JP2005338431A - Image forming apparatus - Google Patents

Abstract

An image forming apparatus capable of obtaining a good image even when cracks occur and enabling a seamless belt to be used for a long time.
A positioning mark provided on the outer peripheral surface side of the belt end in the width direction of the intermediate transfer belt and the presence or absence of a crack on the intermediate transfer belt are detected, and a first optical sensor generates a detection signal. According to the detection signal, the crack and the positioning mark are identified, and the number of the positioning marks identified within the time during which the intermediate transfer belt moves one round is counted to grasp the position of the positioning mark. After the crack that has occurred is identified, the positioning mark that is identified first is set as a reference mark, and the predetermined position from the reference mark whose position is grasped coincides with the leading end of the developer image at the first transfer position. Thus, the exposure start timing of the exposure means is controlled.
[Selection] Figure 2

Description

  The present invention relates to an image forming apparatus provided with a seamless belt carrying a developer image.

  Conventionally, in order to prevent the intermediate transfer belt formed of an endless belt from meandering, an image forming apparatus in which guide ribs are provided at both ends in the width direction of the intermediate transfer belt has been proposed (for example, Patent Document 1).

  The image forming apparatus of Patent Document 1 has a reinforcing member made of a resin film in the vicinity of the joint of the guide rib. This reinforcing member can prevent the intermediate transfer belt from cracking and breaking, and extend the life of the intermediate transfer belt. Usually, the guide rib regulates an unexpected shift in a direction orthogonal to the surface movement direction of the intermediate transfer belt, and prevents the intermediate transfer belt from meandering and shifting. However, the intermediate transfer belt repeatedly bends and extends between a flat portion stretched between the rollers and a curved portion wound around the rollers. At this time, since the belt portion near the joint where the guide rib is interrupted is intensively bent and stretched, a crack is generated in this portion, and the belt is gradually torn. Therefore, if a reinforcing member is attached to the intermediate transfer belt near the joint of the guide rib, even if the intermediate transfer belt repeatedly bends and stretches by driving, stress is not concentrated on the intermediate transfer belt portion corresponding to the joint, and the intermediate transfer belt Generation of cracks is prevented. This extends the life of the intermediate transfer belt.

JP 2000-147950 A

  However, in the conventional technology described above, even if a reinforcing member is provided, cracks may occur due to long-term use. When a crack occurs, there is a possibility that an image transferred to the intermediate transfer belt may be defective.

  Further, the intermediate transfer belt may be broken due to the spread of cracks.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of obtaining a good image even when cracks occur and enabling a seamless belt to be used for a long time.

  In order to achieve the above object, an invention according to claim 1 is an image forming apparatus having a seamless belt carrying a developer image and a developing means for forming a developer image, the crack being formed on the seamless belt. Detecting means for detecting the presence or absence of a crack and generating a detection signal, crack position determining means for determining a crack occurrence position on the seamless belt according to the detection signal from the detecting means, and cracks determined by the crack position determining means And a control means for controlling the development start timing of the developing means so that the developer image does not crack according to the occurrence position.

  According to a second aspect of the present invention, there is provided an exposure means for forming an electrostatic latent image on a photosensitive member, a developing means for developing a latent electrostatic image formed on the photosensitive member to form a developer image, and a plurality of rollers A seamless belt that is stretched and movably provided by the developing means; a first transfer means that transfers the developer image developed by the developing means to the seamless belt at a first transfer position where the photoreceptor and the seamless belt contact; A second transfer means for transferring the developer image transferred to the seamless belt by the transfer means to the recording medium at a second transfer position where the seamless belt and the recording medium contact; and a developer image formed on the seamless belt. A paper feeding means for feeding out the recording medium so that the head and the head of the developer image forming area on the recording medium coincide with each other at the second transfer position; and a recording medium on which the developer image is transferred by the second transfer means. Discharge An image forming apparatus having one or more positioning marks provided on the outer peripheral surface side of the belt end in the width direction of the seamless belt, presence or absence of cracks on the seamless belt, First detection means for detecting presence / absence and generating a detection signal; identification means for identifying a crack and a positioning mark in accordance with the detection signal generated by the first detection means; and identification means within a time during which the seamless belt moves one round The mark counting means that counts the number of the positioning marks identified by the mark and grasps the position of the positioning mark on the seamless belt, and the identification means first identifies the crack that has occurred on the seamless belt after the identification means is identified. Set the positioning mark to be used as the reference mark, Characterized in that the predetermined position from a reference mark which is grasped and the distal end portion of the developer image and a control means for controlling the exposure start timing of the exposure means to match at the first transfer position.

  The invention described in claim 3 is characterized in that guide ribs for preventing meandering are provided on the inner peripheral surface side of the belt end portion in the seamless belt width direction.

  According to a fourth aspect of the present invention, the first detecting means detects the presence / absence of a positioning mark and the presence / absence of a crack by a first optical sensor provided facing the belt end in the seamless belt width direction, and outputs a detection signal. It is generated.

  The invention described in claim 5 is characterized in that the first detecting means is provided at a position facing the roller in a curved surface portion where the seamless belt is wound around the roller.

  The invention described in claim 6 is characterized in that the crack counting means for counting the number of cracks identified by the identification means within the time for which the seamless belt moves once, and two of the plurality of cracks counted by the crack counting means. And a timing means for grasping by measuring the interval between the cracks, and the control means is configured such that the maximum value of the interval between the two cracks ascertained by the timing means is greater than the length from the front end portion to the rear end portion of the recording medium. When it becomes smaller, the image forming operation stopping means is made to stop.

  According to the seventh aspect of the present invention, the image forming operation stop means stops the paper feed means, and after the recording medium is discharged by the paper discharge means, the photosensitive member, the exposure means, the developing means, the seamless belt, the first transfer Each of the means, the second transfer means, and the paper discharge means is stopped.

  In the invention according to claim 8, the predicted value of the number of repetitions of the movement of the seamless belt from the time when the identifying means identifies the crack generated on the seamless belt to the time when the crack reaches a predetermined position in the seamless belt width direction. A storage means for storing, and a movement repetition count counting means for counting the number of repetitions of movement of the seamless belt, and the control means stores the number of movement repetitions of the seamless belt counted by the movement repetition count by the storage means. When the stored predicted value is reached, the image forming operation stopping means is caused to stop.

  The invention according to claim 9 is a second detection means for detecting that a crack has reached a predetermined position and generating a detection signal by a second optical sensor provided at a predetermined position in the seamless belt width direction; Crack determining means for determining the presence or absence of a crack at a predetermined position in accordance with the detection signal generated by the second detecting means, and the control means determines that the crack has reached a predetermined position by the crack determining means. Then, the image forming operation stop means is made to perform a stop operation.

  The invention described in claim 10 is characterized in that the second detection means is provided at a position facing the roller in a curved surface portion where the seamless belt is wound around the roller.

  According to an eleventh aspect of the present invention, there is provided an informing means for informing the user of replacement of the seamless belt when the control means causes the image forming operation stopping means to perform the stopping operation.

  According to a twelfth aspect of the present invention, there is provided an exposure means for forming an electrostatic latent image on a photosensitive member, a developing means for developing a latent electrostatic image formed on the photosensitive member to form a developer image, and a plurality of rollers. And a seamless conveying belt that is movably provided to convey the recording medium, and a developer image developed by the developing means is transferred to the recording medium at a transfer position where the photosensitive member and the recording medium are in contact with each other. Developing by the transfer means, a paper feed means for feeding the recording medium so that the head of the developer image on the photosensitive member and the head of the developer image forming area on the recording medium coincide with each other at the transfer position, and development by the transfer means An image forming apparatus including a paper discharge unit that discharges a recording medium on which the agent image is transferred. The first detection unit generates a detection signal by detecting the presence or absence of a crack on the conveyance belt, and the first detection unit. The generated detection signal is equal to the conveyor belt. The crack position determining means for determining the crack generation position according to the circumferential movement time, and development from the crack generation position determined by the crack position determination means to a predetermined position on the conveyance belt in the direction opposite to the movement direction of the conveyance belt And a control means for controlling the tip of the agent image to be positioned.

  According to a thirteenth aspect of the present invention, the control means grasps the crack generation position according to the detection signal generated from the first detection means and the time for which the conveyor belt moves once, and the control belt detects the position of the conveyor belt from the crack generation position. Control is performed so that the leading end of the recording medium is positioned at a predetermined position on the conveying belt in the direction opposite to the moving direction.

  According to a fourteenth aspect of the present invention, there is provided density detecting means for detecting the density of the developer image, and when the transfer means detects density by the density detecting means, the developer image for density detection is applied to the transport belt. Direct transfer, the control means grasps the crack generation position according to the detection signal generated from the first detection means and the time for which the conveyor belt makes one round movement, from the crack generation position in the direction opposite to the movement direction of the conveyor belt Control is performed so that the front end of the developer image for density detection is positioned at a predetermined position on the transport belt.

  The invention described in claim 15 is characterized in that a guide rib for preventing meandering is provided on the inner peripheral surface side of the belt end in the conveying belt width direction.

  The invention described in claim 16 is characterized in that the first detecting means detects the presence or absence of a crack by a first optical sensor provided at a belt end in the conveying belt width direction.

  The invention described in claim 17 is characterized in that the first detecting means is provided at a position facing the roller in a curved surface portion around which the conveyor belt is wound.

  According to the eighteenth aspect of the present invention, crack counting means for counting the number of cracks detected by the first detecting means within the time for which the conveyor belt makes a round, and among the plurality of cracks counted by the crack counting means, 2 Measuring means for measuring the interval between two cracks, and the control means is configured such that the maximum value of the interval between the two cracks detected by the timing means is the length from the front end portion to the rear end portion of the recording medium. If smaller than this, the image forming operation stopping means is caused to perform a stopping operation.

  According to the nineteenth aspect of the present invention, the image forming operation stop means stops the paper feed means, and after the recording medium is discharged by the paper discharge means, the photosensitive member, the exposure means, the developing means, the transport belt, the transfer means, Each of the paper discharge means is stopped.

  The invention according to claim 20 is the predicted value of the number of repeated movements of the conveyor belt from when the first detecting means detects the crack generated on the conveyor belt until the crack reaches a predetermined position in the conveyor belt width direction. Is stored in advance, and a movement repetition number counting means for counting the number of repetitions of the movement of the conveyor belt, and the control means is configured to determine the number of movement repetitions of the conveyance belt counted by the movement repetition number counting means. When the predicted value stored in the storage unit is reached, the image forming operation stop unit is caused to stop.

  According to a twenty-first aspect of the present invention, the second optical sensor provided at a predetermined position in the conveyance belt width direction includes second detection means for detecting that the crack has reached the predetermined position and generating a detection signal. When the second detection means detects that the crack has reached a predetermined position, the control means causes the image forming operation stop means to perform a stop operation.

  The invention described in claim 22 is characterized in that the second detection means is provided at a position facing the roller in a curved surface portion around which the conveyor belt is wound.

  According to a twenty-third aspect of the present invention, there is provided an informing means for informing the user of the replacement of the seamless belt when the control means causes the image forming operation stopping means to perform the stopping operation.

  According to the image forming apparatus of the first aspect, the detection means detects the presence or absence of a crack, the crack position determination means grasps the occurrence position of the crack, and the control means places the developer image at a position where the developer image is not subject to the crack on the seamless belt. Since the development start timing is controlled so as to transfer the developer image, a good image can be obtained even if a crack occurs, and the seamless belt can be used for a long time.

  According to the image forming apparatus of the second aspect, since the first detecting unit detects one or more positioning marks and the mark counting unit grasps the position of each positioning mark, the first transfer unit grasps the position. The developer image can be accurately transferred to a predetermined position from the reference mark. Further, when the identification means identifies the occurrence of a crack, the transfer position of the developer image onto the seamless belt is changed so that the control means does not transfer the developer image to the crack occurrence area. Therefore, even if a crack occurs, a good image can be obtained and the seamless belt can be used for a long time.

  According to the image forming apparatus of the third aspect, since the guide rib for preventing meandering is provided on the inner peripheral surface side of the belt end portion in the width direction of the seamless belt, the movement of the seamless belt is stabilized and a better image is obtained. Can be obtained.

  According to the image forming apparatus of the fourth aspect, since the first detection unit detects a plurality of positioning marks, the first transfer unit accurately transfers the developer image to a predetermined position from the reference mark whose position is known. It becomes possible. Further, since the crack usually occurs from the belt end in the direction orthogonal to the seamless belt moving direction, the occurrence of the crack can be detected at an early stage by providing the first detection means at the position of the belt end. Furthermore, the use of an optical sensor as the first detection means can accurately detect the occurrence of cracks.

  According to the image forming apparatus of the fifth aspect, the first detecting means is provided on the curved surface portion around which the seamless belt is wound around the roller. Therefore, the crack is wider along the direction of movement of the seamless belt when positioned on the curved surface stretched by the roller than when positioned on the flat surface of the seamless belt. Furthermore, it becomes possible to detect accurately.

  According to the image forming apparatus of the sixth aspect, the crack counting means counts the number of cracks, the time measuring means grasps the interval between the two cracks, and the control means determines that the maximum value of the crack interval is the leading portion of the recording medium. When the length is smaller than the length from the rear end to the rear end, the image forming apparatus is stopped, so that it is possible to prevent poor quality image formation in which an image is formed on the crack. Even if a plurality of cracks occur, the seamless belt can continue to be used as long as the length of the portion where the crack does not occur in the seamless belt is larger than the length from the front end portion to the rear end portion of the recording medium. Therefore, the seamless belt can be used for a long time.

  According to the image forming apparatus of the present invention, the image forming operation stop means stops the paper feeding means, and after the recording medium is discharged, the photosensitive member, the exposure means, the developing means, the seamless belt, the first transfer means. Since each of the second transfer means and the paper discharge means is stopped, if an error occurs during the image forming operation, the recording medium that has been printed at that time is reliably discharged after the printing is completed, This makes it possible to prevent the recording medium from being fed.

  According to the image forming apparatus of the eighth aspect, the storage unit stores in advance a predicted value of the number of repetitions of the seamless belt movement required after the crack occurs until the crack reaches a predetermined position in the seamless belt width direction. Keep it. The image forming operation stopping means stops the image forming operation when the number of seamless belt movement repetitions reaches the stored predicted value. Therefore, even if a crack occurs on the seamless belt, the seamless belt can be used continuously. Furthermore, since the image forming operation is stopped before the crack becomes large, it is possible to prevent the formation of an image with poor quality.

  According to the image forming apparatus of the ninth aspect, the second detecting means detects whether or not the crack has reached a predetermined position in the seamless belt width direction. The image forming operation stopping means stops the image forming operation when the crack determining means determines that the predetermined position has been reached. Therefore, even if a crack occurs on the seamless belt, the seamless belt can be used continuously. Furthermore, since the image forming operation is stopped before the crack becomes large, it is possible to prevent the formation of an image with poor quality. Furthermore, since the size of the crack can be accurately grasped by the optical sensor, the seamless belt can be used to the maximum extent possible.

  According to the image forming apparatus of the tenth aspect, the second detection means is provided on the curved surface portion around which the seamless belt is wound around the roller. Therefore, since the crack is wider along the moving direction of the seamless belt when the crack is located on the curved surface stretched around the roller than when it is on the flat portion of the seamless belt, the crack is further increased. It becomes possible to detect accurately.

  According to the image forming apparatus of the eleventh aspect, after the image forming operation stopping unit stops the image forming operation, the notification unit notifies the user that the seamless belt is to be replaced. Therefore, the user replaces the seamless belt at an early stage. It becomes possible.

  According to the image forming apparatus of the twelfth aspect, the first detection unit detects the occurrence of a crack. The control means is characterized in that the transport position of the recording medium is changed so that the developer image does not overlap the crack occurrence area. Therefore, a good image can be obtained even if a crack occurs, and the transport belt of the seamless belt can be used continuously, so that the transport belt can be used for a long time.

  According to the image forming apparatus of the thirteenth aspect, the first detection means detects the occurrence of a crack. The control means is characterized by changing the transport position of the recording medium so that the recording medium does not overlap the crack occurrence area. Therefore, even if a crack occurs, a good image can be obtained and the conveyor belt can be used continuously, so that the conveyor belt can be used for a long time. In addition, the transportability of the recording medium can be maintained.

  According to the image forming apparatus of the fourteenth aspect, the first detection means detects the occurrence of a crack. The control means is characterized in that the transfer position of the developer image to the conveying belt is changed so that the developer image for density detection is not transferred to the crack occurrence region. Therefore, even if a crack occurs, accurate density detection can be performed, and the conveyor belt can be used continuously, so that the conveyor belt can be used for a long time.

  According to the image forming apparatus of the fifteenth aspect, since the guide rib for preventing meandering is provided on the inner peripheral surface side of the belt end in the conveying belt width direction, the movement of the conveying belt is stabilized and a good image is obtained. Is possible.

  According to the image forming apparatus of the sixteenth aspect, since the crack starts from the belt end in the width direction of the conveying belt, the occurrence of the crack can be detected at an early stage by providing the first detection means at the position of the belt end. . Furthermore, it is possible to accurately detect a crack by using an optical sensor as the first detection means.

  According to the image forming apparatus of the seventeenth aspect, the first detection means is provided on the curved surface portion around which the conveyance belt is wound around the roller. Therefore, since the crack is wider along the moving direction of the conveyor belt when it is located on the curved surface stretched by the roller than when it is on the plane part of the conveyor belt, the crack is further increased. It becomes possible to detect accurately.

According to the image forming apparatus of claim 18, the crack counting means counts the number of cracks, the time measuring means grasps the interval between the two cracks, and the control means determines the maximum value of the crack interval from the beginning of the recording medium. When the length is shorter than the length to the rear end, the image forming apparatus is stopped, so that it is possible to prevent poor quality image formation in which an image is formed on the crack. Even if a plurality of cracks occur, the conveyor belt can continue to be used as long as the length of the non-cracked portion of the conveyor belt is larger than the length from the front end portion to the rear end portion of the recording medium. Therefore, the conveyor belt can be used for a long time.
According to the image forming apparatus of the nineteenth aspect, after the image forming operation stopping unit stops the paper feeding unit and the recording medium is discharged, the control unit includes the photosensitive member, the exposure unit, the developing unit, the transport belt, and the transfer belt. Since each of the means and the paper discharge means is stopped, if an error occurs during the image forming operation, the recording medium that has been printed at that time is discharged after the printing has been completed, and a new recording medium It is possible to prevent the paper from being fed.

  According to the image forming apparatus of the twentieth aspect, the storage unit stores in advance a predicted value of the number of repetitions of the movement of the conveying belt required until the crack reaches a predetermined position in the conveying belt width direction after the occurrence of the crack. deep. The image forming operation stopping means stops the image forming operation when the number of repeated movements of the conveying belt reaches the stored predicted value. Therefore, even if a crack occurs on the conveyor belt, the conveyor belt can be used continuously. Further, since the image forming operation is stopped before the crack becomes large, it is possible to prevent image formation with poor quality.

  According to the image forming apparatus of the twenty-first aspect, the second detection unit detects whether or not the crack has reached a predetermined position in the conveyance belt width direction. Then, if it is detected that it has arrived, the image forming operation stop means stops the image forming operation. Therefore, even if a crack occurs on the conveyor belt, the conveyor belt can be used continuously. In addition, since the image forming operation is stopped before the crack becomes large, it is possible to prevent an image with poor quality from being formed. Furthermore, since the size of the crack can be accurately grasped by the optical sensor, it becomes possible to use the conveyor belt most effectively.

  According to the image forming apparatus of the twenty-second aspect, the second detection means is provided on the curved surface portion around which the conveyance belt is wound around the roller. Therefore, since the crack is wider along the moving direction of the conveyor belt when it is located on the curved surface stretched by the roller than when it is on the plane part of the conveyor belt, the crack is further increased. It becomes possible to detect accurately.

  According to the image forming apparatus of the twenty-third aspect, after the image forming operation stopping unit stops the image forming operation, the notifying unit notifies the user that the conveying belt is to be replaced. Therefore, the user replaces the conveying belt at an early stage. It becomes possible.

  Next, an embodiment of the present invention will be described.

  Hereinafter, embodiments of a four-cycle color laser printer and a direct tandem color laser printer will be described. In the 4-cycle method, each time an intermediate transfer belt, which will be described later, is rotated once, a toner image of one color is formed and the intermediate transfer belt is rotated four times to form a color image on the intermediate transfer belt. This is a method of transferring the upper color image to a recording medium. The direct tandem method is a method in which one photoconductor is arranged for each color, a toner image of each color is formed on each photoconductor, and the toner image is directly transferred to a recording medium conveyed by a conveyance belt described later. It is.

[Configuration of 4-cycle color laser printer]
First, the 4-cycle color laser printer 1 will be described. FIG. 17A is a functional configuration table for controlling a position where a toner image as a developer image is transferred to an intermediate transfer belt 51 described later. As shown in FIG. 17A, the color laser printer 1 includes an identification function 1711, a mark count function 1712, a control function 1713, a crack count function 1714, a time counting function 1715, a stop function 1716, a moving repetition frequency count function 1717, and And a discrimination function 1718. Each of these functions will be described later. FIG. 1 is an overall configuration diagram of the color laser printer 1.

  As shown in FIG. 1, the color laser printer 1 according to this embodiment includes a scanner unit 2 constituting an exposure unit, a process unit 3 having a developing unit, an intermediate transfer belt mechanism unit 5, and a second transfer unit. The transfer roller 6, the sheet feeding unit 7 constituting the sheet feeding unit, the fixing unit 8, and the sheet ejection roller 9 constituting the sheet ejection unit are configured as main components. In the intermediate transfer belt mechanism 5, a first intermediate transfer belt roller 52, which will be described later, constitutes a first transfer unit.

  Hereinafter, the configuration of each component will be described in detail.

(Configuration of scanner unit)
First, the scanner unit 2 will be described with reference to FIG.

  The scanner unit 2 includes a laser light emitting unit (not shown), a polygon mirror, a plurality of lenses, and a reflecting mirror at a central portion in the main body casing 11. The scanner unit 2 applies a laser beam based on image data emitted from a laser light emitting unit to a belt photoconductor (OPC: Organic Photo Conductor) of the belt photoconductor mechanism unit 4 via a polygon mirror, a reflecting mirror, and a lens. ) Irradiate on the surface of 41 by high speed scanning.

(Configuration of process part 3)
The process unit 3 will be described with reference to FIG.

  The process section 3 includes four developing cartridges 31 constituting developing means described later, a belt photoreceptor mechanism section 4 described later, and the like. The four developing cartridges 31 include a yellow developing cartridge 31Y containing yellow toner, a magenta developing cartridge 31M containing magenta toner, a cyan developing cartridge 31C containing cyan toner, and a black toner. And a black developing cartridge 31K accommodated therein. These developing cartridges 31 </ b> Y to 31 </ b> K are sequentially arranged in parallel from the bottom to the top at a predetermined interval in the vertical direction on the front side in the main body casing 11. Each developing cartridge 31 is detachable from the color laser printer 1. Hereinafter, each of these components will be described in detail.

(Developer cartridge configuration)
The four developing cartridges 31 will be described with reference to FIG.

  Each developing cartridge 31 includes a developing roller 32 (a yellow developing roller 32Y, a magenta developing roller 32M, a cyan developing roller 32C, and a black developing roller 32K), a layer thickness regulating blade (not shown), a supply roller, a toner container, and the like. It has. Further, each developing cartridge 31 has a separation solenoid 33 (a yellow separation solenoid 33Y, a magenta separation solenoid 33M, and a cyan separation separation) in order to make each development roller 32 contact or separate from the surface of a belt photoreceptor 41 described later. The solenoid 33C and the black separation solenoid 33K) are configured to be movable in the horizontal direction.

  The developing roller 32 is configured by covering a metal roller shaft with a roller made of an elastic member made of a conductive rubber material. More specifically, the roller of the developing roller 32 is formed by a two-layer structure including a roller portion of an elastic body and a coat layer. The roller portion is made of conductive urethane rubber, silicon rubber, EPDM rubber or the like containing carbon fine particles. The coat layer is coated on the surface of the roller portion, and is mainly composed of urethane rubber, urethane resin, polyimide resin or the like. The developing roller 32 is applied with a predetermined developing bias during development. For example, the predetermined developing bias is + 300V.

  The toner storage portions of the developing cartridges 31 store positively chargeable non-magnetic one-component spherical polymer toners as developers of colors of yellow, magenta, cyan, and black, respectively. During development, the toner is supplied to the developing roller 32 by the rotation of the supply roller. The toner is positively frictionally charged between the supply roller and the developing roller 32. Further, as the developing roller 32 rotates, the toner supplied onto the developing roller 32 enters between the layer thickness regulating blade and the developing roller 32, where it is further sufficiently frictionally charged to a certain thickness. It is carried on the developing roller 32 as a thin layer.

(Configuration of belt photoreceptor mechanism)
The belt photoreceptor mechanism unit 4 will be described with reference to FIG.

  The belt photoreceptor mechanism unit 4 includes a belt photoreceptor 41 wound around a first belt photoreceptor roller 42, a second belt photoreceptor roller 43, and a third belt photoreceptor roller 44, a belt photoreceptor charger 45, and the like. It has.

  The first belt photosensitive roller 42 is disposed opposite to the rear of the four developing cartridges 31, and is disposed below the lowest yellow developing cartridge 31Y. The first belt photoreceptor roller 42 is a roller that is driven to rotate.

  The second belt photosensitive roller 43 is disposed above the first belt photosensitive roller 42 in the vertical direction, and is disposed above the black developing cartridge 31K located at the top. The second belt photosensitive roller 43 is rotationally driven through a driving gear (not shown) by driving a main motor (not shown).

  The third belt photosensitive roller 44 is disposed obliquely above and rearward of the first belt photosensitive roller 42. The third belt photoreceptor roller 44 is a roller that is driven to rotate.

  The belt photoreceptor 41 is wound around a first belt photoreceptor roller 42, a second belt photoreceptor roller 43, and a third belt photoreceptor roller 44. Then, the second belt photosensitive roller 43 is driven to rotate, and the first belt photosensitive roller 42 and the third belt photosensitive roller 44 are driven, so that the belt photosensitive member 41 rotates counterclockwise. To do.

  The belt photoreceptor 41 is an endless belt provided with a base layer (conductive base layer) having a thickness of 0.08 mm and a photosensitive layer having a thickness of 25 μm on one side. The base material layer is made of a nickel conductor formed by nickel electroforming. The photosensitive layer is made of a polycarbonate resin photoreceptor.

  The belt photoconductor charger 45 is located below the belt photoconductor mechanism unit 4 and upstream of the exposed portion of the scanner unit 2 exposed to the belt photoconductor 41 in the vicinity of the first belt photoconductor roller 42. In order not to come into contact with the body 41, they are opposed to each other with a predetermined interval. The belt photoreceptor charger 45 is a positively-charged scorotron charger that generates corona discharge from a charging wire such as tungsten, so that the surface of the belt photoreceptor 41 is uniformly charged positively. It is configured.

  The first and third belt photosensitive rollers 42 and 44 are made of a conductive member such as aluminum, and are in contact with the base material layer of the belt photosensitive member 41 and are connected to a GND terminal (not shown). That is, the first and third belt photoreceptor rollers 42 and 44 keep the potential of the base material layer of the belt photoreceptor 41 at GND (zero potential).

(Configuration of intermediate transfer belt mechanism)
The intermediate transfer belt mechanism 5 will be described with reference to FIG.

  In FIG. 1, the intermediate transfer belt mechanism unit 5 is disposed on the rear side of the belt photosensitive member mechanism unit 4, and a second belt is interposed via a belt photosensitive member 41 and an intermediate transfer belt (ITB: Intermediate Transfer Belt) 51. A first intermediate transfer belt roller 52 disposed opposite to the photosensitive roller 43, a second intermediate transfer belt roller 53 disposed obliquely below and below the first intermediate transfer belt roller 52, and a second intermediate transfer belt roller 53 Is wound around the outer periphery of a third intermediate transfer belt roller 54 and a first to third intermediate transfer belt rollers 52, 53, 54 disposed opposite to a later-described transfer roller 6 via an intermediate transfer belt 51. And an intermediate transfer belt 51 to be rotated. In the intermediate transfer belt mechanism 5, the first intermediate transfer belt roller 52 constitutes a first transfer unit.

  The intermediate transfer belt 51 is formed of a seamless belt made of a resin such as conductive polycarbonate or polyimide in which conductive particles such as carbon are dispersed. Unlike a belt with a seam, the seamless belt is configured such that a developer image can be transferred at any timing. The length of the circumference of the intermediate transfer belt 51 is such that printing can be performed on legal size paper whose maximum length in the intermediate transfer belt moving direction DT is 355.6 mm, and each color developing roller 32 is provided between the papers. Considering the time for performing the switching operation, it is 400 mm.

  The first to third intermediate transfer belt rollers 52, 53, and 54 have an intermediate transfer belt 51 wound around them. Then, the first intermediate transfer belt roller 52 is driven to rotate via the driving device 540 shown in FIG. 4, and the second intermediate transfer belt roller 53 and the third intermediate transfer belt roller 54 are driven to move to the intermediate position. The transfer belt 51 is rotated in the clockwise direction between the first to third intermediate transfer belt rollers 52, 53, and 54.

  As shown in FIG. 2, the intermediate transfer belt 51 includes guide ribs 55 provided on the inner peripheral surface side of the intermediate transfer belt 51 in the width direction DW, and a belt end portion in the width direction DW of the intermediate transfer belt 51. A plurality of positioning marks 56 provided on the outer peripheral surface side, a reflective first optical sensor 57 provided at a position facing the belt end in the width direction DW of the intermediate transfer belt 51, and the width direction of the intermediate transfer belt 51 And a reflective second optical sensor 58 provided at a position facing the belt, a predetermined position inside the belt end of the DW.

(Configuration of guide rib)
The guide rib 55 will be described with reference to FIG.

  The guide ribs 55 are bonded to the inner peripheral surfaces of both end portions in the width direction of the belt in order to prevent the intermediate transfer belt 51 from meandering. The guide rib 55 is made of a rubber material such as urethane rubber, has a thickness of about 0.5 to 1.0 mm, and is not endless, but a single strip-like belt is bonded along the inner peripheral surface of the intermediate transfer belt 51. The end portions thereof face each other to form a seam 59.

(Configuration of positioning marks)
The positioning mark 56 will be described with reference to FIG.

  The position of the positioning mark 56 is grasped by the first optical sensor 57. The surface of the positioning mark 56 is configured to have a predetermined reflectance with respect to the light from the light source of the first optical sensor 57. As a method for increasing the reflectance of the positioning mark 56, for example, the positioning mark 56 is made of a white resin film, a coating material having a high reflectance is applied to the surface of the positioning mark 56, or an ink having a high reflectance. Thus, a configuration in which the positioning mark 56 is printed can be employed. The positioning marks 56 are arranged on the intermediate transfer belt 51 at equal intervals.

(Configuration of optical sensor)
The first optical sensor 57 and the second optical sensor 58 will be described with reference to FIGS.

  As shown in FIG. 3, the first optical sensor 57 includes a light emitting portion 57 a and a light receiving portion 57 b, and the light emitted from the light emitting portion 57 a is applied to the surface of the intermediate transfer belt 51. And the light-receiving part 57b receives the reflected light, and outputs the voltage according to the received light quantity.

  The first optical sensor 57 is provided at a position facing the belt end in the width direction DW of the intermediate transfer belt 51 in order to detect the positioning mark 56 and the crack Pc generated on the intermediate transfer belt 51. In the present embodiment, as shown in FIG. 3, the first optical sensor 57 includes a first to a first curved surface 300 around which the intermediate transfer belt 51 is wound around the first to third intermediate transfer belt rollers 52, 53, and 54. 3 is provided at a position facing any one of the intermediate transfer belt rollers 52, 53, and 54. Therefore, the size of the crack Pc along the moving direction DT of the intermediate transfer belt 51 is larger when the crack Pc is on the curved surface portion 300 than when it is on the flat surface portion 310 of the intermediate transfer belt 51. The light emitted from the light emitting portion 57a is easily transmitted between the cracks Pc, and the difference in reflectance between the surface of the intermediate transfer belt 51 and the positioning mark 56 increases. As a result, the first optical sensor 57 can accurately identify the crack Pc.

  A configuration for identifying whether the position detected by the first optical sensor 57 is the positioning mark 56 or the crack Pc will be described with reference to FIGS. 4 and 5.

  The comparator 401 outputs a high signal as the output signal SO1 if the voltage VS1 output from the light receiving unit 57b is higher than the reference voltage VR1. Conversely, if the voltage VS1 output from the light receiving unit 57b is lower than the reference voltage VR1, a low signal is output as the output signal SO1.

  On the other hand, when the voltage VS1 output from the light receiving unit 57b is lower than the reference voltage VR2, the comparator 402 outputs a high signal as the output signal SO2. Conversely, if the voltage VS1 output from the light receiving unit 57b is higher than the reference voltage VR2, a low signal is output as the output signal SO2.

  When the light emitted from the light emitting portion 57a is reflected on the surface of the intermediate transfer belt 51 where the crack Pc and the positioning mark 56 do not exist (in FIG. 5, time t: t0 <t <t1, t2 <from the start of light emission) When t <t3 and t4 <t), the voltage VS1 output from the light receiving unit 57b is lower than the reference voltage VR1, and a low signal is output as the output signal SO1. The voltage VS1 output from the light receiving unit 57b is higher than the reference voltage VR2, and a low signal is output as the output signal SO2.

  Next, when the light emitted from the light emitting portion 57a is reflected by the positioning mark 56 (in FIG. 5, when the time t from the start of light emission: t1 <t <t2), the voltage VS1 output from the light receiving portion 57b. Becomes higher than the reference voltage VR1, and a high signal is output as the output signal SO1. The voltage VS1 output from the light receiving unit 57b is higher than the reference voltage VR2, and a low signal is output as the output signal SO2.

  When the light emitted from the light emitting unit 57a is reflected by the crack Pc (in FIG. 5, the time t from the start of light emission: t3 <t <t4), the voltage VS1 output from the light receiving unit 57b is the reference voltage VR1. And a low signal is output as the output signal SO1. The voltage output from the light receiving unit 57b is lower than the reference voltage VR2, and a high signal is output as the output signal SO2.

  The output signals SO1 and SO2 are sent to a later-described CPU 530 shown in FIG. When a high signal is sent from the light receiving unit 57b as the output signal SO1, the CPU 530 identifies the signal as a positioning mark detection signal. When a high signal is sent from the light receiving unit 57b as the output signal SO2, the signal is identified as a crack detection signal.

  The second optical sensor 58 as the second detection means has the same configuration as the first optical sensor 57, and a crack generated on the intermediate transfer belt 51 is a predetermined along the width direction DW on the intermediate transfer belt 51. In order to detect that the position has been reached, the intermediate transfer belt 51 is provided at a position facing the belt, a predetermined position inside the belt end in the width direction DW. The predetermined position means that when the crack Pc further extends along the width direction DW of the intermediate transfer belt 51, the intermediate transfer belt 51 irregularly expands and contracts, and the developer images of each color are accurately superimposed and transferred. It refers to the position of the tip of the crack Pc when it reaches a size that cannot be achieved. As shown in FIG. 2, the length Ll is a length between one of the belt end portions in the width direction DW of the intermediate transfer belt 51 and the predetermined position. This length Ll is set in advance by experiments. Further, in the present embodiment, as shown in FIG. 2, the second optical sensor 58 is wound around the first to third intermediate transfer belt rollers 52, 53, and 54 in the same manner as the first optical sensor 57. The curved surface portion 300 is provided at a position facing any one of the first to third intermediate transfer belt rollers 52, 53, and 54. Therefore, the size of the crack Pc along the moving direction DT of the intermediate transfer belt 51 is larger when the crack Pc is on the curved surface portion 300 than when the crack Pc is on the flat surface portion 310 of the intermediate transfer belt 51. Since the light emitted from the light emitting portion 58b of the optical sensor 58 does not reflect and does not go to the light receiving portion 58b of the second optical sensor, and easily passes through the crack Pc, the surface of the intermediate transfer belt 51 and the positioning mark 56 The difference in reflectance value between the two becomes large. As a result, the second optical sensor 58 can accurately identify the crack Pc. In order to determine whether or not the crack Pc generated on the intermediate transfer belt 51 has reached a predetermined position on the intermediate transfer belt 51, the comparator 403 outputs the output voltage VS2 from the light receiving unit 58b of the second optical sensor 58 and A reference voltage VR3 is supplied, and an output signal SO3 is output as a comparison result. The configuration of the comparator 403 is the same as the configuration of the comparator 402 and the like for identifying the crack Pc generated on the intermediate transfer belt 51 by the first optical sensor 57 described above, and a detailed description thereof will be omitted.

(Configuration of transfer roller)
The transfer roller 6 will be described with reference to FIG.

  The transfer roller 6 is disposed so as to oppose the third intermediate transfer roller 54 and the intermediate transfer belt 51 of the intermediate transfer belt mechanism unit 5, and a metal roller shaft is covered with a roller made of a conductive rubber material. And is rotatably supported. The transfer roller 6 is configured to be movable between a standby position separated from the intermediate transfer belt 51 and a transferable position adjacent to the intermediate transfer belt 51 by a transfer roller contact / separation mechanism (not shown). The standby position and the transferable position are determined so as to face both sides of the conveyance path 12 of the sheet 71, and the transfer roller 6 moves the conveyance path 59 between the intermediate transfer belt 51 at the transferable position. It is configured to press the passing sheet 71.

  As will be described later, the transfer roller 6 is positioned at the standby position while the developer images for the respective colors are sequentially transferred to the intermediate transfer belt 51 during printing, and all the developer images are transferred from the belt photoreceptor 41. When it is transferred to the intermediate transfer belt 51, it is located at a transferable position.

  The transfer roller 6 is applied with a predetermined transfer bias to the intermediate transfer belt 51 at a transferable position by a transfer bias application circuit (not shown).

(Configuration of paper feed unit)
The sheet feeding unit 7 will be described with reference to FIG.

  The paper feed unit 7 is configured to contact a paper feed tray 72 in which the papers 71 are stacked and stored, a paper feed roller 73 that contacts the paper 71 at the top of the paper feed tray 72, and takes out the paper 71 one by one by rotation. A conveyance roller 74 that conveys the sheet 71 to the image forming position and a registration roller 75 that performs registration processing are provided. The registration process is an operation in which the registration roller 75 sends out the paper 71 so that the leading edge of the color image on the intermediate transfer belt 51 and the leading edge of the paper 71 coincide with each other.

(Configuration of fixing unit)
The fixing unit 8 will be described with reference to FIG.

  The fixing unit 8 is disposed behind the intermediate transfer belt mechanism unit 5, and includes a heating roller 81, a pressing roller 82 that presses the heating roller 81, and a pair of conveyance units provided on the downstream side of the heating roller 81 and the pressing roller 82. And a roller 83. The heating roller 81 includes a halogen lamp for heating with an outer layer made of silicon rubber and an inner layer made of metal.

(Configuration of paper discharge roller)
The paper discharge roller 9 will be described with reference to FIG.

  The paper discharge roller 9 includes a pair of rollers, and is configured to discharge the paper 71 conveyed by the conveyance roller 83 onto a paper discharge tray 13 formed on the upper portion of the main body casing 11.

[Operation when printing with a 4-cycle color laser printer]
An operation during printing of the color laser printer 1 will be described. This operation is realized by the CPU 530 shown in FIG. 4 controlling each unit.

  Of the sheets 71 stored in the sheet feeding tray 72 of the sheet feeding unit 7, the uppermost sheet is pressed by the sheet feeding roller 73, and the sheet 71 is taken out one by one by the rotation of the sheet feeding roller 73. It is. The taken sheet 71 is fed to the image forming position by the conveyance roller 74 and the registration roller 75. A registration process is performed on the fed paper 71 by a registration roller 75.

  The surface of the belt photoreceptor 41 is uniformly positively charged by the belt photoreceptor charger 45 and then exposed by high-speed scanning of the laser beam from the scanner unit 2 based on the image data. In the exposed portion, the charge is eliminated. Therefore, on the surface of the belt photoconductor 41, an electrostatic latent image composed of a positively charged portion and a portion that is uncharged and uncharged is formed according to the image data. It is formed.

  When the electrostatic latent image is formed, the first belt photosensitive roller 42 and the third belt photosensitive roller 44 maintain the potential of the portion in contact with the base material layer of the belt photosensitive member 41 with which they are in contact with GND. .

  The yellow separation solenoid 33Y moves the yellow developing cartridge 31Y of the developing cartridge 31 rearward in the horizontal direction, and moves the developing roller 32Y of the yellow developing cartridge 31Y to the belt photoreceptor 41 on which the electrostatic latent image is formed. Make contact.

  The yellow toner accommodated in the yellow developing cartridge 31Y is positively charged and adheres only to an uncharged portion on the belt photoconductor 41. As a result, a yellow developer image is formed on the belt photoreceptor 41.

  At this time, the magenta developing cartridge 31M, the cyan developing cartridge 31C, and the black developing cartridge 31K are moved forward in the horizontal direction by the separating solenoids 33M, 33C, and 33K, and are separated from the belt photoreceptor 41.

  The yellow developer image formed on the belt photoreceptor 41 is transferred onto the surface of the intermediate transfer belt 51 when the belt developer 41 moves and faces the intermediate transfer belt 51.

  At this time, the potential of the base material layer of the belt photoreceptor 41 is maintained at GND. On the other hand, a potential of −300 V is applied to the first intermediate transfer belt roller 52. Therefore, a suction force is generated between the positively charged yellow toner and the intermediate transfer belt 51, and the yellow developer image is transferred to the intermediate transfer belt 51.

  Similarly to the above, with respect to magenta, an electrostatic latent image is formed on the belt photoreceptor 41, and then a magenta developer image is formed. Further, a magenta developer image is formed on the intermediate transfer belt 51. Transcribed.

  That is, an electrostatic latent image is formed again on the belt photoreceptor 41, and then the magenta developing cartridge 31M is moved rearward in the horizontal direction by the magenta separation solenoid 33M, and the developing roller 32M of the magenta developing cartridge 31M The yellow developing cartridge 31Y, the cyan developing cartridge 31C, and the black developing cartridge 31K are moved to the front in the horizontal direction by the separation solenoids 33Y, 33C, and 33K while being in contact with the belt photoreceptor 41, and the belt photoreceptor 41 is moved. Spaced apart. As a result, a magenta developer image is formed on the belt photoreceptor 41 only with the magenta toner contained in the magenta developer cartridge 31M. In the same manner as described above, when the magenta developer image is opposed to the intermediate transfer belt 51 by the movement of the belt photoreceptor 41, the yellow developer image is already transferred and transferred onto the intermediate transfer belt 51. Is done.

  Such a similar operation is repeated for the cyan toner accommodated in the cyan developing cartridge 31C and the black toner accommodated in the black developing cartridge 31K, whereby four color toners are transferred onto the intermediate transfer belt 51. A superimposed developer image is formed.

  The developer image formed on the intermediate transfer belt 51 is transferred to the paper 71 by the transfer roller 6 positioned at a transferable position while the paper 71 passes between the intermediate transfer belt 51 and the transfer roller 6. The

  The heating roller 81 of the fixing unit 8 heat-fixes the developer image transferred onto the sheet 71 while the sheet 71 passes between the heating roller 81 and the pressing roller 82.

  Then, the sheet 71 on which the developer image is thermally fixed in the fixing unit 8 is conveyed toward the pair of paper discharge rollers 9 by the conveyance roller 83. The sheet 71 conveyed to the sheet discharge roller 9 is discharged by the sheet discharge roller 9 onto the sheet discharge tray 13 formed on the upper portion of the main body casing 11.

[Control action when a 4-cycle color laser printer cracks]
Next, control of the image forming operation when a crack occurs in the color laser printer 1 will be described.

  FIG. 4 is a block diagram schematically showing the configuration of a control device that controls the image forming operation when the color laser printer 1 is cracked.

The ROM 510 has storage areas for system startup programs, character data, character code information, and the like, and stores programs 511 to 518 described later.
The RAM 520 has a data storage area, is loaded with each program and data represented by a flowchart described later for each of various processes, and can temporarily store image data of a document.

  The CPU 530 executes each of the programs 511 to 518 to perform overall control and arithmetic processing of the color laser printer 1.

  When a drive signal is supplied from the CPU 530, the drive device 540 drives each component of the color laser printer 1.

  When the identification program 511 is executed by the CPU 530, the function of identifying whether it is a positioning mark detection signal or a crack detection signal according to the output signal VS1 generated by the first optical sensor 57 is achieved. This function is an identification function 1711 shown in FIG. 17A, which corresponds to the identification means of the present invention.

  When the mark count program 512 is executed by the CPU 530, the function of counting the number of the positioning marks 56 identified by the identification function 1711 and grasping the position of the positioning marks 56 on the intermediate transfer belt 51 is achieved. This function is the mark count function 1712 shown in FIG. 17A, which corresponds to the mark count means of the present invention. When the total number of positioning marks 56 is counted, the number of positioning marks 56 is counted again from “1”.

  When the control program 513 is executed by the CPU 530, the following functions are achieved. The fact that a crack has occurred on the intermediate transfer belt 51 is identified by the identification function 1711. After that, the intermediate transfer belt 51 moves and the positioning mark 56 first detected by the first optical sensor 57 is set as a reference mark. When the number of positioning marks 56 is counted by the mark counting function 1712, the positioning marks 56 are arranged on the intermediate transfer belt 51 at equal intervals, so that the position of the reference mark is grasped. The above-described transfer control position Px (see FIG. 19E) determined by the reference mark whose position has been determined and the leading portion of the developer image developed by the process unit 3 are the belt photoconductor 41 and the intermediate transfer belt. The exposure start timing of the exposure scanner unit 2 is controlled so as to coincide with each other at the first transfer position Pt (see FIG. 19 (e)) in contact with 51. A function for controlling the exposure start timing of the exposure scanner unit 2 is a control function 1713 shown in FIG. 17A, which corresponds to the control means of the present invention.

  When the crack count program 514 is executed by the CPU 530, the function of counting the number of cracks identified by the identification function 1711 is achieved. When the total number of cracks is counted, the number of cracks is counted again from “1”. The function of counting the number of cracks is a crack count function 1714 shown in FIG. 17A, which corresponds to the crack count means of the present invention.

  When the time measuring program 515 is executed by the CPU 530, the time for which the intermediate transfer belt 51 moves is counted by the length of the interval between adjacent cracks among the plurality of cracks counted by the crack counting function 1714. The function of grasping the interval between two cracks is achieved. This function is the time measuring function 1715 shown in FIG. 17 (a), and corresponds to the time measuring means of the present invention.

  When the stop program 516 is executed by the CPU 530, when the length of the developed crack reaches the above-described length Ll, a plurality of cracks are generated, and the transfer position of the developer image is shifted by the control function 1713. In the case where a part of the developer image is cracked, first, the paper feed unit 7 is stopped so that the paper 71 is not fed. When the paper supply unit 7 is stopped, an image is formed on the paper 71, and when the paper 71 is discharged onto the paper discharge tray 13, the scanner unit 2, the process unit 3, the intermediate transfer belt mechanism unit 5, and the transfer roller 6 and the operation of the paper discharge roller 9 are stopped. A function for stopping the operations of the paper feed unit 7, the scanner unit 2, the process unit 3, the intermediate transfer belt mechanism unit 5, the transfer roller 6, and the paper discharge roller 9 is a stop function 1716 shown in FIG. This corresponds to the image forming operation stop means of the present invention.

  Whether or not a part of the developer image is cracked when a plurality of cracks occur and the transfer position of the developer image is shifted by the control function 1713 is determined as follows. The maximum sheet length is stored in advance in the memory 519 in the ROM 510 for the length of the sheet 71 conveyed in the color laser printer 1 in the conveyance direction. Then, in a plurality of cracks counted by the crack counting function 1714, the time measuring function 1715 measures the time for which the intermediate transfer belt 51 moves by the length of the interval between two adjacent cracks. The interval between two cracks is grasped. Among the grasped intervals, the maximum crack interval having the maximum size is compared with the above-described maximum sheet length read from the memory 519 in the ROM 510. If the maximum crack interval is smaller than the maximum sheet length, it is determined that a part of the developer image is cracked even if the transfer position is shifted.

  The display 550 is operated together with the execution of the stop function 1716 and notifies that the intermediate transfer belt 51 is to be replaced. Normally, whether or not the intermediate transfer belt 51 is replaced is determined by a fuse or an IC chip attached to the intermediate transfer belt mechanism 5. It is determined whether or not the intermediate transfer belt 51 has been replaced at a timing such as opening and closing of the main casing 3 after notification of belt replacement. As a means for notifying the replacement of the intermediate transfer belt 51, a buzzer sounding can be considered in addition to the display.

  When the movement repetition count program 517 is executed by the CPU 530, the function of counting whether or not the number of movement repetitions of the intermediate transfer belt 51 has reached a specified number described later is achieved. This function is the movement repetition number counting function 1717 shown in FIG. 17A and corresponds to the movement repetition number counting means of the present embodiment.

  The determination program 518 is executed by the CPU 530. When the determination program 518 is executed by the CPU 530, the function of determining whether the length of the developed crack has reached the aforementioned length Ll is achieved by the second optical sensor 58. This function is a discrimination function 1718 shown in FIG. 17A and corresponds to the crack discrimination means of the present invention.

  Here, the fact that the CPU 530 cannot control image formation means that the developer images of the respective colors cannot be accurately superimposed. The developer images of the respective colors are not accurately superimposed when a crack is generated from one end in the width direction DW of the intermediate transfer belt 51 and reaches a position in the direction toward the other end. It will be tested in advance. Through this experiment, in the width direction DW of the intermediate transfer belt 51, the length Ll shown in FIG. 2 from the end where the crack occurred to the position where the crack arrived at the time of image formation failure is set. That is, the second optical sensor 58 is provided opposite to the intermediate transfer belt 51 at a position inside the length Ll from the belt end in the width direction of the intermediate transfer belt 51. Then, in order for the length of the crack to reach the length Ll, a specified number of times of how many times the intermediate transfer belt 51 has moved is set in advance by experiments. The memory 519 stores the specified number of times in advance. This memory 519 corresponds to the storage means of the present invention.

  6 and 7 are control flowcharts of the image forming operation when a crack occurs in the 4-cycle color laser printer 1.

  First, the case where the crack Pc generated on the intermediate transfer belt 51 has reached the size at which the image forming operation must be stopped is predicted by the number of repetitions of the movement of the intermediate transfer belt 51 with reference to FIGS. Will be described.

  When the color laser printer 1 is activated (S601), the first optical sensor 57 checks whether a crack has occurred on the intermediate transfer belt 51 (S602).

  The crack Pc is likely to occur in the belt portion near the joint 59 of the guide rib 55 provided on the inner peripheral surface side of the belt end portion in the width direction of the intermediate transfer belt 51. While the intermediate transfer belt 51 is stretched by the first to third intermediate transfer belt rollers 52, 53, and 54 and continues to be driven to move along a predetermined path, the tension is interposed between the rollers. Stretching and bending are repeated in the flat surface portion and the curved surface portion wound around the roller, and stress is applied to the belt portion in the vicinity of the joint 59 of the guide rib 55, so that the crack Pc occurs.

  If the high signal output signal SO2 which is a crack detection signal is not identified (S603: No), the presence / absence of the positioning mark 56 is checked (S605). If the high signal output signal SO1 which is the positioning mark detection signal is not identified (S606: No), the presence / absence of the positioning mark 56 is checked again. When the positioning mark detection signal is identified (S606: Yes), the number of positioning marks 56 is counted (S608).

  The time required for the intermediate transfer belt 51 to move once is counted in advance, and the number of positioning marks 56 is counted while the intermediate transfer belt 51 moves once, and the positioning marks 56 are equidistant on the intermediate transfer belt 51. Therefore, the position of the positioning mark 56 is grasped.

  Then, the image forming position is determined based on the grasped position of the positioning mark 56 (S609), and exposure is started so that the developer image is transferred to the image forming position (S610).

  When the image formation of the final data is confirmed (S611: Yes), the image forming operation is ended (S613). If image formation of the final data has not been confirmed (S611: No), it is checked again whether or not a crack Pc has occurred on the intermediate transfer belt 51 (S602).

  When the crack detection signal is identified (S603: Yes), the number of occurrences of crack Pc while the intermediate transfer belt 51 moves once is counted. When the number of occurrences of cracks is counted as “1” (S615: No), the number of rotations of the intermediate transfer belt 51 is counted (S616).

  When the counted number of movements of the intermediate transfer belt 51 reaches the specified number of times stored in the memory 519 (S618: Yes), it is notified that the intermediate transfer belt 51 is to be replaced (S630).

  When the number of belt movements reaches the specified number, the image forming operation is stopped (S631).

  If the intermediate transfer belt 51 is replaced with a new belt after the image forming operation is stopped (S632: Yes), the control operation is ended (S634). If the intermediate transfer belt 51 has not been replaced with a new belt (S632: No), it is checked whether or not it has been replaced until it is replaced.

  If the counted number of movements of the intermediate transfer belt 51 has not reached the specified number of times stored in the memory 519 (S618: No), the presence / absence of the positioning mark 56 is checked (S619). If the positioning mark detection signal is not identified (S620: No), the presence / absence of the positioning mark 56 is checked again. When the positioning mark detection signal is identified (S620: Yes), the image forming position is determined according to the identified positioning mark 56 (S622), and exposure is started so that the developer image is transferred to the image forming position. (S623). This prevents the developer image from being transferred onto the crack Pc.

When the image formation of the final data is confirmed (S624: Yes), the image forming operation is ended (S626). If image formation of the final data has not been confirmed (S624: No), the number of occurrences of cracks Pc while the intermediate transfer belt 51 moves once again is counted.
When the number of occurrences of cracks is counted 2 or more (S615: Yes), the time required for the intermediate transfer belt 51 to move through the length of each interval between the two adjacent cracks Pc is counted, and between the two adjacent cracks Pc. The length of each interval is grasped (S627).

  If the maximum crack interval among the recognized crack intervals is smaller than the above-described maximum sheet length (S628: Yes), the sheet 71 is applied to any one of the plurality of cracks Pc, so that the intermediate transfer belt is used. The fact that 51 is to be exchanged is notified (S630).

  If the maximum crack interval is wider than the maximum sheet length (S628: No), the number of rotations of the intermediate transfer belt 51 is counted (S616).

  Next, a case where the second optical sensor 58 detects that the crack Pc generated on the intermediate transfer belt 51 has reached a size at which the image forming operation must be stopped will be described with reference to FIGS. I will explain. In FIG. 7, only the portions of S616 and S618 in the flowchart of FIG. 6 are replaced with S716 and S718, and only the changed portions will be briefly described.

  When the number of occurrences of cracks Pc is counted as “1” (S715: No), it is checked whether or not the cracks have reached a predetermined length L1 from the belt end in the width direction of the intermediate transfer belt 51 (see FIG. S716).

  When it is detected by the high signal output signal SO3 from the comparator 403 that the crack Pc has reached the length Ll (S718: Yes), it is notified that the intermediate transfer belt 51 is to be replaced (S730).

  If it is detected that the crack Pc has reached the length L1, the image forming operation is stopped (S731).

  If the intermediate transfer belt 51 is replaced with a new belt after the image forming operation is stopped (S732: Yes), the image forming operation is ended (S734). If the intermediate transfer belt 51 has not been replaced with a new belt (S732: No), it is checked whether or not it has been replaced until it is replaced.

  If it is not detected that the crack Pc has reached the length Ll (S718: No), the presence or absence of the positioning mark 56 is checked (S719). If the positioning mark detection signal is not identified (S720: No), the presence / absence of the positioning mark 56 is checked again. When the positioning mark detection signal is identified (S720: Yes), the identified positioning mark 56 is set as a reference mark, the transfer position is controlled according to the reference mark 56 (S722), and the developer is transferred to the controlled transfer position. Exposure is started so that the image is transferred (S723). This prevents the developer image from being transferred onto the crack Pc.

  As the transfer position control operation, a control operation described later with reference to FIGS. 18 and 19 is executed.

  When the image formation of the final data is confirmed (S724: Yes), the image forming operation is ended (S726). If image formation of the final data has not been confirmed (S724: No), the number of occurrences of cracks is counted while the intermediate transfer belt 51 moves once again.

[Control operation of transfer position at which developer image is transferred to intermediate transfer belt]
The image transfer position to the intermediate transfer belt 51 is controlled by detecting a positioning mark 56 on the intermediate transfer belt 51.

  First, the image transfer position when the crack Pc is not generated on the intermediate transfer belt 51 will be described. In FIG. 18, for example, when it is detected that the positioning mark 56a is located at the detection position PF detected by the first optical sensor 57, the exposure is started. At this time, the moving direction of the intermediate transfer belt 51 from the first transfer position Pt is equal to the length La of the belt photoreceptor 41 from the exposure position Pe to the first transfer position Pt where the belt photoreceptor 41 and the intermediate transfer belt 51 are in contact with each other. The head of the image is transferred to a position Ps that is away from DT. At this time, the maximum length of the image forming area along the moving direction DT of the intermediate transfer belt 51 is 355.6 mm which is the legal size, and therefore the maximum image forming area is as shown by the bold line in FIG. To position. That is, when a part of the intermediate transfer belt 51 at the position Ps is positioned at the first transfer position Pt at the time when it is detected that the positioning mark 56a is positioned at the detection position PF, image transfer is started, When a part of the intermediate transfer belt 51 located at Pg is positioned at the first transfer position Pt, the image transfer is completed.

  Next, an image transfer position when a crack occurs on the intermediate transfer belt 51 will be described. If the exposure is started simultaneously with the detection of the crack Pc at the detection position PF, the maximum image forming area is located as shown by the thick line in FIG. That is, when a part of the intermediate transfer belt 51 located at the position Ps is located at the first transfer position Pt when it is detected that the crack Pc is located at the detection position PF, image transfer is started, and the position Pg The image transfer is completed when a part of the intermediate transfer belt 51 located at the first transfer position Pt is located. As a result, the crack Pc is located in the image forming area. In order for the crack Pc not to be located in the image forming area, the exposure start timing must be controlled so that the crack Pc is located in the non-image forming area.

  If the crack Pc occurs between the positioning mark 56a and the positioning mark 56b, in this case, the reference mark is set to the positioning mark 56b. When the start of exposure is delayed by the time that the intermediate transfer belt 51 moves by the length Lb of the intermediate transfer belt 51 from the position Ps to the first transfer position Pt from the time when the crack Pc is detected at the detection position PF. Further, the image is transferred onto the intermediate transfer belt 51 with a delay by the time that the intermediate transfer belt 51 moves by the length La. That is, when the crack Pc is detected at the detection position PF, the leading end of the image is transferred onto the intermediate transfer belt 51 located at the first transfer position Pt. The maximum image forming area at this time is as shown by a thick line in FIG. Here, the detection accuracy of the crack Pc that is detected each time the intermediate transfer belt 51 moves one round is worse than the detection accuracy of the positioning mark 56b because the detection light diffuses. Therefore, it is preferable that the time point when the positioning mark 56 is detected be a reference rather than the time point when the crack Pc is detected. Therefore, a length (Lb−Lc) obtained by subtracting the distance Lc between the crack Pc and the reference mark 56b from the length Lb described above from the time when the positioning mark 56b set as the reference mark is detected at the detection position PF. If the start of exposure is delayed by the amount of time that the intermediate transfer belt 51 moves, the image is transferred onto the intermediate transfer belt 51 with a delay of the time that the intermediate transfer belt 51 moves by the length La. The maximum image forming area at this time is as shown by a thick line in FIG. However, in the image forming region shown in FIG. 19 (d), the image is applied to the crack Pc. In order for the leading end of the image to be transferred from the crack Pc to the position Px separated by the length x in the direction opposite to the moving direction DT of the intermediate transfer belt 51, it is long from the time when the reference mark 56b is detected at the detection position PF. The start of exposure is delayed by the time that the intermediate transfer belt 51 moves by (Lb−Lc), and the length x is set to the length Ld of the intermediate transfer belt 51 from the first transfer position Pt to the detection position PF. It is only necessary to delay the start of exposure by the time for which the intermediate transfer belt 51 moves by the added length (Ld + x). That is, if the start of exposure is delayed by the time that the intermediate transfer belt 51 moves by the length [(Lb−Lc) + (Ld + x)] from the time point when the reference mark 56b is detected at the detection position PF, the crack Pc The leading edge of the image is transferred to a position Px that is separated by a length x in the direction opposite to the moving direction DT of the intermediate transfer belt 51. The maximum image forming area at this time is as shown by a thick line in FIG.

  Usually, an error occurs in each rotation time of the intermediate transfer belt 51. Therefore, it is preferable to provide a plurality of positioning marks 56 rather than one. This is because the reference mark described above is set to the positioning mark 56 that is detected first after the crack Pc is detected, but if there is only one positioning mark 56, the distance between the crack Pc and the reference mark is large. This is because an error is likely to occur in the position of the detected reference mark as the distance increases. Accordingly, when a plurality of positioning marks 56 are provided rather than one, the transfer position of the image is less likely to shift, so that the four color developer images are more accurately superimposed.

The distance along the moving direction DT on the intermediate transfer belt 51 is measured by counting the number of a plurality of positioning marks 56 arranged at equal intervals on the intermediate transfer belt 51.
The length La is the length of the belt photoconductor 41 from the exposure position Pe to the first transfer position Pt where the belt photoconductor 41 and the intermediate transfer belt 51 are in contact with each other. Therefore, since the value of the length La is constant, it is stored in advance in a memory 519 described later shown in FIG.

  The length Lb is a length obtained by subtracting the length La from the circumference of the intermediate transfer belt 51. Therefore, since the value of the length Lb is constant, it is stored in the memory 519 in advance.

  The length Lc is the distance between the crack Pc and the reference mark 56b. Accordingly, each of the crack Pc and the reference mark 56b is detected by the first optical sensor 57, the position is grasped, and the length Lc is measured.

  The length Ld is the length of the intermediate transfer belt 51 from the first transfer position Pt to the detection position PF. Therefore, since the value of the length Ld is constant, it is stored in advance in a memory 519 described later shown in FIG.

  The length x is a distance between the position on the intermediate transfer belt 51 to which the leading edge of the image is transferred and the crack Pc, and a desired length x is selected in advance and stored in the memory 519. The length x is selected to be smaller than the length of the minimum non-image forming area.

Second embodiment

[Configuration of direct tandem color laser printer]
Next, the direct tandem color laser printer 100 will be described. FIG. 17B is a functional configuration diagram for controlling the position at which the developer image of the color laser printer 100 is transferred to a conveyance belt 154 described later. As shown in FIG. 17B, the color laser printer 100 has a crack position determination function 1721, a control function 1723, a crack count function 1724, a time measurement function 1725, a stop function 1726, and a movement repetition number count function 1727. ing. Each of these functions will be described later. FIG. 8 is an overall configuration diagram of the color laser printer 100.

  As shown in FIG. 8, the color laser printer 100 according to this embodiment includes a scanner unit 102 that constitutes an exposure unit, a process unit 103 that constitutes a developing unit, a transport belt mechanism unit 105, and a transfer that constitutes a transfer unit. A roller 106, a paper feed unit 107 constituting a paper feed unit, a fixing unit 108, and a paper discharge roller 109 constituting a paper discharge unit are configured as main components.

  Hereinafter, the configuration of each component will be described in detail.

(Configuration of scanner unit)
The scanner unit 102 will be described with reference to FIG.

  The scanner unit 102 exposes the surface of the photosensitive drum 104 with a laser beam on the downstream side in the rotation direction DR of the photosensitive drum 104 described later than the charger 142 described later. The scanner unit 102 irradiates the surface of the photosensitive drum 104 with laser light corresponding to the image data, and an electrostatic latent image for each color is formed on the surface of the photosensitive drum 104.

(Process section configuration)
The process unit 103 will be described with reference to FIG.

  The process unit 103 includes four developing cartridges 131 constituting a developing unit, a photosensitive drum 104, a cleaning roller 141, a charger 142, and the like. The entire process unit 103 can be attached to and detached from the color laser printer 100.

  Hereinafter, each of these components will be described in detail.

(Developer cartridge configuration)
The four developing cartridges 131 will be described with reference to FIG.

  The four developing cartridges 131 include a magenta developing cartridge 131M that stores magenta toner, a cyan developing cartridge 131C that stores cyan toner, a yellow developing cartridge 131Y that stores yellow toner, and a black toner. The black developing cartridge 131K is accommodated. These developing cartridges 131M, 131C, 131Y, and 131K are sequentially arranged in parallel from the left to the right in the main body casing 111 at a predetermined interval in the horizontal direction.

  The developing cartridge 131 includes a developing roller 132. The developing roller 132 is formed in a cylindrical shape using conductive silicon rubber as a base material, and further, a coating layer of a resin or rubber material containing fluorine is formed on the surface.

  Each of the developing cartridges 131 includes a supply roller 133. The supply roller 133 is a conductive sponge roller, and is disposed so as to be in pressure contact with the developing roller 132 by the elastic force of the sponge.

  The developing cartridge 131 is formed with a toner accommodating portion that accommodates a positively charged polymerized toner.

(Configuration of photosensitive drum)
The photosensitive drum 104 will be described with reference to FIG.

  As the photosensitive drum 104 (104M, 104C, 104Y, 104K), for example, a member in which a positively chargeable photosensitive layer is formed on an aluminum base material is used.

(Configuration of cleaning roller)
The cleaning roller 141 will be described with reference to FIG.

  The cleaning roller 141 (141M, 141C, 141Y, 141K) is a roller made of an elastic material such as a conductive sponge, and is configured to slide on the photosensitive drum 104 below the photosensitive drum 104. The cleaning roller 141 is configured to be applied with a negative polarity voltage having a polarity opposite to that of the toner by a power source (not shown), and the photosensitive drum 104 is subjected to a rubbing force with respect to the photosensitive drum 104 and an electric field due to the voltage. The residual toner on 104 is configured to be removed.

(Charger configuration)
The charger 142 will be described with reference to FIG.

  The charger 142 (142M, 142C, 142Y, 142K) is a scorotron type charger, and is disposed on the surface of the photosensitive drum 104 from above the photosensitive drum 104 on the downstream side of the cleaning roller 141 in the rotation direction of the photosensitive drum 104. Opposed to each other. Note that a roller-type charger that contacts the photosensitive drum 104 may be employed as the charger 142.

  With the above-described configuration, a positive polarity (positively charged) electrostatic latent image formed on the photosensitive drum 104 at the contact portion between the developing roller 132 and the photosensitive drum 104 is reversed with positively charged toner. Can be developed satisfactorily and an extremely high quality image can be formed.

(Configuration of conveyor belt mechanism)
The transport belt mechanism 105 will be described with reference to FIG.

  The transport belt mechanism 105 includes a first transport belt roller 151 that is one drive roller, a second transport belt roller 152 that is two driven rollers, and a third transport belt roller 153, and a stretch between these three rollers. And a conveyor belt 154 composed of a seamless belt. In the vicinity of the position facing the photosensitive drum 104, transfer rollers 106 (106M, 106C, 106Y, 106K) are provided. The moving direction of the surface of the conveying belt 154 facing the photosensitive drum 104 is set clockwise.

  As shown in FIG. 9, the conveyance belt mechanism unit 105 includes a guide rib 155 provided on the inner peripheral surface side of the belt end in the width direction DW of the conveyance belt 154 and color correction processing for correcting the density of each color during printing ( In order to perform calibration, a density detection sensor 156 provided at a position facing the transport belt 154, a first optical sensor 157 provided at a position facing the belt end in the width direction DW of the transport belt 154, and transport And a second optical sensor 158 provided at a position facing the belt on the inner side by a predetermined position from the belt end in the width direction of the belt 154. Further, the guide rib 155 is bonded in the form of a single elongated band along the inner peripheral surface of the transport belt 154, and ends of the guide rib 155 face each other to form a seam 159.

  Since the guide rib 155, the first optical sensor 157, and the second optical sensor 158 of this embodiment are the same as those described in the four-cycle color laser printer of the first embodiment, the description thereof is omitted. The density detection sensor 156 will be described later together with the density detection processing operation.

(Configuration of transfer roller)
The transfer roller 106 will be described with reference to FIG.

  The transfer roller 106 transfers a toner image formed on the photosensitive drum 104 onto the paper 171 transported by the transport belt 154 when a predetermined voltage is applied from a power source (not shown).

(Configuration of paper feed unit)
The paper feed unit 107 will be described with reference to FIG.

  The paper feed unit 107 is provided at the bottom of the apparatus, and includes a paper feed tray 172 that stacks and stores a plurality of paper sheets 171, and a paper feed roller 173 that separates and feeds the stacked paper sheets 171 one by one. , And a registration roller 174 that performs registration processing. The paper feeding unit 107 is configured to send out the paper 171 at a predetermined timing with the image forming process by the process unit 103. The paper 171 sent out from the paper feed tray 172 is transported to the transport belt 154 by the registration rollers 174.

(Configuration of fixing unit)
The fixing unit 108 will be described with reference to FIG.

  The fixing unit 108 includes a heating roller 181 and a pressure roller 182, and heats and transfers the paper 171 on which the four color developer images are transferred while being nipped and conveyed by the heating roller 181 and the pressure roller 182. The developer image is fixed on the paper 171 by applying pressure.

(Configuration of paper discharge roller)
The paper discharge roller 109 will be described with reference to FIG.

    The paper discharge roller 109 includes a pair of rollers, and is configured to discharge the paper 171 that has passed through the fixing unit 108 onto a paper discharge tray 113 formed on the upper portion of the main body casing 111.

[Operations of direct tandem color laser printer during printing]
Next, the operation during printing of the color laser printer 100 will be described. This operation is realized by the CPU 1030 shown in FIG. 10 controlling each unit.

  First, the surface of the photosensitive drum 104 is uniformly charged by the charger 142, and this surface is exposed by the scanner unit 102 corresponding to magenta, cyan, yellow, and black images. The electrostatic latent image formed on the surface of the photosensitive drum 104 (104M, 104C, 104Y, 104K) by the magenta developing cartridge 131M, the cyan developing cartridge 131C, the yellow developing cartridge 131Y, and the black developing cartridge 131K. Are developed to each color by attaching magenta toner, cyan toner, yellow toner, and black toner, respectively.

  The paper feed unit 107 is configured to send out the paper 171 at a predetermined timing with the image forming process by the process unit 103, and the paper 171 sent out from the paper feed tray 172 is conveyed by the registration rollers 174. It is conveyed to the belt 154.

  The developer images of the respective colors are formed with a slight time difference according to the moving speed of the conveying belt 154 and the positions of the photosensitive drums 104M, 104C, 104Y, and 104K. Then, the developer images of the respective colors are superimposed and transferred onto the paper 171 on the conveyance belt 120 sandwiched between the photosensitive drum 104 and the transfer roller 106.

  The developer image is fixed on the paper 171 in the fixing unit 108 and discharged onto the paper discharge tray. In this way, color printing can be performed on the paper 171.

[Operation when detecting the density of a direct tandem color laser printer]
The operation at the time of density detection for color correction processing of the color laser printer 100 will be described with reference to FIGS. This operation is realized by a later-described CPU 1030 shown in FIG. 10 controlling each unit. This operation is performed when the color laser printer 100 is turned on, when the standby state continues for a certain period of time, or when the toner is newly replaced.

  The paper feed roller 173 is controlled so as not to rotate. Then, a main motor (not shown) is driven, and the photosensitive drum 104 is rotationally driven through a driving gear (not shown). Further, a forward bias is applied to the transfer roller 106, and an electric field is generated for the developer to move from the photosensitive drum 104 to the transfer roller 106.

  The surface of the photosensitive drum 104 is uniformly positively charged by the charger 142, and the color correction processing visible image 1110 is exposed by scanning control of the laser beam from the scanner unit 102. Each color correction processing visible image 1110 has a solid area and a halftone area. Thereafter, when the electrostatic latent image of each color correction processing visible image 1110 formed on the photosensitive drum 104 reaches a position facing the developing roller 132, each color correction image is developed into a visible image for each color correction processing. An image 1110 is formed.

The color correction processing visible images 1110 developed on the photosensitive drum 104 are magenta correction processing visible images 1110M, cyan correction processing visible images 1110C, yellow correction processing visible images 1110Y, and black correction processing. Transferred to the conveyor belt 154 in the order of the visible image 1110K. Each density correction processing visible image 1110 on the transferred conveyance belt 154 is detected by the density detection sensor 156. The density detection sensor 156 is an optical sensor that detects the density of each color correction visible image 1110 by measuring the reflectance of the surface of each color correction visible image 1110 at the position Pd. In this way, density detection is performed.
[Control operation when a crack occurs in a direct tandem color laser printer]
Control of an image forming operation when a crack occurs in the color laser printer 100 will be described with reference to FIGS.

  FIG. 10 is a block diagram schematically showing a control device that controls the image forming operation and the density detection operation when the color laser printer 100 is cracked. In the first embodiment, the description of the components that perform the same operation as the control of the image forming operation when a crack occurs in the 4-cycle color laser printer will be omitted.

  When the crack position determination program 1011 is executed by the CPU 1030, the crack position determination program 1011 has a function of grasping the position of the crack Pc according to the crack detection signal detected by the first optical sensor 157 and the time for which the transport belt mechanism unit 105 travels once. Achieved. This function is a crack position determination function 1721 shown in FIG. 17B, which corresponds to the crack position determination means of the present invention.

  When the control program 1013 is executed by the CPU 1030, the position of the crack Pc generated on the transport belt 154 is grasped by the crack position determination function 1721 and is determined by the position where the crack Pc is generated, and is opposite to the moving direction of the transport belt 905. The leading portion of the sheet is transferred to a predetermined position on the conveying belt 154 in the direction, or the leading portion of each color correction processing visible image 1110 along the moving direction DT of the conveying belt 154 is transferred. A controlled function is achieved. This function is a control function 1723 shown in FIG. 17B, which corresponds to the control means of the present invention.

  The predetermined position is determined as follows. The time required for the conveyance belt 154 to move from the position PD to the position where the magenta toner is transferred, that is, the position Pm sandwiched between the photosensitive drum 104M and the transfer roller 106M, is counted, and this time is stored in the memory 1019 in advance. Is done. The length y is the distance between the position on the conveyor belt 154 to which the leading edge of the image is transferred and the crack, and a desired length y is preset and stored in the memory 519. This length y is set smaller than the length along the moving direction DT of the intermediate transfer belt 51 in the minimum non-image forming area. When the generated crack Pc is located at the position PD detected by the first optical sensor 157 shown in FIG. 9, the crack position determination function 1721 determines the position of the crack Pc. After the crack Pc passes through the crack detection position PD, when the time measured for the length y has elapsed in addition to the time stored in the memory 1019, the leading edge of the magenta toner image is conveyed from the photosensitive drum 104M. The exposure start timing is controlled so as to be transferred to the belt 154. When the image forming operation is executed, the paper feed timing of the registration roller 174 is controlled so that the transferred magenta toner image is accurately aligned with the paper 171 being conveyed.

  When the stop program 1016 is executed by the CPU 1030, when the length of the crack conveying belt 154 along the width direction DW reaches the above-described Ll, or a plurality of cracks are generated, the control function 1723 supplies the paper 171. Even if the timing or the transfer position of the developer image is shifted, the following function is achieved when the paper 171 or a part of the developer image is cracked. First, the paper feeding unit 107 is stopped so that the paper 171 is not fed. Next, when an image is formed on the paper 171, and the paper 171 is discharged onto the paper discharge tray 113 formed on the upper portion of the main body casing 111 by the paper discharge roller 109, the scanner unit 102, the process unit 103, the transport belt The operations of the mechanism unit 105, the transfer roller 106, and the paper discharge roller 109 are stopped. This function is a stop function 1726 shown in FIG. 17B and corresponds to the image forming operation stop means of the present invention.

  The density detection sensor 156 is an optical sensor that detects the density of the color correction processing pattern 1110 by measuring the reflectance of the surface of the color correction processing pattern 1110 for color correction processing of the color laser printer 100.

  12 and 13 are control flowcharts of the image forming operation when the color laser printer 100 is cracked. 14 and 15 are control flowcharts of the density detection operation when the color laser printer 100 is cracked.

(Image formation control operation when a crack occurs)
First, FIG. 10 and FIG. 12 are used to predict that the crack Pc generated on the conveyor belt 154 has reached the size at which the image forming operation must be stopped by the number of repeated movements of the conveyor belt 154. I will explain.

  When the color laser printer 100 is activated (S1201), it is checked whether or not a crack Pc has occurred on the conveyor belt 154 (S1202).

  As with the intermediate transfer belt 51 of the first embodiment, the crack Pc also occurs in the belt portion in the vicinity of the joint 159 of the guide rib 155 provided on the inner peripheral surface side of the belt end portion in the width direction of the conveyor belt 154. It's easy to do.

  If no crack detection signal is detected (S1203: No), the photosensitive drum 104 is exposed so that the developer image is transferred onto the paper 171 fed by the paper feed roller 173 and conveyed by the conveying belt 154. The process is started (S1205). When image formation of the final data is confirmed (S1206: Yes), the image forming operation is ended (S1208). If image formation of the final data has not been confirmed (S1206: No), it is checked again whether or not a crack Pc has occurred on the conveyor belt 154 (S1202).

  When the crack detection signal is detected (S1203: Yes), the number of occurrences of cracks while the conveyor belt 154 moves one round is counted. When the number of occurrences of cracks is counted as “1” (S1210: No), it is counted how many times the conveyor belt 121 has moved (S1211).

  When the counted number of movements of the conveyor belt 154 reaches the specified number of times stored in the storage unit 911 (S1213: Yes), it is notified that the conveyor belt 154 is to be replaced (S1223).

  When the number of belt movements reaches the specified number (S1213: Yes), the image forming operation is stopped (S1224).

  If the conveying belt 154 is replaced with a new belt after the image forming operation is stopped (S1225: Yes), the control operation is ended (S1227). If the transport belt 154 has not been replaced with a new belt (S1225: No), it is checked whether the transport belt 154 has been replaced or not. The determination as to whether or not the conveyor belt 154 has been replaced is as described in the four-cycle color laser printer 1 of the first embodiment.

  If the counted number of movements of the conveyor belt 154 has not reached the specified number of times stored in the memory 1019 (S1213: No), the position of the crack Pc is grasped (S1214). When the position of the crack Pc is grasped, the image forming position is determined according to the grasped crack position (S1215), and exposure is started so that the developer image is transferred to the image forming position (S1216). The image forming position is determined as a position where the image forming area where the developer image is to be transferred onto the paper 171 does not cover the crack Pc.

  This is because, even though the developer image is not directly transferred onto the conveyance belt 154, if there is a crack Pc at the contact position between the photosensitive drum 104 and the transfer roller 106, that is, the developer image transfer position, the developer image is transferred. This is because a discharge due to the application of a transfer bias occurs and the developer may be scattered. Further, at the position covering the crack Pc, it is difficult to apply an electric field, and there is a possibility that the developer does not sufficiently get on the paper 171. Further, it is preferable that the leading end portion of the sheet 171 to which the developer image is to be transferred is determined so as not to get over the crack Pc. This is because if the paper 171 is fed onto the crack Pc by the registration roller 174, the transportability of the paper is deteriorated, and the transfer of the developer of each color may be shifted.

  When image formation of the final data is confirmed (S1217: Yes), the image forming operation is ended (S1219). If image formation of the final data has not been confirmed (S1217: No), the number of occurrences of cracks Pc while the conveyor belt 154 moves once again is counted.

  When the number of occurrences of cracks is counted 2 or more (S1210: Yes), the time for the transport belt 154 to move over the length of each interval between the two adjacent cracks Pc is timed, and the two adjacent The length of each interval between the cracks Pc is grasped (S1220).

  If the maximum crack interval among the recognized crack intervals is narrower than the maximum sheet length (S1221: Yes), the sheet 171 will be applied to one of the plurality of cracks, so the conveying belt 154 is replaced. The effect is notified (S1223).

  If the maximum crack interval is wider than the maximum sheet length (S1221: No), the number of rotations of the conveyor belt 154 is counted (S1211).

  Next, a case where the second optical sensor 158 detects that the crack Pc generated on the conveying belt 154 has reached a size at which the image forming operation must be stopped is described with reference to FIGS. 10 and 13. explain. FIG. 13 is a diagram in which only S1211 and S1213 in the flowchart of FIG. 12 are replaced with S1311 and S1313, and only this changed portion will be described.

  When the number of occurrences of the crack Pc is counted as “1” (S1310: No), the crack Pc reaches the position of the length Ll along the width direction DW from one end of the conveyance belt 154 in the width direction DW. Is checked (S1311). Here, whether or not the length of the crack Pc has reached the position of the length Ll is checked by the second optical sensor 158, but the relationship between the second optical sensor 158 and the tip position of the length Ll is This is equivalent to the relationship between the second optical sensor 58 and the tip position of the length Ll described in the embodiment.

  When it is detected that the crack has reached the position of the length Ll (S1313: Yes), it is notified that the conveyor belt 154 is to be replaced (S1323).

  When it is detected that the crack Pc has reached the position of the length L1 (S1313: Yes), the image forming operation is stopped (S1324).

  If the conveying belt 154 is replaced with a new belt after the image forming operation is stopped (S1325: Yes), the control operation is ended (S1327). If the conveyor belt 154 has not been replaced with a new belt (S1325: No), it is checked whether it has been replaced until it is replaced.

  If it is not detected that the crack Pc has reached the position of the length Ll (S1313: No), the position of the crack is grasped (S1314). When the position of the crack is grasped, the image forming position is determined according to the grasped crack position (S1315), and exposure is started so that the developer image is transferred to the image forming position (S1316). When the image formation of the final data is confirmed (S1317: Yes), the image forming operation is ended (S1319). If the image formation of the final data has not been confirmed (S1317: No), the number of occurrences of cracks Pc while the conveyor belt 154 moves once again is counted.

(Concentration detection control operation when a crack occurs)
First, referring to FIG. 10 and FIG. 14, the case where the crack Pc generated on the transport belt 154 has reached the size at which the image forming operation must be stopped is predicted by the number of repeated movements of the transport belt 154. To explain.

  When the color laser printer 100 is activated (S1401), it is checked whether a crack Pc has occurred on the transport belt 154 (S1402).

  If no crack detection signal is detected (S1403: No), exposure of the photosensitive drum 104 is started (S1405). When each color correction processing visible image 1110 is transferred to the transport belt 154, a density detection operation is performed, and then the density detection operation is terminated (S1406).

  When the crack detection signal is detected (S1403: Yes), the number of occurrences of the crack Pc while the conveyor belt 154 moves once is counted. When the number of occurrences of cracks Pc is counted as “1” (S1408: No), how many rounds the conveyor belt 154 has moved is counted (S1409).

  When the counted number of movements of the conveyor belt 154 reaches the specified number of times stored in the memory 1019 (S1411: Yes), it is notified that the conveyor belt 154 is to be replaced (S1419).

  When the number of belt movements reaches the specified number (S1411: Yes), the image forming operation is stopped (S1420).

  Here, an operation for stopping image formation will be described. In order to prevent the sheet 171 from being conveyed during the density detection operation, the driving of the sheet feeding unit 107 has already been stopped. When the number of belt movements reaches the specified number, the sheet 171 is not conveyed, so immediately, the photosensitive drum 104, the scanner unit 102, the process unit 103, the conveyance belt mechanism unit 105, the transfer roller 106, the fixing unit 108, and the discharge unit. The operation of the paper roller 109 is stopped.

  If the conveyance belt 154 is replaced with a new belt after the image forming operation is stopped (S1421: Yes), the density detection operation is ended (S1423). If the transport belt 154 has not been replaced with a new belt (S1421: No), it is checked whether or not it has been replaced until it is replaced.

  If the counted number of movements of the conveyor belt 154 has not reached the specified number of times stored in the memory 1019 (S1411: No), the position of the crack Pc is grasped (S1412). When the position of the crack Pc is grasped, the image forming position is determined according to the grasped crack position (S1413), exposure is started so that the developer image is transferred to the image forming position, and density detection is performed. (S1414). The image forming position is determined as a position where the leading portion It of the color correction processing visible image 1110 does not cover the crack Pc.

  Thereby, the color correction processing visible image 1110 can be prevented from being transferred onto the crack Pc.

  When the density of each color correction processing visible image 1110 is detected, the density detection operation ends (S1415).

  When the number of occurrences of cracks Pc is counted 2 or more (S1408: Yes), the time for which the conveyor belt 154 moves over the length of all the intervals between the two adjacent cracks Pc is timed, and the two adjacent The length of each interval between the two cracks Pc is grasped (S1416).

  If the maximum crack interval among the grasped crack intervals is shorter than the maximum sheet length (S1417: Yes), the sheet 171 will be caught in any one of the plurality of cracks Pc, so the conveyor belt 154 is replaced. A message to the effect is notified (S1419). If the maximum crack interval is wider than the maximum sheet length (S1417: No), the number of rotations of the conveyor belt 154 is counted (S1409).

  Next, the case where the second optical sensor 158 detects that the crack Pc generated on the conveying belt 154 has reached a size at which the image forming operation must be stopped will be described with reference to FIGS. 10 and 15. To do. FIG. 15 is a diagram in which only the portions of S1409 and S1411 in the flowchart of FIG.

  When the number of occurrences of the crack Pc is counted as “1” (S1508: No), the crack Pc reaches the position of the length Ll along the width direction DW from one end of the conveyance belt 154 in the width direction DW. Is checked (S1509).

  When it is detected that the crack Pc has reached the position of the length Ll (S1511: Yes), it is notified that the conveyor belt 154 is to be replaced (S1519).

  When it is detected that the crack Pc has reached the position of the length Ll (S1511: Yes), the image forming operation is stopped (S1520).

  If the conveyance belt 154 is replaced with a new belt after the image forming operation is stopped (S1521: Yes), the density detection operation is ended (S1523). If the transport belt 154 has not been replaced with a new belt (S1521: No), it is checked whether or not it has been replaced until it is replaced.

  If it is not detected that the crack Pc has reached the position of the length Ll (S1511: No), the position of the crack Pc is grasped (S1512). When the position of the crack Pc is grasped, the image forming position is determined according to the grasped crack position (S1513), and exposure is started so that the developer image is transferred to the image forming position. When each color correction processing visible image 1110 is transferred to the conveyor belt 154, density detection is performed (S1514), and then the density detection operation is terminated (S1515).

[Modification]
In addition, this invention is not limited to the said embodiment, Of course, various improvement and deformation | transformation are possible within the range which does not deviate from the summary of this invention.

  For example, in the intermediate transfer belt 51 and the conveyance belt 154 of the present embodiment, the guide ribs 55 are bonded to the inner peripheral surfaces of both ends in the width direction of the belt to prevent meandering. 16 (a) and 16 (b), a flange 1630 is provided at the end of at least one of the pair of rollers for stretching the seamless belt 1610, and the end of the belt 1610 in the width direction is the flange. By striking 1630, the belt 1610 may be prevented from meandering.

  Further, when a crack occurs on the seamless belt, in the first embodiment, the leading portion of the sheet 71 is aligned with the positioning mark 56 located at a position opposite to the moving direction of the belt from the position where the crack occurs. In the second embodiment, cracks were avoided by transferring the developer image by aligning the leading portion of the developer image at a predetermined position opposite to the moving direction of the belt from the position where the crack occurred. However, the transfer position may be controlled so that the reference position is provided at a predetermined position in the moving direction of the belt from the crack generation position, and the rear end portion of the sheet or developer image is aligned therewith. The predetermined position is set to a position where the leading edge of the sheet or developer image does not get cracked even if the trailing edge of the sheet or developer image is aligned with this position.

1 is an overall configuration diagram of a four-cycle color laser printer 1. FIG. 3 is a perspective view of an intermediate transfer belt 51. FIG. 3 is a side view of a first optical sensor 57 and a second optical sensor 58. FIG. 2 is a block diagram showing a configuration of a control device of a four-cycle color laser printer 1. FIG. It is a timing chart which shows the relationship between the sensor light-receiving part output voltage after a sensor light emission part 57a starts light emission, and an output signal. 4 is a printing operation control flowchart in the case of predicting the size of a crack by the number of repeated movements of the intermediate transfer belt 51 in the 4-cycle color laser printer 1. 5 is a printing operation control flowchart when a second optical sensor 58 inspects the size of a crack in the 4-cycle color laser printer 1. 1 is an overall configuration diagram of a direct tandem color laser printer 100. FIG. 6 is a perspective view of a conveyor belt 154. FIG. 2 is a block diagram illustrating a configuration of a control device of a direct tandem color laser printer 100. FIG. It is a top view of the visible image 1110 for color correction processing. 5 is a printing operation control flowchart in the case where the size of a crack is predicted by the number of repeated movements of the conveyance belt 154 in the direct tandem type color laser printer 100. 5 is a printing operation control flowchart when the second optical sensor 158 inspects the size of a crack in the direct tandem color laser printer 100. FIG. 4 is a density detection operation control flowchart in the case of predicting the size of a crack by the number of repeated movements of the conveyance belt 154 in the direct tandem type color laser printer 100. 5 is a density detection operation control flowchart when the second optical sensor 158 inspects the size of a crack in the direct tandem color laser printer 100. FIG. (A) is a plan view of a portion where the seamless belt 1610 is stretched around a roller 1620 provided with a flange 1630, and (b) is a plan view of a portion where the seamless belt 1610 is stretched around a roller 1620 provided with a flange 1630. is there. (A) is a functional configuration table of the 4-cycle color laser printer 1, and (b) is a functional configuration table of the direct tandem color laser printer 100. FIG. 6 is an explanatory diagram of an image transfer position when a crack occurs in the intermediate transfer belt 51. (A) is an image forming area on the intermediate transfer belt 51 when the positioning mark 56a is located at the detection position PF and exposure is started at the same time, and (b) is exposed at the same time as the crack Pc is located at the detection position PF. (C) shows an image forming area on the intermediate transfer belt 51, and intermediate transfer when the exposure start time is delayed by the time that the intermediate transfer belt 51 moves the length Lb after the crack Pc is located at the detection position PF. (D) is an image forming area on the belt 51. The intermediate transfer when the exposure start time is delayed by the time required for the intermediate transfer belt 51 to move by the length Lb-Lc after the reference mark 56b is located at the detection position PF. The image forming area on the belt 51, (e), the exposure start time is the time required for the intermediate transfer belt 51 to move the length (Lb−Lc) + (Ld + α) after the reference mark 56b is positioned at the detection position PF. This is an image forming area on the intermediate transfer belt 51 when delayed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 4 cycle system color laser printer 2 Scanner unit 3 Process part 4 Belt photoreceptor mechanism part 5 Intermediate transfer belt mechanism part 51 Intermediate transfer belt 52 1st intermediate transfer belt roller 53 2nd intermediate transfer belt roller 54 3rd intermediate transfer belt roller 55 Guide rib 56 Positioning mark 57 First optical sensor 58 Second optical sensor 59 Seam 6 Transfer roller 7 Paper feed unit 71 Paper 75 Registration roller 8 Fixing unit 9 Paper discharge roller 100 Direct tandem color laser printer 102 Scanner unit 103 Process unit 104 Photosensitive drum 105 Conveying belt mechanism 151 First conveying belt roller 152 Second conveying belt roller 153 Third conveying belt roller 154 Conveying belt 155 Guide rib 156 Density detection sensor 157 First optical sensor 158 second optical sensor 159 joint 106 transfer roller 107 paper feeding unit 171 sheet 174 registration rollers 108 fixing unit 109 discharge rollers 510,1010 ROM
519, 1019 Memory 520, 1020 RAM
530, 1030 CPU
540, 1040 Drive device 550, 1050 Display 1711 Identification function 1712 Mark count function 1721 Crack position determination function 1713, 1723 Control function 1714, 1724 Crack count function 1715, 1725 Timekeeping function 1716, 1726 Stop function 1717, 1727 Movement repeat count function 1718 Discriminating function

Claims (23)

A seamless belt carrying a developer image;
Developing means for forming the developer image;
In an image forming apparatus having
Detection means for detecting the presence or absence of cracks on the seamless belt and generating a detection signal;
According to the detection signal from the detection means, crack position determination means for determining the occurrence position of cracks on the seamless belt,
Control means for controlling the development start timing of the developing means so that the developer image does not crack according to the crack occurrence position determined by the crack position determining means;
An image forming apparatus comprising: Exposure means for forming an electrostatic latent image on the photoreceptor;
Developing means for developing a latent image formed on the photoreceptor to form a developer image;
A seamless belt stretched by a plurality of rollers and movable;
First transfer means for transferring the developer image developed by the developing means to the seamless belt at a first transfer position where the photoreceptor and the seamless belt are in contact with each other;
Second transfer means for transferring the developer image transferred to the seamless belt by the first transfer means to a recording medium at a second transfer position where the seamless belt and the recording medium contact;
A paper feeding means for feeding out the recording medium so that the head of the developer image formed on the seamless belt and the head of the developer image forming area on the recording medium coincide with each other at the second transfer position;
A paper discharge means for discharging the recording medium onto which the developer image has been transferred by the second transfer means;
In an image forming apparatus having
One or more positioning marks provided on the outer peripheral surface side of the belt end in the width direction of the seamless belt;
First detection means for detecting the presence or absence of a crack on the seamless belt and the presence or absence of the positioning mark and generating a detection signal;
Identification means for identifying a crack and a positioning mark according to the detection signal generated by the first detection means;
Mark counting means for counting the number of positioning marks identified by the identifying means within a time during which the seamless belt travels once and grasping the position of the positioning marks on the seamless belt;
After the crack generated on the seamless belt is identified by the identification means, a positioning mark that is first identified by the identification means is set as a reference mark, and the reference mark whose position is grasped by the mark counting means is set. Control means for controlling the exposure start timing of the exposure means so that the predetermined position of the developer image and the leading edge of the developer image coincide with each other at the first transfer position;
An image forming apparatus comprising: The image forming apparatus according to claim 2, wherein guide ribs for preventing meandering are provided on the inner peripheral surface side of the belt end portion in the seamless belt width direction. The first detection means detects the presence / absence of the positioning mark and the presence / absence of a crack by a first optical sensor provided facing the belt end in the seamless belt width direction, and generates a detection signal, The image forming apparatus according to claim 2 or 3. The image forming apparatus according to claim 4, wherein the first detection unit is provided at a position facing the roller in a curved surface portion where the seamless belt is wound around the roller. Crack counting means for counting the number of cracks identified by the identifying means within the time that the seamless belt travels once,
Of the plurality of cracks counted by the crack counting means, timing means for grasping by measuring the interval between two cracks;
With
The control means causes the image forming operation stop means to perform a stop operation when the maximum value of the interval between the two cracks grasped by the time measuring means is smaller than the length from the front end portion to the rear end portion of the recording medium. The image forming apparatus according to claim 2, wherein the image forming apparatus is an image forming apparatus. The image forming operation stop means stops the paper feeding means, and after the recording medium is discharged by the paper discharge means, the photosensitive member, the exposure means, the developing means, the seamless belt, and the first transfer means. 7. The image forming apparatus according to claim 2, wherein each of the second transfer unit and the paper discharge unit is stopped. A memory that stores in advance a predicted value of the number of repetitions of movement of the seamless belt until the crack reaches a predetermined position in the seamless belt width direction after the identification means identifies the crack that has occurred on the seamless belt. Means,
A movement repetition number counting means for counting the number of movement repetitions of the seamless belt;
With
The control means causes the image forming operation stop means to perform a stop operation when the seamless belt movement repeat count counted by the movement repeat count count means reaches the predicted value stored in the storage means. The image forming apparatus according to claim 2, wherein the image forming apparatus is an image forming apparatus. Second detection means for detecting that a crack has reached the predetermined position by a second optical sensor provided at a predetermined position in the seamless belt width direction and generating a detection signal;
Crack determination means for determining the presence or absence of cracks at the predetermined position according to the detection signal generated by the second detection means;
With
8. The control unit according to claim 2, wherein when the crack determination unit determines that the crack has reached the predetermined position, the control unit causes the image forming operation stop unit to perform a stop operation. An image forming apparatus according to claim 1. The image forming apparatus according to claim 9, wherein the second detection unit is provided at a position facing the roller in a curved surface portion where the seamless belt is wound around the roller. 11. The image forming apparatus according to claim 7, further comprising a notification unit that notifies the user of replacement of the seamless belt when the control unit causes the image forming operation stop unit to perform a stop operation. . Exposure means for forming an electrostatic latent image on the photoreceptor;
Developing means for developing a latent image formed on the photoreceptor to form a developer image;
A seamless conveyor belt that is stretched by a plurality of rollers and is movably provided to convey the recording medium;
Transfer means for transferring the developer image developed by the developing means to a recording medium at a transfer position where the photoreceptor and the recording medium are in contact;
Paper feeding means for feeding out the recording medium so that the head of the developer image on the photosensitive member and the head of the developer image forming area on the recording medium coincide with each other at the transfer position;
A paper discharge means for discharging the recording medium onto which the developer image has been transferred by the transfer means;
In an image forming apparatus having
First detection means for detecting the presence or absence of cracks on the conveyor belt and generating a detection signal;
Crack position determination means for determining the occurrence position of the crack according to the detection signal generated from the first detection means and the time for which the conveyor belt makes one round movement;
Control means for controlling the front end of the developer image to be located at a predetermined position on the conveying belt in the direction opposite to the moving direction of the conveying belt from the crack occurrence position determined by the crack position determining means;
An image forming apparatus comprising: The control means grasps a crack generation position according to a detection signal generated from the first detection means and a time during which the conveyor belt moves around, and the direction opposite to the movement direction of the conveyor belt from the crack generation position. The image forming apparatus according to claim 12, wherein control is performed so that the leading end of the recording medium is positioned at a predetermined position on the conveyance belt. A density detecting means for detecting the density of the developer image;
When the density is detected by the density detector, the transfer unit directly transfers the developer image for density detection to the transport belt,
The control means grasps a crack generation position according to a detection signal generated from the first detection means and a time during which the conveyor belt moves around, and is reverse to the movement direction of the conveyor belt from the crack generation position. 13. The image forming apparatus according to claim 12, wherein control is performed so that a leading end portion of the developer image for density detection is positioned at a predetermined position on the transport belt. 15. The image forming apparatus according to claim 12, wherein guide ribs for preventing meandering are provided on the inner peripheral surface side of the belt end portion in the conveyance belt width direction. 16. The image forming apparatus according to claim 12, wherein the first detection unit detects the presence or absence of a crack by a first optical sensor provided at a belt end in the conveyance belt width direction. . The image forming apparatus according to claim 16, wherein the first detection unit is provided at a position facing the roller in a curved surface portion around which the transport belt is wound around the roller. Crack counting means for counting the number of cracks detected by the first detection means within the time that the conveyor belt makes a round;
Of the plurality of cracks counted by the crack counting means, timing means for grasping by measuring the interval between two cracks;
With
The control means causes the image forming operation stop means to perform a stop operation when the maximum value of the interval between the two cracks grasped by the time measuring means is smaller than the length from the front end portion to the rear end portion of the recording medium. The image forming apparatus according to claim 12, wherein the image forming apparatus is an image forming apparatus. The image forming operation stop means stops the paper feeding means, and after the recording medium is discharged by the paper discharge means, the photoconductor, the exposure means, the developing means, the transport belt, the transfer means, and the 19. The image forming apparatus according to claim 18, wherein each of the paper discharge means is stopped. Preliminarily storing a predicted value of the number of repetitions of movement of the conveyor belt from when the first detecting means detects a crack generated on the conveyor belt until the crack reaches a predetermined position in the conveyor belt width direction. Storage means,
A movement repetition number counting means for counting the number of movement repetitions of the conveyor belt;
With
The control means causes the image forming operation stop means to perform a stop operation when the number of movement repetitions of the conveying belt counted by the movement repetition number count means reaches the predicted value stored by the storage means. The image forming apparatus according to claim 12, wherein the image forming apparatus is an image forming apparatus. The second optical sensor provided at a predetermined position in the transport belt width direction includes second detection means for detecting that a crack has reached the predetermined position and generating a detection signal,
20. The control unit according to claim 12, wherein when the second detection unit detects that the crack has reached the predetermined position, the control unit causes the image forming operation stop unit to perform a stop operation. The image forming apparatus according to any one of the above. The image forming apparatus according to claim 21, wherein the second detection unit is provided at a position facing the roller in a curved surface portion around which the conveyance belt is wound around the roller. 23. The image forming apparatus according to claim 18, further comprising a notification unit that notifies the user of replacement of the seamless belt when the control unit causes the image forming operation stop unit to perform a stop operation. .

Images