JPH11327246A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive image forming device capable of preventing the deterioration in image quality. SOLUTION: The detection part of a registration sensor 38 is arranged at a specified position on the bearing mechanism of a driving roller 24 being a carrying mechanism positioned on an upstream side in a carrying direction from the just above position A of the rotary shaft of the roller 24 and on a downstream side in the carrying direction from a position B on the most upstream side of the roller 24. The specified position on the bearing mechanism is a position opposed to a specified area where a registration pattern is formed on a carrying belt 21 and also a position where a space between the surface of the belt 21 and a lens at the detection part of the sensor 38 nearly corresponds to the focal distance of the lens.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applicable to a color printer, a color digital copying machine, etc., and forms an image for each color component on a plurality of photoconductors and superimposes the color image on a recording medium. The present invention relates to an image forming apparatus for forming.

[0002]

2. Description of the Related Art An image forming apparatus such as a multi-drum type color printer or a multi-drum type color digital copier has a plurality of image forming units corresponding to color components separated by color separation. An optical scanning device that provides a plurality of laser beams intensity-modulated based on image data, a transport mechanism that transports a sheet as a recording medium in a predetermined direction, and the like are provided.

[0005] A plurality of image forming units are arranged in parallel at predetermined intervals along the transport direction of the transport mechanism. Each image forming unit forms a cartridge type unit integrated for each color component, and is detachably formed in the image forming apparatus main body. Each of these image forming units is provided from a photoconductor drum for holding an image corresponding to a color component, a charging device for charging the surface of the photoconductor drum to a predetermined potential, and an optical scanning device on the surface of the charged photoconductor drum. A developing device that supplies toner as a developer to the electrostatic latent image formed by the laser beam to be formed to form a toner image;
The image forming apparatus includes a transfer device that transfers the toner image formed on the photosensitive drum onto a sheet serving as a recording medium, a cleaning device that cleans the surface of the photosensitive drum onto which the toner image has been transferred, and the like. These image forming units can be replaced in units of each unit according to the lifetime of the photosensitive drum.

The transport mechanism includes a transport belt formed by an endless belt, a drive roller for driving the transport belt in one direction, and a driven roller spaced a predetermined distance from the drive roller. The transport belt is wound and stretched between a driving roller and a driven roller.

In an image forming apparatus having such a structure,
If the toner images of the respective color components that are sequentially superimposed on the paper do not accurately overlap, a color shift occurs in the image formed on the paper. The causes of the color shift include a unique inclination and position shift of each image forming unit, a shift in the formation timing of an image formed through each image forming unit, and a time when each image is superimposed on a sheet. Is known.

For this reason, a predetermined pattern, that is, a registration pattern is formed on the conveyor belt through each image forming section, and these registration patterns are detected by a registration sensor attached to a predetermined position of the conveyor mechanism. The color misregistration is corrected by correcting the exposure position on each photosensitive drum or the relative position of the exposure position between image forming units. According to this method, the position of the image to be actually transferred is detected, and the position shift of the image transferred on the paper is corrected, so that the color shift can be corrected.

[0007]

However, a registration sensor for correcting such a color shift is provided with a driving roller and a driven roller of a transport mechanism via components such as a frame, a stay, and a holder of the image forming apparatus main body. It is attached between. When used in such a state for many years, the transport belt is stretched, and a greater amplitude is generated at a position closer to the center of the transport belt. This amplitude occurs in a direction that changes the distance between the conveyor belt and the registration sensor.

That is, the greater the distance from the driving roller and the driven roller, the greater the amplitude occurs. If the registration sensor is located at a position facing the conveying belt, while the conveying belt is being conveyed, ie, the conveying While the belt has an amplitude, the positional deviation is corrected by detecting the registration pattern. At this time, the distance between the registration sensor and the transport belt is not constant, and there is a possibility that the registration sensor may erroneously detect the registration pattern.

As a result, it is not possible to sufficiently correct the image position shift, and there is a possibility that color shift may occur. Therefore, in such an image forming apparatus, there has been a problem that the image quality of an image transferred to a sheet is significantly impaired when the image forming apparatus has been used for many years.

When the registration sensor is mounted on the frame of the image forming apparatus via a holder or a stay, the distance between the registration sensor mounted on the main body and the transport belt of the transport mechanism is set to a predetermined value. Needs to correct individual mounting errors and the like. For this reason,
It is necessary to make adjustments using jigs or to increase the accuracy using expensive parts.

Therefore, there arises a problem that the cost of the image forming apparatus main body and the manufacturing cost of the image forming apparatus increase. SUMMARY OF THE INVENTION An object of the present invention is to provide a low-cost image forming apparatus capable of preventing image quality deterioration.

[0012]

SUMMARY OF THE INVENTION The present invention has been made based on the above problems, and according to the first aspect of the present invention, there is provided a method for forming a plurality of developer images on a plurality of photosensitive members. An image forming unit, a pair of rollers arranged at a predetermined interval, and a conveying unit having a belt stretched over the pair of rollers, and conveying a recording medium toward the plurality of photoconductors; A detection unit that is disposed on the upstream side in the conveyance direction from the rotation axis of the roller disposed on the downstream side in the conveyance direction of the recording medium by the conveyance unit and that faces the belt surface; Detecting means for detecting a given predetermined image pattern, control means for detecting an image pattern formed on the belt by the detecting means, and adjusting an image forming position on each photoconductor by each image forming means. , Equipped Image forming apparatus is provided, characterized in that the.

According to the second aspect of the present invention, a plurality of image forming means for forming each developer image on a plurality of photosensitive members, a pair of rollers arranged at a predetermined interval, and the pair of rollers Transport means for transporting the recording medium toward the plurality of photoconductors, a bearing mechanism rotatably receiving a rotating shaft of a roller of the transport means, and At a predetermined position on the upstream side in the conveyance direction from the rotation axis of the roller disposed on the downstream side in the conveyance direction, the detection mechanism is disposed integrally with the bearing mechanism, and has a detection unit facing the belt surface. Detecting means for detecting a predetermined image pattern formed by the developer; and detecting the image pattern formed on the belt by the detecting means, and determining an image forming position on each photoconductor by each image forming means. Image forming apparatus is provided, characterized in that and a control means for settling.

According to the third aspect of the present invention, a plurality of image forming means for forming each developer image on the plurality of photosensitive members, a pair of rollers arranged at a predetermined interval, and a pair of the rollers Transport means for transporting the recording medium toward the plurality of photoconductors, a bearing mechanism rotatably receiving a rotating shaft of a roller of the transport means, and a transport mechanism for transporting the recording medium to the plurality of photoconductors. The belt is disposed integrally with the bearing mechanism at a predetermined position on the upstream side in the conveying direction from the rotation shaft of the roller disposed on the downstream side in the conveying direction, and on the downstream side in the conveying direction from the most upstream position of the roller. Detecting means for detecting a predetermined image pattern formed by a developer in a predetermined area on the belt, and detecting an image pattern formed on the belt by the detecting means; An image forming apparatus comprising: the control means for adjusting the image forming position onto the photosensitive member by the image forming means, is provided.

According to the present invention, a plurality of image forming means for forming each developer image on the plurality of photosensitive members, a pair of rollers arranged at a predetermined interval, and the pair of rollers Conveying means for conveying a recording medium toward the plurality of photoconductors, a bearing mechanism rotatably receiving a rotating shaft of a roller of the conveying means, and generating a light beam. A light emitting means for receiving the light beam, generating an electric signal corresponding to the amount of received light, guiding the light beam generated by the light emitting means to the detecting section, and receiving the light beam detected by the detecting section An optical fiber that guides the means, and the detecting unit is located on the upstream side in the transport direction from the rotation axis of the roller disposed downstream in the transport direction of the transport unit, and is located below the most upstream position of the roller in the transport direction. Detecting means for detecting a predetermined image pattern formed by a developer in a predetermined area on the belt, the detection means being provided integrally with the bearing mechanism at a predetermined position on the side of the belt, and having a detection unit facing the belt surface. A control unit for adjusting an image forming position on each photoconductor by each image forming unit based on an electric signal output from a light receiving unit of the detecting unit. Is done.

According to the fifth aspect of the present invention, a plurality of image forming means for forming each developer image on the plurality of photosensitive members, a pair of rollers arranged at a predetermined interval, and the pair of rollers Conveying means for conveying a recording medium toward the plurality of photoconductors, a bearing mechanism rotatably receiving a rotating shaft of a roller of the conveying means, and generating a light beam. A light emitting means for receiving the light beam, generating an electric signal corresponding to the amount of received light, guiding the light beam generated by the light emitting means to the detecting section, and receiving the light beam detected by the detecting section An optical fiber that guides the means, and the detecting unit is located on the upstream side in the transport direction from the rotation axis of the roller disposed downstream in the transport direction of the transport unit, and is located below the most upstream position of the roller in the transport direction. Detecting means for detecting a predetermined image pattern formed by a developer in a predetermined area on the belt, the detection means being provided integrally with the bearing mechanism at a predetermined position on the side of the belt, and having a detection unit facing the belt surface. Determining the distance between the image patterns of each color and the amount of inclination based on the electric signal output from the light receiving means of the detecting means, and calculating the amount of displacement of the image forming position on each photoconductor by each image forming means. And a control unit for adjusting an image forming position on each photoconductor based on a shift amount of an image forming position by each image forming unit calculated by the calculating unit. An image forming apparatus is provided.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of an image forming apparatus according to the present invention and an image forming method applied to the image forming apparatus will be described in detail with reference to the drawings. FIG.
2 is a perspective view schematically showing the appearance of a color digital copying apparatus 1 (hereinafter simply referred to as copying apparatus 1) as an image forming apparatus according to the present invention. This color digital copying apparatus functions as a copying apparatus that reads a document and copies it to a recording medium, and transmits image data of the read document via a general public line and receives image data transmitted via the line. And a printer function for outputting an image based on image data transmitted from a computer connected to the copying apparatus.

As shown in FIG. 1, a document table 81 on which a document is placed is provided at an upper portion of the main body of the copying apparatus 1.
An automatic document feeder 6 (hereinafter, simply referred to as an ADF 6) that feeds a document to an original and presses the document at a predetermined position is provided.

On the front side of the document table 81, a copy button for instructing the image forming apparatus main body to start a copying operation,
A control panel 5 for inputting various copy conditions such as a copy magnification and the number of copies is provided.

At the lower portion of the main body of the copying apparatus 1, there is disposed a paper cassette 30 which is provided detachably from the main body and contains a plurality of recording sheets, ie, sheets P, as recording media. When viewed from the front of the main body of the copying apparatus, the right side is formed to be openable and closable with respect to the main body.
And a cover 7 which functions as a paper feed tray for guiding the recording paper P at the supply port. Below the cover 7, an access cover 8 is provided for this processing when paper jams as supplied from the paper cassette 30.

As shown in FIG. 2, a discharge port 44a for discharging the recording paper P from the main body and a paper discharge receiving the recording paper P discharged from the discharge port 44a are provided on the left side surface of the main body of the copying apparatus 1. A tray 44 is provided.

A power cord 3a for supplying power to the apparatus, an I / F connector 3b for connecting to a computer device such as a personal computer, and a facsimile communication are provided at a lower rear portion of the copying apparatus 1. An I / F connector 3c for connecting to a general public line is provided.

FIG. 3 shows the copying apparatus 1 shown in FIGS.
FIG. 2 is a cross-sectional view schematically showing an internal structure of FIG. As shown in FIG. 3, the copying apparatus 1 includes a scanner unit 2 as a reading unit that reads a document image, a printer unit 4 as an image forming unit that forms an image on a recording medium based on image data,
It has. In addition, an ADF 6
Is set. The ADF 6 is attached to the document table 81 of the scanner unit 2 so as to be openable and closable, feeds the reading object, that is, the document D, one by one toward the document table 81, and also sets the document D placed on the document table. Functions as a document holder for bringing the document into close contact with the document table.

The printer section 4 performs image separation for each color component based on a well-known subtractive color mixing method, that is, yellow (hereinafter referred to as Y), magenta (hereinafter referred to as M), and cyan (hereinafter referred to as M). , C) and first (fourth) image forming units 10Y, 10M, 10C, and 10K that form four color images (hereinafter, referred to as K), respectively. These image forming units 10Y, 10M, 10C,
K is composed of independent cartridge-type units, and each unit is detachably formed from the main body of the copying apparatus. Therefore, as will be described later, replacement can be performed in unit units according to the life of the photosensitive drum included in each image forming unit.

Each of the image forming units 10Y, 10M, 10C, 1
Below 0K, a transport mechanism 20 as a transport unit including an endless belt transport belt 21 that transports the image of each color formed by each image forming unit in the direction of arrow a in the figure is disposed.

The transport belt 21 of the transport mechanism 20 includes a driving roller 24 rotated by a belt motor (not shown) and a driven roller 2 separated from the driving roller 24 by a predetermined distance.
6, and endlessly run at a constant speed in the direction of arrow a. The image forming units 10Y, 10M,
10C and 10K are arranged in series along the transport direction of the transport belt 21.

Each of the image forming units 10Y, 10M, 10C, 1
0K is a photosensitive drum 1 whose outer peripheral surface is formed to be rotatable in the same direction at a position in contact with the conveyor belt 21.
1Y, 11M, 11C, and 11K. A drum motor (not shown) for rotating each photosensitive drum at a predetermined peripheral speed is connected to each photosensitive drum.

Each of the photosensitive drums 11Y, 11M,
The axes of 11C and 11K are arranged so as to be orthogonal to the direction in which the image is conveyed by the conveyor belt 21, and the axes of the photosensitive drums are arranged at equal intervals. In the following description, the axial direction of each photosensitive drum is defined as the main scanning direction, and the direction in which the photosensitive drum is rotated, that is, the transport direction of the transport belt 21 is defined as the sub-scanning direction.

Each photosensitive drum 11Y, 11M, 11C,
Around 11K, charging rollers 12Y, 12M, 12C and 12K as charging means extending in the main scanning direction, developing devices 13Y, 13M and 13C as developing means similarly extending in the main scanning direction, 13K, transfer devices 14Y and 14M1 as transfer means similarly extended in the main scanning direction
4C, 14K, and cleaning devices 15Y, 15M, 15C, 15K similarly extended in the main scanning direction,
Each is sequentially arranged along the rotation direction of the corresponding photosensitive drum.

Each transfer device is disposed at a position where the transfer belt 21 is held between the transfer device and the corresponding photosensitive drum, that is, inside the transfer belt 21. Exposure points by an exposure device described later are formed on the outer peripheral surface of the photosensitive drum between the charging roller and the developing device.

Below the transport mechanism 20, each image forming unit 1
A paper cassette 30 containing a plurality of recording papers P as a recording medium for transferring images formed by 0Y, 10M, 10C, and 10K is arranged.

At one end of the paper cassette 30 and on the side close to the driven roller 26, there is arranged a pickup roller 32 for taking out the recording paper P stored in the paper cassette 30 one by one from the top. . The paper cassette 3 is located between the pickup roller 32 and the driven roller 26.
0 and the image forming unit 10Y
A registration roller 34 for aligning the leading end of the Y toner image formed on the photosensitive drum 11Y is disposed.

The other photosensitive drums 11M, 11C,
The toner image (M, C, K) formed on 11K is supplied to each transfer position in synchronization with the transport timing of the recording paper P transported on the transport belt 21.

The registration roller 34 and the first image forming section 1
0Y, near the driven roller 26, substantially on the outer periphery of the driven roller 26 with the conveyance belt 21 interposed therebetween, the recording paper P conveyed at a predetermined timing via the registration roller 34. A suction roller 36 for providing a predetermined electrostatic suction force is disposed. Note that the axis of the suction roller 36 and the axis of the driven roller 26 are arranged parallel to each other.

At one end of the transport belt 21, near the drive roller 24, substantially on the outer periphery of the drive roller 24 with the transport belt 21 interposed therebetween, a predetermined image formed of toner on the transport belt 21 is formed. A registration sensor 38 functioning as a detecting means for detecting a pattern, that is, a registration pattern, is arranged at a predetermined distance from the surface of the conveyor belt 21.

Further, on the transport belt 21 on the outer periphery of the drive roller 24 and downstream of the registration sensor 38, it functions as a cleaning means for removing the toner adhered on the transport belt 21 or the paper residue of the recording paper P. A belt cleaner unit 40 is disposed. The belt cleaner unit 40 is formed in an integral structure that is configured to be detachable from the copying apparatus main body.

The belt cleaner unit 40 is a blade for removing toner adhered to the conveyor belt 21 by being pressed against the surface of the conveyor belt 21, and waste toner and paper debris removed from the surface of the conveyor belt 21 by the blade. And a waste toner box for storing the same.

In the direction in which the recording paper P conveyed via the conveyance belt 21 is separated from the drive roller 24 and further conveyed, the recording paper P is transferred to the recording paper P by heating the recording paper P to a predetermined temperature. A fixing device 50 is provided for melting the toner image and fixing the toner image to the recording paper P.

A supply port 4a for manually feeding recording paper P is formed on a side surface of the main body of the copying apparatus located on the right side of the printer unit 4, and a paper feed tray 42 is provided in the supply port 4a. Recording paper P fed through supply port 4a
Is guided to the registration roller 34 and supplied to each image forming unit. On the side of the copying apparatus main body located on the left side of the printer section 4, a paper discharge tray 44 for receiving the recording paper P discharged via the fixing device 50 is provided.

The exposing device 60 for forming an electrostatic latent image which is color-separated on the outer peripheral surface of each photosensitive drum is provided with image data (Y, M) for each color component which is color-separated by an image processing unit described later. , C, and K), and has a semiconductor laser device for each color, the light emission of which is controlled based on C, K).

On the optical path of the laser beam emitted from each semiconductor laser device, each laser beam is deflected in the main scanning direction by simultaneously reflecting each laser beam on the same reflection surface while rotating at a predetermined rotation speed. A single polygon mirror 61 is provided.

The polygon mirror 61 has, for example, eight reflecting surfaces, and deflects the laser beam on each of the reflecting surfaces so that the laser beam is linearly formed in the axial direction on the photosensitive drum 11, that is, in the main scanning direction. Scan. The polygon mirror 61 is rotated at a predetermined rotation speed by a polygon motor 61a provided below the polygon mirror 61.

In the direction in which the laser beam is reflected by the polygon mirror 61, each reflected laser beam is corrected to form an image at a predetermined imaging position, that is, an exposure position on each corresponding photosensitive drum. An imaging optical system including the first to third lenses 62, 63, and 64 is provided.

Third lens 64 and each photosensitive drum 11
Between Y, 11M, 11C, and 11K, a first folding mirror 65 (Y, M, and Y) that bends the laser beam of each color that has passed through the third lens 64 toward the exposure position of each photosensitive drum. C, K), and second and third folding mirrors 66 (Y, M, C), 67 (Y, M, C) for further folding the laser beam bent by the first folding mirrors 65Y, 65M, 65C. ) Is arranged.

After the black laser beam is turned by the first turning mirror 65K, it is guided to the photosensitive drum 11K without passing through another mirror. The scanner unit 2 that reads an image of a document has a document table 81 made of transparent glass on which the document D is set, facing the ADF 6 in a closed state. Below the document table 81, an exposure lamp 82 for illuminating the document D placed on the document table 81, a reflector 84 for condensing light from the exposure lamp 82 on the document D, and reflected light from the document D A first mirror 86 and the like, which are bent leftward in the figure, are provided. These exposure lamp 82 and reflector 8
4 and the first mirror 86 are fixed to the first carriage 88.

The first carriage 88 is connected to an unillustrated pulse motor via an unillustrated toothed belt or the like.
The driving force of the pulse motor is transmitted, and the pulse motor is moved in parallel along the document table 81.

In the left side of the drawing with respect to the first carriage 88, that is, in the direction in which the reflected light reflected by the first mirror 86 is guided, a document table is driven via a driving mechanism (not shown) such as a toothed belt and a DC motor. A second carriage 90 movably provided in parallel with 81 is provided. The second carriage 90 has a second mirror 92 for bending the reflected light from the document D guided by the first mirror 86 downward, and a third mirror for bending the reflected light from the second mirror 92 rightward in the figure. 94 are arranged at right angles to each other.

The second carriage 90 includes the first carriage 8
8 and is moved in parallel with the first carriage 88 along the document table 81 at half speed.
An imaging lens 96 that forms an image of the reflected light from the second carriage 90 at a predetermined magnification is disposed in a plane including the optical axis of the light turned back through the second carriage 90. In a plane substantially orthogonal to the optical axis of the light passing through the imaging lens 96,
A CCD image sensor 98 that converts reflected light provided with converging properties by the imaging lens 96 into an electric signal, that is, image data, is provided.

When the light from the exposure lamp 82 is condensed on the original D on the original table 81 by the reflector 84 by the scanner unit 2 having the above-described structure, the reflected light from the original D is reflected by the first mirror 86, The light is incident on the CCD image sensor 98 via the second mirror 92, the third mirror 94, and the imaging lens 96, and the information of the original image is converted into image data as an electric signal. CCD image sensor 98
Are connected to the image processing unit 99. The image processing unit 99 includes an image memory for temporarily storing image data supplied from the CCD image sensor 98. Then, the image processing unit 99 creates image data for each color component based on the image data stored in the image memory.

Then, based on the image data for each color component, the intensity of the semiconductor laser device provided in the exposure device 60 is modulated, each image forming section is driven, and the image is formed on the paper transported by the transport mechanism. An image is formed.

Incidentally, the registration sensor 38 is constituted by a reflection type optical sensor as shown in FIG.
That is, the registration sensor 38 includes a light emitting element 38A as a light emitting unit that generates a light beam of a predetermined light amount, and a light receiving unit that receives a reflected beam from the surface of the conveyor belt 21 and generates an electric signal corresponding to the received light amount. A coaxial optical fiber 38C for guiding the light beam generated by the light emitting element 38A to the surface of the conveyor belt 21 and guiding the reflected beam from the surface of the conveyor belt 21 to the light receiving element 38B; Optical fiber 38C
A lens 38D for condensing the light beam from the light emitting element 38A guided by the optical fiber 38A and condensing the reflected beam from the surface of the conveyor belt 21 to the optical fiber 38C, and holding the other end of the optical fiber 38C and the lens 38D. Lens holder 38E.

The holder 38E constitutes a detection section of the registration sensor 38 by holding the other end of the optical fiber 38C and the lens 38D. Optical fiber 38C
As shown in the cross-sectional view in FIG. 4, a light-emitting optical fiber 38C-1 for guiding the light beam generated by the light-emitting element 38A to the conveyor belt side and a light-receiving element 38B for reflecting the reflected beam from the conveyor belt side. And a plurality of receiving optical fibers 38C-2. Then, the light receiving optical fiber 3
By arranging 8C-2 around the light emitting optical fiber 38C-1, it is possible to reliably detect the reflected beam even if the reflection direction of the light beam is slightly shifted.

In the registration sensor 38, the detection area is narrowed by narrowing the light beam by the lens 38D, and the detection accuracy is improved. That is, the distance between the lens 38D constituting the detection unit of the registration sensor 38 and the surface of the conveyor belt 21 is set to be a distance near the focal length of the lens 38D.

In the registration sensor 38, the light emitting element 38A emits light at a predetermined timing to emit a light beam, and this light beam is incident from one end of the light emitting optical fiber 38C-1 in the optical fiber 38C. And
This light beam propagates through the light emitting optical fiber 38C-1 and is emitted from the other end of the light emitting optical fiber 38C-1.
The light is condensed by the lens 38D and is applied to a predetermined area on the surface of the conveyor belt 21.

The irradiated light beam is reflected on the surface of the conveyor belt 21. The amount of the reflected beam changes according to the concentration of the toner adhered to the surface of the conveyor belt 21, that is, the amount of the adhered toner. That is, as shown in FIG.
When no toner adheres to the surface of the conveyor belt 21, that is, when the toner density = 0, the reflected beam having the maximum light amount is reflected. In contrast, the conveyor belt 21
When the concentration of the toner attached to the surface increases, the scattering of the light beam by the toner increases, and the amount of reflected light decreases.
Accordingly, the presence or absence of toner can be detected based on the amount of reflected light of the reflected beam reflected from the surface of the conveyor belt 21.

Then, the reflected beam from the surface of the conveyor belt 21 is condensed by the lens 38D, and the light receiving optical fiber 3 arranged around the light emitting optical fiber 38C-1.
8C-2 is incident on the other end, and the light receiving optical fiber 38
The light exits from one end of C-2 and enters the light receiving element 38B.

The light receiving element 38B generates an electric signal that changes according to the amount of the incident reflected beam. Accordingly, the registration sensor 38 outputs a signal for determining the presence or absence of the registration pattern.

Further, due to the characteristics of the light emitting element 38A and the light receiving element 38B used in the registration sensor 38, as shown in FIG. 6, a predetermined amount of light beam emitted from the light emitting element 38A is conveyed to the conveyor belt. The light amount of the reflected beam from the surface 21 is the largest, and subsequently, the light is reflected in the order of magenta toner, yellow toner, cyan toner, and black toner on the conveyor belt 21. The light intensity of the beam decreases.

As a result, the registration sensor 38 outputs a signal for determining a registration mark formed by each color toner. Then, based on the signal for determining the presence or absence of the registration pattern of each color, registration correction for correcting the image misalignment between the image forming units is performed.

FIG. 7 is a schematic block diagram showing a control unit for controlling the image forming operation of the image forming apparatus shown in FIG. The image forming apparatus 1 includes an image control unit 1
It has ten.

The image control unit 110 is provided with an image control CPU 11
1. Timing control unit 113 and data control units 115Y, 115M, 115C and 11 corresponding to each color component
It includes multiple control units such as 5K. The image control CPU 111, the timing control unit 113, and the data control units 115 (Y, M, C, and K) are mutually connected via a bus line 112.

The image control CPU 111 operates the mechanical elements of the image forming apparatus 1 such as a motor or a roller and the electric elements such as the charging devices 12 (Y, M, C and K), a main controller 101 for controlling a voltage value or a current amount applied to the developing device 13 (Y, M, C and K) or the transfer device 14 (Y, M, C and K). .

The main control device 101 has a ROM (read only) for storing initial data for initializing the device 1 or a test pattern.
A random access memory (RAM) for temporarily storing input image data or correction data calculated according to the output of the registration sensor 38;
Further, a memory unit 102 including a nonvolatile memory for storing various correction data is connected.

The timing control unit 113 stores image data 114 Y and 11 for storing image data for each color component.
4M, 114C and 114K, and each image memory 1
14 (Y, M, C, and K), based on the image data stored in each of the photosensitive drums 11 (Y, M, C, and K) of each image forming unit 10 (Y, M, C, and K). A laser driving unit 116 (Y, M, C, and K) for driving a semiconductor laser for irradiating a laser beam toward the laser beam is connected.

The timing control unit 113 includes:
Based on the output signal from the registration sensor 38, the registration correction calculation unit 117 and the signal from the registration correction calculation unit 117 function as calculation means for calculating the correction amount of the timing of writing an image with the laser beams LY, LM, LC and LK. , Each image forming unit 10 (Y,
M, C, and K) and a timing setting device 118 that defines various timings for operating the exposure device 60, and a solid-state error for each image forming unit 10 and a difference in the optical path length of each optical path in the exposure device. Oscillation frequency variable circuit (voltage controlled oscillator, ie, VCO, hereafter referred to as VCO)
119Y, 119M, 119C, 119K, etc. are connected. These constitute a control unit that performs registration correction.

Each of the image memories 114 (Y, M, C, and K) stores image data corresponding to an original image read by the scanner unit 2 or image data from an external storage device (not shown) or a host computer. Is stored. The output of the horizontal synchronization detector 23 provided in the exposure device 60 is converted into a horizontal synchronization signal Hsync via a horizontal synchronization signal generation circuit 121, and the main control device 101
Is input to Then, the horizontal synchronization signal input to the main controller 101 is provided to the image control CPU 111 of the image controller 110 via the bus line 112, and then sent to each data controller 115 (Y, M, C and B). Is entered.

The main controller 101 has a control panel 104 having various instruction buttons for giving various instructions to the main body of the copying machine, a display section for displaying the operating state of the main body of the copying machine and various messages. Is connected.

FIG. 8 is a perspective view schematically showing a mounting structure of the registration sensor 38. As shown in FIG. 8, the registration sensor 38 is attached to a bearing mechanism 200 of the drive roller 24 to which the transport belt 21 of the transport mechanism 20 is attached. The bearing mechanism 200 includes a bearing 201 that rotatably receives the rotation shaft of the drive roller 24, and a fiber holder 202 that holds the other end of the optical fiber 38 </ b> C of the registration sensor 38.
And the fiber holding portion 202 are integrally formed.

The fiber holding section 202 is provided with
It is arranged so as to face a predetermined area where the registration pattern 210 formed thereon can be detected, that is, a predetermined area through which the registration pattern 210 passes. The fiber holding section 202 holds a holder 38E that integrally holds the other end of the optical fiber 38C of the registration sensor 38 and the lens 38D. Then, as shown in FIG. 8, the registration sensor 38
1 in the direction perpendicular to the conveying direction.
Are arranged in such a position as to face the predetermined region in

As shown in FIG. 9, the registration sensor 38 is arranged slightly upstream of the rotation axis A of the drive roller 24 in the transport direction with respect to the transport direction of the transport belt 21. I have.

That is, the registration sensor 38 needs to set the distance from the surface of the conveyor belt 21 to a predetermined distance. As shown by the broken line in FIG. 9, when the registration sensor 38 is disposed on the downstream side in the transport direction from the position A directly above the rotation axis of the driving roller, the registration sensor 38 faces the arc portion of the driving roller 24. That is, the distance between the registration sensor 38 and the conveyor belt 21 cannot be set to a predetermined value. Moreover, the light beam emitted from the registration sensor 38 is applied to the conveyor belt 21 along the arc of the drive roller 24.
Since the light is reflected upward, the light is not regularly reflected to the registration sensor 38 side, and exceeds the allowable range in which the registration sensor 38 can receive light. For this reason, the reflected beam from the conveyor belt 21 cannot be sufficiently received.

The registration sensor 38 is connected to the driving roller 2.
4 is located directly above the rotation axis of the drive roller 24 due to the accuracy of the components and mounting errors of the sensor.
The transfer belt 21 may be located at a lower position.
It is difficult to accurately set the interval between them.

Further, a point A just above the rotation axis of the drive roller 24 is provided.
At a position opposing the transport belt 21 on the further upstream side, as the transport belt 21 elongates, as shown in FIG. 9, as the distance to the intermediate portion between the drive roller 24 and the driven roller 25 increases, the amplitude of the transport belt 21 increases. Is formed. Therefore, it is difficult to obtain a stable and accurate signal.

For this reason, in this embodiment, as shown in FIG.
The drive roller 24 is located at a position where the light beam output from the drive roller 8 can be substantially reflected and the distance between the registration sensor 38 and the conveyor belt 21 can be maintained substantially constant.
Is arranged slightly upstream of the rotation axis A in the transport direction. Preferably, the registration sensor 38 is located downstream of the most upstream position B of the drive roller 24.

That is, the registration sensor 38 is located on the upstream side in the transport direction from the position A directly above the rotation axis of the drive roller 24 and on the downstream side in the transport direction from the position B on the most upstream side of the drive roller 24. It is desirable.

By arranging the registration sensor 38 at such a position, it is possible to receive the reflected beam from the conveyor belt 21 within an allowable range in which the light beam output from the registration sensor 38 can be received. . Further, since this position is close to a node where the amplitude is formed on the transport belt 21 and the amplitude is extremely small, the change in the interval between the registration sensor 38 and the transport belt 21 is extremely small.
For this reason, even if an amplitude is formed on the conveyor belt 21, it is possible to detect a stable and accurate signal.

As described above, the registration sensor 38 moves the bearing mechanism 200 of the drive roller 24 at the position as described above.
, It is easy to set the interval with the conveyor belt 21 to a predetermined value, the accuracy of the interval can be improved, and adjustment by a jig after the optical fiber 38C is attached becomes unnecessary.

One end of the optical fiber 38C is provided on the downstream side of the transport mechanism 20 and the transport belt 21
It is connected to a circuit board 38 </ b> F disposed below the transport belt 21 via a transport guide mechanism 220 that separates the paper from the paper. That is, the circuit board 38F includes a circuit for driving the light emitting element 38A and the light receiving element 38B of the registration sensor 30, and causes the light emitting element 38A to emit light at a predetermined timing. An electric signal based on the amount of reflected light is received.

With such a configuration, first, the light emitting element 3
The light beam emitted from the other end of the light emitting optical fiber 38C-1 after being emitted at 8A is condensed on a predetermined area on the conveyor belt 21 by the lens 38D.

Then, a light beam is applied to a predetermined registration pattern formed of yellow, magenta, cyan, and black toners passing through a predetermined area on the conveyor belt 21.

Then, the reflected beam reflected from the predetermined area on the conveyor belt 21 is incident on the other end of the light receiving optical fiber 38C-2 via the lens 38D, and is thereafter received by the light receiving element 38B.

The electric signal generated based on the amount of the reflected beam received by the light receiving element 38B is output to the control circuit 38F. This electric signal is output to the registration correction operation device 117 connected to the registration sensor 38. The registration correction arithmetic unit 117 recognizes a registration pattern formed on the conveyor belt 21 based on the input electric signal, and executes a predetermined registration correction process.

Next, the image forming operation of the copying apparatus 1 configured as described above, for example, the copying operation by the copying function will be described in detail. When the power switch (not shown) is turned on, the copying apparatus 1 is initialized, and the fixing device 5
0 is heated to a predetermined temperature, the rotation speed of each motor is stabilized, and the motor is maintained in a standby state. Then, the document D is optically scanned by the scanner unit 2, and the image of the document D is read via the CCD image sensor 98. The read image data is temporarily stored in an image memory, and image data (Y, M, C, K) for each color is stored in an image processing unit 99.
Then, if necessary, image processing such as scaling, rotation, and the like is performed for each color.

Here, a process of forming a Y (yellow) image using the first image forming section 10Y will be described. Needless to say, the M (magenta) image and the C image are formed by the second to fourth image forming units 10M10C and 10K.
A (cyan) image and a K (black) image are formed similarly.

First, the surface of the photosensitive drum 11Y is uniformly charged by the charging roller 12Y. Subsequently, the light emission of the semiconductor laser device is controlled based on the Y (yellow) image data processed by the image processing unit 99, and the exposure device 60
A laser beam based on the Y image data is applied to a predetermined exposure position of the photosensitive drum 11Y via the. As a result, a Y electrostatic latent image corresponding to the Y image data is formed on the photosensitive drum 11Y.

The Y electrostatic latent image formed on the photosensitive drum 11Y is developed by a developing device 13Y containing Y toner to be visualized, and is converted to a Y toner image on the photosensitive drum 11Y.

The leading end of the Y toner image on the photosensitive drum 11Y is taken out of the paper cassette 30 at a transfer position where the photosensitive drum 11Y and the conveyor belt 21 face each other, and is placed on the conveyor belt 21 by a registration roller 34 at a predetermined position. It is aligned with the leading end of the recording paper P that has been sucked and aligned at the timing. Then, the Y toner image on the photosensitive drum 11Y is transferred onto the recording paper P by a transfer bias supplied from the transfer device 14Y.

Hereinafter, the photosensitive drums 11M, 11C and 11K are respectively controlled by the second image forming section 10M, the third image forming section 10C and the fourth image forming section 10K.
The M toner image, C toner image, and K toner image formed on the recording paper P conveyed by the conveyance belt 21 are sequentially superimposed. That is, in the case of printing of a plurality of colors, each of the image forming units 10Y, 10M, 10C, and 10K
As a result, the image forming operation in the process of charging → exposure → development → transfer is performed in one cycle, and the toner images of a plurality of colors are multiplex-transferred onto the recording paper P.

In this case, each photosensitive drum 11Y, 11
M, 11C, and 11K are arranged at a predetermined distance from each other in the direction in which the recording paper P is conveyed.
In order to superimpose the images of each color on the recording paper P conveyed above, the exposure timing of the semiconductor laser device for each color is shifted.

On the other hand, after the toner images of the respective color components have been transferred onto the recording paper P, the remaining toner that has not been transferred onto the photosensitive drums 11Y, 11M, 11C and 11K is removed by the cleaning devices 15Y, 15M, 15C and Each is cleaned by 15K.

The recording paper P on which the toner images of each color are transferred is
After the toner image is peeled off from the transport belt 21 and transported to the fixing device 50, the toner image heated by the fixing device 50 is melted and fixed on the recording paper P, and is discharged to the paper discharge tray 44.

Further, the toner adhering to the transport belt 21 and paper dust generated from the recording paper P are removed by the belt cleaner unit 40. Next, correction of a beam position shift in the sub-scanning direction which is performed at a predetermined timing, for example, immediately after power-on or immediately after unit replacement in the copying apparatus, that is, registration correction processing will be described.

First, the polygon motor, the conveying belt motor, the photosensitive drum motor and the developing motor included in each image forming unit are driven, and the polygon mirror, the conveying belt, the photosensitive drum, and the developing device are respectively driven at a predetermined number of rotations. Drive.

When each motor reaches a stable rotational speed, image data corresponding to a predetermined resist pattern stored in a memory unit 102 connected to the main control unit 101 is transmitted to each laser drive unit 116. Supplied.

The laser beams emitted from the respective laser driving units 116 are transmitted to the corresponding photosensitive drums 11 via the polygon mirror 61 and the imaging optical system.
At a predetermined exposure position.

Then, a resist pattern of each color toner is formed on each photosensitive drum 11 based on each image data corresponding to the resist pattern, and the formed resist pattern of each color is transferred onto the transport belt 21. .

Subsequently, the registration pattern formed on the conveyor belt 21 is optically read by the registration sensor 38. That is, the registration sensor 38
An electric signal corresponding to the amount of reflected light from the conveyor belt 21 when the light beam is emitted toward the conveyor belt 21 is output.

This electric signal is output to a registration correction arithmetic processing unit 117 as arithmetic means as shown in FIG. The registration correction arithmetic processing unit 117 analyzes the signal output from the registration sensor 38 to calculate the position shift amount, and outputs a correction signal corresponding to the position shift amount to the image control CPU 111 as a control unit.
Then, it outputs the result to the timing control unit 113 to end the registration correction processing.

Then, the resist pattern formed on the conveyor belt 21 is removed by the belt cleaner unit 40. As described above, according to the image forming apparatus of the present invention, when performing the registration correction processing for correcting the mutual image displacement between the image forming units at a predetermined timing, the photoconductor of each image forming unit A registration sensor 38 that detects a predetermined image pattern, that is, a registration pattern, formed on the drum by each color toner includes a light emitting element 38A that generates a light beam, a light receiving element 38B that receives the light beam and generates an electric signal, A coaxial optical fiber 38C that guides the light beam generated by the light emitting element 38A to the detecting section and guides the light beam from the detecting section to the light receiving element 38B, is provided in the detecting section, and is output from the optical fiber 38C. Lens 38 for collecting light
D, and a holder 38E that is provided in the detection unit and holds the end of the optical fiber 38C and the lens 38D.

The detection section of the registration sensor 38 is located at a position upstream of the rotation axis A of the drive roller 24 of the transfer mechanism 20 in the transfer direction and from the position B at the most upstream position of the drive roller 24. It is arranged at a predetermined position of the bearing mechanism 200 of the drive roller 24 located on the downstream side in the direction.
The predetermined position of the bearing mechanism 200 is a position facing a predetermined area on the conveyor belt 21 where a registration pattern is formed, and the distance between the surface of the conveyor belt 21 and the lens 38D in the detection unit of the registration sensor 38. Is a position substantially corresponding to the focal length of the lens 38D.

By arranging the detection section of the registration sensor 38 at such a position, the light beam output from the detection section of the registration sensor 38 can be received within an allowable range within which the light beam can be received.
It is possible to receive the reflected beam from the conveyor belt 21. Further, since this position is close to a node where the amplitude is formed on the transport belt 21 and the amplitude is extremely small, the change in the interval between the registration sensor 38 and the transport belt 21 is extremely small. For this reason, even if the transport belt 21 is extended due to long-term use, or even if the transport belt 21 has an amplitude, a stable and accurate signal can be detected.

As a result, it is possible to stably and accurately perform registration correction over a long period of time, to prevent a mutual image position shift between the respective image forming units, and to prevent a color shift. Therefore, it is possible to prevent the image quality of the image formed on the sheet from deteriorating.

As described above, the registration sensor 38 moves the bearing mechanism 200 of the drive roller 24 at the position as described above.
, It is easy to set the interval with the conveyor belt 21 to a predetermined value, the accuracy of the interval can be improved, and adjustment by a jig after the optical fiber 38C is attached becomes unnecessary. Accordingly, it is an object of the present invention to provide a low-cost image forming apparatus capable of preventing image quality deterioration.

[0104]

As described above, according to the present invention, it is possible to provide a low-cost image forming apparatus capable of preventing image quality deterioration.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing a front external appearance of a digital copying apparatus as an example of an image forming apparatus of the present invention.

FIG. 2 is a perspective view schematically showing an external appearance of a back side of the digital copying apparatus shown in FIG. 1;

FIG. 3 is a sectional view schematically showing an internal structure of the digital copying apparatus shown in FIG. 1;

FIG. 4 is a diagram schematically showing a structure of a registration sensor applied to the copying apparatus shown in FIG. 3;

FIG. 5 is a diagram for explaining a relationship between a light amount of a reflected beam and an amount of toner adhering on a conveyance belt.

FIG. 6 is a diagram for explaining the relationship between the reflection amount of toner of each color adhered to the conveyance belt and the surface of the conveyance belt at the same density.

FIG. 7 is a block diagram schematically showing a configuration of a control system for controlling the copying apparatus.

FIG. 8 is a schematic perspective view for explaining a mounting structure of a registration sensor applied to the copying apparatus.

FIG. 9 is a schematic side view for explaining a mounting structure of the resist sensor shown in FIG. 8;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Digital copying apparatus 2 ... Scanner part 4 ... Printer part 10 ... Image forming part 11 ... Photoreceptor drum 20 ... Conveying mechanism 21 ... Conveying belt 24 ... Drive roller 26 ... Follower roller 38 ... Registration sensor 38A ... Light emitting element 38B ... Light receiving Element 38C Optical fiber 38C-1 Light emitting optical fiber 38C-2 Light receiving optical fiber 38D Lens 38E Holder 38F Circuit board 40 Belt cleaner unit 60 Exposure device 101 Main control device 102 Memory unit 104 ... Control panel 111 ... Image control CPU 117 ... Registration correction arithmetic unit 200 ... Bearing mechanism 201 ... Bearing part 202 ... Fiber holding part 210 ... Image pattern

Claims (5)

[Claims] A plurality of image forming means for forming respective developer images on a plurality of photoconductors, a pair of rollers arranged at a predetermined interval, and a belt bridged over the pair of rollers. Transport means for transporting the recording medium toward the plurality of photoconductors; and a belt surface disposed upstream of the rotation axis of a roller disposed downstream in the transport direction of the recording medium by the transport means. Detecting means for detecting a predetermined image pattern formed by a developer in a predetermined area on the belt, and detecting the image pattern formed on the belt by the detecting means. A control unit for adjusting an image forming position on each photoconductor by each image forming unit. A plurality of image forming means for forming respective developer images on a plurality of photoconductors, a pair of rollers arranged at a predetermined interval, and a belt bridged over the pair of rollers. Transport means for transporting a recording medium toward the plurality of photoconductors, a bearing mechanism rotatably receiving a rotation shaft of a roller of the transport means, and a roller disposed downstream of the transport means in the transport direction. A detection unit disposed integrally with the bearing mechanism at a predetermined position on the upstream side in the transport direction with respect to the rotation axis of the belt and facing a belt surface, and a predetermined image formed by a developer in a predetermined region on the belt Detecting means for detecting a pattern, and controlling means for detecting an image pattern formed on the belt by the detecting means and adjusting an image forming position on each photoconductor by each image forming means. Image forming apparatus characterized by. A plurality of image forming means for forming respective developer images on a plurality of photosensitive members, a pair of rollers arranged at a predetermined interval, and a belt bridged over the pair of rollers. Transport means for transporting a recording medium toward the plurality of photoconductors, a bearing mechanism rotatably receiving a rotation shaft of a roller of the transport means, and a roller disposed downstream of the transport means in the transport direction. A detection unit opposed to the belt surface, which is arranged integrally with the bearing mechanism at a predetermined position on the upstream side in the conveyance direction from the rotation shaft of the roller and on the downstream side in the conveyance direction from the most upstream position of the roller, Detecting means for detecting a predetermined image pattern formed by a developer in a predetermined area on the belt; detecting the image pattern formed on the belt by the detecting means; An image forming apparatus, comprising: control means for adjusting an image forming position on a body. A plurality of image forming means for forming respective developer images on a plurality of photoconductors, a pair of rollers arranged at a predetermined interval, and a belt bridged over the pair of rollers. Transport means for transporting a recording medium toward the plurality of photoconductors, a bearing mechanism rotatably receiving a rotating shaft of a roller of the transport means, a light emitting means for generating a light beam, and receiving the light beam And an optical fiber for guiding the light beam generated by the light emitting unit to the detecting unit and guiding the light beam detected by the detecting unit to the light receiving unit. The detection unit is arranged at a predetermined position on the upstream side in the transport direction from the rotation axis of the roller disposed on the downstream side in the transport direction in the transport unit, and on the downstream side in the transport direction from the most upstream position of the roller. Detecting means for detecting a predetermined image pattern formed by a developer in a predetermined area on the belt, the light receiving means of the detecting means An image forming apparatus comprising: a control unit that adjusts an image forming position on each photoconductor by each image forming unit based on the output electric signal. 5. A plurality of image forming means for forming respective developer images on a plurality of photoconductors, a pair of rollers arranged at a predetermined interval, and a belt bridged over the pair of rollers. Transport means for transporting a recording medium toward the plurality of photoconductors, a bearing mechanism rotatably receiving a rotating shaft of a roller of the transport means, a light emitting means for generating a light beam, and receiving the light beam And an optical fiber for guiding the light beam generated by the light emitting unit to the detecting unit and guiding the light beam detected by the detecting unit to the light receiving unit. The detection unit is arranged at a predetermined position on the upstream side in the transport direction from the rotation axis of the roller disposed on the downstream side in the transport direction in the transport unit, and on the downstream side in the transport direction from the most upstream position of the roller. Detecting means for detecting a predetermined image pattern formed by a developer in a predetermined area on the belt, the light receiving means of the detecting means Calculating means for determining the interval and the amount of inclination of the image pattern of each color based on the output electric signal and calculating the amount of shift of the image forming position on each photoconductor by each image forming means; Control means for adjusting an image forming position on each photoconductor based on a shift amount of an image forming position by each image forming means calculated by the image forming apparatus.