JP7187298B2 - image forming device - Google Patents

Description

The present invention relates to an image forming apparatus that forms an image by sequentially transferring toner images of a plurality of colors onto a transfer material using an electrophotographic method.

Conventionally, in an electrophotographic color image forming apparatus, toner images are sequentially transferred from each color image forming unit to an intermediate transfer member such as an intermediate transfer belt, and then the toner images are transferred collectively from the intermediate transfer member to a transfer material. Transfer configurations are known.

In such an image forming apparatus, each color image forming section has a drum-shaped photosensitive member (hereinafter referred to as a photosensitive drum) as an image carrier. A toner image formed on the photosensitive drum of each image forming section is transferred between the photosensitive drum and the intermediate transfer body by applying a voltage from a transfer power source to a primary transfer member provided facing the photosensitive drum via the intermediate transfer body. is primarily transferred to the intermediate transfer member at the primary transfer portion where the . The toner image of each color, which is primarily transferred from the image forming section of each color to the intermediate transfer member, is transferred from the intermediate transfer member to paper or an OHP sheet by applying a voltage from the secondary transfer power supply to the secondary transfer member in the secondary transfer section. are collectively secondary-transferred onto a transfer material such as The toner images of each color transferred onto the transfer material are then fixed onto the transfer material by fixing means.

In recent years, when forming an image using only black toner (hereinafter referred to as a monochrome image), an image forming unit other than an image forming unit that accommodates black toner, that is, an image forming unit that is not used for image formation of a monochrome image. is known. In this case, by separating the primary transfer member corresponding to the image forming portion not used for monochrome image formation from the intermediate transfer member and stopping the operation of the image forming portion, the image forming portion not used for image formation is removed. It is possible to suppress wear and deterioration of each member.

In Patent Document 1, each primary transfer member corresponding to each image forming portion is provided with a transfer power source and a current detection circuit, and based on the comparison of the detection result of the current flowing from the predetermined primary transfer member to the photosensitive drum, A configuration for determining the contact state between each primary transfer member and the intermediate transfer member is disclosed.

JP-A-2001-83758

The current flowing from the primary transfer member to the photosensitive drum fluctuates due to changes in the potential difference between the primary transfer member and the photosensitive drum and changes in the electrical resistance of each member such as the intermediate transfer member and the primary transfer member. If the current flowing from the primary transfer member to the photosensitive drum fluctuates greatly, it may be difficult to accurately detect the state of contact between the intermediate transfer member and the primary transfer member. In particular, in a configuration in which a voltage is applied from a common transfer power supply to a plurality of primary transfer members, the above-described potential differences and changes in electrical resistance value occur in a plurality of image forming portions, resulting in current flowing from the primary transfer members to the photosensitive drums. tends to have a large amount of fluctuation.

Accordingly, the present invention provides an image forming apparatus in which a voltage is applied from a transfer power source to a plurality of primary transfer members, and the state of contact between an image carrier and an intermediate transfer member is accurately determined based on the current flowing through the primary transfer members. intended to

The present invention provides a first image carrier for carrying a toner image, a first charging member for charging the first image carrier, and a toner image of a color different from that of the first image carrier. a second charging member for charging the second image carrier; and carried on at least one of the first image carrier and the second image carrier. and an intermediate transfer member to which the toner image thus formed is transferred; and a first transfer member for transferring the toner image from the second image carrier to the intermediate transfer member. a second transfer member for transferring; a transfer power supply for applying a voltage to the first transfer member and the second transfer member; and the transfer power supply to the first transfer member and the second transfer member. detecting means for detecting a current flowing through the first transfer member and the second transfer member when a voltage is applied to the intermediate transfer member; a mode in which a toner image is transferred from at least one of the first image carrier and the second image carrier to the intermediate transfer member in a first contact state; a mode in which the toner image is transferred from the first image bearing member to the intermediate transfer member in a second state in which the second transfer member is brought into contact with the transfer member and separated from the intermediate transfer member; and a control unit capable of selecting and executing either one, wherein the control unit controls the first image carrier by the first charging member and the second charging member. and the second image carrier, respectively, and a first current detected by the detecting means in a state in which a voltage is applied from the transfer power supply to the first transfer member and the second transfer member; and after the first current value is detected and after switching the surface potential of the second image carrier, from the transfer power supply to the first transfer member and the second transfer member. It is characterized in that it is determined whether the first state or the second state is formed based on a second current value detected by the detecting means while a voltage is applied. and

According to the present invention, in an image forming apparatus in which a voltage is applied from a transfer power supply to a plurality of primary transfer members, the state of contact between an image carrier and an intermediate transfer member can be accurately determined based on the current flowing through the primary transfer members. It is possible to

1 is a schematic diagram illustrating the configuration of an image forming apparatus according to Example 1; FIG. 4 is a block diagram illustrating control related to image formation in the first embodiment; FIG. 4A and 4B are schematic diagrams for explaining the contact or separation of the primary transfer member in each mode of Embodiment 1. FIG. 4A and 4B are schematic diagrams for explaining a current flowing through a primary transfer member in a full-color mode of Example 1. FIG. 4A and 4B are schematic diagrams for explaining a current flowing through a primary transfer member in a monochrome mode of Example 1. FIG. 4 is a schematic diagram illustrating the relationship between the voltage applied to the primary transfer member and the current flowing through the primary transfer member in Example 1. FIG. 5 is a flow chart for detecting a contact state between a primary transfer member and an intermediate transfer member in Embodiment 1. FIG. FIG. 10 is a schematic diagram for explaining a power supply configuration of Example 2; 8 is a schematic diagram illustrating the relationship between the voltage applied to the primary transfer member and the current flowing through the primary transfer member in Example 2. FIG. 10 is a flow chart for detecting a contact state between a primary transfer member and an intermediate transfer member in Embodiment 2. FIG.

Preferred embodiments of the present invention will be exemplarily described in detail below with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangement of the components described in the following examples should be appropriately changed according to the configuration of the device to which the invention is applied and various conditions. It is not intended to be limited to the following examples.

(Example 1)
[Configuration and Operation of Image Forming Apparatus]
FIG. 1 is a schematic cross-sectional view of an image forming apparatus 100 in this embodiment. FIG. 2 is a block diagram of the control system of the image forming apparatus 100 of this embodiment. As shown in FIG. 2, the image forming apparatus 100 is connected to a host computer 97, which is an external device. An operation start command and an image signal from the host computer 97 are transmitted to the controller 10 as control means, and the image forming apparatus 100 performs image formation by the controller 10 controlling various means. A description of the control will be given later.

As shown in FIG. 1, the image forming apparatus 100 of the present embodiment is an intermediate transfer type color image forming apparatus using an electrophotographic method. , and fourth image forming units 64a, 64b, 64c, and 64d. The first, second, third, and fourth image forming units 64a, 64b, 64c, and 64d form yellow (Y), magenta (M), cyan (C), and black (Bk) images, respectively. It is for These four image forming units 64a, 64b, 64c, and 64d are arranged in a row at regular intervals. In this embodiment, the configurations of the first to fourth image forming units 64a to 64d are substantially the same except that the colors of toners used are different. Therefore, hereinafter, the suffixes a, b, c, and d given to the reference numerals in the drawings are omitted to indicate that the elements are provided for one of the colors, unless a particular distinction is required. explained in detail.

As shown in FIG. 1, the image forming section 64 includes a drum-shaped electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) 56 as an image bearing member, a charging roller 57 as a charging member, and a developing roller 58 as a developing member. and cleaning means 61 . The photosensitive drum 56 is rotationally driven at a predetermined peripheral speed (process speed) in the direction of the illustrated arrow R1. In the vicinity of the image forming unit 64, exposure means 60 (laser scanner) for irradiating light onto a position downstream of the charging roller 57 and upstream of the developing means 5 with respect to the rotational direction of the photosensitive drum 56 is provided. ) are placed.

The charging rollers 57a to 57d are in contact with the photosensitive drums 56a to 56d with a predetermined pressing force. In this embodiment, the charging power source 401 shown in FIG. 2 is connected to the charging rollers 57a to 57c, and the charging power source 402 is connected to the charging roller 57d, which will be described in detail later. That is, by applying a predetermined voltage from the charging power supply 401 to the charging rollers 57a to 57c, the surfaces of the photosensitive drums 56a to 56c are uniformly charged to a predetermined potential by the charging rollers 57a to 57c. By applying a predetermined voltage from the charging power source 402 to the charging roller 57d, the surface of the photosensitive drum 56d is uniformly charged to a predetermined potential by the charging roller 57d.

Further, in this embodiment, the photosensitive drum 56 is negatively charged by the charging roller 57 . In this embodiment, the contact charging method in which the charging roller 57 is brought into contact with the photosensitive drum 56 to charge the photosensitive drum 56 has been described. A non-contact charging method such as a corona charging method may be used.

Further, in this embodiment, the configuration in which the charging power source 401 applies voltage to the charging rollers 57a to 57c and the charging power source 402 applies voltage to the charging roller 57d has been described. However, the present invention is not limited to this, and the charging rollers 57a to 57d may be provided with charging power sources individually, or any two of the charging rollers 57a to 57c may be provided with a common charging power source. Also good.

The exposure unit 60 exposes the surface of the photosensitive drum 56 to form an electrostatic latent image corresponding to image information on the surface of the photosensitive drum 56 charged by the charging roller 57 . That is, in the exposure means 60, a laser beam modulated in accordance with time-series electric digital pixel signals of image information input from the host computer 97 is output from a laser output section, and this laser beam is exposed via a reflecting mirror. The surface of the drum 56 is irradiated.

The developing means 5 in this embodiment employs a one-component contact developing system as a developing system, and has a developing roller 58 as a toner carrier. The toner carried on the developing roller 58 in a thin layer is conveyed to a facing portion (developing portion) where the photosensitive drum 56 and the developing roller 58 face each other as the developing roller 58 is rotationally driven by a drive source (not shown). be done. A voltage is applied to the developing roller 58 from the developing power source 500 (shown in FIG. 2), whereby the electrostatic latent image formed on the photosensitive drum 56 by the exposing means 60 is developed as a toner image. In this embodiment, the normal charge polarity of the toner is negative, and the toner charged to the same polarity as the charge polarity of the photosensitive drum 56 is placed at a position corresponding to the electrostatic latent image formed by the exposure means 60. A toner image is developed on the photosensitive drum 56 by a reversal development method in which the toner adheres to the surface of the photosensitive drum 56 .

Further, each developing means 5a, 5b, 5c and 5d contains yellow, magenta, cyan and black toners, respectively. In the configuration of the image forming apparatus 100 of this embodiment, in the full-color image forming mode in which image formation is performed using all of the image forming units 64a to 64d, all the developing rollers 58a to 58d of the developing means 5a to 5d are used as photosensitive drums. It abuts against 56a-56d. On the other hand, in a monocolor (single-color) image forming mode in which an image is formed using only the image forming unit 64d, the developing roller 58d is brought into contact with the photosensitive drum 56d, and the developing rollers 58a to 58c are in contact with the photosensitive drums 56a to 56c. Separate. This is to prevent deterioration and consumption of the developing rollers 58a to 58c and toner in the image forming sections 64a to 64c which do not perform image formation.

The cleaning unit 61 includes a cleaning blade as a cleaning member that contacts the photosensitive drum 56 and a waste toner box that stores toner collected by the cleaning blade, and collects toner remaining on the photosensitive drum 56 .

When an image forming operation start signal is issued in the image forming apparatus 100, the photosensitive drum 56 is rotationally driven in the illustrated arrow R1 direction. The photosensitive drum 56 is uniformly charged to a predetermined potential with a predetermined polarity (negative polarity in this embodiment) by the charging roller 57 during the rotation process, and is exposed by the exposure means 60 according to the image signal. As a result, an electrostatic latent image corresponding to each color component image of the target color image is formed on each photosensitive drum 56 . Next, the electrostatic latent image is developed by developing means 5 in the developing section and visualized as a toner image. Here, the normal charging polarity of the toner accommodated in the developing means 5 is negative.

An intermediate transfer belt 54 as an intermediate transfer body is an endless movable belt body, and is stretched by tension rollers 55a, 55b and 55c as support members. The intermediate transfer belt 54 is rotationally driven in the illustrated arrow R2 direction at substantially the same peripheral speed as the photosensitive drum 56 . The toner image formed on the photosensitive drum 56 is primarily transferred from the photosensitive drum 56 to the intermediate transfer belt 54 while passing through the primary transfer portion N1 where the photosensitive drum 56 and the intermediate transfer belt 54 are in contact with each other. The primary transfer residual toner remaining on the photosensitive drum 56 after the primary transfer is removed by the cleaning means 61a, and the photosensitive drum 56 is again charged and subjected to the image forming process.

Primary transfer members 59a to 59d, which are conductive brush members, are arranged on the inner peripheral surface of the intermediate transfer belt 54 so as to correspond to the respective photosensitive drums 56 of the image forming portions 64, respectively. A primary transfer power supply 200 is connected to the primary transfer member 59 , and the primary transfer power supply 200 can apply a positive or negative voltage to the primary transfer member 59 . Also, the primary transfer member 59 can come into contact with or separate from the intermediate transfer belt 54 . During image formation, while the primary transfer member 59 is in contact with the intermediate transfer belt 54, the primary transfer power supply 200 charges the primary transfer member 59 with a polarity opposite to the normal charging polarity of the toner (in this embodiment, is positive) voltage is applied. As a result, the toner image formed on the photosensitive drum 56 is primarily transferred onto the intermediate transfer belt 54 .

As shown in FIG. 1, in this embodiment, a voltage is applied from one common primary transfer power supply 200 to each of the primary transfer members 59a to 59d. In this way, by using a common configuration for the primary transfer power source 200 that applies voltage to the plurality of primary transfer members 59, it is possible to achieve cost reduction of the image forming apparatus and space saving of the power supply board.

The toner images of each color formed in each image forming section 64 are sequentially superimposed and primarily transferred onto the intermediate transfer belt 54 in each primary transfer section N1. After that, the four-color toner image on the intermediate transfer belt 54 passes through the secondary transfer portion N2 formed by the intermediate transfer belt 54 and the secondary transfer roller 63, and the transfer material fed by the paper feed roller 51. Secondary transfer is performed collectively on the P surface.

In this embodiment, the secondary transfer roller 63 as a secondary transfer member is made of a nickel-plated steel bar with an outer diameter of 8 mm, and is mainly composed of NBR adjusted to have a volume resistance of 10 ⁸ Ω·cm and a thickness of 5 mm, and epichlorohydrin rubber. One having an outer diameter of 18 mm covered with a foamed sponge body is used. The secondary transfer roller 63 contacts the intermediate transfer belt 54 with a pressure of 50N to form a secondary transfer portion N2. The secondary transfer roller 63 is driven to rotate with respect to the intermediate transfer belt 54, and a voltage of 1800 to 2300 V is applied when the toner image is secondarily transferred from the intermediate transfer belt 54 to the transfer material P at the secondary transfer portion N2. is applied to the secondary transfer roller 63 from the secondary transfer power source 300 .

After that, the transfer material P bearing the four-color toner image is introduced into a fixing means 62, where the four-color toners are melted and mixed and fixed to the transfer material P by being heated and pressurized. Secondary transfer residual toner remaining on the intermediate transfer belt 54 after the secondary transfer is charged by the cleaning brush 65 and moves as the intermediate transfer belt 54 moves. After that, the toner is removed from the intermediate transfer belt 54 by being reversely transferred from the intermediate transfer belt 54 to the photosensitive drum 56 at the primary transfer portion N1, and is collected by the cleaning means 61 of the photosensitive drum 56. FIG. A full-color image is formed on the transfer material P by the above operation.

[Control of Image Forming Apparatus]
FIG. 2 is a block diagram illustrating the configuration of the controller 10 as control means for controlling the image forming apparatus 100 in this embodiment. When image information and an image forming operation start signal are transmitted from the host computer 97 to the image forming apparatus 100 , the controller 10 receives each image signal converted by the video controller 98 . The controller 10 controls each control section (exposure control section 101, charging control section 102, development control section 103) to execute an image forming operation.

The controller 10 has a CPU 150 as a control section. The CPU 150 incorporates a ROM 151 and a RAM 152 . The CPU 150 comprehensively controls the exposure control unit 101 , charging control unit 102 , development control unit 103 , primary transfer control unit 104 , and secondary transfer control unit 105 according to control programs stored in the ROM 151 . An environment table and various tables for transfer control are stored in the ROM 151, and based on environmental information detected by the environment sensor 106 as a detection means for detecting the temperature and humidity in the installation environment of the image forming apparatus 100, the CPU 150 is called from and reflected.

The RAM 152 temporarily holds control data and is used as a work area for arithmetic processing associated with control. The charging control unit 102 controls voltages output from the charging power sources 401 and 402 . The development control unit 103 controls voltage output from the development power source 500 . The primary transfer control unit 104 controls the primary transfer power source 200 and controls the voltage output from the primary transfer power source 200 based on the current value detected by the current detection circuit 201 . The secondary transfer control unit 105 controls the secondary transfer power source 300 and controls the voltage output from the secondary transfer power source 300 based on the current value detected by a current detection circuit (not shown).

[Contact and Separation Operation of Primary Transfer Member]
The image forming apparatus 100 has means (not shown) for bringing the primary transfer members 59a, 59b, 59c, and 59d into contact with or away from the intermediate transfer belt . The controller 10 can perform image formation by selecting either a full-color image forming mode (hereinafter referred to as full-color mode) or a monochromatic image forming mode (hereinafter referred to as monochrome mode). FIG. 3A is a schematic diagram for explaining the full-color mode of this embodiment, and FIG. 3B is a schematic diagram for explaining the monochrome mode of this embodiment.

As shown in FIG. 3A, in the full-color mode, the primary transfer members 59a to 59d are brought into contact with the intermediate transfer belt 54 by a contact/separation mechanism (not shown) to form an image. That is, in the full-color mode, the first state in which the primary transfer members 59a to 59d are in contact with the intermediate transfer belt 54 is formed. On the other hand, in the monochrome mode, as shown in FIG. 3B, an image is formed by bringing only the primary transfer member 59d into contact with the intermediate transfer belt 54 by a contact/separation mechanism (not shown). That is, in the monochrome mode, the second state is formed in which the primary transfer member 59d is in contact with the intermediate transfer belt 54 and the primary transfer members 59a to 59c are separated from the intermediate transfer belt 54. FIG.

In the monochrome mode, as shown in FIG. 3B, the state in which the primary transfer members 59a to 59d are brought into contact with the intermediate transfer belt 54 is released by a contact/separation mechanism (not shown). As a result, when image formation is performed in the monochrome mode, driving of each member in the image forming sections 64a to 64c can be stopped. By adopting such a configuration, it is possible to suppress unnecessary operations and extend the life of each of the image forming units 64a to 64c.

As for the mechanism for bringing the primary transfer member 59 into contact with or separating from the intermediate transfer belt 54, for example, a configuration using an urging means such as a spring is conceivable. In such a configuration, it is possible to separate the primary transfer member 59 from the intermediate transfer belt 54 by releasing the biased state of the spring.

[Path of Current Flowing through Primary Transfer Portion]
Next, paths of current flowing through the primary transfer portion N1 in the full-color mode and the monochrome mode will be described with reference to FIGS. FIG. 4A is a schematic diagram illustrating the path of current flowing through the primary transfer portion N1 in the full-color mode, and FIG. 4B is a schematic diagram illustrating the current detection circuit 201. FIG. Also, FIG. 5 is a schematic diagram for explaining the path of the current flowing through the primary transfer portion N1 in the monochrome mode. The features of this embodiment are that a voltage is supplied from a common primary transfer power supply 200 to a plurality of primary transfer members 59, and that a common current detection circuit 201 detects the primary transfer current flowing through each of the primary transfer portions N1. means).

As shown in FIGS. 4A and 4B, in this embodiment, the charging power source 401 is connected to the charging rollers 57a to 57c, and the charging power source 402 is connected to the charging roller 57d. That is, by applying a predetermined voltage from the charging power supply 401 to the charging rollers 57a to 57c, the surfaces of the photosensitive drums 56a to 56c are uniformly charged to a predetermined potential by the charging rollers 57a to 57c. By applying a predetermined voltage from the charging power source 402 to the charging roller 57d, the surface of the photosensitive drum 56d is uniformly charged to a predetermined potential by the charging roller 57d.

<Full color mode>
The controller 10 sets the value of the primary transfer voltage to be applied from the primary transfer power supply 200 to the primary transfer members 59a, 59b, 59c, and 59d during the primary transfer of the job by ATVC control executed in the pre-rotation process of the job. In the following description, when the same control is performed on the primary transfer members 59a, 59b, 59c, and 59d, an attachment indicating which of the image forming portions 64a to 64d the primary transfer members 59a to 59d correspond to is used. The letters a to d are omitted, and the primary transfer members 59 are simply referred to.

In the ATVC control, first, a voltage that is constant current controlled at a predetermined current value (target current value) is applied from the primary transfer power source 200 to each primary transfer member 59 . At this time, the current detection circuit 201 obtains the current flowing toward each primary transfer portion N1, that is, the total value of the current flowing through each primary transfer member 59 . The controller 10 obtains the voltage value applied to each primary transfer member 59 from the primary transfer power supply 200 based on the detection result of the current detection circuit 201, and sets the value of the primary transfer voltage based on this voltage value.

Here, the current detection circuit 201 will be described with reference to FIG. 4(b). The current detection circuit 201 is electrically connected between the primary transfer power supply 200 and ground. The current detection circuit 201 also has an operational amplifier 204 and resistors 202 , 203 and 205 connected to the primary transfer power source 200 and feeds back the output of the operational amplifier 204 to the controller 10 . A voltage obtained by dividing the power supply voltage Vcc by resistors 202 and 203 (this voltage is hereinafter referred to as Vt) is input to the positive input of the operational amplifier 204 . The voltage value of the voltage Vt is set to approximately several volts in consideration of the rating of the operational amplifier 204 . Here, since the operational amplifier 204 forms a negative feedback circuit with the resistor 205, the potential difference between the positive input and the negative input of the operational amplifier 204 is 0V. That is, the positive input and the negative input of the operational amplifier 204 have the same potential as the voltage Vt.

When the output of the primary transfer power supply 200 is turned on, a voltage is applied to each primary transfer member 59, and as shown in FIG. , Ib, Ic, and Id flow. Here, the current Ia is a current that flows to GND (ground) through the primary transfer member 59a and the photosensitive drum 56a. Current flowing to GND via 56b-56d. A total value of the currents Ia to Id flowing through each primary transfer member 59 flows from GND to the operational amplifier 204 as a total current It. The total current It returns from the output unit of the operational amplifier 204 to the primary transfer power source 200 via the resistor 205 . Due to the current path described above, a voltage is generated across the resistor 205, and the output of the operational amplifier 204 (this voltage is hereinafter referred to as Visns) has a voltage value represented by Equation 1 below.
Vtisns=Vt+R205×It (Formula 1)
where R205 is the resistance value of resistor 205; Equation 1, which is information that associates the voltage value of the voltage Vtisns with the total current It that is the total value of the currents flowing through the primary transfer members 59, is stored in the ROM 151 of the controller 10 in advance. The controller 10 can detect the value of current flowing through each primary transfer member 59 as the total current It based on Equation 1 and the voltage Vtisns output from the current detection circuit 201 .

The value of the primary transfer voltage is set based on the voltage value (generated voltage value) generated across the resistor 205 , and when the toner image is primarily transferred from the photosensitive drum 56 to the intermediate transfer belt 54 , the primary transfer power source 200 , the primary transfer voltage set to each primary transfer member 59 is output. In this embodiment, when primary transfer is performed, constant voltage control is performed in which a predetermined primary transfer voltage set by the method described above is applied from the primary transfer power supply 200 to each primary transfer member 59 .

Note that the value of the primary transfer voltage set by ATVC control may be the generated voltage value itself in ATVC control, or the generated voltage value based on a previously obtained arithmetic expression, lookup table (LUT), or the like. may be determined according to In this embodiment, the primary transfer voltage is controlled by the controller 10 based on process speed information, environment information, and the like, based on a detection signal (voltage signal) from the current detection circuit 201 for each process speed, environment, and other conditions. It is designed to be That is, in this embodiment, a plurality of target current values are set according to conditions such as process speed and environment. Note that the ATVC control can be executed at any timing not only during the pre-rotation process until image formation of a job is started, but also during non-image formation.

<Monochrome mode>
As in the full-color mode described above, the controller 10 sets the value of the primary transfer voltage to be applied from the primary transfer power supply 200 to each primary transfer member 59 during the primary transfer of the job by the ATVC control executed in the pre-rotation process of the job. set.

When the output of the primary transfer power supply 200 is turned on, voltage is applied to each primary transfer member 59 . At this time, as shown in FIG. 5, a current Id' flows through the primary transfer member 59d, but no current flows through the primary transfer members 59a to 59c. More specifically, since the intermediate transfer belt 54 and the primary transfer members 59a to 59c are separated from each other, the current path connected to GND via the primary transfer members 59a to 59c and the photosensitive drums 56a to 56c is eliminated. The currents Ia to Ic shown in FIG. 5(a) do not flow. On the other hand, since the intermediate transfer belt 54 and the primary transfer member 59d are in contact with each other, the current Id' flows through the primary transfer member 59 through the current path connected to GND via the primary transfer member 59d and the photosensitive drum 56d.

A current Id′ flowing through the primary transfer member 59 d flows from GND to the operational amplifier 204 as a total current It, and then returns from the output terminal of the operational amplifier 204 to the primary transfer power source 200 via the resistor 205 . The controller 10 can detect the current value flowing through the primary transfer member 59 d based on Equation 1 and the voltage Vtisns output from the current detection circuit 201 .

[Relationship between primary transfer current and primary transfer voltage]
Next, the relationship between the primary transfer voltage applied to each primary transfer member 59 and the total current It detected by the current detection circuit 201 under each condition will be described with reference to FIGS. . The dotted line graphs shown in FIGS. 6B to 6F correspond to the graph shown in FIG. 6A.

FIG. 6A shows the voltage (primary transfer voltage Vt1) output from the primary transfer power source 200 to each primary transfer member 59 and the total current It detected by the current detection circuit 201 in the full color mode of this embodiment. It is a graph explaining a relationship. FIG. 6B shows the voltage (primary transfer voltage Vt1) output from the primary transfer power source 200 to each primary transfer member 59d and the total current It detected by the current detection circuit 201 in the monochrome mode of this embodiment. It is a graph explaining the relationship between.

Under the conditions of FIG. 6A, each photosensitive drum 56 is charged to -500 [V] by each charging roller 57 in the same manner as during image formation, and then each exposure means 60 performs laser exposure of the image forming area. Thus, the surface potential of each photosensitive drum 56 was set to about -500 [V]. Each primary transfer member 59 was brought into contact with the intermediate transfer belt 54, and the intermediate transfer belt 54 used had a surface resistance ρs of 1.0×10 ^9.5 [Ω/□]. Moreover, the measurement was performed under the environment of room temperature of 25° C. and humidity of 80%.

As shown in FIG. 6A, the relationship between the primary transfer voltage Vt1 and the total current It can be divided into two regions, region A and region B, for consideration. Region A is a region where the primary transfer voltage Vt1 is greater than +100 [V], and region B is a region where the primary transfer voltage Vt1 is +100 [V] or less. Also, when the primary transfer voltage Vt1 was +500 [V], the total current It was 40 [μA].

In the area A, when the primary transfer voltage Vt1 (+100 [V] or more) is applied from the primary transfer power supply 200 to each primary transfer member 59, the potential difference between the surface of each photosensitive drum 56 and the surface of the intermediate transfer belt 54 is exceeds the discharge threshold (approximately 600 [V] in this embodiment). Therefore, discharge occurs between the surface of each photosensitive drum 56 and the surface of the intermediate transfer belt 54 , and current flows through each photosensitive drum 56 .

On the other hand, in area B, even if the primary transfer voltage Vt1 is applied from the primary transfer power supply 200 to each primary transfer member 59, the potential difference between the surface of each photosensitive drum 56 and the surface of the intermediate transfer belt 54 is equal to or less than the discharge threshold. be. Therefore, no electric discharge occurs between the surface of each photosensitive drum 56 and the surface of the intermediate transfer belt 54 , so that no current flows through each photosensitive drum 56 . The relationship between the total current It detected by the current detection circuit 201 and the primary transfer voltage Vt1 is proportional to the position where the primary transfer voltage Vt1 is +100 [V].

Next, FIG. 6B will be described. As already explained with reference to FIG. 5, in the monochrome mode, the primary transfer members 59a to 59c are separated from the intermediate transfer belt 54, so the current flows only through the primary transfer member 59d. As a result, as shown in FIG. 6B, when the primary transfer voltage Vt1 was +500 [V], the total current It was 10 [μA]. Thus, in the monochrome mode, the relationship between the total current It detected by the current detection circuit 201 and the primary transfer voltage Vt1 has a smaller slope than that in FIG. 6A.

In the area A, when the primary transfer voltage Vt1 of +100 [V] or more is applied from the primary transfer power supply 200 to each primary transfer member 59, the potential difference between the surface of the photosensitive drum 56d and the surface of the intermediate transfer belt 54 is exceeds the discharge threshold, and a current flows through the primary transfer portion N1d. On the other hand, in area B, no current flows through each photosensitive drum 56, as in FIG. 6A. The relationship between the total current It detected by the current detection circuit 201 and the primary transfer voltage Vt1 is proportional to the position where the primary transfer voltage Vt1 is +100 [V].

As described above with reference to FIGS. 6A and 6B, the relationship between the total current It and the primary transfer voltage Vt1 changes according to the contact/separation state between the intermediate transfer belt 54 and each primary transfer member 59. .

FIG. 6C is a graph for explaining the relationship between the primary transfer voltage Vt1 and the total current It when the photosensitive drums 56a to 56c are not charged by the charging rollers 57a to 57c in the full color mode of the image forming apparatus 100. be. FIG. 6D illustrates the relationship between the primary transfer voltage Vt1 and the total current It when the photosensitive drums 56a to 56c are not charged by the charging rollers 57a to 57c in the monochrome mode of the image forming apparatus 100. graph.

As shown in FIG. 6C, in area A, when a primary transfer voltage Vt1 of +600 [V] or higher is applied from the primary transfer power source 200 to each primary transfer member 59, the surface of each photosensitive drum 56 and the intermediate transfer voltage Vt1 are applied. The potential difference with the surface of belt 54 exceeds the discharge threshold. At this time, discharge occurs between the surface of each photosensitive drum 56 and the surface of the intermediate transfer belt 54 , and current flows through each photosensitive drum 56 . Therefore, the relationship between the total current It detected by the current detection circuit 201 and the primary transfer voltage Vt1 in the area A has almost the same slope as compared with FIG. 6A. On the other hand, in area B, as in area B in FIG. 6A, no current flows through each photosensitive drum 56 .

Then, as shown in FIG. 6C, in area C, the potential difference between the surface of the photosensitive drum 56d charged by the charging roller 57d and the surface of the intermediate transfer belt 54 exceeds the discharge threshold. However, the potential difference between the surfaces of the photosensitive drums 56a-56c that are not charged by the charging rollers 57a-57c and the surface of the intermediate transfer belt 54 does not exceed the discharge threshold. Therefore, in area C, discharge occurs between the surface of the photosensitive drum 56d and the surface of the intermediate transfer belt 54, and current flows only through the photosensitive drum 56d. As a result, the relationship between the total current It detected by the current detection circuit 201 and the primary transfer voltage Vt1 in the area C becomes a proportional relationship passing through the position where the primary transfer voltage Vt1 is +100 [V]. The slope changes at the +600 [V] position.

Next, FIG. 6(d) will be described. As shown in FIG. 6D, in the second state in which the primary transfer members 59a to 59c are separated from the intermediate transfer belt 54, charging of the photosensitive drums 56a to 56c by the charging rollers 57a to 57c is stopped. , a graph similar to that of FIG. 6(b) was obtained. In the second state where the primary transfer members 59a-59c are not in contact with the intermediate transfer belt 54, no current flows through the primary transfer portions N1a-N1c regardless of the surface potentials of the photosensitive drums 56a-56c.

That is, in the area A, when the primary transfer voltage Vt1 of +100 [V] or more is applied from the primary transfer power supply 200 to each primary transfer member 59, the potential difference between the surface of the photosensitive drum 56d and the surface of the intermediate transfer belt 54 is exceeds the discharge threshold, current flows through the photosensitive drum 56d. On the other hand, in area B, no current flows through each photosensitive drum 56, as in FIG. 6A. The relationship between the total current It detected by the current detection circuit 201 and the primary transfer voltage Vt1 is proportional to the position where the primary transfer voltage Vt1 is +100 [V].

As described above, as shown in FIGS. 6C to 6D, the relationship between the total current It and the primary transfer voltage Vt1 changes according to the surface potential of each photosensitive drum 56 as well.

FIG. 6E is a graph illustrating the relationship between the primary transfer voltage Vt1 and the total current It in the full-color mode when the usage environment of the image forming apparatus 100 changes. In FIG. 6E, regardless of the value of the electrical resistance of the intermediate transfer belt 54, when the primary transfer voltage Vt1 applied to each primary transfer member 59 is +100 [V] or higher, each photosensitive drum 56 current flows through That is, under each condition of FIG. 6E, the relationship between the total current It detected by the current detection circuit 201 and the primary transfer voltage Vt1 is the same as in FIG. A proportional relationship passes through the position of [V].

The surface resistance of the intermediate transfer belt 54 may fluctuate due to changes in the usage environment of the image forming apparatus 100 . In FIG. 6A, the surface resistance ρs of the intermediate transfer belt 54 was 1.0×10 ^9.5 [Ω/□]. On the other hand, the graph R _LOW in FIG. 6E shows the relationship between the primary transfer voltage Vt1 and the total current It when the surface resistance ρs of the intermediate transfer belt 54 is reduced to 1.0×10 ⁷ [Ω/□]. shows the relationship between Graph R _High in FIG. 6E shows the relationship between the primary transfer voltage Vt1 and the total current It when the surface resistance ρs of the intermediate transfer belt 54 increases to 1.0×10 ¹¹ [Ω/□]. is shown.

As shown in the graph R _LOW , when the surface resistance ρs of the intermediate transfer belt 54 decreases to 1.0×10 ⁷ [Ω/□], the total current It is 60 V when the primary transfer voltage Vt1 is +500 [V]. [μA]. As for the graph R _LOW , since the resistance value of the intermediate transfer belt 54 is decreased, the current easily flows through each photosensitive drum 56 as compared with FIG. 6A. Therefore, the relationship between the total current It detected by the current detection circuit 201 and the primary transfer voltage Vt1 has a greater slope than in FIG. 6A.

Then, as shown in the graph R _High , when the usage environment of the intermediate transfer belt 54 changes and the surface resistance ρs increases to 1.0×10 ¹¹ [Ω/□], the primary transfer voltage Vt1 is +500 [V]. , the total current It was 20 [μA]. Regarding the graph R _LOW , since the resistance value of the intermediate transfer belt 54 is increased, compared with FIG. Therefore, the relationship between the total current It detected by the current detection circuit 201 and the primary transfer voltage Vt1 has a smaller slope than in FIG. 6A.

Finally, FIG. 6(f) will be described. FIG. 6F illustrates the relationship between the primary transfer voltage Vt1 and the total current It in the full-color mode when the surface layer thickness of each photosensitive drum 56 becomes thinner as the image forming apparatus 100 is continued to be used. It is a graph that As the film thickness of each photosensitive drum 56 becomes thinner, the potential difference generated in the gap between each charging roller 57 and each photosensitive drum 56 increases, so that the absolute value of the surface potential of each photosensitive drum 56 after charging increases. . That is, as shown in FIG. 6(f), the surface potential of each photosensitive drum 56 after charging is about -600 [V].

Then, in area A in FIG. 6F, when a primary transfer voltage Vt1 of +0 [V] or more is applied from the primary transfer power supply 200 to each primary transfer member 59, the surface of each photosensitive drum 56 and the intermediate transfer belt The potential difference between the surface of 54 exceeds the discharge threshold. At this time, discharge occurs between the surface of each photosensitive drum 56 and the surface of the intermediate transfer belt 54 , and current flows through each photosensitive drum 56 . Therefore, under the condition of FIG. 6(f), the relationship between the total current It detected by the current detection circuit 201 and the primary transfer voltage Vt1 is a proportional relationship passing through the position where the primary transfer voltage Vt1 is 0 [V]. Become.

As compared with FIG. 6A, under the conditions of FIG. 6F, the current easily flows through each photosensitive drum 56. When the primary transfer voltage Vt1 is +500 [V], the total current It is 60 V. became [uA]. That is, as shown in FIG. 6(f), the relationship between the total current It detected by the current detection circuit 201 and the primary transfer voltage Vt1 has a greater slope than that in FIG. 6(a).

6A to 6F, the relationship between the total current It and the primary transfer voltage Vt1 depends on the contact/separation state between the intermediate transfer belt 54 and each primary transfer member 59, the photosensitive drum It fluctuates depending on the surface potential of 56, the resistance value of the intermediate transfer belt 54, and the like.

[Detection of contact state between primary transfer member and intermediate transfer belt]
FIG. 7 is a flow chart illustrating a method for detecting the contact state between the primary transfer member 59 and the intermediate transfer belt 54 in this embodiment.

As shown in FIG. 7, when detecting the contact state between the primary transfer member 59 and the intermediate transfer belt 54, first, in S10, the developing rollers 58a, 58b, 58c, and 58d are separated. As a result, the surface potentials of the photosensitive drums 56a, 56b, 56c, and 56d are conveyed to the positions of the primary transfer members 59a, 59b, 59c, and 59d without toner adhering. Thereafter, in S11, a predetermined voltage A is applied from the charging power sources 401 and 402 to the charging rollers 57a, 57b, 57c and 57d. Then, in S12, a predetermined voltage B is applied from the primary transfer power supply 200 to each of the primary transfer members 59a, 59b, 59c, and 59d. Here, the predetermined voltage A and the predetermined voltage B are determined according to the generated voltage value based on an arithmetic expression, a lookup table, or the like obtained in advance. In this embodiment, the predetermined voltage A is -1000 [V] and the predetermined voltage B is 350 [V].

After that, in S13, after the total current It1 (first current value) is detected by the current detection circuit 201, the application of the predetermined voltage A from the charging power supply 401 to the charging rollers 57a, 57b, and 57c is stopped in S14. This stops the charging of the photosensitive drums 56a, 56b and 56c by the charging rollers 57a, 57b and 57c. In S15, the detection by the current detection circuit 201 is waited for a predetermined time T, so that the surfaces of the photosensitive drums 56a, 56b, and 56c that are not charged by the charging rollers 57a, 57b, and 57c are transferred to the primary transfer portions N1a, N1b, and N1c. to reach

Here, the predetermined time T is at least the distance from the position where the charging roller 57 and the photosensitive drum face each other to the primary transfer portions N1a, N1b, and N1c in the rotational movement direction of the photosensitive drum 56. It is set longer than the time it takes to move. With this setting, the surfaces of the photosensitive drums 56a, 56b, and 56c that are not charged by the charging rollers 57a, 57b, and 57c reach the primary transfer portions N1a, N1b, and N1c after the predetermined time T has passed.

Subsequently, in S16, after detecting the total current It2 (second current value) by the current detection circuit 201, in S17, the value of the total current It1 and the value of the total current It2 are compared. As described with reference to FIGS. 6A and 6C, in the full-color mode, that is, in the first state where each primary transfer member 59 contacts the intermediate transfer belt 54, charging by the charging rollers 57a to 57c is performed. By stopping, the current detected by the current detection circuit 201 decreases. Therefore, when the total current It1 is larger than the total current It2, the controller 10 determines in S18 that the primary transfer members 59 are in contact with the intermediate transfer belt 54 in the first state.

On the other hand, as described with reference to FIGS. 6B and 6D, in the monochrome mode, that is, in the second state where only the primary transfer member 59d contacts the intermediate transfer belt 54, the charging rollers 57a to 57c Even if charging is stopped, the current detected by the current detection circuit 201 does not change. Therefore, when the total current It1 is equal to or less than the total current It2, the controller 10 causes the primary transfer member 59d and the intermediate transfer belt 54 to come into contact with each other and the primary transfer members 59a to 59c to separate from the intermediate transfer belt 54 in S19. It is determined that the state is the second state.

To explain the above determination in more detail, when each photosensitive drum 56 is charged to -500 [V] in the first state and a primary transfer voltage Vt1 of +500 [V] is applied, the total current It is As shown in FIG. 6(a), it becomes 40 [μA]. On the other hand, in the first state, when the photosensitive drums 56a, 56b, and 56c are not charged and only the photosensitive drum 56d is charged, and the primary transfer voltage Vt1 of +500 [V] is applied, the total current It is as shown in FIG. It becomes 10 [μA] as shown in 6(c).

On the other hand, when each photosensitive drum 56 is charged to -500 [V] in the second state and a primary transfer voltage Vt1 of +500 [V] is applied, the total current It is as shown in FIG. becomes 10 [μA]. On the other hand, in the second state, when the photosensitive drums 56a, 56b, and 56c are not charged and only the photosensitive drum 56d is charged, and the primary transfer voltage Vt1 of +500 [V] is applied, the total current It is It becomes 10 [μA] as shown in 6(d).

Thus, in the first state, the value of the total current It changes before and after the charging of the photosensitive drums 56a to 56c by the charging rollers 57a to 57c is stopped. Therefore, in S17 shown in FIG. 7, the controller 10 can determine whether the first state or the second state is formed by comparing the value of the sum current It1 and the value of the sum current It2. .

As described above, in this embodiment, the primary transfer member 59 and the intermediate transfer belt 54 are detected based on the detection results of the current detection circuit 201 before and after stopping the charging of the photosensitive drums 56a to 56c by the charging rollers 57a to 57c. determines the state of contact with the As a result, in a configuration in which a voltage is applied from the primary transfer power supply 200 to a plurality of primary transfer members 59, the state of contact between the primary transfer members 59 and the intermediate transfer belt 54 can be accurately determined based on the detection result of the current detection circuit 201. It is possible to judge

In this embodiment, the current detection circuit 201 detects the sum of the currents flowing through the primary transfer members 59 when the primary transfer voltage Vt1 is applied to the primary transfer members 59. However, the present invention is not limited to this. do not have. If at least the potential difference between the photosensitive drum 56 and the intermediate transfer belt 54 exceeds the discharge threshold, the total current It can be detected. Therefore, for example, when the predetermined voltage A is set to a value with a large absolute value and the surface potential of each photosensitive drum 56 is set to a value that is larger on the minus side than the discharge threshold value of -600 [V], the primary transfer The total current It can be detected without requiring the voltage Vt1.

Further, as shown in FIGS. 6E and 6F, the value of the total current It is affected by the usage state of the image forming apparatus 100. FIG. On the other hand, according to the configuration of this embodiment, it is possible to detect the total current It under the same conditions except for the setting of the surface potential of the photosensitive drum 56 . That is, the state of contact between the primary transfer member 59 and the intermediate transfer belt 54 can be determined with higher accuracy than the configuration in which the total current value is compared with a predetermined threshold value.

In this embodiment, the method for distinguishing between the full-color mode and the monochrome mode has been described, but the present invention can also be used to detect modes other than these modes. For example, a two-color mode in which an image is formed using only the yellow and magenta image forming units 64a and 64b, and a three-color mode in which an image is formed using only the yellow, magenta, and cyan image forming units 64a, 64b, and 64c. etc., various combinations of modes are conceivable. Even in such an image forming apparatus having various color modes, it is possible to determine which primary transfer member and intermediate transfer belt are in contact with each other by using the detection method described in this embodiment. .

Further, in the present embodiment, the predetermined voltage A and the predetermined voltage B are determined according to the generated voltage value based on an arithmetic expression, a lookup table, etc. obtained in advance, but are not limited to this. not something. For example, according to the detection result of the environment sensor 106, the values of the predetermined voltage A and the predetermined voltage B may be further corrected.

Furthermore, in this embodiment, the developing roller 58 is separated from the photosensitive drum 56 to prevent the toner from adhering to the photosensitive drum. You can keep it as is. In this case, for example, the voltage applied from the developing power supply 500 to the developing roller 58 is a voltage having a polarity opposite to that during image formation, thereby preventing the toner carried by the developing roller 58 from moving to the photosensitive drum 56 . should be controlled to

Although a conductive brush member is used as the primary transfer member 59 in this embodiment, it is also possible to use a roller member having a conductive elastic layer, a conductive sheet member, a metal roller, or the like. .

Further, in this embodiment, a configuration has been described in which the primary transfer members 59a to 59d can be separated from the intermediate transfer belt 54, but the present invention is not limited to this. For example, a configuration in which the primary transfer member 59d corresponding to the image forming portion 64d containing black toner is always brought into contact with the intermediate transfer belt 54, that is, a configuration in which the primary transfer member 59d and the intermediate transfer belt 54 are always brought into contact may be employed. good. In this case, an urging structure may be adopted in which only the primary transfer members 59a to 59c can contact or separate from the intermediate transfer belt .

In this embodiment, a configuration is used in which a voltage is applied from the common primary transfer power source 200 to all the primary transfer members 59a to 59d. Also good. More specifically, by sharing a primary transfer power source for applying voltage to at least two primary transfer members, it is possible to obtain the effects described in this embodiment.

(Example 2)
In the first embodiment, the surface potentials of the photosensitive drums 56a to 56c are changed by stopping charging by the charging rollers 57a to 57c in order to determine whether the first state or the second state is formed. A configuration for switching between is described. On the other hand, the second embodiment differs from the first embodiment in that the surface potentials of the photosensitive drums 56a to 56c are switched by exposing the photosensitive drums 56a to 56c by the exposing means 60a to 60c. In the following description, the same reference numerals are given to the configurations and controls that are common to the second embodiment and the first embodiment, and the description thereof will be omitted.

FIG. 8 is a schematic diagram for explaining the current flowing through the primary transfer member in the full-color mode of this embodiment. As can be seen by comparing FIG. 8 and FIG. 4A, in this embodiment, a voltage is applied to each charging roller 57 from a common charging power supply 400. FIG. As will be described in detail below, in this embodiment, the surface potentials of the photosensitive drums 56a to 56c are increased by exposing the photosensitive drums 56a to 56c by the exposure means 60a to 60c without stopping the charging by the charging rollers 57a to 57c. switch. Therefore, it is not necessary to separately provide a charging power source for applying voltage to the charging rollers 57a to 57c and the charging roller 57d, and it is possible to use a common charging power source 400 as shown in FIG.

In this embodiment, the voltage is applied to each charging roller 57 by the common charging power supply 400, but the present invention is not limited to this. For example, the charging rollers 57a to 57d may be individually provided with charging power sources, or some of the charging rollers 57a to 57d may be provided with a common charging power source. A configuration of the charging power supply similar to that of Example 1 may be used.

[Relationship between primary transfer current and primary transfer voltage]
Next, FIG. 9 ( Description will be made using c) to (d). 9A and 9B are graphs showing the relationship between the primary transfer voltage Vt1 and the total current It when the photosensitive drums 56a to 56c are not exposed by the exposing means 60a to 60c. Here, FIGS. 9(a) to (b) are provided as a reference for comparison with FIGS. 9(c) to (d). The same graph.

FIG. 9C is a graph for explaining the relationship between the primary transfer voltage Vt1 and the total current It when the photosensitive drums 56a to 56c are exposed by the exposure units 60a to 60c in the full color mode of the image forming apparatus 100. FIG. FIG. 9D is a graph for explaining the relationship between the primary transfer voltage Vt1 and the total current It when the exposure units 60a to 60c expose the photosensitive drums 56a to 56c in the monochrome mode of the image forming apparatus 100. be. The dotted line graphs shown in FIGS. 9B to 9D correspond to the graph shown in FIG. 9A.

As shown in FIGS. 9C to 9D, the photosensitive drums 56a to 56c are exposed by the exposure means 60a to 60c, so that the surface potential is −100 [V]. The surface potential of the photosensitive drum 56d is -500 [V] because it is not exposed by the exposing means 60d. In FIGS. 9C and 9D, when the primary transfer voltage Vt1 is +500 [V], the total current It is 10 [μA].

As shown in FIG. 9C, in area A, when a primary transfer voltage Vt1 of +500 [V] or higher is applied from the primary transfer power supply 200 to each primary transfer member 59, the surface of each photosensitive drum 56 and the intermediate transfer voltage Vt1 are applied. The potential difference with the surface of belt 54 exceeds the discharge threshold. At this time, discharge occurs between the surface of each photosensitive drum 56 and the surface of the intermediate transfer belt 54 , and current flows through each photosensitive drum 56 . Therefore, in the region A, the relationship between the total current It detected by the current detection circuit 201 and the primary transfer voltage Vt1 has almost the same slope as compared to FIG. 9A. On the other hand, in area B, as in area B in FIG. 9A, no current flows through each photosensitive drum 56 .

Then, as shown in FIG. 9(c), in area C, the potential difference between the surface of the intermediate transfer belt 54 and the surface of the photosensitive drum 56d, which has not been exposed by the exposing means 60d after being charged by the charging roller 57d, is exceeds the discharge threshold. However, the potential difference between the surfaces of the photosensitive drums 56a-56c exposed by the exposure means 60a-60c and the surface of the intermediate transfer belt 54 does not exceed the discharge threshold. Therefore, in area C, discharge occurs between the surface of the photosensitive drum 56d and the surface of the intermediate transfer belt 54, and current flows only through the photosensitive drum 56d. As a result, the relationship between the total current It detected by the current detection circuit 201 and the primary transfer voltage Vt1 in the area C becomes a proportional relationship passing through the position where the primary transfer voltage Vt1 is +100 [V]. The slope changes at the +500 [V] position. Also, the relationship between the primary transfer voltage Vt1 and the total current It in region C has a smaller slope than in FIG. 9A.

Next, FIG.9(d) is demonstrated. As shown in FIG. 9D, in a second state in which the primary transfer members 59a to 59c are separated from the intermediate transfer belt 54, even if the surfaces of the photosensitive drums 56a to 56c are exposed by the exposure means 60a to 60c, , a graph similar to that of FIG. 9(b) was obtained. In the second state where the primary transfer members 59a-59c are not in contact with the intermediate transfer belt 54, no current flows through the primary transfer portions N1a-N1c regardless of the surface potentials of the photosensitive drums 56a-56c.

That is, in the area A, when the primary transfer voltage Vt1 of +100 [V] or more is applied from the primary transfer power supply 200 to each primary transfer member 59, the potential difference between the surface of the photosensitive drum 56d and the surface of the intermediate transfer belt 54 is exceeds the discharge threshold, current flows through the photosensitive drum 56d. On the other hand, in area B, no current flows through each photosensitive drum 56, as in FIG. 9A. In region A, the relationship between the total current It detected by the current detection circuit 201 and the primary transfer voltage Vt1 is proportional to the position where the primary transfer voltage Vt1 passes +100 [V]. Also, the relationship between the primary transfer voltage Vt1 and the total current It in the area A has a smaller slope than in FIG. 9A.

[Detection of contact state between primary transfer member and intermediate transfer belt]
FIG. 10 is a flow chart illustrating a method for detecting the contact state between the primary transfer member 59 and the intermediate transfer belt 54 in this embodiment.

As shown in FIG. 10, when detecting the contact state between the primary transfer member 59 and the intermediate transfer belt 54, first, in S20, the developing rollers 58a, 58b, 58c, and 58d are separated. As a result, the surface potentials of the photosensitive drums 56a, 56b, 56c, and 56d are conveyed to the positions of the primary transfer members 59a, 59b, 59c, and 59d without toner adhering. After that, in S21, a predetermined voltage A is applied from the charging power source 400 to each of the charging rollers 57a, 57b, 57c and 57d. Then, in S22, a predetermined voltage B is applied from the primary transfer power source 200 to each of the primary transfer members 59a, 59b, 59c, and 59d. Here, the predetermined voltage A and the predetermined voltage B are determined according to the generated voltage value based on an arithmetic expression, a lookup table, or the like obtained in advance.

After that, in S23, the total current It1 (first current) is detected by the current detection circuit 201, and in S24, the photosensitive drums 56a, 56b, and 56c are exposed by the exposure means 60a, 60b, and 60c. Thereby, the surface potentials of the photosensitive drums 56a, 56b, and 56c are switched. In this embodiment, in S24, the controller 10 controls the exposure control section 101 so that the surface potentials of the photosensitive drums 56a, 56b, and 56c are approximately −100 [V].

Then, in S25, detection by the current detection circuit 201 is waited for a predetermined time T2. Here, the predetermined time T2 is at least the distance from the position where the photosensitive drum 56 is exposed by the exposing means 60 to the primary transfer portions N1a, N1b, and N1c with respect to the rotational movement direction of the photosensitive drum 56. It is set longer than the time required to rotate. With this setting, the surfaces of the photosensitive drums 56a, 56b, and 56c exposed by the exposing means 60a, 60b, and 60c reach the primary transfer portions N1a, N1b, and N1c after the predetermined time T has elapsed.

Subsequently, in S26, after detecting the total current It2 (second current) by the current detection circuit 201, in S27, the value of the total current It1 and the value of the total current It2 are compared. As described with reference to FIGS. 9A to 9D, in the first state where each primary transfer member 59 contacts the intermediate transfer belt 54, the exposure means 60a to 60c expose the photosensitive drums 56a to 56c. , the current detected by the current detection circuit 201 decreases. Therefore, when the total current It1 is larger than the total current It2, the controller 10 determines in S28 that the primary transfer members 59 are in contact with the intermediate transfer belt 54 in the first state.

On the other hand, as described with reference to FIGS. 9B and 9D, in the second state where only the primary transfer member 59d contacts the intermediate transfer belt 54, the exposure means 60a to 60c expose the photosensitive drums 56a to 56c. is exposed, the current detected by the current detection circuit 201 does not change. Therefore, when the total current It1 is equal to or less than the total current It2, the controller 10 causes the primary transfer member 59d and the intermediate transfer belt 54 to come into contact with each other and the primary transfer members 59a to 59c to separate from the intermediate transfer belt 54 in S29. It is determined that the state is the second state.

As described above, according to the configuration of the present embodiment, the first state or the second state is obtained based on the detection result of the current detection circuit 201 before and after the exposure means 60a to 60c expose the photosensitive drums 56a to 56c to switch the surface potential. It can be determined which of the two states is formed. As a result, in a configuration in which a voltage is applied from the primary transfer power supply 200 to a plurality of primary transfer members 59, the state of contact between the primary transfer members 59 and the intermediate transfer belt 54 can be accurately determined based on the detection result of the current detection circuit 201. It is possible to judge

REFERENCE SIGNS LIST 10 controller 54 intermediate transfer belt 56 photosensitive drum 57 charging roller 59 primary transfer member 200 primary transfer power source 201 current detection circuit

Claims (11)

a first image carrier that carries a toner image;
a first charging member for charging the first image carrier;
a second image carrier carrying a toner image of a color different from that of the first image carrier;
a second charging member for charging the second image carrier;
an intermediate transfer member to which the toner image carried on at least one of the first image carrier and the second image carrier is transferred;
a first transfer member provided at a position corresponding to the first image carrier through the intermediate transfer member, for transferring the toner image from the first image carrier to the intermediate transfer member;
a second transfer member provided at a position corresponding to the second image carrier through the intermediate transfer member, for transferring the toner image from the second image carrier to the intermediate transfer member;
a transfer power supply that applies a voltage to the first transfer member and the second transfer member;
detection means for detecting a current flowing through the first transfer member and the second transfer member when a voltage is applied from the transfer power supply to the first transfer member and the second transfer member;
the intermediate transfer from at least one of the first image carrier and the second image carrier in a first state in which the first transfer member and the second transfer member are brought into contact with the intermediate transfer member; a mode for transferring a toner image onto a body; a mode for transferring a toner image from the image carrier to the intermediate transfer member; and a control means capable of selecting and executing either mode,
The control means charges the first image carrier and the second image carrier with the first charging member and the second charging member, respectively, and charges the first image carrier from the transfer power source. a first current value detected by the detecting means in a state in which a voltage is applied to the transfer member and the second transfer member; and a second current value detected by the detection means in a state in which a voltage is applied from the transfer power source to the first transfer member and the second transfer member after switching the surface potential of the body. , an image forming apparatus which determines whether the first state or the second state is formed. 2. A method according to claim 1, wherein said control means switches the surface potential of said second image carrier by stopping charging of said second image carrier by said second charging member. Image forming device. An exposing means for exposing the second image carrier,
2. The image forming apparatus according to claim 1, wherein said control means switches the surface potential of said second image carrier by exposing said second image carrier from said exposing means. The detection means is electrically connected between the transfer power source and ground, and detects the first transfer member when a voltage is applied from the transfer power source to the first transfer member and the second transfer member. 4. The image forming apparatus according to any one of claims 1 to 3, wherein the total value of the current flowing through the first transfer member and the current flowing through the second transfer member is detected. The control means determines whether the first state or the second state is formed based on a result of comparing the first current value and the second current value. The image forming apparatus according to any one of claims 1 to 4, characterized by: The control means determines that the first state exists when the first current value is greater than the second current value, and determines that the first state is the state when the first current value is less than or equal to the second current value. 6. The image forming apparatus according to claim 1, wherein the second state is determined. 7. The apparatus according to any one of claims 1 to 6, wherein said second current value is detected by said control means after a predetermined time has passed since the surface potential of said second image carrier is switched. The described image forming apparatus. It is capable of contacting or separating from the first image carrier, and an electrostatic latent image formed on the first image carrier in contact with the first image carrier is formed by toner. A first developing member that develops can contact or be separated from the second image carrier, and is formed on the second image carrier while being in contact with the second image carrier. a second development member for developing the applied electrostatic latent image with toner;
The control means separates the first developing member from the first image carrier, separates the second developing member from the second image carrier, and thereafter separates the first developing member from the transfer power source. determining whether the first state or the second state is established based on the detection result of the detection means when a voltage is applied to the transfer member and the second transfer member. 8. The image forming apparatus according to claim 1, wherein: 9. The image forming apparatus according to claim 1, wherein the first image carrier is an image carrier that carries a black toner image. 10. The image forming apparatus according to claim 1, wherein the first transfer member and the second transfer member are composed of conductive brush members. 10. The image forming apparatus according to claim 1, wherein the first transfer member and the second transfer member are conductive roller members.

Images