JP2017068128A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation device that can adjust a process setting as to each of a plurality of photoreceptors using the transfer power source and current detection unit in a configuration making the transfer power source and current detection unit common with respect to a plurality of photoreceptors.SOLUTION: An image formation device 100 includes: a common power source 93 that applies a voltage for transferring a toner image to a moving body 7 from each of a plurality of photoreceptors 1 to a plurality of transfer units N1; a current detection unit 94 that detects a current flowing to the power source 93; and a control unit 15 that causes the plurality of photoreceptors 1 to execute an adjustment operation of adjusting respective process settings upon forming the toner image. In the adjustment operation, the control unit 15 is configured to cause detection of the current by the current detection unit 94 through application of the voltage to the plurality of transfer units N1 by the power source 93 to be conducted in a plurality of states where an area passing through the transfer unit N1 upon detection of the current is different in a combination of the photoreceptor serving as charging part potential and the photoreceptor serving as exposure part potential of the plurality of photoreceptors 1.SELECTED DRAWING: Figure 7

Description

  The present invention relates to an electrophotographic image forming apparatus having a plurality of photoconductors.

  Conventionally, an electrophotographic image forming apparatus uniformly charges a photosensitive member (electrophotographic photosensitive member) and then exposes it to form an electrostatic latent image, and develops the electrostatic latent image with toner. A toner image is formed, and the toner image is transferred to a transfer material directly or via an intermediate transfer member to form an image. In particular, a color image forming apparatus has an image forming unit that forms toner images of different colors independently, and a toner image formed by each image forming unit is transferred onto a transfer material carrier or an intermediate material. There is a tandem type that transfers the image so as to be superimposed on the transfer body. As the transfer material carrier and the intermediate transfer member, a transfer material carrier belt (conveyor belt) and an intermediate transfer belt constituted by endless belts are widely used.

  In a photoconductor used in such an electrophotographic image forming apparatus, in particular, a photoconductor (organic photoconductor) using an OPC (organic photoconductor) as a photosensitive layer, a difference in temperature and humidity, elapse of usage time, etc. As a result, the exposed portion potential VL may fluctuate. If VL fluctuates in the direction of increasing development contrast (difference between development bias and exposed area potential), the amount of toner transferred to the photoconductor during development becomes too large, and line images are likely to scatter or have poor fixing. Become. Further, if the VL fluctuates in the direction in which the development contrast decreases, the image density is lowered.

  As a method for suppressing the problems caused by these VL variations, it is conceivable to detect the VL variations and optimize the development contrast. As a method for detecting the fluctuation of VL, it is conceivable to provide a special surface potential sensor for detecting the surface potential of the photoreceptor, but this is disadvantageous in terms of cost. Therefore, as a method for detecting fluctuations in VL with a configuration advantageous for cost reduction, a method for measuring the amount of charging current that flows when the exposed portion on the photosensitive member is charged again after one rotation of the photosensitive member by the charging member is proposed. (Patent Document 1). The amount of charging current is determined by the potential difference between the charging member and the surface of the photoreceptor. That is, when the VL fluctuates in a direction in which the absolute value of the VL decreases, the potential difference between the charging member and the VL shifts to a larger value, so that the charging current amount increases. On the other hand, when VL fluctuates in the direction in which the absolute value of VL increases, the potential difference between the charging member and VL shifts to the smaller side, and the amount of charging current decreases. By measuring the charging current amount in this way, it is possible to detect a change in VL.

Japanese Patent Laid-Open No. 10-49008

  Here, for example, in an intermediate transfer type image forming apparatus, a primary transfer bias is applied from a primary transfer power source to a primary transfer member provided on the inner peripheral surface side of the intermediate transfer belt corresponding to the photosensitive member. A toner image is primarily transferred from the photoreceptor to the intermediate transfer belt. In such an image forming apparatus, in order to control the primary transfer bias, a current detection circuit (current detection unit) that detects a current flowing through the primary transfer power supply may be provided.

  Therefore, if this current detection circuit is used, it is possible to detect a change in VL with a more advantageous configuration at low cost without providing a new current detection circuit to detect the amount of charging current as described above. It is believed that there is. In other words, the current detection circuit provided for controlling the primary transfer bias is used as a current detection circuit for detecting the amount of current flowing to the primary transfer power supply when the exposed portion on the photosensitive member is charged by the primary transfer portion. Can be considered.

  However, in a tandem type image forming apparatus, a primary transfer power supply (transfer power supply) and a current detection circuit may be commonly used for a plurality of photoconductors in order to reduce the size and cost of the apparatus. In this case, it is necessary to detect the VL fluctuation of each of the plurality of photoconductors with a common primary transfer power supply and current detection circuit. Further, if the electric resistance value of the intermediate transfer belt existing between the primary transfer member and the photosensitive member fluctuates, the current value changes even if VL does not fluctuate. It is necessary to detect the change in VL without being affected by the change.

  Accordingly, an object of the present invention is to adjust process settings for each of a plurality of photoconductors using the transfer power source and the current detection unit in a configuration in which a transfer power source and a current detection unit are shared with respect to the plurality of photoconductors. It is an object of the present invention to provide an image forming apparatus capable of achieving the above.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides a plurality of photoconductors, a plurality of charging means for forming a charged portion potential by charging each of the plurality of photoconductors, and each of the plurality of photoconductors subjected to the charge processing. An exposure unit that exposes to form an exposed portion potential; a plurality of developing units that form toner images by supplying toner to each of the exposed plurality of photoconductors; and a contact with each of the plurality of photoconductors. And a movable body that can be moved around to form a plurality of transfer portions, and a toner image is transferred to the plurality of transfer portions from each of the plurality of photosensitive members to the movable body or a transfer material carried on the movable body. A common power source for applying a voltage; a current detection unit for detecting a current flowing in the power source; and a control unit for executing an adjustment operation for adjusting each process setting when forming toner images on the plurality of photosensitive members; Have In the adjustment operation, the control unit applies a voltage to the plurality of transfer units by the power source and detects a current by the current detection unit, and detects the transfer unit at the time of the detection among the plurality of photosensitive members. An image forming apparatus characterized in that the image forming apparatus is configured to perform a plurality of states in which a combination of a photosensitive member whose passing region is a charging portion potential and a photosensitive member whose exposure portion potential is different.

  According to the present invention, in a configuration in which a transfer power source and a current detection unit are shared with respect to a plurality of photoconductors, it is possible to adjust process settings for each of the plurality of photoconductors using the transfer power source and the current detection unit. It becomes.

1 is a schematic sectional view of an image forming apparatus. It is a schematic diagram which shows the structure of an image formation part. FIG. 6 is a schematic diagram illustrating a potential relationship in a toner image forming process. FIG. 6 is a graph showing a potential relationship in a toner image forming process. FIG. 4 is a schematic diagram and an equivalent circuit diagram showing a configuration of a primary transfer power source. FIG. 6 is a graph for explaining a change in potential relationship in a toner image forming process. It is a flowchart figure of control of Example 1. FIG. It is a flowchart of control of Example 2. FIG. 10 is a flowchart of control in Embodiment 3. FIG. 10 is a graph showing the relationship between the applied bias and the current value in the detection operation of Example 3. It is a schematic sectional drawing of the other example of an image forming apparatus.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

[Example 1]
1. 1 is a schematic cross-sectional view of an image forming apparatus 100 according to an embodiment of the present invention. The image forming apparatus according to the present exemplary embodiment is a tandem type laser beam printer that employs an intermediate transfer method that can form a full-color image using an electrophotographic method.

  The image forming apparatus 100 includes first, second, third, and third images that form yellow (Y), magenta (M), cyan (C), and black (K) images as a plurality of image forming units (stations), respectively. 4 image forming units 10Y, 10M, 10C, and 10K. In the present embodiment, the configuration and operation of each of the image forming units 10Y, 10M, 10C, and 10K are substantially the same except that the color of toner used in the developing process described later is different. Therefore, unless distinction is particularly required, the Y, M, C, and K at the end of the reference numeral indicating any color element will be omitted, and the element will be described generally. FIG. 2 shows the configuration of the image forming unit 10 in more detail.

  The image forming unit 10 includes a photosensitive drum 1 that is a rotatable drum-type electrophotographic photosensitive member (photosensitive member) as an image carrier. The photosensitive drum 1 is rotationally driven in the direction of arrow R1 in the figure by a drum driving motor (not shown) as a photosensitive member driving means. In this embodiment, the photosensitive drum 1 is an organic photoconductor (OPC) photosensitive drum in which a photosensitive layer of an organic material is formed on a conductive support. In the image forming unit 10, the following devices are arranged around the photosensitive drum 1. First, a charging roller 2 that is a roller-type charging member as a charging unit is disposed. Next, an exposure apparatus 3 as an exposure unit is arranged. Next, a developing device 4 as a developing unit is arranged. Next, a primary transfer roller 5 that is a roller-type primary transfer member as a primary transfer means is disposed. Next, a drum cleaner 6 as a photosensitive member cleaning means is disposed. In this embodiment, the exposure apparatus 3 is configured as one unit so as to expose the photosensitive drums 1Y, 1M, 1C, and 1K of the image forming units 10Y, 10M, 10C, and 10K. 10Y, 10M, 10C, 10K may be provided independently.

  The surface of the rotating photosensitive drum 1 is uniformly charged by a charging roller 2 to a predetermined potential having a predetermined polarity (negative polarity in this embodiment). The surface of the charged photosensitive drum 1 is scanned and exposed by the exposure device 3 according to image information, and an electrostatic latent image (electrostatic image) is formed on the photosensitive drum 1. The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) using toner as a developer by the developing device 4, and a toner image is formed on the photosensitive drum 1. The toner image forming process will be described in detail later.

  An intermediate transfer belt 7 composed of an endless belt as an intermediate transfer member is disposed facing the photosensitive drums 1Y, 1M, 1C, and 1K of the image forming units 10Y, 10M, 10C, and 10K. The intermediate transfer belt 7 is wound around a driving roller 71, a tension roller 72, and a secondary transfer counter roller 73 as a plurality of support rollers (stretching rollers) and is stretched with a predetermined tension. The intermediate transfer belt 7 rotates (circulates) in the direction of the arrow R2 in the drawing when the driving roller 71 is rotationally driven by a belt driving motor (not shown) as an intermediate transfer body driving unit. On the inner peripheral surface side of the intermediate transfer belt 7, the above-described primary transfer rollers 5Y, 5M, 5C, and 5K are arranged corresponding to the photosensitive drums 1Y, 1M, 1C, and 1K. The primary transfer roller 5 is urged toward the photosensitive drum 1 via the intermediate transfer belt 7 to form a primary transfer portion (primary transfer nip) N1 where the photosensitive drum 1 and the intermediate transfer belt 7 are in contact with each other. Further, on the outer peripheral surface side of the intermediate transfer belt 7, a secondary transfer roller 8, which is a roller-type secondary transfer member as a secondary transfer unit, is disposed facing the secondary transfer counter roller 73. The secondary transfer roller 8 is urged toward the secondary transfer counter roller 73 via the intermediate transfer belt 7, and a secondary transfer portion (secondary transfer nip) where the intermediate transfer belt 7 and the secondary transfer roller 8 come into contact with each other. ) N2 is formed. The intermediate transfer belt 7 is an example of a movable body that can move around and forms a plurality of transfer portions in contact with each of a plurality of photoconductors.

  The toner image formed on the photosensitive drum 1 as described above is electrostatically transferred (primary transfer) onto the intermediate transfer belt 7 in the primary transfer portion N1. At this time, the primary transfer roller 5 is supplied with a DC voltage having a polarity (positive in this embodiment) opposite to the charging polarity (normal charging polarity) of the toner at the time of development by a primary transfer power supply (high voltage power supply circuit) 91. A certain primary transfer bias (primary transfer voltage) is applied. For example, when forming a full-color image, four color toner images formed on the photosensitive drums 1Y, 1M, 1C, and 1K are superimposed on the intermediate transfer belt 7 in the primary transfer portions N1Y, N1M, N1C, and N1K. Are sequentially transferred. The toner remaining on the surface of the photosensitive drum 1 after the primary transfer process (primary transfer residual toner) is removed from the surface of the photosensitive drum 1 by the drum cleaner 6 and collected. In this embodiment, the drum cleaner 6 scrapes the primary transfer residual toner from the surface of the rotating photosensitive drum 1 by the cleaning blade 61 as a cleaning member, and stores it in the waste toner storage unit 62.

  The toner image formed on the intermediate transfer belt 7 is electrostatically transferred (secondary transfer) onto a transfer material P such as paper at the secondary transfer portion N2. At this time, a secondary transfer bias (secondary transfer) is applied to the secondary transfer roller 8 by a secondary transfer power supply (high-voltage power supply circuit) (not shown) having a DC voltage opposite to the normal charging polarity of the toner. Voltage) is applied. The transfer material P is fed from a cassette 11 as a storage unit, and is conveyed to the secondary transfer unit N2 in synchronization with the toner image on the intermediate transfer belt 7 by a registration roller 12 as a conveyance unit. Further, deposits such as toner (secondary transfer residual toner) remaining on the surface of the intermediate transfer belt 7 after the secondary transfer step are removed and collected from the surface of the intermediate transfer belt 7 by a belt cleaner (not shown). The

  The transfer material P onto which the toner image has been transferred is conveyed to a fixing device (not shown) as a fixing unit, where the toner image is melted and fixed (fixed), and then external to the main body of the image forming apparatus 100. It is discharged (output).

2. Toner Image Forming Process Next, the toner image forming process in the image forming unit 10 will be described in more detail. FIG. 3 is a schematic diagram showing a potential relationship in the toner image forming process.

  The photosensitive drum 1 is rotationally driven at a predetermined peripheral speed in the direction of the arrow R1 in the figure around the center support shaft. In the rotating process, the photosensitive drum 1 is uniformly charged to a negative polarity by the charging roller 2 in this embodiment. As a result, a charged portion potential Vd is formed on the surface of the photosensitive drum 1.

  In this embodiment, the charging roller 2 is disposed in contact with the surface of the photosensitive drum 1. The charging roller 2 is arranged so as to be rotatable while being always in pressure contact with the surface of the photosensitive drum 1, and is driven to rotate as the photosensitive drum 1 rotates.

  In the present embodiment, a charging bias (charging voltage), which is a DC voltage controlled at a constant voltage, is applied to the charging roller 2 from a charging power supply (high voltage power supply circuit) 91. Thereby, the charging roller 2 can charge the surface of the photosensitive drum 1 to an arbitrary potential from a positive potential to a negative potential. In this embodiment, during normal image formation, the charged portion potential Vd of the photosensitive drum 1 is −600V.

  An electrostatic latent image corresponding to image information is formed on the surface of the charged photosensitive drum 1 as follows. The surface of the photosensitive drum 1 subjected to the charging process is scanned and exposed by a laser beam modulated in accordance with an output image signal output from an exposure device 3 (laser scanning unit, laser scanner) 5. The potential of the exposed surface of the photosensitive drum 1 drops due to the charge pair generated in the photosensitive drum 1. As a result, an exposed portion potential VL is formed on the surface of the photosensitive drum 1.

  As described above, the output image is formed as a potential difference on the surface of the photosensitive drum 1 by the charged portion potential Vd which is a non-image portion (non-exposed portion) and the exposed portion potential VL which is an exposed portion (image portion). Is an electrostatic latent image. Here, the decrease in the potential of the photosensitive drum 1 indicates a state in which the absolute value decreases. In this embodiment, during normal image formation, the exposure portion potential VL of the photosensitive drum 1 is −150V.

  In the present embodiment, the exposure apparatus 3 includes a laser light source, a light amount control device for the laser light source, and a current supply unit for the laser light source. The exposure apparatus 3 changes the output light quantity (exposure light quantity) of the laser by adjusting the current supply from the current supply part to the laser light source in accordance with an adjustment signal from the control part 15 described later by the light quantity control apparatus. Is possible. As a result, it is possible to arbitrarily adjust the amount of potential drop from the charged portion potential Vd of the exposed portion potential VL in accordance with the adjustment signal.

  In this embodiment, the electrostatic latent image formed on the photosensitive drum 1 is developed by a reversal development method. That is, in this embodiment, the toner charged to the same polarity as the charged polarity of the photosensitive drum 1 is exposed to the exposed portion on the photosensitive drum 1 where the absolute value of the potential has been lowered by being exposed after being uniformly charged. Adhere to. At this time, a developing bias (developing voltage) Vdc, which is a DC voltage, is applied from a developing power source (high voltage power circuit) 92 to the developing sleeve 41 of the developing device 4. The developing sleeve 41 is an example of a developer carrying member that carries toner as a developer and conveys the toner to a portion (developing portion) facing the photosensitive drum 1. In the reverse development method, the developing bias Vdc is set to a potential between the charged portion potential Vd and the exposed portion potential VL. As a result, the negatively charged toner on the developing sleeve 41 is electrically moved to the area of the exposure portion potential VL due to the potential difference between the exposure portion potential VL and the development bias Vdc.

Here, the potential difference between the exposed portion potential VL and the developing bias Vdc is the development contrast Vcont, the potential difference between the developing bias Vdc and the charged portion potential Vd is the back contrast Vback, and the potential between the exposed portion potential VL and the charged portion potential Vd is the latent image. This is called contrast Vli. That is, here, Vcont, Vback, and Vli are represented by the following equations. Note that Vcont, Vback, and Vli are potential differences, but here, in order to represent the direction of the electric field, a symbol may be attached according to the following formula for convenience.
Vcont = VL−Vdc
Vback = Vdc−Vd
Vli = VL-Vd

  In the developing process, charged toner moves to fill the potential difference of Vcont, and the amount of toner transferred to the photosensitive drum 1 depends on the magnitude of Vcont. That is, when Vcont is relatively small (absolute value), the image density is low, and when Vcont is relatively large (absolute value), the image density is high. If the amount of toner transferred to the photosensitive drum 1 is too large, the line image is likely to be scattered or poorly fixed, so that Vcont needs to be kept at an appropriate value.

  Also, Vback needs to be kept at an appropriate value. When Vback is relatively small (absolute value), so-called fogging, in which toner is transferred to a non-exposed portion (non-image portion), is likely to occur. Conversely, if Vback is relatively large (absolute value), a large potential difference may cause discharge between the charging unit and the developing sleeve 41, and the toner may be positively charged. In addition, so-called reversal fog, in which the toner is transferred to the non-exposed portion, is likely to occur.

  FIG. 4 summarizes the relationship between the above potential relationship and the amount of toner transferred to the photosensitive drum 1. The horizontal axis of FIG. 4 indicates the potential difference from the developing bias Vdc, and the vertical axis indicates the amount of toner transferred to the photosensitive drum 1 (toner development amount). FIG. 4 shows Vback, Vcont, and Vli maintained at appropriate values when the charging portion potential Vd, the exposure portion potential VL, and the developing bias Vdc are set to desired values Vd_ord, VL_ord, and Vdc_ord, respectively. ing. These appropriate values are Vback_ord, Vcont_ord, and Vli_ord, respectively.

  As shown in FIG. 4, when each potential relationship is maintained at an appropriate value, fogging and reversal fogging in the non-exposed part are suppressed, and image defects such as thin image density and scattering in the exposed part are also suppressed. . In this embodiment, Vd_ord is −600V, VL_ord is −150V, and Vdc_ord is −300V. In this embodiment, Vback_ord is −300V, Vcont_ord is 150V, and Vli_ord is −450V.

3. Control Mode As shown in FIG. 2, the operation of each unit of the image forming apparatus 100 is controlled by a control unit 15 provided in the apparatus main body of the image forming apparatus 100. The control unit 15 includes an arithmetic control unit, a storage unit (ROM, RAM), and the like, and comprehensively controls the operation of each unit of the image forming apparatus 100 according to programs and data stored in the storage unit. In particular, in relation to this embodiment, the control unit 15 controls ON / OFF of the charging power source 91, the developing power source 92, and the primary transfer power source 93 and the output value. Further, a current detection circuit 94 described later is connected to the control unit 15. The control unit 15 controls the primary transfer bias based on the detection result of the current detection circuit 94, and can obtain the exposure unit potential and the like in an adjustment operation described later.

  Here, the image forming apparatus 100 executes a series of image output operations (jobs, printing operations) for forming and outputting an image on a single or a plurality of transfer materials P, which is started by one start instruction. In general, a job includes an image forming process, a pre-rotating process, an inter-sheet process when images are formed on a plurality of transfer materials P, and a post-rotating process. The image forming process is a period in which an electrostatic latent image of an image that is actually formed and output on the transfer material P, a toner image, a primary transfer or a secondary transfer of the toner image is performed. This is the period. More specifically, the timing at which the image is formed differs depending on the position where the electrostatic latent image formation, the toner image formation, and the primary transfer and secondary transfer of the toner image are performed. The pre-rotation process is a period for performing a preparatory operation before the image forming process from when the start instruction is input until the actual image formation is started. The inter-sheet process is a period corresponding to the interval between the transfer material P and the transfer material P when image formation is continuously performed on a plurality of transfer materials P (continuous image formation). The post-rotation process is a period during which an organizing operation (preparation operation) after the image forming process is performed. The non-image forming period is a period other than the image forming time, and is a preparatory operation at the time of turning on the power of the image forming apparatus 100 or returning from the sleep state. This is included during the previous multi-rotation process. An adjustment operation described later is executed during non-image formation.

4). Primary Transfer Power Supply and Current Detection Circuit FIG. 5A is a schematic diagram showing the four image forming units 10Y, 10M, 10C, and 10K in a simplified manner. In this embodiment, a primary transfer power source that applies a primary transfer bias to each primary transfer unit N1Y, N1M, N1C, and N1K of each of the image forming units 10Y, 10M, 10C, and 10K in order to reduce cost and reduce the size of the apparatus. 93 is shared. That is, in the present embodiment, the primary transfer power supply 93 that supplies power to the primary transfer rollers 5Y, 5M, 5C, and 5K is shared by the four image forming units 10Y, 10M, 10C, and 10K. The primary transfer power supply 93 is connected to a current detection circuit 94 as a current detection unit, and the current detection circuit 94 monitors the amount of current flowing through the primary transfer power supply.

  FIG. 5B is an electrical equivalent circuit of FIG. Each of the image forming units 10Y, 10M, 10C, and 10K has impedances Ry, Rm, Rc, and Rk including the primary transfer rollers 5Y, 5M, 5C, and 5K and the intermediate transfer belt 7, respectively. The image forming units 10Y, 10M, 10C, and 10K have surface potentials Vy, Vm, Vc, and Vk of the photosensitive drum 1, respectively. In this embodiment, the same primary transfer bias V is applied from the primary transfer power supply 93 to the image forming units 10Y, 10M, 10C, and 10K. Thereby, in each of the image forming units 10Y, 10M, 10C, and 10K, a current represented by the following formula flows.

  When the primary transfer power supply 93 and the current detection circuit 94 are shared by the image forming units 10Y, 10M, 10C, and 10K, the current value that flows through the image forming units 10Y, 10M, 10C, and 10K expressed by the following equation: The sum Iall can be detected.

In this embodiment, the intermediate transfer belt 7 is a resin belt having a volume resistivity of 1 × 10 ¹¹ Ω · cm when a voltage of 100 V is applied and a thickness of 80 μm, in which charged particles are dispersed in a polymer compound to adjust the resistance. The volume resistivity was measured using a general-purpose resistivity meter HIRESTA / UPMCP-HT450 manufactured by Mitsubishi Chemical Analytech. In this embodiment, the primary transfer roller 5 has an elastic layer in which a material obtained by dispersing carbon in EPDM rubber to make it conductive and foaming it is made into a roller shape. The electrical resistance (volume resistance) of the primary transfer roller 5 was set to 1 × 10 ⁶ Ω or less. The electrical resistance of the primary transfer roller 5 is measured by pressing the primary transfer roller 5 against an aluminum roller having an outer diameter of 30 mm at 9.8 N and rotating both rollers at 30 rpm. This was performed by applying a voltage of 50 V to the cored bar.

The impedances of the image forming units 10Y, 10M, 10C, and 10K are caused by the intermediate transfer belt 7 and the primary transfer roller 5. In this embodiment, the region where the photosensitive drum 1, the intermediate transfer belt 7, and the primary transfer roller 5 are all in contact with each other in the primary transfer portion N1 is about 2 mm in the rotation direction of the intermediate transfer belt 7, and the primary transfer roller 5 is about 217 mm in the longitudinal direction. Therefore, the impedance due to the intermediate transfer belt 7 is approximately 1 × 10 ⁸ Ω, which is two orders of magnitude larger than the impedance due to the primary transfer roller 5. For this reason, in this embodiment, the impedance of the primary transfer portion N1 is substantially determined by the electrical resistance of the intermediate transfer belt 7.

5. Potential fluctuation of the photosensitive drum The exposed portion potential VL may fluctuate even if the photosensitive drum 1 is exposed under the same condition (exposure light amount) due to a difference in temperature and humidity or the passage of usage time. This is because the electrical resistance in the photosensitive layer of the photosensitive drum 1 changes due to temperature rise, humidity, and the like. If the exposed portion potential VL fluctuates, the development contrast Vcont fluctuates, so that image defects such as thin image density and scattering are likely to occur as described above. Therefore, it is conceivable to correct the development bias Vdc and set the development contrast Vcont to an appropriate value. However, if the developing bias Vdc is corrected in a state where the exposure portion potential VL fluctuates, that is, an inappropriate latent image contrast Vli, the back contrast Vback deviates from an appropriate value. For example, as shown in FIG. 6A, when the latent image contrast Vli is smaller than an appropriate value (absolute value), the image density becomes light. Therefore, if the development contrast Vcont is increased in the positive direction in order to increase the image density, the back contrast Vback is decreased in the negative direction, and fogging increases. On the other hand, as shown in FIG. 6B, when the latent image contrast Vli is larger than the appropriate value (absolute value), scattering tends to occur. Therefore, if the development contrast Vcont is decreased in the positive direction to suppress this, the back contrast Vback is increased in the negative direction, and the reversal fog increases.

  Thus, when the latent image contrast Vli is not an appropriate value, the above-described problem may occur even if the development contrast Vcont is corrected. Therefore, it is required to set the latent image contrast Vli to an appropriate value even when the temperature and humidity change and the usage time have elapsed. Typically, the latent image contrast Vli is required to be a substantially constant value.

  Here, in this embodiment, it is possible to arbitrarily correct the exposure portion potential VL by changing the output light amount of the laser of the exposure apparatus 3 as described above. In this embodiment, the charging portion potential Vd can be arbitrarily corrected by changing the charging bias applied from the charging power source 91 to the charging roller 2. Therefore, the latent image contrast Vli can be corrected to an appropriate value by directly detecting the charged portion potential Vd and the exposed portion potential VL or by detecting the latent image contrast Vli that is the difference between them. Hereinafter, a description will be given of this detection method and a method (process setting adjustment) in which each potential relationship of Vback, Vcont, and Vli is set to an appropriate value.

  In the photosensitive drum 1, not only the exposure portion potential VL but also the charging portion potential Vd may change as the usage time elapses. This occurs mainly because the electric capacity changes due to wear of the surface layer of the photosensitive drum 1. However, the fluctuation of the charging portion potential Vd can be predicted by calculating the amount of wear of the surface layer based on information (usage time, rotation speed, etc.) regarding the usage amount of the photosensitive drum 1. Therefore, in this embodiment, the amount of wear of the surface layer is calculated from the number of rotations of the photosensitive drum 1, and the charging bias applied to the charging roller 2 is adjusted according to the amount of wear, so that the charging portion potential Vd is always substantially constant. It keeps in. That is, in this embodiment, the control unit 15 stores the number of rotations from the start of use of each photosensitive drum 1 in the storage unit (counter) as information on the usage amount of each photosensitive drum 1 of each image forming unit 10. To do. Further, the storage unit of the control unit 15 stores information related to the relationship between the rotational speed of the photosensitive drum 1 and the wear amount of the surface layer in advance. In the storage unit of the control unit 15, information indicating the relationship between the wear amount of the surface layer of the photosensitive drum 1 and the charging bias necessary for setting the charging unit potential Vd to a desired value is obtained and stored in advance. Has been. That is, the storage unit of the control unit 15 stores information relating the usage amount of the photosensitive drum 1 and the charging bias necessary for setting the charging unit potential Vd to a desired value. Then, when charging the photosensitive drum 1, the control unit 15 obtains a charging bias corresponding to the number of rotations of the photosensitive drum 1 at that time based on the above information, and applies the charging bias to the charging roller 2. By doing so, the charged portion potential Vd is always kept at a substantially constant value.

  Further, the electric resistance value of the intermediate transfer belt 7 varies depending on the environment, the elapsed time of use of the intermediate transfer belt 7, and the like. For example, when an ion conductive material is used as the material of the intermediate transfer belt 7, the electrical resistance of the intermediate transfer belt 7 is likely to fluctuate greatly with the environmental temperature and humidity. In addition, when the electric resistance of the intermediate transfer belt 7 is adjusted by dispersing electronic conductive carbon, the change in the electric resistance due to changes in environmental temperature and humidity is relatively small. However, in this case, the conductive path changes due to the continuous application of the primary transfer bias and the secondary transfer bias, and the electrical resistance value is likely to change as the usage time elapses. These tendencies are the same for the primary transfer roller 5. For this reason, the impedance of the primary transfer portion N1 often changes from the initial value at the timing of detecting the charged portion potential Vd, the exposed portion potential VL, or the latent image contrast Vli that is the difference between them as described below. . Therefore, it is necessary to detect these in a state where the impedance of the primary transfer portion N1 is unknown. Although the values of the impedances of the image forming units 10Y, 10M, 10C, and 10K change depending on the detection timing, there is substantially no difference between the image forming units 10 and are considered to be substantially the same. This is due to the following reason. That is, the impedance of each image forming unit 10 is caused by the common intermediate transfer belt 7 and the primary transfer roller 5 of each image forming unit 10. However, as described above, the impedance of the intermediate transfer belt 7 is much larger than the impedance of the primary transfer roller 5. Therefore, the impedance of each image forming unit 10 depends on the common intermediate transfer belt 7.

6). Adjustment Operation In this embodiment, the control unit 15 executes an adjustment operation for adjusting the process setting when forming a toner image on the photosensitive drum 1 as follows in the non-image formation. In this embodiment, the exposure portion potential VL is detected and the exposure portion potential VL is corrected to correct Vback, Vcont, and Vli to appropriate values. FIG. 7 is a flowchart showing the procedure of the adjustment operation for carrying out this detection method and correction method. In the present embodiment, the adjustment operation is controlled by the control unit 15.

・ Step 1
When the charged portion potential Vd area of the photosensitive drum 1 passes through the primary transfer portion N1 in all the image forming portions 10, the primary transfer bias V1 is applied to each primary transfer roller 5 by the primary transfer power source 93, The current value Iall_1 is detected by the current detection circuit 94. In this embodiment, the primary transfer bias V1 applied here is 300V. At this time, from the equivalent circuit of FIG. 5B, the relationship between the primary transfer bias V1 and the current value Iall_1 is expressed by the following equation (1).

  Since the impedances Ry, Rm, Rc, and Rk of each image forming unit 10 are substantially determined by the electric resistance of the intermediate transfer belt 7 as described above, assuming that the value R is common to all the image forming units 10, the above formula (1) Is arranged as shown in the following formula (2).

・ Step 2
Only the first image forming unit 10Y has the exposure unit potential VL_y, and in the other image forming units 10M, 10C, and 10K, the primary transfer power source 93 performs each primary transfer when the region of the charging unit potential Vd passes through the primary transfer unit N1. A primary transfer bias V <b> 2 is applied to the roller 5. Then, the current detection circuit 94 detects the current value Iall_2 at that time. In this embodiment, the primary transfer bias V2 applied here is 400V. Further, the amount of light output from the laser of the exposure apparatus 3 at the time of current detection is set to a light amount that is set so that the exposure portion potential VL is set to a desired value VL_ord at the present time. At this time, from the equivalent circuit of FIG. 5B, the relationship between the primary transfer bias V2 and the current value Iall_2 is expressed by the following equation (3).

  As in the case of step 1, when the impedances Ry, Rm, Rc, and Rk of the image forming units 10 are set to a common value R, the above equation (3) is arranged as the following equation (4).

  In this embodiment, the charging portion potential Vd is known, and when combined with the equation (2) in step 1, the exposure potential VL_y of the first image forming portion 10Y is arranged as the following equation (5).

  By using the above equation (5), the exposed portion potential VL_y of the first image forming portion 10Y can be calculated from the measured value and the known value without the influence of the impedance R.

・ Steps 3-5
Similarly to step 2, for the second, third, and fourth image forming units 10M, 10C, and 10K, only the corresponding image forming unit is set as the exposure unit potential, and the other image forming units are set as the charging unit potential Vd and the current value. Is detected. At this time, for the second, third, and fourth image forming units 10M, 10C, and 10K, the exposure unit potentials are VL_m, VL_c, and VL_k, the current values are Iall_3, Iall_4, and Iall_5, and the primary transfer bias to be applied is V3, Let V4 and V5. In this embodiment, V2 = V3 = V4 = V5 = 400V. Then, the exposure unit potentials VL_m, VL_c, and VL_k of the corresponding image forming unit are calculated by the following formulas (6), (7), and (8) similar to the above formula (5), respectively.

・ Step 6
The exposure portion potential VL obtained in Steps 2 to 5 is corrected so that each image forming portion 10 has a desired value. In this embodiment, since the charging portion potential Vd is substantially constant, if the exposure portion potential VL is corrected to the above-described desired value VL_ord, the potential relationships of Vback, Vli, and Vcont can be set to appropriate values. it can.

  The exposure portion potential VL is corrected by correcting the amount of laser output from the exposure apparatus 3 for each image forming portion 10. In this embodiment, the change in the potential drop amount of the photosensitive drum 1 with respect to the change in the output light amount of the laser is measured in advance and stored in the storage unit of the control unit 15 as a correspondence table. Based on this information, the control unit 15 can change the output light amount of the laser by a necessary amount. More specifically, the control unit 15 changes the amount of laser output so that the exposure unit potential VL becomes a desired value by changing the amount of current supplied to the laser light source based on the above information. More specifically, the control unit 15 stores the setting changed as described above in the storage unit so that the output light amount of the laser can be adjusted during image formation after the current adjustment operation. Then, the control unit 15 causes image formation to be performed with the stored settings until changed by a subsequent adjustment operation.

  In this embodiment, in order to correct Vback, Vcont, and Vli to appropriate values, the exposure portion potential VL is corrected to a desired value VL_ord. However, the present invention is not limited to this. For example, the exposure portion potential VL is not changed, and the charging portion potential Vd and the developing bias Vdc are corrected, and Vback, Vcont, and Vli can be corrected to appropriate values.

  As described above, the image forming apparatus 100 according to the present exemplary embodiment includes the control unit 15 that performs an adjustment operation for adjusting each process setting when forming toner images on the plurality of photosensitive members 1. In the adjustment operation, the control unit 15 causes the power supply 94 to apply a voltage to the plurality of transfer units N1 and causes the current detection unit 94 to detect current. At this time, the control unit 15 performs the detection by using a plurality of photoconductors 1 in which a combination of a photoconductor whose charging region potential is an area passing through the transfer unit N1 and a photoconductor whose exposure unit potential is different. Let the state do. Typically, at this time, the control unit 15 forms a toner image on each of the plurality of photoconductors so that the difference between the charging unit potential and the exposure unit potential in each of the plurality of photoconductors 1 approaches a predetermined value. At least one of the setting of the charging unit and the setting of the exposure unit when adjusting is adjusted. Here, the number of the plurality of photoconductors 1 is N (N is a natural number of 2 or more). At this time, in the present embodiment, the control unit 15 causes the following operations to be performed in the adjustment operation. First, current detection is performed in a state where the charged portion potential region passes through the transfer portion N1 in all of the plurality of photosensitive members 1. In addition, the current detection is performed in a state where one of the plurality of photoreceptors 1 passes through the transfer portion N1 and the other portion of the photoreceptor 1 passes through the transfer portion N1. Sometimes, the photosensitive member 1 through which the region of the exposed portion potential passes through the transfer portion N1 is changed and repeated N times. As a result, the control unit 15 obtains the exposure unit potential of each of the plurality of photoconductors 1 and brings the difference between the charging unit potential and the exposure unit potential of each of the plurality of photoconductors 1 close to a predetermined value.

  As described above, according to the present embodiment, even when the impedance of the primary transfer portion N1 is unknown and the exposure portion potential VL of each image forming portion 10 is different, each common transfer power supply 93 and current detection circuit 94 are used. The exposed portion potential VL of the image forming unit 10 can be obtained. Then, by correcting the exposure portion potential VL to a desired value based on the result, it is possible to suppress image defects caused by fluctuations in the exposure portion potential VL.

[Example 2]
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of the present embodiment are the same as those of the image forming apparatus of the first embodiment. Therefore, in the image forming apparatus of the present embodiment, elements having the same or corresponding functions and configurations as those of the image forming apparatus of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  The present embodiment is different from the first embodiment in the method for detecting the exposure portion potential VL. In this embodiment, in place of the processing in steps 2 to 5 in the first embodiment, processing is performed in which the number of image forming portions to be exposed portion potential VL is increased as the steps are advanced. FIG. 8 is a flowchart showing the procedure of the adjustment operation for carrying out the detection method and the correction method in the present embodiment.

・ Step 1
The current value Iall_1 is detected in the same manner as in Step 1 of the first embodiment. However, in this embodiment, the primary transfer bias V1 applied here is 200V. At this time, the relationship between the primary transfer bias V1 and the current value Iall_1 is expressed by the above-described equation (1) and is arranged as the above-described equation (2).

・ Step 2
The current value Iall_2 is detected in the same manner as in step 2 of the first embodiment. However, in this embodiment, the primary transfer bias V2 applied here is 250V. At this time, the relationship between the primary transfer bias V2 and the current value Iall_2 is expressed by the above-described equation (3), arranged as the above-described equation (4), and further arranged as the above-described equation (5). .

  By using this equation (5), the exposure portion potential VL_y of the first image forming portion 10Y can be calculated from the measured value and the known value without the influence of the impedance R.

・ Step 3
In the first and second image forming units 10Y and 10M, the exposure unit potentials VL_y and VL_m, and in the other image forming units 10C and 10K, when the charged unit potential Vd passes through the primary transfer unit N1, the primary transfer power supply A primary transfer bias V 3 is applied to each primary transfer roller 5 by 93. Then, the current value Iall_3 at that time is detected by the current detection circuit 94. In this embodiment, the primary transfer bias V3 applied here is 400V. At this time, from the equivalent circuit of FIG. 5B, the relationship between the primary transfer bias V3 and the current value Iall_3 is expressed by the following equation (9).

  As in the case of step 2, assuming that the impedances Ry, Rm, Rc, and Rk of the image forming units 10 have a common value R, the above equation (9) is arranged as the following equation (10).

  And the following formula (11) can be derived from the difference between the formula (4) in step 2 and the above formula (10).

  Further, when combined with the expression (2) in step 1, the exposure part potential VL_m of the second image forming part 10M is arranged as the following expression (12).

  By using the above equation (12), the exposure portion potential VL_m of the second image forming portion 10M can be calculated from the measured value and the known value without the influence of the impedance R.

・ Step 4
In the first, second, and third image forming units 10Y, 10M, and 10C, the exposure unit potentials VL_y, VL_m, and VL_c, and in the fourth image forming unit 10K, the charged unit potential Vd passes through the primary transfer unit N1. During this time, a primary transfer bias V4 is applied to each primary transfer roller 5. Then, the current detection circuit 94 detects the current value Iall_4 at that time. In this embodiment, the primary transfer bias V4 applied here is 500V. At this time, from the equivalent circuit of FIG. 5B, the relationship between the primary transfer bias V4 and the current value Iall_4 is expressed by the following equation (13).

  As in Steps 2 and 3, assuming that the impedances Ry, Rm, Rc, and Rk of the image forming units 10 have a common value R, the above equation (13) is rearranged as the following equation (14).

  Then, the following equation (15) can be derived from the difference between the equation (10) in step 3 and the above equation (14).

  Further, when combined with the expression (2) in step 1, the exposure part potential VL_c of the third image forming part 10C is arranged as the following expression (16).

  By using the above equation (16), the exposure portion potential VL_c of the third image forming portion 10C can be calculated from the measured value and the known value without the influence of the impedance R.

・ Step 5
When the first, second, third, and fourth image forming units 10Y, 10M, 10C, and 10K pass the exposure unit potentials VL_y, VL_m, VL_c, and VL_k through the primary transfer unit N1, the primary transfer power source A primary transfer bias V5 is applied to each primary transfer roller 5 by 93. Then, the current detection circuit 94 detects the current value Iall_5 at that time. In this embodiment, the primary transfer bias V5 applied here is 600V. At this time, from the equivalent circuit of FIG. 5B, the relationship between the primary transfer bias V5 and the current value Iall_5 is expressed by the following equation (17).

  As in Steps 2, 3, and 4, assuming that the impedances Ry, Rm, Rc, and Rk of the image forming units 10 have a common value R, the above equation (17) is rearranged as the following equation (18). .

  Then, from the difference between the expression (14) in step 4 and the above expression (18), the following expression (19) can be derived.

  Further, when combined with the expression (2) in step 1, the exposure part potential VL_k of the fourth image forming part 10K is arranged as the following expression (20).

  By using the above equation (20), the exposed portion potential VL_k of the fourth image forming portion 10K can be calculated from the measured value and the known value without the influence of the impedance R.

・ Step 6
In the same manner as in Step 6 of Embodiment 1, the exposure portion potentials obtained in Steps 2 to 5 are corrected to desired values VL_ord, respectively, and the potential relationships of Vback, latent image contrast, and Vcont are set to appropriate values.

  Thus, in the present embodiment, the control unit 15 causes the following operations to be performed in the adjustment operation. First, current detection is performed in a state where the charged portion potential region passes through the transfer portion N1 in all of the plurality of photosensitive members 1. Of the plurality of photoreceptors 1, m (m is a natural number of 1 or more) photoreceptors 1 are exposed area potential areas, and (N−m) photoreceptors 1 are charged part potentials passing through the transfer section N1. In this state, the current detection is repeated N times from when m is 1 to N. As a result, the control unit 15 obtains the exposure unit potential of each of the plurality of photoconductors 1 and brings the difference between the charging unit potential and the exposure unit potential of each of the plurality of photoconductors 1 close to a predetermined value.

  As described above, according to the present embodiment, the same effects as those of the first embodiment can be obtained. Further, in this embodiment, since it is not necessary to perform current detection after the photosensitive drum 1 once set to the exposure portion potential VL is again set to the charging portion potential Vd in steps 2 to 5, the control time can be shortened compared to the first embodiment. .

[Example 3]
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of the present embodiment are the same as those of the image forming apparatus of the first embodiment. Therefore, in the image forming apparatus of the present embodiment, elements having the same or corresponding functions and configurations as those of the image forming apparatus of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In this embodiment, unlike the first and second embodiments, not only the value of the exposure portion potential VL but also the charging portion potential Vd is detected. In the first and second embodiments, the amount of wear of the surface layer is calculated from the number of rotations of the photosensitive drum 1, and the charging bias voltage Vd applied to the charging roller 2 is adjusted according to the amount of wear so did. That is, in Examples 1 and 2, the charging portion potential Vd is predicted and controlled. On the other hand, in this embodiment, the charged portion potential Vd is actually measured and the charged portion potential Vd is corrected to a desired value, thereby correcting the relationship between Vback, latent image contrast, and Vcont to appropriate values. To increase. FIG. 9 is a flowchart showing the procedure of the adjustment operation for carrying out the detection method and the correction method in the present embodiment. FIG. 10 is a graph showing the relationship between the primary transfer bias applied in the detection method of this embodiment and the current value.

・ Step 1
When the charged portion potential Vd region passes through the primary transfer portion N1 in all the image forming portions 10, the primary transfer power source 93 sequentially applies the two levels of primary transfer biases V1 and V2 to the primary transfer rollers 5. The current detection circuit 94 detects the current values Iall_1 and Iall_2 when the primary transfer bias is applied. In this embodiment, the primary transfer bias V1 applied here is 200V, and V2 is 400V. The charging bias at the time of forming the charging unit potential Vd is set to a value that is currently set to set the charging unit potential Vd to a desired value Vd_ord. As shown in FIG. 10, in the straight line indicating the relationship between the two-level primary transfer bias and the measured value, the intercept when the current value is 0 is the charged portion potential Vd. That is, based on the primary transfer biases V1 and V2 and the current values Iall_1 and Iall_2 from the equivalent circuit of FIG. 5B, the charging unit potential Vd is expressed by the following equation (21).

・ Step 2
Only the first image forming unit 10Y has the exposure unit potential VL_y. In the other image forming units 10M, 10C, and 10K, when the charged unit potential Vd passes through the primary transfer unit N1, each primary transfer roller 5 has two levels. Primary transfer biases V1y and V2y are sequentially applied. The current detection circuit 94 detects the current values Iall_y1 and Iall_y2 when the primary transfer bias is applied. In this embodiment, the primary transfer bias V1y applied here is 300V, and V2y is 500V. At this time, the relationship between the primary transfer biases V1y and V2y and the current values Iall_y1 and Iall_y2 is expressed by the following equation (22) from the equivalent circuit of FIG.

  Regarding the two expressions shown in the above expression (22), the charged portion potential Vd is known from step 1, and the unknowns are the impedance R and the exposure potential VL_y. Therefore, the exposure potential VL_y is expressed by the following equation (23) from these two equations.

  By using the above equation (23), the exposure part potential VL_y of the first image forming part 10Y can be calculated from the measured value and the known value without the influence of the impedance R.

・ Steps 3-5
Similarly to step 2, for the second, third, and fourth image forming units 10M, 10C, and 10K, only the corresponding image forming unit is set as the exposure unit potential, and the other image forming units are set as the charging unit potential Vd and the current value. Measure. At this time, the exposure unit potentials are set to VL_m, VL_c, and VL_k for the second, third, and fourth image forming units 10M, 10C, and 10K, respectively. The current values are Iall_m1 and Iallm2, Iall_c1 and Iallc2, Iall_k1 and Iallk2. The applied primary transfer bias is V1m and V2m, V1c and V2c, V1k and V2k. In this embodiment, V1y = V1m = V1c = V1k = 300V and V2y = V2m = V2c = V2k = 500V. Then, the exposure unit potentials VL_m, VL_c, and VL_k of the corresponding image forming unit are calculated by the following formulas (24), (25), and (26) similar to the above formula (23), respectively.

・ Step 6
The charged portion potential Vd obtained in step 1 and the exposed portion potential VL obtained in steps 2 to 5 are corrected so as to have desired values in each image forming portion. In this embodiment, the charged portion potential Vd is corrected to the above-described desired value Vd_ord, and the exposed portion potential VL is corrected to the above-described desired value VL_ord.

  The charging portion potential Vd is corrected by correcting the charging bias applied to the charging roller 2. In this embodiment, the amount of change in the charging unit potential Vd with respect to the amount of change in the bias applied to the charging roller 2 is measured in advance and stored in the storage unit of the control unit 15 as a correspondence table. Based on this information, the control unit 15 can change the charging bias applied to the charging roller 2 by a necessary amount. More specifically, the control unit 15 stores the setting changed as described above in the storage unit so that the charging bias can be adjusted during image formation after the current adjustment operation. Then, the control unit 15 causes image formation to be performed with the stored settings until changed by a subsequent adjustment operation. Further, the exposure portion potential VL is corrected in the same manner as in the first and second embodiments. As a result, the relationship between Vback, latent image contrast, and Vcont is set to an appropriate value.

  As described above, according to this embodiment, the charging unit potential Vd and the exposure unit potential VL of each image forming unit 10 can be obtained using the common primary transfer power supply 93 and the current detection circuit 94. This can be performed even when the impedance of the primary transfer portion N1 and the charging portion potential Vd are unknown and the exposure portion potential VL of each image forming portion 10 is different. Then, by correcting the charging portion potential Vd and the exposure portion potential VL to desired values based on the result, image defects caused by fluctuations in the charging portion potential Vd and the exposure portion potential VL can be suppressed.

  In this embodiment, in order to correct Vback, Vcont, and Vli to appropriate values, the charging portion potential Vd and the exposure portion potential VL are corrected to desired values Vd_ord and VL_ord, respectively. However, the present invention is not limited to this. Absent. For example, the charging portion potential Vd is not changed, and the exposure portion potential VL and the developing bias Vdc are corrected to correct Vback, Vcont, and Vli to appropriate values.

  In this embodiment, the primary transfer bias applied in step 1 is set at two levels. In other words, in the adjustment operation, the control unit 15 applies current detection to the plurality of transfer units N1 by the power source 93 in a state where the charged portion potential regions pass through the transfer unit N1 in all of the plurality of photosensitive members 1. The voltage to be changed is changed to at least two different voltages to be repeated. The control unit 18 then charges the charging unit potentials of the plurality of photoconductors 1 in the adjustment operation based on the relationship between the at least two different voltages and the current detected by the current detection unit 94 when each voltage is applied. Can be requested. More specifically, when the primary transfer bias at the t level (t is a natural number of 2 or more) is V1 to Vt and the current values when the primary transfer biases are applied are I1 to It, A charging portion potential Vd that is an intercept of the voltage-current characteristic represented by the equation (27) is calculated.

  Further, in this embodiment, in steps 2 to 5, the exposure portion potential VL of the corresponding image forming portion is detected by the method in which only the corresponding image forming portion in step 2 to 5 is set to the exposure portion potential VL. It was. Alternatively, in steps 2 to 5 of the present embodiment, the corresponding image forming section is increased by increasing the number of image forming sections to be the exposure section potential VL as the same steps as steps 2 to 5 of the second embodiment are performed. The exposure portion potential VL may be detected.

[Others]
As mentioned above, although this invention was demonstrated according to the specific Example, this invention is not limited to the above-mentioned Example.

  In the above-described embodiment, the case where the transfer power supply and the current detection unit are shared with respect to the four photoconductors has been described. However, the number of photoconductors with which the transfer power supply and the current detection unit are shared is limited to four. It is not a thing, and it may be more or less. When the transfer power supply and the current detection unit are shared by a plurality of photoconductors, the adjustment operation can be performed according to the above-described embodiment according to the number of photoconductors. Further, the plurality of photoconductors that share the transfer power source and the current detection unit are not limited to all the photoconductors included in the image forming apparatus, and may be a part of the photoconductors. For example, a transfer power supply and a current detection circuit are made common for the photoreceptors for yellow, magenta, and cyan (“color”), and a transfer power supply and a current detection circuit are provided independently for the photoreceptor for black. It may be. In this case, the adjustment operation according to the above-described embodiment can be applied to a plurality of color photoconductors. For the black photoconductor, an independent transfer power source and current detection circuit are used to measure the amount of current flowing by applying a voltage when the charged portion potential and the exposed portion potential pass through the transfer portion. Thus, the charged portion potential and the exposed portion potential can be detected.

  In the above-described embodiments, the intermediate transfer type image forming apparatus has been described as an example, but the present invention can also be applied to a direct transfer type image forming apparatus. FIG. 11 is a schematic cross-sectional view of a main part of a direct transfer type image forming apparatus. 11, elements having the same or corresponding functions and configurations as those of the image forming apparatus of FIG. 1 are denoted by the same reference numerals. An image forming apparatus 100 shown in FIG. 11 includes a transfer material carrying belt 107 constituted by an endless belt as a transfer material carrying body, instead of the intermediate transfer belt 7 in the image forming apparatus 100 shown in FIG. In the image forming apparatus 100 of FIG. 11, the toner image formed on the photosensitive drum 1 in each image forming unit 10 is transferred to the transfer material P carried and transported on the transfer material carrying belt 107 in each transfer unit N. Is done. Also in such a direct transfer type image forming apparatus 100, when the transfer power supply 93 and the current detection circuit 94 are shared with respect to the plurality of photosensitive drums 1, the same problem as the intermediate transfer type image forming apparatus 100 is caused. . Therefore, the present invention can be applied to a direct transfer type image forming apparatus, and the same effects as those of the above-described embodiments can be obtained.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 5 Primary transfer roller 7 Intermediate transfer belt 15 Control part 93 Primary transfer power supply 94 Current detection circuit

Claims (8)

A plurality of photoreceptors;
A plurality of charging means for charging each of the plurality of photoconductors to form a charged portion potential;
Exposure means for exposing each of the plurality of charged photoreceptors to form an exposed portion potential;
A plurality of developing means for supplying toner to each of the plurality of exposed photoreceptors to form a toner image;
A movable body that can move around and forms a plurality of transfer portions in contact with each of the plurality of photoconductors;
A common power source for applying a voltage for transferring a toner image from each of the plurality of photoconductors to the moving body or a transfer material carried on the moving body, to the plurality of transfer units;
A current detector for detecting a current flowing in the power source;
A control unit that executes an adjustment operation for adjusting respective process settings when forming toner images on the plurality of photosensitive members;
Have
In the adjustment operation, the control unit applies a voltage to the plurality of transfer units by the power source and detects a current by the current detection unit, and controls the transfer unit at the time of the detection among the plurality of photosensitive members. An image forming apparatus comprising: a plurality of states in which a combination of a photosensitive member having a charged region potential and a photosensitive member having an exposed region potential is different.   In the adjustment operation, the control unit forms a toner image on each of the plurality of photoconductors so that a difference between the charging unit potential and the exposure unit potential of each of the plurality of photoconductors approaches a predetermined value. 2. The image forming apparatus according to claim 1, wherein at least one of the setting of the charging unit and the setting of the exposure unit is adjusted. When the number of the plurality of photoconductors is N (N is a natural number of 2 or more),
In the adjustment operation, the control unit performs the detection in a state where the charged portion potential region passes through the transfer unit in all of the plurality of photosensitive members, and one of the plurality of photosensitive members. In the state in which the region of the exposed portion potential passes through the transfer portion and the region of the charged portion potential passes through the transfer portion on another photoconductor, the transfer portion is exposed during the detection. Changing the photosensitive member through which the region of the partial potential passes and repeating N times to obtain the exposed portion potential of each of the plurality of photosensitive members, and the charged portion potential in each of the plurality of photosensitive members At least one of the setting of the charging unit and the setting of the exposure unit when forming a toner image on each of the plurality of photoconductors is adjusted so that the difference from the exposure portion potential approaches a predetermined value. The image formation according to claim 1 Location. When the number of the plurality of photoconductors is N (N is a natural number of 2 or more),
In the adjustment operation, the control unit performs the detection in a state where the charged portion potential region passes through the transfer unit in all of the plurality of photoconductors, and m (m Is a natural number equal to or greater than 1), and the region of the exposed portion potential passes through the transfer portion, and the charged portion potential passes through the transfer portion with (Nm) photoconductors. The detection is repeated N times from the case where m is 1 to the case of N, and the exposure portion potential of each of the plurality of photoconductors is obtained, and the charging portion potential of each of the plurality of photoconductors is obtained. Adjusting at least one of the setting of the charging unit and the setting of the exposure unit when forming a toner image on each of the plurality of photoconductors so that the difference between the exposure unit potential and the exposure unit potential approaches a predetermined value. The image forming apparatus according to claim 1, wherein:   The image forming apparatus according to claim 1, wherein charging unit potentials of the plurality of photosensitive members in the adjustment operation are set to a predetermined value.   In the adjustment operation, the control unit applies the detection to the plurality of transfer units by the power source in a state where the charged portion potential region passes through the transfer unit in all of the plurality of photoconductors. In the adjustment operation based on the relationship between the at least two different voltages and the current detected by the current detection unit when each voltage is applied, the voltage is changed to at least two different voltages and repeated. The image forming apparatus according to claim 1, wherein charged portion potentials of the plurality of photosensitive members are obtained.   The plurality of transfer members disposed on the inner peripheral surface side of the movable body corresponding to each of the plurality of photoconductors, and the power source applies a voltage to the plurality of transfer members. Item 7. The image forming apparatus according to any one of Items 1 to 6.   The image forming apparatus according to claim 1, wherein the moving body is an endless belt.

Images