Image forming apparatus, bias voltage determination method, and program

Abstract

The present invention provides an image forming apparatus, a bias voltage determination method, and a program that can determine a development bias corresponding to other process speeds without degrading image quality and without performing calibration of the development bias corresponding to other process speeds. [Solution] The image forming apparatus 10 comprises an image forming unit 3, a calibration processing unit 51, and a bias voltage determination unit 52. The calibration processing unit 51 determines a reference setting value corresponding to the reference process speed, which is set as the DC component Vdc of the development bias VB. The bias voltage determination unit 52 determines a first correction amount Vc based on a first speed difference ΔS1 between the reference process speed and the first process speed, and corrects the reference setting value with the first correction amount Vc to determine the corrected first setting value as the setting value of the DC component Vdc of the development bias VB according to the first process speed.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus, a bias voltage determination method, and a program.

Background Art

[0002] Conventionally, an image forming apparatus that moves toner to a latent electrostatic image formed on the surface of a photosensitive drum based on an electrophotographic method to form a toner image on the photosensitive drum is known. In the image forming apparatus, the charged photosensitive drum is exposed based on image data, and the latent electrostatic image is formed on the photosensitive drum. Then, the image forming apparatus applies a bias voltage (development bias) to a developing roller, and supplies charged toner to an exposed portion (a portion where the latent electrostatic image is formed) of the photosensitive drum according to an electric field between the photosensitive drum and the developing roller. As a result, toner adheres to the exposed portion on the photosensitive drum, and the latent electrostatic image on the photosensitive drum is developed into a toner image.

[0003] Conventionally, in this type of image forming apparatus, a technique for determining process conditions at another process speed from calibration results at a predetermined process speed without degrading image quality has been proposed (see Patent Document 1). Specifically, based on a first density of a measurement image formed at a first process speed by an image forming unit, a second density of a measurement image formed at a second process speed different from the first process speed by the image forming unit, and a first process condition at the first process speed, a second process condition at the second process speed is determined.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] [[ID=3However, the conventional technology described above requires the steps of forming a measurement image at a first process speed, measuring the image density, changing the process speed to a second process speed, forming a measurement image at the second process speed, and further measuring the image density, which makes determining the process conditions time-consuming.

[0006] The object of the present invention is to provide an image forming apparatus, a bias voltage determination method, and a program that can determine a development bias according to other process speeds without degrading image quality and without performing calibration of the development bias corresponding to other process speeds. [Means for solving the problem]

[0007] An image forming apparatus according to one aspect of the present invention includes: an image forming unit that applies a bias voltage between a first carrier whose surface is charged and a second carrier that holds toner to be attached to the first carrier, thereby moving toner from the second carrier to the exposure portion of the first carrier and forming a toner image on the first carrier based on image data; a calibration processing unit that performs a calibration process to determine a reference setting value corresponding to the reference process speed, which is set as the bias voltage, when the image forming unit operates at a predetermined reference process speed; and a bias voltage determination unit that, when the image forming unit operates at a first process speed different from the reference process speed, determines a first correction amount based on a first speed difference between the reference process speed and the first process speed, and determines a corrected first setting value, obtained by correcting the reference setting value with the first correction amount, as the bias voltage corresponding to the first process speed.

[0008] A bias voltage determination method according to another aspect of the present invention is applied to an image forming apparatus that applies a bias voltage between a first carrier whose surface is charged and a second carrier that holds toner to be attached to the first carrier, thereby moving toner from the second carrier to the exposure portion of the first carrier and forming a toner image on the first carrier based on image data. The method is performed by one or more processors and includes: a calibration step in which, when the image forming unit operates at a predetermined reference process speed, a calibration process is performed to determine a reference setting value corresponding to the reference process speed which is set as the bias voltage; and a bias voltage determination step in which, when the image forming unit operates at a first process speed different from the reference process speed, a first correction amount is determined based on a first speed difference between the reference process speed and the first process speed, and the corrected first setting value obtained by correcting the reference setting value with the first correction amount is determined as the bias voltage corresponding to the first process speed.

[0009] A program relating to another aspect of the present invention is a program for causing one or more processors to execute: a calibration step which performs a calibration process to determine a reference setting value corresponding to the reference process speed, which is set as the bias voltage, when the image forming unit operates at a predetermined reference process speed; and a bias voltage determination step which, when the image forming unit operates at a first process speed different from the reference process speed, determines a first correction amount based on a first speed difference between the reference process speed and the first process speed, and determines the corrected first setting value, obtained by correcting the reference setting value with the first correction amount, as the bias voltage corresponding to the first process speed. [Effects of the Invention]

[0010] According to the present invention, it is possible to determine the development bias according to other process speeds without degrading image quality and without performing calibration of the development bias corresponding to other process speeds. [Brief explanation of the drawing]

[0011] [Figure 1] Figure 1 is a block diagram showing the configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] Figure 2 shows the configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 3] Figure 3 shows the configuration of the image forming section of an image forming apparatus according to an embodiment of the present invention. [Figure 4] Figure 4 is an explanatory diagram showing an example of the waveform of the development bias of an image forming apparatus according to an embodiment of the present invention. [Figure 5] Figure 5 is a flowchart showing an example of the procedure for determining the bias voltage performed by the control unit of the image forming apparatus according to an embodiment of the present invention. [Modes for carrying out the invention]

[0012] The embodiments of the present invention will be described below with reference to the attached drawings. The following embodiments are examples that embody the present invention and are not intended to limit the technical scope of the present invention.

[0013] [1] Overall configuration of the image forming apparatus First, the configuration of the image forming apparatus 10 according to this embodiment will be described with reference to Figures 1 and 2.

[0014] For the sake of explanation, the vertical direction is defined as the up-down direction D1 when the image forming apparatus 10 is in a usable installation state (as shown in Figure 2). The front-to-back direction D2 is defined with the left side of the image forming apparatus 10 shown in Figure 2 as the front. The left-to-right direction D3 is defined with the front of the image forming apparatus 10 in its installed state as the reference point.

[0015] The image forming apparatus 10 according to this embodiment is, as an example, a multifunction device having a plurality of functions such as a scan function for reading image data from a document, a print function for forming an image based on the image data, a facsimile function, and a copy function. The image forming apparatus 10 only needs to have a function of forming an image, and may be a printer, a facsimile apparatus, a copy machine, or the like.

[0016] As shown in FIG. 1, the image forming apparatus 10 includes an automatic document feeder 1, an image reading unit 2, an image forming unit 3, a paper feeding unit 4, a control unit 5, a storage unit 6, and an operation display unit 7. Since the automatic document feeder 1 is an ADF (Auto Document Feeder), it is denoted as "ADF" in FIG. 1 and also referred to as "ADF1" in the following description.

[0017] ADF1 conveys the document from which an image is read by the image reading unit 2. ADF1 has a document set unit, a plurality of conveyance rollers, a document holder, a paper discharge unit, and the like.

[0018] The image reading unit 2 reads an image from a document and outputs image data corresponding to the read image. The image reading unit 2 has a document table, a light source, a plurality of mirrors, an optical lens, a CCD (Charge Coupled Device), and the like.

[0019] The image forming unit 3 realizes the print function by forming a color or monochrome image on a sheet based on the electrophotographic method. The image forming unit 3 forms an image on a sheet based on the image data output from the image reading unit 2. Further, the image forming unit 3 forms an image on a sheet based on the image data input from an information processing device outside the image forming apparatus 10, such as a personal computer.

[0020] The paper feeding unit 4 supplies a sheet to the image forming unit 3. The paper feeding unit 4 has a paper feed cassette, a manual feed tray, a sheet conveyance path, a plurality of conveyance rollers, and the like. The image forming unit 3 forms an image on the sheet supplied from the paper feeding unit 4.

[0021] The control unit 5 comprehensively controls the image forming apparatus 10. The control unit 5 mainly consists of a computer system having one or more processors and one or more memories. In the image forming apparatus 10, the functions of the control unit 5 are realized by one or more processors executing a program. The program may be pre-recorded in a memory (storage unit 6), may be provided through an electric communication line such as the Internet, or may be provided by being recorded on a non-temporary recording medium readable by the computer system, such as a memory card or an optical disk. The one or more processors are composed of one or more electronic circuits including semiconductor integrated circuits. Furthermore, the computer system mentioned here includes a microcontroller having one or more processors and one or more memories. The control unit 5 may be a control unit provided separately from the main control unit that comprehensively controls the image forming apparatus 10.

[0022] The storage unit 6 includes one or more non-volatile memories, and information such as a control program for causing the control unit 5 to execute various processes is pre-stored therein. Furthermore, the storage unit 6 is used as a temporary storage memory (working area) for various processes executed by the control unit 5.

[0023] The operation display unit 7 is a user interface in the image forming apparatus 10. The operation display unit 7 has a display unit such as a liquid crystal display that displays various information in response to a control instruction from the control unit 5, and an operation unit such as a switch or a touch panel that inputs various information to the control unit 5 in response to a user's operation.

[0024] [2] Configuration of the Image Forming Unit Next, while referring to FIGS. 1 to 4, the configuration of the image forming unit 3 will be described in more detail.

[0025] As shown in Figure 2, the image forming unit 3 includes four image forming units 31-34, an optical scanning device 35, an intermediate transfer device 36, a secondary transfer roller 37, a fixing device 38, and a paper output tray 39. In Figure 3, an enlarged schematic diagram of one of the four image forming units 31-34, image forming unit 34, is shown within the speech bubble.

[0026] The image forming unit 31 forms a yellow (Y) toner image. As shown in Figure 3, the image forming unit 31 includes a photoreceptor drum 311 (an example of the first carrier of the present invention), a developing device 313 including a charging roller 312 and a developing roller 313A (an example of the second carrier of the present invention), a primary transfer roller 314, and a drum cleaning unit 315. The image forming unit 31 also further includes a toner container 316 (see Figure 2).

[0027] The image forming unit 32 forms a cyan (C) toner image. As shown in Figure 3, the image forming unit 32 includes a photoreceptor drum 321 (an example of the first carrier of the present invention), a developing device 323 including a charging roller 322 and a developing roller 323A (an example of the second carrier of the present invention), a primary transfer roller 324, and a drum cleaning unit 325. The image forming unit 32 also further includes a toner container 326 (see Figure 2).

[0028] The image forming unit 33 forms a magenta (M) toner image. As shown in Figure 3, the image forming unit 33 includes a photoreceptor drum 331 (an example of the first carrier of the present invention), a developing device 333 including a charging roller 332 and a developing roller 333A (an example of the second carrier of the present invention), a primary transfer roller 334, and a drum cleaning unit 335. The image forming unit 33 also further includes a toner container 336 (see Figure 2).

[0029] The image forming unit 34 forms a K (black) toner image. As shown in Figure 3, the image forming unit 34 includes a photoreceptor drum 341 (an example of the first carrier of the present invention), a developing device 343 including a charging roller 342 and a developing roller 343A (an example of the second carrier of the present invention), a primary transfer roller 344, and a drum cleaning unit 345. The image forming unit 34 also further includes a toner container 346 (see Figure 2).

[0030] Furthermore, each of the multiple image forming units 31 to 34, in addition to the above configuration, further includes a power supply circuit 301 and a current detection circuit 302, as shown in Figure 1. In other words, the power supply circuit 301 and the current detection circuit 302 are provided in each of the multiple image forming units 31 to 34. Each power supply circuit 301 includes a developing power supply circuit 301A and a charging power supply circuit 301B.

[0031] Thus, the multiple (in this case, four) image forming units 31-34 each correspond to the four colors Y (yellow), C (cyan), M (magenta), and K (black), and basically employ a common configuration. Therefore, unless otherwise specified, the configuration described for image forming unit 34 is the same for the other image forming units 31-33. In the callouts in Figure 3, only the parts of image forming unit 34, such as the photoreceptor drum 341, developing roller 343A, power supply circuit 301, and current detection circuit 302, are shown.

[0032] An electrostatic latent image is formed on the photoreceptor drum 341. The photoreceptor drum 341 is rotatably supported by a unit housing that houses the photoreceptor drum 341, the charging roller 342, and the drum cleaning unit 345, around a rotation axis extending in the left-right direction D3. The photoreceptor drum 341 rotates in the rotation direction D5 shown in Figure 3, for example, by receiving a driving force supplied from a motor.

[0033] Generally, photoconductor drums are classified into organic photoconductors (OPC), selenium photoconductors, amorphous silicon photoconductors, etc., depending on the type of thin film layer on the charged surface. In recent years, amorphous silicon photoconductors have attracted attention as photoconductor drums due to their high durability, high hardness, and long lifespan.

[0034] The charging roller 342 charges the surface (outer surface) of the photoreceptor drum 341 with positive polarity. Specifically, the charging roller 342 is electrically connected to the charging power supply circuit 301B of the power supply circuit 301, and charges the surface of the photoreceptor drum 341 by receiving high voltage from the charging power supply circuit 301B. However, the charging roller 342 is not limited to charging the surface of the photoreceptor drum 341 with positive polarity; it may also charge it with negative polarity.

[0035] The surface of the photoreceptor drum 341, which has been charged by the charging roller 342, is illuminated by light from the optical scanning device 35 based on image data. As a result, an electrostatic latent image is formed on the surface of the photoreceptor drum 341. In other words, the exposed portion of the surface of the photoreceptor drum 341 that is illuminated by light from the optical scanning device 35 becomes the "image portion".

[0036] The developing device 343 performs a developing process to develop the electrostatic latent image formed on the surface of the photoreceptor drum 341. In this embodiment, the developing device 343 specifically uses a two-component developer containing toner and carrier for development. For example, the developing device 343 includes a case, a pair of stirring members, a magnetic roller, and a developing roller 343A. The case supports the pair of stirring members, the magnetic roller, and the developing roller 343A so that they can rotate around a rotation axis extending in the left-right direction D3. The case also houses the K (black) toner and carrier. The pair of stirring members stir the toner and carrier housed in the case, thereby charging the toner. In this embodiment, the toner is positively charged. However, the charging polarity of the toner is not limited to positive polarity; it may also be negative polarity. The magnetic roller draws up the toner and carrier stirred by the pair of stirring members and supplies the toner to the surface (outer circumferential surface) of the developing roller 343A.

[0037] The developing roller 343A develops the electrostatic latent image formed on the photoreceptor drum 341 using charged toner. Specifically, the developing roller 343A is electrically connected to the developing power supply circuit 301A of the power supply circuit 301, and receives a developing bias VB (see Figure 4) from the developing power supply circuit 301A to supply toner to the surface of the photoreceptor drum 341. In other words, when a high-voltage developing bias VB is applied between the developing roller 343A and the photoreceptor drum 341 by the developing power supply circuit 301A, a developing electric field is formed between the developing roller 343A and the exposure area, and the charged toner moves from the developing roller 343A to the exposure area of ​​the photoreceptor drum 341. As a result, a toner image corresponding to the electrostatic latent image is formed on the surface of the photoreceptor drum 341.

[0038] In this embodiment, the photoreceptor drum 341 is an example of a "first carrier," and the developing roller 343A is an example of a "second carrier." That is, the image forming unit 3 moves charged toner from the developing roller 343A to the photoreceptor drum 341 using a developing electric field, developing the electrostatic latent image on the photoreceptor drum 341 with the toner, and forming a toner image (image) on the photoreceptor drum 341 that corresponds to the electrostatic latent image. In other words, in the development process, the image forming unit 3 moves charged toner from the second carrier to the first carrier and forms a toner image on the first carrier. Here, since the photoreceptor drum 341 rotates in the rotation direction D5 (see Figure 3), the portion of the surface of the photoreceptor drum 341 facing the developing roller 343A changes over time. In other words, the portion of the surface of the photoreceptor drum 341 facing the developing roller 343A moves in the rotation direction D5 of the photoreceptor drum 341.

[0039] Here, the developing bias VB applied between the developing roller 343A and the photoreceptor drum 341 is a voltage in which an AC component Vac is superimposed on a DC component Vdc, as shown in Figure 4. In other words, the developing power supply circuit 301A generates a developing bias VB in which an AC component Vac is superimposed on a DC voltage by superimposing an AC voltage on a DC voltage. Therefore, the developing bias VB has a fluctuating component due to the pulsation (ripple) of the AC component Vac superimposed on the value of its DC component Vdc, and periodically repeats between a value higher and a value lower than the value of the DC component Vdc. In the example in Figure 4, the AC component Vac of the developing bias VB is a square wave with a duty cycle of 50%, but it is not limited to this, and the AC component Vac may be a sine wave or a triangular wave, for example.

[0040] In this embodiment, the value (magnitude) of the DC component Vdc in the development bias VB can be changed. For example, if the surface potential of the charged photoreceptor drum 341 is "Vs", and the potential (exposure potential) of the exposed area on the surface of the photoreceptor drum 341 irradiated with light from the light scanning device 35 is "VL", then the DC component Vdc is set to a value between the surface potential Vs and the exposure potential VL. In other words, the value of the DC component Vdc is set to a voltage lower than the surface potential Vs and higher than the exposure potential VL of the exposed area.

[0041] In this embodiment, the developing bias VB is an example of a "bias voltage" applied between the developing roller 343A and the photoreceptor drum 341. More specifically, the DC component Vdc in the developing bias VB is an example of the bias voltage of the present invention. When the developing bias VB is applied between the developing roller 343A and the photoreceptor drum 341, a developing current due to the DC component Vdc flows between the developing roller 343A and the photoreceptor drum 341.

[0042] The aforementioned developing current includes the toner current that flows as the toner moves. In this embodiment, the current flowing from the developing roller 343A to the photoreceptor drum 341 is defined as "positive," and conversely, the current flowing from the photoreceptor drum 341 to the developing roller 343A is defined as "negative."

[0043] Here, a magnet is placed inside the developing roller 343A, and the developing roller 343A rotates around the stationary magnet. One of the magnetic poles of the magnet faces the photoreceptor drum 341 via the developing roller 343A and the developing gap. The developer carried on the developing roller 343A forms a magnetic brush in the developing gap. The magnetic brush is a magnetic carrier to which toner is attached. Therefore, the developing current includes a toner current that flows as the toner moves, a magnetic brush current that flows through the magnetic brush in the exposed area on the photoreceptor drum 341, and a reverse magnetic brush current that flows through the magnetic brush in the unexposed area in the opposite direction to that of the exposed area.

[0044] The primary transfer roller 344 transfers the toner image formed on the surface of the photoreceptor drum 341 by the developing device 343 to the outer surface of the intermediate transfer belt 361 (see Figure 3). Specifically, the primary transfer roller 344 is electrically connected to the power supply circuit 301, and by receiving high voltage from the power supply circuit 301, it transfers the toner image formed on the surface of the photoreceptor drum 341 to the outer surface of the intermediate transfer belt 361. In other words, a high-voltage transfer bias is applied between the photoreceptor drum 341 and the primary transfer roller 344 by the power supply circuit 301, creating a transfer electric field, and the charged toner moves from the photoreceptor drum 341 to the intermediate transfer belt 361. As a result, a toner image is formed (transferred) to the outer surface of the intermediate transfer belt 361.

[0045] The drum cleaning unit 345 cleans the surface of the photoreceptor drum 341 after the toner image has been transferred by the primary transfer roller 344. For example, the drum cleaning unit 345 has a blade-shaped cleaning member and a transport member. The cleaning member contacts the surface of the photoreceptor drum 341 and removes the toner adhering to the surface. The transport member transports the toner removed by the cleaning member to the toner container.

[0046] The toner container 346 supplies toner to the case of the developing device 343. In the image forming unit 34, which forms a K (black) toner image, the toner container 346 supplies K (black) toner.

[0047] The current detection circuit 302 detects the developing current flowing between the photoreceptor drum 341 and the developing roller 343A. The current detection circuit 302 is, for example, a circuit that includes a current sensor such as a shunt resistor or a current transformer, and is provided on the power supply path from the power supply circuit 301 to the developing roller 343A. The current detection circuit 302 outputs a detection signal to the control unit 5 that corresponds to the magnitude of the developing current flowing from the developing roller 343A to the photoreceptor drum 341.

[0048] Furthermore, in this embodiment, the current detection circuit 302 includes a filter circuit 302A. The filter circuit 302A is, for example, a low-pass filter, or integral filter, that attenuates frequency components above the cutoff frequency of the developing current flowing from the developing roller 343A to the photoreceptor drum 341. By including the filter circuit 302A, the developing current detected by the current detection circuit 302 corresponds to the DC component of the developing current flowing from the developing roller 343A to the photoreceptor drum 341.

[0049] The optical scanning device 35 forms an electrostatic latent image on each of the photoreceptor drums 311, 321, 331, and 341 of the four image forming units 31 to 34. In this embodiment, the optical scanning device 35 includes two optical scanning units 351 and 352. Optical scanning unit 351 forms an electrostatic latent image on the photoreceptor drum 311 by irradiating it with light based on image data in response to the input of Y (yellow) image data. Optical scanning unit 351 forms an electrostatic latent image on the photoreceptor drum 321 by irradiating it with light based on image data in response to the input of C (cyan) image data. Optical scanning unit 352 forms an electrostatic latent image on the photoreceptor drum 331 by irradiating it with light based on image data in response to the input of M (magenta) image data. Furthermore, optical scanning unit 352 forms an electrostatic latent image on the photoreceptor drum 341 by irradiating it with light based on image data in response to the input of K (black) image data.

[0050] The toner images of each color formed by each of the multiple (in this case, four) image forming units 31 to 34 are transferred onto the outer surface of the intermediate transfer belt 361. As a result, a color image (toner image) is formed on the outer surface of the intermediate transfer belt 361.

[0051] As shown in Figure 3, the intermediate transfer device 36 includes an intermediate transfer belt 361, a drive roller 362, a tension roller 363, a belt cleaning unit 364, and a density detection unit 365. The intermediate transfer device 36 uses the intermediate transfer belt 361 to transport the toner image formed by the image forming units 31-34 to the transfer position P1 (see Figure 3) by the secondary transfer roller 37.

[0052] The intermediate transfer belt 361 is an endless belt on which toner images of each color are transferred from each of the photoreceptor drums 311, 321, 331, and 341. The intermediate transfer belt 361 is wrapped around drive rollers 362 and tension rollers 363 which are spaced apart from each other in the front-to-back direction D2 of the image forming apparatus 10. The drive rollers 362 rotate by receiving driving force supplied from a motor. As a result, the intermediate transfer belt 361 rotates in the rotation direction D4 shown in Figure 3. The toner image transferred to the outer surface of the intermediate transfer belt 361 is conveyed to the transfer position P1 by the secondary transfer rollers 37 as the intermediate transfer belt 361 rotates. The belt cleaning unit 364 cleans the outer surface of the intermediate transfer belt 361 after the toner image has been transferred at the transfer position P1.

[0053] The density detection unit 365 detects the density of the image (toner image) transferred to the outer surface of the intermediate transfer belt 361. For example, the density detection unit 365 includes a reflective optical sensor having a light-emitting unit that emits light directed toward the outer surface of the intermediate transfer belt 361, and a light-receiving unit that receives the light emitted from the light-emitting unit and reflected from the outer surface of the intermediate transfer belt 361. As shown in Figure 3, the density detection unit 365 is positioned downstream of the image forming unit 34 in the rotation direction D4 of the intermediate transfer belt 361 and upstream of the secondary transfer roller 37. The density detection unit 365 is also positioned opposite one end of the intermediate transfer belt 361 in the width direction (left-right direction D3) on the outer surface of the intermediate transfer belt 361. The density detection unit 365 may also be positioned opposite both ends of the intermediate transfer belt 361 in the width direction on the outer surface of the intermediate transfer belt 361. The density detection unit 365 may also detect the density of the toner image developed on the outer surface of the photoreceptor drum 341.

[0054] The secondary transfer roller 37 transfers the toner image formed on the outer surface of the intermediate transfer belt 361 to the sheet supplied by the paper feeding unit 4. As shown in Figure 3, the secondary transfer roller 37 is positioned opposite the tension roller 363, with the intermediate transfer belt 361 in between, so as to be in contact with the outer surface of the intermediate transfer belt 361. The secondary transfer roller 37 is pressed towards the tension roller 363 by a biasing member. The secondary transfer roller 37 is electrically connected to the power supply circuit, and by receiving a high voltage from the power supply circuit, it transfers the toner image formed on the outer surface of the intermediate transfer belt 361 to the sheet passing through the transfer position P1 (see Figure 3) where the secondary transfer roller 37 and the intermediate transfer belt 361 are in contact.

[0055] The secondary transfer roller 37 has a length in its axial direction (left-right direction D3) that is shorter than the width of the intermediate transfer belt 361. As a result, the outer surface of the intermediate transfer belt 361 has a contact area that contacts the secondary transfer roller 37 and a non-contact area (blank area) that does not contact the secondary transfer roller 37. The non-contact area is the area on both sides of the contact area on the outer surface of the intermediate transfer belt 361. The density detection unit 365 is positioned opposite one of the non-contact areas. The secondary transfer roller 37 transfers the image formed in the contact area to the sheet, but does not transfer the image formed in the non-contact area to the sheet. The secondary transfer roller 37 may have a length in its axial direction that is the same as the width of the intermediate transfer belt 361.

[0056] The fixing device 38 melts and fixes the toner image transferred to the sheet by the secondary transfer roller 37 to the sheet. For example, the fixing device 38 includes a fixing roller and a pressure roller. The fixing roller is positioned in contact with the pressure roller and heats the toner image transferred to the sheet to fix it to the sheet. The pressure roller presses the sheet as it passes through the contact area formed between it and the fixing roller.

[0057] The image-formed sheet is ejected into the output tray 39.

[0058] Incidentally, the process speed during image formation in the image forming unit 3 is changed, for example, according to the content of the image data. For example, if the image data is a high-density photograph or a high-density solid image, more toner is used compared to a low-density text image, so the process speed is changed to a slower speed than the speed used when printing the text image (e.g., the reference speed). Changing the process speed to another process speed can reduce the degradation of image quality when printing high-density images, but in order to prevent further degradation of image quality, it is preferable that the DC component Vdc of the development bias VB is adjusted to a setting value corresponding to the changed process speed. The process speed is, for example, the linear velocity of the photoreceptor drum 341.

[0059] Conventionally, in image forming apparatuses with adjustable process speeds, a technique has been proposed to determine process conditions at other process speeds from calibration results at a predetermined process speed without degrading image quality. Specifically, the second process conditions at the second process speed are determined based on a first density of a measurement image formed by the image forming means at a first process speed, a second density of a measurement image formed by the image forming means at a second process speed different from the first process speed, and the first process conditions at the first process speed.

[0060] However, the conventional technology described above requires the steps of forming a measurement image at a first process speed, measuring the image density, changing the process speed to a second process speed, forming a measurement image at the second process speed, and further measuring the image density, which makes determining the process conditions time-consuming.

[0061] In contrast, the image forming apparatus 10 according to this embodiment makes it possible to determine the development bias according to other process speeds without degrading image quality and without performing calibration processing for the development bias corresponding to other process speeds, as described below.

[0062] In other words, as shown in Figure 1, the image forming apparatus 10 according to this embodiment comprises at least an image forming unit 3, a calibration processing unit 51, and a bias voltage determination unit 52.

[0063] As described above, the image forming unit 3 applies the development bias VB between the photoreceptor drum 341, whose surface is charged, and the developing roller 343A, which holds the toner to be attached to the photoreceptor drum 341, thereby moving the toner from the developing roller 343A to the exposure portion of the photoreceptor drum 341 and forming a toner image on the photoreceptor drum 341 based on the image data.

[0064] In this embodiment, as an example, as will be described later, the calibration processing unit 51 and the bias voltage determination unit 52 are provided in the control unit 5 as functions of the control unit 5.

[0065] [3] Configuration of the control unit Next, with reference to Figure 1, each functional unit included in the control unit 5 will be described in more detail. The control unit 5 includes various processing units such as a calibration processing unit 51, a bias voltage determination unit 52, a speed change processing unit 53, and a bias upper limit determination unit 54. In other words, the image forming apparatus 10 is equipped with each of these processing units as a function of the control unit 5.

[0066] The calibration processing unit 51 performs a DC calibration process to adjust the voltage value of the DC component Vdc of the development bias VB. The calibration processing unit 51 performs the DC calibration process, for example, when predetermined adjustment execution conditions are met. These adjustment execution conditions include, for example, that initial operations performed after the main power of the image forming apparatus 10 is turned on have been executed, or that a predetermined number of print cycles (for example, 1000) has been counted.

[0067] In this embodiment, the calibration processing unit 51 determines the setting value (reference setting value) of the DC component Vdc when the image forming process is performed at a reference process speed, which is initially set as the standard speed, among a plurality of process speeds that the image forming unit 3 can take. In other words, the calibration processing unit 51 determines the reference setting value (a setting voltage value corresponding to the reference process speed set as the process speed) that corresponds to the DC component Vdc of the development bias VB set when the image forming unit 3 operates at the predetermined reference process speed.

[0068] The DC calibration process involves causing the image forming unit 3 to perform a process to create a predetermined test toner image, and determining and setting the voltage value of the DC component Vdc of the development bias VB in the image forming unit 3 according to the density of the test toner image.

[0069] For example, the calibration processing unit 51 causes the test toner image to be formed on each of the image forming units 31 to 34. As a result, the four color test toner images are developed on the surface of each photoreceptor drum and then transferred to the intermediate transfer belt 361. For example, the test toner image includes a toner patch. The test toner image is formed, for example, on the non-contact area on the outer circumferential surface of the intermediate transfer belt 361. Alternatively, the test toner image may be formed on the contact area of ​​the intermediate transfer belt 361.

[0070] Furthermore, the calibration processing unit 51 acquires the density detection results of the four test toner images by the density detection unit 365. Furthermore, the calibration processing unit 51 corrects the set value (reference set value) of the DC component Vdc according to the difference between the density detection results of the four test toner images and a predetermined target density. Specifically, if the density of the test toner image is lower than the target density, the calibration processing unit 51 determines the set value of the DC component Vdc to be a voltage value that is larger than the current value by a value corresponding to the density difference. Also, if the density of the test toner image is higher than the target density, the calibration processing unit 51 determines the set value of the DC component Vdc to be smaller than the current value by a value corresponding to the density difference.

[0071] If the image forming apparatus 10 is a monochrome printer, the test toner image is formed on the photoreceptor drum 341, and the density detection unit 365 detects the density of the test toner image on the photoreceptor drum 341.

[0072] The bias voltage determination unit 52 performs bias voltage determination processing when the image forming unit 3 operates at a first process speed different from the reference process speed. Specifically, the bias voltage determination unit 52 first determines a first correction amount Vc1 based on a first speed difference ΔS1 between the reference process speed and the first process speed. Furthermore, the bias voltage determination unit 52 corrects the reference setting value with the determined first correction amount Vc1. Then, the bias voltage determination unit 52 determines the corrected first setting value obtained by correcting the reference setting value with the first correction amount Vc1 as the setting value of the DC component Vdc of the development bias VB according to the first process speed.

[0073] In this embodiment, the bias voltage determination unit 52 calculates the first set value by subtracting the first correction amount Vc1 from the reference set value when the process speed is reduced from the reference process speed to the first process speed.

[0074] The speed change processing unit 53 performs a process (speed change processing) to change the process speed of the image forming unit 3. When a print job is input to the image forming unit 3, the speed change processing unit 53 changes the process speed of the image forming unit 3 according to the content of the image data included in the print job.

[0075] The speed change processing unit 53 performs a deceleration process to change the process speed to the first process speed, which is slower than the reference process speed, in order to mitigate the degradation of image quality, for example, when image data such as a photograph or solid image is input.

[0076] For example, when the speed change processing unit 53 acquires image data to be printed, it determines whether the image data is a solid image or a text image. If it is a text image, it maintains the process speed at the initial reference process speed. If it is a solid image, it changes the process speed from the reference process speed to the first process speed. The first process speed is, for example, 3 / 4 of the reference process speed.

[0077] Furthermore, the speed change processing unit 53 determines whether the image data to be printed is a solid image and whether it contains a standard number or more of high-density pixels exceeding a predetermined gradation. If the number of high-density pixels is less than the standard number, the process speed is changed from the standard process speed to the first process speed. If the number of pixels is equal to or greater than the standard number, the process speed is changed from the standard process speed to a second process speed that is slower than the first process speed. The second process speed is, for example, half the speed of the standard process speed.

[0078] The bias voltage determination unit 52 performs the bias voltage determination process, for example, after the DC calibration process is completed. The set value of the DC component Vdc determined by the bias voltage determination process is stored in the storage unit 6 for each process speed.

[0079] Then, when the process speed is changed from the reference process speed to the first process speed by the speed change processing unit 53, the control unit 5 reads a setting value corresponding to the first process speed from the storage unit 6 and applies the development bias VB, which includes the DC component Vdc of the setting value, from the development power supply circuit 301A between the development roller 343A and the photoreceptor drum 341.

[0080] The bias voltage determination unit 52 does not necessarily have to determine the set value of the DC component Vdc of the development bias VB in advance. For example, the first correction amount may be determined when the process speed is changed from the reference process speed to the first process speed by the speed change processing unit 53.

[0081] In this embodiment, the bias voltage determination unit 52 determines the first correction amount Vc1 based on the first speed difference ΔS1, the exposure potential VL of the exposure unit, and the potential difference Vdev between the voltage value of the DC component Vdc of the development bias VB set when the image forming unit 3 operates at the reference process speed (i.e., the reference setting value).

[0082] Specifically, the bias voltage determination unit 52 calculates the first correction amount Vc1 based on the following equation (1), which shows the relationship between the potential difference Vdev between the exposure potential VL of the exposure portion of the photoreceptor drum 341 and the DC component Vdc of the development bias VB, the first speed difference ΔS1, and the first correction amount Vc1. In other words, the bias voltage determination unit 52 calculates the first correction amount Vc1 so as to satisfy equation (1).

[0083] Vc1 = ΔS1(a × Vdev - b) ···(1)

[0084] However, the coefficients a and b in equation (1) are eigenvalues ​​determined for each type of image forming apparatus 10, and are numerical values ​​that can be determined in advance, for example, by experimentation. The coefficients a and b are stored in the storage unit 6 for each type of apparatus. In addition, the formula "a × Vdev - b" in parentheses on the right side of equation (1) is expressed as the unit correction amount Vcom per unit velocity.

[0085] In this embodiment, for example, when the photoreceptor drum 341 is an organic photoreceptor, the coefficient a is determined within the range of 0.05 ≤ a ≤ 4.0, and the coefficient b is determined within the range of -250 ≤ b ≤ 500. Furthermore, in this case, the coefficients a and b are determined such that the unit correction amount Vcom is within the range of 0 ≤ Vcom ≤ 500.

[0086] Furthermore, if the photoreceptor drum 341 is an amorphous silicon photoreceptor drum having an amorphous silicon layer on its surface, the bias voltage determination unit 52 calculates the first correction amount Vc1 to satisfy equation (1), in which case the coefficient a is determined within the range of 0.4 ≤ a ≤ 2.0, and the coefficient b is determined within the range of -150 ≤ b ≤ 100. In addition, in this case, the coefficients a and b are determined so that the unit correction amount Vcom is within the range of 0 ≤ Vcom ≤ 300.

[0087] The above equation (1) can be expanded as follows.

[0088] Vc1 = ΔS1(a × Vdev - b) =ΔS1×a(Vdc-VL)-ΔS1×b =ΔS1×a×Vdc-ΔS1×a×VL-ΔS1×b =ΔS1×a×Vdc-ΔS1(a×VL+b) ···(2)

[0089] In the above expanded equation (2), if we set ΔS1×a as a′ and ΔS1(a×VL+b) as b′, then the above expanded equation (2) can be expressed as follows. The bias voltage determination unit 52 may calculate the first correction amount Vc1 so as to satisfy equation (3).

[0090] Vc1 = a' × Vdc - b' ... (3)

[0091] In addition, as another embodiment of the bias voltage determination unit 52, for example, when the image forming unit 3 operates at a second process speed different from the reference process speed, the bias voltage determination unit may determine a second speed difference ΔS2 between the reference process speed and the second process speed, determine a second setting value obtained by multiplying the ratio of the second speed difference ΔS2 to the first speed difference ΔS1 (ΔS2 / ΔS1) by the first setting value, and determine the bias voltage according to the second process speed using this second setting value.

[0092] The bias voltage determination unit 52 may, for example, calculate the second correction amount Vc2 based on the following equation (4), which shows the relationship between the first speed difference ΔS1, the second speed difference ΔS2, and the first correction amount Vc1 calculated based on equation (1).

[0093] Vc2 = Vc1 × ΔS2 / ΔS1 ... (4)

[0094] In this case, the bias voltage determination unit 52 corrects the DC component Vdc (reference setting value) of the development bias VB corresponding to the reference process speed with the second correction amount Vc2, and determines the corrected second setting value obtained by correcting the reference setting value with the second correction value Vc2 as the setting value of the DC component Vdc of the development bias VB according to the second process speed.

[0095] The bias upper limit determination unit 54 performs a process (bias upper limit determination process) to determine the upper limit of the allowable range (allowable upper limit) that can be taken as the set value of the DC component Vdc of the development bias VB. The bias upper limit determination unit 54 determines an upper limit correction amount based on the first speed difference ΔS1. Furthermore, the bias upper limit determination unit 54 performs a process to determine the corrected first allowable upper limit, obtained by correcting the predetermined reference upper limit with the determined upper limit correction amount, as the set value of the allowable upper limit according to the first process speed. Here, the reference upper limit is, for example, the upper limit of the allowable range that can be taken as the set value of the DC component Vdc of the development bias VB corresponding to the reference process speed.

[0096] In this embodiment, when the process speed is reduced, the bias upper limit determination unit 54 calculates the first allowable upper limit by subtracting the upper limit correction amount from the reference upper limit.

[0097] Here, the bias upper limit determination unit 54 may calculate the first permissible upper limit by further taking into account the environmental conditions of the location where the image forming apparatus 10 is installed. In this case, the environmental conditions are, for example, absolute humidity. Specifically, the bias upper limit determination unit calculates the first permissible upper limit on the condition that the absolute humidity exceeds a predetermined threshold (for example, 80%). Alternatively, the bias upper limit determination unit calculates the first permissible upper limit when the absolute humidity changes significantly, for example, when the difference between the absolute humidity calculated last time and the absolute humidity calculated this time exceeds a predetermined threshold (for example, 30 degrees). The ambient temperature around the image forming apparatus 10 may be used as the environmental condition.

[0098] The calibration processing unit 51 may perform the DC calibration process for each of the multiple speeds that can be adopted as the process speed of the image forming unit 3 (such as the reference process speed, the first process speed, the second process speed, and other process speeds). In this case, if the process speed is changed from the current process speed (for example, the reference process speed) to another process speed (for example, the first process speed or the second process speed) before the conditions for performing the DC calibration process are met, the bias voltage determination unit 52 may determine the set value of the DC component Vdc of the development bias VB according to the changed other process speed without performing the DC calibration process corresponding to the other process speed.

[0099] For example, if the process speed of the image forming unit 3 is set to the reference process speed, and the current process speed is changed from the reference process speed to the first process speed before the conditions for executing the DC calibration process are met, the calibration processing unit 51 does not execute the DC calibration process corresponding to the first process speed, but instead the bias voltage determination unit 52 determines the set value of the DC component Vdc of the development bias VB according to the changed first process speed.

[0100] Furthermore, for example, if the process speed of the image forming unit 3 is set to the first process speed, and the current process speed is changed from the first process speed to the second process speed before the conditions for executing the DC calibration process are met, the calibration processing unit 51 will not execute the DC calibration process corresponding to the second process speed, and the bias voltage determination unit 52 will determine the setting value of the DC component Vdc of the development bias VB according to the changed second process speed.

[0101] Furthermore, for example, if the process speed of the image forming unit 3 is set to the second process speed, and the current process speed is changed from the second process speed to the first process speed before the conditions for executing the DC calibration process are met, the calibration processing unit 51 will not execute the DC calibration process corresponding to the first process speed, and the bias voltage determination unit 52 will determine the setting value of the DC component Vdc of the development bias VB according to the changed first process speed.

[0102] [4] Bias voltage determination process in an image forming apparatus The bias voltage determination method performed in the image forming apparatus 10 will be explained below, along with an example of the procedure for the bias voltage determination process performed by the control unit 5 in the image forming apparatus 10, with reference to the flowchart in Figure 5. Here, steps S1, S2, etc. represent the processing procedure (step) performed by the control unit 5. In the following explanation, the processing procedure for K (black) toner will be used as an example, but the control unit 5 will perform the same processing for Y (yellow), C (cyan), and M (magenta).

[0103] <Step S1> First, in step S1, the control unit 5 determines whether or not the adjustment execution conditions have been met.

[0104] <Step S2> If it is determined in step S1 that the adjustment execution conditions have been met, the control unit 5 executes the DC calibration process corresponding to the currently set process speed in step S2. The process in step S2 is executed by the calibration processing unit 51. Step S2 is an example of the calibration steps of the present invention.

[0105] <Step S3> When the processing in step S2 is completed, the control unit 5 executes the bias voltage determination process in step S3. The processing in step S2 is performed by the bias voltage determination unit 52. The set value for the DC component Vdc of the development bias VB determined in step S3 is stored in the storage unit 6. Note that step S3 is an example of the bias voltage determination step of the present invention.

[0106] <Step S4> In the next step S4, the control unit 5 executes the bias upper limit determination process to determine the upper limit of the acceptable range (acceptable upper limit) that can be taken as the set value of the DC component Vdc of the development bias VB. The process in step S3 is performed by the bias upper limit determination unit 54. The acceptable upper limit determined in step S4 is stored in the storage unit 6.

[0107] <Step S5> In the next step S5, the control unit 5 determines whether the process speed of the image forming unit 3 has been changed. For example, the control unit 5 determines whether the process speed of the image forming unit 3 has been changed from the reference process speed to the first process speed. The process in step S5 is repeated until a change in process speed is determined.

[0108] <Step S6> If a change in the process speed is determined in step S5, the control unit 5 changes the set value of the DC component Vdc of the development bias VB in the next step S6. As a result, in the next image forming process, the development bias VB including the DC component Vdc of the set value is applied between the development roller 343A and the photoreceptor drum 341 by the development power supply circuit 301A.

[0109] [5] Effects of this embodiment As described above, in this embodiment, the calibration processing unit 51 corrects the reference setting value corresponding to the reference process speed, which is set as the DC component Vdc of the development bias VB. The bias voltage determination unit 52 determines the first correction amount Vc1 based on the first speed difference ΔS1 between the reference process speed and the first process speed. More specifically, the bias voltage determination unit 52 determines the first correction amount Vc1 based on the first speed difference ΔS1 and the potential difference Vdev. Then, the bias voltage determination unit 52 determines the corrected first setting value, obtained by correcting the reference setting value with the first correction amount Vc1, as the setting value of the DC component Vdc of the development bias VB corresponding to the first process speed.

[0110] As a result, without performing the DC calibration process for each process speed, the setting value of the DC component Vdc corresponding to other process speeds can be determined by performing the DC calibration process corresponding to at least the currently set process speed. Therefore, the long period of downtime of the image forming apparatus 10 due to multiple calibration processes, as in the conventional method, is prevented. Furthermore, since the setting value of the DC component Vdc of the development bias VB is determined based on the first speed difference ΔS1, the DC component Vdc is determined with accuracy comparable to when the DC calibration process corresponding to other process speeds is performed. As a result, there is no degradation in image quality even in image forming processes after changing the process speed.

[0111] Furthermore, as described above, the first correction amount Vc1 that satisfies equation (1) is calculated, and the DC component Vdc is corrected with this first correction amount Vc1. This determines the optimal DC component Vdc corresponding to the changed process speed.

[0112] Furthermore, as described above, the second correction amount Vc2 is calculated based on equation (2) above, and the DC component Vdc is corrected with this second correction amount Vc2. This determines the optimal DC component Vdc corresponding to the changed process speed.

[0113] [Notes on the invention] The following is an overview of the invention extracted from the above-described embodiments. Note that each configuration and processing function described below can be selected and combined as desired.

[0114] <Note 1> An image forming unit applies a bias voltage between a first carrier whose surface is charged and a second carrier that holds toner to be attached to the first carrier, thereby moving toner from the second carrier to the exposure portion of the first carrier and forming a toner image on the first carrier based on image data. When the image forming unit operates at a predetermined reference process speed, a calibration processing unit performs a calibration process to determine a reference setting value corresponding to the reference process speed set as the bias voltage, An image forming apparatus comprising: a bias voltage determination unit that, when the image forming unit operates at a first process speed different from the reference process speed, determines a first correction amount based on a first speed difference between the reference process speed and the first process speed, and determines the corrected first setting value obtained by correcting the reference setting value with the first correction amount as the bias voltage corresponding to the first process speed.

[0115] <Note 2> The image forming apparatus according to Appendix 1, wherein the bias voltage determination unit determines the first correction amount based on the first speed difference, the potential difference between the potential of the exposure unit and the reference setting value, or the reference potential difference.

[0116] <Note 3> The image forming apparatus according to Appendix 2, wherein the first carrier is an amorphous silicon photoreceptor drum having an amorphous silicon layer on its surface, and the bias voltage determination unit determines the first correction amount based on the first speed difference and the reference setting value.

[0117] <Note 4> The image forming apparatus according to any one of the appendices 1 to 3, wherein when the image forming unit operates at a second process speed different from the reference process speed, the bias voltage determination unit determines a second speed difference between the reference process speed and the second process speed, determines a second correction amount obtained by multiplying the ratio of the second speed difference to the first speed difference by the first correction amount, and determines the bias voltage according to the second process speed.

[0118] <Note 5> The system further includes a bias upper limit determination unit that determines the permissible upper limit value of the bias voltage, The image forming apparatus according to any one of the appendices 1 to 4, wherein the bias upper limit determination unit determines an upper limit correction amount based on the first speed difference, and corrects a predetermined reference upper limit with the upper limit correction amount to determine the corrected first allowable upper limit as the set value of the allowable upper limit according to the first process speed.

[0119] <Note 6> The image forming apparatus according to Appendix 5, wherein the bias upper limit determination unit calculates the first allowable upper limit by further taking into account the environmental conditions of the location where the image forming apparatus is installed.

[0120] <Note 7> The calibration processing unit is capable of performing the calibration process for each of the multiple process speeds that the image forming unit can adopt. An image forming apparatus according to any one of the appendices 1 to 6, which determines the bias voltage by obtaining a correction amount corresponding to a process speed other than the current process speed set in the image forming unit.

[0121] <Note 8> This is applied to an image forming apparatus that applies a bias voltage between a first carrier whose surface is charged and a second carrier that holds toner to be attached to the first carrier, thereby moving toner from the second carrier to the exposure portion of the first carrier and forming a toner image on the first carrier based on image data. A calibration step in which, when the image forming apparatus operates at a predetermined reference process speed, a calibration process is performed to determine a reference setting value corresponding to the reference process speed set as the bias voltage, A bias voltage determination method performed by one or more processors, comprising: a bias voltage determination step in which, when the image forming unit operates at a first process speed different from the reference process speed, a first correction amount is determined based on a first speed difference between the reference process speed and the first process speed, and the corrected first set value obtained by correcting the reference set value with the first correction amount is determined as the bias voltage corresponding to the first process speed.

[0122] <Note 9> This is applied to an image forming apparatus that applies a bias voltage between a first carrier whose surface is charged and a second carrier that holds toner to be attached to the first carrier, thereby moving toner from the second carrier to the exposure portion of the first carrier and forming a toner image on the first carrier based on image data. A calibration step in which, when the image forming apparatus operates at a predetermined reference process speed, a calibration process is performed to determine a reference setting value corresponding to the reference process speed set as the bias voltage, A program for causing one or more processors to execute a bias voltage determination step, which involves determining a first correction amount based on a first speed difference between the reference process speed and the first process speed when the image forming unit operates at a first process speed different from the reference process speed, and determining the corrected first setting value obtained by correcting the reference setting value with the first correction amount to be the bias voltage corresponding to the first process speed, or a non-temporary computer-readable storage medium in which the program is stored. [Explanation of Symbols]

[0123] 1: Automatic document transport device 2: Image reading unit 3: Image forming unit 4:Paper feed section 5: Control Unit 6: Storage section 7: Operation display section 10: Image forming apparatus 31-34: Image forming unit 35: Optical scanning device 36: Intermediate Transfer Device 37: Secondary transfer roller 38: Fixing device 39: Paper output tray 51: Calibration Processing Unit 52: Bias voltage determination unit 53: Speed ​​change processing unit 54: Bias Upper Limit Determination Unit 301: Power supply circuit 301A:Development power supply circuit 301B: Power supply circuit for static electricity 302: Current detection circuit 302A: Filter circuit 311: Photoconductor drum 313A: Developing Roller 321: Photoconductor Drum 323A: Developing Roller 331: Photoconductor Drum 333A: Developing Roller 341: Photoconductor drum 343A: Developing Roller 365: Concentration detection unit

Claims

1. An image forming unit applies a bias voltage between a first carrier whose surface is charged and a second carrier that holds toner to be attached to the first carrier, thereby moving toner from the second carrier to the exposure portion of the first carrier and forming a toner image on the first carrier based on image data. When the image forming unit operates at a predetermined reference process speed, a calibration processing unit performs a calibration process to determine a reference setting value corresponding to the reference process speed set as the bias voltage, An image forming apparatus comprising: a bias voltage determination unit that, when the image forming unit operates at a first process speed different from the reference process speed, determines a first correction amount based on a first speed difference between the reference process speed and the first process speed, and determines the corrected first setting value obtained by correcting the reference setting value with the first correction amount as the bias voltage corresponding to the first process speed.

2. The image forming apparatus according to claim 1, wherein the bias voltage determination unit determines the first correction amount based on the first speed difference, the potential difference between the potential of the exposure unit and the reference setting value, or the reference potential difference.

3. The image forming apparatus according to claim 2, wherein the first carrier is an amorphous silicon photoreceptor drum having an amorphous silicon layer on its surface, and the bias voltage determination unit determines the first correction amount based on the first speed difference and the reference setting value.

4. The image forming apparatus according to claim 1, wherein, when the image forming unit operates at a second process speed different from the reference process speed, the bias voltage determination unit determines a second speed difference between the reference process speed and the second process speed, determines a second correction amount obtained by multiplying the ratio of the second speed difference to the first speed difference by the first correction amount, and determines the bias voltage according to the second process speed.

5. The system further includes a bias upper limit determination unit that determines the permissible upper limit value of the bias voltage, The image forming apparatus according to claim 1, wherein the bias upper limit determination unit determines an upper limit correction amount based on the first speed difference, and corrects a predetermined reference upper limit with the upper limit correction amount to determine a corrected first allowable upper limit as the set value of the allowable upper limit according to the first process speed.

6. The image forming apparatus according to claim 5, wherein the bias upper limit determination unit calculates the first allowable upper limit by further taking into account the environmental conditions of the location where the image forming apparatus is installed.

7. The calibration processing unit is capable of performing the calibration process for each of the multiple process speeds that the image forming unit can adopt. The image forming apparatus according to claim 1, wherein a correction amount corresponding to a process speed different from the current process speed set in the image forming unit is determined, and the setting value of the bias voltage is determined.

8. This is applied to an image forming apparatus that applies a bias voltage between a first carrier whose surface is charged and a second carrier that holds toner to be attached to the first carrier, thereby moving toner from the second carrier to the exposed portion of the first carrier and forming a toner image on the first carrier based on image data. A calibration step in which, when the image forming apparatus operates at a predetermined reference process speed, a calibration process is performed to determine a reference setting value corresponding to the reference process speed set as the bias voltage, A bias voltage determination method performed by one or more processors, comprising: a bias voltage determination step in which, when the image forming unit operates at a first process speed different from the reference process speed, a first correction amount is determined based on a first speed difference between the reference process speed and the first process speed, and the corrected first setting value obtained by correcting the reference setting value with the first correction amount is determined as the bias voltage corresponding to the first process speed.

9. This is applied to an image forming apparatus that applies a bias voltage between a first carrier whose surface is charged and a second carrier that holds toner to be attached to the first carrier, thereby moving toner from the second carrier to the exposed portion of the first carrier and forming a toner image on the first carrier based on image data. A calibration step in which, when the image forming apparatus operates at a predetermined reference process speed, a calibration process is performed to determine a reference setting value corresponding to the reference process speed set as the bias voltage, A program for causing one or more processors to execute a bias voltage determination step, which involves determining a first correction amount based on a first speed difference between the reference process speed and the first process speed when the image forming unit operates at a first process speed different from the reference process speed, and determining the corrected first setting value obtained by correcting the reference setting value with the first correction amount as the bias voltage corresponding to the first process speed.

Images