JP6331508B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a printer, a facsimile machine, and a copying machine.

  In an image forming apparatus using an electrophotographic system, the image density in an output toner image may vary due to changes in the usage environment (temperature / humidity) and changes in the components over time. Therefore, in such an image forming apparatus, in order to obtain a stable image density, the following process called process control is often performed. In the process control, first, a predetermined toner pattern is formed on the peripheral surface of an image carrier such as a photosensitive drum or an intermediate transfer belt, and the amount of toner attached to the toner pattern is detected. Based on the detection result, an image forming condition necessary to obtain a predetermined target adhesion amount is calculated. Examples of the formation conditions calculated at this time include a charging bias when charging the photosensitive drum, an exposure intensity when exposing, a developing bias when developing the electrostatic latent image with toner, and the like. The toner image is formed under the formation conditions calculated by such process control. A stable image density can be obtained by appropriately performing process control.

  Here, the timing for performing the process control includes a non-image forming period in which image formation is not performed in the image forming apparatus, such as immediately after power-on or after a series of image formations are completed. However, if process control is performed only at the time of non-image formation in this way, there is a possibility that it may not be possible to cope with a variation factor of image density during a series of image formation, for example.

  In view of this, a technique has been proposed in which a process control is performed by forming a toner pattern in the following area on the peripheral surface of the image carrier during a series of image formation. For example, a technique for forming a toner pattern in an area between a toner image on a certain sheet and a toner image on the next sheet (hereinafter referred to as a sheet interval) has been proposed (for example, Patent Document 1). In addition, a technique has been proposed in which a toner pattern is formed side by side with a toner image in a main scanning direction that intersects the direction of circular movement of the peripheral surface of the image carrier (for example, Patent Document 2). According to the techniques described in these Patent Documents 1 and 2, since the process control is performed even during a series of image formation, it is possible to cope with a variation factor of the image density during the series of image formation.

  Here, in general, the above-described space between the sheets is a narrow region particularly in the direction of circulation movement of the peripheral surface of the image carrier (that is, the sub-scanning direction). For this reason, in the technique described in Patent Document 1, a toner pattern is formed between a plurality of sheets with a toner image formed therebetween. The formation of the toner image itself may be a factor of fluctuation in image density. In the technique described in Patent Document 1, since the process control is performed with such a factor of fluctuation interposed therebetween, there is a risk that the accuracy of the toner image may be lowered. is there.

  On the other hand, in the technique described in Patent Document 2, since a toner pattern can be created in a wide area adjacent to the toner image in the main scanning direction, process control is performed at a time. For this reason, the technique described in Patent Document 2 has higher accuracy than the technique described in Patent Document 1.

  Here, in the technique described in Patent Document 2, the execution timing of process control is determined in advance by experiments or the like. This also applies to the technique described in Patent Document 1. That is, in any of the techniques described in Patent Documents 1 and 2, process control is executed each time the toner image formation reaches a predetermined number of sheets in terms of the number of sheets. For this reason, it may not be possible to cope with a rapid variation factor between process controls executed at intervals determined in this way. In order to cope with such a rapid variation factor, it is conceivable to increase the execution frequency of process control. However, if the frequency of execution of process control increases, the number of toner pattern formations increases and the toner consumption may increase.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of performing process control with high accuracy while suppressing toner consumption.

In order to solve the above-described problem, the invention according to claim 1 is directed to an image holding body that holds a toner image by forming a toner image on a circumferential surface that is circulated by a process unit, and the image holding body is the circumferential surface. An image forming apparatus comprising: a transfer unit that transfers the toner image held on a sheet-like recording medium; and a fixing unit that fixes the toner image transferred to the recording medium by the transfer unit. An image formation process control execution unit that adjusts the toner image formation conditions during image formation for forming a toner image is a timing determination unit, a formation instruction unit, a pattern formation unit during image formation, and an adhesion amount detection during image formation. and a part of the image forming time adjustment unit, the timing determining section, the execution timing of the process control during the image formation, varying between the image density and the image density of previous toner image bets toner image When the amount is large, the determination is made based on the determination condition that the time is earlier than when the amount is small, and when the amount is small, the delay is greater than when the amount is large. A predetermined toner pattern formation instruction is given, and the image forming pattern forming unit is located in a region aligned with the image forming region in a direction crossing the direction of circulation movement of the peripheral surface of the image carrier by the process unit. A toner pattern is formed in a non-image forming area, the image formation adhesion amount detection unit detects a toner adhesion amount in the toner pattern, and the image formation adjustment unit is an image formation adhesion amount detection unit. The image forming apparatus is characterized in that the formation conditions are adjusted based on the detection result.

  According to the first aspect of the present invention, it is possible to advance the execution time of the process control when the fluctuation of the image density of the toner image is expected. Conversely, when such a change does not occur for the time being or is expected to be small, the process control execution time can be delayed to reduce the toner consumption. As described above, according to the first aspect of the present invention, it is possible to perform process control with high accuracy while suppressing toner consumption.

1 is a schematic configuration diagram of an image forming apparatus common to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram of a process cartridge provided in the image forming apparatus of FIG. 1. FIG. 3 is a diagram showing the developing device shown in FIG. 2 in a state where the developing device shown in FIG. It is a typical hardware block diagram of the control part shown by FIG. It is a functional block diagram showing a non-image forming process control execution unit. FIG. 5 is a flowchart showing process control at the time of non-image formation executed by the functional block shown in FIG. 4. FIG. 7 is a schematic diagram showing a toner pattern at the time of non-image formation, which is formed in step S104 of the flowchart shown in FIG. 7 is a graph showing the relationship between the toner adhesion amount obtained in step S106 of the flowchart shown in FIG. 6 and the development potential obtained in step S105. It is a functional block diagram showing a process control execution unit at the time of image formation. FIG. 10 is a diagram showing functional blocks for determining a process control execution time at the time of image formation by a time determination unit shown in FIG. 9. 11 is a flowchart showing process control at the time of image formation executed by the functional blocks shown in FIGS. 9 and 10. 6 is a graph showing a relationship between an image area ratio of a toner image to be formed and development γ. 6 is a graph showing how development γ increases when the image area ratio of a toner image increases rapidly. FIG. 12 is a schematic diagram showing a toner pattern at the time of image formation, which is formed in step S205 of the flowchart shown in FIG. FIG. 12 is a schematic diagram illustrating adjustment of the developing bias performed in step S207 of the flowchart of FIG. FIG. 6 is a schematic diagram illustrating adjustment of a toner density control reference value by an image forming adjustment unit. It is a figure which shows the functional block for determining the execution time of the process control at the time of image formation in 2nd Embodiment. It is a figure which shows the functional block for determining the execution time of the process control at the time of image formation in 3rd Embodiment. 6 is a graph showing how development γ of the developing device varies depending on the temperature and humidity inside the image forming apparatus. It is a figure which shows the functional block for determining the execution time of the process control at the time of image formation in 4th Embodiment. 6 is a graph schematically showing the relationship between the operation of the developing device and the charge amount of toner.

  Hereinafter, the first to fourth embodiments of the present invention will be described with reference to the drawings.

  First, a schematic configuration of an image forming apparatus common to four embodiments of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic configuration diagram of an image forming apparatus common to the embodiments of the present invention. FIG. 2 is a schematic configuration diagram of a process cartridge provided in the image forming apparatus of FIG.

An image forming apparatus 1 shown in FIG. 1 is used as a copying machine, a printer, a facsimile, or a complex machine for forming and fixing a toner image on a sheet-like recording medium S. The image forming apparatus 1 includes an exposure device 3 that irradiates a laser beam L, and a process unit 5 that forms an electrostatic latent image with the laser beam L and forms a toner image from the electrostatic latent image. . Further, the image forming apparatus 1 includes an intermediate transfer unit 7 to which a toner image is transferred from the process unit 5, and a secondary transfer unit 8 that transfers the toner image from the intermediate transfer unit 7 to the recording medium S. . The image forming apparatus 1 includes a fixing device 9 that fixes the toner image transferred by the secondary transfer unit 8 to the recording medium S. Further, the image forming apparatus 1 includes a stock tray 11 that temporarily holds the recording medium S on which the toner image is fixed, a paper feed tray 13 that stores a plurality of recording media S, a discharge roller 41, and a toner bottle. A bottle housing portion 43 for housing the bottle. The discharge roller 41 discharges the fixed recording medium S to the stock tray 11 . Also, the secondary transfer unit 8 corresponds to an example of a transfer section of the present invention. The fixing device 9 corresponds to an embodiment of the fixing unit referred to in the present invention.

  The exposure device 3 irradiates the surface of the photosensitive drum 15 charged by the charging device 17 described later with a laser beam L to form an electrostatic latent image corresponding to the image data. The exposure apparatus 3 includes a light source composed of a semiconductor laser that emits laser light L, an optical deflector that deflects the laser light L in the main scanning direction, and a photosensitive drum 15 that uses the deflected laser light L as a surface to be scanned. And an optical scanning optical system that collects light toward the surface.

  The process unit 5 is a process for charging the surface of the photoconductive drum 15, a process for developing a latent electrostatic image on the surface of the photoconductive drum 15 to form a toner image, and a transfer residual toner on the surface of the photoconductive drum 15 is removed. The process is repeated in sequence.

  The process unit 5 applies toner images of yellow, cyan, magenta, and black (hereinafter, “Y”, “C”, “M”, and “K” are attached to members corresponding to the respective colors). Process cartridges 10Y, 10M, 10C, and 10K for generation are provided. The image forming apparatus 1 of this embodiment is a so-called tandem type in which these process cartridges 10Y, 10M, 10C, and 10K are arranged in parallel.

  Each of the process cartridges 10Y, 10M, 10C, and 10K is configured to be detachable from the main body of the image forming apparatus 1, and the corresponding process cartridge can be replaced when the life is reached or exhausted. Yes. Hereinafter, the structure of the process cartridge will be described. Since the process cartridges 10Y, 10M, 10C, and 10K for each color have the same structure, the following description will be made without particularly distinguishing the colors. Also in FIG. 2, the reference numerals for identifying colors are omitted.

  As shown in FIG. 2, the process cartridge 10 includes a photosensitive drum 15 on which an electrostatic latent image is formed by the laser light L emitted from the exposure device 3, a charging device 17 that charges the photosensitive drum 15, It has. Further, the process cartridge 10 includes a developing device 19 that develops the electrostatic latent image to form a toner image, and a cleaning device 21 that cleans the surface of the photosensitive drum 15. In the process cartridge 10, toner of any color of YMCK corresponding to the color separation component of the color image is stored in the developing device 19.

  On the photosensitive drum 15, an electrostatic latent image is formed by the laser light L scanned in accordance with the image forming signal, and a toner image as an unfixed image is formed by toner of the developing device 19 described later. The charging device 17 uniformly charges the surface of the photosensitive drum 15 to a desired polarity and a desired potential by applying a charging bias. The developing device 19 performs development by attaching toner to the electrostatic latent image formed on the surface of the photosensitive drum 15. The cleaning device 21 removes transfer residual toner remaining on the surface of the photosensitive drum 15 without being transferred to the intermediate transfer unit 7 described later from the surface of the photosensitive drum 15.

  Hereinafter, the developing device 19 will be described with reference to FIG. 2 and FIG. FIG. 3 is a view showing the developing device shown in FIG. 2 in a state where the internal structure is seen through as seen in the direction of the arrow A1 in the drawing. The developing device 19 is configured by housing a developing roller 192, a first screw 193, and a second screw 194 in a case 191. In the case 191, a developer composed of toner and a magnetic carrier is stored. The developer is stirred while being circulated and conveyed in the direction of the arrow A2 in FIG. 3 by the rotation of the first screw 193 and the second screw 194. By stirring, the toner and the magnetic carrier are mixed and frictionally charged.

  The developing roller 192 includes a magnet roller as a magnetic field generating unit. The developing roller 192 conveys the toner to a developing region facing the photosensitive drum 15 by rotating while holding the developer on the surface. A developing bias is applied to the developing roller 192 from a developing bias power source. For this reason, in the development area, a potential difference is generated between the surface potential of the developing roller 192 and the potential of the electrostatic latent image on the surface of the photosensitive drum 15, and the development electric field formed by this potential difference is affected. The toner in the developer adheres to the electrostatic latent image. As a result, the electrostatic latent image on the photosensitive drum 15 is developed as a toner image.

  When such development is repeated, the toner in the case 191 decreases. A toner concentration sensor 195 that detects the toner concentration in the case 191 is provided below the second screw 194 in the case 191. As the toner concentration sensor 195, a type that detects the toner concentration by measuring the magnetic permeability in the case 191 is employed. In this type of toner concentration sensor 195, the output increases when the toner concentration in the case 191 decreases. When the output value of the toner density sensor 195 rises above a toner density control reference value, which will be described later, toner is supplied from a toner supply port 191a opened in the case 191.

  The intermediate transfer unit 7 shown in FIG. 1 transfers the toner image on the surface of the photosensitive drum 15 to the surface of the recording medium S. The intermediate transfer unit 7 includes an endless intermediate transfer belt 27, and a cleaning backup roller 25 and a secondary transfer backup roller 12 on which the intermediate transfer belt 27 is stretched and around the intermediate transfer belt 27. . Further, the intermediate transfer unit 7 faces a plurality of photosensitive drums 15 corresponding to the respective colors, and a plurality of primary transfer rollers 29Y and 29M that press the intermediate transfer belt 27 against each of the plurality of photosensitive drums 15. 29C, 29K. In addition, the intermediate transfer unit 7 includes a belt cleaning device 33. The intermediate transfer belt 27 is rotated counterclockwise on the drawing while being held at a predetermined tension by the tension roller 35. The intermediate transfer belt 27 corresponds to an example of an image carrier according to the present invention.

  The primary transfer rollers 29Y, 29M, 29C, and 29K are applied with a primary transfer bias with a polarity opposite to the polarity of the charge of the toner. Therefore, the toner is attracted from the surface of the photosensitive drum 15 to the intermediate transfer belt 27 side to primarily transfer the toner image to the intermediate transfer belt 27.

  The secondary transfer unit 8 includes a secondary transfer roller 31 that presses the recording medium S against the intermediate transfer belt 27. The secondary transfer roller 31 is provided to face the secondary transfer backup roller 12. A secondary transfer bias is applied to the secondary transfer roller 31 with a polarity opposite to the polarity of the charge of the toner. Therefore, the toner is attracted from the surface of the intermediate transfer belt 27 to the recording medium S side, and the toner image is secondarily transferred to the recording medium S.

  The belt cleaning device 33 is configured such that a cleaning blade that contacts the intermediate transfer belt 27 is held by a blade holder. The cleaning blade contacts the intermediate transfer belt 27 in the counter direction with respect to the circumferential direction of the intermediate transfer belt 27, and dams and removes transfer residual toner on the surface of the intermediate transfer belt 27.

  The fixing device 9 heats and pressurizes an unfixed toner image on the recording medium S to fix the toner image on the recording medium S. The fixing device 9 includes a heating mechanism 91 having a fixing belt, and a pressure roller 92 that presses the fixing belt and rotates the fixing belt.

  The paper feed tray 13 is provided in the lower part of the image forming apparatus 1. A plurality of recording media S such as paper are accommodated in the paper feed tray 13. The recording medium S is pulled out from the sheet feeding tray 13 one by one by the sheet feeding roller 37 and is conveyed along the recording medium conveying path R formed in the image forming apparatus 1.

  The bottle housing part 43 is provided on the upper part of the image forming apparatus 1. The bottle storage portion 43 stores toner bottles 45Y, 45M, 45C, and 45K. The toner bottle 45Y is filled with Y-color toner corresponding to the color separation component of the color image. The toner bottle 45M is filled with M toner corresponding to the color separation component of the color image. The toner bottle 45C is filled with C-color toner corresponding to the color separation component of the color image. The toner bottle 45K is filled with K-color toner corresponding to the color separation component of the color image.

  The toner of each color in each of the toner bottles 45Y, 45M, 45C, and 45K is supplied to a toner supply port 191a in the case 191 of the developing device 19 of each of the process cartridges 10Y, 10M, 10C, and 10K by a toner supply / delivery device (not shown). It is connected to the. As described above, when the output value of the toner density sensor 195 rises above the toner density control reference value, the toner in the toner bottles 45Y, 45M, 45C, and 45K is supplied to the toner supply port 191a.

  Next, the basic operation of the image forming apparatus 1 configured as described above will be described.

  When the image forming operation is started in the image forming apparatus 1, the photosensitive drums 15 of the process cartridges 10Y, 10M, 10C, and 10K are driven to rotate counterclockwise in the drawing. Then, the surface of each photosensitive drum 15 is uniformly charged to a predetermined polarity by each charging device 17.

  Next, the surface of each charged photosensitive drum 15 is irradiated with laser light L from the exposure device 3 to form an electrostatic latent image on the surface of each photosensitive drum 15. At this time, the image information used for exposure to each photosensitive drum 15 is single-color image information obtained by separating a desired full-color image into color information of Y, M, C, and K colors.

  Next, toner is supplied to each electrostatic latent image on the surface of each photosensitive drum 15 by each developing device 19, and a toner image is formed from the electrostatic latent image. A primary transfer bias is applied to each primary transfer roller 29Y, 29M, 29C, 29K. As a result, the toner images at various places formed on the respective photoconductive drums 15 are sequentially superimposed and transferred onto the intermediate transfer belt 27 that rotates counterclockwise in the drawing. Further, the transfer residual toner remaining on the surface of each photosensitive drum 15 after the transfer of the toner image is removed by the cleaning device 21.

  Further, the paper feed roller 37 is rotated by a driving device (not shown), and one sheet of recording medium S is sent out from the paper feed tray 13 to the recording medium conveyance path R. The recording medium S sent to the recording medium conveyance path R is timed by a pair of registration rollers 39 and is sent between the secondary transfer roller 31 and the secondary transfer backup roller 12 facing the secondary transfer roller 31. At this time, a secondary transfer bias is applied to the secondary transfer roller 31, whereby the toner images on the intermediate transfer belt 27 are collectively transferred onto the recording medium S. Further, the transfer residual toner remaining on the surface of the intermediate transfer belt 27 after the transfer of the toner image is removed by the belt cleaning device 33.

  The recording medium S to which the toner image has been transferred is conveyed to the fixing device 9, and heat and pressure are applied to the recording medium S at the nip portion between the fixing belt of the heating mechanism 91 and the pressure roller 92. Thus, the toner image is fixed on the recording medium S. The recording medium S that has passed through the nip portion is then discharged to the stock tray 11 by the discharge roller 41.

  As shown in FIG. 1, the image forming apparatus 1 includes a control unit 100 that controls the operation of each component described above. FIG. 4 is a schematic hardware block diagram of the control unit shown in FIG. As shown in FIG. 4, the control unit 100 includes a CPU (Central Processing Unit) 101 and an I / O unit 102. The control unit 100 also includes a RAM (Random Access Memory) 103, a ROM (Read Only Memory) 104, and a predetermined nonvolatile memory 105 as storage elements. The CPU 101, the I / O unit 102, the RAM 103, the ROM 104, and the nonvolatile memory 105 are connected by a bus 106. The CPU 101 executes various processes according to a processing program stored in the ROM 104. In the RAM 103, development of a program being processed, temporary storage of various data, and the like are performed. The ROM 104 stores various processing programs and parameters used in the processing programs. The nonvolatile memory 105 stores various information that is stored even after the power is turned off, such as a toner image forming condition described later. The I / O unit 102 exchanges data with the control unit 100 and a drive motor, various devices, or various sensors in the image forming apparatus 1.

  Under the control of the control unit 100, the image forming apparatus 1 forms and fixes a toner image on a sheet. In the image forming apparatus 1, process control described below is executed by the control unit 100 in order to suppress fluctuations in image density due to changes in usage environment (temperature / humidity), changes in component parts over time, and the like. . In the process control, a predetermined toner pattern is formed on the peripheral surface of the intermediate transfer belt 27, and the amount of toner attached to the toner pattern is detected. Based on the detection result, a toner image forming condition necessary for obtaining a predetermined target adhesion amount is calculated.

  Hereinafter, the process control executed in the first embodiment of the present invention will be described.

  As shown in FIG. 1, the image forming apparatus 1 is provided with an optical sensor 107 for detecting the toner adhesion amount on the toner pattern on the intermediate transfer belt 27. The optical sensor 107 is disposed at a position downstream of the K-color process cartridge 10 </ b> K and upstream of the secondary transfer roller 31 in the circulating movement direction of the intermediate transfer belt 27. As shown in FIG. 2, the developing device 19 of each color process cartridge 10 is provided with a potential sensor 196 that detects the surface potential of the photosensitive drum 15. In the process control, the detection result of the optical sensor 107 and the detection result of the potential sensor 196 are used.

  There are two types of process control, one executed during non-image formation when image formation is not performed in the image forming apparatus and the other executed during image formation. First, process control during non-image formation will be described. In the following description, the colors will be described without distinction unless otherwise specified.

  In the present embodiment, process control during non-image formation is executed at two points of time when the power is turned on and when the number of sheets on which image formation has been performed in the image forming apparatus 1 exceeds a predetermined number. Is done. Process control at the time of non-image formation is executed by the following functional blocks in the control unit 100. Hereinafter, a functional block that executes process control during non-image formation is referred to as a non-image formation process control execution unit. FIG. 5 is a functional block diagram showing the process control execution unit during non-image formation. The non-image forming process control execution unit 110 shown in FIG. 5 includes a non-image forming pattern forming unit 111, a development potential calculating unit 112, an adhesion amount calculating unit 113, and a non-image forming adjusting unit 114. And a condition memory 115. The non-image forming process control execution unit 110 corresponds to an example of the non-image forming process control execution unit according to the present invention.

  The non-image forming pattern forming unit 111 causes each color process cartridge 10 and the exposure device 3 to form a non-image forming toner pattern, which will be described later. In the non-image forming pattern forming unit 111, the CPU 101 and the I / O unit 102 shown in FIG. The non-image forming pattern forming unit 111 corresponds to an example of the non-image forming pattern forming unit according to the present invention.

  The development potential calculation unit 112 calculates the development potential based on the detection result of the potential sensor 196 for the electrostatic latent image (pattern latent image) Gr1 of the toner pattern formed on the photosensitive drum 15 in the process cartridge 10 of each color. . The developing potential is a potential difference between the developing roller 192 to which a developing bias is applied and the potential of the electrostatic latent image. The CPU 101 and the I / O unit 102 shown in FIG.

  The adhesion amount calculation unit 113 calculates the adhesion amount of toner in the toner pattern T1 based on the detection result of the optical sensor 107 with respect to the toner pattern T1 on the intermediate transfer belt 27. The CPU 101 and the I / O unit 102 shown in FIG. A combination of the optical sensor 107 and the adhesion amount calculation unit 113 corresponds to an example of the adhesion amount detection unit during non-image formation according to the present invention.

  The non-image forming adjustment unit 114 calculates the formation conditions when the toner cartridge is formed by the process cartridge 10 and the exposure device 3 for each color, the calculation result by the development potential calculation unit 112, and the calculation by the adhesion amount calculation unit 113. Adjust based on results. In the non-image forming adjustment unit 114, the CPU 101 and the I / O unit 102 shown in FIG. The non-image forming adjustment unit 114 corresponds to an example of the non-image forming adjustment unit according to the present invention.

  The condition memory 115 stores the formation conditions adjusted by the non-image forming adjustment unit 114. The process cartridge 10 for each color and the exposure device 3 form a toner image based on the formation conditions stored in the condition memory 115. The condition memory 115 plays the role of the nonvolatile memory 105 shown in FIG.

  The process control at the time of non-image formation is executed in the following processing flow by the above functional blocks. FIG. 6 is a flowchart showing process control during non-image formation executed by the functional blocks shown in FIG. The process control at the time of non-image formation shown in the flowchart of FIG. 6 is performed at two points of time when the power is turned on and when the number of sheets on which image formation has been performed by the image forming apparatus 1 exceeds a predetermined number. When any one of the points arrives. First, power is turned on by the non-image forming pattern forming unit 111 to prepare for process control in various devices and various drive motors used for toner pattern formation in process control (step S101). Next, the non-image forming pattern forming unit 111 performs the following adjustment on the optical sensor 107 (step S102). Here, in the present embodiment, the optical sensors 107 are arranged at three locations, that is, the central portion and both end portions in the width direction (that is, the main scanning direction) of the intermediate transfer belt 27. In step S102, adjustment is performed for each of the three optical sensors 107.

  The optical sensor 107 is a sensor that emits LED light toward the intermediate transfer belt 27 and detects reflected light by a light receiving element. The optical sensor 107 includes two light receiving elements, ie, a regular reflection light receiving element that receives regular reflection light and a diffuse reflection light reception element that receives diffuse reflection light. In step S102, the LED current is adjusted so that the output voltage of the regular reflection light receiving element is 4V when the background light of the intermediate transfer belt 27 is irradiated with LED light. The adjusted LED current value is stored in the condition memory 115.

  In step S102, first, the LED light is irradiated for a predetermined time with the value of the LED current adjusted last time and stored in the condition memory 115. And the average value of the output voltage of the regular reflection light receiving element in the meantime is calculated. It is determined whether or not the calculated average value is within a predetermined range centered on 4V. When it falls within the predetermined range, the LED current is not adjusted. On the other hand, when it is not within the predetermined range, the LED current is adjusted so that the output voltage of the regular reflection light receiving element is 4 V, and the adjustment result is stored in the condition memory 115. The above processing is performed for each of the three optical sensors 107.

  Following step S102, the toner concentration sensor 195 provided in the developing device 19 of each color process cartridge 10 detects the current toner concentration in the case 191 of the developing device 19 (step S103). Subsequently, the non-image forming pattern forming unit 111 forms the following toner pattern (step S104).

  FIG. 7 is a schematic diagram showing a toner pattern at the time of non-image formation, which is formed in step S104 of the flowchart shown in FIG. The toner pattern T1 at the time of non-image formation shown in FIG. 7 is composed of five patches P1 for each color toner of YMCK. Each patch P1 corresponds to one of five gradation levels up to the full tone. The toner pattern T1 at the time of non-image formation is a total of 20 patches P1 arranged in a line in the moving direction (that is, the sub-scanning direction) of the intermediate transfer belt 27 indicated by the arrow D1 for each of the five colors. It is. Here, as described above, the optical sensors 107 are arranged at three locations, that is, the central portion and both end portions in the width direction (that is, the main scanning direction) of the intermediate transfer belt 27 indicated by the arrow D2. In the present embodiment, the toner patterns T1 at the time of non-image formation are arranged in a line on the peripheral surface of the intermediate transfer belt 27 at positions where the LED light is irradiated by the central optical sensor 107. Further, the order of colors in the toner pattern T1 is the same as the order of arrangement of the four-color process cartridges 10 shown in FIG. 1, and YMCK from the upstream side to the downstream side in the moving direction of the intermediate transfer belt 27 indicated by the arrow D1. The order is as follows. This is because the process cartridge 10 of each color forms the patch P1 at the same timing. In the present embodiment, this shortens the process control time during non-image formation.

  In the present embodiment, each patch P1 has a rectangular shape with a width of 10 mm in the main scanning direction (arrow D2) and a width of 14.4 mm in the sub-scanning direction (arrow D1). In the toner pattern T1, such patches P1 are arranged in a line in the sub-scanning direction (arrow D1) with an interval of 5.6 mm. Further, the number of patches P1 of five for each color is such that all the patches P1 for one color fit within the circumference of the photosensitive drum 15 in the process cartridge 10. As a result, the four-color patches P1 are formed at the same timing without overlapping each other. This toner pattern T1 corresponds to an example of a second toner pattern referred to in the present invention.

  In step S104 in the flowchart of FIG. 6, such a toner pattern T1 during non-image formation is performed using the formation conditions stored in the condition memory 115 at that time.

  Here, in the present embodiment, the following potential detection is performed by the potential sensor 196 in the process cartridge 10 of each color when the toner pattern T1 is formed at the time of non-image formation in step S104 (step S105). In step S105, the potential sensor 196 detects the potential (latent image potential) of the electrostatic latent image (pattern latent image) of each patch P1 formed on the peripheral surface of the photosensitive drum 15.

  Further, in step S105, the development potential calculation unit 112 calculates the development potential of each patch P1 forming the toner pattern T1 from the detected latent image potential of the pattern latent image using the following equation.

  Development potential [−V] = Development bias [−V] −Latent image potential [−V] (1)

  In this embodiment, since the development potential, the development bias, and the latent image potential are all negative, the unit is [−V].

  Then, after the toner pattern T1 is formed at the time of non-image formation in step S104, LED light irradiation and regular reflection light and diffuse reflection light are detected by the optical sensor 107 (step S106). Here, in the present embodiment, only the regular reflection light is detected for the K-color patch P1 in which the diffuse reflection hardly occurs, and the regular reflection light and the diffuse reflection light are detected for the other YMC three-color patch P1.

  Next, based on the detection result in step S106, the adhesion amount calculation unit 113 calculates the toner adhesion amount in each patch P1 forming the toner pattern T1 during non-image formation (step S107). In this embodiment, the toner adhesion amount is calculated using linear conversion of the regular reflection light with respect to the output voltage of the light receiving element and linear conversion of the diffuse reflection light with respect to the output voltage of the light receiving element. The toner adhesion amount calculation method using such linear conversion is a known calculation method as described in, for example, Japanese Patent Application Laid-Open No. 2006-139180, and further description thereof is omitted.

  When the toner adhesion amount of each patch P1 forming the toner pattern T1 is calculated in step S106, the non-image forming adjustment unit 114 has a primary relationship between the toner adhesion amount and the development potential calculated in step S105 described above. The equation is obtained as follows (step S108). The primary relational expression is represented by the following expression.

Toner adhesion amount [mg / cm ² ] = development γ × development potential [−V] + development start voltage [−V] (2)

  FIG. 8 is a graph showing the relationship between the toner adhesion amount obtained in step S106 in the flowchart shown in FIG. 6 and the development potential obtained in step S105. In the graph G1 shown in FIG. 8, the development potential is taken on the horizontal axis and the toner adhesion amount is taken on the vertical axis. On the graph G1, the relationship between the toner adhesion amount obtained in step S106 of the flowchart and the development potential obtained in step S105 is plotted with ● marks. In step S108, the linear relational expression (2) shown by the straight line L1 on the graph G1 is obtained by the first square method for the plotted points.

Next, the non-image forming adjustment unit 114 calculates a developing bias necessary for obtaining a predetermined target adhesion amount of toner by the following procedure (step S109). First, as shown in FIG. 8, a development potential (referred to as a target potential) corresponding to a target adhesion amount of toner is calculated in the above equation (2). Here, the target adhesion amount is an adhesion amount necessary to obtain a full tone for each color toner. Although it is determined by the coloring degree of the pigment in the toner and the toner particle size, it is generally about 0.4 to 0.6 mg / cm ² . Next, from the calculated target potential, the development bias necessary to obtain the target adhesion amount is calculated using the following equation.

  Development bias [−V] = target potential [−V] + latent image potential [−V] (3)

  Here, the latent image potential in equation (3) is the latent image potential detected for the full-tone patch P1 in step S105. In step S109, the charging bias is further calculated from the calculated developing bias using the following equation.

  Charging bias [−V] = Development bias [−V] +100 to 200 [−V] (4)

  In step S109, the development bias and the charging bias are calculated in this way for the process cartridges 10 for each color of YMCK. The calculated development bias and charging bias for each color are stored in the condition memory 115.

  Subsequently, the non-image forming adjustment unit 114 sets the light amount of the laser light L irradiated by the exposure device 3 in the following procedure (step S110). First, the target halftone latent image potential for achieving the target halftone density is calculated using the target potential calculated in step S109. The halftone latent image potential is calculated using the following equation.

  Halftone latent image potential = coefficient α × target potential + latent image potential [−V] (5)

  The coefficient α in the equation (5) is a value designed for each process cartridge 10 and is determined from a target halftone density, a line width, and the like. Further, the latent image potential in the equation (5) is the same as the latent image potential in the equation (3). In step S110, after calculating the halftone latent image potential, a light amount adjustment pattern is created. A dither pattern is used as a pattern to be created at this time. The development bias and the charging bias are fixed, and the output of the laser diode (hereinafter referred to as LD power) in the exposure apparatus is changed in a plurality of stages to create a light amount adjustment pattern. Then, during the creation of this pattern, the potential sensor 196 detects the latent image potential of the pattern latent image of each of the plurality of patches forming this pattern. Thereafter, a linear relational expression between the LD power and the latent image potential is obtained by the least square method. Based on the obtained primary relational expression, the LD power corresponding to the target halftone latent image potential is calculated.

  In step S110, the LD power is calculated in this way for the process cartridges 10 for each color of YMCK. The calculated LD power of each color is stored in the condition memory 115.

  Finally, the non-image forming adjustment unit 114 adjusts the toner density control reference value, which is a reference for supplying toner to the developing device 19 of the process cartridge 10, in the following procedure (step S111). The toner density control reference value is stored in the condition memory 115, and the adjustment in step S111 is performed on the stored toner density control reference value.

  The adjustment in step S111 is performed using the toner density detected in step S103 and the development γ in the above equation (2) obtained in step S108. First, the detected toner density is compared with the current toner density control reference value. At this time, if the difference between the two exceeds a predetermined rule, nothing is performed in step S111. On the other hand, when the difference between the two is equal to or less than this regulation, the toner density control reference value is adjusted in the following procedure.

First, Δγ = development γ detection value−development γ target value is calculated. Here, the development γ target value is determined in advance for each apparatus, for example, 1.0 [mg / cm ² / −kV] or the like. For example, the value of “1.0” indicates that a toner having a development potential of 1000 [−V] and 1.0 [mg / cm ² ] adheres to the photoreceptor. In this case, if the development start voltage is 0 [−V] and the target toner adhesion amount is 0.5 [mg / cm ² ], a development potential of 500 [−V] is required. Since the development potential [−V] = development bias−latent image potential, when the latent image potential is 50 [−V], the development bias is 550 [−V].

  If the above Δγ exceeds a predetermined value, the developing bias may exceed the settable range or an abnormal image may occur. Therefore, the toner density control reference value is adjusted so that Δγ falls within the target range. This adjustment is performed by increasing the toner density control reference value by a predetermined value when Δγ is a positive value and decreasing the toner density control reference value by a predetermined value when Δγ is a negative value.

  In step S111, the toner density control reference value is adjusted in this way for the process cartridges 10 for each color of YMCK. The adjusted toner density control reference value for each color is stored in the condition memory 115.

  The process control at the time of non-image formation shown in the flowchart of FIG. The toner image formation executed after the process control is performed under the formation conditions of the development bias, the charging bias, the LD power, and the toner density control reference value adjusted in the process control and stored in the condition memory 115. . In the present embodiment, the process control described below is also performed during image formation performed in this way, and the formation conditions adjusted as described above are further adjusted. Hereinafter, process control at the time of image formation will be described.

  Process control at the time of image formation is executed by the following functional blocks in the control unit 100. Hereinafter, a functional block that executes process control during image formation is referred to as an image formation process control execution unit. FIG. 9 is a functional block diagram showing the process control execution unit during image formation. The image formation process control execution unit 120 shown in FIG. 9 includes a timing determination unit 121, a formation instruction unit 122, an image formation pattern formation unit 123, and an image formation adjustment unit 124. . The image formation process control execution unit 120 also includes an adhesion amount calculation unit 113 and a condition memory 115 shown in FIG. The image formation process control execution unit 120 corresponds to an example of the image formation process control execution unit according to the present invention.

  The timing determination unit 121 determines the execution timing of process control during non-image formation. More specifically, it is determined how many sheets of toner images are formed before the process control is executed. In the time determination unit 121, the CPU 101 and the I / O unit 102 shown in FIG. The time determination unit 121 corresponds to an example of the time determination unit referred to in the present invention.

  Here, the time determination unit 121 further determines the execution time of process control at the time of non-image formation according to the determination conditions obtained by the following functional blocks. FIG. 10 is a diagram showing functional blocks for determining the execution time of process control at the time of image formation by the time determination unit shown in FIG. The timing determination unit 121 determines the execution timing of process control during non-image formation according to the following moving average value calculated by the moving average value calculation unit 125.

  The moving average value calculation unit 125 analyzes the image data Gd representing the toner image to be formed this time, and calculates the moving average value of the image area ratio between the current toner image and a predetermined number of past toner images. In the moving average value calculation unit 125, the CPU 101 and the I / O unit 102 shown in FIG. The moving average value calculation unit 125 corresponds to an example of the moving average value calculation unit referred to in the present invention.

  In the present embodiment, a timing determination correspondence table Tb2 in which moving average values of various image area ratios and execution timings of process control corresponding to the respective moving average values are described in the nonvolatile memory 105 shown in FIG. Is remembered. The time determination unit 121 refers to the time determination correspondence table Tb2 and obtains the process control execution time corresponding to the moving average value of the image area ratio calculated by the moving average value calculation unit 125. The execution timing of the process control based on the moving average value of the image area ratio described above will be described in more detail later.

  When the execution time determined by the time determination unit 121 arrives, the formation instruction unit 122 shown in FIG. 9 gives a formation instruction of a toner pattern T2 at the time of image formation described later to the pattern formation unit 123 at the time of image formation. The formation instruction unit 122 plays the role of the CPU 101 shown in FIG. The formation instruction unit 122 corresponds to an example of the formation instruction unit according to the present invention.

  The image forming pattern forming unit 123 causes the process cartridge 10 and the exposure device 3 of each color to form a toner pattern T2 for image forming which will be described later. In the image forming pattern forming unit 123, the CPU 101 and the I / O unit 102 shown in FIG. The image forming pattern forming unit 123 corresponds to an example of the image forming pattern forming unit according to the present invention.

  When the toner pattern T2 at the time of image formation is formed, the optical sensor 107 performs detection. Then, the adhesion amount calculation unit 113 calculates the toner adhesion amount in the toner pattern T2 based on the detection result. The combination of the optical sensor 107 and the adhesion amount calculation unit 113 corresponds to an example of the image formation adhesion amount detection unit according to the present invention.

  The image forming adjustment unit 124 adjusts the formation conditions such as the developing bias stored in the condition memory 115 according to the toner adhesion amount calculated by the adhesion amount calculation unit 113. Here, in the present embodiment, the non-volatile memory 105 shown in FIG. 4 includes an adjustment amount correspondence table Tb1 in which various toner adhesion amounts and adjustment amounts for the formation conditions corresponding to the toner adhesion amounts are described. It is remembered. The image forming adjustment unit 124 refers to the adjustment amount correspondence table Tb1 and obtains an adjustment amount according to the toner adhesion amount. Then, the image forming adjustment unit 124 adjusts the formation conditions such as the developing bias using the obtained adjustment amount. The adjustment of the formation conditions will be described in detail later. The CPU 101 and the I / O unit 102 shown in FIG. 4 serve as the image forming adjustment unit 124. The image formation adjustment unit 124 corresponds to an example of the image formation adjustment unit according to the present invention.

  Process control at the time of image formation is executed in the following processing flow by the above functional blocks. FIG. 11 is a flowchart showing process control during image formation executed by the functional blocks shown in FIGS. 9 and 10. The process control at the time of image formation represented by the flowchart of FIG. 11 is started when toner image formation based on image data is started in the image forming apparatus 1 of FIG. First, power is supplied to various devices and various drive motors by the image forming pattern forming unit 123 to prepare for image formation, and preparation for detection by the optical sensor 107 is performed (step S201). Here, the shutter of the optical sensor 107 is opened and the LED is turned on.

  Next, the moving average value calculation unit 125 analyzes the current image data Gd, and calculates the moving average value of the image area ratio as follows (step S202). First, the size of the paper on which the current toner image is formed and the image area of the toner image are obtained from the image data Gd, and the current image area ratio is calculated. Then, the moving average value of the image area ratio between the current toner image and a predetermined number of past toner images is calculated by the following equation.

  M (i) = (1 / N) × {M (i−1) × (N−1) + X (i)} (6)

  Here, N is a predetermined cumulative number of image formations including the current time. M (i) is the moving average value of the image area ratio including this time, M (i−1) is the moving average value of the image area ratio up to the previous time, and X (i) is the current image area ratio.

  When the moving average value of the image area ratio is calculated, the time determination unit 121 determines the execution time of the process control with reference to the time determination correspondence table Tb2 (step S203).

  Here, in the present embodiment, the reason for determining the execution timing of the process control based on the moving average value of the image area ratio will be described. As an index representing the ease of toner adhesion from the developing device 19 to the photosensitive drum 15, the development γ in the above equation (2) representing the linear relationship between the development potential and the toner adhesion amount can be given. The higher the development γ, the easier the toner adheres, and the lower the development γ, the less difficult the toner adheres. As a result, the higher the development γ, the higher the density of the toner image tends to be, and the lower the development γ, the lower the density of the toner image. That is, when the development γ changes, the image density of the toner image tends to fluctuate.

  This development γ has the following relationship with the image area ratio of the toner image to be formed. FIG. 12 is a graph showing the relationship between the image area ratio of the formed toner image and development γ. In the graph G2 shown in FIG. 12, the horizontal axis represents the image area ratio, and the vertical axis represents development γ. The relationship between the image area ratio and the development γ is plotted with ◇. As can be seen from this graph G2, the development γ tends to increase as a toner image having a higher image area ratio is formed. When outputting an image with a high image area ratio, the toner replacement amount of the developing device 19 in a certain period is large, so the amount of toner that has been in the developing device 19 for a long time is small. Therefore, since the amount of excessively charged toner is small, it is considered that the development γ is higher than when an image with a low image area ratio is output (a state where the charge amount of the toner is high).

  Such a change in development γ is likely to increase when the image area ratio of the toner image rapidly increases. FIG. 13 is a graph showing how development γ increases when the image area ratio of the toner image increases rapidly. In the graph G3 shown in FIG. 13, the development γ is taken on the vertical axis, and the number of formed toner images is taken on the horizontal axis. Then, after a toner image having an image area ratio of 5% is formed on 100 sheets of paper, a development γ when a toner image having an image area ratio of 80% is continuously formed is plotted by marks. As can be seen from this graph G3, immediately after the image area ratio is switched, the development γ changes rapidly. On the other hand, it can be seen that the development γ is maintained at a certain value when printing a certain number of sheets or more. Immediately after switching to a high image area ratio, the toner replacement amount of the developing device 19 increases rapidly, so the toner charge amount decreases, and the development γ is considered to change suddenly. Thereafter, if the toner replacement amount is not changed in a large state, it is considered that the toner charge amount is kept constant and the development γ becomes constant.

  From the above, it can be seen that when the image area ratio changes, the development γ changes and the image density easily changes. Therefore, it is conceivable to execute process control at an execution time corresponding to the image area ratio to suppress fluctuations in image density. In the present embodiment, the execution timing of process control is determined according to the moving average value of the image area ratio in order to reflect the past image area ratio.

  As described above, the execution time is determined by referring to the time determination correspondence table Tb2. In the time determination correspondence table Tb2, various numerical ranges regarding the moving average value of the image area ratio and the number of sheets as the execution time corresponding to each numerical range are described. In step S203 in the flowchart of FIG. 11, by referring to this time determination correspondence table Tb2, the higher the moving average value of the image area ratio, the earlier the process control execution time, and the fluctuation of the image density is suppressed. Further, the lower the moving average value of the image area ratio is, the later the process control execution time is delayed, and the toner consumption associated with the process control is suppressed.

  As can be seen from the graph G3 in FIG. 13, the development γ varies immediately after the image area ratio varies, and is maintained at a constant value when image formation at a constant image area ratio continues. Therefore, unlike the present embodiment, the execution timing of process control may be determined according to the amount of change in the moving average value of the image area ratio. In other words, the time determination correspondence table Tb2 may be one in which various numerical ranges regarding the amount of change in the moving average value of the image area ratio and the execution time (number of sheets) corresponding to each numerical range are described. In this case, the process control execution time is advanced as the change amount of the moving average value of the image area ratio increases, and the process control execution time is delayed as the change amount decreases. As a result, it is possible to further reduce toner consumption.

  When the execution time (number of sheets) is determined in accordance with the moving average value of the image area ratio in step S203, the formation instructing unit 122 next determines the count value for the current number of sheets and the execution time described above. Are compared (step S204). If the count value does not reach the execution time (No determination in step S204), the process proceeds to step S208. In step S208, the formation instructing unit 122 determines whether a series of image formation started this time has been completed. If the image formation is not completed (No determination in step S208), the formation instruction unit 122 counts up the number of sheets (step S209). Thereafter, the process returns to step S202, and the subsequent processes are repeated.

  On the other hand, when the count value has reached the execution time (Yes determination in step S204), the formation instructing unit 122 gives a toner pattern formation instruction to the image forming pattern forming unit 123 (step S205). In response to the forming instruction, the image forming pattern forming unit 123 forms the following toner pattern.

  FIG. 14 is a schematic diagram showing a toner pattern at the time of image formation formed in step S205 with the flowchart shown in FIG. The toner pattern T2 at the time of image formation shown in FIG. 7 is formed on the peripheral surface of the intermediate transfer belt 27 in the non-image forming area Ar2 arranged as follows in the toner image forming area Ar1. The non-image forming area Ar2 intersects the direction of circulation movement of the intermediate transfer belt 27 indicated by the arrow D1 (that is, the sub-scanning direction), and the image forming area Ar1 extends in the width direction indicated by the arrow D2 (that is, the main scanning direction). Two are provided side by side. The toner pattern T2 at the time of image formation is formed in two rows in total, one row in each non-image forming area Ar2. The toner pattern T2 when these two rows of images are formed is the same toner pattern. And among the optical sensors 107 arrange | positioned at three places as mentioned above, it forms in the position where LED light is irradiated by the optical sensor 107 of both ends.

  The toner pattern T2 at the time of image formation in each row is a total of eight patches P2 arranged in the order of YMCK from the upstream side to the downstream side in the sub-scanning direction (arrow D1). For the three colors of YMC, two full-tone patches P2 are provided for each color. On the other hand, for the K color, two halftone patches P2 are provided. The reason why the K-color patch P2 is a halftone is that the change in the output of the optical sensor 107 becomes smaller as the density of the K color is higher, and the sensitivity to changes in the image density decreases.

  In the present embodiment, the two patches P2 of each color are arranged at an interval of 18.16 mm, and the colors P2 are arranged at an interval of 4 mm between the colors. Each patch P2 has a rectangular shape of 5 mm × 5 mm. Further, the toner pattern T2 at the time of image formation has a position where the most upstream patch P2 is 50.0 mm away from directly below the optical sensor 107 at the timing when the most downstream patch P2 in the sub-scanning direction (arrow D1) is transferred. It is provided to become.

  At the time of image formation, each color patch P2 is formed in the image forming apparatus 1 shown in FIG. 1 together with the toner images of the respective colors that are formed and overlaid in the order of YMCK. As a result, the arrangement of the patches P2 in the toner pattern T2 at the time of image formation is different from the arrangement of the patches P1 in the toner pattern T1 at the time of non-image formation shown in FIG. 7, and the upstream in the sub-scanning direction (arrow D1). From the side to the downstream side, the order is YMCK. This toner pattern T2 corresponds to an example of the toner pattern referred to in the present invention.

  When such toner patterns T2 are formed in two rows in step S205 in the flowchart of FIG. 11, the patch P2 that forms the toner pattern T2 in each row is detected by the two optical sensors 107 arranged at both ends (step S205). S206). At this time, only regular reflection light is detected for the K-color patch P2, and both regular reflection light and diffuse reflection light are detected for the three-color patch P2 of YMC.

  Here, detection by each optical sensor 107 is performed at the following timing. First, from the layout of the toner pattern T2 described above and the process linear speed such as the moving speed of the intermediate transfer belt 27, the timing at which the most upstream patch P2 arrives immediately below the optical sensor 107 is known. Therefore, in the present embodiment, the LED is turned on slightly earlier than such timing. When each patch P2 passes directly below the optical sensor 107, the intensity of both regular reflection light and diffuse reflection light decreases. In the present embodiment, the passage of each patch P2 is recognized when these intensities fall below a predetermined threshold. Then, from the detection results of the regular reflection light and the diffuse reflection light at that time, the toner adhesion amount in each patch P2 is calculated by the same method as step S107 in the flowchart of FIG. Thereafter, for each color, the average value of the toner adhesion amounts in the patches P2 having the same four gradations in total is obtained.

  Next, based on the average value of the toner adhesion amount of each color obtained as described above (hereinafter simply referred to as toner adhesion amount), the image forming time adjustment unit 124 obtains the condition memory 115 obtained by the previous process control. In step S207, the toner image forming conditions stored in the image data are adjusted. In the present embodiment, the development bias among the formation conditions is adjusted as follows.

  FIG. 15 is a schematic diagram illustrating the adjustment of the developing bias performed in step S207 with the flowchart of FIG. FIG. 15A shows a graph G4 representing a change in the toner adhesion amount, and FIG. 15B shows a graph G5 representing a development bias change according to the toner adhesion amount. As shown in FIG. 15A, in the present embodiment, the toner adhesion amount obtained in step S206 has the first upper limit, the second upper limit, the first lower limit, and the third lower limit. The four thresholds are compared. Here, in this embodiment, the table described in the following table is referred to as the adjustment amount correspondence table Tb1 shown in FIG.

  As shown in Table 1, the increase / decrease amount of the developing bias is determined according to the comparison result between the toner adhesion amount and the four threshold values. As a result, for example, when the toner adhesion amount changes as shown in the graph G4 in FIG. 15A, the developing bias is increased or decreased as shown in the graph G5 in FIG. That is, as the toner adhesion amount increases, the development bias decreases, and as the toner adhesion amount decreases, the development bias increases. As the developing bias is higher, the toner charge amount in the developing device 19 is increased, and adhesion to the photosensitive drum 15 is suppressed. On the other hand, as the developing bias is lower, the toner charge amount in the developing device 19 is reduced and the adhesion to the photosensitive drum 15 is increased. This suppresses fluctuations in image density when the toner image is formed next time.

  Here, the object to be adjusted according to the toner adhesion amount is not limited to the developing bias as in the present embodiment, but may be, for example, the above-described toner density control reference value, or the LD light amount in the exposure device 3. There may be. Hereinafter, two different examples of the case where the toner density control reference value is adopted as the adjustment target and the case where the LD light amount is adopted will be described.

  First, another example in which the toner density control reference value is adopted as an adjustment target will be described. As described above, the toner density control reference value is a value used for supplying toner to the developing device 19. That is, when the output value of the toner density sensor 195 increases beyond the toner density control reference value, the developing device 19 is replenished with toner. In another example, the image forming time adjustment unit 124 adjusts the toner density control reference value among the toner image formation conditions obtained in the previous process control and stored in the condition memory 115 as follows.

  FIG. 16 is a schematic diagram illustrating adjustment of the toner density control reference value by the image forming adjustment unit. FIG. 16 (a) shows a graph G6 similar to FIG. 15 (a) showing the change in the toner adhesion amount, and FIG. 16 (b) shows a toner density control standard according to the toner adhesion amount. A graph G7 representing a change in value is shown. In another example, the table described in the following table is referred to as the adjustment amount correspondence table Tb1 shown in FIG.

  As shown in Table 2, the increase / decrease amount of the toner density control reference value is determined according to the comparison result between the toner adhesion amount and the four threshold values. As a result, for example, when the toner adhesion amount changes as shown in a graph G6 in FIG. 16A, the toner density control reference value is increased or decreased as shown in a graph G7 in FIG. That is, the toner concentration control reference value increases as the toner adhesion amount increases, and the toner concentration control reference value decreases as the toner adhesion amount decreases. In the graph G7 in FIG. 16B, changes in the output of the toner density sensor 195 when the toner density control reference value is changed in this way are plotted with ● marks. As described above, the output of the toner concentration sensor 195 increases as the toner concentration in the case 191 in the developing device 19 decreases. Conversely, the output of the toner concentration sensor 195 decreases as the toner concentration in the case 191 increases.

  When the toner adhesion amount is large and the toner density control reference value is increased, the threshold for toner replenishment is raised, so that the toner is not replenished so much that the toner density decreases and the output of the toner density sensor 195 increases. . As the toner density decreases, the charge amount of the toner increases. As a result, toner adhesion to the photosensitive drum 15 is suppressed. On the other hand, when the toner adhesion amount is small and the toner density control reference value is reduced, the threshold for toner replenishment is lowered, so that the toner is replenished immediately and the toner density rises and the output of the toner density sensor 195 is output. Decreases. As the toner density increases, the toner charge amount decreases. As a result, the adhesion of toner to the photosensitive drum 15 is increased. In another example, by increasing or decreasing the toner density in the case 191 in the developing device 19 by increasing or decreasing the toner density control reference value, fluctuations in image density when the toner image is formed next time can be suppressed.

  Next, another example in which the LD light quantity is adopted as an adjustment target will be described. When the toner adhesion amount is large, adjustment is performed so as to suppress the toner adhesion by reducing the LD light quantity. On the other hand, when the toner adhesion amount is small, adjustment is performed to increase the LD light amount to increase the toner adhesion. By such adjustment, fluctuations in image density when the toner image is formed next time can be suppressed.

  As described above, in the first embodiment and the two other examples, as an example of adjustment by the image forming adjustment unit, an example in which the developing bias is an adjustment target, an example in which the toner density control reference value is an adjustment target, and an LD light amount Three examples are shown as examples of adjustment. Note that the adjustment by the image forming adjustment unit is not limited to any one of the above three adjustment targets, and may be performed by combining two or more adjustment targets. For example, when the toner adhesion amount is very small, adjustment may be performed such that the developing bias is increased and the toner density control reference value is adjusted to be small to increase the toner density. According to such adjustment, it is possible to quickly increase the adhesion of the toner and suppress the fluctuation of the image density more quickly.

  Here, in this embodiment, when the count value of the number of sheets on which the toner image is formed reaches the execution time of the process control determined as the number of sheets, the above-described formation conditions are adjusted. In this case, there is a possibility that the adjustment is not performed halfway when a long sheet or the like is used. For this reason, the count value described above may be not the number of sheets on which the toner image is actually formed, but the number of sheets converted to A4, for example. However, in this case, the formation conditions may be adjusted and changed during the formation of the toner image on the long paper. Therefore, when a toner image is formed on a long sheet, the adjustment amount may be adjusted by suppressing the adjustment amount by, for example, multiplying the adjustment amount obtained as described above by a predetermined coefficient.

  Further, in the present embodiment, the formation conditions adjusted as described above are used for the next toner image formation. However, when the adjustment is performed, the current toner image is being formed. Alternatively, the formation conditions after the adjustment may be used immediately.

  When the adjustment described above is performed in step S207 in the flowchart of FIG. 11, the process proceeds to step S208. In step S208, as described above, the formation instruction unit 122 determines whether the series of image formation that has started this time has ended. If image formation has not ended (No determination in step S208), the number of sheets is counted up in step S209, and the process returns to step S202. On the other hand, when the image formation is completed (Yes determination in step S208), the LED of the optical sensor 107 is turned off (step S210). With the processing in step S210, the process control at the time of image formation represented by the flowchart of FIG. 11 ends.

  In the process control at the time of image formation described above, the shutter of the optical sensor 107 is opened and the LED is turned on at the start of toner image formation. The detection by the optical sensor 107 is always performed during execution of process control during image formation. However, the control with respect to the optical sensor 107 is not limited to this. For example, the shutter may be opened and the LED may be turned on only when the toner pattern T2 passes. As a result, power consumption in the optical sensor 107 is suppressed. In addition, since the opening of the shutter is limited, contamination of the optical sensor 107 due to scattered toner or the like can be suppressed.

  According to the image forming apparatus 1 of the first embodiment described above, the timing for forming the toner pattern T2 in alignment with the toner image in the main scanning direction is determined according to the determination condition of the moving average value of the image area ratio. For this reason, it is possible to advance the formation timing of the toner pattern T2 when a change in the image density of the toner image is expected. Conversely, when it is expected that such a change will not occur for the time being, it is possible to delay the formation time of the toner pattern T2 and suppress the toner consumption. As described above, according to the image forming apparatus 1 of the first embodiment, the toner pattern T <b> 2 is formed at regular intervals, and compared with the technique described in Patent Document 2 described above, the amount of toner consumption is suppressed and high accuracy is achieved. Can be used to control the process.

  In the image forming apparatus 1 of the first embodiment, prior to process control during image formation, process control during non-image formation is performed to adjust the toner image formation conditions. The non-image formation has a time margin as compared with the image formation, so that the degree of freedom of the toner pattern T1 formed in the process control is high. For this reason, in the present embodiment, in the process control at the time of non-image formation, the toner pattern T1 including a larger number of patches is formed and the formation conditions are adjusted more precisely than the process control at the time of non-image formation. In the process control at the time of image formation, the finely adjusted formation conditions are further adjusted. In the image forming apparatus 1 of the first embodiment, image density can be controlled with higher accuracy by such two-stage process control.

  Further, in the image forming apparatus 1 according to the first embodiment, the time at which the toner pattern T2 is formed by being aligned with the toner image in the main scanning direction, that is, the process control execution time at the time of image formation is determined as the moving average value of the image area ratio. It is decided according to conditions. As a result, when a toner image having a high image area ratio is formed and the toner charge amount of the developing device 19 is easily changed, it is possible to execute process control at the time of image formation with a fine frequency. ing. In addition, the determination condition has been described with another example of the change amount of the moving average value of the image area ratio. In this case, the process control execution time is advanced as the change amount of the moving average value of the image area ratio increases, and the process control execution time is delayed as the change amount decreases. As a result, it is possible to further reduce toner consumption.

  Next, a second embodiment of the present invention will be described. The second embodiment is different from the above-described first embodiment in the processing content in the toner pattern timing determination unit. Hereinafter, the second embodiment will be described with respect to differences from the first embodiment, and the description of the same points such as the configuration of the image forming apparatus and the process control process will be omitted.

  FIG. 17 is a diagram showing functional blocks for determining the execution timing of process control during image formation in the second embodiment. In FIG. 17, the functional blocks equivalent to the functional blocks of the first embodiment shown in FIG. 10 are denoted by the same reference numerals as those in FIG. Description is omitted. The time determination unit 210 of this embodiment determines the execution time of process control during image formation based on the following equation.

  Execution time = reference value of execution time (number of sheets) x correction coefficient (7)

  The time determination unit 210 uses the execution time reference value corresponding to the moving average value of the image area ratio calculated by the moving average value calculation unit 125 in the same way as the execution time determination method in the first embodiment described above. It is obtained by referring to the time determination correspondence table Tb2. Then, the time determination unit 210 determines the execution time of process control during image formation by multiplying the reference value by the following correction coefficient.

  In this embodiment, the correction coefficient correspondence table Tb3 in which the toner adhesion amounts in Tables 1 and 2 described above are described with various toner adhesion amounts and adjustment amounts for the correction coefficients corresponding to the respective toner adhesion amounts is shown in FIG. Is stored in the nonvolatile memory 105 shown in FIG. The time determination unit 210 refers to the table described in the following table as the correction coefficient correspondence table Tb3.

  In the correction coefficient correspondence table Tb3 shown in Table 3, the five correction coefficients are associated one-to-one with the five ranges divided by the four threshold values described in Table 1 and Table 2 described above. Is. With this correction coefficient correspondence table Tb3, when the formation conditions such as the developing bias are adjusted according to the excessive toner adhesion amount, the smaller the adjustment amount, the smaller the correction coefficient is obtained.

  In the present embodiment, the execution timing of the process control at the time of the first image formation is determined only by the moving average value of the image area ratio, as in the first embodiment. From the second time on, the correction coefficient correspondence table Tb3 is referred to by the toner adhesion amount calculated based on the detection by the optical sensor 107 with respect to the toner pattern T2 in the previous process control. Then, a correction coefficient corresponding to the toner adhesion amount is obtained and is multiplied by the reference value. As a result, the larger the adjustment amount in the previous process control, the earlier the execution timing of the next process control. As a result, whether the adjustment in the previous process control is appropriate is confirmed at an early stage, and if the adjustment is insufficient, the adjustment is performed again. On the other hand, the smaller the adjustment amount in the previous process control, the later the execution timing of the next process control is delayed. As a result, execution of process control at the time of image formation is suppressed to a necessary minimum, and toner consumption is suppressed.

  The correction coefficient for the toner adhesion amount is not limited to the value described in Table 3 above, and may be another example value described in the following table.

  The correction coefficient described in Table 4 is larger than the correction coefficient described in Table 3 above. In another example of Table 4, the amount of toner consumption is suppressed by delaying the execution timing of the process control at the time of image formation as much as possible by increasing the correction coefficient.

  According to the second embodiment described above, the toner adhesion amount in the process control at the time of image formation performed once is reflected in the next process control execution time. That is, in the second embodiment, the determination condition used for determining the execution timing of the process control at the time of image formation is a condition including the toner adhesion amount. As a result, when the adjustment amount in the previous process control is large due to an excessive or small amount of toner adhesion, the next execution timing can be advanced and the control accuracy of the image density by the process control during image formation can be improved. . On the other hand, when the toner adhesion amount is appropriate and the adjustment amount in the process control at the previous image formation is small, the next execution timing can be delayed to suppress the toner consumption amount.

  Next, a third embodiment of the present invention will be described. Similar to the second embodiment described above, the third embodiment differs from the first embodiment in the processing content of the toner pattern timing determination unit. Hereinafter, also in the third embodiment, as in the second embodiment, differences from the first embodiment will be described, and descriptions of the same points will be omitted.

  FIG. 18 is a diagram showing functional blocks for determining the execution timing of process control during image formation in the third embodiment. In FIG. 18, the functional blocks equivalent to the functional blocks of the first embodiment shown in FIG. 10 are denoted by the same reference numerals as those in FIG. Description is omitted.

  Also in the present embodiment, the execution timing of the process control at the time of image formation is obtained based on the above equation (7) as in the second embodiment. Here, in the present embodiment, a temperature / humidity detection unit 301 that detects temperature / humidity around the developing device 19 is provided. Then, in the time determination unit 302, the correction coefficient in the equation (7) is obtained according to the detection result in the temperature / humidity detection unit 301. This is because the development γ of the developing device 19 may vary depending on the temperature and humidity inside the image forming apparatus 1. The temperature / humidity detection unit 301 corresponds to an example of the temperature / humidity detection unit according to the present invention.

  FIG. 19 is a graph showing how the development γ of the developing device varies depending on the temperature and humidity inside the image forming apparatus. In the graph G8 shown in FIG. 19, the horizontal axis represents the moving average value of the image area ratio, and the vertical axis represents the development γ. The development γ with respect to the change of the moving average value of the image area ratio is plotted. In the graph G8, this plot is performed for three types of temperature and humidity environments. Normal temperature and humidity environment (hereinafter referred to as MM environment) is plotted with ◇, high temperature and high humidity environment (hereinafter referred to as HH environment) is plotted with □, and low temperature and low humidity environment (hereinafter referred to as LL environment) Plotted with Δ marks. Here, the MM environment in the graph G8 is an environment where the temperature is 23 ° C. and the humidity is 50%, the HH environment is an environment where the temperature is 27 ° C. and the humidity is 80%, and the LL environment is a temperature of 10 ° C. and the humidity is 70%. The environment is 15%.

  As can be seen from the graph G8 in FIG. 19, compared to the MM environment, the development γ is likely to increase with respect to the variation of the moving average value of the image area ratio in the HH environment, and the variation in the development γ is small in the LL environment. This is because toner aggregation easily occurs in the developing device 19 in the HH environment, making it difficult to come into contact with the magnetic carrier. As a result, the charge amount of the toner decreases, and in the LL environment, the toner charge amount increases. is there. As described above, when the development γ increases, the toner adhesion amount tends to fluctuate, and as a result, the image density tends to fluctuate. For this reason, in the present embodiment, the execution time of process control at the time of image formation is advanced under an HH environment. On the other hand, in the LL environment where the variation in the development γ is small, the execution time is delayed and the toner consumption is suppressed.

  In the present embodiment, there is provided a correction coefficient correspondence table Tb4 that describes three correction coefficients corresponding to three predetermined temperature / humidity environment classifications (HH environment, MM environment, and LL environment). Then, the time determination unit 302 refers to the correction coefficient correspondence table Tb4 based on the detection result of the temperature / humidity detection unit 301 and obtains a correction coefficient corresponding to the detection result. For example, a correction coefficient of “0.4” corresponds to the HH environment, and the execution time of process control at the time of image formation can be advanced by multiplying the reference value of the execution time by this correction coefficient. ing. On the other hand, the MM environment and the HH environment correspond to values larger than the correction coefficient of the HH environment, and the execution time is delayed.

  According to the third embodiment described above, the determination condition used for determining the execution timing of the process control at the time of image formation is a condition including the temperature and humidity environment around the developing device 19. As a result, in an HH environment where development γ tends to increase, the execution timing of process control at the time of image formation can be advanced and the control accuracy of image density can be increased. On the other hand, in the MM environment or LL environment where the fluctuation of the development γ is small compared to the HH environment, the execution time can be delayed to suppress the toner consumption.

  Next, a fourth embodiment of the present invention will be described. Similarly to the second embodiment and the third embodiment described above, the fourth embodiment is different from the first embodiment in the processing content in the toner pattern timing determination unit. Hereinafter, also in the fourth embodiment, similar to the second embodiment and the third embodiment, differences from the first embodiment will be described, and descriptions of the same points will be omitted.

  FIG. 20 is a diagram showing functional blocks for determining the execution timing of process control during image formation in the fourth embodiment. In FIG. 20, the same functional blocks as those of the first embodiment shown in FIG. 10 are denoted by the same reference numerals as those in FIG. Description is omitted.

  Also in the present embodiment, the execution timing of the process control at the time of image formation is obtained based on the above equation (7) as in the second embodiment. Here, in the present embodiment, a timer 401 is provided. The timer 401 measures the stop time during which the developing device 19 has stopped operating. Then, the timing determination unit 402 obtains the correction coefficient in the equation (7) according to the measurement result by the timer 401. This is because as the stop time of the developing device 19 is longer, the charge amount of the toner decreases, and as a result, the development γ may increase. The timer 401 corresponds to an example of a timer according to the present invention.

  FIG. 21 is a graph schematically showing the relationship between the operation of the developing device and the charge amount of the toner. In the graph G9 of FIG. 21, time is taken on the horizontal axis, and the charge amount of the toner is taken on the vertical axis. As can be seen from this graph G9, the toner charge amount decreases as the stop time of the developing device 19 increases. Then, when the developing device 19 starts driving, the charge amount increases. However, as the amount of decrease in the charge amount increases as the previous stop time is longer, the increase fluctuation becomes larger. That is, as the stop time is longer, the developing device 19 is in a state where the increase in the charge amount after the start of driving is larger and the development γ is more likely to change. Therefore, in the present embodiment, the longer the stop time of the developing device 19, the earlier the execution timing of process control during image formation. On the other hand, when the stop time is short, the execution time is delayed so that the amount of toner consumption can be suppressed.

  In the present embodiment, a correction coefficient correspondence table Tb5 is provided in which a correction coefficient is associated with each of a predetermined number of time ranges. Then, the timing determination unit 402 refers to the correction coefficient correspondence table Tb5 at the stop time of the immediately preceding developing device 19 measured by the timer 401, and obtains a correction coefficient corresponding to the detection result.

  Here, the charge amount of the toner in the developing device 19 maintains a constant value when the driving is continued for a while. Therefore, in the present embodiment, the number of times the correction coefficient based on the reference to the correction coefficient correspondence table Tb5 is used is limited to a predetermined number of times, for example, among the process control at the time of repeated image formation. After that, “1.0” is used as the correction coefficient, and the above reference value is substantially used as it is as the execution time. As a result, the amount of toner consumption associated with execution of process control during image formation after the toner charge amount becomes constant can be suppressed.

  According to the fourth embodiment described above, the determination condition used for determining the execution timing of the process control at the time of image formation is a condition including the stop time of the developing device 19. As a result, when the stop time is long and the toner charge amount decreases and the development γ tends to increase, the execution timing of the process control at the time of image formation can be advanced and the control accuracy of the image density can be improved. On the contrary, when the stop time is short and the fluctuation of the development γ is not so large, the execution time can be delayed to suppress the toner consumption.

  In addition, all the 1st-4th embodiment demonstrated above showed only the typical form of this invention, and this invention is not limited to these embodiment. That is, those skilled in the art can implement various modifications in accordance with conventionally known knowledge without departing from the scope of the present invention. Of course, such modifications are included in the scope of the present invention as long as the configuration of the image forming apparatus of the present invention is provided.

  For example, in the above-described second to fourth embodiments, as an example of the determination condition referred to in the present invention, a condition including a moving average value of the image area ratio is exemplified. However, the determination condition referred to in the present invention is not limited to this, and may be any one of the above-described toner adhesion amount, temperature / humidity environment, and stop time of the developing device 19. For example, when only the toner adhesion amount is used as the determination condition, the reference value in the above equation (7) is set to a predetermined fixed value, and this fixed value is multiplied by a correction coefficient corresponding to the toner adhesion amount. Will be.

  For example, in the second to fourth embodiments described above, as an example of the determination condition referred to in the present invention, any one of the toner adhesion amount, the temperature / humidity environment, and the stop time of the developing device 19 is used for the correction coefficient. The included conditions are illustrated. However, the determination condition referred to in the present invention is not limited to this, and may be a condition including two or more of the above three for the correction coefficient, for example. In this case, for example, the correction coefficient is determined by combining the toner adhesion amount and the temperature and humidity environment, the temperature and humidity environment and the stop time, the stop time and the toner adhesion amount, or all three.

  For example, in the first to fourth embodiments described above, the tandem image forming apparatus 1 is illustrated as an example of the image forming apparatus according to the present invention. However, the image forming apparatus according to the present invention is not limited to this, and may be a rotary color image forming apparatus.

1 Image forming apparatus (an example of an image forming apparatus)
3. Exposure device (part of an example of image forming unit)
5 Process unit (part of an example of image forming unit)
7 Intermediate transfer unit (part of an example of image forming unit)
8 Secondary transfer part (an example of transfer part)
9 Fixing device (an example of fixing unit)
DESCRIPTION OF SYMBOLS 10 Process cartridge 15 Photosensitive drum 19 Developing apparatus 27 Intermediate transfer belt (an example of an image carrier)
100 control unit 107 optical sensor (part of an example of an adhesion amount detection unit during image formation, part of an example of adhesion amount detection during non-image formation)
110 Non-image forming process control execution unit (an example of non-image forming process control execution unit)
111 Non-image forming pattern forming unit (an example of non-image forming pattern forming unit)
112 Development potential calculation unit 113 Adhesion amount calculation unit (part of an example of adhesion amount detection unit at the time of image formation, part of example of adhesion amount detection at the time of non-image formation)
114 Non-image forming adjustment unit (an example of a non-image forming adjustment unit)
115 Conditional memory 120 Process control execution unit during image formation (an example of process control execution unit during image formation)
121, 201, 302, 402 Time determination unit (an example of a time determination unit)
122 Formation instruction section (an example of a formation instruction section)
123 Image formation pattern formation unit (an example of image formation pattern formation unit)
124 Image formation adjustment unit (an example of image formation adjustment unit)
301 Temperature / humidity detector (example of temperature / humidity detector)
401 timer (an example of a timer)

JP 2003-14059 A JP 2013-218284 A

Claims (6)

A toner image is formed on the circumferential surface that is circulated by the process unit, and an image carrier that holds the toner image, and the toner image that is held by the image carrier on the circumferential surface is transferred to a sheet-like recording medium. An image forming apparatus including: a transfer unit that fixes the toner image transferred to the recording medium by the transfer unit;
An image formation process control execution unit that adjusts the toner image formation conditions during image formation for forming the toner image includes a timing determination unit, a formation instruction unit, a pattern formation unit during image formation, and an adhesion amount during image formation. A detection unit and an image forming adjustment unit;
The timing determination unit, wherein the execution time of the process control of image formation, earlier than when the change amount of the image density of the past of the toner image and the image density of bets toner image is large is small, if smaller is larger Make a decision based on the decision conditions
The formation instructing unit gives an instruction to form a predetermined toner pattern to the image forming pattern forming unit when the time determined by the time determining unit arrives,
The image forming pattern forming unit causes the process unit to form a toner pattern in a non-image forming region located in a region aligned with the image forming region in a direction crossing the direction of circulation movement of the peripheral surface of the image carrier. ,
The image formation adhesion amount detection unit detects a toner adhesion amount in the toner pattern,
The image forming apparatus, wherein the image forming adjustment unit adjusts the forming conditions based on a detection result of the image forming adhesion amount detection unit. A non-image forming process control execution unit that adjusts the toner image forming conditions during non-image forming except during the image formation;
The non-image forming process control execution unit,
A non-image-forming pattern forming unit that causes the process unit to form a second toner pattern on the peripheral surface;
A non-image-forming adhesion amount detection unit for detecting a toner adhesion amount in the second toner pattern;
A non-image-forming adjustment unit that adjusts the formation conditions based on the detection result of the non-image-forming adhesion amount detection unit;
The image forming apparatus according to claim 1, wherein the image forming process control execution unit further adjusts the forming conditions adjusted by the non-image forming adjusting unit. The image formation process control execution unit,
A moving average value calculating unit for calculating a moving average value of image area ratios of the toner image to be formed by the process unit and the toner image formed in the past;
2. The determination condition is a condition including a moving average value of an image area ratio calculated by the moving average value calculation unit or a change amount of the moving average value of the image area ratio. Or the image forming apparatus of 2.   4. The image forming apparatus according to claim 1, wherein the determination condition is a condition including a toner adhesion amount detected by the adhesion amount detection unit at the time of image formation. A temperature / humidity detection unit for detecting temperature / humidity around the process unit;
5. The image forming apparatus according to claim 1, wherein the determination condition is a condition including a temperature and humidity environment detected by the temperature and humidity detection unit. A timer for measuring a stop time during which the process unit has stopped operating;
6. The image forming apparatus according to claim 1, wherein the determination condition is a condition including a stop time measured by the timer.

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