JP5452000B2 - Image forming apparatus - Google Patents

Description

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

  Conventionally, in an image forming apparatus using toner such as a copying machine, a printer, and a facsimile machine, a photosensitive drum and a developing roller facing the photosensitive drum may be provided. A so-called developing bias in which direct current and alternating current are superimposed is applied to the developing roller. As a result, the charged toner flies from the developing roller to the photosensitive drum, and the electrostatic latent image is developed.

  Here, in order to sufficiently supply the toner to the photosensitive drum, to ensure the density of the formed image and to improve the development efficiency, the peak-to-peak voltage of the AC voltage applied to the developing roller should be increased. However, if it is too large, discharge occurs in the gap between the photosensitive drum and the developing roller. When the discharge occurs, the electrostatic latent image is disturbed due to the potential change on the surface of the photosensitive drum, and the quality of the formed image is deteriorated. Further, depending on the characteristics of the photosensitive drum, a large current may flow depending on the direction in which the discharge current flows, causing damage to the photosensitive drum. Accordingly, an AC voltage that causes discharge should not be applied to the developing roller during image formation.

Therefore, for example, Patent Document 1 provides a toner carrier that is opposed to the image carrier with a required distance in the development region, and a DC voltage and an AC voltage are superimposed between the toner carrier and the image carrier. In a developing device that applies an applied developing bias voltage and supplies toner to an image carrier to develop an electrostatic latent image, a leak that changes a leak detection voltage applied between the image carrier and the toner carrier A generation unit and a leak detection unit for detecting a leak are provided, and the maximum potential difference ΔVmax between the leak detection voltage and the surface potential of the image carrier is gradually increased to flow between the image carrier and the toner carrier. A developing device is described in which when a current continuously increases, a leak detection unit determines that a leak has occurred (see, for example, Patent Document 1: Claim 1).
Japanese Patent No. 3815356

  As described above, in order to increase the development efficiency by causing toner to fly sufficiently without causing adverse effects due to discharge, no discharge occurs between the photosensitive drum and the developing roller, and an AC voltage as large as possible is developed. It will be applied to the roller. Here, the length of the gap between the developing roller and the photosensitive drum is largely related to whether or not discharge is generated. However, this gap length differs in each image forming apparatus due to an error in mounting and supporting the photosensitive drum and the developing roller. In addition, the potential difference at which discharge occurs varies under the influence of atmospheric pressure and the like. Therefore, the potential difference at which discharge occurs varies depending on each image forming apparatus, installation environment, and the like. For this reason, for example, when a product is inspected at a factory or when a product is installed, an AC voltage is initially set as large as possible (between peaks) without discharge. Patent Document 1 is recognized to show one form of this setting.

  However, due to changes over time due to the use of the photosensitive drum and the developing roller, the magnitude of the alternating voltage at which discharge occurs may change. For example, the gap length is subtle due to the impact on the image forming apparatus in the installation environment, the application of force to the photosensitive drum during jamming and maintenance, and the wear on the surface of the photosensitive drum and developing roller. May change. In addition, deterioration of the photosensitive layer of the photosensitive drum, deterioration of an AC voltage application circuit to the developing roller, and deterioration of the charging ability of the charging device for charging the photosensitive drum may be factors. In addition, large changes in atmospheric pressure, temperature, and humidity in the installation environment may change the magnitude of the alternating voltage at which discharge occurs. In other words, even if the AC voltage applied at the time of image formation is set to be optimal at the time of product inspection or the like, at present, discharge occurs or development efficiency due to these time-dependent factors. There is a problem that may be low.

  Therefore, it is necessary to adjust the setting of the AC voltage applied at the time of image formation according to the change over time. However, as in the invention described in Patent Document 1, the maximum potential difference ΔVmax is gradually increased, and the current continues. If the leak detection means determines that the leak has occurred (see Patent Document 1: Claim 1), there is a problem that it takes a very long time to determine that the leak has occurred (for example, the leak occurrence voltage is set). Such as close to the upper limit possible). In particular, when a color machine has a plurality of combinations of photosensitive drums and developing rollers (for example, tandem type), it takes a very long time to adjust each color. During this time, the user cannot use the image forming apparatus, and there is a problem that the convenience of the user and the productivity of the image forming apparatus are impaired.

  In view of the above problems, the present invention is simple and highly efficient for the convenience of the user and the production of the image forming apparatus when it is necessary to adjust the AC voltage applied to the developing roller applied during image formation due to changes over time. It is an object to adjust the AC voltage applied during image formation without impairing the properties.

  In order to achieve the above object, an image forming apparatus according to a first aspect of the present invention opposes a photosensitive drum carrying a toner image on a peripheral surface thereof while providing a gap in the photosensitive drum, and carries the toner during image formation. A plurality of image forming units for forming toner images of different colors, and a storage unit for storing data, including a developing roller connected to an AC voltage application unit for supplying toner to the photosensitive drum. A detection unit that detects the occurrence of discharge between the developing roller and the photosensitive drum; and a control unit that controls each unit of the apparatus and that receives the output of the detection unit and recognizes the occurrence of discharge. The controller checks whether or not discharge has occurred while changing the AC voltage applied to the developing roller, executes adjustment of the AC voltage applied to the developing roller at a predetermined timing, and performs the adjustment once. so , It was decided to control to perform the adjustment for only one of the image forming unit.

  According to this configuration, since the adjustment is performed only for one image forming unit in one adjustment, the adjustment is completed more quickly than in the case where the adjustment is performed for the image forming units of all colors. Therefore, user convenience and productivity of the image forming apparatus are not greatly impaired. In addition, even if the optimum AC voltage applied to the developing roller changes, there is usually no dramatic change with time, and even if only one image forming unit is adjusted by one adjustment, it is sufficient. Further, it is possible to provide a high-quality image forming apparatus in which the development efficiency is maintained in a high state and the image density is maintained.

Further, the prior SL controller, the number of one round of the order of the image forming unit for adjusting a total number of said image forming unit, once for each image forming unit during the number of the one rotation The order of the image forming units that perform the adjustment is determined so that the adjustment is performed, and the order of the image forming units that perform the adjustment within the one round is not fixed. Further, history data indicating a use history of each of the image forming units is stored in the storage unit, and at the time of the adjustment after the second round, the control unit starts from the adjustment in the previous cycle based on the history data. The adjustment is performed from the image forming unit that has been used for a long time.

In this configuration, since the adjustment is performed once for each image forming unit during the number of times of one round, all the image forming units are uniformly subject to adjustment. In addition, since the order of the image forming units to be adjusted for one round is not fixed, for example, the order of the image forming units to be adjusted is determined in consideration of various circumstances such as frequently used image forming units. can do. Furthermore, in this configuration, since the adjustment is performed from the image forming unit having a long use time from the adjustment on the previous circumference to the present based on the history data, the use time from the previous adjustment is long (for example, a black and white image is For example, when printing is frequently performed), it is possible to preferentially adjust an image forming unit that is likely to be greatly affected by changes over time. In other words, it is possible to postpone an image forming unit that is less likely to be affected by changes over time and is not often used. Therefore, the AC voltage applied during image formation can be efficiently adjusted for changes over time, and the AC voltage can be set according to the status of the image forming apparatus.

According to a second aspect of the present invention, in the first aspect of the present invention, the storage unit first includes the storage unit according to a magnitude of an AC voltage applied to the developing roller at the time of the adjustment and at the time of image formation. Setting data relating to an AC voltage to be applied to the developing roller is stored, and at the time of the adjustment, the control unit causes the AC voltage applying unit to apply an AC voltage to the developing roller based on the setting data to generate a discharge. If recognized, the control unit reduces the AC voltage applied to the developing roller during image formation and updates the setting data. If the generation of discharge is not recognized, the control unit performs the development during image formation. The setting data is updated only when the AC voltage applied to the roller is increased or maintained as it is and the AC voltage during image formation is increased.

  According to this configuration, the AC voltage to be applied to the developing roller at the time of image formation can be maintained in a state where no discharge occurs and the development efficiency is high, and there is little variation in density and the like. An apparatus can be provided.

According to a third aspect of the present invention, there is provided an image forming apparatus comprising: a photosensitive drum carrying a toner image on a peripheral surface thereof; the photosensitive drum is opposed to the photosensitive drum while providing a gap; A plurality of image forming units that form toner images of different colors, a storage unit that stores data, and the developing roller. A detection unit that detects the occurrence of discharge between the photosensitive drums; and a control unit that controls each unit of the apparatus and that receives the output of the detection unit and recognizes the occurrence of discharge. And the detection unit is provided for each image forming unit, and the storage unit is first applied to the developing roller according to the magnitude of the AC voltage applied to the developing roller at the time of the adjustment and at the time of image formation. should Setting data relating to the flow voltage is stored, and the control unit determines whether or not discharge has occurred while changing the AC voltage applied to the developing roller, and determines the AC voltage to be applied to the developing roller during image formation. Adjustment is executed at a predetermined timing, and in one adjustment, control is performed so that the adjustment is performed only on one image forming unit, and the number of times of one turn in the order of the image forming units to be adjusted The order of the image forming units to perform the adjustment is determined so that the adjustment is performed once for each image forming unit during the number of times of the one round. Further, the order of the image forming units that perform the adjustment within the one circumference is not fixed, and during the adjustment, the AC voltage application unit applies an AC voltage to the developing roller based on the setting data, and discharge is performed. When recognizing the occurrence of The control unit reduces the AC voltage applied to the developing roller during image formation and updates the setting data. When the controller does not recognize the occurrence of discharge, the control unit applies to the developing roller during image formation. The setting data is updated only when the AC voltage is increased or maintained as it is, and the AC voltage is increased during image formation. When there is a change in the magnitude of the AC voltage to be applied, the control unit performs the adjustment from the image forming unit in which the AC voltage applied during image formation has been changed.

According to this configuration, since the adjustment is performed only for one image forming unit in one adjustment, the adjustment is completed more quickly than in the case where the adjustment is performed for the image forming units of all colors. Therefore, user convenience and productivity of the image forming apparatus are not greatly impaired. In addition, even if the optimum AC voltage applied to the developing roller changes, there is usually no dramatic change with time, and even if only one image forming unit is adjusted by one adjustment, it is sufficient. Further, it is possible to provide a high-quality image forming apparatus in which the development efficiency is maintained in a high state and the image density is maintained. Further, in this configuration, since the adjustment is performed once for each image forming unit during the number of times of one round, all the image forming units are uniformly subject to adjustment. In addition, since the order of the image forming units to be adjusted for one round is not fixed, for example, the order of the image forming units to be adjusted is determined in consideration of various circumstances such as frequently used image forming units. can do. In addition, according to this configuration, the AC voltage to be applied to the developing roller during image formation can be maintained in a state in which no discharge occurs and development efficiency is high, and there is little variation in density and the quality of the formed image. An image forming apparatus can be provided. Further, in this configuration, since the control unit performs adjustment from the image forming unit in which the AC voltage applied during image formation has been changed, it is confirmed at an early stage whether the previous adjustment (change) of the AC voltage is correct. Can do. Therefore, if the previous adjustment of the AC voltage is incorrect, it will be readjusted promptly.

According to a fourth aspect of the present invention, there is provided an image forming apparatus comprising: a photosensitive drum carrying a toner image on a peripheral surface thereof; the photosensitive drum is opposed to the photosensitive drum while providing a gap; A plurality of image forming units that form toner images of different colors, a storage unit that stores data, and the developing roller. A detection unit that detects the occurrence of discharge between the photosensitive drums; and a control unit that controls each unit of the apparatus and that receives the output of the detection unit and recognizes the occurrence of discharge. And the detection unit is provided for each image forming unit, and the storage unit is first applied to the developing roller according to the magnitude of the AC voltage applied to the developing roller at the time of the adjustment and at the time of image formation. should Setting data relating to the flow voltage is stored, and the control unit determines whether or not discharge has occurred while changing the AC voltage applied to the developing roller, and determines the AC voltage to be applied to the developing roller during image formation. Adjustment is executed at a predetermined timing, and in one adjustment, control is performed so that the adjustment is performed only on one image forming unit, and the number of times of one turn in the order of the image forming units to be adjusted The order of the image forming units to perform the adjustment is determined so that the adjustment is performed once for each image forming unit during the number of times of the one round. Further, the order of the image forming units that perform the adjustment within the one circumference is not fixed, and during the adjustment, the AC voltage application unit applies an AC voltage to the developing roller based on the setting data, and discharge is performed. When recognizing the occurrence of The control unit reduces the AC voltage applied to the developing roller during image formation and updates the setting data. When the controller does not recognize the occurrence of discharge, the control unit applies to the developing roller during image formation. The setting data is updated only when the AC voltage is increased or maintained at the same time and the AC voltage at the time of image formation is increased. During the adjustment after the second round, the control unit performs the adjustment for a predetermined number of times. However, the adjustment of the image forming unit without changing the AC voltage applied at the time of image formation is skipped over one or more rounds.

According to this configuration, since the adjustment is performed only for one image forming unit in one adjustment, the adjustment is completed more quickly than in the case where the adjustment is performed for the image forming units of all colors. Therefore, user convenience and productivity of the image forming apparatus are not greatly impaired. In addition, even if the optimum AC voltage applied to the developing roller changes, there is usually no dramatic change with time, and even if only one image forming unit is adjusted by one adjustment, it is sufficient. Further, it is possible to provide a high-quality image forming apparatus in which the development efficiency is maintained in a high state and the image density is maintained. Further, in this configuration, since the adjustment is performed once for each image forming unit during the number of times of one round, all the image forming units are uniformly subject to adjustment. In addition, since the order of the image forming units to be adjusted for one round is not fixed, for example, the order of the image forming units to be adjusted is determined in consideration of various circumstances such as frequently used image forming units. can do. In addition, according to this configuration, the AC voltage to be applied to the developing roller during image formation can be maintained in a state in which no discharge occurs and development efficiency is high, and there is little variation in density and the quality of the formed image. An image forming apparatus can be provided. Further, in this configuration, if there is no change in the AC voltage applied at the time of image formation after the adjustment for a predetermined number of times, the necessity for adjustment is small, and it can be predicted that deterioration in image quality does not easily occur without adjustment for a while. Therefore, the adjustment of the color can be skipped one or more times, and the frequency of adjustment in an image forming unit having a high necessity for adjustment, such as an image forming unit having a high use frequency, can be increased.

According to a fifth aspect of the present invention, in the first to fourth aspects of the invention, at the start-up after the main power supply is turned on, when a predetermined number of sheets have been printed since the previous adjustment, the image formation is completed at the start of image formation. Then, the control unit performs the adjustment by using any one of the cases where no image forming instruction has continued for a predetermined time or a plurality of combinations at these times as the execution timing.

  In this configuration, when the main power is turned on, when a predetermined number of sheets have been printed since the previous adjustment, when image formation is started, and when there is no image formation instruction after image formation has been completed for a predetermined time For example, the image quality is maintained because the adjustment is performed when a large change with time may occur, or when the user does not use or cannot use the image, and the convenience of the user and the productivity of the image forming apparatus are improved. There is no decline.

  As described above, according to the present invention, it is possible to easily and efficiently adjust the AC voltage applied during image formation without impairing the convenience of the user and the productivity of the image forming apparatus.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. In this embodiment, an electrophotographic tandem color printer 1 (corresponding to an image forming apparatus) will be described as an example. However, each element such as the configuration and arrangement described in the present embodiment does not limit the scope of the invention and is merely an illustrative example.

(Schematic configuration of image forming apparatus)
First, the outline of the printer 1 according to the embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view showing a schematic configuration of a printer 1 according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of each image forming unit 3 according to the embodiment of the present invention. As shown in FIG. 1, the printer 1 according to the present embodiment includes a sheet supply unit 2 a, a conveyance path 2 b, an image forming unit 3, an exposure device 4, an intermediate transfer unit 5, a fixing unit 6 and the like in the main body. Provided.

  The sheet supply unit 2a stores various sheets such as copy sheets, OHP sheets, and label sheets toward the intermediate transfer unit 5 and the like, and the sheet is fed by a sheet feeding roller 21 that is rotated by a driving mechanism (not shown) such as a motor. To the transport path 2b. The conveyance path 2 b conveys the sheet in the printer 1 and guides the supplied sheet to the discharge tray 22 through the intermediate transfer unit 5 and the fixing unit 6. The conveyance path 2b includes a pair of conveyance rollers 23, a guide 24, and a registration roller pair 25 that waits for the conveyed sheet in front of the intermediate transfer unit 5 and sends the sheet in time.

  As shown in FIGS. 1 and 2, the printer 1 includes an image forming unit 3 for four colors as a part for forming toner images of different colors based on image data. Specifically, the printer 1 includes an image forming unit 3a (including a charging device 7a, a developing device 8a, a charge removing device 31a, a cleaning device 32a, and the like) that forms a black image, and an image forming unit 3b that forms a yellow image. (Equipped with a charging device 7b, a developing device 8b, a static eliminating device 31b, a cleaning device 32b, etc.) and an image forming unit 3c (charging device 7c, developing device 8c, static eliminating device 31c, cleaning device 32c, etc.) for forming a cyan image. And an image forming unit 3d (including a charging device 7d, a developing device 8d, a charge removing device 31d, a cleaning device 32d, and the like) that forms a magenta image.

  Here, based on FIG. 2, each image forming part 3a-3d is explained in full detail. Each of the image forming units 3a to 3d has basically the same configuration except that the color of the toner image to be formed is different. Therefore, in the following description, the symbols a, b, c, and d in each image forming unit 3 are omitted except for the case where they are specifically described (in FIG. 2, the image forming units 3a, 3b, 3c, and 3d). The reference numerals a, b, c, and d are given to the respective members in the same manner.)

  Each photosensitive drum 9 carries a toner image on its peripheral surface, and has, for example, a positively charged amorphous silicon photosensitive layer on the outer peripheral surface of an aluminum drum base. It is driven to rotate counterclockwise at the process speed.

  Each charging device 7 (corresponding to a charging unit) has a charging roller 71 and charges the photosensitive drum 9 at a constant potential. Each charging roller 71 is in contact with each photosensitive drum 9 and rotates in accordance with the photosensitive drum 9. In addition, a voltage in which direct current and alternating current are superimposed is applied to each charging roller 71 by a charging voltage applying unit 72 (see FIG. 5), and the photosensitive drum 9 has a predetermined positive potential (for example, 200V to 300V). , Dark potential). A cleaning brush 73 for cleaning the surface of each charging roller 71 (for example, a resin brush or the like wound around a shaft) is provided. The charging device 7 may use a corona discharge or a charging brush.

  Each developing device 8 stores a developer (so-called two-component developer) containing toner and a magnetic carrier (the developing device 8a is black, the developing device 8b is yellow, the developing device 8c is cyan, and the developing device 8d is magenta. Of developer). Each developing device 8 includes a developing roller 81, a magnetic roller 82, and a conveying member 83. Each developing roller 81 faces the photosensitive drum 9 and is provided with a predetermined gap (for example, 1 mm or less). Each magnetic roller 82 is disposed diagonally to the upper right of each developing roller 81 and is provided with a gap. Each transport member 83 is provided above each magnetic roller 82.

  The roller shafts 811 and 821 of each developing roller 81 and each magnetic roller 82 are fixed. Magnets 813 and 823 extending in the axial direction are attached to the roller shafts 811 and 821 inside the developing roller 81 and the magnetic roller 82. Each developing roller 81 and each magnetic roller 82 have cylindrical sleeves 812 and 822 that cover the magnets 813 and 823, respectively, and these sleeves 812 and 822 rotate during image formation and adjustment described later (FIG. 3). Further, the magnets 813 and 823 have opposite polarities at the closest positions of the sleeves 812 and 822.

  Thereby, a magnetic brush is formed by the magnetic carrier between each developing roller 81 and each magnetic roller 82. The toner is supplied to the developing roller 81 by rotating the magnetic brush and the sleeve 822 of the magnetic roller 82 or applying a voltage to the magnetic roller 82 (magnetic roller bias applying unit 84: see FIG. 5). A thin layer is formed. The toner remaining after the development is peeled off from the developing roller 81 by a magnetic brush. For example, each conveying member 83 is provided with a screw spirally with respect to the shaft, and conveys and stirs the developer in each developing device 8 to charge the toner to a predetermined level (in this embodiment, the toner is positive). Electrification).

  Each cleaning device 32 cleans the photosensitive drum 9 and has, for example, a cleaning member 33 made of a cylindrical material having elasticity on the outer peripheral portion. The cleaning member 33 abuts on each photosensitive drum 9, and the drum The transfer residual toner on the surface is removed and collected. Further, a neutralization device 31 (for example, an array of LEDs) that performs neutralization by irradiating the photosensitive drum 9 with light is provided below each cleaning device 32.

  An exposure device 4 (corresponding to an exposure unit) above each image forming unit 3 converts an input color-separated image signal into an optical signal by a laser output unit (not shown), and the converted light. A laser beam (illustrated by a broken line), which is a signal, is output, and the photosensitive drum 9 after being charged is scanned and exposed to form an electrostatic latent image. The exposure device 4 may be composed of a large number of LEDs. The exposure device 4 includes an optical system member (not shown) such as a semiconductor laser device (laser diode), a polygon mirror (rotated by a polygon motor), an fθ lens, and a mirror, and irradiates each photosensitive drum 9 with laser light. An electrostatic latent image combined with the image data is formed on the photosensitive drum 9. Specifically, each photosensitive drum 9 of the present embodiment is positively charged, the potential of the light irradiation portion is lowered (for example, approximately 0 V), and the positively charged toner is attached to the portion of the potential decrease (for example, solid image) In the case of irradiating laser light to all lines and all pixels)

  Returning to FIG. 1, the intermediate transfer unit 5 receives the primary transfer of the toner image from the photosensitive drum 9 and performs secondary transfer onto the sheet, and each of the primary transfer rollers 51 a to 51 d, the intermediate transfer belt 52, and the driving roller. 53, driven rollers 54, 55, 56, a secondary transfer roller 57, a belt cleaning device 58, and the like. Each of the primary transfer rollers 51a to 51d is in contact with each photosensitive drum 9 via an endless intermediate transfer belt 52, and is connected to a transfer voltage applying unit 59 (not shown) for applying a transfer voltage. The image is transferred to the intermediate transfer belt 52.

  The intermediate transfer belt 52 is stretched around a driving roller 53 and driven rollers 54, 55, and 56, and rotates in a counterclockwise direction in FIG. 1 by rotational driving of the driving roller 53 connected to a driving mechanism (not shown) such as a motor. To do. The driving roller 53 is in contact with the secondary transfer roller 57 via the intermediate transfer belt 52 to form a secondary transfer portion. The toner image transfer to the sheet will be described. Toner images (black, yellow, cyan, and magenta colors) formed by the image forming units 3 are sequentially applied by applying predetermined voltages to the primary transfer rollers 51. The primary transfer is performed on the intermediate transfer belt 52. At this time, the toner images of the respective colors are primarily transferred while being timed so as to be superimposed without deviation. The superimposed toner images are transferred onto the sheet by a secondary transfer roller 57 to which a predetermined voltage is applied. The residual toner remaining on the intermediate transfer belt 52 after the secondary transfer is removed and collected by the belt cleaning device 58 (see FIG. 1).

  The fixing unit 6 is disposed downstream of the secondary transfer unit in the transfer material conveyance direction, and fixes the toner image secondarily transferred to the sheet by heating and pressing. The fixing unit 6 is mainly composed of a fixing roller 61 having a built-in heat source and a pressure roller 62 pressed against the fixing roller 61 to form a nip. The sheet on which the toner image has been transferred is heated and pressurized as it passes through the nip, and as a result, the toner image is fixed on the sheet. The fixed sheet is discharged to the discharge tray 22 and the image forming process is completed.

(Configuration for discharge detection)
Next, the configuration relating to the application of the developing bias to each developing roller 81 and the detection of the discharge between the respective photosensitive drums 9, which are the features of the present invention, will be described.

  FIG. 3 is a configuration diagram around the developing roller 81 regarding the application of the developing bias to the developing roller 81 and the detection of the occurrence of discharge between the photosensitive drums 9 according to the embodiment of the present invention. However, FIG. 3 shows only one image forming unit 3. Each image forming unit 3 is provided with a DC voltage application unit 85, an AC voltage application unit 86, a detection unit 14, and an amplifier 15, and the output of each amplifier 15 is This is input to the CPU 11 of the control unit 10 to be described later. Here, each of the DC voltage application unit 85, the AC voltage application unit 86, the detection unit 14, and the amplifier 15 may be affixed with symbols a, b, c, and d indicating the distinction of the image forming unit 3. Since the same components are provided in each image forming unit 3, in order to avoid complicated description, the following description will be made with the symbols a, b, c, and d omitted.

  As shown in FIG. 3, the developing roller 81 facing the photoconductor drum 9 with a gap is provided with a roller shaft 811, a sleeve 812 that carries toner during image formation, and a cap 814. The roller shaft 811 is inserted through the sleeve 812, and circular caps 814 are fitted to both ends of the sleeve 812. Further, a DC voltage application unit 85 and an AC voltage application unit 86 are connected to the roller shaft 811 of the developing roller 81 for supplying toner to the photosensitive drum 9.

  The DC voltage application unit 85 is a circuit that generates a DC component to be applied to the developing roller 81, and its output is input to the AC voltage application unit 86. The DC voltage application unit 85 includes an output control unit 87, and the output control unit 87 controls the bias value output from the DC voltage application unit 85 in accordance with an instruction from the CPU 11.

  The DC voltage application unit 85 is a circuit that receives supply of DC power from the power supply device 16 (see FIG. 4) in the printer 1 and whose output voltage is variable under the control of the output control unit 87 in accordance with an instruction from the CPU 11. (For example, there are a plurality of paths to output terminals with different output voltages, and the selection of the path is changed between image formation and discharge detection). Thereby, the alternating voltage applied to the developing roller 81 can be biased.

  The AC voltage application unit 86 is, for example, a rectangular wave (pulse shape), and is a circuit that outputs an AC voltage whose average value is the DC voltage applied by the DC voltage application unit 85. AC voltage application unit 86 includes a Vpp control unit 88 and a duty ratio / frequency control unit 89. The Vpp control unit 88 controls the peak-to-peak voltage of the AC voltage according to an instruction from the CPU 11. Further, the duty ratio / frequency control unit 89 controls the duty ratio and frequency of the AC voltage in accordance with an instruction from the CPU 11.

  For example, the AC voltage application unit 86 includes a switching element or the like, inverts the output polarity by switching, and outputs an AC voltage. The duty ratio / frequency control unit 89 can control the duty ratio and frequency of the AC voltage by controlling, for example, the positive / negative switching timing of the output of the AC voltage application unit 86. Further, the Vpp control unit 88 uses the voltage between the peaks of the AC voltage to be applied to the developing roller 81 and the duty ratio, and the positive peak in the AC voltage by the step-up / step-down of the DC voltage input from the power supply device 16. The value and the negative peak value are varied according to an instruction from the CPU 11. The configuration of the AC voltage application unit 86 and the configuration that varies the peak-to-peak voltage, the duty ratio, and the frequency of the AC voltage only need to change the peak-to-peak voltage, the duty ratio, and the frequency.

  In the AC voltage application unit 86, for example, a boosting circuit such as a boosting transformer can be provided in the output stage, and the developing bias in which the DC and AC are superimposed after the boosting is, for example, the roller of the developing roller 81. Applied to the shaft 811. As a result, a developing bias is also applied to the sleeve 812, and the charged toner carried on the sleeve 812 flies.

  The detection unit 14 is a circuit that converts the current that flows when a discharge occurs between the developing roller 81 and the photosensitive drum 9 into a voltage signal, and detects the occurrence of a discharge between the developing roller 81 and the photosensitive drum 9. The voltage signal thus output is output to the amplifier 15. The amplifier 15 amplifies the voltage signal from the detection unit 14 and outputs it to the CPU 11. The CPU 11 A / D converts the voltage signal from the amplifier 15. From the output of the A / D converted amplifier 15, the CPU 11 can recognize the occurrence of discharge and the magnitude of the discharge (the magnitude of the flowing current).

(Hardware configuration of printer 1)
Next, the hardware configuration of the printer 1 according to the embodiment of the present invention will be described with reference to FIG. FIG. 4 is a block diagram illustrating an example of a hardware configuration of the printer 1 according to the embodiment of the present invention.

  As shown in FIG. 4, the printer 1 according to the present embodiment includes a control unit 10 inside. The control unit 10 controls each unit of the printer 1 and receives the output of the detection unit 14 to recognize the occurrence of discharge. For example, the control unit 10 includes a CPU 11, a storage unit 12, and the like. The CPU 11 is a central processing unit, and controls and calculates each unit of the printer 1 based on a control program stored in the storage unit 12 and developed. The storage unit 12 is configured by a combination of nonvolatile and volatile storage devices such as ROM, RAM, and flash ROM. For example, the storage unit 12 stores a control program, control data, and the like for the printer 1. In addition, regarding the present invention, a program for detecting discharge and setting and adjusting an AC voltage applied to the developing roller 81 is also stored in the storage unit 12.

  The control unit 10 is connected to the sheet supply unit 2a, the conveyance path 2b, the image forming unit 3, the exposure device 4, the intermediate transfer unit 5, the fixing unit 6, and the like. Based on the control program and data in the storage unit 12, the control unit 10 The operation of each unit is controlled so that image formation is performed.

  The control unit 10 is connected to a user terminal 100 (personal computer or the like) as a transmission source of image data to be printed, and the control unit 10 performs image processing on the received image data and transmits it to the exposure apparatus 4. Then, the exposure device 4 forms an electrostatic latent image on the photosensitive drum 9 based on the image data. A magnetic roller bias applying unit 84 shown in FIG. 4 is a circuit that applies a voltage in which alternating current and direct current are superimposed on the magnetic roller 82. The charging voltage application unit 72 is a circuit that applies a charging voltage to the charging roller 71.

  Further, with respect to the present invention, the control unit 10 (CPU 11) is connected to the detection unit 14 (amplifier 15). Further, during the implementation of the present invention, the CPU 11 gives an instruction to change the peak-to-peak voltage of the AC voltage applied to the developing roller 81 to the AC voltage application unit 86 and generates discharge from the output of the detection unit 14 (amplifier 15). Presence / absence detection and discharge magnitude are determined. Then, when the occurrence of discharge is detected, the control unit 10 grasps the potential difference of the photosensitive drum 9 of the developing roller 81 at the time of occurrence of discharge based on values such as the DC voltage at that time and the peak-to-peak voltage of the AC voltage. The setting of the developing bias to be applied during the image forming operation is determined so that no discharge occurs during the formation. The setting value of the developing bias can be stored in the storage unit 12.

  In the present invention, each image forming unit 3 is equipped with, for example, a chip-shaped memory 34 (corresponding to a storage unit) that stores history data. Here, the history data can include data indicating the cumulative number of printed sheets, the print execution date and time, the number of prints, and the usage time (operating time) from the viewpoint of life management of the image forming unit 3. The history data can also include date and time data for adjusting the AC voltage applied to the developing roller 81 described later. In addition, the usage time of each image forming unit 3 from the previous adjustment of the AC voltage to the present time may be stored as data, or converted by multiplying the number of printed sheets after the adjustment by the time required per sheet ( For example, the usage time from the previous adjustment may be stored by the CPU 11 calculating. The history data regarding the history of use and adjustment regarding the image forming unit 3 may be stored in the storage unit 12 of the control unit 10.

(Initial setting of AC voltage applied to developing roller 81)
Next, an example of an initial setting method of the AC voltage applied to the developing roller 81 will be described with reference to FIGS. FIG. 5 is a flowchart showing an example of an initial setting method of the AC voltage applied to the developing roller 81 according to the embodiment of the present invention. FIG. 6 is a timing chart illustrating details of the AC voltage applied to the developing roller 81 according to the embodiment of the present invention. Note that this initial setting operation is performed one by one for each image forming unit 3, and is performed a total of four times.

  This initial setting can be performed, for example, at the time of manufacturing as initial defect detection or initial setting, when the printer 1 is installed, or when the developing device 8 or the photosensitive drum 9 is replaced. The reason why the printer 1 is installed is that the atmospheric pressure changes depending on the altitude of the installation environment (for example, the difference between Japan and the Mexican highlands), and there is a difference in the voltage at which discharge occurs. The reason for performing the replacement of the developing device 8 and the like is that the gap between the photosensitive drum 9 and the developing roller 81 is different from that before the replacement. The implementation timing is not limited to the above example, and the implementation timing can be set as appropriate.

  First, when a predetermined operation is performed in an operation unit (not shown) and the initial setting control is started (start), the photosensitive drum 9, the developing roller 81, the intermediate transfer are performed by a drive mechanism (not shown) according to an instruction from the CPU 11. The rotation of various rotating bodies in the image forming unit 3 such as the belt 52 and the intermediate transfer unit 5 is started (step S1). The driving of each rotating body continues until the initial setting is completed.

  Next, when performing the initial setting, an initial operation as a preliminary operation is performed (step S2). For example, in the initial operation, AC and DC voltages are applied to the developing roller 81 and the magnetic roller 82, respectively. By applying a voltage to the magnetic roller 82 in this initial operation, a small amount of toner is supplied from the magnetic roller 82 to the developing roller 81. In the detection of the occurrence of discharge, basically, toner is not carried on the developing roller 81, but if no toner is carried, the friction between the photosensitive drum 9 and the rotating member (intermediate transfer belt 52, etc.) in contact therewith becomes too large. Therefore, a slight amount of toner is supplied to the photosensitive drum 9.

  Next, the process proceeds to a preparation state for detecting the occurrence of discharge (step S3). For example, in the preparation state, the charging voltage application unit 72 starts voltage application to the charging device 7 in accordance with an instruction from the CPU 11. Note that the voltage applied to the charging device 7 can be turned on until the initial setting operation is completed. Further, the peak-to-peak voltage of the AC voltage applied to the developing roller 81 is increased so as to have a predetermined initial value (for example, a minimum value that can be set).

  In the discharge detection state, the CPU 11 counts the number of times that the output voltage of the amplifier 15 exceeds a predetermined threshold (step # 4). Specifically, the control unit 10 detects and recognizes the occurrence of discharge from the output of the detection unit 14 by applying an AC voltage set in the preparation state or an AC voltage set in a condition change state described later. . At this time, the exposure device 4 continues the exposure in accordance with an instruction from the CPU 11 (in order to expose the entire surface of the photosensitive drum 9 and reduce the surface potential to almost zero V for stabilization). In the printer 1 of this embodiment, the toner and the photosensitive drum 9 are charged with positive polarity, and the toner is deposited on the exposed portion. Therefore, the continuous exposure is the same as the formation of the electrostatic latent image of the solid image. It is. Accordingly, in the discharge detection state, for example, solid image data (for example, stored in the storage unit 12) is sent from the control unit 10 to the exposure apparatus 4.

Here, the voltage applied to the developing roller 81 in the discharge detection state will be described with reference to FIG. The rectangular wave in the timing chart at the time of image formation is an example of the waveform of the developing bias (AC + DC) applied to the developing roller 81. “Vdc1” indicates the bias potential of the DC voltage application unit 85. “V0” indicates the potential of the photosensitive drum 9 after exposure by the exposure device 4 (approximately 0 V = bright potential). “V1” indicates a potential after charging of the photosensitive drum 9 (potential of a portion not exposed to light, for example, about 200 to 300 V). “V ₊₁ ” indicates a potential difference between V 0 and the positive peak value of the developing bias at the time of image formation. “V ₋ ” indicates a potential difference between V1 and the negative peak value of the developing bias. “Vpp1” indicates the peak-to-peak voltage of the AC voltage applied to the developing roller 81 during image formation. “T1” is the time of the high state (positive state) in the rectangular wave. “T01” indicates the period of the rectangular wave.

On the other hand, the rectangular wave in the timing chart of the discharge detection state indicates the waveform of the developing bias applied to the developing roller 81. “Vdc2” indicates the bias potential of the DC voltage application unit 85 at the time of detection. “V0” indicates a potential (approximately 0 V) after exposure of the photosensitive drum 9 by the exposure device 4 as in the upper part of FIG. “V ₊₂ ” indicates a potential difference between the positive peak value of the developing bias at the time of detection and V0. “Vpp2” indicates a peak-to-peak voltage of the AC voltage applied to the developing roller 81 at the time of detection. “T2” is the time of the high state (positive state) in the rectangular wave. “T02” is a period of a rectangular wave.

  First, in the discharge detection state, the output control unit 87 sets the output of the DC voltage application unit 85 to a set value Vdc2 (for example, 100 V to 200 V) for the discharge detection state in accordance with an instruction from the CPU 11. Further, in response to an instruction from the CPU 11, the Vpp control unit 88 sets the Vpp 2 of the AC voltage output from the AC voltage application unit 86. Further, the duty ratio / frequency control unit 89 is instructed by the CPU 11 to detect the duty ratio D2 of the AC voltage output from the AC voltage application unit 86 (the ratio of the high time T2 to the period T02, T2 / T02) for discharge generation detection. And the frequency f2 (= 1 / T02) of the AC voltage output from the AC voltage application unit 86 is set to the setting value for detecting the occurrence of discharge (lower part of FIG. 6).

  Here, the duty ratio D2 (condition: less than 50%) is set smaller than the duty ratio D1 (the ratio of the high time T1 to the period T01, T1 / T01) (for example, D1 = 40%, D2 = 30%). The frequency f2 is set so that the positive time of the AC voltage is the same when the image is formed and when the discharge is detected (ie, T1 = T2, for example, when D1 = 40% and D2 = 30%, If the frequency f1 = 4 kHz during image formation, f2 = 3 kHz). As a result, a positive voltage is applied to the developing roller 818 for the same time as the image formation.

  In the discharge detection state, the duty ratio D2 is made smaller than that at the time of image formation, so that the potential difference between the positive peak value at the developing roller 81 and the potential Vdc2 in relation to the average value (Vdc2) of the AC voltage is It becomes larger than the negative side. The photosensitive layer of the photosensitive drum 9 of the present embodiment is positively charged amorphous silicon, and there are many reasons why the potential of the developing roller 81 is lower than that of the photosensitive drum 9, but a large current flows during discharging. It has been empirically obtained that there are easy characteristics. However, in the discharge detection state of the present embodiment, the potential of the developing roller 81 is made larger than that of the photosensitive drum 9, and it is difficult for a large current to flow during discharging, and damage to the photosensitive drum 9 (for example, the photosensitive drum due to discharge). 9) is prevented.

  Returning to FIG. 5, the description will be continued. After step # 4, control unit 10 confirms whether the count is not 0 (step S5). If it is not 0 (No in step S5), it is determined that a discharge has occurred, and the process proceeds to step # 8 (step S8). Details will be described later). At this time, after decreasing by a predetermined step size ΔV1 from the peak-to-peak voltage of the AC voltage at the time of discharge occurrence, it is increased by a predetermined step size ΔV2 smaller than ΔV1, and a discharge detection state and a condition change state (described later) Step # 7) may be repeated to find the peak-to-peak voltage at which discharge occurs more finely.

  On the other hand, if it is 0 times (No in step S5), the CPU 11 confirms whether or not the current peak-to-peak voltage has reached a settable maximum value (for example, 1500 to 3000 V) as no discharge has occurred (step S6). If it has been reached (Yes in step S6), the process proceeds to step S8 (details will be described later). On the other hand, if not reached (No in step S6), the process shifts to the condition change state. In this condition change state, the Vpp control unit 88 increases the peak-to-peak voltage of the AC voltage output from the AC voltage application unit 86 by a predetermined step size ΔV1 (for example, 30 to 100 V) from the current state in accordance with an instruction from the CPU 11. Setting is performed (step S7). Thereafter, the state returns to the discharge detection state (to step # 3). As a result, the condition change state and the discharge detection state are repeated until the occurrence of discharge is recognized, and during the repetition, the peak-to-peak voltage of the alternating voltage applied to the developing roller 81 is basically stepwise with a constant step size. Enhanced.

Next, step S8 will be described in detail. When discharge is detected (No in step S5) or when the maximum peak-to-peak voltage that can be set cannot be detected (Yes in step S6), the CPU 11 recognizes that the maximum peak-to-peak voltage or discharge occurs. From the voltage Vpp2, the frequency f2, the duty ratio D2, and the bias setting value Vdc2, the potential difference V ₊₂ shown in FIG. 6 (the potential difference between the photosensitive drum 9 and the developing roller 81 when Vpp2 is applied when discharge is detected or at the maximum settable value) ) Is obtained (step S8).

Here, V ₊₂ can be easily obtained. CPU 11 designates the magnitude of the peak-to-peak voltage and issues an instruction to Vpp control unit 88. Therefore, the control part 10 grasps | ascertains Vpp2 at that time, when discharge generation | occurrence | production is detected. Further, based on the duty ratio D2 as a set value and Vdc2 as a reference, the positive side and negative side peak values of Vpp2 and the potential difference between Vdc2 are obtained based on equalizing the positive side and negative side areas. If a potential difference between Vdc2 and V0 (V0 is almost 0 V, it can be treated as Vdc2) is added to this potential difference, V ₊₂ is obtained (see FIG. 6).

Specifically, Vpp2 at the time of discharge occurrence detection operation is changed in stages. If the duty ratio D2 and the bias setting value Vdc2 are constant, V _{+ 2} is calculated in advance according to the magnitude of each Vpp2, The data may be converted into a lookup table, and the CPU 11 may refer to the table to obtain V ₊₂ . In addition, what is necessary is just to memorize | store this table in the memory | storage part 12, for example.

Next, based on the obtained V ₊₂ , the CPU 11 develops the developing roller 81 during image formation so that both V ₊₁ and V ₋ shown in FIG. 5 are smaller than the obtained V _+2. The peak-to-peak voltage Vpp1 of the AC voltage applied to is set, and the control unit 10 stores it in the flash ROM or the like of the storage unit 12 in a nonvolatile manner (step S9). Specifically, there are various methods for determining Vpp1. For example, how much smaller V ₊₁ and V ₋ than V ₊₂ will not cause discharge (how much margin should be taken) depends on the toner used. For example, for the obtained V ₊₂ , a value of Vpp1 that is recognized as causing no discharge during image formation may be tabulated, and the CPU 11 may determine Vpp1 by referring to the table. This table may also be stored in the storage unit 12. This makes it possible to apply as much AC voltage as possible without causing discharge during image formation. When the setting of Vpp1 is completed, the setting of the AC voltage Vpp1 applied to the developing roller 81 at the time of image formation ends (end). Then, after the control is completed, the printer 1 returns to a state where image formation is possible.

(Adjustment of AC voltage applied to developing roller 81)
Next, an example of adjustment of the AC voltage applied to the developing roller 81 corresponding to a change with time will be described with reference to FIGS. FIG. 7 is a flowchart showing an example of control of adjustment of the AC voltage applied to the developing roller 81 according to the embodiment of the present invention. FIG. 8 is a timing chart in adjusting the AC voltage applied to the developing roller 81 according to the embodiment of the present invention.

  Note that “developing roller (AC)” in FIG. 8 indicates the timing at which the AC voltage application unit 86 applies an AC voltage to the developing roller 81. “Vpp” indicates a change in the peak-to-peak voltage of the AC voltage to the developing roller 81. “Developing roller (DC)” indicates a timing at which the DC voltage application unit 85 applies a DC voltage to the developing roller 81. “Charging roller” indicates the timing at which the charging device 7 charges the photosensitive drum 9. “Exposure” indicates the exposure (laser beam irradiation) timing of the photosensitive drum 9 in the exposure apparatus 4. “Discharge detection (detection unit 14 output)” indicates a discharge occurrence detection timing by the detection unit 14.

  Here, the change with time and the necessity of adjusting the AC voltage applied to the developing roller 81 will be described. Use of the photosensitive drum 9 and the developing roller 81 may change the gap length of the photosensitive drum 9 and the developing roller 81. For example, when the layer thickness of the photosensitive layer such as the photosensitive drum 9 is changed due to friction with each member (for example, the charging roller 71), or because a force is applied to the photosensitive drum 9 or the like by jamming or maintenance, the gap When the length changes slightly, when the maintenance member for the gap between the photosensitive drum 9 and the developing roller 81 (for example, a supporting shaft member for supporting the rotating shaft of the photosensitive drum 9 or the like) is worn, or when the printer is dropped The case where there is an impact on 1 is considered.

  The gap length affects the magnitude of the AC voltage that generates a discharge between the photosensitive drum 9 and the developing roller 81. Therefore, when the gap length changes, the magnitude of the AC voltage that causes discharge changes. Note that an environment such as atmospheric pressure, temperature, and humidity in the installation environment, deterioration of a circuit that applies an AC voltage to the developing roller 81, and the like can also cause the discharge start voltage to change.

  Therefore, as described with reference to FIGS. 5 and 6, as an initial setting, even if the AC voltage applied to the developing roller 81 is accurately determined so that no discharge occurs and the development efficiency is increased, the time-lapse Due to the influence of the change, the initial setting is not always optimal as the AC voltage to be applied to the developing roller 81 in the future. Accordingly, it is necessary to adjust (calibrate) the AC voltage to be applied at the time of image formation corresponding to the secular change.

  Therefore, the control unit 10 changes the AC voltage applied to the developing roller 81 at a predetermined timing, confirms whether or not discharge has occurred, and adjusts the AC voltage applied to the developing roller 81 during image formation. explain. This adjustment is performed at a predetermined timing, and at that time, when starting up after turning on the main power, a predetermined number of sheets (for example, several tens to several hundreds) is printed from the previous discharge occurrence detection operation. At the start of image formation, when there is no image formation instruction after completion of image formation for a predetermined time (for example, immediately before entering the sleep mode, etc.), or at a plurality of times at these times Adjustment can be executed using the combination as the execution timing.

  Then, the start of FIG. 7 is the time when the control unit 10 starts the adjustment control of the AC voltage (start) when the predetermined timing for executing the adjustment of the AC voltage is reached. Then, the control unit 10 starts rotation of various rotating bodies such as the image forming unit 3 and the intermediate transfer unit 5 (step # 21).

  Next, the control unit 10 determines an AC voltage to be applied to the developing roller 81 first when adjusting the AC voltage (step # 22). Here, in the present embodiment, in order to avoid damage to the photosensitive drum 9, discharging is performed with the potential of the developing roller 81 being high even during adjustment so that the discharge current flows only in one direction. Therefore, in the present embodiment, the AC voltage that is first applied to the developing roller 81 during the adjustment of the AC voltage is obtained when the table or the like or Vpp1 is obtained from the AC voltage (Vpp1 in FIG. 6) applied during the current image formation. For example, the CPU 11 performs the reverse operation to determine the AC voltage Vpp2 for adjusting the AC voltage (similar to the initial setting) (see FIG. 6).

  In other words, the storage unit 12 of the control unit 10 stores information on the AC voltage applied to the developing roller 81 during current image formation, such as setting data (for example, peak-to-peak voltage, DC bias value, duty ratio, frequency, etc.). Parameter) is stored, and a table or the like is referred to based on the setting data, and the AC voltage to be first applied to the developing roller 81 is determined in the discharge detection during adjustment. For example, after the above-described initial setting, the content of the setting data is data regarding the AC voltage applied to the developing roller 81 during image formation determined by the initial setting. As will be described later, if there is a change in the AC voltage to be applied to the developing roller 81 during image formation by adjusting the AC voltage, the setting data is data regarding the AC voltage after the change. The setting data may include not only information on the AC voltage applied to the developing roller 81 during current image formation, but also information on the AC voltage to be applied to the developing roller first when adjusting the AC voltage. good.

  Then, the operation of the charging device 7 is started, and a transition is made to a preparation state in which the output voltage of the AC voltage application unit 86 is increased to an AC voltage value (determined by setting data) that is first applied to the developing roller during adjustment (step # 23, see FIG. The preparation state in this control is basically the same as the preparation state at the time of initial setting (see FIG. 5). After that, the exposure apparatus 4 shifts to a discharge detection state where exposure is continuously performed (see FIG. 8), and the CPU 11 counts the number of times that the output voltage of the amplifier 15 exceeds a predetermined threshold (step S24). The discharge detection state in this control is basically the same as the discharge detection state at the time of initial setting, such as the duty ratio and the DC bias value (see FIGS. 5 and 6). Then, the control unit 10 confirms whether the count number is 0 (step S25).

  If no discharge is detected (Yes in step 25), the process proceeds to the preparation state, and the control unit 10 develops an AC voltage (for example, +10 to + 50V) whose peak-to-peak voltage is larger than the AC voltage to be applied first. The Vpp control unit 10 is instructed to apply to the roller 81 (step S26, see FIG. 8). Then, the state shifts to the discharge detection state (see FIG. 8), the CPU 11 counts the number of times that the output voltage of the amplifier 15 exceeds a predetermined threshold (step # 27), and the control unit 10 determines whether the count number is not 0 times. Is confirmed (step S28).

If a discharge is detected (No in step 28), the setting data is not changed and the process ends (END). On the other hand, if the discharge is not detected (Yes in step # 28), the control unit 10 determines the potential difference V ₊₂ (at the time of discharge detection) based on the AC voltage in the immediately previous discharge detection state, as in the case of the initial setting. The potential difference between the photosensitive drum 9 and the developing roller 81 when Vpp2 is applied is determined, and the AC voltage Vpp1 to be applied to the developing roller 81 during image formation is determined (step # 29).

  If a discharge is detected in step # 25 (No in step S25), there is a concern that the image quality is deteriorated or the photosensitive drum 9 is damaged as it is. Therefore, the control unit 10 first moves to the preparation state. The Vpp control unit 10 is instructed to apply to the developing roller 81 an AC voltage (for example, −10 to −50 V or the like) whose peak-to-peak voltage is smaller than the AC voltage applied to the developing roller 81 (step S30). Then, the state shifts to the discharge detection state, and the CPU 11 counts the number of times that the output voltage of the amplifier 15 exceeds a predetermined threshold (step # 31), and the control unit 10 confirms whether the count number is not zero (step # 31). S32).

If the number of counts is not 0 and discharge is detected (Yes in step 32), it can be determined that the AC voltage is still too large, so the peak-to-peak voltage is smaller than the AC voltage in the previous discharge detection state. A potential difference V ₊₂ (potential difference between the photosensitive drum 9 and the developing roller 81 when Vpp2 is applied at the time of discharge detection) is obtained with reference to an AC voltage (for example, −10 to −50 V), and is applied to the developing roller 81 during image formation. The power supply AC voltage Vpp1 is determined (step # 33).

  On the other hand, in step # 32, if the count is 0 and no discharge is detected (Yes in step # 32), the AC voltage in the previous discharge detection state is used as a reference and applied to the developing roller 81 during image formation. The power supply AC voltage Vpp1 is determined (step # 29). Then, the AC voltage to be applied at the time of image formation determined at steps # 29 and 33 is updated and stored as setting data (step # 34). Then, the AC voltage adjustment control ends (end).

  In summary, the storage unit 12 stores setting data relating to the AC voltage to be first applied to the developing roller 81 in accordance with the magnitude of the AC voltage applied to the developing roller 81 at the time of adjustment and at the time of image formation. At the time of adjustment, when the control unit 10 causes the AC voltage application unit 86 to apply an AC voltage to the developing roller 81 based on the setting data and recognizes the occurrence of discharge, the control unit 10 recognizes the occurrence of discharge. In the case where the AC voltage to be applied is reduced and the setting data is updated and the occurrence of discharge is not recognized, the control unit 10 increases or maintains the current status of the AC voltage applied to the developing roller 81 at the time of image formation. The setting data is updated only when the AC voltage is increased.

(Determining the order of the image forming unit 3 for adjusting the AC voltage)
Next, an example of determining the order of the image forming unit 3 that adjusts the AC voltage according to this embodiment will be described with reference to FIG. FIG. 9 is a flowchart illustrating an example of order determination of the image forming unit 3 that performs adjustment of the AC voltage according to the present exemplary embodiment.

  In the printer 1 of this embodiment, the AC voltage applied to the developing roller 81 is adjusted. However, in one AC voltage adjustment, the AC voltage is adjusted only for one image forming unit 3. As a result, the time required for one adjustment of the AC voltage is much shorter (1/4) than the time required for adjusting all the image forming units 3. Thereby, a user is not made to wait for a long time until adjustment of an alternating voltage is completed.

  Therefore, since the order and selection of the image forming unit 3 that adjusts the AC voltage applied to the developing roller 81 becomes a problem, the control in determining the order and selection of the image forming unit 3 in the printer 1 of this embodiment is illustrated. 9 will be described.

  First, the start in FIG. 9 is a state immediately after the timing of adjusting the AC voltage. Next, the control unit 10 confirms AC voltage adjustment history data (stored in the storage unit 12 and the memory 34 as described above) (step # 41), and the control unit 10 confirms the history data. However, the image forming unit 3 that has already adjusted the AC voltage in the current cycle is excluded from the selection target (step # 42), and the control unit 10 confirms whether the current AC voltage adjustment is in the first cycle. (Step # 43). Here, one turn is constituted by the number of adjustments of the AC voltage corresponding to the total number of the image forming units 3 (in this example, one turn is four times). In addition, the adjustment of the AC voltage applied to the developing roller 81 is basically performed once for each image forming unit 3 for each rotation (per circumferential unit).

  If it is the first week (Yes in step # 43), the control unit 10 still confirms the history data, and based on a predetermined order (for example, black → cyan → magenta → yellow), the AC voltage is still In step # 44, the image forming unit 3 that performs the adjustment of the AC voltage is determined for the image forming unit 3 of the higher order color.

  On the other hand, if it is not the first week (if it is after the second week) (No in step # 43), the skip target is excluded from the selection target (step # 45). Here, in the printer 1 of the present embodiment, in the past adjustment of the alternating voltage, n times (corresponding to a predetermined number of times), when there is no change in the alternating voltage applied to the developing roller 81 at the time of image formation, image formation is performed thereafter. Since it can be predicted that there is no change in the AC voltage applied to the developing roller 81 from time to time, the AC voltage is set to be skipped (mapped) for m rounds (n and m are arbitrary integers). That is, at the time of adjustment after the second round, the control unit 10 skips the adjustment of the image forming unit 3 without changing the AC voltage applied at the time of image formation even if the adjustment is performed a predetermined number of times. Therefore, the skip target is the image forming unit 3 in which the adjustment of the AC voltage is skipped in the current circumference. Note that n and m can be set arbitrarily. For example, if n = 3, m = 1 can be set. When the skip is completed, n is reset for the image forming unit 3.

  In this way, after narrowing down the selection targets for the adjustment of the AC voltage, the control unit 10 next checks whether there are two or more image forming units 3 to be selected (step # 46). If it does not exist (No in Step # 46), the remaining one image forming unit 3 is determined as a target for adjusting the AC voltage (Step # 47). On the other hand, if there are two or more image forming units 3 to be selected (No in step # 46), the control unit 10 confirms the history data and the image forming unit in which the AC voltage has been changed in the previous cycle. 3 is checked (step # 48). That is, at the time of adjustment after the second round, if there is a change in the magnitude of the AC voltage applied to the developing roller 81 during image formation due to the adjustment of the previous round, the control unit 10 changes the AC voltage applied during image formation. The adjustment is performed from the image forming unit 3 where there is.

  If present (Yes in step # 48), it is confirmed whether or not there are a plurality of image forming units 3 whose AC voltage has been changed in the previous cycle (step # 49). If there are a plurality (Yes in Step # 49), the control unit 10 confirms the history data and becomes the target of the adjustment operation of the AC voltage in the previous cycle, so that the longer use time until now is The image forming unit 3 is determined as a target for adjusting the AC voltage (step # 50). That is, referring to the history data stored in the storage unit 12 or the like and indicating the usage history of each image forming unit 3, the control unit 10 adjusts the previous cycle based on the history data during the second and subsequent adjustments. The adjustment is performed from the image forming unit 3 that has been used for a long time. If there are not more than one (No in step # 49), the image forming unit 3 whose AC voltage has been changed in the previous cycle is determined as the target for adjusting the AC voltage (step # 51).

  In step # 48, if there is no image forming unit 3 in which the AC voltage has been changed in the previous cycle (No in step # 48), the control unit 10 confirms the history data and changes the AC voltage in the previous cycle. The image forming unit 3 that has been used for the adjustment operation and has been used for a long time is determined as the target for adjusting the AC voltage (step # 52).

  In the adjustment order determination, the control unit 10 sets the total number of the image forming units 3 as the number of times of one round, and the adjustment is executed once for each image forming unit 3 during the number of times of one round. In addition, the order of the image forming units 3 to be adjusted is determined, and the order of the image forming units 3 to be adjusted within one round is not fixed.

  In this way, according to the present embodiment, only one image forming unit 3 is adjusted in one adjustment, so that the adjustment is performed on the image forming units 3 for all colors. Adjustment is completed quickly. Therefore, user convenience and productivity of the image forming apparatus are not greatly impaired. In addition, even if the optimum AC voltage applied to the developing roller 81 is changed with time, there is usually no dramatic change even if only one image forming unit 3 is adjusted by one adjustment. Sufficient development efficiency is maintained in a high state, and a high-quality image forming apparatus (for example, printer 1) in which the density is maintained is provided. Further, since the adjustment is executed once for each image forming unit 3 during the number of times of one round, all the image forming units 3 are subject to adjustment all over. In addition, since the order of the image forming unit 3 that performs the adjustment for one round is not fixed, the image forming unit 3 that performs the adjustment is considered in consideration of various circumstances such as the image forming unit 3 that is frequently used. The order can be determined.

  In addition, an AC voltage to be applied to the developing roller 81 at the time of image formation can be maintained in a state in which no discharge occurs and development efficiency is high, and there is little variation in density and the like. can do. Also, since the adjustment is performed from the image forming unit 3 that has been used for a long time from the previous adjustment to the present based on the history data, the use time from the previous adjustment is long (for example, printing monochrome images frequently) In this case, it is possible to preferentially adjust the image forming unit 3 that is easily affected by a change over time. In other words, it is possible to postpone the image forming unit 3 that is less likely to be affected by changes over time and is not often used. Therefore, the AC voltage applied during image formation can be efficiently adjusted for changes over time, and the AC voltage can be set according to the status of the image forming apparatus.

  Further, since the control unit 10 performs adjustment from the image forming unit 3 in which the AC voltage applied at the time of image formation has been changed, it can be confirmed at an early stage whether the previous adjustment (change) of the AC voltage is correct. . Therefore, if the previous adjustment of the AC voltage is incorrect, it will be readjusted promptly. In addition, if there is no change in the AC voltage applied during image formation after adjustment for a predetermined number of times, there is little need for adjustment, and it can be predicted that deterioration in image quality will not occur even without adjustment for a while. For example, the frequency of adjustment in the image forming unit 3 having a high necessity for adjustment, such as the image forming unit 3 having a high use frequency, can be increased by skipping the adjustment by one or more rounds. Also, when starting up after turning on the main power, when printing a predetermined number of times from the previous adjustment, at the start of image formation, when there is no instruction for image formation after completion of image formation, etc. Since the adjustment is performed when there is a large change with time, or when the user is not using or cannot use, there is no decrease in convenience for the user and productivity of the image forming apparatus.

  Next, another embodiment will be described. In the above-described embodiment, the developing roller 81 is used at the time of adjusting the AC voltage (and at the time of initial setting) and at the time of image formation because of the characteristic of the photosensitive drum 9 that a large current is generated depending on the flow direction of the discharge current. The case where the magnitudes of the alternating voltages applied to are not the same has been described as an example. However, the AC voltage applied at the time of image formation may be set as an initial setting value, and may be applied at the time of adjustment to detect whether or not a discharge occurs, and the AC voltage may be adjusted depending on the presence or absence of the detection. In this case, conversion work using a table or the like can be eliminated.

  In the above embodiment, the positively charged photosensitive drum 9 and toner have been described as examples. However, the present invention can also be applied to the case where a negatively charged photosensitive drum 9 and toner are used. In the above embodiment, the order of the image forming unit 3 that adjusts the AC voltage is determined based on both the length of use time and the change of the AC voltage in the previous circumference. The priority order can be set as appropriate (in the above-described embodiment, the AC voltage is preferentially adjusted with respect to the image formation in which the AC voltage has been changed in the previous cycle). Only one of them may be used as a reference. In addition, an example in which the image forming unit 3 to be adjusted is determined every time the adjustment timing is reached has been shown, but when one round is completed, the order of adjustment of the AC voltage in the next round may be determined. good.

  The embodiment of the present invention has been described above, but the scope of the present invention is not limited to this, and various modifications can be made without departing from the spirit of the invention.

  The present invention is applicable to an image forming apparatus that includes a photosensitive drum and a developing roller and applies an AC voltage to the developing roller.

1 is a cross-sectional view illustrating a schematic configuration of a printer according to an embodiment. It is an expanded sectional view of each image forming part concerning an embodiment. FIG. 5 is a configuration diagram around the developing roller regarding application of a developing bias to the developing roller and detection of discharge between the photosensitive drums according to the embodiment. FIG. 3 is a block diagram illustrating an example of a hardware configuration of a printer according to an embodiment. 6 is a flowchart illustrating an example of an initial setting method of an AC voltage applied to the developing roller according to the embodiment. 6 is a timing chart illustrating details of an AC voltage applied to the developing roller according to the embodiment. 6 is a flowchart illustrating an example of control of adjustment of an AC voltage applied to the developing roller according to the embodiment. 6 is a timing chart in adjustment of an AC voltage applied to the developing roller according to the embodiment. 6 is a flowchart illustrating an example of determining the order of image forming units that perform adjustment of an AC voltage according to the embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Printer (image forming apparatus) 3 (3a, 3b, 3c, 3d) Image forming part 34 Memory (a kind of memory | storage part)
81 (81a, 81b, 81c, 81d) Developing roller 86 AC voltage application unit 9 (9a, 9b, 9c, 9d) Photosensitive drum 10 Control unit 12 Storage unit 14 Detection unit

Claims (5)

An AC voltage application unit for carrying a toner image on a peripheral surface of the photoconductive drum, facing the photoconductive drum with a gap provided therebetween, carrying the toner during image formation, and supplying the toner to the photoconductive drum A plurality of image forming units that form toner images of different colors, respectively,
A storage unit for storing data;
A detector for detecting the occurrence of discharge between the developing roller and the photosensitive drum;
A control unit that controls each part of the device and recognizes the occurrence of discharge when the output of the detection unit is input;
The AC voltage application unit and the detection unit are provided for each of the image forming units,
History data indicating usage history of each of the image forming units is stored in the storage unit,
The control unit performs adjustment for determining an AC voltage to be applied to the developing roller at the time of image formation by changing the AC voltage applied to the developing roller and confirming the occurrence of discharge at a predetermined timing,
In one adjustment, control is performed so that the adjustment is performed only on one image forming unit, and the number of one turn in the order of the image forming units to be adjusted is the total number of the image forming units. The order of the image forming units to perform the adjustment is determined so that the adjustment is performed once for each image forming unit during the number of times of the one round, and the order within the one cycle is determined. The order of the image forming units to be adjusted is not fixed.At the time of the second and subsequent adjustments, based on the history data, the image forming unit having a long use time from the previous adjustment to the present time, An image forming apparatus that performs adjustment. The storage unit stores setting data relating to an AC voltage to be first applied to the developing roller according to the magnitude of the AC voltage applied to the developing roller at the time of the adjustment and at the time of image formation.
During the adjustment,
The control unit causes the AC voltage application unit to apply an AC voltage to the developing roller based on the setting data,
When recognizing the occurrence of discharge, the control unit reduces the AC voltage applied to the developing roller during image formation and updates the setting data.
When the occurrence of discharge is not recognized, the control unit increases or maintains the AC voltage applied to the developing roller during image formation, and updates the setting data only when increasing the AC voltage during image formation. The image forming apparatus according to claim 1 . An AC voltage application unit for carrying a toner image on a peripheral surface of the photoconductive drum, facing the photoconductive drum with a gap provided therebetween, carrying the toner during image formation, and supplying the toner to the photoconductive drum A plurality of image forming units that form toner images of different colors, respectively,
A storage unit for storing data;
A detector for detecting the occurrence of discharge between the developing roller and the photosensitive drum;
A control unit that controls each part of the device and recognizes the occurrence of discharge when the output of the detection unit is input;
The AC voltage application unit and the detection unit are provided for each of the image forming units,
The storage unit stores setting data relating to an AC voltage to be first applied to the developing roller according to the magnitude of the AC voltage applied to the developing roller at the time of the adjustment and at the time of image formation.
The control unit performs adjustment for determining an AC voltage to be applied to the developing roller at the time of image formation by changing the AC voltage applied to the developing roller and confirming the occurrence of discharge at a predetermined timing, In one adjustment, control is performed so that the adjustment is performed only on one image forming unit, and the number of one turn in the order of the image forming units to be adjusted is the total number of the image forming units. The order of the image forming units to perform the adjustment is determined so that the adjustment is performed once for each image forming unit during the number of times of the one round, and the order within the one cycle is determined. The order of the image forming units to be adjusted is not fixed, and when the adjustment is performed, the AC voltage application unit applies an AC voltage to the developing roller based on the setting data, and the occurrence of discharge is recognized. The development roller In the case where the setting data is updated and the occurrence of discharge is not recognized, the control unit increases or maintains the AC voltage applied to the developing roller at the time of image formation. The setting data is updated only when the AC voltage at the time of image formation is increased , and the magnitude of the AC voltage applied to the developing roller at the time of image formation is changed by the adjustment at the previous circumference during the adjustment after the second round. If there is, the control unit performs the adjustment from the image forming unit in which the AC voltage applied at the time of image formation is changed. An AC voltage application unit for carrying a toner image on a peripheral surface of the photoconductive drum, facing the photoconductive drum with a gap provided therebetween, carrying the toner during image formation, and supplying the toner to the photoconductive drum A plurality of image forming units that form toner images of different colors, respectively,
A storage unit for storing data;
A detector for detecting the occurrence of discharge between the developing roller and the photosensitive drum;
A control unit that controls each part of the device and recognizes the occurrence of discharge when the output of the detection unit is input;
The AC voltage application unit and the detection unit are provided for each of the image forming units,
The storage unit stores setting data relating to an AC voltage to be first applied to the developing roller according to the magnitude of the AC voltage applied to the developing roller at the time of the adjustment and at the time of image formation.
The control unit performs adjustment for determining an AC voltage to be applied to the developing roller at the time of image formation by changing the AC voltage applied to the developing roller and confirming the occurrence of discharge at a predetermined timing, In one adjustment, control is performed so that the adjustment is performed only on one image forming unit, and the number of one turn in the order of the image forming units to be adjusted is the total number of the image forming units. The order of the image forming units to perform the adjustment is determined so that the adjustment is performed once for each image forming unit during the number of times of the one round, and the order within the one cycle is determined. The order of the image forming units to be adjusted is not fixed, and when the adjustment is performed, the AC voltage application unit applies an AC voltage to the developing roller based on the setting data, and the occurrence of discharge is recognized. The development roller In the case where the setting data is updated and the occurrence of discharge is not recognized, the control unit increases or maintains the AC voltage applied to the developing roller at the time of image formation. The setting data is updated only when the AC voltage at the time of image formation is increased, and at the time of the second and subsequent adjustments, the control unit determines the AC voltage applied at the time of image formation even if the adjustment is performed a predetermined number of times. An image forming apparatus characterized in that the adjustment of the image forming section without change is skipped over one or more rounds. At the start-up after turning on the main power, when a predetermined number of prints have been made since the previous adjustment, at the start of image formation, or when there has been no instruction for image formation after completion of image formation for a predetermined time, or, a plurality of combinations of these times as the execution timing, the control unit, the image forming apparatus according to any one of claims 1 to 4, characterized in that the adjustment.

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