JP2010122375A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten the time required until an electric discharge start voltage is detected by making the value of the peak-to-peak voltage of an AC voltage first applied to a developing roller by an AC voltage applying section, when the peak-to-peak voltage is increased step by step be a value corresponding to an input altitude, in detecting an electric discharge. <P>SOLUTION: An image forming apparatus includes: a photoreceptor drum 9; the developing roller 81; a detection section 14 for detecting the generation of the electric discharge between the developing roller 81 and the photoreceptor drum 9; a control section 10; a storage section 12; and an input section for inputting the altitude of an installation place to the apparatus. When the electric discharge is detected, the control section 10 refers to altitude data for setting the peak-to-peak voltage of the AC voltage first applied by the AC voltage applying section 86, when the peak-to-peak voltage is increased step by step, according to the altitude input to the input section and allows the AC voltage applying section 86 to perform application from the AC voltage of the peak-to-peak voltage set in the altitude data. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

  2. Description of the Related Art Conventionally, some image forming apparatuses using toner, such as a copying machine, a printer, and a facsimile machine, are provided with a photosensitive drum and a developing roller facing the photosensitive drum with a gap. Then, for example, a so-called development bias in which direct current and alternating current are superimposed on the developing roller is applied, and the charged toner flies from the developing roller to the photosensitive drum, and the electrostatic latent image on the photosensitive drum is developed and developed. Printing is performed by transferring and fixing the toner image to the paper.

  In order to supply sufficiently charged toner to the photosensitive drum, to secure 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 is 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, which may cause damage such as a minute hole (pinhole) being formed in the photosensitive drum. Therefore, even if the peak-to-peak voltage is increased, it must be kept within a range where no discharge occurs.

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

  Here, the gap length between the developing roller and the photosensitive drum, which is a major factor that determines the potential difference in which discharge occurs, is an error in the installation and installation of the photosensitive drum and the developing roller, and the ideal photosensitive drum and developing roller. The image forming apparatus varies depending on the shape and the like. In addition, the potential difference in which discharge occurs varies under the influence of atmospheric pressure and the like. For this reason, the occurrence of discharge is detected while changing the peak voltage of the AC voltage (switching), such as by gradually increasing the magnitude of the AC voltage applied to the developing roller, and the AC voltage at which the discharge has occurred. Based on the peak-to-peak voltage, the potential difference between the developing roller and the photosensitive drum is grasped, and the AC voltage applied to the developing roller is determined so as to be slightly less than this potential difference during printing.

  If an AC voltage having a large peak-to-peak voltage is suddenly applied to the developing roller, the photosensitive drum may be damaged by discharge. Therefore, for example, the peak-to-peak voltage is increased stepwise (for example, several tens of V) from the lowest value of the peak-to-peak voltage that can be set, and confirmation of whether discharge occurs is repeated. Further, since the photosensitive drum and the developing roller are fluctuated, in order to accurately detect and measure the discharge start voltage, it is necessary to rotate the photosensitive drum and the developing roller a plurality of times during application of the AC voltage. Accordingly, time is required for discharge detection (discharge start voltage detection) due to repeated stepwise increase in the peak-to-peak voltage, multiple rotations of the photosensitive drum, and the like.

  Discharge detection may be performed at the time of inspection on a production line, but if it takes time to detect discharge, there is a problem in terms of productivity and cost. In addition, the discharge detection may be performed at the time of installation at the customer site. However, if the discharge detection takes time, there is a problem that the setup takes time. For example, when a plurality of combinations of photosensitive drums and developing rollers are provided as in the case of a tandem image forming apparatus, in order to shorten the time until the discharge start voltage is detected, the A / D converter or the like is used for discharge detection. A plurality of components and the like may be provided, and the discharge start voltage detection operation may be performed in parallel by a plurality of image forming units. However, this causes a problem that the cost required for the configuration for discharge detection increases.

  Incidentally, when Patent Document 1 is viewed, Patent Document 1 describes that “the maximum potential difference ΔVmax between the leak detection voltage and the surface potential of the image carrier is gradually increased” (Patent Document 1: Claim). 1, paragraph [0015] etc.), there is no description or suggestion for shortening the discharge detection time. Therefore, the invention described in Patent Document 1 cannot solve the above problem.

  In view of the above problems, the present invention inputs the peak-to-peak voltage value of the alternating voltage that is first applied to the developing roller when the alternating voltage application unit increases the peak-to-peak voltage stepwise during discharge detection. It is an object to reduce the time until the detection of the discharge start voltage by setting the value according to the altitude.

  In order to achieve the above object, an image forming apparatus according to a first aspect of the present invention opposes a photoconductor drum with a gap provided between the photoconductor drum and carries toner at the time of image formation. A developer roller to which an AC voltage application unit is connected, a detection unit for detecting occurrence of discharge between the developer roller and the photosensitive drum, and each unit of the apparatus, and the detection unit A controller for recognizing the occurrence of discharge based on the output of the output, a storage unit for storing data, and an input unit for inputting the altitude of the installation location to the apparatus, wherein the AC voltage application unit includes the development unit At the time of discharge detection in which the voltage between the photosensitive drum and the developing roller is detected by gradually increasing the peak-to-peak voltage of the AC voltage applied to the roller, the control unit stores in the storage unit Remembered According to the altitude input to the input unit, referring to altitude data that determines the peak-to-peak voltage of the AC voltage to be applied first when the AC voltage application unit increases the peak-to-peak voltage stepwise, The AC voltage application unit was applied with an AC voltage having a peak-to-peak voltage determined in the altitude data.

  According to this configuration, when the AC voltage application unit increases the peak-to-peak voltage stepwise according to the altitude, not the lowest value of the peak-to-peak voltage that can be set as in the prior art, The peak-to-peak voltage of the alternating voltage applied to is determined. As a result, it is possible to skip the discharge detection operation at the peak-to-peak voltage that does not cause a complete discharge. Accordingly, the discharge start voltage can be detected and measured quickly, and the time required for discharge detection can be shortened.

  Further, in the invention according to claim 2, in the invention according to claim 1, the altitude data is determined such that the peak voltage of the AC voltage is smaller when the altitude is higher than when the altitude is low. It was decided. When the altitude is high, the atmospheric pressure decreases, and discharge tends to occur at a lower voltage than at a low altitude. According to this configuration, when the altitude data is higher than when the altitude is low, an AC voltage is applied. Since the value of the peak-to-peak voltage of the AC voltage applied first by the AC voltage application unit is determined to be small when the unit gradually increases the peak-to-peak voltage, the peak of the AC voltage at which discharge starts It is possible to quickly find the voltage between the two.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, a plurality of combinations of the photosensitive drum, the developing roller, and the detection unit, and an output from any of the detection units are output to the control unit. A switch for selecting whether to transmit to, and the control unit controls the switch to switch the combination for performing the discharge detection, and performs the discharge detection for each of the combinations one by one. did.

  According to this configuration, when a plurality of combinations of photosensitive drums and developing rollers are provided as in a tandem image forming apparatus, even if the discharge start voltage is detected for each combination, the time required for detection is long. It does not reach. Therefore, as in the past, in order to shorten the discharge detection time, for each combination, a plurality of A / D converters for converting the current generated at the time of discharge from an analog value to a digital value are provided. The need for parallel discharge detection is eliminated. That is, the configuration for detecting discharge can be simplified, and an image forming apparatus that is advantageous in terms of cost can be provided.

  According to the image forming apparatus of the present invention, when detecting the discharge, when the AC voltage application unit gradually increases the peak-to-peak voltage, the value of the peak-to-peak voltage of the AC voltage first applied to the developing roller is input. The time until the detection of the discharge start voltage can be shortened by changing the height according to the altitude.

  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. 1 and 2. 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 has an operation panel 1a (corresponding to an input unit) in the upper part of the main body, and a sheet supply unit 2a, a conveyance path 2b, and an image forming unit in the main unit. 3, an exposure device 4, an intermediate transfer unit 5, a fixing device 6 and the like are provided.

  As shown by a broken line in FIG. 1, the operation panel 1 a is a part where the user performs various inputs to give operation instructions to the printer 1. Specifically, the operation panel 1a is provided with a liquid crystal display unit 1b for displaying an operation menu, a selected menu, and the status of the printer 1, and a plurality of operation keys 1c. In connection with the present invention, a person in charge of inspection at the production line or a service person who performs setup at the customer site operates the operation panel 1a to give an instruction to the printer 1 to detect the discharge start voltage, and The altitude at the installation location can be entered.

  The sheet supply unit 2a accommodates various sheets such as copy sheets, OHP sheets, and label sheets, for example, and feeds the sheets to the conveyance path 2b by a sheet feeding roller 21 that is rotated by a drive mechanism (not shown) such as a motor. . The conveyance path 2 b conveys the sheet and guides the sheet from the sheet supply unit 2 a to the discharge tray 22 through the intermediate transfer unit 5 and the fixing device 6. The conveyance path 2b is provided with 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 it 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 a toner image based on image data of an image to be formed. 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 for identifying which image forming unit 3 belongs are omitted unless specifically described (in FIG. 2, the image forming unit 3a (3b, 3c, and 3d are identified by reference numerals a, b, c, and d)

  Each photosensitive drum 9 is rotatably supported, rotates by receiving a driving force from the motor M, and carries a toner image on its peripheral surface. For example, amorphous silicon or the like is formed on the outer peripheral surface of an aluminum drum base. And is driven to rotate counterclockwise at a predetermined speed by a driving device (not shown). Each photosensitive drum 9 of the present embodiment is a positively charged type.

  Each charging device 7 has a charging roller 71 and charges the photosensitive drum 9 with 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 application unit 72 (see FIG. 4), and the surface of the photosensitive drum 9 has a predetermined positive potential (for example, 200V to 300V, dark potential). The charging device 7 may be a device that charges the photosensitive drum 9 using a corona discharge type or a brush.

  Each developing device 8 accommodates 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. The developing roller 81 is opposed to the photosensitive drum 9 while being provided with a predetermined gap (for example, 1 mm or less), carries toner charged during image formation, and is supplied with AC voltage for supplying toner to the photosensitive drum 9. An application unit 86 (see FIG. 3) is connected. Each magnetic roller 82 faces the developing roller 81 and is connected to a magnetic roller bias applying unit 84 (see FIG. 3). By applying a voltage in which a DC voltage and an AC voltage are superimposed by the magnetic roller bias applying unit 84, each magnetic roller 82 is connected. Toner is supplied to the developing roller 81. Each transport member 83 is provided below each magnetic roller 82.

  The roller shafts 811 and 821 of each developing roller 81 and each magnetic roller 82 are fixed and supported by a support shaft member (not shown) or the like. Magnets 813 and 823 extending in the axial direction are attached to the roller shafts 811 and 821 inside the developing rollers 81 and the magnetic rollers 82, respectively. Each developing roller 81 and each magnetic roller 82 have cylindrical sleeves 812 and 822 that cover the magnets 813 and 823, respectively, and at the time of printing or discharge detection, this sleeve 812, 822 is rotated. In the magnet 813 of the developing roller 81 and the magnet 823 of the magnetic roller 82, different polarities face each other at a position where the developing roller 81 and the magnetic roller 82 face each other.

  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, and a thin layer of toner is formed on the developing roller 81. 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 agitates the developer in each developing device 8 and charges the toner by friction between the toner and the carrier (in this embodiment). The toner is positively charged).

  Each cleaning device 32 extends in the axial direction of the photosensitive drum 9 in order to clean the photosensitive drum 9, and removes residual toner and the like by rubbing the surface of the photosensitive drum 9 and the blade 33 formed of resin, for example. A rubbing roller 34 is provided. The blade 33 and the rubbing roller 34 are in contact with the photosensitive drum 9 and scrape off and remove residual toner after transfer. The removed residual toner or the like is also provided above each cleaning device 32 with a neutralization device 31 (for example, an array of LEDs) that performs neutralization by irradiating the photosensitive drum 9 with light.

  An exposure device 4 below each image forming unit 3 is a laser unit that outputs laser light. Based on an input color-separated image signal, laser light (illustrated by a broken line) that is an optical signal is applied to each exposure unit 4. Output to the photosensitive drum 9 and scanning exposure of the charged photosensitive drum 9 is performed to form an electrostatic latent image. For example, the exposure apparatus 4 is provided with a semiconductor laser device (laser diode), a polygon mirror, a polygon motor, an fθ lens, a mirror (not shown), and the like. With this configuration, laser light is irradiated from the exposure device 4 to each photosensitive drum 9, and an electrostatic latent image combined with 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 this case, all lines and all pixels are irradiated with laser light). The exposure device 4 may be composed of a large number of LEDs.

  The exposure device 4 is provided with a light receiving element (not shown) within the irradiation range of the laser light and outside the irradiation range of the photosensitive drum 9. When the laser beam is irradiated, this light receiving element outputs a current (voltage), and this output is input to, for example, a CPU 11 (Central Processing Unit) to be described later as a synchronization signal when detecting the occurrence of discharge. Used (see FIG. 5).

  Returning to FIG. 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 51a to 51d (corresponding to the transfer unit), the intermediate transfer belt 52, and the drive It comprises a 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 connected to a transfer voltage application unit (not shown) for applying a transfer voltage with the endless intermediate transfer belt 52 sandwiched between the photosensitive drums 9 and intermediate transfer of the toner image. Transfer to the belt 52.

  The intermediate transfer belt 52 is made of dielectric resin or the like, is stretched around a driving roller 53 and driven rollers 54, 55, and 56, and is driven to rotate by a driving roller 53 connected to a driving mechanism (not shown) such as a motor M. 1 orbits clockwise in FIG. The driving roller 53 and the secondary transfer roller 57 sandwich the intermediate transfer belt 52 to form a nip (secondary transfer portion). In the toner image transfer, a predetermined voltage is applied to each primary transfer roller 51, and the toner images (black, yellow, cyan, and magenta colors) formed in each image forming unit 3 are sequentially superimposed without deviation. The primary transfer is performed on the intermediate transfer belt 52. The superimposed toner images are transferred onto the sheet by a secondary transfer roller 57 to which a predetermined voltage is applied. Note that the residual toner and the like on the intermediate transfer belt 52 after the secondary transfer are removed by the belt cleaning device 58 and collected.

  The fixing device 6 is disposed downstream of the secondary transfer portion in the sheet conveying direction, and heats and presses the secondary transferred toner image to fix it on the sheet. The fixing device 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, and forms 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, a configuration relating to discharge detection will be described with reference to FIG. FIG. 3 is an explanatory diagram showing a configuration relating to discharge detection according to the embodiment of the present invention.

  However, FIG. 3 shows only one image forming unit 3, and a DC voltage applying unit 85, an AC voltage applying unit 86, a detecting unit 14, and an amplifier 15 are provided for each image forming unit 3. 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 between the image forming units 3. Since each image forming unit 3 is provided with the same components, 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 cap 814, and a sleeve 812 that carries toner. 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, a DC-DC converter or a plurality of paths to output terminals having different output voltages, and the selection of the path is changed between printing 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 (pulsed), and is a circuit that outputs an AC voltage having an average value of the DC voltage output from 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 is a power supply circuit including a plurality of switching elements and the like, and inverts the polarity of the output by switching to output 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 AC voltage is increased / decreased by the DC voltage input from the power supply device 16 (see FIG. 4). The peak value on the positive side and the peak value on the negative side are varied according to instructions 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.

  The AC voltage application unit 86 can include, for example, a boosting circuit such as a boosting transformer inside in the output stage, and the development bias in which the boosted DC and AC are superimposed 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 for detecting the occurrence of discharge between the developing roller 81 and the photosensitive drum 9, and converts the current flowing when the discharge occurs into a voltage signal to detect the occurrence of the discharge (discharge detection signal). ). Then, the detection unit 14 outputs a discharge detection signal to the amplifier 15. The amplifier 15 amplifies the discharge detection signal from the detection unit 14 and outputs it to the CPU 11.

  A switch 17 and an A / D converter 18 are provided between the amplifier 15 and the control unit 10. The switch 17 (multiplexer) receives a discharge detection signal from any one of the plurality of image forming units 3 (in other words, a combination of the photosensitive drum 9, the developing roller 81, the detecting unit 14, and the amplifier 15). This is a circuit for selecting whether to input to the CPU 11. Then, the CPU 11 gives a switch switching signal to the switch 17 and performs control to select a discharge detection signal from the image forming unit 3 that performs discharge detection. In FIG. 3, the conductive wire input from the other image forming unit 3 to the switch 17 is indicated by a broken line.

  With this switch 17, in the printer 1 of the present embodiment, discharge detection is performed after the image forming units 3 are selected one by one. That is, the printer 1 includes a plurality of combinations of the photosensitive drum 9, the developing roller 81, and the detection unit 14, and a switch 17 for selecting which output from the detection unit 14 is transmitted to the control unit 10. The unit 10 controls the switch 17 to switch the combination for performing discharge detection and performs discharge detection for each combination one by one.

  The A / D converter 18 is a circuit that converts the analog output of the amplifier 15 into a digital signal and inputs it to the CPU 11. From the output of the A / D converted detection unit 14 (amplifier 15), the CPU 11 generates the discharge and the magnitude of the generated discharge (the magnitude of the current flowing between the developing roller 81 and the photosensitive drum 9). Can be recognized. In the printer 1 of this embodiment, discharge detection is performed for each image forming unit 3, so that only one A / D converter 18 is required.

  As will be described later, in the printer 1 of the present embodiment, the time required to detect the discharge start voltage per image forming unit 3 is short, so as to shorten the time required to detect the discharge start voltage as in the prior art. It is not necessary to provide a plurality of A / D converters 18 so that the detection of the discharge start voltages of the plurality of image forming units 3 can proceed simultaneously, and the manufacturing cost of the printer 1 can be reduced. The CPU 11 may incorporate an A / D conversion port and circuit. In this case, the A / D converter 18 is unnecessary, but according to the printer 1 of the present embodiment, a plurality of image formations are performed. Since the detection of the discharge start voltage of the unit 3 is performed in parallel, it is not necessary to occupy a plurality of A / D conversion ports of the CPU 11. Furthermore, when there are not enough A / D conversion ports, a plurality of A / D converters 18 may be externally attached. However, in the printer 1 of this embodiment, a plurality of A / D converters 18 are provided. There is no need to attach externally.

  Next, a configuration for applying a voltage to the magnetic roller 82 and the magnetic roller 82 will be described. As described above, while providing a predetermined gap (a magnetic brush is formed in this gap), the magnetic roller 82 is disposed so as to face the developing roller 81 and the axial directions thereof are parallel to each other. The magnetic roller 82 includes a roller shaft 821, a sleeve 822 that carries toner and a carrier, and a cap 824. The roller shaft 821 is inserted through the sleeve 822, and circular caps 824 are fitted to both ends of the sleeve 822. In addition, a magnetic roller bias application unit 84 that applies a voltage (magnetic roller bias) in which a DC voltage and an AC voltage are superimposed to the magnetic roller 82 is connected to the roller shaft 821 of the magnetic roller 82. Then, the magnetic roller bias applying unit 84 applies the magnetic roller bias, so that the charged toner is supplied to the developing roller 81 by electrostatic force.

(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 apparatus and recognizes the occurrence of discharge based on the output of the detection unit 14. 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 various data such as control data in addition to the control program of the printer 1. In the present invention, the storage unit 12 also stores a program for setting the voltage applied to the discharge detection and the developing roller 81 and the like. Further, when the discharge is detected, when the AC voltage application unit 86 gradually increases the peak-to-peak voltage, altitude data that defines the peak-to-peak voltage of the AC voltage that is first applied to the developing roller 81 is also stored in the storage unit 12. Stored (details will be described later).

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

  Further, the control unit 10 is connected to a motor M, and supplies a driving force for rotating each photoconductive drum 9, each developing roller 81, each magnetic roller 82 and the like of each image forming unit 3. Then, the control unit 10 drives the motor M at the time of printing or discharge detection to rotate each of the photosensitive drums 9 described above. Further, the sleeves of the developing roller 81 and the magnetic roller 82 can be rotated using the driving of the motor M.

  The control unit 10 is connected to a user terminal 100 (such as a personal computer) as a transmission source of image data to be printed via the I / F unit 19 (interface unit). The image data is processed, and the exposure device 4 receives the image data and forms an electrostatic latent image on the photosensitive drum 9. The charging voltage application unit 72 is a circuit that applies a charging voltage to the charging roller 71. The user terminal 100 can input the altitude at which the printer 1 is installed, and data indicating the altitude can be sent from the user terminal 100 to the control unit 10 via the I / F unit 19. Accordingly, the I / F unit 19 serves as an input unit for inputting the altitude.

  Further, regarding the present invention, the output of the detection unit 14 (amplifier 15) is input to the control unit 10 (CPU 11). When detecting the discharge, the CPU 11 gives an instruction to stepwise change the peak-to-peak voltage of the AC voltage applied to the developing roller 81 to any AC voltage application unit 86, and the detection unit 14 (selected by the switch 17 ( From the output after the A / D conversion of the amplifier 15), the presence or absence of occurrence of discharge in the image forming unit 3 is detected and the magnitude of the discharge is determined.

(Discharge occurrence detection operation and setting of AC voltage applied to developing roller 81)
Next, an example of the operation for detecting the occurrence of discharge between the photosensitive drum 9 and the developing roller 81 will be described with reference to timing charts shown in FIGS. FIG. 5 is a timing chart for explaining the outline of the discharge occurrence detection operation according to the embodiment of the present invention. FIG. 6 is a timing chart showing an example of an AC voltage applied to the developing roller 81 according to the embodiment of the present invention. This discharge occurrence detection operation is sequentially performed for each image forming unit 3 one by one.

  First, an outline of the discharge occurrence detection operation will be described with reference to FIG. Note that “developing roller (AC)” in FIG. 5 indicates the timing at which the AC voltage applying 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. “Magnetic roller (AC)” indicates the timing at which the magnetic roller bias unit (see FIG. 4) applies an AC voltage to the magnetic roller 82. “Magnetic roller (DC)” indicates the timing at which the magnetic roller bias unit applies a DC voltage to the magnetic roller 82. “Charging roller” indicates the timing at which the charging device 7 charges the photosensitive drum 9. The “synchronization signal” is a synchronization signal output from the light receiving element 46 of the exposure apparatus 4. “Exposure” indicates the exposure (laser beam irradiation) timing of the photosensitive drum 9 in the exposure apparatus 4. “Discharge detection (detector output)” indicates a discharge occurrence detection timing by the detector 14.

<Initial operation>
When the discharge generation detecting operation according to the present invention is started, after the photosensitive drum 9, the developing roller 81, the intermediate transfer belt 52, and the like start rotating, in the initial operation, the developing roller 81 and the magnetic roller 82 are respectively connected to the alternating current. A DC voltage is applied. 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. After this initial operation, a transition is made to the preparation state.

<Preparation state> and <Default measurement>
In the ready state, charging of the photosensitive drum 9 by the charging device 7 is started. Note that the voltage applied to the charging device 7 remains ON until the discharge occurrence detection operation is completed. Further, the peak-to-peak voltage of the AC voltage applied to the developing roller 81 is increased to the peak-to-peak voltage in the default measurement. Note that the peak-to-peak voltage of the AC voltage applied to the developing roller 81 in the default measurement is set to a minimum value that can be set, for example. Next, the process moves to the default measurement and confirms whether or not a discharge is detected. Note that the default measurement is to confirm the occurrence of discharge in a state where no discharge can occur, and is performed for finding abnormalities in the detection unit 14, etc., member installation positions, circuits, and the like. After the default measurement, the condition shifts to the condition change state (first time).

<Condition change state>
When the condition is changed, the peak-to-peak voltage of the AC voltage applied to the developing roller 81 is changed stepwise (for example, increased). Then, in the middle of the condition change state, the synchronization signal that becomes a guide for the start of exposure of the exposure apparatus 4 becomes High. After the synchronization signal is high, the state shifts to the discharge detection state (first time).

<Discharge detection status>
In the discharge detection state (first time), a developing bias is applied to the developing roller 81, and the exposure device 4 continues exposure (exposure of the entire surface of the photosensitive drum 9). 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. Therefore, in the discharge detection state, for example, solid image data is sent from the control unit 10 to the exposure apparatus 4 (solid image data is stored in, for example, the storage unit 12).

  The discharge detection state continues for a certain period of time (for example, 1 second to several seconds), during which the photosensitive drum 9 and the developing roller 81 rotate a plurality of times. Then, in a fixed case, such as when no discharge is detected from the input of the amplifier 15 to the CPU 11, the state shifts to a condition change state. In the condition change state, the control unit 10 instructs the AC voltage application unit 86 again to issue an instruction to change the AC peak-to-peak voltage. Thereby, in the discharge detection state after the next time, basically, the presence or absence of discharge is confirmed in a state where the peak-to-peak voltage of the AC voltage applied to the developing roller 81 is higher than the previous time. In other words, the condition change state and the discharge detection state are repeated until the AC voltage to be discharged is recognized. During the repetition, the peak-to-peak voltage of the AC voltage applied to the developing roller 81 is basically stepwise with a constant step size. Is increased. FIG. 5 shows that the discharge is detected in the nth discharge detection state.

  Next, application of a voltage to the developing roller 81 in the discharge detection state will be described with reference to FIG. In FIG. 6, a timing chart at the time of printing is shown in the upper part, and a timing chart in the discharge detection state is shown in the lower part.

First, the rectangular wave in the timing chart at the time of printing 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 during printing. “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 printing. “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 when the occurrence of discharge is detected indicates the waveform of the developing bias applied to the developing roller 81 when the discharge is detected. “Vdc2” indicates the bias potential of the DC voltage application unit 85 at the time of detection. “V0” indicates the potential (almost 0 V) of the photosensitive drum 9 after exposure 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, at the time of occurrence of discharge, the output control unit 87 sets the output of the DC voltage application unit 85 to be a set value Vdc2 (for example, 100 V to 200 V) for detecting the occurrence of discharge according to an instruction from the CPU 11. Further, in response to an instruction from the CPU 11, the Vpp control unit 88 sets the Vpp2 of the AC voltage output from the AC voltage application unit 86 (Note that the value of Vpp2 changes for each condition change state). 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 is set smaller than the duty ratio D1 at the time of printing (ratio of High time T1 to period T01, T1 / T01) (for example, D1 = 40%, D2 = 30%). Thus, the duty ratio D2 is set because the photosensitive drum 9 of this embodiment has a characteristic that a large current flows when discharge occurs when the potential of the developing roller 81 is low (at the peak of the negative side) ( This is to make the absolute value of the negative peak voltage as small as possible. The frequency f2 is set so that the positive time of the AC voltage is the same at the time of printing and when the occurrence of discharge is detected (ie, T1 = T2. For example, when D1 = 40% and D2 = 30%, printing is performed. If the frequency at the time f1 = 4 kHz, then f2 = 3 kHz). As a result, a positive voltage is applied to the developing roller 81 for the same time as during printing.

(Altitude data)
Next, an example of the altitude data according to the embodiment of the present invention will be described based on FIG. FIG. 7 is an explanatory diagram showing an example of elevation data according to the embodiment of the present invention.

  First, the relationship between discharge and altitude will be described. In the printer 1 of the present embodiment, it is empirically obtained that the discharge start voltage decreases as the altitude increases (lower atmospheric pressure), and the discharge start voltage increases as the altitude decreases (higher atmospheric pressure). Yes. Further, in other image forming apparatuses shipped in the past, it has been empirically obtained that the discharge start voltage decreases as the altitude increases. The direct reason for such characteristics is not completely clear, but there are many dielectrics such as toner and other dusts between the photosensitive drum and the developing roller compared to normal air. As the atmospheric pressure increases, electrons are likely to collide with dust and the like and their molecules many times, and the average energy of electrons decreases and the discharge start voltage decreases.

  Then, as shown in FIG. 5, when detecting the discharge start voltage by gradually increasing the peak-to-peak voltage, discharge is less likely to occur at low altitudes than at high altitudes. If the voltage between the peaks starts to be applied to the developing roller 81, the discharge start voltage can be detected efficiently. In other words, instead of increasing the peak-to-peak voltage from the lowest value of the peak-to-peak voltage of the AC voltage that can be applied by the AC voltage application unit 86 until the discharge occurs, the altitude is skipped by skipping the period during which the peak-to-peak voltage is small If the discharge detection is started from a somewhat higher peak-to-peak voltage than when the voltage is high, the discharge start voltage can be detected without much time.

  On the other hand, when detecting the discharge start voltage by increasing the peak-to-peak voltage step by step, the discharge is detected before the AC peak-to-peak voltage increases so much at a high altitude. However, the discharge start voltage can be detected without much time if it starts to be applied to the developing roller 81 from the peak voltage of the lower AC voltage.

  Therefore, the printer 1 according to the present embodiment accepts the input of the altitude of the installation location of the printer 1 when the discharge is detected. This altitude can be input to the operation panel 1a. In addition, the altitude can be input at the user terminal 100, and the control unit 10 can receive the input altitude as data from the user terminal 100. Then, based on the input altitude, the control unit 10 determines the peak-to-peak voltage of the AC voltage first applied to the developing roller 81 in order to detect the discharge start voltage at the time of discharge detection, and the determined peak The inter-voltage is instructed to the AC voltage application unit 86. Thereby, when the AC voltage application unit 86 increases the peak-to-peak voltage stepwise according to the local altitude where the printer 1 is installed, the peak-to-peak voltage of the AC voltage first applied to the developing roller 81 is increased. Switches.

  Next, determination of the peak-to-peak voltage of the AC voltage to be applied first when the AC voltage application unit 86 increases the peak-to-peak voltage stepwise according to the input altitude will be described with reference to FIG. In other words, the determination of the peak-to-peak voltage of the AC voltage applied to the developing roller 81 in the first discharge detection state will be described. Of the tables shown in FIG. 7, the table TB <b> 1 in (a) is for explaining the concept of determining the peak-to-peak voltage of the AC voltage applied in the first discharge detection state.

  7 (a) is a numerical value indicating an altitude that can be selected by an inspector on the production line or a service person at the installation location. It is. The values of X1 to Xn are displayed on the liquid crystal display unit 1b of the operation panel 1a and the display of the user terminal 100, and the inspector or the like can set the value closest to the altitude of the place where the printer 1 exists to the operation panel 1a or The user terminal 100 selects and inputs. Note that the magnitude relationship in FIG. 7A is X1 <X2 <X3. That is, the altitude is higher as it gets closer to Xn. Further, n of Xn is an arbitrary integer, and can be set as appropriate. The larger the value of n, the finer the peak-to-peak voltage of the AC voltage applied in the first discharge detection state can be determined according to the altitude. .

  The column of the altitude column shown in FIG. 7A (the column in which Y1 to Yn is written) is a numerical value indicating the peak-to-peak voltage of the AC voltage applied in the initial discharge detection state. Here, in the printer 1 of this embodiment, the higher the altitude, the smaller the discharge start voltage. Therefore, the magnitude relationship between Y1 to Yn in FIG. 7A is Y1> Y2> Y3. Become. The table TB1 composed of these X1 to Xn and Y1 to Yn becomes altitude data for determining the peak-to-peak voltage of the AC voltage applied in the initial discharge detection state according to the altitude. The altitude data is stored in the storage unit 12.

  Note that specific values of Y1 to Yn can be determined based on experiments during development. For example, the atmospheric pressure in the room where the plurality of printers 1 are arranged is set to the atmospheric pressure at each altitude (for example, the atmospheric pressure or the average atmospheric pressure in fine weather), and the discharge start voltage is detected. Then, among the detected discharge start voltages at the respective altitudes, a peak-to-peak voltage lower by about several tens to several hundreds V than the reference value can be determined as Y1 to Yn with the lowest value as a reference.

  Specifically, when detecting the discharge start voltage, the inspector or the like, for example, if the local altitude is 0 ≦ X1 <(X1 + X2) / 2, X1 and (X1 + X2) / 2 ≦ X2 <(X2 + X3). ) / 2, select the closest altitude value displayed on the operation panel 1a or the like and input it as X2. The control unit 10 refers to the altitude data in the storage unit 12 and determines the peak-to-peak voltage of the AC voltage to be applied in the first discharge detection state according to the selected input altitude, and the peak-to-peak voltage is determined as the AC voltage application unit. 86.

  FIG. 7B shows an example of more specific elevation data (table TB2). In the example shown in FIG. 7, the altitude is determined in increments of 500 m. For example, if the installation location of the printer 1 is 0 m to less than 250 m, the inspector selects the nearest altitude 0 m displayed on the operation panel 1 a or the like. Thereby, the control part 10 determines the peak-to-peak voltage of the alternating voltage applied in the first discharge detection state as 1200V.

(Flow of control of discharge occurrence detection operation)
Next, an example of the control flow of the discharge occurrence detection operation of the printer 1 according to the embodiment of the present invention will be described with reference to FIGS. FIG. 8 is a flowchart showing an example of the control flow of the discharge occurrence detection operation of the printer 1 according to the embodiment of the present invention. Note that this flowchart is a control for one image forming unit 3 and is repeated four times in the present embodiment when all colors are used. FIG. 9 is an explanatory diagram showing an example of a table TB3 for determining the peak-to-peak voltage of the AC voltage applied to the developing roller 81 according to the embodiment of the present invention when discharge is detected.

  This discharge occurrence detection operation is performed, for example, at the time of manufacturing as initial defect detection or initial setting, at the time of installation of the printer 1, or at the time of replacement of the developing device 8 or the photosensitive drum 9. 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. Note that the present invention is not limited to the above example. For example, it may be performed every time the printer 1 prints a certain number of sheets, and the execution timing can be set as appropriate.

  First, when a predetermined operation is performed on the input unit of the operation panel 1a and the discharge generation detection operation is started (start), the input unit of the operation panel 1a determines whether or not the altitude is input at the place where the printer 1 is installed. Confirm (step S1). If there is no altitude input (No in step S1), the standby state is continued until an altitude is input (loop in step S1).

  On the other hand, if there is an altitude input (Yes in step S1), an image of the photosensitive drum 9, the developing roller 81, the magnetic roller 82, the intermediate transfer belt 52, and the like by the motor M or a driving mechanism (not shown) is instructed by the CPU 11. The rotation of various rotating bodies in the forming unit 3 and the intermediate transfer unit 5 is started (step S2). The driving of each rotating body is continued until the discharge occurrence detecting operation is completed. Next, the initial operation described in FIG. 5 is performed (step S3). Next, the process proceeds to the preparation state described with reference to FIG. 5 (step S4). For example, the charging voltage application unit 72 starts voltage application to the charging device 7 in accordance with an instruction from the CPU 11.

  Next, the default measurement described in FIG. 5 is performed (step S5). At this time, it is confirmed whether or not the occurrence of discharge has been detected (step S6). This default measurement is performed in a state in which no discharge is generated. If the occurrence of discharge is detected in the default measurement (Yes in step S6), an abnormality in the gap length or an abnormality in the detection unit 14 or the like can be considered. In this case, an error is displayed on the operation panel 13 or the like (step S7), and the discharge occurrence detection operation is ended (END).

  On the other hand, if no signal indicating that a discharge has occurred is input to the CPU 11 (No in step S6), it is confirmed whether the next discharge detection state is the first one (step S8). In other words, it is confirmed whether the next development bias application is applied first when the AC voltage application unit 86 gradually increases the peak-to-peak voltage in order to detect the discharge start voltage.

  If it is the first one (Yes in step S8), the control unit 10 refers to the altitude data in the storage unit 12 and shifts to the input altitude when the condition change state described in FIG. The AC voltage application unit 86 is instructed to determine the peak-to-peak voltage of the AC voltage to be applied to the developing roller 81 in the first discharge detection state and output the determined peak-to-peak voltage. Thereby, the peak-to-peak voltage of the AC voltage to be applied to the developing roller 81 in the initial discharge detection state is set based on the altitude data (step S9).

  That is, the AC voltage application unit 86 increases the peak-to-peak voltage of the AC voltage applied to the developing roller 81 in a stepwise manner, and detects the voltage at which discharge occurs between the photosensitive drum 9 and the developing roller 81. When the AC voltage application unit 86 increases the peak-to-peak voltage step by step according to the altitude stored in the storage unit 12 and input to the operation panel 1 a or the I / F unit 19. The altitude data that determines the peak-to-peak voltage of the AC voltage to be applied first is referred to, and the AC voltage applying unit 86 is applied from the AC voltage of the peak-to-peak voltage determined in the elevation data. As described above, the altitude data has a smaller peak-to-peak voltage value when the altitude is higher than when the altitude is low.

  On the other hand, if it is in the second or subsequent discharge detection state (No in step S8), the process shifts to the condition change state described in FIG. 5, and the Vpp control unit 88 outputs the AC voltage application unit 86 in response to an instruction from the CPU 11. Settings are made to increase the peak-to-peak voltage of the AC voltage by a predetermined step ΔVa (for example, 30 to 100 V, for example) from the previous value (step S10).

  9, the AC voltage application unit 86 applies a peak-to-peak voltage of 600 V to the developing roller 81 in the initial discharge detection state, and the photosensitive drum 9 and the developing roller 81 are rotated a plurality of times. If no discharge is detected even after rotation, in the next discharge detection state, an AC voltage having a peak-to-peak voltage of 700 V increased by ΔVa (ΔVa = 100 V in the example of FIG. 9) is supplied to the AC voltage application unit. 86 is applied to the developing roller 81. In other words, until the first discharge is detected, the peak-to-peak voltage of the AC voltage applied to the developing roller 81 is switched for each discharge detection state from the top to the bottom of the column (1) in FIG. It is done.

  The table TB3 shown in FIG. 9 has a number of stages (1 to n stages). However, in the printer 1 of this embodiment, the stage is switched in the first discharge detection state depending on the input altitude, and the AC voltage is changed. The peak-to-peak voltage applied to the developing roller 81 by the application unit 86 changes. For example, 600V (first stage shown in FIG. 9) at an altitude of 3000 m, 700V (second stage shown in FIG. 9) at an altitude of 2500 m, and the first discharge detection state depending on the altitude. The peak-to-peak voltage of the AC voltage applied to the developing roller 81 changes.

  Next, after step S9 and step S10, the state shifts to a discharge detection state, and a developing bias is applied to the developing roller 81 by the AC voltage applying unit 86 and the DC voltage applying unit. Specifically, a set AC voltage or the like is applied to the developing roller 81, and exposure is performed in accordance with an instruction from the CPU 11. During that time, the CPU 11 counts the number of times that the output voltage of the amplifier 15 exceeds a predetermined threshold (step). S11).

  Then, it is confirmed whether the count number is 0 (step S12). If it is 0 (Yes in step S12), the maximum value (for example, 1500 to 3000 V) at which the current peak-to-peak voltage can be set as no discharge is generated. ), The CPU 11 confirms whether it has reached (step S13). If it has reached (Yes in step S13), the process proceeds to step S14 (details will be described later). If not reached (No in step S13), the process returns to step S8.

  If the count value is 1 or more in step S12 (No in step S12), the discharge voltage is generated and the Vpp control unit 88 (FIG. 3) applies the AC voltage application unit 86 to the developing roller 81 in accordance with the instruction from the CPU 11. The peak-to-peak voltage of the AC voltage is decreased by a predetermined step size ΔVa from the value of the peak-to-peak voltage applied immediately before (step S15), and further set to a value increased by a predetermined step size ΔVb (step S16). . Here, the predetermined step width ΔVb can be obtained by dividing the predetermined step width ΔVa (for example, ΔVb = 10V if ΔVa = 50V, ΔVb = 20V if ΔVa = 100V, etc.). In other words, in order to find the peak-to-peak voltage at which discharge occurs more finely, the step size is stepped back and the step size of the step-by-step change in the peak-to-peak voltage is reduced.

  Here, with reference to FIG. 9, when discharge is detected, the voltage between peaks in the column (1) of the table TB3 is applied to the developing roller 81 to detect discharge, which is applied immediately before. Returning from the stage to which the peak-to-peak voltage belongs, the next step is to switch the peak-to-peak voltage of the AC voltage applied to the developing roller 81 in the row direction shown in FIG.

  Taking FIG. 9 as an example, for example, if discharge is detected when a peak-to-peak voltage of 700 V (second stage) is applied to the developing roller 81, the process returns to the first stage and belongs to the first stage. A peak-to-peak voltage (620 V in FIG. 9) having a value determined in the column (2) is applied to the developing roller 81, and the photosensitive drum 9 and the developing roller 81 are rotated a plurality of times to check for the presence of discharge. If no discharge is detected, the next is 640 V defined in the row (3), and further, if no discharge is detected even at 640 V, the peak applied to the developing roller 81 is 660 V defined in the column (4). The AC voltage application unit 86 changes the inter-voltage. As described above, until the discharge is detected, the AC voltage application unit 86 switches the peak-to-peak voltage in units of ΔVb in the horizontal direction of FIG. 9. If the discharge is detected, the peak-to-peak voltage at the time of discharge detection is changed. The controller 10 recognizes the discharge start voltage.

  After that, as in step S11, the discharge detection state is set, and the CPU 11 counts the number of times that the output voltage of the amplifier 15 exceeds a predetermined threshold (step S17). In other words, if a discharge is detected during the stepwise change of the peak-to-peak voltage at the step size ΔVa, the discharge is detected at the step size ΔVb in order to obtain a more detailed peak-to-peak voltage at which discharge occurs. Until this occurs, the discharge detection state and the condition change state are repeated.

  Next, it is confirmed whether the count number is 0 (step S18). If the count is 0 (Yes in step S18), the current peak-to-peak voltage is changed to the peak-to-peak voltage at which discharge is detected first as no discharge occurs. The CPU 11 confirms whether it has reached (step S19). If it has reached (Yes in step S19), the process proceeds to step S14. If not reached (No in step S19), the process returns to step S16. On the other hand, if the count value is 1 or more (No in step S18), the CPU 11 determines that a discharge occurs at the current peak-to-peak voltage, and proceeds to step S14.

Next, step S14 will be described in detail. When the discharge is detected (No in step S18, Yes in step S19), or even when the maximum peak-to-peak voltage that can be set cannot be detected (Yes in step S13), the CPU 11 determines the maximum peak-to-peak voltage or discharge. From the peak-to-peak voltage Vpp2, the frequency f2, the duty ratio D2, and the bias setting value Vdc2 that are recognized to occur, the potential difference V ₊₂ shown in FIG. 6 (photosensitive drum when discharging is detected or when Vpp2 is applied at the maximum settable value) 9 and the developing roller 81 are obtained (step S14).

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. Then, based on the duty ratio D2 as a set value and Vdc2 as a reference, the positive side area and the negative side area are made equal to obtain the positive side peak value of Vpp2 and the potential difference between Vdc2. If this potential difference is added with the potential difference between Vdc2 and V0 (V0 is almost 0 V, it can be treated as Vdc2), V ₊₂ is obtained.

Specifically, Vpp2 during the discharge occurrence detection operation is changed in stages. Therefore, if the duty ratio D2 and the bias setting value Vdc2 are constant, V ₊₂ is calculated in advance according to the size of each Vpp2. In addition, 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 causes the developing roller 81 to perform printing so that V ₊₁ and V ₋ shown in FIG. 6 are smaller than the obtained V _+2. A peak-to-peak voltage Vpp1 of the AC voltage to be applied is set (step S20). Specifically, a method determining the Vpp1 are diverse, for example, V ₊₁ and V _- than the V _+2, or discharge if much smaller does not occur (or to take much margin), the toner used Based on the experiment at the time of development, for example, for the obtained V ₊₂ , the value of Vpp1 that is recognized that no discharge occurs during printing is tabulated, the CPU 11 refers to the table, and Vpp1 is It may be determined. This table may also be stored in the storage unit 12. Thereby, it is possible to apply an AC voltage as large as possible without causing discharge during printing. When the setting of Vpp1 is completed, the detection of occurrence of discharge and the setting of Vpp1 at the time of printing for one image forming unit 3 are completed (END).

  Thus, according to the configuration of the present embodiment, the AC voltage application unit 86 increases the peak-to-peak voltage stepwise in accordance with the altitude, not from the lowest value of the peak-to-peak voltage that can be set as in the prior art. When this is done, the peak-to-peak voltage of the AC voltage that is first applied to the developing roller 81 is determined. As a result, it is possible to skip the discharge detection operation at the peak-to-peak voltage that does not cause a complete discharge. Accordingly, the discharge start voltage can be detected and measured quickly, and the time required for discharge detection can be shortened.

  In addition, when the altitude is high, the atmospheric pressure decreases, and discharge tends to occur at a lower voltage than at a low altitude. According to this configuration, the altitude data is higher when the altitude is higher than when the altitude is low. When the voltage application unit 86 increases the peak-to-peak voltage stepwise, the value of the peak-to-peak voltage of the AC voltage that is first applied by the AC voltage application unit 86 is determined to be small, so that the discharge is started. The peak-to-peak voltage of the AC voltage can be found quickly.

  According to this configuration, when a plurality of combinations of the photosensitive drum 9 and the developing roller 81 are provided as in the tandem image forming apparatus (for example, the printer 1), the discharge start voltage is detected for each combination. However, it does not take a long time for detection. Therefore, as in the prior art, in order to shorten the discharge detection time, each combination is provided with a plurality of A / D converters 18 or the like for converting the current generated during discharge from an analog value to a digital value for each combination. This eliminates the need for parallel discharge detection. That is, the configuration for detecting discharge can be simplified, and an image forming apparatus that is advantageous in terms of cost can be provided.

  Next, another embodiment will be described. In the above-described embodiment, an example in which primary transfer is performed from each photoconductive drum 9 to the intermediate transfer belt 52 and then secondary transfer is performed to the sheet is described. However, a toner image is directly transferred from each photoconductive drum 9 to the sheet. The present invention can also be applied to the configuration (for example, a mode in which a transfer roller is in direct contact with each photoconductor drum 9 and a sheet passes through the nip, or a conveyance belt is in contact with each photoconductor drum 9 and On a conveying belt, and the sheet passes through the nip.

  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 color image forming apparatus has been described. However, the present invention can be applied to, for example, a monocolor image forming apparatus having only the image forming unit 3a (black).

  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, raises a developing bias applied to the developing roller, and detects discharge.

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. It is explanatory drawing which shows the structure regarding the discharge detection which concerns on embodiment. FIG. 3 is a block diagram illustrating an example of a hardware configuration of a printer according to an embodiment. It is a timing chart for demonstrating the outline of the discharge generation detection operation which concerns on embodiment. 6 is a timing chart illustrating an example of an AC voltage applied to the developing roller according to the embodiment. It is explanatory drawing which shows an example of the altitude data which concern on embodiment. 6 is a flowchart illustrating an example of a control flow of a discharge occurrence detection operation of the printer according to the embodiment. It is explanatory drawing which shows an example of the table for determining the peak voltage of the alternating voltage applied to the developing roller which concerns on embodiment at the time of discharge detection.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Printer (image forming apparatus) 1a Operation panel (input part)
3 (3a, 3b, 3c, 3d) Image forming unit 4 Exposure device 8 (8a, 8b, 8c, 8d) Developing device 81 (81a, 81b, 81c, 81d) Developing roller 82 (82a, 82b, 82c, 82d) Magnetic roller 85 DC voltage application unit 86 AC voltage application unit 9 (9a, 9b, 9c, 9d) Photoconductor drum 10 Control unit 11 CPU 11 (part of control unit 10)
12 storage unit 14 detection unit 17 switch 19 I / F unit (input unit)

Claims (3)

A photosensitive drum;
A developing roller that faces the photoconductor drum with a gap, carries a toner during image formation, and is connected to an AC voltage application unit for supplying the toner to the photoconductor drum;
A detecting unit for detecting 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 based on the output of the detection unit;
A storage unit for storing data;
An input unit for inputting the altitude of the installation location to the device,
When the AC voltage application unit detects the voltage at which discharge occurs between the photosensitive drum and the developing roller by gradually increasing the peak-to-peak voltage of the AC voltage applied to the developing roller, during discharge detection,
The control unit is stored in the storage unit, and according to the altitude input to the input unit, when the AC voltage application unit increases the peak-to-peak voltage stepwise, the peak of the AC voltage applied first An image forming apparatus comprising: referring to altitude data that determines an inter-voltage, and causing the AC voltage applying unit to apply an AC voltage of a peak-to-peak voltage determined in the altitude data.   2. The image forming apparatus according to claim 1, wherein the altitude data is such that the value of the peak-to-peak voltage of the AC voltage is smaller when the altitude is higher than when the altitude is low. A plurality of combinations of the photosensitive drum, the developing roller, and the detection unit;
A switch for selecting which output from the detection unit is transmitted to the control unit;
The image according to claim 1, wherein the control unit controls the switch to switch the combination for performing the discharge detection, and performs the discharge detection for each of the combinations one by one. Forming equipment.

Images