JP7180437B2 - Image forming apparatus and discharge control method - Google Patents

Description

The present invention relates to an image forming apparatus and a discharge control method, and more particularly to an image forming apparatus provided with a high-voltage power supply board used for electrophotographic image formation and a discharge control method in the image forming apparatus.

2. Description of the Related Art Image forming apparatuses such as MFPs (Multi-Functional Peripherals) that form images by electrophotography are equipped with a high-voltage power supply circuit for applying a high voltage during charging, development, and transfer. Conventionally, a circuit that generates a high voltage using an analog signal is used as this high-voltage power supply circuit, and this circuit can output a high voltage with an analog waveform that changes smoothly and has no distortion.

With respect to discharge control using such a high-voltage power supply circuit, for example, Patent Document 1 below discloses that at least an oscillating voltage is applied from an image carrier and a charging bias applying means, and the surface of the image carrier is brought into contact with the above-described discharge voltage. A contact charging member that charges the image carrier to a predetermined potential and an amount of AC discharge current flowing through a minute gap in the vicinity of a charging nip portion between the contact charging member and the image carrier by application of the oscillating voltage is detected. and a control means for controlling the AC voltage applied to the contact charging member so that the amount of the AC discharge current falls within a predetermined set range, the environment in or around the image forming apparatus. and the charging bias applying means switchably generates an oscillating voltage having at least two different waveforms, and the control means is based on the environmental information detected by the environment detecting means. Then, a configuration is disclosed in which the waveform of the oscillating voltage is switched and controlled to be applied to the contact charging member.

Further, Patent Document 2 below discloses a charging mechanism that applies a DC voltage and an AC voltage in a superimposed manner to a charged body to generate discharge between the charged body and the photoreceptor to charge the photoreceptor. and voltage control means for controlling the waveform of the AC voltage, wherein the waveform of the AC voltage has an inflection point at a voltage value smaller than the discharge start voltage, and from the inflection point to the peak voltage of the AC voltage. A charging device is disclosed in which the amount of voltage increase per time until reaching the point of inflection is smaller than the amount of voltage increase per time from the time when the AC voltage is zero to the point of inflection.

Further, Patent Document 3 below discloses a charging device including a charging member facing a latent image carrier and a power supply section for applying an alternating voltage obtained by superimposing a pulsating voltage on a DC voltage to the charging member. The voltage causes positive discharge, which is discharge from the charging member to the surface of the latent image carrier, and reverse discharge, which is discharge from the surface of the latent image carrier to the charging member. Disclosed is a configuration in which the pulse ON time of the voltage component directed to the reverse discharge side with respect to the desired surface potential Vde of the latent image carrier is shortened with respect to the pulse ON time of the voltage component directed to the positive discharge side with respect to the surface potential Vde of the latent image carrier. It is

Japanese Patent Application Laid-Open No. 2005-003728 JP 2018-004714 A JP 2015-165271 A

The above-mentioned Patent Document 1 proposes a method of increasing the current detection sensitivity by changing the shape of the charging voltage waveform when detecting the discharge current of the charging member. It is possible to improve the image quality.

When changing the waveform shape, a high voltage power supply circuit that generates high voltage using a digital signal (digital high voltage power supply circuit) is cheaper than a conventional high voltage power supply circuit that generates high voltage using an analog signal (analog high voltage power supply circuit). Moreover, the shape of the waveform can be changed with a simple configuration. However, in the roller charging method, if the discharge current is excessive, wear of the photoreceptor will be accelerated, shortening the life of the photoreceptor. fine adjustment of the discharge current is necessary in order to cause problems in the image.

If a digital high-voltage power supply circuit is used to generate a high-voltage AC (alternating) waveform in the same way as an analog high-voltage power supply circuit, quantization distortion will occur and the analog signal will be distorted. A current value similar to the discharge current in the case of cannot be obtained. A high-speed CPU (Central Processing Unit) or MPU (Micro-Processing Unit) is required to reduce this quantization distortion, but providing a high-speed CPU or MPU will increase the cost of the high-voltage power supply circuit. I will stay.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and its main object is to increase the discharge current even when a high voltage generated based on a digital signal is applied to a discharge member to generate a discharge. An object of the present invention is to provide an image forming apparatus and a discharge control method that can be controlled accurately.

One aspect of the present invention is a high-voltage power supply board that generates a high voltage based on a digital signal having a waveform obtained by quantizing an analog signal for obtaining a desired discharge current, and applies the high voltage to a discharge member to generate a discharge. obtaining a difference between a discharge current when the high voltage is applied to the discharge member and the desired discharge current, and correcting each voltage value of the digital signal so as to reduce the difference. A correction unit is provided.

One aspect of the present invention is a high-voltage power supply board that generates a high voltage based on a digital signal having a waveform obtained by quantizing an analog signal for obtaining a desired discharge current, and applies the high voltage to a discharge member to generate a discharge. a difference acquisition process for acquiring a difference between a discharge current when the high voltage is applied to the discharge member and the desired discharge current; and a correction process for correcting each voltage value of the digital signal.

According to the image forming apparatus and the discharge control method of the present invention, the discharge current can be accurately controlled even when the high voltage generated based on the digital signal is applied to the discharge member to generate the discharge.

The reason for this is that an image forming apparatus having a high-voltage power supply substrate generates a high voltage based on a digital signal having a waveform obtained by quantizing an analog signal for obtaining a desired discharge current, and applies the high voltage to a discharge member to generate a discharge. 3, the difference between the discharge current when a high voltage is applied to the discharge member and the desired discharge current is obtained, and each voltage value of the digital signal is corrected so that the difference becomes small.

1 is a schematic diagram showing the configuration of an image forming apparatus according to an embodiment of the present invention; FIG. 1 is a block diagram showing the configuration of an image forming apparatus according to one embodiment of the present invention; FIG. 1 is a circuit diagram showing the configuration of a high-voltage power supply board according to one embodiment of the present invention; FIG. FIG. 4 is a circuit diagram showing another configuration of the high-voltage power supply board according to one embodiment of the present invention; It is an example of voltage/current waveforms of an analog high voltage power supply. FIG. 4 is a schematic diagram illustrating discharge control according to an embodiment of the present invention; FIG. 5 is a schematic diagram illustrating another example of discharge control according to one embodiment of the present invention; FIG. 4 is a diagram for explaining discharge control according to an embodiment of the present invention, and is a diagram for explaining a method of predicting discharge start timing from an inflection point of an output current; FIG. FIG. 4 is a diagram for explaining discharge control according to an embodiment of the present invention, and is a diagram for explaining a method of predicting discharge start timing from a voltage waveform and a current waveform; 1 is an example of a digital high-voltage power supply circuit according to an embodiment of the present invention; 4 is a flow chart showing the operation of the image forming apparatus according to one embodiment of the present invention; FIG. FIG. 4 is a waveform diagram of current and voltage in a conventional analog high-voltage power supply; FIG. 4 is a waveform diagram of discharge current and voltage in a conventional analog high voltage power supply; FIG. 2 is a waveform diagram of current and voltage in a conventional digital high voltage power supply; FIG. 4 is a waveform diagram of discharge current and voltage in a conventional digital high voltage power supply;

As described in the background art, an image forming apparatus such as an MFP that forms an image by electrophotography is equipped with a high voltage power supply circuit for applying a high voltage during charging, development, and transfer. can output a high voltage with an analog waveform that changes smoothly and has no distortion.

Here, in order to improve the image quality, it is preferable to be able to change the shape of the charging voltage waveform arbitrarily. Digital high voltage power circuits are cheaper and simpler than conventional analog high voltage power circuits. It is possible to change the shape of the waveform with a simple configuration. However, if a digital high voltage power supply circuit is used to generate a high voltage with an AC (alternating) waveform in the same way as an analog high voltage power supply circuit, quantization distortion will occur. Moreover, if a high-speed CPU or MPU is provided to reduce this quantization distortion, the cost of the high-voltage power supply circuit will increase.

The above quantization distortion will be explained with reference to the drawings. An analog high-voltage power supply circuit uses an analog signal with a waveform whose value changes gently as shown in FIG. It becomes a gentle curve according to the signal, and the current waveform becomes a curve in which the current value increases from the discharge start timing. The portion where the current value increases (the portion marked with + in the figure) becomes the discharge current.

On the other hand, in a digital high-voltage power supply circuit, a digital signal with a jagged waveform whose value changes stepwise as shown in FIG. 14 is used, and this jaggedness becomes quantization distortion. When a high voltage is generated using this digital signal, as shown in FIG. 15, both the voltage waveform and the current waveform reflect this jaggedness. An error occurs depending on the As a result, excessive discharge accelerates wear of the photoreceptor, shortening its life, and insufficient discharge causes image problems because unevenness of the surface potential of the photoreceptor cannot be reduced sufficiently. Let

Therefore, in one embodiment of the present invention, a high voltage is generated based on a digital signal having a waveform obtained by quantizing an analog signal for obtaining a desired discharge current, and the high voltage is applied to the discharge member to generate a discharge. In an image forming apparatus having a power supply board, a difference between a discharge current when a high voltage is applied to a discharge member and a desired discharge current is obtained, and each voltage value of a digital signal is corrected so as to reduce the difference.

Accordingly, even when a high voltage generated based on a digital signal is applied to the discharge member to cause discharge, the discharge current can be accurately controlled.

An image forming apparatus and a discharge control method according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic diagram showing the configuration of the image forming apparatus of this embodiment, FIG. 2 is a block diagram showing the configuration of the image forming apparatus of this embodiment, and FIGS. 3 is a circuit diagram showing the configuration of a power supply substrate; FIG. FIG. 5 shows an example of voltage/current waveforms of an analog high-voltage power supply, and FIGS. 6 and 7 are schematic diagrams for explaining discharge control in this embodiment. 8 and 9 are diagrams for explaining a method of predicting discharge start timing in the discharge control of this embodiment, FIG. 10 is an example of a digital high voltage power supply circuit of this embodiment, and FIG. 4 is a flow chart showing the operation of the image forming apparatus of the example; FIG.

As shown in FIG. 1, the image forming apparatus 10 of this embodiment performs image processing based on image data acquired by reading a document or image data input from an external information device (for example, a client device) via a communication network. It is a device that forms an image by superimposing colors on a sheet of paper. This is a tandem type image forming apparatus in which body drums 83Y, 83M, 83C, and 83K are arranged in series in the running direction of a transfer medium (intermediate transfer belt).

As shown in FIG. 2A, the image forming apparatus 10 includes a control section 20, a high-voltage power supply section 30, a display operation section 40, an image reading section 50, an image processing section 60, a conveying section 70, an image forming section 80, and the like. consists of

The control unit 20 includes a CPU 21, memories such as a ROM (Read Only Memory) 22 and a RAM (Random Access Memory) 23, a storage unit 24 such as a HDD (Hard Disk Drive) and an SSD (Solid State Drive), and a NIC ( network interface card), a network I/F unit 25 such as a modem, and the like. The CPU 21 centrally controls the operation of each part of the image forming apparatus 10 by reading out a program corresponding to the processing contents from the ROM 22 or the storage part 24, developing it in the RAM 23, and executing it. The storage unit 24 stores a program for the CPU 21 to control each unit, information on processing functions of the device itself, image data read by the image reading unit 50, image data input from a client device (not shown), and the like. The network I/F unit 25 connects the image forming apparatus 10 to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network), and exchanges various data with an external information device (for example, a client device). Send and receive.

The high-voltage power supply unit 30 is a circuit that generates a high voltage used for charging, development, and transfer, and supplies an alternating waveform (preferably , a plurality of alternating waveforms) from one output terminal. In particular, in this embodiment, the photosensitive drum is appropriately charged by outputting a high voltage corrected for errors due to quantization distortion to the charging device 84 . A detailed configuration of the high-voltage power supply unit 30 will be described later.

The display operation unit 40 is a pressure-sensitive or capacitive operation unit (touch sensor) in which transparent electrodes are arranged in a grid pattern on a display unit such as an LCD (Liquid Crystal Display) or an organic EL (Electro Luminescence) display. ), and functions as a display unit and an operation unit. The display unit displays various operation screens, image status display, operation status of each function, etc. according to a display control signal input from the control unit 20 . The operation unit receives various input operations by the user and outputs operation signals to the control unit 20 .

The image reading unit 50 includes an automatic document feeder 51 called an ADF (Auto Document Feeder), a document image scanning device (scanner) 52, and the like. The automatic document feeder 51 transports the document placed on the document tray by the transport mechanism and sends it to the document image scanning device 52 . The document image scanning device 52 optically scans the document conveyed onto the contact glass from the automatic document feeder 51 or the document placed on the contact glass, and converts the light reflected from the document into a CCD (Charge Coupled Device). ) The document image is read by forming an image on the light receiving surface of the sensor. An image (analog image signal) read by the image reading section 50 is subjected to predetermined image processing in the image processing section 60 .

The image processing unit 60 includes a circuit that performs analog-to-digital (A/D) conversion processing, a circuit that performs digital image processing, and the like. The image processing section 60 generates digital image data by performing A/D conversion processing on the analog image signal from the image reading section 50 . The image processing unit 60 also analyzes a print job acquired from an external information device (for example, a client device), rasterizes each page of the document, and generates digital image data. Then, the image processing unit 60 performs image processing such as color conversion processing, correction processing (shading correction, etc.), and compression processing on the image data as necessary, and forms the image data after the image processing. Output to unit 80 .

As shown in FIG. 1, the transport unit 70 is configured by a paper feeding device 71, a transport mechanism 72, a paper discharging device 73, and the like. In this embodiment, the paper feeder 71 has three paper feed tray units. In these paper feed tray units, standard paper and special paper identified based on the basis weight, size, etc. of the paper are accommodated for each preset type. Sheets of paper stored in the paper feed tray unit are sent out one by one from the top and conveyed to the image forming section 80 by a conveying mechanism 72 having a plurality of conveying rollers such as registration rollers. At this time, the inclination of the fed paper is corrected and the transport timing is adjusted by a registration section provided with registration rollers. Then, the paper on which the image is formed by the image forming section 80 is discharged to a paper discharge tray outside the machine by a paper discharge device 73 having a paper discharge roller.

As shown in FIGS. 1 and 2C, the image forming unit 80 includes exposure devices 81 (81Y, 81M, 81C, 81K) provided corresponding to different color components Y, M, C, and K, Developing devices 82 (82Y, 82M, 82C, 82K), photosensitive drums 83 (83Y, 83M, 83C, 83K), charging devices 84 (84Y, 84M, 84C, 84K), cleaning devices 85 (85Y, 85M, 85C, 85K), primary transfer rollers 86 (86Y, 86M, 86C, 86K), an intermediate transfer unit 87, a fixing device 88, and the like. In the following description, symbols other than Y, M, C, and K are used as necessary.

The photoreceptor drums 83 for the respective color components Y, M, C, and K are provided with an organic photoreceptor layer (OPC) provided with an overcoat layer as a protective layer on the outer peripheral surface of a cylindrical metal substrate made of an aluminum material. image carrier. The photosensitive drum 83 is rotated counterclockwise in FIG. 1 by being driven by an intermediate transfer belt, which will be described later, while being grounded.

The charging device 84 for each of the color components Y, M, C, and K is, for example, a charging roller type. It is arranged close to the corresponding photoreceptor drum 83, and applies a uniform potential to the surface of the photoreceptor drum 83 by applying a high voltage to the charging member. At the time of this charging, the high voltage power supply unit 30 outputs a high voltage corrected for errors due to quantization distortion.

The exposure device 81 for each of the color components Y, M, C, and K performs scanning parallel to the rotation axis of the photosensitive drum 83 by using, for example, a polygon mirror, and exposes the uniformly charged surface of the corresponding photosensitive drum 83. An electrostatic latent image is formed by performing imagewise exposure based on image data.

The developing device 82 for each of the color components Y, M, C, and K accommodates a two-component developer composed of a small particle size toner of the corresponding color component and a magnetic substance, and the toner is applied to the surface of the photosensitive drum 83 . Then, the electrostatic latent image carried on the photosensitive drum 83 is visualized with toner. During this development, a high voltage corrected for errors due to quantization distortion is output from the high voltage power supply unit 30 as required.

The primary transfer rollers 86 for the respective color components Y, M, C, and K press the intermediate transfer belt against the photoreceptor drum 83 to sequentially superimpose the respective color toner images formed on the corresponding photoreceptor drums 83 to primary transfer onto the intermediate transfer belt. to transcribe. During this primary transfer, a high voltage corrected for errors due to quantization distortion is output from the high voltage power supply unit 30 as required.

The cleaning device 85 for each color component Y, M, C, and K collects residual toner remaining on the corresponding photosensitive drum 83 after the primary transfer. A lubricant application mechanism (not shown) is provided adjacent to the cleaning device 85 on the downstream side of the photosensitive drum 83 in the rotation direction, and applies the lubricant to the photosensitive surface of the corresponding photosensitive drum 83 . there is

The intermediate transfer unit 87 includes an endless intermediate transfer belt 87a as an image bearing member, a support roller 87b, a secondary transfer roller 87c, a separating device (not shown), an intermediate transfer cleaning section 87d, and the like. An intermediate transfer belt 87a is stretched around 87b. When the intermediate transfer belt 87a on which the toner images of each color are primarily transferred by the primary transfer rollers 86Y, 86M, 86C, and 86K is pressed against the sheet by the secondary transfer roller 87c, a pressure contact portion (called a secondary transfer nip portion) is formed. , the toner image is secondarily transferred onto the paper and sent to the fixing device 88 . A separating device (for example, a sawtooth-shaped charge removing needle extending in the axial direction of the secondary transfer roller 87c) is installed downstream of the secondary transfer nip (downstream in the paper conveying direction). The intermediate transfer cleaning section 87d has a belt cleaning blade (BCL blade) that slides on the surface of the intermediate transfer belt 87a. Transfer residual toner remaining on the surface of the intermediate transfer belt 87a after the secondary transfer is scraped off and removed by the BCL blade. During the secondary transfer and paper separation, the high voltage power supply unit 30 outputs a high voltage corrected for errors due to quantization distortion, if necessary.

The fixing device 88 includes a heating roller 88a and a fixing roller 88b serving as heat sources, and a fixing belt 88c and a pressure roller 88d that are stretched over these rollers. The pressure contact portion constitutes a nip portion. Then, the fixing belt 88c heated by the heating roller 88a and the rollers heat and press the paper passing through the nip portion to fix the unfixed toner image formed on the paper.

Then, the paper on which the toner image is fixed by the fixing device 88 is discharged to a paper discharge tray outside the machine by a paper discharge device 73 having a paper discharge roller.

Next, the configuration of the high-voltage power supply section 30 will be described with reference to FIGS. 2(b) and 3. FIG. In a normal high-voltage power supply circuit, output control is performed using a part of the functions of the CPU that performs overall control of the device (especially engine control). Since the board and the high voltage power supply board on which the high voltage power supply circuit is formed are separated, the wiring path between the boards may become long. Therefore, components are arranged to reliably transmit signals, but these components cause signal delays. In particular, high-voltage output needs to be switched at higher speeds in order to handle recent device speed improvements and a wide variety of paper types. However, there may be cases where the requested switching cannot be performed. Further, as the structure of the image forming apparatus becomes more complicated in recent years due to the multifunctionality of the image forming apparatus, the wiring becomes more complicated. Therefore, in this embodiment, a CPU is arranged in the high-voltage power supply board so that a desired waveform can be output by a control signal generated by this CPU.

Specifically, as shown in FIG. 3, the high-voltage power supply section 30 of this embodiment includes a CPU 31, a memory 32, a drive amplifier section 33, a switch element 34, an LR circuit 35, and a transformer (converter) on a high-voltage power supply board 30a. ) 36 and the like.

The memory 32 stores a waveform digital signal (PWM (Pulse Width Modulation) data) obtained by quantizing an analog signal for obtaining a desired discharge current. The CPU 31 reads the PWM data stored in the memory 32. Output as a PWM signal (control signal). The drive amplifier unit 33 amplifies the PWM signal output from the CPU 31 and outputs the amplified signal to the switch element 34 . The switch element 34 is a push-pull circuit (pure complementary class B push-pull circuit) and alternately changes the current polarity of the PWM signal.

The LR circuit 35 is a circuit including resistors, capacitors, etc., converts the signal output from the switch element 34 into a waveform, and outputs the waveform to the transformer 36 . The primary side coil (driving coil) and the secondary side coil (high voltage generating coil) of the transformer 36 are insulated, and the waveform output from the LR circuit 35 is amplified according to the turn ratio, It outputs to the image forming section 80 (particularly, the charging device 84).

In the above configuration, by outputting a PWM signal with a varied duty ratio from the CPU 31, a high voltage with an arbitrary alternating waveform (for example, a sine wave or a trapezoidal wave) can be output.

Further, the CPU 31 of the high-voltage power supply unit 30 functions as a correction unit 31a and a discharge start voltage specifying unit 31b.

The correction unit 31a acquires the difference between the discharge current when the high voltage generated based on the digital signal is applied to the discharge member and the desired discharge current, and adjusts each voltage of the digital signal so that the difference becomes small. Correct the value. At that time, each voltage value of the digital signal corresponding to the high voltage equal to or higher than the discharge start voltage may be corrected. Also, a predetermined correction value may be thinned out in order from a relatively low voltage value, and the voltage value of the digital signal corresponding to the peak voltage of discharge may not be corrected. Then, if the difference does not become equal to or less than the threshold value even after thinning out the predetermined correction value from all the voltage values, the predetermined correction value can be thinned out again in order from the relatively low voltage value. Further, the correction unit 31a can change the predetermined correction value according to the peak value of the digital signal and/or the frequency of the digital signal.

The discharge start voltage specifying unit 31b specifies the discharge start voltage based on the inflection point of the discharge current.

The high-voltage power supply unit 30 may have any structure as long as it can output a high voltage with an alternating waveform. For example, in FIG. 3, the control signal is output from the CPU 31 in the high-voltage power supply board 30a, but as shown in FIG. A control signal may be output from the control board to the high voltage power supply board 30a on which the high voltage power supply circuit is formed. In that case, components (output amplifier, filter, etc.) are arranged to ensure signal transmission.

The correction processing of the correction section 31a will be described below with reference to the drawings.

FIG. 5 is a waveform diagram of an analog signal for obtaining a desired discharge current, and FIG. 6 is a waveform diagram of a digital signal obtained by quantizing this analog signal. In this embodiment, in order to match the current that flows when a high voltage is generated based on a digital signal to the current that flows when a high voltage is generated based on an analog signal, a predetermined voltage value is determined from each voltage value of the digital signal. Each voltage value is corrected by, for example, thinning out the correction value.

Specifically, as shown in FIG. 6B, which is an enlarged right end of FIG. 6A, a predetermined correction value (for example, a voltage value of 1 dgt) is thinned out. Then, the analog waveform current (average value or integral value) is compared with the corrected digital waveform current (average value or integral value). ), a predetermined correction value is thinned out from the next voltage value (here, the voltage value of (2)). Then, even if this process is repeated up to a high voltage value (here, the voltage value of (n)), if the difference does not become equal to or less than the threshold value, the voltage value returns to a relatively low voltage value (the voltage value of (1) above). Then, a predetermined correction value is further thinned out. Then, when the difference becomes equal to or less than the threshold value, the corrected voltage value is converted into the duty of the PWM signal and stored in the memory 32 as a table.

Also, in FIG. 6, each voltage value of the entire digital voltage waveform is corrected, but each voltage value of the digital signal corresponding to the high voltage equal to or higher than the discharge start voltage may be corrected.

Specifically, as shown in FIG. 7, a predetermined correction is made from a relatively low voltage value (here, the voltage value of (k)) among the voltage values corresponding to the high voltage equal to or higher than the discharge start voltage of the digital voltage waveform. Decimate a value (for example, a voltage value of 1 dgt). Then, the analog waveform current (average value or integral value) is compared with the corrected digital waveform current (average value or integral value), and if the difference exceeds a predetermined threshold, the next voltage value A predetermined correction value is thinned out from (here, the voltage value of (k+1)). Then, even if this process is repeated up to a high voltage value (here, the voltage value of (n)), if the difference exceeds the threshold, the voltage value corresponding to the high voltage equal to or higher than the firing voltage is relatively After returning to the low voltage value (the voltage value of (k) above), a predetermined correction value is further thinned out. Then, when the difference becomes equal to or less than the threshold, the corrected voltage value is stored in the table.

In the case of the correction process of FIG. 7, it is necessary to specify the discharge start voltage, but the discharge start voltage can be predicted by the following first to third methods.

The first method is a method of prediction from the inflection point of the output current. For example, a circuit for monitoring the output current (the sum of the discharge current and the induced current) is formed in the high-voltage power supply circuit, and the discharge start voltage specifying unit 31b detects the difference between the output voltage and the output current as shown in FIG. From the correlation, a voltage value (inflection point A, 1 kV here) at which the output current changes greatly with respect to the output voltage is obtained, and that voltage value is specified as the discharge start voltage.

A second method is a method of prediction from a voltage waveform and a current waveform. For example, the discharge start voltage specifying unit 31b acquires a voltage waveform and a current waveform as shown in FIG. The time up to the point C where the voltage value reaches the maximum) is acquired, and the voltage before the point where the voltage value reaches the maximum by the above time is specified as the firing voltage.

A third method is a method of prediction from the value of the atmospheric pressure sensor. For example, the image forming apparatus is provided with a sensor for measuring atmospheric pressure and stores a table that associates atmospheric pressure with discharge voltage. Obtain the corresponding discharge voltage and identify this voltage as the firing voltage.

When the output current is measured by the first method or the second method, a discharge current measuring circuit 37 is formed as shown in FIG. , a current value that is the sum of the discharge current and the induced current can be obtained.

Next, the operation of the image forming apparatus 10 (high-voltage power supply unit 30) of this embodiment will be described with reference to the flowchart of FIG. It is assumed that the desired discharge current is stored in the memory 32 in advance. Also, here, the case of correcting the voltage value of the digital signal corresponding to the high voltage equal to or higher than the discharge start voltage will be described.

First, the high-voltage power supply unit 30 generates a high voltage based on a digital signal and outputs it to the charging device 84 (S101), and the discharge current measuring circuit 37 acquires the current flowing through the charging device 84 (S102). Then, the CPU 31 (discharge start voltage specifying unit 31b) specifies the discharge start voltage using the first method or the second method (S103).

Next, the CPU 31 (correction unit 31a) corrects the voltage value of the digital signal by, for example, thinning out a predetermined correction value from the voltage value equal to or higher than the discharge start voltage and close to the discharge start voltage (S104). For example, when the difference (pp voltage) between the maximum voltage value and the minimum voltage value is represented by 256 bits, the voltage value is corrected by thinning out the correction value for 1 bit from each voltage value. This predetermined correction value can be changed according to the peak value of the digital signal and/or the frequency of the digital signal. can be

Then, the CPU 31 (correction unit 31a) generates a discharge current (average value or integral value) when a high voltage is applied based on the corrected digital signal, and a desired discharge current (average value) stored in the memory 32 in advance. value or integrated value) is less than or equal to a predetermined threshold value (S105), and if the difference is less than or equal to the threshold value (Yes in S105), a series of correction processing ends.

On the other hand, if the difference exceeds the threshold (No in S105), the CPU 31 (correction unit 31a) determines whether the voltage value to be corrected next is the maximum voltage value (S106), If (No in S106), after correcting the next voltage value (S107), the process returns to S105 to determine whether the difference is equal to or less than the threshold. If it is the maximum voltage value (Yes in S106), the process returns to S104, and the voltage values are again corrected in order from the closest to the discharge start voltage.

Thus, by correcting each voltage value of the digital signal of the digital high voltage power supply circuit so that the discharge current is the same as that of the analog high voltage power supply circuit, it is possible to correct minute current differences.

It should be noted that the present invention is not limited to the above embodiments, and its configuration and control can be modified as appropriate without departing from the gist of the present invention.

For example, in the above embodiment, discharge control in the charging device 84 of the image forming apparatus 10 has been described. can be applied as well.

INDUSTRIAL APPLICABILITY The present invention can be used for an image forming apparatus equipped with a high-voltage power supply board used for electrophotographic image formation and a discharge control method for the image forming apparatus.

10 image forming apparatus 20 control section 21 CPU
22 ROMs
23 RAM
24 storage unit 25 network I/F unit 30 high-voltage power supply unit 30a high-voltage power supply board 31 CPU
31a correction unit 31b discharge start voltage identification unit 32 memory 33 drive amplifier unit 34 switch element 35 LR circuit 36 transformer 37 discharge current measurement circuit 40 display operation unit 50 image reading unit 51 automatic document feeder 52 document image scanner 60 image processing Section 70 Conveying Section 71 Paper Feeding Device 72 Conveying Mechanism 73 Paper Discharging Device 80 Image Forming Section 81, 81Y, 81M, 81C, 81K Exposure Device 82, 82Y, 82M, 82C, 82K Developing Device 83, 83Y, 83M, 83C, 83K Photoconductor drum 84, 84Y, 84M, 84C, 84K Charging device 85, 85Y, 85M, 85C, 85K Cleaning device 86, 86Y, 86M, 86C, 86K Primary transfer roller 87 Intermediate transfer unit 87a Intermediate transfer belt 87b Support roller 87c Next transfer roller 87d Intermediate transfer cleaning unit 88 Fixing device 88a Heating roller 88b Fixing roller 88c Fixing belt 88d Pressure roller

Claims (16)

An image forming apparatus comprising a high-voltage power supply substrate that generates a high voltage based on a digital signal having a waveform obtained by quantizing an analog signal for obtaining a desired discharge current, and applies the high voltage to a discharge member to generate a discharge,
a correction unit that acquires a difference between the discharge current when the high voltage is applied to the discharge member and the desired discharge current, and corrects each voltage value of the digital signal so that the difference becomes small;
An image forming apparatus characterized by: A discharge start voltage specifying unit that specifies a discharge start voltage,
The correction unit corrects each voltage value of the digital signal corresponding to a high voltage equal to or higher than the discharge start voltage.
2. The image forming apparatus according to claim 1, wherein: The correction unit thins out a predetermined correction value in order from a relatively low voltage value until the difference becomes equal to or less than a predetermined threshold,
3. The image forming apparatus according to claim 1, wherein: The correction unit does not correct the voltage value of the digital signal corresponding to the peak voltage of the discharge.
4. The image forming apparatus according to claim 3, wherein: If the difference does not become equal to or less than the threshold value even after thinning out the predetermined correction value from all voltage values, the correction unit thins out the predetermined correction value again in order from relatively low voltage values.
5. The image forming apparatus according to claim 3, wherein: The correction unit changes the predetermined correction value according to the peak value of the digital signal and/or the frequency of the digital signal,
6. The image forming apparatus according to claim 3, wherein: The waveform is a sine wave or a trapezoidal wave,
7. The image forming apparatus according to claim 1, wherein: The correction of the voltage value by the correction unit is executed by a CPU arranged in the high voltage power supply board,
8. The image forming apparatus according to claim 1, wherein: Discharge control in an image forming apparatus having a high-voltage power supply substrate for generating a high voltage based on a digital signal having a waveform obtained by quantizing an analog signal for obtaining a desired discharge current, and applying the high voltage to a discharge member to generate a discharge. a method,
a difference acquisition process for acquiring a difference between the discharge current when the high voltage is applied to the discharge member and the desired discharge current;
a correction process for correcting each voltage value of the digital signal so that the difference is reduced;
A discharge control method characterized by: executing discharge start voltage identification processing for identifying a discharge start voltage;
In the correction process, each voltage value of the digital signal corresponding to a high voltage equal to or higher than the discharge start voltage is corrected.
10. The discharge control method according to claim 9, characterized by: In the correction process, a predetermined correction value is thinned out in order from a relatively low voltage value until the difference becomes equal to or less than a predetermined threshold,
11. The discharge control method according to claim 9 or 10, characterized in that: In the correction process, the voltage value of the digital signal corresponding to the peak voltage of the discharge is not corrected.
12. The discharge control method according to claim 11, characterized by: In the correction process, if the difference does not become equal to or less than the threshold value even if the predetermined correction value is thinned out from all voltage values, the predetermined correction value is thinned again in order from relatively low voltage values.
13. The discharge control method according to claim 11 or 12, characterized by: In the correction process, the predetermined correction value is changed according to the peak value of the digital signal and/or the frequency of the digital signal,
14. The discharge control method according to any one of claims 11 to 13, characterized in that: The waveform is a sine wave or a trapezoidal wave,
15. The discharge control method according to any one of claims 9 to 14, characterized in that: executing the correction process by a CPU arranged in the high-voltage power supply board;
16. The discharge control method according to any one of claims 9 to 15, characterized in that:

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