JP2020134644A - Image forming apparatus and discharge control method - Google Patents

Abstract

To accurately control a discharge current, even when a high voltage generated based on a digital signal is applied to a discharge member to cause discharge.SOLUTION: An image forming apparatus comprises a high-voltage power substrate that generates a high voltage based on a digital signal having a waveform in which an analog signal for obtaining a desired discharge current is quantized, and applies the high voltage to a discharge member to cause discharge. The image forming apparatus acquires the difference between a discharge current when the high voltage is applied to the discharge member and the desired discharge current, and corrects voltage values of the digital signal so as to reduce the difference.SELECTED DRAWING: Figure 6

Description

The present invention relates to an image forming apparatus and a discharge control method, and more particularly to an image forming apparatus including a high-pressure power supply substrate used for electrophotographic image forming and a discharge control method in the image forming apparatus.

An image forming apparatus such as an MFP (Multi-Functional Peripherals) that forms an image by an electrophotographic method is provided 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 by an analog signal is used as this high voltage power supply circuit, and this circuit can output a high voltage of an analog waveform without distortion in which the voltage value changes gently.

Regarding discharge control using such a high-voltage power supply circuit, for example, in Patent Document 1 below, at least a vibration voltage is applied from the image carrier and the charging bias applying means, and the voltage is brought into contact with the surface of the image carrier to be abutted. A contact charging member that charges the image carrier to a predetermined potential, and an AC discharge current flowing through a minute void near the charging nip between the contact charging member and the image carrier by applying the vibration voltage is detected. In the image forming apparatus provided with the control means for controlling the AC voltage applied to the contact charging member so that the amount of the AC discharging current falls within a predetermined set range, the environment inside or around the image forming apparatus. The charging bias applying means can freely switch between vibration voltages having at least two different waveforms, and the control means is based on the environmental information detected by the environment detecting means. Therefore, a configuration is disclosed in which the waveform of the vibration voltage is switched and controlled so as to be applied to the contact charging member.

Further, Patent Document 2 below describes a charging mechanism in which a DC voltage and an AC voltage are superimposed and applied to a charged body to generate a discharge between the charged body and the photoconductor to charge the photoconductor. A voltage control means for controlling the waveform of the AC voltage is provided, and the waveform of the AC voltage has a turning point at a voltage value smaller than the discharge start voltage, and the peak voltage of the AC voltage is changed from the changing point. A charging device is disclosed in which the amount of voltage increase per hour until the AC voltage is zero is smaller than the amount of voltage increase per time from the time when the AC voltage is zero to the turning point.

Further, Patent Document 3 below describes the alternation in a charging device including a charging member facing the latent image carrier and a power supply unit for applying an alternating voltage obtained by superimposing a pulsating voltage on a DC voltage on the charging member. The voltage causes a normal discharge, which is a discharge from the charged member to the surface of the latent image carrier, and a reverse discharge, which is a discharge from the surface of the latent image carrier to the charged member, and is desired by the latent image carrier. Disclosed is a configuration in which the pulse ON time of the voltage component toward 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 toward the forward discharge side with respect to the surface potential Vde of. Has been done.

Japanese Unexamined Patent Publication No. 2005-003728 JP-A-2018-004714 Japanese Unexamined Patent Publication No. 2015-165271

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, and by arbitrarily changing the shape of the charging voltage waveform. The quality of the image can be improved.

When changing the shape of a waveform, a high-voltage power supply circuit (digital high-voltage power supply circuit) that generates high voltage by a digital signal is cheaper than a high-voltage power supply circuit (analog high-voltage power supply circuit) that generates high voltage by a conventional analog signal. 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, the wear of the photoconductor is promoted and the life is shortened, and if the discharge current is small, the unevenness of the surface potential of the photoconductor cannot be sufficiently reduced. In order to cause problems in the image, it is necessary to adjust the discharge current finely.

When a high voltage with an AC (alternating) waveform is generated using a digital high voltage power supply circuit for this minute discharge current adjustment in the same way as an analog high voltage power supply circuit, quantization distortion occurs and the analog signal It is not possible to obtain the same current value as the discharge current in the case of. Further, in order to reduce this quantization distortion, a high-speed CPU (Central Processing Unit) and MPU (Micro-Processing Unit) are required, but if a high-speed CPU and MPU are provided, the cost of the high-voltage power supply circuit increases. I will be there.

The present invention has been made in view of the above problems, and a main object thereof is to generate a 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 accurately controlled.

One aspect of the present invention is 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. In the image forming apparatus provided, the difference between the discharge current when the high voltage is applied to the discharge member and the desired discharge current is acquired, and each voltage value of the digital signal is corrected so that the difference becomes small. It is characterized by having a correction unit.

One aspect of the present invention is 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 discharge control method in an image forming apparatus provided, which includes a difference acquisition process for acquiring a difference between a discharge current when the high pressure is applied to the discharge member and the desired discharge current, and a difference acquisition process so that the difference becomes small. It is characterized by executing 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 a high voltage generated based on a digital signal is applied to the discharge member to generate a discharge.

The reason is that an image forming apparatus including a high-pressure 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. This is because the difference between the discharge current when a high voltage is applied to the discharge member and the desired discharge current is acquired, and each voltage value of the digital signal is corrected so that the difference becomes small.

It is a schematic diagram which shows the structure of the image forming apparatus which concerns on one Example of this invention. It is a block diagram which shows the structure of the image forming apparatus which concerns on one Example of this invention. It is a circuit diagram which shows the structure of the high voltage power supply board which concerns on one Example of this invention. It is a circuit diagram which shows the other structure of the high voltage power supply board which concerns on one Example of this invention. This is an example of the voltage / current waveform of an analog high-voltage power supply. It is a schematic diagram explaining the discharge control which concerns on one Example of this invention. It is a schematic diagram explaining another example of discharge control which concerns on one Example of this invention. It is a figure explaining the discharge control which concerns on one Example of this invention, and is the figure explaining the method of predicting the discharge start timing from the inflection point of an output current. It is a figure explaining the discharge control which concerns on one Example of this invention, and is the figure explaining the method of predicting the discharge start timing from a voltage waveform and a current waveform. This is an example of a digital high-voltage power supply circuit according to an embodiment of the present invention. It is a flowchart which shows the operation of the image forming apparatus which concerns on one Example of this invention. It is a waveform diagram of the current and voltage in the conventional analog high voltage power supply. It is a waveform diagram of discharge current and voltage in the conventional analog high voltage power supply. It is a waveform diagram of the current and voltage in the conventional digital high voltage power supply. It is a waveform diagram of discharge current and voltage in the conventional digital high voltage power supply.

As shown in the background technology, image forming devices such as MFPs that form images by electrophotographic methods are equipped with a high voltage power supply circuit for applying high voltage during charging, development, and transfer, and high voltage is generated by analog signals. In the circuit that generates the above, it is possible to output a high voltage of an analog waveform without distortion in which the voltage value changes gently.

Here, in order to improve the quality of the image, it is preferable to be able to arbitrarily change the shape of the charging voltage waveform, and the digital high-voltage power supply circuit is cheaper and easier than the conventional analog high-voltage power supply circuit. The shape of the waveform can be changed with various configurations. However, when a digital high-voltage power supply circuit is used to generate a high-voltage AC (alternating) waveform in the same manner as an analog high-voltage power supply circuit, quantization distortion occurs. Further, if a high-speed CPU or MPU is provided in order to reduce the quantization distortion, the cost of the high-voltage power supply circuit will increase.

The above quantization distortion will be described with reference to the drawings. In the analog high-voltage power supply circuit, an analog signal having a waveform whose value changes gently as shown in FIG. 12 is used, and when a high voltage is generated using this analog signal, the voltage waveform becomes analog as shown in FIG. A gentle curve is formed according to the signal, and the current waveform is 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 the digital high-voltage power supply circuit, as shown in FIG. 14, a digital signal having a jagged waveform whose value changes in steps is used, and this jaggedness becomes quantization distortion. Then, when a high voltage is generated using this digital signal, as shown in FIG. 15, since this jaggedness is reflected in both the voltage waveform and the current waveform, the discharge current does not become the same as that of the analog high voltage power supply circuit, and the quantization distortion. An error occurs according to. As a result, when the discharge is excessive, the wear of the photoconductor is promoted and the life is shortened, and when the discharge is small, the unevenness of the surface potential of the photoconductor cannot be sufficiently reduced, causing a problem in the image. Let me.

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 a high voltage is applied to a discharge member to generate a discharge. In the image forming apparatus provided with the power supply board, the difference between the discharge current when a high voltage is applied to the discharge member and the desired discharge current is acquired, and each voltage value of the digital signal is corrected so that the difference becomes small.

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

In order to explain the embodiment of the present invention in more detail, the image forming apparatus and the discharge control method according to the embodiment of the present invention will be described with reference to FIGS. 1 to 11. 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 and 4 are high voltage of this embodiment. It is a circuit diagram which shows the structure of a power-source board. Further, FIG. 5 is an example of a voltage / current waveform of an analog high-voltage power supply, and FIGS. 6 and 7 are schematic views illustrating discharge control of this embodiment. 8 and 9 are diagrams for explaining the method of predicting the discharge start timing in the discharge control of the present embodiment, FIG. 10 is an example of the digital high-voltage power supply circuit of the present embodiment, and FIG. 11 is the present embodiment. It is a flowchart which shows the operation of the image forming apparatus of an example.

As shown in FIG. 1, the image forming apparatus 10 of this embodiment is based on the image data acquired by reading the original or the 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 paper, and is, for example, photosensitive as a photoconductor corresponding to four colors of yellow (Y), magenta (M), cyan (C), and black (K). The body drums 83Y, 83M, 83C, and 83K are tandem image forming devices arranged in series in the traveling direction of the transferred body (intermediate transfer belt).

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

The control unit 20 includes a CPU 21, a memory such as a ROM (Read Only Memory) 22 and a RAM (Random Access Memory) 23, a storage unit 24 such as an HDD (Hard Disk Drive) and an SSD (Solid State Drive), and a NIC (NIC). It is composed of a network I / F unit 25 such as a Network Interface Card) or a modem. The CPU 21 reads a program according to the processing content from the ROM 22 or the storage unit 24, expands the program into the RAM 23, and executes the program to centrally control the operation of each unit of the image forming apparatus 10. The storage unit 24 stores a program for the CPU 21 to control each unit, information on the processing function of the own device, 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 WAN (Wide Area Network), and connects various data to and from an external information device (for example, a client device). Send and receive.

The high-voltage power supply unit 30 is a circuit that generates high voltage used for charging, developing, and transferring, and has alternating waveforms (preferably) on the charging device 84, the developing device 82, the primary transfer roller 86, and the intermediate transfer unit 87, which will be described later. High voltage (multiple alternating waveforms) is output from one output terminal. In particular, in this embodiment, the photoconductor drum is appropriately charged by outputting a high voltage corrected for an error due to quantization distortion to the charging device 84. The 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. ) Is provided, and functions as a display unit and an operation unit. The display unit displays various operation screens, an image status display, an operation status of each function, and the like according to a display control signal input from the control unit 20. The operation unit receives various input operations by the user and outputs an operation signal to the control unit 20.

The image reading unit 50 includes an automatic document feeding device 51 called an ADF (Auto Document Feeder), a document image scanning device (scanner) 52, and the like. The automatic document feeding device 51 conveys the documents placed on the document tray by the conveying mechanism and sends them out to the document image scanning device 52. The document image scanning device 52 optically scans the document conveyed on the contact glass from the automatic document feeding device 51 or the document placed on the contact glass, and the reflected light from the document is CCD (Charge Coupled Device). ) The original image is read by forming an image on the light receiving surface of the sensor. The image (analog image signal) read by the image reading unit 50 is subjected to predetermined image processing by the image processing unit 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 unit 60 generates digital image data by performing A / D conversion processing on the analog image signal from the image reading unit 50. Further, the image processing unit 60 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 includes a paper feed device 71, a transport mechanism 72, a paper discharge device 73, and the like. In this embodiment, the paper feed device 71 includes three paper feed tray units. In these paper feed tray units, standard paper and special paper identified based on the basis weight and size of the paper are stored for each preset type. The paper contained in the paper feed tray unit is fed one by one from the uppermost portion, and is conveyed to the image forming unit 80 by a conveying mechanism 72 provided with a plurality of conveying rollers such as a resist roller. At this time, the resist portion on which the resist roller is arranged corrects the inclination of the fed paper and adjusts the transfer timing. Then, the paper on which the image is formed by the image forming unit 80 is discharged to the paper ejection tray outside the machine by the paper ejection device 73 provided with the paper ejection roller.

As shown in FIGS. 1 and 2 (c), the image forming unit 80 includes an exposure apparatus 81 (81Y, 81M, 81C, 81K), which is provided corresponding to different color components Y, M, C, and K. Developer 82 (82Y, 82M, 82C, 82K), Photoreceptor drum 83 (83Y, 83M, 83C, 83K), Charging device 84 (84Y, 84M, 84C, 84K), Cleaning device 85 (85Y, 85M, 85C, 85K), a primary transfer roller 86 (86Y, 86M, 86C, 86K), an intermediate transfer unit 87, a fixing device 88, and the like. In the following description, symbols excluding Y, M, C, and K are used as necessary.

In the photoconductor drum 83 of each color component Y, M, C, K, an organic photoconductor layer (OPC) provided with an overcoat layer as a protective layer is formed on the outer peripheral surface of a cylindrical metal substrate made of an aluminum material. It is an image carrier. The photoconductor drum 83 is rotated in the counterclockwise direction in FIG. 1 in a state of being grounded by being driven by an intermediate transfer belt described later.

The charging device 84 for each of the color components Y, M, C, and K is, for example, a charging roller type, in a state where the charging member (charging roller) has its longitudinal direction along the rotation axis direction of the photoconductor drum 83. It is arranged close to the corresponding photoconductor drum 83, and a uniform potential is applied to the surface of the photoconductor 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 the error due to the quantization distortion.

The exposure apparatus 81 for each color component Y, M, C, K scans in parallel with the rotation axis of the photoconductor drum 83 by, for example, a polygon mirror, and is uniformly charged on the surface of the corresponding photoconductor drum 83. An electrostatic latent image is formed by performing image exposure based on the image data.

The developing device 82 for each of the color components Y, M, C, and K contains a two-component developer composed of a toner having a small particle size of the corresponding color component and a magnetic material, and the toner is applied to the surface of the photoconductor drum 83. It is conveyed and the electrostatic latent image carried on the photoconductor drum 83 is visualized with toner. At the time of this development, if necessary, the high voltage power supply unit 30 outputs a high voltage corrected for the error due to the quantization distortion.

The primary transfer roller 86 of each color component Y, M, C, K presses the intermediate transfer belt against the photoconductor drum 83, and sequentially superimposes the toner images of each color formed on the corresponding photoconductor drum 83 on the intermediate transfer belt. Transcribe. At the time of this primary transfer, a high voltage corrected for an error due to quantization distortion is output from the high voltage power supply unit 30 as necessary.

The cleaning device 85 for each of the color components Y, M, C, and K recovers the residual toner remaining on the corresponding photoconductor drum 83 after the primary transfer. Further, a lubricant application mechanism (not shown) is provided adjacent to the photoconductor drum 83 of the cleaning device 85 in the rotation direction, and the lubricant is applied to the photosensitive surface of the corresponding photoconductor drum 83. There is.

The intermediate transfer unit 87 includes an endless intermediate transfer belt 87a which is an image carrier, a support roller 87b, a secondary transfer roller 87c, a separation device (not shown), an intermediate transfer cleaning unit 87d, and the like, and a plurality of support rollers. An intermediate transfer belt 87a is stretched on 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 paper by the secondary transfer roller 87c, the pressure contact portion (referred to as the secondary transfer nip portion). The toner image is secondarily transferred to the paper and sent to the fixing device 88. A separation device (for example, a serrated static eliminator extending in the axial direction of the secondary transfer roller 87c) is installed on the downstream side (downstream side in the paper transport direction) of the secondary transfer nip. The intermediate transfer cleaning unit 87d has a belt cleaning blade (BCL blade) that is slidably contacted with the surface of the intermediate transfer belt 87a. The transfer residual toner remaining on the surface of the intermediate transfer belt 87a after the secondary transfer is scraped off by the BCL blade and removed. At the time of this secondary transfer or paper separation, if necessary, the high voltage power supply unit 30 outputs a high voltage corrected for the error due to the quantization distortion.

The fixing device 88 includes a heating roller 88a and a fixing roller 88b as heat sources, a fixing belt 88c and a pressure roller 88d hung on the fixing roller 88b, and the pressure roller 88d is pressed against the fixing roller 88b via the fixing belt 88c. The pressure contact portion constitutes the nip portion. Then, the fixing belt 88c heated by the heating roller 88a and each roller heat and pressurize 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 the paper ejection tray outside the machine by the paper ejection device 73 provided with the paper ejection roller.

Next, the configuration of the high-voltage power supply unit 30 will be described with reference to FIGS. 2 (b) and 3. In a normal high-voltage power supply circuit, output control is performed using some functions of a CPU that controls the entire device (particularly, engine control), but a control equipped with a CPU that controls the entire device is installed. The board and the high-voltage power supply board on which the high-voltage power supply circuit is formed are separated, and the wiring path between the boards may become long. Therefore, components for reliably transmitting the signal are arranged, but these components cause a signal delay. In particular, it is necessary to switch the high-voltage output at a higher speed in order to improve the device speed in recent years and to handle a wide variety of papers, but a response delay occurs when a time constant is formed at the connection point of each function. However, there are cases where the required switching cannot be performed. Further, when the structure of the device becomes complicated due to the multi-functionality of the image forming apparatus in recent years, the wiring is also complicated, and as a result, noise is easily added to the signal and the device is liable to malfunction. 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 the CPU.

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

The memory 32 stores a digital signal (PWM (Pulse Width Modulation) data) of a waveform obtained by quantizing an analog signal for obtaining a desired discharge current, and the CPU 31 stores 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 it 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 a resistor, a capacitor, and the like, converts a signal output from the switch element 34 into a waveform, and outputs the signal to the transformer 36. The primary side coil (drive coil) and the secondary side coil (high voltage generation coil) of the transformer 36 have an insulated structure, and the waveform output from the LR circuit 35 is amplified according to the turns ratio. The output is output to the image forming unit 80 (particularly, the charging device 84).

In the above configuration, by outputting a PWM signal with a changed duty ratio from the CPU 31, it is possible to output a high voltage of an arbitrary alternating waveform (for example, a sine wave or a trapezoidal wave).

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 described above, and 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 higher than the discharge start voltage may be corrected. Further, a predetermined correction value may be thinned out in order from a relatively low voltage value, or the voltage value of the digital signal corresponding to the peak voltage of the discharge may not be corrected. Then, if the difference does not fall below the threshold value even after thinning out the predetermined correction values from all the voltage values, the predetermined correction values can be thinned out again in order from the relatively low voltage value. Further, the correction unit 31a can change a 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 an inflection point of the discharge current or the like.

The high-voltage power supply unit 30 may have a configuration capable of outputting a high voltage of 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. 4, a CPU that performs overall control (particularly engine control) of the device is mounted. 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, parts (output amplifier, filter, etc.) for reliably transmitting the signal are arranged.

Hereinafter, the correction process of the correction unit 31a will be described 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 the analog signal. In this embodiment, in order to match the current that flows when a high voltage is generated based on a digital signal with the current that flows when a high voltage is generated based on an analog signal, a predetermined value is determined from each voltage value of the digital signal. Each voltage value is corrected by thinning out the correction value.

Specifically, as shown in FIG. 6 (b), which is an enlarged view of the right end of FIG. 6 (a), a predetermined correction value is applied from a relatively low voltage value (here, the voltage value of (1)) of the digital voltage waveform. (For example, a voltage value of 1 dgt) is thinned out. Then, the current of the analog waveform (average value or integrated value) is compared with the current of the corrected digital waveform (average value or integrated value), and if the difference exceeds a predetermined threshold value, FIG. 6 (c) ), The 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 fall below the threshold value, the voltage returns to a relatively low voltage value (voltage value of (1) above). Then, the predetermined correction value is 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 as a table in the memory 32.

Further, in FIG. 6, each voltage value of the entire digital voltage waveform is corrected, but each voltage value of the digital signal corresponding to a 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 higher than the discharge start voltage of the digital voltage waveform. The value (for example, a voltage value of 1 dgt) is thinned out. Then, the current of the analog waveform (average value or integrated value) is compared with the current of the corrected digital waveform (average value or integrated value), and if the difference exceeds a predetermined threshold value, the next voltage value is obtained. (Here, the voltage value of (k + 1)) is thinned out from the predetermined correction value. Then, even if this process is repeated up to a high voltage value (here, the voltage value of (n)), if the above difference exceeds the threshold value, it is relatively relative to the voltage values corresponding to the high voltage higher than the discharge start voltage. It returns to a low voltage value (the voltage value of (k) above) and further thins out a predetermined correction value. Then, when the difference becomes equal to or less than the threshold value, the corrected voltage value is stored in the above 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 methods 1 to 3.

The first method is a method of predicting from the inflection point of the output current. For example, a circuit for monitoring the output current (current obtained by adding the discharge current and the induced current) is formed in the high-voltage power supply circuit, and the discharge start voltage specifying unit 31b has the output voltage and the output current as shown in FIG. From the correlation, a voltage value (turning point A, here 1 kV) at which the output current changes significantly with respect to the output voltage is acquired, and the voltage value is specified as the discharge start voltage.

The second method is a method of predicting from a voltage waveform and a current waveform. For example, the discharge start voltage specifying unit 31b acquires the voltage waveform and the current waveform as shown in FIG. 9, and the time from the change point of the current waveform to the peak of the discharge current (the discharge current is from the change point B in the figure). The time until the maximum point C) is acquired, and the voltage before the above time from the point where the voltage value becomes the maximum is specified as the discharge start voltage.

The third method is a method of predicting from the value of the barometric pressure sensor. For example, the image forming apparatus is provided with a sensor for measuring the pressure, and a table for associating the pressure with the discharge voltage is stored, and the discharge start voltage specifying unit 31b sets the pressure measured by the pressure sensor with reference to this table. The corresponding discharge voltage is acquired and this voltage is specified as the discharge start voltage.

When the output current is measured by the first method or the second method, the discharge current measuring circuit 37 as shown in FIG. 10 is formed, and the current flowing through the discharge current measuring circuit 37 is measured by the CPU 31. , The total current value 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. Further, here, a case of correcting the voltage value of the digital signal corresponding to the high voltage higher than the discharge start voltage will be described.

First, the high-voltage power supply unit 30 generates a high voltage based on the 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 by using the first method or the second method described above (S103).

Next, the CPU 31 (correction unit 31a) corrects the voltage value of the digital signal by thinning out a predetermined correction value from the voltage value close to the discharge start voltage at the discharge start voltage or higher (S104). For example, when the difference (pp voltage) between the maximum voltage value and the minimum voltage value is expressed by 256 bits, the correction value for one bit is thinned out from each voltage value to correct the 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. For example, when the peak value or frequency is doubled, the predetermined correction value is also doubled. Can be.

Then, the CPU 31 (correction unit 31a) has a discharge current (average value or integrated value) when a high voltage generated based on the corrected digital signal is applied, and a desired discharge current (average value) stored in the memory 32 or the like in advance. It is determined whether the difference from the value or the integrated value) is equal to or less than a predetermined threshold value (S105), and if the difference is equal to or less than the threshold value (Yes in S105), a series of correction processes is terminated.

On the other hand, when the difference exceeds the threshold value (No in S105), the CPU 31 (correction unit 31a) determines whether the voltage value to be corrected next is the maximum voltage value (S106), and must be the maximum voltage value. 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 value. If it is the maximum voltage value (Yes in S106), the process returns to S104 and is corrected again in order from the voltage value closest to the discharge start voltage.

In this way, by correcting each voltage value of the digital signal of the digital high-voltage power supply circuit so that the discharge current becomes the same as that of the analog high-voltage power supply circuit, it is possible to correct a minute current difference.

The present invention is not limited to the above embodiment, and its configuration and control can be appropriately changed as long as the gist of the present invention is not deviated.

For example, in the above embodiment, the discharge control in the charging device 84 of the image forming apparatus 10 has been described, but the present invention also applies to the case where a high voltage is applied to the developing device 82, the primary transfer roller 86, the intermediate transfer unit 87, and the like. Can be applied in the same way.

The present invention can be used for an image forming apparatus including a high-voltage power supply substrate used for electrophotographic image forming and a discharge control method in the image forming apparatus.

10 Image forming device 20 Control unit 21 CPU
22 ROM
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 specification 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 reader 51 Automatic document feeder 52 Original image scanning device 60 Image processing Unit 70 Conveying unit 71 Feeding device 72 Conveying mechanism 73 Paper discharging device 80 Image forming unit 81, 81Y, 81M, 81C, 81K Exposure device 82, 82Y, 82M, 82C, 82K Development device 83, 83Y, 83M, 83C, 83K Photoreceptor 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 Pressurizing roller

Claims (16)

In an image forming apparatus including a high-pressure power supply substrate, which 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 is provided 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 in that. Equipped with a discharge start voltage specification unit that specifies the 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.
The image forming apparatus according to claim 1. 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 value.
The image forming apparatus according to claim 1 or 2. The correction unit does not correct the voltage value of the digital signal corresponding to the peak voltage of the discharge.
The image forming apparatus according to claim 3. If the difference does not fall below the threshold value even after thinning out the predetermined correction values from all the voltage values, the correction unit thins out the predetermined correction values in order from the relatively low voltage value.
The image forming apparatus according to claim 3 or 4. 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.
The image forming apparatus according to any one of claims 3 to 5, wherein the image forming apparatus is characterized. The waveform is a sine wave or a trapezoidal wave.
The image forming apparatus according to any one of claims 1 to 6, wherein the image forming apparatus is characterized. The correction of the voltage value by the correction unit is executed by the CPU arranged in the high voltage power supply board.
The image forming apparatus according to any one of claims 1 to 7. Discharge control in an image forming apparatus including 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. The way,
A difference acquisition process for acquiring the difference between the 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 so that the difference becomes small is executed.
A discharge control method characterized by this. Execute the discharge start voltage specification process to specify the 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.
The discharge control method according to claim 9, wherein the discharge control method is characterized. 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 value.
The discharge control method according to claim 9 or 10. In the correction process, the voltage value of the digital signal corresponding to the peak voltage of the discharge is not corrected.
The discharge control method according to claim 11, wherein the discharge control method is characterized. In the correction process, if the difference does not fall below the threshold value even after thinning out the predetermined correction values from all the voltage values, the predetermined correction values are thinned out again in order from the relatively low voltage value.
The discharge control method according to claim 11 or 12, characterized in that. 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.
The discharge control method according to any one of claims 11 to 13, wherein the discharge control method is characterized. The waveform is a sine wave or a trapezoidal wave.
The discharge control method according to any one of claims 9 to 14, characterized in that. The correction process is executed by a CPU arranged in the high-voltage power supply board.
The discharge control method according to any one of claims 9 to 15, characterized in that.

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