JP2008076750A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of continuing power supply to the utmost while coping with an abnormal state such as overcurrent or overvoltage. <P>SOLUTION: If transfer voltage V detected by a voltage detection circuit 130 exceeds upper limit voltage Vlim while performing constant current control to a detection current I, the constant current control is stopped, and the PWM value of a PWM signal S1 is increased/decreased stepwise in a direction where the detection voltage V is lower than the upper limit voltage Vlim regardless of the detection current I. Thereafter, the constant current control is restarted on a condition that the detection voltage V is lower than the upper limit voltage Vlim. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly, to a power supply apparatus that supplies power to an electrical load in the image forming apparatus.

A power supply device provided in the image forming apparatus applies a bias voltage to an electric load such as a charger, a developing device, or a transfer device arranged around a photosensitive member that carries a toner image. By the way, since the impedance of these electrical loads changes greatly due to environmental changes such as temperature and humidity in the image forming apparatus, a large current flows through the electrical load when the power supply device is controlled at a constant voltage, for example. It is possible to change to an abnormal state in which an overcurrent exceeding a predetermined value flows.
Therefore, Patent Document 1 below is a power supply device that performs constant voltage control on an electrical load, and includes a current detection circuit that detects a current flowing through the electrical load, and the detected value indicates the value of the protection signal. A configuration is disclosed in which it is determined that there is an abnormality when it exceeds, and the power supply to the electrical load is stopped.
JP 2006-136136 A

However, in the above-mentioned Patent Document 1, since the power supply is stopped when the detected value of the current flowing through the electric load exceeds the value of the protection signal, the quality of the image transferred onto the print medium is determined. There was a risk that it would fall.
The present invention has been completed based on the above circumstances, and an object thereof is to provide an image forming apparatus capable of continuing power supply as much as possible while dealing with an abnormal state of overcurrent or overvoltage. There is to offer.

As means for achieving the above object, an image forming apparatus according to claim 1 is an electrical load, a voltage generator for generating a voltage to be applied to the electrical load, and an output of the voltage generator. A voltage detection unit that detects a voltage, a current detection unit that detects an output current of the voltage generation unit, a detection voltage of the voltage detection unit, and a detection value of the detection current of the current detection unit are fed back. A PWM control unit that performs PWM control so that the one detected value becomes a target value, and the PWM control unit when the other detected value exceeds a predetermined threshold during the execution of the PWM control. Instead of the feedback control by the protection control unit for executing the protection control for forcibly changing the PWM value of the PWM control unit in the direction in which the other detected value falls below the predetermined threshold, and after the execution of the protection control , If the serial other detection value falls below the predetermined threshold value, and a switching control unit for switching the feedback control by the PWM controller.
The “image forming apparatus” of the present invention may be not only a printing apparatus such as a printer (for example, a laser printer) but also a facsimile machine or a multifunction machine having a printer function and a reading function (scanner function). .

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the switching control unit is configured such that the other detected value is less than the predetermined threshold value and the one detected value has reached the target value. In this case, the control is switched to the feedback control by the PWM control unit.

  According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the protection control unit stops changing the PWM value when the other detected value falls below the predetermined threshold value.

  According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the protection control unit sets the PWM value to a predetermined amount until the other detection value falls below the predetermined threshold. Change it step by step.

According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the electrical load is a transfer mechanism that transfers the developer image carried on the image carrier to the transfer target. It is.
The “transfer object” is not limited to a printing medium such as paper, and may be, for example, an intermediate transfer member (intermediate transfer belt) as long as the developer image is transferred thereto.

<Invention of Claim 1>
For example, in a configuration in which feedback control (constant current control) for maintaining an output current with respect to an electrical load at a constant value is performed in a normal state, a detected value of the output voltage (the other detected value) due to impedance fluctuation of the electrical load, etc. ) Exceeds a predetermined threshold value, the feedback control is temporarily stopped. Then, regardless of the output current detection value (one detection value), the PWM value is forcibly changed in a direction in which the output voltage detection value falls below the predetermined threshold value, and then the output voltage detection value is set to the predetermined threshold value. The constant current control is resumed when the value falls below. Therefore, power supply can be continued as much as possible while dealing with an abnormal state of overcurrent or overvoltage.

<Invention of Claim 2>
For example, in the configuration in which the constant current control is executed in a normal state, if the constant current control is immediately restarted when the detected value of the output voltage falls below a predetermined threshold, for example, the high impedance of the electrical load is still The state continues, and eventually, there is a possibility that the detected value of the output voltage immediately returns to an abnormal state where the value exceeds a predetermined threshold value. Therefore, in this configuration, when the detected value of the output current reaches the target value, it is considered that there is little possibility of returning to the abnormal state even if the constant current control is restarted here, and the detected value of the output voltage is The constant current control is resumed on condition that the value is below a predetermined threshold value and the detected value of the output current has reached the target value.

<Invention of Claim 3>
Even if the other detection value falls below a predetermined threshold value, one detection value is made to reach the target earlier than the configuration in which the protection control unit continues to change the PWM value until one detection value reaches the target value. I can expect that.

<Invention of Claim 4>
If the configuration is such that the PWM value is changed step by step, one detection value can be gradually changed as compared with the configuration in which the PWM value is changed at a time until the other detection value falls below a predetermined threshold value. It is possible to suppress the quality degradation of the output image.

<Invention of Claim 5>
In the transfer mechanism, since the impedance largely changes before and after entering the transfer object, it is particularly useful to apply the present invention.

An embodiment of the present invention will be described with reference to FIGS.
1. Overall Configuration of Printer FIG. 1 is a schematic cross-sectional view showing the internal configuration of a color laser printer (hereinafter simply referred to as “printer 1”) 1 as an image forming apparatus of the present embodiment.
A printer 1 illustrated in FIG. 1 includes a toner image forming unit 4, a paper conveying belt 6 as a belt member, a fixing unit 8, a paper feeding unit 9, a stacker 12, and a control unit 10, and a printing medium. As a result, four color images corresponding to image data input from the outside are formed on the paper P.

  The toner image forming unit 4 includes four developing units 51Y, 51M, 51C, and 51B, and four toners of yellow, magenta, cyan, and black stored in these developing units 51Y, 51M, 51C, and 51B. For each toner image forming step, a photosensitive drum 3 (an example of an “image carrier”) as a photosensitive member, a charger 31 for uniformly charging the photosensitive drum 3, and the charged photosensitive drum 3 is provided with a scanner unit 41 as an exposure unit that exposes the surface 3 with laser light to form an electrostatic latent image according to image data. Note that most of the scanner unit 41 is not shown, and only a portion where laser light is finally emitted is shown.

Hereinafter, the configuration of each component will be described in detail. In the following description, when it is necessary to distinguish each color, it is necessary to add the subscripts of Y (yellow), M (magenta), C (cyan), and B (black) to each part code. If there is not, the subscript is omitted.
The photosensitive drum 3 of the toner image forming unit 4 is formed of a substantially cylindrical member, and four of them are arranged in a horizontal direction at substantially equal intervals so as to be rotatable. As the substantially cylindrical member of the photosensitive drum 3, for example, a member in which a positively chargeable photosensitive layer is formed on an aluminum base material is used. The aluminum base material is grounded to the ground line of the printer 1.

  Further, the charger 31 is a so-called scorotron type charger. The charger 31 is opposed to the photosensitive drum 3 and extends in the width direction thereof. The charging wire 32 is accommodated in the photosensitive drum 3 side. The surface of the photosensitive drum 3 is charged to a positive polarity (for example, +700 V) by applying a high voltage to the charging wire 32. The shield case 33 has a structure in which a grid is provided in the open portion on the photosensitive drum 3 side. By applying a specified voltage to the grid, the surface of the photosensitive drum 3 is substantially the same as the grid voltage. Charged to potential.

  The scanner unit 41 is disposed on each photosensitive drum 3 on the downstream side of the charger 31 in the rotation direction of the photosensitive drum 3, and emits laser light corresponding to one color of image data input from the outside from the light source. The laser beam is emitted and scanned with a mirror surface of a polygon mirror that is rotationally driven by a polygon motor, and is irradiated onto the surface of the photosensitive drum 3. When the scanner unit 41 irradiates the surface of the photosensitive drum 3 with laser light corresponding to the image data, the surface potential of the irradiated portion is reduced (+150 to +200 V), so that the photosensitive drum 3 An electrostatic latent image is formed on the surface.

Each of the developing units 51Y, 51M, 51C, and 51B has a configuration in which a developing unit case 55 that stores toner of each color is provided with a developing roller 52 as a developing unit, and with respect to the rotation direction of the photosensitive drum 3. The developing roller 52 is disposed on the downstream side of the scanner unit 41 so as to contact the photosensitive drum 3. Each developing unit 51 charges the toner to “+” (positive polarity), supplies the toner as a uniform thin layer to the photosensitive drum 3, and in the contact portion between the developing roller 52 and the photosensitive drum 3, The electrostatic latent image formed on the body drum 3 is developed with the toner charged to “+” (positive polarity) being carried by the reversal development method with respect to the electrostatic latent image of “+” (positive polarity). To do.
The developing roller 52 is formed in a cylindrical shape using a conductive silicone rubber or the like as a base material, and a coating layer of a resin containing fluorine or a rubber material is formed on the surface. The toner stored in the developing unit case 55 is a positively chargeable non-magnetic one-component toner, and yellow, magenta, cyan toner, and black toner according to the developing units 51Y, 51M, 51C, and 51B, respectively. Is housed.

  The paper feeding unit 9 is provided at the lowermost part of the apparatus, and includes a storage tray 91 that stores the paper P and a pickup roller 92 that feeds the paper P. The paper P stored in the storage tray 91 is picked up one by one from the paper feeding unit 9 by the pickup roller 92 and is sent to the paper transport belt 6 through the transport roller 98 and the registration roller 99.

  The sheet transport belt 6 is narrower than the width of the photosensitive drum 3 and is endlessly configured to travel integrally with the sheet P while the sheet P is supported on the upper surface. It is bridged between. In addition, transfer rollers 61 are provided in the vicinity of positions facing the respective photosensitive drums 3 with the paper transport belt 6 interposed therebetween. Then, as the driving roller 62 rotates, the surface of the sheet conveying belt 6 facing the photosensitive drum 3 moves from the right in the drawing to the left in the drawing as shown in FIG. The paper P sent from the rollers 99 is sequentially conveyed to the photosensitive drum 3 and sent to the fixing unit 8.

  Further, a cleaning roller 105 as a removing unit is provided at a position near the driven roller 63 on the surface of the sheet conveying belt 6 that is turned back by the driving roller 62. The cleaning roller 105 has a configuration in which a foam material made of silicone is provided around a shaft member extending in the width direction of the paper conveyance belt 6, and a metal provided at a position facing the paper conveyance belt 6. A predetermined bias voltage (for example, −1200 V) is applied between the electrode roller 104 and the electrode roller 104, and the electrode roller 104 is arranged so as to rotate while being in contact with the paper transport belt 6. With this bias voltage, the toner adhering to the paper transport belt 6 is removed by the cleaning roller 105.

  The transfer roller 61 (an example of “electric load, transfer mechanism”) is transferred between the transfer roller 61 and the photosensitive drum 3 by a high-voltage control device 120 described later (for example, −10). .About.-11 .mu.A, a maximum voltage of 6 kV) is applied so that the toner image formed on the photosensitive drum 3 is transferred onto the paper P (an example of "transfer target") transported by the paper transport belt 6. It is configured.

The fixing unit 8 includes a heating roller 81 and a pressure roller 82, and heats and presses the paper P on which the toner image is transferred while nipping and conveying the paper P by the heating roller 81 and the pressure roller 82. Thus, the toner image is fixed on the paper P.
A stacker 12 is formed on the upper surface of the printer 1. The stacker 12 is provided on the paper discharge side of the fixing unit 8 and accommodates the paper P discharged from the fixing unit 8. The control unit 10 includes a control device using a CPU (not shown) and controls the overall operation of the printer 1.

2. Configuration of High Voltage Control Device On the control board of the control unit 10, a bias voltage to be applied to each electrical load provided in the printer 1, such as the transfer roller 61, the developing roller 52, the charger 31, and the toner removal unit 100. Is mounted. FIG. 2 shows a component that generates a transfer voltage V (an example of “voltage applied to an electrical load”) to the transfer roller 61 among them. As shown in the figure, the high voltage generation circuit 121 (an example of a “voltage generation unit”) generates an oscillating current corresponding to a PWM value (duty ratio) of a PWM signal S1 from a PWM control circuit 122 described later. A drive circuit 124 is provided to flow through the primary winding 123A. A first capacitor 125 and a first diode 126 are connected in series to both ends of the secondary winding 123B of the transformer 123, and a second diode 127 and a second capacitor 128 are connected in series. In the two diodes 126 and 127, the flow direction of the transfer current I from the transfer roller 61 is the forward direction. A connection point between the first diode 126 and the first capacitor is connected to the roller shaft of the transfer roller 61 via the output resistor 129. With such a configuration, the high voltage generation circuit 121 functions as a boost (charge pump) circuit that generates a voltage twice the voltage across the first capacitor 125.

  Further, the high voltage control device 120 flows to the transfer roller 61 and a voltage detection circuit 130 (an example of “voltage detection unit”) that detects a transfer voltage V (an example of “output voltage”) applied to the transfer roller 61. A current detection circuit 131 (an example of a “current detection unit”) that detects a transfer current I (an example of an “output current”) is provided. The PWM control circuit 122 mounted on the high-voltage control device 120 receives the detection signal S2 of the current detection circuit 131 at the A / D port 122B, and receives the detection signal S3 of the voltage detection circuit 130 at the A / D port 122C. A PWM signal S1 having a PWM value based on the detected value is output from the PWM port 122A to the drive circuit 124. This will be explained in detail next.

3. Content of Control of PWM Control Circuit The PWM control circuit 122 is constituted by a CPU at its core, and normally the detection signal S2 from the current detection circuit 131 is fed back so that the detection current I is a predetermined target value Is (upper limit value IsU). The constant value control (an example of “feedback control by the PWM control unit”) is performed to adjust the PWM value of the PWM signal S1 so that the lower limit value IsD is, for example, −10 to −11 μA). Accordingly, at this time, the PWM control circuit 122 functions as a “PWM control unit”.

  However, for example, when the inside of the printer 1 becomes high temperature and low humidity and the paper P enters between the transfer roller 61 and the photosensitive drum 3, the ground from the transfer roller 61 through the paper P and the photosensitive drum 3. The impedance between the lines can be very high. Then, under the constant current control, a voltage higher than the upper limit voltage Vlim (an example of “predetermined threshold value”) is continuously applied, so that the high-voltage control device 120 fails or the transfer roller 61 or the like is damaged. There is a risk that.

  Therefore, as described below, when the transfer voltage V detected by the voltage detection circuit 130 exceeds the upper limit voltage Vlim (6 kV in the present embodiment) during execution of the constant current control, the constant current control is performed. And the PWM value of the PWM signal S1 is increased or decreased stepwise (in the present embodiment, the PWM value is decreased) in a direction in which the detected voltage V falls below the upper limit voltage Vlim regardless of the detected current I. At this time, the PWM control circuit 122 functions as a “protection control unit” and a “switching control unit”. The detection current I is an example of “one detection value”, and the transfer voltage V is an example of “the other detection value”. Hereinafter, a description will be given with reference to FIGS.

(1) Setting Target Value For example, when the printer 1 is turned on, the PWM control circuit 122 starts the output sequence control shown in FIG. In S11, first, a target value Is (upper limit value IsU, lower limit value IsD) is set. Specifically, for example, the target value Is is reset to a value corresponding to the setting content such as the type of paper P set in the printer 1. When the printer 1 includes a temperature sensor and a humidity sensor, the target value Is may be reset to a value corresponding to the detection result of each sensor.

(2) Constant Current Control Next, the PWM control circuit 122 initializes a protection control execution flag (PWM_Flag) to zero (does not execute protection control) in S12. Thereby, constant current control is performed by S13. Specifically, as shown in FIG. 4, when the transfer current I based on the detection signal S2 is smaller than the lower limit value IsD (S21: Y), the PWM control circuit 122 increases the PWM value of the PWM signal S1. Thus, the transfer current I is increased so as to reach the lower limit IsD (S22). On the other hand, when the transfer current I based on the detection signal S2 is larger than the upper limit value IsU (S21: N and S23: Y), the PWM value of the PWM signal S1 is decreased and the transfer current I becomes the upper limit value IsU. Decrease so as to head (S24). After that, the system waits for a predetermined time (in this embodiment, for example, 240 μS) in S25, and proceeds to S14 in FIG. Thereby, as shown in FIG. 6, the transfer current I is kept between the upper limit value IsU and the lower limit value IsD.

(3) Moving Average Process In S14, the moving average sequence process shown in FIG. 5 is started. That is, for each of the transfer voltage V and the transfer current I, the average value (moving average value) of the samples for the latest multiple times (four times in this embodiment) including the current sampling timing is calculated as needed. Specifically, first, the transfer voltage V and the transfer current I are detected from the detection signals S2 and S3 in S31, and the sample number k is initialized in S32. In S33, the sample field numbers of the voltage sample field Vdim (k) and the current sample field Idim (k) are added and shifted one by one, and 1 is added to the current sample number k (S34). The process is repeated until the sample number k becomes 3. At the beginning of power-on of the printer 1, the transfer voltage V and the transfer current I are not yet stored in the voltage sample field Vdim (k) and the current sample field Idim (k). For this reason, until the sample number reaches 3, the sample values stored in advance are stored in each voltage sample field Vdim (k) and current sample field Idim (k).

  When the sample number k becomes 3 (S35: Y), the detected values of the transfer voltage V and the transfer current I are stored in the voltage sample field Vdim (3) and the current sample field Idim (3) in S36. To do. In S37, the sample number k, the voltage total Vsum and the current total Isum are initialized, and in S38 to S40, the total values of the voltage sample field Vdim (k) and the current sample field Idim (k) of the sample numbers 1 to 4 are summed up in voltage. Vsum and total current Isum are calculated. In S41, moving average values Vave and Iave of the transfer voltage V and the transfer current I are calculated.

(4) Continuation of Constant Current Control Next, the process proceeds to S15 in FIG. 3, where it is determined whether or not the sequence (printing process) is finished. If it is finished (S15: Y), the output sequence control is finished as it is. If the sequence (printing process) is continuing (S15: N), it is determined in S16 whether the moving average voltage value Vave exceeds the upper limit voltage Vlim. Here, when the impedance between the transfer roller 61 and the ground line is normal, which is below a predetermined value, the moving average voltage value Vave does not exceed the upper limit voltage Vlim under constant current control of the target value Is (S16). : N), and no protection control execution flag is set (S17: N), the process returns to S13 and the constant current control is continued.

(5) Execution of Protection Control On the other hand, as shown in FIG. 6, when the impedance between the transfer roller 61 and the ground line exceeds the predetermined value due to an environmental change in the printer 1, the moving average voltage value Vave is the upper limit. The voltage Vlim is exceeded (S16: Y), and a protection control execution flag is set (set to “1”) in S18. In S19, the PWM value is lowered by a predetermined amount (ΔPWM, for example, a duty ratio of 0.4 to 0.5%), and the PWM value change is transferred after a predetermined time (in this embodiment, for example, after the PWM value is changed). A time until the voltage V is sufficiently reflected (for example, 100 μS) is waited (S20), and the process returns to the moving average sequence process of S14. In this way, the moving average voltage value Vave and the upper limit voltage Vlim are compared approximately every 100 μS, and the change of the PWM value and the passage of the sheet P between the transfer roller 61 and the photosensitive drum 3 are completed. When the moving average voltage value Vave is equal to or lower than the upper limit voltage Vlim (S16: N), the process proceeds to S17. Here, since the protection control execution flag has already been set in S17 (S17: Y), the moving average current value Iave and the target value Is are compared in S21.

(6) Resumption of constant current control When the moving average voltage value Vave is equal to or lower than the upper limit voltage Vlim and the moving average current value Iave is smaller than the target value Is (S21: N), as shown in FIG. The impedance between the roller 61 and the ground line is still large to some extent, and even if the constant current control to the target value Is is resumed in this state, the moving average voltage value Vave eventually soon becomes an abnormal state exceeding the upper limit voltage Vlim. This means that there is a high possibility that Therefore, at this time, the constant current control is not restarted, and is kept constant without changing the PWM value, waits for the predetermined time (S20), and returns to S14.

  On the other hand, when the moving average voltage value Vave is equal to or lower than the upper limit voltage Vlim and the moving average current value Iave is equal to or higher than the target value Is (S21: Y), as shown in FIG. The impedance to the ground line is still somewhat small, and even if the constant current control to the target value Is is resumed in this state, there is little possibility that the moving average voltage value Vave exceeds the upper limit voltage Vlim. Means. Therefore, at this time, the protection control is stopped, and the process returns to S13 to resume the constant current control.

4). Effects of the present embodiment (1) According to the present embodiment, when the transfer voltage V detected by the voltage detection circuit 130 exceeds the upper limit voltage Vlim during the execution of the constant current control with respect to the detection current I, The current control is stopped, and the PWM value of the PWM signal S1 is increased or decreased stepwise so that the detected voltage V is lower than the upper limit voltage Vlim regardless of the detected current I. Thereafter, the constant current control is resumed on condition that the detection voltage V falls below the upper limit voltage Vlim. As a result, it is possible to continue the power supply as much as possible while avoiding the continued abnormal state of the overvoltage.
Further, when the transfer voltage V exceeds the upper limit voltage Vlim, a configuration in which the transfer voltage V is switched to a constant voltage control that maintains a predetermined value smaller than the upper limit voltage Vlim is also conceivable. There is a demerit that a configuration for PWM control is required for both voltage control and voltage control. On the other hand, this embodiment can be realized only with a configuration for PWM control with respect to constant current control.

  (2) Further, the restart of the constant current control to the target value Is is executed when the moving average voltage value Vave is equal to or lower than the upper limit voltage Vlim and the moving average current value Iave is equal to or higher than the target value Is. As a result, the impedance between the transfer roller 61 and the ground line is still large to some extent, the constant current control is resumed in this state, and the abnormal state in which the moving average voltage value Vave exceeds the upper limit voltage Vlim will soon be reached. Can be avoided.

  (3) During the protection control, when the moving average voltage value Vave is equal to or lower than the upper limit voltage Vlim and the moving average current value Iave is smaller than the target value Is, the PWM value is kept constant without being changed. Therefore, it can be expected that the moving average current value Iave reaches the target value Is as compared with the configuration in which the stepwise change of the PWM value is continued even after the moving average voltage value Vave becomes equal to or lower than the upper limit voltage Vlim.

  (4) After the moving average voltage value Vave exceeds the upper limit voltage Vlim, the PWM value is changed step by step by a predetermined amount until the voltage becomes equal to or lower than the upper limit voltage Vlim. Therefore, the transfer current I can be changed more slowly than in the configuration in which the PWM value is greatly changed at a time, and the deterioration of the quality of the output image can be suppressed.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention.

(1) In the above-described embodiment, the example in which the present invention is applied to the case where the constant current control for the transfer current I is performed in the normal state has been described. However, the constant voltage control for the transfer voltage V is performed in the normal state, A configuration may be adopted in which the control shifts to protection control when the average current value Iave) exceeds a predetermined upper limit current value.
(2) In the above-described embodiment, the transfer mechanism (transfer roller 61) whose impedance changes greatly before and after entering the paper P has been described as an example of an electrical load. However, the present invention is not limited to this, and constant current control or constant voltage control is used. The developing roller 52, the charger 31, the cleaning roller 105, and the like to which a bias to be applied is applied may be used.

  (3) In the above embodiment, the constant current control may be resumed when the moving average voltage value Vave becomes equal to or lower than the upper limit voltage Vlim. However, with the configuration of the above embodiment, it is possible to avoid a situation in which the moving average voltage value Vave immediately returns to exceed the upper limit voltage Vlim after resuming the constant current control.

1 is a schematic cross-sectional view illustrating an internal configuration of a printer according to an embodiment of the invention. Block diagram of the components that generate the bias voltage to the transfer roller Flow chart showing main processing contents of PWM control circuit Flow chart showing processing details of high voltage constant current control Flow chart showing moving average processing contents Time chart showing changes in transfer voltage, transfer current, impedance and PWM value

Explanation of symbols

1 ... Printer (image forming apparatus)
3 ... Photosensitive drum (image carrier)
61 ... Transfer roller (electric load, transfer mechanism)
121 .. High voltage generation circuit (voltage generation unit)
122... PWM control circuit (PWM control unit, protection control unit, switching control unit)
130: Voltage detection circuit (voltage detection unit)
131: Current detection circuit (current detection unit)
I: Transfer current (output current)
Is ... target value P ... paper (transferred material)
V: Transfer voltage (output voltage)
Vlim: upper limit voltage (predetermined threshold)

Claims (5)

An electrical load;
A voltage generator for generating a voltage to be applied to the electrical load;
A voltage detector that detects an output voltage of the voltage generator;
A current detector that detects an output current of the voltage generator;
A PWM control unit that feeds back a detection value of one of the detection voltage of the voltage detection unit and the detection current of the current detection unit and performs PWM control so that the one detection value becomes a target value;
When the other detected value exceeds a predetermined threshold during the execution of the PWM control, the PWM control is performed in a direction in which the other detected value falls below the predetermined threshold instead of the feedback control by the PWM control unit. A protection control unit for executing protection control for forcibly changing the PWM value of the unit;
An image forming apparatus comprising: a switching control unit that switches to feedback control by the PWM control unit when the other detection value falls below the predetermined threshold after the execution of the protection control. The switching control unit is configured to switch to feedback control by the PWM control unit when the other detection value falls below the predetermined threshold value and the one detection value reaches the target value. The image forming apparatus according to 1. The image forming apparatus according to claim 2, wherein the protection control unit stops changing the PWM value when the other detection value falls below the predetermined threshold. The image forming apparatus according to claim 1, wherein the protection control unit changes the PWM value step by step by a predetermined amount until the other detection value falls below the predetermined threshold value. The image forming apparatus according to claim 1, wherein the electrical load is a transfer mechanism that transfers a developer image carried on an image carrier to a transfer target.

Images