JP2021043259A - Power supply device and image forming apparatus - Google Patents

Abstract

To prevent a reduction in the accuracy of voltage generated by a voltage generation unit of a power supply device.SOLUTION: A power supply device has: a voltage generation unit that generates a voltage to be supplied to a load; an internal resistance unit that generates an internal current to be supplied to the voltage generation unit; a current detection unit that, from a current obtained by combining the internal current and a load current flowing from the load to the voltage generation unit according to the voltage generated by the voltage generation unit, generates a feedback voltage corresponding to the load current; and a control unit that includes an analog-digital conversion unit converting the feedback voltage into a digital value, and generates a control signal to control the voltage generation unit based on the digital value converted from the feedback voltage.SELECTED DRAWING: Figure 2

Description

The present invention relates to a power supply device and an image forming device.

For example, an electrophotographic image forming apparatus has a power supply device including a high voltage generating circuit that generates a high voltage. The image forming apparatus charges a drum-shaped photoconductor with a high voltage generated by a high voltage generating circuit, exposes the charged photoconductor to form an electrostatic latent image, and develops the electrostatic latent image with toner. Then, the image is formed by transferring it to a recording paper. The power supply device has, for example, a current detection circuit that generates a feedback voltage proportional to the output current of the high voltage generation circuit. The high voltage generation circuit controls the generation of high voltage so that the feedback voltage value converted into a digital value by the analog-to-digital converter becomes a target value.

For example, in an image forming apparatus having a plurality of image forming modes having different image forming speeds, the output current range of the high voltage generating circuit is different depending on the image forming mode, so that the feedback voltage range is different for each image forming mode. .. In this case, the range of the feedback voltage input to the analog-digital converter becomes wide, and the resolution of the feedback voltage becomes low. Therefore, by providing a current detection circuit for each image formation mode and switching the current detection circuit to be used according to the image formation mode, the range of the feedback voltage input to the analog-digital converter is aligned and the resolution of the feedback voltage is lowered. A method for suppressing this has been proposed (Patent Document 1).

By the way, in the image forming apparatus, a bleeder resistor may be provided in order to improve the accuracy of the high voltage generated by the high voltage generating circuit of the power supply device, and a bleeding current may be passed through the high voltage output node of the high voltage generating circuit. .. In this case, since the output current of the high voltage generating circuit and the bleeder current flow to the current detection unit, the current detection unit outputs a feedback voltage corresponding to the sum of the output current and the bleeder current to the analog-to-digital converter. As a result, the area corresponding to the output current in the digital output range of the analog-to-digital converter is reduced, so that there is a problem that the accuracy of the high voltage generated by the high voltage generation circuit is lowered. This problem also occurs when a current detection circuit is provided for each image formation mode.

The present invention has been made in view of the above problems, and an object of the present invention is to suppress a decrease in accuracy of the voltage generated by the voltage generation unit of the power supply device.

In order to solve the above technical problems, the power supply device of one embodiment of the present invention includes a voltage generation unit that generates a voltage to be supplied to a load, an internal resistance unit that generates an internal current to be supplied to the voltage generation unit, and the above. A current detection unit that generates a feedback voltage corresponding to the load current from a total of the load current flowing from the load to the voltage generation unit and the internal current according to the voltage generated by the voltage generation unit, and the feedback voltage. It includes an analog-digital conversion unit that converts the voltage into a digital value, and has a control unit that generates a control signal that controls the voltage generation unit based on the converted digital value.

It is possible to suppress a decrease in the accuracy of the voltage generated by the voltage generation unit of the power supply device.

It is explanatory drawing which shows the structure of the image forming apparatus which concerns on one Embodiment of this invention. It is a block diagram which shows the structure of the hardware which charges a charging roller in the image forming apparatus shown in FIG. It is explanatory drawing which shows the example of the operation of the charge current detection part of FIG. It is explanatory drawing which shows the example of the operation of the charge current detection part when the image formation apparatus of FIG. 1 has two image formation modes in which image formation speeds are different. It is a block diagram (comparative example) which shows the structure of the hardware which charges a charging roller in another image forming apparatus. It is explanatory drawing which shows the example of the operation of the charge current detection part of FIG.

Hereinafter, embodiments will be described with reference to the drawings. In each drawing, the same components may be designated by the same reference numerals, and duplicate description may be omitted.

FIG. 1 is an explanatory diagram showing a configuration of an image forming apparatus 100 according to an embodiment of the present invention. Note that, in FIG. 1, only the main elements of the image forming apparatus 100 are shown for the sake of clarity.

The image forming apparatus 100 includes a drum-shaped photoconductor 10, a charging roller 12, an exposure unit 14, a developing unit 16, a transfer roller 18, an intermediate transfer belt 20, a static elimination unit 22, a cleaning blade 24, and high-voltage power supplies 30 and 40. ing. Then, the image forming apparatus 100 forms an image by an electrophotographic method. The photoconductor 10 is an example of an image carrier, the charging roller 12 is an example of a charging member, and the high-voltage power supply 30 is an example of a power supply device.

The high-voltage power supply 30 superimposes a high-voltage DC voltage and a high-voltage AC voltage to generate a high voltage (for example, a negative voltage), and applies the generated high voltage to the charging roller 12. The high-voltage power supply 40 generates a high voltage (for example, a positive voltage), and applies the generated high voltage to the transfer roller 18.

The charging roller 12 is in contact with or close to the photoconductor 10 at a distance of about several tens of microns, and is discharged between the surface of the photoconductor 10 and the surface of the charging roller 12 by a high voltage applied from the high voltage power supply 30. To generate. As a result, the surface of the photoconductor 10 is uniformly charged to a predetermined potential. In FIG. 1, the photoconductor 10 rotates clockwise, and the charging roller 12 and the transfer roller 18 rotate counterclockwise.

The exposure unit 14 exposes the surface of the photoconductor 10 in response to an image signal to form an electrostatic latent image on the photoconductor 10. The developing unit 16 develops an electrostatic latent image formed on the photoconductor 10 to form a toner image on the photoconductor 10. The transfer roller 18 transfers the toner image on the photoconductor 10 to the intermediate transfer belt 20 by the high voltage applied from the high voltage power source 40. The toner image transferred to the intermediate transfer belt 20 is transferred to a recording material such as paper by a transfer unit (not shown), and then fixed by a fixing mechanism (not shown). As a result, an image is formed on the recording material. In the case of the direct transfer method, a recording material is arranged instead of the intermediate transfer belt 20, and the toner image on the photoconductor 10 is directly transferred to the recording material. In the following description, the formation of an image by an image forming apparatus is also referred to as printing.

The static elimination unit 22 removes the electric charge on the surface of the photoconductor 10 after the toner image on the photoconductor 10 is transferred to the intermediate transfer belt 20. The image forming apparatus 100 does not have to have the static elimination unit 22. The cleaning blade 24 has elasticity, the tip of the cleaning blade 24 is in contact with the photoconductor 10 at an angle, and foreign matter such as toner and paper dust remaining on the photoconductor 10 after transfer to the recording paper is scraped off and collected. Then, the photoconductor 10 is cleaned.

The image forming apparatus for forming a color image has elements on the upper side of the intermediate transfer belt 20 for each of the yellow, magenta, cyan, and black colors in FIG. 1, and is provided in common for the four colors. The toner images of each color are sequentially superimposed and transferred on the intermediate transfer belt. After that, the full-color toner image on the intermediate transfer belt is transferred to a recording material such as paper by the transfer unit, and then fixed by the fixing mechanism. The present embodiment and subsequent embodiments are also applicable to an image forming apparatus for forming a color image.

FIG. 2 is a block diagram showing a configuration of hardware for charging the charging roller 12 in the image forming apparatus 100 shown in FIG. The image forming apparatus 100 has a control unit 50 that controls the high voltage power supply 30 shown in FIG. The control unit 50 may have a function of controlling the high-voltage power supply 40 shown in FIG. Further, the control unit 50 may have a function of controlling the entire image forming apparatus 100. In this case, the control unit 50 may be realized by a controller such as a CPU (Central Processing Unit) that executes a control program that controls the operation of the image forming apparatus 100.

The control unit 50 includes a power supply control unit 52 and an analog-to-digital conversion unit (ADC) 54. The analog-digital conversion unit 54 receives the voltage (feedback voltage) of the charging current feedback signal output from the high-voltage power supply 30, converts the received voltage into a digital value, and outputs the voltage to the power supply control unit 52. The power supply control unit 52 calculates a digital value from the analog-to-digital conversion unit 54 and performs a process of reflecting it on a PWM (Pulse Width Modulation) signal value which is a control signal output to the high-voltage power supply 30.

As will be described later, since the charging current feedback signal (feedback voltage) is generated excluding the component corresponding to the bleeder current, the feedback voltage indicates the value of the charging current and fluctuates in response to the fluctuation of the charging current. .. Therefore, the analog-to-digital conversion unit 54 can use the full scale of the analog input for the conversion of the feedback voltage, and can improve the accuracy of the feedback voltage indicated by the digital value.

The high-voltage power supply 30 has a charge bias generation unit 32, a bleeder resistor 34, and a charge current detection unit 36. The charge bias generation unit 32 generates a high voltage (charge bias) applied to the charge roller 12 at a magnitude and timing corresponding to a control signal (for example, a PWM signal) output from the control unit 50. For example, the charging bias is a negative voltage. The charge bias generation unit 32 is an example of a voltage generation unit.

The bleeder resistor 34 is connected between the output node VOUT of the charge bias in the charge bias generation unit 32 and the ground wire, and supplies the bleeder current to the output node VOUT of the charge bias generation unit 32. The bleeder resistor 34 supplies a combined current of the charging current and the bleeding current to the charging bias output node VOUT. As a result, as compared with the case where the current flows through the bleeder resistor 34 and only the charging current is supplied without supplying the bleeding current, the charging bias generating unit 32 accompanies the time-dependent change and the temperature environment change of the photoconductor 10. Since it is less susceptible to changes in the charging current due to load fluctuations, it is possible to reduce the charging bias generation error. The bleeder resistor 34 is an example of the internal resistance portion, and the bleeder current is an example of the internal current.

The charge current detection unit 36 receives a current that is a combination of the charge current flowing from the photoconductor 10 to the charge bias generation unit 32 via the charge roller 12 and the bleeder current flowing from the bleeder resistor 34 to the charge bias generation unit 32, and is charged. Detect current. Then, the charge current detection unit 36 converts the detected charge current into a charge current feedback signal (feedback voltage) and outputs the detected charge current to the control unit 50. The photoconductor 10 is an example of a load, and the charging current is an example of a load current.

The charge current detection unit 36 has a Zener diode ZD, resistors R1 and R2, and a capacitor C. The cathode of the Zener diode ZD is connected to the current output node IOUT of the charge bias generation unit 32, and the anode of the Zener diode ZD is connected to the input of the analog-to-digital conversion unit 54. The resistor R1 is connected between the cathode and the ground wire of the Zener diode ZD, and the resistor R2 and the capacitor C are connected in parallel between the anode and the ground wire of the Zener diode ZD. Hereinafter, the resistance value of the resistor R1 is also referred to as R1, and the resistance value of the resistor R2 is also referred to as R2.

In the following description, as an example, the maximum value of the charging current generated when the charging bias generating unit 32 outputs a predetermined voltage from the output node VOUT to charge the charging roller 12 is set to 100 μA, and the current is generated at this time. The maximum value of the bleeder current is 400 μA. For example, the resistance value R1 is the Zener voltage (yield voltage) of the Zener diode ZD, which is the voltage generated at the cathode of the Zener diode ZD when the offset current with the minimum charge bias flows through the resistor R1 within the generation range of the charge bias. It is set to be as above. Here, the offset current corresponds to the bleeder current that flows when the charging bias is the minimum value in the generation range.

That is, the resistance value R1 is such that the cathode voltage becomes less than the Zener voltage, which is the breakdown voltage of the Zener diode ZD, when only the bleeder current flows, and the cathode voltage becomes the Zener voltage when the combined current of the bleeder current and the charging current flows. It is set to exceed the voltage. As a result, only the component corresponding to the charging current can flow through the resistor R2, and a voltage corresponding to the charging current can be generated at the anode of the Zener diode ZD which is the input of the analog-digital conversion unit 54. For example, when a Zener diode ZD having a Zener voltage of 12 V is used, the resistance value R1 is set to 10 kΩ and the resistance value R2 is set to 70 kΩ.

The resistance value R2 is such that the feedback voltage generated at the time of the maximum charging bias within the generation range of the charging bias subtracts a predetermined margin from the maximum input value (for example, 3.3V) or the maximum input value of the analog-to-digital converter 54. Is set to the value. As a result, the fluctuation range of the feedback voltage can be made to correspond to the full scale of the analog input, which is the voltage input range of the analog-to-digital converter 54.

In this way, the charge current detection unit 36 generates a feedback voltage corresponding to the charge current from the combined current of the charge current and the bleeder current, so that the analog-digital conversion unit 54 uses the full scale of the analog input. The feedback voltage can be converted to a digital value. As a result, the accuracy of the feedback voltage indicated by the digital value output from the analog-digital conversion unit 54 can be improved, and the accuracy of the voltage generation control by the charge bias generation unit 32 can be improved. In other words, it is possible to improve the detection accuracy of the charging current with an inexpensive and space-saving circuit.

FIG. 3 is an explanatory diagram showing an example of the operation of the charge current detection unit 36 of FIG. The left side of FIG. 3 shows the detection current flowing through the charge current detection unit 36 when the image forming apparatus 100 forms an image. That is, the left side of FIG. 3 shows the operation when the image forming apparatus 100 prints one image. Here, the detection current is indicated by the sum of the charging current and the bleeder current. The offset current is a bleeder current that flows when the charge bias generator 32 generates the minimum charge bias, and is a current that yields the Zener diode ZD. In the figure, the offset current line is shown slightly below the bleeder current for readability. The right side of FIG. 3 shows the feedback voltage generated by the charge current detection unit 36 according to the detection current.

On the left side of FIG. 3, when the printing operation is started, the charge bias generation unit 32 generates a predetermined charge bias (any of −400 to −1000 V), and the photoconductor 10 is charged (discharged) via the charging roller 12. Then, a charging current flows. For example, the charging current flows during a period in which the photoconductor 10 makes one rotation and the entire surface of the photoconductor 10 is charged. The bleeder current always flows while the charge bias generator 32 generates a predetermined charge bias for the printing operation. Therefore, during the period in which the charging current is flowing to charge the photoconductor 10, the detection current is the sum of the charging current and the bleeder current, and shows the maximum value. On the other hand, during the period when the photoconductor 10 is completely charged and the charging current does not flow, the detection current is only the bleeder current.

On the right side of FIG. 3, as described with reference to FIG. 2, due to the action of the Zener diode ZD and the resistor R1, no current flows through the resistor R2 when the current flowing through the resistor R1 is lower than the offset current, and the resistor R1 is pressed. The current flows when the flowing current is equal to or greater than the offset current. Therefore, the feedback voltage is generated by the current corresponding to the charging current flowing through the resistor R2 when the current flowing through the resistor R1 becomes equal to or greater than the offset current. As a result, the full scale of the analog input of the analog-to-digital conversion unit 54 can be used for the conversion of the feedback voltage. Therefore, the resolution of the feedback voltage is improved as compared with the feedback voltage generated by passing a current including the bleeder current through the resistor R2, and the charging current can be detected with high accuracy. The value of the minimum resolution of the analog-to-digital conversion unit 54 in FIG. 3 is represented by the equation (1).
Minimum resolution = (maximum value of detected current-offset current) / (full scale value + 1) ... (1)
Here, the unit of the maximum value of the detected current and the offset current is "μA". The full-scale value is a value obtained by subtracting 1 from 2 (the number of resolution bits), and for example, when the number of resolution bits of the analog-digital conversion unit 54 is 8 bits, the full-scale value is 255.

FIG. 4 is an explanatory diagram showing an example of the operation of the charge current detection unit 36 when the image forming apparatus 100 of FIG. 1 has two image forming modes having different image forming speeds. Detailed description of the same elements as in FIG. 3 will be omitted.

For example, the charge bias generation unit 32 generates a voltage of −1000 V in the high-speed mode in which the printing speed is high, and generates a voltage of −500 V in the low-speed mode in which the printing speed is slow. Therefore, the charging current in the high-speed mode is larger than the charging current in the low-speed mode, and the bleeder current in the high-speed mode is larger than the bleeder current in the low-speed mode. When the image forming apparatus 100 has a plurality of image forming modes having different printing speeds, the offset current for yielding the Zener diode ZD is set according to the bleeding current in the mode in which the bleeding current is the lowest. In other words, the Zener voltage (yield voltage) of the Zener diode ZD and the resistance values R1 and R2 are set according to the lowest bleeder current. Also in FIG. 4, the line of the offset current is shown below the bleeder current in the low speed mode in consideration of legibility.

As a result, even in an image forming apparatus having a plurality of operation modes in which the charging current and the bleeder current are different from each other, the resolution of the feedback voltage can be improved as compared with the case where the offset is not set. As a result, the accuracy of voltage generation by the charge bias generation unit 32 can be improved as compared with the case where the feedback voltage corresponding to the current including the bleeder current is generated.

FIG. 5 is a block diagram (comparative example) showing a configuration of hardware for charging the charging roller 12 in another image forming apparatus 102. The same elements as those in FIG. 2 are designated by the same reference numerals, and detailed description thereof will be omitted. The image forming apparatus 102 is the same as the image forming apparatus 100 shown in FIGS. 1 and 2 except that the high voltage power supply 30 has the charging current detecting unit 37 instead of the charging current detecting unit 36.

The charge current detection unit 37 detects a combined current of the charge current flowing from the photoconductor 10 to the charge bias generation unit 32 via the charge roller 12 and the bleeder current flowing from the bleeder resistor 34 to the charge bias generation unit 32. Then, the charge current detection unit 37 converts the detected current into a charge current feedback signal (feedback voltage) and outputs the detected current to the control unit 50.

The charge current detection unit 37 has a resistor R3 and a capacitor C connected in parallel between the current output node IOUT of the charge bias generation unit 32 and the ground wire. The current output node IOUT is connected to the input of the analog-to-digital converter 54. To the input of the analog-to-digital conversion unit 54, a voltage VR3 generated by flowing a current including a charging current and a bleeder current output from the current output node IOUT through the resistor R3 is supplied as a feedback voltage.

The analog-digital conversion unit 54 converts the feedback voltage VR3 corresponding to the combined current of the charging current and the bleeder current into a digital value and outputs it to the power supply control unit 52. Therefore, the power supply control unit 52 calculates the digital value corresponding to the charging current among the digital values from the analog-to-digital conversion unit 54, and performs a process of reflecting the digital value in the PWM signal value of the control signal output to the high-voltage power supply 30. ..

FIG. 6 is an explanatory diagram showing an example of the operation of the charge current detection unit 37 of FIG. A detailed description of the same operation as in FIG. 3 will be omitted. The left side of FIG. 6 shows the detection current flowing through the charge current detection unit 37 when the image forming apparatus 102 forms an image. The left side of FIG. 6 is the same as the left side of FIG. 3 except that the offset current is not set. The right side of FIG. 6 shows the feedback voltage generated by the charge current detection unit 37 according to the detection current.

The charge current detection unit 37 shown in FIG. 5 generates a feedback voltage corresponding to the combined current of the charge current and the bleeder current, and the analog-digital conversion unit 54 converts the feedback voltage into a digital value and power control unit. Output to 52. For example, the side with a low feedback voltage corresponds to the detection voltage due to the bleeder current, and the side with a high feedback voltage corresponds to the detection voltage due to the charging current. Therefore, the substantial resolution of the charging current by the analog-digital conversion unit 54 is lower than the resolution shown on the right side of FIG. The value of the minimum resolution of the analog-to-digital conversion unit 54 in FIG. 5 is represented by the equation (2).
Minimum resolution = (maximum value of detected current) / (full scale value + 1) ... (2)
The unit of the maximum value of the detected current is "μA".

As described above, in this embodiment, the charge current detection unit 36 removes the bleeder current component and generates a feedback voltage corresponding to the charge current, so that the analog-digital conversion unit 54 converts the full scale of the analog input into the feedback voltage. Can be used for. As a result, the accuracy of the feedback voltage indicated by the digital value can be improved, and even when the bleeder resistor 34 for reducing the generation error of the charging bias is included in the high-voltage power supply 30, the voltage generated by the charging bias generating unit 32 It is possible to improve the generation accuracy of.

By extracting the charging current by the charging current detecting unit 36 using the Zener diode ZD, the charging current detecting unit 36 can be configured by a simple circuit. In other words, it is possible to improve the detection accuracy of the charging current with an inexpensive and space-saving circuit.

For example, the resistance value R1 is such that the cathode voltage becomes less than the Zener voltage, which is the breakdown voltage of the Zener diode ZD, when only the bleeder current flows, and the cathode voltage becomes the Zener voltage when the combined current of the bleeder current and the charging current flows. It is set to exceed the voltage. As a result, only the component of the charging current can flow through the resistor R2, and a voltage corresponding to the charging current can be generated at the anode of the Zener diode ZD which is the input of the analog-digital conversion unit 54.

For example, the resistance value R2 is such that the feedback voltage generated at the time of the maximum charging bias within the generation range of the charging bias has a predetermined margin from the maximum input value (for example, 3.3V) or the maximum input value of the analog-to-digital converter 54. It is set to be the value obtained by subtracting. As a result, the fluctuation range of the feedback voltage can be made to correspond to the full scale of the analog input of the analog-to-digital conversion unit 54.

As a result, the accuracy of the feedback voltage indicated by the digital value output from the analog-digital conversion unit 54 can be improved, and the accuracy of the voltage generation control by the charge bias generation unit 32 can be improved.

Although the present invention has been described above based on each embodiment, the present invention is not limited to the requirements shown in the above embodiments. With respect to these points, the gist of the present invention can be changed without impairing it, and can be appropriately determined according to the application form thereof.

10 Photoreceptor 12 Charging roller 14 Exposure unit 16 Developing unit 18 Transfer roller 20 Intermediate transfer belt 22 Static elimination unit 24 Cleaning blade 30 High-voltage power supply 32 Charging bias generator 34 Breeder resistor 36, 37 Charging current detector 40 High-voltage power supply 50 Control unit 52 Power control unit 54 Analog-to-digital converter 100, 102 Image forming device C Capacitor R1, R2, R3 Resistor ZD Zener diode

Japanese Unexamined Patent Publication No. 9-218567

Claims (5)

A voltage generator that generates the voltage to be supplied to the load,
An internal resistance unit that generates an internal current to be supplied to the voltage generation unit, and an internal resistance unit.
A current detection unit that generates a feedback voltage corresponding to the load current from a total current of the load current flowing from the load to the voltage generation unit and the internal current according to the voltage generated by the voltage generation unit.
A power supply device including an analog-digital conversion unit that converts the feedback voltage into a digital value, and a control unit that generates a control signal that controls the voltage generation unit based on the converted digital value. The current detector
A Zener diode whose cathode is connected to the current output node of the voltage generator and whose anode is connected to the input of the analog-to-digital converter.
A first resistor connected between the cathode and the ground wire,
The power supply device according to claim 1, further comprising a second resistor connected between the anode and the ground wire. The first resistor is set to a resistance value such that the voltage generated at the cathode by the current flowing through the first resistor at the minimum voltage generated by the voltage generator to supply the load is equal to or higher than the Zener voltage. ,
The second resistor makes the voltage of the anode equal to or lower than the maximum input voltage of the analog-to-digital converter when a current corresponding to the maximum load current flows through the second resistor, and also causes the maximum digital. The power supply according to claim 2, which is set to a resistance value to be converted into a value. Image carrier and
A charging member that charges the image carrier and
A voltage generating unit that generates a voltage applied to the charging member,
An internal resistance unit that generates an internal current to be supplied to the voltage generation unit,
A current detection unit that generates a feedback voltage corresponding to the charging current from a total of the charging current flowing from the image carrier to the voltage generating unit and the internal current according to the voltage generated by the voltage generating unit.
An image forming apparatus including an analog-digital conversion unit that converts the feedback voltage into a digital value, and a control unit that generates a control signal that controls the voltage generation unit based on the converted digital value. The image forming apparatus according to claim 4, wherein the current detection unit generates the feedback voltage in a range matched to the voltage input range of the analog-to-digital conversion unit.

Images