JP7536610B2 - Image forming device - Google Patents

Description

The present invention relates to an electrophotographic image forming apparatus.

Conventionally, electrophotographic image forming devices that copy images onto recording paper have been in widespread use. In this image forming device, a photoconductor that is uniformly charged to a positive or negative high potential is irradiated with light such as a laser in accordance with the image to be copied, forming a latent image on the photoconductor by electrostatic charge. Then, a developer such as toner is blown to the part where the latent image is formed by electrostatic force, and developed on the photoconductor. Next, a recording paper is placed on the developed developer on the photoconductor, and a charge of the opposite polarity to the charge held by the developer is applied from the back side of the recording paper, and the developer is attracted to the surface of the recording paper by electrostatic force and transferred. After that, heat and pressure are applied to the recording paper to fix the transferred developer. In this way, in electrophotographic image forming devices, the developer is moved using electrostatic force in each process, so various high voltages with various polarities are required. There are various types of high-voltage power supplies that generate such high voltages, and for example, Patent Document 1 proposes a high-voltage power supply that has a small number of parts and is composed of a circuit that generates high voltages at low cost.

Patent No. 5590956

Figure 8 is a circuit diagram showing the circuit configuration of a development power supply unit 800 that generates a development voltage to be applied to a development roller that attaches toner to an electrostatic latent image formed on a photosensitive drum in an image forming apparatus. The circuit diagram in Figure 8 is a circuit diagram described in the above-mentioned Patent Document 1. In Figure 8, an amplifier unit 802 has a push-pull circuit consisting of transistors 810 and 812, and outputs a square wave amplified based on a pulse signal CLK output from a CPU 801 with the potential of the power supply voltage V1 and the ground potential as references. The square wave output from the amplifier unit 802 is input to the primary winding of a step-up transformer 804, and a stepped-up square-wave AC voltage is output to the secondary winding. The AC voltage output from the step-up transformer 804 is rectified and smoothed, and is output as a development voltage by superimposing a DC voltage generated in a resistor 807, and is applied to the development roller. A detailed explanation of the circuit in Figure 8 will be given later.

However, in the circuit shown in FIG. 8, the duty of the developing voltage output from the output terminal of the developing power supply unit 800 can be controlled by changing the duty of the pulse signal CLK output from the CPU 801. However, in the circuit shown in FIG. 8, the difference between the peak voltage on the upper limit side (positive voltage side) and the peak voltage on the lower limit side (negative voltage side) of the output developing voltage, that is, the peak-to-peak voltage (hereinafter referred to as the peak-to-peak voltage), cannot be changed. The peak-to-peak voltage is an element that affects the image quality in an image forming apparatus, and the optimal value is determined through trial and error in the product development process. In order to further improve the image quality, it is preferable to be able to control the peak-to-peak voltage so that it can be changed depending on the printing time, the paper type, the operating environment, and the degree of toner deterioration. On the other hand, since the circuit shown in FIG. 8 described above has very high cost performance as a circuit for generating the developing voltage, it is not preferable to significantly change the circuit to control the peak-to-peak voltage so that it can be changed, as this increases costs. Therefore, it is desired to control the peak-to-peak voltage of the developing voltage so that it can be changed without changing the circuit of the developing power supply unit 800 shown in FIG. 8 as much as possible.

The present invention was made under these circumstances, and aims to make it possible to change the peak-to-peak voltage of the development voltage.

To solve the above problems, the present invention has the following configuration:

(1) In an image forming apparatus including a photosensitive drum, a developing means for attaching toner to the photosensitive drum and developing an electrostatic latent image formed on the photosensitive drum, a first power supply unit for converting an AC voltage supplied from a commercial power source into a DC voltage and converting the DC voltage to output a base voltage, a second power supply unit for converting the base voltage to output a developing voltage and supplying the developing voltage to the developing means, and a development control unit for controlling the developing means to form a toner image on a recording material, the first power supply unit has a transformer having a primary winding, an auxiliary winding, and a secondary winding, a switching unit for switching the conduction state of the DC voltage to the primary winding of the transformer, and a plurality of resistors including a variable resistor, and a voltage between the secondary winding of the transformer and the auxiliary winding is connected to the secondary winding of the transformer. An image forming apparatus having a voltage divider circuit that divides the base voltage output, an error detection means that outputs a voltage corresponding to the difference between the voltage divided by the voltage divider circuit and a reference voltage, a transmission means that transmits a feedback current corresponding to the output voltage from the error detection means on the secondary side of the transformer to the primary side of the transformer, and a switching control means that controls the switching means to be on or off according to the feedback current and the voltage generated in the auxiliary winding of the transformer, and the development control means changes the resistance value of the variable resistor included in the voltage divider circuit and changes the base voltage output from the first power supply unit so that the peak-to-peak voltage of the development voltage output by the second power supply unit becomes a target voltage value.

According to the present invention, the peak-to-peak voltage of the development voltage can be changed.

1 is a cross-sectional view showing the configuration of an image forming apparatus according to a first embodiment, a second embodiment, and a conventional example; FIG. 1 is a diagram for explaining power supply in a conventional image forming apparatus; FIG. 1 is a diagram for explaining waveforms of developing voltages output from developing power supply units in the first and second embodiments and the conventional example; A circuit diagram illustrating the circuit configuration of a low-voltage power supply unit in a conventional example. A circuit diagram illustrating the circuit configuration of a low-voltage power supply unit according to the first embodiment. A circuit diagram illustrating the circuit configuration of a development power supply unit according to the first embodiment. FIG. 1 is a block diagram illustrating a power supply in an image forming apparatus according to a first embodiment of the present invention. A circuit diagram showing the circuit configuration of a conventional development power supply unit.

[Configuration of a conventional development voltage power supply]
FIG. 8 is a circuit diagram showing a circuit configuration of a development power supply unit 800 that generates a high voltage to be applied to a development roller 104 (see FIG. 1) described later, which is described in the above-mentioned Patent Document 1, among the high-voltage power supplies included in the image forming apparatus. The circuit shown in FIG. 8 is a circuit that generates an AC voltage from a step-up transformer 804 and also generates a DC voltage. In the circuit of FIG. 8, an amplifier unit 802 amplifies a pulse signal CLK output from a CPU 801 at a constant amplification factor. The amplifier unit 802 is composed of resistors 813, 814, 815, and 816, NPN-type transistors 810 and 811, and a PNP-type transistor 812. The resistors 814, 815, and 816, the NPN-type transistor 810, and the PNP-type transistor 812 form a push-pull type drive circuit. The amplifier unit 802 outputs a rectangular wave amplified based on the potential of a power supply voltage V1, which is a reference power supply, and a ground potential (ground).

The CPU 801 is a CPU that controls the operation of the image forming apparatus 100 (see FIG. 1), which will be described later. In FIG. 8, the CPU 801 outputs a pulse signal CLK for generating an AC voltage, and adjusts the DC voltage generated on the secondary side of the step-up transformer 804 by changing the time width (hereinafter, the duty) in one period of the pulse signal CLK. The pulse signal CLK is input to the base terminal of the transistor 811 via a resistor 813. When the pulse signal CLK is at a high level, the transistor 811 turns on, and the current supplied from the power supply voltage V2 flows into the ground (hereinafter, the GND) through the resistor 814 and the collector-emitter of the transistor 811. At this time, the transistor 810 is turned off because no current is supplied to the base terminal. When the transistor 810 is turned off, no current flows through the primary side of the step-up transformer 804, and therefore no high voltage is generated at the output terminal on the secondary side of the step-up transformer 804.

Next, when the pulse signal CLK output from the CPU 801 transitions from high to low, the transistor 811 transitions from on to off. When the transistor 811 turns off, the current supplied from the power supply voltage V2 flows into the base terminal of the transistor 810 via the resistor 814, turning the transistor 810 on and the transistor 812 off. As a result, the current supplied from the power supply voltage V1 flows into the primary winding of the step-up transformer 804 via the resistor 815, between the collector and emitter of the transistor 810, and the coupling capacitor 803, exciting the primary winding of the step-up transformer 804. The coupling capacitor 803 is a capacitor for cutting the DC component of the output from the amplifier 802.

When the primary winding of the step-up transformer 804 is excited, a voltage according to the turns ratio is induced in the secondary winding of the step-up transformer 804, and a voltage according to the voltage induced in the secondary winding is generated at the output terminal of the secondary side. The current flowing in the secondary side of the step-up transformer 804, which is generated from the voltage induced in the secondary winding of the step-up transformer 804, flows into the capacitor 806 via the diode 805. On the other hand, the current flowing in the secondary side of the step-up transformer 804 also flows into the resistor 807 and the capacitor 809 via the Zener diode 817, resistor 818, and GND connected to the cathode terminal of the diode 805. The DC voltage generated in the resistor 807, which is a DC voltage generation circuit, is superimposed on the AC voltage, and is output to the output terminal of the secondary side of the step-up transformer 804 as a development voltage of high AC voltage superimposed on the DC voltage.

Next, when the pulse signal CLK output from the CPU 801 transitions from low level to high level again, the transistor 812 turns on. Then, the current flowing through the primary side of the step-up transformer 804 flows into GND via the coupling capacitor 803, the transistor 812, and the resistor 816. At this time, a voltage is generated in the secondary winding of the step-up transformer 804 in the opposite direction to when the transistor 810 is on, but since the diode 805 is connected to the secondary winding of the transformer 115, no current flows through the secondary side of the step-up transformer 804. By repeating the above operation with the duty of the pulse signal CLK, a development voltage, which is a voltage obtained by superimposing the AC voltage output from the step-up transformer 804 and the DC voltage generated in the resistor 807, is output to the output terminal of the development power supply unit 800 and applied to the development roller.

[assignment]
However, in the circuit shown in FIG. 8, the duty of the developing voltage output from the output terminal of the developing power supply unit 800 can be controlled by changing the duty of the pulse signal CLK output from the CPU 801. However, in the circuit shown in FIG. 8, the difference between the peak voltage on the upper limit side (positive voltage side) and the peak voltage on the lower limit side (negative voltage side) of the output developing voltage, that is, the peak-to-peak voltage Vpp (hereinafter referred to as voltage Vpp) cannot be controlled so as to be changeable. The voltage Vpp is an element that affects the image quality in an image forming apparatus, and an optimal voltage Vpp is determined through trial and error in the product development process. However, in order to further improve the image quality, it is preferable to be able to control the voltage Vpp so as to be changeable according to the image forming conditions that are determined based on the printing time, paper type, operating environment, and the degree of toner deterioration. On the other hand, the circuit shown in FIG. 8 described above is very cost-effective as a circuit for generating a developing voltage, and it is not preferable to significantly change the circuit of the developing power supply unit 800 shown in FIG. 8 in order to control the voltage Vpp so as to be changeable, as this increases costs. For this reason, it is desirable to be able to variably control the voltage Vpp of the developing voltage output from the developing power supply unit 800 without modifying the circuit of the developing power supply unit 800 shown in FIG.

The power supply device to which the present invention is applied is installed, for example, in an image forming device. Therefore, we will first explain a laser printer as an example of an image forming device.

[Configuration of Image Forming Apparatus]
FIG. 1 shows a cross-sectional view of a monochrome laser printer (hereinafter, printer) 100 of the first embodiment. The printer 100 includes a paper feed section 101, a laser scanner 102 as an exposure unit, a toner tank 103, a developing roller 104 as a developing unit, a photosensitive drum 105 as a photoconductor, a transfer roller 106 as a transfer unit, a charging roller 107, and a waste toner tank 108. The photosensitive drum 105, the charging roller 107, the developing roller 104, and the toner tank 103 constitute an image forming section. The printer 100 also includes a fixing roller 109, a pressure roller 110, a discharge section 111, a transport path 112, and a developing blade 114. The paper feed section 101 stores paper P as a recording material to be printed. The laser scanner 102 irradiates the photosensitive drum 105 with a laser beam 113 (the optical path is shown by a broken line in the figure). The toner tank 103 stores magnetic toner therein. The transport path 112 is a path along which the paper P is transported. The developing blade 114 is a blade that regulates the amount of toner on the developing roller 104.

The printer 100 includes a control unit 150, which is a control means for controlling the overall image forming operation described below. The control unit 150 includes a CPU 151, a ROM, and a RAM. The CPU 151 reads out various programs, various tables, constants, etc. stored in the ROM, and executes the read out programs while using the RAM as a working area. The printer 100 also includes the above-mentioned development power supply unit 800, a low voltage power supply unit 200 that converts the AC voltage input from a commercial AC power supply into a predetermined DC voltage, and a transfer/charging power supply unit 220 that applies a high voltage to the charging roller 107 and the transfer roller 106. As described above, the CPU 151 outputs a pulse signal CLK of a predetermined duty to the development power supply unit 800 to control the output of the development voltage.

[Image Forming Operation of Printer]
Next, the image forming operation of the printer 100 will be described. When the printer 100 receives a print job from an external device such as a personal computer, a main motor 160 and a scanner motor 170, which will be described later, are driven, and each roller and the laser scanner 102 provided in the printer 100 start to operate. A negative high voltage is applied to the charging roller 107, which is a charging means, from a transfer/charging power supply unit 220 (third power supply unit) to charge the surface of the photosensitive drum 105. Image data of the print job input from the external device is converted into an image signal, and the laser scanner 102 scans the surface of the photosensitive drum 105 in the longitudinal direction (the direction of the rotation axis of the photosensitive drum 105) while blinking the laser light 113 in response to the image signal. As a result, the charge disappears on the portion of the surface of the photosensitive drum 105 irradiated with the laser light 113, and an electrostatic latent image is formed. A negative high voltage is applied to the developing roller 104 from a developing power supply unit 800. The developing roller 104 has a magnet inside, which attracts the magnetic toner in the toner tank 103 by magnetic force and adheres the toner to the electrostatic latent image on the photosensitive drum 105 by electrostatic force. This forms a toner image on the surface of the photosensitive drum 105. In addition, the developing blade 114 is given a potential difference of, for example, several hundred volts with respect to the developing roller 104. Therefore, the toner on the developing roller 104 is uniformly coated by electrostatic force as well as being physically restricted by the main body of the developing blade 114.

On the other hand, the paper P fed from the paper feed unit 101 is transported along the transport path 112 and is sandwiched by the nip formed by the transfer roller 106 and the photosensitive drum 105. At this time, a positive high voltage is applied to the transfer roller 106 from the transfer/charging power supply unit 220, and the toner on the photosensitive drum 105 is pulled by the transfer roller 106 and transferred to the paper P. The paper P to which the toner has been transferred is then transported toward the discharge unit 111 and sandwiched by the nip formed by the fixing roller 109 and the pressure roller 110. In the nip, the paper P is heated to, for example, several hundred degrees by the fixing roller 109 and pressurized by the pressure roller 110, and the toner (i.e., unfixed toner) that was on the paper P only by electrostatic force is fixed to the paper P. The paper P after the toner has been fixed is then discharged to the discharge unit 111 and stacked on the discharge unit 111.

On the other hand, some toner may remain on the photosensitive drum 105 even after transfer to the paper P. Ideally, all of the toner on the photosensitive drum 105 should be transferred to the paper P, but in reality, the amount of charge that the toner has is not uniform, so some toner remains on the photosensitive drum 105 even after transfer to the paper P. The waste toner tank 108 is a container for scraping off and collecting the toner remaining on the photosensitive drum 105 with a blade that is in contact with the photosensitive drum 105. The toner remaining on the photosensitive drum 105 is removed by the blade, and the photosensitive drum 105 is charged again by the charging roller 107, and the next electrostatic latent image is formed by the laser scanner 102. The printer 100 forms an image on the paper P by repeating the above image forming operations.

[Supply of power supply voltage in image forming apparatus]
The printer 100 includes a low-voltage power supply unit 200 that converts AC voltage input from a commercial AC power supply into a predetermined DC voltage, a development power supply unit 800 that generates high voltages to be applied to the development roller 104, the charging roller 107, and the transfer roller 106, and a transfer/charging power supply unit 220. The printer 100 further includes various devices such as a main motor 160 and a scanner motor 170 that are driven by the DC voltage generated by the low-voltage power supply unit 200 (first power supply unit), a DC/DC converter 210 that converts the power supply voltage to be supplied to control system devices, etc.

Figure 2 is a block diagram explaining the supply relationship of the power supply voltage in the printer 100. In Figure 2, the low voltage power supply unit 200 converts the AC voltage (AC 120V/230V) supplied from a commercial AC power supply (indicated as AC in the figure) into a DC voltage of 24V (DC 24V). The DC 24V, which is the base voltage, is supplied to the DC/DC converter 210, the development power supply unit 800, the transfer/charging power supply unit 220, and the main motor 160 and scanner motor 170, which are driving means.

The DC/DC converter 210 converts the input DC 24V to DC 3.3V, which is a voltage for the control system, and supplies it to the control unit 150 having the CPU 151. The DC/DC converter 210 is equipped with a control circuit that performs on/off control of the built-in switching element so that the output voltage remains 3.3V even if the input voltage of DC 24V changes.

As explained in FIG. 8, the development power supply unit 800 (second power supply unit) generates a development voltage to be applied to the development roller 104 from the input DC 24V (corresponding to voltage V1 in FIG. 8). The transfer/charging power supply unit 220 generates a high voltage to be applied to the charging roller 107 and transfer roller 106 from the input DC 24V. Like the DC/DC converter 210, the transfer/charging power supply unit 220 is equipped with a control circuit that performs on/off control of the built-in switching element so that the output voltage applied to the charging roller 107 and transfer roller 106 does not change even if the input DC 24V changes.

The main motor 160 is a motor that drives each roller (e.g., the photosensitive drum 105, the developing roller 104, the transfer roller 106, etc.) in the printer 100. The scanner motor 170 is a motor that is provided in the laser scanner 102 and drives a rotating polygon mirror (not shown) that deflects the optical path of the laser light 113 so that the laser light 113 can scan the surface of the photosensitive drum 105. The rotation state of the main motor 160 is output to the CPU 151 using an encoder. The CPU 151 performs rotation control to keep the number of rotations of the main motor 160 constant based on the output from the encoder, so that the rotation speed can be maintained even if the DC 24V changes. The scanner motor 170 is also the same as the main motor 160.

As explained above, the power supply units and motors excluding the development power supply unit 800 have circuits and configurations that perform feedback control so that the generated output voltage and rotation speed do not change even if the base voltage DC 24V changes. However, the conventional circuit of the development power supply unit 800 described in Figure 8 does not have a feedback circuit for maintaining the output voltage at a predetermined voltage because it is the circuit configuration that can be manufactured at the lowest cost. Therefore, in the case of the circuit in Figure 8, when the power supply voltage V1, which is the base voltage, changes, the development voltage Vpp output from the output terminal changes.

[Variable control of main voltage]
However, as described above, the DC/DC converter 210 and the transfer/charging power supply unit 220, excluding the development power supply unit 800, to which the DC 24V, which is the base voltage output from the low voltage power supply unit 200 shown in FIG. 2, are supplied, each has a feedback circuit. In addition, the rotation of the main motor 160 and the scanner motor 170 is controlled by the CPU 151. Therefore, even if the base voltage of DC 24V changes, there is no problem with the output voltage or rotation speed. Therefore, in this embodiment, in order to change the voltage Vpp of the development voltage output by the development power supply unit 800, the base voltage of DC 24V output by the low voltage power supply unit 200 is changed within a certain range.

In the circuit diagram shown in FIG. 8, the power supply voltage V1 input to the collector terminal of the transistor 810 is the base voltage DC 24V. When the base voltage increases, the voltage Vpp of the development voltage output from the development power supply unit 800 also increases, and when the base voltage decreases, the voltage Vpp of the development voltage also decreases. FIG. 3 is a diagram explaining the change in the voltage Vpp of the development voltage output according to the change in the base voltage. FIG. 3(a) is a diagram showing a voltage waveform 301 of the development voltage output from the development power supply unit 800 having the circuit configuration shown in FIG. 8. In FIG. 3(a), the horizontal axis indicates time, the vertical axis indicates voltage (unit: V), and voltages above 0V indicate positive voltages (+), and voltages below 0V indicate negative voltages (-). The vertical and horizontal axes are the same for FIGS. 3(b) and (c) described below. As shown in FIG. 3(a), the development voltage is a rectangular wave AC voltage, and the voltage difference between the maximum voltage on the positive voltage (+) side and the minimum voltage on the negative voltage (-) side is the voltage Vpp.

Figure 3(b) is a diagram comparing the voltage waveform 302 of the development voltage output when the base voltage is increased with the voltage waveform 301 when the base voltage is not changed. As shown in Figure 3(b), the development voltage when the base voltage is increased is also a rectangular AC voltage, and it can be seen that the voltage Vpp of the voltage waveform 302 (shown as New_Vpp in the figure) is larger than the voltage Vpp of the voltage waveform 301.

Figure 3(c) is a diagram comparing the voltage waveform 303 of the developing voltage output when the base voltage is reduced with the voltage waveform 301 when the base voltage is not changed. As shown in Figure 3(c), the voltage of the developing voltage when the base voltage is reduced is also a rectangular AC voltage, and it can be seen that the voltage Vpp of the voltage waveform 303 (shown as New_Vpp in the figure) is smaller than the voltage Vpp of the voltage waveform 301. As shown in Figures 3(b) and (c) in the developing power supply unit 800, by increasing or decreasing the input base voltage, the voltage Vpp of the developing voltage output also increases or decreases according to the base voltage.

In this embodiment, the range in which the base voltage DC24V can be changed is limited to the range that other devices other than the development power supply unit 800 shown in FIG. 2 can tolerate. In other words, the output voltage is maintained by feedback control in devices other than the development power supply unit 800 shown in FIG. 2, and the voltage of DC24V is changed within a range in which no problems occur in the withstand voltage or loss of the components. Therefore, it is desirable to keep the range of DC24V that can actually be increased or decreased small. In this embodiment, if the range of the base voltage, which is the output voltage of the low-voltage power supply unit 200, is DC24V±5% (=DC22.8V to DC25.2V), all devices to which the base voltage is supplied are guaranteed to operate normally within this voltage standard range. Therefore, there is no problem in changing the base voltage of the low-voltage power supply unit 200 within the range of DC24V±5% in order to change the voltage Vpp of the development voltage.

[Configuration of conventional low-voltage power supply unit]
FIG. 4 is a circuit diagram showing a circuit configuration of a type of DC/DC step-down converter called a ringing choke converter (hereinafter referred to as RCC) as an example of a conventional low-voltage power supply unit 200. The RCC shown in FIG. 4 includes capacitors C51 to C55, resistors R501 to R509, 511, and 512, a field effect transistor Q51 (hereinafter referred to as a main switching element Q51), a transistor Q52, and diodes D51 to D53. The RCC shown in FIG. 4 further includes a flyback transformer (hereinafter simply referred to as a transformer) T51, a Zener diode VZ51, photocouplers PC51 and PC52, an operational amplifier OP51, and a CPU500 which is a switching control means. The transformer T51 has a primary winding, a secondary winding, and an auxiliary winding. In addition, a DC voltage obtained by full-wave rectification of an AC voltage from a commercial power supply (not shown) via a bridge diode circuit (not shown) is input to both ends of the capacitor C51 shown in FIG. 4, and is smoothed by the capacitor C51.

Diode D51 and capacitor C54 form a rectifying and smoothing circuit that rectifies and smoothes the voltage generated in the secondary winding of transformer T51. Voltage-dividing resistors R507 and R508, operational amplifier OP51, resistor R506, and Zener diode VZ51 form an error detection circuit that compares the divided voltage of the output voltage of the rectifying and smoothing circuit with a reference voltage and outputs a voltage according to the voltage difference. Resistor R505 and photocoupler PC51 form a transmission circuit that transmits information from the secondary side of transformer T51, which is the output of the error detection circuit, to the primary side. Photocoupler PC52, resistor R504, and capacitors C53 and C55 form a determination circuit that determines the on-time of main switching element Q51, which is a switching means. Capacitor C52 is charged with the voltage generated in the auxiliary winding of transformer T51.

When the CPU500 outputs a low-level signal from the output terminal, the LED of the photocoupler PC52 is turned off and the phototransistor of the photocoupler PC52 is turned off. When the phototransistor of the photocoupler PC52 is turned off, all of the current flowing through the resistor R504 charges the capacitor C53. In other words, the on-time of the main switching element Q51 is determined by the time constant of the resistor R504 and the capacitor C53.

On the other hand, when the CPU 500 outputs a high-level signal from the output terminal, the LED of the photocoupler PC52 lights up and the phototransistor of the photocoupler PC52 turns on. When the phototransistor of the photocoupler PC52 is on, the current flowing through the resistor R504 charges both the capacitor C53 and the capacitor C55. In other words, when the LED of the photocoupler PC52 is turned on, the on-time of the main switching element Q51 is switched to be determined by the time constant of the resistor R504 and the capacitors C53 and C55. In this way, the CPU 500 switches the signal level output from the output terminal and switches the capacitance of the capacitor that determines the time constant, thereby switching the time constant that determines the on-time of the main switching element Q51.

In the low-voltage power supply unit 200 shown in FIG. 4, the core of the feedback control is an error detection circuit consisting of a Zener diode VZ51, multiple voltage-dividing resistors R507 and R508, and an operational amplifier OP51. Here, the Zener voltage of the Zener diode VZ51 is 5.1V, and the voltage of the trunk voltage, which is the output voltage output by the low-voltage power supply unit 200, is DC 24V. At this time, the output voltage is divided by the voltage-dividing resistors R507 and R508, and the voltage division ratio by the voltage-dividing resistors R507 and R508 is determined so that the voltage input to the inverting input terminal (-) of the operational amplifier OP51 is 5.1V. The operational amplifier OP51 compares the input voltage of the non-inverting input terminal (+) to which the reference voltage is input, with the voltage input to the inverting input terminal (-). When the voltage input to the inverting input terminal (-) of the operational amplifier OP51 is higher than the reference voltage of 5.1V, the operational amplifier OP51 increases the current flowing through the LED of the photocoupler PC51. This strengthens the light emission state of the LED of the photocoupler PC51, increases the current (feedback current) flowing through the phototransistor, turns off the main switching element Q51, and cuts off the conduction of the primary winding of the transformer T51. As a result, the voltage value of the base voltage, which is the output voltage of the RCC, is reduced. On the other hand, when the voltage input to the inverting input terminal (-) of the operational amplifier OP51 is lower than the reference voltage of 5.1V, the operational amplifier OP51 reduces the current flowing through the LED of the photocoupler PC51. This weakens the light emission state of the LED of the photocoupler PC51, reduces the current flowing through the phototransistor, turns on the main switching element Q51, and conducts the primary winding of the transformer T51. As a result, the voltage value of the base voltage, which is the output voltage of the RCC, is increased. In this way, the error detection circuit and the transmission circuit control the on/off (conducting/non-conducting) state of the main switching element Q51 so that the output voltage is DC 24V.

[Configuration of the low voltage power supply unit of this embodiment]
FIG. 5 is a circuit diagram showing the circuit configuration of the low voltage power supply unit 200 of this embodiment. The difference between the circuit diagram shown in FIG. 5 and the circuit diagram shown in FIG. 4 is that the voltage dividing resistor R507 (first resistor) in FIG. 4 is replaced with a digital potentiometer VR601, which is a variable resistor whose resistance value can be changed by a digital signal from the CPU 151. Here, the voltage dividing resistor R507 in FIG. 4 is replaced with the digital potentiometer VR601, but the voltage dividing resistor R508 (second resistor) in FIG. 4 may be replaced with the digital potentiometer VR601. Also, the voltage dividing resistors R507 and R508 in FIG. 4 may be replaced with a digital potentiometer. In the error detection circuit shown in FIG. 4, the resistance values of the voltage dividing resistors R507 and R508 are determined so that the base voltage is DC 24V. In the circuit of FIG. 5, the voltage dividing resistor R507 is replaced with a digital potentiometer VR601, which is a variable resistor, and the voltage value of the base voltage can be varied by changing the resistance value to control the voltage division ratio of the base voltage output by the low voltage power supply unit 200.

[Configuration of the Development Voltage Dividing Circuit in this Embodiment]
In this embodiment, the development voltage, which is the output voltage of the development power supply unit 800, is detected by the CPU 151, which is the development control means, and the voltage of the base voltage output by the low voltage power supply unit 200 is changed to change the voltage Vpp of the development voltage output by the development power supply unit 800. Since the development voltage is a high voltage, in order for the CPU 151 to detect the development voltage, it is necessary to provide a circuit that divides the development voltage output by the development power supply unit 800 and outputs it to the CPU 151. FIG. 6 is a circuit diagram showing a voltage dividing circuit (voltage dividing unit) that divides the development voltage output from the development power supply unit 800 and outputs it to the CPU 151. In FIG. 6, the voltage dividing circuit 900 is composed of voltage dividing resistors 901 and 902 that divide the development voltage, and the voltage generated in the voltage dividing resistor 902 is output to the CPU 151. The voltage dividing resistors 901 and 902 are set to a voltage dividing ratio that reduces the high development voltage to a voltage that the CPU 151 can detect. As a result, the CPU 151 changes the resistance value of the digital potentiometer VR601 of the low voltage power supply unit 200 based on the detected voltage Vpp of the developing voltage so that the voltage Vpp becomes a desired voltage.

[Supply of power supply voltage in the image forming apparatus of this embodiment]
FIG. 7 is a block diagram for explaining the supply relationship of the power supply voltage in the printer 100 of this embodiment, which is a block diagram in which the voltage control of the base voltage of this embodiment is added to the above-mentioned FIG. 2. As shown in FIG. 7, the voltage dividing circuit 900 divides the development voltage output from the development power supply unit 800, and outputs the divided development voltage to the CPU 151. The CPU 151 can detect the voltage Vpp of the development voltage applied to the development roller from the development power supply unit 800 by acquiring the divided development voltage. Then, the CPU 151 changes the base voltage output from the low voltage power supply unit 200 by changing the resistance value of the digital potentiometer VR601 of the low voltage power supply unit 200 based on the detected voltage Vpp of the development voltage. Then, the CPU 151 acquires the voltage Vpp of the development voltage output from the development power supply unit 800 from the voltage dividing circuit 900 according to the changed base voltage, and judges whether the voltage Vpp has reached the target voltage value. When the CPU 151 determines that the voltage Vpp has not reached the target voltage value, it changes the resistance value of the digital potentiometer VR601 of the low-voltage power supply unit 200 to change the base voltage output from the low-voltage power supply unit 200. In this way, the CPU 151 can control the base voltage output from the low-voltage power supply unit 200 so that the voltage Vpp of the development voltage becomes the target voltage value.

The developing power supply unit 800 has been described as a power supply unit controlled by the CPU 151 that controls the printer 100. For example, the developing power supply unit 800 may be configured to include an independent CPU as a control unit, and to control the developing power supply unit 800 in response to control instructions from the CPU 151.

As described above, in this embodiment, the voltage dividing resistor of the error detection circuit, which is the feedback circuit of the low voltage power supply unit 200 that generates the base voltage from the AC voltage of the commercial AC power supply, is changed to a variable resistor, thereby making it possible to change the base voltage. Furthermore, a voltage dividing circuit 900 is provided that divides the development voltage output from the development power supply unit 800 and outputs it to the CPU 151. This realizes an image forming apparatus that can change the voltage Vpp of the development voltage without changing the configuration of the development power supply unit 800.

As described above, according to this embodiment, the peak-to-peak voltage of the development voltage can be changed.

In the first embodiment, an example was described in which the peak-to-peak voltage of the development voltage output from the development power supply unit is changed by changing the base voltage output from the low-voltage power supply unit. In the first embodiment, a voltage divider circuit is provided to reduce the high development voltage to a voltage detectable by the CPU so that the CPU can detect the development voltage. The development voltage output from the development power supply unit is output to the voltage divider circuit, and the development voltage divided by the voltage divider circuit is input to the CPU. For this reason, it is necessary to use a high-voltage resistor for the voltage divider circuit, which increases costs. Even if the CPU does not change the peak-to-peak voltage during printing, etc., the base voltage output from the low-voltage power supply unit may not be a specified voltage due to the characteristic variations of the parts, and the CPU may change the base voltage output from the low-voltage power supply unit. In the second embodiment, a configuration is described in which the voltage divider circuit added in the first embodiment is not provided to suppress the increase in costs, and the low-voltage power supply unit can output a specified base voltage without the base voltage variation due to the characteristic variations of the parts. The configuration of the printer 100 in Example 2 is the same as that in Example 1, and the same devices and components are designated by the same reference numerals as in Example 1, and the description thereof will be omitted here.

[Configuration of the low voltage power supply unit of this embodiment]
The low voltage power supply unit 200 of this embodiment has a configuration in which a non-volatile memory that is accessible from the CPU 151 and serves as a storage unit for storing the resistance value of the digital potentiometer VR601 is added to the configuration of the circuit diagram shown in Figure 5 described in embodiment 1. The configuration of the development power supply unit 800 is similar to the configuration of the circuit diagram shown in Figure 6 of embodiment 1. Note that in this embodiment, the voltage divider circuit 900 shown in Figure 6 is not provided, and therefore the CPU 151 is configured not to detect the development voltage output from the development power supply unit 800.

[Changing the mains voltage]
In the developing power supply unit 800, the voltage Vpp of the developing voltage output may differ for each device or for each board on which the circuit shown in FIG. 6 is mounted due to the tolerance of the circuit components shown in FIG. 6. In particular, due to differences in the characteristics of the components used, for example, during shipping inspection, a developing power supply unit 800 or board that outputs a voltage Vpp outside the allowable range of the average value of the developing voltage Vpp may be detected. Therefore, in this embodiment, during shipping inspection of the printer 100 with the low voltage power supply unit 200, developing power supply unit 800, etc. mounted, the voltage Vpp of the developing voltage output by the developing power supply unit 800 is measured. In detail, the resistance value of the digital potentiometer VR601 of the low voltage power supply unit 200 shown in FIG. 5 is set to a predetermined value, and the voltage Vpp of the developing voltage output by the developing power supply unit 800 at that time is measured. If the measured voltage Vpp is outside the allowable range of the target voltage Vpp, the value of the digital potentiometer VR601 is changed so that the voltage Vpp of the developing voltage becomes a predetermined voltage value, and the base voltage output by the low-voltage power supply unit 200 is adjusted. The resistance value of the digital potentiometer VR601 when the voltage Vpp of the developing voltage finally becomes the predetermined voltage value is stored in a non-volatile memory provided in the low-voltage power supply unit 200. When the printer 100 is turned on, the CPU 151 reads out the resistance value to be set in the digital potentiometer VR601 from the non-volatile memory of the low-voltage power supply unit 200. The CPU 151 then sets the read resistance value in the digital potentiometer VR601, so that the base voltage output from the low-voltage power supply unit 200 becomes a corrected voltage value, and the voltage Vpp of the developing voltage output from the developing power supply unit also becomes a predetermined voltage value. In addition, if the voltage Vpp of the developing voltage output by the developing power supply unit 800 when the resistance value of the digital potentiometer VR601 is set to a predetermined value is within the allowable range, the predetermined resistance value is stored in a non-volatile memory provided in the low voltage power supply unit 200.

In this embodiment, the development voltage output by the development power supply unit 800 is not changed during image formation as in the first embodiment, but the base voltage is corrected during shipping inspection to correct the voltage Vpp of the development voltage that varies. This makes it possible to reduce the variation in the voltage Vpp of each device of the development power supply unit 800. This embodiment can also be applied to the first embodiment by providing the above-mentioned nonvolatile memory in the low voltage power supply unit 200. In this embodiment, the CPU 151 is configured to directly access the nonvolatile memory provided in the low voltage power supply unit 200, but it may be configured so that only the CPU 500 of the low voltage power supply unit 200 can access it. In this configuration, when the power supply of the printer 100 is turned on, the CPU 151 instructs the CPU 500 of the low voltage power supply unit 200 to set the resistance value of the digital potentiometer VR601. When the CPU 500 of the low voltage power supply unit 200 receives the setting instruction, it reads the resistance value to be set in the digital potentiometer VR601 from the non-volatile memory and sets it in the digital potentiometer VR601. This allows the digital potentiometer VR601 to be set to the desired resistance value. The same can be done when changing the resistance value of the digital potentiometer VR601 depending on the image formation conditions.

As described above, according to this embodiment, the peak-to-peak voltage of the development voltage can be changed.

104 developing roller 151 CPU
200 Low voltage power supply unit 800 Development power supply unit R508 Resistor VR601 Digital potentiometer

Claims (11)

A photosensitive drum;
a developing unit that deposits toner on the photosensitive drum and develops an electrostatic latent image formed on the photosensitive drum;
a first power supply unit that converts an AC voltage supplied from a commercial power supply into a DC voltage and converts the DC voltage to output a base voltage;
a second power supply unit that converts the base voltage to output a development voltage and supplies the development voltage to the developing means;
a development control means for controlling the developing means to form a toner image on a recording material;
In an image forming apparatus comprising:
The first power supply unit is
a transformer having a primary winding, an auxiliary winding, and a secondary winding;
A switching means for switching a conduction state of the DC voltage to the primary winding of the transformer;
a voltage divider circuit having a plurality of resistors including a variable resistor, and dividing the base voltage output from the secondary winding of the transformer;
an error detection means for outputting a voltage corresponding to a difference between the voltage divided by the voltage divider circuit and a reference voltage;
a transmission means for transmitting a feedback current corresponding to an output voltage from the error detection means on the secondary side of the transformer to the primary side of the transformer;
a switching control means for controlling the switching means to be on or off in response to the feedback current and a voltage generated in an auxiliary winding of the transformer;
having
The image forming apparatus is characterized in that the development control means changes the resistance value of the variable resistor included in the voltage divider circuit so that the peak-to-peak voltage of the development voltage output by the second power supply unit becomes a target voltage value, thereby changing the base voltage output from the first power supply unit. the first power supply unit has a storage unit accessible by the development control means,
2. The image forming apparatus according to claim 1, wherein the resistance value to be set in the variable resistor is stored in advance in the storage unit. The image forming apparatus according to claim 2, characterized in that, when the power supply of the image forming apparatus is turned on, the development control means obtains the resistance value of the variable resistor from the memory unit and sets it to the variable resistor. a voltage dividing unit that divides the developing voltage output from the second power supply unit,
4. The image forming apparatus according to claim 2, wherein the voltage dividing section includes a plurality of high voltage dividing resistors. The image forming apparatus according to claim 4, characterized in that the development control means detects the peak-to-peak voltage of the development voltage based on the voltage output from the voltage dividing unit. The image forming apparatus according to claim 5, characterized in that the development control means changes the resistance value of the variable resistor of the voltage divider circuit so that the peak-to-peak voltage of the detected development voltage becomes a peak-to-peak voltage according to the image formation conditions on the recording material. The image forming device according to claim 6, characterized in that the image forming conditions are determined based on the type of recording material, the operating environment of the image forming device, and the degree of deterioration of the toner. The image forming apparatus according to claim 7, characterized in that the development control means changes the resistance value of the variable resistor of the voltage divider circuit so that the voltage value of the base voltage output from the first power supply unit is within the range of the voltage standard. The second power supply unit is
a transformer having a primary winding and a secondary winding;
A drive circuit for driving the transformer;
A generating circuit connected to a secondary winding of the transformer and configured to generate a DC voltage;
A control circuit for controlling the drive circuit;
having
9. The image forming apparatus according to claim 1, wherein the developing voltage is output by superimposing the DC voltage generated by the generating circuit on the AC voltage induced on the secondary side of the transformer. a charging means for charging the photosensitive drum to a uniform potential;
a transfer means for transferring the toner image formed on the photosensitive drum by the developing means onto a recording material;
a third power supply unit that supplies a high voltage generated from the base voltage to the charging means and the transfer means;
The image forming apparatus according to claim 1 , further comprising: A driving means for driving the photosensitive drum is provided,
11. The image forming apparatus according to claim 1, wherein the driving means is driven by the base voltage.

Images