JP2008224861A - Image forming apparatus and piezoelectric transformer system high voltage power unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric transformer system high voltage power unit with a control means for improving rising and falling characteristics of the piezoelectric transformer system high voltage power unit used for an image forming apparatus. <P>SOLUTION: The image forming apparatus comprises: the piezoelectric transformer; a generation means of a piezoelectric transformer driving frequency; an output voltage setting means; an output detection means; and an output control means for controlling output voltage by a signal from the output detection means and a control signal from the output voltage setting means, wherein the piezoelectric transformer driving frequency is controlled according to a setting value of the output voltage setting means. The image forming apparatus is provided with a control means for once setting the output voltage to output voltage with a value larger than difference before and after setting the output voltage to set output voltage to be difference after elapse of fixed time or before and after detecting the output voltage to reset the output voltage when the output voltage is set. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic process, and more particularly to a piezoelectric transformer type high voltage power supply device used in the image forming apparatus.

  In a conventionally known electrophotographic image forming apparatus, when adopting a direct transfer method in which a transfer member is brought into contact with a photoconductor to perform transfer, the transfer member has a roller-like conductivity having a conductor shaft. Using rubber, it is driven to rotate according to the process speed of the photoreceptor. A DC bias voltage is used as the voltage applied to the transfer member. At this time, the polarity of the DC bias voltage is the same as that of a normal corona discharge transfer voltage.

  However, in order to perform good transfer using such a transfer roller, it is usually necessary to apply a voltage of 3 kV or more (required current is several μA) to the transfer roller. In order to generate a high voltage required for the image forming process as described above, a winding type electromagnetic transformer has been conventionally used. However, the electromagnetic transformer is composed of a copper wire, bobbin, and magnetic core. When used in an image forming apparatus having the above specifications, the output current value is a small current of several μA. The leakage current had to be reduced to the maximum. Therefore, it is necessary to mold the winding of the transformer with an insulator, and a large transformer is required as compared with the supplied power, which hinders miniaturization and weight reduction of the high-voltage power supply device.

  Therefore, in order to compensate for these drawbacks, it has been studied to generate a high voltage by using a thin and light high-power piezoelectric transformer. That is, by using a piezoelectric transformer made of ceramic, it is possible to generate a high voltage with an efficiency higher than that of an electromagnetic transformer, and the primary side and the secondary side regardless of the coupling between the primary side and the secondary side. Since it is possible to increase the distance between the electrodes, there is no need to mold for special insulation, so that an excellent characteristic that the high-pressure generator can be made smaller and lighter is obtained.

  Here, a conventional example of a piezoelectric transformer type high voltage power supply will be described with reference to FIG.

  The circuit shown here is a high voltage power source, and 101 is a piezoelectric transformer (piezoelectric ceramic transformer) of the high voltage power source. The output of the piezoelectric transformer 101 is rectified and smoothed to a positive voltage by the diodes 102 and 103 and the high voltage capacitor 104 and supplied to a transfer roller (not shown) as a load. The output voltage is divided by the resistors 105, 106, and 107 and input to the non-inverting input terminal (+ terminal) of the operational amplifier 109 via the protective resistor 108. On the other hand, an inverting input terminal (− terminal) of the operational amplifier 109 receives a high-voltage power supply control signal (Vcont) as an analog signal from an MPU (microcomputer) 207 via a resistor 114.

  By configuring the operational amplifier 109, the resistor 114, and the capacitor 113 as shown in FIG. 8, it functions as an integration circuit, and the control signal Vcont dulled by the integration time constant determined by the component constants of the resistor 114 and the capacitor 113 is sent to the operational amplifier 109. Entered. The output terminal of the operational amplifier 109 is connected to a voltage controlled oscillator (VCO) 110, and the power supply is supplied to the primary side of the piezoelectric transformer 101 by driving the transistor 111 whose output terminal is connected to the inductor 112.

Here, the operational amplifier 109 and its peripheral circuit constitute a general integration circuit, and its output is represented by the following equation.
Output of operational amplifier 109: Vo
Capacitor 113: C
Resistor 114: R
Operational amplifier + terminal input voltage (corresponding to output voltage Vout): Vi0
Vcont: Vi
If
V0 = Vi0− (1 / RC) ∫ (Vi−Vi0) dt (Expression 1)

  FIG. 7 is a timing chart of start-up control in the conventional example.

  The level of the control signal corresponding to the output voltage 0V is Vc0. The level of the control signal from which the output voltage Vout1 is output is Vc1. The rise time at this time is T1 in FIG. Specifically, Vc0 is 0 V, Vc1 is 2.0 V, Vout1 is 2 kV, and T1 is about 120 msec.

  FIG. 6 is a control timing chart of the transfer high voltage of the paper gap bias in the conventional example.

  Vc0 is 0V, Vc1 is 2.0V, and Vout1 is 2 kV, which is the same as in FIG. 7, Vc3 is 0.7 V, Vout2 is 0.3 kV, T3 is 100 msec, and T4 is 90 msec.

  The MPU 207 sets a control signal Vcont corresponding to a paper gap (details will be described later) to Vc3 when the trailing edge of the paper being printed passes the transfer position. The output of the high voltage power supply becomes Vout2 after the time T3. The MPU 207 sets the control signal Vcont corresponding to the transfer bias to Vc1 before the time T4 when the leading edge of the next print paper reaches the transfer position. Then, the output of the high voltage power source becomes Vout1 after the time T4.

In general, the characteristics of the piezoelectric transformer have such a wide shape that the output voltage becomes maximum at the resonance frequency f0 as shown in FIG. 3, and the output voltage can be controlled by the frequency. Increasing the output voltage of the piezoelectric transformer is possible by changing the driving frequency of the piezoelectric transformer from higher to lower.
JP-A-11-206113

  In the conventional piezoelectric transformer type high voltage power supply device, when the minimum voltage is 0 V and the maximum voltage is 3 kV, it is rare to raise from 0 V to 3 kV in high voltage output control. For example, when raising from 0 V to 300 V, 1 kV Control is performed in various voltage regions, such as when starting up from 2 to 2 kV. Therefore, an ideal high voltage power source is required to always be able to quickly start up and shut down in various control areas. However, when the conventional high-voltage power supply configuration is used, the following problems remain.

  For example, when the control region is in a frequency region sufficiently higher than the resonance frequency f0, the control time becomes long and the rise of the output voltage is slow. In this case, the print process is changed, resulting in a longer throughput.

  In addition, when there is no paper between the charged photosensitive drum 305 and the ETB 409, the charge on the photosensitive drum 305 after the transfer is removed by applying a transfer bias when contacting the photosensitive drum 305, and the potential is again set by the primary charging means. Although the original state is restored, the potential on the photosensitive drum 305 is not completely restored when the charge on the photosensitive drum 305 is largely eliminated, such as when the transfer bias is strong. As a result, the potential of the photosensitive drum 305 after charging becomes different between the area corresponding to one rotation of the photosensitive drum 305 at the leading edge of the image having no history of application of the transfer bias and the subsequent areas, and the same image signal is exposed to light. In order to prevent a difference in image density from occurring even when exposed on the drum 305, a paper gap bias is applied. However, if it takes time for the output of the high-voltage power supply to rise and fall, it is necessary to open the paper and reduce the printing speed, and the effect of the paper gap bias is low.

  SUMMARY OF THE INVENTION The present invention solves the above problems, and an object of the present invention is to provide a piezoelectric transformer type high voltage power supply device used in an image forming apparatus capable of quickly controlling the rise and fall of the output voltage regardless of the control frequency region. There is to do.

To achieve the above object, the present invention provides a latent image forming means for forming an electrostatic latent image on an image carrier, a developing means for forming a toner image on the electrostatic latent image, and a transfer for transferring the toner image to a transfer material. And an image forming apparatus including a fixing unit that heats and fixes toner onto a transfer-receiving member to which a toner image has been transferred. And a piezoelectric transformer type high voltage power supply device capable of controlling the piezoelectric transformer driving frequency in accordance with the set value of the output voltage setting means. ,
When setting the output voltage, the output voltage setting means temporarily sets the output voltage to a value larger than the difference before and after setting the output voltage, and the output voltage becomes the difference before and after setting the output voltage after a certain time has elapsed. It is characterized by comprising control means for setting.

  In addition, a latent image forming unit that forms an electrostatic latent image on the image carrier, a developing unit that forms a toner image on the electrostatic latent image, a transfer unit that transfers the toner image to a transfer material, and a substrate to which the toner image is transferred. In an image forming apparatus including a fixing unit that heat-fixes toner on a transfer member, a piezoelectric transformer, a piezoelectric transformer driving frequency generation unit, an output voltage setting unit, an output detection unit, a signal from an output detection unit, and an output voltage setting unit Comprising a piezoelectric transformer type high voltage power supply device capable of controlling a piezoelectric transformer driving frequency in accordance with a set value of the output voltage setting means, wherein the output voltage setting means comprises an output When setting the voltage, once set the output voltage larger than the difference before and after setting the output voltage, the output voltage detected by the output detection means Upon reaching the target value, characterized in that it comprises a control means for setting the output voltage to be a front and rear differential for setting the output voltage.

  Further, the piezoelectric transformer type high voltage power supply device is characterized in that a high voltage is applied to the latent image forming means, the developing means, and the transfer means.

  According to the present invention, the rising and falling characteristics of the high voltage output of the piezoelectric transformer type high voltage power supply device used in the image forming apparatus can be dramatically improved by an inexpensive and simple control means.

(Example 1)
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The same components as those of the conventional example are denoted by the same symbols, and detailed description thereof is omitted.

  FIG. 2 is a configuration diagram of the color laser printer of this embodiment.

  The color laser printer 401 has a deck 402 for storing the recording paper 32, a deck paper presence / absence sensor 403 for detecting the presence or absence of the recording paper 32 in the deck 402, a pickup roller 404 for feeding the recording paper 32 from the deck 401, and the pickup roller A deck paper feed roller 405 that transports the recording paper 32 fed out by 404 and a retard roller 406 that forms a pair with the deck paper feeding roller 405 and prevents double feeding of the recording paper 32 are provided. A registration roller pair 407 that synchronously conveys the recording paper 32 and a pre-registration sensor 408 that detects the conveyance state of the recording paper 32 to the registration roller pair are disposed downstream of the deck paper feed roller 405.

  Further, an electrostatic attraction transfer belt (hereinafter referred to as ETB) 409 is disposed downstream of the registration roller pair 407, and four colors (yellow Y, magenta M, cyan C, black B) to be described later are disposed on the ETB 409. ), The images formed by the image forming unit including the process cartridges 410Y, 410M, 410C, 410B and the scanner units 420Y, 420M, 420C, 420B are sequentially superimposed by the transfer rollers 430Y, 430M, 430C, 430B. As a result, a color image is formed. The formed color image is transferred onto the recording paper 32, and the recording paper 32 is conveyed downstream. In the downstream, in order to thermally fix the toner image transferred onto the recording paper 32, a pair of a fixing roller 433 and a pressure roller 434 provided with a heater 432 for heating therein, and the recording paper 32 from the fixing roller are conveyed. The fixing paper discharge roller pair 435 and the fixing paper discharge sensor 436 for detecting the conveyance state from the fixing unit are provided.

  Each scanner unit 420 also includes a laser unit 421 that emits a laser beam modulated based on each image signal sent from a video controller 440 described later, and a laser beam from each laser unit 421 to each photosensitive drum 305. It comprises a polygon mirror 422 for scanning upward, a scanner motor 423, and an imaging lens group 424. Each process cartridge 410 includes a photosensitive drum 305, a charging roller 303 and a developing roller 302, and a toner storage container 411 necessary for a known electrophotographic process, and is configured to be detachable from the laser printer 401 main body. ing. Further, when the video controller 440 receives image data sent from an external device 441 such as a personal computer, the video controller 440 develops the image data into bitmap data and generates an image signal for image formation.

  Reference numeral 201 denotes a DC controller which is a control means of the laser printer 401. The RAM 207a, the ROM 207b, the timer 207c, the digital input / output port 207d, the MPU (microcomputer) 207 provided with the D / A port 207e, the nonvolatile storage element ( EEPROM) 205 and various input / output control circuits (not shown). Reference numeral 202 denotes a high-voltage power supply (piezoelectric transformer type high-voltage power supply device). The charging high-voltage power supply (not shown) corresponding to each process cartridge 410, the development high-voltage power supply (not shown), and the high voltage corresponding to each transfer roller 430 are supplied. It consists of a transfer high-voltage power supply using a piezoelectric transformer that can output.

  Next, the structure of the piezoelectric transformer type high voltage power source of the present embodiment will be described with reference to FIG.

  Since the high-voltage power supply configuration according to the present invention is effective for both positive voltage and negative voltage output circuits, a transfer high-voltage power supply that typically requires a positive voltage will be described here. The transfer high-voltage power supply corresponds to each transfer roller 430Y, 430M, 430C, and 430B, and is provided with four circuits, but the circuit configuration is the same as that of the conventional example.

  Here, the characteristics of the output voltage with respect to the driving frequency of the piezoelectric transformer 101 are shown in FIG.

  As shown in the figure, the output voltage becomes maximum at the resonance frequency f0, and it can be seen that the output voltage can be controlled by the frequency. Note that the drive frequency when the specified output voltage Edc is output is fx. Further, the voltage controlled oscillator (VCO) 110 performs an operation in which the output frequency increases when the input voltage increases and the output frequency decreases when the input voltage decreases.

  Under this condition, when the output voltage Edc of the piezoelectric transformer 101 increases, the input voltage Vsns of the non-inverting input terminal (+ terminal) of the operational amplifier 109 also increases via the resistor 105, and the voltage of the output terminal of the operational amplifier 109 increases. That is, since the input voltage of the voltage controlled oscillator (VCO) 110 increases, the drive frequency of the piezoelectric transformer 101 also increases. Accordingly, the piezoelectric transformer 101 is driven at a frequency slightly higher than the driving frequency fx, and the output voltage of the piezoelectric transformer 101 decreases as the driving frequency increases. As a result, control is performed in a direction to decrease the output voltage. . That is, this circuit constitutes a negative feedback control circuit.

  On the other hand, when the output voltage Edc decreases, the input voltage Vsns of the operational amplifier 109 also decreases, and the voltage at the output terminal of the operational amplifier 109 decreases. That is, since the input voltage of the voltage controlled oscillator (VCO) 110 decreases, the drive frequency of the piezoelectric transformer 101 also decreases, and as a result, the piezoelectric transformer 101 is controlled in the direction of increasing the output voltage. In this way, the voltage is equal to the voltage determined by the voltage of the control signal (Vcont) from the MPU 207 input to the inverting input terminal (− terminal) of the operational amplifier 109 (control voltage: hereinafter, this control voltage is also expressed by Vcont). The output voltage is controlled at a constant voltage.

  Here, the setting voltage changing sequence of the control signal (Vcont) of the high voltage power supply from the MPU 207, which is a feature of the present embodiment, will be described in detail with reference to the timing chart of FIG.

  First, specific values used for controlling the transfer high-voltage power supply in this embodiment will be shown.

  Vc0 is 0 V, Vc1 is 2.0 V, Vout1 is 2 kV, which is the same as the conventional example, Vc2 is 3.0 V, and T2 is 80 msec.

  Next, the sequence will be described. First, the MPU 207 calculates the value of T2 from a table of output rise times recorded in advance in the EEPROM 205 at the time of factory shipment. Next, Vc2 is set to the control signal Vcont at a timing before T2 from the timing at which a high voltage output is desired. Then, the value of (Vi−Vi0) in Equation 1 of the conventional example becomes larger than when Vc1 is set. The output voltage rises steeply. After setting Vc2 and the time T2 has elapsed, the MPU 207 sets Vc1.

  The description so far has described a transfer high-voltage power supply. However, other high voltage outputs are controlled in the same manner.

  In this embodiment, a high voltage is once applied to the integrating circuit, and the voltage is dropped to a desired voltage after a predetermined time has elapsed, thereby enabling control that can accelerate the rising operation of the high-voltage output.

  The image forming apparatus has been described by taking a tandem color image forming apparatus as an example. However, any image forming apparatus using a high voltage bias is within the scope of the present invention.

  Further, it has been described that the time of T2 is a table. However, it goes without saying that the data recorded in the EEPROM 205 may be one point at which T2 can be estimated, or may be a constant of a calculation formula.

(Example 2)
In the first embodiment, the embodiment that can improve the start-up characteristic of the control in the piezoelectric transformer type high voltage power source has been described. However, in high voltage output control, it may be necessary to improve the falling characteristics as well as the rising characteristics. In view of this, in the second embodiment, a control sequence of a piezoelectric transformer type high-voltage power supply capable of improving both rising characteristics and falling characteristics will be described with reference to FIG. In addition, about the structure similar to a prior art example and Example 1, the same symbol is attached | subjected and the description is abbreviate | omitted. The high-voltage power source described in the present embodiment is the above-described paper bias control of the transfer bias.

  FIG. 4 is a diagram showing a sheet spacing control sequence of the piezoelectric transformer type high voltage power source of the present embodiment.

  The main difference between the present embodiment and the first embodiment is a control sequence when applying a voltage (Vout2) lower than Vout1, which is an inter-paper bias, at a paper interval during continuous printing.

  First, specific values used for controlling the transfer high-voltage power supply in this embodiment will be shown.

  Vc0 is 0 V, Vc1 is 2.0 V, Vout1 is 2 kV, Vc2 is 3.0 V, Vc3 is 0.7 V, Vout2 is 0.3 kV, T5 is 70 msec, and T6 is 60 msec.

  The MPU 207 once sets Vc0 when the trailing edge of the paper being printed passes the transfer position. According to the same theory as in the first embodiment, the output voltage decreases to the level of Vout2 in the time T5. Next, the MPU 207 sets the control signal Vcont corresponding to the paper gap bias to Vc3. The output of the high voltage power supply is Vout2. The MPU 207 once sets Vc2 before the time T6 when the leading edge of the next print paper reaches the transfer position. The output voltage rises to the level of Vout1 in time T6. Next, the MPU 207 sets the control signal Vcont corresponding to the transfer bias to Vc1. Then, the output of the high voltage power supply becomes Vout1. The times T5 and T6 are recorded in the EEPROM 205 as in the first embodiment.

  As described above, in both the rising and falling operations, the control signal level is set so that the difference from the target control voltage is once increased, and the output voltage is brought close to the target control voltage in a short time. As a result, the rise and fall of the paper gap bias are made steep and ideal control is possible.

(Example 3)
Hereinafter, a third embodiment of the present invention will be described with reference to FIG.

  The main difference between the present embodiment and the first and second embodiments is that a feedback signal Vsns capable of monitoring the level obtained by dividing Vout by the resistors 105 and 107 is connected to the A / D input of the MPU 207. is there.

  With such a configuration, the characteristic data of T6 is stored during the initialization operation of the image forming apparatus when the power is turned on, and T2 and T5 monitor the Vsns signal and control Vcont, whereby T2, T5, Without storing T6 data in the EEPROM 205, even if T2, T5, and T6 fluctuate due to changes in the environment or over time, ideal control according to the control signal Vcont is performed for both rising and falling operations. It was possible.

It is a timing chart based on Example 1 of this invention. It is a block diagram of the color laser printer based on the Example. It is a figure showing the characteristic of the output voltage with respect to the drive frequency of a piezoelectric transformer. It is a timing chart based on Example 2 of the present invention. It is a circuit diagram of the piezoelectric transformer type high voltage power supply based on Example 3 of this invention. It is a timing chart of bias control between sheets concerning a conventional example. It is a timing chart of start-up control concerning a conventional example. It is a circuit diagram of a piezoelectric transformer type high voltage power supply according to a conventional example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Piezoelectric transformer 102,103 Diode 104 High voltage capacitor 105,106,107,114 Resistance 108 Protection resistance 109 Operational amplifier 110 Voltage controlled oscillator (VCO)
111 Transistor 112 Inductor 113 Capacitor 201 DC Controller 202 High Voltage Power Supply (Piezoelectric Transformer High Voltage Power Supply Device)
205 EEPROM (nonvolatile memory element)
207 MPU (microcomputer)
401 color laser printer (image forming apparatus)

Claims (3)

A latent image forming unit that forms an electrostatic latent image on an image carrier, a developing unit that forms a toner image on the electrostatic latent image, a transfer unit that transfers the toner image to a transfer material, and a member to which the toner image is transferred In an image forming apparatus including a fixing unit that heat-fixes toner on
Piezoelectric transformer, piezoelectric transformer drive frequency generation means, output voltage setting means, output detection means, and output control means for controlling the output voltage by a signal from the output detection means and a control signal from the output voltage setting means, the output A piezoelectric transformer type high voltage power supply device capable of controlling the piezoelectric transformer driving frequency according to the set value of the voltage setting means,
When setting the output voltage, the output voltage setting means temporarily sets the output voltage to a value larger than the difference before and after setting the output voltage, and the output voltage becomes the difference before and after setting the output voltage after a certain time has elapsed. An image forming apparatus comprising control means for setting A latent image forming unit that forms an electrostatic latent image on an image carrier, a developing unit that forms a toner image on the electrostatic latent image, a transfer unit that transfers a toner image to a transfer material, and a member to which the toner image is transferred In an image forming apparatus including a fixing unit that heat-fixes toner on
Piezoelectric transformer, piezoelectric transformer drive frequency generation means, output voltage setting means, output detection means, output control means for controlling the output voltage by a signal from the output detection means and a control signal from the output voltage setting means, the output A piezoelectric transformer type high voltage power supply device capable of controlling the piezoelectric transformer driving frequency according to the set value of the voltage setting means,
When setting the output voltage, the output voltage setting means once sets the output voltage to a value larger than the difference between before and after setting the output voltage, and when the output voltage detected by the output detection means reaches the target value An image forming apparatus comprising: a control unit that sets an output voltage that is a difference between before and after the output voltage is set.   The image forming apparatus according to claim 1, wherein the piezoelectric transformer type high voltage power supply device applies a high voltage to the latent image forming unit, the developing unit, and the transfer unit.

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