JP4838581B2 - Image forming apparatus - Google Patents

Description

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

  In an electrophotographic process type image forming apparatus, a reduction in size and weight of a high-voltage power supply device for direct current bias related to image formation such as a transfer portion leads to a reduction in size and weight of the image forming apparatus itself. For this reason, as a transformer used in the high-voltage power supply device, it is considered to use a thin, lightweight, high-output piezoelectric transformer instead of a wound electromagnetic transformer. By using a piezoelectric transformer made of ceramic, it becomes possible to generate a high voltage with an efficiency higher than that of an electromagnetic transformer, and the primary and secondary electrodes regardless of the coupling between the primary and secondary sides. The distance between them can be separated. Therefore, there is no need to mold for special insulation, and the high-voltage power supply can be made smaller and lighter.

  A circuit configuration example of a piezoelectric transformer type high-voltage power supply device that outputs both positive and negative polarities will be described with reference to FIG. The circuit shown here is an example of using a high-voltage power supply that outputs both positive and negative polarities. In an image forming apparatus that transports a transfer material by electrostatically attracting the transfer material to the belt, the transfer material is charged to be attracted to the transport belt by charging. It is an example of the high voltage power supply device used for a means.

  In general, it is divided into a positive voltage circuit section that generates a positive output voltage and a negative voltage circuit section that generates a negative output voltage. Although the negative voltage circuit unit is similar in circuit to the positive voltage circuit unit, a negative voltage is generated by reversing the diode polarity of the diode rectification unit in the voltage output stage.

  Further, an off circuit unit 220 is provided in the positive voltage circuit unit, and the voltage divided by the resistors 123 and 124 and the positive voltage setting signal Vcont_ + are compared by the comparator 122, and 24V to the inductance 112 using the transistor 121 is compared. The circuit is configured to turn on and off the supply. Considering the influence of noise and the like, the voltage divided by the resistors 123 and 124 is set to about 0.5 V, and is turned off when the positive voltage setting signal Vcont_ + is about 0.5 V or less. That is, when a negative output detection signal Vsns is input to the operational amplifier of the positive voltage circuit unit during the negative voltage output, the voltage supply to the piezoelectric transformer 101 is stopped.

  The negative voltage circuit unit has a configuration that is partially the same as the configuration of the positive voltage circuit unit, and a reference numeral that is loaded with “′” as the reference number of the positive voltage circuit unit is used for the corresponding part. . Hereinafter, the negative voltage circuit unit will be omitted, and the positive voltage circuit unit will be described. A piezoelectric transformer (piezoelectric ceramic transformer) 101 is a 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 is supplied to a suction roller (500 in FIG. 3). In the output voltage detection circuit 206, 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 through the protective resistor 108.

  Here, the output voltage detection circuit 206 functions as a filter circuit by configuring the resistors 105, 106, and 107 and the capacitor 115 as shown in FIG. Therefore, the output voltage detection signal Vsns is input to the operational amplifier 109 with a circuit time constant determined by the component constants of the resistor and the capacitor. On the other hand, the positive output voltage setting signal Vcont_ + of the high-voltage power supply, which is an analog signal, is input from the DC controller 201 via the resistor 114 to the inverting input terminal (− terminal) of the operational amplifier. Here, the operational amplifier 109, the resistor 114, and the capacitor 113 function as an integrating circuit by being configured as shown in FIG. 2, and have an integration time constant determined by the component constants of the resistor and the capacitor. Further, the output terminal of the operational amplifier 109 is connected to a voltage controlled oscillator (VCO) 110, and the transistor 111 whose output terminal is connected to the inductor 112 is driven to supply power to the primary side of the piezoelectric transformer.

In addition, the output characteristics with respect to the frequency of the piezoelectric transformer generally have a broad shape such that the output voltage becomes maximum at the resonance frequency f ₀ as shown in FIG. Therefore, the output voltage can be variably controlled by changing the drive frequency. For example, it is possible to increase the output voltage of the piezoelectric transformer by changing the drive frequency from a frequency sufficiently higher than the resonance frequency f ₀ to a frequency lower than the resonance frequency f ₀ (a frequency higher than the resonance frequency f ₀ ).

  Such a piezoelectric transformer type high-voltage power supply is disclosed in, for example, Patent Document 1.

  When applying the above conventional example to a high-voltage power supply device that requires a positive output and a negative output, the following problems arise.

  As a general supply output to the adsorbing means, a positive output is applied while the transfer material is being passed, and toner or the like is the adsorbing means during the so-called paper interval between the passing of the transfer material. A negative output having the same polarity as the toner is applied to prevent the toner from adhering to the surface of the suction roller and becoming dirty. For this reason, it is necessary to switch the suction bias output from positive to negative to positive for paper passing → paper spacing → paper passing. As an example of an image forming apparatus, when about 21 sheets of A4 size paper are printed per minute at a process speed of about 120 mm / sec, the time between sheets during continuous printing is about 400 msec.

  An example of output positive / negative switching control of the piezoelectric transformer type high voltage power supply will be described below with reference to FIGS.

  As an integration circuit constant of the input stage of the positive output voltage setting signal Vcont_ + of the circuit of FIG. 2, the resistor 114 is set to 1 MΩ, the capacitor 113 is set to 4700 pF, and the positive output voltage value is about 5V as the positive output voltage setting signal Vcont_ +. In the following, the control in the case of switching from a state of outputting about +1.1 KV DC to a negative output of about −500 V DC and then switching to a positive output of about 1.1 KV DC will be described below.

  In FIG. 7, the horizontal axis indicates time, the vertical axis indicates voltage, the positive and negative output voltage setting signals Vcont are shown in the lower stage, and the output signal Vout is shown in the upper stage.

First, the positive output setting signal Vcont_ + is turned off to temporarily turn off the positive output voltage to 0V. Next, the negative output voltage setting signal Vcont_− is turned on to output a negative target voltage −500V. Next, in order to switch to the positive output, the negative output voltage setting signal Vcont_− is turned off, the negative output voltage is once turned off to 0V, the positive output voltage setting signal Vcont_ + is turned on, and the positive target voltage + 1. 1KV is output. In this way, in the conventional switching control, as shown in FIG. 7, after the output is turned off, after the output is turned off, positive output → positive output off → 0V → negative output → negative output off → 0V → positive output. I was trying to launch the next output. For this reason, the switching time is as long as about 1000 msec, and the switching control cannot be performed within the paper interval time.
JP-A-11-206113

  The object of the present invention is to solve the above problems.

  Another object of the present invention is to provide a piezoelectric transformer type high voltage power supply device capable of switching between positive and negative polarity in a short time and an image forming apparatus using the same.

  In order to achieve the above object, a piezoelectric transformer type high-voltage power supply apparatus according to the present invention generates the positive voltage in a piezoelectric transformer type high-voltage power supply apparatus capable of switching and outputting a positive voltage and a negative voltage. A positive voltage generation circuit, a negative voltage generation circuit that generates the negative voltage, and a positive voltage generated by the positive voltage generation circuit, or an output that outputs a negative voltage generated by the negative voltage generation circuit to a load And each of the positive voltage generation circuit and the negative voltage generation circuit includes a piezoelectric transformer, a piezoelectric transformer drive circuit that drives the piezoelectric transformer, and an output voltage detection circuit that detects a voltage output from the piezoelectric transformer. A control signal for controlling the piezoelectric transformer drive circuit based on a signal from the output voltage detection circuit and an output voltage setting signal for setting a voltage output from the piezoelectric transformer A drive control circuit that outputs a negative voltage from the negative voltage generation circuit from a state in which the positive voltage generation circuit generates a positive voltage and outputs a positive voltage from the output unit to the load. When switching to a state in which a negative voltage is output from the output unit to the load, or a negative voltage is generated from the negative voltage generation circuit and a negative voltage is output from the output unit to the load. When switching to a state in which a positive voltage is generated from the positive voltage generation circuit and a positive voltage is output from the output unit to the load from the output state, the drive control circuit and the negative generation circuit of the positive voltage generation circuit The drive control circuit has a time for outputting the control signal at the same time.

  In addition, the image forming apparatus of the present invention includes a belt member for electrostatically adsorbing and transporting the transfer material, and an adsorption unit that charges the transfer material to electrostatically adsorb the transfer material to the belt member. The image forming apparatus includes: a piezoelectric transformer type high voltage power source that outputs a positive voltage or a negative voltage to the suction unit; and a control unit that controls an operation of outputting a voltage from the piezoelectric transformer type high voltage power source. The piezoelectric transformer high-voltage power supply includes a positive voltage generation circuit that generates the positive voltage, a negative voltage generation circuit that generates the negative voltage, and a positive voltage generated by the positive voltage generation circuit, or the negative voltage generation circuit. An output unit that outputs a negative voltage generated by a voltage generation circuit to a load, each of the positive voltage generation circuit and the negative voltage generation circuit includes a piezoelectric transformer, a piezoelectric transformer drive circuit that drives the piezoelectric transformer, and Piezoelectric An output voltage detection circuit for detecting a voltage output from the output, a signal from the output voltage detection circuit, and an output voltage setting signal for setting a voltage output from the piezoelectric transformer. A drive control circuit that outputs a control signal that controls the negative voltage from a state in which the positive voltage generation circuit generates a positive voltage and outputs a positive voltage from the output unit to the suction unit. When switching to a state in which a negative voltage is generated from the voltage generation circuit and the negative voltage is output from the output unit to the adsorption unit, or a negative voltage is generated from the negative voltage generation circuit and the output unit When switching from a state in which a negative voltage is output to the adsorption unit to a state in which a positive voltage is generated from the positive voltage generation circuit and a positive voltage is output from the output unit to the load, the positive voltage is generated. Circuit Drive control circuit of the dynamic control circuit the negative voltage generating circuit, characterized in that is provided with a time for outputting the control signal at the same time.

  According to the present invention, it is possible to provide an image forming apparatus using a piezoelectric transformer type high voltage power supply device capable of switching the polarity of the output voltage in a short time by a simple method.

  In addition, according to the present invention, the polarity of the output voltage can be switched in a short time regardless of the magnitude of the output value of the piezoelectric transformer type high voltage power supply device.

  Further, according to the present invention, it is possible to switch the polarity of the output voltage of the piezoelectric transformer type high voltage power supply in a short time regardless of the environment (temperature and humidity) in which the image forming apparatus is used.

  Hereinafter, preferred embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings.

  First, a first embodiment according to the present invention will be described.

  FIG. 3 is a configuration diagram of a color laser printer which is an example of the image forming apparatus of this embodiment. The laser printer 401 includes a deck 402 that stores recording paper 32 that is a transfer material, a deck paper presence / absence sensor 403 that detects the presence / absence of the recording paper 32 in the deck 402, a pickup roller 404 that feeds the recording paper 32 from the deck 402, A deck paper feed roller 405 that conveys the recording paper 32 fed out by the pickup roller 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. An electrostatic attraction transfer belt (hereinafter referred to as ETB) 409 is disposed downstream of the registration roller pair 407. On the ETB, a suction roller 500 is disposed as a suction unit for charging the recording paper 32 in order to electrostatically suck the recording paper 32 as a transfer material onto the ETB. On the ETB, process cartridges 410Y, 410M, 410C, and 410B for four colors (yellow Y, magenta M, cyan C, and black B), which will be described later (hereinafter referred to as “process cartridge 410” in the description common to the four colors). Etc., and the transfer roller 430Y and 430M are images formed by the image forming unit including the scanner units 420Y, 420M, 420C, and 420B), and symbols “Y”, “M”, “C”, and “B” are used. A color image is formed by being sequentially superposed by 430C and 430B, and is transferred and conveyed onto the recording paper 32.

  Further downstream, as a fixing device for thermally fixing the toner image transferred onto the recording paper 32, a fixing sleeve 433, which is a fixing member having a heater 432 inside, and a pressure roller, which is a pressing means. A fixing paper discharge roller pair 435 for conveying the recording paper 32 from the fixing sleeve and a 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. 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 unit of the laser printer, and includes a RAM 207a, a ROM 207b, a timer 207c, a digital input / output port 207d, a D / A port 207e, and an MPU (microcomputer) 207 having an A / D port 207f. And various input / output control circuits (not shown).

  Reference numeral 202 denotes a high-voltage power supply unit, which is a charging high-voltage power supply (not shown) corresponding to each process cartridge, a development high-voltage power supply (not shown), and a transfer high-voltage power supply (not shown) capable of outputting a high voltage corresponding to each transfer roller 430. And an adsorption high-voltage power source for the adsorption means.

  In this embodiment, as an example of a high-voltage power supply that performs positive / negative polarity switching output, a piezoelectric transformer type high-voltage power supply device is used as a high-voltage power supply for the suction means.

  Next, the configuration of the piezoelectric transformer type high voltage power source of the present embodiment will be described based on the block diagram of FIG. The high-voltage power supply configuration in this embodiment is largely divided into a positive voltage circuit and a negative voltage circuit section.

  Since the positive voltage circuit section and the negative voltage circuit section are similar in terms of circuit configuration, the positive voltage circuit section will be described below.

  A positive output voltage setting signal Vcont_ + is output from a D / A port 207e from an MPU (microcomputer) 207 mounted on a DC controller 201, which is a control unit, and is configured by an operational amplifier or the like provided on the high-voltage power supply unit 202. Is input to an integration circuit (comparison circuit) 203. Similarly, a negative output voltage setting signal Vcont_− is output from the D / A port 207 e ′ and input to an integration circuit (comparison circuit) 203 ′ configured by an operational amplifier or the like provided on the high voltage power supply unit 202.

  The output of the integration circuit (comparison circuit) 203 is converted into a frequency via the voltage controlled oscillation circuit (VCO) 110, and the switching circuit 204 is driven by the frequency. As a result, the piezoelectric transformer (piezoelectric ceramic transformer) 101 operates and outputs a voltage corresponding to the frequency characteristics and boost ratio of the element. The transformer output is rectified and smoothed to a positive voltage by the rectifier circuit 205, for example, as shown in the figure, and the high voltage output Vout is supplied to a load, for example, the suction roller 500. On the other hand, the output of the integration circuit (comparison circuit) 203 is controlled so that the rectified voltage is fed back to the comparison circuit 203 via the detection circuit 206 and the output voltage detection signal Vsns has the same potential as the output voltage setting signal Vcont. The

  Next, an actual piezoelectric transformer type high voltage power supply circuit will be described with reference to FIG. The inverting input terminal (− terminal) of the operational amplifier 109 receives the output voltage setting signal Vcont of the high voltage power supply from the DC controller 201 via the series resistor 114 and the capacitor 113. On the other hand, in the output voltage detection circuit 206, the output voltage Vout is divided by the resistors 105, 106, and 107, and the divided output is supplied to the non-inverting input terminal (+ terminal) of the operational amplifier 109 via the capacitor 115 and the protective resistor 108. ) As an output voltage detection signal Vsns. The output terminal of the operational amplifier 109 is connected to a voltage controlled oscillator (VCO) 110, and the output terminal of the voltage controlled oscillator 110 is connected to the base of the transistor 111. The collector of the transistor 111 is connected to the power supply (+24 V) via the inductor 112 and simultaneously connected to one of the primary electrodes of the piezoelectric transformer 101. 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 the suction roller 500 as a load.

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 f ₀ , 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 operates to increase the output frequency when the input voltage increases and to decrease the output frequency when the input voltage decreases. Under this condition, if the output voltage Vout slightly rises above the voltage corresponding to the specified output voltage Edc of the piezoelectric transformer 101, the input voltage Vsns of the non-inverting input terminal (+ terminal) of the operational amplifier 109 also rises via the resistor 105. The voltage at the output terminal of the operational amplifier 109 increases. That is, since the input voltage of the voltage controlled oscillator 110 increases, the driving 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 the direction of decreasing the output voltage Vout. That is, this circuit constitutes a negative feedback control circuit.

  On the other hand, when the output voltage Vout decreases below the specified output voltage Edc, 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 output frequency of the voltage controlled oscillator 110 decreases, the piezoelectric transformer 101 is controlled to increase the output voltage. Thus, the voltage Edc determined by the voltage of the output voltage setting signal Vcont from the DC controller 201 input to the inverting input terminal (− terminal) of the operational amplifier 109 (setting voltage: hereinafter, this setting voltage is also expressed as Vcont). So that the output voltage is controlled to be constant.

  Next, the output voltage setting signal Vcont inputted from the DC controller 201 to the inverting input terminal (− terminal) of the operational amplifier 109 and the output voltage detected from the output voltage and inputted to the non-inverting input terminal (+ terminal) of the operational amplifier 109. A circuit constituting the detection signal Vsns will be described in detail. First, the operational amplifier 109, the resistor 114, and the capacitor 113 are configured as shown in FIG. 2, thereby functioning as an integration circuit. When the output voltage setting signal Vcont is determined by the component constants of the resistor 114 and the capacitor 113, A signal that changes according to the constant Tcont is input to the operational amplifier 109.

Here, the time constant Tcont increases as the resistance value of the resistor 114 increases. Similarly, the larger the capacitance of the capacitor 113, the larger the time constant Tcont. In addition, a filter circuit including resistors 105, 106, and 107 and a capacitor 115 is configured, and an output that changes with respect to the output voltage Vout according to a time constant Tsns determined by the component constants of the resistors 105, 106, and 107 and the capacitor 115. The voltage detection signal Vsns is input to the operational amplifier 109. At this time,
Tcont> Tsns
Tcont = R114 × C113
Tsns = Rs × C115
However, R105, R106, R107, R114, C113, and C115 in the formula indicate the resistance values of the resistors 105, 106, 107, and 114 and the capacitances of the capacitors 113 and 115, respectively. Further, by determining the constants of the resistor 114 and the capacitor 113 and the constants of the resistors 105, 106, 107 and the capacitor 115 so that Rs becomes a combined resistance of R105, R106 and R107, control without oscillation is possible. Become. That is, since the time constant of Tsns is small and the rise is fast, the feedback control can operate normally without oscillation.

  In this embodiment, Tcont is set to 5 msec and Tsns is set to 1 msec.

  When the time constants of Tcont and Tsns are large, the feedback control is slowed down, and the rise time of the output bias is slowed down. In addition, when the time constants of Tcont and Tsns are small, a change in the driving frequency to be fed back becomes large and exceeds the resonance frequency f0 of the piezoelectric transformer 101, and feedback control is broken.

  For this reason, Tcont and Tsns are set to optimum values in a timely manner within a range of about 0.5 msec to 100 msec (more preferably, Tcont is about 1 to about 10 msec and Tsns is about 0.5 msec to about 5 msec). It is desirable to do.

  As an example of the embodiment of the first invention according to the present invention, the positive / negative polarity switching control of the output voltage using a piezoelectric transformer type high voltage power supply using such a circuit will be described.

  The switching control will be described below with reference to FIG.

  In FIG. 1, the horizontal axis represents time, the vertical axis represents voltage, the positive output voltage setting signal Vcont_ + and the negative output setting signal Vcont_− are shown in the lower stage, and the output signal Vout is shown in the upper stage.

  In the image forming apparatus used in one example of the present embodiment, about 21 sheets of A4 size paper are printed every minute at a process speed of about 120 mm / sec, and the time between sheets during continuous printing is about 400 msec. Is detected by the pre-registration sensor 408, and the suction between the papers when using an image forming apparatus that requires about 120 msec for the paper to move from the pre-registration sensor to the position of the suction roller as the suction means. The bias output polarity switching control will be described.

  In this embodiment, the positive output is about 1.1 KV and the negative output is about −500 V as the suction bias value.

  The present invention is characterized in that a time for simultaneously turning on the positive output voltage setting means and the negative output voltage setting means is provided.

  In the control of the switching portion from positive to negative, if the rear end of the transfer material is detected by the pre-registration sensor 408 while the positive output voltage setting signal Vcont_ + is being output, the negative output voltage setting signal Vcont_− is output and The positive output voltage setting signal Vcont_ + is turned off when the end is at the suction roller position.

  The time T1 for simultaneously turning on the positive output voltage setting means and the negative output voltage setting means is about 120 msec in this embodiment.

  Next, in the control of the switching portion from negative to positive, when the leading edge of the next transfer material is detected by the pre-registration sensor, the positive output voltage setting signal is turned on, and the positive output voltage setting means and the negative output voltage setting means are simultaneously turned on. The negative output voltage setting signal Vcont_- is turned off after the time T2 for turning on has elapsed. In this embodiment, the T2 time is about 50 msec.

  In this case, since the output obtained by combining the output of the positive circuit unit and the output of the negative circuit unit as shown in FIG. 6 becomes the output voltage Vout, the positive output voltage of the positive circuit unit is expected to rise, and the transfer material The positive voltage output setting signal Vcont_ + is turned ON at the timing of detection of the transfer material, the paper leading edge, and the detection by the pre-registration sensor which is earlier than the time when the leading edge of the paper reaches the suction roller position, and the negative output voltage setting signal Vcont_ From the falling curve when-is turned off, the positive output voltage setting means and the negative output are set so that the composite output Vout becomes the target positive output voltage when the leading edge of the transfer material and paper comes to the suction roller position. The time T2 for simultaneously turning on the voltage setting means is determined. In this embodiment, the output switching time is about 120 msec when switching from negative to positive.

  Thus, according to the first aspect of the present invention, the piezoelectric transformer, the piezoelectric transformer drive frequency generation means, the output voltage setting means, the output voltage detection means, the signal from the output voltage detection means, and the output voltage setting signal A piezoelectric transformer comprising a positive output voltage setting means and a negative output voltage setting means, comprising an output control means for comparing and controlling the output voltage, the piezoelectric transformer drive frequency being controllable according to a set value of the output voltage setting means In an image forming apparatus equipped with a transformer-type high-voltage power supply device, when switching the output polarity of the piezoelectric transformer-type high-voltage power supply, an output is provided by providing a time for simultaneously turning on the positive output voltage setting means and the negative output voltage setting means. The polarity switching time can be shortened, and switching within the paper interval during continuous printing is possible.

  In the present embodiment, the high voltage power source of the suction unit has been described. However, the high voltage power source related to other image formation, such as a transfer unit, can be similarly implemented to obtain the effect. is there.

  In this embodiment, the description of the image forming apparatus is described by taking a tandem color image forming apparatus as an example. However, as long as the image forming apparatus uses a high-voltage bias, other types of image forming apparatuses are applicable to the present invention. To do.

  Example 2 according to the second aspect of the present invention will be described. Description of the parts described in the first embodiment is omitted.

  According to the second and third aspects of the present invention, the positive output voltage setting means and the negative output voltage setting means are simultaneously turned on depending on the use environment of the image forming apparatus, that is, the value of the suction bias target voltage. Is something that changes.

  The optimum adsorption bias target voltage generally varies depending on the environment used in the image forming apparatus.

  Table 1 shows an example of each adsorption bias target value when the environment is changed.

  In a low-temperature and low-humidity environment (referred to as L / L) where the temperature and humidity are 15 ° C. and 10% RH, the resistance value of the transfer material increases and the adsorption bias target also increases to about +1.6 KV. In a high-temperature and high-humidity environment (referred to as H / H) where the temperature and humidity are 30 ° C. and 80% RH, the adsorption bias target is as low as + 500V.

  For this reason, since the start-up time differs depending on the suction bias target voltage, the time during which the positive output voltage setting means and the negative output voltage setting means are simultaneously turned ON is varied.

  In this embodiment, the target voltage is +1.6 KV at L / L and the T2 time is 0 msec, and the target voltage is +500 V at H / H, so the T2 time is 100 msec.

  Although the T1 time is constant in the present embodiment, the time may be optimized depending on each environment and each target voltage.

  For the T2 time, the adsorbability of the transfer material on the front edge of the paper is affected. Therefore, the optimization is performed by changing the time depending on the environment and each target voltage. Since there is no great difference in preventing roller contamination, the roller is kept constant so that control is not complicated.

  As described above, according to the second and third aspects of the present invention, the positive output voltage setting means and the negative output voltage setting means are set according to the use environment of the image forming apparatus, that is, depending on the value of the suction bias target voltage. By changing the ON time at the same time, the polarity switching time of the output voltage can be shortened and optimized.

  In this embodiment, examples of the high voltage output to the suction means are described as the second and third embodiments of the present invention, but the present invention is not limited to this, and other high voltage output sections such as a high voltage output to the transfer section. The same effect can be obtained even if it is used for output polarity switching.

It is explanatory drawing of the output control of the piezoelectric transformer type high voltage power supply in Example 1 concerning the 1st invention of this invention. It is a figure which shows an example of the circuit diagram of a piezoelectric transformer system high voltage power supply. It is a block diagram of the color laser printer based on the Example. It is a block diagram of a piezoelectric transformer high voltage power source according to the embodiment. It is a figure showing the characteristic of the output voltage with respect to the drive frequency of a piezoelectric transformer. It is explanatory drawing of the output switching from negative-> positive in Example 1 concerning the 1st invention of this invention. It is explanatory drawing of the output control of the conventional piezoelectric transformer type high voltage power supply.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Piezoelectric transformer 105,106,107,108,114 Resistance 113,114 Capacitor 108 Protection resistance 109 Operational amplifier 110 Voltage controlled oscillator (VCO)
201 DC controller 202 High voltage power supply (piezoelectric transformer type high voltage power supply device)
207 MPU (microprocessor)
401 color laser printer (image forming apparatus)

Claims (5)

In a piezoelectric transformer type high voltage power supply device capable of switching and outputting a positive voltage and a negative voltage,
A positive voltage generating circuit for generating the positive voltage;
A negative voltage generating circuit for generating the negative voltage;
An output unit that outputs a positive voltage generated by the positive voltage generation circuit or a negative voltage generated by the negative voltage generation circuit to a load;
Each of the positive voltage generation circuit and the negative voltage generation circuit includes a piezoelectric transformer, a piezoelectric transformer drive circuit that drives the piezoelectric transformer, an output voltage detection circuit that detects a voltage output from the piezoelectric transformer, and the output A drive control circuit that outputs a control signal for controlling the piezoelectric transformer drive circuit based on a signal from a voltage detection circuit and an output voltage setting signal for setting a voltage output from the piezoelectric transformer;
From the state where the positive voltage generation circuit generates a positive voltage and outputs a positive voltage from the output unit to the load, a negative voltage is generated from the negative voltage generation circuit and a negative voltage is output from the output unit. From the state in which a negative voltage is generated from the negative voltage generation circuit and a negative voltage is output to the load from the positive voltage generation circuit. When switching to a state in which a positive voltage is generated and a positive voltage is output from the output unit to the load, the drive control circuit of the positive voltage generation circuit and the drive control circuit of the negative generation circuit simultaneously output the control signal. A piezoelectric transformer type high-voltage power supply device characterized in that a time is provided.   The time for the drive control circuit of the positive voltage generation circuit and the drive control circuit of the negative voltage generation circuit to simultaneously output the control signal is changed according to a target value of the voltage output from the piezoelectric transformer. The piezoelectric transformer type high voltage power supply device according to claim 1. In an image forming apparatus comprising: a belt member for electrostatically adsorbing and transferring a transfer material; and an adsorption unit for charging the transfer material to electrostatically adsorb the transfer material to the belt member.
A piezoelectric transformer type high-voltage power supply that outputs a positive voltage or a negative voltage to the adsorption unit;
A controller for controlling the operation of outputting a voltage from the piezoelectric transformer type high-voltage power source,
The piezoelectric transformer high-voltage power supply is
A positive voltage generating circuit for generating the positive voltage;
A negative voltage generating circuit for generating the negative voltage;
An output unit that outputs a positive voltage generated by the positive voltage generation circuit or a negative voltage generated by the negative voltage generation circuit to a load;
Each of the positive voltage generation circuit and the negative voltage generation circuit includes a piezoelectric transformer, a piezoelectric transformer drive circuit that drives the piezoelectric transformer, an output voltage detection circuit that detects a voltage output from the piezoelectric transformer, and the output A drive control circuit that outputs a control signal for controlling the piezoelectric transformer drive circuit based on a signal from a voltage detection circuit and an output voltage setting signal for setting a voltage output from the piezoelectric transformer;
From the state where the positive voltage generation circuit generates a positive voltage and outputs a positive voltage from the output unit to the adsorption unit, a negative voltage is generated from the negative voltage generation circuit and a negative voltage is output from the output unit. When switching to a state in which a voltage is output to the adsorption unit, or from a state in which a negative voltage is generated from the negative voltage generation circuit and a negative voltage is output from the output unit to the adsorption unit When switching to a state in which a positive voltage is generated from the generation circuit and a positive voltage is output from the output unit to the load, the drive control circuit of the positive voltage generation circuit and the drive control circuit of the negative voltage generation circuit are simultaneously An image forming apparatus having a time for outputting the control signal.   4. The image forming apparatus according to claim 3, wherein a time during which the drive control circuit of the positive voltage generation circuit and the drive control circuit of the negative voltage generation circuit simultaneously output the control signal is changed.   The drive control circuit of the positive voltage generation circuit and the drive control circuit of the negative voltage generation circuit simultaneously output the control signal according to the value of the positive voltage generated from the positive voltage generation circuit and applied to the suction unit. 4. The image forming apparatus according to claim 3, wherein the output time is changed.

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