KR20090013655A - High voltage power apparatus of piezoelectric transformer type and image forming apparatus - Google Patents

Abstract

A high voltage power apparatus of a piezoelectric transformer type and an image forming apparatus are provided to use an output voltage detecting unit and a driving control unit to control a driving frequency and a duty ratio at stable high efficiency within a wide output range without unstable production, disable control, or abnormal oscillation. A high voltage power apparatus(10) of a piezoelectric transformer type comprises a driving unit(20), a piezoelectric transformer driving control unit(30), a rectification smoothing unit(40) and an output voltage detecting unit(50). The output voltage detecting unit compares output control voltages for controlling the output voltage with the output voltage. The output voltage detecting unit detects a change of the output voltage based on the comparison result by a digital change value. According to the detected digital change value, the driving control unit controls a driving frequency and a duty ratio.

Description

High voltage power apparatus of piezoelectric transformer type and image forming apparatus

The present invention relates to a high-voltage power supply apparatus and an image forming apparatus of a piezoelectric transformer system.

In an image forming apparatus for forming an image by an electrophotographic process, in the case of using a direct transfer method in which a transfer member is brought into contact with a photosensitive member, a roller-shaped conductive rubber having a rotating shaft of a conductor is used as the transfer member. At this time, the driving of the transfer member is controlled in accordance with the process speed of the photosensitive member. As a voltage applied to the transfer member, a direct current bias voltage is used, and the polarity of the direct current bias voltage is the same as that of a general corona discharge type transfer voltage.

In this way, in order to perform good transfer using the transfer roller, a voltage of about 3 kV (required current is several μA) is generally required to be applied to the transfer roller. Conventionally, coil type electron transformers have been used to generate high voltages required for the image forming process. However, the electron transformer is composed of copper wire, bobbin, and magnetic core, and when the voltage of about 3kV is applied, the output current value is very small, such as several μA, so the leakage current should be minimized in each part. . In order to minimize the leakage current, a method of forming a coil of an electronic transformer into an organic insulator was used. However, in the case of using such a method, there is a risk of smoke and ignition, and a large electronic transformer is required compared to the power supply, and thus there is a problem that the miniaturization and weight reduction of the high-voltage power supply device are not easy.

Thus, in order to compensate for this problem, a method of generating a high voltage using a thin, lightweight, high-power piezoelectric transformer has been examined. In other words, when a piezoelectric transformer made of ceramic material is used, it is possible to generate a high voltage with an efficiency higher than that of the electronic transformer. In addition, since it becomes possible to separate the distance between the electrodes of the primary side and the secondary side irrespective of the coupling between the primary side and the secondary side, there is no need to perform mold processing for insulation in particular, and there is no risk of fuming ignition. Therefore, the outstanding characteristic that a high voltage power supply device can be made small and light can be obtained.

As described above, in the high-voltage power supply device using the piezoelectric transformer, the piezoelectric transformer can control the output by a general frequency. However, in the frequency control by the high-voltage power supply control circuit configuration, there is a problem of limiting the variable width of the output voltage and inefficiency. That is, since a plurality of resonance points exist in the piezoelectric transformer, when the frequency is increased to lower the output voltage, a large change in frequency causes the output voltage to rise rather than at the next resonance point. Therefore, the variable width of the output voltage could not be increased. In addition, the frequency of the driving voltage has an efficient range and a bad range for generating the driving voltage. When the variable width of the output voltage is increased, the frequency of the inefficient range must also be used, so that the overall efficiency is poor. .

In order to solve this problem, a technique for simultaneously controlling the duty ratio of the frequency control and the driving voltage has been proposed. By using the proposed technique to control the frequency ratio and the duty ratio of the driving voltage at the same time to make the output voltage constant, a low output voltage and a wide variable width can be obtained, and thus a stable constant voltage power supply can be obtained. By combining efficient ranges of duty ratios, the efficiency was improved.

However, the frequency and duty ratio simultaneous control circuit of the driving voltage controller in the proposed technique generates a triangular wave by a charge and discharge circuit by a resistor and a capacitor, and simultaneously controls the frequency and duty ratio based on the triangular wave. If the load current is rapidly increased due to the irregularity in manufacturing or fluctuation of the constant value due to temperature, there is a problem that the control is impossible beyond the resonance frequency. In addition, since the driving frequency cannot be used until the resonance frequency, there is a problem that the efficiency cannot be improved.

The technical problem to be solved by the present invention has been made in view of the above problems, and the driving frequency and duty are stable at a high efficiency in a wide range of output values without falling into an uncontrollable or abnormal oscillation state due to manufacturing irregularities or temperature fluctuations of component constants. The present invention provides a piezoelectric transformer-type high-voltage power supply device and an image forming device that can simultaneously control the ratio.

In addition, another technical problem to be achieved by the present invention is to provide a piezoelectric transformer-type high-voltage power supply device and an image forming apparatus capable of high-speed rise of the high-voltage output.

In order to solve the above technical problem, a piezoelectric transformer-type high voltage power supply for supplying an output voltage output from the transformer to a load by applying a driving voltage controlled by a predetermined driving frequency and duty ratio to the piezoelectric transformer according to the present invention. An output voltage detector for comparing the output voltage with an output control voltage for controlling the output voltage to a predetermined value, and detecting a variation of the output voltage as a digital variation value based on the comparison result; And a driving controller for controlling the driving frequency and the duty ratio according to the detected digital variation value.

In order to solve the another technical problem, the imaging apparatus according to the present invention comprises: charging means for charging the surface of the latent image bearing member equally; Exposure means for forming a latent image on a surface of the latent image bearing member after the charging; Developing means for developing the latent image; Transfer means for transferring a toner image formed on the latent image bearing member to a transfer material; And a power supply device supplying a voltage to at least one of the charging means, the developing means, and the transfer means, wherein the power supply device is any one of a piezoelectric transformer-type high voltage power supply device. It features.

The piezoelectric transformer-type high voltage power supply device according to the present invention compares an output voltage with an output control voltage for controlling the output voltage to a predetermined value, and based on the comparison result, an output voltage for detecting a change in the output voltage as a digital variation value Detection unit; And a driving control unit for controlling the driving frequency and duty ratio according to the detected digital variation value, so that it does not fall into uncontrollable or abnormal oscillation due to manufacturing irregularity or temperature variation of a component constant, and has a stable high efficiency over a wide range of output values. The driving frequency and the duty ratio can be controlled at the same time, and there is an effect of enabling a high speed rise of the high voltage output.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has a substantially same functional structure, it represents with the same code | symbol, and overlapping description is abbreviate | omitted.

[About high-voltage power supply device of general piezoelectric transformer method]

Before describing the piezoelectric transformer-type high voltage power supply device according to the preferred embodiments of the present invention, the configuration between the piezoelectric transformer-type high-voltage power supply device and the conventional piezoelectric transformer-type high-voltage power supply device according to the preferred embodiments of the present invention. In order to clarify the differences between the phases, a general piezoelectric transformer-type high-voltage power supply device will be described with reference to FIGS. 1 to 3.

1 is a block diagram illustrating a high-voltage power supply device of a general piezoelectric transformer system.

A piezoelectric ceramic transformer is used as a piezoelectric transformer T901 of a high voltage power source in a general piezoelectric transformer type high voltage power supply device. The AC output of the piezoelectric transformer T901 is rectified and smoothed to a constant voltage by the diodes D902 and D903 and the high voltage capacitor C904, and the rectified smoothed output voltage is supplied to a transfer roller (not shown) which is a load. In addition, the rectified smoothed output voltage is divided by the resistors R905, R906 and R907, and is input to the non-inverting input terminal (+ terminal) of the operational amplifier Q909 through the protective resistor R908. .

Meanwhile, the control signal Vcont of the high voltage power source, which is an analog signal, is input from the DC controller to the inverting input terminal (− terminal) of the operational amplifier through the resistor R914. The operational amplifier Q909, the resistor R914 and the capacitor C913 constitute an integral circuit, and the control signal Vcont integrated with the integral constant determined by the value of the resistor R914 and the capacitor C913 is calculated. It is output from the amplifier Q909.

The output terminal of the operational amplifier Q909 is connected to the voltage controlled oscillator (VCO) 910, and the output terminal thereof drives the transistor Q911 connected to the inductor L912, thereby driving the drive frequency to the primary side of the piezoelectric transformer T901. To supply power. In this way, the high-voltage power supply unit of the electrophotographic image forming apparatus uses such a piezoelectric transformer.

2 and 3 are waveform diagrams for explaining the driving frequency of the piezoelectric transformer in a high-voltage power supply device of a general piezoelectric transformer.

Generally, the piezoelectric transformer has a maximum output voltage at the resonant frequency f0 as shown in FIG. 2, and has a form in which the output voltage is reduced at the high frequency side or the left frequency side based on the resonance frequency. Therefore, the output voltage can be controlled through the driving frequency. When the output voltage of the piezoelectric transformer is increased, the drive frequency fx larger than the resonance frequency may be changed to the resonance frequency f0.

The high voltage power supply unit of the electrophotographic image forming apparatus has a plurality of high voltage power supply circuits shown in FIG. 2, and forms an image by outputting a bias such as charging, developing and transferring.

However, as shown in FIG. 2, since the high-voltage power supply apparatus of the general piezoelectric transformer system controls the driving frequency of the piezoelectric transformer by analog signal processing, a problem of time delay occurs until the desired output control voltage value is reached. .

In addition, a plurality of resonance points may exist in the piezoelectric transformer. For example, as shown in FIG. 3, the piezoelectric transformer may have four resonance points. As shown in FIG. 3, when the first resonant frequency f1 is applied, a first resonant point for obtaining an output voltage of about 3.5 kV exists, and the output voltage is maximum at the other high frequency side of the first resonant frequency f1. There is a second resonance point (resonant frequency f2) and a third resonance point (resonant frequency f3). As shown in Fig. 3, since the resonance point is the point at which the output voltage becomes maximum, the output voltage decreases even if the frequency of the driving voltage is changed to either the high frequency side or the low frequency side based on the resonance frequency at the resonance point.

However, even if the frequency is changed at the resonance frequency, if the maximum value of the output voltage is set to about kv, the output voltage at the changed frequency does not become several OV or less. Because if the frequency is changed greatly, the frequency does not converge to zero but the next resonant frequency is closer, so the output voltage is increased until it is closer to the next resonant frequency.

The frequency of the drive voltage has an efficient range such as near the resonance frequency. However, in order to increase the variable width of the output voltage, the frequency of the range having low efficiency must also be used, so the efficiency is lowered as a whole.

[About high-voltage power supply device of the piezoelectric transformer system according to the first embodiment of the present invention]

In order to solve the problem of a general piezoelectric transformer high voltage power supply device, the piezoelectric transformer high voltage power supply device 10 according to the first exemplary embodiment of the present invention controls the driving frequency and the duty ratio by digital signal processing simultaneously. It is possible to simultaneously control the driving frequency and duty ratio with stable and high efficiency over a wide range of output voltage values without falling into the uncontrollable or abnormal oscillation state due to irregular manufacturing of the purified water or temperature fluctuations, and realize a high-speed rise of the high voltage output.

4 to 9, a high-voltage power supply device of a piezoelectric transformer according to a first embodiment of the present invention will be described in detail. The high-voltage power supply device of the piezoelectric transformer according to the first preferred embodiment of the present invention applies the driving voltage controlled by the predetermined driving frequency and duty ratio to the piezoelectric transformer, thereby supplying the output voltage output from the piezoelectric transformer to the load. . 4 is a block diagram illustrating a high-voltage power supply device of a piezoelectric transformer according to a first embodiment of the present invention.

As shown in FIG. 4, the piezoelectric transformer-type high voltage power supply apparatus according to the first embodiment of the present invention includes a driving unit 20, a piezoelectric transformer driving control unit 30, a rectifying smoothing unit 40, and an output voltage detecting unit ( 50).

The driver 20 includes a piezoelectric transformer T201, an inductance L201, a resistor R201, a capacitor C201, and a switching element S201 of a MOSFET or a transistor.

When the power supply VDD is connected to the inductance L201, a driving voltage frequency controlled by the piezoelectric transformer driving control unit 30 described later is input to the switching element S201, and the input driving voltage is applied to the switching element S201. By controlling ON / OFF, the boosted voltage and the conversion to the pseudo sine wave are performed on the connected power supply voltage. The converted power supply voltage is then applied to the piezoelectric transformer T201.

The piezoelectric transformer T201 of the driving unit 20 is provided with a primary electrode and a secondary electrode in the piezoelectric vibrating body, and the primary side is polarized in the horizontal direction so as to face the piezoelectric vibrating body between them, and the secondary side in the vertical direction. Polarization is carried out and accommodated in a resin case (not shown). The piezoelectric vibrating body is made of piezoelectric ceramics such as Titanium Zirconate Titanium Zirconate (PZT: Plumbum-Zirconate-Titanate), and exhibits a plate shape. In the longitudinal direction of the piezoelectric vibrating body, a primary electrode is provided from one end to about half of the length, for example, and a secondary electrode is provided at the other end. When the driving voltage of the natural resonance frequency determined by the length dimension is input to the primary side, a strong mechanical resonance is caused by the reverse piezoelectric effect, and a high output voltage corresponding to the vibration is output by the piezoelectric effect.

FIG. 6 is a diagram illustrating a relationship between an inductor power supply voltage and an operating waveform when boosted in a piezoelectric transformer-type high voltage power supply device according to a first embodiment of the present invention.

Hereinafter, an operation of power supply voltage boosting will be described with reference to FIGS. 4 and 6. As shown in FIG. 6B, when a driving voltage is applied to the switching element S201, the switching element S201 is turned on and a current flows through the inductance L201. At this time, if the time when the driving voltage is applied is represented by [ON Time] and the time when the driving voltage is not applied is represented by [OFF Time], the current I is represented by the driving voltage * [ON Time]. In addition, the current I flowing through the switching element S201 is determined according to [ON Time], and when the current I flows, energy is accumulated in the inductance L201.

When the switching element S201 is off, resonance occurs between the capacitor C201 and the inductance connected to the primary side of the piezoelectric transformer T201. When such resonance occurs, the voltage applied to the piezoelectric transformer T201 is the piezoelectric transformer driving voltage shown in FIG. 6A, and the voltage value increases according to the amount of energy accumulated in the inductance L201. Therefore, when [ON Time] is made large, the output voltage value which the piezoelectric transformer T201 raises and outputs the drive voltage applied to the piezoelectric transformer T201 becomes large.

In general, when the duty ratio is increased, it is known that the output efficiency of the piezoelectric transformer itself is also improved. Therefore, by controlling the driving frequency and the duty ratio simultaneously, the control of the output voltage becomes easier due to the synergistic effect that the output voltage value of the piezoelectric transformer T201 becomes large. In addition, although FIG. 6 shows the case where [OFF Time] is constant, [OFF Time] can also be made variable.

Referring back to FIG. 4, the piezoelectric transformer driving controller 30 may convert the frequency and duty ratio of the driving voltage for controlling the piezoelectric transformer T201 of the driver 20 to the digital variation value input from the output voltage detector 50. Control accordingly. The piezoelectric transformer-type high voltage power supply device 10 according to the first embodiment of the present invention is characterized by controlling the driving frequency of the piezoelectric transformer by the digital signal processing by the piezoelectric transformer driving control unit 30. Such a piezoelectric transformer driving control section 30 will be described later in detail.

The rectifying smoother 40 includes a capacitor C401 and diodes D401 and D403. The AC output of the piezoelectric transformer T201 is rectified and smoothed at a constant voltage (direct current voltage) by the diodes D401 and D403 and the condenser C401, and is supplied to a transfer roller (not shown) which is a load.

The output voltage detection unit 50 detects a variation in the output voltage as a digital variation value based on a comparison result between the output voltage of the piezoelectric transformer T201 and the output control voltage for controlling the output voltage to a constant value. In order to perform such a function, the output voltage detector 50 includes capacitors C501 and C503, resistors R501 and R503, and a comparator (COMP) 501. The output voltage rectified and smoothed to the DC voltage by the rectifying smoother 40 is divided by the voltage dividing resistors R501 and R503 in the output voltage detector 50, and the comparator 501 as an error detection voltage (Feed back voltage). It is input to the inverting input terminal (-terminal) of. At this time, the capacitors C501 and C503 connected in parallel to the divided resistors R501 and R503 adjust the AC component and the DC component of the output voltage. In addition, an output control voltage, which is a DC voltage for controlling the output voltage, is input to the non-inverting input terminal (+ terminal) of the comparator 501 as the reference voltage Reference_Volt.

The comparator 501 compares the magnitude of the output control voltage Reference_Volt and the output voltage (Feed back voltage) input to the non-inverting input terminal, and outputs the comparison result as a digital variation value. The output of the comparator 501 becomes a low output in the case of the output voltage Feed back> the output control voltage Reference_Volt, and a high output in the case of the output voltage Feed back <the output control voltage Reference_Volt. The comparator 501 can convert the analog variation of the output voltage into a digital variation value. The digital variation value output from the comparator 501 is input to the piezoelectric transformer driving controller 30 as a control signal UP / DOWN of the frequency controller in the piezoelectric transformer driving controller 30.

In addition, the high-voltage power supply device 10 of the piezoelectric transformer system according to the first embodiment of the present invention includes a reset unit 101 for supplying a reset signal, a clock unit 103 for supplying a clock signal, and a piezoelectric transformer T201. It further comprises a controller 105 for supplying a drive control signal to.

The drive control signal (ON / OFF signal) supplied from the controller 105 is inverted by the resistors Rl01, Rl03, and Rl05 and the switching element S101, is converted into an open collector output, and is converted to the piezoelectric transformer driving control unit 30. Is entered.

5 is a block diagram illustrating a piezoelectric transformer driving control unit of a piezoelectric transformer type high voltage power supply apparatus according to a first embodiment of the present invention.

The piezoelectric transformer driving controller 30 of the piezoelectric transformer-type high voltage power supply apparatus according to the first embodiment of the present invention includes a driving frequency controller, an off time setting unit, a selection unit, and a driving voltage generator. Hereinafter, an operation performed by the piezoelectric transformer driving control unit of the piezoelectric transformer type high voltage power supply apparatus according to the first embodiment of the present invention will be described with reference to FIG. 5.

[About driving frequency control part]

The driving frequency control unit variably controls the driving frequency of the piezoelectric transformer T201 according to the digital variation value (UP / DOWN signal) output by the output voltage detector 50. The driving frequency controller includes an updown counter 301, a register 303, and a first comparator 305.

The up-down counter 301 is supplied with a high-speed clock signal according to the required frequency control precision from the clock unit, and the counter when the output voltage detection signal UP / DOWN is high from the output voltage detector whenever the clock signal becomes high. Decreases the value by X, and decreases the counter value by X when it is low. In addition, by setting the number of counter bits for frequency control as the number of counter bits for driving voltage (N) + (N + M) bits of the lower M bits, the lower M bit value is set to correct the error feedback gain, thereby providing stable control. It is desirable to make it. Even when the magnitude of the output voltage (Feed back) and the output control voltage (Reference_Volt) is similar and the amount of change of the up-down counter 301 is very small, when the number of counter bits for frequency control is configured as (N + M) bits, the lower M bits Even if is changed, the upper N bits are not changed, so that a stable count can be obtained.

Here, the counter up-down value (X) is a register value that can be freely set to correct the error feedback gain, and may be set by an external controller (not shown) or a fixed value may be used. The set value of the counter updown value X is stored in the register 303 and is often referred to by the updown counter 301.

7 is a waveform diagram illustrating a driving frequency of a piezoelectric transformer in the piezoelectric transformer-type high voltage power supply apparatus according to the first embodiment of the present invention.

Here, the output voltage changes according to the frequency of the driving voltage applied to the piezoelectric transformer T201. As shown in Fig. 7, the output voltage of the piezoelectric transformer T201 has three kinds of extreme values (resonance points), giving the largest output voltage before and after the first resonant frequency f1 on the low frequency side, and on the high frequency side. As the second resonant frequency f2 and the third resonant frequency f3 become, the value of the output voltage decreases. Therefore, in order to obtain the output voltage of the piezoelectric transformer T201 most efficiently, it is preferable to use the drive frequencies before and after the first resonance frequency f1.

Therefore, the counter value of the up-down counter 301 used for frequency control needs to converge to the frequency variable range shown in FIG. In the frequency variable range, fmin, which is a frequency value considering the manufacturing irregularity of the first resonant frequency f1, is set as the minimum frequency, and the output voltage fluctuation increases between the first resonant frequency f1 and the second resonant frequency f2. It is possible to obtain the maximum frequency by using the fmax value, which is the frequency value before completion. Here, fmin and fmax are register values stored in the register 303 and may be set by an external controller or may be fixed values.

The upper N bits of the counter value are output to the first comparator 305, the off time setting unit 307, and the selecting unit 309. The counter value of the up-down counter 301 is compared with the fmin register value and the fmax register value by the first comparator 305 every time a clock is input from the clock part 103. As a result of the comparison, when the counter value of the up-down counter 301 becomes the frequency variable range boundary, the control signal is output from the first comparator 305 to the up-down counter 301, and the up-down counter 301 stops the count-up down operation. Let's do it.

In addition, when a counter value is input from the up-down counter 301 and a register value for freely setting the off time is input from the off time setting unit 307, the selecting unit 309 selects any one of the input values. Duty ratio can be controlled.

The up-down counter 301 sets the counter value to fmin when the reset signal is supplied from the reset unit 101.

Therefore, as a result of comparing the output control voltage Reference_Volt, which is a DC voltage, with the output voltage Feed back, when the output voltage increases, the counter value of the up-down counter 301 decreases, the driving voltage frequency increases, and the duty ratio is small. The output voltage output from the piezoelectric transformer T201 becomes small. On the other hand, when the output voltage decreases, the counter value of the frequency control up-down counter 301 increases, the drive voltage frequency decreases, the duty ratio increases, and the output voltage output from the piezoelectric transformer T201 increases. As a result, it is controlled to be equal to the desired drive voltage frequency ftarget (see Fig. 7). That is, by simultaneously controlling the driving frequency and the duty ratio in response to the output control voltage Reference_Volt (DC voltage), the output voltage value is kept constant.

In addition, when the output is OFF, the output control voltage Reference_Volt> output voltage becomes low, so that the driving frequency gradually decreases, changes to fmin, and stops. At this time, the duty ratio is maximum. On the contrary, when the output is ON, the output control voltage Reference_Volt < the output voltage is increased, so that the driving frequency gradually increases to become the target frequency ftarget. At this time, the duty ratio is minimum.

The register 303, which is an embodiment of the variable range storage unit, stores the maximum value fmax and the minimum value fmin of the drive frequency of the piezoelectric transformer T201. Further, the register 303 stores the counter updown value X of the updown counter 301. The register 303 also outputs a counter updown value X to the updown counter 301 or fmax or fmin to the first comparator 305.

The first comparator 305, which is an embodiment of the frequency range controller, controls the driving frequency to be variable within the frequency variable range based on the frequency variable range stored in the register 303 and the output value of the up-down counter 301. . More specifically, the first comparator 305 is input with a counter value of the upper N bits of the up-down counter 301 and fmax and fmin. The first comparator 305 compares the counter value with the magnitude relationship between fmax and fmin, and determines whether or not the input counter value exists at the frequency variable range boundary of the piezoelectric transformer T201. When the upper N bits of the counter value exceed the minimum value fmin of the frequency variable range, or when the upper N bits of the counter value become less than the maximum value fmax of the frequency variable range, the first comparator 305 Becomes a high output and transmits an UP / DOWN STOP signal, which is a control signal for stopping the count-down operation of the up-down counter 301.

[About off time setting part]

In the high-voltage power supply apparatus of the piezoelectric transformer system according to the first preferred embodiment of the present invention, the off time setting unit 307 sets the off time for stopping the application of the driving voltage applied to the piezoelectric transformer T201. Specifically, the off time setting unit 307 stores a reference off time setting register value, which is a reference value for setting the off time for which the drive voltage becomes a low output, and at the same time, the off time setting unit 307 turns off based on the output value of the up-down counter 301. And an off time processor (not shown) for setting a time setting register value. At this time, the reference off time setting register value may be set by an external controller.

In addition, the off time setting unit 307 is configured so that the off time can be a variable value or a fixed value, the reference off time setting register value, the output value A of the N-bit up-down counter 301 and the register 303. The off-time setting register value can be output by arithmetic processing using [Equation 1] using the fmin value inputted from the Equation (1).

OFF time setting register value = reference OFF time setting register value + (fmin-A) x α

(0≤α <1)

When [alpha] = O in [Equation 1], since the off time setting register value = the reference off time setting register value, the off time setting unit 307 can make the off time constant, and when O <α <1, The off time setting register value can be set as a change value having a fluctuation range of (fmin-A) × α.

[About selection part]

In the high-voltage power supply of the piezoelectric transformer according to the first embodiment of the present invention, the selector 309 is the output value and the off time setting unit 307 output from the driving frequency control unit according to the output value of the driving voltage generation unit. Selects the output value outputted from the controller, and outputs the selected output value to the driving voltage generator.

The selector 309 receives a counter value (upper N bits) from the up-down counter 301, and an off-time setting register value from the off-time setting register 307. The selector 309 selects the counter value (upper N bits) of the up-down counter 301 when the output of the 1-bit counter 315 is a high output, that is, when the driving voltage is High. When the output of the bit counter 315 is a low output, that is, when the drive voltage is low, the off time setting register value is selected. In addition, the selector 309 outputs the selected output value to the second comparator 313.

[About driving voltage generator]

The driving voltage generation unit generates the driving voltage of the piezoelectric transformer T201 based on the driving frequency controlled by the driving frequency control unit, the off time set by the off time setting unit, and the output value of the selection unit. As shown in FIG. 5, the driving voltage generator includes an N-bit digital reset counter 311, a second comparator 313, a 1-bit counter 315, and AND gates 317 and 319.

N-bit digital reset counter 311 (hereinafter referred to as N-bit counter 311) is a high-speed clock, such as up-down counter 301, is input from clock portion 103 to synchronize with up-down counter 301. Each time the clock goes high, the counter value is increased by +1. The counter value of the N bit counter 311 is output to the second comparator 313.

When the Low signal is input to the reset input terminal of the N-bit counter 311, a reset is performed, and the counter value becomes zero (0). The reset signal input to the N-bit counter 311 is inverted from the system reset signal supplied from the reset unit 101, which initializes all logic circuits when the power is input, and the output signal COMPARE_OUT of the second comparator 313. The signal is generated by ANDing the AND gate 319.

The second comparator 313 has one of an output value of the selector 309, that is, a counter value of the up-down counter 301, which is a counter value for frequency control, or an off time setting register value set by the off time setting unit 307. And a counter value of the N bit counter, which is a counter value for driving voltage generation, are input.

When such a value is input, the second comparator 313 determines that the output of the first bit counter 315 is high (the driving voltage output is High) of the up-down counter 301 selected by the selector 309. The counter value and the counter value of the N-bit counter 311 are compared, and when these values match, the output is high. In addition, the second comparator 313 is configured to select the off time setting register value and the N bit counter value selected by the selector 309 when the output of the first bit counter 315 is Low (the driving voltage output is Low). Compare and output high when these values match.

Therefore, the drive frequency control can be performed by the counter value of the up-down counter 301. The selector corresponding to the control of the on time when the drive voltage output is High by the counter value of the up-down counter 301, the control of the off time by the off-time setting register value, and the reset timing of the N-bit counter 311 ( The duty ratio control may be performed by the conversion timing control of the value selected by 309.

In addition, when the counter value of the N-bit counter 311 becomes equal to or greater than the output value of the selector 309, the second comparator 313 performs high output. The second comparator 313 is reset when the reset signal is supplied from the reset unit 101.

The 1-bit counter 315 inverts the output voltage whenever the output signal from the second comparator 313 is triggered and the output of the second comparator 313 becomes a high signal. The output signal of the 1 bit counter 315 is input to the AND gate 317. The 1-bit counter 315 is reset when the reset signal is input from the reset unit 101.

The output signal of the 1-bit counter 315 is also input to the selector 309. As described above, when the output of the 1-bit counter 315 is High, the selector 309 selects the counter value of the up-down counter 301, and selects when the output of the 1-bit counter 315 is Low. The unit 309 selects an off time setting register value. That is, the value selected by the selector 309 at the timing at which the driving voltage is inverted is high between the counter value of the up-down counter unit 301 controlling the on time and the off time setting register value controlling the off time. Is converted from Therefore, the timing at which the driving voltage is applied to the piezoelectric transformer T201 or the application is stopped by the operation of the one-bit counter 315 and the selection unit 309 can be controlled, thereby controlling the duty ratio of the driving voltage. Can be.

The AND gate 317 is inputted with an inverted signal of the ENABLE signal, which is an inverted signal of the ON / OFF control signal output from the controller 105, and an output signal output from the 1-bit counter 315. The AND gate 317 controls ON / OFF of the high voltage power output. That is, if the ENABLE signal is set to the Low signal, the drive voltage output is output directly from the AND gate 317, and the high voltage power output is output. If the ENABLE signal is set to the High signal, the output from the AND gate 317 is forcibly low. Signal, the high voltage output is stopped. When the high voltage output is stopped, the drive frequency control unit controls the maximum fmin and the duty ratio of the lower limit of the drive frequency to the maximum so that the output voltage is maximum.

The AND gate 319 receives the reset signal from the reset unit 101 and the inverted signal of the output signal COMPPARE OUT of the second comparator 313, and generates a reset signal of the N bit counter 311. . The output of the AND gate 319 is input to the reset terminal of the N bit counter 311.

In addition, the piezoelectric transformer driving control unit 30 includes a D / A converter 321 that converts the output signal of the controller 105 into an analog signal and converts it into an output control voltage Reference_Volt. At this time. The D / A converter 321 is not limited to a specific one, and a D / A converter generally used may be used. The output control voltage Reference_Volt generated by the conversion processing of the D / A converter 321 is input to the comparator 501 constituting the output voltage detector 50.

In addition, instead of the D / A converter 321, a pulse width modulation (PWM) signal generator may be used.

The configuration of the high-voltage power supply device of the piezoelectric transformer according to the first embodiment of the present invention has been described. Each component of the above-described high voltage power supply apparatus may be configured using a general-purpose member or a circuit, or may be configured by hardware specialized in the function of each component. Therefore, whenever implementing this embodiment, the structure used suitably according to a technical level can be changed.

[About operation of high-voltage power supply device of piezoelectric transformer method]

8 is a timing diagram of an operation of the high-voltage power supply device of the piezoelectric transformer according to the first embodiment of the present invention, Figure 9 is an operation stop of the high-voltage power supply device of the piezoelectric transformer method according to a first embodiment of the present invention. Time timing diagram. 8 and 9 assume that the off time setting register value is constant (α = 0).

Hereinafter, the operation of the high-voltage power supply device of the piezoelectric transformer according to the first embodiment of the present invention will be described with reference to FIGS. 8 and 9.

Referring to FIG. 8, FIG. 8 illustrates a control operation timing chart from the high voltage output ready state (OFF state) to ON to the target high pressure output. In the ready state, as shown in FIG. 8, since the output control voltage Reference_Volt> output voltage Feed back is set, the driving frequency FREQ_OUT becomes fmin. Each time the output value Y of the selector becomes High of COMPARE_OUT, the output value Y selects between the counter value of the up-down counter and the off time setting register value (Off Time). When ENABLE goes low and becomes ON, the output voltage (Feed back voltage) gradually rises and UP is input as an UP / DOWN signal to the up-down counter. In addition, when the output voltage (Feed back voltage) becomes larger than the output control voltage Reference_Volt, since the DOWN is output as the UP / DOWN signal, the up-down counter decreases the counter value. In FIG. 8, "CntDown" represents "countdown" which decreases the counter value. In the N bit counter column, "CD1" represents "Cut Down 1", and the counter value is "Cnt Down1"> "Cnt Down2".

8 assumes that the off-time setting register value is constant, and if the counter value of the up-down counter decreases, the on-time when the drive frequency FREQ_OUT is High becomes short, so that the duty ratio becomes small and the drive frequency is high frequency. Move to the side. In Fig. 8, "Hi f" indicates that the driving frequency moves to the high frequency side. In addition, as the on-time is shortened in this manner, the duty ratio becomes small, and as the driving frequency increases, the output voltage FREQ_DRIVE_OUT also becomes small.

In this way, the driving frequency FREQ_OUT moves to the high frequency side and is controlled to be the target driving frequency ftarget. In FIG. 8, "Cnt target 1" in the up-down counter field means counting up to ftarget, and "CT1" in the N-bit counter field means "Cnt target 1".

Referring to Fig. 9, Fig. 9 illustrates a control operation timing chart until a target high pressure output → OFF → high pressure output Ready state is reached. In the state of outputting the target high voltage, as shown in FIG. 9, the N-bit counter and the up-down counter repeat the count until the counter value becomes ftarget (Cnt Target N), and output voltage (Feed back voltage). ) Is similar to the output control voltage Reference_Volt. Here, when ENABLE becomes Hi and becomes OFF, the value of the output voltage (Feed back voltage) gradually decreases, and the value of the output control voltage Reference_Volt increases. As a result, since UP is output as the UP / DOWN signal, the up-down counter increments the counter value. In Fig. 9, "CntUP" means "count up" to increase the counter value.

9 assumes that the off-time setting register value is constant, and as the up-down counter value increases, the on-time in which the driving frequency FREQ_OUT is High becomes long, so that the duty ratio increases, and the driving frequency moves to the low frequency side. In Fig. 9, "Low f" indicates that the driving frequency moves to the low frequency side.

As shown in Fig. 9, when the counter value of the up-down counter increases, the count upper limit value of the N-bit counter also increases accordingly. As a result, the driving frequency FREQ_OUT changes from ftarget to the low frequency side and is controlled to be fmin, which is the minimum value of the frequency variable range. At this time, the duty ratio is controlled to be maximum.

[About image forming apparatus using high-voltage power supply apparatus of piezoelectric transformer system]

An image forming apparatus using a high-voltage power supply apparatus of a piezoelectric transformer according to a first preferred embodiment of the present invention will be described.

The image forming apparatus according to the present embodiment is formed in the charging means for equally charging the surface of the latent image bearing member, the exposure means for forming the latent image on the surface of the latent image carrier after charging, the developing means for developing the latent image, and the latent image bearing member. And a transfer means for transferring the transfer material to the toner image.

At this time, the charging means, the developing means, and the transfer means need to receive a predetermined bias (voltage) from the power supply device set in the image forming apparatus at the time of each processing. Therefore, the image forming apparatus according to the present embodiment is a power supply apparatus for supplying voltage to at least one of the charging means, the developing means and the transfer means, and the high-voltage power supply apparatus of the piezoelectric transformer system according to the first preferred embodiment of the present invention. Apply.

Since the piezoelectric transformer-type high voltage power supply device 10 according to the first embodiment of the present invention is capable of stable frequency control without incurring abnormal oscillation or control, image formation using the piezoelectric transformer type high voltage power supply device 10 is possible. The charging means, the developing means and the transfer means of the apparatus can perform stable processing. Moreover, since the high rise time of a high pressure output becomes possible, the time required for each process process can be shortened.

As described above, in the high-voltage power supply apparatus of the piezoelectric transformer according to the present embodiment, the drive voltage generation unit of the piezoelectric transformer is constituted by an N-bit counter, which is a reset counter, and the frequency control unit is constituted by a digital processing circuit by an up-down counter. At the same time, the variable control range of the frequency variable control up-down counter is settable by the lowest frequency variable range setting register fmin and the highest frequency variable range setting register fmax. Thereby, in the variable range of a wide range of output voltages, stable frequency control and duty ratio control can be performed without falling into abnormal oscillation or uncontrollability caused by irregularity of the part constant or temperature fluctuations.

In addition, in the high-voltage power supply device of the piezoelectric transformer system according to each of the embodiments and modifications of the present invention, when the output is turned off by an external ON / OFF control signal, the piezoelectric transformer driving control section is a variable minimum in which the high-voltage output value is maximum. Since it operates so that it may become the frequency fmin, it enables the high rise time of a high voltage output at the time of output ON.

In addition, by configuring the piezoelectric transformer driving control unit by a logic circuit, it is possible to include in a conventional logic IC (ASIC) for a specific use, it is possible to reduce the cost of the frequency control unit.

As mentioned above, although preferred embodiment of this invention was described with reference to an accompanying drawing, it cannot be overemphasized that this invention is not limited to this example. It is apparent to those skilled in the art that the present invention can be conceived as various modifications or modifications within the scope described in the claims, and they are naturally understood to belong to the technical scope of the present invention.

For example, in the above-mentioned embodiment, the case where the constant voltage control which detects the fluctuation | variation of an output voltage and makes a voltage value constant was described was described, but instead of constant voltage control, a change of an output current is detected and a current value is fixed. It is also possible to do constant current control. Even with this constant current control, the operation is the same as that of the constant voltage control.

1 is a block diagram illustrating a high-voltage power supply device of a general piezoelectric transformer system.

FIG. 2 is a first waveform diagram for describing a driving frequency of a piezoelectric transformer in a general piezoelectric transformer type high voltage power supply device.

3 is a second waveform diagram for describing a driving frequency of a piezoelectric transformer in a general piezoelectric transformer-type high voltage power supply device.

4 is a block diagram illustrating a high-voltage power supply device of a piezoelectric transformer according to a first embodiment of the present invention.

5 is a block diagram illustrating a piezoelectric transformer driving unit of a piezoelectric transformer-type high voltage power supply apparatus according to a first embodiment of the present invention.

FIG. 6 is a diagram illustrating a relationship between an inductor power supply voltage and an operating waveform when boosted in a piezoelectric transformer-type high voltage power supply device according to a first embodiment of the present invention.

7 is a timing diagram of an operation of the high-voltage power supply device of the piezoelectric transformer according to the first embodiment of the present invention.

8 is a timing diagram when operation of the high-voltage power supply device of the piezoelectric transformer according to the first embodiment of the present invention is stopped.

Claims (7)

In the high-voltage power supply device of the piezoelectric transformer system for supplying the output voltage output from the piezoelectric transformer to the load, An output voltage detector for comparing the output voltage with an output control voltage for controlling the output voltage to a predetermined value, and detecting a change in the output voltage as a digital change value based on the comparison result; And And a driving controller for controlling the driving frequency and the duty ratio according to the detected digital variation value. The method of claim 1, The driving control unit A driving frequency controller configured to variably control the driving frequency according to the detected digital variation value; An off time setting unit for setting an off time for stopping the application of the driving voltage applied to the piezoelectric transformer;  A selection unit for selecting an output value output from the driving frequency controller and an output value output from the off time setting unit according to an output value of the driving voltage generator, and outputting the selected output value to the driving voltage generator; And And a driving voltage generation unit generating the driving voltage based on the driving frequency controlled by the driving frequency control unit, the off time set by the off time setting unit, and the output value output by the selection unit. A piezoelectric transformer-type high voltage power supply device. The method of claim 2, The driving frequency control unit If the output voltage is greater than the output control voltage, the digital variation value increases the drive frequency, And the digital variation value decreases the driving frequency when the output voltage is smaller than the output control voltage. The method of claim 2, The driving control unit A storage unit which stores a frequency variable range of the driving frequency; And a frequency range controller for controlling the driving frequency to be changed within the frequency variable range based on the frequency variable range stored in the memory and the output value of the driving frequency controller. High voltage power supply. The method of claim 4, wherein The frequency range control unit If the output value of the drive frequency is out of the frequency variable range, output a control signal to stop the increase or decrease of the drive frequency, The driving frequency control unit The piezoelectric transformer type high voltage power supply device, characterized in that for stopping the increase or decrease of the driving frequency in accordance with the control signal received from the frequency range control unit. The method of claim 2, The driving control unit A timing in which an on time for applying the driving voltage to the piezoelectric transformer is controlled by the driving frequency controller, the off time is controlled by the off time setting unit, and the on time and the off time are changed. And controlling the duty ratio by controlling the selector in the high voltage power supply of the piezoelectric transformer. Charging means for equally charging the surface of the latent image bearing member; Exposure means for forming a latent image on a surface of the latent image bearing member after the charging; Developing means for developing the latent image; Transfer means for transferring a toner image formed on the latent image bearing member to a transfer material; And A power supply device for supplying a voltage to at least one of the charging means, the developing means, and the transfer means, The power supply device is any one of the high-voltage power supply device of the piezoelectric transformer system according to claim 1 characterized in that.

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