JP2007057568A - Power unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power unit that prevents an image carrier and a discharge member constituting an image forming apparatus from deteriorating and decreasing in printing quality. <P>SOLUTION: The power unit 100-1 has a triangular wave generator 11 which generates a triangular wave having the same period with a PWM signal period, a smoothing circuit 12 which generates a smoothed signal by smoothing the PWM signal, a comparator 13 which generates a rectangular wave signal rising and falling alternately in timing where the voltage value of the triangular wave signal and the mean voltage value of the smoothed signal become equal to each other, and an inverting circuit 14 which inverts and outputs the rectangular wave signal, and varies a DC voltage supplied to a charging roll 50 according to the duty ratio of the rectangular wave signal after inversion which is output from the inverting circuit 14. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power supply apparatus that supplies electric power that changes according to a duty ratio of a PWM signal to a discharge member that discharges to an image carrier in an image forming apparatus such as a copying machine or a printer apparatus using an electrophotographic system. .

  In an image forming apparatus such as a printer or a copying machine, a photosensitive drum is uniformly charged by a charging device during printing, and an electrostatic latent image corresponding to an image to be printed is formed on the side surface of the photosensitive member by an exposure device. Further, a toner image is formed in the area of the electrostatic latent image by the developing device, and the toner image is transferred to the paper by the transfer device. The sheet on which the toner image is transferred is peeled off from the photoreceptor or the transfer device by the peeling device.

  When the photosensitive member is charged by the charging device, the output voltage to the charging device is controlled to a voltage value corresponding to a predetermined process speed by constant current control or constant voltage control.

  In such an image forming apparatus, unlike ordinary paper, when high-impedance thick paper or special paper such as OHP is used, it is necessary to slow down the transfer speed in order to enable reliable printing. . At this time, generally, the charging roll (BCR) in the charging device is moved away from the photosensitive member, or the current supplied to the BCR is stopped (see, for example, Patent Documents 1 and 2). However, the former has a complicated mechanism, resulting in an increase in cost and a decrease in reliability. In the latter case, there are problems such as poor response to rising and falling of current.

For this reason, when high-impedance thick paper or special paper such as OHP is used, it is necessary to slow down the transfer speed and also slow down the rotation speed of the BCR and the photoconductor in the charging device. Furthermore, if the voltage and current supplied to the BCR and their operating frequencies are set to the same conditions as those at the constant speed, the life of the BCR and the photoconductor is shortened. It is necessary to reduce the operating frequency.
JP-A-6-83179 JP-A-7-84425

  However, if the voltage or current supplied to the BCR is changed abruptly, an overshoot occurs, which may damage the BCR or the photoconductor and cause streaks or the like in the printed image, leading to a decrease in print quality.

  The present invention has been made in order to solve the above-described conventional problems, and provides a power supply device that prevents deterioration of an image carrier and a discharge member constituting an image forming apparatus and deterioration of print quality. is there.

  The present invention relates to a power supply device that supplies electric power that changes in accordance with a duty ratio of a PWM signal to a discharge member that discharges to an image carrier in an image forming apparatus, and the duty ratio of the PWM signal is the first. Change means for generating and outputting a rectangular wave signal having a duty ratio that changes from the first value to the second value through a step when the value is changed to a second value; The electric power supplied to the discharge member is changed according to the duty ratio of the rectangular wave signal output by the means.

  With this configuration, even if the duty ratio of the PWM signal changes abruptly, the voltage or current supplied to the discharge member that discharges to the image carrier in the image forming apparatus is an electric current such as a current value, a voltage value, or a frequency. Since the target quantities gradually change, the occurrence of overshoot can be prevented, and the deterioration of the image carrier and the discharge member and the deterioration of the print quality can be prevented.

  From the same viewpoint, in the power supply device of the present invention, the changing unit generates a smoothed signal by smoothing the PWM signal with a first generating unit that generates a triangular wave signal having the same period as the period of the PWM signal. Second generation means; and third generation means for generating a rectangular wave signal that alternately repeats rising and falling at a timing at which the voltage value of the triangular wave signal and the average voltage value of the smoothed signal match. Inverting means for inverting and outputting the rectangular wave signal, and changing at least one of voltage and current in accordance with the duty ratio of the inverted rectangular wave signal output by the inverting means. .

The power supply device of the present invention is
Phase control means for outputting the inverted rectangular wave signal output by the inverting means and the rectangular wave signal obtained by shifting the phase of the inverted rectangular wave signal by 90 degrees, and is output by the inverting means. The DC voltage or DC current is changed according to the inverted rectangular wave signal, and the duty ratio of the inverted rectangular wave signal output by the phase control means and the phase of the inverted rectangular wave signal are 90 degrees. The AC voltage or AC current is changed according to the duty ratio of the shifted rectangular wave signal.

  In addition, the power supply device of the present invention includes an oscillator configured by the first generation unit, the third generation unit, and the inversion unit.

  In the power supply device of the present invention, the image carrier is a photoconductor, and the discharge member is a charging member that charges the photoconductor.

  In the power supply device of the present invention, the charging member is a charging roll or corotron that charges the photosensitive member.

  According to the present invention, by gradually changing the electrical quantities of voltage and current supplied to the discharge member that discharges to the image carrier, the occurrence of overshoot can be prevented, and the image carrier and discharge member can be prevented. It is possible to prevent deterioration of printing quality and deterioration of printing quality.

  Hereinafter, a power supply device according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of the first power supply device. A power supply apparatus 100-1 shown in FIG. 1 receives an input PWM signal to a charging roll 50 for charging a photosensitive member (not shown) in an image forming apparatus such as a copying machine or a printer apparatus adopting an electrophotographic system. A DC voltage and an AC voltage whose values are changed according to the duty ratio are supplied in a superimposed manner.

  The power supply apparatus 100-1 includes a triangular wave generator 11 for supplying a DC voltage to the charging roll 50, a smoothing circuit 12, a comparator 13, an inverting circuit 14, a driver circuit 15, a DC power supply control unit 16, and a charging roll 50. A triangular wave generator 21, a smoothing circuit 22, a comparator 23, an inverting circuit 24, a two-phase dividing circuit 25, driver circuits 26 and 27, and an AC power supply control unit 28.

  The triangular wave generator 11 inputs a PWM signal 1 for controlling a DC voltage supplied to the charging roll 50 from, for example, a machine control unit (MCU) (not shown) that is a control unit of the image forming apparatus 100-1. In the case where the PWM signal 1 needs to increase the DC voltage to be supplied to the charging roll 50, the duty ratio increases accordingly, and the DC voltage to be supplied to the charging roll 50 needs to be reduced. Accordingly, the duty ratio is reduced accordingly. Further, the triangular wave generator 11 generates a triangular wave signal having the same period as that of the input PWM signal 1 and outputs the triangular wave signal to the comparator 13.

  When receiving the PWM signal 1, the smoothing circuit 12 smoothes the PWM signal 1 and outputs the smoothed signal to the comparator 13. FIG. 2 is a diagram illustrating a configuration of the smoothing circuit 12. The smoothing circuit shown in FIG. 2 is a CR circuit composed of a resistor 61 and a capacitor 62, which inputs a rectangular PWM signal 1 and outputs a pulsating smooth signal.

  Again, returning to FIG. When the comparator 13 receives the triangular wave signal from the triangular wave signal generator 11 and the smoothed signal from the smoothing circuit 12, the comparator 13 generates a signal (average voltage value signal) indicating the average voltage value of the smoothed signal. The smoothing circuit 12 may smooth the rectangular PWM signal 1 to output an average voltage value signal to the comparator 13 as a smoothed signal. In this case, the comparator 13 does not need to generate an average voltage value signal.

  Further, the comparator 13 compares the triangular wave signal with the average voltage value signal, and repeats rising and falling alternately at the timing when the voltage value of the triangular wave signal matches the voltage value of the average voltage value signal. Is generated. The generated rectangular wave signal is output to the inverting circuit 14. The inverting circuit 14 inverts the rectangular wave signal from the comparator 13 and outputs the inverted signal to the driver circuit 15.

  FIG. 3 is a timing chart showing operations of the triangular wave generator 11, the smoothing circuit 12, the comparator 13, and the inverting circuit 14 in the power supply apparatus 100-1.

  The triangular wave generator 11 and the smoothing circuit 12 receive the PWM signal 1 shown in FIG. The PWM signal 1 changes in duty ratio when the voltage value of the DC voltage to be supplied to the charging roll 50 is changed. In FIG. 3 (a), the PWM signal 1 has an initial (before change) duty ratio of 50%, but is changed to increase the voltage value of the DC voltage to be supplied to the charging roll 50. The duty ratio is greater than 50%.

  The triangular wave generator 11 generates a triangular wave signal (FIG. 3B) having the same period as that of the PWM signal 1 and outputs the triangular wave signal to the comparator 13. On the other hand, the smoothing circuit 12 smoothes the PWM signal 1 and outputs the smoothed signal shown in FIG. The waveform of the smoothing signal changes in accordance with the duty ratio of the PWM signal 1 for each period of the PWM signal 1. In FIG. 3C, the smoothed signal is a first waveform corresponding to the PWM signal 1 before the change, a second waveform corresponding to the PWM signal 1 of the first cycle after the change, and the second and subsequent after the change. There are two types of waveforms of the third waveform corresponding to the PWM signal 1 of the period.

  When the comparator 13 receives the triangular wave signal from the triangular wave signal generator 11 and the smoothed signal from the smoothing circuit 12, the comparator 13 generates an average voltage value signal (FIG. 3D) indicating the average voltage value of the smoothed signal. Generate. The voltage value of the average voltage value signal is maintained at a predetermined value while the PWM signal 1 before the change is input, and increases while the PWM signal 1 of the first cycle after the change is input. While the PWM signal 1 having the second and subsequent cycles is being input, the predetermined value after the increase is maintained.

  Further, the comparator 13 compares the triangular wave signal shown in FIG. 3B with the average voltage value signal shown in FIG. 3D, and the voltage value of the triangular wave signal matches the voltage value of the average voltage value signal. A rectangular wave signal (FIG. 3E) that repeats rising and falling alternately at the timing is generated and output to the inverting circuit 14. The inverting circuit 14 inverts the rectangular wave signal shown in FIG. 3E and outputs the inverted rectangular wave signal (FIG. 3F) to the driver circuit 15.

  While the PWM signal 1 before the change is being input, the inverted rectangular wave signal has the same duty ratio as the PWM signal 1 before the change. On the other hand, when the PWM signal 1 of the first cycle after the change is input, the inverted rectangular wave signal does not immediately have the same duty ratio as the PWM signal 1 of the first cycle after the change. The duty ratio increases through the stages, and becomes the same duty ratio as the PWM signal 1 after the change at the timing when the PWM signal 1 of the second and subsequent cycles after the change is input.

  Again, returning to FIG. The driver circuit 15 controls the operation of a power control switch (power control switch) in the DC power control unit 16 that supplies a DC voltage to the charging roll 50 according to the duty ratio of the inverted rectangular wave signal. . Specifically, the driver circuit 15 turns on the power supply control switch at the rising edge of the inverted rectangular wave signal and outputs a voltage, and turns off the power supply control switch at the falling edge of the inverted rectangular wave signal. Shut off. As a result, the DC power supply control unit 16 supplies the charging roll 50 with a DC voltage having a value proportional to the duty ratio of the inverted rectangular wave signal.

  As described above, the duty ratio of the inverted rectangular wave signal does not immediately follow even if the duty ratio of the PWM signal 1 is changed, and becomes the same as the duty ratio of the PWM signal 1 through the steps. Therefore, by making the voltage value of the DC voltage supplied to the charging roll 50 change according to the duty ratio of the inverted rectangular wave signal, it is compared with the case where it changes according to the duty ratio of the PWM signal 1. As a result, the occurrence of overshoot can be prevented, and the deterioration of the charging roll 50 and the photosensitive member charged by the charging roll 50 and the deterioration of the printing quality can be prevented.

  On the other hand, the triangular wave generator 21, the smoothing circuit 22, the comparator 23, and the inverting circuit 24 are the same as the triangular wave generator 21, the smoothing circuit 22, the comparator 23, and the inverting circuit 24 described above according to the input of the PWM signal 2. Perform the action.

  When receiving the inverted rectangular wave signal from the inverting circuit 24, the two-phase dividing circuit 25 generates a signal (rectangular wave signal after phase control) in which the phase of the inverted rectangular wave signal is shifted by 90 degrees. Then, the two-phase division circuit 25 outputs the inverted rectangular wave signal as it is to the driver circuit 26 and also outputs the phase-controlled rectangular wave signal to the driver circuit 27.

  The driver circuit 26 controls the operation of the AC power supply control unit 28 that supplies an AC voltage to the charging roll 50 according to the duty ratio of the inverted rectangular wave signal. Similarly, the driver circuit 27 controls the operation of the AC power supply control unit 28 according to the duty ratio of the rectangular wave signal after phase control. The AC power supply control unit 28 supplies the charging roll 50 with an AC voltage having a value proportional to the duty ratio of the inverted rectangular wave signal and the duty ratio of the rectangular wave signal after phase control.

  Similar to the control of the DC voltage described above, the duty ratio of the inverted rectangular wave signal does not immediately follow even if the duty ratio of the PWM signal 2 is changed, and becomes the same as the duty ratio of the PWM signal 2 through the steps. . Therefore, by making the voltage value of the AC voltage supplied to the charging roll 50 change according to the duty ratio of the inverted rectangular wave signal, the occurrence of overshoot is prevented, and the charging roll 50 and It is possible to prevent deterioration of the photosensitive member charged by the charging roll 50 and deterioration of printing quality.

  Various configurations of the power supply device are conceivable in addition to the above-described embodiment. FIG. 4 is a diagram illustrating a configuration of the second power supply device. A power supply device 100-2 shown in FIG. 4 is a charging roll for charging a photosensitive member in an image forming apparatus such as a copying machine or a printer employing an electrophotographic method, like the first power supply device 100-1 shown in FIG. 50, a DC voltage and an AC voltage whose values are changed according to the duty ratio of the input PWM signal are supplied in a superimposed manner.

  Compared with the power supply apparatus 100-1, the power supply apparatus 100-2 includes an oscillator 31 having the functions of the triangular wave generator 11, the comparator 13, and the inverting circuit 14, and the triangular wave generator 21, the comparator 23, and the inverting circuit. It has an oscillator 41 having 24 functions.

  In the oscillator 31, the terminal a is grounded, and the voltage Vcc is applied to the terminals d and h. Further, the terminals g and f are applied with a voltage at a connection portion between the other end of the resistor 33 to which the voltage Vcc is applied at one end and the other end of the capacitor 34 with one end grounded.

  The oscillator 31 receives the PWM signal 1 from the terminal b, and generates a triangular wave signal having the same period as that of the PWM signal 1. Further, the oscillator 31 inputs a smoothed signal output from the smoothing circuit 12 from the terminal e. Note that the other end of the capacitor 32 whose one end is grounded is connected between the output end of the smoothing circuit 12 and the terminal e.

  Next, the oscillator 31 generates an average voltage value signal indicating the average voltage value of the smoothed signal input from the terminal e. The oscillator 31 compares the triangular wave signal input from the terminal b with the generated average voltage value signal, and rises and falls at the timing when the voltage value of the triangular wave signal and the voltage value of the average voltage value signal match. A rectangular wave signal that repeats alternately is generated. Furthermore, the oscillator 31 inverts the generated rectangular wave signal and outputs the inverted signal from the terminal c to the driver circuit 15.

  Since the oscillator 41 performs the same operation as the oscillator 31, the description thereof is omitted. In addition, the smoothing circuit 12, the driver circuit 15, the DC power supply control unit 16, the smoothing circuit 22, the two-phase division circuit 25, the driver circuits 26 and 27, and the AC power supply control unit 28 are the same operations as those in the power supply apparatus 100-1. Therefore, the description thereof is omitted.

  By the way, in embodiment mentioned above, although the power supply device 100-1 supplied the DC voltage and AC voltage which changed the value according to the duty ratio of PWM signal in superimposition, it supplies one of DC voltage and AC voltage. The present invention can also be applied to a power supply apparatus that supplies at least one of a direct current and an alternating current that are changed according to the duty ratio of the PWM signal. Furthermore, the present invention can also be applied to a power supply device that supplies a voltage or current whose frequency is changed according to the duty ratio of the PWM signal.

  In the above-described embodiment, the case where a DC voltage and an AC voltage are supplied to the charging roll 50 has been described. However, the DC voltage is applied to other discharge members such as a corotron and a developing unit for charging the photosensitive member. The present invention can also be applied when supplying at least one of an alternating voltage, a direct current, and an alternating current.

  Further, in the above-described embodiment, the power supply apparatus 100-1 realizes control of the DC voltage and the AC voltage by the hardware configuration, but immediately after the duty ratio of the PWM signal is changed by software control by the CPU or the like. Without following, a rectangular wave signal that is the same as the duty ratio of the PWM signal is generated through a stage, and at least one of a DC voltage, an AC voltage, a DC current, and an AC current is set to the duty ratio of the rectangular wave signal. It is also possible to change it accordingly.

  As described above, the power supply device according to the present invention is useful as a power supply device because it can prevent the occurrence of overshoot and can prevent the deterioration of the image carrier and the discharge member and the deterioration of the print quality. .

It is a figure which shows the structure of a 1st power supply device. It is a figure which shows the structure of a smoothing circuit. It is a timing chart which shows operation | movement of a triangular wave generator, a smoothing circuit, a comparator, and an inverting circuit. It is a figure which shows the structure of a 2nd power supply device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11, 21 Triangular wave generator 12, 22 Smoothing circuit 13, 23 Comparator 14, 24 Inversion circuit 15, 26, 27 Driver circuit 16 DC power supply control part 25 Two-phase division circuit 28 AC power supply control part

Claims (6)

A power supply device that supplies electric power that changes according to a duty ratio of a PWM signal to a discharge member that discharges to an image carrier in an image forming apparatus,
When the duty ratio of the PWM signal is changed from a first value to a second value, a rectangular wave signal having a duty ratio that changes from the first value to the second value through a step is generated. A change means for outputting,
The power supply apparatus characterized by changing the electric power supplied to the said discharge member according to the duty ratio of the rectangular wave signal output by the said change means. The changing means is
First generation means for generating a triangular wave signal having the same period as the period of the PWM signal;
Second generating means for smoothing the PWM signal to generate a smoothed signal;
Third generating means for generating a rectangular wave signal that alternately repeats rising and falling at a timing at which the voltage value of the triangular wave signal and the average voltage value of the smoothed signal match;
Inverting means for inverting and outputting the rectangular wave signal,
2. The power supply device according to claim 1, wherein at least one of voltage and current is changed according to a duty ratio of the inverted rectangular wave signal output by the inverting means. Phase control means for outputting the inverted rectangular wave signal output by the inverting means and the rectangular wave signal obtained by shifting the phase of the inverted rectangular wave signal by 90 degrees;
The DC voltage or DC current is changed in accordance with the inverted rectangular wave signal output by the inverting means, the duty ratio of the inverted rectangular wave signal output by the phase control means, and the inverted rectangular wave signal 3. The power supply device according to claim 2, wherein the AC voltage or the AC current is changed in accordance with a duty ratio of the rectangular wave signal obtained by shifting the phase of the wave signal by 90 degrees. 4. The power supply device according to claim 2, further comprising an oscillator configured by the first generation unit, the third generation unit, and the inversion unit. 5. The power supply apparatus according to claim 4, wherein the image carrier is a photoconductor, and the discharge member is a charging member that charges the photoconductor. 6. The power supply device according to claim 5, wherein the charging member is a charging roll or a corotron for charging the photosensitive member.

Images