JP2008020595A - Power source device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power source device capable of supplying electric power at a desired crest factor even when switching a frequency of the power and to provide an image forming apparatus. <P>SOLUTION: A pulse signal meeting the frequency of the electric power supplied from a control circuit 30 to a charging roller 18 is outputted and in a high-voltage power source supply section 34, the pulse signal is converted to a sinusoidal wave by a preset gain according to the frequency corresponding to the pulse signal inputted from the control circuit 30, and the electric power meeting the sinusoidal wave is supplied to the charging roller 18. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a power supply device and an image forming apparatus.

  Conventionally, the surface of a photoconductor is charged to a predetermined potential, and a light beam is irradiated according to image data to form an electrostatic latent image on the photoconductor, and the electrostatic latent image is developed with toner. In an image forming apparatus such as a copying machine that transfers a toner image to a recording medium to form an image, a high-voltage power source is used to drive charging, development, transfer, and the like. The high-voltage power supply supplies driving power having a predetermined potential or current value to components around the photoreceptor.

  Here, there are a non-contact type charger such as a corotron wire and a contact type using a charging roll as a charger for charging the surface of the photosensitive member to a predetermined potential. Since the charging roll requires a smaller charging output than the corotron wire, it is advantageous in terms of low cost and energy saving.

  In recent years, it has been proposed that the image forming apparatus be configured to be compatible with various types of recording media such as plain paper, postcard, coated paper, OHP, and thin paper.

  In order to deal with such diversified recording media, for example, when instructing execution of image formation, an operator inputs information on the type of the recording medium and adjusts the process speed appropriately according to the recording medium. It has been proposed.

  That is, in the fixing process for fixing the toner to the recording medium, it is necessary to melt the toner appropriately by heat and to press the toner to the recording medium. However, the heat transfer efficiency varies depending on the type of recording medium. For example, OHP and coated paper with poor heat transfer efficiency require a longer time for fixing than plain paper. Further, it is necessary to increase the transmittance with OHP, and it is necessary to increase the gloss rate with coated paper.

  There are also models that operate at different process speeds depending on whether color image formation or monochrome image formation, resolution, print quality differences, and the like.

  Here, the charging roll preferably uses a power source in which alternating current is superimposed on direct current in order to charge the surface of the photoreceptor to a constant potential. Furthermore, when using a power supply in which alternating current is superimposed on direct current in this way, the frequency of the alternating current component (charging frequency) depends on the process speed at the time of image formation in order to prevent the occurrence of undulation due to the relationship with the writing frequency, etc. It is preferable to set the frequency.

  That is, when the process speed is adjusted and changed as described above, it is preferable to adjust the charging frequency as well.

  Conventionally, as a technique for changing the charging frequency, Patent Document 1 is configured so that the charging frequency can be changed in order to prevent color unevenness when a color image is formed by overlapping a plurality of color toner images. It describes that the charging frequency or the phase of the waveform is different when forming the toner images of the respective colors.

Further, Patent Document 2 acquires information indicating the type of the charging roller in order to keep the generation level of the charging sound low regardless of the type of the charging roller, and sets a frequency set in advance according to the acquired information. It is described to change.
JP-A-6-242663 JP 2003-156924 A

  An object of the present invention is to provide a power supply device and an image forming apparatus that can supply power at a desired crest factor even when the frequency of power is switched.

  In order to solve the above-mentioned problem, the invention of claim 1 is characterized in that an output means for outputting a pulse signal corresponding to a frequency of power supplied to a load, and the frequency corresponding to the pulse signal output by the output means. Acquisition means for acquiring information indicating, and conversion means for converting the pulse signal output by the output means to a sine wave with a preset gain according to the information indicating the frequency acquired by the acquisition means; Supply means for supplying power corresponding to the sine wave converted by the conversion means to the load.

  According to the first aspect of the present invention, when the pulse signal corresponding to the frequency of the electric power supplied to the load is converted into a sine wave and the electric power corresponding to the sine wave is supplied, the pulse signal is set in advance according to the frequency. Therefore, even if the frequency of the power is switched, the power can be supplied at a desired crest factor.

  The invention of claim 2 is characterized in that the gain is set in advance so that a crest factor of the sine wave becomes a predetermined value.

  According to the second aspect of the present invention, since the gain is set in advance so that the crest factor of the sine wave becomes a predetermined value, the crest factor can be maintained at the predetermined value regardless of the frequency of the power supplied to the load. it can.

  The invention according to claim 3 is characterized in that the acquisition means acquires the information indicating the frequency by converting the pulse signal into a sine wave.

  According to the third aspect of the invention, since the pulse signal output from the output means is converted into a sine wave to obtain information indicating the frequency, the output means is modified so as to perform a special process. The present invention can be realized without it.

  The invention of claim 4 is characterized in that the output means further outputs an identification signal of the frequency, and the acquisition means acquires the identification signal output by the output means.

  According to the fourth aspect of the present invention, it is not necessary to provide a program, a circuit, or the like for executing a process for identifying a frequency by causing the output means to output a frequency identification signal.

  The invention of claim 5 is characterized in that the conversion means includes a filter circuit, and adjusts the gain using the resistance value of the filter circuit.

  According to the fifth aspect of the present invention, the gain can be adjusted only by changing the resistance value of the filter circuit.

  According to a sixth aspect of the present invention, an electrostatic latent image obtained by scanning a light beam on the photosensitive member with the surface of the photosensitive member charged to a predetermined potential is developed with toner, and the toner image is recorded on a recording medium. An image forming apparatus that forms an image by transferring a signal, an output unit that outputs a pulse signal corresponding to a frequency of power supplied to a predetermined part, and the pulse signal output by the output unit Acquisition means for acquiring information indicating the frequency, and conversion for converting the pulse signal output by the output means to a sine wave with a gain set in advance according to the information indicating the frequency acquired by the acquisition means Means and supply means for supplying electric power corresponding to the sine wave converted by the conversion means to the predetermined part.

  According to the sixth aspect of the present invention, when the pulse signal corresponding to the frequency of the electric power supplied to the predetermined part of the image forming apparatus is converted into a sine wave and the electric power corresponding to the sine wave is supplied, Since conversion is performed with a gain set in accordance with the frequency in advance, power can be supplied at a desired crest factor even when the frequency of power is switched.

  The invention according to claim 7 further includes control means for selectively switching a process speed for forming the image to a plurality of preset speeds, and the output means is responsive to the process speed selected by the control means. 7. The image forming apparatus according to claim 6, wherein a pulse signal corresponding to a preset frequency is output, and electric power is supplied by the supply unit to a charging unit that charges the surface of the photosensitive member to a predetermined potential. .

  According to the seventh aspect of the present invention, in the image forming apparatus configured so that the process speed can be changed, the frequency of the power supplied to the charging unit is determined according to the process speed, and the frequency of the power supplied to the charging unit is set. When the corresponding pulse signal is converted into a sine wave, and the power corresponding to the sine wave is supplied, the pulse signal is converted with a gain set in advance according to the frequency. Power can be supplied at a rate.

  The present invention has an excellent effect that power can be supplied at a desired crest factor even if the frequency of power is switched.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 schematically shows a configuration of a main part of an image forming apparatus 10 according to the present embodiment. As shown in the figure, the image forming apparatus 10 is provided with an image forming unit along the transport path of the paper 28 transported in the direction of arrow E.

  The image forming unit includes a photosensitive drum 16 that is disposed in contact with the conveyance path E of the paper 28 and rotates in the direction of arrow F at a predetermined speed.

  On the peripheral surface of the photosensitive drum 16, a charging roller 18, an exposure unit 20, a developing device 22, and a transfer roller 25 are sequentially provided in the direction of arrow F. By rotating in the direction of arrow F, the photosensitive drum 16 is sequentially subjected to various processes by the charger 18, the exposure unit 20, and the developing unit 22, and a toner image is formed on the peripheral surface.

  The charging roller 18 is rotatably provided while being in contact with the peripheral surface of the photosensitive drum 16. The charging roller 18 is supplied with electric power in which alternating current is superimposed on direct current, and charges the peripheral surface of the photosensitive drum 16 to a predetermined potential while being rotated.

  The exposure unit 20 includes a light source (not shown), and forms an electrostatic latent image by scanning and exposing a light beam on the photosensitive drum 16 according to image data.

  The developing device 22 develops the electrostatic latent image by charging the toner to a predetermined potential and attaching the toner to the photosensitive drum 16.

  The transfer roller 25 is provided so that the paper 28 as a recording medium can be nipped and conveyed with the photosensitive drum 16, and a transfer voltage of a predetermined potential is applied during transfer. The toner on each photosensitive drum 16 is attracted to the transfer roller 25 side and transferred to the paper 28 at a transfer position facing the transfer roller 25.

  The final toner image formed on the photosensitive drum 16 is transferred to the paper 28 fed between the photosensitive drum 16 and the transfer roller 25.

  Note that the paper 28 onto which the toner image has been transferred is subjected to a fixing process in which toner is melted and pressure-bonded to the paper 28 by a fixing device (not shown), and then discharged out of the image forming apparatus 10.

  FIG. 2 shows a configuration related to power supply to the charging roller 18 according to the embodiment of the present invention. As shown in FIG. 1, the image forming apparatus 10 includes a control circuit 30 that controls the overall operation and a high-voltage power supply unit 34. The high-voltage power supply unit 34 includes the control circuit 30 and the control circuit 30. The charging roller 18 is connected.

  In the control circuit 30, a pulse signal indicating the frequency and output voltage of the AC component of the power output to the charging roller 18 is output to the high voltage power supply unit 34.

  The high-voltage power supply unit 34 includes a sine wave conversion circuit 36, an amplifier circuit 38, a booster circuit 40, and a detection circuit 42.

  The sine wave conversion circuit 36 converts the pulse signal input from the control circuit 30 into a sine wave. The pulse signal input from the control circuit 30 indicates the frequency of the AC component of the charging bias supplied to the charging roller 18, and the frequency is determined according to the process speed.

  Further, the amplification circuit 38 amplifies the sine wave converted by the sine wave conversion circuit 36 with a predetermined amplification factor and outputs it as a sine wave alternating current. Further, the booster circuit 40 boosts the sine wave input from the amplifier circuit 38 to generate a sine wave AC bias voltage.

  Further, a DC bias generating circuit 41 is connected to the booster circuit 40, whereby the AC bias is superimposed on the DC bias.

  The detection circuit 42 detects the charging bias voltage supplied to the charging roller 18 and feeds back the detection result to the sine wave conversion circuit 36. Thus, the sine wave conversion circuit 36 performs control so that a desired charging bias voltage is output to the charging roller 18.

  Here, the image forming apparatus 10 according to the present embodiment is configured to be operable at a plurality of preset process speeds, and is configured to switch the process speed in accordance with the type of paper. As the process speed is switched, the frequency (pulse signal) of the AC component of the charging bias is also switched.

  In the present embodiment, as an example, a mode in which process speed is switched between plain paper and thick paper will be described. In the case of plain paper, a process speed of 200 mm / sec and a charging frequency of 1500 Hz will be described. In the case of thick paper, a process speed of 100 mm / sec and a charging frequency of 750 Hz will be described.

  Here, FIG. 6 shows the relationship between the gain when the pulse signal is converted into a sine wave and the crest factor of the sine wave obtained by the conversion. As shown in the figure, the relationship between the gain and the crest factor varies depending on the frequency. In order to convert to the same crest factor (1.41 in this embodiment), it is necessary to adjust the gain according to the frequency. For example, it is necessary to increase the gain when the frequency is 750 Hz and decrease the gain when the frequency is 1500 Hz.

  This gain can be changed by adjusting the resistance value of the filter circuit included in the sine wave conversion circuit 36. For this reason, the sine wave conversion circuit 36 is configured to be able to switch the gain when converting the pulse signal into a sine wave to one of two types.

  In the present embodiment, the high-voltage power supply unit 34 further includes a frequency determination unit 32 that determines the frequency indicated by the pulse signal input to the sine wave conversion circuit 36. The frequency determination unit 32 is connected to the sine wave conversion circuit 36.

  The frequency determination unit 32 includes a determination sine wave conversion circuit 44, a low-pass filter circuit 46, a comparison circuit 48, and a determination circuit 50. The determination sine wave conversion circuit 44 converts the input pulse signal into a sine wave having a voltage amplitude Vpp of a predetermined value (5 V in the present embodiment) and outputs the sine wave to the low-pass filter circuit 46.

  In the low-pass filter circuit 46, the input voltage amplitude Vpp of the sine wave is attenuated by an attenuation factor corresponding to the frequency and output to the comparison circuit 48. The attenuation rate is, for example, an attenuation rate of 80% at a frequency of 750 Hz (Vpp after attenuation = 4V), and an attenuation rate of 55% (Vpp after attenuation = 2.8V) at a frequency of 1500 Hz. It is set high.

  The comparison circuit 48 compares a predetermined threshold value with the input voltage and outputs the comparison result to the determination circuit 50. This threshold value is set to a value larger than the peak value of the input voltage with the higher attenuation rate (1500 Hz) and smaller than the peak value of the input voltage with the lower attenuation rate (750 Hz).

  In the present embodiment, it is assumed that the comparison circuit 48 outputs a high level signal when the input voltage is higher than the threshold value, and outputs a low level signal when the input voltage is lower than the threshold value. In this case, when the charging frequency is low (750 Hz), a high level signal is periodically output, and when the charging frequency is high (1500 Hz), a low level signal is always output.

  The determination circuit 50 identifies the frequency of the pulse signal input from the control circuit 30 according to the input comparison result, and outputs a gain control signal to the sine wave conversion circuit 36. In the present embodiment, the gain control signal is at a high level when the input is periodically at a high level, and at a low level when the input is at a low level.

  Here, FIG. 3 shows a circuit diagram relating to gain switching according to the present embodiment. As shown in the figure, in the present embodiment, a plurality of resistors R1 and R2 for determining the gain are connected in series. The resistor R1 has a resistance value corresponding to the gain when the charging frequency is low, and the resistance value of the resistor R2 corresponds to the gain when the sum of the resistance value of the resistor R1 and the charging frequency is high. Is set.

  Further, as shown in the figure, in the present embodiment, the resistor R2 is configured to be opened or short-circuited by a transistor. Further, the transistor performs ON / OFF operation according to the gain control signal. When the gain control signal is at a high level, the transistor is turned on and the resistor R2 is opened. On the other hand, when the gain signal is at a low level, the transistor is turned OFF and the resistor R2 is short-circuited.

  That is, the gain is switched by varying the resistance value used for the sine wave conversion by controlling the opening and short-circuiting of the resistor R2.

  Hereinafter, the operation of the present embodiment will be described.

  When a print job is input to the image forming apparatus 10, the control circuit 30 sets a process speed and a preset charging frequency according to the process speed based on information indicating the type of recording medium included in the print job. To do.

  In the present embodiment, it is determined whether the recording medium is plain paper or thick paper. If the paper is plain paper, the process speed is 200 mm / sec and the charging frequency is 1500 Hz. If the paper is thick paper, the process speed is 100 mm / sec and the charging frequency is 750 Hz. Is set.

  Thereafter, execution of the image forming process based on the image data included in the print job is started at the set process speed and charging frequency.

  The control circuit 30 outputs a pulse signal corresponding to the charging frequency to the high voltage power supply unit 34, and the high voltage power supply unit 34 specifies the charging frequency indicated by the pulse signal input from the control circuit 30 by the frequency determination unit 32. Then, the specific result is input to the sine wave conversion circuit 36 as a gain control signal. The sine wave conversion circuit 36 converts the pulse signal into a sine wave with a gain corresponding to the gain control signal.

  As a result, the high-voltage power supply unit 34 converts the pulse signal into a sine wave having a predetermined crest factor (1.41 in this embodiment), amplifies and boosts it, and charges the charging bias at a desired charging frequency. The roller 18 is supplied.

  As described above in detail, in the present embodiment, a pulse signal corresponding to the frequency of the electric power supplied from the control circuit 30 to the charging roller 18 is output, and the high voltage power supply unit 34 inputs from the control circuit 30. The pulse signal is converted into a sine wave with a gain set in advance according to the frequency corresponding to the pulse signal, and the electric power corresponding to the sine wave is supplied to the charging roller 18. Power can be supplied at a crest factor.

  Here, in the present embodiment, it has been described that the gain corresponding to each frequency is set so that the crest factor is 1.41. A sine wave having a crest factor of 1.41 is an ideal sine wave. If the crest factor at the time of charging is high, the peak voltage may increase, and an excessive potential may be applied to the photoconductor, which may promote wear of the photoconductor. On the other hand, if the crest factor is low, the charging characteristics may be deteriorated and the required surface potential on the photoconductor may not be obtained, so that it may be necessary to increase the potential of the DC component to be superimposed. Therefore, although it is preferable to set the crest factor to 1.41, what value the crest factor is set to can be set as appropriate in consideration of the degree of wear of the photosensitive member and the degree of decrease in charging characteristics.

  In this embodiment, since the gain is set in advance so that the crest factor of the converted sine wave is 1.41, the crest factor can be maintained at 1.41 regardless of the frequency.

  Further, in the present embodiment, a frequency determination unit 32 is provided in the high-voltage power supply unit 34, and the sine wave conversion circuit of the frequency determination unit 32 temporarily converts the pulse signal into a sine wave to acquire information indicating the frequency. Therefore, the sine wave conversion can be performed with a gain corresponding to the frequency in the sine wave conversion circuit 36 without changing the output means to perform special processing.

  In this embodiment, the sine wave conversion circuit 36 includes a filter circuit (see FIG. 3), and adjusts the gain using the resistance values R1 and R2 of the filter circuit. Adjustment is easy.

  In the present embodiment, the mode in which the frequency is switched to two types has been described, but the present invention is not limited to this, and the mode can be switched to three or more types.

  FIG. 4 shows a configuration example of the filter circuit in the case where it is configured to selectively switch to four types of frequencies. As shown in the figure, as many resistors as the number of frequencies to be switched are provided in the filter circuit constituting the sine wave conversion circuit 36. The resistor R1 is always short-circuited, and the resistors R2 to R4 are opened or short-circuited by a transistor connected to an operational amplifier to which a gain control signal is input. Thereby, the operational amplifier to which the resistors R2 to R4 are connected is opened or short-circuited according to the potential of the gain control signal.

  In the case of the configuration shown in the figure, the determination circuit 50 performs so-called D / A conversion. As a result, the gain control signal becomes 0 V when the signal output from the comparison circuit 48 is at the low level (the highest frequency). In addition, when the signal output from the comparison circuit 48 is a high level repetition, the potential of the gain control signal increases as the period of high level becomes longer (lower in frequency).

  That is, since the potential of the gain control signal becomes a potential according to the attenuation rate by the filter circuit 46, the potential of the gain control signal becomes a potential according to the type of frequency. For this reason, when the potential of the gain control signal is the highest, the resistance values of the resistors R5 and R6 are set so that all the resistors R2 to R4 that are controlled to be opened or short-circuited by the gain control signal are short-circuited. Further, when the potential of the gain control signal is the second highest, the resistance value of the resistor R5 is set so that the resistors R2 and R3 are opened.

  That is, the resistance R1 has a resistance value corresponding to the gain when the charging frequency is the lowest, and the sum of the resistance values of the resistance R1 and the resistance R2 is the resistance value corresponding to the gain when the frequency is the second lowest. The resistance value corresponding to the gain when the sum of the resistance values of the resistors R1 to R3 is the third lowest frequency, and the resistance value corresponding to the gain when the sum of the resistance values of the resistors R1 to R4 is the highest frequency Are set to correspond to each other.

  Thereby, the sine wave conversion circuit 36 can execute sine wave conversion with a gain corresponding to the frequency corresponding to the pulse signal.

  Further, in the present embodiment, a description has been given of a mode in which the change of the resistance value according to the frequency is performed by controlling the opening or shorting of a plurality of resistors using a transistor and an operational amplifier, but the present invention is not limited to this. Needless to say, it is only necessary that the resistance value be changed according to the frequency.

  Furthermore, in the present embodiment, the mode in which the high-voltage power supply unit 34 determines the frequency corresponding to the pulse signal has been described, but the present invention is not limited to this.

  For example, as shown in FIG. 5, it is possible to further output a signal corresponding to the frequency corresponding to the pulse signal from the control circuit 30 and switch the resistance value according to the signal. In this case, it is not necessary to provide the high-voltage power supply unit 34 with a program, a circuit, or the like that executes a determination process for identifying the frequency such as the frequency determination unit 32.

  The configuration of the image forming apparatus 10 according to the above-described embodiment (see FIGS. 1 to 5) is an example, and can be changed as appropriate without departing from the spirit of the present invention.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment. It is a block diagram about supply of the high voltage power supply concerning an embodiment. It is a circuit diagram which shows simply a part of sine wave conversion circuit concerning an embodiment. It is a circuit diagram which shows simply a part of sine wave conversion circuit which concerns on another form. It is a block diagram regarding supply of the high voltage power supply which concerns on another form. It is a graph which shows the relationship between the gain at the time of sine wave conversion, and a crest factor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 16 Photosensitive drum 18 Charging roller (charging means)
20 Exposure Unit 22 Developer 25 Transfer Roller 28 Paper (Recording Medium)
30 Control circuit (output means, control means)
34 High-voltage power supply unit 32 Frequency determination unit (acquisition means)
36 Sine wave conversion circuit (conversion means)
38 Amplifier circuit (supply means)
40 Booster circuit (supply means)

Claims (7)

Output means for outputting a pulse signal corresponding to the frequency of the power supplied to the load;
Obtaining means for obtaining information indicating the frequency corresponding to the pulse signal output by the output means;
Conversion means for converting the pulse signal output by the output means into a sine wave with a gain set in advance according to information indicating the frequency acquired by the acquisition means;
Supply means for supplying power to the load according to the sine wave converted by the conversion means;
Power supply unit with   The power supply apparatus according to claim 1, wherein the gain is set in advance so that a crest factor of the sine wave becomes a predetermined value.   The power supply apparatus according to claim 1, wherein the acquisition unit acquires the information indicating the frequency by converting the pulse signal into a sine wave. The output means further outputs an identification signal of the frequency;
The power supply apparatus according to claim 1, wherein the acquisition unit acquires the identification signal output by the output unit.   5. The power supply device according to claim 1, wherein the conversion unit includes a filter circuit, and adjusts the gain using a resistance value of the filter circuit. 6. With the surface of the photoconductor charged to a predetermined potential, the electrostatic latent image obtained by scanning a light beam on the photoconductor is developed with toner, and the toner image is transferred to a recording medium to transfer the image. An image forming apparatus for forming,
Output means for outputting a pulse signal corresponding to the frequency of power supplied to a predetermined part;
Obtaining means for obtaining information indicating the frequency corresponding to the pulse signal output by the output means;
Conversion means for converting the pulse signal output by the output means into a sine wave with a preset gain according to information indicating the frequency acquired by the acquisition means;
Supply means for supplying electric power corresponding to the sine wave converted by the conversion means to the predetermined part;
An image forming apparatus. Control means for selectively switching the process speed for forming the image to a plurality of preset speeds;
The output means outputs a pulse signal corresponding to a preset frequency according to the process speed selected by the control means,
The image forming apparatus according to claim 6, wherein the supplying unit supplies power to a charging unit that charges the surface of the photosensitive member to a predetermined potential.

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