JP4480683B2 - High voltage generation circuit - Google Patents

Description

  The present invention relates to a high voltage generating circuit that applies an oscillating voltage in which a DC voltage and an AC voltage are superimposed on a charging member arranged in contact with or close to an image carrier.

  In recent years, from the viewpoint of low pressure process, low ozone generation, low cost, etc., a charging member such as a roller type or a blade type is arranged in contact with or close to the surface of the image carrier, and a DC voltage and an AC voltage are applied to the charging member. Image forming apparatuses employing a contact charging method that uniformly charges the surface of an image carrier by applying a superposed vibration voltage are becoming mainstream. Here, the vibration voltage is not limited to a sine wave, but may be any vibration waveform that changes periodically, such as a rectangular wave, a triangular wave, and a pulse wave.

  When such a contact charging method is employed in a tandem color image forming apparatus provided with different image carriers corresponding to the four colors of YMCK, a high-voltage DC voltage and an AC voltage are generated on each charging member. Each of the transformers must be provided, which increases the number of parts, which increases the cost and reduces the mounting efficiency of the parts.

  Therefore, in Patent Document 1, in order to improve the mounting efficiency of components on a printed wiring board and realize an inexpensive power supply device, a single DC power supply circuit that outputs a high-voltage DC by a converter transformer, and the DC power supply The voltage value of the DC output from the circuit is converted using a separate high voltage transistor inserted in series between the DC power supply circuit and the corresponding load, and high voltage generation is provided with voltage conversion means for supplying to each load A circuit has been proposed.

JP 2002-162870 A

  However, in order to control the charging potential to each image carrier, it is necessary to measure the current between each charging member and the image carrier to control the high voltage output voltage. In the case of adopting a high voltage generating circuit for applying a voltage to a charging member, it is necessary to provide a current detection circuit separately, which causes the same problem of increased cost and reduced mounting efficiency due to an increase in the number of component circuits. was there.

  Therefore, the inventor of the present application has a single DC transformer in which a plurality of linear DC regulators are connected in parallel on the secondary side, and a plurality of AC transformers in which the output of each linear DC regulator is connected to the secondary side separately. An attempt is made to solve the above-mentioned problem by configuring a high voltage generation circuit having a single current detection circuit connected to the secondary side of the DC transformer and detecting a DC current between the charging member and the image carrier. I thought.

  However, in general, a linear DC regulator is composed of an operational amplifier and a pass transistor driven by the output of the operational amplifier, and the base current of the pass transistor is controlled using the pseudo-short characteristic of the operational amplifier. Although the voltage is stably controlled, the driving power of the operational amplifier is supplied from the outside at that time, so the base current of the pass transistor is supplied from the external power, and the current value detected by the current detection circuit due to the influence thereof There was a problem that was not detected correctly.

  Since such a base current value has a temperature characteristic that becomes larger as the temperature is lower, if the installation environment of the color image forming apparatus fluctuates, the direct current between the charging member and the image carrier cannot be detected in a planned manner.

  In view of the above-described conventional problems, an object of the present invention is to provide a high voltage generation circuit capable of accurately detecting DC currents between a plurality of charging members and an image carrier by a single current detection circuit regardless of environmental temperature fluctuations. Is to provide

In order to achieve the above-mentioned object, the first characteristic configuration of the high-voltage generating circuit according to the present invention is arranged in contact with or in close proximity to a plurality of image carriers, respectively , as described in claim 1 of the claims. a high voltage generation circuit to which a DC voltage and an AC voltage is applied an oscillating voltage which is superimposed on the charging member to each other with a plurality of linear DC regulator for generating a DC voltage applied to each charging member, the secondary-side terminal A single DC transformer in which each linear DC regulator is connected in parallel, one terminal on the secondary side is connected to each charging member, and the other terminal is connected to the output terminal of each linear DC regulator, to each charging member a plurality of AC transformer for generating an AC voltage applied to the DC flowing through the transformer and a single current detection circuit for detecting a direct current discharge start electric outputs of all of the linear direct current regulator A DC current detected by said current detecting circuit when adjusted to a lower pressure than was adjusted to a lower pressure than the discharge starting voltage output of the other linear DC regulators except linear DC regulators corresponding to a predetermined charging member The difference in DC current detected by the current detection circuit is detected as a DC current between the predetermined charging member and the image carrier.

According to the above-described configuration, a predetermined high voltage output from a single DC transformer is input to each linear DC regulator, and the DC voltage to be applied to each charging member is adjusted by each linear DC regulator. An AC voltage to be applied to each charging member is adjusted by an AC transformer, and an oscillating voltage on which the AC voltage is superimposed is applied to each charging member. An offset current caused by a current flowing from the linear DC regulator is detected in the DC current detected by the current detection circuit when all the linear DC regulators are adjusted to a voltage lower than the discharge start voltage . Therefore, the difference between the value and the DC current detected by the current detection circuit when the output of another linear DC regulator is adjusted to be lower than the discharge start voltage except for the linear DC regulator corresponding to the predetermined charging member. Therefore, the offset current due to the current flowing from the other linear DC regulator is eliminated, and the DC current flowing from the predetermined charging member to the image carrier can be accurately detected . For example, when the linear DC regulator is configured to include a pass transistor that performs step-down control of the output voltage of the DC transformer and an operational amplifier that performs feedback control of the base current of the pass transistor so that the step-down voltage becomes the target voltage. The base current flowing through the pass transistor is detected as an offset current by the current detection circuit. According to the above configuration, an output from which the influence of the base current is eliminated can be obtained.

  In the second characteristic configuration, as described in claim 2, in addition to the first characteristic configuration described above, a direct current between the predetermined charging member and the image carrier detected by the current detection circuit is predetermined. A control unit is provided that adjusts the output voltage of the linear DC regulator or the AC transformer so as to achieve a target value.

  According to the above-described configuration, the output voltage of the linear DC regulator or the AC transformer is accurately adjusted so that the DC current between the predetermined charging member and the image carrier becomes a predetermined target value regardless of changes in the environmental temperature. Can now be adjusted.

  The third feature configuration includes storage means for storing the predetermined target value in addition to the second feature configuration described above, and the control unit is stored in the storage means. The output voltage of the linear DC regulator or the AC transformer is adjusted based on the measured value.

  According to the above configuration, for example, the linear DC regulator or the AC transformer is based on the predetermined target value stored as a DC current value detected when the image carrier has a predetermined charging potential. The output voltage can be adjusted.

  In the fourth feature configuration, in addition to the third feature configuration described above, in the storage unit, the predetermined target value is the environmental temperature, environmental humidity, or cumulative use of the charging member. A plurality of points are set based on time or any combination thereof.

  According to the above-described configuration, each of the image carriers is such that the predetermined target value becomes a different value based on the environmental temperature, the environmental humidity or the accumulated usage time of the charging member, or any combination thereof. The predetermined target value suitable for the environment can be set.

  As described above, according to the present invention, it is possible to provide a high voltage generation circuit capable of accurately detecting a direct current between a plurality of charging members and an image carrier by a single current detection circuit regardless of environmental temperature fluctuations. Can now.

  Hereinafter, the high voltage generating circuit according to the present invention will be described. As shown in FIG. 1, the high voltage generating circuit 1 is a direct current applied to a charging member CH formed of a charging roller arranged in contact with or close to four image carriers PC that form four color toner images of YMCK. A single DC transformer for generating an oscillating voltage in which a voltage and an AC voltage are superimposed, wherein a shunt regulator 20 as a linear DC regulator corresponding to the number of image carriers PC is connected in parallel on the secondary side. 10, an AC transformer 30 corresponding to the number of the image carriers PC in which outputs of the shunt regulators 20 are separately connected to the secondary side, and a charging member CH connected to the secondary side of the DC transformer 10. It comprises a single current detection circuit 40 for detecting a direct current between the image carriers PC.

  As shown in FIG. 2, the DC transformer 10 receives a pulse signal from a pulse signal generating unit that outputs a pulse signal based on a remote drive signal input from the control unit CNT, and is input to the primary side of the transformer T10. The high-voltage AC voltage boosted to the voltage is output from the secondary side, and the high-voltage AC voltage is smoothed by the rectifier circuit including the diode D10 and the capacitor C10 so that the high-voltage DC voltage is output from the output terminals t1 and t2. It is configured.

  In the same way as described above, the AC transformer 30 is input to the primary side of a transformer provided with a pulse signal from a pulse signal generating unit that outputs a pulse signal based on a remote drive signal input from the control unit CNT, The high-voltage AC voltage boosted to a predetermined voltage is output from the secondary side. Here, the high-voltage AC voltage is variably controlled by a pulse signal voltage generated based on a variable analog input voltage input from the control unit CNT to the pulse signal generating means.

  The shunt regulator 20 is connected in four circuits in parallel to the terminals t1 and t2 of the DC transformer 10 so as to supply a DC voltage separately to the charging member CH corresponding to each image carrier PC of YMCK. As shown in FIG. 3, an operational amplifier OP20 as a differential amplifier, a pass transistor Q20 driven by an output current of the operational amplifier OP20, and a Zener diode ZD20 having a breakdown voltage of 250 V connected to the collector of the pass transistor Q20. Etc. are provided.

  A divided voltage obtained by dividing the output voltage of the shunt regulator 20 by the resistors R21 and R20 is input to the non-inverting input terminal of the operational amplifier OP20, and a reference voltage is input to the inverting input terminal. Therefore, the base current is supplied from the operational amplifier OP20 to the pass transistor Q20 so that the divided voltage is equal to the reference voltage, and as a result, the output voltage Vdc is adjusted by the current flowing through the resistor R23 and the Zener diode ZD20.

  The reference voltage is variably adjusted by a fixed comparison voltage Vref and a control voltage Vcnt controlled by the control unit CNT, and a direct current applied to each charging member CH by individually adjusting the control voltage Vcnt. The voltage is variably and stably adjusted between 250V and 750V.

  As shown in FIG. 1, the output terminal of the shunt regulator 20 is connected to the secondary terminal of each AC transformer 30 via a bypass capacitor C that bypasses the AC voltage. And an oscillating voltage on which an AC voltage from the AC transformer 30 is superimposed is applied to each charging member CH.

  As shown in FIG. 4, the current detection circuit 40 includes a current / voltage conversion operational amplifier OP41 and an amplification operational amplifier OP40. The inverting input terminal of the operational amplifier OP41 is connected to the secondary low voltage side terminal t2 of the DC transformer 10, and the non-inverting input terminal receives a voltage obtained by dividing the comparison voltage Vref by the resistors R43 and R44 as a reference voltage. The current value flowing through the feedback resistor R42 is converted into a voltage so that the voltage between the reference voltage and the secondary low-voltage side terminal t2 becomes equal, and further amplified by the operational amplifier OP40 and then input to the control unit CNT. .

  When the DC current between the specific charging member CH and the image carrier PC is detected by the current detection circuit 40, the outputs of the other shunt regulators 20 except for the shunt regulator 20 corresponding to the specific charging member CH The output of the AC transformer corresponding to the specific charging member CH is adjusted to be lower than the discharge start voltage.

  Specifically, the control voltage Vcnt of the other three shunt regulators 20 is adjusted by the control unit CNT so that the output is adjusted to about 250 V lower than the discharge start voltage, and is turned off except for one of the AC transformers. Then, the value of the current detection circuit 40 is read. In this way, when detecting a direct current between a specific charging member CH and the image carrier PC, the corresponding shunts are arranged so that no current flows between the other charging members CH and the image carrier PC. The direct current value from the specific charging member CH can be detected by the single current detection circuit 40 by adjusting the direct current voltage to be lower than the discharge start voltage by the regulator 20 and the alternating current transformer.

  In the present embodiment, since the base current Ib of the pass transistor Q20 is supplied from an external power source that drives the operational amplifier OP20, the output voltage of the shunt regulator 20 is adjusted to be lower than the discharge start voltage. Due to the influence of the base current flowing into the secondary side of the DC transformer 10 via the pass transistor Q20, the influence of offset noise appears in the current value detected by the current detection circuit 40. Specifically, the current value detected by the current detection circuit 40 is obtained as Idc-ΣIb.

  The detection of the DC current Idc will be described in detail. In the operational amplifier OP41, the DC current Idc of the current Iac + Idc between the charging member CH and the image carrier PC flowing from each of the image carriers PC to the ground is changed. Each flows from the ground side terminal of the control voltage applied to the operational amplifier OP41 to the output terminal. The DC current ΣIdc, which is the sum of the DC currents Idc, flows to the low-voltage side of the DC transformer 10 via the resistor R42 and forms a DC current component loop of the high-voltage generating circuit 1.

  Of the DC currents ΣIb + ΣIc + ΣIr that is the sum of the DC currents Ib + Ic + Ir flowing from the shunt regulators 20 to the low-voltage side of the DC transformer 10, the drive current ΣIb flows to the ground because it is not output from the DC transformer 10. Further, all of the DC current ΣIdc does not flow from the current detection circuit 40 to the low voltage side of the DC transformer 10, and the DC current ΣIdc−ΣIb is transferred from the current detection circuit 40 to the DC transformer so as to cancel the drive current ΣIb. 10 flows to the low voltage side, and the same ΣIdc + ΣIc + ΣIr as the output current from the high voltage side flows to the secondary low voltage side of the DC transformer 10.

  Here, the high voltage generation circuit 1 is configured to detect the direct current separately by adjusting one of the shunt regulators 20 except for one of the shunt regulators 20 to a voltage lower than the discharge start voltage. Therefore, the DC current Idc flows only from one shunt regulator 20 when the current detection circuit 40 detects the current. That is, the current detection circuit 40 detects the direct current Idc−ΣIb, and cannot accurately detect the direct current Idc.

  If the value of the offset noise is always constant, there is no problem. However, since the current amplification factor of the pass transistor Q20 varies greatly due to the influence of temperature variation, the value of the base current Ib also varies greatly. Become. Due to such temperature characteristics, the current value detected by the current detection circuit 40 may be affected by errors.

  Therefore, first, the current detection circuit 40 detects the DC current −ΣIb when all the shunt regulators 20 are adjusted to a voltage lower than the discharge start voltage, and then excludes the shunt regulator 20 corresponding to the predetermined charging member CH. A DC current Idc-ΣIb is detected when the other output is adjusted to a voltage lower than the discharge start voltage. The control unit CNT stores the DC current −ΣIb, performs a difference calculation when the DC current Idc−ΣIb is input, and detects the DC current Idc between the predetermined charging member CH and the image carrier PC. The control unit CNT adjusts the output voltage of the shunt regulator 20 or the AC transformer 30 so that the DC current Idc becomes a predetermined target value.

  The predetermined target value is stored in the storage means MEM as a plurality of table data set based on environmental conditions such as environmental temperature, environmental humidity or cumulative usage time of the charging member, or any combination thereof. ing.

  The adjustment performed by the control unit CNT so as to maintain the DC current value Idc at the predetermined target value will be described in detail. The control unit CNT refers to the table data of the storage unit MEM based on the environmental condition. Then, the predetermined target value is acquired. The control unit CNT controls the AC transformer 30 to adjust the peak-to-peak voltage value Vpp of the AC voltage so that the DC current Idc becomes the predetermined target value.

  The required peak-to-peak voltage value Vpp cannot be output due to the maximum output voltage value of the AC transformer 30, the withstand voltage characteristics of the charging member CH or the image bearing PC body, and the DC current Idc is set to the predetermined value. When the target value cannot be set, the control unit CNT fixes the peak-to-peak voltage value Vpp, controls the shunt regulator 20 so that the DC current Idc becomes the predetermined target value, and the DC The voltage Vdc is adjusted.

  Here, when the DC current Idc is set to the predetermined target value by adjusting the DC voltage Vdc, the peak-to-peak voltage value Vpp does not reach the predetermined value, and the charged state of the image carrier PC is Since it is not stable, the image quality is expected to deteriorate, but image formation can be executed and consumption of excess toner can be avoided.

  Another embodiment will be described below.

  In the above configuration, the charging member CH is disposed in contact with the image carrier PC. However, the charging member CH may be disposed in proximity.

  In the above-described embodiment, the shunt regulator is provided as the linear DC regulator. However, for example, a series regulator other than the shunt regulator may be provided.

  In the above-described embodiment, the number of image carriers, that is, one high-voltage generation circuit corresponding to four outputs has been described. However, the present invention is not limited to this, and any circuit corresponding to two or more outputs may be used.

  In the above-described configuration, the DC current Idc detected by the control unit CNT based on the DC current detected by the current detection circuit 40 is a plurality of predetermined target values set based on the environmental conditions stored in the storage unit MEM. As shown in FIG. 5, the control unit CNT adjusts the output voltage of the shunt regulator 20 or the AC transformer 30. As shown in FIG. 5, the control unit CNT represents a relationship between the peak voltage value Vpp and the DC current Idc. The voltage at the point where the slope of the straight line changes when the control unit CNT boosts the peak-to-peak voltage value Vpp after adjusting the output of the shunt regulator 20 to the assumed characteristic curve on the dimensional coordinate. DC current value I measured when two different low-voltage side peak-to-peak voltage values Vpp (A) and Vpp (B) that are assumed to be lower than the current value are applied. The straight line L1 passing through the coordinates A (Vpp (A), Idc (A)), B (Vpp (B), Idc (B)) obtained based on c (A), Idc (B), and the inclination changes Coordinates C (Vpp (C), obtained based on a DC current value Idc (C) measured when a high-voltage peak-to-peak voltage value Vpp (C) assumed to be a high-voltage side is applied The AC transformer 30 is controlled so as to output the peak-to-peak voltage value Vpp corresponding to the intersection with the straight line L2 parallel to the coordinate axis representing the peak-to-peak voltage value Vpp through Idc (C)). When the peak-to-peak voltage value Vpp corresponding to is not output, the control unit CNT adjusts the output of the AC transformer 30 to be constant so that the DC current value Idc in the straight line L2 becomes the predetermined target value. To said Shan It may be configured to adjust the DC voltage Vdc by controlling the regulator 20.

  The peak-to-peak voltage values Vpp (A), Vpp (B), and Vpp (C) are stored in advance for each environmental condition as table data having respective values as shown in FIG. 6, for example. The control unit CNT refers to the storage unit MEM based on the environmental conditions, and acquires the peak-to-peak voltage values Vpp (A), Vpp (B), and Vpp (C).

  In the above configuration, a predetermined target value in which a plurality of direct currents Idc detected by the control unit CNT are set based on the environmental conditions stored in the storage unit MEM based on the direct current detected by the current detection circuit 40. The control unit CNT adjusts the output voltage of the shunt regulator 20 or the AC transformer 30 so that all shunt regulators 20 are adjusted to a voltage lower than the discharge start voltage in each of the environmental conditions. The influence of the direct current −ΣIb detected by the current detection circuit 40 is reflected in advance on a predetermined target value stored in the storage unit MEM, and other than the shunt regulator 20 corresponding to the predetermined charging member, The direct current Idc-Σ detected by the current detection circuit 40 when the output is adjusted to be lower than the discharge start voltage. The control unit CNT may adjust the output voltage of the shunt regulator 20 or the AC transformer 30 so that Ib becomes the predetermined target value.

  The above-described embodiments are merely examples of the present invention, and the scope of the present invention is not limited by the description, and the specific configuration of each part is appropriately changed within the scope of the effects of the present invention. It goes without saying that it can be done.

High voltage generation circuit configuration diagram DC transformer circuit diagram Shunt regulator circuit diagram Circuit diagram of current detection circuit Explanatory drawing of the peak-to-peak voltage value Vpp corresponding to the intersection of the straight lines L1, L2 and the coordinates A, B, C obtained in another embodiment and the straight lines L1, L2. Explanatory drawing of the table data of the peak-to-peak voltage values Vpp (A), Vpp (B), and Vpp (C) determined for each temperature and humidity used in another embodiment

10: DC transformer 20: Linear DC regulator (shunt regulator)
30: AC transformer 40: Current detection circuit CNT: Control unit CH: Charging member MEM: Storage means PC: Image carrier

Claims (4)

A high-voltage generating circuit that applies an oscillating voltage in which a DC voltage and an AC voltage are individually superimposed on a charging member that is arranged in contact with or in proximity to each of a plurality of image carriers,
A plurality of linear DC regulators for generating a DC voltage to be applied to each charging member;
A single DC transformer with each linear DC regulator connected in parallel to the secondary terminal;
A plurality of AC transformers, one terminal on the secondary side is connected to each charging member, the other terminal is connected to the output terminal of each linear DC regulator, and generates an AC voltage applied to each charging member;
A single current detection circuit for detecting a direct current flowing in the direct current transformer,
The DC current detected by the current detection circuit when the outputs of all the linear DC regulators are adjusted to be lower than the discharge start voltage, and other linear DC regulators except for the linear DC regulator corresponding to the predetermined charging member . A high voltage generating circuit that detects a difference in DC current detected by the current detection circuit when the output is adjusted to a voltage lower than a discharge start voltage as a DC current between the predetermined charging member and the image carrier.   A controller that adjusts an output voltage of the linear DC regulator or the AC transformer so that a DC current between the predetermined charging member and the image carrier detected by the current detection circuit becomes a predetermined target value; The high voltage generation circuit according to claim 1.   3. The high voltage generation circuit according to claim 2, further comprising storage means for storing the predetermined target value, wherein the control unit adjusts an output voltage of the linear DC regulator or the AC transformer based on a value stored in the storage means. .   4. The high voltage generation circuit according to claim 3, wherein a plurality of the predetermined target values are set in the storage unit based on an environmental temperature, an environmental humidity or an accumulated usage time of the charging member, or any combination thereof.

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