JP6056156B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  Patent Document 1 below discloses a technique in which a power transformer is reduced by generating a grid voltage and a development voltage from a charge voltage.

Japanese Patent Laid-Open No. 9-244481

When the circuit for adjusting the grid voltage and the circuit for adjusting the development voltage are connected in series, adjusting the output in one circuit affects the other circuit and the voltage becomes unstable.
The present invention has been completed based on the above situation, and in a configuration in which a circuit for adjusting the grid voltage and a circuit for adjusting the development voltage are connected in series, the grid voltage and the development voltage can be easily stabilized. To do.

  An image forming apparatus disclosed in this specification includes a photosensitive member, a wire and a grid electrode, and a charger that charges the photosensitive member, a developing device that supplies a developer to the photosensitive member, and the wire. A charging voltage generation circuit that generates a charging voltage to be applied; a grid voltage adjustment circuit that adjusts a grid voltage generated in the grid electrode after the generation of the charging voltage; and a generation in the developer after the generation of the charging voltage. A developing voltage adjusting circuit for adjusting a developing voltage, and the developing voltage adjusting circuit is connected in series with the grid voltage adjusting circuit between the grid electrode and the ground, and develops by dividing the grid voltage. The voltage is generated, and the response speed of the adjustment circuit on the side of the development voltage adjustment circuit and the grid voltage adjustment circuit that starts control later opens the control first. A slower setting than the response speed of the adjustment circuit on the side of.

  In this image forming apparatus, the response speed of the adjustment circuit that starts control later is decreased. Therefore, the adjustment circuit on the side of starting the control first easily absorbs the voltage fluctuation on the side of the adjustment circuit starting the control later. Therefore, the output voltage of the adjustment circuit, that is, the grid voltage and the development voltage can be easily stabilized.

In the image forming apparatus, the following is preferable.
The development voltage control start timing by the development voltage adjustment circuit is set later than the grid voltage control start timing by the grid voltage adjustment circuit. Since the developing unit is used while being pressed against the photosensitive member, if the potential difference between the photosensitive member and the developing unit is small, the developer may adhere to the photosensitive member before exposure. In order to prevent the adhesion of the developer, a separation mechanism for separating the developing device from the photosensitive member is required until the voltage between the photosensitive member and the developing device is stabilized at a target value. In this configuration, since the grid voltage is controlled first and the development voltage is controlled later, the grid voltage rises before the development voltage. Therefore, the potential difference between the photoconductor and the developing device can be maintained, and the developer can be prevented from adhering to the photoconductor before exposure. Therefore, the separation mechanism can be eliminated.

The control device starts control of the development voltage by the development voltage adjustment circuit after the grid voltage is in a stable state that falls within a predetermined allowable range. In this way, after the photosensitive member is charged to a predetermined level, the development voltage is controlled toward the target value, so that the potential difference between the photosensitive member and the developing device can be reliably maintained. For this reason, it is possible to more reliably prevent the developer from adhering to the photoreceptor.

The control device is configured such that when the grid voltage is stabilized, a portion of the photoconductor facing the charger passes through a position facing the developer as the photoconductor rotates, and then the developing voltage is set. Control of the development voltage by the adjustment circuit is started. In this way, the development voltage is controlled toward the target value after the opposed portion charged to a predetermined level in the photoconductor passes through the position facing the developing device, so that the potential difference between the photoconductor and the developing device is reduced. It becomes possible to keep reliably. For this reason, it is possible to more reliably prevent the developer from adhering to the photoreceptor.

  According to the present invention, in a configuration in which a circuit for adjusting the grid voltage and a circuit for adjusting the development voltage are connected in series, the grid voltage and the development voltage are easily stabilized.

1 is a schematic cross-sectional view illustrating an internal configuration of a printer according to a first embodiment of the invention. Schematic sectional view showing the internal configuration of the printer around the black process unit Diagram showing the structure of the charger Block diagram showing the electrical configuration of the printer Circuit diagram showing the electrical configuration of the high-voltage power supply Circuit diagram of development voltage adjustment circuit and grid voltage adjustment circuit Diagram showing grid voltage response Flowchart diagram showing the flow of print processing The circuit diagram which shows the electric constitution of the high voltage power supply device which concerns on Embodiment 2. FIG. Flow chart showing the grid current control procedure FIG. 6 is a diagram illustrating an arrangement of a photosensitive drum, a charger, and a developing roller according to the third embodiment. Flowchart diagram showing the flow of print processing

<Embodiment 1>
A first embodiment of the present invention will be described with reference to FIGS.

1. Overall Configuration of Printer FIG. 1 is a schematic cross-sectional view showing the internal configuration of a printer 1 according to this embodiment (an example of an “image forming apparatus” according to the present invention). In the following description, when distinguishing each component for each color, subscripts of B (black), Y (yellow), M (magenta), and C (cyan) are added to the reference numerals of the respective parts and are not distinguished. In this case, the subscript is omitted.

  The printer 1 includes a paper feeding unit 3, an image forming unit 5, a transport mechanism 7, a fixing unit 9, a belt cleaning mechanism 20, and a high voltage power supply device 100. The paper feed unit 3 is provided at the lowermost part of the printer 1 and includes a tray 17 that accommodates sheets (paper, OHP sheets, and the like) 15 and a pickup roller 19. The sheets 15 accommodated in the tray 17 are taken out one by one by a pickup roller 19 and are sent to the transport mechanism 7 via the transport roller 11 and the registration roller 12.

  The transport mechanism 7 transports the sheet 15 and is installed in the printer 1 above the paper feed unit 3. The transport mechanism 7 includes a driving roller 31, a driven roller 32, and a belt 34, and the belt 34 is bridged between the driving roller 31 and the driven roller 32. When the drive roller 31 rotates, the surface of the belt 34 facing the photosensitive drums 41B, 41Y, 41M, and 41C moves from the right direction to the left direction in FIG. As a result, the sheet 15 sent from the registration roller 12 is conveyed below the image forming unit 5.

  The belt 34 is provided with four transfer rollers 33B, 33Y, 33M, and 33C corresponding to the four photosensitive drums 41B, 41Y, 41M, and 41C. Each transfer roller 33 is disposed at a position facing each of the photosensitive drums 41B, 41Y, 41M, and 41C with the belt 34 interposed therebetween.

  The image forming unit 5 includes four process units 40B, 40Y, 40M, and 40C and four exposure apparatuses 49B, 49Y, 49M, and 49C. The process units 40B, 40Y, 40M, and 40C are arranged in a line in the conveyance direction of the sheet 15 (the left-right direction in FIG. 1).

  Each process unit 40 has the same structure, and each color photosensitive drum (an example of the “photoreceptor” in the present invention) 41B, 41Y, 41M, 41C, and each color toner as a developer (for example, a positively charged non-magnetic single component) The structure includes a toner case 43 containing toner, a developing roller (an example of the “developing device” of the present invention) 45, and chargers 50 </ b> B, 50 </ b> Y, 50 </ b> M, and 50 </ b> C.

  Each of the photosensitive drums 41 </ b> B, 41 </ b> Y, 41 </ b> M, and 41 </ b> C has a positively chargeable photosensitive layer formed on an aluminum substrate, for example, and the aluminum substrate is grounded to the ground of the printer 1. .

  The developing roller 45 is disposed below the toner case 43 so as to face the supply roller 46, and when the toner passes between the two, the toner is triboelectrically charged by friction caused by rotation to form a uniform thin layer. It fulfills the function of supplying the photosensitive drums 41B, 41Y, 41M and 41C.

  Each of the chargers 50B, 50Y, 50M, and 50C is a scorotron charger, and includes a shield case 51, wires 53, and a metal grid electrode 55 as shown in FIGS. The shield case 51 has a rectangular tube shape that is long in the direction of the rotation axis of the photosensitive drum 41. In the shield case 51, the surface facing the photosensitive drum 41 is opened as a discharge port 52.

  The wire 53 is made of, for example, a tungsten wire. The wire 53 is stretched in the direction of the rotation axis (left and right in FIG. 3) in the shield case 51, and a high voltage is applied by a charging voltage generation circuit 200 described later. The wire 53 causes corona discharge in the shield case 51 by applying a high voltage. Then, ions generated by corona discharge flow from the discharge port 52 to the photosensitive drum 41 as a discharge current, so that the surface of the photosensitive drum 41 is uniformly charged to a positive polarity.

  A plate-like grid electrode 55 having slits and through holes is attached to the discharge port 52 of the shield case 51. By applying a voltage to the grid electrode 55 and controlling the applied voltage, the charging voltage of the photosensitive drum 41 can be controlled.

  The chargers 50B, 50Y, 50M, and 50C are provided with a wire cleaner 57. The wire cleaner 57 is slidable along the wire 53. The wire 53 can be removed by the operator reciprocating the wire cleaner 57 along the wire 53.

  Each exposure device 49B, 49Y, 49M, 49C has, for example, a plurality of light emitting elements (for example, LEDs and laser light sources) arranged in a line along the rotation axis direction of the photosensitive drums 41B, 41Y, 41M, 41C. By emitting light in accordance with image data input from the outside, it functions to form an electrostatic latent image on the surface of each photosensitive drum 41B, 41Y, 41M, 41C.

  A series of image forming processes by the laser printer 1 configured as described above will be briefly described. When the printer 1 receives the print data D (see FIG. 4), the printer 1 starts the printing process. As a result, the surfaces of the photosensitive drums 41B, 41Y, 41M, and 41C are uniformly positively charged by the chargers 50B, 50Y, 50M, and 50C as they rotate. Then, laser light is irradiated from each exposure device 49 toward each photosensitive drum 41B, 41Y, 41M, and 41C. As a result, a predetermined electrostatic latent image corresponding to the print data is formed on the surface of each photosensitive drum 41B, 41Y, 41M, 41C, that is, the positively charged photosensitive drums 41B, 41Y, 41M, 41C. Of the surface, the potential of the portion irradiated with the laser light decreases.

  Next, the rotation of the developing roller 45 causes the toner carried on the developing roller 45 and positively charged to be supplied to the electrostatic latent images formed on the surfaces of the photosensitive drums 41B, 41Y, 41M, and 41C. . As a result, the electrostatic latent images on the photosensitive drums 41B, 41Y, 41M, and 41C are visualized, and toner images by reversal development are carried on the surfaces of the photosensitive drums 41B, 41Y, 41M, and 41C.

  Further, in parallel with the processing for forming the toner image described above, processing for conveying the sheet 15 is performed. That is, as the pickup roller 19 rotates, the sheets 15 are sent one by one from the tray 17 to the paper transport path Y. The sheet 15 sent to the paper transport path Y is transported to a transfer position (a point where the photosensitive drum 41 and the transfer roller 33 are in contact) by the transport roller 11 and the belt 34.

  Then, when passing through this transfer position, each color toner image (developer image) carried on the surface of each photosensitive drum 41 is sequentially applied to the surface of the sheet 15 by the transfer bias applied to each transfer roller 33. Superimposed transfer. Thus, a color toner image (developer image) is formed on the sheet 15. Thereafter, when the toner image passes through the fixing unit 9 provided behind the belt 34, the transferred toner image (developer image) is thermally fixed, and the sheet 15 is discharged onto the discharge tray 60.

2. Configuration of High Voltage Power Supply Device 100 As shown in FIG. 5, the high voltage power supply device 100 includes a charging voltage generation circuit 200, grid voltage adjustment circuits 250B, 250Y, 250M, and 250C (collectively 250), and development voltage adjustment circuits 270B and 270Y. 270M, 270C (generally 270), and the control device 110. In the following description, each channel CH refers to each charger 50B, 50Y, 50M, 50C. In this example, the charger 50B is CH1, the charger 50Y is CH2, the charger 50M is CH3, and the charger. Let 50C be CH4.

  The charging voltage generation circuit 200 performs a function of generating a high voltage of about 6 kV to 8 kV from an input voltage of DC 24 V and applying it to each charger 50. In this embodiment, a self-excited flyback converter (RCC) is used for the charging voltage generation circuit 200, and the charging voltage generation circuit 200 is provided on the secondary side of the PWM signal smoothing circuit 210, the transformer 201, and the transformer 201. A smoothing circuit 203 provided and a transistor Tr1 provided on the primary side of the transformer 201 are provided.

  The PWM signal smoothing circuit 210 is an integrating circuit composed of a resistor and a capacitor. The PWM signal smoothing circuit 210 smoothes the PWM signal S0 output from the PWM port P0 of the control device 110, and outputs the smoothed signal to the base of the transistor Tr1 via the drive transistor Tr2. The drive transistor Tr2 is a so-called emitter follower type, and is configured to output a signal input to the base from the emitter side.

  The transistor Tr1 switches the transformer 201. The emitter is connected to the ground, and the collector is connected to the primary winding of the transformer 201. A PWM signal smoothing circuit 210 is connected to the base via a secondary winding (feedback coil) 205 of the primary coil of the transformer 201 and a drive transistor Tr2.

  To the output line Lo of the charging voltage generation circuit 200, the wires 53 of the chargers 50B, 50Y, 50M, and 50C of the channels CH1 to CH4 are commonly connected. As a result, the output voltage Vo of the charging voltage generation circuit 200 is applied to the wires 53 of the chargers 50B, 50Y, 50M, and 50C of each channel.

  The grid voltage adjustment circuit 250 includes a variable resistance circuit, and is provided for each of the channels CH1 to CH4. Similarly, the development voltage adjustment circuit 270 is composed of a variable resistance circuit and is provided for each of the channels CH1 to CH4.

  The grid voltage adjustment circuit 250 and the development voltage adjustment circuit 270 of each channel CH are connected in series between the grid electrode 55 and the ground. Specifically, the development voltage adjustment circuit 270 is provided on the lower side (ground side), and the grid voltage adjustment circuit 250 is provided on the upper side (grid electrode 55 side). An output line is drawn from a common connection point between the grid voltage adjustment circuit 250 and the development voltage adjustment circuit 270, and the developing roller 45 is connected to the end of each output line.

  In addition, each development voltage adjustment circuit 270 and the control device 110 are connected by a signal line, and a control signal (a PWM signal described later) S2 is output from the control device 110 to each development voltage adjustment circuit 270. It has become. The developing voltage adjusting circuit 270 functions to adjust the developing voltage Vd applied to each developing roller 45 by changing the resistance value in response to the input of the control signal S2.

  Similarly, the grid voltage adjustment circuit 250 and the control device 110 of each channel CH are connected by a signal line, and a control signal (a PWM signal described later) S1 is sent from the control device 110 to each grid voltage adjustment circuit 250. Is output. Each grid voltage adjustment circuit 250 functions to adjust the grid voltage Vg of each grid electrode 55 by changing the resistance value in response to the input of the control signal S1.

2-1. Description of Development Voltage Adjustment Circuit 270 Next, a specific configuration of the development voltage adjustment circuit 270 will be described. 6 shows only the development voltage adjustment circuit 270B of the first channel CH1, the development voltage adjustment circuits 270Y, 270M, and 270C of the other channels CH2 to CH4 have the same configuration.

  The development voltage adjustment circuit 270 includes a PWM signal smoothing circuit 271, an amplifier A 2, a transistor Q 2, and a voltage detection circuit 277. The PWM signal smoothing circuit 271 is an integrating circuit composed of a resistor and a capacitor. The PWM signal smoothing circuit 271 smoothes the PWM signal S2 output from the PWM port P2 of the control device 110 and outputs it to the input terminal on the negative polarity side of the amplifier A2. Is. The PWM signal S2 is a control signal for setting a target value for the development voltage Vd, and has a PWM value corresponding to the target value.

  The voltage detection circuit 277 has a function of detecting the development voltage Vd, and is provided between the development roller 45 and the ground. The voltage detection circuit 277 includes two detection resistors RA and RB connected in series, and an intermediate connection point between the detection resistors RA and RB is connected to an input terminal on the positive polarity side of the amplifier A2.

  The amplifier A2 amplifies the difference between the two inputs, that is, the difference between the detection value of the voltage detection circuit 277 and the target value of the development voltage Vd, and outputs it to the transistor Q2. The transistor Q2 is an NPN transistor having an emitter grounded and connected, and a collector connected to the emitter of the transistor Q1 on the grid voltage adjustment circuit 250 side. The base of the transistor Q2 is connected to the output terminal of the amplifier A2 via a smoothing circuit 275 composed of a resistor and a capacitor.

  The transistor Q2 has a collector resistance that changes depending on the magnitude of the base current, and functions as a variable resistance. That is, increasing the base current decreases the resistance value, and conversely decreasing the base current increases the resistance value. The collector resistance is a resistance value obtained by dividing the collector-emitter voltage by the collector current.

  According to the development voltage adjusting circuit 270, when the development voltage Vd is higher than the target voltage, the output of the amplifier A2 becomes positive and the base current of the transistor Q2 tends to increase. For this reason, the collector resistance of the transistor Q2 becomes small, and the development voltage Vd approaches the target value. On the other hand, when the developing voltage Vd is lower than the target voltage, the output of the amplifier A2 becomes negative, and the base current of the transistor Q2 tends to decrease. For this reason, the collector resistance of the transistor Q2 increases, and the development voltage Vd approaches the target value. From the above, the development voltage Vd can be adjusted to the target voltage.

2-2. Description of Grid Voltage Adjustment Circuit 250 Next, a specific configuration of the grid voltage adjustment circuit 250 will be described. In FIG. 6, only the grid voltage adjustment circuit 250B of the first channel CH1 is shown, but the configuration of the grid voltage adjustment circuits 250Y, 250M, and 250C of the other channels CH2 to CH4 is also common.

  The configuration of the grid voltage adjustment circuit 250 includes a PWM signal smoothing circuit 251, an amplifier A 1, a photocoupler 253, a transistor Q 1, and a voltage detection circuit 257. The PWM signal smoothing circuit 251 is an integrating circuit composed of a resistor and a capacitor. The PWM signal smoothing circuit 251 smoothes the PWM signal S1 output from the PWM port P1 of the control device 110 and outputs it to the input terminal on the positive polarity side of the amplifier A1. Is. The PWM signal S1 is a control signal for setting a target value of the grid voltage Vg, and has a PWM value corresponding to the target value.

  The voltage detection circuit 277 has a function of detecting the grid voltage Vg and is provided between the grid electrode 55 and the ground. The voltage detection circuit 277B includes two detection resistors RC and RD connected in series, and an intermediate connection point between the detection resistors RC and RD is connected to an input terminal on the negative polarity side of the amplifier A1.

  The amplifier A1 amplifies the difference between the two inputs, that is, the difference between the detection value of the voltage detection circuit 257 and the target value of the developing voltage Vd, and outputs the amplified difference to the photocoupler 253 provided at the input stage of the transistor Q1. The transistor Q1 is an NPN transistor, and has an emitter connected to the collector of the transistor Q2 and a collector connected to the grid electrode 55. The base of the transistor Q1 is connected to the output terminal of the amplifier A1 via the photocoupler 253 and the smoothing circuit 255.

  Similar to the transistor Q2, the transistor Q1 changes its collector resistance depending on the magnitude of the base current, and functions as a variable resistance. That is, increasing the base current decreases the resistance value, and conversely decreasing the base current increases the resistance value.

  According to the grid voltage adjustment circuit 250 described above, when the grid voltage Vg is higher than the target voltage, the output of the amplifier A1 is negative. As a result, the current flowing through the photocoupler 253 decreases, and the base current of the transistor Q1 tends to increase. Therefore, the collector resistance value of the transistor Q1 becomes small, and the grid voltage Vg approaches the target value. Conversely, when the grid voltage Vg is lower than the target voltage, the output of the amplifier A1 becomes positive. As a result, the current flowing through the photocoupler 253 increases, and the base current of the transistor Q1 tends to decrease. Therefore, the collector resistance value of the transistor Q1 increases, and the grid voltage Vg approaches the target value. From the above, the grid voltage Vg can be adjusted to the target voltage.

  In the grid voltage adjustment circuit 250, the photocoupler 253 is provided between the amplifier A1 and the transistor Q1 because the grid voltage adjustment circuit 250 is connected in series to the development voltage adjustment circuit 270 (in other words, This is because the reference voltage of the circuit is higher by the developing voltage.

  The control device 110 has a function of controlling the charging voltage generation circuit 200 according to the PWM value of the PWM signal S0, and development applied to the development rollers 45Y, 45M, and 45C via the development voltage adjustment circuits 270B, 270Y, 270M, and 270C. The function of controlling the voltage Vd and the function of controlling the grid voltage Vg applied to each grid electrode via the grid voltage adjustment circuits 250B, 250Y, 250M, and 250C are achieved, and the nine PWM ports P0 to P9 are provided. Prepare.

  The control device 110 can be configured with a built-in CPU or an application specific integrated circuit (ASIC). The control device 110 incorporates a nonvolatile storage unit (not shown), and stores various data for controlling each circuit described above.

3. Control start timing and response speed of development voltage adjustment circuit 270 and grid voltage adjustment circuit 250 As described above, grid voltage adjustment circuit 250 and development voltage adjustment circuit 270 are connected in series,
In the configuration in which the development voltage Vd is generated by dividing the grid voltage Vg, if the output is adjusted by one of the adjustment circuits 250 and 270, the influence affects the other adjustment circuit 250 and 270, and the voltage becomes unstable. .

  Therefore, in this embodiment, a time difference is provided in the control start timing of both the adjustment circuits 250 and 270, the grid voltage adjustment circuit 250 is started first, the development voltage adjustment circuit 270 is started later, and the control is started later. The response speed of the developing voltage adjustment circuit 270 on the side to be controlled is set slower than the response speed of the grid voltage adjustment circuit 250 that starts control first. Specifically, the time constant T (for example, 2 ms) of the PWM signal smoothing circuit 271 on the development voltage adjusting circuit 270 side is set to be the time constant T (for example, 0. 0 ms) of the PWM signal smoothing circuit 251 on the grid voltage adjusting circuit 250 side. 2 ms). In this case, the time constant T is “C × R”. The ratio of the time constant T is preferably about 5 to 10 times.

  By providing a time difference between the control start timings of the adjustment circuits 250 and 270, it is possible to suppress control interference between the two adjustment circuits, compared to the case where control is simultaneously started between at least two adjustment circuits. It becomes. In addition, since the response speed of the adjustment circuit on the control start side is slowed down later, the adjustment circuit on the control start side can easily absorb voltage fluctuations on the adjustment circuit side that starts control later. Therefore, the output voltages of the adjustment circuits 250 and 270, that is, the grid voltage and the development voltage are easily stabilized.

  Further, by setting the control start timing of the developing voltage Vd later than the control start timing of the grid voltage Vg, the following effects can be obtained.

  Since the developing roller 45 is used in pressure contact with the photosensitive drum 41, if the potential difference between the photosensitive drum 41 and the developing roller 45 is small, toner as a developer may adhere to the photosensitive drum 41 before exposure. . In order to prevent adhesion of toner as a developer, a separation mechanism for separating the developing roller 45 from the photosensitive drum 41 is necessary until the voltage between the photosensitive drum 41 and the developing roller 45 is stabilized at a target value. In this configuration, since the grid voltage is controlled first and the development voltage is controlled later, the grid voltage rises before the development voltage. Therefore, the potential difference between the photosensitive drum 41 and the developing roller 45 can be maintained, and it is possible to suppress the toner as the developer from adhering to the photosensitive drum 41 before exposure. Therefore, the separation mechanism can be eliminated.

  In the present embodiment, after the grid voltage Vg is stabilized, control of the development voltage Vd by the development voltage adjustment circuit 270 is started. In this way, after the photosensitive drum 41 is charged to a predetermined level, the development voltage Vd is controlled toward the target value (in other words, increases toward the target value), so the photosensitive drum 41 and the developing roller 45 are controlled. It is possible to reliably maintain the potential difference. Therefore, it is possible to more reliably prevent the developer from adhering to the photosensitive drum 41.

  The grid voltage Vg being stable means that the response falls within a predetermined allowable range E (target value ± 5% as an example) (see FIG. 7). In this embodiment, since the settling time Ts from the start of the control of the grid voltage Vg to the stabilization is 50 ms, the PWM signal S1 is output to the grid voltage adjustment circuit 250 to start the adjustment of the grid voltage Vg. Then, after waiting for “50 ms”, the PWM signal S2 is output to the developing voltage adjusting circuit 270 to adjust the developing voltage Vd.

  The settling time Ts until the grid voltage Vg is stabilized can be obtained from the circuit constants of the grid voltage adjustment circuit 250, and the numerical value is used. The settling time Ts can be, for example, an actually measured value by an experimental circuit other than the numerical value obtained from the circuit constant.

4). Printing Process Next, the control flow of the printing process will be described with reference to FIG. As shown in FIG. 4, when print data D is output from a host device such as a host computer, the print data D is received by the printer 1 through the interface IF. Then, the main motor is energized by a command from the main control unit 80 that controls and controls the entire printer 1. As a result, each photosensitive drum 41 starts to rotate (S10).

  Thereafter, a start command for the high-voltage power supply device 100 is given from the main control unit 80 to the control device 110. When the control device 110 receives the activation command, the control device 110 first starts controlling the charging voltage generation circuit 200. Specifically, the PWM value of the PWM signal S0 output from the PWM port P0 of the control device 110 is fixed, and the charging voltage generation circuit 200 is controlled (S20). Accordingly, a charging voltage (7 kV as an example) is applied to the chargers 50B, 50Y, 50M, and 50C of the channels CH1 to CH4 via the charging voltage generation circuit 200. By applying the charging voltage, the grid current Ig flows toward the ground in the path of the thick line shown in FIG. 6, that is, the path of the grid electrode 55, the transistor Q1, and the transistor Q2.

  At this time, the transistors Q1 and Q2 are controlled by the control device 110 so that a predetermined amount of base current flows, and are controlled to be in a low impedance state.

  Then, when a certain time elapses from the start of the control of the charging voltage generation circuit 200 and the output voltage of the charging voltage generation circuit 200 and the grid current Ig become substantially stable, the control device 110 starts to control the grid voltage Vg. . Specifically, the target value (750 V as an example) of the grid voltage Vg is output from the PWM port P1 to the grid voltage adjustment circuit 250 through the PWM signal S1 (S30). Thereby, the level adjustment of the grid voltage Vg by the grid voltage adjustment circuit 250 is performed. That is, when the grid voltage Vg is smaller than the target value, the base current of the transistor Q1 is reduced and the collector resistance is increased. On the other hand, when the grid voltage Vg is larger than the target value, the base current of the transistor Q1 is increased to reduce the collector resistance. Therefore, the grid voltage Vg applied to the grid electrode 55 increases after the start of control and gradually converges to the target value. The grid voltage Vg is controlled individually for each channel CH1 to CH4.

  Then, the control device 110 waits for 50 ms from the start of control of the grid voltage Vg, and starts control of the development voltage Vd when 50 ms elapses (S40, S50).

  Specifically, the target value (500 V as an example) of the development voltage Vd is output from the PWM port P2 to the development voltage adjustment circuit 270 through the PWM signal S2. As a result, the level of the development voltage Vd is adjusted by the development voltage adjustment circuit 270. That is, when the developing voltage Vd is smaller than the target value, the base current of the transistor Q2 is decreased and the collector resistance is increased. On the other hand, when the developing voltage Vd is larger than the target value, the base current of the transistor Q2 is increased to reduce the collector resistance.

  For this reason, the development voltage Vd increases after the start of control and gradually converges to the target value. The development voltage Vd is controlled individually for each channel CH1 to CH4.

  Thereafter, control of the image forming unit 5 by the main control unit 80 is started, and a printing operation is executed. When the printing operation is completed, a cleaning operation for the belt 34 and the photosensitive drum 41 is performed (S60 to S80).

  After the cleaning operation is completed, a process for stopping the high-voltage power supply device 100 is executed according to a command from the main control unit 80, and then a process for stopping the main motor is executed (S90, S100). Thus, a series of processing ends.

5. Explanation of Effects As described above, in this embodiment, the response speed of the development voltage adjustment circuit 270 on the control start side is made slower than the response speed of the grid voltage adjustment circuit 250 that starts control first. Therefore, the grid voltage adjustment circuit 250 on the side that starts control first easily absorbs the voltage fluctuation on the development voltage adjustment circuit 270 side that starts control later. Therefore, the output voltages of the adjustment circuits 250 and 270, that is, the grid voltage Vg and the development voltage Vd are easily stabilized.

<Embodiment 2>
Next, a second embodiment of the present invention will be described with reference to FIGS.
In the first embodiment, an example in which the PWM value is fixed and the charging voltage generation circuit 200 is controlled has been described. In the second embodiment, the grid current Ig of each channel CH is monitored, and the output voltage of the charging voltage generation circuit 200 is controlled so that the minimum value of the grid current Ig becomes a target value (225 μA as an example).

  FIG. 9 is a circuit diagram of the high-voltage power supply device 100 according to the second embodiment, and a current detection resistor RE is added to the high-voltage power supply device 100 according to the first embodiment. The current detection resistor RE is provided between the emitter of the transistor Q2 of the developing voltage adjustment circuit 270 and the ground. The voltage generated in the current detection resistor RE is input to the input port I of the control device 110 through the signal line.

  Therefore, the control device 110 can monitor the current Ia flowing through the collector of the transistor Q2 by checking the voltage level of the input port I.

On the other hand, the grid current Ig is the sum of the current Ia flowing through the collector of the transistor Q2, the current Ib flowing through the detection resistors RA and RB, and the current Ic flowing through the detection resistors RC and RD.
Ig = Ia + Ib + Ic

  Here, “Ib” can be obtained from the target value of the development voltage Vd and the detection resistors RA and RB, and “Ic” can be obtained from the target value of the grid voltage Vg and the detection resistors RC and RD. It is. Therefore, the grid current Ig can be calculated by adding “Ib” and “Ic” obtained by calculation to the detected “Ia”.

  Since the current detection resistor RE and the input port I are provided for each of the channels CH1 to CH4, the control device 110 monitors the voltage level of the input ports I1 to I4, thereby allowing each of the channels CH1 to CH1. The grid current Ig of CH4 can be detected respectively.

Hereinafter, the control flow of the grid current executed by the control device 110 will be described with reference to FIG.
When the print data D is input, the main control unit 80 is given an activation command for the high-voltage power supply device 100 to the control device 110. Then, the control device 110 that has received the start command sets the PWM value to an initial value, and starts control of the charging voltage generation circuit 200 (S200).

  Next, the control apparatus 110 performs the process which detects the grid current Ig of each channel CH1-CH4 (S210). Thereafter, the channel having the smallest current value is selected (S220).

  When the channel with the smallest grid current is selected, the control device 110 next performs a process of determining the magnitude of the grid current Ig of the selected channel. Specifically, it is determined in S230 whether the value of the grid current Ig is 224 μA or less, and in S240, it is determined whether the value of the grid current Ig is 226 μA or more.

  If the value of the grid current Ig is 224 μA or less, YES is determined in S230. In this case, the process proceeds to S250, and the control device 110 increases the PWM value output to the charging voltage generation circuit 200. Thus, the output voltage Vo of the charging voltage generation circuit 200, that is, the charging voltage applied to the wire 53 of each charger 50 is increased and adjusted.

  On the other hand, when the value of the grid current Ig is 226 μA or more, YES is determined in S240. In this case, the process proceeds to S260, and the control device 110 decreases the PWM value output to the charging voltage generation circuit 200. Thereby, the output voltage Vo of the charging voltage generation circuit 200, that is, the charging voltage applied to the wire 53 of each charger 50 is adjusted to decrease.

  Following the adjustment of the charging voltage, a process of waiting for 5 ms is executed, and then a process of determining whether to stop the high-voltage power supply apparatus 100 is performed (S270, S280). If the printing process is not completed, a YES determination is made in S280, and the process returns to S210 to detect the grid current Ig of each channel CH, to select the channel CH having the smallest current value, and to perform PWM according to the current value. Processing to adjust the value is executed.

  By repeatedly executing such processing, the minimum value of the grid current Ig is adjusted to the target value. When the minimum value of the grid current Ig is the target value, NO is determined in S230 and S240, so that the adjustment of the PWM value is not executed and the PWM value of the PWM signal SO is held.

  When the minimum value of the grid current Ig becomes stable at the target value, the control device 110 adjusts the grid voltage Vg to the target value via the grid voltage adjustment circuit 250 as in the case of the first embodiment. After the grid voltage Vg is stabilized at the target value, the development voltage Vd is adjusted to the target value via the development voltage adjustment circuit 270. Similarly to the first embodiment, the response speed of the developing voltage adjustment circuit 270 on the side where control is started later is made slower than the response speed of the grid voltage adjustment circuit 250 where control is started first. Therefore, the grid voltage adjustment circuit 250 on the side that starts control first easily absorbs the voltage fluctuation on the development voltage adjustment circuit 270 side that starts control later. Therefore, the output voltages of the adjustment circuits 250 and 270, that is, the grid voltage Vg and the development voltage Vd are easily stabilized.

  In the second embodiment, since the grid current Ig having the smallest current value is selected and controlled to the target value, the grid currents Ig of all four channels are all equal to or higher than the target value. For this reason, the amount of charge on the photosensitive drum 41 is equal to or higher than an appropriate level for all the four channels, so that the image quality can be kept good.

<Embodiment 3>
Next, Embodiment 3 of the present invention will be described with reference to FIGS.
In the first embodiment, when the high-voltage power supply device 100 is started, control of the grid voltage Vg is started first among the grid voltage Vg and the development voltage Vd. Then, after the control is started, the time until the grid voltage Vg is stabilized (for example, “50 ms”: S40 in FIG. 8) waits, and after the grid voltage Vg is stabilized, the controller 110 causes the developing voltage adjustment circuit 270 to Control of the development voltage Vd was started.

  In the third embodiment, as in the first embodiment, when the high-voltage power supply device 100 is started, control of the grid voltage Vg is started first among the grid voltage Vg and the development voltage Vd. Then, after the control is started, the time until the facing portion A of the photosensitive drum 41 facing the charger 50 when the grid voltage Vg becomes stable passes the facing position B facing the developing roller 45 as the photosensitive drum 41 rotates. (As an example, “500 ms”: S40 in FIG. 12) waits, and then the control of the developing voltage Vd by the developing voltage adjusting circuit 270 is started by the control device 110.

  In this case, the developing voltage Vd is controlled toward the target value after the facing portion A of the photosensitive drum 41 charged to a predetermined level passes through the facing position B facing the developing roller 45, so the photosensitive drum 41 and the developing roller Thus, the potential difference of 45 can be reliably maintained. Therefore, it is possible to more reliably prevent toner from adhering to the photosensitive drum 41.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention.

  (1) Although the color printer is illustrated as an example of the image forming apparatus in the first to third embodiments, the technique of the present embodiment can be applied to a monochrome printer having only one set of the charger 50 and the photosensitive drum 41.

  (2) In the first to third embodiments, control of the grid voltage adjustment circuit 250 is started first, control of the development voltage adjustment circuit 270 is started later, and the response speed of the development voltage adjustment circuit 270 on the side where control is started later is set. The response speed of the grid voltage adjustment circuit 250 that starts control first is set slower than the response speed. The control order of the adjustment circuits 250 and 270 may be reversed, and the development voltage adjustment circuit 270 may be started first and the grid voltage adjustment circuit 250 may be started later. In this case, in order to easily stabilize the grid voltage Vg and the development voltage Vd, the response speed of the grid voltage adjustment circuit 250 on the side to start control later is set to the response of the development voltage adjustment circuit 270 to start control first. It is preferable to set it slower than the speed. In this case, in order to prevent the toner from adhering to the photosensitive drum 41 before exposure, the developing roller 45 is separated from the photosensitive drum 41 until the high-voltage power supply device 100 starts up, and the high-voltage power supply device 100 starts up. Then, the developing roller 45 may be pressed against the photosensitive drum 41.

  (3) In the first to third embodiments, the response speed of the development voltage adjustment circuit 270 is set slower than the response speed of the grid voltage adjustment circuit 250. Specifically, the time constant T of the PWM signal smoothing circuit 271 on the development voltage adjustment circuit 270 side is set to be larger than the time constant T of the PWM signal smoothing circuit 251 on the grid voltage adjustment circuit 250 side. In addition, the response speed of the development voltage adjustment circuit 270 may be set slower than the response speed of the grid voltage adjustment circuit 250 by making a difference in the response of the transistors Q1 and Q2.

  (4) In the first to third embodiments, the grid voltage Vg side is adjusted first, and the development voltage Vd is controlled after the grid voltage Vg is stabilized. The start of control of the development voltage Vd may be at least later than the start of control of the grid voltage Vg, and does not necessarily have to be started after the grid voltage Vg has stabilized. For example, it may be started when the grid voltage Vg reaches a level that is substantially close to the target value (90% as an example) even before the grid voltage Vg is stabilized.

  (5) In the first to third embodiments, the settling time Ts is calculated from the circuit constants of the grid voltage adjustment circuit 250, and after the settling time Ts has elapsed from the start of control of the grid voltage Vg, the grid voltage Vg is stable. Considered to be. The determination as to whether the grid voltage Vg is stable may be made based on the actual measurement value of the grid voltage Vg. That is, a circuit for detecting the grid voltage Vg may be provided separately, and when the measured value of the grid voltage Vg falls within a predetermined allowable range E, it may be determined that the circuit is stable.

DESCRIPTION OF SYMBOLS 1 ... Printer 41B, 41Y, 41M, 41C (generally 41) ... Photosensitive drum (an example of "photoconductor" of the present invention)
50B, 50Y, 50M, 50C (generally 50) ... Scorotron charger 45B, 45Y, 45M, 45C (generally 45) ... developing roller (an example of the "developer" of the present invention)
53 ... Wire 55 ... Grid electrode 80 ... Main control unit 100 ... High voltage power supply device 110 ... Control device 200 ... Charge voltage generation circuit 250B, 250Y, 250M, 250C (collectively 250) ... Grid voltage adjustment circuit 270B, 270Y, 270M 270C (collectively 270)... Development voltage adjustment circuit Q1, Q2... Transistor

Claims (7)

A photoreceptor,
A charger having a wire and a grid electrode to charge the photoreceptor;
A developer for supplying a developer to the photoreceptor;
A charging voltage generation circuit for generating a charging voltage to be applied to the wire;
A grid voltage adjusting circuit for adjusting a grid voltage generated in the grid electrode after the generation of the charging voltage;
A developing voltage adjusting circuit for adjusting a developing voltage generated in the developing unit after the generation of the charging voltage;
A control device that outputs a first control signal according to a target value of the grid voltage to the grid voltage adjustment circuit and outputs a second control signal according to the target value of the development voltage to the development voltage adjustment circuit; Prepared,
The development voltage adjustment circuit is connected in series with the grid voltage adjustment circuit between the grid electrode and ground, and is configured to generate a development voltage by dividing the grid voltage,
The grid voltage adjustment circuit is a circuit that adjusts the grid voltage at a first response speed in accordance with the first control signal output from the control device;
The development voltage adjustment circuit is a circuit that adjusts the development voltage at a second response speed different from the first response speed according to the second control signal output from the control device;
The developing voltage adjustment circuit and of the grid voltage adjustment circuit, one side of the adjustment circuit starts controlling, the first response speed to the control signal input from the control unit and the second response speed after the response speed, on the side of the adjusting circuit to start earlier control, the control device is at a slower setting than the other response speed of the said first response speed second response speed to the control signal input from the Image forming apparatus.   The image forming apparatus according to claim 1, wherein the control device delays a control start timing of the development voltage by the development voltage adjustment circuit from a control start timing of the grid voltage by the grid voltage adjustment circuit.   The image forming apparatus according to claim 2, wherein the control device starts control of the developing voltage by the developing voltage adjusting circuit after a difference between the detected value of the grid voltage and a target value becomes equal to or less than a predetermined value.   The control device adjusts the developing voltage after a portion of the photosensitive member facing the charger when the grid voltage is stable passes a position facing the developing device as the photosensitive member rotates. The image forming apparatus according to claim 3, wherein control of the developing voltage by the circuit is started. The image forming apparatus according to claim 1, wherein the control device delays a timing at which the second control signal is output from a timing at which the first control signal is output. A photoreceptor,
A charger having a wire and a grid electrode to charge the photoreceptor;
A developer for supplying a developer to the photoreceptor;
A charging voltage generation circuit for generating a charging voltage to be applied to the wire;
A grid voltage adjusting circuit for adjusting a grid voltage generated in the grid electrode after the generation of the charging voltage;
A developing voltage adjusting circuit for adjusting a developing voltage generated in the developing unit after the generation of the charging voltage;
A control device that outputs a first control signal according to a target value of the grid voltage to the grid voltage adjustment circuit and outputs a second control signal according to the target value of the development voltage to the development voltage adjustment circuit; Prepared,
The development voltage adjustment circuit is connected in series with the grid voltage adjustment circuit between the grid electrode and ground, and is configured to generate a development voltage by dividing the grid voltage,
The grid voltage adjustment circuit includes:
A first smoothing circuit for smoothing the first control signal output from the control device;
A first detection circuit for detecting the grid voltage;
A first comparator that compares a detection value of the grid voltage detected by the first detection circuit with an output value of the first smoothing circuit;
A first variable resistor connected to the grid electrode and having a resistance value that changes in accordance with an output value of the first comparator;
The development voltage adjusting circuit is
A second smoothing circuit for smoothing the second control signal output from the control device;
A second detection circuit for detecting the development voltage;
A second comparator that compares the detected value of the development voltage detected by the second detection circuit with the output value of the second smoothing circuit;
A second variable resistor connected to the developing unit and having a resistance value that changes in accordance with an output value of the second comparator;
Of the development voltage adjustment circuit and the grid voltage adjustment circuit, the time constant of one smoothing circuit of the first smoothing circuit and the second smoothing circuit provided in the adjustment circuit on the control start side later is An image forming apparatus having a setting larger than the time constant of the other smoothing circuit of the first smoothing circuit and the second smoothing circuit, provided in the adjustment circuit on the control start side. A photoreceptor,
A charger having a wire and a grid electrode to charge the photoreceptor;
A developer for supplying a developer to the photoreceptor;
A charging voltage generation circuit for generating a charging voltage to be applied to the wire;
A grid voltage adjusting circuit for adjusting a grid voltage generated in the grid electrode after the generation of the charging voltage;
A developing voltage adjusting circuit for adjusting a developing voltage generated in the developing unit after the generation of the charging voltage;
A control device that outputs a first control signal according to a target value of the grid voltage to the grid voltage adjustment circuit and outputs a second control signal according to the target value of the development voltage to the development voltage adjustment circuit; Prepared,
The development voltage adjustment circuit is connected in series with the grid voltage adjustment circuit between the grid electrode and ground, and is configured to generate a development voltage by dividing the grid voltage,
The grid voltage adjustment circuit includes:
A first smoothing circuit for smoothing the first control signal output from the control device;
A first detection circuit for detecting the grid voltage;
A first comparator that compares a detection value of the grid voltage detected by the first detection circuit with an output value of the first smoothing circuit;
A first variable resistor disposed between the grid electrode and the first comparator and having a resistance value that varies according to an output value of the first comparator;
The development voltage adjusting circuit is
A second smoothing circuit for smoothing the second control signal output from the control device;
A second detection circuit for detecting the development voltage;
A second comparator that compares the detected value of the development voltage detected by the second detection circuit with the output value of the second smoothing circuit;
A second variable resistor disposed between the developing unit and the second comparator, the resistance value of which varies according to the output value of the second comparator;
The resistance value of one of the first variable resistor and the second variable resistor provided in the adjustment circuit on the control start side of the development voltage adjustment circuit and the grid voltage adjustment circuit. Is set to be slower than the change rate of the resistance value of the other variable resistor of the first variable resistor and the second variable resistor provided in the adjustment circuit on the control start side. An image forming apparatus.

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