JP4863092B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to activation of a transfer voltage thereof.

A conventional image forming apparatus detects a transfer current value and appropriately transfers a transfer roller (or belt) so that an image carried on a photoconductor (image carrier) is appropriately transferred. ) To control the transfer voltage applied. As a technique for applying this transfer voltage, Document 1 describes an image forming apparatus that gradually increases the duty ratio of a PWM signal that is a control signal when a transfer voltage is applied.
JP 2001-296720 A

  In general, the photosensitive member (image carrier) is charged before the high voltage generating circuit for applying the transfer voltage is started, and therefore, an inflow current from the photosensitive member flows into the high voltage generating circuit. If an inflow current from the photosensitive member is received when the high voltage generation circuit is activated, the high voltage generation circuit is difficult to start up due to the influence of the inflow current. Therefore, there is a problem that the transfer voltage cannot be applied quickly.

  In such a state, when the PWM signal is controlled as described in Document 1, the duty ratio of the PWM signal is controlled to gradually increase until the high voltage generation circuit is started. In some cases, the duty ratio becomes too large and an overshoot of the transfer current may occur. Therefore, there is a problem that the transfer voltage cannot be applied suitably.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of quickly and suitably applying a transfer voltage even when there is an inflow current from an image carrier. To do.

  As means for achieving the above object, an image forming apparatus according to a first aspect of the present invention includes an image carrier that carries a developer image developed by a developer, and the developer image according to application of a transfer voltage. A transfer means for transferring the image to a recording medium, an application means for generating the transfer voltage, applying the transfer voltage to the transfer means, and detecting a signal on the output side of the application means to generate a detection signal Generating means, control means for controlling the transfer voltage in response to the detection signal, a first drive signal that is an on / off signal, and a second drive signal that is a signal that increases stepwise. In the driving circuit for driving the applying means according to the first driving signal and the second driving signal, and in the starting mode for starting the applying means, the applying means is driven according to the first driving signal, and the steady mode after starting In Te, as the second said applying means according to the driving signal is driven, and a switching means for switching between the second driving signal and the first drive signal in response to said detection signal.

  According to this configuration, in the startup mode when the application unit is started up, the application unit is driven by the first drive signal that is an on / off signal and has a large level change. Therefore, when the applying means generates a high voltage using a transformer, even if there is an inflow current from the transfer means side at the time of start-up, a large level change of the first drive signal on the primary side of the transformer may cause This effectively works to start up the application means for generating a high voltage on the secondary side, and the application means can be started up reliably and quickly. Thereby, a transfer voltage can be applied quickly and suitably. In this specification, the “start-up mode” means a state in which the applying means is driven by the first drive signal that is an on / off signal, and the “steady mode” is a signal that increases stepwise. This means that the application means is driven by a certain second drive signal.

According to a second aspect, in the image forming apparatus according to the first aspect, the control unit generates a control signal for controlling the drive circuit, and the drive circuit outputs the first drive signal in accordance with the control signal. A startup drive circuit to generate, a steady drive circuit to smooth the control signal and generate the second drive signal according to the smoothed control signal, and according to the first drive signal and the second drive signal And a main drive circuit for driving the applying means, wherein the switching means switches between the first drive signal and the second drive signal according to the detection signal and supplies the first drive signal and the second drive signal to the main drive circuit.
According to this configuration, since the control unit only needs to generate and output a single control signal, the configuration of the control unit is simplified.

According to a third aspect, in the image forming apparatus according to the first aspect, the control unit includes the switching unit and generates a control signal for controlling the drive circuit, and the drive circuit is responsive to the control signal. A start drive circuit that generates the first drive signal, a steady drive circuit that smoothes the control signal and generates the second drive signal in response to the smoothed control signal, the first drive signal, and the A main drive circuit that drives the applying means in response to a second drive signal, wherein the control means supplies the control signal to the start drive circuit and supplies the control signal to the steady drive circuit in response to the detection signal. Switch between supply and supply.
According to this configuration, the switching of the first drive signal and the second drive signal can be performed by software by the control unit, so that the configuration of the switching unit can be simplified.

According to a fourth invention, in the image forming apparatus of the second or third invention, the control signal is a PWM signal.
According to this configuration, the drive circuit can be controlled easily and precisely.

According to a fifth invention, in the image forming apparatus of the first invention, the control means includes the switching means, and the drive circuit drives the application means in accordance with the first drive signal and the second drive signal. The control means includes a main drive circuit, and the control means generates the first drive signal in the start-up mode in response to the detection signal, supplies the first drive signal to the main drive circuit, and the steady mode. , The second drive signal is generated, and the second drive signal is supplied to the main drive circuit.
According to this configuration, since the smoothing circuit and the circuit for forming the drive signal can be omitted, the circuit configuration for generating the transfer voltage can be greatly simplified.

  According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the detection unit detects a current flowing on an output side of the application unit, and the detection signal is a current detection signal. The switching means switches from the startup mode to the steady mode when the value of the current detection signal exceeds a predetermined value.

  According to this configuration, the inflow current from the image carrier (photosensitive member) can be detected by the detection means. Therefore, it is possible to set a predetermined value for mode switching for reliably starting the applying means based on the detected inflow current. For example, when the value of the detected current detection signal exceeds a predetermined value, it can be determined that at least the application unit has been initially activated.

  In a seventh aspect based on the image forming apparatus according to the sixth aspect, the predetermined value is varied in accordance with an initial detection value of the current detection signal.

  According to this configuration, the value of the inflow current, which is the initial detection value of the current detection signal, is usually not constant depending on the material of the image carrier (photoconductor) and the circuit configuration. By changing the predetermined value for switching the mode, it is possible to start the application means in a timely and reliable manner (if the material of the image carrier is different, the virtual load capacity changes, the charge amount changes, and the inflow current value also changes. ).

According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, when the mode is switched from the start-up mode to the steady mode, the signal on the output side in the steady mode immediately after the mode is switched. The first drive signal is switched to the second drive signal so that the value is equal to or greater than the value of the output-side signal in the startup mode immediately before the mode switching.
According to this configuration, a hysteresis characteristic can be provided at the time of mode transition, and chattering at the time of mode transition can be prevented.

  According to a ninth aspect, in the image forming apparatus according to any one of the first to eighth aspects, the signal characteristic of the first drive signal is gradually increased.

  According to this configuration, by gradually increasing the signal characteristics of the first drive signal, for example, the pulse width, amplitude, frequency, and the like of the first drive signal, the transfer current is gradually gradually increased to a predetermined value in the startup mode. Can be raised. In addition, it is possible to reliably prevent overshoot in the startup mode. Thereby, a transfer voltage can be suitably applied.

  According to the image forming apparatus of the present invention, it is possible to quickly and suitably apply the transfer voltage even when there is an inflow current from the image carrier.

<Embodiment 1>
Embodiment 1 of the present invention will be described with reference to FIGS.
1. 1 is a side sectional view of a main part of a monochrome laser printer (an example of an image forming apparatus) 1. Note that the image forming apparatus is not limited to a monochrome laser printer, and may be, for example, a color laser printer, an LED printer, or a multifunction machine having a copy function and a facsimile function. In the following description, the right side in FIG. 1 is the front side of the monochromatic laser printer (hereinafter simply referred to as “printer”) 1 and the left side in FIG. In FIG. 1, a printer 1 includes a feeder unit 4 for feeding a sheet 3 (an example of a recording medium) in a main body frame 2 and an image forming unit for forming an image on the fed sheet 3. 5 etc.

(1) Feeder Unit The feeder unit 4 includes a paper feed tray 6, a paper pressing plate 7, a paper feed roller 8, and a registration roller 12. The uppermost sheet 3 on the sheet pressing plate 7 is pressed toward the sheet feeding roller 8, and the sheet 3 is fed one by one by the rotation of the sheet feeding roller 8.

  The fed paper 3 is registered by the registration roller 12 and then sent to the transfer position X. The transfer position X is a position where the toner image on the photosensitive drum 27 is transferred to the paper 3, and is a contact position between the photosensitive drum 27 (an example of an image carrier) and a transfer roller 30 (an example of a transfer unit). .

(2) Image Forming Unit The image forming unit 5 includes, for example, a scanner unit 16, a process cartridge 17, and a fixing unit 18.
The scanner unit 16 includes a laser light emitting unit (not shown), a polygon mirror 19 and the like. Laser light emitted from the laser light emitting unit (a chain line in the drawing) is irradiated onto the surface of the photosensitive drum 27 while being deflected by the polygon mirror 19.

  The process cartridge 17 includes a developing roller 31, a photosensitive drum 27, a scorotron charger 29, and a transfer roller 30. The drum shaft 27a of the photosensitive drum 27 is grounded.

  The charger 29 uniformly charges the surface of the photosensitive drum 27 to a positive polarity. Thereafter, the surface of the photosensitive drum 27 is exposed by laser light from the scanner unit 16 to form an electrostatic latent image. Next, the toner carried on the surface of the developing roller 31 is supplied to the electrostatic latent image formed on the photosensitive drum 27 and developed.

  The transfer roller 30 includes a metal roller shaft 30a, and a high voltage generation circuit 60 (see FIG. 2) mounted on the circuit board 52 is connected to the roller shaft 30a. During the transfer operation, the transfer voltage Vt is applied from the high voltage generation circuit 60 to the transfer roller 30.

  The fixing unit 18 heat-fixes the toner on the paper 3 while the paper 3 passes between the heating roller 41 and the pressing roller 42. The heat-fixed paper 3 is discharged onto a paper discharge tray 46 via a paper discharge path 44.

2. Configuration of High Voltage Generation Circuit FIG. 2 is a schematic block diagram of a high voltage generation circuit 60 for generating a transfer voltage Vt applied to the transfer roller 30. The high-voltage generation circuit 60 includes a CPU (an example of a control unit) 62, a startup drive circuit 63A, a steady drive circuit 63B, a transformer drive circuit (an example of a main drive circuit) 64, a switching circuit (an example of a switching unit) 65, and a booster circuit ( An example of application means) 66, a current detection circuit (example of detection means) 67, and a memory 72 are included.

  The CPU 62 generates a PWM (Pulse Width Modulation) signal (an example of a control signal) Sc in order to control the transfer voltage Vt according to the current detection signal Si of the current detection circuit 67, and generates the PWM signal Sc. The PWM port 62a supplies the starting drive circuit 63A and the steady drive circuit 63B. The memory 72 stores various programs executed by the CPU 62.

  The activation drive circuit 63A includes a resistor R1, a resistor Ra, and a transistor Tr1, and generates a first drive signal Sd1 that is an on / off signal in accordance with the PWM signal Sc in the activation mode in which the booster circuit 66 is activated (FIG. 3). reference). At this time, the transistor Tr1 is on / off controlled by the PWM signal Sc. At this time, the transistor Tr1 is turned on when the PWM signal Sc is at a logic low level, and the transistor Tr1 is turned off when the PWM signal Sc is at a logic high level. That is, here, the first drive signal Sd1 in which the logic level of the PWM signal Sc is inverted is generated (see FIG. 3). The resistor Ra is a resistor for adjusting the output of the booster circuit 66, and determines the output characteristics of the booster circuit 66.

  The steady drive circuit 63B includes a resistor R2, a capacitor C1, a resistor Rb, and a transistor Tr2, and in the steady mode after startup of the booster circuit 66, the second drive that increases stepwise according to the change in the duty ratio of the PWM signal Sc. A signal Sd2 is generated (see FIG. 3). Here, the resistor R2 and the capacitor C1 form a smoothing circuit, and supply the smoothed PWM signal Sc to the base of the transistor Tr2. That is, in the steady mode, the transistor Tr2 is controlled by the smoothed PWM signal Sc. The resistor Rb is a resistor for adjusting the output of the booster circuit 66, and determines the output characteristics of the booster circuit 66.

  The transformer drive circuit 64 includes a resistor R3 and a transistor Tr3, and starts up the booster circuit 66 according to the first drive signal Sd1 in the startup mode, and changes to the second drive signal Sd2 in the steady mode after startup of the booster circuit 66. Therefore, the booster circuit 66 is driven (see FIG. 3). The first drive signal Sd1 and the second drive signal Sd2 are supplied to the base of the transistor Tr3 via the resistor R3 and the self-excited winding 68c of the booster circuit 66. The transistor Tr3 is configured to turn on / off the current flowing through the primary winding 68b of the booster circuit 66 based on the supplied first drive signal Sd1 and second drive signal Sd2.

  The switching circuit 65 includes a diode (D3, D4), a resistor R4, a transistor Tr4, and a comparison circuit IC1, and the first drive signal Sd1 generated by the activation drive circuit 63A according to the current detection signal (voltage signal) Si of the current detection circuit 67. And the second drive signal Sd2 by the steady drive circuit 63B are switched.

  Specifically, when the current detection signal Si is equal to or lower than a predetermined reference voltage (corresponding to a “predetermined value” in the present invention) Vref, the comparison circuit IC1 generates a logic high level output signal. Accordingly, the transistor Tr4 is turned on, the second drive signal Sd2 is invalidated, and the first drive signal Sd1 is supplied to the transformer drive circuit 64.

  On the other hand, when the current detection signal Si exceeds a predetermined reference voltage Vref, the comparison circuit IC1 generates a logic low level output signal. Accordingly, the transistor Tr4 is turned off, the first drive signal Sd1 is invalidated via the diode D4, and the second drive signal Sd2 is supplied to the transformer drive circuit 64.

  The booster circuit 66 includes a transformer 68, a diode 69, a smoothing capacitor 70, and the like. The transformer 68 includes a secondary winding 68a, a primary winding 68b, and a self-excited winding 68c. One end of the secondary winding 68a is connected to the roller shaft 30a of the transfer roller 30 via a diode 69 and a connection line L1. On the other hand, the other end of the secondary winding 68 a is connected to the ground via a current detection circuit 67. A smoothing capacitor 70 and a discharge resistor 71 are connected in parallel to the secondary winding 68a.

  With such a configuration, the voltage on the primary side of the transformer 68 is boosted and rectified in the boosting circuit 66 in accordance with ON / OFF of the current flowing through the primary winding 68b of the transformer 68, and the roller of the transfer roller 30 A transfer voltage (for example, negative high voltage) Vt is applied to the shaft 30a. At this time, the transfer current It flowing through the transfer roller 30 (the value of the current flowing in the direction of the arrow in FIG. 2 is positive) flows into the resistors 67a and 67b of the current detection circuit 67, and a current corresponding to the transfer current It. The detection signal (voltage signal) Si is supplied to the inverting input terminal of the comparison circuit IC1 and fed back to the A / D port 62b of the CPU 62. The transfer current It includes an inflow current Ir caused by charging of the photosensitive drum 27. Further, the value of the transfer current It is obtained from the relationship V = It × R. Here, V is a voltage value of the current detection signal Si, and R is a resistance value of the resistor 67b.

  Then, after the start-up operation of the booster circuit 66 is completed, when the sheet 3 reaches the transfer position X and the transfer operation for transferring the toner image on the photosensitive drum 27 to the sheet 3 is performed, the CPU 62 flows to the connection line L1. Based on the current detection signal Si corresponding to the current value of the transfer current It, the PWM signal Sc with the duty ratio (an example of the value of the control signal) appropriately changed so that the current value of the transfer current It falls within the target range is steady. The constant current control output to the drive circuit 63B is executed.

3. Mode Switching Next, a mode switching mode between the startup mode and the steady mode when the booster circuit 66 is started will be described with reference to FIGS. 3 and 4. FIG. 3 is a time chart when the booster circuit 66 is started. FIG. 4 is a diagram for explaining a difference in output characteristics of the booster circuit 66 between the startup drive circuit 63A and the steady drive circuit 63B. Here, switching between the start mode and the steady mode is performed by the switching circuit 65 in accordance with the current detection signal Si.

  Specifically, the CPU 62 starts supplying, for example, a PWM signal Sc with a duty ratio of 80% to the start drive circuit 63A and the steady drive circuit 63B at time t0 in FIG. Thereafter, when the PWM signal Sc having a duty ratio of 80% for a predetermined time is supplied, as shown in FIG. 3, the value of the transfer current It including the inflow current Ir is a predetermined reference value (“predetermined value” in the present invention). Iref) has not reached Iref, that is, the value of the current detection signal Si has not reached the predetermined reference value Vref corresponding to the reference value Iref. Therefore, the switching circuit 65 supplies the first drive signal Sd1 generated by the activation drive circuit 63A in response to the PWM signal Sc to the transformer drive circuit 64.

  Here, if the value of the inflow current Ir before the booster circuit 66 is started (corresponding to the “initial detection value” in the present invention) is, for example, 1 μA, the predetermined reference value Iref is, for example, 4 μA, which is four times that value. Set to This is because if the value of the transfer current It including the inflow current Ir reaches four times or more the value of the inflow current Ir before activation, it can be determined that the booster circuit 66 has been activated normally. The predetermined reference value Iref (or reference value Vref) may be varied according to the value of the inflow current Ir before the booster circuit 66 is started. Usually, the value of the inflow current Ir is not constant depending on the material and circuit configuration of the photosensitive drum 27 (if the material of the photosensitive drum 27 is different, the virtual load capacity changes and the charge amount differs, and the inflow current value also varies. Change). Therefore, by changing the reference value Iref (or the reference value Vref) for switching the mode according to the value of the inflow current Ir, the booster circuit 66 can be surely activated in a timely manner.

  Further, the pulse amplitude of the first drive signal Sd1 in the startup mode is adjusted by the value of the resistor Ra. More specifically, here, as shown in FIG. 4, in the output characteristic graph showing the relationship between the duty ratio of the PWM signal Sc and the transfer current It which is the output of the booster circuit 66, the characteristic by the steady drive circuit 63B. The value of the resistor Ra and the value of the resistor Rb are set so that the graph is equal to or higher than the characteristic graph by the activation drive circuit 63A. This is to provide hysteresis at the time of mode transition. FIG. 4 shows a case where the characteristic graph by the steady drive circuit 63B exceeds the characteristic graph by the start drive circuit 63A.

  Next, the CPU 62 supplies, for example, a PWM signal Sc having a duty ratio of 60% to the start drive circuit 63A and the steady drive circuit 63B for a predetermined time. When the value of the transfer current It reaches the reference value (threshold value) Iref at time t1 in FIG. 3, that is, when the value of the current detection signal Si reaches the reference value (threshold value) Vref, the switching circuit 65 performs smoothing. In response to the PWM signal Sc, the second drive signal Sd2, which is generated in a stepwise manner and is generated by the steady drive circuit 63B, is supplied to the transformer drive circuit 64. That is, the switching circuit 65 switches the mode from the startup mode to the steady mode at time t1 in FIG.

  In this way, in the start-up mode, as shown in FIG. 3, the transformer drive circuit 64 causes the primary side of the transformer 68 to respond to the pulsed first drive signal Sd1 which is an on / off signal and has a large level change. Drive. Therefore, even when there is an inflow current Ir from the transfer drum side when the booster circuit 66 is activated, a large level change of the drive signal Sd1 on the primary side of the transformer 68 generates a high voltage on the secondary side of the transformer 68. This effectively works to start up the booster circuit 66. As a result, the booster circuit 66 can be reliably and quickly activated against the inflow current Ir.

  In the start-up mode, the first drive signal Sd1 is formed so that the pulse width is gradually increased while the pulse amplitude remains constant. Therefore, in the startup mode, the transfer current can be suitably gradually increased to a predetermined value, and overshoot in the startup mode can be reliably prevented.

  Further, when the mode is switched from the start mode to the steady mode, the value of the transfer current It in the steady mode immediately after the mode switch is greater than or equal to the value of the transfer current It in the start mode immediately before the mode switch according to the characteristic graph of FIG. Thus, the first drive signal Sd1 is switched to the second drive signal Sd2. Therefore, hysteresis characteristics can be provided at the time of mode transition, and chattering in the comparison circuit IC1 at the time of mode transition can be prevented.

  In the steady mode, the transformer drive circuit 64 drives the primary side of the transformer 68 in accordance with a second drive signal Sd2 that increases stepwise in response to a change in the duty ratio of the PWM signal Sc as shown in FIG. . Accordingly, the transfer current It gradually increases and reaches a predetermined current value, and then the transfer current It is constant-current controlled by the CPU 62 based on the current detection signal Si.

4). Effects of First Embodiment In the first embodiment, since the booster circuit 66 is activated so that the transfer current It gradually increases, generation of an excessive transfer current (overshoot) when the booster circuit 66 is activated is suppressed. be able to.

  In the start-up mode, which is an initial stage when the booster circuit 66 is started, the transformer drive circuit 64 transforms the transformer 68 in response to the pulsed first drive signal Sd1 that is an on / off signal and has a large level change. Drive the primary side. Therefore, even when there is an inflow current Ir from the transfer drum side when the booster circuit 66 is activated, the booster circuit 66 can be reliably and quickly activated against the inflow current Ir.

<Embodiment 2>
Next, Embodiment 2 of the present invention will be described with reference to FIGS. 5 and 6. FIG. 5 is a schematic block diagram of the high voltage generation circuit 60A of the second embodiment. FIG. 6 is a flowchart schematically showing a mode switching processing procedure. Since the second embodiment and the first embodiment are different only in the configuration of the high voltage generation circuit, only the difference will be described. In addition, the same member number is attached | subjected to the structure same as Embodiment 1, and the description is abbreviate | omitted.

  As shown in FIG. 5, the high voltage generation circuit 60 </ b> A of the second embodiment corresponds to a circuit in which the switching circuit 65 is omitted from the high voltage generation circuit 60 of the first embodiment. In the second embodiment, the PWM signal Sc is switched and supplied individually from the first PWM port 62c to the startup drive circuit 63A and from the second PWM port 62d to the steady drive circuit 63B. The CPU 62 performs the switching control and the mode switching control of the PWM signal Sc when starting up the booster circuit 66 in software according to a predetermined program stored in the memory 72 instead of the switching circuit 65. This program is started in response to a predetermined print request.

  In step S10 of FIG. 6, first, the CPU 62 performs initial setting of registers and the like. For example, a predetermined reference value (digital value) Iref of the transfer current It for determining mode switching is set in the current setting register, the start mode is set to “OFF”, and the steady mode is set to “ON” in the PWM setting. Set to Specifically, the second PWM port 62d is selected, the PWM signal Sc is supplied from the second PWM port 62d to the steady drive circuit 63B, and the booster circuit 66 is activated by the second drive signal Sd2 that increases stepwise.

  Next, after a predetermined time has elapsed, in step S20, the CPU 62 reads an FB (feedback) signal, that is, a current detection signal Si, A / D converts the read current detection signal Si, and digitalizes the current detection signal Si. Get the value. At this time, the value of the current detection signal Si, which is a voltage value, is converted into a digital current value according to a predetermined conversion table. In step S30, the CPU 62 determines whether the digital current value (A / D value) is equal to or less than a predetermined reference value Iref. When the A / D value is not less than or equal to the predetermined reference value Iref, that is, when the A / D value exceeds the predetermined reference value Iref (step S30: NO), the steady mode is continued in step S45. This is because it is determined that the booster circuit 66 has been activated in the steady mode, so that the booster circuit 66 is further controlled in the steady mode. After the transfer current It has risen to a value for constant current control, normal transfer circuit control is performed in step S80.

  On the other hand, when it is determined in step S30 that the A / D value is equal to or smaller than the predetermined reference value Iref (step S30: YES), in step S40, the steady mode is turned “OFF” and the start mode is turned “ON”. (Corresponding to time t0 in FIG. 3). This is because the booster circuit 66 is not preferably started in the steady mode from the start of startup, and is therefore an on / off signal, and the booster circuit 66 depends on the startup mode based on the pulsed first drive signal Sd1 having a large level change. It is for starting up. At this time, the second PWM port 62d is switched to the first PWM port 62c, and the PWM signal Sc is supplied from the first PWM port 62c to the start drive circuit 63A.

  Next, after a predetermined time has elapsed, in step S50, as in step S20, the CPU 62 reads the FB signal and obtains a digital value of the current detection signal Si. In step S60, as in step S30, the CPU 62 determines whether the digital current value (A / D value) is equal to or less than the predetermined reference value Iref. When the A / D value is not less than or equal to the predetermined reference value Iref, that is, when the A / D value exceeds the predetermined reference value Iref (step S60: NO), the start mode is turned “OFF” in step S70. Then, the steady mode is turned “ON” (corresponding to time t1 in FIG. 3). This is because the booster circuit 66 is preferably initially started in the start mode, and thus the mode is switched from the start mode to the steady mode. At this time, the first PWM port 62c is switched to the second PWM port 62d, and the PWM signal Sc is supplied from the second PWM port 62d to the steady drive circuit 63B. After the transfer current It has risen to a value for constant current control, normal transfer circuit control is performed in step S80. In other words, the transfer current value is detected, and the transfer voltage applied to the transfer roller (or belt) is controlled so that the value becomes a predetermined value.

  On the other hand, when it is determined in step S60 that the A / D value is equal to or smaller than the predetermined reference value Iref (step S60: YES), the duty ratio of the PWM signal Sc is changed to increase the duty ratio of the first drive signal Sd1. And repeat the process of step S50 and step S60.

  In the flowchart of FIG. 6, the example in which the booster circuit 66 is started in the steady mode, that is, using the smoothed PWM signal Sc is shown, but the present invention is not limited thereto. For example, in step S10, the start mode may be set to “ON” and the steady mode may be set to “OFF”, and step S20, step S30, step S40, and step S45 may be omitted. That is, the start-up control of the booster circuit 66 may be started from the start-up mode at time t0 in FIG.

5. Effects of Embodiment 2 Since the CPU 62 can switch between the first drive signal Sd1 and the second drive signal Sd2 in software, the configuration of the switching means can be simplified.

<Embodiment 3>
Next, Embodiment 3 of the present invention will be described with reference to FIG. FIG. 7 is a schematic block diagram of the high voltage generation circuit 60B of the third embodiment. Since the third embodiment and the first embodiment differ only in the configuration of the high-voltage generation circuit, only the difference will be described. In addition, the same member number is attached | subjected to the structure same as Embodiment 1, and the description is abbreviate | omitted.

  As shown in FIG. 7, the high voltage generation circuit 60B of the third embodiment corresponds to a configuration in which the start drive circuit 63A and the steady drive circuit 63B are further omitted from the high voltage generation circuit 60A of the second embodiment. That is, in the third embodiment, the CPU 62 performs operations corresponding to the operations of the switching circuit 65, the start drive circuit 63A, and the steady drive circuit 63B of the high voltage generation circuit 60 of the first embodiment.

  That is, the CPU 62 drives the current detection signal Si so that the booster circuit 66 is driven in accordance with the first drive signal Sd1 in the start-up mode and is driven in accordance with the second drive signal Sd2 in the steady mode. In response to this, the first drive signal Sd1 and the second drive signal Sd2 are switched. Further, the CPU 62 generates the first drive signal Sd1 in response to the current detection signal Si and supplies the first drive signal Sd1 to the transformer drive circuit 64 via the D / A port 62e in the startup mode. In the mode, the second drive signal Sd2 is generated, and the second drive signal Sd2 is supplied to the transformer drive circuit 64 via the D / A port 62e.

  For this purpose, the waveform data of the first drive signal Sd1 and the second drive signal Sd2 shown in FIG. When the current detection signal Si is equal to or less than the reference value Iref (or Vref), the CPU 62 generates the first drive signal Sd1 from the waveform data of the first drive signal Sd1, and uses the first drive signal Sd1 as the transformer drive circuit. 64. On the other hand, when the current detection signal Si exceeds the reference value Iref, the CPU 62 generates the second drive signal Sd2 from the waveform data of the second drive signal Sd2, and sends the second drive signal Sd2 to the transformer drive circuit 64. Supply. Here, the waveform data of the first drive signal Sd1 and the second drive signal Sd2 stored in the memory 72 stores a plurality of waveform patterns according to printing conditions such as inflow current, and the waveform patterns vary according to the printing conditions. It may be selected.

  Note that the method of forming the first drive signal Sd1 and the second drive signal Sd2 is not limited to the method of storing waveform data. For example, the first drive signal Sd1 is formed by turning on / off a DC signal with a predetermined voltage at a predetermined timing, and the second drive signal Sd2 is increased by a predetermined voltage at a predetermined timing with respect to the DC signal with a predetermined voltage. You may make it form by making it. When the first drive signal Sd1 is formed, the predetermined voltage and / or on-time may be changed.

6). Effects of Embodiment 3 Since the smoothing circuit and the circuit for forming the drive signal can be omitted, the circuit configuration for generating the transfer voltage can be greatly simplified.

<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) In each of the above-described embodiments, an example in which the transfer current It is detected and the transfer current It exceeds a predetermined value is switched from the start mode to the steady mode. However, the present invention is not limited to this. A transfer voltage detecting means for detecting the transfer voltage Vt may be provided, and when the transfer voltage Vt exceeds a predetermined value, the start mode is switched to the steady mode.

  (2) In each of the above embodiments, the example in which the first drive signal Sd1 is formed so as to gradually increase the pulse width while the pulse amplitude remains constant is shown, but the present invention is not limited to this. For example, the first drive signal Sd1 may be formed so as to gradually increase the pulse frequency while keeping the pulse amplitude constant, or gradually increase the pulse amplitude while keeping the pulse width constant. You may form as follows. Alternatively, the first drive signal Sd1 may be formed such that the pulse width and the pulse frequency are gradually increased while the pulse amplitude remains constant.

  (3) In the first and second embodiments, the configuration in which the start drive circuit 63A and the steady drive circuit 63B are provided has been described, but the present invention is not necessarily limited thereto. For example, the steady drive circuit 63B may be omitted, and a smoothing circuit that smoothes the PWM signal Sc may be provided individually. In this case, the PWM signal Sc that is not smoothed is supplied to the startup drive circuit 63A in the startup mode, and the PWM signal Sc that is smoothed is supplied to the startup drive circuit 63A in the steady mode. What should I do? Further, the characteristic adjustment resistor Ra of the activation drive circuit 63A may be configured by a digital potentiometer, and the resistance value may be changed by, for example, the CPU 62 according to mode switching.

1 is a side sectional view of a main part of a printer according to a first embodiment of the invention. 1 is a schematic block diagram of a high voltage generation circuit according to a first embodiment. Time chart related to booster circuit startup Graph showing relationship between transfer current and PWM signal Schematic block diagram of a high voltage generation circuit according to the second embodiment Flow chart of another example for confirming activation of the application circuit Schematic block diagram of a high-voltage generation circuit according to Embodiment 3

Explanation of symbols

1 ... Printer (image forming apparatus)
27. Photosensitive drum (image carrier)
30. Transfer roller (transfer means)
60 ... High voltage generation circuit 62 ... CPU (control means, switching means, part of drive circuit)
63A ... Start-up drive circuit 63B ... Steady drive circuit 64 ... Transformer drive circuit (main drive circuit)
65. Switching circuit (switching means)
66: Booster circuit (applying means)
67 ... Current detection circuit (detection means)
Sd1: first drive signal Sd2: second drive signal Si: current detection signal (detection signal)

Claims (9)

An image carrier that carries a developer image developed by the developer;
Transfer means for transferring the developer image to a recording medium in response to application of a transfer voltage;
Applying means for generating the transfer voltage and applying the transfer voltage to the transfer means;
Detecting means for detecting a signal on the output side of the applying means and generating a detection signal;
Control means for controlling the transfer voltage in accordance with the detection signal;
A drive circuit for generating a first drive signal that is an on / off signal and a second drive signal that is a signal that increases in stages, and that drives the applying means in accordance with the first drive signal and the second drive signal; ,
In the start-up mode for starting the application means, the application means is driven according to the first drive signal, and in the steady mode after start-up, the application means is driven according to the second drive signal. Switching means for switching between the first drive signal and the second drive signal in response to the detection signal;
An image forming apparatus. The image forming apparatus according to claim 1.
The control means generates a control signal for controlling the drive circuit,
The drive circuit is
A startup drive circuit for generating the first drive signal in response to the control signal;
A steady drive circuit that smoothes the control signal and generates the second drive signal in response to the smoothed control signal;
A main drive circuit for driving the applying means in response to the first drive signal and the second drive signal,
The switching means switches between the first drive signal and the second drive signal according to the detection signal, and supplies the first drive signal to the main drive circuit. The image forming apparatus according to claim 1.
The control means includes the switching means and generates a control signal for controlling the drive circuit,
The drive circuit is
A startup drive circuit for generating the first drive signal in response to the control signal;
A steady drive circuit that smoothes the control signal and generates the second drive signal in response to the smoothed control signal;
A main drive circuit for driving the applying means in response to the first drive signal and the second drive signal,
The control means switches between supply of the control signal to the start drive circuit and supply to the steady drive circuit in accordance with the detection signal. The image forming apparatus according to claim 2 or 3,
The control signal is a PWM signal. The image forming apparatus according to claim 1.
The control means includes the switching means,
The drive circuit includes a main drive circuit that drives the application unit according to the first drive signal and the second drive signal,
The control means is responsive to the detection signal,
In the start-up mode, the first drive signal is generated, the first drive signal is supplied to the main drive circuit,
In the steady mode, the second drive signal is generated, and the second drive signal is supplied to the main drive circuit. In the image forming apparatus according to any one of claims 1 to 5,
The detection means detects a current flowing on the output side of the application means,
The detection signal is a current detection signal;
The switching means switches from the startup mode to the steady mode when the value of the current detection signal exceeds a predetermined value. The image forming apparatus according to claim 6.
The predetermined value is varied according to an initial detection value of the current detection signal. The image forming apparatus according to any one of claims 1 to 7,
At the time of mode switching from the startup mode to the steady mode, the value of the output side signal in the steady mode immediately after mode switching is equal to or greater than the value of the output side signal in the startup mode immediately before mode switching. The first drive signal is switched to the second drive signal. In the image forming apparatus according to any one of claims 1 to 8,
The signal characteristic of the first drive signal is formed to gradually increase.

Images