JP2010158111A - Power supply apparatus and image forming apparatus equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply apparatus reducing influence of ripples to output control. <P>SOLUTION: The power supply apparatus includes an output means generating a prescribed output signal It and outputting the output signal It to a load, a detecting means detecting the output signal It outputted by the output means, a control means generating a control signal controlling the output means so that the output signal is within a target signal range based on a detection value of the output signal It, and a range switching means extending the target signal range ΔIt0 when the output signal It is within the target signal range ΔIt0 (time t1, t3 and t5). When the output signal It is out of the extended target signal range ΔIt1 (time t2 and t4), the range switching means narrows the extended target signal range ΔIt1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a power supply device, and more particularly to ripple processing of an output signal of the power supply device.

Conventionally, for example, a technique described in Patent Document 1 is known regarding ripple processing of an output signal of a power supply device. In Patent Document 1, in order to perform stable constant voltage control that does not adversely affect the load, such as ripple current and overcurrent, the current fluctuation detection value is added to the detection value of the output voltage that is the output signal at an appropriate ratio. The value is set as an output detection value. A technique for controlling the output voltage based on the output detection value is shown.
Japanese Patent Laid-Open No. 08-251911

  However, the ripple usually tends to increase as the output signal increases. Therefore, for example, in a power supply device that outputs a high voltage, depending on the degree of setting of the target voltage range (target signal range), the possibility that the output voltage to be controlled is out of the target signal range due to a large ripple increases. To do. When the output voltage deviates from the target signal range, the conventional power supply device and the power supply device described in Patent Document 1 perform control to return the output voltage within the target signal range. There is a possibility that the (output signal) is likely to fluctuate.

  It is an object of the present invention to provide a power supply device that can reduce the influence of ripple on output control when a predetermined output signal is output.

  As means for achieving the above object, the power supply apparatus according to the first invention generates a predetermined output signal and outputs the output signal to a load, and the output means outputs the output signal. Detection means for detecting the output signal; control means for generating a control signal for controlling the output means so that the output signal falls within a target signal range based on a detection value of the output signal; and A power supply apparatus comprising range switching means for expanding the target signal range when the target signal range is entered.

  According to this configuration, when the output signal is out of the target signal range, for example, the target voltage range or the target current range, according to a large ripple caused by generation of a predetermined output signal, for example, the output voltage signal or the output current signal, There are cases where the control of the output signal becomes unstable in response to the ripple of the control means. Even in such a case, by expanding the target signal range, it is possible to reduce the output signal from deviating from the target signal range due to the ripple, and to suppress the influence of the ripple on the output signal control. That is, it is possible to reduce the influence of ripple on the output control when outputting a predetermined signal.

  According to a second invention, in the power supply device of the first invention, the range switching means narrows the extended target signal range when the output signal is out of the extended target signal range.

  According to this configuration, when the output signal is out of the expanded target signal range, there is a high possibility that the cause is not the ripple but the fluctuation of the actual output signal. Therefore, the output signal can be returned to the narrowed target signal range by narrowing the expanded target signal range.

  According to a third invention, in the power supply device according to the second invention, the control means reduces the control change amount of the control signal for a predetermined time after the output signal is out of the expanded target signal range. The range switching means narrows the expanded target signal range after the predetermined time has elapsed.

  According to this configuration, for example, when the output signal is outside the upper limit of the extended target signal range, the extended target signal range is narrowed immediately thereafter, and the output signal is suddenly reduced. It is possible that the output signal is outside the lower limit of the extended target signal range. Therefore, such an inconvenience is suppressed by reducing the control change amount of the control signal for a predetermined time after the output signal deviates from the extended target signal range and then narrowing the extended target signal range. be able to.

  According to a fourth aspect of the present invention, in the power supply device of the second aspect, the detection means shortens the detection interval of the output signal when the output signal is out of the extended target signal range, and the range switching means Is an average value of a plurality of detection values detected at a reduced detection interval, and an average value obtained by removing at least one detection value from the plurality of detection values is obtained, and the average value is expanded. If it is outside the target signal range, the expanded target signal range is narrowed.

  According to this configuration, when the output signal is outside the extended target signal range, immediately after that, at least one detection value, for example, an average value of a plurality of detection values excluding the maximum value and the minimum value is obtained. And determining whether the average value is within the extended target signal range. In other words, it is determined whether the cause of the output signal being out of the expanded target signal range is noise (which is considered to be the cause of the maximum and minimum detection values), and the cause of out of the target signal range is noise. In some cases, the extended target signal range cannot be narrowed. Therefore, the influence of noise in output signal control can be reduced.

According to a fifth invention, in the power supply device of the fourth invention, the at least one detection value includes a maximum value and a minimum value of the plurality of detection values.
According to this configuration, when noise exists, the result is highly likely to be detected as the maximum value and the minimum value of the detection values. Therefore, the influence of noise can be suitably reduced.

According to a sixth invention, in the power supply device according to any one of the second to fifth inventions, the range switching means narrows the target signal range before the expanded target signal range is expanded.
According to this configuration, the target signal range can be returned to the original target signal range.

According to a seventh invention, in the power supply device according to any one of the first to sixth inventions, the range switching means increases the upper limit of the target signal range and decreases the lower limit of the target signal range. , Extending the target signal range.
According to this configuration, the fluctuation of the output signal due to the ripple can be suitably stored within the expanded target signal range according to the shape and size of the ripple waveform.

According to an eighth invention, in the power supply device according to any one of the first to seventh inventions, a setting unit that sets an extension amount of the target signal range by the range switching unit according to a magnitude of a ripple of the output signal. Is further provided.
According to this configuration, the influence of ripple can be reduced without unnecessarily extending the target signal range excessively.

  According to a ninth invention, in the power supply device according to the eighth invention, the setting means estimates the magnitude of the ripple based on at least one of a target signal value of the output signal, the load, and the control signal. To do.

  According to this configuration, for example, table data indicating the relationship between the target signal value of the output signal and the magnitude of the ripple, or table data indicating the relationship between the magnitude of the load and the magnitude of the ripple, or the size of the control signal (control Table data indicating the relationship between the voltage value) and the magnitude of the ripple is provided in the storage device. The setting means can estimate the magnitude of the ripple with a simple configuration by referring to the table data.

According to a tenth aspect of the present invention, in the power supply device of the eighth aspect of the present invention, the power supply device further includes a measuring unit that measures the ripple.
According to this configuration, since the magnitude of the ripple is actually measured, the amount of expansion of the target signal range can be set more suitably than when the ripple is estimated.

According to an eleventh aspect of the present invention, there is provided an image forming apparatus that uses the power supply device according to any one of the first to tenth aspects and the output signal output from the output unit of the power supply device to generate an image on a recording medium. An image forming unit to be formed.
According to this configuration, even when a ripple is included in the output signal used to form an image, a predetermined image quality is maintained.

  According to the power supply device of the present invention, it is possible to reduce the influence of ripple on output control when outputting an output signal.

<Embodiment>
An embodiment in which a power supply device according to the present invention is used in a laser printer as an image forming apparatus will be described with reference to FIGS. The image forming apparatus is not limited to a laser printer, and may be, for example, an LED printer, a facsimile machine, or a multifunction machine having a copy function and a scanner function. Furthermore, the application of the power supply device according to the present invention is not limited to the image forming apparatus, and can be applied to any device using the power supply device.

1. 1 is a schematic sectional side view of a main part of a laser printer. In FIG. 1, a laser printer (hereinafter simply referred to as “printer”) 1 includes a feeder unit 4 for feeding paper (an example of “recording medium”) 3 in a main body frame 2, An image forming unit 5 for forming an image on the sheet 3 is provided.

(1) Feeder unit The feeder unit 4 is provided at the bottom of the main body frame 2, and the one end side (hereinafter, one end side (the right side in FIG. 1)) of the sheet feed tray 6 is the front side and the opposite side. The sheet feeding roller 8 provided above the end (the left side in FIG. 1 is the rear side in FIG. 1), the registration roller 12 provided on the downstream side in the conveyance direction of the sheet 3 with respect to the sheet feeding roller 8, and the like are included.

  The uppermost sheet 3 of the sheet feeding tray 6 is fed one by one by the rotation of the sheet feeding roller 8. The fed paper 3 is sent to the registration roller 12. The registration roller 12 sends the paper 3 to the image forming position after registration. The image forming position is a contact position between the photosensitive drum 27 and the transfer roller 30.

(2) Image Forming Unit The image forming unit 5 includes a scanner unit 16, a process cartridge 17, and a fixing unit 18.
The scanner unit 16 is provided at an upper portion in the main body frame 2 and includes a laser light emitting unit (not shown), a polygon mirror, a reflecting mirror, and the like. The laser beam based on the image data emitted from the laser light emitting unit is irradiated on the surface of the photosensitive drum 27 by high-speed scanning through a polygon mirror, a reflecting mirror, etc., as indicated by a chain line.

  The process cartridge 17 is provided below the scanner unit 16 and includes a drum unit 51 and a developing cartridge 28 accommodated in the drum unit 51. The developing cartridge 28 is detachably accommodated in the drum unit 51, and includes, for example, a developing roller 31, a supply roller 33, a toner hopper 34, and the like.

  The toner hopper 34 is filled with toner (developer). A supply roller 33 is provided at a position behind the toner hopper 34, and a developing roller 31 is provided so as to face the supply roller 33. A predetermined developing bias voltage is applied to the developing roller 31 during development. The toner discharged from the toner hopper 34 is supplied to the developing roller 31 by the rotation of the supply roller 33.

  The drum unit 51 includes a photosensitive drum 27, a scorotron charger 29, a transfer roller 30, and the like. The photosensitive drum 27 is disposed to face the developing roller 31 and includes a cylindrical drum main body and a metal drum shaft 27a that is grounded to the shaft center of the drum main body. A positively chargeable photosensitive layer is formed on the surface of the drum body. An exposure window is provided above the photosensitive drum 27 as a laser beam path.

  The charger 29 is disposed above the photoconductor drum 27 so as to face the photoconductor drum 27 at a predetermined interval so as not to contact the photoconductor drum 27. The charger 29 includes a charging wire 29a and a grid 29b, and the surface of the photosensitive drum 27 is uniformly charged to, for example, positive polarity (for example, about 870 V) through the grid 29b by discharging from the charging wire 29a. Let A predetermined charging voltage (for example, 5 kV to 8 kV) is applied to the charging wire 29a.

  The surface of the photosensitive drum 27 is first uniformly charged positively by the charger 29 as the photosensitive drum 27 rotates. Thereafter, the charged surface is exposed by high-speed scanning of the laser beam from the scanner unit 16, and an electrostatic latent image based on the image data is formed. Next, by the rotation of the developing roller 31, the toner carried on the surface of the developing roller 31 and charged positively is supplied to the electrostatic latent image on the surface of the photosensitive drum 27, and the electrostatic latent image is Developed.

  The transfer roller 30 has a metal roller shaft 30 a and is disposed below the photosensitive drum 27 so as to face the photosensitive drum 27. The roller shaft 30a is covered with a roller made of, for example, a conductive rubber material.

  As shown in FIG. 2, a bias application circuit (an example of a “power supply device” according to the present invention) 60 is connected to the roller shaft 30 a of the transfer roller 30. Then, during a transfer operation for transferring the toner image carried on the developing roller 31 to the paper 3 at the transfer position, a transfer bias voltage (high voltage of −6 kV, for example) is applied to the roller shaft 30 a of the transfer roller 30 from the bias application circuit 60. Voltage) Vt is applied.

  As shown in FIG. 1, the fixing unit 18 is provided on the rear downstream side of the process cartridge 17. In the fixing unit 18, the toner transferred onto the paper 3 is thermally fixed, and then the paper 3 is discharged onto the paper discharge tray 46.

2. Bias application circuit (power supply)
Next, the bias application circuit 60 will be described with reference to FIG. FIG. 2 is a block diagram of a main configuration of a bias application circuit 60 that applies the transfer bias voltage Vt to the transfer roller 30.

  The bias application circuit 60 includes a CPU (an example of “control unit”, “range switching unit”, and “setting unit”) 61 and a transfer bias application circuit that generates and outputs a transfer bias voltage Vt (an example of “output unit”). 62. The transfer bias application circuit 62 is connected to a connection line 90 connected to the roller shaft 30 a of the transfer roller 30. In addition to the control of the bias application circuit 60, the CPU 61 also controls each part of the printer 1 related to image formation.

  The bias application circuit 60 includes an output detection circuit 84 that outputs a detection signal S3 corresponding to the value of a transfer current (an example of an “output signal”) It flowing in the connection line 90. Here, the output detection circuit 84 includes, for example, a detection resistor 89. A control signal Vcn for controlling the transfer bias application circuit 62 is generated based on the detection signal S3. The detection signal S3 is also used to calculate the load (load resistance) of the bias application circuit 60. The calculated load is used to estimate the ripple of the transfer current It, for example, as will be described later. The bias application circuit 60 includes a circuit for generating other high voltage, for example, a charging voltage, but the illustration thereof is omitted.

  The transfer bias application circuit 62 is subjected to constant current control by PWM (Pulse Width Modulation) control of the CPU 61. The memory 61 is connected to the CPU 61. The memory 100 stores a program for controlling the bias application circuit 60, a predetermined count value of the counter, various table data, and the like.

  The transfer bias application circuit 62 is a high voltage (negative voltage) generation circuit, and includes a PWM signal smoothing circuit 70, a transformer drive circuit 71, a boosting / smoothing rectifier circuit 72, and an output voltage detection circuit (an example of “detection means”) 73. including.

  The PWM signal smoothing circuit 70 smoothes the PWM signal S1 from the PWM port 61a of the CPU 61, and provides the smoothed PWM signal S1 to the transformer drive circuit 71. The transformer drive circuit 71 supplies an oscillation current to the primary winding 75b of the step-up / smoothing rectifier circuit 72 based on the smoothed PWM signal S1. The CPU 61 controls the duty ratio (pulse width) of the PWM signal S1 based on the voltage value of the control signal Vcn that controls the transfer bias voltage Vt and the transfer current It.

  The step-up / smoothing rectifier circuit 72 includes a transformer 75, a diode 76, a smoothing capacitor 77, and the like. The transformer 75 includes a secondary winding 75a, a primary winding 75b, and an auxiliary winding 75c. One end of the secondary winding 75 a is connected to the connection line 90 via the diode 76. On the other hand, the other end of the secondary winding 75 a is connected to the output detection circuit 84. A smoothing capacitor 77 and a resistor 78 are connected in parallel to the secondary winding 75a.

  With such a configuration, the voltage of the primary winding 75b is boosted and rectified in the boosting / smoothing rectifier circuit 72, and transferred to the roller shaft 30a of the transfer roller 30 connected to the output terminal A of the bias applying circuit 60. Applied as voltage Vt.

  The output voltage detection circuit 73 is connected to the auxiliary winding 75 c of the transformer 75 of the step-up / smoothing rectifier circuit 72 and the CPU 61. The output voltage detection circuit 73 detects the output voltage Vd generated between the auxiliary windings 75c during the transfer operation by the transfer bias application circuit 62, and supplies the detection signal S2 to the A / D port 61b of the CPU 61. . The CPU 61 detects the transfer output voltage Vt based on the detection signal S2.

  At that time, the CPU 61 further generates a control signal Vcn based on the detection signal S3 corresponding to the transfer current value It flowing in the connection line 90, and the transfer current value It is set to the target current range (“target” based on the control signal Vcn. The duty ratio of the PWM signal S1 is appropriately changed so as to be within an example of “signal range”. That is, the CPU 61 performs constant current control on the transfer current value It.

3. Range Switching Control of Target Current Range (Target Signal Range) Next, range switching control of the target current range of the transfer current It according to the present invention will be described with reference to FIGS. First, a basic concept common to the following embodiments will be described with reference to FIG. FIG. 3 is a time chart schematically showing the present invention. If the transfer current It enters the target current range ΔIt0 at time t1 in FIG. 3 when the transfer current It increases due to the application of the transfer bias voltage Vt, the CPU 61 sets the target current range ΔIt0 to the extended target current range ΔIt1. Switch. In other words, the CPU 61 increases the target upper limit current Itu0 of the transfer current It by the expansion amount “A” to obtain the expansion target upper limit current Itu1, and decreases the target lower limit current Itd0 of the transfer current It by the expansion amount “B”. The lower limit current Itd1 is assumed.

  As described above, the reason why the target current range ΔIt0 is expanded when the transfer current It enters the target current range ΔIt0 is as follows. A ripple also occurs in the transfer current It according to a large ripple caused by the generation of the transfer bias voltage Vt which is a high voltage. When the transfer current It deviates from the target current range ΔIt0 in accordance with the ripple (see P1 to P5 in FIG. 3), the CPU 61 may respond to the ripple and the control of the transfer current It may become unstable. Even in such a case, by expanding the target current range ΔIt0, it is possible to reduce the fact that the transfer current It deviates from the target current range due to the ripple, and to suppress the influence of the ripple on the output control. That is, to reduce the influence of ripple on the output current control. Next, an embodiment based on the basic concept shown in FIG. 3 will be described.

Example 1
First, Example 1 will be described with reference to FIGS. In the first embodiment, when the transfer current It deviates from the extended target current range ΔIt1, the CPU 61 narrows the extended target current range ΔIt1 to the original target current range ΔIt0. FIG. 4 is a flowchart illustrating each process related to the range switching of the target current range of the transfer current It in the first embodiment. Each process is executed by the CPU 61 according to a predetermined program. FIG. 5 is a time chart schematically showing a range switching mode of the target current range of the transfer current It in the first embodiment.

  When the printing process is started by a user's printing instruction to the printer 1, the CPU 61 first performs an initial setting process in step S110 of FIG. The CPU 61 sets a target upper limit current Itu0 and a target lower limit current Itd0 of the transfer current It, that is, a target current range ΔIt0. Further, the CPU 61 sets the control mode MODE to the up mode UP and sets “zero” V to the control voltage Vcn. Here, the control voltage Vcn is a voltage for controlling the transfer bias applying circuit 62 as described above, and the duty ratio of the PWM signal S1 is set based on the control voltage Vcn.

  Next, in step S115, the CPU 61 sets the expansion amount (“A” and “B”) of the target current range ΔIt0 according to the ripple magnitude of the transfer current It. At this time, the magnitude of the ripple is estimated based on at least one of the target current value (or target current range) of the transfer current It, the load of the bias application circuit 60, and the voltage value of the control signal Vcn. At this time, for example, table data indicating the relationship between the target current value (or target current range) of the transfer current It and the magnitude of the ripple, or table data indicating the relationship between the magnitude of the load and the magnitude of the ripple, or a control signal Table data indicating the relationship between the magnitude of Vcn (control voltage value) and the magnitude of ripple is provided in the memory 100. Then, the CPU 61 estimates the magnitude of the ripple by referring to the table data. Then, the expansion amounts (“A” and “B”) are set according to the estimated ripple magnitude.

  Next, in step S120, the CPU 61 reads the transfer current It via the output detection circuit 84. In step S125, the CPU 61 determines whether the transfer current It is larger than the target upper limit current (upper limit value) Itu0. If it is determined in step S125 that the transfer current It is not larger than the target upper limit current Utu0, in step S130, the CPU 61 determines whether the transfer current It is smaller than the target lower limit current (lower limit value) Itd0.

  If it is determined in step S130 that the transfer current It is smaller than the target lower limit current Itd0, that is, for example, before time t1 in FIG. 5, the control mode MODE is currently in the drive mode DRV in step S135. Determine if it exists. Here, the drive mode DRV is a mode in which the transfer bias application circuit 62 is controlled by the constant control voltage Vcn when the transfer current It is in the target current range.

  If it is determined in step S135 that the control mode MODE is not currently the drive mode DRV, in step S140, the CPU 61 increases the control voltage Vcn by the predetermined increase amount UD1, and sets the control mode MODE to the up mode UP. . Then, the process proceeds to step S175, and waits for a predetermined time for which the transfer current It is stabilized, for example, 1 ms. Here, processing up to step S130, step S135, step S140, and step S175 corresponds to time t1 in FIG. That is, it corresponds to a period during which the transfer current It is initially increased to the target lower limit current Itd0.

  On the other hand, when the transfer current It reaches the target lower limit current Itd0 at time t1 in FIG. 5, that is, when the transfer current It enters the target current range ΔIt0, a “NO” determination is made in step S130, and the process proceeds to step S145. Migrate to In step S145, since the control mode MODE is currently the up mode UP, a “NO” determination is made, and the process proceeds to step S150.

  In step S150, since the transfer current It has reached the target lower limit current Itd0, the CPU 61 switches the target current range ΔIt0 to the extended target current range ΔIt1 as described above. In other words, the CPU 61 increases the target upper limit current Itu0 of the transfer current It by the expansion amount “A” to obtain the expansion target upper limit current Itu1, and decreases the target lower limit current Itd0 of the transfer current It by the expansion amount “B”. The lower limit current Itd1 is assumed. Further, the control mode MODE is changed from the up mode UP to the drive mode DRV.

  Next, in step S175, the process waits for 1 ms. In step S180, it is determined whether the printing process is finished and the application of the transfer bias voltage Vt is finished. If the printing process has not been completed, the process returns to step S120 and is repeated until the printing process is completed.

  At this time, for example, as shown at time t2 in FIG. 5, when the transfer current It falls below the target lower limit current, in this case, the expansion target lower limit current Itd1, “YES” determination is made in step S130 and step S135. Then, the process proceeds to step S170.

  In step S170, the CPU 61 narrows the extended target current range ΔIt1 to the target current range ΔIt0. That is, the CPU 61 decreases the target upper limit current Itu0 of the transfer current It by the extension amount “A” to the target upper limit current Itu0, increases the target lower limit current Itd0 of the transfer current It by the extension amount “B”, and sets the target lower limit current. It is assumed to be Itd0. In order to increase the transfer current It, the control mode MODE is changed from the drive mode DRV to the up mode UP in step S140.

  Accordingly, at time t3 in FIG. 5, the transfer current It reaches the target lower limit current Itd0, so that the target current range ΔIt0 is switched again to the extended target current range ΔIt1 (step S150). Then, as shown at time t4 in FIG. 5, when the transfer current It exceeds the target upper limit current, in this case, the extended target upper limit current Itu1, “YES” determination is made in step S125 and step S155, and thus the process is step. The process proceeds to S160.

  In step S160, as in step S170, the CPU 61 narrows the extended target current range ΔIt1 to the target current range ΔIt0. In order to decrease the transfer current It, in step S165, the CPU 61 decreases the control voltage Vcn by a predetermined decrease amount DD1, and sets the control mode MODE to the down mode DOWN. Next, the process proceeds to step S175 and waits for 1 ms.

(Effect of Example 1)
As described above, in the first embodiment, when the transfer current It enters the target current range ΔIt0, the CPU 61 extends the target current range ΔIt0 to the extended target current range ΔIt1, and thereafter, the transfer current It becomes the extended target. When the current range is out of the current range ΔIt1, the extended target current range ΔIt1 is narrowed to the target current range ΔIt0. Usually, when the transfer current It deviates from the extended target current range ΔIt1, there is a high possibility that the cause is not a ripple but a fluctuation of the transfer current It. Therefore, even when the transfer current It varies, the transfer current It can be returned to the narrowed target current range ΔIt0 by narrowing the extended target current range ΔIt1.

(Example 2)
Next, Example 2 will be described with reference to FIGS. FIG. 6 is a flowchart illustrating each process related to the range switching of the target current range of the transfer current It in the second embodiment. Each process is executed by the CPU 61 as in the first embodiment. FIG. 7 is a time chart schematically showing a range switching mode of the target current range of the transfer current It in the second embodiment. In FIG. 6, the same processes as those in the flowchart of FIG. 4 of the first embodiment are denoted by the same step numbers, description thereof is omitted, and only differences from the first embodiment are described.

  The difference of Example 2 from Example 1 is as follows. That is, in Example 2, when the transfer current It deviates from the extended target current range ΔIt1, the CPU 61 reduces the control change amount of the control voltage Vcn for a predetermined time, and after the predetermined time has elapsed, the extended target current range. ΔIt1 is narrowed.

  That is, in the second embodiment, unlike the first embodiment, when the transfer current It deviates from the extended target current range ΔIt1, the extended target current range ΔIt1 is not narrowed immediately thereafter. The reason is as follows.

  For example, when the transfer current It deviates from the upper limit Itu1 of the extended target current range ΔIt1, immediately after that, if the extended target current range ΔIt1 is narrowed to reduce the transfer current It suddenly, depending on the property of the ripple, the transfer current It May continuously deviate from the lower limit Itd1 of the extended target current range ΔIt1. Such a sudden change in the transfer current It affects the stability of the output control. For this reason, the sudden change is suppressed by reducing the control change amount of the control voltage Vcn for a predetermined time after the transfer current It deviates from the extended target current range ΔIt1, and then narrowing the extended target current range ΔIt1. It is to do.

  In the initial setting process in step S110A of FIG. 6, the CPU 61 further sets the count values CNT1 and CNT2 to “zero”. The count value CNT1 is a count value for measuring the predetermined time K1 shown in FIG. 7, and the count value CNT2 is a count value for measuring the predetermined time K2 shown in FIG.

  If the transfer current It deviates from the extended target current range ΔIt1 at time t2 in FIG. 7, “YES” determination is made in step S125 and step S155 in FIG. 6, and the process proceeds to step S220. In step S220, the CPU 61 determines whether or not the count value CNT1 exceeds “2”, for example.

  If the count value CNT1 exceeds “2”, the CPU 61 narrows the extended target current range ΔIt1 to the target current range ΔIt0 in step S160 (time t3 in FIG. 7) assuming that the predetermined period K1 (see FIG. 7) has elapsed. Equivalent). On the other hand, when the count value CNT1 does not exceed “2”, in step S230, the CPU 61 decreases the control voltage Vcn by a predetermined decrease amount (control change amount) DD2. Here, the predetermined decrease amount DD2 is a value smaller than the predetermined decrease amount DD1 in step S165. That is, in the predetermined period K1 shown in FIG. 7, the control change amount of the control voltage Vcn is reduced to suppress the decrease amount of the transfer current It. Then, the count value CNT1 is incremented.

  Next, when the transfer current It enters the target current range ΔIt0 at time t4 in FIG. 7, the target current range ΔIt0 is expanded to the extended target current range ΔIt1. That is, “NO” determination is made at step S125, step S130, and step S145 in FIG. 6, and the process proceeds to step S150. In step S210, the count values CNT1 and CNT2 are cleared to “zero”.

  Next, when the transfer current It deviates from the extended target current range ΔIt1 at time t5 in FIG. 7, “NO” is determined in step S125 in FIG. 6, “YES” is determined in steps S130 and S135, and step The process proceeds to S240.

  In step S240, the CPU 61 determines whether or not the count value CNT2 exceeds “2”, for example. When the count value CNT2 exceeds “2”, the CPU 61 narrows the expanded target current range ΔIt1 to the target current range ΔIt0 (step t6 in FIG. 7) in step S170, assuming that the predetermined period K2 (see FIG. 7) has elapsed. Equivalent). On the other hand, if the count value CNT2 does not exceed “2”, in step S250, the CPU 61 increases the control voltage Vcn by a predetermined increase amount (control change amount) UD2. Here, the predetermined increase amount UD2 is a value smaller than the predetermined increase amount UD1 in step S140. That is, in the predetermined period K2 shown in FIG. 7, the control change amount of the control voltage Vcn is reduced to suppress the increase amount of the transfer current It. Then, the count value CNT2 is incremented.

  Next, when the transfer current It enters the target current range ΔIt0 at time t7 in FIG. 7, the target current range ΔIt0 is expanded to the extended target current range ΔIt1. That is, “NO” determination is made at step S125, step S130, and step S145 in FIG. 6, and the process proceeds to step S150. In step S210, the count values CNT1 and CNT2 are cleared to “zero”. Note that the determination count value “2” in step S220 and step S240 is arbitrary. That is, the predetermined periods K1 and K2 are periods that are set as appropriate, and the predetermined period K1 and the predetermined period K2 may have different time lengths.

(Effect of Example 2)
As described above, in the second embodiment, when the transfer current It deviates from the extended target current range ΔIt1, the CPU 61 reduces the control change amount of the control voltage Vcn for a predetermined time (K1, K2). After the elapse of (K1, K2), the expansion target current range ΔIt1 is narrowed. Therefore, for example, when the transfer current It deviates from the upper limit Itu1 of the extended target current range ΔIt1, immediately after that, if the extended target current range ΔIt1 is narrowed and the transfer current It is suddenly reduced, depending on the property of the ripple, It is possible that the current It continues to deviate from the lower limit Itd1 of the extended target current range ΔIt1. It affects output control. Therefore, the control change amount of the control voltage Vcn is reduced for a predetermined time (K1, K2) after the transfer current It deviates from the expansion target current range ΔIt1, and then the expansion target current range ΔIt1 is narrowed. Inconvenience is suppressed.

(Example 3)
Next, Example 3 will be described with reference to FIGS. FIG. 8 is a flowchart illustrating each process related to the range switching of the target current range of the transfer current It in the third embodiment. FIG. 9 is a flowchart showing the “It multiple reading” routine in the flowchart of FIG. 8. Each process is executed by the CPU 61 as in the first embodiment. FIG. 10 is a time chart schematically showing a range switching mode of the target current range of the transfer current It in the third embodiment. In FIG. 8, the same processes as those in the flowchart of FIG. 4 of the first embodiment are denoted by the same step numbers, the description thereof is omitted, and only differences from the first embodiment will be described.

  The difference between the third embodiment and the first embodiment is as follows. That is, in the third embodiment, when the transfer current It deviates from the extended target current range ΔIt1, the detection interval of the transfer current It is shortened. In addition, the CPU 61 obtains an average value of a plurality of detection values detected in the shortened detection interval and excluding the maximum value and the minimum value of the plurality of detection values. Only when the average value is outside the expansion target current range ΔIt1, the expansion target current range ΔIt1 is narrowed. The reason is as follows.

  When the transfer current It deviates from the extended target current range ΔIt1, the cause may be noise. Therefore, when the transfer current It deviates from the extended target current range ΔIt1, immediately after that, an average value of a plurality of detected values excluding the maximum value and the minimum value of the detected value of the transfer current It is obtained, and the average value is It is determined whether it is within the extended target current range ΔIt1. Thereby, it is determined whether or not the cause of the transfer current It deviating from the extended target current range ΔIt1 is noise. Then, when the factor that deviates from the expansion target current range ΔIt1 is noise, the expansion target current range ΔIt1 is not narrowed to reduce the influence of noise in the output voltage control.

  Assuming that the transfer current It deviates below the extended target current range ΔIt1 at time t2 in FIG. 10, “NO” is determined in step S125 in FIG. 8, “YES” is determined in steps S130 and S135, and step The process proceeds to the S300 “It multiple reading” routine.

  In step S301 of the “It multiple reading” routine shown in FIG. 9, the transfer current It is read, and in step S302, it waits for a predetermined time, for example, 0.1 ms. This standby time is shorter than the standby time of 1 ms in step S175 of FIG. This is to shorten the detection interval of the transfer current It.

  Next, in step S302, it is determined whether or not the number of readings of the transfer current It from time t2 in FIG. 10 has reached a predetermined number, for example, 10 times. If the number of readings has not reached the predetermined number, the process returns to step S301 to read the transfer current It. On the other hand, when the number of readings reaches the predetermined number, in step S304, the CPU 61 obtains an average value of the transfer current It from the detection data read a predetermined number of times. Here, when obtaining the average value, the CPU 61 obtains an average value excluding the maximum value and the minimum value (an example of “at least one detection value”) among the plurality of detection values. This is to eliminate detection values that are considered to be related to noise. And it returns to the process of step S310 of FIG.

  In step S310, the CPU 61 determines whether or not the average value of the transfer current It is smaller than the lower limit value Itd1. When it is determined that the average value is smaller than the lower limit Itd1, the process proceeds to step S170, and the extended target current range ΔIt1 is narrowed to the target current range ΔIt0 (time t3 in FIG. 10). On the other hand, if it is determined that the average value is not smaller than the lower limit Itd1, the process proceeds to step S175. That is, in this case, it is determined that the transfer current It deviated from the extended target current range ΔIt1 due to noise, and the extended target current range ΔIt1 is not narrowed (corresponding to time t6 in FIG. 10).

  Next, when the transfer current It enters the target current range ΔIt0 at time t4 in FIG. 10, the target current range ΔIt0 is expanded to the extended target current range ΔIt1. That is, “NO” determination is made at step S125, step S130, and step S145 of FIG. 8, and the process proceeds to step S150.

  Next, when the transfer current It deviates upward from the extended target current range ΔIt1 at time t5 in FIG. 10, “YES” determination is made in step S125 and step S155 in FIG. 8, and the process proceeds to step S320. In step S320, as in step S300, the “It multiple reading” routine is executed, and the average value of the transfer current It is obtained.

  In step S330, the CPU 61 determines whether the average value of the transfer current It is greater than the upper limit value Itu1. When it is determined that the average value is larger than the upper limit value Itu1, the process proceeds to step S160, and the extended target current range ΔIt1 is narrowed to the target current range ΔIt0. On the other hand, if it is determined that the average value is not larger than the upper limit value Itu1, the process proceeds to step S175. That is, in this case, it is determined that the transfer current It deviated from the extended target current range ΔIt1 due to noise, and the extended target current range ΔIt1 is not narrowed (corresponding to time t5 in FIG. 10).

(Effect of Example 3)
As described above, in the third embodiment, when the transfer current It deviates from the expanded target current range ΔIt1, the CPU 61 immediately after the transfer current It excluding the maximum value and the minimum value, Find the average of the detected values. Then, it is determined whether or not the average value is within the extended target current range ΔIt1. That is, in the third embodiment, it is determined whether or not the factor that causes the transfer current It to deviate from the extended target current range ΔIt1 is noise (considered as the factor of the maximum value and the minimum value of the detection value). When it is considered that the factor that deviates from the expansion target current range ΔIt1 is noise other than the output control, the expansion target current range ΔIt1 is not narrowed. Therefore, the influence of noise in output control is reduced.

<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 the embodiment described above, the magnitude of the ripple is estimated based on the target current value of the transfer current It, and the amount of expansion is determined according to the estimated magnitude of ripple (hereinafter referred to as “ripple amount”). Although an example of setting ("A" and "B") has been shown, the present invention is not limited to this. As shown in FIGS. 11 and 12, the magnitude of the ripple may be measured by a measuring unit that measures the amount of ripple.

  FIG. 11 shows a case where the “ripple measurement” routine process of step S400 is provided instead of the process of step S115 in FIG. The “ripple measurement” routine is executed by the CPU (an example of “measuring means”) 61 when “NO” is determined in step S125, step S130, and step S145 of FIG. That is, the “ripple measurement” routine is executed, for example, at time t1 in FIG. 3 when the transfer current It increases and reaches the lower limit Itd0.

  In step S410 of the “ripple measurement” routine shown in FIG. 12, the transfer current It is read, and in step S420, it waits for a predetermined time, for example, 0.1 ms. This standby time is shorter than the standby time of 1 ms in step S175 of FIG. This is because the detection time of the ripple amount is performed in a short time.

  Next, in step S430, it is determined whether or not the number of readings of the transfer current It has reached a predetermined number, for example, 10 times. If the number of readings has not reached the predetermined number, the process returns to step S410 and the transfer current It is read. On the other hand, when the read count reaches the predetermined count, in step S440, the CPU 61 obtains the maximum value It (MAX) and the minimum value It (MIN) of the transfer current It from the detection data read a predetermined number of times.

  Next, in step S450, the difference between the maximum value It (MAX) and the minimum value It (MIN) is set as the expansion amount ("A" and "B"), and the process returns to step S150 in FIG. That is, here, the difference (MAX−MIN) between the maximum value It (MAX) and the minimum value It (MIN) is measured as the ripple amount, and the ripple amount is set as the expansion amount (“A” and “B”). Is done.

  In this case, since the expansion amounts (“A” and “B”) are set based on the actually measured ripple amount, the expansion amounts (“A” and “B”) are compared with the case where the ripple amount is estimated. ) Can be set more suitably. In addition, the setting mode of the expansion amount (“A” and “B”) by the ripple amount is not limited to this. For example, 70% of the difference (MAX−MIN) may be set as the expansion amount (“A” and “B”). Alternatively, 80% of the difference (MAX−MIN) may be set as the expansion amount “A”, and 50% of the difference (MAX−MIN) may be set as the expansion amount “B”.

  (2) In the above embodiment, when the transfer current It deviates from the expansion target current range ΔIt1, the example in which the expansion target current range ΔIt1 is narrowed to the original target current range ΔIt0 has been described. However, the expansion target current range ΔIt1 is narrowed. The aspect is not limited to this. For example, the extended target current range ΔIt1 may be narrowed to be wider than the original target current range ΔIt0, or may be narrowed to be narrower than the original target current range ΔIt0.

  (3) In the above embodiment, when the target current range ΔIt0 is expanded to the extended target current range ΔIt1, the target upper limit current (upper limit of the target current range) Itu0 is increased and the target lower limit current (lower limit of the target current range) is increased. ) Although an example of decreasing Itd0 has been shown, the present invention is not limited to this. For example, only the target upper limit current Itu0 may be increased, or only the target lower limit current Itd0 may be decreased.

  Also, in the case where the expansion target current range ΔIt1 is narrowed to the target current range ΔIt0, the example in which the expansion target upper limit current Itu1 is decreased and the expansion target lower limit current Itd1 is increased is shown, but the present invention is not limited thereto. For example, only the expansion target upper limit current Itu1 may be decreased, or only the expansion target lower limit current Itd1 may be increased.

  (4) In the above embodiment, the example in which the expansion amount “A”, which is the expansion amount of the target current range ΔIt0, is the same amount as the expansion amount “B” is shown, but the present invention is not limited to this. That is, the expansion amount “A” and the expansion amount “B” may be different amounts.

  Further, when the target current range ΔIt0 is expanded to the expanded target current range ΔIt1, and when the expanded target current range ΔIt1 is narrowed to the target current range ΔIt0, the expansion amount “A” and the expansion amount “B” that are equal amounts, respectively. Although the example which uses is shown, it is not restricted to this. For example, when the expansion target current range ΔIt1 is narrowed to the target current range ΔIt0, the expansion amount “C” that is different from the expansion amount “A” and the expansion amount “B” and the expansion amount that is different from the expansion amount “C” “D” may be used.

  (5) In the above embodiment, the example in which the maximum value and the minimum value are excluded from the plurality of detection values when the average value of the transfer current It is obtained in step S304 in FIG. 9 is shown. I can't. For example, only the maximum value may be excluded, or detection values having a size from the maximum value to the third may be excluded. In short, at least one detection value considered to be related to noise may be removed.

  (6) In each example of the above embodiment, when the transfer current It first reaches the target current range ΔIt0 (time t1), the ripple amount may be detected. Then, when the detected ripple amount exceeds a predetermined value, the target current range ΔIt0 may be extended to the extended target current range ΔIt1. At this time, for example, the “ripple measurement” routine shown in step S400 of FIG. 11 may be executed to detect the ripple amount. When it is assumed that the ripple amount of the transfer current It is smaller than the predetermined amount and the transfer current It does not deviate from the target current range ΔIt0, it is not necessary to extend the target current range ΔIt0. Therefore, according to this configuration, it is possible to omit an unnecessary process of extending the target current range ΔIt0.

  (7) In the above embodiment and other embodiments, the example in which the “output signal” in the present invention is the transfer current It that is a current signal has been described, but the present invention is not limited to this. The present invention can also be applied when the “output signal” is, for example, a voltage signal. In this case, the target voltage range corresponds to the “target signal range” in the present invention, and the expanded target voltage range corresponds to the “expanded target signal range” in the present invention.

1 is a side sectional view showing an internal configuration of a laser printer according to the present invention. The block diagram of the principal part structure of the bias application circuit which concerns on one Embodiment of this invention. Time chart showing the basic concept of the present invention Flowchart showing range switching processing according to the first embodiment. Time chart related to the processing of FIG. Flowchart illustrating range switching processing according to the second embodiment. Time chart related to the processing of FIG. Flowchart showing range switching processing according to Embodiment 3 Flowchart showing the “It multiple reading” routine in the third embodiment Time chart related to the processing of FIG. The flowchart which shows the processing content which concerns on another Example. Flowchart showing "ripple measurement" routine in another embodiment

Explanation of symbols

1. Laser printer (image forming device)
60: Bias application circuit (power supply device)
61 ... CPU (control means, range switching means, setting means, measurement means)
62: Transfer bias application circuit (output means)
84 ... Output detection circuit (detection means)
It ... Transfer current (output signal)

Claims (11)

Output means for generating a predetermined output signal and outputting the output signal to a load;
Detecting means for detecting the output signal output by the output means;
Control means for generating a control signal for controlling the output means so that the output signal falls within a target signal range based on a detection value of the output signal;
When the output signal enters the target signal range, range switching means for extending the target signal range;
Power supply unit with The power supply device according to claim 1,
The range switching means narrows the expanded target signal range when the output signal deviates from the expanded target signal range. The power supply device according to claim 2,
The control means reduces a control change amount of the control signal for a predetermined time after the output signal is out of the extended target signal range,
The range switching means narrows the expanded target signal range after the predetermined time has elapsed. The power supply device according to claim 2,
The detection means shortens the detection interval of the output signal when the output signal is out of the extended target signal range,
The range switching means is an average value of a plurality of detection values detected at a reduced detection interval, and obtains an average value excluding at least one detection value of the plurality of detection values, and the average value is If the extended target signal range is out of range, the extended target signal range is narrowed. The power supply device according to claim 4,
The at least one detection value includes a maximum value and a minimum value of the plurality of detection values. In the power supply device according to any one of claims 2 to 5,
The range switching means narrows to the target signal range before expanding the expanded target signal range. In the power supply device according to any one of claims 1 to 6,
The range switching means expands the target signal range by increasing the upper limit of the target signal range and decreasing the lower limit of the target signal range. In the power supply device according to any one of claims 1 to 7,
There is further provided setting means for setting an extension amount of the target signal range by the range switching means according to the magnitude of the ripple of the output signal. The power supply device according to claim 8, wherein
The setting means estimates the magnitude of the ripple based on at least one of a target signal value of the output signal, the load, and the control signal. The power supply device according to claim 8, wherein
The apparatus further comprises measurement means for measuring the ripple. The power supply device according to any one of claims 1 to 10,
An image forming unit that forms an image on a recording medium using the output signal output from the output unit of the power supply device;
An image forming apparatus.

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