JP2006039133A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for controlling high precision power supply and more responsive power supply to fluctuation of a load resistant value of electrical load. <P>SOLUTION: The image forming apparatus determines the increased and decreased amount of the duty ratio of a PWM signal S1, on the basis of a differential conversion variable α corresponding to the load resistance value Ri of a transfer roller 30, calculated on the basis of detection signals S2 and S4. Furthermore, the image forming apparatus determines the increased and decreased amount of the PWM signal S1 on the basis of a correction deviation amount corrected by a deviation correction variable changed, in response to a current output current value Ii, a constant current setting value It and a deviation amount. In other words, the image forming apparatus determines the increased and decreased amount of the duty ratio of the PWM signal S1, on the basis of the deviation correction variable in which the value is large, when the deviation amount is large as compared with another case that the deviation amount is small. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus, and more particularly to control of power supply to an electrical load provided therein.

  For example, an image forming apparatus such as a printer supplies power from a power supply circuit to each electrical load (for example, a transfer roller) provided therein by constant current control or constant voltage control. Here, in the image forming apparatus, since the load resistance value of the electric load varies depending on the ambient temperature and humidity environment in particular, it is necessary to perform control in consideration of the variation of the load resistance value.

Therefore, Patent Document 1 below discloses a technique for supplying power to an electrical load by PWM (Pulse Width Modulation) control. More specifically, the PWM duty ratio-output characteristic information to the electrical load is stored for each of a plurality of preselected load resistance values. Then, the closest load resistance value is determined based on the current output value to the electric load and the current PWM duty ratio read at a predetermined timing, and the PWM duty ratio-output characteristic information to the electric load. Next, the PWM duty ratio for setting the output value to the control target value is predicted and updated from one PWM duty ratio corresponding to the determined load resistance value-output characteristics to the electric load.
JP-A-11-242502

  However, in the configuration of Patent Document 1, the current output value and the PWM duty ratio may be shifted from a plurality of pre-stored PWM duty ratios-output characteristics to the electrical load. is there. In this case, the current output value and the PWM duty ratio are regarded as being on the closest one PWM duty ratio-output characteristic to the electric load, and the resistance value of the electric load is determined in a pseudo manner. Therefore, when there is a large difference between the current output value and PWM duty ratio and the PWM duty ratio minus the output characteristic to the electrical load, there is a problem that power supply control with high accuracy cannot be performed.

  Further, in the configuration of Patent Document 1 described above, when there is no change in the load resistance value, the increase / decrease amount of the control signal is determined at a constant change rate regardless of the deviation amount between the current output value and the control target value. There was a problem of poor responsiveness of supply control.

  The present invention has been completed based on the above-described circumstances, and a first object of the present invention is an image forming apparatus capable of highly accurate power supply control with respect to fluctuations in the load resistance value of an electrical load. The second object of the present invention is to provide an image forming apparatus capable of more responsive power supply control.

  As a means for achieving the above object, an image forming apparatus according to a first aspect of the present invention comprises a control means and an electric load, and the electric power corresponding to a control signal output from the control means is supplied to the electric device. In the image forming apparatus having a configuration for supplying to an electrical load, the control unit includes a voltage detection unit that detects a voltage value applied to the electrical load, and a current detection unit that detects a current value flowing through the electrical load. The difference calculation means for calculating the difference between the detection value to be controlled among the detection values of the voltage detection means and the current detection means and the target value of the detection value, and the difference calculation means First determining means for determining an increase / decrease amount of a control signal for changing the detected value so as to eliminate the difference amount, and the first determining means includes both the voltage detecting means and the current detecting means. To detected value Flip the difference conversion variables determined, based on the conversion difference amount obtained by multiplying the difference amount, and determines the decrease amount of the control signal.

The “control means” includes, for example, the following.
(A) A pulse train control signal is output to perform control according to this duty ratio, so-called PWM (Pulse Width Modulation) control.
(B) Outputting an analog control signal and performing control according to the amplitude level.
In addition, the “both detection values of the voltage detection means and the current detection means” in the determination means is not limited to both detection values, and includes a load resistance value calculated based on these values.
Further, the “target value of the detected value” is not limited to the control target value to be finally controlled. For example, as in claim 5 below, the deviation amount between the control target value and the current detected value is corrected and temporarily In the configuration in which the target value is temporarily set, the temporary target value may be used.
Further, the “image forming apparatus” includes not only a printer (laser printer) but also a facsimile machine, and a multifunction machine having a printer function and a scanner function.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, both the detection values of the voltage detection unit and the current detection unit or a load resistance value determined by both the detection values and the difference conversion variable First storage means for storing a first arithmetic expression indicating the relationship is provided, and the first determination means is configured to detect the two detected values or the load resistance value based on the first arithmetic expression stored in the first storage means. It is characterized in that a difference transformation variable corresponding to is derived.

  According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the first determining unit includes both the detection values of the voltage detection unit and the current detection unit, or a load resistance value determined by both the detection values. A first arithmetic circuit capable of setting a circuit constant corresponding to the relationship with the difference conversion variable, wherein the first arithmetic circuit receives the signals corresponding to the two detection values or the load resistance value, and A signal corresponding to an increase / decrease amount of the control signal according to a constant is output.

  According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the control unit outputs a PWM control signal as the control signal and applies the PWM control signal to the electrical load. The power supply control is performed, and the increase / decrease amount of the control signal determined by the first determination unit is an increase / decrease amount of the duty ratio in the PWM control signal.

  According to a fifth aspect of the present invention, there is provided an image forming apparatus comprising a control unit and an electric load, wherein the image forming apparatus has a configuration for supplying power corresponding to a control signal output from the control unit to the electric load. In the apparatus, the control means includes a detection means for detecting a voltage value or a current value applied to the electrical load, and a deviation calculation means for calculating a deviation amount between the detection value in the detection means and the control target value. And second determining means for determining an increase / decrease amount of the control signal for changing the detected value so as to eliminate the deviation amount calculated by the deviation calculating means, wherein the second determining means Based on a correction deviation amount that is a deviation amount between the provisional target value obtained by multiplying the control target value by a deviation correction variable that becomes a large value as the deviation amount increases and the detection value, an increase / decrease amount of the control signal is calculated. It is characterized by determining.

  According to a sixth aspect of the present invention, in the image forming apparatus according to the fifth aspect, the correction deviation amount is larger than the deviation amount when the deviation amount is larger than a predetermined reference amount, and is larger than the predetermined reference amount. Is also smaller than the deviation amount.

  According to a seventh aspect of the present invention, there is provided the image forming apparatus according to the fifth or sixth aspect, wherein a second arithmetic expression indicating a relationship between a deviation amount in the deviation calculating means and the deviation correction variable is stored. 2 storage means, wherein the second determination means derives a deviation correction variable corresponding to the deviation amount based on the second arithmetic expression stored in the second storage means.

  According to an eighth aspect of the present invention, in the image forming apparatus according to the fifth or sixth aspect, the second determination unit is capable of setting a circuit constant corresponding to a relationship between the deviation amount and the deviation correction variable. The second arithmetic circuit receives a signal corresponding to the deviation amount, and outputs a signal corresponding to the increase / decrease amount of the control signal according to the circuit constant.

  According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the fifth to eighth aspects, the control unit outputs a PWM control signal as the control signal and applies the PWM control signal to the electrical load by the PWM control. The power supply control is performed, and the increase / decrease amount of the control signal determined by the second determination unit is an increase / decrease amount of the duty ratio in the PWM control signal.

  According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the fifth to ninth aspects, an upper limit value and a lower limit value are provided for the deviation correction variable.

  According to an eleventh aspect of the present invention, in the image forming apparatus according to any one of the fifth to tenth aspects, the second determination is performed when the deviation amount calculated by the deviation calculating means is within a predetermined allowable range. The means does not perform an operation of correcting the increase / decrease amount of the control signal.

  According to a twelfth aspect of the present invention, in the image forming apparatus according to any one of the fifth to eleventh aspects, a predetermined amount of change per unit time of a detection value by the detection unit or a deviation amount by the deviation calculation unit is predetermined. A comparison means for comparing the threshold value of the control signal, wherein the second determination means corrects the increase / decrease amount of the control signal on the condition that the change amount is determined to be less than or equal to the threshold value by the comparison means. It is characterized by performing.

  According to a thirteenth aspect of the present invention, in the image forming apparatus according to any one of the fifth to twelfth aspects, each unit according to any one of the first to fourth aspects is provided, and the second determining unit includes An increase / decrease amount of the control signal is determined based on a conversion difference amount obtained by multiplying the correction deviation amount by the difference conversion variable in the first determination means.

  According to a fourteenth aspect of the present invention, in the image forming apparatus according to any one of the first to thirteenth aspects, the electrical load is a transfer unit.

  According to a fifteenth aspect of the present invention, in the image forming apparatus according to the fourteenth aspect, a forward bias applying unit that applies a transfer bias voltage to the transfer unit, and a reverse polarity of the transfer bias voltage to the transfer unit. Reverse bias applying means for applying a reverse transfer bias voltage, wherein the forward bias applying means and the reverse bias applying means are connected in series to the transfer means, and the control is performed at different timings. The detection means, which is driven and controlled based on a control signal from the means, and detects the applied voltage value or the current value, has a potential level at a point on a series connection line of the forward bias applying means and the reverse bias applying means. A common input terminal to which a corresponding detection signal is input, and the control means, with respect to the detection signal input to the common input terminal, It is recognized as a detection signal corresponding to a detection value for driving control of the forward bias applying means at the time of driving control of the bias applying means, and detection for driving control of the reverse bias applying means at the time of driving control of the reverse bias applying means. Each feedback control is performed by recognizing the detection signal corresponding to the value.

  According to a sixteenth aspect of the present invention, in the image forming apparatus according to the fifteenth aspect, the detection signal is input to the common input terminal via an amplifying unit, and the amplification factor in the amplifying unit is changed in the order. Amplifying factor changing means is provided which changes between driving control of the bias applying means and driving control of the reverse bias applying means.

  According to a seventeenth aspect of the present invention, in the image forming apparatus according to the sixteenth aspect, the control unit outputs a command signal according to the drive control of the forward bias applying unit and the drive control of the reverse bias applying unit. The amplification factor changing unit is configured to include a switching unit that is connected in parallel to a resistor that determines the amplification factor of the amplification unit and that performs an on / off operation based on the command signal from the output unit. It is characterized by being.

  According to an eighteenth aspect of the present invention, in the image forming apparatus according to the fifteenth aspect, the control unit outputs a command signal according to the driving control of the forward bias applying unit and the driving control of the reverse bias applying unit. Output means, and switching means connected in parallel to the series connection line and performing an on / off operation based on the command signal from the output means.

<Inventions of Claims 1 and 4>
This configuration is an invention corresponding to the first object, and according to this configuration, the difference conversion variable corresponding to the actual load resistance value of the electrical load, which is determined by the detection values of the voltage detection means and the current detection means. The increase / decrease amount of the control signal is determined based on the above. Therefore, more accurate power supply control than the conventional configuration in which the PWM duty ratio is predicted and updated based on the PWM duty ratio for each of the plurality of load resistors stored in advance and the output characteristic information to the electrical load. It can be carried out. The present invention can also be applied to the PWM control shown in claim 4.

<Invention of Claim 2>
According to this configuration, the difference conversion variable corresponding to the actual load resistance value is derived based on the arithmetic expression stored in advance. Therefore, for example, the storage capacity can be reduced as compared with the configuration in which the data table indicating the correspondence between each load resistance value and the difference conversion variable is stored in the storage unit.

<Invention of Claim 3>
According to this configuration, the circuit constant corresponding to the relationship between the load resistance value and the difference conversion variable realizes a function equivalent to the arithmetic expression in claim 2, and there is no storage means for this. It becomes possible to do.

<Inventions of Claims 5, 6 and 9>
This configuration is an invention corresponding to the second object, and according to this configuration, the corrected deviation amount corrected by the deviation correction variable that changes according to the deviation amount between the current detected value and the control target value is obtained. Based on this, the increase / decrease amount of the control signal is determined. That is, the amount of increase / decrease in the control signal is determined based on the correction deviation amount that is the deviation amount between the temporary target value and the detection value obtained by multiplying the control target value by the deviation correction variable that increases as the deviation amount increases. It is done. Therefore, compared to the conventional configuration in which the rate of change is fixed, it is possible to perform power supply control with better responsiveness and better stability. In addition, the deviation correction is such that when the deviation is larger than a predetermined reference amount, it is larger than the deviation amount at that time, and when it is smaller than the predetermined reference amount, the deviation is smaller than the deviation amount at that time. It is desirable to derive based on variables. The present invention can also be applied to the PWM control shown in claim 9.

<Invention of Claim 7>
According to this configuration, the deviation correction variable corresponding to the deviation amount is derived based on the arithmetic expression stored in advance. Therefore, for example, the storage capacity can be reduced as compared with the configuration in which the data table indicating the correspondence between each deviation amount and the deviation correction variable is stored in the storage unit.

<Invention of Claim 8>
According to this configuration, the circuit constant corresponding to the relationship between the deviation amount and the deviation correction variable realizes a function equivalent to the arithmetic expression in claim 7, and does not have a storage unit for this purpose. It becomes possible.

<Invention of Claim 10>
According to this configuration, the deviation correction variable has an upper limit value and a lower limit value. That is, when the deviation correction variable is equal to or greater than the upper limit value or less than the lower limit value, the increase / decrease amount of the control signal is determined based on the deviation correction variable corresponding to the upper limit value or the lower limit value. Therefore, it is possible to avoid a situation where the control target value is greatly exceeded.

<Invention of Claim 11>
When the deviation amount calculated by the deviation calculating means is within a predetermined allowable range, that is, when the detected value is close to the control target value, control is performed more smoothly than when the control signal is increased or decreased. There are things you can do. Therefore, according to the present configuration, in such a case, the power supply control is performed based on the control signal as it is without increasing or decreasing.

<Invention of Claim 12>
According to this configuration, when the change amount per unit time of the detection value (or the deviation amount by the deviation calculation means) in the detection unit exceeds a predetermined threshold, the control signal increase / decrease correction operation is not performed. The configuration. As a result, it is possible to avoid erroneous control when the detected value or the deviation amount temporarily changes greatly due to noise or the like.

<Invention of Claim 13>
According to this configuration, it is possible to achieve an image forming apparatus that achieves both the first and second objects and has high responsiveness and high accuracy.

<Invention of Claim 14>
It is particularly beneficial to apply the present invention to power supply control to the transfer means as in this configuration.

<Invention of Claim 15>
According to this configuration, the detection value for feedback control of the forward bias applying unit and the reverse bias applying unit is captured by the common input terminal. Therefore, it is possible to reduce the number of parts and the cost as compared with the configuration in which the detection values of the forward bias applying means and the reverse bias applying means are fetched by separate input terminals.
Further, in the configuration in which the input is taken into separate input terminals, for example, when the forward bias applying unit is driven and controlled, it is not necessary to read the detection value from the input terminal corresponding to the reverse bias applying unit. However, a leakage current flows into this input signal, and as a result, the detection value for the forward bias applying means may fluctuate, which may reduce the accuracy of the drive control. The same applies to the drive control of the reverse bias applying means. On the other hand, since this configuration uses a common input terminal, the influence of leakage current can be eliminated.

<Invention of Claims 16, 17, 18>
The level range shown may differ between the detection value for driving control of the forward bias applying means and the detection value for driving control of the reverse bias applying means. Accordingly, in the configuration of the sixteenth aspect, the amplification factor for the detection signal is changed during the drive control of the bias applying means and during the drive control of the reverse bias applying means. As a more specific configuration, the configuration of claim 17 is a configuration in which the amplification factor is changed by short-circuiting a resistor that determines the amplification factor of the amplification unit by the switching unit that performs an on / off operation based on a command signal from the control unit. .
As another configuration, in the configuration of claim 18, the output resistance value in the detection means is provided by giving a command signal to the switching means connected in parallel to the series connection line to partially short the series connection line. The configuration is changed.

<Embodiment 1>
A first embodiment of the present invention will be described with reference to FIGS.
1. Overall Configuration of Image Forming Apparatus FIG. 1 is a side cross-sectional view showing a main part of a laser printer as an image forming apparatus according to an embodiment of the present invention. In FIG. 1, a laser printer 1 has an image formed on a feeder unit 4 for feeding paper 3 as a recording medium or a fed paper 3 in a main body frame 2 as an apparatus main body of the image forming apparatus. An image forming unit 5 and the like for forming are provided.

(1) Feeder unit The feeder unit 4 includes a paper feed tray 6 that is detachably attached to the bottom of the main body frame 2, a paper pressing plate 7 provided in the paper feed tray 6, and a paper feed tray 6. A feed roller 8 and a separation pad 9 provided above one end side (hereinafter, one end side (the right side in FIG. 1) is the front side and the opposite side (the left side in FIG. 1) is the rear side) The paper dust removing rollers 10 and 11 provided on the downstream side in the conveyance direction of the paper 3 with respect to the paper feed roller 8 and the registration roller 12 provided on the downstream side in the conveyance direction of the paper 3 with respect to the paper dust removal rollers 10 and 11. And.

The paper pressing plate 7 can stack the papers 3 in a stacked manner, and is supported at the end (rear end) far from the paper feed roller 8 so as to be swingable. The (front end) is movable in the vertical direction. Moreover, it is urged | biased by the spring which is not shown in figure from the back side. For this reason, the sheet pressing plate 7 is swung downward against the urging force of the spring with the rear end portion as a fulcrum with respect to the sheet feeding roller 8 as the amount of stacked sheets 3 increases. The paper feed roller 8 and the separation pad 9 are disposed so as to face each other, and the separation pad 9 is pressed toward the paper feed roller 8 by a spring 13 provided on the back side of the separation pad 9.
The uppermost sheet 3 on the sheet pressing plate 7 is pressed toward the sheet feeding roller 8 by a spring (not shown) from the back side of the sheet pressing plate 7, and the sheet feeding roller 8 and the separation pad are rotated by the rotation of the sheet feeding roller 8. After being sandwiched between 9, the sheet is fed one by one.

  The fed paper 3 is sent to the registration roller 12 after the paper dust is removed by the paper dust removing rollers 10 and 11. The registration roller 12 is composed of a pair of rollers, and sends the paper 3 to the image forming position after registration. Note that the image forming position is a transfer position at which the toner image on the photosensitive drum 27 is transferred to the paper 3, and is a contact position between the photosensitive drum 27 and the transfer roller 30 in this embodiment.

The feeder unit 4 further includes a multi-purpose tray 14, a multi-purpose side feed roller 15 and a multi-purpose side separation pad 25 for feeding the paper 3 stacked on the multi-purpose tray 14. ing. The multi-purpose side feed roller 15 and the multi-purpose side separation pad 25 are arranged to face each other, and the multi-purpose side separation pad 25 is supplied to the multi-purpose side by a spring 25 a provided on the back side of the multi-purpose side separation pad 25. It is pressed toward the paper roller 15.
The sheets 3 stacked on the multi-purpose tray 14 are fed one by one after being sandwiched between the multi-purpose side feed roller 15 and the multi-purpose side separation pad 25 by the rotation of the multi-purpose side feed roller 15. Is done.

(2) Image Forming Unit The image forming unit 5 includes a scanner unit 16, a process cartridge 17, and a fixing unit 18.
(A) Scanner Unit The scanner unit 16 is provided in the upper part of the main body frame 2, and includes a laser light emitting unit (not shown), a polygon mirror 19 that is rotationally driven, lenses 20, 21, and reflecting mirrors 22, 23, 24. It has. The laser beam based on the image data emitted from the laser emitting unit passes or reflects in the order of the polygon mirror 19, the lens 20, the reflecting mirrors 22 and 23, the lens 21, and the reflecting mirror 24, as indicated by the chain line, and processes. The surface of the photosensitive drum 27 of the cartridge 17 is irradiated with high-speed scanning.

(B) Process Cartridge The process cartridge 17 is provided below the scanner unit 16. The process cartridge 17 includes a drum cartridge 26 as a photosensitive cartridge that is detachably attached to the main body frame 2, and a developing cartridge 28 as a developer cartridge housed in the drum cartridge 26. As shown in FIG. 1, a front cover 2a that can be opened and closed with the lower end side as a central axis is provided on the front surface of the main body frame 2, and the process cartridge 17 opens the front cover 2a to open the main body frame 2. It is accommodated in a removable manner.

  The developing cartridge 28 is detachably accommodated in the drum cartridge 26 and includes a developing roller 31 as a developer carrier, a layer thickness regulating blade 32, a supply roller 33, and a toner hopper 34.

The toner hopper 34 is filled with positively chargeable non-magnetic one-component toner as a developer. Examples of the toner include polymerizable monomers such as styrene monomers such as styrene, and acrylic monomers such as acrylic acid, alkyl (C1 to C4) acrylate, and alkyl (C1 to C4) methacrylate. Polymerized toners obtained by copolymerization by a known polymerization method such as suspension polymerization are used. Such a polymerized toner has a substantially spherical shape, has extremely good fluidity, and can achieve high-quality image formation.
Such a toner is blended with a colorant such as carbon black, wax, and the like, and an additive such as silica is added to improve fluidity. The particle diameter is about 6 to 10 μm.

  Then, the toner in the toner hopper 34 is agitated by an agitator 36 supported by a rotating shaft 35 provided at the center of the toner hopper 34, and is discharged from a toner supply port 37 opened at the rear side portion of the toner hopper 34. The agitator 36 is rotationally driven in the direction of the arrow (clockwise) by the input of power from a motor (not shown). Note that windows 38 for detecting the remaining amount of toner are provided on both side walls of the toner hopper 34 (both side walls in the depth direction in FIG. 1), and are cleaned by a wiper 39 supported by the rotating shaft 35.

  A supply roller 33 is rotatably provided behind the toner supply port 37, and a developing roller 31 is rotatably provided facing the supply roller 33. The supply roller 33 and the developing roller 31 are in contact with each other in a state where each of them is compressed to some extent.

The supply roller 33 has a metal roller shaft covered with a roller made of a conductive foam material. The supply roller 33 is rotationally driven in the direction of the arrow (counterclockwise) by the input of power from a motor (not shown).
In the developing roller 31, a roller made of a conductive rubber material is coated on a metal roller shaft 31a. More specifically, the roller of the developing roller 31 is coated with a coating layer of urethane rubber or silicone rubber containing fluorine on the surface of a roller body made of conductive urethane rubber or silicone rubber containing carbon fine particles. Has been. A predetermined developing bias voltage is applied to the developing roller 31 during development. The developing roller 31 is rotationally driven in the direction of the arrow (counterclockwise) by the input of power from a motor (not shown).

  A layer thickness regulating blade 32 is provided in the vicinity of the developing roller 31. The layer thickness regulating blade 32 includes a pressing portion 40 having a semicircular cross section made of insulating silicone rubber at the tip of a blade body made of a metal leaf spring material. The layer thickness regulating blade 32 is supported by the developing cartridge 28 near the developing roller 31, and the pressing portion 40 is pressed onto the developing roller 31 by the elastic force of the blade body.

  The toner discharged from the toner supply port 37 is supplied to the developing roller 31 by the rotation of the supplying roller 33. At this time, the toner is positively frictionally charged between the supplying roller 33 and the developing roller 31. Further, the toner supplied onto the developing roller 31 enters between the pressing portion 40 of the layer thickness regulating blade 32 and the developing roller 31 as the developing roller 31 rotates, and is developed as a thin layer having a constant thickness. It is carried on a roller 31.

The drum cartridge 26 includes a photosensitive drum 27 as an image carrier, a scorotron charger 29 as a charger, a transfer roller 30 (corresponding to “electric load, transfer means” of the present invention), and a cleaning brush 64 as a cleaning means. It has.
Among these, the photosensitive drum 27 is disposed behind the developing roller 31 so as to face the developing roller 31 and is supported by the drum cartridge 26 so as to be rotatable in the arrow direction (clockwise). The photosensitive drum 27 includes a cylindrical drum body, and a metal drum shaft 27a that supports the drum body and is provided at the axis of the drum body. The drum body is made of an aluminum tube, and a positively chargeable photosensitive layer made of polycarbonate or the like is formed on the surface thereof. The drum shaft 27a is grounded (see FIG. 2).

  As shown in FIG. 1, the scorotron charger 29 is disposed above the photosensitive drum 27 so as to face the photosensitive drum 27 at a predetermined interval and is supported by the drum cartridge 26. The scorotron charger 29 is a positively charged scorotron charger that generates corona discharge from a charging wire 29 a such as tungsten. The scorotron charger 29 includes a grid 29 b between the charging wire 29 a and the photosensitive drum 27. Is uniformly charged to a positive polarity. A predetermined charging bias voltage is applied to the charging wire 29a.

  The surface of the photosensitive drum 27 is first uniformly charged positively by the scorotron charger 29 as the photosensitive drum 27 rotates, and then exposed by high-speed scanning of the laser beam from the scanner unit 16. An electrostatic latent image based on the image data is formed.

  Next, when the developing roller 31 rotates, the toner carried on the surface of the developing roller 31 and charged positively is formed on the surface of the photosensitive drum 27 when it comes into contact with the photosensitive drum 27. The electrostatic latent image is supplied and selectively supported to be visualized and developed.

  The transfer roller 30 is disposed below the photosensitive drum 27 so as to face the photosensitive drum 27 and is supported by the drum cartridge 26 so as to be rotatable in the direction of the arrow (counterclockwise). In the transfer roller 30, a metal roller shaft 30a is covered with a roller made of a conductive rubber material.

  A bias application circuit 60 mounted on a high voltage power supply circuit board 52 is connected to the roller shaft 30a of the transfer roller 30, and the toner image carried on the developing roller 31 at the transfer position is transferred to the paper 3. For this purpose, a forward transfer bias voltage Va1 (transfer bias voltage) is applied from the bias application circuit 60 during the transfer operation (hereinafter referred to as “forward transfer operation”). Further, in this embodiment, before and after the image forming operation, or during the transfer operation to each sheet 3 during the image forming operation, the reverse transfer having the reverse polarity to the forward transfer bias voltage Va1 is applied to the transfer roller 30. A bias voltage Va2 (reverse transfer bias voltage) is applied from the bias application circuit 60 (hereinafter, this operation is referred to as “reverse transfer operation”). As a result, the toner adhering to the transfer roller 30 is electrically discharged onto the photosensitive drum 27 and is collected by the developing roller 31 together with the residual toner remaining on the surface of the photosensitive drum 27.

  The cleaning brush 64 is provided so as to face the drum body of the photosensitive drum 27. The cleaning brush 64 is made of a conductive member, and is applied with a predetermined cleaning bias voltage and serves to remove paper dust adhering to the photosensitive drum 27.

(C) Fixing Unit As shown in FIG. 1, the fixing unit 18 is provided on the rear downstream side of the process cartridge 17, the heating roller 41, the pressing roller 42 that presses the heating roller 41, and the heating roller 41 and the pressing unit. A pair of transport rollers 43 provided on the downstream side of the roller 42 is provided. The heating roller 41 is made of metal and includes a halogen lamp for heating, and is driven to rotate in the arrow direction (clockwise) by the input of power from a motor (not shown). Further, the pressing roller 42 is rotated in the direction of the arrow (counterclockwise) following the heating roller 41 in a state where the heating roller 41 is pressed. In the fixing unit 18, the toner transferred onto the paper 3 in the process cartridge 17 is thermally fixed while the paper 3 passes between the heating roller 41 and the pressing roller 42, and then the paper 3 is conveyed. A roller 43 conveys the paper to the paper discharge path 44. The paper 3 sent to the paper discharge path 44 is sent to the paper discharge roller 45 and is discharged onto the paper discharge tray 46 by the paper discharge roller 45.

  The laser printer 1 is provided with a reverse conveyance unit 47 in order to form images on both sides of the paper 3. The reverse conveyance unit 47 includes a paper discharge roller 45, a reverse conveyance path 48, a flapper 49, and a plurality of reverse conveyance rollers 50.

2. Bias Application Circuit FIG. 2 shows a block diagram of the main configuration of the bias application circuit 60. As described above, the bias application circuit 60 is for applying the forward transfer bias voltage Va1 to the transfer roller 30 during the forward transfer operation and the reverse transfer bias voltage Va2 during the reverse transfer operation. .

  The bias application circuit 60 includes a CPU 61 (corresponding to “control means” of the present invention), a forward transfer bias application circuit 62 (corresponding to “forward bias application means” of the present invention), and a reverse transfer bias application circuit 63 (present). Equivalent to the “reverse bias applying means” of the present invention. The bias application circuits 62 and 63 are connected to a connection line 90 (“series connection line” of the present invention) connected to the roller shaft 30 a of the transfer roller 30 in the order of the forward transfer bias application circuit 62 and the charging bias application circuit 63. Connected in series. Further, the bias application circuit 60 includes an output detection circuit 83 (which also functions as “current detection means” of the present invention) that outputs a detection signal S4 corresponding to the value of the current flowing through the connection line 90. The forward transfer bias application circuit 62 is subjected to constant current control by PWM (Pulse Width Modulation) control of the CPU 61, and the reverse transfer bias application circuit 63 is constant voltage controlled by PWM control of the CPU 61. The memory 61 is connected to the CPU 61. The memory 100 stores a first arithmetic expression, a second arithmetic expression, and a constant current set value It (corresponding to the “control target value” of the present invention) described later. Therefore, the memory 100 corresponds to “first storage means” and “second storage means” of the present invention.

(A) Forward Transfer Bias Application Circuit First, the forward transfer bias application circuit 62 will be described. The forward transfer bias application circuit 62 includes a forward transfer PWM signal smoothing circuit 70, a forward transfer transformer drive circuit 71, a forward transfer boosting / smoothing rectifier circuit 72, and a forward transfer output voltage detection circuit 73.

  Among them, the forward transfer PWM signal smoothing circuit 70 plays a role of receiving and smoothing the PWM signal S1 from the PWM port 61a of the CPU 61 and supplying it to the forward transfer transformer drive circuit 71. The forward transfer transformer drive circuit 71 is configured to flow an oscillation current through the primary winding 75b of the forward transfer boost / smoothing rectifier circuit 72 based on the received PWM signal S1.

  The forward transfer boost / 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 a connection line 90 connected to the roller shaft 30 a of the transfer roller 30 via a diode 76. On the other hand, the other end of the secondary winding 75 a is commonly connected to the output terminal of the reverse transfer bias application circuit 63. A smoothing capacitor 77 and a discharge resistor 78 are connected in parallel to the secondary winding 75a.

  With such a configuration, the oscillation current of the primary winding 75 b is boosted and rectified in the forward transfer boosting / smoothing rectifier circuit 72, and the roller shaft of the transfer roller 30 connected to the output terminal A of the bias applying circuit 60. The forward transfer bias voltage Va1 is applied to 30a.

  The forward transfer output voltage detection circuit 73 is connected to the auxiliary winding 75 c of the transformer 75 of the forward transfer boost / smoothing rectifier circuit 72 and the CPU 61. The CPU 61 detects the output voltage Vb generated between the auxiliary windings 75c during the forward transfer operation by the forward transfer bias application circuit 62, and inputs the detection signal S2 to the A / D port 61b of the CPU 61. It is configured.

(B) Reverse Transfer Bias Application Circuit Next, the reverse transfer bias application circuit 63 will be described. The reverse transfer bias application circuit 63 includes a reverse transfer PWM signal smoothing circuit 80, a reverse transfer transformer drive circuit 81, and a reverse transfer boosting / smoothing rectifier circuit 82.

  Among these, the reverse transfer PWM signal smoothing circuit 80 plays a role of receiving and smoothing the PWM signal S3 from the PWM port 61c of the CPU 61 and supplying it to the reverse transfer transformer drive circuit 81. The reverse transfer transformer drive circuit 81 is configured to flow an oscillation current to the primary winding 85b of the reverse transfer boost / smoothing rectifier circuit 82 based on the received PWM signal S3.

  The reverse transfer boosting / smoothing rectifier circuit 82 includes a transformer 85, a diode 86, a smoothing capacitor 87, and the like. The transformer 85 includes a secondary winding 85a, a primary winding 85b, and an auxiliary winding 85c. One end of the secondary winding 85 a is connected to the other end of the secondary winding 75 a of the forward transfer bias applying circuit 62 through a diode 86. On the other hand, the other end of the secondary winding 85a is grounded through a resistor 91. A smoothing capacitor 87 and a pair of resistors 88 and 89 are connected in parallel to the secondary winding 85a. In the present embodiment, one resistor 89 of the pair of resistors 88 and 89 is a detection resistor, and the detection signal S4 corresponding to the value of the current flowing through the detection resistor 89 is supplied to the amplifier circuit 92 (the “amplifying means of the present invention”). The A / D port 61d of the CPU 61 (corresponding to the “common input terminal” of the present invention) is fed back via the

  With such a configuration, the oscillation current of the primary winding 85 b is boosted and rectified in the reverse transfer boosting / smoothing rectifier circuit 82, and the roller of the transfer roller 30 connected to the output terminal A of the bias applying circuit 60 is also used. The reverse transfer bias voltage Va2 is applied to the shaft 30a.

  As described above, the CPU 61 applies the PWM signal S1 to the forward transfer bias application circuit 62 and drives it to the connection line 90 during the forward transfer operation ("during drive control of the forward bias application means" in the present invention). Based on the detection signal S4 corresponding to the flowing current value, constant current control for outputting the PWM signal S1 having a duty ratio appropriately changed to the forward transfer PWM signal smoothing circuit 70 so that the current value becomes the constant current set value It. Execute.

  Further, the CPU 61 applies the PWM signal S3 to the reverse transfer bias application circuit 63 to drive it during the reverse transfer operation (“during bias control of the reverse bias applying means” in the present invention), and drives the load of the detection resistor 89. Based on the detection signal S4 corresponding to the voltage, constant voltage control is executed to output the PWM signal S3 with the duty ratio appropriately changed to the reverse transfer PWM signal smoothing circuit 80 so that the load voltage value becomes a predetermined constant voltage value. .

  Here, in the present embodiment, the detection signal S4 from the output detection circuit 83 is fed back by the common A / D port 61d in both the forward transfer operation and the reverse transfer operation. The level range differs between the forward transfer bias voltage Va1 during the forward transfer operation and the reverse transfer bias voltage Va2 during the reverse transfer operation. Therefore, the amplification circuit 92 is provided with amplification factor changing means 93 for changing the amplification factor. More specifically, one feedback resistor 95 of the pair of feedback resistors 94 and 95 that determines the amplification factor of the amplifier circuit 92 (corresponding to “a resistor that determines the amplification factor” in the present invention. May be a transistor 96 (TFT or the like) as a switching means that is connected in parallel to each other and is turned on / off by a command signal S5 output from an output port 61e of the CPU 61 ("output means" of the present invention). .) The transistor 96 has a collector commonly connected to a connection point of the pair of feedback resistors 94 and 95 via a switching resistor 97, and an emitter grounded.

  The CPU 61 does not output the command signal S5 from the output port 61e, for example, during the forward transfer operation that outputs the PWM signal S1. At this time, the detection signal S4 is amplified with an amplification factor determined by the resistance values of the pair of feedback resistors 94 and 95, and is taken into the A / D port 61d. The CPU 61 performs feedback control on the forward transfer bias applying circuit 62 by regarding the detection signal S4 captured at this time as a feedback signal for the forward transfer operation.

  On the other hand, the CPU 61 outputs the command signal S5 from the output port 61e during the reverse transfer operation for outputting the PWM signal S3, for example. At this time, the detection signal S4 is amplified with an amplification factor determined by the resistance values of the feedback resistor 94 and the auxiliary resistor 97 and is taken into the A / D port 61d. The CPU 61 performs feedback control on the reverse transfer bias applying circuit 63 by regarding the detection signal S4 captured at this time as a feedback signal for the reverse transfer operation. The resistance values of the switching resistor 97 and the feedback resistor 95 are adjusted so that the detection signal S4 level during the forward transfer operation and the reverse transfer operation can be taken into the A / D port 61d within the same range (range). .

3. Specific Control Contents in Forward Transfer Operation Now, also in the laser printer 1 of the present embodiment, the load resistance value of the transfer roller 30 as an electrical load varies depending on the ambient temperature and the like. Accordingly, the constant current control with high accuracy is performed by increasing or decreasing the duty ratio of the PWM signal S1 in consideration of the load resistance value that may vary. Further, in the present embodiment, the deviation amount between the output current value Ii (corresponding to the “detected value to be controlled” in the present invention) indicated by the currently acquired detection signal S4 and the constant current set value It is considered. Constant current control with good responsiveness is performed by increasing or decreasing the duty ratio of the PWM signal S1.

Hereinafter, the control content for this will be described with reference to FIGS.
First, the CPU 61 executes the control shown in the flowchart of FIG. 3 during the forward transfer operation. First, in step S1, the constant current set value It is read from the memory 100. In step S2, the timer starts counting, and the start flag X is initialized to 1, and the noise cancellation count Y is initialized to 0. When the timer counts for a predetermined time, for example, 20 ms (“Y” in step S3), the detection signal S4 from the output detection circuit 83 and the detection signal S2 from the forward transfer output voltage detection circuit 73 are set to a predetermined timing in step S4. The operation of setting the duty ratio of the PWM signal S1 is sequentially performed as described below. The reason for waiting for a predetermined time (20 ms) is to perform stable constant current control by starting control after the output current value Ii described below has reached a steady state to some extent from the time of startup.

(A) Calculation of Difference Conversion Variable The CPU 61 calculates the load resistance value Ri of the transfer roller 30 based on the detection signals S2 and S4 read in step S4. That is, the output current value Ii (detected value to be controlled) flowing through the transfer roller 30 is detected from the detection signal S4. Further, the output voltage Vb generated between the auxiliary winding 75c is detected from the detection signal S2. The transfer roller 30 is obtained by adding a voltage Vc obtained by multiplying the output voltage Vb by the voltage ratio n between the auxiliary winding 75c and the secondary winding 75a and a voltage Vd obtained by multiplying the resistors 88 and 89 by the output current value Ii. An applied voltage value Vi is obtained (see the following formula 1). A value obtained by dividing the applied voltage value Vi by the output current value Ii is the load resistance value Ri of the transfer roller 30 in the current environment, and is stored in the memory 100.

(Formula 1)
Load resistance value Ri = {n * Vb + (r1 + r2) * Ii} / Ii
r1, r2: resistance values of the resistors 88 and 89. Then, the CPU 61 determines the difference conversion variable α based on the first arithmetic expression (the following expression 2) stored in advance in the memory 100 in step S5. This first arithmetic expression is derived as follows. First, for each load resistance value, the change amount of the output current value Ii with respect to the unit percentage amount of the duty ratio of the PWM signal S1 is experimentally obtained (see FIG. 4A). The amount of change ΔIi /% per unit percent (the slope of each graph in the figure) changes according to the change in the load resistance value of the transfer roller 30. In the present embodiment, for example, the change rate ΔIi /% at a load resistance value of 200 MΩ is used as a reference, and the relative change rate relative thereto is set as the difference conversion variable α. When this is plotted for each load resistance value, it is experimentally found that a curve as shown in FIG. 4B is drawn. An expression obtained by approximating this curve with the approximate expression of the following expression 2 is defined as a first arithmetic expression.

(Formula 2)
Difference conversion variable α = x / Ri + y
x, y: constants determined by the experimental results Note that, according to the experimental results described in FIG.
α = 160.25 * 10 ⁶ /(Vi/Ii)+0.1715
It becomes. The CPU 61 determines the difference conversion variable α by substituting the currently calculated load resistance value Ri (Vi / Ii) into the first arithmetic expression.

  Next, in step S6, it is determined whether the start flag is 0. If it is 0 (“Y” in step S6), the change amount ΔIi per unit time of the output current value Ii is within a predetermined specified range in step S9. It is judged whether it is in (for example, 0.93 to 1.07 μA). Here, the change amount ΔIi is, for example, a level difference between the output current value Ii acquired at the previous timing and the current timing. If the change amount ΔIi is outside the specified range (“N” in step S9), 1 is added to the noise cancellation count Y in step S10. When the noise cancel count Y has not reached 2 (“N” in step S11), the process returns to step S4 again. On the other hand, when the noise cancel count Y reaches two times, it is considered that the noise cancel count is not affected by the noise, and the process proceeds to step 12 after resetting the noise cancel count Y to 0 in step S20. At this time, the CPU 61 functions as a comparison unit of the present invention.

  In step S12, it is determined whether or not the output current value Ii is within a predetermined allowable range (for example, It * 0.97 to It * 1.03) with respect to the constant current set value It. (“Y” in step S12) The duty ratio of the PWM signal S1 is not corrected. On the other hand, if the output current value Ii is not within the allowable range (“N” in step S12), the output current value Ii differs depending on whether the output current value Ii is smaller than It * 0.97 or larger than It * 1.03. Correct the duty ratio.

  When the activation flag is 1 in step S6, that is, when the activation is in progress (“N” in step S6), it is determined in step S7 whether the output current value Ii is equal to or greater than It * 0.97. If it is smaller than It * 0.97 (“N” in step S7), the process directly proceeds to step S15. On the other hand, if it is greater than or equal to It * 0.97 (“Y” in step S7), it is determined that the activation has been completed, the activation flag is reset to 0 in step S8, and the process proceeds to step S9.

(B) When the output current value Ii is smaller than It * 0.97 When the output current value Ii is smaller than It * 0.97 (“Y” in Step S13), the calculation shown in the following Equation 3 in Step S15 An equation (corresponding to the “second arithmetic expression” of the present invention) is read from the memory 100 and a temporary target value It ′ is calculated based on the equation.

(Formula 3)
Provisional target value It ′ = {(1−Ii / It) * Ka + 0.97} * It
= {(It-Ii) * Ka + 0.97 * It}
Ka: constant according to desired resolution (for example, 0.5)
It−Ii: Corresponding to “deviation amount” of the present invention Here, “(1−Ii / It) * Ka + 0.97” in the above formula 3 corresponds to the deviation correction variable of the present invention, and is constant. The value changes as the deviation amount between the current set value It and the current output current value Ii increases. That is, the temporary target value It ′ is larger than the constant current set value It when the deviation amount between the constant current set value It and the current output current value Ii is larger than a predetermined reference value (deviation correction variable> 1). When the deviation amount is small, it is set to a value closer to It * 0.97.
However, when the temporary target value It ′ is equal to or greater than It * 1.03, this It * 1.03 is set as the temporary target value It ′. That is, the deviation correction variable has an upper limit value (1.03).

  Then, by substituting the temporary target value It ′ and the difference conversion variable α determined in step S5 in the following equation 4 read from the memory 100, the duty ratio Dt of the PWM signal S1 to be output at the next timing To decide.

(Formula 4)
Next duty ratio Dt = Di + (It′−Ii) * K / α
K: amount of change ΔIi /% per unit percentage when the reference resistance value is 200 MΩ
Di: Current duty ratio (It′−Ii): equivalent to “difference amount” and “correction deviation amount” of the present invention (It′−Ii) * K / α: equivalent to “conversion difference amount” of the present invention When the deviation amount between the constant current set value It and the current output current value Ii is large by the calculation, a temporary target value It ′ that is larger than the constant current set value It is set, and the temporary target value It ′ The duty ratio is greatly changed so as to eliminate the difference amount. In addition, at this time, when the duty ratio that eliminates the difference amount is converted, the duty ratio is converted into an appropriate value based on the difference conversion variable α derived in consideration of the current load resistance value Ri. When the deviation amount between the constant current set value It and the current output current value Ii is small, the temporary target value It ′ is smaller than the constant current set value It.

(C) When the output current value Ii is larger than It * 1.03 When the output current value Ii is larger than It * 1.03 (“N” in step S13), the calculation shown in the following equation 5 is performed in step S14. An equation (corresponding to the “second arithmetic expression” of the present invention) is read from the memory 100 and a temporary target value It ″ is calculated based on this.

(Formula 5)
Temporary target value It "= {(1-Ii / It) * Ka + 1.03} * It
= {(It-Ii) * Ka + 1.03 * It}
Ka: constant according to desired resolution (for example, 0.5)
It−Ii: Corresponds to “deviation amount” of the present invention Here, “(1−Ii / It) * Ka + 1.03” in the above formula 5 also corresponds to the deviation correction variable of the present invention, The value changes as the deviation amount between the constant current set value It and the current output current value Ii increases. That is, the temporary target value It ″ is smaller than the constant current set value It when the deviation amount between the constant current set value It and the current output current value Ii is larger than a predetermined reference value (deviation correction variable <1 When the deviation is small, it is set to a value closer to It * 1.03.
However, when the temporary target value It ″ is equal to or less than It * 0.97, this It * 0.97 is set as the temporary target value It ″. That is, the deviation correction variable has a lower limit (0.97).

  Then, the duty ratio Dt of the PWM signal S1 to be output at the next timing is obtained by substituting the provisional target value It ″ and the difference conversion variable α determined in step S5 into the equation 6 read from the memory 100. decide.

(Formula 6)
Next duty ratio Dt = Di + (It ″ −Ii) * K / α
K: amount of change ΔIi /% per unit percentage when the reference resistance value is 200 MΩ
Di: Current duty ratio (It "-Ii): equivalent to" difference amount "and" correction deviation amount "of the present invention (It" -Ii) * K / α: equivalent to "conversion difference amount" of the present invention When the deviation amount between the constant current set value It and the current output current value Ii is large by a simple calculation, a temporary target value It ″ smaller than the constant current set value It is set, and the temporary target value It ″ The duty ratio is greatly changed so as to eliminate the difference amount. In addition, at this time, when the duty ratio that eliminates the difference amount is converted, the duty ratio is converted into an appropriate value based on the difference conversion variable α derived in consideration of the current load resistance value Ri. When the deviation between the constant current set value It and the current output current value Ii is small, the temporary target value It ′ is larger than the constant current set value It.

  Subsequently, in step S16, it is determined whether or not the image forming operation on the sheet 3 has been completed. If completed (“Y” in step S16), the duty ratio correction operation is terminated and the output operation of the PWM signal S1 is performed. Stop (step S17). On the other hand, if not completed, the timer again counts, for example, 20 ms (steps S18 and S19), returns to step S4, and repeats the correction operation.

4). Effects of this embodiment (1) According to this embodiment, the duty ratio of the PWM signal S1 is increased or decreased based on the difference conversion variable α corresponding to the load resistance value Ri of the transfer roller 30 calculated based on the detection signals S2 and S4. It was set as the structure made to do. Therefore, more accurate power supply control than the conventional configuration in which the PWM duty ratio is predicted and updated based on the PWM duty ratio for each of the plurality of load resistors stored in advance and the output characteristic information to the electrical load. It can be carried out.
(2) In addition, the difference conversion variable α corresponding to the actual load resistance value Ri is derived based on the first arithmetic expression (Formula 2) stored in advance in the memory 100. Therefore, for example, the storage capacity can be reduced as compared with the configuration in which the data table indicating the correspondence between each load resistance value and the difference conversion variable is stored in the storage unit.

(3) In this embodiment, the increase / decrease amount of the PWM signal S1 is determined based on the correction deviation amount corrected by the deviation correction variable that changes according to the deviation amount between the current output current value Ii and the constant current set value It. The That is, the amount of increase / decrease in the control signal is determined based on the correction deviation amount that is the deviation amount between the temporary target value and the detection value obtained by multiplying the control target value by the deviation correction variable that increases as the deviation amount increases. It is done. Therefore, compared to the conventional configuration in which the rate of change is fixed, it is possible to perform power supply control with better responsiveness and better stability. In addition, the deviation correction is such that when the deviation is larger than a predetermined reference amount, it is larger than the deviation amount at that time, and when it is smaller than the predetermined reference amount, the deviation is smaller than the deviation amount at that time. The structure is derived based on variables.
(4) Further, a deviation correction variable corresponding to the deviation amount is derived based on the second arithmetic expressions (Equations 3 to 6) stored in advance in the memory 100. Therefore, for example, the storage capacity can be reduced as compared with the configuration in which the data table indicating the correspondence between each deviation amount and the deviation correction variable is stored in the storage unit.

(5) Further, the deviation correction variable includes an upper limit value and a lower limit value (deviation correction variable when the temporary target value It ′ is It * 1.03 or the temporary target value It ″ is It * 0.97). That is, when the deviation correction variable is greater than or equal to the upper limit value or less than the lower limit value, the increase / decrease amount of the PWM signal S1 is determined based on the deviation correction variable corresponding to the upper limit value or the lower limit value. Therefore, a situation where the control target value is greatly exceeded can be avoided.
(6) When the deviation amount between the current output current value Ii and the constant current set value It is within a predetermined allowable range, that is, when the output current value Ii is close to the constant current set value It to some extent (step) In S12, “Y”), there are cases where smoother control is possible when the PWM signal S1 is not increased or decreased. Therefore, in this embodiment, in such a case, the PWM signal S1 is output as it is without increasing or decreasing.

(7) Further, when the change amount ΔIi per unit time of the current output current value Ii exceeds a predetermined threshold (0.93 to 1.07), a predetermined period (until “Y” in step S11) ) A configuration in which the correction operation of the increase / decrease amount of the PWM signal S1 is not performed. As a result, it is possible to avoid erroneous control when the output current value Ii or the like changes temporarily due to noise or the like.
(8) In this embodiment, the detection signal S4 for feedback control of the forward transfer bias application circuit 62 and the reverse transfer bias application circuit 63 is captured by a common A / D port 61d. Therefore, it is possible to reduce the number of parts and the cost as compared with the configuration in which the detected values of the forward transfer bias application circuit 62 and the reverse transfer bias application circuit 63 are fetched by separate input terminals.
Further, in the configuration in which the input is taken into separate input terminals, it is not necessary to read the detection value from the input terminal corresponding to the reverse transfer bias application circuit 63, for example, during the forward transfer operation. However, a leakage current flows into this input signal, and as a result, the detection value for the forward transfer bias application circuit 62 may fluctuate and the accuracy of the constant current control may be reduced. The same applies to the reverse transfer operation of the reverse transfer bias application circuit 63. On the other hand, since this configuration uses a common input terminal, the influence of leakage current can be eliminated.

  (9) The level range shown differs between the detection signal S4 level during the forward transfer operation of the forward transfer bias application circuit 62 and the detection signal S4 level during the reverse transfer operation of the reverse transfer bias application circuit 63. Therefore, in the present embodiment, the amplification factor of the amplifier circuit 92 with respect to the detection signal S4 is changed between the forward transfer operation and the reverse transfer operation.

<Embodiment 2>
FIG. 5 shows Embodiment 2 (corresponding to the invention of claim 18). The difference from the first embodiment is the configuration for changing the detection signal S4 level during the forward transfer operation and the reverse transfer operation to the same range level, and the other points are the same as in the first embodiment. Therefore, the same reference numerals as those in the first embodiment are given and the redundant description is omitted, and only different points will be described next.

  As shown in FIG. 5, in this embodiment, the detection resistor 89 and the resistor 91 connected in series to the connection line 90 are connected in parallel and output from the output port 61 e of the CPU 61 (the “output unit” of the present invention). The transistor 110 (which may be a TFT or the like) is provided as switching means that performs an on / off operation in response to a command signal S5. The collector of the transistor 110 is commonly connected to the connection point of the resistor 88 and the detection resistor 89 via the switching resistor 111, and the emitter is grounded.

  The CPU 61 does not output the command signal S5 from the output port 61e, for example, during the forward transfer operation that outputs the PWM signal S1. At this time, the detection signal S4 is taken into the A / D port 61d at a level corresponding to the combined resistance value of the detection resistor 89 and the resistor 91. The CPU 61 performs feedback control on the forward transfer bias applying circuit 62 by regarding the detection signal S4 captured at this time as a feedback signal for the forward transfer operation.

  On the other hand, the CPU 61 outputs the command signal S5 from the output port 61e during the reverse transfer operation for outputting the PWM signal S3, for example. At this time, the detection signal S4 is taken into the A / D port 61d at a level corresponding to the resistance value of the switching resistor 111. The CPU 61 performs feedback control on the reverse transfer bias applying circuit 63 by regarding the detection signal S4 captured at this time as a feedback signal for the reverse transfer operation. The resistance values of the detection resistor 89, the resistor 91, and the switching resistor 111 are adjusted so that the detection signal S4 level during the forward transfer operation and the reverse transfer operation can be taken into the A / D port 61d in the same range. Has been.

  Even in such a configuration, the detection signal S4 for feedback control of the forward transfer bias applying circuit 62 and the reverse transfer bias applying circuit 63 can be taken in by the common A / D port 61d, and the first embodiment described above. The same effect can be obtained.

<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, and further, within the scope not departing from the gist of the invention other than the following. Various modifications can be made.
(1) The structure which implement | achieves a part or all of the arithmetic processing by said each arithmetic formula (Formula 2-6) with an arithmetic circuit may be sufficient.

(2) In the above embodiment, the first and second objects of the present invention are solved simultaneously. However, the present invention is not limited to this, and only the first object is solved using the first arithmetic expression. It may be. At this time, the calculation formula of the duty ratio of the PWM signal S1 is as follows.
(Formula 7)
Next duty ratio Dt = Di + (It−Ii) * K / α
It: Constant current set value (control target value)
It-Ii: Corresponds to “difference amount” of the present invention (It-Ii) * K / α: Corresponds to “conversion difference amount” of the present invention. Alternatively, only the second object may be solved. At this time, the temporary target values It ′ and It ″ are calculated using the above formulas 3 and 5, and the next duty ratio of the PWM signal S1 is calculated by the following formula.
(Formula 8)
Next duty ratio Dt = Di + (It′−Ii) * K
Next duty ratio Dt = Di + (It ″ −Ii) * K
It′-Ii, It ″ -Ii: equivalent to “correction deviation amount” of the present invention

(3) In each of the above-described embodiments, the transfer roller 30 is a roller body as the transfer unit. However, the transfer unit is not limited thereto, and may be a flat plate transfer unit, for example.
(4) The transfer roller 30 is used as an electrical load. However, as long as power is supplied and constant current or constant voltage control is performed, for example, developing means (developing roller 31), charging means (scorotron charger 29) The present invention may be applied to the charging wire 29a and the grid 29), the cleaning means (cleaning brush 64), and the like.

(5) In the above embodiments, constant current control has been described. However, the present invention is not limited to this, and constant voltage control for setting the applied voltage value Vi to a predetermined level may be used. In this case, the change amount of the output current value Ii with respect to the unit percentage amount of the duty ratio of the PWM signal S1 for each load resistance value is as shown in FIG. For example, the change rate ΔIi /% at a load resistance value of 200 MΩ is used as a reference, and the relative change rate with respect to this is set as the difference conversion variable β. When this is plotted for each load resistance value, it is experimentally found that a curve as shown in FIG. 6B is drawn. An expression obtained by approximating this curve with the following approximate expression of Expression 9 is defined as a first arithmetic expression.
(Formula 9)
Difference transformation variable β = z / Ri + w
z, w: constants determined by the experimental results Note that, according to the experimental results described in FIG.
β = −34.293 * 10 ⁶ /(Vi/Ii)+1.2299
It becomes. The CPU 61 determines the difference conversion variable β by substituting the currently calculated load resistance value Ri (Vi / Ii) into the above formula 9.

1 is a side sectional view showing an internal configuration of a laser printer according to Embodiment 1 of the present invention. Block diagram of main components of bias application circuit Flow chart showing control contents of CPU Explanatory drawing which shows the relationship between load resistance value, duty ratio, and difference conversion variable A block diagram of the principal part composition of the bias application circuit of Embodiment 2 Explanatory drawing which shows the relationship between the load resistance value in a modification, a duty ratio, and a difference conversion variable

Explanation of symbols

1. Laser printer (image forming device)
30. Transfer roller (electric load, transfer means)
61 ... CPU (control means, difference calculation means, determination means, comparison means)
61d: A / D port (common input terminal)
61e ... Output port (output means)
62: Forward transfer bias application circuit (forward bias application means)
63. Reverse transfer bias application circuit (reverse bias application means)
83 ... Current detection circuit (current detection means)
73: Forward transfer output voltage detection circuit (voltage detection means)
90 ... connection line (series connection line)
92 ... Amplifier circuit (amplifying means)
93 ... amplification factor changing means 95 ... resistance 96,110 ... transistor (switching means)
100: Memory (first and second storage means)
Va1: Forward transfer bias voltage (transfer bias voltage)
Va2: Reverse transfer bias voltage (reverse transfer bias voltage)
Vb: Charging bias voltage (charging bias voltage)
Vd: Cleaning bias voltage (divided voltage for cleaning)
Vh: Grid bias voltage (divided voltage for grid)
Ii: Output current value It: Constant current set value (control target value)
Vi: Applied voltage value S1: PWM signal (control signal)
S4 ... Detection signal S5 ... Command signal

Claims (18)

In an image forming apparatus comprising a control means and an electrical load, and having a configuration for supplying power corresponding to a control signal output from the control means to the electrical load,
The control means includes
Voltage detection means for detecting an applied voltage value to the electrical load;
Current detecting means for detecting a current value flowing through the electrical load;
A difference calculation means for calculating a difference amount between a detection value to be controlled among both detection values of the voltage detection means and the current detection means and a target value of the detection value;
First determining means for determining an increase / decrease amount of a control signal for changing the detected value so as to eliminate the difference amount calculated by the difference calculating means;
The first determination unit determines an increase / decrease amount of the control signal based on a conversion difference amount obtained by multiplying the difference amount by a difference conversion variable determined according to both detection values of the voltage detection unit and the current detection unit. An image forming apparatus. A first storage means for storing a first arithmetic expression indicating a relationship between both the detection values of the voltage detection means and the current detection means or a load resistance value determined by the both detection values and the difference conversion variable;
The said 1st determination means derives | leads-out the difference conversion variable corresponding to the said both detection values or the said load resistance value based on the said 1st arithmetic expression memorize | stored in the said 1st memory | storage means. Image forming apparatus. The first determining means is capable of setting a circuit constant corresponding to a relationship between both the detected values of the voltage detecting means and the current detecting means or a load resistance value determined by both detected values and the difference conversion variable. 1 arithmetic circuit,
The first arithmetic circuit receives a signal corresponding to the both detection values or the load resistance value, and outputs a signal corresponding to an increase / decrease amount of the control signal according to the circuit constant. Item 2. The image forming apparatus according to Item 1. The control means is configured to output a PWM control signal as the control signal and perform power supply control to the electrical load by PWM control,
4. The image forming apparatus according to claim 1, wherein the increase / decrease amount of the control signal determined by the first determination unit is an increase / decrease amount of the duty ratio in the PWM control signal. 5. In an image forming apparatus comprising a control means and an electrical load, and having a configuration for supplying power corresponding to a control signal output from the control means to the electrical load,
The control means includes
Detecting means for detecting a voltage value or a current value applied to the electrical load;
Deviation calculation means for calculating a deviation amount between the detection value in the detection means and the control target value;
Second determining means for determining an increase / decrease amount of a control signal for changing the detected value so as to eliminate the deviation amount calculated by the deviation calculating means,
The second determining means is based on a correction deviation amount that is a deviation amount between a provisional target value obtained by multiplying the control target value by a deviation correction variable that increases as the deviation amount increases and the control target value. An image forming apparatus that determines an increase / decrease amount of the control signal. 6. The correction deviation amount is larger than the deviation amount when the deviation amount is larger than a predetermined reference amount, and smaller than the deviation amount when smaller than the predetermined reference amount. The image forming apparatus described in 1. A second storage means for storing a second calculation expression indicating a relationship between the deviation amount in the deviation calculation means and the deviation correction variable;
The image according to claim 5 or 6, wherein the second determination unit derives a deviation correction variable corresponding to the deviation amount based on the second arithmetic expression stored in the second storage unit. Forming equipment. The second determining means includes a second arithmetic circuit capable of setting a circuit constant corresponding to the relationship between the deviation amount and the deviation correction variable,
The said 2nd arithmetic circuit receives the signal corresponding to the said deviation amount, and outputs the signal corresponding to the increase / decrease amount of the said control signal according to the said circuit constant. The image forming apparatus described in 1. The control means is configured to output a PWM control signal as the control signal and perform power supply control to the electrical load by PWM control,
9. The image forming apparatus according to claim 5, wherein the increase / decrease amount of the control signal determined by the second determination unit is an increase / decrease amount of the duty ratio in the PWM control signal. The image forming apparatus according to claim 5, wherein an upper limit value and a lower limit value are provided for the deviation correction variable. 6. The second determination unit does not perform an operation of correcting an increase / decrease amount of the control signal when the deviation amount calculated by the deviation calculation unit is within a predetermined allowable range. Item 11. The image forming apparatus according to Item 10. Comparing means for comparing the amount of change per unit time of the detected value in the detecting means or the deviation amount in the deviation calculating means with a predetermined threshold,
The second determination means performs a correction operation of the increase / decrease amount of the control signal on condition that the change amount is determined to be equal to or less than the threshold value by the comparison means. Item 12. The image forming apparatus according to any one of Items 11. Each means according to any one of claims 1 to 4 is provided,
The increase / decrease amount of the control signal is determined based on a conversion difference amount obtained by multiplying the correction deviation amount in the second determination unit by the difference conversion variable in the first determination unit. The image forming apparatus according to claim 5. The image forming apparatus according to claim 1, wherein the electrical load is a transfer unit. Forward bias applying means for applying a transfer bias voltage to the transfer means;
Reverse bias applying means for applying a reverse transfer bias voltage having a reverse polarity to the transfer bias voltage to the transfer means,
The forward bias applying means and the reverse bias applying means are configured to be connected in series to the transfer means, and are driven and controlled based on control signals from the control means at different timings.
The detection means for detecting the applied voltage value or the current value is a common input terminal to which a detection signal corresponding to a potential level at a point on a series connection line of the forward bias applying means and the reverse bias applying means is input. With
The control means recognizes the detection signal input to the common input terminal as a detection signal corresponding to a detection value for driving control of the forward bias applying means during the driving control of the forward bias applying means, and 15. The image forming apparatus according to claim 14, wherein at the time of driving control of the bias applying unit, the feedback control is performed by recognizing the detection signal corresponding to the detection value for driving control of the reverse bias applying unit. The detection signal is configured to be input to the common input terminal via an amplification unit,
The amplification factor changing unit according to claim 15, further comprising: an amplification factor changing unit configured to change an amplification factor in the amplification unit between driving control of the forward bias applying unit and driving control of the reverse bias applying unit. Image forming apparatus. The control means includes an output means for outputting a command signal according to drive control of the forward bias application means and drive control of the reverse bias application means,
The amplification factor changing means includes switching means that is connected in parallel to a resistor that determines the amplification factor of the amplification means and that is turned on and off based on the command signal from the output means. The image forming apparatus according to claim 16. The control means is an output means for outputting a command signal according to drive control of the forward bias application means and drive control of the reverse bias application means;
The image forming apparatus according to claim 15, further comprising: a switching unit that is connected in parallel to the series connection line and performs an on / off operation based on the command signal from the output unit.

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