JP5530694B2 - High voltage power supply device and image forming apparatus - Google Patents

Description

  The present invention relates to a high voltage power supply device capable of controlling a developing bias voltage and an image forming apparatus including a developing unit.

  In general, in an image forming (electrophotographic) process by an image forming apparatus, a developer (toner) is transferred from a developing sleeve to a photosensitive drum having an electrostatic latent image formed on the surface thereof. The image is being developed. At this time, an electric field (electric field) generated by applying a developing bias voltage is usually used for the transfer of the developer. At this time, for example, the layer thickness of the developer is not uniform on the surface of the developing sleeve. If the developing sleeve or the photosensitive drum is decentered, the distance (interval) between the developing sleeve and the photosensitive drum varies, so that the electric field strength due to the developing bias voltage tends to become unstable. In this case, the transfer of the developer (the amount of the transferred developer) becomes unstable with variations in the electric field strength, so that the developed image has uneven density, excessive development (so-called “fogging”), line width Variations may occur and image quality may deteriorate.

  For this reason, conventionally, there is known a prior art in which a developing bias voltage obtained by superimposing a DC voltage and an AC voltage is applied to the developing sleeve, and the strength of the electric field generated between the developing sleeve and the photosensitive drum is kept constant. (For example, refer to Patent Document 1). This prior art uses a constant voltage DC voltage as the DC component of the developing bias voltage, and uses an AC voltage that is constant current controlled by a control circuit as the AC component. A developing bias voltage obtained by superimposing the constant voltage DC voltage and the constant current AC voltage is applied to the developing sleeve, and the strength of the electric field generated between the developing sleeve and the photosensitive drum is maintained to a certain degree. .

  In addition to this, a capacitor and a resistor are arranged in parallel on the output end side of the developing bias power source, and the DC voltage detection means detects the current of the DC component on the output end side, and a constant output from the DC voltage power source. The prior art of supplying is known (for example, refer to Patent Document 2).

  According to the above-described prior art (Patent Documents 1 and 2), it is possible to suppress fluctuations in electric field strength by constantly controlling the developing bias voltage to be constant, thereby preventing image quality deterioration during development to some extent. It is considered possible.

Japanese Patent Laid-Open No. 6-186830 (page 6, FIGS. 1 and 2) Japanese Patent No. 3096156

  However, in each of the above prior arts (Patent Documents 1 and 2), when adjusting the developing bias voltage, the output of the DC voltage power supply is controlled to be constant (constant voltage control) regardless of the fluctuation of the load on the developing sleeve. ing. For this reason, for example, when the distance between the developing sleeve and the photosensitive drum is changed, or when the developing time is shortened by increasing the rotation of the photosensitive drum, the load on the developing sleeve varies greatly. Therefore, a desired developing bias voltage cannot be applied only by variably controlling the AC component. This can also be understood from the background that the generation of the electric field necessary for developing the electrostatic latent image depends mainly on the DC component, and the AC component is used in an auxiliary manner. Therefore, in the prior art method, when the load on the developing sleeve fluctuates, the control of the developing bias voltage cannot sufficiently follow, and as a result, there is a problem in that the image quality is deteriorated as described above.

  In addition, even if only a constant voltage is output for the DC component by constant voltage control and only the output of the AC component is controlled variably, the desired image quality may not be maintained depending on the characteristics of the photoconductor. For example, as seen in the prior art, if an organic photoreceptor (OPC) is applied to the outer peripheral surface of the photoreceptor drum, the output of the DC component of the developing bias voltage is made constant and the output of the AC component is made. It is considered that desired image quality can be obtained by controlling. However, when amorphous silicon is applied as the photosensitive member, the surface potential of the photosensitive member is higher than that of the organic photosensitive member (OPC), and the load variation of the developing sleeve is increased accordingly. In this case, there is a problem that stable image quality cannot be sufficiently maintained only by adjusting only the output of the AC component as in the prior art.

  Accordingly, an object of the present invention is to provide a technique capable of appropriately controlling the developing bias voltage in accordance with load fluctuations and maintaining the image quality without being influenced by the characteristics of the photoreceptor.

  In order to solve the above-described problems, first, the present invention provides a developer carrying member for developing an electrostatic latent image formed on the surface of an image carrying member with a developer carried on the developer carrying member. On the other hand, a high voltage power supply device is provided that applies a voltage in which a constant voltage DC voltage and a constant voltage AC voltage are superimposed as a developing bias voltage necessary for developing an electrostatic latent image using a developer. In particular, the high-voltage power supply device of the present invention includes a constant voltage DC power supply unit that outputs a DC component included in the development bias voltage, a constant voltage AC power supply unit that outputs an AC component included in the development bias voltage, and an electrostatic latent image And a control circuit that variably controls the output of each of the direct current component and the alternating current component in accordance with fluctuations in the load required for development.

  According to the high-voltage power supply device of the present invention, even if the load required for development fluctuates due to some factor, the output of each of the DC component and the AC component can be variably controlled according to the load variation. In particular, since the direct current component contributes to the generation of a main electric field during the transition of the developer, in the present invention, it is possible to improve the image quality by variably controlling the direct current component of the development bias voltage according to the load fluctuation. It is extremely effective. Further, since the output of not only the direct current component but also the alternating current component is variably controlled, it is possible to appropriately control the developing bias voltage in accordance with various load fluctuations.

  In addition, the high-voltage power supply apparatus of the present invention can further include a load detection circuit that detects a load on the developer carrier required for developing the electrostatic latent image. In this case, it is preferable that the control circuit variably controls the output of each of the direct current component and the alternating current component in accordance with the load variation detected by the load detection circuit.

  If it is said aspect, by detecting the load of a developer carrier with a load detection circuit beforehand, a control signal will be produced | generated with a control circuit according to this load, and each of the direct-current component of a developing bias voltage, and alternating current component of each The output can be controlled in real time.

  In the high-voltage power supply device of the present invention, the load detection circuit can detect the load on the developer carrier based on the strength of the electric field generated between the developer carrier and the image carrier. In addition, the control circuit has a storage unit that stores in advance an appropriate value of the output corresponding to the load of the developer carrier for each of the output of the DC component and the AC component, and is detected from the storage unit by the load detection circuit. It is possible to read out an appropriate value corresponding to the loaded load and control each of the output of the DC component and the AC component.

  In this case, a change in the electric field strength caused by the developing bias voltage can be directly detected as a load fluctuation, so that variable control with higher accuracy is possible. In addition, since an appropriate value for variable control is set in advance according to the load at that time, there is no need to calculate a target value for control each time, and the burden on the control circuit can be reduced accordingly. Generation of unstable control behavior (for example, overshoot or hunting) can be reliably prevented.

  Secondly, the present invention provides an image carrier having an electrostatic latent image formed on the surface, a developer carrier that is disposed opposite to the image carrier and carries a developer for developing the electrostatic latent image, and An image forming apparatus including a power supply unit that applies a necessary developing bias voltage to a developer carrying member is provided. In particular, the power supply unit described above includes a constant voltage DC power supply unit that outputs a DC component of the development bias voltage, a constant voltage AC power supply unit that outputs an AC component of the development bias voltage, and a developer carrying required for developing an electrostatic latent image. And a control circuit that variably controls the output of each of the direct current component and the alternating current component in accordance with fluctuations in body load.

  According to the image forming apparatus of the present invention, even if the load required for development fluctuates due to some factor, the output of each of the DC component and the AC component can be variably controlled according to the load variation. In particular, in the image forming apparatus, in addition to the development of the electrostatic latent image, various operations such as supply (feed) and conveyance of the print medium, transfer and fixing of the developed image onto the print medium, paper discharge, etc. In the case of supplying power from the power supply unit to each part of the image forming apparatus, the load on the developer carrier may fluctuate due to the influence. In addition, since the DC component of the developing bias voltage contributes to the generation of a main electric field when the developer is transferred, the DC component of the developing bias voltage is variably controlled in accordance with load fluctuations in the present invention. Is extremely effective in improving image quality. In addition, the output of not only the direct current component but also the alternating current component is variably controlled, so that it is possible to appropriately control the developing bias voltage according to various load fluctuations. As a result, it greatly contributes to maintaining and improving image quality. can do.

  In the image forming apparatus of the present invention, the power supply unit may further include a load detection circuit that detects a load of the developer carrier required for developing the electrostatic latent image. In this case, the control circuit can variably control the output of each of the direct current component and the alternating current component in accordance with the load variation detected by the load detection circuit.

  In this case as well, since the change in electric field strength caused by the developing bias voltage can be directly detected as a load change, variable control with higher accuracy is possible. In addition to the development of the electrostatic latent image, it is possible to quickly cope with load fluctuations caused by various operations of the image forming apparatus, so that practical control as an image forming apparatus can be realized.

  The load detection circuit preferably detects the load on the developer carrier based on the strength of the electric field generated between the developer carrier and the image carrier. Further, the control circuit has a storage unit that stores an appropriate value of the development bias voltage corresponding to the load in advance for the detected load, and reads the appropriate value corresponding to the load from the storage unit to generate a direct current of the development bias voltage. It is preferable to control the output of each of the component and the AC component.

  In this case as well, the change in the electric field strength caused by the developing bias voltage can be directly detected as a load change. Further, even when the load fluctuates due to various operations necessary for image formation, it is possible to quickly detect the load fluctuation from the change in the electric field strength, so that variable control with higher accuracy is possible. Similarly, since an appropriate value for variable control is set in advance according to the load at that time, it is not necessary to calculate a target value for control each time, and the burden on the control circuit can be reduced accordingly. Thus, it is possible to reliably prevent the occurrence of unstable control behavior (for example, overshoot or hunting).

  The image forming apparatus of the present invention is suitable for a mode in which an amorphous silicon photoconductor is mounted as an image carrier.

  When the photosensitive member is made of amorphous silicon, the potential is higher than that of the organic photosensitive member (OPS), and the proportion of the generation of the electric field necessary for development depends on the DC component. Therefore, if a method of variably controlling not only the AC component of the developing bias voltage but also the DC component output as in the present invention is employed, the load on the developer carrying member caused by the characteristics of the photosensitive member can be reduced. On the other hand, it is possible to maintain or improve the image quality by keeping the electric field strength constant while dynamically responding.

  As described above, the high-voltage power supply device and the image forming apparatus of the present invention can optimize the output of each of the direct current component and the alternating current component of the developing bias voltage applied to the developer carrier in accordance with the load variation, and thereby the image. Quality can be improved.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment. It is a block diagram which shows the structure of a power supply unit roughly. 6 is a flowchart of developing bias voltage control by load variation control processing. It is the schematic which shows the waveform (basic example) of the developing bias voltage which superimposed the DC voltage on the AC voltage. It is the schematic which shows the 1st control example at the time of carrying out the variable control of the direct current component from the basic example of a developing bias voltage. It is the schematic which shows the 2nd control example at the time of carrying out the variable control of the alternating current component from the basic example of a developing bias voltage. It is the schematic which shows the 3rd control example at the time of carrying out the variable control of each output of an alternating current component and a direct current component from the basic example of a developing bias voltage.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus 1 according to an embodiment. The image forming apparatus 1 includes a printer, a copier, a facsimile machine, and a multifunction machine having both functions of transferring a toner image onto the surface of a printing medium such as printing paper based on image information input from the outside. Or the like.

  An image forming apparatus 1 shown in FIG. 1 is, for example, a tandem color printer. The image forming apparatus 1 includes a square box-shaped apparatus main body 2 that forms (prints) a color image on a sheet therein, and discharges the sheet on which the color image is printed on the upper surface of the apparatus main body 2. Paper discharge section (discharge tray) 3 is provided.

  In the lower part of the apparatus main body 2, a paper feed cassette 5 for storing paper is disposed. A stack tray 6 for supplying manually fed sheets is disposed at the center of the apparatus main body 2. An image forming unit 7 is provided on the upper part of the apparatus main body 2. The image forming unit 7 forms an image on a sheet based on image data such as characters and designs transmitted from the outside of the apparatus.

  As shown in FIG. 1, a first transport path 9 for transporting paper fed from the paper feed cassette 5 to the image forming unit 7 is disposed on the left side of the apparatus main body 2. A second transport path 10 for transporting paper fed from the stack tray 6 to the image forming unit 7 is disposed from the right part to the left part of the apparatus main body 2. In the upper left part of the apparatus main body 2, a fixing unit 14 that performs a fixing process on a sheet on which an image is formed by the image forming unit 7 and a sheet that has been subjected to the fixing process are conveyed to the sheet discharging unit 3. 3 conveyance paths 11 are arranged.

  The paper feed cassette 5 can be replenished by pulling it out of the apparatus main body 2 (for example, the front side in FIG. 1). The paper feed cassette 5 includes a storage unit 16 in which at least two types of paper having different sizes in the paper feed direction can be selectively stored. Note that the paper stored in the storage unit 16 is fed out to the first transport path 9 side by sheet by the paper feed roller 17 and the separating roller 18.

  The stack tray 6 can be opened and closed on the outer surface of the apparatus main body 2, and manual sheets are loaded one by one or a plurality of sheets are stacked on the manual feed portion 19. Note that the sheets placed on the manual feed unit 19 are fed out one by one by the pickup roller 20 and the separating roller 21 to the second conveyance path 10 side.

  The first conveyance path 9 and the second conveyance path 10 are joined before the registration roller 22, and the sheet supplied to the registration roller 22 waits for a while and performs skew adjustment and timing adjustment. , And sent to the secondary transfer unit 23. The full color toner image on the intermediate transfer belt 40 is secondarily transferred to the sent paper by the secondary transfer unit 23. Thereafter, the sheet on which the toner image is fixed by the fixing unit 14 is reversed in the fourth conveyance path 12 as necessary, and a full-color toner image is also formed on the surface opposite to the first by the secondary transfer unit 23. Secondary transferred. After the toner image on the opposite surface is fixed by the fixing unit 14, the toner image passes through the third conveyance path 11 and is discharged to the paper discharge unit 3 by the discharge roller 24.

  The image forming unit 7 includes four image forming units 26 to 29 that form black (K), cyan (C), magenta (M), and yellow (Y) toner images, and these image forming units 26 to 29. The intermediate transfer unit 30 is configured to synthesize and carry the toner images of the respective colors formed in 29.

  Each of the image forming units 26 to 29 includes a photosensitive drum 32 (image carrier), a charging unit 33 arranged to face the peripheral surface of the photosensitive drum 32, and a downstream side of the charging unit 33 and photosensitive. A laser scanning unit 34 for irradiating a laser beam to a specific position on the peripheral surface of the photosensitive drum 32; and a downstream side of the laser beam irradiation position from the laser irradiating unit 34 and facing the peripheral surface of the photosensitive drum 32. And a cleaning unit 36 disposed on the downstream side of the developing unit 35 and facing the circumferential surface of the photosensitive drum 32. Further, the developing unit 35 includes a developing sleeve 37 (developer carrying member) that carries a developer, and the developing sleeve 37 and the photosensitive drum 32 face each other.

  Note that the photosensitive drums 32 of the image forming units 26 to 29 are rotated counterclockwise in the drawing by a drive motor (not shown). Further, in the developing units 35 of the image forming units 26 to 29, black toner, cyan toner, magenta toner, and yellow toner are stored in the toner boxes 51, respectively.

  The intermediate transfer unit 30 includes a rear roller (drive roller) 38 disposed near the image forming unit 26, a front roller (driven roller) 39 disposed near the image forming unit 29, and a rear roller. 38 and the intermediate transfer belt 40 disposed between the front roller 39 and the downstream side of the developing unit 35 in the photosensitive drum 32 of each of the image forming units 26 to 29 can be pressed through the intermediate transfer belt 40. The four transfer rollers 41 are provided.

  In the intermediate transfer unit 30, the toner images of the respective colors are superimposed and transferred onto the intermediate transfer belt 40 at the positions of the transfer rollers 41 of the image forming units 26 to 29. Become.

  The first transport path 9 transports the paper fed from the paper feed cassette 5 to the intermediate transfer unit 30 side, and includes a plurality of transport rollers 43 disposed at predetermined positions in the apparatus main body 2. And a registration roller 22 disposed in front of the intermediate transfer unit 30 for timing the image forming operation and the paper feeding operation in the image forming unit 7.

  The fixing unit 14 performs processing for fixing the unfixed toner image on the paper by heating and pressurizing the paper on which the toner image has been transferred by the image forming unit 7. The fixing unit 14 includes a roller pair including, for example, a heating pressure roller 44 and a fixing roller 45. Of these, the pressure roller 44 is made of, for example, metal, and the fixing roller 45 is made of a metal core and an elastic body. It has a surface layer (for example, silicon sponge) and a release layer (for example, PFA). A heat roller 46 adjacent to the fixing roller 45 is provided, and a heating belt 48 is wound around the heat roller 46 and the fixing roller 45.

  When viewed in the sheet conveyance direction, conveyance paths 47 are provided on the upstream side and the downstream side of the fixing unit 14, and the sheet conveyed through the intermediate transfer unit 30 is pressurized through the upstream conveyance path 47. It is introduced into the nip between the roller 44 and the fixing roller 45. The paper that has passed between the pressure roller 44 and the fixing roller 45 is guided to the third conveyance path 11 through the conveyance path 47 on the downstream side.

  The third transport path 11 transports the paper on which the fixing process has been performed by the fixing unit 14 to the paper discharge unit 3. For this reason, a transport roller 49 is disposed at an appropriate position in the third transport path 11, and the discharge roller 24 is disposed at the outlet thereof.

  FIG. 2 is a block diagram schematically showing the configuration of the power supply unit 50. The power supply unit 50 is built in the apparatus main body 2 described above, and the power supply unit 50 supplies electric power necessary for various operations (charging, development, transfer, etc.).

  The power supply unit 50 is an example of a high-voltage power supply device, and this power supply unit 50 applies a developing bias voltage to the developing sleeve 37 for each color (Y, M, C, K) with respect to the image forming operation by the image forming apparatus 1. Can do. In the following description, it is assumed that the power supply unit 50 is provided for each color, and unless otherwise noted, the description of the configuration of each part applies to all colors in common. However, control operations and load detection are performed for each color.

  The power supply unit 50 mainly includes a DC power supply unit 52 and an AC power supply unit 54, and the DC bias power supply unit 52 and the AC power supply unit 54 constitute a developing bias power supply unit 58. Among these, the DC power supply unit 52 converts, for example, an AC voltage transformed by a transformer into a DC voltage by a rectifier, and outputs this as a constant voltage DC voltage (DC component). The AC power supply 54 outputs the AC voltage transformed by the transformer as a constant voltage AC voltage (AC component), and superimposes it on the constant voltage DC voltage to output it as a developing bias voltage.

  An output end 56 is connected to the AC power supply unit 54, and the power supply unit 50 is connected to the developing sleeve 37 via the output end 56. Therefore, the power supply unit 50 can apply a developing bias voltage (a constant voltage DC voltage and a constant voltage AC voltage superimposed) to the developing sleeve 37 through the output end 56.

  The power supply unit 50 is provided with, for example, a load detection circuit 60 for detecting a load on the developing sleeve 37, and the load detection circuit 60 is connected to the AC power supply unit 54. The load detection circuit 60 can detect, for example, a current flowing to the output end 56 as a load on the developing sleeve 37. Here, the load detection circuit 60 is connected to the AC power supply unit 54 as an example. However, the load detection circuit 60 is connected to the output end 56 (or the development sleeve 37), for example, and the development sleeve 37 is connected. It is also possible to detect the load.

  The power supply unit 50 has a control circuit 62, and a load detection signal is input to the control circuit 62 from the load detection circuit 60. The control circuit 62 is connected to the DC power supply unit 52 and the AC power supply unit 54, respectively, and can control the output of the constant voltage DC voltage, the amplitude of the constant voltage AC voltage, the duty ratio, and the like. .

  The control circuit 62 further includes a storage unit 64. The storage unit 64 is, for example, a memory device such as a ROM. In the storage area, a load variation detected by the load detection circuit 60 is written, and an appropriate development bias voltage corresponding to the load variation at that time is written. Value data can be stored in advance. Further, the storage unit 64 stores a control program (software) executed by the control circuit 62 when controlling the developing bias voltage.

  The variation in the load on the developing sleeve 37 may be caused by, for example, a variation in the distance (interval) between the developing sleeve 37 and the photosensitive drum 32. Alternatively, the load on the developing sleeve 37 may fluctuate indirectly due to fluctuations in the power supply voltage caused by various operations in addition to development while the development bias voltage to be applied during development fluctuates.

  The variation in the distance between the developing sleeve 37 and the photosensitive drum 32 is caused by, for example, a change in the layer thickness of the developer formed on the peripheral surface of the developing sleeve 37. For example, when the developing sleeve 37 and the photosensitive drum 32 are decentered, the interval between the developing sleeve 37 and the photosensitive drum 32 fluctuates irregularly with these rotations, and the electric field strength increases. That is, when the distance between the developing sleeve 37 and the photosensitive drum 32 is decreased, the load on the developing sleeve 37 is increased as compared with the distance until then. At this time, the load detection circuit 60 detects an increase in load in real time based on the decrease in the current value, and transmits the detection signal to the control circuit 62.

  When the increase in the load is detected as described above, the control circuit 62 reads the appropriate value of the output corresponding to the load at that time from the storage unit 64, and outputs the DC component of the developing bias voltage based on the appropriate value. The control signal is generated in such a direction that the voltage is decreased and the amplitude (peak voltage) is attenuated for the output of the AC component. Based on this control signal, the development bias power supply unit 58 actually reduces the output of the constant voltage DC voltage, and develops a development bias voltage in which these are superimposed while the amplitude (peak voltage) of the constant voltage AC voltage is attenuated. Applied to the developing sleeve 37. As a result, the strength of the electric field generated between the developing sleeve 37 and the photosensitive drum 32 can be lowered to a certain strength.

  On the other hand, when the load on the developing sleeve 37 is reduced (decreased), the output of the constant voltage DC voltage is increased, and a developing bias voltage in which the amplitude of the constant voltage AC voltage is amplified is applied. . As a result, the strength of the electric field generated between the developing sleeve 37 and the photosensitive drum 32 can be increased to a certain strength. The above-described relationship between the load on the developing sleeve 37 and the electric field strength is an example. When an increase in the load is detected, the electric field strength is increased to a certain level. In some cases, the relationship may be reversed.

  As described above, the control circuit 62 generates a control signal for outputting a desired developing bias voltage based on the load variation detected by the load detecting circuit 60, and the DC power supply unit 52 and the AC power supply unit 54 develop the developing bias. The outputs of the DC component and AC component of the voltage are variably controlled. Then, the controlled developing bias voltage is applied to the developing sleeve 37 via the output end 56 as described above, and as a result, the intensity of the electric field necessary for development is controlled to be constant. As a result, it is possible to suppress the density unevenness and fogging of the developed image, the fluctuation of the line width, and the like and form a high quality image.

  The above is the outline of the variable control of the developing bias voltage by the power supply unit 50. More specifically, the above variable control is realized by the control circuit 62 executing the load fluctuation control process as a control program. Further, the variable control is executed for each color (Y, M, C, K) as described above according to the load variation of the developing sleeve 37 for each color.

  FIG. 3 is a flowchart illustrating a procedure example of the load variation control process. Hereinafter, a method for controlling the developing bias voltage by the control circuit 62 will be specifically described.

  In step S <b> 10, the control circuit 62 detects the load on the developing sleeve 37 based on the detection signal transmitted from the load detection circuit 60. Here, for example, the load applied to the developing sleeve 37 can be detected by detecting the value of the current flowing through the output end 56 with the load detection circuit 60 described above. Usually, if the current value increases, the load decreases. Conversely, if the current value decreases, the load is considered to increase. When the load is detected in step S10, the control circuit 62 next proceeds to step S12.

  In step S <b> 12, the control circuit 62 determines whether or not the detected load is fluctuated as compared to before detection. If it is determined that the detected load has fluctuated (Yes), the control circuit 62 next executes step S14. At this time, the determination as to whether or not the load fluctuates is performed, for example, by taking the difference between the load detected in the previous time and the current time and comparing the value with a reference value (threshold value). That is, if the load difference exceeds the reference value, it is determined that a change has occurred, and if the difference is equal to or less than the reference value, it is determined that no change has occurred. As a result, a stable control operation can be realized without excessively reacting to a small load change that can be ignored in practice.

  On the other hand, if it is determined that no load fluctuation has been detected (No), the control circuit 62 proceeds to step S16 without executing step S14.

  In any case, when the control circuit 62 determines that the load has changed (step S12: Yes), the information on the current load is temporarily stored (written) in the storage unit 64 in the next step S14.

  Next, in step S <b> 16, the control circuit 62 determines whether or not to form an image at this timing (whether or not development with toner is performed). If an image is to be formed (Yes), the control circuit 62 proceeds to step S18. On the other hand, particularly when an image is not formed at the current timing (No), the control circuit 62 temporarily exits from the load fluctuation control process and returns to the previous process (for example, a main program (not shown)) (return). .

  When image formation is performed (step S16: Yes), in the next step S18, the control circuit 62 determines the appropriate values stored in advance in the storage unit 64 (appropriate values for the direct current component and the alternating current component corresponding to the load variation). ) And a control signal to be output is generated.

  In step S20, the control circuit 62 outputs a control signal to the AC power supply unit 54 or the DC power supply unit 52 to be controlled. Thereby, at least one of the constant voltage DC voltage (DC component) and the constant voltage AC voltage (AC component) is variably controlled. In this case, both the constant voltage DC voltage and the constant voltage AC voltage are not always variably controlled, but only one of them may be variably controlled.

  In this way, the control circuit 62 generates a control signal according to the load variation, outputs the control signal to the power supply units 52 and 54 to be controlled, and after the superimposition in a state where each output is variably controlled. A developing bias voltage is generated.

[Basic example]
FIG. 4 is a conceptual diagram showing a waveform of a developing bias voltage in which a constant voltage DC voltage and a constant voltage AC voltage are superimposed. In this embodiment, the waveform shown in FIG. 4 is used as a basic example of the developing bias voltage.

In this basic example, a constant voltage DC voltage of 200 V is superimposed on a constant voltage AC voltage having a frequency of 3 kHz, a duty ratio of 30%, and a peak voltage Vpp of 1.6 kV, so that the output waveform is viewed in the amplitude direction as a whole. Shifting in the positive (+) direction.

[First control example]
Next, FIG. 5 is a schematic diagram showing a first control example when the DC component of the development bias voltage is variably controlled from the waveform of the basic example shown in FIG. In the first control example, the output from the DC power supply unit 52 is changed (increased) from 200 V to 220 V by the control signal output from the control circuit 62. Therefore, as compared with the basic example shown in FIG. 4, it can be seen that the entire AC waveform is shifted in the positive (+) direction in the amplitude direction. Other values are the same as in the basic example.

  The DC component of the development bias voltage greatly contributes to the image quality such as the density and line width of the developed image. Therefore, as in the first control example, by controlling the output of the DC component of the developing bias voltage in accordance with the load on the developing sleeve 37, it is possible to prevent density unevenness, fogging, line width variation, and the like. .

[Second control example]
FIG. 6 is a schematic diagram showing a second control example when the AC component of the developing bias voltage is variably controlled from the basic waveform shown in FIG. In the second control example, the peak voltage Vpp of the AC component is changed from 1.6 kV to 1.7 kV and the duty ratio is changed from 30% to 40% with respect to the basic example of the developing bias voltage shown in FIG. It has changed. As for the constant voltage DC voltage, 200 V is output as in the basic example.

  As described above, the AC component of the developing bias voltage is also variably controlled according to the load variation, so that the developing bias voltage can be finally set to the optimum value.

[Third control example]
FIG. 7 is a schematic diagram showing a third control example when the output of each of the AC component and the DC component of the developing bias voltage is variably controlled from the waveform of the basic example shown in FIG. Here, the waveform of the developing bias voltage in which the direct current component of the first control example shown in FIG. 5 and the alternating current component of the second control example shown in FIG. 6 are superimposed is shown, but the present invention is not limited to this. Absent. In the third control example, the amplitude and duty ratio of the output waveform are increased as compared with the basic example shown in FIG. 4, and the entire waveform is shifted in the positive direction as viewed in the amplitude direction. .

  As described above, according to the image forming apparatus 1 of the present embodiment, it is possible to variably control the output of each of the direct current component and the alternating current component of the developing bias voltage in accordance with the load variation of the developing sleeve 37. is there. Thereby, the strength of the electric field generated between the developing sleeve 37 and the photosensitive drum 32 can be kept constant, and the deterioration of the quality of the developed image can be prevented.

  The present invention is not limited to the above-described embodiment and can be implemented with various modifications. For example, the frequency and duty ratio of the AC component, the peak voltage, the value of the DC component voltage, the shift amount, etc. are not limited to the values given in the embodiment, but are variably controlled to values suitable for the development bias voltage. be able to.

  Further, the load detection circuit 60 can detect the load of the developing sleeve 37 based on not only the current value but also other measurement results such as impedance.

  The control circuit 62 not only changes the load on the developing sleeve 37 caused by fluctuations in the intensity of the electric field generated between the developing sleeve 37 and the photosensitive drum 32 but also changes the power supply voltage. Load variations can also be controlled.

  In one embodiment, the control circuit 62 performs variable control using a control program (software). For example, the outputs of the power supply units 52 and 54 are analogized using the detection signal from the load detection circuit 60 as a feedback signal. A control circuit for variable control may be realized by hardware.

  Furthermore, the present invention can be applied to the photosensitive drum 32 having various photosensitive member characteristics. In particular, the present invention is suitable for an amorphous silicon photoconductor, but the photoconductor drum 32 using an organic photoconductor (OPC) may be applied.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 26, 27, 28, 29 Image forming unit 32 Photosensitive drum 37 Development sleeve 50 Power supply unit 52 DC power supply part 54 AC power supply part 58 Development bias power supply part 60 Load detection circuit 62 Control circuit

Claims (3)

When the electrostatic latent image formed on the surface of the image carrier is developed with the developer carried on the developer carrier, the electrostatic latent image using the developer is developed on the developer carrier. A high-voltage power supply device that applies a voltage in which a constant voltage DC voltage and a constant voltage AC voltage are superimposed as a development bias voltage necessary for development,
A constant voltage DC power supply unit that outputs a DC component included in the development bias voltage;
The AC component included in the developing bias voltage is output, and the developing bias voltage is applied to the developer carrier in a state where the AC component is superimposed on the DC component output from the constant voltage DC power supply unit. Voltage AC power supply,
When the developing bias voltage is applied to the developer carrying member, the electric field generated between the developer carrying member and the image carrying member is determined as the magnitude of the current flowing from the constant voltage AC power source to the developer carrying member. and the strength, and the load detecting circuit for detecting a change in its as fluctuation of the load of the developer carrier required for development of the electrostatic latent image,
It has a storage unit that stores in advance appropriate values of the direct current component and the alternating current component corresponding to the load of the developer carrier, and is required for developing the electrostatic latent image by the load detection circuit. When a load change is detected, a control for reading an appropriate value corresponding to the changed load detected by the load detection circuit from the storage unit and variably controlling the output of each of the DC component and the AC component A high-voltage power supply device comprising a circuit. An image carrier on which an electrostatic latent image is formed on the surface;
A developer carrying member disposed opposite to the image carrier and carrying a developer for developing the electrostatic latent image;
A power supply unit that applies a voltage obtained by superimposing a constant voltage DC voltage and a constant voltage AC voltage as a development bias voltage necessary for developing the electrostatic latent image using the developer to the developer carrier; An image forming apparatus,
The power supply unit is
A constant voltage DC power supply unit that outputs a DC component of the developing bias voltage;
A constant voltage alternating current that outputs an alternating current component of the developing bias voltage and applies the developing bias voltage to the developer carrier in a state in which the direct current component output from the constant voltage direct current power supply unit is superimposed on the alternating current component. A power supply,
When the developing bias voltage is applied to the developer carrying member, the electric field generated between the developer carrying member and the image carrying member is determined as the magnitude of the current flowing from the constant voltage AC power source to the developer carrying member. and the strength, and the load detecting circuit for detecting a change in its as fluctuation of the load of the developer carrier required for development of the electrostatic latent image,
It has a storage unit that stores in advance appropriate values of the direct current component and the alternating current component corresponding to the load of the developer carrier, and is required for developing the electrostatic latent image by the load detection circuit. When a change in the load of the developer carrier is detected, an appropriate value corresponding to the changed load detected by the load detection circuit is read from the storage unit, and outputs of the direct current component and the alternating current component are output. And a control circuit that variably controls the image forming apparatus. The image forming apparatus according to claim 2 ,
The image carrier is
An image forming apparatus having an amorphous silicon photoconductor on a surface.

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