JP6319065B2 - Power supply device and image forming apparatus - Google Patents

Description

  The present invention relates to a power supply apparatus and an image forming apparatus, and more particularly to a technique for applying a voltage to a developer carrier.

  Conventionally, the intensity of the electric field generated between the photosensitive member (image carrier) and the developing roller is kept constant by applying a developing bias voltage in which a DC voltage and an alternating voltage are superimposed on the developing roller (developer carrier). A technique is known in which a latent image is developed while being maintained and deterioration of image quality is suppressed. The DC voltage and AC voltage are optimally determined according to, for example, the magnetic strength of the developer and the photosensitive material (for example, amorphous silicon) that forms the surface of the photoreceptor.

  Even if an optimized development bias voltage is applied, if the distance between the photoconductor and the development roller varies due to some factors such as the eccentricity of the photoconductor under development, the photoconductor and the development are accompanied accordingly. The strength of the electric field generated between the rollers varies. As a result, the amount of developer that should be supplied to the photosensitive member may be excessive or insufficient.

  For this reason, conventionally, as described in, for example, Patent Document 1 below, the electrostatic capacity between the photosensitive member and the developing roller is input to the developing roller as indicating the distance between the photosensitive member and the developing roller. The correction is performed based on the detected current, and the developing bias voltage is decreased as the detected current increase amount is larger, and the developing bias voltage is increased as the detected current decrease amount is larger.

JP2013-250302A

  However, the DC voltage and the AC voltage applied as the developing bias voltage are generated through a process such as transforming an AC voltage supplied from an AC power source such as a commercial power source or converting the AC voltage into a DC voltage. Therefore, after a lapse of time from the application start time, it gradually becomes stable at a predetermined level.

  Therefore, as in the technique described in Patent Document 1, in the case of a configuration in which the developing bias voltage is corrected based on the amount of change in the current input to the developing roller, a DC voltage and an AC voltage that are applied as the developing bias voltage. When the application is started at the same time, during the transitional period from the beginning of the application until the development bias voltage stabilizes at a predetermined level, correction is performed to greatly reduce the development bias voltage due to a large increase in current. There was a risk of being caught.

  In this case, since the development bias voltage is once greatly reduced during the transition period, the time required for the development bias voltage to stabilize becomes stable when the DC voltage and the AC voltage are individually applied one by one. There is a possibility that it may be longer than the total time of the time required for the AC voltage and the time required for the AC voltage to stabilize. As a result, there is a possibility that the time required for starting the developing operation becomes long.

  SUMMARY An advantage of some aspects of the invention is that it provides a power supply device and an image forming apparatus capable of quickly stabilizing a voltage applied to a developer carrying member.

A power supply device according to the present invention is a power supply device that applies a voltage to a developer carrying member that carries a developer, a RAM that stores a DC voltage level and an AC voltage level, and a control that indicates the DC voltage level. When a development control unit that outputs a signal and a control signal indicating the level of the AC voltage and a control signal that indicates a level of the DC voltage greater than 0 are output, the level of the DC voltage indicated by the control signal is gradually increased. When a DC power source for applying a stable DC voltage to the developer carrier and a control signal indicating the level of the AC voltage is output, the AC voltage gradually stabilizes to the level of the AC voltage indicated by the control signal. An AC power supply unit for applying a current to the developer carrying member, a current detecting unit for detecting a current input to the developer carrying member, and a change amount of the current detected by the current detecting unit. The amount of change amount that is generated and the amount that increases or decreases the level of at least one of the DC voltage and the AC voltage according to the amount of change in association with the amount of change detected by the amount of change detector The correction data stored in the change amount storage unit in association with the change amount detected by the change amount detection unit and the change amount storage unit that stores the correction data indicating the correction data is acquired and stored in the RAM. A voltage correction unit that executes a process of increasing or decreasing the level of the at least one voltage indicated by the acquired correction data, and storing the initial level of the DC voltage and the initial level of the AC voltage in the RAM. And the correction data indicates that the greater the amount of change indicating a positive value, the lower the voltage level, and the smaller the amount of change indicating a negative value. The initial setting unit stores an initial level of one of the DC voltage and the AC voltage in the RAM at a first time, and the development level is increased. control unit, after starting the output of the control signal indicating the level of the first voltage stored in the RAM, the to execute the voltage correction unit in the processing, after the first time point or al plants constant time In the second time point, the initial setting unit stores an initial level of the second voltage other than the first voltage among the DC voltage and the AC voltage in the RAM, and the development control unit Output of a control signal indicating the level of the second voltage stored in the RAM is started.

  The image forming apparatus according to the present invention includes the power supply device, an image carrier that carries a latent image, and the developer carrier that is disposed at a position facing the developer carrier, and the power source. By applying the first voltage and the second voltage to the developer carrier by the apparatus, the developer is supplied to the latent image, whereby the image developed on the image carrier is applied to a sheet. An image forming unit to be transferred.

  According to these configurations, application of the second voltage is started at a second time point after a predetermined time has elapsed from the first time point at which application of the first voltage was started. For this reason, even if the current value of the current input to the developer carrying member increases during the period from the beginning of application of the first voltage to the second time point, the level of the second voltage is decreased during the period. It is possible to prevent correction.

  As a result, the level of the second voltage is not once reduced during the above period, so that the time required for both the DC voltage and the AC voltage to stabilize at a predetermined level can be determined separately for the DC voltage and the AC voltage. When applied one by one, it is possible to reduce the possibility of being longer than the total time of the time required for the DC voltage to stabilize at a predetermined level and the time required for the AC voltage to stabilize at a predetermined level. As a result, the voltage obtained by superimposing the DC voltage and the AC voltage applied to the developer carrier can be stabilized at an early stage.

  Further, it is preferable that the predetermined time is determined as an elapsed time from the first time point to the time point when the first voltage is stabilized, which is measured in advance without applying the second voltage.

  According to this configuration, the period from the first time point when the application of the first voltage is started until the predetermined time elapses, that is, after the application of the first voltage is started, until the first voltage is stabilized. During the period up to the time point considered to be necessary, correction for decreasing the level of the second voltage can be avoided even if the current input to the developer carrier increases. As a result, it is possible to reduce the period during which correction for reducing the level of the second voltage is performed.

  As a result, the time required for both the DC voltage and the AC voltage to stabilize at a predetermined level is required until the DC voltage stabilizes to the predetermined level when the DC voltage and the AC voltage are individually applied one by one. It is possible to reduce the possibility that the time is longer than the total time of the time and the time required for the AC voltage to stabilize at a predetermined level.

  Alternatively, the predetermined time may be determined as an elapsed time measured in advance without applying the second voltage, from the first time point to the time point when the current detected by the current detection unit is stabilized. Good.

  According to this configuration, the period from the first time point when the application of the first voltage is started until the predetermined time elapses, that is, the current detected by the current detection unit after the application of the first voltage is started. During the period up to the point in time at which it is considered to be stable, correction for decreasing the level of the second voltage can be avoided even if the current input to the developer carrier increases. As a result, it is possible to eliminate a period during which correction for reducing the level of the second voltage is performed.

  As a result, the time required for both the DC voltage and the AC voltage to stabilize at the initial level is required until the DC voltage stabilizes to a predetermined level when the DC voltage and the AC voltage are individually applied one by one. The possibility of becoming longer than the total time of time and the time required for the AC voltage to stabilize at a predetermined level can be reduced.

  The first voltage is preferably the AC voltage, and the second voltage is preferably the DC voltage.

  Unlike this configuration, when the first voltage is a DC voltage and the second voltage is an AC voltage, when the application of the DC voltage is started before the AC voltage, the application of the voltage to the developer carrier is started In addition, the developer carried on the developer carrying member may be scattered.

  However, according to this configuration, since the application of the AC voltage is started before the DC voltage, the developer carried on the developer carrier at the beginning of the application of the voltage to the developer carrier. Can be moved back and forth from the developer carrier. As a result, it is possible to reduce the possibility that the developer carried on the developer carrying member at the beginning of application of voltage to the developer carrying member is scattered.

  According to the present invention, it is possible to provide a power supply device and an image forming apparatus that can quickly stabilize the voltage applied to the developer carrying member.

1 is a schematic cross-sectional view illustrating an overall configuration of a printer according to an embodiment of an image forming apparatus of the present invention. It is sectional drawing which shows schematic structure of a developing device. It is a block diagram which shows an example of the electrical constitution of the power supply device which concerns on one Embodiment of the power supply device of this invention. It is a figure which shows an example of the waveform of a developing bias voltage. It is a figure which shows an example of the correction data memorize | stored in the variation | change_quantity memory | storage part. It is a flowchart which shows the operation | movement which applies a developing bias voltage. (A) is a figure which shows an example of the waveform of DC voltage and development bias voltage when application of DC voltage and AC voltage is started simultaneously, and (B) is DC after a predetermined time has elapsed from the start of application of AC voltage. It is a figure which shows an example of the waveform of a direct current voltage and development bias voltage when the application of a voltage is started.

  Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings. In this embodiment, a printer is described as an example of the image forming apparatus. However, the present invention is not limited to this, and the image forming apparatus may be, for example, a copying machine, a facsimile machine, or a multifunction machine. FIG. 1 is a schematic cross-sectional view showing the overall configuration of a printer 1 according to an embodiment of an image forming apparatus of the present invention.

  As shown in FIG. 1, the printer 1 includes a paper feeding unit 2 that feeds paper P, an image forming unit 3, and a fixing unit 4 in the apparatus main body 1 a. The image forming unit 3 transfers a toner image based on image data received from an external computer or the like to the paper P while conveying the paper P fed from the paper feeding unit 2. The fixing unit 4 performs a fixing process for fixing the toner image transferred on the paper P by the image forming unit 3 to the paper P. Further, on the upper surface of the apparatus main body 1a, a paper discharge unit 5 for discharging the paper P on which the fixing process has been performed by the fixing unit 4 is provided.

  The paper feed unit 2 includes a paper feed cassette 21, pickup rollers 22 and 27, paper feed rollers 23, 24 and 25, and a registration roller 26. The paper feed cassette 21 stores paper P. The pickup roller 22 takes out the sheets P stored in the sheet feeding cassette 21 one by one. The pickup roller 27 takes out the paper P placed on a manual feed tray (not shown) attached to the left side surface of the device main body 1a shown in FIG. The paper feed rollers 23, 24, 25 send out the paper P taken out by the pickup rollers 22, 27 to the paper transport path. The registration roller 26 temporarily waits for the paper P sent to the paper transport path by the paper feed rollers 23, 24, 25, and then supplies the paper P to the image forming unit 3 at a predetermined timing.

  The image forming unit 3 includes an image forming unit 7, an intermediate transfer belt 31, and a secondary transfer roller 32. The image forming unit 7 primarily transfers a toner image based on image data received from an external computer or the like to the surface (contact surface) of the intermediate transfer belt 31. The secondary transfer roller 32 secondarily transfers the toner image on the intermediate transfer belt 31 onto the paper P sent from the paper feed cassette 21.

  The image forming unit 7 includes a black unit 7K, a cyan unit 7C, a magenta unit 7M, and a yellow unit 7Y. Each unit 7K, 7C, 7M and 7Y includes a photosensitive drum 37 (image carrier). Each photosensitive drum 37 rotates in the direction of the arrow (clockwise) shown in FIG. Around each photosensitive drum 37, a charger 39, an exposure device 38, a developing device 71, and the like are arranged.

  The charger 39 charges the peripheral surface of the photosensitive drum 37. The exposure device 38 irradiates the charged peripheral surface of the photosensitive drum 37 with laser light based on the image data. As a result, the exposure device 38 forms a latent image on the photosensitive drum 37 based on the image data.

  The developing device 71 forms a toner image on the peripheral surface of the photosensitive drum 37 by supplying toner to the peripheral surface of the photosensitive drum 37 on which the latent image is formed. The toner image formed on the peripheral surface of the photosensitive drum 37 is primarily transferred to the intermediate transfer belt 31 as described later.

  The intermediate transfer belt 31 is an endless belt-like rotating body. The intermediate transfer belt 31 includes a plurality of rollers such as a driving roller 33, a driven roller 34, a backup roller 35, and a primary transfer roller 36 so that the surface (contact surface) side is in contact with the peripheral surface of each photosensitive drum 37. It is stretched. Further, the intermediate transfer belt 31 is rotated endlessly by a plurality of rollers in a state where the intermediate transfer belt 31 is pressed against the photosensitive drum 37 by a primary transfer roller 36 disposed to face each of the photosensitive drums 37.

  The driving roller 33 rotates the intermediate transfer belt 31 endlessly with a driving force given by a driving source such as a stepping motor. The driven roller 34, the backup roller 35, and the primary transfer roller 36 rotate following the endless rotation of the intermediate transfer belt 31 by the driving roller 33.

  The primary transfer roller 36 applies a primary transfer bias (a polarity opposite to the toner charging polarity) to the intermediate transfer belt 31. Thus, the toner image formed on each photoconductive drum 37 is driven in the direction of the arrow (counterclockwise) shown in FIG. 1 by driving the drive roller 33 between each photoconductive drum 37 and the primary transfer roller 36. The intermediate transfer belt 31 that is circulated is sequentially overlaid and transferred (primary transfer).

  The secondary transfer roller 32 applies a secondary transfer bias having a polarity opposite to that of the toner image to the paper P. As a result, the toner image primarily transferred onto the intermediate transfer belt 31 is transferred to the paper P between the secondary transfer roller 32 and the backup roller 35, and the color transfer image is transferred to the paper P.

  The fixing unit 4 performs a fixing process on the transfer image transferred to the paper P by the image forming unit 3. The fixing unit 4 includes a heating roller 41 and a pressure roller 42 whose peripheral surface is pressed against the peripheral surface of the heating roller 41. The transfer image transferred to the paper P is fixed to the paper P by a fixing process by heating when the paper P passes between the heating roller 41 and the pressure roller 42. The paper P subjected to the fixing process is discharged to the paper discharge unit 5 by the transport roller 6. The transport roller 6 is disposed at an appropriate position between the fixing unit 4 and the paper discharge unit 5.

  Moreover, the control part 10 is provided in the apparatus main body 1a. The control unit 10 includes, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory) that stores a control program, a RAM (Random Access Memory) that temporarily stores data when various processes are executed, an input / output interface circuit, and the like. It is constituted by a microcomputer provided with a bus for connecting them. The control unit 10 controls the operation of each unit in the apparatus by executing a control program stored in a ROM or the like by the CPU.

  Next, the configuration of the developing device 71 will be described. FIG. 2 is a cross-sectional view illustrating a schematic configuration of the developing device 71. The developing devices 71 provided in each of the image forming units 7K, 7C, 7M, and 7Y have the same configuration.

  The developing device 71 includes a developing roller 72 (developer carrier), a magnetic roller 73, a paddle mixer 74, a stirring mixer 75, a panning blade 76, a partition plate 77, a DC power supply unit 93, and an AC power supply unit 94. . The photosensitive drum 37 is driven by a drum motor M1, and the developing roller 72 is driven by a developing motor M2. That is, the photosensitive drum 37 and the developing roller 72 are driven independently.

  The developing roller 72 is disposed at a position facing the photosensitive drum 37. The developing roller 72 carries toner (developer) on its peripheral surface and transports it, thereby supplying toner to the peripheral surface of the photosensitive drum 37. As a result, a latent image formed in advance on the peripheral surface of the photosensitive drum 37 is visualized (developed) as a toner image. The developing roller 72 has a built-in magnet so that a magnetic pole is formed at a position facing the magnetic roller 73. The magnetic roller 73 forms a magnetic brush with a magnet disposed therein, and supplies toner to the developing roller 72.

  The paddle mixer 74 and the agitation mixer 75 have helical blades, and charge the toner by agitating while conveying the toner in opposite directions. Further, the paddle mixer 74 supplies the charged toner to the magnetic roller 73. The ear cutting blade 76 regulates the thickness of the magnetic brush formed on the magnetic roller 73. The partition plate 77 is provided between the paddle mixer 74 and the stirring mixer 75 so that the toner can freely pass outside both ends of the partition plate 77.

  The toner charged by the paddle mixer 74 and the stirring mixer 75 is supplied to the magnetic roller 73. The toner supplied to the magnetic roller 73 is conveyed as a magnetic brush by a magnet inside the magnetic roller 73. Thereafter, the magnetic brush is moved by the rotation of the sleeve on the surface of the magnetic roller 73, and the thickness thereof is regulated when passing between the ear cutting blade 76 and the magnetic roller 73.

  The DC power supply unit 93 applies a DC voltage to the developing roller 72. The AC power supply unit 94 applies an AC voltage to the developing roller 72. By applying a developing bias voltage, which is a voltage obtained by superimposing a DC voltage output from the DC power supply unit 93 and an AC voltage output from the AC power supply unit 94, to the developing roller 72, the photosensitive drum 37 and the developing roller. A potential difference is generated between the first and second terminals 72. Due to this potential difference, the toner carried on the peripheral surface of the developing roller 72 is supplied to the photosensitive drum 37, and the latent image formed on the photosensitive drum 37 is developed.

  Below, the detail of the power supply device 9 which concerns on one Embodiment of the power supply device of this invention is demonstrated. FIG. 3 is a block diagram illustrating an example of an electrical configuration of the power supply device 9 according to an embodiment of the power supply device of the present invention.

  As shown in FIG. 3, the power supply device 9 includes a DC power supply unit 93, an AC power supply unit 94, a current detection unit 95, and a control unit 10.

  The DC power supply unit 93 is supplied with a control signal output by the development control unit 12 described later. The DC power supply unit 93 transforms an AC voltage supplied from an AC power source such as a commercial power source into an AC voltage of a predetermined level, and then rectifies the AC voltage with a rectifier circuit. As a result, the DC power supply unit 93 outputs a DC voltage having a level (predetermined level) indicated by the input control signal. In this manner, after the control signal is input, the DC power supply unit 93 outputs a DC voltage that gradually becomes stable to the level indicated by the control signal through a process such as transforming the AC voltage supplied from the AC power supply. To do. Note that the DC voltage output method by the DC power supply unit 93 is not limited to this.

  The AC power supply unit 94 receives a control signal output by a development control unit 12 described later. The AC power supply unit 94 converts an AC voltage supplied from an AC power source such as a commercial power source into a DC voltage of a predetermined level, and further converts the DC voltage into a predetermined voltage such as a peak voltage or a duty ratio indicated by the input control signal. Convert to level AC voltage. In this way, the AC power supply unit 94 is subjected to a process such as converting an AC voltage supplied from the AC power supply into a DC voltage after the control signal is input, and the level indicated by the control signal (predetermined level). A stable AC voltage is gradually generated. Note that the AC voltage generation method by the AC power supply unit 94 is not limited to this. The AC power supply unit 94 applies a voltage obtained by superimposing the generated AC voltage and the DC voltage output from the DC power supply unit 93 to the developing roller 72 as a developing bias voltage.

  The current detection unit 95 detects the current value (current) of the current input to the developing roller 72. For example, as illustrated in FIG. 3, the current detection unit 95 is connected to the AC power supply unit 94 and detects the current value of the current flowing to the output terminal of the AC power supply unit 94. Instead of this, a current detection unit 95 may be connected to a wiring unit that connects the AC power supply unit 94 and the developing roller 72 as shown by a one-dot chain line in FIG.

  The DC power supply unit 93, the AC power supply unit 94, the current detection unit 95, and the developing roller 72 shown in the broken line rectangle in FIG. 3 are a black unit 7K, a cyan unit 7C, a magenta unit 7M, and a yellow unit. 7Y is provided, and all have the same configuration.

  The control unit 10 particularly functions as an initial voltage setting unit 11, a development control unit 12, a voltage correction unit 14, a change amount detection unit 13, and a change amount storage unit 15 in connection with the control of the development bias voltage.

  The initial voltage setting unit 11 sets an initial level of a DC voltage to be output to the DC power supply unit 93. The initial voltage setting unit 11 sets an initial level of the AC voltage to be output from the AC power supply unit 94. Specifically, based on experimental values such as test operation, the initial level of the DC voltage to be applied to the developing roller 72, which is necessary for moving the toner of each color from the developing roller 72 of each color to the photosensitive drum 37, and The initial level of the AC voltage is determined in advance and stored in a ROM or the like.

  FIG. 4 is a diagram illustrating an example of a waveform of the developing bias voltage. For example, as illustrated in FIG. 4, the initial voltage setting unit 11 acquires “200 V” as the initial level of the DC voltage from the ROM or the like, and sets the peak voltage “1.5 kV” and the duty ratio “ 30% ". The level of the AC voltage is not limited to the peak voltage and the duty ratio, and may be determined by the amplitude, effective value, frequency, and the like.

  The initial voltage setting unit 11 sets the initial level of the DC voltage by storing the initial level of the DC voltage acquired from the ROM or the like in the RAM. Similarly, the initial voltage setting unit 11 sets the initial level of the AC voltage by storing the initial level of the AC voltage acquired from the ROM or the like in the RAM.

  The development control unit 12 causes the DC power supply unit 93 to apply a DC voltage at a level stored in the RAM by the initial voltage setting unit 11 and the voltage correction unit 14 described later to the developing roller 72. Specifically, the development control unit 12 acquires a DC voltage level stored in the RAM, and outputs a control signal indicating the acquired DC voltage level to the DC power supply unit 93. As a result, the DC power supply 93 applies a DC voltage that gradually becomes stable to the level indicated by the control signal to the developing roller 72.

  Further, the development control unit 12 causes the AC power supply unit 94 to apply the AC voltage at the level stored in the RAM by the initial voltage setting unit 11 and the voltage correction unit 14 described later to the developing roller 72. Specifically, the development control unit 12 acquires the level of the AC voltage stored in the RAM, and outputs a control signal indicating the level of the acquired AC voltage to the AC power supply unit 94. As a result, the AC power supply unit 94 applies an AC voltage that gradually stabilizes to the level indicated by the control signal to the developing roller 72. Details of the operation of the development control unit 12 will be described later.

  The change amount detection unit 13 detects the change amount of the current value detected by the current detection unit 95. Specifically, the change amount detection unit 13 subtracts the current value detected last time from the current value detected by the current detection unit 95, and detects the subtraction result as the change amount of the current value. Then, the change amount detector 13 outputs detection data indicating the detected change amount of the current value.

  That is, when the current value detected by the current detection unit 95 is larger than the current value detected last time, the change amount detection unit 13 outputs detection data indicating a positive (+) value. On the other hand, when the current value detected by the current detection unit 95 is smaller than the current value detected last time, the change amount detection unit 13 outputs detection data indicating a negative (−) value.

  For example, it is assumed that the current value detected last time is “100 μA” and the current value detected this time is “110 μA”. In this case, the change amount detection unit 13 outputs detection data indicating the change amount “+10 μA”. On the other hand, it is assumed that the current value detected last time is “110 μA” and the current value detected this time is “100 μA”. In this case, the change amount detection unit 13 outputs detection data indicating the change amount “−10 μA”.

  The voltage correction unit 14 uses the correction data stored in the change amount storage unit 15 to be described later, and uses the correction data stored in the RAM according to the change amount detected by the change amount detection unit 13. And the level of at least one of the AC voltages) is increased or decreased.

  The change amount storage unit 15 is configured by a part of the storage area of the ROM. The change amount storage unit 15 stores correction data indicating the amount by which the voltage correction unit 14 increases or decreases the DC voltage level in accordance with the change amount in association with the change amount detected by the change amount detection unit 13. ing.

  Hereinafter, the voltage correction unit 14 and the change amount storage unit 15 will be described in detail. FIG. 5 is a diagram illustrating an example of correction data stored in the change amount storage unit 15.

  For example, as shown in FIG. 5, the change amount storage unit 15 indicates that the DC voltage level is decreased by “20 V” in association with the change amount “+10 μA” indicating that the current has increased by “10 μA”. Correction data “DC-20V” is stored. Further, in the change amount storage unit 15, correction data “DC−25 V” indicating that the DC voltage level is decreased by “25 V” in association with the change amount “+20 μA” indicating that the current has increased by “20 μA”. Is remembered.

  As described above, the change amount storage unit 15 indicates that the greater the amount of change indicating a positive value, that is, the greater the current value detected by the current detection unit 95, the lower the DC voltage level. Correction data is stored.

  Further, the change amount storage unit 15 has correction data “DC + 20V” indicating that the DC voltage level is increased by “20V” in association with the change amount “−10 μA” indicating that the current has decreased by “10 μA”. It is remembered. The change amount storage unit 15 also has correction data “DC + 25V” indicating that the DC voltage level is increased by “25 V” in association with the change amount “−20 μA” indicating that the current has decreased by “20 μA”. It is remembered.

  Thus, the change amount storage unit 15 indicates that the smaller the amount of change indicating a negative value, that is, the lower the current value detected by the current detection unit 95, the higher the DC voltage level. Correction data is stored.

  The voltage correction unit 14 acquires correction data stored in the change amount storage unit 15 in association with the change amount indicated by the detection data output from the change amount detection unit 13, and the level of the DC voltage stored in the RAM. Is increased or decreased by the amount indicated by the acquired correction data. Thereby, the voltage correction unit 14 increases or decreases the level of the DC voltage according to the change amount indicated by the detection data output from the change amount detection unit 13.

  For example, it is assumed that correction data is stored in the change amount storage unit 15 as shown in FIG. Further, it is assumed that the detection data output by the change amount detection unit 13 indicates the change amount “+10 μA”. In this case, the voltage correction unit 14 acquires correction data “DC-20V” stored in the change amount storage unit 15 in association with the change amount “+10 μA”. Then, the voltage correction unit 14 decreases the level of the DC voltage stored in the RAM by “20 V” indicated by the acquired correction data. When the detection data output from the change amount detection unit 13 indicates the change amount “+20 μA”, the voltage correction unit 14 performs correction stored in the change amount storage unit 15 in association with the change amount “+20 μA”. Data "DC-25V" is acquired, and the level of the DC voltage stored in the RAM is decreased by "25V".

  Thus, as the correction data stored in the change amount storage unit 15 indicates, the voltage correction unit 14 increases the direct current voltage applied to the developing roller 72 as the current value detected by the current detection unit 95 increases. Decrease the level.

  On the other hand, it is assumed that the detected data indicates a change amount “−10 μA”. In this case, the voltage correction unit 14 acquires the correction data “DC + 20V” stored in the change amount storage unit 15 in association with the change amount “−10 μA”, and sets the level of the DC voltage stored in the RAM. The acquired correction data is increased by “20V”. When the detected data indicates the change amount “−20 μA”, the voltage correction unit 14 acquires the correction data “DC + 25 V” stored in the change amount storage unit 15 in association with the change amount “−20 μA”. Then, the level of the DC voltage stored in the RAM is increased by “25V”.

  Thus, as the correction data stored in the change amount storage unit 15 indicates, the voltage correction unit 14 increases the DC voltage applied to the developing roller 72 as the current value detected by the current detection unit 95 decreases. Increase the level of

  That is, it is considered that the load on the developing roller 72 decreases as the current input to the developing roller 72 increases. For this reason, the voltage correction unit 14 decreases the DC voltage applied to the developing roller 72 as the increase amount of the current increases. On the contrary, it is considered that the load on the developing roller 72 increases as the current input to the developing roller 72 decreases. For this reason, the voltage correction unit 14 increases the voltage applied to the developing roller 72 as the current decrease amount increases.

  Note that the load variation of the developing roller 72 is caused by, for example, a variation in the distance between the developing roller 72 and the photosensitive drum 37. The variation in the distance occurs due to, for example, a change in the layer thickness of the toner on the developing roller 72 or the occurrence of eccentricity in the developing roller 72 or the photosensitive drum 37. When the distance is reduced, the electrostatic capacity between the developing roller 72 and the photosensitive drum 37 is increased, so that the load on the developing roller 72 is increased. On the other hand, as the distance increases, the electrostatic capacity between the developing roller 72 and the photosensitive drum 37 decreases, and the load on the developing roller 72 decreases.

  Hereinafter, an operation for applying the developing bias voltage will be described. FIG. 6 is a flowchart showing the operation of applying the developing bias voltage. Below, in the change amount storage unit 15, similarly to the correction data shown in FIG. 5, correction data indicating the amount by which only the level of the DC voltage is increased or decreased without being increased or decreased in association with the amount of change. Is described as being stored. That is, description will be made assuming that the voltage correction unit 14 increases or decreases only the level of the DC voltage stored in the RAM according to the amount of change in current detected by the change amount detection unit 13.

  When the control unit 10 receives a print job including image data from an external computer or the like, the control unit 10 starts an image forming operation by the image forming unit 7 and starts a developing operation in the process of the image forming operation. To do. In this case, as shown in FIG. 6, the initial voltage setting unit 11 acquires the initial level of the AC voltage to be applied to the developing roller 72, which is stored in the ROM or the like, and the acquired initial level of the AC voltage is acquired. Store in RAM. Thereby, the initial voltage setting part 11 sets the initial level of an alternating voltage (S1).

  Then, the development control unit 12 starts to output a control signal indicating the level of the AC voltage (first voltage) stored in the RAM to the AC power supply unit 94. As a result, the development control unit 12 causes the AC power supply unit 94 to start applying an AC voltage at a level indicated by the control signal (S2). Thereafter, the development control unit 12 continues to output a control signal indicating the level of the AC voltage stored in the RAM until the development operation is completed.

  When the predetermined time T has not elapsed since time t1 (first time point) at which application of the AC voltage is started in step S2 (S3; NO), the development control unit 12 outputs a control signal indicating the level of the DC voltage. It is not output to the DC power supply unit 93. In this case, a DC voltage is not applied to the developing roller 72, and step S7 described later is performed in a state where only the AC voltage is applied to the developing roller 72.

  The predetermined time T is an elapsed time from the start of application of the AC voltage to the time when the AC voltage is stabilized, for example, measured in advance without applying the DC voltage to the developing roller 72 in an experiment such as a test operation. It has been established. The predetermined time T is stored in advance in a ROM or the like.

  On the other hand, when the predetermined time T has elapsed from time t1 (S3; YES) and the application of the DC voltage has not started (S4; NO), the initial voltage setting unit 11 is stored in the ROM or the like. The initial level of the DC voltage to be applied to the developing roller 72 is acquired. The initial voltage setting unit 11 sets the initial level of the DC voltage by storing the acquired initial level of the DC voltage in the RAM (S5).

  Then, the development control unit 12 starts outputting a control signal indicating the level of the DC voltage (second voltage) stored in the RAM to the DC power supply unit 93. Thus, the development control unit 12 causes the DC power supply unit 93 to start applying a DC voltage at a level indicated by the control signal at a time point (second time point) after the elapse of the predetermined time T from the time t1 (S6). Thereafter, the development control unit 12 continues to output a control signal indicating the level of the DC voltage stored in the RAM until the development operation is completed.

  After the application of the AC voltage is started in step S2, the current detection unit 95 detects the current value of the current input to the developing roller 72 regardless of whether or not the application of the DC voltage is started ( S7).

  The change amount detection unit 13 detects the change amount of the current value using the current value detected in step S7 and the current value detected in the previous time stored in the RAM (initial value is 0), and the detected value is detected. Detection data indicating the amount of change is output (S8). When the change amount detection unit 13 outputs detection data in step S8, the change amount detection unit 13 stores the current value detected in step S7 in the RAM as the current value detected last time.

  Next, as described above, the voltage correction unit 14 acquires the correction data stored in the change amount storage unit 15 in association with the change amount indicated by the detection data output in step S8, and is stored in the RAM. The level of the direct current voltage is increased or decreased by the amount indicated by the acquired correction data (S9).

  Thereby, when the application of the DC voltage in step S6 has been started, the development control unit 12 outputs a control signal indicating the level of the increased / decreased DC voltage stored in the RAM to the DC power supply unit 93. The As a result, a DC voltage at the level of the increased / decreased DC voltage is applied to the developing roller 72. On the other hand, if the application of the DC voltage in step S6 has not been started, the control signal indicating the DC voltage level is not output by the development control unit 12, so only the DC voltage level stored in the RAM is obtained. Increased or decreased.

  After the execution of step S9, when the developing operation has not been completed (S10; NO), the processes after step S3 are repeated.

  Hereinafter, an example of waveforms of the DC voltage Vd and the development bias voltage Vb during the development operation will be described. FIG. 7A is a diagram showing an example of waveforms of the DC voltage Vd and the developing bias voltage Vb when the application of the DC voltage and the AC voltage is started simultaneously, and FIG. It is a figure which shows an example of the waveform of DC voltage Vd and development bias voltage Vb when the application of DC voltage is started after time T has passed.

  In FIGS. 7A and 7B, the level of the DC voltage Vd indicates that the level is lower as it goes up, and the level is higher as it goes down. On the other hand, the level of the developing bias voltage Vb indicates a higher level as it goes upward, and indicates a level that becomes lower as it goes lower in the figure.

  For example, it is assumed that the application of the AC voltage and the DC voltage is started simultaneously at time t11 as in the prior art. In this case, as shown in FIG. 7A, the current input to the developing roller 72 greatly increases during the transition period from time t11 to time t12 when the AC voltage level becomes stable. The level of the DC voltage Vd stored in the RAM is reduced to 0 or less by the voltage correction unit 14. As a result, the DC voltage Vd is not output.

  When the AC voltage becomes stable at time t12, the level of the DC voltage Vd stored in the RAM is set to the initial level by the voltage correction unit 14 because the current input to the developing roller 72 gradually decreases. Is gradually increased. As a result, the DC voltage Vd gradually rises to the initial level.

  When the current input to the developing roller 72 becomes stable at time t <b> 13, the level of the DC voltage Vd stored in the RAM is not substantially increased or decreased by the voltage correction unit 14. As a result, the DC voltage Vd becomes stable at the initial level.

  That is, when the application of the AC voltage and the DC voltage is started at the same time, the initial level of the DC voltage and the initial level of the AC voltage are superimposed when the time Td0 has elapsed from the application start time t11 (time t13). The developed developing bias voltage Vb is applied to the developing roller 72.

  On the other hand, in the configuration of the present embodiment, as shown in FIG. 7B, in step S2 (FIG. 6), the control signal Ra indicating the initial level of the AC voltage is output to the AC power supply unit 94 at time t1. Start that. Thereby, only application of an alternating voltage is started at time t1. Then, when a predetermined time T has elapsed from time t1 and time t2 when the AC voltage is considered to be stable at the initial level indicated by the control signal Ra, in step S6 (FIG. 6), the control signal Rd indicating the initial level DC voltage is obtained. Starts to be output to the DC power supply unit 93. Thereby, application of a DC voltage is started at time t2.

  The period from time t2 to time t3 when the AC voltage level is actually stabilized is stored in the RAM by the voltage correction unit 14 due to a slight increase in the current input to the developing roller 72. The level of the DC voltage Vd is slightly reduced.

  When the AC voltage is actually stabilized at time t3, the current input to the developing roller 72 is gradually reduced, so that it is stored in the RAM by the voltage correction unit 14 in step S9 (FIG. 6). The level of the DC voltage Vd is gradually increased to the initial level. As a result, the DC voltage Vd gradually rises to the initial level.

When the current input to the developing roller 72 becomes stable at time t4 , the level of the DC voltage Vd stored in the RAM by the voltage correction unit 14 is not increased or decreased. As a result, the DC voltage Vd becomes stable at the initial level.

  That is, in the configuration of the present embodiment, the development bias voltage obtained by superimposing the initial level DC voltage and the initial level AC voltage at the time (time t4) when the time Td1 shorter than the time Td0 has elapsed from the time t1. Vb is applied to the developing roller 72.

  As described above, according to the configuration of the above embodiment, the application of the DC voltage is started at the time t2 after the elapse of the predetermined time T from the time t1 when the application of the AC voltage is started. For this reason, even if the current value of the current input to the developing roller 72 increases during the period from the beginning of the application of the AC voltage to the time t2, correction for decreasing the DC voltage level is not performed during the period. Can be.

As a result, the level of the DC voltage stored in the RAM during the period is no longer temporarily reduced, so the time required for both the DC voltage and the AC voltage to stabilize at the initial level is the DC voltage and the AC voltage. Reduces the possibility that the time required for the DC voltage to stabilize to the initial level and the time required for the AC voltage to stabilize to the initial level to be longer than the total time required for the voltage to be applied individually be able to. As a result, the developing bias voltage obtained by superimposing the DC voltage and the AC voltage applied to the developing roller 72 can be stabilized at an early stage.

  Further, in the above embodiment, the predetermined time T is set to the elapsed time from the time t1 to the time when the AC voltage is stabilized, measured in advance without applying the DC voltage.

  For this reason, the period from the time t1 when the application of the AC voltage is started until the predetermined time T elapses, that is, until the time when the AC voltage is considered to be stable after the application of the AC voltage is started. During this period, even if the current value of the current input to the developing roller 72 increases, it is possible not to perform correction for decreasing the DC voltage level. As a result, the period during which correction for reducing the level of the DC voltage is performed can be reduced.

  As a result, the time required for both the DC voltage and the AC voltage to stabilize at the initial level is required for the DC voltage to stabilize at the initial level when the DC voltage and the AC voltage are individually applied one by one. It is possible to reduce the possibility that the time is longer than the total time of the time required for the AC voltage to stabilize at the initial level.

  Further, unlike the configuration of the above embodiment, when the application of a DC voltage is started before the AC voltage, the toner carried on the developing roller 72 at the beginning when the application of the voltage to the developing roller 72 is started. There is a risk of scattering.

  However, according to the configuration of the above embodiment, since the application of the AC voltage is started before the DC voltage, the toner carried on the developing roller 72 at the beginning of the application of the voltage to the developing roller 72. Can be moved back and forth between the developing roller 72 and the photosensitive drum 37. As a result, it is possible to reduce the possibility that the toner carried on the developing roller 72 is scattered at the beginning of the application of the voltage to the developing roller 72.

  In addition, the said embodiment is only the illustration of embodiment which concerns on this invention, and is not the meaning which limits this invention to the said embodiment. For example, the following modified embodiment may be used.

  (1) As described in the above embodiment, the control unit 10 is configured by a control circuit such as an ASIC capable of performing the same control as the control instead of the configuration of controlling the operation of each unit by executing a control program. May be.

  (2) The predetermined time T is measured in advance in an experiment such as a test operation without applying a DC voltage to the developing roller 72, for example, from a time point when application of AC voltage is started (first time point). The time point when the current detected by 95 is stabilized, that is, the elapsed time until the change amount detected by the change amount detection unit 13 becomes substantially zero, may be set.

  According to the configuration of the present modified embodiment, the period from when the application of the AC voltage is started until the predetermined time T elapses, that is, after the application of the AC voltage is started, is detected by the current detection unit 95. During the period up to the time point when the current is considered to be stable, even if the current value of the current input to the developing roller 72 increases, it is possible not to perform correction for reducing the DC voltage level. As a result, it is possible to eliminate a period during which correction for reducing the level of the DC voltage is performed.

  As a result, the time required for both the DC voltage and the AC voltage to stabilize at the initial level is required for the DC voltage to stabilize at the initial level when the DC voltage and the AC voltage are individually applied one by one. It is possible to further reduce the possibility of being longer than the total time of the time and the time required for the AC voltage to stabilize at the initial level.

  (3) The change amount storage unit 15 associates the change amount with the change amount, and the larger the change amount indicating a positive value, that is, the greater the current value detected by the current detection unit 95, the greater the direct current voltage and Correction data indicating that both voltage levels are decreased may be stored. Accordingly, the voltage correction unit 14 increases the current value detected by the current detection unit 95 using the correction data stored in the change amount storage unit 15 in step S9 (FIG. 6). The level of the DC voltage and AC voltage applied to the developing roller 72 may be reduced.

  Alternatively, in the change amount storage unit 15, only the level of the AC voltage is associated with the change amount as the change amount indicating a positive value is larger, that is, as the current value detected by the current detection unit 95 is increased. Correction data indicating that the value is reduced may be stored. Accordingly, the voltage correction unit 14 increases the current value detected by the current detection unit 95 using the correction data stored in the change amount storage unit 15 in step S9 (FIG. 6). The level of the AC voltage applied to the developing roller 72 may be decreased.

  That is, the change amount storage unit 15 associates with the change amount, and the larger the change amount indicating a positive value, that is, the greater the current value detected by the current detection unit 95, the more the direct current voltage and the alternating voltage. Correction data indicating that the level of at least one of the voltages is decreased may be stored. In accordance with this, the voltage correction unit 14 uses at least one of the DC voltage and the AC voltage applied to the developing roller 72 as the current value detected by the current detection unit 95 increases using the correction data. The voltage level may be decreased.

  (4) In the above-described embodiment and each of the above-described modified embodiments, the application of the DC voltage is started after the elapse of the predetermined time T from the time when the application of the AC voltage to the developing roller 72 is started (time t1). On the contrary, the application of the DC voltage (first voltage) is first started to the developing roller 72, and the application of the AC voltage (second voltage) is started after a lapse of a predetermined time from the start of application of the DC voltage. You may make it start.

  In accordance with this, the predetermined time in the present modified embodiment is a time point (first time point) at which application of a DC voltage, which is measured in advance without applying an AC voltage to the developing roller 72 in an experiment such as a test operation, is started. ) To the time when the DC voltage stabilizes. Alternatively, for the predetermined time, for example, the current detected by the current detection unit 95 is stabilized from the time when the application of the DC voltage is started (first time) measured in advance without applying the AC voltage to the developing roller 72. The time point, that is, the elapsed time until the change amount detected by the change amount detection unit 13 becomes substantially zero, may be set.

1 Printer (image forming device)
DESCRIPTION OF SYMBOLS 3 Image formation part 9 Power supply device 10 Control part 12 Development control part 13 Change amount detection part 14 Voltage correction part 15 Change amount memory | storage part 37 Photosensitive drum (image carrier)
72 Development roller (developer carrier)
93 DC power supply unit 94 AC power supply unit 95 Current detection unit P paper T predetermined time t1 time (first time point)
t2 time (second time point)

Claims (5)

A power supply device for applying a voltage to a developer carrying member carrying a developer,
A RAM for storing a DC voltage level and an AC voltage level;
A development control unit that outputs a control signal indicating the level of the DC voltage and a control signal indicating the level of the AC voltage;
A DC power supply unit that applies a DC voltage gradually stabilized to the DC voltage level indicated by the control signal to the developer carrier when a control signal indicating the DC voltage level greater than 0 is output;
When a control signal indicating the level of the AC voltage is output, an AC power supply unit that applies an AC voltage that is gradually stabilized to the AC voltage level indicated by the control signal to the developer carrier,
A current detection unit for detecting a current input to the developer carrier;
A change amount detection unit for detecting a change amount of the current detected by the current detection unit;
A change storing correction data indicating an amount to increase or decrease the level of at least one of the DC voltage and the AC voltage according to the change amount in association with the change amount detected by the change amount detection unit. A quantity storage unit;
The correction data stored in the change amount storage unit in association with the change amount detected by the change amount detection unit is acquired, and the level of the at least one voltage stored in the RAM is acquired. A voltage correction unit that executes a process of increasing or decreasing the amount indicated by the correction data;
An initial setting unit for storing the initial level of the DC voltage and the initial level of the AC voltage in the RAM;
With
The correction data indicates that the voltage level is decreased as the change amount indicating a positive value is larger, and the voltage level is increased as the change amount indicating a negative value is smaller.
At a first time, the initial setting unit stores an initial level of one of the DC voltage and the AC voltage in the RAM, and the development control unit is stored in the RAM. After starting the output of the control signal indicating the level of the first voltage is, the voltage correction unit to execute the process,
In the second time after lapse of the first time or al plants constant time, the initial setting unit, the DC voltage and the RAM levels early in the other second voltage and the first voltage of the AC voltage And the development controller starts to output a control signal indicating the level of the second voltage stored in the RAM.   2. The power supply device according to claim 1, wherein the predetermined time is determined as an elapsed time from the first time point to a time point when the first voltage is stabilized, which is measured in advance without applying the second voltage.   2. The predetermined time is set to an elapsed time from the first time point to a time point when the current detected by the current detector is stabilized, which is measured in advance without applying the second voltage. The power supply device described in 1.   4. The power supply device according to claim 1, wherein the first voltage is the AC voltage, and the second voltage is the DC voltage. 5. A power supply device according to any one of claims 1 to 4,
An image carrier that carries a latent image, disposed at a position facing the developer carrier, and the developer carrier, and the first voltage applied to the developer carrier by the power supply device and the developer carrier An image forming unit that transfers an image developed on the image carrier onto a sheet by supplying the developer to the latent image by applying a second voltage;
An image forming apparatus comprising: