JP2011118234A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inexpensively and accurately suppress variation of potential on a photosensitive drum. <P>SOLUTION: An engine control part 202 sets discharge start voltage obtained when the photosensitive drum 101 is newly attached to the image forming apparatus as initial discharge start voltage in advance (YES in S301 to S310), and controls DC voltage to be applied by a charge bias application circuit part 301 based on the discharge start voltage and the initial discharge start voltage (S319 to S323). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus including a charging device that charges a member to be charged via a charging member.

  FIG. 9 shows a schematic configuration of a charging bias applying circuit unit 401 that is a charging DC bias circuit unit for applying a voltage to a charging member of the image forming apparatus. The setting value of the charging bias application circuit unit 401 is changed by the voltage setting circuit unit 402 according to the PWM signal. The transformer drive circuit unit 403 drives the high voltage transformer unit 404. The feedback circuit unit 405 detects a voltage value Vout applied to a charging member (or a charged body (hereinafter referred to as a charged body)) by a resistor R71 and transmits the detected voltage value Vout to the voltage setting circuit unit 402 as an analog value. The charging bias application circuit unit 401 performs control so that a constant voltage is applied to the charging member based on this value. With such a configuration, it is possible to apply a constant voltage value to the charging member by performing a series of controls (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 06-003932

  In a DC charging system that performs pre-exposure, drum memory (residual charge) may occur due to the effect of pre-exposure on the photosensitive drum potential (drum potential). Therefore, image defects such as density unevenness, fogging, and toner scattering may occur depending on the state of the surface potential of the photosensitive drum (hereinafter referred to as memory potential) when the drum memory is generated on the photosensitive drum.

  The present invention has been made under such circumstances, and an object thereof is to suppress the variation in potential on the photosensitive drum at low cost and with high accuracy.

  In order to solve the above problems, the present invention comprises the following arrangement.

  (1) Pre-exposure of a detachable image carrier, and applying a DC voltage to the charging unit uniformly charges the image carrier, and electrostatically charges the image carrier charged by the charging unit. An image forming apparatus that forms a latent image and develops the formed electrostatic latent image by a developing unit to form an image, the first applying unit applying a voltage to the charging unit, and the developing unit A second applying means for applying a voltage; a detecting means for detecting a current flowing in the charging means; and a detection by the detecting means when a DC voltage is applied to the charging means by the first applying means in a non-image area. Control means for setting a voltage applied by the first application means as a discharge start voltage when discharge is started between the charging means and the image carrier based on the current flowing through the charging means. Comprising the control means A discharge start voltage when the image carrier is newly attached to the image forming apparatus is preset as an initial discharge start voltage, and the first applying means is based on the discharge start voltage and the initial discharge start voltage. An image forming apparatus characterized by controlling a DC voltage applied by means of the above.

  According to the present invention, variations in potential on the photosensitive drum can be suppressed at low cost and with high accuracy.

Schematic configuration cross-sectional view and block diagram of image forming apparatuses according to Embodiments 1 and 2 The figure which shows the principal part of the image forming apparatus of Example 1, 2 and the figure which shows a charging bias application circuit part Schematic diagram of VI characteristic when charging bias is applied in Example 1, drum-charging roller applied voltage-drum potential characteristic diagram The figure explaining drum memory and the schematic of the VI characteristic at the time of charging bias application of Example 1 Flowchart for explaining drum memory correction processing according to the first embodiment. The figure which shows the electric potential when there is no drum memory of Example 1 and when it exists Schematic of VI characteristics at the time of charging bias application according to the conveyance speed of Example 2 Flowchart for explaining drum memory correction processing according to the second embodiment. The figure which shows the charging bias application circuit part of a prior art example

  Embodiments of the present invention will be described below with reference to the drawings.

[Configuration of Image Forming Apparatus]
FIG. 1A shows the configuration of a printer that is an image forming apparatus. The photosensitive drum 101 is an image carrier that carries an electrostatic latent image. The rotary polygon mirror 103 is rotated by a scanner motor 104. A laser beam 105 is emitted from a semiconductor laser 102 as a light source, and scans on the photosensitive drum 101 (on the image carrier). The charging roller 106 uniformly charges the photosensitive drum 101. The developing device 107 to which a developing bias is applied by a developing bias applying circuit unit (second applying means) (not shown) develops the electrostatic latent image formed on the photosensitive drum 101 with toner. In this embodiment, the electrostatic latent image is developed with toner by applying a voltage obtained by superimposing an AC voltage on a DC voltage as a developing bias to a developing roller (not shown). As a developing method, a method in which a developing roller is brought into contact with the photosensitive drum 101 and a DC voltage is applied to the developing roller for development can be employed. The photosensitive drum 101, the charging roller 106, and the developing device 107 constitute a detachable cartridge 100. That is, the photosensitive drum 101 can be attached / detached by attaching / detaching the cartridge 100. The transfer roller 108 transfers the toner image developed by the developing device 107 to a recording sheet that is a predetermined recording medium. The fixing roller 109 fuses the toner transferred to the recording paper with heat. The cassette paper feed roller 110 rotates once to feed paper from a cassette having a function of identifying the size of the recording paper and sends it out to the conveyance path. The manual paper feed roller 111 feeds the paper to the transport path from a manual paper feed port that does not have a function of identifying the size of the recording paper. The optional cassette paper feed roller 112 is detachable and feeds the paper from the cassette having a function of identifying the size of the recording paper to the conveyance path. The envelope feeder paper feed roller 113 is detachable, and feeds sheets one by one from the envelope feeder, which can stack only envelopes, to the conveyance path. The transport rollers 114 and 115 transport the paper fed from the cassette.

  The pre-feed sensor 116 detects the leading edge and trailing edge of paper fed from other than the envelope feeder. The pre-transfer roller 117 feeds the conveyed paper to the photosensitive drum 101. The top sensor 118 synchronizes the image writing (recording / printing) to the photosensitive drum 101 and the sheet conveyance for the fed sheet, and measures the length of the fed sheet in the conveyance direction. A paper discharge sensor 119 detects the presence or absence of paper after fixing. A discharge roller 120 discharges the fixed sheet outside the apparatus. The flapper 121 switches the transport destination (external discharge or removable duplex unit) of the printed paper. The conveyance roller 122 conveys the sheet conveyed to the duplex unit to the reversing unit. The reverse sensor 123 detects the leading edge / rear edge of the paper conveyed to the reverse portion. The reversing roller 124 operates the normal rotation / reverse rotation sequentially to reverse the paper, and conveys the paper to the paper re-feed unit. The refeed sensor 125 detects the presence or absence of paper in the refeed unit. The re-feed roller 126 sends the paper in the re-feed section again to the transport path.

[Block diagram of image forming apparatus]
FIG. 1B is a block diagram of a circuit configuration of a control system for controlling the image forming apparatus. The printer controller 201 expands image code data sent from an external device such as a host computer (not shown) into bit data necessary for printing by the printer, and reads internal information of the printer and displays it. The engine control unit 202 controls the operation of each unit of the printer engine in accordance with an instruction from the printer controller 201 and notifies the printer controller 201 of internal printer information. A sheet conveyance control unit 203 drives / stops a motor, a roller, and the like for conveying a recording sheet in accordance with an instruction from the engine control unit 202. The high voltage control unit 204 performs output control of each high voltage in each process such as charging, development, and transfer in accordance with an instruction from the engine control unit 202. The optical system control unit 205 controls driving / stopping of the scanner motor 104 and lighting of the laser beam 105 in accordance with an instruction from the engine control unit 202. The sensor input unit 206 inputs detection results from various sensors to the engine control unit 202. The fixing temperature control unit 207 adjusts the temperature of the fixing device to a temperature designated by the engine control unit 202.

  The option cassette control unit 208 is detachable, drives / stops the drive system according to an instruction from the engine control unit 202, and notifies the engine control unit 202 of paper presence / absence status and paper size information. The duplex unit control unit 209 is detachable, and in accordance with an instruction from the engine control unit 202, performs a paper reversal and refeed operation, and simultaneously notifies the engine control unit 202 of the operation state. The envelope feeder control unit 210 is detachable, and drives / stops the drive system according to an instruction from the engine control unit 202 and notifies the engine control unit 202 of the paper presence / absence state.

[Main parts of image forming apparatus]
FIG. 2A shows a schematic diagram of a main part of the image forming apparatus of the present embodiment, and the same components as those in FIG. The image forming apparatus according to the present exemplary embodiment includes a pre-exposure light source 1205, a charging bias application circuit unit 301 (first application unit), and a cartridge memory 1208. The cartridge memory 1208 stores, for example, information on whether or not a cartridge is newly attached to the image forming apparatus. The engine control unit 202 starts a series of controls to be described later when it is determined that a new cartridge is attached to the image forming apparatus based on information stored in the cartridge memory 1208.

[Charging bias application circuit]
FIG. 2B shows a schematic configuration of the charging bias application circuit unit 301 of this embodiment. The voltage setting circuit unit 302 can change the bias value according to the PWM signal. The transformer drive circuit unit 303 drives a high-voltage transformer unit 304 that generates a high voltage. The feedback circuit unit 306 is provided to monitor the output voltage Vout via the feedback resistor R61 so as to have an output voltage value corresponding to the setting of the PWM signal. The current detection circuit unit 305 detects a current value I63 obtained by adding the current value I62 flowing through the charging body (or a load such as a charging member) and the current value I61 flowing from the feedback circuit unit 306 by the detection resistor R63, and the analog value is detected from J501. The value is transmitted to the engine controller 202 as a value.

Until the discharge between the photosensitive drum 101 and the charging roller 106 starts, the photosensitive drum 101 and the charging roller 106 are insulated. Therefore, until the discharge is started, the current flowing through the detection resistor R63 is only I61 flowing from the feedback circuit unit 306. I61 is determined by Vpwm and Vref, R64, R65 set by the PWM signal.
I61 = (Vref−Vpwm) / R64−Vpwm / R65

Further, the output voltage is also set by the current value I61 flowing through the feedback resistor R61.
Vout = I61 × R61 + Vpwm≈I61 × R61

  That is, as indicated by a line [1] in FIG. 3A, only the current I61 corresponding to the PWM signal flows through the current detection circuit unit 305 (detection resistor R63) until the discharge is started. However, when discharge is started between the photosensitive drum 101 and the charging roller 106, the current detection circuit unit 305 flows I63 obtained by adding the current value I62 flowing through the charged body and the current value I61 flowing through the feedback circuit unit 306. That is, as shown by the line [2] in FIG. 3A, the curve has a branch point when the discharge starts. From this, the current flowing through the charged body at the time when the discharge is started can be calculated by a Δ value that is a predetermined value obtained by subtracting the straight line [1] from the curve [2]. Then, the time when this Δ value reaches a desired current value (also referred to as a discharge current value) is determined as a voltage at which discharge has started (referred to as a discharge start voltage).

[Drum memory (residual charge) problem due to pre-exposure]
In a DC charging system that performs pre-exposure, when light from a light emitting unit such as an LED serving as a pre-exposure unit is applied to the photosensitive drum 101 for each print, a drum memory (residual charge) is placed on the photosensitive drum 101 due to the light. Occurs. For this reason, the reference potential of the drum voltage is shifted as shown in FIG. As a result, compared to the case where there is no drum memory shown in FIG. 4 (a-1), when there is a drum memory of, for example, −100V as shown in FIG. In addition, image defects such as density unevenness, fogging, and toner scattering may occur. In this case, it is necessary to correct the amount of deviation of the drum voltage reference potential, that is, the value corresponding to the drum memory potential. Note that VL is a bright portion potential, Vd is a dark portion potential (charging potential), and Vdc is a DC voltage of the developing bias. Therefore, the initial discharge start voltage before the drum memory is generated on the photosensitive drum 101 when a cartridge is newly mounted (when the cartridge is initial or when it is new) is detected by using the charging bias application circuit unit 301. 1208 is recorded. Thereafter, the discharge start voltage when the optical memory on the photosensitive drum 101 is generated is detected using the charging bias application circuit unit 301 for each print, and the optical memory on the photosensitive drum 101 is calculated based on the difference from the initial discharge start voltage. FIG. 4B is a diagram for explaining the occurrence of a deviation in the discharge start voltage when there is no drum potential and when there is a drum potential. Here, the curve [2] indicates a curve of the current flowing through the photosensitive drum 101 in the initial use of the photosensitive drum 101. A curve [2] ′ represents a curve of a current flowing through the photosensitive drum 101 in a state where the photosensitive drum 101 is deteriorated by use and a drum memory (residual charge) is generated on the photosensitive drum. Therefore, it is necessary to perform control such as calculating the difference between the initial discharge start voltage and the discharge start voltage and correcting the voltage applied to the charging member and the voltage applied to the developing sleeve based on the calculated value.

[Correction based on memory potential]
A flowchart of the present embodiment is shown in FIG. The engine control unit 202 receives a power ON or print command in step S300 (hereinafter referred to as S300). The engine control unit 202 determines whether or not a cartridge (shown as CRG) is newly installed in S301 (that is, whether or not the photosensitive drum 101 is new), and stores information stored in the cartridge memory 1208 or the like. Use to judge. If the engine control unit 202 determines in S301 that a cartridge has been newly installed, the process proceeds to S302. In step S <b> 302, the engine control unit 202 starts rotating the photosensitive drum 101 that is a charged body such as pre-multi-rotation or pre-rotation, and performs pre-exposure with a predetermined drive signal in a non-image area where the photosensitive drum 101 is rotating. The optical element of the light source 1205 is caused to emit light, that is, pre-exposure is performed (S303). Here, the non-image area refers to an area before and after the image forming apparatus performs an image forming operation and during a plurality of image forming operations. The engine control unit 202 applies a predetermined DC bias (PWM [1]) by the charging bias application circuit unit 301 in S304. In step S <b> 305, the engine control unit 202 detects the current I <b> 63, which is the sum of the current values I <b> 62 flowing from the charged body and the current I <b> 61 flowing from the feedback circuit unit 306, as an analog value from J <b> 501. The engine control unit 202 calculates a discharge current from the detection value detected by the current detection circuit unit 305 according to the theory described above.

  In step S309, the engine control unit 202 compares the calculated value calculated in step S306 with the Δ value, and determines whether or not the Δ value is within the tolerance. If the engine control unit 202 determines in S309 that the calculated value is greater than the Δ value, it determines that the discharge start voltage is set to a lower value, and in step S307, steps down the bias value (PWM value). If the engine control unit 202 determines in S309 that the calculated value is smaller than the Δ value, the engine control unit 202 determines that the discharge start voltage is set higher, and in S308, steps up the bias value (PWM value). When this operation is performed and the engine control unit 202 determines in S309 that the calculated value is within the tolerance of the Δ value, in S310, the bias value (PWM [2]) at that time is set as the initial discharge start voltage. . The printer engine is ready to receive a print command at that time. If the engine control unit 202 determines in S301 that the cartridge is not new, the initial discharge start voltage has already been set, and the print command can be received.

  After receiving the print command, the engine control unit 202 starts rotation of the photosensitive drum 101 such as pre-multi rotation or pre-rotation in S311. In the non-image area where the photosensitive drum 101 is rotating, predetermined driving is performed in S312. The optical element of the pre-exposure light source 1205 is caused to emit light by a signal (pre-exposure). In S313, the engine control unit 202 applies a predetermined DC bias (PWM [3]). In step S <b> 314, the engine control unit 202 detects, as an analog value, J <b> 501 from the current I <b> 63, which is the sum of the current value I <b> 62 flowing from the charged body by the current detection circuit unit 305 and the current value flowing to the current I <b> 61 flowing from the feedback circuit unit 306. . In S315, the engine control unit 202 calculates the discharge current from the detection value detected in S314 according to the theory described above. In S318, the engine control unit 202 compares the calculated value with the Δ value, and determines whether or not it is within the tolerance of the Δ value. If the engine control unit 202 determines in S318 that the calculated value is greater than the Δ value, the engine control unit 202 determines that the discharge start voltage is set to a lower setting, and steps down the bias value (PWM value) in S316. If the engine control unit 202 determines in S318 that the calculated value is smaller than the Δ value, the engine control unit 202 determines that the discharge start voltage is set higher, and in S317, steps up the bias value (PWM value).

  This operation is performed, and when the engine control unit 202 determines in S318 that the calculated value is within the tolerance of the Δ value, in S319, the bias value (PWM [4]) at that time is set as the discharge start voltage. Thereafter, in S320, the engine control unit 202 adds a bias value PWM (CHARGE) corresponding to the drum potential to the discharge start voltage (PWM [4]). Here, PWM (CHARGE) is a PWM value (correction amount) corresponding to a voltage for charging the surface of the photosensitive drum 101. In step S321, the engine control unit 202 sets a bias value (PWM [5]) during printing (PWM [5] = PWM [4] + PWM (CHARGE)). In S322, the engine control unit 202 compares the initial discharge start voltage (PWM [2]) and the discharge start voltage (PWM [4]), and calculates a difference ΔPWM (= PWM [2] −PWM [4]). To do. In S323, the engine control unit 202 corrects the calculated value (difference ΔPWM) calculated in S322 with respect to the standard value of the developing bias (set value PWM (DEV) when there is no optical memory on the drum). For example, the difference ΔPWM is added to the standard value PWM (DEV) and set as the development bias value (PWM (DEV) + ΔPWM). After these settings are completed, printing is started in S324.

  By performing such control, as shown in FIG. 6B, the DC potential of the developing bias is corrected and changed to Vdc so that even if a drum memory is generated, the potential state is not affected. A constant contrast potential can be obtained, and a high-quality image without density unevenness can be formed. Further, when it is desired to change the density of an image, it can be realized by changing PWM (CHARGE) and PWM (DEV) to be added.

  According to this embodiment, it is possible to form a high-quality image that is not affected by the drum memory due to the influence of pre-exposure, and it is possible to set a stable contrast on the photosensitive drum. In addition, variation in potential on the photosensitive drum can be suppressed with low cost and high accuracy.

  The schematic configuration of the image forming apparatus according to the second embodiment and the schematic configuration of the charging bias applying circuit unit are the same as those of the first embodiment, and thus description thereof is omitted and the same reference numerals are used.

[Relationship between transfer speed and discharge start voltage]
FIG. 7 shows a schematic diagram of the relationship between the conveyance speed, which is the conveyance speed of the recording paper, the applied voltage, and the discharge current. As shown in FIG. 7, since the impedance between the photosensitive drum 101 and the charging roller 106 with respect to the conveyance speed is different, it can be seen that it is necessary to set a discharge current value suitable for the conveyance speed. For example, as shown in FIG. 7, it is necessary to set a large Δ value when the transport speed is fast, and to set a small Δ value when the transport speed is slow.

[Processing according to transport speed]
A flowchart of this embodiment is shown in FIG. The processing from S400 to S410 is the same as the processing from S300 to S310 in FIG. In step S411, after receiving the print command, the engine control unit 202 determines whether the conveyance speed is ppm [1] or ppm [2]. Here, ppm [1] is the first transport speed, ppm [2] is the second transport speed, and it is assumed that the relationship is ppm [1]> ppm [2]. If the engine control unit 202 determines that the transport speed is ppm [1] in S411, the engine control unit 202 sets ppm [1] as the transport speed in S412 and sets a Δ value for determining that the discharge has started in S413. One predetermined value α is set. The processing from S414 to S427 is the same as the processing from S311 to S324 in FIG. However, in S421, the engine control unit 202 determines whether the calculated value is within the tolerance of the α value by using the α value set as the Δ value in S413 when compared with the calculated value.

  If the engine control unit 202 determines that the transport speed is ppm [2] in S411, the engine control unit 202 sets ppm [2] as the transport speed in S428, and sets a Δ value for determining that the discharge has started in S429 to a second predetermined value. The value β (α> β) is set. Since the processing from S430 to S443 is almost the same as the processing from S414 to S427, only different portions will be described and description of the same processing will be omitted. In S432, the engine control unit 202 applies a predetermined DC bias (PWM [6]). In S437, the engine control unit 202 compares the calculated value with the β value, and determines whether the value is within the tolerance of the β value. In S438, the engine control unit 202 sets the bias value (PWM [7]) when the calculated value is within the tolerance of the β value as the discharge start voltage, and in S439, the drum control value is set to the discharge start voltage (PWM [7]). A bias value PWM (CHARGE) corresponding to the potential is added. In S440, the engine control unit sets a bias value (PWM [8]) at the time of printing (PWM [8] = PWM [7] + PWM (CHARGE)). In S441, the engine control unit 202 compares the initial discharge start voltage (PWM [2]) with the discharge start voltage (PWM [7]), and calculates a difference ΔPWM.

  By performing such control, a constant contrast potential that is not affected by the conveyance speed and is not affected by the optical memory state of the drum as shown in FIG. 6B can be obtained, and a high-quality image can be realized. It becomes.

  According to the present invention, variation in potential on the photosensitive drum can be suppressed at low cost and with high accuracy, a high-quality image that is not affected by the drum memory due to the influence of pre-exposure can be formed, and stable without being affected by the conveyance speed. It is possible to set the contrast.

Claims (4)

A detachable image carrier is pre-exposed, and a DC voltage is applied to the charging means to uniformly charge the image carrier, and an electrostatic latent image is formed on the image carrier charged by the charging means. An image forming apparatus that forms and forms an image by developing the formed electrostatic latent image with a developing unit,
First application means for applying a voltage to the charging means;
Second application means for applying a voltage to the developing means;
Detecting means for detecting a current flowing in the charging means;
When a DC voltage is applied to the charging unit by the first applying unit in a non-image area, a discharge occurs between the charging unit and the image carrier based on a current flowing through the charging unit detected by the detecting unit. Control means for setting the voltage applied by the first application means to the discharge start voltage when starting,
The control means presets a discharge start voltage when the image carrier is newly attached to the image forming apparatus as an initial discharge start voltage, and based on the discharge start voltage and the initial discharge start voltage, An image forming apparatus that controls a DC voltage applied by a first application unit.   The image forming apparatus according to claim 1, further comprising a storage unit that stores the initial discharge start voltage set by the control unit.   3. The image forming apparatus according to claim 1, wherein the control unit determines that the discharge has started by comparing a current value detected by the detection unit with a predetermined value. 4.   The control means uses the predetermined value as a first predetermined value when the recording medium conveyance speed is the first conveyance speed, and when the recording medium conveyance speed is a second conveyance speed slower than the first conveyance speed. The image forming apparatus according to claim 3, wherein the second predetermined value is smaller than the first predetermined value.

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