JP2006039099A - Image forming apparatus and control method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus and a control method thereof which allow a contrast potential for determining a range of brightness of a visible image to be formed on a target image carrier, to be precisely acquired. <P>SOLUTION: The image forming apparatus comprises a photosensitive drum 1, a charging roller 2, an exposure part 3, a developing unit 4, a potential sensor 8, a potential sensor control part 107, a developing high voltage circuit 108, a charging high voltage circuit 109, a switch 110, a controller 111, etc. A voltage equal to a surface potential of the photosensitive drum 1 is generated by a high voltage power source 107b of the potential sensor control part 107 and is attenuated by a voltage dividing output part 107b of the potential sensor control part 107 and is output. A developing DC high voltage output from a developing DC high voltage generation part 108b of the developing high voltage circuit 108 is divided by the voltage dividing output part 107b. The controller 111 controls the developing DC high voltage output of the developing DC high voltage generation part 108b on the basis of a comparison result between a voltage division result and a target value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus capable of detecting a surface potential of an image carrier.

  First, schematic configurations of various image forming apparatuses will be described.

  FIG. 12 is a schematic diagram illustrating a schematic configuration example of an image forming apparatus for forming a monochromatic image.

  In FIG. 12, the image forming apparatus forms a monochrome image on a recording material by an electrophotographic method. The photosensitive drum 201 is an image bearing member in which a photoconductive layer of an inorganic photosensitive member such as amorphous silicon is formed on the outer peripheral surface of a grounded aluminum cylinder, and a predetermined peripheral speed (process speed) in a direction indicated by an arrow by a driving mechanism (not shown). ). The charging roller 202 rotates following the rotation of the photosensitive drum 201, and a predetermined voltage is applied from a charging high voltage power source (not shown), so that the surface of the photosensitive drum 201 is uniformly primary with a predetermined polarity and potential. Charge it. The voltage applied by the charging high-voltage power supply is corrected based on the photosensitive drum surface potential detected by the potential sensor 208.

  Next, the exposure unit 203 exposes the surface of the photosensitive drum 201 subjected to the primary charging process along the scanning line in accordance with target image information to form an electrostatic latent image of the image information. Next, the developing device 204 develops the electrostatic latent image as a toner image by applying a predetermined voltage from a developing high voltage power source (not shown). This toner image is transferred to a recording material P fed at a predetermined timing from a paper feeding unit (not shown) in a transfer nip portion that is a pressure contact portion between the transfer roller 253 and the photosensitive drum 201. A transfer bias voltage having a polarity opposite to the charging polarity of the toner is applied to the transfer roller 253. Thereafter, the fixing device 207 fixes the toner image of the recording material P conveyed by a conveyance mechanism (not shown) as a permanent image, and outputs it as an image formed product. Reference numeral 206 denotes a cleaner for collecting residual toner.

  FIG. 13 is a schematic diagram illustrating a schematic configuration example of an image forming apparatus for forming a color image.

  In FIG. 13, the image forming apparatus forms a color image on a recording material by electrophotography by superimposing a plurality of color toner images. First, an electrostatic latent image is formed on the photosensitive drum 201, and this is sequentially developed as a toner image by developing devices 204a to 204d of four colors (yellow, magenta, cyan, and black). Next, a toner image is transferred onto the intermediate transfer belt 251 each time by the primary transfer roller 253, thereby superimposing a plurality of color toner images, and transferring these onto the recording material P all at once by the secondary transfer roller 257. To do. Thereafter, the fixing device 207 fixes the toner image on the recording material P to obtain a color image.

  FIG. 14 is a schematic diagram illustrating the configuration of a tandem multiple transfer type image forming apparatus.

  In FIG. 14, the image forming apparatus is provided with a process unit such as a photosensitive drum and a developing device for each color of yellow, magenta, cyan, and black, and can form a full color image in one pass. After the photosensitive drums 201a to 201d are uniformly charged by the primary charging rollers 202a to 202d, the exposure units 203a to 203d perform exposure according to the image signal, thereby forming electrostatic latent images on the photosensitive drums 201a to 201d. Form. Thereafter, the toner images are developed by the developing devices 204a to 204d.

  Next, the toner images on the photosensitive drum are multiplex-transferred onto the intermediate transfer belt 251 by the primary transfer rollers 253a to 253d, and the toner images are further transferred to the recording material P by the secondary transfer rollers 256 and 257. Thereafter, the fixing device 207 fixes the toner image on the recording material P to obtain a color image. Reference numerals 206a to 206d and 255 denote residual toner collecting cleaners.

  Next, a method for determining the charging DC high voltage output and the developing DC high voltage output in the image forming apparatus will be described.

  FIG. 15 is a schematic diagram showing the configuration of the periphery of the photosensitive drum of the image forming apparatus according to the conventional example.

  In FIG. 15, around the photosensitive drum 201, a charging roller 202, an exposure unit 203, a potential sensor 208, a developing device 204, a charge removal unit 312 and the like are arranged. The charging roller 202 is uniformly charged with a predetermined potential by supplying a charging high voltage output (AC voltage + DC voltage) generated by the charging high voltage circuit 309. The charging high voltage circuit 309 outputs a predetermined charging high voltage output based on a control value from the controller 411. The exposure unit 203 includes a laser scanner and an optical system, and forms an electrostatic latent image on the surface of the photosensitive drum based on an image signal (not shown). The potential sensor 208 detects the surface potential of the photosensitive drum 201. The potential sensor control unit 407 outputs the detection result of the potential sensor 208 to the controller 411.

  The developing device 204 is supplied with the developing high-voltage output (AC voltage + DC voltage) generated by the developing high-voltage circuit 408, and thereby attaches toner to the electrostatic latent image on the photosensitive drum to form a visible image. The development high-voltage circuit 408 outputs a predetermined development high-voltage output based on the control value from the controller 411. The neutralization unit 312 is disposed upstream of the charging roller 202 in the photosensitive drum rotation direction, and neutralizes residual charges on the photosensitive drum 201.

  Here, the configuration of the development high voltage circuit 408 and the relationship between the development DC high voltage output and the control value will be described.

  FIG. 16 is a block diagram showing the configuration of the development high voltage circuit 408.

  In FIG. 16, the development AC high voltage generator 501 generates an AC component of development high voltage output. The development DC high voltage generation unit 502 generates a DC component of the development high voltage output. The output of the development AC high voltage generation unit 501 is accumulated on the output of the development DC high voltage generation unit 502 and is output as a development high voltage output (AC + DC).

  The development DC high voltage detection unit 503 detects the development DC high voltage, divides the DC high voltage output of the development DC high voltage generation unit 502 with a resistor or the like, and inputs the divided result to the development DC high voltage control unit 504. The development DC high voltage control unit 504 keeps the output of the development DC high voltage generation unit 502 at a predetermined value based on the control value based on the control value input from the controller 411 and the detection result of the development DC high voltage detection unit 503. The development DC high voltage generator 502 is controlled.

  FIG. 17 is a diagram showing a relationship (ideal characteristic) between the development DC output control value and the development DC output.

  In FIG. 17, when the development DC output control value (control voltage) is 2 V or less, the development DC high-voltage output is 0 V (output stopped state), and when the development DC output control value exceeds 2 V, the development DC output control value This indicates that the development DC high voltage output has a linear relationship. When the development DC output control value is 6V, the development DC high voltage output is -500V, and when the development DC output control value is 10V, the development DC high voltage output is -1000V.

  When the development high-voltage circuit 408 has the configuration shown in FIG. 16, the characteristics ideally become as shown in FIG. 17, but in reality, the development high-voltage circuit 408 is shown in FIG. The characteristic deviates from the characteristic. An example is shown in FIG.

  FIG. 18 is a diagram illustrating the relationship (characteristic deviating from ideal characteristics) between the development DC output control value and the development DC output.

  In FIG. 18, when (a) is an ideal characteristic (characteristic of FIG. 17), a characteristic whose inclination is shifted from the ideal characteristic is (b), and a characteristic obtained by offsetting the ideal characteristic is (c). In both (b) and (c), the development DC high-voltage output deviates from −500 V when the development DC output control value is 6 V.

  An example in which the development high-voltage circuit 408 is configured for the purpose of correcting deviation from the ideal characteristic will be described with reference to FIG.

  FIG. 19 is a block diagram showing a configuration of the developing high-voltage circuit 408 in the case where the deviation from the ideal characteristic is corrected.

  In FIG. 19, the difference from the configuration in FIG. 16 is the development DC high voltage detection unit 803. In the example shown in FIG. 19, in order to improve the accuracy of the DC component of the development high voltage output when a predetermined development DC output control value is input, a variable resistor is provided on one side of the voltage dividing resistor of the development DC high voltage detector 803. In this example, the development high-voltage circuit 408 is separately adjusted in advance.

  In the case of FIG. 19, for example, before the development high voltage circuit 408 is incorporated in the image forming apparatus, the development DC output control value 6V is input using a reference power source such as a low voltage source, and the output of the development DC high voltage generation unit 502 at that time. The variable resistance of the development DC high voltage detector 803 is adjusted so that becomes −500V. An example of the adjustment result is shown in FIG.

  FIG. 20 is a diagram showing the relationship between the development DC output control value and the development DC output when the variable resistance of the development high voltage circuit 408 is adjusted.

  20, in the case of the characteristics as shown in FIG. 18B, the characteristics are corrected as shown in FIG. 20A (the same ideal characteristics as FIG. 18A). The In the case of the characteristic as shown in FIG. 18C, the characteristic is corrected as shown in FIG. 20C, and the characteristic around the development DC output control value 6V (development DC high voltage output -around 500V) is greatly improved. Is done. That is, if an output level that is actually used frequently is selected as the development DC output control value at the time of the adjustment, and the adjustment is made with the output level, the characteristics in the actual use region are greatly improved.

  Next, a basic method for determining the charging DC high voltage output and the developing DC high voltage output when performing image formation with the image forming apparatus will be described with reference to FIGS. 15, 21, and 22. FIG.

  FIG. 21 is a diagram showing the relationship between the charging DC high voltage output and the surface potential of the photosensitive drum.

  In FIG. 21, the illustrated characteristics indicate the relationship between the DC component of the charging high voltage output applied to the charging roller 202, that is, the charging DC high voltage output, and the surface potential of the photosensitive drum 201 detected by the potential sensor 208.

  FIG. 22 is a flowchart showing a method for determining a charging DC high voltage output and a developing DC high voltage output.

  This processing is performed, for example, immediately before the image forming apparatus executes the image forming process, or when the temperature of the fixing device reaches a predetermined temperature after the power is turned on, or when a predetermined time has elapsed since the power is turned on, or the temperature is detected. This is performed in various cases such as when the output from the environmental sensor changes by a predetermined value or more.

  In FIG. 22, when entering the determination sequence of the charging DC high voltage output and the development DC high voltage output, first, the controller 411 turns on the potential sensor control remote signal (step S2101). Next, the controller 411 inputs a predetermined controller voltage to the charging high voltage circuit 309 so that the charging DC high voltage output becomes a charging DC high voltage VCHG1 which is a predetermined voltage.

  The charging high voltage circuit 309 outputs the charging DC high voltage VCHG1, and at this time, the exposure unit 203 detects the surface potential of the exposed portion of the photosensitive drum 201 and the surface potential of the unexposed portion by the potential sensor 208, respectively. Here, the potential of the exposed portion of the photosensitive drum 201 in the exposure unit 203 is called a bright portion potential (denoted as VL), and the bright portion potential when the charging DC high-voltage output is VCHG1 is VL1. Further, the potential of the portion of the photosensitive drum 201 that is not exposed by the exposure unit 203 is referred to as dark portion potential (denoted as VD), and the dark portion potential when the charging DC high-voltage output is VCHG1 is defined as VD1 (step S2102).

  Next, the charging DC high voltage output is changed, and VD and VL are measured again. In the case of FIG. 21, the controller 411 inputs a predetermined controller voltage to the charging high voltage circuit 309 so that the charging DC high voltage output becomes VCHG2. The charging high voltage circuit 309 outputs the charging DC high voltage VCHG2 and measures VL2 and VD2 as described above (step S2103).

  Then, the VD characteristics as shown in FIG. 21 can be obtained from the VD1 and VD2, and the VL characteristics as shown in FIG. 21 can be obtained from the VL1 and VL2 (step S2104).

  Next, the controller 411 reads a “fogging potential” (denoted as Vback) determined in advance from a storage unit such as a RAM (not shown) in the controller in order to prevent fogging (attachment of toner to a white background). ) And a detection result of an environmental sensor (not shown), a “target contrast potential” (denoted as VCONT) that is determined in advance by image density adjustment control, gradation characteristic stabilization control, and the like (visible to be formed on the photosensitive drum) The potential that determines the range of brightness of the image is read (step S2105). Next, the controller 411 obtains a development DC output characteristic (VDEV = VD−Vback) in which an offset of Vback is provided in the VD characteristic (step S2106). Further, the controller 411 obtains a difference characteristic (VD−Vback−VL) between the VDEV characteristic and the VL characteristic (step S2107).

  Next, the controller 411 calculates the charging DC high voltage VCHG0 when the difference characteristic (VD−Vback−VL) is equal to the contrast potential VCONT (the range indicated by the double-headed arrow in FIG. 21), and stores it in the storage unit. Store (step S2108). Next, the controller 411 calculates the development DC high voltage output VDEV0 when the charging DC high voltage output calculated in step S2108 is VCHG0, and stores it in the storage unit (step S2109). Thereafter, the controller 411 turns off the potential sensor control remote signal (step S2110), and ends this sequence.

  In the case of the color image forming apparatus shown in FIG. 13, since the characteristics of the toner image are different for each color of yellow, magenta, cyan, and black, the target contrast potential for each color is stored in the storage unit in advance. In step S2105 to step S2109 in FIG. 22, calculation for four colors is performed to calculate a charging DC high voltage output VCHG0 and a development DC high voltage output VDEV0 for each color.

  Regarding the charging DC high-voltage output, the charging DC high-voltage output VCHG0 of the maximum color among the charging DC high-voltage outputs VCHG0 for each color is set as the charging DC high-voltage output VCHG0 common to the colors.

  Further, in the case of the tandem multiple transfer type image forming apparatus shown in FIG. 14, since the characteristics of the toner image are different for each color of yellow, magenta, cyan, and black, the photosensitive drum is not shared for each color. The target contrast potential for each color is stored in the storage unit in advance, and all the processes in steps S2101 to S2110 in FIG. 22 are performed for each color to calculate the charging DC high voltage output VCHG0 and the development DC high voltage output VDEV0 for each color. .

  When actually forming an image, the controller 411 reads the VCHG0 and VDEV0 from the storage unit and inputs a predetermined controller voltage to the charging high voltage circuit 309 so that the charging DC high voltage output becomes VCHG0. At the same time, a predetermined controller voltage is input to the development high voltage circuit 408 so that the development DC high voltage output becomes VDEV0, thereby forming an image.

  In the determination sequence of the charging DC high-voltage output and the development DC high-voltage output described above, the charging DC high-voltage output and the development DC high-voltage output are determined using 2 points of VCHG. .

  A method for controlling the image forming conditions by determining the target contrast potential for each color according to the humidity in the image forming apparatus and using the determination sequence of the charging DC high voltage output and the development DC high voltage output as described above as a basic sequence has been proposed. (For example, refer to Patent Document 1).

Further, the determination sequence of the charging DC high-voltage output and the development DC high-voltage output described above is used as a basic sequence, and the bright portion potential (VL) is measured for each predetermined number of image forming sheets to correct the charging DC high-voltage output and the development DC high-voltage output A method has also been proposed (see, for example, Patent Document 2).
Patent No. 2808107 Japanese Patent No. 3217584

  However, in the conventional image forming apparatus, the target value of the development DC high voltage output during the image forming operation is determined based on the measurement result of the photosensitive drum surface potential by the potential sensor. The development DC high voltage output is controlled on the basis of the output of the output voltage detector of the development high voltage circuit. Therefore, the development DC high voltage output that is actually applied to the developer is the target value due to variations in the constants of the output voltage detector, environmental changes such as temperature and humidity, and deterioration and aging of each part of the circuit. May be off.

  Further, in order to reduce the deviation of the development DC high voltage output from the target value, the development high voltage circuit may be adjusted when the image forming apparatus is assembled. However, when the adjustment is performed, accuracy can be initially obtained. However, in the same manner as described above, the actual development can be performed due to environmental changes such as temperature and humidity, and deterioration of each part of the circuit and changes over time. The development DC high voltage output applied to the device may deviate from the target value.

  If the development DC high voltage output deviates from the target value, the target contrast potential cannot be obtained by the image forming apparatus, and the target gradation property cannot be realized in an image formed by the image forming apparatus, or a continuous image There has been a problem that density change occurs during the forming operation.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of accurately obtaining a contrast potential for determining a light / dark range of a visible image to be formed on a target image carrier and a control method therefor. There is to do.

  In order to achieve the above object, the present invention provides a charging unit for charging an image carrier, an exposure unit for exposing the charged image carrier, and a latent image formed on the image carrier by exposure. A developing means for forming a visible image, a potential detecting means for detecting a surface potential of the image carrier, and a developing DC voltage generating means for generating a developing DC voltage constituting a developing voltage supplied to the developing means, A voltage dividing means that constitutes the potential detecting means and attenuates and outputs a voltage generated by a power source that generates a voltage equal to the surface potential of the image carrier, generates a developing DC voltage generated from the developing DC voltage generating means. It also serves as a detecting means.

  The present invention also provides a charging means for charging the image carrier, an exposure means for exposing the charged image carrier, and a developing means for making a latent image formed on the image carrier by exposure visible. And a potential detecting means for detecting the surface potential of the image carrier, and a developing DC voltage generating means for generating a developing DC voltage constituting a developing voltage supplied to the developing means. A voltage equal to a surface potential of the image carrier is generated by a power source included in the potential detection unit, and the voltage is attenuated and output by a voltage dividing unit included in the potential detection unit. The developing DC voltage generated from the voltage is divided by the voltage dividing means, and the developing DC voltage generated from the developing DC voltage generating means is controlled based on the comparison result between the divided pressure result and the target value.

  According to the present invention, a part of the potential detecting means, that is, the voltage dividing means is configured to also serve as means for detecting the developing DC voltage that constitutes the developing voltage supplied to the developing means. A voltage equal to the surface potential of the image carrier is generated by a power source provided in the potential detection means, and the voltage is attenuated and output by the voltage dividing means. Further, the developing DC voltage generated from the developing DC voltage generating means is divided by the voltage dividing means, and the developing DC voltage generated from the developing DC voltage generating means is controlled based on the comparison result between the divided voltage result and the target value. Thereby, the surface potential detection of the image carrier and the development DC voltage control are performed using the same detection circuit, that is, the voltage dividing means, thereby improving the accuracy over the entire output range of the development DC voltage and making it the target. It is possible to accurately obtain a contrast potential for determining the range of light and darkness of the visible image to be formed on the image carrier.

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

[First Embodiment]
FIG. 1 is a schematic diagram showing the configuration of the periphery of the photosensitive drum of the image forming apparatus according to the first embodiment of the present invention.

  In FIG. 1, the image forming apparatus includes a photosensitive drum 1, a charging roller 2, an exposure unit 3, a developing device 4, a potential sensor 8, a control unit 107a, a high voltage power source 107b, and a voltage dividing output unit (voltage dividing circuit) 107c. A development high voltage circuit 108 having a sensor control unit 107, a development AC high voltage generation unit 108a, and a development DC high voltage generation unit 108b, a charging high voltage circuit 109, a switch 110, and a controller 111 are provided.

  This embodiment is different from the above-described conventional example (FIG. 15) in that a point A which is a connection point between the output of the high voltage power source 107b of the potential sensor control unit 107 and the input of the partial pressure output unit 107c, and the development high voltage circuit The difference is that the switch 110 is connected to the development DC high voltage output of the development DC high voltage generator 108b. The other elements of the present embodiment are the same as the corresponding ones of the above-described conventional example (FIG. 15), and thus description thereof is omitted.

  The potential sensor control unit 107 detects the surface potential of the photosensitive drum 1 by the potential sensor 8 in response to a potential sensor control remote signal from the controller 111. At that time, the potential sensor control unit 107 controls the high voltage power source 107b based on the detection signal from the potential sensor 8, and performs feedback control (zero) so that the high voltage generated by the high voltage power source 107b becomes equal to the surface potential of the photosensitive drum 1. Method). The potential sensor control unit 107 detects the high voltage generated by the high voltage power source 107b equal to the surface potential of the photosensitive drum 1 by the voltage dividing output unit 107c configured by a resistor or the like, and attenuates it to 1/300, for example. Output (when the output of the potential sensor control unit 107 is open).

  In the development high-voltage circuit 108, the development AC high-voltage generator 108a generates an AC high-voltage waveform having a predetermined frequency and a predetermined amplitude. The development DC high voltage generation unit 108b generates a DC high voltage based on the development DC high voltage control signal from the controller 111. The above-described AC high voltage is stacked on this DC high voltage to obtain the development high voltage output of the development high voltage circuit 108. The development high voltage circuit 108 supplies a development high voltage output voltage to the developing device 4.

  The development DC high voltage generator 108b will be described in more detail. The development DC high-voltage output of the development high-voltage circuit 108 is connected via a switch 110 to point A, which is a connection point between the output of the high-voltage power source 107b of the potential sensor control unit 107 and the input of the partial pressure output unit 107c. When the switch 110 is ON (when the potential sensor control remote signal for the potential sensor control unit 107 is OFF), the development DC high voltage output of the development high voltage circuit 108 is divided by the voltage dividing output unit 107c of the potential sensor control unit 107. Pressure and a partial pressure result can be input to the controller 111.

  The controller 111 compares the target development DC high voltage output with the output of the partial pressure output unit 107c of the potential sensor control unit 107, and based on the comparison result, the development DC high voltage generation unit 108b of the development high voltage circuit 108 is developed DC. Input a high voltage control signal. The development DC high voltage generator 108 b generates a development DC high voltage based on a development DC high voltage control signal from the controller 111.

  That is, when the development high voltage circuit 108 starts to operate in response to a development high voltage remote signal (not shown), the development DC high voltage detection circuit (development DC high voltage detection circuit in FIG. This is used as a detection unit 503, a circuit corresponding to the development DC high voltage detection unit 803 in FIG. 19, and performs feedback control to keep the development DC high voltage at a predetermined value.

  FIG. 2 is a block diagram illustrating configurations of the potential sensor 8 and the potential sensor control unit 107 of the image forming apparatus.

  In FIG. 2, the potential sensor 8 includes piezoelectric elements 8a and 8b, a tuning fork vibrator 8e, a measurement electrode 8f, and a detection circuit 8g. The potential sensor control unit 107 further includes a drive circuit 107d in addition to the control unit 107a, the high-voltage power source 107b, and the divided voltage output unit 107c.

  The piezoelectric elements 8a and 8b are disposed on both arms of the tuning fork vibrator 8e. The piezoelectric element 8b is a driving piezoelectric element for vibrating the tuning fork vibrator 8e, and the piezoelectric element 8a is a detecting piezoelectric element for detecting vibration of the tuning fork vibrator 8e.

  Next, the operation will be described. When the potential sensor control remote signal input from the controller 111 to the potential sensor control unit 107 is turned on, the operations of the potential sensor 8 and the potential sensor control unit 107 are started. First, the drive circuit 107 d of the potential sensor control unit 107 inputs a drive signal to the piezoelectric element 8 b of the potential sensor 8. Then, the tuning fork vibrator 8e starts to vibrate, and its tip part vibrates in the directions indicated by the left and right arrows 8c and 8d, respectively. When the tuning fork vibrator 8e starts to vibrate, the piezoelectric element 8a converts the vibration into an electric signal and outputs it as a vibration detection signal.

  The drive circuit 107d controls the frequency of the drive signal so that the phase difference between the drive signal and the vibration detection signal becomes a predetermined value. Thereby, the tuning fork vibrator 8e continues to vibrate in a resonance state. On the other hand, when the tuning fork vibrator 8e vibrates, the electrostatic capacitance between the measurement electrode 8f and the photosensitive drum 1 periodically changes, and the charge amount of the measurement electrode 8f changes accordingly. An AC voltage signal proportional to the potential difference between the measurement electrode 8f and the photosensitive drum 1 can be obtained by converting the change in the charge amount into a voltage by the detection circuit 8g.

  Each part constituting the potential sensor 8 operates using an output of a high-voltage power supply 107b described later (output at point A in FIGS. 1 and 2) as a reference potential.

  And the control part 107a of the electric potential sensor control part 107 controls the output of the high voltage power supply 107b so that the amplitude of the alternating voltage signal which is the output from the detection circuit 8g becomes zero. Here, when the amplitude of the AC voltage signal is zero, the tuning fork vibrator 8e vibrates and the electrostatic capacitance between the measurement electrode 8f and the photosensitive drum 1 periodically changes. In this state, the charge amount of the measurement electrode 8f does not change. This state means that the surface potential of the photosensitive drum 1 and the potential of the measurement electrode 8f, that is, the surface potential of the photosensitive drum 1 and the output of the high voltage generator 107b are the same potential. Thereby, the surface potential of the photosensitive drum 1 can be obtained (zero method).

  The potential sensor control unit 107 divides the output voltage of the high voltage generation unit 107b at this time into, for example, 1/300 and outputs the divided voltage. Note that 1/300 is the case where the output of the potential sensor control unit 107 is open, and the potential of the detection output unit of the potential sensor control unit 107 is connected by connecting some circuit to the potential sensor control unit 107. Is a value different from 1/300 of the output voltage of the high voltage generator 107b.

  Further, the potential sensor control unit 107 uses the point A in FIGS. 1 and 2 which is the output of the high-voltage power supply 107b and the input of the voltage dividing output unit 107c as an external interface, and one side of the switch 110 in FIG. Is connected.

  FIG. 3 is a diagram showing the relationship between the surface potential of the photosensitive drum 1 and the output voltage of the potential sensor control unit 107 when the output of the potential sensor control unit 107 is open.

  In FIG. 3, when the surface potential of the photosensitive drum 1 is −600 V, the output voltage of the detection output unit of the potential sensor control unit 107 is −2 V, and when the surface potential of the photosensitive drum 1 is −900 V, the potential sensor control unit 107. The output voltage of the detection output unit of FIG.

  FIG. 4 is a block diagram showing a configuration of a portion related to the potential sensor control unit 107 in the controller 111.

  4, the controller 111 includes a level shift unit 111a, an A / D conversion unit 111b, a CPU 111c, a storage unit (not shown) such as a RAM, and a lookup table (not shown).

  FIG. 5 is a diagram showing the relationship between the output voltage of the potential sensor control unit 107 and the surface potential of the photosensitive drum 1 and the output of the A / D conversion unit 111b of the controller 111.

  In FIG. 5, the surface potential measurement range of the photosensitive drum 1 required by the image forming apparatus is −900V to + 60V.

  Operations of the level shift unit 111a, the A / D conversion unit 111b, and the CPU 111c in FIG. 4 will be described with reference to FIG. The output voltage of the detection output unit of the potential sensor control unit 107 is input to the level shift unit 111a of the controller 111. The level shifter 111a is detected by the potential sensor controller 107 so that the input of the A / D converter 111b is, for example, 0 to 3.3 V in the surface potential measurement range of the photosensitive drum 1 required by the image forming apparatus. The output voltage level of the output unit is shifted.

  The level shift unit 111a level-shifts the detection value from the potential sensor control unit 107 when the surface potential of the photosensitive drum 1 is −900V so that the output voltage of the level shift unit 111a becomes 3.3V. Further, the detection value from the potential sensor control unit 107 when the surface potential of the photosensitive drum 1 is + 60V is level-shifted, and the output voltage of the level shift unit 111a becomes 0V. The A / D conversion unit 111b is configured with 10 bits, and outputs 3FF (hex) when 3.3V is input to the CPU 111c when inputting 0V.

  The controller 111 is provided with a lookup table in advance, can convert the output of the A / D converter 111b to the surface potential of the photosensitive drum 1, and the converted data is an operation unit (not shown) of the image forming apparatus. Etc. can also be displayed.

  Next, processing relating to a method for determining charging DC high-voltage output and development DC high-voltage output and a method for controlling development DC high-voltage output in the image forming apparatus having the above-described configuration will be described.

  This processing is performed, for example, immediately before the image forming apparatus executes an image forming operation, or when the temperature of the fixing unit reaches a predetermined temperature after the power is turned on, or when a predetermined time has passed since the power is turned on, or the temperature is detected. This is performed in various cases such as when the output from the environmental sensor changes by a predetermined value or more.

  First, a method for determining a charging DC high voltage output and a development DC high voltage output is basically the same as that shown in the flowchart of FIG. However, in step S2101 in FIG. 22, the potential sensor control remote signal from the controller 111 to the potential sensor control unit 107 is turned on with the switch 110 turned off. As a result, the controller 111 can obtain the surface potential of the photosensitive drum 1 based on the potential sensor by the measurement method described with reference to FIGS. In other words, the target charging DC high-voltage output (VCHG0) can be determined and the target development DC high-voltage output (VDEV0) determined based on the potential sensor reference can be obtained by the processing in steps S2102 to S2110.

  In the case of a color image forming apparatus as shown in FIG. 13, the characteristics of the toner image are different for each color of yellow, magenta, cyan, and black. Therefore, the target contrast potential for each color (potential for determining the range of light and darkness of the visible image to be formed on the photosensitive drum 1) is stored in advance, and calculations for four colors are performed in steps S2105 to S2109 in FIG. The charging DC high voltage output VCHG0 and the development DC high voltage output VDEV0 for each color are calculated.

  Regarding the charging DC high voltage output, the charging color high voltage output VCHG0 of the color among the charging DC high voltage output VCHG0 for each color is set to be the common charging DC high voltage output VCHG0.

  Further, in the case of the tandem multiple transfer type image forming apparatus as shown in FIG. 14, the characteristics of the toner image are different for each color of yellow, magenta, cyan, and black, and the photosensitive drum is not shared for each color. Therefore, the target contrast potential for each color is stored in advance, and all the processes in steps S2101 to S2110 in FIG. 22 are performed for each color to calculate the charging DC high-voltage output VCHG0 and the development DC high-voltage output VDEV0 for each color.

  Next, the operation when the target development DC high voltage output (VDEV0) determined as described above is actually output will be described.

  When outputting the development DC high voltage output, the development DC high voltage generator 108b of the development high voltage circuit 108 is controlled by the controller 111 with the development DC output (VDEV0) as a target value. Details will be described below.

  When outputting the development DC high voltage, first, the potential sensor control remote signal to the potential sensor control unit 107 is turned OFF, and the switch 110 is turned ON. As a result, the development DC high-voltage output of the development high-voltage circuit 108 is divided by the partial pressure output unit 107 c of the potential sensor control unit 107, and the partial pressure result is input to the controller 111. The controller 111 compares the target development DC high voltage output with the output of the partial pressure output unit 107c of the potential sensor control unit 107, and based on the comparison result, the development DC high voltage generation unit 108b of the development high voltage circuit 108 is developed DC. Input a high voltage control signal.

  That is, if the signal input from the voltage dividing output unit 107c to the controller 111 is smaller than the target development DC high voltage output (VDEV0), the controller 111 increases the development DC high voltage output to the development DC high voltage generation unit 108b. To output a development DC high voltage control signal. On the other hand, if the signal input from the partial pressure output unit 107c to the controller 111 is larger than the target development DC output (VDEV0), the controller 111 reduces the development DC high voltage output to the development DC high voltage generation unit 108b. To output a development DC high voltage control signal.

  The development DC high voltage generation unit 108b generates a development DC high voltage based on a development DC high voltage control signal input from the controller 111. As a result, the output of the development DC high voltage generator 108b is controlled so that the development DC high voltage output (VDEV0) is always constant.

  Further, the internal temperature and humidity of the image forming apparatus are detected, and when one or both of the internal temperature and humidity changes by a predetermined value or more, the target contrast potential is corrected at a predetermined timing, and the above-described charging direct current The charging DC high voltage output (VCHG0) and the development DC high voltage output (VDEV0) are corrected by the method of determining the high voltage output and the development DC high voltage output. In addition, by controlling the development DC high voltage output described above, it is possible to always perform image formation at a stable density against environmental changes such as temperature and humidity.

  In addition, during the continuous image forming operation, the charging DC high voltage output and the development DC high voltage output are determined every time a predetermined number of images are formed, and the charging DC high voltage output (VCHG0) and the developing DC high voltage output (VDEV0). Correct. In addition, during the continuous image forming operation, the charging DC high voltage output and the development DC high voltage output are determined every predetermined time, and the charging DC high voltage output (VCHG0) and the development DC high voltage output (VDEV0) are corrected. . Further, during a continuous image forming operation, the bright part potential (VL) is measured for each predetermined number of image forming sheets, and when the bright part potential fluctuates by a predetermined value or more, the charging direct current high voltage output (VCHG0) and the development direct current high voltage. The output (VDEV0) is corrected. Thus, by controlling the development DC high voltage output described above, density fluctuations during continuous image forming operations can be reduced.

  Further, when correcting the charging DC high voltage output (VCHG0) and the developing DC high voltage output (VDEV0) during the continuous image forming operation, the set value before correction and the set value after correction are equal to or larger than a predetermined value (for example, 5V). If the set value after correction is immediately set as the target value, the difference in image density between the output image before correction and the output image after correction is conspicuous. Therefore, in such a case, the target value is corrected (recalculated) step by step toward the set value after correction. For example, it is possible to correct by 2V for each image forming sheet, or to calculate a correction amount per sheet so as to reach the target value after correction with 5 image forming sheets, and to perform step correction.

  That is, a method of changing the setting value stepwise toward the setting value after recalculation, the difference between the setting value before recalculation and the setting value after recalculation being a predetermined value or more In the case where there is, a method of changing the setting value stepwise toward the setting value after recalculation, a first value determined in advance as a setting value before recalculation and a setting value after recalculation If there is a difference greater than or equal to the predetermined value, a method of changing the setting value step by step toward the setting value after recalculating each predetermined second predetermined value, the setting value before recalculation, If there is a difference of a predetermined value or more after the recalculated setting value, a correction value is calculated for each image forming process so that the setting value is changed in a predetermined number of image forming processes. Any of the methods to change the setting value step by step toward the setting value after recalculating each calculated correction value It may be.

  As described above, according to the present embodiment, the same detection circuit (the partial pressure output unit 107c of the potential sensor control unit 107) is used both when the development DC high voltage output is determined and when the development DC high voltage output is controlled. Is used to measure the surface potential of the photosensitive drum 1 and control the development DC high voltage output, so that the accuracy is improved over the entire output range of the development DC high voltage output voltage, and the target contrast potential (Vcont) can be obtained with high accuracy. .

  In addition, in order to obtain a desired contrast potential (Vcont) against the influence of environmental changes such as temperature and humidity, and the influence of changes over time and deterioration of each part, a charging DC high voltage output and development DC By correcting the high voltage output, the target contrast potential (Vcont) can always be accurately controlled, the target gradation can be realized in the image formed by the image forming apparatus, and the density change during the continuous image forming operation can be realized. Can be suppressed.

[Second Embodiment]
FIG. 6 is a schematic diagram showing the configuration of the periphery of the photosensitive drum of the image forming apparatus according to the second embodiment of the present invention.

  In FIG. 6, the image forming apparatus includes a photosensitive drum 1, a charging roller 2, an exposure unit 3, a developing device 4, a potential sensor 8, a control unit 107a, a high voltage power source 107b, and a voltage dividing output unit (voltage dividing circuit) 107c. A development high voltage circuit 108 having a sensor control unit 107, a development AC high voltage generation unit 108a, and a development DC high voltage generation unit 108b, a charging high voltage circuit 109, a switch 110, a switch 113, and a controller 111 are provided.

  This embodiment is different from the above-described first embodiment in that a switch 113 is further provided. Since the other elements of the present embodiment are the same as the corresponding ones of the first embodiment (FIGS. 1, 2, and 4) described above, description thereof is omitted.

  The switch 113 switches the connection point between the point A, which is a connection point between the DC high-voltage output of the high-voltage power supply 107b of the potential sensor control unit 107 and the input of the voltage-dividing output unit 107c, and the ground (reference potential unit) to a connected state / non-connected state. . The switch 113 is an A of the offset (the difference between the actual surface potential of the photosensitive drum 1 and the potential read by the controller 111) of the potential sensor measurement system (the potential sensor 8, the potential sensor control unit 107, and the controller 111). It is used to measure the offset due to the controller 111 side from the point. Then, the development DC high voltage output value is corrected using the offset value caused by the controller 111 side from the measured point A.

  Next, offsets related to the potential sensor measurement system in the image forming apparatus having the above configuration will be described with reference to FIG.

  FIG. 7 is a diagram showing the relationship between the surface potential of the photosensitive drum 1 and the detection value of the potential sensor 8.

  In FIG. 7, the ideal characteristic is (a). The characteristics of the potential sensor measurement system shown in FIGS. 3 and 5 are ideal characteristics. However, actually, the assembly variation of the potential sensor 8, the noise component mixed in the measurement electrode 8f of the potential sensor 8, the constant variation of the control unit 107a of the potential sensor control unit 107 and the level shift unit 111a of the controller 111, A / D An offset is generated between the actual surface potential of the photosensitive drum 1 and the potential (reading value) read by the CPU 111c of the controller 111 due to an error in the conversion unit 111b. For example, when the offset of Voffset1V is generated, the characteristics shown in (b) are obtained, and when the offset of Voffset2V is generated, the characteristics shown in (c) are obtained.

  Here, for example, it is assumed that the offset of the potential sensor measurement system in the image forming apparatus shown in FIG. 6 is Voffset1V. There are various factors of the offset Voffset1V as described above, but here, the factor is divided into two such as Voffset1 = offset A + offset B. As shown in FIG. 6, at the point A (the same point as the point A in FIG. 2) that is a connection point between the output of the high voltage power source 107b of the potential sensor control unit 107 and the input of the divided voltage output unit 107c, the potential sensor The offset caused by the 8 side is assumed to be offset A, and conversely, the offset caused by the controller 111 side is assumed to be offset B.

  Next, a method for measuring the above-described offset A and offset B will be described with reference to FIG.

  FIG. 8 is a flowchart showing an offset measurement method for measuring the surface potential of the photosensitive drum 1. The processing shown in this flowchart is executed by the controller 111 based on a program.

  In FIG. 8, when the offset measurement sequence is started, first, the controller 111 turns on the potential sensor control remote signal. At this time, both the switch 113 and the switch 110 are OFF (step S801). Next, the controller 111 neutralizes the charge remaining on the photosensitive drum 1 by the neutralization unit 112 while rotating the photosensitive drum 1 in the direction of the arrow in FIG. 6 (step S802). Thereafter, the controller 111 waits for a predetermined time to elapse or rotates the photosensitive drum 1 by a predetermined number of rotations (step S803).

  After a predetermined time has elapsed or when the photosensitive drum 1 has been rotated by a predetermined number of revolutions, the controller 111 measures the surface potential of the photosensitive drum 1 that has been neutralized by the potential sensor 8 and the potential sensor control unit 107. This measurement result is the above-described offset A + offset B. The controller 111 stores offset A + offset B in the storage unit in the controller (step S804).

  When the measurement of offset A + offset B is completed, the controller 111 turns off the potential sensor control remote signal and turns on the switch 113. Note that the switch 110 is OFF (step S805). In step S805, a state where the output of the high voltage power source 107b of the potential sensor control unit 107 is zero V is forcibly created. Next, the controller 111 measures the detection output output from the partial pressure output unit 107c of the potential sensor control unit 107 at this time. This measurement result is offset B. The controller 111 stores the offset B in the storage unit (step S806).

  Next, the controller 111 calculates the offset A by subtracting the offset B measured in step S806 from the value of the offset A + offset B measured in step S804, and stores the offset A in the storage unit (step S807). . Finally, the controller 111 turns off the switch 113. At this time, the potential sensor control remote signal remains OFF, and the switch 110 also remains OFF (step S808). This completes this sequence.

  Next, a method for determining the charging DC high voltage output and the development DC high voltage output will be described with reference to FIGS.

  FIG. 9 is a diagram showing the relationship between the charged direct-current high-voltage output and the surface potential of the photosensitive drum 1.

  In FIG. 9, the illustrated characteristics indicate the relationship between the DC component of the charging high-voltage output applied to the charging roller 2, that is, the charging DC high-voltage output, and the surface potential of the photosensitive drum 1 detected by the potential sensor 8.

  10 and 11 are flowcharts showing a method for determining the charging DC high voltage output and the developing DC high voltage output. The processing shown in this flowchart is executed by the controller 111 based on a program.

  This processing is performed, for example, immediately before the image forming apparatus executes the image forming process, or when the temperature of the fixing device reaches a predetermined temperature after the power is turned on, or when a predetermined time has elapsed since the power is turned on, or the temperature is detected. This is performed in various cases such as when the output from the environmental sensor changes by a predetermined value or more.

  10 and 11, when entering the determination sequence for determining the charging DC high voltage output and the development DC high voltage output, first, the controller 111 turns on the potential sensor control remote signal. At this time, both the switch 113 and the switch 110 are OFF (step S1001). Next, the controller 111 inputs a predetermined controller voltage to the charging high voltage circuit 109 so that the charging DC high voltage output becomes a predetermined voltage VCHG1 determined in advance. The charging high voltage circuit 109 outputs the charging DC high voltage VCHG1, and at this time, the surface potential of the exposed portion of the photosensitive drum 1 and the unexposed portion of the photosensitive drum 1 are measured by the potential sensor 8 at the exposure unit 3 (step S1002).

  Here, the potential of the exposed portion of the photosensitive drum 1 in the exposure unit 3 is referred to as a bright portion potential (denoted as VL ′), the bright portion potential when the charging DC high-voltage output is VCHG1 is VL′1, and the exposure portion 3 The potential of the unexposed portion of the photosensitive drum 1 is referred to as a dark portion potential (denoted as VD ′), and the dark portion potential when the charging DC high voltage output is VCHG1 is defined as VD′1.

  Note that the bright part potential VL′1 and the dark part potential VD′1 measured here are measured by the potential sensor 8, and thus include the above-described offset A + offset B, so that the bright part potential VL′1 and the dark part potential are measured. For VD′1, the value of surface potential + offset A + offset B of the photosensitive drum 1 is measured.

  Next, the charging DC high voltage output is changed, and VD ′ and VL ′ are measured again. In the case of FIG. 9, the controller 111 inputs a predetermined controller voltage to the charging high voltage circuit 109 so that the charging DC high voltage output becomes VCHG2. The charging high voltage circuit 109 outputs the charging DC high voltage VCHG2 and measures VL'2 and VD'2 by the potential sensor 8 in the same manner as described above (step S1003).

  Note that the bright part potential VL′2 and the dark part potential VD′2 measured here are also measured by the potential sensor 8, and thus include the above-described offset A + offset B, so that the bright part potential VL′2 and the dark part potential are included. For VD′2, the value of surface potential + offset A + offset B of the photosensitive drum 1 is measured.

  9 can be obtained from the VD′1 and VD′2 and the VL ′ characteristic as shown in FIG. 9 can be obtained from the VL′1 and VL′2. Step S1004). As shown in FIG. 9, both the VD ′ characteristic and the VL ′ characteristic are offset from the true VD ′ characteristic and the true VL ′ characteristic by “offset A + offset B”.

  Next, the controller 111 reads a predetermined “fogging potential” (denoted as Vback) for preventing fogging (attachment of toner to the white background) from the storage unit, and an environmental sensor (not shown). A detection result, a target contrast potential (denoted as VCONT) determined in advance by image density adjustment control, gradation characteristic stabilization control, and the like are read (step S1005). Next, the controller 111 obtains a development DC high-voltage output characteristic (VDEV '= VD'-Vback) in which the Vback offset is provided in the VD' characteristic (step S1006). Further, the controller 111 obtains a difference characteristic (VD′−Vback−VL ′) between the VDEV ′ characteristic and the VL ′ characteristic (step S1007).

  Next, the controller 111 calculates the charging DC high voltage VCHG0 when the difference characteristic (VD′−Vback−VL ′) is equal to the contrast potential VCONT (the range indicated by the double arrow in FIG. 9). It memorize | stores in a memory | storage part (step S1008). Next, the controller 111 calculates the development DC high voltage output VDEV (VDEVa) when the charging DC high voltage output calculated in step S1008 is VCHG0, and stores it in the storage unit (step S1009). Next, the controller 111 reads the offset A calculated in step S807 of FIG. 8 and stored in the storage unit (step S1010).

  Next, the controller 111 calculates a value (VDEVa−offset A) obtained by subtracting the offset A from the developing DC high voltage output VDEV (VDEVa) when the charging DC high voltage output calculated in step S1008 is VCHG0, and this value is calculated as VDEV0. Is stored in the storage unit (step S1011). Finally, the controller 111 turns off the potential sensor control remote signal (step S1012). This completes this sequence.

  The step S1011 will be further described. In the image forming apparatus shown in FIG. 6, when outputting the development DC high voltage, the controller 111 turns off the potential sensor control remote signal to the potential sensor control unit 107 and turns on the switch 110. As a result, the output of the development DC high voltage generation unit 108b of the development high voltage circuit 108 is connected to the point A which is a connection point between the high voltage DC output of the high voltage power source 107b of the potential sensor control unit 107 and the input of the voltage division output unit 107c. The Therefore, the output of the development DC high voltage generation unit 108b is detected by the partial pressure output unit 107c of the potential sensor control unit 107, and the controller 111 reads the detection output.

  Here, connecting the development DC high voltage output to the point A and detecting it by the controller 111 means that the above-described offset A can be ignored, and the detected value by the controller 111 includes only the offset B. Therefore, in step S1011, when the offset A is subtracted from VDEVa calculated in step S1009 and the development DC high voltage output is connected to the voltage dividing output unit 107c of the potential sensor control unit 107 and detected by the controller 111, the contrast potential is detected. VDEV0, which is the target value of the development DC high-voltage output, for accurately obtaining Vcont can be calculated.

  In the case of a color image forming apparatus as shown in FIG. 13, the characteristics of the toner image are different for each color of yellow, magenta, cyan, and black. Therefore, the target contrast potential for each color is stored in advance, and the calculations for four colors are performed in steps S1005 to S1011 in FIGS. 10 and 11, and the charging DC high voltage output VCHG0 and the development DC high voltage output VDEV0 for each color are calculated. To do.

  Regarding the charging DC high voltage output, the charging color high voltage output VCHG0 of the color among the charging DC high voltage output VCHG0 for each color is set to be the common charging DC high voltage output VCHG0.

  Further, in the case of the tandem multiple transfer type image forming apparatus as shown in FIG. 14, the characteristics of the toner image are different for each color of yellow, magenta, cyan, and black, and the photosensitive drum is not shared for each color. Therefore, the target contrast potential for each color is stored in advance, and all the processes in steps S1001 to S1011 in FIGS. 10 and 11 are performed for each color, and the charging DC high voltage output VCHG0 and the development DC high voltage output VDEV0 in each color are obtained. calculate.

  In the above-described determination sequence of the charging DC high voltage output and the development DC high voltage output, the charging DC high voltage output and the development DC high voltage output are determined using 2 points of VCHG, but can be determined if VCHG is 2 points or more.

  Next, the operation when the target charging DC high voltage output (VCHG0) and the target development DC high voltage output (VDEV0) determined as described above are actually output will be described.

  When actually forming an image, the controller 111 reads the above VCHG0 and VDEV0 from the storage unit in the controller and inputs a predetermined controller voltage to the charging high voltage circuit 109 so that the charging DC high voltage output becomes VCHG0. At the same time, an image is formed by inputting a development DC high voltage control signal to the development high voltage circuit 107 so that the development DC high voltage output becomes VDEV0.

  The development DC high voltage output (VDEV0) will be further described. During the image forming operation, the development DC high voltage output (VDEV0) is set as a target value, and the controller 111 controls the development DC high voltage generation unit 108b of the development high voltage circuit 108. Details will be described below.

  First, the controller 111 turns off the potential sensor control remote signal to the potential sensor control unit 107 and turns on the switch 110 (the switch 113 is off). As a result, the development DC high voltage output of the development high voltage circuit 108 is divided by the voltage dividing output unit 107 c of the potential sensor control unit 107, and the voltage division result is input to the controller 111. The controller 111 compares the target development DC high voltage output with the output of the partial pressure output unit 107c of the potential sensor control unit 107, and inputs a development DC high voltage control signal to the development DC high voltage generation unit 108b based on the comparison result. To do.

  That is, if the signal input from the voltage dividing output unit 107c to the controller 111 is smaller than the target development DC high voltage output (VDEV0), the controller 111 increases the development DC high voltage output to the development DC high voltage generation unit 108b. To output a development DC high voltage control signal. On the other hand, if the signal input from the partial pressure output unit 107c to the controller 111 is larger than the target development DC output (VDEV0), the controller 111 reduces the development DC high voltage output to the development DC high voltage generation unit 108b. To output a development DC high voltage control signal.

  The development DC high voltage generation unit 108b generates a development DC high voltage based on a development DC high voltage control signal input from the controller 111. As a result, the output of the development DC high voltage generator 108b is controlled so that the development DC high voltage output (VDEV0) is always constant.

  Also in the present embodiment, as explained in the second half of the first embodiment, the development DC high voltage output is controlled after correcting the charging DC high voltage output and the development DC high voltage output, so that the temperature, humidity, etc. Therefore, it is possible to always perform image formation with a stable density against environmental changes. Further, by performing various corrections during the continuous image forming operation and controlling the development DC high voltage output, it is possible to reduce density fluctuations during the continuous image forming operation. The same applies to the step correction during the continuous image forming operation.

  As described above, according to the present embodiment, the same detection circuit (the partial pressure output unit 107c of the potential sensor control unit 107) is used both when the development DC high voltage output is determined and when the development DC high voltage output is controlled. Is used to measure the surface potential of the photosensitive drum 1 and control the development DC output, and to perform correction in consideration of the offset voltage of the surface potential measuring system that measures the surface potential measurement of the photosensitive drum 1. The contrast potential (Vcont) can be obtained with high accuracy.

  In addition, since the contrast potential (Vcont) can be controlled to be constant with respect to the influence due to environmental changes such as temperature and humidity, and also due to the change with time and deterioration of each part, the target in the image formed by the image forming apparatus Can be realized, and a change in density during continuous image forming operations can be suppressed.

[Other embodiments]
In the first and second embodiments, the image forming apparatus of the roller charging method using the charging roller has been described as an example. The present invention is not limited to this, and can also be applied to a charging type image forming apparatus using corona discharge, and similar effects can be obtained.

  In the first embodiment, the example of controlling the development DC high voltage output has been described. In addition to this, for any DC voltage used in the image forming apparatus, the DC voltage output is connected to the connection point between the output of the high voltage power source 107b of the potential sensor control unit 107 and the voltage dividing output unit 107c via a switch. The switch is turned on when the potential sensor control remote signal to the potential sensor control unit 107 is turned off. As a result, any DC voltage can be output with high accuracy.

  In the second embodiment, the example in which the development DC high voltage output is controlled and corrected has been described. In addition, for any DC voltage used in the image forming apparatus, the DC voltage output is connected to the connection point between the output of the high voltage power source 107b of the potential sensor control unit 107 and the voltage dividing output unit 107c via a switch. The switch is turned on when the potential sensor control remote signal to the potential sensor control unit 107 is turned off. If the offset A is subtracted from the reading value obtained by the controller 111, measurement based on the potential sensor can be performed. Similarly, if the offset B is subtracted from the reading value obtained by the controller 111, measurement based on the ground can be performed. As a result, any DC voltage can be output with high accuracy.

  In the first and second embodiments described above, the relative arrangement, shape, material, dimensions, etc. of the components constituting the image forming apparatus can be arbitrarily set without departing from the spirit of the present invention. It is.

  In the first and second embodiments, the image forming apparatus is not limited to a specific type, and various image forming apparatuses (printers, copiers, multifunction peripherals) that perform image formation by an electrophotographic method are used. Applicable.

  The present invention has been described in the first embodiment in step S2101 of the software program that implements the functions of the above-described embodiment (the flowchart in FIG. 8, the flowchart in FIGS. 10 and 11, and the flowchart in FIG. 22). This can be achieved by supplying a computer or CPU with the contents added thereto to the computer or CPU, and reading and executing the supplied program.

  In this case, the program is directly supplied from a storage medium storing the program, or downloaded from another computer or database (not shown) connected to the Internet, a commercial network, a local area network, or the like. Supplied.

  The form of the program may be in the form of object code, program code executed by an interpreter, script data supplied to an OS (operating system), and the like.

  The present invention also supplies a computer or CPU with a storage medium storing a software program that implements the functions of the above-described embodiments, and the computer or CPU reads and executes the program stored in the storage medium. Can also be achieved.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention.

  As a storage medium for storing the program code, for example, ROM, RAM, NV-RAM, floppy (registered trademark) disk, hard disk, optical disk (registered trademark), magneto-optical disk, CD-ROM, MO, CD-R, CD -RW, DVD-ROM, DVD-RAM, DVD-RW, DVD + RW, magnetic tape, nonvolatile memory card, etc.

  The function of the above-described embodiment is not only by executing the program code read from the computer, but the OS or the like running on the computer performs part or all of the actual processing based on the instruction of the program code. Can also be realized.

1 is a schematic diagram illustrating a configuration of a peripheral portion of a photosensitive drum of an image forming apparatus according to a first embodiment of the present invention. 2 is a block diagram illustrating a configuration of a potential sensor and a potential sensor control unit of the image forming apparatus. FIG. It is a figure which shows the relationship between the surface potential of the photosensitive drum in case the output of an electric potential sensor control part is open, and the output voltage of an electric potential sensor control part. It is a block diagram which shows the structure of the part relevant to the electric potential sensor control part in a controller. It is a figure which shows the relationship between the output voltage of a potential sensor control part, the surface potential of a photosensitive drum, and the output of the A / D conversion part of a controller. 7 is a schematic diagram illustrating a configuration of a peripheral portion of a photosensitive drum of an image forming apparatus according to a second embodiment of the present invention. FIG. It is a figure which shows the relationship between the surface potential of a photosensitive drum, and the detected value of a potential sensor. It is a flowchart which shows the offset measuring method regarding the surface potential measurement of a photosensitive drum. It is a figure which shows the relationship between a charging direct-current high voltage output and the surface potential of a photosensitive drum. It is a flowchart which shows the determination method of charging DC high voltage | pressure output and development DC high voltage | pressure output. It is a continuation of the flowchart of FIG. 1 is a schematic diagram illustrating a schematic configuration example of an image forming apparatus for forming a monochrome image. 1 is a schematic diagram illustrating a schematic configuration example of an image forming apparatus for forming a color image. 1 is a schematic diagram illustrating a schematic configuration example of a tandem multiple transfer type image forming apparatus. FIG. 10 is a schematic diagram illustrating a configuration of a peripheral portion of a photosensitive drum of an image forming apparatus according to a conventional example. 2 is a block diagram illustrating a configuration of a development high-voltage circuit of the image forming apparatus. FIG. It is a figure which shows the relationship (ideal characteristic) of development DC output control value and development DC output. It is a figure which shows the relationship (the characteristic shifted | deviated from the ideal characteristic) between the development direct-current output control value and the development direct-current output. FIG. 5 is a block diagram illustrating a configuration of a development high-voltage circuit when correcting deviation from ideal characteristics. It is a figure which shows the relationship between the development DC output control value at the time of adjusting the variable resistance of a development high voltage circuit, and development DC output. It is a figure which shows the relationship between a charging direct-current high voltage output and the surface potential of a photosensitive drum. It is a flowchart which shows the determination method of charging DC high voltage | pressure output and development DC high voltage | pressure output.

Explanation of symbols

1 Photosensitive drum (corresponding to image carrier)
2 Charging roller (supports charging means)
3 Exposure section (corresponding to exposure means)
4 Developer (corresponding to developing means)
8 Potential sensor (corresponding to potential detection means)
107 Potential sensor control unit (corresponding to potential detection means)
107b High voltage power supply (compatible with power supply)
107c Divided pressure output unit (corresponding to voltage dividing means)
108b Development DC high voltage generator (corresponding to development DC voltage generator)
109 Charging high voltage circuit (corresponding to charging DC voltage generating means)
110 switch (corresponding to the second switching means)
111 controller (corresponding to control means)
113 switch (corresponding to the first switching means)

Claims (14)

A charging means for charging the image carrier; an exposure means for exposing the charged image carrier; a developing means for converting the latent image formed on the image carrier by exposure to a visible image; and the image carrier A potential detecting means for detecting the surface potential of the toner, and a developing DC voltage generating means for generating a developing DC voltage constituting a developing voltage supplied to the developing means,
A voltage dividing means that constitutes the potential detecting means and attenuates and outputs a voltage generated by a power source that generates a voltage equal to the surface potential of the image carrier, generates a developing DC voltage generated from the developing DC voltage generating means. An image forming apparatus that also serves as a detecting unit.   The apparatus further comprises control means for controlling the development DC voltage generated from the development DC voltage generation means based on a comparison result between the development DC voltage detected by the voltage dividing means of the potential detection means and a target value. The image forming apparatus according to claim 1. A charging DC voltage generating means for generating a charging DC voltage constituting a charging voltage for charging the image carrier;
The control means is configured to detect the bright part potential of the exposed part of the image carrier and the dark part potential of the non-exposed part of the image carrier when the two or more different charging direct current voltages are output from the charging direct current voltage generating part. The charging DC voltage generating means at the time of image formation based on the bright part potential characteristic and the dark part potential characteristic obtained by detecting the above and the contrast potential that determines the range of light and darkness of the visible image to be formed on the image carrier. 3. The image forming apparatus according to claim 2, wherein a charging DC voltage setting value and a developing DC voltage setting value of the developing DC voltage generator are calculated. A charging DC voltage generating means for generating a charging DC voltage constituting a charging voltage for charging the image carrier;
The control means is configured to detect the bright part potential of the exposed part of the image carrier and the dark part potential of the non-exposed part of the image carrier when the two or more different charging direct current voltages are output from the charging direct current voltage generating part. Based on the bright part potential characteristic and dark part potential characteristic obtained by detecting, the contrast potential that determines the range of light and dark of the visible image to be formed on the image carrier, and the offset value related to the potential detection means, 3. The image forming apparatus according to claim 2, wherein a charging DC voltage set value of the charging DC voltage generating means and a developing DC voltage setting value of the developing DC voltage generating means at the time of image formation are calculated.   The image forming apparatus according to claim 4, wherein the charging DC voltage setting value and the development DC voltage setting value are corrected by the offset value. A first switching means;
The offset value includes a first offset voltage corresponding to a result obtained by detecting the surface potential of the image carrier from which residual charges have been removed by the potential detecting means, and the development DC voltage generating means by the first switching means. The second offset voltage corresponding to the output of the voltage dividing means when the connection point between the output and the voltage dividing means is connected to the reference potential portion of the voltage dividing means. 5. The image forming apparatus according to 1 or 4. A second switching means;
2. The image forming apparatus according to claim 1, wherein the output of the developing DC voltage generating unit and the voltage dividing unit can be connected or disconnected by the second switching unit.   In the measurement of the first offset voltage, the control means disconnects the output of the developing DC voltage generating means from the voltage dividing means by the second switching means, and the potential detecting means During the period in which the potential detection operation is started and the development DC voltage generation means outputs the development DC voltage, the output of the development DC voltage generation means and the voltage dividing means are connected by the second switching means. The image forming apparatus according to claim 2, wherein the potential detecting operation of the potential detecting unit is stopped.   The charging DC voltage setting value and the development DC voltage setting value are calculated immediately before the image forming operation is performed, when the temperature of the fixing unit reaches a predetermined temperature after the power is turned on, and when a predetermined time has elapsed since the power is turned on. The image forming apparatus according to claim 3, wherein the image forming apparatus is selected from a group including:   The conditions for recalculating the charging DC voltage setting value and the development DC voltage setting value are as follows: every predetermined number of image forming sheets during a continuous image forming operation, every elapse of a predetermined time during a continuous image forming operation, When the bright portion potential detected by the potential detecting means during operation fluctuates by a predetermined value or more, it is selected from a group including a case where either or both of temperature and humidity in the image forming apparatus change by a predetermined value or more. The image forming apparatus according to claim 3, wherein:   The setting value changing method when the charging DC voltage setting value and the development DC voltage setting value are recalculated is a method of changing the setting value step by step toward the setting value after recalculation. A method of changing the setting value step by step toward the setting value after recalculation when there is a difference of a predetermined value or more between the previous setting value and the setting value after recalculation; After a recalculation of a predetermined second predetermined value when there is a difference between the pre-recalculated setting value and the recalculated setting value equal to or larger than a predetermined first predetermined value. A method of changing the setting value step by step toward the setting value, and when the setting value before recalculation and the setting value after recalculation have a difference greater than a predetermined value, the predetermined number Calculate the correction value for each image forming process so that the setting value changes in the image forming process. The image forming apparatus according to claim 3 or 4, wherein is selected from the group comprising a method of changing stepwise the set value toward the set value after re-calculated by the correction value. A charging means for charging the image carrier; an exposure means for exposing the charged image carrier; a developing means for converting the latent image formed on the image carrier by exposure to a visible image; and the image carrier A control method for an image forming apparatus, comprising: a potential detecting means for detecting a surface potential of the toner; and a developing DC voltage generating means for generating a developing DC voltage constituting a developing voltage supplied to the developing means,
A voltage equal to the surface potential of the image carrier is generated by a power source provided in the potential detection means, and the voltage is attenuated and output by a voltage dividing means provided in the potential detection means, and generated from the development DC voltage generation means. A control method comprising: dividing a developing DC voltage by the voltage dividing means, and controlling a developing DC voltage generated from the developing DC voltage generating means on the basis of a comparison result between a divided pressure result and a target value. A charging means for charging the image carrier; an exposure means for exposing the charged image carrier; a developing means for converting the latent image formed on the image carrier by exposure to a visible image; and the image carrier A potential detecting means for detecting the surface potential of the toner, a developing DC voltage generating means for generating a developing DC voltage constituting a developing voltage supplied to the developing means, and a charging DC voltage constituting a charging voltage for charging the image carrier. And a charging DC voltage generating means for generating the image, wherein a part of the potential detecting means causes the computer to execute a control method of the image forming apparatus that also serves as a means for detecting the developing DC voltage generated from the developing DC voltage generating means. A program,
At each output of two or more different charging DC voltages from the charging DC voltage generating means, the potential detecting means detects the bright portion potential of the exposed portion of the image carrier and the dark portion potential of the non-exposed portion. The charging DC voltage setting of the charging DC voltage generating means at the time of image formation is based on the bright part potential characteristic and the dark part potential characteristic and the contrast potential that determines the range of light and darkness of the visible image to be formed on the image carrier. And a development DC voltage setting value of the development DC voltage generating means. A charging means for charging the image carrier; an exposure means for exposing the charged image carrier; a developing means for converting the latent image formed on the image carrier by exposure to a visible image; and the image carrier A potential detecting means for detecting the surface potential of the toner, a developing DC voltage generating means for generating a developing DC voltage constituting a developing voltage supplied to the developing means, and a charging DC voltage constituting a charging voltage for charging the image carrier. And a charging DC voltage generating means for generating the image, wherein a part of the potential detecting means causes the computer to execute a control method of the image forming apparatus that also serves as a means for detecting the developing DC voltage generated from the developing DC voltage generating means. A program,
At each output of two or more different charging DC voltages from the charging DC voltage generating means, the potential detecting means detects the bright portion potential of the exposed portion of the image carrier and the dark portion potential of the non-exposed portion. On the basis of the bright part potential characteristic and the dark part potential characteristic, the contrast potential that determines the light and dark range of the visible image to be formed on the image carrier, and the offset value related to the potential detection means, A program comprising a module for calculating a charging DC voltage setting value of the charging DC voltage generating means and a developing DC voltage setting value of the developing DC voltage generating means.

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