JP5820666B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus using an electrophotographic system, and more particularly to an image forming apparatus that uses a two-component developer composed of a carrier and a toner and develops an electrostatic latent image by holding only the toner on a developing roller. About.

  In recent image forming apparatus development systems, attention has been paid to a touch-down development system that has advantages of both a one-component development system that uses only toner as a developer and a two-component development system that uses toner and a carrier. In the touchdown development method, a magnetic brush is formed on the surface of the magnetic roller with a two-component developer containing toner and a carrier, and only the toner is moved from the magnetic brush to the surface of the developing roller to form a thin toner layer. In this method, toner is ejected onto the surface of the photosensitive drum on which the electrostatic latent image is formed, and developed as a toner image. In the touch-down development method, a two-component development method is adopted for the toner charging area to extend the life, and a one-component development method is adopted for the development area to improve the image quality.

  In such an image forming apparatus, a developing bias voltage generated by superimposing an AC voltage and a DC voltage is applied to the developing roller and the magnetic roller. In this case, when the development bias voltage is increased, it becomes easy to supply the amount of toner necessary for forming the toner image to the photosensitive drum, while the peak value of the development bias voltage and the surface potential of the photosensitive drum are reduced. The potential difference between the two increases, and leakage (air discharge) is likely to occur between the photosensitive drum and the developing roller. When the leak occurs, a so-called development leak occurs in which random black spots (noise) are generated on the photosensitive drum, and a toner image having a good image quality is not formed. In addition, peripheral devices are likely to fail.

  Conversely, if the development bias voltage is lowered to avoid leakage, it becomes difficult to supply the amount of toner necessary for forming the toner image to the photosensitive drum, and density unevenness occurs in the toner image. As a result, a good quality toner image is not formed.

  Therefore, it is necessary to set an optimal development bias voltage so that the above-described problems do not occur. However, in reality, the development gap and the resistance value of the development roller vary depending on the molding accuracy and mounting accuracy of the development roller and the wear of the spacer that determines the distance between the peripheral surfaces of the photosensitive drum and the development roller (development gap). For this reason, even if the developing device is the same or the same developing device, the likelihood of occurrence of leaks varies with time. In addition, since the likelihood of leaks also changes depending on the installation environment (temperature and humidity) of the device, even if an optimal development bias voltage that is unlikely to cause leaks is set at a certain time, the leak may occur if the installation environment changes. Sometimes it occurred.

  Therefore, as described in Patent Document 1, a leak detection means for detecting a leak current generated between the photosensitive drum and the developing roller is arranged, and based on the developing bias voltage when the leak is intentionally generated. Thus, there is known a method for setting an optimum developing bias voltage that does not cause a leak.

JP 2010-85592 A

  However, if a developing bias voltage is applied to the developing roller in order to intentionally generate a leak between the photosensitive drum and the developing roller, toner movement also occurs between the photosensitive drum and the developing roller. Since the toner is charged, this toner movement becomes a current, and the leak detection means detects this current. That is, it is unclear whether the current detected by the leak detection means is a leak current due to discharge or a current caused by toner movement, and the leak current due to discharge cannot be accurately detected.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of accurately detecting a leakage current caused by a discharge between a photosensitive drum and a developing roller.

An image forming apparatus according to a first aspect of the present invention includes an image carrier that carries a toner image, a toner carrier that supplies toner to the peripheral surface of the image carrier, and a two-component developer that includes toner and a carrier. A developer carrying body for supplying the toner to the toner carrying body, a constant voltage element having one end connected to the developer carrying body and the other end grounded, and an AC voltage output from an AC power source. An AC voltage output from the transformer means, the transformer means having an AC voltage input from the primary side and outputting an AC voltage transformed from the secondary side; and a first DC power source and a second DC power source outputting a DC voltage; A superimposed voltage of a DC voltage output from the first DC power supply is applied to the toner carrier, and an AC voltage output from the transformer and a superimposed voltage of a DC voltage output from the second DC power supply are applied to the developer carrier. Voltage applying means to be applied to, and Detection means for detecting a leak occurring between the bearing member and the toner carrying member, in which with a.

  In order to suppress the occurrence of leakage between the image carrier and the toner carrier, a discharge was intentionally generated between the image carrier and the toner carrier, which was adopted when the discharge was detected and the discharge occurred. It is necessary to set the development bias voltage based on the development bias voltage. The voltage applying means for outputting the developing bias voltage applies the developing bias voltage to the toner carrying body and the developer carrying body at the same time because the transformer means is common to the toner carrying body and the developer carrying body. . When the developing bias voltage is applied, the toner moves from the developer carrier to the toner carrier, and further moves from the toner carrier to the image carrier. Since this toner movement becomes a current, it is unclear whether the current detected by the detecting means is a current generated by the toner movement or a leakage current due to discharge, and the discharge detection cannot be performed correctly.

  Therefore, the applied voltage at the time of refresh operation is adopted when detecting discharge. By doing so, the toner does not move from the toner carrier toward the image carrier. However, conversely, toner moves from the toner carrier toward the developer carrier. Since the toner moves, that is, the charge, when the charge on the peripheral surface of the toner carrier flows into the developer carrier, no discharge is performed between the image carrier and the toner carrier, and the discharge is detected. Could not be done.

  Therefore, a constant voltage element is connected between the developer carrier and GND so that the potential difference between the developer carrier and GND does not exceed the reference voltage. By doing so, it is possible to prevent a discharge generated between the developer carrying member and the toner carrying member, and to generate a discharge between the image carrying member and the toner carrying member. Therefore, the detection means can improve the detection accuracy of the leak current due to the discharge.

In the above-described configuration, a leak generating means for generating a leak between the image carrier and the toner carrier, and a setting for setting a voltage output by the voltage applying means based on a detection result by the detection means Means.

According to this configuration, the detection unit can correctly detect the leakage current due to the discharge between the image carrier and the toner carrier, and the detection result and the development applied by the voltage application unit when the leak is detected. Based on the bias voltage, the setting unit can set an optimum development bias voltage with the occurrence of leakage suppressed. By applying an optimum developing bias voltage to the toner carrier, a toner image with good image quality can be formed.
An image forming apparatus according to a second aspect of the present invention includes an image carrier that carries a toner image, a toner carrier that supplies toner to the peripheral surface of the image carrier, and a two-component developer that includes toner and a carrier. A developer carrying body for supplying the toner to the toner carrying body, one end connected to the developer carrying body and the other end grounded, and a voltage applied to the developer carrying body is set to a predetermined level. A constant voltage element that is limited to a reference voltage or less; a transformer that inputs an AC voltage output from an AC power supply from the primary side and outputs an AC voltage transformed from the secondary side; a first DC power supply that outputs a DC voltage; A second DC power source, and applying a superimposed voltage of the AC voltage output from the transformer means and the DC voltage output from the first DC power source to the toner carrier, and the AC voltage output from the transformer means Direct output from the second DC power supply A voltage applying means for applying a superimposed voltage to the developer carrying body; a detecting means for detecting a leak generated between the image carrying body and the toner carrying body; and the image carrying body and the toner carrying body. An image forming apparatus comprising: a leak generating unit that generates a leak between the first and second voltages; and a setting unit that sets a voltage output from the voltage applying unit based on a detection result of the detecting unit. The forming apparatus has a normal mode for normal image formation, and a refresh mode in which the developer carrier peels off the toner thin layer formed on the toner carrier to form a new toner thin layer. The potential difference between the toner carrier and the developer carrier in the normal mode and the refresh mode is reversed, and the superimposed voltage applied to the toner carrier is reversed. In order for the superimposed voltage applied to the developer carrier to be a developing bias voltage, and the setting means sets the developing bias voltage, the leak generating means sets the image carrier and the toner carrier. when generating a leak between the voltage applying means, the developing bias voltage during the refresh mode is applied to the toner carrying member and said developer carrying member.

  According to the present invention, by adding a simple element, leakage between the developer carrier and the toner carrier can be prevented, and accurate discharge detection between the image carrier and the toner carrier can be performed. Can do. Since accurate discharge detection can be performed, it is possible to set an optimum developing bias voltage for suppressing the occurrence of leakage between the image carrier and the toner carrier, and high-quality toner images can be formed.

1 is a cross-sectional view showing an internal structure of an image forming apparatus according to an embodiment of the present invention. FIG. 4 is a diagram for explaining a process in which toner is supplied from a developing device to a photosensitive drum. The circuit diagram of a power supply circuit.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing an outline of the internal structure of an image forming apparatus 1 according to an embodiment of the present invention. The image forming apparatus 1 is a tandem color printer. In this embodiment, a printer is described as an example. However, the present invention can be applied not only to a printer but also to a facsimile machine, a copier, a multifunction machine having these functions, and the like. Any image forming apparatus may be used.

  The image forming apparatus 1 includes a sheet storage unit 110, an image forming unit 130, and a fixing unit 160. The sheet storage unit 110 is disposed at the lowermost part of the image forming apparatus 1 and includes a sheet tray 111 that can store a bundle of sheets P. The paper tray 111 is inserted into the image forming apparatus 1 and attached. When replenishing the paper P, the paper tray 111 is pulled out from the image forming apparatus 1. In the bundle of sheets P stored in the sheet tray 111, the uppermost sheet P is fed out toward the sheet conveyance path 115 by driving the pickup roller 113. The paper P is transported to the image forming unit 130 through the paper transport path 115.

  The image forming unit 130 forms a toner image on the conveyed paper P. The image forming unit 130 includes a magenta unit 133M, a cyan unit 133C, a yellow unit 133Y, and a black unit 133Bk arranged in tandem according to the order of transferring the toner images to the transfer belt 131. These units have the same configuration, and a magenta unit 133M will be described as an example.

  The magenta unit 133M includes a photosensitive drum 135. Around the photosensitive drum 135, a charger 137, an exposure device 139, a developing device 141, and a cleaner 143 are arranged. The charger 137 uniformly charges the peripheral surface of the photosensitive drum 135. The exposure device 139 generates light corresponding to magenta data in the image data transmitted from a personal computer or the like, and irradiates the circumferential surface of the uniformly charged photosensitive drum 135. As a result, an electrostatic latent image corresponding to the magenta data is formed on the peripheral surface of the photosensitive drum 135. In this state, by supplying magenta toner from the developing device 141 to the peripheral surface of the photosensitive drum 135, a toner image corresponding to magenta data is formed on the peripheral surface.

  The transfer belt 131 can move in the F direction (clockwise) while being sandwiched between the photosensitive drum 135 and the primary transfer roller 145. The toner image corresponding to the magenta data is transferred from the photosensitive drum 135 to the transfer belt 131. The magenta toner remaining on the peripheral surface of the photosensitive drum 135 is removed by the cleaner 143. The above is the description of the magenta unit 133M.

  A toner image corresponding to magenta data is transferred to the transfer belt 131, and a toner image corresponding to cyan data, a toner image corresponding to yellow data, and a toner image corresponding to black data are superimposed and transferred onto the toner image. The As a result, a color toner image is formed on the transfer belt 131. The color toner image is transferred to the paper P conveyed from the paper storage unit 110 by the secondary transfer roller 149.

  The sheet P on which the color toner image is transferred is sent to the fixing unit 160. The fixing unit 160 includes a heating roller 161 and a pressure roller 163. The paper P on which the color toner image is transferred is sandwiched between these rollers. As a result, heat and pressure are applied to the color toner image, and the color toner image is fixed to the paper P. Then, the paper P is discharged to the paper discharge unit 169.

  Next, the configuration and operation of the developing device 141 will be described. FIG. 2 is a diagram illustrating a process in which the toner 53 in the two-component developer 51 is supplied from the developing device 141 to the photosensitive drum 135. Reference numeral 55 denotes a carrier constituting the two-component developer 51.

  The developing device 141 includes a developing roller 11, a magnetic roller 13, a stirring screw (not shown), and a voltage application unit 6. The agitating screw is disposed in an agitating chamber (not shown) that accommodates the two-component developer 51, and agitates the two-component developer 51 by rotating. As a result, the toner 53 and the carrier 55 are frictionally charged, and the toner 53 and the carrier 55 are electrostatically coupled to each other and are pumped up by the magnetic roller 13.

  The magnetic roller 13 sucks and conveys the two-component developer 51 in which the toner 53 and the carrier 55 are electrostatically coupled while rotating in the rotation direction R2 as the shaft 33 rotates. The blade 35 regulates the thickness of the two-component developer 51 carried on the magnetic roller 13.

  At the facing portion 37, the toner 53 in the two-component developer 51 is supplied to the developing roller 11 that rotates in the rotation direction R1. Specifically, in a state where the carrier 55 is attracted to the magnetic roller 13, only the toner 53 is attracted to the developing roller 11 and attracts to the developing roller 11.

  The developing roller 11 is disposed opposite to the magnetic roller 13, sucks the toner 53 at the facing portion 37, and conveys the toner 53 by rotating in the rotation direction R <b> 1 while carrying the toner 53. Then, the toner 53 is supplied to the photosensitive drum 135 at the facing portion 47.

  Specifically, the photosensitive drum 135 rotates in a rotation direction R3 opposite to the rotation directions R1 and R2. The conveyed toner 53 is attracted by the electrostatic latent image formed on the peripheral surface of the photosensitive drum 135 and moves to the photosensitive drum 135. As a result, the electrostatic latent image on the peripheral surface of the photosensitive drum 135 is developed, and a toner image is formed on the peripheral surface. A transfer belt 131 in contact with the photosensitive drum 135 is disposed on the photosensitive drum 135. The transfer belt 131 moves in the D direction, and the toner image is transferred to the transfer belt 131.

  As described above, the toner 53 in the two-component developer 51 conveyed by the magnetic roller 13 moves to the developing roller 11 at the facing portion 37. Further, the toner 53 conveyed by the developing roller 11 moves to the photosensitive drum 135 at the facing portion 47. Thus, in order to cause the toner 53 to fly and move at the facing portion 47 and the facing portion 37, the voltage applying unit 6 develops a developing bias voltage in which a DC voltage and an AC voltage are superimposed on the developing roller 11 and the magnetic roller 13. Apply. The voltage application unit 6 will be described in detail later.

  The control unit 7 includes a CPU (Central Processing Unit) and the like, and controls the entire image forming apparatus 1, and includes a leak detection unit 71 and a voltage setting unit 72. The leak detector 71 detects a leak current that flows between the photosensitive drum 135 and the developing roller 11. The voltage setting unit 72 sets a development bias voltage that suppresses the occurrence of leaks based on the detection result by the leak detection unit 71. The voltage application unit 6 generates and outputs a voltage according to the developing bias voltage set by the voltage setting unit 72.

  FIG. 3 is a circuit diagram of the voltage application unit 6. Regarding the subscripts of the reference numerals assigned to the respective elements, K indicates black, M indicates magenta, C indicates cyan, and Y indicates yellow, which indicates that the component corresponds to the developing device of each color. In the following description, a subscript is not added and it explains comprehensively.

  An AC power supply 91 is connected to the primary side of the transformer 92. On the secondary side of the transformer 92, a superposed voltage of the transformed AC voltage and the DC voltage output from the developing roller DC power supply 93 is applied to the developing roller 11, and the transformed AC voltage and the magnetic roller DC power supply 94 are applied. The output superimposed voltage is applied to the magnetic roller 13. The resistor R connected to the front stage of the developing roller 11 and the magnetic roller 13 is a resistor for limiting the current flowing to each roller.

  Further, a constant voltage element ZD is connected between the magnetic roller 13 and GND (ground). The constant voltage element ZD is, for example, a Zener diode whose Zener voltage is a predetermined reference voltage. The Zener diode has a cathode connected to the magnetic roller 13 and an anode connected to GND. The constant voltage element ZD is not limited to a Zener diode, and may be any constant voltage circuit that can limit the voltage applied to the magnetic roller 13 to a reference voltage or less.

  When the developing bias voltage applied to the developing roller 11 by the voltage application unit 6 is increased, it becomes easy to supply the amount of toner necessary for forming the toner image to the photosensitive drum 135, while the peak value of the developing bias voltage. And the surface potential of the photosensitive drum 135 become large, and a leak is likely to occur between the photosensitive drum 135 and the developing roller 11. When the leak occurs, a toner image with good image quality is not formed. In addition, peripheral devices are likely to fail.

  On the other hand, if the developing bias voltage is lowered to avoid leakage, it becomes difficult to supply the amount of toner necessary for forming the toner image to the photosensitive drum 135, and density unevenness occurs in the toner image. As a result, a good quality toner image is not formed.

  Therefore, it is necessary to set an optimal development bias voltage so that the above-described problems do not occur. However, in reality, the ease of occurrence of leakage varies depending on the molding accuracy and mounting accuracy of the developing roller 11 and the developing gap G between the photosensitive drum 135 and the developing roller 11 (see FIG. 2). In addition, the ease of occurrence of leaks varies depending on the installation environment (temperature and humidity) of the apparatus, and the ease of occurrence of leaks may vary with time even depending on the development apparatus or the same development apparatus.

  Since the leak generation condition changes as described above, a discharge is intentionally generated between the photosensitive drum 135 and the developing roller 11 at a predetermined timing under the control of the control unit 7, and the leak detection unit 71 performs the discharge. Leak is detected, and based on the detection result, the voltage setting unit 72 sets an optimum development bias voltage that can suppress the occurrence of leak.

  A method for setting the developing bias voltage will be described. First, the voltage application unit 6 applies a development bias voltage in order to generate a discharge between the photosensitive drum 135 and the development roller 11. At this time, since the developing bias voltage is simultaneously applied to the magnetic roller 13, a potential difference is generated between the developing roller 11 and the magnetic roller 13, the toner moves from the magnetic roller 13 toward the developing roller 11, and the developing roller. The toner moves from 11 to the photosensitive drum 135. Since the toner is charged, the leak detector 71 detects this toner movement as a current. In other words, it is unclear whether the current detected by the leak detector 71 is a leak current due to discharge or a current caused by toner movement, and discharge detection cannot be performed correctly.

  Therefore, discharge is generated by setting so that the toner does not move between the photosensitive drum 135 and the developing roller 11. Specifically, the applied voltage during the refresh operation is employed. The refresh operation means that the magnetic roller 13 peels off the toner thin layer formed on the developing roller 11 to form a new toner thin layer. In the touch-down development method, the toner thin layer is formed on the developing roller 11 with a magnetic brush and a developing bias voltage. The toner adheres to the developing roller 11 by continuously applying an electric field in one direction, or from the developing roller 11. There may be a development ghost phenomenon in which an afterimage after the toner has jumped to the photosensitive drum 135 appears in the second round. The refresh operation is for solving this problem, and is generally performed at a timing between sheets, that is, between sheets.

  The development bias voltage during normal image formation (hereinafter referred to as “normal mode”) and during the refresh mode is the same AC because the AC output is composed of one transformer for the development roller 11 and the magnetic roller 13. The component voltage is applied to the developing roller 11 and the magnetic roller 13. Therefore, the potential difference between the developing roller 11 and the magnetic roller 13 in the normal mode and the refresh mode is reversed by changing the DC component.

  However, when the voltage application unit 6 applies the developing bias voltage in the refresh mode to the developing roller 11 and the magnetic roller 13, in the conventional circuit, a discharge may occur between the developing roller 11 and the magnetic roller 13. There was a case where discharge between the body drum 135 and the developing roller 11 was not performed and discharge detection could not be performed.

  However, as shown in FIG. 3, the voltage applied to the magnetic roller 13 does not exceed the reference voltage by connecting the constant voltage element ZD between the magnetic roller 13 and GND. That is, when the voltage between the magnetic roller 13 and GND becomes equal to or higher than the reference voltage, a current flows from the magnetic roller 13 toward the constant voltage element ZD, so that leakage between the developing roller 11 and the magnetic roller 13 can be prevented. it can. That is, it is possible to reliably generate a discharge between the photosensitive drum 135 and the developing roller 11.

  When a Zener diode is used as the constant voltage element ZD, the Zener voltage is larger than the potential difference between the developing roller 11 and the magnetic roller 13 that occurs in the normal mode, and from the potential difference between the developing roller 11 and the magnetic roller 13 that occurs in the refresh mode. Set smaller. By doing so, leakage that occurs between the developing roller 11 and the magnetic roller 13 can be prevented.

  The leak detector 71 detects a leak current that flows due to the discharge generated between the photosensitive drum 135 and the developing roller 11, and the detection result and the developing bias voltage that the voltage applying unit 6 employs when the leak occurs. Based on the above, the voltage setting unit 72 sets an optimum development bias voltage with the occurrence of leakage suppressed. The voltage application unit 6 applies a voltage to the development roller 11 and the magnetic roller 13 according to the development bias voltage set by the voltage setting unit 72.

  As described above, by connecting the constant voltage element ZD between the magnetic roller 13 and GND, the development roller 11 and the magnetic roller 13 can be connected even when the development bias voltage in the refresh mode is adopted when detecting discharge. It is possible to prevent the occurrence of leakage between the photosensitive drum 135 and the developing roller 11, and to reliably discharge. Therefore, the leak detection unit 71 can detect a leak current due to discharge, and the voltage setting unit 72 can set an optimum development bias voltage while suppressing the occurrence of leak. By suppressing the occurrence of leakage between the photosensitive drum 135 and the developing roller 11, the development efficiency is improved, and a toner image with a high quality image can be formed.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 6 Voltage application part (Voltage application means, leak generation means)
7 Control unit 11 Developing roller (toner carrier)
13 Magnetic roller (developer carrier)
71 Leak detection unit (detection means)
72 Voltage setting part (setting means)
91K, 91M, 91C, 91Y AC power supply (AC power supply)
92K, 92M, 92C, 92Y Transformer
93K, 93M, 93C, 93Y DC power supply (first DC power supply)
94K, 94M, 94C, 94Y DC power supply (second DC power supply)
110 Paper storage unit 130 Image forming unit 135 Photosensitive drum (image carrier)
141 Developing Device ZD Constant Voltage Element

Claims (1)

An image carrier for carrying a toner image;
A toner carrier for supplying toner to the peripheral surface of the image carrier;
A developer carrying member for conveying a two-component developer comprising a toner and a carrier and supplying the toner to the toner carrying member;
A constant voltage element that has one end connected to the developer carrier and the other end grounded, and limits a voltage applied to the developer carrier to a predetermined reference voltage or lower;
AC voltage output from the AC power source is input from the primary side, the transformer means for outputting the AC voltage transformed from the secondary side, and a first DC power source and a second DC power source that output DC voltage, A superimposed voltage of the AC voltage output from the transformer means and the DC voltage output from the first DC power source is applied to the toner carrier, and the AC voltage output from the transformer means and the DC voltage output from the second DC power source are applied. Voltage application means for applying a superimposed voltage to the developer carrier;
Detecting means for detecting a leak generated between the image carrier and the toner carrier;
Leak generating means for generating a leak between the image carrier and the toner carrier;
Setting means for setting a voltage output by the voltage applying means based on a detection result by the detecting means;
An image forming apparatus comprising:
The image forming apparatus includes a normal mode for normal image formation, a refresh mode in which the developer carrier peels off the toner thin layer formed on the toner carrier, and a new toner thin layer is formed. Have
The potential difference between the toner carrier and the developer carrier in the normal mode and the refresh mode is reversed,
The superimposed voltage applied to the toner carrier and the superimposed voltage applied to the developer carrier are defined as a development bias voltage,
When the leak generating means generates a leak between the image carrier and the toner carrier in order for the setting means to set the developing bias voltage, the voltage applying means An image forming apparatus that applies a developing bias voltage to the toner carrier and the developer carrier.

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