JP2007108588A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that can optimize an initial surface potential before charging a drum even when performing various discharge/separation sequences for enhancing image quality or even under various environments. <P>SOLUTION: The apparatus includes: an image carrier; a charging means for charging the surface of the image carrier; an electrostatic latent image forming means for forming an electrostatic latent image by exposing a charged surface of the image carrier surface according to image data; a developing means for processing visualization of the electrostatic latent image as a toner image using toner; a transfer means for transferring the toner image to a recording medium; a discharge means for eliminating charges by applying biases onto the recording medium charged by the transfer processing; and a pre-exposure means for performing discharge processing of residual charges remaining on the surface of the image carrier after transfer processing. The light emission quantity of the exposure means is varied depending on the magnitude of bias applied from the discharge means to the recording medium. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic process such as a copying machine or a printer, and more particularly, to an image forming apparatus configured by a contact roller charging method, a transfer method, a static elimination bias method, and a pre-charging exposure method.

FIG. 9 shows an example of a conventional electrophotographic process. The surface of the drum 1 is uniformly charged by a bias applied to the charging roller 2. The drum surface is exposed according to image data by laser light 10 emitted from a laser scanner (not shown), and an electrostatic latent image is formed. The electrostatic latent image on the drum 1 is developed with toner by applying a bias to the developing roller 3, and becomes a visualized image as a toner image. The toner image on the drum 1 is transferred to the printing paper 12 by a bias applied to the transfer roller 4. At this time, the printing paper 12 is charged by the transfer bias 8, so that the printing paper 12 is easily attracted to the drum 1, which adversely affects the process of sending the printing paper 12 to a fixing unit (not shown). For this purpose, a charge having a polarity opposite to that of the transfer bias 8 is applied to the charge eliminating needle 5 so as to eliminate the charge charged on the printing paper 12. Here, for the purpose of improving the image quality, various controls of the static elimination needle bias 9 are performed. For example, by changing the size of the neutralizing needle bias 9 according to the leading and trailing ends of the printing paper 12 and the number of printed sheets, or changing the size of the neutralizing needle bias 9 according to the surrounding environment (temperature / humidity, etc.) The edge of the paper 12 is prevented from being stained. (Refer to Patent Document 1) Or, by changing the magnitude of the static elimination needle bias 9 according to the pattern (halftone / line drawing, etc.) of the print image, the image on the print paper 12 is prevented from being disturbed. (See Patent Document 2)
Japanese Patent Laid-Open No. 2002-40816 JP 11-38771 A

  However, when the neutralizing bias control as described above is performed, the bias applied to the neutralizing needle 6 may affect the drum 1 through the printing paper, and the drum surface may be negatively charged. Depending on the configuration of the image forming apparatus, pre-exposure means may be provided on the upstream side of the charging roller 2, and charges remaining on the drum surface after transfer may be removed by irradiating the drum 1 with light. However, in the system in which the static elimination bias is varied according to various conditions as in the above conventional example, the amount of pre-exposure is insufficient due to the magnitude of the static elimination bias, and the residual charge cannot be completely eliminated. May be too high and generate drum memory.

  The present invention has been made in view of such a situation. Even when various static elimination separation sequences as shown in the above-described conventional example are performed, or even in various ambient environments, the drum is not yet charged. An object of the present invention is to provide an image forming apparatus capable of setting the initial surface potential to an optimum value.

  In order to achieve the above object, an image forming apparatus according to claim 1, wherein an image carrier, charging means for charging the surface of the image carrier, and a charged surface of the image carrier according to image data An electrostatic latent image forming unit that forms an electrostatic latent image by performing exposure, and a developing unit that performs a process of visualizing the electrostatic latent image on the surface of the image carrier as a toner image with charged toner; A transfer means for transferring the toner image on the surface of the image carrier to a recording medium; and applying a bias to the recording medium charged by the transfer process of the toner image to remove the charged charge, A charge eliminating unit for preventing electrostatic adsorption to the image carrier, and a pre-exposure unit for performing a charge eliminating process on the residual charge after transfer processing remaining on the surface of the image carrier by light irradiation. Applied to the recording medium from The amount of light emitted from the pre-exposure means is changed according to the size of the scan.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, in the charging unit that charges the surface of the image carrier, the surface of the image carrier is applied by applying a bias to a cylindrical roller. It is characterized by being charged.

  According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, in the charging unit that charges the surface of the image carrier, an output bias of the charging unit is formed by only a DC component. And

  According to a fourth aspect of the present invention, in the image forming apparatus according to the second aspect, in the charging unit that charges the surface of the image carrier, an output bias of the charging unit is formed from a DC component and an AC component. It is characterized by.

  According to a fifth aspect of the present invention, in the image forming apparatus according to the third or fourth aspect, in the charging unit that charges the surface of the image carrier, the current flowing through the image carrier is controlled to control the magnitude of the output bias. It is characterized in that it is performed based on quantity information.

  As described above, according to the present invention, when the static elimination bias is changed on the static elimination separation sequence, the light amount of the pre-exposure means is changed according to the value, thereby controlling the ability to neutralize the drum surface potential. It is carried out.

  Therefore, it is possible to provide an image forming apparatus capable of setting the drum surface potential to an optimum value in any static elimination separation sequence or in any ambient environment.

Example 1
FIG. 4 is a diagram showing an example of an electrophotographic process of the image forming apparatus according to the embodiment of the present invention. Reference numeral 1 denotes a drum, which is disposed in contact with the charging roller 2, the developing sleeve 3, and the transfer roller 4. The drum 1 is grounded. The charging roller 2, the developing sleeve 3, and the transfer roller 4 are each connected to a power source for applying a bias. A static elimination needle 5 is disposed so as to be in contact with the printing paper after the transfer process. A power source 9 for applying a bias is connected to the static elimination needle 5. Reference numeral 10 denotes a pre-exposure LED disposed between the transfer roller 4 and the charging roller 2. Reference numeral 12 denotes a printing paper as a recording medium.

  The surface of the drum 1 is uniformly negatively charged by the bias applied to the charging roller 2. The drum surface is exposed in accordance with image data by laser light 10 emitted from a laser scanner (not shown), and an electrostatic latent image is formed by removing the exposed portion. The electrostatic latent image on the drum surface is developed by the toner moved to the exposed portion on the drum 1 by the AC bias applied to the developing sleeve 3, and becomes a visible image as a toner image. The toner image on the drum 1 is transferred to the printing paper 12 by a plus bias applied to the transfer roller 4. The printing paper 12 to which the toner image is transferred is sent to a fixing device (not shown), and is discharged as a printing image after fixing processing. Here, as shown in FIG. 6- (a), the printing paper 12 after the transfer process is positively charged by the transfer bias 8, so that it is easily attracted to the negatively charged drum 1. Yes. Therefore, when the printing paper 12 is sent to a fixing unit (not shown) after the transfer process, the printing paper 12 may be attracted to the drum 1 and not separated, causing a conveyance failure. As a countermeasure, a negative bias is applied to the static elimination needle 5 as shown in FIG. 6B to neutralize the printing paper 12 and prevent the paper from adsorbing to the drum 1.

  The output system of the charging bias 6 is a DC charging system formed only with a DC component, and the control of the magnitude of the output bias is constant current control that keeps the current flowing through the drum 1 constant at a predetermined value. That is, when the resistance R is equivalently considered between the drum 1 and the charging roller 2 as shown in FIG. 5- (a), the current value I1 flowing through the resistance R is constant. Since the electrophotographic process is a repetition of charge-exposure-development-transfer, if residual charge remains on the drum 1 after the transfer process, the remaining charge will flow in order to pass a predetermined current value when the next charge is attempted. A bias having a predetermined potential difference must be applied to the potential of. In FIG. 5- (a), the voltage across the resistor R is set to a predetermined constant voltage (I1 (constant) × R (fixed value) = V (constant potential difference)). Accordingly, since the amount of residual charge increases each time the electrophotographic process is repeated, the size of the charging bias 6 increases accordingly (see FIG. 5- (b)). However, since the size of the output bias is limited, a bias sufficient to ensure a necessary potential difference cannot be output over and over, and charging failure occurs. Therefore, after the transfer process, the drum surface is exposed by the LED 11 to remove the residual charge (initialization of the drum surface), thereby preventing an increase in the bias necessary for flowing a predetermined current value.

  The neutralizing needle bias 9 contributes not only for the purpose of separating the printing paper 12 but also for improving the image quality. By promoting the paper separation by the neutralizing needle bias 9, the occurrence of image defects such as image rubbing and edge stains due to the jumping of the edge of the printing paper is prevented. Furthermore, optimization of image quality improvement is attempted by changing the magnitude of the applied bias depending on the first and second sides of double-sided printing or the surrounding environment such as temperature and humidity. Here, the neutralization needle bias 9 is applied to neutralize the charge charged on the printing paper 12, but the printing paper 12 is also in contact with the drum surface during the bias application, so it is applied. It is considered that the bias also affects the drum 1 via the printing paper 12 and may negatively charge the drum surface. The drum surface potential after the transfer process is configured to be neutralized by the pre-exposure of the LED 11, but since the neutralizing needle bias 9 is varied depending on the environmental conditions, it cannot be absorbed by the pre-exposure with a constant light amount. The case comes out. When the bias is increased, the charge amount of the drum 1 also increases, so the neutralization by the LED 11 becomes insufficient. Conversely, when the bias is decreased, the increase in the charge amount of the drum 1 is small and the LED 11 is overexposed. It is considered that the phenomenon that the drum memory is generated occurs.

  Therefore, as shown in FIG. 1, control is performed to vary the amount of light of the LED 11 in accordance with the magnitude of the neutralizing needle bias 9 to be applied. This is a control performed by the CPU 13 that controls each unit in the block diagram showing the configuration of the image forming apparatus shown in FIG. 3. Each bias output of the electrophotographic process is performed by the high-voltage unit 14. A control sequence at the time of duplex printing shown in FIG. 1 will be described with reference to a flowchart shown in FIG. First, a neutralizing needle bias of -1.2k is applied, and the pre-exposure LED 11 is made to emit light with a low light quantity PL in accordance with that, and waits for the leading edge of the first sheet to come. Switch the neutralization needle bias to -2.5k t1 hour after the leading edge of the paper arrives. As a result, the LED 11 emits light with a high light intensity PH. Wait for the trailing edge of the first side of the paper, and after t2 hours from the trailing edge, switch the neutralization needle bias to -1.2k and the LED11 light intensity to PL. Then, after t3 hours, the neutralization needle bias is set to -2.5k, the LED11 light intensity is switched to PH, and it waits for the leading edge of the second sheet to come. When the leading edge of the second side of the paper comes, switch the neutralization needle bias to -1.2k and the LED11 light intensity to PL after t4 hours. After that, after t1 time, the neutralization needle bias is set to -2.5k, the LED 11 light quantity is changed to PH, and the second sheet is waited for the rear end. At t2 hours after the trailing edge comes, switch the neutralization needle bias to -1.2k and switch the LED11 light intensity to PL, and turn off both the neutralization needle bias and the LED11 light intensity after t5 hours. With such control, when the charge eliminating needle bias 9 is increased, the light quantity of the LED 11 is also increased so as to obtain a sufficient charge eliminating capability. On the other hand, when the static elimination needle bias 9 is reduced, the light quantity of the LED 11 is also reduced to prevent excessive irradiation of the drum 1. As a result, the initial drum surface potential during the charging process can be maintained at an appropriate value under various printing conditions and the surrounding environment, and a print image with good image quality can be obtained because printing is performed in an optimum process state. I can do it.

(Example 2)
FIG. 7 is a diagram showing an example of an electrophotographic process of the image forming apparatus according to the embodiment of the present invention. The surface of the drum 1 is uniformly negatively charged by the bias applied to the charging roller 2. The drum surface is exposed in accordance with image data by laser light 10 emitted from a laser scanner (not shown), and an electrostatic latent image is formed by removing the exposed portion. The electrostatic latent image on the drum surface is developed by the toner moved to the exposed portion on the drum 1 by the AC bias applied to the developing sleeve 3, and becomes a visible image as a toner image. The toner image on the drum 1 is transferred to the printing paper 12 by a plus bias applied to the transfer roller 4. The printing paper 12 to which the toner image is transferred is sent to a fixing device (not shown), and is discharged as a printing image after fixing processing. Here, as shown in FIG. 6- (a), the printing paper 12 after the transfer process is positively charged by the transfer bias 8, so that it is easily attracted to the negatively charged drum 1. Yes. Therefore, when the printing paper 12 is sent to a fixing unit (not shown) after the transfer process, the printing paper 12 may be attracted to the drum 1 and not separated, causing a conveyance failure. As a countermeasure, a negative bias is applied to the static elimination needle 5 as shown in FIG. 6B to neutralize the printing paper 12 and prevent the paper from adsorbing to the drum 1.

  The output method of the charging bias 6 is an AC charging method formed by superimposing an AC component on a DC component, and the control of the magnitude of the output bias is a constant that keeps the voltage applied to the drum 1 at a predetermined value. Voltage control is performed. That is, when the resistance R is equivalently considered between the drum 1 and the charging roller 2 as shown in FIG. 8, the voltage R1 across the resistance R is constant. In the DC charging method stop current control described in the first embodiment, a pre-exposure LED is required to initialize the drum surface potential, but in the AC charging method stop voltage control, charging failure occurs. Since the phenomenon does not occur, there is no need for pre-exposure LEDs. However, there are cases where pre-exposure is performed as a role to prevent image quality deterioration such as toner being placed in a region where toner is not originally present in a non-image portion of a printed image. In such a system, after the transfer process, the drum surface is exposed by the LED 11 to remove residual charges (initialization of the drum surface potential).

  The neutralizing needle bias 9 contributes not only for the purpose of separating the printing paper 12 but also for improving the image quality. By promoting the paper separation by the neutralizing needle bias 9, the occurrence of image defects such as image rubbing and edge stains due to the jumping of the edge of the printing paper is prevented. Furthermore, optimization of image quality improvement is attempted by changing the magnitude of the applied bias depending on the first and second sides of double-sided printing or the surrounding environment such as temperature and humidity. Here, the neutralization needle bias 9 is applied to neutralize the charge charged on the printing paper 12, but the printing paper 12 is also in contact with the drum surface during the bias application, so it is applied. It is considered that the bias also affects the drum 1 via the printing paper 12 and may cause the drum surface to be negatively charged. The drum surface potential after the transfer process is configured to be neutralized by the pre-exposure of the LED 11, but since the neutralizing needle bias 9 is varied depending on the environmental conditions, it cannot be absorbed by the pre-exposure with a constant light amount. The case comes out. When the bias is increased, the charge amount of the drum 1 also increases, so the neutralization by the LED 11 becomes insufficient. Conversely, when the bias is decreased, the increase in the charge amount of the drum 1 is small and the LED 11 is overexposed. It is considered that the phenomenon that the drum memory is generated occurs.

  Therefore, as shown in FIG. 1, control is performed to vary the amount of light of the LED 11 in accordance with the magnitude of the neutralizing needle bias 9 to be applied. This is a control performed by the CPU 13 that controls each unit in the block diagram showing the configuration of the image forming apparatus shown in FIG. 3. Each bias output of the electrophotographic process is performed by the high-voltage unit 14. The control sequence during duplex printing shown in FIG. 1 is executed according to the flowchart shown in FIG. By such control, when the charge eliminating needle bias 9 is increased, the light quantity of the LED 11 is also increased so as to obtain a sufficient charge eliminating capability. On the other hand, when the static elimination needle bias 9 is reduced, the light quantity of the LED 11 is also reduced to prevent excessive irradiation of the drum 1. As a result, the initial drum surface potential during the charging process can be maintained at an appropriate value under various printing conditions and the surrounding environment, and a print image with good image quality can be obtained because printing is performed in an optimum process state. I can do it.

The figure which shows the light quantity control method of the pre-exposure means which concerns on this invention 6 is a flowchart showing a light amount control method of the pre-exposure unit according to the present invention. Block diagram showing an example of the configuration of an image forming apparatus The figure which shows the electrophotographic process which concerns on 1st Example of this invention The figure which shows constant current control of the DC charging system which concerns on 1st Example of this invention Diagram showing static elimination separation method for paper The figure which shows the electrophotographic process which concerns on the 2nd Example of this invention. The figure which shows the constant voltage control of the AC charging system which concerns on 2nd Example of this invention A diagram showing a conventional electrophotographic process

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 3 Developing sleeve 4 Transfer roller 5 Static elimination needle 6 Charging bias 7 Development bias 8 Transfer bias 9 Static elimination bias 10 Laser beam 11 Pre-exposure LED
12 Printing paper 13 CPU
14 High-pressure unit 15 Drive / actuator 16 Laser unit 17 Scanner unit 18 Fixing unit 19 Sensor unit

Claims (5)

  An image carrier, a charging unit for charging the surface of the image carrier, and an electrostatic latent image forming unit for forming an electrostatic latent image by exposing the charging surface of the image carrier surface according to image data And a developing means for performing a process of visualizing the electrostatic latent image on the surface of the image carrier as a toner image with charged toner, and a transfer for transferring the toner image on the surface of the image carrier to a recording medium. And a charge eliminating means for preventing electrostatic adsorption of the recording medium to the image carrier by applying a bias to the recording medium charged by toner image transfer processing to remove the charged charge, and the image Pre-exposure means for performing charge removal processing by light irradiation on residual charges after transfer processing remaining on the surface of the carrier, and depending on the magnitude of the bias applied from the charge removal means to the recording medium, the pre-exposure means Changing the amount of light emitted An image forming apparatus comprising.   2. The image forming apparatus according to claim 1, wherein in the charging means for charging the surface of the image carrier, the surface of the image carrier is charged by applying a bias to a cylindrical roller.   3. The image forming apparatus according to claim 2, wherein in the charging unit that charges the surface of the image carrier, an output bias of the charging unit is formed only with a DC component.   3. The image forming apparatus according to claim 2, wherein in the charging unit that charges the surface of the image carrier, an output bias of the charging unit is formed of a DC component and an AC component.   5. The image formation according to claim 3, wherein the charging means for charging the surface of the image carrier performs control of the magnitude of an output bias based on information on an amount of current flowing through the image carrier. apparatus.

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