JP2009008828A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which a stable surface potential on an amorphous silicon photoreceptor can be always obtained by correcting a decrement in the surface potential (dark decay characteristics) due to temperature elevation of the amorphous silicon photoreceptor based on a charging current to the amorphous silicone photoreceptor, without using an expensive device such as a potential sensor or a temperature thermistor. <P>SOLUTION: The image forming apparatus is equipped with: a charging roller 12 for charging an amorphous silicon photoreceptor 11; a detection circuit 21 for detecting a charging current flowing into the amorphous silicon photoreceptor 11; a static eliminator 18 for eliminating the charged potential of the amorphous silicon photoreceptor 11; and a control circuit 22 for controlling an application voltage to the charging roller 12 so as to compensate a difference between the latest detection result of the detection circuit 21 and the current detection result. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that charges a surface of an amorphous silicon photoconductor with a charging roller.

  In recent years, in an image forming apparatus such as a printer or a copier that applies electrophotographic technology, an amorphous silicon photoconductor has come to be frequently used as a photoconductor drum as the image forming process speeds up and the image quality increases. It was.

  This amorphous silicon-based photoconductor has less surface wear due to continuous use and superior durability and higher dot reproducibility than the organic semiconductive photoconductors that have been used so far. There are benefits.

  In addition, as a charging method for charging the surface of such an amorphous silicon photoconductor, mounting a scorotron charging method that generates a large amount of ozone is an environmental problem, and a charging roller that generates a very small amount of ozone is used. The charging method used is becoming mainstream.

  On the other hand, it is also known that an amorphous silicon photoconductor has a demerit that dark decay is large (see, for example, Patent Document 1).

  This dark decay is a phenomenon in which the potential on the surface of the photoreceptor decreases with time after the photoreceptor is charged by a charger. In addition, when the dark attenuation characteristics fluctuate due to environmental changes, the image forming processing conditions such as the exposure conditions and the developing conditions change. Therefore, it is possible to always keep the image forming processing conditions such as the exposure conditions and the developing conditions constant. This is a cause of image defects such as a decrease in visual image density and image fog.

Therefore, in Patent Document 1 described above, a charger for charging the amorphous silicon photoconductor, an exposure device for forming an electrostatic latent image on the surface of the amorphous silicon photoconductor, and a static on the surface of the amorphous silicon photoconductor. A developer unit that visualizes a toner image based on an electrostatic latent image and a transfer unit that transfers the toner image are provided. After non-image formation, the amorphous silicon photoconductor is uniformly charged by a charger and then transferred to the transfer unit. The surface potential of the amorphous silicon photoconductor is detected by detecting the flowing current, and the dark decay of the amorphous silicon photoconductor is measured. Based on the measurement result of the dark decay, the applied voltage of the charger and the exposure of the exposure device are measured. The amount and the developing bias of the developing device are controlled.
JP 2003-015370 A

  However, in the above-described image forming apparatus, since the current flowing through the transfer device at a position rotated 180 degrees from the charger is detected, the control value of the charging potential changes depending on the arrangement relationship from the charger to the transfer device. There has been a problem that complicated control is imposed including the arrangement relationship of the exposure units arranged around the photosensitive member.

  In addition, the dark decay characteristic of the amorphous silicon photoconductor depends on the temperature of the amorphous silicon photoconductor, and in particular, the dark decay characteristic is lowered at a high temperature, that is, the charge potential at the development position of the photoconductor is lowered. There has been a problem that image quality is impaired.

  In view of the above circumstances, the present invention is based on the surface current due to the temperature rise of the amorphous silicon photoconductor without using an expensive device such as a potential sensor or a temperature thermistor from the charging current value to the amorphous silicon photoconductor. An object of the present invention is to provide an image forming apparatus capable of correcting a potential decrease (dark decay characteristic) and always obtaining a stable surface potential of an amorphous silicon photoconductor.

  An image forming apparatus according to the present invention neutralizes a charging roller for charging an amorphous silicon photoconductor, a detection circuit for detecting a charging current value flowing into the amorphous silicon photoconductor, and a charging potential of the amorphous silicon photoconductor. It is characterized by comprising a static eliminator and a control circuit for controlling the voltage applied to the charging roller so as to compensate for the difference between the previous detection result and the current detection result of the detection circuit.

  At this time, the control circuit sets Idc-1 as a charging current value necessary for charging the amorphous silicon photoconductor to a predetermined potential by the charging roller from the neutralization OFF state of the amorphous silicon photoconductor. The charging potential value immediately below the charging roller is Vo-1, and the charging current value required for recharging the amorphous silicon photoconductor to a predetermined potential after one rotation of the amorphous silicon photoconductor is Idc-2. When the charging potential value immediately below the charging roller is Vo-2, the potential decrease due to the dark decay generated in the amorphous silicon photoconductor is calculated from the difference between the charging current value Idc-1 and the charging current value Idc-2. It is preferable to calculate and feedback control the voltage applied to the charging roller.

  The image forming apparatus according to the present invention can reduce the surface potential due to the temperature rise of the amorphous silicon photoconductor without using an expensive device such as a potential sensor or a temperature thermistor from the charging current value to the amorphous silicon photoconductor. It is possible to obtain a stable surface potential of the amorphous silicon photosensitive member by correcting the dark attenuation characteristic).

  Next, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is an explanatory diagram of an image forming apparatus according to an embodiment of the present invention, FIG. 2 is a graph of dark decay characteristics with respect to temperature characteristics of a photoconductor in the image forming apparatus according to an embodiment of the present invention, and FIG. FIG. 4 is a graph of dark decay characteristics at a development position in an image forming apparatus according to an embodiment of the present invention. FIG. 4 is a graph showing temperature characteristics and applied voltages after one rotation of a photoconductor in the image forming apparatus according to an embodiment of the present invention. FIG. 5 is a graph showing the relationship between the charging potential calculation in the image forming apparatus according to the embodiment of the present invention, and FIG. 6 is a graph showing the applied voltage of the charging roller and the photosensitive member in the image forming apparatus according to the embodiment of the present invention. It is a graph which shows the relationship with the surface potential.

  As shown in FIG. 1, an image forming apparatus 1 according to an embodiment of the present invention includes a photoconductor around an amorphous silicon photoconductor (hereinafter simply referred to as “photoconductor”) 11 as an image carrier. A charging roller 12 for charging the surface of the photoconductor 11, an exposure device 13 for forming an electrostatic latent image on the surface of the photoconductor 11, a developing device 14 for developing a toner image on the surface of the photoconductor 11, and a transfer paper ( (Not shown) transfer roller 15, cleaning roller 16 that removes residual toner adhering to the surface of the photoconductor 11 after transfer, cleaning blade 17, and static eliminator 18 that neutralizes the charged potential on the surface of the photoconductor 11. Are arranged in this order.

  The charging current and the charging potential of the photoconductor 11 have a positive correlation, and during normal printing, as described above, the charging / exposure / development / transfer / cleaning / discharging process is one cycle. After the process, a charging process is performed for the next image forming process.

  At this time, the photosensitive member 11 always needs to be charged from the charging potential of 0 V in the discharging step by the discharging unit 18 when the current Idc-0 necessary for obtaining the desired charging potential Vo is obtained. The flow-in current (charging current) to 11 is always Idc-0.

  However, when there is no charge eliminating step, dark decay characteristics occur as shown in FIG. 2 between charging and returning to the original charging position. In this state, the charging region returns to the charging region and recharging is performed. The current required at this time can be obtained by compensating for the dark attenuation, and the desired charging potential Vo can be obtained.

  Further, as shown in FIG. 2, this dark decay characteristic depends on the temperature of the photoconductor 11, and particularly at a high temperature, the dark decay characteristic is lowered, that is, the charging potential at the developing position of the developing device 14 is lowered. Image quality is degraded.

  Note that the time 100 ms shown in FIG. 2 indicates the time required to reach the developing unit 14 from the charging roller 12 at an arbitrary position of the photoconductor 11, and at normal temperature (for example, 25 ° C.) and high temperature (for example, 45 ° C.). ) Indicates that a potential difference of about 20 V is generated in the charging potential after 100 ms. FIG. 3 shows the temperature characteristics of the photoconductor 11 at the development position after 100 ms shown in FIG.

  Accordingly, when the temperature of the photoconductor 11 rises depending on the use state of the apparatus, the recharge current value described above becomes large, so that the darkness at room temperature (25 ° C.) stored in advance in the photoconductor 11 is stored. By comparing with the recharging current obtained from the attenuation characteristics, the amount of charge decrease at the development position is calculated, and the voltage applied to the charging roller 12 (Vdc) is increased to always stabilize the charging potential and image quality. Can be provided.

  Next, experimental examples serving as the basis for charge potential control according to the embodiment of the present invention will be described. The photoreceptor 11 used in this experiment has an outer diameter of 30 (mm), a film thickness of 20 (μm), a length of 254 (mm), and a peripheral speed of 150 (mm / s). The charging roller 12 used had an outer diameter of 12 (mm), a length of 220 (mm), and an outer diameter of a cored bar of 6 (mm). Further, the surface potential of the photoconductor 11 is set to about 300 (V), and the applied voltage of the charging roller 12 is DC = 400 (V), AC = 1.4 (KV), and frequency 1.5. (KHz).

  When the surface temperature of the photoconductor 11 is 25 ° C. at a normal temperature and 45 ° C. under a high temperature, as shown in FIG. 4, after the photoconductor 11 makes one rotation (620 ms), 165 V (Vo−1) due to dark decay. And 135V (Vo-2).

  As shown in FIG. 5, this is because the charging current value Idc-1 required when the photosensitive member 11 is charged to a predetermined potential by the charging roller 12 from the neutralization OFF state of the photosensitive member 11 from the relationship between the charging current and the surface potential. The detection circuit 21 detects (60 μA) and a charging current value Idc-2 (50 μA) required when the photosensitive member 11 is recharged to a predetermined potential after one rotation of the photosensitive member 11. Thus, the dark attenuation correction can be performed by feeding back to the charging roller 12 the amount of decrease in potential (corresponding to 10 μA) caused by the dark attenuation generated in the photoconductor 11 so that a current value of 10 μA flows more than the initial value.

  A control circuit (CPU) 22 performs control based on a control program related to control of the image forming apparatus of the present invention stored in a memory 23 such as a ROM. Therefore, the memory 23 forms a microcomputer with the control circuit 22 that executes the control program. Note that image data and the like when executing the image forming process are temporarily stored in a RAM 24 or the like different from the memory 23 and reflected on the exposure unit 13. Furthermore, the control circuit 22 controls the erase light quantity of the static eliminator 18 and the bias on the photoconductor 11 in addition to the charging current to the charging roller 12. The RAM 24 stores the above-described charging current value Idc-1 and charging current value Idc-2 for the difference calculation by the control circuit 22.

  FIG. 6 shows the relationship between the applied voltage (Vdc) at the charging roller 12 and the surface potential (Vo) of the photoconductor 11.

  As described above, according to the image forming apparatus of the present invention, the charging potential is lowered due to the temperature rise of the photoconductor 11 without using an expensive device such as a thermistor for measuring the temperature of the photoconductor 11 or a surface potential sensor. Therefore, it is possible to provide an image forming apparatus that can prevent the occurrence of the problem and can always obtain a stable image.

It is explanatory drawing of the image forming apparatus which concerns on one Embodiment of invention. FIG. 6 is a graph of dark decay characteristics with respect to temperature characteristics of a photoreceptor in an image forming apparatus according to an embodiment of the present invention. FIG. 6 is a graph of dark attenuation characteristics at a development position in an image forming apparatus according to an embodiment of the present invention. FIG. 6 is a graph showing a relationship between a temperature characteristic after one rotation of the photosensitive member and an applied voltage in the image forming apparatus according to the embodiment of the present invention. FIG. 6 is a graph of charge potential calculation in the image forming apparatus according to an embodiment of the present invention. FIG. 4 is a graph showing a relationship between an applied voltage of a charging roller and a surface potential of a photoreceptor in an image forming apparatus according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 11 ... Amorphous silicon type photoreceptor 12 ... Charging roller 18 ... Static eliminator 21 ... Detection circuit 22 ... Control circuit

Claims (2)

  A charging roller for charging the amorphous silicon photoconductor, a detection circuit for detecting a charging current value flowing into the amorphous silicon photoconductor, a static eliminator for neutralizing the charging potential of the amorphous silicon photoconductor, and a detection circuit An image forming apparatus comprising: a control circuit that controls a voltage applied to the charging roller so as to compensate for a difference between a previous detection result and a current detection result.   The control circuit sets Idc-1 as a charging current value required when the amorphous silicon photoconductor is charged to a predetermined potential by the charging roller from the neutralization OFF state of the amorphous silicon photoconductor, and immediately below the charging roller at that time. The charging potential value is Vo-1 and the charging current value required when the amorphous silicon photosensitive member is recharged to a predetermined potential after one rotation of the amorphous silicon photosensitive member is Idc-2. When the charging potential value immediately below the roller is Vo-2, the potential decrease due to the dark decay generated in the amorphous silicon photoconductor is calculated from the difference between the charging current value Idc-1 and the charging current value Idc-2. The image forming apparatus according to claim 1, wherein feedback control is performed on a voltage applied to the charging roller.

Images