JP2012185198A - Image forming apparatus - Google Patents

Abstract

When a charging roller slips, the photosensitive member is cleaned with the charging roller, so that drum scratches or the like occur, and external additives and toner on the photosensitive member are dammed up at the slip portion to the surface of the charging roller. As a result of the accumulation, a defective charging image on the streak occurs at the moment when the slip is released.
An image forming apparatus comprising means for detecting the follow-up of an image carrier and a charging member, and controlling the follow-up of the charging member by increasing a frictional resistance μ between both members according to the detection result. The device can solve the problem. Whether or not the charging roller in contact with the photosensitive member is driven in real time is detected by a charging current, and driven by performing control to increase the frictional resistance μ of the drum.
[Selection] Figure 11

Description

  The present invention relates to a rotatable image carrier for forming a developer image, the image carrier in contact with the image carrier and rotated by the rotation of the image carrier, and a charging bias applied to the image carrier. The present invention relates to an image forming apparatus having a charging member for charging a surface.

  A typical example of a rotatable image carrier for forming a developer image is a drum type or endless belt type electrophotographic photosensitive member in an electrophotographic image forming apparatus. Also, drum-type and endless belt-type electrostatic recording dielectrics in the electrostatic recording image forming apparatus can be mentioned. A representative example of a charging member that contacts the image carrier and rotates following the rotation of the image carrier and applies a charging bias to charge the surface of the image carrier is a charging roller.

  An electrophotographic image forming apparatus will be described as an example. A contact-type charging device that charges the surface of the photosensitive member by contacting the charging roller with the surface of the electrophotographic photosensitive member and applying a voltage between the charging roller and the photosensitive member in this state is low ozone. There are advantages such as reduction in power consumption and reduction in power consumption.

  In recent years, in order to reduce torque and charge roller contamination in a contact charging device, a photoreceptor having a surface property with a low frictional resistance μ and a charging roller having a highly water-repellent surface (Patent Document 1) have been developed. The frictional resistance between the charging roller and the charging roller is small. Actually, it has been proposed (Patent Document 2) to take a countermeasure against slip by defining a dynamic friction coefficient and a peripheral speed between the photosensitive member and the charging roller and by following the charging roller.

JP 07-134468 A Japanese Utility Model Publication No. 06-130780

  However, this measure does not detect a slip in real time, and cannot cope with a change in the frictional resistance μ due to a sudden external factor (such as adhesion of foreign matter to the image carrier). When the charging roller actually slips, the photosensitive member is cleaned with the charging roller, so that drum scratches may occur due to friction between the two members. Further, since the external additive and toner on the photosensitive member are dammed up at the slip portion and are accumulated on the surface of the charging roller, an image with poor charging on the streak is generated at the moment when the slip is released.

  Accordingly, the present invention has been made to solve the above-described problems, and the object of the present invention is to prevent the charging member from being scratched by the charging member slipping or the adhering substance on the surface of the charging member. It is intended to suppress the generation of defective images such as streaks due to the accumulation on the surface.

  In order to achieve the above object, an image forming apparatus according to the present invention comprises a rotatable image carrier for forming a developer image, and the image carrier is in contact with the image carrier and rotated by the rotation of the image carrier. A charging member that charges the surface of the image bearing member by applying a charging bias, and the charging member is configured to rotate the image bearing member when the image bearing member is rotating. Slip detecting means for detecting the occurrence of slip on the body, and control means for executing slip cancellation control for eliminating the slip when the slip detecting means detects the slip of the charging member. It is characterized by having.

  In the present invention, the slip of the charging member relative to the image carrier is detected in real time, and control is performed to eliminate the slip based on the detection result. Accordingly, it is possible to suppress generation of defective images such as streaks due to scratches on the image carrier due to slippage of the charging member and deposits on the surface of the image carrier.

A longitudinal sectional view showing a schematic configuration of an example of an image forming apparatus Explanatory drawing of the slip detection means example 1 of a charging roller Explanatory drawing of lip state of charging roller The figure which showed the detection result of the charging current value in the slip detection means example 1 The figure which showed the detection result of the charging current value which removed the drive noise and the high voltage noise from the detection result of FIG. Illustration of slip detection examples 2 and 3 The figure which showed the detection result of the position displacement amount (rotation amount for 1 round of a charging roller) in the slip detection means example 2. The figure which showed the detection result of the vibration output value (vibration amount for 1 round of a charging roller) in the slip detection means example 3. A figure showing slip elimination by charging bias up Diagram showing slip elimination due to process speed reduction Flowchart of apparatus control sequence including slip detection and slip cancellation control in the image forming apparatus of the embodiment

[Example]
<Example of image forming apparatus>
FIG. 1 is a longitudinal sectional view showing a schematic configuration of an example of an image forming apparatus M according to the present invention. This apparatus M is a monochrome laser printer using a transfer type electrophotographic process, and an image corresponding to electrical image information input from an external host apparatus H such as a personal computer to a control circuit unit (control means) C is recorded on a recording material P. Form and output as an image formed product.

  In the apparatus main body of the apparatus M, a drum-type electrophotographic photosensitive member (hereinafter referred to as a drum) 1 as a rotatable image carrier (charged body) for forming an electrostatic latent image is disposed. ing. In the drum 1 of this example, an OPC photosensitive layer (organic optical semiconductor) is formed on the outer peripheral surface of a conductive drum base such as aluminum. The rotational force of the drive source motor K controlled by the control circuit C is transmitted to the drum gear G (FIG. 2) via a drive transmission mechanism (not shown), so that the clockwise direction of the arrow R1 is centered on the drum shaft 1a. It is rotationally driven at a predetermined process speed (circumferential speed), in this example, 200 mm / s.

  Around the drum 1, a charging roller 2, an exposure device 3, a developing device 4, a transfer roller 5, and a cleaning device 6 are disposed along the drum rotation direction as electrophotographic image forming process means.

  The surface of the rotating drum 1 is in contact with the drum 1 and is rotated by the rotation of the drum 1, and a charging roller 2 as a charging member that charges the surface of the drum 1 when a charging bias is applied thereto has a predetermined polarity. It is charged uniformly (uniformly) to the potential. The charging roller 2 is in contact with the drum 1 with a predetermined contact force, and rotates (follows rotation) as the drum 1 rotates. A predetermined charging bias is applied to the charging roller 2 from a charging bias application power source S2 controlled by the control circuit unit C. As a result, the peripheral surface of the drum 1 is uniformly contact-charged to a predetermined polarity / potential.

  The charged surface is exposed according to image information by the exposure device 3. The exposure device 3 is a laser beam scanner in this example. The scanner 3 outputs a laser beam L modulated and controlled in accordance with a time-series electric digital image signal of image information input from the apparatus H to the control circuit unit C, and performs main scanning exposure on the charging processing surface of the rotating drum 1. . As a result, the exposed portion potential of the drum 1 is attenuated, and an electrostatic latent image corresponding to the image information is formed on the drum surface.

  Developer (toner) is supplied to the surface of the drum 1 by the developing roller 4 a of the developing device 4. The developing roller 4a is rotationally driven counterclockwise as indicated by an arrow, and a predetermined developing bias is applied from a developing bias applying power source S4 controlled by the control circuit unit C. As a result, the electrostatic latent image on the drum surface is developed as a developer image (toner image) ta.

  The developer image ta on the drum surface is electrostatically transferred onto the surface of the recording material P at the transfer nip T which is a contact portion between the drum 1 and the transfer roller 5. The transfer roller 5 is rotationally driven in a counterclockwise direction indicated by an arrow at a peripheral speed substantially corresponding to the peripheral speed of the drum 1. Further, while the recording material P is nipped and conveyed to the transfer roller 5 from the transfer nip portion T, the transfer bias application power source S5 controlled by the control circuit portion C transfers a predetermined potential with a polarity opposite to the toner charging polarity. A bias is applied.

  The recording material P is loaded on the cassette 8 of the paper feed mechanism unit 7. The recording material P is separated and fed by a sheet feeding roller 9, and a developer image formed (written) on the drum 1 at a predetermined control timing with respect to the transfer nip T by the registration roller 10. It is sent to the transfer nip T so as to be synchronized with ta.

  The recording material P exiting the transfer nip T is separated from the surface of the drum 1 and conveyed to the fixing device 11. An unfixed developer image is heated and pressed on the surface of the recording material by the fixing device 11 and fixed as a fixed image. Then, the recording material P that has undergone image fixing is conveyed to the discharge unit 12 as an image formed product and discharged.

  On the other hand, the developer (transfer remaining developer) tb remaining on the surface of the drum 1 after separation of the recording material is removed from the surface of the drum 1 by the cleaning member 6a of the cleaning device 6, and the drum 1 is repeatedly used for image formation. Is done. In this example, the cleaning member 6a is an elastic cleaning blade counter-contacted to the drum 1, and the drum surface is rubbed and scraped off by the blade 6a, and the transfer residual developer tb is scraped off and accommodated in the cleaning container 6b. Is done.

  The apparatus M of this example is a process in which four process devices, a drum 1, a charging roller 2, a developing device 4, and a cleaning device 6, are integrally incorporated in the cartridge container 13 with a predetermined arrangement relationship and can be attached to and detached from the apparatus main body. A cartridge (process unit) 14 is configured. The cartridge 14 is mechanically and electrically coupled to the apparatus body side by being mounted on the apparatus body in a predetermined manner. The apparatus M can perform an image forming operation in a state where the cartridge 14 is mounted in a predetermined manner.

  FIG. 2 is a schematic cross-sectional view along the length of the cartridge 14. The drum 1 has a drum shaft 1a on one end side (right side in the figure) and the other end side (also on the left side), which is rotatably supported between the first side plates 13a and 13a of the cartridge container 13 via bearing members 15, respectively. It is installed. A drum gear G is disposed on one end side of the drum 1.

  The charging roller 2 is a conductive elastic roller having a metal core 2a and a conductive elastic layer 2b formed concentrically and integrally around the metal core. The charging roller 2 is arranged substantially in parallel with the drum 1, and one end side (right side) and the other end side (left side) of the cored bar 2 a are respectively connected to the second side plates 13 b and 13 b of the cartridge container 13 via the bearing member 16. It is rotatably supported and disposed between them.

  The bearing members 16 on one end side and the other end side are supported so as to be slidable in a direction approaching the drum 1 and a direction away from the second side plate 13b on each side. Each of the pressure springs 17 is urged to move in a direction approaching the drum 1. As a result, the charging roller 2 is brought into contact with the surface of the drum 1 with a predetermined contact pressure against the elasticity of the conductive elastic layer 2b, thereby forming a charging nip N between the surface and the drum surface.

  In a state where the cartridge 14 is mounted on the apparatus main body, the drum gear G is mechanically coupled to a driving force transmission mechanism (not shown) on the apparatus main body side. The charging roller 2 includes a charging bias application power source S2 on the apparatus main body side, an electrical coupling portion a, a pressure spring (conductive) 17 on the other end side, and a bearing member (conductive) 16 on the other end side. And are electrically coupled via a cored bar 2a.

  Therefore, when the motor K on the apparatus main body side controlled by the control circuit unit C is driven, the driving force of the motor K is transmitted to the drum 1 via the drive transmission mechanism and the drum gear G, and the drum 1 is Driven by rotation.

  Further, since the charging roller 2 is in contact with the drum 1, the charging roller 2 is driven to rotate by the frictional force with the drum 1 in the charging nip N as the drum 1 rotates. Then, when a predetermined charging bias is applied to the charging roller 2 from the charging bias application power source S2 through the above-described path, the peripheral surface of the rotating drum 1 is contact-charged to a predetermined polarity and potential.

<Slip detection means>
The slip detection means is means for detecting that the charging roller 2 is slipping with respect to the drum 1 when the drum 1 is rotating. Since the charging roller 2 is in contact with the drum 1, the charging roller 2 is driven to rotate by the frictional force between the drum 1 and the charging roller 2 in the charging nip N as the drum 1 rotates. The driven rotation of the charging roller 2 is greatly related to the frictional resistance of the drum surface.

  Therefore, when the frictional resistance of the charging roller 2 suddenly decreases due to external factors (such as foreign matter adhering to the drum 1), a phenomenon occurs in which the charging roller 2 slips with respect to the drum 1. FIG. 3 shows a situation where the charging roller 2 is slipping. That is, the frictional resistance of the surface of the charging roller 2 is reduced, and the rotation is stopped without being accompanied by the rotation of the drum 1, or the rotation is not the rotation corresponding to the rotation of the drum 1 although the rotation is accompanied. In this state, the drum 1 is rotating at a lower speed than the rotation speed of the drum 1. In this state, the charging roller 2 slips with respect to the surface of the rotating drum 1.

  In this slip state, the surface of the drum 1 is rubbed with the charging roller 2. As a result, drum scratches and the like occur, and transfer residual substances (external additives, toners, and the like of the developer that have passed through the cleaning member 6a) tc are dammed by the slip portion (charging nip N) on the surface of the charging roller 2 The deposit adheres. As a result, a defective charging image on the stripe may occur at the moment when the slip is released.

  Therefore, it is important to detect the slip of the charging roller 2 in real time and to control to eliminate the slip.

  In the present invention, as described below, it is detected that the charging member (charging roller 2) slips with respect to the image carrier when the image carrier (drum 1) is rotating. Slip detecting means for And when the slip detection means detects the slip of the charging member, it has a control means for executing slip elimination control (recovery sequence) for eliminating the slip. In this section, a specific example of the slip detection means will be described.

1) Example 1 of slip detection means
Slip detection can be detected by measuring and monitoring the current value in the circumferential direction (rotation direction) of the current value flowing through the charging roller 2. That is, the current value of the rotation period of the charging roller 2 to which the charging bias is applied is monitored. The difference between the form of the current value period monitored when the charging roller 2 is driven to rotate by the drum 1 and the form of the current value period monitored when the charging roller 2 slips. From this, it is detected that the charging roller 2 is slipping with respect to the drum 1.

  Referring to FIG. 2, in a state where the cartridge 14 is mounted on the apparatus main body in a predetermined manner, the drum shaft 1a on one end side of the drum 1 and the ammeter A on the apparatus main body side are connected via the electrical coupling portion b. Electrically coupled. The charging roller 2 is in contact with the drum 1 with a predetermined contact pressure, and is normally rotated by the rotation of the drum 1. By applying a charging bias, the surface of the drum is charged to a predetermined polarity / potential. A current corresponding to the charged area per area flows. Further, this current has a fluctuation in the period of the current value due to the resistance and outer diameter, which are unique characteristics of the charging roller.

  Therefore, the current value in the circumferential direction of the charging roller was monitored by an ammeter A, and the current value transition of the charging roller cycle was measured. An example of the result is shown in FIG. As a result, the current value period D for one rotation of the charging roller 2 is known, and it can be determined that the charging roller 2 is rotating in the circumferential direction. It can also be seen that this is a driven rotation.

  On the other hand, when the charging roller 2 does not rotate with the rotation of the drum 1 but stops rotating and slips with respect to the surface of the drum 1, the current value for one rotation of the charging roller 2 as shown in FIG. The period D is not detected, and a constant current value is monitored. Therefore, it can be determined that it is not driven.

  In some cases, the charging roller 2 is rotated, but the charging roller 2 is rotating at a lower speed than a predetermined driven rotation speed corresponding to the rotation of the drum 1. The form of the current value period for one rotation of the charging roller 2 in this case is also different from the form of the current value period D when the charging roller 2 is rotated in a predetermined manner. Accordingly, it can be determined that the charging roller 2 is rotating at a lower speed than the rotation of the drum 1 and slipping with respect to the surface of the drum 1.

  The control circuit unit C monitors the current value of the rotation period of the charging roller 2 to which the charging bias is applied with the ammeter A when the drum 1 is rotating. Due to the difference between the form of the current value period D monitored when the charging roller 2 is driven and rotated by the drum 1 and the form of the current value period monitored when the charging roller 2 is slipping. It is detected that the charging roller 2 is slipping with respect to the drum 1. Therefore, in this example, the ammeter A and the control circuit unit C are the slip detection means AC.

  Here, various noises are detected in the above current value detection. The data D in FIG. 4 is actually a result of including noise, and it may be erroneously determined. Therefore, it is important to remove the noise. The various noises described here are the driving noise of the drum 1 and the output noise of the main body transformer. FIG. 5 shows the result of canceling external factors affecting these current values. E is a form of a current value period for one turn of the charging roller 2 calculated by noise cancellation from the result D of FIG.

  As a canceling method, the drum 1 is rotated in a bias-off state to remove drive noise, and then only the charging roller pitch is extracted and determined as noise. First, the drive noise is canceled. Thereafter, a charging bias is applied to the raw data from which the drive noise has been removed when the main body is stopped, the noise of the high voltage transformer is extracted, and the high voltage transformer noise is canceled. As a result, as a result of extracting only the charging roller pitch as shown in FIG.

  Thus, by detecting the period of drive noise and output noise and not counting the output period of this pitch, it is possible to accurately determine the driven rotation and slip state of the charging roller 2. The calculation of the noise cancellation is performed by the calculation function unit of the control circuit unit C, and various noise confirmations and data corrections for canceling drive noise and high voltage noise are performed.

2) Example 2 of slip detection means
The slip detection means of this example digitizes and reads the rotation of the charging roller 2 and grasps the driven rotation state or the slip state. That is, the transition of the rotation amount of the charging roller 2 is monitored. And the difference between the form of the rotation amount period monitored when the charging roller 2 rotates following the drum 1 and the form of the rotation amount period monitored when the charging roller 2 slips. From this, it is detected that the charging roller 2 is slipping with respect to the drum 1.

  In FIG. 6, an encoder (a sensor for converting a mechanical displacement amount into an electrical signal and processing the signal to detect position / speed) 18 is arranged on the bearing member 16 of the drum shaft 1a on one end side of the drum 1. It is installed. The encoder 18 measures the positional displacement (rotation amount) of the drum shaft 1a, that is, the charging roller 2. In a state where the cartridge 14 is mounted on the apparatus main body, the encoder 18 and the control circuit section C on the apparatus main body side are electrically coupled via the electric coupling portion b.

  When the drum 1 is rotating, the control circuit unit C monitors the change in the rotation amount of the charging roller 2 with the encoder 18. FIG. 7 shows a form example of the rotation amount period F for one rotation of the charging roller monitored when the charging roller 2 is rotated following the drum 1 in a predetermined manner. As a result, the rotation amount period of one rotation of the charging roller 2 is known, and it can be determined that the charging roller 2 is rotating in the circumferential direction. It can also be seen that this is a driven rotation. The detection result F in FIG. 7 is a value after driving and removing high-voltage noise by the method described above.

  On the other hand, when the charging roller 2 does not rotate with the rotation of the drum 1 but stops rotating and slips with respect to the surface of the drum 1, the rotation amount of one rotation of the charging roller 2 as shown in FIG. Period F is not detected and a constant measurement is monitored. Therefore, it can be determined that it is not driven.

  In some cases, the charging roller 2 is rotated, but the charging roller 2 is rotating at a lower speed than a predetermined driven rotation speed corresponding to the rotation of the drum 1. The form of the rotation amount period for one rotation of the charging roller 2 in this case is different from the form of the rotation amount period F for one rotation when the charging roller 2 is rotated in a predetermined driven manner. Accordingly, it can be determined that the charging roller 2 is rotating at a lower speed than the rotation of the drum 1 and slipping with respect to the surface of the drum 1. Therefore, in this example, the encoder 18 and the control circuit unit C are the slip detection means 18-C.

3) Example 3 of slip detection means
The slip detection means of this example attaches a pickup to the bearing member of the charging roller, and grasps the driven rotation state or the slip state at the vibration amount period due to the driven rotation of the charging roller 2. That is, the vibration amount transition of the rotation cycle of the charging roller 2 is monitored. Charging is based on the difference between the form of the vibration amount period monitored when the charging roller 2 is rotated following the drum 1 and the form of the vibration amount period monitored when the charging roller 2 is slipping. It is detected that the roller 2 is slipping with respect to the drum 1.

  In FIG. 6, a pickup (a sensor that converts vibration into an electrical signal and processes the signal to detect a vibration amount) 19 is disposed on the bearing member 16 of the drum shaft 1 a on one end side of the drum 1. The pickup 19 measures a vibration amount period corresponding to one rotation accompanying the rotation of the drum shaft 1a, that is, the charging roller 2. In a state where the cartridge 14 is mounted on the apparatus main body in a predetermined manner, the pickup 19 and the control circuit section C on the apparatus main body side are electrically coupled via the electric coupling section b.

  The control circuit portion C monitors the vibration amount transition of the charging roller 2 by the pickup 19 when the drum 1 is rotating. FIG. 8 is a form example of the vibration amount period G for one rotation of the charging roller monitored when the charging roller 2 is rotated following the drum 1 in a predetermined manner. As a result, the form of the vibration amount period for one rotation of the charging roller 2 can be understood, and it can be determined that the charging roller 2 is rotating in the circumferential direction. It can also be seen that this is a driven rotation. Note that the detection result G in FIG. 8 is a value after driving and removing high-voltage noise by the method described above.

  On the other hand, when the charging roller 2 does not rotate with the rotation of the drum 1 but stops rotating and slips with respect to the surface of the drum 1, the vibration amount of one rotation of the charging roller 2 as shown in FIG. Period G is not detected and a constant measurement is monitored. Therefore, it can be determined that it is not driven.

  In some cases, the charging roller 2 is rotated, but the charging roller 2 is rotating at a lower speed than a predetermined driven rotation speed corresponding to the rotation of the drum 1. The form of the vibration amount period for one turn of the charging roller 2 in this case is different from the form of the vibration amount period G for one turn when the charging roller 2 rotates in a predetermined manner. Accordingly, it can be determined that the charging roller 2 is rotating at a lower speed than the rotation of the drum 1 and slipping with respect to the surface of the drum 1. Therefore, in this example, the pickup 19 and the control circuit unit C are the slip detection means 19-C.

  The slip detection means of the charging roller 2 is not limited to the means focusing on the current value, rotation amount (position displacement), and vibration of the above 1), 2), and 3), but other methods that can detect slip. Needless to say, it may be used. Moreover, it can also be set as the structure which uses these various means together or in combination.

<Slip cancellation control>
The slip cancellation control (recovery sequence) is a means for eliminating the slip of the charging roller 2, and is executed when the slip of the charging roller 2 is detected by the slip detection means AC, 18-C, or 19-C as described above. Is done.

  Assume that the slip of the charging roller 2 driven by the rotation of the drum 1 with respect to the drum 1 has a frictional resistance μ on the drum surface smaller than the torque at which the charging roller 2 rotates. Therefore, it is preferable to eliminate the slipping state by increasing the frictional resistance μ between the drum 1 and the charging roller 2. A specific example of the slip elimination control will be described.

1) Example 1 of slip elimination control
In this control example, the charging bias output value is increased, and the charging bias applied to the charging roller 2 is changed to a bias having a higher absolute value than the bias applied during the normal image forming operation. That is, in order to eliminate the state in which the charging roller 2 is slipping with respect to the rotating drum 1, a bias is applied to the charging roller 2 to discharge from the charging roller 2 to the drum 1. Thus, it is effective to increase the frictional resistance between the drum 1 and the charging roller 2 by applying a trace of discharge to the drum surface to roughen the drum surface.

  Here, by applying a higher charging bias to the charging roller 2 than the normal applied DC bias used during image formation, the surface of the drum 1 can be made more rough and the frictional resistance is increased. Thereby, the state where the charging roller 2 slips with respect to the rotating drum 1 can be quickly eliminated. In addition to the bias output value, this method may be used because the slip can be eliminated by extending the bias application time.

  Actually, the effect was verified while monitoring the current value of the charging roller 2 by the above-described slip detection means example 1 (FIG. 2). In a state where the charging roller 2 does not rotate along with the rotation of the drum 1 but stops rotating and slips with respect to the surface of the drum 1, the current value period E for one rotation of the charging roller 2 as shown in FIG. Is not detected, and a constant current value is monitored as indicated by J in FIG. In this slip state, the charging bias output value from the charging bias application power source S2 to the charging roller 2 is increased (for example, 0 to 50 V up).

  Then, the charging roller 2 whose driven rotation is stopped due to slip starts to rotate. As a result, the current value of a normal charging roller cycle such as E monitored when the charging roller 2 is rotated in a predetermined driven manner on the drum 1 from the state where the current value is constant as shown in FIG. was detected. That is, it was found that slip can be recovered early.

  The same applies to the case where the charging roller 2 is rotated, but in a slip state where the charging roller 2 rotates at a lower speed than a predetermined driven rotational speed corresponding to the rotation of the drum 1. That is, when the charging bias output value for the charging roller 2 is increased from the charging bias application power source S2, the charging roller 2 comes to rotate in a predetermined manner on the drum 1, and the current value E of the normal charging roller cycle is detected. That is, it was found that slip can be recovered early.

  If the control circuit unit C determines that the slip of the charging roller 2 has been recovered by detecting the current value E of the normal charging roller cycle, the charging bias output value from the charging bias application power source S2 to the charging roller 2 is set to the normal image. Control to return the charging bias output value at the time of forming is performed.

2) Example 2 of slip elimination control
This control example is based on a process speed down (drum 1 rotation speed down). That is, the control is to change the rotation speed of the drum 1 to a speed slower than the speed during the normal image forming operation. In order to eliminate the slip state of the charging roller 2 with respect to the rotating drum 1, the frictional resistance between the drum 1 and the charging roller 2 is important. Therefore, when the image forming apparatus shifts from the stationary state to the driving state, a higher frictional resistance transmitted to the charging roller is advantageous to follow.

  Therefore, a process speed reduction is proposed as a second method for eliminating the slip. Since the charging roller 2 is intended to charge the drum 1 as before, it has a contact nip N, the drum 1 is formed of a hard resin, and the charging roller 2 is formed of a rubber layer 2b of a soft conductive material. The drum 1 is in contact with a predetermined contact pressure. The charging roller 2 is indented into contact with the contact portion N of both the members 1 and 2.

  When the drum 1 is driven from a stationary state in this state, the charging roller 2 starts to be driven while being slowly crushed by the contact portion N. However, if the process speed (the rotational speed of the drum 1) is high, the process tries to rotate with a small amount of crushing. Therefore, the dent of the contact portion N is maintained as it is, and the charging roller 2 may slip.

  In addition, the contact surfaces of the members 1 and 2 have a frictional resistance of the members 1 and 2 because the contact area cannot be followed and the contact surface is floated and the contact area becomes smaller as the rotational speed increases. May be smaller. Therefore, it is effective to reduce the process speed when the charging roller 2 slips and to enlarge the contact nip N or increase the contact area by the elasticity of the rubber of the charging roller 2.

  Actually, the effect was verified while monitoring the current value of the charging roller 2 by the above-described slip detection means example 1 (FIG. 2). In a state where the charging roller 2 does not rotate with the rotation of the predetermined process speed of the drum 1 and stops rotating and slips with respect to the surface of the drum 1, one charging roller 2 as shown in FIG. Current value period E is not detected, and a constant current value is monitored as shown in J of FIG.

  In this slip state, the process speed was reduced (for example, 0 to 50 mm / sec down). Then, the charging roller 2 whose driven rotation is stopped due to slip starts to rotate. As a result, a predetermined current value as shown in FIG. 10H is monitored when the charging roller 2 rotates in a predetermined manner following the drum 1 with respect to the lowered process speed from a state in which the current value as indicated by J is constant. The current value of the charging roller cycle was detected. That is, it was found that slip can be recovered early.

  The same applies to the case where the charging roller 2 is rotated, but in a slip state where the charging roller 2 rotates at a lower speed than a predetermined driven rotational speed corresponding to the rotation of the drum 1. That is, by reducing the process speed, the current value of a predetermined charging roller cycle as shown in H of FIG. 10 is monitored when the charging roller 2 is rotated by the drum 1 following the process speed. was detected. That is, it was found that slip can be recovered early.

  When the control circuit unit C determines that the slip of the charging roller 2 has been recovered by detecting a current value of a predetermined charging roller cycle as shown in H of FIG. 10, the reduced process speed is set to the normal image forming execution time. Control to return to the process speed. By this return, the form of the current value period for one rotation of the charging roller 2 becomes the form of the current value period E in FIG.

  In addition to the above-described two methods for increasing the frictional resistance μ between the drum 1 and the charging roller 2 and eliminating the slip of the charging roller 2, for example, the following control is also effective. During the non-image formation, the developer is supplied from the developing device 4 to adhere to the drum surface. A bias having the same polarity as the charging polarity of the developer is applied to the transfer roller 5 so that the developer reaches the cleaning device 6. It is also effective to increase the frictional resistance of the drum 1 by rubbing the drum when the developer is removed by the cleaning blade 6a. The slip elimination control is not limited to the above method as long as it is a method of increasing the frictional resistance μ between the drum 1 and the charging roller 2.

<Description of flowchart>
Next, the flowchart of the apparatus control sequence including slip detection and slip cancellation control in the image forming apparatus of the present embodiment will be described with reference to FIG.

  1) When the apparatus M is in a standby state (step S1: main power switch-on, drum drive-off state), a print job start signal is input to the control circuit unit C (step S2). Based on the signal input, the control circuit unit C activates the drive source motor K to rotate the drum 1 at a predetermined process speed (step S3). The period from the rotational driving of the drum 1 to the start of printing is the pre-rotation process.

2) The control circuit unit C executes a predetermined pre-printing operation in this pre-rotation process. In the pre-rotation process, the control circuit unit C detects whether or not the charging roller 2 is slipping by an appropriate slip detection unit such as the above-described slip detection unit examples 1 to 3 (step S4). When it is determined that the charging roller 2 is not slipping based on the detection information of the slip detection means (No in step S4), the apparatus operation is shifted to the image forming operation (step S5).
3) On the other hand, when it is determined that the charging roller 2 is slipping based on the detection information of the slip detection means (Yes in step S4), appropriate slip cancellation control as in the above-described slip cancellation control examples 1 and 2 Is executed (step S10). The control circuit unit C executes this slip cancellation control until slip cancellation is detected by the slip detection means (steps S10 and S11). If the control circuit unit C determines that the slip state of the charging roller 2 has been eliminated based on the detection information of the slip detection means (Yes in step S11), the apparatus operation is shifted to the image forming operation (step S5).
4) The image forming process is from the start of printing execution (step S5) to the completion of printing for a predetermined number of sheets (step S5) until the input print job is completed (step S7). In this image forming process, the control circuit unit C always detects whether or not the charging roller 2 is slipping by the slip detection means (step S12).

  If no slip of the charging roller 2 is detected during the image forming process, a predetermined number of prints are repeatedly executed and the print job is finished (step S7), and then a predetermined post-printing operation is executed in the post-rotation process. Thus, the drive of the drive source motor K is stopped. That is, the driving of the drum 1 is stopped (step S8), and the apparatus M is kept in a standby state until the next print job start signal is input to the control circuit unit C.

  5) When it is determined that the charging roller 2 is slipping based on the detection information of the slip detection means during the image forming process (Yes in step S12), the control circuit unit C performs the next control. That is, the interval between the recording material at the time of the image formation being executed at the time of the determination and the recording material at the time of the next image formation is extended.

  Slip cancellation control similar to that in step S10 is executed between the extended sheets (step S14). The control circuit unit C executes this slip cancellation control until slip cancellation is detected by the slip detection means (steps S14 and S15). If it is determined that the slip state of the charging roller 2 has been eliminated based on the detection information of the slip detection means (Yes in step S15), the image formation is executed from the next recording material in which the interval between sheets is extended.

  In the post-rotation process, slip detection and slip elimination control when slip is detected can also be configured.

  As described above, the slip of the charging roller 2 with respect to the drum 1 is detected in real time, and control for eliminating the slip is performed based on the detection result. Accordingly, it is possible to suppress the occurrence of defective images such as streaks due to the scratches on the drum 1 due to the charging roller 2 slipping and the deposits on the surface of the drum 1 being deposited on the surface of the charging member.

<Others>
1) The rotatable image carrier for forming the electrostatic latent image is not limited to the electrophotographic photosensitive member in the electrophotographic image forming apparatus of the embodiment. It may be an electrostatic recording dielectric in the electrostatic recording image forming apparatus. The image carrier is not limited to a drum type, and may be an endless belt type.

  2) The charging member that contacts the image carrier and rotates following the rotation of the image carrier and applies the charging bias to charge the surface of the image carrier is not limited to the roller type but is an endless belt type. May be.

  M..Image forming apparatus, 1 .... Image carrier, 2..Charging member, AC, 18-C, 19-C..Slip detection means, C..control means

Claims (6)

A rotatable image carrier for forming a developer image, and a rotation of the image carrier in contact with the image carrier, and the surface of the image carrier is charged by applying a charging bias. An image forming apparatus having a charging member,
Slip detecting means for detecting that the charging member is slipping with respect to the image carrier when the image carrier is rotating;
Control means for executing slip elimination control for eliminating the slip when slippage of the charging member is detected by the slip detection means;
An image forming apparatus comprising:   The slip detection means monitors a current value of a rotation period of a charging member to which a charging bias is applied, and a form of a current value period monitored when the charging member rotates in a predetermined driven manner with respect to the image carrier. And detecting that the charging member is slipping with respect to the image carrier based on a difference from a form of a current value period monitored when the charging member is slipping. The image forming apparatus according to 1.   The slip detection means monitors the amount of rotation of the charging member in a rotation period, and the form of the amount of rotation monitored when the charging member rotates in a predetermined driven manner on the image carrier, and the charging member slips. 2. The image according to claim 1, wherein the charging member detects that the image bearing member slips from a difference from a rotation amount period monitored when the image is carried. Forming equipment.   The slip detection means monitors the vibration amount of the rotation cycle of the charging member, and the form of the vibration amount cycle monitored when the charging member rotates with the image carrier in a predetermined manner, and the charging member slips. 2. The image according to claim 1, wherein the charging member detects that the charging member is slipping with respect to the image carrier based on a difference from a vibration amount period monitored when the image is carried. Forming equipment.   5. The slip cancellation control is a control for changing a charging bias applied to the charging member to a bias having a higher absolute value than a bias applied during a normal image forming operation. The image forming apparatus according to one item.   5. The slip elimination control is control for changing the rotation speed of the image carrier to a speed slower than a speed during a normal image forming operation. Image forming apparatus.