JPH0756403A - Image forming device - Google Patents

Abstract

PURPOSE:To achieve uniform electrification at all times and to obtain a satisfac tory image by providing a preliminary drive means which, during the period of time that image formation is not carried out, rotates and drives only an image carrier at speed lower than the speed at which it is rotated during the image formation. CONSTITUTION:A drum drive pulley 25 incorporating a clutch is attached to one end of a photosensitive drum in an axial direction and rotates and drives the drum by means of a motor 24. On the other hand, the power of a main motor 23 is transmitted to the drum drive pulley 25 by means of a drum-drive timing belt 26. In this case, the preliminary drive means is composed of the drum drive pulley 25 and the drum drive motor 24. During the period of time that the image formation is not carried out, only the photosensitive drum is rotated and driven by the preliminary drive means at speed lower than the speed at which it is rotated during the image formation; thereby, the photosensitive drum and an electrifying roller rotate while one follows the other in contact with each other at all times. Thus, partial temperature-difference in the electrifying roller and the occurrence of a trace made by the contact of the photosensitive drum and the electrifying roller are prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copying machine, a printer,
The present invention relates to an image forming apparatus that is used in a facsimile or the like and that charges an image carrier by a charging roller that rotates following the image carrier.

[0002]

2. Description of the Related Art Conventionally, a corona discharger has been generally used for charging in an electrophotographic type or electrostatic recording type image forming apparatus. However, in this type of charging apparatus, ozone is discharged during corona discharge. Occur. This ozone is harmful to the human body and also causes deterioration of rubber parts and the like in the image forming apparatus. Therefore, for reasons such as environmental problems, a roller charging device using a charging roller as a charging means has been put into practical use. By using this device, the amount of ozone generated and the applied voltage can be significantly reduced as compared with the conventional corona discharger, and the overall configuration can be simplified.

However, in this roller charging device, since the charging roller is in contact with the photosensitive drum and is driven to rotate, the surface of the charging roller is contaminated by toner stains or the like on the photosensitive drum that cannot be cleaned by the cleaning device. If so, the surface of the photosensitive drum that is in contact with the portion becomes defectively charged, and it may appear as streaks on the image. Therefore, a charging mechanism of this type is generally provided with a cleaning mechanism for cleaning the surface of the charging roller. The material of the charging roller is 10
^{It is known} that medium resistance rubber with a volume resistivity of about ⁸ to 10 ¹⁰ Ωcm is used, but its temperature dependence is large and the resistance value changes depending on the charging roller temperature, and the charging potential also changes accordingly. Has been. Therefore, at a low temperature, there is a problem that it cannot be actually used due to its characteristics. Therefore, it is proposed to provide a heating mechanism for the charging roller or control the temperature of the charging roller by temperature detection. (JP-A-1-2884872 and JP-A-3-288174).

[0004]

However, in the above conventional image forming apparatus, when the temperature distribution on the surface of the charging roller is observed, there is a partial variation, and in particular, in the contact surface between the photosensitive drum and the charging roller. The temperature is slightly different from the overall temperature, and this temperature difference causes a slight difference in the resistance value of the charging roller, resulting in non-uniform charging. Appears as streaks. In particular, when the photoconductor drum and the charging roller have a heating means, there is a problem that this effect becomes strong. Further, depending on the materials of the photoconductor drum and the charging roller, contact marks may remain or the photoconductor drum and the charging roller may adhere to each other, which adversely affects the image.

In order to deal with this problem, a roller contact / separation mechanism for separating the charging roller from the photosensitive drum during the suspension of copying has been proposed. A temperature difference is inevitable, and due to slip between the photoconductor drum and the charging roller during re-contact, streaks due to toner stains, etc., adhere to the charging roller, resulting in poor charging. There was a problem. Therefore, the present invention solves the above-mentioned problems of the related art, can maintain the temperature of the surface of the photoconductor drum and the surface of the charging roller at the same and uniform, and at the same time, makes a contact mark between the photoconductor drum and the charging roller. It is an object of the present invention to provide an image forming apparatus capable of preventing the occurrence of an image and capable of obtaining a good image.

[0006]

According to a first aspect of the present invention, there is provided an image forming apparatus including an image carrier and a charging roller which is driven to rotate while being in contact with the image carrier. In claim 2, a pre-driving unit that rotationally drives only the image carrier at a speed lower than the rotation speed during image formation is provided, and in Claim 2 (or 3), a heating unit is provided. An image forming apparatus including an image carrier (or a charging roller) having the same includes the same pre-driving unit as in claim 1, and in claim 4, the image carrier and the charging roller are provided on the surfaces of the image carrier and the charging roller, respectively. The temperature detection means and the control means for operating the preliminary drive means when the temperature difference between the detection results of the temperature detection means becomes equal to or more than a predetermined value.

[0007]

Therefore, according to the first aspect, during non-image formation, only the image carrier is rotationally driven by the pre-driving means at a speed lower than the rotational speed during image formation, whereby the image carrier and the charging roller are rotated. Keeps in contact with each other and is driven to rotate, thereby preventing a partial temperature difference of the charging roller and a contact mark between the image carrier and the charging roller. Further, in the present invention, the image carrier has a heating means, and the charging roller and the image carrier are always kept at a temperature at which a predetermined charging characteristic can be obtained without providing a heating means on the charging roller side. The same operation as in claim 1 is provided. Further, in claim 3, since the charging roller has the heating means, the roller temperature is prevented from lowering due to the heat capacity difference at the contact position with the image carrier, and the partial temperature rise on the surface of the image carrier is prevented. The same operation as in claim 1 is provided.

Further, in the present invention, the surface temperature of each of the image carrier and the charging roller is detected by the temperature detecting means, and the temperature difference between them is input to the control means. When the control means determines that the temperature difference exceeds a predetermined value, the control means outputs a signal to the preliminary driving means to drive the image carrier, thereby the minimum operation for driving the image carrier only when necessary. To reduce power consumption. Further, in claim 5, the surface temperature of each of the image carrier and the charging roller is detected by the temperature detecting means, and the temperature difference between them is input to the control means. The control means is
By changing the rotation speed of the image carrier according to the temperature difference, finer control is performed as necessary to reduce power consumption.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 shows a copying machine to which the image forming apparatus of the present invention is applied. In FIG. 2, a light source 5, mirrors 6, 7, and 6 are provided on the lower surface side of a contact glass 3 on which an original 4 is placed.
An optical scanning optical system composed of 8, 10 and a lens 9 is arranged,
Below the optical scanning optical system, the photosensitive drum 1 exposed by the light emitted from the optical scanning optical system is arranged. The transfer charger 1 is placed close to the periphery of the photosensitive drum 1.
2, a separation charger 13, a developing device 17, a charging roller 2, a charge eliminating lamp 16, and a cleaning device 15 are arranged, and a conveyance belt 18 and a fixing device 14 are arranged on a conveyance path of the transfer paper 11. Then, as shown in FIG.
A drum drive pulley 25 with a built-in clutch is attached to one end of the photosensitive drum 1 in the axial direction, and the drum drive pulley 25 is rotationally driven by a drum drive motor 24. On the other hand, the power of the main motor 23 is supplied to the drum drive pulley 25 by the drum drive timing belt 26.
Be transmitted to. The drum driving pulley 25 and the drum driving motor 24 constitute a preliminary driving means.

A cleaning member 22 is arranged on the charging roller 2 so that one end portion in the short side direction thereof is in contact with the charging roller 2, and the end portion of the photosensitive drum 1 opposite to the drum drive pulley 25. , And the end portion of the charging roller 2 on the same side, a temperature detecting thermistor 27 which is a temperature detecting means.
b and 27a are arranged. In the above configuration,
An electrostatic charge is applied to the photosensitive drum 1 by the charging roller 2, and the entire surface is uniformly charged. On the other hand, image scanning is performed by the light source 5 in accordance with the original 4 placed on the contact glass 3, and the scanning light image is passed through the mirrors 6, 7, 8 and the lens 9 and the mirror 10 and the photosensitive drum 1 is scanned. An electrostatic latent image is formed on the photoconductor drum 1 by being projected onto the photoconductor drum 1 and the surface potential of the photoconductor drum 1 being attenuated according to the light and dark light image of the original 4.

Next, the electrostatic latent image is visualized by a toner having a reverse polarity, a transfer paper 11 is superposed on the toner image, and a transfer charger 12 is provided from the back side thereof to reverse the polarity of the toner. The toner image is transferred from the photosensitive drum 1 onto the transfer paper 11 by applying a polar charge.
After this transfer operation, the toner image on the transfer paper 11 separated by the separation charger 13 is fixed by the fixing device 14. On the other hand, the untransferred toner remains on the photosensitive drum 1 after the transfer, and in order to remove the untransferred toner, the cleaning device 15 including a brush and a blade is used to scrape off the untransferred toner and expose it. After cleaning the body drum 1, the residual charge is removed by the static elimination lamp 16.
Return to the initial state. By repeating the series of processes, a copy image is obtained.

Next, the charging operation of the photosensitive drum 1 will be described in detail. As shown in FIG. 1, during a normal copying operation, the photosensitive drum 1 is driven by the main motor 2 via the drum driving timing belt 26 and the drum driving pulley 25.
It is driven by 3. Then, the charging operation is performed by rotating the photosensitive drum 1 and the charging roller 2 being driven. The relationship between the temperature of the charging roller 2 and the charging potential at this time is as shown in FIG. 3 (however, the applied voltage is constant).

Next, after the copying operation is completed, the main motor 2
When 3 is stopped, the clutch of the drum drive pulley 25 is released, and only the photosensitive drum 1 is in a rotatable state while other processes (other units) are stopped. Thereafter, the drum drive motor 24 rotates the photosensitive drum 1 at a preset linear velocity (low linear velocity), and
The charging roller 2 is also driven to rotate and charged. This charging operation is continued until the start of the next copy operation.

Next, the temperature detecting thermistors 27a and 27b.
The operation of the embodiment provided with will be described with reference to FIG. After the copying operation is completed, when the main motor 23 is stopped, the clutch of the drum driving pulley 25 is released, the surface temperature of the charging roller 2 is changed by the temperature detecting thermistor 27a, and the surface temperature of the photosensitive drum 1 is changed by the temperature detecting thermistor 27b. Detected. The signal is output to the detection circuit 30, the temperature difference between them is detected, and the signal is output to the control unit 31 which is the control means. Control unit 3
In No. 1, the input temperature difference is compared with a preset value (for example, x), a control signal corresponding to the comparison result is output to the drive power supply 32, and the drum drive motor 24 is driven to expose the photosensitive drum. The body drum 1 is rotated at a predetermined linear velocity. That is, when the temperature difference exceeds the set value x, the photosensitive drum 1 is rotated at a preset linear velocity (low linear velocity), and the charging roller 2 is also driven to rotate so that uniform charging is performed.

At this time, in the controller 31, according to a preset program, for example, when the temperature difference is 10 ° C. or more, the linear velocity of the photosensitive drum 1 is 1/2 and the temperature difference is 5 when the temperature is normally copied. When the temperature is between 10 ° C and 10 ° C,
The linear velocity of 4 may be set, and the linear velocity may be controlled in multiple stages depending on the temperature difference.
In this case, when the controller 31 determines that the detected temperature difference is smaller than the set value x, the drum drive motor 2
4 is stopped, and the operation of the photosensitive drum 1 is stopped. This series of operations is repeated until the start of the next copy.

However, even if there is no temperature difference between the photosensitive drum 1 and the charging roller 2, in order to prevent the occurrence of contact marks between the photosensitive drum 1 and the charging roller 2 after a certain period of time, the charging roller is prevented. Rotate about 1/2 rotation of 2,
The contact position shifting operation may be performed. Since the temperature at the contact surface between the photoconductor drum 1 and the charging roller 2 is substantially the same as the surface temperature of the photoconductor drum 1, the temperature difference detected by the two temperature detecting thermistors 27a and 27b remains as it is. Can be understood as a partial temperature difference.

[0017]

As described above, according to the first aspect, the pre-driving means is provided for rotationally driving only the image carrier at a speed lower than the rotational speed during image formation during non-image formation. Therefore, the image carrier and the charging roller are always in contact with each other and driven to rotate, which prevents a partial temperature difference of the charging roller and a contact mark between the image carrier and the charging roller from being generated, so that the image carrier is always uniform. Charging can be performed and a good image can be obtained. Also, since only the image carrier is driven during non-image formation,
The operation can be performed silently without burdening other units. Further, according to claim 2, in the image forming apparatus provided with the image carrier having the heating means, since the same pre-driving means as in claim 1 is provided, it is possible to provide the heating means on the charging roller side. The charging roller and the image carrier can always be maintained at a temperature at which a predetermined charging characteristic can be obtained, stable and uniform charging can be performed in all usage environments, and a good image can be obtained. Further, according to claim 3, in the image forming apparatus provided with the charging roller having the heating means, since the same pre-driving means as in claim 1 is provided, there is a difference in heat capacity at the contact position with the image carrier. The roller temperature can be prevented from lowering and the temperature of the image carrier surface can be prevented from rising partially, and the charging roller and image carrier can be maintained at a temperature that provides the desired charging characteristics, and is stable and uniform in all operating environments. Charging can be performed, and a good image can be obtained.

According to a fourth aspect of the present invention, when temperature detection means provided on the surface of the image carrier and the surface of the charging roller, respectively, and the temperature difference between the detection results of these temperature detection means exceeds a predetermined value, Since the control means for operating the pre-driving means is provided, the temperature difference between the charging roller and the partial temperature difference of the charging roller is suppressed while suppressing the power consumption by performing the minimum necessary operation of the image carrier. The generation of roller contact marks can be prevented, uniform charging can be always performed, and a good image can be obtained. Further, according to claim 5, since the control means has a function of changing the rotation speed of the image carrier according to the temperature difference of the detection result by the temperature detection means, more detailed control is required. Various controls can be performed, and the same effect as that of claim 4 can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of an image forming apparatus of the present invention.

FIG. 2 is an overall schematic configuration diagram showing a copying machine to which the present invention is applied.

FIG. 3 is a characteristic diagram showing the relationship between the surface temperature of the charging roller and the charging potential.

FIG. 4 is a block diagram showing control by temperature detecting means.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image carrier 2 Charging rollers 24, 25 Pre-driving means 27a, 27b Temperature detecting means 31 Control means

Claims (5)

[Claims] 1. An image forming apparatus comprising an image carrier and a charging roller which is driven to rotate while being in contact with the image carrier, wherein a speed lower than a rotation speed during image formation during non-image formation. The image forming apparatus is provided with a pre-driving unit that rotationally drives only the image carrier. 2. An image forming apparatus comprising an image carrier having heating means and a charging roller which is driven to rotate while being in contact with the image carrier, and a rotational speed during image formation during non-image formation. An image forming apparatus comprising a pre-driving unit that rotationally drives only the image carrier at a lower speed. 3. An image forming apparatus comprising an image carrier and a charging roller which has a heating means and is driven to rotate while being in contact with the image carrier. An image forming apparatus comprising: a pre-driving unit that rotationally drives only the image carrier at a speed lower than a rotational speed. 4. The temperature detecting means provided on the surface of the image carrier and the surface of the charging roller, and the pre-driving means is operated when the temperature difference between the detection results of these temperature detecting means exceeds a predetermined value. The image forming apparatus according to claim 1, 2 or 3, further comprising a control unit. 5. The control means has a function of changing the rotation speed of the image carrier according to the magnitude of the temperature difference of the detection result of the temperature detection means. Image forming device.