JPH07199580A - Color image forming device - Google Patents

Abstract

PURPOSE:To provide a color image forming device which is free of color slippage and deviation in position. CONSTITUTION:The color image forming device repeats a number of times the process of attaching developer in one color to the surface of a photosensitive drum 1, thereby forming developed images in the separate colors on the photosensitive drum 1, and transfers the images in the many colors to recording paper altogether. As a means for detecting the position of the photosensitive drum 1 in the circumferential direction, the color image forming device uses the encoder 43 of a motor 42 used for driving the photosensitive drum 1. According to the result of the output of the encoder 43, the motor 42 as a means for driving the photosensitive drum 1 is controlled after a photosensitive drum cleaning means 51 is released and before the image in the subsequent color is written by the image exposure means 10, thereby preventing deviation in a position.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, color image forming apparatuses have been known, and various methods are used for forming color images. For example, a method in which the toner image transfer process is repeated for each color, a photosensitive drum is prepared for each color type, and each color is transferred to the recording paper while the recording paper passes through each photosensitive drum, a color image is obtained. There is known a method for forming a toner image, a method for forming a toner image for each color type on a single photosensitive drum in a laminated manner, and a batch transfer of these multicolor images on a recording paper. The method used in the present invention relates to the above-described multicolor image batch transfer type color image forming apparatus.
The operation of the multi-color image batch transfer type color image forming apparatus will be described below.

FIG. 6 is a diagram showing a structural example of a multi-color image batch transfer type color image forming apparatus. In the figure, reference numeral 1 denotes a photosensitive drum which is an image bearing member, and is an OPC photosensitive member coated on the drum, which is electrically grounded and driven and rotated clockwise. Reference numeral 2 denotes a scorotron charger, which uniformly charges the peripheral surface of the photosensitive drum 1 at the potential V _H to the potential V _G.
Given by corona discharge by a grid and corona discharge wire held on. Prior to the charging by the scorotron charger 2, an exposure device using a light emitting diode or the like (for example, P
CL) 3 is used to remove the charge from the peripheral surface of the photoconductor.

After uniformly charging the photoreceptor, the image exposing means 10
Thus, image exposure is performed based on the image signal. The image exposure means 10 uses a laser diode (not shown) as a light emitting source, performs scanning while the optical path is bent by a reflecting mirror 12 via a rotating polygon mirror 11, fθ lens, etc., and rotation of the photosensitive drum 1 (sub scanning). Form an electrostatic latent image. Here, the character portion is exposed to form an inverted latent image in which the character portion has a lower potential V _L.

At the periphery of the photoconductor drum 1, there is provided a developing device 20 in which a developer containing toner such as yellow (Y), magenta (M), cyan (C), black (K) and a carrier is incorporated. First, the development of the first color is performed by the developing sleeve 21 which has a magnet built therein and holds the developer and rotates. The developer is composed of a carrier in which ferrite is used as a core and an insulating resin is coated around the core, and a toner in which a pigment as a main material and a charge control agent, silica, titanium oxide and the like are added, The developer is regulated to a layer thickness (developer) of 100 μm to 600 μm on the developing sleeve 21 by the layer forming means and is conveyed to the developing area.

The gap between the developing sleeve 21 and the photosensitive drum 1 in the developing area is larger than the layer thickness (developer) of 0.2.
The thickness is set to mm to 1.0 mm, and the AC bias of the voltage value V _{AC and} the DC bias of the voltage value V _DC are superimposed and applied during this period. Since V _DC and V _H and the toner charge have the same polarity,
The toner, which has been given the opportunity to leave the carrier by V _AC , does not adhere to the V _H portion, which has a higher potential than V _DC ,
It adheres to the V _L portion having a lower potential than V _DC and is visualized (reverse development).

After the visualization of the first color is completed, the image forming process of the second color is started, the uniform charging is performed again by the scorotron charger 2, and the electrostatic latent image based on the image data of the second color is exposed by the image exposing means. Formed by 10. At this time, the charge removal by the exposure device 3 performed in the image forming process of the first color is not performed because the toner attached to the image portion of the first color scatters due to the rapid decrease in the potential around the image.

Again, an electrostatic latent image similar to that of the first color is formed on the portion of the photoconductor having the potential of V _H over the entire peripheral surface of the photoconductor drum without the image of the first color, Although the development is performed, in the portion where the development of the image of the first color is performed again, the toner attached to the first color shields light and an electrostatic latent image of potential V _M is formed by the electric charge of the toner itself. Development is performed according to the potential difference between V _DC and V _M. In the part where the images of the first and second colors overlap,
When the development of the first color is performed by forming an electrostatic latent image of V _L , the balance between the first color and the second color is lost, so the exposure amount of the first color is reduced and V _H > V _M > V _L Sometimes.

An image forming process similar to that of the second color is performed for the third and fourth colors, and a visible image of four colors is formed on the peripheral surface of the photosensitive drum 1. On the other hand, the recording paper P carried out from the paper feeding cassette 15 via the half-moon roller 16 is temporarily stopped, and when the transfer timing is adjusted, the paper feeding roller 17
The paper is fed to the transfer area by the rotation operation of.

In the transfer area, a transfer roller 18 is pressed against the peripheral surface of the photosensitive drum 1 in synchronism with the transfer timing, and the supplied recording paper P is nipped and a multicolor image is transferred at once. To be done.

Next, the recording paper P is de-charged by the separating brush 19 which is brought into pressure contact with each other almost at the same time, separated by the peripheral surface of the photosensitive drum 1 and conveyed to the fixing device 30, where the heat roller 31 and the pressure roller 32 are heated. After the toner is fused by applying pressure, the toner is ejected to the outside of the apparatus through the paper ejection roller 41. Incidentally, the transfer roller 18 and the separation brush 1 described above.
After the recording paper P has passed through, 9 is retracted from the peripheral surface of the photosensitive drum 1 to prepare for the formation of the next toner image.

On the other hand, the photosensitive drum 1 from which the recording paper P is separated
Removes and cleans the residual toner by pressing the blade 51 of the cleaning device 50, and again receives the charge removal by the exposure device 3 and the charge by the scorotron charger 2 to start the next image forming process. The blade 51 moves immediately after cleaning the surface of the photoconductor and retracts from the peripheral surface of the photoconductor drum 1.

Note that the image forming apparatus shown in the figure can also be manually fed in addition to being fed by an automatic sheet feeding mechanism. The recording paper P manually fed by the manual feed tray 60 is conveyed by the rotation of the pickup roller 61,
The sheet is fed to the transfer area through the same process as the sheet feeding from the sheet feeding cassette 15 described above.

[0014]

In the color image forming apparatus of the multicolor image batch transfer system described above, in order to obtain a good image, the next toner image is accurately formed on the toner image previously formed. It is necessary to stack them well. On the other hand, the operation and release of the cleaning device 50 affects the speed of the photosensitive drum 1 in the circumferential direction. That is, when the cleaning device 50 is operated and the blade 51 is pressed against the photosensitive drum 1, the blade 51 is separated from the photosensitive drum 1, and the load is lightened and accelerated, and the photosensitive drum 1 rotates more than necessary. I will end up.

Therefore, if the cleaning device 50 is operated or released during writing of an image, uneven pitch or uneven color will occur. In addition, the cleaning device 5
Even if 0 is activated or released, the cleaning device 5
Since a toner image formed prior to the operation or release of 0 and a toner image formed after that occur, color misregistration occurs over the entire image.

Conventionally, in order to avoid the influence of this color shift or the like, the cleaning device 50 is released prior to the writing of the image of the first color, and the cleaning is performed after the writing of the image of the last color is completed. The operation of the means 50 was restarted.

For this reason, the rotation of the photosensitive drum 1 is approximately 2
It is necessary for the extra rotation, and when four color toners are used, the printing speed is reduced to 2/3. Further, a method has been considered in which a frictional load is applied to the driving means of the photoconductor drum in advance to relatively reduce the influence of the operation and release of the cleaning device 50, but it is required for the driving means of the photoconductor drum 1. The torque was increased, the size of the device was increased and the cost was increased.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a color image forming apparatus which is free from color misregistration and positional deviation in an image forming apparatus of a multicolor image batch transfer system. There is.

[0019]

SUMMARY OF THE INVENTION In the present invention for solving the above-mentioned problems, a step of adhering a developer of one color onto a photosensitive drum is repeated a plurality of times to form a plurality of types of colors on the photosensitive drum. In a color image forming apparatus configured to transfer a multicolor image onto a recording sheet by forming a visible image, an encoder of a motor for driving the photoconductor drum is used as a means for detecting the circumferential position of the photoconductor drum. In accordance with the output result of the encoder, after the photoconductor drum cleaning means is released, and before the image writing of the next color by the image exposure means is started, the drive means for the photoconductor drum is controlled so that the positional deviation is caused. The feature is that they are prevented.

[0020]

The peripheral speed of the photosensitive drum is detected by the encoder output of the photosensitive drum driving motor, and the driving means for the photosensitive drum is controlled according to the detection result to correct the positional deviation. Specifically, the peripheral speed of the photoconductor drum is increased by releasing the cleaning device 50, so that the image writing start position of the photoconductor drum is extended first. Therefore, the driving means for the photosensitive drum is controlled to slow down the rotation of the photosensitive drum driving motor. As a result, the image writing start position of the image exposure unit and the image start position of the photoconductor drum match.

The above principle will be described with reference to the drawings. FIG. 1 is an explanatory view of the operation of the present invention. The same parts as those in FIG. 6 are designated by the same reference numerals. The process shifts from (a) to (c) in the figure. FIG. 6A shows a state in which the image of the first color is formed. Point A indicates the leading edge of the first color image. In this state, the blade 51 is in pressure contact with the photosensitive drum 1. In (b), the blade 51 is released. When the blade 51 is released, the load on the photosensitive drum 1 is lightened and the photosensitive drum 1 is accelerated.
If the irradiation position of the laser light is not changed, the leading edge of the second color and the leading edge A of the image of the first color are displaced as shown in (c). Therefore, the rotation of the photosensitive drum 1 is slowed down so that the image start position A of the photosensitive drum 1 is aligned with the image writing position of the laser beam as shown in (d).
As a result, the positional deviation between the image exposure unit 10 and the photosensitive drum 1 is eliminated. By doing so, it is possible to provide a color image forming apparatus without color misregistration or position misregistration.

[0022]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 2 is a configuration diagram showing a main part of an embodiment of the present invention. The same parts as those in FIG. 6 are designated by the same reference numerals. In the figure, 1 is a photosensitive drum, 51 is a blade for cleaning the drum surface, and 10 is an image exposing means. A polygon mirror 11 that scans pixels and a reflection mirror 12 that reflects light from the polygon mirror 11 are provided therein.

42 is directly connected to the rotary shaft of the photosensitive drum 1,
A motor for rotating the photosensitive drum 1 and 43 are encoders attached to the rotary shaft of the motor 42. 44
Is a reference pulse generator for generating a reference pulse, 45 is a phase comparison unit for performing a phase comparison between the output of the encoder 43 and the output of the reference pulse generator 44, and 46 is the phase comparison unit 45.
Is a power amplifier that drives the motor 42 according to the output of the. In the circuit that drives the motor 42 in this manner, in the steady state, the phase of the output of the encoder 43 entering the phase comparison unit 45 and the output of the reference pulse generator 44 is fixed to 0 or a fixed value. Phase lock loop) is formed. A control unit 47 receives the output of the encoder 43 and calculates the amount of advance of the photosensitive drum 1 after the blade 51 is removed. The operation of the apparatus configured as described above will be described below.

When the blade 51 moves away from the state in which it is pressed against the photosensitive drum 1, the rotation of the photosensitive drum 1 fluctuates and is accelerated only at that moment. Therefore, the output of the encoder 43 that receives this rotation also changes. FIG. 3 shows the rotation fluctuation of the photosensitive drum 1 and the encoder 4 when the blade 51 is separated.
It is a figure which shows the mode of rotation fluctuation of No. 3. In the figure,
(A) shows the rotation of the photosensitive drum 1, and (b) shows the rotation fluctuation of the encoder 43. In (a), the vertical axis represents rotation, the horizontal axis represents time, and in (b), the vertical axis represents encoder output and the horizontal axis represents time. Assuming that the blade 51 is detached at time t = 0, the rotation fluctuation of the photosensitive drum 1 fluctuates as shown in FIG. 3A, and the output of the encoder 43 also becomes as shown in FIG. fluctuate.

The control unit 70 receives the output of the encoder 43, obtains the delay time Td and the area of the rounded portion (hatched area in the figure), and calculates how far the photosensitive drum 1 advances. Then, based on the calculation, the reference pulse generator 4
A control signal is given to 4 to change the phase of the reference pulse.
As a result, the motor 42 driven by the power amplifier 46
The rotation of can be slowed. Then, the image start position A of the photosensitive drum 1 at the time of starting the next image writing can be matched with the exposure start position of the laser beam output from the image exposure means 10 (see (d) of FIG. 1). As a result, the laser light writing start position coincides with the image start position A of the photosensitive drum 1, and it is possible to form an image without displacement.

Here, the resolution of the encoder 43 required to keep the alignment accuracy within one pixel will be described. Now, the diameter of the photosensitive drum 1 is R (mm), the number of teeth of the encoder 43 is M, the reduction ratio from the encoder 43 to the photosensitive drum 1 is N, and the minimum control length (deviation amount) of the photosensitive drum 1 is Q. (Mm), Q is expressed by the following equation.

Q = πR / N × M (1) Here, R = 120 mm, N = 100, shift amount Q = 0.
If it is set to 02 mm, M becomes M = 188.5 from the equation (1). Therefore, the number of teeth M of the encoder 43 may be set to 200.

FIG. 4 is a block diagram showing another embodiment of the present invention. The same parts as those in FIG. 2 are designated by the same reference numerals.
In the figure, reference numeral 47 denotes a piezoelectric vibrating gyro as a means for detecting the acceleration of the peripheral speed of the photosensitive drum 1, which is attached to the rotary shaft of the photosensitive drum 1. Reference numeral 71 is a first integrator for integrating the output of the piezoelectric vibrating gyro 47 to obtain a speed, and 72 is a second integrator for integrating the output of the first integrator 71 to obtain a distance. The output of the second integrator 72 is input to the control unit 70. The operation of the apparatus thus configured will be described below.

A PLL system composed of a motor 42, a reference pulse generator 44, a phase comparator 45 and a power amplifier 46 rotates the photosensitive drum 1 at a constant speed. here,
It is assumed that the blade 51 is separated from the state in which the blade 51 is pressed against the photosensitive drum 1. At this moment, the peripheral speed of the photosensitive drum 1 fluctuates, and acceleration is generated in the piezoelectric vibrating gyro 47.

The first integrator 71 integrates the output of the piezoelectric vibrating gyro 47 and outputs the velocity. The second integrator 72 integrates the output of the first integrator 71 to obtain the distance. The control unit 70 recognizes the traveling distance of the photosensitive drum 1 due to the acceleration generated by the output of the second integrator 72, and determines the image writing start position A of the photosensitive drum 1 at the time of starting the next image writing. Calculate the deviation from the reference position. Then, according to the calculation result, a control signal is given to the reference pulse generator 44 to change the phase of the reference pulse. As a result, the rotation of the motor 42 driven by the power amplifier 46 can be slowed down. Then, the image start position A of the photosensitive drum 1 at the time of starting the next image writing can be matched with the exposure start position of the laser beam output from the image exposure means 10 (see (d) of FIG. 1). As a result, the laser light writing start position coincides with the image start position A of the photosensitive drum 1, and it is possible to form an image without displacement.

FIG. 5 is a block diagram showing another embodiment of the present invention. The same parts as those in FIG. 2 are designated by the same reference numerals.
In the figure, reference numeral 80 denotes the photosensitive drum 1 when the cleaning means for the photosensitive drum 1 is released (when the blade 51 is separated).
This is a memory for storing the amount of positional deviation in the circumferential direction. Reference numeral 70 denotes a control unit that reads out the contents stored in the memory 81 and predicts the image recording start position of the photosensitive drum 1 according to the amount of positional deviation. The operation of the apparatus configured as described above will be described below.

A PLL system composed of a motor 42, a reference pulse generator 44, a phase comparator 45 and a power amplifier 46 rotates the photosensitive drum 1 at a constant speed. here,
It is assumed that the blade 51 is separated from the state in which the blade 51 is pressed against the photosensitive drum 1.

The control unit 70 predicts the amount of positional deviation of the photosensitive drum 1 at the start of image writing based on the amount of positional deviation stored in the memory 81. Various modes are conceivable for this predicting method. For example, a method is conceivable in which the relationship between the positional deviation amount when the blade is released and the positional deviation amount when the image writing is started is experimentally obtained in advance and tabulated. The control unit 70 gives a control signal to the reference pulse generator 44 based on this prediction to change the phase of the reference pulse. As a result, the rotation of the motor 42 driven by the power amplifier 46 can be slowed down. And
The image start position A of the photosensitive drum 1 at the start of the next image writing can be matched with the exposure start position of the laser beam output from the image exposure means 10 (see (d) of FIG. 1). As a result, the laser light writing start position coincides with the image start position A of the photosensitive drum 1, and it is possible to form an image without displacement.

According to the above-described embodiments, the positional deviation is 1
It can be suppressed within pixels.

[0035]

As described above in detail, according to the present invention, the following effects can be obtained. Higher printing speed can be obtained with the same process speed. Since the photosensitive member driving means having a small output is sufficient, the device becomes small and lightweight. Since the photosensitive member driving means with a small output is sufficient, the rotation noise is small. Since the photosensitive member driving means with a small output is sufficient, the cost is low. Since the number of rotations per print is small, the life of mechanical parts is long.

As described above, according to the present invention, depending on the positional deviation of the photosensitive drum 1, after the photosensitive drum cleaning means is released and before the image exposure means 10 starts writing the image of the next color, By controlling the driving unit of the photoconductor drum 1 to correct the image writing position of the photoconductor drum 1, it is possible to provide a color image forming apparatus having no color shift or position shift.

[Brief description of drawings]

FIG. 1 is an explanatory view of the operation of the present invention.

FIG. 2 is a configuration diagram showing a main part of an embodiment of the present invention.

FIG. 3 is a diagram showing a state of fluctuations in rotation of a photosensitive drum and an encoder.

FIG. 4 is a configuration diagram showing a main part of another embodiment of the present invention.

FIG. 5 is a configuration diagram showing a main part of another embodiment of the present invention.

FIG. 6 is a diagram showing a configuration example of a multi-color image batch transfer type color image forming apparatus.

[Explanation of symbols]

 1 Photoreceptor Drum 10 Image Exposure Means 11 Polygon Mirror 12 Reflection Mirror 42 Motor 43 Encoder 44 Reference Pulse Generator 45 Phase Comparison Unit 46 Power Amplifier 51 Blade 70 Control Unit

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[Procedure amendment]

[Submission date] January 10, 1994

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

[Figure 1]

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display area G03G 21/14

Claims (3)

[Claims] 1. A step of adhering a developer of one color onto a photosensitive drum is repeated a plurality of times to form a visible image of a plurality of colors on the photosensitive drum, and a multicolor image is formed on a recording paper. In a color image forming apparatus configured to perform batch transfer, an encoder of a motor that drives the photosensitive drum is used as a means for detecting the circumferential position of the photosensitive drum, and the photosensitive drum cleaning is performed according to the output result of the encoder. An image forming apparatus, characterized in that, after the releasing of the means, before the image writing of the next color by the image exposing means is started, the driving means of the photosensitive drum is controlled to prevent the positional deviation. 2. The step of adhering the developer of one color onto the photosensitive drum is repeated a plurality of times to form a visible image of a plurality of colors on the photosensitive drum, and a multicolor image is formed on the recording paper. In a color image forming apparatus configured to perform batch transfer, a piezoelectric vibrating gyro is used as a means for detecting the acceleration of the peripheral speed of the photosensitive drum. An image forming apparatus characterized in that after that, before starting the writing of an image of the next color by the image exposing means, the driving means of the photosensitive drum is controlled to prevent the positional deviation. 3. The step of adhering the developer of one color onto the photosensitive drum is repeated a plurality of times to form a visible image of a plurality of types of colors on the photosensitive drum, and a multicolor image is formed on the recording paper. In a color image forming apparatus configured to perform batch transfer, storage means is provided for storing the amount of displacement of the photosensitive drum when the cleaning means for the photosensitive drum is released, and the amount of displacement is stored in the storage means. The image recording start position on the photoconductor drum by the image exposure means is predicted, and according to the prediction result, after the photoconductor drum cleaning means is released and before the image writing of the next color by the image exposure means is started, An image forming apparatus, characterized in that a driving means for the photosensitive drum is controlled to prevent misalignment.