JPH0579991B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drive device for a photosensitive drum used in a color image forming apparatus in information processing equipment such as a copying machine, a facsimile machine, and a printer.

[Prior Art] Taking a copying machine as an example, the color image forming apparatus includes a machine main body 1 having a document table 2 on the upper surface, a light source 3a, a mirror 3b, and a filter, as shown in FIG. - An optical mechanism 3 composed of a lens unit 3c, etc.; a photosensitive drum 4 on which the original image of the document on the document table 2 scanned by the optical mechanism 3 is formed as an electrostatic latent image; A charger 5 that is provided adjacent to the photosensitive drum 4 charges the photosensitive drum 4; a charger 5 that is provided adjacent to the photosensitive drum 4;
Developing units 6a, 6a, and 6c form toner images corresponding to magenta and cyan, a cleaning device 7 that removes residual toner by sequentially removing static electricity from the transfer completed area, and a cleaning device 7 that holds the paper sent out from the paper cassette 8 and A transfer drum 9 for transferring the toner image formed on the photosensitive drum 4 onto this paper
The fixing device 11 fixes the unfixed color image on the paper conveyed from the transfer drum 9 by the conveyor belt 10, and the tray 12 receives the paper on which the color image has been fixed by the fixing device 11. There is.

In such a color image forming apparatus, an optical mechanism 3 is used to form a color image.
When the filter/lens unit 3c transmits light other than yellow, the yellow developing device 6a operates to form a yellow toner image as an electrostatic latent image on the photosensitive drum 4, and transfer this yellow toner image to the paper on the transfer drum 9. When the filter/lens unit 3c transmits light other than magenta, the magenta developer 6a operates to form a magenta toner image as an electrostatic latent image on the photosensitive drum 4, and this magenta toner image is transferred to the transfer drum 9. Transfer it to the paper above, and
When the filter/lens unit 3c transmits light other than cyan, the cyan developing device 6a operates to form a cyan toner image as an electrostatic latent image on the photosensitive drum 4, and transfers this cyan toner image onto a sheet of paper on the transfer drum 9. The toner images of these three primary colors are transferred and superimposed on the paper to synthesize a color image close to natural colors. For this purpose, the toner images of these three primary colors are completely overlapped on the paper of the transfer drum 9. The driving of the optical mechanism 3, photosensitive drum 4, and transfer drum 9 is controlled so that they match.

However, in the conventional color image forming apparatus of this type, the optical mechanism 3, the photosensitive drum 4
The driving means for the transfer drum 9 is composed of mechanical means such as a chain, a sprocket, a gear, a pulley, a belt, and a wire. When transmitting power using
It is extremely difficult to make the toner images of the primary colors perfectly match on the paper on the transfer drum 9, and due to long-term use, each drive means is worn out and the positions of the toner images corresponding to each color are misaligned. This causes a so-called color shift phenomenon in which the periphery or part of the color image formed on the paper becomes blurred and blurred, and the resulting color image becomes unclear. There was a problem. This problem arises especially when providing a reduction/enlargement function that requires controlling the rotation of the photosensitive drum 4 and transfer drum 9 in synchronization with the operation of the optical mechanism 3 by changing the reference clock. It was becoming a big problem.

Therefore, in order to solve this problem, the present applicant et al. separately drove at least one of the optical mechanism 3, photosensitive drum 4, or transfer drum 9 with a servo motor, and controlled the amount of rotation of the servo motor. A color image forming device that counts an instruction pulse train that gives an instruction and an output pulse train of an encoder that detects the amount of rotation of this servo motor, and controls and drives the servo motor so that the difference in the number of counts between the two becomes zero. proposed a drive device (patent application 1986).
−104198 invention).

Although the drive device proposed by the present applicant can greatly improve the problem of color misregistration compared to conventional color image forming devices, it is still possible to completely solve the problem of color misregistration. That was difficult.

[Problems to be Solved by the Invention] The present invention relates to an improvement of the drive device according to the above-mentioned earlier proposal, and relates to a photosensitive drum that can prevent the problem of color misregistration in a color image forming apparatus as much as possible. The present invention provides a drive device for the following.

[Means for Solving the Problems] That is, the present invention provides a photosensitive drum which is exposed to light by an optical mechanism that scans the original image, and which transfers a toner image formed by this exposure and development to a transfer drum. A drive system for a photosensitive drum that is driven in a predetermined relationship with the optical mechanism and the drive system for the transfer drum, wherein a servo motor is used as a power source for the drive system for the photosensitive drum, and the servo motor is used as a power source for the drive system for the photosensitive drum. This is a photosensitive drum driving device in which the photosensitive drum is directly connected to a driven system provided with the photosensitive drum, and the anti-resonance frequency of the driven system is set to 40 Hz or more.

In the present invention, the drive system of the photosensitive drum uses a servo motor as its power source, and the servo motor and the shaft of the driven system on which the photosensitive drum is installed are directly connected to rotate the servo motor. Feedback control is required by means of an encoder that detects the quantity. That is, the drive system of the photosensitive drum counts the instruction pulse train that instructs the amount of rotation of the photosensitive drum and the output pulse train of the encoder that detects the amount of rotation of this servo motor, so that the difference in the number of counts between the two becomes zero. The servo motor is controlled to accurately control the rotation of the photosensitive drum, thereby accurately controlling the relationship between the drive of the optical mechanism and the rotation of the transfer drum, and the electrostatic latent image formed on the photosensitive drum. To accurately generate toner images, and to accurately superimpose toner images transferred from this photosensitive drum to paper on a transfer drum for each color.

By the way, in a driven system in which a photosensitive drum is installed, all the components that make up the system, namely the photosensitive drum, the shaft, and the couplings and flanges that connect them, have a large influence on the torsion and vibration of the shaft. do. Therefore, as shown in FIG.
and a frequency detection detector d, supplying drive power to the motor a via an error amplifier e and a drive amplifier f, and a tachometer b.
The rotational speed detected by the encoder c is fed back between the error amplifier e and the drive amplifier f via the rotational speed detection control circuit g, and the position detected by the encoder c is fed back to the error amplifier e via the position detection control circuit h.
The test signal from the signal generator j of the transfer function measuring device i (HP5420A manufactured by Heuretsu Patscard Co., Ltd.) is input before the error amplifier e to control the motor a. The input signal x to the motor a and the output signal y measured by the detector d are input into the analysis section k of the transfer function measuring device i, and the y/x mode is analyzed, and the frequency characteristics of this driven system are determined by When output as a Bode diagram (gain-phase relationship), as shown in Figure 4, the frequency at the inflection point, which suddenly drops halfway and then rises again, is obtained, that is, the anti-resonant frequency. It has been found that the torsion and vibration of the shaft depend on this anti-resonance frequency.

Therefore, in the present invention, it is necessary to set the anti-resonance frequency of the driven system provided with the photosensitive drum to 40 Hz or more, preferably 50 Hz or more. If the value of this anti-resonance frequency is smaller than 40Hz, the torsion and vibration of the shaft when the photosensitive drum rotates will affect the generation position of toner images corresponding to each color.
This may cause color shift.

In the present invention, in order to make the anti-resonance frequency of the photosensitive drum driven system 40 Hz or more, the shaft diameter of the photosensitive drum driven system is preferably at least 14 mmφ or more, preferably 15 mmφ or more, In addition, the coupling between the shaft and the servo motor is a rigid coupling, and the shaft and photosensitive drum are fixed so that they can be exchanged and are strong enough to prevent rattling during use. Preferably, a positioning collar is attached to the shaft, and the photosensitive drum is attached to the shaft so as to be slidable in the axial direction, and the direction of rotation of the photosensitive drum is regulated between the collar and the photosensitive drum. At the same time, it is preferable to fix the axial direction of the photosensitive drum by pressing the photosensitive drum toward the collar side with a fixing screw via a bush from the shaft end side.

[Function] According to the present invention, a servo motor is used as a power source for the drive system of the photosensitive drum, and since the servo motor and the driven system of the photosensitive drum are directly connected, the amount of rotation of the servo motor is Not only can the amount of rotation of this servo motor be accurately controlled by feeding back the output pulses of the encoder that detects the Vibration is eliminated, toner images corresponding to each color can be reliably generated at accurate positions on the photosensitive drum, and color misregistration can be reliably prevented from occurring.

[Example] Hereinafter, a photosensitive drum driving device according to the present invention will be described based on an example shown in the accompanying drawings.

1 and 2, a photosensitive drum driving device according to an embodiment of the present invention applied to a color copying machine is shown.

This color copying machine basically has a configuration as shown in FIG. 4, and as shown in FIG. Servo motors 21, 22, and 23 are used as drive systems for the drum 4 and the transfer drum 9, which is equipped with a gripper 9a for gripping and wrapping the leading edge of the paper. Encoders 24, 25, and 26 are provided to detect the amount of rotation, and each of the servo motors 21, 22, and 23 has a rotation speed setting device 27 that indicates the amount of rotation thereof.
controllers 28, 29 that control the amount of rotation of each servo motor 21, 22, and 23 by comparing the amount of rotation of each servo motor 21, 22, and 23 actually measured by the encoders 24, 25, and 26;
and 30.

The photosensitive drum 4 applied to this color copying machine is attached to the shaft 3 as shown in FIG.
A positioning collar 32 is provided at a predetermined position of 1, a photosensitive drum 4 is mounted on the shaft 31 so as to be slidable in the axial direction, and the collar 31 and the photosensitive drum 4 are locked by appropriate means. The lever regulates the rotation direction of the photosensitive drum 4, and also controls the shaft 3.
Fixing screw 3 is inserted from the end surface of 1 through the bush 33.
4 fixes the axial direction of the photosensitive drum 4 by pressing the photosensitive drum 4 toward the collar 32 side,
The photosensitive drum 4 is coupled to the servo motor 22 constituting the drive system by using a coupling 35 between the coupling portion 31a formed on the shaft 31 of the photosensitive drum 4 and the rotating shaft 22a of the servo motor 22. This is done by direct connection using a double point method using a plurality of setscrews (not shown) that are highly effective at preventing loosening. Note that in FIG. 2, reference numeral 36 denotes a support member that supports the photosensitive drum 4 via a bearing 37. As shown in FIG.

In this embodiment, the part of the shaft 31 of the photosensitive drum 4 with the smallest diameter is the connecting part 31a connected to the servo motor 22, and its size is 20 mm. Then, when the frequency characteristics of this driven system are measured in the form of a Bode diagram {relationship between gain (dB) and phase (frequency: Hz)} using a transfer function measuring device according to the measurement example shown in Fig. 3, In the Bode diagram shown in Figure 4, a value of approximately 160 Hz was measured as the anti-resonance frequency, which is the frequency at inflection point ₂ where the frequency suddenly drops halfway and then rises again. A value of approximately 350 Hz was measured as the resonance frequency appearing after ₂ .

When color copies were made using a color copying machine (see Fig. 5) equipped with the photosensitive drum drive device of this embodiment, no problem of color shift occurred, and after long-term investigation ( (Number of copies: approximately 1000 copies), satisfactory results were obtained regarding color misregistration.

Next, let us consider the case where the minimum diameter of the shaft 31 is set to 11 mmφ, which is the same as before, and the case where the minimum diameter of the shaft 31 is set to 11 mmφ, which is slightly thicker than that.
When we measured the anti-resonance frequency in the case of mmφ, we found that the anti-resonance frequency in the former case was approximately 20
Hz, and in the latter case it was about 40Hz.
In these cases, we investigated the occurrence of the color shift problem in the same way as in the above case, and found that in the former case, the steady speed accuracy did not improve from about 0.8%, and the color shift was 200 to 400 μm. In the latter case, the steady speed accuracy improved to about 0.4%, and color shift was also improved.
The thickness was 150 μm or less, which was satisfactory.

[Effects of the Invention] According to the photosensitive drum drive device of the present invention, the problem of color shift in a color image device to which the photosensitive drum drive device is applied can be solved as much as possible over a long period of time.

[Brief explanation of the drawing]

FIG. 1 is a perspective explanatory view showing the main parts of a copying machine to which a photosensitive drum driving device according to an embodiment of the present invention is applied, and FIG. 2 shows details of the photosensitive drum driving system and driven system in FIG. 1. Figure 3 is a block diagram showing an example of measurement when measuring the frequency characteristics of a driven system as a Bode diagram using a transfer function measuring device, Figure 4 is a board diagram measured according to Figure 3. A graph diagram showing a line diagram, and FIG. 5 are explanatory diagrams showing the configuration of a color copying machine. Explanation of symbols, 3... Optical mechanism, 4... Photosensitive drum, 9... Transfer drum, 22... Servo motor,
31...Shaft.

Claims (1)

[Scope of Claims] 1. A drive system for a photosensitive drum in which the original image is exposed to light by an optical mechanism that scans the original image, and a toner image formed by this exposure and development is transferred to a transfer drum, the drive system comprising: In a photosensitive drum drive device that drives a mechanism and a transfer drum drive system in a predetermined relationship with each other, a servo motor is used as a power source for the photosensitive drum drive system, and the servo motor and the photosensitive drum are provided with a drive device. A photosensitive drum drive device, characterized in that it is directly connected to a drive system, and the anti-resonance frequency of the driven system is set to 40Hz or higher. 2. The photosensitive drum driving device according to claim 1, wherein the shaft diameter of the photosensitive drum driven system is at least 14 mmφ.