JP2843862B2 - Color image forming equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus that forms a multicolor image by dots based on input image data.

[Background of the Invention]

As a copying apparatus using this type of color image forming apparatus, there is one having a mechanism shown in FIG. This is composed of a scanner section (image reading apparatus) A and a printer section (color image forming apparatus) B.

The scanner unit A exposes the original placed on the original table 1 by the rod-shaped lamp 2 and converts the light image of the original into mirrors 3 to 3.
The light is guided to a lens 6 via a reference numeral 5 and further to a dichroic mirror 7, which performs RGB (red, green, and blue) color separation, and photoelectrically converts the color light with CCDs 8R, 8G, and 8B. Capture as an electrical signal. Then, the image data is subjected to enlargement, reduction, and other image processing as needed.

On the other hand, the printer unit B responds to a laser beam emitted from a laser light source (not shown) with a signal obtained by converting the read image data for recording (RGB data into YMCK
(Yellow, magenta, cyan, black)
A modulator (not shown) that receives one of the YMCK signals) modulates the beam, scans the modulated beam with a polygon mirror 11, and charges the scanned beam with a band electrode 13 at a high voltage in advance by a mirror 12. Incident on the photoreceptor drum 14, and forms a latent image in dot units along the axial direction there, and the latent image is
Of the developing units 15Y, 15M, 15C, and 15K loaded with the CK toner, the developing unit develops a color corresponding to the modulation signal. Then, after the latent image formation / development for all the YMCK modulation signals is completed, that is, after the photosensitive drum 14 is rotated and the YMCK toner superimposed image is formed on the photosensitive surface, the sheet feeding unit 16 The YMCK toner image is transferred to the fed copy paper by the transfer pole 17, separated by the separation pole 18, fixed by the fixing unit 19, and discharged. After that, the photosensitive drum 14 is moved to the cleaner section 20.
It is cleaned in.

[Problems to be Solved by the Invention] As described above, since the printer unit B performs development by superimposing the YMCK color toner on the photosensitive drum 14, precision of the rotation speed of the photosensitive drum is strictly required. You.
In other words, if there is uneven rotation, the formation position of the latent image in the line (axial direction of the rotating drum) is shifted in the sub-scanning direction (rotating direction of the rotating drum), and the dot position at which the YMCK toner is shifted from a predetermined position. To cause unevenness in density and color misregistration.

An object of the present invention is to suppress such density unevenness and color misregistration so that a color image with excellent reproducibility can be obtained.

[Means for solving the problem]

Therefore, the present invention provides a color image forming apparatus including a photosensitive drum on which a latent image is formed and developed a plurality of times to form a superimposed image of toners of a plurality of colors. And a speed detector for detecting the speed of the motor, and a speed control circuit for controlling the speed of the motor by taking in the speed signal detected by the speed detector. The frequency of the detection signal is f (Hz),
The peripheral speed of the photosensitive drum is v (mm / sec), the dot pitch in the rotating direction of the photosensitive drum is d (mm), The above speed control circuit is operated so as to satisfy the following.

〔Example〕

Hereinafter, an embodiment of the present invention will be described. FIG. 2 is a diagram showing a drive system of the photosensitive drum 14. The photoreceptor drum 14 rotates by receiving the rotation of the motor 21 at a reduced speed by the gear unit 22. The rotation of the motor 21 is detected by the speed detector 23 and taken into the speed control circuit 24. Then, the signal processed here (for example, PLL control processing) is applied to the motor 21 as a motor drive signal. The reduction ratio of each gear including the gear portion 22 of the drive system from the rotation axis of the rotor of the motor 21 to the rotation axis of the photosensitive drum 14 is selected so that all gears have an integer ratio. As a result, the starting point of the rotor of the motor 21 and the starting point of the photosensitive drum 14 coincide with each other.

The above-mentioned uneven rotation of the photosensitive drum 14 is caused by uneven rotation of the motor 21. Therefore, in the present embodiment, appropriate control can be performed according to the rotation unevenness. First,
_Assuming that the number of rotations of the motor 21 is N _M and the number of pulses per rotation of the speed detector 23 is N _S , the frequency f of the speed detection signal is f = N _M × N _S while the peripheral speed of the photosensitive drum 14 is Let v be v, the speed control resolution δ converted to the length on the photosensitive drum 14 is δ = v / f. Further, assuming that the dot pitch in the sub-scanning direction, that is, the rotating direction of the photosensitive drum is d, the number of dots 検 出 per pulse of the detection pulse of the speed detector 23 is ζ = δ / d = v / fd. By keeping this ζ within a certain range, the motor
21 rotation unevenness can be compensated.

The present inventor conducted experiments using the following values as the above values, and obtained good results.

Thus, good results were obtained when ζ was 0.897 (1 / pulse).

The value of ζ is desirably a small value as close as possible to 0 (excluding 0), but to achieve this, the speed detector 23
Resolution is increased, and there are technical limitations. The resolution of the speed detector varies depending on the technology employed, but when used in an apparatus such as a copying machine, an extremely expensive system cannot be adopted in view of the cost balance. Actually, there is a photo sensor system combining an LED (light emitting diode) and an optical sensor, or a system using a multi-pole magnetized magnet, but in practice, 5,000 (pulse / r
sound) is the limit in consideration of cost balance. The speed detector rotational speed N _S of the table to this value, calculating the zeta other conditions as the same as the table, zeta = 1/40-speed, and this value is the lower limit value.

On the other hand, the upper limit is determined by the allowable value of the speed unevenness. In the case of line exposure as in a laser printer, the allowable value of positional deviation between adjacent lines in the sub-scanning direction may be up to about 1/5 of the pitch between lines in the sub-scanning direction (drum rotation direction). Conventionally known. Therefore, the rotation unevenness (speed fluctuation) of the photosensitive drum that causes a positional deviation between the lines in the sub-scanning direction is also reduced by the dot pitch d in the sub-scanning direction.
The goal is to reduce it to about 1/5 of the total.

However, motors are generally designed so that in the actual load use condition, rotation unevenness occurs only about 1/10 of the speed control resolution due to the inertia of the load (mainly the drum) on the motor. It is. In other words, the speed fluctuation of the motor can be allowed up to about 10 times the target value of the rotation unevenness of the photosensitive drum.

 Therefore, the speed control resolution δ is δ ≦ (d / 5) × 10, and the number of dots per pulse ζ is ζ (= δ / d) ≦ 2.

〔The invention's effect〕

As described above, according to the present invention, it is possible to minimize density unevenness, color shift, and the like, even if motor rotation unevenness occurs due to load fluctuation or the like.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a mechanism of a copying apparatus, and FIG. 2 is an explanatory view of a rotation drive system of a photosensitive drum. 14 photoconductor drum, 21 motor, 22 gear section, 23 speed detector, 24 speed control circuit.

Claims (1)

(57) [Claims] 1. A color image forming apparatus comprising a photosensitive member on which a latent image is formed and developed a plurality of times to form a superimposed image of toners of a plurality of colors, a motor for rotating the photosensitive member, A speed detector for detecting the speed of the motor; and a speed control circuit for controlling the speed of the motor by taking in the speed signal detected by the speed detector, wherein a frequency of the speed detection signal of the speed detector is provided. Is f (Hz), the peripheral speed of the photoconductor is v (mm / sec), the dot pitch in the rotation direction of the photoconductor is d (mm), A color image forming apparatus that operates the speed control circuit so as to satisfy the following.