JP2000094747A - Color image-forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color image-forming apparatus which can simplify a phase control means in constitution. SOLUTION: The color-image forming apparatus has a plurality of photosensitive bodies, a polygon mirror 2 corresponding to each of the photosensitive bodies, and a transfer belt stretching over the photosensitive bodies. The apparatus transfers overlapping images of colors formed on the photosensitive bodies onto the transfer belt. When the number of faces of the polygon mirror 2 is (n), the mirror is a regular (n)-sided polygon. Rotor magnetic poles N and S are constituted with an equal angle in the circumference and the number of pole pairs of the magnetic poles is (m) (n, m are positive integers). 360 deg./m at every polygon motor is a multiple of 360 deg./n.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic / electrostatic color image forming apparatus such as a copying machine, a printer, a facsimile, etc., and more particularly, to a plurality of photosensitive members and a polygon mirror corresponding to each photosensitive member. The present invention relates to a color image forming apparatus including a transfer belt that straddles each photoconductor, and superimposes and transfers an image of each color formed on each photoconductor onto a transfer belt.

[0002]

2. Description of the Related Art A plurality of photoconductors, a polygon mirror corresponding to each photoconductor, and a transfer belt straddling each photoconductor are provided. Images of each color formed on each photoconductor are transferred onto the transfer belt. As a color image forming apparatus that performs superimposed transfer, for example, there is a technique described in Japanese Patent Application Laid-Open No. 7-239598.

In the color image forming apparatus, the displacement of each color image is a problem. However, in the above-mentioned publication, a displacement detection means for detecting the displacement of the image between the respective colors, First converting means for dividing by the scanning pitch of the means and separating it into a quotient N and a remainder R, first adjusting means for changing the exposure timing by the quotient N, and second means for changing the scanning phase of the exposing means by the remainder R Adjustment means,
Each position shift is adjusted by the first and second adjusting means.

[0004]

When the conventional polygon mirror driving motor is used, the rotation is stopped in a steady state after a transient state when the phase is changed, and the rotation is once stopped and then started again to reach a steady state. In this case, there is a disadvantage that the configuration of the phase control means for obtaining a desired phase becomes complicated.

SUMMARY OF THE INVENTION An object of the present invention is to provide a color image forming apparatus capable of simplifying the structure of the phase control means.

[0006]

According to one aspect of the present invention, there is provided an image forming apparatus comprising: a plurality of photosensitive members; a polygon mirror corresponding to each photosensitive member; and a transfer belt extending over each photosensitive member. In a color image forming apparatus that superimposes and transfers images of each color formed on each photoreceptor on a transfer belt, a mark creation unit that creates a mark of each color, a mark detection unit that detects a mark, and a mark detection unit. Misregistration amount calculating means for calculating various misregistration amounts of each color from the detection result,
A writing timing control unit for correcting the amount of positional deviation; and a phase control unit for controlling a change in the surface phase of the polygon mirror. The number of surfaces of the polygon mirror is n, the mirror shape is a regular n-gon, and the N pole is And the number of poles of the rotor magnetic poles in which S and S poles are formed at the same angle over the circumference is m (n and m are positive integers), and 360 ° / m in all polygon mirror drive motors is a multiple of 360 ° / n. It is characterized by being.

[0007] To achieve the above object, the present invention provides a second aspect.
The invention described in claim 1 is characterized in that the invention has a function of changing the phase of a driving pulse of a polygon mirror driving motor to a desired phase.

[0008] In order to achieve the above object, a third aspect is provided.
The invention described in the first and second aspects is characterized in that the phase of the driving pulse is changed while the polygon mirror driving motor is rotating.

According to another aspect of the present invention, the above object is achieved.
According to the invention described in any one of claims 1 to 3, after the rotation of each polygon mirror drive motor is stabilized, the process shifts to the next job.

[0010] In order to achieve the above object, the present invention is directed to claim 5.
The invention described in the first to third aspects is characterized in that the phase of the drive pulse at the time of rotation of the polygon mirror drive motor and at the time of re-rotation after the stop are the same.

[0011]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a configuration diagram of an image forming system of the color image forming apparatus. In this color image forming apparatus, four combinations of the photoreceptor 1 and the polygon mirror 2 (Y, M,
C, K). The polygon mirror 2 is rotated at high speed by a polygon motor 3 to perform optical writing on the photoreceptor 1 by laser modulation. Around the photoconductor 1, there are a charging unit 4, a developing unit 5, and a transfer unit (transfer roller) 6.

The transfer roller 6 faces the photosensitive member 1 with a transfer belt 7 vertically provided so as to straddle the four photosensitive members 1 arranged in the vertical direction, and is conveyed by the transfer belt 7. Transfer sheet and the transfer belt 7 itself,
The toner image formed thereon is transferred.

Below the photoreceptor 1, there is a paper feed section 8, and above it is a fixing section 9, and further a paper discharge section 10. Further, at a position facing the transfer belt 7 near the photoconductor 1 (upper end photoconductor 1) on the most downstream side, there is a mark detection unit 11 for detecting a color misregistration detection mark formed for each color. . At the time of the misalignment detection and correction operation, the images of the respective colors formed on the respective photoconductors 1 are sequentially transferred from the first color to the transfer belt 7.
The image is transferred to the upper side, detected by the mark detection unit 11, and corrected as described below.

FIG. 2 is a control block diagram of the color image forming apparatus, and FIG. 3 is a timing chart of clocks a, b, c, and d in FIG. As shown in FIG. 2, the mark detection signal of the mark detection unit 11 is taken into the control unit 12. The control unit 12 controls the mark detection unit 11
Based on the mark detection signal from the CPU, various positional deviation amounts of each color are calculated to determine the process timing.

For example, correction of the registration shift in the main scanning direction is performed by changing the exposure timing.
Further, when correcting a registration shift in the sub-scanning direction, 1
The correction for each line is performed at the exposure timing, and the correction for less than one line is performed by changing the surface phase of the polygon mirror 2.

In changing the surface phase of the polygon mirror 2, a drive pulse (clock) of a drive motor (polygon motor) 3 is generated by an oscillator 13. The polygon motor 3 is rotated by the reference phase clock a for the color of the reference color for the alignment, in this case, the first color motor, and the reference phase (a), 1/4 for the other colors. One of the clocks of the phase advance (b), the 2/4 phase advance (c), and the 3/4 phase advance (d) is selected by the selector 15 provided for each.

These phase shifts between the clocks correspond to four divisions of one surface of the polygon mirror 2. Therefore, registration deviation in the sub-scanning direction can be corrected in units of 1/4 line. If the number of divisions is increased, finer correction can be performed.

FIG. 4 is a flowchart showing an example of the displacement correction control. For example, when the power is turned on or when there is a color shift correction request, the mode is set to the position shift detection mode (S
1). In this case, a mark is formed on the transfer belt 7 for each color (S2). Then, this mark is sent to the mark detection unit 11
(S3). Then, the control unit 12 calculates how much the mark interval between the first color and the second, third, and fourth colors deviates from the set value (S4). For a shift of one or more lines, the exposure timings of the shifted second, third, and fourth colors are changed, and the values are stored (S5). If the shift is less than one line, the clock phase of the shifted polygon motor for the second, third, or fourth color is changed, and the information is stored (S6). This ends the position shift detection mode.

When a print start is requested (S
7) The polygon motors 3 for each color are rotated at the clock phase stored in the displacement detection mode (S8). Thereafter, the process operation, mechanism, and electric operation necessary for printing are performed. Although omitted in this flow, 2, 3, 4
The color exposure timing is performed at the timing stored in the displacement detection mode. By performing such correction, a print image with less color shift can be obtained.

Here, the polygon motor and the polygon mirror will be described. FIG. 5 shows an example of the polygon mirror 2 and the polygon motor 3. The same components are provided for each color, and the laser beam is exposed on the photoconductor 1. FIG. 6 is a view of the rotor section viewed from below. The motor shaft 21 rotates with very low friction between the motor shaft 21 and the bearing on the stator side. The magnetic force required for rotation is determined by the rotor magnet 22
And a stator-side coil (not shown). A PLL method is used for controlling the number of rotations, and the rotation can be performed with very high accuracy.

FIG. 7 shows a general positional relationship between the rotor magnet 22 and the polygon mirror 2. In this case, the number of mirror surfaces is six regular hexagons (n =
6), the number of pole pairs of the rotor magnet 22 is 4 (m
= 4), the rotor magnet 22 is provided circumferentially around the rotation speed, and the N pole and the S pole are provided at equal angles. In this case, the angle formed by one pole pair is: 360 ° / m = 360 ° / 4 = 90 °, 360 ° / n =
360 ° / 6 = 60 °, but 360 ° / m is not a multiple of 360 ° / n, and the positional relationship between the boundary line between each N pole and S pole and each mirror surface is all Not equal in plane.

Once the rotation of the motor is P
If the LL is unlocked, even if the phase and frequency of the driving pulse are the same, the surface phase will be different. Further, even when the rotating motor 3 is temporarily stopped and restarted, it is similarly unknown what the surface phase of the polygon mirror 2 of each motor is. Thus, as shown in FIG. 8, the phase shift between the line synchronization signal of each color and the reference line synchronization signal of the first color is compared, and the line synchronization signal (a) of the reference phase and the 1/4 phase leading line synchronization are synchronized. It is conceivable to adjust the phase so that the signal (b) becomes a 2 / 4-phase leading line synchronization signal (c) and the 3 / 4-phase leading line synchronization signal (d). However, in this case, it is necessary to control not to release the PLL lock of each motor, and the drive pulse cannot be instantaneously changed to the selected drive pulse as described above.

FIG. 9 is a diagram showing the relationship between the polygon mirror 2 and the rotor magnet 22 according to the embodiment of the present invention. In this case, the number of mirror surfaces is 6 (n = 6), and the number of pole pairs of the rotor magnet 22 is 6 (m = 6). The angle formed by one pole pair is 360 ° / m = 360 ° / 6 = 60 °, 360 ° / n =
Since 360 ° / 6 = 60 °, and 360 ° / m is a multiple of 360 ° / n, the positional relationship between the boundary line 12 between each N pole and S pole and each mirror surface is all Equal in plane. Therefore, the surface phase of the mirror is uniquely determined by the phase of the drive pulse.

As a result, when the phase changes from the transitional state to the steady state, or when the rotating motor 3 is temporarily stopped and restarted, the surface phase of the polygon mirror 2 of each motor 3 becomes the driving pulse. Is uniquely determined by the phase of
Therefore, unlike the related art, there is no need to perform phase control so as not to deviate from the PLL lock, and the configuration of the phase control means is simple, so that cost can be reduced.

Here, the case where m = 6 has been described, but even when m = 2 or 3, 360 ° / m becomes 360 ° / n.
Therefore, the same effect can be obtained. Further, although the description has been given of the mirror having six surfaces, the same applies to mirrors having other surfaces. For example, in the case of five mirrors (n = 5), m = 5 satisfies the condition, and the same effect can be obtained.

As described above, since the surface phase of the mirror 2 is uniquely determined by the phase of the driving pulse, even if the phase of the supplied driving pulse is instantaneously changed during the rotation of the motor as shown in FIG. Good. In this example, a case where the clock is changed from the reference phase clock to a 1/4 phase advance clock is shown. At the moment when the phase is switched, the rotation of the motor 3 is in a transient state, but after a while, it is settled down to a steady state, a desired surface phase is reached, and the motor 3 rotates at a constant rotational speed.

As described above, at the moment when the phase is switched, the motor 3 is unlocked from the PLL and does not have the desired rotation speed. Therefore, for example, if an image is formed during this transient state, the image will be disturbed. To prevent this, as shown in FIG.
By taking the AND of the lock signal and monitoring this signal, a job such as a print operation can be executed normally.

When the motors 3 of each color are stopped, for example, when the printing operation is not performed for a certain period of time or when the apparatus is put into a standby state, the driving pulse applied while the motors 3 are stopped. Is stored. Then, based on the information, by applying a drive pulse having a changed phase to each motor at the time of rotation start, a desired surface phase can be obtained from the start, and a high-quality image without displacement can be output. Can be.

In the present invention, a plurality of photosensitive members 1, a polygon mirror 2 corresponding to each photosensitive member, and a transfer belt 7 extending over each photosensitive member 1 are provided, and each color formed on each photosensitive member 1 is provided. In the color image forming apparatus for superimposing and transferring the image on the transfer belt 7, if the number of surfaces of the polygon mirror 2 is n, the mirror shape is a regular n-gon and the rotor magnetic pole N pole and S pole
The poles are formed at equal angles around the circumference, and the number of pole pairs of the magnetic pole is m (n and m are positive integers). Then, 360 ° / m in all polygon motors 3 becomes 360 ° / m.
It is a multiple of n. By employing the polygon motor 3 having such a configuration, the intended purpose can be achieved.

[0030]

According to the first aspect of the present invention, the transient state at the time of phase switching and the surface phase relationship of each motor when the rotation is once stopped and restarted do not change, so that the structure of the phase control means is changed. Can be simplified.

According to the second aspect of the present invention, the phase of the driving pulse can be simply changed, so that the configuration of the phase control means can be simplified.

According to the third aspect of the invention, a desired surface phase can be obtained when the phase changes from a transient state to a steady state, so that the configuration of the phase control means can be simplified.

According to the fourth aspect of the present invention, since the transition to the next job is made after the transition from the transitional state at the time of phase change to the steady state, the job currently being executed can be completed normally.

According to the fifth aspect of the present invention, when rotation → stop → rotation, if the phase of the drive pulse is the same, the surface phase does not change, so that the configuration of the phase control means can be simplified.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an image forming system of a color image forming apparatus.

FIG. 2 is a control block diagram of the color image forming apparatus.

FIG. 3 is a timing chart of clocks a, b, c, and d in FIG. 2;

FIG. 4 is a flowchart illustrating an example of misregistration correction control.

FIG. 5 is a diagram illustrating an example of a polygon mirror and a polygon motor.

FIG. 6 is a diagram showing a motor shaft and a rotor magnet of a polygon motor.

FIG. 7 is a diagram showing a general positional relationship between a rotor magnet and a polygon mirror.

FIG. 8 is a general timing chart of a driving pulse of a polygon motor.

FIG. 9 is a diagram illustrating a relationship between a polygon mirror and a rotor magnet according to the embodiment of the present invention.

FIG. 10 is a diagram illustrating a state in which the phase of a drive pulse is instantaneously changed.

FIG. 11 is a diagram illustrating a state in which a lock signal of a motor PLL of each color is ANDed.

[Explanation of symbols]

 Reference Signs List 1 photoconductor 2 polygon mirror 3 polygon motor 4 charging unit 5 developing unit 6 transfer unit 7 transfer belt 8 paper feed unit 9 fixing unit 10 paper discharge unit 11 mark detection unit 12 control unit 13 oscillator 14 driver 15 selector 21 motor shaft 22 rotor magnet

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mitsugu Sugiyama 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Company (72) Inventor Mitsuo Suzuki 1-3-6 Nakamagome, Ota-ku, Tokyo Share F-term within Ricoh Company (reference) 2C262 AA05 AA17 AB15 FA03 FA10 GA04 GA36 GA40 2C362 AA10 BA04 BA39 BA50 BA70 CA39 2H045 AA01 AA52 BA24 CA97 CB51 CB61

Claims (5)

[Claims] A plurality of photoconductors; a polygon mirror corresponding to each of the photoconductors; and a transfer belt extending over each of the photoconductors. Images of each color formed on each of the photoconductors are transferred onto the transfer belt. In a color image forming apparatus that performs overlay transfer, a mark creating unit that creates a mark of each color, a mark detecting unit that detects a mark, a displacement amount calculating unit that calculates various displacement amounts of each color from a mark detection result, A write timing control unit for correcting the shift amount; and a phase control unit for controlling a change in the surface phase of the polygon mirror. The number of surfaces of the polygon mirror is n, the mirror shape is a regular n-gon, and the N pole is Assuming that the number of pole pairs of the rotor magnetic poles whose S poles are formed at the same angle over the circumference is m (n and m are positive integers), 36
A color image forming apparatus, wherein 0 ° / m is a multiple of 360 ° / n. 2. The color image forming apparatus according to claim 1, further comprising a function of changing a phase of a driving pulse of the polygon mirror driving motor to a desired phase. 3. The color image forming apparatus according to claim 1, wherein the phase of the driving pulse is changed while the polygon mirror driving motor is rotating. 4. The color image forming apparatus according to claim 1, wherein after the rotation of each polygon mirror driving motor is stabilized, the process shifts to the next job. 5. The color image forming apparatus according to claim 1, wherein a phase of a driving pulse of the polygon mirror driving motor is the same as a phase of a driving pulse at the time of re-rotation after stopping.