JPH05191605A - Image forming device - Google Patents

Abstract

PURPOSE:To avoid the effect of cogging of a stepping motor onto the image by providing a control circuit controlling the device such that a drive frequency of the stepping motor is an integer number of multiple of a write frequency of main scanning to the device. CONSTITUTION:The device is provided with a control circuit (drive circuit) 10 outputting phase signals 0A, 0A', 0B, 0B' used to drive a stepping motor 6 being a drive source to drive a photosensing body 1 in the subscanning direction and having a CPU (central processing unit section) 11. The control circuit 10 comprising a phase difference detector or a counter or the like matches a drive period (cogging period) of the stepping motor 6 with a period of light writing so that a drive frequency fs of the stepping motor 6 has a relation of fs=N.fw (N:1, 2, 3...; integer) with respect to a light writing frequency fw of the main scanning. Thus, each locus on a photosensitive body formed by a laser beam is of the same shape in the main scanning direction and the interval of the locii is equal to each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a laser beam printer, a facsimile machine, a digital copying machine and the like, and more particularly to an image forming apparatus for rotating a photosensitive member in a sub-scanning direction by using a stepping motor. ..

[0002]

2. Description of the Related Art In recent years, a stepping motor has been used as a photoconductor driving source in the above-mentioned image forming apparatus, instead of a DC (direct current) servo motor which has been widely used in the past.

The DC servo motor has a feedback circuit in the drive circuit and is very expensive as compared with the stepping motor. On the other hand, the stepping motor
Open loop control that does not require a feedback circuit is sufficient, and the circuit configuration is simplified and the cost is reduced.

However, when the stepping motor is rotated at a constant speed, as shown in the characteristic diagram of FIG. 5, no linear displacement is shown, and cogging occurs while deviating from the linear displacement. However, under a constant load condition, the cogging exhibits a substantially constant characteristic and exhibits substantially similar movement (rotation).

On the other hand, in the DC servo motor, when the rotating rotor has a heavy weight and is rotated at a constant speed, as shown in the characteristic diagram of FIG.
(Displacement) shows a linear relationship. Therefore, the main scanning start timing of the photoconductor by the laser light may be any time, and if the optical writing cycle is evenly spaced, the locus (a) can be obtained as shown in the illustration of the light beam locus on the photoconductor in FIG. 6B. _1- a ₂ , a _3- a
₄ , a ₅ -a ₆ , ...) Have a constant linear shape, the electrostatic image obtained by the main scanning of the laser light is constant, and the image quality is not deteriorated.

[0006]

In the above prior art, when a stepping motor is used, it has a cogging characteristic. Therefore, if the cogging cycle and the optical writing cycle do not match as shown in FIG. As shown in FIG. 7 (b), the light beam trajectories (b ₁ -b ₂ , b ₃ -b ₄ , b _5-
b ₆ , ...) becomes non-uniform, and the image is disturbed. That is, if the gaps G ₁ ′ and G ₂ ′ between the adjacent trajectories are narrowed or widened due to the visual relationship, the image defects due to jitter occur. In particular,
When a 1 × 1 dot or 2 × 2 dot continuous pattern in one page is printed, the poor image quality appears remarkably.

Therefore, in the past, in order to make the cogging characteristic as flat as possible, a flywheel was provided on the output shaft of the stepping motor or an appropriate member in the driving force transmission path to increase the effective load. However, if the motor load is increased, it is necessary to use a stepping motor with a larger output in order to cope with step-out due to sudden overload. However, when the output of the stepping motor is large, the cogging also becomes large.

As described above, conventionally, the cogging of the stepping motor cannot be eliminated, and the adverse effect on the image formation due to the cogging cannot be eliminated.

It is an object of the present invention to provide an image forming apparatus capable of forming a high quality image by eliminating the influence of cogging of a stepping motor.

[0010]

In order to achieve the above object, the present invention provides a photoconductor, a laser optical system for optical writing in the main scanning direction of the photoconductor, and a photoconductor in the sub-scanning direction. An image forming apparatus including a stepping motor that is a driving source for rotating the image forming apparatus includes a control circuit that controls a driving frequency of the stepping motor to be an integral multiple of a main scanning optical writing frequency. And

Further, an optical writing synchronizing signal is inputted to the control circuit, and the driving frequency of the stepping motor is generated by matching the driving cycle of the stepping motor and the start time in the optical writing cycle. To do.

Further, the control circuit receives a frequency divider, a phase difference detector for receiving an optical writing synchronizing pulse signal and comparing it with the output of the frequency divider, a stepping motor phase signal generator, and the phase difference detector. And a voltage controlled oscillator that outputs a frequency according to the output of the stepping motor phase signal generator to the stepping motor phase signal generator.

Further, the control circuit includes a stepping motor phase signal generator and a counter which receives the optical writing synchronization pulse signal and outputs a frequency based on the reference clock to the stepping motor phase signal generator. Is characterized by.

[0014]

According to the above means, the relationship between the drive frequency f _S of the stepping motor and the optical writing frequency f _W of the main scan is f _S = N.multidot.N by the control circuit including the phase difference detector or the counter. By setting f _W (N = 1, 2, 3, ...: Integer), the drive cycle of the stepping motor
Since the (cogging cycle) and the optical writing cycle can be matched, each locus formed by the laser light on the photoconductor has the same shape in the main scanning direction and the intervals are substantially equal. A high quality image is obtained without appearing.

[0015] In the control circuit, wherein f _W By matching the start timing of f _S and N · f _W using, can so as not to cause a phase shift, to continue a more stable high-quality image that is obtained Be done.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an explanatory view of the configuration of an embodiment of the present invention. 1 is a drum-shaped photosensitive member, 2 is a polygon mirror rotated by a polygon motor (not shown), 3 is an LD (laser diode), 4 Is the LD reflected by the polygon mirror 2
F-θ lens for scanning the laser beam 3 of laser light at a constant velocity and angle on the photoconductor 1 (main scanning direction), 5 receives the laser light of LD 3 reflected by the polygon mirror 2, A synchronous detection sensor for detecting a synchronous pulse signal for scanning (light writing) by light, 6 is a stepping motor which is a drive source for rotating the photoconductor 1 in the sub-scanning direction, and 7 is an output shaft 6a of the stepping motor 6. , A transmission gear group 10 installed between a drive gear 8 provided on the photoconductor 1 and a driven gear 9 provided on the photoconductor 1, and a phase signal (0A, 0A ', 0B, 0B' for driving the stepping motor 6). Is a drive circuit having a CPU (central processing unit) 11 for outputting

FIG. 2 is a drive circuit which is the control circuit of FIG.
FIG. 10 is a block diagram showing a main part of 10, wherein 20 is a PD (phase difference of a PLL circuit that receives a synchronization pulse signal P exhibiting an optical writing period of main scanning (= optical writing frequency f _W ) detected by the synchronization detection sensor 5). (Detector), 21 is a programmable frequency divider that outputs a value of 1 / N according to an integer value (N = 1, 2, 3, ...) Preset by the CPU 11, 22 is a VCO (voltage controlled oscillator), 23 is a stepping motor phase signal generator.

In FIGS. 1 and 2, the sync pulse signal P obtained by the sync detection sensor 5 is input to the PD 20 and compared with the output of the programmable frequency divider 21. If the phases match, the output of PD20 becomes zero and V at that time becomes V.
The output of CO22 becomes the driving frequency f _S of the stepping motor having a constant value and is output to the stepping motor phase signal generator 23.

FIGS. 3 (a) and 3 (b) are explanatory diagrams of the trajectory of the light beam on the photosensitive member according to the above-mentioned embodiment. As shown in the characteristic diagram of FIG. 3 (a), the cogging of the stepping motor 6 is performed. Since it cannot be eliminated, an example in which the optical writing frequency f _W and the driving frequency f _S are made equal (f _W = f _S ) with the value of N of the programmable frequency divider 21 being “1” will be shown. ing.

The combined start timing by using the f _W as described above, by setting f _W = f _S, FIG. 3 (b)
As shown in, the trajectory of the light beam on the photoconductor 1 (c ₁ -c
_{2, c 3 -c 4, c} 5 -c 6, ···) is fit the period of the driving cycle (cogging period) and the optical writing of the stepping motor, an optical writing corresponding to the displacement of the photosensitive member 1 is made, Moreover, since they are in phase with each other, the distances G ₁ and G ₂ between adjacent trajectories can be maintained at substantially the same distance, although they are not linear.
It is possible to suppress the occurrence of jitter.

Generally, the distance between loci is 85 when the resolution is 300 dpi.
It is said that when the position of c ₃ deviates from the predetermined position by 1/3 dot, jitter is likely to appear. In other words, a deviation of ± 28 μm vertically causes a problem in image quality. However, in the example of FIG. 3, since the loci widths are almost the same distance as described above, the image quality is not deteriorated.

In the above example, V = 1 because N = 1.
The output frequency (= f _S ) of 22 is the same as f _W , but if N = 2 is set, a frequency twice f _w is obtained as f _S.

FIG. 4 is a block diagram showing another example of the drive circuit, in which a counter of a logic circuit is used, 30 is a counter to which the sync pulse signal P detected by the sync detection sensor 5 is inputted, 31 ,. 32 is an OR circuit and 33 is a stepping motor phase signal generator.

In the figure, the synchronization pulse signal (= optical writing frequency f _W ) P obtained by the synchronization detection sensor 5 is the counter 3
When the reset input of 0 is entered, the counter 30 is initialized and simultaneously outputs the stepping motor drive signal (= drive frequency f _S ). That is, the reference clock is input to the counter 30, and when a predetermined number of clocks is counted, carrier up is output and a drive signal is output.

The predetermined number of clocks above, selected by CPU 11, if set the number of clocks to more than one period of the f _W, since it is reset by f _W before the carry-up is output, f _W = f _S. Further, if a value is set such that the number of clocks is 1/2 of one cycle of f _W , f _S becomes f _W and carrier up, totaling 2 pulses, and f _S = 2f _W is obtained. Similarly, 3f _W and 4f _W can be obtained.

[0027]

As described above, according to the present invention,
The relationship between the drive frequency f _S of the stepping motor and the optical writing frequency f _W of the main scan is f _S = Nf _W (N = 1, 1) by a control circuit including a phase difference detector or a counter.
2, 3, ...: Integer), the driving cycle (cogging cycle) of the stepping motor can be matched with the optical writing cycle, so that the occurrence of jitter can be prevented.
Furthermore, by matching the start timings of f _S and N · f _W so that no phase shift occurs, it is possible to provide an image forming apparatus capable of eliminating the effect of cogging of the stepping motor and achieving high quality image formation. ..

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a configuration of an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a block diagram of a main part of the drive circuit in FIG.

FIG. 3 is an explanatory diagram of a trajectory of a light beam on a photoconductor in this embodiment.

FIG. 4 is a block diagram showing another example of the drive circuit of FIG.

FIG. 5 is an explanatory diagram of rotational displacement of a stepping motor.

FIG. 6 is an explanatory diagram of a trajectory of a light beam on a photoconductor when a conventional DC servo motor is used.

FIG. 7 is an explanatory diagram of a locus of a light beam on a photoconductor when a conventional stepping motor is used.

[Explanation of symbols]

1 ... Photosensitive member, 2 ... Polygon mirror, 3 ... LD (laser diode), 4 ... f-θ lens, 5 ... Synchronous detection sensor, 6 ... Stepping motor, 10 ... Drive circuit (control circuit), 20 ... PD (position) Phase difference detector), 21 ... Programmable frequency divider, 22 ... VCO (voltage controlled oscillator),
23, 33 ... Stepping motor phase signal generator, 30 ... Counter, 31, 32 ... OR circuit.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location G03G 15/04 116 9122-2H H04N 1/04 104 Z 7251-5C

Claims (4)

[Claims] 1. An image forming apparatus including a photoconductor, a laser optical system for optically writing in the main scanning direction of the photoconductor, and a stepping motor as a drive source for rotating the photoconductor in the sub-scanning direction. The image forming apparatus according to claim 1, further comprising a control circuit for controlling a drive frequency of the stepping motor to be an integral multiple of a main scanning optical writing frequency. 2. An optical writing synchronization signal is input to the control circuit to generate a driving frequency of the stepping motor by matching the driving cycle of the stepping motor and the start time of the optical writing cycle. The image forming apparatus according to claim 1. 3. The control circuit receives a frequency divider, a phase difference detector for receiving an optical writing synchronization pulse signal and comparing the output with the frequency divider, a stepping motor phase signal generator, and the phase difference detector. 3. The image forming apparatus according to claim 1, further comprising a voltage controlled oscillator that outputs a frequency according to the output of the voltage generator to the stepping motor phase signal generator. 4. The control circuit comprises a stepping motor phase signal generator, and a counter which receives an optical writing synchronization pulse signal and outputs a frequency based on a reference clock to the stepping motor phase signal generator. The image forming apparatus according to claim 1 or 2, characterized in that.