JPH11237579A - Optical writer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical writer capable of evaluating not only the reliability of a polygon mirror but also that of synchronization detection signal generation timing in an actual machine state. SOLUTION: The optical writer is provided with a lighting control part 1, a laser unit 2, a polygon mirror 3, a lens unit 4 consisting of an fθ lens or a cylindrical lens, a reflection mirror 5 and an optical element 6 which are synchronization detecting means, and 1st and 2nd CCD cameras 7, 8. Thus validity not only for the state of the polygon mirror 3 but that for the generation timing of a synchronizing signal is judged based on the light emission detecting timing of the CCD cameras 7, 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a laser printer,
Optical writing devices that apply to digital copiers and perform optical writing on a photoreceptor with a laser, especially processing accuracy of polygon mirror (rotating polygon mirror), assembly accuracy on the device, assembly accuracy, polygon motor rotation accuracy The present invention relates to a technology for evaluating the reliability of a polygon mirror.

[0002]

2. Description of the Related Art The above-described optical writing apparatus includes a lighting control unit for outputting a modulation signal corresponding to an image signal, a laser unit whose lighting is controlled by the lighting control unit, and a laser emitted from the laser unit being rotated by its rotation. A polygon mirror that distributes light in the main scanning direction and performs optical writing on the photoreceptor via the lens unit, and a synchronization detection unit provided outside the effective image area, a laser beam emitted from the laser unit to the polygon mirror, The light is reflected by a polygon mirror that rotates at a high speed, and optical writing is performed in the main scanning direction on the photoconductor. Synchronization detecting means is provided outside the effective image area on the photoreceptor, and light writing to the effective image area is started based on the timing at which the synchronization detection means detects the laser beam reflected by the polygon mirror. It has become.

The synchronization detecting means includes a reflection mirror and an optical element for receiving light reflected from the reflection mirror, and a type in which the reflection mirror is provided at the synchronization detection position, and a type in which only the optical element is provided at the synchronization detection position. In any case, in order to obtain a highly reliable image while keeping the image writing position (optical writing start position) constant, the mounting accuracy of the synchronization detecting means is very important. . Even if the synchronization detection means is installed at a predetermined position outside the effective image area, if the installation angle is shifted, for example, if the reflection mirror is tilted and the optical path toward the optical element is shifted, Means that accurate synchronization timing cannot be obtained.

[0004] On the other hand, even if the synchronization detecting means is accurately assembled at a predetermined position, that does not mean that it is good. That is, there is a problem of the polygon mirror. The laser beam is scanned over the photoreceptor by the polygon mirror, which is a polygon mirror that rotates at high speed, but the processing accuracy, assembly accuracy to the device, and rotation accuracy of the polygon motor must be maintained to a high level. An image to be optically written on the photoreceptor (an electrostatic latent image is first formed by optical writing, and then the electrostatic latent image is visualized by toner) is distorted.

Therefore, various techniques for detecting uneven rotation (jitter) of the polygon mirror have been conventionally proposed (JP-A-2-16523, JP-A-3-26483).
No. 4, JP-A-4-174336, JP-A-5-174.
No. 508939).

[0006]

In each of the prior arts described above, the reliability of the polygon mirror alone is evaluated. Therefore, even if the reliability is secured as a single polygon mirror, there is a problem that the reliability is not necessarily guaranteed as it is when assembled as an optical writing device of a digital copying machine or a laser printer. .

The present invention has been made in view of such a background, and provides an optical writing apparatus capable of evaluating the reliability of a polygon mirror and, more particularly, the reliability of the timing of generating a synchronization detection signal in an actual machine. The purpose is to do.

[0008]

In order to achieve the above object, according to the present invention, there is provided a lighting control unit for outputting a modulation signal according to an image signal, and a laser unit whose lighting is controlled by the lighting control unit. A polygon mirror for distributing a laser beam emitted from the laser unit in the main scanning direction by rotation of the laser unit and performing optical writing on a photoreceptor via a lens unit; and a synchronization detecting means provided outside the effective image area. In the optical writing device, near the optical writing start point at a predetermined distance from the synchronization detecting means, there is provided a light emitting detecting means for detecting a laser scanned by the polygon mirror, and from the light emitting detecting timing of the light emitting detecting means, the state of the polygon mirror, and The control for determining the synchronization detection timing of the synchronization detection signal is performed.

[0009] To achieve the above object, the present invention provides a second aspect.
The described invention provides a lighting control unit that outputs a modulation signal according to an image signal, a laser unit that is controlled to be turned on by the lighting control unit, and a lens that divides a laser emitted from the laser unit in the main scanning direction by rotating the lens. In an optical writing device including a polygon mirror for performing optical writing on a photoreceptor via a unit and a synchronization detecting unit provided outside an effective image area, an optical writing start point located at a predetermined distance from the synchronization detecting unit and an end thereof. In the vicinity of the point, first and second light emission detecting means for detecting a laser beam scanned by the polygon mirror are provided. From the light emission detection timing of the first and second light emission detecting means, the state of the polygon mirror and the synchronization detection signal are detected. The control for determining the synchronization detection timing is performed.

[0010] In order to achieve the above object, a third aspect is provided.
According to a second aspect of the present invention, in the second aspect, control is performed to determine whether or not there is uneven rotation of the polygon mirror based on whether or not there is a change in the difference between the light emission detection timings of the first and second light emission detection means. It is a feature.

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, control is performed to determine the state of the polygon mirror by measuring the position in the height direction of the laser by the light emission detection means. is there.

According to the first aspect of the present invention, the laser is turned on for each surface of the polygon mirror for a moment after a certain period of time corresponding to the light emission detecting means near the optical writing start point with reference to the synchronization detection signal. The presence or absence of a shift in light emission detection timing by the means is detected. If there is no deviation, it is determined that the reliability of the polygon mirror and the synchronization detecting means is guaranteed, and if there is a deviation, it is determined that there is a problem in the polygon mirror (in some cases, the synchronization detecting means).

According to the second and third aspects of the present invention, based on the synchronization detection signal, the polygon is set after a predetermined time corresponding to the first and second light emission detecting means near the optical writing start point and the end point. The laser is turned on momentarily for each surface of the mirror, and the movement amount within a fixed time for each surface of the polygon mirror is obtained from the difference between the light emission detection timings of the first and second light emission detection means. If so, it is determined that there is uneven rotation of the polygon mirror.

According to the fourth aspect of the present invention, the height of the laser in the scanning direction is measured for each surface of the polygon mirror.
The scanning inclination for each surface and the expansion / contraction of printing for each surface are confirmed.

[0015]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a conceptual diagram of an optical writing device showing an embodiment of the present invention. This optical writing device includes a lighting control unit 1, a laser unit 2, a polygon mirror 3, a lens unit 4 formed of an fθ lens or a cylindrical lens, a reflection mirror 5 as a synchronization detecting unit, and an optical element 6. Further, in the present embodiment, First and second CCD cameras 7 and 8 as light emission detecting means are installed near a writing portion (light writing start position) and near a writing end portion (light writing end position).

The lighting control section 1 outputs a modulation signal corresponding to the image signal, and modulates the laser of the laser unit 2 in accordance with the image information. The laser unit 2 emits the modulated laser toward the polygon mirror 3. The polygon mirror 3 reflects the laser beam while rotating at a very high speed and distributes the laser beam in the main scanning direction. The lens unit 4 is interposed between a photoreceptor (not shown) and the polygon mirror 3, and performs laser waveform shaping.

The reflection mirror 5 is provided outside the effective image area of the photoconductor, and when the laser reflected by the reflection mirror 5 enters the optical element 6, a synchronization signal is output.
, Which determines the timing of writing to the effective image area. The above-described optical writing device is incorporated in an image forming apparatus such as a laser printer, a digital copying machine, or the like.

The laser modulated by the image signal is scanned in the main scanning direction of the photoconductor by the high-speed rotation of the polygon mirror 3, so that optical writing is performed line by line, and an electrostatic latent image is formed on the photoconductor. Is done. Thereafter, the electrostatic latent image is developed with toner to become a visible image, and is transferred to a sheet fed from a sheet feeding unit (not shown) by a transfer unit. The sheet onto which the unfixed toner image has been transferred is then conveyed to a fixing unit (not shown), where the unfixed toner image is fixed.

As described above, since the writing of the laser is performed based on the synchronization signal, it is indispensable that the synchronization signal is output at the correct timing. here,
Even if the reflection mirror 5 and the optical element 6 are correctly set, the state of the polygon mirror 3, that is, the surface processing accuracy, the assembling accuracy in the device, the reflectance of each surface, and the uneven rotation of a polygon motor (not shown) ( Jitter) determines the reliability of the synchronization signal. If the state of the polygon mirror is bad, the synchronization signal varies, which causes a shift in the writing start position, which distorts the image, but in this case, the beam in the main scanning direction is not always constant. Will be distorted.

In this embodiment, the first and second CCD cameras 7 and 8 are used to grasp the state of the polygon mirror 3 in the actual machine state.

FIG. 2 is a diagram showing the relationship between the synchronization signal and the light emission timing toward the CCD camera. Lighting control unit 1
Controls the laser unit 2 so as to emit light for a very short time at intervals of α with reference to the synchronization signal, as shown in FIG. This α is set to a time at which light enters the first CCD camera 7 arranged at the scanning image forming position close to the image writing section. Similarly, as shown in FIG. 2, the lighting control unit 1 controls the laser unit 2 so as to emit light for a very short time at intervals of β with reference to the synchronization signal. This β is set to a time at which light enters the second CCD camera 8 arranged at the scanning image forming position near the end of writing of the image.

FIGS. 3 (a) and 3 (b) are diagrams showing the state of the laser beam incident on the CCD camera. The laser incident on the first CCD camera 7 is shown, but the second CCD camera 7
The same applies to the camera 8. As shown in FIG. 3A, if synchronous light is uniformly scanned on all surfaces of the polygon mirror 3 (the laser is always at L1), the first C
Light entering the CD camera 7 is always obtained at the same position. In this case, the polygon mirrors 3 are all normal (assembly accuracy, surface processing accuracy, etc.). That is,
Reliability is guaranteed. However, the reliability of the rotation unevenness is evaluated by the following control.

However, as shown in FIG. 3B, if the synchronous light is scanned in different states depending on the surface of the polygon mirror 3 (the laser is not horizontal like L1 and L2,
That is, if the state of the polygon mirror 3 is not normal, the first CCD camera 7 is shifted by the amount of the shift of the synchronization light.
The light inside is also obtained at the shifted position. By measuring the shift amount X, the synchronization state can be detected, and the larger the shift amount X is, the more the image fluctuates. At this time, as the position of the first CCD camera 7 is closer to the reflection mirror 5, the error of the rotation component of the polygon motor 3 is removed, and correct measurement can be performed.

FIGS. 4A and 4B are views showing laser dots of the first CCD camera and the second CCD camera.
(A), the light emitting position (laser dot) A1 obtained by the first CCD camera 7 and (b), the light emitting position (laser dot) obtained by the second CCD camera 8 ) By calculating B1, the rotation state of each surface of the polygon mirror 3 can be quantified. Then, the presence or absence of uneven rotation of the polygon mirror 3 can be detected based on whether or not there is a change in the difference (B1-A1) between the two. That is, if there is a change in the difference, it means that the polygon mirror 3 has uneven rotation.

Here, the light emission control by the lighting control unit 1 is performed independently for each surface of the polygon mirror 3 so that
Accurate measurement is possible in accordance with the data acquisition timing of the CCD. Next, the first and second CCD cameras 7, 8
The light emitting position (laser dot) in the height direction at, that is, A′1 in FIG. 4A and B′1 in FIG. 4B are calculated for each surface of the polygon mirror 3 in the same manner as described above. ,
The scanning inclination for each surface and the expansion / contraction of printing for each surface can be confirmed. At this time, the accuracy of the measurement can be increased by attaching magnifying lenses to the first and second CCD cameras 7 and 8, including the measurement of A1 and B1.

The optical writing apparatus according to the present embodiment includes a lighting control section 1, a laser unit 2, a polygon mirror 3, a lens unit 4 including an fθ lens and a cylindrical lens,
It includes a reflection mirror 5 and an optical element 6 as a synchronization detecting means, and first and second CCD cameras 7 and 8. Then, based on the light emission detection timings of the first and second CCD cameras 7, 8, the state of the polygon mirror 3, that is, the appropriateness of the generation timing of the synchronization signal is determined. By doing so, it is possible to accurately evaluate the reliability of the polygon mirror 3 in a state similar to an image that is actually scanned (printed).

[0027]

According to the first aspect of the present invention, the laser is momentarily turned on for each surface of the polygon mirror after a predetermined time corresponding to the light emission detecting means near the optical writing start point with reference to the synchronization detection signal. Then, the presence or absence of a shift in the light emission detection timing by the light emission detection unit is detected. If there is no shift, it is determined that the reliability of the polygon mirror and the synchronization detection unit is guaranteed. Depending on the synchronization detection means),
Accurate evaluation of the polygon mirror in the actual machine state becomes possible.

According to the second and third aspects of the present invention, based on the synchronization detection signal, after a lapse of a predetermined time corresponding to the first and second light emission detecting means near the optical writing start point and the end point, respectively. The laser is momentarily turned on for each surface of the polygon mirror, and if there is a change in the difference between the light emission detection timings of the first and second light emission detection means, it is determined that there is uneven rotation of the polygon mirror. Rotation unevenness of the polygon mirror can be accurately detected.

According to the fourth aspect of the present invention, by measuring the height of the laser in the scanning direction for each surface of the polygon mirror, the inclination of the scanning for each surface and the expansion and contraction of the printing for each surface are confirmed. can do.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of an optical writing device showing an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a synchronization signal and light emission timing to a CCD camera.

FIG. 3 is a diagram showing a state of a laser beam incident on a CCD camera.

FIG. 4 is a diagram showing laser dots of a first CCD camera and a second CCD camera.

[Description of Signs] 1 Lighting control unit 2 Laser unit 3 Polygon mirror 4 Lens unit 5 Reflection mirror 6 Optical element 7 First CCD camera 8 Second CCD camera

Claims (4)

[Claims] 1. A lighting control unit for outputting a modulation signal according to an image signal, a laser unit controlled to be turned on by the lighting control unit, and a laser emitted from the laser unit being distributed in the main scanning direction by rotation of the laser unit. An optical writing device comprising: a polygon mirror for performing optical writing on a photoreceptor via a unit; and a synchronization detecting means provided outside the effective image area. A light emission detecting means for detecting a laser beam scanned by the polygon mirror, wherein control is performed to determine the state of the polygon mirror and the synchronization detection timing of the synchronization detection signal from the light emission detection timing of the light emission detection means. Writing device. 2. A lighting control unit for outputting a modulation signal corresponding to an image signal, a laser unit whose lighting is controlled by the lighting control unit, and a laser emitted from the laser unit being distributed in the main scanning direction by rotation of the laser unit. An optical writing apparatus comprising: a polygon mirror for performing optical writing on a photoreceptor via a unit; and a synchronization detecting means provided outside an effective image area. In the vicinity of the point, there are provided first and second light emission detection means for detecting a laser beam scanned by a polygon mirror. From the light emission detection timing of the first and second light emission detection means,
An optical writing device for performing control for determining a state of a polygon mirror and a synchronization detection timing of a synchronization detection signal. 3. The method according to claim 2, wherein control is performed to determine whether or not there is uneven rotation of the polygon mirror based on whether or not the difference between the light emission detection timings of the first and second light emission detection means has changed. Optical writing device. 4. The optical writing apparatus according to claim 1, wherein a control is performed to determine a state of the polygon mirror by measuring a position in a height direction of the laser by the light emission detecting means.