JPS6326366B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to light beam scanning, particularly light beam plane scanning performed using a light deflecting mirror such as a rotating polygonal mirror or a galvano mirror. Alternatively, the present invention relates to a method for correcting, in real time, non-uniformity in scanning line spacing caused by errors in parallelism of a mirror surface with respect to the axis of a polygon mirror.

2. Description of the Related Art Rotary drum scanning methods and plane scanning methods are known as scanning methods for image scanning recording devices such as color scanners and facsimile machines.

In this rotating drum scanning method, a sheet material such as an original image or a recording material is mounted on the rotating drum surface, and the rotating drum is rotated at high speed (for example, 900 rpm) in the circumferential direction (main scanning direction). Because of the scanning, the sheet material can sometimes be lifted off the surface of the rotating drum, and in extreme cases, the sheet material can become detached from the surface of the rotating drum, leading to damage.

Furthermore, as the rotation speed of the rotary drum increases, problems such as vibration occur, so that it is currently difficult to significantly increase the scanning speed.

On the other hand, in the plane scanning method, a sheet material such as an original image or a recording material is moved at low speed in the sub-scanning direction, and the sheet material is moved in a direction crossing the moving direction according to an image signal. By moving a modulated light beam at high speed,
Photoelectric scanning of the original image and scanning recording of the duplicate image are performed. Therefore, the speed increase in such a scanning method is almost determined by the scanning speed of the light beam, and depends on the performance of the light deflection mirror that constitutes the light beam deflection system.

Such optical deflection mirrors have been improved and improved by the recent development of plane scanning methods using laser beams, and have been improved to achieve high speeds that far exceed the speed limit of the rotating drum scanning method. Things are being put into practical use.

However, when scanning with such a light deflecting mirror, especially when using a rotating polygon mirror, the parallelism of each mirror surface to the axis, including the accuracy of mounting the axis to the polygon mirror, as shown by the solid line in Figure 1, is difficult. There are drawbacks to non-uniformity in scan line spacing due to angle errors and mirror flatness errors.

Conventionally, as a method for correcting such non-uniformity in the scanning line spacing, a cylindrical lens is placed in front of the projection surface on which the light beam reflected by the light deflection mirror is projected. A method for reducing non-uniformity in scanning line spacing, and when the optical deflection mirror used is a rotating polygon mirror, the error at each reflective surface is measured in advance and written in a memory device, and then used. Correcting data is read from the memory device according to each reflecting surface, and the acousto-optic light deflection element (hereinafter referred to as AOM) for deflection angle correction is read out from the memory device.
There is a known method for correcting non-uniformity in scanning line spacing on a light beam projection surface by controlling the amount of deflection and applying a deflection amount to the light beam corresponding to the error on each reflecting surface.

However, the former method merely reduces the non-uniformity of the scanning line spacing to make the non-uniformity less noticeable, and the latter method
This is because it is necessary to measure the error on each reflective surface, write correction data to the memory device, and read the corresponding correction data from the memory device depending on the mirror surface used to control the AOM. , the control system is complex and an expensive memory device is required, and when adjusting the optical axis or removing the polygon mirror to clean the mirror surface, the error at each reflective surface must be measured again. The disadvantage is that it is necessary and time-consuming.

The present invention eliminates the disadvantages of such conventional correction methods and uses a detection light beam together with a scanning light beam such as a scanning light beam or a recording light beam to correct errors on each reflective surface of an optical deflector using the detection light beam. The purpose of this is to provide a method for correcting non-uniformity in scanning line spacing in real time by detecting it in advance with a beam, and hereinafter, the correction method according to the present invention will be applied to the recording side. This will be explained using an example.

FIG. 2 shows an example of the optical and electrical configuration for carrying out the method according to the present invention.
2 is an AOM whose incident light beam is modulated according to an image signal and for correcting the deflection angle of the recording light beam by the method according to the present invention;
4 is a rotating polygon mirror, 4 is an F/θ lens, and 5 is a recording material placed on the projection surface of the recording light beam 1 and moved at low speed in a direction intersecting the light beam 1.

Further, 6 is a detection light beam which is, for example, a He--Ne gas laser beam, 7 is a dichroic mirror, 8 is a detection light beam 6, and a detector 9 which will be described later.
The cylindrical lens 9 has its axis perpendicular to the direction of deflection of the detection light beam by the rotating polygon mirror 3 in order to form an image upwardly, and the cylindrical lens 9 is a cylindrical lens in which, for example, two photoelectric conversion elements are arranged side by side in a Japanese character shape. detector, 1
0 is a detection circuit for detecting the state in which the detection light beam 6 is incident on the detector 9, 11 is a voltage/frequency (V/F) converter, 12 is a balanced modulator, and 13 is a power amplifier.

The detection light beam 6 is passed through an optical system (not shown) configured to be parallel to the recording light beam 1.
The light is incident on the rotating polygon mirror 3.

As illustrated in FIG. 3, this detection light beam 6 scans in advance on the same trajectory on each mirror surface of the rotating polygon mirror 3 while maintaining an interval corresponding to a predetermined time difference t with respect to the recording beam 1. It is structured like this.

Strictly speaking, this time difference t varies according to the rotation of the rotating polygon mirror 3, but since the amount of variation is extremely small and can be ignored, the following description will be made assuming that it does not vary.

The recording light beam 1 reflected by the mirror surface of the rotating polygon mirror 3 is transmitted through the dichroic mirror 7, and is reflected by the mirror surface of the rotating polygon mirror 3.
The recording material 5 is passed through the lens 4 and onto the recording material 5.
It moves at a constant speed in a direction (main scanning direction) that intersects the feeding direction (sub-scanning direction) of , and records a predetermined duplicate image on the recording material 5 .

On the other hand, since the detection light beam 6 is a red light beam, it is reflected by a dichroic mirror 7 and passed through a cylindrical lens 8 to a detector 9 in which two photoelectric conversion elements are arranged side by side in a Japanese character shape. incident on . At this time, the detection light beam 6 is incident on a fixed position by the cylindrical lens 8 regardless of the deflection angle by the rotating polygon mirror 3, and the deviation in the direction along the axis of the cylindrical lens 8 due to errors in the mirror surface only detected. The detection light beam 6 incident on the detector 9 is photoelectrically converted by a photoelectric conversion element in the detector 9 and input to the detection circuit 10 .

FIG. 4 shows the connection relationship between the detector 9 and the detection circuit 10. The detection circuit 10 is composed of a current/voltage conversion section consisting of an amplifier and a resistor, and a differential amplifier.

Now, each photoelectric conversion element 9A, 9B of this detector 9
When the state of the detection light beam 6 (shown with hatching in FIG. 4) incident on the detector changes as shown in FIG. 5A, for example, the current/voltage converter in FIG. , detection signals as shown in FIG. 5B and FIG. 5C are outputted, and the detection circuit 10 finally outputs a deviation signal as shown in FIG. 5D.

Thus, partial deviations of the recording light beam 1 that cause non-uniformities in the scan line spacing will cause the detection light beam 6 to
Based on this partial deviation of the detection light beam 6, the non-uniformity of the scanning line spacing in the recording light beam 1 is corrected as follows.

That is, when the detection circuit 10 outputs a deviation signal of the detection light beam 6 as shown in FIG. 6B,
The deviation signal is subjected to voltage/frequency conversion in the next stage V/F converter 11 as shown in FIG.
This frequency-converted signal C is further amplitude-modulated in the next-stage balanced modulator 12 by an image signal as shown in FIG. 6A, and from the balanced modulator 12, a correction signal as shown in FIG. is output.

This correction signal is passed through the power amplifier 13 to
The recording light beam 1 applied to the ultrasonic conversion transducer in the AOM 2 and incident on the AOM 2 is modulated in brightness according to the image signal, and
Detection light beam 6 detected by detection circuit 10
By correcting the deflection angle of the recording light beam 1 according to the deflection signal of the recording light beam 1, non-uniformity in the scanning line spacing of the recording light beam 1 is corrected.

What is important in performing such correction is the delay time t from when the detection light beam 6 scans the same position on the mirror surface of the rotating polygon mirror 3 to when the corresponding recording light beam 1 scans, and the signal The purpose is to make the time (t') from when the signal is applied to the ultrasonic converting transducer in the AOM 2 to when the incident recording light beam 1 is modulated by the signal coincide with each other in advance. To do this, for example, you can do as follows.

That is, by arranging an optical chopper on the optical path of the detection light beam 6, the detection light beam 6 is made incident on a photoelectric converter as pulsed light having a constant width and a constant interval, and the photoelectrically converted pulse signal is converted into an image. Instead of the signal, a constant frequency signal is input to the balanced modulator 12 via a current/voltage converter.

This balanced modulator 12 outputs a signal amplitude modulated according to the pulse signal, and when this output signal is inputted to the ultrasonic modulation transducer of the AOM 2 via the power amplifier 13, the ultrasonic wave propagates through the crystal of the AOM 2, is modulated with a delay of a propagation delay time until it modulates the recording light beam 1, and is output from the AOM 2 as pulsed light.

This recording light beam 1 is made incident on a photoelectric converter (not shown) appropriately placed in the optical path of the light beam 1, and an output signal from the photoelectric converter and an output signal from the photoelectric converter are input into the optical path of the detection light beam 6. The output signals from appropriately placed photoelectric converters are input to, for example, an oscilloscope, the output waveforms from both photoelectric converters are displayed, and the recording light beam 1 is set so that the time difference between the two output waveforms becomes zero. The position of the detection light beam 6 entering the AOM 2 may be adjusted, or the reference position of the detection light beam 6 entering the mirror surface of the rotating polygon mirror 3 may be adjusted. An appropriate delay circuit may be used if necessary.

It goes without saying that the optical chopper and both photoelectric converters are placed in the optical path only during such adjustment.

As described above, the method according to the present invention utilizes the time required for an ultrasound signal to propagate through the crystal of an acousto-optic light deflection element to detect non-uniformity in the scanning line spacing of a recording light beam in real time. The correction signal is applied to the ultrasonic conversion transducer in the acousto-optic light deflection element, and the ultrasonic signal output from the transducer propagates to the incident position of the recording light beam. and the time it takes for the recording light beam to be modulated, and the time from when the detection light beam is incident on the same mirror surface position of the optical deflection device.
The time difference until the recording light beam is incident is adjusted to be equal, the error in each mirror surface of the optical deflection device is detected in advance using the detection light beam, and the recording light beam is modulated with a correction signal corresponding to the error. By applying it to the acousto-optic deflection element along with an image signal for recording, non-uniformity in the scanning line spacing of the recording light beam can be corrected in real time.

In the above description, the method according to the present invention is applied to the recording side of an image scanning recording apparatus. However, if the original image to be scanned is a monochrome original image, the image signal input to the balanced modulator 12 is It can also be applied to the scanning side by simply switching to a constant voltage signal.
In this case, it goes without saying that the AOM only performs optical deflection for correction, and there is no need to perform optical modulation as on the recording side.

In addition, in the above-mentioned embodiment, the case where plane scanning is performed by a light beam is described, but
The method according to the invention can be similarly applied when scanning a cylindrical surface.

As described above, the method according to the present invention deflects the detection light beam with an optical deflection device prior to the main light beam such as the recording light beam or the scanning light beam.
Errors such as non-smoothness and parallelism errors on each mirror surface of the optical deflection device are detected in advance, and non-uniformity in scanning line spacing is corrected in real time.
It has many practical advantages, such as being able to be used as is even after adjusting the optical system, such as when adjusting the optical axis.

[Brief explanation of the drawing]

FIG. 1 is a graph showing an example of non-uniformity in scanning line spacing, FIG. 2 is a graph showing an example of the optical and electrical configuration for carrying out the method according to the present invention, and FIG. FIG. 2 is an enlarged perspective view showing the states of the recording light beam and detection light beam incident on the rotating polygon mirror in FIG. 2, FIG. 4 is a schematic diagram showing an example of the detector and detection circuit in FIG. 2, and FIG. FIG. 2 is a diagram showing an example of the incident state of the detection light beam on the detector and the detection signal, and FIG. 6 is a diagram showing an example of the signal waveform at each part in FIG. 1... Recording light beam, 2... AOM (acousto-optic light deflection element), 3... Rotating polygon mirror, 4... F/θ lens,
5... Recording material, 6... Detection light beam, 7... Gikkreuzk mirror, 8... Cylindrical lens, 9...
Detector, 9A, 9B...Photoelectric conversion element, 10...Detection circuit, 11...Voltage/frequency (V/F) converter, 1
2... Balance converter, 13... Power amplifier.

Claims (1)

[Claims] 1. A scanning light beam is made incident on an optical deflection mirror via an acousto-optic light modulation element, and the scanning light beam deflected by the deflection mirror causes a sheet material placed on a projection surface to be When scanning, a detection light beam having a different light color from the scanning light beam is scanned in advance at the same position on each mirror surface of the light deflection mirror with a predetermined time difference from the scanning light beam, and both light beams are are separated by a dichroic mirror placed in the optical path after the light deflection mirror, and the scanning light beam is projected so as to scan the sheet material surface, while the detection light beam is projected with its axis line for light deflection. Through a cylindrical lens installed perpendicular to the direction of deflection by the mirror, the beam is projected onto a photoelectric conversion device that detects the error in the mirror surface of the light deflection mirror by the deflection of the detection light beam, and based on the detected value of the photoelectric conversion device, The method is characterized in that the deviation of the scanning light beam is corrected by applying a correction signal for the deviation of the detection light beam to the acousto-optic modulation element.
A method for correcting non-uniformity of scanning line spacing in light beam scanning. 2. The time difference between when the detection light beam scans the same position on each mirror surface of the light deflection mirror and when the scanning light beam scans the same position is calculated by applying the correction signal to the acousto-optic light deflection element. Non-uniformity correction of scanning line spacing in light beam scanning according to claim 1, characterized in that the time taken for the scanning light beam incident on the deflection element to be modulated by the correction signal is made equal to the time taken for the scanning light beam to be modulated by the correction signal. Method. 3. Non-uniformity of scanning line spacing in light beam scanning as set forth in claim 1, wherein the photoelectric conversion device is a combination of two photoelectric conversion elements in a Japanese letter shape. Correction method.