JPS62237420A - Image recording device using galvanomirror - Google Patents

Abstract

PURPOSE:To automatically correct the shift of an optical scanning line to one side by simple constitution, by detecting said shift of the optical scanning line, based on a period difference of a photodetecting pulse outputted from each photodetector which is placed in the vicinity of both ends of a scan area, and applying an offset current to a galvanomirror driving circuit so as to correct the period difference. CONSTITUTION:In case the position of an optical scanning line is normal as shown by a full line, a time interval TA of a photodetecting pulse PA outputted from a photodetector 10, and a time interval TB of a photodetecting pulse PB outputted from a photodetector are made equal (TA=TB). On the other hand, if the position of the optical scanning line is deviated as shown by a broken line, a period TA' of the photodetecting pulse PA outputted from the photodetector 10 becomes longer than a period TB' of the photodetecting pulse PB outputted from the photodetector 11 (TA'>TB'), and based on these periods, the shift of the optical scanning line to one side can be detected. Such shift of the optical scanning line can be corrected by applying a DC offset current to a sine wave current for driving a galvanomirror and deviating a vibration of the galvanomirror.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an image recording apparatus using a galvanometer mirror as an optical scanner, and more particularly to correction of offset of an optical scanning line.

(Background of the Invention) A type of image recording device that can perform high-speed, high-quality recording with low noise on plain paper that has not been specially processed is a silent image recording device that uses an optical scanner to scan a light beam over a photosensitive drum. ! ! forming a latent image and visualizing it by attaching toner to the electrostatic latent image;
There are light beam printers that are configured to transfer and fix the toner image onto plain paper.

By the way, galvanometer mirrors that apply the principle of a galvanometer are also often used as optical scanners in such light beam printers. FIG. 4 is a configuration diagram showing an example of a galvano mirror. In FIG. 4, reference numeral 1 denotes a mirror, which is fixed to a rotation support rod 2. As shown in FIG. A coil 3 is attached to the rotation support rod 2.
is also fixed. 4.5 is a permanent magnet for applying a fixed magnetic field to the coil 3, and is disposed opposite to each other so as to sandwich the coil 3.

In such a configuration, when a current is passed through the coil 3, the coil 3 receives a force in relation to a fixed magnetic field and rotates (Fleming's left-hand rule), and the mirror 1 also rotates as a unit.

When using the galvanomirror as an optical scanner, a sine wave current is applied to the coil 3 to enable high-speed scanning. As a result, the mirror 1 also vibrates sinusoidally in the reciprocating direction with the rotation support rod 2 as the rotation center axis.
When the light beam B is irradiated onto the mirror 1, the reflected beam is also captured in a sine wave to perform optical scanning.

FIG. 5 is a schematic diagram of an image recording apparatus using a galvano mirror. In FIG. 5, 6 is a light beam generator such as a semiconductor laser, and the light beam B outputted from the light beam generator 6 is irradiated onto the mirror 1, and the surface of the photosensitive drum 7 rotating in a fixed direction is illuminated. It is reflected so as to scan along the axial direction between the Pl and PG points. Here, by modulating the light beam output from the light beam generator 6 according to the image signal, an electrostatic latent image is formed on the surface of the photosensitive drum 7 according to the image signal, and optical recording is performed. Become. Note that 8 is a photodetector for detecting the recording start point of the optical scanning line.

FIG. 6 is an explanatory diagram showing the behavior of an optical scanning line by a galvano mirror, in which the vertical axis represents the deflection angle θ of the light beam B, and the horizontal axis represents time t. As shown in FIGS. 5 and 6, the optical scanning line reciprocates between points P1 and P8 with sinusoidal vibration.

That is, from the scanning start point Pr to the detection point P2 by the photodetector 8
→ Image recording start point P3 → Image center point P4 → Image recording end point P5 to reach the scan end point P6, and then return to the scan start point P1 again.

Conventionally, image recording devices using this type of optical scanner,
The optical scanners are arranged so that the optical scanning lines are symmetrical about the image center point P4. That is, in the case of FIG. 6, P! The arrangement will be adjusted so as to become ~P4-P4~P6. This is in the vicinity of the image center point P4 within the scanning area of the optical scanning line that vibrates in a sine wave (i.e., P3 to
In P4 to P5), the deflection angle θ of the light beam B and the scanning time t
The relationship is based on the fact that linear approximation can be performed if the angle of view θ is small. On the other hand, if the deflection angle θ becomes large (if the error occurs when linear approximation is performed, it becomes impossible to ignore, and distortion occurs in the recorded image. Therefore, in such cases, the seventh
As shown in the figure, a lens 9 having f·5in-1θ characteristics is used to correct distortion of recorded images. Here, r is the focal length of the lens 9, and θ is the light beam B.
is the deflection angle.

By the way, when correcting distortion of a recorded image using such a lens 9, the optical axis of the lens 9 must be aligned with the image center point P4, and the optical scanning line must be symmetrical about the image center point P4. You need to adjust it accordingly.

(Problems to be Solved by the Invention) However, in conventional devices, no special measures have been taken for such adjustment, and adjustment requires a high degree of skill. Further, after adjustment, there is a possibility that the adjustment may be incorrect due to the influence of vibrations or the like.

The present invention has been made in view of the above points, and an object thereof is to realize an image recording apparatus having an automatic correction means that can automatically correct the deviation of the optical scanning line with a relatively simple configuration. It is in.

(Means for Solving the Problems) The present invention, which solves the above-mentioned problems, is an image recording apparatus using a galvanometer mirror as an optical scanner. The vessel and
A period difference calculation circuit that calculates the difference in the periods of photodetection pulses output from the multiple photodetector, and an offset current that corrects the period difference according to the calculation output of the period difference calculation circuit is output to the galvanomirror drive circuit. The present invention is characterized in that it is provided with an offset current generation circuit.

(Function) In the image recording device of the present invention, deviation of the optical scanning line is detected based on the period difference between the photodetection pulses output from each photodetector arranged near both ends of the scanning area, and The offset of the optical scanning line is corrected by applying an offset current to the galvanometer mirror drive circuit so as to correct the deviation of the optical scanning line.

(Example) Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention.

In FIG. 1, numerals 10 and 11 are photodetectors located on the optical scanning line to detect the light beam, and points P? and 11 whose positions are known mechanically are photodetectors. , Pa.

As a photodetector, a photodiode is used, especially if high speed is required, a pin photodiode or an avalan is used.
There are cheft diodes and the like. In this embodiment, for convenience of explanation, an example is shown in which the positions are placed at points P7 and P8 near both ends of the scanning area that are equidistant from the image center point P4, but as long as the positions are known, good. Further, either one of the photodetectors 10 and 11 can be used also as a photodetector for detecting a recording start point.

FIG. 2 is an explanatory diagram of the operation of FIG. 1. Photodetector 10.1
1 is placed at positions P4-P7-P4-P8 as described above. When the optical scanning line scans back and forth once between the Ps and PG points, the photodetector 10.11 outputs photodetection pulses PA and PB. When the position of the optical scanning line is normal as shown by the solid line, the time interval (period) TA of the photodetection pulse PA output from the photodetector 1o
and the time interval (period>Ta) of the photodetection pulse PB output from the photodetector 11 are equal (TA=T[l).On the other hand, if the position of the optical scanning line is shifted as shown by the broken line, the photodetection The period T^ of the photodetection pulse PA output from the device 10
' is longer than the period T81 of the photodetection pulse PB output from the photodetector 11 (TA'>TB'), and it is possible to detect the deviation of the optical scanning line based on these periods. Such a deviation of the optical scanning line can be corrected by adding a DC offset current to the sine wave current that drives the galvano mirror to make the vibration of the galvano mirror one-sided. This is clear from the fact that galvanometer mirrors operate on the principle of a galvanometer.

In other words, the deviation of the optical scanning line as shown by the broken line in FIG.
This can be corrected by giving an offset to the sine wave current so that it becomes TA-Ttl.

FIG. 3 is a block diagram showing a specific example of a section section that performs such correction control. In FIG. 3, 12 is a period difference calculation circuit that calculates the period difference between the photodetection pulses PA and Pa output from the photodetector 10.11, and the calculation output is added to the offset current generation circuit 13 as a control signal. It will be done. The offset current generating circuit 13 outputs a DC offset current for correcting the period difference to the galvanometer mirror drive circuit 14 in accordance with the period difference output. The galvano mirror drive circuit 14 drives the galvano mirror (coil 3) with a sine wave current to which a predetermined offset current is added.

According to this configuration, the deviation of the optical scanning line caused by the galvanomirror is automatically corrected by feedback control, eliminating the need for adjustments that require advanced technology as in the past. The approach is not a problem either.

(Effects of the Invention) As explained above, according to the present invention, the deviation of the optical scanning line that occurs when a galvano mirror is used as an optical scanner can be automatically corrected with a relatively simple configuration, and at low cost. A high-performance image recording device can be realized.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
3 is a block diagram showing a specific example of a control unit that performs correction control, FIG. 4 is a configuration diagram showing an example of a galvano mirror, and FIG. 5 is an image recording apparatus using a galvano mirror. FIG. 6 is an explanatory diagram showing the behavior of an optical scanning line by a galvano mirror, and FIG. 7 is a schematic diagram of an image recording apparatus configured to correct distortion of a recorded image. 1...Mirror 2...Rotation support rod 3...
Coil 4.5... Permanent magnet 6... Light beam generator 7... Photosensitive drum 8.10.11... Photodetector 9... Lens 12... Period difference calculation circuit 1
3...Offset current generation circuit 14...Galvano mirror drive circuit Patent applicant Roku Konishi Photo Industry Co., Ltd. Agent Patent attorney Fuji Ijima 1 person

Claims (1)

[Claims] In an image recording device that uses a galvanometer mirror as an optical scanner, the difference in the period between the photodetectors that are placed near both ends of the scanning area to detect the light beam and the photodetection pulses output from each photodetector is calculated. 1. An image recording apparatus comprising: a period difference calculation circuit; and an offset current generation circuit that outputs an offset current for correcting a period difference to a galvanomirror drive circuit in accordance with the calculation output of the period difference calculation circuit.