JPS5962821A - Optical scanner - Google Patents

Abstract

PURPOSE:To condense a laser light into a minute spot without an Ftheta lens, by introducing a movable mirror as a focus controller to an optical system and displacing the mirror in the direction of the optical axis by a prescribed quantity in accordance with a deflection angle at which an optical scanner polarizes the laser light. CONSTITUTION:A deflected laser light is total-reflected by a polarizing prism 3 and is reflected by a mirror 6, and the laser light returned to the polarizing prism 3 passes a V4 wavelength plate 4 backward and forward twice to become a laser light which is polarized in the direction orthogonal to the polarization direction of the first incidence to the polarizing prism 3. Therefore, the laser light reflected by the mirror 6 is transmitted through the polarizing prism 3 and is led to an optical scanner 9. A displacing element 7 as the focus controller displaces the mirror 6 in parallel with the optical axis as shown by an arrow 20. A focus control circuit 13 which drives the displacing element 7 converts a scanning signal generated by a scanning signal generator 11 with a proper functional relation and applies the converted signal to the displacing element 7. A piezoelectric material bimorph element has a good frequency responsiveness as the displacing element 7 and has a structure where a reinforcing plate such as a phosphor bronze 18 or the like is interposed between piezoelectric material ceramics 17, and a voltage is applied across electrodes of ceramic plates and the phosphor bronze to displace this element as shown by an arrow 19.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a laser beam scanning device, such as a laser printer.

[Background of the invention]

A conventional laser printer is shown in FIG. Semiconductor laser 1
The laser beam emitted from the coupling lens 2 (focal length f,
incident on . FIG. 1 shows a case where a galvano-mirror optical deflector is used as the optical scanner. In the optical scanner, a scanning signal generated by a scanning signal generator 11 is sent to an amplifier 1.
4, and the optical scanner scans the photosensitive drum 10, which serves as a surface to be scanned, with laser light. The photosensitive drum 10 is rotating in the direction of the arrow, and the entire surface of the photosensitive drum can be scanned with light. Lens 15 (also called Fθ lens) has the function of concentrating the laser beam into a minute spot on the photosensitive drum at the position corresponding to the deflection angle θ, no matter what deflection angle θ the laser beam is deflected by the optical scanner l. A pattern signal generated by a pattern generation circuit 12 is applied to the semiconductor laser 1, and the semiconductor laser 1 outputs a laser beam whose light intensity is modulated according to the pattern signal and optically records the light on the photosensitive drum. .

However, the Fθ lens used in the conventional laser printer shown in Figure 1 has a large diameter and large size in order to obtain the desired performance for all deflection angles scanned by the optical scanner, and is small and inexpensive. This has been a problem when applied to laser printers.

[Purpose of the invention]

The present invention was made in order to eliminate the above-mentioned drawbacks, and it is possible to focus the laser beam into a predetermined minute spot at any laser beam scanning position on the photosensitive drum without using an Fθ lens. ,focus! He gave birth to the l+lJ control device.
The purpose is to provide a small and inexpensive laser printer.

[Summary of the invention]

In order to achieve the above object, the laser printer of the present invention uses a vibrating mirror as a focus control device in the optical system (instead of the F゛θθ lens waste in the conventional laser printer shown in FIG. 1). According to the polarization angle at which the optical scanning device polarizes the laser beam, one mirror is displaced in a predetermined direction in the 11+ direction, and the laser beam is always reflected even at the angle scanning position on the photosensitive drum. Narrow down to a predetermined minute spot and make a characteristic good luck.

[Embodiments of the invention]

Hereinafter, the principle of the present invention will be explained using FIGS. 2 and 3. For example, in Fig. 2, the parallel laser beam is reflected by the semi-transparent mirror I5, and the lens 5 (focal length f2).
and reaches mirror 6.

The laser beam reflected by the mirror 6 passes through the lens 5 and the semi-transparent mirror 15 again. Consider an optical system in which light passes through a lens 8 (focal length f3) and enters an optical scanner 9.

The mirror 6 is placed near the focal point of the lens 5.

Now, if the mirror 6 does not vibrate, the image forming position of the scanning laser beam is formed on the circumference indicated by g116, which is centered on the optical scanner, and the photosensitive drum position 1o is the image forming point. A deviation Δ occurs.In order to correct the imaging deviation Δ, it is necessary to displace the mirror 6.

Δ is expressed by the following equation using the deflection angle θ and the distance R from the optical scanner to the photosensitive drum.

When the deflection angle θ is small, Δ is approximated as follows.

At the same time, the relationship between the displacement amount δ and Δ of the mirror 6 is determined using FIG. When the amount of displacement δ=0, the laser beam reflected by the mirror 6 placed at the focal point of the lens 5 exits the lens 5 as parallel light as shown by the solid line, and forms an image at the focal point of the lens 8. At the same time, the case where the mirror 6 is displaced by δ is shown by a chain line.

When the mirror 6 is displaced by δ, the imaging point of the lens 5 is displaced by 2δ (as shown in the figure), the laser beam emitted from the lens 5 becomes a diverging beam, and the imaging point focused by the lens 8 moves by Δ. .

The relationship between δ and Δ can be determined from the formula for vertical magnification. Therefore, the relationship between δ and deflection angle θ is expressed by the formula (
3), and can be expressed by the following equation using equation (1).

When the deflection angle θ is small, the following equation (5) is approximated.

As explained above, according to equations (4) and (5), the image forming point is shifted at any laser beam scanning position on the optical photosensitive drum when the mirror 6 is displaced by a predetermined value (d) according to the deflection angle θ of the optical scanner. Δ is eliminated, and it becomes possible to always narrow down the laser beam to a predetermined minute spot.

Hereinafter, the present invention will be explained in detail with reference to Examples.

FIG. 4 shows a laser printer according to the present invention (O). Similarly to FIG. 1, laser light emitted from a semiconductor laser 1 (converted into parallel light by four coupling lenses 2).

In FIG. 2, an example is shown in which a semi-transparent mirror 15 is used when explaining the laser printer of the present invention, but instead of the semi-transparent mirror, a deflection prism 3. λ/4 wavelength plate 4
When using this method, the utilization rate of laser light is dramatically improved. That is, first, the polarized laser beam is totally reflected by the polarizing prism, then reflected by the mirror 6, and returned to the polarizing prism again (since it passes through the 4λ/4 wavelength plate twice and returns twice) , the laser light is polarized at right angles to the direction of polarization when it first enters the polarizing prism.

Therefore, the laser beam (i
It passes through a polarizing prism and is guided to an optical scanner. lens 5
, the function of the lens 8 has already been explained in FIG.

The old displacement element 7 of the focus control circuit moves the mirror 6 to the arrow 20.
As shown in , it is displaced in a direction parallel to the optical axis. The focus control circuit 13 that drives the displacement element 7 includes a scanning signal generator 11
The scanning signal generated by the converter converts the scanning signal according to an appropriate functional relationship and applies the converted signal to the displacement element 7.

When the mirror 6 is displaced by the displacement element in proportion to the square of the deflection angle as shown in equation (5), FIG. 5 shows a block diagram of the focal point X1i control circuit that drives the displacement element.

The amplifying section shown in FIG. 5 applies a signal to the displacement element after adjusting the amplification factor.

The displacement element may be one using a piezoelectric material, one called a voice coil made of a coil or a permanent magnet, or one using a magnetostrictive or electrostrictive element. In particular, piezoelectric bimorph elements have good frequency response and are excellent when used as displacement elements. FIG. 6 shows the structure of a piezoelectric bimorph element used in the present invention.

1) ZTθ] Gosaki piezoelectric ceramics 17 and phosphor bronze 1
It has a structure in which reinforcing plates such as No. 8 are sandwiched together. An electrode is applied to the entire surface of the piezoelectric ceramic plate, and by applying a voltage between this electrode and the phosphor bronze, the piezoelectric ceramic plate is displaced in the direction of arrow 19.

In the laser printer of the present invention shown in FIG. 4, a galvano-mirror optical deflector is used as the optical scanner, but a rotating polygonal mirror may also be used. It goes without saying that the present invention uses not only semiconductor lasers but also all other laser devices.Furthermore, although a laser printer is cited as an embodiment of the present invention, devices in general that require a laser scanning optical system, particularly , it goes without saying that the present invention can be effectively utilized in devices that require scanning on a flat surface at a large deflection angle.

〔Effect of the invention〕

As explained above, if the present invention is used, on the scanned surface,
Maintaining a constant laser spot diameter at any scanning deflection angle can be controlled using an electrical circuit, making it possible to perform high-precision, high-quality optical scanning recording, and the entire device can be made lighter and more compact. There are advantages.

[Brief explanation of drawings]

FIG. 1 (e) is a diagram illustrating a conventional printer; FIGS. 2 and 3 are diagrams illustrating a focus control device suitable for the optical scanning device of the present invention; and FIG. 5 is a diagram showing an embodiment of the present invention, FIG. 5 is a diagram showing the configuration of the focal point 1b control circuit,
FIG. 6 is a diagram showing the structure of a piezoelectric bimorph element. Fig. 1 Fig. 5 Sangjing, control port No. 1'Jrq

Claims (1)

[Scope of Claims] 1. A light source that emits a laser beam, an optical scanner that scans the cough laser beam, and a scanned surface made of a display or recording material that displays or records with the scanned laser beam. ,
An optical device comprising an optical means for guiding laser light from a light distribution source to the surface to be scanned, further comprising a focus control device for displacing a mirror constituting the optical means in accordance with the deflection angle of the optical scanner. An optical scanning device with various characteristics. 2. A deflection prism and a λ/4 wavelength plate are used as optical means for guiding the laser beam to the mirror provided with the focus control device,
2. The optical scanning device according to claim 1, wherein the focus control device uses a piezoelectric bimorph element.