JPH0381719A - Laser beam scanning device - Google Patents

Abstract

PURPOSE:To prevent a fault in detecting the write starting position of printing by forming the reflecting surface of a detecting mirror which reflects a part of laser beam reflected by a polygon mirror toward a photodetecting element to a concave surface having curvature with which the photodetecting element is brought into focus. CONSTITUTION:A part of reflected laser beam is made incident on the concave reflecting surface 19a of the detecting mirror 19 and reflected toward a photodiode 8. Therefore, the laser beam reflected in parallel with the exiting optical path of a laser diode 4 by the mirror 19 is made incident on the photodiode 8 to detect the write starting position of printing. When the optical path of the reflected laser beam made incident on a mirror 15 from a mirror 11 is deviated because of the face wobbling of a motor 10 or the surface inclination of the mirror 11, the incident light on the mirror 19 is also deviated. Since the reflecting surface 19a of the mirror 19 is formed of the concave surface having the curvature with which the diode 4 is brought into focus, the laser beam reflected by the mirror 19 is focused by the light receiving part of the photodiode 8 having the highest sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laser beam scanning device used, for example, in a laser beam printer.

[Prior Art] A laser beam printer employs a laser beam scanning device that scans a photoconductor by reflecting a laser beam emitted from a laser beam output element by a polygon mirror.

This laser beam scanning device guides the laser beam emitted from the laser beam output element through an optical system, reflects it on a polygon mirror with multiple reflective surfaces, and then passes the laser beam reflected by this mirror through the optical system to the photoreceptor. image on the photosensitive surface. By rotating the polygon mirror with a motor, the position of the reflective surface is changed relative to the laser beam that enters through the optical system, and each reflective surface corresponds to one line of printing on the photoreceptor. This is a device that repeats scanning with a laser beam.

When scanning the laser beam equivalent to one line of printing, the writing start position is determined by a part of the laser beam reflected by the polygon mirror being reflected by the detection mirror, and the reflected laser beam is incident on the photodetector element. By doing so, it is obtained for each reflective surface of the polygon mirror. Then, by detecting the writing start position of this print, scanning by laser light reflected by the same reflective surface of the polygon mirror is subsequently performed from the predetermined writing start position.

In order to detect the starting position of printing as described above, it is necessary to install the photodetecting element at a position where the sensitivity to laser light is the highest.

Therefore, in the past, when mounting a device supporting a photodetecting element, the angle of mounting a plate and the tightening degree of a plurality of screws were adjusted so that the photodetecting element was installed at an appropriate position.

[Problems to be Solved by the Invention] Incidentally, surface runout of the motor that rotates the polygon mirror (which occurs due to the motor structure; runout in the thickness direction of the polygon mirror centered on the axis of the motor) and Surface inclination (which occurs due to the processing of the polygon mirror, in which each reflective surface is not parallel to the mirror axis but slightly inclined) occurs. These causes movement of the optical path incident on the photodetector element.

If the deviation of the optical path due to the above-mentioned surface deflection or surface tilt is large, the laser beam reflected by the detection mirror will pass through the photodetecting element regardless of the adjustment of the mounting of the photodetecting element as described above. There is a problem in that it is likely to be removed from the light receiving section of the printer, resulting in poor detection of the starting position of the print. Further, there is a problem in that the adjustment work as described above is required to attach the photodetecting element, and the effort is troublesome.

SUMMARY OF THE INVENTION An object of the present invention is to provide a laser beam scanning device that can prevent failure in detecting the starting position of a print and eliminates the need to adjust the mounting position of a photodetector element.

[Means for Solving the Problems] In order to achieve the above object, in the laser beam scanning device of the present invention, the laser beam emitted from the laser beam output element is reflected by a polygon mirror and scanned onto the photoreceptor. The starting position of printing is detected by a photodetecting element that receives part of the laser beam reflected by the polygon mirror, and the part of the laser beam reflected by the polygon mirror is detected by the photodetector. The reflecting surface of the detection mirror that reflects toward the element is formed with a concave curved surface having a curvature that focuses on the detection element.

Furthermore, the laser beam scanning device of the present invention determines the starting position of printing when the laser beam emitted from the laser beam output element is reflected by a polygon mirror and scanned onto the photoreceptor.
In a device that detects a portion of the laser beam reflected by the polygon mirror with a photodetecting element that receives the laser beam, the detection mirror that reflects a portion of the laser beam reflected by the polygon mirror toward the photodetecting element; A cylindrical lens is disposed between the photodetecting element and the convex curved surface provided on the light incident side of the lens is formed to have a curvature that focuses on the photodetecting element.

[Function] In the laser beam scanning device of the present invention, the reflecting surface of the detection mirror that reflects part of the laser beam reflected by the polygon mirror toward the photodetecting element has a curvature that focuses on the detecting element. Because it is formed with a concave curved surface, any laser beam incident from the polygon mirror to any position on the detection mirror will be blocked by the detection mirror due to surface deflection of the motor that rotates the polygon mirror or surface tilt of the polygon mirror. It can be reflected so as to be focused on the detection element.

Further, in the laser beam scanning device of the present invention, a cylindrical lens is disposed between the detection mirror and the photodetection element that reflects a part of the laser beam reflected by the polygon mirror toward the photodetection element. Since the convex curved surface provided on the light incident side of this lens is formed with a curvature that focuses on the photodetecting element, it is possible to prevent the surface from deflecting due to surface deflection of the motor that rotates the polygon mirror or surface tilt of the polygon mirror. Even if a deviation occurs in the optical path from the detection mirror to the photodetecting element, the optical path passes through the cylindrical lens, so that the lens can converge the laser beam so that it is focused on the photodetecting element.

[Example] Hereinafter, a first example of the present invention will be described with reference to FIGS. 1 to 5.

FIGS. 2 to 4 show the overall configuration of the device. In the figure, reference numeral 1 denotes a main body of the apparatus whose top open portion is covered with a cover 2, which is attached to a part of a laser beam printer. A wiring board 3 is disposed outside one end wall 1a of the device main body 1,
A laser diode 4 as a laser light output element is attached to this substrate 3.

Note that 5 is a heat dissipation box screwed to the wiring board 3 via a spacer 6, which houses the laser diode 4 and is connected to the laser diode 4 via a heat transfer plate 7. This suppresses the temperature rise of the laser diode 4 and reduces changes in its output characteristics.

Mounted on the wiring board 3 are peripheral circuit components for the laser diode 4 and other control circuit components (not shown) for gain adjustment of the laser diode 4.

A photodiode 8 is attached to the one end wall 1a of the apparatus main body 1 as a light detection element for detecting the starting position of printing. As shown in FIG. 5, this diode 8 is fitted into a groove 9 formed on one end wall 1a of the device main body 1, and its light receiving surface faces into the device main body 1.

A motor 10 is disposed inside the device main body 1, and this motor 1
A polygon mirror 11 is attached to the rotation axis of 0. This mirror 11 has, for example, a flat hexagonal shape, and each of the six surfaces serves as a reflective surface.

A first mirror 12 is installed in the apparatus main body 1 in the vicinity of the polygon mirror 11 and facing its reflective surface. This mirror 12 is arranged at an angle of about 45 degrees with respect to the incident laser beam in order to reflect the laser beam emitted from the laser diode 4 and make it incident on the reflective surface of the polygon mirror 11.
It is installed at an angle. A collimator lens 13 and a plano-convex lens 14 are arranged between the first mirror 12 and the laser diode 4 in the main body 1 of the apparatus. The collimator lens 13 is attached to pass through the one end wall 1a. The plano-convex lens 14 has a flat surface on the first mirror 12 side and a convex surface on the collimator lens 13 side, and is disposed near the incident side of the first mirror 12.

A polygon mirror 11 is mounted on the inner surface of one side wall 1b of the device main body 1 facing the polygon mirror 11 with the first mirror 12 in between.
A second mirror 15 is attached to which the reflected laser light from the mirror enters. Inside the main body 1 of the apparatus, a third mirror 16 on which the laser beam from the second mirror 15 is incident is attached to the inner surface of the other side wall 1C opposite to the above-mentioned negative side wall. Further, inside the apparatus main body 1, a correction lens 17 is provided facing below the third mirror 16 and through which the laser beam reflected by the third mirror 16 passes.

A photosensitive drum 18 , which is an example of a photosensitive member that forms part of a laser beam printer, is arranged below the main body 1 of the apparatus, and a laser beam that becomes a spot light on the surface of the photosensitive drum 18 passes through a correction lens 17 . It is designed to be incident through the beam.

A detection mirror 19 is mounted inside the apparatus main body 1 on the inner surface of the other end wall 1d that faces the one end wall 1a with the polygon mirror 11 in between. This mirror 1
9 faces each of the second mirror 15 and the photodiode 8, and the optical path reflected by the mirror 19 and reaching the photodiode 8 (that is, the incident optical path to the photodiode 8) is from the laser diode 4 to the first laser diode 8.
It is provided so as to be parallel to the output optical path of the laser diode 4 leading to the mirror 12. The reflective surface 19a of the detection mirror 19 is formed of a concave curved surface having a curvature that focuses on the light receiving portion of the photodiode 8, as shown in FIG.

When the laser beam scanning device having the above configuration is used, the laser beam is modulated based on the printed information and is emitted from the laser diode 4. This laser light passes through each lens 13 , 14 in sequence, is reflected by the first mirror 12 , and enters the reflective surface of the polygon mirror 11 that is being rotated by the motor 10 .

The laser beam reflected by the reflective surface of the polygon mirror 11 is then reflected by the second mirror 15. A part of the reflected laser light enters the concave reflective surface 19a of the detection mirror 19 and is reflected toward the photodiode 8. That is, the laser beam reflected by the detection mirror 19 in parallel to the output optical path of the laser diode 4 is incident on the photodiode 8 . As a result, the starting position of printing is detected. The optical path for this detection is shown in Figures 2 and 3.
This is indicated by the optical path indicated by the solid arrow in the figure.

In such a detection, if the optical path of the reflected laser beam entering the second mirror 15 from the polygon mirror 11 is slightly shifted due to the surface deflection of the motor 10 or the surface tilt of the polygon mirror 11, the second mirror 15 is adjusted accordingly. The optical path incident on the detection mirror 19 also deviates.

Nevertheless, since the reflective surface 19a of one detection mirror is formed of a concave curved surface with a curvature that focuses on the photodiode 4, even if a deviation occurs in the incident optical path to one detection mirror, this The laser beam reflected by the mirror 19,
It is possible to focus and receive light on the light receiving portion of the photodiode 8 having the highest sensitivity.

Therefore, it is possible to prevent failure in detecting the starting position of printing due to the above-mentioned surface wobbling or tilting, and the mounting of the photodiode 8 can eliminate the need for a structure and adjustment work for adjusting the position. Furthermore, since the effects of surface runout and surface tilt can be prevented as described above, the tolerance for these surface runout and surface tilt can be increased, and the manufacture of the motor 10 and the polygon mirror 11 can be facilitated.

After the above detection, the laser beam reflected by the same reflective surface of the polygon mirror 11 (see the optical path indicated by the two-dot chain line in FIGS. 2 and 3) is reflected by the second mirror 12 and reflected by the second dotted line. After being incident on the 3 mirror 16 and being reflected there,
The light passes through the correction lens 17 and reaches the surface of the photosensitive drum 18 to form an image.

As a result, the photosensitive drum 18 corresponding to one line of printing is
The upward scanning of the laser beam is performed from a predetermined writing start position.

Then, the detection of the starting position of printing for each reflective surface of the polygon mirror 11 as described above and the subsequent scanning of one line with the laser beam are repeated, so that the positions of the beginnings of each line are aligned. Can print.

Next, a second embodiment of the present invention will be described with reference to FIGS. 6 and 7. The second embodiment differs from the first embodiment in that an optical path correction means is provided on the optical path from the detection mirror to the photodiode, and this point will be explained below. Note that the other configurations are similar to those of the first embodiment, so the same parts are given the same reference numerals and the explanation thereof will be omitted.

In this second embodiment, the detection mirror 21 used has a flat reflecting surface 21a.

A cylindrical lens 22 serving as optical path correction means is disposed between the detection mirror 21 and the photodiode 8 facing it.

This lens 22 is provided on the photodiode 8 side, and has a flat surface on the diode 8 side, and is connected to the detection mirror 2.
The first side surface is formed as a convex curved surface 22a. The convex curved surface 22a is formed to have a curvature that causes the laser light incident thereon to be focused on the photodiode 8.

In this second embodiment, the optical path of the laser beam is the same as in the first embodiment, but the laser beam reflected by the detection mirror 21 toward the photodiode 8 passes through the cylindrical lens 22 and is converted into a photodiode. The light is focused on the diode 8 and enters the light receiving portion of the diode 8. Therefore, even if a deviation occurs in the optical path from the detection mirror 21 to the photodiode 4 due to surface deflection of the motor or surface tilt of the polygon mirror 11, the deviation is corrected and the laser beam is removed from the light receiving part of the photodiode 8. This can be prevented. Therefore, the intended purpose of the present invention can also be achieved in this second embodiment.

[Effects of the Invention] In the laser beam scanning device of the present invention described above, a detection mirror is used to reflect a part of the laser beam reflected by the polygon mirror toward the photodetecting element at the starting position of printing. Since the reflective surface is formed of a concave curved surface with a curvature that focuses on the photodetecting element, it prevents the laser beam from deviating from the light receiving part of the photodetecting element due to surface wobbling or surface tilt, and makes it possible to start printing. In addition to preventing failure in detecting the starting position, since the light reception of the photodetecting element can be made constant in this way, it is not necessary to adjust the position of the photodetecting element when installing it.

Further, in the laser scanning device of the present invention, a detection mirror that reflects a part of the laser beam reflected by the polygon mirror toward the photodetecting element that is the starting position of printing, and the photodetecting element are provided. In between, a cylindrical lens whose convex surface on the light incident side has a curvature that focuses on the photodetecting element is disposed, so that the laser light does not reach the photodetecting element due to surface deflection or surface tilt. By preventing it from coming off the light receiving area, it is possible to prevent detection errors at the starting position of printing, and since the light reception of the photodetector element can be made constant in this way, there is no need to adjust the position of the photodetector element when installing it. .

[Brief explanation of drawings]

1 to 5 show a first embodiment of the present invention, FIG. 1 is a diagram showing the optical path from the polygon mirror to the photodiode, FIG. 2 is a diagram showing the optical path of the laser beam of the entire device, and FIG. Figure 3 is a partially sectional plan view of the device with the lid removed;
Figure 4 is a sectional view of the entire device along line IV-■ in Figure 3;
FIG. 5 is a perspective view showing the photodiode and its attachment. 6 and 7 show a second embodiment of the present invention, and FIG.
The figure shows the optical path from the polygon mirror to the photodiode, and FIG. 7 shows the optical path of the laser beam throughout the apparatus. 4...Laser diode (laser light output element), 8...
... Photodiode (light detection element), 10 ... Motor, 11 ... Polygon mirror 18 ... Photoreceptor, 1
9...Detection mirror 19a...Reflecting surface, 21...
・Detection mirror 2: lindrical lens, a: convex curved surface.

Claims (1)

[Claims] 1. When the laser beam emitted from the laser beam output element is reflected by a polygon mirror and scanned onto the photoconductor, the starting position of printing is determined by the laser beam reflected by the polygon mirror. A reflective surface of the detection mirror that reflects a part of the laser beam reflected by the polygon mirror toward the photodetector element,
A laser beam scanning device characterized in that the laser beam scanning device is formed of a concave curved surface having a curvature that focuses on the photodetecting element. 2. When the laser beam emitted from the laser beam output element is reflected by the polygon mirror and scanned onto the photoconductor, the starting position of printing is determined by receiving part of the laser beam reflected by the polygon mirror. A cylindrical lens is disposed between a detection mirror that reflects a part of the laser beam reflected by the polygon mirror toward the photodetection element and the photodetection element, in the detection using the photodetection element, A laser beam scanning device characterized in that a convex curved surface provided on the light incident side of the lens is formed to have a curvature that focuses on the photodetecting element.