JPH03269311A - Optical beam position detector - Google Patents

Abstract

PURPOSE:To improve the response speed and sensitivity of the optical beam position detector by arranging two light shielding parts between two photodetectors and two lenses for always making optical beam incident upon the vicinity of the centers of respective photodetectors. CONSTITUTION:Optical beams L1 are made incident upon the ridge line of a prism 1 whose surface forms a reflecting face and its vertex forms an obtuse angle and divided into beams L2a, L2b and respective beams L2a, L2b are detected by respective photosensors 3a, 3b and the center position of the incident beams L1 is found out by the difference between the two detected values. The incident beams are always concentrated into the vicinity of the centers of respective photosensors 3a, 3b by the lenses 2a, 2b inserted between the prism 1 and the photosensors 3a, 3b. Scattered light L4 generated by the photosensors 3a, 3b and the lenses 2a, 2b is shielded by the light shielding parts 4a, 4b and prevented from being made incident upon the opposite sensors as disturbance.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention is directed to measuring the position of a light beam used when measuring the dynamic tilt angle of a rotating polygon mirror (so-called polygon mirror) used in, for example, a laser printer. Concerning a measuring device.

(Prior art) Conventional methods for measuring the incident position of a light beam include COD,
Various methods have been proposed, such as PSD, a method using a two-split sensor, a method using a right-angle prism, and a method using a slit.

First, FIG. 3 shows an example in which a PSD is used in an optical system for measuring the tilt angle of a rotating polygon mirror using these light beam position sensors. Here, 25 is a PSD, 23 is a rotating polygon mirror, 21 is a light source, and 22 is a condensing lens.

The laser beam emitted from the light source 21 is reflected by the reflective surface of the rotating polygon mirror 23 and crosses the photosensitive surface of the PSD 25 . If the angle of the reflecting surface of the rotating polygon mirror 23 is tilted, the angle of the reflected beam changes and the position across the PSD 25 changes.

The PSI 25 can detect this change in the beam incidence position and measure the amount of surface tilt of the rotating polygon mirror 23.

Next, FIG. 4 shows an example in which the same measurement is performed using a slit. Here, 41 is a light source, 42 is a rotating polygon mirror, 43 is a slit, and 44 is a photosensor. The position of the spot incident on the slit 43 and the photosensor 44 is set on the rotating polygon mirror 4.
Suppose that it moves like S1 to S4 with the rotation of 2.

When the spot reaches position 82, the incident beam is not eclipsed by the slit and the entire amount of light enters the photosensor. When the spot moves to the position S3, a portion of the incident beam is eclipsed by the slit 43, and the remaining amount of light enters the photosensor. If the angle of the reflecting surface of the rotating polygon mirror 42 is tilted, the angle of the reflected beam will change and the rate at which it is eclipsed by the slit 43 will change. Even if the angle slightly changes, the light amount at S2 does not change, and the light amount sensed by the photosensor at s3 is affected by the change in angle, so the light amount at 82 and 83
By measuring the change in the beam incident position from the ratio of the light amounts at , it is possible to determine the amount of surface tilt of the rotating polygon mirror 23.

Next, FIG. 5 shows an example in which the same measurement is performed using a right-angle prism. Here, 31 is a right-angled prism whose surface is a reflective surface.
32a and 32b are photosensors, 33 is a rotating polygon mirror,
L31-L33 are beams. The incident beam L31 reflected by the rotating polygon mirror 33 is divided into upper and lower parts at the vertex of the rectangular prism 31, and the beam L32a is directed to the photosensor 32a.
The beam L32b is transmitted to the photosensor 32. b respectively. If the angle of the reflecting surface of the rotating polygon mirror 42 has an error, the angle of the reflected beam changes and the ratio of the upper and lower light amounts divided at the apex of the rectangular prism 31 changes.

For example, when L31 tilts upward in the figure, beam L32a increases and beam L32b decreases. Since the total light amount ratio of the beam L32a and the beam L32b is constant, the incident beam position can be determined from the ratio of the total output of the photosensor 32a and the photosensor 32b and the difference between each output. You can know the amount of trouble.

(Problems to be Solved by the Invention) The conventional light beam position detection method has the following problems.

First, the method using the PSD 25 has a problem in that the PSD 25 has a limited response speed and cannot be used to measure the rotating polygon mirror 23 which rotates at a high number of revolutions.

(5) Next, in the method of using the slit 43, there is no problem in terms of response speed as it is sufficient to use an element with a high response speed for the hook 1-sensor 44. Since there is a time lag at the time S3 when the position of the beam is measured using the method, there is a problem that if the beam itself fluctuates in light intensity due to noise from the light source 41 or the like during that time, it becomes impossible to accurately measure the incident position of the beam. Next, in the method using the right angle prism 31, the beam L
31 and each sensor 32 due to the movement of the beam L31.
Since the output difference between the photosensors a and 32b can be measured at the same time, there is no problem with the noise of the light intensity fluctuation of the light source.

Since the photo sensors 32b are located in facing positions, the reflected light and scattered light L33 of the beam L32a that first entered one photosensor, for example 32a, enters the other photosensor 32b located in the facing position, causing the right angle prism 31 Beam L32a divided by.

It is said that the light intensity of L32b cannot be measured accurately (6) There was a problem.

(Means for Solving the Problems) The present invention has been made to solve the above problems, and as explained with reference to FIGS. 1 and 2 corresponding to embodiments, the light beam position detection device according to the present invention A fixed prism mirror 1 having an obtuse angle of 95 degrees or more divides the beam L1 into two by reflection, and reflected light L2a divided into two by the prism mirror 1.

Comprising two light receiving elements 3a and 3b that receive L2b,
A light beam position detection device is characterized in that the incident position of the light beam L1 is detected from the light amount ratio of the two divided lights L2a and L2b, and the two light receiving elements 3a and 3
Light shielding parts 4a and 4b are provided between the prism mirror 1 and the two light receiving elements 3a and 3b to prevent each scattered light from entering the other light receiving element, and a prism mirror 1 is provided between the prism mirror 1 and the two light receiving elements 3a and 3b. The lens 2 is arranged so that the reflected light beams L2a and L2b always enter near the center of the light receiving elements 3a and 3b.
A, 2b are provided.

Furthermore, instead of the prism mirror I, a fixed prism 11 having an obtuse angle of 95 degrees or more is used to divide the light beam L11 into two by transmission, and the transmitted light L12a is divided into two by the prism 11.

A light beam position detection device comprising two light receiving elements 13a and 13b that receive light L12b, and detecting the incident position of the light beam from the light amount ratio of two divided light beams 2a and L12b. , the two light receiving elements 13
A light shielding part 14 is provided between the prism 11 and the two light receiving elements 13a and 13b to prevent each scattered light from entering the other light receiving element. It is characterized in that lenses 12a and 12b are provided so that the light beams L12a and L12b are always incident near the center of the surfaces of the light receiving elements 13a and 13b.

(Function) A light beam L is applied to the ridgeline of the obtuse prism 1 whose surface is a reflective surface.
Inject the beam and divide it. Each divided beam L2
a and L2b are detected by two photosensors 3a and 3b, and the outputs of the respective photosensors are taken as A and B, respectively, and (A-B)/(A+B) is calculated. This value is O when the center of the light beam L and the ridgeline of the prism L coincide.
This increases in proportion to the amount of deviation from the center. Therefore, the position change of the incident light beam L1 can be determined from this value. Furthermore, since lenses 2a and 2b are inserted between the obtuse prism 1 and the photosensors 3a and 3b, even if the incident position of the light beam LL on the prism l changes, the reflected lights L2a and L2b of the obtuse prism 1 will be reflected from the lenses 2a and 2b. Therefore, the light is always focused near the center of the photosensors 3a and 3b, and a stable signal can be sensed. Further, reflected light L5 and scattered light L4 are generated at the photosensors 3a and 3b and the lenses 2a and 2b, but as for the reflected light L5, since the reflective prism 1 is at an obtuse angle and the photosensors 3a and 3b are not in a position facing each other, for example, on one side. Sensor 3a
The reflected light L5 will no longer be directly incident on the other sensor 3b, and since the light shielding parts 4a and (9) 4b are provided to block the scattered light L4, the same effect can be achieved, making it possible to perform measurements with less disturbance. Become.

(Example) FIG. 1 is an explanatory diagram of a first embodiment according to the present invention.

A light beam L1 is incident on the ridgeline of the prism 1 whose apex has an obtuse angle and whose surface is a reflective surface, and is split.

The divided beams L2a and L2b are detected by two photosensors 3a and 3b, and the outputs of the photosensors 3a and 3b are defined as A and B, respectively (A-B)/
(A+B) is required. This value becomes O when the center of the light beam LL and the ridgeline of the prism 1 coincide, and increases in proportion to the amount of deviation from the center. For example, if the position where the center of the incident beam LL enters the ridgeline of the prism moves upward in the diagram, L2a of the reflected light from the prism increases,
L2b decreases. Therefore, the output of each photosensor is A
increases and B decreases. Since the total amount of light of the incident beam does not change, (A + B) does not change, but (A - B) increases, so (A - B) / (A + B) increases, thereby increasing the incidence of the incident beam L1. (10) The amount of change in position is determined. Furthermore, if the light intensity of the incident beam is halved in this state, the output ratio A:B of each sensor will not change unless the incident position changes, but since the total light intensity has been halved, A and B will each be halved ( A-B
) will also be halved. On the other hand, since (A+B) is also halved, the value of (A-B)/(A+B) does not change after all. Therefore, according to this method, only the variation in the incident position of the beam Ll can be determined without being affected by the variation in the light amount of the incident beam LL.

Furthermore, an obtuse prism l and a photosensor 3a.

Lenses 2a and 2b are inserted between lens 3b. Even if the incident position of the beam L1 changes, the reflected light L2a of the obtuse prism 1,
L2b is always connected to the photo sensor 3 by lenses 2a and 2b.
The light is focused near the centers of a and 3b, and a stable signal can be sensed. Furthermore, reflected light L5 and scattered light L4 are generated at the photosensors 3a and 3b and the lenses 2a and 2b, but the reflected light L5 is reflected at L5 in the figure because the reflective prism 1 is at an obtuse angle and the photosensors 3a and 3b are not in a facing position. As shown, the reflected light from one sensor does not directly enter the other sensor. Regarding the scattered light L4, since the light shielding parts 4a and 4b are provided to block this, the scattered light from one sensor does not directly enter the other sensor as shown in L4 in the figure, so measurement with less disturbance is possible. .

Furthermore, each of the photosensors 3a and 3b is capable of measuring a rotating polygon mirror having an extremely high frequency by selecting and using an element with a fast response speed. Furthermore, the sensitivity of the optical beam position detection device is determined by the beam L incident on the ridge of the obtuse prism 1.
Since the beam diameter of the beam can be made as large as desired by reducing the beam diameter of the beam, the sensitivity can be adjusted in any way by adjusting the beam diameter of the incident beam L1, and an optical beam position sensor with extremely high sensitivity can be realized. It was confirmed that an optical beam position measuring device prototyped using this principle could measure a beam movement amount of 0.5 μm with an incident beam diameter of 150 ILm.

FIG. 2 shows a second embodiment of the present invention, in which 11 is an obtuse-angle transmission prism, 12a and 2b are lenses, 13a and 13b are photosensors, and Li1 and Li2 are light beams. In this example, the same thing as in the first example is performed using a transmission prism. The light beam Lll incident on the vertex of the obtuse-angle transmission prism 11 is split by the refraction of the prism 11, and passes through lenses 12a and 12b, respectively, to each photo sensor 13a.

13b. The rest of the discussion can be the same as in the first embodiment.

(Effects of the Invention) As explained above, according to the present invention, it is possible to construct an extremely sensitive light beam position sensor that has a fast response speed, is unaffected by changes in the light intensity of the light source, and eliminates unnecessary reflected light and scattered light. .

[Brief explanation of drawings]

1 and 2 show a first embodiment of a light beam position detection device according to the present invention, and FIG. 2 shows a second embodiment. FIG. 3, FIG. 4, and FIG. 5 are explanatory diagrams of conventional examples. 1... Obtuse reflective prisms 2a, 2b, 12a, 12b, 2Sl... Lens 3 a
, 3 b, 13 a, 13 b, 32 (1, 32 b. (13) 44... Photosensor 4a, 4b, 14 - Light shielding part 11... Obtuse angle transmission prism 21.41... Light source 23.33 , 42...Rotating polygon mirror 25...PSD 43...3 slits...Right angle reflecting prism L, L 2 a, L 2 b, L 4,
L5, L11. L12a, L12b, L3L, L32a, L32b. L33...Light beam

Claims (2)

[Claims] (1) A fixed prism mirror having an obtuse angle of 95 degrees or more that divides a light beam into two by reflection, and two light-receiving elements that receive the reflected light divided into two by the prism mirror; A light beam position detection device is characterized in that the incident position of the light beam is detected from the light intensity ratio of the two divided lights, wherein each scattered light is transmitted between the two light receiving elements to the other light receiving element. A light shielding portion is provided to prevent the light from entering, and a lens is further provided between the prism mirror and the two light receiving elements so that the light beam reflected from the prism mirror always enters near the center of the surface of the light receiving element. A light beam position detection device characterized by: (2) In place of the prism mirror, a fixed prism with an obtuse angle of 95 degrees or more is used to divide the light beam into two by transmission, and two light receiving methods are used to receive the transmitted light divided into two by the prism. It is equipped with an element and is divided into two parts.
A light beam position detection device is characterized in that the incident position of a light beam is detected from the light intensity ratio of two lights, the light beam position detecting device being characterized in that the light beam position detecting device detects the incident position of the light beam from the light intensity ratio of the two light beams, and the device is configured such that each scattered light does not enter the other light receiving element between the two light receiving elements. A light shielding part is provided for the purpose of transmitting the light, and a lens is further provided between the prism and the two light receiving elements so that the light beam transmitted through the prism always enters near the center of the surface of the light receiving element. Beam position detection device.