JPS5924819A - Mechanism for aligning optical axis of interference measuring device - Google Patents

Abstract

PURPOSE:To facilitate adjustment operation by using a photodetector having quadrisected photodetection surfaces for the spot imaging face of the beams reflected by a reference plane and a sample plane, and controlling a means for driving an adjustment mechanism for the inclination of the sample plane in accordance with the output signal thereof. CONSTITUTION:The position over the entire part of a quadrisected photodetector is adjusted so that the spot 12 by the beam reflected from a reference plane 4 is projected to the central part of the respective photodetectors I , II, III, IV of said photodetector. When a sample 5 is installed, the spot by the beam reflected from the sample plane owing to the inclination of the plane is projected onto any photodetector surface among I , II, III, IV. A control part CPU compares the four outputs of the quadrisected photodetectors, judges the direction and the extent of the rotation where and which the driving motors at fulcrum points A, B, C for adjustment need be rotated and outputs the results thereof to said motors. The inclination of the sample 5 is adjusted by the fine adjusting feed in the optical axis direction of an adjusting screw 17 rotated by the motors 22. The optical axes of the reference plane and the sample plane are easily aligned with good accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical axis alignment mechanism for a sample surface in an interference measurement apparatus used for measuring the surface state of optical elements such as lenses and mirrors, and particularly to an automatic optical axis alignment mechanism.

The above-mentioned interference measurement device is generally called an interferometer, and its principle is to align the optical axes of the reference surface and the sample surface, irradiate them with a laser beam, and place an imaging lens in the optical path of the reflected beam from each. The surface condition of the sample surface is measured by projecting interference fringes generated between the reference surface and the sample surface onto a screen.

Therefore, for accurate measurements, it is essential to accurately align the optical axes of the sample surface and the reference surface.

To align the optical axis of the sample surface in a conventional interferometer, before producing interference fringes, the spots of the beam reflected by the reference surface and the sample surface are projected onto a screen, and while the two spots are viewed with the naked eye, the spots reflected by the reference surface are adjusted. This was done by manually operating an adjustment dial to adjust the inclination of the sample surface so that the reflected spot 47) by the sample surface coincided with the position. Generally, there are three or more dials, and the direction of movement of the spot during the tilt adjustment process generally does not match the direction of the rotational force of the adjustment dial, so that adjustment depends solely on the operator's experience. In addition, the spots have a certain diameter, making it impossible to superimpose them with high precision through observation with the naked eye. Furthermore, depending on the force with which the sample is placed, the spot to be aligned often moves off the screen and does not appear, and in such cases it takes a very long time to align the optical axes.

For these reasons, although interference measurement devices are capable of measuring surface conditions with extremely high precision, they have rarely been used for product inspection on factory lines. However, in recent years, ultra-precise surface shapes have been required, and there has been an increasing desire to use interference measuring devices as inspection means for production lines.

In view of this need, the present invention solves the above-mentioned problems regarding the optical axis alignment of conventional interference measuring devices, allows even non-skilled personnel to align the optical axis of the sample surface with high precision in a short time, and also uses a laser beam. When a single sample has multiple measurement surfaces, such as a rotating polygon mirror commonly used as a deflector in printers, etc., the optical axis can be used to easily measure the relative position of each measurement surface. The object is to provide an alignment mechanism, especially an automatic optical axis alignment mechanism.

EMBODIMENT OF THE INVENTION Hereinafter, the present invention will be described in detail based on drawings showing embodiments thereof.

FIG. 1 is a diagram showing an embodiment in which the present invention is applied to a Fizeau type interference type.

In the optical path of the laser beam emitted from the laser light source 1, a beam diffusing lens 2, a beam splitter 3, and a reference plane 4 are sequentially provided on the -@ line. The beam splitter 3 transmits the beam emitted from the light source 1 and makes it reach the reference surface 4, but the beam reflected by the reference surface 4 is thereby reflected and bent by 90 degrees. An imaging lens 6 and a screen 7 are provided on the imaging surface of the imaging lens 6 on the optical path of the beam reflected by the beam splitter 3. A sample 5 is mounted close to the reference plane 4 with its optical axis aligned therewith. A second beam splitter 8 is provided between the beam splitter 3 and the imaging lens 6 in a direction of 45 degrees with respect to the optical path, and this splits the beam to proceed in a direction perpendicular to the original optical path. A lens 9 and a four-part light-receiving element (photodiode or the like) 10 are provided on the image forming surface of the lens 9 along the path.

- In the structure described above, a laser beam emitted from a laser light source 1 is diffused by a beam diffusing lens 2, transmitted through a beam splitter 3, reflected by a reference surface 4 and a sample surface 5, and then The light reaches the beam splitter 3 again while causing interference due to the optical path difference between the two, where it is reflected in the right angle direction, and interference fringes are projected onto the surface of the screen 7 via the imaging lens 6.

The optical axis alignment of the sample surface, which is performed prior to interference measurement, is performed as follows.

Beam reflected from reference surface 4 (shown by solid line in Figure 1)
The beam reflected by the sample surface 5 (indicated by a broken line) is reflected by the second beam splitter 8, and is imaged as spots on each side on the surface of the 4-split light-receiving element 1O via the lens 9. Generally, this spot is caused by multiple reflections between the reference surface and the sample surface, in which a plurality of beams (indicated by arrows in FIG. 1) are reflected in the direction of the inclination of the sample surface 5. spots are formed.

In the apparatus of the present invention, instead of viewing these spots with the naked eye and adjusting the inclination of the sample surface so that the spot on the sample surface coincides with the spot on the reference surface, the output signal of the 4-split light receiving element 10 is used. The feature is that the driving means for adjusting the inclination of the sample surface is controlled.

FIG. 2 shows an example of the inclination adjustment mechanism for the sample surface 5. As shown in the figure, the sample 5 is placed at three points on the periphery: ■, ■,
0 is held between the tip of a support pin 16 which is elastically movable in the axial direction via a spring 15 on a ring-shaped base plate 11, and the tip of an adjustment screw 17 provided opposite to the support pin 16.

(The figure BL shows the details of the gripping part, and the adjustment screw 1
7 is screwed into a screw hole 19 drilled in a plate member 18 fixed to the device parallel to the reference plane 4 so as to be able to move smoothly in the direction of the axial force, and is adjusted via gear trains 20 and 21. It is rotated υ by the motor 22 and can be finely moved in the axial direction. Therefore, by appropriately rotating the three motors, the inclination of the sample 5 can be adjusted in any direction.

Next, we will discuss the relationship between the output signal of the 4-split photodetector 10, in other words, the position of the spot by the reflected beam on the photodetector surface, and the adjustment of the inclination of the sample supported at the three points ■, ■, and ◎. This will be explained with reference to Figure 3.

In FIG. 3, (al indicates the light-receiving surface of the four-split light-receiving element 10, and the spot 12 by the reflected beam from the reference surface 4 is projected onto the center of the surface of the light-receiving element 1.Il, IIl, IV. Adjust the position of the entire light-receiving element to
The spot due to the reflected beam from the sample surface is lon, m
, rv onto the light receiving element surface.

In Fig. 3 (bl shows the west device of the supporting points of sample 5, ■, ■, where the supporting points ■, ■, 0 are provided at the three vertices of a right-angled isosceles triangle, and ■0 The direction of the straight line that connects is l, ■, and ■ of the four-division light-receiving element 10.

Corresponding to the direction of the boundary line of ■, the direction of the straight line connecting ■0 is 4
■,■ and 1. of the split light receiving element. It is provided so as to correspond to the direction of the boundary line of lV.

Now, the spot 13.1 due to the reflected beam from the sample surface 5
4 is projected onto the surface of the light receiving element I. At this time, the light receiving output from light receiving element 1 is the same as that of other light receiving elements n, m, t.
It becomes larger than the output from v. By driving the point (■) with an adjusting screw, the sample surface is tilted around -0 as the axis. Accordingly, the spora) 13, 1.4 on the light receiving element I move counterclockwise in the circumferential direction. When the outputs of the light-receiving elements I and 2 become equal, that is, when the spora) 13 and 14 are on the boundary line between 1 and 2, the drive at point A is stopped. At this time, sample 5
The upper straight line ■0 is parallel to the reference plane (see the diagram in the center). Next, by moving the zero point back and forth with the adjustment screw, the spot row is concentrated at the center of the light receiving element,
Light receiving element 1. II, In.

Stop the drive of ■ when the outputs of ■ become equal. At this time, the sample surface is parallel to the reference surface (right figure). The driving force direction (rotational force direction of the motor) in (1) and (2) is determined by the control unit so that the required adjustment time becomes the minimum time depending on which light-receiving surface the spot row is initially projected onto. For example, in the center diagram of Figure 3, the spot row is aligned with the vertical axis of the dividing line, but if the horizontal axis forces are close, 5
Reverse the driving force direction. Furthermore, by making the directions of the straight lines connecting the light-receiving element dividing line and the fulcrum of the adjustment mechanism correspond as shown, 1. The driving algorithm can be simplified. Depending on the precision of the sample, the fulcrum position is often specified, but in this case, the fulcrum of the sample and the fulcrum for adjustment should be placed in two stages, or the direction of adjustment at the specified fulcrum should be determined by the controller. Good to consider.

FIG. 4 is a block diagram of the tilt adjustment mechanism. 1 of the 4-split light receiving element. The respective outputs of Il, [1, ■ are input to the multiplexer MPX, and one of them selected by the control unit CPU is A/D converted and taken into the CPU. CPU
changes the selection elements one after another and takes in the entire output. Inside the CPU, the four outputs are compared and the drive motor 22 (
It determines which direction and how much rotation should be made for each of MA, MB, and MC'n, and outputs the result. The CPU performs this operation according to the algorithm described above.

FIG. 5 shows an optical axis tilt adjustment mechanism in an embodiment in which the present invention is applied to an interference measuring device for measuring the surface condition of a rotating polygon mirror used as a laser beam deflector in a laser printer or the like. Rotating polygon mirror 101 is attached to rotating shaft 102 . Of the mirror surfaces of the rotating polygon mirror, only those surfaces that are approximately parallel to the reference surface 103 are measured. Inside the housing 104, a tilt adjustment mechanism 108 is provided that adjusts the tilt in the direction of arrow A about the fulcrum 107. Its configuration is similar to the adjustment mechanism shown in FIG. A rotating shaft 102 is located inside the second housing 105 that is tilted by the tilt adjustment mechanism 108.
A rotation mechanism 112 is provided for adjusting the inclination in the direction of arrow B with the center at , and for switching the surface to be measured of the sample. This rotation mechanism 112 includes a motor MB, a worm 113 provided on the motor shaft, and a worm gear 106. These two tilt adjustment mechanisms 108 and 112 make it possible to make the surface to be measured parallel to the reference surface 103.

Needless to say, the motor kite MB is driven using the spot light receiving output of the four-division light receiving element.

- When the measurement of the surface is completed, the CPU outputs a signal to the motor MB to rotate the rotating polygon mirror by the division angle, and the adjacent surface is brought to the measurement position.

What is important in a rotating polygon mirror is the difference in inclination angle between each surface, and if there is a difference in the inclination angle of each surface, the scanning line by the deflected beam will not form a continuous straight line.

Therefore, if the amount of control signals sent out (the number of pulses given to the motor) during adjustment for each surface is memorized for all measurement surfaces, it is possible to easily measure all the tilting, etc. of each surface.

By the way, in general, there are not very large sizes of 4-split light-receiving elements on the market, so there are 4-split light receiving elements as shown in Figure 6.
By arranging individual light-receiving elements in a ``field'' shape, the permissible movement range of the spot can be expanded, and it is possible to prevent the spot from coming off the light-receiving surface when the sample is first attached.

In the above two embodiments, an example was explained in which the spot light reception output of the 4-split light receiving element is input to the CPU and the drive motor of the tilt adjustment mechanism is controlled by the output to automatically align the optical axis. Using the spot light receiving output of the split light receiving element,
By outputting the information necessary to manually move the sample surface to align the optical axes, manual adjustment can be made without hesitation.

Although FIG. 1 shows an embodiment in which the present invention is applied to a Fizeau type interferometer, the present invention can be applied to various interference measuring devices such as a Twyman-Green type interferometer.

As described above, according to the present invention, it is possible to align the optical axes of the sample surface and the reference surface with high precision in a short time, making it suitable for product inspection at sites where many samples are flowing, such as on a production line in a factory. It becomes possible to use an interference measurement device, and a remarkable effect can be obtained in improving inspection accuracy and work efficiency.

In addition, by memorizing the amount of adjustment, it is possible to simultaneously measure the mutual surface tilt and rotation error of each surface of a rotating polygon mirror, etc., which improves the deflection accuracy of the laser beam and improves the image quality of laser printers. Contribute.

[Brief explanation of the drawing]

Fig. 1 is a diagram of an optical system of an embodiment of an interferometric measuring device to which the present invention is applied, Fig. 2 (at is a perspective view showing the entire sample support part, and (b) is a sectional view showing its tilt adjustment mechanism. , FIG. 3 is a schematic diagram illustrating the relationship between the direction of the dividing line of the 4-split light receiving element and the arrangement of the fulcrum of the sample tilt adjustment mechanism, as well as the tilt adjustment force method.
FIG. 4 is a control block diagram of the tilt adjustment mechanism, FIG. 5 is a sectional view showing the tilt adjustment mechanism in another embodiment of the present invention, and FIG. 6 is a plane view showing another example of the configuration of the 4-split light receiving element. It is a diagram. 1...Laser light source 2...Beam diffusion lens 3...Beam splitter 4...Reference surface 5...Sample 61...Imaging lens 7...Screen lO...4-division light-receiving element 11 ...Sample support substrates 17-22...Sample surface tilt adjustment drive means 101...
Sample 103...Reference surface 108.112...Sample surface tilt adjustment drive means Fig. 1 (a') (b) Fig. 3 Fig. 5 Fig. 6

Claims (1)

[Claims] (1) A laser light source, a beam diffusing lens that diffuses a beam from the laser light source, a beam splitter that transmits the diffused beam and reflects a beam coming from the opposite direction, and the beam splitter. a reference surface that reflects the beam transmitted through the reference surface, a sample surface arranged with its optical axis aligned with the reference surface, and an image formed in the optical path of the reflected beam by the beam splitter. In an optical axis alignment mechanism between a sample surface and a reference surface of an interference measurement apparatus having a lens and a screen for projecting interference fringes generated between the reference surface and the sample surface, reflection by each of the reference surface and the sample surface is used. A light-receiving element having a light-receiving surface divided into four parts is provided on the beam spot imaging plane, and a driving means for adjusting the inclination of the sample surface is provided, and the output signal of the queen light-receiving element is used to control the driving means. Features optical axis alignment mechanism. (2) The method according to claim 1, characterized in that the direction of the dividing line of the light-receiving element is made to correspond to the direction of the tilt axis when adjusting the tilt of the sample surface tilt adjustment mechanism. Optical axis alignment mechanism. (3) The optical axis according to claim 1 or 2, characterized in that the above-mentioned four-division light-receiving element is constructed by arranging four individual light-receiving elements in the shape of a square. Matching mechanism. (4) It has a control section for controlling the tilt adjustment mechanism driving means for the sample surface, and the output of the four-divided light receiving element is input to the control section, and the tilt adjustment mechanism driving means is controlled by the output. Claim 1 characterized in that
The automatic optical axis alignment mechanism according to any one of items 1 to 3. (51) A patent characterized in that a means is provided for outputting information necessary for adjusting the inclination of the sample surface by manually driving the inclination adjustment mechanism driving means of the sample surface using the above-mentioned four-division light-receiving element. The manual optical axis alignment mechanism according to claim 1. (6) When measuring a surface of a sample having a plurality of measurement surfaces, it is characterized by comprising means for storing the amount of tilt adjustment of each surface. An optical axis alignment mechanism according to any one of claims 1 to 5.