JPS6285837A - Adjusting device for pinhole of laser measuring instrument - Google Patents

Abstract

PURPOSE:To improve measuring accuracy of the titled instrument by detecting the quantity of light of laser beams passing through a pinhole at the prescribed position and performing alignment between the pinhole and the laser beams by a feedback mechanism based on the detected value. CONSTITUTION:A part of the irradiated 1 laser beams is directed to the surface (S) of an object to be detected passing through a half mirror 6 via a diverging lens 2 and the pinhole 3 and a part of the rest is reflected on the mirror 6 and irradiated on a photodetection plate 9 and photodetected with detectors 10 (10a-10d) and converted into electrical signals in accordance with the quantities of photodetection. When these signals are compared respectively and the alignment between the pinhole 3 and an optical axis of the laser beams is adjusted and the alignment is made in an accurate state, interference fringes are formed on the laser beams via a collimator lens 4 interfering the reflected light of the surface (S) with the reflected light of a reference plate 5 and the interference fringes are reflected via the mirror 6 and received by a TV camera 8 and an image analysis is performed, by which a surface state of plane accuracy of the surface (S) can be measured.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a pinhole adjustment device in a laser measuring instrument such as a laser beam interferometer that detects the surface condition of an object to be measured by irradiating the surface with a laser beam. It is.

[Conventional technology]

For example, in order to measure the surface accuracy of the surface of a test object, a laser beam is used, and the reflected light of the laser beam from the test object is made to interfere with the light reflected from a reference plate (reference standard surface). A laser beam interferometer is used that analyzes the surface accuracy based on interference fringes generated by interference.

The laser beam interferometer mentioned above generally has a pinhole mechanism installed inside its optical system for noise cutting.
The pinhole in this pinhole mechanism must be placed precisely on the optical axis of the laser beam. For this purpose, in conventional laser beam interferometers, pinholes are formed in a pinhole plate, and this pinhole plate is mounted on a stage assembly that can finely adjust the position in the X and Y directions. Put it on,
By appropriately adjusting the position of this pinhole plate, the laser beam of the pinhole was configured to be finely adjusted 2 for alignment with respect to f,6.

[Problem that the invention seeks to solve]

As mentioned above, if the stage assembly is used to align the pinhole, it is possible to finely adjust the position of the pinhole, but during long-term use of this interferometer, the laser beam device υ where misalignment occurred
Furthermore, deformation of each member due to temperature changes or the like may cause a misalignment between the pinhole and the laser beam. If there is even a slight deviation between the pinhole and the laser beam, the light intensity distribution of the light passing through the pinhole will change, making it impossible to observe interference fringes with a certain contrast. In addition, there have been other inconveniences, such as erroneous recognition of interference fringes when performing image analysis using a computer, for example.

The present invention was made in view of the oblique point, and is a laser that enables automatic alignment between a pinhole and a laser beam, thereby making it possible to always accurately maintain alignment between the pinhole and the laser beam. The object of the present invention is to provide a pinhole adjustment device for a measuring instrument.

[Means for solving problems]

In order to achieve the above-mentioned object, an apparatus according to the present invention includes a laser beam irradiation device that irradiates a laser beam toward the surface of an object to be inspected, and an unnecessary light flux of the laser beam emitted from the laser beam irradiation device. A pinhole forming body is provided with a pinhole for cutting, and a laser beam that has passed through the pinhole is received at a predetermined position to determine the relative positional relationship between the pinhole and the optical axis of the laser beam based on the amount of light. A detector for detecting, and a signal from the detector to move the pinhole forming body to an X perpendicular to the optical axis.
, and a pinhole position adjustment device that finely adjusts the position of the pinhole with respect to the optical axis of the laser beam by displacing it in the Y direction. In order to measure the surface of a test object using a device configured as described above, a laser beam is irradiated from the laser beam irradiation device, the laser beam is passed through a pinhole formed in the pinhole forming body, and the laser beam is passed through a pinhole formed in the pinhole forming body. The passing light is detected by a detector.

Here, when the pinhole and the laser beam are accurately aligned, the light intensity of the laser beam at a two-dimensional position perpendicular to the optical axis of the laser beam is maximum at the center and toward the periphery. In addition, when the amount of irradiation from the laser beam irradiation device is constant, the amount of light at each position is constant. Therefore, a detector that detects the amount of light and converts it into an electrical signal such as a current value or a voltage value is installed at a predetermined position in the area through which this laser beam passes, and the detected value of this detector and the pin The relative positional relationship between the pinhole and the laser beam can be detected by comparing the reference value, which is the amount of light when the hole and the laser beam are aligned. Then, by activating the pinhole position adjustment device based on this detection signal and performing feedback control, the position of the pinhole is displaced so that the above-mentioned detected light amount falls within the reference value range. It is possible to automatically align the pinhole and the laser beam.

In this manner, by automatically aligning the pinhole and the laser beam, the surface of the object to be inspected can be measured accurately and in good condition at all times.

〔Example〕

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

First, in FIG. 1, reference numeral 1 indicates a laser beam irradiation device that irradiates a laser beam.
f: The beam passes through the beam, is focused once, and then expanded in diameter.

A pinhole 3 for noise cutting is provided at the focal position of the laser beam from the dipager lens 2. The laser beam that has passed through the pinhole 3'lc is adjusted by a collimator lens 4 to become parallel light, and is irradiated toward the surface S of the object to be inspected. On the other hand, the irradiated laser beam is partially reflected by the reference plate 5 placed in front of the collimator lens 4, and the laser beam that has passed through it is reflected by the surface S of the object to be inspected, and the light reflected by the reference plate 50 is and composite interference fringes? Occur. The generated interference fringe image is formed on the imaging surface of the television camera 8 via the mirror 6 and the imaging lens 7.

The above-mentioned nose mirror 6 is also capable of reflecting the irradiation light from the laser beam irradiation device 1, and the light reflected by the nose mirror 6 is transmitted to the light receiving plate 9.
It is now possible to receive light. As shown in FIG. 2, the peripheral portions of the light-receiving portions A on the light-receiving plate 9 have a 90° phase with each other. Four detectors 10a at shifted positions.

10b, 10c, and 10d are provided. These detectors receive a laser beam and convert it into electrical signals such as current and voltage values according to the amount of received light.The detectors 10a and 10c are placed on the left and right, and the detectors are placed on the top and bottom. 10b and 10d, it is possible to detect the relative positional relationship between the pinhole and the optical axis of the laser beam in the X direction and the Y direction, respectively.

Next, the aforementioned detectors 10a, 10b, 10c.

In order to fully adjust the position of the pinhole 3 based on the detected value of IQd, the pinhole 3 is formed in a pinhole plate 11 as shown in FIG. It is supported by stepped spring pieces 13.13 attached to the top and bottom of the body 12. These spring pieces 13 are connected to the vertical plate part 13a for displacing the pinhole plate 11 left and right in the X direction, and in the Y direction. It is provided with a horizontal plate portion 13b that is displaced vertically. Positioning rods 14a and 14b are screwed onto the frame 12 to position the pinhole plate 11 at the origin position.A positioning rod 14m is attached laterally to the frame 12 to position the pinhole plate 11''f. , the positioning rod 14b is positioned at the origin position in the x direction, and the positioning rod 14b
It is attached in the vertical direction, and can be positioned at the origin position in the Y direction. By screwing these positioning rods 14a and 14b, the origin position of the pinhole plate 11 can be adjusted.

Furthermore, in order to finely adjust the position of the pinhole plate 11 in the X direction and the Y direction, the frame 12 is provided with a pinhole position adjustment device. It is composed of a device 15 and a Y-direction adjustment device 16. The X-direction adjustment device 15 is a bushing rod 1 that is slidably mounted on the side of the frame 12 by a bearing 17.
8 and a core 19 for displacing the bushing rod 18 in its axial direction. Coils 20 and 21 are wound around each of the bushing rod 18 and the core 19, and between the coil 20 and the power source 22 A variable resistor L1 is interposed so that the repulsive force of the bushing rod 18 against the core 19 can be adjusted based on the resistance value of the variable resistor L1. Further, the Y-direction adjustment device 16 has a bushing rod 23 similar to the aforementioned X-direction adjustment device 15, and the bushing rod 23 has a bearing 24 on the vertical side of the frame 12.
The bushing rod 23 and the core 25 that displaces it by repulsive force are each provided with coils 26 and 27 wound around it.
A variable resistor L2 for adjusting the repulsion force is interposed between the resistor 8 and the repulsion force.

Furthermore, the above-mentioned variable resistor 1. Resistance value control of L2 is performed by X-direction detectors 10a, 10c and Y-direction detectors 10b, 10d, respectively. In order to perform this control, a circuit as shown in FIG. 4 is used. configuration has been adopted. In the figure, detector 1 in the X direction
Although the configuration for controlling the variable resistor Ll using 0a and 10c has been shown, the configuration for controlling the Y direction is also the same, so the reference numerals are shown in parentheses in the drawings for explanation. omitted. That is, the detector 10a.

The detected value of IQe is input to the differential amplifier 30a, and the differential amplifier 30a can output the difference between these detected values.

The output signal of this differential amplifier 30a is input to a threshold setter 31a. In the threshold setter 31a, this differential amplifier 3
The output signal of 0a is compared with a reference threshold value set by the threshold adjuster 32a, and the coil drive circuit 33a is controlled based on the difference between the two signals.
It is now possible to output a drive signal to the

Based on this drive signal, the drive circuit 33 is operated to change the resistance value of the variable resistor L1.

This embodiment is constructed as described above, and its operation will be explained next.

In order to measure the surface S of the object to be measured using this laser beam measuring device, first the threshold hole
2a and 32b, it is necessary to set a predetermined reference threshold value in the threshold setters 31L and 31b. Setting of this reference threshold value is performed as follows. That is, when the pinhole 3 and the optical axis of the laser beam from the laser beam irradiation device 1 are accurately aligned, the light intensity of the laser beam at a two-dimensional position perpendicular to the optical axis of the laser beam As shown by the solid line in Figure 5,
It exhibits a distribution that is maximum at the center C and gradually decreases toward the periphery, and when the amount of light from the laser beam irradiation device 1 is constant, the amount of light at each position is constant. Therefore, if the detectors 10a and 10c and the detectors 10b and 10d are respectively arranged at equal intervals from the center C, the detectors 10a and 10c and the detectors 10b and 10d
The amount of light received at d becomes equal. Therefore, the aforementioned reference threshold value may be set within a predetermined tolerance range, and this reference threshold value may be compared with the detection values of the detectors 10a and 10c and the detection values of the detectors 10b and 10d.

Further, by adjusting the positioning rods 14a and 14b, as shown in FIG. 3, the position of the pinhole plate 11 is shifted to the left by a distance Dl in the X direction with respect to the optical axis P, and by a distance D2 in the Y direction. Hold it in the position shifted downward.

Therefore, a laser beam is irradiated from the laser beam irradiation device 1 toward the surface S of the object to be inspected. This laser beam travels from the dipper lens 2 through the pinhole 3 toward the half mirror 6, and a part of this laser beam passes through the half mirror 6 and passes through the surface of the object to be inspected.
At the same time, a part of the light is reflected by the half mirror 6 and illuminated on the light receiving plate 9, and the detectors 10a, 10b, 10
c and 10d, and is converted into an electrical signal according to the amount of received light. Of these electrical signals, the detected values of the detectors 10a and 10c are input to the differential amplifier 30a, and the detected values of the detectors lQb and 10d are input to the differential amplifier 30b, and these signals are compared. Ru. As mentioned above, since the pinhole 3 is located at a different position from the optical axis P, the amount of light received by the detector 10a and the detector 10c is different, as shown by the chain line in FIG. The amount of light received also differs between the detector 10b and the detector 10d.

1,000, each differential amplifier 3nλ-3nb outputs a signal corresponding to the difference between these detected values, and these output signals are input to the threshold setters 31a and 31b, respectively, and the respective thresholds are set. Hold setting device 31a
It is compared with a reference threshold value of t 3 l b and a drive signal is output based on the difference. and,
These drive signals are input to drive circuits 33a and 33b, respectively, and the resistance values of variable resistors LL and L2 are changed by the drive circuits 33m and 33b. As a result, the repulsive force between the bushing rods 18.23 and the core 19.25 changes, and each bushing rod 18.23 resists the spring force of the pinhole plate In spring piece 13, as shown on the left side in FIG. (X direction) and upward (Y direction). Then, due to the displacement of this pinhole plate 11, the detector 10
The detection signals of a, 10b, 10c, and 10d also change,
Therefore, the output signals from the differential amplifiers 30a and 30b also differ.

Then, due to the displacement of the pinhole plate 11, the pinhole 3
When the alignment between the optical axis P and the optical axis P of the laser beam is achieved, the output signals of the differential amplifiers 30a, 30b fall within the reference threshold values of the hold setters 30a, 30b. The variable resistor L1.
By maintaining the resistance value of L2 by the aforementioned feedback mechanism, the protrusion length of the bushing rod 18.23 into the frame 12 based on the repulsive force with the core 19.25 is fixed, and the pinhole 3 and the laser beam are The pinhole plate 11 is supported in a state in which the optical axis P of the pinhole plate 11 is accurately aligned. Here, the threshold setters 30a, 3
0b serves as a kind of buffer function, and by giving a certain width to the reference threshold value, the pinhole 3 moves even when there is a slight fluctuation in the detectors 10a, 10b, 10c, and 10d. This can prevent the pinhole 3 from becoming unstable during measurement work.

As mentioned above, the pinhole 3 and the optical layer IP of the laser beam
When the laser beam is accurately aligned, the reflected light from the surface S of the object to be measured and the reflected light from the reference plate 5 are caused to interfere with each other through the collimating lens 4 to form interference fringes. This is reflected through a half mirror 6 and received by a television camera 8 to form data regarding interference fringes, which is input into an analysis device such as a computer to perform image analysis. The surface condition of the object surface S with planar accuracy can be measured. Therefore, even if there is a positional shift in the laser beam irradiation device 1 or the device components are displaced due to temperature changes, the pinhole 3 and the optical axis P of the laser beam are automatically aligned. Therefore, interference fringes that accurately represent the surface condition of the surface S of the object to be measured can be obtained, and the measurement accuracy can be improved.

Here, the position adjustment of the pinhole 3 using the bushing rods 18 and 23 described above is for fine adjustment of the laser beam irradiation device 1, and the approximate position adjustment of the pinhole 3 is performed using the positioning rods 14a and 14b. It goes without saying that at least the pinhole 3 must be set so that the laser beam can pass therethrough. By adjusting the position using the bushing rods 18 and 23, fine alignment between the pinhole 3 and the laser beam from the laser beam irradiation device 1 can be performed at all times.

〔Effect of the invention〕

As described in detail above, the pinhole adjustment device in the laser measuring instrument of the present invention detects the laser beam that has passed through the pinhole at a predetermined position using a detector that detects the amount of light, and has a feedback mechanism based on this detected value. Because the structure is configured to align the pinhole and the laser beam, the parts that make up the interferometer may be deformed due to temperature changes, or the position of the laser beam irradiation device may shift during long-term use of the interferometer. Even if this occurs, the alignment between the pinhole and the laser beam can be reliably maintained accurately during measurement, and extremely good measurement accuracy can be maintained.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the principle of the laser measuring instrument of the present invention, Fig. 2 is an explanatory diagram of the arrangement position of the detector, Fig. 3 is an explanatory diagram of the configuration of the pinhole adjustment mechanism, and Fig. 4 is an explanatory diagram of the pinhole position. FIG. 5 is an explanatory diagram of the configuration of a control device for performing adjustment, and is a diagram showing irradiation of a laser beam onto a detector. 1: Laser beam irradiation device 3: Pinhole 5: Reference plate 10a, 10b, 10c, 10d: Detector 11: Pinhole plate 13: Spring piece 15: X direction adjustment device 16: Y direction adjustment device 23: Push rod Ll , L2: Variable resistance P: Optical axis
S: Test object surface Patent applicant: Fuji Photo Kohki Co., Ltd. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] a laser beam irradiation device that irradiates a laser beam toward the surface of an object to be inspected; a pinhole forming body having a pinhole that allows passage of only a necessary beam of the laser beam emitted from the laser beam irradiation device; a detector that detects the relative positional relationship between the pinhole and the optical axis of the laser beam based on the amount of light by receiving the laser beam after the laser beam has passed; Pinhole adjustment in a laser measuring instrument, comprising a pinhole position adjustment device that finely adjusts the position of the pinhole with respect to the laser beam by displacing the pinhole forming body in the X and Y directions perpendicular to the optical axis. Device.