JPS58225305A - Optical shape measuring apparatus - Google Patents

Abstract

PURPOSE:To measure the shape of the surface of an object in a contactless manner by creating an interference fringe from a reflected light from the object to be measured and a reflected light from a double-side mirror. CONSTITUTION:Light from a light source 1 irradiates the surface 30 of an object 3 to be measured and a double-side mirror 4. Lights reflected on these reflective surfaces are reflected with or transmit a half mirror 2 and then, form on interference fringe on image sensors 51 and 52 by interference with each other according to the same theory as in the interference by the Mickelson's optical system. An m-order high harmonic outputted from the image sensors 51 and 52 is heterodyne detected with mixers 61 and 62 and counted 81 and 82 separately through low-pass filters 71 and 72 to compute 9 the Z-direction displacement Z of an object 3 to be measured and the angle DELTApsi of inclination of the surface thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical shape measuring device that utilizes light interference to determine shape changes such as unevenness, inclination, and roughness on the surface of a mirror-surfaced object to be measured.

BACKGROUND ART Conventionally, there is a stylus-type surface roughness meter that measures the surface roughness by bringing a needle into mechanical contact with the surface of an object to be measured and measuring its height. With this device, the needle comes into contact with the surface to be measured, which may cause scratches on the surface to be measured.
There are disadvantages such as it is difficult to know the true shape of the surface to be measured, and it is dangerous to measure the surface of soft objects.

The present invention has been included for the purpose of eliminating such drawbacks in conventional devices.

In the device according to the present invention, the surface of the object to be measured is formed so as to reflect light, and the surface to be measured is irradiated with coherent light of ゛ from a light source, and the optical axis of the light source is and tilt each other by Δθ (:L80'±2・
The light reflected from the surface of the object to be measured and the light reflected from the 2'ms2 are irradiated onto the two image sensors. Interference fringes that move in opposite directions relative to changes in the surface to be measured are formed on top of the sensor, and output signals from each image sensor are processed to determine changes in the shape of the surface to be measured.

FIG. 1 is a block diagram of the configuration of an apparatus according to the present invention.

In the figure, reference numeral 1 denotes a light source, for example, a HeNe laser light source is used, from which coherent surface light is emitted. 2 is bar 7
In the imager, optical axis C4 of light source 1? It is installed at an angle of 45°. Reference numeral 3 denotes an object to be measured, the surface 30 of which is a reflective surface that reflects light, and the light that has passed through the half mirror 2 is irradiated onto this object. Reference numeral 4 denotes a two-sided mirror, which is tilted by Δ0 with respect to the optical axis C1 of light source 1.
Two mirrors 41 that intersect at an angle of 180°-2·Δ.
42, and the light from the light source 1 reflected by the half ξ2-2 is irradiated. Reference numerals 51 and 52 each designate an image sensor, for example a COD, whose light-receiving surface is irradiated with reflected light from the surface 30 of the object to be measured, which is reflected by a half mirror 2;
The reflected light from 4 is irradiated through half mirror 2. These two reflected lights create Michelson interference fringes. Here, one image sensor 51 and the other image sensor 5
2 is located in a region where interference fringes created by light irradiated onto ζ move in opposite directions with respect to deformation of the surface 30 of the object to be measured in two directions.

61 and 62 are mixers for mixing the output frequency signals fa and fb from the image sensors 51 and 52 with the reference frequency signal fR, and 71 and 72 are for mixing specific frequency signals among the output signals from the corresponding mixers. The low-pass filters 81 and 82 are counters that count the frequency signals from the low-pass filters 71 and 72, and 9 is the count signal f□ from each counter 81 and 82,
This is an arithmetic circuit that inputs f2, and for example, a microprocessor is used as this arithmetic circuit. Reference numeral 90 denotes a display device for indicating the calculation results, for example, a CRT is used.

The operation of the device configured as described above is as follows. The light of wavelength λ emitted from the light source 1 is transmitted to the surface 30 of the object to be measured 5.
and the second surface Mi 2-4 is irradiated. Each of the reflected lights reflected by these reflective surfaces, after being reflected and transmitted through the half mirror 2, interferes with each other based on the same principle as interference by Ikelson's optical system, and forms interference fringes on each of the image sensors 51-52.

At this time, the interval d□ of the interference fringes formed on the image sensor 51 is calculated using the formula (1), where the inclination angle 5Δψ of the surface 30 is %.
Equation % (1) Furthermore, the interval d2 between interference fringes formed on the image sensor 52 is expressed by Equation (2).

] One fringe of the interference fringes created on each image sensor 51, 52 is λ12 in two directions of the surface 30 of the object to be measured 30.
corresponds to the change (displacement) in

Each image sensor 51, 521i, with a frequency at one end. The output terminal of each image sensor 51 and 52 is driven by applying a glue signal, and fO-f, /N (where N is the number of pits of image sensor ai, 52) is set as the fundamental frequency (3 ) and the periodic signal fa expressed by equation (4).

fb is output.

fa-A-Z-B smell 9 (S
) fb-A-Z+B-Δψ (
4) However, A and B are coefficients, and 2 is the amount of movement in two directions. Figure 2 is the frequency signal f obtained from each image sensor 51.52.
FIG. 2 is an explanatory diagram showing a frequency spectrum of a(fb). This frequency spectrum has a peak at a point that is an integral multiple of the fundamental frequency fO, and the peak is at each image sensor 5.
The area where the interference fringe spacing is equal to 1/(integer) of the total width of 1.52 is the largest, and when the surface 30 moves by 2 in the direction of the arrow 2, it corresponds to, for example, the m-th harmonic. The peak Pm shifts in frequency by Δfmz, which is proportional to its moving speed di/dt.

In FIG. 1, mixer 61. , 62 performs mixing, that is, heterodyne detection, of the m-th harmonic Pm output from each image sensor 51.52 and its neighboring frequency fR, and passes each output through a low-pass filter 71.72tl- to a counter 81.82. (3), (4
), respectively.

The arithmetic circuit 9 inputs these signals and calculates equations (5) and (
By performing calculations as shown in equation 6), the inclination angle Δψ of the surface of the displacement 21 of the object to be measured 5 in the two directions of the arrows can be determined.

Δψ■ Upper (fb-fa) 2B (6) FIG. 3 is an explanatory diagram showing another example of the configuration of the apparatus according to the present invention. This device uses a polarizing beam splitter 20°λ/4 plate 21, 22 in place of the I-no mirror 2 in the device shown in FIG.
and a polarizing plate 23.

According to this device, power loss of light can be reduced.

In each of the embodiments described above, the two-sided mirrors 4 are arranged to intersect with each other at an angle of (180° - 2∆θ), but it is also possible to intersect with each other at an angle of 180' + 2·Δθ. good. Further, the image sensors 51 and 52 are C
Although it is assumed that a CD is used, a pattern detection device such as a combination of these and a spatial filter may also be used. Furthermore, another circuit may be used as the image sensor signal processing circuit.

As explained above, according to the device according to the present invention, it is possible to measure the object to be measured without contacting it, and it is possible to measure the surface of a soft object without damaging the surface to be measured. can also be done.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the configuration of an apparatus according to the present invention, FIG. 2 is an explanatory diagram showing the frequency spectrum of a signal obtained from an image sensor, and FIG. 5 is an explanatory diagram of the configuration of another embodiment of the apparatus of the present invention. . 1...Light source, 2...Half scold-, 5...Measurement object, 4...Two-sided mirror, 51.52...Image sensor.

Claims (1)

[Claims] (1) When coherent light from a light source is irradiated onto the light reflecting surface of the surface of the object to be measured, Δ0 with respect to the optical axis of the light source
The reflected light from the surface of the object to be measured and the reflected light from the two surfaces are reflected by two mirrors installed at an angle of 180"±2・Δθ- to each other. The image sensor is illuminated on the image sensor to create interference fringes on the two images that move in opposite directions with respect to changes in the shape of the surface of the object to be measured, and the output signals from each image sensor are processed. to know the change in shape of the surface to be measured.
Optical % formula %