JPH07122566B2 - Optical displacement measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION << Industrial Application Field >> The present invention relates to a displacement meter for simultaneously measuring three-dimensional displacement of an object in a non-contact manner.

«Prior art» The first prior art of displacement gauge that simultaneously measures three-dimensional displacement
Is a retro-reflective tape (a light-reflecting tape that has the property that the reflected light returns to the same optical path as the incident light) with a fixed-pitch grating that serves as a scale for displacement measurement. The displacements in the X and Y directions are measured by reading the above, and the displacements in the Z direction are measured by detecting the movement of the interference fringes using a Michelson interferometer.

In the second prior art, there is one in which two-dimensional displacement gauges are combined and measured as shown in FIGS. 4 and 5. FIG. 4 shows the two-dimensional displacement gauges 41 and 42 arranged at right angles, and FIG. 5 shows the two-dimensional displacement gauge 51 and the Z-axis direction one-dimensional displacement gauge.
52 is arranged in the same direction.

<< Problems to be Solved by the Invention >> However, in the case of the first method, there is a problem that the measurement in the Z direction cannot be stabilized, and in the case of the second method, although stable displacement measurement can be performed, It is impossible to measure the displacement of one point in three dimensions. Another drawback is that it takes a long time to hem.

The present invention has been made to solve the above problems, and an object of the present invention is to realize an optical displacement measuring device capable of simultaneously and stably measuring a three-dimensional displacement of a certain point without contact.

<< Means for Solving the Problems >> The present invention relates to an optical displacement measuring device for detecting the displacement of the target based on the movement of the pattern of the target formed on the image sensor. A first image sensor for detecting a displacement of the target in a plane parallel to the target, and a second image sensor for detecting a displacement of the target from a direction forming a predetermined angle with a normal line of the plane, And a processing circuit for calculating the displacement of the target in the plane and the displacement in the vertical direction from the displacement outputs from the two image sensors.

<< Operation >> Since the second image sensor makes a predetermined angle with respect to the direction in which the first image sensor looks into the target, the displacement detected by the second image sensor is the first In addition to the in-plane displacement detected by the image sensor, a vertical displacement component is included and can be separated by the processing circuit from the first and second image sensor outputs.

«Examples» Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a configuration block diagram showing an embodiment of an optical displacement measuring device according to the present invention. 1 is a light source such as a semiconductor laser that emits linearly polarized light having a polarization plane of 45 ° with respect to the polarization beam splitter 2, 2 is a polarization beam splitter for dividing the incident light into two according to the polarization direction of the incident light (hereinafter, PB
S is referred to as S), 3 is a telecentric optical system that forms an image forming optical system and receives the reflected light of PBS2, and 4 is a 1/4 wavelength plate (hereinafter, λ / 4 plate) that receives the light that has passed through the telecentric optical system 3. 5 is a target composed of a retroreflective tape having a lattice pattern with a constant pitch, which is obtained by vertically irradiating light passing through the λ / 4 plate 4, and 50 is an object to be measured to which the target tape 5 is attached. 6 is a PBS arranged with a plane of polarization in the same direction as PBS2, which is transmitted by PBS2, and 7 is this PBS6.
, A second telecentric optical system on which the reflected light of the mirror 7 is incident, and 9 is light transmitted through the telecentric optical system 8, and the transmitted light irradiates the target 5 obliquely. The second λ / 4 plate, 10
A half mirror that receives reflected light from the target 5 of PBS2 and bisects the reflected light, 11 is an image sensor, and the reflected light of the half mirror 10 is incident to detect Y displacement in the Y-axis direction.
Axis photodiode array (hereinafter referred to as PDA), 12 is a Y-axis conversion circuit that converts the electrical output of the PDA 11 into a displacement output, and 13 is the first image sensor that is transmitted by the half mirror 10. For X axis that detects displacement in the X direction
PDA, 14 is an X that converts the electrical output of this PDA 13 into displacement output
Axis conversion circuit, reference numeral 15 is a second image sensor and is a Z-axis PD on which obliquely reflected light from the target 5 is incident.
Reference numerals A and 16 denote Z-axis conversion circuits that convert the electric output of the PDA 15 into displacement outputs, and 17 is a processing circuit that receives the outputs from the conversion circuits 14 and 16 and calculates the displacement in the Z direction. The telecentric optical system 3 (8) has a constant imaging magnification even if the distance to the object changes, and the two lenses 31 (81), 33
(83) is arranged at an interval equal to the sum of the respective focal lengths f ₁ and f ₂ , and irradiates the target 5 with the light emitted from the PBS 2 (6) as parallel light, and The lattice image is formed on the PDA 11, 13 (15). Further, a diaphragm 32 (82) is arranged at the focal position. PDA13 and PDA
15 is arranged so as to detect the movement of the target 5 in the same direction (here, the x direction), and the PDA 11 is 90 degrees relative to the PDA 13,15.
It is arranged in the direction rotated by ° (here, the y direction).

The operation of the optical displacement measuring device having the above configuration will be described below. The light output from the light source 1 is separated into two directions by PBS, and the reflected light is the telecentric optical system 3 and λ.
After passing through the / 4 plate 4, the target 5 is vertically irradiated.
The reflected light of the target 5 returns through the same optical path, passes through the λ / 4 plate 4 twice, and the light whose polarization direction is rotated by 90 ° passes through PBS2 and is separated by the half mirror 10 into two directions. The transmitted light forms the same image on the PDA 11 and PDA 13, respectively. The portion of the light emitted from the light source 1 that has passed through PBS2 is redirected by the mirror 7 after passing through PBS6, and is obliquely irradiated onto the target 5 after passing through the telecentric optical system 8 and the λ / 4 plate 9. This reflected light returns through the same oblique optical path, passes through the λ / 4 plate 9 twice, and the light whose polarization direction is rotated by 90 ° is radiated by the PBS 6 and forms an image on the PDA 15. Here, since the telecentric optical system 8 looks at the target 5 obliquely, a cosine error occurs, so that it is necessary to change the imaging magnification from that of the telecentric optical system 3.
Next, the displacement of the lattice image formed on each PDA is detected and a displacement output is generated. The detection outputs of the PDAs 13 and 11 are converted into displacement outputs S _x and S _y in the X and Y axis directions by conversion circuits 14 and 12, respectively. PDA
The detection output of 15 is once converted into an S _x ′ output by the conversion circuit 16, and is then calculated with S _{x by the} processing circuit 17 to become a displacement output S _z in the Z-axis direction.

Next, the calculation method in the processing circuit 17 will be described with reference to FIG. In FIG. 2, 100 is a part of the optical system of the apparatus of FIG. 1, a is a light beam which is vertically incident on the object 50 (actually the target 5), and b is a light beam which is obliquely incident. To simplify the explanation, consider the xz plane. The object 50 that was on the solid line is now on the broken line The displacement amounts in the X and Z axis directions when moved by (vector) are x and z, respectively, and the displacement amount in the x axis direction at the position where the light beam b irradiates the object 50 is x '. At this time, the conversion circuit 14
The output S _{x of} is the displacement output corresponding to x, and the output S _x ′ of the conversion circuit 15 is the displacement output corresponding to x ′. Processing circuit 17
Calculates the displacement amount z in the Z-axis direction using the following formula and outputs the displacement
Let S _z .

z = (x + x ') / tan θ (1) Since θ is fixed here, tan θ is a constant.

According to the optical displacement measuring device having such a configuration, the three-dimensional side of a certain point on the object can be simultaneously measured without contact. In this case, although the point of sight is slightly displaced when moved in the Z-axis direction, it can be regarded as a single point if the range of movement is small, and there is no problem if the surface is a flat object.

Also, the displacement in the Z-axis direction is measured by the same principle as in the X-axis and Y-axis directions, so the signal is stable.

Further, the optical system can be made compact by using a semiconductor laser or the like as the light source.

FIG. 3 is a block diagram showing the configuration of another embodiment of the optical displacement measuring device according to the present invention. Reference numerals 21 and 22 form first and second image sensors, respectively. This is a commercially available image sensor that uses a photomultiplier tube.
It is called a servo, etc., and when a DUT with a bright / dark boundary line is in the field of view, it can optically detect the motion / displacement of the DUT without contact. The size is output in an analog amount including the sign. The inside of the image sensors 21 and 22 is mainly composed of an imaging optical system and an electron multiplier. The image sensor 21 detects displacement in a two-dimensional plane in the X and Y axis directions, and the image sensor 22 detects X
Align the axis with the direction and set the angle to see the target as θ
It is arranged so that it can be tilted and the displacement in the Z-axis direction can be detected.
Reference numeral 51 denotes a target having a bright / dark boundary line attached to the surface of the object 50, and the image sensors 21 and 22 respectively move reflected light beams c and d from the target 51 by separate illumination to move the boundary line. To detect. As in the case of FIG. 2, the object 50 When the displacement amount in the X-axis direction when moved is x and the displacement amount in the direction perpendicular to the optical path of the light d is x ', the displacement z of the target 51 in the Z-axis direction is obtained by the following equation.

z = (− x′−xcos θ) / sin θ = −x ′ / sin θ−x / tan θ (2) That is, if the processing circuit calculates the above equation for the outputs of the image sensors 21 and 22, the Z axis direction The displacement output can be obtained. Regarding the displacement output in the X and Y axis directions, the output of the image sensor 21 may be used as it is, as in the case of FIG.

Although a retroreflective tape is used as the target tape in each of the above-mentioned embodiments, a normal diffuse reflective tape may be used although there is a problem with the amount of incident light. For example, in the case of FIG. 1, the PBS 6 can be omitted if only the irradiation light perpendicular to the target is used.

If the object 50 originally has a light / dark boundary,
You can take advantage of it.

In the description of the embodiments shown in FIGS. 1 and 3, a semiconductor laser or the like is used to irradiate the target with a light source and the reflected light from the target is used. If an S / N sufficient to form an image with one image sensor is obtained, the light source and its irradiation optical system are not necessary.

<< Effects of the Invention >> As described above, according to the present invention, it is possible to realize an optical displacement measuring device with a simple configuration, which can simultaneously and stably measure a three-dimensional displacement of a point without contact.

[Brief description of drawings]

FIG. 1 is a configuration block diagram showing an embodiment of an optical displacement measuring device according to the present invention, FIG. 2 is an operation explanatory diagram for showing a measuring method of the device of FIG. 1, and FIG. 3 is related to the present invention. FIG. 4 is a constitutional block diagram showing another embodiment of the optical displacement measuring device, and FIGS. 4 and 5 are constitutional perspective views showing a conventional example of the optical displacement measuring device. 5 ... Target, 13, 21 ... First image sensor, 1
5,22 …… Second image sensor, 17 …… Processing circuit, θ…
… Predetermined angle, S _x , S _x ′ …… Displacement output.

Claims (1)

[Claims] 1. An optical displacement measuring device for detecting the displacement of the target based on the movement of the pattern of the target formed on an image sensor, the displacement of the target being detected in a plane parallel to the target. A first image sensor; a second image sensor that detects the displacement of the target from a direction that forms a predetermined angle with the perpendicular of the plane; a displacement of the plane of the target from displacement outputs of the two image sensors; An optical displacement measuring device comprising: a processing circuit for calculating a displacement in a vertical direction.