JPH0543364Y2 - - Google Patents

Description

[Detailed description of the invention] Summary of the invention Projected light from a light source is irradiated onto the top of a reflector fixed to a moving object and has at least two reflective surfaces, and the reflected light from each of the reflective surfaces of the reflector is received. A fixed point between the moving body and the reflector in a position detection device that detects the position of the reflector based on the amount of light received by the reflector is on the ridgeline of the reflector (including on the extension of the ridgeline).
shall be. This can prevent positional displacement of the ridge line due to thermal expansion, and even if the reflector is displaced due to heat, an appropriate reflected light can be obtained and measurement errors can be prevented.

Background of the Invention This invention relates to an apparatus for detecting the position of an object that moves one-dimensionally or two-dimensionally within a plane, such as a stage of a machine tool.

The applicant has already proposed a device that can accurately detect the one-dimensional position of an object by irradiating a light beam onto a reflecting mirror attached to a one-dimensionally moving object and receiving the reflected light (patent application 62−248580,
Patent application 1986-300067, etc.)

In this position detection device, projected light from a light source is irradiated onto the top of a reflector having at least two reflective surfaces fixed to a moving body, and the reflected light from each of the reflective surfaces of the reflector is received. The position of the reflector is detected based on the above.

This position detection device has a detection range of, for example, several tens to several hundred micrometers, and detects the amount of displacement of a moving body to which a reflector is attached with a resolution of about 1 micrometer. Therefore, if the positions of the reflector and the moving body to which it is attached are displaced relative to each other due to thermal expansion and contraction of the reflector, this thermal displacement will appear as a measurement error.

Summary of the invention Purpose of the invention The object of this invention is to provide a position detection device that can prevent measurement errors caused by relative displacement of reflectors due to heat.

Structure of the Invention In the position detection device according to this invention, a fixed point of the reflector relative to the moving body is provided on the ridgeline of the reflector (including an extension of the ridgeline).

Function and effect of the invention According to this invention, the fixed point between the moving body and the reflector is set on the ridgeline of the reflector. Even if the reflector is displaced relative to the moving body due to thermal expansion and contraction of the reflector, its fixing member, and the moving body, the position of the ridgeline of the reflector is not displaced relative to the moving body and is maintained at a constant position. Ru. Therefore, even if the reflector or the like is displaced or deformed due to heat, the reflected light from the reflector will not be affected by the displacement or deformation and will accurately represent the amount of displacement of the moving body.
Thereby, it is possible to prevent errors in position measurement of the moving body caused by changes in reflected light due to displacement of the reflector due to heat. Furthermore, even if the reflector itself expands and contracts thermally, the position of the ridgeline of the reflector does not shift, so a generally inexpensive material with a large coefficient of thermal expansion can be used as the material for the reflector. For example, a resin-molded reflector can be used and can be provided at low cost.

DESCRIPTION OF EMBODIMENTS Hereinafter, an embodiment in which this invention is applied to a one-dimensional position measuring device will be described in detail, but this invention can be applied not only to one-dimensional position detection devices but also to two-dimensional position detection devices. The details of the two-dimensional position detection device are disclosed in a previous application by the same applicant (Japanese Patent Application No. 62-300066), and in this case as well, by setting the ridgeline of the reflector as a fixed point, the reflector can be moved by heat. Even if it is displaced, measurement errors can be prevented from occurring.

The position detection device shown in this embodiment is the one disclosed in the above-mentioned Japanese Patent Application No. 62-300067, but this invention can also be applied to the position detection device disclosed in Japanese Patent Application No. 62-248580, etc. Needless to say.

FIG. 1 shows the optical system of the position detection device.
The moving object 40 is movable, for example, in the X-axis direction (but not in the Y-axis or Z-axis directions), and the reflector 30 is fixedly attached to a predetermined position thereof. Although the configuration of the reflector 30 will be described in detail later, the reflector 30 will be schematically shown here.
The optical system of the detection device is placed at a position separated from the reflector 30 by an appropriate distance in the Z-axis direction. Light emitted from a laser diode 2 as a light source is collimated by a lens 11, and this collimated light (parallel light) is converged by a lens 12. The diffused light after convergence is collimated again by the lens 13. These lenses 11 to 13 convert the parallel light into a smaller beam diameter. The parallel light having a small beam diameter passes through the pinhole of the pinhole plate 14, is slightly diffused, and enters the lens 15. The intensity distribution of the parallel light output from the lens 13 is not necessarily uniform; the intensity is greatest at the optical axis, and the intensity decreases toward the periphery. By passing the parallel light through the pinhole of the pinhole plate 14, only the light at the center where the intensity of the parallel light is substantially uniform is extracted. In this way, light having a substantially uniform intensity distribution is obtained, and this light is slightly converged by the lens 15 and is then directed to the reflector 3.
Projected to 0.

For example, a semiconductor laser diode with a wavelength λ=780 [nm] is used as a light source, and the diameter of the pinhole in the pinhole plate 14 is φ=30 [μm]. Further, as the lens 15, a lens with a focal length of f=10 [mm] is used. Then, the pinhole plate 14 and the lens 1
When the distance between the lens 15 and the lens 15 is set to approximately 12 [mm], a projected light P having a beam diameter φ = 150 [μm] is formed at a position 60 [mm] in front of the lens 15 (on the side from which the light is emitted).

For example, as shown in FIG. 2, the reflector 30 has an isosceles triangular cross section with a low height. The apex angle of this isosceles triangle is, for example, 160°. The slopes of the reflector 30 corresponding to the two sides of the isosceles triangle having the same length serve as reflective surfaces S ₁ and S ₂ . The reflector 30 is arranged so that the ridge line where the two reflecting surfaces S ₁ and S ₂ intersect is parallel to the Y axis as shown in FIG. fixed in position. When light P is projected onto the top of such a reflector 30 perpendicularly to its bottom surface, a portion of the projected light P is reflected in different directions by the reflecting surfaces S ₁ and S ₂ . These reflected lights are denoted by P ₁ and P ₂ .

Photodiodes 51 and 52 are arranged at positions to receive these reflected lights P ₁ and P ₂ , respectively. Photo diodes 51, 52 and reflector 3
The positional relationship between the reflective surfaces S ₁ and S ₂ of 0 is shown in FIG.
FIG. 2 is a view taken from the - line in FIG. 1. The photo diode 51 converts the reflected light P ₁ reflected by the reflecting surface S ₁ into the photo diode 5
2 receives the reflected light P ₂ reflected by the reflecting surface S ₂ . A lens may be arranged between each of the reflecting surfaces S ₁ and S ₂ of the reflector 30 and each of the photo diodes 51 and 52 to converge the reflected light and make it incident on each of the photo diodes 51 and 52.

Next, the principle of detecting the position of the moving object 40 will be explained. When the projected light P is projected onto the reflector 30 and its optical axis coincides with the ridgeline at the top of the reflector 30, the reflected light P ₁ and P ₂ are reflected by the respective reflecting surfaces S ₁ and S ₂ .
have the same amount of light. If the moving object 40 moves in the X-axis direction, the spot of the projected light P moves on the reflector 30 in the -X direction. Therefore, the reflected light P ₂ increases and the reflected light P ₁ decreases (for convenience, the light amount is also
(represented by P ₁ and P ₂ ). Conversely, if the moving object 40 moves in the -X direction, the spot of the projected light P moves on the reflector 30 in the X direction, the reflected light _P1 increases, and the reflected light _P2 decreases. In this way, the reflected lights P ₁ and P ₂ are functions of the X position of the reflector 30. Therefore,
The X position of the reflector 30 is detected by measuring the reflected light P ₁ or P ₂ . A graph showing how the amounts of reflected light P ₁ and P ₂ change as the reflector 30 moves is shown in FIG. In FIG. 3, the position where the optical axis of the projected light coincides with the ridgeline of the top of the reflector 30 is taken as the origin x=0.

On the other hand, the total sum P ₁ +P ₂ of reflected light changes depending on the output light intensity of the laser diode 2. laser·
In order to remove the influence of fluctuations in the output light intensity of the diode 2, the detected value is normalized by the above summation.

Therefore, the position of the reflector 30 in the X direction can be determined by F ₁ (x)=P ₁ /(P ₁ +P ₂ ) (1).

FIG. 4 shows how the moving object 40 (reflector 30) is
FIG. 2 is a block diagram showing a signal processing circuit that calculates a position.

The output light receiving signals of the photo diodes 51 and 52 are respectively given to an adding circuit 61 and added up (the light receiving signals correspond to the above-mentioned light quantities P ₁ and P ₂ , so for convenience, these are also given as P ₁ and P 2 , respectively). (represented by P ₂ ). The output P ₁ +P ₂ of the adder circuit 61 is given to the divider circuit 63. Also, photo diode 5
The output signal P ₁ of 1 is also given to the division circuit 63 .
The divider circuit 63 divides the output signal P ₁ of the photo diode 51 by the output P ₁ +P ₂ of the adder circuit 61, and outputs the result P ₁ /(P ₁ +P ₂ ). This is equivalent to the above-mentioned equation (1) and represents the position of the reflector 30 in the X-axis direction. The calculation result of the division circuit 63 is input to the CPU 64 and displayed on the display 65 as the position in the X-axis direction.

Also, considering the difference P ₁ − P ₂ between the amount of reflected light P ₁ and P ₂ ,
This value changes as the reflector 30 moves in the X direction.
Since it changes more rapidly than P ₁ or P ₂ , the accuracy of detecting the X position of the reflector 30 is increased by determining the above value.

In this case as well, by normalizing the detector by the sum of the reflectors P ₁ and P ₂ as described above, the influence of fluctuations in the output light intensity of the laser diode 2 can be removed.

The position of the reflector 30 in the X direction at this time can be determined by F ₂ (x)=(P ₁ −P ₂ )/(P ₁ +P ₂ ) (2).

A graph of this function F ₂ (x) is shown in FIG. In this figure, as in the case shown in FIG. 3, the position where the optical axis of the projected light P coincides with the ridgeline of the top of the reflector 30 is taken as the origin x=0.

FIG. 6 is a block diagram showing another signal processing circuit that calculates the X position of the moving object 40 (reflector 30) using equation (2).

The output light reception signals of the photo diodes 51 and 52 are applied to an addition circuit 61 and a subtraction circuit 62, respectively. The addition circuit 61 outputs the addition result P ₁ +P ₂ , and the subtraction circuit 62 outputs the subtraction result P ₁ −P ₂
is output. These output signals P ₁ + P ₂ and
P ₁ -P ₂ is given to the division circuit 63. The division circuit 63 divides the output P ₁ −P ₂ of the subtraction circuit 62 into the addition circuit 6.
3 output P ₁ + P ₂ divided by (P ₁ − P ₂ )/(P ₁ + P ₂ )
Output. This is equivalent to the above-mentioned equation (2) and represents the position in the X-axis direction.

The calculation result of the division circuit 64 is input to the CPU 64 and displayed on the display 65 as the position in the X-axis direction.

FIG. 7 shows another example of the reflector 30. Here, the reflector 30 is blazed. It is also possible to use such a reflector 30 in a position detection device. When a blazed reflector is used as the reflector 30, there is an advantage that the thickness of the reflector 30 can be reduced.

8 to 10 show an example of a reflector and its mounting mechanism. Figure 8 shows the reflector 30
and an enlarged front view of its mounting mechanism. FIG. 9 shows a sectional view taken along the - line in FIG. 8, and FIG. 10 shows a sectional view taken along the - line in FIG. 8.

The reflector 30 is formed by depositing aluminum 32 on two slopes of a base material 31 made of, for example, quartz glass and having a low isosceles triangular cross section. The aluminum vapor deposited film 32 is the reflective surface S ₁ and S ₂ . Reflector 30
is fitted into the recess of a fixing member 34 made of stainless steel, which has a recess formed approximately in the center thereof, and is fixed by adhesive or the like. A protective glass plate 33 is provided in the recess opening of the fixing member 34, and the protective glass plate 33 is fixed to the fixing member 34 by adhesive or the like. Reflector 3
0 is protected by this protective glass 33 from the external environment, particularly from dust and dust.

The moving object 40 and the fixing member 34 to which the reflector 30 is fixed are fixed by screws 35, for example. The screw 35 passes through a hole formed in the fixed member 34 and is screwed into the movable object 40.
The center of the hole of the fixing member 34 into which the screw 35 is inserted or the central axis (fixing point) of the screw 35 is on an extension of the ridgeline of the reflector 30. Therefore, even if the reflector 30 is displaced due to heat, the position of the ridgeline of the reflector 30 will not be displaced. Therefore, the reflected lights P ₁ and P ₂ are reflected from the reflector 3.
Always moving object 40 regardless of displacement due to heat of 0
The amount of displacement (movement) or position of is accurately represented, and measurement errors due to thermal expansion and contraction of the reflector 30, fixing member 34, etc. can be prevented.

In the above embodiment, quartz or stainless steel, which have a particularly small coefficient of thermal expansion, is used, so this is a particularly preferable form.

As shown in the embodiment, the reflector 30 is fixed to the fixing member 34.
Instead of forming the reflector 30 and the fixing member 34 separately and fixing them by adhesive or the like, the reflector 30 and the fixing member 34 can be integrally formed of the same material. In this case as well, the fixed point between the reflector 30 and the moving object 40 is an extension of the ridgeline of the reflector 30.

11 to 13 show other examples of reflectors. Figure 11 is a front view, Figure 12 is a cross-sectional view taken along the - line in Figure 11, and Figure 13 is a front view of Figure 11.
FIG. 3 is a sectional view taken along the - line in the figure.

A recess 37 is formed from the back side of the reflector block 36 made of a transparent resin such as acrylic resin, and a 2-shaped reflective surface is formed at the upper base of the recess 37.
Two slopes are formed. Reflecting surfaces S ₁ and S ₂ are formed by vapor-depositing aluminum on these slopes, and the reflector 30 is constructed thereby. In this example as well, a screw insertion hole whose center is on the extension of the ridge line where the two reflective surfaces S ₁ and S ₂ intersect is made, and the screw 35 is inserted into this insertion hole and screwed into the moving object 40. The reflector block 36 is fixed to the moving object 40 by the reflector block 36. Even if the reflector block 36 is made of acrylic resin having a relatively large coefficient of thermal expansion, measurement errors due to thermal expansion and contraction of this material are prevented from occurring.

Although the above description has been about detecting the position of a moving object moving in one direction, the present invention is also applicable to detecting the two-dimensional position of an object moving within the XY plane.

In this case, the reflector is, for example, a rectangular pyramid with a low height. The four slopes of this square pyramid are reflective surfaces. A reflector is attached to a moving object so that the ridgeline of the quadrangular pyramid is parallel to the X-axis and the Y-axis, and the projection light is projected onto the top. The projected light is divided into four directions and reflected by the four reflecting surfaces. Each reflector receives light using four light receiving elements. The position in the Y-axis direction can be calculated based on the amount of reflected light obtained from two groups of reflective surfaces separated by the ridgeline in the X-axis direction of the quadrangular pyramid. Also Y
The position in the X-axis direction can be calculated based on the amount of reflected light obtained from two groups of reflective surfaces separated by the ridgeline in the axial direction. In this way, the position of an object moving two-dimensionally within the XY plane can be detected.

Also in the reflector of the two-dimensional position detection device, by providing a fixed point with the moving object on the extension of the ridgeline of the quadrangular pyramid, the ridgeline is less likely to fluctuate due to thermal displacement. Appropriate reflected light can be obtained, allowing accurate position detection regardless of the presence or absence of thermal displacement.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the optical system of the position detection device;
Figure 2 shows the positional relationship between the reflector and the photodiode as seen from the - line in Figure 1;
The figure is a graph showing the relationship between the position of the reflector and the amount of received light, Figure 4 is a block diagram showing an example of the configuration of a signal processing circuit, and Figure 5 is the relationship between the position of the reflector and the calculation result of the amount of received light. 6 is a block diagram showing another example of the signal processing circuit, and FIG. 7 is a sectional view showing another example of the reflector. 8 is an enlarged front view of the reflector, FIG. 9 is a cross-sectional view taken along the line - in FIG. 8, and FIG. 10 is a cross-sectional view taken along the line - in FIG. 8. 11 to 13 show other examples of reflectors. Figure 11 is the front view, Figure 12 is the first view.
A cross-sectional view taken along the line XII-XII in Figure 1, and Figure 13 is a cross-sectional view taken along the line
It is a sectional view taken along the - line in the figure. 2...Laser diode (light source), 11,1
2, 13, 15... Lens, 14... Pinhole plate, 30... Reflector, 32, 38... Aluminum vapor deposited film, 34... Fixing member, 35... Screw, 3
6... Reflector block, 40... Moving object, 5
1, 52...Photo diode (photoelectric conversion element), 61... Addition circuit, 63... Division circuit.

Claims (1)

[Scope of utility model registration request] Projection light from a light source is irradiated onto the top of a reflector having at least two reflective surfaces fixed to a moving body, and the reflected light from each of the reflective surfaces of the reflector is received, and based on the amount of received light, the reflector is A position detection device for detecting the position of a vehicle, wherein a fixed point between the reflector and the moving body is provided on a ridgeline of the reflector.