JPH0961160A - Measuring apparatus for inclination amount of moving object - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measuring apparatus which can measure the inclination amount of a moving object by a simple structure which does not comprise a mechanical moving part by a method wherein the reflecting face of a reflection reference member reflects a light beam with maximum reflection efficiency according to the position of a measuring part. SOLUTION: In a measuring part 2, light from a light source 21 is changed into a parallel luminous flux by a collimating lens 22, a beam-shaping optical element 23 shapes a beam so as to be radiated to the horizontal direction from a window 24, and a beam LB1 is obtained. The beam LB1 is projected on a reflection reference member 7 when a stage 1 is passed through a measuring position along a linear guide. The reflection face (composed of lattice plates 71, 72 and of a reflecting plate 73) of the member 7 reflects the beam LB1 with maximum reflection efficiency according to the position of the measuring part 2. The reflected means LB1 is incident from the window 24, it is reflected by a semitransparent mirror 25 via the element 23 and the lens 22, it is photoelectrically converted by light receiving element 26, and an electric output signal which expresses the passage of a reference position is created. Thereby, an inclination caused by the pitching operation and the yawing operation of the stage 1 which is moved on the linear guide can be found with good accuracy by a simple structure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for measuring the amount of tilt of a moving object moving on a guide, for example, a device for measuring the amount of tilt of a linear moving stage due to yawing or pitching.

[0002]

2. Description of the Related Art In a machine tool feeding device or a measuring instrument stage, the straightness of a moving object moving on a guide is an important factor in determining the accuracy of the machine tool or measuring instrument. In order to improve the straight traveling accuracy, it is important not only to process the guide itself with high accuracy but also to improve the fitting accuracy between the guide and the moving object. However, there is a limit to the processing accuracy of the guide, and it is impossible to completely eliminate the processing error. Also, with regard to fitting accuracy, play cannot be eliminated at all. Therefore, no matter how highly precise the stage is equipped with a guide, meandering occurs due to yawing, pitching, etc., and the stage itself has a slight inclination with respect to the reference direction at each moving position.

Such a tilt of the stage causes a reduction in machining accuracy in the case of a machine tool feed device, and causes a measurement error in the case of a measuring instrument stage. In order to remove this error, it has been conventionally performed to use data obtained by measuring the amount of inclination of the stage to correct a processing error and a measurement error. As a conventional tilt amount measuring device, a device in which a gyroscope and an accelerometer are combined has been known.

[0004]

However, the gyroscope has the problems that the device becomes large and that it takes time to obtain a mechanically stable state. There is also a problem that the measured values obtained vary due to the influence of shift and drift as characteristics of the gyroscope.

An object of the present invention is to provide an apparatus for measuring the amount of tilt of a moving object, which has a simple structure and does not have a mechanical movable part.

[0006]

A tilt amount measuring device of the present invention is a device for measuring a tilt amount of a moving object moving on a guide laid on the device fixing part, wherein the device fixing part and the moving object are provided. A measuring unit (2) is installed on one side and a reflection reference member (7) is installed on the other side, and a light beam (LB ₁ ) is projected to the measuring unit (2) toward the reflection reference member (7). A light projecting device and a light receiving device for receiving the reflected light of the light beam from the reflection reference member are provided, and the light beam (LB ₁ projected from the measurement unit (2) is projected on the reflection reference member (7). ) Is reflected toward the measurement unit, and the reflection surface maximizes the reflection efficiency of the light beam when the measurement unit faces the reflection reference member in a predetermined positional relationship. , The position of the measuring unit relative to the reflection reference member To those having a different reflection efficiency.

The reflection surface of the reflection reference member is a reflection plate (73).
A first grid plate (71) having a grid pattern arranged at a constant pitch in a direction parallel to the guide and arranged between the guide and the reflection plate; and a first grid plate parallel to the guide. Second grid pattern having a grid pattern arranged at a pitch different from that of the first grid plate and the reflection surface.
It can be composed of a lattice plate (72).

The reflecting plate (73) is formed to have a width larger than that of the first and second lattice plates (71, 72) in the pitch direction of the lattice, and the portions protruding from both sides of the first and second lattice plates are formed. It is preferable to have. Further, the lattice pattern of the first lattice plate is composed of a repeating pattern of the light transmitting portion of the width a and the light shielding portion of the width b, and the lattice pattern of the second lattice plate is the width a.
Of the light transmitting portion and the light shielding portion of width b + Δb, and the distance between the reflection reference member and the measuring portion is L, and the distance between the first lattice plate and the second lattice plate is D.
As the above, it is preferable that Δb / D = (a + b) / L is satisfied.

Further, a plurality of reflecting surfaces each including a reflecting plate, a first grating plate and a second grating plate are provided on the reflection reference member, and the pitch of the first grating plate and the second grating plate is plural. You may comprise so that it may differ for every surface.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 1 shows a schematic cross section perpendicular to the longitudinal direction of the pair of linear guides 4a and 4b at the measurement position, and FIG. 2 shows a plan view. The support column 6 is provided at a position separated by a predetermined distance on the side of the guide from the device fixing portion at the measurement position.
Is installed, and the reflection reference member 7 is attached to the upper part of the support column 6 so as to face the guide.

The stage 1 is fitted with the guides 4a and 4b through a pair of races 5a and 5b, and the guides 4a and 4b.
Move along b. The measuring unit 2 is mounted below the stage 1. The measuring unit 2 horizontally emits the light beam LB ₁ having a linear cross section, which is elongated in the vertical direction, in a plane perpendicular to the guide. This beam LB ₁ is projected onto the reflection reference member 7 when the stage 1 passes through the measurement position, and when reflected by the reflection reference member 7, returns to the measurement unit 2 and undergoes photoelectric conversion.

FIG. 3 shows the measuring unit 2 and the reflection reference member 7.
The schematic configuration of and the positional relationship between the two are shown. The light emitted from the light source 21 is collimated by the collimator lens 22 into a parallel light flux, and is beam-formed into a vertically elongated shape by the beam shaping optical element 23 including, for example, a cylindrical convex lens and a cylindrical concave lens, and is horizontally emitted from the window 24. , Beam LB ₁ . The beam LB ₁ forms a vertically elongated linear spot on the reflection reference member 7. The beam LB ₁ reflected by the reflection reference member 7 enters through the window 24, passes through the optical element 23 and the lens 22, is reflected by the half mirror 25, enters the light receiving element 26 such as a photodiode, and is photoelectrically converted. An electrical output signal is generated that represents the passage of the position.

FIG. 4 shows the detailed structure of the reflection reference member 7. First lattice plate 71, second lattice plate 72, and reflector 73
Are arranged in order from the measurement unit 2 side. Each of the first and second lattice plates 71 and 72 has a lattice pattern, and for example, a striped light-shielding portion is formed by plating a transparent glass substrate with chrome. First lattice plate 71
The grid pattern of is a slit (light transmitting portion) of width a and a width b.
Has a constant pitch P ₁ due to repetition of the light shielding part of
The lattice pattern of the second lattice plate 72 is formed by repeating the slits (light transmitting portions) having the width a and the light shielding portions having the width b + Δb.
Have a pitch P ₂ greater than P ₁ . Each of the lattice plates is arranged so that the pitch direction matches the direction parallel to the guide.

The reflecting plate 73 is arranged behind the second grid plate 72 so as to be close to or in contact with the second grid plate 72.
It has a reflecting surface facing the second side, and the reflecting surface is formed by arranging a large number of fine corner cubes in a matrix. Therefore, the light beam incident on the reflection surface of the reflection plate 73 is reflected in the direction of incidence regardless of the incident angle. The width of the reflector 73 is equal to that of the first and second grid plates 71 and 72.
It is formed to be larger, and therefore has a portion protruding to the left and right by a predetermined width.

The optical characteristics of the reflection reference member 7 with respect to the incident beam will be described with reference to FIG. 5A is a graph showing the light intensity characteristic, and FIG. 5B is a diagram showing the positional relationship of the slits of the first and second lattice plates 71, 72. In the following description, a region where both the first and second grating plates 71 and 72 are slits with respect to the beam LB ₁ is referred to as “aperture”, and an area ratio occupied by the aperture is referred to as “aperture ratio”.

In the figure, a straight line 8 represents the locus of movement of the measuring unit 2 mounted on the stage 1. Since the first and second grating plates 71 and 72 have light-shielding portions having different widths (b, b + Δb), the aperture ratio for the beam LB ₁ having the same incident angle changes in the grating pitch direction. Assuming that the slit having the maximum aperture ratio with respect to the beam LB ₁ incident from the vertical direction is the maximum at n = 0, the aperture ratio w at this time is w.
₀ is represented by w ₀ = a / (a + b) (1). The aperture ratio w _n is expressed by w _n = (a−nΔb) / (a + b) (2) from the position of n = 0 until the aperture becomes 0 (the dark part appears at the beginning (N = 1)). It This first (N = 1) dark portion is a state in which the slits of the first lattice plate 71 and the light shielding portions of the second lattice plate 72 overlap, so that the slit position of n = (a + b + Δb) / 2Δb (3) , It appears at the position of n = 3 in the figure. The first (N = 1) bright part is the slit of the first grid plate 71 and the second bright part.
Since the slit of the lattice plate 72 overlaps, it appears at the slit position of n = (a + b + Δb) / Δb (4), that is, at the position of n = 6 in the figure. If this is generalized, the N-th bright part appears at the slit position of n = N (a + b + Δb) / Δb (5), and the N-th dark part is n = (2N-1) (a + b + Δb) / 2Δb (6) Appears at the position of the slit.

Now, the measuring unit 2 of the stage 1 is a reflection reference
Beam LB for member 7₁Straight while keeping the optical axis of
Consider the case of moving on line 8. Measurement part 2 is on straight line 8
Beam LB when reaching point 81₁Is along a straight line 90
And enters the slit position of n = 0 by the reflector 73.
It is reflected in the same direction. The amount of reflected light at this time is the maximum value
Is shown. The stage moves further and the beam LB₁Is n =
Light intensity of the reflected light when sequentially entering the slit positions 1, 2,
Decreases gradually, and when it enters the slit position of n = 3,
It is the minimum value. Then, the measurement unit 2 reaches the point 82.
When the beam LB ₁Is the slip of n = 6 along the line 106
The light quantity of the reflected light that has been incident on the optical axis reaches the maximum value again. So
As a result, the light intensity of the beam returning to the measuring unit 2 is as shown in FIG.
The light receiving element 26 shows an output signal of a similar waveform.
Issue.

On the other hand, consider a case where the measuring unit 2 of the stage 1 moves on the straight line 8 while the optical axis of the beam LB ₁ is inclined with respect to the reflection reference member 7. In this case, the measuring unit 2 is at point 8
When reaching 1, the beam LB ₁ is incident on the reflection reference member 7 along an inclined straight line as indicated by straight lines 91 to 95. If the beam LB ₁ is slightly inclined, for example, the straight line 9
1 is incident on the slit position of n = 1, and if the inclination is large, for example, it is incident on the slit position of n = 6 along the straight line 95, and in any case, the incident beam is incident on the reflector 73. Reflected in.

Here, straight lines 90 to 95, 101 to 1 in the figure
06 is a line connecting the centers of the slits of the first lattice plate 71 and the second lattice plate 72. Moreover, straight lines 90-9
5 all intersect at a point 81 on the straight line 8 and the straight line 101
~ 106 all intersect at point 82. In other words,
A direction in which the amount of light passing through both slits of the first and second grating plates 71 and 72 is maximum (maximum opening direction)
Will all be directed to points 81 and 82 on the straight line 8.

Therefore, even if the optical axis of the beam LB ₁ moves on the straight line 8 in a tilted state, the amount of reflected light when passing through the points 81 and 82 is the same as when the optical axis is kept vertical. Is the maximum value. Therefore, an output signal having a waveform similar to that of FIG. That is, if the beam tilt is within the allowable angle range, it is understood that a peak appears in the output signal when the measurement unit 2 faces a fixed position (81, 82) on the reflection reference member 7 regardless of the tilt. it can.
Such a fixed position may be used as the measurement reference position of the device fixing portion.

As described above, in order to set the maximum opening of each slit so as to face a fixed position on the straight line 8, a right triangle whose one side is the distance L from the straight line 8 to the first lattice plate 71, and The condition is that the right-angled triangle whose one side is the distance D between the first lattice plate 71 and the second lattice plate 72 is similar. Therefore, if each value is determined so that the relational expression of Δb / D = (a + b) / L (7) holds, it is easy to design, for example, the first (N = 0) bright part to appear in the center. Is possible.

An embodiment of the reflection reference member 7 designed on the basis of the above principle will be described with reference to FIGS. FIG. 6A shows a state where the stage 1 has no yawing and the beam LB ₁ scans the reflection reference member 7 in the direction of arrow A by traveling the stage 1 while vertically irradiating the beam LB ₁ . FIG. 6B shows an output signal waveform from the light receiving element 26 of the measuring section 2 at this time.
At both ends of the reflection reference member 7, first and second grid plates 71, 7 are provided.
Since there is a protruding portion of the reflection plate 73 formed by a width R larger than 2, the scanning of the reflection reference member 7 by the beam LB ₁ causes the reflection reference member 7 to be scanned from time t ₁ to time t ₂ and time t 2.
_{Between 3} and t ₄ , a rectangular wave is generated based on the light directly reflected from the reflection plate 73 without passing through the first and second grating plates 71 and 72. Then, a signal waveform based on the reflected light that has passed through the first and second grating plates 71 and 72 appears between these two rectangular waves.

In this embodiment, it is preferable to determine each dimension of the grating plate so that a signal waveform corresponding to one wavelength of the waveform depicted in FIG. 5A is output. Thereby,
Since the signal waveform having only one peak value can be obtained during the beam scanning of the reflection reference member, the subsequent signal processing is facilitated. When the width of the entire grating is H (where L >> H), the allowable angle range T of beam tilting due to yawing is T = H / L (radian) (8) Further, from N = 0 to N = 1, (a + b +
Since there are Δb) / Δb lattices, HΔb / (a + b + Δb) = a + b (9). Therefore, the design value of the grid is determined based on the equations 7, 8 and 9.

The positional relationship between the first and second grating plates 71 and 72 is such that the amount of reflected light is maximized when the beam LB ₁ from the vertical direction passes through substantially the center of the reflection reference member 7. To set. Therefore, when the beam LB ₁ is vertically incident, the output signal waveform is symmetrical between the two rectangular waves as shown in FIG. 6B. On the other hand, when the beam LB ₁ is obliquely incident on the reflection reference member 7 due to yawing of the stage 1 as shown in FIG. 7A, the peak position of the signal waveform is as shown in FIG. 7B. It shifts and becomes asymmetrical. Since the signal waveform is output along the time axis and the dimension of the reflection reference member 7 is known, this deviation amount d can be converted into the actual dimension.

The edge portion of the rectangular wave does not become an ideal vertical edge as shown in the figure, and the time width of the signal waveform (interval between times t ₂ and t ₃ ) corresponding to the width H of the entire grating is accurately measured. Difficult to do. Therefore, the time width H + R between the center of one rectangular wave (intermediate between times t ₁ and t ₂ ) and the center of the other rectangular wave (intermediate between times t ₃ and t ₄ ) is calculated, and the midpoint of both rectangular waves is calculated. The deviation amount d can be obtained by obtaining the ratio from the (center position of the reflection reference member 7) to the peak position of the signal waveform. Moreover, the displacement amount d thus obtained is an amount irrelevant to the moving speed of the stage 1.

Then, the beam L for the reflection reference member 7
The slope t of B ₁ is calculated by t = d / L (radian) (10). FIG. 8 is a block diagram of a signal processing system in this embodiment. When the stage 1 passes the measurement position, the output signal photoelectrically converted by the light receiving element 26 of the measuring unit 2 is the edge detection circuit 12 and the peak detection circuit 13.
Is input to The edge detection circuit 12 detects the zero-cross point by differentiating the output signal twice, for example. Further, the peak detection circuit 13 detects the zero-cross point by differentiating the output signal, for example. Edge detection circuit 12 and peak detection circuit 13
Each output of is input to the computer 14.

The computer 14 calculates the slope t of the beam LB ₁ from the times t ₁ , t ₂ , t ₃ , t ₄ corresponding to the edges of both rectangular waves and the time at which the peak appears, using the above-mentioned formula (10). . In the present embodiment, the lattice patterns of the first and second lattice plates 71 and 72 are reversed, and the lattice pattern of the first lattice plate 71 is such that the light transmitting portion having the width a and the width b + Δ.
b has a large pitch P ₂ due to repetition with the light-shielding portion, and the grating pattern of the second grating plate 72 has a small pitch P ₁ due to repetition with the light-transmitting portion having the width a and the light-shielding portion having the width b. You may comprise. In this case, the obtained signal waveform is as shown in FIG. 9, and the peak moves in the opposite direction, but the slope can be calculated using Equation 10.

As a modification of this embodiment, the peak position detection accuracy can be improved by changing the ratio of the width a of the slit of the reflection reference member to the width b of the light shielding portion to widen the dark portion. is there. That is, the signal waveform shown in (a) of FIG. 10 is a signal waveform when width a = width b (aperture ratio 50%), which is the same as that of the embodiment in FIGS. 5 to 7 described above. On the other hand, the signal waveform shown in FIG. 10B is when the aperture ratio is 25% (a = b / 2). in this case,
The steeper the rising edge of the waveform, the easier it is to find the peak position.

It is also possible to dispose a plurality of gratings having different design values on the reflection reference member. The reflection reference member 207 shown in FIG. 11 is a combination of two types of gratings, and the design value of each grating is the same. For the upper reflection reference member 207A, the slit width of the first grating plate is a and the width of the light shielding portion is Is b, the width of the slit of the second lattice plate is a, and the width of the light shielding part is b +
The width of the slit of the first grating plate is a / 2, and the width of the light shielding part is b / for the lower reflection reference member 207B.
2, the width of the slit of the second lattice plate is set to a / 2, and the width of the light shielding portion is set to (b + Δb) / 2. The wavelength of the signal waveform obtained from the lower reflection reference member 207B is 1/2 of the wavelength of the signal waveform obtained from the upper reflection reference member 207A. When only the upper reflection reference member 207A is scanned with a beam, a signal waveform as shown in FIG. 12A appears, and when only the lower reflection reference member 207B is scanned with a beam, a signal waveform as shown in FIG. appear. Therefore, when the entire reflection reference member 207 is scanned with a beam, a signal waveform as shown in FIG. 12C is obtained, and this signal waveform is shown in FIG.
It is easier to specify the position of the peak as compared with the waveform of 2 (a).

In the modification of FIG. 11 as well, the reflection plate has portions protruding from both ends of the first and second lattice plates as in the embodiment shown in FIG. By the same method, as shown in Table 1, a composite reflection reference member obtained by combining 10 types of reflection reference members A to J in which the widths a of the slits and the widths b of the light shielding portions of the first lattice plate and the second lattice plate are respectively different. Are formed and scanned with a beam, a signal waveform as shown in FIG. 13 is obtained.

[0031]

[Table 1]

This makes it possible to obtain a higher resolution. In each of the above-described embodiments, the arrangement relationship between the measurement unit 2 and the reflection reference member 7 may be reversed, the reflection reference member may be placed on the stage 1, and the measurement unit 2 may be installed on the apparatus fixing unit. It is feasible.

[0033]

According to the present invention, the inclination of a moving object moving on a linear guide due to pitching or yawing can be accurately obtained as an absolute value with respect to a reflection reference member without offset or drift.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view at a measurement position in an embodiment of the present invention.

FIG. 2 is a plan view of FIG.

FIG. 3 is a cross-sectional view showing a schematic configuration of a measurement unit and a reflection reference member.

FIG. 4 is a perspective view of a reflection reference member.

FIG. 5 is an explanatory diagram showing a detailed configuration of a reflection reference member and a light intensity characteristic.

FIG. 6 is an explanatory diagram showing vertical beam scanning by a reflection reference member and an output signal waveform.

FIG. 7 is an explanatory diagram showing tilted beam scanning by a reflection reference member and an output signal waveform.

FIG. 8 is a block diagram of a signal processing system.

FIG. 9 is an explanatory diagram showing output signal waveforms.

FIG. 10 is an output signal waveform diagram showing a comparison with the modification of the embodiment of the invention.

FIG. 11 is a plan view showing a reflection reference member according to a second modification of the embodiment of the present invention.

12 is an output signal waveform diagram in the modification of FIG.

FIG. 13 is an output signal waveform diagram in the third modified example of the embodiment of the present invention.

[Explanation of symbols]

1 ... Stage 2 ... Measuring section 4a, 4b ... Guide 7,207 ... Reflection reference member 71 ... First grid plate 72-Second grating plate 73-Reflector plate LB _1- Light beam

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G01D 5/36 G01D 5/36 C

Claims (5)

[Claims] 1. A device for measuring an inclination amount of a moving object moving on a guide laid on a device fixing part, wherein a measuring part is provided on one of the device fixing part and the moving object and a reflection reference member is provided on the other. Each of the measuring units is provided with a light projecting device for projecting a light beam toward the reflection reference member and a light receiving device for receiving reflected light of the light beam from the reflection reference member. Is provided with a reflecting surface for reflecting the light beam projected from the measuring section toward the measuring section, and the reflecting surface is provided when the measuring section faces the reflection reference member in a predetermined positional relationship. An apparatus for measuring a tilt amount of a moving object, which has different reflection efficiencies depending on the position of the measurement unit with respect to the reflection reference member so that the reflection efficiency of the light beam is maximized. 2. The reflection surface of the reflection reference member has a reflection plate and a grid pattern arranged at a constant pitch in a direction parallel to the guide, and is arranged between the guide and the reflection plate. A first grid plate and a grid pattern arranged in a direction parallel to the guide at a pitch different from that of the grid pattern of the first grid plate, and arranged between the first grid plate and the reflection surface. The tilt amount measuring device for a moving object according to claim 1, comprising a second lattice plate. 3. The reflection plate is formed to have a larger width in the pitch direction of the grating than the first grid plate and the second grid plate, and a portion protruding from both sides of the first grid plate and the second grid plate. The tilt measuring device for a moving object according to claim 2, further comprising: 4. The lattice pattern of the first lattice plate is a repeating pattern of a light transmitting portion having a width a and a light shielding portion having a width b,
The grating pattern of the second grating plate has a light transmitting portion having a width a and a width b.
When the distance between the reflection reference member and the measurement unit is L and the distance between the first lattice plate and the second lattice plate is D, then Δb The inclination amount measuring device for a moving object according to claim 2 or 3, wherein / D = (a + b) / L is satisfied. 5. The reflection reference member is provided with a plurality of reflecting surfaces each of which includes the reflecting plate, the first grating plate and the second grating plate, and the pitch between the first grating plate and the second grating plate is set. The tilt amount measuring device for a moving object according to any one of claims 2 to 4, wherein each of the plurality of reflecting surfaces is different.