JPS6365315A - Optical displacement detecting device - Google Patents

Abstract

PURPOSE:To perform high-accuracy, high-speed displacement detection by providing a main scale with two arrays of optical gratings which differ in pitch and detecting displacement within a reference length range and displacement in units of the reference length range in relation to the optical gratings. CONSTITUTION:This detecting device is provided with the main scale 10 provided with the different-pitch optical gratings 13 and 15, an index scale 20 provided with reference optical gratings 23 and 25 corresponding to said gratings, an illumination system 40 which illuminates them, photoelectric converters 30A and 30B which receive reflected light from the scales 10 and 20 and output electric signals, and circuits 50 and 90 which count displacement. Then when the scales 10 and 20 move relatively, the circuit 50 counts the displacement quantity of movement with the minimum resolution and the circuit 90 counts the displacement quantity based upon set reference length range as a unit. Here, when they move relatively over plural reference length ranges, the circuit 90 adds the rough counted value obtained by the circuit 90 to the fine counted value obtained by the circuit 50 to detect the displacement quantity with the minimum resolution prescribed by the circuit 50, so high accuracy is secured and the accuracy of the counted value of the circuit 50 is not important, so that the high-speed detection is performed.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to an optical system that has an optical grating that is relatively movable and that processes transmitted light or reflected light from the optical grating in a predetermined manner to detect the amount of relative movement. The present invention relates to a displacement detection device, and is particularly designed to increase the relative movement speed of a corresponding optical grating.

[Background technology and its problems]

Optical displacement detection devices are widely used as a means for determining physical specifications (length, pressure, weight) by detecting relative displacement between independent objects.

Conventionally, a typical transmission type structure of such an optical displacement detection device has been shown in FIG.

That is, a main scale 10 having optical gratings 13 aligned in the longitudinal direction and an index scale 20 having corresponding reference optical gratings 3A and 3B are attached to each of two opposing objects (for example, a stationary body and a movable body). attachment,
The light source 1 and photoelectric converters 2A and 2B are connected to both scales 10.
A signal detection circuit 7 is disposed integrally with the index scale 20 with 20 in between, and selectively includes a waveform shaping circuit, a dividing circuit, a direction discrimination circuit, etc. for processing the output signals from both photoelectric converters 2A and 2B. , a reversible counting counter 8, and a display means 9 consisting of a digital display or the like. Therefore, if the index scale 20 and main scale 10, which are integrated with the light source 1 and the photoelectric converters 2A and 2B, are moved relative to each other in the direction of the arrow For example, 1 μm/
It was possible to count one pulse of a digital signal with the counter 8, display the amount of displacement on the display means 9, and further output an electric signal corresponding to the amount of displacement to other equipment. The reason why the two photoelectric converters 2A and 2B are provided is to demonstrate the direction discrimination function, and also to enable them to be used to double the resolution depending on the division method. Met.

However, the conventional optical displacement detection device described above has the following problems.

That is, if the slit width of the optical grating 13 is 10 μm and the pitch is 20 μm, the output of the photoelectric converters 2A and 2r3 is a substantially sine wave (not necessarily a mathematical sine wave) with one period having a length equivalent to 20 μIn. ) becomes a cyclic signal of the shape. The amount of relative displacement between both scales 10 and 20 is detected as an incremental value. Therefore, in order to detect and display the amount of relative displacement of both scales 10.20 to any point, the signal detection circuit 7, counter 8, etc. must be interrupted while both scales 10.20 are moving relative to each other. It is necessary to perform follow-up operation without any interference.

Moreover, even if both scales 10 and 20 are stationary at any point, they must function so that the specified minimum resolution of 1 μm/pulse in the case of the above example can be obtained. Here, the maximum response speed of the displacement detection device, especially the signal detection circuit 7, counter 8, etc., is limited due to issues such as versatility and economical efficiency. (Selection of speed) is an arbitrary matter on the user's side. Therefore, in actual use, there may be cases where the device is operated at a speed exceeding the maximum response speed. As a result, there was a risk of producing defective products. Although such problems occur even during instantaneous and temporary operations, the high resolution makes it impossible for operators to determine whether or not a counting error has occurred during the process, so it has been recognized as an important technical issue and its solution has been strongly desired. A similar problem exists in the reflective optical displacement detection device shown in FIG.

Furthermore, for example, when used for detecting a feed hack signal for automatic web feed control of a machine tool, high-speed feed to the final target position is not possible for the above reasons even though the amount of relative displacement is clear in advance. This was causing the situation.

[Purpose of the invention]

The present invention has been made in view of eliminating the above-mentioned problems of the conventional art, and has one object to provide an optical displacement detecting device that can operate at high speed while ensuring high accuracy.

[Means and effects for solving the problems] The present invention has the following features:
a first optical grating for detection with minimum resolution;
a second optical grating having a different pitch from the optical grating of the main scale; 1 and the second optical grating involved -l-ζ
Base 1 - A second counting circuit for detecting displacement in units of range length is constructed, and configured so that the amount of relative displacement between the main scale and the index scale can be determined from the counted values of both counting circuits. This is an attempt to speed up the process.

For this reason, there is a main scale in which two rows of optical gratings are provided and each row has a different optical grating pitch, and two rows of reference optical gratings corresponding to each row of optical gratings on the main scale. an intelligence scale provided and movable relative to the main scale; an illumination system for irradiating light to both scales; and a set of two optical gratings arranged for each row of optical gratings of the main scale, Each group receives transmitted light that has passed through the main scale or reflected light that has been reflected from the main scale.
two sets of photoelectric converters that output electrical signals with a phase shift of 0 degrees; and a first set of photoelectric converters that output electric signals output from at least one set of the photoelectric converters to count displacement within a reference range length using human power. a second, il number direction path for counting the displacement in units of base t1-range length by inputting electric signals outputted from the two sets of the counting circuit and the photoelectric converter; and a displacement detection circuit that calculates the relative movement displacement h (between the main scale and the index scale) using both count values of the second 31 number circuit.
It achieves the first goal.

Therefore, when the main scale and the index scale are moved relative to each other, the first 81 number circuit of the displacement detection circuit will count the relative movement displacement amount of both scales with the minimum resolution, and the second counting circuit will count the relative movement displacement amount of both scales with the minimum resolution. Count the relative displacement of both scales in units of length. Here, when there is a relative movement of both scales over the middle range length of multiple bases, the second counting circuit uses the so-called rough old number I, and the first counting circuit of C treats it as a so-called fractional element within the base t1 east range length. By adding the so-called thin count value in , the equivalent movement displacement amount of both scales can be detected with the minimum resolution specified by the first four-number circuit, so high accuracy is guaranteed, and the first count value within the intermediate reference range length can be detected. Since the accuracy of the old number i1^ in the counting circuit can be ignored, speeding up can be achieved as a whole.

〔Example〕

An embodiment of the optical displacement detection device of the present invention will be described in detail with reference to the drawings.

This embodiment is shown in FIGS. 1 to 6, and the apparatus includes a main scale 10 provided with two rows of optical gratings, and second and third scales provided with corresponding reference optical gratings. Index scale 20 that also serves as both scales 10.
a non-parallel illumination system 40 for irradiating the scale 20 with light; and a non-parallel illumination system 40 for irradiating the scale 20 with light;
Mi photoelectric converter 30, a first counting circuit 50 that counts displacement within a reference range length, and a second counting circuit 1190 that counts displacement in units of reference range length. 100, and the whole is a reflection type absolute type optical displacement detection device.

As shown in FIGS. 1 and 2, the main scale IO is in the form of an elongated thin plate made of a glass material 11 with a rectangular cross section, and a first optical grating 13 with a pitch P of 400 pm is located on the lower side of the figure. Pitch P2 (-P-ΔP) is 3 on the upper stage side.
A second optical grating 15 of 98 μm is provided.

Here, the first optical grating 13 has a reference range longer than 80 mm)
is divided into N (-200) equal parts, and the second optical grating 15 is divided into N (-200) equal parts.
Although it is formed to divide into +1 equal parts, L=NP-(N+1)(P-ΔP)...(1)
holds true. The above-mentioned numerical values are selected from this relational expression.

On the other hand, the index scale 20 serves as a second scale placed in front of the main scale 10 and a third scale placed after the optical system. As shown in FIG. 2, there is a first reference optical grating 23A (23B) corresponding to the first optical grating 13 of the main scale 1o on the lower side, and a second reference optical grating on the upper side. A second reference optical grating 25A (25B) corresponding to the optical grating 15
) is provided.

The pitch of the first reference optical grating 23A (23B) is q, the pitch of the second reference optical grating 25A (25B) is q-Δq, and the corresponding first and second optical gratings in the longitudinal direction are Two sets of reference optical gratings 23A, 23B, 25A, 2 whose phase is shifted by 90 degrees with respect to the optical grating 13°15
5B is provided. Note that in this example, q=2P
, Δq-2ΔP (However, in FIGS. 1 and 2, for convenience of drawing, Q=P is shown).

Next, the 2m photoelectric converter 30 (30A, 30B) is 4
photoelectric elements 33A, 33B, 35A.

35B, each reference optical grating 23A, 23B,
25A and 25B, and each photoelectric element 3
3A, 33B, 35A, 35B have preamplifier 37A,
37B, 38A, and 38B are connected to each other. In addition, on the opposite side of the photoelectric converter 3o with both scales 10°20 in between, there are light sources 41A and 41B consisting of I and ED, and lenses 42A and 42B for the purpose of simply condensing light, which are non-parallel to both scales 10 and 20. A non-parallel illumination system 40 for irradiating light is provided, and the non-parallel illumination system 4o is movable relative to the main scale 1o integrally with the index scale 20 and the photoelectric converter 3o in a predetermined relationship in the X direction in the figure. It is said that

Then, the index scale 2o and the non-parallel illumination system 40
A half mirror 45 is interposed between the two. Therefore, the non-collimated light irradiated from the non-collimated illumination system 4o first passes through the half mirror 45 and the index scale 2 as the second scale, and is irradiated onto the main scale 10.
The reflected light from the main scale 10 is configured to pass through an index scale 20 as a third scale, then be refracted in a 45 degree direction by a half mirror 45, and enter the photoelectric converter 3o. In addition, as shown in FIG. =2
p), and if the wavelength of the light from the non-parallel illumination system 40 is λ, the clearance C between both scales 10.20 is C#
Since it is determined by riP2/λ (n is an integer greater than or equal to 1), it can be made extremely large, such as several tens of μm.

Here, as shown in FIG. 2, the point T where the first optical grating 13 and the second optical grating 15 coincide is set as the origin, and the coordinates, that is, the relative position of the index scale 20 with respect to the main scale 10, are set to the right in the figure. Letting the amount of movement displacement be X,
The photoelectric elements 33A and 33B are the first reference optical grating 23A.
, 23B with a phase difference of 90 degrees, the output of the photoelectric element 33A is
If the output of B is S, then the phase difference θ1 between the electrical signals from both optical elements 33A and 33B is, so a+=A sin θ.

(4) It can be approximated as bl=Acosθ 1 . Note that □ in the second term on the right side of equation (3) is introduced as a correction term because the amount of transmitted light is maximum at the origin T.

Similarly, the outputs of the photoelectric elements 35A and 35B are set to "2", respectively.
1 bz, the phase difference θ2 between the electrical signals from the photoelectric elements 35A and 35B can be approximated as t)z=Bcosθ2.

Further, the first counting circuit 50 receives the relative movement displacement X of both scales 10 and 20 from the touch sensor 65 via the CPU 55.
A sample and hold circuit 51 for sample-holding the output signals "+-b," 2+b2 of each photoelectric element 33A, 33I (, 35A, 35B) and this sample The output signals al and bI held from the hold circuit 51
A multiplexer 52 that takes out one of +a2 and +b2, and an A/D converter 53 that converts the output signal, which is an analog signal taken out by this multiplexer 52, into a digital signal.
By processing the output signal of the A/D converter 53 in a predetermined manner in cooperation with the CPU 55, the relative displacement amount of both scales 10.20 within the reference range length is reduced (with the minimum resolution) and the absolute value is It is formed from an absolute displacement counter 56 that counts as . Similarly, the second counting circuit 90 has a configuration as shown in FIG. 5 (details will be described later).

Further, the CPU 55 is connected to the sample hold circuit 5.
1. Provides timely commands to the multiplexer 52 and A/D converter 53, as well as the first and second AL number circuits 50.
The total length relative displacement of both scales 10.20 is determined using a count value of 90. Further, a touch sensor 65 and a display means 60 are connected to the CPU 55. Although the absolute displacement counter 56 may be formed integrally with the CPU 55, it is shown separately as shown in FIG. 1 for convenience of explanation. It is assumed that Here, the first counting circuit 50, the second counting circuit 90, and the CPU 55
to the displacement detection circuit 100. is composed of

Now, the first counting circuit 50 in the displacement detection circuit 100
(Including the cooperative function of the CPU 55) When explaining the thin displacement detection function within the reference range length, the final result is as follows:
The absolute displacement amount X from the origin T is determined as follows. Note that the vertical axis of FIG. 4(B) is set to θ and −□ in relation to the second term on the right side of equation (3). In each case, X is a wide range change within the reference range length of the first optical grating 13 of the main scale 10, and a pitch that is 1ffl different from the pitch l) of the first optical grating 13. Number of P (n is 1
ΔXt is the absolute displacement amount of the first optical grating 13 within the pitch P of the first optical grating 13.

That is, the present invention provides two rows of optical gratings 13.15 on the main scale 10, and the inter-set phase difference (θ2 The reason for using the absolute method using -θ1) is as follows.

That is, the above equation (5) can be converted as follows.

P-ΔP2 ...... (7) Then, by substituting equations (3) and (2) into equation (7), we get
= □ (θ2−θ, ) ・・・・・・
(9) 2 π.

Therefore, in the CPU 55, from equation (9), the photoelectric element 33A corresponding to the first optical grating 13 of the main scale 10,
Phase difference θ1 of output signal aI+ b+ from '33B
and photoelectric elements 35A, 35 corresponding to the second optical grating 15
If the phase difference θ2 of the output signal a2+bg from B is determined, the absolute displacement amount X from the origin T can be determined since the length of the reference range has been determined.

Here, θ1 and θ2 are from 2 (4) and (6)...
・・・・It is obtained as α〔.

Furthermore, in this example, in order to further stabilize the accuracy, θ
Rather than making 1 and 02 independent, they are formed to have a correlation function to determine the absolute displacement X.

If θ2 and θ were found independently and simply subtracted based on equation (9), each photoelectric element 33A, 33B, 35A
, 35B is the pitch P of each optical grating 13.15.

This is because the waveform is cyclic for each P-ΔP, so there is a risk of loss of digits.

Therefore, a and b are newly defined.

This 2〇〇 has the formula f41. (If you substitute 61, a-A
Bsin(θ2-θI) tl=ABcos(θ2-θ1) --tan (θ2-θ1) ...... Therefore, θ2-θr = tan-' ---Ql
, the photoelectric element 35A is obtained by calculating the arctangent function.

Phase difference between strings 35B, 33A, and 33B (θ2−θl
).

By the way, as is clear from equation (b), the phase difference between the pairs (θ
2-01) changes from θ to 2π within the reference range length as seen in Figure 4 (A), so the displacement X' up to point Q in the figure is equal to the absolute value X shown in Figure 4 (B). This is an approximate value. Therefore, the same as equation (9) holds true.

Furthermore, as shown in Fig. 4 (B), the absolute value X of the relative movement amount of both scales 10.20 within the reference range length determines the wide range displacement amount X1 and the narrow range displacement amount ΔX. (Formula %Formula %) Here, from the equation (31, (11), the narrow range displacement amount ΔXL within the pitch P of the first optical grating 13 of the main scale IO
However, the first optical grating 13, the first reference optical gratings 23A, 23B, the photoelectric elements 33A, 33B
Based on (the phase difference θ1 is a periodic function of the pitch P, it is not possible to specify which pitch (counting from the origin 1′) it is within).

Therefore, the above-mentioned phase difference θ1 is converted into a value θ1゛ with a phase shift of □ or more to (2+□) or less. Then, if we set it analogously to equation (3), then the following holds true.

On the other hand, the number n of pitches P of the first optical grating 13 that has passed from the origin T to the relevant point in time is expressed as
It is clear that the number does not exceed P and is an integer.

However, as an exception, in Fig. 4, the measurement resolution Δ
If L is the same as (B) but includes a region where the phase changes by 2π-〇, and ΔXI is closer to 0 than 2π by ΔL, add 1 to the integer that does not exceed (X'--)/P. Bye.

Here, it is a function of X''-f (θ2-0l) as per the second ship, P and ΔL are the values determined as design (a), and θ and ゛ are uniquely the phase from θ. I was asked to spell it out.

Therefore, it can be determined as a function of n=f(θ7-θ1.ΔXI).

From the above, in the CPU 55, X np + ΔX of the above formula 〇61
By calculating 1, the absolute value X of the relative displacement amount of both scales 10°20 can be obtained. In other words, it is assumed that the absolute displacement counter 56 stores this absolute value X.

Next, the second 81 number circuit 9 that goes into the displacement detection circuit 100
A rough displacement detection function that uses the reference range length I as a level by 0 will be explained. First, as shown in FIG. 5 and FIG. 6, the second 41 number circuit 90 is connected to approximately 11:2 to create a sinusoidal wave signal (more specifically, a waveform signal approximately equal to a sine wave shape).
two multipliers 91A, 91B, a subtracter 92, and an approximately cosine wave signal (i!'1'< is a waveform signal approximately equal to the cosine wave shape)
It is formed from multipliers 9IC and 91D that generate , an adder 93, and a counting circuit 94 as a reversible counter having a direction discrimination function. Therefore, the output signal 11 of the subtractor 92
(ABsin (θ2-θ1)) and the output signal I2 of the adder 93 [^Bcos (θ2-θ1)] both have a long reference range and are out of phase by 90 degrees.
Formula (8).

(9)) In the 81 number circuit 94, the dark value is set to zero, for example, and the L-1 scale is roughly calculated by adding and subtracting the number of passing points in the reference range length while distinguishing the relative moving direction of both scales 10.20. Relative displacement can be counted.

Next, the operation of this embodiment will be explained.

For example, main scale I is attached to a stationary object such as a machine tool vent.
O is fixed, and the index scale 20 is fixed to a movable body such as a slider by integrating it with the non-parallel illumination system 40 and the photoelectric converter 30. Therefore, by operating the machine tool, the main scale 10 and the index scale 20
When these move relative to each other, each photoelectric element 33A, 33B, 35
Electrical signals a+ + bl + a from A and 35B
t+ l)z is output, and the cycles of the signals air bl and a2+ bl differ by an amount corresponding to the pitch difference of the optical grating 13.15, and the signal a1 is assumed, and a2 and bl each have a phase difference of 90 degrees. arise.

Now, let us consider a case where the relative displacement amount S of both scales 10.20 from point T to point P is to be detected with point T as the absolute origin, as shown in FIG. 4(C).

First, in the first 31-number circuit 50 of the displacement detection circuit 100, since the detection point is unknown, when the absolute origin specifying signal is input at point T1, it is within the reference range length as shown in FIG. 4 (13). In cooperation with the CPU 55, the absolute displacement i1X is counted. The absolute displacement amount X is stored in the absolute displacement counter 56, and is calculated every reference range length, that is, T 2
, T3.

This order is performed as follows. When the absolute origin specifying signal (in this embodiment, signal 5 is input), the CPU 55 issues a hold command to the sample hold circuit 51 based on the command from the CPU 55, as shown in FIG.

The sample hold circuit 51 is a preamplifier 37A.

Analog electrical signals aI+ bl and a2.37B, 38A, 38B output stage side. Hold bl (steer knob 12).

Next, as in step 14, the multilexer 52
Electrical signals a1, b, and a2+ based on commands from 55
bl is taken in, converted into a digital signal by the A/D converter 53, and then input to the CPU 55.

Hereinafter, CP tJ 55 "il" is the formula 〇θ1,
(Photoelectric element 33A corresponding to the first optical grating 13 based on +51).

The phase difference θ1 from 33B and the narrow range displacement amount ΔX are calculated (step 16). That is, the first optical grating 13
The amount of displacement within the pitch P is determined as an absolute value. Of course, in order to specify which pitch the phase difference θ1 is within, O is a value of □ or more to (2π+□) or less.
It is converted to lo in the cpU55.

Also, in step 18, 2〇〇! +2) definition signals a and b based on these and photoelectric elements 35A, 35B and 3
Inter-group phase difference θ2-θ based on each phase difference with 3A and 33B
1 is determined, and the arctangent function is calculated to calculate the inter-set phase difference θ2−θ1.

Here, the number n of pitches P of the first optical grating 13 that has passed so far, which corresponds to FIG.
).

Therefore, in step 22, the absolute value X of the relative displacement amount within the reference range length of both scales 10 and 20 is determined by calculating the second value.

This absolute value X is displayed on the display means 60 and outputted to the outside if necessary. The above procedure is repeated at regular intervals (step 26). Further, as shown in FIG. 4(C), the count value of the absolute displacement counter 56 is cleared each time the point '1', . . . 'T'3 is reached.

That is, the first counting circuit 50 calculates the absolute displacement amount X within the reference range length with the starting point (points T2, T3) of the reference range length being zero.

On the other hand, in the second counting circuit 90, as shown in FIG.
), bl (Acos θ+), a2 (Bs
in θz ), b2 (Bsin θ2) are manually generated and the sine wave shape signal 1, (ABsin(θ2−
θl)] and cosine wave shape signal 1 z (ABcos
(θ2-θ,)] is determined, and the counting circuit 94 determines direction discrimination (increase/decrease) and counts the length of the reference range as a unit, starting from the absolute origin T. In this embodiment, the count value at point T is "2".

Here, at point P (see Figure 4), both scales 1
When a trigger is input from the touch sensor 65 that is activated when the absolute value of the relative movement displacement amount of 0.20 is desired to be displayed on the display means 60 or output as a feedback signal to the control device (not shown) (step 10), As the displacement amount within the reference range length of the first counting circuit 50, an absolute displacement amount X starting from point T3 is stored. Of course, the count value of the second counting circuit 90 is "2".

Therefore, the CPU 55 can obtain the displacement amount from the absolute origin T1 as the starting point to the current position P1 as the absolute value S by setting 5=2XL+X.

Therefore, according to this embodiment, two rows of optical gratings 13.15 having different pitches (P, P-ΔP) are provided on the main scale 10, and the inter-group position is determined from the relationship with these optical gratings 13.15. The amount of relative displacement between the main scale 10 and the index scale 20 within the reference range length can be detected as an absolute value X using the phase difference (θ2-θ1). Since an absolute type optical displacement detection device can be established here, industrial applicability can be dramatically expanded in terms of accuracy and operational technology.

This ensures stable predetermined accuracy because there is no influence of noise on the way and there is no accumulation of noise, and since continuous tracking is not required, response speed is high and rapid measurement can be achieved. This means that even if the power is cut off, it is possible to immediately re-measure without having to adjust the origin each time, thereby eliminating the drawbacks, disadvantages, and inconveniences of the conventional incremental method.

In particular, both scales 10.20 starting from the absolute origin T1
The relative movement amount S is determined by the value X, which is determined as a high resolution and absolute value by the first counting circuit 50 as described above, and the absolute value (2XL) by the second counting circuit 90, which uses the reference range length as a unit. Therefore, not only can absolute detection be performed over a long span, but also the counted value by the first counting circuit 50 within the reference range length on the way does not have any effect on the accuracy at the target detection point (Pl). As a result, the relative speed of both scales 10.20 can be dramatically increased. For example, if the pitch P is 40 μm and P''/ΔP (#L) is 4 mm, the pitch to be counted by the second counting circuit 90 is 41, so the relative moving speed of both scales is now 10.20. 1m/
sec, the response frequency is only 250)1z, and the design and economic burden of the second counting circuit 90 is light, and it is clear from the fact that the response frequency of the first counting circuit 50 can be further lowered. It is. This means that
When the first counting circuit 50 is an incremental displacement detection circuit as described in FIGS. 8 and 9, it means that the effect and practical benefits are even greater in terms of speeding up. .

In addition, the main scale 10 is provided with two optical gratings 13 and 15 with different pitches, and the first counting circuit 50 is formed to obtain the absolute displacement amount within the reference range length, but the second counting circuit 90 is b) By installing one circuit, it is possible to detect absolute displacement over multiple reference range lengths. Therefore, the second dI number open circuit 90 configuration is useful not only for speeding up the displacement detection circuit 100 but also for the absolute method. This also has the effect of establishing a new displacement detection circuit (first counting circuit 50) and increasing its effectiveness.

Furthermore, two rows of optical gratings 1 provided on the main scale 10
3.15 is assumed to be physically fixed on a glass plate by the etching method, etc., and the inter-set phase difference between optical gratings with different pitches and the position within the same optical grating. Since it is designed to detect the absolute value of the amount of displacement using the phase difference, it is different from, for example, conventional incremental system devices in which the waveform generated within one pitch is electrically subdivided by resistance division, etc. , both scales are 10.20, that is, they are matched with the machine tools used, so true high-precision measurement can be guaranteed.

Furthermore, in order to obtain the phase difference between the two optical gratings 13.15, the phase difference between the two optical gratings 13. Detection without loss of precision can be achieved by making the correlation between High accuracy is guaranteed from this point as well.

In this example, the pitch P of the first optical grating 13 of the main scale lO is 400 μm, the pitch P−ΔP of the second optical grating 15 is 398 μm, and the reference range length is within the range of 80 m++. The number of divisions N was set to 200 to enable detection with a resolution of 2 μm, but these numerical matters can be arbitrarily selected, and the resolution can be set to 0.
It can also be set to 1 μm or less. For example, the pitch P of the first optical grating 13 and the first reference optical gratings 23A, 23
Together with the pitch q of B, 4'Op m (P = q
= 40 μm > , the detection range length is 5 mm (L =
5 mm), that is, the number of divisions n is 125 (N = 12
5), in this case the preamplifiers 37A, 3
Since the cycle pitch of the output signals from 7B, 38A, and 3813 is optically P/2, the result is 20 μm (=
By dividing P/2) into 125 parts, absolute detection with a resolution of 0.16 μm is possible.

In the sense of such arbitrariness, the main scale 10 has two rows of optical gratings 23A, 23B, 25A.

25B were formed from two pieces each with a phase shift of 90 degrees -U, but the point is that if a phase difference can be created in relation to the corresponding optical grating 13.15 of the main scale 10, the pitch q can be slightly changed. It is also possible to form one each by employing a so-called vernier type reference optical grating.

Furthermore, if the two output electric symbols from the photoelectric element having a phase shift of 90 degrees are used, for example, by a differential method, the dynamic range (detection range/resolution) can be further improved. Furthermore, the optical grating 1 of the main scale lO
3 (15) and the reference optical gratings 23A, 23B (25A, 25B) of the index scale 20 are not limited to being equal; for example, the pitch of the reference optical gratings 23A, 23B is P/ It can also be implemented as n (n is an integer of 1 or more).

Further, although the detection device itself is a reflective linear type using a non-parallel illumination system, the present invention is also applicable to a rotary type instead of a linear type. Of course, the first part of the displacement detection circuit 100
Although the counting circuit 50 only needs to detect small displacements within the reference range length 14, the present invention is not limited to the above-mentioned absolute method, but may also be implemented as an incremental method using parallel light as shown in FIG. 7. Further, although the touch center 65 is used to specify the time of displacement detection, the present invention is not limited to this.

Furthermore, in the case of the above embodiment, the reference range length is the length with respect to the relative movement direction between the main scale 10 and the index scale 20, but this can be set and changed in the second detection circuit 90. You can also do that. This detection device detects displacement, and the object to be measured is not limited to length, width, etc., but may also be an angle, velocity, pressure, weight, etc.

〔Effect of the invention〕

In the present invention, two rows of optical gratings with different pitches are provided on the main scale, and the displacement detection circuit is divided into a first counting circuit that subdivides the reference range, and a second counting circuit that performs rough counting using the reference range length as a unit. By designing and configuring the counting circuit, it has the excellent effect of achieving high-speed operation while ensuring high accuracy.

[Brief explanation of the drawing]

Fig. 1 is an overall configuration diagram showing an embodiment of the optical displacement detection device according to the present invention, Fig. 2 is an enlarged view of the main part, and Fig. 3 is a diagram showing the same as the one for calculating the absolute displacement amount within the reference range. 4 is a waveform explanatory diagram, FIG. 5 is a circuit diagram of the second counting circuit, and FIG. 6 is a circuit diagram of the second counting circuit.
FIG. 7 is an overall configuration diagram of an optical displacement detection device showing another embodiment in which the first counting circuit is of an incremental type, and FIGS. 8 and 9 are diagrams of conventional FIG. 8 is a schematic configuration diagram of an optical displacement detection device;
The figure shows a reflective type, and FIG. 9 shows a transmissive type. DESCRIPTION OF SYMBOLS 10... Main scale, 13... First optical grating, 15... Second optical grating, 20... Index scale serving as second and third scales, 23...
- First reference optical grating, 25... Second reference optical grating, 30... Photoelectric converter, 40... Non-parallel illumination system, 5
0...first counting circuit, 90...second counting circuit,
100...Displacement detection circuit.

Claims (6)

[Claims] (1) A main scale provided with two rows of optical gratings and each row having a different optical grating pitch, and two rows of reference optical gratings corresponding to each row of optical gratings of the main scale. an index scale disposed and movable relative to the main scale; an illumination system for irradiating light to both scales; Each time, the transmitted light transmitted through the main scale or the reflected light reflected from the main scale is received.
two sets of photoelectric converters that output electrical signals with a phase shift of 0 degrees; and a first set of photoelectric converters for counting displacement within a reference range length by inputting the electrical signals output from at least one set of the photoelectric converters. The first and second counting circuits are formed to include a counting circuit and a second counting circuit for counting displacement in units of reference range length by inputting electric signals output from the two sets of photoelectric converters. and a displacement detection circuit that determines the amount of relative displacement between the main scale and the index scale using both counted values. (2) In claim 1, the first counting circuit of the displacement detection circuit counts the displacement in an incremental manner using an electric signal output from one set of the photoelectric converters as input. Optical displacement detection device. (3) In claim 1, the first counting circuit of the displacement detection circuit calculates θ_2 when the phase difference between one set of the photoelectric converters is θ_1 and the phase difference between the other set is θ_2. An optical displacement detection device that counts displacement using an absolute method using an inter-set phase difference of −θ_1. (4) In any one of claims 1 to 3, the second counting circuit of the displacement detection circuit sets the optical grating pitch of one row of the main scale to P and the optical grating pitch of the other row. When the pitch is P-ΔP, P^2/Δ
An optical displacement detection device configured to generate a sine wave signal and a cosine wave signal with P as one cycle, and to specify the reference range length from the sine wave signal and cosine wave signal. (5) The optical displacement detection device according to claim 4, wherein the reference range length is one cycle of the sine wave signal or cosine wave signal. (6) In claim 4 or 5, when the sine wave signal and the cosine wave signal have a phase difference of θ_1 between one set of the photoelectric converter and a phase difference of θ_2 between the other set, , θ_2−θ_1, which is an optical displacement detection device, is created using the phase difference between pairs as a variable.