JP2736924B2 - Position detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a position detecting device suitable for use in, for example, a machine tool or a precision length measuring machine.

[Summary of the Invention]

The present invention relates to a position detection device suitable for use in, for example, a machine tool or a precision length measuring device, wherein a first scale on which a periodic pattern is formed and a first scale arranged in parallel with the first scale are provided. A second scale having a non-periodic pattern formed by encoding the absolute position of a periodic pattern, and a phase detection signal corresponding to the periodic pattern that is freely displaceable relative to the first scale. First to generate
A second detector for generating an absolute position signal corresponding to the aperiodic pattern that is relatively displaceable with respect to the second scale in conjunction with the first detector; A first detection circuit for detecting an absolute position within one pitch of the periodic pattern from a phase detection signal, and a second detection circuit for detecting an absolute position of the periodic pattern for each pitch from the absolute position signal And a relative displacement between the first and second scales and the first and second detectors within one pitch of the periodic pattern over the entire length of the aperiodic pattern. By forming the second scale by superimposing it on the first scale so as to detect the absolute position, the scale portion is reduced in size.

[Conventional technology]

In a machine tool or the like, for example, in order to detect the feed amount of a processing tool, a scale having a scale of a periodic pattern formed on one member is arranged, and the scale is read by a sensor on the other member to periodically perform the scale. A so-called incrementala in which a detector for generating an electric signal is arranged, and the electric signal is pulsed and accumulated and counted to measure the relative displacement between the one member and the other member.
l) A type of displacement detection device is used. However, this kind of incremental displacement detection device has the following disadvantages.

For example, when the work is interrupted, the power is turned off, or the work is resumed after a power failure, the accumulated count value is lost. (Initialize).
That is, workability is poor.

If an erroneous count occurs even once during the operation due to noise from another machine tool or the like, all subsequent integrated count values become erroneous, so that initialization is necessary again. That is, the noise resistance is poor.

Since the counting pulse is always counted, the response speed is limited.

In order to solve all of the above-mentioned disadvantages (1) and (2), a scale on which a scale of a non-periodic pattern indicating an absolute position from a certain origin is formed is arranged on one of the two members relatively displaced, and the other member is provided. There are various types of so-called absolute type position detecting devices in which a detector having a sensor for reading the scale is disposed and the relative displacement between the two members is detected as an absolute position from the origin on the scale. Proposed.

FIG. 5 shows a conventional magnetic absolute type position detecting device disclosed in Japanese Patent Publication No. 50-23618. In FIG. 5, (1) is a scale made of a magnetic material. scale (1) the pitch lambda ₁ of the magnetic scale (2) and pitch lambda ₂ (lambda ₂ <lambda ₁₎ magnetic scale (3) of are formed in parallel. (4A) and (4
B) The magnetic head of the pair of magnetic flux response type for reading the respective magnetic scale (2), (5) the phase theta ₁ in one pitch lambda ₁
Phase detection circuit for detecting the (absolute position), (6A) and (6B) of the pair of magnetic flux response type magnetic head for reading the respective magnetic scale (3), (7) within one pitch lambda ₂ showing a phase detection circuit for detecting the phase theta _2.

From phase detection circuit (5) to magnetic heads (4A) and (4B)
Is the excitation signal I _A and I _B of the formula each follows using constants A and the excitation frequency f / 2 is supplied for.

I _A = A cosπft (1) I _B = A cos (πft + π / 4) (2) Also, the interval between the magnetic head (4A) and the magnetic head (4B) is (n + 1/4) λ ₁ ( n is an integer) and their magnetic heads (4
Assuming that the relative displacement (absolute position) of the magnetic scales (2) and (3) of the magnetic scales (A) and (4B) and the scale (1) with the left end as the origin is x, the magnetic heads (4A) and (4B) Is the constant A ₁
And the phase detection signals K _A and K _B represented by the following equations, respectively.
Is supplied to the phase detection circuit (5).

K _A = A ₁ sin (2πx / λ ₁ ) cos2πft (3) K _B = A ₁ cos (2πx / λ ₁ ) sin2πft (4) And, in the phase detection circuit (5), these phase detection signals The displacement signal d is formed by adding K _A and K _B, and d = K _A + K _B = A ₁ sin (2πft + 2πx / λ ₁ ) = A ₁ sin (2πft + θ ₁ ) (5) θ ₁ = 2πx / λ ₁ (6) The phase amount θ ₁ (0 to 2π) of the displacement signal d is measured. The relationship between the phase amount θ ₁ and the displacement amount x is as shown in FIG. 6A. For example, when the phase amount θ ₁ is π, the displacement amount x is x ₀ , x ₁ , x ₂ , x ₃ . Although it is not possible to determine which of the above, but within the range of one pitch λ ₁ of the magnetic scale (2), the phase amount θ ₁ takes a certain value of 0 to 2π, so the displacement amount x is detected as an absolute position. can do.

Similarly, in the phase detection circuit (7) is as shown in Figure 6 B, the phase amount theta ₂ takes a value of 0~2π in period lambda ₂ is measured for displacement x. Accordingly, the following holds: θ ₂ = 2πx / λ ₂ (7)

They phase amount theta ₁ and theta ₂ absolute position detection circuit (8)
The absolute position detection circuit (8) first calculates a phase difference Δθ (= θ ₂ −θ ₁ ). This phase difference Δθ is expressed as follows from equations (6) and (7).

Δθ = θ ₂ −θ ₁ = 2πx (1 / λ ₂ −1 / λ ₁ ) = 2πx (λ ₁ −λ ₂ ) / (λ ₁ λ ₂ ) (8) Further, from the expression (8), x = (Δθ / 2π) λ ₁ λ ₂ / (λ ₁ −λ ₂ ) (9) Since λ ₁ and λ ₂ are known, the absolute position detection circuit (8) is obtained from the equation (9). The displacement x is calculated and supplied to the display (9). In this case, if 0 ≦ Δθ <2π (10), the value of the displacement x can be uniquely obtained, so the maximum measurement length L at which the displacement x can be accurately measured as an absolute position is L = λ ₁ λ ₂ / (λ ₁ −λ ₂ ) (11) Accordingly, the relationship between the displacement x and the phase difference Δθ is as shown in FIG. 6C. Further, in equation (9), the phase difference Δθ can generally be measured with a resolution of about one thousandth of 2π, so the measurement resolution Δx of the displacement x is about Δx ≒ L × 10 ⁻³ (12) . Table 1 shows the values of the maximum measurement length L and the measurement resolution Δx when specific numerical values are substituted for λ ₁ and λ ₂ .

Further, as another conventional absolute position detecting device, a device using a gray code as shown in FIG. 7 is also known. In FIG. 7, (10) is a translucent scale on which a k-bit gray code (11) is formed,
(12) is a light emitting element, (13) is a collimator lens, (14)
Denotes an index plate on which a reference window (15) corresponding to the gray code (11) is formed, and (16) denotes k light receiving elements corresponding to the gray code (11). A detector having 16) is disposed so as to be displaceable in the x direction with respect to the scale (10). When the resolution of the gray code (11) and lambda _3, by multiplying the lambda ₃ to the device obtained by decoding the electric signals output from the light receiving element (16) of the detector, the scale (1
Displacement x of the detector relative 0) is calculated as an absolute position resolution lambda _3.

In this case, the maximum measurement length L that can accurately measure the displacement x as an absolute position is L = λ ₃ × 2 ^k (13). For example, if the resolution λ ₃ is 1 mm and k is 10, the maximum measurement length The length L is 1024 mm.

[Problems to be solved by the invention]

However, among the above-mentioned conventional azo-solut type position detecting devices, the one shown in FIG. 5 has a resolution Δx of approximately 1 mm from the expression (12) when the maximum measuring length L is set to a practical value of approximately 1000 mm. And there was a disadvantage that the resolution was extremely poor.

Note that the above-mentioned Japanese Patent Publication 50-23618 Patent Publication (Fifth illustrated example), the displacement x of the pitch lambda ₁ unit of the scale (1) to identify the absolute position, the final resolution of the displacement x Although it is disclosed can be greatly improved to the pitch lambda ₁ of example 10 about ^-3, there is a disadvantage that the maximum measurement length L is limited when trying to accurately measure the absolute position of its pitch lambda ₁ units.

Further, in the position detecting device of FIG. 7, the resolution λ ₃ is 10 μm.
m is the limit. In this case, when a scale that forms a gray code of about 12 bits, which is a practical limit, is used as the scale, the maximum measurement length L is Δx = 0.
It is about 40 mm from 01 mm and 2 ¹² = 4096, which is not practical.

In view of this, the present invention has a maximum measurement length of, for example, 1000 mm.
And the resolution can be set to, for example, 1 as high as that of an incremental displacement detection device.
It is an object of the present invention to propose an absolute position detecting device having an order of μm.

[Means for solving the problem]

The position detecting device of the present invention is arranged in parallel with the first scale (18) on which a periodic pattern (20) is formed as shown in FIGS. 1 and 2, for example. A second scale (19) on which a non-periodic pattern (21) formed by encoding the absolute position of this periodic pattern (20) is displaced relative to the first scale (18) A first detector (23A) that freely generates a phase detection signal corresponding to the periodic pattern (20);
This second scale (19) in conjunction with the detector (23A)
This aperiodic pattern that can be displaced relative to (21)
A second detector (23) for generating an absolute position signal corresponding to
B) and this periodic pattern (2
0), a first detection circuit (25) for detecting an absolute position within one pitch, and a second detection circuit for detecting the absolute position of this periodic pattern (20) in units of one pitch from the absolute position signal. (32), these first and second scales (18) and (19), and these first and second detectors (23).
When detecting the relative displacement with respect to (A) and (23B) as the absolute position within one pitch of the periodic pattern (20) over the entire length of the aperiodic pattern (21), This second scale (19) is formed so as to overlap the scale (18).

[Action]

According to the present invention, first, the absolute position of the periodic pattern (20) in units of one pitch λ is obtained by the second detection circuit (32). Next, the first detection circuit (2
5) one pitch λ of the periodic pattern (20)
The absolute position within the range is obtained.

Therefore, the length of the aperiodic pattern (21) of the second scale (19) is set to a practical length with a resolution on the order of one pitch λ of the periodic pattern (20), and By setting one pitch [lambda] of the periodic pattern (20) to the same order as that of the incremental displacement detection device, the maximum measurement length can be set to a practical range and the resolution can be improved to the same level as the incremental type.

Further, according to the present invention, the scale portion can be downsized.

〔Example〕

Hereinafter, an embodiment of the position detecting device according to the present invention will be described with reference to FIGS.

FIG. 1 shows a position detecting device of the present example. In FIG. 1, (17) is a scale base, and this base (17)
Is attached to one of two members that are relatively displaced, not shown, and a first scale (18) made of a magnetic material is attached to one surface of the base (17) so as to cover the first scale (18). A second scale (19) made of a non-magnetic material (for example, a non-magnetic stainless sheet) is attached. Then, as shown by notching a part (19a) of the second scale (19), a period of the pitch λ is provided on a surface where the first scale (18) is in contact with the second scale (19). Magnetic scale (2
0) and its second scale (19)
K-bit gray code with resolution λ _m (21)
Is formed. The gray code (21) is, for example, a portion corresponding to the high level "1" on which the antireflection film is deposited except for the portion corresponding to the high level "1" on the outer surface of the reflective second scale (19). A reflective metal film (such as a chrome film) is deposited only on a portion corresponding to a high level "1" on the outer surface of the non-reflective second scale (19) except for roughening the surface by etching, or And the like.

Reference numeral (22) denotes a detection head, and the detection head (22) is arranged so as to be relatively displaceable in the x direction with respect to one of the members to which the base (17) is attached. The detection head (22) is connected to a signal processing device (not shown) by a signal cable (22a).

FIG. 2 shows the internal structure of the detection head (22) and the signal processing device. In FIG. 2, (23A) is a first detector for reading the magnetic scale (20), and (23B) is gray. A second detector for reading the code (21), wherein the first detector (23A) is a pair of magnetic flux-responsive magnets spaced apart by (n + 1/4) λ (n is an integer); Head (24
Formed from (A) and (24B). Reference numeral (25) denotes a phase detection circuit. This phase detection circuit (25) excites the magnetic heads (24A) and (24B) similarly to the phase detection circuits (5) and (7) in FIG. In addition to supplying signals, the phase detection signals output from the magnetic heads (24A) and (24B) are processed to detect the displacement x of the detection head (22) as the phase θ. In the same manner as in the equation (6), the phase amount θ is represented by θ = 2πx / λ (6A). Therefore, the relationship between the phase amount θ and the displacement amount x is as shown in FIG. 3B.

The second detector (23B) is a light-emitting element (26), a collimator lens (27), and converts a parallel ray L into a second scale (19).
, A cylindrical lens (29) for converging the parallel light beam L reflected from the second scale (19), and k reference windows corresponding to the gray code (21). An index plate (30) and a light receiving element array (31) composed of k light receiving elements,
The k-bit output signal of the light-receiving element array (31) is supplied to an absolute position code detection circuit (32), and the absolute position code detection circuit (32) decodes the k-bit output signal and converts the absolute position data. obtain. The phase amount θ obtained by the phase detection circuit (25) and the absolute position data N obtained by the absolute position code detection circuit (32) are supplied to a calculation circuit (33), and the calculation circuit (33) The displacement (ie, absolute position) x obtained in accordance with the procedure described later is supplied to the display (34).
Further, the displacement x may be used as a control signal or the like for the positioning device.

To explain the operation of the arithmetic circuit (33), in this example, the magnetic scale (20) and the gray code (21) actually overlap, but for convenience of explanation, both are shown in FIG. 3A. The first detector (23A) and the second detector (23B), which are arranged in parallel on the same plane and correspond to the magnetic scale (20) and the gray code (21), respectively, are both located at the position P in the x direction. (FIG. 3B). In this case, assuming that the absolute position within one pitch λ of the magnetic scale (20) including the position P is Δx, one pitch of the magnetic scale (20) including the position P is q-th from the origin (x = 0) (x = 0). (q = 0, 1, 2,...)), the displacement x of the position P is represented by x = qλ + Δx (14). In this case, since the phase amount θ is known, Δx is represented by Δx = λθ / (2π) (15) according to the equation (6A). Therefore, the displacement amount x can be calculated by obtaining the integer q. .

To facilitate the calculation of the integer q in this example, the gray code (21) of resolution r _m is r _m = λ / _m ...... using natural number m of the pitch lambda of the magnetic scale (20) (16) Set to the relationship. FIG. 3 shows that r _m = λ, that is, m = 1.
Corresponds to the case of In this case, by generalizing the state shown in FIG. 3, the absolute position data N obtained by decoding the gray code (FIG. 3C) at the position P and an integer q indicating the period of the magnetic scale (20) are obtained. It is clear that there is a relationship between q = INT (N / m) (17). In equation (17), INT (N / m) indicates an integer part of N / m. Incidentally, in the example of FIG. 3, the value of q at the position P is 13.

FIG. 4 shows a state where λ _m = λ / 2, that is, m = 2. In FIG. 4, for example, at positions Q ₁ and Q ₂ , absolute positions obtained from a gray code (FIG. 4C) Data N is different as 12 and 13, respectively. However, equation (17)
The value of the integer q thus obtained is 6 in common at the positions Q ₁ and Q ₂ . Thus, in the position Q ₁ and Q ₂ may be obtained displacement amount x in accordance with the respective equations (14).

When the value of m is set to 2 or more as in the example of FIG. 4, even if the positional relationship between the gray code (21) and the magnetic scale (20) is slightly shifted, the absolute position can be detected with high accuracy. There is a benefit. For example, when m = 2, if the data N Gray code is in the 11 by mistake at the position Q _1, is a directly error of the position Q is one pitch λ is determined that the position Q 'occurs. However, since the Figure 4 example integer q in position Q ₁ it is has been found that not be a pre odd data N, 1 is added to when such odd data N was obtained By converting to an even number, an accurate integer q can be obtained.

As is clear from the above description, the arithmetic circuit (3
In 3), the absolute position Δx within one pitch λ of the magnetic scale (20) is calculated according to the equation (15) using the phase amount θ supplied from the phase detection circuit (25). On the other hand, using the absolute position data N supplied from the absolute position code detection circuit (32), an integer q indicating the position of the magnetic scale (20) in units of one pitch λ is calculated according to equation (17). And
By substituting the calculated absolute position Δx and integer q into equation (14), the displacement x which is the absolute position as a whole is obtained.
Is calculated.

In the example of FIG. 1, for example, the pitch λ of the magnetic scale (20)
The 1 mm, 1 mm resolution r _m Gray code (21) (i.e., r _m
= Λ), and the number of tracks of the gray code (21) is 12 (that is, 12
Bit), the absolute position Δx of the magnetic graduation (20) within one pitch λ can be obtained with a resolution of 1/1000, that is, about 1 μm (see equation (12)). Further, the maximum measurement length L at which the absolute position can be measured is L = 1 × 2 ¹² = 4096 mm (18). That is, according to the present example, after setting the maximum measurement length L to about 4 m, which is a practical value, the absolute type position detecting device having a measurement resolution of about 1 μm comparable to that of the incremental type displacement detecting device is provided. There are benefits that can be realized.

Further, since the example of FIG. 1 has a structure in which the first scale (18) and the second scale (19) are overlapped, there is an advantage that the scale can be reduced in size. In this case, the first scale (18) may be formed using a pattern such as an electromagnetic induction type or a capacitance type.

It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that various configurations can be adopted without departing from the gist of the present invention.

〔The invention's effect〕

ADVANTAGE OF THE INVENTION According to this invention, in an absolute type position detection apparatus, while the maximum measurement length can be set to a practical range, there exists an advantage which can improve a resolution like an incremental displacement detection apparatus.

Further, according to the present invention, there is an advantage that the scale portion can be downsized.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing an embodiment of the present invention, FIG. 2 is a diagram showing a detection head and the like of the example of FIG. 1, and FIG.
FIG. 4 and FIG. 4 are respectively a diagram for explaining the example of FIG.
FIG. 7 to FIG. 7 are diagrams for explaining a conventional position detecting device. (18) is the first scale, (19) is the second scale,
(20) is a magnetic scale, (21) is a gray code, (23A) is a first detector, (23B) is a second detector, (25) is a phase detection circuit, and (32) is an absolute position code detection. Circuit, (33) is an arithmetic circuit, (35) is a scale, (36) is a magnetic scale, (3
7) is a gray code, (42) is a disk, (43) is a grid, (4)
4) is a binary code.

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-189415 (JP, A) JP-A-63-95315 (JP, A) JP-A-64-79619 (JP, A)

Claims (1)

(57) [Claims] 1. A first scale on which a periodic pattern is formed, and a non-periodic pattern arranged parallel to the first scale and encoding an absolute position of the periodic pattern. A second scale, a first detector for generating a phase detection signal corresponding to the periodic pattern that is relatively displaceable with respect to the first scale, and interlocked with the first detector. A second detector for generating an absolute position signal corresponding to the aperiodic pattern that is freely displaceable relative to the second scale; and an absolute position signal within one pitch of the periodic pattern from the phase detection signal. A first detection circuit for detecting a position, and a second detection circuit for detecting an absolute position of the periodic pattern in units of one pitch from the absolute position signal, wherein the first and second scales are provided. The first and second detections The second scale is formed by superimposing the second scale on the first scale so as to detect the relative displacement amount with respect to the entire length of the non-periodic pattern as an absolute value within one pitch of the periodic pattern. A position detecting device characterized in that: