JP2678386B2 - Position detection device - Google Patents

Description

The present invention relates to a position detection device suitable for use in, for example, a machine tool or a precision length measuring and angle measuring device.

[Summary of the Invention]

The present invention is, for example, in a suitable position detection device used in machine tools and precision measuring angle measuring device, a first scale pitch lambda _1, the pitch _{λ 2 (λ 2 ≠ λ 1} ) second scale and A scale in which a third scale having a pitch λ ₁ / m (m is an integer of 2 or more) is formed in parallel, and a first scale that reads the first scale, the second scale, and the third scale to generate a phase detection signal. , A detection head having second and third detectors and arranged so as to be displaceable relative to the scale, and the positions of the first scale and the second scale based on the three types of phase detection signals. A phase detection circuit that detects the phase difference, the phase amount of the first scale and the phase amount of the third scale is provided, and the absolute position of the first scale is obtained from the phase difference in units of pitch λ _{1 and} Based on the phase amount of the first scale, the third scale in the pitch λ ₁ of the first scale By obtaining the absolute position of the scale in units of pitch λ ₁ / m and detecting the relative displacement of the scale and its detection head as an absolute position, it is possible to detect a long absolute position with high resolution. It is a thing.

[Conventional technology]

In a machine tool or the like, for example, in order to detect the feed amount of a processing tool, one member is provided with a scale on which a periodic pattern of scales is formed, and the other member is read by a sensor to periodically measure the scale. A detector that generates an electrical signal is arranged, and the amount of relative displacement between the one member and the other member can be measured by pulsing the electric signal and integrating and counting the so-called incremental.
Type displacement detection device is used. However,
This type of incremental displacement detector has the following drawbacks.

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, the workability is poor.

Noise from other machine tools or the like causes an erroneous count even once during the work, and all the accumulated count values thereafter are erroneous, so initialization is required again. That is, the noise resistance is poor.

The response speed is limited because the counting pulse is always counted.

In order to eliminate all of the above-mentioned disadvantages (1) to (4), a scale having an aperiodic pattern graduation indicating an absolute position from a certain origin is arranged on one member of the two members which are relatively displaced, and the other member is arranged. There are various position detection devices of the so-called absolute type, in which a detector having a sensor for reading the scale is arranged and the relative displacement between these two members is detected as an absolute position from the origin on the scale. Proposed.

FIG. 3 shows a conventional magnetic absolute position detecting device disclosed in Japanese Examined Patent Publication No. 50-23618. In FIG. 3, (1) is a scale made of a magnetic material. A magnetic scale (2) with a pitch λ _{1 and} a magnetic scale (3) with a pitch λ ₂ (λ ₂ <λ ₁ ) are formed in parallel on the scale ( ₁ ). (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 = Acos πft ··· (1) I _B = Acos (πft + π / 4) ··· (2) In addition, the distance between the magnetic head (4A) and the magnetic head (4B) is (n + 1/4) λ ₁ (n is Integer), those 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 the phase detection signals in the phase detection circuit (5) 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 this displacement signal d is measured. The relationship between the phase amount θ ₁ and the displacement amount x is as shown in FIG. 4A. 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 two, the phase amount θ ₁ takes a certain value from 0 to 2π within the range of one pitch λ ₁ of the magnetic scale (2), so the displacement amount x is detected as an absolute position. can do.

Similarly, as shown in FIG. 4B, the phase detection circuit (7) measures the phase amount θ ₂ which takes a value of 0 to 2π in the period λ ₂ for the displacement amount x. Therefore, θ ₂ = 2πx / λ ₂ (7) holds.

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 formula (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) can be calculated from equation (9). The displacement amount x is calculated and supplied to the display (9). In this case, if the value of the displacement amount x is uniquely determined within the range of 0 ≦ Δθ <2π (10), the maximum measurement length L that can accurately measure the displacement amount x as an absolute position is L = λ ₁ λ ₂ / (λ ₁ −λ ₂ ) ... (11) Therefore, the relationship between the displacement amount x and the phase difference Δθ is as shown in FIG. 4C. Further, in the formula (9), since the phase difference Δθ can be generally measured with a resolution of about 1/1000 of 2π, the measurement resolution Δx of the displacement amount x is about Δx≈L × 10 ⁻³ (12) Become. 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 type position detecting device, a device using a gray code as shown in FIG. 5 is also known. In FIG. 10, (10) is a translucent scale formed with a k-bit Gray code (11),
(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). If the resolution of the Gray code (11) is λ _G , the scale (10) is obtained by multiplying the device obtained by decoding the electric signal output from the light receiving element (16) of the detector by λ _G. The displacement amount x of the detector with respect to is determined as the absolute position of the resolution λ _G.

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

[Problems to be solved by the invention]

However, in the conventional absolute type position detecting device shown in FIG. 3, when the maximum measurement length L is set to a practical value of about 1000 mm, the resolution Δx becomes about 1 mm from the formula (12). However, the resolution was extremely poor.

Incidentally, in the above-mentioned Japanese Patent Publication No. 50-23618 (Fig. 3 example), the absolute position of the unit of the pitch λ ₁ of the scale (1) is specified from the displacement amount x, and the resolution of the displacement amount x is finally determined. 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.

Furthermore, the resolution λ _G is 10 μ in the position detection device of FIG.
m is the limit. In this case, when a scale having a gray code of about 12 bits, which is a practical limit, is used as the scale, the maximum measurement length L is Δx =
0.01 mm and 2 ¹² = 4096, which is about 40 mm, 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]

Position detecting device according to the invention, for example, as shown in FIG. 1, the first scale (18) of the pitch lambda _1, pitch lambda _{2 (lambda 2}
Second scale (19) with ≠ λ ₁ and pitch λ ₁ / m (m is 2
A scale (17) in which a third scale (20) of the above integer) is formed in parallel, and first and second scales for reading the first, second and third scales respectively to generate a phase detection signal. And the third
Detection heads (21) having detectors (22) to (24) and arranged so that they can be displaced relative to the scale (17), and those first scales (three scales based on the three types of phase detection signals). 18)
Difference (θ ₂ −θ ₁ ) between the second scale (19) and the second scale (19), the phase amount θ _{1 of} the first scale (18) and the third scale (20)
The phase detection circuits (25) to (27) for detecting the phase amount θ ₃ of are provided, and the absolute position of the first scale (18) is determined by the unit of the pitch λ ₁ from the phase difference (θ ₂ −θ ₁ ). The first scale (1) is calculated from the phase amount θ _{1 of} the first scale (18).
By finding a pitch lambda ₁ / m unit the absolute position of the third scale (20) in the inside of the pitch lambda ₁ of 8), a relative displacement amount between the scale (17) and the detection head (21) The absolute position is detected.

[Action]

According to such present invention, first, the first scale (18) and the phase difference between the second scale (19) the absolute position first of (theta ₂ - [theta] ₁₎ the detection head from (21) Since the resolution is better than the pitch λ ₁ of the scale (18), the pitch of the detection head (21) on the first scale (18) is specified. Then, from the phase amount θ _{1 of} the first scale (18), the absolute position within the pitch λ _{1 of} the first scale (18) is better than the pitch λ ₁ / m of the third scale (20). Since it can be obtained with various resolutions, its detection head (21)
Is located within a certain pitch λ _{1 of} the first scale (18) on the third scale (20).

Therefore, for example, as shown in FIG.
1) is in the first scale (18) N in the _first pitch, further N ₂ th pitch of the third graduation in N within the _first pitch of the first scale (18) (20) Assuming that the phase amount θ _{3 of} the third scale (20) corresponds to the displacement amount Δx, the absolute position x (position P) of the detection head (21) with respect to the scale (17) Can be calculated by the formula x = (N ₁ −1) λ ₁ + (N ₂ −1) λ ₁ / m + Δx.

In this case, the displacement Δx can be measured with a resolution of about 10 ⁻³ of one pitch λ ₁ / m of the third scale (20), whereas the conventional resolution is almost the pitch of the first scale (18). Since it is on the order of λ ₁ , the measurement resolution is improved to approximately 1 / (10 ³ m).

〔Example〕

An embodiment of the phase detector according to the present invention will be described below with reference to FIGS. 1 and 2.

Figure 1 shows a position detecting device of the present embodiment. In FIG. 1, (17) is a scale, the first scale (18) of the pitch lambda ₁ to the scale (17), the pitch lambda _{2 (lambda 2} <λ
The second scale (19) of ₁ ) and the third scale (20) of the pitch λ ₃ are formed in parallel. The scales (18) to (20) may be magnetic scales, optical gratings, electromagnetic induction type conductive patterns, or the like. Then, the pitches λ ₁ , λ ₂ , λ ₃ are determined so as to satisfy the following relationship by using a natural number n having a relatively large value and a natural number m of 2 or more.

λ ₃ = λ ₁ / m (14) nλ ₁ = (n + 1) λ ₂ (= L) (15) Incidentally, as explained in the conventional example of FIG. 3, the pitch λ
_If the scale of _{1 and} the scale of pitch λ ₂ are used, the maximum measurement length L that can be accurately measured with the displacement amount x as the absolute position is λ ₁ λ ₂ /
(Λ ₁ −λ ₂ ) (see Expression (11)), but in this example, because of the relationship of Expression (15), L = λ ₁ λ ₂ / (λ ₁ −λ ₂ ) = nλ ₁ λ ₂ / (Nλ ₁ −nλ ₂ ) = (n + 1) λ ₂ λ ₂ / {(n + 1) λ ₂ −nλ ₂ } = (n + 1) λ ₂ = nλ ₁ holds. Therefore, “(= L)” in equation (15)
It is what it was.

In Fig. 1, (21) is x with respect to the scale (17).
A detection head supported so as to be displaceable in a predetermined direction. The detection head (21) has a first detector (22) for reading a first scale (18) and a phase detection signal, and a second detector (22). A second detector (23) for reading the scale (19) to generate a phase detection signal and a third detector (20) for reading the third scale (20) and generating a phase detection signal are provided. If the scales (18) to (20) are magnetic scales, these detectors (22) to (24) are composed of a magnetic head. If the scales (18) to (20) are optical gratings, a light emitting element and a light receiving element. The scales (18) to (20) are made corresponding to the scales (18) to (20).

The phase detection signal output from the first detector (22) is supplied to the input terminal of the first phase amount detection circuit (25) and one input terminal of the phase difference detection circuit (26), The phase detection signal output from the detector (23) is supplied to the other input terminal of the phase difference detection circuit (26), and the third detector (24)
The phase detection signal output from the above is supplied to the input terminal of the second phase amount detection circuit (27). The detection head (21) has phase amounts θ ₁ , θ with respect to the _first scale (18), the second scale (19) and the third scale (20) of the scale (17), respectively.
Assuming that they are located at positions ₂ and θ ₃ (see FIG. 2), the first phase amount detection circuit (25) detects the phase amount θ ₁ and detects the phase coefficient θ ₁ of the first coefficient discriminating circuit (28). It supplies to one input port and one input port of the second coefficient discriminating circuit (29), and the phase difference detecting circuit (26) detects the phase difference (θ ₂ −θ ₁ ) to detect the first coefficient discriminating circuit. The second phase amount detection circuit (27) detects the phase amount θ ₃ and supplies it to the other input port of the second coefficient determination circuit (29). When the detectors (22) to (24) are magnetic flux response type magnetic heads, the first and second phase amount detection circuits (25) and (27) are respectively the phase detection circuit (5 ), And the phase difference detection circuit (26) can be composed of, for example, the phase detection circuits (5) and (7) and the subtraction circuit shown in FIG.

Further, the detection head (21) of this example is located at the position P with respect to the scale (17) as shown in FIG.
When the displacement amount when 1) is located at the left end of the scale (17) is 0, the displacement amount (that is, absolute position) at the position P is x. Then, the amount of the displacement x is present in the first scale (18) N in the _first pitch from the origin along as shown in Fig. 2 A, the first graduation N _first (18) It is assumed that the displacement amount x within the pitch exists within the N ₂ -th pitch along the third scale (20) as shown in FIG. 2C. The absolute position of the displacement amount x within the N _2nd pitch λ _{3 of} the third scale (20) is Δx, and the length of the first scale (18) is equal to the (N ₁ -1) pitch. To
l ₁ , the length of the (N ₂ -1) pitch of the third scale (20) to l ₂
Then, from FIG. 2, the absolute position x can be represented by x = l ₁ + l ₂ + Δx = (N ₁ -1) λ ₁ + (N ₂ -1) λ ₃ + Δx (16). In Expression (16), Δx has a relationship of the phase amount θ ₃ and θ ₃ = 2πΔx / λ ₃ (17), and therefore can be easily calculated from the phase amount θ ₃ .

In this example, the integers N ₁ -1 and N ₂ -1 in the equation (16) are calculated in the first coefficient discriminating circuit (28) and the second coefficient discriminating circuit (29) of FIG. 1, respectively. First, the coefficient determination circuit (28) calculates the displacement amount y ₁ corresponding to the phase difference (θ ₂ −θ ₁ ) from the following equation corresponding to equation (9).

y ₁ = L (θ ₂ −θ ₁ ) / (2π) (18) This displacement amount y ₁ is within the range of the error Δy ₁ with respect to the true displacement amount x as shown in FIG. 2D. First coefficient determination circuit (2
8) is an integer N ₁ − of one pitch λ ₁ unit of the first scale (18)
1 is calculated from the following equation.

N ₁ −1 = INT (y ₁ / λ ₁ ) (19) In this equation (19), INT (y ₁ / λ ₁ ) represents the integer part of y ₁ / λ ₁ . However, when the detection head (21) is located at the position Q in FIG. 2D relative to the scale (17), the error Δy _{1 in} the expression (19) causes an error of ± 1. Can happen. To avoid this, Δy ₁ is Δy ₁ ≤ λ
_As shown in FIG. 2A, one pitch λ ₁ of the first graduation (18) is adjusted so as to satisfy _1/2 and the front portion R ₂ (0 ≦ θ ₁ <2π /
3), rear part R ₁ (4π / 3 <θ ₁ <2π) and its middle part R ₃
It is divided into (2π / 3 ≦ θ ₁ ≦ 4π / 3). When the phase amount θ _{1 of} the first scale (18) is in the intermediate portion R ₃ , the formula (1
9) is adopted as it is, and when the phase amount θ ₁ is in the rear part R ₁ and the displacement amount y ₁ is in the front part R ₂ , subtracting 1 from the value obtained by the equation (19) is true. Of N ₁ −1, and when the displacement amount y ₁ is in the rear portion R ₁ when the phase amount θ ₁ is in the front portion R ₂ , 1 is added to the value obtained by the equation (19). Make things as if they were true N ₁ -1. In this case, the position difference (θ
Assuming that the displacement y ₁ can be measured with a resolution of 10 ⁻³ of ₂ −θ ₁ ), Δy ₁ ≈L × 10 ⁻³ ≦ λ using L = λ ₁ λ ₂ / (λ ₁ −λ ₂ ). _{1/2 ‥‥ (20) λ} 1 so as to satisfy, it may be set to lambda _2.

At the same time, the second coefficient discriminating circuit (29) calculates the displacement amount y ₂ within one pitch λ ₁ shown in FIG. 2A from the phase amount θ _{1 of} the first scale (18) by using an additional equation.

y ₂ = λ ₁ θ ₁ / (2π) (21) This displacement amount y ₂ falls within the error Δy ₂ range with respect to the true displacement amount, and the second coefficient discriminating circuit (29) determines the third displacement amount. Scale (20)
An integer N ₂ −1 of one pitch λ ₃ unit within one pitch λ ₁ of the first scale (18) of the is calculated from the following equation.

N ₂ −1 = INT (y ₂ / λ ₃ ) ... (22) Even when the formula (22) is used, the error Δy ₂ is ± 1.
Since the error of may occur, assuming can measure the displacement amount y ₂ with a resolution of the phase amount theta ₁ of 10 ^-3, λ _{1 =} mλ ₃ than ^{_{Δy 2 ≒ mλ 3 × 10 -3}} ≦ λ 3/2 ‥ Set the value of m so that (23) is satisfied. Then, the correction is performed similarly to the case of the equation (19).

Subsequently, referring to FIG. 1, a first coefficient discriminating circuit (28)
Calculating circuit integer N ₁ -1 calculated according to equation (19) (3
0) to the first input port, and the second coefficient determination circuit (29) supplies the integer N ₂ −1 calculated according to equation (22) to the second input port of the arithmetic circuit (30), The second phase amount detection circuit (27) supplies the phase amount θ ₃ to the third input port of the arithmetic circuit (30). Then, the arithmetic circuit (30) calculates the absolute position Δx within one pitch λ _{3 of} the third scale (20) from the equation (17), and then it is the total displacement amount based on the equation (16). The absolute position x is calculated and supplied to the display (31).

As described above, according to this example, the displacement amount between the scale (17) and the detection head (21) can be measured as the absolute position x within the range of the maximum measurement length L. Moreover, when the phase amount θ _{3 of} the third scale (20) is also measured with a resolution of about 10 ⁻³ ,
The resolution of the absolute position x is about λ ₃ × 10 ^-3 .

Specifically, the first scale (18), the second scale (19),
Pitch of each scale of the third scale (20) λ ₁ , λ ₂ , λ
_{When 3} (= λ ₁ / m) is set to λ ₁ = 10.00mm λ ₂ = 9.95mm λ ₃ = 0.20mm (that is, m = 50), the maximum measurement length L is L = λ ₁ λ ₂ / (λ ₁ −λ ₂ ) = 1990 (mm). At this time, n (= L / λ ₁ ) in equation (15) is
Since it becomes 199, the first scale (18) and the second scale (1
The phase difference (θ ₂ −θ ₁ ) obtained from 9) should be at least 199
What is necessary is just to divide. However, in order to accurately remove the error of ± 1 in Expression (19), the phase difference (θ ₂ −θ ₁ ) is set to 2 ×.
It is necessary to divide into 199 or more.

Also, since m = 50, in this example, the first scale (18)
3rd scale (20) by dividing the phase amount θ ₁ of at least 50
It is sufficient to calculate an integer N ₂ −1 of 1 pitch λ ₃ unit. However, in order to perform more accurate measurement, it is necessary to divide the phase amount θ ₁ into 100 or more. Finally, 1 on the third scale (20)
By dividing the pitch λ ₃ (0.2 mm) into 200, for example, the absolute position Δx of one pitch λ ₃ can be measured with a resolution of 1 μm.

Therefore, in this case, the absolute position can be detected with a resolution of 1 μm within the entire range of the maximum measurement length of 1990 mm.

As described above, according to this example, in the absolute type position detection device, there is an advantage that the maximum measurement length can be set in a practical range and the resolution can be set to the same level as that of the incremental type displacement detection device.

In the example of FIG. 1, the first to third scales (18)
In parallel with (20), a fourth scale having a pitch that is an integer fraction of the pitch λ ₃ of the third scale (20) is further scaled (1
It is possible to further expand the range of the maximum measurement length and subdivide the resolution by forming a detector in (7) and arranging a detector for reading the fourth scale on the detection head (21). Similarly, it is possible to add the fifth scale and the sixth scale.

Further, the present invention can be naturally applied not only to the linear encoder but also to the rotary encoder. In the case of a rotary encoder, a plurality of scales are formed concentrically on a disk.

As described above, the present invention is not limited to the above-described embodiment, and may adopt various configurations without departing from the spirit of the present invention.

〔The invention's effect〕

According to the present invention, it is possible to set the maximum measurement length or the maximum measurement angle in a practical range, and it is possible to realize an absolute type position detection device in which the resolution is improved to that of an incremental type displacement detection device.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram used to explain the operation of the embodiment, and FIG. 3 is a block diagram showing an example of a conventional absolute type position detecting device. FIG. 4 is a diagram for explaining the operation of the example of FIG. 3, and FIG. 5 is a perspective view showing another example of a conventional absolute type position detecting device. (17) is the scale, (18) is the first scale, (19) is the second scale
Scale, (20) is the third scale, (21) is the detection head,
(22) is the first detector, (23) is the second detector, (24)
Is the third detector, (25) is the first phase amount detection circuit, (2
6) is a phase difference detection circuit, (27) is a second phase amount detection circuit, (28) is a first coefficient determination circuit, (29) is a second coefficient determination circuit, and (30) is an arithmetic circuit. .

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-1-229905 (JP, A) JP-A 64-39522 (JP, A) JP-A 63-247615 (JP, A)

Claims (1)

(57) [Claims] _1. A first scale having a pitch λ 1, a pitch λ ₂ (λ
₂ ≠ λ ₁ ) and a scale in which a third scale having a pitch λ ₁ / m (m is an integer of 2 or more) is formed in parallel, and the first scale, the second scale, and the third scale. A detection head having first, second, and third detectors for reading each to generate a phase detection signal, the detection head being disposed so as to be relatively displaceable with respect to the scale; The phase difference between the first scale and the second scale, the phase amount of the first scale, and the third scale.
And a phase detection circuit for detecting the phase amount of the scale, and the absolute position of the first scale is determined by the pitch λ ₁ from the phase difference.
It is calculated in units and the first scale is used to calculate the first
The absolute position of the third scale within the pitch λ ₁ of the scale is determined in units of the pitch λ ₁ / m to detect the relative displacement between the scale and the detection head as an absolute position. A position detecting device characterized by.