JP2998314B2 - Absolute scale device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an absolute scale device suitable for use in, for example, a machine tool.

[0002]

2. Description of the Related Art In a machine tool or the like, an incremental (in) for detecting a feed amount of a tool to a workpiece is detected.
A cremental type scale device is used. Such a scale device arranges a scale on which a scale of a periodic pattern is formed on one of a workpiece and a tool, and arranges a detection device that reads the scale and generates an electric signal on the other,
The electrical signal is pulsed and counted to measure the relative change between the workpiece and the tool.

Further, in order to streamline the operation of setting the origin of the coordinate system (initialization), there have been proposed various absolute type scale devices which are configured to separately detect the absolute position from the origin. ing.

[0004] FIG. 4 is a schematic diagram of Japanese Patent Publication No.
1 shows a magnetic absolute type scale apparatus according to the prior art disclosed in Japanese Patent Publication No. 23618. This scale device has a scale 10 including two magnetic scales 12a and 12b, and magnetic flux responsive magnetic heads 14a and 14b arranged adjacent to the respective magnetic scales.
Periodic pattern of a pitch lambda _a is formed in 2a, a periodic pattern of a pitch _{λ b (λ b> λ a} ) is formed on the second magnetic scale 12b.

The scale device further includes a first excitation amplifier circuit 22 for supplying an excitation signal to the first magnetic head 14a.
A first head amplifier circuit 24 that receives a phase detection signal supplied from the first magnetic head 14a and generates _a first phase modulation signal PMa; and _a first head amplifier circuit 24.
And _a first waveform shaping circuit 26 for shaping the waveform of the first phase modulation signal PMa supplied from the second magnetic head 14b to form _a rectangular phase modulation signal Sa. a second excitation amplifier circuit 16 supplies a signal, and the second head amplifier circuit 18 for generating a second phase-modulated signal PM _b receives the phase detection signal supplied from the second magnetic head 14b, a The second supplied from the first head amplifier circuit
And a second waveform shaping circuit 20 to form a phase-modulated signal S _b of the rectangular wave of the phase modulation signal PM _b and waveform shaping.

The excitation amplification circuits 16 and 22 include an oscillator 28
A frequency divider 30 is connected to divide the clock signal supplied from the frequency divider to generate a reference signal having a frequency f / 2.

[0007] A first magnetic head 14a, a first excitation amplifier circuit 22, and a first excitation amplifier circuit 22, which are arranged in relation to the first magnetic scale 12a,
First head amplifier circuit 24 and first waveform shaping circuit 26
And a second magnetic head 14b, a second excitation amplification circuit 16, a second head amplification circuit 18, and a second waveform shaping circuit 20 arranged in relation to the second magnetic scale 12b.
The first magnetic scale 12a, the first magnetic head 14a, and the like will be described below.

The magnetic heads 14a mutually (n + ／)
lambda _a only includes a spaced pair of head portions, the excitation signals represented by the excitation amplifier circuit 22 for each such head portion by the following equation is supplied.

[0009]

(Equation 1)

Here, A is a constant, and f / 2 is the excitation frequency. Each of the heads generates a phase detection signal represented by the following equation (2).

[0011]

(Equation 2)

The phase detection signal is supplied to a first head amplifier circuit 24.
To generate _a first phase modulation signal PMa represented by the following equation (3).

[0013]

(Equation 3)

(Equation 4)

[0014] As apparent from the number 4 of the formula, the first pitch of the phase modulation amount theta _a phase modulation signal magnetic graduations 12a lambda
_a is a function of the displacement x with respect to the magnetic scale 12a. The first pitch lambda _a because the known can be obtained displacement x by measuring the phase modulation amount theta _a.

Equation 4 showing the relationship between the amount of phase modulation θ _a and the amount of displacement x is shown in FIG. 5C . The amount of phase modulation θ _a is
A periodic function having a period of the first pitch lambda _a, for example, when the phase modulation amount of theta _a = [pi, the amount of displacement x = X _{0,
X 1, X 2, X 3} , ‥‥ next, it is not possible to determine the value of x, for within a predetermined range of one pitch lambda _a magnetic graduation 12a is phase modulation amount theta _a is 0~2π , it can be determined Displacement <br/> amount x uniquely.

[0016] Similarly in the second head amplifier circuit 18, the second phase modulation signal PM _b is generated.

[0017]

(Equation 5)

(Equation 6)

A graph of the equation (6) is shown in FIG. 5B . The first phase modulation signal PM represented by the equation (3)
_a is being waveform-shaped phase modulation signal S _a rectangular wave generated by the first waveform shaping circuit 26, the second phase modulation signal PM _b represented by the numerical formula 5 by a second waveform shaping circuit 20 phase modulation signal S _b of the rectangular wave is generated to waveform shaping.

These two waveform-shaped phase modulation signals S _a and S _b are supplied to a first counter control circuit, where the phase modulation amounts θ _a and θ _b are compared to obtain a phase difference θ _ab . The phase difference θ _ab is obtained by the following equation (7).

[0020]

(Equation 7)

Here, the pitches λ _a and λ of the two magnetic graduations
Set the ratio of _b to an appropriate value. For example,

[0022]

(Equation 8)

It is assumed that Here, n may be an arbitrary number, but is preferably an integer. The following equation is obtained by substituting equation (8) into equation (7).

[0024]

(Equation 9)

(Equation 10)

Here, λ _c is the synthetic pitch length. FIG. 5D is a graph of Expression 9 showing the relationship between the phase difference θ _ab and the displacement x.

Next, an outline of a procedure for obtaining the variation x will be described with reference to FIGS. 5A to 5D. In FIG. 5, the left end of the magnetic scale is defined as the origin, and the relative displacement between the magnetic head 14 and the scale 10 is defined as x. For the sake of simplicity, it is assumed that the left ends of the two magnetic graduations 12a and 12b coincide. It is assumed that the detection head including the two magnetic heads 14a and 14b moves on the scale and reaches the position P.

In the first pitch λ _a where the position P exists, the absolute displacement amount of the position P is x ₁ , and the composite pitch λ _c
In inside and the absolute amount of displacement of the first pitch lambda _a present position P and x _2, the absolute amount of displacement x from the origin position P is determined by the formula for a number of 11.

[0028]

[Equation 11]

FIG. 5D shows that the position P exists within the first synthetic pitch λ _c counted from the origin,
The position P is the q-th counting from the origin (q = 0, 1, 2, 3,
存在) when it is within the synthetic pitch λ _c ,
Displacement x of the position P by adding q? _C on the right-hand side is determined at the expression.

[0030] As apparent from Equation 11 wherein the absolute change amount x from the origin position P, the absolute amount of displacement of the absolute change amounts x ₁ and the synthetic pitch lambda _c in the first pitch lambda _a It is determined by obtaining the x _2. Therefore, it is possible to increase the accuracy of measurements of the displacement x by reducing the resolution of the displacement x _1, the resolution of the displacement x _2, the first pitch lambda _a is included any number within the It is sufficient that the value is sufficient to determine

FIG. 6 shows an example of the second counter control circuit 42 according to the prior art shown in FIG. The first counter control circuit 40 and the second counter control circuit 42 may have the same configuration.

The counter control circuit 42 includes an input terminal 60 for receiving a reference signal from the frequency divider 30, an input terminal 62 for receiving a phase-modulated signal S _a from the first waveform shaping circuit 26, the clock from the oscillator 28 An input terminal 64 for receiving a signal, an output terminal 70 for sending an enable signal to the second counter 46, an output terminal 72 for sending a latch signal to the second counter 46, and sending a counter clear signal to the second counter 46 And an output terminal 74.

Further, the counter control circuit includes a D flip-flop circuit and a JK flip-flop circuit 66. The JK flip-flop circuit has a J input terminal, a K input terminal, and a Q output terminal. The Q output terminal becomes high level by an input signal from the J input terminal, and becomes low level by an input signal from the K input terminal. Output signal.

FIG. 7 is a timing chart showing the operation of the second counter control circuit 42, the second counter 46, and the second latch circuit 50. The operation of each circuit will be described with reference to FIG. FIG. 7A shows a waveform of the clock signal supplied by the oscillator 28. FIG. 7B shows a waveform of the reference signal supplied by the frequency divider 30. This reference signal is a rectangular wave of frequency f / 2 generated by dividing the frequency of the clock signal.

FIG. 7C shows a waveform of a pulse signal input to the J input terminal of the JK flip-flop circuit 66. The pulse signal is output once every fall of the reference signal shown in FIG. 7B. A pulse is generated. Figure 7D shows the waveform of the supplied phase-modulated signal S _a from the waveform shaping circuit 26.

[0036] Figure 7E, standing of J-K type is input to the K input terminal of flip-flop circuit 66 shows a waveform of an input signal, such input signal is phase-modulated signal S _a shown in FIG. 7D One pulse is generated for each downlink.

FIG. 7F shows the waveform of the output signal output from the Q terminal of the JK flip-flop circuit 66. The output signal from the Q output terminal is connected to the J input terminal as described above. When a pulse signal is input, it becomes high level and when a pulse signal is input to the K input terminal, it becomes low level. The output signal from the Q output terminal is input to the counter 46 as an enable signal. While the enable signal is at the high level, the counter 46 counts the clock signal from the oscillator 28.

FIGS. 7G and 7H show the waveforms of the latch signal and the counter clear signal supplied to the counter 46. One pulse is generated each time the enable signal shown in FIG. 7F falls.

When the latch signal is supplied to the counter 46, the count value of the counter is latched by the latch circuit 50, and when the counter clear signal is supplied, the count value of the counter is cleared. FIG. 7I shows the count value of the counter 46, and FIG.
J indicates the count value of the counter latched by the latch circuit.

As described above, the enable signal shown in FIG. 7F is supplied from the counter control circuit 42 to the counter 46, and the counter 46 counts the clock signal supplied from the oscillator 28 while the enable signal is at the high level. I do. Meanwhile, since Ineburu signal which becomes a low level at the falling edge of the phase modulation signal S _a to the high level at the falling edge of the reference signal, time or pulse width Ineburu signal is at the high level, the reference signal and the phase-modulated signal S _a corresponds to the phase modulation amount theta _a phase difference or phase modulation signal S _a of.

[0041] Thus only the counter 46 time corresponding to the phase modulation amount theta _a counts the clock signal. Thus, the phase modulation amount θ is obtained from the count value of the clock signal by the counter 46.
_a is calculated, and the displacement x is calculated by the equation (4).

[0042] In the counter 46, until the counter clear signal is supplied, the count value of the clock signal corresponding to the displacement amount x ₁ position P shown in Figure 5 is counted, the latch signal is supplied The current value of the count value is latched by the latch circuit. As described above, the second counter control circuit 4
2, the second counter and the second latch circuit 50 have been described, but the first counter control circuit 40, the first counter and the first latch circuit 48 perform the same operation.

[0043] That is, the first counter 44 is counted count value of the corresponding clock signal to the amount of change x ₂ to the synthetic pitch lambda _c is the current value is latched in the first latch circuit of the regimen numeric by a latch signal Is done.

FIG. 8 is a timing chart showing details of the operation of the counter control circuit shown in the prior art example. FIG.
A shows the waveform of the reference signal of frequency f / 2 supplied from the frequency divider 30, and is a diagram corresponding to FIG. 7B.

FIG. 8B shows a waveform of a pulse input to the J input terminal of the JK flip-flop circuit 66, and is a diagram corresponding to FIG. 7C. FIG. 8C shows the waveform of the phase-modulated signal _Sa whose waveform has been shaped, and is a diagram corresponding to FIG. 7D. FIG. 8D illustrates the K-type flip-flop circuit 66 with the K signal.
FIG. 7B is a diagram illustrating a waveform of a pulse input to the input terminal and corresponding to FIG. 7E.

FIG. 8E shows a waveform of the enable signal supplied to the counter 46, and corresponds to FIG. 7F. The pulse signal input to the J input terminal shown in FIG. 8B is generated by the fall of the reference signal shown in FIG. 8A, and the pulse signal input to the K input terminal shown in FIG. 8D has the phase shown in FIG. 8C. generated by the falling edge of the modulation signal S _a.

The enable signal shown in FIG. 8E is made high by an input pulse signal at the J input terminal and made low by a pulse signal at the K input terminal.
Is used only once in two times. That Ineburu signal will not have occurred only once every two out of the falling of the phase modulation signal S _a.

Further, a case may occur in which the input signal to the J input terminal shown in FIG. 8B matches the input signal to the K input terminal. In such a case, the falling of the enable signal shown in FIG. 8E does not occur, so that the latch signal and the counter clear signal are not generated, and the count value of the counter is not latched.

[0049]

The conventional absolute scale apparatus has two counter control circuits and two counters, and has a drawback that the circuit configuration is complicated.
Further, in the conventional absolute scale device, since the count value of the counter is latched only once in two cycles of the phase modulation signal, the displacement amount cannot be measured efficiently.

According to the present invention, a first scale having a periodic pattern formed at a first pitch and a periodic pattern formed at a second pitch different from the first pitch are formed. A first detection head that can be displaced relative to the first scale and generates a detection signal in response to the first excitation signal;
The second scale can be displaced relative to the second scale.
A second detection head for generating a detection signal in response to the excitation signal of the first detection head; and a first phase modulation signal indicating a relative displacement position with respect to the first scale in response to the detection signal generated by the first detection head. First phase detecting means for generating, and second phase detecting means for generating, in response to a detection signal generated by the second detection head, a second transfer modulation signal indicating a relative displacement position with respect to the second scale. And an absolute scale device configured to determine a relative displacement position with respect to the scale based on the first phase modulation signal and the second phase modulation signal, wherein the absolute scale device is generated by the first phase detection means. The first phase modulation signal is configured to be a second excitation signal of the second detection head.

[0050]

The first phase modulation signal is a position signal θ within the first pitch of the first scale as represented by the equation (3).
including _a = _2πx / _{λ a.} According to the present invention, in order to use the first phase modulation signal as the excitation signal for the second detection head, the second phase modulation signal generated by the second phase detection means is expressed by the following equation (12). As represented, the first
Position signal within a first pitch of the graduation of θ _a = 2πx / λ _a
And the position signal θ _b = 2πx within the second pitch of the second scale
/ Including the difference of λ _b. Therefore, according to the present invention, the first scale has the first scale, like the conventional absolute scale device.
A first phase modulation signal including the position signal θ _a = 2πx / λ _a within the pitch of the second pitch and a second phase modulation signal including the position signal θ _b = 2πx / λ _b within the second pitch of the second scale Are separately obtained, and there is an advantage that the circuit configuration is simplified as compared with a case where the two are compared by a counter control circuit or the like. For example,
As shown in FIG. 1, the phase-modulated signal PM _a generated from the first head amplifier circuit 24 is waveform-shaped by the first waveform shaping circuit 26, such waveform shaping phase modulated signal S _a
Is a second magnetic head for supplying an excitation signal to the second magnetic head 14b.
As the reference signal.

In the second head amplifier circuit 18, the first peak
Switch λ_aAnd the second pitch λ_bLonger than any of the
Switch λ_cPhase-modulated signal PM phase-modulated based on
_abIs obtained. Such a phase modulation signal PM_abIs the second
Is shaped into a rectangular wave by the waveform shaping circuit 20 of FIG.
-Modulated phase-modulated signal S_abIs generated. This
These phase modulation signals S_a, S_abAre each the first pick
Λ_aDisplacement x within ₁Phase modulation amount θ_aAnd synthetic
Switch λ_cDisplacement x within_TwoPhase modulation amount θ _abAnd
Including. Therefore, the phase modulation signal S_a, S_abEach phase modulation
Quantity θ_a, Θ_abWith the first latch and the second latch.
And the displacement x₁, X_TwoIs required. Scale
The relative displacement x of the detection head with respect to the
Order x₁, X_TwoIt is obtained as an absolute displacement amount.

[0052]

FIG. 1 is a block diagram showing an embodiment of an abrisolute scale apparatus according to the present invention. The same components as those of the absolute scale device according to the prior art shown in FIG. 4 are denoted by the same reference numerals, and detailed description thereof will be omitted.

[0053] According to absolute scale device according to the present invention, the phase-modulated signal PM _a represented by the formula of the first number by the head amplifier circuit 24 3 is generated, the first waveform shaping on the basis of the phase modulation signal PM _a Circuit 2
6 generates _a phase modulated signal _Sa whose waveform is shaped into a rectangular wave.

[0054] Such phase-modulated signal S _a is supplied to the second excitation amplifier circuit for supplying an excitation signal to the second magnetic head 14b. Thus, the second excitation amplifier circuit a first phase-modulated signal S _a as an excitation signal of the second magnetic head 1
6 differs from the prior art example shown in FIG. The second head amplifying circuit 18 generates a phase modulation signal PM _ab expressed by the following equation (12) instead of the phase modulation signal PM _b expressed by the equation (5).

[0055]

(Equation 12)

The phase modulation amount θ _{ab on} the right side of the equation (12) is represented by the equation (7). Here, similarly as described for FIG. 4, to set the ratio of the pitch lambda _b of the pitch lambda _a and the second magnetic graduations 14b of the first magnetic graduations 14a to an appropriate value. For example, defining a ratio of the first pitch lambda _a and the second pitch lambda _b as the numerical formula 8 to obtain the number 9 and number 10 expression.

The phase modulation signal PM _ab is shaped into a rectangular wave by the second waveform shaping circuit 20 so that the phase modulation signal S
_ab is generated. The displacement amount x ₁ obtained by the equation of the phase modulation amount θ number sought _a 4 of the first waveform shaping circuit 26 from the obtained phase-modulated signal S _a, the second waveform shaping circuit 20
The phase modulation amount θ _ab of the obtained phase modulation signal S _ab is obtained, and the displacement amount x ₂ is obtained by Expression (9).

[0058] In a manner similar to that described prior art about 4, the count value of the counter of the phase modulation signal S frequency divider 30 by _a is latched by the first latch circuit, a phase modulation amount θ From such count value _a is obtained, and the count value of the counter in the frequency divider 30 is changed to the second value by the phase modulation signal S _ab .
And the phase modulation amount θ _ab is obtained from the counted value.

FIG. 2 is a timing chart showing the operations of the binary counter included in the frequency divider 30 and the first latch circuit 34. FIG. 2A shows a waveform of a reference signal having a frequency f / 2 generated by the frequency divider 30. The frequency divider 30, a phase modulation amount theta _a is while changing the 0～2Pai, for example 256 counting pulses are generated, such counting pulses are counted in the binary counter.

[0060] Figure 2B, when the phase modulation amount theta _a formula number 4 is changed to 0～2Pai, is a graph showing the number of pulses counted binary counter. FIG. 2C shows the first
Modulation signal PM generated by the head amplifier circuit 24 of FIG.
indicates the _a waveform, as is clear from equation (3),
Phase modulation amount theta _a is sequentially changed as a function of the position x _1.

[0061] Figure 2D shows a waveform of the waveform-shaped phase modulation signal S _a with a first waveform shaping circuit 26. FIG.
E indicates the count value of the binary counter latched by the falling edge of the phase-modulated signal S _a.

The phase modulation signal S _a shown by FIG. 2D
Is supplied to the first latch circuit, and the phase modulation signal S
_A latch signal is generated by the fall of _a , and when the latch signal is generated, the current value of the binary counter in the frequency divider 30 is latched. The latched count value is converted to _a phase modulation amount θa as shown in the graph of FIG. 2B. The thus obtained phase modulation amount θ _a
More, the displacement amount x ₁ with the number 4 of the formula are obtained.

As is clear from FIG. 2B, the first magnetic eye
Displacement x obtained by the ridge 12a₁Resolution x
_rIs the phase modulation amount θ_aOne cycle of θ, ie θ_aChanges to 0-2π
Depends on the number of counting pulses generated during the conversion. Rank
Phase modulation amount θ_aDisplacement x in one cycle of ₁Is 0 to λ_aChange to
Phase modulation amount θ_aN = 2 in one cycle of^kCounting pal
Is generated, the displacement x₁Resolution x_rIs

[0064]

(Equation 13)

## EQU5 ## Here, the counting pulses of N = 256 pieces (= 2 ⁸⁾ are generated in one period of the phase modulation amount theta _a, the first pitch λ _a λ _a = 0.256mm, number 8
Is n = 16, the second pitch λ _b is given by
From the equation, λ _b = 0.273 mm.

From the equation (13), the resolution x _r of the displacement x ₁ is given by x _r = 0.256 / 256 = 0.001 mm = 1 μ
m. In this calculation example, the lower 8
Using the bit (k = 8), the resolution x _{r of the} displacement x ₁
= 1 μm can be achieved.

FIG. 3 is a timing chart showing the operation of the binary counter and the second latch circuit 32 included in the frequency divider 30 similar to FIG. 3A shows the waveform of the reference signal generated by the divider 30, FIG. 3B, when the phase-modulated signal theta _{a- b} represented by the numerical formula 9 are changed to 0～2Pai, counting binary counter 6 is a graph showing the number of pulses performed. FIG. 3C is a graph showing a waveform of the phase modulation signal PM _ab expressed by the equation (12).

FIG. 3D is a graph showing the waveform of a rectangular phase modulation signal S _ab obtained by shaping the phase modulation signal PM _ab shown in FIG. 3C. FIG. 3E shows the count value of the binary counter latched by the falling edge of the phase modulation signal S _ab .

Here, N = N in one cycle of the phase modulation amount θ _ab.
32 (= 2 ⁵⁾ counting pulse is generated, the first pitch lambda _a and lambda _a = 0.256 mm, the n of the numerical formula 8 n =
Assuming that the resultant pitch is 16, the synthetic pitch λ _c is λ _c
= 4.096 mm. The resolution x _r of the displacement x ₂ is x _r = 4.096 / 32 = 0.128 mm from the equation (13).
Becomes

In this calculation example, the resolution x _r = 0.128 mm of the displacement x ₂ can be achieved by using the upper 5 bits (k = 5) of the 8 bits of the binary counter. As described above, the resolution of the variation x ₂ may be any value sufficient to determine whether the first pitch lambda _a is contained many pieces therein, the accuracy of the measurement of scale displacement It depends on the resolution of the x _1.

Based on the count value of the binary counter latched by the first latch circuit, using a graph as shown in FIG. 2B, the position of the displacement x ₁ within the first pitch λ _a = 0.256 mm Is measured at a resolution of 1 μm. Based on the count value of the binary counter latched by the second latch circuit, the displacement amount x is calculated using a graph as shown in FIG. 3B.
₂ is measured at a certain or resolution 0.128mm at the position of the throat in the composite pitch λ _c = 4.096mm, than the value of such displacement x _2, the first pitch lambda _a within displacement x ₂
Sought number of, whereby more accurate value of the change amount x ₂ is determined.

In this way, the amount of phase displacement with respect to the scale is measured as an absolute value from the equation (11).

Although the embodiments of the present invention have been described above, it will be apparent to those skilled in the art that other configurations can be adopted without departing from the scope of the present invention described in the appended claims.

For example, the frequency divider 30 is configured to include a binary counter.
It is also possible to process with BCD data.

[0075]

According to the present invention, since the first phase modulation signal is used as the excitation signal for the second detection head, the second phase modulation signal generated by the second phase detection means is expressed by the following equation (1).
As represented by 2 in the formula, the position signal within a first pitch of the first scale θ _a = 2πx / λ position signal in the second pitch of _a second graduation θ _b = 2πx / λ Including the difference in _b . If _a relationship such as the equation 8 is provided between the two pitches λ _a and λ _b , the pitch nλ is obtained as the second phase modulation signal.
_The phase modulation signal as obtained from the scale of the scale _a is obtained. Thus, according to the invention, as in a conventional absolute scale device, _a first phase modulation signal including _a position signal θ _a = 2πx / λ _a within a first pitch of the first scale and a second scale Position signal θ _b = 2π within the second pitch of
There is an advantage that the circuit configuration is simpler than when the second phase modulation signal including x / λ _b is separately obtained and both are compared. That is, according to the present invention, the counter control circuits 40 and 42 and the counter which have the same functions as those of the absolute scale device according to the prior art shown in FIG. 44, 46
Becomes unnecessary.

As is apparent from a comparison of FIGS. 8C and 8E with FIGS. 2D and 3D, in the device according to the prior art, the count value of the counter is latched only once in two cycles of the phase modulation signal. In the device according to the present invention, the calculated value of the counter is latched once per cycle of the phase modulation signal, so that the displacement can be measured more efficiently.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an absolute scale device according to the present invention.

FIG. 2 is a timing chart showing the operation of the frequency divider and the latch circuit according to the present invention.

FIG. 3 is a timing chart showing the operation of the frequency divider and the latch circuit according to the present invention.

FIG. 4 is a block diagram showing an example of an absolute scale device according to the related art.

FIG. 5 is a diagram showing the operation of the example of the absolute device according to the prior art of FIG. 4;

FIG. 6 is a diagram showing an example of a conventional counter control circuit.

FIG. 7 is a timing chart showing the operation of a conventional counter control circuit, counter and latch circuit.

FIG. 8 is a timing chart showing details of the operation of the conventional counter control circuit.

[Explanation of symbols]

 Reference Signs List 10 scale 12 magnetic scale 14 magnetic head 16 excitation amplification circuit 20 waveform shaping circuit 22 excitation amplification circuit 24 head amplification circuit 26 waveform shaping circuit 28 oscillator 30 divider 32, 34 latch circuit 40, 42 counter control circuit 44, 46 counter 48 , 50 Latch circuit

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G01D 5/245 101 G01B 21/00

Claims (1)

(57) [Claims] 1. A first scale having a periodic pattern formed at a first pitch and a second scale having a periodic pattern formed at a second pitch different from the first pitch. A scale, a first detection head that can be displaced relative to the first scale and generates a detection signal in response to a first excitation signal, and a first detection head relative to the second scale. A second detection head that can be displaced to generate a detection signal in response to a second excitation signal; and a second detection head relative to the first scale in response to a detection signal generated by the first detection head. First phase detecting means for generating a first phase modulation signal indicating a displacement position; and second phase indicating a relative displacement position with respect to the second scale in response to a detection signal generated by the second detection head. Second phase detection for generating a phase modulation signal Means for calculating a relative displacement position with respect to the scale based on the first phase modulation signal and the second phase modulation signal, wherein the first phase detection means An absolute scale device, wherein the first phase modulation signal generated by the above is used as a second excitation signal of the second detection head.