JP3419132B2 - Displacement detector - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement amount detecting device for detecting a relative displacement amount between a magnetic scale and a detection head composed of a magnetoresistive effect element.

[0002]

2. Description of the Related Art Conventionally, the problems to be solved by the invention
As a displacement amount detecting device for detecting the relative displacement amount between the magnetic scale and the detection head composed of the magnetoresistive effect element, FIG.
The following are proposed.

Referring to FIG. 3, reference numeral 1 in FIG. 3 denotes a magnetic scale having an output signal wavelength, that is, an effective wavelength of λ, and the magnetoresistive effect element moves relative to the magnetic scale 1. 2 channel detection heads 2a and 2b are provided. In this case, the detection head 2
The a and 2b are arranged so as to electrically have a phase difference of 90 ° with respect to the effective wavelength λ of the magnetic scale 1, and output balanced modulation signals modulated by scale signals having different 90 ° phases.

Further, in FIG. 3, reference numeral 3 denotes an excitation signal input terminal to which the rectangular wave signal EX of frequency f is supplied, and the rectangular wave signal E of frequency f supplied to this excitation signal input terminal 3 is shown.
X is supplied to the low pass filter 4, and an excitation signal of a sine wave signal of frequency f is obtained at the output side of the low pass filter 4. The exciting signal obtained at the output side of the low-pass filter 4 is passed through the exciting amplifier 5 to the detecting heads 2a and 2b.
To be supplied to.

The output signals of the detection heads 2a and 2b are supplied to the preamplifiers 7a and 7b via the level adjusting circuits 6a and 6b, respectively, and the output signals of the preamplifier 7a are supplied to the adding circuit 8. Together with this preamplifier 7b
Is supplied to the adder circuit 8 via the phase adjustment circuit 9 and the 90 ° phase shift circuit 10.

In this case, the output signals of the detection heads 2a and 2b are adjusted to the same level by the level adjusting circuits 6a and 6b, and then amplified to appropriate output levels by the preamplifiers 7a and 7b. Further, the phase adjusting circuit 9 adjusts the phase of the excitation signal when the two-channel detection heads 2a and 2b are not correctly maintained in the relationship of 90 ° with respect to the effective wavelength λ of the magnetic scale 1, Two
It functions to correct the deviation from 90 ° between the channel detection heads 2a and 2b.

That is, when the physical dimensions of the individual detection heads 2a and 2b vary greatly, and variations in this 90 ° phase difference are also expected, the phase adjustment circuit 9 is used to eliminate these variation factors. Had to be absorbed.

This preamplifier 7a and 90 ° phase shift circuit 1
The respective output signals e ₁ and e _{2 of 0} are as follows: e ₁ = sin ωt × cos (2πx / λ) (1) e ₂ = cos ωt × sin (2πx / λ) (2) However, ω = 2πf.

Therefore, at the output side of the adder circuit 8, the phase modulation signal e _P as shown in the following equation is obtained. e _P = sin
(Ωt + 2πx / λ) (3)

The phase modulation signal e _P obtained at the output side of the adder circuit 8 is obtained through a waveform shaping circuit 11 to obtain, for example, a rectangular wave phase modulation signal S, which is well known, for example, Japanese Patent Publication No. 49-891.
As shown in Japanese Patent Publication No. 7, a pulse width signal corresponding to the phase difference between the phase modulation signal S and the rectangular wave signal EX for obtaining the excitation signal is obtained, the number of clock pulses corresponding to this pulse width signal is counted, and the position x To get

FIG. 4 shows a detailed configuration example of the adjustment of the DC bias of the detection heads 2a and 2b and the adjustment of the output levels of the preamplifiers 7a and 7b shown in FIG. In FIG. 4, the detection heads 2a and 2b of each channel are respectively provided with four magnetoresistive effect elements (hereinafter referred to as MR elements) 21a and 22.
a, 23a, 24a and 21b, 22b, 23b, 24
It has a bridge configuration of b.

That is, the detection head 2a connects the series circuits of the MR elements 21a and 22a and the series circuit of the MR elements 23a and 24a to each other at one end side thereof, and forms the DC bias adjusting circuit at the other end side thereof. The detection head 2b is connected in parallel via the variable resistor 12a.
One end sides of the series circuit of the elements 21b and 22b and the series circuit of the MR elements 23b and 24b are connected to each other, and the other end sides thereof are connected in parallel via a variable resistor 12b which constitutes a DC bias adjusting circuit. It was done.

The exciting signal obtained at the output side of the low-pass filter 4 is passed through the inverting amplifier 5a which constitutes the exciting amplifier 5, and the inverted signal of the exciting signal is supplied to the variable resistors 12a and 12a.
This inverting amplifier 5a is supplied to each of the movers of FIG.
The excitation signal obtained at the output side of the above is supplied to one end side of each parallel circuit of the detection heads 2a and 2b via the inverting amplifier 5b constituting the excitation amplifier 5.

The middle points of the MR elements 21a and 22a are connected to the inverting input terminal of the differential amplifier constituting the preamplifier 7a via the resistor 25a, and the middle points of connection of the MR elements 23a and 24a are connected to the resistors. The preamplifier 7a is connected to the non-inverting input terminal of the preamplifier 7a via the resistor 25b, and the non-inverting input terminal is grounded via the resistor 26.

Further, a variable resistor forming the level adjusting circuit 6a is connected between the inverting input terminal and the output terminal of the differential amplifier forming the preamplifier 7a, and the output signal of the preamplifier 7a is connected to the variable resistor. It is supplied to the adder circuit 8.

The middle point of connection between the MR elements 21b and 22b is connected to the inverting input terminal of the differential amplifier which constitutes the preamplifier 7b via the resistor 27a, and the middle point of connection between the MR elements 23b and 24b is a resistor. Preamplifier 7 via the device 27b
It is connected to the non-inverting input terminal of the differential amplifier forming b, and this non-inverting input terminal is grounded via the resistor 28.

Further, a variable resistor forming the level adjusting circuit 6b is connected between the inverting input terminal and the output terminal of the differential amplifier forming the preamplifier 7b, and the output signal of the preamplifier 7b is connected to the variable resistor. The 90 ° phase shift circuit 10 is supplied via the phase adjustment circuit 9.

In this case, a balanced modulation signal is obtained at the output side of the differential amplifiers constituting the preamplifiers 7a and 7b, respectively. However, if there is a difference in the potentials at the output terminals, this difference results in a direct current of the balanced modulation signal. Since there is a bias difference, the variable resistors 12a and 12b forming the DC bias adjusting circuit are inserted to correct the DC bias amount.

That is, in the conventional displacement detecting device as shown in FIG. 3, in order to correct the variation in the characteristics of the detecting heads 2a and 2b, the output levels and the DC bias of the detecting heads 2a and 2b of each channel are corrected. In addition to the adjustment, a total of five adjustment elements for adjusting the phase between the two channels were required.

Conventionally, in order to reduce this adjustment element, a displacement amount detecting device as shown in FIG. 5 has been proposed. To explain FIG. 5, parts corresponding to those in FIG.
Detailed description thereof will be omitted.

In FIG. 5, the output signal of the detection head 2a is supplied to the adder circuit 8 via the preamplifier 7a and the output balance adjusting circuit 13, and the output signal of the detection head 2b is moved by 90 degrees to the preamplifier 7b. The power is supplied to the adder circuit 8 through the phase circuit 10 and the output balance adjusting circuit 13. Others are the same as those in FIG.

In FIG. 5, the variation elements of the detection heads 2a and 2b, that is, the clearance between the magnetic scale 1 and the detection heads 2a and 2b, and the detection heads 2a and 2b.
By controlling the output level of each of the detection heads 2a and 2b of each channel within a predetermined level range by controlling the sensitivity and the like, the level adjustment circuits 6a and 6b prepared for each channel of FIG. 3 are output. The phase adjusting circuit 9 is omitted by replacing with the balance adjusting circuit 13 and by accurately managing the reproduction wavelength λ of the magnetic scale and the distance between the detection heads 2a and 2b of the two channels to reduce the number of adjustment elements. However, it still requires three adjustment elements.

However, reducing the variation factor of the parts is to raise the management level, which leads to an increase in the parts cost, which leads to a direct increase in the costs associated with an increase in the number of parts and an increase in the unit price of parts. In addition, an extra space for mounting and man-hours for adjustment are required, which is a factor that hinders cost reduction and downsizing of the device.

In view of the above point, the present invention aims to reduce the number of adjusting elements, and reduce the space for mounting the adjusting mechanism and the number of man-hours for adjusting.

[0025]

DISCLOSURE OF THE INVENTION The displacement amount detecting device of the present invention is provided with first and second magnetoresistive elements which undergo a magnetoresistive effect of 180 ° out of phase with respect to a magnetization pattern corresponding to a wavelength λ of an output signal of a magnetic scale. A first channel detection head in which effect elements are connected in series and a connection point of the first and second magnetoresistive effect elements serves as an output terminal, and a magnetoresistive effect having a phase difference of 180 ° with respect to the magnetization pattern. Receiving the third and fourth magnetoresistive effect elements in series, and using the connection point of the third and fourth magnetoresistive effect elements as an output terminal, the output signal of the detection head of the first channel A second channel detection head adapted to obtain an output signal having a phase difference of 90 ° with respect to the first
And the detection heads of the second channels are driven by two-phase excitation signals having different 90 ° phases, and the output terminals of the detection heads of the first and second channels are input terminals of one and the other of the differential amplifier. And a detection signal is obtained from the output side of this differential amplifier.

[0026]

According to the present invention, the detection heads of the first and second channels are driven by the two-phase excitation signals having different 90 ° phases, and the output terminals of the detection heads of the first and second channels are driven. Is connected to one and the other input terminals of the differential amplifier, and the detection signal is obtained from the output side of this differential amplifier. Therefore, as the adjustment element, the output levels from the detection heads of the first and second channels are adjusted. Balance adjustment,
By adjusting the DC bias of the detection heads of the first and second channels, the number of adjustment points can be reduced, and the space for mounting the adjustment function and the number of adjustment steps can be reduced.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the displacement amount detecting device of the present invention will be described below with reference to FIGS. 1 and 2
It is assumed that a magnetic pattern corresponding to the effective wavelength λ is recorded on the magnetic scale 1 in the example. In general, when the detection heads 2a and 2b are composed of MR elements, a signal having a half of the recording wavelength may be obtained depending on the structure, but here, the signals detected (reproduced) by the detection heads 2a and 2b are The wavelength is defined as the effective wavelength, and the reproduction wavelength, that is, the effective wavelength will be used in the following description.

In this example, two-channel detection heads 2a and 2b made of a magnetoresistive effect element (MR element) are provided so as to move relative to the magnetic scale 1. In this case, the detection heads 2a and 2b are arranged so as to electrically have a phase difference of 90 ° with respect to the effective wavelength λ of the magnetic scale 1, and output balanced modulation signals modulated by scale signals having different 90 ° phases. I will do it.

In this example, the two-channel detection heads 2a and 2b are composed of two MR elements 31a, 32a and 31b, 32b, respectively, as shown in FIGS. The detection head 2a is an MR as shown in FIGS.
The elements 31a and 32a are connected in series, and the MR element 31
The output terminal T _2a is led out from the midpoint of connection of a and 32a, and the detection head 2b has MR elements 31b and 32b.
Are connected in series, and the output terminal T _2b is derived from the midpoint of connection between the MR elements 31b and 32b.

The patterns of the MR elements 31a, 32a, 31b and 32b have substantially the same shape and dimension as shown in FIG. 2, and the MR elements 31a, 31b and 3 are provided.
The distance between the patterns 2a and 32b is d and the effective wavelength λ is 1
/ 4 or (n ± 1/4) λ, and MR elements 31a and 3
The distance between the patterns 2a, 31b and 32b is 2d, which is 1/2 of the effective wavelength λ or (n ± 1/2) λ. However, n
Is an integer.

In this case, the output terminal T of the detection head 2a_2a
That is, from the connection midpoint of the MR elements 31a and 32a, the MR element is
The magnetoresistive effects received by the children 31a and 32a are additive (difference
Output terminal T of the detection head 2b_2bImmediately
The MR element 31b and the MR element from the connection midpoint of 32b
The magnetoresistive effect received by 31b and 32b is additive (differential
Of the two channels of the detection head 2a
And output terminal T of 2b _2aAnd T_2bFor the effective wavelength λ
90 ° phase difference due to the magnetoresistive effect of 90 ° phase difference
An output signal with is obtained.

The other ends T _3a and T _3b of the detection heads 2a and 2b of the two channels are connected via a variable resistor 12 for adjusting the DC bias.

Further, in this example, the rectangular wave signal EX ₁ having the sine wave component of the frequency f is supplied to _one excitation signal input terminal 3a and the frequency f is supplied to the other excitation signal input terminal 3b.
The rectangular wave signal EX ₂ of the cosine wave component of is supplied.

The rectangular wave signal EX ₁ of the sine wave component of the frequency f supplied to the one excitation signal input terminal 3a is supplied to the low pass filter 4a, and the sine of the angular frequency ω = 2πf is supplied to the output side of the low pass filter 4a. The wave excitation signal e _X1 is obtained. e _X1 = sin ωt ··· (4)

The sine wave excitation signal e _X1 obtained at the output side of the low pass filter 4a is passed through the excitation amplifier 5c.
Supply to one end T _1a of the detection head 2a.

The rectangular wave signal EX ₂ of the cosine wave component of the frequency f supplied to the other excitation signal input terminal 3b is supplied to the low pass filter 4b, and the angular frequency ω = 2πf is supplied to the output side of the low pass filter 4b. The excitation signal e _X2 of the cosine wave of is obtained. e _X2 = cos ωt (5)

The cosine wave excitation signal e _X2 obtained at the output side of the low-pass filter 4b is supplied to one end T _1b of the detection head 2b via the excitation amplifier 5d. The square wave signal E
It is also possible to supply X ₁ to the low-pass filter and generate the excitation signal e _X2 of the cosine wave of the output excitation signal e _X1 of the sine wave through the 90 ° phase shift circuit.

The output signals e _X1 and e _X2 of the excitation amplifiers 5c and 5d are supplied to the inverting addition amplifier 5e, and the excitation signal e _X3 is obtained at the output side of the inverting addition amplifier 5e. This excitation signal e _X3 can be expressed as follows. e _X3 =-(sin ωt + cos ωt) (6)

The exciting signal e _X3 obtained at the output side of the inverting addition amplifier 5e is _supplied to the variable resistor 12 for adjusting the DC bias.
Supply to the mover. Therefore, in this case, the detection head 2a
Are equivalently excited by 2 sin ωt, and the detection head 2b
Will be excited at 2 cos ωt.

When the output signals obtained at the output terminals of the detection heads 2a and 2b are e ₁ and e ₂ , they are equivalently as follows. e ₁ = E ₁ sin ωt × cos (2πx / λ) (7) e ₂ = E ₂ cos ωt × sin (2πx / λ) (8)

The output terminal of the detection head 2a, that is, the connection midpoint of the MR elements 31a and 32a is connected to the inverting input terminal of the differential amplifier 34 via the resistor 33a, and the detection head 2a is connected.
The output terminal of b, that is, the midpoint of connection between the MR elements 31b and 32b is connected to the non-inverting input terminal of the differential amplifier 34 via the resistor 33b, and this non-inverting input terminal is grounded via the resistor 35.

Further, in this example, a variable resistor 36 for adjusting the output balance is connected between the inverting input terminal of the differential amplifier 34 and this output terminal, and the variable resistor 36 is adjusted to detect it. Signal level E ₁ from head 2a
Is adjusted, and the signal level E from the detection head 2b is adjusted.
It can be adjusted to be equal to ₂ . Further, the variable resistor 36 may be fixed and the resistor 33a may be a variable resistor. When the signal level E ₁ from the detection head 2a is fixed and the signal level E ₂ from the detection head 2b is adjusted, the variable resistor 36 and the resistor 33a are fixed,
The resistor 35 or the resistor 33b may be adjusted as a variable resistor.

Therefore, the phase modulation signal e _P having the signal level E can be obtained at the output side of the differential amplifier 34. e _P = E sin (ωt-2πx / λ) (9)

Further, in this case, by adjusting the mover of the variable resistor 12 for adjusting the DC bias, the potential difference between the output terminals of the detection heads 2a and 2b of the two channels can be adjusted to zero. MR elements 31a, 3
It is possible to correct the influence of the DC bias of 2a, 31b and 32b.

The phase modulation signal e _P obtained at the output side of the differential amplifier 34 is obtained through the waveform shaping circuit 11 to obtain, for example, a rectangular wave phase modulation signal S, which is well known, for example, Japanese Patent Publication No. Sho 49-.
As shown in Japanese Patent No. 8917, a pulse width signal corresponding to the phase difference between the phase modulation signal S and the rectangular wave signal EX ₁ for obtaining the excitation signal e _X1 is obtained, and the number of clock pulses corresponding to this pulse width signal is counted. To obtain the position x.

As described above, according to the present embodiment, the two-channel detection heads 2a and 2b are excited by the two-phase excitation signals e _X1 = sin ωt and e _X2 = cos ωt which are 90 ° out of phase with each other.
And the output terminals of the two-channel detection heads 2a and 2b are connected to the inverting input terminal and the non-inverting input terminal of the differential amplifier 34, and the phase modulation signal e _P is output from the output side of the differential amplifier 34. Therefore, as an adjusting element, a variable resistor 36 for adjusting the output balance for adjusting the level of the output signals of the detection heads 2a and 2b is used.
With the variable resistor 12 for adjusting the DC bias of the detection heads 2a and 2b, the number of adjustment points is reduced, and the space for mounting the adjustment mechanism and the number of steps for adjustment can be reduced. There is.

Further, according to this example, one differential amplifier 34
Since the phase modulation signal e _P is obtained only by itself, there is an advantage that the configuration of the phase detection circuit is simple and miniaturized.

In the above-described embodiment, the detection heads 2a and 2b for two channels are provided with two MR elements 31 each.
Although an example using a, 32a and 31b, 32b has been described, the detection heads 2a and 2b for each channel can be realized by one MR element. That is, the MR elements 31a and 31b in FIG. 1 may be left as they are, and the MR elements 32a and 32b in FIG. 1 may be replaced with fixed resistors. Alternatively, the MR elements 32a and 32b may be left as they are and the MR elements 31a and 31b may be replaced with fixed resistors, respectively. In this case, the same effect as that of the example of FIG. 1 can be obtained, the detection heads 2a and 2b can be further downsized, and the cost can be reduced.

In the example of FIG. 1, the two-channel detection heads 2a and 2b are excited in a balanced manner by using the three amplifiers 5c, 5d and 5e.
The _purpose is to expand the amplitudes of the excitation signals e _X1 , e _X2 , and e _X3 for the elements 31a, 32a, 31b, and 32b to obtain a large output signal.

Therefore, when the circuit voltage can be set high,
Even if the amplitudes of the output signals of the excitation amplifiers 5c and 5d are enlarged, the inverting addition amplifier 5e is eliminated, and the mover of the variable resistor 12 for adjusting the DC bias is grounded,
It can be easily understood that the same effect as that of FIG. 1 can be obtained.

Further, the present invention is not limited to the above-mentioned embodiments, and it goes without saying that various other configurations can be adopted without departing from the gist of the present invention.

[0052]

According to the present invention, a two-channel detection head is driven by two-phase excitation signals having different 90 ° phases, and each output terminal of the two-channel detection head is connected to one and the other of a differential amplifier. Since it is connected to the input terminal and the phase modulation signal is obtained from the output side of the differential amplifier, the adjustment elements are the adjustment of the output signal level of the 2-channel detection head and the adjustment of the 2-channel detection head. Adjustment of the DC bias is sufficient, the number of adjustment points is reduced, and there is an advantage that the space for mounting this adjustment mechanism and the number of adjustment steps can be reduced.

Further, according to the present invention, since the phase modulation signal is obtained by only one differential amplifier, there is an advantage that the structure of the phase detection circuit can be simplified and downsized.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a displacement amount detection device of the present invention.

FIG. 2 is an enlarged view showing an example of a main part of FIG.

FIG. 3 is a configuration diagram showing an example of a conventional displacement amount detection device.

FIG. 4 is a connection diagram showing a specific configuration example of a main part of FIG.

FIG. 5 is a configuration diagram showing an example of a conventional displacement amount detection device.

[Explanation of symbols]

1 Magnetic scale 2a, 2b detection head 3,3a, 3b Excitation signal input terminal 4,4a, 4b Low-pass filter 5,5a, 5b, 5c, 5d Excitation amplifier 5e Inversion summing amplifier 11 Wave shaping circuit 12 DC bias adjusting variable resistor 31a, 31b, 32a, 32b MR element 34 Differential amplifier 36 Variable resistor for output balance adjustment

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01B 7/00 G01D 5/245

Claims (5)

(57) [Claims] 1. A first and a second magnetoresistive effect element which are subjected to a magnetoresistive effect having a phase difference of 180 ° with respect to a magnetization pattern corresponding to a wavelength λ of an output signal of a magnetic scale, and are connected in series. And a detection head of the first channel having a connection point of the second magnetoresistive effect element as an output terminal,
Third and fourth magnetoresistive effect elements that receive magnetoresistive effects having a phase difference of 180 ° with respect to the magnetization pattern are connected in series, and a connection point of the third and fourth magnetoresistive effect elements serves as an output terminal. And a second channel detection head adapted to obtain an output signal having a 90 ° phase difference with respect to the output signal of the first channel detection head. 9 detection heads
Driving with two-phase excitation signals having different 0 ° phases, and connecting the output terminals of the detection heads of the first and second channels to one and the other input terminals of the differential amplifier, respectively. A displacement amount detecting device characterized in that a detection signal is obtained from an output side. 2. A first magnetoresistive effect element and a first fixed resistor are connected in series, and a connection point of the first magnetoresistive effect element and the first fixed resistor serves as an output terminal. The detection head of the channel, the second magnetoresistive effect element and the second fixed resistor are connected in series, and the connection point of the second magnetoresistive effect element and the second fixed resistor is used as the output terminal. And a second channel detection head for obtaining an output signal having a 90 ° phase difference with respect to the output signal of the first channel detection head, and detecting the first and second channels. The heads are driven by two-phase excitation signals having 90 ° different phases, and the respective output terminals of the detection heads of the first and second channels are connected to one and the other input terminals of the differential amplifier, Obtain the detection signal from the output side of the amplifier Displacement detecting device, characterized in that the the like. 3. The displacement amount detecting device according to claim 1, wherein the differential amplifier is composed of a differential amplifier having a gain adjusting function, and outputs a balanced modulation signal between the first and second channels. A displacement amount detection device characterized in that a phase modulation signal having a constant output amplitude can be taken out while correcting a level imbalance. 4. The displacement amount detection device according to claim 1, wherein the detection heads of the first and second channels are connected via a variable resistor, and the first and the second resistors are connected by the variable resistor. A displacement amount detecting device characterized in that the DC bias voltage of the detection head of the second channel can be adjusted. 5. The displacement amount detecting device according to claim 4, wherein a composite signal of the two-phase excitation signals is supplied to the mover of the variable resistor.