JPH05264293A - Position detecting device - Google Patents

Abstract

PURPOSE:To stabilize the output from a magnetic resistance element and improve the precision of detection value thereby in a position detecting device having a magnetic graduation and the magnetic resistance element. CONSTITUTION:A position detecting device has a magnetic scale having a periodic magnetic graduation, a magnetic resistance element 22 consisting of at least two channels arranged to the magnetic gauge, and a signal processing means for detecting the relative displacement of the magnetic resistance element 22 to the magnetic scale on the basis of the signal from each channel of the magnetic resistance element 22. The signal level from the magnetic resistance element 22 is monitored to control the voltage level for driving the magnetic resistance element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position detecting device suitable for use in, for example, a magnetic linear encoder or a magnetic rotary encoder.

[0002]

2. Description of the Related Art FIG. 10 shows an example of a conventional magnetic linear encoder. The magnetic linear encoder includes a long flat plate type magnetic scale 10A and the magnetic scale 10A.
A detection unit 20 that can move relative to
Signal processing means 30. The magnetic scale 10A includes a base 12 and a magnetic medium 1 mounted on the base 12.
4 and a magnetic scale 16 is formed on the magnetic medium 14.

The detector 20 is a magnetoresistive element (MR sensor).
22 and a holder 24 that supports the magnetoresistive element 22, the magnetoresistive element 22 is arranged so as to face the magnetic scale 16. When the detector 20 relatively moves along the magnetic scale 16 in the direction of the arrow L, the output voltage generated by the magnetoresistive element 22 causes the signal processing means 3 to operate.
0 is supplied. The signal processing unit 30 has, for example, a preamplifier 32 and a detection circuit 34, and is configured to detect the relative displacement amount of the detection unit 20 based on the voltage signal from the magnetoresistive element 22.

FIG. 11 shows an example of a conventional magnetic rotary echo echo. The magnetic rotary encoder includes a rotatable cylindrical magnetic scale 10B and the magnetic scale 1
Detecting section 20 arranged on the side surface of 0B and signal processing means 3
Has 0 and. The magnetic scale 10B is a cylindrical base 1
2 and a magnetic medium 14 mounted on the cylindrical surface of the base 12, and a magnetic scale 16 is formed on the magnetic medium 14 along the circumferential direction.

The detection unit 20 is a magnetoresistive element (MR sensor).
22 and a holder 24 that supports the magnetoresistive element 22, the magnetoresistive element 22 is arranged so as to face the magnetic scale 16. When the magnetic scale 10B rotates in the direction of the arrow R shown, the output voltage generated by the magnetoresistive element 22 is supplied to the signal processing means 30. The signal processing means 30 includes, for example, a preamplifier 32 and a detection circuit 34.
And is configured to detect the relative displacement amount of the detection unit 20 based on the voltage signal from the magnetoresistive element 22.

FIG. 12 shows the operating characteristics of the magnetoresistive element 22. The magnetoresistive element 22 has a characteristic that when the applied magnetic field H changes, the electric resistance R changes accordingly. The position detecting device having the magnetoresistive element 22 changes the magnetic field H acting on the magnetoresistive element 22 by the relative displacement between the magnetic scale 16 and the magnetoresistive element 22.
Is detected as a change in the resistance value R of the magnetoresistive element 22.

FIG. 13 shows an example of a circuit including the magnetoresistive element 22, and the principle of detecting the position by the magnetoresistive element will be described with reference to such an example. In this example, the detection unit 20 is composed of two channels, and the first channel has two pairs of magnetoresistive elements 22-11, 22-12 ,.
22-13, 22-14, and the second channel has two pairs of magnetoresistive elements 22-21, 22-22, 22-.
23, 22-24 are included. The resistivity ρ of the magnetoresistive element 22 changes depending on the position x with respect to the magnetic scale 16, and if the recording wavelength of the magnetic scale 16 is 2λ, then
It is represented by the formula.

[0008]

[Number 1] ρ = ρ- (1/2) (ρ 0 -ρ 1) (H / H S) 2 + (1/2) (ρ 0 -ρ 1) (H / H S) 2 cos (2πx / λ) = ρ-Δρ + Δρcos (2πx / λ) = ρ A -Δρcos (2πx / λ) Δρ = (1/2) (ρ 0 -ρ 1) (H / H S) 2 ρ A = ρ-Δρ

Where x is the position coordinate of the magnetic scale 16, ρ
₀ represents the resistivity at x = 0, ρ ₁ represents the resistivity at x = λ / 2, and H _S represents the saturation magnetic field. In this equation, the magnetic field H as a function of position x is

[0010]

## EQU2 ## H = H ₀ sin (2πx / λ)

Is represented by By optimally arranging four pairs of magnetoresistive elements with respect to the magnetic scale 16, the resistivity ρ of each magnetoresistive element can be expressed by the following equation (3).

[0012]

Ρ ₁₁ = ρ _A −Δρ sin (2πx / λ) ρ ₁₃ = ρ _A + Δρ sin (2πx / λ) ρ ₁₂ = ρ _A + Δρ sin (2πx / λ) ρ ₁₄ = ρ _A −Δρ sin (2πx / λ) ρ ₂₁ = ρ _A −Δρ cos (2πx / λ) ρ ₂₃ = ρ _A + Δρ cos (2πx / λ) ρ ₂₂ = ρ _A + Δρ cos (2πx / λ) ρ ₂₄ = ρ _A −Δρ cos (2πx / λ)

Here, ρ ₁₁ , ρ ₁₂ , ρ ₁₃ , and ρ ₁₄ are magnetoresistive elements 22-11, 22-12, 22-13, respectively.
22-14, and ρ ₂₁ , ρ ₂₂ , ρ ₂₃ , and ρ ₂₄ are magnetoresistive elements 22-21, 22-22, 22-, respectively.
23, 22-24.

Therefore, two input amplifiers (preamplifiers)
The voltages V ₁ and V ₂ output by 41 and 42 are calculated by the following equation (4).

[0015]

V ₁ = A _{1 VA} (Δρ / ρ _A ) sin (2πx / λ) V ₂ = A _{2 VA} (Δρ / ρ _A ) cos (2πx / λ)

Here, A ₁ and A ₂ represent the gains of the input amplifiers (preamplifiers) 41 and 42, respectively, and V _A is the terminal 4
It represents the voltage applied to the magnetoresistive element 22 via 3a and 43b. This input amplifier (preamplifier) 41, 42
The output from the above is used to detect the relative displacement of the magnetoresistive element 22 with respect to the magnetic scale 10 and to discriminate the displacement direction.

However, in the conventional position detecting device, since the magnetic field H applied to the magnetoresistive element 22 is directly converted into a voltage and processed, the level of the output signal varies. Such variations in the output signal occur between the position detecting devices due to instrumental error, and also occur when the magnetic resistance element 22 is relatively displaced with respect to the magnetic scale 10 in one position detecting device. ..

FIG. 14A shows an ideal state in which the level of the output signal, for example, the phase modulation signal V _PM is constant even when the magnetoresistive element 22 is relatively displaced with respect to the magnetic scale 10. FIG. The case where the levels of the output signals, for example, the phase modulation signals V _{PM1 to} V _PM4 change when the magnetoresistive element 22 is relatively displaced with respect to the scale 10 is shown.

The causes of variations or changes in the level of the output signal are as follows. (1) Variation in magnetic characteristics of the magnetic medium 14. (2) Temperature characteristics of the magnetoresistive element 22. (3) Temperature characteristics of electric circuit. (4) Changes in clearance and azimuth due to changes in volume of each part due to changes in temperature.

(5) Relative positional variation between the magnetic head and the magnetic recording surface during recording. This is because, for example, the surface roughness of the magnetic recording surface varies, the magnetic recording surface has undulations, and the followability of the magnetic head to the magnetic recording surface also varies. (6) Output change due to the influence of an external magnetic field.

(7) Change in clearance between the magnetoresistive element 22 and the recording surface of the magnetic scale 16 formed on the magnetic medium 14. This is, for example, a magnetic scale 1 as shown in FIG.
This is because the recording surface of No. 6 has undulations or the position of the magnetoresistive element 22 changes due to vibration. When the magnetoresistive element 22 moves in the direction of arrow L, the magnetoresistive element 22
This is because the distances C1 to C3 between the magnetic scale 16 and the magnetic scale 16 change, and the magnetic field H received by the magnetic resistance element 22 changes accordingly, so that the resistance of the magnetic resistance element 22 changes as shown in FIG.

By removing these causes, it is possible to remove the variation in the level of the output signal, but it is impossible to remove all the causes. In fact, automatic gain control AGC (Auto Gain Control) Is used. The automatic gain control AGC is generally configured to control the gain of the input amplifier section (preamplifier) so that the output level of the input amplifier section (preamplifier) becomes constant regardless of the fluctuation of the level of the input signal. ing.

FIG. 16 shows an example in which a conventional AGC is applied to the signal processing means of the position detecting device. In this example, the detection unit 20 including four pairs of magnetoresistive elements 22, the output stabilizing means 52 connected thereto, the interpolation circuit 54, and the drive signal generation circuit 56 that supplies a signal to the magnetoresistive element drive amplifier 43 are provided. Have. The output stabilizing means 52 is provided with an AGC circuit 44, and the outputs from the input amplifiers (preamplifiers) 41 and 42 are controlled by the AGC circuit 44.

[0024]

However, such an automatic gain control AGC has the following problems when handling a minute output such as an output from a magnetoresistive element. (1) Deterioration of S / N When the output value of the magnetoresistive element decreases, the gain of the input amplifier section increases, but at this time, the noise component is also amplified together with the signal component and increases, so the S / N decreases.
Since the resolution of the position detecting device is limited by the S / N of the signal, it is not possible to obtain high resolution when the S / N decreases.

(2) Increasing the circuit scale of the preamplifier In the position detecting device of the type in which the magnetoresistive element and the detection circuit are arranged apart from each other, in order to prevent a decrease in S / N due to signal transmission, the position is close to the magnetoresistive element. It is necessary to provide an input amplifier section (preamplifier). Since the automatic gain control AGC is provided in this input amplifier section (preamplifier), the shape of the input amplifier sections (preamplifiers) 41 and 42 becomes large, and an integrated circuit is required to prevent this.

The present invention has been made in view of such a point, and the magnetic scale 16
In a position detection device having a magnetic resistance element 22 and
It is an object of the present invention to provide an output stabilizing means which does not need to be arranged close to the magnetoresistive element 22 without reducing the S / N, and thereby improve the accuracy of the detected value.

[0027]

According to the present invention, a magnetic scale 10 having a periodic magnetic scale 16 and at least two channels arranged with respect to the magnetic scale 16 are provided, for example, as shown in FIG. And a signal processing means for generating a phase modulation signal based on a signal from each channel of the magnetoresistance element 22 and detecting a relative displacement of the magnetoresistance element 22 with respect to the magnetic scale 10 based on the phase modulation signal. In the position detecting device having 30 and 30, the level of the phase modulation signal is monitored to detect the magnetoresistive element 22.
Output stabilizing means 52 is provided for controlling the level of the signal output for driving the.

In the position detecting device of the present invention, for example, as shown in FIG. 2, the first channel of the magnetoresistive element 22 is driven by a sine wave signal, and the second channel has a phase more than that of the sine wave of the first channel. Driven by signals of cosine waves different by 90 °, the phase modulation signal is obtained by adding the balanced modulation waves output from each channel, and the output stabilizing means 52 drives the magnetoresistive element 22 by monitoring the phase modulation signal. The sine wave signal output level and the cosine wave signal output level are controlled.

In the position detecting device of the present invention, for example, as shown in FIG. 3, the phase difference between the outputs from the first channel and the second channel of the magnetoresistive element 22 is adjusted to 90 ° by a phase shift circuit, The outputs from the first channel and the second channel are added to generate a phase modulation signal, and the output stabilizing means 52 monitors the phase modulation signal to detect the magnetoresistive element 2.
It is configured to control the level of the sinusoidal signal output driving 2.

In the position detecting device of the present invention, for example, as shown in FIG. 4, the magnetoresistive element 22 is driven by a DC voltage, and the sinusoidal wave output from the first channel and the second channel of the magnetoresistive element 22 is generated. The signal and the cosine wave signal are modulated by the balanced modulation circuits 101 and 102, the balanced modulation waves from the balanced modulation circuit are added to generate a phase modulated signal, and the output stabilizing means 52 monitors the phase modulated signal to detect the magnetic resistance. It is configured to control the level of the DC voltage driving element 22.

In the position detecting device of the present invention, for example, as shown in FIG. 5, the magnetoresistive element 22 is driven by a DC voltage, and a sine wave output from the first channel and the second channel of the magnetoresistive element 22 is generated. The signal and the cosine wave signal are vector-added to thereby generate a position detection signal whose phase is displaced by an arbitrary wavelength, and the output stabilizing means 52.
Is configured to monitor the root mean square value of the signal level of the sine wave and the signal level of the cosine wave to control the level of the DC voltage driving the magnetoresistive element 22.

In the position detecting device of the present invention, the output stabilizing means 52 is configured to include a circuit for generating an alarm signal when the voltage applied to the magnetoresistive element 22 exceeds a predetermined value.

[0033]

According to the present invention, the magnetic scales 10A and 10B having the periodic magnetic scales 16 formed thereon, the magnetoresistive element 22 having at least two channels arranged with respect to the magnetic scales 16 and the magnetoresistive element 22 are provided. Of the magnetoresistive element 2 for the magnetic scales 10A and 10B based on the signal of
In the position detecting device configured to detect the relative displacement of the magnetoresistive element 22, the magnetoresistive element 22 is configured to monitor the output level and control the voltage for driving the magnetoresistive element 22. A stable output can be obtained from the element 22, and the displacement can be detected with high accuracy.

[0034]

Embodiments of the present invention will be described below with reference to FIGS. 1 to 9 and FIGS.
Corresponding portions of 6 are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 1 shows an example of a position detecting device provided with the output stabilizing means of the present invention. In this example, the magnetoresistive element 22
Including the detection unit 20, input amplifiers (preamplifiers) 41 and 42 connected to the respective channels of the detection unit 20, and output stabilizing means 52 arranged on the output side of the input amplifiers (preamplifiers) 41 and 42. An interpolating circuit 54 arranged on the output side of the output stabilizing means 52, and a magnetoresistive element drive amplifier 43 for supplying a drive signal to the magnetoresistive element.
And a drive signal generation circuit 56 for providing a drive signal to the output stabilizing means 52.

The detecting section 20 has a bridge circuit including a magnetoresistive element 22, and is configured to have two channels in the figure. The output from the first channel is the first
Input to the input amplifier (preamplifier) 41, and the output from the second channel is the second input amplifier (preamplifier)
42 is input. Input amplifier (preamplifier) 41, 4
2 may be a differential amplifier, and such a differential amplifier obtains the voltage signal obtained by the equation (4).

The output stabilizing means 52 has a signal processing circuit 62, level detection circuits 64 and 66, and an output stabilizing circuit 60, as shown in the figure. In the signal processing circuit 62, two input amplifiers (preamplifiers)
A phase modulation signal may be generated from the signals from 41 and 42.

The first level detection circuit 64 monitors the signal generated by the signal processing circuit 62 and monitors the output stabilization circuit 6
The signals VD _PM and VD _RMS are supplied to 0. Output stabilizing circuit 60 supplies a drive voltage VA _EX to the magnetoresistive element driving amplifier 43 to input signal VA _C from the drive signal generation circuit 56. The second level detection circuit 66 is the output stabilization circuit 60.
Input the signal VA _EX from the command signal V
The D _EX is supplied to the output stabilizing circuit 60. The output stabilizing circuit 60 supplies a drive voltage to the magnetoresistive element drive amplifier 43 based on the command signal VD _EX .

The output of the signal processing circuit 62 is supplied to the interpolating circuit 54, and the interpolating circuit 54 generates a pulse signal representing the displacement. The output from the interpolation circuit 54 is supplied to, for example, an appropriate counter through the output terminal 54a and counted. In this way, the relative displacement and displacement direction of the magnetoresistive element 22 with respect to the magnetic scale 16 are obtained.

As will be described in detail later, an alarm signal is taken out from the output stabilizing circuit 60 via the output terminal 60a, and the drive voltage supplied to the magnetoresistive element drive amplifier 43 by the alarm signal has a predetermined value. It may be configured such that the crossing is detected.

2 to 5 show more concrete examples of the present example shown in FIG. 1, and FIG. 6 shows the waveform of the voltage signal generated in each example.

FIG. 2 shows a phase modulation method by two-phase AC drive which is the first example of this example. In this example, the frequency is f for the first channel and the second channel of the magnetoresistive element.
AC voltages with different phases are supplied at _c . A second drive amplifier 43 that supplies a drive voltage to the first channel
A phase shifter 78 is provided on the input side of B, so that a phase difference of 90 degrees is generated between the drive voltage of the first channel and the drive voltage of the second channel. The voltage signal input to the first drive amplifier 43A may be, for example, an AC voltage of 50 kHz having a waveform as shown in FIG. 6A, and the voltage signal input to the second drive amplifier 43B may have a waveform as shown in FIG. 6B. May be an alternating voltage.

The outputs of the first channel and the second channel are added by the adding amplifier 70, and the phase modulating signal is generated by the adding amplifier 70. The waveform of the output voltage of the first input amplifier 41 is shown in FIG. 6C, the waveform of the output voltage of the second input amplifier 42 is shown in FIG. 6D, and the waveform of the phase modulation signal output from the summing amplifier 70 is shown in FIG. 6E.

The output signal V ₁ from the first input amplifier 41 connected to the first channel and the output signal V ₂ from the second input amplifier 42 connected to the second channel are expressed by the following equation 5 It is represented by the formula.

[0045]

## EQU5 ## V ₁ = A ₁ V _A (Δρ / ρ _A ) sin (2πx
/ Λ) cos (2πf _c ) V ₂ = A _{2 VA} (Δρ / ρ _A ) cos (2πx / λ) s
in (2πf _c )

The outputs V ₁ and V ₂ are added by the adding amplifier 70 to generate the phase modulation signal V _PM represented by the following equation (6).

[0047]

(6) V _PM = V ₁ + V ₂ = A ₁ V _A (Δρ / ρ _A ) s
in (2πx / λ) cos (2πf _c ) + A _{2 VA} (Δ
ρ / ρ _A ) cos (2πx / λ) sin (2πf _c )

Here, if the coefficients of the first and second terms on the right side are made equal, A ₁ = A ₂ = A and the phase modulation signal V _PM output from the summing amplifier 70 is

[0049]

(7) V _PM = AV _A (Δρ / ρ _A ) sin (2πf _c
+ 2πx / λ)

It can be expressed as In this way, the phase modulation component included in the phase modulation signal V _PM includes the displacement x, and thus the displacement x is obtained.

FIG. 3 shows a phase modulation method by single-phase AC driving which is the second example of this example. In this example, the AC voltage from the drive amplifier 43 is supplied to the magnetoresistive elements 22 of the first channel and the second channel. Drive amplifier 4
The waveform of the AC voltage supplied to No. 3 is shown in FIG. 6A. The outputs of the first input amplifier 41 and the second input amplifier 42 are expressed by the following equation (8).

[0052]

[Formula 8] V ₁ = A ₁ V _A (Δρ / ρ _A ) sin (2πx
/ Λ) sin (2πf _c ) V ₂ = A _{2 VA} (Δρ / ρ _A ) cos (2πx / λ) s
in (2πf _c )

A first phase shifter 91 and a second phase shifter 92 are provided on the output sides of the first input amplifier 41 and the second input amplifier 42, respectively. The phase of the output is displaced by +45 degrees by the first phase shifter 91, and the phase of the output from the second input amplifier 42 is displaced by -45 degrees by the second phase shifter 92. Therefore, the first
Output V _T1 of the second phase shifter 92 and output V _{T2 of} the second phase shifter 92
Is expressed by the following equation (9).

[0054]

[Formula 9] V _T1 = A ₁ V _A (Δρ / ρ _A ) sin (2πx
/ Λ) sin (2πf _c + π / 4) V _T2 = A _{2 VA} (Δρ / ρ _A ) sin (2πx / λ) c
os (2πf _c −π / 4)

The output V _{T1 of} the first phase shifter 91 and the second
The output V _T2 of the phase shifter 92 of FIG.
Shown in. The outputs V ₁ and V ₂ of the phase shifters 91 and 92 are added by the adding amplifier 70, and if the coefficients of the first term and the second term are made equal as in the first example, the following Phase-modulated signal V _PM represented by the equation (10)
Is generated.

[0056]

## EQU10 ## V _PM = AV _A (Δρ / ρ _A ) sin (2πf
_c + 2πx / λ−π / 4)

In this way, the phase modulation component included in the phase modulation signal V _PM includes the displacement x, and thus the displacement x is obtained. Phase modulation signal V output from summing amplifier 70
_{The PM} waveform is shown in FIG. 6E.

FIG. 4 shows a phase modulation method by DC drive which is the third example of this example. In this example, the DC voltage V _A is supplied to the magnetoresistive elements 22 of the first and second channels, and the output signal V _{1 of} the first input amplifier 41 is supplied.
And the output signal V _{2 of} the second input amplifier 42 are expressed by the above-mentioned equation 4
It is expressed by the following equation 11 like the equation of

[0059]

V ₁ = A _{1 VA} (Δρ / ρ _A ) sin (2πx / λ) V ₂ = A _{2 VA} (Δρ / ρ _A ) cos (2πx / λ)

First input amplifier 41 and second input amplifier
The outputs of 42 are shown in Figures 6F and 6G, respectively.
Such output V₁, V₂Are respectively the first balanced modulator 10
It is modulated by the first and second balanced modulators 102. Such
The two balanced modulators 101 and 102 include
From the circuit 104, the phases differ from each other by 90 degrees and the frequency f _c
Carrier signal is supplied by the carrier signal.
Output signal V of the first input amplifier 41₁And the second input
Output signal V of the pump 42₂Is modulated.

The waveform of the carrier signal output from the frequency down-converting circuit 104 is shown in FIGS. 6H and 6I. The outputs V _T1 and V _T2 from the first balanced modulator 101 and the second balanced modulator 102 are represented by the following formula (12).

[0062]

[Equation 12] V_T1= A₁V_A(Δρ / ρ_A) Sin (2π
x / λ) cos (2πf_c+ 6πf _c+…) V_T2= A₂V_A(Δρ / ρ_A) Cos (2πx / λ) s
in (2πf_c+ 6πf _c+…)

The outputs V _T1 , V _T2 from such balanced modulators 101, 102 are shown in FIGS. 6J and 6K. The outputs V _T1 and V _T2 from the balanced modulators 101 and 102 are summing amplifiers 7.
0, and the coefficients of the first term and the second term are adjusted to be equal, and this is further adjusted by the low-pass filter 10
Passing to 3 produces a phase modulated signal V _PM represented by the following equation (13).

[0064]

## EQU13 ## V _PM = AV _A (Δρ / ρ _A ) sin (2πf
_c + 2πx / λ)

In this way, the phase modulation component contained in the phase modulation signal V _PM includes the displacement x, so that the displacement x is generated by the signal.
Is required. The waveform of such a phase modulation signal V _PM is shown in FIG. 6L.
Shown in.

FIG. 5 shows a root mean square value detection method by DC drive which is the fourth example of this example. In this example, the first channel and the magnetoresistive element of the second channel is supplied direct voltage V _A, the output signal V ₂ of the output signal V ₁ of the first input amplifier 41 and the second input amplifier 42 And are expressed by the above-mentioned formula (11). Such an input amplifier 41,
The output signals V ₁ , V ₂ of 42 are shown in FIGS. 6F and 6G. These outputs V ₁ and V ₂ are a: b by resistance division.
Are added at a rate of 1 to generate a voltage signal represented by the following equation (14).

[0067]

V _T1 = √ (a ² + b ² ) AV _A (Δρ /
ρ _A ) sin (2πx / λ + α) α = tan ⁻¹ (a / b)

This signal is

[0069]

(15) α = 2πx / λ

Since the zero point is crossed at the time of, the signal which zero-crosses at the arbitrary point is generated by the arbitrary resistance division ratio a: b, and the position is detected thereby. on the other hand,
The outputs V ₁ and V ₂ of the input amplifiers 41 and 42 are supplied to the RMS converter 108.
Thus, the root mean square value V _{RMS of the two} outputs V ₁ and V ₂ is obtained. The signal representing the root mean square value _VRMS is supplied to the output stabilization circuit 60, which controls the DC drive voltage supplied from the drive amplifier 43.

FIG. 7 shows peak hold amplifiers 74, 76 used in the output stabilizing means of this embodiment shown in FIGS.
An example of 105 is shown. For example, AC voltages VA _PM and VA _EX are input from input terminals 74a and 74b, and output terminals 74c and
DC voltages VD _PM and VD _EX are output from 74d.

FIG. 8 shows the waveforms of the voltages V _PM and V _EX output from the circuit of the peak hold amplifier. FIG. 8A shows AC voltages VA _PM and VA input from input terminals 74a and 74b.
FIG. 8B and FIG. 8C show waveforms of _EX .
The waveforms of the voltages VA _PM and VA _EX output from 74d are shown. When the capacitance of the capacitor C of the peak hold amplifier is small, the undulation of the waveform as shown in FIG. 8B remains, but when the capacitance of the capacitor C is large, a stable output as shown in FIG. 8C is obtained.

FIG. 9 is a modification of the second example shown in FIG. 3, in which a phase shifter 110 is provided on the output side of the first input amplifier 42. The phase of the output of the input amplifier 42 is changed by + π / 2. Further, the part of the output stabilizing circuit 11 is shown as a block, and the output stabilizing circuit 11 is basically a division circuit 60.
A and gm amplifier 60B are included.

According to the output stabilizing means of this embodiment described above, the drive voltage for driving the magnetoresistive element 22 is controlled so as to increase in inverse proportion to the output from the magnetoresistive element 22. Therefore, it is conceivable that the output from the magnetoresistive element 22 is extremely small, which may cause the driving voltage supplied to the magnetoresistive element 22 to be excessive. Therefore, as described above, the output stabilizing circuit 60 may be configured to generate an alarm signal. When the drive voltage supplied to the magnetoresistive element 22 exceeds a predetermined value, the output terminal 60
The alarm signal may be generated via a so that an excessive voltage is not supplied to the magnetoresistive element 22.

Although the embodiments of the present invention have been described above in detail, those skilled in the art will understand that the present invention is not limited to the above-mentioned embodiments and various other configurations can be adopted without departing from the gist of the present invention. Easy to understand.

[0076]

According to the present invention, in the position detecting device having the magnetoresistive element 22 and the magnetic scale 16, the output signal of the magnetoresistive element 22 is monitored to control the drive voltage applied to the magnetoresistive element 22. Therefore, there is an advantage that the output signal of the magnetoresistive element 22 can always be obtained as a constant value.

According to the present invention, since the output signal from the magnetoresistive element 22 is always at a constant level, there is an advantage that the S / N is constant and the position can be detected with high resolution.

According to the present invention, since the output signal from the magnetoresistive element 22 is always at a constant level, the S / N is constant without lowering, and therefore the input amplifiers 41, 4 are provided.
It is not necessary to place 2 close to the magnetoresistive element 22.
Therefore, according to the present invention, the input amplifiers 41 and 42 can be arranged inside the signal processing means 30, and the input amplifier (preamplifier) can be downsized.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration example of a position detection device of the present invention.

FIG. 2 is a diagram showing a first configuration example of a position detection device of the present invention.

FIG. 3 is a diagram showing a second configuration example of the position detection device of the present invention.

FIG. 4 is a diagram showing a third configuration example of the position detection device of the present invention.

FIG. 5 is a diagram showing a fourth configuration example of the position detection device of the present invention.

FIG. 6 is an explanatory diagram showing an example of a signal waveform.

FIG. 7 is an explanatory diagram showing a configuration example of a peak hold amplifier.

FIG. 8 is an explanatory diagram showing an operation of a peak hold amplifier.

FIG. 9 is a diagram showing a fifth configuration example of the position detection device of the present invention.

FIG. 10 is a schematic view showing an example of a conventional position detecting device.

FIG. 11 is a schematic view showing an example of a conventional position detecting device.

FIG. 12 is a characteristic diagram showing characteristics of a magnetoresistive element.

FIG. 13 is an explanatory diagram showing a configuration of a conventional position detection device.

FIG. 14 is a characteristic diagram showing output characteristics of a magnetoresistive element.

FIG. 15 is a diagram showing a relationship between a magnetoresistive element and a magnetic scale.

FIG. 16 is a block diagram of a circuit including an AGC.

[Explanation of symbols]

 10, 10A, 10B Magnetic scale 12 Base 14 Magnetic medium 16 Magnetic scale 16a Signal recording part 16b Signal non-recording part 20 Detection part 22 Magnetoresistive element (MR sensor) 24 Holder 30 Signal processing means 32 Preamplifier 34 Detection circuit 41, 42 Input Amplifier (preamplifier) 43, 43A, 43B Drive amplifier 43a Drive amplifier output terminal 43b Drive amplifier output terminal 44 AGC circuit 52 Output stabilizing means 54 Interpolation circuit 56 Drive signal generating circuit 60 Output stabilizing circuit 60a Output terminal 60A Division circuit 60B gm circuit 62 signal processing circuit 64, 66 level detection circuit 70 summing amplifier 72 waveform shaping circuit 74, 76 peak hold amplifier 78 phase shifter 80 low pass filter 82 frequency reduction circuit 91, 92 phase shifter 93, 94 peak hold amplifier 95 waveform shaping circuit 96 low-pass filter 97 frequency reduction circuit 101, 102 balanced modulator 103 low-pass filter 104 frequency reduction circuit 105 peak hold amplifier 106 constant voltage source 108 RMS converter 110 phase shifter

Claims (6)

[Claims] 1. A magnetic scale having a periodic magnetic scale, a magnetoresistive element having at least two channels arranged with respect to the magnetic scale, and a phase based on a signal from each channel of the magnetoresistive element. A position detecting device having a signal processing means for generating a modulation signal and detecting a relative displacement of the magnetoresistive element with respect to the magnetic scale based on the phase modulation signal; A position detecting device comprising an output stabilizing means for controlling a level of a signal output for driving a magnetoresistive element. 2. The position detecting device according to claim 1, wherein the first channel of the magnetoresistive element is driven by a sine wave signal, and the second channel is 90 ° out of phase with the sine wave of the first channel. Driven by a cosine wave signal, the phase modulation signal is obtained by adding the balanced modulation waves output from each channel, and the output stabilizing means monitors the phase modulation signal and drives the magnetoresistive element. A position detecting device configured to control a level of a signal output of a sine wave and a level of a signal output of a cosine wave. 3. The position detecting device according to claim 1, wherein the phase difference between the outputs from the first channel and the second channel of the magnetoresistive element is adjusted to 90 ° by a phase shift circuit,
Outputs from the first channel and the second channel are added to generate a phase modulation signal, and the output stabilizing means monitors the phase modulation signal and outputs a sine wave signal for driving the magnetoresistive element. The position detection device is configured to control the level of the position detection device. 4. The position detecting device according to claim 1, wherein the magnetoresistive element is driven by a DC voltage, and a sine wave signal and a cosine wave output from the first channel and the second channel of the magnetoresistive element. Signal is modulated by a balanced modulation circuit to add a balanced modulated wave from the balanced modulation circuit to generate a phase modulated signal, and the output stabilizing means monitors the phase modulated signal to drive the magnetoresistive element. A position detecting device configured to control the level of a DC voltage. 5. A magnetic scale having a periodic magnetic scale, a magnetoresistive element comprising at least two channels arranged with respect to the magnetic scale, and each channel when the magnetoresistive element is driven by a DC voltage. Signal processing means for detecting the relative displacement of the magnetoresistive element with respect to the magnetic scale based on the position detection signal by vector-adding the sine wave signal and the cosine wave signal from In the position detecting device having the above, it is configured to monitor the root mean square value of the signal level of the sine wave and the signal level of the cosine wave to control the level of the DC voltage for driving the magnetoresistive element. Characteristic position detection device. 6. The position detecting device according to any one of claims 1 to 5, wherein the output stabilizing means includes a circuit for generating an alarm signal when a voltage applied to the magnetoresistive element exceeds a predetermined value. A position detecting device comprising: