JPH0552583A - Magnetic encoder - Google Patents

Abstract

PURPOSE:To achieve higher measuring accuracy of a magnetic encoder using a phase difference detection system as one electric multiplication method. CONSTITUTION:An amplitude ratio adjusting circuit 20 is inserted between an magnetoresistance effect element 1 (1a, 1b) and a phase difference detection circuit 10 to convert a 2-phase signal to be obtained from the magnetoresistance effect element into two signals of an equal amplitude holding a phase difference therebetween.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic encoder used for detecting the speed and position of an actuator for driving and controlling a robot, a manipulator and the like.

[0002]

2. Description of the Related Art Conventionally, a magnetic encoder, which is an angle detector, has been used as a means for instantaneously and accurately measuring the position and speed of an actuator which is incorporated in a robot or a manipulator and rotates or moves linearly.
FIG. 7 shows a configuration example thereof.

A magnetic recording medium 12 made of a ferromagnetic material is formed on the outer circumference of the drum 11, and a pitch P is formed over the entire circumference thereof.
It is magnetized with multiple poles. On the other hand, a magnetoresistive effect element (hereinafter appropriately abbreviated as MR element) 1 is arranged so as to face each other through a gap G that is sensitive to the leakage magnetic field of these minute magnets. The MR element 1 has (2n + 1) in the rotation direction.
Two sets of MR elements (elements) 1 separated by P / 4 (n is an integer)
By disposing a and 1b, the direction of rotation can be known.

As the drum 11 rotates, the MR element 1
Shows a sinusoidal change with the magnetizing pitch P as a cycle, and by applying a voltage from the DC power supply 13 to the MR element 1, the resistance change can be taken out as a voltage change. Further, the minute two-phase signals (referred to as A-phase and B-phase signals, respectively) from the two sets of MR elements 1a and 1b are amplified.
After being amplified by 4a and 14b and converted into pulse signals by the comparators 15a and 15b, the rotation angle (position) is measured using a counting circuit or the like. In this way, the rotation direction, rotation speed, and position signal output of the drum 11 are obtained from the relationship between the A-phase and B-phase signals. If the rotation of the drum 11 is made to correspond to the movement of the actuator, the position and speed of the actuator can be known.

In such a magnetic encoder, the accuracy of position measurement has been conventionally improved by reducing the magnetizing pitch P. However, as the size of the magnet decreases, the leakage magnetic field also weakens and the MR element 1 Therefore, there is a limit to the reduction of the magnetizing pitch P because it cannot be detected by. Therefore, in recent years, a method of improving the measurement accuracy by electrically multiplying the A-phase and B-phase signals obtained from the MR element 1 has become mainstream.

Next, the flow of signal processing in the phase difference detection method which is one of such electrical multiplication methods will be described with reference to FIG. As the magnetic recording medium moves (rotates), the MR
Minute A phase (sin that is 90 ° out of phase with element 1)
θ) and B-phase (cos θ) signals are output. These signals are amplified by amplifiers 2a and 2b, and the respective outputs and the high frequency two-phase sine wave signals (sin ω) obtained from the oscillator 5 are amplified.
t and cos ωt) (sin ωt · sin θ and co
s ωt · cos θ) is obtained by the multipliers 6a and 6b, and the difference is obtained by the subtractor 7. This difference signal (sin (ωt−
θ)) and the reference signal from the oscillator 5 (sin ω
The phase difference with t) is θ. Therefore, both signals are converted into pulses by the comparators 8a and 8b so that the phase difference can be easily detected, and the digital counter circuit 9 counts the pulses to obtain a position signal output.

[0007]

In the magnetic encoder using the phase difference detection method, which is one of the conventional electrical multiplication methods, the magnetic recording medium 1 is provided over the entire circumference of the drum 11.
The gap G between the MR element 1 and the MR element 1 fluctuates slightly, so that the amplitude ratio of the A-phase signal and the B-phase signal fluctuates, and a slight difference between the stripe direction of the MR element 1 and the rotation axis of the drum 11 occurs. The phase difference between the two signals fluctuates due to the inclination and the like, and the positional measurement accuracy depends on these two fluctuation amounts, particularly the fluctuation of the amplitude ratio. For example, FIG. 9 and FIG. 10 show an example of measuring the fluctuation of the amplitude ratio and the phase difference of the AB phase in the conventional magnetic encoder as described above.
This variation in amplitude ratio and phase difference caused detection errors of 3.0% and 0.2%, respectively. The detection error due to the variation of the amplitude ratio of the A phase and the B phase accounts for 94% of the total detection error of 3.2%.

An object of the present invention is to eliminate the detection error due to the variation of the amplitude ratio of the A phase and the B phase, which has been a great obstacle to the improvement of the position measurement accuracy in the conventional magnetic encoder using the phase difference detection method, and to achieve high measurement accuracy. To get a magnetic encoder.

[0009]

According to the present invention, an A-phase signal and a B-phase signal obtained from an MR element are kept between the MR element and the phase difference detection circuit while keeping the phase information of both signals. An amplitude ratio adjusting circuit for converting into two equal signals is inserted.

[0010]

The position detection circuit obtains the position signal output from the phase difference by using the two signals having the amplitude ratio of 1. Since the influence of the fluctuation of the amplitude ratio of the AB phase, which is the main factor of the detection error, is eliminated, the position measurement accuracy can be improved.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a diagram showing a circuit configuration of the magnetic encoder of the present embodiment, and the same reference numerals as those in FIG. 8 indicate the same or corresponding portions. The MR element 1, the amplifiers 2a and 2b, and the phase difference detection circuit 10 are the same as those shown in FIG. 8. However, in this embodiment, the amplitude ratio adjustment circuit 2 is provided before the phase difference detection circuit 10.
It has 0. The amplitude ratio adjusting circuit 20 includes a subtracter 3a and an adder 3b, each of which includes an operational amplifier.
And external fixed resistors 4a to 4h, and a subtractor 3a.
And the adder 3b have the same amplification degree.

Small signal asin θ obtained from the MR element 1
(A phase) and bcos θ (B phase) are amplified by the amplifiers 2a and 2b. The outputs Asin θ (A phase) and B cos θ (B
The amplitude ratio to the phase) is 0.985 as shown in FIG.
It varies between <A / B <1.015. These A-phase signal and B-phase signal are input to the subtractor 3a and the adder 3b, respectively. As a result, each output (this is A'phase and B '
The phases are as follows.

[0013]

[Equation 1]

Using the A'phase signal and the B'phase signal having the same amplitude as described above, the phase difference detection circuit 10 obtains the position signal output as in the conventional example.

2 and 3 show A'in this embodiment.
The results of measuring the variation in the amplitude ratio and the phase difference between the B phase and the B ′ phase are shown below. The amplitude ratio is 1.
It was 00. The phase difference is 90 ° ± 0.8 °, as shown in FIG.
It is larger than the fluctuation of the phase difference between the A phase and the B phase shown in Fig. 4, but this is because the phase difference 2α between the A'phase and the B'phase is the amplitude ratio A / between the A phase and the B phase. This is because it depends on B. When the amplitude ratio changes between 0.985 <A / B <1.015, 2α is 89.13 ° to 90.85 ° and 1.
It is calculated that it varies within a width of 72 °. Conventional phase A and B
Considering that the phase difference with the phase fluctuates by 0.2 ° over the entire circumference of the drum 11, the fluctuation range of the phase difference between the A ′ phase and the B ′ phase is 1.92 ° at maximum.

Since the amplitude ratio and the phase difference between the A'phase and the B'phase change as described above, the measurement result according to the present embodiment causes a detection error as shown by a white circle in FIGS. 4 and 5. .. In reality, there is no fluctuation in the amplitude ratio, so there is no detection error due to it. In FIG. 4 and FIG. 5, black circles also show the influence of fluctuations in the amplitude ratio between the A phase and the B phase and the phase difference on the detection error in the conventional example. The detection error due to the change in the amplitude ratio of the phase signal is reduced by 3%. Although the detection error due to the fluctuation of the phase difference increases by 1.8%, the total detection error is deducted from 1.
2% improvement, and the position measurement accuracy is 1.6% from the conventional 3.2% (black circle) to 2.0% (white circle) as shown in FIG.
I saw a double improvement.

[0017]

As described above, according to the present invention, an AB 2-phase electric signal obtained from the above-mentioned two sets of MR elements is provided between the two sets of MR elements and the phase detection circuit as phase information of both. By inserting an amplitude ratio adjusting circuit for converting into two signals having the same amplitude, the measurement accuracy of the phase difference detection type magnetic encoder can be improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a magnetic encoder showing an embodiment of the present invention.

FIG. 2 is a diagram showing variations in the amplitude ratio of two-phase outputs of the amplitude ratio adjusting circuit.

FIG. 3 is a diagram showing variations in phase difference between two-phase outputs of an amplitude ratio adjusting circuit.

FIG. 4 is a diagram showing the influence of fluctuations in the amplitude ratio of two-phase outputs on a detection error.

FIG. 5 is a diagram showing the influence of fluctuations in the phase difference between two-phase outputs on a detection error.

FIG. 6 is a diagram showing all detection errors in comparison with a conventional example.

FIG. 7 is a diagram showing a general configuration of a magnetic encoder.

FIG. 8 is a circuit diagram showing a conventional phase difference detection type magnetic encoder.

FIG. 9 is a diagram showing changes in the amplitude ratio of the two-phase output of the MR element.

FIG. 10 is a diagram showing variations in phase difference between two-phase outputs of the MR element.

[Explanation of symbols]

 1 (1a, 1b) Magnetoresistive effect element 10 Phase difference detection circuit 12 Magnetic recording medium 20 Amplitude ratio adjustment circuit

[Procedure amendment]

[Submission date] October 13, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 1

[Correction method] Change

[Correction content]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction content]

Next, the flow of signal processing in the phase difference detection method which is one of such electrical multiplication methods will be described with reference to FIG. As the magnetic recording medium moves (rotates), the MR
Minute A phase (sin that is 90 ° out of phase with element 1)
θ) and B-phase (cos θ) signals are output. These signal amplification unit 2a, amplified by 2b, a high-frequency two-phase sine wave signals obtained from the output and the oscillator 5 of each (sin omega
t and cos ωt) (sin ωt · sin θ and co
s ωt · cos θ) is obtained by the multipliers 6a and 6b, and the difference is obtained by the subtractor 7. This difference signal (sin (ωt−
θ)) and the reference signal from the oscillator 5 (sin ω
The phase difference with t) is θ. Therefore, both signals are converted into pulses by the comparators 8a and 8b so that the phase difference can be easily detected, and the digital counter circuit 9 counts the pulses to obtain a position signal output.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction content]

[0009]

Means for Solving the Problems The present invention is, between the MR element and the phase difference detection circuit, an A-phase signal and the B-phase signal obtained from the MR element, equal amplitude while maintaining both the phase An amplitude ratio adjusting circuit for converting into two signals is inserted.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

[0017]

As described above, according to the present invention, between the two sets of MR elements and the phase detection circuit, the AB two-phase electric signals obtained from the two sets of MR elements are supplied to each other . By inserting the amplitude ratio adjusting circuit for converting the two signals having the same amplitude while maintaining the same, it is possible to improve the measurement accuracy of the magnetic encoder of the phase difference detection method.

[Procedure Amendment 6]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

[Figure 1]

Claims (1)

[Claims] 1. A magnetic recording medium in which at least one magnetization pattern sequence is written at a pitch P to generate a periodic magnetic field, and a magnetic recording medium close to the magnetic recording medium and mutually in the moving direction of the magnetic recording medium. Phase difference detection including two sets of magnetoresistive effect elements arranged at a distance of (2n + 1) P / 4 and a function of electrically multiplying AB two-phase electric signals obtained from these magnetoresistive effect elements, respectively. In a phase-difference detection-type magnetic encoder including a circuit, an A-phase signal and a B-phase signal are held between the magnetoresistive effect element and the phase-difference detection circuit while keeping the phase information of both signals and having the same amplitude. A magnetic encoder characterized in that an amplitude adjusting circuit for converting into a signal is inserted.