JPH0719897A - Magnetic encoder - Google Patents

Abstract

PURPOSE:To heighten measuring precision of a speed and a position by arranging a plurality of magnetic detection means at a symmetrical position of a magnetic record medium and reducing the amplitude fluctuation of a detection signal of a magnetic field. CONSTITUTION:An A-phase signal (B-phase signal) transmitted from leads L1-Ln are added with a group of addition circuits in order. The output of a final stage addition circuit 15 is the total of signals of the leads L1-Ln and its amplitude becomes a sine wave (cosine wave) of nalpha. And the signals of a waveform level are gotten from the leads L1-Ln by averaging the output of the circuits 15 with an operation circuit 16. Thereby a gap between a magnetic record medium and a magnetoresistance effect device fluctuates so that the rotation of a disk may not be in the same plane and, even if an error is produced in the amplitude, a fluctuation part of the amplitude is canceled by averaging the signals of the leads L1-Ln. A detection error caused by the amplitude fluctuation included in the average of the A-phase signal and the B-phase signal, calculated with the circuit 16 are very small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic encoder which detects a magnetic field from a magnetic recording medium and obtains speed and position information for driving and controlling, for example, a photoengraving stepper, robot, manipulator or the like based on the detected value. Regarding

[0002]

2. Description of the Related Art The speed and position of an actuator incorporated in a robot, a manipulator or the like for rotating or linearly moving is determined by a predetermined magnetizing pattern array along a circumferential direction provided on a rotary shaft of a motor for driving the actuator. It is measured by counting the number of pulses based on the magnetic field read from the magnetic recording medium having a magnetized magnet. Then, the actuator is stopped by the drive circuit comparing the number of pulses with the set value and stopping the motor when they match. Traditionally,
In order to stop the actuator at an accurate position, there is a magnetic encoder as a detection device that can accurately measure the speed and position of the actuator by accurately converting the magnetic field read from the magnetic recording medium into pulses and counting the number of pulses. .

FIG. 8 is a basic configuration diagram of a conventional magnetic encoder. As shown in the figure, a magnetic recording medium 2 made of a ferromagnetic material is formed by electroless plating on the surface of a disk 1 provided on a rotating shaft of a motor (not shown) for driving an actuator. A plurality of minute magnets 3 having a magnetizing pitch P are arranged along the circumference with the same poles adjacent to each other.

An MR (magneto-resistive; magnetoresistive effect) is provided with a gap G enough to cover the leakage magnetic field of the minute magnets 3.
The device 4 is arranged to face the micro magnet 3. The magnetoresistive effect device 4 is composed of magnetoresistive effect element groups 4A and 4B composed of a plurality of magnetoresistive effect elements whose resistance changes in accordance with the strength of the magnetic field, and the magnetizing pitch P of the micro magnets 3 is cycled. And the phase of which is shifted by 90 ° A phase signal (sine wave) and B
Outputs a phase signal (cosine wave).

A voltage is applied to the magnetoresistive device 4 by a DC power source 5, the outputs of the magnetoresistive device groups 4A and 4B are amplified by amplifiers 6A and 6B, respectively, and then converted into pulses by comparators 7A and 7B. And is output to a counting circuit (not shown).

FIG. 9 is a diagram showing the magnetoresistive device 4. As shown in FIG. 3A, the magnetoresistive device 4 is
For example, four magnetoresistive effect elements RA1 to RA4 constituting the magnetoresistive effect element group 4A and four magnetoresistive elements RB1 to RB4 constituting the magnetoresistive effect element group 4B are alternately arranged at intervals of 1 / 4P pitch. And each is bridge-connected.

Next, the operation of the above configuration will be described. The resistances of the magnetoresistive effect element groups 4A and 4B are sinusoidal with the magnetizing pitch P as a cycle according to the change in the strength of the magnetic field passing through the magnetoresistive effect element groups 4A and 4B which changes with the rotation of the disk 1. Shows the change of. The resistance changes of the magnetoresistive effect element groups 4A and 4B are output as voltage changes (A-phase signal and B-phase signal, respectively) when a voltage is applied to the magnetoresistive effect device 4 by the DC power supply 5.

Then, the magnetoresistive effect element groups 4A and 4B
The minute A-phase signal and B-phase signal from the amplifiers 6A and 6A
It is amplified by B, converted into a pulse by the comparators 7A and 7B, and the pulse is counted by a counting circuit or the like not shown.

In the circuit of FIG. 8, the A-phase and B-phase signals output from the magnetoresistive effect device 4 are a sine wave and a cosine wave having the magnetizing pitch P of the small magnets 3 as a cycle, and are equal to 1 of the disk 1. Only pulses of the magnetizing number of the micro magnet 3 can be obtained by the rotation.
In order to improve the accuracy of the speed and position measurement of the actuator, it is necessary to enable fine control of the speed and position of the actuator.
It is preferable that the number of pulses detected per one rotation is large.

Conventionally, in order to increase the number of pulses detected for one rotation of the disk 1, the magnetizing pitch P has been reduced, but when the size of the magnet is reduced, the strength of the leakage magnetic field is increased. Becomes weaker, and the magnetoresistive device 4 cannot detect the magnetic field. Therefore, improvement of the speed and position measurement accuracy by reducing the magnetization pitch P is almost at the limit. Therefore,
In recent years, in order to improve the speed and position measurement accuracy, one cycle of a sine wave and a cosine wave of an A phase signal and a B phase signal, which are output signals of the magnetoresistive effect device 4, is divided into several and the A phase and B phase signals are divided. The electrical multiplication method that obtains a plurality of pulses from one cycle of is becoming mainstream.

Next, the flow of signal processing of the phase difference detection method which is one of the electrical multiplication methods will be described with reference to FIG.
As the disk 1 rotates, the magnetoresistive effect device 4 outputs minute A-phase signals (sin θ) and B-phase signals (cos θ) that are 90 ° out of phase with each other.

Amplification of the A-phase and B-phase signals, the respective outputs, and the product (sinω) of the high-frequency reference signals (sinωt, cosωt) from the oscillator 8 serving as a carrier wave.
t · sin θ, cos ωt · cos θ) is obtained by the multipliers 9A and 9B, and these are subtracted by the subtractor 10 to obtain sin ω
t · sin θ−cos ωt · cos θ = sin (ωt−
θ) is obtained. Here, when ωt = aθ (a> 1), the output sin (ωt−θ) of the subtractor 10 is sin (a
−1) θ, and the waveform has a period of 1 / (a−1) times the sin θ1 period.

The output sin (a-1) θ of the subtractor 10 and the high frequency reference signal sinωt from the oscillator 8.
Are converted into pulses by the comparators 11A and 11B, respectively, and then sent to the counting circuit 12. Counting circuit 12
Then, based on the outputs of the comparators 11A and 11B, a-1 pulses are obtained (since it is multiplied by a-1) during the sin θ1 cycle, and this is counted.

As described above, by the phase difference detection method, one of the A phase signal and the B phase signal which is the output signal of the magnetoresistive effect device 4 is obtained.
The position measurement accuracy is improved by generating multiple pulses from the cycle and controlling minute position measurement.

[0015]

The phase difference detection method described above has been described in an ideal case where the disk 1 rotates on the same plane, that is, there is no fluctuation in the A-phase signal and the B-phase signal.
In this case, the A-phase signal sin θ and the B-phase signal cos θ
Since the amplitude ratio of (for the sake of convenience, the amplitude is assumed to be 1) is 1 and does not change, the output of the subtractor 10 is sin (ωt−θ) as described above, and FIG. An ideal sine wave as shown in FIG. 11 is obtained, and therefore the waveform counted by the counting circuit 12 becomes a regular pulse as shown in FIG.

Actually, since the gap G between the magnetoresistive device 4 and the magnetic recording medium 2 slightly fluctuates over the entire disk 1, the amplitudes of the A phase signal and the B phase signal respectively fluctuate, so that the A phase signal. And the amplitude ratio of the B-phase signal changes.

Considering this variation in the amplitude ratio, assuming that the A-phase signal is Asin θ and the B-phase signal Bcos θ (A ≠ B),
The outputs of the multipliers 9A and 9B are Asin ωt ·
sin θ and B cos ωt · cos θ, and the subtracter 1
The output of 0 is Asin ωt · sin θ−Bcos ωt · c
osθ = Asin (ωt−θ) + (A−B) cosθ ·
As a result, cos ωt results in an error of (A−B) cos θ · cos ωt as compared with the ideal case described above.

When such an error is included, the output waveform of the subtractor 10 becomes an irregular sine wave as shown in FIG. 11C, and therefore the pulse waveform counted by the counter circuit 12 is as shown in FIG. As shown in (d), the intervals between the rising edges of the pulses are not constant and an error occurs.

Since the counting circuit 12 counts the pulses at the rising edge thereof, in order to improve the accuracy of the speed and position measurement of the actuator, when the disk 1 is rotating at a constant speed, the rising edge of the pulse is counted. It is preferable that the intervals are constant.

However, due to fluctuations in the amplitude ratio of the A-phase and B-phase signals, the intervals between the rising edges of the pulses counted by the counting circuit 12 are not constant as shown in the waveform of FIG. There is a problem in that an error occurs, which deteriorates the speed and position measurement accuracy of the actuator.

Further, the plurality of magnetoresistive effect elements on the magnetoresistive effect device 4 are arranged so that the lengthwise direction thereof is in the diametrical direction of the disk 1, but the direction in which the magnetoresistive effect elements are arranged and the disk 1 are arranged. Even if the phase difference between the A-phase signal and the B-phase signal fluctuates due to a slight inclination with respect to the diametrical direction, the speed and position detection accuracy will decrease.

Here, the disk 1 is rotated at a constant speed, and the amplitude of the sine wave of the output of the amplifier 6A at an arbitrary portion of the disk 1 and the amplitude of the sine wave of the amplifier 6B at the arbitrary portion of the disk 1 are set. According to the experimental data actually measured by the data recorder, as shown in FIG.
There was a variation in the amplitude ratio of 985 to 1.015, which is almost 3.0%. Further, the disk 1 is rotated at a constant speed, and the sine waves detected from the outputs of the amplifiers 6A and 6B at eight positions around the disk 1 (every 45 ° in the rotation direction) are
According to the experimental data that was enlarged and measured by the data recorder, the phase difference variation between the A-phase signal and the B-phase signal was 0.2% at maximum. Therefore, in the phase difference detection method,
The maximum total detection error is 3.2%, of which the error due to the variation in the amplitude ratio between the A-phase signal and the B-phase signal is 94% of the total detection error.

As described above, the fluctuations in the amplitudes of the A-phase signal and the B-phase signal greatly hinder the improvement of the speed and position measurement accuracy.

The present invention has been made in order to solve such a problem, and reduces the amplitude fluctuation of the detection signal of the magnetic field due to the magnetic recording medium to obtain a magnetic encoder having high speed and position measurement accuracy. The purpose is to

[0025]

A magnetic encoder according to the present invention is a rotary shaft of a motor for driving a driven body of a magnetic recording medium having magnets magnetized in a circumferential direction with a predetermined magnetization pattern sequence. And a signal for controlling the drive of the motor based on the output of the magnetic detection means, which is provided at a position facing the magnet of the magnetic recording medium and detects the magnetic field of the magnetic recording medium. In a magnetic encoder provided with a signal processing circuit for obtaining the above, a plurality of the magnetic detecting means are arranged at mutually symmetrical positions on the circumference of the magnetic recording medium, and in the signal processing circuit,
An addition circuit for calculating the sum of the outputs of the magnetic detection means and an arithmetic circuit for calculating the average value of the outputs of the plurality of magnetic detection means based on the outputs of the addition circuit are provided, and the average value drives the motor. It is used as a signal for controlling.

[0026]

According to the present invention, a plurality of magnets are arranged at symmetrical positions on the circumference of the magnetic recording medium so as to face the magnets of the magnetic recording medium provided on the rotary shaft of the motor for driving the non-driving member. The magnetic field generated by the magnetic recording medium is detected by the detecting means, the sum of the outputs of the magnetic detecting means is calculated by the adding circuit in the signal processing circuit, and the outputs of the plurality of magnetic detecting means are calculated by the calculating circuit based on the outputs of the adding circuits. Calculate the average value of. Then, the obtained average value is used as a signal for driving and controlling the motor.

[0027]

Embodiments of the present invention will be described below. Example 1. 1 is a perspective view showing a first embodiment of the present invention. As shown in the figure, the magnetoresistive effect device 4 faces the magnetic recording medium 2 with the glass substrate 13 on which a plurality of magnetoresistive effect devices 4 similar to those in FIG. 8 are arranged via chromium (Cr) as an adhesive layer. The lead wires are connected to the A-phase and B-phase magnetoresistive effect element groups of all the magnetoresistive effect devices 4. In FIG. 1, for example, the lead wires L _{1 to} L _n connected to the A-phase magnetoresistive effect element group are shown, and the lead wires connected to the B-phase magnetoresistive effect element group are omitted.

When the diameter φ of the disk 1 is, for example, 150 mm, the number of magnetoresistive elements arranged on the glass substrate 13 is, for example, about 4000 elements. In this case, since the magnetoresistive effect device 4 is composed of the A-phase magnetoresistive effect element group and the B-phase magnetoresistive effect element group each composed of four magnetoresistive effect elements, 500 pieces are arranged.

The magnetoresistive effect device 4 is formed by transferring a pattern of a plurality of magnetoresistive effect elements onto a photomask and using a microfabrication technique such as a CVD technique, a sputtering technique, a photoengraving technique or an etching technique. Further, the magnetoresistive effect element includes a ferromagnetic material such as nickel iron (Ni-
Fe) or nickel cobalt (Ni—Co) is used.

FIG. 2 is a circuit diagram for processing a signal output from the magnetoresistive device 4 of FIG. 1 via the lead lines L _{1 to} L _n . As shown in the figure, the A-phase signals of the lead lines L _{1 to} L _n are sequentially added by the adder circuit group 14 including operational amplifiers, and the final-stage adder circuit 15 obtains the sum of the A-phase signals. Arithmetic circuit 1 such as a microcomputer
6 averages the A-phase signals based on the output of the final stage adder circuit 15, and outputs the average to the amplifier 6A in FIG.

As for the B-phase signal, the sum is obtained by another adding circuit group similarly to the A-phase signal, the arithmetic circuit 16 takes an average, and the average is output to the amplifier 6B in FIG.

Next, the operation of the above configuration will be described with reference to the waveform chart of FIG. The A-phase signal (B-phase signal) output from the lead wires L _{1 to} L _n is a sine wave (cosine wave) with an amplitude of α as shown in FIG.
Will be added in sequence. The output of the final stage addition circuit 15 is the sum of the signals of the lead lines L _{1 to} L _n , and
As shown in (b), it becomes a sine wave (cosine wave) with an amplitude of nα. Then, the arithmetic circuit 16 averages the outputs of the final stage adder circuit 15 to obtain the original waveform level signals of the lead lines L _{1 to} L _n .

By doing so, since the rotation of the disk 1 is not on the same plane, the gap G between the magnetic recording medium 2 and the magnetoresistive effect device 4 fluctuates, and for example, the amplitude of the signal on the lead wire L ₁ changes. Even if an error occurs and becomes α-ε,
The magneto-resistive effect device 4 connected to the lead wire L ₁ and the magneto-resistive effect device 4 at a position symmetrical with respect to the rotation axis.
Since the amplitude of the signal of the lead wire connected to is α + ε, the fluctuation ε of the amplitude is canceled by averaging the signals of the lead wires L _{1 to} L _n . Therefore, the arithmetic circuit 16
The detection error due to the amplitude fluctuation included in the average of the A-phase signal and the B-phase signal calculated in step 1 is extremely small.

Here, in general, the number of the magnetoresistive effect element groups forming the A phase and the B phase of the magnetoresistive effect device 4 is n, and A detected by each magnetoresistive effect element group.
The fluctuations of the amplitude ratio between the phase signal and the B-phase signal are represented by ε ₁ , ε, respectively.
₂ , ..., ε _n , the standard deviation of the sum total of the A-phase signal or the B-phase signal is represented by Σε _n / √n, and the detection error when there is only one magnetoresistive device as shown in FIG. 1 / √
n.

Therefore, when the numbers of the magnetoresistive effect element groups forming the A phase and the B phase are each 500 as in this embodiment, the amplitudes of the A phase signal and the B phase signal over one round of the disk 1 are set. The variation is 0.13% (Σε _n / √n = 3 /
√500, where 3 is the experimental data from the conventional device). Even if this is combined with the fluctuation of the phase difference of 0.2%, the total detection error in the phase difference detection method is 0.33 (= 0.13 +).
0.2), which is 3.0% of the conventional value, as shown in FIG.
It is significantly reduced compared to (FIG. 12). Therefore, according to this embodiment, the accuracy of speed and position measurement is 50
It becomes 0 times.

When the diameter φ of the disk 1 is 150 mm and the magnetizing pitch P of the fine magnets 3 is 120 μm, for example, when the magnetizing pitch P = 120 μm is multiplied by 30, the resolution is
{[(Φ150 × π × 1000) / 120] × 100
%} / 0.13% = 3 million pulse / revolution, or 360 ° × 60 ′ × 60 ″) / 3 million≈0.43
/ Pulse.

In the first embodiment, the output of the arithmetic circuit 16 is input to the circuit for performing electrical multiplication in FIG. 10, but it can be applied to the circuit in FIG. 8 that does not perform electrical multiplication. Needless to say. Further, the disk has a magnetized portion and a non-magnetized portion. For example, the magnetized portion is 1 and the non-magnetized portion is 0.
In this way, it can also be applied to an absolute encoder that detects an absolute position by the binary method.

Example 2. Although the addition circuit group 14 such as operational amplifiers and the final stage addition circuit 15 are used when signals from the magnetoresistive device 4 are added in the first embodiment, FIG.
As shown in, while forming the magnetoresistive effect element itself of the magnetoresistive effect device 4 on the silicon substrate 13A,
The adder group 17 in which the device process and the device structure are established is formed, and the magnetoresistive effect device 4 and the adder group 17 are directly connected by the internal wiring on the silicon substrate 13A, and the lead lines L _{1 to} L _n. Even if it eliminates, the same effect can be obtained.

Example 3. Similar effects can be obtained by forming the magnetoresistive effect device 4 and the adder group 17 on the silicon substrate 13B and forming the arithmetic circuit 18 that averages the final output of the adder group 17.

[0040]

As described above, according to the present invention, the magnetic recording medium having the magnets provided on the rotary shaft of the motor for driving the driven body and magnetized in the circumferential direction with a predetermined magnetizing pattern array. A plurality of magnetic detecting means for detecting a magnetic field due to the magnetic recording medium are arranged facing the magnet of the magnetic recording medium and symmetrically arranged on the circumference of the magnetic recording medium, and the sum of outputs of the magnetic detecting means is calculated. A signal processing circuit including an adder circuit and an arithmetic circuit that calculates the average value of the outputs of the plurality of magnetic detection units based on the outputs of the adder circuit is provided, and the average value is used as a signal for controlling the drive of the motor. Even if the gap between the magnetic recording medium and the magnetic detecting means changes, the detection error of the magnetic detecting means due to the change is corrected by the processing in the signal processing circuit. Since the erased, an effect that improves the accuracy of driving control of the motor, thereby improving the speed and position measurement accuracy of the order non driver.

[Brief description of drawings]

FIG. 1 is a perspective view showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a signal processing circuit according to the first embodiment of the present invention.

FIG. 3 is a waveform diagram for explaining the operation of the first embodiment of the present invention.

FIG. 4 is a characteristic diagram showing a detection error according to the first embodiment of the present invention.

FIG. 5 is a comparison diagram for comparing all detection errors between the first embodiment of the present invention and the conventional device.

FIG. 6 is a perspective view showing a second embodiment of the present invention.

FIG. 7 is a perspective view showing a third embodiment of the present invention.

FIG. 8 is a configuration diagram showing a conventional magnetic encoder.

FIG. 9 is a configuration diagram showing a magnetoresistive device of a conventional magnetic encoder.

FIG. 10 is a block diagram of signal processing by an electric multiplication method.

FIG. 11 is a waveform diagram for explaining the operation of the conventional magnetic encoder.

FIG. 12 is a characteristic diagram showing a detection error by a conventional magnetic encoder.

[Explanation of symbols]

 2 Magnetic Recording Medium 3 Micro Magnet 4 Magnetoresistive Device 13 Glass Substrate 13A Silicon Substrate 13B Silicon Substrate 14 Addition Circuit Group 15 Final Stage Addition Circuit 16 Arithmetic Circuit 17 Adder Group 18 Arithmetic Circuit

Claims (1)

[Claims] 1. A magnetic recording medium having magnets magnetized along a circumferential direction with a predetermined magnetization pattern array is provided on a rotary shaft of a motor for driving a driven body, and faces the magnet of the magnetic recording medium. In a magnetic encoder including magnetic detection means provided at a position for detecting a magnetic field from a magnetic recording medium, and a signal processing circuit for obtaining a signal for driving and controlling the motor based on the output of the magnetic detection means. , A plurality of the magnetic detecting means are arranged at positions symmetrical to each other on the circumference of the magnetic recording medium, and the signal processing circuit includes an adding circuit for calculating the sum of outputs of the magnetic detecting means, and an adding circuit of the adding circuit. A magnetic circuit comprising an arithmetic circuit for calculating an average value of outputs of a plurality of magnetic detection means based on the outputs, and using the average value as a signal for driving and controlling the motor. Encoder.