JPH01265113A - Magnetic encoder - Google Patents

Abstract

PURPOSE:To obtain the high-accuracy encoder by supplying a current to magneto-resistance effect elements of the magnetic encoder by a power unit which has a constant current circuit. CONSTITUTION:The magnetic encoder is constituted by magnetizing magnetic records 3 of a magnetic recording medium on the outer periphery of a magnetic drum 2 fixed on a rotary shaft 1 at nearly equal intervals in alternate N and S order and arranging the magnetic sensor 4 which has the magneto-resistance effect elements R1-R4 formed of ferromagnetic thin films oppositely to the outer periphery of the magnetic drum 2 across a proper gap. The current is supplied to terminals (a) and (b) of the magnetic sensor 4 by the constant current power source Is. Consequently, even if the resistance value R0 in the absence of a magnetic field varies with temperature, the current flowing to the magnetic sensor is constant, so the output voltage e1 between terminals (c) and (d) is only an output voltage based upon the variation of a magnetic field and never varies with the temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Purpose of the Invention [Field of Industrial Application] The present invention relates to a magnetic encoder that detects the speed, position, etc. of a rotating body.

[Prior Art] Figure 2 shows a block diagram (a) showing the concept of a conventional magnetic encoder, a developed diagram (b) showing the correlation between magnetic recording on a magnetic drum and a magnetic sensor, and an electric circuit diagram. (Q
) and temperature characteristics (d) and (e).

In the illustrated magnetic encoder, magnetic records 3 of a magnetic recording medium are magnetized alternately N and S at approximately equal intervals on the outer periphery of a magnetic drum 2 fixed to a rotating shaft 1. Magnetoresistive element R formed of a ferromagnetic thin film
Magnetic sensors 4 having □ to R4 are arranged opposite to each other, and the speed or position of the rotating shaft to which the magnetic drum is fixed can be detected by detecting the resistance change of the magnetoresistive element of the magnetic sensor.

The correlation between the magnetic recording 3 of the magnetic drum 2 and the magnetoresistive elements R1 to R4 of the magnetic sensor 4 is as shown in FIG. The arrangement pitch of R4 is λ/2.

Furthermore, as shown in the figure (c), four magnetoresistive elements R1
~R4 is connected to form a bridge, and the a,
The power supply Es is connected to the b terminal, and the rotation shaft 1 is connected to the c and d terminals so that a sine wave or pseudo sine wave voltage can be obtained.The rotation can be determined by measuring this output voltage. Axis position.

Or it can detect speed.

The power source Es that supplies current to the magnetoresistive element is generally a constant voltage circuit.

The resistance value of a magnetoresistive element changes depending on the strength of the magnetic field acting on the element, and the resistance value when the magnetic field strength is zero is Ro.
The resistance value decreases in proportion to the magnetic field strength, and the resistance value reaches a minimum above a certain magnetic field strength.

Here, if the amount of change in the resistance value that changes due to a certain magnetic field is ΔR, then the resistance when the magnetoresistive element is receiving a magnetic field can be expressed as R=R0−ΔR.

(c) Terminal a of the series circuit of R□ and R2 in the figure.

The output voltage e1 appearing at terminals c and b when voltage E is applied to b is expressed as e, = R, e E/ (R, +R,), where R and R2 are respectively R, and the mutual relationship is (b ) Assuming that R1 is at the position shown in the figure, R1 is the position where the acting magnetic field is zero, so ΔR is zero and becomes Ro, and R2 is the position where the acting magnetic field is maximum, so ΔR is maximum and ex = CRo- ΔR)-E/ (2R,-ΔR)-(1
), and a voltage proportional to ΔR is output.

When the magnetic field acting on the magnetoresistive element changes in a sinusoidal manner due to the rotation of the magnetic drum, the output voltage e also changes in a sinusoidal manner, and the output voltage is similarly output between the terminals d and b on the other sides R3R4 of the bridge. A voltage e2 is generated, and the overall output voltage e0 is eo”e, -e2=ΔR-E/(2R,-
ΔR) ・(2)

[Problems to be Solved by the Invention] The output voltage of the magnetic encoder shown in FIG. 2 is a sine wave voltage corresponding to the position or speed of the rotating shaft.
The resistance value of a magnetoresistive element made of a thin film of ferromagnetic material is
Of course, it changes depending on the strength of the applied magnetic field, but as shown in figure (d), it also changes depending on temperature, and has a positive temperature coefficient, while curve (e) shows that it changes due to the magnetic field. This shows that ΔR, which is the minute, has not changed. For this reason, the amplitude of the output voltage changes depending on the ambient temperature, causing a position detection error in a magnetic encoder with a sine wave output used to detect the position of a servo motor. The present invention aims to provide a magnetic encoder that can obtain a voltage of constant amplitude.

(2) Structure of the invention [Means for solving the problems] In order to solve the above problems, the present invention has a structure in which a power supply device having a constant current circuit supplies current to the magnetoresistive element. It is something.

[Function] In the conventional technology, when the temperature of the magnetic sensor increases (1
) As for the output voltage e1 shown by the equation, the Ro of the magnetoresistive element increases, and since the power supply voltage E is constant, the current flow of the magnetic sensor decreases, and the output voltage decreases.

By changing the power supply to a constant current power supply in contrast to the conventional technology described above, the current flowing through the magnetic sensor remains constant even if R11 changes due to temperature changes, so the output voltage e1 becomes only the output voltage due to changes in the magnetic field. It has the effect of not changing depending on the temperature.

[Embodiment of the Invention] Fig. 1 shows an electric circuit of a magnetic encoder according to the present invention, and the new configuration is that current is supplied to terminals a and b of the magnetic sensor via a constant current power supply Is. is the same as that according to the prior art.

In the figure, a current of 1. When flowing (2R0-∆R). Therefore, the voltage at terminals a and b changes in proportion to R, which changes with temperature, resulting in the output voltage.

Since E/(2R-ΔR) is constant in Equation (2), eo only changes ΔR corresponding to changes in the magnetic field, and is not affected by temperature.

ΔR depends on the material of the ferromagnetic material, but is usually 2 to 5% of the resistance value.
Since the temperature coefficient of R is 0.2-0.3%/°C, for example, when the temperature changes by 60 degrees from 20°C to 80°C, R8 changes by 12-18%, whereas the structure of the present invention According to , the output voltage does not change due to temperature.

A constant current circuit is generally known. For example, a semiconductor control element and a current detection resistor are inserted between the power supply and the load side, and the voltage of the current detection resistor is compared with a reference voltage using an operational amplifier. A device or the like is used that controls a semiconductor control element using the output of , and controls the load current to a constant value.

[Effects of the Invention] Since the magnetic encoder according to the present invention has the above-described configuration, its output voltage is not affected by temperature, and it is possible to obtain a highly accurate magnetic encoder that can be used in a position detection device for a servo motor. I can do it.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a magnetic encoder according to the present invention, and FIG. 2 is a conceptual diagram (a) of a conventional magnetic encoder. They are a developed view (b), an electric circuit diagram (C), and temperature characteristic diagrams (d) and (e) of the magnetic sensor. Explanation of symbols 1...rotating shaft, 2...magnetic drum, 3...magnetic recording. 4...Magnetic sensor, Es...constant voltage power supply, Is...
・・Constant current power supply, R engineering ~ R4 ・・Magnetoresistive effect element. Patent applicant Nippon Servo Co., Ltd. (a) (C) Le (J) (e) Figure 2 No. 3-

Claims (1)

[Claims] A magnetic drum in which N and S poles are alternately recorded at approximately equal intervals in the direction of movement of the magnetic recording medium fixed to the outer periphery of a rotating body;
A magnetic encoder having a magnetic sensor formed of a magnetoresistive element made of a thin film of ferromagnetic material, which is disposed opposite to the magnetic drum with a gap therebetween, and configured to supply current to the magnetic sensor via a constant current circuit. A magnetic encoder featuring: