JPH01269014A - Temperature compensation circuit for magnetic encoder - Google Patents

Abstract

PURPOSE:To always obtain output voltages of a constant amplitude even when the temperature changes by providing an adder, square root extracting operator, comparator, etc. CONSTITUTION:The output voltages of sensors 4-A and 4-B at temperature t1 are respectively set at Ea1 and Eb1 and, when the temperature rises, a resistance R increases since the resistance temperature coefficient is positive and, when the output voltages drop, outputs of operational amplifiers 11 and 12 decline. In addition, outputs of adders 25 and 26 also decline and the output voltage of a square root extracting operator 27 drops. Therefore, the output of a comparator 28 increases and the input of a current controller 30 increases. As a result, currents of the sensors 4-A and 4-B are increased and, accordingly, the output voltages of the sensors are increased. Thus the input voltage of the comparator 28 is controlled so that the input voltage can be balanced with a reference voltage. Moreover, the output voltages of the sensors 4-A and 4-B are controlled so that the output voltages appearing at terminals 13 and 14 can have a constant amplitude irrespectively of temperature. When the temperature drops, rises in the output voltages are suppressed so that the output voltages can have the constant amplitude.

Description

Detailed Description of the Invention (1) Purpose of the Invention [Field of Industrial Application] The present invention relates to a temperature compensation circuit for improving the temperature characteristics of a magnetic encoder that can obtain a sine wave output voltage of rotation angle. .

[Prior art] Figure 2 is a diagram showing the concept of a conventional magnetic encoder, in which (a) shows the structure, (b) shows the developed diagram, (Q) shows the output voltage waveform, and (d) shows the equivalent Each shows an electrical circuit.

In the figures (a) and (b), 1 is a rotating shaft, 2 is a magnetic drum, 3 is a magnetic recording device, and 4 is a magnetic sensor.

A magnetic recording medium fixed to the outer periphery of a magnetic drum 2 provided on a rotating shaft 1 is provided with a magnetic recording medium in which N and S magnetic poles are alternately magnetized, and is opposed to the magnetic drum 2 through an air gap to form a magnetic sensor. 4 is arranged, and the plurality of magnetoresistive elements R0 of the magnetic sensor 4 are provided at a pitch of λ/2 with respect to the pitch λ of the magnetic recording 3 of the opposing magnetic drum 2. An A sensor 4-A made up of magnetoresistive elements R0, and a B sensor 4-A made up of four other magnetoresistive elements R0 arranged at a pitch of λ/4 from the A sensor. It is composed of B.

The equivalent electric circuit of the magnetic sensor 4 is as shown in figure (d).
A bridge is configured with magnetoresistive elements R6, and the power supply V is connected to the terminal ab of the bridge, and the 1fe2 terminal is input to the amplifier A1 via resistors R and R, respectively, and the input terminal of the amplifier is A feedback resistor R1 is connected between the output and the + side terminal is grounded via a resistor R4.

If the four magnetoresistive elements R0 receive the magnetic field of the opposing magnetic recording material 3 and change their resistance according to the strength of the magnetic field, and the magnetic flux distribution around the outer periphery of the magnetic recording material 3 changes sinusoidally. The output voltage of the bridge and therefore the output of the amplifier A1 also becomes a sine wave voltage, and an output voltage proportional to the sine of the rotation angle of the rotating body is obtained.

The above configuration is the same for both the A sensor and the B sensor, and the waveform of the output voltage is as shown in figure (c).If the output voltage of the A sensor is sinθ, the output voltage of the B sensor is CO5θ.
A sine wave encoder measures this output voltage and detects the position and rotational direction of a rotating shaft equipped with a magnetic drum, such as a servo motor, thereby constructing a highly accurate servo system.

[Problems to be solved by the invention] However, the magnetic encoder has a property that the output voltage of the magnetic sensor that is the detector changes depending on the temperature, and when the temperature changes, an error occurs in the detected position value. .

(2) Structure of the invention [Means for solving the problem] Focusing on the fact that the output voltage of a magnetic sensor is proportional to sin and aos, the output voltage of the A sensor and the output voltage of the B sensor are respectively multiplied by 2. By multiplying and calculating the sum, a voltage coefficient that is unrelated to the rotation angle and related only to temperature is obtained. This voltage is passed through a calculator to find its square root, and the output voltage of this calculator is used as a reference using a comparator. The configuration is such that the currents of the magnetic sensors A and H are controlled by the output voltage of the comparator in comparison with the voltage.

[Operation] Creates the sum of the squares of the output voltage of sensor A and the output voltage of sensor B via a multiplier and an adder, respectively.

If you calculate the square root of this value using a calculator, you can obtain the coefficient voltage related to the temperature of the magnetic sensor.

This coefficient voltage is compared with a reference voltage by a comparator, and the output voltage of the comparator is used to flow a current to the magnetic sensor.As a result, the output voltage of sensors A and B is controlled to have a constant amplitude regardless of temperature. There is.

[Embodiment of the Invention] FIG. 1 is a circuit diagram showing an embodiment of the present invention, in which 4-A is an A sensor, 4-B is a B sensor, 11 and 12 are operational amplifiers for both the A and B sensors, 13. 14 is A, the output terminal of both 8 sensors, 23.24 is a multiplier, 25.26 is an adder,
27 is a square root calculator, 28 is a comparator, 29 is a Zener diode, 30 is a current control device, and R is a resistor for properly operating each circuit section.

The output voltages of the A sensor 4-A and the B sensor 4-B are output via operational amplifiers 11 and 12, respectively, and Ea=Ktsinθ
, Eb=Ktcosθ, (Kt is a constant at temperature t) are output from the respective output terminals 13 and 14, and input to the multipliers 23 and 24, where they are squared and E
a”, E b” are output, and adder 25.26 outputs Ea
"+Eb" is created.

That is, E a" + E b" = Kt2 (sin "θ
+CO52θ), where sin”θ+cos”θ
= 1, so Ea"+Eb"=Kt", which has nothing to do with the rotation angle θ, and only the constant Kt related to temperature. When the output of the adder 26 is input to the square root calculator 27, the output terminal receives Kt. can get.

The output voltage of the square root calculator 27 and the reference voltage obtained by the Zener diode 29 are compared by the comparator 28, and the output of the comparator 28 controls the current control device 30 to control the magnetic sensors 4-A and 4-B. It has a configuration that controls the current.

To explain the operation of this circuit in detail, when the temperature is now t1, the output voltages of the sensors 4-A and 4-B are Ea, respectively.

When the temperature rises, the resistance temperature coefficient of the magnetic sensor is positive, so when the resistance increases and the output voltage decreases, the output of the operational amplifier 11.12 decreases, and the adder 25.26
The output of the square root calculator 27 also decreases, and the output voltage of the square root calculator 27 decreases.
Therefore, the output of the comparator 28 increases, the input of the current control device 30 increases, the currents of the magnetic sensors 4-A and 4-B increase, and the respective output voltages increase, so that the input voltage of the comparator 28 increases. It operates to control so that it is always balanced with the reference voltage, and as a result, the output voltage of the magnetic sensors 4-A and 4-B appearing at the terminals 13 and 14 has a constant amplitude regardless of the temperature. .

Further, when the temperature decreases, the output voltage is controlled to have a constant amplitude by suppressing the increase in the output voltage, contrary to the above.

[Effects of the Invention] Since the temperature compensation circuit of the magnetic encoder according to the present invention has the above-described configuration, an output voltage with a constant amplitude can always be obtained even when the temperature changes, and it can be used in a position detection device for a servo motor. A highly accurate magnetic encoder can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a temperature compensation circuit of a magnetic encoder according to the present invention, and Fig. 2 is a conceptual diagram of a conventional magnetic encoder, including a structural diagram (a), a developed diagram (b), and an output voltage. They are a waveform diagram (c) and an equivalent electric circuit diagram (d). Explanation of symbols 1...Rotating shaft, 2...Magnetic drum, 3...Magnetic recording. 4... Magnetic sensor, 4-A... A sensor, 4-B.
...B sensor, 11, 12... operational amplifier, 13
．． 14...Output terminal. 23.24... Multiplier, 25.26... Adder, 27... Square root operator, 28... Comparator, 2
9...Zener diode 30...Current control device,
A-1... operational amplifier. Ro...Magnetoresistive element, R, R1-R4...Resistance patent applicant Nippon Servo Co., Ltd.

Claims (1)

[Claims] A magnetic encoder having a magnetic drum in which N and S pole magnetic records are provided at equal intervals on a magnetic recording medium fixed to the outer periphery of a rotating body, and a magnetic sensor disposed opposite to the magnetic drum with an air gap interposed therebetween. In the magnetic sensor outputting an output voltage proportional to the sine and a cosine of the rotation angle of the magnetic drum, the sine wave output voltage is
a multiplier for squaring the cosine wave output voltage; an adder for adding the respective output voltages of the sine wave voltage multiplier and the cosine wave voltage multiplier; A temperature compensation circuit for a magnetic encoder, comprising: an arithmetic unit that obtains a square root; the output voltage of the arithmetic unit and a reference voltage are compared by a comparator; and the current of the magnetic sensor is controlled by the output voltage of the comparator. .