JP3638125B2 - Magnetic detection circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an encoder, and more particularly to a magnetic detection circuit for an encoder.
[0002]
[Prior art]
Conventionally, the magnetic detection circuit of an encoder is as shown in FIG. In FIG. 5, 1 is a magnetoresistive element, 2a and 2b are two fixed resistors set to be equal to the resistance ratio of the resistance wire inside the magnetoresistive element, and 3 is an intermediate point of the magnetoresistive element (two resistances of the magnetoresistive element). A variable resistor for adjusting the offset of the potential of e, 4 is a fixed resistor having a resistance value that is half the maximum value of the variable resistor 3, and 5 is a connection point d of two fixed resistors. This is a comparison means for comparing the potential at the intermediate point e of the magnetoresistive element with reference to the potential.
The operation of this circuit will be described. For example, the change in the resistance value of the magnetoresistive element due to the magnetic field of the magnet disk magnetized alternately in the N and S poles is converted into a sinusoidal potential corresponding to the rotation of the magnet disk. The variable resistor 3 is adjusted so as to swing with equal amplitude above and below the potential appearing at the connection point d of the fixed resistor. The potential at the connection point d of the fixed resistor is input to the non-inverting input terminal of the comparison means, and the potential at the intermediate point e of the magnetoresistive element is input to the inverting input terminal of the comparison means so that the output from the output terminal f of the comparison means. A signal waveform corresponding to the rotation of the magnetic disk is output.
[0003]
[Problems to be solved by the invention]
However, in the conventional technique, the temperature characteristic of the resistance value of the magnetoresistive element and the temperature characteristic of the resistance value of the variable resistor are not the same, so that the potential of the intermediate point e of the magnetoresistive element is equal to the potential of the connection point d of the fixed resistor at room temperature. Even if it is adjusted so as to swing up and down with equal amplitude, there has been a problem that the potential at the intermediate point e of the magnetoresistive element fluctuates due to temperature rise, and the pulse duty of the signal waveform of the output of the comparing means varies with temperature.
Therefore, an object of the present invention is to provide a magnetic detection circuit that obtains a signal waveform whose pulse duty does not vary with temperature.
[0004]
[Means for Solving the Problems]
In order to solve the above problem, in the magnetic detection circuit of the encoder, the present invention has a magnetoresistive element 1 formed of a series connection of two resistance wires whose resistance value varies depending on the direction of the magnetic field as one side, and is used for adjustment. A variable resistor 3 and one terminal connected to the variable resistor 3, and a first and second fixed resistor (2a) connected in series in which the resistance ratio of the two resistance wires of the magnetoresistive element 1 is equal to the resistance ratio. 2b), and a bridge connected to the other terminal of the fixed resistor series connection body and having a series connection body of the third fixed resistor 4 having a resistance value half the maximum value of the variable resistance as the other side Comparing means 5 for comparing the potential of the connection point of the circuit with the first and second fixed resistors (2a, 2b) and the potential of the connecting point of the two resistance lines of the magnetoresistive element 1, and the comparing means One end is connected to the output terminal 5 and the other end is connected to the first terminal. Characterized by comprising a fourth fixed resistor 6 connected to the connection point of the second of the and the fixed resistance of the series connection of the third fixed resistor 4.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be specifically described with reference to the drawings. FIG. 1 is an electric circuit of a magnetic detection circuit of an encoder showing an embodiment of the present invention. In FIG. 1, the offset of the potential appearing at the series connection point d of the magnetoresistive element 1, the two fixed resistors 2a and 2b set equal to the resistance ratio of the resistance line inside the magnetoresistive element, and the fixed resistors 2a and 2b is adjusted. A bridge circuit is formed by the variable resistor 3 and the fixed resistor 4 having a resistance value half of the maximum value of the variable resistor 3, and the power supply voltage Vc is applied to the power supply terminal at the connection point between the magnetoresistive element 1 and the variable resistor 3. The ground terminal at the connection point between the magnetoresistive element 1 and the fixed resistor 4 is connected to the ground level. The intermediate point e of the magnetoresistive element 1 is connected to the non-inverting input terminal of the comparison means 5 formed by a comparator, and the connection point d of the fixed resistors 2 a and 2 b is connected to the inverting input terminal of the comparison means 5. The output terminal f of the comparison means is connected to a connection point g between the fixed resistor 2 b and the fixed resistor 4 through the fixed resistor 6. The fixed resistor 6 applies hysteresis to the input waveform to improve noise resistance. The temperature characteristics of the fixed resistor and variable resistor are the same.
FIG. 2 is a structural diagram illustrating an example of the magnetic detection unit of the encoder. In the figure, 7 is a magnet disk magnetized in NS, and this magnet disk 7 is fixed to the shaft end of the rotating shaft 8 of the servo motor. Reference numeral 1 denotes a magnetoresistive element arranged to face the magnet disk 7. FIG. 3 is a front view showing a magnetized state of the magnetic disk. When the rotary shaft 8 rotates, the resistance value of the magnetoresistive element 1 changes due to the change of the magnetic field, and a sinusoidal potential Ve corresponding to the rotation of the servo motor appears at the intermediate point e. The variable resistor 3 is adjusted so that the potential Vd appearing at the connection point d at the normal temperature is equal to the center potential of the amplitude of Ve, and the low-level duty T1 of the signal waveform Vf at the output terminal f of the comparison means 5 is high. The level duty T2 is set to be T1: T2 = 1: 1. FIG. 4 shows the relationship between the potentials Vd and Ve appearing at the connection point d and the intermediate point e and the signal waveform Vf appearing at the output terminal f of the comparison means 5.
Even if the ambient temperature rises from this adjusted state to a high temperature and the total resistance value of the magnetoresistive element 1 changes, the resistance ratio of the resistance lines inside the magnetoresistive element is kept equal to that at room temperature and appears at the intermediate point e. The central potential of the amplitude of the potential does not change with temperature.
Further, since the other side of the bridge circuit is a circuit configuration with fixed resistors and variable resistors having the same temperature characteristics, the potential Vd appearing at the connection point d does not change with temperature even if the respective resistance values change. Therefore, the duty T1, T2 of the output waveform Vf at high temperature is set to T1: T2 = 1: 1, and a signal waveform whose pulse duty does not vary with temperature can be obtained.
[0006]
【The invention's effect】
As described above, according to the present invention, there is an effect that a magnetic detection circuit that obtains a signal waveform whose pulse duty does not vary with temperature is realized.
[Brief description of the drawings]
FIG. 1 is an electric circuit of a magnetic detection circuit of an encoder according to an embodiment of the present invention. FIG. 2 is a structural diagram showing an example of a magnetic detection unit of the encoder. 4 is a waveform diagram for explaining the operation of the embodiment of the present invention. FIG. 5 is a circuit diagram showing a conventional embodiment.
DESCRIPTION OF SYMBOLS 1 Magnetoresistive element 2a, 2b, 4, 6 Fixed resistance 3 Variable resistance 5 Comparison means 7 Magnet disk 8 Rotating shaft

Claims (1)

In the magnetic detection circuit of the encoder, a magnetoresistive element 1 composed of two resistance wires whose resistance value varies depending on the direction of the magnetic field is connected as one side, and a variable resistor 3 for adjustment and one of the variable resistors 3 The first and second fixed resistors (2a, 2b) connected in series with the resistance ratio of the two resistance lines of the magnetoresistive element 1 being equal to each other and the series connection of the fixed resistors A bridge circuit connected to the other terminal of the body and connected in series with a third fixed resistor 4 having a resistance value that is half the maximum value of the variable resistor, and the first and second fixed circuits Comparing means 5 for comparing the potential at the connection point of the resistors (2a, 2b) with the potential at the connecting point of the two resistance lines of the magnetoresistive element 1, one end connected to the output terminal of the comparing means 5, and the other Ends of the first and second fixed resistors connected in series and the first Magnetic detection circuit 4 which is connected to the connection point between the fixed resistor 4 of the fixed resistor 6, comprising the.

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