JP2002257586A - Magnetic detecting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow electric potential of a midpoint of a magnetic resistance element to fluctuate by a temperature rise, and to allow a pulse duty of an output signal waveform of a comparing means to fluctuate by a temperature since a temperature characteristic of a resistance value of the magnetic resistance element and a temperature characteristic of a resistance value of a variable resistance are not the same. SOLUTION: This magnetic detecting circuit is provided with the variable resistance 3 for an adjustment, first and second fixed resistances 2a and 2b, a third fixed resistance 4 having a resistance value of half of a maximum value of the variable resistance, a comparing means 5 for comparing electric potential of a connecting point of the first and second fixed resistances 2a and 2b with electric potential of a connecting point of two resistance wires of the magnetic resistance element 1, and a fourth fixed resistance 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an encoder and, more particularly, to a magnetic detection circuit of the encoder.

[0002]

2. Description of the Related Art Conventionally, a magnetic detection circuit of an encoder is shown in FIG.
It is like. In FIG. 5, 1 is a magnetoresistive element,
Reference numerals 2a and 2b denote two fixed resistors which are set to be equal to the resistance ratio of the resistance lines inside the magnetoresistive element, and 3 denotes an intermediate point of the magnetoresistive element (the connection point of the two resistance lines of the magnetoresistive element. E) a variable resistor for adjusting the offset of the potential of e; 4 is a fixed resistor having a resistance value that is half of the maximum value of the variable resistor 3; This is a comparing means for comparing the potential of the intermediate point e. The operation of this circuit will be described. For example, a change in the resistance value of the magnetoresistive element due to the magnetic field of the magnet disk alternately magnetized to the north and south poles is converted into a sinusoidal potential corresponding to the rotation of the magnet disk. The variable resistor 3 is adjusted so that it swings at equal amplitudes above and below the potential appearing at the connection point d of the fixed resistor. By inputting the potential of the connection point d of the fixed resistor to the non-inverting input terminal of the comparing means, and inputting the potential of the intermediate point e of the magnetoresistive element to the inverting input terminal of the comparing means,
A signal waveform corresponding to the rotation of the magnet disk is output from the output end f of the comparing means.

[0003]

However, in the prior art, since the temperature characteristics of the resistance value of the magnetoresistive element and the temperature characteristics of the resistance value of the variable resistor are not the same, the potential of the midpoint e of the magnetoresistive element at room temperature is reduced. Even if the amplitude is adjusted so as to swing with equal amplitude above and below the potential of the connection point d of the fixed resistor, the potential at the intermediate point e of the magnetoresistive element fluctuates due to the temperature rise, and the pulse duty of the signal waveform of the output signal of the comparison means becomes lower. There was a problem that fluctuates. Therefore, an object of the present invention is to provide a magnetic detection circuit that obtains a signal waveform whose pulse duty does not fluctuate with temperature.

[0004]

In order to solve the above-mentioned problem, the present invention relates to a magnetic detection circuit of an encoder, comprising: a magnetoresistive element comprising a series connection of two resistance wires whose resistance value changes according to the direction of a magnetic field. 1 is defined as one side, a variable resistor 3 for adjustment, and one terminal connected to the variable resistor 3 are connected in series with the resistance ratio of two resistance lines of the magnetoresistive element 1 being equal to each other. 1, a second fixed resistor (2a, 2b) and a third fixed resistor 4 connected to the other terminal of the series connection of the fixed resistors and having a resistance half the maximum value of the variable resistor. A bridge circuit having another side connected in series with the first and second fixed resistors (2a, 2a,
b) comparing means 5 for comparing the potential at the connection point with the potential at the connection point between the two resistance lines of the magnetoresistive element 1; one end connected to the output terminal of the comparison means 5; 1,
It is characterized in that it comprises a fourth fixed resistor 6 connected to a connection point between the series connection of the second fixed resistors and the third fixed resistor 4.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings. FIG. 1 is an electric circuit of a magnetic detection circuit of an encoder according to 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 wire 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 half of the maximum value of the variable resistor 3, and a power supply voltage Vc is applied to a power supply terminal at a 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. An intermediate point e of the magnetoresistive element 1 is connected to a non-inverting input terminal of a comparing means 5 formed by a comparator, and the fixed resistances 2a, 2a
The connection point d of b is connected to the inverting input terminal of the comparing means 5.
The output end f of the comparing means is connected through a fixed resistor 6 to a connection point g between the fixed resistors 2b and 4. The fixed resistor 6 applies hysteresis to the input waveform to improve noise resistance. The temperature characteristics of the fixed resistor and the 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, reference numeral 7 denotes a magnet disk magnetized to NS, and this magnet disk 7 is fixed to the shaft end of a rotary shaft 8 of a servomotor.
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 magnet disk. When the rotating shaft 8 rotates, a change in the resistance of the magnetoresistive element 1 occurs due to a change in the magnetic field, and a sinusoidal potential Ve corresponding to the rotation of the servomotor appears at the intermediate point e. The potential Vd that appears at the connection point d at normal temperature is V
The variable resistor 3 is adjusted so as to be equal to the center potential of the amplitude of e, and the low-level duty T1 and the high-level duty T2 of the signal waveform Vf at the output terminal f of the comparing means 5 are T1: T2 = 1: Set to 1. The potentials Vd and Ve appearing at the connection point d and the intermediate point e, and the output terminal f of the comparison means 5
FIG. 4 shows the relationship of the signal waveform Vf appearing in FIG. Even if the ambient temperature rises to a high temperature from this adjustment state and the total resistance value of the magnetoresistive element 1 changes, the resistance ratio of the resistance wire inside the magnetoresistive element is kept equal to that at normal temperature and appears at the intermediate point e. The central potential of the potential amplitude does not change with temperature. Further, the other side of the bridge circuit has a circuit configuration including a fixed resistor and a variable resistor having the same temperature characteristic.
Does not change with temperature. Therefore, the duty T1 and T2 of the output waveform Vf at the time of high temperature are T
1: T2 = 1: 1, it is possible to obtain a signal waveform whose pulse duty does not vary with temperature.

[0006]

As described above, according to the present invention, there is an effect that a magnetic detection circuit for obtaining 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.

FIG. 3 is a front view showing a magnetized state of a magnet disk.

FIG. 4 is a waveform chart for explaining the operation of the embodiment of the present invention.

FIG. 5 is a circuit diagram showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic resistance element 2a, 2b, 4, 6 Fixed resistance 3 Variable resistance 5 Comparison means 7 Magnet disk 8 Rotation axis

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (Reference) G01R 33/02 G01R 33/06 R F term (Reference) 2F063 AA35 CB01 DA01 DD02 EA03 GA52 GA67 GA71 LA23 LA27 2F077 AA13 TT06 TT09 TT13 UU09 UU13 2G017 AA01 AB05 AC04 AD55 BA05

Claims (1)

[The claims] In a magnetic detection circuit of an encoder, a side of a magnetoresistive element 1 constituted by a series connection of two resistance lines whose resistance value changes according to the direction of a magnetic field is provided, and a variable resistor 3 for adjustment is provided. One terminal is connected to the variable resistor 3, and the first and second fixed resistors (2a, 2b) connected in series having the same resistance ratio as the resistance ratio of the two resistance lines of the magnetoresistive element 1; A bridge circuit that is connected to the other terminal of the series connection of fixed resistors and has another side connected in series with a third fixed resistor 4 having a resistance value that is half the maximum value of the variable resistor; , A second fixed resistor (2a, 2
b) comparing means 5 for comparing the potential at the connection point with the potential at the connection point between the two resistance lines of the magnetoresistive element 1; one end connected to the output terminal of the comparison means 5; 1,
A magnetic detection circuit comprising: a fourth fixed resistor 6 connected to a connection point between a second fixed resistor connected in series and the third fixed resistor 4.