JPS5868615A - Output circuit of magnetic type rotary encoder - Google Patents

Abstract

PURPOSE:To increase the output with regard to unit current, by using one constant current power source in the output circuit, thereby detecting the change in magnetic field efficiently. CONSTITUTION:A series circuit of magnetic resistance element S1 and S2 is connected to the constant current power source, and a current (i) always flows. When a rotary magnetic field is generated by the movement of a probe, the voltages generated across the element S1 and S2 are detected by differential amplifiers 2 and 3. The amplifier 2 outputs V1=i(R0-DELTAR), and the amplifier 3 outputs V2=i(R0-DELTAR). The outputs are made to be the output V=V2-V1= 2iDELTAR(2iDELTARsintheta) by the operation of a differential amplifier 4.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a measuring instrument for measuring length, etc., in which the distance of movement of a measuring point is detected. The present invention relates to an output circuit that uses a JIJ-z encoder and can electrically accurately detect, in particular, the amount of movement of a probe.

2. Description of the Related Art Rotary encoders are well known for converting the amount of movement of a probe into an electrical signal for measurement in length measuring instruments, and are widely used in, for example, micrometers and other measuring instruments. A rotary encoder has a slit disk in the part that directly or indirectly interlocks with the measuring tip, and detects the rotation angle of the slit disk corresponding to the amount of movement of the measuring tip.
11j The length of a constant object, etc., is displayed digitally, for example.

The present invention provides, instead of the rotating slit disk,
A magnetic rotary rotor is equipped with a magnet (magnet rotor), and a fixed part facing the magnet is equipped with a means for detecting the strength of the magnetic field, which detects the strength of the magnetic field corresponding to the amount of movement of the probe. Regarding encoders. As means for detecting the strength of the magnetic field, a magnetoresistive element whose resistance value changes depending on the strength of the four magnetic fields is generally used. In other words, when a constant current is passed through this element, the voltage between the elements changes depending on the magnetic field, and by detecting this, the amount of movement of the probe can be measured.

Generally, a magnetoresistive element is divided into a portion R6 that does not change and a portion ΔR that changes with respect to changes in the magnetic field. Therefore,
In the output circuit of a magnetic rotary encoder using a magnetoresistive element, it is necessary to output only the JR acid component as a signal component and completely eliminate the DC component due to the Ro component. It is also necessary to compensate for the drift of the DC component due to temperature changes in the resistor R6.

Conventionally, there are output circuits shown in FIGS. 1 and 2 that compensate for the DC component and drift of R8, which does not change. First, in FIG. 1, Sl is a magnetoresistive element, and Rx is a resistor having the same resistance value as the resistance RO, which does not change with respect to the magnetic field of the magnetoresistive element S. A sensing current i is applied to each of the resistor Rx and the magnetoresistive element S1 by a constant current source (not shown). As a result, the magnetoresistive element S1 has V, -1
(RO+ΔR), a voltage of Vz = i RO is generated in the resistor Rx. In other words, the voltage v2 generated across the resistor Rx is the DC voltage of the unchanging resistor R8 of the magnetoresistive element S1. Therefore, by subtracting the voltage += V2 generated across the resistor Rx from the voltage ■ generated across the magnetoresistive element S1, V2 is added to remove the DC component of Ro, and the differential amplifier 1 is the output V=V, -V2=iΔR(
iΔRs inθ) is output.

Therefore, according to the output circuit of FIG. 1, an output of only the voltage 1JR=V outside the variable resistance value of the magnetoresistive element SI can be obtained, making accurate measurement possible. In this output circuit of Fig. 1,
It is not possible to compensate for drift due to temperature changes.

In order to eliminate the drawbacks of the output circuit shown in FIG. 1, FIG. 2 shows a circuit in which drift due to temperature changes is compensated for. In the figure, Sl+S2 are aerobic resistance elements, which are connected so as to have a negative phase relationship with respect to the magnetic field. In other words, the resistance value of the magnetoresistive element S l + 82 is R72R6-ΔR,
They are arranged so that R2=Ro+ΔR. Therefore, as in FIG. 1, from the differential amplifier 1, V=2iΔR(2i
An output of ΔR51nθ) is obtained, which is 2
Double the output voltage can be obtained. Here, for temperature changes, two magnetoresistive elements S1. DC drift can be compensated for by selecting S2s with equal temperature coefficients.

However, due to the circuits of FIGS. 1 and 2, 6', [
, two constant current sources are required based on the sensing current i, and according to FIG. 2, the differential for the unit sensing current i is ΔR51nθ.

The present invention provides an output circuit for a magnetic rotary encoder that is capable of detecting changes in a magnetic field as changes in voltage with only one constant current source.

The present invention comprises two magnetoresistive elements, these elements are connected in series and arranged in an anti-phase relationship, and the voltage generated across each element is outputted through each differential amplifier, and then the output of the step width amplifier is outputted. Furthermore, an output is obtained through a second differential amplifier.

The output circuit of the magnetic rotary encoder of the present invention will be explained in detail below with reference to the drawings. FIG. 3 is a circuit diagram showing a specific example of the output circuit according to the present invention. In the figure, Sl, S
Reference numeral 2 denotes a magnetoresistive element whose ΔR can change depending on changes in the magnetic field, and has an antiphase relationship with respect to the magnetic field.The above magnetoresistive elements S, S2 are, for example, micrometers, etc., on the fixed part side. The resistance ΔR is changed by the magnetic field of a magnet rotor that generates a rotating magnetic field and is provided on the side of the movable measuring element.

In the optical diagram, 2 is the first stage differential amplifier for detecting the voltage generated across the magnetoresistive element S1, and 3 is the magnetoresistive element S.
This is a first-stage differential amplifier used to detect the voltage generated across the two ends of the circuit. The outputs V, V2 of the differential amplifiers 2 and 3 are applied to the respective input terminals of the second stage differential amplifier 4, and an output of V=V2-V is obtained from the output terminal. The series circuit of the magnetoresistive elements S, S2 is connected to a constant current source 5, and has a configuration in which a current 1 always flows.0 With the above configuration, if a rotating magnetic field is generated by the movement of the probe, Accordingly, the magnetoresistive element S1. S2 resistance outside J
R changes. Therefore, when the sensing current i flows, a voltage is generated across each magnetoresistive element S1+ 82. This voltage is detected by the first stage differential amplifier 2.3. The differential amplifier 2 outputs v, -1(RO-ΔR)-, and the other differential amplifier 3 outputs V2=i(R6+Δ
R) Full output. V output from each amplifier 2.3,
V2 is differentially amplified in the next differential amplifier 4, and its output ■ is V2-V, = i (RO + ΔR) t (Ro-Δ
R)=2iΔR(2iΔR51n. That is, 2
The differential amplifier 4 in the second stage is constructed by removing the DC component due to the resistor R8 from among the voltages generated across the magnetoresistive elements Sl and S2. According to the circuit system shown in Fig. 3, there is one constant current source, and the output for a unit current is 2ΔR51nθ.

The output circuit of the present invention is shown in the table below to make it easier to understand the magnitude of the output compared to the output circuits shown in FIGS. 1 and 2.

As shown in the table above, according to the present invention, the output per yearly sensing current is four times that of FIG. 1 and twice that of FIG. 2.

Furthermore, with respect to temperature changes, direct current draft can be compensated for by selecting magnetoresistive elements S, . . . S2 that have equal temperature coefficients.

As explained above, according to the magnetic rotary encoder output circuit of the present invention, changes in the magnetic field can be detected efficiently by using only one constant current source, and the output per unit current is lower than that of the conventional one. It becomes larger compared to other things. Moreover, since the magnetoresistive elements St, 82, etc. are connected in series, even if the number of the magnetoresistive elements increases, the sensing current will not increase.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams showing the output circuit of a conventional magnetic rotary encoder, and FIG. 3 is a circuit diagram showing a specific example of the output circuit of the magnetic rotary encoder according to the present invention. 2.3 D First stage differential amplifier 4: Second stage differential amplifier 5: Constant current source i: Sensing current Sl, 82: Magnetoresistive element R6: Resistance component that does not change ΔR: Resistance component proxy that changes due to magnetic field Person Patent Attorney Aihiko Fukushi Figure 1 2

Claims (1)

[Claims] 1. Two magnetoresistive elements arranged so that the rotating magnetic field given by the magnet rotor has an opposite phase relationship and electrically connected in series, and a constant current that flows a detection current through the series-connected magnetoresistive elements. a first-stage differential amplifier for detecting the voltage generated across the magnetoresistive element; and a second-stage differential amplifier for outputting a detection signal corresponding to only the resistance change due to the magnetic field from the output of the differential amplifier. A magnetic rotary encoder output circuit comprising a differential amplifier and a differential amplifier.