JPH02154128A - Strain detector - Google Patents

Abstract

PURPOSE:To vary the driving parameter of a detection coil with the large degree of freedom, and to improve characteristics and disturbance-resisting magnetic field performance by exciting a test coil and detecting the magnetic permeability of a magnetic layer by using independent circuits. CONSTITUTION:When stress is applied to a driven shaft 1, magnetic layers 2a and 2b are strained and vary in magnetic permeability in mutually opposite directions. An AC driving circuit 7 outputs an AC voltage and an AC current to both ends of detection coils 3a and 3b. The detection coils 3a and 3b detect the magnetic permeability variation rates of the magnetic layers 2a and 2b as variation in self-impedance and the outputs across the detection coils 3a and 3b are based upon an intermediate potential as a reference potential and amplified differentially by differential amplifier circuits 5a and 5b. The outputs of the differential amplifier circuits 5a and 5b are added by an adder 6 and phase-detected 8 with the phase detection signal from an AC driving circuit 7 to remove a noise component, etc. Then the signal which becomes a pulsating current as the result of the phase detection is smoothed and amplified by an AC/DC converting circuit 9 and outputted as a strain detection signal from an output terminal 15.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention detects changes in the magnetic permeability of two detection magnetic layers whose permeability changes in opposite directions due to strain, and detects the amount of strain from the changes. This invention relates to a distortion detection device.

[Prior art] As a conventional device of this type, for example, Japanese Patent Application Laid-Open No. 5918896
There is one shown in No. 8, which is shown in Figure 2. In the figure, 1 is a passive shaft to which stress is applied, 2a and 2b are magnetic layers formed on the passive shaft 1, and the magnetic layer 2a is +45"
The magnetic layer 2b has a magnetic anisotropy of -45°. 3a and 3b are detection coils independently wound around the magnetic layers 2a and 2b at intervals, 1o is an excitation coil commonly wound around the magnetic layers 2a and 2b, and 11 is connected to the excitation coil 1o. 12a and 12b are smoothing circuits that smooth the outputs of the detection coils 3a and 3b, 13 is a differential amplifier circuit that differentially amplifies the outputs of the smoothing circuits 12a and 12b, and 14 is an output terminal.

In the above configuration, the excitation coil 10 driven by the electric 6fX7 generates magnetic flux, and this 6fi east has the magnetic layer 2a,
2b. The passive axis l is strained in response to applied stress, and the magnetic permeability of the magnetic layers 2a and 2b changes in opposite directions in response to this strain. Therefore, excitation [41 coil 10 and detection coil 3
The phase 11-inductance between a and 3b changes, and this change is smoothed by the smoothing circuit 12a.

12b, taken out via the differential amplifier circuit 13 and output terminal 14.

Further, FIG. 3 shows a conventional device disclosed in the 1Y 1985-166828 publication, in which 16 is a magnetostrictive detection circuit consisting of a multi-by-break circuit including detection coils 3a and 3b and a capacitor 17, and the multi-by-break circuit is In addition to the detection coils 3a and 3b, capacitors 1B and 1.9, and resistor 2
0 to 23, a variable resistor 24, and transistors 25 and 26. 27a.

27b is an output terminal. The detection coils 3a and 3b are connected to an excitation power source and also serve as a detection magnetic field drive.

The detection coils 15a, 15b detect changes in magnetic permeability due to strain in the magnetic layers 2a, 2b as changes in self-inductance, and the strain detection circuit 16 detects this inductance change as a change in duty ratio or frequency of the oscillation waveform. , is the distortion amount output.

[Problem to be solved by the invention]

However, the conventional device shown in FIG. 2 requires two coils: detection coils 2a and 2b and excitation coil 10.
The coil manufacturing process took time, and the wiring work also took time.

On the other hand, in the conventional device shown in Fig. It was difficult. Also, in principle, B-1 of the magnetic layers 2a and 2b
Since only the first quadrant on one curve can be used, B −I+
It operates on the minor loop of the curve, and the disturbance magnetic field causes the operating point to move to the node jl'1, resulting in a problem of low sensitivity and vulnerability to the disturbance magnetic field. This point will be explained in more detail in Part 4. FIG. 4(a) shows the main configuration of the multi-by-break circuit, which includes a detection coil 3a.

3b has one end connected to the power supply VCC, and the other end grounded via transistors 25 and 26 and resistors 22 and 23, and transistors 25 and 26 are used as switching elements. Therefore, the collector current I C1+ I r:z of the I transistor 2526 is as shown in FIG. 4 (I)
As shown in Figure 4(C), it flows only in one direction, and IcICff1 also flows in the detection coils 3a and 3b, so in the B-11 curve of magnetic i2a and 2b shown in Figure 4(C), the thick line part A of the minor loop is the operating range. .

I+, is the operating magnetic field region. Here, the disturbance magnetic field II 4
>0 is applied to the magnetic layers 2a and 2b, as shown in FIG.
), it operates in the range of H (thick line) with a deviation of H in the direction from the origin (bold line), and when Ha<O is applied, the range of H as shown in Fig. 4 (el) operates. It operates in the minor loop of Owata c).As the operating point moves greatly due to the disturbance magnetic field, the permeability 451 ratio also moves greatly, resulting in a decrease in sensitivity.

This invention was made to solve the above-mentioned problems, and it is possible to change the drive parameters of the detection coil with a large degree of freedom, improve the characteristics, and create a strain-resistant coil with high resistance to disturbance magnetic fields. The purpose is to detect the device (:).

(Means for Solving the Problems) A strain detection device according to the present invention includes an AC drive circuit that applies an AC voltage to both ends of a detection coil, and a pair of The power to add the output of the differential amplifier circuit and the output of each differential amplifier circuit is γ
It is equipped with a circuit.

In addition to the configuration described in (-), there is a distortion detection device according to another aspect of the invention, in which the drive frequency of the AC drive circuit is within the range of 7.5 to 25 Kllz.

[For production]

In this invention, the circuit for driving the excitation Gel of the detection coil is provided separately from the circuit for detecting changes in magnetic permeability, and excitation driving and magnetic permeability detection are performed in completely separate operations.

Further, in another invention, the driving frequency of the detection coil is limited to a predetermined range, and the offset caused by the disturbance magnetic field is reduced.

〔Example〕

Hereinafter, the first embodiment of the present invention will be explained with reference to the drawings.
The figure shows the configuration of the strain detection device according to this embodiment, 3a,
3b is a detection coil wound independently around the magnetic layers 2a and 2b, and 4 is a detection coil 3 connected in series.
a, 3b intermediate potential output terminal; 7 is the detection coil 3a;
an AC drive circuit that applies an AC voltage to both ends of 3b; 5a;
5b is a differential amplifier circuit that detects the potential difference between the voltages at both ends of the detection coils 3a and 3b using the voltage at the intermediate potential output terminal 4 as a reference; 6 is an adder circuit that adds the outputs of the differential amplifier circuits 5a and 5b; 8 9 is a phase detection circuit that detects the phase of the output of the adder circuit 6 based on the phase detection signal from the AC drive circuit 7;
is an AC that smoothes and amplifies the pulsating current signal output from the phase detection circuit 8.
-DC conversion circuit, 15 is an output terminal.

The fifth part shows the specific configuration of the AC drive circuit 7, Q, -Q
, is a transistor,■. , V, , V is the detection coil 3a
, 3b and the voltages SI to S4 are timing signals for the operation of the transistors Q1 to Q4, and the timing signals 51 to S4 are created by a not shown creation circuit. FIG. 6 shows a timing chart of the operation, and shows the SI
, Sz is L-i? If S3゜S4 is 11, then Q,,Q
, is on and Q,,Q.

is turned off, and V+-Vcc, Vz=0. Therefore, current in the positive direction flows through the detection coils 3a and 3b.

Conversely, if s,,s, is H and Sz, and S- is L, Vz
=Vcc, ■1=0, and the detection coil 3a.

A negative current flows through 3b.

FIG. 7 shows specific configurations of the differential amplifier circuits 5a, 5b and the adder circuit 6, both of which are formed of operational amplifiers and resistors. 28 is an output terminal.

FIG. 8 shows the configuration of the phase detection circuit 8, where Q is a transistor, 30 is an input terminal to which the output of the adder circuit 6 is input,
31 is an output terminal, and 32 is a resistor. FIG. 9 shows a timing chart of the operation. (a) shows the waveform of the phase detection signal, the phase detection signal is input from the AC drive circuit 7 to the base of the transistor Q, and this phase detection signal is at a certain level with the AC drive signal output from the AC drive circuit 7. There is a phase difference. [Yes]) indicates the output waveform of the adder circuit 6,
(C) shows the on/off operation of transistor Q, and (d
) shows the output waveform from the output terminal 31. The transistor Q is on while the phase detection signal is H, and the adder circuit 6
The output is not output from the output terminal 31.

However, when the phase detection signal becomes 1, transistor Q5
is turned off, and the output of the adder circuit 6 is output as is from the output terminal 31. Therefore, the noise component in the output of the adder circuit 6 is removed by the phase detection circuit 8.

Next, the operation of the above configuration will be explained. When stress such as torque is applied to the passive shaft 1, the magnetic layer 2a.

2b is strained, and its magnetic permeability changes in mutually opposite directions. On the other hand, the AC drive circuit 7 outputs an AC voltage and an AC current as shown in FIG.
applied to both ends of. The detection coils 3a, 3b detect the change in magnetic permeability of the magnetic layers 2a, 2b described above as a change in self-impedance, and the output between the respective ends of the detection coils 3a, 3b is output from the differential amplifier circuit 5a using the intermediate potential as a reference potential. ,
5b and differentially amplified. Differential amplifier circuit 5a.

The outputs of 5b are added by an adder 6, and then sent to a phase detection circuit 8.
, the phase is detected by the phase detection signal from the AC drive circuit 7, and noise components and the like are removed. The pulsating signal resulting from this phase detection is smoothed and amplified by the AC-DC conversion circuit 9, and outputted from the output terminal 15 as a distortion detection signal.

In the above embodiment, an AC drive circuit 7 for excitation driving the detection coils 3a, 3b is provided, and since this excitation drive and magnetic permeability detection of the magnetic layers 2a, 2b are performed on separate paths, the frequency and current It is easier to adjust parameters such as values,
It has also become easier to improve temperature characteristics and drift characteristics. Further, the drive current by the AC drive circuit 7 can be made to flow in both directions with a large amplitude, and as shown in FIG. 10(a), the operating magnetic field area H.

can be operated on the major loop of the B-H curve, and as shown in Figure 10(b), the disturbance magnetic field H
Even if 4 is applied, the influence of the operating point shift is reduced, and the detection error of magnetic permeability is also reduced.

Figure 11 shows the detection coil 3a with the disturbance magnetic field as a parameter.
, 3b and the offset fluctuation of the output of this embodiment device. The arrows indicate the strength of the disturbance magnetic field. Second, in the case of the conventional device shown in FIG. 3, the offset fluctuation was about 10 to 100%, but in this embodiment, it can be suppressed to approximately within several percent, especially in the frequency range of 7.5 to 25KIIz.

FIG. 12 shows the differential amplifier circuit 5a shown in FIG.

5b and the adder circuit 6 will be shown. In this example, the circuit is constituted by an operational amplifier ○P and resistors R1 to R3, so that it can have a simple configuration.

However, R, -R, = R, Rs''2R.

In the above embodiment, the detection coils 3a and 3b are made of magnetic Ji.
! Although 2a and 2b are individually wound, they may be wound in common.

〔Effect of the invention〕

As described above, according to the present invention, since the excitation drive of the detection coil and the magnetic permeability detection of the magnetic layer are performed through separate paths, it is easy to adjust parameters such as the drive frequency and drive current, and the operating characteristics are improved. be able to. Furthermore, the driving current can be passed in both the positive and negative directions with a large amplitude, and the operating magnetic field range can be expanded, thereby reducing the influence of disturbance magnetic fields.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the inventive device, Fig. 2 is a block diagram of a conventional device, Fig. 3 is a block diagram of another conventional device, and Fig. 4 is related to the other conventional device shown in Fig. 3. , (a) is the circuit diagram, (b) is the driving current diagram, (C1 is the operating range diagram of the B-H curve of the magnetic layer, ((jl is the operating range diagram when a positive disturbance magnetic field is also applied, ( e) is an operating range diagram when a negative disturbance magnetic field is applied, FIGS. 5 and 6 are circuit diagrams of the AC drive circuit according to the present invention and their operating waveform diagrams, and FIGS. 7 and 12 are diagrams of the AC drive circuit according to the present invention. FIGS. 8 and 9 are circuit diagrams of two embodiments of a differential amplification and addition circuit according to the present invention, and FIGS. It is a relationship diagram. 1... Passive axis, 2a, 2b... Magnetic layer, 3a, 3b
...Detection coil, 4...Intermediate potential output terminal, 5a5
b...Differential amplifier circuit, 6...Addition circuit, 7...AC drive circuit. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (2)

[Claims] (1) A passive shaft to which stress is applied; a pair of magnetic layers mounted on the passive shaft whose magnetic permeability changes in opposite directions due to strain; A wound detection coil, an AC drive circuit that applies an AC voltage to both ends of the detection coil, a pair of differential amplifier circuits that detect the potential difference between the intermediate potential of the detection coil and the potential at both ends, and each differential an addition circuit that adds the outputs of the amplifier circuit;
By the phase detection signal generated by the above AC drive circuit,
A distortion detection device comprising a phase detection circuit that detects the phase of the output from the addition circuit. (2) The frequency of the AC voltage applied to the AC drive circuit is 7.
．． 2. The strain detection device according to claim 1, wherein the distortion detection frequency is within a range of 5 to 25 KHz.