JPH06294690A - Temperature/nonlinearity compensation for magnetostrictive sensor - Google Patents

Abstract

PURPOSE:To enhance compensation for the temperature drift and nonlinearity in the output of a magnetostrictive sensor. CONSTITUTION:An exciting voltage is fed, in the form of an electromagnetic field, from an oscillator 101 through a power amplifier 102 and exciting coils 203, 204 to a magnetostrictive detecting means carried on a sensor shaft. A distortion signal is taken out in proportion to the magnitude of external force and amplified differentially and fluctuation of the exciting voltage due to temperature is detected. Temperature variation and a correction value for corresponding distortion are then extracted from a prestored table ROM 112 and the correction value is added to the differentially amplified distortion signal thus producing a distortion output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing method for temperature compensation of a magnetostrictive sensor and its nonlinear compensation.

[0002]

2. Description of the Related Art First, a structure of a strain detecting portion of a strain sensor of this type is shown in FIG. 201 is a sensor shaft to which an external force is applied. 202 is a thin film magnetic material attached to the outer peripheral surface of the sensor shaft 201.
An external force is applied to this thin film when added to 1, and the magnetic permeability changes according to the strain caused by this external force.
Is an exciting coil which is wound so as to cover a part of the outer peripheral surface of the sensor shaft 201 with a gap therebetween to form a coil, and an exciting current flowing in this coil generates an electromagnetic field for measurement. 205 and 206 are exciting coils. A detection coil that detects the signal voltage that occurs in proportion to the change in the magnetic permeability of the magnetostrictive film 202 that changes in proportion to the strain received from the external force of the electromagnetic field magnetic flux generated in the coils 203 and 204. 207 is a film with the magnetostrictive film 202 On the side, 208 is a filmless side without the magnetostrictive film 202. In the drawings, the same reference numerals represent the same or corresponding parts.

FIG. 6 is a block diagram showing a circuit configuration of a signal processing circuit included in the strain sensor as the first conventional example.
101 is an oscillator that generates an AC voltage of a constant frequency, 102 is the excitation coil of the destination that power-amplifies the voltage signal from the oscillator 101.
A power amplifier for supplying an exciting current to 203, 204. These oscillator 101, power amplifier 102, exciting coil 203, 20
The excitation circuit is composed of 4. 103 and 104 are detection coils 205,
A first-stage amplifier (Pri-Amplifer) that improves the S / N of the voltage signal detected by 206 to amplify the voltage, 105 and 106 are full-wave rectifier circuits that convert AC voltage to DC voltage, and 107 is a full-wave rectifier circuit from 105 and 106 A differential amplifier circuit that amplifies the deviation voltage of the detected DC voltage signal, and 109 is a low-pass filter that removes high frequency noise included in the output detection voltage of the differential amplifier circuit 107.These detection coils 205 and 206, the first stage amplifier 103,
A detection circuit is constituted by 104 or the low-pass filter 109.

In this conventional example 1, when the strain of the magnetostrictive film 202 attached to the sensor shaft 201 to which an external force is applied changes,
The magnetic permeability of the magnetostrictive film 202 changes, and the change in the magnetic flux of the electromagnetic field based on the change in the exciting current flowing through the exciting coil 203 is detected as the voltage change in the detection coil 205. Even if an exchange external force is applied to the sensor shaft 201, as is apparent from FIG. 5, the magnetostrictive film 202 does not exist on the outer peripheral surface of the sensor shaft 201 which the inner peripheral surface of the detection coil 206 opposes through the gap. The magnetic permeability on the detection coil 206 side does not change, and therefore, the magnetic flux of the electromagnetic field based on the excitation current flowing through the excitation coil 204 hardly changes, and the voltage induced on the detection coil 206 side hardly changes. These detection coils
The voltage signals detected by 205 and 206 are respectively the first stage amplifier.
After passing through 103, 104 and converted into a DC voltage signal by the full-wave rectification circuits 105, 106, the signal is differentially amplified by the differential amplifier circuit 107 and then taken out as a distorted signal 110a through the low pass filter 109.

Further, as a second conventional example, Japanese Patent Laid-Open No. 4-286.
There is a sensitivity compensator for the No. 927 torque measuring device. In this prior art example 2, a magnetic anisotropy portion is formed on the outer peripheral surface of the torque transmission shaft, an exciting coil and a detection coil are provided corresponding to the magnetic anisotropy portion, and the torque applied to the torque transmission shaft is set. In the magnetostrictive torque sensor, which outputs a signal according to the magnitude of the detection coil to measure the magnitude of the torque, means for supplying an alternating current to the exciting coil, and a direct current component in the exciting current. Means to bias
A sensitivity compensating device for a torque measuring device, comprising: a means for detecting the temperature of the sensor portion; and a means for controlling a DC bias current based on the temperature detection signal.

[0006]

However, in the prior art example 1, when a temperature change occurs, since the temperature drift on the side where the magnetostrictive film 202 is present is different from that on the side where the magnetostrictive film 202 is not present, the strain output is obtained even if the differential is taken. There was a problem that it caused drift. In addition, the distortion-output characteristic had non-linearity. Further, in the second conventional example, a means for biasing the direct current component in the exciting current in response to the change in the temperature of the sensor is provided, but it is described that the sensor compensates the sensitivity at low temperature or particularly at high temperature. However, the compensation characteristics are linear and rough, and the compensation of the non-linearity of the sensor detection circuit is not taken into consideration at all, and it must be said that the sensor detection accuracy is insufficient. . Here, the present invention eliminates the temperature drift in the detection output of the magnetostrictive sensor that wipes out all the drawbacks of these conventional examples,
It is an object of the present invention to provide a method of compensating for temperature / non-linearity of a magnetostrictive sensor with an aim of improving non-linearity.

[0007]

In order to solve the above problems, the present invention provides a sensor shaft, a magnetostrictive film formed on the sensor shaft, a pair of exciting coils, a pair of detecting coils and an output stage. In the signal processing circuit of the strain sensor including the differential amplifier, the voltage change accompanying the temperature change of the strain sensor is detected through the excitation voltage detection circuit that detects the excitation coil voltage, and the temperature of the strain sensor that is each excitation coil voltage is detected. Table ROM pre-stored as the correction value, the difference between the distortion output characteristic curve corresponding to the above and the ideal characteristic straight line having the ideal distortion / output characteristic for each distortion magnitude applied to the distortion sensor And a voltage corresponding to the temperature obtained by full-wave rectifying the exciting coil voltage and a distortion voltage obtained by full-wave rectifying the distortion output are respectively introduced into the multiplexer, and in the multiplexer, the CP is applied. In accordance with the instruction from, one of the voltages is selected, A / D converted and stored in the RAM, then another voltage is selected, A / D converted and stored in the RAM, and both voltages are selected. It is a method of compensating temperature / non-linearity of a magnetostrictive sensor which extracts a correction value from a designated address of the table ROM, D / A converts the extracted correction value, and adds it to the output of the differential amplifier.

[0008]

By the above means, even if the exciting voltage changes due to the temperature change, the correction value adapted to the temperature / distortion output at the exciting voltage is added to the differential amplifier circuit output, so that there is always no temperature drift. In addition, it is possible to obtain distortion-output characteristics without non-linearity.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a circuit configuration of a magnetostrictive strain sensor including a signal processing circuit according to an embodiment of the present invention. 111 is an excitation voltage detection circuit, 112 is a table ROM,
Reference numeral 113 is a D / A converter, and 108 is an adder. Here, the excitation voltage detection circuit 111 heats the outer peripheral surface of the sensor shaft 201 via a gap, that is, generates an alternating magnetic field by passing an alternating current and detects the induced voltage in the detection coil. There is heat generation due to Joule loss, which forms the ambient temperature of the strain sensor.
However, the film side 207 with this magnetostrictive film 202 and the filmless side
On the 208 side, it is arguable that the environmental temperature is probably different because the temperature coefficient is different. Therefore, this phenomenon is the reason why the temperature drift or the non-linearity occurs despite the differential calculation in the subsequent stages. Therefore, according to the present invention, the exciting voltage extracted from the exciting coils 203 and 204 is treated as information including temperature, and is converted into a value suitable for calculation through an appropriate coefficient unit and then full-wave rectified to the next table ROM. It is given as temperature information. All of these information processes are performed in the excitation voltage detection circuit 111.

Next, details of the internal structure of the table ROM 112 will be described. FIG. 2 is a block diagram showing a main part of a circuit adopted in this embodiment, and a clock circuit for digital operation is omitted. 112a is a multiplexer (Mul-tiplexer), the first input of which introduces a DC signal voltage corresponding to the strain sensor temperature from the excitation voltage detection circuit 111 in the previous stage, and the second input of which is the entire output of the strain sensor. The DC signal voltage corresponding to the distorted output from the wave rectifier circuit 105 is received, and one of these two signal voltages is selected and taken into the inside. 112b is an A / D converter. The analog signal from the multiplexer 112a is digitized to enable internal calculation. The signal passed through the A / D converter is instructed by the CPU (central processing unit) via the bus 112f,
Temporarily stored in RAM. Then, according to a further instruction from the CPU, the multiplexer 112a selects another signal voltage, and the signal is temporarily stored in the RAM in the same manner as before. The CPU makes a determination based on both of these signals, and the address of the ROM in which the correction values are stored in advance in the form of a table is specified.
And is sent to the D / A converter 113 at the next stage.

FIG. 3 is a diagram showing the shape of a ROM in which each correction value is stored in a table. This figure is a state diagram in which the difference between the properly sampled data of each temperature / strain output characteristic of the strain sensor and the ideal characteristic without error is stored for each address. For example, how much the correction value for the strain output S _{2 in} the T ₂ / temperature characteristic is stored. FIG. 4 is an explanatory diagram of the correction value calculation means stored in the table ROM. Is a characteristic curve of the output characteristics shown in FIG. 4 Temperature · T ₄ · Curve - Now, distortion when set to the optimum excitation current (exciting voltage V _ref) at room temperature. That is,
As shown in FIG. 4, even if the optimum excitation current value is set, there is non-linearity from the distortion-output characteristics of the sensor head (the tip of distortion detection consisting of the components such as the sensor shaft 201 or the detection coil 206). To do. From this distortion-output characteristic data, for example, the [ideal straight line] is drawn by the method of least squares, and this [ideal straight line] and the [temperature / T ₄ ·. [Curve] is stored as a correction value in the table ROM 112 [the address is the shaded portion shown in the column (S ₂ ) of the row (T ₂ )]. For example, if the distortion is S ₁ , S ₂ , S ₃ ,
…, S _M-2 , S _M-1 , S _M , the difference correction values are 60-40, 61-41, 62-42, 63-43, ..., 65-45, 66.
It is expressed by the length of the difference between −46 and 67−47.

[0012] Here, when the temperature changes around the strain sensor, the strain of the strain sensor - caused drift in the temperature · T ₂ · curve on the output characteristics. One of the major causes of this drift is the change of the excitation voltage due to the temperature change. This change in the excitation voltage is caused by the temperature drift of the oscillator 101 and the power amplifier 102 that form the excitation circuit, and the excitation coils 203 and 204.
Due to the temperature characteristics of. Further, if the exciting current deviates from the optimum exciting current value, the distortion-output characteristic itself also changes, which causes a drift. Normally, even if the excitation voltage changes, this temperature drift should be canceled because the signal processing circuit uses a differential configuration, but in reality, the side with 207 the magnetostrictive film 202 and the side without 207 Excitation coil 20 with 208
3 and the exciting coil 204, when the exciting voltage changes by the same amount, the drift amount differs between the detection coil 205 side and the detection coil 206 side due to the difference in temperature characteristics in each phase. Therefore, the drift cannot be canceled. Due to the above reason, when the temperature changes, the exciting voltage changes, and the distortion-output characteristic of the strain sensor shows the characteristic curve of [temperature / T ₂ · curve] of the exciting voltage V ₁ of FIG. 4 or the exciting voltage V. ₂
[Temperature / _TN-1 / curve] characteristic curve, that is, zero drift and sensitivity drift occur.

Therefore, according to the present invention, the exciting voltage is applied in advance,
The actual strain at room temperature setting to the optimum excitation current (exciting voltage V _ref) - the difference between the take characteristic curve of the temperature · T ₄ · Curve was described previously for each excitation voltage [ideal straight line on the output characteristics Is stored in the previous table ROM 112 as a correction value. Incidentally, in the correction value of the exciting voltage V _{1 in the case} of the characteristic curve of [Temperature / T ₂ · curve], the distortion is S ₁ , S ₂ , S ₃ , ..., S.
If it changes to _M-2 , S _M-1 , and S _M , the difference correction value becomes 50-
40, 51−41, 52−42, 53−43,…, 55−45, 56−46, 57
It is represented by the length of each difference from −47, and the same applies to the case of the characteristic curve of [temperature / _TN-1 / curve] of the excitation voltage V ₂ . In signal processing, the excitation voltage is detected by the excitation voltage detection circuit 111, full-wave rectified, and corrected according to this DC voltage (temperature) and the distortion at that time (distortion output from the full-wave rectification circuit 105). The value is output from the table ROM 112 and added to the output of the differential amplifier 107 in the adder 108, so that even if there is a change in the excitation voltage due to a temperature change, the strain-output of the strain sensor always follows the [ideal straight line]. The characteristic 110 is obtained. And the present invention provides a torque sensor,
It can be applied to various strain sensors such as a pressure sensor and a tension sensor.

[0014]

As described above, according to the present invention, even if the exciting voltage changes due to temperature change, drifts such as zero-point drift and sensitivity drift do not occur, and the strain of the strain sensor with good linearity is always maintained. -The output characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a circuit configuration according to an embodiment of the present invention.

FIG. 2 is a block diagram showing the internal circuit configuration of a table ROM in one embodiment of the present invention.

FIG. 3 is an explanatory diagram of a ROM address table according to an embodiment of the present invention.

FIG. 4 is a diagram showing a strain-output characteristic of a strain sensor according to an embodiment of the present invention.

FIG. 5 is a side view showing a configuration of a sensor head of a strain sensor with a part cut away.

FIG. 6 is a block diagram showing a circuit configuration of a strain sensor and its signal processing circuit in Conventional Example 1.

[Explanation of symbols]

 101 Oscillator 102 Power amplifier 103 First stage amplifier 104 First stage amplifier 105 Full wave rectification circuit 106 Full wave rectification circuit 107 Differential amplifier 108 Adder 109 Low pass filter 110 Distortion output [present invention] 110a Distortion output [Conventional example 1] 111 Excitation voltage detection Circuit 112 Table ROM 112a Multiplexer 112b A / D converter 112c CPU 112d RAM 112e ROM 113 D / A converter

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[Procedure amendment]

[Submission date] October 27, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Added

[Correction content]

[Fig. 2]

[Figure 1]

[Figure 3]

[Figure 4]

[Figure 5]

[Figure 6]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Koji Uemura Inventor Koji Kurosaki No. 2-1, Kurosaki Shiroishi, Hachimannishi-ku, Kitakyushu, Fukuoka

Claims (1)

[Claims] 1. A signal processing circuit of a strain sensor, comprising: a sensor shaft; a magnetostrictive film formed on the sensor shaft; a pair of exciting coils; a pair of detecting coils; and a differential amplifier in an output stage. The voltage change due to the temperature change of the strain sensor is detected via the excitation voltage detection circuit that detects the strain output characteristic curve according to the temperature of the strain sensor that is each excitation coil voltage, and the ideal strain / output A table ROM that stores in advance the difference between the ideal characteristic line having the characteristics and the magnitude of each strain applied to the strain sensor as a correction value is provided, and the excitation coil voltage is subjected to full-wave rectification at the temperature. The corresponding voltage and the distorted voltage obtained by full-wave rectifying the distorted output are respectively introduced into the multiplexer, and in the multiplexer, one of the voltages is selected according to the instruction from the CPU, A / D converted and stored in RAM, then another voltage is selected, A / D converted and stored in RAM, the address of the table ROM is specified from these both voltages, and the table ROM is specified A method for compensating temperature / non-linearity of a magnetostrictive sensor, characterized in that a correction value from an address is extracted, the extracted correction value is D / A converted and added to the output of the differential amplifier.