JPH0996577A - Torque detecting circuit of torque sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a high sensor output even when the power supply voltage of a torque sensor is low, and to decrease the cost required for a rectifier circuit. SOLUTION: In a torque transmitting shaft 11, a pair of magnetically anisotropic parts 12 and 12 are formed. A pair of AC detected voltages V1 and V2 in correspondence with the respective magnetically anisotropic parts 12 and 12 are generated. The detected torque value is obtained from a pair of these detected voltage V1 and V2. In this torque sensor, a differential amplifier 18, which performs the differential amplification of a pair of the detected voltages V1 and V2, and a rectifying circuit 19, which rectifies the differentially amplified signal, are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a torque detection circuit for a torque sensor.

[0002]

2. Description of the Related Art There is a magnetostrictive torque sensor as a type of torque sensor, an example of which is shown in FIG. here,
On the outer circumference of the torque transmission shaft 1 formed of a material having soft magnetism and magnetostriction, a pair of magnetic anisotropics that are inclined in mutually opposite directions at an angle of about ± 45 degrees with respect to the direction of the axis of the shaft. The characteristic portions 2 and 2 are formed by a large number of machined grooves or the like. Around the magnetic anisotropic portions 2 and 2, a pair of detection coils 3 and 3 corresponding to the magnetic anisotropic portions and a single excitation coil 4 for exciting the detection coils 3 and 3 are provided.
Are provided. The exciting coil 4 is connected to an AC power supply 5.

In the detection coils 3 and 3, detection voltages V1 and V2 having mutually opposite characteristics corresponding to changes in the magnetic permeability of the magnetic anisotropic portions 2 and 2 due to the application of torque to the shaft 1 appear. The output lines from the detection coils 3 and 3 are rectifier circuits 6 and 6 respectively.
Through the subtraction circuit 7 formed of a differential amplifier. That is, the detection voltages V1 and V2 from the detection coils 3 and 3, respectively.
Is rectified by the rectifying circuits 6, 6 and then subtracted by the subtracting circuit 7, so that the subtraction result appears at the output terminal 8 as a torque signal (V1-V2).

[0004]

However, in the case where the detection voltages V1 and V2 are immediately rectified as described above, when the detection voltages V1 and V2 become larger as the voltage becomes closer to the voltage of the power source 5, the operation of the rectification circuit is reduced. It tends to be defective due to its characteristics. As a result, the detection voltages V1 and V2 are restricted by the voltage of the power supply 5, and there is a problem that a high sensor output cannot be obtained under a low power supply voltage.

Further, when the S / N ratio of the sensor is small, high accuracy is required for the rectifier circuits 6 and 6 in order to obtain the required detection accuracy, and as shown in the figure, the rectifier circuits 6 and 6 are provided for each detection line. If installed, there is a problem that two rectifying circuits are required, which causes a cost increase.

Therefore, the present invention solves such a problem so that a high sensor output can be obtained even when the power supply voltage is low, and the cost required for the rectifier circuit can be reduced. With the goal.

[0007]

In order to achieve this object, according to the present invention, a pair of torque detecting portions are formed on a torque transmission shaft, and a pair of alternating detection voltages corresponding to the torque detecting portions are generated. In the torque sensor configured to obtain a torque detection value based on the difference between the pair of detection voltages, means for differentially amplifying the pair of detection voltages, and the differentially amplified signal And means for rectifying.

With such a configuration, since the detection voltage is directly differentially amplified, the differential amplification output becomes smaller than the detection voltage. Since the AC signal after the differential amplification is rectified in this way, a high sensor output can be obtained even when the power supply voltage is low, and a sensor output voltage higher than the power supply voltage can be obtained. is there. Further, since it is only necessary to install one rectifying means and it is not necessary to install a plurality of rectifying means, the cost can be reduced accordingly.

Further, the present invention has means for changing the gain of the differential amplification so as to set the positive and negative signs of the output signal and to output the signal within the range in which the linearity of the rectifier circuit is maintained. Is. Alternatively, it has means for setting the sign of the output signal by applying a bias voltage to the detection voltage to be differentially amplified and outputting the signal within the range in which the linearity of the rectifying circuit is maintained.

That is, if the subtraction is performed after the rectification as in the conventional case, the sensor output will be accompanied by the sign of either positive or negative depending on the direction of torque application to the shaft. When the rectification is performed after that, the output of the rectification circuit, that is, the sensor output increases in accordance with the increase in the applied torque, but can take only a positive value regardless of the direction in which the torque is applied. Therefore, the directionality of the sensor output voltage is lost.

However, when the gain of the differential amplification is changed or the bias voltage is applied to the detection voltage for differential amplification as described above, a bias is generated in the differential amplification output. Then, the sensor output increases or decreases depending on the direction of the applied torque, so that it is possible to determine the torque application direction by confirming the increase or decrease of the sensor output when the torque is applied. That is, the directionality of the sensor output voltage, that is, the positive / negative sign of the sensor output is determined.

In general, a rectifier circuit tends to have a reduced output linearity at a portion where the input level is too low or too high. Normally, when a low level signal is input after differential amplification, the sensor The output linearity may not be guaranteed. However, if a bias is generated in the differential amplification output as described above, the input level of the rectifier circuit can be set appropriately, and the linearity of the sensor output within the range of the magnitude of the applied torque to be detected. Will be maintained.

[0013]

DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows an embodiment of the present invention. Similar to the case of FIG. 5, a pair of magnetic anisotropic portions 12, 12 are formed on the outer periphery of the torque transmission shaft 11, and a pair of corresponding detection coils 13 are provided around these magnetic anisotropic portions 12, 12. ,13
And a single excitation coil 14 connected to an AC power supply 15.

The detection voltages V1 and V2 appear in the respective detection coils 13 and 13, and the output lines 16 from the detection coils 13 and 13
16 is connected to a differential amplifier circuit 18 using an operational amplifier 17. The input resistance a1 and the feedback resistance b1 are connected to the inverting input terminal of the operational amplifier 17, and the input resistance a2 on the output line 16 side and the input resistance on the ground side are connected to the non-inverting input terminal.
b2 and are connected. Of these, the input resistance a1 of the inverting input terminal and the input resistance a2 of the output line 16 side of the non-inverting input terminal
And are composed of variable resistors. The feedback resistor b1 and the ground-side input resistor b2 are fixed resistors.

A rectifier circuit 19 is provided on the output side of the differential amplifier circuit 18.
Is connected.

According to such a configuration, the detection coil 13,
Since the AC detection voltages V1 and V2 of 13 are directly input to the differential amplifier circuit 18 and differentially amplified, the output from the differential amplifier circuit 18 becomes smaller than the detection voltages V1 and V2. Since the AC signal after differential amplification is rectified by the rectifier circuit 19 as described above, a high sensor output can be obtained even when the voltage of the power supply 15 is low. It is also possible to obtain a sensor output voltage higher than the voltage of the power supply 15. Moreover, since only one rectifier circuit 19 needs to be installed, and it is not necessary to install a plurality of rectifier circuits 19, the cost can be reduced accordingly.

The relationship between the torque applied to the shaft 11 and the sensor output in the circuit of FIG. 1 is shown in FIG. For example, in the circuit of FIG. 1, the resistance value of each resistor of the differential amplifier circuit 18 is b1 / a1.
= B2 / a2, the sensor output becomes zero when the torque applied to the shaft 11 is zero. That is, at the origin O, both the applied torque and the sensor output become zero. At this time, the direction of the applied torque is different between the first quadrant and the second quadrant in the figure, and the magnitude of the applied torque increases as the distance from the origin O increases.

However, regardless of the direction of the applied torque,
Since the sensor output increases as the applied torque increases, it cannot be determined in which direction the torque is being applied when the sensor output increases.

However, when the gain of the differential amplifier circuit 18 is changed by establishing the relationship of b1 / a1> b2 / a2 in the resistance value of each resistor of the differential amplifier circuit 18, when the applied torque is zero. Sensor output of the first quadrant of the figure, for example A
Can be biased to the point. Then, when a torque in a certain direction is applied to the torque transmission shaft 11 from the state of the point A, the sensor output increases in the direction of the arrow X, and when a torque in the opposite direction is applied, the sensor output changes. Decrease in the Y direction. As a result, not only the magnitude of the applied torque but also the applied direction can be detected, and the directionality of the sensor output, that is, the positive / negative sign of the sensor output can be determined.

The resistance value of each resistance of the differential amplifier circuit 18 is set to b1 / a1.
If the relationship of <b2 / a2 is established and the gain of the differential amplifier circuit 18 is changed, the sensor output when the applied torque is zero can be set to the second quadrant in the figure, for example, point B. In this case, the relationship between the torque application direction and the increase / decrease in sensor output is opposite to that in the case where the sensor output when torque is zero is set in the first quadrant as described above.

Further, generally, in the portion where the input level of the rectifier circuit 19 is too low or too high, the linearity of the output tends to decrease as shown in FIG. 2, and the gain of the differential amplifier circuit 18 cannot be changed. However, if a low-level signal is input to the rectifier circuit 19, the linearity of the sensor output may not be maintained. However, when the output of the differential amplifier circuit 18 is biased as described above, the input level of the rectifier circuit 19 can be set appropriately, and the sensor can be detected within the range of the magnitude of the applied torque to be detected. Output linearity can be guaranteed.

FIG. 3 shows another embodiment of the present invention.
Here, the resistors a1, b1, a2, and
Both b2 are composed of fixed resistors, and b1 / a1 = b2 /
The gain of the differential amplifier circuit 18 is not changed by setting the relationship of a2.

And instead, the detection coils 13, 13
By connecting the DC power supply 21 in series to one of the two, a bias voltage is applied to the corresponding detection voltage V2. Then
In this case as well, the output of the differential amplifier circuit 18 is similarly biased, and as shown in FIG. 4, the sensor output when the applied torque is zero is the same as in the case of FIG. It can be set to point B in the quadrant. This allows you to determine the sign of the sensor output as well as
It becomes possible to operate the rectifier circuit 19 within the range of good linearity.

Contrary to the above, if a bias voltage is applied to the detection voltage V1 on the opposite side, the sensor output when the applied torque is zero can be set to point A in the first quadrant in FIG.

[0025]

As described above, according to the present invention, the torque sensor is provided with the means for differentially amplifying the pair of detection voltages and the means for rectifying the differentially amplified signals. Since it is possible to directly differentially amplify, the differential amplified output can be made smaller than the detection voltage, and the AC signal after differentially amplified in this way can be rectified. A high sensor output can be obtained even when the power supply voltage is low, and a detection output voltage higher than the power supply voltage can be obtained. Further, since it is only necessary to install one rectifying means and it is not necessary to install a plurality of rectifying means, the cost can be reduced accordingly.

Further, according to the present invention, a bias can be generated in the differential amplification output by changing the gain of the differential amplification or applying a bias voltage to the detection voltage for differential amplification. Since the sensor output can be increased or decreased according to the direction of applied torque, the direction of torque application can be determined by checking the increase or decrease in sensor output when torque is applied. , The sign of the sensor output can be determined. Further, by generating a bias in the differential amplification output, the input level of the rectifier circuit can be set appropriately, and the linearity of the sensor output can be ensured within the range of the applied torque to be detected. You can

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of a torque detection circuit of a torque sensor according to the present invention.

FIG. 2 is a diagram illustrating a sensor output of the torque sensor of FIG.

FIG. 3 is a diagram showing another embodiment of the torque detection circuit of the torque sensor according to the present invention.

FIG. 4 is a diagram illustrating a sensor output of the torque sensor of FIG.

FIG. 5 is a diagram illustrating a torque detection circuit of a conventional torque sensor.

[Explanation of symbols]

 11 Torque transmission shaft 18 Differential amplifier circuit 19 Rectifier circuit V1 detection voltage V2 detection voltage

Claims (3)

[Claims] 1. A pair of torque detectors are formed on a torque transmission shaft to generate a pair of AC detection voltages corresponding to each torque detector, and a difference between the pair of detection voltages. A torque sensor for obtaining a torque detection value based on the above, wherein the torque sensor is provided with means for differentially amplifying the pair of detection voltages and means for rectifying the differentially amplified signal. Torque detection circuit. 2. A means for setting the positive and negative signs of the output signal by changing the gain of the differential amplification and outputting the signal within the range in which the linearity of the rectifier circuit is maintained. The torque detection circuit of the torque sensor according to claim 1. 3. A bias voltage is applied to the detection voltage to be differentially amplified, so that the positive and negative signs of the output signal are set and a signal is output within a range in which the linearity of the rectifier circuit is maintained. The torque detection circuit for a torque sensor according to claim 1, wherein: