JP2831206B2 - Magnetostrictive torque sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art As means for detecting the magnitude of torque applied to a torque transmission shaft, a magnetostrictive torque sensor is known. As this magnetostrictive torque sensor, a pair of magnetic anisotropic parts inclined in opposite directions are formed on the outer peripheral surface of the torque transmission shaft, and an exciting coil and a pair of detecting coils are formed around these magnetic anisotropic parts. Is generally provided.

[0003]

On the other hand, in the case where only one magnetic anisotropic portion is formed on the outer peripheral surface of the torque transmission shaft, the measurement sensitivity is slightly lowered, but there is no practical problem. A magnetostrictive torque sensor can be configured.

However, the higher the measurement sensitivity is, the more preferable. A small and highly sensitive torque sensor having only one magnetically anisotropic portion and high measurement sensitivity can be obtained. Is expected.

Accordingly, an object of the present invention is to improve the measurement sensitivity when a torque sensor is configured with only one magnetically anisotropic portion.

[0006]

In order to achieve the above object, the present invention provides a single magnetically anisotropic portion formed on the outer peripheral surface of a torque transmission shaft, and a single magnetically anisotropic portion provided around the magnetically anisotropic portion. A coil, a means for supplying an exciting voltage to the coil, a means for obtaining a torque detection signal from the coil, and a coil provided in series between the coil and the exciting voltage supplying means, and having substantially the same impedance as the coil. It has a resistor having a resistance value, means for detecting the direction of the torque applied to the torque transmission shaft, and means for switching the gain of the torque detection signal based on the direction of the applied torque.

[0007]

In such a configuration, when a torque is applied to the torque transmitting shaft, the magnetic permeability of the magnetically anisotropic portion changes, thereby changing the coil impedance. At this time, the change in the torque detection voltage with respect to the change in the coil impedance is maximized and the torque detection sensitivity is maximized when the resistance value of the resistor connected in series to the coil is equal to the impedance of the coil. Therefore,
By connecting a resistor having a resistance value substantially equal to the coil impedance to the coil in series, the torque detection sensitivity is improved. Further, when a single magnetic anisotropic portion is provided as described above, the torque detection sensitivity differs between when a clockwise torque is applied and when a counterclockwise torque is applied. According to the present invention, means for detecting the direction of the torque applied to the torque transmission shaft,
By providing the means for switching the gain of the torque detection signal based on the direction of the applied torque, the torque in either direction is detected with equal sensitivity, and the torque in both directions is correctly detected.

[0008]

FIG. 1 shows a first embodiment of the present invention. Here, reference numeral 1 denotes a torque transmission shaft, and a magnetically anisotropic portion 2 is formed on the outer peripheral surface of the shaft at only one position inclined with respect to the axis.
Around the magnetic anisotropic part 2, a coil 3 is arranged.

The coil 3 is connected to an AC excitation power supply 5 for supplying an AC current to the coil 3, and a resistor 4 is connected in series between the coil 3 and the AC excitation power supply 5. This resistor 4 has a resistance value approximately equal to the impedance of the coil 3. A rectifying circuit 6 is connected to the AC exciting power supply 5 so as to be connected in parallel with the exciting coil 3 and the resistor 4, and a low-pass filter 7 is connected to an output side of the rectifying circuit 6, and an exciting voltage detecting circuit 8 is provided. Is composed.

A rectifier circuit 9, a low-pass filter 10, and a gain temperature characteristic correction circuit 11 are connected to an output line from the coil 3, and constitute a torque detection circuit 12. The output side of the correction circuit 11 in the torque detection circuit 12 and the output side of the low-pass filter 7 in the excitation voltage detection circuit 8 are both connected to the input side of the subtractor 13. Also,
The output side of the subtractor 13 is connected to the amplifier 14.

The output side of the amplifier 14 is connected to a polarity determination circuit 15 for detecting the direction of the torque applied to the torque transmission shaft 1 and a gain switching circuit 16. The gain switching circuit 16 can receive the output from the polarity determination circuit 15 and switch the gain of the torque detection signal from the amplifier 14 based on the direction of the torque applied to the torque transmission shaft 1.

In such a configuration, the AC excitation power supply 5
Supplies the exciting voltage Vex to the resistor 4 and the coil 3 connected in series to each other. The output from the coil 3 is V1, the output of the filter 10 is V2, and the output of the correction circuit 11 is V1.
V3. These outputs V1, V2, V3 increase or decrease according to the magnitude of the torque applied to the shaft 1. On the other hand, it is assumed that an output V01 appears on the filter 7 corresponding to the excitation voltage Vex.

When a torque is applied to the torque transmission shaft 1,
The magnetic permeability of the magnetically anisotropic part 2 changes, thereby changing the impedance of the coil 3. At this time, the change in the torque detection voltage corresponding to the change in the impedance of the coil 3, that is, the change in the coil output V1 and the maximum in the torque detection sensitivity are caused by the resistance 4 connected in series with the coil 3.
Is made equal to the impedance of the coil 3. Therefore, by making the resistance value of the resistor 4 substantially equal to the impedance of the coil 3 as described above, the torque detection sensitivity is increased.

If the excitation voltage Vex changes for some reason, the output V1, V2, V3 of the detected voltage and the output
V01 also changes, but their rate of change is equal to the rate of change of the excitation voltage Vex. On the other hand, in the subtractor 13, the output V01 of the filter 7 of the excitation voltage detection circuit 8 is subtracted from the output V3 of the correction circuit 11 of the torque detection circuit 12. Therefore, there is an advantage that no matter how the excitation voltage Vex changes, the torque output does not change. Although FIG. 1 shows a state in which the rectifier circuit 6 is directly connected to the AC excitation power supply 5 for simplicity, the difference between the outputs V01 and V3 is calculated by the subtractor 13 in this manner. , Excitation voltage
In order to prevent the torque output from changing even if Vex changes, actually, the excitation voltage Vex is divided into voltages corresponding to the ratio of the resistance value of the resistor 4 to the impedance of the coil 3 and then supplied to the rectifier circuit 6. Need to supply. This is the same for those shown in other drawings described later.

The temperature characteristics of the outputs V1, V2, V3, and V01 are measured in advance, and the correction of the gain temperature characteristic correction circuit 11 is performed so that V3 = V01 when the torque is not applied to the shaft 1 and the torque is zero. Determine the constant. By doing so, even if a temperature change occurs in the torque sensor, the subtractor 13 outputs an output whose output fluctuation is compensated for in response to the temperature change.
V4 appears. As a result, the output V4 of the subtractor 13 appears as a signal that prevents the occurrence of an error based on the fluctuation of the excitation voltage Vex of the excitation power supply 5 and the temperature change. The output V4 of the subtractor 13
Is amplified by the amplifier 14 to become the output V5.

In the above, a gain temperature characteristic correction circuit is provided on the output side of the low-pass filter 10 in the torque detection circuit 12.
Although the gain temperature characteristic correction circuit 11 is provided, the gain temperature characteristic correction circuit 11 functions similarly when the output side of the low-pass filter 7 in the excitation voltage detection circuit 8 is provided as shown by a broken line in FIG.

The output V5 of the amplifier 14 is input to a gain switching circuit 16 and a polarity judgment circuit 15. Generally magnetic anisotropic part 2
, The torque detection sensitivity is different between the case where the clockwise torque is applied and the case where the counterclockwise torque is applied, and the torque output V1, that is, V5 is different. Therefore, the direction of the applied torque is determined from the output V5 by a polarity determination circuit 15 by a known method, and based on the direction of the applied torque, a gain switching circuit is determined.
16 switches the gain of the output V5. As a result, torques in any direction are detected with equal sensitivity, and torques in both directions are correctly detected and finally output.

FIG. 2 shows a second embodiment of the present invention. Here, the gain temperature characteristic correction circuit 11 includes a torque detection circuit 12
Is provided between the coil 3 and the rectifier circuit 9 or on the input side of the rectifier circuit 6 in the excitation voltage detection circuit 8. Other configurations are the same as those of the first embodiment in FIG.

FIG. 3 shows a third embodiment of the present invention. Here, the gain temperature characteristic correction circuit 11 includes a torque detection circuit 12
Between the rectifier circuit 9 and the filter 10 or between the rectifier circuit 6 and the filter 7 in the excitation voltage detection circuit 8. Other configurations are the same as those of the first embodiment in FIG.

FIG. 4 shows a fourth embodiment of the present invention. Here, the gain temperature characteristic correction circuit 11 is provided between the resistor 4 and the AC excitation power supply 5 or between the coil 3 and the resistor 4. In this embodiment, the gain temperature characteristic correction circuit
Reference numeral 11 denotes a temperature-sensitive resistor whose resistance value greatly changes with a change in temperature. Other configurations are the same as those of the first embodiment in FIG.

[0021]

As described above, according to the present invention, since a resistor having a resistance value substantially equal to the impedance of the coil is provided in series with the coil, the torque transmission shaft has only a single magnetic anisotropic portion. Despite this, the torque detection sensitivity can be maximized and the accuracy of the sensor can be improved, so that the torque transmission shaft can be shortened, and the number of coils and bobbins around which the coils are wound is smaller than before. It is possible to reduce the size of the shield case for accommodating them, thereby simplifying the shape of the shield case. As a result, it is possible to obtain not only a small but high-precision torque sensor, but also the direction of the torque applied to the torque transmission shaft. And a means for switching the gain of the torque detection signal based on the direction of the applied torque. Despite the difference in torque detection sensitivity between the case where a clockwise torque is applied and the case where a counterclockwise torque is applied, torques in any direction can be detected with equal sensitivity to each other. Torque can be detected correctly.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a magnetostrictive torque sensor according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a magnetostrictive torque sensor according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram of a magnetostrictive torque sensor according to a third embodiment of the present invention.

FIG. 4 is a circuit diagram of a magnetostrictive torque sensor according to a fourth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Torque transmission shaft 2 Magnetic anisotropic part 3 Coil 4 Resistance 5 AC excitation power supply

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-60-260821 (JP, A) JP-A-3-183924 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01L 3/10

Claims (1)

(57) [Claims] 1. A single magnetic anisotropic portion formed on an outer peripheral surface of a torque transmission shaft, a coil provided around the magnetic anisotropic portion, and means for supplying an exciting voltage to the coil. ,
Means for obtaining a torque detection signal from the coil, a resistor provided in series between the coil and the excitation voltage supply means and having a resistance value substantially equal to the impedance of the coil, and a torque applied to a torque transmission shaft. Detect direction
And a torque detection signal based on the direction of the applied torque.
Means for switching the gain of the magnetostrictive torque sensor.