JPH04286927A - Compensating apparatus for sensitivity of torque measuring device - Google Patents

Abstract

PURPOSE:To temperature-compensate sensitivity of a sensor when a magnetically anisotropic part formed on an outer periphery of a torque transmission shaft is utilized and torque is measured by means of a torque sensor using a detection coil and an excitation coil. CONSTITUTION:A dc bias current control circuit 8 is added to an ac constant current source 7 to an excitation coil 6. A sum V1+V2 of detected voltages from a pair of detection coils 4,5 is output from an arithmetic device 17, whereby temperature of a sensor part is represented. A signal is sent to the control circuit 8 based on the value of this sum V1+V2 so that dc bias current is increased/decreased. A torque detection output can be varied according to a change in dc bias current, thereby temperature-compensating detection sensitivity.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sensitivity compensation device for a torque measuring device.

0002

[Prior Art] As a known torque measuring device, a pair of magnetic anisotropic parts are formed on the outer periphery of a torque transmission shaft, and the permeability of each magnetic anisotropic part changes when torque is applied to this shaft. is detected by a pair of detection coils placed near these magnetically anisotropic parts, and the magnitude of the torque acting on the shaft is converted into an electrical signal from the difference between both detection signals. , which has an excitation coil for exciting the detection coil is proposed, for example, in Japanese Patent Laid-Open No. 1-173843.

[0003] In this type of torque measuring device, when a temperature change occurs in the shaft portion where the magnetic anisotropic portion is formed, or in the torque detecting portion equipped with the detection coil, excitation coil, etc., the magnetic characteristics and electrical characteristics change. However, the impedance of the excitation coil changes and its excitation current changes. As a result, the torque detection sensitivity changes significantly, causing fluctuations in the detection accuracy. For this reason, industrial machinery, motors, engines, automobiles, etc.
This poses a problem when measuring the torque of equipment that gets relatively hot during operation.

Therefore, in JP-A-1-173843, focusing on the fact that there is a correlation between changes in excitation current and changes in temperature, the sum of the voltages of the output signals of the detection coils, that is, twice the average value of both signals, is The excitation current is controlled by constant voltage control to keep the value constant to prevent such a situation from occurring.

[0005]

[Problem to be Solved by the Invention] However, in such a known device, since the amplification factor of the difference between both detection signals is constant, the sensor There is a problem in that when the temperature becomes particularly high, the torque detection signal is outputted relatively large, and its sensitivity fluctuates, causing an error in the torque measurement value.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to compensate for the sensitivity of a torque sensor at low temperatures, and especially at high temperatures, to prevent such measurement errors from occurring.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present invention forms a magnetically anisotropic portion on the outer circumferential surface of a torque transmission shaft, and provides an excitation coil and a detection coil in correspondence with the magnetic anisotropic portion. and a magnetostrictive torque sensor configured to measure the magnitude of the torque by outputting a signal corresponding to the magnitude of the torque applied to the torque transmission shaft from the detection coil, wherein an alternating current is applied to the excitation coil. means for supplying a current, means for biasing a DC component in the excitation current of the excitation coil, means for detecting the temperature of the sensor section, and means for controlling the DC bias current based on the temperature detection signal;
The configuration has the following.

[0008]

[Operation] In such a configuration, the sensitivity of the sensor increases, for example, as the temperature of the sensor section increases, and conversely decreases as the DC bias current increases. Therefore, when the temperature of the sensor section rises based on the output of the temperature detection means, it is possible to decrease the sensitivity by increasing the DC bias current and achieve sensitivity compensation.

Note that the output waveform of the detection coil, which is the secondary side, is composed of a differential waveform of the waveform of the excitation coil, which is the primary side, so even if the DC current is increased or decreased on the excitation side, the measured torque value will not change. It has no effect on itself.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a first embodiment of the present invention. Here 1
is a shaft for transmitting torque, and is made of a material having soft magnetism and magnetostriction. This shaft 1 is attached to the outer circumference of shaft 1.
Magnetic anisotropic portions 2 and 3 are formed by a large number of grooves, etc., and are inclined in opposite directions at angles of about ±45 degrees with the direction of the axis. Around the magnetic anisotropic parts 2 and 3,
Detection coils 4 and 5 corresponding to each magnetic anisotropy section 2 and 3,
Excitation coil 6 for exciting these detection coils 4 and 5
is provided. The excitation coil 6 is an alternating current constant current source 7
It is connected to the. 8 is a DC bias current control circuit capable of adding a DC bias component to the excitation current of the excitation coil 6. Vex is the AC excitation voltage, Iex
indicates the AC excitation current.

Output lines 9 from each detection coil 4, 5,
10 is connected to the input sides of rectifying filters 11 and 12, respectively, and the output sides of these rectifying filters 11 and 12 are connected to the input side of an arithmetic unit 13 for subtraction. The output side of the arithmetic unit 13 is led to an output terminal 15 via a V/I converter 14. 16 is a load resistance.

The output sides of the rectifying filters 11 and 12 are also connected to the input side of an arithmetic unit 17 for addition. The output side of the arithmetic unit 17 is connected to one input side of a comparator 18, and the other input side of this comparator 18 is connected to the constant voltage generation circuit 1.
9 is connected. The output side of the comparator 18 is connected to a DC bias current control circuit 8, and the control circuit 8 can be controlled to increase or decrease the DC bias current.

With this configuration, the change in magnetic permeability in each magnetically anisotropic portion 2, 3 based on the torque acting on the shaft 1 is detected by the detection coils 4, 5. At this time, since the magnetic anisotropic parts 2 and 3 are inclined in opposite directions, when a tensile force is applied to one magnetic anisotropic part, a compressive force is applied to the other. Therefore, for example, when the detection voltage V1 of one detection coil 4 increases as the torque increases, the detection voltage V2 of the other detection coil 5 decreases accordingly. Therefore, the arithmetic unit 13 uses both detection voltages V1 and V
2, a signal corresponding to the change in torque appears at the output terminal 15, as shown in FIG. t is a torque of a predetermined magnitude, and vt is an output corresponding to the torque t.

The value of the sum V1+V2 of the detected voltages appearing on the output side of the arithmetic unit 17 is compared with a reference voltage from a constant voltage generating circuit 19 in a comparator 18. As shown in FIG. 3, the value of this sum V1+V2 tends to decrease as the temperature of the sensor section increases, so it serves as a signal representing the temperature value of this sensor section. For example, as shown in the figure, when the temperature of the sensor part is 20℃, it takes a value of v20,
Also, when the temperature of the sensor part is 120℃, v120
It takes the value (v20 > v120).

The sensitivity of the sensor, ie, the output signal per unit torque, increases as the temperature increases, as shown in FIG. For example, as shown in the figure, when the temperature of the sensor part is 20°C, the value is S20, and when the temperature of the sensor part is 120°C, the value is S120 (S20 <
S120).

On the other hand, as shown in FIG. 5, when the DC bias current supplied to the excitation coil 6 is increased, the sensor sensitivity tends to decrease accordingly. In FIG. 5, the sensitivities corresponding to the bias currents I0 and I1 are S0 and S1, respectively.

Now, if no bias current is added to the excitation circuit, at high temperatures shown in FIG. 6, the sensor sensitivity will increase as explained in FIG. 4, and when torque t is applied, the output will be lower than the correct output vt. Since a large output vt' appears and a measurement error occurs, this is compensated for. Here, at room temperature (20° C.), no bias current is applied to the excitation circuit, and the DC bias current value is 0 mA. Considering the ratio S0/S1 to find the appropriate bias current, S0/S1 = vt / vt'
(1) becomes. However, S120 = vt' / t
(2) S20 = vt / t
(3), so (
By substituting equations 2) and (3) into equation (1), S120 × S0/S1 = S20
(4) becomes. This ratio S0/S1 becomes a correction coefficient by the bias circuit.

That is, as described above, the sensitivity of the sensor increases as the temperature of the sensor section increases, as shown in FIG. 4, and conversely decreases as the DC bias current increases, as shown in FIG. On the other hand, the sum of detection voltages V1+V
The value of 2 decreases as the temperature of the sensor section increases, as shown in FIG. Therefore, by detecting the temperature of the sensor section from the value of the sum of the detected voltages V1+V2 and controlling the DC bias current based on it, specifically, the sum of the detected voltages V1
By increasing the bias current when the value of +V2 decreases, sensor sensitivity at high temperatures can be compensated.

Note that the output waveforms of the detection coils 4 and 5 on the secondary side are composed of differential waveforms of the waveform of the excitation coil 6 on the primary side, so even if the DC current is increased or decreased on the excitation side, ,
There is no effect on the torque measurement itself.

By temperature-compensating the sensor sensitivity in this way, as shown in FIG. 6, it is possible to reduce the sensitivity error caused by temperature changes in the sensor section and obtain detection output characteristics almost equivalent to those at room temperature. , it is possible to construct a torque sensor that can measure torque with higher accuracy over a wide temperature range.

FIG. 7 shows a second embodiment of the invention. Here, an excitation voltage detection circuit 21 is composed of an arithmetic unit and a rectifying filter, and an AC constant current source 7 similar to that shown in FIG. 1 is used as an excitation power source for the excitation coil 6. As shown in FIG. 8, the excitation voltage Vex when using the constant current source 7 increases in proportion to the rise in temperature of the sensor section, so the detection signal of the detection circuit 21 becomes a signal representing the temperature of the sensor section. . Therefore, the sensor sensitivity can be temperature compensated by inputting the output of the excitation voltage detection circuit 21 to the comparator 18 as in the case of FIG. 1 and controlling the bias current accordingly.

FIG. 9 shows a third embodiment of the invention. Here, a detection resistor 22 is provided in the excitation circuit, and an excitation current detection circuit 23 composed of an arithmetic unit and a rectifying filter is connected to this detection resistor 22 to detect the excitation current Iex. An alternating current constant voltage source 24 is used as an excitation power source for the excitation coil 6. As shown in FIG. 10, the excitation current Iex when using the constant voltage source 24 decreases in inverse proportion to the rise in temperature of the sensor section, so the detection signal of the detection circuit 23 becomes a signal representing the temperature of the sensor section. . Therefore, by controlling the bias current as in the case of FIGS. 1 and 7, the sensor sensitivity can be temperature-compensated.

FIG. 11 shows a fourth embodiment of the present invention. Here, the bias current is controlled using the same detection resistor 22 and excitation current detection circuit 23 as in FIG. A general AC power supply 29 is used as an excitation power supply for the excitation coil 6. This AC power supply 29 is equipped with a constant voltage control circuit 25 similar to that disclosed in the above-mentioned Japanese Unexamined Patent Publication No. 1-173843, which performs feedback control so as to keep the sum of the voltages of the output signals of the detection coil constant. It's a combination. This constant voltage control circuit 25 has a sum V1+V of detected voltages.
2, a comparator 27 that compares the calculation result with the reference voltage from the constant voltage generation circuit 26, and an excitation circuit that controls the excitation voltage Vex based on the signal from the comparator 27. It has an auto gain controller 28 built into the.

With this configuration, the effect of sensitivity compensation by controlling the bias current is synergistic with the effect of sensitivity compensation by controlling the sum of the voltages of the output signals of the detection coil to be constant. This makes it possible to obtain extremely high-precision sensitivity compensation.

[0025]

As described above, according to the present invention, there are provided a means for supplying an alternating current to an excitation coil, a means for biasing a direct current component to an excitation current of an excitation coil, and a means for detecting the temperature of a sensor section. Since the configuration includes means for controlling the DC bias current based on the temperature detection signal,
The sensitivity of the sensor can be compensated by controlling the DC bias current, which reduces sensitivity errors due to temperature changes in the sensor section, making it possible to measure torque with higher accuracy over a wide temperature range. Become.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a sensitivity compensation device for a torque measuring device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing the output characteristics of the torque measuring device at room temperature.

FIG. 3 is a diagram showing the temperature characteristics of the sum of output voltages in the torque measuring device.

FIG. 4 is a diagram showing temperature characteristics of sensitivity of the torque measuring device.

FIG. 5 is a diagram showing the relationship between DC bias current and measurement sensitivity in the sensitivity compensation device of the same torque measuring device.

FIG. 6 is a diagram showing the output characteristics of the torque measuring device at high temperatures.

FIG. 7 is a circuit diagram of a sensitivity compensation device of a torque measuring device according to a second embodiment of the present invention.

FIG. 8 is a diagram showing the temperature characteristics of the excitation voltage in the torque measuring device.

FIG. 9 is a circuit diagram of a sensitivity compensation device of a torque measuring device according to a third embodiment of the present invention.

FIG. 10 is a diagram showing the temperature characteristics of the excitation current in the same torque measuring device.

FIG. 11 is a circuit diagram of a sensitivity compensation device of a torque measuring device according to a fourth embodiment of the present invention.

[Explanation of symbols]

1 Axis 6 Excitation coil 7 AC constant current source 8 DC bias current control circuit 17
Arithmetic unit 21 Excitation voltage detection circuit 23 Excitation current detection circuit 24 AC constant voltage source 25 Constant voltage control circuit

Claims (1)

[Claims] 1. A magnetically anisotropic portion is formed on the outer circumferential surface of a torque transmitting shaft, and an excitation coil and a detection coil are provided corresponding to the magnetically anisotropic portion, so that the torque applied to the torque transmitting shaft is controlled. In the magnetostrictive torque sensor, the magnitude of the torque is measured by outputting a signal corresponding to the magnitude of the torque from the detection coil. A sensitivity compensation device for a torque measuring device, comprising means for biasing a DC component, means for detecting the temperature of a sensor section, and means for controlling a DC bias current based on a temperature detection signal.