JP2806730B2 - Correction method for zero error of 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 method for correcting a zero point error of a torque sensor such as a magnetostrictive torque sensor or a strain gauge type torque sensor.

[0002]

2. Description of the Related Art For example, as a magnetostrictive torque sensor,
A magnetic anisotropic portion is formed on the outer periphery of the torque detecting shaft, and a change in the magnetic permeability of the magnetic anisotropic portion when a torque is applied to the shaft is detected by a coil provided near the magnetic anisotropic portion. Is known. In this magnetostrictive torque sensor, changes in the ambient temperature and the like occur in a sensor unit having a magnetically anisotropic part formed on the shaft, an excitation circuit for exciting the coil, and a detection circuit for processing signals from the coil. When a secular change or the like occurs, it causes a zero point error in the torque signal value.

Therefore, conventionally, in order to correct this zero point error, a torque signal value when no torque is applied to the torque detecting shaft, that is, a zero point signal value is obtained, and the zero point signal value becomes equal to or less than a fixed value. Many methods have been proposed for performing such correction.

On the other hand, in a screw tightening impulse tool, a screw tightening electric tool, a nut runner, a screw tightening machine, and a torque tester for inspecting the performance thereof, the operating torque is measured in real time. It has been proposed to incorporate the aforementioned magnetostrictive torque sensor.

[0005]

However, in a screw tightening impulse tool or the like, since the torque load acts in an impulse manner, torque is applied to the torque detecting shaft when the tool is continuously operated. There is a problem that it is a difficult task to select only when it is not performed and to obtain the torque signal value, that is, the zero point signal value at that time.

Accordingly, the present invention solves such a problem and corrects the zero point signal value of a torque sensor continuously used in a place where a torque load acts in an impulse manner so as to correct it. The purpose is to do.

[0007]

In order to achieve this object, the present invention starts measurement of torque when an absolute value of a torque signal becomes equal to or greater than a first set value, and starts the measurement at predetermined time intervals after the start. The torque signal is sampled and measured, and among a plurality of torque signal values sampled after the absolute value of the measured torque signal value becomes equal to or less than the second set value, the absolute value of the torque signal value is set to be equal to or less than the third set value. An average value of a predetermined number of torque signal values is set as a new zero point.

Further, according to the present invention, immediately after an average value of a predetermined number of torque signal values is calculated and a new zero point is set, the set data is set in a torque detection circuit. Further, in the present invention, immediately after setting the zero point setting data in the torque detection circuit, data for correcting the sensitivity of the torque sensor is set in the torque detection circuit.

[0009]

In this way, among a plurality of torque signal values measured after the pulse-shaped torque is applied, a predetermined number of average values whose absolute values are equal to or less than the third set value are set as new zero points. Therefore, a part of the pulse-like torque waveform is not used for calculating the zero point, and the zero point is accurately calculated using only the torque value when no torque is applied. Since a zero point is obtained by averaging a plurality of torque signal values, the influence of ripples superimposed on the torque signal is less likely to be obtained, and an accurate zero point is set from this point. Each time the pulse waveform of the torque signal is output, a new zero is obtained and the zero correction is performed, so that a zero shift due to hysteresis or a zero drift due to a change in ambient temperature is canceled.

Immediately after an average value of a predetermined number of torque signal values is calculated and a new zero is set, the set data is set in a torque detection circuit, so that a pulse waveform of the next torque signal appears before the next waveform appears. Stabilization of the output of the circuit element in which the data is set is completed.

Immediately after the zero point setting data is set in the torque detection circuit, data for correcting the sensitivity of the torque sensor is set in the torque detection circuit, so that the output of the circuit element in which the sensitivity correction data is set is set. Is completed before the pulse waveform of the next torque signal appears.

[0012]

FIG. 4 exemplifies a waveform of a torque signal value of a torque sensor incorporating an impulse tool. The vertical axis is the signal output voltage, and the horizontal axis is 100 msec / div on the time axis. FIG.
4 shows one waveform in FIG. 4 enlarged in time.
The scale of the vertical axis is the same as that of FIG. 4, but the horizontal axis is 1 msec / di.
Expanded to v. FIG. 6 is an enlarged view of the portion A in FIG. 5, that is, the portion where no torque acts, on both the vertical and horizontal axes. It can be seen that ripple is present as noise.

FIG. 1 shows that a deviation due to the hysteresis H has occurred in the torque signal value when no impulse-like torque is applied. However, the hysteresis H is exaggerated for easy understanding. In this case, if the zero point correction is not performed, an error occurs in the torque measurement value.

Next, a method of correcting a zero point will be described. First, the absolute value of the torque signal value Vtorque (t) is compared with the first value.
, A second set value b, and a third set value c. However, a>b> c. The torque signal value is
The sign changes depending on the direction in which the torque is applied.

When the impulse-like torque is applied and the absolute value of the torque signal value Vtorque (t) exceeds the first set value a, the torque measurement is started. When the torque measurement is started, the torque signal value Vtorque (t) is sampled and measured continuously n times at regular time intervals T0. Vtorque (t ₁₎ of the torque signal value at this time, Vtorque (t _2),
..., and Vtorque (t _n).

As time elapses, the torque signal value Vtorque
When the absolute value of (t) becomes equal to or smaller than the second set value b, the subsequent torque signal values Vtorque (t _i ), Vtorque (t)
Among the ( _{i + 1} ),..., Vtorque (t _n ), an average value of m whose absolute value is equal to or smaller than the third set value c is obtained.

Then, the average value is set as a new zero point. This ensures that a new zero is accurately obtained using only data having a small absolute value. Further, the setting data is immediately transmitted to the D / A in the torque detection circuit.
Set to a zero-point correction circuit element such as a converter. Thus, before the pulse waveform of the next torque signal appears, the stabilization of the output of the zero-point correction circuit element in which the data is set is completed.

Immediately after the zero point setting data is set in the torque detection circuit, data for correcting the sensitivity of the torque sensor is set in a sensitivity correction circuit element such as a D / A converter in the torque detection circuit. . The data for the sensitivity correction is stored in advance in a memory in the torque detection circuit, and is appropriately read according to conditions such as an ambient temperature.

As described above, by setting data for sensitivity correction immediately after setting new zero point setting data in the torque detection circuit, the sensitivity correction data can be obtained before the pulse waveform of the next torque signal appears. The stabilization of the output of the circuit element in which is set is also completed. Therefore, it is possible to prevent the error signal generated based on the settling time of the output of the circuit element such as the D / A converter from being superimposed on the pulse waveform of the next torque signal.

Next, a specific example will be described with reference to FIG.
Here, a fixed time T0 for sampling = 0.5 mse
c, the number of samples n = 15 and the predetermined number m = 5. Also,
When the voltage of the torque signal value at the time of applying the torque is a level of several V, the first set value a = 400 mV and the second set value b =
It is assumed that 300 mV and the third set value c = 100 mV.

At this time, when the impulse-like torque is applied and the absolute value of the torque signal value Vtorque (t) becomes equal to or more than the first set value 400 mV, the torque measurement is started. After the start, the torque signal value Vtorque (t) is sampled and measured 15 times every 0.5 msec for a continuous period of time. Vtorque (t ₁₎ of the torque signal value at this time, Vtorque (t _2),
.., Vtorque (t ₁₅ ).

With the passage of time, the torque signal value Vtorque
When the absolute value of (t) becomes equal to or less than the second set value 300 mV, as shown in the figure, the subsequent torque signal value Vtorque
(T ₄ ), V torque (t ₅ ),..., V torque (t ₁₅ ), the torque signal values V torque (t ₅ ), V torque (t ₆ ),... , Vtorque
The average value of the five (t ₉ ) is calculated. Then, immediately thereafter, it is set as new zero point data in a circuit element for zero point correction such as a D / A converter in the torque detection circuit.

As described above, the torque signal value is measured, the zero point is calculated, and the data is set in a circuit element for correcting the zero point, whereby the torque of the torque sensor incorporating the impulse tool as shown in FIGS. The zero drift of the signal value
Correction can be made accurately.

FIG. 2 shows an example of a circuit configuration of the magnetostrictive torque sensor. Here, reference numeral 10 denotes a torque detection shaft, and a pair of magnetic anisotropic parts 12, 12 inclined in directions opposite to each other with respect to the axis are formed on the outer peripheral surface. Around the magnetic anisotropic parts 12, 12, a pair of detection coils 14, 14 and a pair of excitation coils 16, 16 corresponding to the magnetic anisotropic parts 12, 12 are provided. The excitation coils 16, 16 are connected to an oscillation circuit 18 for supplying an alternating current.

The output lines from each of the detection coils 14, 14 are:
Each is connected to a differential amplifier 22 via rectifier circuits 20, 20. The output line from the differential amplifier 22 is a filter
It is connected to a differential amplifier 26 for zero correction via 24. The differential amplifier 26 receives, via a D / A converter 30 provided with a constant voltage generating circuit 28, zero point data for setting the sensor output to zero when no torque acts on the shaft 10. Is entered.

An output line from the differential amplifier 26 is connected to a D / A converter 32 for sensitivity correction. Numeral 34 denotes a torque signal line, on which the aforementioned torque signal value appears. Both D /
The output lines from the arithmetic control circuit 36 are connected to the A converters 30 and 32. The arithmetic control circuit 36 includes a memory 38
And the data input / output lines 40 are connected. 42 is a temperature sensor whose output line is A /
It is connected to the arithmetic and control circuit 36 via the D converter 44.
Reference numeral 46 denotes a feedback line which is connected from the torque signal line 34 to the arithmetic and control circuit 36 via an A / D converter 48.

According to such a configuration, the torque signal value appearing on the torque signal line 34 is
Is input to the arithmetic and control circuit 36 through the CPU and is subjected to arithmetic processing.
And the shift of the zero point based on the existence of the hysteresis H,
In order to correct a zero point drift or the like generated based on a change in the ambient temperature, zero point data is obtained as described above, and the zero point data is input to the differential amplifier 26 via the D / A converter 30. Is done.

The memory 38 stores data for sensitivity correction in advance. Sensitivity correction data is read from the memory 38 by the arithmetic and control circuit 36 in accordance with conditions such as the ambient temperature, and this data is sent to the D / A converter 32, so that sensitivity correction and sensitivity fluctuation due to temperature change are performed. Correction and the like are performed.

FIG. 4 shows another example of the circuit configuration of the magnetostrictive torque sensor. Here, the differential amplifier 26 for zero correction is used.
Is a rectifier circuit in the output line of one detection coil 14.
It is provided in front of 20. The rest of the configuration is the same as the circuit shown in FIG.

In the above, the case where the method of the present invention is applied to a magnetostrictive torque sensor has been described as a specific example.
Of course, the present invention can be applied to other types of torque sensors such as a strain gauge type torque sensor. It is clear that the technical idea of the present invention can be applied to various sensors other than the torque sensor described above, such as a load cell and a pressure sensor.

[0031]

As described above, according to the present invention, when the absolute value of the torque signal becomes equal to or more than the first set value, the measurement of the torque is started, and the absolute value of the measured torque signal value is changed. In order to set an average value of a predetermined number of torque signal values whose absolute values are equal to or less than the third set value as a new zero point, among a plurality of torque signal values sampled after becoming equal to or less than the second set value, Part of the pulse waveform of the torque signal is not used to calculate the zero point, and the zero point can be calculated accurately using only the torque signal value when no torque is applied, so the pulse width of the pulse waveform is unknown Or it is very advantageous to apply it when it changes.
In addition, since the zero point is obtained by averaging a plurality of torque signal values, the influence of the ripple superimposed on the torque signal is reduced, and the zero point can be set accurately from this point. Each time a pulse waveform of the torque signal is output, a new zero point is obtained and zero point correction is performed, so that zero point shift due to hysteresis and zero point drift due to a change in ambient temperature can be reliably canceled.

According to the present invention, the set data is set in the torque detection circuit immediately after the new zero is set, so that the data is set sufficiently before the pulse waveform of the next torque signal appears. Thus, it is possible to complete the stabilization of the output of the circuit element and prevent the error from being superimposed on the torque detection value.

Further, according to the present invention, immediately after the zero point setting data is set in the torque detection circuit, data for correcting the sensitivity of the torque sensor is set in the torque detection circuit, so that the sensitivity correction data is set. As for the output of the circuit element, the stabilization can be completed before the pulse waveform of the next torque signal appears, and the error signal generated by the settling time of this circuit element can be prevented from being superimposed on the torque detection value.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a state in which a shift due to hysteresis occurs in a torque signal value at a time when an impulse-shaped torque is not applied and a zero point fluctuates.

FIG. 2 is a diagram showing an example of a circuit configuration of a magnetostrictive torque sensor to which the present invention is applied.

FIG. 3 is a diagram showing another example of the circuit configuration of the magnetostrictive torque sensor to which the present invention is applied.

FIG. 4 is a diagram illustrating a waveform of a torque signal value of a torque sensor incorporating an impulse tool.

5 is a diagram showing one waveform in FIG. 4 enlarged in time.

6 is an enlarged view showing a portion A in FIG. 5;

[Explanation of symbols]

 H Hysteresis a First set value b Second set value c Third set value T0 Fixed time

Claims (3)

(57) [Claims] When the absolute value of the torque signal becomes equal to or greater than a first set value, torque measurement is started, and the torque signal is sampled and measured at regular intervals after the start, and the measured torque signal value is measured. The average value of a predetermined number of torque signal values whose absolute values are equal to or less than a third set value among a plurality of torque signal values sampled after the absolute value of the set value becomes equal to or less than a second set value is set as a new zero point. A method for correcting a zero point error of a torque sensor, wherein the method is set. 2. The torque sensor according to claim 1, wherein the set data is set in a torque detection circuit immediately after calculating an average value of a predetermined number of torque signal values and setting a new zero point. How to correct zero point error. 3. The torque sensor according to claim 2, wherein data for correcting the sensitivity of the torque sensor is set in the torque detection circuit immediately after the zero setting data is set in the torque detection circuit. Error correction method.