JP2803966B2 - 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 known magnetostrictive torque sensor, a pair of magnetic anisotropic portions are formed on the outer periphery of a torque detecting shaft, and the magnetic permeability of each magnetic anisotropic portion when a torque is applied to the shaft. Is detected by a pair of detection coils arranged near these magnetic anisotropic parts, and the difference between the two detection signals is obtained, so that the magnitude of the torque acting on this shaft is converted into an electric signal. There is something that I did.

[0003]

In this type of magnetostrictive torque sensor, within a certain period of time after the power is turned on, an exciting portion for exciting a sensor portion having a magnetically anisotropic portion formed on a shaft or a detecting coil is provided. A zero point shift may occur in the torque detection output due to a change in ambient temperature in a circuit or a detection circuit that processes a signal from the detection coil. That is, even if the sensor itself has no abnormality, there is a problem that the zero point of the sensor may shift by warm-up drift. Also, in other types of torque sensors, a zero point shift may occur similarly.

Accordingly, an object of the present invention is to solve such a problem and to make it possible to easily and reliably correct a zero-point shift in a torque sensor immediately after power is turned on.

[0005]

SUMMARY OF THE INVENTION In order to achieve this object, the present invention measures a predetermined number of torque signals after a lapse of a predetermined time after the power supply of a torque sensor is turned on. When the difference between the maximum value and the minimum value is equal to or smaller than the first set value, an average value of the predetermined number of torque signal values is obtained, and when the absolute value of the average value is equal to or smaller than the second set value. Then, the average value is set as a new zero point.

[0006]

In this manner, only when the difference between the maximum value and the minimum value of the predetermined number of torque signal values is equal to or smaller than the first set value, the average value is set as a new zero point.
The signal waveform when the torque is applied after the power is turned on is not used as the basis for calculating the zero point, and the zero point can be accurately calculated using only the data when the torque signal is stable without the torque being applied. Then, the zero point shift is corrected. Since the zero point is obtained by averaging a predetermined number of torque signal values, the zero point is hardly affected by the ripple superimposed on the torque signal, and an accurate zero point is set from this point. Since a new zero point setting is performed only when the absolute value of the average value is equal to or less than the second set value, the zero point setting is not performed by the data when the zero point exceeds the second set value.

[0007]

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. Part A in FIG. 5 shows a part where no torque is applied, and this part A is a zero point when torque is detected.

FIG. 1 shows an example of a zero point shift immediately after the power of the sensor is turned on in a state where no torque is applied to the torque detecting shaft of the torque sensor. As shown,
Even in a normal state, the zero point may shift by the warm-up drift.

Next, a method of correcting the zero point shifted in this manner will be described. First, when the power supply of the torque sensor is turned on, after a predetermined time t ₀ has elapsed,
Start torque measurement. At this time, n
The torque signal value Vtorque (t) is sampled and measured continuously. The torque signal value at this time is Vtorque (t ₁ ),
Vtorque (t ₂ ),..., Vtorque (t _n ).

First, it is checked whether or not the difference between the maximum value and the minimum value of the sampled and measured n torque signal values is equal to or less than a first set value b. That is, [max. ｛Vtorque (t ₁ ), Vtorque (t ₂ ),..., Vto
_{rque (t n)} -.} min {Vtorque (t 1), Vtorque
(T ₂ ),..., Vtorque (t _n )｝] ≦ b is checked.

When this inequality holds,
Torque signal values Vtorque (t _i ), V torque (t _{i + 1} ),
.., An average value M of Vtorque (t _{n−j + 1} ) [i ≧ 1, j ≧ 1] is obtained. Further, it is determined whether or not the absolute value of the average value M is equal to or less than a second set value c.
If it is below, the average value M is set as a new zero point. The sign of this average value changes depending on the direction of the torque load.

At this time, when i = 1 and j = 1 are set, all the sampled torque signal values are used for calculating the average value. However, when i is set to 2 or more, an average value is calculated excluding the first part of a large number of sampled torque signal values.
When j is set to 2 or more, an average value is calculated except for the last part of a large number of torque signal values. After all, by setting both i and j to be 2 or more, a new torque signal value of only a plurality of torque signal values in the remaining intermediate portion excluding the first part and the last part of a large number of torque signal values is obtained. Zeros are calculated. In this way, even if the start of torque measurement and the torque acting on the shaft are not synchronized, a new zero can be accurately obtained using only data having a small absolute value.

If the absolute value of the average value M exceeds the second set value c, it can be determined that the zero point shift is abnormal as shown by the broken line in FIG. Therefore, no new zero is set at this time.

When the difference between the maximum value and the minimum value of the torque signal value exceeds the first set value b, there is a possibility that the torque is applied, so no new zero point is set at that time, too. After a certain time T has passed,
The torque measurement is started in the same manner.

Thereafter, as shown in FIG. 1, since the zero point shift may continue, the above operation is repeated at regular intervals T until the zero point correction is completed. Next, a specific example will be described. Here, a predetermined time t ₀ = 5 sec, a fixed time T0 for sampling = 0.5 msec, and a period T = 20 ms.
Let ec be the number of samples n = 9, i = 3, j = 3. Also,
When the voltage of the torque signal value at the time of applying the torque is several V, the first set value b = 200 mV and the second set value c =
Set to 1000mV.

At this time, after a predetermined time t ₀ = 5 sec has elapsed after the power supply of the torque sensor is turned on, the torque measurement is started, and after the start, the torque signal value Vtorque is continuously set nine times every fixed time T0 = 0.5 msec. (T) is measured by sampling. Then, the result is stored in a memory or the like by A / D conversion or the like. The torque signal value at this time is Vtorq
ue (t ₁ ), Vtorque (t ₂ ),..., Vtorque (t ₉ ).

These torque signal values Vtorque (t ₁ ), Vto
rque (t _2), ..., determine the maximum and minimum values among Vtorque (t _9), if the difference between these maximum and minimum values is equal to or less than the first set value b = 200 mV, a torque signal Value Vtorque
The average value M of the five data of (t ₃ ), Vtorque (t ₄ ),..., Vtorque (t ₇ ) is calculated. When the absolute value of the average value M is equal to or less than the second set value c = 1000 mV,
With this as a new zero point, the magnitude of the applied torque is determined from the subsequent torque signal value.

By doing so, the occurrence of a zero point error due to the zero point shift immediately after the power supply of the torque sensor as shown in FIG. 1 is reliably prevented. When the absolute value of the average value M exceeds the second set value c = 1000 mV, it is determined that the zero point is abnormal, and the zero point correction is not performed, and the elapse of the period T = 20 msec is waited. In this case, the controller connected to the torque sensor can detect the zero point abnormality of the torque sensor. Also, the torque signal values Vtorque (t ₁ ), Vto
When the difference between the maximum value and the minimum value among rque (t ₂ ),..., Vtorque (t ₉ ) exceeds the first set value b = 200 mV, it is determined that torque is applied, and in this case, Does not perform zero point correction and waits for the elapse of a period T = 20 msec.

Thereafter, the above operation is repeated at regular intervals T = 20 msec until the zero point correction is completed and the routine shifts to a normal measurement routine. As described above, by detecting the zero point error when the power supply of the torque sensor is turned on, it is possible to correctly detect the abnormality of the zero point shift of the torque sensor at that time as shown in FIG. If not, the zero point error at the time of turning on the power can be accurately corrected. Also in the torque sensor incorporated in the impulse tool having a torque waveform as shown in FIG. 4 and FIG. 5, since it is usual that no torque is applied to the tool immediately after the power supply of the torque sensor is turned on. In addition, the zero point error based on the zero point shift when the power is turned on can be corrected.

Only when the difference between the maximum value and the minimum value of the sampled torque signal values is equal to or smaller than the first set value b, the average value M is set as a new zero point.
If the difference between the maximum value and the minimum value is increased immediately after the power is turned on and the difference between the maximum value and the minimum value is increased, zero point correction is not performed, and only the data when the torque is not applied and the torque signal is stabilized is used, The zero can be accurately corrected.

FIG. 2 shows an example of a circuit configuration of the magnetostrictive torque sensor. Here, reference numeral 10 denotes a torque detection shaft, and only one magnetic anisotropic portion 12 inclined with respect to the axis is formed on the outer peripheral surface thereof. Around this magnetic anisotropic part 12, a coil
14 are located.

The coil 14 supplies an alternating current to the coil 14 via a resistor 16 and a temperature-sensitive resistor 18 shown by a solid line in the figure and roughly adjusting a zero point fluctuation due to a temperature change. To the oscillation circuit 20 for The temperature-sensitive resistor 18 can be provided between the resistor 16 and the coil 14 as shown by a broken line in the drawing, or can be provided at another place. The resistor 16 has a resistance value substantially equal to the impedance of the coil 14. Oscillation circuit
An excitation voltage detection circuit 22 having a rectifier circuit and a low-pass filter is connected in parallel between the resistor 20 and the temperature-sensitive resistor 18.

The output line from the coil 14 constitutes a torque detecting circuit 24 having a rectifier circuit and a low-pass filter. The output side of the torque detection circuit 24 and the output side of the excitation voltage detection circuit 22 are both connected to the input side of the differential amplifier 26. The output side of the differential amplifier 26 is connected to a differential amplifier 28 for fine adjustment of zero point fluctuation. Zero point data is obtained from the average value M of the above-mentioned sampled measurement data, and the zero point data is input to a differential amplifier 28 via a D / A converter 32 provided with a constant voltage generating circuit 30. The differential amplifier 28 functions to make the torque detection output at that time zero.

The output side of the differential amplifier 28 is connected via an amplifier 34 to a polarity determining circuit 36 for detecting the direction of the torque applied to the torque detecting shaft 10 by a known method, and a gain switching circuit 38. ing. The gain switching circuit 38 is a polarity determination circuit
Based on the output signal 36, the gain of the torque detection signal can be switched according to the direction of the torque applied to the torque detection shaft 10. Numeral 40 denotes a torque signal line, on which the aforementioned torque signal value appears.

The output line from the arithmetic and control circuit 42 is connected to the D / A converter 32 and the gain switching circuit 38. The arithmetic control circuit 42 has a memory 44 arranged in parallel and a data input / output line 46 connected thereto. Reference numeral 48 denotes a temperature sensor whose output line is connected to the arithmetic and control circuit 42 via an A / D converter 50. Reference numeral 52 denotes a feedback line, which is connected to the A / D converter 54 from the torque signal line 40.
Is connected to the arithmetic and control circuit 42 via the.

According to such a configuration, the function of the temperature-sensitive resistor 18 performs a coarse adjustment of the zero point fluctuation accompanying the temperature fluctuation. The torque signal value appearing on the torque signal line 40 is
The data is input to the arithmetic control circuit 42 via the feedback line 52, and is subjected to arithmetic processing. Then, in order to correct the zero point shift immediately after the power is turned on, zero point data based on the above average value M is obtained, and the zero point data is input to the differential amplifier 28 via the D / A converter 32.

In the gain switching circuit 38, sensitivity correction and sensitivity fluctuation correction due to temperature change are performed based on a signal from the arithmetic and control circuit 42. As shown in FIG. 1, despite the fact that only about 10 samplings are performed every fixed time T0 = 0.5 msec, the start of the torque measurement for correcting the zero point fluctuation is started at a fixed period T0.
= Every 20 ms. The reason for this is that the arithmetic processing circuit 42 must perform many arithmetic processes such as the above-described correction of the sensitivity fluctuation due to the temperature change, in addition to the zero point correction, and secures the time.

FIG. 3 shows an example of a magnetostrictive torque sensor of the digital correction type. Here, the output line from the differential amplifier 26 is connected to the arithmetic and control circuit 42 via the A / D converter 56. The torque signal line 40 is derived from the arithmetic and control circuit 42 via a D / A converter 58.

In the torque sensor 1 of the digital correction system, the operation of correcting the zero point shift based on the present invention and various other corrections similar to those of the analog system are performed by the arithmetic control circuit 42 by digital calculation.

In such a case where the correction is performed by the digital operation, in order to accurately measure the pulse torque signal as shown in FIGS.
It must be converted at a high speed by the / D converter 56.
Specifically, for example, a sampling interval of 0.02 msec and a sample number of about 100 to 200 are required.

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.

[0032]

As described above, according to the present invention, in order to set an average value of a predetermined number of torque signal values after turning on the power of the torque sensor as a new zero point, the zero point shift immediately after turning on the power is corrected. Not only is it possible to prevent the occurrence of a zero error based on the zero shift, but also when the difference between the maximum value and the minimum value of the measured predetermined number of torque signal values is less than or equal to the first set value, the predetermined number of torque signal values can be prevented. Since the average value of the torque signal value is obtained, it is possible to prevent the signal waveform when the torque is applied after the power is turned on from being used as a basis for calculating the zero point, and the torque signal is stable without the torque being applied. The zero point shift can be corrected by accurately calculating the zero point based only on the data at the time, and the zero point is obtained by averaging a predetermined number of torque signal values. The new zero point is set only when the absolute value of the average value is equal to or less than the second set value, so the zero point is set by the data when the zero value exceeds the second set value. Can be prevented.

[Brief description of the drawings]

FIG. 1 is a diagram showing a zero point shift immediately after the power supply of a torque sensor is turned on.

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.

[Explanation of symbols]

t ₀ predetermined time T0 fixed time Vtorque (t) torque signal value M average value b first set value c second set value

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-157643 (JP, A) JP-A-5-10777 (JP, A) JP-A-4-49882 (JP, A) JP-A-3-3 78633 (JP, A) JP-A-2-10227 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01L 25/00 G01D 3/028 G01L 3/10

Claims (3)

(57) [Claims] 1. A torque signal is measured at regular time intervals after a lapse of a predetermined time after power-on of a torque sensor,
When the difference between the measured maximum value and the minimum value of the predetermined number of torque signal values is equal to or less than the first set value, an average value of the predetermined number of torque signal values is obtained, and the absolute value of the average value is calculated. A method for correcting a zero point error of a torque sensor, wherein the average value is set as a new zero point when the value is equal to or less than a second set value. 2. The torque sensor according to claim 1, wherein when the absolute value of the average value exceeds the second set value, it is determined that the zero point is abnormal and a new zero point is not set. Method. 3. When the difference between the maximum value and the minimum value of the measured predetermined number of torque signal values exceeds a first set value, the measurement of the torque signal is started again after a certain time. 3. The method for correcting a zero point error of a torque sensor according to claim 1 or 2.