JP2023035345A - Sensitivity determination device and sensitivity determination method - Google Patents

Abstract

To enable a change of sensitivity with time to be determined.SOLUTION: The sensitivity determination device comprises: a signal acquisition unit 301 for acquiring a signal which is outputted by a sensor element 2; an initial sensitivity acquisition unit 304 for acquiring, for each sensor element 2, sensitivity to an external force in the initial state; a coefficient acquisition unit 305 for acquiring information that indicates a coefficient regarding external force computation per sensor element; an external force computation unit 306 for calculating an external force on the basis of the signal having been acquired by the signal acquisition unit 301 and the coefficient indicated by the information having been acquired by the coefficient acquisition unit 305; a signal computation unit 307 for calculating the value of the signal outputted for each sensor element 2 when there is no change in sensitivity, on the basis of the sensitivity having been acquired by the initial sensitivity acquisition unit 304 and the external force having been calculated by the external force computation unit 306; a change amount computation unit 308 for calculating a change amount from the difference between the value of the signal having been acquired by the signal acquisition unit 301 and the value of the signal having been calculated by the signal computation unit 307; and an aging change determination unit 309 for determining whether or not an aging change has occurred to the sensitivity of the sensor element 2 from the change amount having been calculated by the change amount computation unit 308.SELECTED DRAWING: Figure 2

Description

The present invention relates to a sensitivity determination device and a sensitivity determination method for determining changes in sensitivity over time.

A torque sensor is, in principle, a pair (two) of sensor elements, and measures torque (load around a torque axis). Here, if the strain-generating body and the sensor element that constitute the torque sensor are manufactured in an ideal state, the torque sensor can perform measurement according to the principle. However, in practice, it is difficult to manufacture the strain-generating body and the sensor element in an ideal state, and the torque sensor does not always provide sufficient measurement accuracy.
Therefore, there is known a method of increasing the number of sensor elements, obtaining multi-axis outputs, and performing correction by calculation (see, for example, Patent Document 1).

Japanese Patent Publication No. 2008-542735

The conventional method disclosed in this Patent Document 1 can eliminate the influence of the bending moment. However, the conventional method disclosed in Patent Literature 1 cannot determine changes in sensitivity over time, and erroneous outputs continue to be produced.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a sensitivity determination apparatus capable of determining changes in sensitivity over time.

The sensitivity determination device according to the present invention is attached to a strain body at intervals of 90 degrees around the axis of the strain body, and is output by four sensor elements that output signals corresponding to shear stress from the outside. a signal acquisition unit that acquires a signal; an initial sensitivity acquisition unit that acquires the sensitivity to an external force in an initial state for each sensor element; a coefficient acquisition unit that acquires information indicating a coefficient related to external force calculation for each sensor element; An external force calculation unit that calculates the external force based on the coefficient indicated by the signal obtained by the obtaining unit and the information obtained by the coefficient obtaining unit, and the sensitivity obtained by the initial sensitivity obtaining unit and the external force calculated by the external force calculation unit. A signal calculation unit that calculates the value of the signal output to each sensor element when there is no change in sensitivity, the value of the signal obtained by the signal acquisition unit, and the value of the signal calculated by the signal calculation unit based on A change amount calculation unit that calculates the amount of change by comparing the difference between the value and the amount of change, and the amount of change calculated by the change amount calculation unit is compared with a threshold value to determine whether the sensitivity of the sensor element has changed over time. and a change over time determination unit that determines whether or not there is a change.

According to this invention, since it is configured as described above, it is possible to determine the change in sensitivity over time.

2 is a diagram showing a configuration example of a torque sensor according to Embodiment 1; FIG. 3 is a diagram illustrating a configuration example of a calculation unit according to Embodiment 1; FIG. 5 is a flow chart showing an example of calculation operation of coefficients used in the calculation unit according to Embodiment 1; 4A and 4B are diagrams showing examples of states of sensor elements according to Embodiment 1. FIG. 5A and 5B are diagrams showing examples of the first signal group and the second signal group. 5 is a flowchart showing an example of torque calculation operation by a calculation unit according to Embodiment 1; 5 is a flow chart showing an example of a determination operation of a change in sensitivity over time by a calculation unit according to Embodiment 1;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Embodiment 1.
FIG. 1 is a diagram showing a configuration example of a torque sensor according to Embodiment 1. FIG.
The torque sensor, as shown in FIG. In the following description, the two pairs of sensor elements 2 may be distinguished from sensor elements (first to fourth sensor elements) 2a to 2d. Moreover, in FIG. 1, illustration of the calculating part 3 is abbreviate|omitted.

The strain-generating body 1 is made of stainless steel, for example.

A strain-generating body 1 shown in FIG. 1 is a disk-shaped member having a hole in its axis. As shown in FIG. 1, the strain generating body 1 has a fastening portion (first fastening portion) 11, a fastening portion (second fastening portion) 12, a sensing portion 13, and an external force refining portion .

The fastening portion 11 is a portion to which an external device (not shown) is fastened to one surface (one surface of the strain generating body 1). In FIG. 1 , the fastening portion 11 is provided on the outer peripheral side of the strain generating body 1 . Further, in FIG. 1 , a plurality of holes 111 are provided in the fastening portion 11 in the circumferential direction. The hole 111 is configured so that a shaft portion of a fastening member such as a bolt can be inserted. An external device is fastened to the fastening portion 11 by a fastening member through the hole 111 .

The fastening portion 12 is a portion to which an external device (not shown) different from the external device is fastened to one surface (the other surface of the strain generating body 1). In FIG. 1 , the fastening portion 12 is provided on the inner peripheral side of the strain generating body 1 . Further, in FIG. 1 , a plurality of holes 121 are provided in the fastening portion 12 in the circumferential direction. The hole 121 is configured so that a shaft portion of a fastening member such as a bolt can be inserted. An external device is fastened to the fastening portion 12 by a fastening member through the hole 121 .

The sensing portion 13 is provided between the fastening portion 11 and the fastening portion 12 and is a portion where the sensor element 2 is provided.

External force refining portion 14 is a portion provided between at least one of fastening portion 11 and fastening portion 12 and sensing portion 13 . In FIG. 1 , the external force refining section 14 is provided between the fastening section 12 and the sensing section 13 .

The external force refiner 14 has multiple circular discontinuous openings 141 . In FIG. 1, the discontinuous openings 141 are provided in multiples along the radial direction of the torque shaft (the axial center of the torque sensor). The discontinuous opening 141 is composed of non-slit portions 142 positioned rotationally symmetrically and arcuate slit portions 143 provided between the non-slit portions 142 . In FIG. 1 , the external force refining section 14 has three discontinuous openings 141 consisting of eight non-slit sections 142 and eight slit sections 143 in the radial direction of the torque shaft.

At least a part of the non-slit portions 142 has an arrangement angle around the torque axis in a plane perpendicular to the torque axis. Different from the placement angle. At this time, in the non-slit portion 142, the arrangement angle around the torque axis in the plane perpendicular to the torque axis coincides (substantially coincides) with the center of the slit portion 143 in the adjacent discontinuous openings 141 among the discontinuous openings 141. (including the meaning of

Further, at least a part of the non-slit portions 142 in the discontinuous opening 141 closest to the sensing portion 13 among the discontinuous openings 141 has an arrangement angle around the torque axis in a plane perpendicular to the torque axis that is the same as that of the sensor. It is desirable to match (including the meaning of approximately matching) the arrangement angle of the element 2 .

The configuration of the strain-generating body 1 shown in FIG. 1 is an example, and the configuration of the strain-generating body 1 is not limited to this.

The sensor elements 2 are attached to the strain-generating body 1 (the sensing portion 13 in FIG. 1) at intervals of 90 degrees (including the meaning of approximately 90 degrees) around the axis of the strain-generating body 1 . This sensor element 2 outputs a signal corresponding to shear stress from the outside. As the sensor element 2, for example, a semiconductor strain gauge or a metal strain gauge can be used.

In FIG. 1, sensor element 2a and sensor element 2c are provided along a first axis and sensor element 2b and sensor element 2d are provided along a second axis. The axial direction of the second axis differs from the axial direction of the first axis by 90 degrees around the axis of the strain body 1 . In FIG. 1, reference numeral 101 indicates a first axis and reference numeral 102 indicates a second axis.

The computation unit 3 computes torque based on the signal output from the sensor element 2 .
The calculation unit 3 also has a function (function of a sensitivity determination device) to determine a change in sensitivity with respect to external force over time based on the signal output from the sensor element 2 .

As shown in FIG. 2, the calculation unit 3 includes a signal acquisition unit 301, a coefficient acquisition unit 302, a torque calculation unit 303, an initial sensitivity acquisition unit 304, a coefficient acquisition unit 305, an external force calculation unit 306, a signal calculation unit 307, a fluctuation A quantity calculation unit 308 and a time-dependent change determination unit 309 are provided.
The calculation unit 3 is implemented by a processing circuit such as a system LSI (Large Scale Integration) or a CPU (Central Processing Unit) that executes programs stored in a memory or the like.

A signal acquisition unit 301 acquires a signal output by the sensor element 2 .

The coefficient acquisition unit 302 obtains a signal output from the sensor element 2 when a first bending moment is applied to the strain-generating body 1 and a sensor element when a second bending moment is applied to the strain-generating body 1 Based on the signal output by the element 2, information is obtained that indicates a coefficient relating to torque calculation for each sensor element 2, which is calculated according to the restrictions.
A first bending moment is a load about a first axis. A second bending moment is a load about a second axis. A coefficient related to torque calculation is a weighting coefficient used in torque calculation, and is provided for each sensor element 2 . In FIG. 1, reference numeral 103 indicates the first bending moment and reference numeral 104 indicates the second bending moment.

In the following description, the signals output by the sensor element 2 when the first bending moment is applied to the strain-generating body 1 are also referred to as a first signal group. Signals output from the sensor element 2 when the second bending moment is applied to the strain-generating body 1 are also referred to as a second signal group.
An example of a calculation method of coefficients relating to torque calculation for each sensor element 2 will be described later.

Torque calculation section 303 calculates torque based on the signal obtained by signal obtaining section 301 using the coefficient indicated by the information obtained by coefficient obtaining section 302 .

The initial sensitivity acquisition unit 304 acquires the sensitivity to external force in the initial state for each sensor element 2 . The sensitivity to the external force is a function of temperature. The sensitivity to the external force includes sensitivity to torque, sensitivity to the first bending moment, and sensitivity to the second bending moment.

The coefficient acquisition unit 305 acquires information indicating coefficients related to external force calculation for each sensor element 2 . The coefficients related to the external force calculation include a coefficient related to torque calculation, a coefficient related to first bending moment calculation, and a coefficient related to second bending moment calculation.
A coefficient related to the calculation of the first bending moment is a weighting coefficient used in the calculation of the first bending moment, and is provided for each sensor element 2 . A coefficient related to the calculation of the second bending moment is a weighting coefficient used in the calculation of the second bending moment, and is provided for each sensor element 2 .

Note that the coefficient obtaining unit 305 can obtain the information indicating the coefficient related to the torque calculation by the same method as the method used by the coefficient obtaining unit 302 .

In addition, the coefficient acquisition unit 305 can also acquire the information indicating the coefficient related to the first bending moment calculation and the coefficient related to the second bending moment calculation in the same manner as the acquisition method by the coefficient acquisition unit 302. is.
That is, the coefficient acquisition unit 305 obtains the signal output from the sensor element 2 when torque is applied to the strain-generating body 1 and the sensor element 2 when the second bending moment is applied to the strain-generating body 1 . obtains information indicating the coefficient for the first bending moment calculation for each sensor element 2, which is calculated according to the constraints, based on the signal output by .
Similarly, the coefficient acquisition unit 305 obtains the signal output by the sensor element 2 when torque is applied to the strain-generating body 1 and the sensor element when the first bending moment is applied to the strain-generating body 1 . 2, information indicating the coefficients for the second bending moment calculation for each sensor element 2, calculated according to the constraints, is obtained.

Note that FIG. 2 shows a case where the coefficient acquisition unit 305 is provided separately from the coefficient acquisition unit 302 . However, among the functions of the coefficient acquisition unit 305 , the function of acquiring information indicating coefficients related to torque calculation is the same as the function of the coefficient acquisition unit 302 . Therefore, the coefficient acquisition unit 305 may be integrated with the coefficient acquisition unit 302 .

The external force calculation unit 306 calculates an external force (current external force) based on the coefficient indicated by the signal acquired by the signal acquisition unit 301 and the information acquired by the coefficient acquisition unit 305 . That is, the external force calculator 306 calculates the current torque, the current first bending moment, and the current second bending moment.

Based on the sensitivity acquired by the initial sensitivity acquisition unit 304 and the external force calculated by the external force computation unit 306, the signal computation unit 307 computes the value of the signal output to each sensor element 2 when there is no change in sensitivity. do.

The variation calculation unit 308 calculates the variation by comparing the difference between the signal value acquired by the signal acquisition unit 301 and the signal value calculated by the signal calculation unit 307 .

The temporal change determination unit 309 determines whether or not the sensitivity of the sensor element 2 has changed over time by comparing the variation calculated by the variation calculation unit 308 with a threshold value. At this time, if the change amount over time is determined to be less than the threshold value, the change determination unit 309 determines that the sensitivity of the sensor element 2 corresponding to the change amount has not changed over time. On the other hand, when the temporal change determination unit 309 determines that the amount of variation is equal to or greater than the threshold, it determines that the sensitivity of the sensor element 2 corresponding to the amount of variation has changed with time. The threshold is set to an appropriate value in advance.

Next, an example of a calculation method of coefficients relating to torque calculation for each sensor element 2 will be described with reference to FIG.
In the torque sensor according to Embodiment 1, two pairs of sensor elements 2 are used, and torque is calculated using coefficients calculated from actual measurement results. In addition, constraints are given to the torque calculation coefficients. As a result, the torque sensor cancels out the influence of the bending moment by calculation while maintaining the output of its own machine. The bending moment includes a first bending moment, which is a load about a first axis, and a second bending moment, which is a load about a second axis.

Here, the torque measured by the torque sensor is S, the signal output from the i-th sensor element 2 is _si , and the torque calculation coefficients (first to fourth coefficients) for each signal are _ai . In this case, torque is represented by the following formula (1).
S=( _a1 * _s1 )+( _a2 * _s2 )+( _a3 * _s3 )+( _a4 * _s4 ) (1)

In a general four-sensor method, the first to fourth coefficients are all set to 0.25 as shown in the following formula (2). In contrast, the torque sensor according to the first embodiment uses the adjusted coefficient to reduce the measurement error due to the bending moment.
_a1 = _a2 = _a3 = _a4 =0.25 (2)

In the following description, the coefficient of the sensor element 2a (first coefficient) and the coefficient of the sensor element 2c (third coefficient) correspond to the coefficients of the two sensor elements 2 that are greatly affected by the first bending moment. and Further, the coefficient (second coefficient) of the sensor element 2b and the coefficient (fourth coefficient) of the sensor element 2d are assumed to correspond to the coefficients of the two sensor elements 2 which are greatly affected by the second bending moment. .

As shown in FIG. 3, in an example of a calculation method of a coefficient relating to torque calculation for each sensor element 2, first, when a first bending moment is applied to the strain-generating body 1, the signal output by the sensor element 2 is calculated as follows: acquisition (step ST301, first signal group acquisition step). In the following description, the signals output by the sensor element 2 when the first bending moment is applied to the strain-generating body 1 are also referred to as a first signal group. The middle part of FIG. 4 shows an example of the state of the sensor element 2 when the first rated bending moment is applied to the strain generating body 1 . FIG. 5A shows an example of the first signal group (measured values) when the rated first bending moment is applied to the strain generating body 1 . As shown in the middle part of FIG. 4 and FIG. 5A, when the first bending moment is applied to the strain-generating body 1, the signal output by the sensor element 2a and the signal output by the sensor element 2c have opposite signs. increases, and the values of the signal output by the sensor element 2b and the signal output by the sensor element 2d decrease (regardless of sign).
Note that the upper part of FIG. 4 shows an example of the state of the sensor element 2 when torque is applied to the strain generating body 1 .

Also, when the second bending moment is applied to the strain-generating body 1, the signal output from the sensor element 2 is obtained (step ST302, second signal group obtaining step). In the following, the signals output by the sensor element 2 when the second bending moment is applied to the strain-generating body 1 are also referred to as a second signal group. The lower part of FIG. 4 shows an example of the state of the sensor element 2 when the rated second bending moment is applied to the strain generating body 1 . FIG. 5B shows an example of the second signal group (measured values) when the rated second bending moment is applied to the strain-generating body 1 . As shown in the lower part of FIG. 4 and FIG. 5B, when the second bending moment is applied to the strain-generating body 1, the signal output by the sensor element 2b and the signal output by the sensor element 2d have opposite signs. increases, and the values of the signal output by the sensor element 2a and the signal output by the sensor element 2c decrease (regardless of sign).

Next, the initial values of the coefficients of the two sensor elements 2 among the sensor elements 2 that are greatly affected by the second bending moment are set (step ST303, initial value setting step). In the torque sensor shown in FIG. 1, the coefficient (second coefficient) of the sensor element 2b and the coefficient (fourth coefficient) of the sensor element 2d are greatly affected by the second bending moment. corresponds to In the initial value setting step, the initial value of the second coefficient and the initial value of the fourth coefficient are each set to 0.25, for example.

Next, using the coefficient set in the initial value setting step, based on the first signal group acquired in the first signal group acquisition step, according to the restrictions, so that the torque becomes 0, out of the sensor element 2 is calculated (step ST304, first coefficient calculation step). In the torque sensor shown in FIG. 1, the coefficient of the sensor element 2a (first coefficient) and the coefficient of the sensor element 2c (third coefficient) are greatly affected by the first bending moment. corresponds to

Also, the constraint is a constraint on the coefficients. These constraints include a constraint for torque sensitivity and a constraint for radial disturbance force rejection.
As a constraint for torque sensitivity, for example, there is a constraint that the sum of all coefficients is 1, which is represented by the following formula (3).
Constraints for eliminating the effects of disturbance forces in the radial direction include, for example, the sensor elements 2 arranged at 90 degrees tend to be affected by opposite influences, and in order to equalize the sum of the coefficients of the opposing sensor elements 2, There is a constraint that the sum of the coefficients of the sensor elements 2 facing each other out of the elements 2 is 0.5, which is represented by the following equation (4).
_a1 + _a2 + _a3 + _a4 =1(3)
_a1 + _a3 = _a2 + _a4 =0.5 (4)

In the case of FIG. 5A, if a ₂ =a ₄ =0.25, the values of a ₁ and a ₃ that satisfy the constraints and make S equal to 0 are a ₁ =0.256535 and a ₃ =0.25. 243465.

Further, in the first coefficient calculation step, if it is determined in the determination step that at least one of the torques is out of the set accuracy, the coefficient calculated in the second coefficient calculation step is used to perform the first signal group acquisition step. Based on the first group of signals obtained in the following constraints, the values of the coefficients of the two sensor elements 2 that are greatly affected by the first bending moment of the sensor elements 2 are changed so that the torque becomes 0. Calculate.

Next, using the coefficient calculated in the first coefficient calculation step, based on the second signal group obtained in the second signal group obtaining step, according to the constraints, the sensor element 2 is adjusted so that the torque becomes 0. The coefficient values of the two sensor elements 2 among which are greatly affected by the second bending moment are calculated (step ST305, second coefficient calculation step). The constraints used in the second coefficient calculation step are the same as the constraints used in the first coefficient calculation step.

In the case of FIG. 5B, if a ₁ =0.256535 and a ₃ =0.243465, then the values of a ₂ and a ₄ that satisfy the constraints and make S equal to 0 are a ₂ =0.24654 and a ₄ = 0.25346.

Next, using the coefficient calculated in the first coefficient calculation step and the coefficient calculated in the second coefficient calculation step, the torque is calculated based on the first signal group obtained in the first signal group obtaining step. Calculate (step ST306, first torque calculation step). The torque calculated in the first torque calculation step is also referred to as first torque and denoted by S1.

Next, using the coefficient calculated in the first coefficient calculation step and the coefficient calculated in the second coefficient calculation step, the torque is calculated based on the second signal group obtained in the second signal group obtaining step. calculation (step ST307, second torque calculation step). The torque calculated in the second torque calculation step is also called a second torque and denoted by S2.

Next, it is determined whether the torque calculated in the first torque calculation step and the torque calculated in the second torque calculation step are both within the set accuracy (S1, S2≤α in FIG. 3) (step ST308). , decision step). The setting accuracy (α shown in FIG. 3) is a threshold for judging the validity of the coefficient in the judging step, and is set in advance.

If it is determined in the determination step that at least one of S1 and S2 is greater than α, the sequence returns to step ST304.
If it is determined in the determination step that both S1 and S2 are less than or equal to α, the setting is completed.

Next, an example of torque calculation operation by the calculation unit 3 according to the first embodiment shown in FIGS. 1 and 2 will be described with reference to FIG.
1 and 2, the signal acquisition unit 301 first acquires the signal output from the sensor element 2 as shown in FIG. 6 ( step ST601, signal acquisition step).

Further, the coefficient acquisition unit 302 obtains the signal output from the sensor element 2 when the first bending moment is applied to the strain-generating body 1 and the signal output when the second bending moment is applied to the strain-generating body 1. Based on the signal output from the sensor element 2, information indicating the coefficient related to the torque calculation for each sensor element 2 calculated according to the restrictions is obtained (step ST602, coefficient obtaining step).

Next, torque calculation section 303 uses the coefficient indicated by the information obtained by coefficient obtaining section 302 to calculate the torque from equation (1) based on the signal obtained by signal obtaining section 301 (step ST603, torque calculation step).

In the above description, the coefficient acquiring unit 302 acquires information indicating coefficients obtained according to the flowchart shown in FIG. 3 . However, the coefficient acquisition unit 302 is not limited to this, and may acquire information indicating preset coefficients (for example, all 0.25) in the same manner as in a general 4-sensor method.

Next, an example of the determination operation of the change in sensitivity over time by the calculation unit 3 according to the first embodiment shown in FIGS. 1 and 2 will be described with reference to FIG.
1 and 2, the initial sensitivity acquisition unit 304 obtains the initial state of each sensor element 2 as shown in FIG. is obtained (step ST701). The sensitivity to the external force is a function of temperature. The sensitivity to the external force includes sensitivity to torque, sensitivity to the first bending moment, and sensitivity to the second bending moment.

Coefficient acquisition section 305 also acquires information indicating coefficients relating to external force calculation for each sensor element 2 (step ST702). The coefficients related to the external force calculation include a coefficient related to torque calculation, a coefficient related to first bending moment calculation, and a coefficient related to second bending moment calculation.

Next, external force calculation section 306 calculates an external force based on the coefficient indicated by the signal obtained by signal obtaining section 301 and the information obtained by coefficient obtaining section 305 (step ST703). That is, the external force calculator 306 calculates the current torque, the current first bending moment, and the current second bending moment.

Next, based on the sensitivity acquired by the initial sensitivity acquisition unit 304 and the external force calculated by the external force computation unit 306, the signal computation unit 307 determines the value of the signal output to each sensor element 2 when there is no change in sensitivity. is calculated (step ST704).

Next, fluctuation amount calculation section 308 calculates the fluctuation amount by comparing the difference between the signal value acquired by signal acquisition section 301 and the signal value calculated by signal calculation section 307 (step ST705). ).

Next, temporal change determination section 309 determines whether or not the sensitivity of sensor element 2 has changed over time by comparing the variation calculated by variation calculation section 308 with a threshold value (step ST706). At this time, if the change amount over time is determined to be less than the threshold value, the change determination unit 309 determines that the sensitivity of the sensor element 2 corresponding to the change amount has not changed over time. On the other hand, when the temporal change determination unit 309 determines that the amount of variation is equal to or greater than the threshold, it determines that the sensitivity of the sensor element 2 corresponding to the amount of variation has changed with time.

Here, for example, the signal output by the i-th sensor element 2 is assumed to be _si . In this case, s _i is represented by the following formula (5).
In equation (5), a(t) _i represents the sensitivity (coefficient) of the i-th sensor element 2 to torque at temperature (t) in the initial state. Also, S represents the torque applied to the torque sensor. Also, b(t) _i represents the sensitivity (coefficient) to the first bending moment at the temperature (t) of the i-th sensor element 2 in the initial state. Also, M1 represents the first bending moment applied to the torque sensor. Also, c(t) _i represents the sensitivity (coefficient) of the i-th sensor element 2 in the initial state to the second bending moment at the temperature (t). Also, M2 represents the second bending moment applied to the torque sensor. Also, N1 _i represents the zero point output of the i-th sensor element 2 . Also, N2 _i represents the output of the i-th sensor element 2 due to factors other than N1 _i .
s _i =a(t) _i ×S+b(t) _i ×M1+c(t) _i ×M2+N1 _i +N2 _i (5)

Then, the initial sensitivity acquisition unit 304 acquires a(t) _i . At this time, the initial sensitivity acquisition unit 304 acquires a(t) _i by acquiring the sensitivity when only torque is applied to the torque sensor for each predetermined temperature in the initial state.
Similarly, the initial sensitivity acquisition unit 304 acquires b(t) _i . At this time, the initial sensitivity acquisition unit 304 acquires b(t) _i by acquiring the sensitivity when only the first bending moment is applied to the torque sensor for each predetermined temperature in the initial state. do.
Similarly, the initial sensitivity acquisition unit 304 acquires c(t) _i . At this time, the initial sensitivity acquisition unit 304 acquires c(t) _i by acquiring the sensitivity when only the second bending moment is applied to the torque sensor for each predetermined temperature in the initial state. do.

Note that N1 _i is not necessary when correcting the zero point when using a torque sensor. Therefore, in such a case, the calculation unit 3 can exclude N1 _i .
Also, _N2i is small compared to the output change when the torque, the first bending moment and the second bending moment are applied. Therefore, the calculation unit 3 may treat _N2i as a detection error.
In this case, equation (5) is changed to the following equation (6).
s _i =a(t) _i ×S+b(t) _i ×M1+c(t) _i ×M2 (6)

Further, the coefficient acquisition unit 305 determines that when torque is applied to the torque sensor, the torque and the output match, and the torque sensor receives the first bending moment or the second bending moment, as shown in the following equation (7). Obtain information indicating the coefficients (a ₁ -a ₄ ) that, when applied, will result in an output within tolerance. Note that equation (7) is the same as equation (1). That is, the coefficient obtaining unit 305 obtains information indicating the coefficients (a ₁ to a ₄ ) obtained by the processing according to the flowchart shown in FIG.
S=( _a1 * _s1 )+( _a2 * _s2 )+( _a3 * _s3 )+( _a4 * _s4 ) (7)

Similarly, the coefficient acquisition unit 305, as in the following equation (8), when a first bending moment is applied to the torque sensor, the output matches the first bending moment, and the torque or the first Obtain information indicating the coefficients (b ₁ to b ₄ ) that result in an output within tolerance when a bending moment of 2 is applied. That is, the coefficient acquisition unit 305 is obtained by processing performed by replacing “torque” with “first bending moment” and “first bending moment” with “torque” in the flowchart shown in FIG. information indicating the coefficients (b ₁ to b ₄ ) obtained.
M1=( _b1 * _s1 )+( _b2 * _s2 )+( _b3 * _s3 )+( _b4 * _s4 ) (8)

Similarly, the coefficient acquisition unit 305, as in the following equation (9), when a second bending moment is applied to the torque sensor, the output matches the second bending moment, and the torque or the second bending moment is applied to the torque sensor. Information is obtained that indicates the coefficients (c ₁ -c ₄ ) that result in an within-tolerance output when a bending moment of 1 is applied. That is, in the flowchart shown in FIG. 3, the coefficient acquiring unit 305 replaces the "torque" with the "second bending moment", the "first bending moment" with the "torque", and the "second bending moment" with the " Acquire information indicating the coefficients (c ₁ to c ₄ ) obtained by the processing performed by replacing each with "first bending moment".
M2=( _c1 * _s1 )+( _c2 * _s2 )+( _c3 * _s3 )+( _c4 * _s4 ) (9)

Then, when a certain load is applied to the torque sensor, the external force calculation unit 306 calculates the external force (torque, the first bending moment and the second bending moment) from equations (7) to (9). can ask. Then, the signal calculator 307 can obtain the output of the i-th sensor element 2 when there is no change in sensitivity from equation (2).

Here, when the output sensitivity of the torque sensor does not fluctuate, the value calculated by the signal calculation unit 307 and the actual value obtained by the signal acquisition unit 301 match within the threshold. On the other hand, when the output sensitivity of the torque sensor fluctuates, the value calculated by the signal calculation unit 307 and the actual value obtained by the signal acquisition unit 301 do not match within the threshold. Therefore, the secular change determination unit 309 can determine the presence or absence of secular change (failure detection) by making this determination.

Thus, each of the four sensor elements 2 has a unique ratio of output change (sensitivity) to torque, first bending moment and second bending moment. Therefore, in the calculation unit 3 (sensitivity determination device) in the first embodiment, the ratio of the output change in the initial state of the sensor element 2 is obtained, and the ratio in the initial state is established from the current output of the sensor element 2. By confirming, it is determined that there is no change in output due to aging. As a result, the calculation unit 3 according to the first embodiment can determine whether or not the sensitivity changes over time from the output of the sensor element 2, eliminating the need to measure the sensitivity using a separately provided sensor.

Note that FIG. 1 shows the case where the sensor elements 2a and 2c are provided along the first axis, and the sensor elements 2b and 2d are provided along the second axis. However, the present invention is not limited to this, and the sensor elements 2a and 2c may be displaced with respect to the first axis, and the sensor elements 2b and 2d may be displaced with respect to the second axis. may have been On the other hand, from the viewpoint of signal processing, it is desirable that the sensor elements 2a and 2c are provided along the first axis, and the sensor elements 2b and 2d are provided along the second axis.

In the above description, the case where the external force for determining the sensitivity is the torque, the first bending moment, and the second bending moment is shown. However, the external force for determining the sensitivity is not limited to this, and may be one or more of torque, the first bending moment, and the second bending moment.

Moreover, in the above description, the calculation unit 3 included in the torque sensor has the function of the sensitivity determination device. However, the present invention is not limited to this, and the sensitivity determination device may be separate from the torque sensor.

As described above, according to the first embodiment, the sensitivity determination device is attached to the strain-generating body 1 at intervals of 90 degrees around the axis of the strain-generating body 1, and the signal corresponding to the external shear stress is A signal acquisition unit 301 that acquires the signals output by the four sensor elements 2 that output , an initial sensitivity acquisition unit 304 that acquires the sensitivity to the external force in the initial state for each sensor element 2, and each sensor element A coefficient acquisition unit 305 that acquires information indicating a coefficient related to external force calculation, and an external force calculation unit 306 that calculates the external force based on the coefficient indicated by the signal acquired by the signal acquisition unit 301 and the information acquired by the coefficient acquisition unit 305. and a signal calculation unit that calculates the value of the signal output to each sensor element 2 when there is no change in sensitivity, based on the sensitivity acquired by the initial sensitivity acquisition unit 304 and the external force calculated by the external force calculation unit 306. 307, a variation calculation unit 308 that calculates a variation by comparing the difference between the signal value acquired by the signal acquisition unit 301 and the signal value calculated by the signal calculation unit 307; A time-dependent change determination unit 309 is provided for determining whether or not the sensitivity of the sensor element 2 has changed over time by comparing the amount of change calculated by the calculation unit 308 with a threshold value. As a result, the sensitivity determination device according to the first embodiment can determine changes in sensitivity over time.

It should be noted that, within the scope of the present invention, any component of the embodiment can be modified or any component of the embodiment can be omitted.

1 strain-generating body 2 sensor element 3 calculation unit 11 fastening portion (first fastening portion)
12 fastening portion (second fastening portion)
13 sensing part 14 external force purification part 111 hole 121 hole 141 discontinuous opening part 142 non-slit part 143 slit part 301 signal acquisition part 302 coefficient acquisition part 303 torque calculation part 304 initial sensitivity acquisition part 305 coefficient acquisition part 306 external force calculation part 307 signal calculation unit 308 variation calculation unit 309 change over time determination unit

Claims (4)

a signal acquisition unit that acquires signals output from four sensor elements that are attached to the strain body at intervals of 90 degrees around the axis of the strain body and that output signals corresponding to shear stress from the outside;
an initial sensitivity acquisition unit that acquires the sensitivity to an external force in an initial state for each of the sensor elements;
a coefficient acquisition unit that acquires information indicating a coefficient related to external force calculation for each sensor element;
an external force calculation unit that calculates an external force based on the coefficient indicated by the signal acquired by the signal acquisition unit and the information acquired by the coefficient acquisition unit;
a signal calculation unit that calculates the value of the signal that is output to each sensor element when there is no change in sensitivity, based on the sensitivity acquired by the initial sensitivity acquisition unit and the external force calculated by the external force calculation unit;
a variation amount calculation unit that calculates a variation amount by comparing the difference between the signal value obtained by the signal obtaining unit and the signal value calculated by the signal calculation unit;
A sensitivity determination device comprising: a time-dependent change determination unit that determines whether or not the sensitivity of the sensor element changes over time by comparing the variation calculated by the variation calculation unit with a threshold value. The external force is any one or more of torque, a first bending moment, and a second bending moment whose axial direction differs from the first bending moment by 90 degrees about the axis of the strain body. The sensitivity determination device according to claim 1, characterized by: The coefficient acquisition unit receives a signal output from the sensor element when one of the external forces is applied to the strain body and the other one of the external forces applied to the strain body. Acquisition of information indicating a coefficient relating to the calculation of the remaining one of the external forces for each of the sensor elements, which is calculated according to the restrictions based on the signal output by the sensor element when the external force is applied. 3. The sensitivity determination device according to claim 2, wherein: A signal acquisition unit is attached to the strain body at intervals of 90 degrees around the axis of the strain body, and acquires signals output from four sensor elements that output signals corresponding to external shear stress. a step;
an initial sensitivity acquisition unit acquiring the sensitivity to an external force in an initial state for each of the sensor elements;
a step in which a coefficient acquisition unit acquires information indicating a coefficient related to external force calculation for each of the sensor elements;
an external force calculation unit calculating an external force based on the coefficient indicated by the signal acquired by the signal acquisition unit and the information acquired by the coefficient acquisition unit;
A signal calculation unit calculates a value of a signal to be output to each sensor element when there is no change in sensitivity, based on the sensitivity obtained by the initial sensitivity obtaining unit and the external force calculated by the external force calculation unit. a step;
a step of calculating a variation amount by a variation calculation unit by comparing a difference between the signal value acquired by the signal acquisition unit and the signal value calculated by the signal calculation unit;
A sensitivity determination method comprising a step of determining whether or not the sensitivity of the sensor element changes over time by comparing the amount of change calculated by the amount-of-variation calculation unit with a threshold value.

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