JPH0694550A - Ultrasonic torque sensor - Google Patents

Abstract

PURPOSE:To obtain an ultrasonic torque sensor capable of accurately measuring torque over a range from minute torque to large torque with high accuracy, capable of measuring both of static torque and dynamic torque and not requiring a correction circuit correcting the effect of ambient temp. CONSTITUTION:Two sets of ultrasonic transmitters 32a, 34a and ultrasonic receivers 32b, 34b are arranged on the surface of a piezoelectric element 30 so that an ultrasonic wave propagates in directions mutually crossing the surface of the piezoelectric element 30 at a right angle. Further, feedback circuits 36a, 36b applying the signals received by the ultrasonic receivers 32b, 34b to the ultrasonic transmitters 32a, 34a are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic torque sensor for measuring torque acting on a power transmission shaft of a rotating machine.

[0002]

2. Description of the Related Art Conventionally, there are known torque sensors for measuring torque acting on a power transmission shaft and the like as shown in the following (1) to (4). (1) Attach the strain gauge to the surface of the power transmission shaft,
A strain gauge torque sensor that measures torque by measuring changes in electrical resistance and determining strain.

(2) A magnetic torque sensor that measures torque by utilizing the fact that the magnetic permeability of the power transmission shaft changes with the magnitude of the stress acting on the power transmission shaft. (3) A phase difference torque sensor that measures torque by measuring the twist acting on the power transmission shaft. (4) A piezoelectric torque sensor that measures torque by inserting a piezoelectric element into a power transmission shaft and measuring a potential difference generated in the piezoelectric element when the piezoelectric element is twisted due to twisting of the power transmission shaft.

[0004]

The torque sensor is required to have a condition that both static torque and dynamic torque can be measured, and that the measurement accuracy is good and the dynamic range is wide (from small torque to large torque can be measured). ing. However, the above-mentioned conventional torque sensors have their respective drawbacks, and cannot satisfy all of these conditions at the same time.

For example, the piezoelectric element torque sensor has a problem that only static torque can be measured because the response of the measuring circuit is slow. Further, in the strain gauge torque sensor, the magnetic torque sensor, and the piezoelectric torque sensor, in order to measure a minute torque, the torsion bar that is the subject must be thin. However, it is impossible to make the torsion bar thin and measure a large torque because of the strength problem of the torsion bar, so that there is a problem that the dynamic range becomes narrow.

Further, in the magnetic torque sensor and the phase difference torque sensor, the measured voltage is sent as it is through the slip ring. Therefore, when the measured voltage is low, the electromagnetic interference and noise make the measurement inaccurate and the measurement accuracy deteriorates. There's a problem. In view of the above circumstances, the present invention is capable of accurately measuring from a small torque to a large torque with high accuracy, and a static torque,
It is an object of the present invention to provide an ultrasonic torque sensor capable of measuring any dynamic torque.

[0007]

An ultrasonic torque sensor of the present invention which achieves the above object is an ultrasonic torque sensor for measuring a torque acting on an object to be measured. A first ultrasonic transmitter and a first ultrasonic transmitter arranged on the surface of the object to be measured so as to propagate in a first direction of
And the second ultrasonic transmitter and the second ultrasonic transmitter, which are arranged on the surface of the object to be measured so that the ultrasonic waves propagate in the second direction intersecting the surface of the object to be measured. And an ultrasonic receiver of the above.

Further, the first and second ultrasonic transmitters,
And each of the first and second ultrasonic receivers,
It is preferably a comb-shaped electrode arranged on the piezoelectric element.

[0009]

It is known that the velocity of sound propagating in an object changes in accordance with the change of internal stress of the object. Then, in order to measure the torque acting on the measured object from the frequency change of the sound propagating through the measured object, the inventor applies the torque T to the measured object and twists the measured object. As a result, it was verified by experiments that there is a proportional relationship between the torque T and the frequency change Δf when a shear stress is generated in this measured object. This experiment will be described with reference to FIGS. 1, 2 and 3.

FIG. 1 is a perspective view showing the outline of the experimental apparatus, and FIG.
Is a schematic diagram showing a schematic structure of an ultrasonic oscillation circuit used in an experiment, and FIG. 3 is a graph showing an experimental result. As shown in FIG. 1, one set of interdigital electrodes 1 is formed on the surface of a piezoelectric element 12 arranged on the surface of an aluminum plate 10 having a thickness of 3 mm and a width of 50 mm.
4 is attached (the combination of this piezoelectric element and the interdigital transducer is called a surface acoustic wave element), the torque T and the frequency change Δ
The relationship with f was measured.

When a feedback amplifier 16 is connected to the surface acoustic wave device shown in FIG. 1 to form an ultrasonic oscillator circuit as shown in FIG. 2, the ultrasonic oscillator circuit has the following formula: f = (v _s / d) (N−φ _E / 2π) (1) d: distance between electrodes, v _s : velocity of surface wave, φ _E : amount of phase shift of amplifier, n: oscillation at integer frequency.

When the distance d between the electrodes and the surface wave velocity v _s change, the frequency f also changes. Where Δf and Δ
When d and Δv _s are changes in frequency, distance, and speed, respectively, from equation (1), Δf / f = Δv _s / v _s −Δd / d (2) Since Δd / d is very small when the deformation of the piezoelectric element 12 is small, Δf / f = Δv _s / v _s can be obtained.
As a result, a change in the surface acoustic velocity of the piezoelectric element is detected as a change in frequency.

The solid line in FIG. 3 shows the theoretical value, and the broken line shows the measured value. As shown in FIG. 3, a relationship of Δf = K · T (K: constant) is established between the torque T and the frequency change Δf. Therefore, the rate of change of the sound velocity of the ultrasonic wave propagating through the measured object can be detected as a frequency change, and the torque acting on the measured object can be measured by the frequency change of the ultrasonic wave.
In the ultrasonic torque sensor of the present invention, the ultrasonic waves respectively oscillated from the first and second ultrasonic transmitters propagate across the surface of the measured object in the first and second directions, respectively, and respectively propagate to the first and second directions. It is received by the first and second ultrasonic receivers. The sound velocity of the ultrasonic wave propagating in each of the first direction and the second direction changes with a change in the torque acting on the measured object. Therefore, as described above, the frequencies of the ultrasonic waves received by the first and second ultrasonic receivers change according to the magnitude of the torque acting on the measured object. Therefore, the torque value can be obtained by measuring this frequency. The magnitude of the torque acting on the measured object can also be obtained by obtaining the phases of the frequencies received by the first and second ultrasonic receivers.

Since the frequency of the ultrasonic wave is high and the torque is measured by measuring the propagation speed of the ultrasonic wave, the followability is good even when the changing speed of the torque is fast, and the static torque and the dynamic torque can be measured. , High resolution. Moreover, since the frequency is output to the external device as an output signal, the measurement accuracy is good without being affected by the electromagnetic environment. Moreover, since the frequency can be displaced in a wide range, the dynamic range is wide. Further, since the two sets of ultrasonic transmitters and ultrasonic receivers are used, the influences of the ambient temperature on the frequencies cancel each other out. Therefore, it is not necessary to make a correction in consideration of the influence of the ambient temperature.

When each of the ultrasonic oscillator and the ultrasonic receiver is a comb-shaped electrode arranged on the piezoelectric element, an ultrasonic torque sensor that is easy to handle can be obtained.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an ultrasonic torque sensor according to a first embodiment of the present invention will be described with reference to FIGS. 4, 5 and 6. FIG. 4 is a perspective view showing a state in which the interdigital electrode including the ultrasonic transmitter and the ultrasonic receiver of the ultrasonic torque sensor of the first embodiment is attached to the twisted portion connected to the rotating shaft. .

The ultrasonic torque sensor 20 includes a rotary shaft 22.
This is a device for measuring the torque acting on a and 22b, and a torsion bar 26 having a twisted portion 24 that is twisted by the action of the torque is provided on the torsion bar 26 and the rotary shaft 2.
Mounting members 28a, 28b for mounting 2a, 22b
It is attached to the rotating shafts 22a and 22b via. The mounting members 28a and 28b are respectively attached to the rotary shaft 22a and
It is configured to rotate together with 22b. Twisted part 24
2 sets of interdigital electrodes 32 on the surface of the piezoelectric element 30.
The surface acoustic wave element constituted by arranging a, 32b and 34a, 34b is attached. Ultrasonic waves are oscillated from the interdigital electrodes 32a and 34a, and these ultrasonic waves propagate orthogonally to each other on the surface of the piezoelectric element 30 and are received by the interdigital electrodes 32b and 34b, respectively. Also, the interdigital electrodes 32a, 32b and 34a, 34b.
Are connected to feedback amplifiers 36a built in the mounting members 28a and 28b (the feedback amplifier 36b built in the mounting portion 28b is not shown), and are connected to two sets of ultrasonic oscillation circuits (see FIG. 5 described later). Are formed. The feedback amplifier 36a is protected by a cover 38a. The signals representing the frequencies of the ultrasonic waves circulating in the two ultrasonic wave oscillating circuits are respectively slip rings 40a and 4a.
It is input to an arithmetic circuit (not shown) through 0b or the like and converted into torque by this arithmetic circuit.

Next, the operation of the above-described ultrasonic torque sensor will be described with reference to FIGS. FIG. 5 is a configuration diagram showing a schematic configuration of two sets of ultrasonic oscillation circuits, and FIG. 6 is a block diagram showing a schematic configuration of an ultrasonic torque sensor including the ultrasonic oscillation circuit shown in FIG. Rotating shaft 22 shown in FIG.
When torque is applied to a and 22b, the twisted portion 24 is twisted according to the torque, so that strain is generated in the piezoelectric element 30 and the transverse wave velocity of the ultrasonic wave propagating on the surface of the piezoelectric element 30 changes. As a result, two sets of ultrasonic oscillator circuits 42
The oscillation frequencies of a and 42b change. The signals representing the changes in these two oscillation frequencies are converted into converters 44a and 44, respectively.
In b, the frequency signal is converted into a voltage signal, and this voltage signal is input to the arithmetic circuit 46 and converted into a torque value by the arithmetic circuit 46. Thereby, the rotary shafts 22a, 22b
The torque exerted on is measured, and the result is displayed on a display device (not shown).

Next, the calculation performed by the calculation circuit to obtain the torque by measuring the change in frequency using two sets of ultrasonic oscillation circuits will be described. When the measured object is a rigid body, Δf / f = Δv / v holds as described above. Here, v _T0 : When no stress is applied to the piezoelectric element 30,
From the interdigital electrode 32a (34a) to the interdigital electrode 32b (3
4b) Sound velocity of ultrasonic wave v _T1 : Propagation speed of ultrasonic wave from the interdigital transducer 32a to the interdigital transducer 32b when stress is applied to the piezoelectric element 30 v _T2 : Stress is applied to the piezoelectric element 30 At this time, the sound velocity f of the ultrasonic wave propagating from the interdigital transducer 34a to the interdigital transducer 34b f: When no stress is applied to the piezoelectric element 30,
From the interdigital electrode 32a (34a) to the interdigital electrode 32b (3
4b) The frequency of ultrasonic waves propagating to Δf ₁ : When the stress is applied to the piezoelectric element 30, the change in frequency of the ultrasonic waves propagating from the interdigital transducer 32a to the interdigital transducer 32b Δf ₂ : The stress is applied to the piezoelectric element 30. when the added ultrasonic frequency variation k propagating from interdigital electrodes 34a to interdigital electrode 34b: when the _{coefficient, (v T1 -v T0) /} v T0 = k (Δf 1 / f) ... (3 ) (V _T2 −v _T0 ) / v _T0 = k (Δf ₂ / f) (4)

Τ _max : Shear stress acting on the piezoelectric element σ ₁ : Compressive stress generated by τ _max σ ₂ : Tensile stress generated by τ _max C _A : Coefficient: | (1/2) (σ ₂ − _{σ 1) | = | τ max} | ... (5) C a (σ 2 -σ 1) = (v T2 -v T1) / v T0 ... are known to be (6), equation (4) - equation (3), equation (5), (v _T2 -v _T1) from equation _{(6) / v T0 = k} {(Δf 2 / f) - (Δf 1 / f)} = C A (σ 2 - sigma ₁₎ = a _{(C a / 2) τ max} ... (7).

As a result, 2k {(Δf ₂ / f)-(Δf
_{1 / f)} = C A} · τ max τ max = (2k / C A) {(Δf 2 / f) - (Δf 1 /
f)} can be used to measure τ _max . Further, the torque T is T = κa
because it is b ² τ _max (κab ² is a shape ^{factor), T = κab 2 · (} 2k / C A) {(Δf 2 / f) - (Δ
f ₁ / f)} and the torque is obtained.

As shown in FIG. 7, the ultrasonic oscillator circuit 4
The transmitting circuit 48a is connected to 2a to transmit a frequency signal by radio waves, the receiving circuit 50a receives the frequency signal, the converter 44a for converting the frequency signal into a voltage signal converts it into a voltage signal or the like, and the arithmetic circuit 46 calculates the torque. It is also possible to adopt a configuration that allows it. Next, it will be described that the ultrasonic torque sensor does not need to be corrected even if the temperature around the surface acoustic wave element changes.

The torque T is, as described above, T = {(2kκ
ab ² ) / (C _A f)} (Δf ₂ −Δf ₁ ). However, the actually measured frequency is a frequency that is changed under the influence of a change in the ambient temperature of the surface acoustic wave element. If this displacement is δ, then Δf ₁ ′ = Δf ₁ + δ Δf ₂ ′ = Δf ₂ + δ.

Therefore, the torque is T ′ = {(2kκab ² ) / (C _A f)} (Δf ′ ₂ −
Δf ′ ₁ ). However, since the displacement amount δ is canceled by each other, Δf ₂ ′ −Δf ₁ ′ = Δf ₂ −Δf ₁ and T ′ = T, and no correction is necessary.

Therefore, the ultrasonic torque sensor of this embodiment can accurately measure the torque without being affected by the temperature characteristics peculiar to the surface acoustic wave device. On the other hand, when the torque is measured by using only one set of interdigital transducers for transmitting and receiving ultrasonic waves, there is a drawback that a separate correction circuit must be provided because of the influence of temperature.

Next, an ultrasonic torque sensor according to the second embodiment of the present invention will be described with reference to FIG. FIG. 8 shows the second
It is a block diagram showing a schematic structure of an ultrasonic torque sensor of an example. The ultrasonic torque sensor of the present embodiment is a device that measures torque from the phase difference of surface acoustic waves.

In this ultrasonic torque sensor 60, two sets of interdigital electrodes 64a and 64 arranged on the piezoelectric element 62 are provided.
The surface acoustic wave element composed of b and 66a, 66b is provided, and this surface acoustic wave element is used by being attached to the twisted portion 24 shown in FIG. Interdigital transducer 64
a and 66a oscillate ultrasonic waves of frequency f ₀ , and these ultrasonic waves are received by the interdigital electrodes 64b and 66b, respectively.

The surface acoustic wave is represented by φ + 2nπ = (2xf ₀ L
/ V) + φ _E Δφ = − (2πf ₀ L / v ² ) Δv Here, φ _E : Phase delay amount of electric circuit f ₀ : Oscillation frequency L: Distance between electrodes (distance between 64a and 64b) v: Propagation velocity of ultrasonic waves oscillated from interdigital transducer Δφ: Phase difference Δv: It is the difference in the propagation velocity of ultrasonic waves.

Therefore, each phase by two sets of interdigital electrodes
The difference Δφ is detected by the phase difference detectors 64c and 66c, respectively.
The phase difference calculator 68 calculates the difference between these phase differences Δφ.
The change in the propagation velocity v can be detected by obtaining Next
The detection of the change in the propagation velocity v will be described below. This
Where Δφ₁ : When stress is applied to the piezoelectric element 62,
Supersonic waves propagating from the blind electrode 64a to the blind electrode 64b
Wave phase difference Δφ₂ : When stress is applied to the piezoelectric element 62,
Supersonic waves propagating from the interdigital transducer 66a to the interdigital transducer 66b
Wave phase difference v_T0: When no stress is applied to the piezoelectric element 62,
From the interdigital transducer 64a (66a) to the interdigital transducer 64b (6)
Sound velocity of ultrasonic wave propagating to 6b) v_T1: When the piezoelectric element 62 is stressed, the blind
Sound of ultrasonic waves propagating from the electrode 64a to the interdigital electrode 64b
Speed v_T2: When the piezoelectric element 62 is stressed, the blind
Sound of ultrasonic waves propagating from the electrode 66a to the interdigital electrode 66b
Speed C_A : Assuming a coefficient, the above-mentioned Δφ = − (2πf₀ L / v) (Δv /
From v) to (v_T1-V_T0) / V_T0= Δv_T1/ V_T0=-(V / 2πf
₀ L) Δφ₁ (V_T2-V_T0) / V_T0= Δv_T2/ V_T0=-(V / 2πf
₀ L) Δφ₂ From equation (7), (v_T2-V_T1) / V_T0= C_A (Σ₂ −σ₁ ) = (C_A /
2) τ_max Therefore, (v_T2-V_T1) / V_T0= (V / 2πf₀ L) (Δφ₁ −
Δφ₂ ) = (C_A / 2) τ_max T = κab² τ_max (Κab² Is the shape factor)
Phase difference Δφ₁ , Δφ ₂ By calculating
The torque can be detected at 0.

In each of the above embodiments, the surface acoustic wave element is attached to only one surface of the twisted portion. However, when the surface acoustic wave element is attached to both upper and lower surfaces of the twisted portion, bending due to the weight of the twisted portion or the like occurs. Can be canceled.
Examples of the material of the piezoelectric element include ceramics and piezoelectric plastics. Since the material of the piezoelectric element has a certain degree of hardness due to such a material, the above-mentioned Δf / f = Δ
In v _s / v _s −Δd / d, displacement Δ with respect to strain
It is possible to set d / d≈0, and as a result, the change in surface acoustic velocity Δf / f = Δv _s / v _s can be detected as a change in frequency.

In the above embodiment, the ultrasonic oscillator circuit has several MH.
Since ultrasonic waves of z or more are oscillated, the followability is good even when the rate of change of torque is fast, and both static torque and dynamic torque can be measured. Further, the oscillating circuit oscillates ultrasonic waves of several MHz or more, so that the resolution is high. Further, since the frequency is output as a signal, the measurement accuracy is good without being affected by the electromagnetic environment. Moreover, since the frequency can be displaced in a wide range, the dynamic range is wide.

[0032]

As described above, according to the ultrasonic torque sensor of the present invention, since it has two sets of ultrasonic transmitters and ultrasonic receivers, the influence of ambient temperature on the frequency of ultrasonic waves. Therefore, a correction circuit taking into consideration is unnecessary. Further, since the output from each ultrasonic receiver is a change in frequency, it is possible to accurately measure the torque without being affected by the electromagnetic environment. Further, since the torque is detected by obtaining the shear stress using the ultrasonic wave, it is possible to accurately measure from a small torque to a large torque with high accuracy, and it is possible to measure both static torque and dynamic torque.

[Brief description of drawings]

FIG. 1 is a perspective view showing an outline of an experimental apparatus which is the basis of the present invention.

FIG. 2 is a schematic diagram showing a schematic structure of an ultrasonic oscillator circuit used in an experiment.

FIG. 3 is a graph showing a result of an experiment conducted by the experimental apparatus shown in FIG.

FIG. 4 is a perspective view showing a state in which the ultrasonic oscillation circuit of the ultrasonic torque sensor according to the first embodiment of the present invention is attached to a twisted portion connected to a rotating shaft.

FIG. 5 is a configuration diagram showing a schematic configuration of two sets of ultrasonic oscillation circuits.

6 is a block diagram showing a schematic configuration of an ultrasonic torque sensor including the ultrasonic oscillation circuit shown in FIG.

FIG. 7 is a schematic configuration diagram showing an outline of a configuration in which a frequency signal from an oscillation circuit is transmitted by radio waves and a value of torque is calculated by a calculation circuit.

FIG. 8 is a block diagram showing a schematic configuration of an ultrasonic torque sensor according to a second embodiment of the present invention.

[Explanation of symbols]

12, 30, 62 Piezoelectric element 14, 32a, 32b, 34a, 34b 64a, 64
b, 66a, 66b Interdigital electrodes 16, 36a Feedback amplifier 42a, 42b Ultrasonic oscillator circuit

Claims (2)

[Claims] 1. An ultrasonic torque sensor for measuring a torque acting on an object to be measured, wherein the ultrasonic torque sensor is arranged on the surface of the object to be measured so that ultrasonic waves propagate on the surface of the object to be measured in a predetermined first direction. A first ultrasonic transmitter and a first ultrasonic receiver, and the ultrasonic wave so that the ultrasonic wave propagates on the surface of the ultrasonic measurement object in a second direction intersecting the first direction. An ultrasonic torque sensor comprising a second ultrasonic transmitter and a second ultrasonic receiver arranged on the surface. 2. The first and second ultrasonic wave transmitters and the first and second ultrasonic wave receivers are interdigital electrodes arranged on a piezoelectric element. The ultrasonic torque sensor according to claim 1.