A non-contact torque sensor

Abstract

The present invention provides a contactless torque sensor, comprising a swept-frequency laser light source, an optical fiber coupler, a first signal detection arm, a second signal detection arm, a first channel reference arm, a second channel reference arm, a first signal reference mirror, a second signal reference mirror and a signal acquisition system; the first signal reference mirror is connected to the first channel reference arm, and the second signal reference mirror is connected to the second channel reference arm; the optical path difference of light at two positions on the measured object is obtained by the first signal detection arm and the second signal detection arm, which is obtained by the signal acquisition system after coupling by the optical fiber coupler, converted into radial displacement of two positions of the shaft end face, and then converted into corresponding torque angle change after being processed by a signal processing algorithm, so as to measure the change of torque; the technical solution avoids the disadvantage of response lag brought by resistance strain type and other physical principles, effectively reduces the creep, advance and return difference, zero drift and hysteresis of the sensor, and has the characteristics of fast response.

Description

Technical Field

[0001] The invention relates to the technical field of torque measurement and optical sensing, in particular to a non-contact torque sensor. Background Art

[0002] Torque is a very important physical quantity in mechanical transmission, and the state information of mechanical transmission can be obtained from torque. Therefore, whether static torque can be accurately detected or dynamic torque can be monitored is of great significance to the performance, safety, maintenance, and optimization of mechanical transmission systems. Static detection of torque, for example: static torque measurement, rated torque verification of beam-type mechanical components, etc.; dynamic monitoring of torque, for example: torque safety monitoring of wind turbine shafts, real-time monitoring of mechanical arm load, etc.

[0003] According to the working principle, torque sensors can be divided into strain type, magnetic induction type, surface acoustic wave type and photoelectric type. Strain gauge type mainly includes resistance type, fiber Bragg grating type, clamp ring type and so on. Under the action of external load, the elastic element of the strain sensor is deformed, and the deformation is transmitted to the sensitive element (such as strain gauge, fiber Bragg grating, etc.) attached to the elastic element. By measuring the change of electrical signal or optical signal, the torque is measured; magnetic induction torque sensor mainly includes magnetoelastic type, magnetostrictive type, magnetic Barkhausen noise type, magnetoelectric type and so on. When the object to be measured is subjected to torque, the magnetic element attached to the object to be measured will be deformed, so that its magnetic field will change. By converting the change of magnetic field into the change of electrical signal, the torque is measured; surface acoustic wave type generally transmits ultrasonic signal to the surface of the material to be measured, and then detects the reflected wave from the inside of the material to be measured. According to the return time of different signals, the magnitude of the torque applied to the material can be measured; photoelectric torque sensor can be divided into capacitive type, photoelastic type, photoelectric effect type, fiber distributed type and Doppler effect type. This type of sensor converts the torque exerted on the object being measured into a light energy signal or an optical path difference signal carrying information by attaching an optical sensitive element to the object being measured or by laser irradiation, and processes and converts the collected optical signals to obtain the corresponding torque value on the computer.

[0004] For strain-type torque sensors, the deformation generated by external loads needs to be transmitted through multiple layers of elastomer-bonding layer-sensitive element before it can be sensed. Therefore, there is a large hysteresis characteristic, which makes the dynamic response of this type of sensor poor. Moreover, under the action of high-frequency alternating loads, the hysteresis deformation is easy to accumulate, resulting in a large advance and return difference and indication deviation in the measurement results. Although the magnetic induction sensor responds faster, there are many factors that affect the change of the magnetic field, and the magnetic field change is relatively sensitive, so the use conditions of the magnetic induction torque sensor are strictly restricted, the signal processing is difficult, and even in some cases it cannot be used. Although the surface acoustic wave torque sensor has high sensitivity, this method requires the surface treatment of the object to be measured and the use of coupling agent. Therefore, this method has strict requirements on the experimenter, the pasting method and the amount of adhesive used are strict and complicated, and the interference of bending moment and vibration cannot be avoided. Although the photoelectric torque sensor can measure accurately, has a fast response speed and is not affected by the magnetic field, except for the Doppler effect type, the rest are contact measurements, which will cause unnecessary interference to the original system, thereby affecting the accuracy of the measured torque value. For the only non-contact Doppler effect torque sensor, when the object remains stationary or runs at low frequency and low speed, the Doppler frequency shift generated is very small or even disappears, and the system will lose its detection ability. Summary of the invention

[0005] In view of this, an object of the present invention is to provide a non-contact torque sensor, which has high measurement accuracy and sensitivity, small hysteresis creep, few restrictions on use conditions, and has the advantages of non-contact detection.

[0006] To achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a non-contact torque sensor, comprising a swept-frequency laser light source, a 2×4 optical fiber coupler, a first signal detection arm, a second signal detection arm, a first channel reference arm, a second channel reference arm, a first signal reference mirror, a second signal reference mirror and a signal acquisition system; the first signal reference mirror is connected to the first channel reference arm, and the second signal reference mirror is connected to the second channel reference arm; the swept-frequency laser light source, the first signal detection arm, the second signal detection arm, the first channel reference arm, the second channel reference arm and the signal acquisition system are respectively connected to the optical fiber coupler via optical fibers; the optical path difference of light at two positions on the measured object is obtained by the first signal detection arm and the second signal detection arm, and is obtained by the signal acquisition system after coupling through the 2×4 optical fiber coupler, and converted into radial displacement of two positions of the shaft end face, and then converted into corresponding torque angle change after being processed by the signal processing algorithm, thereby measuring the torque change.

[0007] In a preferred embodiment, the swept-frequency laser light source is specifically a swept-frequency laser, the wavelength of the output light beam of the swept-frequency laser is time-modulated, and single-frequency light of different wavelengths is output at different times, and the wavelength changes periodically within the swept-frequency bandwidth; the first signal detection arm and the second signal detection arm include a lens, a lens bracket and an optical fiber connector; the signal acquisition system is mainly composed of a photoelectric detector, a data acquisition card, and a computer.

[0008] In a preferred embodiment, a frequency sweeping laser light source is connected to an optical fiber, and two optical fibers are separated from the optical fiber through a first optical fiber coupler to connect to a second optical fiber coupler and a third optical fiber coupler, and then two optical fibers are separated from the second optical fiber coupler and the third optical fiber coupler to connect to a first signal detection arm and a first channel reference arm and a second signal detection arm and a second channel reference arm, respectively. The first optical fiber coupler is connected to a signal collector through an optical fiber at the other end to collect the measured signal; when the frequency sweeping laser radiates single-frequency light of a starting wavelength, a square wave signal emitted from its A-Trig port will serve as a trigger signal for a data acquisition card; a photoelectric detector is used as a communication bridge between electrical signals and external optical signals, and a data acquisition card is used to realize computer recognition of electrical signals; the detector converts the coherent optical signal from the interferometer into an electrical signal, and sends it to the acquisition card to digitize the electrical signal for reading by the computer; after collecting the data of the set number of points, the data collection of a frequency sweeping cycle can be completed, thereby obtaining the required broadband optical interference signal, and then waiting for the next trigger signal.

[0009] In a preferred embodiment, the position of point A is used as a reference, and the relative position of a point is measured after each interval of Δt. After the shaft makes a complete rotation, the relative position of each point on the shaft is obtained, and the surface contour of the shaft is obtained by contour fitting through Matlab; the above process is called a preprocessing process; after the surface contour of the shaft is obtained, when the shaft is subjected to torque and torsional deformation, the points on the shaft will rotate relative to each other. At this time, the rotated points are measured and compared with the surface contour of the shaft during preprocessing, so that it can be known which point the point is. For example, after the torque is applied, the point rotates from point A to another point, and the relative displacement of the point is measured as x, which matches the relative displacement of point B, so it can be known that the point is point B; after knowing the information of the point, assuming that the center of the circle is O, the angle between OA and OB, that is, the rotation angle θ1, is known; the rotation angle θ2 of another cross section is measured in the same way, The distance between the two cross sections is dx, and the torque T is given by the formula get.

[0010] In a preferred embodiment, the elastomeric shaft to be measured is specific, and the shaft surface has identifiable continuous and complete contour information; the contour information of the shaft surface is reflected near the two shaft ends, and a continuous, identifiable and clear shaft surface contour can be obtained during the measurement preprocessing process; the shaft, as a part of the entire sensing system, is connected to the target shaft to be measured during the actual measurement process, and the connection method is a sleeve connection; when the target shaft to be measured is subjected to torque, the sleeve transfers the torque to the shaft, and the optical interference system is used to measure the two ends of the shaft to obtain the precise torque value.

[0011] Compared with the prior art, the present invention has the following beneficial effects: the sensor is implemented based on the principle of optical interference, and it utilizes the physical property of fast response speed of light propagation, which can avoid the drawbacks of delayed response brought about by resistance strain type and other physical principles, effectively reduce the creep, advance and return difference, zero drift and hysteresis of the sensor, and has the characteristics of fast response. On this basis, combined with the shaft surface profile information, the absolute position of each point on the shaft is accurately located, thereby realizing accurate static / dynamic measurement. The present invention adopts non-contact measurement, which has little impact on the original system, and can accurately and quickly obtain the torque of the measured object. Therefore, the present invention has strong practicality and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a principle diagram of the optical fiber interference optical path of a preferred embodiment of the present invention;

[0013] Figure 2 A signal acquisition and processing system for a preferred embodiment of the present invention;

[0014] Figure 3 It is a schematic diagram of the measuring principle of the measured shaft end face of a preferred embodiment of the present invention;

[0015] Figure 4 The elastic body measured shaft of the preferred embodiment of the present invention;

[0016] Figure 5 A schematic diagram of an optical fiber torque sensor according to a preferred embodiment of the present invention;

[0017] Figure 6 A schematic diagram of a free-space interference optical path of a preferred embodiment of the present invention;

[0018] Figure 7 This is a schematic diagram of a free space torque sensor according to a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0019] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0020] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0021] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application; as used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0022] Example 1

[0023] The entire embodiment system consists of three parts, namely: an engineering shaft and an elastic body measured shaft combination system, a broadband optical coherent ranging system and a signal processing system, which will be further described in detail below in conjunction with the accompanying drawings.

[0024] like Figure 1-5 The embodiment shown provides a non-contact optical fiber torque sensor, including a frequency sweep laser light source, a plurality of optical fibers, an optical fiber coupler, two signal detection heads, two channel reference arms, two signal reference mirrors, a signal acquisition system and a computer, wherein the two signal reference mirrors are respectively connected to the corresponding channel reference arms, and the light source, two signal detection heads, two channel reference arms and the signal acquisition system are respectively connected to the optical fiber coupler via optical fibers. The sensor uses the principle of light interference to obtain the optical path difference of light at two positions on the measured object through two signal detection heads, which is obtained by the signal acquisition system after coupling through the optical fiber coupler and converted into radial displacement of two positions on the shaft end face, and then converted into corresponding torsion angle changes after being processed by the signal processing algorithm, thereby measuring the change in torque.

[0025] The frequency sweeping laser light source is a frequency sweeping laser, the wavelength of the output beam of the frequency sweeping laser is modulated by time, and single-frequency light of different wavelengths is output at different times, and the wavelength changes periodically within the frequency sweeping bandwidth. The signal detection head is mainly composed of a lens, a lens bracket and an optical fiber connector; the signal acquisition system is mainly composed of a photoelectric detector, a data acquisition card and a computer.

[0026] The swept-frequency laser light source is connected to an optical fiber. After passing through the optical fiber coupler 1, two optical fibers are separated to connect to the optical fiber coupler 2 and the optical fiber coupler 3. Then, two optical fibers are separated from the optical fiber couplers 2 and 3 to connect to the signal detection arms 1 and 2 and the channel reference arms 1 and 2 respectively. The optical fiber coupler 1 is also connected to the signal collector through the optical fiber to collect the measured signal. When the swept-frequency laser radiates the single-frequency light of the starting wavelength, the square wave signal emitted by its A-Trig port will serve as the trigger signal of the data acquisition card. The photoelectric detector is used as a bridge for communication between the electrical signal and the external optical signal, and the data acquisition card is used to realize the computer's recognition of the electrical signal, such as Figure 2 As shown. After the detector converts the coherent optical signal from the interferometer into an electrical signal, it is sent to the acquisition card to digitize the electrical signal for the computer to read. After the data of the set number of points are collected, the data collection of a frequency sweep cycle can be completed, thereby obtaining the required broadband optical interference signal, and then waiting for the next trigger signal.

[0027] The non-contact torque sensor is based on the principle of optical interference measurement, combining the scale displacement information of light with the surface profile information of the shaft, thereby realizing broadband light measurement of circumferential displacement, and combining it with the principle of torque calculation to realize torque measurement. The specific implementation process is as follows: Now imagine that a beam of detection light hits a point on the cross section of the shaft (this point is marked as point A). Figure 3 As shown in the figure, when the shaft rotates, the detection light is stationary, but the point on the shaft corresponding to this point will change. For example, after Δt time, the point illuminated by the detection light is point B. At this time, if the shaft is absolutely smooth, then points A and B will not have radial displacement changes, but in fact this is not the case (when the measurement accuracy rises to the nanometer level, the surface of the shaft is not smooth but very rough), but point B is slightly higher or slightly lower than point A. At this time, the interference fringes will change, and the displacement of point B relative to point A can be measured based on the changes in the interference fringes. Taking the position of point A as the reference, the relative position of a point can be measured after each Δt time interval. After the shaft rotates a full circle (hereinafter referred to as a period T), the relative position of each point on the shaft can be obtained, and the surface profile of the shaft can be obtained by contour fitting through matlab software. The above process is called preprocessing. After obtaining the surface profile of the shaft, when the shaft is subjected to torsion deformation due to torque, the points on the shaft will rotate relative to each other. At this time, the rotated points are measured and compared with the surface profile of the shaft during preprocessing to know which point the point is (for example, after applying torque, the relative displacement of the point is measured to be x, which matches the relative displacement of point B, so we know that the point is point B). After knowing the information of the point, let the center of the circle be O, and we can know the angle between OA and OB, that is, the rotation angle θ1. Use the same method to measure the rotation angle θ2 of another cross section. The distance between the two cross sections is dx, and the torque T can be obtained from the formula get.

[0028] The measured elastic shaft is specific, and the shaft surface has identifiable continuous and complete profile information. The profile information of the shaft surface is reflected near the two ends of the shaft, namely the F area and the L area, such as Figure 4 As shown. In the pre-processing process of the measurement, a continuous and discernible clear shaft surface profile can be obtained. As a part of the entire sensing system, the shaft is connected to the target shaft to be measured during the actual measurement process, and the connection method is a sleeve connection. When the target shaft to be measured is subjected to torque, the sleeve transmits the torque to the shaft. According to claim 4, the optical interference system is used to measure the two ends of the shaft to obtain an accurate torque value.

[0029] The entire optical system is based on the theory of optical coherence vibration measurement. The signal processing technology is based on the fast Fourier transform and Hanning window energy centroid method (HnWECM) algorithms to solve the signal time-frequency conversion problem and energy leakage problem respectively, thereby achieving high-precision measurement. The dual-channel data transmission is based on broadband optical coherence ranging multi-channel frequency division multiplexing technology, and accurate torque signals are obtained through dual-channel input and output.

[0030] Example 2

[0031] like Figure 6-7 The embodiment shown provides a non-contact free space torque sensor, including a light source, four double convex mirrors, a fiber collimator, a reflector, two reference mirrors, three beam splitters, and a number of optical brackets. The light emitted by the laser light source is divided into two beams after passing through beam splitter 1 (BS1), and the two beams are respectively divided into reference light and detection light after passing through beam splitters 2 (BS2) and 3 (BS3). The reference light is reflected back to the optical path by the reference mirror, and the double detection light detects the radial displacement of two places on the axial surface. The detection light carrying the displacement information interferes with the reflected reference light and passes through beam splitter 1 (BS1) to form an interference signal. The process after the interference signal enters the signal processing system is consistent with that of Example 1.

[0032] The non-contact torque sensor is implemented based on the principle of optical interference, and is characterized in that the entire optical system is based on optical coherence vibration measurement theory, the signal processing technology is based on the HnWECM algorithm to solve the energy leakage problem and achieve high-precision measurement, and the dual-channel data transmission is based on OCV multi-channel frequency division multiplexing technology to obtain accurate torque signals through multi-channel input and output.

[0033] When the motor rotates, the engineering shaft will rotate, and the engineering shaft will be subjected to a torque load. The torque will be transmitted to the elastomer shaft under test through the sleeve, that is, the elastomer shaft under test will be subjected to the same torque load at this time. At this time, detection arm 1 and detection arm 2 will perform surface profile measurements on the end face of the elastomer shaft under test. The displacement information obtained by the measurement is transmitted through optical fiber and coupled to the signal acquisition system through the optical fiber coupler. The computer compares the measured data with the surface profile data when no torque is applied, and two sets of angle change information can be obtained. The difference between the two sets of angle change information is the torsion angle, and the final torque information can be obtained through the torque calculation formula. Here, the following additional explanations need to be pointed out:

[0034] In the free space type embodiment, the light radiated by the frequency sweeping laser is divided into the first channel light beam and the second channel light beam by the beam splitter BS1. The beam splitter BS2 divides the first channel light beam into the first channel reference light and the first channel detection light. The first channel reference light is focused on the first channel reference mirror by the convex lens 1 and reflected back by it, the first channel detection light is focused on the radial direction I of the end face of the measured shaft by the objective lens, and the detection light is scattered back by the sample surface. The second channel light beam is divided into the second channel reference light and the second channel detection light by the beam splitter BS3, the second channel reference light is focused on the reference mirror by the convex lens 2 and reflected back by it, the second degree of freedom detection light is focused on the radial direction II of the end face of the measured shaft by the objective lens, and the detection light is scattered back by the sample surface. The two reference beams and the two detection beams are respectively coherent and meet again at the beam splitter 1 to form a dual-frequency interference signal, which is transmitted to the signal acquisition device through the main channel.

[0035] In the fiber-optic embodiment, the light emitted by the frequency-sweeping laser enters the fiber 2×4 coupler and is divided into four beams of light, two of which are used as reference light and two as detection light. When the reference light is reflected back by the reference mirror, it interferes with the detection light scattered back by the shaft end face in the same channel and couples with the fiber coupler to form a dual-frequency interference signal, which is transmitted to the signal acquisition device through the main channel.

[0036] For the collected interference signal, the photoelectric detector acts as a bridge between the electrical signal and the external optical signal, and the data acquisition card is used to realize the computer's recognition of the electrical signal. After collecting the data of the set number of points and completing the data collection of a frequency sweep cycle, the required broadband interference signal can be obtained, and then wait for the next trigger signal. The entire optical system is based on the theory of optical multi-point coherent vibration measurement, and obtains accurate torque signals through dual-channel input and output.

[0037] When the number and position of the signal detection heads are different and the number of channel reference arms and signal reference mirrors are different, the measured torque accuracy, error analysis, and signal processing methods are different.

[0038] When the distances between the optical path elements are different, the number and position of the signal detection heads are different, the number of channel reference arms and signal reference mirrors are different, and the signal processing of the signal collection system is different, the torque sensor is used for small / large static torque detection and small / large dynamic torque real-time monitoring.

[0039] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A non-contact torque sensor, characterized in that: It includes a swept-frequency laser light source, a 2×4 optical fiber coupler, a first signal detection arm, a second signal detection arm, a first channel reference arm, a second channel reference arm, a first signal reference mirror, a second signal reference mirror and a signal acquisition system; the first signal reference mirror is connected to the first channel reference arm, and the second signal reference mirror is connected to the second channel reference arm; the swept-frequency laser light source, the first signal detection arm, the second signal detection arm, the first channel reference arm, the second channel reference arm and the signal acquisition system are respectively connected to the optical fiber coupler via optical fibers; the optical path difference of reflected light at two positions on the measured object is obtained by the first signal detection arm and the second signal detection arm, and is obtained by the signal acquisition system after coupling through the 2×4 optical fiber coupler, and converted into radial displacements at two positions of the shaft end face, and then converted into corresponding torque angle changes after calculation by a signal processing algorithm, thereby measuring the torque change.

2. A non-contact torque sensor according to claim 1, characterized in that: The swept-frequency laser light source is specifically a swept-frequency laser, the wavelength of the output light beam of the swept-frequency laser is modulated by time, and single-frequency light of different wavelengths is output at different times, and the wavelength changes periodically within the swept-frequency bandwidth; the first signal detection arm and the second signal detection arm include a lens, a lens bracket and an optical fiber connector; the signal acquisition system is mainly composed of a photoelectric detector, a data acquisition card, and a computer.

3. A non-contact torque sensor according to claim 2, characterized in that: The swept-frequency laser light source is connected to an optical fiber, and the optical fiber passes through a first optical fiber coupler and then two optical fibers are separated to connect the second optical fiber coupler and the third optical fiber coupler, and then two optical fibers are separated from the second optical fiber coupler and the third optical fiber coupler to connect the first signal detection arm and the first channel reference arm and the second signal detection arm and the second channel reference arm, respectively. The first optical fiber coupler is also connected to a signal collector through an optical fiber to collect measured signals; When the frequency-sweeping laser radiates single-frequency light of the starting wavelength, the square wave signal emitted by its A-Trig port will serve as the trigger signal of the data acquisition card; the photoelectric detector serves as a bridge for communication between the electrical signal and the external optical signal, and the data acquisition card is used to realize the computer's recognition of the electrical signal; the detector converts the coherent optical signal from the interferometer into an electrical signal, and sends it to the acquisition card to digitize the electrical signal for the computer to read; after collecting the data of the set number of points, the data collection of a frequency-sweeping cycle can be completed, thereby obtaining the required broadband optical interference signal, and then waiting for the next trigger signal.

4. A non-contact torque sensor according to claim 3, characterized in that: Taking the position of point A as the reference, the relative position of a point is measured after each interval of Δt. After the shaft makes a complete rotation, the relative position of each point on the shaft is obtained. The surface contour of the shaft is obtained by contour fitting through Matlab software. The above process is called the preprocessing process. After knowing the surface contour of the shaft, when the shaft is subjected to torque and torsional deformation, the points on the shaft will rotate relative to each other. At this time, the rotated points are measured and compared with the surface contour of the shaft during preprocessing to know which point it is. For example, after applying torque, the point rotates from point A to another point, and the relative displacement of the point is measured as x, which matches the relative displacement of point B, so it can be known that the point is point B. After knowing the information of the point, set the center of the circle as O, and you will know the angle between OA and OB, that is, the rotation angle θ1. Use the same method to measure the rotation angle θ2 of another cross section. The distance between the two cross sections is dx, and the torque T is given by the formula get.

5. A non-contact torque sensor according to claim 4, characterized in that: The measured elastomer shaft is specific, and the shaft surface has identifiable continuous and complete contour information; the contour information of the shaft surface is reflected near the two shaft ends, and a continuous, identifiable and clear shaft surface contour can be obtained during the measurement preprocessing process; the shaft, as a part of the entire sensing system, is connected to the target shaft to be measured during the actual measurement process, and its connection method is a sleeve connection; when the target shaft to be measured is subjected to torque, the sleeve transmits the torque to the shaft, and the optical interference system is used to measure the two ends of the shaft to obtain the precise torque value.

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