TWI863361B - Micro strain displacement measurement device and measurement method - Google Patents

Abstract

The invention is a micro-strain displacement measurement device and measurement method. The device includes a light source, a strain sensing module and an optical signal processing module. The strain sensing module is attached to a surface of a test object. The strain sensing module includes a flexible columnar array and a liquid crystal layer. The flexible columnar array includes a plurality of closely arranged micro-columns. The gaps are formed between adjacent micro-columns. The liquid crystal layer fills these gaps. Inside the space, the flexible columnar array can be deformed in conjunction with the strain of the device under test, causing the tilt angle of the liquid crystal molecules inside to change accordingly; when the measuring light beam that has undergone the first polarization treatment enters the liquid crystal layer and is changed in its polarization state by the liquid crystal molecules, the optical signal processing module calculates the strain of the device under test based on the second polarization light beam that leaves the strain sensing module and undergoes the second polarization treatment.

Description

Micro strain displacement measurement device and measurement method

The present invention relates to a strain measurement technology, and more particularly to a device and method for measuring strain using optical principles.

A strain gauge is a sensing element for measuring strain. As shown in FIG6 , a common strain gauge is made of a continuously bent planar metal (alloy) wire 100. The metal wire 100 is attached to a carrier film 110, and a signal wire 120 is connected to the two opposite ends of the metal wire 100. In actual application, the strain gauge is glued to the surface of a test piece. When the test piece is strained and elongated or shortened, the metal wire 100 on the strain gauge is slightly deformed, and the resistance value of the metal wire 100 will also change accordingly.

The strain gauge measures the strain of the object under test by using the principle that metal changes its resistance when it is deformed. In order to obtain the change in resistance of the metal wire 100, the signal wires 120 at both ends of the metal wire 100 must be electrically connected to an external signal conversion device, which calculates the strain of the object under test based on the change in resistance of the metal wire 100.

In order to obtain the resistance change of the metal wire 100, the existing strain gauge needs to be electrically connected to an external computing device, generally through a physical wire. However, in some application areas, such as when the DUT itself generates rotational motion, the signal wire 120 of the strain gauge will face the problem of line entanglement. To overcome the entanglement problem, a wireless signal transmission line needs to be added to be applicable to the DUT with rotational motion.

In view of the fact that existing strain measuring sensors require additional electrical connections using wires, the main purpose of the present invention is to provide a "micro-strain displacement measurement device and measurement method" that can measure the surface deformation of a test piece without the need for electrical connection of the sensing element and the non-contact state.

To achieve the above-mentioned purpose, the micro-strain displacement measurement device of this invention includes:

A light source, used to provide a light beam;

At least one linear polarizer is disposed on the transmission path of the light source beam to perform a first polarization process on the light source beam to provide a measurement beam with a fixed intensity;

A strain sensing module is provided on the surface of a test object. The strain sensing module is arranged on the transmission path of the measuring beam so that the measuring beam can be incident on the strain sensing module. The strain sensing module comprises: A flexible columnar array, comprising a plurality of closely arranged microcolumns, with gap spaces formed between adjacent microcolumns. The flexible columnar array is deformed in accordance with the strain of the test object; A liquid crystal layer is filled in the gap space of the flexible columnar array;

An optical signal processing module receives a modulated light beam leaving the strain sensing module. The modulated light beam is the light beam emitted after the measuring light beam enters the liquid crystal layer. The modulated light beam is then polarized for the second time by the at least one linear polarizer to become a secondary polarized light beam. The optical signal processing module calculates the strain of the device to be tested based on the light intensity value of the secondary polarized light beam.

The micro-strain displacement measurement method of this invention includes:

A strain sensing module is attached to the surface of a test object, wherein the strain sensing module includes a flexible columnar array and a liquid crystal layer, the flexible columnar array has a plurality of closely arranged micro-columns, gap spaces are formed between adjacent micro-columns, the liquid crystal layer is filled in the gap spaces, and the flexible columnar array is deformed in accordance with the strain of the test object;

Providing a linearly polarized measuring beam with a fixed intensity, and allowing the measuring beam to be incident on the strain sensing module, wherein the measuring beam is obtained through a first polarization process;

Receiving a modulated light beam leaving the strain sensing module, the modulated light beam being the light beam emitted after the measuring light beam enters the liquid crystal layer, and the modulated light beam undergoes a second polarization process in the same direction as the first polarization process to become a second polarized light beam;

The strain of the test piece is calculated according to the light intensity value of the secondary polarized light beam.

The flexible columnar array deforms with the micro-displacement of the device under test, causing the liquid crystal molecules therein to change their alignment. When the measuring light beam passes through the liquid crystal, the polarization state of the light beam changes due to the tilt angle change of the liquid crystal molecules. When it passes through the linear polarizer in the original polarization direction for secondary polarization, the intensity of the light beam will be attenuated. Therefore, the change in the micro-displacement of the device under test can be calculated based on the light beam intensity value. The strain sensing module does not require physical wire electrical connection. The light beam passing through the strain sensing module can be received by the light receiving device in a non-contact manner to calculate the micro-displacement of the device under test.

Please refer to FIG. 1 , the present invention is a micro-strain displacement measuring device. In a first embodiment, the present invention includes a light source 10 , a strain sensing module 20 , and an optical signal processing module 30 .

The light source 10 is used to provide a light source beam L1, for example, a laser light source outputs the light source beam L1. In this embodiment, the light source beam L1 output by the light source 10 undergoes a first polarization process by a subsequent optical element to become a measurement beam L2 with a fixed intensity, which will be described in more detail later.

The strain sensing module 20 is a strain sensing module based on liquid crystal, comprising a flexible columnar array 21, a liquid crystal layer 22, a first substrate 23 and a second substrate 24. The flexible columnar array 21 is a nano-flexible columnar array structure, and the flexible columnar array 21 comprises a plurality of closely arranged micro-columns 210, and gap spaces 211 are formed between adjacent micro-columns 210; the structure of the flexible columnar array 21 can be made by different methods, such as by nano-imprinting technology, and the present invention uses aluminum anodic oxidation technology to first make a sacrificial porous anodic oxide. By using a porous anodic alumina template, a nanocolumnar structure with a higher aspect ratio (e.g., 4:1-10:1) can be obtained. A flexible polymer is filled in the pores of the porous anodic alumina template. Finally, the porous anodic alumina template is etched away, and the remaining polymer structure becomes the flexible columnar array 21 required for this creation. The aforementioned liquid crystal layer 22 is filled inside the gap space 211.

The first substrate 23 and the second substrate 24 are disposed on the upper and lower surfaces of the flexible columnar array 21, respectively. The sizes of the first substrate 23 and the second substrate 24 are larger than the flexible columnar array 21. The first substrate 23 and the second substrate 24 are used to dispose the strain sensing module 20 on the surface of a device under test O. As shown in FIG. 2 , in order to facilitate the description of how the strain sensing module 20 is disposed on the surface of the device under test O, the flexible columnar array 21 and the liquid crystal layer 22 are combined and simplified in the figure. Assuming that the strain direction of the device under test O moves along the X-axis, the first fixed point 231 of one side (e.g., the side facing the positive X-axis direction) of the first substrate 23 extends and is attached to the surface of the device under test O, and the second fixed point 241 of the second substrate 24 extends and is attached to the surface of the device under test O at the opposite other side (e.g., the side facing the negative X-axis direction), so that the first substrate 23 and the second substrate 24 are respectively fixed to the surface of the device under test O at the first fixed point 231 and the second fixed point 241 in opposite directions. In this embodiment, a reflective film 25 is formed on the surface of the second substrate 24. The reflective film 25 can be formed on the outer surface or the inner surface of the second substrate 24 without limitation.

The optical signal processing module 30 includes a light receiver 31 and a signal processing device 32. The light receiver 31 receives the light beam returned from the strain sensing module 20. The signal processing device 32 is electrically connected to the light receiver 31 and is used to calculate the intensity of the light beam detected by the light receiver 31.

According to the outgoing and return paths of the light beam, the invention can add a spectroscope 40 and a linear polarizer 51 to the path of the light beam as needed. For example, in the embodiment of FIG. 1 , a light source light beam L1 is output from the light source 10. The light source light beam L1 is reflected at an angle of 90 degrees by the spectroscope 40 and is incident on the linear polarizer 51. The linear polarizer 51 allows a light beam with a specific polarization direction to pass through. After passing through the linear polarizer 51, the light beam becomes a linear polarized light beam with a single polarization direction. This is the first polarization process, forming a measurement light beam L2, and the intensity of the measurement light beam L2 remains fixed. After the measuring light beam L2 is incident on the strain sensing module 20 from the surface of the first substrate 23, it is reflected by the reflective film 25 of the second substrate 24 at 180 degrees and passes through the first substrate 23 again before being emitted. FIG. 1 shows that when the DUT has no relative displacement, the modulated light beam R1 leaves the strain sensing module 20 and then passes through the linear polarizer 51 to become a secondary polarized light beam R2. This is the second polarization process. The secondary polarized light beam R2 passes through the spectroscope 40 and enters the optical receiver 31. The light intensity value of the secondary polarized light beam R2' is then calculated by the signal processing device 32.

Please refer to FIG. 3, which is a schematic diagram of the application of the first embodiment. When the surface of the test piece O is strained, that is, a relative displacement occurs between the first substrate 23 and the second substrate 24 fixed on the surface of the test piece O, the flexible columnar array 21 is bent and deformed, thereby changing the orientation arrangement of each plurality of liquid crystal molecules in the liquid crystal layer 22, and the tilt angle of the plurality of liquid crystal molecules will change. The greater the relative displacement between the first substrate 23 and the second substrate 24, the greater the tilt angle of the plurality of liquid crystal molecules. After the measuring light beam L2 is incident on the liquid crystal layer 22 from the first substrate 23, the polarization direction of the measuring light beam L2 will be changed by the twisted liquid crystal molecules. After being reflected by the reflective film 25, it passes through the liquid crystal layer 22 again. The modulated light beam R1 with changed polarization direction passes through the linear polarizer 51 again to filter out the component perpendicular to the first polarization direction and becomes the secondary polarized light beam R2. Therefore, the light intensity value of the secondary polarized light beam R2' entering the light receiver 31 will be reduced. When the relative displacement between the first substrate 23 and the second substrate 24 is larger, the tilt angle of the liquid crystal molecules will be larger, the change of the polarization direction of the modulated light beam R1 will be larger, and the light intensity entering the light receiver 31 will be more attenuated.

The light intensity pre-measured without relative displacement between the first substrate 23 and the second substrate 24 (as shown in FIG. 1 ) is used as a reference value, and the light intensity measured after the first substrate 23 and the second substrate 24 actually undergo relative displacement (as shown in FIG. 3 ) is used as a measurement value. The signal processing device 32 calculates the relative displacement between the first substrate 23 and the second substrate 24 by comparing the difference between the reference value and the measurement value, thereby obtaining the strain of the test piece O.

Please refer to the second embodiment of the present invention shown in FIG. 4 and FIG. 5. The second embodiment is suitable for measuring a light-transmissive test piece O. Compared with the first embodiment, the second embodiment does not need to have a reflective film 25 on the second substrate 24 to allow light to penetrate the second substrate 24. On the other hand, the light source beam L1 emitted from the light source 10 does not need to pass through a spectroscope 40, but directly passes through a first linear polarizer 52 along the beam path for the first polarization process to become a measurement beam L2, and then enters the strain sensing module 20. The measurement beam L2 is After being emitted from the second substrate 24, L2 passes through the device under test O to become a modulated light beam R1, and then passes through a second linear polarizer 53. The second linear polarizer 53 has the same polarization direction as the first linear polarizer 52, and undergoes a second polarization process to become a secondary polarized light beam R2. After the secondary polarized light beam R2 is received by the light receiver 31, the signal processing device 32 calculates the strain of the device under test O according to the light intensity value.

In the second embodiment of FIG. 4 and FIG. 5 , in order to more accurately calculate the strain of the device under test O, when the reference value of the signal processing device 32 is preset, the device under test O can be set in the light transmission path of the modulated light beam R1 and the device under test O can be kept stationary without strain. In this state, the reference value measured can take into account the influence of the light-transmitting device under test O on the light beam, so the light intensity value of the secondary polarized light beam R2 passing through the device under test O can be used as a more accurate reference value.

The present invention utilizes the rotation of liquid crystal molecules in a flexible columnar array to respond to the micro-displacement of the object to be tested. When the light beam leaves the liquid crystal, its polarization state is changed by the tilt angle change of the liquid crystal molecules. After the second polarization treatment, the intensity of the light beam is attenuated, so the change in micro-displacement can be calculated based on the light beam intensity value. The strain sensing module of this invention is a passive element, which does not require additional electrical connection wires or power supply. The micro-displacement of this strain sensing module is measured in a non-contact manner by a remote measurement beam; the flexible columnar array of the strain sensing module is a nano-column matrix structure made using a sacrificial template, and does not require the use of complex and high-cost optical lithography semiconductor processes.

10: Light source 20: Strain sensing module 21: Flexible columnar array 210: Microcolumn 211: Gap space 22: Liquid crystal layer 23: First substrate 231: First fixed point 24: Second substrate 241: Second fixed point 25: Reflection film 30: Optical signal processing module 31: Optical receiver 32: Signal processing device 40: Spectroscope 51: Linear polarizer 52: First linear polarizer 53: Second linear polarizer L1, L1’: Light source beam L2: Measurement beam R1: Modulation beam R2, R2’: Secondary polarization beam O: DUT 100: Metal wire 110: Carrier film 120: Signal wire

Figure 1: Schematic diagram of the first embodiment of the micro-strain displacement measuring device of the present invention. Figure 2: Schematic diagram of the strain sensing module of the present invention set on the surface of the test piece. Figure 3: Schematic diagram of the use of the embodiment of Figure 1 of the present invention. Figure 4: Schematic diagram of the second embodiment of the micro-strain displacement measuring device of the present invention. Figure 5: Schematic diagram of the use of the embodiment of Figure 2 of the present invention. Figure 6: Planar schematic diagram of the existing strain gauge.

10: Light source

20: Strain sensing module

21: Flexible columnar array

210: Micro-columns

211: Gap Space

22: Liquid crystal layer

23: First substrate

24: Second substrate

25: Reflective film

30: Optical signal processing module

31: Optical receiver

32:Signal processing device

40: Spectroscope

51: Linear polarizer

L1, L1’: light source beam

L2: Measurement beam

R1: Modulate the beam

R2, R2’: secondary polarized beam

Claims (10)

A micro-strain displacement measuring device comprises: A light source for providing a light source beam; At least one linear polarizer is arranged on the transmission path of the light source beam, and performs a first polarization process on the light source beam to provide a measurement beam with a fixed intensity; A strain sensing module is provided for being arranged on the surface of a piece to be tested, and the strain sensing module is arranged on the transmission path of the measurement beam so that the measurement beam can be incident on the strain sensing module, and the strain sensing module comprises: A flexible columnar array, comprising a plurality of closely arranged micro-columns, and gap spaces are formed between adjacent micro-columns, and the flexible columnar array is deformed in accordance with the strain of the piece to be tested; A liquid crystal layer is filled in the gap space of the flexible columnar array; An optical signal processing module receives a modulated light beam leaving the strain sensing module. The modulated light beam is the light beam emitted after the measuring light beam enters the liquid crystal layer. The modulated light beam is then polarized for the second time by the at least one linear polarizer to become a secondary polarized light beam. The optical signal processing module calculates the strain of the device to be tested according to the light intensity value of the secondary polarized light beam. A micro-strain displacement measuring device as described in claim 1, wherein: The measuring beam is generated after a laser light source outputs the light source beam, and the light source beam passes through a spectroscope and the at least one linear polarizer in sequence to undergo the first polarization treatment; The strain sensing module further comprises: A first substrate and a second substrate, respectively disposed on the upper and lower surfaces of the flexible columnar array; A reflective film, disposed on the surface of the second substrate; The measuring beam is incident on the liquid crystal layer through the first substrate, and then emitted from the first substrate after being reflected by the reflective film, and becomes the secondary polarized beam after undergoing the second polarization treatment through the at least one linear polarizer, and the secondary polarized beam enters the optical signal processing module. The micro-strain displacement measuring device as described in claim 1, wherein: The at least one linear polarizer includes a first linear polarizer and a second linear polarizer, and the first linear polarizer and the second linear polarizer have the same polarization direction; The measuring beam is generated after a laser light source outputs the light source beam, and the light source beam passes through the first linear polarizer for the first polarization treatment; The strain sensing module further includes: a first substrate and a second substrate, which are respectively arranged on the upper and lower surfaces of the flexible columnar array; The measuring beam is incident on the liquid crystal layer through the first substrate, and then emitted from the second substrate after penetrating the liquid crystal layer, and becomes the secondary polarized beam after the second polarization treatment through the second linear polarizer, and the secondary polarized beam enters the optical signal processing module. The micro-strain displacement measurement device as described in any one of claims 1 to 3, wherein the flexible columnar array is a nano-column array made based on a sacrificial template. A micro-strain displacement measuring device as described in any one of claim items 1 to 3, wherein the optical signal processing module comprises: a light receiver for receiving the secondary polarized light beam; a signal processing device connected to the light receiver for comparing the light intensity value of the secondary polarized light beam with a preset reference value to calculate the strain of the test piece, wherein the reference value is the light intensity value of the secondary polarized light beam measured when the test piece has no strain. A micro-strain displacement measuring device as described in any one of claims 1 to 3, wherein the liquid crystal molecules in the liquid crystal layer change their tilt angles as the flexible columnar array is bent and deformed. A micro-strain displacement measurement method, comprising: Attaching a strain sensing module to the surface of a test piece, wherein the strain sensing module comprises a flexible columnar array and a liquid crystal layer, wherein the flexible columnar array has a plurality of closely arranged microcolumns, gap spaces are formed between adjacent microcolumns, and the liquid crystal layer is filled in the gap spaces, and the flexible columnar array is deformed in accordance with the strain of the test piece; Providing a linearly polarized measurement beam with a fixed intensity, allowing the measurement beam to be incident on the strain sensing module, wherein the measurement beam is obtained through a first polarization process; Receive a modulated light beam leaving the strain sensing module, the modulated light beam is the light beam emitted after the measuring light beam enters the liquid crystal layer, and the modulated light beam is then subjected to a second polarization process in the same direction as the first polarization process to form a second polarized light beam; Calculate the strain of the device to be tested based on the light intensity value of the second polarized light beam. A micro-strain displacement measurement method as described in claim 7, wherein the light intensity value of the secondary polarized light beam is compared with a preset reference value to calculate the strain of the test piece, and the reference value is the light intensity value of the secondary polarized light beam measured when the test piece has no strain. The micro-strain displacement measurement method as described in claim 7, wherein: In the step of providing the measurement beam, the measurement beam is generated after a laser light source outputs a light source beam, and the light source beam passes through a spectroscope and a linear polarizer in sequence to perform the first polarization treatment; In the step of receiving the modulated beam, the modulated beam passes through the linear polarizer to perform the second polarization treatment to become the secondary polarized beam. A micro-strain displacement measurement method as described in claim 7, wherein: The measurement beam is generated by a laser light source outputting a light source beam, and the light source beam is generated after passing through a first linear polarizer to undergo the first polarization treatment; In the step of receiving the modulated beam, the modulated beam is passed through a second linear polarizer to undergo the second polarization treatment to become the secondary polarized beam, wherein the first linear polarizer and the second linear polarizer have the same polarization direction.

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