CN115727882A - Temperature and pressure double-parameter flexible optical fiber touch sensor, preparation method and measurement system - Google Patents
Temperature and pressure double-parameter flexible optical fiber touch sensor, preparation method and measurement system Download PDFInfo
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- CN115727882A CN115727882A CN202211509336.1A CN202211509336A CN115727882A CN 115727882 A CN115727882 A CN 115727882A CN 202211509336 A CN202211509336 A CN 202211509336A CN 115727882 A CN115727882 A CN 115727882A
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Abstract
The invention discloses a temperature and pressure double-parameter flexible optical fiber touch sensor and a measuring system, which are used for simultaneously measuring the contact pressure and the change of the surface temperature of a contact object. The sensor is designed in a spherical structure and is composed of a bending FBG (fiber Bragg Grating) wrapped by a Polydimethylsiloxane (PDMS) elastomer. The Bragg wavelength of the bent FBG and the temperature and pressure response characteristics of the whispering gallery mode interference peak are utilized to realize double-parameter sensing of pressure and temperature, and the problem of pressure and temperature crosstalk in touch sensing can be solved. The PDMS elastomer material can endow the sensor with soft mechanical property and good biocompatibility, and meanwhile, the high thermal elasticity property of the PDMS elastomer material can effectively improve the temperature response of the sensor. In addition, in order to realize the spectrum demodulation of the flexible touch sensor, the invention also provides a miniaturized spectrum measuring system.
Description
(I) the technical field
The invention relates to a temperature and pressure double-parameter flexible optical fiber touch sensor, a preparation method and a measurement system, which are used for rapid and accurate real-time touch monitoring and belong to the field of optical detection and optical fiber sensing.
(II) background of the invention
With the rapid development in the fields of intelligent robots, smart medical treatment, wearable devices, and the like, touch sensors are increasingly valued by researchers because they can simulate the perception of human skin. The touch sense can help human sense the surrounding environment and identify objects, mainly relates to physical attribute information such as temperature, hardness, pressure and surface roughness of target objects, and has important significance in scenes such as medical health and home service of fine operation. With the increasingly complex application scenes of the touch sensor, the requirement on the touch sensor in the real application is higher, while most of the traditional touch sensors are based on the electrical principle and convert the contact pressure and the temperature into electrical signals for processing and outputting, and the traditional touch sensors also have some defects, such as poor electromagnetic interference resistance, complex wiring, signal crosstalk problems and the like. Compared with the traditional electric touch sensor, the optical fiber touch sensor has the advantages of electromagnetic interference resistance, small volume, light weight and adaptability to extreme environments, is various in types, and comprises the optical fiber touch sensor based on optical mechanisms such as an F-P interference cavity, an optical fiber Bragg grating and a micro optical fiber. However, the above-mentioned fiber optic tactile sensors mostly consist of waveguides made of rigid materials (such as silicon and glass), resulting in limited mechanical compliance. In addition, most of the sensors are only limited to the detection of a single physical quantity, cannot completely imitate the multi-dimensional perception of human skin on tactile information, and also limit the application range of the sensors.
The optical fiber touch sensor realizes the sensing function according to the change of the optical characteristics of the optical fiber touch sensor under the action of external factors, so the demodulation mode of the sensor directly influences the sensing precision and reliability. The modulation of the optical fiber touch sensor comprises power modulation, wavelength modulation, phase modulation, polarization modulation and the like, wherein the optical fiber touch sensor with the wavelength modulation has high measurement precision, a wide-spectrum light source is generally used as a light source, and sensing monitoring can be realized by monitoring characteristic wavelength by using a precision spectrometer. The precise spectrometer is generally large in size, expensive, limited in spectral resolution, slow in measurement speed, and not beneficial to rapid and precise measurement of the sensor. Therefore, the problems of miniaturization, stability, multi-dimensional monitoring and the like of the touch sensing system are the development focus of the sensor.
Disclosure of the invention
Aiming at the challenges faced by the application of the optical fiber tactile sensor, the invention provides the optical fiber tactile sensing system for measuring the temperature and the pressure by using the temperature and pressure response characteristics of the FBG and the optical fiber whispering gallery mode, so that the double-parameter sensing of the pressure and the temperature is realized, and the crosstalk problem of the pressure and the temperature in the tactile sensing is solved; in order to realize the spectrum demodulation of the sensor, a double-optical comb laser light source or a sweep frequency laser is used as a laser source, and detection data on a spectrum is inverted in a mode of directly detecting time domain information by a single photoelectric detector, so that real-time and accurate touch (temperature, pressure, hardness, roughness and the like) perception is realized.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
the optical fiber touch sensor is designed in a spherical structure and is formed by a bending FBG (fiber Bragg grating) wrapped by Polydimethylsiloxane (PDMS), and is characterized in that the optical fiber touch sensor realizes double-parameter sensing on pressure and temperature by utilizing the Bragg wavelength of the FBG and the temperature and pressure response characteristics of a whispering gallery mode interference peak, and simultaneously solves the problem of pressure and temperature crosstalk in touch sensing.
The bent FBG is prepared by a method that special femtosecond laser directly penetrates through the optical fiber coating layer to etch the fiber core point by point, and has excellent bending resistance and low bending loss.
The PDMS material has the characteristics of flexibility, stretchability, biocompatibility and high thermal-elastic coefficient, and wraps the bent FBG, so that the bent FBG is protected on one hand, and the mechanical compliance is increased; on the other hand, the temperature response of the sensor can be effectively improved by utilizing the higher thermal elasticity characteristic of PDMS.
The whispering gallery mode interference peak of the optical fiber touch sensor is based on the mode interference principle in the optical fiber, and the bending diameter of the FBG with the bending structure can influence the whispering gallery mode distribution in the optical fiber, so that the whispering gallery mode interference peak is caused to drift. When pressure acts on the bending FBG, the diameter of the bending FBG changes, the echo wall interference spectrum drifts, and high-sensitivity pressure measurement can be realized.
The optical fiber touch sensor is characterized in that the preparation method comprises the following steps:
step (1): the two ends of the fiber Bragg grating are inserted into the support frame central small hole of the hollow sleeve, the bending diameter of the fiber Bragg grating is reduced by pulling the two ends of the optical fiber until the optical fiber Bragg grating can be placed into a spherical mold, the hollow ceramic tube is inserted into the mold, the bent FBG is attached to the inner wall of the mold, and the upper ends of the optical fiber and the hollow ceramic tube are fixed by ultraviolet glue.
Step (2): and (3) mixing the PDMS prepolymer and a curing agent according to a certain proportion to obtain a PDMS mixed solution, injecting the mixed solution into the hollow pipe and the mold in the step (1), curing at room temperature for 24 hours, then disassembling the mold, and taking out the cured sensor.
And (3): and (3) placing the sensor obtained by curing in the step (2) in a temperature box at 120 ℃ for 2 hours for annealing treatment to release residual stress generated by bending in the optical fiber, namely residual stress released by plastic deformation caused by high temperature, and curing and maturing PDMS.
The invention also provides a miniaturized, stable and rapid measurement system, the adopted laser source can be a double-optical comb laser source or a swept-frequency laser, and the detection data on the spectrum is inverted by a photoelectric detector in a mode of directly detecting time domain information. Compared with a measurement method based on a precise spectrometer, the measurement method realizes spectrum detection, is simpler and faster, and has lower cost. Therefore, the method overcomes the difficulty that the high-frequency carrier signal cannot be achieved by only adopting the photoelectric detector, and greatly improves the effectiveness of optical detection. The device comprises a laser light source 1, an optical fiber touch sensor 2, a photoelectric detector 3, a data acquisition card 4 and a computer 5.
1) The demodulation device has the following element relationship: an optical output port 1-1 of a laser light source 1 is connected to an input port 2-1 of an optical fiber touch sensor 2 through a single mode fiber, an output port 2-2 of the optical fiber touch sensor 2 is connected to an input port 3-1 of a photoelectric detector 3 through the single mode fiber, an output port 3-2 of the photoelectric detector 3 is connected to an output port 4-2 of a data acquisition card 4 through a BNC signal wire for acquisition, and an acquisition result is sent to a computer 5 for processing.
2) The demodulation device adopts a frequency demodulation detection mechanism to eliminate the influence of unstable factors of environment and light source light intensity. The laser light source 1 can be a double-optical-comb laser light source or a swept-frequency laser to generate signal light, wherein the effective spectrum of the double-optical-comb laser light source covers the Bragg wavelength and the echo wall transmission peak of the FBG, and sensing is carried out by monitoring the drift of the transmission peak.
3) In the demodulation device, a modulation signal acquired by a data acquisition card is subjected to Fourier transform, signal light and frequency information are extracted, and temperature and pressure information is obtained by calculating a frequency drift difference.
The working principle of the invention is as follows: the Bragg wavelength of the FBG and the resonant wavelength of the echo wall of the bent optical fiber are shifted due to pressure and temperature changes, and quantitative monitoring of double parameters of pressure and temperature is realized by monitoring the shift of the wavelength. PDMS of outside parcel has played the guard action to optic fibre, has improved the mechanical properties of sensor, and the higher thermal elasticity characteristic of PDMS has improved the temperature sensitivity of sensor simultaneously. The hardness of PDMS can be adjusted by adjusting the proportion of PDMS, so that the pressure sensitivity of the sensor can be adjusted, and the pressure sensitivity of the sensor can be adjusted according to actual needs.
1) Thus, λ is obtained by testing the curves of the Bragg wavelength and the whispering gallery wavelength drifts at different pressures (P) at room temperature FBG Formula (1) and λ of bragg wavelength variation with pressure WGM Formula (2) of the echo wall wavelength variation with pressure.
λ FBG ＝k P-FBG ·P+a (1)
λ WGM ＝k P-WGM ·P+b (2)
Wherein k is P-FBG And k P-WGM Sensitivity to pressure variations for Bragg wavelength and whispering gallery wavelength, respectively。
2) Similarly, under the condition of unchanged pressure, the temperature (T) is changed to obtain the function relation of the Bragg wavelength drifting along with the temperature [ formula (3) ] and the function relation of the echo wall wavelength drifting along with the temperature [ formula (4) ].
λ FBG ＝k T-FBG ·T+c (3)
λ WGM ＝k T-WGM ·T+d (4)
Wherein k is T-FBG And k T-WGM Respectively the sensitivity of the bragg wavelength and the whispering gallery wavelength to temperature variations.
3) Establishing the relation between the Bragg wavelength and the spectral drift at the echo wall wavelength along with the changes of pressure and temperature [ formula (5) ],
thus, quantitative detection of haptic sensations (pressure, temperature, stiffness, roughness) can be achieved by measuring the bragg wavelength and the shift in the echo wall wavelength.
Compared with the prior art, the invention has the advantages that:
1) A flexible optical fiber touch sensor can sense the temperature change of a contact object while measuring the contact pressure. The optical fiber touch sensor is characterized by comprising a section of bent Fiber Bragg Grating (FBG) wrapped by Polydimethylsiloxane (PDMS), the Bragg wavelength of the FBG and the temperature and pressure response characteristics of the whispering gallery mode interference peak are utilized to realize double-parameter sensing of pressure and temperature, and the problem of pressure and temperature crosstalk in touch sensing is solved.
2) The optical fiber touch sensor is prepared by wrapping the bent FBG optical fiber with the biocompatible PDMS serving as a base material, can perfectly simulate human body touch perception and measure temperature, pressure, hardness and surface roughness. The sensor has the advantages of simple manufacturing process, low cost and flexible structure, and can be applied to clinical operation robots.
3) The high thermal expansion coefficient of PDMS can increase the temperature sensitivity of the optical fiber touch sensor. Compared with the traditional bending optical fiber sensing, the FBG touch sensor wrapped by the PDMS has good mechanical performance, and the risk that the touch sensor damages biological tissues in clinical operations can be reduced. PDMS of different ratios can obtain the sensor of different pressure sensitivities, can adjust according to actual need.
(IV) description of the drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
Fig. 1 shows a prepared optical fiber tactile sensor.
Fig. 2 is a block diagram of a demodulation apparatus of the optical fiber tactile sensor.
Icon:
1: a laser light source 1;1-1: the light output port of the laser light source 1; 2: a fiber optic tactile sensor 2;2-1: an input port of the optical fiber touch sensor 2; 2-2: an output port of the optical fiber touch sensor 2; 3: a photodetector 3;3-1: an input port of the photoelectric detector 3; 3-2: an output port of the photodetector 3; 4: a data acquisition card 4;4-1: an input port of the data acquisition card 4; 4-2: an output port of the data acquisition card 4; 5: and (4) a computer.
(V) detailed description of the preferred embodiments
To make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings, and it is apparent that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The optical fiber touch sensor prepared by the invention has the following specific preparation process:
the method comprises the following steps that (1) 2 support frames are respectively fixed at the head and the tail of a hollow ceramic tube, the center of each support frame is a small hole with the diameter of 1mm, the two ends of an optical fiber Bragg grating are inserted into the small holes in the centers of the support frames of the hollow sleeves, the bending diameter of the optical fiber Bragg grating is reduced by pulling the two ends of an optical fiber until the optical fiber Bragg grating can be placed into a mold, the hollow ceramic tube is inserted into the mold, the bent FBG is attached to the inner wall of the mold, and the upper ends of the optical fiber and the hollow ceramic tube are fixed through ultraviolet glue.
And (3) mixing the PDMS prepolymer and the curing agent according to a certain proportion to obtain a PDMS mixed solution, injecting the mixed solution into the hollow tube and the mold in the step (1), curing at room temperature for 24 hours, then disassembling the mold, and taking out the cured sensor.
And (3) placing the sensor obtained by curing in the step (2) in a temperature box at 120 ℃ for 2 hours for annealing treatment to release residual stress generated by bending in the optical fiber, namely, releasing the residual stress by plastic deformation caused by high temperature, and curing and maturing PDMS. The final manufactured optical fiber tactile sensor is shown in fig. 1.
The invention also provides a measuring system based on the sensor, and a measuring system block diagram shown in figure 2 is provided. The specific devices adopted in the embodiment are as follows: the laser light source 1 can be a double-optical comb laser light source or a swept-frequency laser; a fiber optic tactile sensor 2; a photodetector 3; a data acquisition card 4 and a computer 5.
The specific process of the embodiment is as follows:
the optical output port 1-1 of the laser light source 1 is connected to the input port 2-1 of the optical fiber touch sensor 2 through a single mode fiber, the output port 2-2 of the optical fiber touch sensor 2 is connected to the input port 3-1 of the photoelectric detector 3 through the single mode fiber, the output port 3-2 of the photoelectric detector 3 is connected to the output port 4-2 of the data acquisition card 4 through a BNC signal wire for acquisition, and the acquisition result is sent to the computer 5 for processing.
The laser light source 1 can be a double-optical comb laser light source or a swept-frequency laser; the optical frequency signal (THz) can be converted into a radio frequency signal (MHz-kHz) by using a double optical comb laser source or a swept-frequency laser can be used, a photoelectric detector can be used for detection, an expensive spectrometer is not used for signal acquisition, a detection system is simplified, the detection precision is improved, real-time and quantitative touch detection is realized, the reliability is good, and long-term continuous touch monitoring can be realized.
The invention adopts the bent FBG combined with PDMS as a matrix material to prepare the flexible optical fiber touch sensor, thereby realizing the measurement of double parameters of pressure and temperature. The FBG and the whispering gallery mode temperature and pressure response characteristics are utilized to realize double-parameter sensing of pressure and temperature, the problem of crosstalk of pressure and temperature in touch sensing is solved, and the device has the advantages of compact structure, convenience in installation, good reliability and the like. The optical fiber touch sensor is prepared by wrapping the bent FBG optical fiber by adopting the biocompatible PDMS as a matrix material, and can perfectly simulate human body touch perception, measure temperature, pressure, hardness and surface roughness. The higher thermal expansion coefficient of PDMS increases the temperature sensitivity of the fiber optic tactile sensor. Compared with the traditional bending optical fiber sensing, the good mechanical property of the PDMS wrapped FBG touch sensor can reduce the risk of damaging biological tissues by the touch sensor in clinical operation. PDMS of different ratios can obtain the sensor of different pressure sensitivities, can adjust according to actual need. The sensor has the advantages of simple manufacturing process, low cost and flexible structure, and can be used for clinical operation robots.
Claims (8)
1. A flexible optical fiber tactile sensor can simultaneously measure the contact pressure and the change of the surface temperature of a contact object. The optical fiber touch sensor is characterized in that the optical fiber touch sensor adopts a spherical structure design and is made of flexible Polydimethylsiloxane (PDMS) material; the spherical structure is internally embedded with a bent Fiber Bragg Grating (FBG), double-parameter sensing of pressure and temperature is realized by utilizing the Bragg wavelength of the bent FBG and the temperature and pressure response characteristics of the whispering gallery mode interference peak, and the problem of pressure and temperature crosstalk in touch sensing can be solved.
2. The optical fiber tactile sensor according to claim 1, wherein the bent FBG is prepared by a method of etching point by point on a fiber core by directly penetrating a fiber coating layer through a special femtosecond laser, and has excellent bending resistance and low bending loss characteristics.
3. The fiber optic tactile sensor according to claim 1, wherein the bent FBG fiber is wrapped with PDMS, which has flexible mechanical properties and good biocompatibility, and the higher thermal elasticity of PDMS can effectively improve the temperature response of the sensor.
4. The optical fiber tactile sensor according to claim 1, wherein different whispering gallery interference spectra are obtained based on the mode interference principle of the optical fiber, wherein the bending diameters of the bending structure FBG are different; pressure acts on the optical fiber touch sensor, and the optical fiber touch sensor deforms, so that the bending diameter of the FBG is changed, interference spectrum change is caused, and high-sensitivity pressure measurement can be realized.
5. The optical fiber tactile sensor according to claim 1, wherein the pressure sensitivity of the optical fiber tactile sensor is adjusted by adjusting the ratio of the PDMS prepolymer to the curing agent so as to adjust the pressure sensitivity of the optical fiber tactile sensor according to actual needs by changing the ratio of the PDMS prepolymer to the curing agent.
6. A fibre-optic tactile sensor according to any of claims 1 to 5, characterized in that the sensor manufacturing method comprises the following steps:
step (1): respectively fixing 2 support frames at the head and the tail of a hollow ceramic tube, wherein a small hole with the diameter of 1mm is formed in the center of each support frame, inserting two ends of a fiber Bragg grating into the small holes in the centers of the support frames of the hollow sleeve, reducing the bending diameter of the fiber Bragg grating by pulling two ends of an optical fiber until the fiber Bragg grating can be placed into a spherical mold, inserting the hollow ceramic tube into the mold, attaching a bent FBG (fiber Bragg Grating) on the inner wall of the mold, and fixing the optical fiber and the upper end of the hollow ceramic tube by using ultraviolet glue;
step (2): mixing the PDMS prepolymer and a curing agent according to a certain proportion to obtain a PDMS mixed solution, injecting the mixed solution into the hollow tube and the mold in the step (1), curing at room temperature for 24 hours, then disassembling the mold, and taking out the cured sensor;
and (3): and (3) placing the sensor obtained by curing in the step (2) in a temperature box at 120 ℃ for 2 hours for annealing treatment to release residual stress generated by bending in the optical fiber, namely residual stress released by plastic deformation caused by high temperature, and curing and maturing PDMS.
7. A measuring system for implementing a fiber optic tactile sensor according to any of claims 1 to 6, wherein the measuring system comprises: the system comprises a laser light source, an optical fiber touch sensor, a photoelectric detector, a data acquisition card and a computer;
wherein, the demodulation device has the following element relationship: the optical output port 1-1 of the laser source is connected to the input port 2-1 of the optical fiber touch sensor through a single mode fiber, the output port 2-2 of the optical fiber touch sensor is connected to the input port 3-1 of the photoelectric detector through the single mode fiber, the output port 3-2 of the detector is connected to the output port 4-1 of the data acquisition card through a BNC signal wire for acquisition, and the acquisition result is sent to the computer 5 for processing.
8. The measurement system according to claim 7, wherein a double optical comb laser light source or a swept-frequency laser is used as a laser source, and detection data on a spectrum is inverted by directly detecting time domain information through a single photoelectric detector, so that real-time and accurate touch (temperature, pressure, hardness, roughness and the like) detection can be rapidly and accurately detected.
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