Pneumatic finger sensor based on three-dimensional S microstructure POF

Abstract

The invention belongs to the technical field of sensors, and particularly relates to a pneumatic finger sensor based on a three-dimensional S microstructure POF. The pneumatic finger sensor comprises an optical fiber body, the optical fiber body is formed through fused biconical taper, and the three-dimensional S microstructure POF is arranged in the length direction of the optical fiber body; the optical fiber body comprises an input optical fiber, a first conical region, a micro optical fiber, a second conical region and an output optical fiber which are sequentially connected, the first conical region and the input optical fiber are coaxially arranged, the second conical region and the output optical fiber are coaxially arranged, the small-diameter end of the first conical region is connected with the small-diameter end of the second conical region through the micro optical fiber, and the input optical fiber and the output optical fiber are arranged in parallel. And the micro optical fiber is S-shaped. According to the pneumatic finger sensor based on the three-dimensional S microstructure POF, the pneumatic finger sensor has sensitive and stable response characteristics to bending deformation, the stress condition, the bending state and the sliding direction can be effectively monitored, and the pneumatic finger sensor has good application potential in closed-loop control and self-adaptive operation of a flexible gripper.

Description

Technical Field

[0001] This invention belongs to the field of sensor technology, and in particular relates to a pneumatic finger sensor based on a three-dimensional S-microstructure POF. Background Technology

[0002] With the rapid development of soft robots, bionic prosthetics, and human-computer interaction systems, we have an urgent need for high-performance flexible sensors that can simulate the tactile functions of human skin, especially those capable of simultaneously sensing contact force, shape curvature, and sliding events. Traditional rigid or semi-flexible sensors, such as those based on metal strain gauges or semiconductor materials, are difficult to conformally fit and seamlessly integrate with continuously deforming soft actuators due to their inherent hardness, brittleness, and limited deformation capabilities. Furthermore, they are prone to fatigue failure under repeated large deformations, severely limiting their application in the dexterous manipulation and precise perception of flexible robots.

[0003] Polymer-plastic optical fibers, due to their excellent mechanical flexibility, high fracture toughness, and low elastic modulus, can adapt to complex deformations and recover quickly, making them an ideal carrier for robotic tactile sensors. However, for specific applications such as slip recognition and curvature measurement, existing methods often employ complex signal processing algorithms involving multi-sensor array data fusion. This approach not only requires the placement of multiple sensor units, increasing system complexity and integration difficulty, but also incurs a large computational burden and limits real-time performance. Furthermore, for curvature measurement, many flexible sensors can only detect the relative degree of bending, making it difficult to synchronously and accurately decouple absolute curvature information during dynamic contact or slippage. Summary of the Invention

[0004] In view of this, the present invention aims to propose a pneumatic finger sensor based on a three-dimensional S-microstructure POF to solve the problem that existing sensors are unable to simultaneously achieve sliding recognition and curvature detection during dynamic contact or sliding.

[0005] To achieve the above objectives, the technical solution of the present invention is implemented as follows: In a first aspect, embodiments of the present invention provide a pneumatic finger sensor based on a three-dimensional S-microstructure POF, comprising an optical fiber body and an elastomer, wherein the optical fiber body is located within the elastomer, and the optical fiber body is formed by melt taper forming. Along the length direction of the optical fiber body, the optical fiber body includes an input optical fiber, a first tapered region, a micro-optical fiber, a second tapered region, and an output optical fiber connected in sequence. The first tapered region is coaxially arranged with the input optical fiber, and the second tapered region is coaxially arranged with the output optical fiber. The small diameter end of the first tapered region and the small diameter end of the second tapered region are connected through the micro-optical fiber. The input optical fiber and the output optical fiber are arranged parallel to each other. The microfiber is S-shaped. Along the axial direction of the input or output optical fiber, there is a first misalignment gap between the small diameter end of the first conical region and the small diameter end of the second conical region. With the axial direction of the input or output optical fiber as the projection direction, in a projection plane perpendicular to the axial direction of the input or output optical fiber, there is a second misalignment gap between the axis of the input optical fiber and the axis of the output optical fiber. The microfiber extends from the input optical fiber to the output optical fiber along the length of the line connecting the axes of the input and output optical fibers. The elastic body has a force-applying surface. The plane where the microfiber is located is perpendicular to the force-applying surface, so that the microfiber undergoes a curvature change when subjected to force, and the light loss is induced by the curvature change to realize pressure measurement and sliding sensing.

[0006] Furthermore, the input optical fiber and the output optical fiber have the same diameter, and the diameter ratio of the input optical fiber to the micro-optical fiber is 25:4.

[0007] Furthermore, the diameter of the microfiber is 40 μm.

[0008] Furthermore, the first conical region and the second conical region have the same shape, and the length of both the first conical region and the second conical region is 1.3-1.6 mm along the length direction of the input optical fiber.

[0009] Furthermore, the length of the first misalignment spacing is 1.6-1.9 mm, the length of the second misalignment spacing is 0.8-1.1 mm, and the straight-line distance between the two endpoints of the S-shape in the micro-optical fiber is 1.9-2 mm.

[0010] Furthermore, the optical fiber body includes a core and a cladding covering the core. The core is made of polymethyl methacrylate, and the cladding is made of fluorinated polymethyl methacrylate.

[0011] Furthermore, the elastic body is an elastic finger body; the optical fiber body is located inside the elastic finger body, and two optical fiber bodies are arranged in parallel, with the length direction of each optical fiber body being the same as the length direction of the elastic finger body; one side of the elastic finger body is provided with a fitting part, and the other side is provided with a deformation part, the force application surface is located on the fitting part, the elastic finger body is provided with an isolation cavity and an inflation cavity, and the elastic finger body is provided with an inflation hole communicating with the inflation cavity; with the length direction of the elastic finger body as the projection direction, in the projection plane perpendicular to the length direction of the elastic finger body, the isolation cavity is located near the fitting part, the inflation cavity is located near the deformation part, one optical fiber body is located between the fitting part and the isolation cavity, and the other optical fiber body is located between the isolation cavity and the inflation cavity.

[0012] Furthermore, taking the length direction of the elastic finger body as the projection direction, in the projection plane perpendicular to the length direction of the elastic finger body, the projection of the bonding portion is a straight line segment, and the line connecting the geometric centers of the two optical fiber body projections is perpendicular to the bonding portion.

[0013] Furthermore, the isolation cavity is connected to the inflatable cavity.

[0014] Furthermore, a protrusion is provided on the bonding portion corresponding to the position of the microfiber.

[0015] Compared with existing technologies, the pneumatic finger sensor based on a three-dimensional S-microstructure POF described in this invention has the following advantages: (1) The pneumatic finger sensor based on a three-dimensional S-shaped microstructure POF described in this invention has sensitive and stable response characteristics to bending deformation, and can effectively monitor bending state and angle changes. Furthermore, by utilizing the asymmetry of the S-shaped microstructure formed by the micro-fiber, sliding shear forces in different directions act on the upper and lower sensitive areas of the micro-fiber, generating distinctly different light intensity response modes, thereby achieving sliding sensing. Therefore, this pneumatic finger sensor has good application potential in the closed-loop control and adaptive operation of flexible grippers.

[0016] (2) The pneumatic finger sensor based on the three-dimensional S-microstructure POF described in this invention, through the simple structural form of setting the optical fiber body with parallel double three-dimensional S-microstructures in the elastic finger body, enables this pneumatic finger sensor to not only measure pressure in the pneumatic finger, but also to measure sliding force and bending effect, which is beneficial to improving the operational controllability and environmental adaptability of the pneumatic finger gripping device, and is very suitable for robot application scenarios that require precise gripping and sliding detection.

[0017] (3) The pneumatic finger sensor based on the three-dimensional S-microstructure POF described in this invention, by setting an isolation cavity in the elastic finger body, can effectively isolate the effect of sliding force transmission by utilizing the isolation cavity, so that this pneumatic finger sensor can realize synchronous and independent measurement of bending signal and sliding signal during the gripping process.

[0018] (4) The pneumatic finger sensor based on the three-dimensional S-microstructure POF described in this invention adopts a protrusion structure design on the elastic finger body, which facilitates the positioning and installation of micro-fibers and can efficiently transmit the normal force to the corresponding fiber, further ensuring the accuracy of the detection signal and the reliability of the structural assembly of this pneumatic finger sensor. Attached Figure Description

[0019] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of the pneumatic finger sensor based on the three-dimensional S-microstructure POF as described in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of a force measurement experiment conducted using a pneumatic finger sensor based on a three-dimensional S-microstructure POF, as described in Embodiment 1 of the present invention. Figure 3 This is an experimental result diagram of the force measurement experiment performed on the pneumatic finger sensor based on the three-dimensional S-microstructure POF as described in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of a sliding experiment conducted on the pneumatic finger sensor based on the three-dimensional S-microstructure POF as described in Embodiment 1 of the present invention. Figure 5 This is an experimental result diagram of the sliding experiment performed on the pneumatic finger sensor based on the three-dimensional S-microstructure POF as described in Embodiment 1 of the present invention. Figure 6 This is an experimental result diagram of the pneumatic finger sensor based on the three-dimensional S-microstructure POF described in Embodiment 1 of the present invention during a bending experiment; Figure 7 This is a schematic diagram of the pneumatic finger sensor based on the three-dimensional S-microstructure POF as described in Embodiment 2 of the present invention; Figure 8 This is a cross-sectional view of the elastic finger body in the pneumatic finger sensor based on the three-dimensional S-microstructure POF described in Embodiment 2 of the present invention. Figure 9 This is a longitudinal cross-sectional view of the elastic finger body in the pneumatic finger sensor based on the three-dimensional S-microstructure POF described in Embodiment 2 of the present invention.

[0020] Explanation of reference numerals in the attached figures: 1. Input optical fiber; 2. First conical region; 3. Micro-optical fiber; 4. Second conical region; 5. Output optical fiber; 6. Elastomer; 61. Force application surface; 62. Elastic finger body; 7. Inflatable cavity; 8. Adhesive part; 9. Deformation part; 10. Protrusion; 11. Slot; 12. Isolation cavity; 13. First optical fiber body; 14. Second optical fiber body. Detailed Implementation

[0021] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0022] Example 1 Figure 1 This is a schematic diagram of the pneumatic finger sensor based on a three-dimensional S-microstructure POF as described in Embodiment 1 of the present invention. See also... Figure 1 This pneumatic finger sensor includes an optical fiber body and an elastomer 6. The optical fiber body is located inside the elastomer 6. The optical fiber body is formed by melt drawing and tapering. Along the length direction of the optical fiber body, the optical fiber body includes an input optical fiber 1, a first conical region 2, a micro-optical fiber 3, a second conical region 4, and an output optical fiber 5 connected in sequence. The first conical region 2 is coaxially arranged with the input optical fiber 1, and the second conical region 4 is coaxially arranged with the output optical fiber 5. The small diameter end of the first conical region 2 and the small diameter end of the second conical region 4 are connected by the micro-optical fiber 3.

[0023] Specifically, the input optical fiber 1 and the output optical fiber 5 are arranged parallel to each other. The micro-optical fiber 3 is S-shaped. Along the axial direction of the input optical fiber 1 or the output optical fiber 5, there is a first misalignment gap between the small diameter end of the first conical region 2 and the small diameter end of the second conical region 4. With the axial direction of the input optical fiber 1 or the output optical fiber 5 as the projection direction, in the projection plane perpendicular to the axial direction of the input optical fiber 1 or the output optical fiber 5, there is a second misalignment gap between the axis of the input optical fiber 1 and the axis of the output optical fiber 5. Along the length direction of the line connecting the axis of the input optical fiber 1 and the axis of the output optical fiber 5, the micro-optical fiber 3 extends from the input optical fiber 1 to the output optical fiber 5. The elastic body 6 has a force application surface 61. The plane where the micro-optical fiber 3 is located is perpendicular to the force application surface 61, so that the micro-optical fiber 3 undergoes a curvature change when subjected to force, and the light loss is caused by the curvature change to realize pressure measurement and sliding sensing.

[0024] In this embodiment, the optical fiber body is composed of a single flexible polymer optical fiber. Its core feature is that a three-dimensional S-shaped microstructure is fabricated in a section of the polymer optical fiber using a fused taper method. This three-dimensional S-shaped microstructure is the micro-optical fiber 3. The elastic body 6 can be made of silicone or PDMS, and the force-applying surface 61 is used by the elastic body 6 to withstand external forces.

[0025] In practical applications, the optical fiber body can be placed inside the elastomer 6, which can be cast using a 3D-printed mold. The mold has an S-shaped structure that mates with the micro-optical fiber 3. For example, PDMS can be filled and cured in two steps to form an "S"-shaped structure with a certain curvature. The input optical fiber 1 and the first conical region 2 are located on the upper layer of the elastomer 6, while the second conical region 4 and the output optical fiber 5 are located on the lower layer of the elastomer 6. The micro-optical fiber 3 is located in the middle of the entire elastomer 6 and is S-shaped. The micro-optical fiber 3 connects the first conical region 2 and the second conical region 4 of the upper and lower parts of the elastomer 6 to form the core area of ​​force sensing, ultimately creating a pneumatic finger sensor.

[0026] It should be noted that the fiber optic sensing system mainly consists of a pneumatic finger sensor, an LED coupled light source (650 nm), and an optical detection component. In actual use, the light source can be connected to the input fiber optic cable 1 in the pneumatic finger sensor. The optical detection component includes a photodetector (TPM-8202-2202), a data acquisition module, a data processing module, and a display module. These parts are connected in sequence, with the photodetector connected to the output fiber optic cable 5 of the pneumatic finger sensor.

[0027] In practical applications, the plane of the three-dimensional "S" microstructure composed of microfibers is perpendicular to the force-acting surface 61. Therefore, the upper and lower segments of the S-shaped microfiber will undergo curvature changes when subjected to force, and this curvature change induces optical loss to achieve pressure measurement. Simultaneously, because the three-dimensional "S" microstructure composed of microfibers is asymmetrically arranged along the normal direction, this normal asymmetry also enables sliding sensing.

[0028] See Figure 2 and Figure 3 When a pressure probe is placed above the pneumatic finger sensor of the sensor, and pressure is applied to the pneumatic finger sensor using the pressure probe, such as a pressure probe with an action area of ​​7.06 square millimeters, the normal force acts on the upper surface of the elastic body 6 (i.e. the force action surface 61), causing the elastic body 6 to undergo longitudinal and transverse deformation. This results in a change in the macro-bending degree of the micro-fiber 3 part of the pneumatic finger sensor, causing changes in the optical loss inside the fiber body, which is reflected in the change in the output light intensity of the output fiber 5.

[0029] The pneumatic finger sensor based on a three-dimensional S-microstructure POF provided in this embodiment reduces the macro-bending of the micro-fiber 3 section when performing force measurement due to the normal force applied to the entire sensing area. As the pressure increases, the bending of the micro-fiber 3 further decreases, leading to a reduction in internal optical loss and an increase in output light intensity. This results in a higher intensity light signal that subsequent devices can receive and detect, which is beneficial for improving the force detection effect and accuracy of this pneumatic finger sensor.

[0030] Since the signal intensity modulation of the sensor's optical signal depends on the curvature of the "S"-shaped microfiber 3, the "S"-shaped region formed by the microfiber 3 can be regarded as being formed by connecting circular arcs, where the arc length is a fixed value. The bending radius is , arc Among them, radians It can demonstrate the degree of curvature of the S-shaped microstructure. The larger the size, the greater the degree of bending. The smaller the arc length, the less curvature. The arc length formula is known.

[0031] There is also the chord length formula:

[0032] From the arc length formula and the chord length formula, we can obtain:

[0033] From the above formula, it can be seen that when When the degree of bending decreases (i.e.) (Reducing) will result in chord length Increase.

[0034] By applying small-scale pressure to five parts—input fiber 1, first conical region 2, microfiber 3, second conical region 4, and output fiber 5—and calculating the chord length, the change in the degree of bending of the S-shaped microstructure in microfiber 3 can be obtained.

[0035] Using the above-described configuration, the micro-fiber 3 in this pneumatic finger sensor adopts a three-dimensional S-shaped microstructure design. This makes the sensing mechanism of this pneumatic finger sensor the opposite of that of traditional signal strength loss-type sensors. When the sensor is subjected to pressure, the bending of the micro-fiber 3 is gradually released, and the signal strength gradually increases. Therefore, this pneumatic finger sensor based on the three-dimensional S-shaped microstructure POF can withstand a greater ultimate force, making it suitable for applications with high stress ranges, such as robotic tactile sensing, and giving it better applicability and versatility.

[0036] Correspondingly, since the micro-fiber 3 adopts an S-shaped structure, a small-range normal force acts on different sensitive parts, and the force response of the curvature of the micro-fiber 3 is different. Based on this, the pneumatic finger sensor can recognize sliding, and the pneumatic finger sensor can distinguish two sliding directions. Therefore, during the process of an object sliding on the surface of the elastic body 6, it passes through the aforementioned force measurement section in different sequences. According to the different characteristics of the output time-domain image, sliding recognition can be clearly achieved, and the sliding force and sliding direction of the object can be effectively identified.

[0037] Similarly, taking curvature measurement as an example, when the pneumatic finger sensor bends, the micro-fiber 3 of the S-microstructure is stretched, resulting in a significant increase in the internal chord length. The relative optical power P / P0 increases linearly with the increase in stretch. Therefore, by detecting the change in the output light intensity of the output fiber 5 under different bending curvatures, the curvature can be measured.

[0038] In one embodiment of this invention, the input optical fiber 1 and the output optical fiber 5 have the same diameter, and the diameter ratio of the input optical fiber 1 to the micro-optical fiber 3 is 25:4. For example, the diameter of the micro-optical fiber 3 is 40 μm. Therefore, the diameters of both the input optical fiber 1 and the output optical fiber 5 are 250 μm.

[0039] For example, the length of the micro-fiber 3 is typically 0.3-0.5 mm longer than the total chord length. By setting the length of the micro-fiber 3 to 1.9-2.3 mm, this size of fiber is thin and flexible, with low bending loss and is not easy to break, allowing for concealed cabling in confined spaces.

[0040] In one embodiment of this example, the first cone region 2 and the second cone region 4 have the same shape, and the length of the first cone region 2 and the second cone region 4 along the length direction of the input optical fiber 1 is 1.3-1.6mm.

[0041] For example, the length of the first cone region 2 and the second cone region 4 is preferably 1.5 mm. By setting the length and shape of the first cone region 2 and the second cone region 4 to be the same, and setting the length of both cone regions to 1.3-1.6 mm, the two cone regions have the same shape and the same length, which can ensure that the response generated by bending deformation is consistent, which is beneficial to improving the detection accuracy of the sensor.

[0042] In one embodiment of this example, the length of the first misalignment spacing is 1.6-1.9 mm, the length of the second misalignment spacing is 0.8-1.1 mm, and the straight-line distance between the two endpoints of the S-shape in the micro-fiber 3 is 1.9-2 mm.

[0043] For example, the first misalignment spacing is 1.7 mm, the second misalignment spacing is 0.9 mm, and the straight-line distance between the two endpoints of the S-shape in the microfiber 3 is 1.97 mm. By setting the length of the first misalignment spacing to 1.6-1.9 mm and the length of the second misalignment spacing to 0.8-1.1 mm, this size range can meet the requirement that the signal strength modulation depends on the bending degree of the "S"-shaped microfiber 3, while maximally matching the theoretical derivation formula.

[0044] In one embodiment of this invention, the optical fiber body includes a core and a cladding covering the core. The core is made of polymethyl methacrylate (PMMA), and the cladding is made of fluorinated polymethyl methacrylate (fluorinated PMMA).

[0045] Specifically, the optical fiber body can be formed by polymer fiber fusion tapering. The following describes the manufacturing process of this pneumatic finger sensor in conjunction with a specific product manufacturing process: Polymer optical fiber: The core layer is polymethyl methacrylate (PMMA), the cladding is fluorinated PMMA, and the total diameter is 250 µm. Elastomer material: Polydimethylsiloxane (PDMS), the main agent is Sylgard 184A, and the curing agent is Sylgard 184B.

[0046] Fiber optic tapering system: consists of a stepper motor (model: 17HS19-2004S1, equipped with TMC2208 driver), a precision displacement platform, a miniature tube furnace (heating zone length 20mm, maximum temperature 300℃) and fiber optic clamps.

[0047] 3D printer: A stereolithography (SLA) 3D printer is used, with rigid resin (Formlabs Rigid4000 Resin) as the printing material, for making encapsulation molds.

[0048] Heating platform: Digital display temperature control heating platform.

[0049] Ultraviolet lamp: 365nm wavelength, 36W ultraviolet point light source.

[0050] Optical testing platform: including LED light source (wavelength 650 nm), photodetector (TPM-8202-2202) and data acquisition card.

[0051] Secondly, the optical fiber body needs to be installed inside the elastic body 6 to form the sensor. The manufacturing process of the sensor is explained below with reference to a specific product: Step 1: Fabricate the optical fiber body. The specific steps are as follows: Use a fiber optic cleaver to process the end faces of a polymer optical fiber about 15cm long to ensure that the end faces are flat.

[0052] The treated polymer fiber is fixed on the clamp of the tapered system to ensure that the fiber is properly straightened.

[0053] Polymer optical fibers with a diameter of 250 μm were melt-drawn and tapered using a stepper motor (set to a stretching speed of 1500 μm / s and a length of 4.5 mm) and a heating device (set to 120 °C) to produce microfibers with a length of 2 mm and a diameter of 40 μm.

[0054] Step 2: Fabricate the S-shaped package lower mold. The specific steps are as follows: The PDMS solution was prepared by mixing the elastomer material (Selge 184A) and the curing agent (Selge 184B) in a ratio of 10:1 and allowing it to stand for later use.

[0055] An S-shaped base mold was created using 3D printing technology.

[0056] Place the micro-fiber onto the S-shaped substrate mold, and insert the soft plug into the pre-reserved grooves on both sides of the substrate mold to make it fit the bottom of the substrate mold.

[0057] Meanwhile, the entire base mold is fixed on the heating table, filled with PDMS that has been left to stand, the heating table is set to 70°C, heated for 15 minutes, and then demolded to obtain a half mold of the sensor.

[0058] Step 3, secondary curing, the specific steps are as follows: Place the half-mold into the 3D-printed flat-bottomed model, repeat step 2, fill with PDMS, heat at 70℃ for 15 minutes, and perform a second curing.

[0059] Step 4: Demolding to obtain the sensor: Cool and demold to obtain the sensor sample.

[0060] The working principle of the pneumatic finger sensor is explained below with reference to a specific testing process: See Figure 2 To test the normal force range of the sensor: Place the sensor on an optical testing platform. Connect input fiber 1 to the light source and output fiber 5 to the photodetector. Apply a normal force to the entire sensing part using a circular probe and record the change in output voltage (proportional to output light intensity).

[0061] Test results: See Figure 3 As pressure increases, the normalized optical power increases linearly, and the sensor's sensitivity can reach 1.55. The measurement range is 0-300 kPa. This linear response characteristic facilitates signal identification and detection. When performing the same test, the pneumatic finger sensor (i.e., the three-dimensional S-microstructure) provided in this embodiment has a significantly larger measurement range than similar sensors, as shown in Table 1 below.

[0062] Table 1. Parameter comparison with other sensors

[0063] See Figure 4 To verify the sensor's ability to distinguish the sliding direction, we conducted a bidirectional sliding test: The experiment used a hemispherical probe with a diameter of 5 mm, which slid unidirectionally along the sensor surface at a constant speed of 10 mm / s: first sliding from the input fiber 1 side to the output fiber 5 side, and then sliding in the opposite direction.

[0064] Test results show that the sensor's output signal exhibits a significant direction dependence. (See also...) Figure 5 When the sliding direction is from right to left, the time-domain signal intensity within a single sliding cycle exhibits a characteristic waveform of "double rising peak - single falling peak"; while when the sliding direction is reversed, the time-domain signal intensity shows a morphological difference of "single rising peak - single falling peak".

[0065] Based on the aforementioned symmetrical and distinguishable signal characteristics, the pneumatic finger sensor in the sensor can not only reliably detect the occurrence of sliding events, but also further identify the direction of the sliding. This function provides an effective means of determining the sliding direction of the object during the gripping process, enhancing the feedback control capability of the soft gripping system.

[0066] Specifically, when the sensor undergoes bending deformation at different curvatures, the pneumatic finger sensor experiences axial stretching, which significantly increases the chord length and consequently alters the transmitted optical signal. Specifically, the normalized relative optical power P / P0 exhibits a good linear upward trend with increasing stretching. To quantify this response characteristic, the sensor was started from a fully extended state (0° bend) and gradually bent at 10° intervals, reaching typical angles of 10°, 40°, and 80°, while simultaneously recording the changes in the sensor's output light intensity.

[0067] See the experimental results. Figure 6 In the figure, the left vertical axis represents the measured light intensity value P, and the right vertical axis represents the corresponding normalized coordinates, i.e., the normalized relative light power P / P0. It can be seen that the sensor output light intensity increases significantly in a stepwise manner with the increase of the bending angle, and the light signal response at each bending stage is stable and distinguishable.

[0068] The above results demonstrate that the pneumatic finger sensor provided in this embodiment exhibits sensitive and stable response characteristics to bending deformation, effectively monitoring bending state and angle changes. Furthermore, by utilizing the asymmetry of the S-shaped microstructure formed by the micro-optical fiber 3, sliding shear forces in different directions act on different sensitive parts of the micro-optical fiber 3, producing distinctly different light intensity response modes. Therefore, this pneumatic finger sensor possesses significant application potential in the closed-loop control and adaptive operation of flexible grippers.

[0069] Example 2 Figure 7 This is a schematic diagram of the pneumatic finger sensor based on a three-dimensional S-microstructure POF as described in Embodiment 2 of the present invention. (Reference) Figures 7 to 9 This pneumatic finger sensor is an improvement and optimization based on the above embodiment. The main improvements are as follows: the elastic body 6 is an elastic finger body 62; the optical fiber body is located inside the elastic finger body 62, and two optical fiber bodies are arranged in parallel, with the length direction of each optical fiber body being the same as the length direction of the elastic finger body 62; one side of the elastic finger body 62 is provided with a fitting part 8, and the other side is provided with a deformation part 9. The force application surface 61 is located on the fitting part 8. The elastic finger body 62 is provided with an isolation cavity 12 and an inflation cavity 7. The elastic finger body 62 is provided with an inflation hole communicating with the inflation cavity 7; with the length direction of the elastic finger body 62 as the projection direction, in the projection plane perpendicular to the length direction of the elastic finger body 62, the isolation cavity 12 is located near the fitting part 8, the inflation cavity 7 is located near the deformation part 9, one optical fiber body is located between the fitting part 8 and the isolation cavity 12, and the other optical fiber body is located between the isolation cavity 12 and the inflation cavity 7.

[0070] Specifically, the pneumatic finger sensor comprises two parallel optical fiber bodies: a first optical fiber body 13 and a second optical fiber body 14. The first optical fiber body 13 is located between the mating portion 8 and the isolation cavity 12, while the second optical fiber body 14 is located between the isolation cavity 12 and the inflation cavity 7. The first optical fiber body 13 simultaneously detects bending deformation and contact surface sliding force; because the isolation cavity 12 effectively isolates the transmission of sliding force, the second optical fiber body 14 only responds to bending deformation. Furthermore, the identical shape and length of the two conical regions of the first and second optical fiber bodies 13 and 14 ensure consistent responses to bending deformation, and decoupling the composite signal from the first optical fiber allows for the separation of pure sliding force data.

[0071] It should be noted that, in the first optical fiber body 13 and the second optical fiber body 14, the lengths of the first cone region 2 and the second cone region 4 are preferably both 1.5 mm.

[0072] In practical applications, the elastic finger 62 is pneumatically driven. An air pump inflates the internal air cavity 7 of the elastic finger 62, causing it to bend and deform, thus enabling the grasping and clamping of objects. During the grasping process, two key data points need to be monitored in real time: first, the sliding force between the grasped object and the soft finger, used to dynamically adjust the inflation amount to ensure grasping stability; second, the degree of bending of the elastic finger 62 under pneumatic drive, used to monitor the soft finger's state in real time and achieve more precise grasping control.

[0073] Since sliding recognition and curvature measurement rely heavily on multi-sensor arrays or complex signal processing algorithms, they suffer from problems such as complex system structure, high integration difficulty, large computational load, and poor real-time performance. Furthermore, it is difficult to synchronously decouple and obtain absolute curvature information during dynamic processes.

[0074] This embodiment integrates parallel dual-dimensional S-shaped microstructures within the elastic finger body 62, enabling simultaneous and independent measurement of pressure, bending, and sliding with high sensitivity. The second optical fiber body 14 provides a pure bending signal to decouple the composite signal from the first optical fiber body 13, thereby separating the sliding force information and allowing for feedback adjustment of the inflation volume. This eliminates the need for a multi-sensor array in this pneumatic finger sensor, reducing the complexity of the sensing system and the data processing burden, improving measurement real-time performance and accuracy, facilitating integration with finger grasping devices, and enhancing the controllability and environmental adaptability of the grasping device operation.

[0075] In one embodiment of this example, the projection direction is the length direction of the elastic finger body 62. In the projection plane perpendicular to the length direction of the elastic finger body 62, the projection of the bonding part 8 is a straight line segment, and the line connecting the geometric centers of the two optical fiber bodies is perpendicular to the bonding part 8.

[0076] By using the above-mentioned setup, it can be ensured that sliding force, normal force, etc. can be accurately transmitted from the bonding part 8 to the two optical fiber bodies, so that the two optical fiber bodies can achieve synchronous and independent measurement, which is beneficial to improving the detection accuracy and precision of this pneumatic finger sensor.

[0077] Optionally, the deformable part 9 is provided with a slot 11 to facilitate the deformation of the elastic finger body 62. When the air cavity 7 is inflated, the rigidity of the elastic finger body 62 increases, making it suitable for clamping objects. The elastic finger body 62 can be made of silicone or PDMS. During the fiber optic casting process of the elastic finger body 62, two identical fiber optic bodies (finger length 110 mm) are embedded inside the elastic finger body 62. The two fiber optic bodies are arranged parallel to each other, and the plane of the microfiber 3 in the two fiber optic bodies is perpendicular to the surface of the mating part 8 of the elastic finger body 62.

[0078] Based on the aforementioned sensing performance, the first optical fiber body 13 simultaneously detects the bending deformation signal of the soft finger and the sliding force signal of the contact surface during the grasping process. An isolation cavity 12 is provided between the second optical fiber body 14 and the first optical fiber body 13, with the two fibers distributed parallel to each other on both sides of the isolation cavity 12. The midpoint of the micro-fiber 3 in both optical fiber bodies is 1.5 mm from the cavity wall of the isolation cavity 12. Since the two optical fiber bodies are completely parallel and have the same bending direction, the response signals of the two optical fiber bodies to the bending of the soft finger are identical.

[0079] The isolation cavity 12 effectively blocks the transmission of sliding force to the second optical fiber body 14. Therefore, the second optical fiber body 14 only responds to the soft finger bending signal. By analyzing the signal of the second optical fiber body 14, the sliding force data can be decoupled from the composite signal of the first optical fiber body 13. Sliding force monitoring helps to adjust the gripping force in real time, while bending degree monitoring can assess the inflation status in real time and feed it back to the pneumatic control system, realizing closed-loop adjustment of the inflation amount of the elastic finger body 62. By simultaneously measuring the sliding force and curvature, the detection and control of the gripping process can be effectively assisted.

[0080] In one embodiment of this example, the isolation cavity 12 is connected to the inflation cavity 7.

[0081] For example, the isolation cavity 12 and the inflation cavity 7 can be connected by a conduit within the elastic finger body 62. When inflation cavity 7 is filled with air, the inflation cavities 7 and the isolation cavity 12 on both sides of the second optical fiber body 14 are in the same air pressure environment, and the air pressures they experience cancel each other out. Therefore, the inflation process does not affect its signal. Since the volume of the isolation cavity 12 is small, compared to the larger volume of the inflation cavity 7, the effect of the inflation process on the gas flow within the isolation cavity 12 is negligible. Therefore, the gas flow and air pressure effects on the first optical fiber body 13 are negligible.

[0082] By using the above configuration, after air is filled into the isolation cavity 12, the blocking effect of the isolation cavity 12 on the sliding force can be improved, which is beneficial to improving the detection accuracy of the pneumatic finger sensor.

[0083] Optionally, the volume of the inflatable cavity 7 is larger than the volume of the isolation cavity 12. For example, the thickness of the cross-section of the isolation cavity 12 is 1.5-2 mm and the length is 20 mm, while the thickness of the cross-section of the inflatable cavity 7 is 16 mm and the length is 80-90 mm.

[0084] By using the above configuration, the isolation cavity 12 is connected to the inflation cavity 7, so that when the elastic finger body 62 is inflated, sufficient air is ensured in the isolation cavity 12, thus ensuring the isolation cavity 12's blocking effect on sliding force.

[0085] In one embodiment of this invention, a protrusion 10 is provided on the bonding portion 8 at the position corresponding to the microfiber 3.

[0086] For example, a hemispherical protrusion, or protrusion 10, is provided at the middle half of the inner surface of the elastic finger body 62. The protrusion 10 extends along the width direction of the elastic finger body 62 and is located in the area where the bending deformation of the elastic finger body 62 is most significant (tested to be the center position in the length direction of the finger). By providing the protrusion 10 on the elastic finger body 62, the protrusion 10 can simultaneously enhance the gripping friction.

[0087] See Figure 8 The first optical fiber body 13 and the second optical fiber body 14 are positioned corresponding to the protrusion 10, and the micro-optical fiber 3 is located in the vertical focal region. By adopting this arrangement, it is not only convenient to position and install the micro-optical fiber 3, ensuring that the micro-optical fibers 3 in the two optical fiber bodies are aligned, but also, during the gripping process, the protrusion 10 can effectively transfer the normal force and frictional force to the first optical fiber body 13, and effectively transfer the normal force to the second optical fiber body 14.

[0088] Using the above configuration, the elastic finger body with parallel double-stereoscopic S-shaped microstructure can measure the sliding force and bending structure effect in the pneumatic finger. This enables the pneumatic finger sensor to achieve synchronous and independent measurement of bending and sliding signals during the gripping process, improving the operational controllability and environmental adaptability of the pneumatic finger gripping device. It is very suitable for robot application scenarios that require precise gripping and sliding detection.

[0089] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A pneumatic finger sensor based on a three-dimensional S-microstructure POF, comprising an optical fiber body and an elastomer (6), wherein the optical fiber body is located within the elastomer (6), the optical fiber body is formed by melt taper forming, and along the length direction of the optical fiber body, the optical fiber body comprises an input optical fiber (1), a first tapered region (2), a micro-optical fiber (3), a second tapered region (4), and an output optical fiber (5) connected in sequence, wherein the first tapered region (2) is coaxially arranged with the input optical fiber (1), the second tapered region (4) is coaxially arranged with the output optical fiber (5), and the small diameter end of the first tapered region (2) and the small diameter end of the second tapered region (4) are connected by the micro-optical fiber (3), characterized in that: The input optical fiber (1) and the output optical fiber (5) are arranged parallel to each other. The micro-optical fiber (3) is S-shaped. Along the axial direction of the input optical fiber (1) or the output optical fiber (5), there is a first misalignment gap between the small diameter end of the first conical region (2) and the small diameter end of the second conical region (4). With the axial direction of the input optical fiber (1) or the output optical fiber (5) as the projection direction, in the projection plane perpendicular to the axial direction of the input optical fiber (1) or the output optical fiber (5), the axis of the input optical fiber (1) and the output optical fiber (5) are aligned. There is a second misalignment spacing between the axes of the output optical fiber (5), and along the length direction of the line connecting the axis of the input optical fiber (1) and the axis of the output optical fiber (5), the micro-optical fiber (3) extends from the input optical fiber (1) to the output optical fiber (5); the elastic body (6) has a force-acting surface (61), and the plane where the micro-optical fiber (3) is located is perpendicular to the force-acting surface (61), so that the micro-optical fiber (3) undergoes curvature change when subjected to force, and the light loss is triggered by the curvature change to realize pressure measurement and sliding sensing.

2. The pneumatic finger sensor based on a three-dimensional S-microstructure POF according to claim 1, characterized in that: The input optical fiber (1) and the output optical fiber (5) have the same diameter, and the diameter ratio of the input optical fiber (1) to the micro-optical fiber (3) is 25:

4.

3. The pneumatic finger sensor based on a three-dimensional S-microstructure POF according to claim 2, characterized in that: The diameter of the micro-optical fiber (3) is 40 μm.

4. The pneumatic finger sensor based on a three-dimensional S-microstructure POF according to claim 1, characterized in that: The first cone region (2) and the second cone region (4) have the same shape. Along the length direction of the input optical fiber (1), the length of the first cone region (2) and the second cone region (4) is 1.3-1.6 mm.

5. The pneumatic finger sensor based on a three-dimensional S-microstructure POF according to claim 1, characterized in that: The length of the first misalignment spacing is 1.6-1.9 mm, the length of the second misalignment spacing is 0.8-1.1 mm, and the straight-line distance between the two endpoints of the S-shape in the micro-optical fiber (3) is 1.9-2 mm.

6. A pneumatic finger sensor based on a three-dimensional S-microstructure POF according to claim 1, characterized in that: The optical fiber body includes a core and a cladding covering the core. The core is made of polymethyl methacrylate, and the cladding is made of fluorinated polymethyl methacrylate.

7. A pneumatic finger sensor based on a three-dimensional S-microstructure POF according to any one of claims 1-6, characterized in that: The elastic body (6) is an elastic finger body (62). The optical fiber body is located inside the elastic finger body (62), and two optical fiber bodies are arranged in parallel. The length direction of each optical fiber body is the same as the length direction of the elastic finger body (62). One side of the elastic finger body (62) is provided with a fitting part (8), and the other side is provided with a deformation part (9). The force application surface (61) is located on the fitting part (8). The elastic finger body (62) is provided with an isolation cavity (12) and an inflation cavity (7). The body (62) is provided with an inflation hole communicating with the inflation cavity (7); with the length direction of the elastic finger body (62) as the projection direction, in the projection plane perpendicular to the length direction of the elastic finger body (62), the isolation cavity (12) is disposed near the fitting part (8), the inflation cavity (7) is disposed near the deformation part (9), one optical fiber body is located between the fitting part (8) and the isolation cavity (12), and another optical fiber body is located between the isolation cavity (12) and the inflation cavity (7).

8. A pneumatic finger sensor based on a three-dimensional S-microstructure POF according to claim 7, characterized in that: With the length direction of the elastic finger body (62) as the projection direction, in the projection plane perpendicular to the length direction of the elastic finger body (62), the projection of the bonding part (8) is a straight line segment, and the line connecting the geometric centers of the two optical fiber body projections is perpendicular to the bonding part (8).

9. A pneumatic finger sensor based on a three-dimensional S-microstructure POF according to claim 7, characterized in that: The isolation cavity (12) is connected to the inflatable cavity (7).

10. A pneumatic finger sensor based on a three-dimensional S-microstructure POF according to claim 7, characterized in that: The bonding part (8) is provided with a protrusion (10) corresponding to the position of the micro-optical fiber (3).

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