Knee joint angle measuring sensor device and measuring system

Abstract

The application provides a knee joint angle measurement sensing device and measurement system, and relates to the technical field of joint angle measurement. The device comprises a cam designed with a constant velocity curve, a flexible conversion structure, a fiber Bragg grating as a sensing element and a sensor frame. The sensor frame comprises an upper cover, a bottom plate and a moving arm. One end of the moving arm is coaxially connected to the cam on the bottom plate. The flexible conversion structure comprises a displacement input boss, two groups of symmetrical fixed bases, a first rigid rod, a second rigid rod and a fiber sticking boss. The displacement input boss is concave. The knee joint angle measurement sensing device and measurement system have the following advantages. The cam is designed with a constant velocity curve to ensure the linearity of the rotation angle and the cam output displacement. Meanwhile, the flexible conversion structure can convert the cam output displacement into the stretching of the fiber Bragg grating at an approximately fixed ratio. Compared with the traditional knee joint rotation angle measurement device, the device has the advantage of high measurement linearity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of joint angle measurement, in particular to a knee joint angle measurement sensing device and a measurement system. BACKGROUND

[0002] The knee joint, as a key joint connecting the thigh and the lower leg, is one of the joints bearing large load in human movement, and plays an important role in ensuring the stability and flexibility of the lower limbs. Long-term knee joint angle measurement can realize quantitative characterization of the movement function of the knee joint, and can be specifically used for diagnosis and evaluation of knee joint diseases such as meniscus injury and knee arthritis, preoperative planning of knee replacement surgery, and optimization of athletes' movement techniques and training methods. Therefore, it is urgent to develop a wearable knee joint angle measurement device.

[0003] Wearable knee angle measurement devices based on inertial measurement unit (IMU), electromechanical sensing principle and fiber-optic sensing principle are widely studied due to their simple structure, low cost and easy implementation. IMU is usually composed of a gyroscope, an accelerometer and a magnetometer. It has the advantages of small size, low cost, easy to wear and support three-dimensional angle detection. Watanabe et al. used accelerometers and gyroscopes to measure lower limb joint angles based on Kalman filter. However, due to the rotation axis deviation between the sensor and the measured joint, the knee joint angle sensor has a serious root mean square error (RMSE) of 2.99°. Liu et al. developed a wearable knee joint monitoring system using a magnetometer and an accelerometer, and used algorithms based on physical sensor difference and virtual sensor difference to estimate the angle value, with a RMSE of 2.52°. However, the fixed position of the IMU-based joint angle sensor will produce a certain offset every time it is used, which will waste a lot of time before use. In addition, the IMU-based method needs to combine multiple devices and rely on a relatively complex data fusion algorithm to improve the measurement accuracy. In addition to the indirect measurement method based on IMU, people also try to use resistance and capacitance electromechanical sensing principles to directly measure the knee joint angle. These sensors are usually integrated into textiles, so they have good flexibility and stretchability, are easy to install on clothing, and have a simple structure. Saggio et al. proposed a cost-effective joint angle sensor with a cylindrical flexible polymer as the sensing element. The sensor has a sensing range of [0, 120°] and an effective error of 1.28°; however, the coupling between bending force and tensile force leads to the non-linear performance of the sensor. Totaro et al. developed a stretchable capacitive sensor with conductive textiles as the two electrodes and an elastic layer as the intermediate dielectric. However, due to parasitic capacitance and partial detachment caused by movement, the maximum RMSE value reaches 4°. However, textile-based sensors face the problem of significant hysteresis caused by relative sliding between the sensing element and the textile. In addition, the electromechanical sensing principle is easily affected by electromagnetic interference and is not suitable for use in humid environments, which limits its application in knee joint angle measurement. Fiber-optic sensor (FOS) technology has great potential due to its high sensitivity, small size, good biocompatibility, strong resistance to corrosion and electromagnetic interference. Based on light intensity modulation (LIM) technology, Stupar et al. proposed a simple and low-cost knee joint angle sensor by sewing a plastic optical fiber (POF) on a knee joint support and etching a tooth-like structure on the optical fiber to improve sensitivity. The sensor has a resolution of 1°, but the linear range is limited to [-45°, 25°]. Leal-Junior et al. improved the above design by using a compensation technology based on the viscoelastic response of polymers and annealing the optical fiber, reducing the average RMSE in the [0, 90°] range to 1.5°.However, sensors based on light intensity modulation (LIM) are susceptible to bending losses and changes in input light intensity.

[0004] To address the limitations and application difficulties of existing sensing technologies, fiber Bragg grating (FBG) sensors have been widely used in joint angle measurement due to their excellent sensing performance. Currently, a common approach is to integrate FBG elements into flexible substrates (such as stretchable textiles and silicone). This method simplifies the sensor structure but still suffers from poor linearity and significant hysteresis. Summary of the Invention

[0005] (a) Technical problems to be solved

[0006] To address the shortcomings of existing technologies, this invention provides a knee joint angle measurement sensing device and measurement system, which solves the problems mentioned in the background art.

[0007] (II) Technical Solution

[0008] To achieve the above objectives, the present invention provides the following technical solution: a knee joint angle measurement and sensing device, comprising a cam designed with a constant velocity curve, a flexible conversion structure, a fiber Bragg grating as a sensing element, and a sensor frame. The sensor frame includes a top cover, a base plate, and a moving arm. One end of the moving arm is rotatably connected to the base plate coaxially with the cam. The flexible conversion structure includes a displacement input boss, two sets of symmetrical fixed bases, a first rigid rod, a second rigid rod, and a fiber optic bonding boss. The displacement input boss is concave. The two sets of second rigid rods, the first rigid rod, and the fixed bases are sequentially connected to both sides of the displacement input boss via flexible hinges. The first rigid rod is located in the X-axis direction, and the first rigid rod and the fixed base are located in the Z-axis direction. The fiber optic bonding boss is connected to the second rigid rod and extends along the X-axis direction. The two ends of the fiber Bragg grating are fixed to the two fiber optic bonding bosses. The flexible conversion structure is fixed to the base plate through the fixed base. The cam is in contact with the bottom of the displacement input boss. When the cam drives the displacement input boss to move in the positive Z-axis direction, the fiber optic bonding boss generates a movement in the XY-axis direction. Its movement component in the X-axis direction is approximately 1:6 with the movement of the displacement input boss. The base plate and the moving arm are respectively connected and fixed to the protective gear on the thigh and calf.

[0009] Preferably, the fiber Bragg grating is fixed to two fiber bonding bosses in a tensioned state with both ends fixed and the middle suspended. The fiber Bragg grating is arranged parallel to the X-axis, and the relationship between the center wavelength shift of the fiber Bragg grating and the strain is as follows:

[0010] Preferably, the cam has a rotation center positioning hole at its center, and one end of the moving arm has a pin hole. The pin hole and the rotation center positioning hole are connected by a positioning pin, and one end of the positioning pin is pivotally connected to the base plate by a bearing.

[0011] Preferably, the cam has a plurality of motion arm connection holes circumferentially arranged around the rotation center positioning hole, and the motion arm is connected to the plurality of motion arm connection holes on the cam through positioning bolts.

[0012] Preferably, the minimum radius of the cam is 15mm, and the maximum width of the cam is a diameter of 30mm + 1.2mm.

[0013] Preferably, the upper cover and the bottom plate are provided with corresponding fixing holes, and the fixing holes between the two are connected by fixing bolts.

[0014] Preferably, the base plate and the fixed base are respectively provided with corresponding mounting holes, and the mounting holes of the two are connected by bolts.

[0015] Preferably, the base plate and the moving arm are respectively provided with a plurality of mounting holes one and two for connecting protective gear.

[0016] Preferably, the flexible conversion structure can be manufactured in one piece using 3D printing technology.

[0017] A measurement system for a knee joint angle measuring sensor includes a fiber Bragg grating demodulator and a computer system. The fiber Bragg grating demodulator is connected to a fiber Bragg grating, and the computer system is connected to the fiber Bragg grating demodulator. The computer system is used to convert the grating strain signal into a digital signal and output the measured knee joint angle.

[0018] (III) Beneficial Effects

[0019] This invention provides a knee joint angle measurement sensing device and measurement system. It has the following beneficial effects:

[0020] 1. This knee joint angle measuring sensor and system uses a constant velocity curve design for the cam stroke, ensuring the linearity between the rotation angle and the cam output displacement. Simultaneously, the flexible conversion structure can convert the cam output displacement into the stretching of a fiber Bragg grating at an approximately fixed ratio; compared with traditional knee joint angle measuring devices, it has the advantage of high measurement linearity.

[0021] 2. The knee joint angle measuring sensor and measuring system, taking into account the maximum strain that the fiber Bragg grating can withstand, calculates the maximum stroke of the cam and the scaling factor of the flexible conversion structure, and achieves high measurement resolution while ensuring that the fiber Bragg grating is not damaged.

[0022] 3. The knee joint angle measuring sensor and measuring system adopts a symmetrical arrangement of flexible conversion structure, which greatly improves the sensor's ability to resist lateral interference and reduces the sensor's hysteresis, thus achieving good dynamic characteristics.

[0023] 4. The knee joint angle measuring sensor and measuring system adopts a rigid body replacement method to design a flexible conversion structure, which avoids complex rigid hinge connection structures. This allows for integrated processing using 3D printing and has the advantages of simple structure, sensitive movement, no friction, and no lubrication.

[0024] 5. The knee joint angle measuring sensor and measuring system uses a flexible conversion structure to convert the movement in the positive Z-axis direction into horizontal movement, so as to realize the parallel arrangement of the fiber Bragg grating in the X-axis direction. This makes the overall structure of the sensor compact and avoids interference with human movement when worn.

[0025] 6. This knee joint angle measurement sensing device and measurement system, when applied to knee joint angle measurement, transmits the knee joint angle to a cam; the cam converts the angle into a displacement along the positive Z-axis and transmits it to the displacement input boss of the flexible conversion structure; the flexible conversion structure converts this displacement into the stretching of a fiber Bragg grating in the horizontal direction, causing strain in the fiber Bragg grating, which in turn causes a shift in the center wavelength of the fiber Bragg grating. The wavelength shift of the fiber Bragg grating is read by a fiber demodulator, thus enabling real-time monitoring of changes in the knee joint angle and providing quantitative reference indicators for knee joint rehabilitation assessment. Attached Figure Description

[0026] Figure 1 This is a three-dimensional exploded view of the knee joint angle measuring sensor device of the present invention;

[0027] Figure 2 This is a camshaft view of the present invention;

[0028] Figure 3 This is a schematic diagram of the cam plane of the present invention;

[0029] Figure 4 This is a schematic diagram of the cam motion trajectory of the present invention;

[0030] Figure 5 This is a schematic diagram of the flexible conversion structure of the present invention;

[0031] Figure 6 This is a three-dimensional assembly schematic diagram of the convex knee joint angle measuring sensor of the present invention.

[0032] Figure 7 This is a schematic diagram illustrating the structural design process of the flexible conversion structure of the present invention;

[0033] Figure 8This is a schematic diagram of a single-sided rigid body model of the flexible conversion structure of the present invention;

[0034] Figure 9 This is a graph showing the relationship between fiber optic strain and knee joint angle in the knee joint angle measuring and sensing device of the present invention.

[0035] Figure 10 This is a schematic diagram of the knee joint angle measurement system of the present invention in a seated position;

[0036] Figure 11 This is a schematic diagram of the measurement results obtained by the knee joint angle measurement system of the present invention in a seated position.

[0037] Figure 12 This is a schematic diagram of the knee joint angle measurement system of the present invention during walking.

[0038] In the diagram: 1 Cam, 11 Motion arm connecting hole, 12 Rotation center positioning hole, 2 Flexible conversion structure, 21 Displacement input boss, 22 Fixed base, 23 First rigid rod, 24 Second rigid rod, 25 Flexible hinge, 26 Fiber optic bonding boss, 3 Fiber Bragg grating, 4 Sensor frame, 41 Top cover, 42 Base plate, 43 Motion arm, 44 Bearing, 45 Positioning pin, 46 Pin hole, 47 Positioning bolt, 48 Fixing hole, 49 Fixing bolt, 5 Fiber grating demodulator, 6 Computer system, 7 Mounting hole, 9 Connection hole one, 10 Connection hole two. Detailed Implementation

[0039] This invention provides a knee joint angle measurement sensing device;

[0040] Example 1: As Figures 1-6 As shown, it includes an angle-displacement conversion cam 1, a flexible conversion structure 2, a fiber Bragg grating 3 as a sensing element, and a sensor frame 4.

[0041] Cam 1 adopts a constant velocity curve design to achieve linear conversion between rotation angle and displacement. A rotation center positioning hole 12 is provided at the center of cam 1, and a pin hole 46 is provided at one end of the moving arm 43. The pin hole 46 and the rotation center positioning hole 12 are connected by a positioning pin 45. Thus, the knee joint rotation angle is transmitted to cam 1. One end of the positioning pin 45 is pivotally connected to the base plate 42 of the sensor frame 4 through a bearing 44.

[0042] like Figure 1 , 2 As shown in Figure 6, four motion arm connection holes 11 are circumferentially formed on the cam 1 around the rotation center positioning hole 12. The motion arm 43 is connected to the four motion arm connection holes 11 on the cam 1 through the positioning bolt 47. This improves the stability and consistency of the motion arm 43 and the cam 1 when they rotate.

[0043] like Figure 3As shown, the minimum radius of cam 1 is 15mm, and the maximum width of cam 1 is a diameter of 30mm + 1.2mm. The maximum stroke of cam 1 driving the displacement input boss 21 is 1.2mm. The stroke angle range is set to 0~140°, the far rest angle range is 140°~220°, and the return angle range is 220°~360°. The stroke profile is designed using a constant velocity curve.

[0044] like Figure 1 As shown, the sensor frame 4 includes an upper cover 41, a base plate 42, and a moving arm 43. Corresponding fixing holes 48 are provided between the upper cover 41 and the base plate 42, and the fixing holes 48 between the two are connected by fixing bolts 49.

[0045] like Figure 1 and Figure 5 As shown, the flexible conversion structure 2 is designed based on a crank-slider structure. The flexible conversion structure 2 includes a displacement input boss 21, two sets of symmetrical fixed bases 22, a first rigid rod 23, a second rigid rod 24, and an optical fiber bonding boss 26. The overall length and width of the two sets of symmetrical fixed bases 22, the first rigid rod 23, the second rigid rod 24, and the optical fiber bonding boss 26 in the XY coordinate axis direction are 30mm and 5mm, respectively. The displacement input boss 21 is concave, and the two sets of second rigid rods 24, the first rigid rod 23, and the fixed bases 22 are sequentially connected to both sides of the displacement input boss 21 via flexible hinges 25.

[0046] The flexible hinge 25 can be an arc-shaped flexible hinge, an elliptical flexible hinge, or a straight beam flexible hinge, or other types of flexible hinges 25. Among them, the straight beam flexible hinge has the characteristics of a large turning angle range and easy processing. Therefore, in the knee joint angle measuring sensing device of this embodiment, the structure of the flexible hinge 25 is preferably a straight beam flexible hinge.

[0047] The second rigid rod 24 and the first rigid rod 23 are located in the X-axis direction, and the first rigid rod 23 and the fixed base 22 are located in the Z-axis direction. The fiber bonding boss 26 is connected to the second rigid rod 24 and extends along the X-axis direction. The two ends of the fiber Bragg grating 3 are fixed on the two fiber bonding bosses 26. The flexible conversion structure 2 is fixed on the base plate 42 through the fixed base 22.

[0048] Cam 1 contacts the bottom of displacement input boss 21, and displacement input boss 21 maintains close contact with cam profile at all times.

[0049] When the cam 1 drives the displacement input boss 21 to move in the positive direction of the Z coordinate axis, the fiber optic bonding boss 26 generates a motion in the XY coordinate axis direction. Its motion component in the X-axis direction is approximately 1:6 with the motion of the displacement input boss 21.

[0050] The base plate 42 and the fixed base 22 are respectively provided with corresponding mounting holes 7, and the mounting holes 7 of the two are connected by bolts.

[0051] The flexible transformation structure 2 is an integrally formed flexible hinge mechanism obtained by the rigid body replacement method. The flexible transformation structure 2 can be manufactured in one piece using 3D printing technology.

[0052] The fiber Bragg grating 3 is fixed to the two fiber bonding bosses 26 in a tensioned state with both ends fixed and the middle suspended. The fiber Bragg grating 3 is arranged parallel to the X-axis.

[0053] This device can be used with commercial protective gear to achieve long-term wearable measurement. The base plate 42 and the moving arm 43 are respectively provided with several mounting holes 9 and 10 for connecting connectors. This allows the knee joint angle measuring device to be fixed to the commercial protective gear for wearable measurement. The commercial protective gear includes braces strapped to the thigh and calf. The base plate 42 and the moving arm 43 are connected and fixed to the braces on the thigh and calf using straps through mounting holes 9 and 10, respectively.

[0054] Furthermore, such as Figure 7 As shown, in this embodiment, the rigid body model of the flexible conversion structure 2 is obtained through the following steps:

[0055] 1. Traditional crank-slider mechanism;

[0056] 2. Extend the connecting rod of the crank-slider mechanism in the opposite direction and change its input and output directions:

[0057] 3. Arrange the structures obtained in step 2 symmetrically to obtain the rigid body model of the flexible transformation structure 2;

[0058] Through the above steps, the flexible conversion structure 2 of this embodiment 1 can convert vertical displacement into horizontal tension between two fiber optic bonding platforms 26 in the horizontal direction, making the overall structure of the knee joint angle measurement sensing device compact. At the same time, the ratio of the vertical displacement input to the horizontal tension output by the flexible conversion structure 2 is approximately constant, which helps the knee joint angle measurement sensing device to better measure linearity. Since the flexible conversion structure 2 is symmetrically arranged from the result in step 2, it can greatly improve the anti-interference ability of the flexible conversion structure 2 and reduce the hysteresis of the measurement device.

[0059] like Figure 1As shown, in this embodiment 1, the fiber Bragg grating 3, under preload, is bonded at both ends to the fiber bonding protrusions 26 of the two flexible conversion structures 2 using a two-point bonding method. When the displacement input protrusion 21 of the flexible conversion structure 2 is subjected to vertical displacement along the Z-axis by the angle-displacement conversion cam 1, the fiber bonding protrusions 26 stretch the fiber Bragg grating 3, thereby causing strain. The suspension arrangement of the fiber Bragg grating 3 can improve its sensitivity and avoid the chirping phenomenon caused by the traditional full bonding method.

[0060] The specific working principle of this embodiment 1 is as follows:

[0061] like Figure 1 , 2 As shown in Figure 3, in this embodiment 1, the knee joint rotation angle is transmitted to the angle-displacement conversion cam 1 via the motion arm 43. The cam 1 outputs a vertical motion along the positive Z-axis, which pushes the displacement input boss 21 of the flexible conversion structure 2. The second rigid rod 24 converts this motion into a horizontal stretch along the X-axis, causing strain to be generated in the fiber Bragg grating 3 arranged on the fiber bonding boss 26. The relationship between the center wavelength shift of the fiber Bragg grating 3 and the strain is as follows:

[0062]

[0063] Where λ is the initial center wavelength of fiber Bragg grating 3, Δλ is the center wavelength drift of the grating, αf is the thermal expansion coefficient of the fiber, ξ is the thermo-optic coefficient of the fiber material, Pe is the elastic-optic coefficient of the fiber, and Δε is the strain change generated by the fiber grating.

[0064] Since the reflection center wavelength of the fiber Bragg grating 3 changes with the knee joint angle, the corresponding grating strain signal can be obtained by detecting the reflection center wavelength, and the corresponding knee joint angle information can be output. In this knee joint angle measuring device, the relationship curve between the rotation angle and the fiber Bragg grating 3 is as follows: Figure 9 As shown in Figure 9, the relationship between knee joint rotation angle and fiber wavelength offset is as follows, with a measurement range of 0–140°, a measurement linearity of 0.9992, a linearity error of 1.36%, and a resolution of 0.015°.

[0065] Furthermore, in this embodiment, the flexible conversion structure 2 is a displacement reduction mechanism that can output a reduced horizontal stretch. The specific principle is explained as follows:

[0066] like Figure 8 As shown, since the flexible conversion structure 2 is a symmetrical structure, the structure on the left is exactly the same as the flexible linkage structure on the right. Therefore, we will take one set of flexible linkage structures as an example for explanation as follows:

[0067] In this design, link OP represents the first rigid link 23, link MN represents the second rigid link 24, point M represents the displacement input boss 21, point N represents the fiber optic bonding boss 26, and points O and P are two flexible hinges 25. In the structural design, the lengths of different links conform to the following dimensional parameters:

[0068] l op =l PN =l PM =d1

[0069] l MN =d2

[0070] α0=θ0

[0071] The coordinates of points M and N can be represented as:

[0072]

[0073] The displacement reduction factor of this mechanism can be expressed as the ratio of the ordinate of point M to the abscissa of point N:

[0074]

[0075] Under these design conditions, the value of θ+α is approximately constant, and the reduction factor of the flexible conversion structure can be calculated to be approximately 6.

[0076] Example 2: Figure 10 As shown, a measurement system for a knee joint angle measuring sensor includes a signal processing unit and the knee joint angle measuring sensor as described in Embodiment 1 above. The signal processing unit includes a fiber Bragg grating demodulator 5 and a computer system 6. The fiber Bragg grating demodulator 5 is connected to a fiber Bragg grating 3, and the computer system 6 is connected to the fiber Bragg grating demodulator 5. It is used to convert the grating strain signal into a digital signal and output the measured knee joint angle. Volunteers sit comfortably in a chair and wear the knee joint angle measuring sensor on the knee joint to be measured. The volunteers then perform a series of flexion, hold, extension, and hold movements of their knee joint. The measurement results are shown below. Figure 11 As shown.

[0077] Example 3: As Figure 10As shown, a measurement system for a knee joint angle measuring sensor includes a signal processing unit and the knee joint angle measuring sensor as described in Embodiment 1 above. The signal processing unit includes a fiber Bragg grating demodulator 5 and a computer system 6. The fiber Bragg grating demodulator 5 is connected to a fiber Bragg grating 3. The computer system 6 is connected to the fiber Bragg grating demodulator 5 and is used to convert the grating strain signal into a digital signal and output the measured knee joint angle. Volunteers stand in a normal posture and wear the knee joint angle measuring sensor on both knees. The volunteers then walk a distance at a normal speed, and the measurement results are as follows. Figure 12 As shown.

[0078] Example 4: The knee joint angle measurement system of Examples 2 and 3 of the present invention is only used for knee joint angle measurement. However, in fact, the knee joint angle measurement system is not limited to knee joint angle measurement. It can also measure ankle, hip, elbow, shoulder and wrist joints by adjusting the wearing position of the measuring device.

[0079] In summary, this knee joint angle measuring device can assist doctors in the diagnosis and treatment monitoring of knee joint diseases. By accurately measuring the knee joint angle and movement trajectory, doctors can better understand the patient's condition and develop more effective treatment plans. For patients recovering from knee surgery, this device can monitor knee joint movement during the rehabilitation process, helping rehabilitation doctors and patients understand rehabilitation progress and adjust rehabilitation plans in a timely manner to improve rehabilitation outcomes. In the field of sports, this device can monitor athletes' knee joint movement, helping coaches and athletes analyze and improve movement techniques, prevent sports injuries, and improve athletic performance. Furthermore, with the increasing trend of population aging, knee joint problems among the elderly have become an increasingly serious social issue. This device can be used for health management of the elderly, timely detection and prevention of knee joint problems, and improvement of their quality of life. In research fields such as exercise physiology and biomechanics, this device is also of great significance, helping researchers to delve deeper into the mechanisms of human movement and providing theoretical support and experimental data for sports injury prevention, rehabilitation, and performance improvement.

[0080] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A knee joint angle measuring sensor, characterized in that: The system includes a cam (1) designed with a constant velocity curve, a flexible conversion structure (2), a fiber Bragg grating (3) as a sensing element, and a sensor frame (4). The sensor frame (4) includes a top cover (41), a base plate (42), and a motion arm (43). One end of the motion arm (43) is coaxially rotatably connected to the base plate (42) with the cam (1). The flexible conversion structure (2) includes a displacement input boss (21), two sets of symmetrical fixed bases (22), a first rigid rod (23), a second rigid rod (24), and a fiber optic bonding boss (26). The displacement input boss (21) is concave. The two sets of second rigid rods (24), first rigid rods (23), and fixed bases (22) are sequentially connected to both sides of the displacement input boss (21) via flexible hinges (25). In the X-axis direction, the first rigid rod (23) and the fixed base (22) are in the Z-axis direction. The fiber bonding boss (26) is connected to the second rigid rod (24) and extends along the X-axis direction. The two ends of the fiber Bragg grating (3) are fixed on the two fiber bonding bosses (26). The flexible conversion structure (2) is fixed on the base plate (42) through the fixed base (22). The cam (1) is in contact with the bottom of the displacement input boss (21). When the cam (1) drives the displacement input boss (21) to move in the positive direction of the Z-axis, the fiber bonding boss (26) generates a movement in the XY-axis direction. Its movement component in the X-axis direction is approximately 1:6 with the movement of the displacement input boss (21). The base plate (42) and the moving arm (43) are respectively connected and fixed on the protective gear on the thigh and calf.

2. The knee joint angle measuring and sensing device according to claim 1, characterized in that: The fiber Bragg grating (3) is fixed to two fiber bonding bosses (26) in a tensioned state with both ends fixed and the middle suspended. The fiber Bragg grating (3) is arranged parallel to the X-axis. The relationship between the center wavelength shift of the fiber Bragg grating (3) and the strain is as follows: ;in, This is the initial center wavelength of fiber Bragg grating 3. The center wavelength shift of the grating. This is the coefficient of thermal expansion of the optical fiber. is the thermo-optic coefficient of the optical fiber material, and Pe is the elastic-optic coefficient of the optical fiber; This refers to the strain change generated by the fiber Bragg grating.

3. The knee joint angle measuring and sensing device according to claim 1, characterized in that: The cam (1) has a rotation center positioning hole (12) at its center, and the moving arm (43) has a pin hole (46) at one end. The pin hole (46) is connected to the rotation center positioning hole (12) by a positioning pin (45), and one end of the positioning pin (45) is pivotally connected to the base plate (42) by a bearing (44).

4. The knee joint angle measuring and sensing device according to claim 3, characterized in that: The cam (1) has several motion arm connection holes (11) circumferentially arranged around the rotation center positioning hole (12). The motion arm (43) is connected to the several motion arm connection holes (11) on the cam (1) through the positioning bolt (47).

5. The knee joint angle measuring and sensing device according to claim 1, characterized in that: The minimum radius of the cam (1) is 15mm, and the maximum width of the cam (1) is 30mm + 1.2mm.

6. The knee joint angle measuring and sensing device according to claim 1, characterized in that: The upper cover (41) and the bottom plate (42) are provided with corresponding fixing holes (48), and the fixing holes (48) between the two are connected by fixing bolts (49).

7. The knee joint angle measuring and sensing device according to claim 1, characterized in that: The base plate (42) and the fixed base (22) are respectively provided with corresponding mounting holes (7), and the mounting holes (7) of the two are connected by bolts.

8. The knee joint angle measuring sensor device according to claim 1, characterized in that: The base plate (42) and the moving arm (43) are respectively provided with a number of mounting holes 1 (9) and 2 (10) for connecting protective gear.

9. The knee joint angle measuring and sensing device according to claim 1, characterized in that: The flexible conversion structure (2) can be manufactured in one piece using 3D printing technology.

10. A measurement system for a knee joint angle measuring sensor, characterized in that, The knee joint angle measuring sensing device according to any one of claims 1 to 9 is used. The measuring system includes a fiber Bragg grating demodulator (5) and a computer system (6). The fiber Bragg grating demodulator (5) is connected to a fiber Bragg grating (3), and the computer system (6) is connected to the fiber Bragg grating demodulator (5) to convert the grating strain signal into a digital signal and output the measured knee joint angle.

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