A variable stiffness flexible knee exoskeleton and method of controlling the same

Abstract

The application discloses a variable-rigidity flexible knee exoskeleton, which comprises a wearing assembly, an exoskeleton support arranged on the wearing assembly, a variable-rigidity joint connected with the exoskeleton support, the variable-rigidity joint comprising a shell, a fixed-axle gear A, a planetary gear, a fixed-axle gear B and a variable-rigidity driver, the fixed-axle gear A and the fixed-axle gear B are positioned in the shell through gear shafts and rotate relative to the shell, and an elastic element is arranged between the fixed-axle gear B and the shell; a sliding rail is arranged in the shell, the gear shaft of the planetary gear is driven by the variable-rigidity driver to move along the sliding rail, the meshing and disengaging of the planetary gear and the fixed-axle gear B are realized, and the planetary gear is always meshed with the fixed-axle gear A; the exoskeleton support comprises a thigh support and a shank support, the thigh support is fixedly connected with the gear shaft of the fixed-axle gear A, and the shank support is connected with the shell. The meshing and disengaging of the planetary gear and the fixed-axle gear realize two different rigidity transformations, the man-machine interaction is comfortable, and the assisting effect is good.

Description

Technical Field

[0001] This invention relates to exoskeleton assistive robots, specifically to a variable stiffness flexible knee joint exoskeleton and its control method. Background Technology

[0002] Knee exoskeletons can enhance mobility and significantly reduce physical strain, holding immense promise for applications in military and medical fields. They can provide assistance and support to individuals with limited mobility or mobility impairments, aiding in daily activities such as walking and climbing stairs. Through the strength support of the exoskeleton, users can reduce load, decrease physical exertion, improve exercise efficiency, and enhance their quality of life. They can also be used in rehabilitation training to assist in motor recovery and muscle function reconstruction. Exoskeletons can assist in rehabilitation training to restore normal movement patterns, strengthen muscle strength and stability, promote the rehabilitation process, and improve rehabilitation outcomes.

[0003] Currently, knee exoskeletons include the REX Exoskeleton wearable knee exoskeleton developed by Rex Bionics and the HAL knee exoskeleton developed by Cyberdyne. Existing exoskeleton technologies include an assistive knee exoskeleton (application number CN202310205484.2) and a knee exoskeleton device (application number CN202120741041.1), but these exoskeletons have fixed stiffness and cannot adjust to the user's needs and changes in movement. This means that the exoskeleton may not provide adequate support and control in different activity scenarios. Furthermore, some mainstream active variable stiffness exoskeletons rely on external power sources. Using too much power increases the overall weight and reduces wearer comfort, while using too little power results in insufficient battery life. Summary of the Invention

[0004] Purpose of the invention: To address the above-mentioned shortcomings, this invention provides a variable stiffness flexible knee exoskeleton that features variable stiffness, low energy consumption, and good comfort.

[0005] The present invention also provides a method for controlling a variable stiffness flexible knee exoskeleton.

[0006] Technical Solution: To solve the above problems, the present invention employs a variable stiffness flexible knee exoskeleton, including a wearable component, an exoskeleton support mounted on the wearable component, and a variable stiffness joint connected to the exoskeleton support. The variable stiffness joint includes a housing, a fixed-axis gear A, a planetary gear, a fixed-axis gear B, and a variable stiffness actuator. Both fixed-axis gear A and fixed-axis gear B are positioned within the housing via gear shafts and rotate relative to the housing. An elastic element is provided between fixed-axis gear B and the housing. A slide rail is provided within the housing, and the variable stiffness actuator drives the gear shaft of the planetary gear to move along the slide rail, realizing the engagement and disengagement of the planetary gear with the fixed-axis gear B; and the planetary gear is always engaged with the fixed-axis gear A.

[0007] The exoskeleton support includes a thigh support and a lower leg support. The thigh support is fixedly connected to the gear shaft of the fixed-axis gear A, and the lower leg support is connected to the shell.

[0008] Furthermore, the variable stiffness actuator includes a power source, a crank transmission mechanism, a slider, and a slide groove. The crank transmission mechanism is connected between the power source and the slider. The power source drives the slider to move within the slide groove via the crank transmission mechanism. The slide groove is connected to the inner housing via screws. The slider pushes the gear shaft of the planetary gear to move along the slide rail. The slider can switch between two extreme positions under the control of the power source. Variable stiffness can be achieved by controlling the position of the planetary gear shaft to control whether it meshes with the fixed-axis gear B.

[0009] Furthermore, the crank transmission mechanism includes a crank and a connecting rod, with the crankshaft connected to a power source. The dimensions L1 of the crank and L2 of the connecting rod satisfy the following conditions:

[0010]

[0011]

[0012]

[0013]

[0014] Where D is the difference between the distance from the slider hinge to the edge of the inner shell and the radius of the motor when the slider just contacts the gear shaft; Δs is the displacement of the slider from the moment it contacts the gear shaft of the planetary gear. δ is the angle between the crank and the slide; δ is the distance the planetary gear needs to move to disengage from the fixed-axis gear B; [γ] = 40°.

[0015] Furthermore, the elastic element is a spiral spring, which is sleeved on the gear shaft of the fixed-axis gear B. One end of the spiral spring is fixedly connected to the housing, and the other end is fixedly connected to the gear shaft of the fixed-axis gear B. One end of the gear shaft of the fixed-axis gear B is provided with two annular bosses on both sides for twisting the spiral spring.

[0016] Furthermore, the stiffness K of the spiral spring is:

[0017]

[0018] Where η is the assist effect coefficient; Z B Z represents the number of teeth of fixed-axis gear B; A The number of teeth for fixed-axis gear A.

[0019] Furthermore, one end of the gear shaft of the fixed-axis gear A extends through the housing and is fixedly connected to the thigh support, while the other end rotates relative to the housing through a rolling bearing. Both ends of the gear shafts of the planetary gear and the fixed-axis gear B are provided with rolling bearings that rotate relative to the housing.

[0020] Furthermore, the calf support and the housing are connected by a double-hinge structure, which includes three hinges connected in sequence. Adjacent hinges are rotated relative to each other via pins. The calf support and the housing are respectively connected to the hinges at both ends of the double-hinge structure. The double-hinge structure allows the calf support to have multiple degrees of freedom in the coronal plane, and the lower strap can effectively fix it to the wearer's calf.

[0021] Furthermore, the wearable component includes several straps, a waist belt, and two leg straps. One end of each strap is connected to the waist belt via a buckle, and the other end is connected to the thigh support. The strap adjustment devices on the thigh and calf supports are fixed to the supports with screws, and the straps are fixed to the strap adjustment devices. Both the thigh and calf supports are provided with several mounting holes. The strap adjustment devices fix the straps into different mounting holes to adjust the position of the wearable component. The strap adjustment devices on the thigh and calf supports can be fixed to different positions with screws according to the wearer's actual leg parameters to adjust the vertical position.

[0022] Furthermore, it also includes a variable stiffness joint control system, which comprises several inertial sensors, a controller, and an electronic speed controller (ESC). The inertial sensors are used to detect the wearer's motion data. The inertial sensors include inertial sensor A and inertial sensor B, which are respectively fixed to the thigh support and the calf support and connected to the controller. The controller is fixed to the waist belt and connected to the power source through the ESC. The power source is also fixed to the waist belt and connected to the controller and the power source to provide energy. The power source is fixed to the outer shell with screws. The controller is used to identify changes in the wearer's gait based on the motion data collected by the inertial sensors and output control signals to the ESC to control the operation of the power source.

[0023] The present invention also employs a control method for the above-mentioned variable stiffness flexible knee joint exoskeleton, comprising the following steps:

[0024] Step S100: Use the exoskeleton module to perform actual tasks and collect exoskeleton operation data through inertial sensors;

[0025] Step S200: The controller receives exoskeleton operation data collected by the inertial sensor, performs attitude calculation, and obtains the current attitude angle of the carrier;

[0026] Step S300: Gait judgment is made by observing changes in leg posture angles during human movement;

[0027] Step S400: Based on the gait judgment result, output a PWM signal to the ESC, and the ESC controls the operation of the power source;

[0028] Step S500: Repeat steps S200 to S400 until the actual task is completed.

[0029] Beneficial effects: Compared with the prior art, the significant advantage of this invention is that it achieves two different stiffness transformations through the meshing and disengagement of planetary gears and fixed-axis gears, resulting in strong human-machine interaction comfort, good assistive effect, enhanced human mobility, reduced physical load, reduced physical exertion, improved exercise efficiency, and improved quality of life. Attached Figure Description

[0030] Figure 1 The diagram shown is a schematic representation of the overall structure of the variable stiffness flexible knee exoskeleton of this invention.

[0031] Figure 2 The diagram shown is a structural schematic of the variable stiffness joint in this invention.

[0032] Figure 3 The diagram shown is a structural schematic of the variable stiffness actuator in this invention.

[0033] Figure 4The diagram shown is a schematic diagram of the structural parameters of the crank transmission mechanism in this invention;

[0034] Figure 5 The diagram shown is a schematic representation of the thigh support structure in this invention.

[0035] Figure 6 The diagram shown is a schematic representation of the lower leg support structure in this invention.

[0036] Figure 7 The diagram shown is a schematic of the double-hinge structure in this invention. Detailed Implementation

[0037] like Figure 1 As shown, this embodiment of a variable stiffness flexible knee exoskeleton includes a variable stiffness joint, a variable stiffness joint control system, a wearable component, and an exoskeleton support mounted on the wearable component. The upper end of the variable stiffness joint is connected to the thigh support of the wearable component via a gear shaft of a fixed-axis gear A, and the lower end is connected to the lower leg support of the wearable component via a double-hinge structure. The variable stiffness joint control system is connected to the thigh support of the wearable component via screws. By performing attitude calculations on data from inertial sensors, the current posture angle of the vehicle is obtained. Gait is then determined by observing changes in leg posture angles during human movement, and the variable stiffness joint is controlled to achieve different stiffnesses, satisfying the characteristic of piecewise linear variable stiffness of the human knee joint during walking and squatting.

[0038] like Figure 2 As shown, the variable stiffness joint includes a housing 901, a fixed-axis gear A902, a planetary gear 903, a crank-slider mechanism 905-908, a fixed-axis gear B909, and a spiral spring 910. The housing 901 has numerous holes and bosses inside to facilitate mating with other parts. The fixed-axis gear A902 is fixed to the gear shaft via a spline, with a bearing at one end to reduce friction. The gear shaft is also fixed to the support bracket via screws. In terms of absolute motion, the fixed-axis gear A is fixed; it rotates the gear set through relative motion with the housing. Planetary gear 903 is fixed to both housings using a dual-shaft fixing method, with bearings at both ends to reduce friction. The planetary gear shaft can move via a slide rail on the inner housing. To ensure that the planetary gear shaft can achieve meshing and non-meshing states at two extreme positions, the slide rail angle range on the inner housing should be no less than 10°. Fixed-axis gear B909 is also fixed to both housings using a dual-shaft fixing method, with bearings at both ends to reduce friction. Two annular bosses are provided at the end of the gear shaft near the spiral spring 910 to twist the spiral spring 910.

[0039] Considering the size of the housing, the internal space distribution, and the difficulty of processing, the pitch circle diameter range of the three gears given in this embodiment is as follows: fixed-axis gear A902 is 45mm-60mm, fixed-axis gear B909 is 26mm-30mm, and planetary gear 903 is 40mm-45mm. Correspondingly, considering that the more teeth a gear set has, the smoother the transmission will be, and the number of teeth of the smallest gear should be as small as possible without undercutting to ensure processing accuracy, the module of the gear can be selected between 1mm and 1.5mm.

[0040] The spiral springs 910 can be divided into non-contact planar spiral springs (Type A) and contact planar spiral springs (Type B). Non-contact planar spiral springs are often used to generate reaction torque, while contact planar spiral springs are often used to store energy. Based on the function of the spiral spring in this embodiment, a non-contact planar spiral spring should be selected.

[0041] The input torque is transmitted to the fixed-axis gear B via the spiral spring, then to the fixed-axis gear A through the gear set, and finally to the exoskeleton structure as output torque. Based on the properties of the gear set, the stiffness formula for the planar spiral spring can be derived:

[0042]

[0043] Where K is the stiffness of the spiral spring, and T B The torque of the fixed-axis gear B, i.e., the input torque, T A The torque of the fixed-axis gear A, i.e., the output torque, is Z. B For the number of teeth of fixed-axis gear B, Z A Let A be the number of teeth on a fixed-axis gear. For a person walking, the torque on the knee joint during the support phase can be approximated as a linear change from 0 to 60 Nm, with the swing angle varying approximately 0.1 rad. For a non-contact planar spiral spring, its rotation angle is proportional to the generated torque. Since the ratio of the output torque to the torque required for walking is the assist effect, it can be seen that, given a fixed assist effect, the gear set... The smaller the ratio, the smaller the required stiffness of the spiral spring. When a boosting effect with a ratio of η is required, the required spiral spring stiffness can be calculated as follows:

[0044]

[0045] like Figure 3As shown, the crank-slider mechanism includes a crank 905, a connecting rod 906, a slider 907, and a slide 908. The power source 904 rotates a specific angle after receiving information from the controller 1 to control the slider 907 to switch between two extreme positions. Both the crank 905 and the connecting rod 906 are hinged, and each hinge is equipped with a retaining ring to limit the position of the crank 905 and the connecting rod 906. When the slider 907 is in its extreme position close to the planetary gear 903, it can be lifted to achieve a non-engaged state. When the slider 907 is in its extreme position away from the planetary gear 903, the planetary gear 903 can switch back to the engaged state under gravity. The slide 908 is fixed to the housing 901 with screws. To ensure that the slider 907 can move well within the slide 908, the slide 908 is designed with a mortise and tenon structure.

[0046] The parameters of the crank-slider mechanism are as follows: Figure 4 As shown, to maximize the efficiency of the crank-slider mechanism when the slider disengages the gear shaft, the transmission angle γ1 at the input end of the crank mechanism is designed to be 90° when the slider contacts the gear shaft. Simultaneously, the values ​​of L1 and L2 are designed to maximize the transmission angle γ2 at the output end. For ease of design, we take the crank's rotation angle... The range is (20°, 90°). When γ1 = 90°, due to the influence of the size of the casing and the size of the motor, we can obtain:

[0047]

[0048] Where D is the difference between the distance from the slider hinge to the edge of the inner shell and the radius of the motor when the slider just contacts the gear shaft. Assume that a movement of δ on the planetary gear shaft will completely disengage it from gear B. Therefore, we can obtain:

[0049]

[0050] Where Δs is the displacement of the slider from the moment it comes into contact with the planetary gear shaft. It is the angle between the crank and the slide.

[0051] The input transmission angle γ1 satisfies:

[0052] γ1≥[γ] (5) that is:

[0053]

[0054] Where, [γ] = 40°, γ1 ≤ 90°.

[0055] The input transmission angle γ2 satisfies:

[0056] γ2≥[γ] (7)

[0057] Right now:

[0058]

[0059] Where, [γ] = 40°, γ2 ≤ 90°.

[0060] When designing L1 and L2, equations (3), (4), (6), and (8) must be satisfied. (Corner) The value of can be calculated using equation (4).

[0061] Considering the size of the motor, the size of the housing, the internal space distribution, and the difficulty of processing, the value of D in this embodiment is given as 29mm and the value of δ as 4mm. Therefore, through complex surface analysis, the range of crank and connecting rod is obtained as follows: 8.5mm≤L1≤14.3mm, 9.05mm≤L2≤24.0mm.

[0062] The variable stiffness joint control system includes an inertial sensor A8, an inertial sensor B13, a controller 1, an electronic speed controller 5, a power supply 2, and a power source 904. Inertial sensors A8 and B13 are fixed on the thigh support 6 and the lower leg support 11, respectively, and are connected to the controller 1. The controller 1 is fixed on the waist belt 3 and is connected to the power source 904 through the electronic speed controller 5. The power supply 2 is also fixed on the waist belt 3 and is connected to the controller 1 and the power source 904 to provide energy. The power source 904 is fixed to the outer shell with screws.

[0063] During human walking, the inertial sensor collects the changes in the three-axis Euler angles of the legs during human movement and transmits the data to the controller 1. The controller 1 performs attitude calculation on the data from the inertial sensor to obtain the current attitude angle of the carrier. Based on this, the controller 1 identifies the wearer's gait changes and makes a gait judgment. Then, based on the current gait position, it outputs a PWM signal to the ESC 5 to control the rotation of the power source 904, thereby controlling the variable stiffness joint to realize the transformation between two stiffnesses.

[0064] The exoskeleton frame includes two thigh supports 6 and two lower leg supports 11. The wearable components include a waist belt 3 and two slings 4. The thigh supports 6 and lower leg supports 11 are as follows: Figure 5 and Figure 6 As shown, it includes an upper strap 7, a lower strap 12, and two strap adjustment devices 601 and 1101. Each strap adjustment device is fixed to the bracket by screws. The position of the strap can be adjusted by selecting different threaded holes on the bracket according to the wearer's actual leg parameters, so as to adjust the up and down position.

[0065] The lower leg support 11 and the variable stiffness joint 9 are connected by a double hinge structure 10, such as Figure 7As shown, it consists of three hinges 1001 and two pins 1002. Because the human thighs and calves are of different thicknesses, and the overall structure of this exoskeleton is in the same plane parallel to the coronal plane, the distances between the thigh support 6 and the calf support 11 and the thigh and calf are different, making it difficult to secure the lower strap 12 to the calf effectively. To solve this problem, this invention designs a double-hinge structure 10. This structure allows the calf support 11 to have multiple degrees of freedom in the coronal plane, and the lower strap 12 can effectively secure it to the wearer's calf.

Claims

1. A variable stiffness flexible knee joint exoskeleton, comprising a wearable component and an exoskeleton support disposed on the wearable component, characterized in that, It also includes a variable stiffness joint connected to the exoskeleton frame. The variable stiffness joint includes a housing (901), a fixed-axis gear A (902), a planetary gear (903), a fixed-axis gear B (909), and a variable stiffness actuator. The fixed-axis gear A (902) and the fixed-axis gear B (909) are both positioned inside the housing (901) via gear shafts and rotate relative to the housing (901). An elastic element is provided between the fixed-axis gear B (909) and the housing (901). A slide rail is provided inside the housing (901). The stiffness actuator drives the gear shaft of the planetary gear (903) to move along the slide rail, thereby realizing the meshing and disengagement of the planetary gear (903) with the fixed shaft gear B (909); and the planetary gear (903) is always meshed with the fixed shaft gear A (902); the elastic element is a spiral spring (910), which is sleeved on the outside of the gear shaft of the fixed shaft gear B (909). One end of the spiral spring (910) is fixedly connected to the housing (901), and the other end is fixedly connected to the gear shaft of the fixed shaft gear B (909); The exoskeleton support includes a thigh support and a lower leg support. The thigh support is fixedly connected to the gear shaft of the fixed-axis gear A (902), and the lower leg support is connected to the housing (901).

2. The variable stiffness flexible knee joint exoskeleton according to claim 1, characterized in that, The variable stiffness actuator includes a power source (904), a crank transmission mechanism, a slider (907), and a slide (908). The crank transmission mechanism is connected between the power source (904) and the slider (907). The power source (904) drives the slider (907) to move within the slide (908) through the crank transmission mechanism. The slider (907) pushes the gear shaft of the planetary gear (903) to move along the slide rail.

3. The variable stiffness flexible knee exoskeleton according to claim 2, characterized in that, The crank transmission mechanism includes a crank (905) and a connecting rod (906), wherein the crank (905) has the following dimensions: Dimensions of connecting rod (906) The following conditions must be met: ， ， ， ， Where D is the difference between the distance from the slider hinge to the edge of the inner shell and the radius of the motor when the slider just contacts the gear shaft; This is the displacement of the slider from the moment it comes into contact with the gear shaft of the planetary gear. The angle between the crank and the slide; The distance the planetary gear needs to move horizontally to disengage from the fixed-axis gear B; ]=40 .

4. The variable stiffness flexible knee joint exoskeleton according to claim 3, characterized in that, The stiffness of the spiral spring (910) for: in, To enhance the effectiveness coefficient; The number of teeth for fixed-axis gear B; The number of teeth for fixed-axis gear A.

5. The variable stiffness flexible knee joint exoskeleton according to claim 1, characterized in that, One end of the gear shaft of the fixed-axis gear A (902) passes through the housing (901) and is fixedly connected to the thigh support. The other end rotates with the housing (901) through a rolling bearing. Both ends of the gear shafts of the planetary gear (903) and the fixed-axis gear B (909) are provided with rolling bearings and rotate with the housing (901) through each other.

6. The variable stiffness flexible knee exoskeleton according to claim 1, characterized in that, The lower leg support and the housing (901) are connected by a double hinge structure, which includes three hinges connected in sequence. Adjacent hinges can rotate relative to each other through pins. The lower leg support and the housing (901) are respectively connected to the hinges at both ends of the double hinge structure.

7. The variable stiffness flexible knee exoskeleton according to claim 1, characterized in that, The wearable component includes several straps, and both the thigh support and the calf support are provided with several mounting holes. The straps are fixedly installed in different mounting holes to achieve position adjustment of the wearable component.

8. The variable stiffness flexible knee joint exoskeleton according to claim 2, characterized in that, It also includes a variable stiffness joint control system, which includes several inertial sensors, a controller (1), and an electronic speed controller (5); the inertial sensors are used to detect the wearer's motion data, and the controller (1) is used to identify the wearer's gait changes based on the motion data collected by the inertial sensors and output control signals to the electronic speed controller (5) to control the operation of the power source (904).

9. A control method for the variable stiffness flexible knee joint exoskeleton as described in claim 8, characterized in that, Includes the following steps: Step S100: Use the exoskeleton module to perform actual tasks and collect exoskeleton operation data through inertial sensors; Step S200: The controller receives exoskeleton operation data collected by the inertial sensor, performs attitude calculation, and obtains the current attitude angle of the carrier; Step S300: Gait judgment is made by observing changes in leg posture angles during human movement; Step S400: Based on the gait judgment result, output a PWM signal to the ESC, and the ESC controls the operation of the power source; Step S500: Repeat steps S200 to S400 until the actual task is completed.

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