Robotic lower limb variable stiffness soft actuator

Abstract

The application provides a robot lower limb variable stiffness soft body driving mechanism, which comprises a single degree of freedom driver, the single degree of freedom driver comprises a gas bag and fixed connectors located at both ends of the gas bag, the end of the gas bag is connected with the fixed connector, and the gas bag can be elongated and bent in the axial direction when being inflated; a variable stiffness structure comprises an internal skeleton located in the gas bag and an external wire-driven antagonistic structure located outside the gas bag, the two ends of the internal skeleton are fixedly connected with the fixed connectors, and the internal skeleton can realize bending movement consistent with the bending direction of the gas bag; the two ends of the external wire-driven antagonistic structure are fixedly connected with the fixed connectors and used for controlling the bending stiffness of the single degree of freedom driver. The soft body driving mechanism has the advantages of good flexibility, high flexibility, good safety, self-adaptation to the change of the human joint axis, realization of stiffness regulation and control and satisfaction of different user requirements, thereby providing the possibility of assisting walking for the soft body exoskeleton.

Description

Technical Field

[0001] This invention relates to the field of soft robot technology, and more specifically, to a variable stiffness soft drive mechanism for the lower limbs of a robot. Background Technology

[0002] Soft robots, mimicking the soft-bodied animals of nature, are made of highly elastic soft materials capable of withstanding large strains. Theoretically, they possess unlimited deformation freedom and continuous deformation capabilities, allowing them to arbitrarily change shape and size over a wide range. Soft materials endow soft robots with excellent flexibility and interactivity. They are compatible with objects through passive continuous deformation, eliminating the need for complex mechanical transmission systems, resulting in a more compact overall structure and more diverse actuation methods, including wire-driven, fluid-driven, electric-driven, magnetic-driven, and thermal-driven actuation. Soft robots possess advantages such as flexibility, adaptability, and safe interaction. Due to these characteristics, the concept of soft robots is applicable to the design of wearable exoskeleton robots, whose biomimetic and ergonomic design makes them lightweight, highly flexible, and comfortable to wear.

[0003] The actuation problem of robots is crucial to their movement; the actuation mechanism converts energy from other sources into energy for robot motion. Current main actuation methods for robots include electric actuation, hydraulic actuation, and pneumatic actuation. These methods often provide sufficient force or torque and are suitable for rigid robots. Soft robots primarily use soft materials such as silicone rubber and shape memory alloys, and are driven by pneumatic pressure, wire tension, or electrothermal effects.

[0004] In soft actuators, pneumatic soft actuators have attracted widespread attention from scientists and engineers due to their large range of motion, high force output, and fast response speed. Pneumatic artificial muscles are the most commonly used pneumatic soft actuators in industry and exoskeletons, consisting of an elastic internal cavity and a fabric sheath, and are driven by air pressure. The inventors of this application previously proposed a soft actuator structure for lower limb rehabilitation robots (application number 202011384605.7) for training antagonistic muscles, which has advantages such as large bending angle and large bending moment. However, its problems are: 1. Low bending stiffness, which cannot assist when the human body is standing and cannot provide sufficient stiffness; 2. The bending stiffness is not variable. In different gait states, the patient's stiffness requirements are different. In the swinging phase, a small amount of stiffness is needed to achieve joint bending, while in the support phase, a large amount of stiffness is needed to support one leg to achieve the swinging of the other leg; 3. Unwanted movements such as circumferential torsion and radial bending exist in the bending motion, which reduces energy utilization. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a variable stiffness soft drive mechanism for the lower limbs of a robot.

[0006] According to one aspect of the present invention, a variable stiffness soft actuation mechanism for a robot lower limb is provided, comprising:

[0007] A single-degree-of-freedom actuator includes an airbag and fixed connectors located at both ends of the airbag. The ends of the airbag are connected to the fixed connectors. The airbag can extend and bend axially when inflated.

[0008] The variable stiffness structure includes an internal skeleton located inside the airbag and an external linear drive antagonistic structure located outside the airbag. The two ends of the internal skeleton are fixedly connected to the fixed connector, and the internal skeleton can achieve bending motion in the same direction as the bending of the airbag. The two ends of the external linear drive antagonistic structure are fixedly connected to the fixed connector and are used to control the bending stiffness of the single-degree-of-freedom actuator.

[0009] Optionally, the airbag includes a soft airbag core and a fabric layer wrapped around the outside of the soft airbag core. The fabric layer includes a sheath and a neutral restraint layer. The sheath is made of a rubber-blended polyester-knitted fabric, and the neutral restraint layer is made of a polyvinyl chloride-coated polyester-woven fabric reinforcement. The fabric layer allows the airbag to stretch longitudinally and restricts its radial expansion.

[0010] Optionally, the soft airbag core has a semi-elliptical cylindrical chamber, the neutral restraint layer is in close contact with the plane of the semi-elliptical cylindrical chamber, and the sheath is in close contact with the arc surface of the semi-elliptical cylindrical chamber.

[0011] Optionally, the connection points between the two ends of the airbag and the fixed connector are provided with a first conical surface.

[0012] Optionally, the fixed connector includes:

[0013] An internal conical connector has a second conical surface that fits against the outer side of the first conical surface. The two ends of the internal frame are respectively contacted and fixed to the inner side of the internal conical connector. An air vent is provided on the internal conical connector, through which air is inflated into the airbag.

[0014] An external conical connector covers the internal conical connector. The external conical connector has a third conical surface that fits against the second conical surface. The external conical connector has a through hole. One end of the vent pipe passes through the through hole and is exposed outside the external conical connector. The exposed part of the vent pipe is fixed by a nut.

[0015] Optionally, the exposed end of the vent pipe is provided with a pneumatic interface for connecting to an external air source.

[0016] Optionally, the internal skeleton includes multiple skeleton bones and multiple skeleton connectors;

[0017] Multiple skeleton bones and multiple skeleton connectors are arranged alternately along the height direction of the single-degree-of-freedom actuator. The skeleton bones and the skeleton connectors are hinged together by hinge rods, and the internal skeleton can bend and move around the axis of the hinge rods.

[0018] Optionally, the external line drive antagonistic structure includes:

[0019] End caps are located at both ends of the external wire drive antagonistic structure. The end caps are fixed to the external tapered joint by an interference fit. The outer periphery of the end caps is provided with multiple through holes.

[0020] A steel wire rope passes through the through hole at the corresponding position on the end cap to connect the two ends of the end cap.

[0021] Optionally, the wire rope is connected to the end caps at both ends by a single fold, and the ends of all the wire ropes are located on the same side of the single-degree-of-freedom actuator.

[0022] Optionally, one side of the external tapered connector is provided with an insertion hole for inserting a connecting rod, thereby connecting the variable stiffness soft drive mechanism between any two of the waist rigid connecting rod, thigh rigid connecting rod, calf rigid connecting rod, and foot rigid connecting rod of the lower limb rehabilitation robot.

[0023] Compared with the prior art, the present invention has at least one of the following beneficial effects:

[0024] This invention employs a single-degree-of-freedom actuator, which can reduce structural mass, improve motion performance, simplify assembly processes, reduce assembly workload, and effectively extend the actuator's service life, reduce component wear, and improve actuator efficiency. When the single-degree-of-freedom actuator is inflated and bent, the internal frame does not impede the actuator's bending motion but prevents torsional motion in other directions, thereby improving energy utilization efficiency and reducing the risk of injury to the human body from the actuator. By employing an external wire drive antagonistic stiffness control structure to control the bending stiffness of the single-degree-of-freedom actuator, it is possible to achieve assistive walking.

[0025] The variable stiffness soft drive mechanism for robot lower limbs provided by this invention has advantages such as good flexibility, high flexibility, good safety, adaptability to changes in the human joint axis, stiffness control, and meeting the needs of different users, thus providing possibilities for assistive walking with soft exoskeletons. Attached Figure Description

[0026] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0027] Figure 1 This is a schematic diagram of the structure of each part of the variable stiffness soft drive mechanism for the lower limb of a robot in one embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of a single-degree-of-freedom actuator in one embodiment of the present invention;

[0029] Figure 3 for Figure 2 Corresponding AA cross-sectional view;

[0030] Figure 4 This is a schematic diagram of the internal skeleton structure in one embodiment of the present invention;

[0031] Figure 5 This is a schematic diagram of the external line drive antagonistic structure in one embodiment of the present invention;

[0032] Figure 6 This is a schematic diagram of the overall structure of the variable stiffness soft drive mechanism for the lower limbs of a robot in one embodiment of the present invention;

[0033] The corresponding labels in the figure are: 1 for a single-degree-of-freedom actuator, 2 for the internal skeleton, and 3 for the external line drive antagonistic structure.

[0034] 1-1A is the first nut, 1-1B is the second nut, 1-2A is the first external conical connector, 1-2B is the second external conical connector, 1-3A is the first internal conical connector, 1-3B is the second internal conical connector, 1-4 is the soft airbag core, 1-5 is the neutral restraint layer, 1-6 is the sheath, 1-7A is the first vent tube, 1-7B is the second vent tube, 1-8A is the first through hole, 1-8B is the second through hole, 1-9A is the first insertion hole, and 1-9B is the second insertion hole;

[0035] 2-1 is the skeleton, 2-2 is the skeleton connector, and 2-3 is the hinge rod;

[0036] 3-1A is the first end cap, 3-1B is the second end cap, and 3-2 is the wire rope. Detailed Implementation

[0037] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0038] In the description of this invention, it should be understood that the terms "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the purpose of simplifying the description of this invention and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.

[0039] Reference Figures 1-6 An embodiment of the present invention provides a variable stiffness soft drive mechanism for the lower limb of a robot, comprising a single-degree-of-freedom actuator 1 and a variable stiffness structure. The single-degree-of-freedom actuator 1 includes an airbag and fixed connectors located at both ends of the airbag. The ends of the airbag are connected to the fixed connectors. When inflated, the airbag can extend and bend axially. The variable stiffness structure includes an internal skeleton 2 located inside the airbag and an external linear drive antagonistic structure 3 located outside the airbag. The two ends of the internal skeleton 2 are fixedly connected to the fixed connectors. The internal skeleton 2 can achieve bending motion consistent with the bending direction of the airbag. The two ends of the external linear drive antagonistic structure 3 are fixedly connected to the fixed connectors and are used to control the bending stiffness of the single-degree-of-freedom actuator 1.

[0040] In this embodiment of the invention, the stiffness characteristics of the single-degree-of-freedom actuator 1 are adjusted by a variable stiffness structure, increasing torsional stiffness, controlling bending stiffness, and improving energy conversion efficiency. This embodiment integrates the single-degree-of-freedom actuator 1 and the variable stiffness structure. Inflating the single-degree-of-freedom actuator 1 enables bending actuation, while the variable stiffness structure allows for stiffness control of the single-degree-of-freedom actuator 1, providing possibilities for assistive walking in lower limb rehabilitation robots.

[0041] Continue to refer to Figure 2 and Figure 3In some embodiments, the airbag includes a soft airbag core 1-4 and a fabric layer covering the outside of the soft airbag core 1-4. The soft airbag core 1-4 may be made of silicone rubber. The fabric layer includes a sheath 1-6 and a neutral restraint layer 1-5. The sheath 1-6 is unidirectionally elastic and made of a rubber-blended polyester-knitted fabric. The rubber-blended polyester-knitted fabric has high uniaxial nonlinear elasticity, which can limit radial expansion and only allow axial elongation. The neutral restraint layer 1-5 is made of a polyvinyl chloride-coated polyester-woven fabric reinforcement material. The polyvinyl chloride-coated polyester-woven fabric reinforcement material has high in-plane strength, which can limit elongation deformation at the inner position of the actuator. The sheath 1-6 and the neutral restraint layer 1-5 are fixed by sewing, which can completely cover the soft airbag core 1-4 and together form the outer fabric layer of the soft airbag core 1-4. The inner soft airbag core 1-4 ensures airtightness, while the outer sheath 1-6 and neutral restraint layer 1-5 protect the soft airbag core 1-4. The fabric layer is formed by sewing two types of fabric together to create a restraint layer that allows for longitudinal stretching of the airbag while limiting its radial expansion.

[0042] The driving torque of the single-degree-of-freedom actuator 1 is proportional to the static moment of its cross-section. Preferably, the soft airbag core 1-4 has a semi-elliptical cylindrical chamber. The semi-elliptical cross-section has a larger static moment than the semi-circular cross-section, which is beneficial to improving the driving torque of the actuator under inflation conditions. On the one hand, compared with a semi-circular cross-section, the cross-sectional size of the single-degree-of-freedom actuator 1 can be increased, thereby increasing the static moment of the cross-section and thus increasing the driving torque of the actuator. On the other hand, compared with a semi-circular cross-section, using a semi-elliptical cross-section can reduce the width dimension of the cross-section and increase the height dimension of the cross-section, which is beneficial to increasing the static moment of the cross-section under the same area conditions, thereby increasing the driving torque of the actuator. The neutral restraint layer 1-5 is tightly attached to the plane of the semi-elliptical cylindrical chamber, and the sheath 1-6 is tightly attached to the arc surface of the semi-elliptical cylindrical chamber. The airbag includes upper and lower ends, which are connected by a fixed connector. The connection between the two ends of the airbag and the fixed connector is provided with a first conical surface, which is located at both ends of the soft airbag core 1-4.

[0043] To achieve a seal at both ends of the airbag and for connection with other components, in some embodiments, the fixing connector includes an internal tapered joint and an external tapered joint, such as... Figure 2 and Figure 3The airbag consists of a first internal conical connector 1-3A and a first external conical connector 1-2A located at the upper end, and a second internal conical connector 1-3B and a second external conical connector 1-2B located at the lower end. The internal conical connectors have a second conical surface and are positioned at both ends inside the airbag. The second conical surface fits against the outer side of the first conical surface, and the internal conical connectors are sealed to the airbag. The two ends of the internal frame 2 are respectively fixed in contact with the inner side of the internal conical connectors. The internal conical connectors are equipped with protruding venting tubes, including a first venting tube 1-7A located at the upper end and a second venting tube 1-7B located at the lower end, through which air is inflated into the airbag. The external conical connectors cover the internal conical connectors. The external conical connector has a third conical surface that mates with the second conical surface. The external conical connector has a through hole, through which one end of the vent tube passes and protrudes from the external conical connector. The outer wall of the vent tube is threaded, and the inner side has a sealing thread for inserting an air nozzle. The exposed portion of the vent tube is secured with a nut. Specifically, the first external conical connector 1-2A has a first through hole 1-8A, and the second external conical connector 1-2B has a second through hole 1-8B. The upper first vent tube 1-7A passes through the first through hole 1-8A and is secured with a first nut 1-1A. The lower second vent tube 1-7B passes through the second through hole 1-8B and is secured with a second nut 1-1B. During installation, the internal conical connector is inserted into the airbag, with the second conical surface of the internal conical connector mates with the inner conical surface of the airbag, and the external conical connector mates with the outer conical surface of the airbag. The clamping force of the internal and external conical connectors on the airbag can be adjusted by tightening the nut on the threaded outer wall of the vent tube. Furthermore, during the tightening of the nut, by reducing the distance between the second conical surface of the inner conical joint and the third conical surface of the outer conical joint, the friction between the various parts can be increased, enabling the soft drive mechanism to withstand greater air pressure values.

[0044] To inflate the airbag, the exposed end of the ventilator is equipped with a pneumatic interface. The pneumatic interface is used to connect to an external air source and can be used to connect and disconnect the air source from the soft drive mechanism.

[0045] Continue to refer to Figure 4 In some embodiments, the internal skeleton 2 includes multiple skeleton bones 2-1 and multiple skeleton connectors 2-2. The multiple skeleton bones 2-1 and multiple skeleton connectors 2-2 in the internal skeleton 2 are arranged alternately along the height direction of the single-degree-of-freedom actuator 1. The shape of the skeleton bones 2-1 matches the shape of the airbag. The skeleton bones 2-1 and the skeleton connectors 2-2 are hinged together by hinge rods 2-3, allowing the internal skeleton 2 to bend around the axis of the hinge rods 2-3. Because of the hinged connection, the internal skeleton 2 can only achieve bending motion around the axis of the hinge rods 2-3, without translation or rotation in other directions. Therefore, it does not hinder the original bending motion of the single-degree-of-freedom actuator 1 and prevents torsional motion in other directions.

[0046] In this embodiment of the invention, the internal skeleton 2 is placed inside the airbag, and the two ends of the internal skeleton 2 are fixed in contact with the inner side of the internal conical joints on both sides of the airbag. When the single-degree-of-freedom actuator 1 is inflated and bent, the internal skeleton 2 will not hinder the bending movement of the actuator and can prevent torsional movement in other directions, thereby improving the energy utilization rate of the single-degree-of-freedom actuator 1.

[0047] Continue to refer to Figure 5 To achieve stiffness control of the single-degree-of-freedom actuator 1, in some embodiments, the external wire drive antagonistic structure 3 includes end caps and steel wire ropes 3-2. The end caps are located at both ends of the external wire drive antagonistic structure 3, including a first end cap 3-1A at the upper end and a second end cap 3-1B at the lower end. The two end caps are fixed to the external tapered joint by interference fit. The outer periphery of the end caps is provided with multiple through holes. The steel wire rope 3-2 passes through the through holes at corresponding positions on the end caps to connect the end caps at both ends.

[0048] Preferably, the end caps of the wire ropes 3-2 are connected by a single fold, and the ends of all the wire ropes 3-2 are located on the same side of the single-degree-of-freedom actuator 1, such as... Figure 5 The ends of the steel wire rope 3-2 described herein are all located at the lower end caps. By controlling the locking and unlocking of the steel wire rope 3-2, the bending stiffness of the single-degree-of-freedom actuator 1 can be controlled, making it possible to assist in lower limb rehabilitation.

[0049] In some embodiments, an insertion hole is provided on one side of the external tapered connector, such as... Figure 2 A first insertion hole 1-9A is located on one side of the first external conical connector 1-2A, and a second insertion hole 1-9B is located on one side of the second external conical connector 1-2B. The first insertion hole 1-9A and the second insertion hole 1-9B are located on the same side, and connecting rods can be inserted to connect any two of the rigid connecting rods of the waist, thigh, calf, and foot to form a complete rehabilitation exoskeleton. In this embodiment of the invention, the variable stiffness soft drive mechanism is connected between any two of the rigid connecting rods of the waist, thigh, calf, and foot of the lower limb rehabilitation robot, which can realize bending deformation and stiffness change, drive the movement of the human lower limb joints, and achieve assisted walking through stiffness control.

[0050] The variable stiffness soft actuation mechanism for the lower limbs of this embodiment includes an airbag, which simplifies the structural design, reduces mass, and increases the energy density of the actuation structure. It also enables stiffness control, improving the energy utilization of the actuation structure and providing assistive walking assistance for lower limb rehabilitation robots, meeting the needs of different patients. The internal skeleton 2 can only perform bending movements around the hinge axis, without hindering the original bending movement of the single-degree-of-freedom actuator 1, and preventing torsional movements in other directions. The external wire drive antagonistic structure 3 can control the bending stiffness of the single-degree-of-freedom actuator 1 by controlling the locking and unlocking of the steel wire rope 3-2.

[0051] The variable stiffness soft drive mechanism for robot lower limbs in the above embodiments of the present invention has the advantages of high flexibility, good safety, high energy density, adjustable stiffness, high energy utilization, and convenient installation. It overcomes the problems of existing airbags with low bending stiffness, invariable bending stiffness, unnecessary movements such as torsion during bending motion, and low ratio of torque to mass of the structure, thereby improving the installation efficiency, drive efficiency and service life of the exoskeleton.

[0052] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention. The above preferred features can be used in any combination without conflict.

Claims

1. A variable stiffness soft drive mechanism for a robot's lower limb, characterized in that, include: A single-degree-of-freedom actuator includes an airbag and fixed connectors at both ends of the airbag, the ends of the airbag being connected to the fixed connectors. The airbag is capable of axial elongation and bending when inflated. The airbag includes a soft airbag core and a fabric layer wrapped around the soft airbag core. The fabric layer includes a sheath and a neutral restraint layer. The sheath is made of rubber-blended polyester-knitted fabric and is unidirectionally elastic. The neutral restraint layer is made of polyvinyl chloride coated polyester-woven fabric reinforcement. The fabric layer allows longitudinal stretching of the airbag and restricts its radial expansion. The variable stiffness structure includes an internal skeleton located inside the airbag and an external linear drive antagonistic structure located outside the airbag. The two ends of the internal skeleton are fixedly connected to the fixed connector, and the internal skeleton can achieve bending motion in the same direction as the bending of the airbag. The two ends of the external linear drive antagonistic structure are fixedly connected to the fixed connector and are used to control the bending stiffness of the single-degree-of-freedom actuator. The internal skeleton includes multiple skeleton bones and multiple skeleton connectors; Multiple skeleton bones and multiple skeleton connectors are arranged alternately along the height direction of the single-degree-of-freedom actuator. The skeleton bones and the skeleton connectors are hinged together by hinge rods. The internal skeleton can bend and move about the axis of the hinge rods. The external line drive antagonistic structure includes: End caps are located at both ends of the external line drive antagonistic structure, and the outer periphery of the end caps is provided with multiple through holes; A steel wire rope passes through the through hole at the corresponding position on the end cap to connect the two ends of the end cap.

2. The variable stiffness soft drive mechanism for the lower limb of a robot according to claim 1, characterized in that, The soft airbag core has a semi-elliptical cylindrical chamber, the neutral restraint layer is closely attached to the plane of the semi-elliptical cylindrical chamber, and the sheath is closely attached to the arc surface of the semi-elliptical cylindrical chamber.

3. The variable stiffness soft drive mechanism for the lower limb of a robot according to claim 1, characterized in that, The airbag has a first conical surface at the connection between its two ends and the fixed connector.

4. The variable stiffness soft drive mechanism for the lower limb of a robot according to claim 3, characterized in that, The fixed connector includes: An internal conical connector has a second conical surface that fits against the inner side of the first conical surface. Both ends of the internal frame are respectively contacted and fixed to the inner side of the internal conical connector. An air vent is provided on the internal conical connector, through which air is inflated into the airbag. An external conical connector covers the internal conical connector. The external conical connector has a third conical surface that fits against the second conical surface. The external conical connector has a through hole. One end of the vent pipe passes through the through hole and is exposed outside the external conical connector. The exposed part of the vent pipe is fixed by a nut.

5. The variable stiffness soft drive mechanism for the lower limb of a robot according to claim 4, characterized in that, The exposed end of the vent pipe is provided with a pneumatic interface, which is used to connect to an external air source.

6. The variable stiffness soft drive mechanism for the lower limb of a robot according to claim 4, characterized in that, The end cap is fixed to the external tapered joint by an interference fit.

7. The variable stiffness soft drive mechanism for the lower limb of a robot according to claim 6, characterized in that, The wire rope is connected to the end caps at both ends by a single fold, and the ends of all the wire ropes are located on the same side of the single-degree-of-freedom actuator.

8. The variable stiffness soft drive mechanism for the lower limb of a robot according to claim 4, characterized in that, The external tapered connector has an insertion hole on one side, which is used to insert a connecting rod to connect the variable stiffness soft drive mechanism between any two of the waist rigid connecting rod, thigh rigid connecting rod, calf rigid connecting rod and foot rigid connecting rod of the lower limb rehabilitation robot.

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