A bidirectional multi-branch planar volute torsion spring

Abstract

The present invention relates to an elastic element of a robotic series elastic actuator, specifically a bidirectional multi-branch planar scroll torsion spring, which is installed by stacking two torsion spring elastic bodies with opposite helix directions; each torsion spring elastic body has a plurality of elastic body branches with the same helix direction, in the shape of an Archimedean spiral, and deformable. The elastic body branches are evenly arranged circumferentially clockwise or counterclockwise around the rotation center of the torsion spring. There is a gap as the deformation space of the torsion spring elastic body between adjacent two elastic body branches in the no-load state; a single elastic body has the problem of insufficient load-bearing capacity in both positive and negative directions under the action of torque. The method of pre-tightening and installing two torsion spring elastic bodies with different helix directions can enable the torsion spring to have a large load-bearing capacity in both positive and negative directions. The structure of the present invention is compact and has good mechanical properties. It can be used as an elastic element of a robotic flexible joint, and is particularly suitable as an elastic element of a rotary series elastic actuator.

Description

Technical Field

[0001] The present invention relates to an elastic element of a robot series elastic actuator, and more particularly to a bidirectional multi-branch planar scroll torsion spring. Background Art

[0002] With the development of robot technology, more and more robots need to interact with humans or work in unstructured environments, such as exoskeleton robots, collaborative robots, service robots, humanoid robots, etc. In the process of human-robot interaction, in order to ensure the safety of humans, the robot joints need to be flexible; when the robot works in an unstructured environment, in order to avoid impact loads generated when the robot contacts the environment, the robot joints also need to be flexible.

[0003] At present, there are mainly three ways to achieve robot joint flexibility: using impedance control, force-position hybrid control, and designing joints with series elastic actuators. Among them, the robot joints of series elastic actuators connect the output end of the reducer and the end effector through an elastic element. The elastic element cuts off the rigid connection between the end effector and the motor, making the end effector have inherent flexibility. At the same time, the deformation of the elastic element is measured by an encoder, and the force of the end effector can be calculated by combining Hooke's law, which can reduce the use of expensive torque sensors. In recent years, more and more research has been done on series elastic actuator technology at home and abroad, and series elastic actuator technology has broad application prospects in exoskeleton robots, robotic arms and legged robots.

[0004] In a series elastic actuator, the elastic element is a key part restricting its application and development. An ideal elastic element has various performance requirements, among which appropriate stiffness, large load-bearing capacity, and compact structure are very important. With the development of series elastic actuators, various elastic elements have also been designed. For example, the series elastic actuator developed by N.G. Tsagarakis uses three groups of linear springs as elastic elements, with two compression springs in each group. The planar torsion spring proposed by Chris A. Ihrke et al. in the US Patent No. US8176809B2 includes two rigid wheels, an inner wheel and an outer wheel, and an elastic curved beam connecting the two wheels in the middle. The double helical torsion spring proposed by Claude Lagoda et al. of the University of Tokyo in Design of an electric SeriesElastic Actuated Joint for robotic gait rehabilitation training has a stiffness of 219 Nm / rad and a maximum load-bearing capacity exceeding 100 Nm. The "Planar Torsion Spring Suitable for Robot Joints" published on August 15, 2012, with the publication number CN102632508B, is an early-developed planar torsion spring for robot joints in China. Other planar torsion springs for robot joints include the "Unidirectional Planar Torsion Spring" published on December 13, 2019, with the publication number CN110566614A, and the "Planar Torsion Spring and Method for Series Elastic Actuator" published on July 7, 2017, with the publication number CN106931060A, etc.

[0005] Analyzed from the structure, most planar torsion springs are composed of three parts: an inner wheel, an outer wheel, and an intermediate elastic structure. The design of the intermediate elastic structure is the key to the design of planar torsion springs. The planar torsion spring has the same mechanical properties in both forward and reverse directions, requiring the elastic structure to be symmetric left and right; it is difficult for the intermediate elastic structure to simultaneously meet the requirements of having a large stiffness and a large deformation ability for the elastic element. Some springs will undergo plastic deformation under overload conditions, resulting in permanent damage to the spring. In order to prevent overload, it is also necessary to design a limit to restrict the relative rotation angle of the inner and outer wheels of the spring. In addition, if the shape of the intermediate elastic structure is too complex, it will bring great difficulties to the design and processing, and the compactification and lightweight of the spring are also great challenges. The above problems bring great difficulties to the design of planar torsion springs and also limit the development of robot joints equipped with series elastic actuators. Summary of the Invention

[0006] In order to meet the needs of series elastic actuators for rotary elastic elements, the purpose of the present invention is to provide a bidirectional multi-branch planar scroll torsion spring.

[0007] The object of the present invention is achieved by the following technical solutions:

[0008] The present invention includes a torsion spring inner wheel, a torsion spring outer wheel and a torsion spring elastomer. The torsion spring inner wheel is located inside the torsion spring outer wheel. There are two torsion spring elastomers, namely torsion spring elastomer A and torsion spring elastomer B with the same structure. Each of the torsion spring elastomer A and the torsion spring elastomer B includes an elastomer rigid wheel and a plurality of elastomer branches. The elastomer branches of the torsion spring elastomer A have the same helix direction. The inner sides of the elastomer branches of the torsion spring elastomer A are respectively connected to the elastomer rigid wheel of the torsion spring elastomer A. The elastomer branches of the torsion spring elastomer B have the same helix direction. The inner sides of the elastomer branches of the torsion spring elastomer B are respectively connected to the elastomer rigid wheel of the torsion spring elastomer B. The helix direction of the elastomer branches of the torsion spring elastomer A is opposite to that of the elastomer branches of the torsion spring elastomer B. The number of elastomer branches of the torsion spring elastomer A is the same as that of the torsion spring elastomer B and they correspond one by one. The outer sides of the elastomer branches of the torsion spring elastomer A are respectively connected to the outer sides of the corresponding elastomer branches of the torsion spring elastomer B and are connected to the torsion spring outer wheel. The elastomer rigid wheel of the torsion spring elastomer A and the elastomer rigid wheel of the torsion spring elastomer B are respectively connected to the torsion spring inner wheel.

[0009] Wherein: the elastomer branches in the torsion spring elastomer A are evenly arranged in a circumferential direction clockwise or counterclockwise around the torsion spring rotation center. There is a gap as the deformation space of the torsion spring elastomer A between adjacent two elastomer branches in the no-load state. The elastomer branches in the torsion spring elastomer B are evenly arranged in a circumferential direction clockwise or counterclockwise around the torsion spring rotation center. There is a gap as the deformation space of the torsion spring elastomer B between adjacent two elastomer branches in the no-load state.

[0010] Each outer side of the elastomer branch has a torsion spring outer wheel connection hole. The torsion spring outer wheel connection holes on the elastomer branches of the torsion spring elastomer A are connected to the corresponding torsion spring outer wheel connection holes on the elastomer branches of the torsion spring elastomer B through a torsion spring outer wheel connection pin. And the torsion spring outer transmission line connection pin is connected to the torsion spring outer wheel.

[0011] The part of each elastomer branch except the torsion spring outer wheel connection hole is a deformation section in the shape of an Archimedean spiral. The rotation centers of the deformation sections in the shape of an Archimedean spiral on the elastomer branches of the torsion spring elastomer A coincide. The rotation centers of the deformation sections in the shape of an Archimedean spiral on the elastomer branches of the torsion spring elastomer B coincide.

[0012] The starting positions of the deformed sections in the shape of Archimedean spirals on each elastic body branch of the torsion spring elastic body A are evenly distributed along the circumferential direction of the elastic body rigid wheel of the torsion spring elastic body A, and are respectively tangent to the elastic body rigid wheel of the torsion spring elastic body A; the starting positions of the deformed sections in the shape of Archimedean spirals on each elastic body branch of the torsion spring elastic body B are evenly distributed along the circumferential direction of the elastic body rigid wheel of the torsion spring elastic body B, and are respectively tangent to the elastic body rigid wheel of the torsion spring elastic body B; at the starting and ending points of the deformed sections, arcs with smooth transitions for eliminating stress concentration are provided.

[0013] The cross-section of the elastic body branch is rectangular, and the length of the rectangle is the same as the axial direction of the torsion spring; the spiral twist angle of the deformed section in the shape of an Archimedean spiral is ≤ 360°.

[0014] On the outer torsion spring wheel, grooves are evenly opened along the circumferential direction, and the number of the grooves is the same as and corresponds one by one to the number of the outer torsion spring wheel connection holes in the torsion spring elastic body A or the outer torsion spring wheel connection holes in the torsion spring elastic body B. Any one of the outer torsion spring wheel connection holes in the torsion spring elastic body A and the corresponding outer torsion spring wheel connection hole in the torsion spring elastic body B are both accommodated in one of the grooves, and a pin hole A for connecting the outer torsion spring wheel connection pin is opened at the bottom of each groove.

[0015] An outer torsion spring ring for supporting the outer torsion spring wheel connection pin is connected to the outer torsion spring wheel. One end of each outer torsion spring wheel connection pin is connected to the outer torsion spring wheel, and the other end is inserted into the outer torsion spring ring.

[0016] The outer edge of the central hole of the inner torsion spring wheel extends axially towards the torsion spring elastic body A and the torsion spring elastic body B to form an extension part that is inserted into the central holes of the elastic body rigid wheels of the torsion spring elastic body A and the torsion spring elastic body B. A plurality of inner torsion spring wheel connection grooves B are evenly opened on the outer surface of the extension part along the circumferential direction; on the inner wall of the central holes of the elastic body rigid wheels of the torsion spring elastic body A and the torsion spring elastic body B, inner torsion spring wheel connection grooves A with the same number as and corresponding one by one to the inner torsion spring wheel connection grooves are evenly opened along the circumferential direction. A torsion spring inner wheel connection pin for connecting the elastic body rigid wheel and the inner torsion spring wheel is inserted between each inner torsion spring wheel connection groove A and the corresponding inner torsion spring wheel connection groove B.

[0017] Both the torsion spring elastic body A and the torsion spring elastic body B are pre-tightened during installation; when the torque is small, the elastic body branches of the torsion spring elastic body A and the torsion spring elastic body B do not come into contact, and the stiffness of the torsion spring is a constant value; when a larger torque is applied, the elastic body branches of the torsion spring elastic body A or the torsion spring elastic body B will come into contact. As the torque increases, the contact part of the elastic body branches becomes longer, and the stiffness of the torsion spring increases non-linearly.

[0018] The advantages and positive effects of the present invention are:

[0019] 1. The present invention adopts the design of a pair of positive and negative torsion spring elastomers, enabling the torsion spring to have the same mechanical properties in both positive and negative directions.

[0020] 2. The elastomer branches in the torsion spring elastomer of the present invention adopt an Archimedean spiral shape, which has a simple shape and greatly simplifies the design process of the planar torsion spring.

[0021] 3. The torsion spring stiffness of the present invention has non-linear characteristics.

[0022] 4. The present invention can adjust the stiffness characteristics of the torsion spring according to the different pre-tightening degrees of the two torsion spring elastomers. The torsion spring has a large load-bearing capacity in both positive and negative directions and generally does not require limit protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is an exploded view of the present invention;

[0024] Figure 2 is one of the structural schematic diagrams of the torsion spring elastomer of the present invention;

[0025] Figure 3 is another structural schematic diagram of the torsion spring elastomer of the present invention;

[0026] Figure 4 is one of the structural schematic diagrams of the bi-directional torsion spring of the present invention;

[0027] Figure 5 is another structural schematic diagram of the bi-directional torsion spring of the present invention;

[0028] Figure 6 is the structural schematic diagram of the inner wheel of the torsion spring of the present invention;

[0029] Figure 7 is the sectional view of the cross-section of the torsion spring elastomer of the present invention;

[0030] Among them: 1 is the torsion spring elastomer A, 2 is the torsion spring elastomer B, 3 is the outer wheel connecting pin of the torsion spring, 4 is the inner wheel connecting pin of the torsion spring, 5 is the inner wheel of the torsion spring, 6 is the outer wheel of the torsion spring, 7 is the outer ring of the torsion spring, 8 is the outer ring screw, 9 is the inner wheel connecting groove A of the torsion spring, 10 is the outer wheel connecting hole of the torsion spring, 11 is the elastomer branch, 12 is the elastomer rigid wheel, 13 is the deformation section, 14 is the inner wheel connecting groove B of the torsion spring, 15 is the groove, 16 is the pin hole A, and 17 is the extension part. DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention will be further described in detail below with reference to the drawings.

[0032] As Figure 1As shown in the figure, the present invention includes a torsion spring inner wheel 5, a torsion spring outer wheel 6 and a torsion spring elastomer. The torsion spring inner wheel 5 is located inside the torsion spring outer wheel 6. The torsion spring inner wheel 5 and the torsion spring outer wheel 6 are respectively connected to other parts of the robot joint or integrally designed. There are two torsion spring elastomers, namely torsion spring elastomer A1 and torsion spring elastomer B2 with the same structure. Both the torsion spring elastomer A1 and the torsion spring elastomer B2 include an elastomer rigid wheel 12 and a plurality of elastomer branches 11. The helical directions of the elastomer branches 11 of the torsion spring elastomer A1 are the same. The inner sides of the elastomer branches 11 of the torsion spring elastomer A1 are respectively connected to the elastomer rigid wheel 12 of the torsion spring elastomer A1. The helical directions of the elastomer branches 11 of the torsion spring elastomer B2 are the same. The inner sides of the elastomer branches 11 of the torsion spring elastomer B2 are respectively connected to the elastomer rigid wheel 12 of the torsion spring elastomer B2. The helical direction of the elastomer branches 11 of the torsion spring elastomer A1 is opposite to the helical direction of the elastomer branches 11 of the torsion spring elastomer B2. A single torsion spring elastomer has two deficiencies. First, the unidirectional load-bearing capacity is large, while the load-bearing capacity in the other direction is insufficient. Second, the stiffness and allowable torsional angle of the positive and negative angular displacements of a single torsion spring elastomer are inconsistent. In this embodiment, two torsion spring elastomers with opposite helical directions are installed. Both the torsion spring elastomer A1 and the torsion spring elastomer B2 are pre-tightened during installation, and the above problems can be eliminated simultaneously. The number of elastomer branches 11 of the torsion spring elastomer A1 is the same as that of the torsion spring elastomer B2 and they correspond one by one. In this embodiment, both the torsion spring elastomer A1 and the torsion spring elastomer B2 have five elastomer branches 11. The outer sides of the elastomer branches 11 of the torsion spring elastomer A1 are respectively connected to the outer sides of the corresponding elastomer branches 11 of the torsion spring elastomer B2 and are connected to the torsion spring outer wheel 6. The elastomer rigid wheel 12 of the torsion spring elastomer A1 and the elastomer rigid wheel 12 of the torsion spring elastomer B2 are respectively connected to the torsion spring inner wheel 5.

[0033] In this embodiment, the elastomer branches 11 in the torsion spring elastomer A1 are evenly arranged in a clockwise or counterclockwise direction along the circumferential direction with the torsion spring rotation center as the center. There is a gap as the deformation space of the torsion spring elastomer A1 between adjacent two elastomer branches 11 in the no-load state. The elastomer branches 11 in the torsion spring elastomer B2 are evenly arranged in a clockwise or counterclockwise direction along the circumferential direction with the torsion spring rotation center as the center. There is a gap as the deformation space of the torsion spring elastomer B2 between adjacent two elastomer branches 11 in the no-load state.

[0034] On the outer side of each elastomer branch 11 in this embodiment, there is a torsion spring outer wheel connection hole 10. The torsion spring outer wheel connection holes 10 on the respective elastomer branches 11 in the torsion spring elastomer A1 are connected to the torsion spring outer wheel connection holes 10 on the corresponding elastomer branches 11 in the torsion spring elastomer B2 through a torsion spring outer wheel connection pin 3, and the torsion spring outer transmission line connection pin 3 is connected to the torsion spring outer wheel 6. The part of each elastomer branch 11 except the torsion spring outer wheel connection hole 10 is a deformed section 13 in the shape of an Archimedean spiral. The centers of rotation of the deformed sections 13 in the shape of an Archimedean spiral on the respective elastomer branches 11 of the torsion spring elastomer A1 coincide, and the centers of rotation of the deformed sections 13 in the shape of an Archimedean spiral on the respective elastomer branches 11 of the torsion spring elastomer B2 coincide. The starting positions of the deformed sections 13 in the shape of an Archimedean spiral on the respective elastomer branches 11 of the torsion spring elastomer A1 are evenly distributed along the circumferential direction of the elastomer rigid wheel 12 of the torsion spring elastomer A1 and are respectively tangent to the elastomer rigid wheel 12 of the torsion spring elastomer A1; the starting positions of the deformed sections 13 in the shape of an Archimedean spiral on the respective elastomer branches 11 of the torsion spring elastomer B2 are evenly distributed along the circumferential direction of the elastomer rigid wheel 12 of the torsion spring elastomer B2 and are respectively tangent to the elastomer rigid wheel 12 of the torsion spring elastomer B2; at the starting and ending points of the deformed section 13, there are arcs with smooth transitions for eliminating stress concentration.

[0035] The cross-section of the elastomer branch 11 in this embodiment is rectangular, and the length of the rectangle is the same as the axial direction of the torsion spring; the rectangular dimensions of the cross-sections of the deformed sections 13 in the shape of an Archimedean spiral on the elastomer branch 11 are the same; the spiral twist angle of the deformed section 13 in the shape of an Archimedean spiral is ≤ 360°.

[0036] On the outer torsion spring wheel 6 of this embodiment, a plurality of grooves 15 are evenly arranged along the circumferential direction. The number of grooves 15 is the same as and corresponds one by one to the connecting holes 10 of the outer torsion spring wheel in the torsion spring elastomer A1 or the connecting holes 10 of the outer torsion spring wheel in the torsion spring elastomer B2. Any one of the connecting holes 6 of the outer torsion spring wheel in the torsion spring elastomer A1 and the corresponding connecting hole 6 of the outer torsion spring wheel in the torsion spring elastomer B2 are both accommodated in a groove 15. A pin hole A16 for connecting the outer torsion spring wheel connecting pin 3 is provided at the bottom of each groove 15. The outer wall shapes of the groove 15 and the connecting hole 10 of the outer torsion spring wheel are the same, but the size of the groove 15 is slightly larger to achieve a large clearance fit and avoid mutual friction between the groove 15 and the connecting hole 10 of the outer torsion spring wheel. During installation, each connecting hole 10 of the outer torsion spring wheel in the torsion spring elastomer A1 and each connecting hole 10 of the corresponding outer torsion spring wheel in the torsion spring elastomer B2 are inserted with an outer torsion spring wheel connecting pin 3. After insertion, the connecting hole 10 of the outer torsion spring wheel and the outer torsion spring wheel connecting pin 3 have a small clearance fit, and the pin hole A16 for fixing the outer torsion spring wheel connecting pin 3 in the groove 15 of the outer torsion spring wheel 6 and the outer torsion spring wheel connecting pin 3 have an interference fit, so as to realize that the connecting hole 10 of the outer torsion spring wheel rotates around the outer torsion spring wheel connecting pin 3 while the outer torsion spring wheel connecting pin 3 does not rotate in the pin hole A16, reducing future maintenance costs. The shapes of the groove 15 on the outer torsion spring wheel 6 and the outer edge of the connecting hole 10 of the outer torsion spring wheel in the plane of the torsion spring are both cylindrical.

[0037] To avoid the connection strength between the outer torsion spring wheel 6 and the outer torsion spring wheel connecting pin 3, an outer torsion spring ring 7 for supporting the outer torsion spring wheel connecting pin 3 is connected to the outer torsion spring wheel 6 of this embodiment. The outer torsion spring ring 7 is fixed to the outer torsion spring wheel 6 by an outer ring screw 8. One end of each outer torsion spring wheel connecting pin 3 is connected to the outer torsion spring wheel 6, and the other end is inserted into the outer torsion spring ring 7.

[0038] The outer edge of the central hole of the inner torsion spring wheel 5 of this embodiment extends axially towards the torsion spring elastomer A1 and the torsion spring elastomer B2 to form an extension part 17 that is inserted into the central hole of the elastomer rigid wheel 12 of the torsion spring elastomer A1 and the torsion spring elastomer B2. A plurality of inner torsion spring wheel connecting grooves B14 are evenly arranged along the circumferential direction on the outer surface of the extension part 17, and the inner torsion spring wheel connecting grooves B14 are evenly distributed along the circumferential direction about the rotation center of the inner torsion spring wheel 5; along the circumferential direction on the inner wall of the central hole of the elastomer rigid wheel 12 of the torsion spring elastomer A1 and the torsion spring elastomer B2, inner torsion spring wheel connecting grooves A9 with the same number as and corresponding one by one to the inner torsion spring wheel connecting grooves 14 are evenly arranged. The inner torsion spring wheel connecting grooves A9 and the inner torsion spring wheel connecting grooves B14 are both semi-cylinders with the same shape. Each inner torsion spring wheel connecting groove A9 and the corresponding inner torsion spring wheel connecting groove B14 are combined into a cylindrical hole, and a inner torsion spring wheel connecting pin 4 for connecting the elastomer rigid wheel 12 and the inner torsion spring wheel 5 is inserted into each cylindrical hole, realizing the torque transmission between the inner torsion spring wheel 5 and the torsion spring elastomer A1 and the torsion spring elastomer B2.

[0039] Before preloading, the positions of the torsion spring inner wheel connection grooves A9 of the torsion spring elastomer A1 and the torsion spring inner wheel connection grooves A9 of the torsion spring elastomer B2 do not coincide. During installation, first use the torsion spring outer wheel connection pin 3 to connect the torsion spring outer wheel connection hole 10 of the torsion spring elastomer A1 with the corresponding torsion spring outer transmission line connection hole 10 of the torsion spring elastomer B2. Then, through a tooling, align the torsion spring inner wheel connection groove A9 of the torsion spring elastomer A1 with the torsion spring inner wheel connection groove A9 of the torsion spring elastomer B2 and insert the torsion spring inner wheel connection pin 4 embedded on the torsion spring inner wheel 5.

[0040] When the torque on a single torsion spring elastomer is small, the branches of each elastomer do not contact, and the stiffness of the torsion spring is a constant value. When the torque on a single torsion spring elastomer is large, the branches of each elastomer on the torsion spring elastomer come into contact, and the change in the stiffness of the torsion spring is non-linear.

[0041] According to different preloading degrees, the preloaded torsion spring has two states. First, when the preloading force is small, the branches 11 of each elastomer of the torsion spring elastomer A1 and the branches 11 of each elastomer of the torsion spring elastomer B2 do not contact, and the stiffness of the torsion spring shows a segmented phenomenon, including a constant stiffness stage and a non-linear stiffness stage. Second, when the preloading force is large, the branches 11 of each elastomer of the torsion spring elastomer A1 contact, and the branches 11 of each elastomer of the torsion spring elastomer B2 contact, and the stiffness of the torsion spring only has a non-linear stage.

[0042] Insert the extension 17 of the torsion spring inner wheel 5 with the torsion spring inner wheel connection groove B14 into the torsion spring elastomer A1 and the torsion spring elastomer B2 in reverse parallel connection. Align the torsion spring inner wheel connection groove B14 on the torsion spring inner wheel 5 with the torsion spring inner wheel connection groove A9 on the corresponding torsion spring elastomer A1 and the torsion spring elastomer B2, and press twelve torsion spring inner wheel connection pins 4 into the cylindrical holes formed by the combination of the torsion spring inner wheel connection groove A9 and the torsion spring inner wheel connection groove B14 respectively. Since the torsion spring elastomer A1 and the torsion spring elastomer B2 are not preloaded at this time, the torsion spring inner wheel 5 and the torsion spring inner wheel connection pin 4 are very easy to fall off. The torsion spring inner wheel 5 at this time should be placed on the platform with the extension 17 of the torsion spring inner wheel connection pin 4 facing up for the next preloading assembly. After aligning the axes of the corresponding torsion spring outer wheel connection holes 10 of the torsion spring elastomer A1 and the torsion spring elastomer B2, insert the torsion spring outer wheel connection pin 3 to preload the torsion spring elastomer A1 and the torsion spring elastomer B2. At this time, turn the extension 17 of the torsion spring inner wheel 5 with the torsion spring inner wheel connection groove B14 away from the torsion spring outer wheel 6, press the solid outer edges of five pairs of concentric torsion spring outer wheel connection holes 10 into the five grooves 15 of the torsion spring outer wheel 6, and insert the exposed part of the torsion spring outer wheel connection pin 3 into the pin hole A16 in the groove 15 on the torsion spring outer wheel 6. Align the five pin holes B on the torsion spring outer ring 7 with the other exposed part of the torsion spring outer wheel connection pin 3 and press them in. Finally, pass eight outer ring screws 8 through the light holes of the torsion spring outer ring 7 and screw them into the threaded holes of the torsion spring outer wheel 6 to complete the assembly.

[0043] This embodiment is used for the development of a flexible joint of a robot. In the flexible joint of the robot, the inner wheel 5 of the torsion spring is connected to the output end of the reducer of the joint. In this embodiment, the inner wheel 5 of the torsion spring is connected to the output end of the reducer by bolts.

[0044] The outer wheel 6 of the torsion spring is connected to the link at the end of the robot joint. In this embodiment, the outer wheel 6 of the torsion spring is connected to the end effector of the robot joint by bolts.

[0045] Due to the pre-tightening force existing in the two torsion spring elastomers A1 and B2 connected in reverse parallel, the clearance at the beginning of the rotation of the inner wheel 5 of the torsion spring is eliminated, realizing an accurate torque response. For a single-piece torsion spring, due to its own special structural characteristics, the load-bearing capacity and stiffness allowed in its forward and reverse directions are different, and the load-bearing capacity in the winding direction of the torsion spring is greater than that in the unwinding direction. The poor load-bearing capacity in the unwinding direction of the torsion spring easily leads to damage to the mechanism or plastic deformation of the torsion spring. After adding a set pre-tightening force between the two identical torsion spring elastomers A1 and B2 and connecting them in parallel with opposite helix directions, the combined structure has the same load-bearing capacity in both forward and reverse directions.

[0046] When the adjacent elastomer branches 11 do not come into contact, the stiffness of the torsion spring shows linearity. Continuing to wind until the adjacent elastomer branches 11 come into contact, the stiffness of the torsion spring shows non-linearity.

[0047] The lengths of the elastomer branches 11 of the torsion spring elastomer A1 and the torsion spring elastomer B2 can be designed according to the requirements of the series elastic actuator for the torsion spring. Under the condition that other parameters remain unchanged, the smaller the length of the elastomer branch 11, the greater the stiffness of the torsion spring.

[0048] In this embodiment, the outer diameter of the outer wheel 6 of the torsion spring is 105 mm, the total thickness of the torsion spring elastomer A1 and the torsion spring elastomer B2 in the axial direction of the joint is 8 mm, and the axial and radial dimensions of the torsion spring are very compact. This flexible joint is used for the hip joint of an exoskeleton robot, with a maximum joint diameter of 105 mm and a maximum joint thickness of 72 mm. The total weight of the torsion spring elastomer A1 is 111 grams.

[0049] In this embodiment, the parametric equations of the Archimedean spiral in the torsion spring elastomer A1 and the torsion spring elastomer B2 and the parameters of the torsion spring elastomer A1 and the torsion spring elastomer B2 are:

[0050] ρ = α + βθ

[0051] Constant α: α = 26.5;

[0052] Constant β: β = 12.5 / π;

[0053] The helix angle θ of the torsion spring: 0 ≤ θ ≤ 4 / 3π (rad);

[0054] Radius ρ of the Archimedean spiral

[0055] Cross-sectional parameters of the elastomer branch 11: b = 4 mm, h = 2.9 mm

[0056] Number n of torsion springs: n = 5

[0057] Processing method of the torsion spring elastomer: middle-wire electrical discharge machining

[0058] Material of the torsion spring elastomer: 60Si2CrA

[0059] Elastic modulus E: 206 GPa

[0060] Yield limit: ≥1568 MPa

[0061] Tensile strength: ≥1764 MPa

[0062] Helix angle Ф of the Archimedean spiral: 4 / 3π

[0063] The present invention is applied to a series elastic actuator. Power is input by the inner wheel 5 of the torsion spring. The inner wheel 5 of the torsion spring transmits the power to the torsion spring elastomer A1 and the torsion spring elastomer B2 through the connecting pin 4 of the inner wheel of the torsion spring. The torsion spring elastomer transmits the power to the outer wheel 6 of the torsion spring through the connecting pin 3 of the outer wheel of the torsion spring, and finally the power is output by the outer wheel 6 of the torsion spring.

[0064] The present invention avoids some common disadvantages and deficiencies of a single multi-branch planar spiral torsion spring, and solves the problems of insufficient single-way load-bearing capacity and inconsistent forward and reverse stiffness of a single multi-branch planar spiral torsion spring.

Claims

1. A bidirectional multi-branch planar scroll torsion spring, comprising a torsion spring inner wheel, a torsion spring outer wheel and a torsion spring elastic body, wherein the torsion spring inner wheel is located inside the torsion spring outer wheel; characterized in that: There are two torsion spring elastomers, namely torsion spring elastomer A (1) and torsion spring elastomer B (2) with the same structure. Each of the torsion spring elastomer A (1) and the torsion spring elastomer B (2) includes an elastomer rigid wheel (12) and a plurality of elastomer branches (11). The elastomer branches (11) of the torsion spring elastomer A (1) have the same helix direction. The inner sides of the elastomer branches (11) of the torsion spring elastomer A (1) are respectively connected to the elastomer rigid wheel (12) of the torsion spring elastomer A (1). The elastomer branches (11) of the torsion spring elastomer B (2) have the same helix direction. The inner sides of the elastomer branches (11) of the torsion spring elastomer B (2) are respectively connected to the elastomer rigid wheel (12) of the torsion spring elastomer B (2). The helix direction of the elastomer branches (11) of the torsion spring elastomer A (1) is opposite to that of the elastomer branches (11) of the torsion spring elastomer B (2). The number of the elastomer branches (11) of the torsion spring elastomer A (1) is the same as that of the elastomer branches (11) of the torsion spring elastomer B (2) and they correspond to each other one by one. The outer sides of the elastomer branches (11) of the torsion spring elastomer A (1) are respectively connected to the outer sides of the corresponding elastomer branches (11) of the torsion spring elastomer B (2) and are connected to the torsion spring outer wheel (6). The elastomer rigid wheel (12) of the torsion spring elastomer A (1) and the elastomer rigid wheel (12) of the torsion spring elastomer B (2) are respectively connected to the torsion spring inner wheel (5). The elastomer branches (11) in the torsion spring elastomer A (1) are evenly arranged in a circumferential direction clockwise or counterclockwise around the torsion spring rotation center. There is a gap serving as the deformation space of the torsion spring elastomer A (1) between two adjacent elastomer branches (11) in the no-load state. The elastomer branches (11) in the torsion spring elastomer B (2) are evenly arranged in a circumferential direction clockwise or counterclockwise around the torsion spring rotation center. There is a gap serving as the deformation space of the torsion spring elastomer B (2) between two adjacent elastomer branches (11) in the no-load state. The outer edge of the central hole of the torsion spring inner wheel (5) extends axially towards the torsion spring elastomer A (1) and the torsion spring elastomer B (2) to form an extension part (17) inserted into the central holes of the elastomer rigid wheels (12) of the torsion spring elastomer A (1) and the torsion spring elastomer B (2). A plurality of torsion spring inner wheel connection grooves B (14) are evenly arranged on the outer surface of the extension part (17) in the circumferential direction. The inner wall of the central hole of the elastomer rigid wheels (12) of the torsion spring elastomer A (1) and the torsion spring elastomer B (2) is evenly provided with torsion spring inner wheel connection grooves A (9) having the same number as and corresponding one by one to the torsion spring inner wheel connection grooves B (14). A torsion spring inner wheel connection pin (4) for connecting the elastomer rigid wheel (12) and the torsion spring inner wheel (5) is inserted between each torsion spring inner wheel connection groove A (9) and the corresponding torsion spring inner wheel connection groove B (14).

2. The double-direction multi-branch planar volute torsion spring according to claim 1, wherein: On the outer side of each of the elastomer branches (11), there is a torsion spring outer wheel connection hole (10). The torsion spring outer wheel connection holes (10) on the elastomer branches (11) of the torsion spring elastomer A (1) are connected to the corresponding torsion spring outer wheel connection holes (10) on the elastomer branches (11) of the torsion spring elastomer B (2) through torsion spring outer wheel connection pins (3), and the torsion spring outer wheel connection pins (3) are connected to the torsion spring outer wheel (6).

3. The bi-directional multi-branch planar volute torsion spring according to claim 2, characterized in that: The part of each of the elastomer branches (11) except the torsion spring outer wheel connection hole (10) is a deformed section (13) in the shape of an Archimedean spiral. The centers of rotation of the deformed sections (13) in the shape of an Archimedean spiral on the elastomer branches (11) of the torsion spring elastomer A (1) coincide. The centers of rotation of the deformed sections (13) in the shape of an Archimedean spiral on the elastomer branches (11) of the torsion spring elastomer B (2) coincide.

4. The bidirectional multi-branch planar volute torsion spring according to claim 3, wherein: The starting positions of the deformed sections (13) in the shape of an Archimedean spiral on the elastomer branches (11) of the torsion spring elastomer A (1) are evenly distributed along the circumferential direction of the elastomer rigid wheel (12) of the torsion spring elastomer A (1) and are respectively tangent to the elastomer rigid wheel (12) of the torsion spring elastomer A (1). The starting positions of the deformed sections (13) in the shape of an Archimedean spiral on the elastomer branches (11) of the torsion spring elastomer B (2) are evenly distributed along the circumferential direction of the elastomer rigid wheel (12) of the torsion spring elastomer B (2) and are respectively tangent to the elastomer rigid wheel (12) of the torsion spring elastomer B (2). At the starting and ending points of the deformed section (13), there are arcs with smooth transitions for eliminating stress concentration.

5. The double-direction multi-branch planar scroll torsion spring according to claim 3, wherein: The cross-section of the elastomer branch (11) is rectangular, and the length of the rectangle is the same as the axial direction of the torsion spring. The spiral twist angle of the deformed section (13) in the shape of an Archimedean spiral is ≤360°.

6. The double-direction multi-branch planar scroll torsion spring according to claim 2, wherein: On the torsion spring outer wheel (6), there are evenly arranged grooves (15) along the circumferential direction, and the number of grooves (15) is the same as and corresponds one by one to the number of torsion spring outer wheel connection holes (10) in the torsion spring elastomer A (1) or the number of torsion spring outer wheel connection holes (10) in the torsion spring elastomer B (2). Any one of the torsion spring outer wheel connection holes (10) in the torsion spring elastomer A (1) and the corresponding torsion spring outer wheel connection hole (10) in the torsion spring elastomer B (2) are both accommodated in one of the grooves (15), and a pin hole A (16) for connecting the torsion spring outer wheel connection pin (3) is provided at the bottom of each groove (15).

7. The bi-directional multi-branch planar volute torsion spring according to claim 2, characterized in that: Connected to the torsion spring outer wheel (6) is a torsion spring outer ring (7) for supporting the torsion spring outer wheel connection pin (3). One end of each torsion spring outer wheel connection pin (3) is connected to the torsion spring outer wheel (6), and the other end is inserted into the torsion spring outer ring (7).

8. The double-direction multi-branch planar volute torsion spring according to claim 1, wherein: Both the torsion spring elastomer A (1) and the torsion spring elastomer B (2) are pre-tensioned during installation; when the torque is small, the elastomer branches (11) of the torsion spring elastomer A (1) and the torsion spring elastomer B (2) do not come into contact, and the stiffness of the torsion spring is a constant value; when a large torque is applied, the elastomer branch (11) of the torsion spring elastomer A (1) or the torsion spring elastomer B (2) will come into contact. As the torque increases, the contact part of the elastomer branch (11) becomes longer, and the stiffness of the torsion spring increases non-linearly.

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