Robot joint finger based on tendon drive and automatic rebound mechanism

Abstract

The utility model discloses a kind of robot joint fingers based on tendon transmission and automatic rebound mechanism, the finger structure adopts tendon to reverse winding three joints in 8 character back loop mode, two ends are fixed in first joint and third joint respectively, and the synchronous rotation of second joint and third joint is realized using double pulley symmetrical winding.Tendon sliding path is provided with spring fixed position one, connecting spring one end, and spring other end is fixed in the spring fixed position two of second joint, and tendon sliding drives spring stretching or compression energy storage, spring drives tendon back after external force release, and realizes joint automatic rebound.The utility model integrates driving and reset function, compact structure, spring is arranged using tendon path space, reduce space occupancy;Linear motion spring assembly prolongs service life, and 8 character winding design ensures joint synchronism, applicable to high-precision robot scene such as bionic hand, dexterous hand, improve operation flexibility and reliability.

Description

Technical Field

[0001] This utility model belongs to the field of robot bionic drive technology, specifically relating to a robot joint finger based on tendon cable transmission and automatic rebound mechanism. Background Technology

[0002] As a biomimetic drive technology that mimics the function of biological tendons, chord drive has shown unique advantages in the field of robot joints and is gradually becoming a key technology to promote the development of robots towards high flexibility and lightweight. Its core principle is to connect the distal actuator to the joint through a flexible chord, and the motor drives the ball screw through the gearbox. The nut converts the rotational motion into linear motion, pulling the chord wrapped on the nut, thereby driving the robot joint to rotate around the axis. This design separates the actuator from the execution mechanism, allowing the motor to be centrally located in the robot's forearm or hand, significantly reducing the end effector load and rotational inertia, and greatly improving the speed and flexibility of movement.

[0003] In the design of chord-driven robot joints, the design of the rebound mechanism is a key technical aspect in order to improve the dynamic response capability and energy utilization efficiency of the joint. Currently, the two mainstream rebound technologies—torsion spring-assisted rebound and tension spring (including tension rope) rebound—each have their advantages, but both face significant technical bottlenecks in practical applications, which restrict the performance improvement and reliability assurance of robot joints.

[0004] Torsion spring-assisted rebound technology achieves passive joint reset by embedding a torsion spring into the joint's rotation axis and utilizing its elastic potential energy. Its core advantage lies in its compact structure, allowing direct integration into the joint's rotation axis without requiring additional space. Furthermore, the torsion spring's torque output is linearly related to the joint's rotation angle, facilitating control algorithm modeling. For example, in bionic dexterous hand design, the torsion spring can simulate the rebound characteristics of the flexor tendons in human fingers, enabling the joint to automatically return to its initial posture without driving input, thus reducing energy consumption. However, this technology has two major drawbacks: (1) Conflict between space occupation and structural design: Torsion springs need to be embedded inside the joint's rotation axis, and their diameter and length directly occupy the effective rotation space of the joint. Taking the knee joint of a humanoid robot as an example, if a torsion spring rebound is used, the torsion spring needs to be arranged in a rotation axis with a diameter of only 20~30mm, which limits the maximum rotation angle of the joint (usually not exceeding 120°) and makes it difficult to meet the requirements of high torque drive. In addition, the preload of the torsion spring needs to be adjusted by changing the axial compression, which further compresses the internal layout space of the joint, forcing designers to compromise between joint size and performance.

[0005] (2) Fatigue life and reliability risk: The fatigue life of torsion springs is significantly affected by material properties and stress cycle number. In high-frequency reciprocating motion scenarios (such as robot running and jumping), torsion springs need to withstand millions of alternating loads. Their materials (such as spring steel) are prone to microcracks due to stress concentration, which leads to torque output attenuation or even breakage.

[0006] Spring return technology fixes one end of a spring to the joint base and the other end to the joint output end, using the rebound force generated by the spring tension to achieve reset. A variant—wire return—further optimizes layout flexibility by adding a flexible wire rope (such as a steel wire rope or fiber rope) to transmit the tension. The core advantage of this technology is that the spring can be placed in the non-rotating area of ​​the joint, avoiding occupying rotational space, and the tension output has a non-linear relationship with the joint angle, adapting to complex motion trajectories. For example, in the design of a robotic arm shoulder joint, the spring can be arranged along the joint arm direction, and the rebound force can be transmitted to the rotation axis via a wire rope to achieve passive reset at large angles (such as ±180°). However, this technology also has significant drawbacks: (1) Insufficient dynamic tracking: The rebound force of the tension spring is linearly related to the displacement, while the load torque (such as gravity and inertial force) that needs to be overcome during joint rotation usually changes with the rotation angle. This results in insufficient rebound force of the tension spring in the early stage of joint movement (small rotation angle) and excessive rebound force in the late stage of movement (large rotation angle), causing joint vibration or overshoot. For example, in robot grasping tasks, the lag of the tension spring rebound may cause the joint to fail to stop accurately at the target position, requiring additional compensation from the actuator, increasing energy consumption and control complexity.

[0007] (2) Increased wear induced by tangential force: The connection point between the tension spring (or rope) and the joint base must withstand the combined effects of tension and tangential force. Especially during high-speed motion, the tangential force will exacerbate friction and stress concentration at the connection point. Experiments show that under the conditions of 300 rpm and 50 N tension, the wear rate of the contact surface between the fixed end of the tension spring and the base can reach 0.1 mm / 1000 h, leading to loosening of the connection or breakage of the tension spring. Although the rebound of the rope disperses some of the tangential force through flexible transmission, the friction between the rope and the pulley will still cause energy loss (efficiency reduction of about 15%) and life reduction (rope life is about 500,000 cycles). Summary of the Invention

[0008] In view of the above, this utility model provides a robotic joint finger based on tendon cable transmission and automatic rebound mechanism, which combines the functions of tendon cable and elastic element, saving space, achieving rebound, and effectively reducing friction loss and increasing service life.

[0009] A robotic finger joint based on chordal transmission and an automatic rebound mechanism includes a first joint, a second joint, and a third joint arranged sequentially from the base of the finger to the tip. The first, second, and third joints are connected by chordal transmission. The chordal is arranged in a figure-eight loop, symmetrically wound around two cylinders of equal radius. One end of the chordal is fixed at a chordal fixing point in the first joint, and the other end is fixed at a chordal fixing point in the third joint, forming a cross-joint mechanical coupling transmission path, enabling the second and third joints to rotate synchronously. A spring fixing position one is provided on the chordal, and a spring fixing position two is provided on the second joint. The two ends of the spring are connected to spring fixing position one and spring fixing position two, respectively. When an external force drives the chordal to rotate the joint, the chordal slides within the second joint, causing spring fixing position one to move, resulting in tensile or compressive deformation of the spring to store elastic potential energy. When the external force is released, the spring releases its elastic potential energy, driving the chordal to retract, causing the second and third joints to automatically rebound to their initial positions. This structure achieves a combined function of synchronous movement and automatic rebound through the integration of the chordal transmission path and the spring's common path.

[0010] Furthermore, the tendon cord is a single independent tendon cord with a fixed terminal in its middle. The fixed terminal is installed on the first joint or the third joint, and forms a figure-eight loop around the cylindrical pulley of the second joint. The two ends are fixed to the tendon cord fixing points of the first joint and the third joint, respectively. Alternatively, two independent tendon cords are arranged on a symmetrical path, with one end of each tendon cord fixed to the first joint and the other end fixed to the third joint, together forming a dual-path mechanical coupling system.

[0011] Furthermore, the spring is a tension spring or a compression spring. When a tension spring is used, the spring fixed position one is located on the tension side of the tendon ligament. When a compression spring is used, the spring fixed position one is linked with the tendon ligament sliding node, and the spring compression is triggered by axial displacement to store energy.

[0012] Furthermore, the springs can be arranged in a single-sided or double-sided symmetrical manner; in the single-sided arrangement, the spring is only set on one side of the tendon cord path; in the double-sided arrangement, independent springs are mounted on both sides of the tendon cord path to form a redundant elastic reset system.

[0013] Furthermore, the second joint is equipped with a tendon sheath or slide rail structure to constrain the sliding trajectory of the tendon rope and reduce friction loss; the second spring fixing position is installed on the second joint through an adjustable base to support dynamic adjustment of the spring preload to adapt to different load requirements.

[0014] Furthermore, the tendon cord is wrapped or lubricated with a low-friction coefficient material in the figure-eight loop path to reduce transmission energy loss; the spring adopts a linear motion configuration, with its axis collinear with the sliding direction of the tendon cord to ensure maximum force transmission efficiency.

[0015] Furthermore, the rotation angle of the third joint is linearly mapped to the spring deformation, and the joint rebound speed and damping characteristics can be controlled and adjusted by optimizing the spring stiffness parameters.

[0016] This utility model has a compact structural design. Springs can be mounted on the tendon ropes on both sides separately or together to achieve rebound. This makes use of the space that would otherwise be needed for the rope path and achieves rebound at the same time, combining the effects of synchronous movement and automatic rebound. In addition, the linear rebound path has a longer service life. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the structure of the robotic joint finger based on tendon cable transmission and automatic rebound mechanism of this utility model.

[0018] In the diagram: 1—First joint, 2—Second joint, 3—Third joint, 4—Third joint tendon ligament fixation point, 5—Tendon ligament, 6—Spring fixation point one, 7—Spring, 8—Spring fixation point two, 9—First joint tendon ligament fixation point. Detailed Implementation

[0019] To describe the present invention in more detail, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] This utility model relates to a robotic joint finger structure based on tendon chord transmission and an automatic rebound mechanism, as follows: Figure 1 As shown, it includes a first joint 1, a second joint 2, and a third joint 3 arranged sequentially from the base of the finger to the tip. A tendon cord 5 is used to connect the three joints by winding the cord in opposite directions. One end of the tendon cord 5 is fixed to the first joint 1, and the other end is fixed to the third joint 3. It is symmetrically wound around two cylinders of equal radius to form a figure-eight loop, which allows for synchronous rotation of the second joint 2 and the third joint 3. A spring fixing position 6 is added to the tendon cord 5, connected to one end of a spring 7. Another spring fixing position 8 is installed on the second joint 2. When an external force drives the joint to rotate, it causes the tendon cord 5 to slide within the second joint 2. The spring fixing position added to the tendon cord 5 moves along with the tendon cord 5 during joint rotation, simultaneously stretching or compressing the spring 7. When the external force is released, the spring 7 returns the tendon cord 5 to its initial position.

[0021] like Figure 1As shown, the tendon cord 5 is arranged in a figure-eight loop. The tendon cord fixing points need to be fixed to the corresponding joints. The tendon cord 5 can be a single independent tendon cord to achieve the left-right wrapping effect, such as fixing the middle to the first joint 1 or the third joint 3, and fixing both ends to the third or first joint 1; or two tendon cords arranged left and right can be used for wrapping, with one end fixed to the first joint 1 and the other end fixed to the third joint 3; the spring 7 can be a compression spring or a tension spring, both of which can achieve the same effect. One end of the spring 7 is fixed to the tendon cord 5, and the other end is fixed to the second joint 2; when the first joint 1 is driven to rotate, it will drive the second joint 2 to rotate, and at the same time drive the spring fixing position 6 fixed to the tendon cord 5 to slide. The sliding spring fixing position 6 will drive the corresponding spring 7 to compress or stretch, thereby storing energy in the spring 7. When the driving force is released, the stored spring energy will be automatically released, causing the third joint 3 and the second joint 2 to rebound simultaneously. The spring 7 can be arranged alone on one side, on both sides separately, or on both sides simultaneously, all of which can achieve the same effect.

[0022] In this embodiment, the joints are connected in series through a shell or skeleton structure to form the main frame of the finger. The tendon cord transmission system adopts a figure-eight loop layout with reverse symmetrical winding. Its core consists of a single continuous tendon cord or two independent tendon cords: When a single tendon cord is used, the middle of the tendon cord 5 winds around two cylindrical pulleys of equal radius set in the second joint 2 to form a spatially symmetrical loop, and its two ends are respectively anchored to the tendon cord fixing point 9 of the first joint and the tendon cord fixing point 4 of the third joint; if a double tendon cord scheme is adopted, the two tendon cords are arranged on both sides of the transmission path, with one end of each fixed to the first joint 1 and the other end correspondingly fixed to the third joint 3, together forming a redundant transmission channel. The tendon cord fixing point adopts a wedge-shaped clamping or winding locking structure, and achieves reliable anchoring through mechanical interlocking or friction self-locking to prevent transmission loosening.

[0023] The second joint 2 integrates a tendon sheath or low-friction slide rail. The tendon sheath is coated with polytetrafluoroethylene or a solid lubricant to constrain the sliding trajectory of the tendon chord and reduce frictional loss. The tendon chord 5, wound within the second joint 2, is mounted in the joint cavity via two cylindrical pulleys of equal radius through bearings or bushings. The pulley surfaces are machined with annular guide grooves to prevent the tendon chord 5 from slipping out. The cross-section of the guide groove matches the shape of the tendon chord 5 to ensure transmission stability. A spring fixing position 6 is dynamically set in the tendon chord transmission path. This position forms a rigid connection point with the tendon chord 5 via a slider, knot, or special clamp, allowing linear displacement as the tendon chord 5 slides. A second spring fixing position 8 is preset on the second joint housing. This position can be equipped with an adjustable base, allowing for fine-tuning of the installation position via a threaded adjustment mechanism or elastic shims, thereby changing the spring preload to adapt to different load requirements.

[0024] The elastic reset system in this embodiment consists of at least one linear motion spring. The spring type can be either a tension spring or a compression spring. When a tension spring is used, the spring fixing position 6 is located on the tension side of the tendon ligament 5, and the spring axis is collinear with the sliding direction of the tendon ligament. When a compression spring is used, the sliding displacement of the tendon ligament needs to be converted into the spring compression stroke through a lever mechanism or auxiliary slider. In this case, the spring fixing position 6 is connected to the tendon ligament 5 through an intermediate transmission component. The other end of the spring 7 is directly fixed to the spring fixing position 8 of the second joint 2, forming a single-sided elastic reset unit. In the case of double-sided implementation, each tendon ligament path on both sides is equipped with an independent spring. The spring parameters can be the same or different, forming a redundant reset system. The spring material is selected from high fatigue strength alloys or composite materials, and the elastic performance is optimized through heat treatment or pre-compression processes.

[0025] The working cycle of this embodiment includes a transmission stage and a reset stage: When an external force drives the third joint 3 to rotate, the tendon rope 5 generates differential displacement in the transmission path—the tendon rope on the tension side tightens, and the tension is transmitted to the second joint pulley through a figure-eight loop, driving the second joint 2 to rotate synchronously; at the same time, the tendon rope 5 slides, causing the spring fixed position 6 to generate axial displacement, forcing the spring 7 to undergo tensile or compressive deformation, converting mechanical energy into stored elastic potential energy. During this process, the rotational resistance of the second joint pulley and the spring deformation force form a dynamic balance, ensuring smooth transmission; when the external force is released, the spring 7 releases the stored elastic potential energy through a straight path, pulling the spring fixed position 6 to move in the opposite direction along the original displacement trajectory, driving the tendon rope 5 to retract to the initial tension state; during the tendon rope retraction process, the mechanical interlocking effect of the pulley drives the second joint 2 and the third joint 3 to rebound synchronously, achieving passive automatic reset.

[0026] This embodiment deeply integrates the mechanical structure, embedding the elastic reset function within the tendon cable transmission path: spring 7 directly utilizes the tendon cable sliding space for energy storage and release, eliminating the need for additional elastic element mounting positions and significantly improving space utilization; the linear motion characteristics ensure that spring 7 is always in a unidirectional stress state, avoiding the torque attenuation problem of rotary springs, and in conjunction with the tendon sheath constraint mechanism, effectively preventing lateral instability of the spring and extending its service life. In the transmission system, the figure-eight loop layout of tendon cable 5 and the pulley guide groove design ensure complementary changes in the length of the two paths, eliminating single-path transmission errors, and ensuring that the angular displacement of the second joint 2 and the third joint 3 strictly follows the transmission ratio determined by the pulley radius ratio, achieving precise synchronous control; by adjusting the spring preload or replacing springs with different stiffnesses, the joint rebound speed and damping characteristics can be flexibly adjusted to meet diverse operational needs.

[0027] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. Those skilled in the art can readily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made to the present invention by those skilled in the art based on the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A robot joint finger based on tendon drive and automatic rebound mechanism, comprising a first joint, a second joint and a third joint arranged in sequence from the finger root to the finger tip, characterized in that: The first, second, and third joints are connected by a tendon cord. The tendon cord is arranged in a figure-eight loop and symmetrically wound around two cylinders of equal radius. One end of the tendon cord is fixed at the tendon cord fixing point of the first joint, and the other end is fixed at the tendon cord fixing point of the third joint, forming a mechanical coupling transmission path across the joints, enabling the second and third joints to rotate synchronously. The tendon cord has a spring fixing position one, and the second joint has a spring fixing position two. The two ends of the spring are connected to the spring fixing position one and the spring fixing position two, respectively. When an external force drives the tendon cord to rotate the joint, the tendon cord slides within the second joint and drives the spring fixing position one to move, causing the spring to undergo tensile or compressive deformation to store elastic potential energy. When the external force is released, the spring releases its elastic potential energy, driving the tendon cord to retract, causing the second and third joints to automatically spring back to their initial positions.

2. The robot joint finger based on tendon drive and automatic rebound mechanism according to claim 1, characterized in that: The tendon cord is a single independent tendon cord with a fixed terminal in the middle. The fixed terminal is installed on the first joint or the third joint and forms a figure-eight loop around the cylindrical pulley of the second joint. The two ends are fixed to the tendon cord fixing points of the first joint and the third joint, respectively. Alternatively, two independent tendon cords are arranged on a symmetrical path, with one end of each tendon cord fixed to the first joint and the other end fixed to the third joint, together forming a dual-path mechanical coupling system.

3. The robot joint finger based on tendon drive and automatic rebound mechanism according to claim 1, characterized in that: The spring is either a tension spring or a compression spring. When a tension spring is used, the spring's fixed position is located on the tension side of the tendon ligament. When a compression spring is used, the spring's fixed position is linked to the tendon ligament's sliding node, and the spring is compressed and stored through axial displacement.

4. The tendon-driven and automatically resilient mechanism-based robotic joint finger according to claim 1, wherein: The springs can be arranged on one side or symmetrically on both sides. When arranged on one side, the spring is only placed on one side of the tendon cord path. When arranged on both sides, independent springs are mounted on both tendon cord paths to form a redundant elastic reset system.

5. The tendon-driven and automatically resilient mechanism-based robotic joint finger according to claim 1, wherein: The second joint has a tendon sheath or slide rail structure inside to constrain the sliding trajectory of the tendon rope and reduce friction loss; the second spring fixing position is installed on the second joint through an adjustable base to support dynamic adjustment of the spring preload to adapt to different load requirements.

6. The tendon-driven and auto-rebound mechanism based robotic joint finger of claim 1, wherein: The tendon cord is wrapped or lubricated with a low-friction coefficient material in the figure-eight loop path to reduce transmission energy loss; the spring adopts a linear motion configuration, and its axis is collinear with the sliding direction of the tendon cord to ensure maximum force transmission efficiency.

7. The tendon-driven and auto-rebound mechanism based robotic joint finger according to claim 1, wherein: The rotation angle of the third joint is linearly correlated with the spring deformation. The joint rebound speed and damping characteristics can be controlled and adjusted by optimizing the spring stiffness parameters.

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