A finger figure-eight rope structure for underactuated dexterous hands

Abstract

This invention relates to a figure-eight cord structure for underactuated dexterous hands. A driving tendon cord is crisscrossed in a figure-eight pattern between the distal and mid-joint winding reels. The driving tendon cord forms two transmission arcs β1 and β2 tangent to the winding reels. Transmission arc β1 is wound around the distal joint winding reel, and transmission arc β2 is wound around the mid-joint winding reel. The two ends of the driving tendon cord are respectively fixed to binding points P1 on the distal joint and P2 on the mid-joint winding reel, forming a closed figure-eight loop. This invention uses a single tendon cord crisscrossed in a figure-eight pattern around the winding reels of adjacent joints. Through the conservation of arc length between the two relatively sliding arc segments, the precise fixation of the rotation angle ratio of the two joints is achieved mechanically. This structure also possesses self-tensioning characteristics, reducing control nonlinearity caused by changes in tendon cord length. Furthermore, it requires no additional elastic elements, has a compact structure, and provides direct transmission, making it suitable for lightweight, highly coordinated underactuated dexterous hands.

Description

Technical Field

[0001] This application belongs to the field of robotic dexterous hand technology, specifically relating to a finger figure-eight rope structure for an underactuated dexterous hand. Background Technology

[0002] Against the backdrop of the national strategy to comprehensively promote the high-quality development of intelligent manufacturing and the robotics industry, dexterous hands, as core technological components of robot end effectors, directly affect grasping adaptability, motion coordination, and structural compactness through the design level of their transmission and coupling mechanisms. Underactuated dexterous hands, due to their fewer actuators, simpler control, and higher reliability, have become the mainstream research and application direction. And chordal drive is one of the commonly used methods to achieve underactuated joint coupling.

[0003] A review of existing patents and literature on underactuated dexterous hands and rope-driven finger coupling mechanisms revealed that most designs use a single tendon rope to connect multiple joints and rely on elastic elements or rope pulleys for proportional transmission to achieve joint motion distribution. However, these designs still have the following shortcomings in terms of transmission accuracy, structural simplicity, and long-term operational stability: 1. The transmission lag and nonlinearity problems of joint coupling are prominent. Existing underactuated fingers mostly use springs or elastic bands to provide reset and tension, and the kinematic coupling between joints depends on the elastic deformation of the tendons and the deformation recovery of the elastic elements.

[0004] Patent CN101797753B discloses a parallel-connected tendon cord dexterous underactuated bionic robot finger device, which utilizes a motor, rope wheel, tendon cord, and reset spring to achieve variable initial finger configuration and adaptive grasping. However, in this type of solution, the tendon cord is prone to loosening and creep during repeated stretching, resulting in significant lag in joint transmission, and the angular relationship between the two joints is difficult to control precisely, limiting the naturalness of the grasping posture and the uniformity of force distribution.

[0005] 2. Existing rope-driven coupling mechanisms are complex in structure or have unclear coupling relationships. Patent CN211729167U discloses a tensioning structure for pneumatic muscles in a robot's dexterous finger. It achieves continuous tension by winding a tendon rope in a figure-eight shape around a pulley and combining it with a tension spring, which to some extent extends the working space of the robotic hand and reduces control difficulty. However, this solution only focuses on the tensioning of a single tendon rope and does not address the transmission ratio design and motion coupling relationship between multiple joints, making it impossible to achieve coordinated motion at a fixed angle ratio between two joints. CN101633170A discloses a coupled three-joint robot finger device, using a motor, two sets of figure-eight rope pulleys, and a parallel pulley transmission mechanism to achieve three-joint coupled bending. However, its transmission links are redundant, and the structure is large, which is not conducive to the miniaturization and integration of dexterous hands.

[0006] 3. The control nonlinearity caused by changes in chord length is difficult to overcome. In configurations where a single chord drives multiple joints in series, the wrap angle and arc length of the chord on each joint wheel dynamically change with joint rotation. This results in a highly nonlinear mapping relationship between joint driving torque and rotation angle, increasing the difficulty of precise control. Existing solutions generally lack a design approach that directly constrains the joint rotation angle ratio at the mechanical structure level, often relying on complex sensor feedback and algorithm compensation. Summary of the Invention

[0007] The purpose of this application is to overcome the shortcomings of the prior art and provide a finger figure-eight rope structure for underactuated dexterous hands. It uses a single tendon rope to cross and wrap around the winding wheel of adjacent joints in a figure-eight shape. Through the conservation of arc length of two relatively sliding segments, the mechanical aspect achieves precise fixation of the rotation ratio of the two joints. This structure also has self-tensioning characteristics, reducing control nonlinearity caused by changes in tendon rope length. It does not require additional elastic elements, has a compact structure, and direct transmission, making it suitable for lightweight, highly coordinated underactuated dexterous hands.

[0008] The technical problem solved by this application is achieved through the following technical solution: A figure-eight rope structure for underactuated dexterity hands includes a distal phalanx winding reel, a mid-phalanx winding reel, a distal phalanx, a mid-phalanx, and a driving tendon rope. The driving tendon rope is crisscrossed and wound in a figure-eight shape between the distal phalanx winding reel and the mid-phalanx winding reel. The driving tendon rope forms two transmission arcs β1 and β2 tangent to the winding reels. Transmission arc β1 is wound on the distal phalanx winding reel, and transmission arc β2 is wound on the mid-phalanx winding reel. The two ends of the driving tendon rope are respectively fixed to binding points P1 on the distal phalanx and P2 on the mid-phalanx to form a figure-eight closed loop.

[0009] Moreover, when the finger flexion and extension is driven, the middle phalanx rotates θ2 (11) around the middle phalanx winding wheel, and the transmission arc β2 releases the rope length from the middle phalanx winding wheel. At the same time, the transmission arc β1 segment winds an equal amount of rope length onto the distal phalanx winding wheel. Due to the conservation of the driving tendon rope length, the distal phalanx is forced to rotate θ1 (12) around the distal phalanx winding wheel. The lengths of the two arc segments satisfy the geometric constraint β1× R1=β2× R2, where R1 is the radius of the distal phalanx winding wheel and R2 is the radius of the middle phalanx winding wheel. The ratio of the two joint rotation angles satisfies θ2× R2=θ1× R1.

[0010] Moreover, the drive tendon rope is fixed at the binding point P1 of the distal phalanx, passes sequentially around the winding wheel of the middle phalanx, crosses the guide bearing between the middle phalanx and the distal phalanx, passes around the winding wheel of the distal phalanx, and is finally fixed at the binding point P2 of the middle phalanx, forming a seamless continuous figure-eight closed loop structure.

[0011] Moreover, the driving tendon rope is a continuous, jointless ultra-high molecular weight polyethylene tendon rope.

[0012] Moreover, in the initial state, the fingers are straight and the figure-eight rope is in a slightly open, low-tension state; when the driving tendon rope contracts, the middle phalanx bends first, followed by the distal phalanx, and the movement of the two joints is coordinated without lag, presenting a smooth and natural gripping posture.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention can achieve precise mechanical coupling of joint rotation ratio. By using the "8" shaped cross-winding and the principle of arc length conservation, the rotation ratio of adjacent finger joints (θ2×R2= θ1×R1) is directly fixed at the mechanical structure level. It does not rely on sensor feedback or complex control algorithms, which greatly improves the coordination and predictability of grasping action.

[0014] 2. This invention has self-tensioning characteristics, which reduces control nonlinearity. The figure-eight knot always maintains a dynamic balance between the two arc lengths during the movement, the overall rope length is conserved, and the tendon rope always remains in a slightly tensioned state. This effectively avoids the driving dead zone and control nonlinearity caused by tendon rope slack or creep, and reduces the difficulty of precise control.

[0015] 2. The present invention has a compact structure and does not require additional elastic elements. Compared with existing coupling schemes that rely on springs, parallel pulleys or multiple sets of rope pulleys, the present invention only requires a single tendon rope and two winding pulleys to achieve coupling transmission between adjacent joints. It has fewer transmission links, smaller size, lighter weight, and is easy to integrate into the limited finger joint space of underactuated dexterous hands.

[0016] 4. This invention improves the flexibility and adaptability of gripping. When the finger touches an object, the unobstructed joints continue to bend, while the already touched joints stop moving, thereby passively adapting to the shape of the object, achieving flexible gripping, and reducing impact and damage to the object. Attached Figure Description

[0017] Figure 1 This is a simplified diagram of the figure-eight rope structure of the present invention, showing its initial state and principle. Figure 2 This is a simplified diagram of the figure-eight rope structure and a schematic diagram of the finger joint flexion and extension principle of the present invention; Figure 3 This is a diagram showing the initial state of the figure-eight knot's position when wrapped around the rope, according to the present invention. Figure 4 This is a diagram showing the bending and stretching motion of the figure-eight knot around the rope according to the present invention. Figure 5 This is a model diagram of the figure-eight rope of the present invention.

[0018] Explanation of reference numerals in the attached figures 1-Distal finger joint winding reel, 2-Figure-eight knot, 3-Middle finger joint winding reel, 4-Drive arc β2, 5-Drive arc β1, 6-Distal finger joint, 7-Middle finger joint, 8-Drive tendon rope, 9-Binding point P2, 10-Binding point P1, 11-Turn angle θ2, 12-Turn angle θ1. Detailed Implementation

[0019] The present application will be further described in detail below through specific embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present application.

[0020] like Figure 1 , 2 As shown, an innovative finger figure-eight rope structure for underactuated dexterity hands includes: a distal phalanx winding wheel 1, a mid-phalanx winding wheel 3, a distal phalanx 6, a mid-phalanx 7, and a driving tendon rope 8; the driving tendon rope 8 is crisscrossed in a figure-eight shape between the distal phalanx winding wheel 1 and the mid-phalanx winding wheel 3; the driving tendon rope 8 forms two transmission arcs β1 and β2 tangent to the winding wheels, with transmission arc β15 wound around the distal phalanx winding wheel 1 and transmission arc β24 wound around the mid-phalanx winding wheel 3; the two ends of the driving tendon rope 8 are respectively fixed to the binding point P110 on the distal phalanx 6 and the binding point P29 on the mid-phalanx 7 to form a figure-eight closed loop.

[0021] like Figure 3 As shown, the driving tendon rope 8 is fixed at the binding point P110 of the distal phalanx 6, passes sequentially around the middle phalanx winding wheel 3 of the middle phalanx 7, crosses the guide bearing between the middle phalanx 7 and the distal phalanx 6, passes around the distal phalanx winding wheel 1 of the distal phalanx 6, and is finally fixed at the binding point P29 of the middle phalanx 7, forming a continuous figure-eight closed loop structure without joints, forming a figure-eight knot 2. The driving tendon rope 8 is a continuous, jointless ultra-high molecular weight polyethylene tendon rope, which has high strength, low friction, and fatigue resistance, and is suitable for long-term reciprocating movements.

[0022] like Figure 4 As shown, when the finger flexion and extension is driven, the middle phalanx 7 rotates θ211 around the middle phalanx winding wheel 3, and the transmission arc β24 releases the rope length from the middle phalanx winding wheel 3. At the same time, the transmission arc β1 segment 5 winds an equal amount of rope length onto the distal phalanx winding wheel 1. Due to the conservation of the length of the driving tendon rope 8, the distal phalanx 6 is forced to rotate θ112 around the distal phalanx winding wheel 1. The lengths of the two arc segments satisfy the geometric constraint β1×R1=β2×R2, where R1 is the radius of the distal phalanx winding wheel and R2 is the radius of the middle phalanx winding wheel. The ratio of the two joint rotation angles satisfies θ2×R2=θ1×R1.

[0023] In the initial state, the fingers are straight and the figure-eight rope is slightly open and under low tension. When the driving tendon rope 8 contracts, the middle phalanx 7 bends first, followed by the distal phalanx 6. The two joints move in a coordinated manner without lag, presenting a smooth and natural gripping posture.

[0024] This invention reduces control nonlinearity caused by changes in chord length through reverse coupling and continuous tension in the mechanical structure, thereby reducing the difficulty of precise control. The torque from a single drive source is distributed to multiple joints in a fixed proportion, achieving mechanical coupling between the joints. When a finger contacts an object, the unobstructed joints continue to bend, while the contacting joints stop moving, thus passively adapting to the object's shape and improving grip flexibility.

[0025] Although embodiments and drawings of the present invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A finger figure-eight rope structure for an underactuated dexterous hand, characterized in that: It includes a distal phalanx winding wheel (1), a middle phalanx winding wheel (3), a distal phalanx (6), a middle phalanx (7), and a drive tendon rope (8); the drive tendon rope (8) is wrapped in a figure-eight shape between the distal phalanx winding wheel (1) and the middle phalanx winding wheel (3), and the drive tendon rope (8) forms two transmission arcs β1 and β2 that are tangent to the winding wheel. The transmission arc β1 (5) is wrapped around the distal phalanx winding wheel (1), and the transmission arc β2 (4) is wrapped around the middle phalanx winding wheel (3); the two ends of the drive tendon rope (8) are respectively fixed to the binding point P1 (10) on the distal phalanx (6) and the binding point P2 (9) on the middle phalanx (7) to form a figure-eight closed loop.

2. The finger figure-eight rope structure for underactuated dexterous hands according to claim 1, characterized in that: When the finger flexion and extension is driven, the middle phalanx (7) rotates θ2 (11) around the middle phalanx winding wheel (3), and the transmission arc β2 (4) releases the rope length from the middle phalanx winding wheel (3). At the same time, the transmission arc β1 segment (5) winds an equal amount of rope length onto the distal phalanx winding wheel (1). Due to the conservation of the length of the driving tendon rope (8), the distal phalanx (6) is forced to rotate θ1 (12) around the distal phalanx winding wheel (1). The lengths of the two arc segments satisfy the geometric constraint β1 × R1 = β2 × R2, where R1 is the radius of the distal phalanx winding wheel and R2 is the radius of the middle phalanx winding wheel. The ratio of the two joint rotation angles satisfies θ2 × R2 = θ1 × R1.

3. The finger figure-eight rope structure for underactuated dexterous hands according to claim 1, characterized in that: The drive tendon rope (8) is fixed at the binding point P1 (10) of the distal phalanx (6), passes through the middle phalanx winding wheel (3) of the middle phalanx (7) in sequence, crosses the guide bearing between the middle phalanx (7) and the distal phalanx (6), passes through the distal phalanx winding wheel (1) of the distal phalanx (6), and is finally fixed at the binding point P2 (9) of the middle phalanx (7), forming a seamless continuous "8" shaped closed loop structure.

4. The finger figure-eight rope structure for underactuated dexterous hands according to claim 1, characterized in that: The driving tendon rope (8) is a continuous, jointless ultra-high molecular weight polyethylene tendon rope.

5. The finger figure-eight rope structure for underactuated dexterous hands according to claim 1, characterized in that: In the initial state, the fingers are straight and the figure-eight rope is in a slightly open, low-tension state; when the driving tendon rope (8) contracts, the middle phalanx (7) bends first and the distal phalanx (6) follows closely behind. The two joints move in a coordinated manner without lag, presenting a smooth and natural gripping posture.

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