Humanoid arm kinematics with rolling contact joints and cable drive

Abstract

Arm kinematics for a robot, in particular for humanoid robots, comprising: a. an arm swivel joint (1) with one rotational degree of freedom for connection to a base or a torso, b. a serial sequence of three rolling joints (2, 3, 5) or four rolling joints (2, 3, 4, 5) each with two rotational degrees of freedom, c. wherein the rolling joints (2-5) have a movement characteristic with spherical rolling contact and d. the joints (2-5) are driven exclusively by cables (A), e. all actuators (D) are arranged outside the arm and f. the cables (A) are guided in pairs antagonistically through the rolling joints (2-5) so that, due to the geometry of the joint type and the cable guide, the total length of each cable pair remains constant during the joint movement.

Description

[0001] The invention relates to arm kinematics for robots, in particular for humanoid robots, lightweight robots, and other handling devices. The term "arm kinematics" refers to the sequence, type, and arrangement of the joints, as well as their mechanical implementation. The kinematics are modular in design and consist of a serial sequence of joints whose movement characteristics correspond to the external kinematics of a rolling contact joint, each with two rotational degrees of freedom, as well as an additional rotary joint at the base. Control is via a cable drive, with all actuators located in the base or torso of the robot.

[0002] Serially constructed robot arms with multiple individual joints are well known (e.g., DE 102013019869 B4, DE 102016222255 B3). In humanoid robotics, seven or more serial rotational degrees of freedom are often used to replicate human arm kinematics, such as in the ARMAR-6 (KIT), HRP-4 (Kawada Industries), or TALOS (PAL Robotics) systems. However, these systems have disadvantages, such as high weight due to actuators integrated into the joints, high inertia, kinematic singularities, and limited range of motion.

[0003] Remote drives using belts, gear drives (CN106272399B) or rods (JP7373212B2) allow the actuators to be relocated outside the moving links, but result in increased design effort and do not offer a solution to the problem of kinematic singularities.

[0004] Cable pulleys represent a proven method for transferring actuators from the moving arm segments to the robot base or torso of a humanoid robot. Cable-driven robot arms are characterized by low moving mass, high mobility, and mechanical compliance, making them particularly suitable for safe human-robot interactions and service robotics. Such systems are used in areas such as surgical robotics (EP2846725B1) and robotic hands (DE102016209639A1, KR100997140B1). However, cable-driven joint structures require complex mechanisms for guiding the cables through upstream joints (US5710870A, Kim 2018). In soft, flexible, worm- or trunk-like robots (so-called “continuum robots”), actuation is typically achieved via several cables arranged radially around the circumference (cf. Wang 2022).However, such soft or under-actuated systems make precise and predictable positioning of the hand or other end effector difficult, as their position depends not only on the motor positions but also on external forces. Another disadvantage of many known cable-driven solutions is the fluctuation of the cable tension during the movement of the robot arm, whereby consistent cable tension is essential for precise and reproducible control of the joints.

[0005] Various alternative designs have already been proposed for individual joints of humanoid robots, for example in the wrist area (DE102010045525B4). Some of these approaches implement kinematic rolling contact, with so-called "omni-wrist" mechanisms (EP1023653B1, EP0393024B1, EP0295244B1) in particular enabling two-dimensional rolling contact motion without an actual physical rolling process and with a large range of motion of approximately ±90°. Similar concepts are known under various names such as "quaternion joint," "high-angle active link," "i-wrist," or "LIMS2-AMBIDEX." These known solutions have so far been used exclusively for the implementation of individual joints and not as repeatedly used structural elements within a complete humanoid arm kinematics. However, such reuse of a uniform joint type offers significant advantages in terms of modularity, manufacturability, and maintenance.

[0006] Due to the limitations of existing solutions, there is still a need for robot arm kinematics that combine the advantages of a cable drive with a mechanically simple, cost-effective, low-backlash, and modular design. Especially for lightweight and humanoid robots, optimized solutions that equally combine high performance, low weight, and compactness, exhibit clearly predictable kinematics, and allow for enclosing with a continuous shell are lacking. Likewise, a design that allows for the passage of numerous additional cables to control a hand with many degrees of freedom is lacking. Bibliography [Kim 2018] Kim, Y.-J.; Kim, J.-I.; Jang, W.: Quaternion Joint: Dexterous 3-DOF Joint Representing Quaternion Motion for High-Speed ​​Safe Interaction, IEEE / RSJ Int. Conf. on Intelligent Robots and Systems (IROS), 2018, pp. 935-942. [Wang 2022] Wang, Y.; Yang, G.; Zheng, T. et al.: Tension Reduction Method for a Modular Cable-Driven Robotic Arm with Co-Shared Cables, Intelligent Service Robotics 15 (2022), pp. 27-38.

[0007] The present invention is based on the object of providing a robot arm kinematics system for executing human-like movements with at least seven degrees of freedom that overcomes the disadvantages of the prior art. In particular, an arm structure is to be created that is characterized by a mechanically simple, cost-effective, and modular design, exhibits low backlash, offers high structural robustness, enables a large, largely singularity-free range of motion, and offers good feasibility for a variety of ropes or cables. At the same time, clear and predictable kinematics are to be ensured.

[0008] The invention pursues in particular the following technical requirements: • All drive motors are housed in the base or torso; the arm itself remains completely motor-free to reduce mass, inertia, and complexity. • The kinematics should enable human-like movements in terms of hand, arm and elbow position. • A uniquely calculable inverse kinematics must be realized. • The cable pulleys must be guided in such a way that the total length of a pair of cables – consisting of two opposing cables – remains constant throughout the arm movement to ensure consistent cable tension. A preferred embodiment provides for the drive of such a pair of cables via a common cable pulley. • The kinematics should enable a continuous outer shell without twisting or wrinkling caused by torsion. • The design should allow simple and safe installation of additional cables to control a hand with multiple degrees of freedom. • The rope guidance and arrangement should enable flexible adaptation of the movement synergies to parameters favourable for human-like movement sequences, for example through targeted positioning of the rope guides.

[0009] The arm kinematics according to the invention consists of a modular sequence of joints, which together enable a humanoid range of motion. The design is such that all drives are via cables arranged in the base or torso. The reference numbers and letters are shown in the drawing references. Fig. 1 to Fig. 5 used consistently.

[0010] The kinematics begins with an arm pivot joint (1) with one rotational degree of freedom, to which four rolling joints, each with two rotational degrees of freedom, are connected. These joints—whose motion characteristics correspond to the external kinematics of a spherical rolling contact and which are also known as rolling contact joints, quaternion joints, or 2D rolling joints—are referred to collectively as rolling joints. The rolling joints preferably have a uniform or similar mechanical structure, which facilitates modular production.

[0011] The sequence of joints is as follows: • a shoulder rolling joint (2), • a first elbow rolling joint (3), • a second elbow rolling joint (4) and • a wrist rolling joint (5), the • a hand, a tool or another end effector (6) follows.

[0012] The drive is provided by cables (A) that are routed between the joints through protective tubes or sheaths (B). In front of the arm's swivel joint (1), the cables run in flexible, bendable Bowden cable sheaths (C), which do not change length when bent. These compensate for the relative movement between the cable guides on the arm and the fixed motors with cable pulleys (D).

[0013] The invention solves the problem by the following features: a. The central component of the arm kinematics consists of several 2D rolling joints. These enable a biaxial rolling movement of the distal joint part relative to the base. The schematically illustrated joint placeholder ( Fig. 2) can be achieved by different mechanical implementations (e.g. Fig. 3). A range of motion of ±90° in all directions is preferred. A. The rolling joints are each driven by pairs of opposing cables (A). These two pairs of cables (four cables in total) actuate the two degrees of freedom of the joint. Additional pairs of cables run through the joint to actuate subsequent degrees of freedom. These also run through the respective joint as pairs of opposing cables. The total length of the opposing cables remains constant, regardless of the joint position. B. Between the joints, the cables can be guided through cable sheaths (B). b. The transmission of the cable movement from the rotating joints to the fixed motor arrangement is carried out via flexible, preferably constant-length Bowden cable sheaths (C), as shown in Fig. 5 shown. c. The motors (D) drive the rope pairs synchronously via rope pulleys. d. The first joint of the kinematics is the arm pivot joint (1) with one degree of freedom for connecting to the basic structure of the robot, e.g. the torso. e. The arm swivel joint (1) is followed by a shoulder rolling joint (2) with two rotational degrees of freedom, which is controlled by cables and also traversed by further cables. f. Following this, a first elbow rolling joint (3) with two degrees of freedom is provided, which is driven and traversed in the same way via pairs of cables. g. This is followed by a second elbow rolling joint (4) with two degrees of freedom, which, like the previous joints, is cable-driven and designed to pass additional cables. h. At the distal end of the rolling joint row is the wrist rolling joint (5) with two degrees of freedom, which is also controlled by cables and allows further cable passages. i. At the distal end, a hand, a tool or another end effector (6) is provided, which is controlled via the remaining cables. j. The design allows the passage of numerous additional cables or ropes, particularly for the actuation of complex hands with many degrees of freedom. k. The design of the joints and their arrangement enable a continuous outer shell without wrinkling due to torsional distortion. Rotation of the hand around its longitudinal axis can be achieved through coordinated control of the rolling joints (2-5) and the arm pivot joint (1). I. The resulting torques from multiple cable pairs can be combined to create synergistic effects. By carefully selecting the cable routing in the joints, synergistic effects can be specifically influenced and adapted to movement-physiologically favorable parameters.

[0014] The individual roller joints are controlled via defined pairs of drive cables (A), each assigned to a degree of freedom. The cables run through protective cable sleeves (B), which reduce friction and stabilize the guide. At transition points with relative movement, Bowden cable sleeves (C) are used, preferably of a design that does not exhibit any significant change in length when bent.

[0015] Each pair of ropes is driven by a motor (D) via a shared pulley, with one rope being wound up and the opposite one being unwound simultaneously. Due to the constant overall length of the pair of ropes, the tension remains largely constant. Each combination of rope lengths clearly corresponds to a specific pose of the robot arm.

[0016] The rotation of the hand around its longitudinal axis (third axis), which is not controlled by the wrist joint (5), is realized through a coordinated combination of the rotation of the arm pivot joint (1) and the targeted control of the rolling joints (2)-(5). This allows all hand and elbow positions, as well as hand orientations in space, to be created, analogous to the human arm. However, for the same pose of human and inventive arm kinematics, the rotation of the individual arm segments around their longitudinal axis does not always correspond to the rotation of the segments in the human model.

[0017] Because the roller joints used function as constant velocity joints, all arm segments are not twisted relative to each other. This allows for the use of continuous, torsion-free covers from the hand to the shoulder roller joint, for example in the form of a spiral tube or a closed elastic sheath, which can also be used to create a waterproof enclosure.

[0018] Human arm kinematics can be approximated by a serial arrangement with seven rotational degrees of freedom (plus the degrees of freedom of the hand). To achieve a sufficiently large range of motion in the elbow area of ​​almost 180°—as required to replicate all natural arm positions—the inventive kinematics provides two consecutive elbow joints, each with a range of motion of approximately ±90°. This results in an overall kinematics with nine degrees of freedom.

[0019] For certain applications, the additional degrees of freedom of the kinematics according to the invention can be advantageous; however, they are generally not required for simulating human arm movements. Reducing the degrees of freedom is possible in various ways: For example, the movement of both elbow joints can be functionally coupled by appropriately controlling the motors, which enables a higher movement speed in the elbow area. Alternatively, both joints can also be mechanically coupled, for example, by a diagonal cable guide using cross sheaths (E) according to Fig. 4, so that two pairs of cables actuate both joints simultaneously. If a range of motion of 90° is sufficient, the second elbow joint can be omitted.

[0020] Although changes in the length of the cables passing through them must be taken into account when moving upstream joints, this also results in design advantages: In particular, synergistic effects can be utilized, for example, to generate coordinated movements of multiple joints or to specifically increase the output torque. The positioning of the cable feedthroughs can be specifically adjusted to optimize such synergies for specific movement requirements.

[0021] The cable lengths required to achieve a desired arm configuration—and thus the corresponding motor positions—can be calculated by applying established inverse kinematics methods to a kinematics system consisting of coupled cardan joints, or determined using a model. The cable lengths are derived from the geometric distances between the defined deflection points. This calculation can be performed in real time.

[0022] The arm kinematics according to the invention has the following technical advantages over the prior art: • The kinematics are free of singularities within the intended working space. This applies both to the individual rolling joints and to their combination with the basic rotary joint. • The arm's movement is clear and predictable. The inverse kinematics is clearly defined and can be solved in real time. • All drive units (motors) are located outside the arm, preferably in the robot base or torso. This significantly reduces the moving mass and improves dynamics and safety in collaborative operation. • The kinematics enable human-like arm, elbow and hand positions. • The design allows for simple and cost-effective production using standardized components. The roller joints can also be made from readily available materials (see utility model AZ 20 2025 001 421.8). Cable pulls and Bowden cable housings represent a particularly simple, lightweight, and cost-effective solution compared to other drive systems. • The structure of the arm kinematics and the type and arrangement of the joints ensure excellent access for numerous supply lines and drive cables. In particular, the integration of additional cables for controlling complex multi-finger hands is feasible. • The essentially constant total length of paired drive cables (A) during the joint movement leads to a constant cable tension even when the arm is moving and thus to a considerably simplified drive mechanism and motor control. • The mechanical design of the kinematics allows a closed outer shell without torsional folds or twists, which allows, for example, a covering with elastic or liquid-tight materials. • The continuous cables enable structural synergies, for example, through the targeted coupling of multiple joints for increased strength or coordination. These synergy effects can be adjusted by carefully positioning the cable guides.

[0023] Fig. 1a-c show an embodiment of the arm kinematics according to the invention in different positions; Fig. 1a shows a perspective view of the kinematics in neutral position; Fig. Figure 1b shows a perspective view of the arm kinematics with the hand in front of the body. Fig. 1c an enlarged view of the wrist.

[0024] Fig. 2a-d show a schematic placeholder for a rolling joint in different views and positions. Fig. 2a shows a side view in neutral position; Fig. 2b shows a perspective view in neutral position; Fig. 2c shows a joint position deflected by 30◦ in side view; Fig. Figure 2d shows a perspective view of a joint position deflected by 30°. This placeholder can be replaced by various types of rolling joints, such as those according to AZ 20 2025 001421.8 ("Double universal joint with rolling contact movement through flexible cross elements"), omni-wrist mechanisms (e.g., EP 1023 653 B1, EP 0 393 024 B1, EP 0 295.244 B1), or other joint types such as "High Angle Active Link" or "i-Wrist."

[0025] Fig. 3a-d show an embodiment of a rolling joint according to utility model application AZ 20 2025 001 421.8 (“double cardan joint with rolling contact movement by flexible cross elements”) in different views and positions for replacing the placeholder; Fig. 3a shows a side view of the joint in neutral position; Fig. 3b shows a perspective view of the joint in neutral position; Fig. 3c shows a joint position deflected by 70◦ in side view; Fig. 3d shows a perspective view of a joint position deflected by 70◦.

[0026] Fig. Figure 4 shows a variant with coupled elbow joints. The four degrees of freedom of two consecutive elbow joints are reduced to two degrees of freedom by cross-coupling them using cross sleeves (E).

[0027] Fig. 5 shows the connection of the cables rotating through the arm swivel joint (1) to fixed motors (F) by means of flexibly bendable, length-constant Bowden cable sheaths (D).

[0028] Fig. 6 shows the image of a realized prototype of the arm kinematics according to the invention.

[0029] The invention is described below with reference to Fig. 1 illustrated embodiment will be explained in more detail. Fig. The placeholder for a rolling joint shown in Figure 2 can be replaced by the Fig. 3 can be replaced by the specific embodiment of a rolling joint mechanism shown. Fig. Figure 5 shows an exemplary arrangement of the drive units with cable pulleys (motors) and their connection to the cable inputs of the arm kinematics by means of flexibly bendable Bowden cable sheaths.

[0030] The arm kinematics shown comprise an arm pivot joint (1) with one rotational degree of freedom, which is intended to connect the following arm kinematics to the torso, a shoulder roll joint (2) with two degrees of freedom, the first elbow roll joint (3) with two degrees of freedom, the second elbow roll joint (4) with two degrees of freedom, the wrist roll joint (5) with two degrees of freedom and an adjoining hand (6).

[0031] Each rolling joint is actuated by two opposing pairs of cables (four cables); additional cables for actuating subsequent degrees of freedom are routed through the joint. The rolling joints allow for large ranges of motion while maintaining a constant total length of the opposing cables. This allows each joint to be driven by a simple cable pulley without negatively affecting the cable tension.

[0032] The Fig. 1 and Fig. The exemplary embodiment shown in Figure 5 shows the following cable routing: Four cables drive the hand (6). A total of eight cables run through the wrist (5): four for direct actuation of the wrist, four for the hand. Twelve cables run through the second elbow joint (4): eight for the hand and wrist, and four for its own control. Sixteen cables run through the first elbow joint (3): the twelve mentioned above plus four for direct drive of the first elbow joint. A total of 20 cables therefore run through the shoulder joint (2) and the arm pivot joint (1).

[0033] The design shown allows for the passage of up to 36 ropes or cables. In the illustrated embodiment, up to 16 ropes can be used to control a complex hand.

[0034] In a Fig.In the variant shown in Figure 4, the number of cables required to control the two elbow joints is reduced from eight to four. Additionally, four cross-guided cables (E) enable coupled movement of the two joints while simultaneously reducing the degrees of freedom and the number of motors required. List of designations 1 arm swivel joint 2 shoulder-roll joint 3 First elbow rolling joint 4 Second elbow joint 5 Wrist rolling joint 6 hands A Cable pulleys B Cable housings C Bowden cable housings D engines E Cross covers QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 102013019869 B4

[0002] DE 102016222255 B3

[0002] CN 106272399B

[0003] JP 7373212B2

[0003] EP 2846725B1

[0004] DE 102016209639A1

[0004] KR 100997140B1

[0004] US 5710870A

[0004] DE 102010045525B4

[0005] EP 1023653B1 [0005, 0024] EP 0393024B1 [0005, 0024] EP 0295244B1 [0005, 0024] Cited non-patent literature

[0000] Kim, Y.-J.; Kim, J.-I.; Jang, W.: Quaternion Joint: Dexterous 3-DOF Joint Representing Quaternion Motion for High-Speed Safe Interaction, IEEE / RSJ Int. Conf. on Intelligent Robots and Systems (IROS), 2018, S. 935-942

[0006] Wang, Y.; Yang, G.; Zheng, T. et al.: Tension Reduction Method for a Modular Cable-Driven Robotic Arm with Co-Shared Cables, Intelligent Service Robotics 15 (2022), S. 27-38

[0006]

Claims

[1] Arm kinematics for a robot, in particular for humanoid robots, comprising: a. an arm swivel joint (1) with one rotational degree of freedom for connection to a base or a torso, b. a serial sequence of three rolling joints (2, 3, 5) or four rolling joints (2, 3, 4, 5) each with two rotational degrees of freedom, c. wherein the rolling joints (2-5) have a movement characteristic with spherical rolling contact and d. the joints (2-5) are driven exclusively by cables (A), e. all actuators (D) are arranged outside the arm and f. the cables (A) are guided in pairs antagonistically through the rolling joints (2-5) so that, due to the geometry of the joint type and the cable guide, the total length of each cable pair remains constant during the joint movement. [2] Arm kinematics according to claim 1, characterized bythat each pair of ropes is driven by a common pulley, with one rope being wound up and the opposite one being unwound. [3] Arm kinematics according to one of the preceding claims, characterized by that the cables (A) are guided through cable sheaths (B) and, at transition points with relative movement, through Bowden cable sheaths (C) which have an essentially constant effective length when bent. [4] Arm kinematics according to one of the preceding claims, characterized by that the joints (2-5) are modular and largely identical in design. [5] Arm kinematics according to one of the preceding claims, characterized by that one or more of the rolling joints (2-5) are designed to carry further pairs of cables, these cables serving to actuate distal joints or a hand (6). [6] Arm kinematics according to one of the preceding claims, characterized bythat the cable is guided in such a way that the combination of drive cables (A) creates a synergistic effect that enables a coordinated movement of several joints to increase power or facilitate movement. [7] Arm kinematics according to one of the preceding claims, characterized by that the first elbow joint (3) and the second elbow joint (4) are mechanically coupled, in particular via diagonally running cables in cross sheaths (E), so that both joints are actuated synchronously. [8] Arm kinematics according to one of the preceding claims, characterized by that the kinematics has a continuous outer shell which is free of torsional folds and can in particular be designed to be liquid-tight. [9] Arm kinematics according to one of the preceding claims, characterized bythat a plurality of ropes or cables are guided through the kinematics, wherein the ropes or cables in addition to those for controlling the joints (2-5) are provided for controlling a complex hand (6) with several degrees of freedom. [10] Arm kinematics according to one of the preceding claims, characterized by that the inverse kinematics is uniquely calculable and can be determined in real time based on known methods.

Images