The application requirements of the tendon-sheath mechanism in the field of precision machinery are becoming increasingly extensive. However, the contact friction between the tendon and sheath seriously affects the transmission accuracy. In the case of unavoidable friction, optimizing the tendon transmission path to reduce tension loss and elastic deformation has become an important research direction. In this article, the influence law of the tendon transmission path on the tension and displacement transmission is obtained using the two parameters related to the curvature of the transmission path: total bending angle and equivalent tendon length. Then, based on the optimal control theory and minimum principle, the different transmission path solutions of the minimum tension loss, the minimum tendon deformation, and the coupling of tension and displacement are obtained; the numerical optimization method verifies the correctness of the proposed theory. Finally, an optimal design of a tendon-constrained synchronous rotation mechanism for the manipulator is carried out, and the linkage performance is greatly improved by optimizing the transmission path.

Cooperative planning is one of the critical problems in the field of multi-agent system gaming. This work focuses on cooperative planning when each agent has only a local observation range and local communication. We propose a novel cooperative planning architecture that combines a graph neural network with a task-oriented knowledge fusion sampling method. Two main contributions of this paper are based on the comparisons with previous work: (1) we realize feasible and dynamic adjacent information fusion using GraphSAGE (i.e., Graph SAmple and aggreGatE), which is the first time this method has been used to deal with the cooperative planning problem, and (2) a task-oriented sampling method is proposed to aggregate the available knowledge from a particular orientation, to obtain an effective and stable training process in our model. Experimental results demonstrate the good performance of our proposed method.

To date, soft robots have been increasingly designed and analyzed, especially, Soft Continuum Manipulators (SCMs). Due to dexterous deformability, their Inverse Kinematics (IK) is still difficult to solve. Cyclic Coordinate Descent (CCD) algorithm is one of the classical optimization algorithms to solve IK of rigid manipulators with prismatic or rotational joints. However, it cannot be directly extrapolated to SCMs with configuration space parameters such as center arc, bending angle, and torsion angle. Here, we modified the CCD algorithm from a new view and proposed several tricks to set constraints. Numerical and experimental results show that the soft-CCD algorithm can quickly and accurately generate solutions for IK of SCMs. This study provides the necessary kinematic foundation for fault tolerance, obstacle avoidance, trajectory planning, and other further explorations of SCMs.

Accurate tracking control of nonminimum phase systems relies on the calculation of the ideal internal dynamics (IID). Traditional IID calculation methods fail when applied to nonminimum phase nonhyperbolic systems (systems with nonhyperbolic zero dynamics). Recently, we propose the optimal bounded inversion method for IID calculation, which obtains IID by solving a trajectory optimization problem. In this paper, we extend our previous result and show that optimal bounded inversion can also deal with nonminimum phase nonhyperbolic systems. More than that, it is also possible to achieve different control goals by setting different cost functions. Particularly, three cases are investigated in this paper. The first uses minimal initial value deviation as the cost function, resulting in "T-IID" which can achieve accurate output tracking. The second applies minimal terminal value as the cost function, resulting in "S-IID" which leads to a final rest for the system. The last combines "T-IID" and "S-IID" to achieve a compound goal. The effectiveness is verified through Matlab simulations of a two-cart inverted-pendulum system.

Continuum robots composed of elastic backbones have a broad application prospect in the narrow and restricted environment because they overcome the disadvantages of traditional articulated robots, such as being bulky and inflexible. Statics plays an important role in the planning and control of the continuum robot composed of the elastic backbone. Pseudo-Rigid Body (PRB) theory has shown great potential in the description of flexible body statics. The PRB 3R model accurately describes the large deformation of the flexible body and has high computational efficiency. However, PRB 3R models mostly focus on the planar static modeling, and there are few applications in three-dimensional (3D) statics. In this paper, a 3D static modeling method of cable-driven continuum robot based on PRB 3R theory is proposed. By introducing the equilibrium constraint equations of resultant force/moment and bending plane normal of the elastic backbone, the state of the continuum robot is determined. The 3D static equations established by the proposed method take into account the comprehensive effects of the elastic force, external force, gravity and friction. A static verification experiment system of the cable-driven continuum robot is designed to verify the proposed method. The accuracy of the proposed method is verified by comparison with experimental data. The maximum position error between simulation and experimental results is 7.6%.

In a multiarm space robotic system, one or more manipulators can be used to stabilize the base through counteracting the disturbance caused by other manipulators performing on-orbital tasks. However, singularities are inevitably present in the traditional methods based on differential kinematics solutions. In this paper, we propose a singularity-free trajectory planning method to simultaneously keep the attitude and centroid position of the base stabilized in inertial space; the balance arms are also designed. First, we derive the coupling motion equations of a free-floating multiarm space robotic system. Then, the singularity problems are theoretically analyzed, and the theoretical basis for singularity-free trajectory planning is established. Second, we decompose the six degrees of freedom pose (attitude and position) stabilization problem into two 3DOF subproblems related to attitude and position balancing. We then design two robotic arms: 1) a position balance arm and 2) an attitude balance arm, to maintain the base centroid position and attitude, respectively. Third, we plan the coordinated trajectories of the two balance arms according to holonomic and nonholonomic constraints. As long as the desired motion is not beyond its balance ability, the reasonable joint variables can always be determined without encountering a singularity problem. Finally, the proposed methods are verified using simulations of typical on-orbital missions, including joint trajectory tracking and target capturing.

In this paper, we study the effect of mechanical compliance on the impact force of human-robot interactions, more specifically the maximum impact force during a collision. Here we consider two methods of introducing compliance to industrial manipulators: joint compliance and link compliance. To compare their effect on the maximum impact force, we study two designs of a 2D robot link: a rigid link with torsion spring at the joint and a uniform compliant link. The dynamic impact model is based on the Hertz contact model. The results show that the compliant joint solution could produce a larger impact force than that of the compliant link solution if the arm mass is larger than that of the end mass, given the same lateral stiffness and all other inertial parameters (e.g. mass). Simulations and experiment have been done and verified this conclusion. The research demonstrates that the compliant link solution could be a promising approach for addressing safety concerns of human robot interactions.

In this article, we build dynamic models of 2D compliant links to evaluate injury level in a human-robot interaction. Safety is a premium concern for co-robotic systems. It has been studied that using compliant links in a robot can greatly reduce the injury level. Since most safety criteria are based on tolerance of acceleration of the operator's head during the impact, an efficient and yet accurate dynamic model of compliant links is needed. In this paper, we compare three dynamic models for calculating acceleration and head injury criterion: the compliant Beam-Spring-Mass (BSM) model, the Mass-Spring-Mass (MSM) model and the Link-Spring-Mass (LSM) model. For the MSM model and LSM model, we obtain analytic expressions of acceleration. While numerical results are achieved for the compliant BSM model. To develop the compliant BSM model, we compared three different methods: the Pseudo-Rigid-Body (PRB) model, the Finite-Segment-Model (FSM), and the Assumed-Mode-Method (AMM). Finally, all these models are validated by human-robot impact simulation programs built in Matlab. The acceleration from these simulations can be used to quantitatively measure the injury level during an impact.

Autonomous target capturing is the key for space robot to perform on-orbital servicing tasks. To meet the requirement of complex and long-term task, large flexible appendages, such as solar paddles and antenna reflectors are usually mounted on the base of a space robot. Due to the structure vibration, it is very challenging to capture a free-floating target satellite. In this paper, we derived the kinematics equations and proposed the autonomous target capturing method for free-floating flexible-base space robots. The kinematics equation established the mapping from the base velocities, joint rates and elastic motion to the end-effector velocities. Based on this equation, we designed resolved motion rate control with vibration compensation for the space manipulator. Another contribution of this paper is that we modeled the dynamic coupling between the rigid movement of the end-effector and the flexible vibration of the solar paddles. Based on this model, we analyzed the coupling effect which was very important for the design of the manipulator and determining the trajectory planning and control strategy. At last, a simulation system was created and simulation studies of the proposed methods were carried out. The simulation results verify the proposed methods.