AbstractKinematic estimations and dynamic performance assessments are fundamental theoretical issues to realize the mechanism from conceptual design to engineering application. In this article, the closed-form dynamic formulations of a 4-degrees-of-freedom (DoFs) parallel driving mechanism are derived by combining the Lagrange method and the virtual work principle. The selection principle of generalized coordinates and the steps for inverse dynamics modeling of the manipulator are proposed. Simulation results verify the correctness of the dynamic model, and a physical prototype has been built. Based on the dynamic modeling, the concise algebraic expression of the operational space inertia matrix of the parallel driving mechanism is deduced. Because the translation and rotation degrees-of-freedom are inconsistent in the operational space, the Jacobian matrix is adopted to map the inertia matrix from the operational space to the joint space. Based on the inertia matrix in joint space, the average energy transfer efficiency (AETE) index is proposed. Finally, two control techniques for the manipulator implementable in joint space are compared. The AETE index and dynamic modeling method suggested in this article can be further used in other manipulators for dynamic analysis and motion system design.

AbstractIn the field of grasping application, continuum robots are characterized by flexible grasping and high adaptability. Based on research on the physiological structure and winding method of seahorses, a continuum robot with a helical winding grasping function is presented in this paper. The continuum robot is driven by cables and uses a new flexural pivot with large deformation as a rotation joint. Firstly, based on the Serret–Frenet frame of the spatial cylindrical helix, the helical winding continuum robot is modeled and solved. The change rules of parameters such as the rotation angle of the joint and the helix parameters under the helical winding method are derived. Then, the compliance matrix of the joint is solved using the structural matrix method, and a stiffness model is established to analyze the relationship between the load and deformation of the continuum robot. The kinematics model of the continuum robot is established by using the modified Denavit–Hartenberg parameter method. The static model of the continuum robot is solved by vector analysis under the condition of considering gravity, and the relationship between the length change of cables and joint curvature is obtained. Finally, the stiffness model and static model of the continuum robot are verified by simulations and experiments. The test results show that within a certain radial range, the continuum robot has the function of helical winding and grasping for objects. Compared to the previous imitation seahorse tail robot, the helical winding structure not only provides a larger grasping area compared to in-plane form but also achieves a better bionic effect.

AbstractRigidly foldable origami tubes are widely used in origami-inspired engineering designs. Here, using a mechanism construction process, we show that these tubes can be combined with tapered adding parts to form new tubes with different-sized cross sections that are rigidly foldable. A tapered tube is proposed, whose geometries are provided based on the kinematics of spherical 4R linkages. Several variations of the tapered tubes are presented, and the flat-foldability of these tubes is studied, leading to the right-angled and non-right-angled tubes which can be folded along their radial direction. The approach can be applied to both single and multilayered tubes. Moreover, the thick-panel form of the right-angled tubes is developed. Our work provides designers great flexibility in the design of tubular structures that require large shape changes. The results can be readily utilized to build new structures for engineering applications ranging from deployable structures, meta-materials to origami robots.

AbstractIn type synthesis of mechanisms, isomorphic identification of kinematic chains is a key issue, which has been studied for many years. In this paper, a new topological invariant, a character array of edge is constructed based on a novel model called an equivalent mechanical model. This invariant is used as a necessary condition for recognizing the edges of two topological graphs. On this basis, a method of constructing mapping by closed loop is proposed. The constructed mapping is used as the adequacy of identification so as to accurately identify the isomorphism of two graphs. This method is sufficient and necessary, which has been successfully tested in the 10-vertex, 12-vertex, 15-vertex, 28-vertex topological graphs. This method is limited to planar mechanisms that consist of revolute joints.

AbstractFor practical applications of interactive manipulation, active contact control is one of the fundamental functions that flexible-link parallel mechanisms (FLPMs) should be equipped with. In this paper, a force control approach is proposed for FLPMs to make active adjustment toward their payload, which cannot be directly achieved by their intrinsic passive compliance. To begin with, at a starting configuration the Jacobian matrix is accurately calculated with the finite difference method, while at non-starting configurations it is deduced with an increment-based approach. The compliance model is derived through mapping from the joint stiffness within each elastic rod. On this basis, the differential relation among pose, payload, and actuation variables is constructed to form the control logic, whose correctness and feasibility are then verified with simulations. Finally, interaction experiments under fixed environment and cooperative motion are carried out, and the results demonstrate that force control for a quasi-translational FLPM can be accomplished with enough pose accuracy.