Parallel mechanisms is used in the large capacity servo press to avoid the over-constraint of the traditional redundant actuation. Currently, the researches mainly focus on the performance analysis for some specific parallel press mechanisms. However, the type synthesis and evaluation of parallel press mechanisms is seldom studied, especially for the four degrees of freedom(DOF) press mechanisms. The type synthesis of 4-DOF parallel press mechanisms is carried out based on the generalized function(G_F) set theory. Five design criteria of 4-DOF parallel press mechanisms are firstly proposed. The general procedure of type synthesis of parallel press mechanisms is obtained, which includes number synthesis, symmetrical synthesis of constraint G_F sets, decomposition of motion G_F sets and design of limbs. Nine combinations of constraint G_F sets of 4-DOF parallel press mechanisms, ten combinations of G_F sets of active limbs, and eleven combinations of G_F sets of passive limbs are synthesized. Thirty-eight kinds of press mechanisms are presented and then different structures of kinematic limbs are designed. Finally, the geometrical constraint complexity(GCC), kinematic pair complexity(KPC), and type complexity(TC) are proposed to evaluate the press types and the optimal press type is achieved. The general methodologies of type synthesis and evaluation for parallel press mechanism are suggested.

This article presents the design, control, and implementation of a novel four-legged rover for planetary exploration. A novel active-passive coupled leg mechanism is proposed for the design of the planetary rover. Then, based on the design of the actuator and leg mechanism, the novel wheel-legged robotic system is developed. Furthermore, the kinematic model of the robot is established and then a kinematics-based control strategy is presented, incorporating roll-and-pitch control, contact force control, wheel speed allocation, and steering modules. Experiments are carried out on regular indoor terrain and irregular outdoor terrain. The variations of rover attitude angles and contact forces in regular terrain decrease by more than 90% and 60%, respectively. In the outdoor environment, rover attitude angles are regulated within 1 ^o and variations of contact forces are reduced by more than half. In addition, the proposed control strategy decreases the slippage on hard unstructured terrain by almost half. Finally, the robustness and failure responses of the robot are investigated, which are also verified by simulations and experiments.

We propose a novel hybrid robot with seven degrees-of-freedom (DOF) and variable topology for operation in space. Design specifications of the space robot are presented for the type synthesis of hybrid mechanisms. Based on GF set theory, three design rules are given, thus providing the design method of the 7DOF hybrid space robot mechanism. Twenty-four combinations of the hybrid robotic mechanisms are obtained. The final synthesized configuration for the design of the space robot has a 3DOF parallel module and a 4DOF serial module with four revolute (RRRR) joints. The parallel module consists of a limb with universal-prismatic (UP) joints and two limbs with universal-prismatic-spherical (UPS) joints. The topology of the hybrid robot can be changed, and it will become an RPRR four-bar mechanism when it is folded for launch. The closed-form solution for the inverse displacement model is developed, and then the forward displacement equations are also obtained. After that, the Jacobian matrix is derived from the displacement model; the Jacobian matrix will analyze the singularity and workspace. We find that there are four singularities of mechanisms. The dexterous workspace of the hybrid robot is a good match for the grapple operation in space. An experiment with the prototype shows the present hybrid robot can grapple to a satellite-rocket docking ring and therefore validates the kinematic equations.

In this paper, we investigate potential singularity issues in prescribed performance control induced by actuator faults and propose a global nonmonotonic prescribed performance scheme for strict-feedback nonlinear systems. This scheme allows for parameterized relaxation of constraint boundaries in the presence of actuator faults. Unlike existing prescribed performance control schemes that rely on redesigning nonmonotonic rate functions to modify boundary relaxation properties, the proposed method introduces a novel adjustment module into the prescribed performance function, enabling the parametric design of nonmonotonic boundaries. Moreover, the proposed method simultaneously addresses the removal of the initial feasibility condition and the imposition of asymmetric constraints by introducing a global asymmetric design with an error correction module. This module enables flexible conversion from asymmetric to symmetric boundaries at a predetermined time instant, thereby reducing transient overshoot while maintaining steady-state tracking precision. Simulation results validate the effectiveness and superiority of the proposed scheme.

This paper presents a kinematics modeling and hybrid motion planning framework for wheeled-legged rovers. It is a unified solution for wheeled-legged rovers to traverse multiple challenging terrains using hybrid locomotion. A kinematic model is first established to describe the rover’s motions. Then, a hybrid motion planning framework is proposed to determine the rover’s gait patterns and parameterize the legs’ and the body’s trajectories. Furthermore, an optimization algorithm based on B-spline is utilized to minimize the motors’ energy dissipation and generate smooth trajectories. The wheeled and legged hybridization allows the rover for faster locomotion while maintaining high stability. Besides, it also improves the rover’s ability to overcome obstacles. Prototype experiments are carried out in more complex environments to verify the rover’s flexibility and maneuverability to traverse irregular terrains. The proposed algorithm reduces the swing amplitude by 83.3% compared to purely legged locomotion.