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Parallel mechanisms (PMs) having three translational (T) and one rotational (R) movement capability draw continuous attention from academia and industry. The existing 3T1R PMs can only generate Schoenflies motion and bifurcation of Schoenflies motion. This paper proposes a new 3T1R motion that features one rotation about a varying axis plus three pure translations. Drawing mainly on finite screw theory, a hierarchical approach for type synthesis of limb structures of the PMs having 3T1R motion with variable rotational axis is presented by developing the basic limb bonds first and then their equivalent substitutions using the properties of screw triangle product. The assembly conditions for the PMs of this kind are discussed. Consequently, numerous novel PMs consisting of four identical limbs are synthesized using this technique. [ABSTRACT FROM AUTHOR]

• Topology characters are parameterized and identified by analytical expression • Algebraic mapping between performance with topology and dimension is constructed • Two algorithms are provided for topology generation and performance modeling • Synchronous optimal design for topologies and dimensions is carried out Parallel robots have attracted much attention from both academia and engineering in last two decades. For development of novel parallel robots, topology and dimensions are brought into sharper focus, which are associated closely and have coupled influence on both motion pattern and performance together. However, currently topology design and dimension design are always performed individually with independent aims, leading to local optimal solutions and difficulties in further modification. Actually, the intrinsic relationship between topology and performance is concerned far from abundant. In this article, a method for topology and dimension synchronous optimization is investigated by employing finite screw theory. Within this approach, two algorithms are formulated to parameterize and deliver topology characters in the same format with dimensions. Topology design and dimension design are converted into a synchronous optimization model with mixed variables and multi-objectives, resulting in global optimal solutions of both optimal topology and dimensions. Topology and dimension synchronous optimization of a kind of 1T2R parallel robots is presented and discussed by comparing with state-of-the-art methods. [ABSTRACT FROM AUTHOR]

• A novel modular self-crossing mechanism is proposed. • Kinematic analysis of the self-crossing mechanism is conducted based on FIS theory. • Degree of freedom and gait of self-crossing locomotion is obtained. • Simulation is carried out to prove feasibility of self-crossing mechanism. In this paper, a novel mobile mechanism based on Bennett mechanism is proposed, which can realize self-crossing locomotion. Unlike the most of the self-crossing mechanisms, the proposed mechanism can be assembled modularly, which has better environment adaptability. Firstly, on the basis of revealing mechanism of the self-crossing movement, configuration of the self-crossing mechanism is designed. The mechanism consists of n Bennett mechanisms connected in series by 2(n -1) 3 R limbs that are symmetrically distributed on both sides of n Bennett mechanisms. Then, kinematic analysis of the mechanism is carried out based on finite and instantaneous screw theory, including mobility analysis and gait analysis. For the former, the number of degrees of freedom that the mechanism can achieve self-crossing locomotion is obtained, and for the latter, the trajectory of end point of the mechanism in the self-crossing movement is obtained. Finally, On the basis of theoretical analysis, simulation is conducted, and the results show that the proposed novel mechanism can realize self-crossing locomotion without interference, which verified the rationality of the mechanism. This paper provides a useful reference for the design and analysis of self-crossing mobile mechanism. [ABSTRACT FROM AUTHOR]