Abstract: A novel two degrees-of-freedom (DOF) rolling mechanism constructed by three spatial-crossed parallelograms is proposed. The mechanism whose appearance presents three pairwise orthogonal parallelograms consists of 10 links, 12 universal joints and 4 revolute joints. It can realize rolling by taking advantage of the mechanism of the parallelogram’s instability caused by its deformation. By the arrangement of the joints and the structure design, the mechanism can achieve locomotion functions of going straight and flexible turning. The DOF of the mechanism is obtained by using the screw theory and applying the analytical sequence from local to whole. According to the simplified configuration which is established by geometric relations, kinematic analysis is carried out, such that the center of gravity of the links can be derived. The stability is analyzed, and the tumbling condition is discussed. The dynamic model of the mechanism is established and simulated by software, and the gait planning is completed. A prototype is manufactured, and the experiment research is done. The result shows that, by a simple control means, the proposed rolling mechanism can achieve the functions of going straight and flexible turning, and good stiffness and carrying capacity are revealed.

Key words: mobile robot, parallelogram mechanism, rolling mechanism, screw theory