Basic Research On Hybrid-driven Planar 3-RRR Mechanism

Today, with the rapid development of high technology, modern machine has put forward higher requirements, such as the flexible output, one machine with more versatile uses, meeting the needs of increasingly diverse functions and so on. Traditional mechanisms lack of flexibility, which can only complete the single task. All servo-driven robot mechanisms have disadvantages like high costing and poor carrying capacity, while having good flexibility. Integrating with the advantages of both, hybrid-driven mechanism becomes one hotspot of modern mechanism.Hybrid-driven mechanism synthesizes the constant speed motor and the servo motor as the power source through a multi degree of freedom mechanism. Among them, the constant speed motor provides the main imputes and the servo motor performs the regulation role. Throughout the research situation, current research is focused on the planar 2-dof mechanisms like five-bar and seven-bar mechanism, more than 3-dof mechanism is not involved.This paper first study hybrid-driven planar 3-dof mechanism, the main contents include:(1) Based on compatible link combinations, all possible basic configurations of planar 3-dof kinematic chains were derived. Based on the requirements of hybrid-driven mode, the kinematic chains were selected one by one. Planar 3-RRR mechanism was determined to be the research object finally.(2) The basic research of kinematic analysis on planar 3-RRR mechanism had completed, including the position and attitude solution, the Jacobian matrix, workspace analysis. These conclusions provide the basis for further research.(3) The linkage length constraint conditions which must be considered on designing hybrid-driven planar 3-RRR mechanism were put forward. Using the assemblability of planar single-loop linkages, the crank conditions were studied. After the analysis of singularity of 3-RRR mechanism, the geometric conditions to avoid direct singular positions were presented. After that, a simulation example demonstrated the conclusions.(4) The trajectory planning of hybrid-driven planar 3-RRR mechanism was studied. Based on the conclusions of inverse kinematic analysis, using the cubic spline function on point to point path planning, the servo motor rotation laws were presented. Comparing the different speed situation of constant motor, the influence trends on planning results were analyzed.As the three degrees of freedom is the transition between plane and space. So this paper is hoped to provide a reference value for the study of hybrid-driven space mechanisms in future.