Jin Dewen

Control strategies and topological invariance of human prehension

Control strategies and topological invariance of human prehension are discussed through the analysis and comparison of upper-limb reaching-grasping tasks. Five subjects were asked to perform different reaching-grasping tasks with different indices of difficulty, and the movements were captured using a Vicon 3D motion analysis system. Topological invariance was observed in the trajectories of different task performances. After normalization, the trajectories of the hand had very close patterns for different reaching-grasping tasks. Synergy control in the reaching-grasping movements of the upper limbs was also found among the different joint angles. Despite joint redundancy, the joint angles can be fitted using the same format of functions proposed in this study. The parameters in the function can be taken as a characteristic feature of reaching-grasping movement patterns.

Effects of Part Flexibility on Dynamic Behaviors of Machine Systems with Clearances in the Joints

Part flexibility and joint clearance are two of important factors that affect motion precision of machines. The fixed-boundary component modal synthesis (CMS) method and nonlinear impact model was used to study dynamic behaviors of mechanism with flexible parts and clearances at the joints. A test model of slider-crank mechanism was created and numerical simulation was made under several cases. After a coordinate transformation is applied for the fixed-boundary CMS method, the CMS method can be employed easily, improve the precision of computing and efficiency of CMS method and also present the effects of boundary constraints and impact. The coupling effects of flexible parts and clearances at the joints make the mechanism show particular dynamic behaviors that are different from the mechanism without clearances at joints or flexible parts.

THE EFFECTS OF JOINT CLEARANCE ON THE MOTION PRECISION OF THE MACHINES

Joint clearance is one of important factors which affect motion precision of machines. In this paper the mathematical model of a new-type joint, tripod-ball sliding joint, is established, and the new concepts of basal system and active system are put forward. Based on the mode-change criterion established here, the consistent equations of motion in full-scale are derived by using Kane method. The dynamic behavior of the crank-slider mechanism with clearance in the tripod-ball sliding joint is investigated. The results including motion error and impact acceleration are obtained and the advantage of this new joint is shown.