Static Stability Analysis of a Planar Object Grasped by Multifingers with Three Joints

This paper discusses static stability of a planar object grasped by multifingers with three joints. Each individual joint (prismatic joint or revolute joint) is modeled as a linear spring stiffness. The object mass and the link masses are also included. We consider not only pure rolling contact but also frictionless sliding contact. The grasp stability is investigated using the potential energy method. This paper makes the following contributions: (i) Grasp wrench vectors and grasp stiffness matrices are analytically derived not only for the rolling contact but also for the sliding contact; (ii) It is shown in detail that the vectors and the matrices are given by functions of grasp parameters such as the contact conditions (rolling contact and sliding contact), the contact position, the contact force, the local curvature, the link shape, the object mass, the link masses, and so on; (iii) By using positive definiteness of the difference matrix of the grasp stiffness matrices, it is analytically proved that the rolling contact grasp is more stable than the sliding contact grasp. The displacement direction affected by the contact condition deviation is derived; (iv) By using positive definiteness of the differential matrix with respect to the local curvatures, it is analytically proved that the grasp stability increases when the local curvatures decrease. The displacement direction affected by the local curvature deviation is also derived; (v) Effects of the object mass and the joint positions are discussed using numerical examples. The numerical results are reinforced by analytical explanations. The effect of the link masses is also investigated

An intelligent robot control system for physiotherapic applications

An intelligent robot control system for physiotherapic applications has been developed. The intelligent robot control system consists of a specially designed robotic hand with built-in sensors, an interfacing module between the robot system and the computer, an intelligent path planning module and a fuzzy logic based intelligent control module. The robotic hand with the integrated palm and two fingers has been used to perform the padding and kneading opeartions. The sensory information of the robotic hand have been used in the intelligent control process. The intelligent path planning and control modules have been constructed with the knowledge bases (KBS) and the fuzzy logic based inference mechanism, which are able to deal with uncertainties by manipulating the fuzzy terms. Thus, with the fuzzy/linguistic input terms, the required parameters can be generated for the path planning module. The massaging path can be planned by using the KBS in the intelligent path planning module. While the task execution is monitored by the intelligent control module. The intelligent control module allows error-correction strategies to be formulated. The required corrections can be carried out by using the on-line KBS and fuzzy inference mechanism in the intelligent control module. Experimental results are presented, which show the feasibility and the effectiveness of the designed intelligent control system