Design and Test of Adaptronic Joints With Quasi-Statical Clearance Adjustment in a Parallel Robot

Robots based on parallel kinematic structures feature low moved masses, allowing for better dynamic performance compared to serial mechanisms, eventually resulting in shorter cycle-times in handling and assembly. A side effect of this high dynamics is a higher level of vibration which has to be addressed in order to reach the full potential for short cycle-times. Some active measures for vibration-suppression were already presented previously. Another problem of parallel robots is a small ratio between working-space to installation-space. In order to overcome the problem (e.g. by changing configurations) specific components (e.g. joints) are needed. In this paper the use of an adaptronic joint with quasi-statical clearance adjustment integrated in the five-bar parallel structure is presented, addressing both vibration-suppression and configuration changes. Dimensioning of the adaptronic joint covers two aspects. Firstly increasing of friction up to blocking the joint in order to change configuration of the five-bar-structure. Secondly friction variation is used to optimize vibration damping and thus indirectly shorten cycle-times. The design and the test-setup for use of adaptronic joints in a parallel robot is presented.