|Ph.D Student||Bamberger Hagay|
|Subject||Kinematics of Micro Parallel Robots|
|Department||Department of Mechanical Engineering||Supervisor||Professor Moshe Shoham|
|Full Thesis text|
Micro-Electro-Mechanical-Systems (MEMS) is a relatively new technology, enabling fabrication of mechanical devices on silicon wafers. A micro parallel mechanism fabricated by MEMS technology can be part of the electro-mechanical system, for such applications as switching, focusing, steering, vibration stabilizing, or aberration compensation. The present investigation takes into consideration the micro manufacturing limitations, and suggests special robot architectures, and special kinematic treatment to realize robots on the sub-millimeter scale. This approach is denoted as MEMS kinematics, since it comprises both MEMS constraints and fundamental kinematic rules in mechanism design.
Kinematic architectures of parallel mechanisms, which are suitable for MEMS fabrication, are introduced. The mechanisms consist of only revolute passive joints, and linear actuators located at the base for the active ones. A new micro robot architecture that contains three single loop sub-mechanisms, and actuates the moving platform in six degrees-of-freedom (DOF) is developed. In addition, translational parallel mechanisms, which actuate the moving platform in three linear DOF, are investigated taking into account the constraint singularities of limited DOF mechanisms. A systematic design for kinematic architectures of pure translational mechanisms is also developed.
The second part of the research deals with the effect of large joint clearances on the resulting moving platform motion. Manufacturing techniques of micro-mechanisms may cause large clearance at the joints - only one order smaller than the links length themselves. Due to these relatively large clearances, the direct kinematics solutions are no longer considered discrete, but rather constitute significant volume defined as clearance space. When two separate regions of these clearance spaces merge, uncontrolled assembly mode (AM) changes may occur. The formation of the clearance space is described, its volume is depicted, and merging of clearance space volumes in 3PRR planar mechanism is exemplified.
Assembly mode changing is an important issue not only in micro-mechanisms. Parallel mechanisms usually have several direct kinematics solutions that are attributed to different AM. Besides the known encircling of cusp points, a new way for AM changing is first described in the present investigation. The changing may occur by moving on a path like a ramp, while encircling an a-curve in the singularity map drawn in the joint-space.
Due to the large clearances, the moving platform may deviate considerably as a result of external forces. Tools for analyzing the static behavior of the mechanism, using Hough and Force dual transforms, were developed, enabling graphical representation of the external forces that the moving platform withstands with no motion even in the presence of large joint clearances.