Design and Fabrication of Electrothermal Micromotors and Compliant Mechanisms for Spatial Parallel Micromanipulators (Mechanical Project)

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In this project a new class of spatial micromechanisms employing compliant joints and electrothermal motors has been developed. The spatial micromechanisms contain three limbs driven by individual electrothermal linear motors to form multiple degree-of-freedom (DOF) manipulators.

At the coaxial point of the actuated limbs, a platform acts as the end effector of the device. Each limb in this spatial mechanism interconnects compliant pseudo-revolute joints, which are capable of providing either in-plane or out-of-plane rotations. Mechanisms are demonstrated using polysilicon surface micromachining, and a new four-layer UV-LIGA fabrication process is also presented for future production of high aspect ratio spatial micromechanisms. Linear motors are developed to provide bi-directional continuous motions to drive the spatial mechanism.

Individual electrothermal actuators within a linear motor employ saw-toothed impactors to provide a synchronized locking/pushing motion without needing a secondary clamping actuator. These saw-toothed linear motors provide a platform for accurate open-loop position control, continuously smooth motion, high motion resolution, and long life operation. Electrothermal V-beam actuators using multiple arrayed beams have been shown to provide large output forces up to several mN, sufficient for the spatial micromechanisms developed in this work. Taking advantage of a modeling approach based on the pseudo-rigid-body model, a new force and displacement model for the electrothermal V-beam actuators is developed and shown to provide good agreement with experimental results.

The optimization design for the thermal actuators is also discussed to reduce actuation power. Pseudo-rigid-body modeling is used to simplify the designed compliant spatial mechanisms, allowing the well-known rigid body method to replace the cumbersome matrix method for compliant mechanism analysis. Based on the pseudo-rigid-body model, inverse kinematics is used to find the workspace of a typical microscale mechanism, together with the required movement for each linear motor to allow the end effector to reach a desired position.

Dynamic analysis of the mechanism is applied to determine the maximum required forces for each actuator. The manipulator workspace volume defined by maximum link lengths and joint rotation angles is determined by using the Monte Carlo method. A systematic design procedure is finally proposed to enable effective compliant micromanipulator designs.
Source: University of Maryland
Author: Cheng, Wei-Jen

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