Kinematic, dynamics, and control of a particular micro-motion system

Abstract

In many applications such as chip assembly in the semiconductor industry, cell manipulation in biotechnology, and surgery automation in medicine, there is a need for devices which can perform very small motions (less than 100 μm) with very high positioning accuracy (in the submicron range) and complex trajectories. This range of motion is known as micro-motion. In this thesis, the research is described concerning the design of micro-motion systems. A particular interest of this research lies in a particular system that produces planar micro-motions and has been found useful in semi-conductor industries.

The general methodology of designing such systems is based on an observation made by the author. It is not difficult to find that most of the micro-motion systems commercially available were developed based on the ball-screw and DC-servo or stepper motor component systems. These systems have their inherent problems, such as backlash, friction, and assembly errors, which usually call for high precision manufacturing technologies and, thus, cause high cost. The compliant mechanism concept, which suggests generating motions based on deformations in a member of compliant material, was proposed around the 1990s. The compliant mechanism concept has been used in mechanism design for years; however, it has not been used for systems with a feedback control need. Therefore, using the compliant mechanism concept for building micro-motion systems appears to be a promising methodology and worth studying.

The goal of the research described in this thesis is to develop an understanding of and a design tool for a particular planar micro-motion system (called the RRR compliant mechanism) which is constructed based on the compliant mechanism concept. This system consists of three PZT actuators and a specially shaped member of compliant material. The structure of this system is symmetrical to the center of the system which serves as the end-effector of the system to perform two translations and one rotation in a plane. As a result, the following contributions of this research are described in this thesis.

A Constant-Jacobian method for kinematic analysis of the RRR compliant mechanism is developed and verified using the pseudo rigid body model (PRBM) concept. The result of the kinematic calibration based on this method shows an excellent agreement with the experimental result. The PRBM concept leads to a lumped model of materially continuous systems and, hence, to a computationally efficient model.

The finite element analysis of the RRR compliant mechanism, using the ANSYS program, is performed. In this analysis, mesh is directly generated on a compliant material, which differs from the lumped approximation procedure associated with PRBM. This finite element model is a parametric one and is completely determined by nine parameters. A change in any one of these parameters will update the mesh automatically. This is very useful for an optimal selection of parameters to achieve some set of design objectives. The result of the finite element analysis is compared with those obtained using other methods, including the Constant-Jacobian method and the experiment, which further confirms that the Constant-Jacobian method is an excellent method for kinematic analysis in terms of computational efficiency and modeling accuracy.

A novel dynamic model is further developed based on the Constant-Jacobian kinematics, the PRBM concept, and other simplification procedures that leave out the terms of order o(Δl²) and above (Δl=0-12 μm). Consequently, this dynamic model achieves both computational efficiency and modeling accuracy. This dynamic model is used for feedback control simulation studies for the RRR compliant mechanism.

***Note: There was a floppy disk with the original thesis***