Daniel C. Handley

A three‐DOF compliant micromotion stage with flexure hinges

Micromanipulation has enabled numerous technological breakthroughs in recent years, from advances in biotechnology to microcomponent assembly. Micromotion devices commonly use piezoelectric actuators (PZT) together with compliant mechanisms to provide fine motions with position resolution in the nanometre or even sub‐nanometre range. Many multiple degree of freedom (DOF) micromotion stages have parallel structures due to better stiffness and accuracy than serial structures. This paper presents the development of a three‐DOF compliant micromotion stage with flexure hinges and parallel structure for applications requiring motions in micrometres. The derivation of a simple linear kinematic model of the compliant mechanism is presented and simulation results before and after calibration are compared with results from finite element (FE) modeling and experiments. The position control system, which uses an experimentally determined constant‐Jacobian, and its performance are also presented and discussed.

Loop closure theory in deriving linear and simple kinematic model for a 3 DOF parallel micromanipulator

Various types of micro-motion devices have been developed in the past decade for applications including the manipulation of cells in micro-surgery and the assembly of micro-chips in micro-assembly industries. Most of the micro-motion devices are designed using the compliant mechanism concept, where the devices gain their motions through deflections. In addition, closed-loop parallel structures are normally adopted due to better stiffness and accuracy compared to the serial structures. However, the forward kinematics of parallel structures are complex and non-linear; to solve these equations, a numerical iteration technique has to be employed. This iteration process will increase computational time, which is highly undesirable. This paper presents a method of deriving a simple, linear and yet effective kinematic model based on the loop closure theory and the concept of the pseudo-rigid-body model. This method is illustrated with a 3 DOF (degree-of-freedom) micro-motion device. The results of this linear method are compared with a full kinematic model for the same micro-motion system. It is proved that the derived kinematic model in this paper is accurate and the methodology proposed is effective. The static model of the micro-motion device will also be presented. The uncoupling property of the micro-motion systems, based on the static model, will be briefly discussed.

A simple and efficient dynamic modeling method for compliant micropositioning mechanisms using flexure hinges

In this paper we consider the dynamic modelling of compliant micropositioning mechanisms using flexure hinges. A simple modelling method is presented that is particularly useful for modelling parallel micropositioning mechanisms. This method is based upon linearisation of the geometric constraint equations of the compliant mechanism. This results in a linear kinematic model, a constant Jacobian and linear dynamic model. To demonstrate the computational simplicity of this methodology it is applied to a four-bar linkage using flexure hinges. Comparisons are made between the simple dynamic model and a complete non-linear model derived using the Lagrangian method. The investigation reveals that this new model is accurate yet computationally efficient and simple to use. The method is then further applied to a parallel 3-degree of freedom (dof) mechanism. It is shown that the method can be simply applied to this more complex parallel mechanism. A dynamic model of this mechanism is desired for use in optimal design and for controller design.

Workspace investigation of a 3 DOF compliant micro-motion stage

This paper investigates the workspace of a three degree-of-freedom (DOF) compliant micro-motion stage with flexure hinges. This micro-motion stage has parallel structure for better stiffness and accuracy than serial structures and is driven by three PZT stack actuators. This kind of micro-motion stage can be used in applications including micro system assembly, biological cell manipulation and microsurgery. Nevertheless, workspace is fundamental. When selecting or designing micro-motion stage(s) for a particular application, its workspace must be studied to ensure the end-effector can reach the desired points with required orientations. In this paper the workspace of the presented micro-motion stage is investigated and presented, both mathematically and empirically.

An experimental observation of uncoupling of multi-DOF PZT actuators in a compliant mechanism

The control of a dynamic system with multiple degrees-of-freedom (DOF) is far simpler if the system is uncoupled. The property of an uncoupled system can be achieved with careful design of mechanical structures in the case of conventional mechanisms. The study reported in this paper will show via experiment the uncoupling property in a compliant mechanism, which is driven by three PZT actuators. This observation has the significance to motivate study on a new methodology for designing uncoupled multi DOF compliant mechanisms.

Multiple-degree-of-freedom compliant mechanism possessing nearly uncoupled dynamics: experimental findings

Micromanipulation has enabled numerous technological breakthroughs in recent years, from advances in biotechnology to micro-component assembly. Micromanipulators commonly use piezoelectric actuators (PZT) and a compliant mechanism to provide fine motions with position resolution in the nanometre or even sub-nanometre range. Parallel compliant mechanisms are used to provide motion with multiple degrees-of-freedom (DOF) as parallel mechanisms provide greater rigidity and positioning accuracy than serial mechanisms. However, parallel mechanisms with multiple DOF often have dynamic behavior that is coupled, non-linear and highly complex. This leads to difficulties in modeling and controller design, often requiring sophisticated control techniques such as model-based or neural networks to provide fast, accurate control. This paper presents the findings of an experimental study into the dynamics of a particular 3 DOF compliant mechanism, specifically considering actuator-space coupling at a range of frequencies and poses. It was expected that the dynamics would be coupled as a dynamic model developed for this mechanism suggested this to be the case. However the experimental results reveal the surprising and useful finding that this mechanism possesses almost completely uncoupled dynamics for the operating bandwidth of the manipulator. This result simplifies the problem of controller design and suggests that the micromanipulator could be effectively controlled using simple independent joint control without requiring development of a decoupling controller.