Design of a 6-DoF Miniature Maglev Positioning Stage for Application in Haptic Micromanipulation

Abstract

This thesis presents the design of a six degree of freedom micropositioning stage. It is a part of a research project on haptic tele?operation, applied to micromanipulation, at the TU Delft. The micropositioning stage will be used as the fine range positioning stage of a slave robot, in a haptic tele?operated control scheme. The technology used to build the stage is magnetic levitation. The stage has a movement range of 200 x 200 x 200 ?m and rotations of about ±1°. The stage MIM (Minimum Incremental Motion) is designed to be 40 – 100 nm. The focus of this thesis is mainly on the modelling and design of the system and its components, the design of actuator and sensor electronics, and the mechanical design of the stage. Control aspects have been taken into account since the stage is open?loop unstable, but do not constitute a main topic. The position sensors used in the micropositioning stage are infrared reflective sensors. These affordable sensors have previously been implemented in various projects at the TU Delft. Existing optical sensor readout electronics have been investigated; an improved version has been developed with lower noise levels. The achieved sensor noise is 14 – 28 nm, peak?to?peak over a measurement range of 200 ?m. A three?channel readout circuit board has been designed and tested. It can be used in other future applications as well as the current project. The actuators are a novel Lorentz type actuator. They consist of two fixed coils and a permanent magnet attached to the moving mass. One actuator can generate two independent force components, namely a vertical force and a horizontal force. The actuator characteristics have been extensively investigated using FEM modelling. These characteristics are position dependent, and exhibit crosstalk and parasitic forces. The overall system modelling and actuator FEM modelling has shown that these effects are manageable over the motion and force ranges of the stage. The actuator can generate an 80 mN vertical force and a 10 mN horizontal force, continuously. A threechannel current amplifier circuit board has been designed and tested. It is used to drive the Lorentz actuators, but can also be used in other future applications. Simulation diagrams have been developed of the mechanical system and its controller. The mechanical system is essentially a rigid free?floating mass that has 6 degrees of freedom. The eigenmodes of this mass have been investigated using FEM based modal analysis. Its eigenfrequencies lie far above the closed?loop system bandwidth, and are therefore not considered further. The control system is implemented as six independent SISO PD?controllers. The closed loop system bandwidth is 100 Hz. Using the system model in a Monte Carlo?type simulation, the effect of manufacturing and assembly tolerances on stage performance have been investigated. The results showed that the stage can be built with standard manufacturing technology, provided that extra care is taken during assembly of the actuators to reduce misalignment of the actuator components. An alignment tool has been developed for this purpose. A mechanical design has been made of the micropositioning stage. In this design the conclusions of the modelling phase and sensor and actuator characterisation have been taken into account. Fabrication drawings have been made, and all mechanical parts have been manufactured. The fine stage and its associated electronics have been fully assembled; the stage is currently in the test and characterisation phase.