Modelling and Control of Flexure Mechanism Driven by Electromagnetic Linear Motors for Ultraprecise Continuous Path Positioning over a One-Millimetre Stroke

The topic discussed is the Continuous-Path (CP) control performance of a planar positioning mechanism with three degrees of freedom using flexure guides and electromagnetic linear motors. A stage of cube configuration with 60 mm sides is supported by leaf springs made of phosphor bronze, which form double compound rectilinear springs with three degrees of freedom. Three pairs of VCM-type linear motors are set around the stage, and laser interferometers with a resolution of 0.6 nm measures the stage motion in the X-Y-θ directions. To achieve ultraprecise CP positioning, a dynamic model is derived from the equations of motion of the mechanism, and a simulation system is constructed to demonstrate the dynamic performance of the developed positioning system. Some experiments are performed to evaluate the performance of the control methods to obtain high-precision circular motion. The simulation system reproduces the performance in single-axis positioning. The multiaxis control is affected by interference among the axes X-Y-θ . To eliminate the interference, the input-output property of the mechanismconsidered as a Multiple-Input Multiple-Output (MIMO) system is measured in quasi-static and dynamic domains, and a static inverse model of the MIMO system is adopted for a FeedForward (FF) controller. Fine circularmotion with a roundness of 66 nm and a tracking deviation of 20 nm is achieved over a 1-mm stroke, and thus, the potential of the mechanism is demonstrated.