| Abstract |
From the viewpoint of freedom from contamination, wafer handling systems with contactless mechanisms are required in the production of VLSl. Authors have developed a clean and vacuum-compatible wafer handling robot using an electro-magnetic suspension system. This two d.o.f. (gedree of freedom) wafer handling robot can be applied to a wafer-hoist, a turn-table and a swing-arm in an ultra-high vaccum. This robot performs two d.o.f. motion (0-axis rotation and Z-axis linear motion). For the two d.o.f. motion, a synchronous AC servo motor whose winding is installed in the air gap and a voice coil type actuator are used. These actuators are compactly integrated to fit a vacuum environment. The robot controller is fully digitalized by multi-DSP system. And the following advanced control methods are implemented: 1) Electro-magnetic suspension control by decoupling control scheme, 2) Precise positioning control by predictive observer and auto-tuning of the control parameters, 3) Linearization of gap sensor signal by curve fitting technique. The decoupling control enables to hold the position of the rotational axis precisely, regardless of the arm position. the predictive observer using the coarse signal (72 pulse/rev.) of position sensor significantly improves the precision of the rotational positioning. Auto-tuning controller save the time to adjust the parameters manually. These control schemes are introduced and experimental results are shown in this paper. |
