Projects in the MIT Precision Motion Control Laboratory

We have designed, implemented, and tested an electromagnetically driven fast tool servo for diamond turning precision contoured surfaces with nanometer resolution. Our device is based on a novel ultrafast motor utilizing permanent magnets for flux bias in conjunction with steering coils used to control the actuator force. Experimental results demonstrate that our ultrafast tool servo has a stroke of 30 micrometers, achieves 23kHz closed-loop bandwidth, as low as 1.7nm RMS tracking error, 500G peak acceleration at 10kHz open-loop operation, and 2.1nm (0.04%) error in tracking a 3kHz sinusoid of 16mm p-v.   To drive and control this ultrafast tool servo, a 1kW linear power amplifier and a high-speed real-time computer with 1MHz sampling rate have been designed and implemented. [More Info]

We are designing and building a prototype hybrid machine tool axis as a key component of new manufacturing machines for meso-scale parts. By hybrid we mean that the two axes of motion are compounded in a single moving component. We define meso-scale parts as having a size on the order of centimeters and thus falling between the domains of microfabrication and standard machining. Such parts include dental restorations, molds, dies, and turbine blades. We currently have built a prototype rotary-linear axis. It consists of a central shaft which is driven in both rotation and translation. This hybridization minimizes machine inertias and thereby maximizes accelerations allowing for the production of complex parts rapidly and accurately. The minimization of inertias also increases the frequency of structural resonances allowing for control at higher bandwidths.[More Info soon.]

Together with UNC Charlotte, we have built a magnetically-suspended stage designed to achieve 0.1-nm resolution, 1-nm repeatability, and 10-nm accuracy over a macroscopic range of 25 mm in X,Y and 100 microns in Z. To complete the project, we are currently developing an atomic force microscope head to allow accurate characterization of the performance of the LORS stage. This probe senses tip-sample separation using a miniature piezoelectric quartz tuning fork. When driven with an AC voltage at its resonant frequency and with a sharp tip mounted to one end, this sensor can resolve topographic features on the atomic scale. Development of integrated metrology with the inherent accuracy of the system remains one of the key design challenges. Scanned probe microscopy typically relies on open-loop control of PZT actuators, which may introduce errors due to hysteresis. Our design will incorporate closed-loop positioning of a PZT tube, thereby improving the probe's accuracy. [More Info]

We have built a prototype turning machine specialized for the production of plastic spectacle lenses. This machine features a novel rotary fast-tool servo, which can track trajectories at frequencies up to 500 Hz, and accelerations of 500 m/s^2. Thus the machine can turn 100 mm diameter toric lenses having surface asymmetries of up to 3 cm in depth. The control system consists of a conventional inner position loop, feedforward filtering, and repetitive control. This high-bandwidth, high-accuracy system allows us to turn a toric surface with tracking errors of less than 2 microns. [More Info]

Last Updated: May 05, 2005