Ultra-high Speed and Ultra-precision Positioning by Friction Drive

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The positioning apparatus is made which consists of the DC servometer, the drive wheel, the slider moved longitudinally by the friction force between the drive wheel and a slider, the table, its displacement measuring apparatus by laser and the controller. The following results can be obtained ;1. For 1mum step responses repeated 100 times by PI control, the mean of the positioning errors E at 0.5 s after the table start, e.is -1.7nm, and their standard deviation, sigma, is 3.2 nm.2. For 300 mm step responses, the modified velocity control is applied at the large displacement difference DELTAx between the target position x and table position y (DELTAx=x-y). Afterwards, at the small displacement of DELTAx, the table displacement feed-back control is applied. As a result of 100 times positioning trials, e=0.016 mum and sigma=0.17 mum at 2 s after the table start. The setting time, when the table comes into (〕SY.+-.〔)1 mum from the target position, is Ts=1.26s(mean).3. There is a nonlinear elastic relationship between the small torque of the motor, T, and resultant small table displacement, y. Furthermore, for much smaller torque and table displacement, its relationship shows a better linearity, and plays an important role for obtaining nm positioning accuracy.4. In comparison with the apparatus by the leadscrew drive, the driving force is larger for the apparatus by the friction drive. The noise and vibration during operation can not be measured.5. This friction drive is applied to the driving system for the newly-developed nm surface grinder.