Many fields such as microelectronics, storage media, and gene technology, require resolution in the nanometer range and over long travel distances. In the case of microelectronics, travel can be as long as 14 in. to cope with 12-in. wafers. These requirements were traditionally met by combining two motion mechanisms, one for long travel and another for high resolution. But this combination poses other problems due to complexity of mechanics, drive and control, natural frequencies, and cost.
Standing wave ultrasonic motors from Nanomotion, Ronkonkona, N.Y., provide an alternative. The motors hit speeds up to 300 mm/sec, have no travel limits, and achieve submicron resolutions. Additional advantages include a small footprint, direct-drive capability which simplifies the control scheme, and a single motion mechanism for both linear and rotary applications.
Nanomotion's approach combines the standard resonant mode for long travel with nonresonant motion for small, nanometer-scale motion. Once within the target radius, the nonresonant mode takes over for distances up to 200 nm with 1-nm resolution.
The motors normally operate in resonance, but they can be operated in nonresonant mode as well. In resonant mode, a rectangular component resonates or vibrates inside the motor at 40 kHz. The up and down motion bends into an elliptical path. This component presses against a bearing surface producing motion. Motors can contain from one to eight elements, each producing 1 lb of force.
In nonresonant mode, voltage applied directly to a crystal causes the piezoelement to bend right or left with the sign of the applied voltage, thereby determining the direction of motion. Movements of 1 to 250 nm are possible.
Traditional piezomotors are limited in their travel range and by hysteresis effects. The Nanomotion motor, however, is unaffected by hysteresis because the motor element is perpendicular to the axis of travel. The motor is also unaffected by temperature changes that would cause the elements to change size.
A closed-loop servocontrol can be provided with standard offthe-shelf servocontrollers or with the Nanomotion servocontroller that offers full PID control at 20 kHz.