Many medical devices such as blood analyzers, cell imagers, MRI, and microelectronics require resolutions in the nanometer range, and long travel distances. These requirements are traditionally met by combining two motion mechanisms, one for travel and another for resolution. But the combination poses problems of complexity of mechanics, drive and control, natural frequencies, and cost.

Standing-wave ultrasonic motors from Nanomotion, Ronkonkona, N.Y., (nanomotion.com) provide an alternative. The motors hit speeds up to 300 mm/sec, have no travel limits, and have submicron resolutions. Additional advantages include a small footprint, direct-drive, which simplifies control, and a single motion mechanism for linear and rotary applications.

Nanomotion's approach relies on a standard resonant mode for long travel. Then, when close to the target (within 200 nm) a nonresonant mode takes over with its 1-nm resolution. The motors normally operate in resonance, but they can operate in nonresonant mode as well. In resonant mode, a rectangular component resonates or vibrates at 40 kHz inside the motor.

Up and down motion of the resonating components bends into an elliptical path and presses against a bearing surface producing motion. Motors contain one to eight resonating components, each producing 1-lb of force. In nonresonant mode, voltage applied to a crystal causes the piezoelement to bend right or left with the sign of the applied voltage, thereby determining direction of motion.

Movements of 1 to 250 nm are possible. Traditional piezomotors are limited in travel range and by hysteresis effects. Nanomotion motors, however, are unaffected by hysteresis because its elements are perpendicular to the axis of travel. The motor is also unaffected by temperature changes that might cause the elements to change size. A closed-loop servocontrol can be provided with standard off-the-shelf servocontrollers or with the Nanomotion servocontroller that offers full PID control at 20 kHz.