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Non-resonant piezo motors can offer much higher resolutions and forces than ultrasonic piezo motors. They usually consist of several individual piezo actuators and generate motion through succession of coordinated clamp/ unclamp and expand/contract cycles. Each extension cycle provides only a few microns of movement, but running at hundreds of Hertz, achieves continuous motion in the mm/second range. PI offers two types of non resonant motors, the high-force NEXLINE® drives and the new ultra-compact NEXACT® motors. NEXLINE® provides higher forces while NEXACT® drives (Fig. 13) are more economical, with smaller dimesions, lower forces and higher speeds to 10 mm/sec.
The latest NEXLINE® and NEXACT® piezo motor designs address the drawbacks of existing nanopositioning drives. NEXLINE® systems are based on very rugged, high-efficiency shear actuators and incorporate a preloading mechanism to provide pushing and holding forces up to 600 N (see Fig. 8) with basically unlimited lifetime. Such motors combine two operating modes: in long-range step mode, motion consists of user-defined (or auto-ranging) steps with widths from less than 1 nm to 6 µm in size; in fine-adjustment mode analog piezo motion with subnanometer resolution (see Fig. 10) over a travel range up to 6 µm is provided.
NEXACT® piezo motors are generally smaller, the N-310 (Fig.13) measuring only 25x25x12mm. These piezo stepping drives also run on lower voltages (~40 V), provide higher speeds (to 10 mm/sec) and are more economical than the ultra-high performance NEXLINE® systems.
Features and Advantages of NEXLINE® and NEXACT® Motors
- Very high resolution, limited typically only be the sensor. In fine-adjustment, analog mode, resolution of 50 picometers has been shown.
- High force generation and stiffness. NEXLINE® drives can hold and generate forces to 600 N. The rigid design with resonant frequencies of hundreds of Hz allows the construction of very stiff structures and helps to suppress vibration. The analog operating mode can actively be used for dithering and vibration cancellation.
- Can be run in open-loop and closed-loop mode. NEXLINE® digital controllers can process incremental position signals from linear encoders or laser interferometers andfor ultra-high precisionabsolute position signals from capacitance sensors. If the absolute position information is not important, NEXLINE® drives can also be operated in open-loop mode.
- Can hold a stable position to nanometer level in power-off mode. Due to the very high preload force and the intrinsic stability of the shear actuator design, NEXLINE® piezo drives are perfectly suited for applications where very precise adjustments have to be made occasionally. Also, experiments where strong electromagnetic radiation could affect the position stability or integrity of a motion control system can benefit from NEXLINE®.
- Extremely long lifetime. Because a position is held with zero operating voltage, leakage currents cannot affect the integrity of the piezo drive. Once a new position has been set, the digital controller ensures that after removal of the operating voltage no position change will occur. NEXLINE® drives were designed to achieve lifetimes greater 10 years.
- Non-magnetic, negligible EMI. NEXLINE® drives are available for non-magnetic applications such as super-conductivity experiments. They do not create magnetic fields nor are they influenced by them (see Fig. 9).
- Can be used in difficult environmental conditions. The active parts in NEXLINE® drives are made of vacuum-compatible ceramics. NEXLINE® also works in UV-light environments.
- Very rugged. NEXLINE® drives can survive shock loads of several g during transportation.
- Flexibility for OEMs: NEXLINE® drives are available in three levels of integration: OEM motors, packaged actuators and integrated into complex positioning systems such as multi-axis translation stages or 6-DOF hexapods see Figs. 8, 9, 11, 12.
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