Stepper motor driven precision actuators have a good track record for precision alignment applications. They provide high resolution, force, and relatively high speed. Their downside is size and heat generation (especially when used in high-resolution micro-step mode, the motor will not hold a position when powered off).
Piezo-ratchet-motor-driven actuators can be designed much smaller than conventional stepper motor actuators. They provide nanometer resolution, very low energy consumption (heat dissipation), and are self-locking when powered down. Due to the compact size / form factor, they can be easily used to replace manual micrometers. For applications where the absolute position is not relevant (feedback is provided by a system parameter such as optical power, focus, etc), open-loop actuators can be used. This situation also allows for simple control solutions, where one driver can be used to operate multiple actuators in sequence, by an internal electronic switch. Compared to traditional motorized precision-actuators, piezo-ratchet motor actuators provide lower velocity and are ideal for “set-and-forget” applications that would typically be handled by manuals micrometers.