Abstract: An actuator able to move along a track. The actuator has an elastic coupling member that surrounds the track. The coupling member has a regularly grooved internal surface. There are pairs of piezo electric transducers surround the coupling member. These transducers are polarized with each member of a pair being polarized in a direction different from the other member of the pair. There is an insulator between neighbouring pairs of transducers and absorber means at each end of the actuator. Voltage can be applied to the transducers whereby the application of voltage expands and contracts the transducers, generating waves in the coupling member causing it to move along the track.