Piezoelectric Bending Actuators

An important step in making fully functional robotic systems is making the structure move.  We accomplish this through the addition of actuators.  Even for this size scale (millimeter-sized),  there are several types of actuators that we could use.  However, because they are easily incorporated into our structures, we often look to piezoelectric actuators, more specifically, clamped-free bending cantilever PZT actuators.   The drawback of these actuators is that they require a high voltage source and drive electronics which is addressed in the power and control electronics section.

PZT actuators with examples

Made from composite material (some of the same material as used in our structural parts) and PZT (an amorphous piezoceramic), a typical biomorph layup is shown below.  In practice, we use both unimorphs (single layer) and bimorphs (two layers of piezoceramic material).

cross section of a PZT bimorph

Given the geometric constraints usually dictated by the structure itself, the parameters of the actuator like length, width, extension ratio, and width ratio are determined based upon laminate plate design as discussed in the paper reference given below.

Paper reference:
Optimal Energy Density Piezoelectric Bending Actuators
             R.J. Wood, E. Steltz, and R.S. Fearing
             Sensors and Actuators, Vol 119/2 pp 476-488, 2005.