Large Stroke High Fidelity PZN-PT Single-Crystal "Stake" Actuator

A new piezoelectric actuator design, called "Stake" actuator, is proposed and demonstrated in this paper. As an example, the stake actuator is made of four d(32)-mode PZN-5.5% PT single crystals (SCs), each of 25 mm (L) x 8 mm (W) x 0.4 mm (T) in dimensions, bonded with the aid of polycarbonate edge guide-cum-stiffeners into a square-pipe configuration for improved bending and twisting strengths and capped with top and bottom pedestals made of 1.5-mm-thick anodized aluminum. The resultant stake actuator measured 9 mm x 9 mm x 28 mm. The hollow structure is a key design feature, which optimizes SC usage efficiency and lowers the overall cost of the actuator. The displacement-voltage responses, blocking forces, resonance characteristics of the fabricated stake actuator, as well as the load and temperature effects, are measured and discussed. Since d(32) is negative for [011]-poled SC, the "Stake" actuator contracts in the axial direction when a positive-polarity field is applied to the crystals. Biased drive is thus recommended when extensional displacement is desired. The SC stake actuator has negligible (<1%) hysteresis and a large linear strain range of >0.13% when driven up to +300 V (i.e., 0.75 kV/mm), which is close to the rhombohedral-to-orthorhombic transformation field (E-RO) of 0.85 kV/mm of the SC used. The stake actuator displays a stroke of -36.5 mu m (at +300 V) despite its small overall dimensions, and has a blocking force of 114 N. The SC d(32) stake actuator fabricated displays more than 30% larger axial strain than the state-of-the-art PZT stack actuators of comparable length as well as moderate blocking forces. Said actuators are thus ideal for applications when large displacements with simple open-loop control are preferred.