Ambulatory robots driven by piezoelectric bimorph benders: design, drive and control methods

This thesis describes the design, manufacture and testing of a small scale autonomous robot, as well as methods for driving piezoelectric benders that can be used in miniature robotics. This research creates a foundation for a new range of miniature robots that can be used across a wide range of applications, such as remote sensing in dangerous conditions, assembly or maintenance in larger machines or devices, in-vitro administration of medical aid, search and rescue and agricultural robots for pollination and pest control. Piezoelectric actuators have a high stiffness, resolution and fast response compared to other actuators, however they can generally only achieve very small strains. A bimorph bender is a type of piezoelectric actuator that features two piezoelectric elements joined together as a beam and when driven with a voltage will produce a bending motion. The idea of using piezoelectric benders in miniature robotics is a relatively new one and ways of improving the driving and operation of these benders are explored. A new method for driving a bimorph bender was developed that utilises both the polling, and coercive electric field strengths to provide a 38% improvement in deflection over previous methods. A charge drive for a piezoelectric bimorph was also developed that reduced the hysteresis non-linearity by 92%. An integral part of any miniature robot is the locomotion mechanism. A two degree of freedom miniature robotic leg that utilises piezoelectric bimorph actuators was designed and then tested. This leg measured approximately 15 mm x 15 mm x 15 mm and is intended to be used in a hexapod style robot driven at resonance. An analytical model was derived using three independent lumped mass models and superposition. This model can be used to tune the first two resonance modes such that they overlap by altering the size and shape of the flexure and end-effector. By driving the leg at this resonance an ambulatory motion is produced. This analytical model was then verified using FEA and experimentally.