J. Clark, J. Clark
Auburn University,
United States
Keywords: s-drive, connectable actuators, artificial muscle, piezomuscle, piezoelectric
Summary:
We propose a new type of microscale piezoelectric actuator that can be arrayed with a multitude of others to form a larger actuator, which behaves as a single actuator. Microelectromechanical systems (MEMS) have matured to the level of being ubiquitously employed to transduce information (sound, temperature, pressure, movement, etc.) between the cyber and physical domains. However, they are typically deployed in hermetically sealed packages and are confined to transducing only micrometer level displacements. This limitation has severely limited their utility compared to their highly-successful biological counterpart, the muscle cell (or myocyte). Although muscle cells are the size of MEMS, muscle cells differ by their ability to connect to one another and magnify their displacement and force to behave like a single large actuator (or muscle). The building block attributes of muscle cells have enabled them to provide locomotor abilities across five orders of length scale, from insects to whales. The s-drive appears to be the first manufacturable microactuator that is connectible like muscle cells. This attribute has the potential to bridge the barrier between the microscale and macroscale. That is, the s-drive will enable the beneficial physics of the microscale to be extended to the macroscale, as muscle cells have done. Some interesting attributes of the s-drive include the following. (1) Packaging is not required. The s-drive is able to operate in liquid or in dusty environments. (2) The s-drive is able to operate in the direct piezoelectric mode for energy harvesting. (3) Several piezoelectric materials are available for the s-drive including ceramics like PZT and biocompatible polymers like PVDF. (4) If a part of an array of s-drives is damaged, the rest of the array is still operable. Prior efforts by others have demonstrated how piezoelectric bimorph microactuators can be used for microrobotic actuation [1] and energy harvesting [2]. What is different here is the formation of the slight ‘S’ shape upon deflection, which is the unique novelty that enables this actuator to be connectable and form large arrays. The array of building blocks is continuous. The building blocks share the same electrodes and structural material. This enables a whole array of s-drives to actuate in unison when just one building block is supplied with voltage. The ability to be connectable enables this method to achieve the largest deflections and largest forces in MEMS. Through modeling and simulation, in the full paper we will characterize the s-drive by comparing it to conventional actuators (i.e. energy density, deflection, force, connectability), demonstrate how s-drives can be connected in an array to form artificial muscle-like actuators, and demonstrate various array patterns affect the actuator’s force and deflection characteristics. [1] C-H Rhee, J. S. Pulskamp, R. G. Polcawich, and K. R. Oldham, "Multi-Degree-of-Freedom Thin-Film PZT-Actuated Microrobotic Leg", Journal of Microelectromechanical Systems, Vol. 21, No. 6, Dec 2012 [2] S. Nadig, S. Ardanuç, and A. Lal, "Monolithic 2-Axis In-Plane PZT Lateral Bimorph Energy Harvester with Differential Output", MEMS 2015, Estoril, Portugal, Jan 2015