A piezoelectric ultrasonic micro-motor for In Vivo micro-robots
thesisposted on 13.01.2017, 01:30 by Watson, Brett
A need for improvement in minimally invasive surgical techniques is well documented. A method of achieving this improvement is through the development of a tetherless micro-robot capable of conducting medical procedures in vivo. Such a device could circumvent many of the problems associated with current minimally invasive procedures, and ultimately, may carry out procedures previously impossible and open up new areas of treatment. A key obstacle that must be overcome in the development of such a device is the realisation of a motor capable of acting as the drive system. Such a motor needs to be approximately 200 um in diameter, produce a start-up torque in excess of 15 nNm/mm^2, and produce an output power of more than 65 uW/mm^2. Existing micro-motors have separately met the geometric or performance requirements, but never both. In this thesis, we report a design methodology that results in a piezoelectric ultrasonic resonant micro-motor that, for the first time, effectively meets these requirements. The design methodology of the motor uses the piezoelectric element as a vibration generator, rather than as an integral part of the stator design. This simplifies the design, resulting in a reduction in size compared with existing micro-motor designs. The application of this methodology requires a stator design that can produce an elliptical stator tip motion from a single excitation source through resonant frequency matching. The design of such a stator is achieved through the development of three novel modelling techniques, which facilitate an understanding of how the system geometric parameters affect the resonant frequencies of interest, and affect the generation of the desired elliptical stator tip motion. The resulting motor has a stator dimension of 241 um and an overall diameter of 400 um, the larger dimension resulting from the commercial availability of magnetic elements. The peak measured start-up torque was 230.4 nNm/mm^2, with a peak output power of 72.4 uW/mm^2. This exceeded the requirements for torque and power to drive a tetherless micro-robot by 15-times and 10%, respectively. By overcoming the challenge of the drive system design, this work has opened up the opportunity to progress to the next stage of research in in vivo micro-robotics, full prototype development.