Design of a Hydraulic Low-Speed, High-Torque, Cycloidal Actuator/Motor for Use in Medical Devices

The thesis presents the design of a meso-scale, hydraulic, rotary actuator/motor. While there are some existing devices, both hydraulic and pneumatic, it was ascertained that there are opportunities for other devices. Some particularly relevant devices that are discussed in the thesis are the PneuStep from John Hopkins University and a meso-scale linear actuator from Oak Ridge National Laboratory. The PneuStep is a pneumatic stepper motor for use in the MRI environment that achieves a max output torque of 5.31 lb·in. (600 N·mm) at an approximate speed of 15 RPM under operating pressures of 120 PSI (0.83 MPa) [1, 2]. In addition, researchers at the Oak Ridge National Laboratory (Oak Ridge, Tennessee) have developed a meso-scale linear actuator with a diameter of 0.09 in. (2.3 mm) that generates a force of 2.4 lb (10.69 N) with a stroke length of 0.3 in. (7.6 mm) [3].;The meso-scale, hydraulic, rotary actuator/motor that is the subject of this thesis incorporates an integral cycloidal speed reducer while utilizing hydraulic cylinders for actuation in a pancake-style configuration. Initial testing with a pneumatic powered rotary actuator, which was designed and fabricated, revealed a number of important considerations that were used in the final design. Piston rod side-loading, friction losses, and cylinder alignment were found to be particularly important.;The final design of the hydraulic, rotary actuator/motor was limited in its pressure supply to 85 PSI but achieved a maximum holding torque of 23 lb·in. (2.6 N·m). A Simulink model was developed that included compressibility effects, dynamics/inertial effects, and the effects of changing effective mass moment of inertia. Simulink model runs predicted a speed of 55 RPM with a resisting torque of 4 lb·in. (450 N·mm). Experimental results, under similar conditions resulted in a speed of 45 RPM.;The development of a novel rotary actuator may lead to further progress in the field of medical devices for situations where a low-speed, high-torque actuation is particularly suited. Furthermore, these developments add valuable design knowledge to both the fields of meso-scale hydraulic componentry and cycloidal actuators/motors.