Harmonic and cycloid drives are both compact, high ratio transmissions appropriate for use in anthropomorphic robots, although cycloid drives are rarely used in the field. This paper describes the design parameters for cycloid drives and shows the results of six cycloid models designed to match corresponding harmonic drives. Cycloid drive models were compared with manufacturing data from corresponding harmonic drives with respect to maximum gear ratio, transmission thickness, efficiency, backlash/gear ratio ripple, and reflected inertia. Cycloid drive designs were found to be thinner, more efficient, and to have lower reflected inertia than corresponding harmonic drives. However, the cycloid designs had larger gear ratio ripple and substantial backlash, and they could not meet the maximum gear ratio provided by the corresponding harmonic drives in two out of six models for equal applied torques. Two cycloid drives were manufactured to confirm efficiency predictions and demonstrated moderate to high efficiency across a range of output torques. Cycloid drives should be considered for robotic and prosthetic applications where smaller thickness/higher efficiency requirements dominate over low backlash/gear ratio ripple considerations.

A piezoelectric (PZT) stack-based actuator was developed to provide a means of actuation with dynamic characteristics appropriate for small-scale manipulation. In particular, the design incorporates a highly nonlinear, large-ratio transmission that provides approximately two orders of magnitude motion amplification from the PZT stack. In addition to motion amplification, the nonlinear transmission was designed via optimization methods to distort the highly non-uniform properties of a piezoelectric actuator so that the achievable actuation force is nearly constant throughout the actuator workspace. The package also includes sensors that independently measure actuator output force and displacement, so that a manipulator structure need not incorporate sensors nor the associated wires. Specifically, the actuator was designed to output a maximum force of at least one Newton through a stroke of at least one millimeter. For purposes of small-scale precision position and/or force control, the actuator/sensor package was designed to eliminate stick-slip friction and backlash. The overall dimensions of the actuator/sensor package are approximately 40/spl times/65/spl times/25 mm.