Development and Testing of a Reliability Performance Index for Modular Robotic Systems

Using a probabilistic representation of manipulator kinematics and a reliability block diagram model of the manipulator system, a Reliability Performance Index RPI representing the probability of no hardware or software failure and the manipulator achieving a specified position and orientation is developed. The RPI is tested with a case study consisting of a three degree-of- freedom planar manipulator assembled from a choice of six joint modules of varying reliability and precision and a choice of six link module combinations of varying lengths and machining tolerances. A straight-line, square trajectory is specified and the RPI is calculated for each combination of joint modules and links, a total of 1296 different combinations. Using statistical testing, a 70 reduction in the module design space is achieved using the RPI. Optimization using other appropriate manipulator criteria can then be performed to generate the final configuration. Additional extensive case studies are needed to fully develop the RPI to a stage necessary for implementation into a computer-aided design system for modular robot configuration design. The RPI may also be useful in the quantification of the overall system reliability and performance of any system based upon measured error, such as control systems.