Design of lightweight lead screw actuators for wearable robotic applications

A wearable robot is a controlled and actuated device that is in direct contact with its user As such, the implied requirements of this device are that it must be portable, lightweight, and most importantly safe. To achieve these goals, all actuator with a good power to weight ratio, good mechanical efficiency, good strength to weight ratio, and that is safe is desired. The design of the standard lead screw does not normally perform well in ally of these categories. The typical lead screw has low pitch angles and large radii, thereby yielding low mechanical efficiencies and heavy weight. However, using the design procedure outlined in this text, both efficiency and weight are improved; thus yielding a lead screw system with performances that rival human muscle. The result of an example problem reveals a feasible lead screw design that has a power to weight ratio of 277 W/kg, approaching that of the dc motor driving it, at 312 W/kg, as well as a mechanical efficiency of 0.74, and a maximum strength to weight ratio of 11.3 kN/kg (1154 kgf/kg).