Series Parallel Elastic Actuator: Variable Recruitment of Parallel Springs for Partial Gravity Compensation

In several applications, the gravitational load is dominant and requires high torque or force from the actuation. This load can be reduced using gravity compensaters which can provide a counter-torque/force passively. For applications with several degrees of freedom, providing perfect compensation can be extremely challenging and thus methods to provide partial compensation are used. The Series-Parallel Elastic Actuators use compliant elements, placed in series and parallel which can be tensioned separately. Through this recruitment, they can provide partial gravity compensation for complex tasks. Two Series parallel Elastic Actuators will be presented: the iSPEA which combines one motor which can recruit an arbitrary number of springs and the +SPEA which uses several units composed of a motor and a spring. It will be shown that both actuators can reduce the peak and RMS value of the actuation torque through partial gravity compensation.