Control system and method for non-gait ankle and foot motion in human assistance device

A human assistance device has a rate gyro, first accelerometer, and second accelerometer disposed on a mobile body for sensing a physical state of the mobile body to provide a physical state measurement. The human assistance device can be a prosthetic, orthotic, and robotic device. An ATAN2 function is performed on an output of the first accelerometer and an output of the second accelerometer. An output of the rate gyro and an output of the ATAN2 function is filtered to provide a filtered physical state measurement. The filtered physical state measurement is applied to a reference function to generate a reference command to control a non-gait motion of an actuator in the human assistance device. The reference command controls the human assistance device, for example to provide a shifting foot position while seated, with a natural, biological motion, without an artificial or mechanical appearance.