A pelvic belt worn by the participant is connected by multiple wires to a fixed frame. The wires are controlled in tension using servomotors based on real-time motion capture data of the pelvis. A desired force can be applied to the pelvis either continuously or intermittently in any direction of the space. The system design allows the use of any number of motors and the ease of changing the locations of motors and pulleys to achieve different cable configurations.
The control is implemented using a high and a low level structures. The high level controller plans the desired cable tension vector Td to apply a desired force-moment vector Fd. The low level controller implements these cable tensions using a feedback PID loop and a reference feed-forward. A friction compensation model based on the motor velocity is also included in the low level controller