Architecture for robust force and impedance control of series elastic actuators

A series elastic actuator architecture for providing force control for a series elastic actuator that actuates a robotic link, said architecture comprising:

• a rotary spring coupled to the robotic link;
• a motor including a motor shaft and a gear box, said motor shaft being coupled to the spring;
• a first position sensor provided at an output of the gear box of the motor and measuring the absolute orientation of the motor shaft;
• a second position sensor provided at a location where the spring is coupled to the robotic link and measuring the absolute orientation of the robotic link;
• an embedded processor provided proximate the motor and receiving sensor position signals from the first and second sensors, said embedded processor calculating the actual torque on the spring based on the difference between the first position sensor and the second position sensor;
• and
• a remote controller providing a reference torque signal to the embedded processor, said embedded processor determining the difference between the reference torque and the actual torque on the spring and controlling the position of the motor shaft so that the reference torque and the actual torque are the same, said embedded processor operating at a higher speed than the remote controller.

A series elastic actuator architecture for providing force control for a series elastic actuator that actuates a load, said architecture comprising:

• a set of series elastic actuator joints, where the set contains two or more series elastic actuator joints and where each series elastic actuator joint includes:
• a spring coupled to the load;
• a motor including a motor shaft and a large reduction gear box, said motor shaft being coupled to the spring;
• a first absolute position sensor provided at an output of the gear box of the motor, said first sensor measuring the orientation of the motor shaft;
• a second absolute position sensor provided at an opposite end of the spring and measuring the orientation of the load;
• and
• an embedded processor provided proximate the motor and receiving sensor position signals from the first and second sensors, said embedded processor calculating the actual torque of the spring based on the orientation of the motor shaft and the load and the spring rate;
• a high speed communication bus;
• and
• a remote controller that communicates with the set of series elastic actuator joints through the high speed communication bus providing each embedded processor with a reference torque signal, said embedded processor determining the difference between the reference torque and the actual torque on the spring and controlling the position of the motor shaft so that the reference torque and the actual torque are the same, said embedded processor operating at a higher speed than the remote controller, wherein a servo loop within the embedded processor controls the position of an actuator according to a relation between position and the torque in the spring.