Arm

One focus of research for Cardea is to explore behavior based methods of mobile and dexterous manipulation in an unstructured environment. To this end, we have given special attention to the development of a new generation of series elastic actuator robotic arms. Cardea will eventually have three of these arms. Each arm will likely be kinematically unique and designed such that different pairings of arms can be specialized to different manipulation tasks.

Series elastic actuators were invented here at MIT CSAIL. These actuators have a spring in series with the output of a DC motor. By sensing the spring deflection, we can determine joint torque. The spring also serves to protect the gear train from impact forces the arm may encounter. By knowing the torque at each arm joint, we can simulate virtual springs at each joint using Virtual Spring Control. This provides us a compliant and intuitive interface for doing behavior based manipulation.

The current prototype arm under development has 5 DOF. There is a 2 DOF differentially driven shoulder which provides pitch and yaw, a 1 DOF elbow, and a 2 DOF differentially driven wrist. The arm has been designed to roughly match the speed, power, weight, and proportions of a human arm.

The arm has analog torque and angle feedback at each joint. Each actuator is driven by a custom brushless DC motor amplifier. High bandwidth control (~1Khz) processing is done on a custom Motorola DSP 56F807 board. This controller interfaces with a microcontroller running our in-house behavior language called CREAL.

A second generation prototype is currently under development. This arm will add a roll degree-of-freedom at the shoulder and will incorporate a 4 DOF series elastic actuator hand.

The arm was developed by Aaron Edsinger.