The Rehabilitation Robotics Research Program

Combined Rate and Position Control


A combined rate and position control mode has been implemented on the telerobot. The system starts up in rate control mode where the master robot behaves as a head-mounted manipulandum centered in its workspace using software springs. The slave robot's end effector moves at a velocity proportional to the cartesian deflections of the master while the wrist maintains the master robot's orientation. The presence of this mode is very advantageous because it allows the user to perform gross motions in the workspace without having to move the manipulandum much. Once the slave's end-effector is in the vicinity of the task, the user can switch to position mode.

In the position control mode, the slave robot mimics the motion of the master - this has been implemented in two ways - with and without orientation update. In one case, the Zebra's wrist has a fixed orientation while in the other, the slave's wrist matches the master's end effector's orientation. In both cases, the slave's end-effector translates according to the master's motion along its cartesian axes. There is force feedback in this mode along with adjustment of stiffness and damping to create realistic soft and hard contact environments.

The user can switch between rate control and position control modes at any time. This allows great amount of flexibility along with excellent mobility and reach within the workspace.

Last Updated: July 15, 1996 by Vijay Jayachandran (