A dynamically consistent hierarchical control architecture for robotic-assisted tele-echography with motion and contact dynamics driven by a 3D time-of-flight camera and a force sensor

This paper discusses a new control approach for robotic-assisted tele-echography where contact dynamics are driven by a 3D time-of-flight camera and a force sensor. Based on 3D camera and force data, contact stiffness is anticipated, allowing adaptation before contact. This approach enables to slow down robot dynamics before contact which is adequate for tele-echographic tasks. Additionally, free space inertial forces can also be eliminated from the control loop. In contact, environment stiffness is estimated online using only force data. The control architecture features a dynamically consistent hierarchical approach, where an explicit Cartesian force control arises as the primary task while orientation control is designed in the null space. Control performance is boosted by Kalman active observers (AOBs). Experiments with a 7-DOF WAM™ validate the architecture, where an ultrasound probe is teleoperated in 6 Cartesian dimensions, executing typical echographic tasks.