  We believe that the future of robot motion planning will look very different
than how it looks today: instead of complex collision avoidance trajectories
with a brittle dependence on sensing and estimation of the environment, motion
plans should consist of smooth, simple trajectories and be executed by robots
that are not afraid of making contact. Here we present a "contact-aware"
controller which continues to execute a given trajectory despite unexpected
collisions while keeping the contact force stable and small. We introduce a
quadratic programming (QP) formulation, which minimizes a trajectory-tracking
error subject to quasistatic dynamics and contact-force constraints. Compared
with the classical null-space projection technique, the inequality constraint
on contact forces in the proposed QP controller allows for more gentle release
when the robot comes out of contact. In the quasistatic dynamics model, control
actions consist only of commanded joint positions, allowing the QP controller
to run on stiffness-controlled robots which do not have a straightforward
torque-control interface nor accurate dynamic models. The effectiveness of the
proposed QP controller is demonstrated on a KUKA iiwa arm.
