  Many robot manipulation tasks require the robot to make and break contact
with objects and surfaces. The dynamics of such changing-contact robot
manipulation tasks are discontinuous when contact is made or broken, and
continuous elsewhere. These discontinuities make it difficult to construct and
use a single dynamics model or control strategy for any such task. We present a
framework for smooth dynamics and control of such changing-contact manipulation
tasks. For any given target motion trajectory, the framework incrementally
improves its prediction of when contacts will occur. This prediction and a
model relating approach velocity to impact force modify the velocity profile of
the motion sequence such that it is $C^\infty$ smooth, and help achieve a
desired force on impact. We implement this framework by building on our hybrid
force-motion variable impedance controller for continuous contact tasks. We
experimentally evaluate our framework in the illustrative context of sliding
tasks involving multiple contact changes with transitions between surfaces of
different properties.
