  With the goal of enabling the exploitation of impacts in robotic
manipulation, a new framework is presented for control of robotic manipulators
that are tasked to execute nominally simultaneous impacts. In this framework,
we employ tracking of time-invariant reference vector fields corresponding to
the ante- and post-impact motion, increasing its applicability over similar
conventional tracking control approaches. The ante- and post-impact references
are coupled through a rigid impact map, and are extended to overlap around the
area where the impact is expected to take place, such that the reference
corresponding to the actual contact state of the robot can always be followed.
As a sequence of impacts at the different contact points will typically occur,
resulting in uncertainty of the contact mode and unreliable velocity
measurements, a new interim control mode catered towards time-invariant
references is formulated. In this mode, a position feedback signal is derived
from the ante-impact velocity reference, which is used to enforce sustained
contact in all contact points without using velocity feedback. With an eye
towards real implementation, the approach is formulated using a QP control
framework, and is validated using numerical simulations both on a rigid robot
with a hard inelastic contact model and on a realistic robot model with
flexible joints and compliant partially elastic contact model.
