  Articulated and flexible objects constitute a challenge for robot
manipulation tasks but are present in different real-world settings, including
home and industrial environments. Current approaches to the manipulation of
articulated and flexible objects employ ad hoc strategies to sequence and
perform actions on them depending on a number of physical or geometrical
characteristics related to those objects, as well as on an a priori
classification of target object configurations.
  In this paper, we propose an action planning and execution framework, which
(i) considers abstract representations of articulated or flexible objects, (ii)
integrates action planning to reason upon such configurations and to sequence
an appropriate set of actions with the aim of obtaining a target configuration
provided as a goal, and (iii) is able to cooperate with humans to
collaboratively carry out the plan.
  On the one hand, we show that a trade-off exists between the way articulated
or flexible objects are perceived and how the system represents them. Such a
trade-off greatly impacts on the complexity of the planning process. On the
other hand, we demonstrate the system's capabilities in allowing humans to
interrupt robot action execution, and - in general - to contribute to the whole
manipulation process.
  Results related to planning performance are discussed, and examples of a
Baxter dual-arm manipulator performing actions collaboratively with humans are
shown.
