  This paper considers the problem of retrieving an object from many tightly
packed objects using a combination of robotic pushing and grasping actions.
Object retrieval in dense clutter is an important skill for robots to operate
in households and everyday environments effectively. The proposed solution,
Visual Foresight Trees (VFT), intelligently rearranges the clutter surrounding
a target object so that it can be grasped easily. Rearrangement with nested
nonprehensile actions is challenging as it requires predicting complex object
interactions in a combinatorially large configuration space of multiple
objects. We first show that a deep neural network can be trained to accurately
predict the poses of the packed objects when the robot pushes one of them. The
predictive network provides visual foresight and is used in a tree search as a
state transition function in the space of scene images. The tree search returns
a sequence of consecutive push actions yielding the best arrangement of the
clutter for grasping the target object. Experiments in simulation and using a
real robot and objects show that the proposed approach outperforms model-free
techniques as well as model-based myopic methods both in terms of success rates
and the number of executed actions, on several challenging tasks. A video
introducing VFT, with robot experiments, is accessible at
https://youtu.be/7cL-hmgvyec. The full source code is available at
https://github.com/arc-l/vft.
