We consider the problem of reorienting a rigid object with arbitrary known shape on a table using a two-finger pinch gripper.
Reorienting problem is challenging because of its non-smoothness and high dimensionality. In this work, we focus on solving reorienting using pivoting, in which we allow the grasped object to rotate between fingers. Pivoting decouples the gripper rotation from the object motion, making it possible to reorient an object under strict robot workspace constraints. We provide detailed mechanical analysis to the 3D pivoting motion on a table, which leads to simple geometric conditions for its stability.
The algorithm is hierarchical. Low level motion planning algorithm only needs to solve reorienting given a particular grasp location on the object; high level planning is concerned with finding the right sequence of grasping locations, which is done by performing graph search on the stable placements graph:
To handle the uncertainties in modeling and perception, we make conservative plans that work in the worst case, and propose a robust control strategy for executing the motion plan.
We demonstrate the effectiveness of our method in simulations and multiple experiments. Our algorithm can solve more reorienting problems with fewer making and breaking contacts, when compared to traditional pick-and-place based methods.
We provide a “two-phase” gripper design to implement pivoting without slipping, and to switch between pivoting grasp and firm grasp conveniently.
The idea of using pivoting for 3D reorienting was first presented in the following paper:
Paper · Video
A more general version of the algorithm, detailed analysis of the mechanical design, along with a lot more experimental results were summarized into the following paper:
Paper · Video