A robot that's sorting through a bin of objects and attempting to get a good grasp on one of them is performing a computationally taxing maneuver. Before even attempting the move, it must calculate a litany of properties and probabilities such as the friction and geometry of the table, the pen, and its two fingers, and how various combinations of these properties interact mechanically based on fundamental laws of physics.

A new method was developed to significantly speed up the planning process required for a robot to adjust its grasp on an object by pushing that object against a stationary surface. Whereas traditional algorithms would require tens of minutes for planning out a sequence of motions, the new approach cuts the pre-planning process down to less than a second. The faster process will enable robots, particularly in industrial settings, to quickly figure out how to push against, slide along, or otherwise use features in their environments to reposition objects in their grasp.

Existing algorithms typically take hours to pre-plan a sequence of motions for a robotic gripper, mainly because for every motion that it considers, the algorithm must first calculate whether that motion would satisfy a number of physical laws such as Newton's laws of motion and Coulomb's law describing frictional forces between objects. The new method solves the physics of these manipulations in advance of deciding how the robot's hand should move using “motion cones” that are essentially visual, cone-shaped maps of friction.

The inside of the cone depicts all the pushing motions that could be applied to an object in a specific location, while satisfying the fundamental laws of physics and enabling the robot to keep hold of the object. The space outside of the cone represents all the pushes that would in some way cause an object to slip out of the robot's grasp. The algorithm calculates a motion cone for different possible configurations among a robotic gripper, an object that it is holding, and the environment against which it is pushing in order to select and sequence different feasible pushes to reposition the object.

The algorithm was tested on a physical setup with a three-way interaction in which a simple robotic gripper was holding a T-shaped block and pushing against a vertical bar. Multiple starting configurations were used, with the robot gripping the block at a particular position and pushing it against the bar from a certain angle. For each starting configuration, the algorithm instantly generated the map of all the possible forces that the robot could apply and the position of the block that would result. The algorithm's predictions reliably matched the physical outcome in the lab, planning out sequences of motions — such as reorienting the block against the bar before setting it down on a table in an upright position — in less than a second, compared with traditional algorithms that take over 500 seconds to plan out.

For more information, contact Abby Abazorius at This email address is being protected from spambots. You need JavaScript enabled to view it.; 617-253-2709.

Motion Design Magazine

This article first appeared in the December, 2019 issue of Motion Design Magazine.

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