non-prehensile manipulation

Non-prehensile manipulation means moving an object around without ever gripping it. Instead of closing fingers and holding on, the robot pushes, slides, rolls, taps, pivots, or topples the object — it changes where the object is by nudging it, the way you might slide a heavy book across a table with one hand rather than picking it up. The word prehensile means able to grasp (like a monkey's tail), so non-prehensile simply means not grasping.

Why bother, when grabbing seems simpler? Sometimes the object is too big, too heavy, too flat, or too fragile to grip — a sheet of glass, a coin lying flat on a table, a pancake. Sometimes the robot's hand is busy or it only has a simple poker or a flat plate, not a clever hand at all. And sometimes pushing is just faster: shoving three boxes into a corner at once beats picking them up one by one. The trade-off is that a pushed object is not held, so it can slip, spin, or drift in ways that are hard to predict, which makes this a surprisingly tricky skill.

The heart of the difficulty is friction and physics: when you push an object, exactly how it moves depends on where you push, how hard, and how it rubs against the surface — and small errors grow. So non-prehensile manipulation leans heavily on understanding contact and motion, often nudging an object a little, watching what happened, and correcting. It is a key tool for handling things that simply cannot be grasped, and for setting an object up into a better position before a real grasp.