grasp quality metric
A grasp quality metric is a number that scores how good a particular way of gripping an object is — how firmly and reliably it will hold. When a robot looks at an object, there are usually many possible places and angles to grab it: by the rim, by the body, edge-on, top-down. The metric is the yardstick that lets the robot compare these candidate grasps and pick the best one, the way a number from 0 to 10 lets you rank choices instead of just guessing.
What does a high score actually mean? Roughly, a strong grasp is one that will not let the object slip, twist, or fall no matter which direction it gets nudged from — you could shake it and the object stays put. A weak grasp is one where a small bump or a slightly heavier-than-expected object would break the hold. Good metrics reward grips where the contacts press from opposing sides so the object is trapped, where the contact patches are wide and well placed, and where the hold resists pushes and twists coming from any direction. They penalize a grasp that pinches one tiny corner the object can easily pivot out of.
The point of having a single score is automation: a robot can generate hundreds of possible grasps in a fraction of a second, run each through the metric, and act on the highest-scoring one — no human picking by eye. The catch is that the score is only as honest as its assumptions; if the real object is heavier or more slippery than the metric expected, a top-scoring grasp can still fail, which is why quality scores are usually paired with planning that allows for being wrong.
Offered two ways to grip a hammer — across the thick head versus pinching the thin handle tip — the robot scores the head grasp higher, because that hold stays put when the heavy head swings, while the tip pinch would let the hammer rotate and drop.
The metric ranks grasps so the robot grips near the heavy center, not the wobbly tip.
A grasp where the contacts press from opposing sides so the object is trapped tends to score high, because it resists being slipped or twisted free from any direction — the property classic metrics call force closure.