Why hasn’t anyone heard of cuspidal robots?

A cuspidal (ˈkəspədᵊl ; having cusps) robot changing postures without passing through a singularity. That unique ability comes with tricky motion planning.

A familiar motion planning problem

The Kinova Mico had trouble executing simple motions without leaving the intended path, which could cause collisions. These movements are different from instabilities arising from passing through a singularity when using the Jacobian transpose.

The class of robots you haven’t heard of

Simple robot arm moving from the elbow up posture (IK solution) to elbow down. It must pass through a singularity (middle). Unlike your arm, this robot can’t rotate its shoulder, however it can ‘superflex’ its elbow. The manipulability ellipsoid (oval shape at the hand) is flat at the singularity.

Small changes, large impact

Announcement of the IRB 6400C in ABB Review 3/1996. I spoke with a (now retired) engineer who oversaw the project. Engineers working on the project weren’t familiar with the discovery of cuspidal robots.

Modifying an industrial robot can make it cuspidal

A simple cuspidal robot that has issues following a straight path. White lines in the middle and right graphs are singularity surfaces. For an in-depth explanation, see part 2 of cuspidal robots.

Is my robot cuspidal?

Are there any upsides?

Roboticist, geometer, plant-person, Belgian living in the Bay Area

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Achille Verheye

Achille Verheye

Roboticist, geometer, plant-person, Belgian living in the Bay Area

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