A collaborative robot ("cobot") is designed to share workspace with people without a fixed safety cage. ISO/TS 15066's Speed and Separation Monitoring (SSM) method keeps that safe by continuously measuring the distance between the robot and the nearest person and holding it above a protective separation distance Sp that shrinks as the robot slows down.
S(t) = Sh + Sr(t) + C + Zd + Zr
Sh ≈ vh · (Tr + Ts) (human approach)
Sr ≈ vr · Ts (robot stopping distance)
C, Zd, Zr — intrusion + position-uncertainty margins
- Green zone (beyond the slow-down threshold) — the operator is far enough that the robot runs at full programmed speed.
- Yellow zone — as the operator crosses the slow-down threshold, the robot's speed is scaled down continuously and proportionally to the shrinking distance, exactly as SSM requires.
- Red zone — inside the minimum protective separation, the robot executes a protective stop (zero speed) until the operator retreats.
The Smin readout is a simplified version of the ISO/TS 15066 separation-distance formula: it grows with the robot's own current speed, since a faster-moving arm needs more stopping distance and therefore a larger safety margin.