Power & Force Limiting (ISO/TS 15066)

Contact point

Contact mode

Arm approach speed 0.5 m/s

Effective robot mass 8 kg

Force-limiting setting 120 N

Effective mass μ

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Region limit

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Computed contact force

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Margin to limit

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How it works

ISO/TS 15066 Power and Force Limiting (PFL) sets two separate ceilings on how hard a collaborative robot may contact a person, because a brief glancing hit and a sustained clamp injure very differently. Free (transient) contact is modelled as an elastic spring impact between the robot's reduced mass and the body region's own effective mass and stiffness; clamped (quasi-static) contact — where the person is trapped against a fixture — is bounded only by the robot's own force-limiting controller setting, independent of speed.

μ = (m_H · m_R) / (m_H + m_R)
F_transient = v · √(k · μ)
F_quasi-static = controller force-limit setting

Approach speed / effective robot mass — only matter in free contact; a lighter, slower-moving tool keeps the spring-impact force below the region's transient limit.
Force-limiting setting — the safety parameter an integrator programs into the controller; it alone determines the clamped-contact force, so it must sit under the stricter quasi-static limit even though free contact could tolerate more.
Region — sensitive rigid areas (skull, face) carry much lower limits than compliant, well-padded ones (chest, forearm) per ISO/TS 15066 Annex A.

Figures shown are illustrative teaching values in the shape of ISO/TS 15066 Annex A's biomechanical limit tables, not a substitute for the certified standard during an actual risk assessment.

Robot tool Under limit Over limit

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