Limits must differ by contact location, not follow one uniform standard

What it is

Body-region-specific contact limits distinguish constraints by anatomical site, contact type, and consequence instead of assigning a robot one “human-safe force.” Forehead, back of the hand, abdomen, and finger differ in bony support, soft-tissue depth, pain sensitivity, and entrapment consequence. Equal mechanical exposure does not imply equal risk.

Why it happens

Superficial bony sites provide little cushioning and concentrate pressure. Compliant tissue can lengthen impact yet deform under sustained clamping. Small regions such as fingers enter geometric pinch points, while head and neck contact can produce consequences not represented by local pain alone. A body region is therefore a risk variable linking geometry, withdrawal, injury mode, and exposed population—not merely a threshold-table label.

Studying it

Studies and verification should predefine anatomical location, loading direction, contact area, and transient or quasi-static condition, then report participant characteristics or surrogate-tissue properties. Outcomes may include pain onset, peak force, pressure map, deformation, and duration, but volunteer studies necessarily stop within an ethically low-risk range. Engineering tests map each credible contact to a body region; if a region cannot be excluded, use a conservative applicable condition rather than the most permissive category.

Where it stops holding

Regional data come from bounded samples and specified apparatus; decimal precision does not remove uncertainty. Children, older adults, pregnant people, anticoagulated people, and those with impaired sensation may be poorly represented by healthy-adult data. Posture changes support and withdrawal at the same named location: an unrestrained palm strike and a palm trapped against a bench do not share one conclusion.

Applying it

• Run a contact-location analysis on the task posture first, establishing which body regions the end-effector could realistically reach under normal and off-nominal trajectories, then select the corresponding zone's limit.
• For tasks where the contact location is uncertain or straddles multiple zones, set limits to the most sensitive zone involved rather than an average or optimistic estimate.
• After adjusting zoned limits through a control-strategy change, re-measure with a calibrated force probe under real task postures to confirm the trajectory change hasn't drifted contact into a stricter zone.

Related

• Same group: X5.04.1 Contact force and pressure need injury-based upper limits · X5.04.3 Collision-detection response time directly sets the achievable safety limit · X5.04.4 Compliant mechanisms and passive force limiting are more reliable than software speed limiting alone
• Adjacent: X5.06 Presence of vulnerable populations · X5.07 Safety Standards and Certification
• Search terms: region-specific limits · pain threshold · body region force table