Contact force and pressure need injury-based upper limits

What it is

Biomechanical force and pressure limits for human-robot contact constrain mechanical exposure to a range judged acceptable through risk assessment and testing. Force describes total load; pressure describes its concentration over contact area. A broad rounded surface and a narrow edge can apply equal force with different tissue consequences, so the measures are not interchangeable.

Why it happens

Transient collision peaks depend on relative velocity, effective mass, contact stiffness, and damping as energy transfers rapidly into tissue. Quasi-static clamping may sustain load without a large initial peak and may prevent withdrawal. Tool edges concentrate pressure, while an opposing surface turns a yielding impact into crushing. The contact chain includes robot, end effector, workpiece, and environment, not robot rated force alone.

Studying it

Hazard identification first separates foreseeable transient, quasi-static, and trapping contacts by pose. A pressure-force measurement device with characterized stiffness, damping, and contact face then reproduces the encounter. Peak force, pressure distribution, impulse, duration, and residual load are measured across speed, effective mass, tool orientation, and control settings. ISO/PAS 5672 supplies a measurement and analysis framework for professional collaborative applications, but neither identifies hazards nor covers friction, shear, and other injury modes.

Where it stops holding

One result below a tabulated value cannot establish “no injury.” Population variability, repeated contact, sharp features, sensitive body regions, shear, puncture, and fall consequences may escape a normal force-and-pressure test. Industrial collaborative-robot values and methods do not transfer automatically to children, medical use, or consumer robots; each standard has a defined scope.

Applying it

• Inventory worst contacts by robot surface, tool, workpiece, body region, ability to withdraw, adverse pose, and opposing trapping structure.
• Derive force and pressure constraints from risk assessment and bind speed, torque, geometry, and payload to the validated configuration; reassess after changes.
• Reproduce the real path with a measurement device matched to contact stiffness. Check peaks, spatial distribution, and sustained load, while evaluating edges, shear, and falls separately.

Related

• Same group: X5.04.2 Limits must differ by contact location, not follow one uniform standard · 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: X5.01 Physical safety boundaries · X5.03 Emergency Stop
• Search terms: biomechanical limits · power and force limiting · ISO/TS 15066