Detection latency directly sets the achievable safety limit

What it is

Collision detection-to-reaction latency spans physical contact, threshold crossing, recognition, safety command, and actual unloading or braking. The relevant quantity is this physical end-to-end interval, not a detection timestamp in a log. Motion and force continue until the mechanical response takes effect.

Why it happens

During early contact, structural deflection and successive control cycles build force. Threshold filtering, communication, scheduling, brake-torque rise, and elastic rebound postpone unloading, so the peak can occur after detection. Raising a threshold suppresses nuisance events but allows greater force before recognition; filtering likewise trades noise rejection for delay. Effective mass, speed, and contact stiffness make the same latency produce different peaks and impulse, coupling controller settings to mechanics.

Studying it

Measuring response time requires recording the full chain from physical contact to the control command taking effect, using high-speed force sensors and motion capture on the real end-effector and representative task loads, covering worst-case conditions across different payloads, sensor sampling rates, and network or bus latency — not an average or typical value. Engineering verification also needs repeated testing of sensor noise and false-detection-driven variability in response time, because the worst case tends to appear at the system's boundary conditions rather than in normal operation.

Where it stops holding

Fast detection alone does not ensure safety when braking travel, stored mechanical energy, contact misclassification, or trapping geometry dominates. Very low thresholds may repeatedly trip on process forces, floor shock, or payload changes and motivate bypasses. Unsynchronized device clocks produce false precision, while insufficient sampling misses brief force peaks.

Applying it

• Back-calculate the maximum permitted operating speed from the integrated system's end-to-end latency, not a single sensor's nominal spec, and re-check under worst-case payload and communication conditions.
• Keep a safety margin on detection latency for safety-critical functions rather than treating the best measured value as the design baseline.
• After deployment, periodically re-measure response time with a calibrated impact rig to confirm firmware updates, sensor aging, or bus-load changes haven't degraded latency past the original force-limit configuration.

Related

• Same group: X5.04.1 Contact force and pressure need injury-based upper limits · X5.04.2 Limits must differ by contact location, not follow one uniform standard · X5.04.4 Compliant mechanisms and passive force limiting are more reliable than software speed limiting alone
• Adjacent: X5.01 Physical safety boundaries · X5.05 Handling humans entering the workspace
• Search terms: detection latency · speed and separation monitoring · collision response time