Stop actuators must sit within reach
Aliases: emergency stop reach envelope · e-stop placement · stop button layout
What it is
Reachability of emergency stop actuators means a person who may need to intervene can trigger a stop without crossing the hazard, finding a hidden control, or completing a complex unlock sequence. A button somewhere in the cell is insufficient; count, placement, and actuation must match real postures, routes, and sightlines.
Why it happens
Response time serially adds hazard detection, device identification, travel and actuation, and physical machine stopping. Distance, a cabinet door, or stored material adds human movement to braking delay; placement across a hazardous path can draw a rescuer toward moving machinery. Multi-station and two-sided cells add occlusion, so the nearest bystander may neither see nor reach the same actuator.
Studying it
Task analysis first enumerates personnel locations during operation, loading, teaching, maintenance, and jam clearance. Anthropometric data can screen inaccessible points, followed by harmless surprise drills measuring first correct actuation, errors, detour distance, and hazard-zone entry. Seated, kneeling, gloved, one-hand-limited, and mobility-aid conditions reveal barriers that a standing percentile range misses.
Where it stops holding
Emergency stop complements other protection; it does not replace guarding, presence sensing, or automatic protective stopping. Wireless and software controls expand coverage but add battery, connectivity, focus, and interface-freeze failures, making them poor sole channels. Public robots also face accidental or malicious actuation, yet anti-tamper treatment must not turn a real stop into a dexterity sequence.
Applying it
- Trace an unobstructed route from every foreseeable person location to the nearest actuator; eliminate routes that cross robot motion, require unlocking, or depend on moving stored material.
- Provide consistent, recognizable physical actuation at fixed stations, teach pendants, and likely mobile-robot stopping points. Design other protective devices as distinct safety functions rather than presenting them as emergency stops.
- Run drills with actual gloves, tools, and mobility aids from randomized locations. Record the slowest correct actuation and detour, and repeat after layout changes.