Light Curtain
A safety light curtain (ESPE) is a non-contact, electro-sensitive protective device that creates an invisible array of infrared beams between a transmitter and receiver. When any beam is interrupted by a person or body part entering the protected zone, the device outputs a safety stop signal, removing power from hazardous machine motion. It functions as a presence-sensing safeguard at the point of operation or access opening, without physical contact.
In manufacturing environments, light curtains are installed across openings to robotic work cells, automated stations, or at the point of operation on presses and packaging lines. They act as invisible safety gates, triggering an emergency stop when beams are broken, allowing frequent access without physical barriers. The receiver's OSSD outputs connect to safety relays or controllers in dual-channel, self-monitoring circuits. Engineers calculate minimum safety distance based on machine stopping time and curtain response time. Muting logic may allow material passage while stopping for humans, but requires strict safety-rated control.
- Incorrect safety distance or improper placement: Light curtains installed too close to the hazard without proper calculation, allowing reach before machine stops, violating CSA Z432/OSHA standards.
- Inadequate resolution or coverage: Using coarse beam spacing (e.g., body protection) where finger/hand protection is needed, or gaps allowing reach-over/under, rendering the curtain ineffective.
- Defeating or poorly managed muting: Operators blocking beams, disabling outputs, or configuring muting logic that masks human entry, leading to serious incidents and regulatory citations.
How is the minimum safety distance for a light curtain determined on a press or robot cell?
The safety distance is calculated using standard formulas from CSA/ANSI/IEC: S = K × (Tm + Tc) + C, where S is safety distance (mm), K is approach speed (mm/s), Tm is machine stopping time (s), Tc is light curtain response time (s), and C is a constant for resolution. Engineers measure machine stopping time, use manufacturer response time, and apply conservative margins to ensure the machine stops before contact.
What safety circuit features are essential for compliant light curtain integration?
Essential features include dual-channel OSSD outputs from the light curtain that switch OFF on beam interruption or fault. These connect to a safety relay or controller that monitors for discrepancies, shorts, opens, or cross-faults, and enforces fail-safe behavior. The controller must immediately remove power from hazardous motion and require manual reset outside the hazard zone after clearing.
How do resolution (beam spacing) and protected height impact risk reduction?
Smaller beam spacing (e.g., 14 mm for finger protection) detects smaller body parts, while larger spacing (e.g., body protection) only detects torso entry. If resolution is too coarse, hands or fingers can reach hazards undetected. Protected height must prevent reach-over/under, with top high enough and bottom low enough, sometimes requiring additional barriers to close all approach paths.