From Injury to Zero Accidents: A Food Plant’s Journey with DAIDISIKE Safety Light Barriers

DAIDISIKE photoelectric safety light curtain on a sanitary line

Client Background: Safety Challenges in Food Processing

In the fast-paced environment of a food processing plant, operators work in close proximity to high-speed blades, heat-sealing knives, and powered conveyor lines, often just centimeters away. Despite training and warning labels, the facility faced recurring injuries in two key areas:

• Hand Crush Injuries During Changeovers: While clearing jammed film in a Vertical Form Fill Seal (VFFS) machine, operators reached into the heat-sealing zone. If a sensor mistakenly detected the guard as “closed,” the sealing knife would cycle, crushing hands.
• Finger Cuts at Pick-and-Place Stations: When adjusting misaligned cartons, operators’ fingers entered the robot’s transfer path. If the robot unexpectedly restarted, fingers could be caught between the carton and guide rails.

The Challenge: In a washdown, highly reflective environment, implement intrusion detection to stop motion before contact without compromising productivity or causing excessive false triggers. Mechanical guards alone couldn’t accommodate the variable openings required for frequent changeovers. The Health, Safety, and Environment (HSE) team therefore deployed DAIDISIKE Type 4 safety light curtains to retrofit the most hazardous areas.

Risk Assessment and Hazard Mapping

Key Findings:

• Hazardous Areas: Heat-sealing knives (VFFS), infeed conveyors, robot pick-and-place paths, and carton compacting zones.
• Detection Requirements: 14 mm resolution at the heat-sealing knife for fingertip protection; 30 mm at the robot infeed for hand/forearm protection.
• Environment: Surrounded by stainless steel, exposed to steam and daily washdowns, requiring IP67 protection and resistance to interference from water droplets and reflective films.
• Control Level: Performance Level e (PL e) / Safety Integrity Level 3 (SIL 3), with dual-channel OSSD outputs and External Device Monitoring (EDM) for the main contactor.

Retrofit Solution

Light Curtain Specifications

• Type 4 compliant with IEC 61496; 14 mm resolution for heat-sealing knives, 30 mm for robot infeed.
• Protective Height: 450–600 mm at heat-seal entry; 900–1200 mm at conveyor entry. (For a 500 mm effective protective height, the DQC or DQE series, such as DQC16-40-600A, is suitable. Here, 600 mm refers to the effective protective height with 16 beams, and the total height is approximately 666 mm, fully covering the heat-seal entry.)
• Operating Distance: 0.2–6 m, allowing installation on a frame outside the splash zone.
• Features: Fixed blanking for unavoidable fixtures, restart interlock, EDM, and alignment diagnostics.

 
Safety light screen guarding a sealing-jaw entry

Safety Distance Calculation (Per ISO 13855)

Formula: S = K × T + C, where K = 1600 mm/s (hand speed), T = total stopping time (controller + actuator), and C = 8 mm (fingertip) or additional encroachment allowance.

Example (Heat-Sealing Knife): Measured stopping time T = 120 ms (0.12 s). Thus, S = 1600 × 0.12 + 8 ≈ 200 mm. The light curtain was installed at ≥220 mm to account for alignment tolerances and provide a safety margin.

Mounting and Framework

Used 316L stainless steel posts with vibration-damping rubber mounts; toe-kick blocks prevented floor blind spots. (Contact DAIDISIKE representatives for 3D product drawings to finalize mounting hole positions based on site-specific safety distances.) Quick-release protective covers were designed to withstand daily foam cleaning without misalignment.

Safety Circuit Integration

• Light curtain OSSD1/2 connected to a PL e-rated safety relay, with EDM feedback from the main contactor.
• Dual safety relay outputs cut off drive enable and motion hold signals, integrated with the existing emergency stop circuit.
• Manual reset button placed outside the protected area; automatic restart disabled after intrusion clearance.

Control Logic

• PLC received status signals for HMI diagnostics only; safety functions were not implemented in the standard PLC.
• Muting for pallet sections used directional, time-limited logic to allow product passage while blocking personnel and avoiding false triggers.

Stainless frame with quick-release cover for washdown environments

Installation Steps

1. Performed Lockout-Tagout (LOTO) on VFFS, robot units, and conveyors to ensure zero energy.
2. Positioned and drilled stainless steel framework; used spacers to ensure post parallelism within ±1 mm.
3. Routed cables through IP67 conduits, separating OSSD and 24 V lines from motor power cables to prevent interference.
4. Connected OSSD1/2 to the safety relay and linked the main contactor’s auxiliary contacts (13-14) to EDM.
5. Configured parameters: resolution, protective height, restart interlock, fixed blanking (at film-forming area), and muting where needed.
6. Aligned using built-in indicators; retested after washdown to confirm operation in the “green zone” for stability.

Testing and Validation

• Measured worst-case stopping time with a portable tester and updated safety distance labels on the framework.
• Conducted intrusion tests with 14 mm / 30 mm test rods at multiple heights and angles.
• Verified no automatic restart: equipment remained disabled after beam restoration until manual reset.
• Tested EDM by simulating contactor sticking—safety relay rejected reset and triggered an HMI alarm.
• Performed functional tests post-washdown to ensure no false triggers or misalignment.

Results (Six Months Post-Retrofit)

• Recordable Injuries: Reduced from 3 incidents in the prior six months to 0.
• Unplanned Downtime: Decreased by 27% through optimized muting and fixed blanking.
• Changeover Time: Improved by 11% by eliminating the need to remove/install hard guards.

Maintenance Guidelines for Long-Term Reliability

• Daily: Wipe lenses, confirm green light, and perform a quick hand-pass test at shift start.
• Weekly: Inspect mounting brackets, cable strain relief, and EDM logs on the HMI.
• Quarterly: Recheck stopping time, verify safety distances, and retrain operators.

Common Pitfalls Avoided

• Installing Too Close to Hazards: Insufficient reaction time was prevented by calculating safety distances per ISO 13855 with added margins.
• Enabling Automatic Restart: Explicitly disabled, requiring visual inspection and manual reset.
• False Triggers from Reflections: Mitigated by angled installation and adding dark backplates near reflective film paths.

Conclusion

This retrofit transformed a high-risk production line into a safe, reliable asset. DAIDISIKE safety light curtains instantly halt hazardous motion upon human intrusion, replacing reliance on chance with engineered precision.