Light Barrier (Safety Light Curtain): Working Principle, Types & Machine Guarding Guide

First, the introduction: what is categorized at type 2 and category 4 safety levels

It also refers to the process of using the guide in light curtain principle of work, but it is a one-off.

In industrial safety, classification level of type 2 (Category 2) and type 4 (Category 4) safety light curtains based on international IEC 61496-1/-2. Technical-wise, Type 2 is directly related with the DC output of the PLC for single output; however, Type 4 needs dual-channel outputs, including dual npn or dual pnp and is implemented in conjunction with a safety relay module. Based on the appearance of the shell, the light curtain for category 2 will seem thin. Usually there is a blind spot at the top, we take the JER light synchronisation this, look at it visually, these 2 values are blind when P + 12 and J + 12 taken together, we can see this, these 2 values are blind, light curtain cannot protect the place. Like H is the effective protection height, this area is the effective protection range.

Next, 4 types of light curtains are like DQT4 this kind of a models, this whole surface can take up the protective surface, the safety factor is a very high.

Secondly, the principle of operation of grating (safety light curtain): from infrared emission to milliseconds in time stop (response time length)

the grating protection capability originates from the ‘launch - receive - control’ closed-loop system, the essential mechanism can be divided into crucial components as follows:

1. The infrared beam matrix ensures the grating by transmitter and receiver is symmetrically placed on both sides of the hazardous area, the transmitter to 20-50kHz frequency emission modulated infrared beam (850nm near infrared invisible light), the formation of a density of up to 14–40mm with respect to the beam matrix, complete coverage of the protection area.
2. Real-time signal verification receiver real-time receives the beam synchronously through a high-sensitivity PIN photodiode, carries out full-beam scan every 1ms, identifies only the matching coded infrared signals, and effectively filters out sunlight, factory lighting and other stray light interference.
3. Intrusion Signal Detection Human body (finger, arm) or foreign objects entering the protection area and blocking 1 or more beams causes the receiver to detect the signal interruption in 1μs and sends the ‘blocking event’ to the controller.
4. Millisecond safety stop Industrial MCU controller activates the OSSD safety output within ≤10 ms, stops the controlled apparatus’s power source, and immediately stops the moving parts within the inertia range (e.g., braking of the press slider in the braking time ≤50 ms).
5. Reset recovery mechanism after the intrusion of the object and to remove the object from the system, the receiver to reclaim the complete beam, the manual / automated reset to confirm the safe state, the controller will restore the OSSD output, the equipment can be restarted.

Third, the grating (the safety light curtain) between the core types

Based on the safety level to ensure the safety level and protection needs

1. As for the professional view, according to the safety level (IEC 61496 standard) in order to explain the two kinds
   • Type 2 grating has single channel design, no redundancy self-test function, suitable for very low-risk cases (like small conveyor belt), economic costs are great but only limited fault tolerance is possible.
   • Type 4 encoder: dual channel redundant design, all core circuit and optical equipment are dual channels, every 10 ms to accomplish a full-system self-test and even if a single point of failure can still maintain the press protection, robots, automation equipment and other high-risk equipment must be selected.
2. In proportion with detection potential (resolution)
   • finger protection type (10,14mm resolution): beam-distance ≤ 14mm, can detect fingers and other small parts, suitable for precision machine tool protection, precision instrument protection.
   • Hand protection type (20, 25, 30mm resolution): Suitable for typical hand protection scenes including injection moulding machines, packaging machines and spring automation equipment.
   • body protection type (40, 80, 200mm resolution or higher): for full body protection or for large equipment peripheral isolation such as AGV trolley travelling path.
3. Based on the environmental flexibility
   • waterproof/dustproof type (IP65/IP67/IP68): sealed structure design, best for dusty and humid food processing, lithium fabrication facility.
   • Light Intrusion Resistance capability: In the presence of pulse code modulation technology, a 100,000 lux direct sunlight can be resisted and used in outdoor or high brightness scenes.

Fourth, the grating (safety light curtain) machine protection scene: from stamping to logistics of the whole industry coverage

1. Safety of metal processing machines Protection in punching machines, shearing machines, bending machines and other equipment, Type 4 grating is in the real-time monitoring of the location of operator hands, helps in the prevention of accidental action caused by extrusion, cutting accident, without altering the replacement of mold and the delivery of material.
2. Industrial robot work area protection grating enclosing the robot movement range, when personnel mistakenly enter the work area immediate trigger a shutdown, to protect the safety of human-robot collaboration, especially for automotive welding, electronic assembly and other scenes. Automated production line protection on conveyor belt, packaging machine, injection moulding machine material import and export, and grating can identify the human body invasion and material through the difference, only to the personnel triggered by shutdowns, enhance efficiency of production. If automated and automated loading and unloading AGV equipment in warehouse logistics equipment protection to place grating in vehicles, we can avoid the hazard of the collision between personnel and vehicles, suitable for heavy traffic logistics case.

Fifth, grating (safety light curtain) selection and install guide: so as to counter common misconceptions

1. Selection of core parameters
   • protection height: per the height of equipment hazard area chosen (typically 300 mm-1800 mm), such as punching presses, upper and lower mould travel range should be covered.
   • Protection distance: 0.5-20m conventional, long distance models up to 50m are recommended, should be compatible with the width of the equipment and installation environment.
   • Response time: In order to ensure that the shutdown event takes place before the human body interacts with the hazardous point, we recommend selecting high-risk equipment within ≤10ms.
   • Certification: Select products with CE, TUV, SIL/PL certificates to comply with international safety standards.
2. Installation Key Points
   • Precision alignment: Alignment of transmitter and receiver deviation ≤±0.5°, can be fitted via laser alignment, or
   • Safety distance calculation: Determine the safety distance according to braking behavior of the apparatus (safety distance = Response time × maximum speed of equipment + buffer distance), avoiding the personnel touching the risky point before the machine stops.
   • Anti-interference arrangement: Do not let it interfere with strong direct lights or reflection, and if needed, add a light shield; next to grating to use different frequency encoding to avoid cross-interference.

VI. Typical Troubleshooting and Maintenance Specifications

1. Troubleshooting
   • False Trigger: Verify whether filter lens is dusty, poorly installed or noisy light/vibration interference; you may choose the size threshold through the ‘Material Exemption Function’, to minimise the misjudgment.
   • Beam Interruption Alarm: Calibrate transmitter and receiver alignment, verify power supply stability (needs 12-30V DC regulated power supply).
   • OSSD Output Incorrect: Verify the redundant channels function by testing controller circuit and wiring.
2. Maintenance Recommendations
   • Once a month, clean lenses to test beam smoothness.
   • Perform quarterly functional tests to check the downtime response time.
   • Record a fault log to conduct periodic faults assessments to detect issues such as loose wiring and light source attenuation. If there is broken wiring or a loose interface, it must be addressed immediately in order to avoid the short circuit.

VII. Conclusion: technology-based safety, efficiency and balancing protection

The fundamental reason why those light barriers (safety light curtains) have such value is to break free from the limitations of the physical fence, to attain the ‘safety and efficiency’ of double guarantee. A local brand that has been around for over 20 years in the sensor area, DAIDISIKE Type 4 light barriers enjoy IP67 protection, 10ms response time and can be applied in stamping, robotics, logistics and other industries. For tailored protection or free of cost selection, reach out to our professional technical team to turn encoders into an ‘invisible umbrella’ for industrial production. Understanding the difference between class 2 light curtains and class 4 light curtains and different application environments, the future for their own equipment selection model will not take a detour. Here is the light curtain factory application environment showing, I hope that you know the light curtain better.