Cengiz Özemli
Akademisyen
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## Leuze – Advancements in Machine Safety: Limitations of Muting Applications and Safer Alternatives
In industrial automation, the limitations of muting applications used to ensure uninterrupted material flow and alternative solutions to close the safety gaps arising from these applications are discussed.
Muting temporarily deactivates safety functions in machines and systems, allowing for uninterrupted material entry and exit through protective devices such as light curtains or laser scanners. However, personal safety must be guaranteed in all circumstances. In practice, muting applications sometimes reach their limits, leading to misuse and manipulation. In such cases, alternative safety concepts are needed.
### Unconscious Risks in Muting Applications
In industrial automation, 2-sensor, 4-sensor, time-controlled, or sequence-controlled muting types are used. The international DIN EN IEC 62046 standard regulates the requirements for entry and exit stations where muting is performed. The basic rules are:
- Muting must be activated by at least two independent signals.
- Muting must provide protection against foreseeable faulty operations or manipulations.
However, in the field, applications sometimes do not fully comply with these rules, either because the actual conditions are unknown or because risky compromises are made for high process stability. As a result, safety functions are weakened, the risk of manipulation increases, and serious occupational safety issues arise for operators.
### Hazard 1: Safety Gap Due to Pallet Muting
In automated systems, objects that are difficult for sensors to detect, such as metal cage boxes, can be loaded onto and unloaded from pallets. Gaps in the cage structure prevent sensors from generating stable signals. Therefore, sometimes the pallet is mistakenly used as a muting trigger. This procedure is prohibited because, for example, an empty pallet can disable the protective device.
### Solution with Smart Process Gating (SPG)
To close this type of safety gap, Leuze's Smart Process Gating system is recommended. Here, bridging is done with two independent control signals, eliminating the need for an external muting sensor:
- CS (control signal) from the system control is the first trigger.
- PFI (protective field intrusion) in the light curtain is the second verification signal.
When load-bearing objects enter the protective field, muting is activated by the CS signal sent by the PLC. Objects must be less than 200 mm from the protective field, so another person cannot pass immediately before. When objects enter the area within 4 seconds, the PFI signal prevents a safety shutdown during muting.
### Hazard 2: Safety Gap in Insufficiently Loaded Pallets
If the pallet is partially loaded or the loads are much narrower than the carrier, gaps form at the sides of the pallet during muting. A person can enter the danger zone through this gap, and the safety function may not be activated. According to the standard, the side gap should be a maximum of 200 mm, but in real applications, these gaps are often wider.
### Solution with Access Protection with Dynamic Format Adaptation
This risk is eliminated with access protection with dynamic format adaptation. Two safety laser scanners create a combined, closed vertical protective field. Distance sensors placed at the edges of the conveyor belt or the measuring functions of the laser scanners detect the position and width of the load on the pallet. The system opens an aperture in the protective field to allow the transported material to pass; the sides continue to be protected in accordance with standards. Human or vehicle access is safely detected. This solution provides Performance Level d according to EN ISO 13849-1 standard.
### Hazard 3: Safety Gap Due to Forklift Muting
Two induction loops or ultrasonic sensors detect the entry of the forklift and muting is initiated, deactivating the safety function of the light barrier. However, according to the draft standard DIN EN 415-4, this method is not acceptable. This is because a person might assume the machine is safe and enter the danger zone.
### Solution with Sequential Restart
This safety solution stops all hazardous movements when the light curtain is violated. When the forklift leaves the danger zone, specially positioned induction loops generate a sequential signal, and the system automatically restarts. If a floor sensor cannot be installed, movement can also be monitored with radar sensors. This method complies with EN ISO 13849-1 standard, ensuring safety with Performance Level d.
### Muting Limitations and Alternative Solutions
Muting distinguishes between objects and people, enabling automation and efficiency, but it always requires protection against faulty operations and the risk of manipulation. The risk increases especially when muting sensors cannot reliably detect the transported load or when the load width varies greatly at the sides. Forklift muting is generally not considered current safety technology. In these situations, danger zones are accessible and risky. Leuze offers safe solutions that comply with standards, with comprehensive support from planning to validation.
### Leuze's Safe Solution Path
The solution begins with the customer's specific requirements. After a risk analysis, the safety designer develops application-specific safety functions. The engineering team integrates, programs, and tests the appropriate hardware and sensors. The dual-check principle ensures safe application. After functional tests and field validation, it is delivered to the customer with CE conformity documents.
This structure offers three main advantages:
- Simplified operation: Functional safety can be complex; it is simplified with Leuze's expertise.
- Safety: All solutions are fully compliant with standards and documented.
- Efficiency: Functional safety guarantees uninterrupted, economical operation.
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