Safety Devices for Robot Cells: Key Components and Their Role in Achieving Performance Levels (PL)
Safety is a critical consideration when designing robot cells, especially as the integration of robotics into industrial processes continues to increase. Ensuring that robot cells are equipped with the right safety devices is essential not only for the protection of human workers but also for compliance with international safety standards. Safety devices such as safety sensors, emergency stop systems, light curtains, and guarding systems work together to ensure that the robot cell operates safely and minimizes the risk of accidents.
In this article, we will explore the key safety devices used in robot cells, their role in achieving the required Performance Level (PL), and how they contribute to meeting ISO 13849-1 and IEC 62061 requirements. Understanding the role of each safety device and how they interact within the robot cell’s safety system is crucial for both designing safe systems and ensuring compliance with safety regulations.
What Are Safety Devices in Robot Cells?
Safety devices are components integrated into a robot cell’s control system to monitor, detect, and react to hazardous situations. These devices are designed to protect workers by either stopping the robot's movement when an unsafe condition is detected or by preventing access to hazardous areas.
Key Types of Safety Devices in robot cells include:
Safety Sensors (e.g., Light Curtains and Proximity Sensors)
Emergency Stop Devices (e.g., Emergency Stop Buttons and Pull Cords)
Safety Interlocks
Guarding Systems (e.g., Safety Gates and Fences)
Safety Mat Systems
Each of these devices contributes to the overall Performance Level (PL) by enhancing the robot cell's ability to mitigate risks and prevent accidents. Let’s examine each device in detail.
1. Safety Sensors: Light Curtains and Proximity Sensors
Safety sensors are critical components in ensuring the protection of workers from the moving parts of a robot. These sensors can detect the presence of a worker or an object within the robot's workspace and trigger an emergency stop or safety shutdown.
Light Curtains
Light curtains are optical sensors consisting of multiple beams of light, which are placed across the perimeter of a robot’s working area. If a beam is broken (i.e., if a worker enters the dangerous zone), the light curtain sends a signal to the control system to stop the robot immediately.
Key Role in Performance Level (PL):
Redundancy: Light curtains typically use dual channels for higher reliability, improving fault detection and ensuring that the robot stops when a person or object is detected.
Category 3 or 4: Depending on the system design, light curtains can achieve Category 3 or Category 4 systems (as defined in ISO 13849-1), which support higher PL levels due to their ability to detect faults and failures effectively.
Proximity Sensors
Proximity sensors detect objects or workers within a specified range of the robot. They are commonly used to create safety zones around the robot, ensuring that the robot’s motion stops if a worker enters these zones.
Key Role in Performance Level (PL):
Proximity sensors can contribute to higher PL by offering diagnostic coverage and fail-safe mechanisms that ensure the system reacts quickly when a worker is detected within a dangerous area.
2. Emergency Stop Devices: Emergency Stop Buttons and Pull Cords
Emergency stop devices are critical safety components that allow operators to stop the robot or other machinery in case of an emergency. These devices are manually activated, providing a last line of defense in preventing injury or damage.
Emergency Stop Buttons
Emergency stop buttons are located around the robot cell, easily accessible to workers. When pressed, these buttons immediately cut power to the robot, halting any movement.
Key Role in Performance Level (PL):
Redundancy: Emergency stop buttons are often part of a redundant circuit, ensuring that even if one part of the system fails, there is still another pathway to stop the robot.
Category 3 or 4: Depending on their integration, emergency stop systems can help achieve Category 3 or Category 4, providing high reliability for worker safety.
Pull Cords
Pull cords are a type of emergency stop mechanism that is commonly used in robot cells where workers may need to stop the robot from a distance. These cords are placed around the perimeter of the robot cell, and pulling the cord immediately triggers the emergency stop sequence.
Key Role in Performance Level (PL):
Pull cords provide a redundant mechanism to ensure that the robot will stop in case of an emergency, contributing to a higher PL for the system.
3. Safety Interlocks
Safety interlocks are devices that prevent the robot from operating when a safety barrier (such as a gate or door) is opened. These devices are crucial for preventing access to hazardous areas while the robot is in operation.
How Safety Interlocks Work
Safety interlocks are typically mechanical or electronic locks connected to safety doors or gates. If a door or gate is opened, the interlock disables the robot’s operation until the door is securely closed again.
Key Role in Performance Level (PL):
Redundancy and Reliability: Interlocks often use dual-channel systems to ensure that a single failure does not result in a hazard, thereby increasing the reliability of the safety system.
Category 4: Well-designed interlocks can achieve Category 4, offering maximum protection with no single point of failure.
4. Guarding Systems: Safety Gates and Fences
Guarding systems, such as safety gates and fences, create physical barriers that prevent workers from entering the robot cell during operation. These barriers are a fundamental safety feature, as they ensure that workers remain outside of hazardous zones.
How Guarding Systems Work
Safety Gates: Safety gates are equipped with electrical interlocks that disable the robot’s movement when the gate is opened. These gates may also feature light curtains to detect if a worker is attempting to bypass the gate.
Safety Fences: Safety fences prevent unauthorized access to the robot cell. These fences may also be equipped with proximity sensors or light curtains to monitor whether workers are too close to the robot.
Key Role in Performance Level (PL):
Redundancy: Guarding systems with interlocks and safety devices ensure maximum safety by combining physical barriers with electrical shutdowns.
Category 4: With the integration of light curtains and dual-channel safety devices, these systems can achieve Category 4, ensuring high diagnostic coverage and reliability.
5. Safety Mat Systems
Safety mats are placed on the floor around robot cells, and they detect when a worker steps on them. If the mat is triggered, it sends a signal to the robot's control system to stop the robot immediately.
How Safety Mats Work
When a person steps on the mat, it completes a circuit, sending a signal to the robot’s control system. This causes the robot to stop to avoid injury to the worker.
Key Role in Performance Level (PL):
Redundancy: Safety mats are often designed with redundant sensors to ensure that a failure in one sensor does not compromise safety. This helps achieve a higher PL.
Category 3: When integrated with other safety devices, safety mats can contribute to achieving Category 3 systems.
Integrating Safety Devices to Achieve Required PL
Achieving the required Performance Level (PL) for a robot cell is not solely dependent on individual safety devices. The architecture of the entire system, the redundancy of safety circuits, and the interconnection between safety devices all play a crucial role in determining the PL.
To achieve a high PL, robot cells need to integrate multiple safety devices, ensuring that no single point of failure can jeopardize worker safety. By choosing the right combination of light curtains, safety sensors, emergency stops, safety interlocks, guarding systems, and safety mats, manufacturers can design a robot cell that offers both high reliability and compliance with international safety standards.
Conclusion: The Vital Role of Safety Devices in Achieving Performance Levels
In robot cells, safety devices are not just accessories—they are the foundation of a system’s ability to meet the required Performance Level (PL) and mitigate risks. Understanding the role and capabilities of each safety device, as well as how to integrate them effectively, is crucial for creating safe and compliant automated systems.
By ensuring that robot cells are equipped with the appropriate safety devices and that these devices are integrated in accordance with ISO 13849-1 and IEC 62061, manufacturers can create safer working environments, reduce accidents, and maintain compliance with industry standards.
Citations:
ISO 13849-1: Safety of machinery—Safety-related parts of control systems—Part 1: General principles for design.
IEC 62061: Safety of machinery—Functional safety of safety-related electrical, electronic, and programmable electronic control systems.
ANSI/RIA R15.06: Industrial Robots and Robot Systems – Safety Requirements.
