A Mobile Robot should be safe, not colliding against people or goods as a result of potential failures. In order to ensure this is possible, Safety Systems should be able to control the movement of the Mobile Robot even if the Main System fails. A Safety System may allow the Main System to try to avoid an obstacle, but if the Mobile Robot gets dangerously close to the obstacle, the Safety System may stop directly the motors, overriding the control from the Main System, although informing to it.
This short post gives a quick overview of what are Safety Systems for Mobile Robots and why they are so important.
Safety Standards
In order to make the Mobile Robot system safe, there are some safety standards. To comply with these safety standards, Mobile Robots must include some safety sensors and devices to avoid and prevent risks
AGVs (Automated Guided Vehicle) are a specific set of Mobile Robots for Industry, able to perform specific tasks usually critical for production. This kind of Mobile Robots have very specific mandatory standards to follow:
- AGV safety standards in the USA are defined by ANSI B56.5 - 2012, Safety Standard for Driverless, Automatic Guided Industrial Vehicles and Automated Functions of Manned Industrial Vehicles.
- AGV safety standards in Europe are found in EN1525: 1997 “Safety of industrial trucks – Driverless trucks and their systems”
While both safety standards are important, there are gaps that fail to cover some of the latest technology. As mobile robots become more autonomous, correct their path while in motion, and gain new features and functions such as robotic arms, new safety standards are required. One of the most promising safety standards for new technologies in Mobile Robotics is ANSI/RIA 15.08 – Safety Standard for Industrial Mobile Robots and Mobile Manipulators – (in progress)
Safety Devices
A safety system as defined in the safety standards mentioned may require one or more safety elements. Typical Mobile Robots Safety devices are:
- Safety Laser scanner
- Contact Bumpers for stopping Mobile Robots (Quite uncommon nowadays)
- Emergency Stop Buttons
- Safety PLC
The different safety devices could be used together, usually controlled by a Safety PLC, as it is shown in the following image of a typical Mobile Robot safety system: Two safety laser scanners, two safety stop buttons, motor encoder and motor brake, all connected to a Safety PLC. In this kind of system, the safety PLC could know the speed of the Mobile Robot and activate different laser detection fields. Also, could stop the Mobile Robot activating the motor brake in case an emergency stop button or in case the laser scanner detect an object in the protective field. Usually Safety PLCs are connected to other systems that control the kinematics and behavior of the Mobile Robot. This other system could reduce the speed of the Mobile Robot in case the laser scanner detects an object in the warning field, so the Safety PLC informs this other system in such case.
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| Typical integration of safety system in a Mobile Robot. Source: Sick AG |
This post just gives a general overview of Safety Systems. If you want more information about Safety Systems implementation, I would recomend you to read the thirteen pages document "Safety Systems for Mobile Robots" I prepared.
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Reference:
- AGV Network. Understanding AGV Safety Systems
- Robot Safety Standards for Industrial Mobile Robots. RIA, Robotics Industries Association. 2017.
- EN 1525
- ANSI B56.5
- EN ISO 13855
- S300 Safety laser scanner operating instructions. SICK AG.
- Keyence. Safety Laser Scanner SZ Series Manual
- What Are Safety PLCs. Huffman Engineering. 2017.
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