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Robot Safety Begins with the Design Process

by Stacy Kelly , Safety Systems Product Manager
SICK, Inc.

To realize the many benefits that robots offer a production facility, safety considerations are THE top priority in protecting the operator, maintenance personnel and other personnel that interact with the robot.  These safeguards should be designed into and around the robotic cell early in the design process to maximize the inherent safety of the overall system.  Beyond the safeguarding products, the planning and implementation of these products are of critical importance for good safeguarding practices and factor heavily into optimizing system design and cost.  What are the potential hazards of the robotic cell?  What safeguarding technologies are available?  How do I keep out unnecessary personnel, yet protect necessary personnel?  How much panel space must be used for relays?  How difficult or easy will the troubleshooting of the system be?  And, of course, what is the overall reliability and safety of the system?

Risk Assessment
The first step in designing a safe robot system is to understand the hazards that exist in the system.  This is commonly achieved through a formal risk assessment process that identifies and documents all production and non-production tasks and the hazards associated with them.  The hazards are then classified based on the criteria, such as the severity, the potential injury, frequency of access to the hazard and the possibility of avoidance.  Risk assessments should be performed during the design phase and prior to the commissioning to ensure that no new hazards have arisen in the integration process. 1

Safeguarding Technology – Availability and Implementation
System designers must understand the current safeguarding technology and how this technology will save them time and money, both now and in the future.  For example, the capabilities and size of the safety relays will dictate the amount of panel space that will be needed for wiring and relays.  Availability of safety bus technologies will also have serious impact on the design and implementation.  Optimizing this system will also provide flexibility for future expansion and minimize troubleshooting.

System designers must then know how to properly apply the safeguards.  For instance, designers must understand safety distance, or the distance from a hazard the safeguard must be mounted to ensure the hazard will cease to exist before personnel can reach it.  These calculations should be done at the initial commissioning of the system and periodically thereafter to ensure that the safety distance has not changed due to mechanical wear or other changes in the system.

Perimeter Guarding
To keep unnecessary personnel out of the restricted space of a robot cell, one of two safeguarding methods are often used.  Hard-guarding is a fencing-type solution.  With hard-guards, door access will likely be needed, and these doors must contain interlocking devices (e.g. safety interlocks) to guarantee safe access.  Optical perimeter guards (e.g. light curtains) are a more flexible solution that can easily adapt to layout changes.  These guards must be located at a safe distance from the hazard and must interface with the robotic control system.2  Optical perimeter guards are often used in combination with hard-guards.  An additional requirement for either perimeter solution is that the operator control, such as a system reset, be located outside the safeguarded area. 2

Protection on the Inside
If there is a danger to the operator, maintenance personnel or other personnel from robotic motion within the restricted or operating space, this area must also be safeguarded. Area safety scanners are often used in these areas, as the scanner coverage area is wider and more flexibly programmed than with other devices.  Light curtains have also been used.  Again, these safeguarding devices must be located at a distance that provides adequate stopping time of the system and accounts for the speed of approach from the personnel in the area as well as a depth penetration factor, as defined in the ANSI/RIA R15.06-1999 standard. 2

The Solution
How should a company ensure that it has a reliable and safe robot system?  Good planning, proper installation and ongoing support are paramount.  Some companies may decide to develop this expertise internally, while others turn to outside safety consultants and manufacturers of safeguarding systems.  Safety consultants and manufacturers would certainly be in a better position to keep up with the rapidly changing technologies and industry standards.  Either way, the goals of a safe and productive environment are better achieved when considered together.

Stacy Kelly is a Safety Systems Product Manager at SICK, an RIA member company since 1988. 

1 Above are summarizations from ANSI/RIA R15.06-1999, Section 9.
2 Above are summarizations from ANSI/RIA R15.06-1999, Section 11.

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