Integrating Safety into Automation: Implications and Considerations for Safety Engineers
October 16, 2013
Designing a Safe Machine is Easy – Right?
Designing a machine to be safe can be quite easy for an engineer; simply build a metal box around the hazards and never allow access to any part of the operation. Unfortunately, every engineer knows this can be a huge nightmare for efficiency and productivity. The next logical thought in improving efficiency would be to start replacing pieces of this proverbial “box” with newer electrical, mechanical, and programmable machine safety devices. This would allow you as an engineer to do what you do best; use your experience and creativity to design the functionally ideal solution.
As long as you use safety-rated devices everything is still safe, right?
Not so fast….
Advancements in Machine Safety = Integrated, Safer, More Productive Manufacturing Processes
Traditional safety circuits are hierarchically at the top of any machine’s control scheme, basically either allowing a machine to run normally or abruptly removing all power to all devices which can create a machine safety hazard. With only these two extreme choices available, there weren’t many options for designing safety systems, until recently…
In the past couple of years, much advancement has been made in safety input devices (e.g. laser scanners, safety cameras, RFID key access systems, etc. ) and embedding safety technology in traditional logic (e.g. PLCs) and traditional motion (e.g. Servos). Now safety is not just a separate system, but highly integrated into the functionality of each and every unique manufacturing process.
By properly taking advantage of this technology you can not only make the machine safer, but improve manufacturing productivity.
Engineering Improvements through Safety Technological Advancements
From an engineering standpoint, these technologies can create many improvements:
- Reduced wiring
- Decreased component count
- Allowing for smaller control panels
- Increased longevity of electro-mechanical devices
- Increased diagnostics for easier troubleshooting of safety systems
Operations Improvements through Safety Technological Advancements
From a production standpoint, machine down time can be minimized by slowing a machine down to a safe speed or even “pausing” a machine as opposed to just completely removing power. This can avoid re-homing of robotics and re-synchronization of coupled axis, reducing start-up time from minutes to seconds.
Understanding New Machine Safety Standards
Prior to recent international safety standards, there has been a reluctance to accept newer programmable safety devices as reliable. In fact, antiquated safety standards made it difficult to demonstrate compliance if you tried to use these new devices. Single-function hard-wired safety devices have been easy for everyone to understand and simple to properly implement, therefore, staying the standard for machine safeguarding for far too long. Understanding a few key safety standards and how they relate to new technologies can give you the confidence and flexibility to design the best possible safeguarding solution for your application.
ISO 13849-1 Design Principles for Safety-Related Parts of Control
Lets start with ISO 13849-1, which in 2010 officially replaced the long standing “Safety Categories” with “Performance Levels.” This standard had a major overhaul in conventional methods, essentially giving you the capability to design more advanced safety functions. This is mainly accomplished by requiring safeguard manufactures to provide reliability data on every product, giving you the ability to determine the reliability of your overall safety system. In addition, this means you can get “credit” for using non-safety rated devices (e.g proximity sensors, heat sensors, camera systems, etc. ) in your safety system. Components of performance levels:
- Mean Time to a Dangerous Failure (MTTFd)
- Common-Cause Failures (CCF)
- Diagnostic Coverage
- System Structure (Categories)
IEC 61508-5-2 Functional Safety Requirements for Adjustable Speed Electrical Power Drive Systems
IEC 61800-5-2 is an international safety standard which defines safety functions for adjustable speed electrical power drive systems. There are roughly 20 defined safety functions established in this standard, however, not all of them have been developed by drive manufactures yet. Stay tuned, because this gives us a glimpse into the future of safety technology. Safe Braking and Holding (SBS) is probably the most unique, providing fall protection for axes with gravity loads. Typically this is accomplished by independent brakes separately controlled and monitored by redundant, diverse channels in the drive. Imagine the impact on the culture of a company to now safely be able to hold a load over someone’s head. Examples of popular integrated safety functions:
- Safe Torque Off (STO)
- Safe Stop 1 (SS1)
- Safe Stop 2 (SS2)
- Safe Operating Stop (SOS)
- Safety-Limited Acceleration (SLA)
- Safe Acceleration Range (SAR)
- Safety-Limited Speed (SLS)
- Safe Speed Range (SSR)
- Safe Speed Monitor (SSM)
- Safe Brake Control (SBC)
ANSI/RIA R15.06 Safety Requirements for Industrial Robots and Robot Systems
The new 2012 edition of the Robot Safety Standard, ANSI/RIA R15.06, has also made major improvements in integrating safety technology. This new revision identifies four requirements for collaborative robot operation, which allow humans to be in the vicinity of an operating robot without safety enclosures:
- Safety-Rated Monitored Stop,
- Hand Guiding,
- Speed and Separation Monitoring,
- Power and Force Limiting.
In addition, TS 15066 is a supplemental guideline currently being developed to provide assistance for the setup of human-robot-collaboration and the appropriate risk assessment procedures.
Designing Machine Guarding with New Technologies and Caution
As engineers put on their thinking caps and start designing safeguarding schemes with these new technologies, remember to proceed with caution. The last thing any company wants to do is make a machine seemly “look safe” when it is actually quite dangerous. As exciting as these new machine safety technologies are, make sure your company has a full understanding of their proper use and associated design requirements.