Machine & Operator Safety
Design your safety system for improved uptime
By Chris Brogli
By Chris Brogli
Sept. 29, 2014 – It’s a belief that has persisted for decades — safety and productivity are squarely at odds with each other in the manufacturing environment. Safety has traditionally been associated with compliance, while productivity has been associated with competitiveness — both with separate, sometimes competing, paths to meet their individual goals.
Top-performing manufacturers, however, are showing this age-old notion the door with their use of contemporary approaches to safety. These leaders are using a combination of integrated safety solutions and standards to optimize machinery uptime. Simply put, safety is no longer just about safety; it’s also about minimizing the safety-related downtime events that hinder productivity.
The key is to expect safety events, and to utilize safety technologies that can minimize the length of those events. This begins in the design stage.
Designing safety into your machinery upfront, with an architectural view rather than a bolt-on solution, can result in a more holistic system that can be optimized for faster recovery. Understanding the standards that apply to various machinery designs — and when they make allowances for the latest safety technologies — is also crucial.
Safety and productivity: The new normal
The advent of integrated safety — technologies that connect and/or combine your safety and standard control systems — has opened new doors to productivity. Integrated safety helps ensure your safety system has a far lower impact on productivity by improving machinery availability, reducing mean time to repair (MTTR), and streamlining maintenance.
Integrated safety is at the core of what’s known as a design-for-recovery strategy, which requires that you treat safety events as expected events and design your machinery to recover as quickly as possible. That recovered downtime translates to more production time, which accumulates and can add up to significant profit improvements.
Consider a typical lockout/tagout downtime event: A safety system that is designed for recovery can speed up or perhaps eliminate some of the processes within a lockout/tagout event. Consider an improvement of just one minute to an entire lockout/tagout process that averages 12 minutes. If the production value per minute equals $1,000, and you have an average of eight downtime events per day in 350 production days per year, your savings would amount to $2.8 million annually.
Here’s how to realize these savings:
1. Lockout/Tagout: Minor service exceptions
Canadian standards require lockout/tagout during machinery servicing to prevent unexpected startup or release of stored energy that could cause injury. That often means performing the exhaustive lockout/tagout process several times per day for servicing events.
The standards, however, provide exceptions for minor tool adjustments and other minor servicing activities. Guidance for developing safety systems for these alternative measures is available in the standard CSA Z460.
The minor service exception should never be used as a safety workaround that seeks to improve productivity at the expense of safety. Plan to conduct a risk assessment, document the reliability of your alternative measure, and train your employees.
If used according to the letter and intent of the standards, alternative measures can provide significant productivity gains.
2. Safe speed
Machinery servicing functions can be dangerous if they’re carried out when machinery is operating, but they’re also time consuming when machinery must be shut down. Because of this, plant floor personnel will too often find a workaround to a machinery safeguard and service the machinery while it’s running in an effort to save time — a recipe for disaster.
A safe-speed monitor device, part of your safety motion control system, allows you to bring machinery to a safe speed so operators can carry out tasks without completely stopping the machinery.
In some instances, a worker may need to interact with machinery, and safe speed can keep production running while this happens. In other instances, safe speed can help speed up tasks that might take longer if the machinery must go through the lockout/tagout cycle several times.
Safe-speed technology can be deployed through a dedicated speed-monitoring relay or embedded into drives and control modules with no need for additional wiring, making it easy to implement.
3. Zone control
Similar to safe speed, zone control maintains worker safety while limiting machinery downtime to help optimize productivity.
Using zone control, a specific area of your production process can stop or slow down while other zones continue to run at normal speed. This allows operators to safely enter a zone to carry out tasks while the rest of your production processes continue as normal.
The safety control system is responsible for providing protection for workers within the different zones, and interfacing between the different zones.
A simple and low-cost safety relay architecture can suffice for two- or three-zone machinery configurations. For larger, more sophisticated configurations, a safety PAC should be used to ease implementation and recovery.
Like any other part of machinery, safety systems are subject to wiring faults, open gates or other machinery events that require maintenance or repairs and lead to downtime. When these events occur, they can send operators into a scurry trying to fix the machinery and identify the root of the problem.
Diagnostics play a critical role in your design-for-recovery strategy. Controlled from a safety PAC, distributed safety I/O modules can be located on the machinery close to sensors and actuators. These modules do more than ensure safety functions are operating correctly; they also pinpoint the source of a stoppage on your safety system and more quickly guide technicians to an effective restart.
The best approach to integrating safety systems for faster recovery is to connect each individual gate interlock to the safety logic device. This allows safety logic devices to communicate critical detailed information to the machinery control system so operators can stay informed of diagnostics within the safety circuit.
A safer future
When you look at where manufacturing is headed — specifically with people and machinery working together in increasingly collaborative ways — the use of integrated safety is only becoming more important. Ultimately, designing your machinery for the fastest possible recovery using contemporary safety technologies will translate to greater productivity and a stronger bottom line.
Chris Brogli is the global business development manager for safety at Rockwell Automation. He has 27 years of experience in electrical engineering, industrial automation and manufacturing.
This column originally appeared in the September 2014 issue of Manufacturing AUTOMATION.