Safety-system design, standard and technology changes now allow OEMs and end users to boost efficiencies and compliance and be more profitable.
By George Schuster, TÜV Functional Safety Expert and business development manager and Brad Prosak, safety commercial engineer, Rockwell Automation
It happens all the time: Machine safety systems are built to the incorrect safety level and create big problems in production.
Under-designed systems that fall short of the required safety level can put workers at risk. They also can generate big expenses from lost production time, worker-compensation costs and fines. On the other hand, over-designed systems can lead to unnecessarily complex and expensive machines. These machines are more difficult to operate, require more maintenance, may create nuisance trips and take up more space on the plant floor.
So how do machine designers and users make sure that safety systems are specified, designed and built to the proper safety level?
The most important thing they can do is follow the Functional Safety Life Cycle (see illustration) to define and meet their safety performance requirements. As part of this optimization process, they also should be looking for ways to maximize their safety system’s performance to realize additional business value beyond injury reduction or compliance.
Understand the Safety Life Cycle
There’s a recurring theme for why many machine safety systems are built to the incorrect safety level: uncertainty.
Sometimes, end users specify a safety system to the highest possible performance level (PL) because they don’t know what level is required. Or they may request a specific PL in a new machine but don’t know how to verify that the constructed machine achieves it. Many machine builders simply don’t know how to correctly identify, realize or verify the required PL in their offerings.
The Functional Safety Life Cycle can help avoid these problems. It outlines a rigorous, systematic set of processes for assessing, mitigating and verifying machine-safety systems.
This can help confirm machines are designed and built to the proper safety level. And it can help set clear expectations for what’s required in a machine-safety system for both machine designers and end users.
The Functional Safety Life Cycle is defined in the IEC 61508 standard and involves five steps:
- Risk or Safety Assessment: Performing an assessment to identify tasks and hazards and estimate the associated risks while outlining mitigations.
- Functional Requirements: Defining the safety functional requirements that help mitigate the hazards identified in the assessment.
- Design and Verification: Selecting the appropriate safety devices, architecture and monitoring and verifying that the system has achieved the required PL defined in the risk assessment.
- Installation and Validation: Installing the system and validating that mitigation solutions perform as intended under normal and fault conditions.
- Maintain and Improve: Using change management to maintain compliance over the machine’s life.
By following these steps, engineers can design and build safety systems to the right safety level, while avoiding unnecessary cost and complexity.
Consider a machine end user who traditionally has specified that all safety systems be built to a SIL 3/PLe safety level. If that user discovers through risk assessment that a new machine requires only a SIL 2/PLd safety level, the safety system’s cost might be lowered by 25% to 40% with a reduction in control panel size of as much as 40%. Proper design targets can help right-size engineering and contain system costs.
Machine designers and users can use a variety of industry tools to demonstrate system design compliance.
Automated design tools provide a simple, consistent way to design machine safety systems within the safety life cycle. These tools can help engineers select the right safety devices, verify that a safety system meets all requirements and document the process to help achieve compliance.
Pre-engineered safety-function documents also can give engineers guidance for incorporating proven safety functions that include documented functional requirements, equipment bill of materials (BOM), wiring and configuration details, programming examples and PL verification analysis.
Maximize Safety System Performance
The latest smart, scalable and high-performing safety technologies can help machine designers right-size safety systems to the required safety level. But the technologies also can help machine users get more value from their safety systems and the machines under control.
For example, consider a presence-sensing safety function such as a tripped light curtain that de-energizes a machine. In a conservative calculation, the latest high-performing safety controller on the market could reduce the safety function’s response time by as much as 200 ms compared to other controllers in use. Now, a light curtain can be mounted 12 in. closer to a machine while still achieving the required stopping time.
This can take a full step out of an operator’s task when moving in and out of a machine. That might seem like a minor change, but one small step for an operator can be a giant leap for improving productivity. Specifically, taking a step out of a task can reduce an operator’s cycle time by 0.5 sec. and improve operator utilization by as much as 5%. This helps make labor more efficient and lessens the ergonomic load.
A shorter safe stopping distance also can reduce a machine’s footprint. If a light curtain safety function saves 12 in. of floor space and is used at 150 load points in a plant, and each operator load window is 4 ft. wide, that adds up to 600 sq. ft. of space savings. This is floor space that can be put to productive use.
Faster and smarter safety technologies also are helping redefine what modern production can look like, and how people and machinery can interact more productively.
New collaborative applications, for example, use safety systems that allow robots and humans to work nearer to each other. The robots are ideal for taking on heavy-lifting and repetitive tasks and can slow down, change course or come to a stop based on the distance to a human. Smart safety technologies that provide access to safety-system usage data can help manufacturers understand risks better, enhance safety, improve production efficiencies, reduce safety-related downtime and improve compliance.
Safety’s Sea Change
Many people in the industrial world still believe that safety improvements degrade production. But safety-system designs, standards and technologies all are evolving in a way that allows companies to use safety to complement and even improve production.
Machine builders and users increasingly are embracing these changes in thinking and method. Doing so might require a fundamental shift in how safety is viewed — from seeing it as a burdensome requirement to something that can help them meet their business and production goals. And the rewards are worth it: making jobs easier and faster, improving efficiencies and ultimately creating more competitive and profitable operations.
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