Exploring the updated safety standard for integrated manufacturing systems

As automation and manufacturing systems continue to advance in various industries to keep up with emerging trends, the safety of those who work on or near these systems remains a critical issue. A newly updated standard is now available to help industry stay updated on guidelines, trends, and requirements related to worker safety, ANSI B11.20-2017 – Safety Requirements for Integrated Manufacturing Systems.

With the convergence of Industrie 4.0, the Industrial Internet of Things (IIoT), smart manufacturing, and new automation technologies (such as power and force limited robots and servo-drive equipment), mass customization will drive the next generation of flexible, on-demand manufacturing. At the core of this paradigm in industries are integrated manufacturing systems (IMS).

An IMS is defined as a system which: 

• Incorporates two or more industrial machines that:
  • Can operate independently of each other, and
  • Are intended for the purpose of manufacturing, treatment, movement or packaging of discrete parts or assemblies;
• Linked by a material handling system; and
• Interconnected by a control system(s) for coordinated operation.

An IMS is most often associated with robot systems because robots are frequently combined into a cell with at least one other machine (see Figure 1). However, a system does not require a robot for the system to be classified as an IMS. 

Safety standards

As existing IMSs are continually updated and additional systems are introduced to keep up with market demands, the safety of people working on or around an IMS is paramount. ANSI B11.20-2017 is designed to address potential safety concerns and help achieve a safe work environment. This standard has been updated to a third edition, which was approved on Sept. 12, 2017, and is the U.S. equivalent of ISO 11161: Safety of machinery – Integrated manufacturing systems – Basic requirements, which has been harmonized in Europe since 2007. It is important to note that this standard will most likely begin a new (third) revision starting in April 2018.

ANSI B11.20 was the first document to address complex automation systems’ safety resulting from integrating individual machines into a larger coordinated system. The first edition of ANSI B11.20 was published in 1991, followed by its European equivalent, ISO 11161, in 1994. The next revision cycle for ANSI B11.20 was concluded in 2004; ISO 11161 was updated in 2011. The 2017 edition of B11.20 addresses current industry best practices applicable to an IMS which have been developed and refined over the past quarter century.

The purpose of ANSI B11.20 is to guide suppliers, users, modifiers, and personnel working on or near an IMS. Each IMS can differ in size and complexity and can incorporate different technologies that require diverse expertise and knowledge.

An IMS should be considered as a new and different machine rather than the sum of its combined parts. Hazards are frequently unique to a particular IMS. The number and types of hazards are directly related to the nature of the automation process and the complexity of the installation. The risks associated with these hazards vary with the type of machinery used, their purpose, and the way in which they are installed, programmed, operated, and maintained.

Combining individual machines intended by the supplier to operate independently into an IMS for coordinated operation typically introduces new or additional hazards not foreseen by each original equipment manufacturer (OEM). This standard only addresses the safety aspects important for the safety-relevant interconnection of the machinery and equipment. In other words, there may also be existing machine-specific standards to provide guidance to reduce risks associated with each component machine and the unique hazards they present. 

Partitioning complex automation systems into control zones

In the 2017 edition, the standard now further emphasizes a process called "layout analysis." This process is similar to-and can be incorporated into-a risk assessment, and is recommended to create individual zones within a larger system. Protecting personnel within these zones often requires flexible presence sensing technologies and safety-related logic systems to determine when hazardous conditions are (or are not) permitted within specific zones.

The biggest benefit of partitioning an IMS into smaller control zones is to allow workers access to certain portions of the automation system in a safe condition while still allowing other sections to remain in motion, such as in production mode. This helps maximize productivity and throughput of the system; any modifications required (e.g. maintenance, change over, set-up, etc.) to individual component machines do not require the entire system to be shut down (See Figure 2).

To determine control zones within the system, the layout analysis process consists of the following steps: 

• Specify the limits of the machine(s) and/or system
• Identify task/hazard pairs from a risk assessment
• Identify task zone(s) and/or control zone(s)
• Select risk reduction measures
• Identify span(s) of control of safety-related control devices.

Additionally, the layout analysis process is an iterative process that can be repeated as part of risk reduction, and can result in one or more of the following: 

• Modify the layout, the IMS functionality, or IMS limits
• Modify or add new special modes of operation
• Change or modify equipment to suppress or modify tasks
• Determine new access means
• Modify how tasks are performed.

The layout analysis is complete when the acceptable residual risk and IMS functionality have been achieved.

ANSI B11.20-2017 thoroughly explains the layout analysis process and provides detailed examples of the process in use in a dedicated 30-page annex.

Special operating modes

A decision process is also presented for determining when any additional "special" modes are required to operate equipment within an IMS that are not necessary when the equipment is operated independently or in a typical manner foreseen by the equipment supplier. The concept for "special mode" has been around in some form for a decade. When first introduced, this concept was called "process observation" and has since been included in the current safety standard for industrial robot systems and integration, ISO 10218-2:2011- Robots and robotic devices. This standard has been adopted in the United States as ANSI/RIA R15.06-2012: Industrial Robots and Robot Systems – Safety Requirements and in Canada as CAN/CSA Z434-14: Industrial Robots and Robot Systems. However, ANSI B11.20-2017 recognizes that process observation is not the only special mode of operation where this decision process is still applicable.

Operating an IMS in a special mode requires a combination of specific risk reduction measures and safe work procedures to provide protection to the operator when the special mode is active. A special mode usually limits potentially hazardous situations by restricting velocities, movement, torque, access, etc. It also restricts potential hazards not required for the special mode (for example, allowing slow speed motion of an auger to permit cleaning but prohibiting other motions or transfers). The decision process provided in ANSI B11.20 helps integrators and system users conduct focused communications to determine if a special mode can be safely implemented into an IMS. Once implemented, each special mode should then be uniquely named so personnel know its function.

As the latest version of ANSI B11.20 begins to circulate within industries, these elements will be tested and refined by design engineers. It is anticipated that the decision process supporting "special mode" can be effectively applied to safe design of robot systems using collaborative operation, defined as a state in which purposely designed robots work in direct cooperation with a human within a defined workspace.

As robots with power and force-limiting features (also known as collaborative robots or "cobots") continue to gain in popularity, end users will continue to find new and creative ways to interact with a system that was not previously considered by the component supplier(s) or system integrator. The concepts of "layout analysis" and "special mode" described in ANSI B11.20 will continue to be useful and become essential tools for complex automation systems designers.

Christopher Soranno is the safety standards and competence manager at SICK Product and Competence Center Americas and chairman of the ANSI B11.20 subcommittee; Edited by Emily Guenther, associate content manager, Control Engineering, CFE Media, eguenther@cfemedia.com.

MORE ANSWERS

KEYWORDS: Industrial Internet of Things (IIoT)

• The updated version of ANSI B11.20-2017
• Special operating modes within an IMS
• Explaining the layout analysis in ANSI B11.20-2017.

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How can your facility adopt the new safety standard to increase worker safety?

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