Integration of Machinery into a System – ISO 11161 and B11.20
ISO 11161 Safety of Machinery – Integrated manufacturing systems – Basic requirements is not a standard that catches the eye as a go to standard for the designer of machinery safety systems, but should it be?
Incorporating two or more interconnected machines for a specific application constitutes an Integrated Manufacturing System (IMS), and in the modern automated manufacturing environment this is very common, just think of a packaging line with machines putting products into boxes, palletising and then wrapping pallets all in one space. An IMS is much greater than just two or more separate machines, it can be highly complex and require multiple layers of expertise and knowledge.
The pace of change in automation and the use of diverse manufacturing technologies within the same safeguarded space is making ISO 11161 even more relevant. First published in 1994 and revised and republished in 2007 with minor revisions in 2010, ISO 11161 is once again under revision by the ISO Technical Committee 199, workgroup 3. The revision has taken the 2017 publication of the US standard B11.20 – Safety of Machinery – Integration of Machinery into a System as the basis for its working draft. (Including the title.) The current version of ISO 11161 views an IMS as a whole new and different machine rather than the parts simply combined, this is especially important where frequent manual interventions are required as it may not be possible to stop the whole IMS. This raises new challenges that may not be present with the individual machines.
The onus for risk assessment and the provision of risk reduction measures falls upon the integrator, who may be the manufacturer, assembler, engineering company or the user, depending upon the terms of any contract.
The risk assessment process follows ISO 12100 paying additional attention to the interfaces between the different parts of the IMS and the hazards and tasks associated with the integration of the component machines and associated equipment.
Specifying the limits and scope of the IMS leads to two key considerations. The first is the determination of task zones and this brings us back to the potential for operators entering a particular portion of the IMS without shutting down the entire system.
Secondly there is a need to identify the span of control of risk reduction measures. As an example, and in layman’s terms, this means knowing what happens when a device, such as an emergency stop, is pressed. What parts of the IMS are controlled by that E-Stop?
The term span of control appears in other ISO and B11 machinery safety standards but is perhaps even more relevant when it comes to an IMS. The devices requiring a defined span of control are emergency stops, enabling devices, gate interlocks, presence sensing devices, means for disconnecting and local control mode. It is possible for a single device e.g. an emergency stop to have a span of control combined from other devices e.g. multiple gate interlocks.
Given the potential for an IMS to cover a large floorspace and have the potential for whole body access the importance of the reset function cannot be stressed enough. Protection of personnel within the hazard zone(s)(safeguarded space) can be achieved through continuous presence detection but if this is not practicable then visibility of the hazard zone(s)(safeguarded space) becomes key. The reset is required to be installed outside of the danger zone (safeguarded space) and the operator is required to have good visibility to ensure nobody is within the hazard zone(s).
Where visibility is not complete a trapped key system, providing safety or personnel keys, or a “special reset” is required. It is important to remember that reset and restart are two separate functions. Look upon the reset as a permissive action within the safety related part of the control system that allows, for example, a restart button to issue the start command.
This brings us to some potential changes in ISO 11161 that as things currently stand will introduce some new terminology and concepts.
The term proactive inhibit function, emanating from B11.20, is introduced and is used to describe a means of preventing unintended start-up. It is an administrative control but places control into the hands of a person entering into the safeguarded space. In the example of the trapped key system the safety or personnel key carried by the operator ensuring the reset cannot be performed until it is returned.
Another example of a proactive inhibit function is an interlock blocking device e.g. a device used to prevent an interlocked movable guard being closed and the reset actuated.
Where it is not possible to utilise a proactive inhibit function, a reactive inhibit function could be used and this would be, for example, an escape release or a latching actuating device.
Surprisingly, whole body access is defined for the very first time in an ISO machinery safety standard, assuming ISO 11161 is published before the revision of ISO 14119.
Safeguarded space is another term that has been introduced in the current draft and is defined as the area or volume enclosing (a) hazard zone(s) where guards and / or protective devices are intended to protect persons. Space is, perhaps, more important than is first imagined as it refers to the third dimension as opposed to area which relates to the 2D footprint.
ISO 11161 will grow in in importance as industrial tasks become further automated. Generally robotics comes to mind when considering IMS, but there are many other systems without robotics where two or more machines are integrated. A good example is a line that bends and punches material – it also has a conveyance system.
As of March 2021 the revision of ISO 11161 is at the working draft stage and will be at least a couple of years away from publication. Follow Fortress to keep up to date!
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