Out in all weathers - the quest for certifiable sensor safety outdoors

The difficulties associated with validating the performance of optical sensors intended to protect people from machinery outdoors are clear. The unpredictability of conditions like bright sunlight, rain, fog, snow and dust are the most obvious of many complex challenges. Agreeing a certifiable technical safety standard that defines what such devices can achieve, and sets out their limitations, in an almost infinitely-variable outside environment, seems an almost impossible task.

Manufacturers, machine-builders and systems integrators have, therefore, been unable to provide their customers with a sensor safety solution that can be certified for use in the open air. For some time now, there have been growing calls from industry for a technical standard that can complement and correlate with those used to certify safety systems indoors.

Proven technologies

Of course, there are many well-proven optical technologies already operating all over the world in all sorts of outdoor applications. Their technological sophistication and refinement to be able to cancel out the false signals caused by challenging conditions, such bright light, moisture, visibility and temperature, have made them extremely capable and reliable. From laser distance sensors, to LiDAR Scanners and vision cameras, manufacturers like SICK offer devices with a robust capability to perform in all weathers.

SICK’s recent investment in a new Outdoor Technology Centre, on the site of its Buchholz international distribution centre, near Freiburg, is an indication of just how important these technologies are – and how there are likely to develop in future. At Buchholz, a growing portfolio of outdoor sensors of all types is tested under real environmental conditions. The products, destined for use in plant and machinery for the construction, agriculture or traffic industries, or to be deployed for building security and anti-collision in cranes and ports are put through their paces to ensure their high availability and robustness under harsh operating conditions.

So, where will a safety-certified outdoor sensor most likely be needed?

The development of autonomous, or, more accurately, semi-autonomous systems more than any other technology is driving the need for an internationally-recognised technical standard for the use of safety sensors outdoors.  There may be requirement not only in industry and factory automation, but in mobile automated vehicle technologies in logistics, ports, agriculture and mining for example. In the longer term, technological developments made now will pave the way for future refinements and understanding of the operation of semi-autonomous driving systems in future.

We are have seen some early interest and development where mobile vehicles must operate safely both within a factory or warehouse, as well as outdoors.  For example, in heavy industries where large AGVs may travel between nearby buildings to transport tooling or parts, perhaps needed to cross roads or yards without endangering the safety of people nearby.

Another area is likely to be in industries where providing a validation of safety compliance is important, for example, for outdoor automated systems such as passenger boarding bridges in airports.

Safety standards indoors

The functional safety standard IEC 61496 contains the design and performance requirements for Electro-Sensitive Protective Equipment (ESPE) for the detection of people. It gives clear, but limited, guidelines for a variety of subjects including typical conditions representing indoor use in an industrial environment and the design, functional requirements and test to determine the ESPE’s “Type” (2, 3 or 4).

Venturing outdoors

However, there is an increasing demand for safety certification in applications that may not necessarily be in an indoor industrial environment. In such cases generic functional standards like IEC 61508, IEC 62061 or ISO 13849 can be used, but applying these standards requires an in-depth analysis of systematic capabilities of the sensor or sensor system. Furthermore, there is not enough guidance in these standards to prevent design failures, or insufficient capability to detect in certain environmental conditions such as outdoors, which could result in an intolerable risk to the safety of people.

Technical standard

Since 2016 a working committee, initiated by industry leaders including SICK, has been working on developing a Technical Standard, IEC 62998, which is forecast for publication some time in 2019. It is intended that IEC 62998 will complement the existing functional safety standards to provide a safety classification system for electro-protective devices used in certain environments such as outdoors.

While it is still early days, the development has been greeted with interest and excitement by the industry as one that will encourage the development of new technologies, particularly in automated and mobile applications.

Balancing availability & productivity

The conundrum for safety laser scanners is that their ultimate strengths, their utmost sensitivity to changes in conditions, are at the same time a potential weakness in outdoor environments. The system, by nature, is designed to stop working when the environment cannot be guaranteed to be safe, so the availability of the system could potentially be limited in extreme weather conditions or dusty or sandy environments.

More than anything, the development of outdoor applications using safety laser scanners will, therefore, depend upon the assessment of each individual case in close discussion with the sensor manufacturer to balance the need for detection sensitivity with availability of the overall system. Delivering a flexible and productive material flow will be a key requirement of the automation concepts of the future, as well as real-time condition monitoring.

IEC 62998 only applies if product-specific standards do not contain all of necessary provisions, or product specific sensor standards are not developed. It classifies outdoor safety devices as Class A to F, to distinguish them from interior safety device classifications. Performance classes of sensors and sensor systems are defined in accordance with existing safety standards but there is no definition, of or interconnection to, the “types” as defined in IEC 61496. For example, IEC 62998 Class D would correspond to PLd (ISO 13849), SILCL2 (IEC 62061) and SIL 2 (IEC 61508) but has no link to Type 3.

Industry first

The industry caught its first glimpse of a safety laser scanner to be certified to IEC 62998 for use in outdoor applications at the SPS IPC DRIVES show in Nuremberg last November.

The SICK outdoorScan3 allows automated guided vehicle systems to navigate safely through outdoor industrial environments. Using SICK’s innovative outdoor-safeHDDM scanning technology, a development of the technology already used successfully in our indoor MicroScan3 safety laser scanner, it promises exceptional reliability in rugged outdoor conditions such as bright sunlight, rain, snow, and fog.

As well as being Type 3, PLd and SIL2, the SICK outdoorScan3 will be IEC 62998 Performance Class D, certified for use outdoors. With a broad range of applications and a whole host of other potential uses, the SICK outdoorScan3 is scheduled to become available worldwide in mid-2019.

Dr Martin Kidman is SICK’s UK Product Specialist for Machinery Safety.