Safety and productivity can be compatible!

13 July 2023

Dr Martin Kidman discusses the options for safely optimising material flows in access protection applications without affecting productivity.

Highly productive and dynamic automation depends on optimising the flow of materials between individual processes. Achieving close to a continuous flow is the ultimate aim, including at the end of a production line where goods need to be packed, palletised and transferred for onward distribution.

As the automation of materials handling increases – for example with the use of mobile transportation systems, conveyors or articulated robots – so does the risk of injury to personnel. At the same time, production teams may well be under pressure to introduce greater manufacturing flexibility, minimise machine set-up time and to improve space utilisation on shop floors.

In such circumstances, safety systems can easily – and unjustifiably - become characterised as necessary but counterproductive to achieving the most fast-moving and uninterrupted processes. The nuisance of physical guards, or manual stops and restarts, can be perceived as a barrier to productivity. They could even cause irritation that could tempt impatient operators to override systems and indulge in unsafe practices.

The good news is that developments in intelligent sensing systems have opened up more opportunities to optimise the onward flow of goods in high-speed production environments by using robust safety systems. They avoid unnecessary stoppages and downtime, while continuing to protect people. 

Especially for small objects such as bottles, workpieces or chocolate bars on a conveyor, a physical tunnel, designed with the correct safety distances to the hazardous area often could be used as a low-tech way of protecting personnel.

However, there are production set-ups where physical guards or tunnels may be unsuitable or take up too much space. Once built, tunnels cannot easily be adapted for variations in the shapes of products or cartons or to accept larger objects than the guard is built for. So, on many machines, for example conveying lines, Electro-Sensitive Protective Equipment (ESPE), like safety light curtains and safety laser scanners, is used.

To ensure a continuous flow of materials, the ESPE must allow objects through the protective field without triggering a safety response that stops the machinery, but must still react if a person breaks the field by reaching into the area. The most common implementation is to temporarily ‘mute’ the ESPE while the material is passing, by using additional sensors to detect either a recognised object or a person. But there are some disadvantages – muting systems still have a residual risk while the protective system is briefly bypassed. Muting sensors need extra space, take more time and effort to set up and maintain and they are at risk of getting dislodged or damaged. 

Light curtain systems can offer greater flexibility to install safe access protection with integrated entry/exit monitoring (muting). Pre-configured, plug-and-play solutions can now be specified as complete muting sets designed for rapid mounting, connection and commissioning. 

Safety laser scanners
Like safety light curtains, safety laser scanners are ESPEs that can be used for human/material differentiation. Safety laser scanners are more commonly used to set up horizontal protective fields – for example on an AGV – but safety laser scanners can also be used vertically. Their benefit is that, where safety light curtains can only mute a certain number of beams, a safety laser scanner can be set up to recognise shapes with more complex contours, and its fields can be changed dynamically. This removes the need for additional guarding or sensors to detect if a person is trying to gain access to a machine whilst the ESPE is muted.

Additionally, using a scanner with a safe communications interface such as CIP Safety, PROFISAFE or SICK EFI-Pro, multiple fields can be evaluated simultaneously to develop more complex applications for human-material differentiation. SICK’s Safe Portal is a pre-certified solution, originally developed for material transfer stations in automotive assembly. It uses intelligent protective field evaluation to enable adaptive production processes so different vehicles or other objects can pass through. Detection fields alter dynamically to allow, for example, a vehicle to pass through while still protecting the rest of the aperture. 

Classic muting alternatives
The development in intelligent sensing systems has also enabled safety light curtain solutions to be marketed as pre-certified alternatives to classic muting. For example, SICK’s Safe Entry Exit is a pre-certified safety system that reliably differentiates between humans and materials without additional muting sensors. Any Type 4 ESPE can be configured to use the Safe Entry Exit, using just one safety controller to evaluate several material gates simultaneously.

SICK’s Safe Entry Exit gets around the limitations of muting sensors by using process information to generate a signal to tell the safety logic to by-pass the protective device. Such systems can be TÜV-certified to save time and money. 

Smart box detection
More recently, plug and play safety light curtain solutions have become available that use intelligent pattern recognition to detect pre-determined objects without muting sensors. The SICK C4000 Fusion and deTec4 Smart Box Detection can facilitate safe material flow without having to receive signals from an external machine controller.  The C4000 Fusion can be programmed to allow complex patterns through its horizontal array of beams. This could, for example, be pallets or car skids while still reliably detecting a person walking through. 

People are often surprised when I tell them that manufacturers with the best safety records are often also those with the highest productivity. Of course, machinery safety regulations and standards are there to protect employees, but a well-designed safety system will also be one that enables operating efficiency, rather than hinders it. Choosing the right safety solution is, therefore, paramount to achieving optimum material flows.

Intelligent sensing systems and software are now being developed for machinery safety that can enable operators to progress quickly to installed and fully-certified systems that can avoid unnecessary machinery downtime, while continuing to safeguard their workforce.

Dr Martin Kidman is Safety Solutions Market Product Manager at SICK. 

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