Safe presence detection or machine guarding?
With the arrival of the Collaborative Robot (CoBots) and the introduction of safety devices with presence detection, the question is whether fixed Machine guarding still has a future. Users see the opportunity to limit their production space, but is everything what it seems at first sight?
ISO 13855 (2010) Safety of machinery – Positioning of protective devices in relation to the approach speed of parts of the human body.
It may not be the most catchy title for a standard, but it is essential when designing machine safety devices for robots.
The standard states that when applying safety devices, the time needed to stop the machine (total machine stop) must be taken into account, taking into account the minimum distance to the hazard. ISO 13855 gives values for approach speeds (walking speed) that have been tested in practice.
When physical machine guarding is replaced by safe presence detection such as safety light curtains, pressure mats, safety laser scanners or safe radar systems, they must be placed at such a distance that the operator can never reach the hazard when a machine stop is generated. Even when the machine has hardly any downtime, the reaction time of the safety detection and the safety relay/PLC must be taken into account.
The minimum distance from the hazard can be calculated using the following equation.
S = (K x T) + C
S | minimum distance in mm
K | is the approach speed in mm/s of the body or body part
T | is the total stop time of the system in seconds
C | is the intrusion distance in mm
If it is not possible to stop a machine during the cycle or if the stopping action of the system cannot be predicted, ISO 13855 cannot be used and presence detection devices cannot be used as primary protection.
In addition, the correct positioning of fixed guards also provides the opportunity to reduce the surface area of the factory, with the added benefit of providing impact protection in the event of materials coming loose or being ejected. By using steel safety interlocks , the operator can only gain access when the cycle has been completed and the machine has come to a complete standstill, so that the distances specified in the ISO 13855 standard do not have to be taken into account.
While more and more CoBots are used in the production environment, we also see the emergence of the “integrated production system”, where multiple machines work together. This creates additional complexity when designing the safety system. fixed guards then provide an excellent option, especially in combination with safety interlocks fitted with a safety key to protect operators from being trapped inside.
It is expected that safety systems that work with presence detection will continue to be used in combination with machine guarding. It is expected that safety systems that work with presence detection will continue to be used in combination with machine guarding in many cases, this combination will ensure that production environments can be set up more efficiently.
USP offers a wide range of both safe presence detection and machine guarding for safely shielding machines. For electrical applications you can think of safety key switches or bolt locks in combination with a door lock. For valves, valve interlocks, where key release is only possible in the closed position.
Are you interested in free advice on presence detection, such as light curtains, laser scanners, radar scanners or machine guarding ? Please contact our sales engineers.
On our webshop www.machinesafety-shop.com you will find a selection of our range of machine safety products, including light curtains, laser scanners, radar scanners and machine guarding.