Chapter 3.5
Safe access to large machinery systems
Today, large machinery systems are often enclosed by guard fencing. The integrated machinery behind the guard fence may include production machines, conveyors, robots etc. and cover an entire factory hall or extent across several levels of a building.
Integrated manufacturing systems
These systems are often divided into task zones that can operate independently, ensuring efficiency. Safety features like presence sensing devices and warning signals protect workers, adhering to ISO 11161 standards.
For instance, a packaging machine may be able to run independently of a robot that places material to be packed in its feed zone. An output conveyor at the other end of the packaging machine may run independently of the machine or at intervals controlled by the packaged goods output.
When an error occurs in one task zone, it may be possible to resolve the error without having to stop the entire system or adjacent task zones. This results in higher production efficiency, as faults can be resolved “on the fly.” The same may be true of retooling operations and even some maintenance jobs.
Safety features
To be able to utilize versatile operating concepts, each task zone must have its own safety features allowing workers to enter a zone and work while the rest of the system continues running:
- Presence sensing devices like light barriers, laser scanners, and contact mats inside the hazard zones to detect a worker and stop the hazardous operation.
- Reset and open individual doors while others remain locked.
- Switch-over to a set-up mode in one task zone while the others keep operating in automatic mode.
- Fences inside the fenced-in area which prevents a worker from migrating into a task zone that keeps running automatically.
Of course, this brings up numerous safety issues that need to be considered carefully. In 2008 already, ISO published a standard that contains many valuable rules for the safety of so-called integrated manufacturing systems – ISO 11161.
One of the most difficult risks to deal with is that a system part may restart or accidentally be started while a person is still inside. To avoid that, several strategies have been developed to protect workers during such “whole body access.”
Visual or Audible Warning Devices
When a worker presses a start button outside the system, a warning light flashes or a horn sounds long enough for them to leave the hazard zone. At the end of the warning signal, the system starts.
Combined with:
- Start prevention buttons
- Rope switches
- Emergency stop buttons inside the safeguarded area
Additionally, install guard locking switches with escape release.
