Machinery safety 

Technological advances over the last twenty years have made a huge difference to the
way safety is implemented on machines. Today's machinery safety technologies are
bringing significant additional benefits to machine builders and end users alike.
Before considering the benefits, however, it is worth analyzing what it is that machine
builders and end users are seeking from machinery safety. Obviously they want a safe
machine and one that complies with current safety standards and regulations, but they
also want ease of set-up and reliability. Machine builders and system integrators are
keen to have diagnostics that can help them when they are commissioning the machine,
and end users want diagnostics so they can identify and rectify faults as fast as possible.
Although it is an extreme example, a modern car plant produces one car every 48
seconds, or 75 per hour, so you can see why the potential cost of lost production is
massive.
Fortunately modern safety technologies can help to achieve these goals, whether we are
talking about an automotive production line or a machine on a smaller scale. Starting at
the lower end, simple machines still tend to use one or two safety relays and guard
interlocks, emergency stop switches, safety light curtains, and so on. Having said that,
traditional electromechanical safety relays are limited in their functionality and
diagnostics, so many companies are now using Pilz PNOZsigma relays that are capable
of performing one of several different functions. This makes circuit design, ordering and
stockholding easier for machine builders, plus the LEDs aid fault-finding during
commissioning and operation.
Drag-and-drop logic
As the complexity of a machine increases, the complexity of the safety-related control
system also increases. Once you need more than a few safety relays, the benefits of a
configurable controller - such as the Pilz PNOZmulti - come into their own. Configuring
the logic with drag-and-drop software is much easier than using relay logic, and the
chance of wiring errors being made is greatly reduced. For series machines, the
configuration can just be copied to all of the machines, and diagnostics are also far
superior as well. Another thing to be aware of with medium-complexity machines is that
they are more likely to require changes. With safety relays, this could require significant
amounts of rewiring but, with PNOZmulti, all you have to do is connect the new safety
sensors/actuators and make the necessary changes to the configuration.
Once you have a project the size of an automotive production line, you really need a
programmable safety system (sometimes called a safety PLC) to handle the I/O and the
logic, and probably a safety field bus for communications - such as SafetyBUS p or the
forthcoming SafetyNET p.
Having considered the monitoring and control of the safety-related functions, we can
now look at how safety sensor technologies can help machine builders and end users. In
most cases safety sensors can be used across the board, on machines of all sizes and
complexities. For example, whatever the machine, tongue-actuated guard switches or
interlocks are still appropriate for physical guards that are opened on an occasional
basis, while guards that are opened more frequently will benefit from non-contact
magnetic switches. And if you need higher integrity, there are coded non-contact
switches available.
Light curtains are very popular, but you have to remember that they are not suitable for
something like a CNC machine tool where parts might be ejected at high speed should
the tool or workpiece break. Light curtains are also limited to the extent that they can
only guard a flat plane. Mirrors can be used to 'bend' the plane around a corner, but
setting up the light curtain and integrating it with physical guarding is time-consuming
and, consequently, expensive.