Modularising machine design and build

Ray Barnes of Hoebiger-Origa explains how mechatronic subsystems, modular design and intelligent controls can be used to ensure food packaging machines have a long and productive working life.

The European market for packaging machinery is forecast to grow at an Olympian 8% per annum to reach Eur 13 million by 2008.

And with developing nations coming on-stream as producers, but still looking to Europe for machine design and build, some analysts put the figure higher yet.

This is in contrast to growth of 1.6% predicted for the UK economy as a whole.

So packaging machinery would seem to be a good market in which to operate, especially as other engineering sectors do not appear to be in such good shape.

However there are some significant barriers to entry, most notably the level of expertise that is needed.

Designing a packaging machine is not easy.

Packaging machines need to be very efficient (and that usually means high speed) to safeguard the slim margins in which food processors operate.

They also have to be long-life machines, robust enough to run and run, often with low maintenance for many years.

They also have to be very flexible so that they are able to accommodate the constant changes driven by supermarkets and their customers.

There are many reasons driving the constant changes; the steady stream of tempting special offers, free gifts attached to the packaging, requirements for multi-packs, different packaging for different customers.

And there are new reasons emerging at quite an alarming rate too.

For instance, new materials are constantly emerging.

To date these have tended to be new multi-material high performance laminates that may need special handling.

More and more "green" materials are emerging, for instance starch-based plastics replacements have different tolerances to temperature and may be less pliable.

Another green issue is the energy consumption of the machine, prompting a switch for some applications from hydraulics and pneumatics, which require constant power, to electric drive which requires power only during actual operation.

So a packaging machine needs to be robust, high speed, ultra reliable, energy efficient flexible and easily adaptable.

To accommodate these requirements, four key technologies are emerging in mechatronic design; linear motion, servodrives and programmable control.

All have been around for some time, but continue to evolve.

Simpler machines are typically controlled by a small "brick" PLC (programmable logic controller).

But the performance level of these increases year on year, allowing every greater control of machines.

Additionally fieldbuses and Industrial Ethernet are making "wiring up" far less daunting and encouraging greater take up of comprehensive controls.

Similarly servo drives are getting faster, more controllable, more powerful and more compact as time goes on.

Significantly their purchase prices are more attractive and setting them up is becoming increasingly user friendly They are not yet plug and go, and will probably always require specialist installation knowledge, but they are more widely installed than 10 years ago and look set to become more and more popular.

But perhaps surprisingly, the greatest advances are being made in linear motion technology.

The need for linear motion has existed as long as there have been machines, but for a long time this was generated using bespoke solutions.

The first linear actuators were probably hydraulic and pneumatic cylinders, which became standardised engineering components in the 1960s (and have evolved considerably since then).

These were a great leap forward in technology, and although it predates many of today's engineers, pneumatic cylinders in particular advanced machine design considerably.

The 1980s saw the development of the rodless pneumatic cylinder.

This had many advantages over older designs but was significantly more expensive.

The extra cost meant rodless had to carve a niche for itself, and significantly further costs could also be justified in order to integrate extra functions such as positioning or intermediate stops.

Soon rodless was finding uses way beyond those normally associated with pneumatic and this encouraged the manufacturers to rethink their designs.

Several variations of the concept emerged, features such as guides, sensors, encoders and controls were incorporated, such that they became intregrated structural and actuation elements within a machine.

Demands for ever greater positional accuracy and the very compressibility of air meant that a practical limit was reached for some packaging applications, which spawned the birth of electromechanical linear actuators.

The greatest positional accuracy is achieved with linear actuators based on ballscrews or lead screws.

These also have good load carrying capacity - but there are downsides too, most notably with regard to weight, unit cost and limited high end operating speeds.

For many packaging machinery applications, a more effective, faster and lower cost solution is achieved with belt-based linear actuators.

These are able to satisfy the levels of precision, flexibility, robustness and reliability demanded, particularly for longer stroke applications.

However machine design is not only about speed and throughput.

There are also growing demands for shorter stroke, applications that do not require high speeds and cycle rates, but provide for the flexibility required to adapt to constant change.

And this is where spindle (screw) drive actuators can be indispensable.

A typical application may be a machine filling individual containers of various sizes and involving frequent batch changes In this case, a screw driven linear actuator could be used to automatically make the necessary machine adjustments to accommodate the changes in container size.

Similarly demands for multi-packing flexibility, for varying pack sizes and special offer runs will also necessitate machine setting adjustments that may readily be automated with linear actuators.

Before linear actuators, resetting machines as described here would have been a time consuming task.

A machine would be idle and nonproductive, so change overs would have been minimised with long production runs.

However long runs are not flexible in terms of meeting customer orders, so expensive stock holding was required.

Nowadays programmable changeover using the memory of a PLC and the precision of a linear actuator has replaced stock holding with short run flexible working.

While the basic mechanical principles of the various types of linear actuator are well established, new forms are still being developed to meet the evolving needs of machine designers as they meet the evolving needs of their machine users, as they satisfy the evolving demands of the consumer.

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