Electropneumatic boxes simplify fieldbus control

Colortronic is installing streamlined intelligent ancillary equipment faster than ever by formulating the control and actuation features around a single fieldbus communications cable.

Colortronic is installing streamlined intelligent ancillary equipment - used to help produce plastic parts - faster than ever, by formulating the control and actuation features around a single fieldbus communications cable.

This competitive edge was achieved after adopting compact flexible electropneumatic Airboxes from Kuhnke, in place of valve islands; a move which has circumvented convoluted hard wiring and led to increased repeat business Colortronic (UK) provides a full range of ancillary equipment used in the production of plastic parts around the world.

In addition to providing discrete components, the company also acts as a systems integrator by corralling and adapting its technology into tailored working solutions.

Most of Colortronic's systems customers are plastic processing companies that require a bespoke control subsystem to form an integral part of a larger turnkey production facility.

In addition they service original equipment manufacturers around the world.

Mark Gregory, Technical Support Engineer at Colortronic, confirmed: "In terms of plastics production, we produce everything for a typical system; apart from the plastic machines themselves".

"This ancillary equipment includes: dryers, blenders, metal detectors, temperature controllers, vacuum-operated conveyors, silos and storage hoppers, control gear and industrial control systems".

The subsystems Colortronic are asked to create at its engineering facility in Chesterfield, Derbyshire, vary considerably from one order to the next - requiring it to use its considerable design experience.

However, a typical contract might involve the integration of ancillary equipment for a plastic extrusion or moulding facility whereby 28 hoppers, containing polymers of varying grades and colours, are drawing granular plastic stock, as required, from a central silo.

Gregory adds: "Many people assume that an array of hoppers is utilised to create different colours of plastic component".

"Although this is often a factor, it's more usual for our customers to vary the properties of the plastic, by introducing different grades of polymer".

Plastic granules are moved from silo to hoppers; as level sensors in the receiver indicate that more stock is required.

This flow of plastic is moved under vacuum, via a matrix of enclosed tubes.

Traditionally, vacuums are created by a matrix of electropneumatic valves, mounted on bulky island housings.

Such vacuums are created for a time interval sufficient to move the requisite volume of plastic, from silo to hopper on demand.

However, the use of conventional valve technology presents significant drawbacks, particularly for the installer, by necessitating a complex control network where valve islands are individually wired to a central controller.

Such installations are cumbersome, bulky, labour intensive to create and thereby difficult to expand or otherwise modify.

In this area, Colortronic has made a major breakthrough by spurning valves in favour of electropneumatic Airboxes manufactured by Kuhnke.

Airbox technology is based around a modular network of small footprint electropneumatic boxes, which perform the functions usually associated with valves.

Each box contains two I/Os which can be configured to operate either one or two actuators.

In terms of the typical 28-hopper one-silo setup outlined earlier, such installations typically move around 2t of plastics per hour, ready for processing by the machines; pulling stock as required.

In such a scenario, Colortronic uses 28 Airboxes of two inputs and two outputs capacity each, mounted directly onto a single daisychained communications pair that feeds into a host Siemens controller.

Specifically, Colortronic uses the ASi (actuator sensor interface) fieldbus protocol on its Airbox-based installations.

This bright yellow two-wire cable, which carries both power and communications data, and is typically 150-200m long in such plastic processing installations.

"Airbox is the only pneumatic product designed specifically for use with ASi", highlights Kuhnke UK's Managing Director, Brod Bass.

"Our boxes connect directly onto the yellow cable; in contrast to valve islands, which each link onto ASi by means of dedicated adapter cables".

This inability to directly interface standard valves and ASi cable creates two problems.

First, the linking adapter cables reintroduce a level of clutter, akin to dedicated hard wiring, which the use of a single looped fieldbus cable seeks to eliminate.

Secondly, diagnostics become significantly more difficult.

Mark Gregory at Colortronic explains: "With our ASi based systems, a series of LED indicators show what the I/O is doing at all times".

"In particular, if a fault occurs, the source is easy to identify and isolate because all Airboxes sit on the yellow cable".

"If we were to use valve islands, the adapter cables would require time and space to install, and it would be far more difficult to pinpoint the cause of a problem".

Therefore, as far as Colortronic is concerned, the availability of Kuhnke's Airbox means the difference between using ASi fieldbus and sticking with conventional hard wiring.

Gregory adds: "If Airbox didn't exist we wouldn't be able to use ASi fieldbus".

"There would be no point".

"The advantages you gain by using ASi - which is a simple to use reliable fieldbus - are lost once you try to start to combine it with conventional valves".

"We'd be stuck with hard wired valve islands".

He suggests there are five key benefits to adopting ASi fieldbus when creating control systems for plastic processing: far fewer cables in comparison to dedicated hard wiring; higher reliability through simplicity; ease of modification and expansion (the combination of ASi and Airbox allows the engineer to "plug and play" until they are satisfied with performance); faster installation speed; and transparent diagnostics.

Colortronic first used Airbox and ASi technology some four and a half years ago to form the basis of a control system for ancillary components within a plastics mouldings production unit.

Since then, it has increasingly come to rely on the technology to make flexibility and ease of use its watchwords when dealing with OEMs and end-users alike.

Mark Gregory adds: "We now install around 20 large subsystems per year based around ASi and Airbox technology".

Each of these control pyramids is headed by an industrial controller provided by Kuhnke's alliance partner, Siemens.

Colortronic sources Siemens controllers from authorised distributor, Parmley Graham, as required.

"We've rewritten the codes provided in the Siemens software so that the whole system is completely compatible with ASi", says Gregory.

The only other change we've made is the base unit of the Airbox, which was refined to better suit our area of application".

Initially, when plastics systems' integration first began working with fieldbus linked Airboxes, there was the occasional teething problem created by its unfamiliarity with the technology.

But, as Mark Gregory confirms: "Kuhnke was excellent at problem solving these initial issues".

"Today, there are no problems to solve".

Colortronic is now in a position to identify occasions where its use of ASi, in turn facilitated by its use of Airboxes, has won it repeat business it wouldn't otherwise have achieved.

"We recently installed five systems into one plastic moulding factory".

"Space was incredibly tight and this would have been particularly tough if we'd had to accommodate a clutter of hard wired valves".

"Thankfully we didn't and the customer could see the benefit of the technology we were using".

"The result was more business", recalls Gregory.

He concludes: "Our business is all about establishing a reputation for reliable operating systems".

"We have to go in, quickly install a system, which then has to work reliably first time".

"ASi is simple to use and suits our purpose perfectly, Airbox, as well as allowing us to use ASi, provides a flexibility and compactness that ensures the customer is immediately comfortable with the new technology".

"As a result, they are much more inclined to award us repeat business".

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