HMI has recipe for successful baking

An intelligent HMI and three inverters are emulating the performance of a full function control system as Hamden Systems drives it mid-range food processing machines to new levels of capability.

An intelligent HMI and three inverters are emulating the performance of a full function control system as Hamden Systems drives it mid-range food processing machines to new levels of capability.

Poole-based Hamden is a major OEM for the food manufacturing industries, supplying systems from high volume fully integrated processing lines to standalone machinery for craft producers.

One of the development strategies upon which it builds its success is to regularly transfer technologies from its largest systems into smaller machines.

To achieve this Hamden works closely with its key suppliers such as control systems specialist TM Automation.

"Our top end processing lines have become more and more sophisticated over the years", says Hamden's John Phillippo.

"So I was only half serious when I asked TM Automation's Andy Cross if we could achieve the same leave of control for our craft machinery without pricing us out of our market".

Cross kept a cool head and knew how to proceed.

"I've been asked this question by several other customers, and I have realised that OEMs see engineering as a series of mechanical functions - the principles of control theory are lost on them.

So I asked John to list out the functions he required and the variables that define these".

"As I expected John's list, once written down, was actually quite short and I was confident I could develop a control system based on either a microcontroller or, better yet, intelligent field devices".

Hamden's speciality is foodstuff spraying, using a high-speed spinning disk to generate the spray pattern rather than the more usual compressed air techniques which can cause misting or irregular patterns.

The machines, typically used in the bakery industry could be spraying oil onto pizza bases or white chocolate onto meringues to stop the cream from soaking in or one of many other food applications.

The food products are usually presented to a spray head via a conveyor, often the same conveyor as runs through the bakers' oven.

The conveyor's speed defines the amount of coating that is picked up by the product.

These are the three key variables associated with the performance of a disc spraying machine: the conveyor speed, the pump throughput (set by the pump motor speed) and the rotational speed of the discs.

These are interactive and require critical adjustment to achieve the specified coverage at a given production rate.

The conveyor speed is set by the product line speed, which in turn is dictated by other processes - more often than not by the cooking time in the pass through oven.

Once Cross had understood this basic principle he could start looking at possible control solution architectures.

Hamden had already fitted inverters, but was looking for a lower cost unit that provided the functionality and reliability of more expensive units.

TM Automation is the European distributor for Toshiba inverter drives, and has a superb range of low power drives ideally suited to Hamden's needs.

Cross and Phillippo then had a series of brainstorming meetings during which they realised that food manufacture at the craft level is a batch process, and that each processor has a relatively small product range.

"For instance an Italian baker may make 6, 9, 12 and 15in pizzas and three or four type of bread", says Phillippo, "while a confectionary baker will produce say meringues, pastries, sponges and fruit cakes, all of which need to be sprayed before the application of icing or cream".

It was not long before these two engineers realised that each product had two recipes, one of ingredients and another of process parameters, such as cooking time, spraying diameter etc.

These process recipes could be written into the memory of the control system, and then any one of them could be selected with a single keystroke prior to the start of each new batch of products.

Each recipe was quite short, so even if a particular customer needed several dozen the memory requirement was quite modest.

This lead Cross to considering leaving a computer, PLC or even a microcontroller out of his architecture and going for an intelligent HMI (human-machine interface).

Again TM Automation had just the product, a Horner OCS.

"The OCS has more than enough memory", he says, "and better yet is its user-friendliness with a nice big screen and relatively few hardware pushbuttons - too many buttons can be rather intimidating, particularly for first time users".

Another advantage of the integrated display is its diagnostic capabilities.

In today's world it is no longer acceptable for machine to stop due to an internal problem without being able to report the cause of the disruption.

On earlier Hamden craft machines standard beacons were used to indicate problems such as 'product shortage' or 'tank overfill', but with each of the Toshiba drives able to provide several different fault indications, this form of annunciation was not sufficient.

Now the drives supply information to the Horner OCS, which instantly display a discrete message identifying the fault.

The OCS and the Toshiba drives both have RS485 communications ports as standard, so linking them up was straightforward.

The cost of a PLC or computer has been saved, as has the cost of manual potentiometers for speed trimming the drives (plus a panel to food industry hygiene standards to mount them in).

The only extra component is an emergency stop button, and all systems are required to have one of those.

Phillippo sums up for Hamden: "With TM Automation's help we have pulled off a design coup that our competitors thought was impossible - integrated systems standards of control on craft industry machines, at a price our market is happy to pay.

We have been successfully exporting our big systems for many years and now our craft machines are going down the same sales channels too, thanks to the new control system".

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