Batch-weighing innovation via automation design

Fieldbus-controlled weighing/handling system with intelligent carts fully automates production of minor ingredient recipes for plastic, rubber and chemical processing

A ground-breaking minor-ingredient weighing system that can multiply process throughput has been developed by John P Waterhouse Co - with the aid of fieldbus-compatible automation components from Festo.

The first system, which has just been commissioned, implements probably the most automated weighing system of its type ever deployed in the UK.

Unlike conventional minor-ingredient batch weighing systems, the John P Waterhouse Co new Smart Cart employs mobile and intelligent carriages for accurate ingredient weighing.

These electric motor-powered carriages move beneath the feeding devices on a monorail track, and many carriages can be deployed simultaneously - allowing the throughput of the automated dispensing system to be tailored to the needs of the downstream process.

This approach is capable of multiplying productivity compared with a conventional system with a single weigh station.

Moreover, as all the ingredients are dispensed and weighed into their own bag, the system eliminates the cross-contamination that can take place when only a single centralised weighing vessel is used.

Each Smart Cart is equipped with a PLC controller to manage weighing, communications, and anti-collision control for the track.

It takes its power, and connects with the master PLC controlling the overall process and recipes, using fieldbus communications over a busbar system running alongside the monorail.

The monorail system with its intelligent carts is served by automatic bag-making and bag-offloading stations - based on Festo pneumatics and electrical drives.

The inline bag manufacturing machine - the EVA30 - produces bags from a roll of low-melt temperature tubular plastic.

A combination of pneumatically and electrically controlled movement and handling functions automatically create the desired bag size, and transfer it to a passing Smart Cart, where it is held in place by sprung mechanical retention arms.

The bag material on the roll is manipulated by simple pneumatic grippers.

The gripped material is fed forwards to create the desired bag height by a rotary stepper motor axis with an encoder, connected to a pair of belt-driven linear actuators.

A pneumatic rotary actuator with a knife blade then separates the bag length, the gripper jaws open to 180 degrees to release the material - so that retraction is not necessary - and the motor drives it on to a pneumatic handling stage where two sets of vacuum cups open the bag, and a pair of swinging pneumatically-controlled arms transfer it onto the cart.

Back-to-back cylinders are used for the swinging arms, to provide the necessary articulation for the final pick-and-place operation.

The bag-making system is controlled by the modular Festo CPA valve terminal fitted with an interface option for the CC-Link fieldbus protocol - to suit the Mitsubishi PLCs that John P Waterhouse Co chose for controlling the process and carts.

Once equipped with a bag, a Smart Cart travels around the track beneath the ingredient dispensing system - stopping under the appropriate feeders to accept the programmed ingredients required by the recipe - before moving to the unload station.

This station requires only simple pneumatics to complete the operation - heat-sealing the bag and offloading it onto an accumulation conveyor for intermediate storage before use.

Over some 12 years in the automated batch weighing business, John P Waterhouse Co Ltd has built up a considerable knowledge of pneumatics.

However, the novel concept behind this system took the required level of automation into completely new territory for this OEM - demanding levels of positioning precision, cycle times, and co-ordinated real-time control that could only be achieved economically with the addition of electrical drives and fieldbus communications.

The design task was considerable, and the OEM development team sought to minimise the system integration risk as much as possible.

The solution came in the shape of Festo, who could provide a complete package of pneumatic and electrical drive components - compatible with the CC-Link protocol - and technical design assistance.

Festo simplified the development cycle further with a number of design tools and logistics services.

These included CAD configuration software that allowed the developers to simulate the pneumatic functions and specify pneumatic cylinders accurately sized for the application.

Festo additionally advised on electrical drive selection - providing a matched stepper motor and linear actuator package for the bag feeding mechanism.

This part - which was custom-assembled in the Festo system building facility in Northampton - and is now available to the OEM as a single part number, simplifying machine building as they start to sell their new product.

"Festo was the only company we found that could supply a complete electro/pneumatic handling component package to our specific requirements, and offer support for the CC-Link fieldbus", says Mike Fisher, Senior Mechanical Engineer at John P Waterhouse Co Ltd.

"They provided invaluable technical support during the design cycle, which included bringing a stepper drive assembly along for trials, and providing valuable advice on implementing a fieldbus-connected system".

John P Waterhouse Co has just completed the commissioning phase of its first fully automated Smart Cart system at the largest UK custom compounding facility.

For this application, a total of six weigh carriages are deployed which can provide in excess of 60 completed minor ingredient batches per hour, to service the company's multiple mixing lines.

The newly-operational system currently has approximately 25 bulk feed stations, and commissioning tests demonstrated the speed of the networked control system.

Weighing is carried out utilising force motion platform scales with typical accuracies of better than +/-5g.

The entire system can be run by a single operator, who is responsible for selection of scheduled recipes and ensures feed hoppers are replenished.

"The Smart Cart concept introduces a new degree of automation into the minor-ingredients batch-weighing arena", says Chris Waterhouse, Sales and Marketing Manager of John P Waterhouse Co Ltd.

"It's the most significant design project our company has ever undertaken, and we were pleased to find an automation supplier who could help us to minimise the risk involved, and take such a big technological step forward".

"Being able to supply both the electrical drive and pneumatic automation components required for this system ensured there were no integration problems, and made it easy for us to help with design assistance", adds Neil Lewin of Festo.

"The resulting system is a showcase for our technology".

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