Driven to succeed

Today’s drives — with built-in software, frequency inverters, vector control drives, soft start drives and even drives that can interconnect via Ethernet — are a far cry from the simple components of yesteryear.

In applications as diverse as machine control, through traditional process applications and communications systems used by top broadcasters, the drive is adding to the functionality, durability and flexibility of modern devices.

Crane control software incorporated into Unidrive SP AC drives from Control Techniques has enabled NTK Technik to build in extra operational features into a design of crane recently launched by Jost Cranes of Germany.

‘We have worked to produce sophisticated control software that runs in the drives’ application modules,’ said managing director Bernd Niehoff. ‘This incorporates two completely new features that include a method of assessing load during the lift to eliminate the weighing delay — and its accompanying jolt — and a selectable operating mode that provides a constant load height, irrespective of the luffing position of the crane.’

Unlike other crane control systems, this one weighs the load during the smooth S-ramp lift, using the 55kW hoist drive’s internal torque measurement. This eliminates the need for static weighing by a load cell after initial lift, making the process more comfortable for the operator without the usual jolt caused by the start-stop-start of the hoist.

The constant load height feature is designed to make the crane operation both easier and safer. The 30kW luffing (jib) drive can lift the jib from horizontal (0°) up to 89°.

This would normally change the height of the load above the ground. During cargo loading and unloading, there is a need to keep the load at a constant height after an initial lift.

This is achieved by operator key selection, at which point the drives take over. The hoist and luffing drives operate in digital lock mode, with feedback from absolute encoders on both motors directly into the application module software. These then calculate the take-up or payout of the hoist cable, as the jib drops or lifts, to maintain load height throughout the operation.

The third Unidrive SP, again 30kW, provides the 360° slewing movement of the crane. Another software-generated mode is the joystick-selected ‘constant power-hoisting mode’.

This instructs the hoist drive to increase the speed of the motor over its nominal speed when a part-load is detected, giving more efficient lifts without any increase in power consumption.

‘The Unidrive SP has many features that are ideal for crane control,’ said Niehoff.

‘Its vector control, integrated space-saving braking and its superb dynamic response are all important, of course. But it is the best for our needs because of the application modules — with pre-loaded crane-specific software — which make the process of design much easier. They are a key part of our double-redundancy ultra-safe design that meets grade 4 — the very highest level of crane safety. Because the drives are compact and programmable, we can also keep the panel size to a minimum, which has been important in the overall crane design.’

In the more traditional machine building sector Kallfass is using frequency inverter drives and geared motors to improve the efficiency and accuracy of its packaging machines. The packaging machinery company Kallfass, in Nurtingen near Stuttgart, is a specialist in high-speed packaging machinery.

Its fully-automatic side sealer machine features a particularly sturdy design where Lenze frequency inverters and geared motors are used for the film transport operations which requires accurate indexing at up to 85 operations/min.

The Universa 400 packaging machines offer fully automatic overwrapping and edge heat sealing without film overlap, allowing products of randomly varying lengths to be packed at speeds of up to 85 packs/min. The products are fed in via an in-feed conveyor and at the same time are wrapped in a centre-folded film by means of a forming shoe.

After wrapping, the cross seal is made with a permanently heated sealing system, and excess film is cut away with a knife.

Contracting packaging companies in particular need machines that can be quickly converted for new tasks. That is why the machine is equipped with an integrated product data memory that keeps changeover times to a minimum, thus ensuring higher productivity. The memory can be used to store up to 250 different products for packaging.

The data stored is not limited to the format but also includes the seal bar temperature, sealing times or temperature of the downstream shrink tunnel.

By using software on a PLC machine control system with Profibus communication, it takes only a fraction of a second to switch drive parameters.

Lenze 8200 vector inverters — equipped with two parallel communication interfaces — control the film feed, into which optional communication modules are plugged.

They include an integrated RFI filter compliant with Class B levels and occupy a minimal amount of space. Easy plug-in connections are provided with large surface special shield sheets for optimum EMC behaviour.

In this case the helical geared motors for variable speed operation are equipped with incremental encoders for closed loop feedback, connected into the plug-in I/O module on the frequency inverters.

According to Tino Kraut, technical director at Kallfass, the degree of speed synchronism achieved is sufficient to ensure the level of accuracy required by the machine.

For this reason the company has decided that there is no need to use servo technology to transport the product through the machine.

Advances in AC drive technology have helped Fibre Extrusion Technology of Leeds win a valuable machine order from Korea and subsequently Japan. The commpany is to manufacture two machines to manufacture a hi-tech suture material for the medical industry. Synthetic absorbable polyglycolic acid (PGA) sutures biodegrade within the human body, whereas previous synthetic sutures, based on monofilament nylon, were not dissolvable, making them unsuitable for internal stitching.

PGA is manufactured using a melt spinning process originally developed for the manufacture of polypropylene which, when woven, was used for high-strength straps such as seatbelts, lifting straps and cordage. Following polymerisation of the raw material, the PGA is extruded through specialised heated dies.

It is crucial for the speed of the melt pumps to be controlled very accurately to ensure constant denier of the fibre. In the original evolution of the machines, synchronous or synchronous reluctance motors were driven by standard inverters. Modern drives, however, have more accurate vector control, which has enabled standard 1.5kW induction motors fitted with encoder feedback to be adopted.

Passing from the die, the fibre is air quenched to solidify and stabilise it before being passed to a series of four pairs of heated draw rolls, each pair being driven by a single inverter drive. Here again, high-speed accuracy and stability is critical as the accuracy of draw-ratio between roll pairs imparts molecular orientation and governs the material denier.

There is a final relaxation to condition the yarn before it passes to a wind-up section where the fibre is laid on to a bobbin in an accurately-controlled pattern to ensure a stable pack.

Managing director Richard Slack said his company selected the new Danfoss AutomationDrive FC302 for a number of reasons. ‘In addition to the highly accurate vector control, there are a number of features that simplified their adoption and gave us confidence. Not least of these is the ability to connect the drives on an Ethernet network that enables us to interrogate the machine set-up remotely.’

Variable speed drives, or adjustable speed drives, are not new to industry but continue to provide significant benefits. Paper manufacturer UPM’s plant at Shotton, Flintshire, has achieved its goal of producing all its paper from recovered waste paper, rather than virgin wood, with the help of ABB’s variable speed drives.

Known as the ‘100 per cent Shotton project’, it has involved the building of a new recycled fibre plant, a sludge plant and modifications to two paper machines. The drives are used mainly on pumps in the process, using variable speed to match pump speed to the production rate.

They are also used on chemical dosing pumps to accurately add chemicals to the pulp, helping manage the process better, adjusting the inputs to the plant to maintain the correct pressure and temperature conditions, as well as making it easier to control the production rate.

So well did the implementation phase go that on start-up, the drives and automation system were switched on at the exact scheduled time. ‘It was like switching on a light,’ said projectautomation manager Ray von der Fecht.

He said that compact size was part of the client’s demand, to save on space, improve efficiency and heat loss and cut cooling costs. Another useful feature was the ability to communicate over Profibus, the industry standard for communication in paper production.

Holkirk Communications is changing satellite news-gathering with its Cyclone compact fly-drive system. This uses a backlash-free Sumitomo Fine Cyclo unit, which allows it to find satellites automatically, obviating the need for specialist staff in the news-gathering process.

The fly-drive system can be mounted on an ordinary vehicle and then dismantled for shipment to the latest world trouble spot or disaster area without the need for weighty support structures.

When disassembled for shipment by air, Cyclone fits into three cases that can be checked in on a flight, all of which weigh less than 32kg.

The system can be easily installed on the roof bars of standard vehicles, with no tools required for assembly, so it can be deployed quickly and easily in the harshest of environments.

The unit is used for the elevation drive of the antennas. ‘The positioning accuracy provided by the backlash-free operation of the Fine Cyclo enables the system to find satellites without any trouble and, because it’s such a positive drive, it can do this without the aid of skilled personnel,’ said director of Holkirk Communications Steve Kirkwood. ‘Importantly, the unit is very light for the torque capability that it provides.’

Andrew Riddle, Sumitomo’s area sales manager, said: ‘Its combination of zero backlash, minimal lost motion (down to one arc/min) and high torsional stiffness ensure the ultimate in positioning accuracy. This makes it the ideal unit for this type of application.’

One of the first Cyclone systems has been supplied to a company that provided live feeds from outside of the grounds hosting World Cup matches in Germany this summer.

The company’s main broadcasts were made via cable, but the Cyclone system was used to provide coverage of teams while training, as well as for interviews and press conferences at the team hotels.