Commander SK Drives Keep Cinema Trailers And Ads On Schedule

What they probably don’t realise is that each such commercial presentation is carefully worked out to be relevant to the target audience and is changed weekly at each screen and each cinema throughout the UK. This massive logistical task is the responsibility of one company based in Slough – Bucks Laboratories – and the special purpose machines for the editing task, designed and built by the company, all feature intelligent AC drives from Emerson Control Techniques.

“Control Techniques was instrumental in us winning this prestigious contract,” comments managing director David Buck. “The reliability and flexibility of the drives – with their in-built PLC functionality - was crucial to us. We simply could not have achieved this without Control Techniques!”

Bucks Laboratories, an established film processing laboratory serving the UK film industry, has an extensive engineering capability, with a reputation in the market for upgrading and re-engineering equipment for both positive and negative processing – and film copiers / printers as well .

“We use the on-board PLC processing of both Unidrive SP drives and Commander SK AC drives to bring older, mechanically sound machines to the standards required in today’s market,” explains engineering manager Graham Greenfield. “The drives’ capabilities eliminate the need for an extra PLC and they communicate directly with our PC and touch-screen interface, which has the same control ‘buttons’ as the old machine controller to provide a straightforward changeover to our up-dated machines. So we are used to using the intelligence of Control Techniques’ drives to the full. We use Control Techniques drives for many applications exclusively throughout the company and have never had a failure in over 13 years!”

So, when the company had the opportunity to take on the ambitious UK-wide contract for advertisements for cinemas, Graham Greenfield felt confident that, using the capabilities of Control Techniques Commander SK AC drives, they could build the machines needed for the tasks – with an initial deadline to meet of just three weeks!

“We conceived unique machines to provide fast, reliable and easy-to-control editing of the filmreels” says Graham Greenfield. “We call them ‘White Winders’ because of the melamine board construction of the editing desks. Each uses Commander SK’s for both drives and overall machine control too, utilising their in-built PLC capability. The design is simple, elegant – and it works!”
When the company initially won the contract, Graham raced against time to produce the first machines, which were operated manually with foot-pedal control. As time went on, he was able to introduce more sophisticated control, including automatic recognition of film joins using ultra-sonic attenuation sensors that allow the film to be stopped with millimetre accuracy and very precise tension control.

“Film is heavy,” he explains. “There is a lot of inertia in the reels, so stopping a film from 1,000 ft/minute speed very quickly requires very precise control to prevent breakage or, worse, ending up with a pile of film on the floor.” The take-up drive determines the speed, in closed loop mode with feedback from a diameter sensor, using PID control to keep film speed constant between edits. The feed drive controls the torque, with a spring-loaded dancer control feeding back a 1-10V signal to the drive. For each edit, the operator determines which join on which to stop. The take-up drive counts the signals from the ultrasonic thickness sensor and initiates a stop signal that simultaneously ramps down both drives whilst maintaining precise tension control and stops the film to within one millimetre accuracy. Since film has 16 frames/ foot, 64 perforations /foot, this effectively gives exact position control of the film to allow the operator to carry out the appropriate action specified on the work-sheet.

Conservatively dimensioned Emerson Leroy Somer motors ensure that slippage is eliminated. The winders can be used in four basic modes, feeding from the top or bottom of either reel and with a third reel that can be designated to run as either feed or take-up if required. This means that each drive has to be capable of performing different roles as needed and is programmed accordingly with numerous ‘recipes’. The operator’s control simply designates duty to each drive by code number that selects the appropriate programme.

“Because the real-time response is carried out in the drive, it is so much faster,” comments Graham Greenfield. “I like the flexibility of these drives with on-board processing, including PID control which is standard – on many drives this is extra. It means that there’s no additional PLC required, even though the Commander SK is marketed as a general purpose drive.”

“In reality, it’s very powerful, very intelligent and keeps the cost of each machine down and our costs competitive. You can’t buy something like our white winders off the shelf. Every bit of their functionality is done by the SKs.”
Bucks Laboratories now has a total of 18 white winders. Each has one 0.37 kW, one 0.75 kW and one 1.1 kW Commander SK drives, complete with LogicStick and no additional I/O or special plug-in modules are needed. Graham Greenfield carried out all of the programming.

Bucks Laboratories’ cinema contract is complex. There are two reels for each cinema screen, one at the cinema and the second at Bucks for preparation – cutting, inserting and changing content order. Thousands of reels have to be completed and delivered in time for the weekly changeover. In addition, Bucks Laboratories holds the national stock of cinema advertisements and Graham has written the stock control programme too! Currently, some 70% of UK cinemas still use film for trailers and advertisements, although the trend is to digital – and Bucks Laboratories provide this service too.