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10/02/2006
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A novel three-axis control system that reduces vibration in camera lenses has been developed that enables the filming of tiny insects in the undergrowth. Dean Palmer reports
 A novel three-axis control system that reduces vibration in camera lenses has been developed that enables the filming of tiny insects in the undergrowth. Dean Palmer reports
A novel system that comprises worm wheel gearboxes, lead screw actuator rail assemblies and DC motors has been developed, specifically to reduce vibration in a miniature camera lens used for filming tiny insects in the undergrowth.
Bristol-based company Ammonite, set up by film maker Martin Dohrn, is responsible for the design, construction and funding of the system, which was used to support special camera and video equipment for filming and photographing the BBC's recent nature programme 'Life in the Undergrowth', presented by David Attenborough.
The camera support system is called 'Frankencam', which is one of a series of eight unique camera support systems developed by Dohrn over the last decade or so. Other systems are used for filming underwater ('Guppycam') and another is used specifically for filming ants ('Antcam').
Frankencam is Dohrn's latest development and is based on a complex-looking assembly of mechanical and electronic systems. However, on closer inspection, the system is made up from relatively simple, off-the-shelf linear motion systems, motors and gearboxes, but integrated by some rather unique mechanical connections and pivot points. The system was developed and refined over the last two years.
Dohrn demonstrated Frankencam to Eureka and explained some of the design problems he was faced with initially: "When it comes to filming tiny insects at ground level, you need a camera support system that reduces vibration to a minimum so that the lens doesn't move and ruin the shot. The first version of Frankencam suffered from too much vibration because it was hand held. The body's balance is not particularly steady when you're filming in such awkward places close to the ground and so the lens kept moving too much and a lot of time and shots were wasted."
So Dohrn then decided to try to counter these vibration problems by eliminating the human element and introducing a unique camera support system that could be controlled remotely by joysticks.
At the core of Frankencam is a Panasonic 'Varicam 27F' high definition variable speed, three-chip video camera and a 10mm diameter wide angle lens for filming the insects. The lens is fixed to the video camera via Dohrn's custom-designed 'miniscope' assembly, which allows the lens to get closer to the ground for filming small insects.
The video camera itself is fixed to an aluminium support bar, again, custom designed by Dohrn, which is basically a bent piece of aluminium, which pivots on a nylon bearing and attaches to a leadscrew actuator rail assembly.
The leadscrew actuator assembly is fixed to a carbon fibre tripod via a baseplate. The lead screw actuator itself is an off-the-shelf 'LA8' unit supplied by Chesterfield-based company Ondrives, who has a long-standing collaboration with Dohrn.
The LA8 unit is a 600mm medium duty leadscrew actuator which Dohrn adapted to a focus slide giving the lens backwards and forwards movement. The leadscrew itself is a ZBX Teflon-coated stainless steel design. The base, rails supports and carriage are made from anodised aluminium and the anti-backlash nut is a self-lubricating polyacetal. Shafts and bearings are hardened steel. The complete actuator assembly weighs around 3kg and lead accuracy is 0.0006mm/mm, more than enough for Dohrn's requirements.
The actuator assembly has two worm wheel reduction 'P type' anodised aluminium gearboxes, supplied by Ondrives. A flexible coupling, again supplied by Ondrives, sits between the leadscrew actuator assembly and a DC drive, supplied by Maxon Motor.
The drive comprises a DC motor, a 23:1 or 256:1 ratio reduction gearbox and an encoder/tachometer unit.
But, as well as backward and forwards movement of the camera and lens, Dohrn needed other axes of motion, up and down and left to right. For the vertical axis, Dohrn used another identical 600mm leadscrew actuator assembly from Ondrives fixed to another (smaller) tripod mount. This assembly was then attached via a polished steel rod and linear bearing (both from Ondrives) to the main central tripod, giving Dohrn a total of three axes of movement for his camera.
One really clever component which Dohrn designed and built himself, is a
The whole camera support assembly is counter-balanced by weights but offers Dohrn the level of precision he needed to film the BBC's 'Life in the Undergrowth' programme. Eureka was able to see first-hand how the system helped reduce vibration and how it gave Dohrn the precision he needs to film such tiny insects.
The camera system can be controlled remotely via two joysticks and a controller unit, through a 10 metre-cable. This means Dohrn can sit up to 10 metres away from where the filming is taking place and so not disturbing the insects, which means better quality film can be taken.
To develop the complete Frankencam system, Dohrn required the expertise of a number of engineer-colleagues. "Without the support of these engineers and Ondrives, the system would have been very difficult to develop," enthused Dohrn. "The high quality equipment sourced from Ondrives and Maxon Motor has been instrumental in taking the system from concept to reality."
Dohrn has been described by those that worked with him on 'Life in the Undergrowth' as "an optical and mechanical wizard". Eureka certainly agrees with this statement, after seeing the system in action. Frankencam, whilst developed for a unique application, solves a common problem for many design engineers, that is, to create control systems that reduce or eliminate vibration for high precision applications.
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Author
Tom Shelley
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