EUREKA OCTOBER 2003 COVER FEATURE STORY

Golden chain thrusts into actuation

Tom Shelley reports on a device that could revolutionise linear actuation in a very wide range of products

In a novel actuator, a chain of links in a guide are coiled round in such a way as to form a strong, rigid rod, which emerges at 90 degrees to the chain guide.

Exceptionally ingenious, its Danish developers have named it the 'Kataka', Sanskrit for golden chain, in the hope that it will yield appropriate profits.

It requires very little space in its direction of actuation when retracted. It therefore offers benefits to designers of a vast range of products from window openers through hospital bed height adjusters to car jacks.

Soren Jensen, of promoters, VKR Holding, based in Copenhagen, told Eureka that Jens Sorensen, its inventor, was inspired by the feeding of cartridges into machine guns. The original intention of the invention was to devise an improved window opener whose mechanism could be concealed in its frame.

Locking chains have been made before, and the 'Indian rope trick' with slats locked together by a tightened cord has been known for centuries. Previous designs, however, have tended to lack something in their load carrying capacity when free standing, which is why the rope trick was only ever performed with a small boy climbing it.

The secret of the new device lies in its links. These are parallelogram shaped, with a hook shaped hinge member at each end. Each link is made up of two elements that can slide over each other in a direction parallel to the axes of the hinge members. The inner elements possess helical grooves on their insides, and the outer members, curving grooves on their outsides. Each inner element also has a tongue at one end, and a fork at the other.

In unextended mode, the links sit in a rectangular guide, linked by their hook shaped hinge members. They are drawn into the actuator assembly device by an advancing wheel with helical protuberances that fit into the helical grooves on the insides of the links. Fixed protuberances on the inside of the assembly device fit into the curving grooves on the outsides of the outer elements, guiding them into position.

When the links are fed into the assembly device, they are turned relative to each other so that the hook shaped hinge members engage fully with each other. At the same time, the links slide relative to each other so that the parallelogram links form a continuous, long parallelogram, coiled into a spiral. Because the inner and outer elements of each link are displaced relative to each other, the boundaries between adjacent inner elements and outer elements are similarly displaced relative to each other, giving the formed rod rigidity. This is enhanced by engagement between tongues and forks at each end of the inner elements.

The device presently exists in the form of a working proof of concept prototype. This extrudes a rod of 18mm diameter and has a maximum stroke of 500mm. In its retracted position, it has a height of 35mm. Speed is 3mm/s and the machine has so far been put through 10,000 cycles, lifting a 50kg load. Maximum dynamic force is 250kgf.

The prototype draws its chain links from a rectangular guide, but they could be stored in containers of many shapes, including coiled configurations, requiring little space. The hollow central core of the extruded actuator offers a space for wires, tubes or cables.

The idea is patented or has patents applied for in various forms and configurations and in all "Significant markets." The developers and promoters are looking for partnerships with companies able to turn the prototype into a family of industrial products. Partnerships could take the form of joint venture agreements, licensing or marketing. Potential markets have been identified in satellites, aerospace, the automotive sector, furniture, hospitals, the military, automation and special purpose machines.

Used as car jacks, the devices could be built into a vehicle chassis, so the car could be raised off the ground for a tyre change at the touch of a button. This would be most useful in a world where many drivers are unable to use a conventional jack while others cannot be relied on to use one at all safely. For large commercial vehicles, including cranes and construction equipment, the units offer a sleeker and tidier way of making stabilisers. They could also simplify the construction of caravans and campers that have extendible or liftable sections to allow the provision of maximum space when stopped, while causing minimum wind resistance when driving.

Being light and portable, it has been suggested that they might be used in avalanche rescue equipment. By heating the tip of a drill on the end, it could quickly reach a buried person, presumably located by GPS, allowing the supply of oxygen and other vital supplies. For the same reasons of lightness and compactness, the actuators offer promise in shop window and exhibition trade stand displays.

In security applications, extended rods could be made to protect windows and doorways. Door openers could be made more discrete, with the mechanism concealed in the frame and new kinds of blinds designed that could extend from one side, or rise from below. As awning extenders, the actuators offer the possibility of running lighting cables down the centres of the rods, protecting cables as well as making them look tidier. They have also been suggested as suitable for the rapid erection of military tents and mobile hospitals. Banners, tables and road signs could all be made to extend outward from walls or ground. Disappearing bollard lamps could be made that would not require the digging of deep holes. Queue divider posts in airports or posts for tennis or volleyball nets in sports halls could be erected instantly when required. Chairs and beds could also be easily height adjusted using compact mechanisms hidden in framework. It has further been suggested that wardrobes or clothes shop racks could be made with extendible rods for hangers. Kitchen drawers could be electrically opened or closed or work surfaces raised or lowered, to suit the needs of the disabled or lazy. Cooker hoods could be made to disappear or fold behind appliances when not required as could loudspeakers, television and other items of furniture. Many other applications are also possible, limited only by designer's imagination.
VKR-Holding
or email Soren Jensen

Pointers

* Special links are coiled into a spiral to form a strong, rigid rod

* The links can be stored in a container of arbitrary shape or within a window or door frame or vehicle chassis member

* The device exists as a working proof of concept prototype

For more technical developments see www.eurekamagazine.co.uk

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