Requirements for components used on therapeutic equipment

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Nigel Pritchett, the Managing Director of Elesa (UK) Ltd, discusses the particular requirements for components used on therapeutic equipment and postural seating.

Requirements for components used on therapeutic equipmentThe specifications for components of postural seating and therapeutic equipment – such as chairs, wheelchairs, wheeled walker frames, massage couches, beds and support frames – have developed substantially in recent years, together with the industry. This is perhaps especially true of those products designed to improve the quality of life for children with special needs.

Widespread requirements have been identified for seating of able-bodied individuals to maintain good posture and good health, as well as seating for people with special needs to aid greater comfort and stability. In these cases individual adjustment is essential to provide properly distributed support to, for example, feet, arms, buttocks, thighs, the back/lumbar region and head. This often complex seating can require fully adjustable components, frequently customised with additional items such as lateral supports. Similar needs were found in transport conversions, adjustable desking and tables for home or office working, as well as adjustable beds and access equipment. Not only are these extremely functional mechanisms, but they are also required to be of a high standard aesthetically.

Elesa has found that applications into this product group require standardised but specialised components for the locating and clamping of adjustable assemblies. Specific categories of mechanism have been identified:

  • Extensible tubes with clamping actions
  • Rotating joints with indexing positions
  • Rotating joints with continuous clamping adjustments
  • Temporary locating and clamping of equipment
  • Operating levers for actuating mechanisms

Consequently Elesa's engineers initiated a development programme that sought to accommodate the needs of this important industry.

Sliding tube arrangements

Initially the engineers found that, typically, the design of these types of adjustments can involve an inner tube sliding within an outer tube or sleeve. The inner tube that extends to achieve the required distance setting is invariably of a high surface finish for aesthetic reasons and may often be chrome-plated for aesthetic or hygienic reasons.

In addition, the engineers listened to manufacturers of postural seating who often commented on problems of achieving sufficient torque on clamping components to achieve the necessary clamping forces required to hold adjustments in place, specifically those that could experience a lot of weight such as foot plates and back rests. It also became evident after a period of use that the inner adjustment tubes were becoming scratched and damaged from the clamping systems then being used. Invariably this was down to the use of poorly designed clamping products that were not of an ergonomic design and, as such, did not allow sufficient torque to be applied - and in many cases this was further compounded by the incorporation of conventional bolts to form the clamping point, rather than custom-designed inserts.

Other factors found to be influencing design requirements were the need, in some cases, for adjustment to be made by occupational therapists or under parental control and protected from misuse, or the ability to make adjustment when the grip of an operator may be impaired in some way.

All of these factors were taken into account by the Elesa technical department while understanding that cost would also be an issue when investigating suitable designs. The specification mix defined a number of new products and variants derived from the Elesa range, thereby extending the established lineage of quality, functionality and value.

Soft-touch overmoulding

Elesa took its well proven VCT five-lobe knob design, which already incorporated purpose-designed inserts with faced and chamfered ends, and overmoulded a 'soft-touch' thermoplastic elastomer (TPE) to improve grip and aid the application of torque. In instances where the end of the stud is clamping highly finished tube, a further enhancement was the addition of a Delrin insert in the end of the studs.

The standard range of VCT Clamping Handknobs is said to represent a significant improvement over older style products manufactured in thermosetting material (which can shatter on impact) and, in this case, the glass-reinforced thermoplastic construction not only confers high ruggedness and impact strength, but is also suitable for overmoulding. A major additional feature of the VCT series is the availability of coloured centre caps in blue, red, yellow, orange, grey and black (standard). These allow for colour-coding of equipment functions or matching of the finish to the equipment for improved aesthetics. For alternate functions, female and through-threaded versions are offered with brass inserts, while male versions have zinc-plated steel studs. The VC range of five-lobe grip knobs also offers the aesthetically striking chrome version – known as the VC.692-CR - as a cost-effective alternative to stainless steel, which also addresses the hygiene issues involved in frequent-use medical situations.

For applications requiring a level of protected adjustment, Elesa introduced the VLS security knob, which is a further derivative of the VCT five-lobe design incorporating a security key. VLS security lobe knobs (for which Elesa has a patent) have been designed to be unsecured only by authorised personnel provided with the ingenious security key. Without the key inserted, the knob can be clamped in the conventional manner and, with the key in place, it unscrews as normal; but when the key is removed, an internal ratchet mechanism operates with an audible click warning so the knob cannot be undone and the knob head simply rotates while the clamping action remains fixed. This ensures that important settings are not lost and that adjustments are not made by unskilled personnel.

Two types of key are available: a fold-down type to be left in place (eg for use throughout the working day, and then removed); and a ball-top key to be kept on a key ring for occasional use. Both have red moulded handles for ready identification.

Quick clamping

For ultra-quick clamping operation, the Elesa range of eccentric cam-operated levers is suited to equipment mounting on tubular frameworks. The LAC series are designed for attachment to medical furniture, wheelchairs, trolleys, orthopaedic seating, therapeutic products, bicycles or other mobile equipment where rapid fixing/removal or re-positioning is required (eg rapid assembly of mobile stands or supports).

LAC cam-clamps feature a smooth-action cam clamping plate arrangement with fine adjustment by means of a knurled knob, or they are available in a non-adjustable configuration. This cam with plastic clamping plate design ensures smooth, torque-free clamping to eliminate movement or 'wriggle' during the clamping process, as well as ensuring that the clamping force cannot exceed set limits - which can be as high as 5000N. Both adjustable and non-adjustable types are available in female or male M8 threaded formats. Since the LAC clamps are intended for frequent manual operation, Elesa has paid special attention to ergonomic features such as touch comfort, feel and fit, using well-proven glass-reinforced polyamide technopolymer for the hand lever itself.

For adjustments where high forces are involved, Elesa recommends the use of indexing plungers to give a positive lock in a number of pre-determined positions as opposed to relying on the clamping force of a handknob. These are the type of item that are vital in many situations, but they often require space that is difficult to achieve, and give an awkward appearance if too large. Mini indexing plungers of the GN 822 series feature an AISI 303 stainless steel plunger that provides accurate positioning, while the technopolymer knurled knob offers a safe and solid grip during operations. They are useful for these applications due to their low overall height and shortened threaded body. Options are available with and without lock out 'rest' positions.

In the Elesa technical department many other components are also coming under scrutiny for medically-related applications – items such as handles, clamping handles, castors and even handwheels come into this arena where increasingly special considerations are becoming the norm.

Further information on components for therapeutic equipment is available from the Elesa website at

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