Keeping patient mobility on track

Author : Robert Kershaw, Business Development Manager at Magnet Schultz

02 November 2017

Figure 1. Ceiling hoists provide valuable mobility, but can benefit from more  advanced tracking design

A medical technology supplier envisaged an innovative diverter unit for tracked ceiling hoists, designed to enhance efficiency and comfort when transporting patients between hospital treatment and consulting rooms. This article discusses how Magnet Schultz took on the design aspects of the critical 'diverter' component… and ended up delivering the entire system prototype – all in a two month development window.

This piece originally appeared in the September 2017 issue of Electronic Product Design & Test; to view the digital edition, click here – and to register to receive your own printed copy, click here.

Used widely in hospitals, hydrotherapy areas, schools and care centres, tracked ceiling hoists (Figure 1) are invaluable mobility aids for people with disabilities and for rehabilitation (for example after a stroke or sports accident), helping patients reach areas that are difficult to access. A hydrotherapy pool is a good example: the therapy is known to be highly effective for managing chronic conditions or aiding recovery, but entering and leaving the pool can be challenging for patients – and support is needed throughout the treatment session for safety reasons.

Eliminating the turntable Conventional ceiling track systems typically use a rotary turntable mechanism in a central location. To move a patient from one area to the next, the hoist is driven to the turntable, rotated around the mechanism until it aligns with the exit track, and then driven on to its destination. The journey can be frustratingly long, even when a patient simply needs to move to an adjacent room. An efficiency improvement was conceived that deploys a function equivalent to a set of railway line points in the track. This required the design of a special ‘diverter’ device with the ability to switch on demand – a solenoid actuator being the optimum solution.

Magnet Schultz Ltd (MSL) is a leader in the design and development of special-purpose electromagnetic subassemblies, as well as an astute outsource partner for electromechanical development teams. That was the basis upon which the company was initially contracted to design and prototype the diverter unit.

The customer had limited design and prototype capabilities in-house. The original diverter unit design and improvised mechanical mock-up used an imported conventional solenoid – that would neither deliver the required performance, nor provide the working life needed. Upon studying this, MSL’s experts advised immediate changes, and quickly took over the task of engineering the complete diverter mechanism, offering a faster, more reliable and cost-effective route to a testable pre-production model (Figure 2).

Figure 2. The track diverter system is  fast and easy to use, eliminating the  waiting time associated with conventional rotating diverters

Rethinking design at the module level A focus on the complete subassembly solution allowed MSL to base its prototype on a powerful standard solenoid to fit the electrical design, but then to further customise this to suit the diverter application. Re-imagining the design for the physical ‘pivoting blade’ mechanism greatly informed the development process about how best to position the actuator within the diverter module to achieve the dependable physical switching required.

The function of the diverter called for a strong, single-acting solenoid, which actuated in one direction to move the blade, with a spring mechanism to return. Position sensing would use a pair of microswitches to confirm mechanical actuation and provide feedback to the controller. The standard solenoid was customised to feature an over-moulded and encapsulated coil to prevent moisture ingress, along with corrosion-inhibiting nickel-plated armature and stainless-steel return spring. It is continuously rated to cater for a constant power-on state.

During the electromechanical design process, the design team also developed many novel interchangeable features that meant one set of parts would work for both a left-hand and right-hand variant of the diverter module. Such design enhancements helped to simplify the manufacturing of the diverter blade and reduce bill of materials costs. MSL engineers designed the mechanism to minimise power consumption and respond quickly to user commands received from the hoist’s remote controller.

In its quiescent state – the ‘straight on’ default position on the ceiling track – the solenoid draws no power. Such low consumption helps to minimise demands on the system power supply, in turn allowing the use of a small and lightweight unit to help ensure a competitive price tag for the diverter.

Figure 3. Ultra-low-power actuator  latches for automatic window shutter closure during fire containment

An expanding design brief After the diverter module design proved a success, MSL was then invited to take on development aspects of other key parts of the transporter system. While MSL’s core competency is the design and customisation of application-specific solenoid mechanisms, the company increasingly provides whole system electromechanical solutions and has a broad portfolio of successful projects in its ‘back catalogue’. Among these are concealed sub-floor door locking solutions for historic buildings, rapid lockdown anti-piracy protection mechanisms for superyachts, and fire containment systems for portable buildings.

Each project features solenoid actuation at its heart. On some projects, MSL is called in at the outset: the informed design community knows where the focused expertise lies. But many begin life when MSL is called in to address design problems, typically where either an off-the-shelf actuator function becomes a development bottleneck or there’s a knowledge shortfall in-house. Such was the case with the diverter module for the patient transport system.

Moving the design brief beyond the actuator assembly is common. In its simplest form, MSL frequently develops custom housings for a variety of reasons, including requirements to conceal a mechanism or make it environmentproof; some solenoid actuators are even customised to be ATEX-rated for certified use in hazardous or explosion-sensitive settings. Other projects are more sophisticated – for instance, the fire containment challenge for portable accommodation buildings (worksite cabins).

Here, a system-wide, battery-powered and ‘ready-to-install’ solution was developed for the client by MSL from the ground up. It comprises: ultra-low-power purpose-designed actuator latches for automatic window shutter closure (Figure 3); the critical torsion spring mechanism to close those shutters with a predetermined acceleration (not too fast to avoid endangering the safety of nearby personnel); the control panel with status indicators; sensors; wiring looms; connectors; evacuation alarm and mounting hardware; as well as defined test functions and procedures.

For the patient hoist transport project, the expanded brief saw the MSL engineering team undertake the development of the wall-mounted power supply and controller for the diverter, including environmental considerations based on likely installation locations. The mains-powered control box design uses an IP-rated enclosure. The electrical internals are simple, comprising IP-rated switches and LED indicators to show the direction of the ceiling-mounted diverter, alongside a transformer – needed to drive the electrical system and the solenoid – to supply the 12V rail.

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