Aorangi Mt Cook summit ridge
Aorangi Mt Cook
Aorangi Mt Cook
Glacier fed river
Out on a Limb
The eastern side of Aoraki Mt Cook has two great faces; the 2,500-metre Caroline Face and the 1,800-metre East Face. Winding between the two is the East Ridge, an arête of ice and snow leading directly to the middle peak of the mountain.
Aorangi Mt Cook summit ridge
Aorangi Mt Cook
Aorangi Mt Cook
Glacier fed river
In late November 1982, two young mountaineers climbed the ridge, reaching the top around 6pm. In good conditions, they would have rested a while on the summit, enjoying the uninterrupted view to the Tasman. But when the pair reached the summit conditions were atrocious. Their planned descent route to the west was closed by the full blast of a storm roaring in off the sea and returning via their ascent route was out of the question. They settled into a small crevasse just below the summit and waited. It was an uncomfortable night – their refuge was too short to lie down in properly and too low to sit up in – but they were confident the storm would soon pass, as it would normally have done, in a day or so. But the airstream proved unusually persistent and they were trapped for 13 days.
Temperatures touched minus 20 degrees Celsius, and before rescuers could reach them the climbers were severely frostbitten. On Christmas Eve 1982, both of them underwent double below-the-knee amputations.
Almost exactly 20 years on one of the pairs, Mark Inglis, returned to the mountain. After one abortive attempt, he climbed it, using a pair of prosthetic legs designed and built by Dashfoot Ltd, which at the tune was a subsidiary of the Britten Motorcycle Company of Christchurch. The story of those climbing legs is a story about an approach to engineering that is both medieval and utterly contemporary.
The Development of Dashfoot Ltd
This case study is reproduced with permission from e.nz magazine. Subscriptions to e.nz are discounted for schools and TENZ members.
The Concept
Prosthetic foot and socket
Dynamic Response Foot 2
The Palmer Leg
In recent years there have been huge advances in prosthetics, mostly in materials, progressing from wood and metal to plastics and, more recently, carbon fibre. But amputees still face the same fundamental problems: unlike living legs, artificial legs produce no power of their own and they can't receive sensory information.
An amputee, where once they relied on the complex interaction of muscles, tendons, and ligaments to provide just the right amount of thrust while maintaining balance, has to fling forward what is essentially a dead-weight. To address this problem, energy-storing feet were developed in the 1980s, featuring a spring that captures the power created at the strike of the heel and uses it to propel the leg forward.
A healthy leg continuously receives information from its nerves about positioning, terrain and speed, and sends this information to the brain. The brain, in turn, sends instructions to the leg on how it should bend and adjust. Without signals travelling in both directions, amputees find it difficult to maintain a normal gait and are at constant risk of falls and injury. A new generation of computer-controlled prosthetics promises to alleviate this problem; computer chips paired with sophisticated sensors may ultimately allow artificial limbs to replicate the complex functions of healthy limbs.
While a truly bionic leg – an artificial limb "wired" to the brain – is still the stuff of science fiction, rudimentary microprocessor-controlled limbs are available. But they come with a hefty price tag: the C-Leg, produced by German company Otto Bock, costs around US$40,000. What was required, Wayne Alexander reasoned, was a robust but light energy-storing limb that could be cheaply mass-produced.
In 1997, Wayne Alexander was introduced to Mark Inglis through the Para Fed organisation. He set about producing what he calls a "graft" – a quickly assembled prototype, brazed together from panel steel – that embodied his ideas. The aim was to establish the first principles from which a sporting limb could be produced (Conceptual statement).
From the outset it was clear that it would be a waste of time re-engineering the sockets connecting Mark's stumps to his artificial legs. An artificial leg is fitted by means of a socket that fits snugly over the stump like a thimble on a finger. The socket is custom-made of fibreglass or plastic, and held on either by suction or by a system of belts or straps. Much of the prosthetist's art lies in fitting the socket, creating a comfortable connection that minimises irritation, blistering and tissue breakdown. To complicate matters stumps swell and shrink, changing the fit. (A relatively new approach is to bypass the socket and connect the artificial limb directly via a titanium-coated stainless steel pin implanted in the cavity of the femur.)
COP Outcome development and evaluation
Mark sacrificed the sockets from an old pair of legs and mounted them on the prototypes. He describes the prototypes as looking "heavy enough to anchor a boat"; but they worked – "After two steps I wanted to run and jump".
Design
Saint Maria del Fiore, Cathedral or Duomo of Florence
Church of San Lorenzo, interior, ceiling detail
Church of San Lorenzo, exterior overview
COP Outcome development and evaluation
The design incorporated a urethane block in the ankle joint, the aim being to create a foot with a dexterous ankle and a solid heel (DASH). The industry standard has a solid ankle and cushioned heel (SACH). The original idea was to use the resilient plastic – originally developed for mountain-bike suspension systems – as if it were a torsion bar on a car's suspension, and lever it in different ways.
Eventually, this approach was abandoned. Wayne says the freedom to change part-way through a design project is critical. "An open mind is one of the best things you can have... you have to be really careful to maintain the freedom to push any of it off your bench at any point."
The approach is artisanal, very hands-on. Before the Renaissance artisans made things directly. Ideas may have been sketched on paper or on the materials from which the thing was made, models may have been made, but artisans worked directly with their materials. During the Renaissance, the role of the artisan was split into that of the worker and that of the engineer. Rather than make things directly, engineers began to use drawings to explain their visions to other people who would build them.
(Some of the earliest such drawings were made in the early 15th century by Filippo Brunelleschi , who designed and supervised the building of the great masonry dome of the Cathedral of Santa Maria del Fiore in Florence. Wishing to prevent his original design for a crane from being pirated, Brunelleschi sent drawings of various components to separate workshops outside the city and assembled the parts when he received them.)The artisanal/bespoke approach incorporates the application of what Eugene Ferguson terms non-verbal/non-visual knowledge – practical skills and the intuitive "feel" for materials that comes with experience.
There's nothing precious about this approach, Wayne argues. It's simply a way of establishing the first principles of a particular design problem. Most design challenges are ill-defined in their early stages; there are no single "right" answers, merely many better or worse solutions. Developing prototypes is a way of clarifying an idea and bringing it into focus. A working prototype can be modeled and reverse-engineered, detailed and refined for manufacture later.
The performance of disabled athletes is greatly enhanced by the custom engineering of prosthetics, not only for the individual body, but also for the specific requirements of the individual's particular sport. In the early 1990s Mark Inglis collected a clutch of medals in international disabled skiing events, then become obsessed with cycle racing. He was committed to attending the 1998 Paralympic World Cycling Championships in Denver, Colorado, mere months away when the focus of the design task changed from a walking leg to a cycling leg.
Development
Cyclists
Even for the able-bodied cycling is an unnatural thing to do. Moving the feet in a pair of circles, with the two feet at opposite points in their respective circles, bears little resemblance to any gait of any bipedal or quadrupedal animal. Neither gravitational nor elastic energy storage, used in normal walking and running, play much of a role. About the only "normal" aspect of cranking a bike is the opposite movements of the two legs and the use of the powerful extensor muscles.
COP Outcome development and evaluation
Cyclists obsess over their pedalling action and spend years perfecting what has been described as "the classical ballet of graceful pedalling". Cyclists lacking finesse stamp on their pedals, "chopping" them up and down, wasting energy; a good cyclist pedals in neat, fluid circles, maximising power transmission. The trick lies in the ankle – as the foot goes round, the toe moves from being level with the heel to a toe-down attitude at the top and bottom of each cycle. Mark Inglis' walking limbs stayed fixed through the cycle, giving him appearance of a waddling duck as he pedalled.
Wayne Alexander modified a pair of American legs, giving each foot a 15-degree downward rake toward the toe. Despite Mark's initial skepticism, the modification produced immediate results: he gained ninth place in the 16km time trial at the Paralympic World Cycling Championships. (In his recent book No Mean Feat Mark confesses he abandoned the legs at a New York airport, rather than pay exorbitant excess baggage charges – something Wayne still can't quite bring himself to talk about.)
Encouraged by the success of the concept, Wayne created a new pair of racing legs with aerodynamic carbon-fibre twin spars and a polymer "ankle", which Mark used at the 1999 Southern Cross Multidisability Games in Sydney. (After the event these legs found a permanent home at Te Papa). A third set, with toe-axis movement, was built for the Sydney 2000 Paralympic Games, where Mark won a silver medal in the 1km time trial.
In these legs, the pedal cleat bolted directly onto the footplate, doing away with the need for a shoe and reducing the rotating mass by about 400gm; but the key advance was the movement of the foot-plate relative to the pedal. As the foot passed through the bottom of the cycle, a spring in the plate flung the foot into a toe-down position, shortening the time spent in the null or dwell spot, where the leg is neither pulling or pushing.
Outcome
Sketch of prosthetic foot
e.nz magazine, March/April 2003, p. 6
Following the paralympics Mark Inglis decided the time had come to tidy up some unfinished business and return to Mount Cook. However unnatural, cycling is an extremely energy-efficient way of getting around; climbing, on the other hand, is sheer hard work – even more so for a person who must continuously fight for balance and who must bodily lift and throw his or her leg forward to take a step. (It is estimated that a person with an above-the-knee prosthesis uses about 80 percent more energy than an able-bodied person just to walk on a flat surface.) Something special in the way of prosthetics was clearly required.
Lightness was critical. Carbon fibre is light and immensely strong and has good energy-storing properties, but it becomes brittle at low temperatures. For this reason Wayne opted for a mixture of spring steel and titanium for the working components of what became known as the alpeds. A single carbon-fibre spar connected the foot to the socket.
To allow Mark to ascend and descend the steep route, it was important to find some way of placing his knees over his feet or behind them, depending on whether he was going uphill or down. It's a subtle adjustment, which normally isn't noticed, but a critical one.
COP Outcome development and evaluation
After some trials and breakages ("If it doesn't break during design then it's over-engineered") an 8mm spring was used to capture energy on heelstrike.
The energy stored was released as the front of the foot left the ground and effectively "kicked" the prosthesis through itself, saving Mark energy. During slope trials Inglis found the action so active that "they almost levitated me up the hill, with the spring off the toe almost throwing my feet up." The heel had a soft action and narrow profile, which gave great stability and cushioning on downhill sections, always the hardest on the stumps.
At 1pm on 7 January 2002, in near-perfect conditions, Mark Inglis reached the summit of Aoraki/Mt Cook. Wayne Alexander accompanied him on the climb.
Post script: Later this year Mark Inglis hopes to climb the 8000m Mount Shishapangma in Tibet, and the following year Mount Everest.
Wayne Alexander is busy reinventing the Solex and is negotiating with American interests over something he believes will make jetskis passé.
Intellectual property issues
The following questions were put to prosthetics developer Wayne Alexander in late 2007 by Susan Corbett, of Victoria University of Wellington, as part of her study, Intellectual property in Technology teaching, identifying intellectual property implications and issues that emerge from selected Techlink case studies. Their replies take the form of edited reported speech.
Wayne believes there are pros and cons in claiming intellectual property rights in a prototype. The cost of registering an intellectual property (IP) right such as a patent or registered design at the Intellectual Property Office of New Zealand (www.iponz.govt.nz) is an overhead that might be difficult for a new business to afford.
On the other hand, registration provides evidence of ownership of the IP in the prototype.
Until the prototype is developed, and until he is confident that it is worth protecting, Mr Alexander relies upon secrecy , sometimes using confidentiality agreements to protect his ideas.
The word DASH® is a registered trade mark . It was arrived at from an acronym for the words that describe the invented prosthetic foot (Dextrous Ankle Solid Heel).
It is not usually possible to obtain a registration for a trade mark that actually describes a product because this would prevent other traders in similar products from using appropriate words to describe their own product. For instance you could not obtain a registration for the word 'sweet' in relation to chocolate. However the choice of an acronym for the DASH® trade mark is acceptable – it will not for instance prevent another trader from using the word 'ankle'.
Wayne Alexander used a strategy of time management in relation to the patent application for the prototype. He reasoned that the longer he was able to draw out the process, the more opportunity he would have for clarifying and focussing his ideas (while still maintaining some intellectual property protection) before arriving at the ultimate final product.
The first step was to file a provisional application for a patent on the prototype with IPONZ. This application provided the prototype with a priority date – evidence of ownership of an invention which helps prevent it being patented by anyone else. In addition, a provisional application number was allocated to the prototype and could be used with the words 'patent pending' whenever the prototype was displayed in public, for example when it was tested in the marketplace.
After a maximum time of 15 months the inventor is required by IPONZ to file a complete specification and apply for a full patent. Mr Alexander chose to file a complete specification for just one aspect of his invention at a time. This strategy allowed him to refine his invention over a number of years.
The approach could be seen as a modern 'take' on the Brunelleschi story mentioned in the case study.