Exoskeleton 101

On a hot January in 2016, about 60 people – the cream of Australia’s design and technology consultants – expectantly assembled at a site north of Adelaide and adjacent to RAAF Base Edinburgh. We were there to be briefed on a fascinating project, by the Defence, Science and Technology Group (DST) – Australia’s lead science and technology agency supporting the country’s defence and security needs.

A couple of months later, Cobalt was selected in the competitive tender to take DST’s exoskeleton idea to the next level of design refinement. We believe one of the factors Cobalt was chosen was the load-carriage experience we’d established whilst designing the successful ONE299 adjustable backpack frame.

Our inspiration came from the concept of an exoskeleton, which is an external skeleton that supports the load of an animal or insect. Common examples of exoskeletons include grasshoppers and lobsters who can carry far greater loads than their simple muscular systems could usually accommodate.

To date, exoskeleton development for military applications has been primarily focussed on powered and motorised systems. These mechanically complex devices effectively turn wearers into hybridised robots. So far, this approach has been favoured by big defence industry players and have resulted in heavy, complex and expensive devices that need to be tailored for each wearer. The impracticalities of batteries and regular recharging within tactical operations also pose fundamental safety and redundancy limitations to these systems.

DST’s concept, developed by Tom Chapman – or OX as it is known – takes a completely different, almost acoustic approach.

The human gait has evolved to be a very efficient process, and any disruption to this results in a steep rise in metabolic cost. OX aims to offset loads from the user, without providing any additional energy input, therefore requiring the wearer to support and actuate the system. The challenge with this approach is to balance the metabolic cost of this against the ‘benefit’ of reduced loads and impacts on the wearer’s musculoskeletal system.

DESIGN ACHIEVEMENTS

  • Improved metabolic efficiency
  • Total system weight: 5.2kg
  • Maximum system payload: 35kg
  • Load transfer of up to 60%
  • Dynamic adjustment of load transfer proportion
  • Limited restriction to mobility
  • Improved design integration
  • Stronger and more robust construction
  • Adjustable to suit a range of users

PROJECT IMPACT

  • Will greatly assist the well-being of Australian Defence Force personnel
  • Holds commercial viability outside of the defence force
  • Has already seen interest from overseas markets
  • Similarities to the One299 Backpack Frame project has increased initial interest
  • Development from TRL-3 to TRL-5

COBALT TASKS

  • Anthropometric analysis and application
  • Ergonomics
  • Load calculations and analysis
  • Product engineering
  • FEA (Finite Element Analysis)
  • Prototyping
  • Testing and analysis
  • External trial support
  • Kynan Taylor
  • Ben Goodwin
  • Nat Hunt
  • Chris Morrish
  • Libby Christmas
  • Marcus Krigsman
  • Nathan Scanlon
  • Steve Martinuzzo

Standing tall

OX is a passive (unpowered) exoskeleton system that uses a semi-flexible cable system to transfer a controlled proportion of the weight of a heavy backpack off the wearer’s skeletal system.  In contrast to powered exoskeletons, OX is lightweight, low cost, adjustable and easily put on and removed.

According to DST’s Project Lead Tom Chapman, load-carriage exoskeletons face three primary challenges:

  • Minimising the energy (metabolic) cost of wearing the device
  • Fitment to be as universal as possible whilst being intuitive/rapidly deployable, lightweight and reliable
  • Capable of transferring loads in bent leg positions without motors or actuators

DST’s Project Lead had developed his idea for a simpler exoskeleton using flexible cables. His early (TR3-level) prototypes successfully transferred loads, even during bent leg positions.  His work had enough merit to justify external development to further validate the concept and take it to a more advanced level.

Cobalt started our work by researching the science of walking; the physical forces in carrying loads through the phases of a person’s gait, and how these might be partially transferred via a flexible cable.

During this process, it became obvious that a seemingly simple principle was actually very complex, and developing a system that maximised the performance of the Bowden cables whilst minimising the impact on the user would be key to its success.

Early stages of our development were focused on understanding the behaviours of the system and how each had to integrate with the human form and external inputs. We started this mathematically; quantifying the forces to show how and where they acted. And then practically through engineering design, simulation and prototyping.  A number of demonstration prototypes were constructed and tested in-house to verify ideas, performance and usability. This culminated in laboratory trials conducted in collaboration with Victoria University at their world class sports science facility.

The second phase of the project focused on the design’s optimisation. Data generated from the first phase lab test highlighted areas for further focus including improved user fit and adjustability, enhanced bracing of the cables to the user and overall weight minimisation. The final design included a number of key improvements including use of advanced materials such as carbon fibre composites, miniaturised mechanisms and refined sub-system integration.

Our on-time and on-budget deliverables were handed over in May 2018;  three TRL5 level working prototypes able to be tested by a variety of military personnel replicating operational demands.  Currently the subject of university and defence force testing, the prototypes and project are being considered for further commercialisation by DST.

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