Related Work
\label{rel}
Limitations of Rigid Robotic Systems
Hand exoskeletal system that utilize rigid mechanic has been for a long in both hand rehabilitation systems, master/slave control, and strength assistance. In rehabilitation process, it provides strength for patients that suffered a stroke and lost their strength in their hands, which increase their rate of recovery and increase patient’s involvement and responsibility in his or own rehabilitation process.
Moreover, various sensors can be attached to the hand exoskeletal system to measure the strength exerted by the users and track the human finger movements \cite{foumashi2011state}. Through reading and analysis of information, hand exoskeletal system is then able to amplify the strength exerted to provide additional strength for users to lighten the difficulty of the task that requires significant amount of strength to be complete. The same data collection system can also be used in master/slave control, where slave robotic systems can be controlled at faraway distance, mimicking or even amplify the actions of the master.
However, it is also found that rigid mechanics has its limitation. Due to the rigidity of the materials, hand exoskeletal system that utilized rigid mechanics are unable to perform delicate or flexible task due to limitations in their degree of freedom unlike the rich multi-functionality of natural organisms \cite{majidi2014soft}. Increasing degree of freedom for the exoskeletal system will require large number of components that are small, thus increasing the complexity of the mechanical system, which is tedious for both users and manufacturers in the process. The HANDEXOS has only 1 Degree of Freedom (DOF) for each finger \cite{chiri2009handexos}. However, multiple components are needed to assemble a single finger mechanism. The PERCO Hand I is a haptic device which has its motor and electronic box located on top of the hand \cite{fontana2009mechanical}. However, it is observed that this arrangement will be inconvenient for the user due to its bulkiness.
Soft Robotics in Biomedical Applications
In recent years, soft robotics has been found to have solve the problems faced by rigid mechanical systems.
Soft robotics reduces the components involved in the hand exoskeletal system and increase the flexibility and maneuverability of the system. Thus, soft robotic hand exoskeletal system could perform task that are delicate and complex.
This will minimize dependency on the physical therapist and provide patient new opportunities to relearn.
The soft robotic glove by Polygerinos of Wyss Institute and Harvard University \cite{polygerinos2013towards)|\@@cite[cite]{[\@@bibref{Refnum}{polygerinos2015soft}{}{}]}|isagreatexample.Hydraulicallyactuated,thesystemusessoftfiber-enforcedactuatorsmadeofrubber|\@@cite[cite]{[\@@bibref{Refnum}{polygerinos2013towards}{}{}]}|andtheadditionofastrainlimitinglayersuchasfiberglassisappliedforbendingandtwistingability|\@@cite[cite]{[\@@bibref{Refnum}{polygerinos2015soft}{}{}]}|.TheOkayamaUniversityHandisanotherassistiveexoskeletalsystemmadeupofrubbermusclesandfiberfellows,wherethereisnomechanismtocouplethejoints’movementsasitismovedbycompressedairsuppliedintotherubbermuscles\@@cite[cite]{[\@@bibref{Refnum}{noritsugu2008power}{}{}]}|\@@cite[cite]{[\@@bibref{Refnum}{foumashi2011state}{}{}]}|.\parHowever,therearealsolimitationsinthedevelopmentofsoftroboticsduetolackofunderstandinginsoftmaterials.Dynamicsofsoftmaterialsaredifficultandslowtosimulatebecauseofthemanydegreesoffreedomandnonlinearmaterialeffects|\@@cite[cite]{[\@@bibref{Refnum}{lipson2014challenges}{}{}]}|.Thenonlineareffectsimplythatextensivecomputationalprocessesneedtobeemployedforcorrectsimulation.Evenifthesimulationiscorrect,predictionsaredifficulttomatchtorealityduetomanyempiricalcoefficientsthatneedtobecalibratedexperimentally,forexample,nonlinearelasticbehavioranddampingcoefficients,interfacesbetweenmaterials,andfriction.ManysoftmaterialsalsocontradicttheintuitionbyexhibitingnegativePoissonratios|\@@cite[cite]{[\@@bibref{Refnum}{trimmer2014journal}{}{}]}|,changingtheirapparentstiffnessunderrapidforcesoreven‘‘creeping’’andhardeningunderconstantloads.Thesepropertiesmakeitchallengingtocreateaccuratemathematicaldescriptionsofcomplexstructures.Therequiredcalculationscanmakefiniteelementanalysistoocumbersomeandslowtobepractical.|\@@cite[cite]{[\@@bibref{Refnum}{trimmer2014journal}{}{}]}|\parBarryTrimmer|\@@cite[cite]{[\@@bibref{Refnum}{trimmer2014journal}{}{}]}|suggestedthiscanbesolvedbystudyingevolvedsolutionsinlivingcreaturesasanimalsarecomposedalmostentirelyofsoftmaterialsandliquids.Likeanimals,humanshaveastiffinternalskeletonthatcomprisesonly11to15\parTheothersolutionmaybeahybridrobotsystemsthatcombinesbothhardandsoftrobots.InaresearchconductedbyStokes|\@@cite[cite]{[\@@bibref{Refnum}{stokes2014hybrid}{}{}]}|,thehybridcombinesacommerciallyavailablewheeledhardrobot,andaleggedsoftrobotcapableofversatilegrippingandmovementoverunstableterrain.Thehardrobotsuppliescompressedairtothesoftrobotthroughaflexibletether,andcarriesthecontroller,micro-compressors,andvalvesthatoperatethesoftrobot|\@@cite[cite]{[\@@bibref{Refnum}{stokes2014hybrid}{}{}]}|.\par\@@section{subsection}{S1.SS3}{1.3}{1.3}{{\@tag[][]{1.3}KirigamiInspirationDesigninSoftRobotics}}{{\@tag[][]{1.3}KirigamiInspirationDesigninSoftRobotics}}\parAmongthesub-categoriesofsoftroboticsystems,kirigami-inspiredsystemisoneofthesystemhasnotbeenfullyutilizedinhandexoskeletalsystem.Manydeployablestructureshaventakeninspirationfromkirigamifolding.Researchfoundthatcertainkirigamifoldinghasproducedphysicalpropertiesthatwasdifferentfromthematerial,whichcanbeseenfromtheincreaseofstrengthinpaper.Origamistructurehasalsoobservedtoincreaseaccessibilityofcomponentsastheycanbereducedinsizethroughmultiplefolding.\par\parOrigamihasbeenutilizedinthefieldofbiomedicalrobotics.Origamidesignscanstartinacompactformandthendeployintoafunctionalform,thusenablinganovelandlessinvasivemethodoftreatmentdeliveryinwhichmedicaldevicestravelthroughthebodytopreviouslyunreachableareas|\@@cite[cite]{[\@@bibref{Refnum}{johnson2017fabricating}{}{}]}|.\parForbiomedicaldevices,whichhasgrippingabilitiessimilartoexoskeleton,theresearchersofBYUareintegratingorigamitechniquestocreatesmallergrippers(3mmindiameter)forIntuitiveSurgical’sDaVinciSurgicalSystem.TheDaVinciSurgicalSystemperformssurgeriesroboticallywiththeuseofgrippers.Thegripperscanholdaneedle,suture,graspobjects,etc.BYU’snewdesignwasinspiredbytheorigamipatternknownas“Choppers”.Thesimpleorigamidesignallowsone-thirdofthenumberofpartsastheoriginal.Duetothedesign,thepartsarelesscomplex,givingthegrippertheabilitytobescaleddownfurther.Thegripperisinsertedintoatinyincisionandthendeployedinsidethebodytocarryoutaspecificsurgery.Theseorigami-inspireddesignsmayenablelessinvasiveroboticsurgeryduetothesmallscale|\@@cite[cite]{[\@@bibref{Refnum}{johnson2017fabricating}{}{}]}|.\parAstheresearchonorigami-inspiredroboticsystemsdeepen,anextensionoforigamiwasbeennoticed:Kirigami.Kirigamimeans“papercutting”|\@@cite[cite]{[\@@bibref{Refnum}{rossiter2014kirigami}{}{}]}|.Comparedtoorigamistructure,thestretchabilityofkirigamistructureisnotlimitedbytheplanarstate|\@@cite[cite]{[\@@bibref{Refnum}{song2016studies}{}{}]}|.\parThispaperpresentadesignofkirigami-inspiredthree-fingeredhandexoskeletalsystem.Excludingthethumb,thedesignofeachfingermechanismfocusedonthemovementinoneDegree-of-Freedom(DOF)ofmovementincontractionandextension.ThethumbhastwoDOFofmovementwhichincludesadductionandabduction.Whileadvantagesofthesystemarediscussed,thelimitationsandconstraintsoftheproposeddesignarealsodiscussedattheendoftheexperimentsection.}