ApplicationofFilmSensorsforFeedbackonCyclists’SagittalAnkleFlexionKyleSimon1,DixiongWang2,SusanTrolier-McKinstry2

1SouthWesternHighSchool,2ThePennsylvaniaStateUniversity

ResearchExperiencesforTeachersandYoungScholarsinAdvancedSelf-PoweredSystemsofIntegratedSensorsandTechnologies

(ASSIST)

The ASSIST RET and Young Scholar programs are funded by NSF nanosystems engineering research center grant EEC 1160483.

ProblemIdeal flexion of the talocrural joint about the sagittal plane forcyclists range from -2° plantar flexion to +22°dorsiflexion. Flexionoutside of this range is more common with fatigued riders. Inaddition,outsideoftheidealrangemuscularefficiencyisnotedtodecreases.

Provide simple “coaching” that allows for both novice andexperiencedcyclists to ridewithankle flexion that fallswithin theideal range, increasingefficiencyandoverallperformancewhile inthesaddle.

Response

Engineered Solutions

ApplicationConstraints• must be designed small enough to remaincomfortablefortheuser—nonoticeableincreaseinloadontheankleduringflexion• mustwithstandasignificantamountofrepetitivecyclesofflexureandrelaxation• materialsmustbeaffordable

• Filmsmustbethinenoughtoflexfreelyinnarrowprotectiveplasticsleeve

Modeling the Talocrural Joint

Angle Measured Using Flex Sensor

Conceptual Model of PVDF Film as Sensor

Future WorkThenextstepinthedevelopmentofthisdeviceis establishing a means of collecting high-frequencycurrentmeasurementusingacurrentsensor breakout such as the Adafruit INA219.Thiswillallowforfurtherdevelopmentofa

Poor ergonomics may result in reduceddesire touse cyclingas ameansof activehobbyorexercise. Fortechnicalcyclistsorprofessionals,reductionsofefficiencymayhave a significant impact on theirperformance.

Currently,cyclistscanreceiveformfeedbackfromacyclingcoachoranalyzevideoofstationarycyclingexercises,butthosesolutions are either cost prohibitive or requires complexequipmentorsoftware.

A small, film-based sensor that analyzesankle motion and alerts the rider whentheir range of sagittal ankle flexion isoutside of the rangeof -2° plantar flexionand +22° Dorsiflexion. The sensors,investigated for installation over theanterior talus, were made of either aserpentine resistor or a piezoelectricmaterial.

TwopiecesofPVCpipewerecutandjoinedatapivotpointusingabolt. Thefootandlowerlegwererepresentedby4”diameterand3”diameterPVCpipe,respectively.Thejointhadfreemotionfromwhat would model 25° dorsiflexion to approximately 90° plantarflexion.

A coupling rod and drivingwheelwith five attachment points were3D printed and driven by alittleBits DCmotor. This allowedforavarietyoftotalflexionstobetested. The actuation rate wascontrolled using a littleBits SlideDimmer.Sensors were connected to an Arduino Uno R3 and transferredthroughitsserialporttoCoolTermfordatacollectionandanalysis.

AlargeFlexSensorelementwithleadssuppliedbySpectraSymbolwasinstalledonthetalocruraljointmodel.Thesignalwasanalyzedand a relationshipbetween themodel flexion and resistancewasestablished.

During manufacturing conductive ink is printed in a serpentinepatternontoaflexiblesubstrate. Whenbenttheconductiveinkisstretched,andthe lengthandresistanceof thematerial increases.Theelementprovidesa resistanceasa functionof itsbendangle.Resistance through the element is static and does not requireconstantactuationinorderforasignaltobeproduced.

According to the model, theminimumandmaximumvaluesofresistancethatshouldbedetectedwhile a rider is maintaining idealtalocruralflexionare16,200Ωand22,500 Ω, respectively. ThesevalueswereusedasthresholdsinordertoproductvisualfeedbacktotheriderusingtheArduinoUno.

Below-2°plantarflexion

Above22°dorsiflexion

The rateofankleflexionwas alsomeasured andnoted to haveminimal impacton the sensor’sdata(<0.4%).

PolyvinylideneDifluoride(PVDF) ismaterialthat iscommonlyusedaspiezoelectricelementinfilmapplications.Whenthefilmisbentorvibrated,acurrentisproducedacrossthefilmthatcanbeanalyzed. Utilized in a talocruraljointsensor,PVDFprovidessomechallengeswhencomparedtotheserpentine resistor, as thematerial only produces a signalwhen actuated. Using a highsampling rate, there is potentialto approximate the total chargeproducedbythefilmasaproductof the sum of discrete measurement and the total time ofmeasurement.

Despite the challenges in using PVDF, the material present someadvantages that make it worth exploring. Because the sensor isproducingacurrent,thereispotentialtousethePVDFelementasamechanicalenergyharvester.ThismayservetoreducetheloadonthebatteryusedtooperatetheArduino,prolongingitslifebetweencharges.PVDFmayalsoshowlessvarianceinsignalduringextremehotandcoldthanaresistance-basedsensor.

Acknowledgements

References

PVDF-basedsensor. Becauseof the flexiblenatureof thePVDFfilm,integrationofthematerialintothefabricofcyclists’clothesmaybearealistic possibility. Finally the opportunity also exists to develop ameans of wireless communication between either device and ahandlebar-based display to increase usability and reduce accidentaldamage.

SpecialthankstotheSTMgroup,especiallyDr.SusanTrolier-McKinstryandDixiongWangfortheir assistance during my time at Penn State. Also, thank you to Dr. Kathleen Hill, Dr.MatthewJohnson,AmandaSmith,AmberCesare,andTaylorWoodfor therichprofessionaldevelopmentthroughoutmyexperiencesatanRET

Abt,J.P.,Smoliga,J.M.,Brick,M.J.,Jolly,J.T.,Lephart,S.M.,&Fu,F.H.(2007).RelationshipBetweenCyclingMechanicsandCoreStability.TheJournalofStrengthandConditioningResearch,21(4),1300.doi:10.1519/r-21846.1

Dorsiflexionandplantarflexion[Digitalimage].(2013,November14).RetrievedJuly15,2018,fromhttps://foundation.wikimedia.org/wiki/File:Dorsiplantar.jpg

Ronner,A.(n.d.).Shoesizeimage[Digitalimage].RetrievedJuly20,2018,fromhttps://d2gqkshisthvn1.cloudfront.net/blog/wp-content/uploads/fietsschoenmeetsysteem1.jpg