Application of Film Sensors for Feedback on Cyclists ...Application of Film Sensors for Feedback on...
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Application of Film Sensors for Feedback on Cyclists’ Sagittal Ankle Flexion Kyle Simon 1 , Dixiong Wang 2 , Susan Trolier-McKinstry 2 1 South Western High School, 2 The Pennsylvania State University Research Experiences for Teachers and Young Scholars in Advanced Self-Powered Systems of Integrated Sensors and Technologies (ASSIST) The ASSIST RET and Young Scholar programs are funded by NSF nanosystems engineering research center grant EEC 1160483. Problem Ideal flexion of the talocrural joint about the sagittal plane for cyclists range from -2° plantar flexion to +22° dorsiflexion. Flexion outside of this range is more common with fatigued riders. In addition, outside of the ideal range muscular efficiency is noted to decreases. Provide simple “coaching” that allows for both novice and experienced cyclists to ride with ankle flexion that falls within the ideal range, increasing efficiency and overall performance while in the saddle. Response Engineered Solutions Application Constraints • must be designed small enough to remain comfortable for the user — no noticeable increase in load on the ankle during flexion • must withstand a significant amount of repetitive cycles of flexure and relaxation • materials must be affordable • Films must be thin enough to flex freely in narrow protective plastic sleeve Modeling the Talocrural Joint Angle Measured Using Flex Sensor Conceptual Model of PVDF Film as Sensor Future Work The next step in the development of this device is establishing a means of collecting high- frequency current measurement using a current sensor breakout such as the Adafruit INA219. This will allow for further development of a Poor ergonomics may result in reduced desire to use cycling as a means of active hobby or exercise. For technical cyclists or professionals, reductions of efficiency may have a significant impact on their performance. Currently, cyclists can receive form feedback from a cycling coach or analyze video of stationary cycling exercises, but those solutions are either cost prohibitive or requires complex equipment or software. A small, film-based sensor that analyzes ankle motion and alerts the rider when their range of sagittal ankle flexion is outside of the range of -2° plantar flexion and +22° Dorsiflexion. The sensors, investigated for installation over the anterior talus, were made of either a serpentine resistor or a piezoelectric material. Two pieces of PVC pipe were cut and joined at a pivot point using a bolt. The foot and lower leg were represented by 4” diameter and 3” diameter PVC pipe, respectively. The joint had free motion from what would model 25° dorsiflexion to approximately 90° plantar flexion. A coupling rod and driving wheel with five attachment points were 3D printed and driven by a littleBits DC motor. This allowed for a variety of total flexions to be tested. The actuation rate was controlled using a littleBits Slide Dimmer. Sensors were connected to an Arduino Uno R3 and transferred through its serial port to CoolTerm for data collection and analysis. A large Flex Sensor element with leads supplied by Spectra Symbol was installed on the talocrural joint model. The signal was analyzed and a relationship between the model flexion and resistance was established. During manufacturing conductive ink is printed in a serpentine pattern onto a flexible substrate. When bent the conductive ink is stretched, and the length and resistance of the material increases. The element provides a resistance as a function of its bend angle. Resistance through the element is static and does not require constant actuation in order for a signal to be produced. According to the model, the minimum and maximum values of resistance that should be detected while a rider is maintaining ideal talocrural flexion are 16,200 Ω and 22,500 Ω, respectively. These values were used as thresholds in order to product visual feedback to the rider using the Arduino Uno. Below -2° plantar flexion Above 22° dorsiflexion The rate of ankle flexion was also measured and noted to have minimal impact on the sensor’s data (< 0.4%). Polyvinylidene Difluoride (PVDF) is material that is commonly used as piezoelectric element in film applications. When the film is bent or vibrated, a current is produced across the film that can be analyzed. Utilized in a talocrural joint sensor, PVDF provides some challenges when compared to the serpentine resistor, as the material only produces a signal when actuated. Using a high sampling rate, there is potential to approximate the total charge produced by the film as a product of the sum of discrete measurement and the total time of measurement. Despite the challenges in using PVDF, the material present some advantages that make it worth exploring. Because the sensor is producing a current, there is potential to use the PVDF element as a mechanical energy harvester. This may serve to reduce the load on the battery used to operate the Arduino, prolonging its life between charges. PVDF may also show less variance in signal during extreme hot and cold than a resistance-based sensor. Acknowledgements References PVDF-based sensor. Because of the flexible nature of the PVDF film, integration of the material into the fabric of cyclists’ clothes may be a realistic possibility. Finally the opportunity also exists to develop a means of wireless communication between either device and a handlebar-based display to increase usability and reduce accidental damage. Special thanks to the STM group, especially Dr. Susan Trolier-McKinstry and Dixiong Wang for their assistance during my time at Penn State. Also, thank you to Dr. Kathleen Hill, Dr. Matthew Johnson, Amanda Smith, Amber Cesare, and Taylor Wood for the rich professional development throughout my experiences at an RET Abt, J. P., Smoliga, J. M., Brick, M. J., Jolly, J. T., Lephart, S. M., & Fu, F. H. (2007). Relationship Between Cycling Mechanics and Core Stability. The Journal of Strength and Conditioning Research, 21(4), 1300. doi:10.1519/r-21846.1 Dorsiflexion and plantar flexion [Digital image]. (2013, November 14). Retrieved July 15, 2018, from https://foundation.wikimedia.org/wiki/File:Dorsiplantar.jpg Ronner, A. (n.d.). Shoe size image [Digital image]. Retrieved July 20, 2018, from https://d2gqkshisthvn1.cloudfront.net/blog/wp- content/uploads/fietsschoenmeetsysteem1.jpg
Transcript of Application of Film Sensors for Feedback on Cyclists ...Application of Film Sensors for Feedback on...
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
