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A method to estimate relative orientations of body segments during movement using accelerometry

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A  method  to  estimate  relative  orientations  of  body  segments  during  movement    

using  accelerometry  

Kortier  HG1,  Schenk  O1,  Luinge  H.J.2,  Veltink  PH1  

1MIRA  Institute,  University  of  Twente,  Enschede,  The  Netherlands   2Xsens  Technologies,  Enschede,  The  Netherlands  

 

INTRODUCTION    

Quantitative   assessment   of   human   body   movements   includes   the   analysis   of   joint   orientations.   We  propose  a  new  method  to  estimate  relative  orientation  between  body  segments  using  a  single  3D   accelerometer  per  segment  under  the  following  conditions:  

(1) The   total   acceleration   on   both   segments   is   the   same.   They   are   only   measured   in   different   coordinate  frames.  

(2) The  direction  of  the  total  acceleration  changes  with  time.  

(3) The  relative  orientation  changes  relatively  slowly  with  respect  to  the  total  acceleration.   These  conditions  may  be  satisfied  in  certain  situations,  for  example  on  the  segments  of  the  fingers  of   a  hand  during  functional  movements.  

 

METHODS  

We  tested  this  method  using  an  experimental  setup  with  inertial  sensors  on  a  kinematic  body   chain  with  fixed  relative  orientations.  The  relative  distance  between  the  accelerometers  was  47  mm.      

RESULTS  

Accurate  relative  orientations  were  obtained  when  performing  horizontal  translational  

movements  (Figure  1  Left),  but  as  expected,  errors  occurred  at  higher  angular  velocities  during  pure   rotations  (Figure  1  Right).  

DISCUSSION  AND  CONCLUSION  

The   proposed   method   may   be   useful   to   estimate   relative   orientations   between   body   segments   using  only  a  single  accelerometer  per  segment.  The  application  in  estimating  relative  orientation  of   finger  segments  of  the  hand  during  functional  movements  needs  to  be  further  evaluated.    

 

ACKNOWLEDGEMENT  

This   study   was   financially   supported   by   the   Dutch   technology   foundation   STW   under   the   PowerSensor  project.    

Figure  1.    Two  experimental  measurements:  The  plots  on  the  first  and  second  row  show  the  magnitude  of  accelerations  and   angular  velocities  in  the  sensor  frames  of  both  accelerometers.  The  plots  on  the  third  row  show  the  angle  between  the   estimated  and  actual  orientation.  Left:  cyclic  translational  movements  over  45  cm  in  the  horizontal  plane  at  approximately   0.8  Hz.  Right:  cyclic  rotational  movements  over  180  degrees  at  approximately  0.8  Hz.  The  distance  between  the  axis  of   rotation  and  accelerometers  was  35  mm  and  75  mm  respectively.    

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