ArmTrak: I am a Smartwatch and I can Track my User's Arm

What is ArmTrak?

ArmTrak is a system designed to track the geometric motion of the human arm using only the motion and magnetic sensors on the smartwatch.

Core Idea

While arm posture space can be very large, ArmTrak continuously estimates the orientation of the smartwatch (worn on the wrist), and together with human arm kinematics, ArmTrak reduces its uncertainty on elbow/wrist location to a small area (called point clouds). The remaining uncertainty is further mitigated by feeding the inferred elbow acceleration into modified HMM framework and inferring the correct elbow/wrist locations within the point clouds.

Demo 1: Use ArmTrak as a Kinect

Demo 2: Use ArmTrak to Write in the Air

Key Research Components

• Arm posture is essentially determined by 5 joint angles.

  While arm posture contains elbow location, wrist location and wrist/watch orientation, they are essentially a function of 5 joint angles. Given 5 angle values and upper/lower arm lengths, the whole arm posture is fixed.

  
  
  

• Measured (noisy) elbow acceleration is fed into modified HMM framework for elbow tracking.

  We modified the traditional HMM framework so that the best sequence of elbow/wrist locations within the point clouds can be inferred efficiently with Viterbi algorithm, using elbow acceleration as the observation.

Publication

• I am a Smartwatch and I can Track my User’s Arm
  Sheng Shen, He Wang, Romit Roy Choudhury
  ACM MobiSys, 2016 [pdf]

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