Reference Frame Unification of IMU-Based Joint Angle Estimation: The Experimental Investigation and a Novel Method

Area of Science:

• Biomechanics
• Robotics
• Clinical applications

Background:

• Inertial measurement unit (IMU)-based joint angle estimation is widely used but hindered by reference frame deviations.
• Existing methods lack systematic investigation and clear metrics, leading to conceptual confusion and accuracy limitations.

Purpose of the Study:

• To clarify reference frame unification (RFU) and differentiate it from drift correction.
• To investigate the time-varying characteristics of IMU reference frame deviations.
• To propose a novel, comprehensive method for unifying IMU reference frames to enhance joint angle estimation accuracy.

Main Methods:

• Defined reference frame unification (RFU) and distinguished it from drift correction.
• Designed a mechanical gimbal-based experiment to isolate and study reference frame deviations.
• Developed a novel method utilizing joint axis consistency, gravity, and magnetic fields for frame unification.

Main Results:

• Experimental study revealed time-varying characteristics of reference frame deviations.
• The proposed method effectively unifies reference frames, addressing nonlinear and time-varying deviations.
• Demonstrated significant improvement in joint angle estimation accuracy compared to previous methods across ten subjects.

Conclusions:

• The novel reference frame unification method enhances IMU-based joint angle estimation accuracy.
• This work provides a new perspective for addressing IMU orientation errors in biomechanical and clinical settings.
• The findings contribute to more reliable and precise motion analysis using IMUs.