Magnetometer-Based Drift Correction During Rest in IMU Arm Motion Tracking

Abstract

Real-time motion capture of the human arm in the home environment has many usecases, such as video game and therapy applications. The required tracking can be based onoff-the-shelf Inertial Measurement Units (IMUs) with integrated three-axis accelerometers, gyroscopes,and magnetometers. However, this usually requires a homogeneous magnetic field to correctfor orientation drift, which is often not available inside buildings. In this paper, RPMC (RestPose Magnetometer-based drift Correction), a novel method that is robust to long term drift inenvironments with inhomogeneous magnetic fields, is presented. The sensor orientation is estimatedby integrating the angular velocity measured by the gyroscope and correcting drift around the pitchand roll axes with the acceleration information. This commonly leads to short term drift aroundthe gravitational axis. Here, during the calibration phase, the local magnetic field direction for eachsensor, and its orientation relative to the inertial frame, are recorded in a rest pose. It is assumed thatarm movements in free space are exhausting and require regular rest. A set of rules is used to detectwhen the user has returned to the rest pose, to then correct for the drift that has occurred with themagnetometer. Optical validations demonstrated accurate (root mean square error RMS = 6.1), lowlatency (61 ms) tracking of the user’s wrist orientation, in real time, for a full hour of arm movements.The reduction in error relative to three alternative methods implemented for comparison was between82.5% and 90.7% for the same movement and environment. Therefore, the proposed arm trackingmethod allows for the correction of orientation drift in an inhomogeneous magnetic field by exploitingthe user’s need for frequent rest.

Upper Limb Physical Rehabilitation Using Serious Videogames and Motion Capture Systems: A Systematic Review

“…Understanding the advantages of the use of inertial sensors, some works focused on an improvement in their efficiency and, taking into account that one of the limitations that IMUs have shown is the problem of drift, in [ 12 ], a drift correction method was proposed on the basis of a rest pose magnetometer (RPMC), for the measurement of combined inertia and the following of the arm in real time with a magnetometer. This method corrected drift while the user was relaxing, involving a precalibrated direction of the magnetic field.…”

“…Another commercial product used was the videogame therapy software included in the ArmeoSenso system, which has been previously mentioned, which is oriented toward the recovery of the function of the arm. In [ 12 ], a therapy game called “Meteors” was implemented in ArmeoSenso. This game involves a virtual robotic arm that coincides with the movement of the arm of the player and is used to catch meteors which fall on a planet.…”

“…Concerning the evaluation and analysis of the range of movement, and the lesions in the upper limbs derived from different clinical conditions, in [ 7 , 9 , 12 , 16 ], and in one of the experiments presented in [ 15 ], it was identified that the contribution of these technologies to a patient’s motor recovery is positive, as it helps to overcome the limitation of traditional rehabilitation methods.…”

“…In the face of this, individual, cooperative, and competitive video games have been used. Commercial video games were used in [ 7 , 12 , 19 , 20 , 21 ], which, despite encouraging the execution of physical activity and supporting the player’s motivation, were not adapted to the particular characteristics of physical rehabilitation. For this reason, most of the studies proposed active video games specifically for rehabilitation, to increase motivation and adherence to therapies [ 8 , 11 , 13 , 15 , 16 , 17 , 18 , 22 , 23 , 25 ], in some cases associated with a configuration module allowing the health professional to adjust the characteristics of the game according to the diagnosis and progress of the patient in treatment [ 9 , 10 , 14 , 24 ].…”

Classifying Elite From Novice Athletes Using Simulated Wearable Sensor Data

“…IMUs contain an accelerometer, gyroscope, and magnetometer, allowing measurement of linear accelerations and angular velocities in three axes and the triaxial magnetic fields of the earth. IMUs are susceptible to drift, especially when close to metal, although more robust algorithms are continuously being developed to mitigate these effects (Madgwick et al, 2011;Wittmann et al, 2019), making them more suitable for use in the field.…”