Joint angle estimation with accelerometers for dynamic postural analysis

Determining anatomical frames via inertial motion capture: A survey of methods

Despite the exponential growth in using inertial measurement units (IMUs) for biomechanical studies, future growth in "inertial motion capture" is stymied by a fundamental challenge - how to estimate the orientation of underlying bony anatomy using skin-mounted IMUs. This challenge is of paramount importance given the need to deduce the orientation of the bony anatomy to estimate joint angles. This paper systematically surveys a large number (N = 112) of studies from 2000 to 2018 that employ four broad categories of methods to address this challenge across a range of body segments and joints. We categorize these methods as: (1) Assumed Alignment methods, (2) Functional Alignment methods, (3) Model Based methods, and (4) Augmented Data methods. Assumed Alignment methods, which are simple and commonly used, require the researcher to visually align the IMU sense axes with the underlying anatomical axes. Functional Alignment methods, also commonly used, relax the need for visual alignment but require the subject to complete prescribed movements. Model Based methods further relax the need for prescribed movements but instead assume a model for the joint. Finally, Augmented Data methods shed all of the above assumptions, but require data from additional sensors. Significantly different estimates of the underlying anatomical axes arise both across and within these categories, and to a degree that renders it difficult, if not impossible, to compare results across studies. Consequently, a significant future need remains for creating and adopting a standard for defining anatomical axes via inertial motion capture to fully realize this technology's potential for biomechanical studies.

An application of scissored-pair control moment gyroscopes in a design of wearable balance assistance device for the elderly

Impaired balance control ability and degraded functional mobility increases the risk of falling in elderly people. The elderly show more postural sway when standing compared with young people. A sway fall occurs when the center of gravity moves outside the limit of stability. In order to reduce the fall risk from the excessive sway, this study presents the design of wearable balance assistance device for the elderly. Scissored-pair control moment gyroscopes were selected as a torque actuator. A two-axis inclination sensor was used to detect the inclined angle of the wearer's body. The direction of sway was calculated from the detected inclined angle. The designed device weighs 8.2 kg with a height of 32 cm × width of 40 cm × depth of 22 cm. A multi-segment model of a standing human was used to investigate the device's performance for balance recovery. According to the simulations, balance recovery in any direction was successfully accomplished with the appropriate initial angle. The relationship between the effective initial angle and detected inclined angle was subsequently established. The stability provided by activation of the device was able to limit the unstable user's sway boundary. The designed device shows promise for use as a balance assistance device for the elderly.