Slip and fall is a major cause of injury in the elderly and outdoor workers. This paper presents the development of a wearable knee assistive device aimed to prevent slip-induced falls. The proposed novel approach relies on providing active assistance to the trailing leg during slip onset. The assistive device, when slip is detected and device is activated, actively extends the knee of the trailing leg creating contact with the ground. This immediately extends subject's base of support and helps with balance recovery. The lightweight device is powered by compressed CO2 gas from a small cartridge that can be used for a single slip assistance and easily replaced. The results of device characterization and human subject testing demonstrate that the device can assist with rapid knee extension during gait, forming an active slip and fall recovery strategy.
We present a human postural balance study on quiet stance and kneeling gaits on inclined and high elevated surfaces for construction workers. To simulate the high elevation, an immersive mixed reality environment is built with an actual inclined roof surface to create somatosensory haptic feedback. We quantify the postural balance during quiet kneeling and stance through measurements of the center of pressure and sway motion of the upper-body under various inclined angles and heights. The results of center of pressure and trunk acceleration measurements show smaller postural sway during kneeling compared to standing. A mathematical model is also presented to help understand the experimental results and potentially provide design guidance for further intervention to prevent and mitigate the fall risk for construction workers. The model and controller parameters are optimized to precisely capture and explain the experimental results.
This study presents a method for trip detection using inertial sensors, and a controller for balance recovery in the sagittal plane after trip using exoskeleton devices. Trip detection was performed using a computed root mean square of the lower back angular acceleration in a sagittal plane and a fixed threshold resulting in mean detection times of 51 ± 16 ms. The foot placement estimator-based controller was designed for bilateral, pneumatic, constant-torque output exoskeleton devices to provide assistance to reposition the foot to prevent a fall. At the moment of detection, foot placement estimation (FPE) for recovery is calculated, and a human-inspired response (lift/lower) is chosen for the perturbed leg. A pendulum model is used to determine the necessary torque injections to achieve FPE. Sensitivity analysis of this pendulum model is performed to influence the outputs chosen. The controller is validated through simulation results of the applied strategies showing successful fall prevention.
Construction workers regularly perform tasks that require kneeling, crawling, and squatting. Working in awkward kneeling postures for prolonged time periods can lead to knee pain, injuries, and osteoarthritis. In this article, we present lightweight, wearable sensing, and knee assistive devices for construction workers during kneeling and squatting tasks. Analysis of kneeling on level and sloped surfaces (0 ° , 10 ° , and 20 ° ) is performed for single- and double-leg kneeling tasks. Measurements from the integrated inertial measurement units are used for real-time gait detection and lower limb pose estimation. Detected gait events and pose estimation are used to control the assistive knee joint torque provided by lightweight exoskeletons with powerful quasi-direct drive actuation. Human subject experiments are conducted to validate the effectiveness of the proposed analysis and control design. The results show reduction in knee extension/flexion muscle activation (up to 39%) during stand-to-kneel and kneel-to-stand tasks. Knee-ground contact forces/pressures are also reduced (up to 15%) under robotic assistance during single-leg kneeling. Increasing assistive knee torque shows redistribution of the subject's weight from the knee in contact with the ground to both supporting feet. The proposed system provides an enabling intervention to potentially reduce musculoskeletal injury risks of construction workers.
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