Balance and Task Evaluation of Construction Workers Assisted by Knee Exoskeletons

Background Introduction

Construction workers face serious safety and health risks in hazardous working environments, especially when working at heights. Prolonged standing and kneeling postures can lead to knee injuries, musculoskeletal disorders, and visual disturbances, which may affect workers’ balance. To prevent falls and other work-related injuries, researchers have begun exploring technological solutions to enhance the balance of construction workers in these high-risk environments. Knee exoskeletons, as wearable devices, are considered a promising intervention to reduce knee joint stress and help workers maintain balance in various postures.

The core of this study lies in exploring the influence of lower limb joints, particularly the knee joint, on neural balance control strategies during standing and kneeling postures. Additionally, the research evaluates the impact of elevated environments and knee exoskeletons on construction workers’ postural balance and welding task performance. Through virtual reality (VR) and mixed reality (MR) technologies, researchers simulated elevated environments and welding tasks, providing new tools for studying workers’ balance strategies.

Source of the Paper

This paper was co-authored by Gayatri Sreenivasan, Chunchu Zhu, and Jingang Yi from Purdue University and Rutgers University. The paper was presented at the 2023 IEEE International Conference on Automation Science and Engineering from August 26 to 30, 2023, and is scheduled for formal publication in the IEEE Transactions on Automation Science and Engineering in 2025.

Research Process

1. Experimental Design and Model Construction

The study first analyzed balance control strategies during standing and kneeling postures using multi-link inverted pendulum models. Specifically, the standing posture was modeled using a triple-link inverted pendulum (TIP), while the kneeling posture was modeled using a double-link inverted pendulum (DIP). These models were used to quantify neural balance control strategies, particularly through the frequency behavior of the intersection point (IP) height of ground reaction forces.

2. Virtual Reality Environment Setup

Researchers used the HTC Vive Pro virtual reality system to simulate elevated construction environments and built various visual scenes using the Unity game engine, including low-elevation (LE) and high-elevation (HE) construction environments. Welding tasks were also simulated in the virtual environment to evaluate workers’ balance and task performance during task execution.

3. Experimental Subjects and Procedures

The study recruited 11 healthy subjects (4 females, 7 males), who participated in experiments involving both standing and kneeling postures. Each subject completed a series of tests under different conditions, including: - Protocol A: Balance Evaluation: Subjects maintained standing or kneeling postures for 60 seconds with or without exoskeleton assistance, assessing their balance ability. - Protocol B: Welding Task Evaluation: Subjects performed welding tasks in the virtual environment, evaluating their balance and task performance during task execution.

Experimental data included ground reaction forces (GRF), center of pressure (COP), acceleration (measured via IMU sensors), and heart rate data. Researchers synchronized and analyzed this data using custom Python scripts.

4. Data Analysis and Model Validation

The study used a linear quadratic regulator (LQR) as the neural balance controller to quantify subjects’ balance strategies under different conditions. By analyzing the IP height frequency curves, researchers derived the subjects’ balance control strategies at different frequencies. Additionally, the acceleration ellipse area (A_acc) and sway ellipse area (A_sway) were calculated to quantify subjects’ dynamic control and postural stability.

Research Results

1. Balance Strategy Analysis

The experimental results showed that the knee joint played a crucial role in balance control during both standing and kneeling postures. Particularly in elevated environments, the knee exoskeleton significantly reduced subjects’ postural sway. Specific data indicated that in elevated environments, the center of pressure sway area decreased by 62% in standing posture and by 39% in kneeling posture when wearing the exoskeleton.

2. Task Performance Evaluation

During welding tasks, subjects wearing the exoskeleton showed significant improvement in task performance in elevated environments. The completion rate, accuracy, and precision of the welding tasks all improved, with the exoskeleton’s assistance being particularly noticeable in elevated environments.

3. Heart Rate and Physiological Responses

The study also found that elevated environments led to increased heart rates in subjects, while wearing the exoskeleton alleviated this physiological stress to some extent. Although the statistical significance of heart rate changes was not strong, the trend suggested that the exoskeleton helped mitigate the psychological stress associated with elevated environments.

4. Model Validation and Parameter Fitting

Through the optimal parameter fitting of the LQR controller, researchers found significant differences in balance control strategies between standing and kneeling postures. During standing, subjects tended to use ankle and knee strategies, while kneeling relied more on the knee joint. These findings provide important references for the design of exoskeletons.

Conclusions and Significance

This study, through virtual reality technology and multi-link inverted pendulum models, delved into the critical role of the knee joint in construction workers’ balance control and validated the effectiveness of knee exoskeletons in elevated construction environments. The results demonstrated that exoskeletons not only significantly improve workers’ postural stability but also enhance their task performance, particularly in elevated environments. These findings provide a scientific basis for the future design and optimization of exoskeleton devices.

Research Highlights

1. Innovative Models: This study is the first to use triple-link and double-link inverted pendulum models to quantify balance control strategies during standing and kneeling postures, particularly the role of the knee joint.
2. Virtual Reality Technology: The successful simulation of complex construction environments using VR and MR technologies provides new tools for balance control research.
3. Exoskeleton Application Validation: The study validated the practical application value of knee exoskeletons in construction workers’ balance control and task performance, especially in elevated environments.
4. Multidimensional Data Analysis: The study comprehensively assessed subjects’ balance control strategies through IP height frequency analysis, acceleration, and sway area metrics.

Additional Valuable Information

The researchers also noted that future studies could expand the subject pool to include experienced construction workers and introduce more direct physiological measurement methods (e.g., electromyography, EMG) to further analyze the impact of exoskeletons on muscle activation. Additionally, developing adaptive control systems that respond to real-time balance changes is an important direction for future research.