Ingo Hermanns

Workload Assessment in Field Using the Ambulatory CUELA System

Ambulatory assessment of physical workloads in field is necessary to investigate the risk of work-related musculoskeletal disorders (MSD). Since more than ten years the BGIA is developing and using the motion and force capture system CUELA (computer-assisted recording and long-term analysis of musculoskeletal load), which is designed for whole-shift recordings and analysis of work-related postural and mechanical loads in ergonomic field analysis. This article gives an overview of the actual state of development and some applications of the system.

Optimization of inertial sensor-based motion capturing for magnetically distorted field applications.

Inertial measurement units (IMU) are gaining increasing importance for human motion tracking in a large variety of applications. IMUs consist of gyroscopes, accelerometers, and magnetometers which provide angular rate, acceleration, and magnetic field information, respectively. In scenarios with a permanently distorted magnetic field, orientation estimation algorithms revert to using only angular rate and acceleration information. The result is an increasing drift error of the heading information. This article describes a method to compensate the orientation drift of IMUs using angular rate and acceleration readings in a quaternion-based algorithm. Zero points (ZP) were introduced, which provide additional heading and gyroscope bias information and were combined with bidirectional orientation computation. The necessary frequency of ZPs to achieve an acceptable error level is derived in this article. In a laboratory environment the method and the effect of varying interval length between ZPs was evaluated. Eight subjects were equipped with seven IMUs at trunk, head and upper extremities. They performed a predefined course of box handling for 40 min at different motion speeds and ranges of motion. The orientation estimation was compared to an optical motion tracking system. The resulting mean root mean squared error (RMSE) of all measurements ranged from 1.7 deg to 7.6 deg (roll and pitch) and from 3.5 deg to 15.0 deg (heading) depending on the measured segment, at a mean interval-length of 1.1 min between two ZPs without magnetometer usage. The 95% limits of agreement (LOA) ranged in best case from -2.9 deg to 3.6 deg at the hip roll angle and in worst case from -19.3 deg to 18.9 deg at the forearm heading angle. This study demonstrates that combining ZPs and bidirectional computation can reduce orientation error of IMUs in environments with magnetic field distortion.

A Person-Centered Measurement System for Quantification of Physical Activity and Energy Expenditure at Workplaces

Accurate quantification of physical activity (PA) and energy expenditure (EE) is a basic prerequisite to evaluate activity promoting measures. A novel approach for determining EE by a person-centered measurement system which operates with motion sensors is presented. The new EE prediction model combines information on the type and intensity of PA as well as personal characteristics. For model calibration eight subjects performed standardized office and locomotion tasks while wearing the measurement system and an indirect calorimeter simultaneously. Via multiple regression analyses different EE prediction equations for sitting, standing, walking, climbing downstairs and climbing upstairs are developed. Model fit statistics revealed good results (adjusted R2 = 0.51 - 0.90). The developed model seems promising for precise EE prediction during the investigated activities.

Influence of different safety shoes on gait and plantar pressure: a standardized examination of workers in the automotive industry

Working conditions, such as walking and standing on hard surfaces, can increase the development of musculoskeletal complaints. At the interface between flooring and musculoskeletal system, safety shoes may play an important role in the well‐being of employees. The aim of this study was to evaluate the effects of different safety shoes on gait and plantar pressure distributions on industrial flooring.