Why it is important to use the right motion capture system in the field of ergonomics
This is a guest blog post from Dr Jason Konrath,Product manager at Xsens.
Ergonomics is a field aimed at optimizing the design of systems, products or processes by taking into account the way people interact with them. The goal of ergonomics should be to reduce human error, as well as improve productivity, safety and comfort. To this end, accurate assessment of human motion is needed, including the postures and movements undertaken, as well as the interactions with the external environment. Such knowledge is fundamental to achieve optimal design.Traditional laboratory set-ups containing camera-based and force plate systems have been proven as an effective tool to accurately measure human motion,however just as the name suggests they are limited to a laboratory setting. In the case of a factory station, the entire station would need to be replicated within the laboratory to accurately define the human’s movement and interaction with the environment. Furthermore, laboratory based methods are limited by costant availability of laboratories, constrained measurement space and marker occlusion. Inertial motion capture addresses these short comings, providing an alternative solution for human motion analysis, especially for ambulatory assessment in the natural environment of the participant.
An inertial motion capture system is composed of several inertial measurement units (IMU) placed on an individual’s main body segments. Each inertial measurement unit consists of an accelerometer, gyroscope and magnetometer, from which the position and orientation of a body segment can be estimated, via a process of sensor fusion. The Xsens MVN system uses a total of 17 IMUs mounted on the body, following scaling and calibration, the data is applied to a biomechanical model, from which segment and joint kinematics can be determined. Importantly, IMUs are relatively inexpensive and portable, making them accessible to wide variety of settings.
In the past, due to the use of magnetometers in an IMU, magnetic disturbance soften caused a degraded performance due to the presence of ferro-magnetic objects. Considering ergonomics analysis often takes place in factory settings, this could be a major limitation given the amount of metallic objects present such as chairs, tables and workstations. However, Xsens has now solved this issue following the release of the MVN analyze engine. The latest advances instatistical state estimation and numerical optimization algorithms, combined with specific calibration routines, complex biomechanical models and innovative sensor fusion frameworks, can provide solutions to this typical limitation of inertial motion capture. As a result of this, highly accurate and consistentf ull body human motion measurement is now possible in any environment despite the influence of magnetic interference.
The recent developments in the MVN analyze engine delivers a huge performance boost under all conditions due to many improvements, from signal processing to how the data is handled. The latest developments in foot contact detection, now make it possible to track height changes of the subject, such as walking up a set of stairs. In addition to this, algorithms to reduce the effect of soft tissue artefact have also been employed to ensure more accurate tracking of the segments, as well as prevent artefacts being projected to the feet.
Collectively, the use of the Xsens MVN system ensures lab quality data in the factory or plant floor and is a revolutionary step for the industry. The evaluation of workstation set-ups, ergonomic design, body posture assessment can be enabled in a fast and reliable way without relying on a laboratory. This has both enormous value and potential to help companies and individuals undertake their work activities in an optimal way, so that performance can be improved, whilst reducing the risk of work related injury.
