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Taking human motion measurement out of the lab and into industry

01 April 2015

With the advent of inertial sensing technology, research can now be taken outside of the usual laboratory settings to track human movement outdoors, in factories or even in homes. Colleen Monaghan reports.

Motion capture systems fall predominantly into two categories: inertial and optical. Optical systems use cameras to track the motion of markers mounted onto the subject. While this is sufficient for studio and lab use, it also comes with some restrictions. Inertial motion capture technology, enabled by microelectromechanical systems (MEMS), is opening doors to human motion capture outside of studios and labs to much more everyday or even extreme environments.

Inertial motion sensors were initially used to stabilise the V-2 rockets during World War 2. Since then, the technology has evolved, with mechanical gyroscopes and accelerometers being replaced by solid state technology. This allows for smaller and lighter sensors able to accurately measure human motion without the need for an external reference. This is particularly beneficial for industrial applications. 

Inertial motion trackers contain discreet sensors which detect movements in the form of angular velocity and acceleration. This allows the system to measure human motion in three dimensions. Effective autocalibration, combined with sensor fusion algorithms, has been a significant breakthrough in inertial motion capture technology, allowing drift free measurement.

The system only needs calibration at the factory assembly stage, while the sensor fusion technology combines the data produced by the sensors to exactly replicate the motion with a very high degree of accuracy. A benefit of the solid state components within inertial motion sensors is that there is almost no degradation over time, reducing the need for maintenance or replacements.

The small size of inertial motion sensors, combined with the fact that no external reference is needed, make the systems suitable for use outdoors, in clinics and in industrial settings. Attached to the body using a suit or straps, the entire hardware can be worn under clothing making it possible to measure movement of factory workers actually working on the factory floor, generating true data in the natural environment without the need for simulations or props. 

MVN Biomech
Xsens’ new MVN Biomech is an inertial motion capture system which has already been used in various applications, such as rehabilitation, ergonomics, human machine interaction and sports.

The system is made up of 17 motion trackers that transmit data wirelessly to the dedicated software, MVN Studio Biomech. The initial set up is very basic, generating a 3D character which is scaled with the subject and, using biomechanical models, the movement is replicated perfectly, including orientation and position.

The system even detects changes in height, a feature that is unique in inertial sensing systems. MVN Studio Biomech also provides 3D graphs representing joint angles, segment kinematics, segment global positions, body centre of mass and sensor component data. It fits into an average sized backpack, facilitating the freedom of movement and possibility to measure anywhere.

Inertial motion tracking for industry
MVN Biomech is being used by Vanderlande Industries to measure the shoulder load of employees at order pick workstations. Distribution warehouses are becoming increasingly automated, easing the workload of operators. It allows operators to remain stationary, picking products from product bins and placing them into order bins. While this is beneficial, it does pose some risks due to the long periods of high frequency movements. 

Vanderlande Industries was faced with the challenge of finding a location for the bins that would best reduce the shoulder load of the operators. To do this, the company analysed the movement of operators as they transferred products between bins and confirmed the packing of the order. MVN Studio Biomech analysed the data to calculate left and right upper arm elevation and to find the maximum elevation angle that was considered safe for operators.  

Inertial motion capture technology, like MVN Biomech, is being used more widely. Human motion measurement no longer needs to be confined to a lab or studio, which has seen it increasingly being used in factories and outdoors. This will be helped by the increasing power efficiency of motion sensors. In addition, sensors are likely to reduce further in size making it a more widely used technology in industry. 

Inertial motion capture technology has already been shown to help reduce the risk of strain and injury for employees and the coming advances in the technology could make this easier in the future.

Dr Colleen Monaghan is product manager, Xsens

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