Product Optimisation: Data Loggers Record Usage Behaviour of Wheelchair Users

Measurement data acquisition at Otto Bock Mobility Solutions with MSR145 and MSR160 data loggers

In order to obtain well-founded insights regarding the intensity of use of an electric wheelchair that is geared towards golfing, development engineers at Otto Bock Mobility Solutions GmbH recorded the usage behaviour of wheelchair users over a period of several weeks, using MSR data loggers.

Author: Thomas Brendel, Development Engineer in the R&D division at Otto Bock Mobility Solutions GmbH

Mobility is quality of life – this has been the vision of German Otto Bock HealthCare GmbH since its founding. With its four business units of Prosthetics, Orthotics, Mobility Solutions and Medical Care, the medical technology company founded in 1919, is able to offer people with an impairment a wide range of products and comprehensive services for leading a more independent and self-determined life. Otto Bock HealthCare GmbH, which is based in Duderstadt, employs more than 6,000 staff worldwide. In the Mobility Solutions business unit, the engineers at Otto Bock develop technical aids for rehabilitation purposes. This includes rehabilitation products such as standing supports and seating systems, as well as manual and electric wheelchairs for the most varied demands and needs. From a sturdy, flexible folding wheelchair to a high-tech electric piece of equipment featuring sophisticated control functions, wheelchairs must meet the highest standards in terms of technology, functionality, customisation, sturdiness and design.

The consistent advancement of the products that are geared clearly towards the current customer requirements is of key importance to the company’s success. The focus of its endeavours to optimise the products is currently on the ParaGolfer sports wheelchair – a success story of the company. The electric wheelchair, which has been specifically geared towards golfing, has a function that assists the user in assuming a standing position and has been designed in a way that enables the user to stand securely for teeing off in spite of their walking impairment. The adjustable seat helps the golfer position themselves optimally towards the ball. At the same time, the three-wheeled chassis meets the specific demand for cross-country mobility on the golf course.

Data loggers help identify weak spots

In order to be able to improve a product, you must first identify any potential weak spots and analyse their impacts. Therefore, the engineers at Otto Bock used various data loggers of the Swiss MSR Electronics GmbH Company to obtain well-founded insights into the product utilisation of the ParaGolfer. MSR Electronics specialises in the development of miniaturised data loggers and has made a name for itself in particular in the field of modular measurement technology. With sophisticated sensor and processor technology, the compact, autonomous MSR data loggers record a variety of physical environmental parameters over long periods of time.

For the electric golfing wheelchair by Otto Bock, the engineers used Typs data loggers of the type MSR145 and MSR160 to examine how often an average player uses the electric seat adjustment function when playing an 18-hole golf course. In addition, they examined the total number of cycles to be assumed to ensure the fault-free operation over the product life.

In the case of the Otto Bock golf power wheelchair, the engineers used MSR145 and MSR160 data loggers to investigate the question of how often an average player uses the electric seat stand-up adjustment when mastering an 18-hole golf course and what total number of cycles should be assumed in order to guarantee perfect functioning over the product’s service life. For this purpose, the data loggers recorded the parameters range, speed, frequency of the stand-up cycles, power consumption and temperature development. The aim was to be able to design the functional components of the ParaGolfer precisely so that they reliably fulfil the typical requirements of the customers after evaluating the data.

Objective measured values provide clarity

Within the context of a field test, the golfing wheelchairs of several users were equipped with MSR data loggers and subsequently, the mechanical and electrical behaviour was recorded over a period of several weeks. The data loggers were equipped with an internal 3-axis acceleration sensor (±15 g). Furthermore, sensors connected to four analogue inputs recorded electricity, voltage, speed and temperature. By default, the memory capacity of the mini data loggers is two million measured values. This capacity can be increased by means of a micro SD card; this is how the engineers were eventually able to record over 1 billion measured values. The USB port ensured the power supply of the respective data logger from the batteries of the wheelchair. The signal of the y-axis of the internal acceleration sensor was stored at a measurement frequency of 1 Hz and subsequently analysed. A specialist software counted the instances of standing up as a change of angle over time as soon as they exceeded a defined limit value. In addition, the MSR160 data logger recorded the measured values of electricity, voltage, speed and temperature at a frequency of 16 Hz. The continuous recording of 16 measurements per second accumulated a very high data volume. Therefore, the memory cards had to be read quite frequently. In principle, the volume of the recorded measured data can be reduced by setting limit values. However, the engineers initially decided to record all the values and extract the relevant data ranges at a later stage during the analysis. This enabled them to make sure they would be able to evaluate all events of interest.

The 32-bit PC application by MSR was used to convert sections that each corresponded to approximately one day of use. This data was exported as a CSV file and subsequently analysed. In the meantime, this program has also been made available as a 64-bit version that is capable of processing significantly greater data volumes per session.

LabVIEW helps with the analysis

On the basis of the LabVIEW (Laboratory Virtual Instrumentation Engineering Workbench) graphical programming environment from National Instruments, the Otto Bock engineers developed an analysis software that is geared to this specific application. Among other things, this software examines the measured values of the acceleration sensors recorded over time. It calculates the respective seat angle in degrees compared with the horizontal and recognises events that exceed or fall below a threshold of 20°. The program highlights these events in green in the charts so that they can be clearly identified, irrespective of the zoom factor.

This information obtained by means of the data loggers is extremely valuable to the company: It helps to improve the products on the basis of real usage data, which has been recorded over a long period of time and which is therefore objective. This enables the staff at Otto Bock to select the components best suited for the respective intended use and thus enhance the product quality. This results in fewer complaints and repairs, whilst increasing the customer satisfaction.