Tools and methods for the quality assurance of force platforms in human movement analysis
Creators: name: Cedraro, Andrea <1979>
Publisher: name: Alma Mater Studiorum - Università di Bologna
Year: 2008
Subjects: ING-INF/06 Bioingegneria elettronica e informatica

description: The human movement analysis (HMA) aims to measure the abilities of a
subject to stand or to walk. In the field of HMA, tests are daily performed
in research laboratories, hospitals and clinics, aiming to diagnose a disease,
distinguish between disease entities, monitor the progress of a treatment and
predict the outcome of an intervention [Brand and Crowninshield, 1981; Brand,
1987; Baker, 2006]. To achieve these purposes, clinicians and researchers use
measurement devices, like force platforms, stereophotogrammetric systems, accelerometers,
baropodometric insoles, etc.
This thesis focus on the force platform (FP) and in particular on the quality
assessment of the FP data. The principal objective of our work was the design
and the experimental validation of a portable system for the in situ calibration
of FPs.
The thesis is structured as follows:
Chapter 1. Description of the physical principles used for the functioning
of a FP: how these principles are used to create force transducers, such as strain
gauges and piezoelectrics transducers. Then, description of the two category
of FPs, three- and six-component, the signals acquisition (hardware structure),
and the signals calibration. Finally, a brief description of the use of FPs in
HMA, for balance or gait analysis.
Chapter 2. Description of the inverse dynamics, the most common method
used in the field of HMA. This method uses the signals measured by a FP to
estimate kinetic quantities, such as joint forces and moments. The measures of
these variables can not be taken directly, unless very invasive techniques; consequently
these variables can only be estimated using indirect techniques, as the
inverse dynamics. Finally, a brief description of the sources of error, present in
the gait analysis.
Chapter 3. State of the art in the FP calibration. The selected literature
is divided in sections, each section describes: systems for the periodic control
of the FP accuracy; systems for the error reduction in the FP signals; systems
and procedures for the construction of a FP. In particular is detailed described
a calibration system designed by our group, based on the theoretical method
proposed by ?. This system was the “starting point” for the new system presented
in this thesis.
Chapter 4. Description of the new system, divided in its parts: 1) the algorithm;
2) the device; and 3) the calibration procedure, for the correct performing
of the calibration process. The algorithm characteristics were optimized by a
simulation approach, the results are here presented. In addiction, the different
versions of the device are described.
Chapter 5. Experimental validation of the new system, achieved by testing
it on 4 commercial FPs. The effectiveness of the calibration was verified
by measuring, before and after calibration, the accuracy of the FPs in measuring
the center of pressure of an applied force. The new system can estimate
local and global calibration matrices; by local and global calibration matrices,
the non–linearity of the FPs was quantified and locally compensated. Further,
a non–linear calibration is proposed. This calibration compensates the non–
linear effect in the FP functioning, due to the bending of its upper plate. The
experimental results are presented.
Chapter 6. Influence of the FP calibration on the estimation of kinetic
quantities, with the inverse dynamics approach.
Chapter 7. The conclusions of this thesis are presented: need of a calibration
of FPs and consequential enhancement in the kinetic data quality.
Appendix: Calibration of the LC used in the presented system. Different
calibration set–up of a 3D force transducer are presented, and is proposed the
optimal set–up, with particular attention to the compensation of non–linearities.
The optimal set–up is verified by experimental results.