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Research Papers

A Direct Method for Mapping the Center of Pressure Measured by an Insole Pressure Sensor System to the Shoe's Local Coordinate System

[+] Author and Article Information
Brian T. Weaver

Mem. ASME
Orthopaedic Biomechanics Laboratories,
Michigan State University,
A407 East Fee Hall,
East Lansing, MI 48824;
Explico Engineering Co.,
40028 Grand River Avenue,
Suite 300,
Novi, MI 48375,
e-mail: Brian@explico.com

Jerrod E. Braman

Orthopaedic Biomechanics Laboratories, Michigan State University,
A407 East Fee Hall,
East Lansing, MI 48824
e-mail: Bramanj1@msu.edu

Roger C. Haut

Fellow ASME
Orthopaedic Biomechanics Laboratories,
Michigan State University,
A407 East Fee Hall,
East Lansing, MI 48824
e-mail: Roger@msu.edu

1Corresponding author.

Manuscript received September 9, 2015; final manuscript received April 11, 2016; published online May 5, 2016. Assoc. Editor: Kristen Billiar.

J Biomech Eng 138(6), 061007 (May 05, 2016) (7 pages) Paper No: BIO-15-1444; doi: 10.1115/1.4033476 History: Received September 09, 2015; Revised April 11, 2016

A direct method to express the center of pressure (CoP) measured by an insole pressure sensor system (IPSS) into a known coordinate system measured by motion tracking equipment is presented. A custom probe was constructed with reflective markers to allow its tip to be precisely tracked with motion tracking equipment. This probe was utilized to activate individual sensors on an IPSS that was placed in a shoe fitted with reflective markers used to establish a local shoe coordinate system. When pressed onto the IPSS the location of the probe's tip was coincident with the CoP measured by the IPSS (IPSS-CoP). Two separate pushes (i.e., data points) were used to develop vectors in each respective coordinate system. Simple vector mathematics determined the rotational and translational components of the transformation matrix needed to express the IPSS-CoP into the local shoe coordinate system. Validation was performed by comparing IPSS-CoP with an embedded force plate measured CoP (FP-CoP) from data gathered during kinematic trials. Six male subjects stood on an embedded FP and performed anterior/posterior (AP) sway, internal rotation, and external rotation of the body relative to a firmly planted foot. The IPSS-CoP was highly correlated with the FP-CoP for all motions, root mean square errors (RMSRRs) were comparable to other research, and there were no statistical differences between the displacement of the IPSS-CoP and FP-CoP for both the AP and medial/lateral (ML) axes, respectively. The results demonstrated that this methodology could be utilized to determine the transformation variables need to express IPSS-CoP into a known coordinate system measured by motion tracking equipment and that these variables can be determined outside the laboratory anywhere motion tracking equipment is available.

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Figures

Grahic Jump Location
Fig. 4

Illustration of two coordinate systems that have a translation (R) and an angle of rotation (θ) relative to one another

Grahic Jump Location
Fig. 3

Illustration of the push tests to determine the location of discrete sensors in the local shoe coordinate system (tip of the probe) and the coordinate system of the IPSS

Grahic Jump Location
Fig. 2

Illustration of the custom fabricated probe

Grahic Jump Location
Fig. 1

Illustration of the marker placement on the right Nike shoe used to create the local shoe coordinate system with an origin at the height of the insole pressure measurement system

Grahic Jump Location
Fig. 5

(a) Temporal plot CoP from subject 3 performing internal rotation of the body relative to the foot. (b) Temporal plot of CoP from subject 5 performing external rotation of the body relative to the foot. (c) Temporal plot of CoP from subject 2 performing AP Sway.

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