• Specifications
• PressureAnalysis

Additional information can be found on the Discussion page.

Target Outcome

To process Tekscan pressure data for a static loading condition (exported as csv file) and generate:

• an XML file containing: averaged pressure data for all temporal frames, contact metrics (force, area, peak pressure)
• an image (png) displayng the averaged pressure data

Prerequisites

Infrastructure

Previous Protocols

• Specifications/SpecimenPreparation

• Specifications/ExperimentationJointMechanics

• Specifications/PressureCalibration

Requirements

• Python [Version 3] [tested with Version 3.3.2] (https://www.python.org)

• NumPy [tested with Version 1.9.2] (https://www.numpy.org)

• matplotlib [tested with Version 1.4.3] (https://matplotlib.org/)

Python Script

https://simtk.org/websvn/wsvn/openknee/utl/PressureAnalysis/Tekscan_contact_metrics.py

Input

• Tekscan pressure data exported as a csv file, which includes an arbitrary number of temporal frames, at a static loading condition.
• Pressure Sensor:
  • VERSION: Tekscan Pressure Measurement System 7.60-18I
  • HARDWARE: 102-4201
  • MAP_VERSION: 6.4
  • SENSOR_TYPE: 5051

Procedures

Import Tekscan Parameters

The script is robust in that in imports both values and units (defaults listed below) from the csv file. Tekscan data imported includes:

• Sensor dimensions
  • number of sensel rows
  • number of sensel columns
  • sensel row dimension (mm)
  • sensel column dimension (mm)
  • sensel area (mm^2)
• Calibration data
  • noise threshold (raw)
  • scale factor (MPa/raw)
  • exponent
  • saturation pressure (MPa)
  • calibration points
    • force (N)
    • sum (raw)
    • number of loaded cells
• Pressure array data
  • accumulate all temporal pressure frame arrays (MPa) into a single array (for subsequent averaging)
  • record number of temporal frames

Compute contact metrics

• contact area (mm^2) = 'number of loaded sensels' * 'sensel area'
• contact force (N) = SUM( 'averaged sensel pressure' * 'sensel area' )
• peak average pressure (MPa)
  • location, sensel indices [row,column]

Compute averaged pressure array data

• divide accumulated pressure array by the number of frames

Output

XML file

Includes (as specified above):

• input filename (Tekscan csv)
• imported Tekscan parameters
• contact metrics
• averaged pressure data (numpy array, as string)

Average pressure sensor image

File type: png

• Plot of averaged pressure sensor data (MPa)
• Title includes:
  • name of associated xml file that contains the average pressure sensor data
  • contact metrics: force (N), area (mm^2)
  • peak average pressure (MPa)
• Sensor dimensions: mm
• Colormap scale: [0.0 - 'peak average pressure'] (MPa)

Sample Results

Following are example output files (xml, png) for analysis of oks007 at a flexion angle of 60 degrees and and quadriceps force of 600N.

XML file

<Pressure_Sensor>
        <Input_File type="csv">oks007-intact-60-600-2_M.csv</Input_File>
        <Dimensions>
                <rows units="sensels">44</rows>
                <cols units="sensels">44</cols>
                <sensel_area units="mm^2">1.6129</sensel_area>
        </Dimensions>
        <Calibration>
                <noise_threshold units="raw">3</noise_threshold>
                <scale_factor units="MPa/raw">0.0011882</scale_factor>
                <exponent>1.5754</exponent>
                <saturation_pressure type="Exponential Extrapolation" units="MPa">7.34773</saturation_pressure>
                <Points>
                        <Point num="1">
                                <force units="N">49.9998</force>
                                <sum units="raw">3173</sum>
                                <loaded_cells units="count">109</loaded_cells>
                        </Point>
                        <Point num="2">
                                <force units="N">100.0</force>
                                <sum units="raw">5370</sum>
                                <loaded_cells units="count">135</loaded_cells>
                        </Point>
                        <Point num="3">
                                <force units="N">200.0</force>
                                <sum units="raw">9195</sum>
                                <loaded_cells units="count">176</loaded_cells>
                        </Point>
                        <Point num="4">
                                <force units="N">400.0</force>
                                <sum units="raw">15543</sum>
                                <loaded_cells units="count">231</loaded_cells>
                        </Point>
                        <Point num="5">
                                <force units="N">599.998</force>
                                <sum units="raw">21169</sum>
                                <loaded_cells units="count">268</loaded_cells>
                        </Point>
                </Points>
        </Calibration>
        <Contact_Metrics>
                <area units="mm^2">783.8694</area>
                <force units="N">387.19987076</force>
                <Peak_Pressure>
                        <value units="MPa">2.1456</value>
                        <Location>
                                <row units="sensels">19</row>
                                <col units="sensels">40</col>
                        </Location>
                </Peak_Pressure>
        </Contact_Metrics>
        <Pressure_Array processing="averaged" type="numpy array" units="MPa">array([[0.0000,...],...])</Pressure_Array>
</Pressure_Sensor>

Average pressure sensor image

Anatomical orientation of pressure sensor