Pitch Moment Compensation for Belt Acceleration of an Instrumented Treadmill

This is the source code which reproduces the results for the paper entitled:

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The acceleration of the belt of a treadmill which is instrumented to measure the ground reaction loads may introduce an undesired superimposed pitch moment. This source code provides a computational method for reducing the effect the belt accelerations have on the pitch moment measurement and produces all of the results in the aforementioned publication.

Dependencies

• Matlab R2014b (8.3.0.532)
• Optimization Toolbox (Version 7.0)
• Signal Processing Toolbox (Version 6.21)

Basic Installation

Download the source code and data from the Git repository:

$ wget https://github.com/csu-hmc/pitch-moment-compensation/archive/master.zip
$ unzip pitch-moment-compensation-master.zip
$ cd pitch-moment-compensation-master

Usage

The complete results can be computed by starting Matlab with the main source code directory in your Matlab path and typing the following at the command prompt:

>> compensation_test

Once the function has run you will find all of the plots in the Results directory. For the cutoff frequency of interest, a table of results including the reduction in the root-mean-square (RMS) between uncompensated and compensated pitch moment and the R^2 fit between the model simulation output and the measured acceleration.

Computation Steps

The data processing pipeline follows this general process:

1. Specifies filenames located in the Data directory.
2. Loads data from tab separated ACSII data files (load_data.m). Data includes the timestamps, recorded belt velocities, and recorded pitch moment (Mx) from four data files (two slow speeds at 1.2 m/s and two fast speeds at (2.0 m/s).
3. Computes belt acceleration by numerical differentiation.(obtain_derivative.m)
4. Sets a range of desired cutoff frequencies for the lowpass filter (1-20 Hz). Also sets a cutoff frequency of interest (6 Hz).
5. Filters signals (acceleration and pitch moment) with the cutoff frequency(filter_data.m)
6. Computes model coefficients for the belt acceleration pitch moment model. (pitch_moment_calibration.m)
7. Simulates the model with the acceleration as the independent variable. (simulate.m)
8. Truncates the filtered data to avoid end effects (one second from beginning and end of the trial. (simulate.m)
9. Subtracts the difference in the pitch moment due to belt acceleration. (simulate.m)
10. Computes the coefficient of determination (R^2) of the model with respect to the data from the other trial. (calculate_statistics.m)
11. Computes the RMS of the uncompensated and compensated pitch moment of the trials, as well as the percent reduction (calculate_statistics.m)
12. Displays the table of results for the desired frequency (6 Hz).
13. Shows a plot of simulation versus actual data at the desired frequency (6 Hz). (plot_simulation_graphs.m)
14. Shows a comparison of RMS with respect to the filter frequency for compensated and uncompensated. (plot_frequency_graphs.m). If the range of the cutoff frequencies is 1, then the graph will not generate.
15. Saves the graphs to the Results data directory.