Dynamic Force Platforms

Introduction

Some force platforms have the ability to move during a trial. However, the C3D file format is only set up to handle static force platforms, which makes it difficult to account for a dynamic force platform. This page is devoted to handling a moving platform within Visual3D.

Please note that although some treadmills can be inclined, you will most likely want to use a jig to account for the motion of the treadmill. All information about treadmills can be found here.

IMPORTANT Please note these instructions are specific to force platforms.

To be added Instrumented Pedal Example with out center of pressure.

Example 1

This example would be relevant if the instrumented device will not be placed in the same location at the start of each trial.

Examples 1A and 1B will result in the same answer. The only difference between the two is that Example 1A creates force platforms to do the "heavy lifting". This means that the analog signals are scaled and the center of pressure is calculated by creating "fake" force platforms. Example 1B manually scales the analog signals and calculates the center of pressure. Example 1B is really only provided to give the user a better idea of the internal calculations when using this method.

When defining the model:

• The origin of the force platform segment should be defined at the top center surface of the platform
• The segment coordinate system should be aligned with the internal force platform coordinate system - except the Z axis should be vertical and the X should be pointed in the opposite direction
• The segment should be tracked using targets placed directly on the platform

When updating the script for your purposes:

• The calibration matrix should represent the scale factors/calibration matrix for your platform
• The force platform origin should represent the vector from the mechanical center to the top center surface of the platform
• The force platform corners do not need to be modified

Example 1A Download

A sample CMO file, with a script to create the force signals can be found here.

Example 1B Download

A sample CMO file, with a script to create the force signals can be found here.

Example 2

This example would be relevant if you have a force platform which is always at the same location when the lab origin is defined.

When defining the model:

• The origin of the segment coordinate system should be at the origin of the lab coordinate system
• The segment coordinate system should be aligned with the lab coordinate system
• The segment should be tracked using targets placed directly on the platform

When updating the script for your purposes:

• The calibration matrix should represent the scale factors/calibration matrix for your platform
• The force platform origin should represent the vector from the mechanical center to the top center surface of the platform
• The force platform corners should represent the location of the force platform in your global coordinate system

Example 2 Download

A sample CMO file, with a script to create the force signals can be found here.