Biomechanical Measurement and Modeling & Inverse Dynamics Flashcards
Motion Capture
Qualify the movements of the body
Accuracy
How accurately position can be estimated - sub-mm desirable
Capture rate
Number of still frames captured per unit time - 60 frames/sec (Hz) or higher desirable
Measure Volume
Volume of space in which marker position can be accurately determined -full movement cycle desirable
Motion Capture Non-Optical Systems
Mechanical, Inertial, Magnetic
Mechanical
- Premise: electronic goniometers/exoskeletons
that use potentiometers to sense joint angle - Strengths: inexpensive, unlimited capture vol
- Limitations: cumbersome, few angles possible
Inertial
- Premise: accelerometer and rate gyro signals
integrated over time to determine the position - Strengths: untethered, unlimited capture
volume - Limitations: accuracy because of drift
Magnetic
- Premise: sensors detect position with respect
to a source magnetic field - Strengths: no optical occlusion
- Limitations: wires, complex, metal occlusion
Motion Capture Optical Systems
Passive Marker, Active Marker, Markerless
Passive Marker
- Premise: light often IR is reflected off of
retroreflective markers captured by
cameras - Strengths: no wires required
- Limitations: marker overlap and occlusion
Active Marker
- Premise: IR LED markers emit light in
sequence, captured by cameras - Strengths: no marker confusion
- Limitations: wires required and occlusion
Markerless
- Premise: automatically identify the body
landmarks from images - Strengths: no markers, no overlap or occlusion
- Limitations: early stages
Marker Positions
Marker positions in space are expressed relative to some arbitrary origin point
Segment Positions
Marker positions can be used to solve for segment positions
Segment Angles
Segment positions can be used to solve for angles - relative and absolute
