Biomechanics Part 4 Kinematics . Study of motion without reference to the forces that cause the motion. · Linear and angular characteristics · Examples: Displacement, Velocity, Acceleration Kinetics · Study of forces and moments acting on a person or object Measurement in biomechanics Kinematics Optical tracking Non-optical tracking Medical imaging Strain gauges Displacement sensors Kinetics Load cells Force plates Muscle Activity Electromyography (EMG) Motion Capture . Defined as "the process of recording movement of obiects or neonle"
... --. Types of Motion Capture Systems · Optical passive systems 1. High-speed cameras 2. Reflective markers · Optical active systems · Electromagnetic systems · Markerless · Inertial sensors Optical passive tracking · Motion capture using passive (not powered) markers to identify locations on a person or object. Optical systems - High-speed cameras · Markers are placed and imaged during loading · Multiple cameras can be used to measure 3D motion · Requires software and time to post-process video Optical systems - Reflective passive markers · Uses reflective markers placed on person or object · Markers reflect infrared (IR) light emitted by cameras · Real-time tracking · Specific issues · Markers must to close to cameras · Cannot be used outside Why Do Need Multiple Cameras · Ambiguous distance to markers
· Noise in measurement · Spurious markers · Single camera tracking is possible in special cases · Need to know relative arrangement of markers · Need more markers visible to camera General issues with passive optical tracking · Soft tissue artifacts · Marker placement · Field of view (FOV) · Camera alignment and calibration · Image distortion Optical systems - Active markers · Typically, highest accuracy · Each marker emits IR light · Markers uniquely identified · Real-time tracking · Specific issues: Requires wires or battery, Soft tissue artifacts, Marker placement, Field of view Electromagnetic (EM) tracking · Sensors in electromagnetic fields · Advantages 1. Versatile 2. No need for lines of sight · Limitations 1. Sensors are wired or require battery 2. Soft tissue artifacts 3. Field of view