Force & Motion Measurement Flashcards
What are the three different types of imaging systems?
Cinematography
Videography
Optoelectronic systems.
What is Cinematography?
The method traditionally used in commercial film making, as the quality of picture is higher and editing of the reel is done with a pair of scissors and glue!
What is Videography?
The best-known method – usually using a camcorder. It is inexpensive and can be transferred to computer systems for editing and analysis.
What are Optoelectronic systems?
Expensive systems which use reflective markers picked up by infra-red cameras to produce an image that can have models ‘mapped’ onto it.
What are the 6 processes in kinematics?
Set-up of equipment.
Recording of equipment.
Downloading and treatment of kinematic data.
Noise reduction.
Body segment parameter model selection.
Extraction of analysed data.
What is frame rate?
The number of pictures taken per second.
Every frame is made up of two fields. These two fields can be separated by computer software (so that 25 frames allows analysis of 50 fields). This obviously doubles the amount of analysis possible.
We rarely record above 500 Hz.
What does the lens/aperture do?
The aperture is what controls the amount of light entering the camera.
This is also known as the f-stop or f-ratio and the smaller the aperture, the less focal range possible.
What does the shutter do?
Controls the exposure time.
What happens in effect is that when each frame is in place, the shutter opens and lets light in. The image is recorded on the frame.
What is resolution important for?
Precision.
What 4 steps must be taken to set up the camera?
Manual focus setting
Shutter speed – The faster the better (reduces blurring) although the image will be darker.
F-stop – Controls the amount of light entering the camera iris. Note that a low f-stop means a narrow range of focus.
ISO – This is a measure of the camera sensor’s
sensitivity to light. (Higher ISO values mean the camera can get better pictures in dark conditions but the image is more grainy)
What is Two-Dimensional Analysis (2D)?
Single camera.
The movement is measured in only one plane (2 dimensions - x, y).
What is Three-Dimensional Analysis (3D)?
At least two cameras.
The movement is recorded for more than one view (3 dimensions - x, y, z).
What is the most popular method in processes in kinematics?
Direct Linear Transformation (DLT).
DLT requires knowledge of the x, y, z coordinates of known points in the field of view. This is provided by the calibration object (frame).
DLT coordinate reconstruction can only be guaranteed within the calibration volume.
What are Force platforms (force plates) used for?
They are used to measure the ground reaction forces (GRF) in three dimensions (x, y, z).
What direction of motion are:
Fy
Fx
Fz
Fy= Vertical
Fx= Anteroposterior
Fz= Side-to-side
