Biomedical Engineering Reference
In-Depth Information
Figure 2.1.
Principal of an optical system with passive markers
Systems with photosensitive
cells and active sensors are
based on the synchronized photographing of three
photosensitive cells arranged on the same unit of
measurement that detect sensors (which emit an infrared
signal) at different angles. The synthesis of 3D coordinates is
done directly, in real-time. No calibration is necessary, since
the three cells in the system are fixed to the origin in a rigid
structure and are precalibrated using a dynamic test battery
after assembly. This technique allows the 3D coordinates of
each active sensor to be calculated in the sensor volume to a
high degree of accuracy, and the automatic recognition of
sensors associated with the multiplexing of the signal over
time, which requires a compromise between the number of
sensors monitored and the sampling frequency. The main
inconvenience of these systems is that the active sensors
require an electrical power source, which requires the
presence of wires and batteries on the subject, which may
hinder movement. Currently, the main manufacturers of
motion
capture systems with
photosensitive
cells
are
Northern digital Inc., Codamotion and PhaseSpace.
