User guide

Charnwood Dynamics Ltd. Coda cx1 User Guide – Coda Basics I - 1
CX1 USER GUIDE - COMPLETE.doc 26/04/04 13/162
SETTING UP AND USING THE SYSTEM
Coda cx1 Scanner Units
Each Coda scanner unit contains three special cameras which detect infra-red pulses of
light emitted by the Coda markers and locate the marker positions with very high
resolution and linearity. The cameras are rigidly mounted in the scanner units so that the
system can be precalibrated by Charnwood Dynamics before delivery to the customer.
This relieves the user of the task of calibrating the system before use. The calibrated
system measures the positions of markers within a three dimensional co-ordinate system
which is fixed in relation to the scanner unit. (The nominal origin is usually relocated by
the user and the orientation of the co-ordinate frame can be reset by an alignment
transform in the software.)
Siting the Scanner Units
If you will be using more than one Coda scanner, a number of extra possibilities arise for
which the siting and alignment issues are considerably more complex. It is advisable to
consult with Charnwood Dynamics before making any structural decisions for the
laboratory.
Each scanner unit should be placed on a solid table or bench, mounted on a suitable
tripod, or attached to a solid wall or ceiling. It is important that the scanner unit(s) should
be solidly fixed with reference to the space which constitutes the field of view. Any small
translational movements will register as unwanted variations of similar magnitude in the
co-ordinate values measured by Coda, and if a scanner unit moves in a rotational sense
about any axis then the resulting variations in co-ordinate values can become quite large
as they are magnified with distance. For example, if a Coda unit tilts by 1mm, the
measured co-ordinate of a marker at 3m distance will change by 30mm. Rotational
stability is especially important when more than one scanner unit is used.
The scanner units do not need to be mounted parallel to the room co-ordinate frame (i.e.
the floor), as a co-ordinate alignment transform can be performed in the software. The
mounting angle of each scanner unit should be chosen to centralize the field-of-view.
If the Coda unit is fixed to a tripod, or to a wall or ceiling fixing, it is also important that no
bending or twisting stress is applied, as this might change the relative alignment of the
cameras and distort the co-ordinate frame.
Interconnections
A single Coda interface cable is supplied with each Coda scanner unit. The cable
provides both the 12V DC power and high speed serial communications link via:
i) A mini hub unit which in turn is connected to the host computer using a serial
cable.
ii) An active hub unit consisting of a Charnwood Dynamics Quad UART board and a
Single Board Computer (SBC) connected through a compact PCI (cPCI)
backplane.
The Coda interface cable is fitted with a 26-way high density D plug (male) at each end.