Clarke, Tim
6. 6DOF ESTIMATION
The assembly operation that this project is investigating involves the computation of the six parameters describing the
position and orientation of the rib and spar. The general arrangement is illustrated in figure 4.
Component No 2
Figure 4. Assembly configuration
The process can be split into two steps: Step 1. Determine object to camera transformation relationship To using a target
datum interface (TDI) on spar as illustrated in figure 5 and Step 2. Determine rib movement parameters in the robot co-
ordinate system as illustrated in figure 6.
oc desired
CAD data TDI. CAD data
: Tote Photogrammetric
Photogrammetric D measurement
T T cum
measurement
(a) (b)
Figure 5. Co-ordinate transformation relationships
7. TOOL CENTRE POINT ESTIMATION
The previous step allowed the relative orientation of the rib and spar to be estimated with respect to the desired assembly
position. The next step is to determine how the command the robot move in it's co-ordinate systems. A procedure of
moving the robot end-effector into a number of positions while measuring a number of stationary points has been devised to
enable the TCP of the robot to be estimated (figure 6).
Robot movements
Photogrammetric
measurement
Figure 6. Estimation of the relationship between camera system and robot tool centre point
Stationary points
ctr
The accuracy of this process may be a critical error source but a feedback loop should be used to avoid this problem.
8. PRACTICAL REALISATION
Two versions of the system will have been developed by the end of the project. In the first system the functionality was
demonstrated using a KUKA robot at Sowerby Research Centre (figure 7). In the second system, which is currently under
development, a Staubli Puma robot will be used to assess the capability.
140 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B5. Amsterdam 2000.
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