|
For a multi-sensor machine vision system, relating each sensor's measurement to a master gage coordinate system has been a difficult task. This is especially true for sheet metal gaging in the automotive industry where sensors may be separated by four or five meters. The current approach used to establish this master coordinate system, which is difficult at best, has been the following. First, the part is placed in the gage. The exact location, that is being measured by each sensor, is marked on the part. Then the marked part is transported to a coordinate measuring machine (CMM), where the location of each of the marked points is measured. These CMM measurements establish a master coordinate system. The procedure just described has major drawbacks including: the accuracy of marking the exact location being measured; the sensors orientation must be known with respect to the master coordinate system; and deformation of the sheet metal part when it is transported to the CMM. The mastering process can be significantly improved by optical coupling a theodolite pair with each machine vision sensor. This optical coupling is established by locating a target in a position that can be accurately measured by both a sensor and the theodolite system. First, the theodolite system is calibrated in gage coordinates by sighting on reference points placed on the machine vision gage. Then, for each sensor, the target location is measured by both the sensor and theodolite pair at three or more positions (or alternately one target may have three or more points that can be measured). From this data, the transforms from sensor coordinates to gage coordinates can be calculated. This report will present the configuration and calculations for coordinate mastering using optical coupling.
|
