This invention relates to workpiece handling apparatus, and more particularly to apparatus for centering and aligning a workpiece having at least one planar surface.
Workpieces such as printed circuit boards ("PCBs") or ceramic substrates for integrated circuits ("ICs") must be precisely centered and aligned in the apparatus which carries out the various steps involved in fabricating the PCB or IC (e.g., printing the required circuitry on a PCB). Among the known techniques for locating and aligning such workpieces are holding two perpendicular reference edges of the workpiece against registration stops in the fabrication apparatus ("edge alignment"), or providing registration holes in the workpiece and placing the workpiece on the fabrication apparatus so that the holes fit over registration pins in that apparatus ("pin alignment").
The known centering and aligning techniques have various shortcomings. The accuracy of edge alignment decreases with the distance from the reference edges. If the workpiece is subject to distortion due to thermal expansion or the like, edge alignment may not be satisfactory for the portions of the workpiece remote from the reference edges. Pin alignment allows the alignment points to be located within the boundaries of the workpiece, thereby affording the possibility of reducing the maximum distance from the alignment points to any working portion of the workpiece. However, locating a workpiece on alignment pins is more difficult and time-consuming than edge alignment, and the difficulty increases if the workpiece is even moderately distorted.
It is therefore an object of this invention to improve workpiece centering and aligning apparatus.
It is another object of this invention to provide workpiece centering and aligning apparatus which combines the ease of use of edge alignment with the increased accuracy of pin alignment.