Apparatus and method for measuring properties of cylindrical objects

Abstract

A system for rapidly measuring, during production, various properties of cylindrical products, such as aluminum cans, uses both optical and non-contact air gauge measurements. The system is configured with three dimensional control to receive cans for optical and air gauge analysis on a movable platform having spaced apart receiving positions. A video camera inspects and identifies cans in one position, using X, Y and Z axis control. Wall thickness is measured using a reference mandrel and a movable air gauge having an end nozzle directed toward a linear reference surface on the mandrel. The air gauge uses hydrodynamic balance to maintain a specified gap relative to the opposing surface, with a high degree of accuracy. Before a measurement is taken, the air nozzle is traversed along the length of the mandrel, and its position sensed and converted to digital form, with the recorded points being entered into storage. A can inserted on the mandrel is drawn tightly against the mandrel by vacuum pressure, and the air nozzle is run along the length of the can, with readings being taken at high speed but relatively small increments. These readings are then stored and utilized, in relation to the prior reference readings, to provide accurate mapping of all thicknesses to less than 1 micron. When one scan is completed, the can is released, rotated and again drawn onto to the reference mandrel for another in a series of readings providing rapid mapping of the entire surface.