Apparatus and method for automatic monitoring of lids of beverage and food cans

A device for the automated optical inspection of a plurality of three-dimensional inspection objects, in particular metallic lids and containers of beverage and food cans, in the ongoing production process, which objects can be moved via a conveyor device, the device comprising:

• a camera which captures digital images of the moving test objects,
• lighting units,
• and a controller for controlling the camera and the lighting units,
• characterized in that
• the camera captures at least two digital image recordings of the moving test objects in series during transportation on the conveyor device, so that a first digital image recording of the test object in a first position and a second digital image recording of the test object in a second position are obtained, the first and second positions of the test object differing as a result of the movement of the conveyor device by a corresponding offset,
• and in that the plurality of illumination units are composed of at least one or more dark-field illumination units and one or more bright-field illumination units, which are each controlled synchronously with the camera by the controller in such a way that the first image recording generates a first contrast by a first specific activation of the dark-field illumination units and bright-field illumination units, and in that the second image recording generates a second contrast by a second specific actuation of the dark-field illumination units and bright-field illumination units, the first and second specific actuation of the dark-field illumination units and bright-field illumination units differing from one another to form the first and second contrast,
• characterized in that the illumination units comprise, in addition to the dark-field illumination units and the bright-field illumination units, a reflected coaxial illumination by a half-mirror, which can be variably controlled by the controller for individual image exposures, so that the contrast of the image exposures can be varied.