Apparatus for monitored control of the processing process of systems processing the surface of a workpiece, in particular wide belt sanders, taking into account safety-relevant long-term aspects, comprising: a first transverse rail for bridging over a product, wherein the surface of the product is moved past during a processing process underneath the first transverse rail and wherein an illumination carriage having an illumination device and a controller for the illumination device is provided on the first transverse rail for illuminating the product by means of a beam path running obliquely to the first transverse rail in a measurement region extending linearly transversely to the processing direction, a height adjustment device of the illumination device for adapting the measurement region to the thickness of the object, the beam path and the illuminating surface of the product, and an apparatus for evaluating the shadows caused by the illumination device on the surface of the product and for generating a surface analysis signal, characterized by a further, second transverse rail, which extends in the direction of the movement of the product parallel to the first transverse rail and bridges over the product, wherein the second transverse rail carries a camera carriage and a replacement camera carriage with in each case a camera controller, each having a plurality of cameras (3, 16) for optically recording the measurement region, and a control apparatus for controlling the processing process on the basis of the surface analysis signal, and wherein the apparatus is furthermore configured to use, after the processing process has finished, corresponding operating data for fundamentally improving the processing process and the processing system. a first transverse rail for bridging over a product, wherein the surface of the product is moved past during a processing process underneath the first transverse rail and wherein an illumination carriage having an illumination device and a controller for the illumination device is provided on the first transverse rail for illuminating the product by means of a beam path running obliquely to the first transverse rail in a measurement region extending linearly transversely to the processing direction, a height adjustment device of the illumination device for adapting the measurement region to the thickness of the object, the beam path and the illuminating surface of the product, and an apparatus for evaluating the shadows caused by the illumination device on the surface of the product and for generating a surface analysis signal, characterized by a further, second transverse rail, which extends in the direction of the movement of the product parallel to the first transverse rail and bridges over the product, wherein the second transverse rail carries a camera carriage and a replacement camera carriage with in each case a camera controller, each having a plurality of cameras (3, 16) for optically recording the measurement region, and a control apparatus for controlling the processing process on the basis of the surface analysis signal, and wherein the apparatus is furthermore configured to use, after the processing process has finished, corresponding operating data for fundamentally improving the processing process and the processing system.