Scanning of workpieces such as lumber cants

Abstract

An array camera used to scan elongated workpieces moving through a measuring zone transversely to their lengths has its photoresponsive detector elements aligned lengthwise of the workpieces, with optical axes of the elements lying in a common plane intersecting the measuring zone. Each element 'sees' only a small (e.g., 8.times.8 mm) pixel. Radiation sources are located at opposite sides of said plane and emit radiation towards the measuring zone to be reflected to the elements from workpieces. During each of a succession of short measuring cycles (e.g., 4 millisecond duration) each element is exposed successively to radiation originating from each radiation source to the exclusion of the other, to thus produce an A output and a B output during each cycle, and is also exposed to substantially low level radiation to produce an R output. For each cycle, the R output of at least certain elements is subtracted from the A and the B outputs of the same elements for the same cycle, to produce .DELTA.A and .DELTA.B difference signals. Timing is such that .DELTA.A and .DELTA.B signals for the same element and cycle originate from one and the same small surface area on the workpiece, and therefore inclination of that surface area is ascertainable as a function of the .DELTA.A and .DELTA.B values. During a fourth interval in each cycle, certain elements detect radiation from a laser that has its beam in said plane and oblique to the workpiece surface, and such elements then produce an L output. From the particular elements that produce L outputs, local thickness of the workpiece is ascertainable.