Procedure and device to control the position of books provided with a marking

摘要

The method controls the position of transported books (1) having reinforcing strips (3) on their spines. The strips (3) have a marking (4) essentially perpendicular to the transport direction. An analogue voltage signal is generated by each of a first and a second photocell (7,8) arranged one after another in the transport direction. When a book (1) moves along to a photocell (7) the voltage signal is dependent on light reflected by the strip (3) or the marking (4). The book (1) enters the scanning region of the second cell (8) before the marking (4) leaves the scanning region of the first cell (7). The analogue signals are converted into digital signals which have only one of two possible values. A first difference signal is obtained by subtracting the digital signal of the first photocell (7) from the signal of the second cell (8). A second difference signal is obtained by subtracting the digital signal of the second photocell (8) from the signal of the first cell (7). The time of the difference signals together have two sections with the higher digital value caused by the edge region of the book (1). Between these sections are further sections with the higher digital value caused by the marking (4). The position of the marking (4) on the reinforcing strip (3) is determined using the difference signal pattern.