Patent GB-1483399-A (GB)
Title: Curve follower
IPC: B23Q35/128
Filed: 1975-04-01
Abstract: 1483399 Line followers ERWIN SICK GmbH OPTIK-ELEKTRONIK 1 April 1975 [9 April 1974] 13220/75 Heading G1A [Also in Division G3]  In a curve following system in which a photoelectric head may be required to follow one or other of two paths at a junction, information about the desired course is coded on to the path a given distance upstream of the junction; when the head reaches the coded section it is instructed which way it must subsequently turn, and also an integrator commences accumulating a voltage representing head displacement so that the head circuitry can determine where the turn will have to be made. In Fig. 1 the head 11 is to initially follow a curve leading to junction 20. It traverses section 19 and the closed loop 13 back to junction 20; then it is required to traverse section 19 again and branch off to the right at junction 21. An instruction to prepare to turn right is coded on to the path in the form of narrow sections 12a, 12b. The integrator starts integrating at 12a and gives a first signal after the head has covered distance S1; after this signal the head will follow any branch to the right, i.e. the one at junction 21. A second signal from the integrator, after S2 has been covered, resets the system so as to prevent subsequent right turns. Head and circuitry: the head scans across the path in a circular manner, as seen in Fig. 2, though a linear transverse scan could be used. Its field of view is normally limited optically or electrically to the width of the wider section of the path, and when it is so limited the head will not branch off the path. When the turn right signal is received, the field of view is enlarged at the right, so that the head branches off to the right at the next right hand junction; similarly, for a turn left signal the'field is enlarged at the left. When the head crosses a narrow portion of the path such as 12, the interval between the pulses it produces becomes shorter. These pulses Ul are inverted at (17), Fig. 4 (not shown), filtered at 18a, 18b and thresholded at K4 to produce a squarewave which exists as long as the head takes to traverse the narrow section. When the squarewave U5 starts an integrator 12 begins integrating a voltage UV which represents head displacement; the integrator output is thresholded at K3 to give a pulse U7 towards the end of the squarewave. The number of pulses U7 corresponds to the number of narrow sections crossed, and is counted at 15; the number of sections is chosen to signify either turn left, turn right, no turn, or brake; the counter output is later decoded at 14 to give a signal on one of four lines corresponding to these four codings.  As soon as the counter signal is received at 14, an integrator 11 also starts to integrate the head displacement signal UV, and two comparators K1, K2 give signals when the distances S1, S2 have been covered. When S1 has been covered, the unit 14 is enabled and the signal appears on one of its four outputs to prepare the head to turn, carry on or brake; when S2 is reached a signal to input 16 resets the counter, cancelling the unit 14. To maintain maximum curve following ability, the field of view may normally be wider than the path, and would then be narrowed appropriately between the times when a coded section of the path is encountered and when S2 has been reached.