Patent GB-920881-A (GB)
Title: Improvements in the control of steerable vehicles
IPC: G05D1/02
Filed: 1958-04-22
Abstract: 920,881. Automatic control systems; phase sensitive circuits. HUNTING ENGINEERING Ltd., A. HANN, H. R. LEGGE, and F. A. RICHARDS. April 21, 1959 [April 22, 1958], No. 12786/58. Class 38 (4). [Also in Group XL (c)] A self-propelled vehicle follows a line marked on a surface providing a background having a different reflectivity from that of the line, and comprises a vehicle steering motor M2, a scanning unit SH movable by means M1 across the width of the vehicle and including illuminating means LP1, LP2 affording periodic light outputs having a phase difference and a light - sensitive device PC2, means for analyzing the output of device PC2 to provide an output signal so that the scanning unit is caused to move to a position in which the areas of illumination produced by means LP1, LP2 fall symmetrically on the line, means for producing a first signal indicative of the position of the scanning unit in the width of the vehicle, means for producing a second signal indicative of the direction in which the vehicle is being steered, and means controlled by the first and second signals for actuating steering motor M2 to steer the vehicle so that the scanning unit is moved to a predetermined position in the length of its movement. In the embodiment lamps LP1, LP2 are fed in anti-phase (90 degrees, 270 degrees) from a master oscillator and are arranged to project light patches 1a 1b Fig. 13, on to the ground. A photo-cell PC1 receives light directly from both lamps for automatic stabilization of their light outputs. An A.C. error signal of magnitude dependent on displacement from the guide line, and of phase-dependent on sense of displacement, is fed from photo-cell PC2 to phase-sensitive rectifier PSR1 which affords an output D.C. voltage of amplitude proportional to displacement magnitude, and polarity dependent on sense of displacement. The rectifier is fed with anti-phase reference voltages (0/180 degrees, 180/0 degrees) from the master oscillator via lines X, Y, Fig. 3 (not shown) ; it is stated that the light outputs from the lamps lag their energizing signals by 90 degrees. The rectifier is arranged to be in a detecting condition for brief intervals only on either side of the peak values of the " error " signals. Permanent-magnet motor M1 is energized from the rectifier to return the search head to a symmetrical position above the guide line and motor M2 steers the vehicle to follow the line. To ensure stability of the control system the gain of amplifier A3 is controlled by the voltagedelayed output of a phase-sensitive rectifier PSR2, which is responsive to a signal indicative of the contrast between guide line and background and obtained from two signals the first of which is obtained from the response of photocell PC2 to a 0 degrees phase signal fed to amplifiers A1, A2 and the second of which is obtained from a photo-cell PC3 contained, together with a lamp LP3, in a fixed head on the vehicle. Photocell PC4 provides for constancy of peak light output from lamp LP3. The output of a further phase-sensitive rectifier PSR3 is a D.C. voltage proportional to the peak value of signal varying with changing contrast between the guide line and background ; the D.C. voltage is fed to a polarized relay via a voltage delay VD2 such that when the contrast is below a predetermined value the relay is not operated and the vehicle control system is rendered inoperative, Fig. 2 (not shown) ; the polarity of the contrast signal determines the sense of phase of the inputs to rectifiers PSR1 and PSR2, Figs. 3 and 4 (neither shown). Traverse of scanning head SH is reversed at either end by micro-switches. Transistor circuits are described for the amplifiers shown in Fig. 1, the master oscillator and the regulator for lamps L1, L2, Figs. 6 and 8 . . . 12 (none shown). Phase-sensitive circuits. Fig. 7.-Phase sensitive rectifier PSR1 comprises a transistor T8 to the base of which is fed the output of amplifier A3, Fig. 1, transistors T9, T11 having their collectors fed from the respective outputs of transistors T8, T10 and having their emitters commoned and connected to the base of a transistor T12 from the emitter of which the circuit output is taken. Shaped pulses from the 0 degrees and 180 degrees phase angle outputs of the master oscillator, Fig. 1, are fed to the bases of transistors T9, T11, respectively. Phasesensitive rectifier PSR2 is similar. Route selection. Figs. 1, 13.-If a vehicle is to follow a route other than A a signal is given and fed into the control system through resistor R4, and a relay is energized to move contacts RLF1, RLF2 to their upper positions; the search head is moved until the light patches are displaced to position 2, Fig. 13, for travel along route B &c. Contacts RLF1, RLF2 then revert to their lower positions.