Patent GB-824781-A (GB)
Title: Improvements in or relating to automatic traffic signalling systems
Inventor: SHAND GEORGE
IPC: G08G1/081
Filed: 1956-08-29
Abstract: 824,781. Road-traffic signals. METROPOLITAN-VICKERS ELECTRICAL CO. Ltd. Aug. 29, 1957 [Aug. 29, 1956], No. 26417/56. Classes 40 (1) and 118 (2). An automatic traffic signalling system employs a programme which defines at least the end of each clearance period and each holding period (viz. changes from clearance to hold and vice versa) for a traffic phase at an intersection, which programme is translated into corresponding control signals operating a programme responsing device which governs the traffic lights but allows for an extended main road clearance in the absence of side road traffic. The programme may originate at a distance from the intersection and is transmitted thereto by a pulse sequence, and the invention can be applied to the simultaneous control of a number of intersections. The programme is in binary form on a recording track and alternative programme can be switched in to suit the varying traffic conditions. Preferably the track carries suitably spaced holes through which an electric contact is made and a marking signal is thus originated. However, conductive portions on a tape may be read by contacts or photoelectric reading of a track having opaque and transparent portions can be used. Arrangements are made to allow for manual control, one way working and " filter left. " Basic control circuit (Fig. 3).-A tape reader TR has a finger F which transmits current to a bar E in the presence of a hole in the tape A. The motor TRM is stepped by breaking a switch S1. In the presence of a hole relay RL1 makes contacts 12-14 and RL1-2, in the absence of the hole the relay makes back contact 12-13. 12-14 makes before 12-13 breaks and RL1-2 makes before 12-13 breaks. Switches 81-84 are contacts on a rotary timing disc (Fig. 4, not shown). The signal lights are under control of a 4-way stepping switch LS1-5 stepped by LSM on breaking S4. As shown, main red cross green is displayed and LSM is disconnected when RL2 is energized through RL-1(12-14); two successive S4 pulses cause the lights to step through amber to main green cross red. LSM is now disconnected by LS3 until RL2-1 changes over. This change over normally works to programme through RL1-1 in the presence or absence of a marking signal. Main clearance from side clearance no side traffic waiting.-A marking signal from tape reader energizes RL1 which makes RL1-1 (12-14) to energize RL2 which makes RL2-1 (22-23) allowing LSM to step twice (under control of S4 timer contacts) to main green side red. As there is no side traffic the relays RL5, RL6 (only one shown) are energized by photosensitive device PEC1 and RL6-1, RL5-1 are closed. RL3 is energized whn S3 closes ande holds (RL3-1, 15-17), RL3-2 is thus closed and RL2 is supplied with power so that when RL1 is de-energized (loss of marking signal being side clearance conditions from programme reader) RL2 remains energized and lights remain at main green. Main clearance side traffic waiting.-RL6-1 or RL5-1 or both are broken so that RL3 cannot be energized as described above and RL2 is deenergized by the absence of a marking signal on RL1, thus changing over RL2-1 and stepping LS through amber to main red side green. Side clearance. Traffic cleared.-When S2 makes 5-6 (5 times a minute) RL4 is energized and holds (RL4-2). RL3 is now connected to S2 (7) which will energize RL3 11 seconds later unless relays RL5 or RL6 are opened by a vehicle passing a detector. RL3 is now energized through RL4-1 and thus held (RL3-2) providing an alternative energizing circuit for RL2 other than through RL1-1. This changes over RL2-1 and allows LSM to step twice, giving main green. If a vehicle passes a detector before RL3 is energized, RL4 is deenergized and opens RL4-1, thus isolating RL3 from S2 and the main clearance is postponed for 11 seconds. This continues as long as traffic passes the detectors or until RL1 is energized by the marking signal from the programme reader. Main clearance initiated after truncated side clearance.-RL1 is energized by the programme reader keeping RL2 energized through 12-14 and breaking 12-13. This causes RL3 to become de-energized by opening of RL6-1, RL5-1 or S3. Contact 6 is isolated from the supply by the breaking of RL1-1 (12-13) so that RL3 and RL4 becomes inoperative until the end of the clearance period. End of main clearance, no waiting vehicles.- Contacts RL1-2 being closed RL3 is energized through RL5-1 and RL6-1 and held so by S3 for 1 second. TRM steps to give blank in tape (side clearance), RL1-1 makes 12-13 and thus holds RL3 through 15-17. When S3 breaks RL3 remains energized and holds RL2 through RL3-2. Modifications, Fig. 3B (not shown).-Extra relay to prevent extension of main clearance by " remembering " waiting vehicle in side road. It is possible to remove the reading apparatus to a distance and control the lights by two signals, one to control RL1, the other to control the rotary timer. Fig. 5 (not shown) discloses a circuit for this purpose substantially that of Fig. 3, with a modified timing switch driven by a synchronous motor and having a slip clutch and electromagnetically operated stop means for ensuring synchronization of the timer if it slips out due to a fault &c. An additional relay is provided for releasing the stop means at the correct times. Manual control of the lights is provided by a switch MS. In position 1 the control is from the programme reader, in position 2 main clearance, and in position 3 side clearance, are obtained. The vehicle control means (detectors, relays RL2, RL3, RL5, RL6, S2 and S3 and the extra relay of Fig. 3B (not shown)) may be omitted and RL1 will have a set of change-over contacts substituted for RL2-1. S4 will still control the stepping action of LSM. This is done in Fig. 8A which shows a control circuit allowing individual control of each direction of traffic. Separate light sequence switches SM1, SM2, 8C1, SC2 are provided, each under control of programme responding relays RL11-RL14 each having a change-over switch controlling the LS5 bank of switches (as RL2-1 controls LS in Fig. 3). Each switch is separately controlled by the programme tape and interlock circuits are provided to prevent conflicting signals being given. Bank LS6 lights " cross now " signals C when all red is shown. The amber timing is still effected by S4. To eliminate the necessity for a timer at the intersection, the circuit of Fig. 8B can be used. Here RL15 and RL16 control the main road and RL17 and RL18 control the cross road. The relay contacts are shown de-energized. RL15 is energized for main hold and RL16 is de-energized. RL15-1 is closed to illuminate main red and supplies power to side green if required. RL15-3 is open to prevent main green and RL15-2 breaks main amber. On main clearance RL16 is energized thus displaying main redamber (right-hand contacts RL15-2, RL16-2) and then RL15 de-energizes, breaks RL15-1 and RL15-2 (right hand) and RL15-3 closes. Provided that RL17 is energized and RL18 is not, the main green and side red both light. At the end of main clearance RL16 is deenergized, opens RL16-1 and closes main amber by changing RL16-2 to left hand. RL15 is then energized for main red. RL17 and RL18 similarly control the side lights. " All red " conditions give a circuit through RL15-5, RL17-5, RL16-4 and RL18-4 to illuminate a " cross now " sign. At other times " wait " is illuminated. If RL15 and RL17 are both deenergized (usually a " fault " condition) the amber circuits are completed through RL15-4, RL17-4 and flasher FL. A modified circuit (Fig. 8C, not shown) is given, in which each direction on the main road is separately controlled and " one way street " or " filter left " working is possible. Programme transmission apparatus.-The marking signals from the programme readers, presented simultaneously, are serialised by gating circuits controlling timing pulse circuits, the information comprising a train of clock impulses whose amplitude denotes " mark," " space " or " sync." The receiver extracts the " sync." pulse to control a pulse ring counter triggered by the clock impulses and extracts the space and mark impulses to control the programme responding relay. The rotary timing switch (referred to above, Fig. 5, not shown) is synchronized by one of the counter pulses releasing the stop means. Transmitter.-This comprises a timing waveform generator, two ring counters defining digit slots and a mixing circuit for deriving digit signals and mixing them with timing and synchronizing signals. Timing waveform generator, Fig. 12.-A.C. is squared by TR1, TR2 acting as two state devices and emitter follower TR3 gives the resultant " clock " signal. TR4 produces short duration negative signals (Strobe) determined in length by C2R6. An " AND " gate D4, D5 fed with clock and strobe signals allows TR5 to follow the most negative of these signals to give a delayed clock signal. This is fed to inverter TR6 and emitter follower TR7 to produce an inverse delayed clock signal. The programme cycle is initiated and terminated by a bi-stable flip-flop TR8, TR9. S5 initiates by a signal on TR8 base rendering TR8 conducting. The output from TR9 is applied together with the strobe signal to an " AND " gate D14, D15 which passes the strobe when TR8 is conducting (TR9 cut off). TR10 supplies the ring counters (two banks each four signals P1-P4 and B1- B4, the latter being the " tens "). The transmission cycle terminates when P4, B4 and clock all go negative on an " AND " gate D11- D13 thus passing a negative signal to C4 and triggering the flip-flop. The ring counter is that disclosed in Specification 823,226, [Group XXVI], and has 4 X 4 stages. Digit deriving and mixing circuit, Fig. 16.- Each programme reader marking signal is supplied to a gate, only those for programmes 2-4 being shown. With no signal on OD3 the current flow OR3, OD3, OR4 is arranged to give a potential to cut-off OD4 and thus P2 (P and