Patent GB-916773-A (GB)
IPC: G08G1/081
Filed: 1959-02-04
Abstract: 916,773. Road signals for controlling traffic. LABORATORY FOR ELECTRONICS Inc. Feb. 4, 1959 [Feb. 12, 1958], No. 3998/59. Class 118. In a traffic control system having more than two mutually interfering traffic lanes of which the signals in at least one lane are not trafficactuated and the signals in at least two lanes are so actuated, the right of way periods in the traffic-actuated lanes are variable between minimum and maximum limits and the maximum limit is remotely controlled (e.g. from a master controller). General.-The invention is described in relation to a control system of the kind disclosed in Specifications 843,916 and 906,716, in which the total length of the signal cycle is controlled by the period between successive coincidences of two sine waves, of slightly different frequencies, derived-from a master controller as applied to an intersection of three roads, A, B and C. The reference frequency FR is generated in the master controller by the three-phase generator FRG (Fig. 2) and the control frequency FC by the differential generator DG, being transmitted to the local controllers (Fig. 3) over lines FR and FC respectively. At each local controller sine wave outputs are taken from the deltaconnected potentiometers PA1 and PA2, respectively and fed to spike pulse forming networks PF2 and PF1. The spike pulses are applied to a coincidence gate CG1 and at coincidence, determined by the setting of the rotor arms RA1 and RA2, they operate a control device which controls the associated signal lights. Offset control.-The offset or time of commencement of a signal cycle is determined at any particular local controller by the setting of a delta-connected potentiometer designated PA1 in Fig. 3 and the length of that cycle by the setting of a similar potentiometer PA2. In the preferred embodiment (Figs. 4a-4e) the particular offset desired for preponderance of incoming traffic, preponderance of outgoing traffic, average conditions or simultaneous operation at each intersection, is selected by closing switches SW1, SW2 or SW3 (Fig. 2) at the master controller either manually or as the result of traffic or time control. The particular switch closed operates a corresponding relay OT, IN, or SIM (Fig. 4b), and if both switches SW1 and SW2 are closed relays OT and IN together, to connect spike pulses derived from respective potentiometers PO2, PO1, PO4 or PO3 (each equivalent to PA1 in Fig. 3) to coincidence gate CG2 and square pulses derived from the same potentiometer to coincidence gate CG3. Each pulse is compared with a reference spike pulse derived via potentiometer PO5, from the reference frequency but offset as determined by the last setting of the switches SW1-SW3, and non-coincidence in coincidence gate CG2 alone releases a relay OS and energizes a relay OD to drive the motor RDM and potentiometer PO5 counter-clockwise until coincidence is again achieved, when both relays OS and OD operate and the drive is removed from the motor RDM. Non-coincidence in both of the gates CG2 and CG3 releases both of the relays OS and OD and drives the motor RDM and its associated potentiometer PO5 clockwise until coincidence is again achieved. With a switch SS2 in position 1 and none of the relays IN, OT or SIM operated, a relay FRR operates to provide free offset operation of the local controller. With switch SS2 in any other position, when free operation is called for by the master controller average offset operation is provided. During free offset operation the input to pulse former PF1 is shorted out by contact 681 of relay FRR operated and the start of the selector switch cycle is initiated by local vehicle or pedestrian demand. Changes in the vehicle phase B minimum interval and the vehicle phase C maximum interval are also made. Change of split.-The percentage of each time cycle occupied by each of the traffic phases A, B or C is determined by jumpering leads FREESIM<SP>1</SP> (Fig. 4b) to terminals SPLIT 1, 2 and 3, as desired. No connection at all is equivalent to a connection to the unconnected terminals labelled SPLIT 1. When a particular offset condition, e.g. SIM or simultaneous operation is selected by the master controller switches SW1-SW3, the corresponding lead, e.g. SIM<SP>1</SP>, is earthed. A change of split can take place only in the rest position 1 of a rotary selector switch A-F (Figs. 4a and 4c) when a corresponding combination of relays SB2, SB3, SC2, SC3 is operated over contacts of a relay LO operated, to select potentiometers PB1, PC1 or PB2, PC2 or PB3, PC3 according to the split selected. The outputs of the selected potentiometers are applied in positions, Figs. 7 and 11, of the selector switch to the pulse former PF1 and the resulting spike pulse applied to coincidence gate CG1 and compared with the spike pulse derived from the reference frequency. At coincidence valve 205 passes anode current and operates its anode relay MAX which on release steps the selector switch to its next position. The termination of the phase B and phase C vehicle green interval is thus decided by the setting of the potentiometers PB1-PB3 and PC1-PC3 respectively, the desired pair being selected by the jumpering of the leads FREESIM<SP>1</SP> and their selected earthing by switches SW1-SW3 chosen at the master controller. Signal cycle.-The operation of various cycles of signal changes are described. The local controller of Fig. 4 is shown in the rest position with right of way accorded to street A and in simultaneous operation with split 1 in effect. Signal changes are effected by a thirteen position sixbank rotary selector switch A-F which at rest remains in position 1. In this position by means of associated relays AG, AW, AGR, and AGD, street A has green vehicle and pedestrian signals showing and all other signals are at red, except filter (or overlap) signals on roads B and C for non-interfering traffic. This condition is independent of traffic on street A and will continue until traffic or pedestrian actuation in street B or C, or both. Operation of, e.g., the vehicle detector VDB in street B will release the relay BM and at contact 259 complete the cathode circuit of valve 205. This valve has reference pulses and control pulses applied to its respective control-grids and at the next coincidence the valve fires, operating its anode relay MAX which in turn energizes the selector drive magnet MM. Contact 118 of the drive magnet MM discharges capacitor 120 which blocks the valve 165, thus stopping the anode current of valve 205 and releasing the anode relay MAX. The drive magnet MM thus releases and steps the selector switch to its next position. The selector switch is driven step-by-step through the complete signal cycle under control of a timing condenser TC which, when sufficiently charged, discharges through a gas discharge tube FA to operate a relay INT and hence the drive magnet MM. The timing condenser is charged through various pre-set timing potentiometers such as TP1 according to the time interval for which each different display of the signal lights is required to last. When there is no call for a particular display, then the corresponding selector position is skipped, the timing capacitor TC charging rapidly. Actuation of a pedestrian push-button alone causes the same operation as if the corresponding vehicle detector had also been operated. In positions 7 and 11 the phase B and C vehicle intervals are timed. These intervals are extendible by vehicle actuation subject to an over-riding maximum control. The phase B extendible vehicle interval in position 7, for example, is timed by charging the timing condenser TC through a pre-set potentiometer TP2 and the wiper C1 of the selector. Passage of a vehicle during this charging interval actuates detector VDB and thus operates relay BD which over contact 463 discharges the timing capacitor TC, and hence, so long as vehicles operate the detector VDB at sufficiently short intervals, capacitor TC will not charge sufficiently to operate the gas discharge tube FA to step the selector on. The control of the maximum interval time is exercised by the particular split potentiometer in use, here assumed to be PB1 since split 1 is in effect on phase B. As stated above, the choice of pre-set potentiometer PB1, PB2, or PB3 is made from the master controller switches SW1-SW3 over lines OC1, OC2, SM1 and jumper wires FREESIM<SP>1</SP>. The locally phase-adjusted sine wave output of potentiometer PB1, derived from the control frequency over lines FC, is applied to pulse former PF1. The spike pulse output from pulse former PF1 is compared in the coincidence gate CG1 with a similar reference pulse derived from potentiometer PO5 (and hence from the reference frequency over lines FR). At the predetermined point in the signal cycle, coincidence of the two pulses causes valve 165 to pass current and hence causes valve 205 to operate its anode relay MAX and to step on the selector. Thus the maximum phase B (or C) green interval is determined by the particular split potentiometer selected by the master controller. Position 13 is either a skip position, or if switch SS8 is opened, provides an all-red period. Timing of this position is over potentiometer TP5 which is suitably adjusted according to whether an all-red period is desired or not. Upon termination of the interval the selector steps to position 1 and awaits further calls. Isolated operation.-When the ganged switches SS3-SS4 are in the central position, simultaneous offset is eliminated, and when they are in the lower position the local controller assumes isolated operation without any control from the master controller. Relay PR operates, shorting out transformer T3 and applying 60-cycle mains voltage to the transformer T2. This latter prevents coincidence in the coincidence gate CG2 and prevents the relay OS operating. The coincidence gate CG3 will similarly n