Patent GB-792047-A (GB)
Title: Improvements in or relating to traffic control systems and apparatus
IPC: G08G1/082
Filed: 1954-12-03
Abstract: 792,047. Road signals for controlling traffic. EASTERN INDUSTRIES, Inc. Dec. 3, 1954 [Dec. 4, 1953], No. 35126/54. Class 118 (2). Traffic signal control apparatus comprises a master controller providing two variable frequency power sources, local traffic signal controllers for operating right-of-way signal circuits for each of a plurality of interfering traffic lanes and selectively driven from the said variable frequency power sources whereby the speed of operation of the local traffic signal controllers is varied by varying the frequency of the power sources during the respective green signal periods, the local controller being driven from one of the said variable frequency sources during one green signal period, and from the other variable frequency source during the other green signal period, thereby permitting the split of the cycle time between the respective green periods to be determined by remote control from the master controller. The A.C. motor-driven rotary dial assembly operating the signals at a local controller may thus be set, for example, to a basic 50-50 per cent split which may be varied at any time by the master controller without regard to the particular signal display in operation at the time and this avoids the need for complex auxiliary apparatus at each local controller normally provided to assure that there will be no sudden reversal or other unexpected change in signal display in systems where the split is varied by switching to a different dial assembly. A fixed frequency power supply is provided for use in the yellow clearance periods so that these do not vary with change in the split proportions. The fixed frequency power supply is indicated in the Figures by the plus and minus signs in circles. The master controller (Fig. 2) comprises two variable frequency generators GN1 and GN2 driven by motors MM1 and MM2 whose speeds are independently adjustable by rheostats PR1 and PR2 respectively. The variable frequency supplies are fed by lines VFL1, VFL2 and common return VFC to the master control unit MCU and to local control units (such as the one shown in Fig. 3). The master control unit MCU has an amplifier MA feeding a motor MSM which drives a synchronizing cam MCR and also cams MC1, MC2 which switch the supply to the motor MSM between the two variable frequencies and the fixed frequency at various parts of the cycle such that the total cycle time is of the same order as that at a local control unit. Cams MC1 and MC2 overlap twice per cycle-once (as shown) where both associated contacts MS1 and MS2 are open, and once half a cycle later where both contacts are closed. When relays R1 and R2 are thus both released or both operated their contacts supply the motor MSM from the fixed frequency source; this corresponds to the yellow clearance periods. When one relay is operated and the other released one or other, respectively, of the two variable frequencies is connected to the motor, and these two periods correspond to the green " go " periods in the two traffic lanes at local units. The synchronizing signal comprises a break of a few seconds once per cycle in the fixed frequency supply to line RSL, due to the cam MCR and associated contacts MSR. The function of this and selection of return synchronization line RSR or RSR<SP>1</SP> by switch SW is described below. The green, yellow and red signals of lanes A and B are operated by cams CAG, CAY, CAR and CBG, CBY, CBR in the local control unit (Fig. 3). These cams are moved by ratchet-drive wheel DRW which is stepped by contacts LDS1 closed by pins DP on a rotary dial LD1 driven by a synchronous motor LM. This is fed from the amplifier LA which is supplied from the variable frequency lines VFL1 or VFL2 or the fixed frequency respectively by cams CG1, CG2 and CY, also driven by the ratchet wheel DRW. These cams close their associated contacts respectively during the green period for lane A, the green period for lane B, and the two yellow clearance periods. The pins DP may be. set to a basic 50-50 per cent split between the two lanes A and B for steady speed of motor LM, and the split could then be made, for example, 60- 40 per cent or 40-60 per cent by increasing the variable frequency on line VFL1 and decreasing the frequency on line VFL2, or vice versa. The total cycle time can also be controlled without variation in split by increasing or decreasng both frequencies equally. The motor LM is stopped once per cycle by operation of the relay LRS when pin RP on dial LD2 closes its associated contacts, if the switch SW in the master control unit is in the position shown in Fig. 2. If switch SW is in the alternative position, line RSRI is normally energized and the relay LRS is operated by pin RP<SP>1</SP> on dial LD3. In either case the motor LM cannot start again until the cam MCR in the master controller (Fig. 2) opens contact MSR to release relay LRS (Fig. 3). To ensure that the local unit cycle is effectively synchronized in this manner by the master controller the motor MSM is arranged to give a slightly longer cycle time than that of the slowest local controller. This may be obtained for example by a slightly greater reduction ratio in the gear train between motor MSM and its camshaft than between motor LM and rotary dials LD. Phasing of the signal cycle of a local control unit is determined by the offset or relative position of synchronizing pin RP with respect to signal-operating pins DP. The arrangement shown with two pins RP and RP<SP>1</SP> provides remote selection (by switch SW in the master control unit) of two offsets for use where a system is to be phased on a simultaneous basis at one time and on a progressive basis at another time, the respective local control units having their pins RP, for example, set at similar offsets and pins RP<SP>1</SP> set at predetermined different offsets. Overlap of green and yellow periods is treated as part of the clearance period and green on its own is considered as the true "go" period for application of the variable frequency supplies. The switching of the amplifiers in either master or local control units may be performed directly from cams (as exemplified in Fig. 3) or by means of intermediate relays (as in Fig. 2). Specifications 674,590 and 791,832 are referred to.