US3271734A - Traffic signal controller - Google Patents

Description

Sept. 6, w CABE ETAL TRAFFIC SIGNAL CONTROLLER 3 Sheets-Sheet 1 Filed March 16, 1964 INVENTORS RAY W CABE MgjfLIAM C. SONDERGARD AT'TOR N EY Sept. 6, 1966 CABE ETAL 3,271,734

TRAFFIC SIGNAL CONTROLLER 3 Sheets-Sheet 2 Filed March 16, 1964 RAY W. CABE WILLIAM C. SONDERGARD AT ,TORNEY R. w. CABE ETAL 3,271,734

TRAFFIC SIGNAL CONTROLLER Sept. 6, 1966 I5 Sheets-Sheet 5 Filed March 16, 1964 18 SOLENOID &

ASSEMBLY -15 AC. POWER SOU RCE INVENTORS RAT CH ET RAY W. CABE WILLIAM C. SONDERGARD ATTORNEY United States Patent 3,271,734 TRAFFIC SIGNAL CONTROLLER Ray W. Cabe, Manhattan Beach, and William C. Sundergard, Torrance, Califl, assignors to Tamar Electronics Industries, Inc., Anaheim, Calif., a corporation of Delaware Filed Mar. 16, 1964, Ser. No. 352,025 7 Claims. (Cl. 340-37) This invention relates to a traffic signal controller and more particularly to such a device capable of alternative operation either in a pre-timed mode or a semi-actuated mode.

Control systems for trafiic lights generally operate either in a pre-timed cyclical manner in response to a program or in response to traffic conditions as appropriately sensed by road switches or the like in what is generally termed a semi-actuated type of operation. A pretimed controller operating in response to a program is described in Patent #2,745,086, entitled Trafiic Signal Controller, issued May 8, 1956, ltO R. A. Reid et al. In this controller, the signal lights are operated cyclically in accordance with a pre-set program. The lights are thus periodically turned on and off in accordance with the program regardless of trafiic conditions. This type of operation is generally suitable where the intersecting streets being controlled both have a relatively regular flow of traflic.

In a situation, however, where the controlled intersection in question is between a main artery and a side street having a very small amount of intermittent trafiic, such regular pre-timed cycling of the lights unnecessarily holds up traflic on the main artery in view of the small and intermittentrequirement for allowing traflic to pass on the cross street. This type of situation is best handled by semi-actuated type operation in which the signal facing the main artery is constantly maintained green except when the presence of a vehicle is detected at the cross street, at which time the signal on the main artery is switched to red to allow such vehicle to pass.

Devices of the prior art are generally either adapted to operate in a pre-timed fashion or a semi-actuated fashion, and a separate system for accomplishing one or the other types of operation must be installed as the situation may demand. Often, however, the requirements at any particular intersection may change at different times of the day or week making the choice of one system or the other a compromise. Then too, what may be an intersection requiring a particular type of controller at the time of installation may completely change in its traflic conditions, especially in rapidly growing areas.

With the traffic control systems of the prior art, it has generally been necessary to install a completely new unit in changing over from pre-tirned to semi-actuated type of operation or vice versa. This not only presents additional expense but ties up the traflic signal while the changeover is being made. Often too, when making an initial traflic light installation, it is difficult to accurately determine what type of operation is 'best suited to the situation. Thus, a semi-actuated type controller might be installed and a short time thereafter it may be discovered that a pre-timed system is more suitable for the particular situation involved. This often leaves an intersection which should have a pre-timed controller or vice versa with improper traflic control. This can only be remedied with prior art devices by installing a new system.

The device of this invention overcomes the shortcomings of prior art traffic signal controllers in providing a system that can be alternatively operated either in a pretimed or a semi-actuated mode of operation. Operation can be changed from one type to the other by simply throwing a switch without the necessity for disabling the trafiic lights or undertaking an expensive installation. In the device of the invention, utilization is made of substantially all of the equipment needed for pre-timed operation when operating in the semi-actuated mode. The equipment of the pre-timed controller is utilized in semiactuated operation with a semi-actuator unit being added and connected into the existing pre-timed controller. This enables the ready conevrsion of existing pre-timed units to dual operation in either mode.

Such alternative operation is achieved in the device of the invention by providing switch means for alternatively connecting the power source of the system either directly to the pre-timed controller unit to operate in the pretirned mode or connecting the power through timer means so that the pre-timed operation is disabled, with the green light being held on the main street. The timing operation under these conditions is taken over by a timer device which operates in response to a road switching device located in the cross street, thus providing semi-actuated operation. The timer means includes a unique type of timer unit which provides two distinct delay periods in controlling switchover of the lights on the cross street from red to yellow, and from yellow to green.

It is therefore an object of this invention to provide an improved traflic signal controller.

It is another object of this invention for providing a trafiic signal controller which can be alternatively operated in either a pre-timed or semi-actuated mode.

Is is still another object of this invention to provide a semi-actuated trafiic controller which utilizes the circuitry and equipment of a pre -timed controller and has the advantages of the features thereof.

It is still another object of this invention to enable the conversion of existing pre-timed trafiic controllers to alternative operation in either a semi-actuated mode or a pre-timed mode.

It is still another object of this invention to increase the versatility of operation of traffic signal controllers.

Other objects of this invention will become apparent from the following description taken in connection with the accompanying drawings of which FIG. 1 is a block diagram illustrating the basic operation of the device of the invention,

FIG. 2 is a schematic drawing illustrating a preferred embodiment of the device of the invention, and

FIG. 3 is a schematic drawing showing the timer unit utilized in the preferred embodiment of the device of the invention.

Referring now to FIG. 1, the basic operation of the device of the invention is illustrated. For pre-timed operation, switch 27 is thrown over to the position indicated by the dotted line. This continually supplies power to pre-timed control means 8. Pre-tirned control means 8 may include a program timer drum as shown in the aforementioned Patent #2,745,086 which rotates continually and cyclically causes power to be applied to actuator means 18. Actuator means 18 operates in response to the output of pre-timed control means 8, and advances sequencing switching means 9 to actuate signal lights 21 in a predetermined sequence and for predetermined time intervals.

If operation is desired in the semi-actuated mode, switch 27 is thrown to the position indicated by the solid line, thereby removing the power connection from power source 15 through switch 27 to pre-timed control means 8 and connecting pre-timed control means 8 to timer switching means 7. With switch 27 in the position indicated by the solid line, as to be explained in detail in connection with FIG. 2, pre-t-imed control means 8, is incapable of driving actuator means 18 further once se- 3 quencing and switching means 9 has advanced to the point where signal lights 21 present a green signal on the main artery.

This static condition of the signal lights is maintained continually in the absence of any actuation of timer switching means 7 by road switch 49. When, however, road switch 49 is actuated by a vehicle approaching the intersection on the cross street, timer switching means 7 generates an output signal to actuator means 18 so as to actuate sequencing and switching means 9, thus changing the signal light on the main street from green to yellow. Once so started, sequencing and switching means 9 continues to be driven through a predetermined cycle and next switches on the red signal on the main street and the green signal on the cross street. At this time, a signal from timer switching means 7 is sent to timer unit 40. Timer unit 40 effectively provides a delay in this signal and after a first predetermined time interval sends a control signal back to timer switching means 7. This delayed control signal causes timer switching means 7 to actuate actuator means 18 so as to again advance the signal light, now causing the light on the cross street to go from green to yellow. It is to be noted that such operation is controlled by timer unit 40 and is independent of the timing action of pre-timed control means 8 which nevertheless continues in its predetermined cyclical operation. It is to be further noted that the timing action of timer unit 40 occurs in a substantially shorter time than the timing cycle of pre-timed control means 8. An additional delay signal is similarly provided by timer unit 40 to set the time interval that the yellow signal on the cross street remains on. As to be explained in connection with FIG. 2, the pre-timed control means 8 finally reaches the end of its cycle, at which time, operation is restored to a continual green condition on the main artery. Thus in going from pre-timed to semi-actuated operation, timer unit 40, timer switching means 7, and road switch 49 take control from pro-timed control means 8.

Referring now to FIG. 2, the schematic drawing of a preferred embodiment of the device of the invention is shown. Program timer means 11 comprises a continuously rotating motor driven drum assembly having cam means thereon. With rotation of the drum of program timer means 11, switch 12 is momentarily closed at predetermined time intervals. Assuming that contact a of switch 16 is closed, which is the case at all times except at the end of the timing cycle, power is fed from power source 15 through switch contacts 16a and switch 12 to solenoid and ratchet assembly 18. Solenoid and ratchet assembly 18, as fully explained in the aforementioned Patent #2,745,086 provides a predetermined rotation of sequence controller means 19, each time switch 12 is closed. Sequence controller means 19 may comprise a drum assembly having a plurality of prepositioned cams thereon so that switch contacts 16a-16g are successively closed in a predetermined sequence as the drum of the sequence controller means 19 rotates. Switch contacts Me, i and g connect power from power source 15 to the green, yellow and red lights at signal light 21. Thus, these lights are successively actuated and maintained on for time periods determined by the program set up in program timer means 11. At the end of each timing cycle which coincides with a green light actuated in the signal light, contact 16a which is normally closed is opened by its associated cam. This cuts ofi further power to the drum advance contact 12 and thus prevents further actuation of sequence controller means 19 by the ratchet assembly 18.. However, further rotation of program timer means 11 causes an appropriate cam thereon to close drum release contact 30. In pre-tirned operation, switch contact is connected by means of switch 27 to power source 15 as indicated by the dotted line and thus provides power to solenoid and ratchet assembly 18 to commence a new operating cycle. In such pre-timed operation, drum release contact is utilized to synchronize the operation of program timer means 11 with that of sequence control means 19 to assure that their cycles start at the same time.

In changing over operation from pre-timed to semiautomatic operation, switches 27 and 28 are thrown to the positions indicated in FIG. 2. In semi-actuated operation, it is desired that the system be controlled in response to existing traffic conditions. Thus for example, it may be desired that a green signal be maintained constantly along a main tr-aific artery without any cycling from green to red in response to the program timer and that the red signal be switched on the main trafiic artery and the green switched on a cross street only in response to detected traffic appearing on the cross street. After this cross traflic has been allowed to pass through, the green signal on the main artery is to be restored. It is further necessary that the red signal on the main artery be held on for no longer than a predetermined maximum period in response to the cross traffic. This type of operation is achieved in the semi-actuated mode. The timer unit 40 operating in conjunction with relays 42-45 operate to control solenoid and ratchet assembly 18 to provide this desired operation. It is to be noted that only one set of signal lamps 21 is shown. An additional similar set of lamps for the cross street control actuated in the same manner by cams on the sequence controller means 19 is of course utilized as fully described in the aforementioned Patent #2,745,086.

Let us now see how the semi-actuated control is achieved. The unit as shown in FIG. 2 is operating with a continous green signal on light unit 21 (along the main artery) in the absence of any vehicles waiting at the cross street. This is because, as already noted, the sequence controller means is held at the end of its cycling, namely with the green signal on, by the drum locking contact 16a being open and drum release switch 30 not being able to provide the power signal to solenoid and ratchet assembly 18 because it has been connected by switch 27 over to contact b of relay 42.

Road switch 49 is located at the cross street and when a vehicle passes over this switch, a ground connection is made to one end of relay 42 thereby completing the power circuit thereto from power source 15. When relay 42 is momentarily actuated, it is latched closed by latching contact 42a which provides a ground connection through switching contact 16c, which is closed at the start of the operation with the main artery in green condition. With relay 42 closed, power is supplied from power source 15 through contact 42b to switch 30. The next time program timer means 11, which is either rotating continuously (or is caused to commence rotating in response to the actuation of road switch 49) closes switch 30, a pulse is supplied to solenoid and ratchet assembly 18 to advance the sequence controller means 19 so as to cause contact 16a to open and 16 to close and the main artery signal light 21 thereby to go from green to yellow. Such movement of the sequence controller also causes contact 16a to close so that when switch 12 is closed by program timer means 11, another pulse will be applied to the solenoid and ratchet assembly 18 to advance the sequence controller so as to now close contact 163 and open contact 16] so that the red light of trafiic signal 21 will be actuated. Simultaneously with this operation, the signal lamps (not shown) for the cross street will be actuated by similar cams and switches (not shown) in sequence controller means 19 to go from red to green. Program timer means 11 continuing to rotate, drum advance contact 12 will again be momentarily actuated (drum lock contact 16a now being closed) to advance sequence controller means 19 one more step. This further advance does not change the signal light contacts but opens switch contact 160. This removes the ground connection to latching contact 42a thereby deactuating relay 42. With this advance of the sequence controller means 19, switch contact 16d is now driven closed, thereby applying power from power source through contacts 420, 43a and 44a to timer unit 40. Timer unit 40 as to be explained in connection with FIG. 3 includes delay circuitry which, a predetermined time period after power is applied thereto from power source 15 produces an output signal to relay 44 causing this relay to momentarily close. The cross street green timing cycle is a function of this time period. When relay 44 closes, power is applied to solenoid and ratchet assembly 18 through contact 44a thereof and thereby simultaneously disconnected from timer unit 46. Solenoid and ratchet assembly 18 advances sequence controller means 19 one step to change the signal light facing the cross street from green to yellow. With the momentary actuation of relay 44, and the resultant actuation of solenoid assembly 18 to close contact 16d, power is also applied through contact 44b to the coil of relay 45. Contact a of relay 45 latches it in the closed position. As the cross street light goes to the yellow condition, power is also applied to relay 43 to energize this relay, through contact16b which is now closed by the action of sequence controller means 19. This again causes power to be applied to timing unit 40, this time through contacts 43a and 44a. After a second predetermined timing interval as set by the parameters of the timer (to be explained in connection with FIG. 3) relay 44 is momentarily energized, again advancing the sequence controller means 19 to bring the opera-tion back to the original standby condition with the green light facing the main traffic artery and the red light facing the cross street. The timing period of the yellow signal light is a function of this second timing interval.

If succeeding vehicles should actuate switch 49 during the timing operation of timing uni-t 40, the timing operation of this unit is re-cyclecl to its starting point as to be explained in connection with FIG. 3, this by virtue of the removal of power therefrom with the actuation of relay 42 and a timing restart circuit which is illustrated in detail in FIG. 3.

If there should be a continuous line of cars such as to prevent timing unit 40 from completing a timing cycle, the cross street green condition is nevertheless terminated when program timer means 11 runs through one complete cycle so as to advance the lights by virtue of the power connected periodically to solenoid and ratchet assembly 18 through switch contacts 16a and 12. Thus, the cross street green is held on only for a maximum period of time as determined by the pre-set timing cycle of the program timer means 11.

There is always the possibility that one or more cars may be left waiting at the cross street when the cross street green is terminated by the cycling action of program timer means 11. This exigency is taken care of in the following manner: Near the end of the timing cycle, switch contacts 16b and 160 are simultaneously closed. A ground connection is thereby applied through contact 16b to energize relay 43. A ground connection is thus applied through contacts 160, 43b and 45b to the coil of relay 42. This momentary ground connection causes relay 42 to be actuated and latched closed through contact 42a. This initiates a timing cycle of time-r unit 40 just as if a car had actuated switch 49 at that moment. In this manner it is assured that cars will not be left waiting indefinitely at the cross street.

Referring now to FIG. 3, a schematic diagram of the timer unit utilized in the device of the invention is shown. As already noted in connection with FIG. 2, the timing action of timer unit 40 is initiated when sequence controller means 19 causes contact 160 to open and contact 16d to close. The opening of contact 160 causes relay 42 to unlatch so that contact 420 closes. With the closing of contact 16d, AC. power is applied from power source 15 through contacts 16d, 420, 43a, and 44a to bridge rectifier 50. The rectified power is fed from rectifier 50 through dropping resistor 52 to zener diode 54. Zener diode 54 regulates the voltage so that a constant DC. voltage is applied through variable resistor 56 and contact 430 to resistor 47. Resistor 58 and thermistor 59 provide a temperature compensating network to minimize voltage fluctuations with variations in temperature.

Capacitor 60 commences to charge by virtue of the voltage fed thereto through resistor 57. When capacitor 60 charges to an appropriate value after a time period determined by the time constant of its charge circuit, switching diode 62 triggers which results in a current flow from capacitor 60 to the coil of relay 44. Switching diode may be, for example, a four layer PNPN switching type diode. Relay 44 is thus energized a predetermined time. interval after power is first applied to rectifier bridge circuit 50. When relay 44 is energized, contact 44a is drawn to the down position to remove the power from bridge rectifiier circuit 50 and to apply such power to solenoid and ratchet assembly 18. Relay 44 is kept energized long enough to properly actuate solenoid and ratchet assembly 18 byvirtue of the discharge of capacitor 64 through the coil of relay 44, this capacitor being conneced across the coil of the relay through contacts 44c. In this manner, the signal light on the cross street is held in the green condition for a predetermined time interval as determined by the timing circuit of timer unit 40 and then switched to yellow.

In the event that an additional car should actuate switch contact 49 (see FIG. 2) during the timing cycle of timer unit 40, relay 42 will be momentarily actuated to draw the arm of contact 42c down, thereby cutting off power to bridge rectifier circuit 50. At the same time, a ground discharge circuit is provided for capacitor 60 through contact 42d to remove any charge that may have collected on this capacitor. After the momentary energization of relay 42 and the relay again is deenergized, the timing power is reapplied to bridge rectifier 50 to start a brand new timing cycle. Thus, as each succeeding vehicle actuates switch 49, a new and complete timing interval for this vehicle is provided.

As already noted, in connection with FIG. 2, when the first complete timing interval of timer unit 40 is over, relay 45 is actuated and latched in the closed position. Solenoid and ratchet assembly 18 having been actuated by the momentary closing of relay 44 in response to the discharge current from capacitor 60, the vehicle light on the cross street changes from green to yellow. Relay 43 also is actuated at this time by virtue of the closing of contact 16b in response to sequence controller means 19 (see FIG. 2). This provides power from power source 15 through contacts 16a, 43a and 44a to bridge rectifier 50. At the same time, potentiometer 66 is thrown into the charging circuit for capacitor 60 in lieu of potentiometer 56 through relay contacts 430 and 45c by virtue of the actuation of relays 43 and 45. Thus, a new timing circuit dependent upon the resistance of potentiometer 66 rather than that of potentiometer 56 is provided. This circuit operates similarly to the circuit described in connection with potentiometer 56, to time the yellow condition of the cross street light. At the completion of the timing interval as determined by the charging of capacitor 60 to fire diode 62, relay 44 is again actuated to advance solenoid and ratchet assembly 18 to change the signal on the cross street to red and that on the main street to green. The resistance of potentiometer 56 is pre-set to determine the interval during which the green light will be displayed on the cross street and potentiometer 66 is pre-set to determine the time interval during which the yellow light will be displayed. In this manner independent timing control for each of these signal lights is provided.

While the device of the invention has been described in connection with semi-actuated operation whereby a green signal is continually facing the main street in the absence of cross street road switch actuation, this is merely illustrative of one type of semi-actuated operation possible with the device of the invention, and other types of such operation can be obtained by appropriate adjustment of the system.

The device of this invention thus provides a traffic signal controller which utilizes most of the circuitry of a pre-timed controller to obtain semi-actuated type operation such that operation can be changed over from one type operation to the other by means of a simple switch. This enables the installation of a unit capable of alternatively operating in either mode of operation and facilitates the conversion of existing pre-timed controller units so they are capable of such alternative operation.

While the invention has been described and illustrated in detail, it is to be clearly understood that this is intended by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of this invention being limited only by the terms of the following claims.

We claim:

1. In a traffic signal controller for controlling traffic signals at an intersection between streets, said signals including a set of signal lights for each such street,

a power source,

pro-timed control means for providing control signals for said lights in accordance with a predetermined program,

semi-actuated control means for providing control signals for said lights in accordance with trafiic conditions on one of said streets, sequencing and switching means interposed between said power source and said signal lights and said power source and said semi-actuated control means for connecting power to said lights and to said semiactuated control means in a predetermined sequence,

actuator means responsively connected to said pre-timed for actuating said sequencing and switching means, and

means for alternatively connecting said power source either directly to said pre-timed control means to cause said pre-timed control means to drive said actuator means in accordance with said predetermined program or connecting said pre-timed control means to said semi-actuated control means to cause said actuator means to be driven in response to said semiactuated control means,

said semi-actuated control means comprising road switch means adapted to be actuated in response to vehicles arriving at said intersection on said one of said streets, timer switching means connected for actuation by said road switch means, and electronic timer unit means connected to said timerswitching means for generating predetermined timing signals in response to the actuation of said road switch means, said power source being connected to said electronic timer unit means through said sequencing and switching means and said timer switching means to initiate the generation of said timing signals, said actuator means being actuated by said timer switching means in response to said timing signals.

2. The system as recited in claim 1 wherein said timer unit means includes a first delay circuit for timing the duration of the green signal on said one of said streets and a second delay circuit for timing the duration of the yellow signal on said one of said streets.

3. The system as recited in claim 1 wherein said timer switching means includes a plurality of relays interconnecting said power source with said timer unit, said pretimed control means, said actuator means and said sequencing and switching means.

4. The system as recited in claim 3 wherein said timer unit means includes a capacitive delay circuit, the coil of one of said relays being energized in response to the discharge currents of the capacitors of said delay circuit.

5. In combination, pre-timed control means for generating control signals in accordance with a predetermined program,

actuator means connected to receive the output of said pre-timed control means for producing an actuation signal in response thereto,

a power source,

trafiic signal lights,

sequencing and switching means for connecting said power source to said signal lights in a predetermined sequence in response to the output of said acuator means,

timer switching means connected to operate said actuator means, road switch means for initiating the operation of said timer switching means in response to traffic,

electronic timer unit means connected to said timer switching means for delaying signals received therefrom a predetermined time interval, said actuator means being caused to actuate said sequencing and switching means at the end of said time interval, and

switch means for alternatively connecting said pre-timed control means directly to said power source or to said timer switching means,

whereby when said pre-timed control means is connected directly to said power source, said signal lights are operated in pre-timed type operation, and when said pre-timed control means is connected to said timer switching means, said signal lights are operated in semi-actuated type operation in response to said road switch means.

6. The device as recited in claim 5 wherein said timer switching means includes a plurality of relays for selectively feeding pulses of power from said power source to said timer unit means, said timer unit means including resistive-capacitive delay circuits for delaying said pulses, said delayed pulses being fed to actuate one of said relays, said one of said relays being connected to feed power from said power source to said actuator means in response to said pulses.

7. The device as recited in claim 6 wherein said relays are connected to said delay circuits to discharge said delay circuits and initiate a new timing cycle when said road switch means is again actuated by trafiic during said predetermined time interval.

References Cited by the Examiner UNITED STATES PATENTS 2,908,891 10/1959 Cass 340-37 3,056,946 10/1962 Brockett 34037 3,106,695 10/1963 Baltayan 34037 NEIL C. READ, Primary Examiner.

THOMAS B. HABECKER, Examiner.

Claims (1)

1. IN A TRAFFIC SIGNAL CONTROLLER FOR CONTROLLING TRAFFIC SIGNALS AT AN INTERSECTION BETWEEN STREETS, SAID SIGNALS INCLUDING A SET OF SIGNAL LIGHTS FOR EACH SUCH STREET, A POWER SOURCE, PRE-TIMED CONTROL MEANS FOR PROVIDING CONTROL SIGNALS FOR SAID LIGHTS IN ACCORDANCE WITH A PREDETERMINED PROGRAM, SEMI-ACTUATED CONTROL MEANS FOR PROVIDING CONTROL SIGNALS FOR SAID LIGHTS IN ACCORDANCE WITH TRAFFIC CONDITIONS ON ONE OF SAID STREETS, SEQUENCING AND SWITCHING MEANS INTERPOSED BETWEEN SAID POWER SOURCE AND SAID SIGNAL LIGHTS AND SAID POWER SOURCE AND SAID SEMI-ACTUATED CONTROL MEANS FOR CONNECTING POWER TO SAID LIGHTS AND TO SAID SEMIACTUATED CONTROL MEANS IN A PREDETERMINED SEQUENCE, ACTUATOR MEANS RESPONSIVE CONNECTED TO SAID PRE-TIMED FOR ACTUATING SAID SEQUENCING AND SWITCHING MEANS, AND MEANS FOR ALTERNATIVELY CONNECTING SAID POWER SOURCE EITHER DIRECTLY TO SAID PRE-TIMED CONTROL MEANS TO CAUSE SAID PRE-TIMED CONTROL MEANS TO DRIVE SAID ACTUATOR MEANS IN ACCORDANCE WITH SAID PREDETERMINED PROGRAM OR CONNECTING SAID PRE-TIMED CONTROL MEANS

Images