US2908891A - Traffic actuated traffic light control system - Google Patents

Description

Oct. 13, '1959 I s. CASS ETAL 2,908,891

TRAFFIC ACTUAIED TRAFFIC LIGHT CONTROL SYSTEM Filed June 17, 1957 FIXED TIME SEMI ACCUATE D SOLENOID RATCHET CAM SHAFT AMBER GREEN MAIN STREET GREEN CROSS STREET INVENTOR. SAM UEL CAS 5 BY OHN T-yN AT TORNEY United States Patent() 571cc TRAFFIC ACTUATED LIGHT 3 CONTROLSYSTEM Samuel Cass and John T. Hewton, Toronto, Ontario, Canada, assignors, by mesne assignments, to Canadian General Electric Company, Limited, Toronto, Ontario, Canada, a company. of Canada Application June 17, 1957, Serial No. 665,976 4 Claims. cram-31 2,908,891 Patented Oct. 13, 1959 vance contacts and every key which actuates the drum advance contacts will operate to advance the drum one position. When the drum lock cam rotates to its single open position, however, the drum lock contacts open, and the drum advance contacts are inoperative. If the mechanism is in synchronization, however, at this point the drum release key will close the drum release contacts feeding power to the drum and advancing the drum and thus closing the drum lock contact again.

If the dial and drum are not in synchronization, the drum will remain stationary until the drum release key does engage and close the drum release contacts at which time both will be back in positive synchronization.

The drum release key is usually placed in a period of main street green to minimize the inconvenience in case of a delay in synchronization.

timed sequence are well known in the art. One of the H most successful and widely used controllers of this type comprises a constant speed motor, which, by means of a gear train of variable ratio, drives a timing dial at a constant rate-ot'speed. A number. of slots are provided on the timing-dial and keys may be inserted into selected slots. *As the dial rotates, the keyseach in turn momentarily olosefa contact. Each time such a contact is closed, a coil isenergized which operates a ratchet mechanism, advancing a'drum one position, i.e. a predetermined degree of rotation. A number of cams are mounted on the drum," each cam having" a" contact arm 'bearingthereagainst. The cams may conveniently be formed; in segments; each section representin'gone drum position, One or more segments'ofeach cam maybe broken off.

, 'When the drumrotates {to a position where the contact arm for a cam encounters a brokn out cam sectio n, the contact arm closes azcircuit which will actuate alight, either gr'een, amber or red on either the main street or thecross street or perform-some other function inthe system.

fIn' oir'e revolution 'ofth'e tirnin'g 'dialg a-cofnplete "see contact main street green .hasiI-a broken out section in position with its contact, and cam 4 corresponding to contact arm cross street red also has a broken out section in positionwith its contact. other camshave their sections in placeandthus all lights are out except main street; green and cross street red. -At the %5position, a ke'y could be insertedin the timing dial which, when it actuated the contact would cause rotation of the drum and thus of the cams, one position, i.e. a rotation corresponding to one cam section. At this position on cam 2 (main street amber) and cam 4 (cross street red) will be broken away, and so on through a-cornplete sequence of light changes.- The sequence-isdetermined by the lo cation ofdrum advancing keys on the timing-dial and by breaking away appropriate cam segments on the drum.

; sinceperfect synchronization between the timing dial and the cam drum is required to operate the lights in the prearranged sequence, systems .of. thiskind contain a means for synchronizingthe ,dial and the drum... A drum rele q ta kisr o d si dap ed to be p d y a e m iee k ie t m n di T drum advance contact already described gets power from the line' throu gh a drum lock contact actuated by a drum lock ,caIngThis carn i s;g-su ch ,tlratthe drum lock contact is w xs-ql sed $@P 9 cli ii i ie A n as this contact is closed power is supplied to the drum ad- These signals, operating on a predetermined timed sequence have the adyantage of being reliable, easy to service and maintain. They are, however, subject mall the limitations of a fixed time signal, for while the sequences can be changed, it requires the services of a trained technician to. effect a change in sequence--a course obviously impractical to follow with every change in demand.

Many intersections in metropolitan locations demand changes from hour to hour, and the need has arisen for a traflic signal control capable of adjusting to the actual traffic flow rather than adhering to a fixed sequence of operation.

Many traffic operated signal control systems have been proposed, but none of them has successfully combined the advantages of the variable sequence based upon traffic flow.with the rugged dependability and ease of maintenance and service characteristic of the dial and drum type of, control already described.

It is a principal object of this invention, therefore, to provide a trafiic signal controller in which the signals may be operated according to the demands of traific flow or in a fixed predetermined sequence as desired.

It is another important ,object of this invention to provide such'a trafiic signal controller as will be reliable in operation and easily maintained and serviced.

It is a still further object of this invention to provide a means of adapting the known dial and cam drum type of fixed sequence traffic controller to traflic demand operation. e

These and other advantageous objects will become apparent through a consideration of the following detailed description taken in conjunction with the attached draw- Referring to the single figure, 1 represents a timing dial having a plurality of slots 51 in which keys 52 are inserted. These keys have protruding contact portions 53 adapted to engage the contacts 5, 12, or Z as the case may be.

Contact 5 is the drum advance contact. Each time this contact is closed, power is supplied to a ratchet which actuates the drum moving it one position.

Contact 12. is the drum release contact already described, having onlyone key adapted to close it once per revolution of the timing dial.

The cams on the drum operate to open or close signal contactsISC S0 86 etc. to complete circuits to the traffic lights, and to open and close contact DLC, being the lock contact already described.

' All of the above is the conventional timed sequence trafiic control, and this conventional predetermined sequence will operate from the switch 8C in the fixed time position as viewed in the figure. V The improvement which formsthis invention involves the use of tw'o additional cams on the drum, and a switch and key position on the timing dial which is additional to/the drum advance and the-drum release positions to- 3 gether with certain relays and switches as hereinafter described in detail.

Since fixed time controllers are readily available with this additional switch, and with extra cams, the adaptation of the invention to the conventional fixed time controller is a simple and inexpensive matter.

In the drawings a detector D of any desired type is mounted so as to give a signal when actuated by a passing vehicle. Detectors are available in many types. The simplest form is a pneumatic type having a treadle mounted in the road which is depressed by the wheels of a passing vehicle to close a contact. One of the more acceptable types at least (for climatic and traific conditions prevailing in the northern United States and Canada) is the magnetometer type which is actuated by the distortion in the earths magnetic field caused by the metal mass of a. passing vehicle. A radar type is also available, but at present the cost of this type makes its widespread use impractical.

All detectors, however, are adapted to momentarily close a circuit, and since the detector itself does not form part of this invention, the construction of various types will not be discussed in detail here.

The detector is mounted in the side street at a predetermined distance from the intersection.

One detector will be mounted on each side of the main street intersection, and, if pedestrian trafiic across the main street is a factor, push buttons located at the intersection may give a response identical to that of a detector.

The detectors and push buttons are in circuit with relay R which, when actuated, closes contacts R A, R B, and R C. A relay R is also provided actuating contacts R A, R B and R C.

The timing dial is provided with an additional contact Z, with a number of keys ZK being located in the timing dial adapted to actuate this contact. In addition to the 6 cams required for completion of the circuits to the light, and to the drum lock cam, two additional cams X and Y are employed. The contacts actuated by cam X are closed only in side street green, while the contacts actuated by cam Y are closed only in side street amber.

The operation of the circuit as shown in the wiring diagram is as follows when the switch SC is in the semi actuated position as shown on the drawings:

The lights are set to give side street red and main street green until a vehicle in the side street approaches the intersection. In the absence of such a vehicle, the detector is open, relay R de-energized, and contacts R A, R B and R C are all open. In this condition, actuation by the drum advance keys of the drum advance contacts is inoperative to advance the drum because relay contacts R A are open thereby breaking the drum release circuit and rendering it inoperative with the result that the drum remains stationaly in its lock position, i.e., in main street green.

If a vehicle approaches in the side street, however, it will actuate the detector momentarily, supplying current to relay R which will cause contacts R A, R B and R C to close. Closing of R C completes a circuit in parallel with the detector keeping R activated and the contacts R A, R B and R C closed. The closing of contact R A completes the dnim release circuit, and when the drum release key DRK closes the drum release contacts the drum is advanced one position, at which position main street amber is illuminated. The next key is a drum advance key DAK, which will now actuate the drum advance contact, moving the drum a further position; At this further position, side street green and main street red are'illuminated.

The next key is the first of the Z ofi set keys ZK Actuation of the Z contact by this key completes a circuit through the X cam contacts (which are. closed only in side street green), and through R B to relay R which is breaks the hold circuit for R de-energizing R and allowing contacts R A, R B, and R C to open. Contact R C holds R closed as long as" the Z ofiset contacts are closed, thus preventing false actuation of the drum.

The next key in the timing dial is a second Z offset ZK Assuming that no further vehicle has actuated the detector in the interval between ZK and ZK ZK will close contact Z feeding power through the X cam contact. But relay R and R being open, the power is fed through R B and R B to the drum coil advancing the drum one position at which side street amber is illuminated, cam contacts Y being closed and cam contacts X open in this position. The next key is 2K which, upon closing Z contacts, feeds power through the Y cam contacts R B and R B to the drum, advancing the drum and illuminating main green whereupon X and Y cam contacts are open. Thus until the detector is again actuated, closing of DA contact, DR contact or Z contact is inoperative to advance the drum once it has reached its lock position.

If, however, in the interval between ZK and ZK a subsequent vehicle actuates the detector, R is again energized and the closing of Z by ZK instead of energizing the drum, energizes R through R B releasing R and the lights remain unchanged. If there is no further actuation of the detector between ZK and ZK ZK upon closing Z contacts will bring on side street amber as before. If a vehicle actuates the detector between ZK and ZK ZK upon closing Z contacts will release R again.

A maximum for side street green is, of course, a necessity regardless of the repeated actuation of the detector. In this system, the first drum advance key following the ZK keys, will advance the drum regardless of the actuation of R bringing on side amber, and the next drum advance being side red and main green.

The number of the ZK contacts will determine the possible variations in side street green related to the flow of traffic in the lSlde street. The ZK keys are preferably spaced an amber period apart since, depending upon side .then actuated; closing contacts R A, R B and R C. R A

street traific flow, any pair of ZK contacts after ZK can cause first side amber and then side red.

Following side red and main green, X and Y cam contacts both being open in the absence of energization of R subsequent closing of Z contacts by ZK keys is, of course, inoperative to change the lights.

With the switch, in the fixed time position, the controller will operate in a normal timed sequence, the keys ZK 2K etc. being inoperative and the keys DAK DAK DAK etc. upon closing contact 5 each advancing the drum one position thereby a light sequence is effected in the conventional manner.

EXAMPLE As an example of the operation of the invention described, in a common form of signal control system, the dial is divided into slots in which keys may be in- Iserted, while there are 6 positions for one rotation of the drum. A typical application could be set up as follows:

and the cams will be disposed as follows, X indicating a closed contact, and a blank space an open cam contact.

aoos, s9 1 According to this arrangement, if on a fixed time basis (switch SC in the fixed time position) the lights will be, assuming a dial rotation time of 60 seconds.

Percent Sec.

Main Gre 5O 30 Main Amber" 6 3. 6 Main Red- 44 26. 4 Side Red 56 33. 6 Side Amber 6 3. 6 Side Green 38 20. 8

If working on an actuation basis, switchSC in the timed position, the minimum green for side street would be 14% or 8.4 sec. and the maximum side street green would be 38% or 20.8 see.

What we claim as our invention is:

1. A traffic signal controller for controlling at least a pair of trafiic lights each including at least a red and a green signal and positioned to control traffic on amain street and an intersecting side street, comprising a switch for each signal operable when closed to energize the signal, rotatable switch control means operable when rotated through a complete revolution to open and close said switches sequentially to operate said signals through a complete cycle, means operable each time energized to index said switch control means through a selected portion of said revolution, timing means including a continuously rotatable cylindrical member having a plurality of switch-operating members thereon, an advance switch operable by several of said switch-operating members, said advance switch being operable to energize said indexing means, a control switch operable in one position to connect said advance switch to said indexing means, means for detecting the passage of a vehicle along the side street, relay means controlled by said detecting means, said control switch being operable in another position to connect said advance switch to said indexing means only through said relay means, said relay means being operable in the absence of operation of said detecting means to disconnect the advance switch from the indexing means to maintain the switches in positions to keep the green signal on the main street and the red signal on the side street energized but operable when said detecting means operates to connect the advance switch to the indexing means to complete one cycle of operation of the switches and signals.

2. The apparatus of claim 1 including a release switch operable by one of said switch-operating members, a locking switch, said switch control means being operable to maintain said locking switch closed except during one selected portion of the cycle thereof, said locking switch being in series with said advance switch and said indexing means and said release switch being connected directly across the series combination of the advance switch and the locking switch when said control switch is in said one position and being connected in series with normally open contacts of said relay means across the series combination of the advance switch and the locking switch When the control switch is in said other position, Whereby said lock switch and said release switch provide for synchronization of the timing means with the indexing means when the control switch is in said one position but said release switch is effective only when said detecting means operates said relaymeans when said control switch is in said other position. i c r T 3. The apparatus of claim 2 in which said relay means includes a pair of'relays, one of said relays having its operating coil connected to said detecting means to be energized by operation thereof and having one of its sets of normally open contacts in series with said release switch when said control switch is in said other position, another set of normally open contacts of said one relay and a set of normally closed'contacts 0f the other relay furnishing a holding circuit forsaid-'one.relay, aldelay switch, a plurality of operating members for said delay switch on said cylindrical member of the timing means, a second control switch closed only when the green signal on the cross street is energized, the series combination of a third set of normally open- .contacts of said one relay, said second control switch and said delay switch being connected in series with the operating coil of said second relay and operable when closed to energize the second relay and thereby to de-energize the first relay, a set of normally closed contacts of said second relay being connected in series with said indexing means to permit operation thereof only when said second relay is de-energized.

4. A trafiic signal controller for controlling at least a pair of traffic lights each including at least a red and a green signal and positioned to control traffic on a main street and intersecting side street, comprising a switch for each signal operable when closed to energize the signal, a rotatable drum carrying a cam for each switch, said drum and cams being operable when rotated through a com,- plete revolution to open and close said switches sequentially to operate said signals through a complete cycle, solenoid and ratchet means operable each time the solenoid is energized .to index the drum through a selected portion of said revolution, timing means including a con- I tinuously rotatable cylindrical member having a plurality of advances, one release, and a plurality of delay switchoperating members spaced arcuately along its periperal extent, an advance switch operable when closed to energize said solenoid and said advance switch-operating members to index the drum through a complete revolution for each revolution of said cylindrical member, a control switch operable in one position to connect said advance switch directly to said solenoid, means including a switch for detecting the passage of a vehicle along the side street to close the switch when a vehicle passes, a pair of relays, said control switch being operable in another position to connect said advance switch to said solenoid only through a first set of normally-closed contacts of a first of said relays, a circuit-controlling switch operable by a cam on said drum, the circuit-controlling switch being closed only when the green signal on the cross street is energized, a delay switch operable by said delay switch-operating members, a locking switch operable by one of said cams and closed in all but one position of said drum, the series combination of said first set of contacts of the first relay the advance switch and the locking switch being connected in series to furnish an energizing circuit for said solenoid when said control switch is in said other position, the series combination of said release switch and a first set of normally open contacts of the second relay being connected in parallel with the series combination of the advance switch and the locking switch when said control switch is in said other position and said release switch being connected directly across the series combination of the advance switch and the locking switch when the control switch is in said one position, said detecting switch being operable when closed and when the control switch is in said other position to complete an energizing circuit for said second relay, a second set of normally open contacts of the second relay and a second set of normally closed contacts of the first relay being connected across said detector switch to provide a holding circuit for said second relay, a third set of normally open contacts of the second relay being connected in series with said circuit-controlling switch, said advance switch and said locking switch to provide an energizing circuit for the first relay after the second relay energizes, whereby when said control switch is in said one position, the signals are periodically energized cyclically according to .the positions of the advance switch-operating members on said drum, but, when said control switch is in said other position, said. drumis maintained in one position, to keep one set of signals continuously energized until a car actuates said detector switch and the drum is then rotated through one complete revolution to accomplish a complete cycle of signal-operation.

References Cited in the file of this patent UNITED STATES PATENTS

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