US2531153A - Traffic signal control system - Google Patents

Description

Nov. 21, 1950 w. c. PENNELL TRAFFIC SIGNAL CONTROL SYSTEM Filed Dec. 29, 1949 we p C 0 m n.@ M

H i5 Attorney Patented Nov. 21, 1950 TRAFFIC SIGNAL CONTROL SYSTEM William C. Pennell, Saugus, Mass assig'nor to General Electric Company, a corporation of New York Application December 29, 1949, Serial No. 135,616

8 Claims. l

My invention relates to traflic signal control systems, and more particularly to systems wherein one or more individual intersection controllers are brought into and maintained in synchronism with a master controller in any one of a plurality of selectable phase displaced or offset relations with respect to .the master.

In systems of the above type, it is common to provide synchronizing means operable at any one of a plurality of predetermined selectable instants during each cycle of the intersection controller to stop the intersection controller in the event that a predetermined synchronous positional relationship between the intersection controller and the master controller does not exist. Such synchronizing means stops the intersection controller .and maintains it at standstill until the master and intersection controllers again assume the desired synchronous relationship, whereupon the intersection controller is released and synchronous operation is continued. Since the intersection controller is ordinarily provided with but a single rotatable timing member or dial, and since the signal interval timing means as well as the offset synchronizing means is actuated by this single timing dial, stoppage of the intersection controller, either for the purpose of restoring a synchronous relationship or for the purpose of changing the. ofiset with respect to the master controller, may occur in any part of the signal interval timing cycle. It has been found desirable in many instances to ensure that any stoppage of the intersection signal interval timer, either for the purpose of reestablishing a synchronous relationship with the master or for the purpose of efiecting a change from one ofiset synchronous relation to a different offset synchronous relation, can occur during only one predetermined signal display interval, for example, the main street green interval.

Accordingly, it is a general object of my in- 4 vention to provide new and improved multiple oifset synchronizing means for a synchronized system of traflic signal controllers including master and intersection controllers.

secondary, or sub-master, element which is continuously maintained in a fixed synchronous relationship with respect to a master timer, and the other being a signal interval timing element which is maintained in synchronism with the secondary timing element in any one of a plurality of phase displaced positions or offsets. In providing such a selectable phase positional relation between the secondary timing element and interval timing element of the intersection controller, '1 preferably provide means for stopping the interval timer at only one fixed predetermined instant or position in its cycle, and means actuated by the secondary timing element, or sub-master timer, for releasing the interval timer at any one of a plurality of selectable instants or positions during the cycle of the secondary element. In this way, any stoppage of the interval timing element, either for resynchronizing or for changing of the offset, occurs always at a predetermined fixed point in the cycle of the interval timer, and therefore during a predetermined-signal display interval, for example, main street green interval.

My invention will be more fully understood and its various objects and advantages further appreciated by referring now to the following detailed specification taken in conjunction with the accompanying drawing, the single figure of which illustrates diagrammatically a traffic signay control system embodying my invention.

Referring now to the drawing, the system there shown comprises a master controller I connected through an interconnecting cable 2, 2a, 2b to a plurality of intersection controllers 3, 3a. For the purpose of illustration only the intersection controller 3 has been shown in detail, the identical controller 311 being indicated in block form only. As the description proceeds, it will be evident that any desired number of intersection controllers, one or more, may be used.

The master controller I includes a master timing element shown as a rotatable cam 4 driven counterclockwise by a synchronous timing motor having an armature 5 and an energizing or running winding 5a connected to a suitable source of alternating current supply. The timing cam 4 is arranged to open momentarily once each revolution or cycle a normally closed master synchronizing contact 6 connected between the interconnecting cable wire 2b and a suitable source of alternating current supply. The master controller includes also a selector switch I having an off position and two operating positions. The selector switch I is shown in its on" position, and

in its operating positions it is arranged to connect one or the other of the interconnecting cable wires 2 or 2a to the alternating current supply source at the master controller. The interconnecting cable wire 2b is a synchronizing line between the master timer and the intersection timers, and the interconnecting wires 2 and 2a are oilset selector lines, as will become more evident hereinafter.

The intersection controller 3 comprises a secondary timing unit 8 and an interval timing unit 9 and a signal switching mechanism 26. The timing units 8 and 9 are separately driven by timing motors in, lUa, illb and ii, lla, lib, respectively, connected to a local source of alternating current supply.

Th interval timing unit 8 and switching mechanism 26 per se are fully described and claimed in Patent 2,236,298 issued to Ralph A. Reid on March 25, 1941. As described in the foregoing patent, the interval timing motor is provided with an armature ii, an energizing or running winding Ila and a retarding or braking winding lib, and is connected through suitable gearing l2 to drive a rotatable timing dial IS in a clockwise direction as viewed in the drawing. The timing dial i3 is provided with a peripheral row of radially disposed slots within which may be adiustably positioned a plurality of contact actuating keys l4, l5, i6, l1, l8 and i9. The timing dial i3 is also provided with a fixed contact actuating stud positioned radially inward from the key supporting slots and in an angular position which will be more fully described hereinafter. Adjacent the timing dial l3 there are provided three resilient contact arms 2i, 22 and 23. The contact arms 22 and 23 are arranged, when lifted by certain of the keys in the peripheral row of slots, to close respective associated pairs of normally open contacts 24 and 25. The contacts 24 and 25 control the switching mechanism 26,

which is, in turn, arranged to control the various lighting circuits of two groups of traific signal lamps 21 and 21a. The contact 25 is disposed to be closed by any of the keys l4, l5, l6, H, or l9 and the contact 24 is disposed to be closed only by the key l8. The mode of operation of the interval timing unit 9 in conjunction with the switching mechanism 26 and trafiic signal lamps 2i and 21a is more fully described in the aforementioned Patent 2,236,298. The contact arm 2i is arranged when raised by the stud 20 to close a pair of normally open contacts 28. The normally open contacts 28 are connected in series with the interval timing motor brake winding lib in a synchronizing circuit between the interval timing unit 9 and the secondary, or sub-master, timing unit 8, as will be more fully described hereinafter.

The secondary or sub-master timing unit 8 comprises a timing motor having an armature ill, a running or energizing winding lila and a braking or retarding winding li'lb connected through suitable gearing 29 to drive a rotatable timing dial 30 in a clockwise direction as viewed in the drawing. The timing dial 30, like the dial i3, is provided with a peripheral row of radially disposed slots within which may be adjustably mounted a plurality of contact actuating keys. The timing dial 30 is provided also with a fixed contact actuating stud 3i mounted upon the dial at a position radially inward from the key slots. Adjacent the timing dial 3!! there are provided four resilient contact arms 82, 33, 34 and 35. The contact arm 32 is arranged when 'the intersection secondary timing unit 8. the

running winding Illa of the timing motor is connected to a suitable local source of alternating current supply, as shown. The retarding or braking winding lilb of the secondary timing motor is connected through the normally open secondary timer dial contacts 36, the interconnecting cable wire 2b-and the master synchronizing contact 8 to a source of alternating current supply at the master controller. This constitutes a synchronizing circuit between the master timer and the sub-master or secondary timing unit I.

In the intersection interval timing unit 9, the timing motor driving coil Ila is connected to a suitable local source of alternating current supply. The braking coil lib for the interval timing motor is connected to a local source of alternating current supply through a series circuit'including the normally open interval timer dial contacts 28, the contacts of a pair of selector relays 43, 44 and any one selected pair of the secondary timer dial contacts 40, 4| or 42.

For the purpose of determining which one of the secondary timer dial contacts 40, 4| or 42 is connected in circuit with the interval timer braking winding l lb at any time, the relay 44 is provided with a pair of normally closed contacts 45 and a pair of normally open contacts 46, while the relay 43 is provided with a pair of normally closed contacts 41 and a pair of normally open contacts 48. The contacts 45, 46, 41 and 4B are' so interconnected that when both the relays 43 and 44 are deenergized the secondary timer dial contact 40 is connected in the synchronizing circuit between the timers 8 and 9, when the relay 43 alone is energized the secondary timer dial contacts 4i are connected in the synchronizing circuit, and when the relay 44 alone is energized, the secondary timer dial contacts 42 are connected in the synchronizing circuit. The selector relays 43 and 44 are provided with energizing windings 49 and 50, respectively, and these windings are connected to be energized from a suitable source of current supply at the master timer I through the selector switch 1 and the interconnecting wires 2a and 2, respectively.

It will be understood that the intersection controller 3a, and any other desired number of connected intersection controllers, are constructed in the same manner as the controller 3 described above.

In operation, it will be understood that as the intersection interval timing dial l3 rotates through successive revolutions or cycles, this dial, through the dial contacts 24 and 25, controls the switching mechanism 26, which in turn controls the signal lamps 21, 21a, all as more fully described and claimed in the aforementioned Patent 2,236,298-Reid. The intersection secondary timer 8 together with the selector relays 43 and 44 serve to maintain the interval timer 9 in synchronism with the master timer l and to determine its offset or phase displaced positional relation with respect thereto. In the embodiment of the invention shown, three such phase positional relationships are selectable by means of the selector relays 43, 44 and the secondary timer 8 dial contacts 40, M and 42. This selectable synchronizing arrangement operates in the manner described below.

Assuming that the selector switch I is in the on position shown, and that power is supplied to themaster and intersection controllers, the selector relays 43 and 44 will both be deenergized and in the positions shown in the drawing. The running winding Ca of the master timing motor is energized, so that the master timing cam 4 rotates. Similarly, the running windings Illa and Ma respectively of the secondary and interval timing motors are energized, so that the intersection timing dials i3 and 30 rotate.

It will first be noted that the synchronizing circuit between the master timer and the intersection secondary or sub-master timer 8 includes, in series circuit relation, the secondary timer braking winding ib, the normally open secondary timing dial contacts 36, the interconnecting wire to and the normally closed master synchronizin contact 6. The secondary timer braking winding Nib therefore can not be energized except at that position of the secondary timing dial where the fixed stud 3i raises the contact strip 32 and closes the dial contacts 36. If the secondary timer 8 and the master timer II are not in the desired fixed synchronous positional relationship, such closing of the contacts 36 will complete a circuit for the braking coil iilb, and the secondary timer 8 will be stopped with the dial it! in this position. The secondary timer dial 30 will remain in this position until the master timer comes to that position of its rotation where the synchronizing contact 6 is momentarily opened. Upon opening of the master contact 6-, the master synchronizing circuit is interrupted, the braking winding Hlb is deenergized,. and the secondary timer 8 is released for rotation. By the time the master synchronizing contact 6 is reclosed, the secondary timing dial 30 has moved to a position where the dial contacts 36 are reopened. If now the secondary timing dial 30 and the master timing cam 4 continue to rotate at the same speed, there is one instant during each revolution when the synchronizing contacts 36 at the secondary timer are momentarily closed while at the same time the master timing contact 6 is momentarily opened. This acts as a check upon synchronization, and this check occurs momentarily once per revolution or cycle. The secondary timer 8 is maintained in this fixed synchronous positional relationship by reason of the fact that, if the secondary timer gets ahead or behind this position, the contacts 36, when closed, complete the master synchronizing circuit and stop the secondary timer 8 until the master timing contact 6 again releases it. In this manner, the secondaryintersection timer 8 maintained in synchronism and in fixed phase positional relationship with the master timer I.

For the purpose of maintaining the intersection interval timing dial I3 in synchronism with the intersection secondary timing dial 30 but in a selected one of a plurality of phase displaced positional relationships therewith, a similar synchronizing circuit is provided between the intersection timers 8 and 9 and controlled by one of the selectable normally closed dial contacts on the intersection secondary timer 8. This circuit comprises the intersection interval timer brake coil lib, connected in series circuit relation with the normally open interval dial contacts 28 and, through the selector relays 43 and 44, with one of the secondary dial contacts 40, M or 42. In

the position of the apparatus shown in the drawing, the'secondary dial contacts 40 are connected in the local intersection synchronizing circuit, and'are actuated by the dial key 31 on the secondary timing dial 30. The key 31 is selectably positionable in the slots in the timing dial 30, but is shown by way of example as being positioned at about 55% of the cycle time. For the purpose of illustration, both intersection timing dials l3 and 30 are shown in arbitrarily chosen zero positions with zero at the top of the dial.

The local synchronizing circuit between the intersection timers 8 and 9 functions in a manner similar to the master synchronizing circuit, so that the local intersection timing dials l3 and 30 are maintained in synchronism. However, in this local synchronizing circuit the relative phase position, or offset, is selectable by means of the relays 43, 44 and the dial contacts 40, 4|, 42. In the illustrated offset conditions the phase relationship is determined by the position of the dial key 31 in the secondary dial 30. It will be evident from the foregoing that in operation, the dials l3 and 30 are maintained in such a relative phase position or ofiset relation that the secondary timer dial key 31 normally opens its associated dial contacts 40 momentarily at the same instant that the fixed stud 20 on the intersection interval timer dial i3 closes its dial contacts 28.

Thus, the intersection secondary timing dial 30, being maintained as previously described in a fixed synchronous positional relationship with the master timer, and the intersection interval timing dial i3 being maintained in a predetermined selectable phase displaced or offset positional relation with respect to the intersection secondary timing dial 30, the intersection interval dial 30 is consequently maintained in synchronism with and in a predetermined phase displaced positional or ofiset relation with respect to the master timer.

It will now be evident that the phase positional relationship of the intersection interval timing dial [3 with respect to the intersection secondary timing dial 30, and thus with respect to the master timer, may be selected by energizing either the relay 43 or the relay 44 or maintaining both deenergized. With th relays in their deenergized positions, the secondary dial key 31 and dial contacts 40 are effective in the local synchronizing circuit, as described above. If the relay 43 alone is energized, the dial contacts 4| are substituted in the local synchronizing circuit and the secondar dial key 38 is effective to control the positional relationship of the interval timer 9. Similarly, if the relay 44 alone is energized, the dial contacts 42 are substituted in the local synchronizing circuit and the secondary timer dial key 39 iseifective to control the relative positional relationship of the secondary and interval timers.

It may now be particularly noted that, regardless of which dial contacts 40, 4| or 42 is selected for use in the loca1 synchronizing circuit, the interval timer dial contacts 28, which are also in this circuit, are always controlled solely by the fixed dial stud 20 on the interval timing dial l3. This means that any stoppage of the interval timing dial l3 which may occur, either for the purpose of resynchronization or for re-setting with respect to the secondary timing dial. 30 (and thus with respect to the master timer), necessarily occurs in only the one fixed predetermined position of the interval timer dial l3 wherein the fixed stud 20- lifts the contact strip 2| to close the contacts 2|. This synchronizing or dwell position of the intersection intervaltlmer I may thus be made to occur during only one predetermined signal interval, regardless of which oflset relation is selected. By way oi. example, I have shown the fixed stud 20 in the interval timing dial l3 positioned at about 5% of the cycle time and in the main street green interval oi the dial ll. This arrangement is selected by way of 11- lustration merely because it is ordinarily desirable that any dwell oi the intersection interval timer should take place in the main street green interval.

The fixed stud 3| on the intersection secondary or submaster timing dial 30 may be positioned at any desired angular location with respect to the arbitrarily selected zero position, since this dial is always maintained 'by the stud in one fixed predetermined positional relation with respect to the master timer. For the purpose of illustration, however, I have shown the stud 3| as positioned at about 5% of the cycle time of the intersection secondary dial 30.

To illustrate the reason for providing selectable oifset of the intersection interval timer 9 with respect to the master time I, assume a plurality of intersection controllers 3, 3a, etc., of the type described, positioned at various intersections along a length of street or roadway. The various signal intervals, or'percentage split, may be similarly set up on each interval timing dial l3 by means of the keys l4, l5, l8, I1, l8 and I9. However, the zero positions of the interval timing dials l3, or the initiation of main street green at the successive intersections, may be made to occur sequentially to accommodate traffic proceeding in one direction by setting the secondary dial keys 31, for example, in progressively greater percentage positions on the secondary timing dial 30, thereby to establish a progression along the main street in one direction. Thus, for trafllc proceeding in that direction, the beginnings of the main street green intervals will occur sequentially at successive intersections along the main street. This sequence, however, is not effective for traffic in the opposite direction. In order to set up a similar sequence for traflic in the opposite direction (to be used, for example, at a different time of the day) the secondary dial keys 38 may be progressively positioned so that the main street green intervals are initiated sequentially for traffic in such opposite direction. Similarly, a third desired arrangement may be set up by suitably arranging the dial keys 39 in the various controllers. In order to select any one thus predetermined sequence, it is only necessary to utilize the selector switch 1 at the master controller.

It will now be evident that with such an arrangement, any dwell or stoppage of the intersection timing dial l3 which occurs by reason of necessary resynchronization or by reason of a change in the selected oilset can occur only' durin the main street green interval of that particular controller. This result is effected in accordance with my invention by providing at each intersection one timer which controls only the signal intervals, or percentage split, and a separately driven timer which is synchronized in oil'set relation with the interval timer.

It will now be apparent to those skilled in the art that, while I have shown a triple offset arrangement by way of example, my invention is equally applicable to double offset or other multiple ofiset arrangements. Moreover, while I have illustrated the selector switch I as being manually operated. it will be further evident that, if desired, a program controller or time switch may be utilized to actuate the selector switch. Furthermore, while I have shown fixed cycle time timers wherein the various timing dials and cams are directly connected to the timing motor through fixed gearing, it will be clear to those skilled in the art that, ii desired, means may be provided for controlling the normal cycle time from the master controller. Such remote cycle change meansare described and claimed in Patent 2,328,473, issued to Vincent W. Leonard. It will be evident that if a remote cycle change arrangement such as disclosed in the Leonard patent is utilized in conjunction with my invention, the impulsed clutch of the Leonard patent will be necessary between each of the intersection timing dials and its timing motor.

Finally. while I have illustrated my invention in connection with a system where a rotating master timing element is connected by interconnecting cable to the secondary timing elements, it will be understood by those skilled in the art that the invention is equally applicable to controllers which are each provided with synchronous alternating current motors and connected only locally to the same alternating current supply system. In such an arrangement, the impulsed synchronizing circuit between the master timer and the intersection secondary timer would be omitted, and the supply system frequency would be relied upon to maintain a fixed synchronous positional relationship of the intersection secondary timer 8 with the system generator, such generator then acting as a master timing element.

Thus, while I have described only a preferred embodiment 01' my invention by way of illustration, many modifications will occur to those skilled in the art, and I therefore wish to have is understood that I intend in the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim is:

1.In a trafllc signal control system, a master timing element, a secondary timing element, means for maintaining said master and secondary timing elements in a predetermined fixed synchronous relationship, an interval timing element, and selectable synchronizing means controlled by said secondary timing element for maintaining said secondary and interval timing elements in any one of a plurality of selectable phase displaced synchronous positional relationships.

2. In a trafllc signal control system, a, master timing element, an intersection controller located remotely with respect to said master timing element and including a rotatable secondar timing member, means for maintaining said master element and said secondary timing member in a predetermined fixed synchronous relationship, a rotatable interval timing member in said intersection controller, and selectable synchronizing means actuated by said secondary timing member for maintaining said secondary and interval timing members in any one of a plurality of selectable phase displaced synchronous positional relationships.

3. In a traflic signal control system, a rotatable master timing member having a predetermined cycle time, an intersection controller comprising separately driven rotatable secondary and interval timing members, synchronizing means actuated by said master and secondary timing members for maintaining said master and secondary members in a predetermined fixed phase relation, and selectable synchronizing means including a plurality of selectable synchronizing devices ac-.

timing element having a predetermined cycle time, an intersection controller including sepa-.

rately driven rotatable secondary and interval timing members, means for maintaining said master timing element and said secondary timing member in a predetermined fixed synchronous relation, and local synchronizing means including a device actuated momentarily by said interval timing member at a predetermined fixed position during each revolution and a plurality of selectable devices each actuated momentarily by said secondary timing member at difi'erent predetermined adjustable positions during-each revolution, thereby to maintain said secondary and interval timing members in synchronius relation at any one of a plurality of selectable positions of relative phase displacement.

5. In a traflic signal control system, a master timing element having a predetermined cycle time, an intersection controller including separately driven rotatable secondary and interval timing members, means for maintaining said master timing element and said secondary timing member in a predetermined fixed synchronous relation, means actuated by said interval timing member at a predetermined fixed position in each revolution to stop said interval timing member, and selectable means each actuated momentarily by said secondary timing member once per revolution to disable said stopping means at different selectable positions ofsaid secondary timing member, thereby to maintain said secondary and interval timing members in synchronism in any one of a plurality of selectable phase positional relationship.

6. In a traiiic signal control system, a master timing element having a predetermined cycle time, an intersection controller including separately driven rotatable secondary and signal interval timing members, synchronizing means for maintaining said secondary timing member in fixed synchronous relation with said master timing element, a synchronizing circuit at said intersection controller including means actuated by said interval timing member at a predetermined fixed position during each revolution thereof to stop said interval timing member, a plurality oi selectable means actuated by said secondary timing member for disabling said synchronizing circuit at diflerent predetermined positions during each revolution of said secondary timing member thereby to release said interval timing member, and selector means for rendering said selectable disabling means alternatively operable.

7. In a traillc signal control system, a master timing element having a predetermined cycle time, an intersection controller including separately driven rotatable secondary and signal interval timing members, synchronizing means for maintaining said secondary timing member in fixed synchronous relation with said master timing element, means for stopping said interval timing member comprising a synchronizing circuit interconnecting said secondary and interval timing members and having a pair of normally open contacts and one pair of a plurality of pairs of selectable normally closed contacts connected in series circuit relation, means actuated by said interval timing member to close said normally open contacts momentarily at a predetermined fixed instant once per cycle of said interval timing member thereby to stop said interval timing member, means actuated by said secondary timing member to open each of said plurality of selectable pairs of normally closed contacts momentarily at diflerent predetermined adjustable instants once per cycle of said secondary timing member thereby to release said interval timing member, said closing and selected opening instants coinciding whenever a predetermined synchronous positional relationship exists between said secondary and interval timing members, and switching means for selecting a desired one of said normally closed contacts for operation in said synchronizing circuit.

8. In a traiiic signal control system, a master timing element having a predetermined cycle time, an intersection controller remotely located and including a secondary timing element and a signal interval timing element each having a normal cycle time synchronously related to said predetermined cycle time, means for maintaining said master and secondary timing elements in fixed synchronous relation, local intersection synchronizing means between said secondary and interval timing elements and including a member actuated momentarily once per cycle at a predetermined fixed instant in the cycle of said interval timing element, and selector means for determining a displaced phase relationship of said secondary and interval timing elements including a plurality of members selectably and alternatively included in said local synchronizing means and each actuated momentarily once per cycle at diflerent predetermined instants in the cycle 01' said secondary timing element.

WILLIAM C. PENNELL.

No references cited.

Images