US3023327A

US3023327A - Remotely settable timer

Info

Publication number: US3023327A
Authority: US
Inventors: John D Freeman; Kull Leo
Original assignee: General Time Corp
Current assignee: General Time Corp
Priority date: 1959-10-02
Filing date: 1959-10-02
Publication date: 1962-02-27
Anticipated expiration: 1979-02-27

Description

Feb. 27, 1962 J. D. FREEMAN ET AL 3,023,327

REMOTELY SETTABLE TIMER Filed Oct. 2, 1959 3 Sheets-Sheet 1 Laeo Dull gfh-"romav Feb. 27, 1962 J. D. FREEMAN ET AL 3,023,327

REMOTELY SETTABLE TIMER 3 Sheet-Sheet 2 Filed Oct. 2, 1959 all Leo

United States Patent Ofifice 3,023,327 Patented Feb. 27, 1962 3,023,327 REMOTELY SETTABLE TIMER John D. Freeman, Forest Hills, N.Y., and Leo Kull, Jersey City, N.J., assignors to General Time Corporation, New York, N.Y., a corporation of Delaware Filed Oct. 2, 1959, Ser. No. 844,125 10 Claims. (Cl. 307--141.8)

This present invention relates to control systems for actuation after a given count and relates particularly to remotely-settable interval timers.

Interval timers are often employed for initiating electrical switching operations or other functions at the end of a preset time interval. Their usefulness in many instances depends upon combined high degrees of accuracy, compactness, and reliability. The time interval must often be settable by precise small increments over a very wide range and furthermore, resettable from a remote station. It is the primary purpose of the present application to provide a timer meeting these requirements.

More specifically, it is an object to provide an improved remotely resettable interval timer. It is also an object to provide a portable interval timer in which the interval is conveniently and quickly adjusted and initiated by remote control. It is also an object to provide a simple remote control interval timer which is both compact and reliable. A still further object is to provide an adjustableinterval resetting mechanism for an interval timer which is quickly and conveniently operated. More generally, it is an object to provide a count-responsive automatic control system.

Further advantages and objects of the invention will be apparent in the following description, taken with the drawings in which:

FIGURE 1 schematiaclly illustrates the differential drive and other mechanical elements of a remote control timer;

FIG. 2 is a sectional view taken along line 22 of FIG. illustrating the load program switch operated by the timer upon completion of a timed interval;

FIG. 3 is a sectional view taken along line 33 of FIG. 5 illustrating the position of the first coincidence switch and latch;

FIG. 4 is a sectional view along line 44 of FIG. 5 and with portions further broken away to particularly show the drive stepping means;

FIG. 5 is a side elevation, partially in section, of a remote control timer incorporating the invention and in cluding the mechanism of FIG. 1;

FIG. 6 is a schematic diagram of the electrical and mechanical elements of a system in which the FIG. 5 apparatus is employed.

While the invention is susceptible of various modifications and alternative constructions, a preferred embodiment has been shown in the drawings and will be described below in considerable detail. It should be understood, however, that there is no intention to limit the invention to the specific form disclosed, but on the contrary, the intention is to cover all modifications and alternative constructions falling within the spirit and scope of the invention as expressed in the appended claims.

In the following description, the differential stepping system of a timing mechanism of a preferred embodiment is described in connection with the schematic representation of FIG. 1, prior to the further description of the timing mechanism as compactly arranged and particularly illustrated by FIG. 5. The description of the electrical stepping means and timed switches illustrated in FIGS. 2, 3, and 4 follows. The overall electrical system for both timing and remotely setting the timer is explained in connection with the schematic diagram of FIG. 6. Finally,

the method of operation is further described and summarized.

Referring now to FIG. 1, a switch cam 10 represents the timed element for program control of one or more switches in a timed sequence, which may be extended over the entire period of revolution of the cam. A stepper rotor or ratchet wheel 11 carries the cam 10, suitably on a shaft 12 in the common axis of rotation for the timer mechanism. In the particular example here, the ratchet was selected with 94 steps or teeth. With a stepplng impulse provided every five seconds by a pawl 13 of a stepping mechanism, one rotation of the ratchet wheel 11 repeats the switch cam cycle in 470 seconds, or slightly under eight minutes. While such a cycle can provide a several-minute interval from the initiation of cam rotation to a possible first switching operation, much longer intervals are desired. The simple apparatus here described is designed to provide such intervals adjustably by five-second increments up to 12 hours duration between the initiation of a stepping impulse train and a switching programcontrolled by the cam 10.

To provide a long delay interval without resorting to large ratchet wheels or gear trains, the switching program controlled by cam 10 is disabled until the switching cam has rotated a controlled number of times from a start position. This is effectively accomplishing electrically, and without limitation as to adjustment of the interval, by switches controlled by coincidence of given angular position of first and

second coincidence cams

14 and 15 rotated at a different speed. A latch 16 is suitably employed to lock one switching or tripping mechanism in its actuated position after the cams have passed at the given'angular position. An unlatching device, here shown as a latch pin 17, located on the second coincidence cam 15 several steps after the coincidence position resets the switch or trip to terminate the switching program.

Rather than rotate the second coincidence cam 15 an integral number of times slower than the first cam 14, the cams are preferably driven at only slightly differing speeds. As shown in FIG. 1, a 93-tooth gear 18 coupled to the second coincidence cam 15 is advanced by 94/93 revolution for each revolution of the first coincidence cam 11, which, as previously stated, undergoes one revolution in 94 steps. Starting with a given angular reference position of each coincidence cam, the next coincidence does not occur until the first cam 14 has rotated 93 times and the second cam 94 times. This calls for 8742 ste pping impulses applied to the pawl 13 of the stepping mechanism. A suitable drive for the 93-tooth gear 18 meeting this requirement is provided by a 94-tooth gear 19 mounted on the same shaft with the 94-tooth ratchet 11, the two gears being coupled by

idler gears

21 and 22 on a common shaft (and having the same number of teeth).

Accordingly, for each revolution or ratchet step of cam 14, the second coincidence cam 15 is driven of a revolution. Each cam or ratchet is advanced during each step by the angle subtended by the circular pitch of its gear or ratchet teeth. Two rotor assemblies stepped or indexed simultaneously but at a slight differential rate are thus provided.

:In order to permit the coincidence earns 14 and 15 to be adjusted relative to each other for quick setting of the time interval, ratchet wheel 23 can be independently advanced a step at a time by a pawl 24 of a resetting stepping means. This 93-step ratchet wheel is directly connected to the coincidence cam 15 and is connected through a one-way drive to the 93-tooth gear 19. Such a one-way drive is suitably provided by a 93-step internal ratchet 25 on the ratchet gear 23 through a pawl 26 pivotally connected to the gear 18. With the rotation of the elements on the axis of rotation in a counterclockwise eoaasav the coincidence cam to be advanced in the direction.

of rotation by the resetting stepper by steps of the same angular extent as those transmitted from the rotor assembly driven by the timing stepper pawl 13. Smooth operation of the differential system thus described is assured with reliable and precise stepping in the angular ratio required from a single stepper pawl.

Turning now to FIG. 5, a side view of the FIG. 1 mechanism is presented with the timing and resetting rotor assemblies compactly arranged in a frame defined by

end plates

27 and 28 supported by spacers 29. As shown, the switch cam 10, the stepper ratchet 11, and the 94- tooth gear 19 of the timing rotor are coupled by pins 30 to the first coincidence cam 14 which has a hub portion 31 mounted on the shaft 12. The shaft 12 is supported from the left-side end plate 27 in a bearing 32 and is journaled at its other end in a bushing 33 in turn carried by a bushing 34 mounted in the right-hand end plate 28. As shown, the 93-tooth gear 18 for driving the second coincidence cam rotates on the bushing 34 and has an opening 36 (best viewed in FIG. 4) through which the pawl 26 of the one-way drive extends to advance the internal ratchet 25 of the adjacent ratchet gear 23. The pawl 26 is suitably mounted on a pivot 37 extending as shown from the right-hand side of the gear 18. A pawl spring 38 is mounted on the left-hand side of the gear to assure a driving engagement. The idler gears 21 and 22 for coupling the 93-tooth and 94-

tooth gears

18 and 19 are shown in the lower portion of FIG. 5.

The stepping or indexing actuators employed in this instance for the

stepper pawls

13 and 24 shown in FIG. 4 are suitably solenoid-actuated. Looking to the stepper pawl 13 which advances the ratchet 11 of a revolution for each impulse received, the pawl is pivoted on a stepper magnetic armature member 39. A torque spring 40 urges the pawl 13 against the ratchet wheel 11. To advance and withdraw the pawl, the armature 39 rotates on a pivot 41 alined between spaced pole pieces 42 in a magnetic circuit energized by solenoid coils 43. When the solenoid coils, which may be treated as a single winding, are not energized, an armature tension spring 44 rotates the armature out of alinement with the pole pieces as portrayed in FIG. 4 to pull the pawl away from the ratchet. A stop 45 limits armature movement and a second stop 46 limits the pawl movement for single-step advance. Energization of the solenoids by a stepping pulse rotates the armature in alinement over them to retract the pawl and position it for advancing the ratchet when the armature is withdrawn by its spring 44 after the stepping pulse ends. An anti-reversal pawl 47 directed against the ratchet wheel 11 prevents reverse or counterclockwise (as viewed in FIG. 4) movement of several rotors of the mechanism.

A similar stepping mechanism (shown in the right-hand portion of FIG. 4) is employed for the resetting stepper pawl 24. As shown, an armature assembly 48 is again pivotally mounted in or out of alinement with pole piece 49 of solenoid coils St) to which the resetting impulses are applied.

Referring now to FIG. 2, an exemplary switching cycle controlled by the switch cam 10 is illustrated. For this purpose the circular cam disk, suitably made of insulating material, although permissibly metallic as are the other rotary members of the mechanism, is notched or relieved at circumferentially spaced locations to define cam edges 51 and 52. Thus the full radius leading edge (referring to the direction of rotation) is abruptly cut away for an angular length suitably equal to several steps of cam advance.

Switches

53 and 54 are of a type having a pair of normally open contacts mounted on parallel extended spring fingers. They are supported and positioned on the frame plate 27 for actuation by the cam edges 51 and 52 respectively. An extension 55 of one spring finger of each switch serves as a cam follower urged by that spring finger toward the cam periphery. With the cam follower portion of a switch riding the full radius portion of the cam, the switch is held open. When the edge 51 or 52 of a reduced diameter portion passes the cam follower, the switch snaps closed and remains closed for a number of step advances corresponding to the relieved length of the cam notch. In this embodiment, the cam surfaces and the switch positions are arranged so that switch 54 shown open in FIG. 2 is closed one step (five seconds) after switch 53 is closed (shown closed in FIG. 2). The arrangement of switches is not crowded since none of the cam length is reserved for measuring the interval prior to the initiation of a switching cycle. Obviously further switches can be actuated by the same cam disk or multiple cam disks can be added as desired for a larger program.

A switching assembly 56 is shown in FIGS. 3, 4, and 5 for signalling the end of the timed interval after which the cam 10 control cycle is initiated. Two contact pairs or switches 57 and 53, each mounted side by side on extended parallel spring fingers, are operated simultaneously, and in this instance the upper spring finger is common to both switches. Fo convenience of reference herein, the down direction or movement is toward the cam disk axis of rotation; the upward direction is radially away from the cam. A rigid leaf or member 59 stationed above the lower contact fingers prevents them from springing upward to close the switches. Accordingly the switches can be closed only when the common upper switch finger 58 is depressed. A tongue 60 extends beyond the contact end of the upper spring finger for engagement by a latch when the switch closes. The switches are suitably supported from the end plate 28 and extend adjacent the periphery of the

coincidence cam disks

14 and 15.

Switches 57 and 58 close at what is defined as a first coincidence position of the coincidence earns 14 and 15 and open a given number of incremental steps later. The cam surfaces for establishing the coincidence position are sharply defined notches 61 and 62 in the otherwise circular

respective cam disks

14 and 15. The first coincidence position is defined by that incremental timing step when the notches are angularly alined under a tooth-like edge 63 of a cam follower member 64 which straddles the periphery of both cams. As best shown in FIGS. 3 and 4, the cam follower member 64 swings on pivot means 65 by the frame end plates and bears against the common upper finger of the switches to close the switches when the follower edge 63 bottoms in both notches at the first coincidence position. FIG. 3 illustrates the closed and latched position of the switches 57 and 58 at the first coincidence position, and FIG. 4 illustrates the open and unlatched position.

Since the cams do not stop or otherwise maintain their first coincidence position beyond one five-second stepping interval, a latching action is provided to maintain the switches 56 and 57 closed during a select number of additional incremental steps. A latch member 16 swings on a pivot 68 carried between the frame end plates and its lower end extends downwardly past the end of the switch tongue extension 61 A cam followe spring 611 connected between an ear 7%) on the pivoted cam follower and the latch member 16 provides the tension for both pressing the cam follower tooth 63 against the

cam disks

14 and 15 and for also pulling the latch member against the end of the switch tongue 60. A detent position or shoulder 71 on the latch member keeps the switches closed once the cam follower 64 has entered the cam notches by blocking the upward movement of the tongue 60. When the cams are past the coincidence step, cam follower pivots upwardly against the pressure of spring 69. The switches 57 and 58 remain closed, since the latch member 16 remains in place and its detent 71 does not release the tongue 64).

In order to unlatch the switches, the lower or radially inward end of the latch member 16 is engaged by the unlatching pin 17 carried on coincidence cam 15. The pin is located a selected number of incremental steps behind (i.e., angularly counterclockwise in FIG. 4) the cam notch 62 for an interval sufiicient to complete switching cycle programmed by switch cam 10. In the embodiment illustrated, with pin 17 angularly displaced by 19 steps behind the notch 62, a 95-second interval is provided.

A second coincidence position marks the initiation of a new timed interval before the next switching cycle is operated by cam 1t and suitably coincides with the unlatching of switches 57 and 58. A shut-off switch 73 is accordingly provided for shutting off the stepper at the second coincidence position and is preferably actuated directly from the coincidence cams. This normally-open switch, shown in FIG. 4, is also of the type having parallel spring fingers upon which the switch contacts are mounted. It is stationed on end plate 28 and spaced to follow both

cam disks

14 and 15. A cam follower 74 attached to the end of the upper switch spring finger is urged by that spring finger against the two cams. The switch closes when the follower 74 bottoms in the cam disk notches 61 and 62. The cam follower end portions 75a and 75b riding the respective cams are slightly offset with respect to each other to match the slight angular misalinement of the cam notches occurring 19 steps after the first coincidence position. This mis-alinement is due to the slight differential speed of the timing and resetting rotor assemblies but defines a coincidence position just as unique as the first coincidence position.

The overall electrical and mechanical system is illustrated schematically in FIG. 6. As shown therein a source of power-011 signals 76 is applied to a switchclosing winding 77a of a latching relay 77 connecting a power source 78 to an oscillator 79. The oscillator is suitably a conventional crystal controlled type designed to produce a fixed frequency. Frequency divider circuits 80 reduce the frequency to that desired for the timing steps and suitably amplify each pulse so obtained to meet the power requirements of the stepper winding 43. In a vehicle-mounted apparatus incorporating the preferred embodiment mechanism thus far described, an oscillator frequency of 6553.6 cycles per second was divided by successive magnetic counter stages to ultimately produce a 24 volt, .50 milliampere pulse of 50 milliseconds duration every five seconds. After the oscillator is warmed up, a starting impulse from start source 81 is provided to unblock the frequency divider output and thus initiate the application of stepping signals. In independent vehicles the oscillator and frequency divider are preferably carried by the vehicle with the power-on and starting signals received by wire or radio from a remote control station.

The maximum period defined betweenthe second and first coincidence positions in the direction of rotation is 93 times 94 in five-second steps minus the 19 interval steps allowed between the first and second coincidence positions. Something less than this period is desired as the maximum interval to be chosen in order that the mechanism be advanced from. its off-position and in readiness for actuation by the stepper pulses from the oscillator. The mechanism is reset for timing the selected intervals by the receipt of M and N pulses. The M pulse source 82 is connected to the solenoid coils 50 of the resetting impulse stepper which actuates the pawl 24 driving coincidence cam 15. A source of N reset pulses 83 is connected to the solenoid coil 43 for the timing stepper which drives both of the coincidence cams i4 and 15 as previously described. This pulse source contains switching circuits to effectively disengage them from the solenoid coils when timing pulses are transmitted by the oscillator after the initiation of the timing cycle. The

sources

82 and 83 are advantageously located at a remote control station with the setting pulse signals transmitted by radio and received at the vehicle. There is no requirement that the resetting M and N pulses be limited to the relatively slow five-second repetition rate but the convenience and speed of resetting does not rely upon high frequency resetting signals, as is subsequently described.

Switches

53 and 54 operated by the program cam 10 connect respective loads, termed simply the 30-second load 84 and 35-second load 85, through one of the normally open first coincidence switches 57 to a power source 86.

With the frequency divider connected to the stepper solenoid 43 and actuated by a start signal, the switch cam 10 may rotate several times as the

coincidence cams

14 and 15 differentially rotate from their reset position to the first coincidence position. Until switch 57 closes when the first coincidence is reached at the exact end of the preset interval, the load circuits are disabled. Thirty and thirty-five seconds after the first coincidence, the

switches

53 and 54 then close to perform their programmed functions. The other first coincidence switch 58 provides in this instance an alarm indication by connecting an alarm circuit 87 to the power source 78. The alarm (or further function served) continues until the switches 57 and 58 are unlatched seconds after the first coincidence.

The mechanism is shut off at the second coincidence by closing of the shut-0E switch 73. This switch is in series with the closing coil 77b of one latching relay 77., one of the latching relay contact pairs, and power source 78. When relay 77 is opened, the oscillator is turned off and the power source is disconnected. The coincidence cams remain at the second coincidence position awaiting resetting before another timing cycle can be instituted.

Turning now to the operation of the apparatus, the versatility of the equipment is demonstrated by illustrating the remote setting operation of the time delay interval between a starting pulse supplied from source 81 and the activation of the alarm means 86 which marks the beginning of the load switching program.

The starting point in the cycle is automatically defined by the operation of the shut-ofi switch 73 which leaves the coincidence cams in their second coincidence position. The interval for which the apparatus is thus set is 8723 five-second pulses or 12 hours, 6 minutes and 55 seconds. it will be appreciated that a count of 8723 steps (the product 94x93 minus 19) is required to reach the first coincidence position. First, however, the apparatus must be moved away from the second coincidence position in order to open the shut-off switch 73 and allow the latching relay 77 to be closed by a power-on pulse from source 76.

Accordingly, resetting pulses both put the mechanism in condition to begin a timing operation and also select the timing period. The number of resetting pulses corresponds to the timed diiference between the maximum interval and the one to be programmed. The remaining or programmed interval can be completed through a given interval after pulses are initiated from the frequency divider 80.

Rather than transmit the possibly large number of difference pulses in incremental steps to the timing stepper, a lesser number of pulses is required by applying one reset pulse, from source 82, here called M pulses, to the reset stepper coil 50 for each 94 timing pulses in the difference quantity. The remaining pulses of the difference quantity are then applied as N pulses from source 83 to the timing stepper coil 43.

For example, if an interval of zero hours, 26 minutes and 35 seconds is desired, 319 timing steps are required where each step corresponds to a five-second time unit.

The difference in steps between the maximum available on the mechanism and the selected number is 8723 minus 319 or 8404 steps. Such a number of steps, converted to revolutions of the 93 step coincidence cam, is 8404/94

aoaaear

7 or 89 and 38/94. Accordingly, 89 M pulses are transmitted from the control station to the stepper coil t of the reset mechanism. The fractional remainder is applied as 38 N pulses from source 83 to the stepper coil 43 of the timing stepper.

With the timer interval thus established, the oscillator 79 can be turned on through a power-on pulse from source 76. The starting impulse from source 81 may be delayed for as long as desired. The load program is initialed and the alarm is energized 319 pulses (26 minutes and 35 seconds) after the starting impulse is transmitted. No further signals are required from the control station since the equipment automatically closes itself off at the second coincidence position and erases the previously set time interval.

The particular example of 93 and 94 step ratchets is but one of various differential speeds which may be ob tained. The example here illustrates a large count of steps or increments available for precise resetting with minimum requirements in gear and ratchet sizes. Smaller and larger programs may be designed accordingly. A sole coincidence is always defined in such a differential drive at a number of steps equal to the product of the steps in each rotor where the steps of each rotor are unequal and have no common factors other than one. The angular steps referred to herein and in the claims are those subtended by the ratchet or gear tooth (i.e., corresponding to the circular pitch) where the teeth or steps are uniformly disposed in a circular array. 1t will be further appreciated that by having only a small difference in steps between the two rotors, quite similarly dimensioned teeth and radii are involved, and mechanical stepping problems are avoided.

The intervals represented by each step may be adjusted as desired. They also may represent numerical sequences other than those involved in time delays. As a counter, for example, the mechanism will count or integrate a given number of pulses from a source of either constant or varying frequency.

We claim as our invention:

1. A control means responsive to a predetermined impulse count comprising first and second stepped rotors each having an angular reference position, means for advancing said rotors by uniform single steps in response to each impulse received, the stepping angles of said rotors being of different magnitude to provide a differential rotor rotation, count-initiating means for coupling an impulse train source to said rotor advancing means, means operable in response to the coincidence of said angular reference positions to mark the end of the impulse count, stop means for disconnecting said source of impulses at a given angular displacement of said rotors past said first coincidence position, and resetting means for advancing the rotors relative to each other to select the number of impulses required to advance the rotors to the coincidence position.

2. A control means responsive to a predetermined count of impulses comprising first and second stepped rotors each having an angular reference position, first means for advancing each rotor by a single step in response to each count impulse received, said first and second rotor steps having different magnitudes to provide a differential cam rotation, a second means for advancing one of said rotors independently of the other by a single step in response to each resetting impulse, countinitiating means for coupling an impulse train source to said first rotor advancing means, controlled means operable in response to the coincidence of said angular reference positions, stop means for disconnecting said impulse train source at a given number of steps of said rotors past said first coincidence position, and resetting means for supplying a selected number of resetting impulses to said second rotor advancing means for adjusting said predetermined impulse count required to further advance both rotors to the coincidence position.

3. In an electrical control system for actuation following a preselected number of stepping impulses, a diferential cam system having first and second rotary cams advanced by a uniform angular increment in response to each stepping impulse, the angular increments of the first and second cams being of different angular extent to provide a differential cam movement, said cams having first and second angular coincidence positions, means for starting a train of stepping impulses for advancing said cams to said first coincidence position, a first cam-controlled switch means rcsponsive to the arrival of said cams at said first coincidence position to actuate said control system, a second cam-controlled switch means responsive to arrival of said cams at said second coincidence position for stopping said train of impulses, and resetting means for advancing said cams relative to said second coincidence position independently of said train of impulses to select the number of impulses required to further advance the cams to said first coincidence position.

4. An adjustable-count control system comprising first and second multi-step rotors each having an angular reference position, means for advancing both rotors by a single step in response to each stepping impulse received, the stepping angle of said second rotor differing slightly from that of said first rotor whereby several revolutions of each rotor is required to advance said rotors from one coincidence of said rotor reference positions to the next occurrence thereof, means operable in response to the coincidence of said angular reference positions of said rotors to signify the end of the timed interval, means for stopping said rotors at a predetermined stop position beyond said coincidence position, a first source of stepping impulses having a constant repetition rate, adjusting means for advancing each rotor directly from said stop position to a reset position for the desired number of stepping impulses required to further advance the rotors to the coincidence position, and means for coupling said impulse source to the first and second rotors to initiate the count.

5. An adjustable interval timer comprising first and second stepped rotors each having an angular reference position, means for advancing both rotors by a single step in response to each stepping impulse received, the stepping angle of said second rotor differing from that of said first rotor to provide a differential rotation, means operable in response to the coincidence of said angular reference positions of said rotors to signify the end of the timed interval, means for stopping said rotors at a predetermined stop position beyond said coincidence position, a source of stepping impulses having a constant repetition rate, adjusting means for advancing the rotors from said stop position to a reset position from which the number of stepping impulses required at said repetition rate to differentially advance the rotors to the coincidence position equals the desired interval, and means for coupling said source of stopper impulses to the first and second rotors to initiate the timer interval.

6. A remotely resettable interval timer comprising twomulti-step rotors having different numbers of steps per revolution, a constant repetition rate source of stepping impulses for which each impulse corresponds to an incremental time unit of the timer interval, stepping means for advancing both rotors by their respective stepping angles for each stepping impulse received, a cam carried by one of said rotors for operating an output circuit switch during each revolution of said one of said rotors, means responsive to the angular position of both rotors for disabling the operation of said output circuit except upon coincidence of given angular positions of said rotors. means for rotating one of said rotors independently of the other, resetting means for advancing each of said rotors directly to an angular position of each from which the required number of stepping impulses required to advance both rotors to said co-incidence position equals the desired interval, and means for coupling said impulse source to said stepping means for initiating the timed interval.

7. A remotely resettable interval timer comprising two multi-step rotors having diiferent numbers of steps per revolution, a constant repetition rate source of stepping impulses for which each impulse corresponds to an incremental time unit of the timer interval, stepping means for advancing both rotors by their respective stepping angles for each stepping impulse received, a cam carried by one of said rotors for operating an output circuit switch during each revolution of said one of said rotors, coincidence switch means responsive to the angular position of both rotors for disabling the operation of said output circuit except upon coincidence of given angular position of said rotors, stop switch means responsive to the angular position of both rotors a fixed number of steps beyond said coincidence position to stop said rotors, means for rotating one of said rotors independently of the other, resetting means for advancing each of said rotors directly to an angular position of each from which the required number of stepping impulses required to advance both rotors to said coincidence position equals the desired interval, and means for coupling said impulse source to said stepper for initiating the timed interval.

8. A remote settable interval timer comprising two multi-step rotors having different numbers of steps per revolution, a constant repetition rate source of timing impulses for which each impulse corresponds to an incremental time circuit of the timer interval, a first stepper for advancing each rotor by its own stepping angle for each stepping impulse received, a second stepper for advancing only one of said rotors for each stepping impulse received, means responsive to the angular position of both rotors, operative upon coincidence of given angular positions of said rotors to define the end of the timed interval, means for supplying a given number of setting pulses to said second stepper and a further number to said first stepper for advancing each of said rotors directly to angular positions of each from which the required number of timing impulses required to advance both rotors to said coincidence position equals the desired interval, and means for coupling said source of timing impulses to said first stepper for initiating the timed interval 9. In an interval timer for actuating a control circuit in a desired time interval corresponding to a selected number of impulses of an impulse train, a difi'erential cam system having first and second rotary cams advanced by a uniform angular increment in response to each received impulse, the angular increments of the first and second cams being of different extent to provide a differential movement thereof, said cams having first and second angular coincidence positions, a first cam-controlled switch means responsive to the arrival of said cams at said first coincidence position to actuate said control circuit, a second cam-controlled switch means responsive to arrival of said cams at said second coincidence position to stop the cams, and resetting means for advancing the cams from said second coincidence position to select the number of impulses required to further advance the cams to said first coincidence position.

10. In an interval timer for actuating a control circuit after a preselected time interval corresponding to a selected number of impulses of an impulse train, a differential cam system having first and second rotary cams advanced by a uniform angular increment in response to each received impulse, the angular increments of the first and second cams being of different extent to provide a differential movement thereof, said cams having first and second angular coincidence positions, means for applying a train of impulses to said cam system at a selected instant to initiate the time interval and advance said cams towards said first coincidence position, a first cam-controlled switch means responsive to the arrival of said cams at said first coincidence position to actuate said control circuit, a second cam-controlled switch means responsive to arrival of said cams at said second coincidence position for removing impulse train from said cam system and resetting means for advancing the cams from said second coinsidence position independently of said train of impulses to select the number of such impulses required to further advance the cams to said first coincidence position.

References Cited in the file of this patent UNITED STATES PATENTS