US3732685A

US3732685A - Clock mechanism

Info

Publication number: US3732685A
Application number: US00240623A
Authority: US
Inventors: A Haydon
Original assignee: Tri Tech Inc
Current assignee: Tri Tech Inc
Priority date: 1970-06-12
Filing date: 1972-04-03
Publication date: 1973-05-15
Anticipated expiration: 1990-05-15

Abstract

A clock mechanism driven by a pulsed stepper motor and having planetary reduction gearing which provides a continuous but resilient connection between the motor and the minute hand of the clock at all times. The motor includes a permanent magnet rotor in direct driving relationship with the minute hand, and the rotor poles serve as a magnetic detent to hold the minute hand in discrete angular positions. The mechanism may be employed either in individual clocks or in the secondary clocks of a mastersecondary clock system. In these latter embodiments the secondary clocks additionally include a pair of switches respectively controlled by the minute hand gearing and the hour hand gearing. The switches greatly facilitate the automatic resetting of the clocks in response to appropriate resetting signals from the master unit.

Description

United States Patent 1 1 Haydon 1111 3,732,685 1451 May 15, 1973 SUPPLY 541 CLOCK MECHANISM 902,224 8/1962 Great Britain ..5s 23 D [75] Inventor: Arthur W. Haydon, Middlebury,

Conn. Primary ExammerR1chard B. W1lk1nson 73 A T T h I b Assistant ExaminerEdith C. Simmons Jackmon ss1gnee. r1- ec nc., West ury, Conn. AttorneyLe C. Rbbinson Jr [22] Filed: Apr. 3, 1972 [57] ABSTRACT [21] Appl. No.: 240,623 I v A clock mechamsm driven by a pulsed stepper motor Related U.S. Application Data and having planetary reduction gearing which pro- 63 f I I vides a continuous but resilient connection between 1 fgy gg g g gg NO June the motor and the minute hand of the clock at all times. The motor includes a permanent magnet rotor 52 us. 01 ..58/26,58/8, 58/23 1), in diieet driving reiaeienehip with the minute hand 58/355, 58/855 and the rotor poles serve as a magnetic detent to hold 51 1111. c1 ..G04c 11/04, G046 9/00 the minute hand in diserete angular pesiiiens- The 58 Field of Search ..58/7, 23 R, 23 v, mechanism y be p y either in individual 53 23 1 24 25, 2 34 35 R, 35 w 425 43 clocks or in the secondary clocks ofa master-secondary clock system. In these latter embodiments the [56] References Cited secondary clocks additionally include a pair of switches respectively controlled by the minute hand UNITED STATES PATENTS gearing and the hour hand gearing. The switches 3,011,111 11/1961 Clifford ..58/23 R greatly iaeiiiiate the autemaiie resetting Of the eieeks 3,184,909 5/1965 Lohf et l. in response to appropriate resetting signals from the 3,233,400 2/1966 Haydon ..58/34 master unit.

FOREIGN PATENTS OR APPLICATIONS 21 Claims, 9 Drawing Figures 1,129,446 10/1966 Great Britain ..58/23 D IO r I i 1 5 5 l I I l PIIIJLNSII1NG\ E [9 cLt'iicK I l i I6 {I I I CLgCK 2/ i 5 i 1 i I2 I l i i I 1 4 g I was? 2 l i I l I 1 23 E 12 i n. 1 i STAND-BY 22 POWER I l PATENTED RAY I 51873 SHEET 3 [IF 4 CLOCK MECHANISM CROSS REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of copending application Ser. No. 45,609, filed June 12, 1970 by Arthur W. Haydon now US. Pat. No. 3,685,278.

BACKGROUND OF THE INVENTION This invention relates to clock mechanisms and more particularly to a novel drive arrangement between the motor of the clock and the hands or other time indicating indicia.

The present invention, while of general application, is particularly well suited for use in clocks which are driven by pulsed stepper motors. One advantageous motor of this type is disclosed, for example, in Arthur W. Haydon U. S. Pat. No. 3,495,107 granted Feb. 10, 1970. Rather than being operated continuously, such motors are supplied with intermittent pulses of current and provide a significant reduction in the power consumption of the clocks when compared with more conventional synchronous motors. As more fully explained in Arthur W. Haydon US. Pat. No. 3,643,420 granted Feb. 22, 1972, the stepper motors also exhibit advantages when used to drive the secondary clocks in a master-secondary clock system.

Clock mechanisms of the type employed heretofore have exhibited certain disadvantages. For example, it often was necessary to provide a friction device, clutch or similar interruption in the drive train between the motor and the minute hand of the clock in order to facilitate resetting and to avoid other deleterious effects. In addition, in prior clocks of the type powered by stepper motors a continuous driving connection between the motor and the minute hand resulted in the application of a series of sharp impulses thereto, with the result that the minute hand as well as the second hand, if any, tended to vibrate or jiggle during each movement. Furthermore, in clock mechanisms of the type previously employed, problems arose because of the inertia of the reduction gears, hands, etc., with the result that the energy needed to properly drive the clock was excessive in many instances. These and other difficulties were compounded in cases in which the clocks were used in a clock system, employing a number of secondary clocks, and additional problems resulted from attempts to automatically reset the secondary clocks at periodic intervals to denote the correct time.

SUMMARY One general object of this invention, therefore, is to provide a new and improved drive arrangement for a clock.

More specifically, it is an object of this invention to provide a clock mechanism which has a continuous driving connection between the motor and the hands or other time indicating indicia but which is arranged such that the clock may be readily reset to indicate the correct time.

Another object of the invention is to provide a clock mechanism of the character indicated which is driven by a pulsed stepper motor and includes novel reduction gearing to insure a smooth transfer of motion from the motor to the time indicating indicia.

An additional object of the invention is to provide such a clock mechanism in which the time indicating indicia is affirmatively held in successive discrete positions by the rotor of the motor.

A further object of the invention is to provide a master-secondary clock system in which all of the secondary clocks are automatically and simultaneously resettable to the correct time.

Still another object of the invention is to provide a clock mechanism utilizing comparatively simple mechanical and electrical elements which is economical to manufacture and thoroughly reliable in operation.

In one illustrative embodiment of this invention, the clock mechanism is disposed within a suitable housing or other support member and is driven by a two-wire stepper motor. The stepper motor is of the type which includes a permanent magnet two-pole rotor and an output pinion connected to the rotor. A minute hand gear and an hour hand gear are rotatably carried by a central shaft on the support member and are respectively affixed to the minute hand and the hour hand of the clock. These gears are interconnected by reduction gearing which maintains the minute hand gear in direct driving relationship with the hour hand gear. Interposed between the motor pinion and the minute hand is a resilient planetary reduction gear assembly which drives the minute hand gear in response to each successive increment of motion of the motor.

In accordance with one feature of the invention, in certain particularly important embodiments, the planetary reduction gear assembly serves as a direct but resilient connection between the output pinion of the motor and the minute gear. The resiliency of the planetary gearing enables an extremely smooth transfer of motion to the minute gear without unwanted vibration as a result of the successive increments of energy applied by the stepper motor.

In accordance with another feature of the invention, in several advantageous arrangements, the rotor poles of the motor provide a magnetic detent which holds the minute gear in successive discrete angular positions. Upon the automatic or manual resetting of the clock, the rotor poles automatically maintain the minute gear in its proper time indicating position.

In accordance with a further feature of certain preferred embodiments of the invention, the planetary reduction gearing is supported by a resilient arm member for limited orbital movement relative to the central shaft, and this arm member biases the gearing toward a particular orbital position with respect to the shaft. Upon the application of an input current pulse to the stepper motor, the planetary gearing is rotated in a direction to move it away from its particular orbital position against the bias of the resilient member. The resilient member thereupon returns the gearing toward the particular orbital position and advances the minute gear from one of its discrete angular positions to the succeeding angular position. The arrangement is such that the driving'energy applied to the minute gear is continued after the termination of each input pulse, with the result that the minute gear receives a smooth flow of energy without unwanted vibration.

In accordance with a still further feature of the invention, in some good arrangements, the mechanism is provided with novel circuit means for detecting whether the minute and hour gears are in their correct angular positions, thus facilitating the automatic resetting of the gears in response to appropriate resetting signals.

The term clock", as used herein, means any sort of time indicating, controlling or recording mechanism such as a clock with a dial and hand, a digital clock, a time switch, a repeat cycle timer, an elapsed time indicator, a chart drive, or other instrument where the essential function of the mechanism is dependent on timing intelligence.

g The present invention, as well as further objects and features thereof, will become more fully apparent from the following detailed description of certain preferred embodiments, when read with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic block diagram ofa clock system in accordance with an illustrative embodiment of the invention.

FIG. 2 is a schematic wiring diagram of the electrical circuit for one of the clocks of FIG. 1.

FIG. 3 is a vertical sectional view of a clock mechanism in accordance with an illustrative embodiment of the invention which is suitable for use in the clock sys tem of FIG. 1.

FIG. 4 is a vertical sectional view taken along the line 4-4 in FIG. 3.

FIG. 5 is a vertical sectional view taken along the line 55 in FIG. 3.

FIG. 6 is a fragmentary perspective view of certain of the components shown in FIGS. 3-5.

FIG. 7 is an enlarged fragmentary sectional view similar to a portion of FIG. 4 but with certain parts omitted for purposes of clarity.

FIG. 8 is a fragmentary perspective view of the switch contact structure illustrated in FIG. 7.

FIG. 9 is an enlarged fragmentary sectional view similar to a portion of FIG. 3 but showing certain additional parts.

DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS Before describing the construction and mode of operation of the driving mechanisms for the individual clocks, there will first be given a brief discussion of a master-secondary clock system with which the clock mechanisms are particularly useful. Following the description of the mechanisms themselves, there will be presented a discussion of the way in which the clocks are reset when used in a system of this character.

THE MASTERSECONDARY CLOCK SYSTEM Referring to FIG. 1 of the drawings, there is shown a clock system which comprises a master unit 10 and a series of remotely located secondary units 12. The master unit 10 may or may not include appropriate time-indicating indicia, while each of the secondary units is in the form of a clock. The unit 10 comprises a voltage reducing transformer 16 and a pulsing circuit 18 having a pair of output leads 19 and 20 which are connected to the secondary clocks 12. The pulsing circuit 18 is effective to generate clock pulses at a uniform frequency dependent on the frequency of an alternating current source 21 such as that available from the.

local power company. In the illustrated embodiment, the source 21 comprises a standard 110 volt, 60 cycle ac. power supply, and during normal operation the pulsing circuit 18 is constructed to send out a +6 volt d.c. signal over the

leads

19 and 20. The transmitted signal is interrupted once per minute to provide negative going pulses of from +6 volts to 0 volts. These pulses are simultaneously applied to each of the secondary clocks 12 to advance the hands of the clocks in accordance with the timing intelligence of the source 21.

An auxiliary or stand-by power supply 22 is maintained in electrical circuit relationship with the pulsing circuit 18. Although a wide variety of stand-by power supplies may be employed for this purpose, one particularly advantageous supply is disclosed in U.S. Pat. application Ser. No. 837,774 filed June 30, 1969 by Arthur W. Haydon. Power supplies of this character include a battery or other direct current source and are effective to produce an alternating wave form at an extremely precise and constant frequency. The connection between the supply 22 and the pulsing circuit 18 includes a normally closed relay 23. The relay 23 is normally maintained in its energized or open condition by the alternating current signal from the source 21, thus preventing the transmission of auxiliary power to the pulsing circuit 18. In the event of a power failure or other interruption in the signal from the source 21, the relay moves to its closed position to furnish standby power from the supply to the pulsing circuit. With this arrangement, the individual secondary clocks 12 continue to advance during the interruption.

THE CLOCK DRIVE MECHANISMS As best shown in FIG. 3, each of the secondary clocks 12 includes a pulsed stepper motor 25. The motor 25 illustratively comprises a two-wire stepper motor of the type disclosed in Haydon U.S. Pat. No. 3,495,107 referred to above, although other types of twoand threewire stepper motors also may be employed with good results. The motor 25 is provided with an energizing winding 26 having input leads 27 and 28 which are electrically connected in the secondary clock circuit of FIG. 2 in a manner that will become more fully apparent hereinafter.

The stepper motor 25 is externally mounted on one end of a generally cylindrical housing member 30. A stationary shaft 32 is centrally located within the housing 30, and this shaft protrudes from the housing adjacent the motor 25 to provide support for a rotor 33. The rotor 33 is in the form of a sleeve of ceramic magnetic material which is permanently magnetized to provide a single pair of rotor poles. In a manner more fully described in the above noted Haydon U.S. Pat. No. 3,495,107, the rotor turns through a complete 360 revolution in response to each pulse applied to the energizing winding 26.

The rotor 33 is affixed to a central sleeve 40 which is rotatably carried on the shaft 32 and is integral with a drive pinion 41. The sleeve 40 and the pinion 41 are made from an acetal resin such as Delrin, for example, a registered trademark of E.I. duPont de Nemours & Company. The pinion 41 protrudes into the housing 30 and is in meshing engagement with a planetary reduction gear 42. A pinion 43 is integrally formed with the gear 42 and meshes with a secondary planetary reduction gear 44 having an integrally formed pinion 45. These gears and pinions, as well as the remaining gears and pinions within the clock mechanism, similarly are fabricated from Delrin acetal resin or other suitable material.

As best shown in FIG. 6, the planetary reduction gear 42 and its attached pinion 43, and the planetary reduction gear 44 and its attached pinion 45, are supported by a resilient arm member indicated generally at 50. The arm member 50 is of arcuate configuration and includes two integrally formed

stub shafts

51 and 52 which extend in directions parallel to the central shaft 32 in spaced orbital relationship therewith. The stub shaft 51 is located intermediate the ends of the arm member 50 and rotatably carries the planetary gear 42 and the pinion 43, these components being held in place on the shaft by a push-on fastener 53 (FIG. 4). The stub shaft 52 is disposed at the outer end of the arm member 50 on an offset portion 54, and the planetary gear 44 and attached pinion 45 are rotatably carried by the shaft 52 and are similarly held in place by a push-on fastener 55. The gear 44 protrudes through an opening 57 in the housing 30, for purposes that will become more fully apparent hereinafter.

The arm member 50 is fabricated from Delrin acetal resin or other material which is relatively stiff but exhibits a certain amount of resiliency. The member 50 includes a comparatively thin arcuate portion 60 and a wider, more rigid portion 61. One end of the portion 60 is rigidly held between two inwardly extending

protrusions

62 and 63 which are integrally formed on the interior of the housing 30. The portion 60 extends from the

protrusions

62 and 63 around the central shaft 32 in spaced relationship therewith, and its opposite end merges with the portion 61. This latter portion is provided with an integral bushing 65 for the shaft 32. The portion 61 extends in a radial direction with respect to the shaft 32 and supports the stub shaft 51 for the planetary gear 42 and attached pinion 43 and the offset portion 54 carrying the stub shaft 52 for the planetary gear 44 and attached pinion 45. The arrangement is such that the portion 61 maintains the respective planetary gear and pinion assemblies at fixed but different radial distances from the shaft 32, while the flexibility of the portion 60 permits each assembly to move orbitally relative to the shaft against the resilient bias of the arm member. The planetary gear and pinion assemblies are thus resiliently biased toward particular orbital positions (the positions shown in FIG. 4) with respect to the shaft.

Disposed around the central shaft 32 in meshing engagement with the pinion 45 is a timing or minute hand gear 70. As a result of the planetary gearing on the comparatively rigid portion 61 of the arm member 50, the output pinion 41 of the stepper motor 25 is maintained in direct driving relationship with the minute gear 70 at all times. The various gear ratios are such that the gear 70 rotates through an angle of six degrees in response to each complete revolution of the output pinion 41. In cases in which the motor winding 26 is pulsed at a rate of once per minute, the rotor 33 and the pinion 41 rotate 360 during each minute, with the result that the gear 70 turns through a complete revolution once per hour. A minute hand sleeve 71 is integrally formed with the gear 70, and this sleeve is disposed around the central shaft 32 and protrudes from the side of the housing 30 opposite that adjacent the motor 25. The protruding end of the sleeve 71 is provided with a self-tapping screw 72 which serves to affix the minute hand (not shown) to the sleeve.

An hour gear 75 is rotatably positioned around the minute hand sleeve 71 between the minute gear 70 and the adjacent wall of the housing 30. The hour gear 75 is driven by the minute gear through reduction gearing which comprises a pinion 77 integral with the sleeve 71, a planetary gear 78 rotatably carried on a stub shaft 79 and a pinion 80 integral with the gear 78. The stub shaft 79 protrudes from the adjacent inner wall of the housing 30 in spaced parallel relationship with the central shaft 32 and is provided with a push-on fastener 81 to hold the gear and pinion in place. The minute pinion 77 meshes with the planetary gear 78 and the pinion 80 meshes with the hour gear 80 to maintain the minute gear in direct driving relationship with the all times. The gear ratios are such that the hour gear rotates through an angle of 30 in response to each complete revolution of the minute gear. A sleeve 82 is affixed to the hour gear, and this sleeve protrudes from the housing 30 in coaxial relationship with the minute hand sleeve 71 and the central shaft 32. As will be understood, an hour hand (not shown) is suitably secured to the sleeve 82.

DRIVE MECHANISM OPERATION Upon the application of each successive current pulse to the energizing winding 26 of the stepper motor 25, the rotor 33 of the motor turns through a complete revolution. The output pinion 41 similarly rotates through a complete revolution about the central shaft 32, the pinion being driven in a clockwise direction, as viewed in FIG. 4. The pinion 4] drives the planetary gear 42 and the attached pinion 43 in a counterclock wise direction, and this latter pinion in turn drives the planetary gear 44 and the attached pinion 45 clockwise.

Particularly during the initial portion of the rotation of the planetary reduction gear 44 and the attached pinion 45, the inertia of the succeeding gears and pinions in the train, and particularly the minute and hour hands of the clock, tend to hold the minute gear 70 stationary. As a result, the rotational axis of the planetary gear 44 and the pinion 45, as well as the rotational axis of the planetary gear 42 and the pinion 43, undergo limited orbital movement relative to the central shaft 32 against the resilient bias provided by the flexible arm member 50. This movement carries the planetary gears and pinions to the right (clockwise) from the particular orbital positions illustrated in FIG. 4. Thereafter, the stored energy in the arm member 50 returns the planetary gears and pinions to their particular orbital positions, and the pinion 45 acts on the minute gear 70 to advance the gear through a six degree angle. The

minute gear in turns moves the sleeve 71 and the minute hand of the clock to the next discrete position corresponding to the succeeding minute.

As the minute gear 70 steps forward, the pinion 77 thereon drives the reduction gear 78 and the attached pinion 8 0 to advance the hour gear 75. The reduction gear train comprising the gear 78 and the pinion 80 is in meshing engagement with both the minute gear 70 and the hour gear at all times, thus maintaining the minute gear in direct driving relationship with the hour gear. The hour gear, its attached sleeve 82 and the hour hand of the clock complete one revolution every 12 hours in the usual way.

As indicated heretofore, the planetary reduction gearing carried by the resilient arm member 50 is in continuous meshing engagement with both the motor pinion 41 and the minute gear 70 at all times during the rotation of the minute gear, thus maintaining the pinion 41 and the attached permanent magnet rotor 33 in direct driving relationship with the gear 70. The poles of the rotor 33 provide a magnetic detent which holds the minute gear 70 and hence the minute hand in discrete angular positions relative to the central shaft 32 which correspond to the successive minutes of the clock. In order to manually reset the clock to the correct time, the protruding portion of the planetary reduction gear 44 is turned in the desired direction to bring the minute hand into its approximate correct position. Because of the magnetic detent provided by the rotor 33, the minute hand thereupon automatically moves to its proper time indicating position.

THE RESETTING MECHANISM In cases in which the clock mechanism is arranged for automatic resetting at preselected intervals, the minute gear 70 and the hour gear 75 are respectively provided with rectangular openings 85 and 86 (FIGS. 7 and 9) at preselected positions. In the illustrated embodiment the opening 85 in the minute gear 70 is oriented with respect to the minute hand of the clock at the 58 minute position, and the opening passes this position once each hour. The opening 86 in the hour gear 75 is located at the 2:58 position, and for a 12 hour clock the opening passes this position twice a day.

The minute gear opening 85 cooperates with a pair of normally closed

contact wires

88 and 89, and the hour gear opening 86 cooperates with a pair of normally closed

contact wires

90 and 91. The

wires

88 and 91 are stationary, while the

wires

89 and 90 are resiliently biased toward the

respective gears

70 and 75 and are arranged to move into and out of the

opening

85 or 86 as the corresponding gear rotates. The movement of the

wire

89 or 90 into the

opening

85 or 86 serves to carry the wire away from its

adjacent wire

88 or 91 to open an electrical circuit.

The

contact wires

88, 89, 90 and 91 are supported by a terminal block 95 which is integrally formed with the adjacent portion of the housing 30. The

wires

88, 89, 90 and 91 are respectively connected within the block 95 to corresponding leads 97, 98, 99 and 100. These leads are arranged in the secondary clock circuit shown schematically in FIG. 2. The lead 97 is connected through a resistor 106 to the input line 19, and the lead 98 is connected to the anode of a diode rectifier 105, the cathode of which leads to the motor terminal 27. The

minute gear contacts

88 and 89 are thus in series with the motor 25. The

hour gear contacts

90 and 91 are in parallel with the

minute gear contacts

88 and 89. The lead 99 for the contact 90 is connected to the lead 98 for the contact 89, while the lead 100 for the contact 91 is connected to the cathode of a Zener diode 107. the anode of the diode 107 is connected to the lead 97 for the contact 88. A second Zener diode 108 is connected across the

contacts

90 and 91 with its cathode connected to the lead 99 and its anode connected to the lead 100.

The base of a P-N-P transistor 110 leads through a resistor 111 to the common terminal of the

switch contacts

89 and 90. The emitter of the transistor 110 is connected to the cathode of the diode 105, while the collector is connected through a resistor 112 to the base of an N-P-N transistor 113 and through a biasing resistor 114 to the grounded input lead 20. The emitter of this latter transistor likewise is connected to the input lead 20, and the collector is connected to the motor terminal 28. The circuit additionally includes a condenser 115 connected between the motor terminal 27 and the emitter of the transistor 113 and a low voltage battery 116 in parallel with the condenser.

CIRCUIT OPERATION The pulsing unit 18 (FIG. 1) normally maintains a low level direct current signal, illustratively +6 volts, across the

leads

19 and 20. With the

minute contacts

88 and 89 and the

hour contacts

90 and 91 in their closed positions, the incoming signal maintains the transistor 110 in a nonconducting condition and charges the condenser 115 through the diode 105. The transistor l13'also is nonconducting at this point to break the circuit for the motor 25.

As indicated heretofore, the incoming signal is interrupted once per minute to provide negative going pulses to the individual clock mechanisms. Upon the receipt of each of these pulses, the transistor 110 is rendered conducting and the transistor 113 also conducts to connect the condenser 115 across the motor 25 and apply a sharp stepping pulse to the motor winding. The rotor of the motor 25 steps a full 360 in response to the applied pulse to advance the clock mechanism one minute in the manner described above.

The master unit 10 additionally includes a reset unit indicated generally at 120. The unit 120 is arranged to send out particular resetting pulses over the

leads

19 and 20 at preselected intervals corresponding to the times at which the secondary clocks 12 are to be reset. If, for example, the clocks 12 are to be reset at 58 minutes after each hour, in the illustrated embodiment the unit 120 causes the generation of a 30 second pulse train at the rate of 30 pulses per second beginning at the 58th minute. This pulse train is produced by shorting the low voltage d.c. signal on the leads l9 and 20 at the selected rate.

For those secondary clocks 12 which are on time at the 58th minute, the contact wire 89 (FIGS. 7-9) is located within the minute gear opening to break the circuit between the

wires

88 and 89. The Zener diode 107 (FIG. 2) is thus connected in series with the triggering transistor 110 to block the triggering of the transistor and momentarily prevent the further advance of the minute hand. For those clocks which are too fast, a similar blocking occurs. If a particular clock is too slow, the 30 pulse per second signal from the master unit rapidly steps the rotor of the motor 25 until such time as the minute hand gear for that clock reaches the 58 minute position, at which point the

contacts

88 and 89 open and the diode 107 blocks the further pulsing of the motor.

At 58 minutes and 30 seconds after each hour, the train of resetting pulses from the master unit is arrested, and the normal low voltage d.c. signal appears across the

leads

19 and 20. At 59 minutes after each hour, the reset unit 120 sends a single -l2 volt pulse over the leads l9 and 20 to each of the secondary clocks. The voltage of this pulse is outside the operating range of the Zener diode 107, and the pulse accordingly is transmitted through the diode and the closed hour hand contacts and 91 to turn on the transistor 110. The transistor triggers the transistor 113 to switch it to its conducting condition and thereby apply a pulse from the condenser to the motor 25. The minute hands for all of the clocks are thus simultaneously advanced from the 58 minute position to the 59 minute position. Thereafter, the application of the successive minute pulses to the clocks continues in the manner described heretofore.

Similarly, at 2:58 am. and p.m., the reset unit 120 transmits a train of 30 pulses per second to the secondary clocks 12 for 30 seconds. These latter pulses comprise voltage variations across the

leads

19 and 20 of from +6 volts to 6 volts. If both the

minute hand contacts

88 and 89 and the

hour hand contacts

90 and 91 are in their open positions, indicating that the minute and hour hands are at the correct time or are too fast, the incoming train of pulses is blocked by the

seriesconnected Zener diodes

107 and 108. If, on the other hand, the

contacts

88 and 89 are closed, representing a slow minute hand, the resetting pulses trigger the secondary clock circuit and rapidly advance the rotor of the motor 25 until the minute hand reaches the correct position. Should the

hour hand contacts

90 and 91 be closed, the resetting pulses likewise trigger the circuit to advance the rotor until the hour hand reaches its correct position. In this latter situation, if the

contacts

88 and 89 are closed the resetting pulses are transmitted across the contacts to the base of the transistor 1 10, while if the

contacts

88 and 89 are open the pulses proceed to the transistor through the Zener diode 107 and the

contacts

90 and 91.

At 2:59 am. and p.m., a single l2 volt pulse is transmitted from the reset unit 120 over the

leads

19 and 20 to the secondary clocks 12. The pulse passes through the series-connected

Zener diodes

107 and 108 to simultaneously advance the minute hands of all of the clocks and thus close the minute and hour hand contacts and restore the system to normal operation.

The reset rate of thirty pulses per second is 1800 times the normal rate of one pulse per minute. With this arrangement, the maximum amount of time required to reset the minute hand is at most less than 2 seconds, depending upon the amount of error, and the maximum time required to reset the hour hand as well as the minute hand is less than 30 seconds. Of course, many types of clock systems exhibit sufficient timing accuracy that the reset rate may be substantially less than 30 pulses per second, and some systems may be sufficiently accurate that the resetting circuitry may be dispensed with entirely.

The current applied to the condenser 115 after each incoming pulse from the master unit should be sufficient to recharge the condenser preparatory to the receipt ,of the next pulse. During resetting and in other cases in which the line current from the master unit may be at too low a level for this purpose, such as when there are a large number of secondary clocks onthe line, the battery 116 provides the desired recharging current. For comparatively low reset pulse rates or in other situations in which sufficient charging current is available from the master unit, the battery 116 may be eliminated from the circuit without deleterious effect.

In the illustrated embodiment of the invention the

minute hand contacts

88 and 89 and the

hour hand contacts

90 and 91 are opened in response to the movement of the gear openings 85 and 86 (FIG. 7) into their preselected positions. In other advantageous arrangements the contacts may be in the form of reed switches, for example, and the openings'85 and 86 may be replaced by small permanently magnetized elements at the selected positions on the minute gear 70 and the hour gear 75. The reed switches are normally closed but are opened as the magnetic elements move into juxtaposition therewith.

The terms and expressions which have been employed are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions of excluding equivalents of the features shown and described, or portions thereof, it being recognized that various modifications are possible within the scope of the invention claimed.

What is claimed is: 1. In a clock, in combination: a support member; drive means mounted on the support member; a shaft carried by the support member; timing means rotatable about the axis of the shaft; planetary reduction means interconnecting the drive means and the timing means for maintaining the drive means in direct driving relationship with the timing means at all times during its rotation;

means for supporting the planetary reduction means for limited orbital movement relative to the shaft and for resiliently biasing said planetary reduction means toward a particular orbital position with respect thereto; and

means for actuating the drive means to move the planetary reduction means away from said particular orbital position against its resilient bias and to rotate the timing means.

2. In a clock as defined in claim 1, the drive means comprising a pulsed stepper motor having a rotor including a plurality of permanently magnetized rotor poles, the rotor poles providing a magnetic detent to hold the timing means in discrete angular positions relative to said shaft.

3. In a clock, in combination:

a support member;

drive means mounted on the support member;

a shaft carried by the support member;

timing means rotatable about the axis of the shaft;

planetary reduction means in continuous engagement with both the drive means and the timing means at all times during its rotation, to maintain the drive means in direct driving relationship with the timing means;

means for rotatably supporting the planetary reduction means for limited orbital movement relative to the shaft and for resiliently biasing said planetary reduction means toward a particular orbital position with respect thereto; and

means for actuating the drive means to rotate the planetary reduction means in a direction to move the same away from said particular orbital position against its resilient bias, the planetary reduction means thereupon returning toward said orbital position to advance the timing means.

4. In a clock, in combination:

a support member;

drive means mounted on the support member and having an output pinion;

a central shaft carried by the support member;

timing gear means rotatable about the axis of the central shaft;

planetary reduction gearing in continuous meshing engagement with both the output pinion and the timing gear means at all times during its rotation,

to maintain the pinion in direct driving relationship with the timing gear means;

resilient means for rotatably supporting the planetary reduction gearing for limited orbital movement relative to the central shaft and for resiliently biasing said planetary reduction gearing toward a particular orbital position with respect thereto; and

means for actuating the drive means to rotate the planetary reduction gearing in a direction to move the same away from said particular orbital position against the bias of the resilient means, the resilient means thereupon returning said planetary reduction gearing toward said orbital position to advance the timing gear means.

5. In a clock, in combination:

a support member;

drive means including a pulsed stepper motor mounted on the support member, the motor having a permanent magnet rotor and an output pinion connected to the rotor;

a shaft carried by the support member;

timing gear means rotatable about the axis of the shaft;

to maintain the pinion in direct driving relationship with the timing gear means, the rotor of the motor providing a magnetic detent to hold the timing gear means in discrete angular positions relative to the shaft;

resilient means for rotatably supporting the planetary reduction gearing for limited orbital movement relative to the shaft and for resiliently biasing said planetary reduction gearing toward a particular orbital position with respect thereto; and

means for applying electrical pulses to the stepper motor to rotate the planetary reduction gearing in a direction to move the same away from said particular orbital position against the bias of the resilient means, the resilient means thereupon returning said planetary reduction gearing toward said orbital position to move the timing gear means from one of its discrete angular positions to an adjacent angular position.

6. In a clock, in combination:

a support member;

drive means mounted on the support member;

a central shaft carried by the support member;

minute gear means rotatable about the axis of the central shaft;

hour gear means rotatable about the axis of the central shaft;

means for maintaining the minute gear means in direct driving relationship with the hour gear means;

planetary reduction means interconnecting the drive means and the minute gear means;

means for supporting the planetary reduction means for limited orbital movement relative to the central shaft and for resiliently biasing said planetary reduction means toward a particular orbital position with respect thereto; and

means for actuating the drive means to move the planetary reduction means away from said particular orbital position against its resilient bias and to rotate the minute gear means.

7. In a clock as defined in claim 6, in which the means for supporting the planetary reduction means comprises a flexible arm member mounted on said support member.

8. In a clock as defined in claim 6, in which the planetary reduction means comprises a plurality of planetary gears supported at different distances from the central shaft.

9. In a clock, in combination:

a support member;

drive means including a pulsed stepper motor mounted on the support member, the motor having a permanent magnet rotor and an output pinion connected to the rotor; I

a shaft carried by the support member;

minute gear means rotatable about the axis of the shaft;

hour gear means rotatable about the axis of the shaft;

planetary reduction means interconnecting the output pinion and the minute gear means;

resilient means for supporting the planetary reduction means for limited orbital movement relative to the shaft and for resiliently biasing said planetary reduction means toward a particular orbital position with respect thereto; and

means for applying electrical pulses to the stepper motor to move the planetary reduction means away from said particular orbital position against the bias of the resilient means and to rotate the minute gear means.

10. In a clock as defined in claim 9, which further comprises means for applying resetting pulses to the stepper motor at preselected intervals; and

means for disabling the minute gear means during the application of the resetting pulses when the minute gear means is in its correct angular position.

11. In a clock, in combination:

a support member;

drive means including a pulsed stepper motor mounted on the support member and an output pinion driven by the motor;

a central shaft carried by the support member;

minute gear means rotatable about the axis of the central shaft;

hour gear means rotatable about the axis of the central shaft;

first reduction gearing in meshing engagement with both the minute gear means and the hour gear means for maintaining the minute gear means in direct driving relationship with the hour gear means;

planetary reduction gearing in meshing engagement with both the output pinion and the minute gear means, to maintain the pinion in direct driving relationship with the minute gear means; a

means for applying electrical pulses to the stepper motor to rotate the planetary reduction gearing in a direction to move the same away fromsaid particular orbital position against the bias of the resilient means, the resilient means thereupon returning said planetary reduction gearing toward said orbital position to rotate the minute gear means.

12. In a clock, in combination:

a support member;

drive means including a pulsed stepper motor mounted on the support member, the motor having a permanent magnet two-pole rotor and an output pinion connected to the rotor;

a central shaft carried by the support member;

minute gear means rotatable about the axis of the central shaft;

hour gear means rotatable about the axis of the central shaft;

first reduction gearing in meshing engagement with both the minute gear means and the hour gear means for maintaining the' minute gear means in direct driving relationship with the hour gear means;

planetary reduction gearing in continuous meshing engagement with both the output pinion and the minute gear means at all times during its rotation, to maintain the pinion in direct driving relationship with the minute gear means, the rotor poles of the motor providing a magnetic detent to hold the min ute gear means in discrete angular positions rela tive to the central shaft;

means for applying electrical pulses to the stepper motor to rotate the planetary'reduction' gearing in a direction to move the same away from said particular orbital position against the bias of the resilient means, the resilient means thereupon returning said planetary reduction gearing toward said orbital position to move the minute gear means from one of its discrete angular positions to an adjacent angular position.

13. In a clock, in combination;

a support member;

a central shaft carried by'the support member;

minute gear means rotatable about the axis of the central shaft;

hour gear meansrotatable about'the axis of the central shaft;

first reduction. gearing in meshing engagement with both the minute gear means and the hour gear means formaintaining the minute gear means in direct driving relationship with the hour gear means;

planetary reduction gearing in meshing engagement with both the output pinion and the minute gear means, to maintain the pinion in direct driving relationship with the minute gear means;

means for rotatably supporting the planetary reduction gearing for limited orbital movement relative to the central shaft and for resiliently biasing said planetary reduction gearing towarda particular orbital positionwith respect thereto;

means for applying clock pulses to the stepper motor to move the planetary reduction gearing away from said particular orbital position against its resilient bias and to rotate the minute gear means and the hour gear means at timing speed; and

means for applying resetting pulses to the stepper motor to rotate at least one of said gear means at a speed higher than said timing speed. 14. In a clock as defined in claim 13 which further comprises switching means controlled by said one gear means for disabling the stepper motor when said one gear means is in a particular angular position; and

means for thereafter enabling the stepper motor to condition the same for the receipt of successive clock pulses.

15. In a clock as defined in claim 14, in which said one gear means is the minute gear means.

16. In a clock as defined in claim 14, in which the switching means comprises a pair of normally closed contacts, and said one gear means includes actuating means for opening said contacts when the one gear means is in said particular angular position.

17. In a clock, in combination:

a support member;

a central shaft carried by the support member;

minute gear means rotatable about the axis of the central shaft;

hour gear means rotatable about the axis of the central shaft;

planetary reduction gearing in meshing engagement with both the output pinion and the minute gear means, to maintain the pinion in direct driving relationship with the minute gear means; resilient means for rotatably supporting the planetary reduction gearing for limited orbital movement relative to the central shaft and for resiliently biasing said planetary reduction gearing toward a particular orbital position with respect thereto; means for applying clock pulses to the stepper motor to move the planetary reduction gearing away from said particular orbital position against the bias of the resilient means and to rotate the minute gear means and the hour gear means at timing speed;

means for applying resetting pulses'to the stepper motor to rotate the minute gear'means and the hour gear means at a speed higher than said timing speed; and

means including first and second switch contacts respectively controlled by theiminute gear means and the hour gear meansilfoi disabling the stepper motor when the corresponding gear means is in a selected angular position.

18. In a clock, in combination:

a support member;

drive means including a pulsed stepper motor mounted on the support member, the motor having a permanent magnet rotor and an outputpinion connected to the rotor;

a central shaft carried by the support member;

minute gear means rotatable about the axis of the central shaft; hour gear means rotatable about the axis of the central shaft;

planetary reduction gearing in continuous meshing engagement with both the output pinion and the minute gear means at all times during its rotation, to maintain the pinion in direct driving relationship with the minute gear means, the rotor poles of the motor providing a magnetic detent to hold the minute gear means in discrete angular positions rela tive to the central shaft;

resilient means for rotatably supporting the planetary reduction gearing for limited orbital movement relative to the central shaft and for resiliently biasing said planetary reduction gearing toward a particular orbital position with respect thereto;

means for applying clock pulses to the stepper motor to rotate the planetary reduction gearing in a direction to move the same away from said particular orbital position against the bias of the resilient means, the resilient means thereupon returning said planetary reduction gearing toward said orbital position to move the minute gear means at timing from one of its discrete angular positions to an adjacent angular position; and

means for applying resetting pulses to the stepper motor to rotate the minute gear means at a speed higher than said timing speed.

19. In a clock as defined in claim 18, in which the resilient means includes a flexible arm member mounted on the support member, and in which the planetary reduction gearing includes a plurality of planetary gears carried by the arm member.

20. In a clock as defined in claim 19, in which the planetary gears are carried by the arm member at different distances from the central shaft.

21. In a clock, in combination:

a support member;

a central shaft carried by the support member;

minute gear means rotatable about the axis of the central shaft and having an opening in a preselected position thereon;

hour gear means rotatable about the axis of the central shaft;

planetary reduction gearing in continuous meshing engagement with both the output pinion and the minute gear means at all times during its rotation, to maintain the pinion in direct driving relationship with the minute gear means, the rotor poles of the motor providing a magnetic detent to hold the minute gear means in discrete angular positions relative to the central shaft;

means for applying clock pulses to the stepper motor to rotate the planetary reduction gearing in a direction to move the same away from said particular orbital position against the bias of the resilient means, the resilient means thereupon returning said planetary reduction gearing toward said orbital position to move the minute gear means at timing speed from one of its discrete angular positions to an adjacent angular position;

means for applying resetting pulses to the stepper motor to rotate the minute gear means at a speed higher than said timing speed;

switching means including a contact member movable into the opening in the minute gear means for disabling the stepper motor when the minute gear means is in its correct timing position; and

means for thereafter applying an enabling pulse to the stepper motor to condition the same for the receipt of said clock pulses.

Claims

1. In a clock, in combination: a support member; drive means mounted on the support member; a shaft carried by the support member; timing means rotatable about the axis of the shaft; planetary reduction means interconnecting the drive means and the timing means for maintaining the drive means in direct driving relationship with the timing means at all times during its rotation; means for supporting the planetary reduction means for limited orbital movement relative to the shaft and for resiliently biasing said planetary reduction means toward a particular orbital position with respect thereto; and means for actuating the drive means to move the planetary reduction means away from said particular orbital position against its resilient bias and to rotate the timing means.

3. In a clock, in combination: a support member; drive means mounted on the support member; a shaft carried by the support member; timing means rotatable about the axis of the shaft; planetary reduction means in continuous engagement with both the drive means and the timing means at all times during its rotation, to maintain the drive means in direct driving relationship with the timing means; means for rotatably supporting the planetary reduction means for limited orbital movement relative to the shaft and for resiliently biasing said planetary reduction means toward a particular orbital position with respect thereto; and means for actuating the drive means to rotate the planetary reduction means in a direction to move the same away from said particular orbital position against its resilient bias, the planetary reduction means thereupon returning toward said orbital position to advance the timing means.

4. In a clock, in combination: a support member; drive means mounted on the support member and having an output pinion; a central shaft carried by the support member; timing gear means rotatable about the axis of the central shaft; planetary reduction gearing in continuous meshing engagement with both the output pinion and the timing gear means at all times during its rotation, to maintain the pinion in direct driving relationship with the timing gear means; resilient means for rotatably supporting the planetary reduction gearing for limited orbital movement relative to the central shaft and for resiliently biasing said planetary reduction gearing toward a particular orbital position with respect thereto; and means for actuating the drive means to rotate the planetary reduction gearing in a direction to move the same away from said particular orbital position against the bias of the resilient means, the resilient means thereupon returning said planetary reduction gearing toward said orbital position to advance the timing gear means.

5. In a clock, in combination: a support member; drive means including a pulsed stepper motor mounted on the support member, the motor having a permanEnt magnet rotor and an output pinion connected to the rotor; a shaft carried by the support member; timing gear means rotatable about the axis of the shaft; planetary reduction gearing in continuous meshing engagement with both the output pinion and the timing gear means at all times during its rotation, to maintain the pinion in direct driving relationship with the timing gear means, the rotor of the motor providing a magnetic detent to hold the timing gear means in discrete angular positions relative to the shaft; resilient means for rotatably supporting the planetary reduction gearing for limited orbital movement relative to the shaft and for resiliently biasing said planetary reduction gearing toward a particular orbital position with respect thereto; and means for applying electrical pulses to the stepper motor to rotate the planetary reduction gearing in a direction to move the same away from said particular orbital position against the bias of the resilient means, the resilient means thereupon returning said planetary reduction gearing toward said orbital position to move the timing gear means from one of its discrete angular positions to an adjacent angular position.

6. In a clock, in combination: a support member; drive means mounted on the support member; a central shaft carried by the support member; minute gear means rotatable about the axis of the central shaft; hour gear means rotatable about the axis of the central shaft; means for maintaining the minute gear means in direct driving relationship with the hour gear means; planetary reduction means interconnecting the drive means and the minute gear means; means for supporting the planetary reduction means for limited orbital movement relative to the central shaft and for resiliently biasing said planetary reduction means toward a particular orbital position with respect thereto; and means for actuating the drive means to move the planetary reduction means away from said particular orbital position against its resilient bias and to rotate the minute gear means.

9. In a clock, in combination: a support member; drive means including a pulsed stepper motor mounted on the support member, the motor having a permanent magnet rotor and an output pinion connected to the rotor; a shaft carried by the support member; minute gear means rotatable about the axis of the shaft; hour gear means rotatable about the axis of the shaft; means for maintaining the minute gear means in direct driving relationship with the hour gear means; planetary reduction means interconnecting the output pinion and the minute gear means; resilient means for supporting the planetary reduction means for limited orbital movement relative to the shaft and for resiliently biasing said planetary reduction means toward a particular orbital position with respect thereto; and means for applying electrical pulses to the stepper motor to move the planetary reduction means away from said particular orbital position against the bias of the resilient means and to rotate the minute gear means.

10. In a clock as defined in claim 9, which further comprises means for applying resetting pulses to the stepper motor at preselected intervals; and means for disabling the minute gear means during the application of the resetting pulses when the minute gear means is in its correct angular position.

11. In a clock, in combination: a support member; drive means including a pulsed stepper motor mounted on the support member and an output pinion driven by the motor; a central shaft carrieD by the support member; minute gear means rotatable about the axis of the central shaft; hour gear means rotatable about the axis of the central shaft; first reduction gearing in meshing engagement with both the minute gear means and the hour gear means for maintaining the minute gear means in direct driving relationship with the hour gear means; planetary reduction gearing in meshing engagement with both the output pinion and the minute gear means, to maintain the pinion in direct driving relationship with the minute gear means; resilient means for rotatably supporting the planetary reduction gearing for limited orbital movement relative to the central shaft and for resiliently biasing said planetary reduction gearing toward a particular orbital position with respect thereto; and means for applying electrical pulses to the stepper motor to rotate the planetary reduction gearing in a direction to move the same away from said particular orbital position against the bias of the resilient means, the resilient means thereupon returning said planetary reduction gearing toward said orbital position to rotate the minute gear means.

12. In a clock, in combination: a support member; drive means including a pulsed stepper motor mounted on the support member, the motor having a permanent magnet two-pole rotor and an output pinion connected to the rotor; a central shaft carried by the support member; minute gear means rotatable about the axis of the central shaft; hour gear means rotatable about the axis of the central shaft; first reduction gearing in meshing engagement with both the minute gear means and the hour gear means for maintaining the minute gear means in direct driving relationship with the hour gear means; planetary reduction gearing in continuous meshing engagement with both the output pinion and the minute gear means at all times during its rotation, to maintain the pinion in direct driving relationship with the minute gear means, the rotor poles of the motor providing a magnetic detent to hold the minute gear means in discrete angular positions relative to the central shaft; resilient means for rotatably supporting the planetary reduction gearing for limited orbital movement relative to the central shaft and for resiliently biasing said planetary reduction gearing toward a particular orbital position with respect thereto; and means for applying electrical pulses to the stepper motor to rotate the planetary reduction gearing in a direction to move the same away from said particular orbital position against the bias of the resilient means, the resilient means thereupon returning said planetary reduction gearing toward said orbital position to move the minute gear means from one of its discrete angular positions to an adjacent angular position.

13. In a clock, in combination: a support member; drive means including a pulsed stepper motor mounted on the support member and an output pinion driven by the motor; a central shaft carried by the support member; minute gear means rotatable about the axis of the central shaft; hour gear means rotatable about the axis of the central shaft; first reduction gearing in meshing engagement with both the minute gear means and the hour gear means for maintaining the minute gear means in direct driving relationship with the hour gear means; planetary reduction gearing in meshing engagement with both the output pinion and the minute gear means, to maintain the pinion in direct driving relationship with the minute gear means; means for rotatably supporting the planetary reduction gearing for limited orbital movement relative to the central shaft and for resiliently biasing said planetary reduction gearing toward a particular orbital position with respect thereto; means for applying clock pulses to the stepper motor to move the planetary reduction gearing away from said particular orbital position against its resilient bias anD to rotate the minute gear means and the hour gear means at timing speed; and means for applying resetting pulses to the stepper motor to rotate at least one of said gear means at a speed higher than said timing speed.

14. In a clock as defined in claim 13 which further comprises switching means controlled by said one gear means for disabling the stepper motor when said one gear means is in a particular angular position; and means for thereafter enabling the stepper motor to condition the same for the receipt of successive clock pulses.

17. In a clock, in combination: a support member; drive means including a pulsed stepper motor mounted on the support member, the motor having a permanent magnet rotor and an output pinion connected to the rotor; a central shaft carried by the support member; minute gear means rotatable about the axis of the central shaft; hour gear means rotatable about the axis of the central shaft; first reduction gearing in meshing engagement with both the minute gear means and the hour gear means for maintaining the minute gear means in direct driving relationship with the hour gear means; planetary reduction gearing in meshing engagement with both the output pinion and the minute gear means, to maintain the pinion in direct driving relationship with the minute gear means; resilient means for rotatably supporting the planetary reduction gearing for limited orbital movement relative to the central shaft and for resiliently biasing said planetary reduction gearing toward a particular orbital position with respect thereto; means for applying clock pulses to the stepper motor to move the planetary reduction gearing away from said particular orbital position against the bias of the resilient means and to rotate the minute gear means and the hour gear means at timing speed; means for applying resetting pulses to the stepper motor to rotate the minute gear means and the hour gear means at a speed higher than said timing speed; and means including first and second switch contacts respectively controlled by the minute gear means and the hour gear means for disabling the stepper motor when the corresponding gear means is in a selected angular position.

18. In a clock, in combination: a support member; drive means including a pulsed stepper motor mounted on the support member, the motor having a permanent magnet rotor and an output pinion connected to the rotor; a central shaft carried by the support member; minute gear means rotatable about the axis of the central shaft; hour gear means rotatable about the axis of the central shaft; first reduction gearing in meshing engagement with both the minute gear means and the hour gear means for maintaining the minute gear means in direct driving relationship with the hour gear means; planetary reduction gearing in continuous meshing engagement with both the output pinion and the minute gear means at all times during its rotation, to maintain the pinion in direct driving relationship with the minute gear means, the rotor poles of the motor providing a magnetic detent to hold the minute gear means in discrete angular positions relative to the central shaft; resilient means for rotatably supporting the planetary reduction gearing for limited orbital movement relative to the central shaft and for resiliently biasing said planetary reduction gearing toward a particular orbital position with respect thereto; means for applying clock pulses to the stepper motor to rotate the planetary reduction gearing in a direction to move the same away from said particular Orbital position against the bias of the resilient means, the resilient means thereupon returning said planetary reduction gearing toward said orbital position to move the minute gear means at timing from one of its discrete angular positions to an adjacent angular position; and means for applying resetting pulses to the stepper motor to rotate the minute gear means at a speed higher than said timing speed.

21. In a clock, in combination: a support member; drive means including a pulsed stepper motor mounted on the support member, the motor having a permanent magnet two-pole rotor and an output pinion connected to the rotor; a central shaft carried by the support member; minute gear means rotatable about the axis of the central shaft and having an opening in a preselected position thereon; hour gear means rotatable about the axis of the central shaft; first reduction gearing in meshing engagement with both the minute gear means and the hour gear means for maintaining the minute gear means in direct driving relationship with the hour gear means; planetary reduction gearing in continuous meshing engagement with both the output pinion and the minute gear means at all times during its rotation, to maintain the pinion in direct driving relationship with the minute gear means, the rotor poles of the motor providing a magnetic detent to hold the minute gear means in discrete angular positions relative to the central shaft; resilient means for rotatably supporting the planetary reduction gearing for limited orbital movement relative to the central shaft and for resiliently biasing said planetary reduction gearing toward a particular orbital position with respect thereto; means for applying clock pulses to the stepper motor to rotate the planetary reduction gearing in a direction to move the same away from said particular orbital position against the bias of the resilient means, the resilient means thereupon returning said planetary reduction gearing toward said orbital position to move the minute gear means at timing speed from one of its discrete angular positions to an adjacent angular position; means for applying resetting pulses to the stepper motor to rotate the minute gear means at a speed higher than said timing speed; switching means including a contact member movable into the opening in the minute gear means for disabling the stepper motor when the minute gear means is in its correct timing position; and means for thereafter applying an enabling pulse to the stepper motor to condition the same for the receipt of said clock pulses.