US3657875A - Electro-mechanical drive mechanism for watches and related devices - Google Patents

Electro-mechanical drive mechanism for watches and related devices Download PDF

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Publication number
US3657875A
US3657875A US73770A US3657875DA US3657875A US 3657875 A US3657875 A US 3657875A US 73770 A US73770 A US 73770A US 3657875D A US3657875D A US 3657875DA US 3657875 A US3657875 A US 3657875A
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United States
Prior art keywords
control arm
clutch
escapement wheel
drive shaft
electro
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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US73770A
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English (en)
Inventor
Joseph L Radnik
Edward E Hahn
Wayne F Ridenour
Helen L Ridenour
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GRUEN IND Inc
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GRUEN IND Inc
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    • G—PHYSICS
    • G04—HOROLOGY
    • G04B—MECHANICALLY-DRIVEN CLOCKS OR WATCHES; MECHANICAL PARTS OF CLOCKS OR WATCHES IN GENERAL; TIME PIECES USING THE POSITION OF THE SUN, MOON OR STARS
    • G04B11/00—Click devices; Stop clicks; Clutches
    • G04B11/001—Clutch mechanism between two rotating members with transfer of movement in both directions, possibly with limitation on the transfer of power
    • G—PHYSICS
    • G04—HOROLOGY
    • G04B—MECHANICALLY-DRIVEN CLOCKS OR WATCHES; MECHANICAL PARTS OF CLOCKS OR WATCHES IN GENERAL; TIME PIECES USING THE POSITION OF THE SUN, MOON OR STARS
    • G04B11/00—Click devices; Stop clicks; Clutches
    • G04B11/02—Devices allowing the motion of a rotatable part in only one direction
    • G04B11/04—Pawl constructions therefor, e.g. pawl secured to an oscillating member actuating a ratchet
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T74/00—Machine element or mechanism
    • Y10T74/15—Intermittent grip type mechanical movement
    • Y10T74/1526—Oscillation or reciprocation to intermittent unidirectional motion

Definitions

  • ABSTRACT mechanical transducer for driving an escapement wheel of a timing device such as an electr mechanism coupled to the shaft of the esc through an electro-magnetically actuated mechanically to drive the escapement wheel st to effect time-spaced incremental an 24 Claims, 8 Drawing Figures PATENTEDAPR 25 I972 3, 657, 875
  • This invention relates generally to improvements in drive systems of the type finding utility in precision timing devices such as electronic watches and chronometers. More particularly, the invention is directed to a miniature electromechanical actuator system effective to produce stepped, precise, incremental angular rotation of an output shaft at very low input power levels and with very low duty cycle operation.
  • the invention includes a nonresonant electro-magnetic energy converter and a miniature clutch drive subassembly, the converter and the clutch and drive components cooperating to produce translational mechanical motion upon energization by low-amplitude, small duration current pulses supplied by a low voltage miniature battery and a transistor switch controlled through a precision oscillator.
  • the translational motion is converted into rotational motion through the expedient of a toothless ratchet" clutch sub-system. Precision angular stepping is achieved through the use of a pallet stone index wheel arrangement.
  • an electrical watch mechanism utilizing a standard frequency transmitter stabilized by means of a resonant element and an electronic frequency reducer, an improved electro-mechanical transducer or electro-mechanical converter in which frictional losses are minimized and power demands are extremely low.
  • the electro-mechanical converter includes electro-magnetic means for dictating the movement of a control arm, the latter acting upon and driving a clutching assembly whereby electrical and electro-magnetic energy are effective to produce rotative motion of an escapement wheel.
  • a novel spring clutch and drive assembly utilized includes a pair of coaxial, wound spring elements embracing a drive shaft of an escapement wheel, the spring elements serving both as escapement wheel holding and advancing means.
  • a fiber clutch assembly serves as a coupling means by which a control arm advances an escapement wheel.
  • An important feature of the driving mechanism of the present invention is that there are invoked intermittent, timespaced stepping pulses rather than a harmonic drive.
  • the power requirement is microwatts or less and that the duration of the control-arm-actuating pulse is exceedingly short.
  • Yet another feature of the invention is that frictional losses are minimized through the use of a flexural pivot in place of conventional bearings.
  • FIG. I is an exploded perspective view of an electromechanical drive mechanism in accordance with one preferred embodiment of the present invention, and showing the interrelationship of its component parts;
  • FIG. 2 is an enlarged plan view of the spring clutch drive of the invention
  • FIG. 3 is an elevational view showing the escapement wheel support and drive structure
  • FIG. 4 is a fragmentary perspective view showing, schematically, the indexing pawl cooperating with the control arm of the clutching and drive mechanism, in two different positions;
  • FIG. 5 is a perspective view showing a second embodiment of a drive and clutch assembly in accordance with the invention.
  • FIGS. 6 and 7 are cross sectional views taken respectively on the lines 6-6 and 7-7 of FIG. 5 and showing the fibercarrying drive arm, the cooperating clutch plate, and the fiber filament check means for preventing counter rotation of the driven clutch plate;
  • FIG. 8 is a perspective view showing an alternative fiber clutch drive assembly, in accordance with the invention.
  • the present invention provides an improved system of conversion of electrical and electro-magnetic energy to rotative energy.
  • the electro-magnetic energy converter produces translational mechanical motion when energized by low-amplitude, small duration current pulses supplied by a low voltage miniature battery and a transistor switch which is in turn controlled by a precision oscillator.
  • the battery is conventional, and the precision oscillator does not broadly, as such, constitute an inventive feature of the invention. Accordingly, no detailed description is provided herein.
  • the translational mechanical motion is converted into rotational motion by means of a toothless ratchet, clutch sub-system, and precision angular steps are ensured through the use of a pallet stone index wheel arrangement.
  • the miniature energy converter is a non-resonant, polarized electro-magnetic device which transforms low voltage electrical power into mechanical power at extremely low input power levels and low duty cycle rates.
  • the intended use of the energy converter is as a power unit for miniature precision timing devices such as electronic watches and chronometers.
  • the device itself is extremely versatile and is capable of operating and driving many mechanical systems including ratchet wheels, indexing mechanisms, and other drive systems to provide precision, incremental mechanical motion.
  • FIGS. 1 through 4 for the purposes of illustrative disclosure, one preferred embodiment of the electro-mechanical drive mechanism of the invention, incorporating the teachings thereof.
  • the physical components of the electromagnetic drive and the electromechanical transducer include a solenoid assembly comprising a solenoid coil 24 and an armature or control arm 28 extending axially into the coil 24 and projecting outwardly from one end thereof.
  • the solenoid coil 24 is carried on a platen or plate 30 and is cradled between a pair of opposed permanent magnets 36 and 38 extending generally parallel to the axis of the coil 24.
  • a bar 64 of non-magnetic material is attached to plate 30 and supports the rear end 66 of the coil armature 28.
  • the forwardly projecting portion 70 of the coil armature 28 carries at its end a jeweled receptacle 74. Also secured to the armature 28 and extending generally forwardly thereof is a ratchet arm 78 terminating in a jeweled probe or pallet stone 80.
  • An escapement wheel assembly 90 is mounted onand rotatably supported by the magnet-carrying plate 30.
  • the escapement wheel assembly includes a plate jewel 92 secured in an opening 96 formed in the plate 30.
  • Rotatably engaged in the plate jewel 92 and extending upwardly therefrom is a drive shaft, output shaft or pinion staff 100, and carried by the staff are a coaxial pinion 102, a toothed ratchet wheel or escapement wheel 106, and a ratchet drum 1 10.
  • a clutch assembly includes a pair of wound, coaxial springs 114 and 116 encircling and embracing the shaft-mounted drum 110.
  • a bridge plate 120 surmounts the ratchet and pinion staff assembly 90, the bridge having formed therein a jeweled bushing 124 in which the upper end 126 of the pinion staff 100 is rotatably received.
  • a locking spring support arm 130 Secured to the bridge plate 120 and extending outwardly therefrom is a locking spring support arm 130 provided with a jeweled opening, socket or receptacle 134 into which an end 136 of the locking spring .114 is received.
  • An end 140 of the other spring 116 is received in the jeweled receptacle 74 carried by the coil armature 28.
  • the jeweled probe or pallet stone 80 extending from the coil armature 28 projects into and seats in an interdental space 144 between teeth or cogs 148 of the ratchet wheel 106.
  • the solenoid assembly 20 which functions as a part of the miniature energy converter of the invention is a non-resonant, polarized, electro-magnetic device which transforms low voltage electric power to mechanical power at extremely low input power levels and low duty cycle rates.
  • the energy converter consists of the combination of soft iron pole pieces, a soft iron armature, permanent magnets, and a coil.
  • the converter incorporates a flexural pivot in the form of a cantilever armature 28.
  • a unique and very important feature of the converter is that during its unenergized state, the armature 28 is sealed or stopped adjacent one pole or pole face 52 of the working gap 152. This condition is achieved through the use of the permanent magnets 36 and 38 and mechanical unbalance.
  • a lowamplitude, short-duration current pulse of the appropriate polarity produces an electro-magnetic force which overcomes the permanent magnet seal force, causing armature shifting and releasing the stored energy of the deflected cantilever.
  • the established electro-magnetic force also acts directly on the armature to urge it from its rest position.
  • the armature returns to its stand-by, seal, or rest position under the influence of the permanent magnet forces.
  • the armature 28 remains distorted and stressed in this position until the next current pulse.
  • the current pulses themselves may be derived from a 1.5 volt miniature battery through a transistor switch controlled by a precision oscillator (not shown).
  • the battery, transistor switch and the precision oscillator form no part of the instant invention and, accordingly, no detailed description is provided, many appropriate and useful circuits being known in the prior art.
  • the dynamics of the armature are preferably selected to provide a mechanical response time which permits extremely low duty cycle operation of the converter.
  • Current pulses of about 0.8 to 2.0 millisecond duration are adequate to operate ratchet wheels, indexing mechanisms, and other rotational drive systems.
  • the converter On a 1 stroke per second basis, the converter is capable of operating with an average power input of 5 microwatts or less from a miniature battery. The low power demand and consumption are particularly valuable in ensuring extended battery life.
  • the power stroke of the energy converter at pulsing of the electromagnet, causes a shift of the armature 28 between the poles 52 and 58 of the pole pieces 46 and 48. Since the armature is mechanically coupled to the upper spring (ratchet spring) 116, the effect of annature shifting is to wind or unwind that spring. During the power stroke, the spring 116 is unwound, rotating freely on the ratchet drum 110. At the same time, the output shaft or pinion staff 100 of the escapement wheel assembly is prevented from rotating by the frictional gripping or looking action of the lower clutch spring 114. At termination of the applied driving pulse, the armature 28 returns to its quiescent position under the influence of the permanent magnets 36 and 38.
  • the return path executed by the armature 28 produces rotation of the clutch spring 116 in a direction to tighten the spring 116 which then grips and causes the ratchet drum 110 and the output shaft 100 secured thereto to rotate.
  • the lower spring or locking spring 114 is unwound" and exerts minimal locking torque to obviate interference with the rotation of the encircled ratchet drum 110.
  • the load upon the energy converter during the power stroke is of extremely low inertia and friction since the upper spring 116 has low mass and low friction in the unwound condition. Frictional losses are further minimized through the use of the flexural pivot of the armature 28 in place of conventional bearings. All of the above factors contribute to low duty cycle, fast response, and minimal damping of the mechanical system. An extremely simple structure having low input power requirements is achieved.
  • the electro-mechanical converter of the invention provides controlled intermittent stepping rotational movement of the output shaft or drive shaft 100 of the escapement wheel assembly through an impulse stepping system rather than through a harmonic drive.
  • the output arm or armature 28 shifts at a frequency of 1 cycle per second and the output shaft is driven 6 each shifting cycle, or I rotation per minute.
  • the output shaft 100 may serve as the shaft for a second hand of a watch mechanism.
  • the pallet stone 80 moves into engagement with a face of the next cog 148 of the escapement wheel 106. That is, the clearances provided are such that the rotational shift of the drum 110 efi'ects an advancement of one tooth position before the pallet stone 80 reengages the escapement wheel 106.
  • This indexing procedure ensures a precise, controlled rotational shift for each shifting cycle of the driving armature 28, and limits further rotation of the wheel 106.
  • each step is 6.
  • the pallet stone 80 ensures a completion of the step.
  • the mechanism is simple, highly shock resistant, unusually reliable, has relatively few moving parts, and provides highly accurate control of the rotational motion and assurance of uniform precise incremental steps. It will be appreciated that, if desired, the physical arrangement of elements may be such that advancement of the escapement wheel occurs as the armature 28 moves from position 1 to position 2, that is, during shift from the rest position to the displaced position.
  • FIGS. 57 A second embodiment of the clutch assembly, fabricated in accordance with the concept of the instant invention and finding utility as a drive shaft advancing mechanism, is illustrated in FIGS. 57.
  • the clutch assembly 200 differs from the dual spring embodiment of FIG. 2, previously described, principally in the form of mechanical elements through which the drive shaft 100 and the escapement wheel 106 carried thereby are advanced.
  • a clutch plate 204 mounted on the drive shaft 100 for rotation therewith, is provided on a principal surface 206 thereof extending generally normally of the drive shaft 100, with a plurality of elements establishing surface irregularities and constituting abutment means for cooperative interengagement with extremities of fiber-like projections 214 carried on the projecting end portion of the armature or control arm 28 of the solenoid assembly 20.
  • the surface of the plate 204 is formed with an array of raised, radial spokes or ribs 216 whose side wall facets constitute abutment faces through which the contacting end of the fibers 214 impel the clutch plate 204 annularly about the drive shaft 100 as the armature 28 is energized to execute shifting steps.
  • the fiber-like elements 214 are oriented to form an angle of about 20 to about 45 with the plate 204.
  • the angle is not critical, but is to ensure that, during the return movement or reset of the armature 28, the fibers 214 will wipe smoothly across the surface of the clutch plate with minimumfriction. Any tendency of the clutch plate to rotate in a reverse direction is further obviated through the use of positive check means consisting of a fixed array of fiber elements 220 carried on a bar 222 secured to the support arm 130. As indicated in FIG. 5, the fibers 220 are oriented to contact the surface of the clutch plate at an angle to permit the plate to advance under the applied stepping force of the armature, but to check and to preclude reverse rotation of the plate 204.
  • the exemplary clutch plate is shown with ribs, it is contemplated that any other suitable surface treatment may be utilized, including a 'wire mesh or latticed surface, or an etched surface.
  • the fibers may be natural or synthetic filaments or may be metal wires.
  • an appropriately surfaced drum or cylinder 230 encircling and coaxial with the drive shaft 100 may be used to fulfill the function of the clutch plate 204.
  • the driving fibers or drum advancing fibers 234 are oriented to abut the drum at an angle and at a disposition to effect annular advancement thereof.
  • a second set of fiber elements 240, carried on a bar 242 secured to the support arm 130 prevents counter rotation of the drum 230.
  • An electro-mechanical transducer actuable through an electrical current applied thereto to convert electrical energy to rotative motion, and comprising:
  • control arm and means supporting said control arm for shifting movement in a plane substantially normal to a rotational axis of the drive shaft of said escapement wheel
  • clutch means intercoupling said control arm with said escapement wheel for driving said escapement wheel through said control arm
  • magnetic means including electro-magnetic means operationally coupled to said control arm
  • said magnetic means being responsive to electrical energy applied thereto to provide electro-magnetic pulses at time-spaced intervals
  • first and second wound spring means encircling and embracing said drive shaft
  • said first and second spring means being axially spaced and coaxially mounted on said drive shaft for tensioned gripping engagement therewith,
  • said second spring means being a fixed spring and comprising shaft gripping means wound about said drive shaft in a direction to prevent rotation of said drive shaft during unwinding of said first spring means and to permit rotational advancement of said drive shaft during winding of said first spring means.
  • said second spring means is wound in a sense to grip and hold said drive shaft during unwinding of said first spring means and to slip relative to said drive shaft during winding of said first spring means.
  • said escapement wheel is formed with an encircling array of teeth about the periphery thereof, and wherein said control arm periodically to interject into interdental spaces between said teeth of said escapement wheel to abut and bear against said teeth to serve as means to regulate stepwise angular advancement of said escapement wheel and to provide exact, incremental rotative steps.
  • said magnetic means includes permanent magnet means operatively disposed to impress a magnetic force upon said control arm to hold said control arm at a rest position and to retain said control arm in said rest position in a mechanically stressed state
  • control arm being responsive to said electro-magnetic force and being operable to shift from and then to return to said rest position to effect an annular incremental rotative advancement of said escapement wheel.
  • An electro-mechanical transducer comprising the combination with a rotatively supported escapement wheel of toothless ratchet means coupled to said escapement wheel and operable to advance said escapement wheel in incremental steps at controlled time-spaced intervals,
  • said toothless ratchet means comprising drive means rotatively shifting said escapement wheel
  • cooperating clutch means restricting rotative shifting of said escapement wheel to only one annular direction
  • electro-mechanical means for actuating said drive means.
  • said electro-mechanical means including electro-magnetic means operative periodically to-shift said control arm from a quiescent rest position to an electro-magnetically established displaced position, 1
  • said electro-mechanical means including electro-magnetic means operative periodically to shift said control arm from a quiescent rest position to an electro-magnetically established displaced position,
  • an electrical transmitter having a resonant element as a frequency stabilizer
  • said electro-mechanical transducer comprises, in combination:
  • first and second spring means encircling and embracing said drive shaft
  • said first and second spring means being axially spaced and coaxially mounted on said drive shaft for tensioned gripping engagement therewith,
  • control arm and means supporting said control arm for angular movement in a plane substantially normal to a rotational axis of the drive shaft
  • magnetic means including electro-magnetic means responsive to electrical energy applied thereto to provide magnetic pulses at time-spaced intervals to effect angular displacement of said control arm,
  • said second spring means being a fixed spring and comprising clutch means wound about said drive shaft in a direction to prevent rotation of said drive shaft during unwinding of said first spring means and to permit rotational advancement of said drive shaft during winding of said first spring means.
  • said clutch means comprises a fiber clutch assembly including:
  • said clutch element having an irregular surface defining abutment means adapted to engage ends of cooperating fiber means presented thereagainst
  • said fiber means projecting in planes intersecting said abutment means and angled in a direction to effect rotation of said clutch element upon actuation of said control arm;
  • said clutch means comprises a fiber clutch assembly including:
  • said fiber means projecting in planes intersecting said facets of said clutch plate, and angled forwardly with respect to a direction of rotation of said clutch plate;
  • said fixed fiber means being angled in a direction to permit annular advance of said clutch plate and said escapement wheel secured thereto,
  • said fixed fiber means being angled in a direction to permit annular advance of said clutch element and said escapement wheel secured thereto,
  • said fixed fiber means allow sliding passage of said clutch element in contact therewith and constitute check means limiting rotation of said clutch element to one direction only.
  • said clutch 75 means comprises a fiber clutch assembly including:
  • said fiber means projecting in planes intersecting said abutment means of said cylinder and angled in a direction to effect rotation of said cylinder upon actuation of said control arm;
  • said fixed fiber means being angled in a direction to permit annular advance of said rotatable cylinder and said escapement wheel secured thereto,
  • said fixed fiber means allow sliding passage of said rotatable cylinder in contact therewith and constitute check means limiting rotation of said rotatable cylinder to one direction only.
  • said clutch means comprises first and second cooperating clutch elements
  • said first and said second clutch elements being disposed to interengage upon actuation of said control arm;
  • said clutch means comprises a fiber clutch assembly including:
  • one of said clutch elements having an irregular surface defining abutment means for engaging ends of cooperating fiber means presented thereagainst
  • the other of said clutch elements comprising fiber means projecting in planes intersecting said abutment means for stressing engagement therewith during actuation of said control arm to effect stepped advancement of said escapement wheel at said time spaced intervals.
  • an electrical transmitter having a resonant element as a frequency stabilizer
  • control arm and means supporting said control arm for shifting movement in a plane substantially normal to a rotational axis of the drive shaft of said escapement wheel, and
  • clutch means intercoupling said control arm with said escapement wheel for driving said escapement wheel through said control arm
  • said clutch means comprises, in
  • said fiber means projecting in planes intersecting said facets of said clutch plate
  • shifting displacement of said control arm presents projecting free end portions of said fiber means into stressing abutment contact with said facets of said clutch plate effects annular shifting of said clutch plate and said escapement wheel about said drive shaft.
  • an electrical transmitter having a resonent element as a frequency stabilizer
  • control arm and means supporting said control arm for shifting movement in a plane substantially normal to a rotational axis of the drive shaft of said escapement wheel, and
  • clutch means intercoupling said control arm with said escapement wheel for driving said escapement wheel through said control arm
  • said clutch means comprises, in
  • shifting displacement of said control arm effects annular shifting of said clutch and said escapement wheel about said drive shaft.
  • said indexing pawl shifts into and out of successive interdental spaces about said escapement wheel and into abutting contact with faces of said teeth to provide positive, precise, incremental stepping of said escapement wheel.
  • said magnetic means comprises a non-resonant, polarized assembly including, in combination, both permanent and electromag- 5 netic elements.
  • Claim 4 column 6, line 50 after "arm” insert includes pawl means operabl e claim 16 column 9 line 2, cancel "and” and substitute said 4. same line 2, "to” should read of claim 20 column 10 line 23, before “effects” insert and claim 21., column 10, line 49, cancel "consisting” and substitute constituting Signed and sealed this 6th day of February 1973.
  • column 6, line 50, after "arm” insert includes pawl means operable claim 16 column 9, line 2, cancel “and” and substitute said same line 2, "to” should read of claim 20 column 10 line 23 before “effects” insert r and claim 2].
  • column 10 line 49 cancel "consisting” and substitute constituting Signed and sealed this 6th day of February 1973.
US73770A 1970-09-21 1970-09-21 Electro-mechanical drive mechanism for watches and related devices Expired - Lifetime US3657875A (en)

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US7377070A 1970-09-21 1970-09-21

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US3657875A true US3657875A (en) 1972-04-25

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US73770A Expired - Lifetime US3657875A (en) 1970-09-21 1970-09-21 Electro-mechanical drive mechanism for watches and related devices

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US (1) US3657875A (de)
CA (1) CA929357A (de)
DE (1) DE2120357C3 (de)
FR (1) FR2112958A5 (de)
GB (1) GB1352790A (de)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4207733A (en) * 1978-09-07 1980-06-17 Datcon Instrument Company Elapsed time indicator
US5932940A (en) * 1996-07-16 1999-08-03 Massachusetts Institute Of Technology Microturbomachinery
EP2302468A1 (de) * 2009-09-24 2011-03-30 MPS Micro Precision Systems AG Kupplungsvorrichtung

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2347425A (en) * 1944-04-25 Clutch for fare registers
US2977811A (en) * 1958-11-24 1961-04-04 North Electric Co Ratchet and pawl stepping mechanism

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2347425A (en) * 1944-04-25 Clutch for fare registers
US2977811A (en) * 1958-11-24 1961-04-04 North Electric Co Ratchet and pawl stepping mechanism

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4207733A (en) * 1978-09-07 1980-06-17 Datcon Instrument Company Elapsed time indicator
US5932940A (en) * 1996-07-16 1999-08-03 Massachusetts Institute Of Technology Microturbomachinery
US6392313B1 (en) 1996-07-16 2002-05-21 Massachusetts Institute Of Technology Microturbomachinery
EP2302468A1 (de) * 2009-09-24 2011-03-30 MPS Micro Precision Systems AG Kupplungsvorrichtung
CH701883A1 (fr) * 2009-09-24 2011-03-31 Mps Micro Prec Systems Ag Dispositif d'accouplement.

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DE2120357C3 (de) 1974-07-18
DE2120357B2 (de) 1974-01-03
CA929357A (en) 1973-07-03
FR2112958A5 (de) 1972-06-23
GB1352790A (en) 1974-05-08
DE2120357A1 (de) 1972-03-30

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