US3699764A - Tuning-fork type electronic clock having push-pull indexing mechanism - Google Patents

Abstract

An electronic clock making use of an electromagneticallyactuated tuning fork whose vibrations are converted into rotary motion for driving the gear train of the clock. The conversion is effected by an indexing mechanism including two oppositely directed V-shaped indexing elements whose ends are attached to the tines of the fork. The vertex of each element is flattened to define a rectangular tongue whose edge engages the ratchet teeth of an index wheel whereby as the tines vibrate, the tongues reciprocate in phase opposition in a rectilinear path at right angles to the direction of vibration. In the course of each cycle, as the tines move together, one tongue acts to push the wheel as the other tongue retracts, and when the tines move away from each other, the other tongue acts to pull the wheel as the one tongue retracts.

Description

United States Patent Van Haaften [54] TUNING-FORK TYPE ELECTRONIC CLOCK HAVING PUSH-PULL INDEXING MECHANISM [72] Inventor: Egbert Van Haaften, Closter, NJ.

[73] Assignee: Bulova Watch Company, Inc., New

York, NY.

22 Filed: Jan. 28, 1972 21 Appl. No.: 221,690

Related US. Application Data [63] golngglluation-in-part of Ser. No. 160,835, July [52] US. Cl. ..58/23 TF, 58/23 D, 310/25 [51] Int. Cl. ..G04c 3/00, H02k 33/00 [58] Field of Search...58/23 D, 23 TF, 23 V; 84/457;

[56] References Cited UNITED STATES PATENTS 3,425,210 2/1969 Barth ..58/23 R FOREIGN PATENTS OR APPLICATIONS 1 Oct. 24, 1972 1,519,243 2/1968 France ..5s/23 TF Primary Examiner-Richard B. Wilkinson Assistant Examiner-Edith C. Simmons .lackmon Att0meyMichael Ebert ABSTRACT An electronic clock making use of an electromagnetically-actuated tuning fork whose vibrations are converted into rotary motion for driving the gear train of the clock. The conversion is effected by an indexing mechanism including two oppositely directed V- shaped indexing elements whose ends are attached to the tines of the fork. The vertex of each element is flattened to define a rectangular tongue whose edge engages the ratchet teeth of an index wheel whereby as the tines vibrate, the tongues reciprocate in phase opposition in a rectilinear path at right angles to the direction of vibration. In the course of each cycle, as the tines move together, one tongue acts to push the wheel as the other tongue retracts, and when the tines move away from each other, the other tongue acts to pull the wheel as the one tongue retracts.

5Claims,6DrawingFigures IOA TUNHQG-FORK TYPE ELECTRONIC CLOCK HAVING PUSH-PULL INDEXING MECHANISM RELATED APPLICATION This application is a continuation-in-part of my copending application Ser. No. 160,835 filed July 8, 1971.

BACKGROUND OF THE INVENTION This invention relates generally to electronic timepieces, and more particularly to a clock incorporating an electromagnetically-actuated tuning fork as a time base, the vibratory motion of the fork being converted into rotary motion by a push-pull indexing mechanism.

In U.S. Pat. No. 2,971,323 of Hetzel, there is =disclosed an electronic timepiece including a tuningfork having a relatively high frequency, a battery-powered transistorized drive circuit acting to sustain the vibratory motion of the fork. The reciprocating motion of the fork, which serves as a time-keeping standard, is transformed into rotary motion by means of a ratchet and pawl mechanism whose index finger is attached to one tine of the fork. The finger engages and advances a ratchet wheel provided with a pinion for operating the timepiece hands through a train of gears.

U.S. Pat. No. 3,184,981 of Bennett, Mutter and Van Haaften discloses an improved form of a motion converter for a timepiece of the Hetzel type, whereby the ratchet wheel is caused to advance only one tooth for each forward stroke of the index finger attached to the tine, regardless of minor variations in the length of the stroke arising from changes in the amplitude of fork vibration. This is accomplished by means of an auxiliary pawl attached to the pillar plate of the timepiece, the pawl engaging the ratchet wheel at a position relative to the index finger at which the phase between the finger and pawl is several ratchet teeth plus one-half tooth. Motion converters of this type operate efficiently and reliably, and are presently used in tuning fork watches sold commercially under the trademark, AC- CUTRON.

When the tuning fork principle as disclosed in the above identified patents is applied to electronic timepieces in clock form, the relatively delicate index finger-auxiliary pawl ratchet wheel arrangement, which requires careful adjustment, may not be suitable for a low-cost clock, particularly for clocks intended for a somewhat rugged environment such as the dashboard of a vehicle. Though clocks are larger than watches, clocks are generally marketed at a much lower cost. Watches, because of their fine workmanship, are treated as jewelry items, whereas clocks are household or industrial articles. Hence expensive mechanisms which are acceptable for fine watches cannot, as a practical matter, be used in a low-cost clock.

In an attempt to overcome these drawbacks, batteryoperated tuning-fork clocks have been developed, making use of so-called magnetic escapements to convert the vibratory motion of the fork into rotary motion, rather than mechanical motion converters of the type disclosed in the above-identified patentsqHowever, a magnetic escapement wherein a wheel having a magnetic track or teeth is associated with magnets secured to the vibrating tines of the fork has serious disadvantages, for such escapements are inefficient and produce relatively little torque. Moreover, they are not self-starting and it is necessary to include a mechanical starter in the clock to set the wheel of the magnetic escapement into motion.

In my copending application, previously identified, there is disclosed an electronic clock comprising a tuning fork having a permanent magnet assembly secured to one time thereof, and a coreless coil assembly to the other tine thereof, the magnet being inserted in the coil to provide an electromagnetic transducer for sustaining the fork in vibration. Bridged between the tines is a V- shaped indexing element whose ends are secured to corresponding points on the tines and whose vertex is flattened to define a rectangular tongue, the lower edge of which engages the ratchet teeth of an index wheel. The tongue is caused to undergo rectilinear motion at right angles tothe direction of tine vibration, thereby to drive the index wheel. The index wheel is mounted on a worm gear supported between end pivots, one of which is spring-biased to create sufficient friction preventing retrograde movement of the index wheel. The worm gear engages the first wheel in a gear train serving to drive the hands of the clock.

While a clock, as disclosed in my copending application, is self-starting, accurate and reliable as well as being produceable at low cost, in a practical embodiment, the magnitude of voltage necessary to power the mechanism is such that more than one battery cell is required. In order to drive the fork with sufficient amplitude to advance the ratchet wheel one tooth per vibratory cycle, one needs a voltage at a level of 2.8 volts. In practice, this dictates the use of two 1.4 volt mercury cells in series.

Mercury cells are preferred in that such cells are characterized by a voltage which remains substantially constant during the full operating life of the cell and does not decline as is the case with conventional dry batteries. Since the amplitude of the tuning fork is governed with respect to battery voltage, which serves as a set point, a constant battery voltage makes possible effective amplitude stabilization. However, mercury cells are costly, and the need for two cells is objectionable.

Moreover, in the arrangement disclosed in my copending application, in the course of each vibratory cycle, when the two tines move away from each other, the V-shaped indexing element produces a forward stroke that advances the ratchet wheel one tooth, but when the two tines draw toward each other, the indexing element produces a return stroke which tends to cause retrograde motion of the wheel. In the prior arrangement, the ratchet wheel is subjected to sufficient friction to prevent such retrograde motion.

There are practical drawbacks to this prior arrangement. First, the movement of the fork which produces a return stroke of the index wheel is wasted, for this action does not advance the ratchetwheel. Second, by introducing friction to prevent retrograde motion of the ratchet wheel, the mechanical efficiency of the clock is degraded.

' SUMMARY OF THE lNlENTION In view of the foregoing, it is the main object of this invention to provide a tuning-fork type electronic clock which is accurate and reliable in operation, which requires but a single battery cell to operate and which may be produced and sold at low cost.

More specifically, it is an object of this invention to provide an efficient and rugged motion transformer for an electronic clock of the above-noted type, which converter is constituted by an indexing mechanism adapted to exploit both the in and out movements of the tuning fork, whereby unidirectional rotary motion results from both movements.

A significant advantage of the motion converter in accordance with the invention is that because both the in and out movements of the fork are converted into rotary motion, the amplitude of fork vibration necessary to provide a predetermined advance of the indexing wheelis only half that required by the prior arrangement. This makes it possible to operate with half the fork amplitude to produce the same wheel advance, as a consequence of which the battery voltage for operating the system need be only half of that previously required.

Also an object of the invention is to provide a motion converter which is provided with a pair of V shaped indexing elements that function to drive a ratchet wheel in a push-pull manner, whereby in the course of each vibratory cycle, first one element acts to advance the wheel while the other element is retracted, and then the other element acts to advance the wheel while the one element is retracted. Because of this arrangement, no pawl or other means is required to prevent retrograde motion of the wheel.

Briefly stated, these objects are attained in an electronic clock in which a tuning fork is sustained on vibratory motion at its natural frequency by an electromagnetic drive circuit or equivalent means. Bridged between the tines of the fork are two V-shaped indexing elements, each having a flattened vertex to define a rectangular tongue. The two elements are attached in opposing relationship to the tines of the fork, whereby when the two tines move toward each other, one of the tongues advances at right angles to the direction of tine vibration, while the other tongue retracts at right angles to this direction, whereas when the two tines move away from eachother, the one tongue retracts while the other advances.

The tongues of the two indexing elements engage the ratchet teeth of an indexing wheel at displaced points thereon, whereby in the course of each vibratory cycle of the fork as the tines move toward and away from each other, first one tongue pushes the index wheel and then the other tongue pulls the wheel to advance it unidirectionally, Retrograde motion is prevented, for when the one tongue is retracting, the other is pushing and when the other tongue is retracting, the one tongue is pulling, so that at no time is the wheel free to reverse direction.

OUTLINE OF THE DRAWING For a better understanding of the invention, as well as other objects and further features thereof, reference is made to the following detailed description to be read in conjunction with the accompanying drawing wherein:

FIG. 1 is a plan view of an electronic clock of the tuning fork type including a push-pull indexing mechanism in accordance with the invention;

FIG. 2 is a separate perspective view of the tuning fork and the indexing elements attached thereto;

FIG. 3 is a perspective view of one of the indexing elements;

FIG. 4 is a sectional view taken through the clock;

FIG. 5 shows in side view, the relationship between the indexing elements and the index wheel; and

FIG. 6 is a plan view of the indexing mechanism.

DESCRIPTION OF THE INVENTION Referring now to FIG. 1, there is shown a tuning-fork type electronic clock in accordance with the invention, comprising a U-shaped fork generally designated by numeral 10, having a pair of tines 10A and 10B. The fork is constructed of a single strip of metal having indentations at nodal points 10C and 10D adjacent the base 10E. The fork is attached to a mounting post 1 1 by a pair of spaced tabs 12, each of which is bent to embrace base 10E. Mounting post 11 is anchored in pillar plate 13.

The free ends of tines 10A and 10B are provided with cut-outs to define mounting fingers for holding a coil assembly 14 and a magnet assembly 15, which together constitute the electromagnetic transducer for sustaining the fork in vibration. The operating frequency of the fork is preferably 180 Hz, for while the clock is designed for battery operation, at this frequency it becomes possible to synchronize the operation of the fork from a 60 Hz power line (60 Hz is an integral submultiple of 180 Hz), thereby providing a timepiece of high accuracy. But should AC power fail, the fork would still continue to function accurately on battery power. In practice, sync pulses may be derived inductively from the power line, thereby avoiding the need for a wired connection thereto.

The vibratory action of the fork is converted into rotary motion by a mechanical motion transformer constituted by a pair of generally V-shaped indexing elements 16 and 16'. The ends of element 16 are attached at corresponding positions to tines 10A and 10B so That mmry'aiieeteajtnee nds fitting into holes in the tines and being epoxied or otherwise bonded thereto. The ends of element 16' are similarly attached to tines 10A and 103, but this element is positioned so that the vertex thereof is rearwardly directed. The indexing elements are preferably made from a single piece of stainless steel round wire having a diameter of 0.006 inches.

As best seen in FIG. 3, the round wire of each element is flattened at the vertex thereof to define a vertically oriented rectangular tongue 16A, and the ends of the element are bent outwardly and flattened to define verticaly oriented feet 168 and 16C. The sides of the indexing element are also flattened to define horizontally oriented legs 16D and 16E, whereby all that along the same axis. But since elements 16 and 16 are 5 in opposing relationship, when tines A and 10B move toward each other, element 16 executes a forward stroke while element 16 concurrently executes a return stroke, and when tine 10A and 10B move away 1 from each other, the elements reverse direction.

The lower edge of tongue 16A of the indexing element 16 engages the ratchet teeth on an index wheel 17 such that with each forward stroke of the tongue 16A thereof, the wheel is pushed to advance one increment.

The tongue element 16 engages the ratchet teeth at another point such that with each forward stroke of the tongue, the wheel is pulled to advance another increment. The tuning fork has no pivots or bearing and its timekeeping action is therefore independent of the ef- 2 fects of friction. No pawl is used to prevent retrograde motion of the wheel, for as one element undergoes a return stroke, the other undergoes a forward stroke, and the wheel cannot therefore reverse direction.

Index wheel 17 is integral with a worm gear 18, the

two members being preferably made of high-strength, low-friction plastic material, such as Delrin. The worm gear is mounted for rotation between two tapered pivots l9 and 20, which project into holes bored in the opposite ends of the worm gear. Pivot 19 is rigidly sup- 3o ported whereas pivot 20 is borne on the free end of a flat spring 21, mounted on a bracket 22. In practice, the pivots are formed of hardened, highly polished stainless steel and are pointed to a 20 included angle.

The direction of pitch'in the worm is chosen so that as it rotates, should there by any load imposed on the index wheel and the worm integral therewith, its direction is toward the fixed pivot 19, thereby preventing the worm from moving away from the fixed pivot under load conditions.

Because the teeth in the ratchet wheel are engaged by the broad lower edge of the tongue of the indexing elements, shock or vibration causing lateral displacement of the tongue relative to the wheel will not effect disengagement therebetween. The indexing elements are downwardly biased against the index wheel which also serves to preve it disengagement therebetween Thus the clock is capadale of uninterrupted operation under the most arduous field conditions, for the clock includes no delicate balance wheel or motion transformer that may be rendered inoperative or upset by shock forces. Y

lntermeshing with worm gear 18 is a worm wheel 23 mounted on a center shaft 24 whose end, as shown in FIG. 4, terminates in the second hand 25 of the clock. The various time-indicating hands are associated with a dial plate 26. Worm wheel 23 has teeth, the worm gear having a single lead pitch. Index wheel 17 has essentially the same as that disclosed in my copending application, and the description thereof will therefore not be repeated.

Coil assembly 14, as shown in FIG. 1 is constituted by a tubular coil form 31 divided by an annular partition into two sections, one having a drive coil wound therein, and the other a phase-sensing or pick-up coil. In practice, since the drive coil has more turns than the 0 phase sensing coil, a portiongftl hase-sensing coil section may be occupied by drive coil turns, so that the drive coil is then made up of two series-connected parts.

Coil form 31 is provided with a cylindrical extension 32 projecting axially from one end thereof, which extension has one groove adapted to receive the U- shaped cutout on the end of tine 10A, and a second groove for accommodating a timing regulator 33.

The regulator is in the form of an unbalanced loading mass constituted by a round piece of wire with a loop and a circular portion to fit into the coil form groove, such that by turning the regulator to different angular positions, the orientation of the unbalanced loading mass is shifted to bring about a fine adjustment in timmg.

The three wires from the drive and phase sensing coils are connected to an electronic circuit housed in a module 34 secured to the pillar plate. The wires from coil assembly 14 run along the length of tine 10B and are fastened thereto, the wires at the nodal point 10C then leaving the tine to go to module 34. Since there is virtually no motion at nodal point 10C, negligible flexing of the wires is experienced despite the fact that the tine carrying the wires is in constant vibration.

Magnet assembly 15 is constituted by three parts, namely a permanent magnet rod 35, a mounting plug 36, preferably made of brass and cemented or otherwise bonded to one end of the magnet rod, and a regulator 37. Because the plug is made of non-ferromagnetic material, the open magnetic flux path extends from the magnet rod, coaxially disposed within coils on assembly 14 through these coils, but is magnetically isolated from tine 10A on which the magnet assembly is mounted.

' Plug 36 is provided with a groove to receive the cutout in tine 10A and a groove to receive the regulator 37 which is identical in form and function to regulator 33 on the coil assembly.

The electronic circuit housed in module 34 is powered by a replaceable battery cell 37 held in a suitable socket or by clips on pillar plate 13. The circuit is the same as that disclosed in my copending application.

The operating frequency of the fork is determined not by the fork per se, but by the combined mass of the tines and the assemblies mounted thereon. For highest operating efficiency, it is essential that symmetry exist as between the centers of gravity of the two oscillating masses with respect to the axis of symmetry of the fork.

teeth to match the 180 Hz fork frequency. With this 60 In practice, therefore, magnetic assembly 15 is made combination, worm wheel 23 makes one revolution per minute so that the second hand completes a full turn every minute.

Also keyed to shaft 24 directly at a position below worrn wheel 23 is a pinion 27 having six teeth which, in turn, drives a 60-tooth gear 28. The gear train arrangement for operating hour hand 29 and minute hand 30 is such that its mass and center of gravity substantially match that of the coil assembly 14.

While there has been shown and described a preferred embodiment of a tuning fork clock in accordance with the invention, it will be appreciated that many changes and modifications may be made therein without, however, departing from the essential spirit of the invention. For example, the indexing elements, rather than being made of round wire as described herein, with flattened sections, may be made entirely of flat wire twisted at appropriate points to define the flat lip and tongue sections of the element. In a clock of the type disclosed in my copending application, it is now possible with a redesigned transducer, to operate with only a single (1.4 v) power cell, rather than two cells. But even with this redesigned transducer, the double index finger arrangement is advantageous, for with the resultant reduction in fork amplitude, the current drain is reduced by about one-half, thereby almost doubling the life of the single power cell.

1 claim: 1. An electronic timepiece comprising; a. a tuning fork having a pair of tines, b. means operatively coupled to said fork to sustain said fork in vibration at its natural frequency, and c. means including an indexing mechanism to convert the vibratory action of said fork'into rotary motion for driving a gear train coupled to time-indicating hands, said means including two oppositelydirected V-shaped indexing elements whose ends are secured to the tines, whereby the vertex of one element is caused to reciprocate in a rectilinear path substantially at right angles to the direction of tine motion and the vertex of the other element is caused to reciprocate in phase opposition to the one element, the teeth of said wheel being engaged at different points by the vertices of said elements whereby said wheel is pushed by one vertex and pulled by the other in the course of each vibratory cycle of the tuning fork.

2. A timepiece as set forth in claim 1, wherein each vertex is constituted by a rectangular tongue whose lower edge engages said teeth, said tongue lying in a plane transversely disposed relative to said rectilinear path.

3. A timepiece as set forth in claim 2, wherein each V-shaped indexing element is formed by a piece of round wire whose ends are bent outwardly and are attached to said tines, the vertex being flattened to define said tongue.

4. A timepiece as set forth in claim 3, wherein the sides of said element are also flattened.

5. A timepiece as set forth in claim 1, wherein said means to sustain said fork in vibration includes an electromagnetic transducer coupled to an electronic drive circuit, said transducer being constituted by a magnet assembly mounted on one tine of said fork and cooperating with a coil assembly mounted on the other tine.

Claims (5)

1. An electronic timepiece comprising; a. a tuning fork having a pair of tines, b. means operatively coupled to said fork to sustain said fork in vibration at its natural frequency, and c. means including an indexing mechanism to convert the vibratory action of said fork into rotary motion for driving a gear train coupled to time-indicating hands, said means including two oppositely directed V-shaped indexing elements whose ends are secured to the tines, whereby the vertex of one element is caused to reciprocate in a rectilinear path substantially at right angles to the direction of tine motion and the vertex of the other element is caused to reciprocate in phase opposition to the one element, the teeth of said wheel being engaged at different points by the vertices of said elements whereby said wheel is pushed by one vertex and pulled by the other in the course of each vibratory cycle of the tuning fork.

2. A timepiece as set forth in claim 1, wherein each vertex is constituted by a rectangular tongue whose lower edge engages said teeth, said tongue lying in a plane transversely disposed relative to said rectilinear path.

3. A timepiece as set forth in claim 2, wherein each V-shaped indexing element is formed by a piece of round wire whose ends are bent outwardly and are attached to said tines, the vertex being flattened to define said tongue.

4. A timepiece as set forth in claim 3, wherein the sides of said element are also flattened.

5. A timepiece as set forth in claim 1, wherein said means to sustain said fork in vibration includes an electromagnetic transducer coupled to an electronic drive circuit, said transducer being constituted by a magnet assembly mounted on one tine of said fork and cooperating with a coil assembly mounted on the other tine.

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