US3140376A - Contact member for electric clocks and watches - Google Patents

Description

y 7, 1964 i w. TlLSE ETAL 3,140,376

CONTACT MEMBER FOR ELECTRIC CLOCKS AND WATCHES Filed Dec. 28, 1960 3 Sheets-Shee t 1 I 1| [I ll 9 l I l I JIWENTOES. WIL HELM TILSE JOSEF EGGER A TTORNEYS.

July 7, 1964 w, TlLSE ETAL 3,140,376

CONTACT MEMBER FOR ELECTRIC CLOCKS AND WATCHES Filed Dec. 28, 1960 3 Sheets-Sheet 2 A T TOR rs July 7, 1964 1 w. TILSE ETAL 3,140,376

CONTACT MEMBER FOR ELECTRIC CLOCKS AND WATCHES Filed Dec. 28, 1960 s Sheets-Sheet :5

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United States Patent 3,140,376 CONTACT MEMBER FOR ELECTRIC CLOCKS AND WATCHES Wilhelm Tilse, Pforzheim-Birkenfeld, and Josef Egger, Pforzheim, Germany, assignors to The United States Time Corporation, Waterbury, Conn., a corporation of Connecticut Filed Dec. 28, 1960, Ser. No. 78,964 Claims priority, application Germany Jan. 9, 1960 2 Claims. (Cl. 200166) This invention relates to electric clocks and watches of the type having an oscillating balance wheel or pendulum powered by the reaction between a steady magnetic field and a pulsating magnetic field. In particular, the invention relates to improvements in electrical switches for generating the magnetic impulses in mechanisms of this type where the switch is periodically closed by the rotating member at fixed points in each cycle of oscillation.

Devices of this type are generally divided into two classes, the first comprising a plurality of fixed permanent magnets and a moving coil, the second comprising a fixed coil and moving permanent magnets disposed on the oscillating member. Both classes use a mechanically activated electrical switch member intermittently to connect a source of direct current to the coil to provide a pulsed magnetic field which reacts with the permanent magnetic field to push the oscillating rotary member either once or twice .during each cycle of oscillation. The current source thus supplies energy to the system to overcome frictional losses and to power the gear train which drives the hands of the watch.

One of the principal disadvantages of systems in current use has resided in the mechanical switch, which is necessarily subjected to millions of closures in normal usage, the consequent wear resulting in a decrease of dependability with age. Aside from the normal wear resulting from friction, there occurs physical deterioration of the contacts resulting from the inherent sparking which occurs during the making and breaking of the electrical circuit. Where, as in the usual case, one of the contact members is spring mounted, and thereby subject to vibrational movements, the problem is magnified, because on each primary closing of the contacts the spring-mounted contact is subjected to natural transverse oscillations induced by the shock of the main impact. This results in bounce or chatter of the contacts which occurs prior to making complete connection. This bouncing or chattering increases the erosion of the contacts resulting from the numerous spark discharges, causing a proportionate decrease in contact life.

My present invention is directed to methods and apparatus for minimizing contact bounce and sparking between contacts in order to extend the useful life of contact members.

A feature of my invention is the addition of a loosely coupled damping weight disposed on the vibrating contact member to dampen the vibrations which occur first when the contacts close and second when the contacts break as the moving contact member swings beyond and free from the fixed contact member. Damping of this secondary vibration which occurs on separation is necessary to insure :that the spring contact member has substantially ceased vibrating by the time the second impact takes place.

Another feature of my invention resides in a novel arrangement of the oscillating contact member. To further guard against contact bounce and chatter on the closing impact, I arrange an insulating member either on the contact spring or on the moving contact in such a manner that the first physical connection takes place between one contact and the insulating member. With this arrangement no electrical contact, and consequently no sparking,

3,140,376 Patented July 7, 1964 occurs until all vibrations are effectively terminated. Thereafter, sliding electrical contact is made giving a wiping action between the contacts that promotes selfcleaning.

A further feature of the invention involves the shaping of the stationary spring contact area to minimize the electrical contact area to a virtual point contact and to promote wiping action of the contacts.

These and other features of the invention will be better understood by reference to the accompanying drawings, showing a preferred embodiment, in which:

FIG. 1 is an elevation view, partly in section, of an electric watch, embodying the invention along line 11 of FIG. 2;

FIG. 2 is a plan view of the principal elements of the electro-mechanical portion of the watch of FIG. 1 as viewed along line 22 of FIG. 1;

FIGS. 3 to 6 illustrate the switching action, step-by-step, during one sweep of the balance wheel;

FIGS. 7 to 10 illustrate various forms of the damped spring contact member; and

FIGS. 11 to 13 are sectional views of the preferred type of contact member as illustrated in FIGS. 7 to 10.

The main elements of an electric watch embodying the present invention are shown in elevation and partly in section in FIG. 1, the section being taken along line 11 of FIG. 2. A balance wheel body 20 of non-magnetic material is arranged on a balance staff 14 which is journaled at its upper end in the balance cock 10 and at its lower end in the pillar plate 11. Also included on the staff 14 are the hair-spring 16, secured to the collet 18 at its inner end and to the stud 17 at its outer end in the usual manner, and upper and lower roller tables 30 and 35, respectively. The lower roller table 35 has an eccentric roller jewel 37 adapted to engage and drive the gear train, generally indicated at 38, in the normal arrangement. The upper roller table 30 has a flanged portion 31 supporting a crescent-shaped pin 32 which may be a jewel or other non-conducting material.

The balance wheel body 20 carries a sector-shaped coil 25 which is adapted to react magnetically to a series of three alternately polarized permanent magnets 40 which are disposed on the pillar plate 11. The magnetic axes of the magnets are parallel to the axis of the balance staif 14. One end 28 of the coil 25 is electrically connected to the balance wheel which is grounded to the pillar plate via hair-spring 16 and stud 17. The other end 27 of the coil 25 is electrically connected to a cylindrical contact pin 26 aligned along a radius of the balance staff directly outside the upper roller jewel 32. The pin 26 is mounted on but insulated electrically from the balance wheel body 20 by the insulated insert 24.

An electrical contact member, generally indicated at 43, includes an elongated spring member 44, mounted at its extremity in an insulated block or base 49 secured in any suitable manner to the pillar plate 11, as by stud 41. The contact member 43 is electrically connected via wire 51 to a source of voltage 50 which may be a small dry cell enclosed either internally within the movement or externally in the watch band, not illustrated. The other electrode of the battery 50 is suitably connected to the ground circuit which includes the pillar plate 11 and the watchcase itself, not shown. The electrical contact member 43 as shown in FIG. 2, includes a spring finger 44 having at its other extremity a contact area 45 which is adapted periodically to contact the pin 26 twice during each cycle of oscillation of the balance wheel 20.

One of the features of this invention resides in the physical arrangement of the spring contact member 43, and a preferred embodiment thereof is illustrated in FIGS. 1 through 6 inclusive. Other suitable forms of the spring contact member, to be hereinafter described, are illustrated in FIGS. 7 to 10 inclusive.

FIG. 2 illustrates the preferred form of spring contact member 43. The spring 43 is preferably of hairpin shape, having a longer leg 44 and a shorter leg 46 interconnected by the curved contact portion 45. The member is mounted in such a manner that the center of the radius of curvature of the portion 45 lies along a line which intersects the axis of staff 14. A damping member 48 is disposed on the leg 44 at a point to be hereinafter described. The shorter leg 46 is bent at its outer extremity into the form of an inwardly projecting V so that the apex of the V lies close to the inside edge of the leg 4-4. The ringshaped damping member 48 is arranged to loop loosely the two legs 44 and 46 at their closest point. The weight of the damper 48 is selected so that its natural resonant frequency of vibration in a transverse direction differs from the natural resonant frequency of transverse vibration of the spring member 43, thus serving to damp vibrations of the spring member resulting from the impact of the oscillating balance wheel assembly. It is to be noted that the damper 48 is free to vibrate transversely to the longitudinal axis of the spring member 48 but is restricted from longitudinal movement along the leg 44.

It is advantageous to select the longitudinal location of the damper member 48 on the basis of the following criteria. It is well-known that transverse vibrations of a bar clamped at one end include a fundamental resonant frequency of vibration which may be calculated from known formulae, as, for instance, those illustrated and discussed in the book by Harry F. Olson entitled Elements of Acoustical Engineering, published in 1940 by the D. Van Nostrand Company, Inc., in Section 3.3 at pages 38 and 39. As also pointed out by Olson, harmonic vibrations or overtones also are present in the vibrating bar. These secondary vibrations have antinodes, or points of maximum deflection, existing at discrete points along the bar. For example, the first overtone has an antinode located approximately halfway along the bar while the second overtone has an antinode located approximately two-thirds the way along the length of the bar, as measured from the fixed end. It has been found that surprisingly effective damping occurs if the damper member 48 is located at any point within the region between onehalf and two-thirds of the length of the member as measured from the fixed end.

Systems subjected to vibrational oscillation as a result of some initially applied force are known to have specific vibration decay characteristics dependent on such factors as length, density, modulus of elasticity and radius of gyration of the body. For example, a certain spring member may have a vibration decay characteristic of one-tenth of a second. This represents the length of time, as measured from the initial application of energy, to the point when for all practical purposes the vibrations have ceased. When a damping weight is attached to the body in the proper manner it is possible to shorten the vibration decay characteristic from one-tenth of a second to, say, one-twentieth of a second or less. The weight of the damping member may be increased, however, further to shorten the decay characteristic to, say, one-fortieth of a second if desired. A further factor must be considered in determining the weight of the damping memher, that is, if the Weight is too heavy, the impedance which the weighted spring contact member presents to the rotating balance wheel during each sweep of the balance may disturb the natural period of oscillation sufficiently to cause it to lose its inherent isochronous properties essential to its accurate timekeeping function. Thus the Weight as well as the position of the damping member 48 must be selected from optimum performance.

A still further factor to be considered in obtaining optimum performance of the spring and damper assembly is the physical size of the damping member. By that is meant primarily the size of the internal opening with respect to the dimensions of the spring. The actions of these two combined members may not be analyzed by simple harmonic motion theory since the damping weight is only loosely interconnected with the spring member. The damping ring is essentially free to move transversely in space but limited in the vertical and longitudinal directions. The ring once set in transverse motion in a given direction continues moving in that direction until it strikes the spring or is struck by the spring and moved in a different direction. It has been found that the optimum size and weight of the damping member are achieved when the contact spring and the damping member strike each other after the contact spring has undergone one complete cycle of oscillation (from zero to maximum deflection in the direction of movement of the contact pin, to zero, to maximum deflection in the opposite direction, and back to zero) and is about to commence its second oscillation, and after the damping ring has completed only one half an oscillation (from zero to maximum deflection and back to zero) and is passing through zero in the opposite direction. It has been determined that the optimum sized damping weight will undergo deflections of substantially one-half the deflection of the contact spring measured at the point of contact.

For a preferred embodiment of the invention it has been determined, in a system of the type illustrated in FIGS. 1 through 6 having a balance 20 weighing 0.3 gram and having a periodicity, in combination with the hairspring, of 6 beats per second, that a contact spring 44 of precious metal having a cross-sectional dimension of 0.2 millimeter by 0.04 millimeter, an overall length of 9.0 millimeters and weight of 1.3 micrograms; a damping member of toroidal shape having an internal diameter of .32 millimeter and an external diameter of 0.6 millimeter, weighing 1.0 microgram positioned 5.5 millimeters from the fixed end thereof provides satisfactory operation.

Other suitable forms of the spring contact member 43 are illustrated in FIGS. 7 through 10 inclusive, where the spring member is a straight rod or bar fixed at one end. In FIG. 7 the damper 63 comprises an L-shaped member, having an outer ring part 65, and an inner ring part 64 coupled to a ring 62 disposed in the holding member 61. FIG. 8 illustrates a form of spring 70 having a one-turn loop '71 which interlinks the annular damper weight '72. FIG. 9 shows a further form wherein the hailpin-shaped spring is inverted with the shorter leg having a loop 76 at its extremity interconnecting the annular damper 77. FIG. 10 depicts a further variation in form wherein a straight spring member 80 has a transverse slotted opening therethrough to receive a freely sliding member 81. The member 81 has weights 82 and 83 at its extremities which provide the damping action and prevent separation of the members.

Another feature of my invention resides in the shaping of the end of the spring member to provide for eflicient and long-wearing electrical connection between it and the pin 26. The active contact area 45 of the spring contact 43 may be curved. This promotes removal of oxidation products from the contact surfaces that form as a result of the sparking. However, the most desirable arrangement results if the end of the spring finger has a spherical shape in its contact area. With the preferred form of contact spring, as shown in FIGS. 1 to 6, the arcuate portion 45 may be ground or formed as illustrated in FIGS. 11 through 13. FIG. 11 is an enlarged plan view of the end of the spring member 85. FIG. 12 illustrates the cross-sectional shape of the member taken along line 121l2 of FIG. 11. FIG. 13 illustrates the cross-sectional shape of the arcuate portion 87 as taken along line 1313 of FIG. 11. When the end of the fixed contact member is spherical, as depicted, only line contact is established between the contacts during a sweep of the balance wheel, and at any particular instant of time during the contact period only virtual point contact exists between the bodies. The wiping action which is inherent serves to clean the surface of the contact areas of any oxidation products produced by sparking.

A further feature of my invention resides in the arrangement of the rotating contact pin 26 and the insulated member 32. In describing the function of the insulating member 32, reference is made to FIGS. 3 to 6 inclusive, which illustrate the various positions assumed by the two electrical contacts during one counterclockwise sweep of the balance wheel. In FIG. 3, the spring finger 43 is in its neutral or at-rest position and the balance wheel is turning counterclockwise, as indicated by the arrow P. As seen in FIG. 4, the first impact between the two met bers occurs between the arcuate portion 45 of the spring member 43 and an edge of the insulating pin 32. At this position, the member 43 undergoes vibrating oscillations as a result of the impact, and any residual contact bounce which has not been completely eliminated by the damper 48 will rapidly subside or decay prior to the first electrical contact and therefore without the usual numerous spark discharges, energy loss and pitting. As seen in FIG. 5, after the vibration of spring contact 43 has dissipated, the further counter-rotation of the balance wheel causes electrical connection to be established gradually between member 43 and pin 26. FIG. 6 depicts further counter-rotation of the balance wheel to the point where the member 43 is about to slide ofi the pin 26 and break the electrical circuit. Member 43 now being under tension snaps away from the pin 26 to minimize the spark discharge resulting from the collapse of the magnetic field in coil 25. At this point, member 43 again enters upon a vibratory state which is quickly arrested by the action of damper 48 prior to the subsequent impact by the opposite edge of insulating pin or bumper 32, during the reverse half-cycle of oscillation of the balance wheel.

While each of the features described above including the addition of a damping weight to the spring, the shaping of the contacts to provide only point contact at any instant and use of an insulated bumper to provide initial physical connection and vibration absorption prior to electrical connection of the contacts in themselves, tend to reduce sparking, combinations of any two of the features will yield further reduction in sparking. In the preferred embodiment of the invention I include all three features simultaneously to virtually eliminate all sparking problems.

What is claimed is:

1. A fixed electrical switch contact member adapted to cooperate with a rotating switch contact member comprising an elongated member of spring material supported at one end thereof at a point remote from the rotating contact member, the other end of said spring member being adapted to contact periodically said rotating contact member, said spring member having a damping member thereon disposed at a point intermediate the ends thereof, wherein the switch member is of hairpin shape and has two leg portions and an arcuate portion interconnecting said leg portions, one of said legs is longer than the other and adapted for mounting said member at its extremity, the shorter of said legs has an inward V-shaped bend near its extremity, and said damping member is ringshaped and disposed to link loosely both legs at the notch of the V bend.

2. A fixed electrical switch contact member adapted to cooperate with a rotating switch contact member comprising an elongated member of spring material supported at one end thereof on a base at a point remote from the rotating contact member, the other end of said spring member being adapted to contact periodically said rotating contact member, said spring member having a damping member thereon disposed at a point intermediate the ends thereof, wherein the switch member is of hairpin shape and has two legs and an arcuate portion interconnecting said legs, one of said legs is longer than the other and adapted for mounting said member at the legs extremity, means on a leg portion of the switch member holds the damping member against longitudinal movement along said switch member and permits movement transverse to the axis of the spring member, and said damping member is ring-shaped, loosely surrounds a leg of the switch member, and is unconnected to the base and the legs.

References Cited in the file of this patent UNITED STATES PATENTS 2,088,411 Fagley July 27, 1937 2,494,622 Lamb Jan. 17, 1950 2,599,953 Summers June 10, 1952 2,847,529 Munn Aug. 12, 1958 2,874,251 Dreyfus Feb. 17, 1959 2,887,551 Detwiler May 19, 1959 FOREIGN PATENTS 161,786 Australia Aug. 27, 1953 1,001,719 Germany Jan. 31, 1957 1,037,676 France June 9, 1958

Claims (1)

1. A FIXED ELECTRICAL SWITCH CONTACT MEMBER ADAPTED TO COOPERATE WITH A ROTATING SWITCH CONTACT MEMBER COMPRISING AN ELONGATED MEMBER OF SPRING MATERIAL SUPPORTED AT ONE END THEREOF AT A POINT REMOTE FROM THE ROTATING CONTACT MEMBER, THE OTHER END OF SAID SPRING MEMBER BEING ADAPTED TO CONTACT PERIODICALLY SAID ROTATING CONTACT MEMBER, SAID SPRING MEMBER HAVING A DAMPING MEMBER THEREON DISPOSED AT A POINT INTERMEDIATE THE ENDS THEREOF, WHEREIN THE SWITCH MEMBER IS OF HAIRPIN SHAPE AND HAS TWO LEG PORTIONS AND AN ARCUATE PORTION INTERCONNECTING SAID LEG PORTIONS, ONE OF SAID LEGS IS LONGER THAN THE OTHER AND ADAPTED FOR MOUNTING SAID MEMBER AT ITS EXTREMITY, THE SHORTER OF SAID LEGS HAS AN INWARD V-SHAPED BEND NEAR ITS EXTREMITY, AND SAID DAMPING MEMBER IS RINGSHAPED AND DISPOSED TO LINK LOOSELY BOTH LEGS AT THE NOTCH OF THE V BEND.

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