US2690646A - Escapement mechanism - Google Patents

Description

1954 c. F. CLIFFORD ESCAPEMENT MECHANISM 2 Sheets-Sheet 1 Filed June 2, 1949 Oct, 5, 1954 c. F. CLIFFORD ESCAPEMENT MECHANISM 2 Sheets-Sheet 2 Filed June 2, v 1949 Patented Oct. 5, 1954 UNITED STATES 2,690,645 PATENT OFFICE Claims priority, application Great Britain June 10, 1948 ll Claims.

This invention relates to magnetic escapement mechanism for timepieces, and more particularly to mechanism in which the timekeeping oscillator consists of a vibratory magnet attached to a spring and coupled to a magnetic escapement wheel by magnetic forces acting across one or more air gaps between the escape wheel and the magnet. Such mechanism is described in my prior British patent specification N 0. 596,216.

The present invention concerns primarily, but not exclusively, magnetic escapement mechanisms for portable timepieces wherein the vibratory magnet is carried by the spring to which it is attached and is capable of operating in any position.

The reed and like spring-controlled vibratory armatures capable of operating in any position which have hitherto been used for controlling magnetic escapements -(e. g. as described in my prior specification above referred to) have suffered from the disadvantage that they are liable to be disturbed by impact or vibration and thus brought out of step with the escape wheel. They are also liable to position error due to the eliect of gravity upon the oscillatory mass. These undesirable eflects can be minimised by increasing the natural frequency of the oscillatory system, but they cannot be reduced as much as is desired for ordinary purposes, except by using an oscillatory system of inconveniently high natural frequency.

According to the present invention, in order to remove these disadvantages, the magnet and the leaf-type spring that carries it are arranged so that the oscillatory axis of the oscillator extends transversely of the spring intermediate the iongitudinal extent of the oscillator lengthwise of the spring, and preferably through the cent-er of gravity of the oscillator. The oscillatory system is thus substantially balanced about its oscillatory axis and is thereby rendered substantially insensitive to gravitational forces. The risk of derangement by inertial forces due to shock is also materially reduced.

While the invention includes arrangements in which the vibratory movement of the magnet or keeper is substantially a rocking movement about an axis passing approximately through the centre of gravity of the oscillatory system, it is not restricted to such arrangements, but includes a modification or development in which a rectilinear vibratory movement is employed.

The nature of the invention and the manner in which the same is to be performed will be understood from the following description of several different examples of escapement mechanisms constructed according to the invention, reference being made to the accompanying drawings in which:

Figure l is a perspective view showing the essential parts of an escapement mechanism constructed according to a form of the invention 2 having a vibratory magnet which extends on op=- posite sides of the support to which the spring is attached,

Fig. 1A is a perspective view similar to Fig. .l, the oscillator of the escapement mechanism shown having, however, an oscillatory'axis which passes substantially through the center of gravity of the oscillator,

Figures 2, 3 and 4 are similar views of three different examples of construction in which the magnet is located on one side only of the support, the required balance being obtained by arranging the spring so that it extends on both sides of the support,

Figure 5 is a similar view of another modification in which a diiferentm'ode of vibration of the oscillatory system is employed, and

Figure 6 illustrates another modification in which a magnet is arranged to have a rectilinear vibratory movement due to a third mode of vibration, i. e. longitudinal.

Corresponding parts are designated by the same reference numerals in the different modifications oi the invention shown in different figures or the drawings.

The mechanism shown in Figure l of the drawings comprises a vibratory magnet I carried by a spring 2 that permits its vibration and provides its support, and a magnetic escape wheel 3 on a rotatable spindle 4 adapted to be driven by an external driving mechanism such as the clockwork mechanism of a timepiece.

As shown in Figure l, the magnet l is a generally U-s'haped permanent magnet having inturned ends 5 forming parallel pole faces of opposite magnetic polarity facing one another across a gap into which the wheel 3 projects so that there is a small air gap between each of the pole faces of the magnet l and the adjacent side of the wheel 3.

The spring 2 consists of a fiat leaf-type spring or reed, preferably made of beryllium, copper or chronovar and is attached to the magnet i the end thereof remote from the ends 5. It extends in the plane of the magnet I and is attached to a fixed support 6 at a point located, in this instance, approximately midway between the ends of the magnet I. The spring 2 is thus supported at a point located approximately at the centre of gravity of the oscillatory system (consisting of the magnet I and spring 2).

The magnet l is adapted to vibrate under the control of the spring 2 by rocking about an axis parallel to the axis of the spindle 4, so that the pcle-iaces formed by the inturned ends 5 of the magnet vibrate towards and away from the spindie 4 in planes parallel to the plane of the escape wheel 3.

The vibratory movement of the magnet causes the pole faces of the magnet to move in a wavy oath relatively to the wheel 3 as the wheel rotates. The wheel has a highly permeable magnetic rim l which is shaped to correspond as closely as possible with this wavy path having regard to the varying amplitudes of poles 5. The magnet is thus coupled to the wheel by the magnetic attractive forces acting across the gaps between the inturned ends 5 of the magnet and the rim '1 of the wheel. The magnetic attraction is suiiiciently powerful to control the rotation of the wheel against the torque applied to it through the spindle t so that the wheel is constrained to rotate at a speed determined by the natural frequency of vibration of the oscillatory system consisting of the magnet I and spring 2.

The oscillatory system is impulsed by the rotation of the wheel 3; and, in order to enable the oscillatory system to vibrate freely at an amplitude determined by the energy of its vibration, the rim I is formed with magnetic extensions 8 and 9 which form branch extensions of the wavy path and which are arranged so that the polefaces of the magnet can leave the wavy path 1 and move along one of the extensions 8 or 9 at each extreme of the vibratory movement of the magnet. The extensions 8 on one side of the rim I project outwardly, and the extensions 9 on the other side project inwardly and are formed by spokes connecting the rim I to the hub of the wheel.

It will be evident that the axis about which the magnet I vibrates is located near to the fixed support 6 and on the side thereof remote from the inturned ends 5 of the magnet. More particularly, the oscillatory axis lies midway of the spring length which connects the magnet I with the support 6.

The length of the spring 2 is, in this particular instance, so chosen that the fixed support 6 is located approximately at the centre of gravity of the oscillatory system. Extremely accurate adjustment of the position of the support in relation to the centre of gravity is not necessary, as the system is not overly sensitive to small discrepancies between the position of the support 6 and its theoretically perfect position to be described presently. Thus, in Fig. 1A the magnet and support are so coordinated that the oscillatory axis (do't-and-dash line) of the oscillatory system passes through the center of gravity of the latter. The efiect of these arrangements, and especially that of Fig. 1, is that the magnet and spring assembly is substantially balanced about the oscillatory axis thereof which extends at right-angles to the plane in which the magnet can be moved by flexing the spring 2. By reason of this substantial or complete balance, the escapement is much more resistant to adverse effects of shock and vibration than would be the case if the oscillatory system were not so balanced. The balanced mounting of the magnet also minimises position error in the timekeeping of the oscillatory system due to the efiect of gravity on said oscillatory system.

Figure 2 of the drawings shows a modified construction according to the invention in which the oscillatory system comprises two magnets I in the form of rods or bars attached to the arms of a generally U-shaped spring 2 attached to a fixed support 6 by means of a spring tongue 2a which is located between the outer arms of the U and projects inwards from the base of the U towards the magnets I. In this construction, the magnets I are located entirely on one side of the support 6 but the spring 2 extends on both sides of the support. The vibratory system consisting of the magnets I and spring 2 is substantially balanced in a similar way as the system described in Figure l, the weight of the magnets I and portion of the spring 2 on one side of the support 6 being in this instance approximately balanced by the weight of the portion of the spring 2 on the opposite side of the support 8. The oscillatory axis of the instant vibratory system extends transversely of the spring tongue 2a somewhere between the ends thereof. Of course, the spring 2 of the instant vibratory system could, in view of the teaching of Fig. 1A, be readily arranged so that the oscillatory axis would pass approximately through the center of gravity of the vibratory system.

In the construction shown in Figure 2, the magnets i are not permanently magnetised but are made of low-loss magnetic material, e. g. Mumetal and are magnetised by means of a fixed permanent magnet I9 having pole faces II and I2 of opposite magnetic polarity which are located near to but do not touch the outer ends of the magnets. The escape wheel 3 cooperates with the pole faces on the inner ends of the magnets I in the same way as the wheel 3 described with reference to Figure 1 cooperates with the pole faces of the magnet shown in that figure.

Figure 3 of the drawings illustrates another modified construction in which a permanent bar magnet I is carried by a generally T-shaped spring 2 having extensions 3a at the end of the bar of the T, which extensions are parallel with the stem 3b thereof. The magnet I is fixed to the free end of the stem 3b, and the spring is supported by attaching the ends of the extensions 3a to a pair of fixed supports 6 located on an axis X which passes approximately through the centre of gravity of the oscillatory system consisting of the magnet I and spring 2. This construction is similar to that shown in Figure 2, in the respect that the spring 2 with its stem 31) extends on both sides of the supports 6, so that the magnet l and the portion of the spring 2 to which the magnet is attached is substantially balanced by the portion of the spring 2 which extends on the side of the supports 6 remote from the magnet I. Here again, the oscillatory axis of the vibratory system I, 2 extends transversely of the spring extensions 3a somewhere between the ends thereof. If desired, the spring 2 could be so arranged that the oscillatory axis of the system would pass substantially through the center of gravity of the latter.

The magnet I, in the construction shown in Figure 3, cooperates with a pair of escape wheels 3 on a common spindle 4 and aligned axially so that each end of the bar magnet I cooperates with the rim 1 and extensions 8 and 9 on one of the wheels 3. There is, of course, a small air gap between each end of the magnet i and the adjacent wheel 3.

Figure 4 shows another construction in which a magnet I is carried by a generally T-shaped spring 2 fixed by extensions 3a to a pair of fixed supports 6 located on an axis X which passes approximately through the centre of gravity of the oscillatory system consisting of the magnet I and spring 2. In this construction, the magnet I is a bar magnet, one end of which cooperates with an escape wheel 3 on a spindle 4 having its axis at right angles to the axis X and to the plane of the spring 2 in the repose condition of the latter. The escape wheel 3 is of generally cylindrical shape and is formed with a wavy magnetic path I and with extensions 8 and 9 on its circumferential surface of rotation. The magnet I vibrates, as indicated by the arrows in Figure 4, about an axis extendi-ng transversely of the spring extensions 3a somewhere between the ends thereof, and the surface of the escape wheel 3 is. curved in the direction of its length to correspond to the curved path of movement of the cooperating pole of the magnet I. There is of course a small air gap between the wheel 3 and the adjacent pole face of the magnet I.

Figure. 5 of the drawings shows another form of construction comprising a vibratory magnet I attached to the stem 3b of a generally T- shaped spring having extensions 3a by which it is attached to a pair of fixed supports 6., these supports being located on an axis X which passes approximately through the centre of gravity of the system consisting of the magnet I and spring 2. In this construction, the magnet I is adapted to vibrate rotationally about the axis of the stem 31) of the spring, the stem 3?) acting as a torsion spring. The magnet I is a generally U-shaped permanent magnet and has inturned ends 5 adapted to cooperate with an escape wheel 3 mounted between the poles 5 upon :a spindle 4 which has its axis at right-angles to the plane of the spring 2 in its repose condition and at right-angles to the axis of rotational vibration of the magnet I and reed 3b. The escape wheel in this construction consists of :a low-loss magnetic disc, e. g. Mumetal, formed with radial corrugations arranged so that the edge of the disc forms the Wavy path I which cooperates with the pole faces 5 of the armature. The disc is shaped so that the wavy path 1 comprises an odd number of waves, this being necessary to enable the diametrically opposed pole faces of the magnet I to operate in unison.

In the construction shown in Figure 5., the previously described extensions 8 and 9 of the wavy magnetic path are not used. The vibration of the magnet must therefore conform approximately in amplitude to the amplitude of the wavy path I. To obtain satisfactory operation under these conditions, it "is necessary to regulate the torque applied to the spindle 4 so that the amplitude of the oscillation of the magnet due to the energy transmitted to the oscillatory system conforms very nearly to the amplitude set by the wavy path I, or the poles of the magnet may be made thicker (in. the direction of vibration) to give tolerance for varying amplitudes of vibration.

Figure 6 of the drawings shows another modification of the invention which employs a U- shaped permanent magnet 1 similar to that described with reference to Figure l and having inturned ends 5 forming poles of opposite polarity which face one another across a gap .in which an escape wheel 3 similar to that described with reference to Figure 1 is located. In the construction shown in Figure 6', the magnet is supported by means of a control spring 2 in a plane which intersects the axis of the escape wheel 3; and it is adapted to vibrate rectilinearly as indicated by the arrows in Figure .6. The spring 2 may be constructed so that it is more flexible in the direction of its length to make this mode of vibration easier, although a straight spring will vibrate longitudinally at high frequency. The support -6 to which the spring 2 is attached is located approximately at the centre of gravity of the oscillatory system consisting of the magnet I and spring 2, so that the magnet is substantially balanced about the support.

As compared with the conventional balance wheel, the vibratory magnet used according to the present invention has the advantage of having no bearings and hence no bearing friction or'wcar.

The balanced arrangement of the magnet enables an oscillatory system having a comparatively low natural frequency (e. g. of the order of from 50 cycles per second) to be used without rendering the mechanism unduly sensitive to shock and without introducing a serious position error. As will be well understood by those skilled in the art, the liability to position error and the degree of sensitiveness of the mechanism to shock will depend on the frequency at which the oscillatory system is adapted to operate. A system of relatively high frequency is inherently more resistant to shock and less liable to position error. By balancing the assembly in accordance with the present invention, the resistance to shock is considerably increased, and liability to position error is reduced, as compared with. an unbalanced assembly adapted to operate at the same frequency.

For a portable timepiece such as an alarm clock, it is convenient to adapt the magnet to vibrate at a frequency corresponding to the frequency of public electricity supply mains (e. g. 50 cycles per second) as this facilitates stroboscopic adjustment of the oscillatory system by merely viewing the magnet assembly in a light fed from the mains.

Any convenient method may be employed for adjusting the natural frequency of vibration of the oscillatory system for the purpose of regulating the timepiece. For instance the frequency may be adjusted by loading the magnet I or by altering the effective length of the spring 2. Figure l of the drawings shows a simple regulating device which consists of an eccentric clamping disc I 2a controlled by means of a lever-arm I3. The spring 2 is tightly clamped between a shoulder of the screw it and the fixed support '6. The disc I2a is spring loaded by a Thackery washer I5 against the spring 2. By rotating the eccentric disc 32a. by means of the lever I3, the effective length of the spring 2 can be adjusted for the purpose of regulating the natural frequency of the oscillatory system.

It is to be observed that the spring 2 used in the several constructions described is inherently rigid in one plane and is arranged so that this inherent rigidity prevents movement of the magnet or keeper I towards or away from the escape wheel, and thus maintains the air gap or air gaps between the magnet or keeper and escape wheel. It appears further from the drawings that the spring 2 is, in its own plane, sufficiently stiff or rigid to be substantially resiliently non-bent in its repose position in any disposition of the vibratory system.

Unless the magnet is of negligible thickness '(as, for example, in the construction shown in Figure 1) it should be halved where it joins the spring so that the latter lies in the thickness of the magnet. Alternatively, the spring could be bent to achieve the same purpose.

I claim:

1. A magnetic escapement mechanism comprising an escape wheel and a cooperating oscillator, said oscillator being coupled to said wheel by magnetic forces and comprising a magnet carried by a leaf-type spring and a support to which said spring is attached at a point such that the oscillating movement takes place about an axis extending transversely of said spring and passing substantially through the center of gravity of the oscillator.

2. An escapement mechanism according to claim 1 wherein the magnet is adapted to vibrate by bending the spring and the vibratory movement thereof is substantially a rocking movement about a transverse axis of the spring passing approximately through the center of gravity of the oscillator.

3. An oscillator, comprising a rigid inertiamember, a leaf-type spring carrying said memher and forming with the latter an oscillatory unit, a support on which said spring is mounted so that a length of said spring connects said member and support, said member and spring being arranged so that the latter will, on oscillation of said unit, flex about a fixec. transverse axis of said spring which passes substantially through the center of gravity of said unit and is spaced from said said support so that the unit is substantially immune to shock, and means for impulsing said unit for oscillation of same at its natural frequency.

4. An oscillator, comprising a rigid inertiamember, a leaf-type spring-member carrying said inertia-member, and forming with the latter an oscillatory unit, a support on which said spring-member is mounted intermediate the ends of one of said members so that a length of said spring member connects said inertia-member and support, said members being arranged so that said spring-member will, on oscillation of said unit, flex about a fixed transverse axis thereof which passes substantially through the center of gravity of said unit to provide a substantially isochronous oscillator which is substantially immune to shock, and means for impulsing said unit for oscillation of same at its natural frequency.

5. An oscillator, comprising a rigid inertiamemoer having spaced opposite legs and at least one connecting yoke at adjacent ends of said legs, a leaf-type spring extending between said legs and being secured at one end to said yoke, said spring and inertia member together forming an oscillatory unit, a support on which the ther end of said spring is mounted, said member and spring being arranged so that the latter will. on oscillation of said unit, flex about a fixed transverse axis of said spring which passes substantially through the center of gravity of said unit, and means for impulsing said unit for oscillation of same at its natural frequency.

6. A magnetic escapement mechanism, comprising an escape wheel, a magnet, a leaf-type spring of uniform cross section, said spring carrying said magnet and forming with the latter an oscillatory unit coupled to said wheel by magnetic forces, and a support on which said spring is mounted so that a length of said spring connects said magnet and support, the oscillatory axis of said unit extending transversely of said spring between said spring length, and said magnet being arranged so that the center of gravity of said unit lies substantially in said oscillatory axis.

7. A substantially isochronous oscillator for use with an escape wheel of a magnetic escapement, comprising a magnet, a leaf-type spring carrying said magnet and forming with the latter an oscillatory unit, a support on which said spring is mounted so that a length of said spring connects said magnet and support, said magnet and spring being arranged so that the latter will, on oscillation of said unit, flex about a fixed transverse axis of said spring which passes substantially through the center of gravity of said unit, and magnetic means for impulsing said unit for oscillation at its natural frequency.

8. A magnetic escapement mechanism, comprising an escape wheel, a magnet member, a. leaf-type spring member carrying said magnet member and forming with the latter an oscillatory unit coupled to said wheel by magnetic forces, and a support on which said spring member is mounted intermediate the ends of one of said members so that a length of said spring member connects said magnet member and support, said members being arranged so that said spring member will, on oscillation of said unit, flex about a transverse axis thereof which passes substantially through the center of gravity of said unit.

9. A magnetic escapement, comprising an escape wheel, a generally U-shaped magnet having spaced opposite legs and a connecting yoke, a leaf-type spring extending between said legs and being secured at one end to said yoke, said spring and magnet together forming an oscillatory unit coupled to said wheel by magnetic forces, and a support on which the other end of said spring is mounted, said magnet and spring being arranged so that the latter will, on oscillation of said unit, flex about a transverse axis of said spring which passes substantially through the center of gravity of said unit.

10. An oscillator, comprising a leaf-spring type inertia member adapted to serve as an oscillatory unit, a support on which said member is mounted intermediate its ends, said member being shaped so that the same will, on oscillation, flex about a fixed transverse axis thereof passing substantially through the center of gravity of said member and spaced from said supports so that said unit is substantially isochronous and substantially immune to shock, and means for impulsing said unit for oscillation of same at its natural frequency.

11. An oscillator, comprising a rigid inertia member, a leaf-type spring of uniform cross section, said spring carrying said member and forming with the latter an oscillatory unit, a support on which said spring is mounted so that a length of said spring connects said memher and support, the oscillatory axis of said unit being fixed and extending transversely of said spring midway between said spring length, said member being arranged so that the center of gravity of said unit lies substantially in said oscillatory axis, and means for impulsing said unit for oscillation of same at its natural frequency.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 554,700 Kohler Feb. 18, 1896 1,522,217 Warren Jan. 6, 1925 1,771,383 Roe July 22, 1930 1,825,382 Baker Sept. 29, 1931 2,061,047 Schweitzer Nov. 17, 1936 2,427,990 Coake Sept. 23, 1947 FOREIGN PATENTS Number Country Date 277,760 Germany Sept. 4, 1914 451,035 Germany Oct. 22, 1927

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