US2340182A - Electric clock - Google Patents

Description

Jan. 25, 1944 T. B. GIBBS ET AL ELECTRIC CLOCK Filed Sept. 9, 1940 INVENTQRS. Thomas 5. Gabbs Patented Jan. 25, 1944 ELECTRIC CLOCK Thomas B. Gibbs and Jean assignors to George W. cago, 111., a corporation of Delaware Application September 9, 1940, Serial No. 355,952

Fink, Delavan. Wis.,

Borg Corporation, Chi- 19 Claims. (01. 58-28) The present invention relates in general to electric clocks, and more in particular to clocks of the type in which the mainspring is omitted and an electromagnet is employed to maintain the balance in oscillating condition, the magnet being intermittently energized under control of the balance. Clocks of this type are well adapted for use in automobiles, and the object of the inven tion may therefore be considered to be the pro-- vision of a new and improved autombile clock, although certain features of the invention are not necessarily so limited and are adapted for use in other types of clocks.

A feature of the invention is a new and improved contact device for controlling the circuit of the drive magnet. A small permanent magnet is used, which actuates the contact device at each oscillation of the balance.

A further feature is a new and improved magnetic circuit for the drive magnet, so designed that the rate of the clock is substantially independent of voltage variations over a range which is at least as great as that which is usually met with in practice.

A further feature is a new and improved drive mechanism by means of which the oscillatory motion of the balance is converted into a unidirectional motion of the clock train.

A still further feature is a new and improved drive mechanism which also functions as a contact device for controlling the circuit of the drive magnet, thus permitting a separate contact device to be dispensed with.

There are other features which with those mentioned above will be described in detail hereinafter, reference being had to the accompanying drawing, in which- Fig. l is a rear view of a clock constructed in accordance with the invention;

Fig. 2 is another rear view of the clock, on a larger scale, and with the back frame plate removed;

Fig. 3 is a side view looking toward the balance as seen in Fig. 2;

Fig. 4 is another side view taken from the as the clock is seen in Fig. 3;

Fig. 5 is a fragmentary view showing details of the magnetic type contact device for controlling the circuit of the drive magnet;

Figs. 6, '7 and 8 are diagrammatic views showing the essential parts of the new drive mechanism in different positions which they assume during oscillation of the balance; and

Figs. 9 and 10 are fragmentary views showing left - as shown in Figs. 2, 3, and 4.

how the drive mechanism can be used for controlling the magnet circuit.

Referring to the drawing, the various parts of the clock are mounted on a frame which comprises the front plate 2, the plate 3, and three posts 5, 6, and I. The front plate 2 may be circular in shape, and has the three posts secured to it by a riveting or staking operation, as indicated in Figs. 3 and 4 of the drawing. Each post is reduced in diameter for about half its length, as shown by the dotted lines, and the ends of these reduced portions are threaded. The shape of the plate 3 can be seen from Fig. 2, which indicates that in the vicinity of posts 5 and 5 the plate conforms to the inner surface of the pole pieces l0 and II, except fo the two cars 8 and 9, which'pass through slots if]. the pole pieces and are drilled to receive the reduced portions of the posts. Plate 3 is also drilled at a point corresponding to the location of post I.

In assembling the frame, the two pole pieces are forced onto the ears Band 9 of frame plate 3, where they are retained by the press fit. The .plate 3may then be placed in position against the shoulders on posts 5, 6, and I, after which tubular spacers IZ are assembled on posts 6 and l, and a short spacer l3 on post 5. The contact springs I l and m, formed integrally with one another, are then piaced on post 5 above spacer 13, after which the spacer I5 is added. The assembly is then secured together firmly by means of nuts It. It Will be understood that other parts may also be mounted on plate 3 before it is assembled in me frame if desired.

The back plate 4 may be regarded as part of the frame, although it IS readily removable. The plate 4 is prelerably made of some suitable sheet insulat ng material. It has holes drilled to correspond to the locations of posts 5, ii and l, andis clamped in position against the nuts lb by three nuts I1. I

The balance comprises a ring I B, of brass or other suitable material, and a four-pole armature which also functions as a support for the ring. The armature is a sheet-metal stamping of high grade magnetic material, as will be subsequently explained more in detail, and is shaped The four poles are indicated at I9, 20, 2|, and 22, and are connected to a central hub section by means of spokes 23 formed integrally therewith. The ends of the poles are bent at right a circle of the same diameter as ference of ring l8, thus forming a partial enclothe" outline of sure for the ring, which may be held in position by a press fit, or in any suitable manner.

The balance is mounted on an arbor 25, which has a jeweled bearing at one end in the downturned portion 26 of frame plate 3, as shown in Figs. 2 and 4. At the other end the arbor 25 has a plain jeweled bearing and also a thrust bearing, which are supported on the balance cock 2! in known manner. The thrust bearing is required because the clock is intended to be mounted with the balance arbor in a vertical position. The balance cock is provided with a base portion 28, which is secured to the frame plate 2 by means of screw 29. It will be noticed that the bearings for the balance arbor are located so close to the frame plate 2 that the rim of the balance projects slightly beyond the face of the plate, the latter having an opening therein, as shown in Fig. 2, in which the balance oscillates. The purpose of this construction is to enable the oscillating balance to be observed from the front of the clock, it being understood that the dial will be provided with a similar opening.

The usual hairspring is indicated at 39 and has one end secured to the balance arbor and the other end secured to a stud 3| which projects from the base 28 of the balance cock. A regulating mechanism is also provided, as shown, and includes a toothed sector 32 which is rotatably mounted on the balance cock in known manner. The sector 32 is in mesh with a gear 33 which is mounted on the under side of the plate 4 and may be rotated by means of a pointer 34. These parts are of the usual construction and will require no extended description. It will sufflce to say that rotation of pointer 34 rotates the gear 33 and sector 32, and that the latter moves the regulator pins along the hairspring to change the effective length thereof.

Mounted on the balance arbor, as shown in Fig. 2, there are a safety roller 35 and a pinion 38 having a single tooth 31, which cooperate,'respectively, with the safety wheel 38 and the lever 39. The safety wheel 38 is mounted on an arbor 40, which has a bearing at one end in the post I. At the other end, the arbor 46 has a bearing in the member 4|, which forms part of a bracket including the base 42. Thebracket is secured to the frame plate 2 by means of a screw 43. The arbor 49 drives the clock movement by means of the worm 44 and a gear in mesh therewith which is mounted on the shaft 45. The rest of the gear train may be of known construction and has been omitted in order to avoid confusing the drawing.

The lever 39 is pivotally mounted on a stud 41 which is secured to the bracket 4|. The lever is adapted to be rotated on its pivot by the tooth 31 of pinion 36 during the oscillatory motion of the balance, and is restored to normal each time by the spring 14 which bears on the two projections .48 and 49. Spring l4 may be formed integrally with spring l4. At the end of the lever 39 there is a pin 50, which cooperates with the teeth of the safety wheel 38 in a manner which will be explained.

Attention may now be directed to the construction of the electromagnet which drives the balance. This magnet comprises the two pole pieces i and H previously referred to, which terminate in poles 55 and 56, and which are connected to opposite ends of the core 51. The core is formed with a shoulder at each end and the pole pieces are clamped against the shoulders by means of nuts, as shown clearly in Figs. 2 and 4. The magnet winding is indicated at 58. Associated with the electromagnet there is a condenser 59. The electrical connections for these parts will be described shortly.

The contact device for controlling the electromagnet is best seen in Fig. 5. As previously explained, the double contact spring, comprising spring 14 and i4, is clamped between the spacers l3 and I5 on the frame post 5. Spring 14 cooperates with a fixed contact member 63, which is clamped to the frame plate 3 by means of a screw 65 and nut 69. A terminal member 64, best seen in Fig. 2, is assembled just above the contact member 63, and these parts, as well as the screw 65, are insulated from the frame plate 3 by means of insulators 66, 61, and 68. It will be understood also that the members 63 and 64 have openings therein which are large enough to avoid contact with screw 65.

The contact spring 14 is tensioned in an up ward direction, as seen in Fig. 5, so that it tends to break contact with the contact member 63. The spring is operated to close the contact by means of an armature 62, secured to the spring, and a small permanent magnet 69, which is mounted on the balance arbor. The magnet 60 is preferably of Alnico and has an opening in which there is fitted a bushing 6|, which has a press fit on the arbor 25. The poles of the magnet are at the opposite ends thereof, and the magnet is eccentrically mounted on the arbor so that during the oscillation of the balance one of the poles comes much closer to the armature 62 than the other pole. The distances are so proportioned to'the strength of the magnet that the armature can be attracted only by the pole which comes the closest to it. The drawing Fig. 5 shows the armature 62 in attracted position, the contact between spring i4 and contact member 63 being closed. When the arbor 25 and magnet 60 are rotated in either direction, the armature is released and the contact is opened. Rotation of the magnet through degrees will not close the contact because the pole at the rounded. end of the magnet passes the armature at too great a distance for it to be operatively attracted.

The magnet 66 is so located as regards its angular position on the arbor that a line passing centrally through the poles of the magnet and the arbor will bisect the angle formed by the spokes 23 which support the poles l9 and 20 of the balance armature. This relation can be seen from Fig. 3, which also shows that when the balance is symmetrically located with respect to the poles 55 and 56, with pole 56 midway between the armature poles I9 and 22, the operative pole 3; magnet 60 is in alignment with the armature The circuit connections for the electromagnet 58 may now be described. The condenser 59 may be provided with heavy terminal conductors Ill and H, as seen in Fig. 2. The conductor 16 is formed as shown in the drawing, and its end is soldered to the terminal member 64. The conductor H is bent down around the edge of the frame plate 3 and extends along the under side of the frame plate to the screw 65, where the end of the conductor may be formed in a loop.-

as shown in Fig. 5, and secured under the head of the screw, a suitable washer being interposed if desired. The ends of the winding 58 are brought out at opposite ends of the coil by way of conductors I2 and i3, which are soldered to conductors and II, respectively. It will be understood, therefore, that the condenser 59 and winding 58 are connected in parallel; that is, the condenser is bridged around the magnet winding.

There is a binding post 81 mounted on the frame plate 4, which is provided with a spring clip 88 beneath the frame plate. This clip presses against the end of the screw 65, as seen in Fig. 3. Assuming that the clock is used in an automobile, the ungrounded pole of the storage battery is connected to the binding post. With the battery connected in this manner, the complete circuit for the electromagnet may be traced from the ungrounded pole of the battery by way of binding .post 81, spring clip 88, screw 65, conductor ll, conductor I3, winding 58, conductor 72, conductor I8, terminal member 64, contact member 63, and spring 14 (armature 62 being in attracted position) to the frame. Since the frame of the clock is grounded on the car, the circuit is completed by way of the chassis of the car to the grounded pole of the battery. It will be clear that this circuit is closed intermittently dunng oscillation of the balance by means of the magnet 60, armature 62, and spring I4.

The circuit arrangements described are capable of various modifications. A non-grounded circuit can be used if desired, and may be necessary under some conditions. In order to keep the circuit clear of the frame, the contact spring i4 is made separate from spring 14' and is suitably insulated at the fixed end where it is clamped between the spacers l3 and I5. A terminal member similar to 64 may be assembled next to the spring I4 to provide for the convenient attachment of a conductor.

The construction of the clock and the various parts thereof having been described, considei'ation may be given to the operation, with special attention to the novel features provided by the invention.

The hairspring 30 is so assembled and adjusted with respect to the balance that when the battery is disconnected the hairspring will tend to return the balance to the position in which it is shown in Fig. 3. In this position the poles 55 and 56 of the electromagnet are midway between the adjacent armatures poles on the balance, and the operative pole of magnet 60 is adjacent the armature 62. The adjustment of the hairspring is not at all critical, since the attraction between the magnet 60 and armature 62 will rotate the balance to the position in which it is shown, provided the hairspring adjustment is even approximately correct. In other words, the magnet 68 will pull itself in, if brought within range of the armature 62 by the hairspring, and will maintain the circuit of the electromagnet 58 closed at contact spring l4. This feature presents a decided advantage over the usual type of contact arrangement in which the hairspring alone is depended on to maintain the contact closed when the battery is disconnected.

When the battery is connected, a flow of current over the previously traced circuit is established and the electromagnet 58 is energized. The resulting magnetic field passes through the armature and the balance is thus placed in a condition of unstable equilibrium. The rotative forces tending to rotate the balance in opposite directions will not be exactly equal, for obvious reasons, and the balance will start to rotate in one direction or the other. As soon as the rota- 36 and the direction of the rotation is shortly reversed, with the result that the circuit of the electromagnet is again closed when the magnet 68 comes within operating distance of the armature 62. Thus the balance is given another rotative impulse. but in the opposite direction The operation continues in this manner and in a very short time the balance will attain its normal amplitude, a power impulse being received during each oscillation or beat, when the operative pole of magnet 60 passes the armature 62.

The oscillation of the balance drives the clock movement through the medium of the lever 39 and the safety wheel 38, the latter being fixed to the arbor 40 carrying the 'worm 44, which is the first element of the gear train. The manner in which the drive operates can best be explained in connection with Figs. 6, 'I, and 8, which show the essential parts on a larger scale and with the view unobstructed by other parts.

It may be assumed that the balance arbor 26, safety roller 35 and pinion 36 are rotating in the direction shown by the arrow toward the position in which these parts are shown in Fig. 6. As the rotation continues, the notch in the safety roller 35 will pass the tooth 8| of the safety wheel 38 without engaging the said tooth, for there is no rotative force being applied to the safety wheel. When the parts reach the position in which they appear in Fig. 6, the tooth 31 of pinion 36 engages the end of lever 39 and, as the rotation of the pinion continues, rotates the lever in aclockwise direction on its pivot 41 far enough to permit the pinion tooth to pass by. The lever is rotated against the tension of spring 14 and is instantly restored to normal as soon as it is released by the pinion tooth.

The balance and associated parts continue to rotate in the direction indicated in Fig. 6 until stopped by tensioning of the hairspring, whereupon the direction .of rotation is reversed, and these parts, including the safety roller 35 and pinion 36, start rotating in the direction shown by the arrow in Fig. 7. When the pinion 36 reaches the position in which it is shown in Fig. 7, the tooth 31 comes into engagement with the end of lever 39, and the lever is rotated on its pivot 41 as the pinion tooth passes by. In the normal position of the lever pin 50 is just outside the circle defined .by the extremities of the teeth of wheel 38, but when the lever is rotated in a counterclockwise direction the pin crosses the circle and engages tooth 83, thereby starting the rotation of wheel 38. The safety roller 35 is so positioned on arbor, 25 with respect to pinion 36 that the notch in the safety roller arrives at the tooth 82 just as the lever 39 starts the rotation of wheel 38. The tooth 82 is therefore caused to enter the notch in the safety roller by the further rotation of wheel 38.

As the parts reach the position last described, the lever 39 is released by tooth 3'! and is instantly restored to its normal position. The safety roller 35 now carries on with the rotation of wheel 38 and completes its rotation through the angular distance of one tooth, the tooth 84 and the wheel is locked against overrun by the engagement of tooth 85 with the periphery of the safety roller.

The operations just described are repeated during the next two beats of the balance and continue in the same manner. It will :be appreciated that since the safety wheel 38 is fixed on the arbor 40, each rotative movement of the safety wheel will advance the clock movement. It will be clear also that the safety wheel is rotated only during alternate beats of the balance, when the balance and associated parts are moving in a clockwise direction, as seen in Figs. '7 and 8, the operations of the lever 39 which take place during those beats in which the balance is moving in a counterclockwise direction being ineffective. Thus the clock movement is always driven in a forward direction by the oscillation of the balance.

It will be desirable now to consider the operation of the electromagnet and the control of the electromagnet circuit somewhat more in detail. Assuming that the :balance and magnet 60 are rotating in a clockwise direction as seen in Figs. 3 and 5, the magnet 60 is able to operatively attract the armature 62 before coming to exact alignment therewith, and accordingly the electromagnet circuit is closed by spring l4 shortly before magnet 60 reaches the position in which it is shown in Fig. 5, even though sometime is required for the operation of armature 62. When the circuit is closed, therefore, the armature poles l9 and 2|, through the medium of which the next rotative impulse is to be given to the balance, are farther from the electromagnet poles 56 and 55 than are the armature poles 22 and 20; in fact, at the time the circuit is closed the poles 22 and 20 may not be entirely out from between poles 56 and 55. The building-up of the magnetic field is delayed, however, due to the inductance of the magnet winding and also due to the momentary short-circuiting effect of condenser 59, which charges when the circuit is closed, so that by the time an appreciable amount of flux begins to pass through the armature it has reached approximately the position of Fig. 3. As the armature advances from this position, the poles l9 and 2| approach and begin to enter between the electromagnet poles 56 and 55, with the result that the energization of the electromagnet applies a strong rotative force or torque to the balance.

The magnet 60 releases armature 62 and opens the circuit at a time when the armature poles I6 and 20 have entered about halfway, more or less, between the magnet poles 56 and 55. The release is delayed somewhat due to the increased pull between the magnet and armature when the latter is in operated position. When the circuit is broken, the inductance of the electromagnet winding tends to maintain the current fiow, in which it is aided by the discharge of the condenser, with the result that the energization of the electromagnet is prolonged for an appreciable length of time during which it continues to apply a driving torque to the balance.

From the foregoing, it will be seen that an eflective driving torque is applied to the balance, notwithstanding the completely symmetrical arrangement of the magnet 60, balance armature poles, and electromagnet poles, which offhand might lead one to believe that substantially equal and opposite rotative forces would be applied to the balance. That such is not the case is due to the several factors discussed. Although the electromagnet circuit may be closed in advance of dead center (the position in which the parts are shown in Fig. 3), the opening of the circuit is delayed for more than an equivalent amount; that is, the opening of the circuit occurs at an angle past dead center which is considerably greater than the angle of advance. When the circuit is closed, the building-up of the magnetic neld'is delayed, and when the circuit is broken the decay of the field is also delayed, for reasons explained. All these factors cause an effective magnetic field to be established and maintained over a time interval which substantially coincides with the time interval during which the poles I9 and 2| are moving into alignment with the field poles from the position in which these parts are shown in Fig. 3, a time interval during which the attraction of the field poles for the armature poles l9 and 2| is increasingly preponderant over their attraction for armature poles 22 and 20. Thus the balance is given a strong rotative impulse in the direction in which it is assumed to be moving, that is, in clockwise direction.

When the balance reverses its direction of rotation, the same operations occur as have been described in detail above. The various factors discussed cause the establishment and disestablishment of the field to be delayed with respect to the motion of the balance, but since the balance is rotating in the opposite direction the field is effective at a time when the armature poles 22 and 20 are operatively related to the field poles. Thus the balance is given a rotative impulse in a counter clockwise direction.

The condenser 59 plays an important part in the operations just described. In addition to its function of preventing arcing at the contact when the circuit is broken, the condenser receives energy from the battery when the circuit is closed, which it delivers to the electromagnet when the circuit is opened, and thus provides for a more powerful energization of the electromagnet than could otherwise be obtained during the short time in which the circuit is closed. The condenser should preferably be of the electrolytic type in order to obtain a fairly high capacity within the size limits which are imposed by the dimensions of the other parts of the clock.

When the clock described herein is used in an automobile it is subjected to variations in voltage, which ordinarily would have a considerable errect on the rate of the clock. While the normal voltage is about 6 volts, it may drop as low as 4 volts or even less on starting and rise to 7.5 volts -or thereabouts when the battery is charging.

These varying voltages tend to afiect the rate of the clock by varying the amplitude of the balance. That a considerable eifect on the amplitude is produced may be appreciated from a consideration of the fact that with a given load the power delivered varies as the square of the voltage. Thus with an automobile clock, it the voltage is raised from 4 volts to 8 volts, or doubled, the power delivered is quadrupled, unless some means is employed to prevent it.

For the best results as regards accuracy in the rate, it is desirable that the balance should have an amplitude of about one and three-eighth:

turns. This value oi! amplitude may be considered to be the approximate optimum, from which a variation of about one quarter turn above or below may be permitted without appreciably affooting the rate. We have discovered that by properly designing the magnetic circuit the power delivered to the balance may be maintained constant enough to keep the balance oscillating within the permissible range, with the voltage variation of from 4 volts or slightly less to over 7.5 volts. The manner in which this is done will now be explained.

The amplitude of the balance is a function of the power delivered to it by the armature and the stillness of the hairspring. The power that the armature can deliver depends on the amount of flux it can carry when the electromagnet is energized, which in turn depends on the crosssection of the magnetic path through the armature. The armature poles preferably should have a certain minimum width circumferentially or the balance in order to properly distribute themagnetic pull during the motion of the balance, and hence at the poles the cross-section of the magnetic circuit is necessarily more or less fixed, but at points between the poles it can be varied within rather wide limits. As a first consideration, therefore, the cross-section of the poleconnecting spokes such as 23 (see Fig. 3) is so proportioned to the strength of the hairspring that when the spokes are substantially saturated the power delivered will be sufiicient to produce oscillations of the desired amplitude. The electromagnet is then designed so that at a minimum energizing voltage, say 4 volts or somewhat less, it will produce the requisite saturating flux for the armature.

It will be understood that the values of the factors under discussion at this point canbe varied considerably, so long as the correct proportions are substantially maintained. The stiffness of the hairspring and the power delivered by the armature when saturated (as determined by the cross-section of the magnetic clrcuit between the poles) should be so related that the correct amplitude is obtained, and the electromagnet should be capable of delivering the necessary saturating flux at the minimum operating voltage. The power of the electromagnet at the minimum voltage should not greatly exceed this requirement. The requirement as to the' relation between the stiffness of the hairspring and the saturation flux in the armature will in general make it necessary to use spokes 23 of considerably less width than the best pole width, as shown in the drawings, particularly Fig. 3, from which it can be seen that the spokes 23 have a width of about one-third the width of the poles such as l9.

The variation in balance amplitude in response to voltage variations is greatly reduced by adherence to the foregoing principles, but this does not entirely solve the problem due to considerations which will be pointed out. As the voltage rises the flux passing through the armature poles is not strictly limited to the amount of flux that can be carried by the spokes, but includes the leakage fiux between poles, which is sufficiently great so that the total flux rises considerably faster than the magnetization curve of the spokes alone. It is desirable therefore to limit, insofar as possible, the amount of flux that can be delivered to the armature poles by the pole pieces of the electromagnet. This result can be obtained in a satisfactory manner by reducing the cross-section of the pole pieces i ii and ii throughout a portion 01 their length. The pole pieces could be of reduced cross-section throughout, but it is desirable to have the poles 55 and 56 of approximately the same width as the armature poles, and the pole pieces have to be of sturdy construction between the poles and points beyond the posts 5 and 6 for obvious mechanical reasons. The reduction in cross-sec tion is limited, therefore, to the portions of the pole pieces which extend between the posts and the magnet core, as illustrated in Fig. 4 in the case of pole piece I0. I

As can be seen from the drawing, that portion of the pole piece ill which extends from the vertical portion which is secured to the core to the portion which is slotted to receive the ear 8 is greatly reduced in width, and'forms a section of reduced crosssectlon which tends to limit the amount of flux that can be delivered to the pole 55. A certainsmall amount of leakage flux will by-pass this reduced section at high voltages, but it is very effective nevertheless, and the whole arrangement produces very satisfactory results. Taking into account the leakage flux, the pole pieces l0 and II should be so dimensioned that the portions thereof which are reduced in cross section will carry somewhat less flux than the spokes of the armature, which generally requires that the pole pieces have a smaller cross-section in the reduced portions than the cross-section of the armature spokes. The required cross-section depends on several factors, however, such as the strength of the eleotromagnet and the material of which the pole pieces are constructed and can be determined by trial within the principles explained.

The selection of the proper magnetic materials for the balance armature and the pole pieces is of importance for the best results. For the balance armature nickel iron alloys, such as Allegheny metal, .Mu metal, or Permalloy, are desirable, as these materials have high permeability at low flux densities and have magnetization curves which are quite flat above the knee. as contrasted with the magnetization curves of other magnetic materials which show a more gradual increase in flux over a wide range of increasing magnetization forces. The armature is operated just above the knee of the curve, where it is substantially flat over the range of voltages which is met with in practice.

The nickel iron alloys mentioned above are also suitable for the pole pieces and magnet core, but a less expensive material such as Armco iron can also be used with good results. A pure soft ir'on such as Armco iron is all right for the field; but in the case of the armature, where considerable stifiness and rigidity are required, thenickel iron alloys are more suitable.

As previously intimated, very excellent accuracy is obtained in a clock of this type by means of the armature and field construction described. Magnetization curves for the armature, which have been made under test conditions, show a flat top characteristic over the voltage range 4-8 volts, which is much superior as regards low change in flux over the operative voltage range to that exhibited by the magnetization curve of any known material. This result is due to the use of the proper material in the armature, in the first place, and to the advantage which is secured by the limitation as to the amount of flux that can be delivered to the armature by the field. The total armature flux therefore remains nearly constant when the clock is operating on different voltages within the specified range and the amplitude of the balance is not subject to variations which would deleteriously affect the accuracy of the clock.

Attention may now be directed to the modifica tion shown in Figs. 9 and 10, in which the drive mechanism is made to perform the function of a contact device for controlling the circuit of the drive magnet.

When this modification is used the springs M and i4, contact member 63, and the magnet 6!! are omitted. In placeof contact member 63, a spring 94 is provided, which functions as a restoring spring for the lever 39. The lever is insulated from the frame in any suitable manner, as shown in Fig. 10, for example, where the lever is pivoted on the shoulder screw 90. This screw is insulated from the bracket M by means of a bushing 92 and washer 93, and is secured to the bracket by a nut a l.

The circuit of the magnet extends from the binding post 8'! by way of spring clip 88, screw 65, conductors ii and is, winding of magnet 58, conductors l2 and i0, terminal member 64, spring 94, lever 39, tooth 31, pinion 36, and thence to the frame through the balance arbor and hairspring. This circuit is closed and opened by the engagement and disengagement of lever 39 by the tooth iii of the pinion 35. These parts, or at least their contact surfaces, should be made of some non-corrosive metal.

The hairsprlng normally tends to return the balance to the position in which it is shown in Fig. 3, and the parts of the drive mechanism are so adjusted that when the balance is in this position the radius of the tooth 3? will coincide with a line connecting the center of arbor 25 with the center of the shoulder screw on which lever 39 is pivoted. The end of lever 39 also lies in this line and when the battery is disconnected, therefore, the tooth ill will engage the end of the lever on one side or the other, and the circuit of the magnet will be closed inside the clock. This position of the parts is illustrated in Fig. 9. The tooth 31 is in engagement with the end of lever 39, and the tension of the hairspring tending to rotate the balance to the position of Fig. 3 is opposed by the tension of spring 94 which tends to prevent the rotation of the lever from its normal position. In equilibrium the lever is slightly out of normal position, while the rotation of the balance is arrested slightly short of its Fig. 3 position.

When the battery is connected, the drive magnet as is energized and an impulse will be applied to the balancetending to rotate it in a clockwise direction as seen in Fig. 3. since the armature poles is and iii are closer to the magnet poles Elli and 55 than the armature poles 22 and 2!]. The rotation of the balance in a clockwise direction breaks the circuit of the magnet, but it stores up tension in the hairspring and the direction of rotation is shortly reversed, with the result that the circuit is again closed. This time tension in the hairspring will be aided by the inertia of the balance, which will carry the balance past dead center and the impulse resulting from the closure of the circuit will be effective to continue the rotation of the balance in the same direction. The circuit is broken when the lever is released by tooth 3?. The balance continues its rotation until the motion is arrested by the hairspring, whereupon the direction of motion is reversed and the circuit is again closed, giving another operative impulse to the balance. Thus the normal oscillating motion of the balance is quickly established.

When the clock is running, the circuit of the drive magnet is closed each time by the engagement of the tooth 31 with the end of lever 35 as described, and during each oscillation or beat in a counterclockwise direction the circuit is also broken at the same point. During each beat in a clockwise direction, however, the circuit is actually broken when the pin 50 disengages from a tooth of the wheel 38 just'after the lever is re leased by the tooth 31 of the pinion. That this is true will be evident from the fact that the wheel 38 and arbor 40 afford an alternative circuit path to the frame of the clock. The pin 50 and the wheel 38 should also be made of some satisfactory contact material therefore.

If it is desired to confine the circuit control to the make and break between the lever and pinion tooth, this result can be readily secured by insulating the pin 50 from the lever 39.

It will be seen from the foregoing that the invention provides an improved electric clock having a number of features which tend to enhance the utility of a device of this character. While the invention has been described in considerable detail, this has been done for convenience in explaining the principles employed and to facilitate a clear understanding of suitable means by which the invention may be carried out in practice, but without any intention to limit the invention to the specific construction shown and described. Modifications may be made within the principles of the invention, and We do not wish to be restricted, therefore, to the exact structure described, but desire to include and have protected by letters patent all forms and adaptations of the invention which come within the scope of the appended claims.

We claim:

1. In a clock, a balance, an electromagnet for driving said balance, a circuit for said electromagnet including a switch having a fixed contact, a magnetic device for operating said switch, said device comprising an armature operatively associated with the switch and a permanent magnet oscillating with the balance, and means including said fixed contact for limiting the movement of said armature under the influence of said magnet sufliciently to'prevent said armature from engaging said magnet.

2. In a clock, a balance, an electromagnet for driving said balance, a permanent magnet mounted on the balance arbor and having one pole at a greater distance from th arbor than the other pole, an armature located adjacent the path of the remote pole and adapted to be op-- erated thereby but not by the other pole, a switch operated by said armature, and a circuit for said electromagnet controlled by said switch.

3. In a clock, an oscillating system including an armature, an electromagnet associated with said armature for supplying power to operate said oscillating system, a hair-spring forming part of said oscillating system and adapted to maintain said armature approximately in a predetermined position relative to the poles of said electromagnet when the clock is not running, means including a permanent magnet for moving said armature exactly to said predetermined position, a circuit for said electromagnet, and a switch operated by said permanent magnet in said position to render said circuit effective, whereby said clock is able to start when current is supplied to said circuit, said switch including two contact members both mounted independent of the balance arbor.

4. In a clock, an electromagnetically driven balance, a toothed wheel for driving the clock train, a pivoted lever actuated during alternate beats of the balance to start the rotation of said wheel, and means supported on the balance for completing the rotation of said wheel through an angular distance of one tooth each time its rotation is started by said lever.

5.111 a clock, an electromagnetically driven balance, atoothed Wheel for driving the clock train, a pivoted lever, means supported on the balance arbor for oscillating said lever on its pivot responsive to oscillation of the balance, means carried by said lever for starting the rotation of said wheel when the lever moves in one direction on its pivot, and means supported on the balance arbor for completing the rotation of said wheel through an angular distance of one tooth each time its rotation is started.

6. In a clock, an electromagnetically driven balance, a toothed wheel for driving the clock train, a pivoted lever, means rotating with the balance for moving said lever on its pivot dur ing each beat of the balance, and additional means rotating with the balance and cooperating with said wheel and with said lever for rotating said wheel during alternate beats of the balance only.

'7. In a clock, an electromagnetically driven balance, a locking roller mounted on the balance arbor and having a single notch therein, a Wheel coupled with the clock train and having teeth cooperating with said roller, a pivoted lever adapted to advance said wheel to cause a tooth thereof to enter the notch in said roller, and means rotating with said balance for actuating said lever.

8. In a clock, a balance, an electromagnet for driving said balance, a toothed wheel for driving the clock train, means supported on the balance arbor for advancing said wheel, an actuating member supported on the balance arbor, a pivoted lever operated by said member to render said means effective during alternate beats of the balance, and a circuit for said magnet including said lever and actuating member.

9. In a clock, a balance, an electromagnet for driving said balance, a toothed wheel for driving the clock train, a pivoted lever. a member sup ported on the balance arbor for oscillating said lever, means including said lever for advancing said wheel, and a circuit for said magnet including said lever and said member.

10. In a clock, means for driving the balance comprising an armature on the balance arbor and an electromagnet, the magnetic circuit through said armature including a portion the cross-section of which is so related to the stiffness of the hairspring that when the armature is substantially saturated sufficient power will be delivered to the armature to give the balance the desired amplitude, and pole pieces for said electromagnet including portions of such reduced cross-section as to substantially prevent the electromagnet from supplying flux to the armature in excess of the amount required for saturation thereof.

11. In a clock, an armature for driving the balance, said armature having its carrying capacity for magnetic flux related to the stiffness of the halrspring that at approximate saturation values of flux the armature will develop sufficient power to oscillate the balance at the desired amplitude, an electromagnet for producing flux in said armature, and field members included in the magnetic circuit adapted to prevent delivery of excess flux to the armature in case the electromagnet is energized at a higher voltage than that which is required in order to produce approximate saturating flux in the armature.

12. In a clock, means for driving the balance comprising an armature on the balance arbor and an electromagnet, a Winding for the magnet -'adapted to be energized at different voltages, a .member forming part of the armature and having such a restricted cross-section that it becomes saturated at the minimum voltage, and members forming part of the magnet core and including sections of such limited cross-section as to substantially prevent delivery of excess flux to the armature when the electromagnet is energized at higher voltages.

13. In a clock, means for driving the balance comprising an armature on the balance arbor and an electromagnet, a winding for the electromagnet adapted to be energized at diiferent voltages, and a magnetic circuit including an armature section and a magnet section which are of such limited cross-section that they become substantially saturated when the said winding is energized at a predetermined mini mum voltage.

14. In a clock, an armature mounted on the balance arbor, said armature having poles con ected by a member of limited cross-section less than that of the poles, a magnet core having extensions terminating in poles adapted to cooperate with said armature poles, each of said extensions including a portion adjacent the core whi h has a limited cross-section less than that -of the magnet poles, and a winding on said core so designed that when the winding is energized at a predetermined minimum voltage the armature member and extension Dnlfiions of limited Cross-section will be substantially saturated.

15. In a clock, an electromagnet for driving the clock, an armature for said magnet mounted on the balance arbor, poles for said magnet and armature, a magnetic circuit including a magnet section and an armature section and air gaps at said poles, said sections each including a portion having a smaller cross-section than the portions adjacent said poles, and a winding forming part of said electromagnet and so designed that when energized at a predetermined minimum voltage the said portions of the magnetic circuit of smaller cross-section will be substantially saturated.

16. In a self-starting electrical clock having a frame, a balance, an electromagnet for drlving said balance, a circuit for said electiomagnet, a switch for controlling the said circuit, said switch including two contact members both mounted on the clock frame, a hair spring adjusted to bring the balance to rest in a predetermined angular position when the current supply to the electromagnet is cut off, and means responsive to movement of the balance to said predetermined position to apply power independent of said hairspring to operate said switch and hold the same operated while the balance remains in said position.

17. In a clock, an oscillatory balance having an arbor, an electromagnet, for driving said balance, a movable contact. an armature for moving said contact, a permanent magnet mounted on the balance arbor and adapted to attract said armature on each oscillation of the balance, a stationary contact engaged by said movable contact when the latter is moved by said armature, the entire movement of said movable contact being produced by said permanent magnet, said stationary contact being so located that the movement of the movable contact and armature is arrested before the armature can engage the permanent magnet, and a circuit for said electromagnet controlled by said movable and stationary contacts.

18. In a clock having a frame, a balance having an arbor, means including a hairspring and an electromagnet for oscillating said balance, a circuit for said electromagnet, and means for controlling said circuit without physical engagement between any part mounted on the clock frame and any part mounted on the balance arbor, whereby mechanical interference with the motion of the balance is avoided, said controlling means comprising a switch mounted on the clock frame and a magnetic device ineluding a part operatively associated with said switch and a part mounted on the balance arbor and effective at each oscillation of the balance to operate said switch solely by the attraction through space between said parts.

19. In a self-starting clock having a frame, a balance having an arbor, a hairspring, an electromagnet cooperating with said hairspring to cause said balance to oscillate in both directions from a central position, a permanent magnet mounted on the balance arbor, an armature supported on the clock frame in such angular position around the balance arbor that the attraction between the magnet and armature is a maximum when the balance is in said central position, whereby the mutual attraction between said magnet and armature aligns the balance in said central position when the clock stops and moves the armature toward the magnet, a switch operated by said armature and adapted to arrest the movement thereof before it engages said magnet, and a circuit for said electromagnet controlled by said switch.

THOMAS B. GIBBS. JEAN FINK.

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