US3660737A

US3660737A - Magnetic escapement

Info

Publication number: US3660737A
Application number: US84324A
Authority: US
Inventors: Satoshi Sakai; Kenzo Shirakawa; Norio Shimizu
Original assignee: Matsushita Electric Works Ltd
Current assignee: Panasonic Electric Works Co Ltd
Priority date: 1969-11-15
Filing date: 1970-10-27
Publication date: 1972-05-02
Anticipated expiration: 1989-05-02
Also published as: FR2067320B1; FR2067320A1; DE2052941A1; GB1338084A; DE2052941B2; DE2052941C3

Abstract

A magnetic escapement including a rotor driven by an external force, and escape wheel made of a magnetic material and having along its periphery radially extending magnetic teeth, said escape wheel being coupled through a coil spring to the rotor, and an oscillator having a magnetic pole piece secured at the end of one of its tines and coupled magnetically to the escape wheel teeth. The oscillator is preferably formed in a W-shape and supported at a point near its center of gravity for extension parallel to the plane of the escape wheel, and its pole piece being magnetically coupled to that tooth of the escape wheel which is farthest from the supporting point. A driving circuit of a constant output for the rotor is provided, which includes a compensating transistor and a temperature compensating element for eliminating load and temperature variations.

Description

May 2,1972

United States Patent Sakaiet a].

Dinerstein el Sit/I16 lshikawa et a]. .5

45 66 mm MW 27 28 J 78 0 33 T N E M E P A C S E m T E N G A M m [72] Inventors: Satoshi Sakai, Hirakata; Kenzo Shiraknwa;

Norio Shimizu, both of Neyagawa. all of E i Milw K f Japan AtrorneyPierce. Scheffler & Parker Primary ABSTRACT [73] Assignee: Mlttsushita Electric Works. Limited,

Osaka, Japan [22] Filed: 0cL 27 1970 A magnetic escapement including a rotor driven by an external force. and escape wheel made ofa magnetic material and [2i] 84,324 having along its periphery radially extending magnetic teeth,

Appli No.2

said escape wheel being coupled through a coil spring to the rotor, and an oscillator havin a ma netic ole iece secured [30) Foreign Application Priority Dam at the end of one of its tines 5nd cofipled agnstically to the Nov. 15 I969 escape wheel teeth. The oscillator is preferably formed in a W- Nov. [8, 1969 Nov. 2i, 1969 shape and supported at a point near its center of gravity for exn a D. a J

tension parallel to the plane of the escape wheel, and its pole piece being magnetically coupled to that tooth of the escape wheel which is farthest from the supporting point, A driving circuit ofa constant output for the rotor is provided, which includes a compensating transistor and a temperature compen- [52] US. [Si] Int.

sating element for eliminating load and temperature variations.

6 Claims, 13 Drawing Figures References Cited UNITED STATES PATENTS 2946,183 7/1960 Clifford.........m.............m....74/l.5X

Patented May 2, 1972 5 Sheets-Sheet 1 EDUmG oz mo OP Pahntod Mny 2, 1972 3,660,737

5 Shun-Shut 2 Patented May 2, 1972 5 Shuts-Shut 5 m2; "94 08 mo @3162 RESONANU FREQMNCY Patented May 2, 1972 3,660,737

5 Sheets-Sheet 4 29 fil fi --H- 0 ii i b i 5 ed;

Fig. 8 (PRIOR ART) MAGNETIC ESCAPEMENT This invention relates to improvements in magnetic escapements used in such devices specifically as electric clocks or the like in which a constant velocity is required.

In magnetic escapements generally, there has been suggested a type in which permanent magnets are secured to forward ends of a mechanical oscillator as, for example, a tuning fork which has a specific constant frequency, and a rotary plate made of a magnetic material, that is, a so-called escape wheel is arranged so as oppose to the permanent magnets, said magnets being oscillated at a constant frequency by means of the mechanical oscillator, according to which the escape wheel is rotated at a constant speed. In the above arrangement, however, there is a drawback, because, since the magnet and rotary plate are coupled only magnetically, the rotation of the rotary plate is apt to become unstable because of shocks or the like given externally, whereby mis-synchronizing or even interrupting the rotation of the plate will be caused. The present invention removes the above defect of conventional escapements.

According to the present invention, the above mentioned defect is removed with an arrangement by which the escape wheel and driving shaft of the wheel are coupled by a spring having a low rigidity. That is, the external shocks are effectively absorbed by the resiliency of said spring and any deviation from the normal relative position of the oscillator to the escape wheel is also damped by the resiliency of the spring, whereby the defect that the magnetic couple is readily broken is effectively avoided.

A main object of the present invention is therefore to provide an improved magnetic escapement which is stable against any external shocks and produces constant rotation at uniform speed, causing less likelihood of mis-synchronization.

Another object of the present invention is to provide a magnetic escapement having a large exciting force and may be made in compact form.

A further object of the present invention is to provide a magnetic escapement which is capable of adjusting the speed of the escape wheel.

Other objects and advantages of the present invention will be made apparent as the following detailed disclosures proceed with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of the magnetic escapement according to the present invention.

FIG. 1B shows a circuitry diagram ofa driving circuit for the escapement.

FIG. 2 is a plan view showing partly in section the main part of the escapement in FIG. 1.

FIG. 3 is a vertical view showing partly in section the main part in FIG. 2.

FIG. 4 is a vertical section of escape wheel unit showing details of the same.

FIG. 5 is a diagram showing resonance curve of the oscillator used in the present invention.

FIGS. 6 8 are circuitry diagrams of conventional driving circuits for the magnetic escapement.

FIGS. 9 and 10 show diagrammatically voltage-current characteristics at the collector and base of the transistor used in the driving circuit, respectively.

FIG. 11 is a diagram showing voltage characteristics.

FIG. 12 is a diagram showing output variations with respect to temperatures.

While the present invention shall be disclosed in detail with reference to a preferable embodiment, it should be understood that the true intention is not to limit the invention to the particular embodiment as illustrated, but is rather to cover all possible alterations, modifications and equivalent arrangements which are included in the scope of the invention as defined in the appended claims.

Referring now to FIG. 1, l is an oscillator or oscillating governer, which is formed substantially in a W-shape as shown in FIG. 3 and is fixed to a supporting member 8 at the center of gravity, shown at 17, of the oscillator l. The supporting member 8 is secured to a fixed base 16 by means of screws [8, and said base 16 in turn is secured to a frame plate l5. 9 is a dead weight secured to a free end of the supporting member 8. The oscillator 1 is provided with a permanent magnet 2 and a balance weight 2' made of a magnetic material, respectively secured to each free end of the oscillator I.

3 is an escape wheel, of which details are shown in FIG. 4. That is, the escape wheel 3 is secured to a boss 7, which is fixed to a driving shaft 6. 4 is a rotor consisting of a cylindrical permanent magnet in which N and S poles are alternately arranged along its peripheral surface. Said rotor 4 is fixed around a sleeve 12 which is mounted over the driving shaft 6 for free rotation therearound. The sleeve 12 is provided ad jacent the lower end with a threaded part 12' for starting the rotor. 13 is a driving gear secured to the shaft 6 and the sleeve 12 rests on the upper surface ofthe gear 13. I1 is a coil spring, which is fixed at an end to the escape wheel 3 and at the other end to the rotor 4. 22 is a worm gear fixed on the shaft 6.

Referring again to F IG. 1, means for supporting the driving shaft 6 is provided in the form of a pair of pedestal plates 14 and 14', respectively formed by bending a part of the frame plate 15 at right angles thereto, so as to support the shaft 6 between said plates 14 and 14' for free rotation. A further frame plate 20 is arranged in parallel relation to the frame plate 15 and is secured thereto by means of screws through spacers 19. The worm 22 is in mesh with a gear wheel 23, which in turn is in mesh with a gear 24, so that the escapement is connected to a gear system for driving hour-hand, minutehand and secondhand. Sis a coil assembly including a driving coil for the rotor 4 and a detecting coil. The coil assembly 5 is mounted to the frame plate 15 by means of screws 26 through an insulating board 25. A speed adjusting member 34 made of a magnetic material is provided adjacent the permanent magnet 2 mounted on the tine of the oscillator I. The member 34 is fixed on an adjusting screw 35, which is screwed at one end into a threaded hole of the frame plate 15 so that the position of the speed adjusting member 34 will be varied by turning the screw 35, thereby influencing the specific frequency of the oscillator I so as to vary it and consequently the number of rotation of the escape wheel 3.

The escape wheel 3 is made of a magnetic material and is provided with radial magnetic teeth 36 at regular intervals. The oscillator 1 is supported by means of the fixed base 16, so that its longitudinal axis will be parallel to the plane of the escape wheel 3 and the permanent magnet 2 secured to one of the tines of the oscillator 1 will be disposed above the escape wheel 3 so as to oppose that tooth 36 of the wheel 3 which is remote from the fixed base 16. 21 is a manual driving lever provided for kicking the threaded part 12' of the sleeve 12 and the driving gear l3 simultaneously so that the driving shaft 6 and rotor 4 will be started in the desired direction.

According to the present invention, as referred to in the foregoing, the oscillating governor or oscillator l is supported by the supporting member 8 which has the dead weight 9. This dead weight 9 is provided for the purpose of reducing the amplitude of unnecessary oscillations of the oscillator 1, so that the accuracy of the oscillator is very high. That is, as diagrammatically shown in FIG. 3, in the case when the both tines of the oscillator are oscillated in the same phase, that is, in the asymmetrical mode at a lower specific frequency f, the oscillation amplitude is relatively smaller than in the case of the reverse phase or symmetrical mode oscillation at a higher specific frequency f,. It means that the resonance sharpness value at the frequency f, is low and the oscillator is unable to accomplish higher accuracy while it oscillates at this frequency. Further, when the oscillation frequency is low, such as f, the output of the rotor rotating at the speed corresponding to this frequency f 1 is insufficient and hence the motor is no longer rotatable and, consequently, the synchronized rotation of the wheel 3 is no longer established. In order to prevent such inadequate oscillation of the oscillator in the asymmetrical mode at the lower frequency f, therefore, the weight 9 having a suitable weight for absorbing such oscillation of the frequency f, is provided at the opposite end of the supporting member 8 to a connecting part 8' with respect to the supporting point I7. Thus. the oscillator 1 according to the present invention can be oscillated always in the symmetrical mode at the higher frequency f, and, therefore, a highly accurate and synchronized rotation of the escape wheel 3 can be accomplished.

Turning now to FIG. 1B. an electric circuit for controlling the coil assembly 5 in the magnetic escapement of FIG. 1 is shown. In the drawing, 27 is a detecting coil and 28 is a driving coil. These two

coils

27 and 28 are wound as stacked so as to form the coil assembly 5. 29 is a PNP type transistor, 30 is a compensating NPN type transistor. 3l is a condenser for preventing parastic oscillation, 32 is a DC source. and 33 is a temperature compensating element. An end a of the detecting coil 27 is connected to the base of the transistor 29 and the other end I: is connected to an end of the driving coil 28 and also to the emitter of the transistor 29. The other end d of the driving coil 28 is connected to the collector of of the compensating transistor 30. The base of the transistor 29 and the emitter of the transistor 30 are connected to each other through the temperature compensating element 33. and between the collector of the transistor 29 and the collector of the transistor 30 the DC. source 32 is inserted. The condenser 31 is inserted between the base and collector of the transistor 29.

The operation of the device according to the present invention shall now be explained.

When the manual driving lever 21 is operated under the condition in which the direct electric current is supplied to the coil assembly 5, the driving shaft 6 and the permanent magnet rotor 4 are started in a fixed rotating direction, so that the rotor 4 begins to rotate. Since the escape wheel 3 is coupled to the rotor 4 through the coil spring 11, the rotation of the rotor 4 is transmitted to the wheel 3 and thus the wheel 3 is also caused to rotate together with the rotor. As the escape wheel 3 is thus rotated, the oscillator I carrying at a tine thereof the permanent magnet 2 which is magnetically coupled to the magnetic teeth of the wheel is excited by the teeth each time a tooth passes beneath the magnet 2. Here, at the time when the frequency of this excitation coincides with the specific frequency of the oscillator 1. the oscillator 1 will be in its resonant state. The escape wheel 3 is restricted, at this time, to a speed conforming with the specific frequency of the oscillator I.

As described in the foregoing, the speed adjusting member 34 made of a magnetic material is mounted on a movable screw 35 in the oscillating direction of the oscillator I, so that the member 34 is located at a position opposite to one of the poles of the permanent magnet 2 in attractive relation to the latter and is movable together with the screw 35. If the speed adjusting member 34 is moved so as to vary the attracting force acting between the member 34 and magnet 2. the specific frequency of the oscillator l is caused to vary. Therefore, it is possible to adjust the number of revolutions per unit time period of the escape wheel 3.

FIGS. 6. 7 and 8 show conventional driving circuits. In the circuit shown in FIG. 6. the detecting coil 27 is inserted between the base and the emitter of the transistor 29, the DC. source 32 and driving coil 28 are connected in series between the collector and the emitter of the transistor 29, and the parastic oscillation preventing condenser 31 is connected between the base and the collector of the transistor 29. In the circuit of FIG. 7, an NPN type transistor is used for the transistor 29, and a DC. blocking condenser 36 and a bias resistance 37 are used. These elements cause, however, the circuitry output to be varied depending on variations in the prevailing conditions such as temperature. source voltage and the like and, in the case when these are used for the transistor motor, its drive is unstable due to the relation of the torque and load That is, when the temperature is varied and reaches a high temperature. the base voltage V, base current I,

characteristics are transferred as shown by the broken line in FIG. 10. and the base current is increased from i to i Due to this increase. the collector voltage is varied from i to i in the collector voltage V collector current I characteristics shown in FIG. 9. and consequently the circuitry output is increased. If the voltage is decreased, on the other hand. in the case when a biasing circuit is accompanied or the transistor is made to operate close to its saturation point. the voltage is varied from E. to E, and the collector current is varied from i to i in the V l characteristics of FIG. 9, so that the circuitry output is decreased. Further, in the case when the transistor is unsaturated, even a slight variation of the base current will influence the output. In order to prevent this, there has been suggested such a circuit as shown in FIG. 8. in which a diode 38 is connected between an end of the driving coil 28 and the base of the transistor 29. However. this circuit has such inconveniencies that its compensation is insufficient and the temperature characteristics are dependent upon the transistor 29 and diode 38. According to the present inven tion. the above described defects of the conventional driving circuits can be overcome.

In the driving circuit according to the present invention, for the purpose of making the base current of the transistor 29 constant at all times, the compensating current i, is determined by the voltage V across base and emitter and the resistance value of the temperature compensating element 33.

The state of the compensation shall be explained now in detail. When the prevailing temperature rises. the V, I, characteristics of the transistor are changed to the state of the broken line shown in FIG. 10 and the base current is increased from i to i In order to reduce this increased base current of the transistor 29, it may be sufficient to increase the compensating current i Since, on the other hand, the base current at the compensating transistor 30 is also increased, the compensating current i is also made to be increased so as to make the base current of the transistor 29 constant. It is possible to further compensate for possible differences between the respective characteristics of the

transistors

29 and 30. That is, for the temperature compensating element 33, either type of such element having positive or negative temperature coefficient is used depending on the requirement. In the case when the load of the motor or the like is reduced, the motor speed is increased and the induction voltage of the detecting coil 27 is increased, so that the base current i is increased. On the other hand. the respective terminal voltages e, and e of the detecting coil 27 and driving coil 28 are increased. Due to these increases. the emitter-base voltage V of the compensating transistor 30 is also increased, so that the compensating cur rent i, is made to increase so that the base current i of the transistor 29 is not increased and, thus, the motor speed can be kept at a constant rate.

The above described effects shall be explained with reference to the embodiment. In the voltage characteristic diagram of FIG. II. the solid line curve shows the case of the present invention and the broken line curve shows the conventional case. As is clear from the curves, an excellent result has been obtained according to the present invention. The diagram shown in FIG. 12 shows output variations due to the temperature, in which the broken line curve shows the case where no compensating means is used.

Next, the features of the present invention shall be explained.

A. As has been described in the foregoing, according to the present invention, the driving shaft 6 and the escape wheel 3 are coupled by means of the coil spring I] which is low in rigidity and, therefore. any shocks given from outside the device are softened (or absorbed) by the resiliency of the coil spring, so that no large influence will be exerted upon the magnetic coupling of the escape wheel to the oscillator.

B. The oscillator is arranged in such manner that its longitudinal axis will be parallel to the plane of escape wheel and that at least one of its forward ends will be positioned adjacent the tooth of the escape wheel which is remote from the supporting point of the oscillator. Therefore, it is possible to make the dimension of the magnetic escapement smaller than in the conventional cases so that the forward end or ends of the oscillator will be positioned substantially at the center of the escape wheel or near the supporting point of the oscillator,

C. As the oscillator l is formed substantially in a W-shape and supported at the point 17 which is close to the center of gravity any shocks given to the oscillator through the

frames

15, 20 will be transmitted always near the center of gravity of the oscillator 1. Therefore, it is practically impossible that the moment due to the shock will be reproduced in the oscillator and, thus, the oscillator l is less influenced by the shock.

D. In the driving circuit, the compensating transistor is inserted in such manner that its base and collector are connected to the intermediate tap and collector side terminal of the driving coil, respectively, and the emitter of this transistor is connected through the temperature compensating element to the base of the transistor. Therefore, any variations in the prevailing temperature will be compensated for by the temperature characteristics of the compensating transistor and temperature compensating element, and any variations in the load will be compen sated for by the compensating transistor with a detection of the voltage at the detecting coil and driving coil, whereby the output of the driving circuit may always be stable.

What is claimed is:

l. A magnetic escapement comprising a rotor, means providing a force for rotating said rotor, an escape wheel, a coil spring for coupling said escape wheel to said rotor, said escape wheel being formed of a magnetic material and having a plurality of magnetic teeth extending radially from the peripherey thereof at regular intervals, an oscillator extending in a direction parallel to said escape wheel, means for supporting said oscillator, and a permanent magnet at one only of the forward ends of said oscillator for oscillation in a direction parallel to the plane of the escape wheel.

2. A magnetic escapement as claimed in claim I wherein said permanent magnet is secured to said one forward end of said oscillator opposed to the magnetic tooth of the escape wheel which is remote from the point of support of the oscillator.

3. A magnetic escapement as claimed in claim 1 wherein said oscillator is formed substantially in a W-shape and is supported by said support means at a position near its center of gravity.

4. A magnetic escapement as claimed in claim 1 wherein said oscillator is formed substantially in a Wshape and is supported by said support means at a position near its center of gravity, and further comprising a weight attached to the other of said forward ends of said oscillator, said weight being suffi cient to absorb the specific frequency corresponding to the frequency in the asymetrical mode.

5. A magnetic escapement as claimed in claim I wherein said permanent magnet is provided with a magnetic pole at each end thereof, one of said poles being opposed to the magnetic force of the said escape wheel and further comprising means for adjusting the speed of oscillation of said oscillator made of a magnetic material and movable in the oscillating direction of said oscillator, the other of the poles of said permanent magnet being opposed to the magnetic force of said adjusting means.

6. A magnetic escapement as claimed in claim 1 wherein said means for rotating said rotor comprises a rotor driving circuit including a first transistor, a detecting coil connected between the emitter and base of said first transistor, a driving coil connected in series with said detecting coil for exciting said rotor and connected between the emitter and collector of said first transistor through a source of current, the junction point of said detecting coil and driving coil being connected to the emitter of said irst transistor, a second compensating

Claims

1. A magnetic escapement comprising a rotor, means providing a force for rotating said rotor, an escape wheel, a coil spring for coupling said escape wheel to said rotor, said escape wheel being formed of a magnetic material and having a plurality of magnetic teeth extending radially from the peripherey thereof at regular intervals, an oscillator extending in a direction parallel to said escape wheel, means for supporting said oscillator, and a permanent magnet at one only of the forward ends of said oscillator for oscillation in a direction parallel to the plane of the escape wheel.

2. A magnetic escapement as claimed in claim 1 wherein said permanent magnet is secured to said one forward end of said oscillator opposed to the magnetic tooth of the escape wheel which is remote from the point of support of the oscillator.

4. A magnetic escapement as claimed in claim 1 wherein said oscillator is formed substantially in a W-shape and is supported by said support means at a position near its center of gravity, and further comprising a weight attached to the other of said forward ends of said oscillator, said weight being sufficient to absorb the specific frequency corresponding to the frequency in the asymetrical mode.

5. A magnetic escapement as claimed in claim 1 wherein said permanent magnet is provided with a magnetic pole at each end thereof, one of said poles being opposed to the magnetic force of the said escape wheel and further comprising means for adjusting the speed of oscillation of said oscillator made of a magnetic material and movable in the oscillating direction of said oscillator, the other of the poles of said permanent magnet being opposed to the magnetic force of said adjusting means.

6. A magnetic escapement as claimed in claim 1 wherein said means for rotating said rotor comprises a rotor driving circuit including a first transistor, a detecting coil connected between the emitter and base of said first transistor, a driving coil connected in series with said detecting coil for exciting said rotor and connected between the emitter and collector of said first transistor through a source of current, the junction point of said detecting coil and driving coil being connected to the emitter of said first transistor, a second compensating transistor having the base connected to an intermediate tap on said driving coil and the collector connected to an end terminal of said driving coil, and a temperature compensating element inserted between the emitter of said second compensating transistor and the base of said first transistor.