US2301870A - Vibratory reed drive - Google Patents

Description

D. HANCOCK, .1Rv VIBRATORY REED DRIVE Filed May 1, 1941 Nov. 10 1119421 CONTACT CLEHNCE CONT/967' CLOSED C ove electromagnetic driving ineens ein 1;/ which is effective nutomstiefrliy if s en eniarged fragmentary sectional View te s er. the line 5.5 of Fig. i.;

Figure ii e. wiring diagram; 'and Figure i e diagram illustrating the method lend operation-of the apparatus.

The invention maybe employed generally for the maintenance in vibration of a vibratory element such as reed, but is disclosed herein as employed in the vibrato mechanism of an electrical musical instrument. Such vibrato mechanism is more fully disclosed in the co-pending application of lLourens Hammond, Serial No. 362,018, filed October 21, 1940.

Referring to Figs. 1 and 2, the vibrato mechaniszn comprises generally a ferromagnetic part ll which is securely riveted to a leaf spring i2, while the letter is rigidly attached to the upwardly extending portion cfa. bracket i4 suitably mounted on a supporting plate ll. y The les! spring l2 together with the part I l thus composes s freely vibratory reed.

Rigidly secured to the' part il is a.v core il preferably of the powdered iron type, a plurality of washers 2i being likewise secured to the part IB to provide the necessary mass to obtain the desired frequency of vibration. Additional washers may be added. or some of the washers shown may be removed, for adjusunent'of the mass of the reed. The desired frequency of vibrational e ement o displacement being exeg long@ ti ement @3o ciilnticn ci the reed im" are rivet ,ci the perf im, l Lying al' 1e core lotes the iicllow'cent disclosed t e store-seid applic* Kommen y he located in. of en 'ce ne ductelnce The coii il other form circuit n its in csciiletcr. im. for any i may be deu the term ef suoli meg electrical osf to any u l c regnet, the coil plein i t ecrip und en ins' edt-c the @non sides i connection to the i adjacent t o st pe extending beyond Lower edge its l contact il its end portion Z med in e. vertical piene,t and has e lfirieontal f entending contest wire 32 welded er otherwise suitably secured. thereto. The contact wire 2 is cooperable with o similar vertically extending contact wire 3i `which is welded or otherwise secured adjacent the formed lower end oi the contact strip il. The arm 28 is mounted for rotation between a pair of insulating friction washers 3l. El, the washer 3B being shouldered to provide a. ilnnge I8 forming a, centrai bearing for the arm 2l. The armi! is clamped with light pressure between the two washers li and 31 by the force .applied byla compression coil spring Il which is compressed between the washer It and a. washer 42. A spacing sleeve Il is clamped between the washer IZ and a. similar washer I8 by a. bolt 48 which also passes through the mounting plate i6 and thus Y moved, but is insuillcient to place e material load upon the vibratory reed.

Referring to Figs. 3 and 4, it will be apparent that when the reed is moving on the counterclockwise portion of its vibretory cycle, the insulating strip 26 will contact the end portion n' of the arm 2l and swing the latter oounterclockwise with the reed. Y

Upon the commencement of the clockwise porthe clockwise stroke of the reed. Immediately upon commencement of the counterclockwise stroke of the reed, the contact wire 34 will move away from the contact wire 32 and the arm 28 will remain stationary during the initial portion of this counterclockwise stroke until the insulating strip 28 engages the end portion 30 of the arm 28 and swings the latter counterclockwise with the reed.

The means for driving the reed comprises an electromagnet having a laminated core Il and winding 52. `As shown in Fig. 6, the winding 32 is connected in series with a resistor 34 across a source of alternating voltage indicated as 6.3 v. A. C. The reed Ill, I2 is connected to ground to which one terminal of the alternating current source is also connected so that when the contact 32 makes contact with the contact 3,4, the resistance 54 is shunted out of the energizing circuit for the winding 52, the latter then being connected directly across the alternating current source. The resistor 54 is of relatively high value compared to the impedance of the winding 52 so that no appreciable amount of current flows through the winding 52 when the contacts 32, 34 are open. The resistor 54, however, acts to suppress sparking across the contacts upon making and breaking the circuit. It will be noted that when the reed Ill is in its position of rest, its free end lies close to the end of the core 50, and that the center line of the reed is displaced from the center line of the core 50. The amount of this displacement is a substantial fraction of the oscillatory stroke of the end of the reed. Since the electromagnet l0, 52 is energized only during the clockwise swinging stroke of the reed, it is necessary, in order to make it possible to eilect a net transfer of energy from the electromagnet to the reed, that the major part of the clockwise stroke of the reed be located in that portion of the magnetic field which applies an accelerating force to the reed. It will be clear that this is accomplished when the reed, in its rest position, is displaced a substantial distance counterclockwise of the magnetic center of the end of core SII.

The operation of the reed driving mechanism may best be explained by reference to the diagram, Fig. 7, wherein the end of the core 50 is diagrammatically shown, while the curves illustrate the displacement of the end of the reed relative to the core 50. Assuming that the reed has been set into low amplitude vibration by any suitable means, its displacement through a cycle of vibration will follow substantially the curve A. 4

At the origin of the curve 1A, the reed is in normal or rest position and travelling in a coun-f terclockwise direction, during which time the contacts 32, 34 are separated. Shortly after the commencement of the clockwise stroke at the point c, the contacts will close and remain closed throughout the remaining portion of the clockwise .stroke of the reed, that is', until the reed reaches the position d on'the curve 1A. It will be understood, however, that after the reed passes the center line 'lC of the core 5l, the magnetic attraction of the core 3l, instead of tending to accelerate the reed, tends to retard it. Such retardlng action occurs during the movement of the reed from the point e on the curve 1A to the point d on said curve. The length of time that the magnetic attraction is effective to accelerate the reed is thus represented by the dimension a, while the length of time during which the magnetic attraction retards the reed is represented by the dimension b.

Assuming that the frequency of the altemating current supplied to the winding 52 is high relative to the frequency of vibration of the reed, the magnetic field may be assumed to be constant, and thus, the amount of energy supplied to the reed by the electromagnet may-be consid- .ered as a function of the difference between the dimensions a and b. This energy which is supplied to the reed by the electromagnet is of course dissipated in air friction and in the slight amount of internal friction in theleaf spring I2. If the energy suppliedto the reed by the electromagnet is greater than that thus dissipated in friction,

the amplitude of vibration of the reed must necessarily'increase. If the system did not 1nclude some compensatory factor, the amplitude of vibration of the reed would tend to increase far beyond that desired, and thus buil'er stops would have to be provided (as in the aforesaid application of Laurens Hammond), to limit. the extent of vibration of the reed. The striking of the reed against such buffer stops would cause undesirable noise and would cause the vibration of the reed to depart from substantially simple harmonic or sine wave motion. Both of these effects are generally undesirable.

How the above undesirable effects are eliminated may be explained by reference to the curve 1B of Figure 7, which shows the instantaneous position of the reed when it is vibrating at high amplitude. Under these circumstances, the contacts 32, 34 close at the point c and remain closed until the reed completes its clockwise stroke at the point d'. However, as the reed passes the center line 1C at the point e', the magnetic attraction of the core acts to retard the reed. Thus, while the reed is moving from the point c' to the point e', energy'is being supplied to the reed. On the other hand, as the reed moves from the point e' to the point d', energy is being taken from the reed by the electromagnetic system. The time during which energy is being supplied is thus represented by the dimension a', while the time that energy is being subtracted from the reed is indicated by the dimension b.

By comparison of the dimensions a and b with the dimensions a and b', it will be apparent that as the amplitude of vibrationof the reed increases, the net energy added to the reed during each cycle decreases. Thus, the driving electromagnetic system in itself forms the braking or energy absorbing means effective to limit the amplitude of vibration of the reed because with increasing amplitude of vibration of the reed, the time during which energy is subtracted from the reed approaches in duration the time interval during which energy is being added to the reed, and thereby decreases the net amount of energy added to the reed necessary to overcome the frictional loses. From the foregoing, it will be apparent that while the voltage of the alternating current supplied remains constant and other conditions remain uniform, the reed will fend to vibrate at an equilibrium amplitude condition in which the net energy supplied to the reed is just sufficient to overcome the losses, mainly air friction losses. It will also be apparent that reasonably wide variations in the supply voltage will produce relatively small variations in the amplitude of vibration of the reed.

The reed driving apparatus of the invention is of particular advantage because an alternating current source may be used to supply the necessary energy, although it will be apparent that the apparatus will also operate when the energizing source is direct current. When the energizing source is alternating current it should be of a frequency higher than that of the frequency of vibration of the reed. For example, an alternating current source of 25 to 6D C. P. S. or higher will be satisfactory provided the reed frequency is in the order of 7 C. P. S. This is a considerable economic advantage because of the, elimination of a direct current supply system which would be required if the apparatus had to be operated on direct current.

While the electromagnet is disclosed herein as being located beyond the end of the reed,- it may, for example, be located above or below the magnetic part of the reed, or the core of the electromagnet may be U-shaped with its poles adjacent opposite edges of the magnetic part of the reed. In each instance, the electromagnet should be so located with respect to the magnetic part of the reed that the center of attraction of the electromagnetic iield (the position toward which the magnetic forces tend to move the reed), is displaced from the neutral position of the reed, the neutral position being the rest position assumed by the reed when the electromagnet is deenergized. The center of attraction of the electromagnet should also lie in the path of oscillation of the magnetic part of the reed, so that retarding as well as accelerating forces may be applied to the reed. In the following claims the terms clockwise and counterclockwise are not intended to have absolute, but instead merely relative, signiiicance.

While I have shown and described a particular embodiment of my invention, it will be apparent to those skilled in the art that numerous modiiications and variations may be made in the form and construction thereof, without departing from the more fundamental principles of the invention. I therefore desire, by the following claims, to include within the scope of my invention, all such similar and modiiied forms of the apparatus disclosed by which substantially the results of the invention may be obtained by substantially the same or equivalent means.

I claim:

l. In a vibrator, the combination of a reed having an oscillatory magnetic part, an electromagnet for driving said reed,` said electromagnet having the center of attraction of its magnetic field located within the path of oscillation of said part but displaced clockwise with respect to said part when the reed is in neutral position, an energizing circuit for said electromagnet including a switch, and means operated by said reed to close said switch during substantially the whole of the clockwise stroke of said reed and to open said switch during the counterclockwise stroke of said reed.

2. In a vibrator, the combination of a reed having an oscillatory magnetic part, an electromagnet for driving said reed, said electromagnet having the center of attraction of its magnetic field positioned in the path of oscillation of said magnetic part so as to be capable of exerting both accelerating and retarding forces on said reed, an energizing circuit for said electromagnet including a switch, and means operated by said reed to close said switch during substantially the whole of the forward stroke of said reed and to open said switch during the return stroke of said reed.

3.In a vibrator, the combination of a reed having an oscillatory magnetic part, an electromagnet for driving said reed, said electromagnet having the center of attraction of its magnetic field located in the path of oscillation of said part but to the side of said part when the reed is in neutral position, an energizing circuit for said electromagnet including4 a switch, vand means controlled by said reed to close said switch during substantially the whole of the forward stroke of said reed and to open said switch during the return stroke of said reed.

4. In an electromagnetic vibrator, the combination of a vibratory reed having an oscillatory magnetic part, an electromagnet having its field traversed by said part, said electromagnet being so located with respect to said part that the latter is displaced from the center of attraction of the iield of said electromagnet when the reed is in its neutral position, means for energizing said electromagnet including a switch, and means to close said switch during substantially the whole of the stroke of said reed in one direction and to open said switch throughout the stroke of said reed in the opposite direction.

5. In an electromagnetic vibrator, the combination of a vibratory reed having a magnetic part at its free extremity, an electromagnet positioned beyond but closely adjacent the path of oscillation of said magnetic part and having its center of attraction displaced from said part when said reed is in neutral position, and means for energizing said electromagnet during substantially all of the forward stroke of the reed and de-energizing said electromagnet throughout the return stroke of said reed.

6. In an electromagnetic vibrator, the combination of a vibratory reed having a magnetic part at itsfree extremity, an electromagnet positioned closely adjacent the path of oscillation of said magnetic part and having its center of attraction displaced from said part when said reed is in neutral position, and means controlled by said reed for energizing said electromagnet during substantiallyl thewhole of the forward stroke of the reed and de-energizing said electromagnet throughout the return stroke of said reed.

7. In an oscillatory element having a magnetic part, an electromagnet positioned closely adi acent the path of oscillation of said magnetic part and having its center of attraction displaced from said part when said element is in neutral position, and means for energizing said electromagnet during substantially the whole of the forward stroke of said element and de-energizing said electromagnet throughout the return stroke of said element.

8. In an oscillatory element having a magnetic part, an electromagnet having its iield traversed by said part, said electromagnet being so located with respect to said part that the latter is displaced from the center of attraction of the field of said electromagnet when said element is in its neutral position, but passes through said center DAVID HANCOCK, Jn.

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