US2471542A - Phonograph pickup unit using magnetostrictive wire - Google Patents

Description

May 31, 1949. s. R. RICH PHONOGRAPH PICKUP UNIT USING MAGNETOSTRICTIVE WIRE Filed Oct. 25, 1945 M m wk W F B 5 2 a 6 W5 L m 1 m w F r\\ F 5v: 2 .l O B .1 q 2 3 F ///,,,\V U \\\.\\N\ m :P F. 3 WM MS l. 4 7 m n F F F.

Patented May 31, 1949 PHONOGRAPH PICKUP UNIT USING MAGNETOSTRICTIV E WIRE i Stanley R. Rich, Cambridge, Mass.

Application October 25, 1945, Serial No. 624,362

8 Claims.

The present invention relates to a phonoraph pick-up unit for converting mechanical vibrations into corresponding electric vibrations.

The present invention is particularly useful in reproduction of sound from phonograph records, but may of course be applicable to any other type of energy conversion between mechanical vibrations and corresponding electric current.

There are many various units in current use for reproduction of sound recorded on phonograph records and for cutting records from sound. Some of these are comparatively large and heavy, particularly the parts entering into the vibrating system, with a general result that while vibrations of lower frequencies are faithfully reproduced, nevertheless, the presence of the large vibrating masses interferes substantially with the faithful and full reproduction of higher frequencies. A further difficulty has been found in obtaining sufficient sensitivity and response with pick-up units now generally used.

In the present invention as applied to reproducing of sound, the vibrating element in the unit is hardly more than the stylus itself. Full and efficient use is made of the vibrational stresses in the portion of the unit which is actuated by the stylus. It will also be noted that the coupling between the vibrating element and the pick-up coil is extremely close and made to function in such a way that the potential generated in the coil is additive for the pick-up operation and arranged to balance out extraneous electrical or mechanical disturbances. The phonograph unit of the present invention is further extremely simple to manufacture, requires substantially no adjustment and is durable, rugged and will not be injured even with extremely rough treatment. No fine or accurate adjustment need be made to this device, and since no crystal elements are employed, dropping the unit on the floor or the like will not injure it.

The present invention will be more fully explained in connection with the embodiment described in the specification below when read in connection with the drawings, in which- Figure 1 shows an elevation of the phonograph pick-up unit.

Figure 2 shows an end view of the unit seen in Figure l as viewed from the right of that figure.

Figure 3 shows a section taken on the line 33 of Figure 1.

Figure 4 shows a further modified form of the unit of Figure 1, the needle being positioned in a different direction.

Figure 5 shows an elevation as seen when looking at the lower end of Figure 4.

Figure 6 shows an end view of Figure 4 as Viewed from the right of that figure, and,

Figure 7 shows a further modified form of Figure 1.

In the arrangement of Figures 1, 2 and 3, the unit comprises a pair of C-shaped magnets, I and 2, which may be of the alloy material such as Alnico, comprising aluminum, nickel and cobalt, or Cunico comprising copper, nickel and cobalt or any other powerful permanent magnet elements.

The two C-shaped pieces may be fittted face I: to face and are held together at convenient places,

as for instance at the corners by the bolts 4, 4, passing through the two pieces.

In the present construction it is preferable to assemble the two pieces I and 2 together and then to drill at the joining line of each arm elements of the c magnets, holes 5, 5 aligned together, or if the surfaces are too hard to drill, semi-circular holes may be ground in each edge surface. These holes may be sufficiently large for a sliding fit to accommodate a magnetostrictive wire 6, or if additional tension on the wire is desired, the two halves of the G magnet may serve to clamp the wire firmly, which passes through the holes 5, 5, adjacent the end of the elements or prongs of the C. The wire 6 terminates at either end in hooked or angle elements I and 8 with small inwardly extending terminal pieces 9 and In which are at angles to the portion 1 and 8 and lay over the faces of the magnet.

As indicated more clearly in Figures 2 and 3, the end angle elements I and 8 are twisted, so so that the wire at one end is given a torsional stress in one direction of rotation of the wire, and the other end is given a torsional stress in the other direction of rotation of the wire.

As indicated in Figures 1 and 2, the wire 6 at its right end is twisted to bring the end 9 on the forward face of the magnet I, while the end 8 is twisted to bring the end N) of the wire at the forward face of the magnet 2. The wire is therefore given a torsional twist which approximates in the arrangement of Figures 1 and 2 about 90. The wire may be given a greater or less stwist, angle of twist not being critical since considerable leeway is permitted in the present design. It is desirable to provide however a twist of such a magnitude, taking into consideration the length of the wire, that the magnetostrictive forces employed may be used most efiiciently. The torsional stress so exerted on the wire 6 will place the fibers of the wire longitudinally in tension and will at the same time provide shearing forces, both of which will tend to increase the magnetostrictive variations brought about through the operation of the device.

A coil of fine wire H is wound about the wire 6 and serves to pick up the flux variations produced by the mechanical twisting force acting on the wire 6 at the point of the wire 8 where the stylus is. Between the two ends, and at the midpoint preferably, the stylus I2 is attached by welding, soldering or any other suitable manner. The stylus may be a round or flat element and carries at its end a jewelled point 13 such as sapphire or diamond or any other similar type of point which will wear substantially indefinitely or for a very long time when used on phonograph records. The point may be removable by having a screw threaded connection to the stylus. The coil or wire need not be ultra fine but may be of No. 40 and Wound in one or more layers with the desired resistance. The coils, one on either side of the stylus, will be connected to an electrical system, such as an amplifier with proper matchmg by means of a suitable transformer. The coils II are connected in such a manner that current flows in opposite directions of rotation over the two halves of the wire 6, that is on one half and counterclockwise on the other half.

In the arrangement in Figure 1 it is assumed that the pick-up unit will move in the direction or the arrow A over the phonograph record, the point l3 following in the record groove substantially in the same direction with the stylus I2 vibrating perpendicularly to the plane of the paper as viewed in Figure 1. This action will produce torsional vibration of the wire 6, which one half will tend to relieve the tension in the longitudinal direction and reduce the magnitude of the shearing forces. In the other half of the wire 6, the opposite action will take place. The reluctance of the first mentioned half of the wire '6 will decrease and that of the second mentioned h'al'f wi'll increase. The change in the first half will be to reduce the flux, while in the other half 'to increase the flux so that by winding the coils in the two halves in opposite directions, the direction of the generated potential will be additive.

I have found that the lines of force or flux on account of this action leaves the magnetostrictive wire along its length as the torsion is varied. As the reluctance increases in a portion of the wire, more lines of force leave in that portion, and when the reluctance decreases, less flux leaves the wire so that while the reluctance of the whole wire path may remain the same within the limits of operation, the flux in each half of the wire changes in opposite directions to produce additive electromotive force in oppositely wound coils. A 7 It will be noted further in the arrangement of Figures 1, 2 and 3, that the operation is one of torsion of the wire 6, so that the wire 6 occupies the same position throughout its torsional vibrations. There is no substantial motion of the wire as a whole. As a mechanical protection for the wire, and as a clamping means, if desired, a support It in the shape of a wedge, may be extended to a point adjacent the center of the wire where the stylus is attached to prevent excessive mechanical forces not encountered in the operation of the wire from injuring it. This wedge M may be retained in a recess between the magnet sections I 'and 2 as indicated at M.

For so called hill and dale record, the same arrangement indicated in Figures 1, 2 and 3, may be used. The only change necessary in such an arrangement is that the stylus l2 would be positioned to provide torsional vibrations when drawn over the hill and dale record. As viewed in Figures 2 or 3, the stylus under these conditions would be inclined to the right or left instead of straight down.

While it is preferable and of simple construction to have the wire t in a free sliding fit in the holes 5, nevertheless it may be desirable, as mentioned above, to obtain longitudinal tension, to clamp the wire 8 rigidly in place between the two magnet elements l and 2. This of course be accomplished by making the hole 5 smaller so that the two magnets l and 2 when pressed together will act to clamp the wire in the groove. In such a case the end sections or the wire 1, 9, and 8, It, may be eliminated after the desired torsional stress has been applied to the wire 6.

In the arrangement of l 'gures e, 5 and 6, the device substanti .e as of Fig ure 1 and like eiements are referred to by the same numbers.

In these figures the stylus 3t is directed at an angle with the plane of the device which is drawn over the record plate in the direction of the arrow B. The vibrations of the stylus due to the record is assumed to be perpendicular to the plane of the paper.

In the arrangement of Figures 4, 5 and 6, a pair of formed coils 3| and 32 may be mployed. These may be slipped over the wire ii which is arranged and constructed in the same Way as in Figures 1, 2 and 3.

The guard element corresponds substantially to that of the element i l, with the exception that it extends over the wire E at the side of t". midsection as indicated at the end 35 in Figures 4 and 5 to protect the wire The operation of he mod. mien of Figures 4, 5 and 6, is substantially the same as that of Figures 1, 2 and 3. The action in the two coils '31 and 32 is made to be additive by suitable connection.

In the arrangement indicated in Figure 7, the par-ts are substantially the same as in Figure 1, and to that extent they are similarly numbered. The difference in structure resides principally in the use of a balanced magnetic circuit in which the magnet has a central arm til, the magnetic potential of which is neutral, or half way between the end arms 42 and 23. A coll li is wound around the central section lEl which extends to a, point mid-way between the ends of the wire 6. Under normal conditions when no torsional vibration is impressed upon the wire, the reluctance of both halves of the wire ii is th same, and the flux passing through. the central section 6Z3, remains balanced. When the torsional stresses on one half of the wire 6 are released, the reluctance of this half increases and that of the other half decreases, because of increased torsional stresses. This changes the balance in the section it and provides an increasing in magnetic flux which induces the voltage in the coil M which is impressed upon the electrical phoncgraph or amplifier circuit.

The device as indicated above will also operate in the reverse manner. If current is impressed on the coils II or H, the flux in the wire 6 will change and the mechanical forces will be altered 'or varied in the wire to produce motion which will vibrate the stylus for the purposes of cutting a sound groove or producing a sound film.

Having now described my invention, I claim:

1, A phonograph pick-up device comprising a permanent magnet of high flux retentivity, providing two opposing pole elements, a magnetostrictive wire bridging said pole elements and supported thereby, means maintaining said magnetostrictive wire in torsion between the pole elements the torsional stresses acting in the same direction along its entire length, a stylus attached to said magnetostrictive wire in free equilibrium and extending from said magnetostrictive wire at the mid section thereof and a coil wound about said magnetostrictive wire on both sides of said stylus for converting the magnetic flux variations produced by said magnetostrictive wire to eleetro motive force.

2. A phonograph pick-up device, comprising a C-shaped permanent magnet formed of two 0- shaped sections supported together in face to face relation, a magnetostrictive wire bridging the pole elements of said magnet and supported between the C-shaped sections, means providing and sustaining torsional stress in said magnetostrictive wire between the supported portions thereof, a free stylus extending from said magnetostrictive wire between its supported portions and coil means for converting the magnetic flux variations produced by said magnetostrictive wire to electromotive force.

3. A phonograph pick-up device, comprising a C-shaped permanent magnet formed of two C- shaped sections supported together in face to face relation, a magnetostrictive wire bridgingthe pole elements of said magnet and supported between the C-shaped sections, means providing torsional stress in said magnetostrictive wire between the supported portions thereof, a. free stylus extending from saidmagnetostrictive wire between its supported portions and coil means wound about said magnetostrictive wire for converting the magnet flux variations produced by said magnetostrictive wire to electromotive force.

4. A phonograph pick-up device comprising a permanent C-shaped magnet formed in two similar C-shaped sections, means retaining said C-shaped sections together, a magnetostrictive wire extending between the poles of said C-shaped magnets, said magnetostrictive wire being supported between the faces of said C-shaped sections, means providing a torsional stress on said magnetostrictive wire, said means comprising end sections of the wire twisted in opposite directions and having end elements lying over the pole elements of the G-shaped magnets, a free stylus attached to said magnetostrictive wire between its end support and coil means wound around said magnetostrictive wire for converting the magnetic flux variations produced by said magnetostrictive wire to electromotive force.

5. A phonograph pick up device comprising a magnetostrictive wire, means supporting said magnetostrictive wire at its ends and placing the wire in torsion between the supporting ends, the torsion acting in opposite angular directions at its ends as viewed from either end, a stylus free at one end and attached at its other end to the magnetostrictive wire at a point between the supported ends of the magnetostrictive wire, means for polarizing said wire with magnetic flux longitudinally of the wire, and coil means for converting magnetic flux variations produced by said wire to electromotive force.

6. A phonograph pick up device comprising a magnetostrictive wire, means supporting said wire at two spaced points in alignment with said Wire, means providing a torsional stress acting in the same angular direction along the wire between its supported points, a free stylus attached at one end to said magnetostrictive wire between said two points of support, means for polarizing said wire with magnetic flux, and coil means surrounding the wire for converting the magnetic flux variations into electromotive force.

7. A phonograph pick up device comprising a magnetostrictive wire, means supporting said magnetostrictive wire at its ends and placing the wire in torsion between the supporting ends, means providing a torsional stress acting in the same angular direction along the wire between its supported ends, a free stylus attached at one end to said magnetostrictive wire, said stylus adapted to vibrate to relieve the torsional stress in the magnetostrictive wire at one side of the mid-point thereof and increase it at its other side, means for polarizing said wire with magnetic flux, and coil means for converting the magnetic flux variations produced in the magnetostrictive wire to electromotive force.

8, A phonograph pick up device comprising a magnetostrictive wire, means supporting said wire at two spaced points in alignment with said wire, means providing a torsional stress acting in the same angular direction along the wire between its supported points, a free stylus attached at one end to said magnetostrictive wire substantially at the midpoint thereof, means for polarizing said wire with magnetic flux, and coil means positioned at each side of said midpoint of the magnetostrictive wire and wound about it for converting magnetic flux variations therein to electromotive force, said coil means being wound to make the effect of said variations additive in producing said electric force.

STANLEY R. RICH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 351,905 Eichemeyer Nov. 2, 1886 1,821,836 Hull Sept. 1, 1931 1,882,400 Pierce Oct. 11, 1932 2,343,352 Mallina May 9, 1944 FOREIGN PATENTS Number Country Date 513,062 Germany Jan. 25, 1928

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