US 3556537 A
Description (OCR text may contain errors)
United States Patent  inventor William E. Stacy North Wilbraham, Mass.  AppLNo. 749,767  Filed Aug. 2, 1968  Patented Jan. 19, 1971  Assignee The Poly-Choke Company, Inc.
East Hartford, Conn. a corporation of Connecticut  TONE ARM 6 Claims, 6 Drawing Figs.
 U.S.Cl 274/23  lnt.Cl Gllb 3/10  Field ofSearch 274/1,23, 23.1; 308/237, 158; 252/12 (lnquired); 58/140A [5 6] References Cited UNITED STATES PATENTS 2,983,517 5/1961 Klein 274/23 2,983,516 5/1961 Bauer et al. 274/23 2,878,638 3/1959 Fauvelot.... 58/140 3,261,609 7/1966 Geiger.... 274/23 3,244,422 4/1966 Hathaway 274/9 3,169,774 2/1965 Daellenbach 274/14 Primary Examiner-Leonard Forman Assistant Examiner-Steven L. Stephan Att0rney--Fishman and Van Kirk ABSTRACT: A tone arm is provided in which the tone arm is mounted on a horizontally disposed shaft, the shaft in turn being pivotally mounted in a vertical pivot assembly to allow vertical motion of the tone arm. The vertical pivot assembly has large diameter sapphire bearing elements against which opposite ends of the shaft bear. The bearing elements are contained in housings which are in turn mounted in resilient isolation mounts which allow for some movement to provide protection and isolation while a stabilization ring limits the amount of movement. A resilient potting compound is contained in a recess along most of the length of the arm, and this potting compound and the isolation rings contribute to the achievement of highly desirable resonance characteristics.
TONE ARM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to phonograph tone arms.More particularly, this invention relates to a tone arm having highly desirable resonance absorption or damping characteristics, 7
especially as achieved by construction of the arm itself and by a pivot assembly which provides isolation from shock, stray vibrations, and system resonance, including low frequency mechanical resonance of the system.
2. Description of the Prior Art Among the more important requirements of a high-quality tone arm are'that it be a structure of low mass and of high sensitivity, i.e., good tracking in response to light impulses. The
overall total quality of a tone arm is directly related to the horizontal and vertical pivot characteristic of the arm. That is, the pivot assemblies must be highly frictionless and must also provide damping and isolation from extraneous vibrations, shock and resonance.
Just as it is true that the development of pickup cartridges has proceeded at a more rapid pace and to a higher level of sophistication than tone arm development, it is also true that the problems associated with horizontal tone arm movement have received more attention than the problems associated with vertical tone arm movement, and the development of horizontal pivot assemblies for horizontal tonearm movement have reached a higher level of sophistication than vertical pivot assemblies for allowing vertical tone arm motion. Among the reasons for this disparity in the development of horizontal and vertical pivot assemblies are the facts that the problems and needs associated with each are different so that solutions applicable to one are not necessarily applicable to the other, and
, previously available vertical pivot assemblies have been consistent with and adequate for the overall quality of available tone arms. However, overall tone arm development has progressed, along with the development of horizontal pivot assemblies, to the pointwhere problems associated with vertical pivoting and vertical pivot assemblies have becomeof prime importance.
Typical prior art approaches to the vertical'pivot assembly construction problem include: v
U.S. Pat. No. 3,261,609 to Geiger, .Ir. wherein the vertical pivot assembly'has a miniature ball bearing construction;
U.S. Pat. No. 3,003,772 to Snow, Jr. et al. in which the vertical pivot assembly is in the form of a fluid mounting at the head; and
U.S. Pat. No. 2,983,5l6 to Bauer et al. in which a jewel bearing arrangement is shown at the head.
' However, these typical prior art arrangements and other arrangements available in the art are not compatible with an optimized overall tone arm design.
Of course, an optimized overall tone arm design has for its overall objective high dependability and sensitivity in tracking so that there will be tracking fidelity in response to very light impulses. Tracking pressure is a measure of the force of the stylus on the record at which dependable tracking will occur; and, of. course, a light tracking pressure is desirable since record wear is directly related to tracking pressure. However, as attempts are made to reduce tracking pressure, problems such as groove hopping and other problems associated with vertical movement of the tone arm become paramount and mechanical resonance becomes of increasing concern. Prior to the present invention, the best, i.e., lightest, obtainable tracking force was on the order of 0.5 grams. While that tracking force of 0.5 grams is significantly better than was available to I0 years ago, lighter forces are still desirable for the more sophisticated and higher quality applications and equipment such as, but not limited to, professional broadcastmg.
2 SUMMARY OF THEINVENTION The present invention overcomes the problems heretofore present in resonance and in vertical pivot structures, and results in an optimized tone arm which is capable of dependable tracking at tracking pressures below 0.5 grams and down to as low as 0.1 grams. Of course, although the difference between 0.5 grams and 0.1 grams is a small absolute difference, it is an extremely large relative difference with respect to equipment heretofore available, and it represents a significant advance in the tone arm art. In the'vertical pivot assembly of the present invention, the tone arm is mounted on a shaft which has reduced end portions at both 'ends. Thereduced end portions of the shaft have rounded ends which are both supported by and bear against large diameter spherical jewel surfaces which are in turn mounted in isolation mounts of resilient material to allow movement of the bearings. Stabilization rings limit the allowable movement.
' The vertical pivot assembly is contained in a casing through which the body of the tone arm passes so that excess vertical movement is constrained and the forces generated thereby are transmitted to the casing to protect both the vertical pivot assembly and the horizontal pivot assembly. Furthermore, in the present invention the vertical pivot assembly is mounted on the axis of the horizontal pivot assembly so that the pivot assemblies are in alignment and at the same position along the length of thetone arm so that the interrelationship between the operation of the two pivot assemblies remains constant as the tone arm moves across the record in the playing operation.
In a further feature of the present invention, the body of the 7 tone arm is an extremely lightweight unit formed of highly dried wood vacuum impregnated with a phenolic or epoxy resin material. This material from which the body of the tone arm is formed is low weight, has high strength, and has a very low mechanical resonance point, all of which characteristics make it especially suitable for tone arm use. A recess along the underside of the arm is filled with a resilient compound to provide damping and thus improve the resonance characteristics.
In addition, a novel arm rest structure is provided to bridge the gap between the turntable and the rest position of the arm so that'stylus damage resulting from accidental dropping of the arm is eliminated. j v
Accordingly, one object of the present invention is to provide a novel'and improved tone arm.
Another object of the present invention is to provide a novel and improved tone arm having significantly improved tracking characteristics and ability.
Still another object of the present invention is to provide ,a novel and improved tone arm having low overall mass and improved resonance characteristics.
Still another object of the present invention is to provide a novel and improved vertical pivot assembly for a tone arm.
Still another object of the present invention is to provide a novel and improved vertical pivot assembly wherein the vertical pivot assembly provides a high degree of isolation from shock, extraneous vibrations and resonance.
Other objects and advantages of the present invention will be apparent and understood from the following detailed description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, wherein like elements are numbered alike in the several FIGS.
FIG. 1A is a top plan view of the phonograph tone am of the present invention.
FIG. 1B is a side elevation view of the phonograph tone arm FIG. 4 is an enlarged detailed showing of the jewel bearing and isolation structure of the vertical pivot assembly.
FIG. 5 is a view showing the improved arm rest structure of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings, the tone arm of the present invention is shown in FIG. 1A in a top plan view and in FIG. 1B is side elevation view. The overall appearance of the tone arm can be seen from FIGS. 1A and 1B and reference is also made to U.S. Pat. application No. 9824, filed Dec. 18, I967 and assigned to the same assignee of the present application, for a more detailed showing of the overall appearance of the tone arm. A base plate having a plurality of mounting holes l2 is provided for mounting the tone arm on a suitable base. A horizontal pivot assembly 14 passes through a central opening in base plate 10 and is secured thereto by any suitable fastening means such as a set screw 16. A vertical pivot assembly 18 is mounted on horizontal pivot assembly 14 at the top end thereof, the center of gravity of vertical pivot assembly 18 being preferably on the axis of horizontal pivot assembly 14. An arm 20 is pivotally supported within vertical pivot assembly l8, and arm 20 has a head 22 at one end thereof and a counterbalance weight 24 at the other end thereof. Head 22 is preferably an aluminum casting, and counterbalance weight 24 is preferably a brass casting, both having their outer surfaces brushed for the sake of appearance. A pickup cartridge and needle are mounted in any standard fashion in head 22 and plugs into contact prongs (not shown) at the forward end of arm 20. Transmission wires encased in a cable 23 extend from the contact prongs rearwardly along arm 20 toward pivot assembly 18 to be connected to amplifying apparatus in standard fashion. The wires may preferably be positioned in a recess 25 in the underside of arm 20.
Counterbalance weight 24 is releasably secured to arm 20 such as by a set screw 26 so that the position of the counterbalance weight can be adjusted on the arm. Also, balance weights may be attached to head 22 in the form of shims, and these head shims and the position of counterbalance weight 24 can be adjusted to provide a desired downward pressure or force at the head end so as to establish and regulate the tracking pressure of the tone arm assembly. As previously indicated, particularly because of the structure of the horizontal pivot assembly of the present invention (to be described in detail hereinafter) the tracking pressure of the present tone arm can be substantially less than 0.5 grams and as low as 0.1 grams. Also contributing to this low tracking force capability is the overall low mass of the tone arm assembly wherein the head 22 is a lightweight aluminum casting and arm 20 is a highly dried wood which is vacuum impregnated with a phenolic or epoxy resin and counterbalance weight 24 can be of low weight because of the low weight of the rest of the system. The vacuum impregnated wood of arm 20 possesses extremely desirable high strength characteristics for its weight (for example, about 35,000 p.s.i. shear strength and 20,000 p.s.i. tensile strength with a specific weight of only .051 pounds per cubic inch) and it also exhibits extremely good resonance characteristics in that it has a low mechanical resonance point. Also, as can best be seen in FIG. 3, recess 25 in arm 20 is filled with a resilient epoxy resin potting compound 27in which cable 23 is enclosed and which forms an important part of the resonance system of the arm by providing resonance damping. The potting compound must always remain resilient to perform its damping function. By way of example, the resilient epoxy resin potting compound 27 can be formed by mixing equal parts of an epoxy resin known as Eccobond 045 and Catalyst 015, both of which are available from Emerson & Cuming, Inc. Canton, Mass.
Referring now to FIGS. 2 and 3, it can be seen that vertical pivot assembly 18 has a casing 26 with a horizontally disposed central passageway 28 through which arm 20 passes. Arm 20 is firmly mounted on a pivot shaft 30 and is locked to pivot shaft 30 by a press fit. As can be seen from FIGS. 2 and 3,
pivot shaft 30 spans passageway 28, and it will be understood that arm 20 is firmly secured with respect to pivot shaft 30 by the press fit so that there is no relative rotational motion between arm 20 and pivot shaft 30. Pivot shaft 30 is mounted for rotation about its axis in a horizontal plane so that arm 20 pivots vertically about the axis of pivot shaft 30.
As can best be seen in FIG. 3, the casing 26 of the vertical pivot assembly has an integral depending collar 34 which is secured as by means of a set screw 36 to the rotatable structure of horizontal pivot assembly 14. Thus, vertical pivot assembly 18 is mounted for rotation on the axis of horizontal pivot assembly 14, and arm 20 is mounted for rotation on the axis of pivot shaft 30. Accordingly, it can be seen that arm 20 is mounted for horizontal and vertical rotation about intersecting axes. Reference is hereby made to US. Pat. No. 3,003,772 to Snow, Jr. et al. for a disclosure of a fluid damped horizontal pivot assembly of the type contemplated for use as pivot assembly 14 in the present invention, and it will be understood that vertical pivot assembly 18 would be mounted on structure corresponding to the rotating pintle of the pivot assembly disclosed in US. Pat. No. 3,003,772.
Still referring to FIGS. 2 and 3, each end of pivot shaft 30 has a reduced portion forming mounting pins 38 centrally located on the axis of the pivot shaft and' the mounting pins 38 preferably have a minimum yield strength of 75,000 psi. in shear. Mounting pins 38 may be integral with shaft 30 with the reduction in size being accomplished by machining, or the pins 38 may be separate elements press fitted into recesses in shaft 30. Each of the pins 38 is rotatably mounted in a jewel bearing element 40 which is in turn mounted in an isolation ring 42. Isolation ring 42 is retained in a recess in an end screw 44 which screws into a central opening at the side of casing 26 to form the vertical pivot assembly. A stabilization ring 43 extends from screw 44 to limit movement, as will be described hereinafter. Of course, it will be understood that the structure consisting of jewel bearing element 40, isolation ring 42, stabilization ring 43 and end screw 44 is present at both sides of casing 26 to form the support structure for each of the mounting pins 38. i
Referring now to FIG. 4, the details of one side of the vertical pivot assembly are shown in an enlarged view. Jewel bearing element 40 includes a brass shell or casing 46 which houses the jewel elements. The jewel elements are preferably of sapphire and are in two pieces, one piece being a thrust bearing element 48, and the other being a rotating support bearing element 50. The bearing surface 52 of bearing element 48 is a portion of a large diameter convex spherical surface. Similarly, the annular central opening through support bearing 50 defines bearing surface 54 in the shape of a body of revolution of an arc of a large diameter circle or other broad curve. The end 56 of mounting pin 38 extending into the jewel bearing structure is also rounded in a semicircular shape to define a spherical surface at end 56 of smallef diameter than the diameter of bearing surface 52. Thus, the radius defining end 56 is smaller than the radius defining bearing surface 52. The bearings 48 and 50 are mounted in a cavity in casing 46 and are held in place by end portions 58 of the casing swaged to overlap part of bearing 50.
The large diameter spherical surfaces of bearing surfaces 52 and 54 and the rounded end 56-of mounting pin 38 result in a reduction in the contact area between pin 38 and either of the bearings 48 and 50 to minimize contact friction, while at the same time the rounded surfaces provide enough contact area to avoid load concentrations. Thus, the combined structure of bearings 48 and 50 with their rounded bearing surfaces 52 and 54, respectively, and the pins 38 with their rounded ends 56 combine to produce a very low friction mounting (i.e. essentially frictionless) while at the same time avoiding load and stress concentrations.
As stated earlier, each of the bearing cases 46 is mounted in an isolation ring 42 which is resilient and preferably of rubber or similar material having a hardness of approximately 30 durometer. The bearing cases 46 fit in conformingly-shaped recesses 60- in the isolation rings 42, and the isolation rings allow for some movement of bearing elements 40 and thus provide isolation from shock, resonance and stray vibrations to thereby protect the relatively fragile sapphire bearings. Stabilization ring 43 extends from screw 44 and slightly overlaps a cylindrical portion of shaft 30 extending beyond the side of arm 20. Ring 43 is spaced from shaft 30 and bearing element 40 to allow movement of shaft 30 and bearing element 40 as determined by the size of the spacing, but ring 43 prevents any excessive movement or twisting of shaft 30 or bearing 40 since they will contact ring 43 if they move more than the distance of the spacing.
As previously stated, the overall objective of the present design is to provide a tone arm of low mass with high sensitivity response in tracking to light impulses. The horizontal pivot assembly 14 is of known construction and incorporates the known advantages thereof. The vertical pivot assembly 18 is of novel and improved construction providing significant advantages over previous tone arms. Excessive vertical movement of arm 20, such as by accidental jarring or movement of the arm, is constrained by the vertical dimension of passageway 28. if arm 20 is vertically pivoted an amount greater than that permitted by the size of opening 28, the arm will come into contact with casing 26 which is a cast unit. and the forces will be transmitted to the casting and to its support structure for absorption so that the relatively fragile and expensive sapphire bearings are not harmed. ln addition, the isolation rings 42 in which each of the bearing elements is mounted provides the previously mentioned isolation from shock, resonance and other stray vibrations while forces causing excessive movement of bearing 40 or shaft 30 are also transmitted to casing 26 through ring 43 and screw 44. The tone arm of the present invention, especially as a result of the vertical pivot assembly, will track dependably at 0.1 grams of tracking pressure so that tracking is more dependable than heretofore available and results in significantly less wear on records than was encountered with previous tone arms.
Referring now to FIG. 5, a new and improved armrest assembly of the present invention is shown, and the assembly is shown as it would be operatively positioned with respect to a turntable 62 and a record 64. The armrest assembly includes a body 66 having a recessed rest portion 68 and a bridge 70. The tone arm 20 would sit in recessed'rest portion 68 when the arm has been properly removed from the record. Bridge 70 spans the gap between rest 68 and the outer edge of turntable 62 and record 64 so that arm 20 cannot inadvertently be dropped or otherwise fall when it is being removed from the record it is being moved toward rest 68. Thus, damage to the arm, head or stylus is eliminated. A post 72 on the side of rest 68 opposite to bridge 70 prevents movement of arm 20 past the post so that damage to the arm, head or stylus which 'might result from moving it beyond the rest is also avoided. To complete the description of the rest assembly, body 66 is mounted on a cylindrical shaft 74 which in turn is positioned in a passageway in a base 76. Shaft 74 is slidable in base 76, and thus the height position of body 66 can be adjusted by loosening and retightening a set screw 78. Base 76 is mounted, as by a threaded portion 80, on any suitable mounting structure so that the arm rest assembly can be appropriately positioned with respect to table 62.
While a preferred embodiment has been shown and described, various modifications and substitutions may be made without departing from the spirit and scope of this in vention. Accordingly, it is to be understood that this invention has been described by way of illustration rather than limitation.
lclaim: l. A tone arm assembly including: horizontal pivot assembly means; vertical pivot assembly means, said vertical pivot assembly means including a casing having an opening therethrough and said casing being mounted on said horizontal pivot assembly means; 4 a tone arm having a head member, said tone arm passing through saidopening in said casing;
a pair of opposed resilient isolation rings in said casing for isolating said tone arm from resonance vibration;
a recess in each of said isolation rings;
a bearing housing in each pf said recesses, said housing hav ing an opening at one end;
a jewel thrust bearing elemeitt in each housing having a large diameter spherical bearing surface facing the open end of said housing;
a jewel support bearing element in each housing between said thrust bearing and the open end of said housing, said support bearing having a central toroidal opening with the walls thereof in the shape of a body of revolution of a curve;
mounting means extending from said tone arm into said housings in said casing, said mounting means having reduced end portions with a spherical end surface;
one of said reduced end portions extending into each of said housings and through the central opening of a support bearing to the spherical surface of a thrust bearing, the spherical end surface of the reduced end portion opposing and being of smaller diameter than the spherical surface of the thrust bearing; and
a stabilization ring extending from each of said resilient isolation rings beyond said bearing housing toward said tone arm, said stabilization ring extending beyond said reduced end portion of the mounting means to overlap the enlarged portion thereof to define a movement limiting space therebetween.
2. A tone arm assembly as in claim 1 wherein:
said casing surrounds a part of said tone arm; and
wherein said opening in said casing is a central passageway therethrough, said tone arm passing through said passageway.
3. A tone arm assembly as in claim 2 wherein said tone arm is a lightweight dried wood impregnated with a resin.
4. A tone arm assembly as in claim 2 wherein said tone arm has a recess therein for transmission wires, said recess having a resilient potting compound therein.
5. A tone arm assembly as in claim 2 including an armrest assembly having a rest portion for said tone arm and a bridge portion extending between said restportion and a turntable associated with said arm, said rest portion being recessed with respect to said bridge portion.
6. A tone arm assembly as in claim 1 wherein said casing has a pair of opposed sidewalls, one of said isolation rings being mounted in each of said sidewalls.