Abstract:
The invention relates to tonearm tracking mechanisms in phonograph players and mechanical devices constructed for the purpose of reproducing or playing back recorded audio material previously impressed, in the form or grooves, onto a surface of a disk, which are commonly called phonograph players or turntables. Such disk is commonly called, among other similar words, a phonograph record or a vinyl disk. The present invention is a tangential tracking tonearm mechanism, wherein the tonearm bearing subassembly has two rotary bearings in the lateral plane and a coupling linkage built into a compact subassembly. The collective contribution of these elements, when properly configured and appropriately adjusted, make, during playback of audio material on a disk, reduced playback distortion over radial tracking mechanisms and closely mimics the conditions under which nearly all masters are made.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to tonearm tracking mechanisms in phonograph players. More particularly, the present invention relates to mechanical devices constructed for the purpose of reproducing or playing back recorded audio material previously impressed, in the form or grooves, onto a surface of a disk. Such devices are commonly called phonograph players or turntables. Such disk is commonly called, among other similar words, a phonograph record or a vinyl disk. Even more particularly, the present invention describes a novel design of the tonearm mechanism, a component part of a phonograph player which is capable of tracking a groove in a phonographic disk in a controlled fashion, most especially in a tangential manner. 
     Conventional tonearm mechanisms fall generally into two categories: 1) a radial tracking mechanism wherein the path of a stylus, which is attached via several subcomponents to the end of one end of a tonearm, follows a curved path over the surface of a grooved disk. The curved path is a portion of a circle centered about a point near and outside the outer circumference of the disk; and 2) a tangential tracking mechanism wherein the path of a stylus, which is attached via several subcomponents to the end of a tonearm, follows a linear path over the surface of a grooved disk. The linear path over the surface corresponds to a radial line from the center of the disk and the mechanism that is employed to achieve the linear path is a form of linear bearing. 
     Known in the art is a third category of tonearm mechanism, namely one that has a tracking characteristic that achieves the groove-to-stylus relationship of a tangential tracking mechanism but is constructed from rotational bearings similar to those found in a radial tracking mechanism. In this third category of tonearm mechanisms, the stylus need not follow a single radial line coming from the center of the phonograph disk. Tangential tracking mechanisms are considered to be capable of more accurately rendering the recorded material on a disk because the motion of a playback stylus relative to a groove of a disk more accurately mimics the manner in which the original audio material was cut into a surface of a master disk. Tangential tracking mechanisms are not as common as radial tracking mechanisms because tangential tracking mechanisms tend to be more complicated, physically larger, and more costly to produce than radial tracking mechanisms. The present invention falls into this third category of tonearm mechanisms. U.S. Pat. Nos. 3,476,394; 3,813,100; 3,826,505; 4,153,256; 4,344,168; 4,346,466; and 4,580,258 disclose various tonearms of this category. 
     SUMMARY OF THE INVENTION 
     Lathes used to cut masters of analog audio material on lacquer disks have (commonly) a cutting head that moves slowly in a radial direction, thus assuring that a groove created by a cutting diamond stylus is always oriented perpendicular to a radius of the disk. Positive (grooves, versus molded inverse “hills”) copies or such masters may be played back using a phonograph player with a playback transducer having a stylus, a cartridge with internal components that hold the stylus, a headshell that supports the cartridge, the headshell attached to a tonearm which in turn is held by a tonearm bearing subassembly. When, during playback, the manner of playback closely matches the manner in which the original or master disk was produced, particularly with regard to the relative angular orientation of the stylus and the groove, one key source of systematic reproduction errors is essentially eliminated. 
     The various components of the tonearm mechanism must work together to allow a faithful rendering of audio material recorded on a disk. To achieve this result, the tonearm bearing subassembly must apply a force on the stylus to hold the stylus in the groove during tracking (i.e. while the disk is rotating about its axis) without applying so much force that the stylus wears surfaces of the groove; and the headshell, cartridge and stylus must rise and fall during tracking to accommodate changes in the vertical height of the top surface of the disk (e.g. due to a warped condition of the disk); and the tonearm bearing assembly should not allow the tonearm to rock about its own axis significantly; and the tonearm bearing assembly must allow the tonearm to track the groove in the disk as successive revolutions of the disk change the position of the stylus relative to the center of the disk. 
     The tracking properties of a tonearm assembly govern the fidelity of a signal created by a playback transducer. A tangential tracking tonearm allows the cartridge to play back the audio material in a way that very closely approximates the way in which the original master was created, and leads to superior sound fidelity compared to an otherwise similar, radial tracking tonearm (in the reproduced). A radial tracking tonearm plays back the audio material in a way that loosely approximates the way in which the original master was created, and leads to reduced sound fidelity. Terms commonly used to describe signal errors due to inaccurate rendering of the recorded material because the tracking during playback does not closely match the conditions under which the original master was created are “playback distortion” and “tracking distortion.” 
     The present invention is a tangential tracking tonearm mechanism, wherein the tonearm bearing subassembly has two rotary bearings in the lateral plane and a coupling linkage built into a compact subassembly. The collective contribution of these elements, when properly configured and appropriately adjusted, make, during playback of audio material on a disk, reduced playback distortion over radial tracking mechanisms and closely mimics the conditions under which nearly all masters are made. 
     It is an object of the present invention to reduce tracking distortion by orienting the playback stylus in the disk&#39;s groove during playback in a manner designed to closely mimic the motion of the cutting stylus used during creation of the master. 
     It is an object of the present invention to maintain tangency of the stylus in the groove during playback. 
     It is an object of the present invention to provide a tonearm mechanism that may be attached, or retrofitted, to an existing turntable. 
     It is an object of the present invention to incorporate bearing technology that reduces frictional losses in order to minimize wear on the walls of the groove being played back and to assist in maintaining accurate tangency in the orientation or the stylus with respect to the groove throughout playback. 
     It is an object of the present invention to incorporate magnet technology to reduce the degree of error from tangency in tracking. 
     It is also an object of the present invention to incorporate specially shaped magnetic components in the path of a linkage magnetic field for setting the tracking characteristics of a stylus in a tonearm mechanism. 
     It is an object of the present invention to incorporate, into a tonearm mechanism, linkage mechanisms comprising non-magnet and non-magnetic components and two vertically-oriented rotary bearings to control the angular and translational disposition of a stylus during playback to achieve substantially tangential tracking. 
     It is an object of the present invention to provide a linkage means for tailoring the path a stylus follows, both in angular orientation and in displacement, during playback. 
     Further objects and advantages will be described in succeeding sections of this specification. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a top view of a phonograph player and shows where the tonearm subassembly resides relative to other components of a phonograph player; 
         FIG. 2  is a schematic diagram, side view, of the bearings and linkage of the tonearm mechanism, where the magnet is at an inner end of the magnet guide; 
         FIG. 3  is a schematic diagram, side view, of the bearings and linkage of the tonearm mechanism, where the magnet is at an outer end of the magnet guide; 
         FIG. 4  is a schematic diagram, top view, of a portion of the tonearm mechanism showing the disposition of the vertical bearings when the magnet is at an inner end of the magnet guide; 
         FIG. 5  is a schematic diagram, top view, of a portion of the tonearm mechanism showing the disposition of the vertical bearings when the magnet is near the outer end of the magnet guide; 
         FIG. 6  is a schematic diagram, top view, of a portion of the tonearm mechanism showing the path followed by the magnet during playback of a phonographic disk. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     Referring now to the drawings, the invention is shown in  FIGS. 1 through 6  as a set of components of a tonearm mechanism  10  assembled atop a planar surface of a phonograph turntable. In  FIG. 1 , attached above turntable surface  11  is tonearm bearing subassembly  12 , which in turn supports tonearm  13 . A component of tonearm bearing subassembly  12 , shown in  FIG. 3 , is tonearm mounting collar  14  which is affixed, via base screw  15  to turntable surface  11 . Supported by tonearm mounting collar  14  is a vertically-oriented base bearing subassembly  16 . Referring to  FIG. 3 , attached or incorporated within base bearing subassembly  16  are vertical bearing housing  17 , base bearing  34 , guide platform  18  and magnet guide  19 , and base shaft  20 . 
     Referring again to  FIG. 3 , attached to the top of base shaft  20  is swivel platform  21 . Inserted in a hole in swivel platform  21  and rigidly affixed is vertically-oriented tonearm bearing-housing  22 , containing upper swivel bearing  35  and lower swivel bearing  36 , into which is placed tonearm shaft  23 . The top of tonearm shaft  23  supports tonearm pivot housing  24 . To the bottom of tonearm shaft  23  is attached magnet platform  25  upon which is affixed magnet  26 . 
     Referring now to  FIG. 2  and  FIG. 3 , within tonearm pivot housing  24  are two point pivot bearings, left point pivot bearing  27  and right point pivot bearing  28  which, together, support tonearm  13 . Left point pivot bearing  27  and right point pivot bearing  28  together define a horizontally-oriented bearing and serve to restrict, within tonearm pivot housing  24 , tonearm  13  to rotation about tonearm pivot axis  45 . To the rear of tonearm  13  is attached counterweight  29 . The counterweight  29  features an inner sleeve, made from a marginally compliant material, such as an acetal resin, Delrin (a registered trademark of, and manufactured and sold by E. I. DuPont De Nemours and Company) or a fluorinated hydrocarbon polymer such as Teflon (a registered trademark of, and manufactured and sold by E. I. DuPont De Nemours and Company). A grub screw, accessible from above, compresses the sleeve such that the effective coupling intensity can be adjusted by varying the screw torque. In other words, the counterweight can be slid—against varying friction—to adjust the tracking force unless the grub screw is tightened sufficiently to secure the position. To the front of tonearm  13  is attached headshell  30 . Contained within or held below headshell  30  is a cartridge, not shown, containing components, not shown, leading to a cantilever  37  to which a playback stylus  31  is attached. 
     In further detail, again referring to  FIGS. 1 through 5 , the combined effect of the various components is to produce a desired motion of playback stylus  31 , during playback of recorded material embodied in a groove  32 , impressed, in a spiral fashion, on phonograph disk  33 . Tangential tracking is achieved by providing two paths for the force applied to playback stylus  31  to reach the vertically-oriented bearings. One such path is strictly mechanical and can be regarded as setting the angular position of tonearm shaft  23 ; another path incorporates a linkage that, in effect, sets the angular position of base shall  20 , which, in the process of rotating, shifts the position of tonearm pivot housing  24 . The shape of magnet guide  19  provides a means for continuously controlling the degree of such shifting as the position of playback stylus  31  changes during playback. The simplified drawing of  FIG. 6  illustrates magnet path  44 , shown as a dashed line, as followed during playback of a phonograph disk. 
     The two paths, generally described above, by which lateral (i.e. in the plane of the top surface of phonograph disk  33 ) forces acting upon stylus  31  are transmitted throughout the bearings and linkage, shall now be described in greater detail. 
     A first path for the force applied to playback stylus  31  starts with tonearm mounting collar  14 , which is attached to turntable surface  11  by base screw  15 . Tonearm mounting collar  14  contains within it vertically-oriented base bearing subassembly  16  which allows the rigid connection of tonearm bearing subassembly  12  to the turntable or its “tonearm board” via a single eccentrically oriented screw. Its second function is to allow for setting the height of the tonearm  13 , or more correctly, vertical tracking angle (“VTA”). This can be achieved by a grub screw in tonearm mounting collar  14 , effectively clamping bearing subassembly  16  when in regular operation, but, after loosening the grub screw, allowing for the bearing subassembly  16  to be slid up or down to account for different turntable/platter and or cartridge dimensions, one component of which is vertical bearing housing  17  into which base shaft  20 , free to rotate about base vertical axis  38  is inserted. Attached to base shaft  20  is swivel platform  21 , which rotates in a horizontal plane as base shaft  20  rotates. Swivel platform  21  supports and is rigidly affixed to tonearm bearing subassembly  12 . Tonearm bearing subassembly  12  contains a second bearing assembly, also having a vertical axis of rotation, herein referred to as vertical bearing housing  22 . Into this vertical tonearm bearing is inserted tonearm shaft  23 , which extends from below the bottom of tonearm bearing subassembly  12  to above the top of tonearm bearing subassembly  12 . Rigidly attached to tonearm shaft  23  at a point above tonearm bearing subassembly  12  is tonearm pivot housing  24 , which can be connected by a screw or manufactured such that it is a one piece component. Tonearm pivot housing  24  has horizontally-oriented tonearm clearance hole  39  through which tonearm  13  is placed. Tonearm clearance hole  39  is larger in diameter than the diameter of tonearm  13 , which enables tonearm  13  when following vertical motion or playback stylus  31 , to move within a vertical tracking plane that contains a center axis of tonearm clearance hole  39 . To constrain tonearm  13  to angular motion in the vertical tracking plane, tonearm pivot hole  41 , perpendicular to tonearm clearance hole  39  and perpendicular to the vertical tracking plane is constructed in tonearm pivot housing  24 . Tonearm pivot housing  24  intersects tonearm clearance hole  39 , forming two distinctly separate sections of the tonearm pivot hole. One of the two sections shall be called left pivot hole  42  and-the other section shall be called a right pivot hole  43 . The axis of left pivot hole  42  and the axis of right pivot hole  43  are collinear. Into left pivot hole  42  is placed left point pivot bearings  27  and into right pivot hole  43  is placed right point pivot bearing  28 . These two pivot point bearings serve in concert, once aligned with receptacle features, not shown in the figures, on tonearm  13  and fixed in place, to create a tonearm pivot axis about which tonearm  13  is free to rotate. Counterweight  29  is placed on one end of tonearm  13 , the exact position of counterweight  29  along tonearm  13  being easily adjustable. On the other end of tonearm  13  is attached headshell  30  or similar supporting assembly. To headshell  30  is attached a transducer subassembly having various components, one of which is playback stylus  31 . Playback stylus  31 , supported by cantilever  37 , is the one and only element that touches groove  32  in phonograph disk  33 . The force with which playback stylus  31  presses down and into groove  32  is set by an adjustment procedure that involves placing and fixing counterweight  29  in a position along tonearm  13  such that a desired amount of force is applied. In tonearm assemblies designed to track (tangentially) a groove in a phonograph disk, the stylus, at the point where the stylus contacts a groove, is oriented to track the groove such that the stylus orientation equals that of the cutting stylus, i.e. runs parallel to, the vertical tracking plane is in, or at least runs parallel to, the vertical tracking plane. 
     A second path for the force applied to playback stylus  31  starts with the tonearm mounting collar  14 . A separate component, not described previously, is part of vertically-oriented base bearing subassembly  16 . This part shall be called guide platform  18 ; it is attached to the outside of vertical bearing housing  17 . The angular orientation of guide platform  18 , about the axis of base shaft  20 , is adjustable. Once adjusted and fixed in place, guide platform  18  is not permitted to move, unlike base shaft  20 . To the bottom of guide platform  18  is attached a magnetically active magnet guide  19 . Magnet guide  19  is contoured in such a way that tangential tracking is achieved. Finally, to the bottom of tonearm shaft  23  is attached magnet platform  25 , which can be attached by a screwed connection, press fit, glued or riveted means. Magnet platform  25  moves in concert with any angular motion, in a horizontal plane, of tonearm  13 . To the far end of magnet platform  25  is attached magnet  26 , which is press fit or interference fit and can be glued or secured by a screw, or preferably a small horizontal grub screw. The top of magnet  26  is disposed just below magnet guide  19 . Magnet guide  19  never touches magnet  26 , but magnet  26  is magnetically linked to magnet guide  19 . While this magnetic linkage between two components permits the transmittal of a mechanical force, there is no mechanical friction associated with the magnetic linkage at the linkage point between magnet  26  and magnet guide  19 . 
     To describe the various transfers of force with tonearm mechanism  10 , consider the very slow drift of playback stylus  31  as it plays back the recorded material on phonograph disk  33 . The inward motion of playback stylus  31  toward the center of phonograph disk  33  during playback occurs because the outside wall of the groove imparts a small radially directed inward force upon playback stylus  31 . This force is effectively reduced to zero or even directed towards the center of the record due to the remaining, albeit small skating force. It takes nearly no force to move the arm either inward or outward other than what is required to overcome lateral arm bearing friction. Tonearm  13  responds to such a force by rotating (typically clockwise when viewed from above the turntable). In turn tonearm shaft  23  must rotate. This angular motion is transmitted to magnet  26 , which in turn moves slightly relative to magnet guide  19 . In particular, magnet  26  becomes misaligned with respect to magnet guide  19  and creates a magnetically induced force in the horizontal plane between guide platform  18  and magnet platform  25 . Since guide platform  18  is itself fixed to vertical bearing housing  17  and pivot base  14 , both stationary components, the only component left to rotate in response to the magnetically induced force is base shaft  20 . The direction of rotation of base shaft  20  must be such that the magnetically-induced horizontal force diminishes and this is only achieved when tonearm  13  moves, now both in rotation and translation, such that any tangential tracking error is reduced. 
     In practice, due to the actual spiral groove, due to center hole (of phonograph disk  33 ) placement and size errors, and due to other manufacturing imperfections, the dynamic forces that are angularly applied to tonearm  13  by the walls of groove  32  during playback shift in direction and magnitude very frequently. Tonearm mechanism  10  must respond continuously and rapidly to correct any tangential tracking errors created by such dynamic forces. 
     In again further detail, also referring to  FIGS. 1 through 6 , regarding the sizes of the various parts, tonearm mechanism  10 , including counterweight  29 , is contained within a four inch diameter circle, approximately. While an overall smaller size could be contemplated, the compact organization of the component parts is sufficiently small for product design purposes. Reducing the size of parts comprising tonearm mechanism  10  would reduce mass that moves during operation of the invention, would permit a smaller footprint on turntable surface  11 , would reduce the moments of inertia about the axes of the bearings and would potentially reduce the accuracy of tangential tracking. On the other hand, bearing susceptibility to damage and bearing rotational friction might rise. Generally, the size of components like guide platform  18 , magnet guide  19 , and swivel platform  21  can range from a ⅛″ to ½″ in thickness, and most preferably, approximately ¼″ in thickness wherein the actual size is selected to exceed a desired level of mechanical stiffness, while being selected to reduce the unnecessary mass. The size of tonearm pivot housing  24  is determined by the requirements imposed by the size of point pivot bearings  27  and  28 , the diameter of tonearm shaft  23 , and the desired vertical swing of tonearm mechanism  10 ; the diameter of tonearm pivot housing  24 , viewed from the top, can range from 0.5 to 1 inch, and preferably about 0.9 inches, or most preferably is 23 mm, and the height of tonearm pivot housing  24 , viewed from the side, can range from 0.5 to 1 inch and preferably, is about 0.8 inches. 
     In further detail, also referring to  FIGS. 1 through 6 , regarding the materials from which the various parts are fabricated, most parts are constructed from aluminum. Parts such as magnet platform  25  and guide platform  18  must be constructed from materials that have no, or have properly controlled, influence upon the main function of the magnetic linkage that is composed of magnet guide  19  and magnet  26 . Magnet  26 , in a preferred embodiment, is constructed of rare earth elements. Magnet guide  19  is made of a magnetic material which can be any ferromagnetic material, like pure iron, nickel and it&#39;s alloys, i.e. Permalloy, Cobalt and its alloys or even made from another magnetic material, i.e. rare earth, bariumferrite, AlNiCo. The magnet  26  and/or magnet guide  19  can, among others, be substituted with an electromagnet, likewise is it possible to use, e.g., a permanent or electromagnet that is arc shaped to replace the magnet guide  19 . The quality of the bearings having vertically-oriented axes, i.e. base bearing  34  and swivel bearing  35 , largely controls the performance of tonearm mechanism  10 . These bearings should have low rolling friction. Ball bearing type bearings are used, and bearing balls constructed of ceramic compounds are particularly preferred. 
     The tonearm mechanism  10  could alternatively be governed by a servo system. Here the magnet guide  19  may be traced optically, inductively or capacitively. Any deviation from a maximally close proximity (or maximal proximity, i.e., a maximal distance that allows the sensor to trace the magnet guide  19  of sensor and magnet guide  19  would generally call for rotating the swivel platform  21  so that minimum proximity is maintained. This can be achieved by, e.g., driving the swivel platform  21  via a motor (e.g., Brushed DC, Stepper, piezo, geared or not) attached to and driving the base shaft  20 . The magnet  26  is merely the equivalent of a position sensor against magnet guide  19 . Once the proximity is minimal or, alternatively, if one senses/monitors the angular orientation of tonearm bearing subassembly  12 , the proper (tangential) orientation of tonearm  13  and the connected phono cartridge can be restored by rotating tonearm bearing subassembly  12  either clockwise or counterclockwise (in case of a strongly eccentric record). The swivel platform  21  would in such an embodiment become the holder/mount of the sensor. 
     While the preferred embodiment has been described in rich detail, various alternatives to the basic design as presented to this point are also considered within the scope of the invention. 
     Referring to  FIGS. 2 through 5  regarding the linkage, the mechanical placement of magnet platform  25  and magnet  26  can be switched with guide platform  18  and magnet guide  19 . 
     Referring to  FIGS. 2 through 5 , regarding magnet  26  and magnet guide  19 , contoured surfaces of these parts, near the gap between these parts, different from those shown in the figures, are anticipated. 
     Referring to  FIGS. 2 through 5 , regarding the angular orientation of magnet platform  25  to tonearm  13 , alternate angular separations of those parts may be selected from that shown in the figures. 
     Referring to  FIG. 3 , regarding base bearing  34 , ball bearing components such as those used for upper swivel bearing  35  and lower swivel bearing  36  may be used to replace the simple bearings shown for base bearing  34 . 
     Referring to  FIG. 2  and  FIG. 3 , regarding the construction of tonearm housing  24  and in particular the point pivot bearings  27  and  28 , the desired degree of freedom provided by such bearings (in this case, pivoting about a horizontal axis and over a small range) may be achieved by alternate means such as ball bearings, roll or cylindrically shaped bearings, or by other physical structures known in the art that accomplish the same goal.