Floating head shell for a self propelled, tangentially tracking tone arm

A pivoting, passive servo controlled, self propelled and tangentially tracking tone arm, featuring a floating head shell/transducer assembly that tracks the groove in a disk-record independently of the tone arm itself and utilizing the so-called inward force to propel the tone arm across the disk record.

All references to left, right, front, rear, horizontal and vertical assume that the observer/narrator is facing the front of a common turn table with the tone arm located to the right of said turn table and the head shell facing the front of said turn table.

BACKGROUND OF THE INVENTION

The present invention applies to the field of gramophones, turn tables and record players, including their various tone arms and it particularly applies to pivoting, tangentially tracking tone arms therefor.

There are many pivoting tone arms that are claimed to be tangentially tracking. They include parallelograms, servo motor drives and designs that are driven by the camming action of the right channel flank of the groove in the record disk. Most of them have head shells that are constrained to the main body of the tone arm. The head shell is that part of the tone arm which is located at the end of the tone arm, which is opposite to the tone arm's pivot. Said head shell serves as a platform for mounting the transducer cartridge which carries the cantilever/stylus assembly that is in contact with the modulated groove of said record disk for playing back the sound contained in said modulated groove. In addition, many of the above tone arms have offset head shells and are subject to the so-called inward force. Said inward force occurs when the vertical center line of the pivot for horizontal rotation of the tone arm does not occupy the vertical center plane of said head shell and where said head shell has been rotated horizontally in a clockwise direction by the designer of the tone arm.

All of the tone arms mentioned in the above paragraph exhibit some degree of tracking error, especially the ones featuring servo motors to drive them.

The center line of said cantilever/stylus assembly occupies the vertical center plane of said transducer cartridge when at rest. Said modulated groove deflects said cantilever/stylus assembly equally to either side of said transducer cartridge's center plane when groove modulation is equal in both channels. When said inward force is present, and is under-compensated, the total excursion of said cantilever/stylus assembly is shifted to that side of said transducer cartridge that faces away from the center of said record disk, and when said inward force is present and is over-compensated, the total excursion of said cantilever/stylus assembly is shifted to that side of said transducer cartridge that faces toward said center of said record disk. The result is excessive wear of the record disk and distortion of the sound during playback.

A serious fault of servo motor driven tangential tone arms is that the servo requires the tone arms to display a small degree of tracking error before said servo can make a correction, thus “crabbing” their way across said record disk by alternating from one side to the other side of true tangency by hundreds of times during the playing time of the average record disk.

BRIEF SUMMARY OF THE INVENTION

It is therefore the general object of my present invention to provide a tangentially tracking tone arm assembly that will overcome the above, as well as other disadvantages of existing tangentially tracking tone arm assemblies.

It is the principal object of my present invention to introduce two new, heretofore unknown components, that I call “The Floating Head Shell”, and “The Cradle”, applicable to all tone arm assemblies to completely eliminate any and all tracking errors in all existing tone arm assemblies.

It is also an object of my present invention to provide a tangentially tracking tone arm assembly that is driven across said record disk solely by the frictional force between the stylus of said transducer cartridge and said modulated groove in said record disk.

It is another object of my present invention to provide a tangentially tracking tone arm assembly that does not require an active servo to drive the tone arm assembly across the record disk.

It is a further object of my present invention to provide a passive servo that acts in variable opposition to said inward force.

It is yet another object of my present invention to reduce the translation of said tone arm pivot, necessary for tangential tracking, by ˜50% as related to my U.S. Pat. No. 4,722,080.

It is a final object of my present invention to provide an offset cradle/head shell combination to utilize said inward force for the purpose of driving said tone arm across the surface of said record disk.

THE FOLLOWING IS A DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OF MY PRESENT INVENTION

I like the classical appearance of common pivoting tone arms installed in the upper right hand corner of the vast majority of turn tables.

All turn tables provide a flat surface dedicated to the mounting of all existing tone arms. Base1represents said flat surface in drawing1. Resting upon base1is column2, comprised of a cylinder with an integral mounting flange2awhich is designed to be immovably fastened to said flat surface of base1.

Projecting from column2, to the right hand side of the turn table and pivoting about the vertical center line of column2, is shelf3. Shelf3supports cam means4on its top surface and magnet assembly10and servo amplifier6on its bottom surface. Shelf3is designed to be manually rotated by ˜30°.

Also projecting from column2, above shelf3, and also pivoting about said vertical center line of column2, is beam5. Beam5supports cam follower housing7for rotation in the horizontal plane. Beam5is designed to rotate ˜30° and does so independently of shelf3.

Cam follower housing7supports cam followers9(2) and pivot8for rotation in the horizontal plane. When cam follower housing7is assembled to integral bearing housing5aof beam5, cam followers9(2) engage cam means4. At this point, any rotation of beam5causes a corresponding rotation of cam follower housing7and vice versa.

Tone arm assembly12comprises all of the usual components expected by those skilled in the art, with the special addition of the components that comprise the heart of my present invention, namely cradle assembly13and floating head shell assembly16, located at the front of tone arm assembly12. Floating head shell assembly16comprises phono cartridge17, attachment means33(2), magnet support18and magnet19. The vertical center plane of cradle assembly13is offset by ˜12° in a clockwise direction with respect to the vertical center plane of the tone arm tube.

Cradle assembly13incorporates ball bearing15(5) to support floating head shell assembly16. Four, of ball bearing15, support floating head shell assembly16against gravity, two at the front of cradle assembly13and two at the rear of cradle assembly13. The two ball bearings15at the rear of cradle assembly13are inclined ˜45° toward the front of cradle assembly13. When floating head shell assembly16is placed upon ball bearings15(4) it tends to be urged in a forward direction. To check this tendency, a fifth ball bearing15is located at the front center of cradle assembly13with the pivotal center line disposed perpendicularly with respect to the horizontal plane of cradle assembly13. This arrangement insures that all ball bearings15(5) are loaded and that floating head shell assembly16can only move in a lateral direction, perpendicular to the vertical center plane of cradle assembly13.

When tone arm assembly12is assembled to the tone arm bearing locating means in the top of cam follower housing7, the geometrically perfect feature of my present invention is established.

When tone arm assembly12is now pivoted in the horizontal plane to any random location above disk record21, controlled by the rotation of beam5, cam follower housing7and cam followers9(2) and guided by cam means4, a horizontal line projected from platter spindle20aof platter20and intersecting the center line of cradle assembly13in a perpendicular fashion, will be stylus path27upon which stylus26of transducer cartridge17will travel without deviation.

When tone arm assembly12is lowered until stylus26of transducer cartridge17makes contact with the groove in disk record21, the friction between stylus26and rotating disk record21immediately pulls floating head shell assembly16against ball bearing5at the front of cradle assembly13thus forcing tone arm assembly12and cradle assembly13to rotate clockwise by virtue of the inward force being the result of the offset angle of cradle assembly13. To check this uncontrolled rotation, a voice coil motor is provided and located on the underside of shelf3. Magnet assembly10of the voice coil motor is attached to the under side of shelf3and voice coil11is attached to beam5in such a fashion that it applies an equal and opposite force to beam5. Because said friction constantly varies based on tracking force, vinyl composition and the modulated content of said groove, a servo amplifier6is provided, and is located on the underside of shelf3and constantly varying the current supplied to said voice coil motor, synchronous with the variation of said friction. The varying control signal required by servo amplifier6to supply the correct amount of current comes from analog Hall Effect sensor14located in cradle assembly13. The output of Hall Effect sensor14is governed by magnet19, hovering above it and being supported by laterally moving floating head shell assembly16. This arrangement allows floating head shell assembly16to follow the groove independently and unhindered by tone arm assembly12, cradle assembly13silently following head shell assembly16keeping a position˜central to the underside of floating head shell assembly16. Precise central location of cradle assembly13and head shell assembly16is not necessary for 100% accurate tangential playback, as long as cradle assembly13and head shell assembly16do not collide with one another.

A secondary embodiment would apply my invention of the floating head shell assembly16and its control servo to tangential tone arms of the type shown on drawing10. These tone arms allow a small degree of rotation of the tone arm to trigger the servo motor into action. They are not really tangentially tracking tone arms because they constantly rotate fractions of degrees in an alternating clockwise and counterclockwise direction, thus “crabbing” their way across the disk record. They do that hundreds of times per LP side.

Tone arm assembly12rolls on carriage path29driven by carriage motor31. The revolutions per minute of carriage motor31are determined by the relative position of magnet19, supported by magnet support18, being integral to floating head shell assembly16, to the position of Hall Effect sensor14, which is integral with cradle assembly13. As head shell assembly16is guided across disk record21, by the modulated spiral groove, tone arm assembly12follows in the manner of the classic follow-up system, well known to those skilled in the art.

A tertiary embodiment would apply my invention of the floating head shell assembly16, and its control servo, to standard pivoting tone arms of the type shown on drawing11. The purpose of this embodiment is not tangential tracking, but to eliminate disk record wear and the distortion of the sound contained in the modulated groove upon playback. As everyone knows, standard pivoting tone arms with offset head shells, are subject to the so-called inward force. This force constantly varies while the disk record rotates based on the vinyl composition, the frequency content and the volume level of a given disk record. The various mechanisms employed, known as “antiskating”, don't come close to mitigating the effects of the inward force. By applying my invention of the floating head shell to pivoting tone arms, the transducer cartridge is completely isolated from the tone arm proper, thus allowing the head shell/transducer cartridge to follow the modulated groove without interference from the tone arm itself. While the inward force still exists, it does not have to be precisely controlled by the servo, as long as the head shell assembly and the cradle assembly do not collide.

LIST OF REFERENCE CHARACTERS