US3078100A

US3078100A - Tone arm for phonographs

Info

Publication number: US3078100A
Application number: US47012A
Authority: US
Inventors: Krober Klaus
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-02-25
Filing date: 1960-08-02
Publication date: 1963-02-19
Anticipated expiration: 1980-02-19

Description

Feb. 19, 1963 K. KRBER 3,078,100

TONE: ARM FOR PHONOGRAPHS Filed Aug. 2, 1950 sgfllllrlII/l/J r I-l l Il .jf-l (C gl l() l l T I l w (Q i I I l LJ ,l ...l

INVE TOR ATTO R N EY5 ilnited tates 3,078,100 TGNE ARM FR PHONSGRAPHS Klaus Krller, Gutenbergstrasse 65, Potsdam, Germany Filed Ano. 2, 1960, Ser. No. 47,912 Claims priority, application Germany Feb. 2S, 1960 3 tlaims. (Cl. 274-23) The present invention relates to a bearing arrangement `for the tone arm of a record player.

Several kinds of bearing arrangements for tone arms of record players are known which are all based on two associated bearing elements, eg., knife edge bearings, slide bearings, or point bearings. The shortcomings of these bearings are due to the more or less considerable friction forces which will become active between the bearing elements. In ball bearings these forces are, of course, least felt, but ball bearings will not function without play; that, however, is a necessity for the vertical movement of the tone arm because of the scanning of the needle.

The microgrooves which are now generally used in long-playing records, require a very light, sensitive scanning by the needle of the pick-up device. The pendulum movement of the tone arm in vertical as well as in horizontal direction, which is a consequence of the produc tion tolerances of the records, causes the oil film between bearing elements to disappear so that a dry friction results. The friction forces are very much increased thereby and in point bearings an increase of up to 2/3 of the original force has been found.

It is known that to save the record and the needle from excessive wear, a certain maximum contact force is admissible, which is determined by the necessary guidance of the needle in the very line micro groove in order that it may render all recorded undulation in true form. An attempt has to be made to keep the minimum Contact force as low as possible.

The indicated friction forces caused by dry friction in slide bearings lead to the following undesirable occurrences, particularly noticeable at a low pitch:

(l) Due to the friction loss in the bearing the contact force has to be undesirably increased when the tone arm head oscillates up and down in order to guarantee the guidance of the needle in the microgroove and to avoid slipping of the needle out of the groove when the record moves down. The increase in the contact force results in undue wear of the needle and the record. At the same time, during rotation, the contact force of the needle will vary continually. The varying contact forces are transmitted to the resilient rubber bearing of the needle which therefore is under unequal tension and the needle will scan undulations unevenly and this, in turn, will lead to tone distortions in the loudspeaker.

(2) Due to the friction forces in the slide bearing the lateral contact pressure of the needle is subject to variations by oscillating movements occuring in the scanning of the record spiral, which will likewise intiuence the loudspeaker and lead to distortions due to uneven lateral scanning by the needle.

It is the object of the present invention to overcome the above-mentioned disadvantages of the present pick-up devices.

In accordance with the invention, the disadvantages of bearing friction are overcome for the vertical movement Patented Feb. 19, 1963 of the tone arm by providing a connection for the arm with a supporting portion in the form of a flexible band, for example, a short leaf spring which, due to its particular arrangement, is permanently under tension. This flexible connection has no friction except internal molecular friction. The contact force for the needle can thus be considerably reduced, a factor which will not only reduce wear of the records and the needle, but will also result in much improved sound and result in very natural tone rendition in the loud speaker over the entire frequency range.

The invention will be fully understood from the following description and the accompanying drawings in which:

FIG. 1 is a longitudinal section through the tone arm; and

FIG. 2 is a front view of the flexible connection.

ln the drawing, the tone arm is designated by l. The weight of the arm acts against the spreading pressure of a spring 3 which is adjustable by a screw 2. The needle is shown at 4. The resulting contact force of the needle is, for instance, adjusted to be 6 grams. A leaf spring 5 replaces the known bearings for resiliently connecting the tone arm 6 with a supporting member 7 and is permanently under tension, as for instance the pendulum spring in a pendulum clock. Leaf spring 5 is fastened to brackets or tianges 10 and 11 by screws 12 extending through backing plates 13 and 14.

A ball bearing 9 is provided for the vertical shaft 8 of the supporting member 7. The bearing 9 is protected by an enclosure and runs with only a dry dusting of molybdenum disulfide. At this location, the play of the ball bearing does not produce any disadvantage, because it is unilaterally loaded by the total weight of the tone arm.

The invention has been illustrated by one embodiment thereof, but it will be understood that the invention is not to be construed as limited except as defined in the following claims.

I claim:

1. A tone arm for use in phonographs, having a lower supporting member adapted to be rotatably supported from the phonograph, an upper elongated member adapted to support a needle, and means connecting said upper and lower members, said means including first substantially vertically disposed spring means and second spring means.

2. A tone arm according to claim l, wherein said second spring means is adjustable for controlling the weight of the contact force of said needle on a phonograph record.

3. A tone arm according to claim 1, wherein said first vertically disposed spring means comprises a leaf spring, the longitudinal axis of said leaf spring being perpendicular to the longitudinal axis of said tone arm.

References Cited in the tile of this patent UNITED STATES PATENTS 2,224,332 Alsbrook Dec. 10, 1940 2,622,993 McCullough Dec. 23, 1952 2,941,810 Wagner June 21, 1960 FOREIGN PATENTS 722,876 Germany July 23, 1942 555,519 Great Britain Aug. 26, 1943

Claims

1. A TONE ARM FOR USE IN PHONOGRAPHS, HAVING A LOWER SUPPORTING MEMBER ADAPTED TO BE ROTATABLY SUPPORTED FROM THE PHONOGRAPH, AN UPPER ELONGATED MEMBER ADAPTED TO SUPPORT A NEEDLE, AND MEANS CONNECTING SAID UPPER AND LOWER MEMBERS, SAID MEANS INCLUDING FIRST SUBSTANTIALLY VERTICAL DISPOSED SPRING MEANS AND SECOND SPRING MEANS.