GB2109979A

GB2109979A - Tone arm

Info

Publication number: GB2109979A
Application number: GB08134834A
Authority: GB
Inventors: Vladimir Fedorovich Vinogradov
Original assignee: RIZH ELEKTROMEKHANICHESKY Z PR
Current assignee: RIZH ELEKTROMEKHANICHESKY Z PR
Priority date: 1981-11-19
Filing date: 1981-11-19
Publication date: 1983-06-08
Also published as: GB2109979B; DE3146989A1; FR2517098B1; DE3146989C2; FR2517098A1

Abstract

A tone arm comprises a lever 1 with a pickup cartridge 11 and a pressing- force setup assembly 12, two bases 2 and 3 facing each other, the movable base 3 being coupled to the lever 1, while the second base 2 is a fixed member, a vertical pivot 4, and ball 6. The pivot is attached to one of the bases 2 or 3 and cooperates with a spherical thrust bearing 5 in the other base 3 or 2, while the ball 6 is disposed between the bases 2 and 3 so that it makes contact with one of them and cooperates with a guiding element (slot 8) in the other base. <IMAGE>

Description

SPECIFICATION Tonearm The present invention relates to electric record players and in particular to tonearms.

The tonearm forming the subject of the invention may be used to advantage in high4idelity electric record players.

The invention resides in that in a tonearm comprising a lever with a pickup cartridge on its end and a pressing-force setup assembly, two bases facing each other, one of the bases being a movable member integral with the lever, while the second base is a fixed member to be affixed to a panel of an electric record player, a vertical pivot attached to one base and cooperating with a spherical thrust bearing in the other base, a vertical geometrical axis of rotation being extended through an interaction point thereof, according to the invention, a ball disposed between the bases is in contact with one of the bases and cooperates with a guiding element in the other base, a horizontal geometrical axis of rotation of the lever being formed by a straight line passing through the point of interaction between the pivot and the spherical thrust bearing, and through a point of contact between the ball and the base.

Preferably the guiding element represents an arched slot extended along a circumference with its centre on the vertical geometrical axis.

The guiding element may represent a spherical hole, the radius of its sphere exceeding slightly the radius of the ball, or two equidistant arched lugs, while the second base mounts an additional guiding element, which is structurally similar to the main guiding element and is arranged opposite said guiding element.

To change a pressing force in the course of reproduction, the pressing-force setup assembly desirably represents a magnetic pair comprising a magnet and a ferromagnetic element separated therefrom by a suitable gap, one element of the magnetic pair being rigidly coupled to the movable base, while the second element of said magnetic pair is rigidly attached to the fixed base.

When both bases mount the guiding elements, it is of advantage that the element of the magnetic pair rigidly attached to the fixed base is arranged so that a maximum flow from the magnetic pair passes through a perpendicular to a bisector of an angle formed by extremes of the horizontal geometrical axis with the tonearm lever being turned a complete revolution about the vertical geometrical axis to reproduce sound within the entire grooved surface of a record, the perpendicular intersecting the vertical geometrical axis.

The tonearm forming the subject of the present invention is characterized by high-fidelity reproduction and substantially reduced frictional forces in a gimbal. Provision is also made for changing a pressing force during reproduction, a factor resulting in such apparent advantages as a longer service life of a record and a reproducing stylus. Furthermore, a rolloff force may be compensated for in accordance with its variation law by locating, in compliance with the invention, the electromagnet of the pressing-force setup assembly in proper position with respect to geometrical axes of the tonearm.

A simple novel structure of a gimbal in the hereinproposed tonearm provides minimum friction in horizontal and vertical axes of rotation of the tonearm (less than 7 mg), which is an apparent advantage over most of foreign-made high-fidelity tonearms. A pressing force may be changed in quite a number of ways in various embodiments of the invention.

The tonearm in compliance with the invention entails a simple production process. The number of parts in the herein-proposed tonearm is reduced by about two times, as compared with prior art tonearms.

Moreover, most of its parts are cast and stamped items, another advantage being reduced dimensions of the pickup.

Minimum friction in geometrical axes of rotation of the tonearm, the possibility of adjusting a pressing force and the associated asvantages provide technical-and-economic indices enabling the use of the tonearm in high-class electric record players.

The invention will now be described further with reference to specific embodiments thereof, taken in conjunction with the accompanying drawings, wherein: Figure 7 is a top view of a tonearm according to the invention; Figure 2 is a section along Il-Il of Figure 1 depicting a guiding element on a movable base; Figure 3 is a section A of Figure 2 depicting the guiding element on a fixed base; Figure 4 is a top view of a preferred embodiment of the tonearm compensating for a rolloff force; Figure 5 is a diagram illustrating distribution of forces acting on the tonearm of Figure 4; Figure 6 is a top view of another embodiment of the tonearm with the guiding element representing a spherical hole in the fixed base according to the invention; Figure 7 is a section along VII-VII of Figure 6;; Figure 8 illustrates the embodiment of Figure 6 with the hole in the movable base; Figure 9 is a section along IX-IX of Figure 8; Figure 10 is a plot illustrating variations of a pressing force acting on the tonearm of Figures 8, 9; Figure 11 is a plot illustrating variations of a rolloffforce in the tonearm according to the invention; Figure 12 is a top view of one more embodiment of the tonearm with the guiding elements disposed on the two bases according to the invention; Figure 13 is a section along Xlll-Xlll of Figure 12; and Figure 14 is a view along arrow L of Figure 12 depicting a pressing-force setup assembly according to the invention.

The tonearm illustrated in Figures 1 and 2 comprises a lever 1, a lower fixed base 2 affixed to a panel of an electric record player (not shown in the drawing), an upper movable base 3 integral with the lever 1, a vertical pivot 4 secured, in a preferred embodiment of the invention, to the movable base 3 and cooperating with a spherical thrust bearing in the base 2. Besides, a ball 6 disposed between the bases 2 and 3 is in contact with a supporting plate 7 on the base 2 and cooperates with a guiding element (an arched slot 8 in the preferred embodiment of the invention).A vertical geometrical axis a-a of rotation of the lever 1 passes through a point 9 of interaction between a pointed portion of the pivot 4 and the thrust bearing 5, while a horizontal geometrical axis b-b of rotation of the lever 1 is formed by a straight line passing through the same point 9 and through a point 10 of contact between the ball 6 and the supporting plate 7 on the base 2.

The generating lines of the arched slot 8 are found on a circumference with its centre on the vertical axis a-a.

The length of the slot 8 is chosen to provide free movement of the lever 1 throughout the entire recorded area from the starting to the final grooves. Besides, one end of the lever 1 mounts a pickup cartridge 11, while the opposite end carries a pressing-force setup assembly 12 of the cartridge 11 (a counterbalance in the preferred embodiment of the invention). A point 0 in Figure 1 illustrates a possible position of the centre of mass of the tonearm.

As the pickup stylus moves over uneven surfaces of a record, i.e., during movement of the cartridge 11 in a vertical plane, the working bearing surfaces the pivot 4 and the ball 6 (the points 9 and 10, respectively) rock over the bearing surface of the plate 7 of the base 2.

The invention allows appreciably reducing friction in horizontal and vertical axes of the tonearm due to exclusion of sliding-friction sources. In the horizontal and vertical axes of the tonearm there occurs rolling friction of said bearing surfaces whereby a moment of frictional forces in the tonearm support is substantially reduced, an advantage assuring movement of the pickup over the record without a braking effect. The obtained friction is about 5 mg, as referred to a force applied to the pickup stylus.

Figure 3 illustrates another embodiment of the invention with the ball 6 installed in a different manner. In the preferred embodiment of the invention the slot 8 is made in a lower fixed base 13, while the plate 7 of an upper movable rests against the ball 6 at the point 10. The guiding element may be constructed in different ways, say, as a hinge secured to one of the bases, etc.

In the tonearm forming the subject of the present invention an undesirable gap is eliminated, which is an apparent advantage over the prior art. The performance of the pickup is improved to a considerable extent by increasing structural rigidity and reducing the unbalance of cartridge channels, other positive features being improved isolation of channels, decreased wow and flutter, and the possibility of longitudinal stabilization of the tonearm.

In the embodiment of Figures 4 and 5 there occurs useful distribution of frictional forces as the tonearm rotates about the vertical axis a-a whereby the rolloff4orce compensation effect is achieved.

As distinct from the tonearm of Figures 1 and 2, in the preferred embodiment of the invention the length of the slot 8 is somewhat shorter than the length required to move the lever 1 through the entire grooved surface of a record. Also, one of the bases (the movable base 3 in the preferred embodiment of the invention) is inclined with respect to the base 2 in the direction opposite to the direction of movement of the lever 1 during reproduction.

Without a radial runout (eccentricity) created by a record and electric record players, a rolloff force could be compensated by merely increasing a frictional force in a vertical axis of the tonearm.

However, under actual conditions any disc record is characterized by eccentricity of a central opening with respect to a record field. So, during reproduction the tonearm performs a reciprocating motion. As the tonearm moves with respect to the centre of the record, a frictional force is added to a rolloff force in a vertical axis. Thus, in the known devices the frictional force in the vertical axis is reduced to a minimum, which, as a rule, is achieved by utilizing expensive methods, say, by using ruby and sapphire balls in bearings. The rolloff force is compensated for by applying a compensating force equal in magnitude but opposite in direction. This is accomplished by utilizing springs, magnetic and gravitational forces.

In the embodiment of Figures 4 and 5 the rolloff force is compensated for in the following manner.

Assume that the base 3 mounting the pickup cartridge 11 and the counterbalance 12 turns about the vertical axis a-a of the tonearm while the lever 1 moves towards the centre of a record as indicated by arrow B. ihe ball 6 restring against an edge 15 of the slot 8 moves with sliding friction over the plate 7 of the base 2.

A force of sliding friction determined by the position of the counterbalance 12, i.e., by the position of the centre of gravity 0, is chosen to be equal to the value of a rolloff force but has an opposite direction. As a result, the rolloff force will be adequately compensated.

The base 3 rolls away while the lever 1 moves from the centre of a record as indicated by arrow C (due to eccentricity). The ball 6 moves (rolls) over the plate 7 of the base 2 with minimum rolling friction, whereas sliding friction is eliminated.

In this case, an antirolloff moment is set up due to the fact that at least one of the bearing surfaces of the upper or lower base (the base 3 in the embodiment of Figure 3) is inclined.

Thus, as the lever 1 moves towards the centre of the record, the rolloff force is compensated for due to sliding friction between the ball 6 and the plate 7 of the base 2. As the lever 1 stops or moves back from the centre of the record, the compensation occurs due to a force F set up as a result of decomposition of a gravitational force P into components.

As distinct from the embodiment of Figures 1 and 2, the tonearm illustrated in Figures 6 and 7 has the guiding element representing a spherical hole 16, the radius of its sphere exceeding slightly the radius of the ball 6, said spherical hole being provided in the fixed base 3. Besides, in the preferred embodiment of the invention the pressing-force setup assembly represents a magnetic pair comprising an electromagnet 17 and an armature 18 separated therefrom by a suitable gap. The electromagnet is secured to the fixed base 3, while the armature 18 is attached to the movable base 2. The attachment may be reversed with the electromagnet 17 secured to the base 2 and the armature 18 attached to the base 3. The armature 18 is held in place with a screw 19. The electromagnet 17 may be secured at different points on the base 3, say, in positions l, ll, or Ill.

When the tonearm operates (turns as indicated by arrow D), the upper base 3 slides over the ball 6, while the ball 6 and the lower base 2 remain stationary.

The dashed line in the drawing shows the position of the lever 1 as it moves towards the centre of a record.

During reproduction, the pressing force is changed as follows.

When the pickup stylus k tracks the starting grooves of the record, the pressing force is determined by the relationship F F2.12 11 where F1 is the pressing force; 11 is an arm of the force F1, i.e., the distance from the stylus k to the horizontal axis b-b of the tonearm; F2 is a force developed by the electromagnet 17 (F2 = const); and 12 is an arm of the force F2, i.e., the distance from the electromagnet 17 to the horizontal geometrical axis b-b of the tonearm. In the drawing the electromagnet 17 is in position I, E-E indicates the position of the lever 1 on the starting grooves of the record, and H-H indicates the position of the lever 1 on the final grooves of the record.

As the stylus k moves from the position E to the position H, 11 (the arm of the force F1) increases by Awl1, while 12 does not change. As a result, the pressing force F1 decreases. A similar relationship betwee the forces and arms is obtained when the electromagnet 17 is located at other points on the base 3, say, in positions II or lil.

Figures 8 and 9 illustrate one more embodiment of the invention. As distinct from the previous embodiment, the guiding element (spherical hole 20) is provided in the movable upper base 3, and the ball 6 is displaced together with the base 3 relative to the fixed base 2 during movement of the lever 1.

In operation with the electromagnet 17 in position I, the arm 11 does not change, and the arm 1 2-l increases.

Consequently, F1 increases at F2 = const.

When the electromagnet 17 is set to position 11 (turned through a certain angle) as the tonearm is operative, the arm 11 does not change, and the arm 12.11 increases and then, after a certain maximum value 12.11 is reached, decreases equalling the initial value of 12.11. The pressing force F1 being directly proportional to the quantity 12will change in a similar manner.

The above process is illustrated in the plot of Figure 10 depicting variations of the pressing force F1. In the drawing the ordinate is the pressing force F1, and the absissa is radius R of the reproducing groove (mm), R1 being the radius of the starting groove and R3 being the radius of the final groove.

In the preferred embodiment of the invention a rolloff force is compensated for in accordance with its variation law.

From the existing publications it is known that the rolloff force F3 in electric record players changes in accordance with a complicated law, as in Figure 11, and depends on the value of the pressing force F1.

A principal difficulty involved in designing means for compensating the rolloff force F3 lies in providing a compensating force changing in the same manner as the force F3.

Table I illustrates the dependence of the rolloffforce F3 on the reproduction radius R with the pressing force F1 being a constant value. Table II illustrates the dependence of the rolloff force F3 on the radius R with the pressing force F1 being a variable quantity.

TABLE I F F3 R1 1.0 0.12 R2 1.0 0.1 R3 1.0 0.12 TABLE II F7 F3 R1 1.0 0.12 R2 1.2 0.12 R3 1.0 0.12 Referring to Table lit is seen that a minimum value F3=0.1 is obtained with the mean groove radius R2.

Referring to Table II it is apparent that, if the tonearm provides for a variation of the pressing force F1, the rolloff force F3 will be constant over the entire grooved area regardless of the reproduction radius R. Its compensation by a force equal in magnitude and opposite in direction will, then, be a simple problem solved virtually in every electric record player.

With the electric magnet 17 in position Ill while the tonearm is operative, the arm 11 does not change, the arm 12 decreases, and the pressing force F1 decreases, accordingly.

In the embodiment of Figures 12 and 13 the guiding element represents two equidistant arched lugs on the base 3 extended along circumferences with a centre in the vertical geometrical aixs a-a, while the base 2 mounts an additional guiding element comprising two equidistant lugs 22 structurally similar to the main guiding element and arranged opposite said main guiding element. In the illustrated embodiment of the invention the ball 6 is displaced with respect to the bases 2 and 3 when the lever 1 turns. As a result, there may be obtained the following relationships between the pressing force F1 and the arms 11, 12 depending on the position of the electromagnet 17. Reference numerals 23 and 24 denote fastening screws.

In position I of the electromagnet 17, as the lever 1 moves towards the final grooves of the record, the arm 12 of the force F2 will increase more rapidly than the arm 1, of the force F1. Since the pressing force F F2#12 11 then at A12 > A11. the force F1 will smoothly change but in a slower manner as compared with the embodiment of Figures 7 and 8.

With the electromagnet 17 in position II, the arm 12 changes by a smaller amount than the arm 11. Thus, the pressing force F1 decreases.

In position Ill of the electromagnet 17, as distinct from the previous two embodiments (positions I and II of the electromagnet 17), the arms 12.111 will decrease, a condition resulting in a sharp decrease of the force F1.

The electromagnet 17 is advantageously secured in a position at which a maximum flow from the magnetic pair passes through a perpendicular to a bisector of an angle formed by extremes of the horizontal geometrical axis b-b with the lever 1 turned through a complete revolution about the vertical geometrical axis a-a to reproduce the entire grooved surface of a record, the perpendicular intersecting the vertical geometric axis a-a.

In all the preferred embodiments of the invention the force of the magnetic pair contributes to distribution of a vertical pressure among the supporting elements of the gimbal (the pivot 4, the thrust bearing 5, the guiding elements, and the ball). The performance of the tonearm is not impaired due to the absence of an adverse lateral pressure.

Using the preferred embodiments of the invention allows obtaining different laws of variation of a pressing force, a feature advantageous in many aspects in designing pickups, say, in compensating for a rolloff force in accordance with its variation law orland in automatically changing the value of a pressing force.

Figure 14 illustrates an embodiment of an electromagnetic device for creating a pressing force (a view along arrow L in Figure 12). The electromagnet 17 is secured to the fixed base 2 by means of the screws 23 and 24. The armature 18 is installed on the lever 1. The electromagnet 17 and the armature 18 may be arranged in quite a number of different ways. For example, the armature 18 may be installed on the base 2, while the lever 1 mounts the electromagnet 17.

Claims

1. A tonearm comprising a lever with a pickup cartridge on its end and a pressing-force setup assembly, two bases facing each other, one of the bases being a movable member integral with the lever, while the other base is a fixed member to be affixed to a panel of an electric record player, a vertical pivot attached to one base and cooperating with a spherical thrust bearing in the other base, wherein a ball disposed between the bases is in contact with one of the bases and cooperates with a guiding element on the other base, a horizontal geometrical axis of rotation of the lever being formed by a straight line passing through a point of interaction between the pivot and the spherical thrust bearing, and through a point of contact between the ball and the base, while a vertical geometrical axis thereof passes through the point of interaction between the pivot and the spherical thrust bearing.

2. A tonearm as claimed in Claim 1, wherein the guiding element represents an arched slot extended along a circumference with its centre on the vertical geometrical axis.

3. A tonearm as claimed in Claim 1, wherein the guiding element represents a spherical hole, the radius of its sphere exceeding slightly the radius of the ball.

4. Atonearm as claimed in Claim 1, wherein the guiding element represents two equidistant arched lugs, while the second base mounts an additional guiding element, which is structurally similar to the main guiding element and is arranged opposite said main guiding element.

5. A tonearm as claimed in any claim from 1 to 4, wherein the pressing-force setup assembly represents a magnetic pair comprising a magnet and a ferromagnetic element separated therefrom by a suitable gap, one element of the magnetic pair being rigidly coupled to the movable base, while the second element of said magnetic pair is rigidly attached to the fixed base.

6. A tonearm as claimed in Claim 5 in conjunction with Claim 4, wherein the element of the magnetic pair rigidly attached to the fixed base is arranged so that a maximum flow from the magnetic pair passes through a perpendicular to a bisector of an angle formed by the extremes of the horizontal geometrical axis with the tonearm lever being turned a complete revolution about the vertical geometrical axis to reproduce sound within the entire grooved surface of a disc record, the perpendicular intersecting said vertical geometrical axis.

7. A tonearm substantially as hereinabove described with reference to, and as shown in the accompanying drawings.