GB1587196A - Disc record players - Google Patents

Description

(54) IMPROVEMENTS RELATING TO DISC RECORD PLAYERS (71) We, THE PLESSEY COMPANY LIMITED, a British Company of 2/60 Vicarage Lane, Ilford, Essex, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: In co-pending British Application No. 44399/ 75, (Serial No. 1554407) hereinafter called the Main Patent, we have described anti-skating arrangements for gramophone record players, and in this connection we have described and claimed a device for applying to the pick-up arm of a disc-record player of the kind in which the playing groove of the record is scanned by a stylus carried on a pick-up arm which is mounted in the player for pivotal movement about a vertical axis, a torque about the vertical pivot axis about which the arm is moveable. In the device a magnet member having an annular flux-emitting surface concentric with said vertical axis, is arranged to emit through the fluxemitting surface a magnetic flux substantially normal or parallel to said axis, and a winding member comprises a winding having conductor elements which extend through said flux at a distance from the emitting surface in a direction substantially normal to the flux, one of said members being arranged to move with the pickup arm about said axis, and the other to be fixed relative to the player.

In connection with this device the main patent describes an electric circuit arrangement for passing through the winding of the device, during the playing of a record, a current of such direction and strength as to substantially balance the so-called skating force which is caused in disc-record players by the tangential friction force acting upon the pick-up stylus owing to its radial distance from the vertical pick-up axis about which the pick-up arm moves during the play of a record. The main patent also describes means for automatically cutting off this current when the pick-up arm is raised from the record, so as to prevent the device from causing socalled pick-up arm drift during cueing operation.

According to the present invention the torque applying device according to the main patent is equipped with an electric circuit incorporating the winding of the device, and switch means which can be operated to selectively pass through the winding when the pick-up arm is raised from the record, motor current from a source in one or the other of two opposite directions and of such strength as to produce, in cooperation with the flux from the pole faces, a torque of such magnitude about the vertical axis of pick-up arm movement as to move the pick-up arm about the said vertical axis in one or the other direction according to the selected direction of the current, damping means being additionally provided for controlling the speed of this movement. Preferably these circuit means are combined with the circuit means according to the main patent which produce anti-skating torque when the pick-up arm is lowered for the play of a record. Preferably the circuit arrangement for applying to the winding current to produce a reversible motor torque for movement of the arm incorporates switch means which render that arrangement inoperative when the arm is lowered on to a record, and these switch means may be operated by a pick-up arm lifting element, which thus is arranged, if anti-skating means are also provided, to perform both the cutting of the circuit for the arm-moving motor current when the arm is lowered onto the record, and the cutting-off of the current for producing the anti-skating torque when the arm is lifted off the record. According to a subsidiary feature of the invention, time-delay means may be provided for delaying the completion of the circuit for the anti-skating current for a short time immediately following the putting-down of the stylus on to the record.

In order that the invention may be more readily understood, reference will now be made to the accompanying drawings, in which Figures 1 to 8 are identical with the drawings of the main patent.

Figure 1 is a somewhat diagrammatic view of part of the unit plate assembly of a gramophone record player and shows the pick-up arm and also, somewhat diagrammatically together with electric circuit means for its use as an antiskating device according to the main patent, one form of a device according to the main patent, which forms part of the device according to the present invention.

Figure 2 is a sectional plan view showing, to a larger scale, the permanent magnet element means and the coil constituting the winding of this device.

Figure 3 is a radial section of the permanent magnet means and coil, in which the permanent magnet means is equipped with a yoke portion for the flux-return path, thus providing an annular air gap which is crossed by the flux from the flux-emitting surface of the magnet to a complementary surface provided by the yoke portion.

Figure 4 is an exploded perspective view of an embodiment of the invention which employs a magnetic flux disposed radially relative to the vertical arm-pivot axis.

Figure 5 is a perspective view showing the magnet elements employed in the permanent magnet means of the embodiment of Figure 4.

Figure 6 is an exploded perspective view of a preferred embodiment of the invention which employs a magnetic flux disposed in an axial direction relative to the vertical arm-pivot axis.

Figure 7 is a perspective view of the magnet elements of the embodiment of Figure 6.

Figure 8 is a diagrammatic side elevation showing the pick-up arm together with a portion of the arm-lifting mechanism and a record being played, and also shows diagramatically the arrangement of a switch in the electric circuit for the winding which automatically ensures that the anti-skating current through the winding is cut-off when the pick-up arm is lifted by the arm-lifting pin during a cueing operation, Figure 9 is a view similar to that of Figure 1, in which the energizing circuit for the winding is modified to provide in accordance with the present invention, for the control of electrodynamic movement of the pick-up arm, Figure 10 is a diagrammatic elevation of an embodiment incorporating means for automatically controlling the change-over between armdisplacement operation effective when the arm is raised, and skating-force balancing operation, effective when the arm is in its playing position with the stylus in contact with a record, and Figure 11 illustrates an alternative for the current-reversing switch arrangement of Figure 9.

Referring now first to Figures 1 and 2, the pick-up arm 2 of a disc-record player, which may be arranged for manual, semi-automatic, or fully automatic playing of a record or a succession of records, is, in a conventional manner, mounted in an arm support arranged for movement in the player about a vertical axis 3 to permit the arm to be moved to a desired starting point and then to follow the record groove on a disc record, and also to be moved outwardly of the record to a position of rest. The arm carries a pick-up head 8, which is fitted with a cartridge arranged along an axis ga and having a stylus 8b for engagement of the record groove.

As shown in the illustration, the axis 8a of the pick-up head 8 and cartridge is arranged at an angle to the pick-up arm 2 in order to ensure that during the play the axis 8a approximately corresponds to the tangential direction of the record groove at a point at which it is engaged by the stylus 8b, and it will be readily appreciated that, since the frictional force between the record and the stylus extends substantially in the direction of the axis 8a, it will exert upon the pick-up arm 2 a torque about a vertical axis 3 which is substantially equal to the product of the radial distance of the stylus 8b from the arm-pivot axis 3 multiplied by that component of the friction force acting upon the stylus 8b which acts at right angles to the said radial distance, and as is generally known, this torque tends to move the arm towards the centre of the turntable.

In order to compensate for the effect of this torque, or if desired to permit the arm to be moved electrodynamically or both, a permanent magnet means 1 comprising two elements la and lb in the form of adjacent sectors of a cylindrical sleeve, is secured to a drum 6 fixed on the arm support constituted by the pick-up arm spindle, coaxially with the vertical pivot axis 3, so as to move round that axis jointly with the pick-up arm 2. Both elements la and are permanently magnetized in the radial direction in such a manner that the North pole of the one element, for example of element la, is at its outer cylinder surface while the North pole of the outer element is at its inner surface, as indicated by N and S in Figure 2, and each extends over an angle sufficient to cover the total operative movement of the pickup arm. A winding in the form of a coil 4 which is curved according to a cylinder coaxial with that of the magent elements la and Ib, is secured to the stationary part of the recordplayer structure and is arranged to be energized with direct current from any suitable source, indicated as a battery 7, through an antiskating circuit which includes an adjustable resistor 5 and an on-off switch 9. The coil 4 is so arranged that two portions 4a and 4b of it, which preferably are substantially rectilinear, and in which the current flows substantially parallel to the axis 3, are respectively placed in the radial field emitted by the two permanent magnet elements la and ib. Since, when the on-off switch 9 is closed to energize the coil, current will flow through the two portions 4a and 4b in opposite directions, and these two portions are also arranged in parts of the field of the permanent-magnet member in which the radial directions of the flux are opposite to each other, both elements 4a and 4b will contribute to a torque about the pivot axis 3 in one and the same direction, which is arranged to be such as to tend to move the arm 2 away from the centre of the record, i.e. opposite to the torque exerted by the skating force, and by adjustment of the vertical resistor 8, the torque exerted by the device can be made equal to the above-mentioned skating torque.

It will also be observed that, while in all mechanical skating-force compensators of which we are aware, the provision of the compensator will produce a tendency for the pick-up arm to move outwardly when the arm has been set to a cueing position, (so-called cueing drift) due to the presence of the compensator torque in the absence of a skating torque, the present invention offers the possibility of eliminating such interference with cueing procedure by simply opening the switch 9 until the stylus rests on the record.

In practice the arrangement as so far described with reference to Figures 1 and 2 suffers from the drawback that the flux path of the flux passing through the conductors of the winding coil from one pole of a permanentmagnet element has to traverse a long distance through air to establish a closed path to the other pole, and that therefore a relatively strong magnet is required for producing a given strength of effective flux, and for this reason the permanent-magnet means comprises, as illustrated in Figure 3, a yoke member 10 which extends from that surface of the permanentmagnet elements which faces away from the winding 4, round the edge of the winding coil 4 to provide a complementary pole face 10a which faces the opposite surfaces of the permanent-magnet elements 1 across an air gap, in which the portions 4a and 4b of the winding 4 are accommodated.

A practical form of the magnet structure and the winding structure of an arrangement as described with reference to Figures 1 to 3 is illustrated in Figures 4 and 5, in which the yoke structure is constituted by a member 12 pressed in mild steel, with the yoke in the shape of an inverted U-channel curved to form a sector of an annulus about the arm-pivot axis 3 and formed integral with a flat, sector-shaped portion 13 which has a bore 38 extending along the axis 3 for centering the member 12 on the pick-up arm support spindle of a disc recordplayer. The permanent-magnet elements la and ib are secured, inside the channel, to the outer wall 12a of the U-channel in order to accommodate a maximum circumferential length of magnet. The winding is formed as a coil 14 wound in substantially rectangular shape but curved cylindrically in accordance with mean curvature of the air gap formed between the inner wall 12b of the channel 12 and the inner surface of the magnet elements la, lb. This coil is mounted between two similarly curved ribs 15a and 15b extending from a plate-like base 15c of a coil holder 15. The base 1 5c is provided with bores 16, through which screws may be passed for attaching the coil holder to the fixed structure of the record-player.

Figures 6 and 7 similarly illustrate a preferred construction of the magnet means and the winding of an arrangement employing a magnetic flux in the direction of the axis 3. The permanent-magnet means comprise two flat permanent-magnet plates 17 and 18, which are formed as plates shaped and arranged as adjacent sectors of a flat ring, coaxial with the arm-pivot axis 3 and magnetized across their thickness with opposite polarities. These magnet plates 17 and 18 are secured to the underside of a part-annular flange l9a formed of mild steel and integral with, but axially offset relative to, a flat centering portion I9b which jointly with it forms a yoke element 19, and which is provided with a centering bore 19c fitting round the pick-up arm support spindle of a record-player, and with two fixing bore l9d.

A further yoke element 20, also of mild steel, and of similar general outline but flat, is similarly provided with a centering bore 20e and with fixing and locating bores 20d, all of which are arranged to be aligned with the bores 19c and 19d respectively of yoke element 19. The two yoke elements 19 and 20 are arranged with their outlines aligned in the direction of the axis 3, and the amount of axial offset of the annular portion 1 9a relative to the attachment portion 1 9b of element 19 is so dimensioned as to leave, when the element 20 is in surface contact with the portion 19b of the element 19, an air gap between the free surface of the magnet elements 17, 18 and the adjacent surface of the plate-like element 20, which is sufficient to accommodate the thickness of a winding constituted by a coil 21. The latter has a flat, near-triangular shape to provide two conductor portions 21a and 21b and a connecting portion 21c formed approximately as a sector of flat ring, and a coil holder 22 is provided, which can be secured to the stationary portion of the record-player by a screw extending through a bore 22a. The coil holder 22 is formed as a plate with a side portion 22b which is formed with a lateral groove 22c for holding engagement with the outer edge of the connecting portion 21c of the coil 21, whereby the coil 21 is held in such a position that its conductor portions 21a and 21b extend substantially radially relative to the axis 3 of the pivot-arm spindle.

An arrangement such as that described with reference to Figures 6 and 7, in which a magnetic flux in the direction of the spindle axis 3 is employed, offers the advantage over an arrangement such as that described with Figures 4 to 5, in which a radial flux is employed, that it avoids the need for making a coil whose turns are arranged in a cylindrically curved surface.

Both the embodiments described respectively with reference to Figures 4 and 5 and to Figures 6 and 7 may be modified in detail; in particular, while in the embodiments described the two permanent-magnet elements are arranged to form abutting sectors of a circular configuration these two elements may be spaced from each other along such circle, thereby improving the quality of the magnetic flux in the vicinity of the adjacent ends, but at the cost of a decrease in compactness of the arrangement.

In the arrangement of Figure 8, the circuit for the energization of the winding 4 with current to produce anti-skating action incorporates, in addition to the current-adjustment resistor 5, a microswitch 24, which is spring-biassed to its closed position and has an operating member 24a, while an arm-lifting pin 23 has a platform forming spur 23a, on which the operating element 24a of the microswitch rests. The relative position of the microswitch and this platform is so determined that the switch is closed when the spur 23a is in its lowermost position, but will open when the lifting pin 23 is raised to reach a height at which it makes contact with an abutment 2a of the pick-up arm 2 to raise the latter from the position illustrated in the Figure, in which the stylus 8b of the pick-up 8 rests on a record 25b which has been placed on the turntable 25 of the record-player; during downward movement of the lifting pin 23, the microswitch is arranged to close its contact only when the pin 23 has moved a certain distance below the point at which the stylus 8b makes contact with the record, thus preventing the device from exerting an outwardly acting force on the pick-up arm before the stylus has engaged the record groove.

Referring now to Figures 9 and 10 in which the same references as in Figures 1 to 8 have been used for corresponding parts, the turntable 25, with which the pick-up arm 2 is to co-operate, is rotatable about a centre spindle 35 extending, along the axis 3, from a unit plate 31, its direction being vertical when the player is in use. The pick-up 2 is carried by the centre spindle 35 in such a manner as to be also capable of movement relative to the spindle 35 about a horizontal axis 35a extending transversely to the length of the arm, as shown in Figure 10, to enable the pick-up 8 with its stylus 8b to be lifted off the surface of a record 25b resting on the turntable or to follow any minor up and down movement of the record surface when the stylus 8b rests on the record.

The device employed for producing electrodynamically movement of the pick-up arm 2 about the axis 3 of the spindle 35 for movement of its pick-up 8 towards and away from the record centre, is generally similar to that described with reference to Figure 3, the same references being used to indicate corresponding parts with the additional use of a reference 42 for the air gap between the outer faces of the magnet plates la and lb and the opposed faces of the yoke member 10. No repetition of the detailed explanation of the motor device is therefore required. Current flow in the winding coil 4 to produce pivotal movement of the pickup arm either towards or away from the turntable centre, according to the direction of a current flow, is obtained by suitably connecting the coil 4 to a d.c. voltage source 46, which has been shown as a battery but is in practice likely to be a voltage source derived, via suitable voltage-reducing and rectifying means, from an a.c. mains supply employed for energization of a tunatable drive motor. To produce movement of the pick-up arm 2 in one direction or the other about the axis 3, a two-pole reversing switch 47 is moved to one or the other of its two end positions, thereby respectively closing circuits for supplying the winding coil 4 with current in two opposite directions through a path including in each case a suitably preset adjustable resistor 48. A second two-pole switch 49, arranged to be open when the switch 47 is put into one of its operating positions, can be closed when the pick-up stylus rests on the surface of a record 25b on the turntable 25, in order to provide compensation for the aboveexplained skating force. When this switch 49 is closed, it completes a circuit which includes a second adjustable resistor 50, and it will pass through the winding 4 a current which tends to move the pick-up arm 2 away from the turntable centre 25a with a force which is less than that applied when displacement of the pick-up arm is effected by energization of one of the circuits controlled by the switch 47, and the effective resistance of the adjustable resistor 50 is set to a value at which the torque applied electrodynamically to the pick-up arm 2 balances the torque produced by the so-called skating force. A switch 55 is interposed in the line connecting one terminal of the d.c. source 46 to the reversing switch 47. This switch 55 is interlocked with the two-pole switch 49 so that only one of the switches 49 and 55 can be closed at any one time, thus ensuring that the winding 4 cannot be energized simultaneously both via the movement-control resistor 48 and via the bias-compensating resistor 50.

The arrangement illustrated in Figure 10 includes an arm-lifting pin 51, which in a customary manner serves for lifting the pick-up from the record surface when the pick-up arm is to be moved across the turntable otherwise than by the guiding action of the record groove exerted on the stylus 8b during the play of a record. The movement of this pin 51 is utilised to ensure that the anti-skating torque is applied to the pick-up arm when, and only when, the pick-up stylus rests on the surface of a record 25b and becomes operative with a slight delay after the moment of deposition of the pick-up arm, and on the other hand to ensure that application of the arm-moving torque under the control of the change-over switch 47 can only become effective when the pick-up has been lifted off the record surface. For this purpose the pick-up lifting pin 51 has a projection 52 co-operating with the spring-loaded actuating element 53 of a two-pole microswitch 54. This microswitch incorporates the two switches 49 and 55 of Figure 9 and is arranged to close the switch 49 when the actuating element 53 is in the illustrated position, which corresponds to the lowermost position of the arm-lifting pin 51, and which the pin reaches after contact between the stylus 8b and a record being played has been established. Switch 55 is open at this position of the arm 2;it will close when the lifting pin 51 has been raised sufficiently to ensure that the stylus 8b is clear of the surface of any record 25b resting on the turntable 25, while the switch 49 is arranged to be open at this position of the arm 2. A damping electromagnet 56, co-operating with a disc 57 of electrically conductive material, arranged for rotation with the arm spindle 35 is arranged to be likewise controlled by the switch 55 so that the winding 56a of this electromagnet is energized to produce an eddy-current damping action whenever the switch 55 is closed.

It should be appreciated that the arrangements of Figures 9 and 10 have been described by way of example only and that, for example, the eddy-current damping device described with reference to Figure 10 may be replaced by a suitable viscosity damping device. Furthermore the form of the electro-dynamic torqueproducing means may be varied from the constructions shown somewhat diagrammatically in Figures 9 and 10 and may, for example, be constructed as described hereinabove with reference to Figures 4 and 5, or to Figures 6 and 7.

It will also be readily appreciated that, while the acutation of the arm-lifting pin 57 to raise and lower the pick-up arm may be effected mechanically, the raising and lowering of the arm may alternatively be effected electromagnetically or electrodynamically and that the damping during the deposition may be effected by mechanical, hydromechanical, or electrical means.

Furthermore, instead of providing a reversing switch 49 connected to a d.c. supply, a simple change-over switch 47a may, as indicated in Figure 11, be arranged to selectively connect an a.c. supply 46a to a pair of input terminals 47c, 47d via one or the other of two rectifier systems 47f, 47g to respectively supply to these terminals 47c, 47d d.c. current of two opposite polarities.

WHAT WE CLAIM IS: 1. A device for applying a torque to the pick-up arm of a disc-record player as claimed in the main patent, the pick-up arm being movable vertically between a playing position and a raised position, wherein the winding forms part of an electric circuit arrangement including switch means which, when the circuit is connected to a source of direct current, can be operated to pass selectively, when the pick-up arm is in such raised position, motor-driving-direct current from the source through the winding in one or the other of two opposite directions at such strength that the winding will produce, by electrodynamic co-operation with the flux from the flux-emitting surface of the magnet member of the device, a torque. about the vertical axis of pick-up arm movement, whose magnitude is such that the torque will move the pick-up arm about the vertical axis in one or the other direction according to selected direction of the current, and wherein the device also includes damping means for controlling the speed of the arm movement thus produced.

2. A device as claimed in Claim 1, wherein the electric circuit also contains switch means which when the pick-up arm is in the playing position, cause direct current from the source to flow through the winding in such direction as to produce a torque urging the pick-up arm away from the centre of the turntable and of such magnitude as to substantially balance the so-called skating force.

3. A device as claimed in Claim 1 or Claim 2, for a record-player equipped with an armlifting member mechanically acting on the pickup arm to raise the latter when required, wherein a switch device is so arranged so as to be mechanically actuated by the arm-lifting member so as to cut-off flow of arm-moving current through the winding when the arm is lowered to the playing position.

4. A device as claimed in Claim 3, wherein the switch device operated by the arm-lifting member also completes, when the arm is in the playing position, a circuit for passing antiskating current through the winding and cutsoff the flow of this current when the arm is in the raised position.

5. A device according to Claim 4, wherein time-delay means are provided to delay the commencement of the flow of anti-skating current until a short time after the arm has reached the playing position.

6. A device as claimed in Claim 1, and incorporating a motor drive constructed substantially as described with reference to Figure 2, or Figure 3, or Figures 4 and 5, or to Figures 6 and 7, of the accompanying drawings.

7. A device as claimed in any preceding claim, including an electric circuit arrangement as described with reference to Figure 9, or to Figure 10 or to Figures 10 and 11, of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. lifting pin 51 has been raised sufficiently to ensure that the stylus 8b is clear of the surface of any record 25b resting on the turntable 25, while the switch 49 is arranged to be open at this position of the arm 2. A damping electromagnet 56, co-operating with a disc 57 of electrically conductive material, arranged for rotation with the arm spindle 35 is arranged to be likewise controlled by the switch 55 so that the winding 56a of this electromagnet is energized to produce an eddy-current damping action whenever the switch 55 is closed. It should be appreciated that the arrangements of Figures 9 and 10 have been described by way of example only and that, for example, the eddy-current damping device described with reference to Figure 10 may be replaced by a suitable viscosity damping device. Furthermore the form of the electro-dynamic torqueproducing means may be varied from the constructions shown somewhat diagrammatically in Figures 9 and 10 and may, for example, be constructed as described hereinabove with reference to Figures 4 and 5, or to Figures 6 and 7. It will also be readily appreciated that, while the acutation of the arm-lifting pin 57 to raise and lower the pick-up arm may be effected mechanically, the raising and lowering of the arm may alternatively be effected electromagnetically or electrodynamically and that the damping during the deposition may be effected by mechanical, hydromechanical, or electrical means. Furthermore, instead of providing a reversing switch 49 connected to a d.c. supply, a simple change-over switch 47a may, as indicated in Figure 11, be arranged to selectively connect an a.c. supply 46a to a pair of input terminals 47c, 47d via one or the other of two rectifier systems 47f, 47g to respectively supply to these terminals 47c, 47d d.c. current of two opposite polarities. WHAT WE CLAIM IS:

1. A device for applying a torque to the pick-up arm of a disc-record player as claimed in the main patent, the pick-up arm being movable vertically between a playing position and a raised position, wherein the winding forms part of an electric circuit arrangement including switch means which, when the circuit is connected to a source of direct current, can be operated to pass selectively, when the pick-up arm is in such raised position, motor-driving-direct current from the source through the winding in one or the other of two opposite directions at such strength that the winding will produce, by electrodynamic co-operation with the flux from the flux-emitting surface of the magnet member of the device, a torque. about the vertical axis of pick-up arm movement, whose magnitude is such that the torque will move the pick-up arm about the vertical axis in one or the other direction according to selected direction of the current, and wherein the device also includes damping means for controlling the speed of the arm movement thus produced.

2. A device as claimed in Claim 1, wherein the electric circuit also contains switch means which when the pick-up arm is in the playing position, cause direct current from the source to flow through the winding in such direction as to produce a torque urging the pick-up arm away from the centre of the turntable and of such magnitude as to substantially balance the so-called skating force.

3. A device as claimed in Claim 1 or Claim 2, for a record-player equipped with an armlifting member mechanically acting on the pickup arm to raise the latter when required, wherein a switch device is so arranged so as to be mechanically actuated by the arm-lifting member so as to cut-off flow of arm-moving current through the winding when the arm is lowered to the playing position.

4. A device as claimed in Claim 3, wherein the switch device operated by the arm-lifting member also completes, when the arm is in the playing position, a circuit for passing antiskating current through the winding and cutsoff the flow of this current when the arm is in the raised position.

5. A device according to Claim 4, wherein time-delay means are provided to delay the commencement of the flow of anti-skating current until a short time after the arm has reached the playing position.

6. A device as claimed in Claim 1, and incorporating a motor drive constructed substantially as described with reference to Figure 2, or Figure 3, or Figures 4 and 5, or to Figures 6 and 7, of the accompanying drawings.

7. A device as claimed in any preceding claim, including an electric circuit arrangement as described with reference to Figure 9, or to Figure 10 or to Figures 10 and 11, of the accompanying drawings.