GB2119996A - Speed selection device for turntables - Google Patents

Abstract

A device for the speed selection of a record turntable 4 with a motor driven pulley 1 consisting of two coaxial closely arranged disks of different diameters, a flat belt 3 connecting the turntable with one of said disks and a change-over element 2 adapted to be moved in a horizontal direction and consisting of a lower part and of an upper part, with a substantially rectangular opening 23 passing at the top over into a slot 24 inclined upwards separating both said parts. <IMAGE>

Description

SPECIFICATION Speed selection device for turntables The invention relates to an arrangement for the speed selection of a gramophone, record player or music centre turntable driven by a flat belt from a motor pulley.

It is common knowledge that present turntables of the hifi class are using predominantly a drive by means of a flat belt from a pulley of a driving motor situated in front of the rotating turntable. The motor pulley on the shaft of a motor running at constant rotating speed has for two required numbers of revolutions of 33 and 45 rpm two stages of different diameter, a larger for 45 and a smaller for 33 rpm. The flat belt is running on the first or second stage, whereby it is automatically stabilized at the place of the maximum diameter of each of both stages of the motor pulley. A change of revolutions is achieved by shifting the belt from the higher stage to the lower one or vice versa. A mechanical element of a U-fork shape serves for the change-over, which element urges the belt from the higher stage to the lower one and vice versa.This solely used method of change of revolutions requires the provision of a relatively high transition part of conical shape at the place between the upper and lower stage of the motor pulley in order to allow the belt a continuous shifting in the course of a vertical movement of the changeover fork. The required conical transition part between both stages however increases the height of the whole motor pulley and thus also the height of the driven turntable and of the whole turntable.

It is an object of this invention to eliminate these mentioned drawbacks of arrangements for speed selection of the turntable. The arrangement acording to this invention utilizes the circumstance that in a top view of the arrangement, the respective positions of the driving belt on different stages of the pulley are at an angle a (see Fig. 3 of the drawings) so that they are close to the pulley at a distance, allowing a change-over by a horizontal shifting of a suitable change-over element.

According to this invention the motor pulley comprises two coaxial, adjacently arranged disks of different diameter, having at the centre of their height a maximum diameter, which diameter is continuously decreasing toward their borders and the pulley is provided on its upper side and on its lower side with flat safety plates. The change-over element of the flat belt has a shorter upper part and a longer lower part, between which parts a substantially rectangular opening is provided terminating in a slot inclined in an upward direction between an inclined edge of the shorter upper part of the change-over element and an opposite inclined edge of the lower part of the change-over element.

The upper disk of the motor pulley which can be advantageously of larger diameter than the lower disk has a not symmetrical cross section with respect to a plane determined by the maximum diameter, whereby the upper half of the upper disk adjacent to the upper safety front plate has a larger inclination from a perpendicular line to the centre of the disk.

The change-over element can be formed by a flat plate or by a shaped wire.

The upper horizontal edge of the lower part of the change-over element can be bent toward the pulley so that this edge is situated just below the lower edge of the upper disk of the pulley.

Both parts of the change-over element can be arranged mutually off-set.

Advantages of the solution according to this invention are in a substantial reduction of the height of the pulley, of the thereof derived height of the driven turntable and thus a reduction of the height of the whole turntable.

The arrangement is from the point of view of operation completely resistant to possible incompetent handling in the course of operation, for instance against a forcible braking of the turntable by hand, against vibrations of the apparatus and the like. The reliable guiding and inclination of the belt in the intermediate position by the narrow inclined slot of the change-over element in the course of change-over prevents an unwelcomed twisting of the belt. The arrangement is also advantageous from the point of view of manufacture as the apparatus can be assembled from a minimum number of individual parts.

The arrangement for speed selection of the turntable according to this invention will be in the following described on an examplary embodiment on hand of attached drawings, where Figure 1 is a perspective view of the arrangement with the flat belt on the upper disk of the pulley, Figure 2 the same view with the belt on the lower disk of the pulley, Figure 3 a top view of the arrangement, Figure 4 an elevation of the pulley with the driving motor, Figure 5 a perspective view of a changeover element made of wire.

The motor pulley 1 is in case of a motor running at constant speed combined of two stages formed by two coaxial, adjacently arranged disks 11 and 12 of different diameter, having at the centre of their height a maxi mum diameter, decreasing toward the edges.

A flat belt 3 stabilizes automatically at the place of the maximum diameter of each disk 11 or 12. Flat security plates 13 and 14 are provided at the upper and lower face of the pulley 1 preventing any shifting of the flat belt 3 beyond the pulley 1, particularly at not expert handling of the turntable. The upper half of the upper, in the case given larger disk 11 of the pulley 1 has a larger inclination from a perpendicular line to the centre of the disk so that the flat belt 3 which in case of a forcible stoppage of the turntable 4 is sliding in direction upwards, is reliably caught below the safety front plate 13 without a possibility of winding on its circumference and of leaving the pulley 1 in an upward direction. The lower front plate 14 has a similar safety function.

A change-over element 2 is provided at the approaching strand of the flat belt 3 close to the pulley 1, said element 2 being in a vertical position and adapted to be moved by a control means in direction from the driving motor 5 to the driven turntable 4 and vice versa. The change-over element 2 which has in Fig. 1, 2 and 3 the shape of a flat vertical plate, but may be also made of wire as shown in Fig. 5, has a substantially rectangular opening 23 from which a narrow slot 24 starts in an upward inclined direction. The opening 23 and the slot 24 divide the vertical surface of the change-over element 2 to a shorter upper part 21 and to a longer lower part 22.The inclined edge 211 of the upper part 21 comes in the course of movement of the change-over element 2 in direction from the motor 5 to the turntable 4 in contact with the upper side of the belt 3, inclines it and shifts it in this inclined position from the upper stage 11 of the pulley 1 to its lower stage 12.

The belt 3 is in the course of the whole change-over reliably guided in this inclined position by the narrow slot 24 in an optimum inclined position so that it cannot be twisted in the course of contacting the lower stage 12 of the pulley 1. As soon as the belt 3 is in reliable contact with the respective disk of the pulley, the change-over element 2 finishes its movement toward the turntable 4 up to its extreme position determined by a stop. The belt 3 passes now freely through the opening 23 in a safe distance from the circumference of the opening 23. The turntable 4 obtains in that case the speed of 33 rpm.

In case of a change-over to 45 rpm the change-over element 2 starts to be shifted back from the turntable 4 toward the motor 5.

The inclined edge 221 of the lower part 22 of the change-over element 2 contacts the lower side of the belt 3, inclines it and urges it in this position upwards, whereby its optimum inclined position is again secured by guiding in the narrow slot 24. As soon as the belt 3 is shifted by the inclined edge 221 sufficiently high, it is caught by the lower edge of the upper stage 11 and is instantaneously wound on its maximum diameter. Only at this moment the belt 3 looses contact with the inclined edge 221 in the lower part 22 of the change-over element 2, which proceeds in its movement from the turntable 4 toward the motor 5 up to a stop.The belt 3 runs in this position on the upper stage 11 of the pulley 1 and is stabilized at the plane of the largest diameter, again in a safe distance from the upper horizontal edge of the lower part 22 and of the inclined edge 211 of the upper part 21 of the change-over element 2. The stabilization effect of the lower part 22 of the change-over element is substantially improved if its upper horizontal edge is bent toward the pulley 1 and is as close as possible to the lower stage 12 of the motor pulley 1 or if both parts 21, 22 of the change-over element 2 are offset, the lower part 22 being closer to the pulley 1.

In the described device the upper disk 11 of the pulley 1 has a larger diameter than the lower disk 12. it is of course also possible to situate the larger disk below the smaller disk.

In that case the change-over element 2 has to be situated within the space determined by the belt 3 between the pulley 1 and the turntable 4.

The change-over element 2 is in the examplary embodiment shifted in a direction parallel to a line connecting the centres of the pulley and of the turntable 4. The changeover element 2 can be of course also shifted at an inclination to this connecting line.

Claims (7)

1. Speed selection device for turntables using a belt drive from a two stage motor pulley, wherein the motor pulley comprises two coaxial, closely arranged disks of different diameter, each of said disks having substantially at the center of its height its maximum diameter, which diameter is continually decreasing toward both sides of the disk, a flat security plate of larger diameter than each of said disks provided at the top of the upper disk and below the lower disk, a change-over element of the flat belt arranged in the space between the motor pulley and the driven turntable in a substantially vertical position and in front of the pulley, this change-over element consisting of a smaller upper part and of a larger lower part with a substantially rectangular opening passing over at its top into a slot separating both parts of the change-over element, said slot situated between an inclined edge of the upper part of the change-over element and an opposite inclined edge of the lower part of the changeover element.

2. Speed selection device as claimed in claim 1, wherein the upper disk of the motor pulley has a larger diameter than the lower disk.

3. Speed selection device as claimed in claim 1, wherein the upper disk of the motor pulley has a not symmetrical cross section with respect to a plane determined by the maximum diameter of the disk, with a larger inclination against a perpendicular line to the axis of the pulley of the part of the disk, adjacent to the upper security plate of the pulley.

4. Speed selection device as claimed in claim 1, wherein the change-over element is made of a flat plate or of wire.

5. Speed selection device as claimed in claim 1, wherein the upper horizontal edge of the lower part of the change-over element is bent in a direction toward the pulley and is arranged close to the lower edge of the upper disk of the pulley.

6. Speed selection device as claimed in claim 1 wherein both parts of the change-over element are mutually offset.

7. Speed selection device substantially as herein described with reference to the accompanying drawings.