GB2423626A

GB2423626A - Record player drive arrangement

Info

Publication number: GB2423626A
Application number: GB0603787A
Authority: GB
Inventors: Arthur Haroutoun Khoubesserian
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-02-24
Filing date: 2006-02-24
Publication date: 2006-08-30
Also published as: GB0503809D0; GB0603787D0

Abstract

A drive arrangement for a record player, comprising support means 4 for supporting a disc record, an arrangement of pulleys 1, 2, 3, belt means 5 for rotating the pulleys and drive means for rotating at least one of the pulleys, wherein the pulleys are asymmetrically arranged with respect to the centre of rotation of the support means. The invention is said to address the problem of the large sideways force exerted by the belt in conventional belt driven turntables.

Description

IMPROVEMENTS IN A DRWE ARRANGEMENT

FOR A RECORD PLAYER

The present invention relates to improvements in a drive arrangement for a record player To date it has been assumed that once turning the action of the platter and bearing arrangement of a record player exhibits pure rotation and no translational components. For this to be so, however, the centre of mass of the platter, the bearing axis and the axis of rotation must at all times remain co-linear and all non-rotational forces must balance out to zero.

In known belt drive turntables there is a very large uni-directional force of the belt against the platter pulling the bearing point out of colinearity with the bearing axis and causing continuous instability. In an attempt to regain stability, the platter must precess about the bearing point; in other words, there is a lateral translational component as the bearing moves out of position and the motion is no longer purely rotational. This degree of translation is dependant on the gap existing between the bearing spindle and the bearing sleeve, which permits rotation. As the gap is considerably in excess of the maximum groove modulation found, this movement is audible.

In suspended turntable systems, the above mentioned precession of the centre of mass of the platter, and hence precession of the suspended system, continuously alters the extension of the various isolating springs and hence continuously varies the state of balance of the suspended system overall.

This results in varying non-linear forces being applied against the wall of the

-F

bearing and thus varies the uniformity of the platter and therefore the record.

Although such variation may be detected by the motor's drive circuitiy and correction subsequently applied, further undesirable, audible phase modulated distortions are now introduced.

In an effort to balance the tension of the belt about the bearing spindle, designs have been tried where either one or two additional motors have been positioned symmetrically about the axis of the platter. This would mean a second motor positioned diametrically opposite the first motor (180 degrees) or two motors at 120 degrees. Unfortunately, this does not work. Drive to the platter is supplied by a combination of the pulley and belt dimensions acting together. Even with all the motors turning at the same speed, necessary, impossible to attain, additional conditions are now apparent.

Firstly, all motor pulleys need to be precisely identical in driving diameter.

Anything less than perfection will result in any one motor driving another.

Secondly the belt thickness needs to be precisely constant at all times.

However, the inherent necessary resilience of the belt, which enables the belt to absorb vibration, means that it has to compress variously, thereby altering its thickness and so altering the previously stated precise driving ratio. Any deviation from those two initial conditions would, and do, result in the relative drive from one motor acting against any other motor and so called hunting of drive occurs as each motor attempts to apply its power not to the platter but to the other motors.

An alternative solution which has been tried is where instead of using an additional motor as mentioned above, an undrivable pulley is introduced.

Again, this does not solve the problem. Firstly, for a drive to operate, there must be greater tension on the takeup side of the pulley than on the return side. This will have a vector, which does not pass through the axis of the bearing and will thus not be balanced by the opposing pulley.

Secondly, although the platter is planner, the two pulleys acting to provide support to the platter act only along a bi-directional axis of that plane. Such geometry is itself inherently unstable, for under the action of any various remaining forces, such as the tracking weight acting on the platter! bearing there will result a side-to-side instability. Stability in a plane or in three dimensions can only be achieved with at least three supports and thus, the optimum solution is to utilise at least three pulleys. One pulley would be used to apply the drive force with the other two pulleys acting passively with no independent drive mechanism, save that supplied via the first motor. This expedient is used in order to distribute the load evenly. For a stationary system this would mean positioning the at least three pulleys equidistant and equiangular about the bearing,when all the vectors act directly through the bearing.

In a dynamic system as found in a record player, however, the forces are unbalanced and thus optimisation is neither equiangular nor equidistant.

According to the present invention there is provided a drive arrangement for a record player, comprising support means for supporting a disc record, an arrangement of belt supports or pulleys, belt means for rotating the supports or pulleys and drive means for rotating at least one of the supports or pulleys, wherein the supports or pulleys are asymmetrically arranged with respect to the centre of rotation of the support means.

The drive arrangement may comprise three belt supports or pulleys.

The asymmetrical arrangement of the supports or pulleys may comprise an arrangement wherein the supports or pulleys are angularly asymmetrically disposed with respect to the axis of rotation of the support means.

The asymmetrical arrangement may comprise an arrangement wherein the supports or pulleys are radially asymmetrically disposed with respect to the axis of rotation of the support means.

Although the resultant positions are neither equiangular nor equidistant, the relevant vectors act about the bearing and still sum to provide stability of support to the platter and a balanced rotation of drive results.

The force applied to the platter via the belt should be applied so as not to exert a moment about the bearing and should thus be directed in line with the bearing point. For stability this point should itself be inline with or below the centre of gravity of the platter.

An embodiment of the present invention will now be described by way of example and with reference to the accompanying drawing, the single figure of which schematically shows an arrangement of pulleys and drive belt for a disc record player.

The drawing shows an underneath plan view of a record player which includes only those parts pertinent to the present invention. Three belt supports or pulleys 1, 2 and 3 are located beneath a disc record platter or support 4 and a drive belt 5 is situated around and engages with the pulleys 1,2 and 3. The drive belt 5 also engages a bearing or drive shaft 6 which is connected to and provides rotation to the platter or disc support 4. The pulley 1 is connected to and is driven by a motor (not shown). In operation, the motor positively rotates the pulley 1. This causes the belt 5 to rotate around the freely moveable passive pulleys 2 and 3 and to rotate the shaft 6 and thereby the platter or disc support 4.

The radial distance between the axis of rotation of the platter or support 4 and the pulley 1 is different from the radial distance from the axis of rotation of the support 4 and the pulleys 2 and 3. This difference may, for example, be plus or minus 5 mm, although this difference is not crucial.

The angle A between the pulleys 1 and 2 may, for example, be 110 to 119 degrees or 121 to 130 degrees. In this case the angle B between the pulleys 1 and 3 may correspondingly be 121 to 130 degrees or 110 to 119 degrees.

It can be seen from the above described example that the pulleys are both angularly and radially asymmetric or offset with respect to the axis of rotation of the platter or disc support 4.

Claims

Claims 1. A drive arrangement for a record player, comprising support

means for supporting a disc record, an arrangement of belt supports or pulleys, belt means for rotating the belt supports or pulleys and drive means for rotating at least one of the belt supports or pulleys, wherein the belt supports or pulleys are asymmetrically arranged with respect to the centre of rotation of the support means.
2. A drive arrangement according to claim 1, comprising three belt supports or pulleys.
3. A drive arrangement according to claim 1 or claim 2, wherein the asymmetrical arrangement of the supports or pulleys comprises an arrangement in which the supports or pulleys are angularly asymmetrically disposed with respect to the axis of rotation of the support means.
4. A drive arrangement according to any one of the preceding claims, wherein the asymmetrical arrangement comprises an arrangement in which the supports or pulleys are radially asymmetrically disposed with respect to the axis of rotation of the support means.
5. A drive arrangement for a record player, substantially as hereinbefore described with reference to the accompanying drawing.