GB2244538A

GB2244538A - Reducing gear train backlash

Info

Publication number: GB2244538A
Application number: GB9011646A
Authority: GB
Inventors: David Braithwaite
Original assignee: MAUL TECHNOLOGY CO; VHC Ltd
Current assignee: MAUL TECHNOLOGY CO; VHC Ltd
Priority date: 1990-05-24
Filing date: 1990-05-24
Publication date: 1991-12-04
Also published as: GB9011646D0

Abstract

Apparatus for substantially eliminating backlash in a train of three bevel gear wheels 21, 22, 23 mounted for rotation in a housing 11 and having substantially parallel axes of rotation comprises biasing means 34 to urge the intermediate gear wheel into engagement with the outermost gear wheels of the train. As shown the biasing means comprises a stack of disc springs. <IMAGE>

Description

APPARATUS AND METHOD FOR REDUCING GEAR TRAIN BACKLASH This invention relates to a method and apparatus for reducing or substantially eliminating backlash in a gear train, and especially to a backlash eliminator for the drive gear train of a bottle transfer mechanism in a glass bottle moulding machine.

Glass bottles are usually blow moulded in a two stage process. Firstly a gob of molten glass is fed into the open top of a blank mould where a parison, or partially formed bottle, is blown or pressed into shape. On one type of machine the parison is normally formed with the bottle neck at bottom of the mould. Secondly the parison is transferred by the neck to a blow mould where the moulding process is completed. The parison transport mechanism usually comprises an arm which swings through approximately 1800 from the blank mould to the blow mould; accordingly the bottle is normally blown with the neck at the top.

Once the blow mould opens, the bottle is transported by the neck to a dead plate and conveyor mechanism. The bottle transport mechanism also usually comprises an arm which swings through approximately 1800, but in contrast to the parish transport mechanism the bottle hangs by the neck throughout The bottle transport mechanism usually includes a tong arm operable to grip and release the bottle neck and an internal gear train, or chain and sprocket arrangement, which ensures that the bottle is held vertical throughout the transfer.

The bottle is still quite soft when transferred and it is therefore essential that the transfer mechanism operates smoothly. However after long periods of use the bottle transfer mechanism can develop significant backlash in the gear or chain and sprocket arrangement; this results in damage to the neck and finish of the bottle which may result in rejection at the subsequent inspection stage.

Elimination of backlash is a particular problem in bottle transport mechanisms since as the weight of bottle, tong arm and supporting head is transferred from one side of the transport mechanism to the other, the load on the drive gear teeth reverses; any backlash in the system will result in a shock being transmitted to the bottle as it passes through the mid-point position. Such shocks may damage the bottle neck and finish. Further shocks may be transmitted as the actuating mechanism, usually a piston and cflirsd-r, reaches the end of its stroke.

These frequent shocks increase wear of the gear teeth which leads to further backlash.

A secondary shock occurs each time the bottle transport mechanism reverses and a further shock may occur as the transport mechanism itself passes through tie over centre position in the returnt journey to the blow mould.

The present invention provides a backlash eliminator for the bottle transport mechanism.

According to the invention there is provided a method of substantially eliminating backlash in a train of three bevel gear wheels having parallel axes of rotation, the method comprising biasing the intermediate gear wheel into engagement with the outermost gear wheels of the train. The method-may further include the step of biasing one only of the outermost gear wheels into engagement with the intermediate gear wheel, the biasing force of the outermost gear wheel being less than the biasing force of the intermediate gear wheel.

In a further aspect, the invention provides a train of three gear wheels having substantially parallel axes of rotation, the gear wheels being bevel gear wheels and the intermediate gear wheel being biased into engagement with the outermost gear wheels.

Preferably the gear wheels are rotatable in a substantially common plane.

In one embodiment the invention further comprises means for biasing one only of the outermost gear wheels of the train into engagement with the intermediate gear wheel, the biasing load on said outermost gear wheel being less than the biasing force on said intermediate gear wheel.

Preferably the biasing force is provided by one or more disc springs.

In a preferred embodiment the intermediate gear wheel is journalled on a shouldered bearing, the shoulder of said bearing being adapted to receive the biasing load from said disc springs. The disc springs may be mounted on a tubular member having an outwardly extending circumferential flange at one end, the flange abutting the shoulder of said bearing.

Other features of the invention will be apparent from the following description of a preferred embodiment shown by way of example only in the accompanying drawings in which: Fig 1 is a schematic illustration of a typical bottle transport mechanism; and Fig 2 is an axial section through a drive gear train for the mechanism of Fig 1.

With reference to Fig 1 there is illustrated a housing 11 connected for rotation with a pinion 12; the wheel 12 is driven for rotation through 1800 by a rack 13 coupled to the piston 14 of a double acting hydraulic cylinder 15.

Movement of the piston is effected by fluid supplied under pressure from a conventional hydraulic control valve 16.

Arcuate movement of the pinion 12 results in movement of the housing 11 to and from a position shown in dotted outline above a bottle mould 17.

With additional references to Fig 2, the housing cor.air,s a train of tnree gear wheels 2;, 22, 2 in and rotatable with respect to the housing 11. The drive gear wheel 21 is connected to a shaft 24 which passes out of the housing and is in use anchored to a fixed part of the moulding machine. The driven gear wheel 23 is connected for rotation with a shaft 25 by a plurality of roll pins 28 (one shown). The shaft protrudes from the housing 11 and carries at its free end a tong arm head 26. Tong arms 27 attached to the head are operable by a fluid actuator (not shown) to grip and release the neck of a bottle 29.

The gear train 21, 22, 23 ensures that the orientation of the tong arm head 26 does not change as the housing 11 moves arcuately through 1800.

Each of the gear wheels 21, 22, 23 is bevelled at approximately 150 to the horizontal axis as shown.

The idler wheel 22 is journalled on a shouldered thrust bearing 31 which is itself journalled on a fixed shaft 32; the thrust ring is of any suitable plastics material, such as PTFE. A thrust ring 33, also journalled on the shaft 32, abuts the shoulder of bearing 31 and transmits the load of a stack of disc springs 34; the reaction of the disc springs is taken by the housing 11.

Idler wheel 22 is consequently urged into engagement with the input and output gear wheels and backlash is thus eliminated. Thrust from the disc springs is taken equally through conventional thrust bearings for the gear wheels 21 and 23. Sufficient clearance is allowed in the housing to perm t the idler wheel to move further into engagement as the gear teeth wear.

The spring force exerted by the disc spring stack may be readily adjusted to suit the load carried by the bottle transfer mechanism; springs may for example be added or substituted, or the load may be adjusted by means of a rotatable reaction member screw-threaded in the housing 11.

In some circumstances thrust from the disc springs may not be equally shared between the gear wheels 21 and 23; for example a thrust bearing for one of these gear wheels may wear prematurely. In such circumstances a small amount of backlash may develop in the gear train.

A modification to the arrangement of Fig 2 includes a thrust spring for one of the gear wheels 21 and 23 and acting to urge the respective wheel into engagement with the idler wheel 22. The load of this second thrust spring must be less than the idler wheel thrust spring 34 to ensure that the resultant thrust load is taken by the unbiased gear wheel.

For example the second thrust spring may be located between gear wheel 21 and the left side of the gear housing 11 as viewed, the resultant thrust being taken by gear wheei 23.

In use the tong arms grip the neck of the bottle as it is released fro the mould 17. Clearly at the start of the transfer movement the bottle imposes an anti-clockwise load on the mechanism whereas at the end of the transfer stage the ioaa is ciockwise, the direction G loadin changin abruptly as the housing 11 passes through the mid-position The mechanism illustrated in the accompanying drawings is for illustration only, many parts being omitted in the interests of clarity.

Claims

CLAIMS:

1. Apparatus for substantially eliminating backlash in a train of three gear wheels mounted for rotation in a housing and having substantially parallel axes of rotation wherein the gear wheels are bevel gear wheels and the apparatus includes biasing means to urge the intermediate gear wheel into engagement with the outermost gear wheels of the train.

2. Apparatus according to Claim 1 and further including biasing means to urge one of said outermost gear wheels into engagement with the intermediate gear wheel, the biasing force of said outermost gear wheel being less than the biasing force of said intermediate gear wheel.

3. Apparatus according to Claim 1 or Claim 2 wherein said gear wheels are rotatable in a substantially common plane.

4. Apparatus according to any preceding Claim wherein biasing means for said intermediate gear wheel comprises a stacli cf three or more disc springs arranged between said intermediate wheel and housing about the axis of rotation of said intermediate wheel.

5. Apparatus according to Claim 4 wherein said intermediate wheel is journalled for rotation on a snouldered bearing, said biasing means acting on the should c- sa

6. Apparatus according to any of Claims 1-5 wherein the bevel angle of said gear wheels is in the range 10-300 to the axis of rotation.

7. A method of substantially eliminating backlash in a train of three bevel gear wheels having parallel axes of rotation, the method comprising biasing the intermediate gear wheel into engagement with the outermost gear wheels of the train.

8. A method according to Claim 7 and further including the step of biasing one only of the outermost gear wheels into engagement with the intermediate gear wheel, the biasing force of the outermost gear wheel being less than the biasing force of the intermediate gear wheel.