Table drive for multi-axis machine tool

Details Table drive for multi-axis machine tool Table drive for multi-axis machine tool

1996-01-29

2000-06-27

Morgan, Eilleen P.

Abrading

Precision device or process - or with condition responsive...

With indicating

451213, 451218, 74826, 74 27, 408129, 409162, 409159, 409167, B24B 700

Patent

active

060800399

DESCRIPTION:

BRIEF SUMMARY
FIELD OF INVENTION

This invention concerns machine tools particularly apparatus for grinding piece parts and other components to a very high accuracy, particularly but not exclusively components which have complex shapes and forms.


BACKGROUND TO THE INVENTION

Due to forces exerted on a workpiece, the worktable and workpiece supporting structures of such machines, distortions and misalignments occur. These result in inaccuracies in the dimensions and shape of the final machined article.
Where the dimensional errors are of the same order as the accuracy to which the article is to be machined it is impossible reliably to machine the article.
Distortions, misalignments and other error producing effects which can arise and tend to be cumulative must therefore be reduced to a level which is such that the magnitude of the cumulative error in the final article is much less than the error which can be permitted therein.
One of the primary controlling parameters in a machining operation is the accuracy with which the workpiece position relative to a machining tool is known. This parameter has been addressed and solutions proposed in our co-pending applications filed concurrently herewith. Other factors affecting accuracy are addressed in other copending applications.
It is an object of the present invention to provide an improved Z-axis drive for accurately moving a worktable and workpiece thereon, relative to a worktool in a machine tool.
The invention is of particular relevant to a cylindrical grinding machine.


PRIOR ART

A friction worktable drive for a machine tool is known from U.S. Pat. No. 4,934,278, wherein wheels engage one side of a rectangular sectioned guide bar.


SUMMARY OF THE INVENTION

According to one aspect of the invention a machine tool comprises a machine tool comprising a machine bed incorporating a linear slideway along which a worktable is slidable under a friction drive comprising a pair of wheels engaging opposite sides of a guide member mounted parallel to the slideway, whereby the worktable can be driven along the slideway in either direction in accordance with the sense of operation of the friction drive, characterised in that the guide member comprises a tensioned rod of circular cross-section and in that the wheels of the friction drive, at least one of which is a driven wheel, comprise wheels in the form of pulleys the flanged peripheries of which are urged against opposite sides of the tensioned rod.
According to another aspect of the invention a machine tool comprises a machine tool comprising: by said machine frame and a second portion of which is carried by said carriage, for moving said carriage along a predetermined path with respect to said machine frame, wherein said second portion of said friction drive assembly comprises a tensioned rod extending along said predetermined path and fixedly secured to said machine frame, and said first portion of said friction drive assembly comprises a pair of spaced wheels which grip therebetween said friction rod, at least one of said wheels being driven to effect movement of said carriage along said friction rod.
Preferably both wheels are in the form of pulleys and the elongate member is a rod of generally circular cross-section having a diameter which is sufficiently large to prevent the flanges of one pulley on one side of the rod from touching the flanges of the other pulley on the other side of the rod.
Both wheels may be driven by the drive means.
The wheel means may be resiliently biased into contact with the track.
The invention is of particular application to a machine tool in which the tool comprises a grinding wheel mounted on a wheelhead itself slidable towards and away from the worktable to permit engagement of the grinding wheel with a workpiece carried by the worktable.
Conveniently the position of the worktable along its slideway is determined by an optical reading head cooperating with a scale in which one is stationary and the other is mounted on the worktable.
The scale may be carried by the worktable in which even

REFERENCES:
patent: 3043056 (1962-07-01), Decker et al.
patent: 3299577 (1967-01-01), Pernack et al.
patent: 3616576 (1971-11-01), Piat
patent: 4086730 (1978-05-01), Kobayashi et al.
patent: 5649853 (1997-07-01), Kuo

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