Abrading – Precision device or process - or with condition responsive... – With indicating
Patent
1996-01-30
1998-03-24
Smith, James G.
Abrading
Precision device or process - or with condition responsive...
With indicating
451 11, B24B 4900, B24B 5100
Patent
active
057306435
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention concerns machine tools and particularly apparatus for grinding piece parts, typically cylindrical components such as spindles-and shafts, particularly for grinding such articles to a very high accuracy.
BACKGROUND OF 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 cummulative 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. Other factors are the accuracy by which the machining tool can be positioned and moved from one position to another, the accuracy by which the worktable can be positioned along the Z-axis of the machine and the degree to which extraneous influences such as vibration, distorting loading forces due to the weight of umbilical service chutes providing services to the workhead, tailstock and worktable, and the distortions and misalignments which can arise as a result of thermal imbalance of workpieces working environment and forces exerted on the sensitive parts of the machine due to the need for movable protective covers for some parts of such machines.
It is an object of the present invention to provide a machine tool and working environment therefor which seeks to overcome these problems and allow accurate machining to accuracies of the order of nonometers.
In particular it is an object of the design of the machine to permit the very precise positioning of the various movable parts of the machine before and during machining.
The invention is of particular relevance to a cylindrical grinding machine.
PRIOR ART
Japanese patent publication No. JP-A-02160457 discloses a machine tool in which a reference surface parallel to one axis and a sensor cooperating therewith are used to generate error signals fed to a servo-motor in order to correct errors of movement along an orthogonal axis.
SUMMARY OF THE INVENTION
According to one aspect of the invention, there is provided a machine tool in which a reference straight-edge is mounted on the worktable of the machine tool and the position of the worktable and therefore the workpiece along the x-axis of the machine is determined by sensing the straight edge; a linear scale is mounted to move with the tool and a reading head associated therewith provides a measure of the position of the tool along the x-axis of the machine, and a linear scale is mounted to move with the worktable and a reading head associated therewith provides a measure of the position of the worktable and therefore the workpiece along the z-axis of the machine; wherein the linear scale mounted to the tool and the reference straight edge mounted to the worktable, and also the reading head and sensing means respectively associated therewith are all mounted in the same plane, and the machine is mounted so that the said plane is horizontal.
Preferably the linear tool scale is aligned with the tool axis which intersects the point of-application of the tool to the workpiece.
Preferably the reference straight edge sensor is also located on the same axis so as to be on the same straight line as the linear tool scale and the point of application of the tool to the workpiece.
Preferably the reading head for the linear scale mounted to the worktable is also located in the same vertical plane containing the said tool axis.
Where the tool is a grinding wheel the wheel axis of rotation is preferably at the same height as the reference str
REFERENCES:
patent: 3578043 (1971-05-01), Menge
patent: 3634975 (1972-01-01), Hensley
patent: 4747689 (1988-05-01), Aldred
patent: 5534692 (1996-07-01), Nakayama
Bartlett Christopher David
Lavcock Michael
Leadbeater Peter Brian
Banks Derris H.
Pollack Morris I.
Smith James G.
Western Atlas UK, Limited
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