Brown & Sharpe Manufacturing Co.

William J McCabe

Vitaly I Pesikov

In a coordinate measuring machine, apparatus for compensating the sensing means for determining the position of a probe for changes in temperature, where the machine base and the support column for the probe have differing coefficients of thermal expansion. In a preferred embodiment, the apparatus of this invention is used to prevent 'zero shift' in the Z-direction for a Z-rail. The compensating apparatus is associated either with the support column or Z-rail. The apparatus offsets the greater expansion of the machine component having the greater coefficient of thermal expansion. Typically, the position sensing means for the Z-rail includes an encoder and a scale. In one embodiment, either the encoder or the scale is secured to a mount which is affixed to the column. One element of the mount which extends upwardly from the support column has a coefficient of thermal expansion which is substantially less than that of the aluminum of which the column is composed. In another embodiment of this invention, the encoder the scale is secured to a lower end of a rod depending downwardly from the support column. In this alternative embodiment, the rod is composed of a material having a coefficient of thermal expansion substantially greater than that of the component of the support column, which is especially aluminum. In a third embodiment, two supports can be used, one having a coefficient of thermal expansion substantially greater than aluminum and another having a coefficient of thermal expansion substantially less than aluminum. Similar apparatus also is used to prevent 'zero shift' in the X and Y directions.

Apparatus for temperature compensation of sensing means of a machine

A base assembly for a machine tool includes a support arrangement between a metal base and a granite worktable which eliminates distortion caused by differential thermal expansion and contraction and which isolates the base from deformation due to the weight of a workpiece. The support arrangement preferably includes three spaced-apart blocks, each with a V-groove track, attached to the bottom of the granite worktable. The axes of the V-groove tracks intersect at a common point. The metal base includes three spherical projections located for engagement in each of the V-groove tracks. The support arrangement permits the granite worktable and the base to expand, contract and distort separately, while providing vertical support and lateral and rotational restraint. Several configurations of tracks and projections are disclosed.

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North Kingstown, RI, United States of America

William J McCabe