Bearings – Linear bearing – With detection – nonbearing magnetic or hydraulic feature
Patent
1994-07-14
1996-06-04
Footland, Lenard A.
Bearings
Linear bearing
With detection, nonbearing magnetic or hydraulic feature
384 12, 384 37, 384 38, 384 40, F16C 3206
Patent
active
055226647
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a slide assembly, especially an assembly which provides precision guidance of a sliding member.
Highly accurate and low-friction guidance of sliding elongate members is necessary in many different types of machines or instruments, of which a three-dimensional co-ordinate measuring machine can be considered to be a representative example. Co-ordinate measuring requires movement of a measuring element relative to a stationary article, for example a sensor probe which contacts the article, and recording the movement of the element in relation to a reference point so as to build up a two-dimensional or three-dimensional measurement profile of the article. In a typical construction of such a measuring machine, a probe is carried by a square-, oblong- or circular-section spindle which is mounted in a carriage on a bridge movable relative to a support table for the article. Movement of the probe in the Z axis direction is by way of axial displacement of the spindle in a bearing mount on the carriage, movement in the Y axis direction is by way of displacement of the carriage on the bridge and movement in the X axis direction is by way of displacement of the bridge over the table. The accuracy of the measurements obtained from signals generated through co-operation of the probe with the article is critically dependent on the accuracy of the spindle displacement, in particular its travel along a precisely fixed axis. Any deviations from this axis will ultimately be reflected in the measurement result.
In order to ensure precise and low-friction guidance of the spindle in such a measuring machine, it is common practice to construct the bearing mount for the spindle as an air bearing sleeve encasing a portion of the spindle. The peripheral surface of the spindle and the guide passage of the sleeve must be finished to a superaccurate standard of parallelism and uniformity of section, which imposes substantial costs on manufacturing of the assembly. Problems that can result from machining of the spindle surface and sleeve passage are local fluctuations in diameter or width and also gradual change resulting in a taper. If there are any such departures of the spindle and bore diameters or widths from their nominal values the spindle displacement in the sleeve may deviate from a fixed axis.
SUMMARY OF THE INVENTION
It is therefore the principal object of the invention to provide a slide assembly in which highly accurate guidance of an axially displaceable member may be achieved by more economically producible measures. A further object of the invention is to provide an assembly which includes an adjustment facility allowing precise setting of the guidance of the member.
Other objects and advantages of the invention will be apparent from the following description.
According to the present invention there is provided a slide assembly comprising an axially displaceable member, and guidance means for guiding displacement of the member and comprising at least one set of air bearings which are co-operable with the peripheral surface of the member and mutually aligned in a common transverse plane of the member, wherein the bearings of the or each set are substantially equidistantly spaced around the periphery of the member and are each held by resilient mounting means.
Due to the substantially equidistantly spacing of the air bearing of the or each set around the periphery of the member and the disposition of the bearings to be symmetrical about a transverse plane of the member, each being arranged so that the bearing force it exerts, by way of a compressed air film, on the surface of the member is opposed by the force exerted by another bearing of that set or the resultant force of two or more bearings of that set. Any changes in the diameter or width of the member due to production tolerances can be absorbed by equal deflection of the resilient mounting means for all bearings of the set without deviation of the displacement of the member from a fixed axis. It is p
REFERENCES:
patent: 5391002 (1995-02-01), Eigenbrod
patent: 5431527 (1995-07-01), Yamazaki
Eastman Machine Company Limited
Footland Lenard A.
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