GB2291193A

GB2291193A - Co-ordinate measuring machine

Info

Publication number: GB2291193A
Application number: GB9413688A
Authority: GB
Inventors: Ray Hudson
Original assignee: Eastman Machine Co Ltd; Eastman Machine Co
Current assignee: Eastman Machine Co Ltd; Eastman Machine Co
Priority date: 1994-07-07
Filing date: 1994-07-07
Publication date: 1996-01-17
Anticipated expiration: 2014-07-07
Also published as: GB2291193B; GB9413688D0

Abstract

A co-ordinate measuring machine (10) comprises a support table (11) for articles (17) to be measured and a co-ordinate measuring system (13 to 15) with components movable in X-axis, Y-axis and Z-axis directions to obtain co-ordinate measurements from an article profile. The table is provided in its centre with a bore (19) and with a separately constructed article support member (18) arranged to support articles in or over the opening, depending on the configuration of the member. The member can be a rotary turntable to enable rotation of an article in conjunction with axial travel of the components of the measuring system. The turntable may include on its underside equidistantly spaced air bearings. The support member may be a disc arranged in or above the bore (19). <IMAGE>

Description

CO-ORDINATE MEASURING MACHINE The present invention relates to a co-ordinate measuring machine and has particular reference to support, within the machine, of articles to be measured.

Co-ordinate machines essentially consist of an article support table of a material having a very low co-efficient of expansion, for example granite, a bridge extending over the table and movable in one horizontal direction, generally that of the X axis, a carriage mounted on the bridge and movable in an orthogonal horizontal direction, thus that of the Y axis, and a spindle mounted on the carriage and movable in a vertical direction, i.e. the Z axis. The spindle carries a probe at its lower end. By movement of the bridge, carriage and spindle the probe can be brought into contact with or predetermined proximity to different points on an article placed on the table, whereupon signals are issued from which, by correlation with a movement reference point or origin, co-ordinate measurements can be obtained to construct a two-dimensional or three-dimensional profile of the article.The article is stationary throughout the measurement process, which may entail a considerable amount of controlled movement of the bridge, carriage and spindle so that the probe can approach the article from any direction.

Relatively complicated manoeuvring of the probe, which prolongs the measuring process, may be needed and the task is even more difficult if the article possesses an awkward size and shape. Problems in the latter respect can even result in insufficient working clearance between the top of the article and the tip of the probe in its uppermost setting.

The invention has, as its principal object, enhancement of the utility of a co-ordinate measuring machine with regard to article support within the machine. Subsidiary objects of the invention are the formulation of specific constructions which inter alia may reduce the movement effort of travelling components of the machine and more readily accommodate articles with shapes or dimensions otherwise causing loss of clearance.

Other objects and advantages of the invention will be apparent from the following description.

According to the present invention there is provided a coordinate measuring machine comprising a support table for articles to be measured and co-ordinate measuring means for obtaining coordinate measurements from the articles, the table being provided in a central region thereof with an opening and with an article support member constructed separately from the table and arranged to support articles in or over the opening.

The inclusion of an opening through the table, which is preferably a hard natural material having a low co-efficient of expansion, and provision of an article support member as a component constructed separately from the table constitutes a departure from conventional thinking that such a table must be an entirely integral structure with an uninterrupted top surface. A prior art table of such a construction can play no part in adaptibility of the machine and constitutes, in effect, an unchanging component to which all other machine components must relate and be adapted as necessary.

In the machine of the present invention, however, the opening and/or the separate support member can be structured according to specific requirements, with the result that reduced demands may be imposed on other, more complex components of the machine, particularly components with electrical, electronic and/or pneumatic drives and controls.

For preference, the support member is provided in a top surface thereof with fixing points for attachment of at least one fixture. As a separately produced component the support member can readily be constructed with threaded bores, smooth bores, slots, grooves and other forms of fixing points which may allow clamps, chucks, stops and similar fixtures to be secured to the support member.

If it is envisaged that the machine will be used for measuring articles likely to create clearance problems the support member can be arranged to be removable, so that protruding portions of articles can be accommodated in the passage opening.

The support member itself can be a selectable one of a number of interchangeable members of different shape or construction.

These members thus form a system which can be supplied with the machine to allow customer adaptation to requirements.

The support member can define an article support surface above or below the plane of the top surface or substantially co-planar with that top surface. According to the type of support member, the member can be mounted above, within or below the opening.

Provision can also be made for adjustment of the support member in position to vary the height of its support surface relative to the plane of the table top surface. This adjustment in position preferably takes the form of a capability to reduce the height of the support surface down from the plane of the table top surface.

In a particularly advantageous embodiment of the machine, in which the article itself can be moved as well as components of the measuring means, the support member is mounted to be rotatable. For this purpose the support member can be provided at its underside with air bearings co-operating with the table top surface, and preferably also with an axle journalled in a carrier attached, preferably detachably attached, to the table. The axle can be journal led by way of air bearings co-operating with the circumferential surface of the axle and can serve as a rotary drive input point for the support member. The machine may include means to allow the support member to be located in predetermined rotational settings, such as by way of an indexing system with defined arrest points, or in selectable rotational settings, such as by way of freely selected stopping of a drive.The rotational position of the support member can be detectable by way of a detector, for example a disc with markings and a reader for reading the markings, and rotational position data from the detector can be correlated with co-ordinate measurement data from the measuring means by way of data processing means so that measurements can be linked with the article rotational position.

Embodiments of the present invention will now be more particularly described with reference to the accompanying drawings, in which: Fig. 1 is a schematic side elevation of a co-ordinate measuring machine embodying the invention; Fig. 2 is a sectional view, to an enlarged scale, of the detail II of Fig. 1, showing an article support arrangement in a support table of the machine; Fig. 3A is a simplified sectional view, similar to Fig. 2 but of reduced scale, showing another form of article support arrangement; and Fig. 3B is a view corresponding to Fig. 3, but showing a variant of the article support arrangement.

Referring now to the drawings there is shown in Fig. 1, in diagrammatic form, a three-dimension co-ordinate measuring machine 10 comprising a support table 11 mounted on a base 12 and measuring means in the form of a bridge 13 guided on the table to be horizontally movable in the X-axis direction, a carriage 14 guided on the bridge to be horizontal movable in the Y-axis direction, and a spindle 15 guided in the carriage 14 to be vertically movable in the Z-axis direction. Guidance of the bridge and spindle can be by way of, for example, air bearings, and electric and/or pneumatic drives are provided for driving the bridge, carriage and spindle.

The table consists of a hard, rigid material with a low coefficient expansion, preferably a dressed granite slab. Other materials are possible, including ceramic material or cast iron.

The spindle 15 carries a probe 16 which is brought, by movement of the bridge, carriage and spindle, into contact with different points of an article 17 to be measured. When each contact of the probe with the article takes place a signal is generated and, by evaluation of the movement of the bridge, carriage and spind-le with respect to a reference point up to the time when the signal is issued, a co-ordinate measurement is obtained and stored. A threedimensional profile of the article is then derived from the stored measurement data. These aspects of construction and operation of co-ordinate measuring machines are generally known and accordingly are not described in greater detail. Contactless measuring can equally well be carried out by way of a proximity sensing probe.

The article 17 is supported on the support table 11 by way of a rotary turntable 18 disposed over a through bore 19 in the table 11. The arrangement for support of the article is shown in more detail in Fig. 2. The turntable is provided at its underside and in the region of its periphery with a plurality, in particular at least three, of equidistantly spaced air bearings 20 co-operating with the top surface, which is finished to a high degree of planarity, of the table 11. By way of compressed air feeds, which are not shown, a film of air is generated between each air bearing and the table top surface so as to provide low-friction guidance of the turntable 18 relative to the support table 11. A downforce opposing the action of the air bearings is provided by the weight of the turntable and associated components described further below.

Lateral location of the turntable 18 is provided by an axle 21 which extends downwardly from the underside of the turntable and is journalled in a carrier spider 22 by way of a further plurality, preferably four, of air bearings 23 equidistantly spaced around the axle circumference. The air bearings 23 are resiliently mounted on the spider and the effective centre of each air bearing 23 coincides with the plane of the top surface of the support table 11. The air bearings 23 are supplied with compressed air by way of suitable feeds and a film of air is generated between each bearing and the circumferential surface of the axle so as to provide low-friction journalling of the axle.

The spider 22 is detachably secured to the support table 11 by way of threaded fasteners 24 screwed into insert sleeves let into the top of the support table 11 and bonded in place.

The axle 23 projects down into the bore 19 and is provided at its lower end with a pinion which is drivably coupled by way of a cogged belt 25 with a pinion on a drive output shaft of an electric motor 26. The motor 26 is suspended by a mounting bracket from the spider 22.

Also arranged on the axle is a disc 27 with markings which can be read off by a reader 28 located on the wall of the bore to obtain an indication of the rotational position of the turntable 18. An indexing system can be included to locate the turntable in predetermined rotational settings.

The turntable 18 has fixing points, in the form of threaded bores 29 in its uppermost surface, to enable clamps, chucks or the like to be attached so that articles can be secured in defined positions.

In use of the machine, rotation of the turntable 18 is employed in conjunction with X, Y and Z axial travel of the bridge, carriage and spindle to expedite the measuring process. The positioning travel of the bridge and carriage, in particular, can be considerably reduced in the case of some articles if the article is rotated by way of the turntable. Thus, for example, a cylindrical article can be rotated for checking dimensional accuracy with the bridge stationary and with a short-stroke reciprocating movement of the carriage to produce probe contact with the article at a series of points around its circumference. These points can be determined by, for example, rotation of the turntable under the control of the indexing system.The selective use of the facility for rotation of the article may not only expedite the measuring procedure, but also, in conjunction with reduced travel strokes of the more complex assembly of bridge, carriage and spindle, potentially save wear and energy consumption.

As will be apparent from the foregoing description, provision of the bore 11 to accommodate components of the article support arrangement is fundamental to the arrangement. Different forms of support arrangements making use of the bore can be provided, as illustrated diagrammatically in Figs. 3A and 3B. In Fig. 3A a support disc 30 is arranged in the bore 19 with its top surface substantially coplanar with the top surface of the support table 11.

The disc 30 is seated on a plurality, in particular at least three, of legs 31 which in turn rest on a base member 32 attached to the underside of the table 11. A cylindrical article 33 of medium axial length is shown disposed on the disc 30. In the configuration shown in Fig. 3B, the legs 31 have been removed and the disc 30 is seated directly on the base member 32, thus is located entirely within the bore 19. A cylindrical article 34 of much greater cylindrical length is shown disposed on the disc 30. The article 34 is thus partly accommodated in the bore 19 and the extent to which the article projects above the support base 11 is correspondingly reduced, which allows greater working clearance in relation to the probe 16.

The arrangements shown in Figs. 3A and 3B are merely examples.

The support disc 30 can be seated on longer legs or supported in other suitable manner, so as to be elevated above the level of the top surface of the table 11. The length of the legs can be reducible in stages and the legs or an alternative form of mount for the support disc, such as a central sleeve or shaft, can incorporate an adjustment system to enable stepped or stepless change in the height of the disc. The support member itself can be of any suitable shape. An arrangement such as that of Figs. 3A and 3B can be provided as an alternative to that of Fig. 2, either as sole equipment of the machine or as part of a universal support system supplied with the machine for the user to select from and fit as appropriate. It is also possible for the support arrangement to be removed entirely, so that the bore 19 can accommodate a protruding part of an awkwardly shaped article which is then supported directly on the top surface of the support table 11. Irrespective of the form of support arrangement provided in association with the bore 19 it remains possible to use outlying areas of the top surface of the table for direct support of articles in conventional manner. In that case the measurement process is carried out away from the table centre.

Other variations of the support arrangement, including combination of a rotary turntable with a height adjustment system, are possible.

Claims

1. A co-ordinate measuring machine comprising a support table for articles to be measured and co-ordinate measuring means for obtaining co-ordinate measurements from the articles, the table being provided in a central region thereof with an opening and with an article support member constructed separately from the table and arranged to support articles in or over the opening.

2. A machine according to claim 1, wherein the support member is provided in a top surface thereof with fixing points for attachment of at least one fixture.

3. A machine according to claim 1 or claim 2, wherein the support member is removable to allow the opening to receive a protruding portion of an article to be measured.

4. A machine according to any one of the preceding claims, wherein the support member is a selectable one of a plurality of interchangeable support members of different shape or construction.

5. A machine according to any one of the preceding claims, wherein the support member defines an article support surface above the plane of the top surface of the table.

6. A machine according to claim 5, wherein the support member comprises a cover plate covering the opening and a portion of the top surface of the table bounding the opening.

7. A machine according to any one of claims 1 to 4, wherein the support member defines an article support surface substantially coplanar with the top surface of the table.

8. A machine according to claim 7, wherein the support member is mounted within the opening.

9. A machine according to any one of claims 1 to 4, wherein the support member defines an article support surface below the plane of the top surface of the table.

10. A machine according to claim 9, wherein the support member is mounted within or below the opening.

11. A machine according to any one of claims 1 to 4, wherein the support member defines an article support surface and is adjustable in position to vary the height of the support surface relative to the plane of the top surface of the table.

12. A machine according to claim 11, wherein the support member is adjustable in position to reduce the height of the support surface down from the plane of the top surface of the table.

13. A machine according to any one of claims 1 to 6, wherein the support member is mounted to be rotatable.

14. A machine according to claim 13, wherein the support member is provided at its underside with air bearings co-operating with the top surface of the table.

15. A machine according to claim 13 or claim 14, wherein the support member is provided at its underside with an axle journalled in a carrier attached to the table.

16. A machine according to claim 15, wherein the carrier is detachable from the table.

17. A machine according to claim 15 or claim 16, wherein the axle is journalled in the carrier by way of air bearings co-operating with the circumferential surface of the axle.

18. A machine according to any one of claims 14 to 17, wherein the support member is rotationally drivable by way of the axle.

19. A machine according to any one of claims 13 to 18, comprising drive means operable to rotationally drive the support member.

20. A machine according to any one of claims 13 to 19, comprisng means to cause the support member to be located in predetermined rotational settings.

21. A machine according to any one of claims 13 to 19, comprising means to cause the support member to be located in selectable rotational settings.

22. A machine according to any one of claims 13 to 21, comprising a detector to detect the rotational position of the support member.

23. A machine according to claim 22, wherein the detector comprises a disc connected to the support table and a reader for reading markings on the disc.

24. A machine according to claim 22 or claim 23, comprising data processing means to correlate rotational position data from the detector with co-ordinate measurement data from the measuring means.

25. A machine substantially as hereinbefore described with reference to Figs. 1 and 2 of the accompanying drawings.

26. A machine substantially as hereinbefore described with reference to Figs. 3A and 3B of the accompanying drawings.