Similar to the major part of present-day co-ordinate measur- ing machines, the first co-ordinate measuring machines de- signed and manufactured in the beginning of the 1970s were equipped with three mutually perpendicular linear guides.

These guides were provided with linear scales for measuring the displacement of a measuring probe along these guides, similar to the guides of present-day co-ordinate measuring machines.

Distinct from present-day co-ordinate measuring machines, in which the guides are moved in the direction of their respec- tive axes with the aid of servomotors almost without excep- tion, and in which a measuring probe having a spring-away measuring tip triggers reading of the values on the measuring scales, movement of the guides in said first co-ordinate machines was effected manually. The probes of these earlier machines were thus direct-sensing. For example, hole dis- tances were measured with the aid of conical probes which were centred in a hole when inserted down thereinto.

In order to achieve perfect centring of the probe, it is necessary to avoid all"jamming effects", which, in turn, requires a friction-free bearing. This has often been achieved with the aid of an air bearing, with which the move- able elements are supported by an air film between slide and axle. Although this solution provides for practically fric- tion-free movement, the air bearing is encumbered with a

number of drawbacks. One such drawback resides in poor bear- ing stiffness, i. e. the bearing gap varies quite signifi- cantly at different loads. Another drawback. resides in the amount of power required as a result of continuous air con- sumption. Moreover, the bearings become large and bulky, due to said low bearing stiffness. Construction is also compli- cated, due to the requirement for a continuous supply of air.

In the case of the earlier co-ordinate measuring machines described above, the point of attack with respect to the mechanical power flow in the system was the measuring probe itself. The position of the measuring probe in relation to the position of the hole was centred by drawing the probe manually to its desired position and moving the probe cone into contact with the sides of the hole. The force applied to the measuring probe was passed"backwards"in the system and resulted in longitudinal displacements along the various co- ordinate axes. This required the linear bearings to be fric- tion-free, since a"jamming"effect in respect of such use would have been devastating with respect to measuring accu- racy.

The power flow is the reverse in the case of present-day co- ordinate measuring machines. A spring-away measuring probe is guided to a desired position with the aid of separate servo- motors that act in the longitudinal direction of respective co-ordinate axes, either directly through the medium of a joystick (manual measuring) or through the medium of CNC- guiding. Consequently, present-day requirements regarding linear bearings in co-ordinate measuring machines differ in essential points than the requirements placed on earlier co- ordinate measuring machines. Because the power flow does not take place in a direction away from the co-ordinate axes out

towards the measuring probe, and because the measuring probe springs away in response to a specific measuring force, the requirement of a friction-free bearing is no longer a domi- nating factor. This results in new possibilities of con- structing novel types of co-ordinate measuring machines of a highly accurate class which, nevertheless, combine simple and compact construction with a low price.

Accordingly, the object of the present invention is to pro- vide a bearing arrangement in a co-ordinate measuring machine that includes at least two mutually perpendicular co-ordinate axes, wherein a fixedly mounted beam is disposed parallel with the first of said co-ordinate axes and a movable slide is disposed parallel with a second co-ordinate axis that extends perpendicular to said first co-ordinate axis, and wherein said bearing arrangement enables the movable slide and the fixed beam to be readily mounted in relation to one another on said bearing.

This object is achieved with an inventive bearing arrangement which includes a bearing plate that can be moved in the lon- gitudinal direction of the fixed beam and in that the movable slide carried by the bearing plate is mounted for movement in its longitudinal direction perpendicular to the longitudinal direction of the fixed beam.

The invention will now be described with reference to a non- limiting exemplifying embodiment thereof and with reference to the accompanying drawings, which show solely those fea- tures significant of the present invention and of which Figs.

1-5 illustrate the construction principles of known co- ordinate measuring machines ; Fig. 6 illustrates schematically a first embodiment of a co-ordinate measuring machine that

includes an inventive bearing arrangement; Fig. 7 illustrates schematically a second embodiment of a co-ordinate measuring machine that includes inventive bearing arrangements ; Fig. 8 illustrates in larger scale a beam and two slides for a co- ordinate measuring machine that includes an inventive bearing arrangement; Fig. 9 is a perspective view of a bearing plate included in an inventive bearing arrangement; and Fig. 10 is a side perspective view of the bearing plate shown in Fig. 9.

Seen generally all linear-type co-ordinate measuring machines are constructed in the way shown in Fig. 1. A beam 1 is mounted for movement in the Y-direction (the bearing is not shown in the figure). The beam 1 carries a slide 2, which is mounted for movement in the X-direction. A further slide 3 is mounted in the slide 2 for movement in the Z-direction. This further slide 3 carries a measuring probe 4 at one end.

The difference between the various illustrated types of ma- chine consists essentially in the method of fixing and mount- ing the beam 1 for movement in the Y-direction. The bearings in the co-ordinate measuring machines are normally mechanical linear bearings based on ball bearings or roller bearings, although they may, of course, equally as well be applied to co-ordinate measuring machines that have other types of bear- ings, such as the earlier mentioned conventional air bearing, hydrostatic bearings, magnetic bearings or other conceivable types of linear bearings.

Fig. 2 illustrates a"cantilever-type"co-ordinate measuring machine. In this case, the beam 1 is mounted in a bearing on one end of an axle 5 in a fixed stand. This bearing model places high demands on the ability of the linear bearing 6 to take up torque caused by extension of the beam 1. Movement of

the sleeve 2 along the beam 1 also gives rise to changes in the magnitude of the torque. However, different types of measures can be employed to detect or anticipate any rotary movement thereby enabling such movement to be eliminated in the presentation of the final result.

Fig. 3 illustrates a variant of the machine shown in Fig. 2, for eliminating undesired torque in the bearing 6 of the fixed axle 5, by providing the beam 1 with a support leg 7 mounted on a surface 8 that extends parallel with the axle 5.

Fig. 4 illustrates a so-called"gantry-type"machine. In this case, the beam 1 is mounted for movement on two parallel guides 5 and 5'that are situated on mutually the same level.

Fig. 5 illustrates a portal-type co-ordinate measuring ma- chine, which is characterised by fixed beams 9,9'placed in the plane of the measuring table, and by a cross beam 1 which carries a slide 2 and which is placed in a portal-like ar- rangement which can be displaced along the fixed beams 9,9' through the medium of its support legs 10.

A common feature of the aforedescribed geometries is that they are comprised of a large number of components and that these components must be manufactured to high degrees of precision and require accurate adjustment of their mutually relative positions.

The present invention enables the geometric construction of a co-ordinate measuring machine to be greatly simplified so as to reduce the number of machine components and therewith reduce manufacturing costs, while, nevertheless, enhancing the precision and the reliability of said machine at the same

time. Although the invention is chiefly intended for types of machines that are based on mechanical linear bearings in the form of linear ball bearings or roller bearings, it may also be applied beneficially to other types of linear bearings, such as conventional air bearings or other types of existing linear bearings.

Fig. 6 illustrates schematically part of a co-ordinate meas- uring machine in which a fixed beam 11 is connected to a stand (not shown) and extends in the Y-direction. The fixed beam 11 carries a movable slide 12 which extends perpendicu- lar to the longitudinal direction of the beam 11, in the X- direction. The whole of the X-slide 12, which actually corre- sponds to the beam 1 in Figs. 1-5, is not only displaceable in the Y-direction but also in the X-direction relative to the fixed beam 11, this being achieved through the medium of the inventive bearing arrangement. The bearing arrangement enables all bearing elements required for movement of the slide in the horizontal plane, X-Y, to be placed in a single element, namely in a bearing plate 20. The bearing plate 20 includes two sets of mutually perpendicular guide elements, linear bearing units 21,21'of a known kind, wherein one linear bearing unit 21 is mounted on the underside of the plate 20 and co-acts with rail arrangements 22 mounted on the lower fixed beam 11 in its longitudinal direction, and the other linear bearing unit 21'is mounted on the upper side of the plate 20 and co-acts with rail arrangements 22'mounted on the upper movable slide 12 in its longitudinal direction.

The collection of storing elements for the two perpendicular directions of movement into one single component facilitates assembly, adjustment and pre-checking of the angle between the X and Y guides. Moreover, the number of components is

significantly reduced, owing to the omission of the separate X-slide required in earlier known apparatus.

In the earlier co-ordinate measuring machines described above, the mechanical power transmission took place in the system. A further simplification can now be made, by placing drive means, such as drive motors, for movement in the X-and Y-directions in the bearing plate 20. This reduces the number of"movable"electric cables in the system, which affects significantly both the reliability and the price of such machines.

Another advantage is that the vertical Z-axis can be placed symmetrically in the cross-section of the X-slide 12, as opposed to earlier described geometries of the known arrange- ments in which it was necessary to position the Z-axis asym- metrically. The embodiments illustrated in Figs. 6 and 8 include a further slide 13 parallel with the Z-axis and ar- ranged at one end of the movable slide 12. A measuring probe 14 is carried on the bottom end of said further slide 13. The further slide 13 can be moved up and down in its longitudinal direction. The further slide 13 can be mounted for movement in the movable slide 12 in any appropriate manner, for in- stance by means of all bearings or roller bearings.

A further significant advantage is that the space available for the insertion and the removal of measurement objects can be greatly increased, since a wide free surface is obtained on the measuring table when the X-beam is withdrawn to its furthest rear position.

In the case of a movable slide 12 freely mounted in a bear- ing, as in the case of the Fig. 6 embodiment, it may be nec-

essary to provide the slide with a movable counterweight (not shown) in order to maintain the centre-of gravity of the slide in relation to the fixed beam 11. This enables the centre-of gravity of the slide 12 to be maintained unchanged in the X-direction, by moving the movable counterweight in an opposite direction to movement of the movable slide 12 in relation to the fixed beam 11, so that the fixed beam 11 will not be subjected to a changed bending moment.

Fig. 7 illustrates another variant in which the movable slide 12 is carried by two fixed beams 11,11'with the aid of two bearing plates 20,20'which are arranged between respective fixed beams 11,11'and the movable slide 12. The movable slide 12 is able to move in the same way as in the embodiment shown in Fig. 6, i. e. is movable in both the X-and the Y- directions. As in the Fig. 6 embodiment, a measuring probe 14 is carried by a further slide 13. However, the probe is lo- cated approximately midway of the sleeve 12 instead of at its end, and movement of the movable slide 12 in the X-direction is limited to the distance between the fixed beams 11, also Fig. 8 illustrates in more detail the mounting achieved be- tween the fixed beam 11 and the movable slide 12 with the aid of the bearing plate 20. The figure illustrates the rail arrangements 22 and 22'on the fixed beam 11 and the movable slide 12, which co-act with the linear bearing units 21,21' on the bearing plate 20. Also shown in the figure are drive belts 23 connected to a drive motor (not shown) by means of pulleys 24,25 on the bearing plate 20 and on the fixed beam 11 respectively, therewith enabling movement of the bearing plate and the movable slide 11 along the fixed beam 11 in its longitudinal direction.

Figs. 9 and 10 illustrate more clearly a possible embodiment of the bearing plate 20 with the linear bearing unit 21,21' and the pulleys 24 mounted thereon. It is clearly shown in Fig. 10 that the linear bearing units 21 are rotated through 90° in relation to the linear bearing units 21'on the other side of the bearing plate 20.