Coordinate measuring machine

The coordinate measuring machine comprises a basic frame structure including a bearing portion having a steel track with a crossbeam support for traveling on the steel track which carries a spindle sleeve. At least one of the frame structure parts comprises a cast resin concrete with a steel track embedded in the cast part. The composition of the synthetic resin concrete at least in the zones adjacent the steel track is such that the coefficient of thermal expansion of the concrete is substantially equal to that of the steel track.

FIELD AND BACKGROUND OF THE INVENTION 
This invention relates in general to the construction of machines for 
measuring coordinates and in particular to a coordinate measuring machine 
including a frame structure having guide ways formed by steel embedded in 
a resin concrete. 
An embodiment of a measuring machine similar to the invention is disclosed 
in German OS No. 24 13 335. 
The supporting basic frame of such measuring machines is formed by a welded 
structure which is coated with metallic plates. This is expensive. 
SUMMARY OF THE INVENTION 
The invention is directed to a measuring machine having an improved 
supporting structure. 
In accordance with the invention, the coordinate measuring machine 
comprises a basic frame structure with a crossbeam which includes a 
bearing portion in the form of a steel track which is embedded in a 
concrete structure of the basic frame. The basic frame comprises a 
synthetic resin concrete which is cast with the steel track embedded 
therein and the composition of the concrete is such that the coefficient 
of thermal expansion of the concrete will be substantially equal to that 
of the steel track. 
Synthetic resin concretes are described in German OS NO. 27 43 396, for 
example. They substantially comprise a mixture of a granular stone 
material and of a synthetic resin as the binder. The employed synthetic 
resin may be an expoxy resin or an acrylic resin. By varying in the 
mixture the proportion of synthetic resin to granular stone material, 
desired properties of the concrete can be adjusted. More particularly, a 
suitable mixing ratio may result in a coefficient of thermal expansion of 
the set synthetic resin concrete, which is substantially equal to that of 
steel. The modulus of elasticity and the strength factors of the cast 
parts may also be adjusted to the specific requirements. As compared to a 
hydraulically setting concrete, a synthetic resin concrete has the further 
advantage of a small absorption of water. 
Casting parts is a simple manufacture which also ensures that such a basic 
frame structure is dimensionally accurate. If large casting molds are to 
be avoided, the basic frame structure may be assembled of a plurality of 
cast parts. They are then connected to each other with the same synthetic 
resin concrete. 
A basic frame structure of synthetic resin concrete absorbs well mechanical 
oscillations which are imposed to the basic frame structure. Such 
oscillation occur, for example, at the start and stop of the cross beam. 
The measuring operation can be performed only after the oscillations have 
damped out. Due to the favorable damping properties of the basic frame 
structure, the oscillations decay substantially faster than in a basic 
frame of welded steel. The cross beam can therefore travel at a higher 
speed than in prior art measuring machines. 
Another advantage of the inventive basic frame structure is the low thermal 
conductivity of synthetic resin concrete. For this reason, short-time 
zonal temperature variations of the frame do not take effect as 
dimensional variations. Such temperature variations may be caused in the 
room accommodating machine by incident sum beams or by draft. 
The inventive design is further advantageous in that the guide tracks of 
hardened steel can be fixed in the cast part in a simple and stable manner 
be inserting the part into the casting mold. Since the coefficient of 
thermal expansion of the synthetic resin concrete is adjusted to that of 
the guide elements, no mechanical stresses therebetween can occur under 
temperature variations. 
In a development of the invention, the advantages of synthetic resin 
concrete may further be utilized by designing the bearing portion of the 
cross beam also as a part cast of synthetic resin concrete. 
On the basic frame of prior art measuring machines, a granite plate is 
provided as the measuring table. To obtain such a table surface on the 
inventive basic frame structure, a development of the invention provides a 
layer of synthetic resin concrete with a particle size which is finer than 
that of the respective cast parts. In another embodiment, granite plates 
are embedded in a layer of synthetic resin concrete, to form the measuring 
table surface. 
Further advantageous developments of the invention may be learned from the 
following description of different embodiments. 
Accordingly it is an object of the invention to provide a coordinate 
measuring machine which comprises a basic frame structure which has a 
steel track bearing portion with cross beam means supported on the bearing 
portion for movement therealong and which carries a spindle sleeve and 
wherein at least one of the basic frame structure parts is made of a 
synthetic resin concrete having a steel track embedded in the concrete and 
with the concrete being such that the coefficient of thermal expansion is 
substantially equal to that of the steel. 
A further object of the invention is to provide a coordinate measuring 
machine which is simple in design, rugged in construction and economical 
to manufacture.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the drawings in particular the invention embodied therein 
comprises a coordinate measuring machine which comprises a basic frame 
structure 1 having a steel track bearing portion 5. Crossbeam means which 
in the embodiment of FIG. 1 comprises upright columns 2 and 3 and a head 
beam 4 with a crossbeam 7 movable along a guideway or steel track 6 and 
having an arm 8, bearing on a guideway including steel track 5 is mounted 
on the basic frame to provide movement for the crossbeam supported on the 
trackeways 5 and 6. At least one of the basic frame parts comprises a cast 
synthetic resin concrete having this bearing portion 5 or 6 which is 
embedded in the cast part. The composition of synthetic resin concrete at 
least in the zones adjacent the steel tracks 5 or 6 is such that the 
coefficient of thermal expansion of the concrete is substantially equal to 
that of the steel track. 
The basic frame 1 and the columns 2 and 3, and headbeam 4 are cast of 
synthetic resin concrete. To reduce the weights cavities are provided in 
the cast parts, which may be filled with hard foam material. The mixture 
of synthetic resin concrete is made to have a coefficient of thermal 
expansion substantially equal to that of hardened steel. 
In the basic frame 1 and in the headbeam 4, guideways 5 and 6 of hardened 
steel are embedded as tracks. On guideway 6, crossbeam 7 is supported 
which bears through arm 8 against guideway 5. Crossbeam 7 is mounted for 
traveling on guideways 5 and 6 in the X direction. A carriage 9 is 
provided on a bearing portion of crossbeam 7, supporting a spindle sleeve 
carrier 9' which is mounted for traveling in the Y direction. A spindle 
sleeve 10 is adjustable in the Z direction in its carrier 9'. Arm 8 and 
the bearing portion of crossbeam 7 may also be designed as parts cast of 
synthetic resin concrete. 
Basic frame 1 at the same time forms a measuring table. The surface of the 
measuring table is formed by a layer 11 of synthetic resin which is 
deposited on the cast basic frame 1. The particle size of the granular 
stone material of concrete layer 11 is smaller than that of underlying 
basic frame 1, to be able to obtain a very smooth surface. If it is 
desired to give the measuring surface a granitic aspect, corresponding 
coloring matter is added to the synthetic resin concrete. 
The measuring table surface may also be formed by granite plates placed on 
cast basic frame 1 and connected thereto by a layer of synthetic resin 
concrete of such composition that the layer elastically compensates for 
the differences in thermal expansion between the basic frame and the 
granite plates. 
In the measuring machine shown in FIGS. 3 and 4, a basic frame 1' supports 
on a side thereof a single upright member 2'. On the top of member 2', 
guideways 12 and 13 for crossbeam 7' are embedded. Basic frame 1' is 
designed in the same way as in the embodiment of FIGS. 1, 2. 
In the measuring machine shown in FIGS. 5 and 6, a basic frame 1" comprises 
two parts 14 and 15 cast of synthetic resin concrete. In cast parts 14, 
for example, a straight and supporting guideway of hardened steel for the 
crossbeam is embedded, while the surface of part 15 is designed as a guide 
plane for an air cushion support. A crossbeam 7" is supported by a 
guideway 16 of a cast part 14 and bears through arm 8' against a guideway 
17 of a part 15. As to the design of cast parts 14 and 15, substantially 
the same applies as to the embodiment of FIGS. 1 and 2, only an air 
cushion support is provided as the backing, because of the considerable 
weight. In the embodiment of FIGS. 5,6 again, a supporting portion of 
crossbeam 7" and arm 8' may be formed by a part cast of synthetic resin 
concrete. 
While specific embodiments of the invention have been shown and described 
in detail to illustrate the application of the principles of the 
invention, it will be understood that the invention may be embodied 
otherwise without departing from such principles.