The present invention relates to a coordinate measuring machine for determining 2D or 3D coordinates of a test object. More particularly, the invention relates to coordinate measuring machines designed for providing extremely high 2D or 3D measurement accuracies.
Coordinate measuring machines of this type might be used for determining the object form of a test object with high accuracy. For example, they might be used for checking the object form of machine-produced workpieces for quality control. Typically, a touch probe having a movably mounted stylus is used as a measuring probe, and this touch probe is moved, by means of a suitable traversing mechanism of the coordinate measuring machine, up to the test object until the touch probe stylus touches a desired measurement point on the test object. The spatial coordinate of the sensed measurement point can then be determined from the position of the touch probe and the displacement of the stylus relative to the touch probe. The invention is not, however, restricted to coordinate measuring machines with tactile touch probes, and can also be used in coordinate measuring machines with different measuring probes, such as optical probes.
Various concepts are known for the traversing mechanisms. In the case of machines for three-dimensional measurement (3D coordinate measuring machines), typical concepts are the portal design, horizontal-arm coordinate measuring machines and coordinate measuring machines having a column design. Coordinate measuring machines of portal design comprise a portal moveable in the X-direction and having a cross beam on which a carriage moveable in the Y-direction is arranged. The Y-carriage carries a quill, which is moveable in the Z-direction. Such a coordinate measuring machine is known for example from DE 101 24 493 A1.
Horizontal-arm coordinate measuring machines have a pillar that is moveable in the X-direction, on which a carriage moveable in the Z-direction is arranged. The Z-carriage carries an arm that is adjustable in the Y-direction, the free end of the arm carries the touch probe.
Coordinate measuring machines of column design have a column, which carries the quill that is moveable in the Z-direction. The column itself can be moved in the X- and/or Y-direction. Alternatively, the X- and Y-guide axes can also be provided by a correspondingly moveable table for mounting the test object.
The known concepts each have design-related advantages and disadvantages, in particular with respect to the accessibility of the measurement volume and susceptibility to static and dynamic deformations and the resultant measurement errors. As will easily be understood, there is for example deformation of the cantilever horizontal arm in a horizontal-arm coordinate measuring machine in relation to the Y-position of the touch probe, under the effect of gravity.
Another kind of a coordinate measuring machine traversing mechanism is disclosed by the thesis “High-Precision 3D-Coordinate Measuring Machine” by Marc Vermeulen, which is deposited at the Eindhoven Technical University and is available under ISBN number 90-386-2631-2. The thesis can also be found on the Internet at the address http://alexandria.tue.nl/extra2/9902695.pdf.
In the aforementioned thesis, a coordinate measuring machine having a novel traversing mechanism is proposed, which makes it possible to eliminate at least some sources of errors due to static and dynamic deformations, so that the measurement accuracy can be increased. Basically the proposed coordinate measuring machine has two bearing supports arranged in a V-shape relative to each other and acting as linear guideways for the X- and Y-direction. Each bearing support carries a carriage that can be displaced longitudinally, and a beam that can be displaced perpendicularly to the bearing support is arranged on each carriage. The two beams are once again arranged in a V-shape relative to one another, with the first beam extending substantially parallel to the second bearing support and vice versa. The free ends of the beams, facing one another, are connected to a platform, which is thus moveable in the X- and Y-direction and carries a quill that is moveable in the Z-direction. Practical tests with the proposed coordinate measuring machine have shown that a traversing mechanism of this type allows to achieve far higher measurement accuracy than with the designs known hitherto.
Although the modified design of the traversing mechanism already eliminates some sources of errors, or reduces their effects, it is still desirable to achieve even greater measurement accuracy.