DE19830646A1 - Correcting geometrical collection of errors in axis of coordinate measuring machine by applying correction factor derived from part of volume to measurement result - Google Patents

Abstract

Method stores correction value derived for at least part of the volume being measured in control unit, and this value is applied, depending on the result of measurement during measurement of a workpiece.

Description

The invention relates to a method for correcting Geometric sequence errors of at least one axis of one Coordinate measuring machine.

According to the prior art, a computational Correction of residual errors in the straight lines of axes from Coordinate measuring machines performed. Here are with tels test specimens or laser devices the six spatial Chen degrees of freedom of an axis of the coordinate measuring machine measured and the deviations from the ideal straight guidance Right.

The recording of the deviations is necessary because a Linear guide three translatory and three rotary Has errors. The three translational ones Errors are generally referred to as "straightness" and "position". The three rotational errors Possibilities are roll, yaw and pitch errors.

These measured deviations are then actually used Chen measuring operation for correcting the probing coordinates of a Measuring point.

To record these deviations, an axis of the Coordinate measuring device over its entire length in the same divided moderate sections. The measuring devices, esp special interference optics for lasers, then step wisely driven to the location of the support points and there ever occurring deviations measured and together with the base coordinates are saved.  

The distance between these nodes is mainly determined by the parameters

• - accuracy,
• - length of the axis to be corrected,
• - Short or long ripple of the expected Error,
• - Storage space in the machine control for storage the correction data,
• - Measuring time to record the errors certainly.

For machines with axis lengths of several meters especially the last parameter of importance, since here the measuring device if the corresponding support density is used and the environmental conditions, if necessary, over several Have to be stable for hours. When using a La sers, whose measuring accuracy depends on the stability of the Bre index of the air is a measurement time of this Order of magnitude no longer realistic, so that a reasonable ger compromise between spatial resolution and measuring accuracy must be found. This is usually 50 to 100 support points per measuring line.

Furthermore play with measuring lengths greater than one meter un avoidable air turbulence plays a role in the laser signal add noise and affect the measurement accuracy pregnant. Because the tolerances to be measured for workpieces usually proportional to their external dimensions men, this method works even with large measurement seem as long as the workpieces to be measured are large enough are.  

For measuring smaller workpieces on a Koordi natenmeßmaschine with a large measuring volume kick everyone However, the disadvantages of the longer measurement time and the measurement accuracy with longer measuring paths. For smaller workpieces to measure with the required accuracy is in In principle, a second, smaller measuring machine is necessary.

The technical problem underlying the invention is a method of correcting geometri to indicate the procedural errors with which it is possible to Make correction such that at least in part range of the entire measuring volume a measurement accuracy is enough, the approximate accuracy of a small neren measuring machine corresponds.

This technical problem is caused by the characteristics of the Claim 1 solved.

According to the method of claim 1, the Kor rectification of the geometric sequence errors of at least one Made axis of a coordinate measuring machine, with a measuring device a little recording of the sequence errors least one axis over the entire measuring volume with a be agreed base grid. In addition, a further inclusion of the sequence errors of at least one axis in with at least a partial volume of the total measuring volume an increased support density, the Measuring device, for example a laser interferometer, we at least approximately at a virtual zero mark, at least an axis of the partial volume is arranged and on finally the inclusion of the sequence errors in the partial volume is carried out.  

This means that after correcting the total volume mens a partial volume of the measuring machine like a separate Ma machine is treated, which due to the now shortened ten measuring lengths work with a higher support density what is the accuracy of the correction for this Partial volume increased considerably. Receives the partial volume plus virtual zero marks for the individual axes, so as whether it would be a different, smaller machine. Like a small machine, the laser is now in the Near these new zero marks, so that not only the Travels, but also the laser beam paths as a whole be shortened. So you have the same Precision requirements like a real small one Machine.

The correction data determined during this measurement that as an independent correction data record in the machine control saved. Through software control, depending on Need between the original (large) and the virtual (small) machine can be switched, with the associated correction data record is activated. The Meßvo lumen of the "large" machine includes that of the "small" Machine, but with a low support point density for the correction.

The "small" machine only exists in the associated one Partial volume, so that overlapping measurements in the mode "large Machine ".

According to the invention, the correction files are optional used, depending on whether the workpiece is exclusively  is located within the at least a partial volume or completely or partially outside the at least one partial vo lumens is arranged.

The machine control advantageously switches within of the partial volume automatically to the correction file with the higher support density around.

Preferably, the Cor correction values of the two "machines" at the interfaces creates a uniform correction file that is in the subvolume The coarse support post automatically increases accuracy interpolated lenraster. The one when measuring with high Correction values generated in support point density are thus adjusted to match those at the measurement with lower Base density generated correction values at their Digits match.

The geometrical deviations of the at least one axis are, for example, with a laser interferometer with Ge Raditätsoption and / or rotation option detected.

But it is also possible to ver other measuring devices turn.

Further details of the invention can be found in the sub claims are taken.

In the drawing is an embodiment of the He finding, namely show:

Figure 1 is a coordinate measuring machine with total volume and partial volume.

Fig. 2 is a support points scanning;

Fig. 3 another grid grid.

Fig. 1 shows a coordinate measuring machine ( 1 ) with a measuring table ( 2 ). The coordinate measuring machine ( 1 ) has guides ( 3 , 4 ) for portals ( 5 ) with a crossmember ( 6 ). The portals ( 5 ) are designed to be displaceable in the X direction. A carriage ( 7 ) which can be displaced in the Y direction is arranged on the crossmember ( 6 ). The carriage ( 7 ) carries a quill ( 8 ) which can be moved in the Z direction.

To determine the geometric deviations of the X axis, a laser interferometer ( 9 ) is used, which has a light source with a beam path ( 10 ) in the direction of a measuring axis ( 11 ). In the direction of the measurement axis (11) in the beam path (9), a linear beam splitter (12) and a retroreflector (14) is provided. The linear beam splitter ( 12 ) is arranged on the quill ( 8 a), which is shown in dashed lines.

The quill ( 8 , 8 a) is moved in the direction of the measuring axis ( 11 ), and in a predetermined grid of reference points, the geometric deviations are recorded over the entire measuring volume of the coordinate measuring machine ( 1 ).

For a partial volume ( 13 ), the laser interferometer ( 9 ) is moved from a first position (I) to a second position (II). The position (II) of the laser interferometer ( 9 ) is determined by virtual zero marks for the part volume ( 13 ). The retroreflector ( 14 ) is also moved from position (I) to position (II), position (II) of the retroreflector ( 14 ) being immediately outside but near the partial volume ( 13 ).

The geometric deviations in the partial volume ( 13 ) who determined the with an increased support density. However, it is also possible to use the same support point density as in the total volume. In this case you have at least the advantages of small beam lengths.

The coordinate measuring machine ( 1 ) has a measuring line in the X direction with a measuring length of several meters. The partial volume ( 13 ) has an edge length of one meter. As already stated, the laser devices ( 9 , 14 ) are attached in the vicinity of the partial volume limits, with all the advantages of short beam lengths.

Fig. 2 shows a grid of nodes ( 15 ), with "a" the nodes of the entire measuring volume of the coordinate measuring machine ( 1 ) are designated and with "b" the nodes of the partial volume ( 13 ).

Referring to FIG. 3, the measuring lines are sequentially fitted attached. The support points scanning (16) of FIG. 3 shows provide support (a) for the Gesamtmeßvolumen and supporting points (b) for the partial volume (13).

The adjustment is made according to the following formula:

The prerequisite for this is that every kth b-point coincides with an a-point. If this is not the case, as shown in FIG. 2, the values of a _n and must be interpolated a _{n + 1,} respectively, before they go into the mel For.

Reference list

1

Coordinate measuring device

2nd

Measuring table

3rd

guide

4th

guide

5

Portals

6

traverse

7

carriage

8th

Quill

8th

aPinole

9

Laser interferometer

10th

Beam path

11

Measuring axis

12th

Linear beam splitter

13

Partial volume

14

Retroreflector

15

Interpolation grid

16

Interpolation grid
I, II positions

Claims (8)

1. A method for correcting geometric sequences of at least one axis of a coordinate measuring machine, in which the measuring errors of at least one axis are recorded over the entire measuring volume with a grid of reference points using a measuring device,
characterized by

• 1. that in addition a recording of the sequence errors of at least one axis ( 11 ) in at least one partial volume ( 13 ) of the entire measuring volume with an increased support density is carried out, the measuring device ( 9 ) at least approximately at a virtual zero mark we least one axis of the partial volume ( 13 ) is arranged, and then the recording of the sequence errors in the partial volume ( 13 ) is carried out,
• 2. that the correction values determined in the entire measurement volume and in the at least one partial volume ( 13 ) are stored in the machine control, and
• 3. that the determined correction values are used depending on the measurement task when measuring a workpiece.

2. The method according to claim 1, characterized in that the correction values of the entire measurement volume and we at least a partial volume ( 13 ) are each stored in separate files. 3. The method according to claim 2, characterized in that the correction files are used selectively, depending on whether the workpiece is located exclusively within the at least one partial volume ( 13 ) or entirely or partially outside of the at least one partial volume. 4. The method according to claim 2, characterized in that at least two correction files are matched be such that they are at common support points tune in. 5. The method according to any one of claims 1 to 4, characterized in that the machine control within the partial volume ( 13 ) automatically switches to the correction file with the higher support density. 6. The method according to claim 2, characterized in that at least two correction files for a single cor rectification file can be summarized.   7. The method according to claim 1, characterized in that a laser interferometer ( 9 ) with at least one mirror and / or retroreflector ( 14 ) and a rotary beam splitter or linear beam splitter ( 12 ) arranged in the beam path is provided as the measuring device. 8. The method according to claim 1, characterized in that the measurement of the deviation components with an elec tric protractor and a physical straightness standard times and / or with a laser interferometer, a mirror and a reflector and a physical straightness standard is carried out.