DE3132383C2 - Length standard for checking the measuring accuracy of coordinate measuring machines - Google Patents

Description

a) the two balls (5,6,6 ', 6 ") are on one common carrier (8, 8 ') supported that the The distance between the two balls (5, 6, 6 ', 6 ") can be changed;

b) on the carrier (8,8 ') is an interferometer arrangement to measure the change in the distance between the two balls (5,6,6 ', 6 ") attached;

c) the beiöea balls (5,6,6 ', 6 ") are along the The course of the measuring beam (20) is provided with bores (21);

d) the line connecting the two balls (5,6,6 ', 6 ") coincides with the measuring axis (19);

e) in which one of the two balls (5,6,6 ', 6 ") is a triple reflector (18) arranged in such a way that its centrally symmetrical point is in the center of the sphere lies, while in the other of the two balls (5, 6, 6 ', 6 ") either one further triple reflector (18) is arranged such that its centrally symmetrical point in The center of the sphere lies, "which is an interferometer divider (13) is arranged concentrically to the sphere in such a way that its active layer (14) runs through the center of the sphere

2. Length standard for checking the measuring accuracy of coordinate measuring machines, the two in known distance to each other, touchable balls with a precisely machined surface -to has, which at the ends of a carrier that is adjustable in its relative position to the base «; are supported, characterized in that

a) the carrier (8 ') is constructed and suspended symmetrically with respect to its longitudinal extension with support parts adjustable in length on both sides (10),

b) a ball (6 ', 6 ") is arranged in the end area of both support parts (10),

c) an interferometer arrangement on the carrier (8 ') for measuring the change in the distance is attached between the two balls (6 ', 6 "),

d) the two balls (6 ', 6 ") along the course of the measuring beam (20) with bores (21) have passed away

e) the line connecting the two balls (6 ', 6 ") coincides with the measuring axis (19),

a triple reflector (18) is arranged in each of the two balls (6 ', 6 ") in such a way that whose centrally symmetric point lies in the center of the sphere and

g) an interferometer divider (13) is arranged approximately in the middle of the carrier and is designed so that an interferometric determination of the distance between the two opposing spheres (6 ', 6 ″) is possible with it, the interferometer divider (13) being designed and arranged in this way is that it lies on two opposite sides transversely to the direction of incidence of light Sides measuring beams (20) can exit and on these sides with polarization plates (15) is provided

3. Length standard according to claim 1 or 2, characterized characterized in that at least one ball (6, 6 ', 6 ") is attached to the end of the carrier (8,8') and that this due to telescopically nested and mutually longitudinally guided carrier sections (9) can be changed in length

4. Length standard according to one of claims 1 to

3, characterized in that a laser head (12) including a receiver for the interferometer arrangement is fixedly arranged on the carrier (8, 8 ')

5. Length standard according to one of claims 1 to

4, characterized in that the measuring beam (20) of the interferometer arrangement and the balls (5, 6, 6 ', 6 ") run or are arranged next to the carrier (8, 8').

6. Length standard according to one of claims 1 to 4, characterized in that the measuring beam of the Interferometer arrangement runs inside the carrier and the balls are coaxial with the carrier are arranged.

7. Length standard according to one of claims 1 to 6, characterized in that the carrier (8, 8 ') gimbaled (22) is with horizontal (23) and vertical pivot axis (24), with it in each any pivot position can be locked

8. Length standard according to claim 7, characterized in that the interferometer divider (13) is arranged relative to the cardanic suspension (22) that the pivot axis intersection comes to rest on the active layer (14) of the interferometer divider (13).

9. Length standard according to claim 7 or 8, characterized in that the cardanic suspension (22) is provided with a vertical guide for height adjustment

10. Length standard according to one of claims 7 to

9, characterized in that for measuring the individual movements of the cardanic suspension (22) a distance or angle measuring system is provided in each case.

11. Length standard according to one of claims 1 to

10, characterized in that for the azimuth, the Elevation, vertical and / or extension movement of the carrier (8, 8 ') a servo drive (11, 25) is provided.

The invention relates to a length standard for checking the measuring accuracy of coordinate measuring devices according to the preamble of claim 1 and a length standard for checking the measurement accuracy of coordinate measuring devices according to the preamble of claim 2, as for example from DE-OS 03 376 appear as known.

In this publication, a dumbbell-shaped ball gauge block is proposed in which one ball rests in a pan on the measuring table and the other ball of a height-adjustable, likewise

braced with a pan is supported.

In addition to the use of such dumbbell-shaped ball gauge blocks, multi-coordinate measuring devices can also be checked with regard to their accuracy by means of parallel gauge blocks and crenellated step gauge blocks; in this connection, reference is made, for example, to a publication in the VDI magazine 1980, pages 535 to 548.

In DE-AS 21 43 655 a displacement comparator with laser interferometer is shown with the dimensions of bodies can be precisely determined along a single measuring axis. When moving the The light-dark transitions of the interfering laser light are the moving part of the comparator counted, with the number of light-dark transitions It is known that displacement paths are also used in other applications to be accurately determined in an interferometric manner.

However, the use of gauge blocks and step gauge blocks has various disadvantages, which are particularly evident in when checking coordinate measuring machines: the temperature, possibly also the temperature distribution within the gauge block or in the step-gauge base body would be in the calibration state as well as when used on the coordinate measuring machine for everyone To record the time of measurement in order to use the coefficient of linear expansion to make the necessary expansion correction to calculate. All distances to be used later on on a coordinate measuring machine must be known about five times as reliably as the expected one, according to a basic metrological rule Measurement uncertainty of the coordinate measuring device. This requires a complex prior calibration measurement for the gauge blocks used in the check. The inevitable dimensional changes due to bending in different spatial arrangements or fixtures in an inclined state in comparison to the situation during the calibration measurement can reach considerable values. Precision manufacturing a set of gauge blocks or a step gauge block with many lapped measuring surfaces and their periodic ones Calibration to determine a possibly age-related change in length is a high cost factor for the user. Gauge blocks and step gauge blocks are currently only manufactured up to a length of 1 m, while for accuracy testing of coordinate measuring machines with medium measurement ranges in the In the room diagonal direction, length standards of approx. 2.5 m are required. The handling and clamping Such long physical precision length standards on the coordinate measuring machine would be very problematic. It can be done with parallel gauge blocks or step gauge blocks and also with the known ball gauge blocks necessarily only determined distances between the actually existing touchable surfaces finer gradations or distances cannot be represented. The surface of each measuring surface must be very be well educated. Existing ripples or misalignments cause an undesirable error influence, if it is not touched exactly in the measuring line.

The object of the invention is to provide a largely temperature-independent, easily manageable length standard to accomplish.

According to the invention, this object is achieved by the characterizing features of claim 1 or by the characterizing features of claim 2 solved. This creates a ball gauge block in which the distance of the balls directly to the wavelength definition of the meter is connected. Due to the arrangement of the optical components in the centers of the spheres is the influence of tilting movements of the balls - be it due to a deflection of the Carrier by its own weight, be it due to a bending of the ball holder when probing - Also eliminates temperature-related changes in length of the carrier and changes in distance between the balls, which is due to a bending or deformation of the beam are due, have no effect on errors, since only the distance due to the interferometer arrangement the spherical center is detected. The coordinate measuring machine now has the fundamental measuring task It is possible to determine the spatial distance between two spheres in terms of coordinates by means of multi-point probing. This process can advantageously be carried out in different positions of the carrier within the Measurement volume of the coordinate measuring device are repeated, so that a closed picture of the Accuracy of the entire coordinate measuring machine results

Appropriate refinements of the invention can be found in the subclaims. the The invention is explained in more detail by the following description of the exemplary embodiments shown in the drawings; thereby shows

F i g. 1 shows the perspective view of an exemplary embodiment a length standard according to the invention,

F i g. 2 and 3 side view (FIG. 2) and cross section along the section line EII-III (FIG. 3) of the length standard according to FIG. 1 and

4 shows the side view of a further embodiment with variable length support parts for the measuring balls on both sides.

In the drawings, the coordinate measuring device to be checked by the length standard is only through the measuring table 1 and indicated by the probe head 2 with button 3 and 4 feeler ball

The length standard shown in FIGS. 1 to 3 has a first (5) and a second measuring ball 6, the distance of which can be changed via feet 7 on a carrier 8 are held. The measuring balls 5, S are very precise and have a high surface quality Manufactured precision spheres whose spatial position is determined by the coordinate measuring device through a multi-point probe can be determined. The carrier 8 consists of several carrier sections 9, the telescopic are so telescoped and guided exactly to one another, so that the carrier 8 itself can be changed in length as a whole is. This has the advantage that the length of the carrier 8 corresponds to the size of the MeCvoIumen to be checked Coordinate measuring device adapted and on different Intermediate lengths can be set and protruding support parts can be avoided. At least the second measuring ball 6 is always at the outer end of the, regardless of the distance between the balls Carrier 8.

An interferometer arrangement for ongoing interferometric determination of the distance between the spheres is attached to the carrier 8 Relative position to the carrier 8 participates In itself it would also be conceivable to place the measuring beam 20 of the interferometer arrangement in the interior of the hollow carrier 8

'to run and to arrange the balls 5, 6 coaxially with the carrier 8. In the illustrated embodiments however, the measuring beam 20 is arranged parallel to the carrier 8 and the balls are 5, 6 held at a distance from him via little feet 7. The interior of the hollow carrier 8 is for needs other purposes, as described below.

The first measuring ball 5 lying next to the laser head 12 is for the passage of the measuring beam 20 and of the reference beam 20 'completely pierced (hole 21). Inside this measuring ball 5 is a small one Interferometer splitter 13 with a triple reflector 17 attached on top. The ones from Laser head 12 emitted light beam are exactly concentric to the measuring axis 19 through the Connecting line of the two spherical centers is determined.

The! F! T £ rferorr.etertei!? R 1? he is essentially of two triangular prisms placed one on top of the other, which enclose an active layer 14 between them. These has the property, only light rays linearly polarized light of a single very specific one Polarization plane, for example horizontally. The light beams of a different polarization direction are reflected by the active layer 14. In the arrangement according to FIGS. 1 to 3, the measuring beam 20 is in the transmission direction of the active layer 14 polarized, whereas the reference beam 20 'is polarized transversely to the transmission direction and to the upper one Triple reflector 17 is deflected, of which it - again reflected on the active layer 14 - in the Receiver part of the laser head 12 is thrown back.

The measuring beam 20 measures the first ball 5 and the measuring section and strikes the second measuring ball 6, in the interior of which a triple reflector 18 is arranged, the centrally symmetrical point of which with the center of the sphere coincides. This triple reflector 18 throws the measuring beam 20 through the measuring section and the first Measuring ball 5 through into the receiver part of the laser head 12 back. It comes with the reference beam 20 'to an interference formation.

To determine the exact distance between the spheres, an initial distance must be exact in terms of its absolute dimension be known. This starting distance can, for example, be the mutual contact of the two measuring balls 5, be 6. The starting distance must always be able to be retracted very precisely and reproducibly. By counting the interference signals that occur when the distance between the spheres is increased, the actual ball spacing can be determined. Since the active layer 14 of the interferometer part 13 so is arranged within the first ball 5 that it runs through the center of the sphere and there also the centrally symmetrical point of the triple reflector 18 with coincides with the center of the sphere of the second measuring sphere 6, pivoting of the spheres 5 remains, 6 z. B. due to deformations of the carrier 8 or the feet 7 in the determination of the distance ineffective. The interferometric measurement always detects the center distance of the balls 5, 6 regardless of the pivot position. In order to move the second measuring ball 6 to different positions within the measuring volume in quick succession of the coordinate measuring machine to be able to position test measurements on all possible To be able to make places within the measuring volume, the carrier 8 is movably mounted. In fact a cardanic suspension 22 is provided with a horizontal (23) and a vertical axis 24, the intersect at a certain point. This axis intersection is chosen so that it is also on of the active layer 14 of the interferometer part 13 and lies on the measuring axis 19, it falls accordingly at the in the F i g. 1 to 3 illustrated embodiment with the center of the first measuring ball 5 together. Of the Carrier 8 can be locked in any desired pivoting position, so that the carrier 8 assume a rigid position can.

In the illustrated embodiment, the cardanic suspension is vertical by one A turntable 26 realizing the axis and a swing 28 realizing the horizontal pivot axis created, the cheeks 27 fixed in two opposite on the turntable 26 pivotable is stored and the carrier 8 holds. The turntable 26 can in turn still with a vertical guide for a Be provided height adjustment, but this is not shown in the embodiment shown. As a result, the position of the first measuring ball 5 can also be changed at least in one coordinate direction will.

For the turntable 26, so the azimuth movement, for the swing 28, so the elevation movement and for the extension movement of the carrier 8 is each provided with a servo control. And zwcr is graphic illustrated servo drive 11 for the extension and retraction movement of the carrier 8 at its rear Arranged at the end. The carrier sections 9 can be extended, for example, by means of an inside Compression spring and the retraction of the carrier 8 by a running inside the carrier 8 be made of windable steel belt. On a scaled turntable on the outside of the servo drive 11, the The extension length of the beam can be read off. The swivel drive 25 for the elevation movement is arranged laterally on one of the two cheeks 27.

Here, too, as on the turntable 26, there is a scale for setting and checking a specific one Swivel position attached. Appropriately, the respective servo drives are each also with connected to a very precisely working distance or angle measuring system. As a result, due to a corresponding program control of the servo drives certain positions of the carrier 2 or the measuring ball 6 can be retracted automatically. Through this sirh lets in Complete the measuring program at greater speed.

The embodiment according to FIG. 4 differs from that according to FIGS. 1 to 3 essentially in that here the two measuring balls 6 'and 6 "are changed in their position when the carrier 8' is pivoted, so that no measuring ball is arranged in the area of the stationary interferometer part 13 two measuring balls 6 ', 6 "extends beyond the center of the carrier, the laser head 12 must be moved out of the measuring axis 19, for which a deflecting prism 16 is arranged below the interferometer part 13. In this arrangement, the reference beam 20" is aligned linearly with the transmission direction of the active layer 14 polarized, whereas the measuring beam 20 is linearly polarized transversely thereto. The reference beam 20 ⁵ thus passes through the active layer 14 and hits the triple reflector 17, from which it immediately returns to the receiver part via the deflecting prism 16

of the laser head 12 is thrown back.

The interferometer divider 13 is across the two to the direction of incidence of light sides are each provided with a polarizing plate 15, which have the property, the plane of polarization of a linear polarized light beam after passing twice through the polarizing plate 15 by 90 ° seem crazy. The first across The measuring beam 20 polarized to the transmission direction of the active layer 14 is therefore reflected by it to the right, reaches the triple reflector 18 ir. the right measuring ball 6 ', is thrown back to the interferometer splitter 13 and is now - after the second passage through the right polarization plate 15 - polarized in the forward direction of the active layer 14, so that it is to left measuring ball 6 ″. From there it is thrown back to the interferometer splitter 13. After the second passage through the left polarization plate 15 is the measuring beam! 20 again. "» »Mier polarized to the forward direction of the active layer 14, so that it follows is deflected into the triple reflector 17 at the top. This throws him back on the active layer 14, which him turn to the left so that the game just described is repeated once more. The measuring beam 20 traverses the measuring section a total of two times and is then finally via the active layer 14 and the deflecting prism 16 in the receiver part of the Laser head 12 thrown back, thanks to such an arrangement, the distance between two is more movable Measuring balls interferometrically detectable. In itself, one of the two measuring balls could be on one arranged in its length invariable support part be; a change in position of the ball would then only be with azimuth and elevation movements of the Carrier possible. The illustrated embodiment shows, however, that the carrier 8 'by two carrier parts 10 is formed, each according to the type of carrier 8 according to FIGS. I to 3 can be changed in length. Through this Larger elevation angles can also be retracted by moving the lower support part 10 accordingly is withdrawn.

is The length standard according to F i g. 4 offers over the 1 to 3 have the advantage that with approximately the same mutual spacing of the measuring balls and with an unchanged position at least the cardanic suspension of the beam the measuring section can be moved within the measuring volume of the coordinate measuring machine.

The movements of the carrier can be controlled by a control computer via the servo drives which is also laser interferometric determined ball distance values and the measured values of the Coordinate measuring device detected and compares with the ball contact.

For this purpose 3 sheets of drawings

Claims (1)

Claims; 1. Length standard for checking the measuring accuracy of coordinate measuring machines, the two in known distance from each other held, touchable balls with a precisely machined surface has, of which one in a fixed relative position to the base and the other in an adjustable position Carrier is supported, characterized by the combination of the following features: to