DE102011012981B3 - Standard hybrid spherical cap for calibration of coordinate measuring machine, has recess whose edge extends from slope of acute angle to planar measuring surface such that calotte is provided in contact points at another edge - Google Patents

Abstract

The cap (10) has a base body (12) provided with a planar measuring surface. The planar measuring surface projects cross-sectionally circular cap-shaped calotte. The base body has a recess (18) dividing an edge (22) with the measurement surface. The calotte is formed on an insert body (16) i.e. ball segment. The calotte is received in the recess. Another edge (20) of the recess extends from a slope of an acute angle to the planar measuring surface such that the calotte is provided in contact points at the former edge. The base body is formed from a single crystal. An independent claim is also included for a method for manufacturing a standard hybrid spherical cap.

Description

The invention relates to a hybrid calotte standard with (a) a basic body having a planar measuring surface, and (b) a dome projecting over the planar measuring surface, circular cap in cross-section, (c) the base body having a recess and (d) the dome an insert body is formed, which is received in the recess. In a second aspect, the invention relates to a method of making a hybrid dome standard.

For calibrating measuring means, such as coordinate measuring machines, hybrid dome standards are used. Such hybrid dome standards are used in particular to determine the accuracy of the measuring system to be calibrated in the situation in which both a plane surface and a spherical surface are to be measured. It is known in the art to prepare hybrid dome normal by first making a uniform body, such as a cube. In this uniform body spherical aberrations are then eroded into it by means of spark erosion. The disadvantage of this is that the achievable surface quality, which can be characterized, for example, by the roughness, is limited. Another disadvantage is that the spark erosion is not completely reproducible, so that each cap differs from the other and must be calibrated separately. This makes the production of hybrid calotte normal consuming.

From the DE 10 2006 014 509 A1 is a generic Hybridkalottennormal known in which holes are drilled in a body and inserted into the holes balls. This has the advantage that the balls can be manufactured separately and thus with high accuracy. The disadvantage, however, is that it is inherently impossible to perform the hole in exactly the same size as the ball. This means that there is a furrow between the sphere and the plane surface. Such grooves, in particular, present the evaluation software of optical surveying methods with, in some cases, great difficulties, without the furrow forming a realistic structure to be tested. Another disadvantage of such hybrid dome normal is their elaborate production.

In the DE 100 81 572 B4 is a comparably constructed normal known, in which the holes are inserted into the bottom of a groove.

The US 2004/0036867 A1 describes a glass ceramic rod having inwardly tapered bores in which steel balls are inserted.

The invention has for its object to provide a Hybridkalottennormal reproducing a well-defined Tastweg.

The invention solves the problem by a Hybridkalottennormal according to claim 1. According to a second aspect, the invention solves the problem by a method according to claim 9.

An advantage of the inventive solution is that a precisely defined Tastweg is obtained, which initially runs straight along the plane measuring surface and then merges into a circular arc shape in a kink steadily. Thereafter, the Tastweg can again go continuously in a straight line. There is no gap at the point of transition between the calotte and the flat measuring surface.

Another advantage is the high achievable accuracy. It is possible to form the flat measuring surface with a slight deviation in shape from a perfect plane. Such techniques are well known in the art. It is also possible to produce the insert body, which may be, for example, a ball or a cylinder, with high accuracy also with well-controlled techniques. The fact that the edge of the recess rests against the insert body, the plane measuring surface goes steadily into the dome, at least at the point of contact. In this way, a hybrid dome normal is obtained which can be manufactured with high precision both with respect to the flat measuring surface and with respect to the dome.

It is a further advantage that the insert bodies can be produced in a reproducible manner. This makes it unnecessary to calibrate the calotte surfaces. A hybrid calotte standard according to the invention can therefore be produced easily and also has an increased accuracy compared to known hybrid calotte standards.

In the context of the present description, the feature that the calotte bears against the edge, in particular, means that there is a cross section through the hybrid calotte standard, in which the planar measuring surface merges continuously into the calotte. It is based on the mathematical concept of continuity. Along this cross section exists a Tastweg, which is a straight line in one section and a circular arc in a second section, wherein both sections merge into each other continuously. At the point where both sections merge into each other, the measurement path thus defined has a kink. The measuring path can be described as a function. In known hybrid calotte normal, undercuts can occur at the transition between the flat measuring surface and the calotte.

Under the feature that the edge of the recess extends on at least one side at an acute slope angle to the measuring surface, so that the dome rests on the edge, in particular also understood that a cross section exists, with respect to which a measuring path exists, as described above is trained and has a monotonous course in the mathematical sense. In known hybrid dome normal, as indicated above, at the transition between the dome and the planar measurement surface, a groove may be formed. At this point, the measurement path drops in conventional hybrid dome models to then re-enter the calotte. Such a metrologically problematic transition does not usually exist in the hybrid calotte standard according to the invention.

In particular, the planar measuring surface is understood to mean a surface which is formed on the basic body and, in an environment of the edge, has a flatness deviation from an ideal plane of at most 1 μm to 1 cm.

The insert body is understood to mean, in particular, a body which is separated from the basic body at least at one point in time during the production of the hybrid calotte standard. It is possible that the insert body is permanently attached to the base body, for example glued. But it is also possible that the insert body is releasably secured and is pressed against the base body, for example by means of a spring element. The spring element may be integrally connected to the substrate, for example, the spring element is etched out of the main body.

The calotte is understood in particular to be that portion of the insert body which is circular-cap-shaped in at least one cross-section. This is to be understood in particular that a shape deviation from an ideal circular cap is at most 1 μm.

The slope angle is understood in particular to be that angle which is present directly at the edge. As a rule, the edge of the recess is formed by a plane. In principle, however, it is also conceivable that the edge is curved, so that the slope angle changes with increasing distance from the measuring surface. in this case the relevant slope angle is the one that exists directly at the edge.

The term "hybrid calotte standard" is to be understood as meaning in particular the entirety of the material measure as described by the features of the respective claim and a measurement certificate. In principle, any body is suitable as normal, provided that it is sufficiently stable in its geometric dimensions. In order to be able to calibrate measuring instruments using this standard, it is necessary for the variables represented by the standard to be recorded in a test certificate. The fact that a test certificate is available is inherent in the concept of the standard. Preferably, the Hybridkalottennormal allows a calibration with an error of below 10 ^-3 .

According to a preferred embodiment, the insert body is a spherical segment or a ball or a part of a spherical segment or a ball, so that the dome is a spherical cap. Balls can be produced with a particularly high accuracy, so that a high accuracy for the Hybridkalottennormal can be achieved in this way.

Preferably, at least the base body is formed from a single crystal. It is also possible that additionally or alternatively the insert body is formed from a single crystal. It is particularly favorable if the monocrystal is a semiconductor monocrystal, for example a silicon monocrystal. For the processing of silicon monocrystals there is a sophisticated process technology, so that particularly flat measuring surfaces can be produced, which increases the accuracy that can be achieved with the Hybridkalottennormal. It is particularly favorable if the recess has been etched into the base body. It is possible for the edge of the recess to run along a crystal plane. Particularly preferred is the slope angle between 54 ° and 55 °, in particular, the slope angle is 54.7 °. Such a slope angle can be adjusted by crystal-direction-selective etching in silicon with high process reliability.

Preferably, the measuring surface and / or an insert body surface are specularly smooth. Mirror-smooth surfaces can not be achieved with the hitherto available methods for producing a hybrid dome standard without a circumferential groove forming around the dome. The fact that the measuring surface or the insert surface are specularly smooth, particularly accurate measurements are possible, so that the measuring device to be calibrated can be brought to a high measurement accuracy.

The insert body preferably has an insert body refractive index which differs from a main body refractive index of the main body. Optical methods for detecting surface topography should be tolerant of variations in the refractive index of the object to be measured. To test this, it is advantageous to provide objects with different indices to test the property of the instrument under test to accurately measure, independent of refractive index. In particular, the real parts of the refractive indices differ by at least 5%.

According to a preferred embodiment, the base body and the insert body are designed such that in an environment, in particular a 1 millimeter environment, of the insert body, the measuring surface deviates by at most 1 micrometer, in particular 100 nanometers, from a compensating plane through the measuring surface. This information relates in particular to a measuring path in a cross section through two points, in which the insert body rests on the edge.

In the following the invention will be explained in more detail with reference to the accompanying drawings. It shows

1 a perspective view of a Hybridkalottennormals invention,

2a a view from below of the Hybridkalottennormal according to 1 .

2 B a scanning path along a cross-section AA through the hybrid calotte standard,

3 a cross section through the Hybridkalottennormal according to 2 .

4 a perspective view of a second embodiment of a Hybridkalottennormals invention and

5 a cross section through the Hybridkalottennormal according to 4 ,

1 shows a Hybridkalottennormal invention 10 with a basic body 12 , which has a plane measuring surface 14 which has in 1 points down and an insert body 16 includes. In the embodiment according to 1 is the insert body 16 a sphere that has an insert surface 17 Has.

The main body 12 has a recess 18 that from one edge 20 is bounded. The edge 20 goes in an edge 22 into the measuring area 14 above. In the present case, the edge 20 partially even.

The main body 12 is made of a silicon single crystal, with the measuring surface 14 as well as the opposite surface 24 extend along a crystal plane, preferably in the <111> plane in 100 wafers.

2a shows a view from below of the Hybridkalottenormal 10 , It can be seen that the insert body 16 in the form of the sphere in two opposing points of contact P1 and P2 at the edge 22 is applied. It thus exists a cross section, which is characterized by AA, along which a measuring path M exists, as in the overlying 2 B is shown.

2 B shows that the measuring path M has a first section m1, which is rectilinear. This is followed by a second section m2, in which the measuring path M extends in a circular arc. This is followed by a third section m3 in which the measuring path again runs in a straight line. At the transition points of the individual sections, for example between m1 and m2, the measuring path M is continuous, although of course not differentiable.

If the measuring path M is aligned as in 2 B is shown, namely so that the straight sections m1 and m3 can be described as a constant function, the measuring path M is either monotonically increasing namely in the first section m1 and in the half of the second section m2, or monotonically decreasing, namely in the second Half of the second section m2 and in the third section m3.

3 shows a cross section according to the section AA after 2 , It can be seen that the insert body 16 so in the recess 18 it is arranged that he is on the edge 22 is applied. The edge 22 is the imaginary line in which the edge 20 into the measuring area 14 passes. The edge 20 runs around the recess 18 , It follows that the edge 22 in the present case describes a rectangle, namely a square. 3 also shows the imaginary measuring path M. It can be seen that although there is a kink in the measuring path M in the contact points P1, P2, there is no point of discontinuity. 3 also shows the section where the insert body 16 over the measuring surface 14 protruding, which is referred to as calotte K.

3 shows a slope angle α between the edge 20 and the measuring surface 14 , In the present case, the slope angle α = 54.7 °.

4 shows an alternative embodiment of a Hybridkalottennormals invention 10 in which the insert body 16 is cylindrical.

5 shows a bottom view of the Hybridkalottenmodell 10 according to 4 , It can be seen that the insert body 16 along two lines L1, L2 on the main body 12 is applied. The lines L1, L2 run along the edge 22 , The hybrid dome normal described above 10 are in particular prepared so that initially the main body 12 , For example, is made of a silicon single crystal. For this purpose, the basic body is polished until it is mirror-smooth. There are also the recesses 18 introduced, for example by wet-chemical etching or reactive ion etching. This can be done by the basic body 12 Covered with a mask made of acid-resistant material and then etched out of the recess with the acid. Since the etching rate is crystal direction selective, the recess is formed 18 ,

In addition, the insert body 16 manufactured, for example, also based on silicon or a metal, for example steel. The insert body is then fitted into the recess of the base body so that the base body rests in at least one contact point on the edge between the edge and the measuring surface. For example, the insert body is glued in this position or biased by a spring in this position. This spring can be supported for example against a support element which is connected to the main body.

LIST OF REFERENCE NUMBERS

10

Hybridkalottennormal

12

body

14

measuring surface

16

insert body

17

Use of body surface

18

recess

20

edge

22

edge

24

area

α

angle of repose

P1

contact point

P2

contact point

M

measuring path

m1

first section

m2

second part

m3

third section

K

dome

L1, L2

line

Claims (10)

Hybrid calotte standard with (a) a basic body ( 12 ), which has a flat measuring surface ( 14 ), and (b) one over the planar measuring surface ( 14 ) projecting, in cross-section circular cap-shaped dome (K), (c) wherein the main body ( 12 ) a recess ( 18 ) having an edge ( 22 ) with the measuring surface ( 14 ), and (d) the dome (K) on an insert body ( 16 ) is formed in the recess ( 18 ), characterized in that (e) an edge ( 20 ) of the recess ( 18 ) at at least one point at an acute slope angle (α) to the measuring surface ( 14 ) runs, so that the dome (K) in at least one contact point (P1, P2) at the edge ( 22 ) is present. Hybridkalottennormal according to claim 1, characterized in that - the insert body ( 16 ) is a spherical segment or a ball, so that the dome (K) is a spherical cap. Hybrid calotte standard according to one of the preceding claims, characterized in that the basic body ( 12 ) is formed of a single crystal. Hybrid calotte standard according to one of the preceding claims, characterized in that - the recess ( 18 ) in one edge ( 22 ) into the measuring surface ( 14 ) and the slope angle (α) is selected so that the insert body ( 16 ) the edge ( 22 ) touched. Hybridkalottennormal according to any one of the preceding claims, characterized in that the measuring surface ( 14 ) and / or an insert body surface ( 17 ) are mirror-smooth. Hybridkalottennormal according to any one of the preceding claims, characterized in that the insert body ( 16 ) has an insert body refractive index which differs from a basic body refractive index of the main body ( 12 ) is different. Hybridkalottennormal according to any one of the preceding claims, characterized in that in an environment, in particular a 1 millimeter environment, of the insert body ( 16 ) the measuring surface ( 14 ) by a maximum of 1 micron from a leveling plane through the measuring surface ( 14 ) deviates. Hybridkalottennormal according to any one of the preceding claims, characterized in that a relative deviation between a coefficient of thermal expansion of the main body material of the base body ( 12 ) and the insert body material of the insert body ( 16 ) is at most 10%. Method for producing a hybrid dome standard, comprising the steps of: (a) producing a basic body ( 12 ), which has a flat measuring surface ( 14 ) and a recess ( 18 ), wherein one edge ( 20 ) of the recess ( 18 ) on at least one side at an acute angle of repose to the measuring surface ( 14 ), (b) producing an insert body ( 16 ) which has a constant curvature at least in segments in at least one plane, and (c) introduction of the insert body ( 16 ) in the recess ( 18 ) of the basic body ( 12 ), so that the insert body ( 16 ) in at least one contact point (P1, P2) at the edge ( 22 ) between edge ( 20 ) and measuring surface is applied. Method according to claim 9, characterized in that the recess ( 18 ) is produced at least by etching.

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