EP1080339A1

EP1080339A1 - Feeling method and a device for determining the surface characteristics of a test piece according to the feeling method

Info

Publication number: EP1080339A1
Application number: EP99926478A
Authority: EP
Inventors: Ralf Christoph; Frank HÄRTIG
Original assignee: Werth Messtechnik GmbH
Current assignee: Werth Messtechnik GmbH
Priority date: 1998-05-29
Filing date: 1999-05-29
Publication date: 2001-03-07
Also published as: WO1999063299A1; AU4371899A; DE19824107A1

Abstract

The invention relates to a feeling method for determining the surface characteristics of a test piece comprising a feeler element which is supported on the surface. The position of the feeler element or a position of at least one reticle which is directly assigned to the feeler element is directly detected using an optical sensor. In addition, the surface characteristic is determined while taking the relative movement between the test piece and the feeler element into account.

Description

description

Tactile cut method and arrangement for determining the characteristic size of a surface of a test object according to the tactile cut method

The invention relates to a probe cut method for determining the characteristic size of a surface of a test specimen, in particular for determining the waviness and / or roughness depth and / or smoothing depth of the surface, with a probe element of a probe that is supported on the surface and includes a probe extension. Furthermore, the invention relates to an arrangement for determining the characteristic size of a surface of a test specimen according to the tactile cut method, in particular for determining the ripple and or roughness depth and / or smoothing depth of the surface, comprising a probe element that can be supported on the surface of a probe comprising a probe extension.

The surface inspection is used to assess the boundary surface of a body. For this purpose, stylus devices are known, with which, for example B. a sapphire, diamond or simple steel tip, the surface is scanned, which is drawn at the desired speed evenly relatively over the surface to be tested. The surface is then assessed based on the deflection of the needle perpendicular to the surface. These displacements can e.g. B. be measured with a sensitive mechanical pointer. In the most common stylus devices, the needle deflections are converted into an electrical signal, amplified and used as an upper area characteristic displayed or registered by a high-speed recorder. In a mechanical optical stylus device, an oscillating needle is guided along the surface and is connected to a mirror. A light mark is deflected by this mirror and deflected onto light-sensitive material.

With the previously known methods, an indirect measurement of the surface parameters takes place, relatively high probing forces being required in particular in the case of mechanical and electrical amplification devices. As a result, small probe tips cannot be used, since they would otherwise be destroyed. If small probe tips are nevertheless used, the probe element will wear due to the probing force required on hard surfaces, with the result that there is a high degree of measurement inaccuracy. Due to the relatively high probing force, it is also not possible to measure sensitive surfaces, since otherwise there would be a risk of destruction. Similar disadvantages arise with the optical measuring method not used in practice due to the necessary oscillating movement of the needle. Therefore, the previously known methods are only suitable to a limited extent, very small object geometries such. B. measure holes.

Non-contact methods are also known, such as e.g. B. the light section process according to Schmaltz. Here, a thin, sharply delimited band of light is radiated onto a surface to be tested and then viewed as a profile curve through a microscope.

Scanning force microscopy is used to measure the technical surfaces of small areas. A very fine tip is not necessarily touching a sample surface. The probe tip is attached to a small leaf spring, the surface of which faces away from the tip is acted upon by a laser light which is detected to detect the movement of the spring by means of a PSD sensor (Technica 5/96, pages 13 to 20). Inner surfaces of small bores or undercuts cannot be measured or can only be measured with considerable effort. Coordinate measuring machines can be used to determine the geometries of objects such as bores in these, in which, according to DE 297 10 242 Ul, a probe element originating from a resilient shaft comes into direct contact with the body to be measured, in order to directly contact the probe element itself to detect the assigned target mark by means of a photogrammetry system.

A coordinate measuring machine is described in the magazine VDI-Z 131 (1989) No. 11, pages 12 to 16, in which the geometries of a body are determined purely mechanically both optically and with tactile sensors.

In a measuring system according to DE 40 02 043 C2 known for determining geometric machining data on shapes to be measured, an optical fiber is moved manually along a shape to be measured, the optical fiber forming a luminous vector which is optically recorded.

The present invention is based on the problem of developing a method and an arrangement of the type mentioned at the outset, which follow the mechanical measuring principle, in such a way that measurements with minimal contact forces of, for. B. 1 μN and less can be carried out, with very small surface characteristics should be measured with high measurement accuracy.

According to the invention, the problem is solved in terms of the method in that a flexurally elastic shaft is used as the stylus extension and that the position of the feeler element directly or a position of at least one target mark directly associated with the feeler element that originates from the flexurally elastic shaft is detected with an optical sensor and taking into account the relative movement between the DUT and the probe element as well as the deflection of the probe element caused by the touch of the object, the surface measured variable is determined. According to the invention, an optical method is used using an optical sensor, by means of which the position of the probe element supported on the surface is determined directly or a target mark clearly assigned to the probe. In particular, the position of the probe element and / or the at least one target mark is determined by means of reflecting radiation and / or radiation emitting from the probe element or the target mark.

According to the invention, the deflection of the sensing element caused by touching the object is optically determined in order to measure the course of the surface. The deflection of the probe element can be detected by shifting the image on a sensor field of an electronic image processing system such as an electronic camera. There is also the possibility of determining the deflection of the sensing element by evaluating a contrast function of the image using an electronic image processing system. Another possibility for determining the deflection is to determine this from a change in size of the image of a target mark, from which the radiation-optical relationship between the object distance and the magnification results. The deflection of the probe element can also be determined by the apparent size change of a target mark, which results from the loss of contrast due to defocusing. Alternatively, the position of the feeler element or the at least one target mark assigned to it can be determined by means of a photogrammetry system. If there are several target marks, their position can be optically recorded and the position of the sensing element can then be calculated, since there is a clear, fixed relationship between these and the target marks.

An arrangement for determining the characteristic size according to the tactile cut method is characterized in that the stylus extension is designed, at least in sections, as a flexible shaft and that the arrangement detects the optical element emanating from the stylus extension and / or at least one target mark directly associated with the stylus element and originating from the stylus extension Includes sensor that with the probe element as a unit relative to the measuring surface is adjustable. The feeler element and / or the target should preferably be designed as a body that radiates or reflects radiation such as a sphere or cylinder.

The feeler element can be made with the feeler extension such as a shaft by gluing, welding or other suitable connection types. The feeler element and / or the target can also be a section of the feeler extension itself. In particular, the push button extension or the shaft is designed as a light guide or comprises such a light guide in order to supply the required light to the push button element or the target.

The end of the shaft can be designed as a button or comprise such a button. In particular, the feeler element and / or the target should be interchangeably connected to the feeler extension for the shaft.

According to the invention, a stylus device is proposed which is designed in particular as a coordinate measuring machine or has the basic structure, or is integrated in a coordinate measuring machine, the stylus device combining the advantages of optical and mechanical methods without accepting their disadvantages, one use in particular in the mechanical measurement of very small structures and in particular sensitive surfaces is possible, since only extremely low contact forces of e.g. B. 1 μN and less are required with small dimensions of the probe element itself in order to determine surface parameters with high accuracy and reproducibility.

According to the invention, a touch or probe element or a target mark assigned to it is determined in its or its position by a sensor such as an electronic camera after the former has been brought into mechanical contact with the surface of a test specimen to be measured. Because either the probe element itself or the target mark, which is directly connected to the probe element, in position is measured, deformations of a shaft receiving the probe have no influence on the measurement signals. When measuring, the elastic behavior of the shaft does not have to be taken into account, nor can plastic deformations, hysteresis and drift phenomena of the mechanical coupling between the probe element and the sensor influence the measurement accuracy.

To implement the teaching according to the invention, it is not necessary for an active light-emitting probe element or another active target to be used. Particularly high accuracies can be achieved with light-emitting probe balls or other light-emitting target marks on the probe extension. The light from a light source is the probe element such as ball or other target marks of the probe extension via z. B. an optical fiber is supplied, which itself can represent the stylus shaft or the stylus extension. The light can also be generated in the barrel or in the target marks by z. B. contain LEDs.

In particular, the probe element should have a disk-shaped or disc-shaped geometry.

The reason for these construction methods is that electronic imaging systems require a high light intensity, especially for the determination of microscopic structures. If this light is directly supplied to the probe element, the necessary light output is considerably reduced and thus the thermal load on the object during the measurement.

When using spheres as the probe element, an ideally contrasting and ideally circular image of the probe ball results from all viewing directions. This applies in particular when using a volume-scattering ball. Disturbances caused by the depiction of structures of the object itself are avoided, since the object itself is only brightly illuminated in the immediate vicinity of the probe ball. However, the image of the probe ball created by reflection on the object will practically always appear less bright than the probe ball itself. Errors can therefore be corrected easily. There is also the possibility of making the target mark fluorescent, so that incident and emitted light are separated in terms of frequency and thus the target marks in the image can also be more clearly isolated from the surroundings. The same considerations apply to the touch element itself.

It is also possible to attach further illuminated spheres or other target marks to the optical fiber, to record the position of these target marks in particular photogrammetically and then to calculate the position of the sensing element accordingly. Balls represent comparatively ideal, clear target marks. Good light coupling into the balls can be achieved by disturbing the light-guiding properties of the shaft, in which, for example, B. the pierced volume-scattering balls on the shaft, d. H. of the push button extension and glued to it. The volume-scattering balls can also be glued to the side of the shaft, and light can also be coupled in, provided the shaft guides light up to its surface, ie does not have a jacket at the point of adhesion.

A particularly high level of accuracy is achieved if the probe element position is experimentally recorded (calibrated) as a function of the fiber position and fiber curvature (zones of the fiber at some distance from the probe element). Here too, the dimension of target marks applied along the fiber is possible instead of the dimension of the fiber itself. The separation of the elements of the probe element such as the probe ball and target marks additionally reduces the probability of a disturbance in the measurement of the probe element position due to reflections of the target mark on the object surface.

In principle, the touch element, the target marks or the shaft can be illuminated not only from the inside by the shaft, but also by suitable lighting devices from the outside. The tactile element or target mark can be designed as retro-reflectors. In particular, the button extension can be designed as a light guide and a - diameter of z. B. 20 microns. The diameter of the probe element such as the probe ball should then preferably be 50 μm.

In order to increase the breaking strength of the stylus extension, when using light guides as the material, they can have a surface coating such as Teflon or another break-resistant substance. A casing can e.g. B. generated by sputtering.

Further details, advantages and features of the invention result not only from the claims, the features to be extracted from them - by themselves and / or in combination - but also from the following description of preferred exemplary embodiments which can be found in the drawing.

Show it:

Fig. 1 is a schematic diagram of a first embodiment of an arrangement for performing a probe cut method and

Fig. 2 is a schematic diagram of a further arrangement for performing the probe cut method.

In the figures, in which the same elements are basically provided with the same reference numerals, purely in principle different embodiments of arrangements for determining the characteristic size of a surface 10 of a test specimen 12 are illustrated using the tactile cut method.

A characteristic surface characteristic such as roughness depth, smoothing depth, average roughness value. To determine the waviness, the proportion of profile support and / or the shape of the body, the surface 10 is mechanically scanned according to the invention by means of a sensing element 14. continuously and the position of the sensing element 14 or a target mark 16 associated therewith is detected by means of an optical sensor 18, in order then to determine the desired surface parameter from the position of the sensing element 14 or the target mark 16 and the relative movement between the test object 12 and the sensing element 14. Probe element 14 and target mark are based on probe extensions 22, 26, which together form a probe.

In the embodiment of FIG. 1, the sensor 18 is aligned with its optical axis 20 directly on the probe element 14, whereas in the embodiment of FIG. 2 there is an alignment with the target mark 16.

In the exemplary embodiment, the pushbutton element 14 is arranged at the end of the pushbutton extension designed as a light guide 22, which extends from a holder 24 which preferably has a light source. Alternatively, there is the possibility of the touch element 14 being self-illuminating, for. B. by means of an LED or to apply light from the outside, so that the reflected light is evaluated by the sensor 18 for determining the position of the probe element 14.

In the exemplary embodiment in FIG. 2, the sensor 18 does not use the touch element 14 itself, but rather the target mark 16 directly associated with it, i. H. the position of which is evaluated, the target mark 16 likewise starting from the push-button extension, such as light guide 26, which is received by the holder 24.

The probe element 14 or the target mark 16 are adjusted for the measurement to be carried out with respect to the optical axis 20 and the focal plane. After the adjustment of the sensing element 14 or the target mark 16, the corresponding element is observed by means of the optical sensor 18. Deflections due to the structure of the surface 10 of the test object 12 are evaluated by electronic image processing.

Is mentioned the button extension 22 or 24 leading to the holder 24 W 99/63299

PCT / EP99 / 0374S

10 is preferably formed as an optical fiber, other suitable and known from the prior art ^~ shafts are also suitable for implementing the invention.

When using an optical fiber, there is the advantage that light itself can be guided to the feeler element 14 or the target mark 16 through it.

In the exemplary embodiment, the feeler element 14 and the target mark 16 each have a spherical shape radiating in terms of volume. The feeler element 14 or the target 16 can be connected to the feeler extension 22, 26 by gluing, welding or in any other suitable manner. An interchangeable connection via a coupling is also possible.

However, the touch element 14 should preferably have a disk or disc shape.

Alternatively, the end of the push button extension, that is to say in the exemplary embodiments of the optical fibers 22, 26, can be designed as a push button element. For this purpose, the respective end section is preferably shaped accordingly at the end.

The touch element 14 or the target mark 16 can consist of different materials such as ceramic, ruby or glass. Furthermore, the optical quality of the corresponding elements can be improved by coatings with scattering or reflecting layers. The use of fluorescent material is also possible.

The diameter of the push button extension 22, 26 is preferably less than 100 μm, in particular approximately 20 μm. The feeler element 14 or the target mark 16 has a larger diameter, preferably a diameter that is between 1.5 and 3 times larger than that of the feeler extension 22, 26.

The image of the touch element 14 or the target mark 16 associated therewith can, for. B. are imaged on a CCD field of the optical sensor 18. The displacement of the light spot in the CCD field can be measured with sub-pixel accuracy. Consequently, with the method according to the invention, reproducible measurements with an accuracy in the μm range are possible, wherein only probing forces are required that can be in the range of 1 μN and less.

The body 12 can be arranged on a measuring table of a coordinate measuring machine, to which buttons with holder 24 and optical sensor 18 can be aligned in CNC technology.

Claims

Tactile cutting method and arrangement for determining the characteristic size of a surface of a test specimen according to the tactile cutting method

1. Probe cut method for determining the characteristic size of a surface of a test specimen, in particular for determining the waviness and / or roughness depth and / or smoothing depth of the surface, with a probe element of a probe that is supported on the surface, characterized in that a flexurally elastic shaft is used as the probe extension and that the position of the feeler element directly or a position of at least one target mark directly associated with the feeler element and emanating from the flexible shaft is detected by an optical sensor and, taking into account the relative movement between the test object and the feeler element and deflection of the feeler element caused by touching the object, the surface measurement variable is determined.

2. The method according to claim 1, characterized in that the probe element with the sensor as a unit is relatively moved relative to the test object.

3. The method according to claim 1 or 2, characterized in that the position of the sensing element and / or the at least one target mark is determined by means of reflecting radiation and / or shading by this and / or radiation emitting from the sensing element or target mark.

4. The method according to at least one of the preceding claims, characterized in that the deflection of the sensing element is detected by shifting its image or one of a target mark on a sensor field.

5. The method according to at least one of the preceding claims, characterized in that the deflection of the probe element is determined by evaluating a contrast function.

6. The method according to at least one of the preceding claims, characterized in that the deflection of the probe element is determined from a change in size of an image of a target mark, which results from the radiation-optical relationship between the object distance and magnification.

7. The method according to at least one of the preceding claims, characterized in that the deflection of the probe element is determined by an apparent change in size of a target mark, which results from the loss of contrast due to defocusing.

8. The method according to at least one of the preceding claims, characterized in that the deflection perpendicular to the optical axis of an electronic image processing system is determined by this.

9. The method according to at least one of the preceding claims, characterized in that the spatial position of the probe element is determined by means of at least 3 target marks assigned to it by means of a two-dimensional measuring system.

10. The method according to at least one of the preceding claims, characterized in that a probe extension or a portion of this is used as a spatially extended target, the position of which is measured relative to the probe body in freely selectable cross sections.

11. The method according to at least one of the preceding claims, characterized in that target marks arranged on the probe extension are determined photogrammetrically (at least 2 cameras) to determine the position of the probe element.

12. The method according to at least one of the preceding claims, characterized in that the position of the sensing element is measured photogrammetrically (at least 2 cameras).

13. Arrangement for determining the characteristic size of a surface (10) of a test specimen (12) according to the tactile cut method, in particular for determining the ripple and / or roughness depth and / or smoothing depth of the surface, comprising a probe element (14) that can be supported on the surface and a probe extension (22 , 26) comprising the push button, characterized in that the push button extension (22, 26) is designed at least in sections as a flexible shaft and that the arrangement of the push button element (14) emanating from the push button extension and / or at least one that is directly assigned to the push button element and that of the Includes an optical sensor (18) that detects a target extension (16) and is adjustable with the probe element as a unit relative to the surface to be measured.

14. Arrangement according to claim 13, characterized in that the arrangement is designed as a coordinate measuring machine or is part of such.

15. The arrangement according to claim 13 or 14, characterized in that the sensing element (14) and / or the target mark (16) is designed as a reflector and / or self-radiating.

16. The arrangement according to at least one of the preceding claims, characterized in that the sensing element (14) and / or the target mark (16) is a radiation of spatially radiating or reflecting bodies such as spheres or cylinders, in particular has a disc or disc shape.

17. The arrangement according to at least one of the preceding claims, characterized in that the push button extension (22, 26) is at least partially designed as a light guide or comprises such.

18. Arrangement according to at least one of the preceding claims, characterized in that the button extension (22, 26) or at least a portion of this is the button element and / or the target mark.

19. The arrangement according to at least one of the preceding claims, characterized in that the pushbutton element (14) is assigned a plurality of target marks (16) which preferably originate from the pushbutton extension (26) or form sections thereof.

20. The arrangement according to at least one of the preceding claims, characterized in that the push button extension is designed at the end as a push button (14).

21. The arrangement according to at least one of the preceding claims, characterized in that the pushbutton element (14) and / or the target mark (16) are interchangeably connected to the pushbutton extension (30).

22. The arrangement according to at least one of the preceding claims, characterized in that the feeler element (14) and / or the target mark (16) are connected to the feeler extension (22, 26) by gluing or welding.

23. The arrangement according to at least one of the preceding claims, characterized in that the button starts from a holder (24) which forms a unit with the sensor (18) or is connected to the sensor.

24. The arrangement according to at least one of the preceding claims, characterized in that the sensing element (14) and / or the target mark (16) has or is a self-illuminating electronic element such as LED.

25. Arrangement according to at least one of the preceding claims, characterized in that the sensor (18) is an image processing sensor.

26. The arrangement according to at least one of the preceding claims, characterized in that the sensor (18) is a position-sensitive area sensor.

27. The arrangement according to at least one of the preceding claims, characterized in that the diameter of the probe element (14) is approximately 1 to 3 times larger than that of the probe extension (22, 26).

28. The arrangement according to at least one of the preceding claims, characterized in that the push button extension has a cylindrical shape at the end and is designed as a push button element.

29. Arrangement according to at least one of the preceding claims, characterized in that the push button extension (30) is spherically rounded to form the push button element.