DE20002978U1 - Auxiliary device for an optical distance sensor - Google Patents

Description

GEITZ & GEITZ Patent Attorneys

Kriegsstr. 234 · 76135 Karlsruhe

Attorney file: 004181

Applicant: Ulrich Breitmeier

Erzbergerstrasse 115
D-76133 Karlsruhe
10

AUXILIARY DEVICE FOR AN OPTICAL DISTANCE SENSOR

The invention relates to an auxiliary device for an optical distance sensor, which preferably enables a distance measurement by means of classical or white light interferometry, with an objective lens designed as a collimating lens, wherein a first light inlet and a first light outlet, preferably coinciding with this, are provided for light rays reflected or backscattered from a surface of an object, so that the auxiliary device can be coupled to the distance sensor via a first beam path, wherein the light rays assigned to the first beam path are essentially collimated in front of the objective lens, and wherein a second light outlet and a second light inlet, preferably coinciding with this, are provided for the light rays reflected or backscattered from the surface of the object, so that the auxiliary device can be coupled to the object via a second beam path.

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Various methods are known for optical distance measurement, particularly of surface profiles and/or the roughness of test objects, for example interference optical, triangulation, stripe projection, moiré or autofocus methods. When scanning workpiece surfaces with optical distance sensors, a number of parameters are particularly important for the user and the quality of the measurement data acquisition. These include the measuring range, the measurement accuracy or resolution in the direction of the measuring beam, the achievable lateral resolution, i.e. the measuring point density, the maximum permissible tilt of the measuring object, and the dependence of the measurement result on the color, material and consistency of the test object as well as on environmental influences.

Distance sensors used for optical distance measurement usually contain an objective lens, the numerical aperture of which is the instrumental parameter that has a greater or lesser influence on almost all of the above parameters. Because a significant portion of the light information reflected or scattered back from the object surface is in the higher frequency range, and this is precisely where it is located in the marginal rays, it is important to capture as much of the light reflected or scattered back from the surface of the object as possible and to feed it to a photodetector. For this purpose, an objective lens with the largest possible numerical aperture is usually selected. In practice, however, the use of high-aperture objective lenses has the disadvantage that only a small working distance and a small depth of field can be achieved. Even if the actual distance sensor had a large measuring range, depending on a specific distance detection principle, this would

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This advantage may be negated by the limited depth of field of the objective lens.

In general, distance sensors that enable high resolution or measurement accuracy have a short characteristic curve, i.e. a correspondingly small measuring range. A larger measuring range can therefore only be achieved at the expense of a lower resolution or measurement accuracy. In industrial practice of optical distance measurement, however, the ideal goal is exactly the opposite, namely high measurement accuracy with a large measuring range at the same time.

Sensors are known for optical distance measurement which work with collimated light beams for this purpose, so that, for example, an interferometric or holographic distance measurement is possible. In contrast to classical holography, in which the radiation emanating from the object and a reference beam of coherent light form the interference image, in the recently discovered conoscopic holography using a linear conoscope, the ordinary and extraordinary parts of a single beam are used instead of the two separate coherent beams, which are guided through a uniaxial prism. In this way, holograms are also created with incoherent light, which can be precisely evaluated and on the basis of which the exact distance to the measured point can be determined. The optical distance sensors constructed in this way have an objective lens which acts as a collimating lens and is firmly connected to the respective distance sensor. For optical distance measurement, however, from many points of view, the largest possible measuring range is required with a variation of the measuring scale, i.e. the

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Working distance between the optical distance sensor and the object is the goal. To do this, these objective lenses have to be exchanged. The measurement options with such distance sensors are limited and exchanging the lenses is complex and expensive because several interchangeable lenses have to be provided.

Accordingly, it is an object of the invention to provide an auxiliary device for an optical distance sensor which expands the measuring possibilities of conventional optical distance sensors, in particular for measuring surface contours or profiles and/or the roughness of objects while maintaining a high measuring accuracy or resolution.

This is achieved according to the invention by the features of claim 1, in particular by the auxiliary device being arranged at a distance from the distance sensor, forming a separate unit. This makes it possible to create a particularly favorable distance measurement even with test object surfaces that are difficult to access, without the distance sensor and/or the test object or the object itself having to be moved. Such an auxiliary device can be produced inexpensively, can be used flexibly and enables high measurement precision.

According to a particularly advantageous embodiment, the objective lens is designed to be translationally movable relative to the distance sensor, preferably displaceable, rotatable and/or tiltable. This allows the objective lens to be positioned at an optimal working distance from the object surface, so that favorable measurement results can be achieved with a

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At the same time, an advantageously enlarged measuring range can be achieved for a fixed lens while maintaining a high level of measurement accuracy and resolution and keeping the diameter of the scanning light spot constant. If the objective lens is mounted so that it can rotate and/or tilt, the rotation or tilt can be controlled so that as much light as possible always falls on the photoreceiver of the distance sensor, so that even undercut surfaces can be measured to a limited extent.

Conveniently, the objective lens is connected to an actuator, preferably a piezoelectric actuator, a coil-magnet system or an electric motor for translating, rotating and/or tilting the objective lens.

If the auxiliary device or actuator is coupled to a control circuit for tracking the objective lens depending on a measured value provided by the distance sensor, the objective lens can always be automatically moved to such an extent that its distance from the surface of the object to be tested is maintained without leaving the sensor characteristic curve. Analogue or digital PID controllers are suitable for this, for example, because a displacement of the objective lens will generally occur more slowly than the measured value is recorded.

Advantageously, a beam-deflecting element, in particular a preferably partially transparent mirror, a prism or a diffraction grating, is arranged in the first beam path, i.e. between the distance sensor and the objective lens and/or in the second beam path, i.e. between the objective lens and the surface of the object.

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These measures make it particularly advantageous to arrange the actual distance sensor on a conventional feed device, such as that used for tactile roughness measurement. If the distance sensor is arranged horizontally, the beam deflecting element can deflect the measuring beam vertically downwards to the actual measuring location, i.e. to the surface of the object to be measured. In this way, object surfaces can be scanned particularly easily, precisely and cost-effectively with an advantageous measuring arrangement.

Advantageously, the beam-deflecting element is arranged so that it can be moved in translation, preferably displaced, rotated and/or tilted, preferably by means of an actuator to which the objective lens can also be attached. This allows the beam-deflecting element to be moved in the direction of the incident or reflected light beams in such a way that the measuring light spot of the light beams projected onto the surface of the object can be moved in a linear or planar manner over the object surface. In this way, advantageous linear or planar surface scanning can also be achieved without the object itself having to be moved.

The auxiliary device expediently has a measuring means for quantitatively measuring a translation, rotation and/or tilting of the objective lens and/or the beam-deflecting element, preferably in terms of amount and direction, wherein the measuring device preferably also comprises a control circuit for translation, rotation and/or tilting of the objective lens and/or the beam-deflecting element as a function of a signal from a photodetector, preferably

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of the distance sensor, measured intensity of the light rays reflected or backscattered from the surface of the object is coupled in such a way that the photodetector can receive the greatest possible light intensity.

The auxiliary device is expediently coupled to a calibration unit which enables a correction of a measured value detected by the measuring means and/or the distance sensor, preferably as a function of a degree of collimation of the light beams, by means of a fixed or dynamic calibration factor, so that the measured values can be subjected to a corresponding calibration factor as a function of the angular position of the beam-deflecting element and/or the objective lens.

Advantageously, at least one further collimation lens is arranged in the first beam path, i.e. between the distance sensor and the objective lens. This allows, for example, the distance between the distance sensor and the objective lens to be made as large as possible. It is also expedient if the collimation lens is arranged so that it can be moved in translation, preferably displaced, rotated and/or tilted, by means of an actuator, wherein preferably the auxiliary device has a measuring device for quantitatively measuring a translation, rotation and/or tilting of the collimation lens. Expediently, the auxiliary device or the collimation lens is coupled to a control circuit for translating, rotating and/or tilting the collimation lens depending on a measured value measured by the measuring device, preferably in such a way that even if the distances of the object or the object surface change during a measuring process, the

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the sensor characteristic can be measured and/or optimized lighting conditions can be created at the photodetector. Preferably, the controllers used for this purpose are
also as analogue or digital controllers, especially
designed as a PID controller.

The auxiliary device is expediently connected to the optical
Distance sensor, preferably with a first
This provides good protection against contamination and a compact measuring setup.

Furthermore, it may be advantageous if the auxiliary device is connected to the optical distance sensor (25) via a mono- or
Multimode fiber optic cable. This is especially important when using white light interference sensors of the
case, where a corresponding fiber optic cable of the same length is then inserted into a reference branch.

Consequently, according to the invention, a sensor is available

which is characterized by a miniaturized measuring head that can be used close to the measuring object, while the
Distance sensor itself including evaluation electronics further away
can be set up. In the last mentioned

In this case, the connection between the measuring head and the distance sensor can be established via a movable fiber optic cable.

The above measures contribute both individually and in
Combination with each other to extend the measuring capabilities of conventional optical distance sensors while maintaining a high measurement accuracy and resolution
at.

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. Further features, aspects and advantages of the invention are described below with reference to the single figure.
Description section can be removed.
5

A preferred embodiment of the invention is described below with reference to Fig. 1. This shows a
Schematic view of the auxiliary device coupled to the distance sensor and the object to be tested.

The auxiliary device 20 for the optical distance sensor 25 has the objective lens 26, the beam-deflecting element 31 and the collimation lens 35 and is spaced apart from the distance sensor 25 to form the separate unit 21.

For this purpose, the auxiliary device is preferably
provided with a housing.

The auxiliary device 20 has a first light inlet 42 for the light emitted by the optical distance sensor 25.

light rays and a first light exit 41 for the light rays reflected or scattered by the surface 37 of the object 38, so that the auxiliary device
20 is coupled to the distance sensor 25 via the first beam path 43. In the embodiment shown in Fig. 1,

game, the first light entry 42 and the first
Light exit 42 together or are identical. To generate
the light rays used for distance measurement
the optical distance sensor 25 has a not shown
light source, for example a laser diode.

The light rays penetrate the collimation lens 35 and emerge as substantially collimated light rays 30 in the direction of the beam-deflecting element 31.

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There, the light rays are deflected in the direction of the objective lens 26. The collimated light rays 30 then penetrate the objective lens 26 and leave the auxiliary device 20 through the second light exit 22 in the direction of the surface 37 of the object 38 to be tested, forming the second beam path 40 between the auxiliary device 20 or the objective lens 26 and the surface 37 of the object 38. There, the light rays are reflected or backscattered in the direction of the objective lens 26, after which they enter the objective lens 26 of the auxiliary device 20 through the second light entry, which coincides here with the second light exit 22. After penetrating the objective lens 26, the light rays leave it as essentially collimated light rays 30 in the direction of the beam-deflecting element 32, with the help of which they are deflected in the direction of the collimation lens 35. After penetrating the collimation lens 35, the light rays leave the auxiliary device 20 through the first light exit 41 in the direction of the distance sensor 25 and are available there for further measurement data evaluation.

The objective lens 26, which is designed as a collimation lens, can be moved relative to the distance sensor 25 or relative to the object 38 to be tested parallel to the optical axis 28 with the aid of the actuator 27, as indicated in Fig. 1 with the double arrow 29. In this way, the objective lens 26 can be positioned at an optimal working distance from the surface 37 of the object 38. This allows an enlarged measuring range for a fixed objective while maintaining a high measuring accuracy or resolution and keeping the diameter of the scanned object constant.

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The measuring light spot 33 is positioned at the same time. A measuring device (not shown in detail in the figure) for quantitatively measuring the translation or displacement path in terms of amount and direction is coupled to the objective lens. The measured values associated with the displacement of the objective lens 26 are added with the correct sign to the distance to the object 38 measured by the distance sensor 25 in order to obtain a total measured value which can then be displayed in a suitable manner or evaluated in another way.

If the light beams arranged on the sensor side in front of the objective lens 26 or between it and the distance sensor 25 are not perfectly collimated, the correct distance measurement value still depends on the movement, in particular the displacement of the objective lens 26. In this case, the sensor measurement value can advantageously be corrected using a correction table. The auxiliary device 20 is therefore expediently coupled to a calibration unit which enables a correction of a measurement value recorded by the measuring device and/or the distance sensor 25, preferably depending on a degree of collimation of the light beams, using a fixed or dynamic calibration factor, so that the measurement values can also be subjected to a corresponding calibration factor depending on the angular position of the beam-deflecting element 31 and/or the objective lens 26 .

The beam-deflecting element 31 and the collimating lens 35 are arranged so as to be translationally movable or displaceable by means of the actuators 32 and 36, respectively, as indicated in Fig. 1 by the double arrows 44, 46 and 34, respectively. It is understood that both the beam-deflecting element 31 and the

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Collimation lens 35 as well as the objective lens 26 by means of the mentioned actuators 46, 36 and 27 respectively by several
Axes can be moved, tilted and/or rotated.

If the objective lens 26 is tiltable and, if necessary,

is rotatably mounted and whose movement is controlled by means of suitable measuring devices (not shown in the figure) as well as analogue or digital controllers, in particular PID controllers, so that as much light as possible always falls on the photoreceiver preferably arranged in the distance sensor 25, even undercut surfaces of the object 38 can be measured. If the light rays are directed relative to the optical axis 28 or in the direction of the incident
or reflected light rays are deflected,

for example by tilting and/or rotating the beam-deflecting
Elements 31, by tilting and/or rotating
the objective lens 26 or by tilting and/or rotating the auxiliary device 20 itself, a
appropriate deflection of the measuring light spot 33 to achieve a linear or planar surface scanning of the object 38,
without having to move it yourself.

The auxiliary device 20 can be used particularly advantageously together with distance sensors which have a collimated or approximately collimated light beam on the sensor side
in front of the objective lens. Preferably
These enable interferometric or holographic distance measurement, whereby distance sensors in particular
with a so-called "phase shift" evaluation, especially linear conoscopes can be used. These distance sensors
can be used with the auxiliary device 20 in such a way
be extended or supplemented so that for a fixed predetermined

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an objective lens, this can be positioned at an optimal working distance from the surface 37 of the object 38 and consequently favorable measurement results can be achieved with a simultaneous increase in the measuring range and while maintaining a high measurement accuracy and resolution.

The distance sensor 25 and/or the auxiliary device 20 can advantageously be attached to a conventional high-precision feed device (not shown in the figure), for example a tactile roughness measuring device. This provides a particularly cost-effective solution for high-precision measurement of the surface contours or roughness of objects.

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GEITZ & GEITZ Patent Attorneys

Kriegsstr. 234 · 76135 Karlsruhe

Attorney file: 004181

Applicant: Ulrich Breitmeier

Erzbergerstraße D-76133 Karlsruhe 10

LIST OF REFERENCE SYMBOLS

20 Auxiliary device 21 Separate unit

22 second exit

23 second entry

25 Distance sensor

26 Objective lens

27 Actuator

28 Optical axis

29 Double arrow

30 rays of light

31 beam deflecting element

32 Actuator

33 Measuring light spot

34 Double arrow

35 collimation lens 36 actuator

37 Surface

38 Object

40 second beam path

41 first exit 42 first entry 43 first beam path

Claims (15)

1. Auxiliary device ( 20 ) for an optical distance sensor ( 25 ), which preferably enables a distance measurement by means of classical or white light interferometry, with an objective lens ( 26 ) designed as a collimating lens, wherein a first light inlet ( 42 ) and a first light outlet ( 41 ) preferably coinciding therewith are provided for light rays ( 30 ) reflected or backscattered from a surface ( 37 ) of an object ( 38 ), so that the auxiliary device ( 20 ) can be coupled to the distance sensor ( 25 ) via a first beam path ( 43 ), wherein the light rays ( 30 ) assigned to the first beam path ( 43 ) are essentially collimated in front of the objective lens ( 26 ), and wherein a second light outlet ( 22 ) and a second light inlet (23) preferably coinciding therewith are provided for the light rays (30) reflected or backscattered from the surface ( 37 ) of an object ( 38 ). ) of the object ( 38 ) is provided, so that the auxiliary device ( 20 ) can be coupled to the object ( 38 ) via a second beam path ( 40 ), and wherein the auxiliary device ( 20 ) is arranged at a distance from the distance sensor ( 25 ) to form a separate unit ( 21 ). 2. Auxiliary device according to claim 1, characterized in that the objective lens ( 26 ) is designed to be translationally movable, preferably displaceable, rotatable and/or tiltable, relative to the distance sensor ( 25 ). 3. Auxiliary device according to claim 2, characterized in that the objective lens ( 26 ) is connected to an actuator ( 27 ) for translating, rotating and/or tilting the objective lens ( 26 ). 4. Auxiliary device according to one of claims 2 or 3, characterized in that it is coupled to a control circuit for tracking the objective lens ( 26 ) as a function of a measured value supplied by the distance sensor ( 25 ). 5. Auxiliary device according to one of claims 2 to 4, characterized in that a beam-deflecting element ( 31 ), in particular a preferably partially transparent mirror, a prism or a diffraction grating, is arranged in the first beam path ( 43 ) and/or in the second beam path ( 40 ). 6. Auxiliary device according to claim 5, characterized in that the beam-deflecting element ( 31 ) is arranged to be translationally movable, preferably displaceable, rotatable and/or tiltable, preferably by means of an actuator ( 32 ). 7. Auxiliary device according to one of claims 5 or 6, characterized in that it comprises a measuring means for quantitatively measuring a translation, rotation and/or tilting of the objective lens ( 26 ) and/or the beam-deflecting element ( 31 ). 8. Auxiliary device according to claim 7, characterized in that it is coupled to a control circuit for translating, rotating and/or tilting the objective lens ( 26 ) and/or the beam-deflecting element ( 31 ) as a function of an intensity of the light rays reflected or backscattered by the object ( 38 ) measured by a photodetector in such a way that the photodetector can receive the greatest possible light intensity. 9. Auxiliary device according to one of claims 7 or 8, characterized in that it is coupled to a calibration unit which enables a correction of a measured value detected by the measuring means and/or the distance sensor ( 25 ), preferably depending on a degree of collimation of the light beams, by means of a fixed or dynamic calibration factor. 10. Auxiliary device according to one of claims 1 to 9, characterized in that at least one collimation lens ( 35 ) is arranged in the first beam path ( 43 ). 11. Auxiliary device according to 10, characterized in that the collimation lens ( 35 ) is arranged to be translationally movable, preferably displaceable, rotatable and/or tiltable, by means of an actuator ( 36 ). 12. Auxiliary device according to one of claims 10 or 11, characterized in that it comprises a measuring means for quantitatively measuring a translation, rotation and/or tilting of the collimation lens ( 35 ). 13. Auxiliary device according to claim 12, characterized in that it is coupled to a control circuit for translating, rotating and/or tilting the collimating lens ( 35 ) as a function of a measured value measured by the measuring means. 14. Auxiliary device according to one of claims 1 to 13, characterized in that it is firmly connected to the optical distance sensor ( 25 ), preferably to a tube containing the first beam path. 15. Auxiliary device according to one of claims 1 to 14, characterized in that it is connected to the optical distance sensor ( 25 ) via a mono- or multimode fiber optic cable.