DE102008062458B4 - Measuring method for laser-based measurement of workpieces, assemblies and tools - Google Patents

Abstract

Measuring method for laser-based measurement of workpieces, assemblies and tools using a laser (1) as a light source and an optical sensor (2) designed as a CCD or CMOS matrix sensor as Messsignalempfänger (2), wherein an object to be measured (4) in the Beam path of the laser (1) is introduced such that only one of the object to be measured (4) uncovered part of the laser radiation (3) on the optical sensor (2), characterized in that the object to be measured (4) and the laser (1) are positioned relative to one another such that the polarization direction of the linearly polarized laser radiation (3) corresponds to the direction of a main edge of the object (4) to be measured, such that at least one polarization filter (5) is introduced into the beam path of the laser (1) is that its orientation of the plane of polarization corresponds to the direction of the linear polarization of the laser radiation (3) that the optical sensor (2) gegenüb it is the main edge of the object to be measured (4) is rotated about an approximately in the direction of the beam path of the laser radiation (3) facing axis, in such a way that the alignment of the lines of the CCD or CMOS matrix sensor (2) by an angle > 0 ° and <45 ° relative to the main edge of the object to be measured (4) is rotated, and that a signal processing by means of the sensor (2) detected pixel signals for detecting and measuring a running in the direction of the main edge contour of the object to be measured (4 ) is performed by means of a regression calculation.

Description

The invention relates to a measuring method for laser-based measurement of workpieces, assemblies and tools during manufacturing processes in mechanical and plant engineering.

The measured data obtained can be used to compensate in particular the dimensional trends or the dimensional drift due to thermally induced deformations and / or as a result of tool wear. Depending on the design of the measuring procedure for the laser-based measurement of workpieces, assemblies and tools, dimensions and shapes as well as the position of geometric elements relative to each other can be measured.

At present, tactile, inductive and optical measuring systems are used for workpiece measurement.

Tactile and inductive measuring systems are less suitable for the process-accompanying measurement of workpieces and tools, since they either have a high mechanical and wear sensitivity or have unsatisfactory accuracies in the case of inductive measuring systems.

The more suitable optical systems operate as either incident or backlight systems, with only the backlight systems achieving reasonably satisfactory measurement accuracy.

The basic concept of a backlight system is based on a diffuse light source (eg halogen lamp, fluorescent tube, flash lamp, etc.) and a high-resolution camera, between which the measurement object is located and its recorded by the camera silhouette is computer-aided evaluation, for. B. to determine the target-actual deviation of a measured object. Such solutions are for. As in the measuring systems of Omron and Zoller included (Pfeifer, T. et al., Optoelectronic method for measuring geometric sizes in manufacturing, contact & study, Volume 405, expert-Verlag, Ehningen at Böblingen, 1993, p 166 ff.) ,

According to another concept - the laser scanner - a laser beam is deflected by means of a mostly rotating mirror system in order to scan an object to be measured. Photodiode-triggered the respective actual measurement of an object is calculated with the aid of the simultaneously detected mirror deflection. Such solutions can be found at www.betalasermike.com. The main disadvantage of the aforementioned optical surveying solutions is the high cost that the very expensive camera or scanner-based systems cause in their implementation. An additional disadvantage is the fault influence, which can cause incident extraneous light.

Devices for laser-based measurement of workpieces outside of machines are z. B. after DE 37 13 109 C2 known, however, the laser beam is moved here with a separate complex device and determined from the context of measured interruption time of the laser beam through the workpiece whose dimension. Such a method is inconvenient for the detection of workpiece geometries in operational machining processes because of its complicated and expensive implementation.

According to the DE 40 30 994 A1 For example, a geometric inspection of rotationally symmetrical workpieces can be carried out by combining a laser measuring head with a mechanical probe. Again, the field of application is limited to the non-operational area. The implementation effort is disproportionately large, since even with this solution laser measuring head and button must be moved and controlled separately.

In all the above-mentioned optical systems for measuring workpieces, assemblies and tools is also the requirement for a dense positioning of the optical sensor on the measurement object in order to limit extraneous light influences.

From the US Pat. No. 6,055,329 For example, a method and apparatus for determining dimensional deviations of a workpiece from predetermined pattern workpieces are known. Using a laser light source, a parallel beam is generated which impinges on discrete light sensor elements to generate pixel data. In the beam path of the parallel beam, the workpiece to be measured is introduced, so that the silhouette of the workpiece to be measured is displayed as a shadow image on the light sensor elements. The discrete pixel data of the light sensor elements are electronically processed to determine and the dimensional deviation of the workpiece. However, the achievable with the solution described above accuracy of the measurement results is unsatisfactory.

In the US 4,781,463 A For example, a method and apparatus for determining the location and dimensions of an article are described. The object is imaged on a matrix formed by rows and columns of pixels, the edges of the object not being parallel to the rows or columns of the matrix. The position and dimensions of the object are calculated using statistical calculation methods, such as regression or compensation calculations. For measuring workpieces, assemblies and Tools during manufacturing processes in mechanical and plant engineering, the solution described is not suitable.

The disadvantages of the prior art can be summarized in high implementation costs, often unsatisfactory measurement accuracy and reliability, lack of robustness during use in the manufacturing process and ultimately limited application.

To avoid the disadvantages of the solutions of the prior art, the object is to develop a measuring method for laser-based measurement of workpieces, assemblies and tools that can be executed by simple and robust assemblies, has a high accuracy even under unfavorable lighting conditions and with reduced Cost is feasible. In addition, a small size of the device with which the measuring process can be carried out is generally desirable.

According to the invention this object is achieved by a measuring method for laser-based measurement of workpieces, assemblies and tools, having the features of the first claim. Claim 2 describes an advantageous embodiments of the measuring method.

Here, the essence of the invention consists in the fact that in the combination of a laser as a measuring light source emitting linearly polarized light, and an optical sensor in the form of a CCD or CMOS matrix sensor as Messsignalempfänger a polarization of the linearly polarized laser radiation adapted polarization filter in the laser beam is introduced, that the object to be measured is positioned in the linearly polarized laser radiation, that the polarization direction of the linearly polarized laser radiation corresponds to the direction of a major main edge of the object to be measured that the measuring signal receiver, ie the CCD or CMOS matrix sensor, with respect to this Is arranged rotated in such a way that the alignment of the rows of the matrix sensor with respect to the main edge of the object to be measured by an angle greater than 0 ° and less than 45 °, preferably by an angle between 4 ° and 10 °, is rotated and a signal processing by means of the sensor ( 2 ) detected pixel signals for detecting and measuring a running in the direction of the main edge contour of the object to be measured by means of a regression calculation is performed.

In this case, the measuring signal receiver is preferably rotated about an axis pointing approximately in the direction of the beam path of the laser radiation.

By introducing a polarization filter adapted to the polarization direction of the linearly polarized laser radiation into the laser beam, a considerable part of the extraneous light can be masked out and kept away from the optical sensor.

It may be expedient, in particular in unfavorable light conditions, to provide two polarization filters, one of which is oriented such that its polarization plane corresponds to the polarization direction of the laser radiation, whereas the second polarization filter is introduced so that its polarization plane is rotated relative to the first polarization filter. In such an arrangement, a considerable part of the extraneous light is retained by the first polarization filter, while the laser radiation passes through the polarization filter almost undamped. By the second polarizing filter of the remaining part of the extraneous light is almost completely retained and attenuated the laser radiation. An optimization can be achieved by changing the direction of the polarization plane of the second polarization filter.

It may also be expedient to provide, in addition to one or two polarization filters, a color filter whose transmission wavelength corresponds to the wavelength of the mostly monochrome laser light. As a result, the extraneous light influence on the optical sensor can be further reduced.

The filters should be placed as close to the optical sensor as possible. It is advantageous to accommodate the sensor and the filter in a predominantly opaque housing with a filter as an inlet window for the laser radiation.

The resolution and thus possible measurement accuracy of the device for laser-based measurement of workpieces, assemblies and tools is primarily dependent on the line spacing of the sensor matrix. Therefore, an increase in resolution is possible by inclining the matrix with respect to the direction of the laser radiation. Another way to increase the resolution is to fan out the laser radiation cone-shaped.

The arrangement of the measuring signal receiver, which is rotated with respect to the main edges of the workpiece to be measured, avoids line-parallel impingement of the laser light passing the main edge of the measuring object on the matrix sensor, thereby achieving a very considerable improvement in the measuring accuracy.

A further improvement of the measuring accuracy is achieved by the signal processing of the Sensor signal can be achieved by means of a regression calculation by known mathematical methods. Thus, the measurement accuracy can be increased beyond the resolution of the CCD or CMOS matrix sensor. In the simplest case this can be a linear regression calculation to improve edge detection.

The following advantages are associated with the inventive, surprisingly simple solution of a measuring method for laser-based measurement of workpieces, assemblies and tools:
The construction of a device with which the measuring method can be carried out is very simple with small dimensions in relation to previous camera and scanner solutions. Instead of elaborate optical systems or complicated movement mechanisms, only one or two polarization filters and possibly a color filter are required in addition to the robust components laser light source and optical matrix sensor.

Due to a high realizable light intensity of the laser radiation compared to extraneous light this is in a variety of applications already by the first polarization significantly attenuated extraneous light for subsequent image evaluation of the sensor image without significant influence, so that the invention in its simple design, d. H. with only one polarizing filter, a large number of practical applications.

The measuring method for the laser-based measurement of workpieces, assemblies and tools thus offers the possibility, with little effort, d. H. with simple and robust assemblies to achieve a high quality of measurement. An elaborate lens optics, as used on camera systems, is not required.

The invention will be explained in more detail below using an exemplary embodiment.

The accompanying drawing shows a schematic representation of a device for carrying out the measuring method for the laser-based measurement of workpieces, assemblies and tools with two polarizing filters and a color filter.

According to the drawing, the device consists of a laser 1 and a CCD matrix sensor 2 , In the beam path of the laser radiation 3 the laser 1 is the measuring object 4 while two polarizing filters 5 and 6 as well as a color filter 7 between the measuring object 4 and the CCD matrix sensor 2 in the beam path of the laser radiation 3 are arranged. The measurement object 4 is so in the beam path of the laser radiation 3 positioned that it is the laser radiation 3 not completely obscured and that the measurement object 4 and the laser 1 are positioned to each other so that the polarization direction of the linearly polarized laser radiation 3 the direction of a main edge of the measurement object 4 equivalent. The CCD matrix sensor 2 is opposite the main edge of the measurement object 4 around one in the direction of the beam path 3 the laser radiation 3 pointing axis rotated by an angle between 4 ° and 10 °. The CCD matrix sensor 2 and the polarizing filter 6 as well as the color filter 7 are in an opaque housing 8th with the polarization filter 5 as an inlet window for the laser radiation 3 accommodated.

The polarization filter 5 is oriented so that the orientation of its polarization plane of the orientation of the linearly polarized laser radiation 3 corresponds during the polarization filter 6 oriented in a different orientation of the polarization plane. In this way, the quasi-series polarizing filter 5 and 6 diffuse foreign light components to a proportion of at least 50% and usually retained more than 80%. Further filtering of extraneous light is carried out by the color filter 7 , whose transmission curve is wavelength-wise designed so that the color filter 7 the wavelength of the laser light of the laser 1 optimal passage and light of different wavelength is maximally damped.

The filter series from polarizing filters 5 and 6 as well as color filters 7 continuous laser radiation 3 then partially hits the target 4 and is reflected or absorbed there, leaving only the contour of the measured object 4 unlocked part of the laser radiation 3 on the CCD matrix sensor 2 meets. Depending on whether a sensor point of the CCD matrix of a laser beam 3 is lit or not, creates a corresponding pixel signal. From the totality of the signals of the individual sensor points is then in a known manner, the geometric detection and metrological evaluation of the measurement object 4 possible.

The fineness of the evaluation, ie the measurement accuracy, is dependent on the resolution of the CCD matrix sensor 2 ie the size, number and spacing of the sensor points within the matrix.

A regression calculation is performed to determine the measurement result.

LIST OF REFERENCE NUMBERS

1

laser

2

CCD matrix sensor

3

laser beams

4

measurement object

5

polarizing filter

6

polarizing filter

7

color filter

8th

casing

Claims (2)

Measuring method for the laser-based measurement of workpieces, assemblies and tools using a laser ( 1 ) as a light source and a CCD or CMOS matrix sensor formed as an optical sensor ( 2 ) as measuring signal receiver ( 2 ), where an object to be measured ( 4 ) in the beam path of the laser ( 1 ) is introduced such that only one of the object to be measured ( 4 ) not hidden part of the laser radiation ( 3 ) on the optical sensor ( 2 ), characterized in that the object to be measured ( 4 ) and the laser ( 1 ) are positioned relative to one another such that the polarization direction of the linearly polarized laser radiation ( 3 ) the direction of a main edge of the object to be measured ( 4 ) corresponds to that in the beam path of the laser ( 1 ) at least one polarizing filter ( 5 ) is introduced such that its orientation of the plane of polarization of the direction of the linear polarization of the laser radiation ( 3 ) corresponds to that the optical sensor ( 2 ) opposite the main edge of the object to be measured ( 4 ) about in the direction of the beam path of the laser radiation ( 3 ) is rotated in such a way that the alignment of the lines of the CCD or CMOS matrix sensor ( 2 ) by an angle> 0 ° and <45 ° with respect to the main edge of the object to be measured ( 4 ) and that a signal processing by means of the sensor ( 2 ) detected pixel signals for detecting and measuring a running in the direction of the main edge contour of the object to be measured ( 4 ) is performed by means of a regression calculation. Measuring method according to claim 1, characterized in that the optical sensor ( 2 ) opposite the main edge of the object to be measured ( 4 ) about in the direction of the beam path of the laser radiation ( 3 ) is rotated in such a way that the alignment of the lines of the CCD or CMOS matrix sensor ( 2 ) by an angle between 4 ° and 10 ° with respect to the main edge of the object to be measured ( 4 ) is twisted.

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