DE102004053659B3 - Non-contact measurement of the temperature profile of a surface, along a line, uses a rotating and transparent polygon scanner to pass emitted and/or reflected light from the surface to a focusing lens - Google Patents

Abstract

For the non-contact detection of thermal characteristics of the surface of an object, along a line (24), emitted and/or reflected light is detected by a focusing lens (22) with a transparent and rotating polygon scanner (16). The scanner has an even number of paired facets so that, according to the angular lie of the scanner, the temperature-related emission and/or reflected light is detected continuously through the parallel offset of the lens. For the actual measurement position on the surface to be made visible, a multi-spectral light source (40) with a wavelength outside the measurement wavelength band is coupled coaxially to the light beam. A mechanism (28) determines the angular position of the polygon scanner and an integrated confocal distance measurement system (40,42,44,45) determines the geometric height profile of the surface along the line, using the multi-spectral light source (40) and a spectral analysis unit (44). The assembly has a rapid Ge detector (14) to detect temperatures from 300[deg]C.

Description

The The invention relates to a method and a device for non-contact Detection of thermal properties of an object surface after the The preamble of claim 1 or claim 4.

In In many areas of technology, it depends on temperature profiles to pinpoint. This is in principle also with discrete point temperature sensors possible, along the surface of the specimen to be detected a desired one Line are applied. In general, this procedure sets a stationary one and possibly unparalleled application not considered here ahead. The present application is about continuous Processes, so that one such solution out of the question

Around to carry out the measurement proposed here as completely as possible can, does she have to contactless and done very fast.

It sensors are known which measure the temperature of a measuring point contactless to capture. With most known sensors of this kind can be only temperature profiles of the scanned surface along the direction of movement of the process. The task at hand is a (nearly) complete one and spatially resolving Detection of temperature profiles perpendicular to the direction of movement of the Process to implement. The known sensors leave one such measurements are not, since they are either stationary mounted and thus only in the "field of view" of the sensor located Workpiece surface and along the line of movement can capture the temperature or, when they are swung back and forth across the line of motion or translational with a parent electromechanical system to be moved, never at fast-running Processes due to the existing mechanical inertia of the sensor and the parent Movement system, the desired workpiece surface temperature lükkenlos (or almost completely) can capture.

It For example, sensors are known in which only the measuring beam via a or deflecting multiple reciprocating mirrors so that one perpendicular (or nearly perpendicular) to the line of motion lying measuring track is formed. Here is actually a certain spatial resolution achieved, but the process still has significant limitations, because the swivel mirrors due to its own mechanical inertia no linear, but mostly perform a sinusoidal motion, so that the Dwell time of the measuring spot is position dependent on the workpiece surface and thus also the detected measurement affected. Although the achievable measuring speed relatively high, but limited by the mirror inertia anyway, so that the Measurement in very fast processes can not be complete. One Another important disadvantage of the mentioned method is that that the measuring beam always the angle and thus the distance to the workpiece surface during the Swinging motion changes and thus the measurement of the most unknown emission characteristic strong to the surface to be measured affected becomes. Add to that the "field curvature" of the measuring line, i.e. that without an expensive corrective optics the measurement points on a curved line lie in the scan plane. The "punctiform contactless measuring temperature sensors " Furthermore the surface temperature is not in a nearly dimensionless point, but usually in a round one measuring spot with a diameter of about 3 to 15mm. Capture these sensors gapless the integral of the temperature of a wide trace according to the spot diameter along the direction of movement of the workpiece surface, here due to optical imaging nonlinearities, due to the shape of the measuring spot and due to the temperature profiles to be detected transversely to the direction of movement systematic measurement errors occur, which is a spatially resolving Temperature measurement impossible do. As an indication, it should be noted that a circular Temperaturmeßfleck a much higher nonlinear measuring sensitivity in the middle than at the edge of the measuring spot, since the length of the measuring distance in the middle of the measuring spot corresponds to the diameter and is shorter at the edge of the measuring spot, that the finally detected temperature-dependent measured value of the local emissivity and from the fourth power of the local Lich existing temperature as well as the location-dependent radiation characteristic depends on the workpiece surface.

Another known class of sensors, which allows a spatially resolved temperature measurement transverse to the direction of movement, consists of line-shaped point-shaped temperature-sensitive sensors (similar to line scan cameras). These sensors are closest to the task at hand, but they also have serious disadvantages. Thus, the material selection of the sensor is limited and thus the measurable temperature range depends on the available sensor materials. Furthermore, the sensor line has gaps between the individual sensors, so that the gaplessness of the measurement is no longer given with sharp imaging optics. Another disadvantage is the uneven sensitivity of the individual dot sensors of the line (manufacturing tolerance). This can usually be calibrated, but represents a further complication and increase in the cost of the measuring system. The cost of such a measuring system are very high and almost exponentially dependent on the number of individual sensors of the line, whereby the complicated required imaging optics has a significant share. Due to the line costs and available materials as well as due to the size of such components, the realization of two- or multi-wavelength pyrometers is unthinkable and not yet realized on an industrial scale.

The only temperature sensor class, which in principle is a solution of task, consists of individual sensors, the measuring beam via rotating mirrors (such as e.g. Polygon scanners) is deflected. In this case, the Problems associated with the mechanical inertia of the scanner. at very big Must have rotational speeds Although the scanner balanced and equipped with air bearings (or similar) be, but with this technique can be sufficient in principle size and constant measuring speeds be achieved. However, problems with polygon scanners are: a) the polygon size, b) the in the axis of rotation of the polygon lying drive element with his Size, c) the above-mentioned Field curvature, which can only be compensated with expensive lenses, d) the most unused relatively large measuring angle and e) the constant change the measuring angle to the workpiece surface. outgoing from a common one Facet size of 10mm × 10mm, for example the diameter of a 12-fold polygon already about 40mm. The rest here mentioned disadvantages were already in the other sensor classes treated.

In the field of non-contact temperature measuring numerous patents have been filed, but compared to the present invention have one or more disadvantages, the present method and the exemplary device not the temperature measurement itself, but claimed the spatial resolution of the measurement and the technically advantageous solution. For the one- or two-wavelength pyrometers with and / or without the use of a reference radiation source, the following patent applications are cited in detail without being exhaustive: US 3,433,052 / US 3,442,591 / US 3,611,806 / US 3,619,059 / US 3,796,099 / US 4,225,230 / US 4,465,382 / US 4,470,710 / US 4,647,774 / US 4,647,775 / US 4,924,478 / US 5,231,595 A , For the multispectral measurement methods with and without the use of a reference measurement, the following patent applications are cited without any claim to completeness: US 3,822,098 / US 4,708,493 / US 4,880,314 / US 5,868,496 A ,

For measuring methods with targeted measurement of surface reflectivity, the following patent applications are cited without any claim to completeness: US 4,417,822 / US 4,579,463 , For temperature scanners, the US 4,439,049 cited. For measuring methods for determining the position of the Planck curve, the US 4,605,314 and finally the US 4,605,314 and US 5,231,595 A cited for the wavelength-dependent separation of the measured signals. For the confocal distance measurement, the following patent applications are cited without any claim to completeness: US 3,788,741 / U.S. 4,081,215 /
US 4,600,831 / US 4,711,578 / US 5,033,856 and GB 2 077 421 A , The cited protective rights have strong deviations from the device claimed here and in particular by the claimed scanning method. For completeness, the class of Triangulationsmeßmethoden with fixed beam profile projection or the projection generated by means of moving deflecting mirror called here with respect to the claimed Profilmeßverfahren the object surface without citing specific property rights, since they have significant disadvantages compared to the claimed method of measurement and also in principle in State of the art have been described.

Out The prior art is the principle of the plane-parallel plate to correct the offset of a beam path known. this will mostly stationary used as manual fine adjustment. The generated parallel beam offset depends on Angle of the plate used to the optical axis, of the thickness and the refractive index of the plate.

A fast profile measurement can be only realize, in the first place, the inertia of the mechanical Scanner system is minimized or eliminated. This can be easiest by transforming the back and forth movement in realize a rotational movement at a constant speed. Further are the geometric conditions of a temperature measurement for accuracy the measurement crucial, i. the measuring angle to the object surface must be accurate Measurement be the same, because the emissivity is dependent on the measuring angle and should therefore be Scan as possible be equal. In the assumption that the Therefore, most of the technical surfaces to be measured are flat ensure a corresponding profile measurement that the measuring beam in each point of the profile measurement satisfies this condition, i. it becomes a telecentric measuring arrangement needed. Further, the object of this invention is to limit the scan angle to limit to the required range.

The DE-OS 2 310 472 discloses an arrangement with which an infrared image an object scanned line by line and on a video monitor is pictured.

The JP 05 026 733 A discloses a thermo meter with a rotating mirror.

The EP 1 118 848 A2 discloses a device for detecting the surface temperature of a heating element whose thermal radiation is directed onto a pyrometer by means of a rotating reflector.

task The invention is a method and an apparatus of the initially mentioned type to improve such that with simple means and high Accuracy one (almost) complete and spatially resolving Acquisition of temperature profiles can be achieved.

Is solved This object is achieved by a method according to claim 1 or by a Device according to claim 4th

advantageous Embodiments are the subject of the dependent claims.

One embodiment The invention results from the following description in FIG Connection with the drawings. Show:

1 Schematic representation of a temperature scanner according to the invention;

2 perspective view of a scanner cage with air drive pockets and holders with air nozzles;

3 Schematic representation of an adjustment device with a visible laser diode;

4 Schematic representation of an embodiment of a temperature scanner with integrated confocal distance meter;

5 perspective view of a standard transparent cube scanner;

6 Side view of in the 5 shown cube scanner, in which the generation of an offset of the beam path is perpendicular to the scan plane recognizable.

To implement the measuring method according to the invention, here is a sensor system 10 proposed in which a measuring beam 12 between a measuring point on the object surface and a detector device 14 for detecting the surface temperature of the object via a transparent polygon scanner for the measuring wavelengths 16 with an even number of facets A, AA, B, BB (see 5 ) in a rotatably mounted and air driven cage 18 (please refer 2 ) is mounted, so that the measuring beam 12 according to the plan parallel plate principle of rotating polygon scanner 16 is deflected, wherein for detecting the current scanner angular position, a second measuring device 20 is used, which preferably optically (like a light barrier) works and transverse to the optical axis OA of Sen sorsystems 10 is arranged. The angular position detection of the polygon can of course be done by other means.

In the 1 is with 21 a screen and with 23 a filter indicated.

The cage 18 has the same even number of openings as the transparent polygon scanner 16 , and the position of the cage openings corresponds to the position of the polygon facets. The opposing facets are arranged parallel to each other. Preferably, the number of polygon facets 4 ie the transparent polygon scanner 16 is a transparent cube scanner. In the following, only the cube scanner will be referred to. The remaining webs between the cage openings of the cylindrical outer wall are used to attach the transparent cube (at the corners) and to cover the optically ineffective angle of the scanner (s. 1 and 2 ).

The cube scanner becomes the focal length of a focusing lens 22 somewhat shortened, and it also creates a small, for normal applications negligible field curvature of about 50 .mu.m at a measuring line length of the test section 24 of ± 2 mm. At the same time, the transmission of the cube scanner changes depending on the instantaneous angle of the irradiated optical surfaces to the optical axis OA of the measuring device and is at most 90 ° (perpendicular to the optical axis OA).

The device 10 is designed so that the field curvature with respect to the detected Temperaturmeßwert at a flat object surface compensates for the angle-dependent transmission of the cube scanner at least partially. This compensation can also be realized for differently shaped object surfaces.

In an advantageous variant of the device according to the invention, at least one pair of the above-mentioned polygon facets is not parallel to the scanner rotation axis 29 designed so that the beam path exits the plane of rotation of the scanner, so that on the object surface two or more measuring lines offset in the direction of the process movement, or perpendicular to the scanning plane arise (s. 6 ). This is advantageous since the measurement is a quasi-stationary overall picture of the item to be measured le on the object surface.

If required (e.g., limited space for sensor mounting), the Beam path between the dice scanner and the object surface over another Mirror to be deflected (not shown).

The air drive was designed to keep the size of the scanner as small as possible. The scanner speed can be adjusted via the air pressure and is not regulated for cost and space reasons. There are also other constructive variants for driving the scanner conceivable. For example, the drive required here can act electromagnetically, without contact, like a stir bar in the chemical industry. The air drive mentioned here consists of one or more nozzles that blow tangentially on the side end faces of the cage, where small pockets 25 are formed in the outer wall of the cage. Preferably, two air nozzles 27 (one on each side of the cage) used (s. 2 ).

There detects the speed of the scanner can, in the case of higher claims to the accuracy of maintaining a constant speed of Air pressure of the scanner drive via a controllable throttle or over a valve and a corresponding controller are controlled so that a desired speed is set and held.

The angular position of the cube scanner indirectly corresponds to the position of the temperature measuring spot in the plane of rotation of the scanner. As a light source for the angular position detection is preferably a fiber-coupled LED 26 and for position detection a position sensitive diode (PSD) 28 used. The resolution of the reference measurement is virtually infinite since the PSD 28 micrometer accurate forms the position of the center of gravity of the incident light beam. By using a short piece of optical fiber, the reference beam was sufficiently well shaped to be homogeneous and completely on the face of the PSD 28 was projected (s. 1 ). The measured value (s) detected are correlated with the respective angular position of the rock scanner and correspondingly taken into account by a higher-level evaluation device.

The setup was done, for example, with a fast Ge detector 14 equipped, whereby temperatures from about 300 ° C can be detected. A two-wavelength temperature measurement can also be realized in the manner presented. The chopping effect of the cube scanner also makes it possible to use inexpensive IR pyrodetectors as sensors for detecting the surface temperature of the object.

The local resolution the temperature measurement is in practice <0.1 mm. At the edge of the measuring range decreases the sensor sensitivity, since the transparency of the cube at huge Deflection angles decreases. However, this systematic mistake can be wegkalibrieren. For example, the working distance of the scanner is 130mm and the scanning distance on the object surface ± 2 mm. At the maximum achievable Speed of the dice scanner reaches the actual Scan speed 120 m / s. Despite the low compressed air consumption For example, speeds up to 60,000 rpm have been reliably achieved, i. 4000 Temperature profiles per second (4 profiles per revolution). For one permanent use at this speed, the scanner must be balanced and possibly air bearings are used. The example here These dimensions can be scaled arbitrarily. The used Compressed air must be free of particles, oil and be water.

• a) Falls ein unbeweglicher Punkt in der Mitte der Meßstrecke auf der zu messenden Objektoberfläche benötigt wird, so ist die Einkopplung zwischen Scanner und Objekt vorzunehmen, oder
• b) Falls ein sichtbarer Strich im Bereich der Meßstrekke auf der Objektoberfläche benötigt wird, so ist die Einkopplung im kollimierten Teil des Strahlenganges zwischen Würfelscanner und Temperaturmeßvorrichtung vorzunehmen.

In order to improve the practical use of the device according to the invention, a visible marking on the object surface is required in order to make the exact position of the measuring area visible for adjustment purposes. Due to the special features of the device, two basic application-dependent arrangements are proposed here for advantageous coupling of the visible radiation of a laser diode into the beam path of the scanner:

• a) If an immovable point in the middle of the measuring section on the object surface to be measured is required, then the coupling between scanner and object is to be made, or
• b) If a visible line is required in the area of the measuring path on the object surface, the coupling in the collimated part of the beam path between the cube scanner and the temperature measuring device must be carried out.

Particularly advantageous is a separate arrangement in which the collimated radiation of a visible laser diode 30 , which is associated with a Kollimationsoptik, by a 90 ° prism 32 two equal beams are shared, using two adjustable mirrors 34 be deflected symmetrically to the optical axis of the measuring device so that they are exactly in the middle at 36 cross the scanner temperature measuring section. This will be the exact location of the test section 24 displayed (s. 3 ). This device can be located either in the scanning plane or in the mounting flange of the scanner (not shown) and inclined to the optical axis of the scanner so that the intersection of the two marking beams of the visible laser diode is exactly in the middle of the scanner track.

The visible marking device may be combined with a device measuring at the same wavelength to provide the back-reflection from the object surface for the purpose of obtaining further surface information. Among other things, such a measurement is suitable for determining the surface reflectivity and / or emissivity and can be extended by one or more visible and / or invisible wavelengths for complex and irregular courses of said properties. In this case, a very precise and rapid measurement of the temperature along the scanner Temperaturmeßstrecke is possible.

Further is the incorporation of a matrix camera in the Strahlgan the device according to the invention provided to improve the practical use of the device, the camera always at a certain preselectable angular position of the scanner cube is triggered to get a stationary picture (not shown). Because the scanner speed is much larger than the refresh rate is the matrix camera, the trigger time of the camera takes place respectively after a settable number of scanner revolutions. Preferably the camera is triggered in the 0 position of the cube, i. if the scanner cube faces perpendicular stand on the optical axis of the device. It is the through the scanner cube captured image detail the object surface big enough, around the entire measuring range for documentation and control purposes.

One typical field of application of such a measuring device is the detection the thermal properties of a weld just made or The supervision thermal processes on endless workpieces such as drawing of wire.

In these cases are also the geometric properties of the objects to be detected in conjunction and at the same time with their thermal properties of highest importance. On the one hand, the claimed device offers a good lateral Resolution, so that e.g. the width of a hot one Weld or the molten pool during welding or the wire diameter when wire drawing reliable and quickly detected can be.

Simple tasks can be realized with the help of the above-mentioned marking devices with visible light, but irregular structures such as a weld bead can be measured only with the help of an additional extension of the measuring device to a confocal distance measurement sufficiently accurate, as in the 4 is shown. A confocal distance measurement can be carried out according to the back-reflection principle with one or more wavelengths, which preferably also serve as a visible light marking. This is the focus lens 22 the claimed device designed with the largest possible and linear chromatic aberration, so that the focal points of different wavelengths, which are simultaneously projected onto the object to be measured, are at different distances. The aforementioned back-reflection measuring device is then supplemented with a spectral separating and analyzing device which is capable of continuously detecting the wavelength and the intensity of the back-reflection outside and / or including the wavelength-measuring region in which the temperature measurement takes place.

For simple Tasks range from two or three discrete wavelengths to determining a coarse one geometric height profile from the focus of the claimed device. For complex Tasks can be white Light can be used, wherein the focusing lens claimed Device the existing spectrum of white light source in the field of Temperaturmeßlinie decomposed into spectral components, so that a lying in this area surface only the light components reflected back, which are focused exactly on the surface to be measured. Therefore corresponds to the wavelength the return reflex the position of the object surface in focus, so that in Connection with the scanner movement the entire profile shape of the object surface in focus is measured four times per scanner revolution.

There the beam offset by the cube scanner is wavelength dependent, creates a small angle-dependent systematic measurement error, in relation to the instantaneous angular position of the cube scanner can be calculated and compensated.

In the in the 4 shown sensor system 10 ' is via the focusing lens 22 is using the non-contact temperature measuring device 14 occasionally the temperature-induced emission of an object surface in the area 24 detected. To increase the spatial resolution of the temperature measurement is the rotatably mounted transparent polygon scanner 16 integrated into the beam path, so that by the resulting parallel offset of the beam path, in the 6 Denoted by d, the surface emission along the measuring line 24 is detected.

To detect the angular position of the polygon scanner (shown here as a cube) is transverse to the optical axis of the measuring device, the collimated light of the LED 26 through the polygon scanner to the PSD 28 projected. This allows each Temperaturmeßwert a position along the measuring line 24 be assigned. At the same time, the light becomes a multispectral light source 40 over an optical fiber 45 Coaxially coupled into the beam path of the measuring device. Due to the chromatic aberrations of the focusing lens 22 will the spectrum of light source 40 disassembled and in the Höhenmeßbereich 46 focused. When the light strikes the surface of the object, the exactly focused wavelength is reflected back and can be removed from the fiber 45 over a branch 42 decoupled and with a spectral analyzer 44 be evaluated. The wavelength measured here corresponds to the position of the point of impact of the light in the height measuring range 46 , Thus, the geometrical object surface shape along the measurement line can be obtained from the obtained temperature measurement data 24 determine.

Claims (7)

Method for non-contact detection of thermal properties of an object surface along a line ( 24 ), in which light emitted and / or reflected by the object surface is detected, characterized in that in the beam path of a focusing lens ( 22 ) for detecting the temperature-induced emission of the object surface, a transparent rotatably mounted polygon scanner ( 16 ) is interposed with an even number of pairwise opposite parallel arranged facets (A, AA, B, BB), so that according to the angular position of the polygon scanner ( 16 ) continuously the temperature-induced emission and / or the reflected radiation of the object surface along the line ( 24 ) by the polygon scanner ( 16 ) caused parallel offset (d) of the beam path of the focusing lens ( 22 ) is detected. Method according to Claim 1, characterized in that the light of a multispectral visible light source (16) is made visible for visualizing the instantaneous measuring position on the object surface ( 40 ) is coupled coaxially with a wavelength range outside the detected wavelength range of the object surface emission in the same beam path. Method according to claim 1 or 2, characterized in that the geometric height profile of the object surface along the line ( 24 ) by the spectral and intensity evaluation of the back reflection of the multispectral light source ( 40 ) is detected at the object surface and at the same time as the detection of the temperature-induced emission of the object surface. Device for non-contact detection of thermal properties of an object surface along a line ( 24 ), in which light emitted and / or reflected by the object surface is detected, characterized by: a) a focusing lens ( 22 ), b) a transparent and rotatably mounted polygon scanner ( 16 ) with an even number of pairwise oppositely parallel facets (A, AA, B, BB) placed between the focusing lens ( 22 ) and the object surface is arranged, whose temperature-induced emission is to be detected. Device according to claim 4, characterized by means ( 26 . 28 ) for determining the angular position of the polygon scanner ( 16 ). Apparatus according to claim 4 or 5, characterized by an integrated confocal distance measuring device ( 40 . 42 . 44 . 45 ) for determining the geometric height profile of the object surface along the line ( 24 ). Device according to Claim 6, characterized in that the confocal distance-measuring device is a multispectral light source ( 40 ) and a spectral analyzer ( 44 ).