DE102008015133A1 - Apparatus for collecting process light during laser machining, comprises lens in machining head, narrow annular mirror over lens edge and reflective ellipse for directing light to detector - Google Patents

Abstract

In apparatus for collecting process light during laser machining, the intensity of light emitted from the machining site is detected with a lens in the machining head through a narrow annular mirror (R) over the lens outer edge. The light is reflected through 90[deg] ; focused onto the first focal point (F1) of a reflective ellipse (E); guided out of the side of the head; collected at the second focal point (F2); turned 90[deg] ; and focused onto the detector. In apparatus for collecting process light during laser machining of a workpiece, the intensity of light emitted from the machining site is detected with a lens in the machining head (in the laser direction), through a narrow annular mirror (R) applied over the outer edge of the lens. The light is reflected through ca. 90[deg] (i.e. perpendicular to the laser beam) and focused onto the first focal point (F1) of a reflective ellipse (E) in a higher or lower plane. The light is directed from the ellipse out of the side of the machining head and collected at a second focal point (F2) of the ellipse, and then turned through a cone angle of ca. 90[deg] and focused onto the detector.

Description

The The invention relates to a new method for decoupling the process radiation, the collection and focusing of the same on a sensor, for monitoring and regulation of processes in laser material processing.

at Laser material processing is in certain cases necessary for process control emitted by machining point To measure electromagnetic radiation and from it to parameters determine the quality of the Editing and used to control the editing process can be.

Examples for this are monitoring during laser welding, the power control of the piercing process and the determination of the Punctuation before the start of cutting, monitoring and control of the cutting process itself, detection of plasma formation and more.

at the laser material processing, in particular with CNC supported Portal machines and robots are required for high accelerations. The sensors for process control must be close to the processing point be attached to a measurable intensity proportion of To detect process radiation. Therefore, the demand exists Integrate sensor into the machining head, taking into account small size and weight. The advantage of the sensors in the head is the constant distance to the processing point.

By way of illustration is in 1 a laser material processing head shown schematically. With the lens L, the laser radiation LA is focused on the material M. To protect the lens from splashes of gas G is supplied laterally below the lens which exits through the nozzle D and thus pushes the splashes substantially laterally. In Focus F, the material glows, melts, burns or vaporizes (depending on the power and process) and emits electromagnetic radiation in all directions - referred to below as process radiation P. The portion of the process radiation which penetrates through the nozzle into the machining head, falls onto the lens and is guided back by the lens more or less parallel to the incident laser beam LA.

• a, Rückreflektierte Laserstrahlung,
• b, ein kontinuierliches Spektrum in Abhängigkeit von der Temperatur und des bearbeiten Materials,
• c, sowie ein Linienspektrum, falls ionisiertes Gas vorhanden ist.

The electromagnetic radiation emitted by the processing point contains:

• a, back-reflected laser radiation,
• b, a continuous spectrum depending on the temperature and the material being processed,
• c, and a line spectrum if ionized gas is present.

ever after editing process can be made of intensity, Frequency spectrum, temporal change of the signal and others more, corresponding parameters for the regulation of material processing measured and determined with an electronic evaluation.

State of the art

• 1, Die Sensoren werden außerhalb des Bearbeitungskopfes und nahe am Bearbeitungspunkt angebracht, wie in der Patentschrift DE4433675A1 beschrieben. Um genügend Intensität zu erhalten benötigt man meistens mehrere Sensoren. Der Nachteil ist, dass die Sensoren durch Spritzer und Dämpfe verunreinigt werden, die bei der Materialbearbeitung auftreten. Die Sensoren im Inneren des Bearbeitungskopfes unterhalb der Linse anzubringen, hat dieselben Nachteile wie oben beschrieben, da auch durch die Düse Spritzer und Dämpfe eindringen, wenn auch in geringeren Maße.
• 2, Die nachfolgend beschrieben Verfahren, nützen die Tatsache, dass das Prozesslicht, welches im Fokus des Laserstrahles entsteht durch dieselbe Linse, die den Laserstrahl bündelt, annähernd parallel, entgegen der Richtung des einfallenden Laserstrahles zurückgeworfen wird. Sensoren, die sich im geschützten Raum hinter der Linse befinden, können aber nur ringförmig außerhalb des einfallenden Laserstrahles angeordnet werden, da sie sonst verbrennen, wie in der Patentschrift DE19644101C1 beschrieben. Mit dieser ringförmigen Anordnung mehrerer Sensoren, wird nur eine geringe Intensität des Prozesslichtes erfasst wird. Eine Verbesserung dieses Verfahrens, ist der Scraper-Spiegel, der das ringförmig um den Laserstrahl zurückreflektierte Prozesslicht unter 90° zum Laserstrahl seitlich ausleitet, wo es durch eine Linse oder Hohlspiegel gebündelt wird und auf einen Sensor fällt. Der Nachteil dieser Anordnung ist die Größe und das Gewicht, was bei hochbeschleunigten Bearbeitungsköpfen stört. Deshalb wird diese Anordnung meist im unbewegten Teil des Strahlenganges eingebaut, was aber wiederum den Nachteil nicht konstanter Intensität des Prozesslichtes hat, aufgrund des sich bewegenden Bearbeitungskopfes, der mal näher oder weiter weg vom Sensor arbeitet.
• 3, Eine weitere Methode besteht darin, den nach dem Bearbeitungskopf nächsten 90° Umlenkspiegel in Richtung des Bearbeitungspunktes zu durchbohren, wie in der Patentschrift US6,596,961B2 beschrieben. Das Prozesslicht kann durch diese Bohrung auf den dahinter liegenden Sensor gelangen, während das Laserlicht durch die senkrecht dazu angebrachte Bohrung nicht direkt und gradlinig eindringen kann. Der Nachteil ist, dass die Bohrung sehr klein sein muss um den gespiegelten Laserstrahl nicht zu schwächen. Durch die kleine Bohrung gelangt daher nur eine geringe Intensität des Prozesslichtes auf den Sensor.

The following describes the previously used methods for decoupling and measuring the process light.

• 1, The sensors are mounted outside the machining head and close to the machining point, as in the patent DE4433675A1 described. To get enough intensity you usually need several sensors. The disadvantage is that the sensors are contaminated by splashes and vapors that occur during material processing. Installing the sensors inside the machining head below the lens has the same disadvantages as described above, as splashes and vapors also enter through the nozzle, albeit to a lesser extent.
• 2, The method described below, the fact that the process light, which arises in the focus of the laser beam through the same lens, which focuses the laser beam, approximately parallel, is reflected against the direction of the incident laser beam. Sensors that are located in the protected space behind the lens, but can only be arranged in a ring outside of the incident laser beam, otherwise they burn, as in the patent DE19644101C1 described. With this annular arrangement of several sensors, only a small intensity of the process light is detected. An improvement of this method is the scraper mirror, which laterally emits the process light reflected back annularly around the laser beam at 90 ° to the laser beam, where it is focused by a lens or concave mirror and falls onto a sensor. The disadvantage of this arrangement is the size and weight, which interferes with high-speed machining heads. Therefore, this arrangement is usually installed in the stationary part of the beam path, which in turn has the disadvantage of non-constant intensity of the process light, due to the moving processing head, which works nearer or farther away from the sensor.
• 3, Another method is to pierce the next 90 ° deflection mirror after the machining head in the direction of the machining point, as in the patent US6,596,961B2 described. The process light can pass through this hole on the underlying sensor, while the laser light through the vertically mounted hole can not penetrate directly and straight. The disadvantage is that the hole must be very small so as not to weaken the mirrored laser beam. Due to the small bore, only a small intensity of the process light reaches the sensor.

task

• 1, klein, leicht und robust ist, um in einem bewegten Beschleunigten Bearbeitungskopf integriert zu werden,
• 2, die den einfallenden Laserstrahl nicht abschattet,
• 3, die sich hinter der Linse im geschützten Raum des Bearbeitungskopfes befindet,
• 4, die ringförmig die gesamte Prozessstrahlung im Bereich außerhalb des Laserstrahles bis zum Rand der Linse erfasst und damit eine hohe Intensität des Prozesslichtes auf den Sensor leitet, wodurch es möglich ist, auch noch schwach leuchtende Vorgänge zu detektieren,
• 5, die nur einen Sensor enthält auf den das gesamte erfasste Prozesslicht fokussiert wird, anstatt mehrere Sensoren was einen höheren elektronischen Aufwand erfordert,
• 6, deren Konstruktion es erlaubt, ein Schutzfenster anzubringen, welches den Sensor vor der rückreflektierten Laserstrahlung schützt.

It is an object of the invention to provide a device for detecting and bundling the process light, which:

• 1, small, lightweight and sturdy to be integrated in a moving accelerated machining head,
• 2, which does not shade the incident laser beam,
• 3, which is located behind the lens in the protected space of the machining head,
• 4, which detects in a ring the entire process radiation in the area outside the laser beam to the edge of the lens and thus directs a high intensity of the process light to the sensor, whereby it is possible to detect even weakly glowing processes,
• 5, which contains only one sensor on which the entire detected process light is focused, rather than multiple sensors which requires a higher electronic effort,
• 6, the construction of which allows to install a protective window which protects the sensor from the back-reflected laser radiation.

embodiment

The The invention describes a new method for decoupling the process light and collection thereofb and focusing and redirecting to one Sensor.

The Device for collecting the process light is close above (in Towards the laser) of the lens in the machining head.

The principle of the device:

The Process light falling through the lens L becomes utmost Rim of the lens collected by a narrow ring mirror R and in the focussed focus F1 of an ellipse, which sideways the process light from the processing optics and in the second focal point F2 focused. In the 2nd focal point is a mirror cone of the process light is deflected by 90 ° and directed to the detector.

Ring mirror, Detector and electronics are in one plane, in the 2nd Level, below or above, is the ellipse and the cone mirror.

The invention will be described below with reference to 1 . 2 and 3 described in detail.

The process light P occurring in the laser material processing is emitted almost point-like from the processing point F, it passes partly through the nozzle D and falls on the lens L. Since the processing takes place approximately in the focus of the lens L, the process light after passing through the lens L approximates parallel to the incoming laser beam LA (see 1 ). For safety reasons, the laser beam has a smaller diameter than the lens L (about 70%). In the area of the laser beam it is impossible to decouple the process light P because of the high intensity, but the fraction of the radiation which is returned approximately parallel to the edge of the lens L but outside the area of the laser beam is returned. This portion of the radiation is detected by the device and focused on the detector DE.

Drawing 2 shows the structure of the device.

The from the processing point F emitted process light P, which on the Edge of the lens L occurs approximately from the lens L. directed onto a ring mirror R parallel to the incoming laser beam, the few mm from the outer free edge of the lens L protrudes. The ring mirror R is arranged to absorb the radiation slightly inclined downwards in the first focus F1 of the underlying Ellipse E focuses, turning it back to the second focal point F2 collects. There is a mirror cone K of the radiation focused on the detector DE. The center of the ring mirror R and the focal point F1 of the ellipse E are concentric with the lens center arranged.

In 3 is again the beam path seen from above.

The Arrangement and size of the ring, ellipse E and cones K are according to the optics used and the diameter of the Lens L interpreted by geometric calculation of the beam path. The surfaces of ring, ellipse E and cone K need reflect the process light, preferably in the wavelength range for which the corresponding detector DE is designed. Preferably they are made of polished, reflecting metal. The detector DE is preferably undesirable through a window F. Laser radiation and dust to protect. Ring and detector DE are in the upper level - around the detector EN around is enough space for an electronic evaluation. The arrangement can also be carried out in mirror image, Ring and detector in the lower, ellipse and mirror in the upper Level.

By suitable design, the device has a thickness of 15-30 mm, it is small and light, because it consists essentially of cavities consists. It is thus suitable for mounting on a high acceleration moving optics suitable.

Especially the device is characterized by the fact that the process light that hits the lens L with a high intensity component directed to the detector DE.

Example:

Application in a cutting machine with CO ² laser, moving optics and a lens L with free diameter of 35 mm.

at a width of the ring mirror R of only 1 mm (the free lens opening reduced to 33 mm) becomes 10% of the process light incident on the entire lens L. directed to the detector DE, at a width of the ring mirror R by 3 mm it is already 30%. This high intensity is especially decisive if a low radiation intensity of the Process light due to processing occurs.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 4433675 A1 [0008]
• - DE 19644101 C1 [0008]
• - US 6596961 B2 [0008]

Claims (6)

Device for collecting the process light the machining of a workpiece by means of a laser beam, where the intensity of the emitted by the processing station Radiation, after the lens in the processing head (towards the laser) at the very edge of the lens through one above attached narrow ring mirror captured to approximate 90 ° mirrored (almost perpendicular to the laser beam) and focused on the first focus of a specular ellipse, which is in a plane below or above, discharged laterally from the ellipse from the machining head and collected in the 2nd focal point of the ellipse and from there through a cone mirror deflected by approximately 90 ° and focused on the detector. Device according to claim 1, characterized that the device consists of 2 levels: 1st level: ring mirrors, Detector, windows, electronics 2nd level: ellipse and cone mirror As well can be arranged reversed 1st and 2nd level (Mirror image arrangement). This is easy to produce, essentially hollow and narrow, thus small and light to to be used in accelerated processing heads. Device according to claim 1, characterized that the reflective surfaces are preferably polished Metal are executed. Device according to claims 1 and 3, characterized that the ring mirror is designed as a concave mirror to the process radiation to focus on the detector. Device according to claim 1, characterized that a window is placed in front of the detector that the detector protects against back-reflected laser radiation. Device according to claim 1, characterized that in front of the detector, a diaphragm or filter is attached to Matching of detector sensitivity and received intensity of the detector Process radiation.