DE102008015133B4 - Device for detecting the process radiation during laser material processing - Google Patents

Abstract

Device for detecting a process radiation (P) during processing of a workpiece (M) by means of a laser beam (LA), in which the intensity of the process radiation (P) emitted by the processing point (F) passing through the outermost edge of a processing head ( B) arranged lens (1) passes, detected by a in the processing head (B) behind the lens (L) in the direction of the laser mounted narrow annular mirror (R) by approximately 90 ° and thus approximately perpendicular to the laser beam (LA) mirrored and on focusing a first focus (F1) of a specular ellipse (E) disposed in a plane below or above, laterally out of the specimen head (B) from the specular ellipse (E), and the specular ellipse at the second focus (F2) (E) is collected and from there by a cone mirror (K) is deflected by approximately 90 ° and focused on a detector (DE).

Description

The Invention relates to a new device 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 necessary in certain cases for process control the electromagnetic emitted from the processing point Radiation to measure and to determine parameters that provide information about the quality edit and used to control the editing process can be.

Examples for that are The supervision in 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.

Such devices are disclosed in the patents. EP 1886757A1 . DE 10 2004 020 704 A1 . DE4433675A1 . DE19644101C1 and US6,596,961B2 described, the demarcation on the next page.

at Laser material processing, especially with CNC-supported gantry machines and robots, are called for high accelerations. The sensors for process control be attached near the processing point by a measurable intensity component to detect the process radiation. That is why the demand exists to integrate the 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 machining 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), emitting 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 from intensity, Frequency spectrum, temporal change of the Signals and other 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, wie in der Patentschrift DE 10 2004 020 704 A1 und EP1886757A1 beschrieben, 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, as in the patent DE 10 2004 020 704 A1 and EP1886757A1 described is the scraper mirror, which laterally deflects 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 can not penetrate directly and straight through the vertically mounted hole. 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 device 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 P falling through the lens L becomes the outermost one Rim of the lens collected by a narrow ring mirror R and in the focused focus F1 of an ellipse E, which is the process light sideways from the processing optics and in the second focal point F2 focused. In the second focal point is a mirror cone K which deflects the process light by 90 ° and to the detector DE conducts.

Ring mirror, Detector and electronics are in one plane, in the 2nd Level, below or above, there 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 is approximately parallel to the lens L. directed to the incoming laser beam on a ring mirror R, the few mm from the outside free Edge of the lens L protrudes. The annular mirror R is arranged so that he tilted the radiation slightly down in the first focus F1 of the underlying ellipse E focused, which in turn collects it in the second focus F2. There there is a mirror cone K of the radiation on the detector DE focused. The center of the ring mirror R and the focus F1 the ellipse E are arranged concentrically to the lens center.

In 3 is again the beam path seen from above.

The arrangement and size of the ring, ellipse E and cone K are to be interpreted according to the optics used and the diameter of the lens L by geometrical calculation of the beam path. The surfaces of ring, ellipse E and cone K must reflect the process light, preferably in the wavelength range for which the corresponding detector DE is designed. Preferably they are off polished, reflective metal perform. The detector DE is preferably to be protected by a window FE against unwanted laser radiation and dust. Ring and detector DE are in the upper level - there is enough space around the detector DE for an electronic evaluation system. The arrangement can also be performed 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. It is thus for mounting on a moving with high acceleration 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 annular mirror R of only 1 mm (the free lens opening on Reduced by 33 mm) becomes 10% of the process light falling 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 particular crucial if a low radiation intensity of the process light due to processing occurs.

Claims (6)

Device for detecting a process radiation (P) during the machining of a workpiece (M) by means of a laser beam (LA), where the intensity of the process radiation (P) emitted by the processing station (F), by the utmost Edge of a lens (1) arranged in a machining head (B) passes through one in the processing head (B) behind the Lens (L) in the direction of the laser mounted narrow ring mirror (R) captured to approximate 90 ° and thus approximate mirrored perpendicular to the laser beam (LA) and at a first focal point (F1) of a specular ellipse (E) is focused in a Level below or above is appropriate, from the reflecting one Ellipse (E) discharged laterally from the machining head (B) and in the 2nd focal point (F2) of the specular ellipse (E) is collected and from there by a cone mirror (K) deflected by approximately 90 ° and a detector (DE) is focused. Apparatus according to claim 1, characterized in that the Device consists of 2 levels: 1st level: ring mirror (R), Detector (DE), window (FE), electronics 2nd level: ellipse (E) and cone mirror (K) Apparatus according to claim 1, characterized in that the reflecting surfaces are preferably made of polished metal. Apparatus according to claim 1 or 3, characterized in that the ring mirror (R) is designed as a concave mirror to the process radiation (P) to focus on the detector (DE). Apparatus according to claim 1, characterized in that a Window (FE) is placed in front of the detector (DE), which is the detector (DE) before backreflected Laser radiation protects. Apparatus according to claim 1, characterized in that before the detector (DE) a shutter (BL) or a filter (FI) attached is used to match the sensitivity of the detector (DE) and received intensity the process radiation (P).