Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J1/00—Photometry, e.g. photographic exposure meter
  • G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
  • G01J1/4257—Photometry, e.g. photographic exposure meter using electric radiation detectors applied to monitoring the characteristics of a beam, e.g. laser beam, headlamp beam
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K26/00—Working by laser beam, e.g. welding, cutting or boring
  • B23K26/02—Positioning or observing the workpiece, e.g. with respect to the point of impact; Aligning, aiming or focusing the laser beam
  • B23K26/04—Automatically aligning, aiming or focusing the laser beam, e.g. using the back-scattered light
  • B23K26/042—Automatically aligning the laser beam
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J1/00—Photometry, e.g. photographic exposure meter
  • G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
  • G01J1/4257—Photometry, e.g. photographic exposure meter using electric radiation detectors applied to monitoring the characteristics of a beam, e.g. laser beam, headlamp beam
  • G01J2001/4261—Scan through beam in order to obtain a cross-sectional profile of the beam

Definitions

• the invention relates to a method for determining the position of a laser beam, in which at least part of the temperature-dependent electrical sensor absorbing some of the radiation energy is arranged around the beam at predetermined positions near the edge of the beam, and in which sensor measurement values are used the beam position is inferred.
• the constant position of the laser beam within the beam guidance system is important for a constant quality of the processing, because deviations of the beam position from the target position can change the position, shape and size of the focus.
• the precise adjustment of the beam axis to the resonator axis is a necessary prerequisite in order to obtain the maximum laser power and an intensity distribution of high quality.
• the shift and Movement of the beam axis with respect to the resonator axis manifests itself in a shift in the intensity distribution relative to the Resonatorach.se.
• the beam center must be determined with an accuracy of 0.1 mm - 1 mm so that when adjusting a laser resonator, the beam axis can be adjusted to the resonator axis with an accuracy of at least 1/10 of the beam diameter. This is necessary in order to be able to achieve the maximum laser power through optimal use of the discharge volume.
• the measurement should influence the beam only slightly or not at all, so that the intensity distribution and the laser power are changed only slightly during the measurement within a resonator. The same requirement applies when used in beam guidance systems, where several devices may be used at the same time, and any change in the intensity distribution or the laser power can have a negative impact on the result of the material processing.
• the beam center is given by the symmetry axis of the distribution. If the distribution is asymmetrical, the center of the beam can be determined by calculating the center of gravity of the beam area. The measurement of the intensity distribution is therefore necessary for an exact determination of the beam center of radiation of any shape. Assuming that the intensity distribution to be measured is point-symmetrical, the center of gravity can also be determined without precise knowledge of the intensity distribution. This boundary condition is not restrictive because almost all commercial laser systems have a rotationally symmetrical, elliptical or rectangular intensity distribution. In this case, to determine the beam position, it is sufficient to determine the edge of the beam on two axes.
• the electrical sensors are four needles, which are grouped around the desired position of the laser beam and can be advanced more or less to the beam center. Laser radiation hitting the needles warms the needles and the warming of everyone. The needle is measured with a temperature sensor.
• This known method can only be used very slowly, owing to the large thermal capacity of the needles. The measuring accuracy is low due to the limitation of the measuring range to the edge of the beam and when the diameter of the laser beam changes, the needles have to be readjusted in a cumbersome manner.
• the invention has for its object to improve the method of the type mentioned so that it can be used quickly, even with variable beam diameters.
• the senor is moved step by step on a predetermined path between the beam edge and the beam center, that after each step the measured value of the sensor is registered and then a certain percentage of the maximum registered measured value per coordinate axis is determined as a threshold value for determining the beam edge will be that starting from the measured values corresponding to the threshold values, parallel sterang edge tangents are defined starting from the coordinate axes, and that the position of the beam axis is then determined in accordance with the center of gravity of the surface enclosed by the beam edge tangents.
• the beam position can be detected in a simple manner by the sensors sweeping over the area comprising the beam and thereby registering a large number of measured values in rapid succession, with the aid of which an area approximately corresponding to the beam cross-section can be registered is determined and used arithmetically to determine the beam axis.
• the area enclosed by the beam edge tangent can be determined quite precisely as a means for determining the position of the beam axis, and thus also the position of the beam center or the position of the Laser beam.
• the method includes measuring and computing processes that can be automated, so that the method can in principle be carried out very quickly and, as a result, can also be used in control and regulating circuits which affect the position of a laser beam.
• the method is advantageously carried out in such a way that the entire beam diameter of two pairs of opposing sensors is progressively recorded from the beam edge to the beam center, and that the sensors are then moved back into their rest position on the beam edge.
• Each sensor of a pair of sensors measures half of the total beam diameter, so that there is a corresponding process acceleration.
• the step-by-step measurement should take place with short cycle times, but the heating of the sensor by the laser beam can only take place with a certain delay, the measured values of the sensors are recorded via a differential proportional element. This is the low-pass behavior of the sensor compensated and the measuring speed increased considerably.
• the method according to the invention is carried out during a machining process of a workpiece using the laser beam, and the beam position determined in the process is used to set the beam position.
• the accuracy and / or the speed can be improved or increased when processing with laser radiation.
• the method is designed such that it is carried out at two points located one behind the other in the beam direction and the laser beam is aligned using the parameters determined by both measuring points.
• the invention also relates to a device for determining the position of a laser beam, in particular with four temperature-dependent electrical sensors which are adjustable in a holder transverse to the beam and arranged opposite one another and connected to a measuring device.
• the known sensors are needles that can be adjusted across the laser beam.
• the needles are heated by laser radiation and the heating is measured using a temperature sensor.
• the known needles have a comparatively large heat capacity, so that they can only be measured slowly. Measurement errors can also result from the needles being arranged at the wrong locations for these with a corresponding intensity distribution.
• the invention has for its object to verbes a device of the aforementioned type Ensure that a complete detection of the laser beam cross section is achieved with little construction effort and favorable time behavior.
• the sensors are wires enclosing a measuring surface and in that the holder is motor-adjustable in the sense of changing the measuring surface.
• wires as sensors results in low irradiated sensor surfaces, correspondingly low power absorption and thus a small reduction in laser beam power due to the measurement, combined with a favorable behavior over time when the beam intensity changes.
• wires With wires, a measuring surface can be completely enclosed and thereby complete detection of the entire cross section of the laser beam can be achieved.
• the motorized drive of the holder is a prerequisite for the automation of the measuring process and the quick acquisition of the entire beam cross-section.
• the wires are advantageously arranged in pairs parallel to one another and the wire pairs are arranged at right angles to one another.
• the parallel arrangement of two wires means that they each cover half of the measuring range to be recorded with respect to one coordinate, while the two wires of the other pair of wires serve the measuring process in a second coordinate that is perpendicular to the first.
• the forks can be adjusted towards or away from each other on a slide guide frame transversely to the laser beam.
• the structural effort for the movement mechanics is kept small by the fact that the sliding guide frame consists essentially of two parallel slide rods with slidable slides thereon, each carrying a fork, which are attached to opposite runs of a drive belt driven by an actuator.
• An advantageous embodiment of the measuring device is that for each wire it has an upstream signal transmitter, a downstream analog / digital converter and a computer evaluating all measuring signals, which is connected to the servomotor and has a display device.
• An adder is connected upstream of the analog / digital converter, which can impress the wire signal with a signal component obtained therefrom with a differentiator. As a result, an evaluable pulse signal is made available to the converter very quickly.
• the computer is connected to the drive of a mirror system influencing the beam position.
• 1 is a partially sectioned side view of a measuring device for determining the position of a laser beam
• the device has a holder 12 for sensors 2.
• the latter are wires 14 to 14 ''', which are arranged in pairs in parallel.
• the wire pairs 14, 14 '' and 14 ', 14''' are arranged at right angles to each other.
• the wires 14 to 14 ''' consequently enclose a measuring surface 15 which is arranged transversely to a laser beam 1 and is approximately matched to its cross section.
• the wires 14 'to 14''' are in the position shown on the beam edge 3.
• the beam diameter enclosed by them is D.
• the bracket 12 consists of two U-shaped forks
• Each fork 16 holds two wires 14, 14 'and 14' ', 14' '' tensioned crosswise. Initially serve for wire guidance
• Insulating material e.g. Polyethylene
• existing diverter pins e.g. Polyethylene
• each wire is arranged between the deflection pin 30 and the tensioning element 31, which has one end on the wire, e.g. 14 'attacks, and is attached at its other end to an anchor pin 33.
• This also consists of insulating material.
• Each wire is guided from a deflecting pin 30 located at the end of a fork arm to a deflecting pin 30 of the fork base 16 ′ distant from the beam 1, which is designed as a trough in accordance with FIG. 1.
• the brackets 16 are arranged one behind the other in the beam direction 34 and carry the wires 14, 14 'on the one hand and 14' ', 14' '' on sides facing away from one another, where accordingly the required deflection and anchor pins 30, 33, Springs 32 and the clamping elements 31 are arranged, so that there is an overall flat construction.
• the forks 16 are each held by a carriage 21. Each carriage is slidable on carriage rods 20, for which purpose it has the plain bearings 35 shown in FIG. 1.
• the slide rods 20 are fastened in pillow blocks 3, which in turn are fastened in a manner shown in FIG. 2 to a bottom 36 of a frame 37 with screws 38. 2 shows a servomotor 23 for driving the slides 21 and thus the forks 16.
• the servomotor 23 is attached to a pillow block 3 and drives a drive shaft 39 on which a drive pinion 40 is seated in a rotationally fixed manner.
• a drive belt 41 engages, which is designed as a toothed belt and rotates in a tensioned manner via a corresponding pinion of the other plummer block bearing 3.
• the left carriage 21 in FIG. 1 is attached to the upper run 41 ′ and the right carriage 21 in FIG. 1 is attached to the lower run 41 ′′.
• the forks 16 are moved in opposite directions with each adjustment of the belt 41, namely towards each other Rotation of the servomotor 23 according to FIG. 1 clockwise and away from one another when the motor 23 rotates counterclockwise.
• 1, 2 also show a frame 37 seated on the floor 36 for receiving a power supply 42, a computer board 43 and a traveling board 44, so that all parts of the device required for the measuring process are arranged in a compact design around the laser beam 1 are.
• Fig. 3a explains the adjustment of the forks 16 in such a way that moving the forks 16 apart leads to a complete removal of the wires 14 to 14 '' 'from the area of the laser beam 1, while according to Fig. 3b the forks 16 in the direction of the arrow are moved towards each other so that the wires 14 to 14 '' 'held by them travel through the cross section of the laser beam 1 until the measuring surface 15 enclosed by them becomes zero and the entire beam cross section can thus be measured.
• Fig. 4 explains the required measuring device.
• This is generally designated 13 and essentially contains the wires 14 to 14 '''and the in the measuring head 48 Actuator 23 and signal generator 25 for these wires. It can be seen from the illustration that a measurement voltage is applied to each wire for measurement at a specific step position, a measurable voltage change taking place via an impressed current if the resistance of the wire changes as a result of its temperature coefficient because the wire has been heated accordingly by the laser beam .
• the computer 27 acts on the servomotor 23 via a motor interface 51 after it has received the measurement signals. It also controls a display device on which the positions of the wires 14 to 14 '''and the position of the beam center ultimately determined or the beam diameter can be read. In addition, the computer 27 is connected to an interface 52 for controlling the mirror system 22 shown in FIG. 6.
• This mirror system 22 consists of a first adjustable mirror 54 and a second adjustable mirror 53, which influence the position of the laser beam 1.
• two devices 55, 56 for determining the position of the laser beam 1 are arranged in FIG. 6.
• the first device 56 is arranged as close as possible to the second mirror 53 in order to be able to detect the position of the beam 1 on this mirror 53 as precisely as possible.
• This position is set with the mirror 54 by pivoting it about its horizontal axis and / or about its vertical axis with the servomotors 59, 60.
• the direction of the beam 1 is set with the second mirror 53, in that the mirror 53 is pivoted about its horizontal axis by means of the servomotor 58 and / or about its vertical axis with the aid of the servomotor 57. While the servomotors 57, 58 are acted upon by the device 55, the mirror 54 is set by the device 56.
• the two devices 55, 56 are arranged at a distance from one another in order on the one hand to be able to detect the position of the beam 1 (device 56) and on the other hand to determine the beam direction (device 55). From the.
• the distance of the devices 55, 56 from the mirror 53 and the measured deviation of the beam from the desired position can be determined with the line equation, the position of the beam 1 on the second mirror 53 and thus the direction of the beam.
• the beam position is therefore set in two steps. First, with the aid of the first mirror 54, the beam 1 is set so that it falls on the center of the second mirror 53 and in a second step the beam position is set with the mirror 53 to the desired axis.
• the measurement with a device 55, 56 is carried out as follows:
• the forks 16 are brought into their rest position shown in FIG. 3a, in which the wires 14 to 14 '' 'are arranged outside the area of the laser beam 1 and are not heated by it. Then the forks 16 and thus the wires 14 'to 14' '' are moved step by step towards the beam center 4 on a linear path. In each measuring position, the temperature of the wires 14 to 14 '' 'is measured and saved with the circuit shown in FIG. 4. In this case, a comparison is made, not shown, with a fixed, predetermined maximum value which is matched to the maximum permissible temperature in order to prevent the wires 14 to 14 ''' 'from melting through during the measurement.
• the forks 16 immediately move outward into the rest position.
• the forks 16 are moved towards each other until the measuring surface 15 enclosed by the wires 14 to 14 '' 'has become zero.
• the forks 16 are then moved back into the rest position according to FIG. 3a.
• FIG. 5a shows the laser beam 1 and the rest positions r to r3 'of the wires 14 to 14''' when the forks 16 are in the rest position according to FIG. 3a.
• the forks 16 are moved towards one another, they are moved into the positions a, b, c or a ′′, b ′′, c ′′, that is to say they advance linearly from the beam edge 3 to the beam center 4.
• the measured values 5 determined in the respective positions a, b, c and a ′′, b ′′, c ′′ are plotted with respect to the coordinate axis x and with respect to the coordinate axis y, so that the measurement curves shown in FIG. 5a are even .
• the measurement curves have a maximum value of 5m. Before evaluating these curves, the rest value is subtracted from the individual measured values.
• FIG. 5b shows the measurement curves of FIG. 5a for evaluating the measurement result.
• Threshold values 6 determined. For example, the percentage is assumed to be 20%. These threshold values 6 are determined on the measured curves and from there the
• Coordinate axes x, y define parallel beam edge tangents 7x, 7y, with which an equivalent beam surface 10 is determined.
• the centroid 9 corresponds to the position of the beam axis 8 of the laser beam 1.
• the beam radius can also be approximately determined from the position of the threshold values 6.
• a sensor which takes the step-by-step measurement on several concentric circular paths or on a spiral path.
• a combination of the above-described and the aforementioned step-by-step measurements consists in designing the sensor in the manner of an iris diaphragm and having it measured step by step.
• the simple mechanical construction is important for the practical use of the method for determining the position of the laser beam and for the use of the measuring device.
• the wire can withstand high thermal loads and absorbs a small proportion of the beam power, for example less than 1%, so that the measurement can also be carried out without repercussions during material processing.
• the independence of the measuring device from the beam diameter and from precise adjustment with wear-free measurement make the device suitable for use in automated processes.
• the method according to the invention serves to improve the method for determining the position of a laser beam so that it can be worked with quickly, even with variable beam diameters.

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• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Engineering & Computer Science (AREA)
• General Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Plasma & Fusion (AREA)
• Mechanical Engineering (AREA)
• Laser Beam Processing (AREA)
• Length Measuring Devices By Optical Means (AREA)

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Citations (5)

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• 1988
  • 1988-04-12 DE DE3812091A patent/DE3812091C1/de not_active Expired
• 1989
  • 1989-04-11 DE DE89904008T patent/DE58906596D1/de not_active Expired - Fee Related
  • 1989-04-11 WO PCT/DE1989/000216 patent/WO1989009928A1/de not_active Ceased
  • 1989-04-11 EP EP89904008A patent/EP0409857B1/de not_active Expired - Lifetime

Patent Citations (5)

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