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1. US5340962 - Automatic control of laser beam tool positioning

Note: Text based on automatic Optical Character Recognition processes. Please use the PDF version for legal matters

[ EN ]
I claim:
1. In a system for machining a workpiece with a laser beam tool, control means for maintaining a controlled distance between the tool and a workpiece surface, said control means comprising, in combination:
a. capacitive sensor means for measuring the capacitance between the tool and the surface of the workpiece;
b. beam control means for driving the laser beam for the tool with periodic pulses separated by a refractory interval
b. sampling means for taking a measurement of the capacitance between the tool and the workpiece during the refractory interval.
2. In a system having an automatic focus control for moving the focal point of a laser beam by movements along orthogonal machine translation axes x, y, and z and orthogonal rotational axes C and D of a multiaxis processing head mounted on the machine, a method for determining a unit normal vector at a point on the surface of a workpiece, said method comprising the steps of:
a) positioning the focal point of the beam on a reference point on the surface of the workpiece;
b) adjusting the C and D processing head axes to orient the beam substantially normal to the surface of the workpiece and the x, y, and z axis to position the focal point coincident with the reference point to orient the beam axis, d' of the directing head approximately normal to the surface of the workpiece at the reference point;
c) defining a local orthogonal coordinate system u, v, and w where w is the unit normal vector of the workpiece, is aligned with the -d by varying the C and D axis rotations and the origin of said local coordinate system is positioned coincident with the focal point of the beam by variation of the x, y, and z axis positions;
d) creating a beam focal point moving program in the local coordinate system to move the focal point of the beam to three points Pl, P2 and P3 on the workpiece surface which are non-collinear and define a plane to which the true unit normal vector is normal, said points positioned preferably equidistant from the origin of the local coordinate system;
e) executing the beam focal point moving program in the local coordinate system while the automatic focus control is active thereby to avoid collision between the adjustable head and the workpiece and while recording the coordinates of the x, y, z, C and D axes at points p1 p2 and p3 while the AFC maintains a constant gap;
f) computing the orientation of a true unit normal vector to the workpiece at the reference point by calculating the cross product of the vectors v1 between Pl and P2 and v2 between Pl and P3, or g) adjusting the angles of C and D rotational axes to orient d of the adjustable head such that an adjusted d is aligned with and in opposition to the unit normal vector n at the reference point of the workpiece.
3. In a system having an automatic focus control for moving the focal point of a laser beam by movements along orthogonal machine translation axes x, y, and z and C and D rotational axes of an adjustable beam directing head mounted on the machine, a method for positioning the focal point of a laser beam at selected points on a surface of a workpiece, comprising the steps of:
a) varying the orientation of the C and D rotational axes thereby to adjust the beam axis of the directing head an expected predetermined orientation relative to the surface of the workpiece and aligning the x, y, and z axes to place the beam on one of the selected points;
b) using a gap sensor for generating a signal proportional to the displacement between the directing head and the surface of the workpiece and moving the directing head along a selected x, y, and z coordinate axis to maintain a predetermined displacement as the beam focal point is moved through selected points.
4. The invention of claim 2 wherein the predetermined orientation of the beam axis, d is normal to the surface of the workpiece.
5. In a system for machining a workpiece with a laser beam tool which includes control means for maintaining a controlled distance between the tool and a workpiece surface, a method for determining when the focal point of the laser beam is optimally positioned at the surface of the workpiece, said method comprising the steps of:
a. monitoring an indicia of optimal beam interaction with the surface of the workpiece as the focal point of the beam is moved toward the surface of the workpiece from above and below the workpiece;
b. recording the coordinates corresponding to the point where the indicia indicated maximum activity for movement of the beam in both directions toward the surface of the workpiece; and
c. analyzing the coordinate points obtained in a. and b. above by a least squares method to obtain the optimum gap distance for positioning the focal point of the beam at the surface of the workpiece.
6. The method of claim 5 wherein the indicia of optimal beam interaction with the workpiece is the acoustic noise generated as the beam cuts the surface of the workpiece.
7. The method of claim 5 wherein the indicia of optimal beam interaction with the workpiece is the intensity of the blue spark generated as the beam cuts the surface of the workpiece.
8. In a system for machining a workpiece with a laser beam tool which includes control means for maintaining a controlled distance between the tool and a workpiece surface, apparatus for determining when the focal point of the laser beam is optimally positioned at the surface of the workpiece, said apparatus comprising, in combination:
a. means for monitoring an indicia of optimal beam interaction with the surface of the workpiece as the focal point of the beam is moved toward the surface of the workpiece from above and below the workpiece;
b. means for recording the coordinates corresponding to the point where the indicia indicated maximum activity for movement of the beam in both directions toward the surface of the workpiece; and
c. means for analyzing the coordinate points obtained in a. and b. above by a least squares method to obtain the coordinates for commanding the machine to maintain an optimum gap distance for positioning the focal point of the beam at the surface of the workpiece.
9. The apparatus of claim 8 wherein means for monitoring the indicia of optimal beam interaction with the workpiece is acoustic means for measuring the acoustic noise generated as the beam cuts the surface of the workpiece.
10. The method of claim 8 wherein the means for monitoring the indicia of optimal beam interaction with the workpiece is an optical means for detecting the intensity of the blue spark generated as the beam cuts the surface of the workpiece.
11. In a system for machining a workpiece with a laser beam tool including means for measuring the distance between a sensor positionable by the automatic focus control of the machine and a workpiece surface, means for determining the programs to be run by the machine to process a workpiece in accordance with one of a plurality of processing programs, said means comprising, in combination:
a. sensor means for measuring an indicia applied to a fixture for a workpiece;
b. means for automatically and sequentially moving the sensor means to a series of reference points at predetermined locations on the fixture in accordance with a fixture identification program and measuring the indicia at each point; and
c. means for decoding the indicia pattern to identify and select the program to be run by the machine in accordance with the coding on the particular fixture.
12. In a system for machining a workpiece with a laser beam tool including means for measuring the distance between a sensor positionable by the automatic focus control of the machine and a workpiece surface, means for determining the programs to be run by the machine to process a workpiece in accordance with one of a plurality of processing programs, said means comprising, in combination:
a. sensor means for measuring the capacitance between it and the surface of the workpiece;
b. means for automatically and sequentially moving the sensor means to a series of reference points at predetermined locations on a fixture in accordance with a fixture identification program and measuring the capacitance at each point to determine whether or not a peg is present; and
c. means for decoding the peg pattern to identify and select the program to be run by the machine in accordance with the coding on the particular fixture.