Method for the Thermal Processing of a Workpiece with a Thermal Processing Machine

Abstract

A method for thermal processing of a workpiece uses a thermal processing machine. The method includes the following steps carried out in an automated manner: setting up the processing machine by producing contact between the processing tool and the workpiece and recording the spatial position of a workpiece surface, positioning the processing tool at a predetermined first and second distance from the workpiece surface and recording the associated signal values of the distance sensor as first and second measured values, and calibrating the distance controller which includes determining a height derivative of the distance sensor signal and an amplification factor for the signal of the distance sensor taking in account the first measured value, the second measured value, the first distance and the second distance; positioning the processing tool at a predetermined working distance from the workpiece surface with the inclusion of the amplification factor; and thermally processing the workpiece.

Claims

1. A method for the thermal processing of a workpiece (1) with a thermal processing machine (2) which has a processing tool (3), which is displaceable relative to the workpiece (1) by means of a CNC controller (6) and, for fine tuning, by means of a distance controller (8), and a distance sensor (4) which is displaceable with the processing tool (3), wherein the following method steps are carried out in a fully automated manner: (a) setting up the processing machine (2) by (aa) producing contact between the processing tool (3) and the workpiece (1) and recording the spatial position of a point on a workpiece surface (5), (bb) positioning the processing tool (3) at a predetermined first distance h.sub.1 from the workpiece surface (5) and recording the associated signal value of the distance sensor (4) as a first measured value, (cc) positioning the processing tool (3) at a predetermined second distance h.sub.2 from the workpiece surface (5) and recording the associated signal value of the distance sensor (4) as a second measured value, (dd) calibrating the distance controller (8), which comprises determining a height derivative of the distance sensor signal and an amplification factor amp for the signal of the distance sensor (4) taking into account the first measured value, the second measured value, the first distance h.sub.1 and the second distance h.sub.2, (b) positioning the processing tool (3) at a predetermined working distance h.sub.cut from the workpiece surface (5), with the inclusion of the amplification factor amp, and (c) thermally processing the workpiece (1).

2. The method according to claim 1, wherein setting up the processing machine (2) according to method step (a) comprises positioning the processing tool (3) at the working distance h.sub.cut from the workpiece surface (5) and recording the associated signal value of the distance sensor (4) as the reference measured value for the distance controller (8).

3. The method according to claim 2, wherein, in the thermal processing of the workpiece (1) according to method step (c), the distance of the processing tool (3) from the workpiece surface (5) is maintained at the working distance h.sub.cut by the distance controller (8), wherein the control variable is the amplified signal of the distance sensor (4).

4. The method according to claim 1, wherein the signal value recorded on production of the contact between the processing tool (3) and the workpiece (1) according to method step (aa) is a reference value which is taken into account in the calibration of the distance controller (8).

5. The method according to claim 4, wherein the reference value is taken into account in the calibration of the distance controller (8) in the determination of the amplification factor amp, according to method step (dd).

6. The method according to claim 1, wherein on the basis of the contact between the processing tool (3) and the workpiece (1) produced according to method step (aa) and on the basis of the predetermined working distance h.sub.cut from the workpiece surface (5), a safety distance from the workpiece surface (5) for rapid positioning of the processing tool (3) is determined.

7. The method according to claim 1, wherein for recording the spatial position of the workpiece surface (5) according to method step (aa), a second contact between the processing tool (3) and the workpiece (1) is produced and the spatial position of a second point on the workpiece surface (5) is recorded.

8. The method according to claim 1, wherein for recording the spatial position of the workpiece surface (5) according to method step (aa), two further contacts between the processing tool (3) and the workpiece (1) are produced at points on the workpiece surface (5) which are spaced apart from one another.

9. The method according to claim 1, wherein the distance sensor records the electrical capacitance between a measuring electrode of the distance sensor (4) and the workpiece (1).

10. The method according to claim 1, wherein the distance sensor (4) records the distance between the workpiece (1) and the processing tool (3) by an optical method.

11. The method according to claim 1, wherein the contact between the processing tool (3) and the workpiece (1) is identified by the feedback of a drive amplifier (torque, current, etc.) or by a mechanical lever on-off switch.

12. The method according to claim 1, wherein the contact between the processing tool (3) and the workpiece (1) is identified with the aid of the sensor signal and a default parameterisation of a closed-loop control circuit for setting the working distance.

13. The method according to claim 1, wherein the positioning of the processing tool (3) according to method step (bb) and/or (cc) is carried out on the basis of a processing machine coordinate system, the zero point of which is a contact point produced on production of the contact between the processing tool (3) and the workpiece (1) according to method step (aa).

14. The method according to claim 1, wherein the thermal processing of the workpiece (1) comprises a first thermal processing and a second thermal processing, independent of the first thermal processing, of the same workpiece (1), and in that method steps (a) and (b) are carried out before the first thermal processing and before the second thermal processing.

15. The method according to claim 1, wherein there is used as the processing tool (3) a plasma torch which has a ferromagnetic torch head and at least one ferromagnetic cutting or welding tool fixed to the torch head, and in that the distance sensor (4) comprises a field coil for generating a magnetic field and two measuring coils, wherein the measuring coils and the field coil extend around the torch head and the cutting and welding tool, and in that the distance of the plasma torch from the workpiece surface (5) is determined on the basis of the relative position between the phases of the measurement signals recorded by the measuring coils.

16. The method according to claim 1, wherein there is used as the processing tool (3) a plasma torch and as the distance sensor (4) a capacitive sensor or an optical sensor or an inductive sensor.

17. The method according to claim 1, wherein there is used as the processing tool (3) a laser cutting head and as the distance sensor (4) a capacitive sensor or an optical sensor or an inductive sensor.

18. The method according to claim 1 wherein, for producing the contact between the processing tool (3) and the workpiece (1) according to method step (aa), the processing tool (3) is moved in the direction towards the workpiece (1) at a speed ν in the range of from 0.3 m/min to 30 m/min.

Description

EXEMPLARY EMBODIMENTS

[0044] The method according to the invention is explained in greater detail hereinbelow with reference to drawings, in which, in diagrammatic form:

[0045] FIG. 1 shows a thermal processing machine having a processing tool which is moved in the direction towards the workpiece in order to produce contact with the workpiece,

[0046] FIG. 2 shows the thermal processing machine from FIG. 1 at the time at which contact between the processing tool and the workpiece is produced,

[0047] FIG. 3 shows the thermal processing machine from FIG. 1 during positioning of the processing tool at a first distance h.sub.1 from the workpiece surface,

[0048] FIG. 4 shows the thermal processing machine from FIG. 1 during positioning of the processing tool at a second distance h.sub.2 from the workpiece surface, and

[0049] FIG. 5 shows the thermal processing machine from FIG. 1 with the processing tool positioned at the working distance h.sub.cut during thermal processing of the workpiece.

[0050] FIG. 1 shows a thermal processing machine, to which reference numeral 2 is generally allocated. The thermal processing machine 2 is designed for the thermal processing of ferromagnetic workpieces. By way of example, FIG. 1 shows a workpiece 1 of structural steel S235, which has a length of 2000 mm, a width of 4000 mm and a height of 12 mm. The thermal processing machine 2 comprises a processing tool 3 in the form of a plasma cutting torch, as is described in EP 1 498 209 A2. The plasma cutting torch is provided with a distance sensor 4. The distance sensor 4 is an inductive sensor. It comprises a field coil and two measuring coils, through which the plasma cutting torch extends as the sensor body. The thermal processing machine additionally has an open-/closed-loop control unit 9. The open-/closed-loop control unit has a module 7 for recording the signal of the distance sensor 4. The processing tool is additionally displaceable in the x-, y- and z-direction relative to the workpiece via the open-/closed-loop control unit 9. In order to be able to displace the processing tool relative to the workpiece with high guiding accuracy, the open-/closed-loop control unit 9 further has a CNC controller 6 and a distance controller 8. The CNC controller 6 allows the processing tool to be positioned in the machine space as a whole. By contrast, the distance controller 8 only works reliably when the processing tool is in the vicinity of the workpiece to be processed, that is to say at a distance of not more than 200 mm from the workpiece surface 5. The CNC controller 6 therefore serves for rough positioning while the distance controller 8 serves for fine positioning of the processing tool 3 relative to the workpiece 1.

[0051] Setting Up the Processing Machine

[0052] Setting up the processing machine 2 serves on the one hand to record the spatial position of the workpiece surface 5 and on the other hand to calibrate the distance controller 8, in particular the distance sensor signal. It is carried out with the distance controller 8 switched off.

[0053] Producing a First Contact Between the Processing Tool and the Workpiece

[0054] First of all, contact between the processing tool 3 and the workpiece 1 is produced in a fully automated manner. For this purpose, the processing tool 3 is moved towards the workpiece 1 by means of the CNC controller 6 at a speed ν of 5 mm/s in a direction as perpendicular as possible to the workpiece surface 5. The processing tool 3 on the one hand and the workpiece 1 on the other hand are part of an open electric circuit (not shown in FIG. 1), which is closed when the processing tool 3 touches the workpiece surface 5. Contact between the processing tool 3 and the workpiece 1 is identified by the fact that the electric circuit is closed. FIG. 2 shows the thermal processing machine 2 from FIG. 1 at the time at which contact between the processing tool 3 and the workpiece 1 is produced. The closed electric circuit used for detecting the contact is symbolised by the arrow 10.

[0055] Recording the Spatial Position of a Point on the Workpiece Surface

[0056] At the time of contact between the processing tool 3 and the workpiece 1, the position of the nozzle tip of the processing tool 3 in the space is recorded via the CNC controller 6. Since this point corresponds approximately to the spatial position of a point on the workpiece surface 5, it is set as the zero point of the processing machine coordinate system.

[0057] In addition, two further contacts between the processing tool 3 and the workpiece 1 are produced. The first contact and the two further contacts are so chosen that the contacts are at as great a distance as possible from one another. Preferably, the first contact and the two further contacts are produced at three different corners of a rectangular workpiece surface.

[0058] Determining a Safety Distance for Rapid Positioning

[0059] The safety distance for rapid positioning is calculated from the distance of the uppermost position of the z-axis from the workpiece surface minus the pierce height and minus a safety margin of about 5 mm. The pierce height is about 175% of the working distance h.sub.cut. Within the safety distance for rapid positioning, the processing tool 3 is moved by the CNC controller 6 at a maximum speed of, depending on the z-axis, up to 30 m/min.

[0060] Positioning the Processing Tool at a First and Second Distance from the Workpiece Surface

[0061] The processing tool 3—as shown diagrammatically in FIG. 3—is then displaced to a first distance h.sub.1 from the workpiece surface 5. There, the signal value of the distance sensor 4 associated with the first distance h.sub.1 is recorded and stored by the module 7 before the processing tool 3—as shown diagrammatically in FIG. 4—is moved to a second distance h.sub.2 from the workpiece surface 5. In this case, the signal value of the distance sensor 4 associated with the second distance h.sub.2 is recorded and stored by the module 7. In an alternative embodiment of the method (not shown), the first distance h.sub.1 corresponds to the working distance h.sub.cut to be set during thermal processing of the workpiece. The associated signal value of the distance sensor 4 is used as the reference measured value for the distance controller 8.

[0062] Calibrating the Distance Controller

[0063] In a first step, module 7 calculates on the basis of the measurement points (h.sub.1/signal value 1 reference value) and (h.sub.2/signal value 2 reference value) a regression line and the gradient thereof (which corresponds in the case of a regression line to the height derivative f′(h) of the distance sensor signal) for calibrating the distance controller 8. Although the distance controller is thus calibrated in principle, the measurement range of the distance sensor must not be used optimally. Therefore, in a second step, the module 7 determines an amplification factor amp for the signal of the distance sensor.

[0064] Calculation of the amplification factor amp is illustrated by the following example:

[0065] It is assumed that the measurement signal of the distance sensor 4 increases as the distance of the distance sensor 4 from the workpiece surface 5 increases. If the distance sensor has a measurement range of +/−10 V, for example, the measurement range must be so shifted that the distance to be controlled corresponds as far as possible to a sensor signal that lies in the region of about 0 V. The gradient of the distance sensor signal is then determined on the basis of the first and second measured values. The gradient is a value for the agility of the adjustment to interfering variables, that is to say deviation of the distance. The amplification is to be so chosen that it is possible to react as quickly as possible to deviations but the controller is nevertheless quiet during normal operation.

[0066] When an amplification factor amp is used, it must, however, also be applied to the calibration. Consequently, in a third step, the amplification factor amp must also be applied to the first and second signal values, and the calibration of the distance controller 8, in particular the height derivative f′(h) of the distance sensor signal, must at least be corrected by computation. Alternatively, the processing tool 3 can, however, also be positioned at the first and second distance from the workpiece surface 5 again and the associated measured values can be recorded again with application of the amplification factor amp.

[0067] Determining a Safety Distance from the Workpiece Surface

[0068] The safety distance is calculated on the basis of the contact produced according to method step (aa) between the processing tool 3 and the workpiece 1 and a predetermined working distance h.sub.cut from the workpiece surface. For this purpose, a safety distance of 50 mm is applied to the recorded spatial position of the workpiece 1 and a plane parallel to the workpiece surface is calculated, which divides the processing space in which the processing tool 3 can be displaced into two sub-spaces, namely a first sub-space facing the workpiece, in which the processing tool 3 can be displaced only slowly in order to avoid collisions with the workpiece 1, and a second sub-space facing away from the workpiece, in which the processing tool 3 can be displaced with maximum speed.

[0069] Positioning the Processing Tool at the Working Distance and Thermal Processing of the Workpiece

[0070] Finally, the processing tool 3—as shown diagrammatically in FIG. 5—is positioned at a predetermined working distance h.sub.cut relative to the workpiece surface 5 and the distance controller 8 is switched on in order to maintain the distance of the processing tool from the workpiece surface at the working distance h.sub.cut. The signal of the distance sensor 4 multiplied by the amplification factor amp serves as the control variable for the distance controller 8. Thermal processing of the workpiece 1 is then begun.

[0071] After a first cutting contour has been cut, a second cutting contour is cut into the same workpiece. In the simplest case, it is sufficient in order to process the same workpiece multiple times to configure the processing machine a single time. The reason for this is that, after rapid positioning of the processing tool with the distance controller, an adjustment is made to a signal value which represents a distance between the processing tool and the workpiece. Alternatively, method steps (a) to (b) are repeated before the second cutting contour is cut.