Transactions on Engineering Sciences vol 16, © 1997 WIT Press, www.witpress.com, ISSN 1743-3533
Laser system for non-contact tool setting and breakage detection W. Reiser Blum-Novotest GmbH, Production Metrology, Testing Equipment, P.O.Box 7202, D-&S7&2 #m E-Mail: blum-novotest@t-o]
Abstract In principle, as for a high-precision photo-electric barrier, the Laser-System is capable of monitoring (within the entire machining-range) even the smallest tools for breakage as well as precisely measuring length and diameter of rotating tools. All this can be realized under the rough environmental conditions within a machining center. By measuring tools in the spindle and at operating speed, clamping errors, run out, "flight-circle"-deviations and thermal drift of the machine can be determined and compensated. The integrated electronics react to the shading of the laser beam by each cutting edge and, after having detected the longest cutting edge, transmits the respective information to the machine tool control. The visible red-light laser (wavelength 670 nanometres, output capacity 0.05 mm) where there is always a distinct broken shank. It is easy to program and to evaluate without problems. There is no need for a precise calibration of the laser-system. The evaluation can be done with the CNC or PLC. Tool-check passing through the beam lengthwise in feed direction or backwards.Using this method it is also possible to check the tip of the tool. The calibration can be done by going through the measuring cycle using the new tool. The signal requires eveluation using the interrupt measuring input of the connected CNC, as both methods of interrupting and clearing the beam lead to a measuring impulse, allowing different strategies of controlling the tool can be developed.
Transactions on Engineering Sciences vol 16, © 1997 WIT Press, www.witpress.com, ISSN 1743-3533
Laser Metrology and Machine Performance
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Figure 5: Control position for single cutter monitoring. Besides the relatively simple control of the length, the system - due to its precision - is able to detect even smallest defects down to micron dimensions of wear. Under such circumstances the cutter in use will be compared with the new one. Example: A ball-nose cutter can be measured in both its length and diameter. After that, the cutter will be fed along the beam by using circular interpolation. Any change of the signal will then be interpreted as a broken cutter or a worn tool. The high measuring frequency of the system permits such a control and also allows measurement during working revolutions on a multiple-insert tool. Applying this method we are able to measure five different defects: broken cutter, run out of the tool, worn tool, built-up edge, clamping error.
Figure 6: Tool control by scanning its geometric shape.
Transactions on Engineering Sciences vol 16, © 1997 WIT Press, www.witpress.com, ISSN 1743-3533
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Laser Metrology and Machine Performance
3.4 Supervision of the Machine If we apply the measuring cycle the opposite way around, the laser can be used in an ideal way to supervise the machine. By measuring several times during the day the same tool (calibration-tool), the thermal displacement of the machine can be monitored and compensated. Besides the "growing" of the Y- and Z-axes it is also possible to measure the oblique-angled spindle of a 5-axis-machine which can be detected and then compensated for by the system. Temperature-drift of the y-axis
turned off the heating of the machine-base
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No. of measurement Figure 7: Thermal displacement of the y-axis of a machining center, measured by Laser-System, reference: Micro-Switch. Temperature-drift of the z-axis
turned off the heating of the machine-base
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