| Summary: | 博士 === 國立彰化師範大學 === 電機工程學系 === 98 === Abstract
High speed spindle is the heart of vertical machining center ( VMC ), especially applied to high speed machining ( HSM ). However, the spindle vibration and thermo growth are two main problems for precise machining industry. Therefore, the quality and selling price of VMC are determined by the ability to maintain the vibration control and thermo growth of spindle within a reasonable tolerance. In general, the PT-100 thermo coupler is usually applied to compensate the thermo growth of high speed spindle. And the value of thermo growth is converted by indirect measuring method, which causes larger measuring error. The experiment verified the existence of 23 μm thermal growth at the beginning of PT-100 test while the spindle is running at constant 18000 rpm. Moreover, actual value of thermo growth could not be detected by indirect temperature measurement. Hence, this dissertation proposes single and dual displacement measurement sensors as the monitoring elements to detect thermo growth of high speed spindle in VMC and design its amplifier and compensation control. After comparing the value of laser checking and the value of PT-100 thermo coupler, the single displacement measurement sensor shows excellent compensation under condition of high temperature and high speed spindle. However, the measuring error of single displacement measurement sensor is about 20μm at maximum during low speed spindle running. In contrast, the measuring error is only 3μm at maximum by applying dual displacement measurement sensor.
As for vibration, the vibration value of vertical machining center can be 8.6 mm/s, which is going to cause serious damage to high speed spindle. The
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vibration monitoring system proposed by this dissertation can reduce the vibration value to less than 2mm/s in 10.7 seconds while the spindle vibration value is 3mm/s. To protect the spindle, the machine will be shut down by the monitoring system in a short time when the vibration value reaches 4.4mm/s. At last, this dissertation applies single and dual displacement measurement sensors to compensate on the vertical machining center and conduct 3 axes precise machining. After comparing with the compensation of PT-100, the result shows the single or the dual displacement measurement sensor can reduce the measuring error from -60μm to -10μm and increase the machining accuracy significantly. In addition, without 45 minutes machine warming period, the thermo compensation design in this dissertation saves up to 1%~1.56% electric consumption and 9.38% working time. The efficiency of working time and energy saving is improved tremendously, especially for the long time running of VMC. The cost of the vibration monitoring system and the thermo growth compensation system proposed by this dissertation is both under NT$ 11,000.00, which is around 0.5% of one machine cost. Comparing with the same product of similar standards in European Union area, additional value and commercialization potential are significantly increased.
Keywords: displacement sensor, thermo growth, vibration monitoring
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