On Machine Measurement Methods For The Geometric Parameters Of Large Workpiece By Laser

Large workpieces are basic components in the large equipment manufacturingindustries including aerospace, energy and power, marine engineering etc. Thepurposes of upgrading the machining precision, efficiency and reliability of largeworkpieces are relentless pursuits for these industries. However, the improvement ofthese parameters is not only dependent on the manufacturing technologies, but alsothe measurement means, especially the means of detection in the machining process.The requirements of high accuracy for the large workpieces are mostly decided by theinner structure for fitting to other parts. In this paper, the backwards of the existingdetection techniques applied to large workpieces are analyzed for this type ofstructure. Then, we combine the laser measurement technology and CNC machinetools to propose several measurement methods about position and dimension whichare high-precision, non-contact, on machine and easy of automation. Lastly, somemeasurement methods for the errors of machine tool are introduced.The first part of the paper is for the position measurement. The idea of themachine rotary axis centering is proposed. A single sensor rotary probe whose core isa triangulation laser displacement sensor is developed based on this idea. Using thechange of the limited values of the probe when it is rotating, the approximation centerposition models for the standard round and the elliptical are established. Finally, thehole-center distance measurement method and the corresponding experimental deviceare designed based on the approximation centering model. The function of thehole-center distance measurement experiment doesn’t only verify the approximationcenter position model, but also extends the methods from the position measurement tothe dimension measurement.The second part is about two kinds of non-contact inner dimension measurementmethods. The one is: It utilizes the single sensor rotary probe as a measurement bodywith the single laser rotating, so a method about the single laser rotary searching limitpoint is proposed. The searching model could find the limited point from anywhere ofan arbitrary surface to a fixed point of the rotation axis. The measurement methods ofthe inner dimension including the hole diameter and distance between inner parallelplanes are constructed based on the single laser rotary limited point searching model and comparative measuring method. Both of the measurement methods have beenverified by the experiments in a CNC machine tool. The other is: A non-contactconstant-value-comparing probe is developed, which is similar to a micrometerdiameter. We analyze the collinearity tolerance of the reverse dual laser beam of theprobe, and design a corresponding collinearity measurement and calibration method.Then, it uses a standard objects constructed by some standard ring gauges, quicklyand easily achieving the calibration of the initial value of the probe. The measurementmethods of the inner dimension including hole’s diameter and distance between innerparallel planes are constructed through the extreme characteristics of the probe whenit is moving and scanning along a trajectory that could make the optical axis anddimension line of the hole or the inner plane overlap each other. Finally, it iscombined with the comparative measurement method to achieve measurementdimension of the inner parallel plane and the hole.The third part is about the measurement methods for the some errors of machinetool. Firstly, the upside down mode of the probe and the approximation hole-centerlocation method are used to realize dynamic measurement of parallelism between therotation axis of the machine tool and guideway in the synthetic direction. Secondly,the laser test method for radial runout based on twice deviation elimination isproposed, which could dynamically measure the radial runout of the machine toolspindle.The results of this study has some practical promotional value, which is expectedto be used as new means to complete some rigorous tasks for the on machinemeasurement of the large workpieces, as well as some tasks of machine tools. Thesemethods are expected to improve the efficiency and accuracy of these measurementtasks.