| Multi-axis CNC machine tools is more and more important in modern machiningindustry due to its flexibility and high efficiency for complex curved surface machining.To satisfy the increasing demand in accuracy and quality of productions, high accuracyis becoming the most important indicator for a machine tool. Multi-axis CNC machinetools are3-axis CNC machine tools with additional rotary axis, the rotary axis could bea rotary table or a rotary spindle head. The dissertation modeling models for machinetool with one rotary table and machine tool with two rotary tables based on themulti-body kinematics theory, the author also implement measurement experiment on amulti-axis machine tool. At last, a compensation experiment was executed on themachine tool based on an algorithm which improves the accuracy of the machine tool.Based on the HTM (Homogeneous transformation matrices), the author modeling amulti-axis CNC machine tool mathematic model including geometric error terms, anddeduce a relationship of tool coordinate system and work coordinate system in idealcondition and actual condition. In additional, a measurement of geometric errors ofrotary axis with the DBB (double ball bar) was proposed, for multi-axis with only onerotary axis, the measurement has no effect from linear axis, which is an advantagecompare with the traditional method. The author also developed a simulator withVC++6.0, the simulator can give a simulated tract of the DBB with the given geometricerrors, which can be used to gain a qualitative errors effect when use a DBB on a rotarytable. To improve the accuracy, DBB, geometric errors of rotary could be estimated withan identification program and recording data, and the estimated data of geometric errorvalues are used to compensate the G code.The measurement and identification methods are applied to an experiment, in a tworotary table machine tool, the experiment verified the model, measurement and thecompensation method. |
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