Study On Some Technologies In Fixture System Errors

With the rapid development of manufacturing and precision measurement technology, higher demands are put forward on the quality and precision of the fixture. Because the errors of fixture system affect the precision of workpiece by changing the localization datum, so it is of great significance to detect and control the fixture system error. The fixture system errors model, tolerance assignment and error optimal adjustment of the locators are talked about in this paper.First of all, the mathematical model between fixture system errors and position and orientation deviation of the workpiece (PODW) is established, of which parameters are set based on 3-2-1 localization scheme. Then the individual locator error model is established after in-depth study. And the relationship between the geometric error of workpiece surface features, such as vertical error, parallelism error, position error and slope error etc, and the geometric error of individual locator is presented.Secondly, a method is proposed to distribute the locators'tolerance according to workpiece surface feature tolerance. The tolerance is assigned based on the different influence of each locator on workpiece surface feature, for multiple machining surface tolerances, the tightest tolerance is selected as the final tolerance for each locator. Then a method of optimizing the fixture errors by adjusting the locators'position is presented, which can get to accuracy localization. Set composite position error model of workpiece as an example, position of locator with greater impact on it can be adjusted based on localization sensitivity. Adjustment amount along the contact surface normal direction is calculated by program, which can instruct optimization of locator error and lead to minimum localization error. A simulation study is used to verify the method.Finally, based on the simulation verification, with Renishaw OMP60 probe and SKY2003 open CNC system, the On Machine Verification Platform is built to measure geometric errors of the fixture, and verify the fixture error adjustment method. The simulation and experiment to verify the above deductions and methods show that the conclusion is correct, and methods to distribute tolerance and adjust error are effective and practical.