Research On Multi-objective Fixture Layout Modeling And The Optimization Based On Memetic Algorithm

Machine tool fixture is sustaining equipment, which is widely used in the process of manufacturing. It is used for locating and clamping of workpiece in the machine tool table. The manufacturing and installation errors of the fixture locating elements,localization stability will cause the workpiece position deviation, namely there are errors between the actual position and the theory position, and eventually led to the workpiece machining errors. By the analysis of fixture locating layout on the workpiece location accuracy and stability, a multi-objective fixture layout model is established. We can obtain the workpiece machining errors caused by the known error source and localization stability, and then we can optimize the fixture layout. In this paper, the fixture layout was studied and the following work has been completed:First of all, the relationship between the errors of fixture locating elements and the workpiece position errors was analyzed. Then, the model of the relationship between the position error of workpiece and the fixture locating elements errors was established. By analyzing the relationship between localization stability of workpiece and the overall geometry shape distribution of locating elements. We can establish the model of localization stability which is related with overall geometry shape distribution.Then, a multi-objective fixture layout optimization, involving workpiece position errors objective function and localization stability objective function was established.Both the objective function of the multi-objective problem is related with the position of locating elements. The model considering the errors of locating elements and the localization stability related to machining precision of workpiece. By minimum position error of workpiece and maximum the localization stability, we can obtain improve machining precision of workpiece.Finally, we describe a new approach based on Memetic Algorithm(MA) to multi-objective fixture layout optimization, considering both location accuracy and stability. This approach uses an entropy method to obtain the weights of each objective functions, and establishes a fitness function. Then, a Memetic Algorithm is developed to properly select the positions of locators to minimize the fitness function.By comparing with a single objective model based on GA to validate that themulti-objective fixture layout model is corrected and the method for a multi-objective problem is reliability effectively and efficiently.