Parallel Analysis And Calculation Of Multi-geometric Positioning Errors Based On Theoretical Datum

The analysis and calculation of the positioning error of the workpiece in the fixture is one of the important contents in the fixture design of the machine tool.The magnitude of the positioning error is the basic basis to judge whether the positioning scheme of the workpiece is reasonable or not and to improve the positioning scheme.When the workpiece is positioned on the fixture,the error must be related to the fixture,but the current definition of positioning error can not be connected with the fixture and the workpiece.At present,the calculation method of positioning error only aims at a single geometric quantity and lacks generality.in order to improve this problem,this paper analyzes the cause of workpiece positioning error,finds its essence and gives a clear definition of positioning error.according to the definition,the universal calculation method of positioning error is studied.This paper puts forward the concept of theoretical benchmark,judges the positioning status of the workpiece on various modular fixtures,sums up its determination method by using the geometric principle and the correlation of the theoretical benchmark,and summarizes the characteristics and application value of the theoretical benchmark.On this basis,the formation mechanism of the positioning error is improved,the size and position relationship between the process datum and the corresponding theoretical datum is taken as the source geometric quantity,and the positioning error is defined as the projection of the source geometric error in the process dimension direction.Taking this definition as the starting point,the positioning errors of multi-geometric quantities are analyzed and calculated in parallel according to the theoretical benchmark,so as to realize the generalization of the calculation method of positioning errors,which has a certain practical value for computer-aided positioning error calculation.According to the relationship between the machining allowance and the blank size and the process size,the size correlation of the machining allowance is established,and it is concluded that the rough machining margin is related to the blank size and process size,and the finishing margin is only related to the process size.The principle of minimum size relation is determined to reduce the number of relevant blank dimensions to reduce the error of rough machining allowance.According to the characteristics of rough datum,it is put forward that the blank size design should be based on the rough datum of the blank as the design basis.