An Automatic Calculation Method Of The Fixture Location Error

Calculation of fixture location error is an important part of fixture design.The accuracy and efficiency of calculation of fixture location error will affect the production cycle of fixture,and then affect the production efficiency of enterprise products.Computer aided tolerance analysis is the most powerful method and means for tolerance design.The expression,organization and processing of tolerance information are the foundation and core content of computer aided tolerance design software.In this paper,an automatic method of calculation of fixture location error is proposed based on the "Research on the application and inspection method of tolerance principle based on the linkage mechanism model(51675147)”.Firstly,An automatic calculation method of the fixture location error is presented in this paper.The automatic calculation mechanism of the method,the coordinate system hierarchy of workpiece-fixture assembly system and its establishment rules are introduced and discussed firstly.Then,the fixture locating elements are grouped into the compound location element based on the machine assembly model,and the compound rules of the compound location element which contact with same location datum of the workpiece are described.At the last,a prototype software to calculate the location error automatically is illustrated and an examples are given to verify the prototype software.The main contents of this paper include the following parts:1)In the first chapter,this paper introduces the concept of fixture location error and its causes,the general calculation method of fixture location error,analyzes the research status of location error analysis at home and abroad,discusses the significance of this topic,and gives the main research content and innovation points of this paper.2)In the second chapter,the principle of automatic calculation of fixture location error is given,and the error transmission relationship of fixture assembly is introduced.In order to realize the automation of the calculation process,the establishment rules of the workpiece coordinate system are given.An example is given to illustrate the establishment process of workpiece coordinate system under the mode of three plane location and one side two hole location.3)In The third chapter,this paper introduces the tolerance information representation model of spherical feature,cylinder feature and plane feature based on control point variation model.This paper introduces the establishment rules of datum reference frame based on construction elements,and illustrates the establishment process of reference frame with examples,analyzes the meaning of geometric element error transfer diagram and serialization output,and gives the automatic establishment algorithm and serial output algorithm of geometric element error transfer diagram.4)In the fourth chapter,the meaning of error transfer diagram and serialization output is analyzed,and the automatic establishment algorithm and serialization output algorithm of assembly part error transfer diagram are given.This paper analyzes the significance and rules of the recognition and sequencing of parts assembly mode,and gives the calculation method of assembly error based on real machine,and illustrates the calculation process of assembly error under three plane of assembly with an example.5)In the fifth chapter,the processing method of the composite positioning element is given,and the sampling function of the changing simulation probability between the actual positioning element and the workpiece is given.It also introduces how to use probability sampling function and tolerance value of geometric elements to generate the position of actual geometric elements.6)The sixth chapter introduces the secondary development method of Solidworks,and gives the result description of fixture positioning error.This paper introduces the development framework and process of the automatic calculation software of positioning error,and verifies the correctness of the software with several examples.