Metrology of Non-Rigid Objects

Blaedel, K L ; Smith, D W ; Claudet, A A ; Kasper, E P ; Patterson, S R

Lawrence Livermore National Laboratory

关键词: Usa;    Dimensions;    Shape;    Geometry;    Compliance;   

DOI  :  10.2172/15005129
RP-ID  :  UCRL-ID-146957-REV-1
RP-ID  :  W-7405-ENG-48
RP-ID  :  15005129

美国|英语

来源: UNT Digital Library

【 摘 要 】

Dimensional characterization of non-rigid parts presents many challenges. For example, when a non-rigid part is mounted in an inspection apparatus the effects of fixturing constraints cause significant deformation of the part. If the part is not used in normal service with the same load conditions as during inspection, the dimensional characteristics in service will deviate from the reported values during inspection. Further, the solution of designing specialized fixturing to duplicate ''as-installed'' conditions does not fully resolve the problem because each inspection requires its own methodology. The goal of this project is to formulate the research problem and propose a method of assessing the dimensional characteristics of non-rigid parts. The measured dimension of a rigid component is traceable at some level of confidence to a single source (NIST in the USA). Hence the measurement of one component of an assembly can be related to the measurement of another component of that assembly. There is no generalized analog to this pedigreed process for dimensionally characterizing non-rigid bodies. For example, a measurement made on a sheet-metal automobile fender is heavily influenced by how it is held during the measurement making it difficult to determine how well that fender will assemble to the rest of the (non-rigid) car body. This problem is often overcome for specific manufacturing problems by constructing rigid fixtures that over-constrain the non-rigid parts to be assembled and then performing the dimensional measurement of the contour of each component to check whether each meets specification. Note that such inspection measurements will yield only an approximation to the assembled shape, which is a function of both the geometry and the compliance of the component parts of the assembly. As a result, non-rigid components are more difficult to specify and inspect and therefore are more difficult to purchase from outside vendors compared to rigid components. The problems are compounded as the requirements come to include higher and higher precision. The central idea for this project is the concept of a ''free shape.'' The free shape is the geometry of the part when no loads are present. That is, when those loads produced by fixturing, gravity and others are not present. Since it is impossible to directly measure the free shape, some method for inferring it must be developed. Once the free shape is known some metric must be developed for acceptance or rejection of the part.