Constraint Analysis and Reduction of Over-Constraints for Tolerance Design of Assemblies - A Case Study of Ball Valve Design

조립체 공차설계를 위한 제약해석과 과잉제약 개선 - 볼밸브 설계 사례연구

Park, Jun Il;Yim, Hyunjune

  • Received : 2016.02.22
  • Accepted : 2016.07.09
  • Published : 2016.08.01


Mechanical designers often make mistakes that result in unwanted over-constraints, causing difficulty in assembly operations and residual stress due to interference among parts. This study is concerned with detection and elimination of over-constraints. Screw theory is a general method that is used for constraint analysis of an assembly and motion analysis of a mechanism. Mechanical assemblies with plane-plane, pin-hole, and pin-slot constraint pairs are analyzed using screw theory to illustrate its utility. As a real-world problem, a ball valve design is analyzed using the same method, and several unwanted over-constraints are detected. Elimination measures are proposed. Nominal dimensions of some parts are adjusted, and dimensions and tolerances of the pins and holes are modified using the virtual condition boundary concept. The revised design is free of over-constraints. General procedure for applying screw theory to constraint analysis is established and demonstrated; it will contribute to improving quality of assembly designs.


Over-Constraint;Assembly design;Screw theory;Tolerance design;Ball valve


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Supported by : 홍익대학교, 대우조선해양주식회사