A workholding fixture should ensure a stable and precise positioning of the workpiece with respect to the machine tool. This requirement is even more important when modular fixtures are used for the sake of efficiency and reconfigurability. They include standard locating elements, which set the part in a predefined spatial orientation by contacting its datum surfaces. In the computer-based design of a fixture, the layout of locators must be tested against two main sources of problems. Kinematic analysis verifies that any relative motion between the part and the worktable is constrained. Tolerance analysis evaluates the robustness of part orientation with respect to manufacturing errors on datum surfaces. We propose a method to carry out both tests through a common set of geometric parameters of the fixture configuration. These derive from the singular value decomposition of the matrix that represents positioning constraints in screw coordinates. For a poorly designed fixture, the decomposition allows us to find out either unconstrained degrees of freedom of the part or a possible violation of tolerance specifications on machined features due to geometric errors on datum surfaces. In such cases, the analysis provides suggestions to plan the needed corrections to the locating scheme. This paper describes the procedure for kinematic and tolerance analysis and demonstrates its significance on a sample case of fixture design.
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June 2010
Research Papers
A Unified Approach to Kinematic and Tolerance Analysis of Locating Fixtures
Antonio Armillotta,
Antonio Armillotta
Dipartimento di Meccanica,
Politecnico di Milano
, Via La Masa 1, 20156 Milano, Italy
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Giovanni Moroni,
Giovanni Moroni
Dipartimento di Meccanica,
Politecnico di Milano
, Via La Masa 1, 20156 Milano, Italy
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Wilma Polini,
Wilma Polini
Dipartimento di Ingegneria Industriale,
Università degli Studi di Cassino
, Via Di Biasio 43, 03043 Cassino (FR), Italy
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Quirico Semeraro
Quirico Semeraro
Dipartimento di Meccanica,
Politecnico di Milano
, Via La Masa 1, 20156 Milano, Italy
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Antonio Armillotta
Dipartimento di Meccanica,
Politecnico di Milano
, Via La Masa 1, 20156 Milano, Italy
Giovanni Moroni
Dipartimento di Meccanica,
Politecnico di Milano
, Via La Masa 1, 20156 Milano, Italy
Wilma Polini
Dipartimento di Ingegneria Industriale,
Università degli Studi di Cassino
, Via Di Biasio 43, 03043 Cassino (FR), Italy
Quirico Semeraro
Dipartimento di Meccanica,
Politecnico di Milano
, Via La Masa 1, 20156 Milano, ItalyJ. Comput. Inf. Sci. Eng. Jun 2010, 10(2): 021009 (11 pages)
Published Online: June 8, 2010
Article history
Received:
February 26, 2008
Revised:
March 11, 2010
Online:
June 8, 2010
Published:
June 8, 2010
Citation
Armillotta, A., Moroni, G., Polini, W., and Semeraro, Q. (June 8, 2010). "A Unified Approach to Kinematic and Tolerance Analysis of Locating Fixtures." ASME. J. Comput. Inf. Sci. Eng. June 2010; 10(2): 021009. https://doi.org/10.1115/1.3402642
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