M.S. Thesis Presentation by Anand Raghu
Tuesday, May 9, 2003

(Dr. Shreyes Melkote, advisor)

"Prediction of Workpiece Location as a Function of Fixture-Induced Errors"


An integral part of any manufacturing system is the fixturing mechanism used. The fixture serves two important purposes: accurate location and holding the workpiece. Most fixtures consist of locators (that serve to uniquely position the part) and clamps (that serve to hold the part in place). However, there are several fixture-induced error sources that effect the position and orientation of the workpiece in the fixture. Error sources include but are not limited to bulk deformation of the workpiece/locators/clamps due to the clamping force, geometric errors at the locators, and the effect of clamping sequence. Although these error sources have been modeled independently, no model exists that represents their aggregate effect on workpiece position and orientation. Hence, the primary goal of this thesis is to develop and experimentally verify a model for predicting workpiece location that integrates the aforementioned error sources. With this model, both fixture designers and manufacturers using the fixture will have a better understanding of the effect of each error source on the quality of the part being produced.

Analytical and numerical models are developed to model the major sources of compliance in the system. Models to determine the intermediate and final workpiece position and orientation to describe part loading and clamping are also developed. Lastly, a relatively simple yet accurate model to capture the effect of clamping sequence on part position and orientation is developed. The model is implemented in MATLAB. Experimental validation of the model using a 3-2-1 fixture layout is presented. The model is useful in predicting workpiece location as a function of fixture compliance, workpiece compliance, contact geometry, fixture geometric errors, and clamping sequence.