Tolerance Prediction in Modular Fixtures and Proposal of Sensor-Based Modular Fixtures

This paper presents a methodology to predict manufacturing tolerances when the most important source of error is the locators variability. The locators variability is modeled as a multivariate normal system where the dependence among locators errors due to clamping deformations is considered. The tolerance of a feature is modeled as a function of the deviations among the points that define the feature. A case study with a 3-2-1 modular fixture is presented and both simulations and experiments were conducted to validate the methodology proposed. The experimental results confirm a good approximation between the predicted tolerance and the measured one (1.9 mm and 2.1 mm, respectively). To improve workpiece location, this paper also presents the potential use of precision sensors integrated in modular systems. For the case study, it is estimated a parallelism tolerance improvement from 1.9 mm to 0.47 mm when the workpiece is set up in a sensor-based fixture. Published in the Transactions of NAMRI/SME, Vol. 36, 2008, pp. 557-564.