Opto-Mechanical Method for Measurement of Ferrule Concentricity and Roundness Error

摘要

A novel method for determining ferrule concentricity and roundness error of the outside diameter is presented, based on a Fast-Fourier Transform (FFT) of microhole position at different angular orientations of the ferrule. The resulting concentricity value is independent of the roundness error. Connector insertion loss is one of the most important parameters in fiber-optic transmission system design. Because concentricity error in the ferrule is a major contributor to insertion loss, accurate measurement and control of this parameter is very important to the connector manufacturing industry. Currently, all measurements of concentricity error are influenced by the roundness error of the outside diameter of the ferrule, which reduces the precision and accuracy. At the same time ferrule roundness error is an important parameter that characterizes the quality of the ferrule. A separation between ferrule concentricity and roundness error will improve the control of connector insertion loss and identify ferrules with poor roundness error. A standard opto-mechanical method for ferrule concentricity measurement positions a ferrule in a v-groove as shown in Figure 1. The position of the center of the microhole is measured, then the part is rotated through 180° and the position of the microhole is measured again. The difference between the two microhole positions is calculated as concentricity. This measurement is accurate and precise when the roundness error of the outside diameter is small compared to the concentricity. As the roundness error increases the concentricity measurement accuracy reduces because the roundness error contributes to the movement of the ferrule microhole as it is rotated. Other standard methods improve the measurements precision by monitoring the position of the center of the microhole at several different angular orientations of the ferrule. However the accuracy would still suffer because of the contribution of roundness error. This paper proposes that an appropriate application of a FFT to the microhole position data can be used to separate pure concentricity and roundness error achieving improved precision and accuracy in the measurement of concentricity while obtaining an accurate roundness error measurement.