A Low-Cost Calibration Strategy for Measurement-While-Drilling System

The measurement-while-drilling (MWD) system is mainly used to draw borehole trajectory in a coal mine. However, its measurement error directly demonstrates a deviation between the drawing locus and the actual path. Thus, it is imperative to effectively compensate the error in advance. In this study, the traditional-integrated error model is adopted and a low-cost calibration strategy, namely an incomplete calibration strategy, is proposed. In this strategy, the ellipsoid-fitting method is quoted to determine the combined bias and orthogonalize the coordinate frame of the triaxial accelerometer, and a new plane-fitting method is exploited to align the orthogonal accelerometer coordinate frame with the body coordinate frame of the MWD system; meanwhile, the theoretical basis is also stated with the simulation verification of MATLAB. Besides this, the scalar product constant method is finally employed to acquire the error model of the triaxial magnetometer on the condition of the previously calibrated accelerometer coordinate system. In the end, the newly designed calibration strategy was experimentally tested with the MWD prototype developed by ourselves. The results reveal that the strategy can not only be implemented without the help of other expensive auxiliary equipment but also has good performance in attitude reconstruction.