This paper describes a computational procedure to obtain the vertical railroad track irregularities using the signals of an accelerometer and a gyroscope (IMU, inertial measurement unit) installed on a bogie of a railway vehicle. The procedure is designed to be implemented in a real-time on-board track geometry measurement system. The paper includes algorithms for constant and variable forward velocity of the laboratory vehicle. In each case, individual numerical methods to obtain the track vertical irregularities from the accelerometer signal and the gyroscope signal are presented. In addition a sensors fusion algorithm based on the concept of complementary filters is presented. In the sensors fusion algorithm the gyroscope’s based irregularity is used to measured low spatial frequencies while the accelerometer’s based irregularity is used to measure the high spatial frequencies. The numerical examples are developed on the basis of a synthesized irregular track profile that is numerically obtained from a known PSD (power spectral density) used in the railway industry. In the numerical tests the measured acceleration and angular velocity are corrupted with a bias error and a Gaussian white noise to account for the sensors errors. The numerical results compare the original irregularity profile with the measured profile in the space and frequency domains using the PSD and coherence function. Results include the algorithms for a constant and a variable forward velocity of the laboratory vehicle. A good agreement is found.

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