Off-line displacement error correction method for servo-hydraulic testers

Purpose: This paper presents an approach towards improving the test rig performance in reproduction of random excitation to which a prototype hydraulic damper is subjected. The method is intended to be implemented as a software solution without modifications either in hardware or the settings of the servo-hydraulic tester. These are the conditions of fatigue tests when a specific signal sequence (block) is repeated until failure of the sample. Design/methodology/approach: Experimental validation of the proposed correction method was conducted using a servo-hydraulic test rig and a transfer function inverse model which was identified based on the operational data. Findings: The proposed method, both in the frequency and time domain, improves the tracking of the test signal and allows an accuracy of more than 95% to be gained using the best fit measure in the case of reproduction of coloured noise signals. Research limitations/implications: It is possible to consider more advanced model-based methods for performing off-line error correction, e.g. state-space models. Practical implications: The proposed method was validated and implemented in the LabVIEW® software to automatically perform the correction of the test signal before the test. The method was validated for the test rig with and without the tested object. Originality/value: The paper proposes an off-line control strategy that improves the reproduction of the load signal in case of repeatable test sequences achieving more than 99% agreement between the applied and measured load.