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2 Journal of Achievements in Materials and Manufacturing Engineering

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

Braska D., Huchla M., Czop P., Wszołek G.

Journal of Achievements in Materials and Manufacturing Engineering

2012

Vol. 55, nr 2

431--438

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.

Application of off-line error correction method software to reproduce random signals on servo-hydraulic testers

Braska D., Czop P., Sławik D., Wszołek G.

Journal of Achievements in Materials and Manufacturing Engineering

2010

Vol. 40, nr 1

41-49

Purpose: This paper presents an approach towards improving the test rig performance for road signals used in automotive shock absorber tests. The goal is to develop a method for correction of the test signal profile in the off-line mode. The method is intended to be implemented as a software solution without any changes either in hardware or the settings of the servo-hydraulic tester. Design/methodology/approach: A two-stage validation of the proposed correction method was conducted using a servo-hydraulic test rig and its first-principles model. The model is capable of capturing key dynamical properties over a wide operating range while being only moderately complex. Both simulation and experimental performance results are presented and discussed. Findings: The proposed method, both in the frequency and time domain, improves the tracking of the test signal by 10-20% and allows an accuracy of more than 90% to be gained using the best fit measure in the case of reproduction of white noise signals. Research limitations/implications: It is possible to consider more advanced model-based methods for performing off-line error correction. These methods can be used if an accuracy close to 100% is expected. Practical implications: The result of the investigations is the algorithm implemented in the LabView software to automatically perform the correction of the test signal before the test. Originality/value: The paper proposes a modern approach towards the validation process by applying a simulation environment. This ensures the involvement of arbitrary disturbance models to investigate key parameters of the correction method without expensive and time-consuming experimental validation. The developed model can be extended to a model of a shock absorber to simulate full interaction between the servo-hydraulic test rig and the tested product.