This study considers a fifth order theoretical model for an electrohydraulic servo system. The experiments were conducted with various values of load stiffness and inertia of the electrohydraulic servo system to compare with the fifth-order theoretical model. It was found that the theoretical results showed good agreement with the experiments. The load stiffness was found to give little influence on the frequency response at the frequency where the phase lag is less than 180 degrees. The higher stiffness ratio gives more damping to the servo system at the frequency where the phase lag is over 180 degrees: however, its influence on the response becomes less when the stiffness ratio exeeds 2, 6. The higher inertia ratio of the load to the servo drive gives more damping as well as slower speed of response.
In this study, a hydraulic servo system is considered to be theoretically expressed in the fifth-order, and the gain margin of the fifth-order hydraulic servo system was calculated in terms of the natural frequency ratio of load to servo drive with various values of load-damping ratios and inertia ratios of load to servo drive. The experiments were conducted with various values of load stiffness and inertia of the hydraulic servo system to compare with the fifth-order theoretical model. It was found that the theoretical results showed good agreement with those of the experiments. It was also found from the theoretical model that the natural frequency ratio of load to servo drive must be greater than unity for a servo system to be stable. The relationship between the natural frequency ratio and the inertia ratio for a servo system to have optimal response was qualitatively clarified.
Contamination has been long recognized as the main source of failure to systems including pulp and paper making machines. Many researches has been conducted and concluded that the contamination control is the most effective means of preventing system malfunction. Unfortunately, the potential benefits are not being fully realized as often a ‘fix’ is implemented without considering other factors in the process.This paper explains the practice of Total Cleanliness Control (TCC) which involves a systematic and complete approach to the subject of fluid system cleanliness. The implementation of this practice by component producers, system builders and operators alike will enable them to realize the benefits and the subsequent contribution to the profitability of the company.
The Multi-pass filter test is the most common method to evaluate the performance of hydraulic filters. The test is conducted at a constant flow rate at constant temperature and very high dirt ingression in order to evaluate filter performance at accelerated test condition. This standard test does not represent operating condition of the modern hydraulic control systems. In order to precisely represent filter performance in the field in the laboratory, the Cyclic Stabilization Test (CST) has been developed. The CST can reliably measure the ability of the filter to control contamination in an even lower ingression environment. It also simulates cyclic flow condition to measure filter performance. In this paper, the CST is proposed as a more effective method for filter performance evaluation method.
