Minimization of Crosstalk in Multi-Actuator Hydraulic Systems

Abstract

The field of material testing is dominated by servo-hydraulic control systems owing to their large power to weight ratio compared to servo-electric control systems. Hydraulic systems are capable of producing large forces and torques with a fast response time, making them ideal to conduct fatigue, failure, and wear type tests. Material testing requires high positional and force control accuracy, which is achieved in hydraulics with fast responding servo-hydraulic valves. In this thesis, the impact on the accuracy in positional control of hydraulic test systems is explored, specifically in the case of multiple actuators simultaneously being powered by a singular pressurized flow source. The reduction in performance and position control accuracy of a loadframe due to the dynamics introduced in the system by another loadframe connected to the same hydraulic circuit is called crosstalk.A system model is developed of a hydraulic testing laboratory as a tool to model pressure and flow dynamics in the hydraulic circuit and position dynamics of the actuators. The aim of this model is to measure impact on the position control accuracy of loadframes during simultaneous operation. The model consists of sub-system models of the components of a hydraulic testing laboratory - the loadframes, hydraulic pipeline and a hydraulic power unit. These sub-system models are developed and experimentally validated. The system model is then used to evaluate crosstalk in a baseline test case. Three methods of crosstalk reduction, namely close coupled accumulation, RC Filtering, and 2nd Order RC Filters are analyzed and modelled and shown to be effective tools for the mitigation of crosstalk. The components involved in each method are sized to reduce the pressure fluctuations and improve the position control accuracy of the loadframes to an acceptable value in the baseline test case. The effectiveness of these methods is then evaluated by measuring the reduction of pressure fluctuations and improvement in position control accuracy showing that RC filters are the most effective tools for crosstalk mitigation tools. A cost comparison is conducted on the methods to corelate the expense with their effectiveness, concluding that 2nd order RC filters are the most cost-effective method for crosstalk reduction within the scope of this study.