Velocity control of single-rod hydrostatic actuators: component sizing and controller design
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Date
2018
Authors
Rafiq, Moosa
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Abstract
Pump-controlled hydraulic actuation of single-rod actuators is more challenging than double-rod actuators due to difference in areas on two sides of single-rod actuators and a need to compensate for differential flow. The performance of a single-rod pump-controlled hydraulic circuit can be significantly affected by variations in load, velocity and circuit design. Designing a simple-to-implement velocity controller for such hydraulic configurations is challenging under these conditions. This thesis presents velocity control of two typical hydraulic circuits; one is commonly used while the other is a novel design. Two issues involved are controller design and component sizing.
The design of velocity controllers is based on Quantitative Feedback Theory (QFT) as the design criteria are graphically illustrated for whole range of plant uncertainties in this design procedure. In order to design QFT controllers for closed-loop velocity control of pump-controlled single-rod hydraulic actuators, smooth open loop performance of hydraulic circuit becomes important. Hence component sizing, i.e., choosing optimal hydraulic components and having an optimal hydraulic design becomes necessary. Hence, a methodology to choose hydraulic components and hence improve system performance is proposed. First, a mathematical model of hydraulic circuit is developed, which is later used in simulations. Next, initial values of selected parameters of circuit components (pilot operated check valves and counterbalance valves) to be used in system are chosen based on manufacturer’s specifications, experimental data and conservative judgement. This is followed by choosing few parameters which need to be optimised. Next, an optimisation algorithm is used on the simulation model to optimize parameters chosen based on an optimization criteria. In optimization, particle swarm optimization (PSO) and modified Nelder-Mead (MNM) algorithms are used to obtain smooth, least jerky system performance.
Next QFT Controllers are designed based on uncertainties found where families of transfer functions are to be obtained. For this purpose, system identification is used in order to obtain frequency responses from measured data and hence uncertainties. All the development reported in this research is experimentally validated. First hydraulic circuit is a commonly used circuit incorporating pilot-operated check valves, while as the second novel circuit uses counterbalance valves.
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Keywords
Hydraulic circuit, Optimization, Optimisation, Parameter, Control, Pilot operated check valve, Counterbalance valve, Valve, PSO, MNM, Nelder, Ten parameters, Hydrostatic, Pump, Pump Control, Algorithm, Simulation, Experiment, Cracking pressure, Optimal, Novel, Design, Methodology, Criteria, Particle, Swarm, Hydraulic design, Optimal design, Validation, Component sizing, Sizing, Sizing hydraulic circuits, Monika, Vibrations, Undesirable region, Multistep, Multistep polynomial, Single rod, Double rod, Single-rod, Double-rod, QFT, Quantitative Feedback Theory, Velocity control, Velocity, Component, Hydraulic component, Jerk, Objective, Objective function, ten parameter, Quadrants, System identification, Chirp, Chirp signal, Transfer function, Uncertainities, Feedback, Frequency, Gain margin, Phase margin