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Control of a Fast Switching Valve for use in Digital Hydraulics

Control of a Fast Switching Valve for use in Digital Hydraulics. Nathan Sell Nigel Johnston and Andrew Plummer University of Bath. Introduction. Pumps, motors and actuators >90% efficient. High flow, low loss valves. Very complicated and specialised circuits and control.

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Control of a Fast Switching Valve for use in Digital Hydraulics

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  1. Control of a Fast Switching Valve for use in Digital Hydraulics Nathan Sell Nigel Johnston and Andrew Plummer University of Bath UKACC PhD Presentation Showcase

  2. Introduction • Pumps, motors and actuators >90% efficient. • High flow, low loss valves. • Very complicated and specialised circuits and control. • But still get system efficiencies <50% common. • Premise of most hydraulic control is throttling, which is intrinsically dissipative. UKACC PhD Presentation Showcase

  3. Digital Hydraulics • Uses fast switching “digital” valves so that fluid power produced tracks power requirements. • Digital Cylinders • Digital Pumps and Motors • Digital Transformers • University of Bath has created a valve for use in a Switched ReactanceHydraulic Transformer. • Allows the transformation of flow into pressure or visa-versa. • Similar operating principal to a buck converter. UKACC PhD Presentation Showcase

  4. Fast Switching Valve • Three stage valve • 37.7mm2 flow area • 0.2mm stroke • Overlapped spool • Three ports (HP, LP and service) • Integrated position and velocity sensors • Switching at >100Hz • Needs to rise quickly • Overshoot less than 0.1mm • Variable width and frequency PWM UKACC PhD Presentation Showcase

  5. Controller Design • Utilises an Iterative Learning Control • Passes error through inverse model to discover the “incorrect” input • Subtracts this from the previous input • Able to adjust for changes properties or inaccuracies in valve model • Inverse model (L(s)) • Position sensor and accelerometer used with complimentary filters to provide accurate position, velocity and acceleration estimates. • These values are used to numerically implement a 2nd order inverse model, along with a negative delay. UKACC PhD Presentation Showcase

  6. Simulated Results UKACC PhD Presentation Showcase

  7. Summary • Digital hydraulics offers large efficiency savings in a host of fluid power applications. • University of Bath has developed a valve with a view to create a SRHT. • ILC has been shown to be a powerful tool to control the required fast switching valve. • Valve model needs validating on test rig. • Control scheme needs proving in real time. UKACC PhD Presentation Showcase

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