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

Slide 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 Slide 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 Reactance Hydraulic Transformer.  Allows the transformation of flow into pressure or visa-versa.  Similar operating principal to a buck converter.

UKACC PhD Presentation Showcase Slide 4 Fast Switching Valve  Three stage valve  37.7mm 2 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 Slide 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 2 nd order inverse model, along with a negative delay.

UKACC PhD Presentation Showcase Slide 6 Simulated Results

UKACC PhD Presentation Showcase Slide 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.