Rana Saha

Effects of flow inertia modelling and valve-plate geometry on swash-plate axial-piston pump performance

The present work aims at developing a methodology for designing a swash-plate axial-piston pump whose barrel kidneys are wider than the bridges separating the kidney ports on the plate. Besides reducing pressure ripples and avoiding cavitation for minimizing the fluid-borne noise, maximization of the pump discharge has also been considered in formulating an objective function to be minimized. A comprehensive mathematical model considering oil compressibility and inertia has been developed and implemented in MATLAB/Simulink for dynamic simulation of the pump flow. The model has been found acceptable by observing a good match between its predictions of mean discharge and delivery pressure and available experimental results. A detailed parametric study has been performed and the optimum angles for the valve-plate pre-compression and the barrel kidneys have been obtained.

Design of an Adaptive Fuzzy-Bias SMC and Validation for a Rugged Electrohydraulic System

An adaptive fuzzy-bias sliding-mode controller has been designed by adding biasing to an existing controller for motion tracking by an electrohydraulic system. The system has a proportional valve with large deadband and a cylinder with jump in static friction and nonlinear but continuous dynamic friction. While the biasing controller takes care of the discontinuous features, the fuzzy controller approximates the other system nonlinearities. The sliding-mode controller compensates the approximations. By a number of real-time experiments, the appropriate choices for the number of fuzzy rule base and some free parameters have been established. Then, starting with the same set of initial parameters for tracking step and sinusoidal demands of different frequencies, the responses have demonstrated sufficient adaptability of the controller.

GA-Optimized Fuzzy-Feedforward-Bias Control of Motion by a Rugged Electrohydraulic System

An electrohydraulic system with a proportional valve and industry-grade cylinder has been used to target the servoclass tracking performance. Such systems have a wide range of heavy-duty applications, where the environment could be quite dirty along with the demands becoming faster and more precise every day. High static friction in the cylinder and large deadband of the valve in the system pose control challenges that are more severe than in a system with a servovalve and a low-friction cylinder. A fuzzy-feedforward-bias controller has been developed and a genetic algorithm has been used to optimize the controller parameters. The real-time control experiments revealed excellent tracking throughout the cycle for sinusoidal displacements beyond 1.5 Hz.

Real-time fuzzy-feedforward controller design by bacterial foraging optimization for an electrohydraulic system

High power-to-weight ratio rugged electrohydraulic systems are extensively used for land tilling, harvesting, construction and various industrial control operations. Flow, friction and valve deadband nonlinearities of these systems make the controller design quite challenging, especially for meeting fast and precise motion tracking requirements. For such a system, a bacterial foraging optimization, or BFO, has been employed with a simple swarming method proposed here to design a real-time controller. With a fuzzy voltage compensating the flow-related continuous nonlinearities, a feedforward voltage has been employed to cater for known external loading and discontinuous internal nonlinearities due to the valve deadband and cylinder stiction. Acceptability of the optimized controller has been demonstrated by testing the performances for square, trapezoidal and triangular demands for the piston position variation with time.

Actuation dynamic modeling and characterization of an electrohydraulic system

The physical model of an electrohydraulic actuation system with pressure-reducing cylinder end cushioning has been obtained. In order to arrive at the closure of the model, experimental models for actuator friction and the characteristics of the relief, non-return and proportional valves have been constructed. The variation in discharge through the proportional valve with both pressure and command signal has been modeled by training a neural network with experimental data. For the characterization of the discharge through the proportional valve, besides square root of the pressure drop in each metered orifice, polynomial forms of command signal for the discharge coefficients have been used. Such a direct characterization of the discharge with the command signal eliminates the orifice opening as an intermediate variable. A simple friction model that retains all the features of the existing complex models has been developed. Parameters such as maximum dynamic friction and the corresponding velocity have been introduced for this purpose. All these nonlinear subsystem models have been integrated together in MATLAB/Simulink frame to predict the actuation dynamics. The variations in the predicted and experimental displacements of the piston against different command signals have been found to be quite close to each other.

Lessons learned from using some bio-inspired optimizers for real-time controller design for a low-cost electrohydraulic system

Display Omitted Controller design for an electrohydraulic system with proportional valve.Fuzzy control with suitable feedforward and bias compensations.Controller parameter optimization by Artificial Bee Colony technique.Real-time position demands of Regulation, tracking and composite types.Superior controller performance than that of other existing optimized servosystem. Well-designed searching procedures following natural processes have been developed for finding optimized solutions of complex systems. Here, a comparison of performances of some optimizers, namely differential evolution, genetic algorithm, bacterial foraging and artificial bee colony technique, have been carried out for designing a fuzzy-feedforward real-time controller of an electrohydraulic motion actuation system. The first two optimizers execute dominatingly exploratory search, while the latter two execute a combination of exploratory search with intensified exploitive search in prospective regions, thus providing faster convergence. The optimized controller has been designed by minimizing a response error integral for some standard displacement demands of the highly nonlinear system. The strong nonlinearities in the system arise from the friction of low-cost industry-grade cylinder and large deadband of rugged proportional valve. The convergences to the minimum of zero for a number of nonlinear functions have also been demonstrated for all the optimization processes. These optimizers with faster convergence rate have been shown to be robust against arbitrary demands like variable frequency sinusoidal demands and sinusoidal demands with superimposed log concave-convex variations.

Study of leakage flow through a spool valve under blocked-actuator port condition—Simulation and experiment

The spool valve is the key component of hydraulic control system, and the performance of spool valve depends on its leakage behaviour. Again, the leakage flow of spool valve is highly susceptible to valve uncertain dimensions, radial clearance and overlap or underlap. In the present work, the relative performance of critically lapped, underlapped and overlapped valves has been demonstrated in terms of leakage flow rate and pressure sensitivity about the metered ports. An approach to explore uncertain dimensions of the valve has been developed using CFD as an investigating tool. The comparison of CFD prediction against experimental results has also been carried out. It is found that the CFD predictions are in excellent agreement with the experimental results.

Designing Aerostatic Bearing With Counterbalancing Gaps for Lifting a Heavy Payload

An aerostatic bearing has been designed for supporting a heavy payload. The bearing involves an axial gap on the stator top that provides an upward lift, a bottom gap for counterbalancing the tendency of large lift-off, and a feeding orifice at the bearing inlet that is connected with the gaps by a network of holes or inherences yielding the damping. Notable contributions of the work are proving the concept by numerical simulation through first-principle order-separated modeling and evolving a simple solution strategy. The predicted vertical motion dynamics of the payload reveals that, depending on the target range of the payload weight, alternatives could be free or choked orifice designs.

Real-Time Pole Placement Control of the Rugged Electrohydraulic System

Features like high power to weight ratio, self lubrication, heat dissipation and fast control make hydraulic systems superior to mechanical and electric systems. Such systems are used in aircraft, motion simulators, metal-cutting, universal-testing machines and material handling for heavy industries. For a precision operation, it is usual to employ electrohydraulic servo systems that are more sophisticated than systems with proportional valve. Due to larger deadband and higher flow nonlinearities, the low-cost rugged proportional valves together with standard PID controllers result in poor response for tracking demand. A controller has been designed through a novel state estimation algorithm and the usual pole placement (PP) technique by carefully choosing the operating points. One high friction cylinder and another industrial grade cylinder have been driven separately by using the same proportional control valve. The designed controller has yielded better performance compare to the PID controller.

Designing an optimized model-free controller for improved motion tracking by rugged electrohydraulic system

Electrohydraulic actuation systems with proportional valves and industry-grade cylinders have widespread use due to their low cost and ease of maintenance. Achieving good tracking of output position of the piston in such a system by a proper controller design is the objective of this study. Due to various parameter uncertainties and complex nonlinearities like piston friction, valve deadband and flow characteristics, the variation of oil property with working temperature and air entrapment volume, the implementation of a model-based control becomes quite difficult for such systems. A notable contribution of this work is to couple a model-free fuzzy controller with a feedforward controller with all the parameters estimated by a real-coded genetic algorithm. Also, the optimizer has been used for identifying an appropriate fuzzy structure that is easy to implement in real time. A comprehensive experimental study has revealed the best fuzzy structure to be achieved through a Gaussian fuzzification of linear combination of the position and velocity errors as the input and singleton membership function for the output voltage actuating the proportional valve. Excellent responses with good disturbance rejection capability and energy efficiency have been achieved. These responses have emerged superior to those achieved in a similar system with different controller structures and in systems with much costlier components.