Saikat Mookherjee

Approaching Servoclass Tracking Performance by a Proportional Valve-Controlled System

An industry-grade proportional valve is much cheaper and rugged than a servovalve. A feedforward controller for a proportional valved system has been developed here to achieve tracking controls beyond 1 Hz that are usually attained by servovalves. For compensating the higher nonlinearities, feedforward controllers have been designed offline by proposing appropriate static models for friction and valve flow and executing the supporting experiments. These controllers have been implemented with real-time PID feedback of only the piston displacement. Excellent tracking performance has been obtained up to 2 Hz that has deteriorated with an increase in cylinder friction.

GA-optimized feedforward-PID tracking control for a rugged electrohydraulic system design

Rugged electrohydraulic systems are preferred for remote and harsh applications. Despite the low bandwidth, large deadband and flow nonlinearities in proportional valves valve and highly nonlinear friction in industry-grade cylinders that comprise rugged systems, their maintenance are much easier than very sophisticated and delicate servocontrol and servocylinder systems. With the target of making the easily maintainable system to perform comparably to a servosystem, a feedforward control has been designed here for compensating the nonlinearities. A PID feedback of the piston displacement has been employed in tandem for absorbing the unmodeled effects. All the controller parameters have been optimized by a real-coded genetic algorithm. The agreement between the achieved real-time responses for step and sinusoidal demands with those achieved by modern servosystems clearly establishes the acceptability of the controller design.

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.

Static-Performance Based Computer-Aided Design of a DDV and its Sensitivity Analysis

Abstract Direct Drive valves (DDV) are gaining increasing acceptability for their simple configuration, low leakage, and low cost. Two major components of the present single-stage DDV are a spool valve and a linear force-motor. The objective of the present investigation was to formulate a design methodology and a static performance simulation tool for the DDV. The present work includes lumped and chiefly one-dimensional, non-linear field modelling of flow through the spool valve and magnetic flux in the motor. Detail modelling has been done only for leakage flow in the spool-bushing radial clearance of the spool valve, since it has critical bearing in the performance analysis. A computer-aided tool for designing a single stage valve, based on some additional simplifying assumptions of the lumped model, has been presented. The static performance algorithm was developed on SIMULINK, without invoking the design-level simplifications. The simulation tool has been used to carry out a design validation against the known performance of Moog Series D633 valve. Different designs of the valve, corresponding to different actuation specifications were obtained, and their static performances have been investigated. Also a sensitivity analysis has been carried out to study the effects of tractive air gap area ratio in the motor and port lap conditions in the spool valve.

Pressure Compensator Design for a Swash Plate Axial Piston Pump

An in-line axial-piston swash-plate pump with pressure compensator is widely used for its fast speed of response and power economy. Although several simulation based design approaches exist to minimize issues like fluid-born noises, ample scope exists for more exhaustive design analysis. The most popular pressure compensator for a variable displacement pump with a spool valve actuating the control and bias cylinders has been taken up here. With an existing comprehensive flow dynamics model, an updated model for swiveling dynamics has been coupled. The dynamics also includes the force containment and friction effects on the swash plate. A design optimization has been accomplished for the pressure compensator. The target of the optimal design has been set as minimizing the transient oscillations of the swash plate, the compensator spool, pressures in the bias and control cylinders along with avoidance of both over-pressurization and cavitation in the bias cylinder. It has been found that the orifice diameters in the spring-side and at the metering port of the spool valve and in the backside of the bias cylinder have critical role in arriving at an optimum design. The study has led to a useful design procedure for a pressure compensated variable displacement pump.

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.

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.