R. Burton

The Variable Structure Filter

This paper presents a new strategy for state estimation. The strategy may be applied to linear systems and is referred to as the variable structure filter. The filter is considered for discrete-time systems subject to random disturbances and measurement noise. It requires a parametric model and can be formulated to accommodate modeling uncertainties. A proof of stability for the filter is provided. For stability this concept requires a specification of an upper bound for uncertainties, disturbances, and measurement noise. The application of this filter to a third-order linear system is demonstrated.

Parameter Identification for a High-Performance Hydrostatic Actuation System Using the Variable Structure Filter Concept

Parameter estimation is an important concept that can be used for health and condition monitoring. Estimation or measurement of physically meaningful parameters and their evaluation against predetermined thresholds allows detection of gradual or abrupt deteriorations in the plant. This early detection of faults enables preventative unscheduled maintenance that is of benefit to industries concerned with reliability and safety. In this paper, a recently proposed state estimation strategy referred to as the smooth variable structure filter (SVSF) is reviewed and extended to parameter estimation. The SVSF is applied to a novel hydrostatic actuation system referred to as the electrohydraulic actuator (EHA). Condition monitoring of the EHA for preventative unscheduled maintenance would increase its safety in applications pertaining to aerospace and would reduce its operational and maintenance costs.

Analysis of a Pressure-Compensated Flow Control Valve

A pressure-compensated valve (PC valve) is a type of flow control device that is a combination of a control orifice and a compensator (often called a hydrostat). The compensator orifice modulates its opening to maintain a constant pressure drop across the control orifice. In other words, the PC valve is so designed that the flow rate through the valve is governed only by the opening of the control orifice and is independent of the total pressure drop across the valve. Because of the high nonlinearities associated with this type of valve, it is impossible, in practice, to design such a valve where the flow rate is completely unaffected by the pressure drop across the valve. In this paper, the effect of the nonlinearities on the performance of the PC valve is investigated. First, a generic nonlinear model of a PC valve is developed. Using this model, all possible operating conditions can be determined. Then a linearized model is developed and used to analyze the dynamic behavior of the PC valve. The model can then be used to evaluate and improve the design and operation of the valve for specific applications.

Sliding mode control for an electrohydraulic actuator system with discontinuous non-linear friction

This paper considers the application of a sliding mode controller (SMC) to a high-precision electrohydraulic actuator (EHA) system with non-linear discontinuous friction effects. An important consideration in such systems is the oscillations that occur in the system response owing to friction for small input signals at cross-over regions where the velocity changes sign. A new model for a high-precision hydrostatic actuation system is developed to investigate the effects of discontinuous and non-linear friction. This model is used in the development of a sliding mode control strategy. A significant result from this study is that the SMC can suppress such oscillations. In addition, the paper uses a linear quadratic approach for defining a discrete-time sliding surface for non-linear systems. A comparative study involving the application of the proposed SMC versus a gain-scheduled proportional controller is presented.

Sliding mode control for a model of an electrohydraulic actuator system with discontinuous nonlinear friction

This paper considers the application of sliding mode control (SMC) to a high precision hydrostatic actuation system with nonlinear discontinuous friction. An important consideration in such systems is the oscillations that occur in the system response due to friction for small input signals at cross-over regions where the velocity changes sign. A new model for a high precision hydrostatic actuation system is developed assuming discontinuous and nonlinear friction in the actuator. This model is used in the development of a sliding mode control strategy. A significant result from this study is that the SMC can suppress such oscillations. In addition, the paper introduces for the first time, a linear quadratic approach for defining a discrete-time sliding surface for nonlinear systems. A comparative study involving the application of the proposed SMC versus a gain-scheduled proportional controller is presented. This comparison demonstrates the performance improvements resulting from the SMC and the added robustness of this strategy given large modeling uncertainties

Parameter Identification for a High Performance Hydrostatic Actuation System Using the Variable Structure Filter Concept

Parameter estimation is an important concept that can be used for health and condition monitoring. Estimation or measurement of physically meaningful parameters and their evaluation against predetermined thresholds allows detection of gradual or abrupt deteriorations in the plant. This early detection of faults enables preventative unscheduled maintenance that is of benefit to industries concerned with reliability and safety. In this paper, a recently proposed state estimation strategy referred to as the Smooth Variable Structure Filter (SVSF) is reviewed and extended to parameter estimation. The SVSF is applied to a novel hydrostatic actuation system referred to as the ElectroHydraulic Actuator (EHA). Condition monitoring of the EHA for preventative unscheduled maintenance would increase its safety in applications pertaining to aerospace and would reduce its operational and maintenance costs.Copyright

Filtering controller in sliding mode: From the estimation to control

Abstract The paper introduces the concept of a filtering controller (FC), which uses sliding mode control as its basis. The FC ‘seamlessly’ integrates a smoothed variable structure filter with a variable structure controller. The paper provides the conceptual derivations of variable structure filtering and its integration with a controller in the presence of uncertainties and non-linearities in control systems. Concepts supported with basic describing equations are used to demonstrate how the FC is developed.

Modeling of a novel fan clutch pneumatic actuation system

A variable speed fan clutch system has been developed to help improve engine temperature regulation efficiency in heavy-duty commercial vehicles. This system is currently in a prototype phase and a detailed physical model of the actuation system is required for control system design and design trade-off analysis. This paper proposes the use of model identification techniques to estimate a minimal model structure. Parametric models of the fan clutch pneumatic system are developed and the system dynamic behavior examined. The fan clutch pneumatic system is composed of three subsystems. Model structure estimates for these subsystems are realized using system identification techniques. The physical and parametric models are validated by comparing simulation and test results. A comparison of the physical and parametric models shows that the physical models outperform the identified parametric models and are able to closely predict the system response to a range of inputs.

Micro-Precision Hydrostatic Actuation System

This paper reports on an important discovery that is: hydrostatic actuation systems are able to manipulate heavy loads with sub-micron precision and large stroke. In this relation, the design of a high-precision hydrostatic actuation system referred to as the ElectroHydraulic Actuator (EHA) is presented. A laboratory prototype of this system has achieved an unprecedented level of performance by being able to move a large load of 20Kg with a precision of 50 nanometers and a stroke of 12cm. This level of performance places the hydrostatic actuation concept in competition with piezoelectric platforms in terms positional accuracy. Experimental results from this prototype are reported and analyzed.Copyright