Ganga P. Jayaraman

Active sidestick design using impedance control

The active sidestick is a mechanical sidestick assembly for fly-by-wire flight control that uses motors, electronics and a high bandwidth closed loop control system to provide grip feel of spring return, breakout forces, and soft-stops. The grip feel characteristics can be user-configured. Also, advanced features such as two-stick cross-coupled operation can be implemented using only electronic feedback signals instead of a mechanical link connecting the two sticks. The goal of this project is to develop a proof of concept system that implements the most important functional requirements of the active sidestick. Safety-critical issues and other flight-worthiness issues are not considered here. The intention is to demonstrate the functionality of the active sidesticks to potential customers in order to generate interest in a request for proposal. This paper describes the system architecture and functional operation of the proof of concept system.

An observer design for a poppet type pressure reducing valve

This paper presents an observer design that may be used to improve the response and stability characteristics of a solenoid operated pressure-reducing valve. Most pressure-reducing valves have very little inherent damping, and can potentially exhibit unstable behavior due to fluid velocity effects during the opening of the poppet. One solution is to improve the dynamic characteristics of the valve by using a closed-loop control strategy. Here, the solenoid current, poppet position, the poppet velocity and the control pressure are feedback signals, used to increase the stability margin and the response time. The cost of the sensors and problems associated with taking derivatives make direct measurement infeasible. We propose to obtain estimates of the poppet position and poppet velocity from only measurements of the valve control pressure and the solenoid current. This is done using a state observer that estimates the poppet position and the poppet velocity without calculating derivatives. These estimates may then be used in a feedback controller that is designed to meet the valve transient response specifications.

Modeling and analysis of an electronic load sensing pump

This paper describes the modeling and analysis of the dynamics of an electronic load sensing hydraulic system consisting of a load sensing pump, a flow control valve, a hydraulic cylinder and an effective mass representing the linkage inertia. Load sensing hydraulic circuits are prone to instabilities and frequently require hydraulic filters in the form of orifices and control volumes to remove unwanted oscillations. Closed loop controllers for such systems are difficult to design due to the nonlinearities and high order transfer functions. In this paper a linear model is derived from equations of motion, and validated against a nonlinear simulation model based on MATLAB. Then, a third order model is derived that can be used for controller design.

Parameter estimation of an electronic load sensing pump using the Recursive Least Squares algorithm

This paper describes a method to estimate in realtime the parameters of a linear model of an electronic load sensing (ELS) pump. It consists of a pressure sensor to measure the load pressure, a pressure sensor to measure the pump discharge pressure, and a Recursive Least Squares (RLS) algorithm implemented in software that runs on an Electronic Control (ECM) in real-time. The RLS algorithm estimates a linear model of the electronic load-sensing pump by measuring the load pressure data, which is the input to the model, the pump discharge pressure data which is the output of the model, and obtaining recursively a least-squares fit to the input-output data. This method can be used to design robust, adaptive controllers for load-sensing systems, or simply to monitor the dynamic performance of the load-sensing pump. The feasibility of this concept has been verified using models of the electronic load-sensing system, and a floating-point implementation of the RLS algorithm.

Simulation analysis of a pitch trim actuator

This paper describes the architecture and modeling of a pitch trim actuator servo drive system designed by Woodward Inc. for a typical midsize business jet aircraft. The PTA system provides secondary pitch control by adjusting a set of trim tabs located on the trailing edge of the elevator surface. Trim tab commands are issued by the trim wheel or the trim switches located on the control stick in the cockpit. Thrust compensation commands and flap position commands may also be sent by the flight computer directly to the PTA system for appropriate pitch corrections. The solution consists of a linear actuator and two electronic control units. Simulation results are presented that demonstrate the accuracy and dynamic performance of the speed control system.

An optimal state estimator for a fuel valve actuator

We describe a digital implementation of a Kalman filter to estimate the true values of the angular position, the angular velocity and the coil current of a motor used to drive a fuel valve. By modeling the effect of coil current on the position sensor as a linear additive term, and the uncertainties in the actuator parameters as an additive random noise on the angular position, angular velocity and coil current, we have attempted to improve the robustness of the estimator. We believe that the storage and execution time requirements of this algorithm as implemented on the TI-320C2407 based actuator are comparable or less than the current model based algorithm.

Motion control of the SOFIA cavity door drive system

This paper describes the architecture and modeling of the motion control system for the cavity door drive system developed by Woodward MPC Inc., for the SOFIA aircraft. We also describe some of the fault tolerance features in the system architecture designed to meet the safety requirements. Finally, simulation results are presented that demonstrate the tracking capabilities of the door drive control system.