Nonlinear Control Algorithms for Low-Cost Seeker Head

Gilad Fursht
Work towards M.Sc. degree under the supervision of Prof. M. Idan
Faculty of Aerospace Engineering
Technion – Israel Institute of Technology

Low-cost seeker head line-of-sight (LOS) control design presents a great challenge due to system uncertainty and internal disturbances caused by the simple mechanical and electromechanical system components. One of the most severe phenomena that are difficult to model is friction. Conventional controllers, such as the commonly used proportional-derivative or proportional-integral-derivative (PID) controllers cannot guarantee that the required performance characteristics are met over the entire field-of-regard, which is quite large in nowadays seeker heads designs. Therefore it is suggested to utilize nonlinear robust control methods, such Sliding-Mode-Control (SMC), which may introduce enhanced capabilities to deal with system uncertainties and disturbances. In this work, two such nonlinear controllers are proposed to address the line-of-sight control task: a conventional SMC and high order (2-SM) Super-Twisting SMC. The higher order sliding-mode controller was introduced in order to better deal with the chattering phenomenon accompanied with the conventional SMC design. Due to the strong nonlinearities and the multi-input-multi-output (MIMO) coupled structure of the seeker head setup MIMO SMC design methods were used.
The performance of the proposed controllers is compared to a commonly used PID controller. The comparison is based on numerical simulation and laboratory tests carried out with a real low-cost seeker head. The controllers were tested in command tracking task. In addition, axes decoupling and disturbance rejection in a LOS stabilization tasks were evaluated. The numerical simulation is based on the simplified seeker head mathematical model. It was used to tune the compared controllers and access their performance bounds.
In the numerical simulation, study, performed without severe modeling errors and disturbances, all controllers exhibit similar performance. The performance difference between the controllers was revealed in the laboratory tests that clearly demonstrated the advantage of the robust nonlinear SMC methods in meeting system performance characteristics, while facing system nonlinearities, un-modeled dynamics, coupling and disturbances. In addition, the performance of the high order super-twisting controller both in command following and in coupling/disturbance rejection, was superior to both the PID and conventional SMC controllers.

The talk will be given in English

Wed, 09-04-2014, 16:30 (Gathering at 16:00)

Classroom, ground floor, Library, Aerospace Eng.

Light refreshments will be served before the lecture

Nonlinear Control Algorithms for Low-Cost Seeker Head