Controller design and implementation for a guidance kit used at spinning rockets and projectiles

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2022-4-28
Günay, Görkem
Traditional spin-stabilized projectiles have disadvantages due to low accuracy and precision with respect to guided munitions. There are two main solutions to eliminate these disadvantages. The first one uses a drag brake mechanism to make 1-D guidance by making range correction. The second solution makes 2-D guidance. Since rotation dynamics of a spin-stabilized projectile is faster than existing servo actuators this solution requires isolation of the guidance kit from the rotation of the projectile body. It is possible to use traditional control actuation systems with movable aerodynamic surfaces for 2-D guidance but it requires complicated electronics and a battery. In the scope of this thesis, the feasibility of an actuation solution to 2-D guidance problem of spin-stabilized projectiles is examined. The examined solution uses a fixed canard structure which is isolated from body rotation. The actuator part consists of an alternator. The stator of the alternator rotates with the projectile body and the rotor of the alternator rotates with a fixed canard structure. There is a net torque and a net force generated by fixed canards and guidance can be done by controlling the direction of the net force. Therefore, the main actuation problem is position control of an alternator. Since the actuation problem is reduced to one-axis position control, required driver electronics and actuators are simplified. And also, it is possible to use power generated by the alternator instead of using a battery. A test system is developed to simulate the rotation of the projectile body and aerodynamic torque on the guidance kit. Mathematical model of the test system with the alternator is created. To make position control of the alternator, a cascade PI controller is designed and applied in the test system. Requirements of the controller are satisfied with PI controller in the velocity loop and P controller in the position loop. Clamping anti-windup method is used to overcome the overshoot problem caused by the limitation of the controller output in the velocity loop. Also, in the scope of this thesis, flight dynamics of a spin-stabilized artillery projectile is examined. Firstly, the model is established in 6-DOF, then it is extended to 7-DOF with the addition of 1-DOF generated by the free rotating part of the guidance kit. This 7-DOF flight simulation model is used to find the angular velocity of the projectile body and aerodynamic torque on the guidance kit. The designed controller is tested with changing aerodynamic torque and body angular velocity. The aerodynamic torque found by using 7-DOF simulation is directly applied to the test system but the angular velocity of the body is scaled down to be inside of the limits of the test system. A disturbance observer is designed to be able to find the sum of the aerodynamic torque and friction torque generated by body angular velocity. The saturation parameters are updated with respect to total disturbance torque on the system to have control ability through to fight time.

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Citation Formats
G. Günay, “Controller design and implementation for a guidance kit used at spinning rockets and projectiles,” M.S. - Master of Science, Middle East Technical University, 2022.