Bülent E. Platin

A Complete Analysis and a Novel Solution for Instability in Pump Controlled Asymmetric Actuators

This paper addresses the stability problem of pump controlled asymmetric hydraulic actuators and proposes a physical solution for it. The system under consideration utilizes a shuttle valve to compensate for unequal flow rates due to the asymmetry in the actuator. Possible hydraulic circuit configurations resulting from various valve positions are defined on the load pressure versus velocity plane and a generalized linear model of the system is derived. The investigation shows that there exists a critical load pressure region in which any equilibrium point requiring a partially open spool position is unstable during the retraction of the actuator. A particular valve underlap is proposed in order to avoid the instability and a shuttle valve selection guide is presented. Theoretical findings are validated by both numerical simulations and experimental tests. Results show that the undesired pressure oscillations are removed up to certain actuator velocities with the use of an underlapped shuttle valve.

An Application of Equation Error Method to Aerodynamic Model Identification and Parameter Estimation of a Gliding Flight Vehicle

This paper describes the application of the equatio n error method to aerodynamic parameter estimation of a gliding flight vehicle. T he flight test data used is not originally designed for estimation, causing data collinearity. A strategy is devised to deal with this situation so that the model identification and para meter estimation can be performed. A computer tool is developed in Matlab ® environment for the flight test data processing an d aerodynamic identification/estimation. The results of the study show that, although the stepwise regression and equation error method have some potential to be used for flight vehicles other than aircraft, the quality of the fl ight test data and input design is crucial for aerodynamic parameter identification.

Compensation of friction effects in gyro-stabilized motion platforms

A frequent problem encountered in the stabilization of gyro-stabilized motion platforms is the disturbance rejection associated with moving components. Due to relative motion of adjacent components, friction is induced by the destabilizing force from the base motion to the stabilized object, degrading its motion accuracy. Hence, a compensation of frictional effects is necessary in order to obtain a highly precise stabilization performance. In this paper, applications of both single-state disturbance observer and well-known LuGre friction model on gyro-stabilized motion platforms is presented to compensate for friction. The compensation techniques are described for a generalized control system and simplified for a specific case. The success of these techniques is validated via experiments and simulations by constructing a block diagram of the system stabilization loop. An added disturbance observer yields a similar improvement in the stabilization performance as the LuGre friction model does at low frequencies. However, the performance of disturbance observer degrades as the frequency of disturbances increases although it still improves the overall stabilization performance of the system.

External Configuration Optimization of Missiles in Conceptual Design

The main area of emphasis in this paper is to investigate the methods and technology for aerodynamic configuration sizing of missiles and to develop a software platform in MATLAB® environment as a design tool which has an ability of optimizing the external configuration of missiles for a set of flight requirements specified by the user through a graphical user interface. A genetic algorithm based optimization tool is prepared by MATLAB® that helps the designer to find out the best external geometry candidates in the conceptual design stage. Missile DATCOM is employed as the aerodynamic coefficient prediction package to determine aerodynamic coefficients of each external geometry candidate in finding their performance merits by integrating their dynamic equations of motion. Numerous external geometry candidates are rapidly eliminated according to objectives and constraints specified by designers, which provide necessary information in preliminary design. In this elimination, the external geometry candidates are graded according to their flight performances in order to discover an optimum solution. All of the flight performance data are obtained by running a two degree-of-freedom simulation in the vertical plane. In order to solve the resulting multi-objective optimization problem with a set of constraint of linear and nonlinear nature and in equality and inequality forms, geneticalgorithm-based methods are applied. Hybrid encoding methods in which the integer configuration variables (i.e., nose shape and control type) and real-valued geometrical dimension (i.e., diameter, length) parameters are encoded in the same individual chromosome. An external configuration design tool (EXCON) is developed as a synthesis and external sizing tool for the subsonic cruise missiles. A numerical example, the reconfiguration problem of an anti-ship cruise missile, is presented to demonstrate the accuracy and feasibility of the conceptual design tool.

Aeroservoelastic Analysis of Missile Control Surfaces via Robust Control Methods

Abstract in this study the effect of uncertainties on the flutter and instability speeds of the control actuation system of a missile is analyzed. The control surface is modeled as a typical section wing with uncertainties in damping and stiffness coefficients. The analyses are carried out for incompressible flow with some uncertainties in aerodynamic coefficients. The actuator dynamics of the aeroservoelastic system is modeled as a second order system with a frequency varying uncertainty.

A Control System for Hydraulic Single Axis Durability Test Rig

In this study, a controller is designed for a hydraulic actuator of a single axis durability test rig. The mathematical equations of the system are derived and a MATLAB Simulink® model is developed. The non-linear equations defining the system dynamics are linearized and the system is represented in state space. For the position control of the hydraulic actuator, a combined feedforward and feedback controller is designed. The feedforward controller estimates the force transmitted between the vehicle and the hydraulic actuator. Considering this force as a disturbance, a feedforward valve command signal is generated for compensation. In the design of feedback controller, the hydraulic actuator is considered independent of the load. Neglecting the valve dynamics and assuming the actuator chamber pressures are linearly dependent, a third order actuation system model is derived and a LQR controller is designed. In the design of LQR controller, the matrix penalizing the states is formed by approximating the impulse response of the closed loop system to an ideal second order response profile rather than by using iteration. The closed loop state space representation of the complete system is derived and its response is compared with the non-linear model.Copyright

Synthesis of an Hinf Controller for Fully Movable Aeroelastic Control Surfaces of Air Vehicles

A controller synthesis method is proposed for fully movable aeroelastic control surfaces of air vehicles. The proposed synthesis method is based on the mu flutter analysis method. The performance of the method is compared with an alternative flutter suppression controller synthesis method available in literature. The methods are implemented to a theoretical aeroservoelastic control actuation system based on the aeroservoelastic test system constructed in TUBITAK-SAGE for incompressible subsonic flow. The synthesis and analysis are performed by using the codes developed on MATLAB®. The airfoil is modeled via typical section model. The aerodynamics is modeled at distinct Mach numbers of 0.5, 0.6 and 0.7 by using the indicial functions. Hinf type controllers are synthesized by using the two synthesis methods. Aeroservoelastic analyses of the systems are performed considering the stability, performance and the effect of backlash type nonlinearity. Comparing the two methods, it is seen that the proposed method has better stability and performance characteristics.

CHARACTERISTIC PHASE PLANE PATTERN OF HUMAN POSTURAL SWAY

Abstract Reasons for the everlasting complex oscillatory behavior of human postural sway have been explored by constructing the phase-plane representation of the Center of Pressure data recorded experimentally. For this purpose, 275-seconds time records are received from a healthy subject while standing still in an upright posture. A Sensorial threshold has been proposed as being one of the nonlinear sources governing postural dynamics. Ethyl alcohol has also been introduced to the subject for provocation of the nonlinear behavior associated with the sensorial dynamics.

An Application of Variable Structure Systems with Sliding Mode Control to a Remotely Operated Vehicle

Abstract 3-D rigid body motion has been restudied for Remotely Operated Vehicles. The particular structure under investigation is a submersible platform whose position and orientation are to be controlled in depths of water via forces of its three thrusters. A Sliding Mode Control(SMC) application is attempted for the guidance problem which is intrinsically uncontrollable and nonlinear. A fragmented point-to-point control strategy has been implemented in order to demonstrate the abilities of SMC technique in ROV guidance.

Modelling and Analysis of a Stepper Motor Driven Feed-Drive System of a CNC Lathe

Abstract A sixth order mathematical model of the feeddrive of a stepper motor driven CNC lathe is developed. The effects of the system parameters, such as the center distance and the speed ratio between the lead screw and the motor shaft, damping on the lead screw and on the slideways, axial stiffness of the lead screw are investigated in terms of eigenvalue loci on the complex plane. A series of guidelines are given describing how these parameters influence the dynamic performance of the machine tool.