Modeling and control of a flexible robotic manipulator

Successful control of the flexible robotic manipulator arm available to grapple the Space Station Freedom and maneuver it into a berthed position with the Shuttle depends on accurate modeling of the flexural dynamics of the arm and development of a controller capable of quickly settling the system transient dynamics without exceeding the servomotor capability.;During berthing, periodic attitude corrections of the combined vehicles and contact interaction dynamics of the latch system present two transient load critical events. These result from (1) attitude maneuvers using reaction control jets and (2) trunnion contact with latch guide surfaces.;This dissertation is concerned with modeling and optimal control of the system flexural dynamics. A new transient response simulation is developed which includes the total system modal characteristics, nonlinear joint dynamics, and system servomotor joint control. Conventional system modeling using individual modal characteristics fails to accurately represent joint boundary conditions. To obtain total system modal characteristics with accurate joint boundary conditions, a new finite element model of the manipulator is developed and added to finite element models of a Shuttle and space station. The transient response model is validated using test data obtained during actual orbital flight.;A new suboptimal digital redesigned controller weighting algorithm automatically determines the manipulator servocontrol characteristics to be used in the transient response simulation, while satisfying the desired minimum settling time within the fixed torque limits of the servomotors. The controller uses an optimal linear quadratic regulator to place the closed-loop poles of a multivariable continuous-time system within the common region of an open sector with the sector angle +/-45° from the negative real axis and the left-hand side of a line parallel to the imaginary axis in the complex s-plane. Moving the poles to the left-hand side of a designated line parallel to the imaginary axis allows control of both settling time and maximum actuator torques, features lacking in earlier pole placement methods as is shown by comparison with control methodology recently published by Skelton. Also shown are controller stability sensitivity studies for changes in system mass.