Thesis. 1976. M.S.--Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. / Microfiche copy available in Archives and Barker. / Bibliography: p.80-81. / M.S.

Typescript (Photocopy) Includes paper co-authored by the author as attachment. Bibliography: leaves 133-140.

The effectiveness of linear control of a planar manipulator is presented for robot operation markedly exceeding the limits of linearity assumed in the design of the linear controller. Wolovich's frequency domain pole placement algorithm is utilized to derive the linear controller. The control scheme must include state estimation since only link position is measured in the planar manipulator studied. Extensive simulations have been conducted not only to verify the linear control design but also to examine the behavior of the controlled system when inputs greatly exceed those assumed for linear design. The results from these studies indicate the linear model performs exactly as designed. The non-linear realistic simulation reveals that the linear model results are obtained when the inputs do not exceed linearity limits. However, when large inputs are applied, the nature of the system response changes significantly. Regardless of the change in behavior, for the cases considered, there was no instability detected and steady-state values were realized with reasonable settling times which increased in length as the size of the inputs were increased. From the simulation results, it is concluded that the linear controller scheme studied is suitable for use in moving objects from one position to another but would not work well in the rapid drawing of lines and curves. / Graduation date: 1992

A new decentralized nonlinear controller for Robot Manipulators is presented in this thesis. Based on concepts of Lyapunov stability theory and some control ideas proposed in [3]-[7], we obtain continuous nonlinear decentralized control laws which guarantee position and velocity tracking to within an arbitrarily small error. Assumptions based on physical constraints of manipulators are made to guarantee the existence of the controller and asymptotic stability of the closed loop system. Simulations show how well this rather simple control scheme works on two of the links of the Puma 560 Manipulator. The main contribution of this thesis is that it extends the results of a class of complex centralized control algorithms to the decentralized robust control of interconnected nonlinear subsystems like robot manipulators. / Graduation date: 1992

This thesis presents a control system for a walking machine leg. The leg is representative of one of the six legs required for a proposed walking machine based on the geometry of the darkling beetle. Each of the three joints is controlled by a DC servo motor mounted to the base of the leg. The speed of the motors is controlled with pulse width modulation. Feedback of joint positions is accomplished with potentiometers mounted on the actual joints. A five-point path, forming a rectangle in the global coordinate system, is used as a skeleton of the path of movement. Desired times and accelerations from point to point are used to develop the path of movement, which smoothes corners and velocity transitions along the path. To create a model of the dynamics of each joint, a constant motor speed is output and the joint velocity and joint angle are recorded. From several trials at several different motor speeds, relationships between the joint velocity, joint angle, and motor speed can be found. This data is then least squares fit in two dimensions to give two second order functions. The first function uses the desired joint angle to calculate the variance from the mean joint velocity. This variance is then added to the desired joint velocity and is used in the second function to calculate the needed motor signal. Feedback control is accomplished using a PID control system. Because of the high level of noise in the feedback signal, a digital noise filter is used. Both moving average and linear regression techniques are examined. Performance of the system is measured by comparing the actual path in Cartesian coordinates to the desired path of movement. The RMS error is taken along the path, during the time frame of the ideal system. The maximum Cartesian error along the path is also used in evaluation. To determine suitable feedback gain combinations, several experiments are run and evaluated. Data is plotted and suitable values are chosen for the feedback gains based on their performance and sensitivity to change in performance. The performance of the leg is measured for a basic rectangular path, the basic path with a variation in step angle, and the basic path with a constant body velocity. / Graduation date: 1992

An adaptive decentralized nonlinear controller for a robot manipulator is presented in this thesis. Based on the adaptive control schemes designed by Seraji [18], Dai [30], and Jimenez [31], we redesigned and further simplified the control algorithm and, as a consequence, we achieved better path tracking performance. The proposed adaptive controller is made of a PD feedback controller which has time varying gains, a feedforward compensator based on the idea of inverse dynamics, and an auxiliary signal. Due to its adaptive structure, the controller shows robustness against disturbances and unmodeled dynamics. In order to ensure asymptotic tracking we select a Lyapunov function such that the controller forces the negative definiteness of the time derivative of such a Lyapunov function. To do this, the tracking position and velocity error are penalized and used as a part of the adaptive control gain. The main advantages of this scheme are the comparably faster convergence of tracking error, relatively simpler structure, and smoother control activity. This controller only requires the position and angular speed measurement, it does not require any knowledge about the mathematical model of the robot manipulator. Simulation shows the capacity of this controller and its robustness against disturbances. / Graduation date: 1993

published_or_final_version / abstract / Industrial and Manufacturing Systems Engineering / Master / Master of Philosophy

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