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Robot trajectory planning via dynamic programming

Description: The method of dynamic programming is applied to three example problems dealing with robot trajectory planning. The first two examples involve end-effector tracking of a straight line with rest-to-rest motions of planar two-link and three-link rigid robots. These examples illustrate the usefulness of the method for producing smooth trajectories either in the presence or absence of joint redundancies. The last example demonstrates the use of the method for rest-to-rest maneuvers of a single-link manipulator with a flexible payload. Simulation results for this example display interesting symmetries that are characteristic of such maneuvers. Details concerning the implementation and computational aspects of the method are discussed.
Date: March 1, 1994
Creator: Dohrmann, C. R. & Robinett, R. D.
Partner: UNT Libraries Government Documents Department

Input shaping for three-dimensional slew maneuvers of a precision pointing flexible spacecraft

Description: A method is presented for input torque shaping for three-dimensional slew maneuvers of a precision pointing flexible spacecraft. The method determines the torque profiles for fixed-time, rest-to-rest maneuvers which minimizes a specified performance index. Spacecraft dynamics are formulated in such a manner that the rigid body and flexible motions are decoupled. Furthermore, assembly by making use of finite element analysis results. Input torque profiles are determined by solving an associated optimization problem using dynamic programming. Three example problems are provided to demonstrate the application of the method.
Date: April 1, 1994
Creator: Dohrmann, C. R. & Robinett, R. D.
Partner: UNT Libraries Government Documents Department

Self-repairing control for damaged robotic manipulators

Description: Algorithms have been developed allowing operation of robotic systems under damaged conditions. Specific areas addressed were optimal sensor location, adaptive nonlinear control, fault-tolerant robot design, and dynamic path-planning. A seven-degree-of-freedom, hydraulic manipulator, with fault-tolerant joint design was also constructed and tested. This report completes this project which was funded under the Laboratory Directed Research and Development program.
Date: March 1, 1997
Creator: Eisler, G.R.; Robinett, R.D.; Dohrmann, C.R. & Driessen, B.J.
Partner: UNT Libraries Government Documents Department

Adaptive external torque estimation by means of tracking a Lyapunov function

Description: A real-time method is presented to adoptively estimate three-dimensional unmodeled external torques acting on a spacecraft. This is accomplished by forcing the tracking error dynamics to follow the Lyapunov function underlying the feedback control law. For the case where the external torque is constant, the tracking error dynamics are shown to converge asypmtotically. The methodology applies not only to the control law used in this paper, but can also be applied to most Lyapunov derived feedback control laws. The adaptive external torque estimation is very robust in the presence of measurement noise, since a numerical integration is used instead of a numerical differentiation. Spacecraft modeling errors, such as in the inertia matrix, are also compensated for by this method. Several examples illustrate the practical significance of these ideas.
Date: March 1, 1996
Creator: Schaub, H.; Junkins, J.L. & Robinett, R.D.
Partner: UNT Libraries Government Documents Department

Distributed Sensing and Cooperating Control for Swarms of Robotic vehicles

Description: DISTRIBUTED SENSING AND COOPERATING CONTROL FOR SWARMS OF ROBOTIC VEHICLES Key words: Distributed Sensing, Cooperative Control. ABSTRACT We discuss an approach to effectively control a large swarm of autonomous, robotic vehicles, as they per- form a search and tag operation. In particular, the robotic agents are to find the source of a chemical plume. The robotic agents work together through dis- tributed sensing and cooperative control. Distributed sensing is achieved through each agent sampling and sharing his information with others. Cooperative con- trol h accomplished by each agent u-sing its neighbors information to determine an update strategy. INTRODUCTION There is currently considerable interest in expanding the role of robotic vehicles in surveillance and inspec- tion; searching, following and t aggir-g and locating and identifying targets. In particular, researchers are beginning to focus on using small autonomous robotic vehicles for these tasks. This focus has been brought about largely because of the many recent advances in microelectronics and sensors, which include small, low power, CCD cameras; small microprocessors with ex- panded capabilities; autonomous navigation systems using GPS; and severrd types of small sensors. It seems likely that these technological advances will lead to in- expensive, easy to fabricate, autonomous vehicles out- fitted with an array of sensors. This, in turn, will allow researchers to consider teams, or even swarms, of these agents to perform a particular task. It is natural then to wonder how one might effectively control a team, or even a swarm, of robotic agents. In this paper, we discuss an approach to effectively control a large swarm of autonomous, robotic vehicles as they perform a search and tag operation. In par- ticular, the robotic agents are to find the source of a chemical plume. The robotic agents work together through distributed sensing and cooperative control. Distributed sensing is ...
Date: October 9, 1998
Creator: Dohrmann, C. R.; Goldsmith, S. Y.; Hurtado, J. E. & Robinett, R. D.
Partner: UNT Libraries Government Documents Department

Operator in-the-loop control of rotary cranes

Description: An open-loop control method is presented for reducing the oscillatory motion of rotary crane payloads during operator commanded maneuvers. A typical rotary crane consists of a multiple degree-of-freedom platform for positioning a spherical pendulum with an attached payload. The crane operator positions the Payload by issuing a combination of translational and rotational commands to the platform as well as load-line length changes. Frequently, these pendulum modes are time-varying and exhibit low natural frequencies. Maneuvers are therefore performed at rates sufficiently slow so as not to excite oscillation. The strategy presented here generates crane commands which suppress vibration of the payload without a priori knowledge of the desired maneuver. Results are presented for operator in-the-loop positioning using a real-time dynamics simulation of a three-axis rotary crane where the residual sway magnitude is reduced in excess of 4OdB.
Date: March 1, 1996
Creator: Parker, G.G.; Robinett, R.D.; Driessen, B.J. & Dohrmann, C.R.
Partner: UNT Libraries Government Documents Department

Optimized input shaping for a single flexible robot link

Description: This paper will discuss the design of an input shaped open-loop control for a single flexible robot link. The authors develop the equations of motion, including the first flexible mode shape and the actuator dynamics. Additional content includes the hardware system identification iterative runs used to update the model. Optimized input shaped commands for the flexible robot link to produce a rest-to-rest, residual vibration-free, 90 degree maneuver are developed. Correlation between both experimental and analytical results of the 90{degree} slew, using two different identification models, are reviewed.
Date: March 1, 1996
Creator: Wilson, D.G.; Stokes, D.; Starr, G. & Robinett, R.D.
Partner: UNT Libraries Government Documents Department

New attitude penalty functions for spacecraft optimal control problems

Description: A solution of a spacecraft optimal control problem, whose cost function relies on an attitude description, usually depends on the choice of attitude coordinates used. A problem could be solved using 3-2-1 Euler angles or using classical Rodriguez parameters and yield two different ``optimal`` solutions, unless the performance index in invariant with respect to the attitude coordinate choice. Another problem arising with many attitude coordinates is that they have no sense of when a body has tumbled beyond 180{degrees} from the reference attitude. In many such cases it would be easier (i.e. cost less) to let the body complete the revolution than to force it to reverse the rotation and return to the desired attitude. This paper develops a universal attitude penalty function g() whose value is independent of the attitude coordinates chosen to represent it. Furthermore, this function will achieve its maximum value only when a principal rotation of {plus_minus}180{degrees} from the target state is performed. This will implicitly permit the g() function to sense the shortest rotational distance back to the reference state. An attitude penalty function which depends on the Modified Rodriguez Parameters (MRP) will also be presented. These recently discovered MRPs are a non-singular three-parameter set which can describe any three-attitude. This MRP penalty function is simpler than the attitude coordinate independent g() function, but retains the useful property of avoiding lengthy principal rotations of more than {plus_minus}180{degrees}.
Date: March 1, 1996
Creator: Schaub, H.; Junkins, J.L. & Robinett, R.D.
Partner: UNT Libraries Government Documents Department

Moving mass trim control system design

Description: This paper describes the design of a moving mass trim control system for maneuvering axisymmetric reentry vehicles. The moving mass trim controller is composed of three equal masses that are independently positioned in order to deliver a desired center of mass position. For a slowly spinning reentry vehicle, the mass offset creates a trim angle-of-attack to generate modest flight path corrections. The control system must maintain the desired position of each mass in the face of large disturbances. A novel algorithm for determining the desired mass positions is developed in conjunction with a preliminary controller design. The controller design is based on classical frequency domain techniques where a bound on the disturbance magnitude is used to formulate the disturbance rejection problem. Simulation results for the controller are presented for a typical reentry vehicle.
Date: March 1, 1996
Creator: Byrne, R.H.; Robinett, R.D. & Sturgis, B.R.
Partner: UNT Libraries Government Documents Department

Command shaping for residual vibration free crane maneuvers

Description: Cranes used in the construction and transportation industries are generally devices with multiple degrees of freedom including variable load-line length, variable jib length (usually via a trolley), and variable boom angles. Point-to-point payload maneuvers using cranes are performed so as not to excite the spherical pendulum modes of their cable and payload assemblies. Typically, these pendulum modes, although time-varying, exhibit low frequencies. Current crane maneuvers are therefore performed slowly contributing to high construction and transportation costs. This investigation details a general method for applying command shaping to various multiple degree of freedom cranes such that the payload moves to a specified point without residual oscillation. A dynamic programming method is used for general command shaping for optimal maneuvers. Computationally, the dynamic programming approach requires order M calculations to arrive at a solution, where M is the number of discretizations of the input commands. This feature is exploited for the crane command shaping problem allowing for rapid calculation of command histories. Fast generation of commands is a necessity for practical use of command shaping for the applications described in this work. These results are compared to near-optimal solutions where the commands are linear combinations of acceleration pulse basis functions. The pulse shape is required due to hardware requirements. The weights on the basis functions are chosen as the solution to a parameter optimization problem solved using a Recursive Quadratic Programming technique. Simulation results and experimental verification for a variable load-line length rotary crane are presented using both design procedures.
Date: July 1, 1995
Creator: Parker, G.G.; Petterson, B.; Dohrmann, C. & Robinett, R.D.
Partner: UNT Libraries Government Documents Department

Two-axis hydraulic joint for high speed, heavy lift robotic operations

Description: A hydraulically driven universal joint was developed for a heavy lift, high speed nuclear waste remediation application. Each axis is driven by a simple hydraulic cylinder controlled by a jet pipe servovalve. Servovalve behavior is controlled by a force feedback control system, which damps the hydraulic resonance. A prototype single joint robot was built and tested. A two joint robot is under construction.
Date: April 1, 1994
Creator: Vaughn, M. R.; Robinett, R. D.; Phelan, J. R. & VanZuiden, D. M.
Partner: UNT Libraries Government Documents Department

Vibration suppression of fixed-time jib crane maneuvers

Description: A jib crane consists of a pendulum-like end line attached to a rotatable jib. Within this general category of cranes there exist devices with multiple degrees of freedom including variable load-line length and variable jib length. These cranes are commonly used for construction and transportation applications. Point-to-point payload maneuvers using jib cranes are performed so as not to excite the spherical pendulum modes of their cable and payload assemblies. Typically, these pendulum modes, although time-varying, exhibit low frequencies. The resulting maneuvers are therefore performed slowly, contributing to high construction and transportation costs. The crane considered here consists of a spherical pendulum attached to a rigid jib. The other end of the jib is attached to a direct drive motor for generating rotational motion. A general approach is presented for determining the open-loop trajectories for the jib rotation for accomplishing fixed-time, point-to-point, residual oscillation free, symmetric maneuvers. These residual oscillation free trajectories purposely excite the pendulum modes in such a way that at the end of the maneuver the oscillatory degrees of freedom are quiescent. Simulation results are presented with experimental verification.
Date: February 1, 1995
Creator: Parker, G. G.; Petterson, B.; Dohrmann, C. R. & Robinett, R. D.
Partner: UNT Libraries Government Documents Department

Input shaping for vibration-damped slewing of a flexible beam using a heavy-lift hydraulic robot

Description: An input shaping scheme originally used to slew flexible beams via a tabletop D.C. motor is modified for use with an industrial-type, hydraulic-drive robot. This trajectory generation method was originally developed to produce symmetric, rest-to-rest maneuvers of flexible rotating rods where the angular velocity vector and gravitational vector were collinear. In that configuration, out-of-plane oscillations were excited due to centripetal acceleration of the rod. The bang-coast-bang acceleration profile resulted in no oscillations in either plane at the end of the symmetric slew maneuver. In this paper, a smoothed version of the bang-coast-bang acceleration is used for symmetric maneuvers where the angular velocity vector is orthogonal to the gravitational vector. Furthermore, the hydraulic robot servo dynamics are considered explicitly in determining the input joint angle trajectory. An instrumented mass is attached to the tip of a flexible aluminum rod. The first natural frequency of this system is about 1.0Hz. Joint angle responses obtained with encoder sensors are used to identify the servo actuator dynamics.
Date: August 1, 1994
Creator: Parker, G. G.; Eisler, R.; Phelan, J. & Robinett, R. D.
Partner: UNT Libraries Government Documents Department

Explaining finite state machine characteristics using variable structure control

Description: This paper describes how variable structure control can be used to describe the overall behavior of multiple autonomous robotic vehicles with simple finite state machine rules. The importance of this result is that it allows for the design of provably asymptotically stable group behaviors from a set of simple control laws and appropriate switching points with variable structure control. The ability to prove convergence to a goal is especially important for applications such as locating military targets or land mines.
Date: October 1, 1997
Creator: Feddema, J. T.; Robinett, R. D. & Driessen, B. J.
Partner: UNT Libraries Government Documents Department

Designing stable finite state machine behaviors using phase plane analysis and variable structure control

Description: This paper discusses how phase plane analysis can be used to describe the overall behavior of single and multiple autonomous robotic vehicles with finite state machine rules. The importance of this result is that one can begin to design provably asymptotically stable group behaviors from a set of simple control laws and appropriate switching points with decentralized variable structure control. The ability to prove asymptotically stable group behavior is especially important for applications such as locating military targets or land mines.
Date: March 10, 1998
Creator: Feddema, J.T.; Robinett, R.D. & Driessen, B.J.
Partner: UNT Libraries Government Documents Department

Adaptive Remote-Sensing Techniques Implementing Swarms of Mobile Agents

Description: In many situations, stand-off remote-sensing and hazard-interdiction techniques over realistic operational areas are often impractical "and difficult to characterize. An alternative approach is to implement an adap- tively deployable array of sensitive agent-specific devices. Our group has been studying the collective be- havior of an autonomous, multi-agent system applied to chedbio detection and related emerging threat applications, The current physics-based models we are using coordinate a sensor array for mukivanate sig- nal optimization and coverage as re,alized by a swarm of robots or mobile vehicles. These intelligent control systems integrate'glob"ally operating decision-making systems and locally cooperative learning neural net- works to enhance re+-timp operational responses to dynarnical environments examples of which include obstacle avoidance, res~onding to prevailing wind patterns, and overcoming other natural obscurants or in- terferences. Collectively',tkensor nefirons with simple properties, interacting according to basic community rules, can accomplish complex interconnecting functions such as generalization, error correction, pattern recognition, sensor fusion, and localization. Neural nets provide a greater degree of robusmess and fault tolerance than conventional systems in that minor variations or imperfections do not impair performance. The robotic platforms would be equipped with sensor devices that perform opticaI detection of biologicais in combination with multivariate chemical analysis tools based on genetic and neural network algorithms, laser-diode LIDAR analysis, ultra-wideband short-pulsed transmitting and receiving antennas, thermal im- a:ing sensors, and optical Communication technology providing robust data throughput pathways. Mission scenarios under consideration include ground penetrating radar (GPR) for detection of underground struc- tures, airborne systems, and plume migration and mitigation. We will describe our research in these areas anti give a status report on our progress.
Date: November 25, 1998
Creator: Asher, R.B.; Cameron, S.M.; Loubriel, G.M.; Robinett, R.D.; Stantz, K.M.; Trahan, M.W. et al.
Partner: UNT Libraries Government Documents Department

Techniques for controlling a two-link flexible arm

Description: The long length and relatively small cross sectional area of the robotic arms envisioned for use inside of the underground nuclear waste storage tanks will require the control of flexible structures. This will become an important problem in the characterization and remediation of these tanks. We are developing control strategies to actively damp residual vibrations in flexible robotic arms caused by high speed motion and abrupt external forces. A planar, two-link flexible arm is currently being used to test these control strategies. In this paper, two methods of control are discussed. The first is a minimum-time control approach which utilizes a finite element model and and optimization program. These tools plan the motor torque profiles necessary for the tip of the arm to move along a straight line, in minimum time, within the motors' torque constraints, and end in a quiescent state. To account for modeling errors in the finite element model, errors in joint angles, velocities, and link curvatures are added to the optimal torque trajectory. Linear quadratic Gaussian (LQG) regulatory design theory is used to determine the feedback gains. The second method of control is a teleoperated joystick controller which uses an input shaping technique to alter the commands of the joystick so as to reduce the residual vibration of the fundamental modes. Approximating the system as linear, the natural frequency and damping ratio are estimated on-line for the complete system, which includes the structure plus a lower level proportional derivative controller. An input shaping filter is determined from the estimated natural frequency, estimated damping ratio, and the desired transfer function of the system. 11 reps., 9 figs.
Date: January 1, 1990
Creator: Feddema, J.T.; Eisler, G.R.; Segalman, D.J.; Robinett, R.D. III; Morimoto, A.K. & Schoenwald, D.A.
Partner: UNT Libraries Government Documents Department