Optimal large angle maneuvers with simultaneous shape control/vibration arrest

A relaxation method is demonstrated which reliably solves the nonlinear two point boundary value problem which arises when optimal control theory is applied to determination of large angle maneuvers of flexible spacecraft. The basic ideas are summarized and several idealized maneuvers are determined. The emphasis is upon demonstrating the basic ideas and practical aspects of the methodology

Large Angle Satellite Attitude Maneuvers

Two methods are proposed for performing large angle reorientation maneuvers. The first method is based upon Euler's rotation theorem; an arbitrary reorientation is ideally accomplished by rotating the spacecraft about a line which is fixed in both the body and in space. This scheme has been found to be best suited for the case in which the initial and desired attitude states have small angular velocities. The second scheme is more general in that a general class of transition trajectories is introduced which, in principle, allows transfer between arbitrary orientation and angular velocity states. The method generates transition maneuvers in which the uncontrolled (free) initial and final states are matched in orientation and angular velocity. The forced transition trajectory is obtained by using a weighted average of the unforced forward integration of the initial state and the unforced backward integration of the desired state. The current effort is centered around practical validation of this second class of maneuvers. Of particular concern is enforcement of given control system constraints and methods for suboptimization by proper selection of maneuver initiation and termination times. Analogous reorientation strategies which force smooth transition in angular momentum and/or rotational energy are under consideration

Autonomous attitude estimation via star sensing and pattern recognition

Results are reported on the development of an autonomous, onboard, near real time spacecraft attitude estimation technique. The approach uses CCD based star sensors to digitize relative star positions. Three microcomputers are envisioned, configured in parallel, to: (1) determine star image centroids and delete spurious images; (2) identify measured stars with stars in an onboard catalog and determine discrete attitude estimates; (3) integrate gyro rate measurements and determine optimal real time attitude estimates for use in the control system and for feedback to the star identification algorithm. Algorithms for the star identification are presented. The discrete attitude estimation algorithm recovers thermally varying interlock angles between two star sensors. The optimal state estimation process recovers rate gyro biases in addition to real time attitude estimates

Data acquisition and reduction for the University of Virginia superconducting magnetic suspension and balance facility

The problems associated with data acquisition and reduction in the U. Va. superconducting magnetic suspension and balance facility are similar to those in free-flight ranges (or tunnels). The model undergoes a quasi-six-degree-of-freedom motion which must be monitored both in position and angular orientation from which the aerodynamics must be inferred. The data acquisition problem is made more difficult because geometric constraints prevent direct visual access to the model in the Mach 3 wind tunnel. The methods, accuracies, and problems associated with the acquisition of data are discussed

CSI sensing and control: Analytical and experimental results

Recent work on structural identification and large-angle maneuvers with vibration suppression was presented. The recent work has sought to balance structural and controls analysis activities by involving the analysts directly in the validation and experimental aspects of the research. Some new sensing, actuation, system identification, and control concepts were successfully implemented. An overview of these results is given

ROBUST NONLINEAR LEAST SQUARES ESTIMATION USING THE CHOW- YORKE HOMOTOPY METHOD

No abstract available

A quasi-analytical method for non-iterative computation of nonlinear controls

An optimal control solution process was developed for a general class of nonlinear dynamical systems. The method combines control theory, perturbation methods, and Van Loan's recent matrix exponential results. A variety of applications support the practical utility of this method. Nonlinear rigid body optimal maneuvers are routinely solved. Flexible body dynamical systems of an order greater than 40 were solved. The method fails occasionally due to poor convergence of the perturbation expansion or numerical difficulties associated with computing the matrix exponential. The method is attractive because it appears to be a good candidate for semi-automation; no initial guess is required, and it usually converges at 2nd or 3rd order in minutes of machine time

Assessing unmet anaesthesia need in Sierra Leone: a secondary analysis of a cluster-randomized, cross-sectional, countrywide survey.

Objectives: To determine the unmet anaesthesia need in a low resource region. Introduction: Surgery and an\ue6sthesia services in low- and middle-income countries (LMICs) are under-equipped, under- staffed, and unable to meet current surgical need. There is little objective measure as to the true extent and nature of unmet need. Without such an understanding it is impossible to formulate solutions. Therefore, we re-examined Surgeons OverSeas (SOSAS) unmet surgical need data to extrapolate unmet anaesthesia need. Methods: For the untreated surgical conditions identified by SOSAS, we assigned anaesthetic technique required to carry out the procedure. The chosen anaesthetic was based on common practice in the region. Procedures were categorized into minimal anaesthesia, spinal an\ue6sthesia, regional anaesthesia, ketamine/monitored anaesthesia care (MAC), and general endotracheal an\ue6sthesia (GETA). Discussions: Ninety-two per cent (687 of 745) of untreated surgical conditions in Sierra Leone would require some form of anaesthesia. Seventeen per cent (125 of 745) would require MAC, 22% (167 of 745) would require spinal anaesthesia, and 53% (395 of 745) would require GETA. Conclusion: Analyses such as this can provide guidance as to the rational and efficient production and distribution of personnel, drugs and equipment

GLOBAL ASYMPTOTIC STABILIZATION OF THE SPINNING TOP

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/57818/1/WanOCAMTop1995.pd

Viking Thrust Vector Control Dynamics Using Hybrid Coordinates to Model Vehicle Flexibility and Propellant Slosh

Control System Design Implementation of the linear feedback control system with time varying feedback gains and command forces may be accomplished with a fairly simple analog controller. The feedback gains and command forces consist of well behaved sinusoidal functions, constants, and simple ramp functions. The difficulty caused by the gain fluctuation near the simulation final time may be overcome by cycling the control gain functions back to the beginning before the fluctuations take place. Cycling the control gain functions is not a problem because the control is in a feedback form. The effect of cycling the control gain functions may be interpreted in the analysis as restarting the nonlinear simulation with an initial state closer to the final state. Simulation of the nonlinear system within the region of operation always resulted in a stable response so the effect of restarting the simulation when the system state has moved closer to the final state is valid. A consequence of cycling the control is that the functional in Eq. Conclusions This study has shown that the dynamic instability caused by sloshing fluid stores carried in the main rigid body of a spacecraft may be controlled by use of a linear quadratic regulator with the fluid modeled as an equivalent spherical pendulum and only the first mode of fluid oscillation included. The control system presented stabilized a highly nonlinear system for a large deviation from the nominal operating point and uses easily measured state variables (only main body fixed angular rates and attitude) and was shown to be stable for a wide variation in fluid level. It was shown that sensing the dynamic state of the fluid was not necessary for the specific spacecraft under study. A pointing maneuver was also successfully accomplished by this control system and a control design based on the analysis was outlined for the specific spacecraft. Acknowledgments This study was completed under partial support of contract no. AFOSR-86-0080 and subcontract 83RIP33, U.S. Air Force. The authors wish to acknowledge the support of Iowa State University in accomplishing the lengthy digital computer simulation required in this study. References Introduction An interesting problem in robotics is cloth handling. Applications include composite lay-up and apparel and upholstery manufacturing. Rebman (1986) describes an application of a tactile sensor to assembly of a flexible diaphram and a plastic cap. Hertzanu and Tabak (1986) described an adaptive controller for an industrial sewing machine. For most applications, cloth must be held taut and unwrinkled. It was postulated that this requires multi-axis force control, and a suitable control system was designed and constructed. The system chosen is an adaptive force feedback loop with position accommodation. Non-adaptive force feedback control schemes have been described and tested by many researchers, such as Whitney (1977). An adaptive force feedback loop for coordination of two robot arms was described by Because cloth stiffness varies depending on whether the individual cloth fibers are taut or slack, a nonadaptive loop is unsuitable for cloth handling. An adaptive control loop was designed with cloth stiffness as the adaptive variable. The system design was constructed and tested using a PUMA 560 robot with a LORD 15/50 force/torque sensor mounted on its wrist. Control System Description The parameter estimator is a least mean square (LMS) estimator. Let y=KH(z)u = K a x z ' + + a"z~ -r-"u, \+b x z + ... +b"z~ where a it ..., a" and b\ b" axe found from the ordinary least squares plant identification, y is the error in the force, and u is the position command. Then the LMS estimator for A-is K* =K*^i+r{y-y*)w-l , where K* is the estimated stiffness, +a"u""), and Vf_ 1 =ff 1 «_ 1 + The position control law is where u, is the change in the position of the /th degree of freedom (DOF), y t is the force (or torque) error of the ith DOF, and K* is the stiffness of the rth DOF. end of a cloth of dimensions 36 by 36 in., the other end of which was attached to a table. Both ends of the cloth were stapled to wooden rods; proper robot end effectors would eliminate the need for these rods. Two 8086 microprocessor cards were also built. The 1st microprocessor calculated the cloth stiffness and end effector position changes; the 2nd microprocessor was used for communication with the robot and the force/torque sensor. Experimental Procedure The experiments were run with one end of the cloth fixed. The initial slack and misalignments of the cloth were as follows: Stretch (x) direction Lateral (y) direction 6 direction 6 to 10 in. of slack 2 to 4 in. of misalignment 5° to 20° of misalignment The robot straightened out the misalignments and pulled 4 lb of tension on the cloth. After it had done so the end effector was moved inward to produce 6 in. of slack in the x-direction. This movement draped the cloth over 2 boxes without wrinkling. Test Setup Experimental Results The visual results showed consistency between the experiments. In all of them, the cloth was successfully draped over the boxes without wrinkles, the motion was smooth, and the times were approximately the same. Transactions of the ASME position, the robot pulls a 4 lb tension on the cloth and adjusts the lateral (y) force and the moment to zero. This requires approximately 12 s. At 14 s the robot drapes the cloth; at this point the tension (x-force) falls to zero. This experiment was successfully repeated several times. Conclusions A force feedback control loop implemented on a robot has been used successfully to straighten and draw a tension on a cloth. Further work will include using more sophisticated end effectors to grip the cloth, and applications in upholstery and composite manufacture. Reference