Gordon G. Parker

Control for slosh-free motion of an open container

This article describes two methods for controlling the surface of a liquid in an open container as it is being carried by a robot arm. Both methods make use of the fundamental mode of oscillation and damping of the liquid in the container as predicted from a boundary element model of the fluid. The first method uses an infinite impulse response filter to alter the acceleration profile so that the liquid remains level except for a single wave at the beginning and end of the motion. The motion of the liquid is similar to that of a simple pendulum. The second method removes the remaining two surface oscillations by tilting the container parallel to the beginning and ending wave. A double pendulum model is used to determine the trajectory for this motion. Experimental results of a FANUC S-800 robot moving a 230 mm diameter hemispherical container of water are presented.

Study of Interspacecraft Coulomb Forces and Implications for Formation Flying

In the course of exploiting spacecraft formations for use in separated interferometry (or other missions), it is possible that the separation distance between vehicles will be on the order of 10 m. The effects of spacecraft charging on the dynamics of very closely spaced formations are investigated. For certain high-Earth orbits, the ambient plasma conditions will conspire to produce significant spacecraft charging in an environment with a plasma Debye length of more than 100 m. For such conditions, it is shown that the potential exists to develop disruptive interspacecraft Coulomb forces and torques, with magnitude comparable to candidate formation-keeping thrusters over distances of tens of meters. Because of the unexpectedly large interaction forces, the concept of purposely charging spacecraft to affect formation-keeping Coulomb forces is also explored. Analytic methods are developed that show the existence of static equilibrium formations in Earth orbit using only inter-vehicle coulomb forces for one-, two-, and three-dimensional formations. Such Coulomb formations would be free of the risk of plume contamination due to thrusters firing in close proximity. Figures of merit for the proposed Coulomb control system are calculated in a manner analogous to traditional propulsion systems, and it is shown that required forces can be created with milliwatts of power, can be controlled on a millisecond timescale, and imply specific impulses that can be as high as 1013 seconds.

Survey of multi-agent systems for microgrid control

Multi-agent systems (MAS) consist of multiple intelligent agents that interact to solve problems that may be beyond the capabilities of a single agent or system. For many years, conceptual MAS designs and architectures have been proposed for applications in power systems and power engineering. With the increasing use and modeling of distributed energy resources for microgrid applications, MAS are well suited to manage the size and complexity of these energy systems. The purpose of this paper is to survey applications of MAS in the control and operation of microgrids. The paper will review MAS concepts, architectures, develop platforms and processes, provide example applications, and discuss limitations.

Model-Based Estimation and Control System Development in a Urea-SCR Aftertreatment System

In this paper, a model-based linear estimator and a nonlinear control law for an Fe-zeolite ureaselective catalytic reduction (SCR) catalyst for heavy duty diesel engine applications is presented. The novel aspect of this work is that the relevant species, NO, NO2 and NH3 are estimated and controlled independently. The ability to target NH3 slip is important not only to minimize urea consumption, but also to reduce this unregulated emission. Being able to discriminate between NO and NO2 is important for two reasons. First, recent Fe-zeolite catalyst studies suggest that NOx reduction is highly favored by the NO2 based reactions. Second, NO2 is more toxic than NO to both the environment and human health. The estimator and control law are based on a 4-state model of the urea-SCR plant. A linearized version of the model is used for state estimation while the full nonlinear model is used for control design. An experimentally validated, higher order simulation is used to evaluate the performance of the closed loop system. For the cases considered, the control strategy uses less urea, produces less NH3 slip, and less tailpipe NOx than a similar strategy where NO and NO2 are assumed as all NO during estimation and control law implementation.

Experimental verification of a command shaping boom crane control system

Presents experimental results of a command shaping control method for suppressing payload swing caused by operator commanded manoeuvres, in rotary, ship-based, boom cranes. The crane configuration investigated, consists of a payload mass that swings on the end of a spherical pendulum of varying lift-line length (hoisting). The lift-line is attached to a boom capable of elevation (luffing) and rotation about a vertical axis (slewing). Positioning of the payload is accomplished through luff, slew and hoist commands issued in real-time by an operator. The command shaping strategy, consisting of a time-varying filter, reduces payload oscillation by 18 dB in experiments using the 1/16th scale Navy Crane Testbed at Sandia National Laboratories.

Flexible Robot Dynamics and Controls

Contents. 1. Introduction. 2. Mathematical Preliminaries. 3. Flexible Robot Dynamic Modeling. 4. System Identification. 5. Input Shaping for Path Planning. 6. Linear Feedback Control. 7. Nonlinear Systems and Sliding Mode Control. 8. Adaptive Sliding Mode Control. Appendix A: VF02AD Optimization. Appendix B: MATLAB%% Optimization. Appendix C: Hardware & Software Support.

Command shaping control of an operator-in-the-loop boom crane

This paper presents a control method for suppressing payload sway caused by operator commanded maneuvers, in rotary boom cranes. The crane configuration studied, consists of a payload mass that swings at the end of a spherical pendulum, which is attached to a boom capable of hub rotation and elevation. Positioning of the rotary crane is accomplished through the hub and boom angles, and the lift line length. Since the configuration of the crane affects the excitation and response of the lift line, the sway control scheme must account for the varying geometry of the system. Adaptive forward path command filters are employed to remove the components of the command signal which induce oscillation of the lift line. A real-time operator-in-the-loop simulation, is used to demonstrate results for a simultaneous three-axis maneuver.

A Study Describing the Performance of Diesel Particulate Filters During Loading and Regeneration - A Lumped Parameter Model for Control Applications

A computational lumped parameter model (MTU-Filter- Lumped) was developed to describe the performance of diesel particulate filters (DPFs) during loading and regeneration processes. The model was formulated combining three major sub-models: a filtration model, a pressure drop model, and a mass and an energy balance equation for the total filter volume. The first two submodels have been widely validated in the literature, while the third sub-model is introduced and combined with the first two sub-models in the present study. The three sub-models combined can give a full description of diesel particulate filter behavior during loading and regeneration processes, which was the objective of the present work. The total combined lumped parameter model was calibrated using experimental data from the literature covering a range of experimental conditions, including different catalytic regeneration means and engine- operating conditions. The model predictions showed very good agreement with the experimental data in terms of pressure drop across the filter, mass retained in the filter, and filter temperature. A diesel particulate filter system was selected to illustrate the control application of the lumped model equations. This system involves a diesel particulate filter for the collection and oxidation of the engine out particulate matter emissions, and the injection of hydrocarbons upstream of an oxidation catalytic converter (OCC) in order to raise the exhaust gas temperature and in turn achieve filter regeneration. Two model-based control strategies were developed aiming to minimize the fuel penalty of the regeneration process described above.

Command shaping for residual vibration free crane maneuvers

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.

Topology Optimization of Smart Structures Using a Homogenization Approach

Engineers are often required to design mechanical structures to meet specific loading conditions. Topology optimization automates the process of finding an optimal structural design, allowing for size, shape, and topology variations. For a given set of boundary conditions and design specifications, an optimal structure is computed, based on a formulated cost function. In this paper, the optimization considers not only the distribution of conventional material, but also simultaneously the distribution of active piezoelectric material within the domain. In the formulation of the topology optimization problem, a microstructure consisting of smart as well as conventional material is used. Instances of the microstructure occur in a rectangular grid and cover the design domain. Since the microstructure is defined parametrically, the density of each material can be controlled individually at each point. This enables us to formulate the problem of finding an optimal material distribution as a parameter optimization problem. A homogenization approach is used to find and use effective material properties for the limiting case of an infinitely small microstructure. Several numerical examples are provided to demonstrate the application of the method to find structures that maximize the deflection at a point when the piezoelectric material is activated.