Browsing by Subject "Actuators"
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Item Coordinated and reconfigurable vehicle dynamics control(2007-05) Wang, Junmin, 1974-; Longoria, Raul G.This dissertation describes a coordinated and reconfigurable vehicle dynamics control system. With the continuous development of vehicle actuation/sensing technologies, coordinating all the available actuation resources to improve system performance and expand system operational envelope has become an active research topic that has received significant attention from both academia and industry. Given the complex nature of tire forces that are relied upon for inducing generalized forces for vehicle motion control, the main challenge is how to coordinate all the tire forces in a unified and optimal manner to achieve the overall control objectives even under adverse conditions. In this dissertation, a hierarchically-coordinated and reconfigurable vehicle dynamics control system is proposed. A higher-level robust nonlinear controller is designed to produce the generalized forces/moment for controlling vehicle planar motions. An innovative control allocation scheme is designed to distribute the generalized forces/moment to slip and slip angle of each tire with the considerations of vehicle dynamics and environmental variations. Individual tire slip and slip angles are selected as the control variables to resolve the inherent tire force nonlinear constraints which otherwise may make the system more complex and computationally expensive. A real-time adaptable, computationally efficient accelerated fixed-point method with improved convergence rate when actuation saturates is proposed to solve the amplitude and rate constrained quadratic programming (QP) control allocation problem. To track the desired allocated slip and slip angle of each tire and therefore the required tire longitudinal and lateral forces to fulfill the control objectives, a combined tire slip and slip angle tracking control system is developed to manipulate the driving/braking/steering actuation of each wheel independent to vehicle body states. The overall system is evaluated on a commercial full-vehicle model provided by CarSim® under various adverse driving conditions including scenarios where vehicle actuator failures occur. Compared with those of existing vehicle control systems, significantly expanded system operational envelop and greatly reduced driver efforts were observed.Item Design and electrodynamic analysis of active magnetic bearing actuators(2003-05) Pichot, Mark Allen, 1956-; Driga, Mircea D.For more than a century, engineers have imagined bearing systems that use magnetic fields to levitate rotors in rotating machines, eliminating contact between bearing surfaces. In the past twenty-five years, magnetic bearing systems have moved from laboratory novelty to an accepted industrial product, and are now being used in an impressive variety of applications. This dissertation deals with the development and verification of design codes for permanent magnet bias, homopolar magnetic bearing actuators. A design code using magnetic circuit analysis is developed that can provide quick evaluation of candidate bearing actuators. Non-linear material properties are represented, and force versus current bearing characteristics can be calculated as a function of operating speed. Details of code development and description of a user interface created with a commercially available spreadsheet program are presented. To verify magnetic circuit design code predictions, three-dimensional finite element analysis is performed for a magnetic bearing system of interest. For experimental verification, an inside-out topology test bearing actuator and testing fixture were designed and fabricated in which bearing parameters were directly measured. Test results are presented and compared to theoretical predictions of the circuit analysis code and finite element program. In high-speed rotating machines, rotating losses are a prime concern because heat transfer mechanisms to remove rotor heat are limited. Losses inherent in permanent magnet bias homopolar magnetic bearings are discussed and the dependence of losses on bearing geometry is explored. Studies to reduce rotor losses by optimizing stator winding slot geometry are presented. Finally, a thrust-bearing concept designed to further reduce bearing losses is evaluated. In this concept, the static rotor weight of a vertical-axis machine can be supported by bearing actuator bias fields, minimizing required control effort. This concept holds the promise of reducing actuator power input and bearing losses, thus increasing bearing system efficiency.Item Direct numerical simulation of microjets for turbulent boundary layer control(2004) Lee, Conrad Yuan Yuen; Goldstein, David B.A direct numerical simulation approach is used to simulate an array of MEMS slot jets in a turbulent boundary layer for the purposes of flow control. Initial studies were used to first ascertain the correctness of the model and give insight into the performance characteristics of the devices. To this end, a flow and geometric parameter study was conducted on a 2-D simulation of the devices and the results used in the design of 3-D devices. Then, once the performance characteristics of the 3-D devices were determined, a series of parametric studies were conducted involving quasi-steady, periodic and single pulses into a turbulent boundary layer. Results indicate that low Re devices can substantially affect the flow but the arbitrary actuation tended to introduce new disturbances in the flow. Hybrid methods involving passive surface texture elements and active devices were briefly examined in an attempt to extract some form of useful flow control from the actuators but the results were still insufficient. Instead, a real-time, adaptive feedback method was selected to calibrate the strength of the actuators. The feedback method was first tested by itself to verify that the numerical approach used here was capable of implementing such control. The feedback method was then modified and used with a single, isolated slot. Subsequent simulations increased the number of slots to form a row of actuators and eventually actuator arrays. Results showed that an actively-controlled actuator array provided a small turbulent drag decrease despite having only a small impact on the turbulence levels in the flow. This result suggested a different mechanism of drag reduction from the original feedback method based on the presence of cavities which are seen as low-shear stress regions by the mean flow.Item Fundamental development of hypocycloidal gear transmissions(2005) Park, Sang-Hyun; Tesar, DelbertThe objective of this research is to push the Electro-Mechanical (EM) actuator technology forward and make it capable of meeting increasingly demanding requirements by improving gear transmission technology which has the most significant effects on actuator performance. The research presents in-depth parametric design and analysis of the Hypocycloidal Gear Transmission (HGT) and its circular-arc tooth profile. This unique combination is claimed to provide exceptional advantages including very high torque to weight/volume ratio, quiet and smooth operation under load, almost zero lost motion and backlash, very high efficiency, and insensitiveness to the manufacturing errors. Careful parametric design of the highly conformal, convex-concave circular-arc tooth profile and its tip relief can further enhance the performance of the HGT by dramatically improving the Hertz contact property, and maximizing the contact ratio. This high contact ratio leads to ideal load distribution and gradual pickup/release of the vii load (minimization of tooth-to-tooth impact). One of the key deliverables of this research is to provide a parametric design guideline for the HGT employing the circular-arc teeth. Several analyses were performed to establish the claimed advantages. In the tooth meshing analysis, clearances/interferences and kinematics of the contacts were analyzed for understanding of the contact characteristics of the HGT. Parametric decision based on this analysis also provided an exceptionally low pressure angle for one of the prototype HGTs. In the loaded tooth contact analysis, real contact ratio under tooth deformation and load sharing factor were analyzed for demonstration of an effective ‘self-protecting’ feature, which made the HGT suitable for extremely heavy load applications. In the efficiency analysis, friction power losses in the prototype HGTs were evaluated to verify the claimed high efficiency. Finally, effects of manufacturing errors on the contact properties were analyzed for visualization of the error-insensitiveness of the HGT. This report successfully proves that the HGT is a promising architecture for use in EM actuators. Sponsored by Navy and DOE, two EM actuator prototypes which employ the HGT as a key component have been built, and set up for performance tests. The design and analysis of these prototype HGTs have been fully documented in this report.Item Influence of actuator parameters on performance capabilities of serial robotic manipulator systems(2008-08) Rios, Oziel, 1980-; Tesar, DelbertA serial robotic manipulator arm is a complex electro-mechanical system whose performance is primarily characterized by the internal parameters of its actuators. The actuator itself is a complex nonlinear system whose performance can be characterized by the speed and torque capabilities of its motor and its accuracy depends on the resolution of the encoder as well as its ability to resist deformations in its gear train under load. The mechanical gain associated with the gear train transmission is critical to the overall performance of the actuator since it amplifies the motor torque thus improving the force capability of the manipulator housing it, reduces the motor speed to a suitable output speed operating range, dominates the inertia content of the manipulator and amplifies the stiffness improving the precision under load of the overall system. In this work, a basic analytic process that can be used to manage the actuator parameters to obtain an improved arm design based on a set of desired/required performance specifications is laid out. The key to this analytic process is the mapping of the actuator parameters (motor speed, motor torque, rotary stiffness, encoder resolution, transmission efficiency, mass, rotary inertia) to their effective values at the system output via the mechanical gains of the actuator transmissions as well as the effective mechanical gains associated with the manipulator geometry. This forward mapping of the actuator parameters allows the designer to determine how each of the actuator parameters influences the functional capacity of the serial manipulator arm. The analytic formulation is demonstrated to be effective in addressing the issue of configuration management of serial robotic manipulators where the goal is to assemble a system from a finite set of actuator modules that meets some required performance specifications. To this end, four design case studies demonstrating the solution of the configuration management problem are presented where the application domains include designing for light to heavy-duty force applications, designing for responsiveness and designing for Human-Robot Interactions (HRI). The design trade-offs for each of the application domains are analyzed and design guidelines are presented. This research also formulates a new approach to characterizing the dynamic behavior of serial chain mechanisms via the kinetic energy distribution. In any mechanism, the amount of kinetic energy in the system is a very important quantity to analyze. Since the inertial torques are directly related to the rate of change of the kinetic energy, better design (and operation) is achieved by having an understanding of how kinetic energy is distributed along the mechanism structure as well as how rapidly kinetic energy is flowing within it. In this work, a description of the Kinetic Energy Partition Values (KEPV) for serial chain mechanisms, as well as their rates of change, are presented. The KEPVs arise from the partitioning of the mechanism’s kinetic energy. Two design criteria, one based on the KEPVs and another based on their rates of change, are developed. These design criteria are indicators of both the dynamic isotropy of the system as well as the amount of kinetic energy flow within the system. A six-axis spatial manipulator is used to illustrate the solution of a design optimization problem where the goal is to demonstrate how the inertial parameters of the actuators and mechanical gains of the actuator transmissions alter the kinetic energy of the system which is “measured” via an effective mass criterion and its distribution which is measured via the KEPV criterion. It is demonstrated that the mechanical gains in the actuators significantly influence the magnitude of the kinetic energy as well as its distribution within the system.Item Investigation of magnetohydrodynamic plasma actuators for aerodynamic flow control(2013-05) Pafford, Brent Joel; Sirohi, JayantThis thesis describes the analysis, fabrication and testing of a novel magnetohydrodynamic plasma actuator for aerodynamic flow control, specifically, retreating blade stall. A magnetohydrodynamic plasma actuator is comprised of two parallel rail electrodes embedded chord-wise on the upper surface of an airfoil. A pulse forming network generates a low-voltage, high-current repetitive pulsed arc. Self-induced electromagnetic fields force the pulsed arc along the length of the rail electrodes at high velocities, transferring momentum to the surrounding air, creating a high-velocity pulsed air wall jet. A systematic experimental investigation of the effect of plasma actuators on the surrounding air is conducted in stagnant air conditions to gain an understanding of the physical characteristics. These characteristics include voltage and current measurements, pulsed arc velocity measurements, and high speed video imaging. The results show typical pulsed arc velocities of about 100 m/s can be induced with discharge energies of about 300 J per pulse. Additional experimental studies are conducted to quantify the performance of the pulsed arc for potential use in subsonic flow control applications. To gain an estimate of the momentum transferred from the pulsed arc to the surrounding air the plasma actuator is placed in a subsonic open-circuit wind tunnel at a Reynolds number of 4.5 x 105. The induced velocity of the pulsed wall jet is measured using a Laser Doppler Anemometer. The measurements show that the pulsed arc creates a high-velocity pulsed wall jet that extends 40 mm above the airfoils surface and has an induced velocity of 15 m/s greater than the unaltered air flow over the airfoil, with peak velocities of 32 m/s. The magnetohydrodynamic plasma actuator proved to induce velocities an order of magnitude greater than the velocities attained by current state-of-the-art plasma actuators. Moreover, the RailPAc is found to posses the potential for alleviation of retreating blade stall. Future work will include experiments to gain a detailed understanding of the improvements to the static stall angle, the optimal actuator geometry, excitation duty cycle, magnetic field augmentation, and behavior of the plasma armature at high Mach/Reynolds numbers. Particle Image Velocimetry (PIV) will be utilized to improve the induced flow velocity measurements acquired with the LDA.Item Math framework for decision making in intelligent electromechanical actuators(2007-05) Ashok, Pradeepkumar, 1977-; Tesar, DelbertSignificant progress has been made in the science of designing sophisticated electromechanical actuators to serve the ever growing needs of complex motion. There are many controllable parameters that can be managed in an actuator in real time to obtain significant operational benefits. However, normally only one parameter (usually current) is managed in real time. The focus has not been managing the available resources to maximize performance but on traditional control for stability. Actuators are very nonlinear and the operation of an actuator is full of uncertainties. The nonlinearity is trivialized by using simplified linear control. The uncertainties are also neglected. Actuators are often discarded before they have been fully utilized for lack of reliable knowledge with regards to the actual condition (degradation) of the actuator. Here we strive for the best operational decision or course of action. Optimization is definitely one way to tackle this problem. But that approach, for the most part, is not transparent to the end user who might like to have some assurance that the decisions suggested by these optimization algorithms are not flawed. The objective of this report is to develop a math framework for decision making in actuators to overcome the previously cited obstacles. The framework should allow for human involvement in the decision making process. It should use test data models (as opposed to simple physics based models) for maximum utilization of actuator capabilities and representation of the nonlinearities. The model should be updatable as new information about the actuator is obtained from a sensor suite. The framework should be capable of handling uncertainties in the parametric model, the in-situ sensor data and the decision process itself. It should allow the generation and full utilization of decision making criteria for performance maximization, condition based maintenance, fault tolerance, layered control and force motion control. Based on the above requirements a framework was developed in this report that requires the following math techniques; Bayesian causal network modeling of actuators, design of experiments for data collection, Bayesian regression for model fitting, Sensor data fusion techniques for accurate modeling, combining maps to obtain decision surfaces and applying norms on the decision surfaces We show that Bayesian causal network modeling is the best suited for our task. It offers the advantage of isolating only those parameters that are important during the operation of the actuator. Also it enables the inclusion of uncertainties and propagation of uncertainties to other parameters through causal links. We demonstrate how Bayesian regression techniques make it straightforward to update the model when new data becomes available and how this in turn helps condition based maintenance. Using the actuator Bayesian causal network we then generate 3 dimensional decision surfaces. We illustrate eight different ways of arriving at these decision surfaces from primary performance maps (maps that were generated through experiments). The illustrations were done using data gathered on a test bed built specifically for the purpose of developing the decision making framework. The test bed is modular and has a controller architecture that allows for different types of actuators (with any type of prime mover; switched reluctance motors, brushless DC motors, brushed DC motors and stepper motors) to be tested on it. We then proceed to develop norms mathematically. They are applied to the decision surfaces and their physical meaning is brought out through example scenarios. The framework was demonstrated on a simple actuator model and found to work satisfactorily for performance maximization and condition based maintenance. In future, the framework needs to be further developed to treat specific decision making situations relating to fault tolerance, layered control and force/motion control.Item Simplifying the programming of intelligent environments(2011-05) Holloway, Seth Michael; Julien, Christine, D. Sc.; Bias, Randolph; Perry, Dewayne E.; Kim, Miryung; Khurshid, SarfrazIn the future, computers will be virtually everywhere: carried by everyone and integrated into the environment. The increased computation and communication capabilities will enable intelligent environments that react to occupants through automated decision-making. Devices (sensors and actuators) are the key to making intelligent environments a reality. We believe that devices must be made more approachable for average users. Existing approaches to application development for intelligent environments require detailed knowledge about devices and their low-leveling programming interfaces, which greatly limits the number of potential users. Instead of limiting users, we must enable everyone to program the devices around them. Intelligent environments will not be commonplace until average people can set up and manage the hardware and software necessary for their personalized applications. In simplifying the programming of intelligent environments, we first made sensors and actuators accessible to average programmers then extended our work to end-users. We term the former contribution Sensor Enablement for Average Programmers (SEAP); the latter work is Sensor Enablement for End-Users (SEEU). In our experience, devices’ disparate, niche programming languages and communication protocols presented great difficulty in developing intelligent environments. To ease the development effort for average programmers, we abstracted and standardized complex sensor and actuator interactions, allowing users to instead think in terms of well-understood web applications. Users have said that SEAP is easy-to-use and exciting. But what about average people, end-users? We found that end-users are incredibly interested in intelligent environments. By engaging end-users we can create intelligent environments even faster and allow domain experts to tailor their environment. This dissertation’s second contribution, Sensor Enablement for End-Users (SEEU) provides a visual programming interface that allows users to create personalized automated behaviors given available devices and data. We performed several user studies to uncover people’s desires for intelligent environments and determine the best interface for managing an intelligent environment. SEEU combines an intuitive interface with the power and flexibility of SEAP. SEEU is a usable end-user programming framework that allows average people to create useful applications for their intelligent environments. With SEEU and SEAP, we simplified the development of intelligent environments, reducing barriers to adoption of emerging sensing and actuation technologies. We demonstrated the feasability with a series of user studies.