Browsing by Author "Dr. Gregory D. Buckner, Committee Member"

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Low Power Valve Actuation Using Trans-Permanent Magnetics
(2003-11-21) Duval, Luis Denit; Dr. Richard F. Keltie, Committee Member; Dr. Mohammed A. Zikry, Committee Member; Dr. Lawrence M. Silverberg, Committee Chair; Dr. Gregory D. Buckner, Committee Member
The subject of magnetic actuators is very broad, and encompasses a wide range of technologies, magnetic circuit topologies, and performance characteristics for an ever-increasing spectrum of applications. As a consequence of recent advances in soft and hard magnetic materials and developments in power electronics, microprocessors and digital control strategies, and the continuing demand for higher performance motion control systems, there appears to be more research and development activity in magnetic actuators for applications spanning all market sectors than at any time. Thus many actuator types and topologies are emerging with widely varying operational characteristics, in terms of displacement (rotary or linear), speed of response, position accuracy and duty cycle. In this dissertation, a rational approach for switching the states of permanent magnets through an on-board magnetization process is presented. The resulting dynamic systems are referred to as trans-permanent magnetic systems (T-PM). The first part of this research focuses on the governing equations needed for the analysis of trans-permanent magnetic systems. Their feasibility is demonstrated experimentally. In doing so, a method that has the potential of leading to new ultra-low power designs for electromechanical devices is introduced. In the second part of this research, the aforementioned developments in T-PM are applied to the problem of low power valves. Whereas alternate approaches to low power valve control may utilize latching to maintain valve position during inactive periods, an approach that eliminates the need for latching mechanisms is presented. Instead, the principles of T-PM are employed to switch the states of permanent magnets; the used of permanent magnets instead of electromagnets eliminates power consumption during inactive periods, thereby reducing power consumption to ultra-low levels. The magnets in a T-PM actuator are configured in a stack. The relationships between the strength and number of magnets in the stack and the stroke and resolution of the actuator are developed. This dissertation reports on the design and testing of a prototype valve actuator that uses a stack pf T-PM with alternating polarity. It is shown that this stack is well suited for discrete state process valves having a small number of states. It is concluded that the trans-permanent valve represents a promising valve actuation technology.
Modeling and Control of a Magnetostrictive System for High Precision Actuation at a Particular Frequency
(2002-12-05) Mou, Gang; Dr. Gregory D. Buckner, Committee Member; Dr. Fen Wu, Committee Member; Dr. Paul I. Ro, Committee Chair
A magnetostrictive actuator made of Terfenol-D alloy can generate high mechanical strains with broadband response and provide accurate positioning. These characteristics have been employed as controllers and vibration absorbers in industrial and heavy structural applications, such as fast tool servo systems and precision micropositioners. Full utilization of magnetostrictive transducers in these applications requires a suitable controller as well as quantification of the transducer dynamics in response to various inputs. However, at moderate to high drive levels, the output from a magnetostrictive actuator is highly nonlinear and contains significant magnetic and magnetomechanical hysteresis. The control of this nonlinear system is a challenge. In order to simplify this problem, 50Hz is chosen as the working frequency for the actuator in the experiments since it shows near linear property at 50Hz and the approach used at 50Hz could be extended to a broader frequency range in the applications. First, with an optical sensor, the dynamics of the actuator are measured under voltage inputs at different frequencies and amplitudes. Using SAS System V8, a second order dynamic model is obtained at one frequency (50Hz). This model matches the open loop behavior very well. A PID controller is then developed. The control command signal generated through the DSP board is directed to the actuator. A close loop control system is thus formed. As a nonlinear control approach, sliding mode control can offer some ideal properties, such as insensitivity to parameter variations or uncertainties, external disturbance rejection, and fast dynamic response. In order to obtain better tracking performance and robustness, a sliding mode control algorithm is introduced into the system. The experiment results from the sliding mode controller are compared with those from the open loop and PID control. The comparison shows improvement in the displacement tracking performance at this frequency. Further work will involve the modification of the sliding mode controller using a time-varying switching gain and improvement in modeling of the actuator over a broader frequency range.
Two-Axis Force Feedback Deflection Compensation of Miniature Ball End Mills
(2004-10-26) Freitag, Karl P.; Dr. Gregory D. Buckner, Committee Member; Dr. Thomas A. Dow, Committee Chair; Dr. Ronald O. Scattergood, Committee Member
The primary objective of this research is to improve dimensional tolerances and reduce total manufacturing time of precision milling operations through the implementation of force-feedback machining. Force-feedback machining consists of using real-time cutting force measurement integrated with high bandwidth actuation to provide active error compensation of tool deflection. This research focuses on the development and implementation force-feedback machining using miniature (< 1 mm diameter) ball end mills. Due to the thin geometry of these tools, deflection of the tool during machining results in significant form error of the machined part. A piezoelectric two-axis force feedback actuator was designed and developed to measure and compensate for tool deflection errors of miniature ball end mills. Geometric form error was reduced by 75 % thru the application of force feedback machining.
Vibration Energy Harvesting by Magnetostrictive Material for Powering Wireless Sensors
(2008-05-11) Wang, Lei; Dr. Gianluca Lazzi, Committee Member; Dr. Gregory D. Buckner, Committee Member; Dr. Kara J. Peters, Committee Member; Dr. Fuh-Gwo Yuan, Committee Chair
Wireless Sensor Networks (WSN) have been increasingly applied to Structural Health Monitoring (SHM). For WSN to achieve full potential, self-powering these sensor nodes needs to be developed. A promising approach is to seamlessly integrate energy harvesting techniques from ambient vibrations with the sensor to form a self-powered node. The objective of this study is to develop a new magnetostrictive material (MsM) vibration energy harvester for powering WISP (Wireless Intelligent Sensor Platform) developed by North Carolina State University. Apart from piezoelectric materials which currently dominate in low frequency vibration harvesting, this new method provides an alternate scheme which overcomes the major drawbacks of piezoelectric vibration energy harvesters and can operate at a higher frequency range. A new class of vibration energy harvester based on MsM, Metglas 2605SC, is deigned, developed, and tested. Compared to piezoelectric materials, Metglas 2605SC offers advantages including ultra-high energy conversion efficiency, high power density, longer life cycles, lack of depolarization, and high flexibility to survive in strong ambient vibrations. To enhance the energy conversion efficiency and shrink the size of the harvester, Metglas ribbons are transversely annealed by a strong magnetic field along its width direction to eliminate the need of bias magnetic field. Governing equations of motion for the MsM harvesting device are derived by Hamilton's Principle in conjunction with normal mode superposition method based on Euler-Bernoulli beam theory. This approach indicates the MsM laminate wound with a pick-up coil can be modeled as an electro-mechanical gyrator in series with an inductor. Then a generalized electrical-mechanical circuit mode is obtained. Such formulation is valid in a wide frequency range, not limited to below the fundamental natural frequency. In addition, the proposed model can be readily extended to a more practical case of a cantilever beam element with a tip mass. The model resulting in achievable output performances of the harvester powering a resistive load and charging a capacitive energy storage device, respectively, is quantitatively derived. An energy harvesting circuit, which interfaces with a wireless sensor, accumulates the harvested energy into an ultracapacitor, is designed on a printed circuit board (PCB) with plane dimension 25mm*35mm. It mainly consists of a voltage quadrupler, a 3F ultracapacitor, and a smart regulator. The output DC voltage from the PCB can be adjusted within 2.0˜5.5V which is compatible with most wireless sensor electronics. In experiments, a bimetallic cantilever beam method is developed to determine the piezomagnetic constant d from the measured Lambda-H curve. The maximum output power and power density on the resistor can reach 200 uW and 900 uW⁄cm3, respectively. For a working prototype, the average power and power density during charging the ultracapacitor can achieve 576 uW and 606 uW⁄cm3 respectively, which compete favorably with the piezoelectric vibration energy harvesters.