581 research outputs found

    Electromagnetically-driven ultra-fast tool servos for diamond turning

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    Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 343-351).This thesis presents the design, implementation, and control of a new class of fast tool servos (FTS). The primary thesis contributions include the design and experimental demonstration of: novel ultra-fast electromagnetic actuators, integration of these actuators in a new class of FTS, a novel real-time control computer with 1 million samples per second throughput, MIMO loop shaping techniques for parallel power amplifiers, and a novel configuration and controller tuning method for implementing adaptive feed-forward cancellation control. All of these elements have been successfully used for diamond turning of contoured surfaces. Fast tool servos (FTS) are high bandwidth positioning devices, which, in conjunction with an ultra-precision lathe and diamond tooling, can produce free form surfaces with nanometer-scale resolution, such as required in micro-optical devices and light-enhancing films. The increasing complexity of such surfaces requires more components in shorter spatial wavelengths, and thus drives simultaneously the need for high bandwidth, high acceleration and high accuracy of the FTS. Conventional FTS solutions are based on piezoelectric stacks, which are typically limited to a few micron stroke at 1 kHz operation if not operated in a resonant mode.(cont.) As a promising alternative, this thesis demonstrates electromagnetically driven solutions for fast tool servos. The key new technology in these alternative designs is a new class of ultra fast electromagnetic drivers with thousands of G's acceleration capability in continuous operation. By separating the flux-biasing surfaces from the normal-flux working surfaces, this new driver design has a number of advantages: (1) actuating force linear to both excitation current and displacement, (2) modularity and parallel operating ability, (3) full magnetic stress utilization of normal surfaces, and (4) low heat dissipation. We analyze the operation characteristics, and also provide soft magnetic material selection criteria and motor design guidelines. Based on this ultra fast driver, we designed a linear fast tool servo with the theoretical capability for 1200 G acceleration in continuous operation. To control such positioning devices at bandwidth of over 10 kHz, we developed a real-time computer architecture, utilizing three floating point digital signal processors (DSPs) in conjunction with a field-programmable gate array (FPGA) to significantly increase the processing rate.(cont.) The real-time computer prototype experimentally demonstrated 1 million samples per second real-time control execution with a total latency of 1.9 microseconds when implementing a representative control algorithm of significant complexity. This processing system has capabilities far beyond what is commercially available for such real-time high-accuracy control tasks. The power amplifier driving the FTS must supply 1 kVA (primarily reactive power) with over 100 kHz bandwidth. We present a solution of using 4 power operational amplifiers in parallel, each capable of supplying one fourth of the total power. To address the coupling issues among channels, a decoupling theory is developed to convert the associated MIMO plant into several SISO sub-plants, and thus ease the analog decentralized controller design of the power amplifier current feedback loops. In order to enhance the FTS repetitive position trajectory tracking and disturbance rejection, adaptive feed-forward cancellation is embedded into a conventional motion control loop in our system. We provide a consistent loop shaping framework and intuitive parameter tuning and trade-off guidelines for this controller structure.(cont.) Experimental results with the first prototype FTS using powder iron cores demonstrate 23 kHz closed-loop bandwidth, as low as 1.7 nm RMS error, 30 micron stroke, 500 G peak acceleration at 10 kHz open-loop operation, and 2.1 nm (0.04%) error in tracking a 3 kHz sinusoid of 16 micron p-v. (The full 1200 G capability is expected to be experimentally demonstrated by the second prototype FTS using Ni-Fe tape cores). Using this FTS, we have diamond-turned two-dimensional sinusoidal surfaces in copper and aluminum with 0.5 degree azimuthal spatial period, 160 micron radial spatial period, and 2 micron peak-to-valley amplitude, at 500 RPM spindle speed.by Xiaodong Lu.Ph.D

    Development, Design, Manufacture and Test of Flapping Wing Micro Aerial Vehicles

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    The field of FlappingWing Micro Air Vehicles (FWMAV) has been of interest in recent years and as shown to have many aerodynamic principles unconventional to traditional aviation aerodynamics. In addition to traditional manufacturing techniques, MAVs have utilized techniques and machines that have gained significant interest and investment over the past decade, namely in additive manufacturing. This dissertation discusses the techniques used to manufacture and build a 30 gram-force (gf) model which approaches the lower limit allowed by current commercial off-the-shelf items. The vehicle utilizes a novel mechanism that minimizes traditional kinematic issues associated with four bar mechanisms for flapping wing vehicles. A kinematic reasoning for large amplitude flapping is demonstrated namely, by lowering the cycle averaged angular acceleration of the wings. The vehicle is tested for control authority and lift of the mechanism using three servo drives for wing manipulation. The study then discusses the wing design, manufacturing techniques and limitations involved with the wings for a FWMAV. A set of 17 different wings are tested for lift reaching lifts of 38 gf using the aforementioned vehicle design. The variation in wings spurs the investigation of the flow patterns generated by the flexible wings and its interactions for multiple flapping amplitudes. Phase-lock particle image velocimetry (PIV) is used to investigate the unsteady flows generated by the vehicle. A novel flow pattern is experimentally found, namely “trailing edge vortex capture” upon wing reversal for all three flapping amplitudes, alluding to a newly discovered addition to the lift enhancing effect of wake capture. This effect is believed to be a result of flexible wings and may provide lift enhancing characteristics to wake capture

    Minimally invasive instrument for in vivo measurement of solid organ mechanical impedance

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    Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001.Includes bibliographical references (p. 161-165).The medical field, and surgeons in particular, are turning to engineers to develop systems that help them learn their craft better. Mannequin-based systems, animal labs and surgery on cadavers each have drawbacks that could be addressed through realistic computer-based surgical simulation systems. To generate a simulation that includes both tactile/haptic and visual feedback, one must know what the material properties of tissue are, so that a finite element or other model can generate the proper predictions for interactions between surgical instruments and tissue. This thesis presents the design, construction, characterization, and use of a mini- mally invasive surgical instrument designed to measure the linear visco-elastic prop- erties of solid organs. The Tissue Material Property Sampling Tool, or TeMPeST 1-D, applies a small amplitude vibration normal to the surface of an organ such as liver or spleen, and records the applied force and displacement. It has a range of motion of up to lmm, and can apply up to 300mN force with a 5mm right circular indenter. The open loop bandwidth of the system is approximately 100Hz, which is greater than the bandwidth of both the human visual and motor control systems. The relationships between indentation force and displacement and material prop- erties such as the elastic modulus of tissue are presented, and models are developed that show the expected response to a standard tissue model. Characterization and calibration tests demonstrate the response of the prototype components. Experi- ments performed on spring and mass elements and on silicone gel samples, which mimic tissue response, show that the TeMPeST 1-D can accurately measure their force-displacement responses.(cont.) The TeMPeST 1-D and its data acquisition system are intended to be portable, to be easily transported to and used in an operating room. The system was used in proof-of-concept experiments performed on live pigs; an example of the measured properties of porcine liver is presented. The TeMPeST 1-D is the first in a series of instruments that will be developed to support the generation of a comprehensive atlas of tissue material properties.by Mark Peter Ottensmeyer.Ph.D

    Design and Optimal Control of a Magnet Assisted Scanning Stage for Precise and Energy Efficient Positioning

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    Scanning stages are characterized by repeated back and forth motions and are widely used in advanced manufacturing processes like photo-lithography, laser-scribing, inspection, metrology, 3D printing, and precision parts assembly, many of which are closely related to the semiconductor (i.e., integrated circuit) manufacturing industry. In order to deliver more high- performance semiconductor chips, i.e., to keep up with predictions made by Moore’s Law, the scanning stages employed by the industry need to move faster while maintaining nanometer-level precision. Achieving these two goals simultaneously requires extensive use of thermal and vibration-induced error mitigation methods, because the motors, and subsequently the surrounding stage components, become heated and flexible parts of scanning stages are easily excited by their aggressive motions (with high acceleration/deceleration). Most of the available solutions tackle the heat and vibration mitigation problems separately, even though the two problems originate from one source, i.e., the large inertial loads generated by the scanning stage’s actuators. Much benefit (e.g., size and cost reductions) can be achieved by considering the two problems simultaneously by addressing their root cause. This dissertation proposes a design-based approach to simultaneously mitigate thermal and vibration-induced errors of scanning stages. Exploiting the repeated back-and-forth motions of scanning, permanent magnet (PM) based assist devices are designed to provide assist force needed during the motion reversal portions of scanning trajectories. The PM-based assist devices store the kinetic energy of the moving table during deceleration and release the stored energy when the table accelerates. Consequently, the force requirements of the primary actuator decrease, thus lowering its heat generation due to copper (resistive) losses. Moreover, the reaction forces borne by the PM assistive devices are channeled to the ground, bypassing the vibration isolated base upon which the scanning stage rests, thus reducing unwanted vibration. To increase the force density of the PMs, a 2D Halbach arrangement is adopted in a prototype scanning stage. Moreover, an efficient and low-cost servo system, optimized for versatility, is integrated into the scanning stage for automatic positioning of the PMs. The designed magnet assisted scanning stage is an over-actuated system, meaning that it has more control inputs than outputs. For the best utilization of its actuators, a feedforward approach for optimal allocation of control efforts to its actuators is developed. The stage, controlled with the optimal feedforward control inputs, achieves significant reductions of actuator heat and vibration-induced errors when applied to typical scanning motions used in semiconductor manufacturing (silicon wafer processing). To further improve the positioning accuracy of the stage, an Iterative Learning Control (ILC) approach for over-actuated systems is developed, exploiting the repeated motion of scanning stages. The optimal ILC update law is designed, considering model and input force uncertainties, for robust monotonic convergence of tracking errors, and the resultant control force is efficiently allocated to multiple actuators. Applied to the magnet assisted scanning stage, the proposed ILC approach additionally reduces tracking errors arising from the mismatch between the model and actual system, thus significantly improving the positioning accuracy of the stage.PHDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/149847/1/yydkyoon_1.pd

    The 31st Aerospace Mechanisms Symposium

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    The proceedings of the 31st Aerospace Mechanisms Symposium are reported. Topics covered include: robotics, deployment mechanisms, bearings, actuators, scanners, boom and antenna release, and test equipment. A major focus is the reporting of problems and solutions associated with the development and flight certification of new mechanisms

    Full state feedback control of galvanometer scanning system

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    Voice coil actuators are devices used for moving an inertial load at extremely high accelerations and relocating it within micrometers over a limited range of travel. The motion produced may be linear or rotational and the travel times may be in the order of milliseconds or less. These actuators have applications in computer disk drives, high speed lens focusing, servo valves and laser scanning tools. In this thesis a digital controller is developed for use in voice coil actuator applications. The controller is designed for high accuracy and a fast dynamic response. Two design methods are presented both of which are developed, simulated and implemented using a laser-scanner experimental rig. In voice coils based systems, the instantaneous rotor position is normally measured using an electro-mechanical sensor connected to the shaft. The elimination of the electo-mechamcal sensor is considered. Simulation and experimental results are presented for the laser scanning system operating under normal (with a sensor) and 'sensorless' control

    Volume 2 – Conference: Wednesday, March 9

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    10. Internationales Fluidtechnisches Kolloquium:Group 1 | 2: Novel System Structures Group 3 | 5: Pumps Group 4: Thermal Behaviour Group 6: Industrial Hydraulic
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