A Study of dynamic force measurement based on the levitation mass method

In this thesis, methods based on the levitation mass method (LMM) for evaluating the frictional characteristics of a linear ball bearing, the electro-mechanical characteristics of a voice coil and a piezo-electric actuator and for removing the velocity limitation of laser Doppler interferometer (LDI) are proposed. In the LMM, the inertial force of a levitated mass used as the reference force for measuring dynamic force is measured as the product of the mass and acceleration. For evaluating the dynamical friction of linear ball bearing, two corner-cube prisms (CC) are attached to a moving part which is connected to the ball bearing. The acceleration of the gravity center of the moving part is estimated from the accelerations of the two CCs which are measured using a dual axis LDI. The frictional force is measured as the product of the mass of the moving part and the acceleration of the gravity center. For evaluating the voice coil actuator, a moving part levitated using an aerostatic linear bearing is connected to the coil. The dynamic force generated by the coil is measured as the inertial force of the moving part. The velocity of the moving part is measured using a LDI. Other mechanical characteristics such as position, acceleration and force are calculated from the measured velocity. With the electrical characteristics mea-sured using a digital voltmeter, the relationships between electrical and mechanical characteristics are evaluated. For measuring the electro-mechanical characteristics of piezo-electric actuator, a CC considered as an inertial mass is attached to the top of the actuator instead of the moving part. The dynamic force generated by the actuator is measured as the inertial force of CC. Based on this method, the force-displacement behavior of the actuator under dynamic condition is evaluated. The relationship of energy conversion between electrical and mechanical domains is also evaluated based on the observed results. In the LMM, the velocity of moving part is measured using a LDI whose laser source is a Zeeman-type two-frequency laser. However, the measurable velocity of LDI is limited by the frequency di.erence of laser in back and forth motion. In order to get high measurable velocity in back and forth motion, a dual beat-frequencies laser Doppler interferometer (DB-LDI) is developed and applied. In DB-LDI, two laser beams with di.erence frequency (f1,f2) are divided into reference beams and signal beams by a non-polarized beams splitter. They are used to produce two beat signals. When the object moving, the beat frequencies of beat signals are detected as |f ′ . f2| and |f ′ . f1|, respectively. For back and forth motion, although the 12 velocity of the object calculated from one beat frequency reaches critical velocity, the velocity calculated from the other one is far from critical velocity. The DB-LDI has been applied to realize a high-speed impact testing. During the collision, the velocity of the mass, even higher than the critical velocity, is accurately measured using the DB-LDI.学位記番号：工博甲47

Static, dynamic and levitation characteristics of squeeze film air journal bearing: Designing, modelling, simulation and fluid solid interaction

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Bearings today need to be able to run at very high speed, providing high positional accuracy for the structure that it supports, and requiring very little or no maintenance. For this to happen, bearings must have tight tolerances and very low or zero friction during operation. This pushes many traditional contact-type bearings to their limits as they often fail due to friction, generating heat and causing wear. By comparison, existing non-contact bearings fare better because of their very low or zero friction. But some have their own problem too. For example, the fact that aerostatic bearings require an air supply means having to use a separate air compressor and connecting hoses. This makes the installation bulky. Aerodynamic and hydrodynamic bearings cannot support loads at zero speed. Both hydrodynamic and hydrostatic bearings may cause contamination to the work-pieces and the work environment because of the use of lubricating fluid. A potential solution to the above-mentioned problems is the new squeeze film air bearing. It works on the rapid squeeze action of an air film to produce separation between two metal surfaces. This has the benefit of being compact with a very simple configuration because it does not require an external pressurized air supply, can support loads at zero speed and is free of contamination. For this research, two squeeze film air journal bearings, made from material of Al 2024 – T3 and Cu - C101 with the same geometry, were designed. The bearing is in the shape of a round tube with three fins on the outer surface and the journal, a round rod. When excited at a certain normal mode, the bearing shell flexes with a desirable modal shape for the squeeze film action. The various modes of vibration of Al bearing were obtained from a finite-element model implemented in ANSYS. Two Modes, the 13th and 23rd, at the respective frequencies of 16.320 kHz and 25.322 kHz, were identified for further investigation by experiments with respect to the squeeze film thickness and its load-carrying capacity. For Cu bearing, the two Modes are also 13th and 23rd at the respective frequencies of 12.184 kHz and 18.459 kHz. In order to produce dynamic deformation of the bearings at their modes, a single layer piezoelectric actuator was used as a driver. The maximum stroke length and the maximum blocking force of the single layer piezoelectric actuator were determined using manual calculation and ANSYS simulation. In the coupled-field analysis, the single layer piezoelectric actuator was mounted on the outside surface of the bearing shell and loaded with an AC and a DC voltage in order to produce the static and dynamic deformation. For the static analysis, the maximum deformation of Al bearing shell is 0.124 μm when the actuators are driven at the DC of 75 V. For the dynamic analysis, the actuators are driven at three levels of AC, namely 55, 65 and 75V with a constant DC offset of 75V and the driving frequency coincided with the modal frequency of the bearing. The maximum dynamic deformation of Al bearing shell is 3.22μm at Mode 13 and 2.08μm at Mode 23 when the actuators were driven at the AC of 75 V and the DC of 75 V. Similarly, the FEA simulation was used for analyzing Cu bearing. Furthermore, the dynamic deformation of both Al and Cu bearing at Mode 13 and 23 are validated by experiments. This research developed two theoretical models that explain the existence of a net pressure in a squeeze film for the levitation. The first model uses the ideal gas law as first approximation whilst the second uses the CFX simulation to provide a more exact explanation. In terms of the load-carrying capacity, Mode 13 was identified to be better than Mode 23 for both bearings. However, at Mode 13, Al bearing has a higher load-carrying capacity than Cu bearing. This is due to Al bearing having a higher modal frequency and amplitude. Finally, the coupled-field analysis for fluid solid interaction (FSI) was studied at both Mode 13 and 23 for Al bearing. The findings are that: a) the fluid force in the squeeze film can affect the dynamic deformation of the bearing shell, especially at high oscillation frequency, more at Mode 13 than at Mode 23 due to the relatively high pressure end-leakage in the latter; b) the dynamic deformation of the bearing shell increases with the gap clearance in a logarithmic manner at Mode 13; and c) the micron levels of gap clearance provide a damping effect on the dynamic deformation of the bearing shell at Mode 13 and at Mode 23, though much less dominant

Alternative plate deformation phenomenon for squeeze film levitation

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonThis thesis deals with a theoretical and an experimental exploration of squeeze film levitation (SFL) of light objects. The investigations aimed to find the important design parameters controlling this levitation mechanism and also to suggest an alternative way to implement SFL. The study, through computer modelling and experimental validation, focused on Poisson’s contraction effect for generating SFL. A finite element model (ANSYS) was verified by experimental testing of five different plate designs. Each plate was subjected to a uniaxial plain stress by an arrangement of two hard piezoelectric actuators (PZT) bonded to the bottom of the plate and driven with DC or AC voltages. It was observed that pulsation of a dimple or crest shaped elastic deformation along the longitudinal axis in the central area of the plate was created because of Poisson’s contraction. This Poisson’s effect generated the squeeze-film between the plate and the levitated object. The separation distance between a floating lightweight object and the plate was analysed using computational fluid dynamics (ANSYS CFX) through creation of a modelling model for the air-film entrapped between the two interacting surfaces – a typical three-dimensional fluid-solid interaction system (FSI). Additionally, the levitation distance has been experimentally measured by a Laser Sensor. A satisfactory agreement has been found between model predictions and experimental results. Two levitation systems, one based on a horn transducer (Langevin type) and the other one in the form of a plain rectangular plate made of Aluminium and firmly fastened at both ends with a surface-mounted piezoelectric actuator, were compared in this thesis. Both devices were based on SFL mechanism. Evidently, the performances of both designs were greatly influenced by the design structure and in particular by the driving plate characteristics such as plate size and geometry as well as the driving boundary conditions. To this end, physical experiments were carried out and it was found that the device utilising horn-type transducer yields better levitation performance. Ultimately, the research explained the confusion between three approaches to non-contact levitation through literature review and also pointed out some essential parameters like piezoelectric actuators location, material of the driving structure, coupled-field between the actuators and the driving structure and the fluid-solid interface that was existed between the excited plate and the levitated object

Using time delay in the nonlinear oscillations of magnetic levitation for simultaneous energy harvesting and vibration suppression

In this paper, the nonlinear oscillations of magnetic levitation in the presence of a time delay is investigated, with the purpose of simultaneous energy harvesting and vibration suppression. To harvest energy, a coil with seven layers of 36 gauge wire wound around the outer casing is utilized. Although the proposed control feedback consumes some power, the results show the harvestable power can be much larger than the consumed power, which makes the proposed concept feasible. The first-order perturbation method is utilized to examine the possibility of energy harvesting and vibration suppression for different selections of the delay parameters, the distances between the magnets and the external load resistances. In addition, the stability map of the time-delayed control is analytically determined. The influence of the time delay parameters chosen from Single Periodic Solutions (SPS) and Multiple Periodic Solutions (MPS) on the vibration and power amplitudes is studied. It is shown that a point chosen from the MPS region enables the system to harvest power over a broad range of excitation frequencies. Also, the effect of the distance between the magnets on the frequency response of the system is examined. In addition, to select the optimum value for the distance between the magnets for different values of the time delay parameters, a parameter called the Perfection Rate (PR), which reflects both the electrical and mechanical behavior of the system, is used. Finally, it is shown that the presence of the time delay and a point chosen from the MPS region enables the system to harvest more power over a broad range of excitation frequency and to suppress higher levels of vibration, than for a point chosen from the SPS region and without time delay

Design and optimal control of a multistable, cooperative microactuator

In order to satisfy the demand for the high functionality of future microdevices, research on new concepts for multistable microactuators with enlarged working ranges becomes increasingly important. A challenge for the design of such actuators lies in overcoming the mechanical connections of the moved object, which limit its deflection angle or traveling distance. Although numerous approaches have already been proposed to solve this issue, only a few have considered multiple asymptotically stable resting positions. In order to fill this gap, we present a microactuator that allows large vertical displacements of a freely moving permanent magnet on a millimeter-scale. Multiple stable equilibria are generated at predefined positions by superimposing permanent magnetic fields, thus removing the need for constant energy input. In order to achieve fast object movements with low solenoid currents, we apply a combination of piezoelectric and electromagnetic actuation, which work as cooperative manipulators. Optimal trajectory planning and flatness-based control ensure time- and energy-efficient motion while being able to compensate for disturbances. We demonstrate the advantage of the proposed actuator in terms of its expandability and show the effectiveness of the controller with regard to the initial state uncertainty

Design, Optimization, and Experimental Characterization of a Novel Magnetically Actuated Finger Micromanipulator

The ability of external magnetic fields to precisely control micromanipulator systems has received a great deal of attention from researchers in recent years due to its off-board power source. As these micromanipulators provide frictionless motion, and precise motion control, they have promising potential applications in many fields. Conversely, major drawbacks of electromagnetic micromanipulators, include a limited motion range compared to the micromanipulator volume, the inability to handle heavy payloads, and the need for a large drive unit compared to the size of the levitated object, and finally, a low ratio of the generated magnetic force to the micromanipulator weight. To overcome these limitations, we designed a novel electromagnetic finger micromanipulator that was adapted from the well-known spherical robot. The design and optimization procedures for building a three Degree of Freedoms (DOF) electromagnetic finger micromanipulator are firstly introduced. This finger micromanipulator has many potential applications, such as cell manipulation, and pick and place operations. The system consists of two main subsystems: a magnetic actuator, and an electromagnetic end-effector that is connected to the magnetic actuator by a needle. The magnetic actuator consists of four permanent magnets and four electromagnetic coils that work together to guide the micromanipulator finger in the xz plane. The electromagnetic end-effector consists of a rod shape permanent magnet that is aligned along the y axis and surrounded by an electromagnetic coil. The optimal configuration that maximizes the micromanipulator actuation force, and a closed form solution for micromanipulator magnetic actuation force are presented. The model is verified by measuring the interaction force between an electromagnet and a permanent magnet experimentally, and using Finite Element Methods (FEM) analysis. The results show an agreement between the model, the experiment, and the FEM results. The error difference between the FEM, experimental, and model data was 0.05 N. The micromanipulator can be remotely operated by transferring magnetic energy from outside, which means there is no mechanical contact between the actuator and the micromanipulator. Moreover, three control algorithms are designed in order to compute control input currents that are able to control the position of the end-effector in the x, y, and z axes. The proposed controllers are: PID controller, state-feedback controller, and adaptive controller. The experimental results show that the micromanipulator is able to track the desired trajectory with a steady-state error less than 10 µm for a payload free condition. Finally, the ability of the micromanipulator to pick-and-place unknown payloads is demonstrated. To achieve this objective, a robust model reference adaptive controller (MRAC) using the MIT rule for an adaptive mechanism to guide the micromanipulator in the workspace is implemented. The performance of the MRAC is compared with a standard PID controller and state-feedback controller. For the payload free condition, the experimental results show the ability of the micromanipulator to follow a desired motion trajectory in all control strategies with a root mean square error less than 0.2 mm. However, while there is payload variation, the PID controller response yields a non smooth motion with a large overshoot and undershoot. Similarly, the state-feedback controller suffers from variability of dynamics and disturbances due to the payload variation, which yields to non-smooth motion and large overshoot. The micromanipulator motion under the MRAC control scheme conversely follows the desired motion trajectory with the same accuracy. It is found that the micromanipulator can handle payloads up to 75 grams and it has a motion range of ∓ 15 mm in all axes

Superconducting non-contact linear slider for precision positioning in cryogenic environments

In this thesis, a novel device for precision positioning in a long stroke suitable for cryogenics environments has been proposed, designed, built and tested. The device is based on superconducting magnetic levitation. A set of high temperature superconductors allows a long permanent magnet to levitate stably over them. Furthermore, due to the high translational symmetry of the magnetic field applied on the superconductors for any position of the slider in its path, the superconductors not only provide stable levitation to the slider, but al so guide it. Therefore, a sliding kinematic pair is established between the permanent magnet and the superconductors. Finally, using a pair of coils, the position of the slider can be controlled with an open-Ioop control strategy of the current in the coils with nanometre resolution and reduced power consumption. Besides, a set of design rules has been proposed and experimentally verified at 77 K. Parameters of the performance of the mechanism such as the stroke, sensitivity, stiffness, natural frequency, run outs or the power consumption can be modified and optimized by an appropriate designo After this, two prototypes of a long stroke nanopositioner based on these design rules have been built and tested in a relevant environment (T~15 K, in a high vacuum < 10⁻⁶ Pa). Nanometre resolution in the positioning of a mass of about 170 g has been demonstrated in a stroke up to 18 mm. ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------En esta tesis doctoral se propone, diseña, construye y demuestra un dispositivo de alta resolución para posicionado en una carrera larga para entornos criogénicos. Este dispositivo está basado en levitación magnética superconductora de manera que, un conjunto de superconductores de alta temperatura (superconductores de tipo II) permiten a un imán permanente levitar de manera estable sobre ellos y, al mismo tiempo, ser guiado. De hecho, se establece un par cinemático de deslizamiento entre el imán y los superconductores gracias a la alta simetría traslacional del campo magnético aplicado en estos últimos. Además, la posición de la deslizadera puede ser controlada mediante una estrategia de control en bucle abierto de la corriente circulante en un par de bobinas diseñadas específicamente para esta tarea, obteniéndose una excelente resolución y un consumo de energía muy reducido. Así mismo, se proponen una serie de reglas de diseño que fueron verificadas a una temperatura de operación de 77 K. Estas reglas demuestran que hay una serie de parámetros característicos del desempeño del mecanismo como la sensibilidad, la rigidez, la frecuencia natural, las desviaciones o el consumo energético que pueden ser modificados mediante un diseño apropiado. Tras obtener estas reglas de diseño, un par de prototipos de un nanoposicionador de larga carrera han sido diseñados en consecuenCIa, construidos y probados en un ambiente relevante (T ~ 15 K, alto vacío < 10⁻⁶ Pa). Una resolución nanométrica en el posicionamiento de una masa de 170 gramos ha sido demostrada en una carrera de hasta 18 mm

Autonomous shock sensing using bi-stable triboelectric generators and MEMS electrostatic levitation actuators

This work presents an automatic threshold shock-sensing trigger system that consists of a bi-stable triboelectric transducer and a levitation-based electrostatic mechanism. The bi-stable mechanism is sensitive to mechanical shocks and releases impact energy when the shock is strong enough. A triboelectric generator produces voltage when it receives a mechanical shock. The voltage is proportional to the mechanical shock. When the voltage exceed a certain level, the initially pulled-in Microelectromechanical system (MEMS) switch is opened and can disconnect the current in a safety electronic system. The MEMS switch combines two mechanisms of gap-closing (parallel-plate electrodes) with electrostatic levitation (side electrodes) to provide bi-directional motions. The switch is initially closed from a small bias voltage on the gap-closing electrodes. The voltage from the bi-stable generator is connected to the side electrodes. When the shock goes beyond a threshold, the upward force caused by the side electrodes on the switch becomes strong enough to peel off the switch from the closed position. The threshold shock the system can detect is tunable using two control parameters. These two tuning parameters are the axial force on the bi- stable system (clamped-clamped beam) and the bias voltage on the MEMS switch (gap-closing electrodes). The actuation in macro-scale is thus directly connected to a sensor-switch mechanism in micro-scale. This chain makes an autonomous actuation and sensing stand-alone system that has potential application on air bag deployment devices and powerline protection systems. We provide a theoretical frame work of the entire system validated by experimental results