DEVELOPMENT OF A NOVEL Z-AXIS PRECISION POSITIONING STAGE WITH MILLIMETER TRAVEL RANGE BASED ON A LINEAR PIEZOELECTRIC MOTOR

Piezoelectric-based positioners are incorporated into stereotaxic devices for microsurgery, scanning tunneling microscopes for the manipulation of atomic and molecular-scale structures, nanomanipulator systems for cell microinjection and machine tools for semiconductor-based manufacturing. Although several precision positioning systems have been developed for planar motion, most are not suitable to provide long travel range with large load capacity in vertical axis because of their weights, size, design and embedded actuators. This thesis develops a novel positioner which is being developed specifically for vertical axis motion based on a piezoworm arrangement in flexure frames. An improved estimation of the stiffness for Normally Clamped (NC) clamp is presented. Analytical calculations and finite element analysis are used to optimize the design of the lifting platform as well as the piezoworm actuator to provide maximum thrust force while maintaining a compact size. To make a stage frame more compact, the actuator is integrated into the stage body. The complementary clamps and the amplified piezoelectric actuators based extenders are designed such that no power is needed to maintain a fixed vertical position, holding the payload against the force of gravity. The design is extended to a piezoworm stage prototype and validated through several tests. Experiments on the prototype stage show that it is capable of a speed of 5.4 mm/s, a force capacity of 8 N and can travel over 16 mm

Deformation Mechanisms in Pd Nanowhiskers

The reduced length scales inherent in nanoscale materials enable access to properties that are otherwise not achievable in bulk. The application of their novel structural and functional responses however is hindered by a lack of understanding of their mechanical behavior, which affects their assimilation into device fabrication as well as their reliability during performance. In contrast to bulk materials, nanoscale materials possess a non-negligible proportion of surface atoms, which can exert significant influence on the overall mechanical response. In addition, structures with small volumes can possess much lower defect densities, which could potentially be driven out of the volume instead of interacting and promoting traditional deformation behavior. Systematic experimental investigations will be crucial to developing the necessary understanding, although they remain challenging due to limited access to suitable test specimens and testing methodologies for directly extracting pertinent results. By employing a MEMS-based tensile testing system and a temperature-controlled cryostat configuration to test defect-free and -scarce Pd nanowhiskers, we have been able to systematically investigate some of the important deformation mechanisms in nanoscale single crystals. We first address the elastic behavior in nanoscale crystals, which is predicted to differ from bulk behavior due to the reduced coordination of surface atoms. We measured size-dependent deviations from bulk elastic behavior in nanowhiskers with diameters as small as ~30 nm. In addition to size-dependent variations in Young\u27s modulus in the small strain limit, we measured nonlinear elasticity at strains above ~1%. In addition to providing the first measurements of higher-order elasticity in Pd, our study shows that the elasticity response in Pd nanowhiskers can be attributed to higher-order elasticity in the bulk-like core upon being biased from its equilibrium configuration due to the role of surface stresses in small volumes. Comparison of the size-independent values of δ in our nanowhiskers with studies on bulk FCC metals lends further insight into the role of length scales on both elastic and plastic mechanical behavior. We then consider incipient plasticity in nanoscale Pd nanowhiskers, which is governed not by the initial motion of pre-existing dislocations but rather the nucleation of dislocations. Whereas nucleation strengths are weakly size- and strain-rate-dependent, strong temperature dependence is uncovered, corroborating predictions that nucleation is assisted by thermal fluctuations. We measure activation volumes as small as singular atomic volumes, which explain both the ultrahigh athermal strength as well as the temperature-dependent scatter, evident in our experiments and well captured by a thermal activation model. Our experiments highlight the pronounced probabilistic nature of surface dislocation nucleation, which is crucial input to device design using nanoscale building blocks. In total, this body of work demonstrates that distinctly different processes are responsible for the deformation behavior in small volumes and underscores the importance of comprehensive characterization of material properties at the relevant length scales

Microtweezers For Studying Vibrating Carbon Nanotubes

Vibrational modes in suspended carbon nanotubes (CNTs) are incredibly soft, which makes them sensitive to small forces and prime candidates as force sensors. This same property, combined with the stiffness of the CNT to stretching, makes them an unusual mechanical system characterized both by large thermally-activated fluctuations and strong nonlinear interactions between the resonance modes. To understand how these thermal fluctuations manifest themselves in the resonance of CNTs, we developed an electrically-contacted micro-tweezer platform. The platform is capable of lifting a pristine CNT off of its growth substrate, directly applying strain to the free-standing doubly-clamped CNT, and controlling its proximity to electrical gates. Using the unprecedented level of measurement precision offered by our novel setup, we preformed the firstever single-shot ring-down measurements on CNTs, to map the resonance spectra as a function of strain and we directly measured the thermal motion of single-walled CNTs at room temperature. These measurements, in agreement with our original theoretical predictions, convincingly show that thermally-inducted fluctuations of CNT resonance modes are in fact the source of the remarkably high mechanical dissipation that has been ubiquitously observed in room-temperature CNT resonators. This result is not material dependent and the underlying physics should apply to all nanoscale 1D resonators. In addition to this key result, we use the microtweezer platform to couple CNT resonators to high-Q optical microdisk resonators. With this hybrid system, we demonstrate remarkably strong optomechanical coupling and make the first-ever observation of the optical spring-effect on CNT mechanical resonators

Theoretical and Experimental Investigation on the Multiple Shape Memory Ionic Polymer-Metal Composite Actuator

Development of biomimetic actuators has been an essential motivation in the study of smart materials. However, few materials are capable of controlling complex twisting and bending deformations simultaneously or separately using a dynamic control system. The ionic polymer-metal composite (IPMC) is an emerging smart material in actuation and sensing applications, such as biomimetic robotics, advanced medical devices and human affinity applications. Here, we report a Multiple Shape Memory Ionic Polymer-Metal Composite (MSM-IPMC) actuator having multiple-shape memory effect, and is able to perform complex motion by two external inputs, electrical and thermal. Prior to the development of this type of actuator, this capability only could be realized with existing actuator technologies by using multiple actuators or another robotic system. Theoretical and experimental investigation on the MSM-IPMC actuator were performed. To date, the effect of the surface electrode properties change on the actuating of IPMC have not been well studied. To address this problem, we theoretically predict and experimentally investigate the dynamic electro-mechanical response of the IPMC thin-strip actuator. A model of the IPMC actuator is proposed based on the Poisson-Nernst-Planck equations for ion transport and charge dynamics in the polymer membrane, while a physical model for the change of surface resistance of the electrodes of the IPMC due to deformation is also incorporated. By incorporating these two models, a complete, dynamic, physics-based model for IPMC actuators is presented. To verify the model, IPMC samples were prepared and experiments were conducted. The results show that the theoretical model can accurately predict the actuating performance of IPMC actuators over a range of dynamic conditions. Additionally, the charge dynamics inside the polymer during the oscillation of the IPMC are presented. It is also shown that the charge at the boundary mainly affects the induced stress of the IPMC. This study is beneficial for the comprehensive understanding of the surface electrode effect on the performance of IPMC actuators. In our study, we introduce a soft MSM-IPMC actuator having multiple degrees-of-freedom that demonstrates high maneuverability when controlled by two external inputs, electrical and thermal. These multiple inputs allow for complex motions that are routine in nature, but that would be otherwise difficult to obtain with a single actuator. To the best of our knowledge, this MSM-IPMC actuator is the first solitary actuator capable of multiple-input control and the resulting deformability and maneuverability. The shape memory properties of MSM-IPMC were theoretically and experimentally studied. We presented the multiple shape memory properties of Nafion cylinder. A physics based model of the IPMC was proposed. The free energy density theory was utilized to analyze the shape properties of the IPMC. To verify the model, IPMC samples with the Nafion as the base membrane was prepared and experiments were conducted. Simulation of the model was performed and the results were compared with the experimental data. It was successfully demonstrated that the theoretical model can well explain the shape memory properties of the IPMC. The results showed that the reheat glass transition temperature of the IPMC is lower than the programming temperature. It was also found that the back-relaxation of the IPMC decreases as the programming temperature increases. This study may be useful for the better understanding of the shape memory effect of IPMC. Furthermore, we theoretically modeled and experimentally investigated the multiple shape memory effect of MSM-IPMC. We proposed a new physical principle to explain the shape memory behavior. A theoretical model of the multiple shape memory effect of MSM-IPMC was developed. Based on our previous study on the electro-mechanical actuation effect of IPMC, we proposed a comprehensive physics-based model of MSM-IPMC which couples the actuation effect and the multiple shape memory effect. It is the first model that includes these two actuation effects and multiple shape memory effect. Simulation of the model was performed using finite element method. To verify the model, an MSM-IPMC sample was prepared. Experimental tests of MSM-IPMC were conducted. By comparing the simulation results and the experimental results, both results have a good agreement. The multiple shape memory effect and reversibility of three different polymers, namely the Nafion, Aquivion and GEFC with three different ions, which are the hydrogen, lithium and sodium, were also quantitatively tested respectively. Based on the results, it is shown that all the polymers have good multiple shape memory effect and reversibility. The ions have an influence on the broad glass transition range of the polymers. The current study is beneficial for the better understanding of the underlying physics of MSM-IPMC. A biomimetic underwater robot, that was actuated by the MSM-IPMC, was developed. The design of the robot was inspired by the pectoral fish swimming modes, such as stingrays, knifefish and cuttefish. The robot was actuated by two soft fins which were consisted of multiple IPMC samples. Through actuating the IPMCs separately, traveling wave was generated on the soft fin. Experiments were performed for the test of the robot. The deformation and the blocking force of the IPMCs on the fin were measured. A force measurement system in a flow channel was implemented. The thrust force of the robot under different frequencies and traveling wave numbers were recorded. Multiple shape memory effect was performed on the robot. The robot was capable of changing its swimming modes from Gymnotiform to Mobuliform, which has high deformability, maneuverability and agility

Structure evolution in tribological interfaces studied by multilayer model alloys

Recent studies of deformation mechanisms of metals and alloys pioneer the better investigation of the friction and wear behavior of materials with well-defined initial microstructures. Within this scope, in this work, the effect of sub-surface deformations on the resulting friction and wear behavior has been searched by means of a systematic experimental study on Au-Ni metallic multilayer model alloy system