Nonprehensile Dynamic Manipulation: A Survey

Nonprehensile dynamic manipulation can be reason- ably considered as the most complex manipulation task. It might be argued that such a task is still rather far from being fully solved and applied in robotics. This survey tries to collect the results reached so far by the research community about planning and control in the nonprehensile dynamic manipulation domain. A discussion about current open issues is addressed as well

Micro-Object Manipulation Using Oscillating Bubbles

This thesis deals with the development of novel manipulation techniques of micro/mini objects using oscillating bubbles. Two major physical principles studied and applied are cavitational microstreaming flows and electrowetting on dielectric (EWOD) actuation in gaseous bubbles. Micro/mini bubbles oscillated and handled in 2-D and 3-D spaces using these two principles are key components serving as carriers of objects to be manipulated. The first type of manipulation system allows us to manipulate mini/micro objects on a 2-D space. A series of bubble operations (creation, elimination, and transportation) and object manipulations (capturing, carrying, and releasing) is extensively investigated in this configuration along with modeling and analysis. The capturing force is identified and completely confirmed as the acoustic radiation force through several experiments. Effects of the frequency and amplitude of acoustic excitation on capturing are quantified with high-speed imaging. The bubble elimination process is modeled by two sequential steps: catalytic reaction and dissolving process.In addition, the similar operations of capturing, carrying, releasing of objects are accomplished only using AC-EWOD, not using the acoustic excitation. In this case, the AC voltage (optimal frequency of 100 Hz) not only oscillates the bubble but also transports the oscillating bubble on the surface. However, the carrying efficiency is lower than the simultaneous actuations of acoustic excitation and EWOD. The second type of object manipulation system utilizes the capturing phenomenon by oscillating bubble. The main feature is that the oscillating bubble is deposited on a 3-D traversing rod tip, rather than a two-dimensional surface. So, it allows for object manipulation in a 3-D space. It is concluded from multiple experiments that the maximum carrying speed is highest near the bubble resonant frequency, meaning that the capturing force is proportional to the bubble oscillation amplitude.Finally, the cavitational streaming flow is extended to underwater propulsion. The key concept is to utilize the net momentum flux around the oscillating bubble. As a reaction force, the net momentum flux pushes or pulls the solid substrate on which the oscillating bubble sits. Using mini/micro glass rods, the propulsion mechanism is experimentally proved. The propulsion force is measured to be hundreds of nano-Newtons in a pendulum configuration

The influence of magnetic cohesion on the stability of granular slopes

This thesis presents an investigation into the influence of magnetic cohesion on the stability of granular slopes. We consider magnetic cohesion that results from the interaction between dipole moments induced in grains by a uniform magnetic field. The repose angle of spheres is known to increase much more slowly with magnetic cohesion than in experiments with liquid-bridge cohesion. To our knowledge, nowhere in the literature has anyone offered a satisfactory explanation of this discrepancy. Our two-dimensional molecular dynamics simulations of granular piles show that shear occurs deep in the pile. The addition of a magnetic field causes the motion to shift farther down into the pile, preventing the angle from increasing substantially. We investigate different models of wall friction, and discover that wall interactions have a significant influence on the rate of increase of the slope angle with magnetic cohesion. In three-dimensional simulations we observe an initial decrease in the repose angle as the cohesion is increased, contrary to expectations. We explain this effect by considering how the transverse magnetic force influences the particle distribution of the pile. In contrast, draining-crater experiments reveal that the angle of repose of diamagnetic bismuth grains increases dramatically with cohesion in a vertical field. We argue that this difference is due to the non-spherical shape of the grains, and investigate further the influence of grain shape by using non-magnetic `voids' of different shapes in a paramagnetic solution. We discover a strong positive correlation between the grain aspect ratio and the size of the effect of magnetic cohesion on the slope angle. This is because a non-spherical grain accumulates magnetic charge on sharp edges and corners, increasing the magnetic field in its immediate vicinity and leading to stronger interactions with neighbouring grains. Also, in piles of grains with larger aspect ratios, avalanches occur closer to the surface, thus increasing the stability of the pile

Magnetoresistive and Thermoresistive Scanning Probe Microscopy with Applications in Micro- and Nanotechnology

This work presents approaches to extend limits of scanning probe microscopy techniques towards more versatile instruments using integrated sensor concepts. For structural surface analysis, magnetoresistive sensing is introduced and thermoresistive sensing is applied to study nanoscale phonon transport in chain-like molecules. Investigating with these techniques the properties of shape memory polymers, a fabrication method to design application-inspired micro- and nanostructures is introduced

Characterization of Biomaterials by Atomic Force Microscopy

AFM microscopy is a very promising tool for the understanding and the study of biological materials. This abstract briefly shows the results obtained during the period of my Ph.D. studies in the Chemistry and Industrial Chemistry Department at the University of Pisa. A commercial atomic force microscope (AFM) was used to investigate different kinds of biomaterials such as oligo peptides, polymers and proteins but also some hard materials as silicon and metals. The AFM consists of a microsized cantilever with a sharp tip (probe) at its end that is used to scan the specimen surface. The cantilever is typically made of silicon or silicon nitride with a tip radius of curvature on the order of few nanometers. When the tip is brought into proximity of a sample surface, forces between the tip and the sample lead to a deflection of the cantilever ruled by Hooke's law. Depending on the situation, forces that are measured in AFM include mechanical contact force, Van der Waals forces, capillary forces, chemical bonding, electrostatic forces etc. Traditionally, the sample is mounted on a piezoelectric scanner, that can move the object under examination in the z direction for maintaining a constant force, and in the x and y directions for scanning the sample. An image of the surface is obtained by mechanically moving the probe in a raster scan (that is the pattern of image detection and reconstruction in a computer image) over the specimen, line by line, and recording the probe-surface interaction as a function of position. The operating mode described above represents the typical way to use the atomic force microscope. But a whole world of capabilities of the instrument can be used. In particular we focused our attention on three research lines: • The phase imaging • The mechanical analysis of materials • The chemical force microscopy The AFM, developed first to explore atomic details on hard materials, has evolved to an imaging method capable of achieving fine structural details on biological samples and soft matter. The first one in fact, was used in order to characterize the shape and the morphology of particular bio samples: some oligopeptides that could auto aggregate on complex structures depending on the concentration of the starting solutions from which they are prepared and on the presence or not buffer salt. The measurements were performed in the so called “tapping mode” which is capable of acquiring both the morphological maps and also the phase maps. This signal is a powerful extension of AFM that provides nanometer-scale information about surface structure and properties often not revealed by traditional techniques. In phase imaging, the phase lag of the cantilever oscillation, relative to the drive signal, is simultaneously monitored with topography data. The phase lag is very sensitive to variations in many material properties such as viscoelastic properties and this allows for a precise determination of the presence of organic materials What we have found is a dependence of peptide aggregates dimensions from the starting concentration. Essentially a growing trend is found with the augmentation of concentration regarding both the mean dimension and the dispersion of aggregates. Moreover a similar trend was found also in peptides prepared from a salt solution. Nevertheless in this case the dispersion was quite minimal: the presence of the salt strongly influences the dimension of peptides structures. For a better understanding of the aggregation process it would be interesting, for future works, to monitor the dynamics of the peptide aggregations during the cast of the solvent and to make more measurements of samples from solution at different concentration. The second argument we deal with was the mechanical analysis of materials. Tissues are a challenging class of materials as they are composed in hierarchical structures with important features down to the nanometer scale. Continuing developments in indentation data model and analysis will increase the usefulness of the method for the characterisation of biomaterials and in particular for tissue regeneration. The nanoindentation, also known as depth sensing indentation (DSI), involves the application of a controlled load over the surface to induce local deformations. Load and displacement are monitored during the loading- unloading curves enabling the calculation of the interested mechanical properties. Some theoretical models were considered and new ones were developed in order to get a better understanding of phenomena involved during the indentation process. A technique that can probe mechanical properties at these scales has the potential to answer numerous questions that are relevant in the field of nanotribology and nanomechanics. Several tests were performed over a large variety of materials including PMMA, polystyrene, silicon, metals and so on in order to obtain two of the most important mechanical properties: the hardness and the Young modulus. Moreover other deeper studies allow for the determination of the hardness in function of the indentation depth, the stiffness and other important features. Anyway the results obtained have to be fully understood due the large variety of theories and method of analysis of the data. We have also to take in account the instrument data distortion and the different materials response to indentation tests that could affect the final results. The last research addressed to biomaterials in this work is the chemical force microscope, exploited to monitor the forces involved in a protein swelling experiment. The potential of the AFM to reveal ultra low forces at high lateral resolution has opened an exciting way for measuring inter and intra molecular forces at the single molecule level. In particular Human Serum Albumin was used for this test. The idea is to detect and study the binding of ligands on tips to surface-bound receptors by applying an increasing force to the complex that reduces its lifetime until it dissociates at a measurable unbinding force. During the loading unloading curves a couple of step (revealing the sudden change) have been found revealing the first a small detachment of the protein from the surface, while the second is properly due to the uncoiling of albumin. Several measurements were collected in order to have statistically significant data

Reliable measurement of slip using colloid probe atomic force microscopy

Recent research has shown that Newtonian liquids can slip at solid surfaces in confined geometries, which contradicts the classical no-slip boundary condition in which the liquid is stationary at the solid surface. The study of liquid boundary conditions that provides a fundamental understanding of the physics of liquid flow in confined geometries, such as in porous media, and also could benefit various commercial applications, such as micro and nanofluidic applications. The aim of our work was to build a reliable experimental and theoretical framework to investigate liquids slip on solid surfaces by colloid probe atomic force microscopy (AFM). Colloid probe AFM provides an accurate way to study slip at a solid surface by measuring the hydrodynamic drainage force between a colloid probe and a solid substrate as the two surfaces approach to contact. In our studies, we have investigated the slip of a one-component viscous liquid (di-n-octylphthalate) on bare silicon substrates and hydrophobised silicon substrates. In order to obtain reliable slip results, we solved experimental problems in previously published experiments and improved the theoretical modeling which affects the reliability and accuracy of the measured slip lengths. In the new improved experimental protocol we used a closed loop scanner to produce a constant driving velocity, minimised the virtual deflection due to top-scan AFM by removing a constant slope in the force curve, and clarified the true compliance and zero separation in the force curve. The need for tight control over experimental conditions in slip measurements was highlighted, such as extremely careful surface cleaning, the use of a one-component liquid, continuous monitoring of the liquid temperature, and repeat measurements in different locations of the substrate. By performing slip measurements in symmetric and asymmetric systems, a new method was developed to self-assess the accuracy and reproducibility of the slip force measurements. A new mathematical algorithm was built to predict the hydrodynamic drainage force independently of experimental data. This new mathematical algorithm reduced the noise greatly in the theoretical forces over that in the previous treatments; it was demonstrated by blind test that this new calculation method provides reproducible and reliable slip length values and spring constant values with the uncertainty within 3%. The new mathematical algorithm can be easily applied to simulate slip lengths and hydrodynamic forces in different experimental conditions, such as the presence of nanoparticle contamination on the substrate surface and the flattening of the colloid probe, which were both demonstrated to affect the measured slip lengths. The exact variable drag force on soft cantilevers was calculated for the first time and applied to fit the experimental force. This calculation revealed that the dependence of slip on the driving velocity and the cantilever shape found in literature could be a spurious effect due to the assumption that the drag force on the cantilever is constant during force measurements. In our studies, it was also shown that the measured slip length actually decreases with increasing shear rate, rather than being a constant value as commonly assumed. A new shear dependent model for slip fitted well experimental hydrodynamic forces for all separations down to a few nanometres. A possible molecular explanation was proposed for the mechanism of shear rate dependent slip in our experiments