A survey of non-prehensible pneumatic manipulation surfaces : principles, models and control.

International audienceMany manipulation systems using air flow have been proposed for object handling in a non-prehensile way and without solid-to-solid contact. Potential applications include high-speed transport of fragile and clean products and high-resolution positioning of thin delicate objects. This paper discusses a comprehensive survey of state-of-the-art pneumatic manipulation from the macro scale to the micro scale. The working principles and actuation methods of previously developed air-bearing surfaces, ultra-sonic bearing surfaces, air-flow manipulators, air-film manipulators, and tilted air-jet manipulators are reviewed with a particular emphasis on the modeling and the control issues. The performance of the previously developed devices are compared quantitatively and open problems in pneumatic manipulation are discussed

Diamagnetic Levitation of Bubbles and Droplets

This thesis describes the use of diamagnetic levitation to study fluids in a zero-gravity environment, particularly focusing on bubbles and droplets. We use a strong nonhomogeneous magnetic field (maximum field strength 18.5~T) generated by a superconducting solenoid magnet to repel/attract materials at a molecular level allowing for a net zero body force to be experienced by bubbles/droplets. A new technique that allows for the suspension of spherical gas bubbles in liquids at room temperature is presented. The development of this technique allowed for several novel experiments to be carried out. Firstly, we use this technique to observe the coalescence of multiple pairs of air bubbles in water, starting from hydrostatic equilibrium. The coalescence creates large axisymmetric perturbations to the surface of the bubble which leads to the ejection of satellite bubbles. For the first time, we experimentally observe the simultaneous ejection of two satellite bubbles from the coalescence of a pair of air bubbles. After satellite bubbles are ejected, the bubble formed from the coalescence of the parent bubbles undergoes large nonlinear axisymmetric surface oscillations. We analyse these surface oscillations for two cases: a symmetric case, where the initial parent bubbles have equal radii (within experimental error) and an asymmetric case where the ratio of the radii of the two parent bubbles is $\sim1.5$. We compare our results to the analytical model of Tsamopoulos and Brown and find that in the symmetric case, when only a single large amplitude surface mode is dominant, that experiment and simulation agree well with theory and the oscillation frequency of the dominant mode behaves as a function of the square of its amplitude. But, in the case several surface modes are oscillating with moderate or large amplitudes, agreement between the model of Tsamopoulos and Brown and what is observed in experiment and simulation is seen to be less accurate. Secondly, we use this technique to observe and manipulate bubble clusters. We show that if a small amount of surfactant is added to the liquid, that air bubbles levitating in the liquid may remain in contact with each other without coalescing for an indefinite period of time. This allows for the creation of clusters of multiple diamagnetically levitated spherical air bubbles. We present bubble clusters created from up to 21 bubbles and show how the arrangement of these clusters may be altered by simply altering the current in the superconducting solenoid. Future use cases are hypothesised for bubble clusters, such as the production of new acoustic metamaterials and a new technique for the study of the nonlinear interaction of bubbles in an oscillating acoustic field. The final section of this thesis describes a new experimental technique ‘Sonomaglev’. This new technique combines both acoustic and diamagnetic levitation, allowing for the manipulation of multiple levitated spherical water droplets, using a superconducting magnet fitted with low-power ultrasonic transducers. We show that multiple droplets, arranged horizontally along a line, can be stably levitated with this system, and demonstrate controlled contactless coalescence of two droplets. Numerical simulation of the magnetogravitational and acoustic potential reproduces the multiple stable equilibrium points observed in our experiments

Thick film PZT transducer arrays for particle manipulation

This paper reports the fabrication and evaluation of a two-dimensional thick film PZT ultrasonic transducer array operating at about 7.5 MHz for particle manipulation. All layers on the array are screen-printed and sintered on an Al2O3 substrate without further processes or patterning. The measured dielectric constant of the PZT is 2250 ± 100, and the dielectric loss is 0.09 ± 0.005 at 10 kHz. Finite element analysis has been used to predict the behaviour of the array and impedance spectroscopy and laser vibrometry have been used to characterise its performance. The measured deflection of a single activate element is on the order of tens of nanometres with 20 Vpp input. Particle manipulation experiments have been performed by coupling the thick film array to a capillary containing polystyrene microspheres in water

Investigating the motility of Dictyostelium discodeum using high frequency ultrasound as a method of manipulation

Cell motility is an essential process in the development of all organisms. The earliest stages of embryonic development involve massive reconfigurations of groups of cells to form the early body structures. Embryos are very complex systems, and therefore to investigate the molecular and cellular basis of development a simpler genetically tractable model system is used. The social amoeba Dictyostelium Discoideum is known to chemotax up a chemical gradient. From previous work, it is clear that cells generate forces in the nN range. This is above the limit of optical tweezers and therefore we are investigating the use of acoustic tweezers instead. In this paper, we present recent progress of the investigation in to the use of acoustic tweezers for the characterisation of cell motility and forces. We will describe the design, modelling and fabrication of several devices. All devices use high frequency (>15MHz) ultrasound to exert a force on the cells to position and/or stall them. Also, each device is designed to be suitable for the life-sciences laboratory where form-factor and sterility is concerned. A transducer (LiNo) operating at 24 MHz excites resonant acoustic modes in a rectangular glass capillary (100um by 2mm). This device is used to alter the directionality of the motile cells inside the fluid filled capillary. A quarter-ring PZT26 transducer operating at 20.5MHz is shown to be useful for manipulating cells using axial acoustic radiation forces. This device is used to exert a force on cells and shown to pull them away from a coverslip. The presented devices show promise for the manipulation of cells in suspension. Currently the forces produced are below that required for adherent cells; the reasons for this are discussed. We also report on other issues that arise when using acoustic waves for manipulating biological samples such as streaming and heating

Diamagnetic Levitation of Bubbles and Droplets

This thesis describes the use of diamagnetic levitation to study fluids in a zero-gravity environment, particularly focusing on bubbles and droplets. We use a strong nonhomogeneous magnetic field (maximum field strength 18.5~T) generated by a superconducting solenoid magnet to repel/attract materials at a molecular level allowing for a net zero body force to be experienced by bubbles/droplets. A new technique that allows for the suspension of spherical gas bubbles in liquids at room temperature is presented. The development of this technique allowed for several novel experiments to be carried out. Firstly, we use this technique to observe the coalescence of multiple pairs of air bubbles in water, starting from hydrostatic equilibrium. The coalescence creates large axisymmetric perturbations to the surface of the bubble which leads to the ejection of satellite bubbles. For the first time, we experimentally observe the simultaneous ejection of two satellite bubbles from the coalescence of a pair of air bubbles. After satellite bubbles are ejected, the bubble formed from the coalescence of the parent bubbles undergoes large nonlinear axisymmetric surface oscillations. We analyse these surface oscillations for two cases: a symmetric case, where the initial parent bubbles have equal radii (within experimental error) and an asymmetric case where the ratio of the radii of the two parent bubbles is $\sim1.5$. We compare our results to the analytical model of Tsamopoulos and Brown and find that in the symmetric case, when only a single large amplitude surface mode is dominant, that experiment and simulation agree well with theory and the oscillation frequency of the dominant mode behaves as a function of the square of its amplitude. But, in the case several surface modes are oscillating with moderate or large amplitudes, agreement between the model of Tsamopoulos and Brown and what is observed in experiment and simulation is seen to be less accurate. Secondly, we use this technique to observe and manipulate bubble clusters. We show that if a small amount of surfactant is added to the liquid, that air bubbles levitating in the liquid may remain in contact with each other without coalescing for an indefinite period of time. This allows for the creation of clusters of multiple diamagnetically levitated spherical air bubbles. We present bubble clusters created from up to 21 bubbles and show how the arrangement of these clusters may be altered by simply altering the current in the superconducting solenoid. Future use cases are hypothesised for bubble clusters, such as the production of new acoustic metamaterials and a new technique for the study of the nonlinear interaction of bubbles in an oscillating acoustic field. The final section of this thesis describes a new experimental technique ‘Sonomaglev’. This new technique combines both acoustic and diamagnetic levitation, allowing for the manipulation of multiple levitated spherical water droplets, using a superconducting magnet fitted with low-power ultrasonic transducers. We show that multiple droplets, arranged horizontally along a line, can be stably levitated with this system, and demonstrate controlled contactless coalescence of two droplets. Numerical simulation of the magnetogravitational and acoustic potential reproduces the multiple stable equilibrium points observed in our experiments