Feasibility of Non-contact Manipulation of a Small Object using Standing Wave Acoustic Levitation

In this dissertation a novel method of non-contact manipulation using standing wave acoustic levitation (SWAL) was investigated. Multiple ultrasonic bolt-clamped Langevin transducers (BLTs) were used to generate pressure nodes in a unique acoustic standing wave field. Small light objects of any shape or material can be trapped in these pressure nodes. It was proposed that the frequency, amplitude and phase of standing waves can be modulated to transport the object along desired trajectories. From simulation and experiments, phase modulation proved to be superior to modulating the other parameters and produced smooth motion long range capability and was simple to control. Furthermore, the angle between the two transducers was found to affect the trajectory of the trapped object during phase modulation. At certain tilt angles, modulating a combination of parameters resulted in sinusoidal and elliptic paths of the object both in simulations and experiments.;To understand the nature of levitation forces acting on objects, analysis of non-linear second order radiation pressure was conducted for a simple case. In accordance with the analysis of the radiation pressure, a finite element method was employed to validate the complex radiation pressure field and its levitation forces. According to the simulation results, radiation pressure increased at 180 ·n degree phase angles (n=0, 1, 2, 3...) if the distance between two facing transducers is changed by a certain fraction of the wave length. This observation led to proposing a new distance modulation technique to enhance the acoustic levitation forces. The distance modulation technique changes the distance between two opposing transducers at the certain phase angles to increase levitation forces without moving the pressure nodes. This was proven numerically and experimentally. The results showed that the additional distance modulation can increase overall levitation force more than two times and it allows for longer controlled movements than that achieved by phase modulation alone.;A three-transducer experimental system was developed for SWAL. A three-channel function generator controlled by a micro-controller was adapted for parameter modulation. Stepper motors and servo motors were attached to the transducers for the linear and angular movements and two other micro-controllers operated the motors. An integrated graphical user interface (GUI) was developed to control each component. A USB camera and object tracking algorithm served as the feedback sensor for the controller.;For two-dimensional motion control, direct inverse control using artificial neural networks (ANN) with PID feedback was adopted to follow a desired trajectory. Two different operational methods were developed for control bases. The first uses two BLTs attached to two horizontal linear actuators, and a vertical linear actuator moves the entire structure. In this setup, distance modulation was applied for accuracy and stability. In the second method, three BLTs were attached to the two horizontal linear actuators and one rotational servo motor respectively to form a Y-shape. Angular modulation of the lower servo motor was adapted to achieve straight movement of objects in the acoustic field.;Experiments were performed for each method with two different trajectories: linear and circular. The results show that the second method has a higher overall control error than the first due to the complexity of the pressure field generated by the larger number of transducers. In addition, circular trajectory control had a higher mean square error (MSE) than the linear trajectory because the phase modulation is only used for single axial motion control. This causes both x- and y- axial movement and this extra error results in more frequent movement when following a complex circular trajectory. The results of experiments confirm that two-dimensional motion control using acoustic levitation can be achieved with acceptable errors.