[Paper Review] A rotational traveling wave based levitation device - Modeling, design, and control

Ran Gabai, Dotan Ilssar+3 more|arXiv (Cornell University)|Aug 24, 2016

Microfluidic and Bio-sensing Technologies19 references3 citations

TL;DR

This paper presents a non-contact rotational manipulation system for acoustically levitated objects using a vibrating ring that generates ultrasonic standing and traveling waves. By controlling the ratio of these waves via a closed-loop system, the device precisely manipulates rotational torque through shear forces in a thin air layer, achieving rapid and accurate angular positioning with a simplified single-parameter control approach.

ABSTRACT

Described is a device acting on an acoustically levitated object by manipulating the pressure and flow of a thin layer of air such that its rotation can be precisely controlled without mechanical contact. Virtual work analysis assists in simplifying the multi-actuator control problem into a problem governed by a controllable parameter. Actuation is done with a vibrating ring capable of producing ultrasonic standing and traveling waves, creating the acoustic excitation that affects the pressure in a thin, intermediate layer of gas. A distinctive vibration pattern is required to generate the temporal and spatial pressure field of the squeezed air layer that gives rise to both acoustic levitation force and rotational torque. Described are the physical and design development stages leading to an optimized structure, all followed by verifying and dynamics-calibration experiments. Moreover, by precisely controlling the ratio of standing and traveling waves in a closed-loop, one can affect the shear forces applied by the squeezed air layer, thus creating a non-contacting manipulation mechanism. An over-actuated set-up is converted via an algebraic transformation, into a simplified single control-parameter problem. The transformation ties the standing waves ratio, and hence the rotational torque, to the amplitudes and phases of the actuators. This arrangement leads to an effective closed loop methodology that was implemented experimentally showing good performance and exhibiting rapid angular positioning.

Motivation & Objective

• To develop a non-mechanical method for controlling the rotation of acoustically levitated objects.
• To address the complexity of multi-actuator control in acoustic levitation systems.
• To simplify the control problem by transforming over-actuated actuator inputs into a single controllable parameter.
• To achieve precise, rapid angular positioning of a levitated object without physical contact.

Proposed method

• Utilizes a vibrating ring capable of generating both ultrasonic standing and traveling waves.
• Employs virtual work analysis to reduce the multi-actuator control problem to a single controllable parameter.
• Applies an algebraic transformation linking actuator amplitudes and phases to the ratio of standing to traveling waves.
• Uses closed-loop control to dynamically adjust the wave ratio and modulate shear forces in the air layer.
• Designs and optimizes the mechanical structure through physical and dynamic calibration experiments.
• Employs a thin intermediate gas layer where pressure and flow variations generate both levitation force and rotational torque.

Experimental results

Research questions

• RQ1 How can rotational torque be precisely controlled on a levitated object without mechanical contact?
• RQ2 What is the optimal configuration of standing and traveling waves to generate controllable shear forces in the air layer?
• RQ3 Can a complex multi-actuator system be simplified into a single control parameter for effective manipulation?
• RQ4 How does the ratio of standing to traveling waves affect the resulting torque and angular positioning performance?
• RQ5 What experimental validation confirms the effectiveness and responsiveness of the control methodology?

Key findings

• The system successfully achieves precise, non-contact angular positioning of a levitated object through controlled shear forces in the air layer.
• The closed-loop control method enables rapid response and accurate angular positioning, validated experimentally.
• The algebraic transformation effectively reduces the over-actuated system to a single control parameter, simplifying implementation.
• The device demonstrates effective manipulation by tuning the standing-to-traveling wave ratio, directly influencing rotational torque.
• Dynamics calibration and experimental verification confirm the model's accuracy and the system's robust performance.