Abstract
Acoustic levitation forces can be used to manipulate small objects and liquids without mechanical contact or contamination. This work presents analytical models based on which concepts for the controlled insertion of objects into the acoustic field are developed. This is essential for the use of acoustic levitators as contactless robotic grippers. Three prototypes of such grippers are implemented and used to experimentally verify the lifting of objects into an acoustic pressure field. Lifting of high-density objects (ρ > 7 g/cm3) from acoustically transparent surfaces is demonstrated using a double-sided acoustic gripper that generates standing acoustic waves with dynamically adjustable acoustic power. A combination of multiple acoustic traps is used to lift lower density objects (ρ≤0.25g/cm3) from acoustically reflective surfaces using a single-sided arrangement. Furthermore, a method that uses standing acoustic waves and thin reflectors to lift medium-density objects (ρ≤1g/cm3) from acoustically reflective surfaces is presented. The provided results open up new possibilities for using acoustic levitation in robotic grippers, which has the potential to be applied in a variety of industrial use cases.
Highlights
Trapping of objects by means of acoustic forces is used in various areas such as chemistry [1], bioreactors [2,3], blood analysis [4], the study of organisms in microgravity [2,5], control of nanomaterial self-assembly [6], containerless processing [7,8,9], and to study droplet dynamics [10,11].The main advantage of acoustic levitation over other levitation methods is its independence from the material properties of the object
Based on the presented results, acoustic grippers can be used for the automation of processes that involve small and fragile objects and/or require contamination-free handling of small objects
For objects that were picked from acoustically reflective surfaces, the density was limited to ρ = 0.25 g/cm3 for the single-sided arrangements due to the small vertical forces generated by vertical twin trap (VTT) and ρ = 1 g/cm3 for the reflector arrangement
Summary
Trapping of objects by means of acoustic forces is used in various areas such as chemistry [1], bioreactors [2,3], blood analysis [4], the study of organisms in microgravity [2,5], control of nanomaterial self-assembly [6], containerless processing [7,8,9], and to study droplet dynamics [10,11]. New concepts have been developed that use transducer arrays instead of a single or few transducers and can manipulate levitated objects [18,19]. To enable such manipulations, a system capable of adjusting the pressure field by exciting the transducers individually is required [20,21]. The transport range is limited to the range of the acoustic field To increase this range, the device that generates the acoustic field can be mounted to a robot arm as a gripper, as shown in Figures 1 and 2 [22]. This work demonstrates acoustic grippers for different boundary conditions, namely, for high-density objects placed on acoustically transparent surfaces and low- or medium-density objects placed on reflective surfaces
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