Vision-Based Closed-Loop Control With Spatiotemporal Multiplexing Strategy for Noncontact Trapping of Multiple Micro-Particles

Noncontact trapping of micro objects has great application potential in fields like material science and biomedical engineering due to its label-freeness and biocompatibility. In this paper, an automated acoustic micro-particle trapping system implemented with phased transducer array (PTA) is prototyped. The system is incorporated with a stereo vision to provide visual feedback benefited from localization of the invisible acoustic field through hydrophone scanning. Binocular vision calibration and stereo matching are realized using image Jacobian matrix. An efficient phase modulation algorithm is proposed for the calculation of desired PTA phase profile in real-time and a spatiotemporal multiplexing control strategy is adopted to dynamically generate multiple trappings. Experimental results well demonstrated that the stable trapping of multiple particles can be robustly realized by the system, leading to the improvements of robotic noncontact manipulation with invisible acoustic end-effector.
Note to Practitioners
—This paper is motivated by the problem that previous classic acoustic trapping was achieved as a physical phenomenon that particles within the trapping zone would be automatically trapped and thus required people to place the particle into the invisible trapping zone, which is neither precision nor efficient. Such problem is a crucial factor that limits acoustic tweezer to be further readily usable in bioengineering, surface manufacturing, and quantitative micromechanical characterization. In this work, automated acoustic trapping is presented in the context of robotics, as grasping task in conventional industrial robots, that can generate the acoustic trap exactly in the location where particles are detected (by microscopic vision, or micro-CT or acoustic imaging, etc.). This paper proposes a full pipeline to automatically trap multiple particles using ultrasonic transducer array and binocular microscopic vision. The experiments verified the ability of proposed method in simultaneously trapping three micro particles with opposite acoustic properties. Such trapping method is the foundational technology for further acoustic manipulation such as arraying and sorting, which will be the tasks in our future work.