Xiangpeng Li

A bounded controller for multirobot navigation while maintaining network connectivity in the presence of obstacles

Maintaining the connectivity of networked robots is a challenge in multirobot applications. In this paper, this challenging problem is addressed through the development of a novel controller that can guarantee that robots will approach their individual desired positions while maintaining existing network topology and avoiding obstacles. A new concept of connectivity constraint, along with a continuous modeling approach to obstacle avoidance, is utilized in building the navigation function. The designed potential field integrates the navigation requirement, connectivity constraint, and obstacle avoidance simultaneously, based on which a bounded control input is generated for multirobot control. It is shown that if the initial configurations of the robots are connected and the desired configuration is reachable, the proposed controller is capable of driving multirobots to their individual goal positions conditionally while keeping the underlying network connected. Simulations and experiments are finally performed using a group of mobile robots to demonstrate the effectiveness of the proposed controller.

Design of a robust unified controller for cell manipulation with a robot-aided optical tweezers system

With the advantages of non-physical contact, high precision, and efficiency, optical tweezers have been increasingly used to manipulate biological cells in various biomedical applications. When trapping a cell with optical tweezers, the cell must be located within the optical trap. The lack of an efficient control technique that can automatically control cell motion while consistently locating such cell within the optical trap causes the trapped cell to escape easily, thus resulting in the failure of the manipulation task. Therefore, the development of a unified controller that can manipulate both cell trapping and cell motion simultaneously while possessing robustness to environmental disturbances is urgently needed. In this paper, we develop a novel unified controller that manipulates cell positioning and cell trapping simultaneously. First, we establish a geometric model to confine the cell within a local region around the optical trap. The connection between the cell and the optical tweezers is formulated by using the concept of cell-tweezers (C-T) coalition. Second, we develop a controller based on a defined potential field function to drive the C-T coalition to the desired state while avoiding collisions with other obstacles in the environment. Finally, we perform experiments of transferring yeast cells to demonstrate the effectiveness of the proposed approach.

Dynamic Path Planning for Inserting a Steerable Needle Into a Soft Tissue

Steerable bevel-tip needles are widely used in modern, minimally invasive percutaneous procedures to reach specific areas inside the body. In this paper, we propose an optimized path planner for manipulating such steerable needles, which can generate the shortest path from the starting position to the target position with the least number of rotation times. The shortest traveling path produces less damage to the body, thus shortening the recovery period. We first investigate the insertion problem in a nondeformable environment, which is termed as the static environment in this paper. As the needle is flexible, the moving path is a curve. We propose to regulate the curved path within two parallel lines and then determine the optimal distance between the two parallel lines such that the generated moving path of the needle has the shortest length with the least number of needle rotations. We then investigate the insertion problem in a deformable environment, which is termed as the dynamic environment. Taking deformation and nonhomogenous properties of soft tissue into account, the target position and the radius of the curve path vary as the needle is inserted. By using a mass-spring model to formulate the deformable environment and a vision system to measure the time-varying radius of the curve, we propose a dynamic path planner that replans the path to adapt to the change of the target position and the curve radius. Simulations and experiments are performed to demonstrate the effectiveness of the proposed approach.

Preserving Multirobot Connectivity in Rendezvous Tasks in the Presence of Obstacles With Bounded Control Input

Maintaining the connectivity of an underlying robot network during a rendezvous task in the presence of obstacles is a challenge in control systems technology. In this brief, a navigation-function-based potential field approach is developed to address this challenging problem. A concept called connectivity constraint is used to establish a navigation function. A new potential field that simultaneously integrates rendezvous requirement, connectivity maintenance, and obstacle avoidance is also developed. On the basis of this potential field, we design a bounded control input for multirobot control. The proposed controller can drive multiple robots to an agreement state while maintaining connectivity of the underlying network provided that the initial configurations of the robots are connected. Simulations and experiments are performed to verify the effectiveness of the proposed approach.

Modeling and development of a magnetically actuated system for micro-particle manipulation

This paper presents the modeling and development of a micromanipulation system that can provide continuous force to manipulate a micro-particle through an externally applied magnetic field. This system consists of six electromagnetic coils and the size of the micro-particle to be manipulated is less than 30μm. The magnetic field maps generated from the electromagnets are first simulated using a finite element method. Based on the result, we then calculate the force that can be provided by the system. A prototype of the system is designed and constructed, which is used to precisely control the navigation of a super-paramagnetic micro-bead in a microfluidic environment. This system can be used for drug delivery as well as medical applications such as minimally invasive surgery, diagnosis and sensing.

Multirobot consensus while preserving connectivity in presence of obstacles with bounded control inputs

In the existing literatures of multirobots, it is usually assumed that the networked robots remain connected in topologyduring the task execution. In pracice, however, it is not easy to guarante connectivity of the networked robots in a clustered environment. Failure to maintain connectivity may decrease the performance of the networked robots or even fail the task. In this paper, we propose a multirobot motion coordination strategy that can maintain multirobot connectivity as well as guarante obstacle avoidance. A potential function is proposed to generate bounded control inputs for networked robots. The efficiency of the proposed apporach is demonstrated in both simulation and experiment performed on multirobot consensus tasks.

Modeling and closed-loop control of electromagnetic manipulation of a microparticle

Precise manipulation of microparticles has received considerable attention for its great potential applications to clinical medicine. Among the existing manipulation techniques, the method of magnetic force based manipulation exhibits great advantages for its minimally-invasive feature and insensitivity to biological substance, making it ideally suitable to in vivo environment. On the other hand, increasing demand for accurate and high throughput magnetic manipulation highlights the need of incorporating automation technology in the manipulation. In this paper, we propose an automated control approach to manipulating a magnetic microparticle (bead) with a home-designed electromagnetic coil system. A simplified two-order dynamic model for a microparticle suspended in fluidic environment is established first. A closed-loop controller with utilizing visual feedback is then developed based on input-to-state stability and backstepping methodology. The proposed controller guarantees that the microparticle follows the desired trajectory even in presence of environmental uncertainties and disturbances. Experiments are performed to demonstrate the effectiveness of the proposed approach.

Automated manipulation of magnetic micro beads with electromagnetic coil system

Magnetic manipulation of micro particles has exhibited a great potential in clinical applications due to its non-invasive feature. The demand for precise motion control with high throughput highlights the necessity of bringing the automation technology to this important area. In this paper, we attempt to use an electromagnetic coil system for achieving automated manipulation of micro beads. Utilizing visual position feedback, a closed-loop control law based on input-to-state stability and backstepping is proposed, which guarantees that the bead can successfully follow the desired trajectory in three dimensions while maintaining stability of the overall system.

Automated Transportation of Biological Cells for Multiple Processing Steps in Cell Surgery

Most studies on automated cell transportation are single-task oriented. Results from these investigations hardly meet the increasing demand for emerging cell surgery operations that usually require a series of manipulation tasks with multiple processing steps. In this paper, automated cell transportation to accomplish a multistep process in cell surgery was investigated. A novel control system that can manipulate grouped cells to move into different task regions sequentially and continuously without interruption was developed based on a robot-aided optical tweezers manipulation system. A potential field-based controller was designed to achieve multistep processing control, where the new concepts of contractive coalition and switching region were incorporated into tweezers–cell coalition. The success of this controller lies in simultaneously controlling the positions of the optical tweezers, trapping multiple cells effectively, and avoiding collisions in a unified manner. Simulations and experiments of transferring a group of cells to a number of task regions were performed to demonstrate the effectiveness of the proposed approach. Note to Practitioners—This paper was motivated by the challenging problem of automated transportation of grouped cells to several predefined task regions in emerging cell surgery with multiple processing steps. Existing automated cell transportation studies are mainly single-task oriented, thereby making them inapplicable to cell surgery operations, because a series of sequential processing steps are usually involved in these operations. This paper provides a novel control strategy based on a robot-aided optical tweezers manipulation system to efficiently transport cells into different task regions sequentially without interruption. Unlike the previous cell transportation studies where the goal positions of single cells must be specified early, here only the desired task regions are identified in the controller implementation, making the proposed strategy a better fit for actual cell surgery practice.

A switching controller for high speed cell transportation by using a robot-aided optical tweezers system

Abstract Rapid and efficient cell manipulation is critical to many cellular operations at the single-cell resolution. In this paper, we propose a new approach for high speed manipulation of a single suspended cell using a robot-aided optical tweezers cell manipulation system. A switching geometrical model for achieving automatic cell trapping, maintenance of optical trapping, and obstacle avoidance is developed based on an objective of confining the trapped cell inside the high speed transfer region, which can help attain high speed cell transportation velocity. With the switching geometrical model, a controller for high speed cell transportation is proposed to transfer the target cell to the destination efficiently. Experiments of manipulating human leukemia cancer NB-4 cells to the specific testing area for property characterization are performed to demonstrate the effectiveness of the proposed approach.