Jinchuan Zheng

Collective Behaviors of Mobile Robots Beyond the Nearest Neighbor Rules With Switching Topology

This paper is concerned with the collective behaviors of robots beyond the nearest neighbor rules, i.e., dispersion and flocking, when robots interact with others by applying an acute angle test (AAT)-based interaction rule. Different from a conventional nearest neighbor rule or its variations, the AAT-based interaction rule allows interactions with some far-neighbors and excludes unnecessary nearest neighbors. The resulting dispersion and flocking hold the advantages of scalability, connectivity, robustness, and effective area coverage. For the dispersion, a spring-like controller is proposed to achieve collision-free coordination. With switching topology, a new fixed-time consensus-based energy function is developed to guarantee the system stability. An upper bound of settling time for energy consensus is obtained, and a uniform time interval is accordingly set so that energy distribution is conducted in a fair manner. For the flocking, based on a class of generalized potential functions taking nonsmooth switching into account, a new controller is proposed to ensure that the same velocity for all robots is eventually reached. A co-optimizing problem is further investigated to accomplish additional tasks, such as enhancing communication performance, while maintaining the collective behaviors of mobile robots. Simulation results are presented to show the effectiveness of the theoretical results.

Novel active LiFePO4 battery balancing method based on chargeable and dischargeable capacity

Abstract A lithium iron phosphate battery (LiFePO4) pack is one of the main power resources for electric vehicles and the non-uniformity of cells in the battery pack has become the bottleneck to improve the pack capacity. An active balancing method based on chargeable and dischargeable capacities, derived from the dynamically estimated state of charge (SOC) and capacity in the pack, is proposed to tackle this problem in both the charging and discharging processes. To determine the current of each cell in balancing operation, one extra current sensor is added with a chosen flyback balancing circuit. The balancing simulation of a LiFePO4 battery pack has been conducted in the moderate and severe capacity imbalance scenarios. The simulation results show that the proposed battery balancing method has better performance than the other balancing methods based on voltage or SOC in increasing the charged and discharged pack capacity in the charging and discharging process.

Connectivity control and performance optimization in Wireless Robotic Networks: Issues, approaches and a new framework

In Wireless Robotic Networks (WRNs), robots interact with each other to fulfill complex tasks such as target tracking, area coverage or environment monitoring. When designing the interactive controller with a more realistic consideration, connectivity needs to be maintained instead of simply assumed. In this paper, we give an introduction on how to maintain the connectivity of a communication graph which corresponds to a WRN. Due to the limited communication range of robots, proximity-limited communication models are used for the co-operative control problem and the connectivity maintenance problem in WRNs. Therefore, we review two kinds of proximity-limited communication models in this paper: the disk-based communication model and the hysteresis-based communication model. In addition, we present some network performance optimization work that based on communication metrics of Bit Error Rate (BER) and Signal to Interference plus Noise Ratio (SINR). Finally, we propose a new framework that involves the connectivity control and the network performance optimization, and potential solutions are discussed accordingly.

Design of a robust discrete time sliding mode repetitive controller

This paper presents the design of a robust discrete-time sliding mode repetitive controller (DSMRC) which combines the features of repetitive control (RC) and sliding mode control (SMC) to achieve fast transient response, improved robustness to various matched uncertainties, and improved steady state performance. The new control structure consists of a repetitive control component and a sliding mode control part. The task of the sliding mode component is to provide a fast dynamic response and improve the robustness of the system against various uncertainties. The repetitive control part is added to the system to reduce the periodic error and improve the steady state performance of the system. A small pure phase lead component is added to the RC structure to ensure system stability and achieve high bandwidth tracking performance in the presence of bounded uncertainties. The proposed control structure is applied to a linear actuator (LA) system subjected to payload variations. A detailed analysis of the new control structure is presented in this paper to show the significance of the proposed scheme. Simulation results verify the effectiveness of the proposed method.

New on-line approach for lithium iron phosphate battery pack balancing based on state of charge

Lithium iron phosphate batteries (LiFePO4) are becoming one of the main power resources for electric vehicles (EVs), and the non-uniformity of cells in a battery pack has become the bottleneck to improve battery usable capacity. Many active balancing approaches are proposed to transfer charge among the cells to achieve the uniformity based on terminal voltage. This paper proposes a new balancing approach based on the battery state of charge (SOC) to equalize the cells in the LiFePO4 battery pack in charging process. The hybrid extended Kalman filter is adopted to dynamically estimate the cell SOCs which serve as a balancing criterion. A current sensor is added to detect balancing current for the SOC estimation. Simulations are carried out to compare the proposed approach with terminal voltage approaches and show that the proposed approach has charged more capacity into the pack in charging process.

Design of a new phase lead repetitive compensator for fast transient response

This paper proposes a simple design of a new discrete phase lead repetitive controller (RC) for fast transient response. The proposed phase lead RC provides a phase lead angle to compensate the phase lag of the closed loop system. This increases the range of the RC learning gain for which the system is stable and allows a large value of the learning gain to be used to achieve a faster convergence rate. The proposed compensator design is applied to a piezoactuator (PA) plant. A comprehensive analysis of the proposed RC structure and a comparison study are also presented in this paper. Simulation results show faster convergence rate and improved tracking performance of the system with the proposed phase lead RC.

Robust sliding mode control design for a dual-stage actuator system

To improve the positioning accuracy of servomechanisms with one single actuator only, the dual-stage actuator (DSA) systems have been proposed and widely used for industrial applications for the benefits of both large working range, high positioning accuracy and fast response. However, it is common that servomechanisms suffer from plant uncertainties and external disturbances which will affect the positioning accuracy. As such, this paper studies a robust control method called fast non-singular terminal sliding mode (FNTSM) control for a class of DSA systems. Compared with conventional sliding mode control, the FNTSM control can guarantee a faster convergence rate of the tracking error in the presence of system uncertainties including payload variations and external disturbances. Furthermore, it has the inherent feature of chattering-free in the control input. We also discuss the selection criteria of the controller parameters and then the FNTSM control method is applied to design the two control inputs of the DSA system. Simulations are studied to verify that the FNTSM controller can offer robust performance with respect to the mass variations and disturbance. Tracking performance achieved by conventional linear controllers is also presented for comparison.

Design and implementation of a vision-based robotic air hockey table

Air hockey has been an arcade favourite since the early 70s and has gained as much popularity to even schedule a yearly world championship. Unfortunately, this game requires a minimum of two players making it impossible for users who wish to train or play by themselves. To solve this issue, a robotic air hockey table capable of emulating a human player has to be created. In this paper, we have developed a computer vision system to detect and track the movements of the puck which is used to predict the final position of the puck in real time. Once the system predicts the final location of the puck, an electrical linear actuator capable of high speed and acceleration is activated which drives the mallet to block the goal. This paper will also discuss various problems encountered and possible future solutions to eradicate them.

An improved phase lead repetitive controller for a linear actuator

This paper presents an improved phase lead repetitive compensator (RC) for a linear actuator (LA) system. The linear phase lead compensation provided by the proposed compensator structure compensates the phase lag of the feedback system caused by payload variations and nonlinear friction present in the LA system. Unlike conventional phase lead RC structures which use a pure linear phase advance compensator zm to cancel the phase lag of the uncertain system, the proposed phase lead structure incorporates a phase lag compensator to counterbalance and reduce the large fixed phase angle of zm. This produces a control structure with a larger stability region and improved tracking performance in the presence of payload variations, and nonlinearities such as nonlinear friction. A comprehensive study and a detailed analysis of the proposed method are presented in this paper. Simulation results and a comparison study are also presented to support and verify the effectiveness of the proposed method when applied to a perturbed LA system.

An improved battery pack equalizer based on a DC/DC converter with fuzzy logic controller

This paper presents an improved battery pack equalizer (BPE) based on a DC/DC converter using fuzzy logic controller (FLC). This BPE can be designed without the necessity of a cell model in the pack. It is simple and robust. The simulation results have demonstrated that the BPE with the FLC has better performance than the BPE with the PI controller in terms of the balancing speed and efficiency.