@article {Li2022,
	title = {3-D Inter-Robot Relative Localization via Semidefinite Optimization},
	journal = {IEEE Robotics and Automation Letters},
	volume = {7},
	year = {2022},
	pages = {10081{\textendash}10088},
	publisher = {IEEE},
	abstract = {In this letter, the 3-D inter-robot relative localization problem is addressed using noise-corrupted odometric and distance measurements. Unlike the existing solutions, we are devoted to providing a relative localization method that has an {\textquotedblleft}overall best performance,{\textquotedblright} which means that the tradeoffs between the estimation accuracy (EA), the number of measurements (NoMs), and the computation efficiency (CE) are considered. We demonstrate that an existing formulation of the 3-D relative localization problem, the square distances weighted least square (SD-WLS), can be equivalently reformulated as a non-convex quadratic constrained quadratic programming (QCQP) problem. Further, to handle the non-convex nature of the QCQP problem, we adopt the semidefinite programming (SDP) relaxation approach, which drops the rank constraint and recovers the solution of the QCQP via an eigenvalue decomposition strategy. Finally, a refinement step is introduced to solve the problem that the quadratic constraints might not be satisfied due to the SDP relaxation. The simulation and experiment results show that, compared to existing methods, our method has the best overall performance when the three factors, i.e., EA, NoMs, and CE, are important for a relative localization application.},
	keywords = {3-D inter-robot relative localization, Distance measurement, Global Positioning System, Location awareness, non-convex optimization, QCQP, Quaternions, Robots, SDP, sensors, Sun},
	issn = {2377-3774},
	doi = {10.1109/LRA.2022.3192888},
	author = {Ming Li and Tin Lun Lam and Zhiyong Sun}
}
@article {Luo2022,
	title = {Adaptive Flow Planning of Modular Spherical Robot Considering Static Gravity Stability},
	journal = {IEEE Robotics and Automation Letters},
	volume = {7},
	year = {2022},
	pages = {4228{\textendash}4235},
	publisher = {IEEE},
	abstract = {Modular robots have a unique obstacle-crossing method, flow. Flow is realized by constantly changing the connection relationship between modules, namely reconfiguration. Existing flow planning methods do not consider the static stability in their adaptation to obstacles. This letter proposes a flow planning method with scalability, adaptability, and static gravity stability. The criterion of static gravity stability is always satisfied through the following two innovations. First, each target configuration in the flow process is designed to grasp obstacles like vines. Second, in motion planning, each module maintains contact with the obstacle or a fixed module to maximize the supporting polygon of the configuration. What{\textquoteright}s more, the simplified path output by the connection planning and the precise calculation based on the mesh model realize the scalability and adaptability of the flow planning method. In simulation, we evaluate the adaptability to various obstacles and the margin of static gravity stability.},
	keywords = {Cellular and modular robots, Gravity, Hardware, path planning for multiple mobile robots or agents, Planning, Robot kinematics, Robots, scheduling and coordination, Stability criteria, Three-dimensional displays},
	issn = {2377-3774},
	doi = {10.1109/LRA.2022.3150028},
	author = {Haobo Luo and Tin Lun Lam}
}
@conference {Liang2022,
	title = {Energy Sharing Mechanism for a Freeform Robotic System - FreeBOT},
	booktitle = {2022 International Conference on Robotics and Automation (ICRA)},
	year = {2022},
	pages = {4232{\textendash}4238},
	publisher = {IEEE},
	organization = {IEEE},
	address = {Philadelphia, PA, USA},
	abstract = {Energy sharing in modular self-reconfigurable robots ensures the energy balance of the modules, thus allowing the system to work sustainably. This paper proposes an energy sharing mechanism for a novel modular self-reconfigurable robot that allows free connections among modules, termed as FreeBOT, such that each FreeBOT can share energy with peers through surface contact. Corresponding energy sharing rules are proposed to achieve an energy sharing network structure without invalid components. As alternative choices, several types of networks subjected to the above requirements are provided, which also maximize the number of FreeBOTs joining to share energy. We implement and test the prototype of the energy sharing mechanism on FreeBOT. The experimental results show that the mechanism can effectively achieve energy sharing among FreeBOTs.},
	keywords = {Automation, Prototypes, Robots},
	isbn = {978-1-7281-9682-4},
	doi = {10.1109/ICRA46639.2022.9811860},
	author = {Guanqi Liang and Yuxiao Tu and Lijun Zong and Junfeng Chen and Tin Lun Lam}
}
@conference {Tu2022,
	title = {FreeSN: A Freeform Strut-node Structured Modular Self-reconfigurable Robot - Design and Implementation},
	booktitle = {2022 International Conference on Robotics and Automation (ICRA)},
	year = {2022},
	pages = {4239{\textendash}4245},
	publisher = {IEEE},
	organization = {IEEE},
	address = {Philadelphia, PA, USA},
	abstract = {This paper proposes a novel freeform strut-node structured modular self-reconfigurable robot (MSRR) called FreeSN, consisting of strut and node modules. A node module is mainly a low-carbon steel spherical shell. A strut module contains two freeform connectors, which provide strong magnetic connections and flexible spherical motions. The FreeSN system shares the benefits of freeform connection and strut-node structures. The freeform connection brings good adaptability to the environment. The triangle substructures inside the system configuration significantly improve the structural stability. The parallel execution of module motions can superpose the module capabilities and makes the system more scalable. The modules can combine these robot features by selecting the system configuration and better fit different circumstances and tasks. Four demonstrations, including assembly, obstacle crossing, transportation, and object manipulation, are designed to show the capabilities of the FreeSN system in different aspects. The results show the great performance and versatility of this MSRR system.},
	keywords = {Automation, Connectors, Robots, Steel, Structural engineering, Task analysis, Transportation},
	isbn = {978-1-7281-9682-4},
	doi = {10.1109/ICRA46639.2022.9811583},
	author = {Yuxiao Tu and Guanqi Liang and Tin Lun Lam}
}
