Dongjun Lee

In this note, we consider the flocking of multiple agents which have significant inertias and evolve on a balanced information graph. Here, by flocking, we mean that all the agents move with a common velocity while keeping a certain desired internal group shape. We first show that flocking algorithms that neglect agents' inertial effect can cause unstable group behavior. To incorporate this inertial effect, we use the passive decomposition, which decomposes the closed-loop group dynamics into tw

In this paper, we propose a novel framework, passive set-position modulation (PSPM), which enables us to connect a (continuous-time) robot's position to a sequence of slowly updating/sparse (discrete-time) set-position signal via the simple (yet frequently used in practice) spring coupling with damping injection, while enforcing passivity of the closed-loop robotic system. The PSPM modulates the original set-position signal in such a way that the modulated signal is as close to the original sign

We propose a novel semiautonomous haptic teleoperation control architecture for multiple unmanned aerial vehicles (UAVs), consisting of three control layers: 1) UAV control layer, where each UAV is abstracted by, and is controlled to follow the trajectory of, its own kinematic Cartesian virtual point (VP); 2) VP control layer, which modulates each VP's motion according to the teleoperation commands and local artificial potentials (for VP-VP/VP-obstacle collision avoidance and VP-VP connectivity

We propose a control framework for the bilateral teleoperation between a single master robot and multiple cooperative slave robots with communication-delay in the master-slave communication channel. Using passive decomposition, we first decompose the dynamics of multiple slaves into two decoupled systems while preserving energetic passivity: the shape system describing cooperative grasping aspect, and the locked system representing overall behavior of the multiple slaves. Then, by locally contro

We propose a novel agreement framework for multiple (possibly heterogeneous) agents evolving on a directed information graph with non-uniform delays. Our proposed framework can ensure agreement of a certain scalar quantity among the agents, as long as 1) for each agent, we can design a local control s.t. its closed-loop transfer function has unit gain at dc and gain strictly less than unity elsewhere; 2) the information graph has a globally reachable node (i.e. there exists a path from it to eve

We consider bilateral teleoperation of a wheeled mobile robot over communication channels with constant delays. Our main objective is to enable humans to control the mobile robot much as they drive a car: i.e. by operating a master haptic joystick, they can control the linear velocity and heading angle of the mobile robot, much like they do so with the gas pedal and steering wheel. Passivity of the closed-loop system is also enforced so that, even with communication delays, humans can stably and

We propose a passive bilateral teleoperation control law for a pair of n-degree-of-freedom (DOF) nonlinear robotic systems. The control law ensures energetic passivity of the closed-loop teleoperator with power scaling, coordinates motions of the master and slave robots, and installs useful task-specific dynamics for inertia scaling, motion guidance, and obstacle avoidance. Consequently, the closed-loop teleoperator behaves like a common passive mechanical tool. A key innovation is the passive d

Presents a passive bilateral feedforward control scheme for linear dynamically similar (LDS) teleoperated manipulators with kinematic scaling and power scaling. The proposed control law renders the teleoperator as a passive rigid mechanical tool with programmable apparent inertia to the human operator and the work environment by utilizing bilateral force feedforward and kinematic feedback control. The passivity of the closed-loop system is robust to force measurement inaccuracies and model uncer

State-of-the-art technologies for hand (and finger) motion tracking do not always provide accurate and robust tracking. For example, severe occlusions can affect tracking with vision sensors, electromagnetic interference affects tracking with inertial measurement units (IMUs) and compasses, and ambiguous mechanical contact can affect tracking with soft sensors (i.e., the inability to distinguish motion-induced deformation). Here, we report a visual-inertial skeleton tracking (VIST) framework tha

We propose a novel haptic teleoperation control framework for multiple unmanned aerial vehicles (UAVs) over the Internet, consisting of the three control layers: 1) UAV control layer, where each UAV is abstracted by, and is controlled to follow the trajectory of, its own kinematic virtual point (VP); 2) VP control layer, which modulates each VP's motion according to the teleoperation commands and local artificial potentials (for inter-VP/VP-obstacle collision avoidance and inter-VP connectivity

We propose nonholonomic passive decomposition, which enables us to decompose the Lagrange-D'Alembert dynamics of multiple (or a single) nonholonomic mechanical systems with a formation-specifying (holonomic) map into 1) shape system, describing the dynamics of (i.e., formation aspect), where is the systems' configuration; 2) locked system, describing the systems' motion on the level set of with the formation aspect being fixed (i.e., maneuver aspect); 3) quotient system, whose nonzero motion per

Low-cost light scattering particulate matter (PM) sensors have been widely researched and deployed in order to overcome the limitations of low spatio-temporal resolution of government-operated beta attenuation monitor (BAM). However, the accuracy of low-cost sensors has been questioned, thus impeding their wide adoption in practice. To evaluate the accuracy of low-cost PM sensors in the field, a multi-sensor platform has been developed and co-located with BAM in Dongjak-gu, Seoul, Korea from 15