Hyeonbeom Lee

Onboard flight control of a micro quadrotor using single strapdown optical flow sensor

This paper considers autonomous onboard hovering flight control of a micro quadrotor using a strapdown optical flow sensor which is conventionally used for desktop mice. The vehicle considered in this paper can carry only a few dozen grams of payload, therefore conventional camera-based optical flow methods are not applicable. We present autonomous hovering flight control of the micro quadrotor using a single-chip optical flow sensor, implemented on an 8-bit microprocessor without external positioning sensors. Detailed description of all the system components is provided along with evaluation of the accuracy. Experimental results from flight tests are validated with the ground-truth data provided by a high-accuracy motion capture system.

Estimation, Control, and Planning for Autonomous Aerial Transportation

This paper presents estimation and control synthesis for an aerial manipulator to carry an unknown payload. Online estimation is based on parametrization of the aerial manipulator, which consists of a multirotor and a robotic arm. With the estimated physical properties, an augmented adaptive controller is proposed so that the end effector of the robotic arm can track the desired trajectory. Relying on this control structure, finally, we propose a flight motion generation method satisfying the joint angle limitation based on the analysis of the allowable flight area with respect to the joint angle variation. To validate our approach, the simulation results with comparison of conventional adaptive controller are shown. We also perform load carrying experiments using a custom-made aerial manipulator.

Path planning and control of multiple aerial manipulators for a cooperative transportation

This paper presents planning and control of multiple aerial manipulators for cooperative transportation. Individual aerial manipulators which consist of a hexacopter and 2-DOF robotic arm are controlled by an augmented adaptive sliding mode controller based on a closed-chain robot dynamics. The desired path for each aerial manipulator is obtained by using RRT* to transport an object to the desired position. It also considers the constraints about the grasping point at the end effector. To validate the proposed planning and control algorithm, an experimental result with multiple custom-made aerial manipulators is presented, which involves two aerial manipulators tracking the user-guided command and planned trajectory.

Robust control of a quadrotor using Takagi-Sugeno fuzzy model and an LMI approach

This paper presents robust control for a quadrotor using TS (Takagi-Sugeno) fuzzy model and an LMI (Linear Matrix Inequality) approach. TS fuzzy model can provide an effective representation of nonlinear systems with a set of local linear models. We present TS fuzzy model for the quarotor which is composed of local linear models valid in different operation points. Also, a state feedback controller is designed based on LMIs with the pole placement method. Simulation results illustrate the more stable tracking performance of the proposed controller in comparison with a conventional LQR controller.

Planning and Control for Collision-Free Cooperative Aerial Transportation

This paper presents planning and control synthesis for multiple aerial manipulators to transport a common object. Each aerial manipulator that consists of a hexacopter and a two-degree-of-freedom robotic arm is controlled by an augmented adaptive sliding mode controller based on a closed-chain robot dynamics. We propose a motion planning algorithm by exploiting rapidly exploring random tree star (RRT*) and dynamic movement primitives (DMPs). The desired path for each aerial manipulator is obtained by using RRT* with Bezier curve, which is designed to handle environmental obstacles, such as buildings or equipments. During aerial transportation, to avoid unknown obstacle, DMPs modify the trajectory based on the virtual leader–follower structure. By the combination of RRT* and DMPs, the cooperative aerial manipulators can carry a common object to keep reducing the interaction force between multiple robots while avoiding an obstacle in the unstructured environment. To validate the proposed planning and control synthesis, two experiments with multiple custom-made aerial manipulators are presented, which involve user-guided trajectory and RRT*-planned trajectory tracking in unstructured environments.Note to Practitioners—This paper presents a viable approach to autonomous aerial transportation using multiple aerial manipulators equipped with a multidegree-of-freedom robotic arm. Existing approaches for cooperative manipulation based on force decomposition or impedance-based control often require a heavy or expensive force/torque sensor. However, this paper suggests a method without using a heavy or expensive force/torque sensor based on closed-chain dynamics in joint space and rapidly exploring random tree star (RRT*) that generates the desired trajectory of aerial manipulators. Unlike conventional RRT*, in this paper, our method can also avoid an unknown moving obstacle during aerial transportation by exploiting RRT* and dynamic movement primitives. The proposed planning and control synthesis is tested to demonstrate performance in a lab environment with two custom-made aerial manipulators and a common object.

Control of an aerial manipulator using on-line parameter estimator for an unknown payload

This paper presents an estimation and control algorithm for an aerial manipulator using a hexacopter with a 2-DOF robotic arm. The unknown parameters of a payload are estimated by an on-line estimator based on parametrization of the aerial manipulator dynamics. With the estimated mass information and the augmented passivity-based controller, the aerial manipulator can fly with the unknown object. Simulation for an aerial manipulator is performed to compare estimation performance between the proposed control algorithm and conventional adaptive sliding mode controller. Experimental results show a successful flight of a custom-made aerial manipulator while the unknown parameters related to an additional payload were estimated satisfactorily.

Design concept for autonomous operation of KITSAT-3, an experimental LEO microsatellite

KITSAT-3 is a 3-axis stabilized technology demonstration satellite weighing 100 kg and was launched into the 720 km altitude sun synchronous circular orbit by Indian PSLV rocket in May, 1999. As we have only one command groundstation, the contact time is limited and hence, satellite operation was required to be highly autonomous. KITSAT-3 is heavily dependent on centralized on-board computer (OBC) for its autonomous in-orbit operation. Autonomous operation of KTTSAT-3 is implemented in the normal mode housekeeping and the safe mode operation. Battery charge control, operation mode based attitude control, scenario based payload operation and flexible on-board software management are the techniques used for the normal mode operation. For the safe mode operation, two levels of power safe mode control, OBC back-up mode and attitude safe mode control are used. Initial in-orbit operation was successful and the autonomous operation has been achieved by the implemented design concepts.

Backstepping Control on SE(3) of a Micro Quadrotor for Stable Trajectory Tracking

This paper presents a back stepping controller based on SE(3) to track the desired trajectory for a quad rotor unmanned aerial vehicle. The controller consists of two parts: 1) a position control part and 2) an attitude control part. The position controller is used to track the desired Cartesian coordinates using position and velocity errors, while the attitude controller uses the rotation matrix error and body angular velocity error to stabilize attitude dynamics expressed on SO(3). Simulation results illustrate the more stable tracking performance of the proposed controller in noisy environments in comparison with geometric controller. Experimental results on a micro quad rotor show the satisfactory performance of the proposed controller.

A robust watermarking method for high quality image

We propose a new image watermarking method for copyright protection. This method is a block based approach in the spatial domain. In addition to the perceptual invisibility and robustness, the image quality is also considered during the embedding procedure. Block activity is calculated to embed watermark. The watermark strength and the spread of the signal into a block are controlled by the block activity measurement. Experimental results show that the proposed method is suitable for the high quality image.

Constraint-Based Cooperative Control of Multiple Aerial Manipulators for Handling an Unknown Payload

This paper presents the planning and control synthesis of cooperative aerial manipulators to carry an unknown object together. The online parameter estimation algorithm is designed to estimate the unknown physical parameters of the common payload such as mass and moment of inertia, without the need of multiaxis force/torque sensors. Based on the augmented adaptive sliding mode controller with the estimated physical parameters, the desired trajectory of each aerial manipulator is generated to track the desired trajectory of corresponding end effector. In order to carry an unknown object safely considering the actuation limit of the hexacopter, we use the task priority to satisfy the unilateral constraints determined by the allowable flight envelope. To validate our approach, the experimental result on a successful transportation by using multiple custom-made aerial manipulators is shown. This result suggests that the proposed approach can be utilized for safe cooperative aerial transportation.