We propose a novel robotic platform for aerial operation and manipulation, a spherically connecte... more We propose a novel robotic platform for aerial operation and manipulation, a spherically connected multiquadrotor (SmQ) platform, which consists of a rigid frame and multiple quadrotors that are connected to the frame via passive spherical joints and act as distributed rotating thrust generators to collectively propel the frame by adjusting their attitude and thrust force. Depending on the number of quadrotors and their configuration, this SmQ platform can fully (or partially) overcome the issues of underactuation of the standard multirotor drones for aerial operation/manipulation (e.g., body-tilting with sideway gust/force, dynamic interaction hard to attain, complicated arm-drone integration, etc.). We present the dynamics modeling of this SmQ platform system and establish the condition for its full actuation in SE(3). We also show how to address limited range of spherical joints and rotor saturations as a constrained optimization problem by noticing the similarity with the multifingered grasping problem under the friction-cone constraint. We then design and analyze feedback control laws for the S3Q and S2Q systems as a combination of high-level Lyapunov control design and low-level constrained optimization and show that the (fully actuated) S3Q system can assume any trajectory in SE(3), whereas the S2Q system in 3 × S 2 with its unactuated dynamics is still internally stable. Experiments are also performed to show the efficacy of the theory.
International Journal of Control, Automation and Systems, 2017
Positioning control of an underwater robot is a challenging problem due to the high disturbances ... more Positioning control of an underwater robot is a challenging problem due to the high disturbances of ocean flow. To overcome the high disturbance, a new underwater robot with tilting thrusters was proposed previously, which can compensate for disturbance by focusing the thrusting force in the direction of the disturbance. However, the tilting motion of the thrusters makes the system nonlinear, and the limited tilting speed sometimes makes the robot unstable. Therefore, an optimized controller is necessary. A new positioning controller is proposed for this robot using a vector decomposition method. Based on the dynamic model, the nonlinear force input term of the tilting thrusters is decomposed in the horizontal and vertical directions. Based on the decomposition, the solution is determined by a pseudo-inverse and null-space solution. Using the characteristics of the decomposed input matrix, the final solution can be found by solving a simple second-order algebraic equation to overcome the limitations of the tilting speed. The positioning was simulated to validate the proposed controller by comparing the results with a switching-based controller. Tracking results are also presented. In future work, a high-level control strategy will be developed to take advantage of the tilting thrusters by focusing the forcing direction toward the disturbance with a limited stability margin.
2015 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), 2015
We propose a new aerial tool operation system consisting of multiple quadrotors connected to a to... more We propose a new aerial tool operation system consisting of multiple quadrotors connected to a tool by spherical joints to perform tool operation tasks. We model the system and show that the attitude dynamics of each quadrotor is decoupled from the tool dynamics, so that we can consider the quadrotors as thrusters and control the tool by adjusting the orientation and magnitude of these thrusters. We also show that the 6-DOF tool dynamics could be under-actuated or fullyactuated, depending on the number of quadrotors attached to the tool and the geometric configuration of their attachments. We then design control laws for the tool-tip position/orientation tracking of the (under-actuated) tool system with two quadrotors and the (fully-actuated) tool system with three quadrotors. We use Lyapunov approach to find the desired thrust command for each quadrotor while also taking into account the spherical joint limits in a form of constrained optimization. Simulation and implementation results are performed to support the theory.
2015 12th International Conference on Ubiquitous Robots and Ambient Intelligence (URAI), 2015
We introduce a new aerial manipulator system that consists of an airborne base actuated by multip... more We introduce a new aerial manipulator system that consists of an airborne base actuated by multiple spherically-connected quadrotors and a manipulator rigidly connected to that base. We first model the dynamics of the system and show that attitude dynamics of each quadrotor is decoupled from the base-manipulator dynamics. Therefore, we can consider the quadrotors as thrusters to control the base-manipulator dynamics. We then use Lyapunov approach to design a pose-tracking control for the end-effector of the manipulator and optimally distribute that control to each quadrotor on the base and each joint rotor on the manipulator. The simulation of a system of three quadrotors and a 2 degree-of-freedom (DOF) manipulator is presented to support the theory.
We propose a novel control framework to enable a quadrotor to operate a tool attached on it. We f... more We propose a novel control framework to enable a quadrotor to operate a tool attached on it. We first show that any Cartesian control at the tool-tip can be generated if and only if the tool-tip is located strictly above or below the quadrotor's center-of-mass. We then fully characterize the internal dynamics of the spatial quadrotor tool operation, which arises due to the quadrotor's under-actuation, and elucidate a seemingly counter-intuitive necessary condition for the internal stability, that is, the tool-tip should be located above the quadrotor's center-of-mass. We further manifest that this internal dynamics can exhibit finite-time escape and propose a stabilizing action to prevent that. The theory is then illustrated for the problems of rotating tool operation and hybrid force/position control with relevant simulation results.
2013 13th International Conference on Control, Automation and Systems (ICCAS 2013), 2013
In this paper, we consider the problem of rotation coordination of a group of bodies in SO(3), wh... more In this paper, we consider the problem of rotation coordination of a group of bodies in SO(3), which has significant applications in coordinating spinning spacecraft and diving underwater vehicles. By exploiting passive decomposition, the system is divided into: 1) the shape system representing the group formation shape, and 2) the locked system describing the movement of the whole the group. We then design centralized controller which can be easily achieved by canceling out the coupling between two systems and controlling the shape and locked systems individually.
2013 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2013
This paper presents a hybrid force/motion control framework for quadrotors with a rigid/light too... more This paper presents a hybrid force/motion control framework for quadrotors with a rigid/light tool attached on it. By transforming the quadrotor dynamics into that of the tool-tip position y and applying the passive decomposition to decompose its dynamics into tangential and normal components w.r.t. a contact surface, we design hybrid position/force control. We also elucidate the internal dynamics (i.e., the dynamics hidden from the tool-tip position and yaw angle output and not directly affected by the control action due to the quadrotor's under-actuation), reveal a (seemingly counter-intuitive) necessary condition for internal stability (i.e., tool above the quadrotor, not beneath it), and propose a stabilizing control action to ensure the angular rates still be bounded while preventing the finite-time escape. Simulations are performed to support the theory.
We propose a novel robotic platform for aerial operation and manipulation, a spherically connecte... more We propose a novel robotic platform for aerial operation and manipulation, a spherically connected multiquadrotor (SmQ) platform, which consists of a rigid frame and multiple quadrotors that are connected to the frame via passive spherical joints and act as distributed rotating thrust generators to collectively propel the frame by adjusting their attitude and thrust force. Depending on the number of quadrotors and their configuration, this SmQ platform can fully (or partially) overcome the issues of underactuation of the standard multirotor drones for aerial operation/manipulation (e.g., body-tilting with sideway gust/force, dynamic interaction hard to attain, complicated arm-drone integration, etc.). We present the dynamics modeling of this SmQ platform system and establish the condition for its full actuation in SE(3). We also show how to address limited range of spherical joints and rotor saturations as a constrained optimization problem by noticing the similarity with the multifingered grasping problem under the friction-cone constraint. We then design and analyze feedback control laws for the S3Q and S2Q systems as a combination of high-level Lyapunov control design and low-level constrained optimization and show that the (fully actuated) S3Q system can assume any trajectory in SE(3), whereas the S2Q system in 3 × S 2 with its unactuated dynamics is still internally stable. Experiments are also performed to show the efficacy of the theory.
International Journal of Control, Automation and Systems, 2017
Positioning control of an underwater robot is a challenging problem due to the high disturbances ... more Positioning control of an underwater robot is a challenging problem due to the high disturbances of ocean flow. To overcome the high disturbance, a new underwater robot with tilting thrusters was proposed previously, which can compensate for disturbance by focusing the thrusting force in the direction of the disturbance. However, the tilting motion of the thrusters makes the system nonlinear, and the limited tilting speed sometimes makes the robot unstable. Therefore, an optimized controller is necessary. A new positioning controller is proposed for this robot using a vector decomposition method. Based on the dynamic model, the nonlinear force input term of the tilting thrusters is decomposed in the horizontal and vertical directions. Based on the decomposition, the solution is determined by a pseudo-inverse and null-space solution. Using the characteristics of the decomposed input matrix, the final solution can be found by solving a simple second-order algebraic equation to overcome the limitations of the tilting speed. The positioning was simulated to validate the proposed controller by comparing the results with a switching-based controller. Tracking results are also presented. In future work, a high-level control strategy will be developed to take advantage of the tilting thrusters by focusing the forcing direction toward the disturbance with a limited stability margin.
2015 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), 2015
We propose a new aerial tool operation system consisting of multiple quadrotors connected to a to... more We propose a new aerial tool operation system consisting of multiple quadrotors connected to a tool by spherical joints to perform tool operation tasks. We model the system and show that the attitude dynamics of each quadrotor is decoupled from the tool dynamics, so that we can consider the quadrotors as thrusters and control the tool by adjusting the orientation and magnitude of these thrusters. We also show that the 6-DOF tool dynamics could be under-actuated or fullyactuated, depending on the number of quadrotors attached to the tool and the geometric configuration of their attachments. We then design control laws for the tool-tip position/orientation tracking of the (under-actuated) tool system with two quadrotors and the (fully-actuated) tool system with three quadrotors. We use Lyapunov approach to find the desired thrust command for each quadrotor while also taking into account the spherical joint limits in a form of constrained optimization. Simulation and implementation results are performed to support the theory.
2015 12th International Conference on Ubiquitous Robots and Ambient Intelligence (URAI), 2015
We introduce a new aerial manipulator system that consists of an airborne base actuated by multip... more We introduce a new aerial manipulator system that consists of an airborne base actuated by multiple spherically-connected quadrotors and a manipulator rigidly connected to that base. We first model the dynamics of the system and show that attitude dynamics of each quadrotor is decoupled from the base-manipulator dynamics. Therefore, we can consider the quadrotors as thrusters to control the base-manipulator dynamics. We then use Lyapunov approach to design a pose-tracking control for the end-effector of the manipulator and optimally distribute that control to each quadrotor on the base and each joint rotor on the manipulator. The simulation of a system of three quadrotors and a 2 degree-of-freedom (DOF) manipulator is presented to support the theory.
We propose a novel control framework to enable a quadrotor to operate a tool attached on it. We f... more We propose a novel control framework to enable a quadrotor to operate a tool attached on it. We first show that any Cartesian control at the tool-tip can be generated if and only if the tool-tip is located strictly above or below the quadrotor's center-of-mass. We then fully characterize the internal dynamics of the spatial quadrotor tool operation, which arises due to the quadrotor's under-actuation, and elucidate a seemingly counter-intuitive necessary condition for the internal stability, that is, the tool-tip should be located above the quadrotor's center-of-mass. We further manifest that this internal dynamics can exhibit finite-time escape and propose a stabilizing action to prevent that. The theory is then illustrated for the problems of rotating tool operation and hybrid force/position control with relevant simulation results.
2013 13th International Conference on Control, Automation and Systems (ICCAS 2013), 2013
In this paper, we consider the problem of rotation coordination of a group of bodies in SO(3), wh... more In this paper, we consider the problem of rotation coordination of a group of bodies in SO(3), which has significant applications in coordinating spinning spacecraft and diving underwater vehicles. By exploiting passive decomposition, the system is divided into: 1) the shape system representing the group formation shape, and 2) the locked system describing the movement of the whole the group. We then design centralized controller which can be easily achieved by canceling out the coupling between two systems and controlling the shape and locked systems individually.
2013 IEEE/RSJ International Conference on Intelligent Robots and Systems, 2013
This paper presents a hybrid force/motion control framework for quadrotors with a rigid/light too... more This paper presents a hybrid force/motion control framework for quadrotors with a rigid/light tool attached on it. By transforming the quadrotor dynamics into that of the tool-tip position y and applying the passive decomposition to decompose its dynamics into tangential and normal components w.r.t. a contact surface, we design hybrid position/force control. We also elucidate the internal dynamics (i.e., the dynamics hidden from the tool-tip position and yaw angle output and not directly affected by the control action due to the quadrotor's under-actuation), reveal a (seemingly counter-intuitive) necessary condition for internal stability (i.e., tool above the quadrotor, not beneath it), and propose a stabilizing control action to ensure the angular rates still be bounded while preventing the finite-time escape. Simulations are performed to support the theory.
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