Practical Model Construction and Stable Control of an Unmanned Aerial Vehicle With a Parafoil-Type Wing

This correspondence paper presents a framework for practical model construction and stable altitude control of an unmanned aerial vehicle with a parafoil-type wing (UAV-PW). To design a stable controller, we first construct a dynamical longitudinal model of the UAV-PW. Since there exist no aerodynamics data of the parafoil shape in our UAV-PW, aerodynamics coefficients balanced at the trimmed equilibrium are employed. The model accuracy is investigated by comparing the model outputs with the real test flight experimental data. Next, stable controller design conditions for the UAV-PW model with uncertainties are derived in terms of linear matrix inequalities (LMIs). By solving the LMI conditions, we design a stable controller that asymptotically stabilizes the UAV-PW model with the uncertainties on a considered operation domain. The experimental results demonstrate the viability of the model construction and the stable altitude control

A Waypoint Following Control Design for a Paraglider Model With Aerodynamic Uncertainty

This paper presents a waypoint following control design for a powered paraglider (PPG) model. After constructing a dynamic model with six degrees of freedom of the PPG, a dynamical lateral model around a trim equilibrium in the steady-state flight is obtained. Unknown parameters, such as the moment of inertia, the drag coefficient, etc., in the lateral model are optimized by real flight experimental data. The model output with the optimized parameters agrees with the real flight experimental data. Since the aerodynamics-related parameter, i.e., the drag coefficient, might be slightly changed even near the considered trim equilibrium, this paper considers its uncertainty in the constructed lateral model. A nonlinear controller to stabilize the lateral model (with the aerodynamic uncertainty) on a considered operation domain is designed by solving robust controller design conditions expressed in terms of linear matrix inequality. The experimental results including automatic landing demonstrate the effectiveness of the control system design framework, i.e., the model construction and the robust stable control, considering the model uncertainty

Control of a Snake Robot for Ascending and Descending Steps

This paper proposes control method for a snake robot to ascend and descend steps. In a multiplane step environment, it is necessary for locomotion to transfer from one plane to another. When a snake robot moves, it touches several planes as its body is long and thin. In this paper, we propose a control method to track the trajectory of a snake robot in a step environment. We decomposed the 3-D motion of the robot into two simple models by introducing an assumption that simplifies the model and controller, and derive a model of the robot as a hybrid system with switching. The control method consists of a tracking controller, a method for shifting the robot\u27s part connecting the planes, and active lifting to control the shape of the robot. Ascent and descent experiments confirm the effectiveness of the proposed controller and the method for shifting the connecting part of the robot\u27s body

Singularity Analysis of a Snake Robot and an Articulated Mobile Robot With Unconstrained Links

In this paper, we analyze the conditions related to singular configurations with unconstrained links and present related theorems and lemmas for a snake robot and an articulated mobile robot. A snake robot and an articulated mobile robot have links that have passive or active wheels and the links are serially connected by active joints. The singular configuration should be avoided if the robots are automatically controlled because they cannot execute intended motion when they are in the singular configuration. We derive a novel necessary and sufficient condition for the singular configurations of the snake robot; this removes some limitations of the traditional condition for a snake robot without unconstrained links. We also derive the necessary and sufficient conditions for the singular configurations of the articulated mobile robot, and the structural conditions under which a real articulated mobile robot does not have a singular configuration. These conditions are proved by analyzing the elements of matrices included in the kinematic model and considering the geometrical meaning of the elements. In addition, we propose evaluation indices representing the distance from the singular configurations of a snake robot. We verify the effectiveness of these indices through simulations

Shape Control of a Snake Robot With Joint Limit and Self-Collision Avoidance

This paper proposes a shape control method for a snake robot, which maintains head position and orientation, and avoids joint limits and self-collision. We used a passive wheeled snake robot that can switch the grounded/lifted status of its wheels. We derived a kinematic model of the robot that represents its redundancy as both joint angles [the shape controllable points (SCPs)] and the null space of the control input. In the control method, the shape is changed by sequential control of the SCPs, and the null space of the control input is used for joint limit and self-collision avoidance. Jumps in control input do not occur, although the controlled variable and the model are switched. Simulations and an experiment were used to demonstrate the effectiveness of the proposed method

Approximate Path-Tracking Control of Snake Robot Joints With Switching Constraints

This paper presents an approximate path-tracking control method for all joints of a snake robot, along with the verification of this method by simulations and experiments. We consider a wheeled snake robot that has passive wheels and active joints. The robot can switch the wheels that touch the ground by lifting the required parts of its body. The model of the robot becomes a kinematically redundant system if certain wheels are lifted. Using this kinematic redundancy, and selecting the appropriate lifted parts, we design a controller for approximate path tracking. Simulations and experimental results show that the proposed controller effectively reduces the path-tracking error for all joints of the snake robot

Range-Sensor-Based Semiautonomous Whole-Body Collision Avoidance of a Snake Robot

This brief presents a control system for a snake robot based on range sensor data that semiautonomously aids the robot in avoiding collisions with obstacles. In the proposed system, an operator indicates the desired velocity of the first link of the robot using a joystick, and the joint input which accomplishes both the desired velocity of the first link and collision avoidance between subsequent links and obstacles is automatically calculated by the controller, which selects the links needed to be grounded and exploits redundancy. The controller uses real-time data from range sensors for obstacle positions. The experimental system, which has range sensors and the function generating environmental map using simultaneous localization and mapping, was developed with decreasing calculation cost, and experiments were performed to verify the effectiveness of the proposed system in unknown environments

Smooth control of an articulated mobile robot with switching constraints

The paper describes a smooth controller of an articulated mobile robot with switching constraints. The use of switching constraints associated with grounded/lifted wheels is an effective method of controlling various motions; e.g. the avoidance of a moving obstacle. A model of an articulated mobile robot that has active and passive wheels and active joints with switching constraints is derived. A controller that accomplishes the trajectory tracking of the robot’s head and subtasks using smooth joint input is proposed on the basis of the model. Simulations and experiments are presented to show the effectiveness of the proposed controller

Mixed Integer Programming-Based Semiautonomous Step Climbing of a Snake Robot Considering Sensing Strategy

We propose a control method for semiautonomous step climbing by a snake robot. Our method is based on mixed integer quadratic programming to generate the reference trajectory of the head of the snake robot online. One of the features of the method is that it determines suitable positions and time duration in which to sense the surroundings before approaching the step. Furthermore, constraints on velocity and acceleration are taken into account, so that the snake robot can securely follow the generated trajectory. Our method was applied to a snake robot equipped with a laser range finder, which is used for step detection. Experiments were performed to verify the efficacy of the method