This paper proposes a distributed coverage control strategy for quadcopters equipped with downward-facing cameras that prevents the appearance of unmonitored areas in between the quadcopters' fields of view (FOVs). We derive a necessary and sufficient condition for eliminating any unsurveilled area that may arise in between the FOVs among a trio of quadcopters by utilizing a power diagram, i.e. a weighted Voronoi diagram defined by radii of FOVs. Because this condition can be described as logically combined constraints, we leverage nonsmooth control barrier functions (NCBFs) to prevent the appearance of unmonitored areas among a team's FOV. We then investigate the symmetric properties of the proposed NCBFs to develop a distributed algorithm. The proposed algorithm can support the switching of the NCBFs caused by changes of the quadcopters composing trios. The existence of the control input satisfying NCBF conditions is analyzed by employing the characteristics of the power diagram. The proposed framework is synthesized with a coverage control law that maximizes the monitoring quality while reducing overlaps of FOVs. The proposed method is demonstrated in simulation and experiment.

This paper presents novel quadrotor structures composed of only clockwise rotors. A multirotor unmanned aerial vehicle (UAV) generally has both clockwise and counterclockwise rotors to counteract the torques from the rotors. While the proposed structures have only clockwise rotors, those rotors are tilted to cancel the torques around the yaw angle of the body. This paper investigates the conditions for the proposed structures to achieve static hovering. More specifically, we provide a guideline to design the rotor tilt angles of the proposed structure. Then, this paper presents the design example of the rotor tilt angles and develops a prototype of the proposed quadrotor. The cascaded controller is also developed for the proposed structure. Finally, experimental validation is conducted with a developed prototype and controller.

This paper presents a method for biped gait generation along a predefined curve with fully stretched knees. First, we design a spatial gait pattern as a function of the traveled distance on the path without considering dynamics. Then, a consistent dynamic walking motion is obtained by optimization that minimizes the zero-moment point and the speed errors while considering the trade-off between kinematics and dynamics. This method generalizes the spatially quantized dynamics-based gait generation, which is our former method restricted to straight paths, to walk on arbitrary curves. The generated gaits are validated by dynamic simulation.

This article proposes a novel geometric method to investigate whether a multirotor unmanned aerial vehicle (UAV) can achieve static hovering, i.e., hoverability. Hoverability is indispensable for a multirotor UAV to conduct its tasks safely and should be satisfied even after its rotors fail to prevent accidents. The proposed geometric method reveals the relationship between the position of the center of mass (CoM) and the rotor placement of a multirotor UAV with upward-oriented rotors to satisfy hoverability. It can be applied to a multirotor UAV with any number and positioning of rotors. This article also demonstrates that our proposed method can be applied to the investigation of a robust structure against rotor failures. This investigation provides a geometric proof that a pentarotor UAV with robustness against an arbitrary rotor failure cannot be developed. Furthermore, a quantitative measure of hoverability is newly presented based on the analysis method. This enables us to design a multirotor UAV with an optimal structure by maximizing it. Finally, experimental validation is performed by using a hexrotor UAV whose CoM position is adjusted.

A new approach for solving an optimal control problem of ball pitching with an underactuated human-like robot arm is proposed. The system dynamics is simplified to a planar two-link robot with actuation only at the shoulder joint and a passive spring at the elbow joint representing the stiffness of the arm. The objective is to accelerate the ball from an initial configuration at rest in such a way that the projection of its velocity along a certain elevation angle is maximal at a predefined release line. The suggested procedure makes use of a parameterization of the robot motion in terms of geometric relations among the generalized coordinates. We systematically formulate a necessary condition for an optimal motion resulting in a nonlinear differential equation that describes a synchronization of the joint angles. A suitable solution is found by numerically searching over a finite number of free initial conditions.

This paper investigates the running control problem for the 7-link, 6-actuator planar bipedal robot including ankle joints. The control strategy is based on the “synchronization structure” with the angular momentum of the pivot point. The synchronization not only follows the simplified joint angle dynamics of human running but also generates the uniform running speed from wide range of initial speed, which claims that the controller is robust for the error of initial speed. Moreover, it successfully verifies the acceleration of running speed from 0.1[m/s], which is almost zero speed, to a uniform running speed “without” switching controllers. Finally, the controller is applied for the running on an uneven terrain, and it successfully achieves running with the maximum slope angle 6[deg], which is highly steep terrain in the real situation.

This paper describes an experiment for swing up control for the acrobot with the compliance of the high bar based on the energy pumping method. The energy interaction exists between the gymnast and the high bar, because the high bar is bending during gymnastics. Therefore, more efficient motion would be constructed by controlling this energy interaction. Based on this probability, swing up control which considers the compliance and the energy interaction with each component is proposed. To confirm this discussion, an experiment using the acrobot is carried out, and the advantage and the disadvantage by using compliance are examined by comparing experimental results for with and without compliance case.

This paper deals with the ball-plate manipulation problem considered as a typical but complicated model of a driftless nonholonomic system. Due to a strong nonlinearity of the ball-plate system, a state equation of the kinematic model cannot be transformed into a chained form, which is known to be effective in constructing a feedback control law for some driftless nonholonomic systems. To address this problem, we utilize a time-state control form, a kind of canonical form which covers a broader class of systems than the chained form. This form is first applied to two separate subproblems, position control, in which the planar position of the ball is controlled but not the orientation, and orientation control, in which the orientation is controlled without changing the positional relation between the ball and the plates. It turns out that there exists a linearly uncontrollable subspace in the transformed subsystem, which turns into controllable by a change of coordinates. This implies that the system has the structure of a system with two generators. We propose a control strategy using iterative changes of coordinates, ensuring convergence in the neighborhood of the origin. Finally, we unify the subproblems into simultaneous control of position and orientation, i.e., the whole configuration of the system. The important idea in the simultaneous control is the coordinate transformation, which enables us to avoid a singular point. Results of simulations show that the proposed method achieve robustness to a measurement noise and perturbation of radius of the ball.

The present paper is concerned with an adaptive fuzzy control approach to control one linear actuator hopping robot. Our simple approach uses linearized model to design a state feedback servo controller. Thereafter, by using fuzzy networks we developed model reference adaptive fuzzy control in which a fuzzy network is used to compensate the nonlinearity of robot dynamics. The role of the fuzzy network is to construct a linearized model by minimizing the output error caused by nonlinearity in the robot control system through the proposed learning mechanism. The continuous hopping gait was realized by simulation.

This paper deals with hopping motion analysis of spherical robot with a typical impact condition like 'superball'. A horizontal velocity of super ball after an impact depends on the angular velocity before the impact where it doesn't slip at the contact point. Our robot model consists of an elastic spherical shell with such an impact condition and of an internal rotary input. Assuming the perfectly elastic impact in a vertical direction, a feedback control strategy for generating the horizontal velocity after an impact by the rotary input during flying phase is derived. Simulation results show that some hopping motion is achieved by the proposed method. In addition, this paper shows the possibility and necessary condition that a climbing motion with impacts against two parallel vertical planes is achieved.

Balance control analysis of humanoid robot based on Zero Moment Point (ZMP) feedback control is presented. ZMP is mostly used as standard evaluation of stability of humanoid robot, and balance control is conducted by controlling ZMP position so that it is always in convex hull of the foot-support area. To simplify the design of controller, it is mainly used as one mass inverted pendulum model which represents lower body of humanoid robot model. However this model causes system to become non-minimum phase and performance limitation of the system occurrs, because of the presence of Waterbed effect in frequency domain and unavoidable undershoot in time domain. This paper proposes ZMP feedback control using two masses inverted pendulum model which represents lower and upper body of humanoid robot and creates minimum phase system. The design of the controller based on the proposed model using linear quadratic by considering output is described and confirmed using simulation.

We discuss autonomous locomotion control of a snake-like articulated robot with passive wheels. Such a robot has a quite different mechanism in locomotion from that of other locomotion systems, namely, it has no driving wheel and moves only by bending its body. Hence the locomotability depends on its posture. In order to evaluate the locomotability, we utilize a notion of dynamic manipulability which has been applied to a robot manipulator. We also propose a simple controller based on this manipulability. Simulation results show that a certain periodic winding motion is automatically generated.

Proposes a classification of nonholonomic systems from a viewpoint of classical mechanics as well as nonlinear control theory. We clarify this connection by recalling our previous results (1998) that the asymptotic stabilizability of the target equilibrium holds only if the dimension of the equilibria set is equal to the number of control inputs. We summarize a lot of nonholonomic control problems by relating their equilibria set and the numbers of control inputs, their mechanical properties (nonintegrability of constraints) and the existing control strategies proposed in recent years.

This paper investigates the position estimation of wheeled mobile robots governed by nonholonomic constraints. Using time-scale transformation and a proper choice of state variables, the problem is formulated as state estimation of nonlinear SISO systems. To deal with this problem, we construct the nonlinear observers via Lyapunov's direct method. Simulation results are also provided.

The authors design a path tracking controller for a trailer-like mobile robot which has the following properties: (1) the stability of the control can be evaluated analytically; (2) the trailer-like mobile robot tracks the desired path even when it moves backward; and (3) the control varies according to the environment and/or the velocity of the robot without violating the stability of the control.>

An alternative method is proposed for designing a robot-controller in Cartesian coordinates using a time-scale transformation. The proposed controller achieves slow poles in the area of poor manipulative ability and fast poles in the area of good manipulative ability. Therefore, the robot can be properly controlled in the neighbourhood of singular points without reducing the performance outside the neighborhood of these points.>

In this paper, we propose an alternative method for designing a robot controller in Cartasian coordinates using a time scale transformation. We will show how a suitable choice of the time scale allows us to control the robot in the neighborhood of singular points without reducing the performance outside the neighborhoods of these points. The resultant controlled system has slow poles in the area of poor manipulative ability and fast poles in that of good manipulative ability.