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Human-demonstrated motion transferred to a robotic platform often needs to be adapted to the current state of the environment or to modified task requirements. Adaptation, i. e. learning of a modified behavior, needs to be fast to enable quick utilization of the robot either in industry or in future household-assistant tasks. In this paper we show how to accelerate trajectory adaptation based on learning...
The overall performance of sampling-based motion planning algorithms strongly depends on the use of suitable sampling and connection strategies, as well as on the accuracy of the distance metric considered to select neighbor states. Defining appropriate strategies and metrics is particularly hard when considering robot dynamics, which is required to treat constrained motion planning problems for quadrotors...
Navigating non-holonomic mobile robots in dynamic environments is challenging because it requires computing at each instant, the space of collision free velocities, characterized by a set of highly non-linear and non-convex inequalities. Moreover, uncertainty in obstacle trajectories further increases the complexity of the problem, as it now becomes imperative to relate the space of collision free...
This paper explores the manipulation of a grasped object by pushing it against its environment. Relying on precise arm motions and detailed models of frictional contact, prehensile pushing enables dexterous manipulation with simple manipulators, such as those currently available in industrial settings, and those likely affordable by service and field robots.
Computing time optimal motions along specified paths forms an integral part of the solution methodology for many motion planning problems. Conventionally, this optimal control problem is solved considering piece-wise constant parametrization for the control input which leads to convexity and sparsity in the optimization structure. However, it also results in discontinuous control trajectory which...
In this article, we build dynamic models of 2D compliant links to evaluate injury level in a human-robot interaction. Safety is a premium concern for co-robotic systems. It has been studied that using compliant links in a robot can greatly reduce the injury level. Since most safety criteria are based on tolerance of acceleration of the operator's head during the impact, an efficient and yet accurate...
Given an articulated rigid body, we define the problem of estimating its dynamics as the problem of computing all the forces and accelerations acting on the bodies which constitute the articulated system. Similarly, we define the state estimation problem as the problem of computing the system positions and velocities. In the present paper we propose a framework for simultaneous state and dynamics...
This paper presents a trajectory tracking control strategy based on the subspace stabilization approach to accurately manipulate an under-actuated flying robot from a known initial state to the desired terminal state. To facilitate the development of this tracking strategy, the dynamical model of the quadrotor is firstly proposed. Subsequently, an optimal trajectory generation algorithm is adopted...
Traditional performance and energy scaling benefits based on technology improvements have slowed greatly. At the same time the demand for computing capability is unsatiated with new killer applications emerging in the domains of robotics, automotive, and machine-intelligence. Lack of progress in technology scaling will necessarily place more demands on the computer architecture and software layers...
Time optimal trajectory planning under various hard physical constraints plays a significant role in simultaneously meeting the requirements on high productivity and high accuracy in the fields of both machining tools and robotics. In this paper, the problem of time optimal trajectory planning is first formulated, and then a novel back and forward check algorithm is proposed to solve the minimum time...
In this paper a method is introduced that combines Inertial Measurement Unit (IMU) readouts with low accuracy and temporarily unavailable velocity measurements (e.g., based on kinematics or GPS) to produce high accuracy estimates of velocity and orientation with respect to gravity. The method is computationally cheap enough to be readily implementable in sensors. The main area of application of the...
The dynamics research of folded-deployable suspension of a new planetary exploration robot is carried out. The first three-order natural frequency and vibration mode of planetary robot in folded and deployable states are obtained respectively by finite element simulation analysis; the robot's natural frequencies in folded and deployable states are achieved respectively through vertical and horizontal...
Attitude Estimation is critical for balance control of Unicycle Robot, Accelerometers and gyroscopes are always used for posture detecting, and unscented Kalman filter(UKF) is adopted as sensors information fusion algorithm. Because the accelerometer is sensitive to external vibration and non-gravitational acceleration, the results of attitude estimation are extremely inaccurate. In order to overcome...
An adaptive energy-based swing-up controller for simple pendulums is presented. A state transformation from cartesian to polar phase space followed by approximation steps leads to the fundamental dynamics of the controlled simple pendulum. Based on the fundamental dynamics, the unknown natural frequency is estimated and a control gain is adjusted such that the system energy follows desired reference...
This paper is concerned with the development of motion safety criteria and associated proofs of safe operation for the class of reciprocal collision avoidance methods based on the relative velocity paradigm; including Velocity Obstacles (VO), Reciprocal Velocity Obstacles (ORCA), and Continuous Control Obstacles (CCO) - thus covering both holonomic and non-holonomic configurations. In the first part...
This paper addresses distributed average tracking for a group of physical double-integrator agents under an undirected graph without using velocity measurements. We introduce a discontinuous algorithm and filter to allow the agents to track the average of time-varying signals, where each agent needs the relative positions between itself and its neighbors and its neighbors' filter outputs but the requirement...
This paper investigates the behavior of central Jacobi differentiator in robot identification applications. Jacobi differentiator is a Jacobi orthogonal based algebraic differentiator. It is applied to compute acceleration from noisy position measurements. Moreover, its frequency domain property is analyzed via a finite impulse response (FIR) filter point of view, indicating clearly the differentiators...
In this paper we propose a new method to tackle the problem of discontinuous curvature observed in the time-optimal Dubins trajectories of car-like robots. The discontinuous curvature profile renders the paths untraceable by a real robot due to the existence of infinite accelerations at the transition points. To make way for a continuous curvature profile, we relax the idealized nonholonomic constraint...
This paper presents a compliant locomotion framework for torque-controlled humanoids using model-based whole-body control. In order to stabilize the centroidal dynamics during locomotion, we compute linear momentum rate of change objectives using a novel time-varying controller for the Divergent Component of Motion (DCM). Task-space objectives, including the desired momentum rate of change, are tracked...
Learning motion tasks in a real environment with deformable objects requires not only a Reinforcement Learning (RL) algorithm, but also a good motion characterization, a preferably compliant robot controller, and an agent giving feedback for the rewards/costs in the RL algorithm. In this paper, we unify all these parts in a simple but effective way to properly learn safety-critical robotic tasks such...
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