3D Coordinated Path Following with Disturbance Rejection for Formations of Under-actuated Agents

In this paper coordinated path following for formations of under-actuated agents in three dimensional space is considered. The agents are controlled to follow a straight-line path whilst being affected by an unknown environmental disturbance. The problem is solved using a twofold approach. In particular, the agents are controlled to the desired path using a guidance law that rejects an unknown, but constant, disturbance. Simultaneously each agent utilises a decentralised nonlinear coordination law to achieve the desired formation. The closed-loop system of path-following and coordination dynamics is analysed using theory for feedback-interconnected systems. In particular, a technique from [1] is used that allows us to analyse a feedback-interconnected systems as a cascaded system. The origin of the closed-loop error dynamics is shown to be globally asymptotically stable. A case study with simulation results is presented to validate the control strategy.(c) 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works

Underactuated leader-follower synchronisation for multi-agent systems with rejection of unknown disturbances

Author preprintIn this paper leader-follower synchronization is considered for underactuated followers in an inhomogeneous multi-agent system. The goal is to synchronise the motion of a leader and an underactuated follower. Measurements of the leader's position and velocity are available, while the dynamics and trajectory of the leader is unknown. The leader velocities are used as input for a constant bearing guidance algorithm to assure that the follower synchronises its motion to the leader. It is also shown that the proposed leader-follower scheme can be applied to multi-agent systems that are subjected to unknown environmental disturbances. Furthermore, the trajectory of the leader does not need to be known. The stability properties of the complete control scheme and the unactuated internal dynamics are analysed using nonlinear cascaded system theory. Simulation results are presented to validate the proposed control strategy.Preprint version. © IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works

Autonomous ROV inspections of aquaculture net pens using DVL

This article presents a method for guiding a remotely operated vehicle (ROV) to autonomously traverse an aquaculture net pen. The method is based on measurements from a Doppler velocity log (DVL) and uses the measured length of the DVL beam vectors to approximate the geometry of a local region of the net pen in front of the ROV. The ROV position and orientation relative to this net pen approximation are used as inputs to a nonlinear guidance law. The guidance law is based upon the line-of-sight (LOS) guidance law. By utilizing that an ROV is fully actuated in the horizontal plane, the crosstrack error is minimized independently of the ROV heading. A Lyapunov analysis of the closed-loop system with this guidance law shows that the ROV is able to follow a continuous path in the presence of a constant irrotational ocean current. Finally, results from simulations and experiments demonstrating the performance of the net pen approximation and control system are presented.acceptedVersio

Line-of-Sight Path Following for Dubins Paths with Adaptive Sideslip Compensation of Drift Forces

This is the author’s final, accepted and refereed manuscript to the article.We present a nonlinear adaptive path-following controller that compensates for drift forces through vehicle sideslip. Vehicle sideslip arises during path following when the vehicle is subject to drift forces caused by ocean currents, wind and waves. The proposed algorithm is motivated by a lineof-sight (LOS) guidance principle used by ancient navigators, which is here extended to path following of Dubins paths. The unknown sideslip angle is treated as a constant parameter, which is estimated using an adaptation law. The equilibrium points of the cross-track and parameter estimation errors are proven to be uniformly semiglobally exponentially stable (USGES). This guarantees that the estimated sideslip angle converges to its true value exponentially. The adaptive control law is in fact an integral LOS controller for path following since the parameter adaptation law provides integral action. The proposed guidance law is intended for maneuvering in the horizontal-plane at given speeds and typical applications are marine craft, autonomous underwater vehicles (AUVs), unmanned aerial vehicles (UAVs) as well as other vehicles and craft where the goal is to follow a predefined parametrized curve without time constraints. Two vehicle cases studies are included to verify the theoretical results.http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6868251 "(c) 2014 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works.

Experimental Results for Set-based Control within theSingularity-robust Multiple Task-priority Inverse KinematicsFramework

Inverse kinematics algorithms are commonly used in robotic systems to achieve desired behavior, and several methods exist to ensure the achievement of numerous tasks simultaneously. The multiple task-priority inverse kinematics framework allows a consideration of tasks in a prioritized order by projecting task velocities through the null-spaces of higher priority tasks. Recent results have extended this framework from equality tasks to also handling set-based tasks, i.e. tasks that have an interval of valid values. The purpose of this paper is to further investigate and experimentally validate this algorithm and its properties. In particular, this paper presents experimental results where a number of both set-based and equality tasks have been implemented on the 6 Degree of Freedom UR5 which is an industrial robotic arm from Universal Robots. The experiments validate the theoretical results.(c) 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works

Keefektifan Strategi Pembelajaran antara Metode Tutor Sebaya dengan Metode Tanya Jawab dalam Pengajaran Remidial Materi Fungsi Limit

Aktivitas belajar tidak selamanya dapat berjalan dengan lancar, peserta didik seringkali mengalami kesulitan dalam belajar, baik dalam hal menerima pelajaran, menyerap pelajaran, atau kedua-duanya. Kesulitan belajar dapat dilihat dengan adanya seorang atau sekelompok peserta didik yang tidak dapat mencapai hasil belajar yang diinginkan.Tujuan penelitian ini adalah untuk mengetahui ada tidaknya perbedaan prestasi belajar matematika antara peserta didik yang diremidi menggunakan metode tutor sebaya dengan peserta didik yang diremidi menggunakan metode tanya jawab. dan jika ada, manakah yang lebih efektif dari dua metode pembelajaran tersebut.Hasil penelitian ini mengambil lokasi di Madrasah Aliyah Negeri Kota Tegal tahun pelajaran 2011/2012. Populasi dalam penelitian ini adalah para peserta didik kelas XI IPS yang nilai ulangan harinya dibawah KKM pada materi fungsi limit semester genap. Sampel sebanyak 2 kelas diambil menggunakan teknik cluster random sampling terambil kelas XI IPS 1 dan XI IPS 2 dengan jumlah 76 peserta didik. Metode pengumpulan data yang dipakai adalah metode dokumentasi dan tes untuk mempereoleh data tentang populasi dan sampel serta prestasi belajar sebelum dan sesudah pengajaran remidial. Analisis data menggunakan uji-t dua pihak digunakan untuk menentukan ada tidaknya perbedaan prestasi belajar matematika antara peserta didik yang diremidi menggunakan kedua metode tersebut dan uji-t satu pihak untuk untuk menetukan metode pembelajaran yang lebih efektif.Hasil penelitian menunjukan bahwa ada perbedaan prestasi belajar matematika antara peserta didik yang diremidi menggunakan metode tutor sebaya dengan peserta didik yang diremidi menggunakan metode tanya jawab. Penerapan metode pembelajaran tutor sebaya lebih efektif daripada metode pembelajaran tanya jawab

Distributed MPC for Formation Path-Following of Multi-Vehicle Systems

The paper considers the problem of formation path-following of multiple vehicles and proposes a solution based on combining distributed model predictive control with parametrizations of the trajectories of the vehicles using polynomial splines. Introducing such parametrization leads indeed to two potential benefits: A) reducing the number of optimization variables, and b) enabling enforcing constraints on the vehicles in a computationally efficient way. Moreover, the proposed solution formulates the formation path-following problem as a distributed optimization problem that may then be solved using the alternating direction method of multipliers (ADMM). The paper then analyzes the effectiveness of the proposed method via numerical simulations with surface vehicles and differential drive robotspublishedVersio

Formation Control of Underactuated Bio-inspired Snake Robots

This paper considers formation control of snake robots. In particular, based on a simplified locomotion model, and using the method of virtual holonomic constraints, we control the body shape of the robot to a desired gait pattern defined by some pre-specified constraint functions. These functions are dynamic in that they depend on the state variables of two compensators which are used to control the orientation and planar position of the robot, making this a dynamic maneuvering control strategy. Furthermore, using a formation control strategy we make the multi-agent system converge to and keep a desired geometric formation, and enforce the formation follow a desired straight line path with a given speed profile. Specifically, we use the proposed maneuvering controller to solve the formation control problem for a group of snake robots by synchronizing the commanded velocities of the robots. Simulation results are presented which illustrate the successful performance of the theoretical approach.© ISAROB 2016. This is the authors' accepted and refereed manuscript to the article. Locked until 2017-07-27

Stability Analysis for Set-based Control within the Singularity-robust Multiple Task-priority Inverse Kinematics Framework

Inverse kinematics algorithms are commonly used in robotic systems to accomplish desired behavior, and several methods exist to ensure the achievement of several tasks simultaneously. The multiple task-priority inverse kinematics framework allows tasks to be considered in a prioritized order by projecting task velocities through the nullspaces of higher priority tasks. This paper extends this framework to handle set-based tasks, i.e. tasks with a range of valid values, in addition to equality tasks, which have a specific desired value. Examples of such tasks are joint limit and obstacle avoidance. The proposed method is proven to ensure asymptotic convergence of the equality task errors and the satisfaction of all high-priority set-based tasks. Simulations results confirm the effectiveness of the proposed approach.(c) 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works

Analysis of underwater snake robot locomotion based on a control-oriented model

This paper presents an analysis of planar underwater snake robot locomotion in the presence of ocean currents. The robot is assumed to be neutrally buoyant and move fully submerged with a planar sinusoidal gait and limited link angles. As a basis for the analysis, an existing, controloriented model is further simplified and extended to general sinusoidal gaits. Averaging theory is then employed to derive the averaged velocity dynamics of the underwater snake robot from that model. It is proven that the averaged velocity converges exponentially to an equilibrium, and an analytical expression for calculating the forward velocity of the robot in steady state is derived. A simulation study that validates both the proposed modelling approach and the theoretical results is presented.Prepint - (c) 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works