Omnidirectional Base Research Articles

Optimization of Circularly Polarized Omnidirectional Base Station Antenna by Machine Learning

Machine learning (ML) is a scientific technology related to data learning that can help machines learn patterns from existing complex data to predict future behavioral outcomes and trends. In this paper, we use 16 different ML algorithms and 5 different hyper-parameters optimal methods to model a circularly polarized omnidirectional base station antenna. The mean absolute error is 8.431, the root mean squared error is 11.100, the coefficient of determination is 0.967, and the adjusted coefficient of determination is 0.944, which means evaluation metrics are excellent.

Machine-Learning-Assisted Antenna Optimization With Data Augmentation

In this letter, a machine learning assisted antenna optimization method is proposed based on the random forest (RF) algorithm with data augmentation (DA). Using only a small number of samples, the prediction and optimization accuracy of the RF algorithm is ensured with repeated data augmentation, which balances different types of samples during the training. With the proposed DA-RF method, the AR bandwidth of a circularly polarized omnidirectional base station antenna is optimized. By learning the relationship between the loop orientations and the AR bandwidth efficiently, the AR bandwidth is improved by 41% compared with the best one in the samples. The estimation accuracy of the proposed method outperforms other similar methods, with fewer iterations as well. The method is also successfully applied to multi-objective optimizations.

Autonomous Wall-building and Firefighting: Team NimbRo’s UGV Solution for MBZIRC 2020

Autonomous robotic systems for various applications including transport, mobile manipulation, and disaster response are becoming more and more complex. Evaluating and analyzing such systems is challenging. Robotic competitions are designed to benchmark complete robotic systems on complex state-of-the-art tasks. Participants compete in defined scenarios under equal conditions. We present our UGV solution developed for the Mohamed Bin Zayed International Robotics Challenge 2020. Our hardware and software components to address the challenge tasks of wall-building and firefighting are integrated into a fully autonomous system. The robot consists of a wheeled, omnidirectional base, a 6 DoF manipulator arm equipped with a magnetic gripper, a highly efficient storage system to transport box-shaped objects, and a water-spraying system to extinguish fires. The robot perceives its environment using 3D LiDAR, as well as RGB and thermal camera-based perception modules and is capable of picking box-shaped objects and constructing a pre-defined wall structure. Its sensor modules also facilitate detecting and localizing heat sources to extinguish potential fires. A high-level planner coordinates and applies the robot’s skills to complete the Challenge tasks. We analyze and discuss our successful participation during the MBZIRC 2020 finals, present further experiments, and provide insights to our lessons learned.

Dynamic End Effector Tracking With an Omnidirectional Parallel Aerial Manipulator

To address the challenge of precise, dynamic and versatile aerial manipulation, we present an aerial manipulation platform consisting of a parallel 3-DOF manipulator mounted to an omnidirectional tilt-rotor aerial vehicle. The general modeling of a parallel manipulator on an omnidirectional floating base is presented, which motivates the optimization and detailed design of the aerial manipulator parameters and components. Inverse kinematic control of the manipulator is coupled to the omnidirectional base pose controller with a dynamic compensation term, going beyond common decoupled approaches. This presents a baseline for the control of redundant omnidirectional aerial manipulators. Experimental flights show the advantages of an active manipulator vs. a fixed arm for disturbance rejection and end effector tracking performance, as well as the practical limitations of the dynamic compensation term for fast end effector trajectories. The results motivate future studies for precise and dynamic aerial manipulation.

M-FABRIK: A New Inverse Kinematics Approach to Mobile Manipulator Robots Based on FABRIK

The inverse kinematics of mobile manipulators is a challenging problem due to the high degree of kinematic redundancy added by the coupling of the mobile platform and the manipulator. Some different approaches have been proposed to solve this problem, but most of them are either complex in terms of modelling and matrix calculation, with high computational cost and even with singularity problems, or slow in terms of convergence. This paper proposes a new approach for inverse kinematics of mobile manipulators based on the algorithm FABRIK. This new method, named M-FABRIK, has as main advantages the simplicity to implement, a fast convergence and a low computational cost, allowing real-time applications. Furthermore, this solution allows the robot to be positioned according to various criteria, such as decreasing convergence time, avoiding contact with obstacles, avoiding joint angle limits, increasing robot manipulability or even decreasing joint effort, besides avoiding matrix inversion and being robust to singularities. The proposed approach is illustrated by simulation considering a 5 DOF manipulator mounted on an omnidirectional base for a path-tracking task in different environments, including obstacles. A comparison between the proposed approach and classical methods is also presented.

Dynamical Obstacle Avoidance of Task- Constrained Mobile Manipulation Using Model Predictive Control

Task-constrained motion planning (TCMP) is involved in many practical applications, such as opening the door, opening the drawer, twisting the screw, and so on. Because of the trend of man-machine collaboration and the existence of dynamic in environments, planning the collision-free motions for task-constrained manipulation is a significative problem. This paper explores the TCMP issue for mobile manipulation, which uses a mobile base to enhance the working range and flexibility but simultaneously makes the problem harder than that of single manipulation because of the additional degrees of freedom (dofs). We propose an optimization-based method to plan the obstacle avoidance motion in real-time. First, the global robotic Jacobian matrix that combines the omnidirectional base and the robotic arm is derived. Second, model predictive control is used to plan the control rule in order to maximize the closest distance between the obstacles and the mobile manipulator and minimize the velocities of null space at the same time. We have deduced the model with four differential equations that represent the law of the distance over time. Third, the distances are calculated and sent to the model to calculate the velocity of each joint of the arm and the base using ACADO that is an open-source toolkit. Using the velocities, the mobile manipulator can move away from the approaching people while still fixing the end of the arm to manipulate tool at the same time. Our method is verified on the mobile manipulator that consists of four Mecanum wheels, a base, a UR10 arm, and four kinect cameras in Gazebo simulation with using the ROS operation.

Team NimbRo at MBZIRC 2017: Autonomous valve stem turning using a wrench

AbstractThe Mohamed Bin Zayed International Robotics Challenge (MBZIRC) 2017 has defined ambitious new benchmarks to advance the state‐of‐the‐art in autonomous operation of ground‐based and flying robots. In this study, we describe our winning entry to MBZIRC Challenge 2: the mobile manipulation robot Mario. It is capable of autonomously solving a valve manipulation task using a wrench tool detected, grasped, and finally used to turn a valve stem. Mario’s omnidirectional base allows both fast locomotion and precise close approach to the manipulation panel. We describe an efficient detector for medium‐sized objects in three‐dimensional laser scans and apply it to detect the manipulation panel. An object detection architecture based on deep neural networks is used to find and select the correct tool from grayscale images. Parametrized motion primitives are adapted online to percepts of the tool and valve stem to turn the stem. We report in detail on our winning performance at the challenge and discuss lessons learned.

Optimal Paths for Polygonal Robots in SE(2)

We consider planar navigation for a polygonal, holonomic robot in an obstacle-filled environment in SE(2). To determine the free space, we first represent obstacles as point clouds in the robot configuration space (C). A point-wise Minkowski sum of the robot and obstacle points is then calculated in C using obstacle points and robot convex hull points for varying robot configurations. Using graph search, we obtain a seed path, which is used in our novel method to compute overlapping convex regions for consecutive seed path chords. The resulting regions provide collision-free space useful for finding feasible trajectories that optimize a specified cost functional. The key contribution is the proposed method's ability to easily generate a set of convex, overlapping polytopes that effectively represent the traversable free space. This, in turn, lends itself to (a) efficient computation of optimal paths in ℝ3 and (b) extending these basic ideas to the special Euclidean space SE(2). We provide simulated examples and implement this algorithm on a KUKA youBot omnidirectional base.

A RECONFIGURABLE BROADBAND DUAL-MODE DUAL-POLARIZED ANTENNA FOR SECTORIAL/OMNIDIRECTIONAL MOBILE BASE STATIONS

© 2018, Electromagnetics Academy. All rights reserved. This paper proposes a new design of reconfigurable three-sector dual-mode dual-polarized antenna for use primarily in mobile communication base stations. The design offers the flexibility to be used as a sectorial (directive) or omnidirectional base station antenna whenever required. The two different radiating modes (omnidirectional and sectorial) depend only on the excitation scenario. The proposed antenna has the advantages of offering broadband, stable radiation pattern and high polarization purity within the desired frequency band, and a simple feeding structure with a very compact size (less than 800 cm3) and low profile. The achieved fractional bandwidth is 55.3% (1.7 - 3GHz). A prototype antenna was constructed and tested with the two modes of operation. Results demonstrate the principle of the design and show how the design may be packaged in a compact size to offer excellent omnidirectional or sectorial performance which makes this new design an ideal candidate for reconfigurable dual-mode mobile base stations.

A novel design of an omnidirectional wheelchair

Wheelchair users are not able to move around as easily as someone on foot. For those not in a wheelchair, to move sideways, perhaps alongside a work surface, generally just requires a step to the left or right. Someone in a wheelchair however must shuffle his/her wheelchair forwards and backwards several times. The more restricted the space available, the more difficult this is. A solution to this is to use an omnidirectional wheelchair, which can translate left and right, and rotate on the spot as well as the more conventional movements. Several projects have addressed this problem in the past but have been complex and expensive and haven't worked on all floor surfaces. The authors have developed concepts for a simple and robust omnidirectional base and plan to integrate this into a new wheelchair design. This paper will describe these concepts, and discuss work in progress on realising these aims.

28 GHz omni-directional quasi-optical transmitter array

Omni-directional base stations are needed in many emerging wireless communication systems. This paper presents the first adaptation of a quasi-optical oscillator array for this purpose. A 28 GHz active oscillator element containing a modified Vivaldi endfire antenna is utilized as the unit cell. Twelve of these are incorporated into the circular array, which is powered from a single DC power supply. The array has a high combining efficiency and remains frequency-locked over a span of 600 MHz. >

Radio propagation at microwave frequencies for line-of-sight microcellular mobile and personal communications

A propagation experiment has been designed and conducted at 900 MHz and 11 GHz to characterize microcell channels using various antennas at two distinct frequencies. It is found that propagation in rural areas is dominated by interference between the direct, line-of-sight ray and a specular roadway-reflected ray. In urban areas, the addition of four specular wall-reflected rays adequately represents microcell propagation. The dependence of mean power falloff, measured mean power and calculated power on distance was determined. The lambda /2 scale microvariations of the received power are reduced compared to the variations in present cellular radio systems. For urban sites using omnidirectional base and mobile antennas, the RMS delay spread due to road- and wall-reflected rays was obtained from a six-ray model. Using a 20-dB horn for the mobile antenna can reduce this delay spread.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Experimental study of UHF mobile radio transmission using a directive antenna

Propagation experiments were run at 836 Mc between a fixed omnidirectional base station and a mobile station using a directional antenna. On typical residential streets it was found that the antenna orientation had only a small effect on the average signal level and that the fading rate was significantly reduced. It was also discovered that the fading rate expressed as a function of antenna direction has definite minima and maxima. These are related to two factors, the direction of motion of the vehicle and the direction from the vehicle to the base station. In general, minimum fading occurs along and at right angles to the direction of motion and in the direction of the base station.