A novel model for layer jamming-based continuum robots

Continuum robots with variable stiffness have gained wide popularity in the last decade. Layer jamming (LJ) has emerged as a simple and efficient technique to achieve tunable stiffness for continuum robots. Despite its merits, the development of a control-oriented dynamical model tailored for this specific class of robots remains an open problem in the literature. This paper aims to present the first solution, to the best of our knowledge, to close the gap. We propose an energy-based model that is integrated with the LuGre frictional model for LJ-based continuum robots. Then, we take a comprehensive theoretical analysis for this model, focusing on two fundamental characteristics of LJ-based continuum robots: shape locking and adjustable stiffness. To validate the modeling approach and theoretical results, a series of experiments using our \textit{OctRobot-I} continuum robotic platform was conducted. The results show that the proposed model is capable of interpreting and predicting the dynamical behaviors in LJ-based continuum robots

Simultaneous Position-and-Stiffness Control of Underactuated Antagonistic Tendon-Driven Continuum Robots

Continuum robots have gained widespread popularity due to their inherent compliance and flexibility, particularly their adjustable levels of stiffness for various application scenarios. Despite efforts to dynamic modeling and control synthesis over the past decade, few studies have focused on incorporating stiffness regulation in their feedback control design; however, this is one of the initial motivations to develop continuum robots. This paper aims to address the crucial challenge of controlling both the position and stiffness of a class of highly underactuated continuum robots that are actuated by antagonistic tendons. To this end, the first step involves presenting a high-dimensional rigid-link dynamical model that can analyze the open-loop stiffening of tendon-driven continuum robots. Based on this model, we propose a novel passivity-based position-and-stiffness controller adheres to the non-negative tension constraint. To demonstrate the effectiveness of our approach, we tested the theoretical results on our continuum robot, and the experimental results show the efficacy and precise performance of the proposed methodology

Mathematical Modelling of Container Transfers for a Fleet of Autonomous Straddle Carriers

Abstract-The main contribution of this paper is a mathematical model describing performance metrics for coordinating multiple mobile robots in a seaport container terminal. The scenario described here requires dealing with many difficult practical challenges such as the presence of multiple levels of container stacking and sequencing, variable container orientations, and vehicular dynamics that require finite acceleration and deceleration times. Furthermore, in contrast to the automatically guided vehicle planning problem in a manufacturing environment, the container carriers described here are free ranging. Although, the port structure imposes a set of "virtual" roadways along which the vehicles are allowed to travel, path planning is essential in preventing contention and collisions. A performance metric which minimises total yard-vehicle usage, while producing robust traffic plans by encouraging both early starting and finishing of jobs is presented for different vehicle fleet sizes and job allocation scenarios. I. INTRODUCTION T seaport terminals, reducing the turnaround time of berthed ships and docked trucks in a highly uncertain and dynamic environment are the most significant factors in reducing the overall transportation cost of containers. A secondary, but competing objective is to minimise the utilisation of yard resources, in this case a fleet of autonomous straddle carriers (SCs). Any delays experienced while performing yard jobs using the SCs will impact the throughput of the entire seaport. In this paper, we formulate a mathematical model which incorporates many of the challenging practicalities of an operational seaport container terminal. Including various nonlinear constraints related to the spatial and temporal aspects of SCs interacting with containers. Unlike many seaport terminals, which utilise yard vehicles that are either manned or fixed upon a circuit of tracks We have also proposed a sequencing parameter to account for multiple levels or stacks of containers stored in the yard. Stacking, creates an exclusion constraint for the set-down and pickup of containers, i.e. it is not possible to place a container on the upper tier without a container on the ground tier and it is not possible to pickup a container on the ground tier without initially removing a container present on the upper tier. Similarly, a sequencing parameter is proposed to solve the problem of loading and unloading of containers from trucks in a required order. Another significant challenge is to address the orientation of containers as they are transported between the yard, ship(s) and truck(s). Since the orientation of containers placed onto ships and onto trucks is fixed in a single direction, path planning must consider the orientation at both the initial and destination nodes. In order to guarantee the required orientation prior to loading containers onto ships or trucks we model the changes in alignment during transportation (flip movement) as a container is transported from its initial node to destination node. Furthermore, we have developed an objective function which considers the competing objectives of minimising the total SC utilisation while maximising the throughput of yard jobs. Here, the throughput of yard jobs is increased by encouraging the early starting and early finishing of jobs. Our approach does not introduce bias towards the allocation of short or long jobs, which can result in traffic plans that are more robust to uncertainties within the seaport. Once a method for determining optimal yard operations is established, prudent investment in capital and changes to the seaport infrastructure can be more accurately measured. Apart from providing an excellent survey of the principle logistics processes and operations within current container terminals, the authors in In a recent study, Preston and Kozan [4] examined mathematical modelling and optimisation using genetic algorithm and tabu search of the sea interfaces, specifically the transfer of export containers from the storage to berthed ships. Their implementation of the model and optimisation algorithms is capable of handling large problems that arise in the quay side operations. However, this study deals exclusively with import and export containers between the ship and the yard and does not include a comprehensive model that considers yard-to-yard and yard-truck transportations or other practicalities. Also, Hartmann [5] proposed a general model for various scheduling problems that occur in container terminal logistics. The scheduling model consists of the assignment of jobs to resources and the temporal arrangement of the jobs subject to precedence constraints and sequence-dependent setup times. The model was applied to solve problems for SCs, AGVs, stacking cranes, and workers who handle reefer containers in the port of Hamburg. Good solutions where obtained using a resource constrained genetic algorithm. Mathematical Modelling of Container Transfers for a Fleet of Autonomous Straddle Carriers The main contributions of this paper include the formulation of a mathematical model of a large and difficult multi-objective optimisation problem involving a fleet of fully autonomous SCs. The model formulation includes all container handling subsystems of an automated container terminal operating in Brisbane, Australia II. MATHEMATICAL MODEL A. Overview of Container Terminal Environment A yard environment map has been developed to model the actual Fisherman Islands Depot located within the Port of Brisbane, Australia. The yard environment map consists of 18380 positional nodes and 83155 predefined links. Currently, there are 23 autonomous SCs operating within the actual yard environment. The working area is strictly confined and SCs can travel freely from position to position, along predefined paths (links). Thus, the problem of optimising the assignment of tasks to SCs (task allocation) is complicated by the additional requirement to ensure safety through collision-free path planning, while attempting to meet the overall objective of minimizing the turnaround time of berthed ships and trucks docked at the truck import area. Considering the requirements, let the map be represented by a graph Using a graph to represent the seaport map allows for the accurate determination of position and trajectory information at any time. As a result, both collision-free paths and optimal task allocation (online scheduling) can be calculated at any time for the purpose of the replanning problem. B. Definitions of Parameters and Variables This section further describes the model parameters and variables. Considering yard operations only, we can establish the following definitions. Since the orientation of containers is fixed in a single direction for both ships and trucks, path planning must consider the orientation at the initial and destination nodes. To guarantee the orientation at the destination node we model the alignment and changes in alignment during transportation (flip movements) as a container is transported from its initial node to destination node. C. Definition of Container Orientation and Vehicle Trajectory 1263 In order to achieve optimal task allocation of SCs at anytime, we must be able to accurately determine the relative timings for all jobs. D. Objective Functions and Constraints The fundamental idea of implementing cost functions as part of the model formulation is to permit input of a desired work throughput, which can be translated by an additional controller into required rates and resourcing levels. In this paper, we assume that the sequence of both import and export containers for ships and trucks are specified a priori and provided to the task allocation and path planning algorithms. The cost function for SC usage V V i is given by: Given the highly dynamic nature of the yard operations and the other seaport resources, the probability of unexpected events which result in delays to the short term traffic plan (schedule) can be quantified. As such, the robustness of a given traffic plan may be assessed by the level of impact such stochastic delay events have on the short term traffic plan. In order to improve the robustness of traffic plans, the following bonus function aims to encourage early start and finish times for both short jobs and long jobs. The bonus function is given by: Where, from Eq(2) and the problem definitions

Direct observation of precipitation along twin boundaries and dissolution in a magnesium alloy annealing at high temperature

Precipitation along twin boundaries and dissolution in a cold-rolled Mg-Y-Nd alloy was directly observed for the first time during annealing at 490 °C. Precipitation occurred concurrently with recrystallization and the combined effect of precipitation and solute segregated to twin boundaries modified the recrystallization behaviour. Precipitates later dissolved into the matrix at the point where full recrystallization was nearly complete. The precipitates and higher solute concentration along original twin boundaries hindered grain growth of newly formed recrystallized grains. Even where twin boundaries had been consumed by recrystallization, the size of recrystallized grains were still controlled by the pre-existing twin boundaries

An Enhanced Dynamic Model for McKibben Pneumatic Muscle Actuators

Abstract An enhanced dynamic force model of a type of small and soft McKibben-type pneumatic muscle (PM) actuator has been developed. This model takes the factor of external loads and a more sophisticated form of friction into account, and is presented as a polynomial function of pressure, contraction length, contraction velocity and external load. The coefficients in this model are determined from a series of experiments with constant loads and step pressure inputs. Comparison study with other models is conducted assuming the Coulomb friction as a constant force. The results demonstrate a solid enhancement of the presented model

Design of autonomous land vehicle

This report is the final report of the Final Year Project A081 Design of Au- tonomous Land Vehicle of School of Mechanical and Aerospace Engineering, Nanyang Technological University, Singapore. In this project, an autonomous land vehicle is designed with input capabilities, processing capabilities, output capabilities and communication capabilities. Especially, this vehicle is designed to serve as an Urban Search and Rescue (USAR) robot after earthquake and will be put in test for RoboCup Rescue Robot League competition. The robot is equipped with one pair of triangular tracked wheels, one pair of flipper tracked wheels and a mechanical arm to explore and interact with the disaster environment. Equipped with an embedded AI computing device and a mini PC, the robot is designed to have fully autonomous control capability with the support of rich environment data from stereo camera, LiDAR, IMU and other sensors. The robot can be accessed by WiFi from any portable smart device, like laptops and smart phones. With the connection, the robot state can be monitored and the user’s command can be sent to the robot. To achieve autonomous navigation capability, 2D and 3D map will be generated with SLAM and the data will be used for path planning and object detection and recolonization in real time.Bachelor of Engineering (Mechanical Engineering

Decoupling control law for structural control implementation

Multi-story buildings, subjected to wind or earthquake excitation, can be modeled as multi-degree of freedom (MDOF) systems defined by a set of coupled second order ordinary differential equations. In this paper, the dynamic coupling characteristics of multi-story building are examined, and it is found that the coupled property in a system can be described as a positive feedback from the control theory point of view. This positive feedback property of a MDOF system may intensify structural vibration. For the structural control implementation, open-loop and closed-loop decoupling control laws are proposed. All coupled “channels” of the system are “broken off” when the vibration control design is based on the proposed control laws. A complex MDOF structural system, therefore, is equivalent to a set of single degree of freedom (SDOF) systems, and the control design can be carried out independently for any specific degree of freedom. Thus, the proposed control laws provide an efficient tool by which the vibration of a selected floor can be suppressed without any effect on its neighboring floors because the control is one to one. Meanwhile, the computational procedure of the control design can be significantly simplified because all analyses and design are conducted based on SDOF systems