Wheeled Mobile Robots: State of the Art Overview and Kinematic Comparison Among Three Omnidirectional Locomotion Strategies

In the last decades, mobile robotics has become a very interesting research topic in the feld of robotics, mainly because of population ageing and the recent pandemic emergency caused by Covid-19. Against this context, the paper presents an overview on wheeled mobile robot (WMR), which have a central role in nowadays scenario. In particular, the paper describes the most commonly adopted locomotion strategies, perception systems, control architectures and navigation approaches. After having analyzed the state of the art, this paper focuses on the kinematics of three omnidirectional platforms: a four mecanum wheels robot (4WD), a three omni wheel platform (3WD) and a two swerve-drive system (2SWD). Through a dimensionless approach, these three platforms are compared to understand how their mobility is afected by the wheel speed limitations that are present in every practical application. This original comparison has not been already presented by the literature and it can be used to improve our understanding of the kinematics of these mobile robots and to guide the selection of the most appropriate locomotion system according to the specifc application

Mobile Robots Navigation

Mobile robots navigation includes different interrelated activities: (i) perception, as obtaining and interpreting sensory information; (ii) exploration, as the strategy that guides the robot to select the next direction to go; (iii) mapping, involving the construction of a spatial representation by using the sensory information perceived; (iv) localization, as the strategy to estimate the robot position within the spatial map; (v) path planning, as the strategy to find a path towards a goal location being optimal or not; and (vi) path execution, where motor actions are determined and adapted to environmental changes. The book addresses those activities by integrating results from the research work of several authors all over the world. Research cases are documented in 32 chapters organized within 7 categories next described

Mobile Robot Localization Based on Kalman Filter

Robot localization is one of the most important subjects in the Robotics science. It is an interesting and complicated topic. There are many algorithms to solve the problem of localization. Each localization system has its own set of features, and based on them, a solution will be chosen. In my thesis, I want to present a solution to find the best estimate for a robot position in certain space for which a map is available. The thesis started with an elementary introduction to the probability and the Gaussian theories. Simple and advanced practical examples are presented to illustrate each concept related to localization. Extended Kalman Filter is chosen to be the main algorithm to find the best estimate of the robot position. It was presented through two chapters with many examples. All these examples were simulated in Matlab in this thesis in order to give the readers and future students a clear and complete introduction to Kalman Filter. Fortunately, I applied this algorithm on a robot that I have built its base from scratch. MCECS-Bot was a project started in Winter 2012 and it was assigned to me from my adviser, Dr. Marek Perkowski. This robot consists of the base with four Mecanum wheels, the waist based on four linear actuators, an arm, neck and head. The base is equipped with many sensors, which are bumper switches, encoders, sonars, LRF and Kinect. Additional devices can provide extra information as backup sensors, which are a tablet and a camera. The ultimate goal of this thesis is to have the MCECS-Bot as an open source system accessed by many future classes, capstone projects and graduate thesis students for education purposes. A well-known MRPT software system was used to present the results of the Extended Kalman Filter (EKF). These results are simply the robot positions estimated by EKF. They are demonstrated on the base floor of the FAB building of PSU. In parallel, simulated results to all different solutions derived in this thesis are presented using Matlab. A future students will have a ready platform and a good start to continue developing this system

Formation Navigation and Relative Localisation of Multi-Robot Systems

When proceeding from single to multiple robots, cooperative action is one of the most relevant topics. The domain of robotic security systems contains typical applications for a multi-robot system (MRS). Possible scenarios are safety and security issues on airports, harbours, large industry plants or museums. Additionally, the field of environmental supervision is an up-coming issue. Inherent to these applications is the need for an organised and coordinated navigation of the robots, and a vital prerequisite for any coordinated movements is a good localisation. This dissertation will present novel approaches to the problems of formation navigation and relative localisation with multiple ground-based mobile robots. It also looks into the question what kind of metric is applicable for multi-robot navigation problems. Thereby, the focus of this work will be on aspects of 1. coordinated navigation and movement A new potential-field-based approach to formation navigation is presented. In contradiction to classical potential-field-based formation approaches, the proposed method also uses the orientation between neighbours in the formation. Consequently, each robot has a designated position within the formation. Therefore, the new method is called directed potential field approach. Extensive experiments prove that the method is capable of generating all kinds of formation shapes, even in the presence of dense obstacles. All tests have been conducted with simulated and real robots and successfully guided the robot formation through environments with varying obstacle configurations. In comparison, the nondirected potential field approach turns out to be unstable regarding the positions of the robots within formations. The robots strive to switch their positions, e.g. when passing through narrow passages. Under such conditions the directed approach shows a preferable behaviour, called “breathing”. The formation shrinks or inflates depending on the obstacle situation while trying to maintain its shape and keep the robots at their desired positions inside the formation. For a more particular comparison of formation algorithms it is important to have measures that allow a meaningful evaluation of the experimental data. For this purpose a new formation metric is developed. If there are many obstacles, the formation error must be scaled down to be comparable to an empty environment where the error would be small. Assuming that the environment is unknown and possibly non-static, only actual sensor information can be used for these calculations. We developed a special weighting factor, which is inverse proportional to the “density” of obstacles and which turns out to model the influence of the environment adequately. 2. relative localisation A new method for relative localisation between the members of a robot group is introduced. This relative localisation approach uses mutual sensor observations to localise the robots with respect to other objects – without having an environment model. Techniques like the Extended Kalman Filter (EKF) have proven to be powerful tools in the field of single robot applications. This work presents extensions to these algorithms with respect to the use in MRS. These aspects are investigated and combined under the topic of improving and stabilising the performance of the localisation and navigation process. Most of the common localisation approaches use maps and/or landmarks with the intention of generating a globally consistent world-coordinate system for the robot group. The aim of the here presented relative localisation approach, on the other hand, is to maintain only relative positioning between the robots. The presented method enables a group of mobile robots to start at an unknown location in an unknown environment and then to incrementally estimate their own positions and the relative locations of the other robots using only sensor information. The result is a robust, fast and precise approach, which does not need any preconditions or special assumptions about the environment. To validate the approach extensive tests with both, real and simulated, robots have been conducted. For a more specific evaluation, the Mean Localisation Error (MLE) is introduced. The conducted experiments include a comparison between the proposed Extended Kalman Filter and a standard SLAM-based approach. The developed method robustly delivered an accuracy better than 2 cm and performed at least as well as the SLAM approach. The algorithm coped with scattered groups of robots while moving on arbitrarily shaped paths. In summary, this thesis presents novel approaches to the field of coordinated navigation in multi-robot systems. The results facilitate cooperative movements of robot groups as well as relative localisation among the group members. In addition, a solid foundation for a non-environment related metric for formation navigation is introduced

Modular Omni-directional AGV Developmental Platform with Integrated Suspension, Power-plant and Control Systems

The thesis focuses on the development of an industrial automatic guided vehicle (AGV) with omni-directional capabilities. The omni-directional strategy used was the "swerve drive" system, a system whereby a wheel can be rotated about both its y axis (rolling axis) and z axis (vertical axis). Unlike most commonly used swerve drive systems that have swerve capabilities on each wheel attached to the body of the vehicle, this research seeks to reduce cost by only having swerve capabilities on two diagonal wheels. The remaining two wheels will act as castor units. AC drives are used on the system in place of more traditional DC drives, due to their cost vs capability advantage over DC and their prevalence in the industrial environment. Since an AGV is a mobile platform any power source found on it is usually derived from batteries, a DC source. Usage of DC introduces several limitations including difficulty transforming voltage levels for different systems, inability to run AC drives directly from the power source and comparably larger conduction wires. These limitations were overcome by adding a stand-alone power-plant on the AGV in the form of an inverter. The inverter transformed the DC power supplied by a battery bank from 48 volts DC to 230 volts AC. Thus, the primary focus of this research is on the development and validation of a novel two wheel omni-directional drive system that makes use of inexpensive and readily available components that have already been proven to work in industry.Thesis (PhD) -- Faculty of Engineering, the Built Environment, and Technology, 202

Developing a Semi-autonomous Robot to Engage Children with Special Needs and Their Peers in Robot-Assisted Play

Despite the wide variety of robots used in human-robot interaction (HRI) scenarios, the potential of robots as connectors whilst acting as play mediators has not been fully explored. Robots present an opportunity to redefine traditional game scenarios by being physical embodiments of agents/game elements. Robot assisted play has been used to reduce the barriers that children with physical special needs experience. However, many projects focus on child-robot interaction rather than child-child interaction. In an attempt to address this gap, a semi-autonomous mobile robot, MyJay, was created. This thesis discusses the successful development of MyJay and its potential contribution in future HRI studies. MyJay is an open-source robot that plays a basketball-like game. It features light and color for communicative feedback, omni-directional mobility, robust mechanisms, adjustable levels of autonomy for dynamic interaction, and a child-friendly aesthetically-pleasing outer shell. The design process included target users such as children with special needs and therapists in order to create a robot that ensures repeated use, engagement, and long-term interaction. A hybrid approach was taken to involve stakeholders, combining user-centered design and co-design, exemplifying that children can be included in the creation process even when it is not possible to hold in-person co-design sessions due to COVID-19. Aside from the care taken to meet user requirements, the robot was designed with researchers in mind, featuring extensible software and ROS compatibility. The frame is constructed from aluminum to ensure rigidity, and most functional parts related to gameplay are 3D printed to allow for quick swapping, should a need to change game mechanics arise. The modularity in software and in mechanical aspects should increase the potential of MyJay as a valuable research tool for future HRI studies. Finally, a novel framework to simulate teleoperation difficulties for individuals with upper-limb mobility challenges is proposed, along with a dynamic assistance algorithm to aid in the teleoperation process

Distributed navigation of multi-robot systems for sensing coverage

A team of coordinating mobile robots equipped with operation specific sensors can perform different coverage tasks. If the required number of robots in the team is very large then a centralized control system becomes a complex strategy. There are also some areas where centralized communication turns into an issue. So, a team of mobile robots for coverage tasks should have the ability of decentralized or distributed decision making. This thesis investigates decentralized control of mobile robots specifically for coverage problems. A decentralized control strategy is ideally based on local information and it can offer flexibility in case there is an increment or decrement in the number of mobile robots. We perform a broad survey of the existing literature for coverage control problems. There are different approaches associated with decentralized control strategy for coverage control problems. We perform a comparative review of these approaches and use the approach based on simple local coordination rules. These locally computed nearest neighbour rules are used to develop decentralized control algorithms for coverage control problems. We investigate this extensively used nearest neighbour rule-based approach for developing coverage control algorithms. In this approach, a mobile robot gives an equal importance to every neighbour robot coming under its communication range. We develop our control approach by making some of the mobile robots playing a more influential role than other members of the team. We develop the control algorithm based on nearest neighbour rules with weighted average functions. The approach based on this control strategy becomes efficient in terms of achieving a consensus on control inputs, say heading angle, velocity, etc. The decentralized control of mobile robots can also exhibit a cyclic behaviour under some physical constraints like a quantized orientation of the mobile robot. We further investigate the cyclic behaviour appearing due to the quantized control of mobile robots under some conditions. Our nearest neighbour rule-based approach offers a biased strategy in case of cyclic behaviour appearing in the team of mobile robots. We consider a clustering technique inside the team of mobile robots. Our decentralized control strategy calculates the similarity measure among the neighbours of a mobile robot. The team of mobile robots with the similarity measure based approach becomes efficient in achieving a fast consensus like on heading angle or velocity. We perform a rigorous mathematical analysis of our developed approach. We also develop a condition based on relaxed criteria for achieving consensus on velocity or heading angle of the mobile robots. Our validation approach is based on mathematical arguments and extensive computer simulations

Engineering and Clinical Evaluation of the VA-PAMAID Robotic Walker

The Veterans Affairs Personal Adaptive Mobility Aid (VA-PAMAID) is a robotic walker that is designed to provide physical support and obstacle avoidance and navigational assistance to frail visually impaired individuals. The goal of this study was to develop and implement testing protocols to determine the performance and safety capabilities of the device and use the results to redesign the walker to make it more reliable and effective.Engineering tests were performed to determine factors such as stability, range, speed, and fatigue strength. Additional tests to characterize the reliability and accuracy of the sensors and avoidance/navigation algorithms were also conducted. The walker traveled 10.9 kilometers on a full charge, and was able to avoid obstacles while traveling at a speed of up to 1.2 m/s. There were no failures during static stability, climatic, or static, impact, and fatigue testing. Some problems were encountered during obstacle climbing and sensor and control testing. Several significant differences were found with respect to the detection distance of the device when varying the obstacle height, material, approach angle, and lighting source. The walker also failed to detect 40-50% of the doorways during the hallway test.Clinical trials were conducted to compare the VA-PAMAID to a low-tech mobility aid (AMD). Subjects were recruited and trained to use both devices efficiently. Each participant was then asked to traverse an obstacle course several times. The time to complete the course, number of wall and obstacle collisions, and number of reorientations were all recorded and averaged. There were no significant differences between the VA-PAMAID and the AMD with respect to collisions or reorientations. The AMD had a significantly lower completion time (p=0.017) than the VA-PAMAID on the obstacle course. The results of the engineering and clinical tests were then used in a house of quality model to determine what factors of the walker needed to be revised. Specific modifications were recommended that would make the device safer, more reliable, and more marketable. Changing the wheel size, mass, component positions, detection algorithm, and other variables would make the VA-PAMAID easier to use and more effective for elderly visually impaired individuals

Specialization of Perceptual Processes

In this report, I discuss the use of vision to support concrete, everyday activity. I will argue that a variety of interesting tasks can be solved using simple and inexpensive vision systems. I will provide a number of working examples in the form of a state-of-the-art mobile robot, Polly, which uses vision to give primitive tours of the seventh floor of the MIT AI Laboratory. By current standards, the robot has a broad behavioral repertoire and is both simple and inexpensive (the complete robot was built for less than $20,000 using commercial board-level components). The approach I will use will be to treat the structure of the agent's activity---its task and environment---as positive resources for the vision system designer. By performing a careful analysis of task and environment, the designer can determine a broad space of mechanisms which can perform the desired activity. My principal thesis is that for a broad range of activities, the space of applicable mechanisms will be broad enough to include a number mechanisms which are simple and economical. The simplest mechanisms that solve a given problem will typically be quite specialized to that problem. One thus worries that building simple vision systems will be require a great deal of {it ad-hoc} engineering that cannot be transferred to other problems. My second thesis is that specialized systems can be analyzed and understood in a principled manner, one that allows general lessons to be extracted from specialized systems. I will present a general approach to analyzing specialization through the use of transformations that provably improve performance. By demonstrating a sequence of transformations that derive a specialized system from a more general one, we can summarize the specialization of the former in a compact form that makes explicit the additional assumptions that it makes about its environment. The summary can be used to predict the performance of the system in novel environments. Individual transformations can be recycled in the design of future systems