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Design and implementation of Omni-directional spherical modular snake robot (OSMOS)
Abstract
Control, motion estimation, and planning of highly articulated snake robots have been challenging tasks for researchers. Even traversal on simple flat trajectory requires complex models of planar snake robot locomotion. This paper presents a novel design of an Omni-directional planar snake robot (OSMOS) consisting of mechanically and software linked spherical robot modules. This new design eliminates the problems of planar snake robots to handle versatile motions with complex gait analysis, by leveraging Omni-directional motion capabilities of spherical robots. This paper also presents the basic robot gaits which clearly demonstrate its design advantages such as fast turn speed and present simpler motion planning strategies. Experimental results that verify the effectiveness of this robot architecture and gaits that have been designed to traverse flat terrain are included.
... In our previous work [20], we presented the design of omnidirectional snake robot (OSMOS) on the basis of above considerations. But the robot links connecting the adjacent modules were rigid and incapable of bending in the vertical plane. ...
... Though obstacle avoidance is a solution a wider obstacle needs to be overcome by climbing it. This intrigued us to introduce compliance in the links such that the robot can also now bend in the vertical direction using passive compliance of the links [20].Compliance with the link is incorporated by adding a pair of symmetric torsional springs in the links. The calculation of the spring constants are done mathematically by using a quasi-static analysis similar to the spring modelling calculations done in [21,22]. ...
... In our previous work [20] link assemblies were connected by passive rigid rods as shown in Fig.6. However, the the updated design focuses on introducing a compliant joint at the end of each passive rod near to the central spherical module as shown in Fig (7) such that the link can now bend about this the pivot point in the vertical plane. ...
Control, motion estimation, and planning of highly articulated snake robots have been challenging tasks for researchers. Even traversal on simple flat trajectory requires complex models of planar snake robot locomotion. Apart from flat trajectories formulating gaits for the modular structure to overcome obstacles is mathematically complicated. This paper presents a novel design of an Omni-directional snake robot (OSMOS) consisting of mechanically and software linked spherical robot modules. This new design eliminates the problems of planar snake robots to handle versatile motions with complex gait analysis, by leveraging Omni-directional motion capabilities of spherical robots. The robot is also capable of climbing smooth obstacles by introducing compliant joints in the links interconnecting adjacent modules. This paper also presents the basic robot gaits which clearly demonstrate its design advantages such as fast turn speed and present simpler motion planning strategies. Experimental results that verify the effectiveness of this robot architecture and gaits that have been designed to traverse flat terrain are included. Also, the spring stiffness of the passive joints in the links is calculated and simulation results for obstacle climbing are included.
... In our previous work [20], we presented the design of omnidirectional snake robot (OSMOS) on the basis of above considerations. But the robot links connecting the adjacent modules were rigid and incapable of bending in the vertical plane. ...
... Though obstacle avoidance is a solution a wider obstacle needs to be overcome by climbing it. This intrigued us to introduce compliance in the links such that the robot can also now bend in the vertical direction using passive compliance of the links [20].Compliance with the link is incorporated by adding a pair of symmetric torsional springs in the links. The calculation of the spring constants are done mathematically by using a quasi-static analysis similar to the spring modelling calculations done in [21,22]. ...
... In our previous work [20] link assemblies were connected by passive rigid rods as shown in Fig.6. However, the the updated design focuses on introducing a compliant joint at the end of each passive rod near to the central spherical module as shown in Fig (7) such that the link can now bend about this the pivot point in the vertical plane. ...
Control, state estimation and motion planning of highly articulated snake robots have been challenging tasks for researchers. As a result, formulating gaits for the modular structure, for motion on flat trajectories as well as overcoming obstacles is mathematically complicated. This paper presents a novel design of a Compliant Omni-directional snake robot (COSMOS) consisting of mechanically and software linked spherical robot modules. This design eliminates the problems of planar snake robots to handle versatile motions with complex gait analysis, by leveraging Omni-directional motion capabilities of spherical robots. The robot is also capable of climbing smooth obstacles by introducing compliant joints in the links interconnecting adjacent modules. This paper also presents the basic robot gaits and their motion analysis which clearly demonstrate the robot design advantages such as fast turn speed and simpler motion planning strategies. Experimental results that verify the effectiveness of this robot architecture and gaits that have been designed to traverse flat terrain are included. Also, the spring stiffness of the passive joints which provide the vertical compliance in the links joining the modules is calculated and simulation results for obstacle climbing are included.
... Fig. 1 shows different mobility modes considered in this research, and Fig. 2 provides a summary of the strengths and weakness of each mobility mode. Snake robots, due to their hyper redundancy and narrow cross-section of their body, are versatile and can navigate within limited space, rough terrains, move underwater [1], traverse through pipes, slopes, and uneven ground [2], [3], [4]. Snake robots can be deployed for various practical applications like locating hazardous chemical leaks, search and rescue operations [5], reconnaissance; they can function as self-propelled inspection devices [6], [7], [8]. ...
The selection of mobility modes for robot navigation consists of various trade-offs. Snake robots are ideal for traversing through constrained environments such as pipes, cluttered and rough terrain, whereas bipedal robots are more suited for structured environments such as stairs. Finally, quadruped robots are more stable than bipeds and can carry larger payloads than snakes and bipeds but struggle to navigate soft soil, sand, ice, and constrained environments. A reconfigurable robot can achieve the best of all worlds. Unfortunately, state-of-the-art reconfigurable robots rely on the rearrangement of modules through complicated mechanisms to dissemble and assemble at different places, increasing the size, weight, and power (SWaP) requirements. We propose Reconfigurable Quadrupedal-Bipedal Snake Robots (ReQuBiS), which can transform between mobility modes without rearranging modules. Hence, requiring just a single modification mechanism. Furthermore, our design allows the robot to split into two agents to perform tasks in parallel for biped and snake mobility. Experimental results demonstrate these mobility capabilities in snake, quadruped, and biped modes and transitions between them.
... On a different direction, the propulsion of the OmniTread snake robots was achieved by tank treads on all four sides of every link, which can help the robot move in complex environments (Armada et al., 2005). More recently, the OSMOS snake utilizes spherical shaped modules to help realize gaits without changing the robot body shape and orientation (Singh et al., 2017). Meanwhile, a lot of researchers have made progress on the study of snake robot locomotion. ...
Snake robotics is an important research topic with a wide range of applications, including inspection in confined spaces, search-and-rescue, and disaster response. Snake robots are well-suited to these applications because of their versatility and adaptability to unstructured and constrained environments. In this paper, we introduce a soft pneumatic robotic snake that can imitate the capabilities of biological snakes, its soft body can provide flexibility and adaptability to the environment. This paper combines soft mobile robot modeling, proprioceptive feedback control, and motion planning to pave the way for functional soft robotic snake autonomy. We propose a pressure-operated soft robotic snake with a high degree of modularity that makes use of customized embedded flexible curvature sensing. On this platform, we introduce the use of iterative learning control using feedback from the on-board curvature sensors to enable the snake to automatically correct its gait for superior locomotion. We also present a motion planning and trajectory tracking algorithm using an adaptive bounding box, which allows for efficient motion planning that still takes into account the kinematic state of the soft robotic snake. We test this algorithm experimentally, and demonstrate its performance in obstacle avoidance scenarios.
... MorpHex, in Figure 4a [118], is a reconfigurable hybrid robot that can move either by rolling or as a hexapod. A reconfigurable snake/biped robot is shown in Figure 4b [119], while the robot in [120] combines omni-directional wheels and slithering. ...
This paper presents a survey on mobile robots as systems that can move in different environments with walking, flying and swimming up to solutions that combine those capabilities. The peculiarities of these mobile robots are analyzed with significant examples as references and a specific case study is presented as from the direct experiences of the authors for the robotic platform HeritageBot, in applications within the frame of Cultural Heritage. The hybrid design of mobile robots is explained as integration of different technologies to achieve robotic systems with full mobility.
Although substantial advancements have been achieved in robot-assisted surgery, the blueprint to existing snake robotics predominantly focuses on the preliminary structural design, control, and human–robot interfaces, with features which have not been particularly explored in the literature. This paper aims to conduct a review of planning and operation concepts of hyper-redundant serpentine robots for surgical use, as well as any future challenges and solutions for better manipulation. Current researchers in the field of the manufacture and navigation of snake robots have faced issues, such as a low dexterity of the end-effectors around delicate organs, state estimation and the lack of depth perception on two-dimensional screens. A wide range of robots have been analysed, such as the i²Snake robot, inspiring the use of force and position feedback, visual servoing and augmented reality (AR). We present the types of actuation methods, robot kinematics, dynamics, sensing, and prospects of AR integration in snake robots, whilst addressing their shortcomings to facilitate the surgeon’s task. For a smoother gait control, validation and optimization algorithms such as deep learning databases are examined to mitigate redundancy in module linkage backlash and accidental self-collision. In essence, we aim to provide an outlook on robot configurations during motion by enhancing their material compositions within anatomical biocompatibility standards.
To solve problems of conventional mobile robots, such as constrained mobility due to nonholonomic wheels or complicated structure due to specialized wheels, we propose a novel omnidirectional mobile robot named slidable-wheeled omnidirectional mobile robot (SWOM). SWOM has three conventional wheels connected to the main body by passive sliding joints, which enable the main body to make omnidirectional movement in spite of the nonholonomic constraints on the wheels. Thus, SWOM achieves both superb mobility and simple structure. However, its behavior is described as a nonlinear system with nonholonomic constraints, which has difficulty with control because this type of system does not have a general design method for a stabilizing controller. This study aims to develop a controller for SWOM using state feedback linearization. This paper presents the following achievements: An exactly linearized state equation is derived using feedback and coordinate transformation based on the kinematics of SWOM. The unwanted singular configurations of the system are discussed and a control strategy to avoid them is proposed. Then, a stabilizing controller that enables SWOM to reach a designated position and orientation is designed. Through a numerical simulation and an experiment using a SWOM prototype, the effectiveness of the developed control system was verified.
Mobile robots for automatically transporting products in factories and warehouses contribute to an increase in efficiency. Omnidirectional mobile robots can move immediately in an arbitrary direction and overcome the disadvantages of lack of mobility in conventional mobile robots. However, the omnidirectional mobile robots proposed in the past have not been as reliable as the conventional mobile robots such as AGVs due to their complicated wheel mechanisms. This research proposes a novel omnidirectional mobile robot named SWOM (slidable-wheeled omnidirectional mobile robot), which has three wheels that connect to the robot body by three passive sliding joints. The relative movements of the sliding joints allow SWOM to use conventional wheels. Thus, SWOM realizes both omnidirectional mobility and structural reliability. In this paper, we discuss the kinematic conditions for omnidirectional mobile robots and prove theoretically that SWOM can achieve omnidirectional movement. We present a kinematic analysis, a reachable region evaluation considering the limited movable range of the sliding joints, and trajectory generation that enables SWOM to move unlimitedly. We develop a prototype of SWOM and conduct experiments that show SWOM actually moves according to the theory. From the above, we verify the effectiveness of SWOM as an omnidirectional mobile robot.
As a step toward enabling snake robots to move in cluttered environments, this paper proposes a control strategy that combines environment adaptation with directional control in order to achieve straight line path following control in environments with obstacles. Moreover, the paper presents the design of a mechanical snake robot with tactile sensing capabilities that allow the robot to sense its environment. Experimental results are presented where the snake robot is successfully propelled through different obstacle environments with the proposed control strategy.
Snake Robots is a novel treatment of theoretical and practical topics related to snake robots: robotic mechanisms designed to move like biological snakes and able to operate in challenging environments in which human presence is either undesirable or impossible. Future applications of such robots include search and rescue, inspection and maintenance, and subsea operations. Locomotion in unstructured environments is a focus for this book.
The text targets the disparate muddle of approaches to modelling, development and control of snake robots in current literature, giving a unified presentation of recent research results on snake robot locomotion to increase the reader’s basic understanding of these mechanisms and their motion dynamics and clarify the state of the art in the field. The book is a complete treatment of snake robotics, with topics ranging from mathematical modelling techniques, through mechatronic design and implementation, to control design strategies. The development of two snake robots is described and both are used to provide experimental validation of many of the theoretical results.
Snake Robots is written in a clear and easily understandable manner which makes the material accessible by specialists in the field and non-experts alike. Numerous illustrative figures and images help readers to visualize the material. The book is particularly useful to new researchers taking on a topic related to snake robots because it provides an extensive overview of the snake robot literature and also represents a suitable starting point for research in this area.
Advances in Industrial Control aims to report and encourage the transfer of technology in control engineering. The rapid development of control technology has an impact on all areas of the control discipline. The series offers an opportunity for researchers to present an extended exposition of new work in all aspects of industrial control.
Snake robots are controlled by implementing gaits inspired from their biological counterparts. However, transitioning between these gaits often produces undesired oscillations which cause net movements that are difficult to predict. In this paper we present a framework for implementing gaits which will allow for smooth transitions. We also present a method to determine the optimal time for each module of the snake to switch between gaits in a decentralized fashion. This will allow for each module to participate in minimizing a cost by communicating with a set of modules in a local neighborhood. Both of these developments will help to maintain desired properties of the gaits during transition.
The design of a hyper-redundant serial-linkage snake robot is the focus of this paper. The snake, which consists of many fully enclosed actuators, incorporates a modular architecture. In our design, which we call the Unified Snake, we consider size, weight, power, and speed tradeoffs. Each module includes a motor and gear train, an SMA wire actuated bistable brake, custom electronics featuring several different sensors, and a custom intermodule connector. In addition to describing the Unified Snake modules, we also discuss the specialized head and tail modules on the robot and the software that coordinates the motion.
This article presents AmphiBot II, an am- phibious snake robot designed for both serpentine loco- motion (crawling) and swimming. It is controlled by an on-board central pattern generator (CPG) inspired by those found in vertebrates. The CPG is modelled as a chain of coupled nonlinear oscillators, and is designed to produce travelling waves. Its parameters can be modi- fled on the ∞y. We present the hardware of the robot and the structure of the CPG, then the systematic parameter tests done in simulation and with the real robot to char- acterize how the speed of locomotion depends on the parameters determining the frequency, amplitude and wavelength of the body undulation.
Based on the experience with our first GMD-SNAKE, we now present
the next generation robot, the GMD-SNAKE2, which is a robot for
inspection tasks in areas difficult to access by humans. We aim to
imitate the natural scale-driven propulsion of a snake by wheels around
the body. After a description of our robot we concentrate on a method
for motion control. It allows a very flexible and consistent method of
path planning and calculation where smooth curves are desired. It is
applicable not only to snake-like movement, but to any wheeled robot
which is able to control the curvature of its path
The paper presents the design and motion planning for a mechanical
snake robot that was built at the University of Michigan. The structure
of the robot enables it to move without wheels. It is constructed of a
series of articulated links, each one with a motor and linear solenoid.
Although each link has only one motor, this structure allows the body
configuration to be easily controlled thereby enabling the robot to move
in very cluttered environments. The motion planning system provides the
robot with a basic motion pattern that can be easily modified for
different tasks and environments. The mechanical snake does not avoid
obstacles on its way, but rather “accommodates” them by
continuing its motion towards the target while in contact with the
obstacles. With the authors' design and motion planning, each link has a
different number of degrees-of-freedom in each motion stage, providing
the robot with great adaptability even during contact with obstacles in
a cluttered environment
Physical parameters of modules and gait parameters affect the overall snake-inspired robot performance. Hence the system-level optimization model has to concurrently optimize the module parameters and the gait. The equations of motion associated with the rectilinear gait are quite complex due to the changing topology of the rectilinear gait. Embedding these equations in the system-level optimization model leads to a computationally challenging formulation. This paper presents a system-level optimization model that utilizes a hierarchical optimization approach and meta-models of the pre-computed optimal gaits to reduce the complexity of the optimization model. This approach enabled us to use an experimentally validated physics-based model of the rectilinear gait and yet at the same time enabled us to create a system-level optimization model with a manageable complexity. A detailed case study is presented to show the importance of concurrently optimizing the module parameters and the gait using our model to obtain the optimal performance for a given mission.
The characteristics and the applications of the articulated body
mobile robot, `Koryu (KR)', a mobile robot with a new style of
articulated body is identified, and the construction of the newly
developed `Koryu-II (KR-II)' is discussed. KR-II takes the form of seven
linked articulations and its total length is 3.3 m, and its total weight
is 350 kg. KR-II introduces new mechanisms and control systems such as:
easily detachable unified segments; self-contained driving system with
wireless control; traction wheels attached on one side of the segment;
long stroke vertical prismatic joint to cope with a steep inclination;
robot hand driven by the coordination control of the body articulation;
force sensor based on photodetective technology; and an analog bus
system to simplify the electrical installation. Finally, the paper
describes KR-II's fundamental results of experimental trials, to show
the validity of it as a robot to move and operate in an unstructured
environment
Even though many researchers have studied spherical mobile robots, a robot with an elastic external frame can hardly be in the literature. Therefore in this study the pendulum-driven spherical mobile robot is introduced. The external frame of the robot is designed as glass fiber sticks which show good elastic characteristics. All control modules, such as a Zigbee wireless communication module and battery, are embedded into the spherical mobile robot. Atmega 2560-based embedded system is adopted as a main controller to drive the robot along desired path. This study also introduces driving and steering dynamic model of the pendulum-driven type spherical robot and performs experiments to verify the models. Based on the model, a PID controller is implemented and good mobility of the robot is verified.
In this paper, we present a technique for approx- imating the net displacement of a locomoting system over a gait without directly integrating its equations of motion. The approximation is based on a volume integral, which, among other benefits, is more open to optimization by algorithm or inspection than is the full displacement integral. Specifically, we develop the concept of a body velocity integral (BVI), which is computable over a gait as a volume integral via Stokes's theorem. We then demonstrate that, given an appropriate choice of coordinates, the BVI for a gait approximates the displacement of the system over that gait. This consideration of coordinate choice is a new approach to locomotion problems, and provides significantly improved results over past attempts to apply Stokes's theorem to gait analysis. I. INTRODUCTION Locomotion is everywhere. Snakes crawl, fish swim, birds fly, and all manner of creatures walk. The facility with which animals use internal joint motions to move through their environments far exceeds that which has been achieved in artificial systems; consequently there is much interest in raising the locomotion capabilities of such systems to match or surpass those of their biological counterparts. A fundamental aspect of animal locomotion is that it is primarily composed of gaits - cyclic shape motions which efficiently transport the animal. Examples of such gaits include a horse's walking, trotting, and galloping, a fish's translation and turning strokes, and a snake's slithering and sidewinding. The efficacy of these motions, along with the abstraction that they allow from shape to position changes, suggests that gaits will form an equally important part of artificial locomotion. Here, we are specifically interested in producing tools for designing gaits for mechanical systems which result in desired net position changes. Much prior work in gait design has taken the approach of choosing parameterized basis functions for gaits and simulating the motion of the system while executing the gaits, optimizing the input parameters to find gaits which meet the design requirements. Such optimization with forward simulation is computationally expensive and vulnerable to local minima. Therefore, there is growing interest in using curvature analysis tools, such as Stokes's theorem, to replace the simulation step with a simple volume integration, which is more amenable to optimization. Unfortunately, these Stokes's theorem methods as previously developed are not completely applicable to most interesting systems; either they are restricted to designing small, inefficient motions, or they provide incomplete information about the actual displacement of the system over the course of a gait. In this paper we address these limitations by developing the concept of a body velocity integral (BVI), which provides an expanded and physically meaningful interpretation of previous locomotion work based on Stokes's theorem. We then identify conditions under which this body velocity integral is a good estimate of the true displacement resulting from a gait. We finish by introducing the notion that rather than being intrinsic to the system, the presence of these conditions is dependent on the choice of parameterization of the system, and demonstrat- ing that this choice of parameterization can be manipulated to ensure their existence.
This paper presents a novel design of an omni-directional spherical robot that is mainly composed of a lucent ball-shaped shell and an internal driving unit. Two motors installed on the internal driving unit are used to realize the omni-directional motion of the robot, one motor is used to make the robot move straight and another is used to make it steer. Its motion analysis, kinematics modeling and controllability analysis are presented. Two typical motion simulations show that the unevenness of ground has big influence on the open-loop trajectory tracking of the robot. At last, motion performance of this spherical robot in several typical environments is presented with prototype experiments.
We present a comparison of methods to estimate the shape and orientation of a locomoting snake robot by fusing the robot's redundant internal proprioceptive sensors using and Extended Kalman Filter (EKF). All of the estimators used in this work represent the shape of the snake with gait parameters to reduce the complexity of the robot configuration space. The compared approaches for representing shape and pose of the snake robot differ primarily in the use of a body frame fixed to the pose of a single module versus one that is aligned with the virtual chassis. Additionally, we evaluate a state representation that explicitly tracks joint angles for improved estimates. For one particular gait, rolling, we present experimental data where motion capture data of the snake robot is used as ground truth to compare the accuracy of the state estimates from these techniques. We show that using the virtual chassis body frame, rather than a fixed body frame, results in improved accuracy of the snake robot's estimated pitch and roll. We also show that, in general, representing the robot's shape with gait parameters is sufficient to accurately estimated shape and pose, though it can be improved upon in specific cases by explicitly modeling joint angles.
Mobile robots having good terrain adaptability, sufficient payload capability, and high mobility are now urgently in de mand. In this paper, design of a practical mobile robot is attempted, with an inspection task in a nuclear reactor as a concrete objective for development. The configuration of the mobile robot is first discussed. A wheel with crawler track, legs, and a snake-like articulated body are shown to be three fundamental configurations. A hybrid configuration consist ing of an articulated body and a crawler track is most ade quate for the nuclear reactor robot because of its excellent terrain adaptability, sufficient payload capability, and high mobility. Design of the joint structure of the articulated body is discussed. Basic control problems such as signal process ing for tactile sensors and control of statically indeterminant forces are also investigated. A mechanical model KR I, a robot with six articulated body segments, 16 degrees of free dom, length 1391 mm, and weight 27.8 kg, is constructed and several experiments are done to demonstrate the basic mobility of the robot and to show the validity of introducing force control.
Body undulation used by snakes and the physical architecture of a snake body may offer significant benefits over typical legged or wheeled locomotion designs in certain types of scenarios. A large number of research groups have developed snake-inspired robots to exploit these benefits. The purpose of this review is to report different types of snake-inspired robot designs and categorize them based on their main characteristics. For each category, we discuss their relative advantages and disadvantages. This review will assist in familiarizing a newcomer to the field with the existing designs and their distinguishing features. We hope that by studying existing robots, future designers will be able to create new designs by adopting features from successful robots. The review also summarizes the design challenges associated with the further advancement of the field and deploying snake-inspired robots in practice.
This paper describes the development of ACM-R3, which is a new
version of the active cord mechanism with three-dimensional mobility.
This ACM-R3 is equipped with large passive wheels which wrap its overall
body, and has frictional characteristic as snake-like skin. It is also
equipped with radio controlled servomotors with some gears added to
them, and held tightly by shell flames so that it can move steadily and
with high power. Each unit of ACM-R3 consists of a very simple
structure, batteries, and electronic circuits to control itself.
Consequently, ACM-R3 consists of as many units as we want to use, and is
suitable for the platform of snake-like robotics researchers. ACM-R3 can
demonstrate new propulsion methods and motions, combining the ability of
a manipulator and a propulsion unit