Improving motion speed and efficiency remains a critical challenge in snake robots gait control. This paper introduces the Loop gait, a novel locomotion gait designed to enhance both speed and energy efficiency of snake robots without passive wheels. Compared to Crawler gait and S-pedal gait, which are more widely used, the Loop gait has a better motion speed (1.8 times of the Crawler gait in the same parameter) and a better motion efficiency (1.6 times of the Crawler gait in the same parameter) due to its more loop body morphology. A static stability model is developed to guide parameter optimization, addressing potential instability caused by elevated center of mass of snake robots. Experiments confirm the Loop gait’s exceptional energy efficiency and propulsion, validating the static stability model’s utility in selecting parameters.

Omni-directional mobile manipulators (OMMs) are typically nonlinear, strongly coupled, multiple-input and multiple-output systems, for which the development of mechanistic models is often complex and time-consuming. Koopman operator theory is a fully data-driven modeling approach that leverages input-output data to generate high-dimensional linear models, but it often has modeling errors. In this paper, a completely data-driven online learning linear model predictive control (MPC) framework is proposed for an OMM, without using any prior knowledge of the robot system. A finite-dimensional approximate linear Koopman model is established for an OMM using the input-output data. The model errors (including external disturbances) are online learned by Gaussian process regression (GPR) using the collected data and compensated for in real time within the controller. Selective forgetting and incremental inverse computation methods are employed to reduce the computational cost of online GPR. Finally, a total of 11,400 experimental data pairs are generated for Koopman modeling of an OMM prototype, utilizing randomly generated control inputs under different initial states. Then experimental tests are carried out to verify the control performances and robustness of the proposed control scheme.

A building information model for existing pipes is essential for maintenance tasks such as repairs, reconstruction, and modernization. However, current automatic recognition methods are not well-suited for handling complex piping systems on mobile devices. To address this, an attention mechanism-based recognition network is proposed. First, a decoder network is designed to minimize information loss during feature extraction. Its ability to integrate with various encoder networks allows for flexible network design tailored to different applications. Second, an extended convolution pyramid, tailored to the geometric characteristics of pipes, is introduced to enhance computational efficiency. The proposed network’s performance was evaluated through ablation studies and comparison experiments with state-of-the-art methods. To address the challenge of data scarcity, a hybrid dataset was developed using neural style transfer techniques, and an evaluation experiment demonstrated its effectiveness.

Rescue robots require versatility and the capability to operate in various environments to carry out a diverse set of tasks effectively. The eccentric paddle (ePaddle) mechanism stands out for its high efficiency and adaptability. Generally, it is designed as a quadruped robot with a combined structure for fully-actuated control, this approach is often both inefficient and inflexible due to the requirement for repeated front-to-back paths. Unlike the fully-actuated controller that assume torso is fixed, this study proposes an under-actuated controller, consisting of a single ePaddle mechanism and a free torso for more efficient and flexible movement. Inspired by human gait, precision walking, and non-precision walking are introduced to discuss the stability of zero dynamics. Additionally, the stability condition is presented and demonstrated by numerical simulation. Since this control is based on robot dynamics, it has a high fault-tolerance and benefited from its dynamics attractor. The concept of under-actuated controller we proposed in this study is not only applicable to the ePaddle mechanism, but also to other under-actuated legged locomotion models.

This paper mathematically conceives a novel walking support device that leverages passive dynamics and coupling effects. In this model, a passive human walker is flexibly connected to an active humanoid, where the coupling effect induces a stable walking gait of the human. To understand the key mechanism of such indirect gait regulation, different actuation modes are designed for the humanoid and compared via phase-plane analysis of the steady-state gaits. Moreover, stability analysis is conducted via Poincaré map. The results show that it is difficult to enhance the human walker's stability when coupled to a humanoid robot using additional sensory information, compared to using a humanoid robot actuated with a predetermined force that employs no state feedback. The present mathematical model and our theoretical findings contribute to analysis and control design for locomotion systems with robot-human or inter-robots cooperation.

Enlightened by the creeping gait of natural snakes, snake-like robots swing joints side to side at similar tracks for generating propelling forces. However, it is not always essential to control all joints of a snake-like robot to realize the creeping gait. Therefore, in this paper, a creeping snake-like robot with partially actuated joints has been investigated, towards reducing the redundancy caused by full actuation. Essentially, this approach is composed of the following two concepts: 1) joint equipped with torsion spring mechanism bridges the passive joint to generate rhythm oscillation, and 2) harmonic joint trajectories assist the robot in generating more efficient locomotion. We hereafter demonstrated that the actuated joint dominates passive dynamics of the system, which contributes to overall motion. Meanwhile, different spring stiffness affects the motion performance. Additionally, the interaction between robot and environment through Coulomb friction has been considered to reveal the contributing factors that assist the snake-like robot to yield better locomotion performance.

The goal of this paper is to develop an ultrasonic detection device that can be mounted on an underwater snake vehicle (USV) for underwater district heating pipe (DHP) detection in the future. Ultrasonic detection technology (UDT) is the detection means used, and the cavitation defects in polyurethane (PUR) layer of DHPs are the object being detected. Due to the large thickness of PUR layer and the complex interface information of multi-layer structure, detecting defects of DHPs quantitatively is a difficult task. To address this issue, this paper proposes an approach that combines feature extraction and crow search algorithm (CSA) optimized support vector machine (SVM). Firstly, the main parameters and detection method of UDT are designed after investigation. Secondly, defective signals are pre-processed by signal processing to extract the features form three domains. Finally, four different classifiers are used to identify cavitation defects based on the feature-set. When compared among optimized random forest (RF), k-nearest neighbor (KNN), and ordinary SVM, the experimental results show that CSA-SVM had the highest accuracy in defect size prediction, and the validation-experiment verifies the practicability and feasibility of the CSA-SVM classifier. All experiments illustrate that the issue could be well solved by our method.

The performance of a robot is closely related to its structure. From the initial design of link lengths to structural optimization, it is still the research hotspot in recent years. To make the manipulator lightweight and ensure its working range and flexibility, researchers have proposed many optimization methods, most of which are for specific working scenarios, requirements, and robot structures, therefore their generality is limited. The optimization of the manipulator should be a comprehensive method. That is, we should pay attention to the joint configuration and each link length at the beginning of the design. Particularly, the geometric parameters of each link, which not only affect the range of the workspace but also have a direct impact on the working space, working efficiency, and flexibility of the manipulator. In this paper, a generalized optimization framework is proposed for multi-link manipulators. Starting from the optimization of manipulator link lengths, firstly, the geometry of the manipulator and workspace is parameterized; then the performance indicators are established; lastly, the geometric size of the manipulator is optimized according to the workspace limits and task requirements. Besides, we verified its feasibility and generality by applying this method to different TBM scenarios.

Reinforcement learning commonly suffers from slow convergence speed and requires thousands of episodes, which makes it hard to be applied for physical robotic applications. Little research has been studied for snake robot control using RL because of the additional difficulty of high redundancy of freedom. Existing methods either adopts an asynchronous A3C structure or a joint state representation. We propose a distributed coach-based deep learning method for snake robot control, which can greatly expedite the training speed with less episodes. The major contributions include: 1) a completely distributed graphical formulation; 2) an explicit stochastic density propagation rule for each robot link; 3) various interaction models with uncertainty estimation. The preliminary results of both simulation and real-world experiments have demonstrated the promising performance in comparison with state-of-the-art.

This paper presents a method of drawing pipeline routes using a sensing unit with a rotary encoder and IMU (Inertial Measurement Unit), which is towed by a self-propelled in-pipe inspection robot. However, the IMU information generally contains integration errors, making it difficult to draw accurate pipeline routes. In this study, we propose a method combining gradient descent using a gyroscopic sensor and an accelerometer, and the correction of the route based on the standard information of the pipe. First, the method of identifying the start point, end point, direction of straight pipes, and bending direction of curved pipes is explained. Then, an experiment is conducted using the developed robot system on a 11.6-meter-long pipeline course that includes nine curved pipes and horizontal and vertical straight pipes. Consequently, the mean absolute error of the route dimension was reduced to 2.74 %.

The paper reports the performance verification of vertical bend and T-branch travels of an articulated wheeled in-pipe inspection robot. The robot is composed of only a single active compliant middle joint, two passive compliant joints, three drive wheels, and two roll wheels. The passage of the bend pipe is achieved only by the joint torque control, while the T-branch travel is achieved by controlling both joint angle and torque. Instead of using a torque sensor, a polyurethane-based series elastic actuator (SEA) is installed in the middle joint. In this paper, the travel performances of our developed in-pipe robot were tested on bend pipes and 10 types of T-branch with different gravity directions. From the experiments, in all cases, the effectiveness of the bend and T-branch travels performance was confirmed.

Undulation is the most common gait generated by legless creatures, which enables their robust and efficient locomotion in various environments. Such advantages inspired the control design of many kinds of locomotion robots. Despite their technical details, most of them realize the undulation gait via tracking predetermined trajectories called serpenoid curves, which are a group of sinusoidal waveforms with specified phase differences. This technique, however, sounds quite redundant in terms of sensing and control. Here, we investigate the research question: whether the sinusoidal waveform is necessary to be encoded in the control signal to make the whole body an “S-shape”? We use a 4-link rigid body dynamics model as a simple example, by which numerical simulations are conducted. Together with theoretical analysis, we show that undulation gait emerges naturally based on embodied position controller and filter, where binary actuation torques are required only. Our results not only discover locomotion mechanisms for significantly reducing the sensing and control requirement of generating artificial undulation gait, but also provide additional understandings for biological systems from the mechanical engineering point of view.

Compliance is good. However, it is challenging for one compliant continuum robot to finish both high precision manipulation and environmental-adapted motions. In this paper, a modular continuum robot with the alterable compliance characteristic is proposed. Besides, an actuation module is also proposed using a tubular-screw mechanism for non-slippage transmission. Kinematic analyses and dynamic co-simulation are performed to study the continuum robot. Furthermore, two potential application scenarios of pick-and-place manipulation and confined space navigating are carried out to demonstrate the advantages of the alterable compliance design. This study presents a capable continuum robotic solution for non-structural inspection tasks, with potential for in-situ applications in restricted and hazardous environments.

Regular maintenance of pipelines is an important task to ensure oil transportation and other operation (sewers, nature gas). Precise localization of pipeline damage can greatly improve the efficiency of maintenance work. Since the texture similarity and illumination change of pipe, traditional local descriptors for image matching like SIFT, SURF and ORB are easy to suffer from false correspondences. As to remove the false matches, the local neighborhood constraints (LNC) that contain spatial constructs around feature points are proposed. Good correspondences are essential for the high-accuracy localization and mapping solution given the limited textures and illumination in the pipes. The LNC method is also integrated into the state-of-the-art visual SLAM system. The proposed LNC image matching method and the SLAM system are evaluated on datasets gathered from the pipe environment. Compared with other state-of-the-art methods, our LNC image matching method achieves similar or better performance in precision, recall and runtime. The SLAM system provides state estimation and map reconstruction of the pipe in real-time, and the localization error is within 1%.

Active disturbance rejection control (ADRC) is an efficient control technique to accommodate both internal uncertainties and external disturbances. In the typical ADRC framework, however, the design philosophy is to "force" the system dynamics into a double-integral form by an extended state observer (ESO) and then the controller is designed. Especially, the systems' physical structure has been neglected in such a design paradigm. In this article, a new ADRC framework is proposed by incorporating at a fundamental level the physical structure of the Euler-Lagrange (EL) systems. In particular, the differential feedback gain can be selected considerably small or even 0, due to the effective exploitation of the system's internal damping. The design principle stems from an analysis of the energy balance of EL systems, yielding a physically interpretable design. Moreover, the exploitation of the system's internal damping is thoroughly discussed, which is of practical significance for applications of the proposed design. Besides, a sliding-mode ESO is designed to improve the estimation performance over traditional linear ESO. Finally, the proposed control framework is illustrated through tracking control of an omnidirectional mobile robot. Extensive experimental tests are conducted to verify the proposed design as well as the discussions.

Biological observations on tetrapods locomotion deduce that anti-phase synchronization (APS) between fore and rear parts is beneficial for achieving a high-speed walking. On the other hand, theoretical analysis and experimental studies on quadruped robots suggest that a flexible spine potentially improves the gait efficiency and adaptability via smoothing the ground collisions. However, these two mechanisms have never been placed together by a comprehensive investigation in terms of their synergetic effect. Namely, an advanced principle is still lacking in combining the APS and the spine flexibility for quadruped walking robots. To address this issue, we construct a mathematical model for a quadruped dynamic walker under different spine conditions. First, the APS effect is generated via entrainment-based control method under a rigid spine condition. Then, flexible spines realized by three kinds of springs are compared with the rigid one via theoretical analysis. The results suggest that the APS mechanism and the flexible spine can be synergized via an appropriate deformation control. The theoretical findings not only uncover locomotion control mechanisms for quadruped walking robots, but also provide additional understandings of tetrapods dynamic walking from a mechanical engineering point of view.

This paper presents a wheeled V-shaped in-pipe robot in which the two outputs of the wheel shaft and roll joint are driven solely by a single actuator input. This underactuation is generated by a simple miter gear mechanism. Generally, to control two movements easily, one of the outputs of the underactuated mechanism is constrained by the resilience force of springs or by the friction force. However, this complicates the control of each output. In this study, a one-way clutch is installed to completely constrain one of the outputs (wheel movement). By using this clutch, the proposed mechanism enables a hemispherical wheel to switch between pitch and roll rotations by selecting the drive direction of a single motor. The one-way clutch constrains the wheels to rotate in only one direction. To take advantage of this constraint, the robot changes its direction of movement between forward and backward by using the rolling movement of the robot. After describing the configuration of the proposed robot and a roll-angle model of the robot, experiments are conducted in straight pipes, bending pipes, and an out-of-plane double elbow.

To cope with the requirements on efficiency and labour-saving of the out-pipe surface grinding tasks in the wild, several proposals are revealed and discussed. The one benefiting from the characteristics of planetary gear transmission and friction actuating mechanism are expatiated. To realize full coverage of out-pipe surface, the self-rotation and revolution motions of every polishing tool (cutter) are actuated by the same motor, and the friction force produced in grinding process acts as suitable tractive force for the forward travel of the grinding system. The friction statics analysis is established to illustrate the force transmission. Compression spring system are utilized to realize force equilibrium and support passive diameter adaptability. The proposed robotic grinding system is characterized by less actuator, online grinding capability and high working efficiency. It has clear advantages regarding manufacturing costs and control complexity. As the result of prototype experiments, performance of smooth grinding the out-pipe surface is confirmed.

Compared with torque-control techniques, a position-controlled quadruped robot is lower cost, easier to build, and more direct to drive. However, the stiff actuation of position-controlled actuators makes it difficult for the quadruped to achieve dynamically stable locomotion. This paper presents an implementation of joint velocity programming technique to regulate the body’s moving speed and orientation for a position-controlled quadruped robot that performs trotting or pacing locomotion. The robot model is mapped to a new coordinate space in order to decouple the control of its body. In one plane of the new coordinate space, the robot is simplified to an inverted pendulum model to generate attitude and velocity tracking actions. In the other planes, body regulating problems are formulated in velocity forms and solved by designing support leg motions. The controllers in these planes are integrated to produce joint velocities that enable robust trotting and pacing locomotion at a variety of speeds and directions, despite lacking force control or feedback techniques. Physical test results as well as simulating results demonstrate control of the quadruped robot SmarQ to perform omni-directional locomotion, impact recovery, and adaptability to uneven terrains.

This paper presents a novel Bayesian-based controller for snake robots in cluttered environment. It extends the conventional shape-based compliant control into statistical field providing an explicit mathematical formulation with Bayesian network. A sequential density propagation rule is derived by introducing several probability densities in a unified framework. Specifically, two input influence densities are proposed to model the cumulative effect of various external forces that the snake robot undergoes. Moreover, the measurement likelihood model is exploited to give a more robust closed-loop feedback. Overall, the proposed approach provides an innovative way to handle challenging tasks of snake robot control in complicated environment. Experimental results have been demonstrated for both simulation and real-world data.

AIRo-5.1 an in-pipe inspection robot comprised of two passive compliant joints and a single active compliant joint that is driven by a series elastic actuator (SEA) is presented in the course of this study. As an aid in pipeline maintenance, AIRo-5.1 controls joint angles and the torque of middle joints, to enable them to adapt to bend, branch, vertical pipes, and slippery surfaces. To sense the joint torques, an improved durable polyurethane rubber spring was installed. To smoothly pass through T-branches, the angle trajectory of middle joints was calculated based on the pipe geometry and thus, was interpolated using a cosine curve. Experiments to verify robot performance in bent and T-branch pipes, its joint angle and torque control was conducted.

To access rough terrain and enhance the mobility in sandy terrain, a configurable paddle-wheel robot was pro-posed. This report addresses the paddle terradynamics, and the experimental verification of the locomotion performance of the robot over dry sandy terrain. To study the interactive forces between the paddle and the media, a terradynamic model is built and verified through experiments. To explore the locomotion performance, an indoor platform that allows the paddle-wheel module to move freely in both horizontal and vertical directions is created. Forward locomotion speed, height variant, and specific resistance are evaluated with different con-figurations. The protruding paddles have successfully reduced the slippage so as to increase the locomotion efficiency in sandy terrain. The performance of the whole robot has also been verified in outdoor sandy terrain.

Creative design of grippers on their configurations, mechatronics control system, and multi-component collaborative algorithms is often utilized to realize complex operations in industrial applications, due to the environmental constraints or specific task requirements. Firstly, this paper introduces the background problems. As the main automatic equipment -- the shield machine -- in the field of tunnel boring construction, needs frequent tool (cutter) replacement during underground process, but has no practical automatic method yet, due to heavy payload, complex environment and work procedure. Thus, an integrated solution was proposed by developing a specific gripper and a snake-like manipulator to accomplish tool replacement in a cooperative way. Through simple and unique design of relative components, the solution realizes a fully automatic and precise approach including heavy load tool grasping and regrasping, posture adjustment, unlocking and disassembly, and installation and locking. Finally, this paper also describes the experimental process of tool replacement by the prototype under a real working condition, and discusses the feasibility of putting the scheme into practical application through comparison.

In this paper, we updated an inspection robot with passive adaptation ability, which is used to detect small size water supply pipeline. By geometric calculation and kinematic verification, static model of the robot is checked for flexible movement in the pipeline. Besides, inertial measurement unit is leveraged to simultaneously detect the attitude of robot, and different algorithm is tested to compensate the camera image rotation, stabilizing the image output.

A floating base system is inevitably to contact the environment while it is moving. This paper explores the contact force estimation and regulation algorithm for a position-controlled floating base system without joint torque information. First, the joint space dynamic model of the system is presented and transformed into the contact space. Then, the inverse dynamics method is employed to estimate the contact forces. After that, a proportional-integral (PI) regulator is designed to drive the contact forces to track the desired values. Finally, the feasibility of this algorithm is demonstrated on a simulated bipedal platform.

Nonprehensile manipulation produces underconstraint motions that are sensitive to environmental dynamics. Legged locomotion constitutes a floating-based movement, whose dynamic is underactuated with respect to the inertial frame. When these two tasks are combined, system motion planning and control are complex due to their inherent underactuated features. This article presents a motion planning framework for a legged robot that uses its limbs for nonprehensile manipulation, as well as locomoting motions. First, issues related to the description of the robot-object-environment system and the task are presented. The velocity constraint that prevents separation and the force constraint that restricts interactive forces are then integrated into the system dynamic model to produce bounds on the system acceleration as a function of the system state. Then, we solve the motion planning problem by reducing the system dimensions in operational space and programming feasible trajectories within the phase plane. This approach is employed to control the quadruped robot TITAN-VIII to manipulate objects and locomote itself using Drive Mode, Inchworm Mode, Scoot Mode, and Throw Mode. Experimental results obtained through simulations and physical tests are reported to demonstrate the effectiveness of our approach.

This study presents an in-pipe inspection robot module, called AIRo-2.3s. This robot module can control its joint angle and torque and adapt to any directed bent pipe regardless of its orientation. Stretching the drive wheels against the inner wall of pipes is essential for adapting robots to be used in vertical pipes and slippery inner surfaces. To achieve this, a series elastic actuator (SEA) with a high reduction system and a polyurethane rubber is installed to sense the joint torque. More than 100 N constant traction force and a wide range of adaptive inner diameters (4 to 6 in.) are achieved despite the short body length, a minimum number of the drive wheels, and a simple joint of 1 degree of freedom. Experiments to verify the performance in bent pipes are conducted after the robot module configuration is described.

This study presents a differential elastic joint for use in multi-linked pipeline inspection robots. Active joints to stretch against the pipe wall are essential for adapting robots to use in vertical pipes and slippery inner surfaces where a large traction force is required. Series elastic actuators with a high reduction system have typically been used to sense force/torque in such applications. However, compactness, power, and bi-directional series elasticity are required to conduct in-pipe inspections. In this study, we propose an active joint using a differential elastic actuator with a rubber spring for decreasing the size and increasing the stiffness of the joint. After describing the configuration of the differential elastic actuator that is suitable for our robot and the design theory of the rubber spring cross-section, we conducted experiments to verify its torque property.

In this paper, we present a multi-link articulated wheeled in-pipe robot that can drive the wheel and roll joint by using only a single actuator installed in each link. The proposed mechanism enables the robot to move forward or backward and helically in pipes owing to rotation of the drive wheel and twisting of the body. These two movements are generated by a miter-geared differential mechanism installed in each joint, and the magnitudes of these movements depend on the load applied to the wheels and roll joints. However, controlling of two outputs independently and aligning the rotation of the roll joints as desired are extremely challenging. Therefore, in this study, we switch those two movements by driving the rear wheels and the front wheels of the robot alternately. In addition, a stopper is used to constrain the roll joint movement. By calculating the angle of elevation of the robot's helical movement in the pipe by using a kinematic model, we can design a stopper to precisely adjust the roll angle. We verified that the robot can twist using the differential mechanism, and we validated experimentally the effectiveness of the stopper.

This paper presents the dynamic modelling and motion planning method for a quadruped robot that uses its legs for nonprehensile manipulation as well as locomotion. Three different working modes named Drive Mode, Inchworm Mode and Scoot Mode are proposed to enable the robot to move forward together with the object. We firstly introduce a universal model for these modes and deduce its dynamic equation. Then the contact force constraints are combined and mapped to the system state variables. Based on the acquired state acceleration constraints, the motion planning problem can be solved by designing system state paths in the phase space. After that, we described the mathematical problems within the three working modes and generate the robot motions accordingly. Finally, experimental results obtained through simulations and physical tests are reported to demonstrate the effectiveness of our method.

This paper explores the control strategy for a multi-limb robot nonprehensilely pushing an object to slide on the floor. The robot's limb distals perform point contacts with the object and the floor. The contact velocity constraint and force constraint are proposed to prevent separation and restrict the system forces. Then the constraints are combined with the system dynamic models to obtain bounds on the system states. We solve the motion planning problem by selecting a feasible path in the reduced-dimensional space and generating the system trajectory along the selected path. An example is provided to illustrate the application of our technique on the physical platform.

A novel gait planning and control framework was developed for quadruped locomotion of a robot. It modeled the quadruped robot as two bipeds carrying the body from the front and rear ends. We first mapped the relationship between the joint torques of support legs and the torso forces of the bipedal sub-robots. Then the equations describing the relationship between the quadruped body forces and the bipedal torso forces under various operating modes of the robot were deduced and solved. Virtual forces were generated on the quadruped body to manipulate its velocity and orientation. Then these virtual forces were distributed to the front and hind sub-robots to generate support leg torques. The state machines and gait generators for the two bipedal sub-robots were designed individually, resulting in the decoupling of the gait parameters in the front legs and hind legs. The effectiveness of the controller was validated through dynamic simulations.

In this paper, active disturbance rejection control is designed for position/force control of a holonomic constrained mobile manipulator in presence of uncertainties and disturbances. A dynamic model of the mobile manipulator is derived, based on the Lagrange formulation. The basic idea of the proposed control design is to estimate the unknown internal dynamics of the mobile manipulator and external disturbances by the linear extended state observer and to actively compensate them by the control input. The stability of the proposed control system is analyzed. Simulation results validate the effectiveness and strong robustness of the proposed control system.

The planar rimless wheel (PRW) is a classic and simple passive dynamic mechanism to simulate biped walking, different simplified PRW models have respective descriptions and limited applications. This paper focus on constructing the general PRW model, and analyzing the intrinsic and mathematical relation between different PRW models. Based that, the limit cycle of symmetric PRW and asymmetric PRW are proposed separately. Moreover, the stability in universal domain are investigated in detail. Furthermore, simulation and experiment results show that the 2-period limit cycle motion of the asymmetric PRW is more effective, flexible and self-adaptive compared with regular rimless wheel, and more actual applications would be achieved by adopting the general model.

This paper presents an anisotropic shadow-based operation assistant method for a multilink-articulated wheeled pipeline-inspection robot by using a single illuminator and camera. By displacing the position of the illuminator relative to that of the head camera, a crescent-shaped shadow appears in the images captured in a bent pipe. The size, position, and orientation of the shadow depend on the robot's orientation around the pipe axis, and the shadow disappears in a certain robot's orientation (anisotropic shadow). Generally, as for shadow based navigation systems, disappearances of the shadow should be avoided because the robot loses its way. However, our previously developed robot (AIRo-2) adapts to a bent pipe without any control when the robot's orientation and the pathway direction of the bent pipe are aligned. By aligning those two specific orientations, we propose operation assistant system to pass through winding pipes. In this paper, the shadow region is extracted using two types of image binarization. The proposed system was experimentally verified in pipelines including seven bent pipes by applying the pathway direction of the bent pipe (obtained from the shadow) to the rolling movement of the robot.

Snake robots have been researched for locomotion in unstructured environments due to its unique and adaptable gaits, however, they have not been used to interact with the environment in a dexterous manner, for example to grasp or push an object. In this paper, the effect of both the configuration of the snake robot (shape) and the friction between the snake robot and ground on a wrench applied to another object are studied. It is assumed that the snake robot has anisotropic friction with the ground, a property that has been proved to be essential for locomotion. The extreme cases of no friction and ideal unbounded friction can be both studied at the same time, making the model and conclusions very versatile and possible to apply to any coefficient of friction. The model and metrics are tested in a study case.

This paper designs a guide rail for a wall-climbing robot based on passive suction cups. The designed guide rail can guarantee stable climbing of a wall-climbing robot. Firstly, to design the parameters of the guide rail, properties of the utilized passive suction cup are experimentally studied. Then a guide rail is designed to distribute the forces of the attached suction cups. It guarantees that the front attached suction cup of the robot obtains a large enough reaction force from the attached surface. Experimental results show that the robot prototype with the designed guide rail is able to stably climb a surface without falling off, since the front suction cup of the robot prototype can be completely attached to the climbing surface.

This paper presents a multilink-articulated robot with omni and hemispherical wheels (AIRo-II) for inspecting and exploring winding pipes. To quickly adapt to winding pipes, holonomic rolling movement without moving forward and backward is more useful. However, this requires the replacement of driving actuators with rolling actuators at the expense of the driving force. In this paper, we investigate the possibility of high maneuverability of multilink-articulated robots in winding pipes by using less actuators and by designing spring joints. We further validate this by experimental verification.

The safety of working on walls has been improved by several adsorption mechanisms most of which sustain the absorption by pumps or other actuators. This research proposes an alternative method (a spring-suspended suction cup with a buckled plate spring) that can be attached for long durations without any vacuum pumping system. The negative pressure of the spring suspended suction cup is analyzed and the buckled plate spring is appraised by the energy efficiency and force over long adsorption times of the suction cup. The adhesion time of the suction cup is calculated and compared with that of the volume-fixed suction cup. Under high air inflow conditions, the spring-suspended suction cup adhered to the test surface for longer than the fixed-volume cup. The advantages of the spring-suspended suction cup were verified in experiments on a developed prototype.

This paper presents and discusses the trajectory tracking control design with friction compensation for a three wheeled omnidirectional mobile robot. Firstly, a dynamic model without considering the friction forces is derived. Part of the control effort is used to compensate the friction effects, which is estimated by an extended state observer without using a friction model. Then traditional resolved acceleration control is applied to the robot, based on the derived dynamic model. In addition, stability analysis of the controller and observer is presented. Experimental results show that the proposed control design is efficient in compensating the friction effects and in improving the tracking control performances.

Robots capable of both locomotion and interaction with the environment are necessary for robots to move from ideal laboratory situations to real applications. Snake robots have been researched for locomotion in unstructured environments due to its unique and adaptable gaits. However, they have not been used to interact with the environment in a dexterous manner, for example to grasp or push an object. In this paper, the model of a snake robot in contact with external objects (or the environment) is derived. Metrics that are coordinate-independent are derived in order to quantify the wrench that a snake robot could exert into these objects. In particular, we show that the configuration of the robot plays a significant role in these metrics. The model and metrics are tested in a study case.

Snakes and worms are capable of travelling along a straight line on a resistance medium using rectilinear locomotion. To apply this kind of gait in snake-inspired robots, some fundamental properties remain elusive. In this paper, we study the directional migration of a three-segment self-propelled system on a rough horizontal surface with Coulomb's dry friction. We elucidate the possibility that the system achieves directional migration through the propagation of extension and contraction wave. The necessary and sufficient conditions are certified to insure that the system is able to start from the state of rest. To analyze the approximately steady-state motion of the system, we provide explicit formulas for the mean velocity of the whole system by method of averaging. It is confirmed that for isotropic friction, the average speed and direction of the motion can be excited controlled.

Snake robots are highly redundant robots that could potentially be used as robotic arms, allowing them to interact with the environment. However they do not have a fixed base, making them difficult to control accurately. In this paper, a complete modeling approach and an optimization algorithm are presented that show the torques that allow a snake robot to track a trajectory while keeping one of its links from slipping. To do this, it is essential to consider the static friction between the ground and a snake robot. The forces of static friction are modeled as bounded constraints, in a similar fashion as the constraint forces studied in grasping with robotic hands. Simulations are carried out to analyze the problem.

To gain high mobility on challenging terrains, a mobile robot based on eccentric paddle mechanism (ePaddle) with locomotion versatility has been proposed. In this paper, a paddle-aided stair-climbing motion is presented for this ePaddle-based robot. The robot can roll on the stair as a traditional wheeled vehicle and also can climb up the stair under the help of its paddles. Robot-stair interaction modes are presented and typical feasible postures of the robot in stair-climbing are discussed. Frictional requirements for the robot to hold a desired posture are evaluated by modelling statics of the robot. Analyzed results reveal that two critical scenarios in wheeled mode occur when the front-wheel is at the bottom of the riser, and when the rear-wheel is at the top of the riser, respectively. In contrast, frictional requirements of the paddle-aided stair-climbing postures confirm that the robot can climb up the stair with all feasible postures by touching the stair with the paddle, which verifies the effectiveness of the proposed paddle-aided stair-climbing.

Snakes and worms are capable of travelling through tightly confined spaces on a resistance medium using rectilinear locomotion. To apply this kind of gait into snake-inspired robots, some fundamental properties remain elusive. In this paper, we present a n-segment kinematic model of the snake robot based on an ideal anchor assumption. Then, the relationships between the motion performance and the gait patterns are identified based on two force constraints hypothesises. To validate theoretical analysis of kinematic model and prediction of average velocity, the experiments are conducted on a novel snake-like robot prototype. Each module of the robot contains unique one-direction wheels, which generate sufficient backward friction force severing as anchoring force.

In this paper, we present a new in-pipe robot with independent underactuated parallelogram crawler modules, which can automatically overcome inner obstacles in the pipes. The parallelogram crawler modules are adopted to maintain the anterior-posterior symmetry of forward and backward movements, and a simple differential mechanism based on a pair of spur gears is installed to provide underactuated mechanisms. A central base unit connects each crawler module through foldable pantograph mechanisms. To verify the basic behavior of this robot, primary experiments in pipes with different diameters and at partial steps were conducted.

This paper presents a biomimetic approach based on central pattern generator (CPG), to control turning motion of a snake-like robot. One of the interesting features of a biological snake is its ability to avoid obstacles or a barrier by turning its whole body from its trajectory. This special obstacle avoidance motion is different from other types of animal, and thus, it is worth to be analyzed and realized into a snake-like robot. The paper first briefly explains: 1) the phase oscillator model which represents the CPG model and 2) the CPG network. Next, we address several issues related to the existing/typical turning control of a snake-like robot. We then propose the phase transition method utilizing the phase difference control parameter to realize the turning motion of a snake-like robot. We also introduce a new parameter to control the turning of the robot, where it provides a way to incorporate sensory feedback into the CPG model. Simulation results show that the proposed turning method can be used efficiently as an obstacle avoidance method for a snake-like robot.

The omnidirectional mobile robots with MY wheels-II are discontinuous dynamic systems. This paper derives a continuous model from a given discontinuous dynamic model. Firstly, the problem of a previously proposed dynamic model, average dynamic model, is analyzed. It shows that the effectiveness of the average dynamic model is limited to robots under a certain class of configurations. To overcome this problem, we first derive the switching conditions of MY wheel-II. Then a continuous dynamic modeling method, using adaptive continuous curves instead of the real discontinuous contact radius in the discontinuous dynamic model, is proposed based on the switching conditions. The resulting dynamic model is a smooth NLPV model, which may then be used as one solution for the model-based control design. The effectiveness of the proposed NLPV model is verified and compared through open-loop simulations against the average model.

Sandy terrains are widely distributed on this planet and include desert, beach, and area affected by volcanic eruption where covered with ash. Currently, these environments still present a challenge for mobile robots due to their poor trafficability. One of the most essential requirements on such terrains for mobile robots is to generate enough drawbar pull with a small amount of slippage. For this purpose, protrusions or convex patterns called lugs (i.e. grousers) are attached on the wheels. However, oscillational drawbar pull generated by lugs results vibration of the robot body and therefore disturb the stability of the robot. In this paper, we aim to reduce the oscillation of the drawbar pull by proposing a novel wheeled mechanism integrated with an actively actuated lug. The drawbar pull on the sandy terrain in fabricated testbed is firstly measured on a prototype mechanism. Based on measured force, a strategy of tuning sinkage length of the active lug for generating stable drawbar pull is proposed. This method has the advantage of that it requires neither prior knowledge on terramechanic models nor physical properties of the terrain. The performance of the proposed method is finally verified by comparing the generated drawbar pull with that of a wheel with a fixed lug.

This paper presents a new suction cup with a disc spring for exiting adsorption mechanisms (for example, wall-climbing robots). The center of the suction cup can be pulled up manually through the use of buckling of the disc spring. When deformation of the disc spring reaches a certain balance point, it can sufficiently generate adsorption force. However, with time, the adsorption force will gradually decrease because of air inflow into the suction cup. Then, the spring can be automatically pulled up again to next balance point according to the air inflow. Repeating this process enables the adsorption for a long duration. By pushing back the disc spring to the original position manually, the suction cup is easily detached from the wall. This proposed suction cup can achieve long adsorption, easy attachment and detachment, and energy saving. In this paper, analysis of the adsorption force, design of the suction cup, and experiment of the prototype are conducted.

An eccentric paddle locomotion mechanism (ePaddle) was proposed to enhance the mobility of amphibious robots for multi-terrains tasks. There are several feasible terrestrial and aquatic gaits for an ePaddle-based robot. In this paper, we present the method for modelling thrust in one of the aquatic gaits, namely the oscillating-paddling gait, for an ePaddle mechanism. The conception of the oscillating-paddling gait is introduced firstly and followed by the thrust model. In order to verify the proposed model, a thrust measuring facility is built. A series of experiments are carried out with this facility. From the results, we verify the thrust model for the oscillating-paddling gait. Furthermore, we characterize how the amplitude and direction of the generated net thrust force relate with the amplitude, period and oscillation ratio of the oscillating-paddling gait.

The use of rescue robots in disaster response has become increasingly common, but few of them can operate on harsh amphibious terrain, especially on soft terrain. To access such challenging environments, we have proposed a novel eccentric paddle mechanism (ePaddle) which exhibits high environmental adaptability and can achieve six major types of gait, such as wheel-like rolling, two legged walking gaits, wheel-paddle-integrated rolling, and aquatic paddling gaits. In this paper, we present the details of the paddle trajectory generation method for ePaddle to access soft terrain. On such conditions, the paddle can operate as a lug to generate additional pull and lift forces that improve traction performance and prevent wheel sinkage than using wheel-like rolling. We adopt the passive pressure theory to model the pull and lift forces acting on the paddle; these forces are determined by soil parameters and the inclination angle, sinkage length, and moving direction angle of the paddle. Based on this model, we propose a motion planning strategy to control the inclination angle and protruded length of the paddle to generate required pull and lift forces and weaken any fluctuations in them. Then, we verify the effectiveness of our proposed method by using simulations.

This paper presents the dynamic modeling and analysis of a three-wheeled omnidirectional mobile robot with MY wheels-II, whose dynamics is nonlinear and piecewise-smooth. Firstly, the detailed dynamic model of the robot is derived, which shows that the robot is actually a switched nonlinear system. Analysis of the robot dynamic properties based on the detailed dynamic model is presented in detail. Then to facilitate the controller design for the switched nonlinear system, based on the detailed dynamic model, an average dynamic model is proposed by simply averaging the wheel contact radius. The resulting average dynamic model is nonlinear and smooth, which may then be used as one solution for the model-based control design. Open-loop simulation results show the dynamic properties of the mobile robot. In addition, the effectiveness of the proposed average model in predicting characteristics of the detailed dynamic model is also illustrated through open-loop simulations.

Stair-climbing is a necessary capacity for mobile robots. This paper presents an online control method for the stair-climbing of a transformable tracked robot, Amoeba-II, and this robot is also an isomerism-modules robot with different mechanism modules. Based on the reasonable compartmentalization and kinematics analysis of the stair-climbing process, the coordination of the rotations of modules can reduce the slippage between tracks and terrain. To ensure that the robot can climb stairs with enough capability and stability, the stair-climbing criterion for the robot has been established based on the force analysis of each stage of the stair-climbing procedure. Meanwhile, the interference-avoiding criterion has been set up to avoid the interference between the non-tracked module of the robot and the stair. The experiment for the stair-climbing of the robot has been implemented to certify the validity of the online stair-climbing control method for a transformable tracked robot.

This paper presents an optimal design method for a new robot called amphibious transformable robot which can not only perform reconfiguration but also implement tasks in amphibious environment. To satisfy a range of performance requirements for the robot in aquatic and terrestrial environments, the multi-objective optimization method is adopted to design the robot which can achieve the optimal comprehensive performance in the amphibious environment. Based on the kinematics and dynamic analysis of the robot, the multi-objective optimization problem of the mechanism parameters design is established on the mapping relationships between the performance indexes, and then Multi-Objective Genetic Algorithm is proposed to get Pareto solution. Based on combination weighting method of multi-attribute decision-making, the result can be extracted and used to direct the mechanism design of the amphibious transformable robot, Amoeba-II. The experiment for the maneuverability of Amoeba-II in the amphibious environment is performed to verify the validity and applicability of the mechanism-parameters design method of amphibious transformable robot based on Multi-Objective Genetic Algorithm.

To enhance the mobility of amphibious robots for multi-terrains tasks, we have proposed an eccentric paddle locomotion mechanism (ePaddle) with several feasible terrestrial and aquatic gaits. In this paper, we present a rigid paddle model for predicting the thrust force in one of the aquatic gaits, namely the rotational paddling gait. Thrust forces calculated by this model demonstrate the idea that by relocating the paddle shaft eccentrically from its wheel center, the rotating paddles will generate vectored thrust force for swimming. The paddling motion and the validity of the rigid paddle model are verified by experiments in a water tank.

In this paper, we propose a novel configuration of a multi-legged robot which has only one degree of freedom in each leg and a passive body segment joint between each pair of body segments. With this configuration, a robot can perform planar legged locomotion with less actuators than the conventional legged robots. To model the mobility of a robot with this novel configuration, we firstly select candidate configurations from all of the possible configurations by performing mobility analysis on the robot. Then, feasible gait patterns for achieving planar locomotion are designed with these candidate configurations. The idea that legged locomotion is achievable by less actuators as well as the gait planning methods are verified finally by simulations.

Connectionist Central Pattern Generator models (CCPG) are helpful to understand how the CPG neural mechanism functions, and have relatively small complexity which makes them suitable for controlling snake-like robots. However, there are few CCPG models are constructed to generate the snake-like robot's three-dimensional gaits, which are important for adapation, and their gaits generation ability is also very inadequate. According to the CPG mechanism, a hierarchical CCPG model (HCCPG) with small complexity is proposed to implement the three-dimensional gaits better. The HCCPG has a two-layers structure, namely the basic rhythmic signal generation layer and the output signal modulation layer. The HCCPG can generate three-dimensional gaits well and is extendable. Based on the HCCPG, a three-dimensional gait control method is proposed. The simulations and experiments validate this method.

In this paper we present a decoupled control method based on kinematic models of an amphibious reconfigurable robot called ePaddle-based quadruped robot (eQuad). The locomotion mechanism of eQuad is a novel eccentric paddle mechanism (ePaddle) that can perform wheeled, legged and paddling actions in both terrestrial and aquatic environments. We first introduce five terrestrial and aquatic gaits. A duty factor of up to 1.0 can be achieved for the legged walking. Therefore, the proposed robot eQuad can walk with a unique gait by eliminating the swing phase of the legs, and it has a large stable margin because all its legs are in contact with ground during walking. Kinematic models of this robot suggest that with this unique gait the reconfigurable ePaddle mechanism has the potential to achieve both legged and wheeled locomotion with the aid of a simple controller. A decoupled controller adapted from the wheeled robot is then built to evaluate this idea. Finally, simulations are performed to verify our proposed decoupled control and gait sequence planning methods.

Biologically inspired control approaches based on the central pattern generator (CPG) have been studied to apply to a snake-like robot. One of the important problems is to determine how to construct a sensor-driven neural system in order to control the robot for adaptive locomotion. To solve this problem, a sensor-based neural network is presented in this paper. To realize collision-free behavior of the snake-like robot, three IR range sensors were used to obtain the obstacle information. By analyzing the motion strategies for the snake like robot, a signal feedback network was constructed based on the neuron model. The sensory signals were used as the adjusted values for the input of CPG oscillators. By changing the driving input of the extensor neurons or flexor neurons in the CPG network, the snake-like robot could perform the desired turning motion to avoid the obstacles. The performance of the proposed sensor-driven neural controller was verified by conducting an experiment on a snake robot in an environment with obstacles.

Our amphibious snake-like robot conquers the terrestrial and aquatic environments with different kinds of gait. Future work has been planned to apply the robot in inspection tasks in complicated wild environments.

To achieve versatile locomotion in complex amphibious environments, a robot should be capable of performing different gaits. In this paper we present such a versatile amphibious robot based on a novel eccentric paddle mechanism (ePaddle). We first illustrate the concept of the ePaddle with five major possible gaits and conceptual gait sequences. We then summarize five types of configurations from these gaits. Based on these configurations, two motion behaviors are found and modeled by using kinematic equations for the future gait planning tasks. To verify the proposed ideas, we develop an ePaddle prototype module. Several simulations on these gaits are performed to verify the conceptual locomotion gait and the developed kinematic models. Experiments on five possible configurations demonstrate the valid of the ePaddle concept and the prototype design.

Making biomimetic robots move like natural animals is an interesting problem, because this topic involves not only the low level algorithm that controls the movement of robots' bodies and limbs but also the high level control strategy that deals with different kinds of situations. Based on a certain biological assumption, a self-tuning multi-phase CPG for snake robots is proposed. This method imitates the control strategy of natural snake's movement in different environments, which enables the snake robot to move more quickly and naturally. Through kinematic and dynamic analysis of snake robots, optimal control parameters are chosen for the decision strategy. Due to the intrinsic property of the multi-phase CPG, this model can change the movement patterns and control parameters autonomously according to external information. As a result, such neural control provides a powerful but simple way to self-tune adaptable behaviors in snake robots.

This paper presents a self-rescue mechanism for a screw drive in-pipe robot, which only uses one DC motor. The robot has two working modes, Normal Working Mode and Self-rescue Mode. Under normal working mode, the robot propels itself in the pipe just as other classical screw drive robots. When the robot encounters the obstacle and gets jammed, the lock up mechanism and motion control mechanism of the robot are activated. Then, the robot changes from working mode to self-rescue mode and moves away in the reverse direction to avoid jamming in the pipe. The change of the working mode is determined by the characteristics of the mechanism. The proposed mechanism can be used as a safety protection method for the pipe robot. Experiments have been conducted to testify the proposed mechanism. Compared with those with screw drive mechanisms, robots with self-rescue mechanism are able to avoid jamming in the pipe.

The mobile robots often perform the dangerous missions such as planetary exploration, reconnaissance, anti-terrorism, rescue, and so on. So it is required that the robots should be able to move in the complex and unpredictable environment where the ground might be soft and hard, even and uneven. To access to such terrains, a novel robot (NEZA-I) with the self-adaptive mobile mechanism is proposed and developed. It consists of a control system unit and two symmetric transformable wheel-track (TWT) units. Each TWT unit is driven only by one servo motor, and can efficiently move over rough terrain by changing the locomotion mode and transforming the track configuration. It means that the mobile mechanism of NEZA-I has self-adaptability to the irregular environment. The paper proposes the design concept of NEZA-I, presents the structure and the drive system of NEZA-I, and describes the self-adaptive principle of the mobile mechanism to the rough terrains. The locomotion mode and posture of the mobile mechanism is analyzed by the means of simulation. Finally, basic experiments verify the mobility of NEZA-I.

The control of a snake-like robot is a challenging problem because of the complex dynamics and the unknown environment. We have proposed an energy-based method, called passive creeping, to control the serpentine locomotion. This paper lays emphasis on the stability and the adaptability of the method. First, the local orbital stability of the movement is explicated based on the maximal Lyapunov exponent and the recurrence plot. Second, the adaptability to the environment is analyzed, and an optimal adaptive law based on the energy proportion is put into use to perfect the method. The particular advantages of the passive creeping include the comprehensive concept, the explicit control, and the inherent adaptability.

Inspired from the natural motion of snakes, a head-navigated locomotion is proposed for snake-like robots in this paper. Different from the traditional serpentine motion, the head of the snake-like robot would always maintain its direction along the forward direction of the whole robot. By utilizing this particular characteristic, the obstacles in front of the undulatory motion could be detected conveniently by a distance sensor installed on the head module. Based on the analysis of the configuration of the snake-like robot in the head-navigated locomotion, CPG-based control is introduced for the control system. Two kinds of control strategies for the realization of the automatic obstacle avoidance are proposed. Both simulation and experiment have been carried out to verify the proposed motion pattern.

This paper deals with a tracked robot that consists of the proposed crawler module, in which a planetary gear reducer is used as the power transmission device to give two different outputs with just one actuator. This under-actuated system could perform posture control through the interaction between the front and rear modules. On occasion, the posture that the front module is lifted up can make the robot overcome obstacles actively and easily. To find out the controllable postures, the static analysis of the robot has been conducted. In this paper, we provide the control strategy for performing the posture control, and propose the control methods including direct, indirect, and cooperative control to conduct the posture control. Experimental tests show the effectiveness of the control methods.

This paper presents a tracked robot composed of the proposed crawler mechanism, in which a planetary gear reducer is employed as the transmission device and provides two outputs in different forms with only one actuator. When the crawler moves in a rough environment, collision between mechanism and environment inevitably occurs. This under-actuated crawler can absorb the impact energy that should be transmitted to the actuator. A modular concept for the crawler is proposed for enlarging its use in robot systems and mechanical design of a modular crawler is conducted. Using this crawler module, a four-crawler-driven robot is realized by easily assembling. Experiments are conducted to verify the proposed concept and mechanical design. A single crawler module can well perform the proposed three locomotion modes. The four-crawler-driven robot has good adaptability to the environment which can get over obstacles both passively and actively.

A snake-like robot can locomote in various environments; and it can manipulate objects when one end is fixed. A method of dynamic modeling for locomotion-manipulation of the snake-like robot is developed in order to unify the dynamic equations of two states. A virtual structure for orientation and position and the product-of-exponentials formula describe the mechanism and the kinematics of the robot. The dynamics of the robot are established in a Riemannian manifold. Furthermore, the dynamics of manipulation can be directly degenerated from those of locomotion. This method unifies the dynamics of locomotion and manipulation of the snake-like robot in the differential geometry formulation. Finally, simulation results of the method are presented.

In this paper, a mobile mechanism with driving capability and detecting function is proposed for in-pipe inspection task. Based on this mechanism, a robot is designed and fabricated. The advantage of this robot is that it has mobile ability in the pipe and detecting function for inspection, while only one DC motor is installed. This results in low energy consumption and low cost to make. The robot propels itself in the pipe under a driving mode, and it is used for finding the defect of the pipe under a detecting mode. By switching these two working modes, the robot performs the inspection task without other extra DC motors. Moreover, a velocity change mechanism is introduced to adapt the change of the payload through adjusting the incline angle of the roller. The characteristics of this mechanism are analyzed by comparison with a classical screw drive robot and a direct drive robot. Finally, basic experiments are conducted to testify the mobility and efficiency of this robot.

Robots are efficient and economic for in-pipe inspection tasks. In this paper, we deal with versatility and multifunction of in-pipe inspection robots. A versatile platform equipped with one driving motor is the main body of multifunctional mobile unit (MMU) that performs inspection tasks. We have developed three kinds of MMU by fixing different assemblies on the proposed versatile platform. MMU1 is an adaptive mobile mechanism that changes its working mode autonomously and gets over the obstacle without any extra motorpsilas help, in the case that the pipe diameter changes. MMU2 is a mechanism that has both driving ability and detecting function; MMU3 is equipped with assemblies that integrate the wheel and propeller function together, thus, MMU3 is able to propel both in dry pipe and watery pipe. These MMUs are all constructed from a same platform, which makes little increase of the cost but realizes of more kinds of robots. Several basic experiments have been conducted to confirm the effectiveness and mobility of the MMUs.

In this paper, development of a CPG-based controllers for meandering locomotion of a snake-like robot that can adapt to changing friction is presented. The controllers are composed of two kinds of CPG models and receives environmental information from friction force sensors attached on the bottom of the robot. Adaptive CPG parameters are obtained using genetic algorithm with environments with different friction conditions.

A robot, which is composed of adaptive mobile mechanism, is developed for the purpose of performing the internal inspection tasks of pipelines. Adaptability and efficiency are the basic considerations for this robot. Based on these concepts, a prototype is designed and fabricated. The proposed adaptive mobile mechanism equipped with one actuator can perform two working modes, a normal working mode and an assistant enhanced mode. Robot under the normal working mode is used for moving in pipe or monitoring the inner surface of the pipe. On the other hand, robot under the assistant enhanced mode will produce a larger torque to help itself surmount an obstacle in the pipe without any other driving actuator. This special feature is achieved by applying a power transmission mechanism. The rotation problem of the stator is solved according to the calculation results of the robot kinematics. Basic experiments have been conducted to testify the adaptability and efficiency of the robot.

The paper analysis a kinematic model for a wheeled mobile robot (WMR) traversing uneven terrain. A new form of the kinematics for wheeled mobile robot is deduced, through analyzing Jacobian matrices of individual wheel and rearranging the variables. The performance and characters of the kinematic formulation are explained using physical conception. A new method is proposed to set up the kinematics formulation for wheeled mobile robots. After analyzing the actuation kinematics, simulation results are provided to validate the motion of wheeled mobile robot over a special terrain

With 3D (3-dimensional) movement's ability and rhythmic locomotion mode, a nature snake makes itself survive in rugged terrains. The rhythmic activities of most creatures are generated by the CPG (central pattern generator). Based on this fact, the sustained-type neuron has been adopted to construct a cyclic inhibitory CPG model for a snake-like robot whose joints are perpendicularly connected in series. Having compared with the sustained-type neuron and the mutual inhibitory CPG, the cyclic inhibitory CPG was proven to generate capably rhythmic output with the least number of differential equations. In this paper, we introduce the neuron network organized by the cyclic inhibitory CPGs connected in line with unilateral excitation to control the 3D locomotion of a snake-like robot, and present the necessary condition for the CPG neuron network to sustain a rhythmic output. By implementing this control architecture to a simulator with consideration of mechanical dynamics of a real snake-like robot "Perambulator", preliminary parameter setting of the CPG neuron network for its 3D locomotion is obtained. Moreover, it is shown that "Perambulator" can successfully exhibit 3D locomotion by using the output of the proposed CPG network. The obtained results have also provided a bran new approach to understand the unknown neuron network of nature snakes

A reconfigurable modular planetary robot system (RMPRS) consists of the parent body and multiple asymmetric wheel-manipulator child-robot modules. The module, which can independently locomote and manipulate, possesses the orientation of posture and the direction of locomotion. The modules have reconfiguration capability so that a group of the modules can construct a variety of configurations. The aim of the robot reconfiguration is to generate better configuration with respect to the directional locomotion adapted to the environment. Module state vector (MSV) and configuration state matrix (CSM) are presented and constructed for representing the asymmetric module and the configurations, and supporting the transformation operation for triggering the elementary motions of the module and the reconfiguration. The algorithm for optimizing the assembly reconfiguration of discrete modules is proposed and the result is evaluated through numerical simulation in an example

The recent natural and man-made devastations have urged the research on the urban search and rescue (USAR) robot systems. This paper presents a novel shape-shifting mobile robot system named as Amoeba II (A-II) for the urban search and rescue application. It has been designed with three degrees of freedom (DOFs) and two tracked drive systems. This robot consists of two modular mobile units and a joint unit. The mobile unit is a tracked mechanism to enforce the propulsion of robot. The joint unit can transform the robot shape for getting high mobility. A-II robot not only can adapt to the environment but also can change its body corresponding to locus space. It behaves two states including the parallel state (named as II state) and the linear state (named as I state). The parallel state enables the robot with high mobility on rough ground. With the linear state the robot can climb upstairs and go through narrow space such as the pipe, cave etc. Also, the joint unit can propel the robot to roll in sidewise direction. Especially, two modular A-II robots can be connected through jointing common interfaces on the joint unit to compose a stronger shape-shifting robot, which can transform the body into four wheels-driven vehicle. Finally, the elementary experimental results validate the adaptation and its mobility

Several insights gained from observing quadruped robots in omnidirectional static walking experiments at high speed on a slope are presented here. In order to allow a robot to move as fast as possible, the height of center of gravity (COG) and three rotating axes, i.e., roll, pitch, and yaw, were used to discuss the COG with the corresponding optimal body posture (COBP). The COBP is the posture in which the motion velocity is maximized according to the height of COG, stability, degree of slope, and direction. Successive gait transition with a minimum number of steps is achievable with the use of a common foot position before and after a gait transition. The time required to change gaits may be reduced by designing the foot positions during crawling and rotating while limiting reachable region of the foot on a slope. The robot, thus, walks in any direction fast and statically with COBP by dynamically changing the height of COG and body posture during gait transitions

In this paper, we discuss the optimal body postures of a quadruped robot to perform omni-directional static walking on a slope. The optimal body posture is the posture with the maximum possible moving speed w. r. t. slope and moving direction. The proposed method based on dynamically changing body posture during gait-transitions, is used to maintain high robot motion velocity on slope. The timing of changing body posture is designed by considering the stability during gait-transition. Using the proposed method, the robot can walk into any direction with the fastest moving speed on a slope. Through walking experiments by computer simulation, the validity of the proposed method has been verified.

A new Reconfigurable Planetary Robot System (RPRS) is introduced in this paper. The locomotion mechanism, especially the static force analysis and the climbing ability for different configurations of the multiple child-robots are presented in detail. The basic configurations of two child-robots systems were given in three modes: connecting in series with arm in front or back and combining to a loop with grasper. The simulation results of these three configurations based on static analysis demonstrate that the climbing ability is closely correlated to their configurations. Compared the results, the conclusion can be obtained that the loop configuration has the best effect than others on slope climbing. The actual experiments of the child-robots system have illustrated the simulating results, and an exciting phenomenon has emerged, which shows that all the configurations can climb bigger gradient than the simulating results. The phenomenon rightly discloses the characteristic of the novel architecture of the child-robot.

A reconfigurable planetary rover system (RPRS) is presented, including the parent body and some child robots. The child robot composed with the arm part and the wheel part has two moving modes: locomotion mode and manipulation mode. According to the mechanical characteristics, we proposed the two methods for the motion planning of swerving locomotion. The results of experiments showed that the robot can achieve turn during locomotion by adjusting the arm's attitude. But the child robot's radius of left-hand turning motion during locomotion is bigger much than the radius of right-hand turning motion during locomotion and the effect is not obvious. The method of spot turning is presented by use of the difference between radial frictional force and tangential frictional force of ground and direction wheel, which is important for robot for autonomous locomotion.

Based on the structure of both biological snakes and snake-like robots and their rhythm locomotion, the theory of the cyclic inhibitory CPG is adopted as a control method to construct a neuron network model of the snake-like robot. The relation between the CPG parameters and the serpentine locomotion of the snake-like robot is defined in this paper. The validity of the serpentine locomotion controlled by the CPG model is verified through a snake-like robot model. The modulating methods of the CPG parameters are brought forward and simulated to realize the required turn motion and the reconfiguration. Moreover, we present that real snake-like robot can successfully exhibit serpentine locomotion by using controller output of the proposed architecture. Finally, the aspects of future researches are discussed.

Based on the structure of both biological snakes and snake-like robots and their rhythmic locomotion, the musical theory is adopted as a control method to study on a snake-like robot. The relation between the rules and symbols of the musical theory and the control process of the snake-like robot is defined in this paper. Thus the data sequence of the relative angles in the serpentine locomotion is melodized. The gait score of the serpentine locomotion is utilized to control a snake-like robot named "Perambulator-I". Finally, the aspects of the future researches are discussed.

In this paper, we propose a successive gait-transition method for a quadruped robot to realize omnidirectional static walking. The gait transition is successively performed among the crawl gaits and the rotation gaits, while the feet hold in common positions before and after gait transition. The gait-transition time is reduced by carefully designing the foot positions of the crawl gait and the rotation gait, while limiting the feet in rectangular reachable motion ranges. Computer simulations and experiments were executed to show the validity and the limitation of the proposed gait-transition method.

Simulating platform plays a crucial role in multi-robot research, as a tool to quickly and efficiently test new concepts, strategies, and algorithms. In this paper, OpenGL and Visual C++ based modeling method has been discussed in detail to establish a platform for the 3D simulating of multi-link mobile robots and their collaboration. The cooperation strategies, the control methods and the communication mechanisms of multi-robot system can be explored and verified by this platform. A planetary robot system is used to verify the validity of the developed platform. The effectiveness and the practicability of the platform are successfully demonstrated by a four-robot motion coordination simulating results.

Docking is an essential function for reconfigurable planetary robot system (RPRS), it supports almost all metamorphic characteristics of the system. This paper presents a space docking method for self-reconfigurable modular robot system. The method adopts a position sensory detector (PSD) to get the space geometrical relation between modular child robots. By using the kinematics and inverse kinematics modeling of the child robot, a docking control algorithm is developed to achieve space dock automatically. To validate the method, simulation experiments were done on a platform based on OPENGL, and the simulating results were given as well.

A reconfigurable modular snake robot has been developed, which can not only move on a plane but aIso achieve some f-dimensional motions while reconfigured. Control equations of 3-dimensional locomotion were established by the composition of two bending motions in mutual orthogonal plane. Three types of lateral rolling locomotion, flapping, linear rolling and curved rolling, were achieved by controlling the amplitudes and the number of two waves in the two bending motions. Using the three types of locomotion the snake robot can realize net lateral translation, alternation of its contact base and rolling over some obstacles. The lateral rolling locomotion obtains its driving force through the interaction with the environment. The rolling shape and its direction depend on the transferring direction and phase difference of the two waves respectively.

In this paper, we propose a control architecture for meandering locomotion of snake-like robots based on neural oscillator network (NON). The proposed architecture is composed of a network of central pattern generators (CPGs) to realize propagation of purposive oscillation with specific phase shift. By implementing this architecture to a simulator with consideration of mechanical dynamics of a real snake-like robot, we present realization of meandering motion and preliminary policies about parameter settings of the NON. Moreover, we present that real robot can successfully exhibit meandering movement by using controller output of the proposed architecture.

To fit well the needs of autonomous mobile manipulator, two robust adaptive Neuro-Fuzzy motion controllers are developed. The first controller, based on a computational efficient processing scheme for fuzzy reactive navigation, is used to generate the commands for the servo-systems of robot arm so that, locally, it may choose its way to its goal autonomously. The second fuzzy reactive navigation is implemented in mobile platform so that it maintains a permanent flexible path between two nodes in network generated by a probabilistic roadmap approach. In order to consider the compatibility of stabilisation, mobilisation and manipulation, we derive a coordinated fuzzy local planner algorithm so that the mobile manipulator can avoid stably unknown and/or dynamic obstacles The purpose of an integration of robust controller and Modified Elman Neural Network is to deal with unmodeled bounded disturbances and/or unstructured unmodeled dynamics.

With high adaptability to environments snakelike robots offer a variety of advantages over other mobile robots. Such a robot with passive wheels has quite different mechanism in locomotion from that of other locomotion systems. We have developed a snakelike robot for rescue applications. The unit composing the snakelike robot of Shenyang Institute of Automation (SIA) is a module including actuating system and control system. To let the snakelike robot perform turning motion and compensate offset and orientation errors of the robot, we propose an amplitude modulation method and a phase modulation method based on analysis of the serpenoid curve. The side motion of the snakelike robot can also be generated by the amplitude modulation. The tracking control method is also proposed based on sensor information. Computer simulations and experimental tests are performed to show the validity of the proposed methods.

Hyper-redundant manipulator has more degrees of freedom than the least necessary to perform a given task, thus it has the features of overcoming conventional industrial robot's limitation such as improving its kinematics and dynamic performances. Crucial as it is, effective control of hyper-redundant manipulator is difficult for its redundancy. A novel shape control technique based on the concept of variable structure regular polygon and subsystem has been proposed. This technique, using variable structure regular polygon and neural networks models, is completely capable of solving the control problem of a planar hyper-redundant manipulator with any number of links following any desired path. With regular polygon side number's variety and its shape's transformation, the manipulator's configuration changes accordingly and moves actively to perform the task form point to point or following a path. Compared with other methods to our knowledge, this technique has such superiorities as fewer control parameters, higher precision and less computation. Simulation of a six-link modularized manipulator's inspection work in a bottle-like concave has demonstrated that this control technique is available and effective.

Snake-like robots that behaves biological snakes' characteristics have possibility to make them supremely adapted for environment. In this paper, we firstly formulate the kinematics and the dynamics of 3-dimensional snake robots and then analyze the sinus-lifting creeping motion as an example. In this study, the sinus-lifting motion was imaged as the creeping motion in 2-dimensional plane with different distribution of normal reaction forces for simplicity. Comparison has been made between the creeping locomotion with uniform normal reaction forces, and the sinus-lifting creeping motion where the normal reaction forces are distributed by the weight with respect to the body curvature. As a result, we know that the snake-like robot in the sinus-lifting creeping motion mode with curvature-weighted normal reaction forces moves at higher speed than that in the creeping motion mode with uniform normal reaction forces.

It is essential to design a joint mechanism for snake-like robots to exhibit more mobility, no singularity and powerful actuation for many applications. By adding a series of passive wheels to the perimeter of the newly designed joint mechanism with 3 DOFs, a snake-like robot provided with the characteristic of omnidirectional mechanism can traverse rough terrain and compensate the lack of actuation due to passive wheels. The nonholonomic constraints and kinematics are analyzed as well as the redundancy. The composite motion method and grouping alternation motion control method are thus proposed for the locomotion of robot and the avoidance of singularity. Also, the grouping alternation motion adds a new explanation to the sinus lifting locomotion of natural snake. Computer simulations validate both mobility of mechanism and effectiveness of control methods.

Biological snakes' diverse locomotion modes and physiology make them supremely adapted for environment. The special structure of snakes and their unique movement offer them peculiar ability of climbing and moving even in some ill-conditioned environments such as on the marshland or in narrow tubes. In this paper, we first discuss the controllability of a 3-dimensional snake-like robot, and then show the controllability of the robot by computer simulation.

Biological snakes' diverse locomotion modes and physiology make them supremely adapted for environment. To realize these snakes' noticeable features, we have developed a snake-like robot that has no any forward direction driving force. To enlarge the environment-adaptable ability of our robot, in this study we discuss the creeping locomotion of our snake-like robot on a slope. A computer simulator is presented for analysis of the creeping locomotion of our snake-like robot on a slope, and the environment-adaptable body shape for the creeping locomotion of the snake-like robot on slope is also derived through this simulator.

In this paper we propose a successive gait-transition method for a quadruped robot to realize omni-directional static walking. The gait-transition is successively performed among the crawl gaits and the rotation gaits while the feet are held in a common position before and after the gait transition. The gait-transition time is reduced by carefully designing the foot position of the crawl gait and the rotation gait while limiting the feet in rectangular reachable motion ranges. Experiments were executed to show the validity and the limitation of the proposed gait-transition method.

Dexterity is an important issue for design, trajectory planning, and control, of manipulators. In this study, we introduce anew kinematic/static dexterity measure for manipulator manipulation. The measure is to evaluate how efficient a manipulator system is, while the limit driven characteristics of its actuators (DC motors) is included into consideration. The possible maximum velocity and force of the required task are derived in subjection to the heat-converted power limit of the DC motor, and two examples are used to show that the proposed dexterity measure is of task-dependent and changed due to the tasks.

Snakes perform many kinds of movement that are adaptable to the environment. Utilizing the snake (its forms and motion) as a model to develop a snake-like robot that emulates a snakes' function is important for generating a new type of locomotor and expanding the possible use of robots. We developed a simulator to simulate the creeping locomotion of a snake-like robot, in which the robot dynamics is modeled and its interaction with the environment is considered through Coulomb friction. This simulator makes it possible to analyze the creeping locomotion with the normal-direction slip coupled to gliding along the tangential direction. Through the developed simulator, we investigated the snake-like robot creeping locomotion which is generated only by swinging each of the joints from side to side, and discussed the optimal creeping locomotion of the snake-like robot that is adaptable to a given environment.

In this study, we present a time-optimal control scheme for kinematically redundant manipulators to track a predefined geometric path, subject to the limit heat characteristics of actuators (DC motor was assumed to be the used actuator). Constraints due to the rated torque and the rated velocity of the motor would not be valid for continuous use of manipulators, since the required mechanical output of the actuator (DC motor) exceeds its maximum power capacity and far more exceeds its heat-converted power limit. The heat-converted power limit of DC motor is thus considered as the actuation bound of actuator and the time-optimal trajectories are generated by using the phase-plane analysis and the linear programming technique in subjection to this bound. Computer simulation was also executed on a three-link planar rotary manipulator to demonstrate the effectiveness of the proposed scheme.

We propose a time-optimal control scheme for kinematically redundant manipulators to track a predefined geometric path, subject to joint torque limits. The scheme makes full use of redundancy to increase the path-tracking velocity, and the the optimal trajectory planning problem is solved by using phase-plane analysis and linear programming technique. Computer simulation is also executed on a three-link planar rotary manipulator to show that, 1) the redundancy of the manipulator is fully used to increase the path-tracking velocity, and 2) redundant joints plus one more joint use their bound values of torque all the the while the minimum time path-tracking task is performed.

Hyper-redundant manipulators have very large degrees of redundancy, thus possessing unconventional features such as the ability to enter a narrow space while avoiding obstacles. In this study a time-optimal control scheme was proposed for the coupled tendon-driven manipulators, in which a pair of tendons for driving a joint is pulled from base actuators via pulleys mounted on the base-side joints and the degrees of actuation redundancy exist. The time-optimal trajectory planning problem was solved by using the phase-plane analysis and the linear programming technique. Computer simulations were also performed to demonstrate the validity of the proposed scheme.

This research aims to discover the mechanism and principle for the emergence of the snakes' movement in order to realize a snake-like robot. In this study, we elucidate the standard creeping movement form of a snake, which is the typical locomotive motion shown by snakes. The so called serpentine curve in the constant steady-state velocity is derived for the uniform creeping locomotion of the snake, through analyzing physiologically its muscle characteristics. Muscular force is then discussed for this uniform locomotive curve. We also compare the locomotive efficiencies for various creeping movement curves of snake locomotion, by analyzing the ratio of the tangential force to the normal force and the power required for snake locomotion. The results show that the proposed serpentine curve is more valid as the snake creeping locomotion shape than the formerly suggested curves.

We propose a time-optimal control scheme for the manipulator to track a predefined geometric path, subject to constraints due to the limit heat characteristics of actuators (DC motor was assumed to be used as actuator). The generated heat of DC motor is considered as the driven bound, and the time-optimal trajectories are generated in this bound. Computer simulation was also performed to demonstrate the effectiveness of the proposed scheme with comparison to the former schemes subject to torque and velocity bounds.

A hyper redundant manipulator has a very large or infinite degree of kinematic redundancy, thus it is possessed of unconventional features such as the ability to enter a narrow space while avoiding obstacles. We propose a novel obstacle avoidance technique for the hyper redundant manipulator to perform a payload location task from point to point while avoiding existing static obstacles in the environment. The scheme is based on analysis in the defined posture space, where three parameters were used to determine the hyper redundant manipulator configurations. The scheme is verified by computer simulation in case of using the model of the developed Hyper-R Arm. It shows that our method works perfect and the obstacles are well avoided globally.

We develop further our singularity-consistent approach to arrive at a parameterized form of the dynamics of a nonredundant robotic mechanism tracking a desired path in Cartesian space. It is shown that this form is suitable for incorporating joint torque limits, which is an important issue for practical applications. We propose a closed-loop controller which behaves as a "conventional" resolved-acceleration type controller at regular points of the kinematic function. Around any singularity and at so-called instantaneous self-motion singularities the controller is able to truck the direction of the specified path exactly. The limit on the torque norm results in some position error, without deteriorating, however, the direction tracking ability. It is shown also that motion through the bifurcation type singularity can be easily controlled in practice as well.

A technique that stabilizes the existing local torque optimization solutions for redundant manipulators is proposed in this paper. The technique is based on a balancing scheme, which balances a solution of joint torque-minimization against a solution of joint velocity-minimization. Introducing the solution of joint velocity-minimization in the approach prevents occurrence of high joint velocities thus results in stable optimal arm motions, and guarantees the joint velocities at end of motion to be near zero. Computer simulations were executed on a three-link planar rotary manipulator to verify the performance of the proposed local torque optimization technique and to compare its performance with existing ones for various straight line trajectories.

A new type of a swarm, named multi-agent supporting system (MASS), is introduced for supporting structures where the configuration formed by many agents must be maintained even though there exist unknown disturbances. A control system for a MASS is also proposed on the basis of a new estimator of disturbance. The proposed disturbance estimator is described by inverting the stable digital inverse system. With this disturbance estimator, the unknown disturbance acting on each agent in the MASS is cancelled by the input, and influences less the output of the system. A computer simulation has been executed to demonstrate the effectiveness of the proposed method in comparison with the control method without the disturbance estimator.>

A nine-degree-of-freedom multijoint manipulator called the CT ARM-I has been developed. The CT ATM-I is based on the concept of coupled drive and the connected differential mechanism, and thus the force for lifting a payload does not concentrate on one actuator but is distributed among all actuators. This manipulator has a specific tendon traction force transmission mechanism in which a pair of tendons for driving a joint are pulled from base actuators via pulleys mounted on the base-side joints. The mechanism uses the coupled drive function of the tendon traction forces and thus enables the lightweight manipulator to exhibit high payload capability. Through the experimental study, it was demonstrated that the CT ARM-I has an active compliance arm and offers payload capability far superior to conventional designs.>

A coupled tendon-driven manipulator called the CT arm is introduced, an its control is discussed. The CT arm has a specific tendon traction force transmission mechanism in which a pair of tendons for driving a joint are pulled from base actuators via pulleys mounted on the base-side joints. The mechanism makes the most of the coupled drive function of the tendon traction forces and thus can exhibit enormous payload capability. The CT arm is solidly structured and can be inexpensively manufactured because of its mechanical simplicity. A control algorithm which minimizes the square sum of the traction force of tendons while satisfying given restrictions is introduced. The validity of the control method is shown by computer simulation.>

A coupled tendon-driven manipulator, CT arm, is presented. In its tendon traction force transmission mechanism, the pair of tendons driving a joint is pulled by base actuators via pulleys mounted on the base-side joints. The mechanism uses coupled drive function of the tendon traction forces and thus exhibits a large payload capability for such a light-weight manipulator arm. CT arm has a solid structure and can be manufactured inexpensively because of its mechanical simplicity. Through experimental simulation, it is known that CT arm has the structure of a variable compliance arm and has an unusually large payload capacity.>

A control method called redundancy decomposition control is proposed for the resolved acceleration control of a manipulator equipped with redundant degrees of freedom. In this method, the redundant degrees of freedom of a given manipulator are decomposed into nonredundant subsets. For every time interval from t to t+ Delta t, the acceleration of the corresponding subset of degrees of freedom is assumed to be controlled and the inverse kinematics and dynamics as well as the evaluation function are calculated using the nonredundant inverse Jacobian matrix. The calculation is performed in parallel for all the combinations of degrees of freedom. The optimum set of degrees of freedom is selected and it is used for the control of the time interval t to t+ Delta t. The proposed method is reviewed in comparison with conventional approaches, including the pseudoinverse matrix and null-space vector techniques. It is demonstrated that the proposed method almost always realizes better motion planning than the other two techniques, and is effective in real-time control.>