Near-Optimum Folding for a Reconfigurable Snake-Like Robot

To improve reachability of a snake-like robot depending on the problem, the links of the robot need to be resizable. In such a case folding links of the robot help to better plan obstacle avoidance. Optimum folding of the robot is the aim of our paper. We introduce a practical idea to construct reconfigurable and resizable snake robots which can be folded and an approximation algorithm to find near-optimum folding for the robot. Since an open chain is an abstract model of a snake-like robot, folding algorithms for the proposed robot are given in terms of an open chain. Ruler folding is a well-known NP-Complete problem. It considers folding of an n-link open chain linkage to the minimum length. The best previously known approximation algorithm for this problem has been developed by Hopcroft et al. They achieved the upper bound of 2m ₁ for the length of the folded chain in all cases, where m ₁ is the length of the longest link of the given chain. Already there are no any algorithms for open chain folding which guarante that the folded length of the open chain is less than 2m ₁. In this paper, we introduce an approximation algorithm which runs in O (n log n) using O (n) space. We introduce a function for the upper bound of the folded chain which depends to the lengths of all links in the given chain. Our experimental results show that for more than 95% of the problem instances we can achieve the same results in O (n) time. Using our folding algorithm, we can design the length of each link in an open chain to get x · m ₁ folded length where 1 < x < 2 is given and m ₁ is the length of the longest link of the chain. We introduce how to design a snake-like robot for which it can be folded in the given interval.     

Fluid-Filled Soft-Bodied Amoeboid Robot Inspired by Plasmodium of True Slime Mold

This paper presents a fluid-filled soft-bodied amoeboid robot inspired by the plasmodium of the true slime mold. The significant features of this robot are 2-fold. (i) The robot has a fluid circuit (i.e., cylinders and nylon tubes filled with fluid), and a truly soft and deformable body stemming from real-time tunable springs — the former seals protoplasm to induce global physical interaction between the body parts and the latter is used for elastic actuators. (ii) A fully decentralized control using coupled oscillators with a completely local sensory feedback mechanism is realized by exploiting the global physical interaction between the body parts stemming from the fluid circuit. The experimental results show that this robot exhibits adaptive locomotion without relying on any hierarchical structure. The results obtained are expected to shed new light on the design scheme for autonomous decentralized control systems.     

Control System Design for an Upper-Limb Rehabilitation Robot

Control system implementation is one of the major difficulties in rehabilitation robot design. The purpose of our study is to present newly developed control strategies for an upper-limb rehabilitation robot. The Barrett WAM Arm manipulator is used as the main hardware platform for the functional recovery training of the past-stroke patient. Passive and active recovery training have been implemented on the WAM Arm. A fuzzy-based PD position control strategy is proposed for the passive recovery exercise to control the WAM Arm stably and smoothly to stretch the impaired limb to move along predefined trajectories. An adaptive impedance force controller is employed in the active motion mode in which a fuzzy logic regulator is used to adjust the desired impedance between the robot and impaired limb to generate adaptive force in agreement with the change of the impaired limb's muscle strength. In order to evaluate the change of the impaired limb's muscle power, the impaired limb's mechanical impedance parameters as an objective evaluation index is estimated online by using a recursive least-squares algorithm with an adaptive forgetting factor. Experimental results demonstrate the effectiveness and potential of the proposed control strategies.     

Dynamic Rolling-Walk Motion by the Limb Mechanism Robot ASTERISK

New dynamic rolling-walk motion for a multi-legged robot with error compensation is proposed. The motion is realized by using the isotropic leg arrangement and the dynamic center of mass control inspired by bipedal robots. By using the preview control of the zero moment point (ZMP) with a cart-table model based on the bipedal robot's technique, the robot's center of mass trajectory is planned for the dynamic motion. The resolved momentum control for manipulating the multi-links robot as a single mass model is also implemented in the system to maintain the stability of the robot. In the new dynamic rolling-walk motion, the robot switches between the two-leg supporting phase and three-leg supporting phase to achieve dynamic motion with the preview control of the ZMP and resolved momentum control as dynamic motion controllers. The authors analyzed the motion and confirmed the feasibility in the Open Dynamics Engine before testing the motion with an actual robot. Due to the difficulties of controlling the ZMP during the two-leg supporting phase, the authors implemented error compensation by using a gyro sensor and compared the results.     

Modified PID Control of a Single-Link Flexible Robot

The use of flexible links in robots has become very common in different engineering fields. The issue of position control for flexible link manipulators has gained a lot of attention. Using the vibration signal originating from the motion of the flexible-link robot is one of the important methods used in controlling the tip position of the single-link arms. Compared with the common methods for controlling the base of the flexible arm, vibration feedback can improve the use of the flexible-link robot systems. In this paper a modified PID control (MPID) is proposed which depends only on vibration feedback to improve the response of the flexible arm without the massive need for measurements. The arm moves horizontally by a DC motor on its base while a tip payload is attached to the other end. A simulation for the system with both PD controller and the proposed MPID controller is performed. An experimental validation for the control of the single-link flexible arm is shown. The robustness of the proposed controller is examined by changing the loading condition at the tip of the flexible arm. The response results for the single-link flexible arm are presented with both the PI and MPID controller used. A study of the stability of the proposed MPID is carried out.     

Controlling Ensembles of Robots via a Supervisory Aerial Robot

We consider the task of controlling a large team of non-holonomic ground robots with an unmanned aerial vehicle in a decentralized manner that is invariant to the number of ground robots. The central idea is the development of an abstraction for the team of ground robots that allows the aerial platform to control the team without any knowledge of the specificity of individual vehicles. This happens in much the same way as a human operator can control a single robot vehicle by simply commanding the forward and turning velocities without a detailed knowledge of the specifics of the robot. The abstraction includes a gross model of the shape of the formation of the team, and information about the position and orientation of the team in the plane. We derive controllers that allow the team of robots to move in formation while avoiding collisions and respecting the abstraction commanded by the aerial platform. We propose strategies for controlling the physical spread of the ensemble of robots by splitting and merging the team based on distributed techniques. We provide simulation and experimental results using a team of indoor mobile robots and a three-dimensional, cable-controlled, parallel robot which serves as our indoor unmanned aerial platform.     

可重构模块化机器人研究

可重构模块化机器人是机器人学的一个新的发展方向,其研究的核心和基础问题是可重构机器人的模块设计以及模块组合的运动规划。设计了一种新型可重构模块化机器人,该机器人具有独特的平面连接机构,实现了结构、驱动、运动和功能的模块化,能够根据需要重新构形,完成实时任务。分别介绍了模块单元的机械结构设计、连接机构以及基于CAN总线的控制系统结构。构建了基于OpenGL技术和VC++开发平台的机器人仿真实验系统,仿真机器人构形和运动,验证了模块设计的正确性和整体运动构形规划方法的有效性。     

Mobile Robot Control Architecture for Reflexive Avoidance of Moving Obstacles

In this paper, a three-layer (deliberative, sequencing, reflexive) architecture is adopted and the structure of the reflexive layer is discussed. The objective of this architecture is to extract the basic actions that require hard-real-time execution from non-real-time-allowed behaviors by separating them into the reflexive and sequencing layers, respectively. The reflexive layer consists of resources, actions, an action coordinator and a motion controller. To guarantee the hard-real-time execution, a set of simple actions and an action coordinator are designed using the functions provided in the RTAI (Real-Time Application Interface for Linux) environment. Also, an obstacle avoidance algorithm based upon data from a laser range scanner is developed. For the purpose of avoiding a moving obstacle, which is treated as a moving circle through segmentation and circularization processes, a Kalman filter is developed to estimate the distance and the heading of the center of the moving circle. The effectiveness and real-time characteristics of the proposed reflexive layer and the developed algorithms are examined through experiments using scattered stand-still obstacles as well as a moving human.     

Transporting an Object by a Passive Mobile Robot with Servo Brakes in Cooperation with a Human

In this paper, we introduce a passive mobile robot called PRP (Passive Robot Porter) to realize transportation of an object in cooperation with human, which is developed based on a concept of passive robotics. PRP consists of three omni-directional wheels with servo brakes and a controller. It can manipulate an object by controlling an external force/moment applied by a human based on the control of the servo brakes. We consider the characteristics of the servo brakes and control the brake torque of each wheel based on the brake force/moment constraint so that several motion functions of PRP are realized based on the applied force. This allows PRP to track a path which includes motion perpendicular to the pushing direction of the human without using servo motors. The impedance-based motion control is also realized with respect to the perpendicular to the pushing direction. These functions are implemented on PRP experimentally, and the experimental results illustrate the validity of PRP and its control method.     

Investigations on the Hybrid Tracking Control of an Underactuated Autonomous Underwater Robot

The problem of trajectory tracking control of an underactuated autonomous underwater robot (AUR) in a three-dimensional (3-D) space is investigated in this paper. The control of an underactuated robot is different from fully actuated robots in many aspects. In particular, these robot systems do not satisfy Brockett's necessary condition for feedback stabilization and no continuous time-invariant state feedback control law exists that makes a specified equilibrium of the closed-loop system asymptotically stable. The uncertainty of hydrodynamic parameters, along with the coupled, nonlinear dynamics of the underwater robot, also makes the navigation and tracking control a difficult task. The proposed hybrid control law is developed by combining sliding mode control (SMC) and classical proportional–integral–derivative (PID) control methods to reduce the tracking errors arising out of disturbances, as well as variations in vehicle parameters like buoyancy. Here, a trajectory planner computes the body-fixed linear and angular velocities, as well as vehicle orientations corresponding to a given 3-D inertial trajectory, which yields a feasible 6-d.o.f. trajectory. This trajectory is used to compute the control signals for the three available controllable inputs by the hybrid controller. A supervisory controller is used to switch between the SMC and PID control as per a predefined switching law. The switching function parameters are optimized using Taguchi design techniques. The effectiveness and performance of the proposed controller is investigated by comparing numerically with classical SMC and traditional linear control systems in the presence of disturbances. Numerical simulations using the full set of nonlinear equations of motion show that the controller does quite well in dealing with the plant nonlinearity and parameter uncertainties for trajectory tracking. The proposed controller response shows less tracking error without the usually present control chattering. Some practical features of this control law are also discussed.     

Improved Control Strategy of 2-Sliding Controls Applied to a Flexible Robot Arm

Controlling a flexible robot arm driven by McKibben artificial muscles with direct transmission is delicate. The usual PID controller rapidly reveals itself to be inadequate and robust control tools are unavoidable. Classical sliding control, although robust, generates chatter. Several solutions are available to attenuate this phenomenon, among them the twisting and super twisting algorithms, which belong to the 2-sliding control set. It will be shown when to use the equivalent control and the effect of a noised sensor signal on control performance. Also, the use of an additional discontinuous term that increases robustness, performance and stability is put forward. Experimental results are presented and discussed.     

An Adaptive Controller Dominant-Type Hybrid Adaptive and Learning Controller for Trajectory Tracking of Robot Manipulators

This paper proposes a new hybrid adaptive and learning control method based on combining model-based adaptive control, repetitive learning control (RLC) and proportional–derivative control to consider the periodic trajectory tracking problem of robot manipulators. The aim of this study is to obtain a high-accuracy trajectory tracking controller by developing a simpler adaptive dominant-type hybrid controller by using only one vector for estimation of the unknown dynamical parameters in the control law. The RLC input is adopted using the original learning control law, adding a forgetting factor to achieve the convergence of the learning control input to zero. We will improve and prove that the adaptive dominant-type controller could be applied for tracking a periodic desired trajectory in which adaptive control input increases and becomes dominant of the control input, whereas the other control inputs decrease close to zero. The domination of the adaptive control input gives the advantage that the proposed controller could adjust the feed-forward control input immediately and it does not spend much time relearning the learning control input when the periodic desired trajectory is switched over from the first trajectory to another trajectory. We utilize the Lyapunovlike method to prove the stability of the proposed controller and computer simulation results to validate the effectiveness of the proposed controller in achieving the accurate tracking to the periodic desired trajectory.     

可重构模块机器人倾翻稳定性研究

介绍了一种可重构模块机器人,它可以通过构形的变化来提高系统的稳定性和抗倾翻能力．该机器人由3个模块组成,采用履带驱动,具有直线、三角、并排3种对称构形．在对移动机器人的倾翻因素和倾翻对策等问题进行分析的基础上,提出稳定锥方法,用倾翻性能指数对移动机器人的静、动态稳定性进行综合判定. 讨论了变形机器人3种对称构形在仰俯、偏转、倾斜等干扰组合作用下的倾翻性能指数和综合稳定性,并进行了仿真实验和非结构环境实验．     

Coordination of Multiple Control Schemes for Mobile Robot Navigation on the Basis of the Generalized Stochastic Petri-Nets

There have been two major streams of research for the motion control of mobile robots: model-based deliberate control and sensor-based reactive control. Since the two schemes have complementary advantages and disadvantages, each cannot completely replace the other. There are a variety of environmental conditions that affect the performance of navigation. The motivation of this study is that multiple motion control schemes are required to survive in dynamic real environments. In this paper, we exploit two discrete motion controllers for mobile robots. One is the deliberate trajectory tracking controller and the other is the reactive dynamic window approach. We propose the selective coordination of two controllers on the basis of the generalized stochastic Petri net (GSPN) framework. The major scope of this paper is to clarify the advantage of the proposed controller based on the coordination of multiple controllers from the results of quantitative performance comparison among motion controllers. For quantitative comparison, both simulations and experiments in dynamic environments were carried out. In addition, it is shown that navigation experiences are accumulated in the GSPN formalism. The performance of navigation service can be significantly improved owing to the automatically stored experiences.     

Design of Robust Stabilization and Fault Diagnosis for an Auto-balancing Two-Wheeled Cart

This paper investigates robust fault diagnosis strategies for the auto-balancing of an ergonomically designed two-wheeled cart which is inherently unstable and has a non-minimum phase. To endow the rider with robust stabilization, the normalized coprime factorization for steering is employed for allowing maximum model uncertainties and the driving orientation is achieved with an electronic differential steering control. A model-based fault-detection filter is designed to detect sensor faults. The observer gain obtained by solving an algebraic Riccati equation in the normalized coprime factorization approach offers some design convenience associated with the fault diagnosis filter. In order to promptly alert the rider for safety purposes in the event of a malfunction, the decision-making process to identify a critical failure is also investigated. Finally, evaluation examples are given to illustrate the performance of the proposed robust fault diagnosis strategies.     

Mechanism Design and Gait Experiment of an Amphibian Robotic Turtle

In this paper we describe the design of a new bio-inspired amphibian robot with high environmental adaptability. The robot, called MiniTurtle-I, can transform terrestrial and aquatic locomotion configurations through a new variable topology mechanism (Leg-Flipper). Based on the modular design philosophy, four rotatory joint modules (Joints I–IV) constitute a Leg-Flipper module. Variable topology structure transformation of Leg-Flipper by actuation redundancy enables the robot to achieve a variety of locomotion. Our motivation is to provide another solution to achieve amphibious movement both easily and efficiently. A prototype of MiniTurtle-I is built to exam the configuration transformations. Terrestrial, aquatic and semiaquatic gait experiments are performed to verify the locomotion functions of the MiniTurtle-I.     

The development and control of a flexible-spine for a human-form robot

In this paper, the development of a robot which has a flexible spine is presented. By embedding a multi-d.o.f. soft structure into a robot body as a spine, the robot can increase its ability to absorb shock and to work in various environment such as narrow places. As a result of these abilities, the robot can expand its opportunity to work in the human environment. Moreover, its motion could be more natural. The developed full-body human-form robot has a five-jointed flexible spine. Each joint (vertebra) has 3 d.o.f. Between each vertebrae is a 'disk' made of silicone rubber. The spine is controlled by eight tendons, whose tensions can be controlled using tension sensors and locally distributed microcontrollers. This paper describes the development of the flexible spine and the control of the posture of the spine and body.     

Development of a steerable,wheel-type,in-pipe robot and its path planning

This paper presents the development of a steerable, wheel-type, in-pipe robot and its path planning. First, we show the construction of the robot and demonstrate its locomotion inside a pipe. The robot is composed of two wheel frames and an extendable arm which links the centers of the two wheel frames. The arm presses the frames against the interior wall of a pipe to support the robot. The wheels of the frames are steered independently so that the robot can turn within a small radius of rotation. Experimental results of the locomotion show that the steering control is effective for autonomous navigation to avoid obstacles and to enter the joint spaces of L- and T-shaped pipes. Generally, autonomous navigation is difficult for wheel-type robots because the steering angles required to travel along a desired path are not easily determined. In our previous work, the relationship between the steering angles and locomotion trajectories in a pipe has already been analyzed. Using this analysis, we propose the path planning in pipes.     

Final-state control of a two-link cat robot

In this study, we deal with the twisting motion of a falling cat robot by means of two torque inputs around her waist. The cat robot consists of two rigid columns and has two internal actuators at the joint to generate torque inputs around normal coordinates. This system is a nonholonomic system whose angular momentum is conserved. We formulate the state equation that has torque inputs to the joint by using the nonholonomic constraint and the Lagrange-d'Alembert principle. Then, we transform the system into a linear parameter varying system. In order to improve error learning of a final-state control method, we provide the initial inputs in order to determine the appropriate rotation direction in the early stage of the twisting motion. Next, we introduce the method of the artificial potential function to the final-state control in order to make the maximum bending angle small. The feedforward torque inputs can be obtained by the final-state control in order to bring the system from the initial state to the final state in the desired time. In simulations, we also demonstrate that the twolink cat robot can land on her feet by using the 2-d.o.f. control system even when her waist damping coefficient varies.     

Kinematic Design of Modular Reconfigurable In-Parallel Robots

This paper describes the kinematic design issues of a modular reconfigurable parallel robot. Two types of robot modules, the fixed-dimension joint modules and the variable dimension link modules that can be custom-designed rapidly, are used to facilitate the complex design effort. Module selection and robot configuration enumeration are discussed. The kinematic analysis of modular parallel robots is based on a local frame representation of the Product-Of-Exponentials (POE) formula. Forward displacement analysis algorithms and a workspace visualization scheme are presented for a class of three-legged modular parallel robots. Two three-legged reconfigurable parallel robot configurations are actually built according to the proposed design procedure.