A Back-stepping Based Trajectory Tracking Controller for a Non-chained Nonholonomic Spherical Robot

Spherical robot has good static and dynamic stability, which provides it with strong viability in hostile environment, but the lack of effective control methods has hindered its application and development. This article deals with the dynamic trajectory tracking problem of the spherical robot BHQ-2 designed for unmanned environment exploration. The dynamic model of the spherical robot is established with a simplified Boltzmann-Hamel equation, based on which a trajectory tracking controller is designed by using the back-stepping method. The convergence of the controller is proved with the Lyapunov stability theory. Numerical simulations show that with the controller the robot can globally and asymptotically track desired trajectories, both linear and circular.

Design of a spherical robot based on novel double ballast masses principle

A spherical robot based on a novel double ballast masses principle is developed for military reconnaissance and unknown environment exploration. The robot is driven by two DC motors, each of which drives one ballast mass, and the two ballast masses are placed symmetrically on the major axis. Compared with the traditional ballast mass principle, the robot has featured high speed, the ability of slope climbing and obstacle overcoming in linear motion. The robot has two inputs and three DOF, which is a nonholonomic and underactuated system. The dynamic model of the robot is constructed, and the linear motion performance of robot in theory is proved by Adams simulation. The control system is briefly introduced, and the performance of the prototype is tested by experiments at last.

Research on the structure design of double eccentric coaxial spherical robot

The paper design a double eccentric mass driven spherical robot, the ball is also subject to eccentric force and inertia force that generate by internal drive units in movement. Due to the unique spherical shell, the robot in the dynamic state transition process, Friction cannot offset the robot motion state change due to internal driving motion error of small units. In order to make linear movement of the spherical robot that can smooth start, stop and speed control, the paper design a method for linear motion driven spherical robot with double eccentric mass control. The improved driving eccentric mass of robot total mass ratio is larger, that can provide the eccentric torque and inertia moment more, the robot has higher motion velocity.

Dynamical Analysis of a Novel Spherical Robot with Retractable Arms

A novel structure of a spherical robot with retractable arms was presented in order to fulfill the requirements of omni-direction movement and operation mission. Under the assumption of rolling without slipping, nonholonomic constraints were revealed and a dynamics model of the proposed robot was constructed by use of Kane＇s method. Numerical simulations about rectilinear motion and sigmoid curve motion of the system were carried out in Matlab, and as a comparison, the same trajectories were also implemented by a virtual prototype in ADAMS, which validate the derived dynamical model accordingly. With the derived dynamical model, torques/forces of joints were analyzed. The results indicate the disturbance forces or torques on each joint are not zero under the state of sphere moving, and with rational planning for the trajectory of the robot, there will be a great decrease of the disturbance forces or torques acting on the spherical caps and arms.

Control of a Spherical Robot: Path Following Based on Nonholonomic Kinematics and Dynamics

This paper presents the controller design for the path following of a spherical mobile robot, BHQ-1. Firstly, a desired velocity for the reference path is deduced from the kinematic model, which cannot be transformed into the classic chained form. Secondly, a necessary torque for the desired velocity is obtained based on the dynamic model. As to the kinematics, a one-dimensional function is selected to measure the two-directional tracking error, and the velocity of rolling forward is reasonably assumed to be constant; therefore the multiple-input multiple-output （MIMO） system is transformed into a single-input single-output （SISO） system. As to the dynamics, both exact dynamics and inexact dynamics with modeling error as well as bounded unknown disturbance are taken into account, based on which a proportional-derivative （PD） controller and a sliding mode controller with adaptive parameters are proposed respectively. Finally, convergence analysis and simulation results are provided to validate these controllers.

A Fuzzy PID Algorithm for a Novel Miniature Spherical Robots with Three-dimensional Underwater Motion Control

We proposed and developed a small bionic amphibious spherical robot system for tasks such as coastal environment monitoring and offshore autonomous search and rescue.Our third-generation bionic small amphibious spherical robots have many disadvantages,such as the lack of maneuverability and a small operating range.It is difficult to accomplish underwater autonomous motion control with these robots.Therefore,we proposed a fourth-generation amphibious spherical robot.However,the amphibious spherical robot developed in this project has a small and compact design,with limited sensors and external sensing options.This means that the robot has weak external information collection capabilities.We need to make the real time operation of the robot's underwater motion control system more reliable.In this paper,we mainly used a fuzzy Proportional-Integral-Derivative(PID)control algorithm to design an underwater motion control system for a novel robot.Moreover,we compared PID with fuzzy PID control methods by carrying out experiments on heading and turning bow motions to verify that the fuzzy PID is more robust and exhibits good dynamic performance.We also carried out experiments on the three-dimensional(3D)motion control to validate the design of the underwater motion control system.

Implementation of Caterpillar Inspired Rolling Gait and Nonlinear Control Strategy in a Spherical Robot

This paper presents a novel Central Pattern Generator （CPG） based rolling gait generation in a small-sized spherical robot and its nonlinear control mechanism. A rhythmic rolling pattern mimicking Pleurotya caterpillar is produced for the spherical robot locomotion. A synergetically combined feedforward-feedback control strategy is proposed. The feedforward component is generated from centrally connected network of CPGs in conjunction with nonlinear robot dynamics. Two nonlinear feedback control methods namely integral （first order） Sliding Mode Control （SMC） and High （or second） Order Sliding Mode Control （HOSMC） are proposed to regulate robot stability and gait robustness in the presence of matched parameter uncertainties and bounded external disturbances. Design, implementation and experimental evaluation of both roll gait control strategies for the spherical robot are done on smooth （indoor） and irregular （outdoor） ground surfaces, The performance of robot control is quantified by measuring the roll angle stability, phase plane convergence and wheel velocities. Experimental results show that proposed novel strategy is efficient in producing a stable rolling gait and robust control of a spherical robot on two different types of surfaces. It further shows that proposed high HOSMC strategy is more efficient in robust rolling gait control of a spherical robot compared to an integral first-order SMC on two different ground conditions.

Design, Implementation and Control of an Amphibious Spherical Robot

We proposed and implemented a leg-vector water-jet actuated spherical robot and an underwater adaptive motion control system so that the proposed robot could perform exploration tasks in complex environments.Our aim was to improve the kinematic performance of spherical robots.We developed mechanical and dynamic models so that we could analyze the motions of the robot on land and in water.The robot was equipped with an Inertial Measurement Unit(IMU)that provided inclination and motion information.We designed three types of walking gait for the robot,with different stabilities and speeds.Furthermore,we proposed an online adjustment mechanism to adjust the gaits so that the robot could climb up slopes in a stable manner.As the system function changed continuously as the robot moved underwater,we implemented an online motion recognition system with a forgetting factor least squares algorithm.We proposed a generalized prediction control algorithm to achieve robust underwater motion control.To ensure real-time performance and reduce power consumption,the robot motion control system was implemented on a Zynq-7000 System-on-Chip(SoC).Our experimental results show that the robot’s motion remains stable at different speeds in a variety of amphibious environments,which meets the requirements for applications in a range of terrains.

Design and test of stem diameter inspection spherical robot

Stem diameter is an important parameter in the process of plant growth which can indicate the growth state and moisture content of the plant,its automatic detection is necessary.Traditional devices have many drawbacks that limit their practical uses in general case.To solve those problems,a stem diameter inspection spherical robot was developed in this study.The particular mechanism of the robot has turned out to be suitable for performing monitoring tasks in greenhouse mainly due to its spherical shape,small size,low weight and traction system that do not produce soil compacting or erosion.The mechanical structure and hardware architecture of the spherical robot were described,the algorithm based on binocular stereo vision was developed to measure the stem diameter of the plant.The effectiveness of the prototype robot was confirmed by field experiments in a tomato greenhouse.The results showed that the machine measurement data was linearly correlated with the manual measurement data with R^(2) of 0.9503.There was no significant difference for each attribute between machine measurement data and manual measurement data(sig>0.05).The results showed that this method was feasible for nondestructive testing of the stem diameter of greenhouse plants.

MECHANISM DESIGN AND MOTION ANALYSIS OF A SPHERICAL MOBILE ROBOT

A new spherical mobile robot BHQ-1 is designed. The spherical robot is driven by two internally mounted motors that induce the ball to move straight and turn around on a fiat surface. A dynamic model of the robot is developed with Lagrange method and factors affecting the driving torque of two motors are analyzed. The relationship between the turning radius of the robot and the length of two links is discussed in order to optimize its mechanism design. Simulation and experimental results demonstrate the good controllability and motion performance of BHQ-1.

Optimal trajectory planning based on Hamiltonian function of a spherical mobile robot

Designed for planetary exploration,a spherical mobile robot BHQ-1 was briefly introduced.The mo-tion model of BHQ-1 was established and quasi-velocities were introduced to simplify some dynamic quan-tities.Based on the model,the time- and energy-based optimal trajectory of BHQ-1 was planned withHamiltonian function. The effects of three key coefficients on the shape and direction of the planned tra-jectory were discussed by simulations.Experimental result of the robot ability in avoiding an obstacle waspresented to validate the trajectory planning method.

Tracking Control in Presence of Obstacles and Uncertainties for Bioinspired Spherical Underwater Robots

During marine missions,AUVs are susceptible to external disturbances,such as obstacles,ocean currents,etc.,which can easily cause mission failure or disconnection.In this paper,considering the strong nonlinearities,external disturbances and obstacles,the kinematic and dynamic model of bioinspired Spherical Underwater Robot(SUR)was described.Subsequently,the waypoints-based trajectory tracking with obstacles and uncertainties was proposed for SUR to guarantee its safety and stability.Next,the Lyapunov theory was adopted to verify the stability and the Slide Mode Control(SMC)method is used to verify the robustness of the control system.In addition,a series of simulations were conducted to evaluate the effectiveness of proposed control strategy.Some tests,including path-following,static and moving obstacle avoidance were performed which verified the feasibility,robustness and effectiveness of the designed control scheme.Finally,a series of experiments in real environment were performed to verify the performance of the control strategy.The simulation and experimental results of the study supplied clues to the improvement of the path following capability and multi-obstacle avoidance of AUVs.

Development of an Amphibious Turtle-Inspired Spherical Mother Robot

Robots play an important role in underwater monitoring and recovery operations, such as pollution detection, submarine sampling and data collection, video mapping, and object recovery in dangerous places. However, regular-sized robots may not be suitable for applications in some restricted underwater environments. Accordingly, in previous research we designed several novel types of bio-inspired microrobots using Ionic Polymer Metal Composite （IPMC） and Shape Memory Alloy （SMA） ac- tuators. These microrobots possess some attributes of compact structure, multi-functionality, flexibility, and precise positioning. However, they lack the attributes of long endurance, stable high speed, and large load capacity necessary for real-world appli- cations. To overcome these disadvantages, we proposed a mother-son robot system, composed of several microrobots as sons and a newly designed amphibious spherical robot as the mother. Inspired by amphibious turtles, the mother robot was designed with a spherical body and four legs with two Degrees of Freedom （DOF）. It is actuated by four vectored water-jet propellers and ten servomotors, and it is capable of walking on land and cruising underwater. We analysed the mother robot＇s walking and underwater cruising mechanisms, constructed a prototype, and carried out a series of experiments to evaluate its amphibious motions. Good motion performance was observed in the experiments.

Task Planning and Collaboration of Jellyfish-inspired Multiple Spherical Underwater Robots

Task planning and collaboration of multiple robots have broad application prospects and value in the field of robotics.To improve the performance and working efficiency of our Spherical Underwater Robot(SUR),we propose a multi-robot control strategy that can realize the task planning and collaboration of multiple robots.To complete real-time information sharing of multiple robots,we first build an acoustic communication system with excellent communication performance under low noise ratio conditions.Then,the task planning and collaboration control strategy adjust the SURs so that they maintain their positions in the desired formation when the formation moves.Multiple SURs can move along desired trajectories in the expected formation.The control strategy of each SUR uses only its information and limited information of its neighboring SURs.Finally,based on theoretical analysis and experiments,we evaluate the validity and reliability of the proposed strategy.In comparison to the traditional leader–follower method,it is not necessary to designate a leader and its followers explicitly in our system;thus,important advantages,such as fault tolerance,are achieved.

Path Optimization Method for the Spherical Underwater Robot in Unknown Environment

One of the major respects of the autonomous capability of underwater robots in unknown environment is to be capable of global path planning and obstacles avoiding when encountering abrupt events.For the Spherical Underwater Robot(SUR)to fulfill autonomous task execution,this paper proposed a novel fuzzy control method that incorporates multi-sensor technology to guide underwater robots in unknown environment.To attain the objective,a SUR we designed is used to design the controller.According to its kinematic model,the safety distance was calculated and sensors(US1000-21 A)were arranged.The novel fuzzy control method was then explored for robot's path planning in an unknown environment through simulation.The simulation results demonstrate the capability of the proposed method to guide the robot,and to generate a safe and smooth trajectory in an unknown environment.The effectiveness of the proposed method was further verified through experiments with a SUR in a real platform.The real environment experiments by using the novel fuzzy control method were compared with the basic control method.The experimental results show that in unknown environments,the proposed method improves the execution efficiency and flexibility of the SUR.

Mechanics Unloading Analysis and Experimentation of a New Type of Parallel Biomimetic Shoulder Complex

The structure design for high ratio of carrying capacity to deadweight is one of the challenges for the bionic mechanism,while the problem concerning high carrying capacity has not yet be solved for the existing shoulder complex.A new type biomimetic shoulder complex,which adopts 3-PSS/S（P for prismatic pair,S for spherical pair） spherical parallel mechanism（SPM）,is proposed.The static equilibrium equations of each component are established by using the vector method and the equations for constrain forces with certain load are solved.Then the constrain force on the middle limb and that on the side limbs are compared in order to verify the unloading performance of the mechanism.In addition,the prototype mechanism of the shoulder complex is developed,and the force feedback experiment is conducted to verify the static analysis,which indicates that the middle limb suffers most of the external force and the effect of mechanics unloading is achieved.The 3-PSS/S spherical parallel mechanism is presented for the shoulder complex,and the realization of mechanics unloading is benefit for the improvement of the carrying capacity of the shoulder complex.

A decoupling three-dimensional motion control algorithm for spherical underwater robot

Underwater spherical robots are good assistants for ocean exploration,where motion control algorithms play a vital role.Conventional motion control algorithms cannot eliminate the coupling relationship between various motion directions,which will cause the motion control of various directions to interfere with one other and significantly affect the control effect.This study proposes a new decoupling motion control algorithm based on the robot attitude calculation for an underwater spherical robot designed for offshore,shallow water,and narrow terrain.The proposed method uses four fuzzy proportional-integral-derivative(PID)controllers to independently control the robot’s movement in all directions.Experiments show that the motion control algorithm proposed in this study can significantly improve the flexibility and accuracy of the movement of underwater spherical robots.