Adaptive Trajectory Tracking Control for Nonholonomic Wheeled Mobile Robots:A Barrier Function Sliding Mode Approach

The trajectory tracking control performance of nonholonomic wheeled mobile robots(NWMRs)is subject to nonholonomic constraints,system uncertainties,and external disturbances.This paper proposes a barrier function-based adaptive sliding mode control(BFASMC)method to provide high-precision,fast-response performance and robustness for NWMRs.Compared with the conventional adaptive sliding mode control,the proposed control strategy can guarantee that the sliding mode variables converge to a predefined neighborhood of origin with a predefined reaching time independent of the prior knowledge of the uncertainties and disturbances bounds.Another advantage of the proposed algorithm is that the control gains can be adaptively adjusted to follow the disturbances amplitudes thanks to the barrier function.The benefit is that the overestimation of control gain can be eliminated,resulting in chattering reduction.Moreover,a modified barrier function-like control gain is employed to prevent the input saturation problem due to the physical limit of the actuator.The stability analysis and comparative experiments demonstrate that the proposed BFASMC can ensure the prespecified convergence performance of the NWMR system output variables and strong robustness against uncertainties/disturbances.

A finite-time fuzzy adaptive output-feedback fault-tolerant control for underactuated wheeled mobile robots systems

This paper investigates the adaptive fuzzy finite-time output-feedback fault-tolerant control (FTC) problemfor a class of nonlinear underactuated wheeled mobile robots (UWMRs) system with intermittent actuatorfaults. The UWMR system includes unknown nonlinear dynamics and immeasurable states. Fuzzy logic systems(FLSs) are utilized to work out immeasurable functions. Furthermore, with the support of the backsteppingcontrol technique and adaptive fuzzy state observer, a fuzzy adaptive finite-time output-feedback FTC scheme isdeveloped under the intermittent actuator faults. It is testifying the scheme can ensure the controlled nonlinearUWMRs is stable and the estimation errors are convergent. Finally, the comparison results and simulationvalidate the effectiveness of the proposed fuzzy adaptive finite-time FTC approach.

A Wheeled Wall-Climbing Robot with Bio-Inspired Spine Mechanisms

This paper presents a wheeled wall-climbing robot with the ability to climb concrete, brick walls using circular arrays of miniature spines located around the wheel. The robot consists of two driving wheels and a flexible tail, just like letter “T”, so it is called Tbot. The simple and effective structure of Tbot enables it to be steerable and to transition from horizontal to vertical surfaces rapidly and stably. Inspired by the structure and mechanics of the tarsal chain in the Serica orientalis Motschulsky, a compliant spine mechanism was developed. With the bio-inspired compliant spine mechanism, the climbing performance of Tbot was improved. It could climb on 100° （10° past vertical） brick walls at a speed of 10 cm·s^-1. A mechanical model is also presented to analyze the forces acting on spine during a climbing cycle as well as load share between multi-spines. The simu- lation and experiment results show that the mechanical model is suitable and useful in the optimum design of Tbot.

Motion mechanism and gait planning of a wheeled micro robot

Based on a novel shape memory alloy （SMA） actuator, a micro worming robot is presented. The robot adopts a wheeled moving mechanism. The principle of the robot＇s enlarged pace is introduced, and the structure and motion mechanism of the SMA actuator and the wheeled moving mechanism are discussed. The gait about the robot＇s rectilinear movement and turning movement is also planned. Under the effect of the eccentric wheel self-locking mechanisms and changing-direction mechanisms, the robot can move forward and backward, and turn actively, which overcomes the disadvantages of the traditional SMA micro robots to a certain extent. Furthermore, some experiments on the heating current of the SMA actuator and the robot＇s motion capability are carded out.

Adsorption Performance of Sliding Wall-Climbing Robot

Sliding wall-climbing robot （SWCR） is applied worldwide for its continuous motion, however, considerable air leakage causes two problems： great power consumption and big noise, and they constraint the robot＇s comprehensive performance. So far, effective theoretical model is still lacked to solve the problems. The concept of SWCR＇s adsorption performance is presented, and the techniques of improving utilization rate of given adsorption force and utilization rate of power are studied respectively to improve SWCR＇s adsorption performance. The effect of locomotion mechanism selection and seal＇s pressure allocation upon utilization rate of given adsorption force is discussed, and the theoretical way for relevant parameters optimization are provided. The directions for improving utilization rate of power are pointed out based on the detail analysis results of suction system＇s thermodynamics and hydrodynamics. On this condition, a design method for SWCR-specific impeller is presented, which shows how the impeller＇s key parameters impact its aerodynamic performance with the aid of computational fluid dynamics （CFD） simulations. The robot prototype, BIT Climber, is developed, and its functions such as mobility, adaptability on wall surface, payload, obstacle ability and wall surface inspection are tested. Through the experiments for the adhesion performance of the robot adsorption system on the normal wall surface, at the impeller＇s rated rotating speed, the total adsorption force can reach 237.2 N, the average effective negative pressure is 3.02 kPa and the design error is 3.8% only, which indicates a high efficiency. Furthermore, it is found that the robot suction system＇s static pressure efficiency reaches 84% and utilization rate of adsorption force 81% by the experiment. This thermodynamics model and SWCR-specific impeller design method can effectively improve SWCR＇s adsorption performance and expand this robot applicability on the various walls. A sliding wall-climbing robot with high adhesion efficiency is developed, and this robot has the features of light body in weight, small size in structure and good capability in payload.

Development and control of flexible pneumatic wall-climbing robot

A new kind of flexible pneumatic wall-climbing robot,named WALKMAN-I,was proposed. WALKMAN-I is basically composed of a flexible pneumatic actuator (FPA),a flexible pneumatic spherical joint and six suction cups. It has many characteristics of low-cost,lightweight,simple structure and good flexibility. Its operating principle was introduced. Then three basic locomotion modes,which are linear motion,curvilinear motion and crossing the orthogonal planes,were presented. The safety conditions of WALKMAN-I were discussed and built. Finally,the control system was designed and experiments were carried out. Experimental results show that WALKMAN-I is able to climb on the vertical wall surface along a straight line or a curved path,and has the ability of crossing orthogonal planes and obstacles. The maximum rotation angle reaches 90°,the maximum velocity reaches 5 mm/s,and the rotation angle and the moving velocity of WALKMAN-I can be easily controlled.

Analytical modeling and multi-objective optimization(MOO) of slippage for wheeled mobile robot(WMR) in rough terrain

Good understanding of relationship between parameters of vehicle, terrain and interaction at the interface is required to develop effective navigation and motion control algorithms for autonomous wheeled mobile robots （AWMR） in rough terrain. A model and analysis of relationship among wheel slippage （S）, rotation angle （0）, sinkage （z） and wheel radius （r） are presented. It is found that wheel rotation angle, sinkage and radius have some influence on wheel slippage. A multi-objective optimization problem with slippage as utility function was formulated and solved in MATLAB. The results reveal the optimal values of wheel-terrain parameters required to achieve optimum slippage on dry sandy terrain. A method of slippage estimation for a five-wheeled mobile robot was presented through comparing the odometric measurements of the powered wheels with those of the fifth non-powered wheel. The experimental result shows that this method is feasible and can be used for online slippage estimation in a sandy terrain.

Robust simultaneous tracking and stabilization of wheeled mobile robots not satisfying nonholonomic constraint

A robust unified controller was proposed for wheeled mobile robots that do not satisfy the ideal rolling without slipping constraint.Practical trajectory tracking and posture stabilization were achieved in a unified framework.The design procedure was based on the transverse function method and Lyapunov redesign technique.The Lie group was also introduced in the design.The left-invariance property of the nominal model was firstly explored with respect to the standard group operation of the Lie group SE(2).Then,a bounded transverse function was constructed,by which a corresponding smooth embedded submanifold was defined.With the aid of the group operation,a smooth control law was designed,which fulfills practical tracking/stabilization of the nominal system.An additional component was finally constructed to robustify the nominal control law with respect to the slipping disturbance by using the Lyapunov redesign technique.The design procedure can be easily extended to the robot system suffered from general unknown but bounded disturbances.Simulations were provided to demonstrate the effectiveness of the robust unified controller.

Wheeled foot quadruped robot HITAN-I

In view of the robot running environment, the structure of wheeled foot and quadruped are adopted in this robot system, which combines the priorities of both wheeled robot and legged robot. Based on CAN bus, the two-class robot control system using multiple controllers and drivers is constructed. At the same time, serial inverse kinematics of swaying leg and parallel inverse kinematics of supporting legs are analyzed independently. The forward gait and turning gait are planned and experiment image is given at last.

Dynamics and Wheel's Slip Ratio of a Wheel-legged Robot in Wheeled Motion Considering the Change of Height

The existing research on dynamics and slip ratio of wheeled mobile robot （WMR） are derived without considering the effect of height, and the existing models can not be used to analyze the dynamics performance of the robot with variable height while moving such as NOROS- Ⅱ. The existing method of dynamics modeling is improved by adding the constraint equation between perpendicular displacement of body and horizontal displacement of wheel into the constraint conditions. The dynamic model of NOROS- Ⅱ in wheel motion is built by the Lagrange method under nonholonomic constraints. The inverse dynamics is calculated in three different paths based on this model, and the results demonstrate that torques of hip pitching joints are inversely proportional to the height of robot. The relative error of calculated torques is less than 2% compared with that of ADAMS simulation, by which the validity of dynamic model is verified, Moreover, the relative horizontal motion between fore/hind wheels and body is produced when the height is changed, and thus the accurate slip ratio can not be obtained by the traditional equation. The improved slip ratio equations with the parameter of the vertical velocity of body are introduced for fore wheels and hind wheels respectively. Numerical simulations of slip ratios are conducted to reveal the effect of varied height on slip ratios of different wheels. The result shows that the slip ratios of fore/hind wheels become larger/smaller respectively as the height increases, and as the height is reduced, the reverse applies. The proposed research of dynamic model and slip ratio based on the robot height provides the effective method to analyze the dynamics of WMRs with varying height.

Adaptive trajectory tracking control of two-wheeled self-balance robot

Wheeled mobile robot is one of the well-known nonholonomic systems. A two-wheeled sell-balance robot is taken as the research objective. This paper carried out a detailed force analysis of the robot and established a non-linear dynamics model. An adaptive tracking controller for the kinematic model of a nonhotonomic mobile robot with unknown parameters is also proposed. Using control Lyapunov function （CLF）, the controller＇s global asymptotic stability has been proven. The adaptive trajectory tracking controller decreases the disturbance in the course of tracking control and enhances the real-time control characteristics. The simulation result indicated that the wheeled mobile robot tracking can be effectively controlled.

Modeling and Adaptive Control of an Omni-Mecanum-Wheeled Robot

The complete dynamics model of a four-Mecanum-wheeled robot considering mass eccentricity and friction uncertainty is derived using the Lagrange’s equation. Then based on the dynamics model, a nonlinear stable adaptive control law is derived using the backstepping method via Lyapunov stability theory. In order to compensate for the model uncertainty, a nonlinear damping term is included in the control law, and the parameter update law with σ-modification is considered for the uncertainty estimation. Computer simulations are conducted to illustrate the suggested control approach.

Sensor-less Terrain Estimation and Torque Control of a Wheeled Mobile Robot

As unmanned electric wheeled mobile robots have been increasingly applied to high-speed operations in unknown environments,the wheel slip becomes a problem when the robot is either accelerating,decelerating,or turning at high speed.Ignoring the effect of wheel slip may cause the mobile robot to deviate from the desired path.In this paper a recently proposed method is implemented to estimate the surface conditions encountered by an unmanned wheeled mobile robot,without using extra sensors.The method is simple,economical and needs less processing power than for other methods.A reaction torque observer is used to obtain the rolling resistance torque and it is applied to a wheeled mobile robot to obtain the surface condition in real-time for each wheel.The slip information is observed by comparing the reaction torque of each wheel.The obtained slip information is then used to control the torque of both wheels using a torque controller.Wheel slip is minimized by controlling the torque of each wheel.Minimizing the slip improves the ability of the unmanned electric wheeled mobile robot to navigate in the desired path in an unknown environment,regardless of the nature of the surface.

Real-time Non-linear Target Tracking Control of Wheeled Mobile Robots

A control strategy for real-time target tracking for wheeled mobile robots is presented.Using a modified Kalman filter for environment perception,a novel tracking control law derived from Lyapunov stability theory is introduced.Tuning of linear velocity and angular velocity with mechanical constraints is applied.The proposed control system can simultaneously solve the target trajectory prediction,real-time tracking,and posture regulation problems of a wheeled mobile robot.Experimental results illustrate the effectiveness of the proposed tracking control laws.

Mathematical modeling and simulation application for a wheeled mobile robot applied on pipe welding

A geometric model was built to represent the position relation of a wheeled mobile robot relative to a pipe. The relationship between the deviation of falling off for the robot and the curvature of the pipe was formulated quantitatively. Based on the relationship, a mathematical model was derived and a fuzzy control algorithm for the robot was developed. Simulations were carried out to confirm the dynamic index and the validity of the mathematical model of the fuzzy control algorithm for seam tracking of pipe welding. Experiments for pipe welding with the mobile robot were also carried out to verify the algorithm, and the results showed that the seam has a good quality with a preferable appearance of weld.

Fault detection and identification based on combining logic and model in a wall-climbing robot

A combined logic- and model-based approach to fault detection and identification （FDI） in a suction foot control system of a wall-climbing robot is presented in this paper. For the control system, some fault models are derived by kinematics analysis. Moreover, the logic relations of the system states are known in advance. First, a fault tree is used to analyze the system by evaluating the basic events （elementary causes）, which can lead to a root event （a particular fault）. Then, a multiple-model adaptive estimation algorithm is used to detect and identify the model-known faults. Finally, based on the system states of the robot and the results of the estimation, the model-unknown faults are also identified using logical reasoning. Experiments show that the proposed approach based on the combination of logical reasoning and model estimating is efficient in the FDI of the robot.

Research on Alternatively Moving Vacuum Absorbing Wall-climbing Robot

In conection with the complex working-surroundings of the wall-climbing Robot, this paper researched akind of alternatively moving mechanism with good obstacle-surmounting ability and high moving speed, making use ofthe thought of bionics. This paper designed a kind of self-adjusting multi-vacuum sucker. Furthermore, it employedthe theory of vacuum system to establish the work mathematics madel of control switch to are sucking disc and presented the design parameter of the control switch. In addition, this paper made use of the thought of bionics to design aobstacle-surmounting mechanism used in wall-climbing robot. Also it employed the theory Of robotics to analyze the kinematics and the dynamics movement of die robot.

High-performance wall-climbingrobot for inspection and maintenance

A wall-climbing robot that can continuously work on many types of wall surfaces has been developed. This robot based on low-vacuum adsorption principle consists of a locomotion mecha- nism, a sealing device, a fluid machine and a detecting system. The adsorption force is analyzed in details and its influencing factors are given. The robot prototype, which has the features of high ad- hesion efficiency, light body in weight, small size in structure and good capability in payload, is test- ed in outdoor and indoor environments. Through the experiments, the influences of the impeller slit and the seal clearance are discussed. In addition, the robot functions such as adsorption perform- ance, locomotion performance and wall adaptability are tested by experiments. The experiments have verified that the robot not only can climb on many types of wall surfaces, but also has outstand- ing locomotion ability and payload capacity.

On Transit Gait Programming of Six-legged Wall-climbing Robot

Transit gait programming is a key problem for a multi-legged robot to climb automatically from the ground up the wall, as well as between wall intersections. In this paper, a new idea is put forward by which the complex transit gait is decomposed into a sequence of two relatively simpler parts - single-leg motion and body pitching motion. An algorithm based on the above concept shows its feasibility and effectiveness in the graphic kinematics simulation.

Motion design of a hybrid wheeled/legged robot for lunar exploration

The robot consists of a quadruped mechanism and two active dual-wheel casters possesses the advantages of wheeled and legged mechanism, and can quickly move on the relatively plane ground with the wheeled mechanism, and can walk on the extremely uneven terrain with the legged mechanism. The effectiveness of the motion design of the hybrid robot is iHustrated by simulation results.