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.

Design and Test of Closed Hydraulic Transmission System of 4WD High-clearance Wheeled Sprayer

In conjunction with the working characteristics of the high-clearance wheeled sprayer and the benefits of the closed hydraulic system,a series of reasonable working parameters should be established,and a hydraulic system that fulfills the requisite specifications should be designed.The AMESim software model is employed to construct a closed hydraulic transmission system,and the simulation analysis is then performed according to the data of hydraulic components.According to analysis results,the prototype can be optimized and upgraded,and a verification test is further carried out.The test results demonstrate that the designed closed hydraulic transmission system meets the actual working requirements of the high-clearance wheeled sprayer and provides a stable experimental platform for intelligent control of agricultural machinery.

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.

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.

Obstacle performance of cobalt-enriching crust wheeled mining vehicle

A cobalt-enriching crust mining vehicle with four independent driven wheels was proposed. The influence of center-of-gravity position of mining vehicle on obstacle performance was studied. The results show that the mining vehicle has optimal obstacle performance with center-of-gravity position in the middle of suspension. A virtual prototype based on ADAMS software was built and its obstacle performance was simulated. Simulation results show that the mining vehicle with four independent driven wheels has excellent obstacle performance, the maximum climbing capacity is no less than 30°, the maximal ditch width and shoulder height are no less than wheel radius of mining vehicle. Thus wheeled mining vehicle is feasible for cobalt-enriching crust commercial mining.

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.

Effects of wheeled cable skidder on rut formation in skid trail-a case study in Hyrcanian forest

The impact of skidding operations on forest soils can be divided into three major categories： soil profile disturbance, soil compaction, and soil puddling and rutting. The present study was designed as a factorial experiment in the Kheyrud Forest with a Timberjack cable skidder to evaluate the influences of number of machine passes and soil moisture of skid trails on rutting over a fine-grained soil, and to quantify these effects. The effects of soil moisture of 20% 30%, 30% 40% and 40% 50% and different levels of compaction were studied. Compaction treatments were applied using different numbers of skidding passes （1, 5, 10, 15, 20, 25, 30 times）. Result shows that an increase in the number of machine passes could increase rut depth, but the majority of rutting was occurred after the initial few machine passes. Also rut depth at soil moisture of 40% 50% was higher than rut depths at soil moisture of 30% 40% and 20% 30%. The average rut depth in soil with 20% 30%, 30% 40% and 40% 50% moisture was 17, 22 and 35 cm, respectively. Rut depths were increased significantly with soil moisture and number of machine passes. It is suggested that skidding operations should be planned when soil conditions are dry in order to minimize rutting., but if skidding must be done under wet conditions, the operations should be stopped when machine traffic could create deep ruts.

Steering Control of Wheeled Armored Vehicle with Brushless DC Motor

Considering the steering characters of one type of wheeled armored vehicle, a brushless direct current （DC） motor is adapted as the actuator for steering control. After investigating the known algorithms, one kind of algorithm, which combines the fuzzy logic control with the self-adapting PID control and the startup and pre-hrake control, is put forward. Then a test-bed is constructed, and an experiment is conducted. The result of experiment confirms the validity of this algorithm in steering control of wheeled armored vehicle with brushless DC motor.

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.

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.

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.

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.

Use of Accelerators for Biomechanical Analysis of Walking Motion Aided by Wheeled Walking Frames

Walkers improve self-reliability. We examined the effectiveness of a newly developed wheeled walking frame for use by physically handicapped persons. Unstable gaits in walker users were analyzed by tri-axial accelerometers and a motion capture system. Several markers were placed on subjects＇ backs and legs. Subjects were requested to walk around a test course at a comfortable speed, while their motion was recorded by two high-speed video cameras. The activities performed on the test course comprised standing, normal walking, fast walking, and walking over a barrier. Any accidental falls were also recorded. We established the characteristic rules of gait motion using a walker. Furthermore, we demonstrated that gait characteristics are more conveniently extracted from acceleration sensors than from motion capture systems, since the sensors can be affixed to subjects for self-monitoring and goal achievements. The methods employing acceleration sensors are considered suitable for determining the average gait motions of elderly persons living in nursing homes, and can be used to evaluate walking motion before and aider rehabilitation.

New steering mechanism for wheeled mobile robots

A new castor wheel mechanism for omni-directional mobile platform is presented. A motion of translation is transformed into a rotation to steer the wheel with the help of a helical path fits into a translation joint and three rollers whose axes are connected to the driving shaft of the wheel. When the path moves in translation it acts on the rollers for steering. The path-roller friction transmission, the wheel kinematics and the maneuverability have been analyzed.

Data-driven iterative learning trajectory tracking control for wheeled mobile robot under constraint of velocity saturation

Considering the wheeled mobile robot(WMR)tracking problem with velocity saturation,we developed a data‐driven iterative learning double loop control method with constraints.First,the authors designed an outer loop controller to provide virtual velocity for the inner loop according to the position and pose tracking error of the WMR kinematic model.Second,the authors employed dynamic linearisation to transform the dynamic model into an online data‐driven model along the iterative domain.Based on the measured input and output data of the dynamic model,the authors identified the parameters of the inner loop controller.The authors considered the velocity saturation constraints;we adjusted the output velocity of the WMR online,providing effective solutions to the problem of velocity saltation and the saturation constraint in the tracking process.Notably,the inner loop controller only uses the output data and input of the dynamic model,which not only enables the reliable control of WMR trajectory tracking,but also avoids the influence of inaccurate model identification processes on the tracking performance.The authors analysed the algorithm's convergence in theory,and the results show that the tracking errors of position,angle and velocity can converge to zero in the iterative domain.Finally,the authors used a simulation to demonstrate the effectiveness of the algorithm.

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.

Fuzzy Behavior-based Control of Three Wheeled Omnidirectional Mobile Robot

In this paper, a fuzzy behavior-based approach for a three wheeled omnidirectional mobile robot(TWOMR) navigation has been proposed. The robot has to track either static or dynamic target while avoiding either static or dynamic obstacles along its path. A simple controller design is adopted, and to do so, two fuzzy behaviors "Track the Target" and "Avoid Obstacles and Wall Following" are considered based on reduced rule bases(six and five rules respectively). This strategy employs a system of five ultrasonic sensors which provide the necessary information about obstacles in the environment. Simulation platform was designed to demonstrate the effectiveness of the proposed approach.