Robust Adaptive Control for Mobile Manipulators

This paper addresses the trajectory tracking control of a nonholonomic wheeled mobile manipulator with parameter uncertainties and disturbances. The proposed algorithm adopts a robust adaptive control strategy where parametric uncertainties are compensated by adaptive update techniques and the disturbances are suppressed. A kinematic controller is first designed to make the robot follow a desired end-effector and platform trajectories in task space coordinates simultaneously. Then, an adaptive control scheme is proposed, which ensures that the trajectories are accurately tracked even in the presence of external disturbances and uncertainties. The system stability and the convergence of tracking errors to zero are rigorously proven using Lyapunov theory. Simulations results are given to illustrate the effectiveness of the proposed robust adaptive control law in comparison with a sliding mode controller.

Control of a 6DOF Mobile Manipulator with Object Detection and Tracking Using Stereo Vision

A supportive mobile robot for assisting the elderly is an emerging requirement mainly in countries like Japan where population ageing become relevant in near future.Falls related injuries are considered as a critical issue when taking into account the physical health of older people.A personal assistive robot with the capability of picking up and carrying objects for long/short distances can be used to overcome or lessen this problem.Here,we design and introduce a 3 D dynamic simulation of such an assistive robot to perform pick and place of objects through visual recognition.The robot consists of two major components;a robotic arm or manipulator to do the pick and place,and an omnidirectional wheeled robotic platform to support mobility.Both components are designed and operated according to their kinematics and dynamics and the controllers are integrated for the combined performance.The objective was to improve the accuracy of the robot at a considerably high speed.Designed mobile manipulator has been successfully tested and simulated with a stereo vision system to perform object recognition and tracking in a virtual environment resembling aroom of an elderly care.The tracking accuracy of the mobile manipulator at an average speed of 0.5 m/s is 90%and is well suited for the proposed application.

Dexterity Analysis for Omni-directional Wheeled Mobile Manipulator Based on Double Quaternion

The unified analysis of omni-directional wheeled mobile manipulator(OWMM) through the dimensionally nonhomogeneous Jacobian matrix may lead to unreliable results. The existing researches focus on the integrated performance evaluation of OWMM, without taking the influence of velocity difference into consideration. This paper presents a new approach to formulate the dimensionally homogeneous Jacobian matrix and a new index for OWMM. First, the universal transformational matrix of the link coordinate frame is derived based on double quaternion. The degree of locomotion of a mobile platform and the degrees of manipulation of a manipulator are treated equally as the joints of a redundant composite robot. Then the integrated modeling of OWMM is established, and the non-dimensional Jacobian matrix is obtained from the above matrix. Next, by examining the concept of directional manipulability, a new index is proposed to evaluate the directional manipulability of OWMM along the specified task direction. Furthermore, for the same task and the time of simulation, the kinematic performance of the fixed base operation of the manipulator and the operation of OWMM are analyzed by numerical simulation. The results suggest that the proposed approach is equivalent to the method of traditional kinematic modeling, with the error of numerical solution being 10-7 , and the varying frequency of DMTR is higher than that of the condition number. This indicates that DMTR is more effective to reflect the variation of the task direction. The proposed method can be used to analyze the manipulating capability of OWMM, and has a simple structure and generality in the unified analysis of OWMM.

Base position planning of mobile manipulators for assembly tasks in construction environments

With good mobility and flexibility,mobile manipulators have shown broad applications in construction scenarios.Base position(BP)planning,which refers to the robot autonomously determining its working station in the environment,is an important technique for mobile manipulators when performing the construction assembly task,especially in a large-scale construction environment.However,the BP planning process is tedious and time-consuming for a human worker to carry out.Thus,to improve the efficiency of construction assembly tasks,a novel BP planning method is proposed in this paper,which can lead to appropriate BPs and minimize the number of BPs at the same time.Firstly,the feasible BP regions are generated based on the grid division and the variable workspace of the mobile manipulator.Then,the positioning uncertainties of the mobile manipulator are considered in calculating the preferred BP areas using clustering.Lastly,a set coverage optimization model is established to obtain the minimum number of BPs using an optimization algorithm according to the greedy principle.The simulated experiment based on a 9-degree of free(DoF)mobile manipulator has been performed.The results illustrated that the time for BP planning was significantly reduced and the number of BPs was reduced by 63.41%compared to existing manual planning,which demonstrated the effectiveness of the proposed method.

The visual fiducial based pose estimation of mobile manipulator in large-scale components manufacturing

The accurate estimation of the end-effector’s pose in large operating spaces is the key for the mobile manipulator to realize efficient manufacturing of large and complex components.We propose a novel pose tracking method in large-range using visual fiducial markers,and further propose the layout optimization method for the encoded fiducial markers.A metric named orientational dilution of precision(ODOP)is proposed to evaluate the magnification of the pose estimation error compared with the measurement error of the coded fiducial markers.The distribution pattern of the coded markers is analyzed based on ODOP,and the square-shaped layout is determined to be a satisfactory distribution pattern for the minimum positioning unit of markers,and the side length of the square-shaped layout is further selected.The simulations and experiments prove the effectiveness of the ODOP index.Finally,the square-shaped layout and the designed distribution density for positioning coded markers are adopted to realize the high-precision measurement of large components by the mobile manipulator.

Neuro-fuzzy and model-based motion control for mobile manipulator among dynamic obstacles

This paper focuses on autonomous motion control of a nonholonomic platform with a robotic arm, which is called mobile manipulator. It serves in transportation of loads in imperfectly known industrial environments with unknown dynamic obstacles. A union of both procedures is used to solve the general problems of collision-free motion. The problem of collision-free motion for mobile manipulators has been approached from two directions, Planning and Reactive Control. The dynamic path planning can be used to solve the problem of locomotion of mobile platform, and reactive approaches can be employed to solve the motion planning of the arm. The execution can generate the commands for the servo-systems of the robot so as to follow a given nominal trajectory while reacting in real-time to unexpected events. The execution can be designed as an Adaptive Fuzzy Neural Controller. In real world systems, sensor-based motion control becomes essential to deal with model uncertainties and unexpected obstacles.

Adaptive Tracking Control of Mobile Manipulators with Affine Constraints and Under-actuated Joints

Adaptive motion/force tracking control is considered for a class of mobile manipulators with affine constraints and under-actuated joints in the presence of uncertainties in this paper. Dynamic equation of mobile manipulator is transformed into a controllable form based on dynamic coupling technique. In view of the asymptotic tracking idea and adaptive theory, adaptive controllers are proposed to achieve the desired control objective. Detailed simulation results confirm the validity of the control strategy.

Input-Constrained Hybrid Control of a Hyper-Redundant Mobile Medical Manipulator

To reduce the risk of infection in medical personnel working in infectious-disease areas, we proposed ahyper-redundant mobile medical manipulator (HRMMM) to perform contact tasks in place of healthcare workers.A kinematics-based tracking algorithm was designed to obtain highly accurate pose tracking. A kinematic modelof the HRMMM was established and its global Jacobian matrix was deduced. An expression of the trackingerror based on the Rodrigues rotation formula was designed, and the relationship between tracking errors andgripper velocities was derived to ensure accurate object tracking. Considering the input constraints of the physicalsystem, a joint-constraint model of the HRMMM was established, and the variable-substitution method was usedto transform asymmetric constraints to symmetric constraints. All constraints were normalized by dividing bytheir maximum values. A hybrid controller based on pseudo-inverse (PI) and quadratic programming (QP) wasdesigned to satisfy the real-time motion-control requirements in medical events. The PI method was used whenthere was no input saturation, and the QP method was used when saturation occurred. A quadratic performanceindex was designed to ensure smooth switching between PI and QP. The simulation results showed that theHRMMM could approach the target pose with a smooth motion trajectory, while meeting different types of inputconstraints.

A hybrid visual servo control method for simultaneously controlling a nonholonomic mobile and a manipulator

Visual servo control rules that refer to the control methods of robot motion planning using image data acquired from the camera mounted on the robot have been widely applied to the motion control of robotic arms or mobile robots.The methods are usually classified as image-based visual servo,position-based visual servo,and hybrid visual servo(HVS)control rules.Mobile manipulation enhances the working range and flexibility of robotic arms.However,there is little work on applying visual servo control rules to the motion of the whole mobile manipulation robot.We propose an HVS motion control method for a mobile manipulation robot which combines a six-degreeof-freedom(6-DOF)robotic arm with a nonholonomic mobile base.Based on the kinematic differential equations of the mobile manipulation robot,the global Jacobian matrix of the whole robot is derived,and the HVS control equation is derived using the whole Jacobian matrix combined with position and visual image information.The distance between the gripper and target is calculated through the observation of the marker by a camera mounted on the gripper.The differences between the positions of the markers’feature points and the expected positions of them in the image coordinate system are also calculated.These differences are substituted into the control equation to obtain the speed control law of each degree of freedom of the mobile manipulation robot.To avoid the position error caused by observation,we also introduce the Kalman filter to correct the positions and orientations of the end of the manipulator.Finally,the proposed algorithm is validated on a mobile manipulation platform consisting of a Bulldog chassis,a UR5 robotic arm,and a ZED camera.

A Review on Cooperative Robotic Arms with Mobile or Drones Bases

This review paper focuses on cooperative robotic arms with mobile or drone bases performing cooperative tasks. This is because cooperative robots are often used as risk-reduction tools to human life. For example, they are used to explore dangerous places such as minefields and disarm explosives. Drones can be used to perform tasks such as aerial photography, military and defense missions,agricultural surveys, etc. The bases of the cooperative robotic arms can be stationary, mobile(ground), or drones. Cooperative manipulators allow faster performance of assigned tasks because of the available "extra hand". Furthermore, a mobile base increases the reachable ground workspace of cooperative manipulators while a drone base drastically increases this workspace to include the aerial space.The papers in this review are chosen to extensively cover a wide variety of cooperative manipulation tasks and industries that use them.In cooperative manipulation, avoiding self-collision is one of the most important tasks to be performed. In addition, path planning and formation control can be challenging because of the increased number of components to be coordinated.

A survey of the development of quadruped robots: Joint configuration, dynamic locomotion control method and mobile manipulation approach

Some quadruped robots developed recently show better dynamic performance and environmental adaptability than ever, and have been preliminarily applied in the field of emergency disposal, military reconnaissance and infrastructure construction. The development route, mechanisms design, control methods and mobile manipulating approaches of the quadruped robots are surveyed in this article. Firstly, the development route of the quadruped robot is combed, as the references of the forecast of the future work on quadruped robots. Then the bionic structure and the motion control method of the quadruped robot is summarized, the advantages and disadvantages are analyzed in aspects of gait switching, terrain adaption and disturbance resistance. Subsequently, aiming at the mobile manipulation of the quadruped robot, the representative leg-arm collaborative robots and the multi-task-oriented Whole-body Control (WBC) methods are introduced. Finally, the summary and future work of the quadruped robots is given.

Different manipulation mode analysis of a radial symmetrical hexapod robot with leg-arm integration

With the widespread application of legged robot in various fields,the demand for a robot with high locomotion and manipulation ability is increasing.Adding an extra arm is a useful but general method for a legged robot to obtain manipulation ability.Hence,this paper proposes a novel hexapod robot with two integrated leg–arm limbs that obtain dexterous manipulation functions besides locomotion ability without adding an extra arm.The manipulation modes can be divided into coordinated manipulation condition and single-limb manipulation condition.The former condition mainly includes fixed coordinated clamping case and fixed coordinated shearing case.For the fixed coordinated clamping case,the degrees of freedom(DOFs)analysis of equivalent parallel mechanism by using screw theory and the constraint equation of two integrated limbs are established.For the fixed coordinated shearing case,the coordinated working space is determined,and an ideal coordinated manipulation ball is presented to guide the coordinated shearing task.In addition,the constraint analysis of two adjacent integrated limbs is performed.Then,mobile manipulation with one integrated leg–arm limb while using pentapod gait is discussed as the single-limb manipulation condition,including gait switching analysis between hexapod gait and pentapod gait,different pentapod gaits analysis,and a complex six-DOF manipulation while walking.Corresponding experiments are implemented,including clamping tasks with two integrated limbs,coordinated shearing task by using two integrated limbs,and mobile manipulation with pentapod gait.This robot provides a new approach to building a multifunctional locomotion platform.

Design and control of a robotic system with legs,wheels,and a reconfigurable arm

Unmanned robotic systems are expected to liberate people from heavy,monotonous,and dangerous work.However,it is still difficult for robots to work in complicated environments and handle diverse tasks.To this end,a robotic system with four legs,four wheels,and a reconfigurable arm is designed.Special attention has been given to making the robot compact,agile,and versatile.Firstly,by using separate wheels and legs,it removes the coupling in the traditional wheeled–legged system and guarantees highly efficient locomotion in both the wheeled and legged modes.Secondly,a leg–arm reconfiguration design is adopted to extend the manipulation capability of the system,which not only reduces the total weight but also allows for dexterous manipulation and multi-limb cooperation.Thirdly,a multi-task control strategy based on variable configurations is proposed for the system,which greatly enhances the adaptability of the robot to complicated environments.Experimental results are given,which validate the effectiveness of the system in mobility and operation capability.