Effects of Joint Controller on Analytical Modal Analysis of Rotational Flexible Manipulator

Modal analysis is a fundamental and important task for modeling and control of the flexible manipulator. However, almost all of the traditional modal analysis methods view the flexible manipulator as a pure mechanical structure and neglect feedback action of joint controller. In order to study the effects of joint controller on the modal analysis of rotational flexible manipulator, a closed-loop analytical modal analysis method is proposed. Firstly, two exact boundary constraints, namely servo feedback constraint and bending moment constraint, are derived to solve the vibration partial differential equation. It is found that the stiffness and damping gains of joint controller are both included in the boundary conditions, which lead to an unconventional secular term. Secondly, analytical algorithm based on Ritz approach is developed by using Laplace transform and complex modal approach to obtain the natural frequencies and mode shapes. And then, the numerical simulations are performed and the computational results show that joint controller has pronounced influence on the modal parameters： joint controller stiffness reduces the natural frequency, while joint controller damping makes the shape phase non-zero. Furthermore, the validity of the presented conclusion is confirmed through experimental studies. These findings are expected to improve the performance of dynamics simulation systems and model-based controllers.

Dynamics of luffing motion of a hydraulically driven shell manipulator with revolute clearance joints

In this study,a modeling method for investigating the dynamic characteristics of a hydraulically driven shell manipulator with revolute clearance joints is presented.This model accounts for the effect of the clearance,the flexibility of the rotating beam,and the coupled dynamic characteristics of the hydraulic cylinder.A modified contact force model was developed to simulate the physical properties of realistic revolute joints with small clearances,heavy loads,and variable contact stiffnesses and damping coefficients with variations of the indentations.Considering the strong coupling relationship between the hydraulic cylinder and the flexible beam,a system equation of motion combining the state variables of the hydraulic cylinder and mechanical system was established.The complex nonlinear friction force of the hydraulic cylinder motion was constructed using a modified Lu Gre model,and the parameters of the friction model were identified using intelligent identification algorithms.Moreover,a test system for the shell manipulator was established to achieve experimental validation.Finally,the effects of the clearance size and the stiffness of the cylinder support on the dynamic response were investigated.

MODELING AND CONTROLLING OF PARALLEL MANIPULATOR JOINT DRIVEN BY PNEUMATIC MUSCLES

A parallel manipulator joint driven by three pneumatic muscles and its posture control strategy are presented. Based on geometric constraints and dynamics, a system model is developed through which some influences on dynamic response and open-loop gain are analyzed including the supply pressure, the initial pressure and the volume of pneumatic muscle. A sliding-mode controller with a nonlinear switching function is applied to control posture, which adopts the combination of a main method that separates control of each muscle and an auxiliary method that postures error evaluation of multiple muscles, especially adopting the segmented and intelligent adjustments of sliding-mode parameters to fit different expected postures and initial states. Experimental results show that this control strategy not only amounts to the steady-state error of 0. 1° without overshoot, but also achieves good trajectory tracking.

Fault tolerant motion planning based on joint torque limit for redundant manipulators

First, two fault tolerant planning algorithms with avoidance of joint static torque limit or joint dynamic torque limit are proposed respectively. The former is suitable for the low-speed manipulators, and the latter is suitable for the high-speed manipulators. These algorithms not only can insure manipulation tasks to lie within the fault tolerant workspace but also can avoid joint torque limit, and hence can insure a redundant manipulator to be. fault tolerant in both kinematical sense and dynamic sense. Then, the simulation examples for a planar 3R manipulator demonstrate the validity of these algorithms.

Dynamic analysis of multi-link spatial flexible manipulator arms with dynamic stiffening effects

The dynamics for multi-link spatial flexible manipulator arms is investigated. The system considered here is an N-flexible-link manipulator driven by N DC-motors through N revolute flexiblejoints. The flexibility of each flexible joint is modeled as a linearly elastic torsional spring, and the mass of the joint is also considered. For the flexibility of the link, all of the stretching deformation, bending deformation and the torsional deformation are included. The complete governing equations of motion of the system are derived via the Lagrange equations. The nonlinear description of the deformation field of the flexible link is adopted in the dynamic modeling, and thus the dynamic stiffening effects are captured. Based on this model, a general-purpose software package for dynamic simulation of multi-link spatial flexible manipulator arms is developed. Several illustrative examples are given to validate the algorithm presented in this paper and to indicate that not only dynamic stiffening effects but also the flexibility of the structure has significant influence on the dynamic performance of the manipulator.

Kinematic Research on Hinged Synchronous Universal Joint Applied for Snake-like Manipulator

The structure and motion principle of a hinged synchronous universal joint (HSUJ) is introduced, also whose kinematics is theoretically analyzed. As a result, a few kinematic characters of the HSUJ are obtained,which establish the foundation of its application for snake-like manipulator. Making use of the HSUJ ss actuating mechauism, the developed snake-like manipulator has the merits of small curve radius, fewer actuator, and small volume etc.

Motion planning for redundant prismatic-jointed manipulators in the free-floating mode

This paper investigates the motion planning of redundant free-floating manipulators with seven prismatic joints. On the earth, prismatic-jointed manipulators could only position their end-effectors in a desired way. However, in space, the end-effectors of free-floating manipulators can achieve both the desired orientation and desired position due to the dynamical coupling between manipulator and satellite movement, which is formally expressed by linear and angular momentum conservation laws. In this study, a tractable algorithm particle swarm optimization combined with differential evolution （PSODE） is provided to deal with the motion planning of redundant free-floating prismatic-jointed manipulators, which could avoid the pseudo inverse of the Jacobian matrix. The polynomial functions, as argument in sine functions are used to specify the joint paths. The co- efficients of the polynomials are optimized to achieve the desired end-effector orientation and position, and simulta- neously minimize the unit-mass-kinetic energy using the redundancy. Relevant simulations prove that this method pro- vides satisfactory smooth paths for redundant free-floating prismatic-jointed manipulators. This study could help to recognize the advantages of redundant prismatic-jointed space manipulators.

Analysis and Design of Control Dynamics of Manipulator Robot’s Joint Drive

A system of automatic control(SAC)of the electric drive of rotary link of manipulator robot(MR)is considered.The variables of mechanical load of drive,depending of changes of a spatial configuration of MR in the course of motion,mass and dimensions of the moved payloads,etc.,are received from the motion equation of rotary link of MR.Changes of mechanical load can be unknown and cause the essential deterioration in dynamical properties(speed,damping,etc.)of the SAC of drive.With the aim to stabilize the desired dynamical properties of SAC the algorithm of drive control is proposed which is adaptive to changes of mechanical load.The unknown parameters of drive load,necessary to form the adaptive control algorithm,are identified via observing device(OD).The work algorithm of OD to identify the unknown parameters of drive load is proposed.For the proposed control and work of OD algorithms the block diagram of drive control is construction.The simulation results on computer proved that in considered SAC of drive the stabilization of desired dynamical properties ensured.

Development of A Deep Ocean Electric Autonomous Manipulator

This paper describes an underwater 3500 m electric manipulator （named Huahai-4E, stands for four functions deep ocean electric manipulator in China）, which has been developed at underwater manipulation technology lab in Huazhong University of Science and Technology （HUST） for a test bed of studying of deep ocean manipulation technologies. The manipulator features modular integration joints, and layered architecture control system. The oil-filled, pressure-compensated joint is compactly designed and integrated of a permanent magnet （PM） brushless motor, a drive circuit, a harmonic gear and an angular feedback potentiometer. The underwater control system is based on a network and consisted of three embedded PC/104 computers which are used for servo control, task plan and target sensor respectively. They communicate through User Datagram Protocol （UDP） multicast communication in Vxworks OS. A supervisor PC with a virtual 3D GUI is fiber linked to underwater control system. Furthermore, the manipulator is equipped with a sensor system including a unique ultra-sonic probe array and an underwater camera. Autonomous grasp strategy based multi-sensor is studied. The results of watertight test in 40 MPa, joint＇s efficiency test and autonomous grasp experiments in tank are also presented.

Method for optimizing manipulator's geometrical parameters and selecting reducers

A geometrical parameters optimization and reducers selection method was proposed for robotic manipulators design. The Lagrangian approach was employed in deriving the dynamic model of a two-DOF manipulator. The flexibility of links and joints was taken into account in the mechanical structure dimensions optimization and reducers selection, in which Timoshenko model was used to discretize the hollow links. Two criteria, i.e. maximization of fundamental frequency and minimization of self-mass/load ratio, were utilized to optimize the manipulators. The NSGA-II (fast elitist nondominated sorting genetic algorithms) was employed to solve the multi-objective optimization problem. How the joints flexibility affects the manipulators design was analyzed and shown in the numerical analysis example. The results indicate that simultaneous consideration of the joints and the links flexibility is very necessary for manipulators optimal design. Finally, several optimal combinations were provided. The effectiveness of the optimization method was proved by comparing with ADAMS simulation results. The self-mass/load ratio error of the two methods is within 10%. The maximum error of the natural frequency by the two methods is 23.74%. The method proposed in this work provides a fast and effective pathway for manipulator design and reducers selection.

Takagi–Sugeno Fuzzy Modeling and Control for Effective Robotic Manipulator Motion

Robotic manipulators are widely used in applications that require fast and precise motion.Such devices,however,are prompt to nonlinear control issues due to the flexibility in joints and the friction in the motors within the dynamics of their rigid part.To address these issues,the Linear Matrix Inequalities(LMIs)and Parallel Distributed Compensation(PDC)approaches are implemented in the Takagy–Sugeno Fuzzy Model(T-SFM).We propose the following methodology;initially,the state space equations of the nonlinear manipulator model are derived.Next,a Takagy–Sugeno Fuzzy Model(T-SFM)technique is used for linearizing the state space equations of the nonlinear manipulator.The T-SFM controller is developed using the Parallel Distributed Compensation(PDC)method.The prime concept of the designed controller is to compensate for all the fuzzy rules.Furthermore,the Linear Matrix Inequalities(LMIs)are applied to generate adequate cases to ensure stability and control.Convex programming methods are applied to solve the developed LMIs problems.Simulations developed for the proposed model show that the proposed controller stabilized the system with zero tracking error in less than 1.5 s.

TREATING DISLOCATION OF SMALL JOINTS OF THORACIC VERTEBRAE BY MANIPULATION WITH PALM PRESSING AND SHAKING

Dislocation of small joints of thoracicvertebrae is frequently seen in the clinic.Theauthor treated 25 such cases using palmpressing and shaking manipulation and ob-tained satisfactory results.The following is areport on the work.

CLINICAL STUDY ON MANIPULATIVE TREATMENT OF DERANGEMENT OF THE ATLANTOAXIAL JOINT

The derangement of the atlantoaxial joint is one of main cervical sources of dizziness and headache, which were based on the observation on the anatomy of the upper cervical vertebrae, analysis of X-ray film of the atlantoaxial joint, and the manipulative treatment in 35 patients with cervical spondylosis. The clinical diagnosis of derangement consists of: dizziness, headache, prominence and tenderness on one side of the affected vertebra, deviation of the dens for 1 mm-4 mm on the open-mouth X-ray film, abnormal movement of the atlantoaxial joint on head-rotated open-mouth X-ray film. An accurate and delicate adjustment is the most effective treatment.

THEORETICAL DESIGN AND MOTION PLANNING OF NONHOLONOMIC MANIPULATOR

A new nonholonomic transmission mechanism is proposed based on thenonholonomic theory and nonlinear control principle, and combined with conditions of thenonholonomic motion planning and control, that is researched to compose method of the motiontransfer chain from this transmission mechanism, on which a new nonholonomic manipulator isdesigned. This nonholonomic manipulator is a controllable multi-joint manipulator that actuated onlyby two-servo electromotor. Its motion expresses the characteristic of nonholonomy constraint andnonlinear, and that also satisfies the chained form convertibility. And then, using the nonlinearcontrol principle of chained system, motion characteristic of the nonholonomic manipulator isapplied. From simulation verification and analysis, the usefulness of the theoretical design andcontrol strategies is shown, and that is important in design and research of handiness robot andmulti-finger robot hand.

基于无奇异工作空间和关节空间的5R并联机构性能分析

针对并联机构的性能分析多集中于工作空间,而针对关节空间的研究较少这一问题,以5R并联机构为研究对象,对其在无奇异工作空间和关节空间中的性能进行了分析。首先,建立了机构的运动学方程,得到了装配模式、工作模式的定义;然后,利用一种无量纲化的参数模型,将机构运动学参数的无限设计空间转化为一个有限的平面设计区域,得到了机构不同尺寸参数下的工作空间和关节空间的分布;之后,绘制了机构设计空间中奇异轨迹的分布,得到了机构的无奇异工作空间,以无奇异工作空间面积最大化为指标,对机构的尺寸参数进行了优化设计;最后,在最大无奇异工作空间和关节空间中,对机构进行了性能分析,得到了机构的最大内切矩形、可操作度与奇异边界距离性能指标分布图。研究结果表明:机构在工作空间内具有较好的运动学性能,基于可操作度对机构进行轨迹规划,平均可操作度可提高17%;并联机构的优化设计需综合考虑奇异边界距离和可操作度性能指标,确保机构在远离奇异位形的同时,保持较高的运动灵活性。

A multi-stage regulation strategy of space manipulators with a free-swinging joint failure

To ensure tasks can be completed after a free-swinging joint failure occurs,a multi-stage regulation strategy of space manipulators is proposed.Considering all terms of the dynamics equation,an evaluation model of the regulation ability(EMRA)of active joints over the fault joint is established based on the fuzzy entropy.And then a multi-stage regulation strategy based on the EMRA is designed to regulate the fault joint.The strategy divides the regulation process into several stages,and select a certain active joint to regulative the fault joint in every stage.With this multi-stage regulation strategy,the fault joint can be regulated to the desired angle without huge torque on regulative joints.The simulation is carried out with a 7-DOF space manipulator,verifying the correctness and effectiveness of the multi-stage regulation strategy.The strategy has three advantages:Coriolis and centrifugal terms are both considered for the first time in selecting the regulative joint,making the selection result more in line with the actual regulation process;The influence of the model uncertainty is eliminated in establishing the EMRA,making the evaluation of regulative ability more precise;The fault joint is successfully regulated to the desired angle without huge torque on regulative joints.

Learning synergies based in-hand manipulation with reward shaping

In-hand manipulation is a fundamental ability for multi-fingered robotic hands that interact with their environments.Owing to the high dimensionality of robotic hands and intermittent contact dynamics,effectively programming a robotic hand for in-hand manipulations is still a challenging problem.To address this challenge,this work employs deep reinforcement learning(DRL)algorithm to learn in-hand manipulations for multi-fingered robotic hands.A reward-shaping method is proposed to assist the learning of in-hand manipulation.The synergy of robotic hand postures is analysed to build a low-dimensional hand posture space.Two additional rewards are designed based on both the analysis of hand synergies and its learning history.The two additional rewards cooperating with an extrinsic reward are used to assist the in-hand manipulation learning.Three value functions are trained jointly with respect to their reward functions.Then they cooperate to optimise a control policy for in-hand manipulation.The reward shaping not only improves the exploration efficiency of the DRL algorithm but also provides a way to incorporate domain knowledge.The performance of the proposed learning method is evaluated with object rotation tasks.Experimental results demonstrated that the proposed learning method enables multi-fingered robotic hands to learn in-hand manipulation effectively.

Inverse Kinematics Analysis of a Five Jointed Revolute Arm Mechanism

This paper presents some initial solutions to the problem of accuracy and repeatability of the arm position placement in applied kinematics by solving the inverse kinematics problem of a serial jointed manipulator whose forward kinematics solution was earlier presented to solve the position placement problem of a mobile manipulator for Lunar Oxygen production. The problem herein is that of identifying a combination of joint angles to effectively position the end-effecter at a specified location in space. The reverse solution as presented in this paper is predicated on DH＇s （Denavit-Hartenberg＇s） technique for robot arm position analysis. The generalized solution for the 5-degrees of freedom DOF （degree of freedom） revolute joint variables which comprises 2-1inks and a spade-like 3-DOF end-effecter was obtained by solving a set of algebraic equations emerging from series of transformation matrices. The proposed solution herein has a high degree of accuracy and repeatability for workspace reachable domains where joint combination is analytic.

柔性关节空间机械臂传感容错无模型自适应控制

针对传感信号畸变、丢失等故障状态严重影响空间机械臂控制系统性能的问题,提出基于空间机械臂运动传感器故障观测的无模型自适应容错控制方法。采用动态线性化和递推参数估计思想设计传感故障监测器,实现对传感畸变及数据丢失等故障的判定,并进行运动状态预测估计;建立包含跟踪误差变化率项的无模型自适应控制准则函数,有效惩罚由传感故障引起的参数估计突变问题;设计面向柔性关节空间机械臂的新型传感容错无模型自适应控制(SFT-MFAC)算法。仿真结果表明,在不同传感故障情况下,所提控制策略均能快速准确识别传感故障信息,避免系统瞬时发散,有效延长系统响应时间,增加控制系统的鲁棒性。