Synchronous tracking control of 6-DOF hydraulic parallel manipulator using cascade control method

The synchronous tracking control problem of a hydraulic parallel manipulator with six degrees of freedom (DOF) is complicated since the inclusion of hydraulic elements increases the order of the system.To solve this problem,cascade control method with an inner/outer-loop control structure is used,which masks the hydraulic dynamics with the inner-loop so that the designed controller takes into account of both the mechanical dynamics and the hydraulic dynamics of the manipulator.Furthermore,a cross-coupling control approach is introduced to the synchronous tracking control of the manipulator.The position synchronization error is developed by considering motion synchronization between each actuator joint and its adjacent ones based on the synchronous goal.Then,with the feedback of both position error and synchronization error,the tracking is proven to guarantee that both the position errors and synchronization errors asymptotically converge to zero.Moreover,the effectiveness of the proposed approach is verified by the experimental results performed with a 6-DOF hydraulic parallel manipulator.

Time delay control of hydraulic manipulators with continuous nonsingular terminal sliding mode

For the position tracking control of hydraulic manipulators,a novel method of time delay control(TDC) with continuous nonsingular terminal sliding mode(CNTSM) was proposed in this work.Complex dynamics of the hydraulic manipulator is approximately canceled by time delay estimation(TDE),which means the proposed method is model-free and no prior knowledge of the dynamics is required.Moreover,the CNTSM term with a fast-TSM-type reaching law ensures fast convergence and high-precision tracking control performance under heavy lumped uncertainties.Despite its considerable robustness against lumped uncertainties,the proposed control scheme is continuous and chattering-free and no pressure sensors are required in practical applications.Theoretical analysis and experimental results show that faster and higher-precision position tracking performance is achieved compared with the traditional CNTSM-based TDC method using boundary layers.

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.

Compound Impedance Control of a Hydraulic Driven Parallel 3UPS/S Manipulator

The hydraulic parallel manipulator combines the high-power density of the hydraulic system and high rigidity of the parallel mechanism with excellent load-carrying capacity.However,the high-precision trajectory tracking control of the hydraulic parallel manipulator is challenged by the coupling dynamics of the parallel mechanism and the high nonlinearities of the hydraulic system.In this study,the trajectory control of a 3-DOF symmetric spherical parallel 3UPS/S manipulator is evaluated.Focusing on the highly coupling and nonlinear system dynamics,a compound impedance control method for a hydraulic driven parallel manipulator is proposed,which combines impedance control with the spatial motion characteristics of a parallel manipulator.The control strategy is divided into the inner and outer loops.The inner loop controls the impedance of the actuator in the joint space,and the outer loop controls the impedance of the entire platform in the task space to compensate the coupling of the actuators and improve the tracking accuracy of the moving platform.Compound impedance control does not require force or pressure sensors and is less dependent on modeling precision.The experimental results show that the compound impedance control effectively improves the tracking accuracy of the moving platform.This research proposes a compound impedance control strategy for a 3-DOF hydraulic parallel manipulator,which has high tracking precision with a simple and cheap system configuration.

Modeling and controlling of a flexible hydraulic manipulator

A mathematical model was developed combining the dynamics of an Euler-Bernoulli beam, described by the assumed-mode method and hydraulic circuit dynamics. Only one matrix, termed drive Jacobian, was needed in the modeling of interaction between hydraulic circuit and flexible manipulator mechanism. Furthermore, a new robust controller based on mentioned above dynamic model was also considered to regulate both flexural vibrations and rigid body motion. The proposed controller combined sliding mode and backstepping techniques to deal with the nonlinear system with uncertainties. The sliding mode control was used to achieve an asymptotic joint angle and vibration regulation by providing a virtual force while the backstepping technique was used to regulate the spool position of a hydraulic valve to provide the required control force. Simulation results are presented to show the stabilizing effect and robustness of this control strategy.

Singular perturbation approach for control of hydraulically driven flexible manipulator

The hydraulic flexible manipulator system is divided into two parts: flexible arm dynamics and hydraulic servomechanism, a driving Jacobian is derived to connect these two parts. Taking hydraulic actuator force as virtual input, a singular perturbed composite model is formulated and used to design composite controllers for the flexible link, in which the slow subsystem controller dominates the trajectory tracking, and then a fast controller is designed to damp out the vibration of the flexible structure. Moreover, the backstepping technique is applied to regulate the spool position of a hydraulic valve to provide the required force. Simulation results are provided to show the effectiveness of the presented approach.

Parameter Identification for the Valve Control Cylinder System of a Hydraulic Manipulator

In mechanical, hydraulic and electronic systems, the determination of system parameters is often challenging because liquid parameters often change significantly, due to variations in working and environmental conditions. Therefore, it is of significant practical importance to identify those parameters through experimental procedures. A systematic approach to identifying parameters in the valve controlling cylinder system of hydraulic manipulators is provided. It first derives the transfer function of the system, and then uses P control of PID control to predict system parameters. The predicted parameters are further validated using PID control. The prediction through simulation using MatLab language is utilized, which agrees well with experimental results.

Compliance motion control of the hydraulic dual-arm manipulator with adaptive mass estimation of unknown object

Given the limited operating ability of a single robotic arm,dual-arm collaborative operations have become increasingly prominent.Compared with the electrically driven dual-arm manipulator,due to the unknown heavy load,difficulty in measuring contact forces,and control complexity during the closed-chain object transportation task,the hydraulic dual-arm manipulator(HDM)faces more difficulty in accurately tracking the desired motion trajectory,which may cause object deformation or even breakage.To overcome this problem,a compliance motion control method is proposed in this paper for the HDM.The mass parameter of the unknown object is obtained by using an adaptive method based on velocity error.Due to the difficulty in obtaining the actual internal force of the object,the pressure signal from the pressure sensor of the hydraulic system is used to estimate the contact force at the end-effector(EE)of two hydraulic manipulators(HMs).Further,the estimated contact force is used to calculate the actual internal force on the object.Then,a compliance motion controller is designed for HDM closed-chain collaboration.The position and internal force errors of the object are reduced by the feedback of the position,velocity,and internal force errors of the object to achieve the effect of the compliance motion of the HDM,i.e.,to reduce the motion error and internal force of the object.The required velocity and force at the EE of the two HMs,including the position and internal force errors of the object,are inputted into separate position controllers.In addition,the position controllers of the two individual HMs are designed to enable precise motion control by using the virtual decomposition control method.Finally,comparative experiments are carried out on a hydraulic dual-arm test bench.The proposed method is validated by the experimental results,which demonstrate improved object position accuracy and reduced internal force.

Reliability Analysis of Heavy-Duty CNC Machine Hydraulic System Based on Fuzzy Goal Oriented Method

There is a common sense that heavy-duty CNC machine strongly depends on its foundation and can be easily affected by many factors.Hydraulic system,the most important part in CNC machine,is a complex and multi-loop system.In order to make up for the shortcomings of traditional fault tree analysis method and traditional GO method,the most effective method named fuzzy GO method is proposed to analyze the reliability of hydraulic system.And then some ideas are provided for system reliability assessment,fault diagnosis and maintenance by qualitative and quantitative analysis.

Dynamics of electromagnetic slip coupling for hydraulic power steering application and its energy-saving characteristics

To improve high-speed road feel and enhance energetic efficiency of hydraulic power steering(HPS) system in heavy-duty vehicles, an electromagnetic slip coupling(ESC) was applied to the steering system, which regulated discharge flow of steering pump to realize variable assist characteristic as well as uniquely transfer on-demand power from engine to steering pump. The model of ESC was established and the dynamic characteristics of ESC were presented by the way of simulation and experiment. Upon the layout of the assist characteristics, output torque of ESC was derived. Based on the ESC model, the output torque characteristics of ESC were simulated under steering situation and straight driving situation, respectively. The consistency of simulated ESC output torque and the one deduced from assist characteristics verifies the correctness of the ESC dynamic model. To illustrate energy saving characteristics of ESC-HPS, energy consumption comparison of ESC-HPS and conventional HPS was carried out qualitatively and quantitatively. It follows that the energy consumption of ESC-HPS decreases by 50% compared with that of HPS.

Inverse kinematics of a heavy duty manipulator with 6-DOF based on dual quaternion

An iterative method is introduced successfully to solve the inverse kinematics of a 6-DOF manipulator of a tunnel drilling rig based on dual quaternion, which is difficult to get the solution by Denavit-Hartenberg(D-H) based methods. By the intuitive expression of dual quaternion to the orientation of rigid body, the coordinate frames assigned to each joint are established all in the same orientation, which does not need to use the D-H procedure. The compact and simple form of kinematic equations, consisting of position equations and orientation equations, is also the consequence of dual quaternion calculations. The iterative process is basically of two steps which are related to solving the position equations and orientation equations correspondingly. First, assume an initial value of the iterative variable; then, the position equations can be solved because of the reduced number of unknown variables in the position equations and the orientation equations can be solved by applying the solution from the position equations, which obtains an updated value for the iterative variable; finally, repeat the procedure by using the updated iterative variable to the position equations till the prescribed accuracy is obtained. The method proposed has a clear geometric meaning, and the algorithm is simple and direct. Simulation for 100 poses of the end frame shows that the average running time of inverse kinematics calculation for each demanded pose of end-effector is 7.2 ms on an ordinary laptop, which is good enough for practical use. The iteration counts 2-4 cycles generally, which is a quick convergence. The method proposed here has been successfully used in the project of automating a hydraulic rig.

Sheet material lifting mechanism of the manipulator

At present, machine fixed up and down repeatedly work is done by human. Although it is low cost and easy to change plate, there are many shortcomings of the work injury and the low work efficiency. Foreign automatic loading and unloading device has been developed, but the principle is more complex, the cost is higher, the energy consumption is larger, so the automatic loading and unloading robot came into being. Aiming at the transportation of mechanical raw material, an automatic device is designed to transport the scheduled raw materials to the specified position according to the processing requirements. The device has the characteristics of the simple operation, the rapid response and the large range of activities, and has obvious economic and environmental benefits. There is certain popularization value.

水液压扭转关节的结构优化设计与试验

针对压力流体驱动的柔性机械手操作空间有限、支撑刚度不足等问题,提出一种由水液压驱动的新型扭转关节。通过有限元分析方法,对不同结构参数以及不同系统压力下关节的扭转变形特性进行了分析。基于Kriging代理模型混合优化算法获得扭转关节最大扭转角度对应的最佳结构参数组合,并对水液压扭转关节进行了试验研究。结果表明:试验与仿真的关节扭转角随系统压力变化的趋势基本一致,当系统压力为0.6 MPa时,扭转关节达到最大扭转角度,约为40°,且试验与仿真结果误差低于2%。为扭转关节设计和驱动方式提供了新思路、新方法。

液压支架自动化组装技术的研究与应用

为解决人工组装液压支架存在安全隐患和工作效率低的问题,通过分析实现液压支架自动化组装需要解决的技术难点,设计了一种采用工业机械臂、自动化行车、深度传感相机和深度视觉算法的液压支架自动化组装系统。实践效果表明,该系统能够在安全生产的前提下自动完成液压支架的组装工作,降低了安全风险、提高了工作效率,具有较高的实际应用价值。

液压机械臂驱动关节的非线性摩擦力自适应补偿控制

液压机械臂在重载任务中至关重要,但在精细化作业中却普遍存在“力量够大、精细不足”的问题。无论采用全自主还是半自主的作业方式,精密运动控制都是实现精细作业的首要基础。液压机械臂多采用液压缸直动推动关节转动的非线性驱动关节构型,摩擦分别来自液压缸和转动轴,但现研究大多忽略直动摩擦而仅考虑转动摩擦,因而运动控制中的摩擦补偿不到位。建立了面向模型补偿控制的液压机械臂非线性驱动关节动力学模型,全面考虑液压缸和转动轴的摩擦特性,进而提出摩擦补偿控制方法。结合基于最小二乘的在线参数自适应律,设计了直接/间接自适应鲁棒控制器。最后开展多组仿真对比,验证所提控制方法对液压机械臂驱动关节控制精度的提升效果。

水下液压机械臂主被动柔顺控制系统设计与验证

水下液压机械臂是用于水下特种作业的重要装备。目前控制液压机械臂进行水下作业时主要基于视觉反馈来确定作业位置,由于摄像头畸变、水流干扰等存在多种作业误差,容易在抓取、定位等作业时产生卡滞、楔紧等问题,严重影响作业效率和安全性。对此,提出了一种面向水下液压机械臂的主被动柔顺控制方法。通过末端夹具设计,补偿定位误差和偏转误差,实现被动柔顺;基于虚拟解耦控制方法建立精确位置控制器,结合接触力观测器和变阻抗控制,实现主动柔顺。实验验证了主被动柔顺控制的有效性,为水下液压机械臂的安全柔顺控制作业提供了参考。

重型液压机械臂的模型前馈补偿自抗扰控制

液压驱动的重型机械臂被广泛应用于工程机械和矿山机械,对其进行自动控制在行业内具有迫切的需求。然而,液压系统的强参数不确定性和难以建模的动态等因素的影响,给其自动控制带来了一定的挑战。文中以某锚杆钻车为例,研究了一类重型液压机械臂驱动液压缸的位置跟踪控制问题,提出了一种模型前馈补偿自抗扰控制器。为解决重载下变负荷、死区、参数不确定以及摩擦等非线性因素带来的控制难题,采取模型前馈与自抗扰反馈相结合的控制方法,将重型液压机械臂的机构动力学模型和比例阀控液压缸模型相结合,建立了系统的机理模型,然后基于系统的机理模型,构建了控制器的前馈补偿部分;设计了扩张状态观测器对系统的未建模因素进行实时观测,再加上基于状态误差的反馈调整构成了自抗扰控制器。最后在实际的重型液压机械臂上进行了实验研究,结果表明:基于模型前馈补偿的自抗扰控制器相比于PID控制器,具有更小的滞后和跟踪误差,整体跟踪精度比PID控制器提升了63.5%,说明所设计的控制器可以很好地克服液压系统的非线性因素的不利影响,比PID控制器具有更高的鲁棒性,因此所设计的控制方法更适用于此类重型液压机械臂的位置跟踪控制。

面向喷浆机械臂电液比例控制系统的降噪处理研究

考虑到系统辨识数据的预处理能够提高喷浆机械臂电液比例控制系统的建模精度,采用小波变换滤波算法对采集的传感器数据进行滤波降噪处理。应用表明,在以sym5为小波基函数时,信噪比数值最大且均方根误差最小,降噪效果最好。滤波降噪结果能够为电液比例控制系统数学模型的精确辨识奠定基础。

考虑动态倾覆稳定性的液压重载机械臂路径规划方法

针对液压重载机械臂的动态倾覆稳定性问题,提出了一种基于改进快速扩展随机树(Rapidly-exploring Random Tree,RRT)算法的路径规划方法。与只对危险工况的静态稳定性校核不同,该算法以机械臂运动过程中的动态倾覆稳定性最优为目标,在机械臂的关节空间内进行路径规划。以7个关节变量组成的七维数组作为采样点,结合正运动学与力矩法建立机械臂的动态倾覆稳定性计算模型,利用双采样点择优原则,选择其在对应位姿下抗倾覆稳定力矩最优的随机点作为采样点,以增强算法的启发性。在Matlab平台进行的仿真实验表明,改进RRT算法规划路径的倾覆裕度在3种典型工况下分别提升了37%、28%和38%,有效地改善了液压重载机械臂作业平台的抗倾覆稳定性。

电液伺服系统驱动机械臂的自适应反步法控制

在实际应用中,电液伺服系统存在非线性和参数不确定的特性,并且在作动器运动过程中可能受到外部随机干扰,会对电液伺服系统的控制造成较大影响。为了改善电液伺服系统在参数不确定性和未知扰动(即水力参数和外部负载)下的动态行为。首先,利用基于李亚普诺夫的反步法对电液伺服系统进行控制。然后,利用基于李亚普诺夫的参数自适应反步法对外部随机干扰和系统非线性进行抑制或补偿的控制方法进行了研究,比较了这两种控制策略的优缺点。表明了基于李亚普诺夫的的参数自适应反步法对于多个未知参数的情况下进行估计系统仍能保证具有的良好性能。