Constraint operator for the kinematic calibration of a parallel mechanism

This paper introduces a constraint operator for the kinematic calibration of a parallel mechanism. By adopting the concept of a constraint operator, the movement between two poses is constrained. When the constrained movements are satisfied, the active joint displacements are taken and inputted into the kinematic model to compute the theoretical movements. A cost function is derived by the errors between the theoretical movement and the actual movement. The parameters that minimize the cost function are estimated and substituted into the kinematic model for a kinematic calibration. A single constraint plane is employed as a mechanical fixture to constrain the movement, and three digital indicators are used as the sensing devices to determine whether the constrained movement is satisfied. This calibration system represents an effective, low cost and feasible technique for a parallel mechanism. A calibration algorithm is developed with a constraint operator and implemented on a parallel manipulator constructed for a machining center tool.     

Development and kinematic calibration for measurement structure of a micro parallel mechanism platform

This paper presents a micro-positioning platform based on a unique parallel mechanism developed by the authors. The platform has a meso-scale rectangular shape whose size is 20 × 23 mm. The stroke is 5 mm for both the x-and y-axes and 100 degrees for the α-axis. The platform is actuated by three sets of dual stage linear actuators: a linear motor for rough positioning and a piezo actuator for fine positioning. The developed micro-positioning platform has a measurement system that consists of three linear sensors. The position and orientation values of the movable platform can be measured directly and used in a feedback control system. Selecting 18 kinematic error parameters of a measurement system (feedback control system), a two-stage kinematic calibration method is proposed. Constant error parameters are found in the first stage and variable error parameters are found in the second stage of kinematic calibration. After kinematic calibration the position error is reduced to within 0.5 μm and error reduction rate is over 90%.     

Site calibration for the wind turbine performance evaluation

The accurate wind speed information at the hub height of a wind turbine is very essential to the exact estimation of the wind turbine power performance testing. Several methods on the site calibration, which is a technique to estimate the wind speed at the wind turbine’s hub height based on the measured wind data using a reference meteorological mast, are introduced. A site calibration result and the wind resource assessment for the TaeKwanRyung test site are presented using three-month wind data from a reference meteorological mast and the other mast temporarily installed at the site of wind turbine. Besides, an analysis on the uncertainty allocation for the wind speed correction using site calibration is performed.     

6-PSS并联机构误差分析及标定

为提高6-PSS并联机构的运动精度,需对其进行误差分析和标定研究。利用矢量法构建并联6自由度机构的误差模型,根据MATLAB计算得到机构的误差源对动平台末端位姿影响的灵敏度。对机构进行误差综合分析,结合运动学正解和逆解,提出一种新的基于机构坐标轴姿态约束的运动学标定方法。根据测量初始值,利用标定算法解算得到机构的标定值。借助外部检测设备测量得机构标定前和标定后的位移和角度误差,标定后位移误差由10mm减小到1mm,角度误差由0．3°减小到0．1°。以实际测量数据验证了该标定方法的有效性和正确性,并最终提高了并联机构的运动精度。     

一种三自由度并联机构的运动学标定

以一种三自由度并联机构测量机为研究对象,给出了机构的正解运动学模型,在此基础上阐述了运动学标定方法,给出了标定步骤,通过计算机编程对其进行了参数辨识.对标定前后的运动学参数与实际值进行了比较,标定前后的测头误差也进行了比较,从而验证了标定方法的正确可行性.     

一种六自由度海浪模拟并联平台的零点标定与性能评估

针对并联机器人中存在的运动精度欠缺的问题,对一种用于海浪模拟的六自由度并联平台进行了零点标定与性能评估。确立了并联平台的运动控制模型,通过齐次坐标方法建立了该并联平台的运动学反解,并且在运动学反解的基础上采用边界搜索法确定了平台定姿态时的工作空间。采用"PC机+运动控制卡"的控制模式对该平台进行了运动控制系统的设计,实现了并联平台的运动控制。首先运用矢量推导法建立了平台的零点误差模型,然后借助于激光跟踪仪对平台进行了零点标定,提高了平台的运动性能。最后针对特定的海浪谱,利用该平台对其进行了模拟实验,并根据实验结果对平台的跟踪性能进行了分析。研究结果表明,经过零点标定后的并联平台能够很好地对海浪进行跟踪模拟。     

6-PUS/UPS并联机构运动学标定理论与实验研究

基于6-PUS/UPS并联机构,首先建立含结构误差的运动学反解模型;使用遗传算法建立其标定模型,通过Matlab编程验证了模型的正确性和有效性;提出了一种利用球杆仪、高度游标卡尺和双轴倾角传感器配合测量动平台位姿的标定方案;最后进行标定实验及误差补偿,提高了该并联机构的精度。     

Development of synchronized control system through a pneumatic parallel mechanism and its 3D CG model

This study developed a rehabilitation system that can improve the patient care services provided by physical therapists. Wristparalyzed patients were given arbitrary force through a six-Degree of freedom (6DoF) parallel mechanism composed of six pneumatic cylinders, and recovery training was performed. Each pneumatic cylinder was used to apply force control using a pulse width modulation control, and the force of the 6DoF direction was directed to the wrist of the patient. The thrust force of each cylinder and the force of the 6DoF direction of the parallel mechanism were analyzed. The analysis results conformed well to the experimental results. The developed rehabilitation system was designed to help a physical therapist remotely treat multiple patients at the same time. To monitor the operation of the parallel mechanism of each patient’s side, a 3D computer graphic model was created through OpenGL. The movement of this model was investigated to further examine the movement of the 6DoF direction of the parallel mechanism. Results confirmed that both movements can be controlled synchronously.     

3-RPS并联机构运动学标定方法的研究

针对六轴混联机床中因3-RPS并联机构结构参数误差引起的精度问题,分析了影响3-RPS并联机构几何精度的误差因素,给出了并联机构的误差模型;基于影响并联机构定平台运动精度较大的几何误差参数;建立了运动学标定模型.采用阻尼最小二乘法,经多次优化迭代实现了利用一组测量数据完成非线性超越矛盾标定方程组的求解.利用激光干涉仪完成了标定用数据的测量,通过3-RPS并联机构运动学逆解和各铰链的几何标定参数,得到动平台的实际位姿.通过对标定前后的Z轴定位精度的检测及实际零件加工试验,验证了3-RPS并联机构运动学标定模型和方法的正确性和有效性.     

3-PPPS并联机翼调姿机构运动学标定

为解决一种3-PPPS并联机翼调姿机构因制造、装配过程中存在的误差因素所引起的调姿精度不高的问题,考虑了调姿系统结构误差因素对调姿机构位姿精度的影响。采用空间矢量链建立机翼部件调姿位移逆解方程,通过微分机构运动学方程,得到包含39项误差源的调姿机构位姿误差与几何误差之间的映射方程。利用激光跟踪仪测量调姿机构测量机翼参考点位置和定位器各轴的实际驱动量。通过最小二乘迭代法辨识出定位器结构误差,修正定位器反向驱动位移求解参数。经过运动学标定实验后,调姿平台的位置最大误差由2.68 mm降为0.82mm,角度最大误差由0.481°降为0.167°,从而验证了标定方法的有效性。     

Design and control of a 3DOFs parallel actuated mechanism for biped application

In this paper, a novel approach to carry out the design of a three degrees of freedom (3DOF) actuated mechanisms for humanoid robots joints is presented. Instead of common serial mechanism, a more robust parallel mechanism was developed. This kind of structure gives the terminal body the ability to move within a cone from the nominal position and permits unlimited rotation about the cone pointing axis. Kinematic analysis are presented in this paper. A biped robot ROBIAN with parallel hip and ankle mechanisms was developed and experimental tests were carried out to evaluate the performances of the adopted structure.     

Analysis and evaluation of objective functions in kinematic calibration of parallel mechanisms

This paper analyses different objective functions for the parameter identification of parallel mechanisms and studies the influence in the position and orientation errors to improve their accuracy. A new objective function considering deviation terms is presented. This function is compared with other widely used functions and the advantages and disadvantages of each function are presented. The geometric parameter identification is performed by external calibration by means of the direct kinematic model. First, the objective functions are defined considering error position, error orientation and deviations in measurement. These functions compare the measured and calculated moving platform coordinates in order to obtain the identified model parameters that minimize this difference. The measured coordinates are obtained by measuring three sphere centres, fixed to the moving platform of a parallel mechanism, and the computed coordinates are given by the kinematic model. Second, the model is solved by the Levenberg–Marquardt algorithm for a number of identification positions. Finally, the calibration is verified in test positions. The results obtained show that the consideration of the deviations in measurement in the objective function with respect to classical approaches allows us to better identify those kinematic parameters corresponding with passive joints that cannot be measured. These findings confirm that a suitable objective function can improve the mechanism accuracy by more than one order of magnitude in both position and orientation errors.     

On the modeling and composite control of flexible parallel mechanism

One of the key problems in high speed motion control of a flexible parallel mechanism (PM) is to damp out the mechanical vibration arising from high inertial force acting on the linkages and other components. In this paper, the dynamic equations of a 2 degree-of-freedom (DOF) planar PM with flexible links are established by taking the singular perturbation approach (SPA). Thus the model of the mechanism can be separated into slow time-scale and fast time-scale subsystems. Based on the feedback linearization theory and input shaping technique, the large range rigid motion controller and the flexible link vibration controller can be designed separately. A composite control with the two separate controllers can then be applied in the PM to achieve the desired fast and accurate positioning.     

Research on stiffness control of a redundant cable-driven parallel mechanism

Journal of Mechanical Science and Technology - Controlling the stiffness of cable-driven parallel mechanisms (CDPM) is of great significance for improving performance in different tasks. A method...     

采用KPCA-BP神经网络的并联机构全局综合性能评价方法研究

基于并联机构单一性能指标的多样性和各单一性能指标之间的非线性关系,将核主成分分析(Kernel Principal Component Analysis,KPCA)方法与误差反传播(Back Propagation,BP)神经网络技术相结合,建立一个对可完成不同工作任务的并联机构进行综合性能评价的KPCA-BP神经网络模型。通过合理的系统抽样,利用KPCA对BP神经网络的输入数据进行预处理,既能处理各单一性能指标间的非线性关系,又能简化BP神经网络结构,加快网络学习速度,提高预测精度,进而提出一种基于多种单一性能指标的并联机构全局综合性能评价新方法,为并联机构工作任务优序关系研究提供科学的参考依据。     

并联机构动力学建模及控制策略的研究

在总结并联机构动力学分析目标的基础上,对并联机构的动力学建模方法,包括拉格朗日方法、牛顿-欧拉法、虚功原理、凯恩方程法等进行了比较研究,并对控制策略的研究现状进行了综述。     

3-RRR并联机构动力学参数辨识模型

根据运动学模型,推导了3-RRR并联机构的雅可比矩阵.在每一个运动构件上选择一个适当的关键点,从而使运动构件的偏角速度矩阵和关键点的偏速度矩阵中不包含基本动力学参数.相对于这些关键点,计算出每一个运动构件的惯性力和力矩.基于虚功原理,从惯性力和力矩中提取基本动力学参数,推导出3-RRR并联机构动力学参数辨识模型.     

利用正交位移测量系统进行六自由度并联机构参数标定

为了简化六自由度并联机构的参数标定过程,提高标定效率,降低标定成本,提出了基于正交位移测量系统的位姿测量装置及方法.首先,研究了该装置的位姿解算方法,利用空间解析几何的方法,求解其运动学正解与逆解.其次,利用微小位移合成法,建立了并联机构及正交位移测量系统组合体的误差模型.然后,基于误差模型,构建了组合体参数误差辨识的...     

面向在轨装配的冗余索并联机构变刚度控制

为了提高一种面向在轨装配的索并联机构的工作性能,提出了变刚度控制算法.建立了索并联机构的完整刚度模型,分析了绳索张力分布对不同方向刚度的影响.然后,考虑影响绳索张力分布的矢量λ的安全边界,建立了变刚度控制算法,该算法消除了刚度模型中对整体影响较小的耦合刚度,提高了计算效率,并且通过分配权重的方式对不同方向的刚度进行不同...     

模糊控制在并联机器人中的应用

分析了一种三平移并联机构中的驱动电动机,求出其动态方程及传递函数.简述了模糊控制器的设计与仿真,模糊控制中引入一个Ⅰ型积分环节用来消除模糊控制固有的静态偏差.仿真结果及实际结果均表明有较好的控制效果.