Research on the parallel load sharing principle of a novel self-decoupled piezoelectric six-dimensional force sensor

This paper presents a novel integrated piezoelectric six-dimensional force sensor which can realize dynamic measurement of multi-dimensional space load. Firstly, the composition of the sensor, the spatial layout of force-sensitive components, and measurement principle are analyzed and designed. There is no interference of piezoelectric six-dimensional force sensor in theoretical analysis. Based on the principle of actual work and deformation compatibility coherence, this paper deduces the parallel load sharing principle of the piezoelectric six-dimensional force sensor. The main effect factors which affect the load sharing ratio are obtained. The finite element model of the piezoelectric six-dimensional force sensor is established. In order to verify the load sharing principle of the sensor, a load sharing test device of piezoelectric force sensor is designed and fabricated. The load sharing experimental platform is set up. The experimental results are in accordance with the theoretical analysis and simulation results. The experiments show that the multi-dimensional and heavy force measurement can be realized by the parallel arrangement of the load sharing ring and the force sensitive element in the novel integrated piezoelectric six-dimensional force sensor. The ideal load sharing effect of the sensor can be achieved by appropriate size parameters. This paper has an important guide for the design of the force measuring device according to the load sharing mode.     

Dynamic characteristics of piezoelectric six-dimensional heavy force/moment sensor for large-load robotic manipulator

This paper presents research on dynamic characteristics of a piezoelectric six-dimensional heavy force/moment sensor for a large-load robotic manipulator. The theory on dynamic characteristics of the sensor structure is analyzed, and a mathematical model of the sensor dynamics, decoupled into separate vibration modes, is provided. This model is complemented by dynamic mode analysis of the sensor by finite-element modeling (FEM; ANSYS software). A dynamic calibration experiment is designed, and methods and principles for measurements and data analysis are provided. The characteristic dynamic vibration modes of the piezoelectric force/moment sensor are extracted by analyzing experimental data, yielding amplitude frequency and phase frequency curves of the transfer function linking the excitation loads with the output signals of the transducer. The results of the dynamic calibration experiment demonstrate the good dynamic characteristics of the piezoelectric six-dimensional heavy force/moment sensor. The natural frequencies in the three force directions are high, with values close 2000 Hz. This demonstrates the applicability of the presented six-dimensional heavy force/moment sensor to large industrial robotic manipulators.     

新型过约束正交并联六维力传感器测量模型与静态标定试验

面向航空航天领域对重载大吨位多维测力传感器的急需,通过引入冗余测力分支,提出一种适用于重载测力场合的新型过约束正交并联六维力传感器结构,在提高传感器结构刚度和承载能力的同时有效抑制了关节摩擦对多维力传感器测量精度的影响。基于螺旋理论,推导得到了该并联传感器一阶静力影响系数矩阵,建立理想状态下该新型过约束正交并联六维力传感器测量数学模型。考虑各测量分支的初始预紧力与刚度,基于传感器静力平衡方程与补充建立的位移协调方程,推导建立考虑初始预紧力与分支刚度因素下该新型过约束正交并联六维力传感器测量数学模型。在此基础上,设计并研制该新型过约束正交并联六维力传感器样机,搭建传感器加载标定与信号采集及处理试验系统,对新型过约束正交并联六维力传感器进行了加载标定试验。根据试验结果计算了传感器测量误差矩阵,分析得到了传感器测量精度,从而为重载过约束并联六维力传感器的开发与应用提供了参考。     

基于6维力/力矩传感器的并联机器人惯性参数辨识方法

提出了基于6维力/力矩传感器的并联机器人惯性参数辨识新方法,这种方法不需要了解关节摩擦和驱动器动力学特性的精确模型,推导了一般并联机器人的惯性参数辨识模型,分析了并联机器人的基惯性参数,提出了并联机器人惯性参数辨识轨迹的选择原则,并给出了两种新型空间并联机器人的分析实例。     

3/6-SPS 并联机构刚度和弹性变形的解析法分析

针对并联机构中机构的刚度和弹性变形随外载荷变化的问题,以3/6-SPS 并联机构为例,采用解析法求解分析其总刚度矩阵和弹性变形。首先,分析该并联机构受力位置并确定驱动力及其姿态;然后,分析该机构的驱动约束分支的弹性变形,导出驱动约束分支的伴随矩阵;最后求解出该并联机构的总刚度矩阵和弹性变形。得到结论：当建立3/6-SPS 并联机构的总刚度矩阵和求解弹性变形时,必须理清刚度和位姿、广义六维力之间的关系。     

A novel parallel sensor with six rigid compliant limbs for measuring six- component force/torque

A novel parallel sensor with six rigid/compliant hybrid limbs and six standard force sensors is developed for measuring the six-component force/torque. The measuring theory and performances are studied. A prototype of the robot hybrid hands with the parallel sensor is developed. A prototype of the parallel sensor is built up and its merits and performances are analyzed. A statics equation among the forces of the standard force sensors and the whole external load and a stiffness model of the parallel sensor are established based on its equivalent parallel mechanism. The force/torque of the parallel sensor is measured under the given external load. The theoretical solutions of the statics model of the parallel sensor are obtained and verified by both the experimental measuring solutions of the prototype of the parallel sensor and the simulation solutions of a FE model.

     

Torque sensor calibration using virtual load for a manipulator

Accurate load sensing of a manipulator becomes increasingly important in performing various tasks involving contact with an environment. Most of the research has been focused on improving the hardware of a force/torque sensor. The torque sensors for a manipulator suffer from crosstalk, which is difficult to compensate for even with sophisticated calibration. This research proposed a novel calibration method composed of two steps. Through the primary calibration, the torque sensor output can be related to the joint torques. The secondary calibration, which is based on a virtual load, is conducted to compensate for the crosstalk of a torque sensor. The virtual load is obtained from the sensed joint torques and manipulator configuration. Using the proposed calibration method, the external load acting on the end-effector of a manipulator can be accurately measured even with relatively low-quality torque sensors. The experimental results showed that the error in the load sensing was significantly reduced by the proposed calibration method.     

拔长工艺中锻造操作机液压系统能耗分析

扩展了锻造操作机整机的能量流模型和能耗计算模型,研究了拔长工艺下锻造操作机液压系统的控制特性和能耗特性,得出了液压系统的能耗分布规律,分析了能量浪费的关键环节,为锻造操作机液压控制系统的优化以及节能控制方法的提出提供指导。研究结果表明,锻造操作机液压系统的能耗特性具有如下特点：夹钳上升和旋转动作的能量传递效率较高,均可达60%以上;大车行走动作的能量传递效率仅为17%;夹钳下降时重力势能几乎全部转化为升降控制阀的节流损失;多执行器不同负载与单压力源不能合理匹配会造成巨大的节流损失。     

Design and fabrication of a six-dimensional wrist force/torque sensor based on E-type membranes compared to cross beams

This paper presents a novel device for measuring components of forces and moments along and about three orthogonal axes based on E-type membranes compared to conventional sensor based on cross beams. After design and analysis of both types of sensors, we chose to fabricate a six-dimensional wrist force/torque sensor based on E-type membranes. Furthermore, the calibration and decoupling based on Neural Network method were performed, and the sensor possesses excellent characteristics such as high measurement sensitivity, overload protection, good linearity, and weak couplings between components. Finally, its maximum interference error and nonlinearity error are 1.6% F.S. and 0.17% F.S., respectively.     

四自由度锻造操作手模拟实验台动力学建模与控制

锻造操作手在时变工况下的动力学特性直接影响着锻件的成形质量.采用拉格朗日方程法建立四自由度锻造操作手模拟实验台动力学模型,并将数学模型与ADAMS虚拟样机的动力学仿真结果进行对比验证,证明了模型的合理性.在此基础上,设计基于重力补偿的PID控制器,仿真结果显示控制性能良好.研究结果为实际锻造操作手的动力学研究和轨迹规划提供了有价值的参考.     

一种可用于微创手术的并联机构运动学分析与性能优化

与串联机构相比,并联机构具有刚度好,精度高,响应快等优点,适合用于医疗领域。微创穿刺活检等手术要求机器人机构能够输出远中心运动。提出了一种用于微创手术的新型远中心并联机构,其分支内部包含平行四边形闭环子链。采用螺旋理论对机构自由度进行了分析,证明其能输出两个转动运动和一个移动运动,且所有运动均通过远端固定中心。对机构进行位置分析,建立了驱动参数与末端参数之间的映射。通过速度分析建立了雅可比矩阵,并分析得到了机构的奇异位形,包括逆解奇异、正解奇异和混合奇异。应用搜索法分析了机构的工作空间。采用运动/力传递指标对机构进行了性能分析,绘制工作空间内的性能图谱。以优质空间大小为目标对机构进行了尺度优化。     

Impedance analysis of forging process and strategy study on compliance for forging manipulator

In the field of heavy forging, there are numerous researches on deformation rule in forging process by FEM simulation, however, not many scholars take the equipment constraint and the mutual reaction load between the forging manipulator clamp and the forging blank into account, which will impact on safety of manipulator body and quality of forging blank. This paper presents an impedance model to describe the load and formulates compliance strategies correspondingly to reduce the mutual reaction load for forging manipulator. Firstly, an FEM model of forging process is built. Meanwhile, the clamp of forging manipulator is added to the model as movement constraint and interaction part between the manipulator and the forming process. Secondly, a typical forging process is simulated by changing the movement constraint, and then an impedance model is established to describe the relationship between the load and movement constraint. Finally, two kinds of compliance strategies are formulated according to the impedance model, one is called free compliance, and the other is initiative/passive compliance. The simulation results show that compliance strategies reduce the load amounting to 5 000 kN in z direction between the manipulator clamp and the forging blank obviously, which may lead to serious accidents, such as the capsizing of forging manipulator, the fracture of manipulator clamp, and so on. The proposed research simulates the more real forging process, gets the initiative/passive compliance strategy which is more simple and suitable to the real producing and better for forming a forging process planning and control system in the modern production, and improves the quality and efficiency of heavy forging.     

The effect of base replacement on the dynamic load carrying capacity of robotic manipulators

The problem of establishing the load carrying capacity of mobile base manipulators operated by limited force or torque actuators is presented. It is shown the maximum allowable load on a given load trajectory, is a function of base position. The load workspace is defined as the union of places where the base can be located on them and it carries a load by the manipulator on a desired trajectory. The load workspace is discretised into some grid points, and the base is positioned on each grid point. The recursive Newton-Euler method is used to compute the dynamic effects of the load and manipulator on each joint actuator, then the load carrying capacity of the mobile manipulator at each base location is computed by considering the manipulator joints and actuator torque constraints. By applying a simple procedure, a smaller subspace of the load workspace is selected, so that the load carrying capacity is near to a maximum. This procedure is repeated until the optimum base location is found so that the load carrying of the manipulator is a global maximum in the load workspace for the desired dynamic trajectory. Finally, the effect of base mobility on optimising the dynamic load carrying capacity for different robotic arms is investigated in separate case studies.     

双锻造操作机大车行走系统控制方法探析

双锻造操作机配合压机联动完成大型高精长轴类锻件的锻造,可以有效提高锻造效率,提升锻件品质。针对双操作机夹持锻件同步行走控制难题,以燕山大学的两台20 kN锻造操作机为研究对象,综合考虑了吊挂系统、大车行走机械和液压系统的特点,搭建了双锻造操作机大车行走系统的数学模型。在此基础上,仿真研究了独立反馈位置同步控制方法、位置速度复合独立反馈同步控制方法和位置速度复合状态差值校正同步控制方法对双操作机大车行走系统控制特性的影响。仿真结果表明,对于动力性能差异较大的两台重载机械手,基于位置速度复合状态差值校正同步控制方法的控制效果最为理想,同时设定操作机A和操作机B的给定位移200 mm、加速度1000 mm/s2时,双操作机大车行走系统的动作响应时间为105 s,同步位置误差为［-0.28 mm,0.02 mm］。研究结果可为双锻造操作机控制提供技术支撑和理论指导,对于提升锻造产品质量和实现锻造生产线的智能控制具有重要意义。     

A new sheet metal forming system based on the incremental punching, part 1: modeling and simulation

In heavy forging, a manipulator is indispensable to assist and help the precision of the forming process. This paper presents a multi-system simulation methodology combining the forging finite element method (FEM) simulation and the kinematics analysis to evaluate the mutual reaction loads between the forging process and the assisting manipulator. The forging is realized by the thermal–mechanical FEM simulation and the kinematics movements are analyzed based on the statics and dynamics modeling of the manipulator. The reaction load generating from the forging process to the manipulator clamps is treated as an input parameter for the kinematics analysis system, which will then calculate the movement of the manipulator. And this movement is regarded as the passive compliant movement constraint and applied on the forging process through the manipulator clamps. Using this coupled system, the study compares the reaction loads with and without the active vertical compliant movement and/or the passive horizontal compliant movement and reveals the effect of these compliant movements on the reaction loads.     

STRUCTURE SYNTHESIS OF 4-DOF PARALLEL ROBOT MECHANISMS BASED ON SCREW THEORY

Structural synthesis for 4-DOF parallel manipulators using screw theory is systematically studied. Motion properties and constraint conditions of 4-DOF parallel manipulators according to the relationship between screw and reciprocal screw are analyzed. Mathematical expressions for constraint screws and twist screws of moving platform are constructed, and all possible limbs, which provide one or more force constraints, are enumerated. Finally, a parallel manipulator with 3-rotation-DOF and 1-translation-DOF is used as an example to describe the synthesis procedure for symmetrical and non-symmetrical 4-DOF parallel manipulators.     

锻造操作机钳口夹紧力和夹紧缸能力的计算

在锻造操作机设计中，钳口夹紧力和夹紧缸能力的计算是首要的和关键的问题，它的分析、计算、选择是否正确，对操作机整体设计至关重要。     

并联机器人力传递性能分析

并联机器人雅可比矩阵中包含了输入输出力/力矩关系的信息,以此为基础可以进行一些力学性能评价。然而,力和力矩具有不同的量纲,因而,直接对雅可比矩阵进行分析计算不尽合理。据此,将雅可比矩阵分为力雅可比和力矩雅可比,在此基础上,研究并联机器人在工作空间内的力传递性能和力矩传递性能。所提方法自然直观,避免了不同量纲的物理量之间的混合,所得结果物理意义明晰,可用于并联机器人结构优化。     

A novel piezoelectric 6-component heavy force/moment sensor for huge heavy-load manipulator's gripper

This paper presents the development of a piezoelectric 6-component heavy force/moment sensor which may be used to detect forces F_x, F_y and F_z, and moments M_x, M_y and M_z on huge heavy-load manipulator's gripper, simultaneously. The structure of the sensor is newly modeled. Piezoelectric quartz is chosen as force sensing element to realize real-time measurement. In order to investigate the validity of the proposed method, a prototype of piezoelectric 6-component heavy force/moment sensor is developed, and a characteristic test of the piezoelectric 6-component heavy force/moment sensor is performed. The experiments show that the linearity of the sensor is no more than 1%, and the interference errors are less than 3%. The carrying capability of force sensor is improved greatly by using load distribution.     

Measurement method of six-axis load sharing based on the Stewart platform

In this paper, a measurement method of six-axis load sharing based on the Stewart platform is presented. The force Jacobin matrix of the Stewart platform, the solution of forward kinematics of the Stewart platform and the deep beam element stiffness matrices were combined in the decoupling algorithm. The FEM model was established, and the results of FEM analysis agreed well with the calculation results from proposed method, which proves the effectiveness of the method of six-axis load sharing. Moreover, a six-axis heavy force sensor based on the Stewart platform was demonstrated in order to investigate the reasonability and validity of the six-axis load sharing model. And the experiment results verified the feasibility of the method.