A new 3-DOF Z-tilts micropositioning system using electromagnetic actuators and air bearings

A new 3-DOF Z-tilts (z, pitch, and roll motion) micropositioning system has been developed. It uses electromagnetic actuators and air bearings. An electromagnetic actuator produces an attraction force between the air bearing and the base plate. An air bearing has the role of suspension and guidance, with a clearance of several tens of micrometers in the z-direction. Therefore, this system has design features of guiding 3-DOF XYθ motion without limiting the plane motion and playing the role of a z-directional position actuator. With the control of current, the equilibrium position between magnetic attraction force and air bearing thrust force can be controlled with inherently infinite resolutions. The theoretical background of an electromagnetic actuator is explained. Then, an air bearing is analyzed in the point of z-directional positioning mechanism. The air bearing can be modeled as a second-order system with parameter variation—stiffness and damping vary with respect to the z-directional displacement. Therefore, a simple robust control algorithm is applied to improve the control performance. With the aid of robust control, this system provides 25 nm positioning resolution over the total range of 40 μm along the z-direction and, accordingly, 0.29 μrad resolution over the total range of 460 μrad in pitch and roll motion.     

一种新型6-DOF并联机构的运动学分析

提出了一种新型6自由度2支链并联机构:2-S*RU;其中S*为3自由度球面机构,为复合球铰,R为转动副,U为虎克铰。采用余弦矩阵方法得出了该并联机构的位置正反解的封闭解形式,其中正解的最终方程为一元4次方的多项式。采用余弦矩阵的优点是:第一,与欧拉角不同,方向余弦矩阵不会有任何有代表性的奇异位形。第二,在计算过程中不会出现三角函数,提高了计算效率。该机构可应用于机器人手臂,结构简单紧凑,易于实现模块化。     

基于正弦输入的球形机器人运动控制

球形移动机器人具有结构紧凑,动作灵敏,适合在缺少人为干预的恶劣环境中应用。由于球形移动机器人属于非完整约束系统,传统的运动控制理论在这种机器人上无法应用。论文首先介绍BHQ-1球形移动机器人机构和运动原理,其次根据欧拉角描述方法建立了球形机器人的运动学模型,并对输入量进行变换得到一个可用正弦输入进行控制的双链系统。最后利用正弦输入方法得到轨迹仿真图。     

Design, modeling, and testing of a novel 6-DOF micropositioning stage with low profile and low parasitic motion

We developed a novel piezoelectrically actuated 6 degree-of-freedom (DOF) stage for micropositioning. To achieve a parallel mechanism with high stiffness, compact size, and low parasitic motion for 6-DOF positioning, an orthogonal actuator configuration is proposed and actuation units are carefully designed. For the purpose of suppressing parasitic motion in the overall stage, the ratios of the lateral stiffness to actuating directional stiffness of the actuation units are minimized under the condition that the stress at any point in the stage does not exceed the allowable strength. Flexure hinges and lever linkages are effectively applied to the horizontal and vertical actuation units. A physics-based model of the stage is developed to ensure low system order and high reliability. The model parameters are estimated by experiment and finite element analysis. Open-loop tests including sinusoidal and step responses verify low parasitic motion and reliability of the model. Closed-loop step responses with a model-based controller validate the high micropositioning performance of the stage.     

基于惯性冲击原理的3DOF微小型机器人系统

提出一种由4组压电陶瓷驱动器驱动的微小型移动机器人系统.基于惯性冲击原理,4组压电陶瓷驱动器在不同形式锯齿波电压的驱动下,能够实现机器人2个平动运动自由度和一个旋转运动自由度.基于DDS波形发生原理,为机器人设计了由C8051F040高速单片处理器、FPGA和功率放大器所构成的机器人驱动控制系统.机器人运动性能测试试验表明,提出的微小型移动机器人统具有亚毫米级的运动速度和亚微米级的运动分辨力,可以作为微操作系统中的移动式精密定位机构.     

Design of a slider-crank leg mechanism for mobile hopping robotic platforms

Legged locomotion has been widely researched due to its effectiveness in overcoming uneven terrains. Due to previous efforts there has been much progress in achieving dynamic gait stability and as the next step, mimicking the high speed and efficiency observed in animals has become a research interest. The main barrier in developing such a robotic platform is the limitation in the power efficiency of the actuator: the use of pneumatic actuators produce sufficient power but are heavy and big; electronic motors can be compact but are disadvantageous in producing sudden impact from stall which is required for high speed legged locomotion. As a new attempt in this paper we suggest a new leg design for a mobile robot which uses the slider-crank mechanism to convert the continuous motor rotation into piston motion which is used to impact the ground. We believe this new mechanism will have advantage over conventional leg mechanism designs using electronic motors since it uses the continuous motion of the motor instead of sudden rotation movements from stall state which is not ideal to draw out maximum working condition from an electronic motor. In order to control impact timing from the periodic motion of the piston a mechanical passive clutch trigger mechanism was developed. Dynamic analysis was performed to determine the optimal position for the mechanical switch position of the clutch trigger mechanism, and the results were verified through simulation and experiment. Development of a legged locomotion with two degrees of freedom, slider-crank mechanism for impact and additional actuation for swing motion, is proposed for future work.     

DESIGN AND CONTROL OF AN ULTRAPRECISION STAGE USED IN GRATING TILING

In petawatt laser system, the gratings used to compose pulse compressor are very large in size which can be only acquired currently by arraying small aperture gratings to form a large one instead, an approach referred to as grating tiling. Theory and experiments have demonstrated that the coherent addition of multiple small gratings to form a larger grating is viable, the key technology of which is to control the relative position and orientation of each grating with high precision. According to the main factors that affect the performance of the grating tiling, a 5-DOF ultraprecision stage is developed for the grating tiling experiment. The mechanism is formed by serial structures. The motion of the mechanism is guided by flexure hinges and driven by piezoelectric actuators and the movement resolution of which can achieve nanometer level. To keep the stability of the mechanism, capacitive position sensors with nanometer accuracy are fixed on it to provide feedback signals with which to realize closed-loop control, thus the positioning precision of the mechanism is within several nanometers range through voltage control and digital PID algorithm. Results of experiments indicate that the performance of the mechanism can meet the requirement of precision for grating tiling.     

6自由度绳牵引并联机构的运动轨迹规划

首先,基于6自由度绳牵引并联机构的运动学逆解模型,给出了可用于运动轨迹规划的绳的速度和加速度 的一般结论:绳的速度值始终不大于动平台上相应铰链点的速度值;而正的绳加速度值始终不大于动平台上相应 铰链点沿绳拉力方向的加速度值。接着,提出一种适用于大部分工作空间的绳拉力的计算算法。然后,选择一个 结构紧凑的6自由度完全约束定位机构,以末端执行器能实现空间螺旋∞型的轨迹为目标,进行运动规划,研究 绳的运动特性。仿真结果验证了以上所得到的一般性结论。同时表明,一些绳的拉力的变化不大;而另外一些绳 的拉力的变化很大。这些运动轨迹规划的仿真结果,能为以后该机构的运动控制方案的研究提供依据。提出的运 动轨迹规划方法对一般的6自由度绳牵引并联机构都适用。     

运动副间隙对汽车摆振系统非线性动力学行为影响分析

在前期研究中发现运动副间隙对机构的动力学响应影响显著,因此做出转向系统中的间隙也会对转向摆振系统的响应产生重要影响的推断。为此,将转向梯形机构简化为一个连杆机构,并就机构中运动副间隙对转向系统摆振的影响进行了分析。借助拉格朗日方程建立考虑转向机构运动副间隙的6自由度转向系统摆振动力学模型,基于该摆振模型,应用四阶龙格－库塔法对间隙参数发生变化时摆振系统的响应进行仿真分析。通过仿真分析结果发现：转向机构运动副间隙是诱发转向轮摆振系统混沌运动的重要因素,在摆振系统建模过程中应予以充分考虑;随着运动副间隙增大,转向摆振系统会由周期运动状态经过拟周期运动状态逐渐进入混沌状态,造成摆振运动加剧。相关结论可为转向系统摆振的有效控制奠定理论基础。     

一种新型3自由度大行程微定位平台设计与分析

为解决微定位平台大行程与高精度之间的矛盾,提出一种新型的3自由度柔性并联机构。该机构三条支链采用特殊方式与动平台相连,使整体机构结构紧凑且具有良好的力学传递性能。同时,机构采用行程大,分辨率高,便于控制的电磁驱动器作为驱动部件,保证机构在不需要引入放大机构的前提下便可获得较大的行程和较高的分辨率。使用大行程柔性铰链代替普通的球铰,降低了加工制造难度和机构刚度模型的求解难度。采用螺旋理论分析了3-P(4S)并联机构末端运动特征,结合单元刚度矩阵法和矩阵位移法推导了3-P(4S)柔性并联机构的静刚度模型,并采用ANSYS进行了分析验证。     

基于变胞铰链的并联机构结构设计与构型分析

为了拓展变胞机构的种类,提出了一种变胞运动单元,该变胞单元采用三个旋转关节,并且三个旋转关节可以通过位置调节形成等效球铰、虎克铰以及转动副。与传统的锁定运动副来实现变胞功能的变胞单元相比,此变胞单元三种构型的切换只需对轴线位置调整,无需额外增加关节锁死电机。通过研究由线矢量构成的螺旋系统的相关性,揭示了变胞运动单元构态变化的基本原理。提出了可用于构造新型变胞并联机构的支链构型设计方法,并基于螺旋的互易性分析了各支链构型所必须满足的几何约束条件。提出了两种变胞并联机构,通过不同的支链装配形式可将其从6自由度构型转换为3自由度构型,并对支链安装形式进行改进,构造出了具有3自由度平移模式和3自由度转动模式的并联机构。对变胞支链作为中心支链组装而成的并联机构的构型及对应的运动类型进行了分析,获得了六种不同构型的并联机构。     

Dynamic Modeling and Eigenvalue Evaluation of a 3-DOF PKM Module

Due to the structural complexity, the dynamic modeling and quick performance evaluation for the parallel kinematic machines (PKMs) are still to be remained as two challenges in the stage of conceptual design. By using the finite element method and substructure synthesis, this paper mainly deals with the dynamic modeling and eigenvalue evaluation of a novel 3-DOF spindle head named the A3 head. The topological architecture behind the proposed A3 head is a 3-RPS parallel mechanism, which possesses one translational and two rotational capabilities. The mechanical features of the A3 head are briefly addressed in the first place followed by inverse position analysis. In the dynamic modeling, the platform is treated as a rigid body, the RPS limbs as the continuous uniform beams and the joints as lumped virtual springs. With the combination of substructure synthesis and finite element method, an analytical approach is then proposed to formulate the governing equations of motion of system using the compatibility conditions at interface between the limbs and the platform. Consequently, by solving the eigenvalue problem of the governing equations of motion, the distribution of lower natural frequencies of the A3 head throughout the entire workspace can be predicted in a quick manner. Modal analysis for the A3 head reveals that the distributions of lower natural frequencies are strongly related to the mechanism configuration and are axially symmetric due to system kinematic and structural features. The sensitivity analysis of the system indicates that the dimensional parameters of the 3-RPS mechanism have a slight effect on system lower natural frequencies while the joint compliances affect the distributions of lower natural frequencies significantly. The proposed dynamic modeling method can also be applied to other PKMs and can effectively evaluate the PKM's dynamic performance throughout the entire workspace.     

空间曲面线切割多轴联动加工系统开发及应用

开发了能实现空间曲面零件电火花线切割加工的多轴联动加工系统,分析了系统的组成和运动参数。依据空间解析几何直纹曲面形成原理,建立了五轴联动加工的数学模型体系,获得了五轴联动加工三导线曲面零件的数学模型。研制了多轴联动加工系统的执行机构转摆摆数控工作台及数控系统,加工出理想的实验样件。解决了空间曲面零件的加工难题,拓宽了高速走丝电火花线切割加工的应用范围。该方法在模具制造及空间曲面零件加工中得到广泛应用。     

气囊抛光进动机构的运动建模与仿真

气囊抛光工具的进动由一类特殊的2自由度空间机构实现。针对此2自由度空间机构运动,运用机构学理论,推导了这一空间机构的基本坐标变换,建立了各参数之间的内在关系。在此基础上,根据进动要求建立了这一空间机构的进动运动方程,通过仿真研究了气囊进动过程中运动参数的变化规律。结果表明在进动过程中,合成进动运动的2自由度运动有一定的运动规律,同时所建立的模型为该空间机构的进一步分析和运动控制提供了依据。     

阀门驱动装置——电控液动执行机构的研究

电控液动执行机构是一种自动化程度较高的阀门驱动装置 ,其结构简单、形式紧凑、操作方便、运行可靠 ,产品体积小、重量轻、出力大 ,耐恶劣环境。本文介绍了电控液动执行机构的结构、工作原理和使用情况等     

Steering control algorithm for efficient drive of a mobile robot with steerable omni-directional wheels

Omnidirectional mobile robots are capable of arbitrary motion in an arbitrary direction without changing the direction of wheels because they can perform 3-DOF motions on a plane. This paper presents a novel mobile robot design with steerable omnidirectional wheels. This robot can operate in either omnidirectional or differential drive modes, depending on the drive conditions. In the omnidirectional mode, the robot has 3 DOF in motion and 1 DOF in steering, which can function as a continuously variable transmission (CVT). The CVT function can be used to enhance the efficiency of the robot operation by increasing the range of the velocity ratio of the robot velocity to wheel velocity. The structure and kinematics of this robot are presented in detail. In the proposed steering control algorithm, the steering angle is controlled such that the motors may operate in the region of high velocity and low torque, thus operating with maximum efficiency. Various tests demonstrate that the motion control of the proposed robot works satisfactorily and the proposed steering control algorithm for CVT can provide a higher efficiency than the algorithm using a fixed steering angle. In addition, it is shown that the differential drive mode can give better efficiency than the omnidirectionaldrive mode.     

Vision guided dual arms robotic system with DSP and FPGA integrated system structure

Usually, a humanoid robot has two arms and stereo vision system to execute human daily actions. It has complicate mechanism and mechatronics control system structure. The hardware control structure should be planned ingeniously to execute the complicate computation of 3D image processing and manipulate a multi degree of freedom dual arms motion control, especially for mobile robot system. Here a 7 DOF dual arms robot with FPGA hardware control structure and a digital signal processor (DSP) based CMOS stereo vision system are designed and built in our lab. The intelligent fuzzy sliding mode control strategy is employed to establish the visual guided robotic motion control software. This low cost humanoid robotic system has compact control structure and mechanism integration for mobile application purpose. Object detecting and tracking schemes in 3D space were developed for locating the target position and then guided the robot arm to pick and place objects or track the specified moving target. Experimental results show that this delicate robotic system has basic humanoid function.     

大型刚体调姿系统最优时间轨迹规划

研究基于三坐标支撑柱的大型刚体位姿调整系统。系统可等效为6自由度冗余驱动并联机构,动平台初始位姿和目标位姿已知,而运动时间和路径不确定。为了使支撑柱运动平稳并提高调姿精度,在考虑工程实际中的关节驱动力约束和驱动速度约束的基础上,提出一种最优时间轨迹规划算法。首先运用冗余驱动并联机构的分析方法建立该系统的运动学和动力学模型,并通过Moore-Penrose广义逆矩阵得到关节驱动力的最小范数解,然后以时间为参数,运用5次多项式拟合调姿物体的位姿变化轨迹,再通过二分法求解出满足关节空间约束的最优调姿时间,从而生成相应的关节运动轨迹。仿真结果表明算法只需经过较少次迭代就能获得理想的调姿运动轨迹。总之,该轨迹规划方法是有效的。     

Development of a piezoelectrically actuated two-degree-of-freedom fast tool servo with decoupled motions for micro-/nanomachining

The limited degrees of freedom (DOFs) of servo motions is an inherent deficiency in conventional, fast-tool-servo-(FTS)-assisted, diamond-turning, highly blocking applications of the FTS technique. In this paper, the concept of two-DOF FTS (2-DOF FTS)-assisted diamond turning is proposed and demonstrated. A piezoelectrically actuated 2-DOF FTS mechanism is developed to enable the cutting tool to move along two directions with decoupled motions. A novel guidance flexural mechanism constructed using the newly proposed Z-shaped flexure hinges (ZFHs) is introduced to generate motions along the z-axis, which is based on the bending deformation of the beams of the ZFHs. Additionally, using the differential moving principle (DMP), bi-directional motions in the x-axis direction can be achieved. Using the matrix-based compliance modeling method, the kinematics of the mechanism are analytically described, and the dynamics are also modeled using the Lagrangian principle. The theoretical results are then verified using finite element analysis (FEA). Certain increases in performances over conventional two-DOF flexural mechanisms are achieved: (a) a more compact structure with lower moving inertia, (b) theoretically decoupled motions of the output end, and (c) less than one actuator per DOF. To investigate the practical performance of the 2-DOF FTS system, both open-loop and closed-loop tests are conducted. Finally, the developed 2-DOF FTS technique is implemented to realize an innovative Pseudo-Random Diamond Turning (PRDT) method for the fabrication of micro-structured surfaces with scattering homogenization. The cutting results demonstrate not only the superiority of the concept but also the efficiency of the developed 2-DOF FTS system.     

新型三平移一转动并联机构及运动学分析

根据并联机器人机构结构综合理论，以单开链支路为单元，提出了一种能实现空间三维移动和一维转动的四自由度并联机构。分析了该机构的运动特性，运用连杆DH矩阵，探讨了具有5R支链的建模方法，给出了机构位置反解的数学模型，并在ADAMS虚拟样机软件及MATLAB数学计算软件上进行了数值验证。这种机构具有4个自由度运动特性，在结构上具有较好的对称性，且支链结构可进行模块化组装，有较好的应用前案。为机构建立的反解模型较简单，数值验算证明是正确的。机构的运动学反解模型为该机构作进一步的运动学动力学及优化设计研究打下基础，并为系统控制提供了理论依据。