APPROACH TO IMPROVEMENT OF ROBOT TRAJECTORY ACCURACY BY DYNAMIC COMPENSATION

Some dynamic factors, such as inertial forces and friction, may affect the robot trajectory accuracy. But these effects are not taken into account in robot motion control schemes. Dynamic control methods, on the other hand, require the dynamic model of robot and the implementation of new type controller. A method to improve robot trajectory accuracy by dynamic compensation in robot motion control system is proposed. The dynamic compensation is applied as an additional velocity feedforward and a multilayer neural network is employed to realize the robot inverse dynamics. The complicated dynamic parameter identification problem becomes a learning process of neural network connecting weights under supervision. The finite Fourier series is used to activate each actuator of robot joints for obtaining training samples. Robot control system, consisting of an industrial computer and a digital motion controller, is implemented. The system is of open architecture with velocity feedforward function. The proposed m     

Dynamic characteristics and dual control of a ball screw drive with integrated piezoelectric actuator

This paper describes the precision continuous path tracking control by using a dual-actuated single stage. First, fine-drive mechanism and the dynamic model of the entire drive system are described. In the simulation model, the dynamic characteristic of the dual-actuated stage is investigated to see whether it can provide precise motion by using dual control. Second, the fine motion controller is designed. Adjusting the control parameters, a positioning resolution of 20 nm and a bandwidth of 260 Hz were obtained. Third, the frequency responses of coarse and fine drives are experimentally investigated. After that, the dual controller is designed based on the investigated dynamics. Finally, whether coarse motion and fine motion could work complimentarily by the dual servo is examined in the experiments. By using the simultaneous dual controller, tracking errors were reduced sufficiently compared to the single coarse control.     

惯性参考单元的变增益PI位置控制技术

基于惯性参考单元的视轴稳定方式是克服运动载体光电跟瞄系统外部扰动,实现微弧度甚至亚微弧度级跟瞄的主要技术手段。惯性参考单元的初始校准需要构建以电涡流线位移传感器作为角位置反馈元件的闭环控制回路,角位置控制精度是影响光电跟瞄系统指向精度的主要因素。为了解决惯性参考单元系统位置控制面临的基座扰动、传感器噪声等问题,提出基于频段估计的变增益PI控制方法。设计改进扰动观测器,降低中低频传感噪声对控制精度的影响,设计频段估计器实现外部扰动频段的细分,据此动态调节控制器增益。仿真和实验结果表明,基于VGPI-IDOB控制算法能够有效提高系统的位置控制精度,无输入条件下,系统的静态输出均方根较PI控制降低了67.3%;15 Hz, 1 mrad正弦输入,20 Hz, 0.097 mrad扰动作用下,VGPI-IDOB的位置控制精度相较PI控制提升了72%。     

基于前馈解耦的振动与加载电液混合试验系统力加载跟踪控制研究

针对振动与加载电液混合试验系统力加载跟踪过程中的多余力抑制问题,分析了振动与加载电液混合系统的组成及工作原理,建立了混合系统的动力学模型,并对动力学模型的准确性进行了验证。在此基础上,分析了混合系统加载多余力的产生机理,提出了振动与加载电液混合系统力加载前馈解耦控制算法。搭建了振动与加载电液混合试验台及嵌入式控制系统,利用振动与加载电液混合试验台进行了力加载控制策略的试验研究。结果证明,与传统PI控制器相比,提出的力加载前馈解耦控制算法可以更有效地抑制系统多余力,提高力加载的跟踪精度。     

Computational parametric analysis and experimental investigations of a compact flexure-based microgripper

This paper presents a flexure-based piezoelectric actuated microgripper for high precision grasping/releasing tasks. The design of the microgripper consists of a three-stage amplification and transmission mechanism, and the parallel grasping technique. A bridge-type mechanism and two sequential lever-type mechanisms are symmetrically connected to amplify the output displacement of the embedded piezoelectric actuator. The parallelogram mechanisms assist in linearizing the output displacement of both jaws of the microgripper. The computational analysis is conducted to investigate the effect of the dimensional parameters on the characteristics of the microgripper. A computational parametric optimization methodology is established to achieve the required attributes of the microgripper. The design optimization resulted in a compact design, a high displacement amplification ratio, and a large output displacement of the microgripper. The experimental studies are conducted to investigate the key characteristics of the microgripper such as the displacement amplification ratio, the output displacement, tracking performance. Further, the parasitic motion, input-end and output-end motion resolution of the microgripper are identified. The experimental results indicate that the compact microgripper can achieve a high displacement amplification ratio and large output displacement with a high positioning accuracy.     

基因测序仪运动平台的高精度定位控制

为了实现对基因测序仪运动平台的高精度定位控制,建立了基因测序仪运动平台控制系统。对该系统所采用的数学建模、模型辨识、控制器设计、输入整形等方法进行研究。根据运动平台动力学方程和永磁同步直线电机电压-推力关系构建了运动平台数学模型,利用频域扫描法在实物实验的基础上辨识出运动平台的模型参数。最后,基于运动平台模型设计了双闭环控制器和前馈控制器组成的复合控制器来保证运动平台的稳定性和高精度,同时根据整个系统的主导极点设计了输入整形器以抑制运动平台的残余振荡。实验结果表明:加入了输入整形的复合控制器将运动平台的稳态重复定位精度从±1.47μm提高到±0.354μm。较传统复合控制器,本文提出的方法能使基因测序仪运动平台更快进入可用重复定位精度范围,并基本满足基因测序仪采集图像时所需的稳定性强、精度高等要求。     

液压驱动单元位置控制系统前馈补偿控制研究

液压驱动型足式机器人在运动过程中各关节液压驱动单元（Hydraulic drive unit,HDU）多采用基于液压控制内环的外环阻抗控制方法,其中液压控制内环可分为位置闭环控制和力闭环控制。当液压控制内环采用位置闭环控制时,其位置控制性能直接决定了外环阻抗控制性能,所以,一种针对HDU的高精度的位置控制方法具有重要研究意义。针对以上研究意义,首先对HDU位置控制系统6阶数学模型进行简化,求出位置控制系统中各部分传递函数。其次,推导位置控制输入前馈补偿控制器,该控制器中含有液压系统固有非线性和负载特性。最后,在HDU性能测试试验平台上,在多种典型输入信号以及对角小跑输入信号下,对系统的位置控制性能进行试验研究并给出定量分析。试验结果表明,在不同输入信号下,加入所提出的输入前馈补偿控制器可以大幅提高系统位置控制性能,并且该控制器具有良好的多工况适应性。以上研究成果可结合相应的针对位置控制系统的抗干扰控制策略,一起为基于位置的阻抗控制液压内环控制提供控制策略重要参考和试验基础。     

A study on tracking error based on mechatronics model of a 5-DOF hybrid spray-painting robot

Industrial robots suffer from difficulties in predicting and guaranteeing tracking performance due to the complex dynamic behavior and inaccurate mechatronics model. This study investigates the tracking error and motion accuracy improvement based on a mechatronics model of a 5-degree of freedom hybrid spray-painting robot. The dynamic model of the robot is derived by using Lagrange equation, and an identification method is presented to identify the torque coefficient and joint friction synchronously. An accurate mechatronics model is established after the theoretical dynamic modeling and friction identification. The tracking error generation mechanism of the robot control system is studied, and its analytical equation is derived on the basis of a transfer function. A multichannel feedforward controller is synthesized to reduce the tracking error from different sources. The effectiveness of the proposed method in improving tracking accuracy is verified by physical experiments.

     

Development of a microgripping system for handling of microcomponents

This paper reports the development of a semi-automatic microgripping system that consists of a microgripper and an x, y, z positioning system. The microgripper has two 1DOF fingers fabricated by an amorphous, soft magnetic material and is actuated electromagnetically. The microgripper is embedded in the 3DOF positioning system with the help of a stainless steel holder under an angle, which is manually adjusted, in respect to the working field. The position of the microgripper is observed optically and by three digital indicators¹ from Mitutoyo, which offer easy reading and continuous position tracking. All axes are actuated by step motors which allow precise positioning of the microparticles under manipulation. The microgripping system was tested in pick and place cases, under an optical microscope in atmospheric conditions. Optical fibres (125 μm in diameter) and bonding wires (50 μm in diameter) were handled. The temperature on the actuator, on the microgripper fingers and on the microgripper tips during manipulation was measured using K type (Ni/CrNi) thermocouples. The gripping force was evaluated as well.     

Pneumatic actuating device with nanopositioning ability utilizing PZT impact force coupled with differential pressure

This paper reports a new actuating method using piezoelectric (PZT) impact force coupled with differential pressure for the pneumatic positioning device. Fundamental experiments show that the sliding table can be actuated to move with precise step motions in both the forward and backward directions based on the proposed method. A two degree-of-freedom (DOF) analytic model is established and verified for expressing the impact actuation. Furthermore, a pulse width, which is equal to the period of second-mode vibration of the actuating device, is experimentally examined for the actuation of PZT actuator. Finally, position control based on a hybrid controller is implemented. The experimental result shows that the sliding table is successfully positioned from the reference origin to the target position of 4 mm in 0.924 s with the positioning accuracy of 5 μm due to the actuation of the pneumatic cylinder, and that the final positioning accuracy of 10 nm is obtained by the actuation of PZT impact force coupled with differential pressure. The total control time is 2.683 s. It is shown that the proposed method is capable of significantly improving the positioning performance of the pneumatic actuating device. It is expected that the proposed method will be widely applied in the precision industry using pneumatic cylinders.     

电液马达伺服系统积分鲁棒自适应高精度位置控制

电液马达伺服系统中存在各种类型的扰动,包括参数不确定性和不确定非线性,制约着其高精度位置控制。针对电液马达伺服系统高精度位置跟踪控制,考虑系统的黏性摩擦特性以及外干扰等建模不确定性,提出了一种基于鲁棒自适应的电液马达伺服系统高精度位置控制策略。所提出的全状态控制器通过自适应对模型不确定性进行估计及前馈补偿,提高了系统的低速伺服性能;通过自适应对未建模干扰等不确定性的上界进行估计并前馈补偿,提高了系统对外干扰的鲁棒性。所设计的闭环控制器还能保证系统获得渐近跟踪性能,对比仿真验证了其可行性。     

Controller design for high-frequency cutting using a piezo-driven microstage

Controller design consists of a feedforward and a feedback controller to support a microstage with flexure hinge structure driven by piezoelectric ceramic actuator for high-frequency nanoscale cutting is developed in this article. The feedforward controller is designed based on a hysteresis dynamic model in order to reduce the nonlinear hysteresis effect of piezoelectric actuator. The position feedback controller is designed based upon an exponentially weighted moving average (EWMA) method embedded in an internal model control (IMC) structure constructing a run-to-run IMC (RtR-IMC) control scheme in order to deal with system bias or modeling inaccuracy. Also, disturbance due to temperature rise will influence actuator's performance, hence an additional compensator is included in the IMC structure. Surfaces dimple micro-machining utilizes piezoelectric-driven microstage for high-speed cutting is selected as an example to investigate system performance. The developed control algorithm is implemented on a DSP-based system to provide 1 kHz operating speed. In experiment, the proposed feedforward and feedback controller is verified to be able to overcome those negative factors efficiently and preserve good positioning accuracy.     

Research on the control systems of a precision linear motor drive device

The model of a precision linear motor drive device (PLMDD) and its control requirements are analyzed. In order to enhance the tracking and anti-disturbance performance of the system, its third-order model is established, and disturbance-observer based input revising feedforward error compensation robust control algorithm, combined with integral-separated proportional integral derivative (PID) control algorithm is proposed. This includes feedback control algorithm and feedforward control algorithm. The feedback controller improves system tracking performance and suppresses load and mechanical disturbance while the feedforward controller compensates phase hysteresis introduced by feedback control. Theoretical analyses, simulations and experiments show that this control method increases the tracking precision of PLMDD from ±5 μm to ±2 μm and dramatically improves its anti-disturbance ability.     

基于LuGre模型的自适应摩擦补偿

为提高开放式伺服系统的动态性能,使其具有良好的适应能力,提出一种基于LuGre模型的自适应摩擦补偿方法.建立开放式伺服系统的动力学模型,并通过LuGre模型来描述系统的摩擦特性.考虑到摩擦模型的参数会随系统变化而发生改变,采用Backstepping方法设计自适应摩擦补偿控制器,并采用Lyapunov定理证明系统的全局渐进稳定性.通过可编程多轴控制器(Programmable multi-axis controller,PMAC)编写伺服算法实现该自适应摩擦补偿方案,并通过试验验证该方案的有效性.试验结果表明:与传统的速度加速前馈补偿相比,该自适应摩擦补偿方案在正弦运动作为输入信号时,其跟踪误差由±40 μn降低到±7 μm.采用该补偿方案能有效地抑制摩擦干扰对伺服系统的不利影响,为提高伺服系统的动态跟踪性能奠定基础.     

考虑安装基座影响的光电平台等价捷联惯性稳定控制

采用陀螺仪直接测量光电平台内部载荷的惯性角速度构建反馈,可以在运动载体上控制视轴惯性角速度,实现稳定成像。陀螺捷联惯性稳定控制能够构建前馈,有效提高系统带宽、减小控制误差,但对陀螺安装位置有要求。本文提出了在陀螺直接反馈的机械安装条件下等价捷联稳定的控制方法,并考虑平台基座约束条件建立了动力学模型。该模型显露了光电平台基座安装刚度引入的谐振问题。针对被控对象中的一对谐振和反谐振环节,基于稳定的零极点对消设计滤波器消除谐振。综合利用陀螺直接测量的框架惯性角速度和编码器测量的机械框架相对转角构建等价捷联惯性稳定回路。在等价捷联惯性稳定回路中,采用内回路干扰抑制结合基于逆模型前馈的复合控制方法,有效拓展控制带宽,提高对指令的跟踪精度和对载体姿态晃动的隔离性能。仿真和实验结果表明:该方法有效抑制了安装基座弹性约束力矩的谐振,且与陀螺直接反馈控制相比性能更优。对幅值为1(°)/s、频率为1 Hz的典型正弦角速度指令进行跟踪,均方根误差由1.75(°)/s减小到0.23(°)/s,在1 Hz处扰动隔离度由18%减小到2%。     

A novel driving principle by means of the parasitic motion of the microgripper and its preliminary application in the design of the linear actuator

This paper presents a novel driving principle by means of the parasitic motion of the microgripper. Actuators based on this principle can realize the large displacement range and high speed easily. Also the structure can be simple. A parasitic motion principle linear actuator mainly consisting of two piezoelectric stacks, two microgrippers and a mover was designed. Experimental results indicate that at a low driving frequency of 5 Hz, large velocity over 40 μm/s is obtained with the driving voltage of 100 V. Backward motion was observed and analyzed. Experimental results verify the feasibility of the new principle and it can be used to design new linear or rotary actuators.     

轴向柱塞泵壳体降噪区域识别

为了精确识别轴向柱塞泵壳体降噪区域,首先,搭建液压-多体动力学耦合模型,求解结构噪声激振力;然后,分析零部件模态并试验验证,建立装配体有限元模型,开展基于模态的振动响应分析,通过振动实验验证模型准确性,搭建轴向柱塞泵声学边界元模型,分析其辐射噪声特性;最后,基于声学传递向量原理,开展模态及板面声学贡献量分析,对壳体噪声辐射板面进行合理划分,分析其对关键频率下辐射噪声的贡献量。研究表明:轴向柱塞泵振声模型具有良好的准确性;某板面在辐射噪声突出的1350 Hz频率下,其声学贡献量达到46.1%。精确识别了轴向柱塞泵壳体降噪区域,为其降噪优化设计提供有效指导。     

New method to improve dynamic stiffness of electro-hydraulic servo systems

Most current researches working on improving stiffness focus on the application of control theories.But controller in closed-loop hydraulic control system takes effect only after the controlled position is deviated,so the control action is lagged.Thus dynamic performance against force disturbance and dynamic load stiffness can’t be improved evidently by advanced control algorithms.In this paper,the elementary principle of maintaining piston position unchanged under sudden external force load change by charging additional oil is analyzed.On this basis,the conception of raising dynamic stiffness of electro hydraulic position servo system by flow feedforward compensation is put forward.And a scheme using double servo valves to realize flow feedforward compensation is presented,in which another fast response servo valve is added to the regular electro hydraulic servo system and specially utilized to compensate the compressed oil volume caused by load impact in time.The two valves are arranged in parallel to control the cylinder jointly.Furthermore,the model of flow compensation is derived,by which the product of the amplitude and width of the valve’s pulse command signal can be calculated.And determination rules of the amplitude and width of pulse signal are concluded by analysis and simulations.Using the proposed scheme,simulations and experiments at different positions with different force changes are conducted.The simulation and experimental results show that the system dynamic performance against load force impact is largely improved with decreased maximal dynamic position deviation and shortened settling time.That is,system dynamic load stiffness is evidently raised.This paper proposes a new method which can effectively improve the dynamic stiffness of electro-hydraulic servo systems.     

Ultra-precise tracking control of piezoelectric actuators via a fuzzy hysteresis model

In this paper, a novel Takagi-Sugeno (T-S) fuzzy system based model is proposed for hysteresis in piezoelectric actuators. The antecedent and consequent structures of the fuzzy hysteresis model (FHM) can be, respectively, identified on-line through uniform partition approach and recursive least squares (RLS) algorithm. With respect to controller design, the inverse of FHM is used to develop a feedforward controller to cancel out the hysteresis effect. Then a hybrid controller is designed for high-performance tracking. It combines the feedforward controller with a proportional integral differential (PID) controller favourable for stabilization and disturbance compensation. To achieve nanometer-scale tracking precision, the enhanced adaptive hybrid controller is further developed. It uses real-time input and output data to update FHM, thus changing the feedforward controller to suit the on-site hysteresis character of the piezoelectric actuator. Finally, as to 3 cases of 50 Hz sinusoidal, multiple frequency sinusoidal and 50 Hz triangular trajectories tracking, experimental results demonstrate the efficiency of the proposed controllers. Especially, being only 0.35% of the maximum desired displacement, the maximum error of 50 Hz sinusoidal tracking is greatly reduced to 5.8 nm, which clearly shows the ultra-precise nanometer-scale tracking performance of the developed adaptive hybrid controller.     

Inertial parameter estimation for the dynamic simulation of a hydraulic excavator

This paper presents a systematic method for estimating the inertial parameters of an excavator. The method utilizes dynamic excavator models with the pressure and displacement measurements of the hydraulic actuators. Provided that the geometrical parameters of the mechanical linkages are obtained with relatively high accuracy, the dynamic model is factored into the unknown inertial parameter vector and the known kinematic matrix. The contribution of each inertial parameter on the actuator force under the specific motion is explored through a dynamic sensitivity analysis. The results are then used to investigate various properties of the inertial parameters and categorize them into identifiable, unrelated to dynamics, and known parameter groups, according to numerical properties of the kinematic matrix. Then the identifiable inertial parameters are estimated sequentially, and the guideline for the optimal excavator position at each estimation step is suggested in order to minimize estimation error. The practicality of this method is demonstrated via data acquired using an actual hydraulic excavator.