HOSIDF-based feedforward friction compensation in low-velocity motion control systems

The paper describes an application of a recently introduced methodology for modeling of a class of nonlinear systems — Higher-Order Sinusoidal Input Describing Function technique (HOSIDF) — to a motion control platform for which a precisely controlled motion at low velocity is required. One of the key challenges for these systems is to compensate for the friction, which is particularly difficult to model at low velocities. The frequency-domain HOSIDF modeling framework is used to assist in designing a feedforward compensator. Experiments with a laboratory benchmark system (gimballed camera platform) prove the technique useful.     

Nonlinear identification and optimal feedforward friction compensation for a motion platform

In this study, we present a method of nonlinear identification and optimal feedforward friction compensation for an industrial single degree of freedom motion platform. The platform has precise reference tracking requirements while suffering from nonlinear dynamic effects, such as friction and backlash in the driveline. To eliminate nonlinear dynamic effects and achieve precise reference tracking, we first identified the nonlinear dynamics of the platform using Higher Order Sinusoidal Input Describing Function (HOSIDF) based system identification. Next, we present optimal feedforward compensation design to improve reference tracking performance. We modeled the friction using the Stribeck model and identified its parameters through a procedure including a special reference signal and the Nelder–Mead algorithm. Our results show that the RMS trajectory tracking error decreased from 0.0431 deg/s to 0.0117 deg/s when the proposed nonlinear identification and friction compensation method is utilized.     

Increasing stroke and output force of linear shape memory actuators by elastic compensation

Shape memory actuators are a class of very interesting actuators due to the high power to weight ratio, plus the fact that they can work in harsh environments and can be easily constructed. The main defects of this technology are the short strokes and the non-uniformity of the useful force over the stroke. This paper aims to limit these two problems by introducing a passive system of elastic compensation. We first develop a functional design procedure of the active elements and of the compensation system in order to obtain the force and stroke desired. We also show two compensation mechanisms that are able to execute the laws required, and we provide expressions for the kinematic design. A numerical example for an actuator with a single shape memory element shows that, all other conditions being equal, the elastic compensation produces increases in stroke (for equal useful force) or useful force (for the same stroke) that are more than 2.5 times greater. A proof-of-concept actuator including a rocker-arm compensating mechanism is also built and tested to confirm the theoretical predictions.     

Parameter identification and hysteresis compensation of embedded piezoelectric stack actuators

A novel method for the identification of embedded piezoelectric stack actuator parameters in combination with a real-time capable hysteresis compensation measure is presented. The presented algorithms are based on the Maxwell resistive capacitor model and are particularly useful for the identification of piezoelectric actuators embedded in a high-precision micropositioning system where the disassembly of the complete system for separate actuator identification is not recommended or not possible. The parameter identification can be performed in a fully automated way and enables the adaptation of the compensation routine to the changed circumstances (temperature difference, wearing of actuators) as well. The hysteresis compensation method proposed here does not require significant CPU or memory resources. It can be implemented as an additional task on the already existing controller or a low-budget FPGA. As an example, the proposed method was validated experimentally by the parameter identification and hysteresis compensation of the piezoelectric actuators incorporated in a commercially available hybrid micropositioning system. The achieved experimental results are in very good agreement with the theoretical ones.     

Optimal two-vector combination-based model predictive current control with compensation for PMSM drives

The duty-ratio-based model predictive control (D-MPC) is rapidly researched for permanent-magnet synchronous machine (PMSM) drives. Existing D-MPC methods produce large current ripple and distortion. To solve this issue and promote the system performance, an optimal two-vector combination MPC (OTC-MPC) is proposed for current control in this paper. The collection of the combination is firstly produced for the proposed OTC-MPC by combining the two vectors and corresponding duty-ratio, and then the optimal combination is selected among all feasible two-vector combinations, thus, the output vectors and duty-ratio are simultaneously optimised. The optimising process is simplified so that the proposed OTC-MPC can be easily implemented. Moreover, a simplified repetitive control with feed-forward compensation method is added to eliminate the predictive current errors of MPC, and also to improve the system robustness against external disturbances. Theoretical analysis, simulation and experimental results demonstrate that the proposed OTC-MPC effectively reduces current ripple and distortion while retaining fast dynamic response compared with the conventional D-MPC.     

基于预测控制的自适应PID控制器设计与仿真

从数学上建立了预测控制与PID控制的广义联系,并结合某火电厂300MW锅炉机组,针对烟气氧含量控制回路,在不改变原有控制系统框架的基础上,采用基于GPC的PID控制方法,很好地解决了在锅炉负荷和氧含量设定值同时变化的情况下系统的动态响应不理想的问题。通过MATLAB仿真,验证了该控制系统具有较好的控制品质,适合具有一定延迟的复杂控制系统。     

基于速度估计的成像器稳定装置摩擦补偿

针对成像器稳定装置中由于摩擦力距造成的跟踪误差这一问题,采用自适应滑模控制的方法对摩擦力矩进行有效补偿,并且提出了基于改进欧拉近似法从位置测量信号中获取速度信号的方法。通过在成像器稳定装置控制系统中的实际应用,表明提出的方法有效地减小了成像器稳定装置的跟踪误差,算法简单、易于实现。     

数字PID控制在运动控制系统中的应用

在半导体设备运动过程中,有效的调节数字PID控制参数可以提高设备运动的稳定性和可靠性,利用积分分离的算法来实现具有最佳组合的PID控制。     

Coordinated motion control and event-based obstacle-crossing for four wheel-leg independent motor-driven robotic system

This work investigates the coordinated motion control and obstacle-crossing problem for a four wheel-leg independent motor-driven robotic system via a model predictive control (MPC) approach based on an event-triggering mechanism. The modeling of a wheel-leg robotic control system with a dynamic supporting polygon is organized. The system dynamic model is 3 degrees of freedom ignoring the pitch, roll, and vertical motions. The single wheel dynamic is analyzed considering the characteristics of the motor-driven and the Burckhardt nonlinear tire model. As a result, an over-actuated predictive model is proposed with the motor torques as inputs and the system states as outputs. As the supporting polygon is only adjusted at certain conditions, an event-based triggering mechanism is designed to save hardware resources and energy. The MPC controller is evaluated on a virtual prototype as well as a physical prototype. The simulation results guide the parameter tuning for the controller implementation in the physical prototype. The experimental results on these two prototypes verify the efficiency of the proposed approach.     

Control of a 2-DOF ultrasonic piezomotor stage for grommet insertion

The treatment of a common disease called “Otitis Media with Effusion (OME)” involves the surgeon inserting a grommet in the eardrum to bypass the Eustachian tube for draining fluid when medication fails. In this paper, a novel device for myringotomy and grommet insertion is first designed and introduced. Due to the advantages of high precision and fast response, a 2-DOF ultrasonic piezomotor (USM) stage is chosen to provide the motion sequences of the device, especially a precise path tracking during the grommet insertion. This paper briefly presents the mechanical design of the device and the configuration and control of the 2-DOF USM stage. The model of the USM consisting of a linear and nonlinear term is built. A PID controller is used as the main controller and tuned with the help of LQR technique. Since there are nonlinear dynamics caused by friction and hysteresis existing in the system, a nonlinear compensation including a sign function and sliding mode control is designed to reject the nonlinearity. Moreover, a decoupling controller is designed to eliminate the coupling effects between the two USM stages. The experimental results show that the LQR-assisted PID controller with compensation can achieve very good system performance and the decoupling controller can further improve the performance.     

星载光机扫描仪像移模型及补偿方法

针对地球自转运动形成的星载光机扫描式成像仪的图像畸变问题,详细描述了畸变量与地球纬度及仪器工作参数之间的关系,给出了太阳同步轨道扫描成像仪的畸变量计算公式。针对传统地面畸变校正算法的不足,提出了基于光学补偿扫描和星上软件补偿采样的两种像移补偿方法。详细分析两种方法的特点与可行性,并给出仿真结果。该研究工作对于提高星载光机扫描式成像系统的图像质量具有参考意义。     

Spatiotemporal texture synthesis and region-based motion compensation for video compression

In this paper, a content-based approach for video compression is proposed. The main novelty relies on the complete texture analysis/synthesis framework, which enables the use of multiple algorithms, depending on texture characteristics. The idea comes from the efficient MPEG prediction based on a best mode selection. Existing synthesis algorithms cannot be efficient in synthesizing every kind of texture but a certain range of them.This approach is designed to be jointly used with current and future standard compression schemes. At encoder side, texture analysis includes segmentation and characterization tools, in order to localize candidate regions for synthesis: motion compensation or texture synthesis. The corresponding areas are not encoded. The decoder fills them using texture synthesis. The remaining regions in images are classically encoded. They can potentially serve as input for texture synthesis. The chosen tools are developed and adapted in order to ensure the coherency of the whole scheme. Thus, a texture characterization step provides required parameters to the texture synthesizer. Two texture synthesizers, including a pixel-based and a patch-based approach, are used on different types of texture, complementing each other.The scheme is coupled with a motion estimator in order to segment coherent regions and to interpolate rigid motions using an affine model. Inter frame adapted synthesis is therefore used for non-rigid texture regions.The framework has been validated within an H.264/MPEG4-AVC video codec. Experimental results show significant bit-rate saving at similar visual quality levels, assessed using subjective tests. The method can be coupled with the future HEVC in which blocks can be skipped by the encoder to be synthesized at decoder side.     

基于惯导系统的机载SAR运动补偿精度分析

该文分析了典型飞机惯性导航系统(INS)的误差特性及其对机载合成孔径雷达(SAR)运动补偿精度和高分辨率成像的影响。分析结果表明INS定位漂移误差是低频误差,并随时间呈级数增加。初始阶段INS漂移误差较小,与杂波锁定和自聚焦方法相结合,可以实现机载SAR高分辨率成像。     

MPEG-4运动补偿的VLSI结构设计

针对MPEG．4解码中运动补偿控制复杂、数据吞吐量大、实现较困难，提出了一种适合MPEG-4的运动补偿硬件实现方案，解决了时序分配、输入输出控制等较难处理的问题。此方案已经在Xilinx ISE6．li集成开发环境下，采用了VHDL进行描述，并使用了电子设计自动化（EDA）工具进行了模拟和验证。仿真和综合结果表明，设计的运动补偿处理器逻辑功能完全正确，而且可以满足MPEG-4 Core Profiles ＆ Level 2的实时编码要求，可用于MPEG-4的VLSI实现。     

双面光刻机运动控制系统设计分析

针对双面光刻机运动控制需求,提出模块化的设计方案,重点分析了对准工作台PID 调节方法,实现了高动态响应、高精度运动控制。     

一种改进的步进频率雷达信号的运动补偿研究

为解决步进频率雷达一维距离像失真和运动补偿的问题,提出了一种精确的速度估计方法。文中首先阐述了步进频率信号的改进原理及其处理方法,该方法先使用互相关FFT测速法对目标速度进行粗估计,然后再以最大脉组乘积求和为准则搜索精确速度,最后实现对运动目标的速度补偿从而得到精确的一维距离像。仿真结果表明,在信噪比为-4dB的时候仍能得到准确的结果,改进后的信号性能有了很明显的改善,一维距离像不会随目标的运动而产生失真,该运动补偿方法具有估计精度高、抗噪性能好的优点。     

多标准视频解码器运动补偿存储架构设计

设计了一种适用于多标准视频解码器的存储架构,采用并行多级流水线用以实现AVS,MPEG-2,H.264标准中不同模式的图像预测计算,缓存机制避免了频繁访问外部存储器SDRAM,提高了运动补偿计算性能,减少了计算周期。使用90 nm的CMOS工艺库,在135 MHz的工作频率下综合,电路规模为45 kgate(千门)左右,处理一宏块需要大约520个时钟周期,结果表明该设计满足高清视频处理的要求。     

Friction modeling,identification, and compensation based on friction hysteresis and Dahl resonance

This paper studies effects of friction on control systems and utilizes the observed frictional behavior to develop a parameter identification method for a friction model using frequency domain measurements. Friction exists in a wide range of drive systems due to physical contacts in bearing elements, transmissions, or motion guides. Friction in a control system can deteriorate performance by causing limit cycles or stick–slip, as well as larger tracking errors. Friction compensation can help to reduce following errors, but requires physical understanding and a reliable model of friction in both the gross- and the pre-sliding regimes. In this paper, we adopt the Generalized Maxwell-Slip (GMS) model and develop a frequency-domain method to identify the model parameters based on the frictional resonances, which occur due to the elastic behavior of friction at small amplitudes. With the experimentally identified parameters, the friction model is utilized to compensate the friction effects in a motion control system. The resulting system performance of a compensated and uncompensated control system is then compared in both the frequency and time domains to demonstrate the Dahl resonance identification method for a GMS model.