Impact of features of control systems of the tunneling microscope on the measurement accuracy

A significant number of measurement errors of the surface nanotopography by a tunneling microscope is caused by features of the probe motion control. If the geometry of the needle tip is taken into account in the interpretation of measurements, it is possible to significantly reduce the influence of these errors. It is shown that the shape and size of the tip can be determined from the mathematical model of the scanning process using existing measurements of the nanotopography.     

Steady-state behavior in the vibrational control of a class ofnonlinear systems by AP-forcing

Vibrational control is an open-loop control technique that uses zero mean parametric vibrations for shaping the response of a linear or nonlinear dynamical system. Several theoretical results are available, based on averaging techniques, assuring the possibility of modifying the equilibrium properties of a system. For nonlinear systems, computational difficulties arise and theoretical results cannot easily be applied. In this note, the stationary behavior of a class of nonlinear systems vibrationally controlled by AP-forcing is investigated. A practical formula linking the amplitude and the frequency of the vibration and the amplitude of the steady-state oscillation in the controlled variable is obtained. As test cases, the well-known Rayleigh equation, a catalytic reactor equation, and the phase locked loop equation are considered     

Dynamic boundary control of a Euler-Bernoulli beam

A flexible beam, clamped to a rigid base at one end and free at the other end is considered. To stabilize the beam vibrations, a dynamic boundary force control and a dynamic boundary torque control applied at the free end of the beam are proposed. It is proved that with the proposed controls, the beam vibrations decay exponentially. The proof uses a Lyapunov functional, based on the energy functional of the system     

受振动影响的手部操作仿真与操作精度研究

在手及手臂参与控制的操作中,由操作端传递给手及手臂的振动会对操作精度产 生影响。利用计算机程序仿真了一种在虚拟空间中的直线路径追踪操作,以可编程的力觉交互 设备Phantom 作为操作端,研究低频率段不同参数的振动对用户操作精度的影响。振动频率对 操作误差的影响呈非线性,显著的影响出现在2 Hz 附近。振动幅值对操作误差的影响近似线性, 振动方向对操作误差也有一定影响。     

高精度磁场式时栅传感器激励信号对测量误差的影响分析及系统设计

为提高磁场式时栅传感器测量精度,本文从理论上推导分析了时栅传感器激励信号源幅值和相位不一致产生的谐波成分对时栅传感器测量精度的影响,提出了一种基于DDS原理并采用完整闭环调节的高性能时栅激励信号源设计方案。以FPGA为微处理器,通过编程分频系统时钟,设置频率、相位控制字对DDS输出的信号频率、相位进行调节,使用增益控制器配合相位累加器实现相位到幅值精确转换。搭建了信号调理电路和信号反馈电路,通过实时对比反馈控制,解决了系统电路阻抗不匹配及干扰导致的激励信号相位不正交性和幅值不一致性的问题。实验结果表明：本文所设计的激励信号源输出信号幅值相对误差只有0.4%,正交性相对误差只有0.05%,并且采用该激励信号源,磁场式时栅传感器测角原始误差从±103.4"降低到了±20.3",有效抑制由于激励信号源幅值不一致和相位不正交带来的谐波误差。经修正后对极内角位移测量误差只有±1.3",整周角位移测量精度达到±2",满足高精度位移测量要求。     

Decentralized stabilization of Markovian jump interconnected systems with unknown interconnections and measurement errors

This paper investigates the decentralized output feedback control problem for Markovian jump interconnected systems with unknown interconnections and measurement errors. Different from some existing results, the global operation modes of all subsystems are not required to be completely accessible for the decentralized control system. A decentralized dynamic output feedback controller is constructed using neighboring mode information and local outputs, where the measurement errors between actual and measured outputs are considered. Subsequently, a new design method is developed such that the resultant closed‐loop system is stochastically stable and satisfying an L_∞‐norm constraint. Sufficient conditions are formulated by linear matrix inequalities, and the controller gains are characterized in terms of the solution of a convex optimization problem. Finally, an example is given to illustrate the effectiveness of the proposed theoretical results.     

Digital signal processing and test rig testing results

Digital processing method of the vibrating system rotation angle in the measuring test rig is considered; it allows evaluating the eigenfrequency, amplitude and phase of the signal. The measurement results of the mass, center of gravity coordinates and inertia moments of the reference objects are provided. The measurement errors are determined.     

小正弦振动幅度的测量与实验

基于迈克耳逊干涉原理 ,设计了一种测量装置 ,采用连续间隔幅度的测量算法 ,对小正弦振动幅度进行了测量。这个理论在研究石英晶体振动中得到证实。利用这种方法 ,参照高准确度的模型 ,可测量纳米级的振动幅度     

Active optimal vibration control for a lumped system

A dynamic absorber with active torque generating DC motors has been studied as an actively suppressing vibration system. A typical two-level spring-lumped mass system with slider undergoing internal excitation vibrations has been considered. Both the main mass and the secondary absorber mass have DC servo motors planned to suppress the amplitude of vibration. State variable techniques are used to formulate the complete system and three optimal control schemes are used to control such a system. First, the discrete time optimal disturbance rejection control for a system with known disturbance is considered, in the second approach a digital optimal control for a linear quadratic regulator problem is studied and in the last approach a discrete optimal control with selected system characteristic matrix is investigated. The response of the system obtained from these optimal control approaches are compared with the response without control action first. The performance of these optimal control approaches are also compared and the availability of implementations of them are evaluated.     

Modelling and motion control of a mechatronic system using BGM with intelligent controllers

In this research paper, a mechatronics system such as a pan tilt platform (PTP) has been considered for motion control under intelligent controllers. A proportional-derivative (PD) controller is considered for comparison of results obtained from fuzzy and hybrid controllers. The trajectory following performance of the mechatronics system is found against these controllers. The results of simulations show that hybrid fuzzy controller reduce the tracking error effectively in lesser settling time. The intelligent controllers require knowledge base of error and derivative of error to compensate the PTP dynamics. The intelligent controllers have similar trends as the PD controllers and compensated both electrical and mechanical dynamics. The PD controller requires position measurement. The intelligent controllers have knowledge base consisting of position and velocity data. Thus intelligent controllers have position measurement along with knowledge base for position control system. The best results were achieved with hybrid fuzzy controllers. They meet the desired specifications.     

Issues in closed-loop needle steering

Percutaneous needle insertion is amongst the most prevalent clinical procedures. The effectiveness of needle-base interventions heavily relies on needle targeting accuracy. However, the needle interacts with the surrounding tissue during insertion and deflects away from its intended trajectory. To overcome this problem, a significant research effort has been made towards developing robotic systems to automatically steer bevel-tipped needles percutaneously, which is a comprehensive and challenging control problem. A flexible needle inserted in soft tissue is an under-actuated system with nonholonomic constraints. Closed-loop feedback control of needle in tissue is challenging due to measurement errors, unmodelled dynamics created by tissue heterogeneity, and motion of targets within the tissue. In this paper, we review recent progress made in each of the complementary components that constitute a closed-loop needle steering system, including modelling needle-tissue interaction, sensing needle deflection, controlling needle trajectory, and hardware implementation.     

Development of a new frequency weighting filter for the assessment of grinder exposure to wrist-transmitted vibration

The risk assessment of hand tool workers exposed to hand-arm vibrations is still problematic. It is based, accordingly to ISO 5349, on a frequency-weighted measurement recorded at the handle of the tool. Unfortunately, the frequency-weighted filter recommended by ISO 5349 does not take into account any amplification of the hand-arm system and underestimates the global rms acceleration transmitted to the hand. In this study, the vibration transmitted from the tool handle to the worker's wrist is investigated in an industrial environment for seven commercial grinders, two subjects and three push forces. The results are compared with the ISO-5349 and ACGIH threshold limit values, and a new frequency weighting filter is proposed, by which the amplification close to the natural frequencies of the hand-arm system can be considered in the evaluation of the vibration transmitted to the wrist from vibration measurements at the tool handle in a grinding operation.     

Reducing flexible base vibrations through local redundancy resolution

Future space systems will use teleoperated robotic systems mounted on flexible bases such as the Shuttle Remote Manipulator System. Due to dynamic coupling, a major control issue associated with these systems is the effect of flexible base vibrations on the performance of the robot. If uncompensated, flexible vibrations can lead to inertial tracking errors and an overall degradation in system performance. One way to overcome this problem is to use kinematically redundant robots. Thus, this article presents research results obtained from locally resolving kinematic redundancies to reduce or damp flexible vibrations. Using a planar, three-link rigid robot example, numerical simulations were performed to evaluate the feasibility of three vibration damping redundancy control algorithms. Results showed that compared to a zero redundancy baseline, the three controllers were able to reduce base vibration by as much as 90% in addition to decreasing the required amount of joint torque. However, similar to locally optimizing joint torques, excessive joint velocities often occurred. To improve stability, fixed weight, multi-criteria optimizations were performed. © 1995 John Wiley & Sons, Inc.     

一种混沌测量系统的设计与分析

为设计一种高灵敏度、高分辨率的测量系统，文中从混沌的原理出发，采用简单混沌信号测量电压信号的数学模型，研究了相应的电路实现方法，设计出了一套混沌测量系统，给出了具体电路、单元电路分析和实验结果。实验结果表明了利用混沌实现信号测量的可行性。     

On the estimation of the linear relation when the error variances are known

The problem of consistent estimation in measurement error models in a linear relation with not necessarily normally distributed measurement errors is considered. Three possible estimators which are constructed as different combinations of the estimators arising from direct and inverse regression are considered. The efficiency properties of these three estimators are derived and the effect of non-normally distributed measurement errors is analyzed. A Monte-Carlo experiment is conducted to study the performance of these estimators in finite samples.     

Design,kinematic modeling and sliding mode control with sliding mode observer of a novel 3-PRR compliant mechanism

Compliant mechanisms have great advantages to be used as micropositioning stages for high-precision applications but they are very sensitive to manufacturing tolerances and assembling errors. In this work, a novel compliant stage having 3-PRR kinematic structure and actuated by piezoelectric actuators is introduced. A kinematic modeling based on compliance of the flexible elements and finite element analysis based model have been extracted. It is found out that the experimental results are not compatible with the theoretical results due to the manufacturing, actuator assembly errors. The position control of the mechanism has been achieved using sliding mode control which is a great method for unpredictable varying parameters in the system. Sliding mode observer has also been used for the hysteresis and nonlinearities of the piezoelectric actuators. Experimental models for each actuation axis have been used as the nominal models for the sliding mode observer. In order to see the advantage of the control method simple PID control has also been implemented. It is seen that sliding mode control with sliding mode observer using experimental models reduces the position tracking errors to the range of the accuracy of our available measurement.     

Consequences of the digitization on the performance of a fuzzylogic controller

The consequences of the finite wordlength on the performance of a digital fuzzy logic controller (FLC) based on Mamdani's inference algorithm are investigated. Digital implementations of FLCs involve three main types of errors due to the finiteness of the wordlength: analog-to-digital errors, membership function errors, and arithmetic errors. First, a statistical evaluation of the consequences of these errors is performed. The effects of the digital resolution on the controller response are discussed. Then, the dynamic behavior of a closed-loop fuzzy system composed of a digitized FLC and a second-order plant is evaluated; a qualitative evaluation of time-domain parameters as a function of the universe discretization is carried out. The results show that, as in the case of conventional control strategies, bias effects and limit cycles are generated as a consequence of the digitization. Although these distortions diminish when the discretization is sufficiently refined, they are very difficult to predict because of the nonlinear nature of both quantization and fuzzy operation. In this sense, the availability of computer-aided design (CAD) tools that permit the specification of the wordlength is essential to validate the design     

Learning control of mobile robots using a multiprocessor system

A real-time multiprocessor system is proposed for the solution of the tracking problem of mobile robots operating in a real context with environmental disturbances and parameter uncertainties. The proposed control scheme utilizes multiple models of the robot for its identification in an adaptive and learning control framework. Radial Basis Function Networks (RBFNs) are considered for the multiple models in order to exploit the net non-linear approximation capabilities for modeling the kinematic behavior of the vehicle and for reducing unmodeled contributions to tracking errors. The training of the nets and the tests of the achieved control performance have been done in a real experimental setup. The proposed control architecture improves the robot tracking performance achieving fast and accurate control actions in presence of large and time-varying uncertainties in dynamical environments. The experimental results are satisfactory in terms of tracking errors and computational efforts.     

大射电望远镜馈源指向系统轨迹跟踪自抗扰控制

采用独立控制策略实现新一代大射电望远镜馈源指向跟踪系统的高精度轨迹跟踪 .将两组成子系统之间的动力学耦合及其他扰动视为对精调Stewart平台子系统的未知扰动 ,设计了强鲁棒自抗扰控制器实现扰动补偿 .大射电望远镜馈源指向系统 5 0m缩比模型实验 ,验证了独立控制策略和自抗扰控制器的工程有效性和可行性 .为将来建造新一代大射电望远镜工程奠定了坚实的基础