Large travel ultra precision x-y-/spl theta/ motion control of a magnetic-suspension stage

This paper presents an indirect adaptive-control approach and its implementation for realizing large travel ultra precision x-y-theta motion control of a magnetic-suspension stage, which is actuated by ten electromagnets and is capable of six-degrees-of-freedom motion. Feedback linearization of the nonlinear force relationship of the electromagnet in terms of the coil current and the air gap is implemented. Due to modeling errors, perfect feedback linearization is not possible, and parameter variations of the feedback-linearized system are demonstrated through closed-loop system identification. Each axis of the feedback-linearized system is then modeled as a double integrator having gain value depending on the position of the stage and subjected to a disturbance. For the purpose of large travel x-y-theta motion control, an indirect adaptive-control algorithm is designed and implemented for each axis of the feedback-linearized system. The developed control algorithm consists of three procedures: a) real-time parameter estimation; b) model cancellation; and c) nominal linear control. Experimental results demonstrate that the indirect adaptive controllers have superior tracking ability when compared to constant gain robust linear H/sup /spl infin// controllers.     

A Robust Position and Force Control Strategy for 7-DOF Redundant Manipulators

This paper is concerned with robust position and contact force control for 7-DOF redundant robot arms. An outer-inner loop controller, called the augmented hybrid impedance control scheme is developed. A 6-DOF force/torque sensor is used to measure the interaction forces. These are fed back to the outer-loop controller that implements either a force or an impedance controller in each of the 6 DOF of the tool frame. The force controller is provided with a force set point, and desired inertia and damping are introduced in the force control loop to improve transient performance. The inner loop consists of a Cartesian-level potential difference controller, a redundancy resolution scheme at the acceleration level, and a joint-space inverse dynamics controller. Experimental results for two 7-DOF robot arms (redundant, dextrous, isotropically enhanced, seven-turning pair robot (REDIESTRO) and Mitsubishi PA10-7C) are given to illustrate the performance of the force control strategy. A successful application of the proposed scheme to a surface cleaning task is described using the REDIESTRO, while position and force tracking experiments are described for the Mitsubishi PA10-7C robot.     

Development of a totally active magnetically suspended gyro

A magnetically suspended gyro (MSG) is developed and its performances is estimated. In the MSG, a disk-type rotor is connected to a synchronous motor through a fluid bearing and the motor is fixed to the frame of the floator. The floator is suspended by magnetic force without any mechanical contact so that highly accurate measurement is possible. In accordance with this concept, a three-degrees-of-freedom (DOF) active MSG was developed. However, because of poor damping in the passive suspension and the low resolution of the displacement sensors, the measurement accuracy was relatively low. To solve these problems, a six-DOF (totally) active MSG is designed and fabricated. The frame of this gyro is an octagonal. The motion of the frame is controlled by eight electromagnets. The performance of the gyro is evaluated through measurement of the double-axis angular velocity. The advantages of totally active suspension are investigated. Sufficient damping rapidly reduces the influence of disturbances. Then, the influence of sensor noise is examined. The results of this examination show that the accuracy of the angular velocity measurement is improved by using highly sensitive displacement sensors. Next, the dynamic range is measured. This experiment shows that the MSG can provide precise angular velocity measurement in a low-frequency region.     

A low-cost driving simulator for full vehicle dynamics simulation

This paper describes the construction of a low-cost PC-based driving simulator that can perform five degree-of-freedom (DOF) motions similar to a road vehicle. The mathematical equations of vehicle dynamics are first derived from the 2-DOF bicycle model and incorporated with the tire, steering, and suspension subsystems. The equations of motion are then programmed by MATLAB, transferred into C++ code in the MIDEVA environment, and further developed into a motion platform control program by C++Builder. To achieve the simulator functions, a motion platform that is constructed by five hydraulic cylinders is designed, and its kinetics/inverse kinetics analysis is also conducted. Driver operation signals such as steering wheel angle, accelerator pedal, and brake pedal positions are measured to trigger the vehicle dynamics calculation and further actuate the cylinders by the motion platform control program. In addition, a digital PID controller is added to achieve the stable and accurate displacements of the motion platform. The experiments prove that the designed simulator is adequate in performing some special road driving situations discussed in this paper.     

Precision stage using a non-contact planar actuator based on magnetic suspension technology

The precision stage using a novel contact-free planar actuator based on magnetic forces, magnetized force and Lorentz force, is suggested. In the promising magnetic structure, a mover is levitated by magnetized force between iron-core electromagnets attached under the upper-side of a stator and ferromagnetic plates belonging to the mover. And the mover is driven by Lorentz force that acts on permanent magnets with an identical polarity put under magnetic field by air-core coils. Namely, the mover is driven directly without any transmission mechanism, and does not need any auxiliary driver for its posture calibration. Then it is estimated that the proposed operating principle is very suitable for work requiring high accuracy and cleanness, or general-purpose nano-stage. In this paper, we discuss a driving principle of the planar system including the magnetic force generation mechanism, a framework for the force model, governing characteristics of the levitated plate, and a planar motion control of the constructed prototype. And experimental results are given to verify the derived theoretical model and the feasibility of the system.     

Development of micromanipulator and haptic interface for networkedmicromanipulation

Telemicromanipulation systems with haptic feedback, which are connected through a network, are proposed. It is based on scaled bilateral teleoperation systems between different structures. These systems are composed of an original 6 degree of freedom (DOF) parallel link manipulator to carry out micromanipulation and a 6-DOF haptic interface with force feedback. A parallel mechanism is adopted as a slave micromanipulator because of its good features of accuracy and stiffness. The system modeling and control of the parallel manipulator system are conducted. Parallel manipulator feasibility as a micromanipulator, positioning accuracy and device control characteristics are investigated. A haptic master interface is developed for micromanipulation systems. System modeling and a model reference adaptive controller are applied to compensate friction force, which spoils free motion performance and force response isotropy of the haptic interface. These systems aim to make the micromanipulation more productive constructing a better human interface through the microenvironment force and scale expansion     

超精密磁悬浮工作台的一种低功耗磁悬浮设计

超精密磁悬浮工作台的磁悬浮部分的设计，将直接影响到系统的动力学性能、空间结构以及热性能等。针对这些性能上的要求，给出了一种三磁极电磁铁及相应的磁悬浮设计，并结合常规双磁极电磁铁的情况，对性能进行了分析和比较。相比之下，该设计可使静态功耗(或发热量)降低50％，具有更合理的空间结构。只需要两个这样的电磁铁便可以实现工作台的磁悬浮(采用双磁极电磁铁则通常需要四个)。最后通过一个应用实例及实验结果，验证了该设计的正确性和有效性。     

空间光学次镜平台的运动学分析和控制系统设计

为解决空间光学次镜的高精度定位需求设计了一种六自由度并联次镜平台,对并联平台进行运动学分析,并设计了平台的闭环控制系统。根据设计的并联次镜平台结构,搭建了实验硬件系统,编写了软件控制程序,对运动分析结果及控制系统进行实验验证。实验结果表明,所设计的控制系统可以实现六自由度并联次镜平台的运动控制,运动控制精度能够达到0.02mm。     

Robust disturbance rejection for improved dynamic stiffness of a magnetic suspension stage

Magnetic suspension is an attractive approach in realizing ultraprecision multiple-degree-of-freedom actuation for precision engineering. However, improving the dynamic stiffness of magnetic-suspension systems is an engineering challenge due to their noncontact nature. Two disturbance rejection algorithms that improve the dynamic stiffness of a magnetic-suspension stage (MSS) are presented in this paper. For rejection of narrow-band disturbances with unknown frequencies, an internal model principle-based control together with a frequency estimation algorithm based on adaptive-notch filtering is proposed. A chattering-free sliding mode (CFSM) disturbance rejection algorithm is developed in order to reject wide-band disturbances. The CFSM disturbance rejection scheme includes a continuous approximation of the switching function to avoid chattering, an integral control term to reduce the switching magnitude, and a derivative control term to elevate the bandwidth of disturbance rejection. Experimental results verified that the disturbances can be effectively rejected with the two developed algorithms. Consequently, the dynamic stiffness of the MSS is greatly improved.     

A new MAGLEV system for magnetically levitated carrier system

A power-saving electromagnetic suspension system has been developed in which electromagnets with permanent magnets are used to suspend the vehicle. The electromagnets are controlled to maintain air gap length so that the attractive force by the permanent magnet always balances the total weight of the vehicle and its loads, based on modern control theory. This technology realizes a significantly power-saving system in which the electromagnetic coil current required to keep a vehicle levitating was extremely small, ideally zero. The 8-kg weight test vehicle with 4-kg load could be levitated continuously over 8 h, without recharging the on-board 1300-mAh batteries. This technology realized a completely contact-free material transportation system when combined with a contact-free driving system using linear motors. The attractive force characteristics of a permanent magnet with control electromagnets and the newly developed electromagnet control system that can eliminate power collecting devices from the electromagnetic suspension system are described     

MagTable: A tabletop system for 6-DOF large range and completely contactless operation using magnetic levitation

This paper presents a new magnetic levitation system, MagTable, which provides six-degrees-of-freedom (6-DOF) and completely contactless operation of a magnetized object. The MagTable consists of a planar array of square coils and a permanent magnet type carrier. The maximum levitation height of the carrier is 30mm within a 400mm × 200mm horizontal translation range. The novelty of this research lies in the fully untethered manipulation of levitated carriers in such a large area, and in the fast and accurate computation of wrench matrix using the magnetic nodes method and the Lorentz force law. In this paper, the design method is firstly provided. Then, the optimization of the carrier's magnet topology, based on better controllability and minimum power consumption, is documented. Experimental results of the 5-DOF motion control of two single-permanent-magnet carriers and the 6-DOF motion control of a three-permanent-magnets carrier are presented. The results demonstrate the performance of the MagTable in 100mm × 40mm horizontal translation range with maximum levitation height of 20mm. The rotation range are ±6° in both roll and pitch, and ±12° yaw motion about the vertical axis. The proposed system has potential applications in fast and high precision manipulation tasks.     

Implementation of a novel large moving range submicrometer positioner

A novel, compact and two degree-of-freedoms (DOF) submicrometer positioner with a large moving range is presented in this paper. The design of the positioner utilizes a monolithic parallel flexure mechanism with built-in electromagnetic actuators and eddy current sensors to achieve the precision 2-DOF motion. The travel range of the positioner is 1000 μm/5 mrad and which depend on the eddy current sensor’s range of measurement (ROM) and electromagnetic actuator’s effective length. The analytical model and its dynamics were analyzed and derived. The whole control architecture takes the measured configuration parameters and endeavors to control the positioner motion by regulating the currents in the electromagnetic actuators. To increase the compactness and stability of the positioner, a self-tuning adaptive (STA) controller was analyzed and proposed. From the experimental results, satisfactory performances of the system, including stiffness and precision, have been successfully demonstrated.     

PID-type sliding mode-based adaptive motion control of a 2-DOF piezoelectric ultrasonic motor driven stage

This paper presents a new scheme of adaptive sliding mode control (ASMC) for a piezoelectric ultrasonic motor driven X–Y stage to meet the demand of precision motion tracking while addressing the problems of unknown nonlinear friction and model uncertainties. The system model with Coulomb friction and unilateral coupling effect is first investigated. Then the controller is designed with adaptive laws synthesized to obtain the unknown model parameters for handling parametric uncertainties and offsetting friction force. The robust control term acts as a high gain feedback control to make the output track the desired trajectory fast for guaranteed robust performance. Based on a PID-type sliding mode, the control scheme has a simple structure to be implemented and the control parameters can be easily tuned. Theoretical stability analysis of the proposed novel ASMC is accomplished using a Lyapunov framework. Furthermore, the proposed control scheme is applied to an X–Y stage and the results prove that the proposed control method is effective in achieving excellent tracking performance.     

A fuzzy disturbance observer based control approach for a novel 1-DOF micropositioning mechanism

This paper presents the design, analysis, and control of a novel compact, large range 1-DOF micro manipulation mechanism. Leaf flexures were incorporated into a modular multilayer design configuration to achieve large range motion with a high natural frequency. The modular design of the proposed mechanism makes it usable as a building block to construct higher DOF-mechanisms. Computational analysis was conducted to verify the static and dynamic responses of the proposed mechanism and to ensure low flexures stress, high natural frequency, and large workspace. The mathematical model was developed to establish the derivation of a robust observer-based Sliding Mode (SM) controller. To improve the precision of tracking performance, the SM controller was augmented with adaptive Fuzzy Disturbance Observer (SM-FDO). Another robust control technique (H_∞) was implemented in this work to characterize and compare the performance of SM-FDO. The mechanism was fabricated using 3D printing technology and a Voice Coil Motor (VCM) was used to deliver the actuation for its capability to provide large displacements. Experiments were performed to verify the computational modeling of the proposed mechanism and to evaluate the performance of the developed controllers. Several experimental results showed that the adaptive nature of SM-FDO allowed this controller to have superior robustness and tracking performance over the other implemented robust controller.     

Hybrid fuzzy-logic and neural-network controller for MIMO systems

This study developed a hybrid fuzzy-logic and neural-network controller (HFNC) for multiple-input multiple-output (MIMO) systems. The HFNC consists of a fuzzy logic controller (FLC) which was designed to control each degree of freedom (DOF) of a MIMO system individually and an additional coupling neural network which was incorporated into the FLC to compensate for the dynamic coupling effects between each DOF of the MIMO system. Stability and robustness of the HFNC have been demonstrated using a state-space approach. From the simulation results of the 2-link robotic manipulator application and the experimental results of the 6-DOF robot tests, the HFNC demonstrated more superior control performance than the FLC.     

一种六维加速度传感器原理的研究

提出并研究了一种基于6只单轴加速度传感器的六维加速度传感器的原理及结构,建立了获取6维加速度的传感模型,并利用建立的传感模型在Matlab/Simulink环境下对提出并研究的6维加速度传感器的传感特性进行了数字仿真分析。研究结果表明,该6维加速度传感器能够实现6维加速度传感。     

A magnetically levitated, automated, contact analytical probe tool

With the challenge of the shrinking dimensions in the fabrication process, demands are growing for higher precision and more powerful analytical probing stations to be used for characterization and failure analysis of integrated circuits. A magnetic levitation-based approach to analytical probing stations is proposed and investigated in this paper. This approach permits the process to be automated while maintaining better resolution and easier operation than is currently available. Further, force control can be implemented to ensure that the probe contact does not scratch the device under testing. Feedback controllers are designed and used in both the suspension and the XY positioning. The suspension motion controller is implemented in analog circuitry while the XY motion controller is implemented in a digital controller. An air gap sensor and optical position sensors are used for the position feedback. A simple open loop control method is derived for the force control. A positioning repeatability of 0.2 μm and a force repeatability of 80 mgf are observed from the experimental results     

Dipole Models for Forward/Inverse Torque Computation of a Spherical Motor

This paper presents an alternative method to model a multilayer voice coil or an air-cored electromagnet as an equivalent permanent magnet (ePM) such that its magnetic field can be characterized by a distributed set of multipoles model. We validate the ePM model by comparing the computed results against exact solutions and illustrate its effectiveness in computing the magnetic force using the dipole force equation. Unlike methods that are based on the Lorentz force equation or the Maxwell stress tensor, which require computing the volume or surface integrals to derive the forces, the closed-form dipole force method that replaces integrations with summations dramatically reduces computation time. We compare the dipole force computation against results of the Lorentz force equation and the Maxwell stress tensor method, and validate the comparisons against published experimental data. To demonstrate the effectiveness of the method, we compute the inverse torque model of a 3-DOF orientation stage operated on the principle of a spherical motor that has more controlling inputs than its mechanical DOF.      

Modeling and control of a six-axis precision motion control stage

This work presents a newly developed six-axis magnetic suspension stage for precision motion control. The designed travel volume is 4/spl times/4/spl times/2 mm in translation and 1/spl deg//spl times/1/spl deg//spl times/2/spl deg/ in rotation. A dynamic model of the feedback linearized and uncoupled stage is developed for the purpose of motion control. Model parameter variations are demonstrated through closed-loop system identification. In motion control, a parameter variation model is proposed in conjunction with a reduced order observer to compensate the joined effect of disturbance, modeling error, and cross coupling. Experimental results in terms of positioning stability, motion resolution, rotational motion control, model regulation, large travel multiaxis contouring, and disturbance rejection are shown. Uniform positioning stability and invariant dynamic response within the designed travel volume are illustrated.