Zichen Chen

Structural Parameter Identification for Articulated Arm Coordinate Measuring Machines

Errors of structural parameters are the most important factors causing uncertainty of articulated arm coordinate measuring machines (AACMMs). Therefore these parameters must be identified to insure the accuracy of AACMMs. The kinematic model of six degree of freedom (6-DOF) AACMMs was established, and the structural parameters influencing the accuracy of AACMMs were achieved through analysis. A method to acquire data for identification with a cone-shape hole was presented. With single-point repeatability as the objective function, a modified simulated annealing algorithm (MSAA) was presented to identify structural parameters. A 6-DOF AACMM was used to carry out experimental tests in order to evaluate the efficiency of the MSAA, showing that after identification the repeatability and length measuring accuracy are improved greatly.

Kinematic Calibration for Articulated Arm Coordinate Measuring Machines Base on Particle Swarm Optimization

Kinematic calibration is one of the most important ways to improve the accuracy of articulated arm coordinate measuring machines (AACMMs). The kinematic model of six degree of freedom (6-DOF) AACMMs was established by Denavit-Hartenberg method. One calibration technology base on particle swarm optimization (PSO) was presented, which used single-point repeatability as the fitness function and kinematic parameters as the position vector. An adaptive inertia weight was presented to improve the ability of global exploration and local exploitation of the PSO. A 6-DOF AACMM was used to carry out experimental tests in order to evaluate the efficiency of the self-calibration technology, showing that after calibration the accuracy is improved greatly.

Simulation Analysis on Characteristics of a Planar Capacitive Sensor for Large Scale Measurement

Measuring multi-dimensional linear displacements in large scale range with high precision is always focused on by researchers. This paper presents the results of simulation analysis on characteristics of a planar capacitive sensor (PCS), which is proposed for X and Y direction linear displacement measurement by measuring the periodic change of capacitance between two periodic plates, one fixed (i.e. fixed plate) and the other movable (i.e. movable plate). Since the capacitive electrode array on the fixed plate is periodically positioned, large scale measurement is realizable as long as the electrode array is large enough. The use of two geometrical orthogonal (90-degree out-of-phase) electrode arrays on the movable plate promises either axial displacement can be measured simultaneously without the coupling of another axial movement. The result of simulation proves 2-dimensional large scale measurement is feasible, meanwhile, different strategies are presented to fulfill structural optimization, including sensitivity optimization and linearity optimization.

Design and analysis of two dimensional X-Y micropositioning stage

This paper presents a novel piezodriven X-Y stage utilizing flexure hinges. Levers of high amplifying rate were adopted to magnify the output displacement of the piezoelectric actuator and a complex parallel four-bar mechanism was used to guide the mobile platform. In order to describe the static and dynamic behaviour of the stage, an analytical model was built and a series of formulae were deduced. Based on mathematical analysis, the configuration of the stage was optimized. Then Finite Element Analysis was applied to analyze travel ranges, natural frequencies and stress distribution. The simulation computation results demonstrate that the stage could reach a motion range of 200mby 200m and has a first order natural frequency of 265 Hertz, which is of good concordance with the theoretical estimate. Now a prototype is being fabricated.

A New Friction Estimation Approach for Precision Positioner

Precision positioner has been significantly developed as the rapid growth of MEMS and IC industries. As for short-stroke position, the loss of friction can be avoided by using flexible hinges. Long-stroke postioner, however, in which moved-to-be mass always stands on the guide-way part, a main source of friction, makes friction unavoidable. Friction estimation is based on certain filters, such as Extended Kalman filter (EKF). However, estimation accuracy of Kalman filter, especially at low-velocity movement, is not very well. To solve this problem, the paper proposes an estimation method based on DD2 to make an accurate estimation. And the result shows this method is promising in real-time friction estimation. After background introduction, in section 2, the relation of EKF and Taylor series and EKF implementation are reviewed and its limitations are noted as well. A briefly introduction to DD2 is given in Section 3 and friction estimation case comparing the simulation results of DD2 estimation with that of EKF described in Section 4, respectively. At last, conclusions are summarized.Copyright

Sliding Mode Based Controller for Magnetostrictive Actuator in Precision Positioner

Magnetostrictive actuator, for its merits of relatively low voltage and high force, has been increasingly applied in many applications, such as vibration control, aviation, positioner, etc. At low drive level, magnetostrictive actuator presents linear relation between strain or displacement and input voltage or input current, while non-linear appears when applied moderate or high drive level. To achieve accurate control for high drive level, non-linear, including saturation and hysteresis, must be compensated. Sliding mode control, a robust control scheme, can handle these non-linear. As magnetostrictive actuator modelled in Jiles-Atherton model, the relation of magnetic field H and bulk magnetization M, hysteresis, is divided into anhysteresis and deviation from anhysteresis. Saturation can be compensated by inversion of anhysteresis (free-hysteresis) and then, hysteresis, represented as the deviation from anhysteresis, is compensated with sliding mode control.Copyright