Measurement of multi-degree-of-freedom error motions of a precision linear air-bearing stage

This paper describes the measurement of straightness error motions (vertical straightness and horizontal straightness) and rotational error motions (pitch, yaw and roll) of a commercial precision linear air-bearing stage actuated by a linear motor. Each of the error motions was measured by two different methods for assurance of reliability. The stage was placed in the XY-plane and moved along the X-direction. The pitch error and yaw error, which were measured by an autocollimator and the angle measurement kit of a laser interferometer, were about 8.7 and 1.6 arc-s, respectively, over a travel of 150 mm with a moving speed of 10 mm/s. The roll error was measured by the autocollimator through scanning a flat mirror along the X-direction. The second method for roll error measurement was to scan two capacitance-type displacement probes along the flat surface placed in the XZ-plane. The two probes with their sensing axes in the Y-direction were aligned with a certain spacing along the Z-axis. The roll error can be obtained by dividing the difference of the outputs of the two probes by the spacing between the two probes. The roll error was measured to be approximately 11.8 arc-s over the 150 mm travel. The horizontal straightness error and the vertical straightness error (Y- and Z-straightness errors) were measured by using the straightness measurement kit of the laser interferometer. The second method for straightness measurement was to scan the flat surface with a capacitance-type displacement probe. The horizontal and vertical straightness errors of the stage over the 150 mm travel were measured to be approximately 207 and 660 nm, respectively.     

多圈光电轴角编码器在直线位移测量中的应用

多圈光电轴角编码器是一种适用于大量程轴角位移精密测量的光电数字测角仪,其测量范围可超过整周(360°)的几百倍,甚至上千倍.利用多圈光电轴角编码器具有分辨力高、精度高、体积小、量程大以及数字量输出等优点,设计了由高精度齿轮同步带传动机构与16位多圈编码器组合而成的直线位移测量系统,并对系统的测长精度进行了检定.实验结果表明,修正后的系统测长误差低于0.065 mm,可满足中低精度的工业测量要求.     

An evaluation of a modulated laser encoder

This paper introduces a new method of interpolation for sub-nanometer-resolution linear encoders. This method, called SPPE (scanning position probe encoder), uses high-order harmonics information obtained by a sinusoidal scanning pickup located on a periodic grating surface. The proposed encoder uses a current-modulated laser diode with diffractive grating optics. Since the electrical current changes the laser-diode wavelength, the interference light intensity is modulated as a sinusoidal scanning pickup on the scale grating. Phase-detection circuits can decode the position information in the pickup signal by using phase-locked loop techniques. The decoder achieves an interpolation rate of over 1/40,000 with interpolation errors of less than ±1 nm. A new interpolation-error measuring system was developed for the encoder. Finally, the evaluation results reveal that the presented encoder shows both high resolution and strong robustness.     

Performance evaluation of a new taut wire system for straightness measurement of machine tools

This paper describes evaluation of a method of measuring the straightness of motion of machine tool axes using a taut wire and an optical sensor head mounted at the tool point location. In contrast to commonly used taut wire instruments, straightedges or laser-based methods, this solution combines low cost, simplicity of setup and automated data capture while achieving state of the art accuracy suitable for application on precision machine tools. A series of tests are discussed which examine the performance of the new sensing head and different wires which highlight the suitability of the taut wire properties as a straightness reference. Experimental results obtained on a production machine tool are provided with respect to the accuracy and repeatability of both the proposed taut wire system and a laser interferometer operated under the same conditions. The reference errors of wires made of different materials are compared and the wire catenary is separated from the measurement results. The uncertainty budget for taut wire and laser systems is presented and expanded uncertainty of 4 μm obtained for both. During the experiment, the method showed excellent repeatability with two standard deviations of 1.5 μm over a measuring range of 1.5 m; this performance matches that of a commercial laser interferometer-based straightness reference to within 0.1 μm.     

Design and experimental validation of an ultra-precision Abbe-compliant linear encoder-based position measurement system

The design and development of an Abbe-compliant linear encoder-based measurement system for position measurement with a targeted 20 nm uncertainty (k = 2) in machine tools and CMMs is presented. It consists of a linear scale and a capacitive sensor, mounted in line on an interface which is guided in the scale's measurement direction and driven by a linear motor based on the output signal of the capacitive sensor. The capacitive sensor measures the displacement of a target surface on the workpiece table. The functional point, which is the center of a tool or touch probe, is always aligned with the scale and capacitive sensor such that this configuration is compliant with the Abbe principle. Thermal stability is achieved by the application of a thermal center between the scale and capacitive sensor at the tip of the latter, which prevents both components to drift apart. Based on this concept, a prototype of a one-DOF measurement system was developed for a measurement range of 120 mm, together with an experimental setup aimed at verifying the reproducibility of the system for changing ambient conditions of ±0.5 °C and ±5%rh and the repeatability during tracking of a target surface over a short period of time. These experiments have shown that the measurement uncertainty of the one-DOF system is below 29 nm with a 95% confidence level.     

An international length comparison at an industrial level using a photoelectric incremental encoder as transfer standard

A Japanese–German interlaboratory comparison of length measurements was conducted. A photoelectric incremental encoder with a measurement length of 270 mm was used as transfer standard. An agreement of better than 27 nm over the entire length was ascertained, and the “short-range” deviations within a length interval of approximately 10 mm could be characterized with a standard deviation of σ=0.8 nm. The results attained are considered as consistent with the estimated uncertainties of measurement. Since the measurements performed are directly traceable to the SI unit of the “metre”, the comparison supports ideas currently being discussed by some National Metrology Institutes and dealing with the question of how foundations can be laid for a generally accepted application of this method of traceability.     

Development of a three-degree-of-freedom laser linear encoder for error measurement of a high precision stage

In this study, a laser linear encoder with three degrees of freedom (3-DOFs) based on diffraction and interference was developed to measure the linear displacement and two angular errors of a linear moving stage. Parts of the linear motion errors induced from the two angular errors can be calculated by this prototype 3-DOF laser encoder. It was an effective method for online error calculation and compensation to improve precision stage performance. This new function was superior to other laser encoders. The verification results showed that the resolution is 20 nm. It detected displacements relative to an external grating scale with accuracy of about +/-150 nm for a measuring range of +/-1 mm, and detected the angular errors with related accuracy of about +/-1 arc sec for a measuring range of +/-100 arc sec.     

A high performance one-dimensional homodyne encoder and the proof of principle of a novel two-dimensional homodyne encoder

Displacement laser interferometers and interferometric encoders currently are the dominating solutions to the displacement measurement applications which require measurement uncertainties in the order of a few nanometers over hundreds of millimeters of measurement range. But, in comparison with interferometric encoders, to achieve nanometer order or even lower measurement uncertainties, displacement laser interferometers require much stricter environmental control if not vacuum, which will increase their Total Cost of Ownership (TCO). Therefore interferometric encoders are getting more and more preferable. Furthermore, for some applications, the measurement of the out-of-plane displacement is required as well. Therefore, in this work, a one-dimensional interferometric encoder was built and investigated, a novel two-dimensional (one is in-plane, the other one is out-of-plane) interferometric encoder was devised and its principle was proven experimentally. For the one-dimensional encoder, a periodic nonlinearity of ±50 pm with HEIDENHAIN EIB 741 and a periodic nonlinearity of less than ±10 pm with a home built phase meter and off-line Heydemann correction were identified through a comparison measurement with a differential heterodyne interferometer. In addition, this one-dimensional encoder was identified to have a better measurement stability compared to the differential heterodyne interferometer.     

A fast and simple algorithm for evaluation of minimum zone straightness error from coordinate data

Various methods have been suggested in the past to determine the minimum zone straightness error, but suffer from various drawbacks. A new, fast and simple algorithm is proposed to calculate the straightness error from planar coordinate data. It guarantees the minimum zone solution. An example and test data are provided. Results of simulation experiments to establish the time computational complexity of the algorithm are also presented.     

An Improved Fourier Five-Sensor (IF5S) method for separating straightness and yawing errors of a linear slide based on multiple sensor parameter sets and least square regression technique

In this paper, an Improved Fourier Five-Sensor (IF5S) measurement method is proposed for separating the straightness and yawing motion errors as well as determining the profile of a linear slide. The previous F5S method [3] used the constant parameters initially to estimate the profile function based on three sensor equations for different angle ranges. The profile estimation and error separation are implemented via an iterative method which can only yield acceptably accurate results with tremendous computational efforts. Here, the improved F5S method applies the least square regression technique instead of the iterative method to estimate the profile functions by using three distinct sets of parameters and different fused sensor data according to the travel of the linear slide. Various errors can then be separated based on the calculated profile function. Simulation results confirm that the IF5S method provides better performance and effectiveness as compared to the previous F5S method.     

Surface profile measurement of a sinusoidal grid using an atomic force microscope on a diamond turning machine

This paper describes the surface profile measurement of a XY-grid workpiece with sinusoidal microstructures using an atomic force microscope (AFM) on a diamond turning machine. The sinusoidal micro-structures, which are fabricated on an aluminum plate by fast tool servo-assisted diamond turning, are a superposition of periodic sine-waves along the X- and Y-directions (wavelength (XY): 150 μm, amplitude (Z): 0.25 μm). A linear encoder with a resolution of 0.5 nm is integrated into the AFM-head for accurate measurement of the Z-directional profile height in the presence of noise associated with the diamond turning machine. The spindle and the X-slide of the machine are employed to spirally scan the AFM-head over the sinusoidal grid workpiece. Experiments fabricating and measuring the sinusoidal grid workpiece are carried out after accurate alignment of the AFM cantilever tip with the spindle centerline.     

基于51单片机的光电编码器接口装置设计

光电编码器以其分辨率高、测量精度高、形式多样等优点,被广泛运用于现代工业、航天航空领域。在工程中对光电编码器信号的采集一般使用专用PCI卡,这无形中增加了工程的成本,本文介绍了一种基于AT89S52单片机的绝对式光电编码器的接口装置及软件设计,该装置使用LCM12684作为显示模块,实现了对绝对式光电编码器的数据采集、处理及输出。     

Development of a piezoelectrically actuated two-degree-of-freedom fast tool servo with decoupled motions for micro-/nanomachining

The limited degrees of freedom (DOFs) of servo motions is an inherent deficiency in conventional, fast-tool-servo-(FTS)-assisted, diamond-turning, highly blocking applications of the FTS technique. In this paper, the concept of two-DOF FTS (2-DOF FTS)-assisted diamond turning is proposed and demonstrated. A piezoelectrically actuated 2-DOF FTS mechanism is developed to enable the cutting tool to move along two directions with decoupled motions. A novel guidance flexural mechanism constructed using the newly proposed Z-shaped flexure hinges (ZFHs) is introduced to generate motions along the z-axis, which is based on the bending deformation of the beams of the ZFHs. Additionally, using the differential moving principle (DMP), bi-directional motions in the x-axis direction can be achieved. Using the matrix-based compliance modeling method, the kinematics of the mechanism are analytically described, and the dynamics are also modeled using the Lagrangian principle. The theoretical results are then verified using finite element analysis (FEA). Certain increases in performances over conventional two-DOF flexural mechanisms are achieved: (a) a more compact structure with lower moving inertia, (b) theoretically decoupled motions of the output end, and (c) less than one actuator per DOF. To investigate the practical performance of the 2-DOF FTS system, both open-loop and closed-loop tests are conducted. Finally, the developed 2-DOF FTS technique is implemented to realize an innovative Pseudo-Random Diamond Turning (PRDT) method for the fabrication of micro-structured surfaces with scattering homogenization. The cutting results demonstrate not only the superiority of the concept but also the efficiency of the developed 2-DOF FTS system.     

Multi-probe method for straightness profile measurement based on least uncertainty propagation (1st report): Two-point method considering cross-axis translational motion and sensor's random error

In the straightness profile measurement of a mechanical workpiece, hardware datums have been the traditional standard. However, error separation techniques of the surface profile from parasitic motions have been developed. These are known as software datums, which separate the surface profile from the parasitic motions using multiple sensors and/or multiple orientations and realize higher accuracy than that of the hardware datum. However, the conventional software datum cannot measure a large-scale workpiece because the large sampling number causes random error amplification. Furthermore, the conventional software datum assumes that sensor's random noise is small enough in comparison with the parasitic motions. But, the accuracy of the hardware datum has become high. Then, the accuracy of the sensor's random noise is not so small, relatively. In this paper, a next-generation software datum, the two-point method based on the least uncertainty propagation, is proposed. The proposed two-point method consists of weighting and inverse filtering, resulting in the least uncertainty of the estimated surface profile by choosing suitable weighting.     

基于FPGA的LDPC编码器设计与实现

设计了一种用于近地空间通信的CCSDS标准下编码速率为7/8的(8176,7154)低密度奇偶校验(Low density parity check,LDPC)编码器。基于LDPC编码理论,完成了基于现场可编辑逻辑门阵列(Field-programmable gate array,FPGA)的编码算法设计。利用LDPC生成矩阵的特点,引入循环移位寄存器作为编码电路核心,采用移位寄存器加累加器(Shift-register-adder-accumulator,SRAA)结构实现了矩阵乘法的快速运算,从而构建了以部分并行编码电路为核心的编码模块。此外,还设计了串口输入输出模块、随机存储模块和控制模块,共同组成了编码器系统。最后,利用FPGA完成硬件设计,并进行了仿真和实验验证。结果表明,所设计的LDPC编码器测试结果与理论结果具有一致性。因而该编码系统具有实用性,且设计方法简单、高效。     

脉冲编码器、测速发电机性能自动测试分析系统

脉冲编码器、测速发电机是传动系统中常用的速度传感器,其性能分坏直接影响控制系统的品质指标。本文设计实现了一种基于微机脉冲编码器,测速发电机性能自动测试系统,对该系统的硬件构成和软件分析功能进行了详细讨论。     

一种新的拉线式位移传感器的设计及其应用

研究了一种新的拉线式位移传感器的设计及其应用。简要分析了传统拉线式位移传感器的工作原理及其不足,针对此从结构上对这种传感器进行了优化设计,并从性能上对所设计的传感器进行了分析。实验证明所设计的传感器测量精度高、耐磨性好、具有良好的研究和应用价值。     

基于光电编码器轴的转速测量系统设计实例

设计了由半导体激光器、光电码盘、光电二极管、放大保护电路、89S52单片机、显示模块组成的转速测量系统,给出了定时器初装值的计算过程以及程序主要代码,最后给出了一部分测量数据.     

Design and control of a new linear magnetic actuator for squeeze film damper

A new model of a linear magnetic actuator (LMA) that can be applied to the controllable squeeze film damper (CSFD) was proposed, designed, and fabricated. To validate the operation of the proposed actuator, a mathematical model of the proposed LMA was derived through experiments. From the experimental results it was verified that the electromagnetic force depends upon the position of the mover (the outer damper ring of the CSFD) and the applied current. Also, the electromagnetic force varies symmetrically with the position of the mover within the working region. A self-tuning fuzzy PID controller was applied to control the position of the novel LMA. Further, the proposed LMA was assembled in the squeeze film damper (SFD), where the clearance can be controlled by LMA. To investigate the damping effect of the damper under various clearances by controlling the LMA, experiments on the rotor test-rig were conducted. From the experimental results, the proposed device, which is composed of SFD and LMA, was verified to be very effective for attenuation of the vibration of the rotor system. This paper was recommended for publication in revised form by Associate Editor Dong Hwan Kim Kyoung Kwan Ahn received the B.S. degree in the department of Mechanical Engineering from Seoul National University in 1990, the M. Sc. degree in Mechanical Engineering from Korea Advanced Institute of Science and Technology (KAIST) in 1992 and the Ph.D. degree with the title “A study on the automation of out-door tasks using 2 link electro-hydraulic manipulator” from Tokyo Institute of Technology in 1999. He is currently a Professor in the School of Mechanical and Automotive Engineering, University of Ulsan, Ulsan, Korea. His research interests are design and control of smart actuator using smart material, fluid power control and active damping control. He is a Member of IEEE, ASME, SICE, RSJ, JSME, KSME, KSPE, KSAE, KFPS, and JFPS. Truong Quoc Thanh received the B.S degree in the department of Mechanical Engineering from Hochiminh City University of Technology in 1998, and the M.Sc. degree with title “Dynamic stiffness method in calculation vibration of structure” from the master program of mechanics under Inter-University Cooperation Program between Liege University (Belgium) and HCMUT (Vietnam) in 2000. From 2000 to 2004, he worked as a lecturer in the mechanical department of Hochiminh City University of Technology. His teaching subjects are relevant in Advanced Manufacturing Methods, Measuring Technique and Manufacturing Technique. He is currently a Ph.D. candidate at the University of Ulsan. His research interests focus on designing and manufacturing of new actuators, vibration control theory and application theories.     

Positioning and tracking of a linear motion stage with friction compensation by fuzzy logic approach

In this paper, the development of a fuzzy controller that compensates for nonlinear friction in a linear motion stage is presented. The experimental work and instrumentation set up is presented for this research. Based upon a nonlinear friction model, friction parameters were estimated from experimental results. Simulation and experimental validation on a ball-screw mechanism is presented, showing the effectiveness of the proposed controller. Furthermore, it is shown that the proposed fuzzy control scheme offers several implementation advantages such as smaller control effort, and reduced effect of measurement noise. Moreover, the fuzzy logic methodology displays superior performance when compared to a conventional PID controller. It also shows good and robust tracking with respect to system parameters variation.