基于光栅编码器的柔性测量臂位置精度研究

光栅编码器的误差使得柔性测量臂(AACMM)在不同位置、不同构型下的精度呈现一定的规律。掌握由光栅编码器精度引起的位置精度在工作空间的分布规律,有利于指导柔性测量臂的标定和测量。以六关节测量臂为研究对象,分析末端执行器位置精度与光栅编码器精度区间之间的关系,并定义了基于光栅编码器精度的位置精度评价指标,在整个工作空间下描述其分布情况。验证试验包括:比较不同关节下光栅编码器精度区间对末端执行器位置精度的影响;与目前常用Monte Carlo方式进行柔性测量臂精度分布特性对比;利用其分布特性,对不同区域进行单点和标准球直径测量。实验结果表明,本方法能更直观、全面地描述光栅编码器精度对柔性测量臂位置精度在工作空间分布情况,通过该分布确定优化测量区域,指导实际操作。     

Design and construction of a two-degree-of-freedom linear encoder for nanometric measurement of stage position and straightness

This paper presents a two-degree-of-freedom (two-DOF) linear encoder which can measure the position along the moving axis (X-axis) and the straightness along the axis vertical to the moving axis (Z-axis) of a precision linear stage simultaneously. The two-DOF linear encoder is composed of a reflective-type scale grating and an optical sensor head. A reference grating, which is identical to the scale grating except the scale length, is employed in the optical sensor head. Positive and negative first-order diffracted beams from the two gratings are superposed with each other in the optical sensor head to generate interference signals. The optical configuration is arranged in such a way that the direction of displacement in each axis can also be detected. A prototype two-DOF linear encoder is designed and constructed. The size of the optical sensor head is about 50 mm (X) × 50 mm (Y) × 30 mm (Z) and the pitch of the grating is 1.6 μm. It has been confirmed that the prototype two-DOF linear encoder has sub-nanometer resolutions in both the X- and Z-axes.     

空间高精度扫描伺服系统的驱动控制

研究了空间飞行器扫描伺服系统的高精度驱动控制技术。针对有效载荷对地面目标进行扫描时多要求其伺服系统提供高精度的低速性能,本文提出采用交流永磁同步电机直接驱动伺服系统,省去中间的减速器传动环节来提高伺服系统的驱动控制精度。伺服驱动控制系统用现场可编程门阵列(FPGA)作为高速信号处理芯片,提高信号的处理速度和控制精度;用高精度的绝对式光电编码器检测转动位置,提高位置检测和速度的精度;主电路采用功率线性放大技术,得到光滑,力矩脉动小的驱动波形。系统实验表明,由于该方法采用模拟正弦信号驱动,在低速时避免了脉宽调制(PWM)驱动信号开关和死区造成的速度波动,实现了高精度的速度控制,速度波动范围在1%以内;得到的电压、电流测试曲线光滑,无高次谐波干扰。该扫描伺服系统满足动态和静态要求,为实现空间低速高精度扫描提供了一种新的方法。     

星载差分吸收光谱仪摆镜控制系统设计

针对差分吸收光谱仪搭载于地球同步轨道卫星时对地成像的要求,设计了一种扫描摆镜转动控制系统。从摆镜控制结构设计、控制电路设计两个方面阐述了摆镜系统的方案。摆镜系统受载荷主控器控制,接收控制指令并回传当前摆镜位置状态,通过LMD18200驱动芯片进行功率输出,由步进电机和谐波减速器构成的驱动器驱动摆镜转动,编码器读取摆镜角度信息。给出了PWM(Pulse Width Modulation)波占空比的测定办法,并提出通过回转到成像起始点之前的方式,消除回程误差对成像区域步距不确定性的影响。实验结果表明该系统的步距角均值偏差小于1″,最大偏差小于5″,标准偏差小于2″。该光谱仪摆镜控制系统满足步距精度指标要求。     

应用于光栅测量的新型多段式距离码研究

介绍了应用于精密位置测量的光栅尺位移传感器的编码方法,根据对光栅尺传统距离码编码原理的研究,提出了一种新型距离码的编码方法——新型多段式距离码。这种编码方法使任意连续的3个参考标记之间的两段间隔距离是唯一的,可通过判断相邻的两段间隔距离来确定绝对位置。将这种编码方法与传统距离码作比较,并利用软件MATLAB建立数学模型,研究结果表明新型多段式距离码在精密位置测量上具有明显优势。     

LS7266R1在双轴位置信号检测中的应用

在数控机床和加工中心等设备中,大多利用直线光栅或圆光栅编码器来测量直线位移或角位移,该传感器输出信号经放大、整形后转换为两路正交编码脉冲信号。针对闭环位置控制系统中的光栅编码器多轴位置信号检测装置,介绍和分析了双轴正交信号鉴相器LS7266R1的功能及内部结构,提出了基于LS7266R1的位置采集电路和软件设计,给出了在数控系统位置检测装置中利用LS7266R1芯片对多组数字信号进行检测的实例并证实采用该芯片不仅组态灵活,适用于多种应用场合,计数范围广、计数频带宽,而且可以简化系统硬件设计,提高系统的可靠性。     

数控机床伺服进给系统无传感器检测技术

提出一种基于光栅尺与编码器信号的机床伺服进给系统定位精度检测方法;深入研究电流、扭矩、润滑特性之间关系,获取伺服电动机电流并据此对机床润滑状态进行分析和监测.在全闭环和半闭环条件下进行单轴直线和两轴联动圆测试,实验表明位置、瞬时速度等光栅尺、编码器信息可以用于机床伺服进给系统精度评定和控制特性评估;进行了不同进给速度下的恒速、润滑特性测试,试验分析表明机床润滑特性符合Stribeck摩擦效应,能够实现对机床润滑和运行状态进行监测.     

Precision nano-fabrication and evaluation of a large area sinusoidal grid surface for a surface encoder

This paper describes the fabrication of a large area sinusoidal grid surface, which is used as the measurement reference of a surface encoder for multi-axis position measurement. The profile of the grid surface is a superposition of sinusoidal waves in the X-direction and the Y-direction with spatial wavelengths of 100 μm and amplitudes of 100 nm. Diamond turning with a fast tool servo (FTS) was chosen as the fabrication method. The constructed FTS, which employs a piezoelectric tube actuator (PZT) to actuate the diamond tool and a capacitance probe as the feedback sensor, was confirmed to have a bandwidth of approximately 2.5 kHz and a tool displacement accuracy of several nanometers in the closed-loop mode. Experiments of fabricating the sinusoidal grid surface were performed on a commercially available precision diamond turning machine. An aluminum alloy workpiece was vacuum chucked on the spindle and the FTS was mounted on the X-slide. Efforts were made to position the tool tip to the center of the spindle (center-alignment) since it was verified that the center-alignment is important for the fabrication accuracy of the sinusoidal grid surface. An evaluation technique based on the two-dimensional (2D) discrete Fourier transform (DFT) of interference microscope images was also developed to evaluate the fabricated grid surface effectively. The fabrication result of a grid surface over an area of 150 mm has indicated the effectiveness of the fabrication system.     

单圈绝对式电子经纬仪测角信号处理

为实现快速、高精度角位移测量,提出了一种单圈绝对式电子经纬仪测角信号处理算法。只需刻画脉冲左右边沿在阈值附近各2个采样点就可以快速估计出脉冲宽度和脉冲中心坐标;对现有文献细分方法进行改进,给出了基于多组刻画脉冲中心求解高分辨力细分角的公式;并对算法时间复杂度和抗噪声性能分别进行了分析与仿真。实验结果表明,本方法在水平方向上测角误差标准差仅为2.5″,平均每秒钟可测角输出25次,具有实现简单、只需较少计算量就可以获得较高测量精度的优点。研究结果可以为单圈绝对式电子经纬仪、全站仪提供一种新的测角信号处理实用方法。     

增量式光学编码器 IAS 信号误差建模及补偿

增量式光学编码器在制造与安装的过程中不可避免的会出现刻线误差和细分误差,这些误差会降低角度测量的精度并导致瞬时角速度(IAS)信号波动,研究刻线与细分误差的补偿途径有重要意义,但现有方法存在误差补偿效率低,不易现场应用等局限。针对上述问题,本文首先对增量式光学编码器的刻线误差与细分误差进行分析并建立误差模型,揭示了刻线误差、细分误差与IAS信号波动之间的联系。在此基础上提出了一种使用IAS信号对增量式光学编码器刻线与细分误差进行补偿的方法,该方法具有效率高、无需对编码器进行改装等优点。通过仿真分析对本文所建立的误差模型的正确性与误差估计方法的可行性进行了验证,并在RV传动实验台上对伺服电机末端的增量式光学编码器进行刻线与细分误差补偿,最后使用光学旋转平台对增量式光学编码器误差进行测量,通过对比分析验证了本文所提方法的有效性。     

论绝对编码器

说明了数控机床所使用的增量编码器、旋转变压器、绝对值编码器、绝对编码器以及光栅编码器与磁栅编码器的特点与区别,指出了绝对编码器的本质,介绍了绝对位置输出的方式与接口。     

Large-area profile measurement of sinusoidal freeform surfaces using a new prototype scanning tunneling microscopy

This paper presents large-area profile measurement of ultra-precision diamond turned sinusoidal surfaces by using a specially developed scanning tunneling microscopy (STM). The new prototype of STM system employs a long stroke PZT servo actuator as the Z-directional scanner, an integrated capacitance displacement sensor to accurately measure the Z-directional profile height, a motorized stage with long traveling stroke for carrying out large-area scanning. A simple method for self-calibration of the inevitable sample tilt is proposed in order to achieve large-area measurement without tip-crashing or losing of tip-sample interaction. Several types of ultra-precision machined sinusoidal freeform surfaces with different geometrical parameters are measured by the new STM system over large scanning areas at the scale of millimeters. Specially, a sinusoidal surface with peak-valley amplitude of 22 μm and periodical wavelength of 550 μm is successfully measured and imaged by the STM system. The measurement repeatability error, repeatability standard deviation and measured profile deviation are also evaluated. It is confirmed that the new STM system is capable of carrying out large-area as well as large-amplitude measurement of the ultra-precision machined sinusoidal surfaces.     

非均匀采样莫尔条纹信号的分析与处理

为了动态、实时地测量光电编码器在变速转动情况下的细分误差,提出了一种莫尔条纹信号的非均匀采样分析与处理方法。利用傅里叶级数原理构造了实际情况下的莫尔条纹信号方程,根据编码器在不同转速下的实时采样,揭示了莫尔条纹信号的非均匀采样特征。鉴于信号采样的非均匀性,采用曲线拟合的最小二乘法重构莫尔条纹信号,利用离散傅里叶变换算法分析重构信号并求出波形参数。通过信号参数与细分误差的关系式,测量了编码器动态细分误差。采用该方法对21位绝对式光电编码器莫尔条纹信号进行了分析和处理,两次测试得到其动态细分极值误差为+3.21″、-4.69″和+3.45″、-4.81″。实验结果表明,该方法可以有效地分析和处理编码器在非匀速转动下产生的变频莫尔条纹信号,精确地测量编码器的动态细分误差,为工作现场编码器误差的实时检测与修正奠定了基础。     

On the magnification of two-dimensional contouring errors by using contour-parallel offsets

The cross grid encoder is a diffraction grating type encoder to measure two-dimensional position of a optical head by using a grid plate, and is widely used in the industry to evaluate the two-dimensional contouring performance of a machine tool. In the graphical display of measured contouring error profiles, the error is often magnified to some given scale with respect to the reference trajectory. The conventional algorithm to compute the magnified contouring error profile, adopted in a commercial software to analyze an error profile measured by the cross grid encoder, makes the magnified trajectory discontinuous when the given reference trajectory is unsmooth, which makes it difficult to understand the magnified trajectory especially at corners. This paper proposes a new algorithm to compute the magnified trajectory of two-dimensional contouring error profiles such that the magnified trajectory becomes continuous even when the reference trajectory is unsmooth. Application examples are presented with error profiles obtained by using a cross grid encoder applied to a commercial machining center.     

数控齿条磨齿机分齿精度控制方法的研究

阐述了一种基于PLC的数控齿条磨齿机分齿精度控制方法.以PLC为控制核心,在现有伺服电机旋转编码器和滚珠丝杠基础上增加了光栅尺构成闭环控制,利用PLC的高速计数模块和高速计数中断作位置反馈处理.给出了控制结构框图,详细介绍了光栅尺测量系统和控制方法的实现.     

Development of a grating disk of a microrotary encoder for measurement of meshing accuracy of microgears

Grating disks of a microrotary encoder are developed to measure the rotational accuracy of microgears. In gear engagement, transmission error plays an important role to grasp the meshing performance of gear pairs. For measurement of transmission error of microgears, it is necessary to utilize a couple of microrotary encoders whose diameters are smaller than the reference diameter of microgears to be measured. The designed grating disk has a diameter of 1 mm, and the number of gratings is up to 1,000. It is manufactured with photo-lithography method on trial, and the grating patterns are successfully achieved homogeneously. The accuracy of the pitch and the line width is enough for realizing grating disks of a microrotary encoder.     

精密衍射光栅信号的椭圆拟合与细分校正算法

讨论了对相位差为非严格 90°的衍射光栅干涉条纹两路正弦信号的椭圆拟合算法的实现 ;提出了基于光栅正弦信号实际相位差进行残余相移识别的软件细分校正方法 ;分析了常规软件细分处理方法的缺陷并对常规细分处理方法所引起的测量误差进行了仿真。测量系统稳定下的噪声测量实验证明了本文提出的细分校正方法在提高光栅测量精度方面的有效性     

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.     

Computer automation of data acquisition from a Knudsen, torsion-effusion pendulum

A computer-automated data acquistion system has been developed for a dynamic torsion pendulum applied to measurement of vapor pressures at high temperatures by the torsion-effusion method. Laser beams reflected from mirrors on the pendulum are detected by a bank of photodetectors which, in turn, transmit signals representing pendulum positions through an encoder and interface to a laboratory computer with an internal clock. The computer uses pendulum position and time data with stored information to solve the equation of motion of the pendulum and to calculate vapor pressures. The physical parts, electronic circuits, and software are described and discussed. The rest point of a dynamic torsion pendulum has been reproduced within 1 min of arc.     

High-throughput accurate-wavelength lens-based visible spectrometer

A scanning visible spectrometer has been prototyped to complement fixed-wavelength transmission grating spectrometers for charge exchange recombination spectroscopy. Fast f/1.8 200 mm commercial lenses are used with a large 2160?mm(-1) grating for high throughput. A stepping-motor controlled sine drive positions the grating, which is mounted on a precision rotary table. A high-resolution optical encoder on the grating stage allows the grating angle to be measured with an absolute accuracy of 0.075 arc sec, corresponding to a wavelength error ≤0.005?A?. At this precision, changes in grating groove density due to thermal expansion and variations in the refractive index of air are important. An automated calibration procedure determines all the relevant spectrometer parameters to high accuracy. Changes in bulk grating temperature, atmospheric temperature, and pressure are monitored between the time of calibration and the time of measurement to ensure a persistent wavelength calibration.