The contribution of the grating ruler in modern industry is also very huge, not only to further improve the current processing accuracy, but more importantly, to improve the current processing efficiency. Now that China's processing industry and manufacturing industry are becoming more and more mature, and the precision of processing is getting higher and higher, gratings can be installed on various machine tools, such as milling machines, grinding machines, lathes, wire cutting, EDM and other machine tools. Ruler, its working environment requirements are relatively not very harsh, and it is also very simple for the operator to use.

　　What needs to be explained here is that the grating ruler is just a reaction device, it can feedback the displacement and displacement direction through signal output, but it cannot be displayed directly. It also needs a display device, which we call digital display for short. Display box, also known as digital display. Only when the grating ruler and the digital display are connected together, can the numerical value be reflected to each operator normally. Therefore, we still need to know more about the use of the grating ruler. With some professional knowledge, the grating ruler can be used alone as a feedback device.

　　Device classification

　　The grating scale displacement sensor is divided into transmission grating and reflection grating according to the different manufacturing methods and optical principles.

　　Transmission grating refers to a glass grating.

　　Reflection grating refers to the steel tape grating.

　　Device structure

　　The grating scale displacement sensor is composed of a scale grating and a grating reading head. The scale grating is generally fixed on the movable part of the machine tool, the grating reading head is installed on the fixed part of the machine tool, and the indicating grating is installed in the grating reading head. The figure on the right shows the structure of the grating scale displacement sensor.

　　Grating detection device

　　Structure of grating detection device The key part of the grating detection device is the grating reading head, which is composed of a light source, a converging lens, an indicating grating, a photoelectric element and an adjustment mechanism. There are many structural forms of grating reading heads, which are divided into direct receiving reading heads (or silicon photocell reading heads, mirror reading heads, spectroscopic reading heads, and metal grating reflective reading heads) according to the structural characteristics and application occasions of the reading head.

　　working principle

　　常见光栅的工作原理都是根据物理上莫尔条纹的形成原理进行工作的。当使指示光栅上的线纹与标尺光栅上的线纹成一角度来放置两光栅尺时，必然会造成两光栅尺上的线纹互相交叉。在光源的照射下，交叉点近旁的小区域内由于黑色线纹重叠，因而遮光面积最小，挡光效应最弱，光的累积作用使得这个区域出现亮带。相反，距交叉点较远的区域，因两光栅尺不透明的黑色线纹的重叠部分变得越来越少，不透明区域面积逐渐变大，即遮光面积逐渐变大，使得挡光效应变强，只有较少的光线能通过这个区域透过光栅，使这个区域出现暗带

　　莫尔条纹

　　以透射光栅为例，当指示光栅上的线纹和标尺光栅上的线纹之间形成一个小角度θ，并且两个光栅尺刻面相对平行放置时，在光源的照射下，位于几乎垂直的栅纹上，形成明暗相间的条纹。这种条纹称为“莫尔条纹” (右图所示)。严格地说，莫尔条纹排列的方向是与两片光栅线纹夹角的平分线相垂直。莫尔条纹中两条亮纹或两条暗纹之间的距离称为莫尔条纹的宽度，以W表示。

　　莫尔条纹

　　W=ω /2* sin(θ/2)=ω /θ 。

　　莫尔条纹具有以下特征：

　　(1)莫尔条纹的变化规律

　　两片光栅相对移过一个栅距，莫尔条纹移过一个条纹距离。由于光的衍射与干涉作用，莫尔条纹的变化规律近似正(余)弦函数，变化周期数与光栅相对位移的栅距数同步。

　　(2)放大作用

　　在两光栅栅线夹角较小的情况下，莫尔条纹宽度ω和光栅栅距W、栅线角θ之间有下列关系。式中，θ的单位为rad，W的单位为mm。由于倾角很小，sinθ很小，则

　　W=ω /θ

　　若ω =0.01mm，θ=0.01rad，则上式可得W=1，即光栅放大了100倍。

　　莫尔条纹计算

　　(3)均化误差作用

　　莫尔条纹是由若干光栅条纹共用形成，例如每毫米100线的光栅，10mm宽度的莫尔条纹就有1000条线纹，这样栅距之间的相邻误差就被平均化了，消除了由于栅距不均匀、断裂等造成的误差。

　　检测与数据处理

　　光栅测量位移的实质是以光栅栅距为一把标准尺子对位称量进行测量。高分辨率的光栅尺一般造价较贵，且制造困难。为了提高系统分辨率，需要对莫尔条纹进行细分，目前(2006年)光栅尺位移传感器系统多采用电子细分方法。当两块光栅以微小倾角重叠时，在与光栅刻线大致垂直的方向上就会产生莫尔条纹，随着光栅的移动，莫尔条纹也随之上下移动。这样就把对光栅栅距的测量转换为对莫尔条纹个数的测量。

　　在一个莫尔条纹宽度内，按照一定间隔放置4个光电器件就能实现电子细分与判向功能。例如，栅线为50线对/mm的光栅尺，其光栅栅距为0.02mm，若采用四细分后便可得到分辨率为5μm的计数脉冲，这在工业普通测控中已达到了很高精度。由于位移是一个矢量，即要检测其大小，又要检测其方向，因此至少需要两路相位不同的光电信号。为了消除共模干扰、直流分量和偶次谐波，通常采用由低漂移运放构成的差分放大器。由4个光敏器件获得的4路光电信号分别送到2只差分放大器输入端，从差分放大器输出的两路信号其相位差为π/2，为得到判向和计数脉冲，需对这两路信号进行整形，首先把它们整形为占空比为1：1的方波。然后，通过对方波的相位进行判别比较，就可以得到光栅尺的移动方向。通过对方波脉冲进行计数，可以得到光栅尺的位移和速度。

　　安装指导

　　光栅尺位移传感器的安装比较灵活，可安装在机床的不同部位。

　　一般将主尺安装在机床的工作台(滑板)上，随机床走刀而动，读数头固定在床身上，尽可能使读数头安装在主尺的下方。其安装方式的选择必须注意切屑、切削液及油液的溅落方向。如果由于安装位置限制必须采用读数头朝上的方式安装时，则必须增加辅助密封装置。另外，一般情况下，读数头应尽量安装在相对机床静止部件上，此时输出导线不移动易固定，而尺身则应安装在相对机床运动的部件上(如滑板)。

　　安装基面

　　安装光栅尺位移传感器时，不能直接将传感器安装在粗糙不平的机床身上，更不能安装在打底涂漆的机床身上。光栅主尺及读数头分别安装在机床相对运动的两个部件上。用千分表检查机床工作台的主尺安装面与导轨运动的方向平行度。千分表固定在床身上，移动工作台，要求达到平行度为0.1mm/1000mm以内。如果不能达到这个要求，则需设计加工一件光栅尺基座。

　　基座要求做到：(1)应加一根与光栅尺尺身长度相等的基座(最好基座长出光栅尺50mm左右)。(2)该基座通过铣、磨工序加工，保证其平面平行度0.1mm/1000mm以内。另外，还需加工一件与尺身基座等高的读数头基座。读数头的基座与尺身的基座总共误差不得大于±0.2mm。安装时，调整读数头位置，达到读数头与光栅尺尺身的平行度为0.1mm左右，读数头与光栅尺尺身之间的间距为1~1.5mm左右。

　　主尺安装

　　将光栅主尺用M4螺钉上在机床安装的工作台安装面上，但不要上紧，把千分表固定在床身上，移动工作台(主尺与工作台同时移动)。用千分表测量主尺平面与机床导轨运动方向的平行度，调整主尺M4螺钉位置，使主尺平行度满足0.1mm/1000mm以内时，把M2螺钉彻底上紧。

　　在安装光栅主尺时，应注意如下三点：

　　(1) 在装主尺时，如安装超过1.5M以上的光栅时，不能象桥梁式只安装两端头，尚需在整个主尺尺身中有支撑。(2)在有基座情况下安装好后，最好用一个卡子卡住尺身中点(或几点)。(3)不能安装卡子时，最好用玻璃胶粘住光栅尺身，使基尺与主尺固定好。

　　读数头安装

　　在安装读数头时，如果发现安装条件非常的有限，可以考虑使用附件，如角铝、直板，首先应保证读数头的基面达到安装要求，然后再安装读数头，其安装方法与主尺相似。最后调整读数头，使读数头与光栅主尺平行度保证在0.1mm之内，其读数头与主尺的间隙控制在1~1.5mm以内。安装完毕后，可以用大拇指接触度数头与光栅尺尺身表面是否平滑、平整。

　　限位装置

　　After all the grating line displacement sensors are installed, a limit device must be installed on the machine guide rail to prevent the reading head from colliding with both ends of the main ruler when the machine tool moves, thereby damaging the grating ruler. In addition, when purchasing a grating linear displacement sensor, the user should try to choose a grating ruler that exceeds the processing size of the machine tool by about 100mm, so as to leave a margin.

　　Sensor check

　　After the grating line displacement sensor is installed, you can turn on the digital display, move the worktable, and observe whether the counting of the digital display is normal.

　　Select a reference position on the machine tool, and move the work point back and forth to the selected position. The DRO should read the same (or return to zero). In addition, a dial indicator (or dial indicator) can also be used to adjust the dial indicator and the digital indicator to zero at the same time (or memorize the initial data), return to the initial position after going back and forth several times, and observe the digital indicator and the dial indicator. Whether the data in the table is consistent.

　　Through the above work, the installation of the linear displacement sensor of the grating ruler is completed. But for the general machine tool processing environment, there are many iron filings, cutting fluid and oil pollution. Therefore, the sensor should be equipped with a protective cover. The design of the protective cover is determined by leaving a certain space size according to the enlarged cross-section of the sensor. The protective cover is usually sealed with rubber to make it have a certain waterproof and oil-proof ability.