FEANOR LP30 Laser Calibration Ensures Machine Tool and CMM Accuracy

激光校准，确保精度机床和三坐标测量机.

Linear measurements with Feanor LP30 heterodyne laser interferometer.

In the heterodyne method, shown on figure, two different laser frequencies are used. Therefore a two-frequency laser is needed, e.g. a Zeeman laser. A two-mode laser is not suitable for the heterodyne method interferometer, because the difference between f₁ and f₂ is usually too high for an electronic counter. The output beam of a Zeeman laser consists of two circularly polarized beams, one with left polarization and the with right polarization. A l/4 waveplate changes circular polarization to linear.

The main difference between two described methods is that in the heterodyne one the beam frequency in reference arm differs from the beam frequency in the measuring arm.

Measurement set

Linear measurements are the most often used measuring option. Using this option it is possible to measure:

- Linear displacement

- Speed of moving element

- Linear positioning

- Vibrations

Measurements may be executed in three mutually perpendicular measuring axes X, Y, Z. Change of a measured axis requireswill demand displacements of optics.

Required measuring set: a computer, a laser head with a power supply, a stand Tripod, two magnetic holders UM1 (or two UM2), a Environmental Compensation Unit (ECU) - SM1, sensors of basis temperature T1, T2, T3, a linear interferometer IL1, a linear retro-reflector RL1, remote control Strobe (option)

Linear displacement measurement

To setup the measurement system for the measurement of a linear displacement, electric connections and adjustment of the optical path must be carried out. When the laser system is ready to work – green LED light on the forehead of the laser head. Following step is check of optical path, the measuring signal should be at least 80% on the entire axis. The measurements now can start. A measuring unit (mm, µm), a number of significant positions on a display, a measured axis, a sign (“+” or “-“) and base’s material may be chosen. After resetting, the display system is ready for measurements. When the retro-reflector is moved, the displacement in relation to a starting point is displayed on the screen (it is also possible to move the interferometer and keep retro-reflector in fixed position).

以激光波长为已知长度、利用迈克耳逊干涉系统(见激光测长技术)测量位移的通用长度测量工具。激光 干涉仪有单频的和双频的两种。单频的是在20世纪60年代中期出现的，最初用于检定基准线纹尺，后又用于在计量室中精密测长。双频激光干涉仪是1970年 出现的，它适宜在车间中使用。激光干涉仪在极接近标准状态（温度为20℃、大气压力为101325帕、相对湿度59％、C O2含量0.03％）下的测量精确度很高，可达1×10-7。
单频激光干涉仪。从激光器发出的光束，经扩束准直后由分光镜分为两路，并分别从固定反射镜和可动反射镜反射回来会合在分光镜上而产生干 涉条纹。当可动反射镜移动时，干涉条纹的光强变化由接受器中的光电转换元件和电子线路等转换为电脉冲信号，经整形、放大后输入可逆计数器计算出总脉冲数， 再由电子计算机按计算式式中λ为激光波长(N 为电脉冲总数)，算出可动反射镜的位移量L。使用单频激光干涉仪时，要求周围大气处于稳定状态，各种空气湍流都会引起直流电平变化而影响测量结果。

双频激光干涉仪 。在氦氖激光器上，加上一个约0.03特斯拉的轴向磁场。由于塞曼分裂效应和频率牵引效应，激光器产生f1和f2两个不 同频率的左旋和右旋圆偏振光。经1/4波片后成为两个互相垂直的线偏振光，再经分光镜分为两路。一路经偏振片1后成为含有频率为f1-f2的参考光束。另 一路经偏振分光镜后又分为两路：一路成为仅含有f1的光束，另一路成为仅含有f2的光束。当可动反射镜移动时，含有f2的光束经可动反射镜反射后成为含有 f2±Δf的光束，Δf是可动反射镜移动时因多普勒效应产生的附加频率，正负号表示移动方向(多普勒效应是奥地利人C.J.多普勒提出的，即波的频率在波 源或接受器运动时会产生变化)。这路光束和由固定反射镜反射回来仅含有f1的光的光束经偏振片 2后会合成为f1-(f2±Δf）的测量光束。测量光束和上述参考光束经各自的光电转换元件、放大器、整形器后进入减法器相减，输出成为仅含有±Δf的电 脉冲信号。经可逆计数器计数后，由电子计算机进行当量换算（乘 1/2激光波长）后即可得出可动反射镜的位移量。双频激光干涉仪是应用频率变化来测量位移的，这种位移信息载于f1和f2的频差上，对由光强变化引起的直 流电平变化不敏感，所以抗干扰能力强。它常用于检定测长机、三坐标测量机、光刻机和加工中心等的坐标精度，也可用作测长机、高精度三坐标测量机等的测量系 统。利用相应附件，还可进行高精度直线度测量、平面度测量和小角度测量。