-
基于Moore Nanotech 450 UPL超精密单点金刚石车削机床搭建了光学原位检测系统,进行环境误差抑制方法的验证实验。相较于离线检测,原位检测更容易受到环境扰动的影响,因此对其进行实验具有实际的应用价值,图6为实验装置的实物图。
机床由一个主轴(C轴)和两个运动轴(X轴和Z轴)所组成。如表1所示为机床关键性能参数的实测结果,其中Z轴的水平直线度为0.063 μm(总量程为300 mm),X轴的水平直线度为0.129 μm(总量程为300 mm)。X轴和Z轴的分辨率为0.034 nm,定位精度均优于10 nm,C轴的定位精度为0.6″,高精度的位移系统可以对检测点进行精确地定位。
Performance test Result X-axis horizontal straightness/μm 0.129 X-axis vertical straightness/μm 0.360 Z-axis horizontal straightness/μm 0.063 Z-axis vertical straightness/μm 0.753 X-Z axes squareness/(″) 0.486 C-axis motion error (radial)/μm 7.21 C-axis motion error (axial)/nm 6.58 C-axis positioning accuracy/(″) 0.60 Table 1. Performance test of the lathe
检测用的光学探针选用Precitec公司的彩色共焦探头,并通过垂直调整架针安装于机床之上,如图7所示。调整架和机床轴系的相互配合可以实现探针中心和机床旋转中心的精确对准。表2为探针的检测参数,其测量范围为300 μm,检测精度约为0.1 μm,重复精度为30 nm,Z轴分辨率为3 nm。
装置搭建完成后,基于所提出的抑制方法,对一个直径为60 mm的镍平面进行原位检测。图8(a)为平面的实物图,在表面上粘贴了定位标记,用于数据处理时确定数据点的角度。图8(b)为表面在离线式Zygo干涉仪上的面形检测结果,面形PV值为0.611 μm,RMS值为0.140 μm。
Parameter Specification Measuring range/μm 300 Working distance/mm 4.5 Resolution/nm 3 Spot diameter/μm 5 Lateral resolution/μm 2.5 Numerical aperture 0.5 Measurement angle/(°) 90±30 Measuring accuracy/μm 0.1 Reproducibility/nm 30 Table 2. Parameters of the probe
Figure 8. The measured surface. (a) Nickel flat mirror with diameter of 60 mm; (b) Interferometer test results
首先进行圆周路径检测,工件转速维持60 r/min,探针沿着X轴每间隔0.2 mm进行一次圆环测量,总体检测时间为800 s。圆周检测的面形误差如图9所示,PV值为0.791 μm,RMS值为0.173 μm。
随后进行径向路径检测,以45°为间隔,进行了8次径向测量,每一次径向检测的探针速度设置为15 mm/min。基于所得到的径向数据校正圆周检测面形,结果如图10所示。
抑制后的面形误差PV值为0.697 μm,RMS值为0.146 μm。对环境误差抑制前后的表面形貌做差,如图11所示,偏差的PV值为0.145 μm,RMS值为0.029 μm。由于圆周和径向检测依次进行,且整体测量行程较短,在测量过程中由机床运动所引起的误差可以忽略,二者间检测数据的偏差主要是由环境扰动所引起。
为了验证方法的可重复性,进行了5次重复实验,对比抑制环境误差前后的面形RMS值如图12所示。通过将面形误差的RMS值于与离线式干涉仪进行了对比,处理后的实验数据如表3所示。
Unsuppressed Suppressed Interferometer RMS value/μm 0.174 0.146 0.140 Standard deviation/μm 0.006 0.009 - Deviation from
interferometer/μm0.034 0.006 - Relative error 24.3% 4.3% - Table 3. Experimental data
可以看到,抑制误差前面形RMS均值为0.174 μm,标准差为0.006 μm。抑制后的RMS均值为0.146 μm,标准差为0.09 μm。对比离线式干涉仪的检测结果,抑制前面形的RMS值与离线式干涉仪的偏差为0.034 μm,抑制后RMS的偏差降到了0.006 μm,测量相对误差从24.3%降到了4.3%。证明了提出的离散化路径检测和拼接方法的可靠性,能有效提高环境扰动下的光学检测精度。
High-precision optical measurement method based on discrete path and splicing
doi: 10.3788/IRLA20210144
- Received Date: 2021-03-09
- Rev Recd Date: 2022-06-10
- Publish Date: 2022-11-30
-
Key words:
- optical measurement /
- environmental error /
- path generation /
- data splicing
Abstract: In the manufacturing of ultra-precision optical elements, high-precision optical detection technology is the key to further improve the optical processing accuracy and to characterize and evaluate the optical surface morphology. Non-contact optical detection method has been widely used because of its high efficiency and no damage detection. But the external environment disturbance can easily affect the optical probe and reduce the detection accuracy. Therefore, a method of discrete detection path and splicing is proposed in this paper. The traditional spiral path is divided into multi-circular and multi-path paths. The compensation of environmental disturbance error is realized by the data splicing between paths. The parameter setting of discrete detection path is analyzed, and a uniform distribution strategy of circular path is given. Finally, based on the optical detection platform, the verification experiment of the compensation method of environmental error is carried out. Compared with the uncompensated results, the measurement relative error is reduced from 24.3% to 4.3%.