Variable image distance bending using an elliptical bending mechanism with a constant cross-section mirror
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摘要: 针对新设计的等截面反射镜椭圆压弯机构在固定物距(即反射镜在光路中位置不变)的情况下,研究了实现大范围像距调整(即样品位置发生改变)时镜面面形误差等问题。通过理论分析并借助有限元分析软件计算等截面平面镜压弯至不同(反射点处像距不同)椭圆柱面时的理论斜率误差,最后对椭圆压弯机构样机进行了实际压弯测试。实验结果与计算分析均表明:保持物距、掠入射角不变,压弯镜面与理想椭圆柱面之间的斜率误差会随着像距的减小而增大,并且像距越小,镜面斜率误差的增加速度越大。实验测得在反射镜面初始斜率误差为0.397 μrad的情况下,全部像距范围(21.5~3.8 m)内压弯镜面的实际斜率误差在0.402~0.560 μrad之间,重复精度为0.051 μrad,均满足上海光源光束线的设计要求。本文研究证明了使用等截面反射镜压弯机构进行椭圆柱面压弯可以实现聚焦镜工作像距在大范围内的连续调节。Abstract: In this paper, the surface shape error of latest elliptical bending mechanism with a constant cross-section mirror is studied when the object distance is fixed (when the position of the mirror in the light path is invariable) and the image distance is adjusted drastically (when the position of the sample is changed). Based on theoretical analysis and the finite element analysis, theoretical slope error is calculated when it is caused by bending a mirror with a width equal to an elliptical cylinder with a different shape (different image distances at the reflection point). Then, a bending experiment of a prototype of the elliptical bending mechanism is conducted. Experimental results and analysis indicate that the slope error between the bending mirror and an ideal elliptic cylinder will increase with a decrease in image distance, and the slope error of the mirror will increase more quickly as the image distance is shortened. When the initial slope error of the reflecting mirror is 0.397 μrad, the slope error of the bent mirror in the whole range of image distance (21.5~3.8 m) is 0.402~0.560 μrad and the repeatable accuracy is 0.051 urad, which meets the design requirements of the beamline of the Shanghai Synchrotron Radiation Facility (SSRF). It is proven that in elliptically bending mirrors, continuous adjustment of the image distance from the focusing mirror can be achieved by using a bending mechanism with constant cross-section mirror.
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Key words:
- synchrotron radiation /
- bending mechanism /
- elliptical cylindrical mirror /
- slope error
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表 1 椭圆压弯反射镜的参数及设计指标
Table 1. Parameters and design indexes of elliptical bending mirror
材料 聚焦镜尺寸/mm 镜面有效尺寸/mm 自身斜率误差/μrad 单晶硅 1000×70×50 700×20 0.4 物距p/m 掠入射角θ/mrad 像距q/m 要求压完后
斜率误差/μrad26.5 3.5 21.5~3.8 <0.60 表 2 压弯部件材料属性
Table 2. Material properties of the bending mechanism,s parts
材料 泊松比 杨氏模量/GPa 密度/kg·m−3 Si 0.3 169 2330 结构钢 Structural steel (OCr18Ni9) 0.33 206 7800 轴承钢 Beering steel (Gcr15) 0.3 208 7800 表 3 不同像距下镜面斜率误差RMS值的有限元计算结果
Table 3. FEA results of RMS values of slope error at different image distances
理论像距/m 斜率误差RMS 左右驱动杆位移/mm 21.5 0.013 3.96 4.27 16.5 0.015 4.53 5.18 11.5 0.027 5.57 7.32 8.5 0.035 6.10 7.93 6.5 0.078 7.42 8.96 4.8 0.128 9.05 12.83 3.8 0.242 10.10 17.20 表 4 实际压弯测试结果
Table 4. Actual bending experiment results
理论像距/m 斜率误差RMS/μrad 重复精度/μrad 驱动杆位移/mm 21.5 0.402 0.011 4.13,4.30 16.5 0.409 0.021 4.65,5.05 11.5 0.415 0.013 5.67,6.30 8.5 0.413 0.021 6.35,7.80 6.5 0.439 0.026 7.70,9.55 4.8 0.478 0.023 9.70,13.10 3.8 0.560 0.051 10.55,17.60 -
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