基于圆锥曲线参数方程的渐进多焦点镜片设计 下载: 531次
Progressive addition lenses (PALs) not only solve the problem that the elderly need different focal powers for distance and near visions but also overcome the image jump of bifocal lenses owing to their continuously varying focal power along the meridian. Therefore, PAL design methods have a broad development prospect. PALs are mainly designed by a direct method and an indirect method. Although the indirect method offers convenient design, its prism is large when the focal power changes. The design of PALs by the direct method has the disadvantage that the maximum peripheral astigmatism exceeds two times the addition power (ADD) according to the Minkwitz theorem. Nevertheless, the direct method has relatively favorable advantages for the distance and near areas. The optimization of the direct method in China and abroad mainly focused on the changes in the focal power along the meridian, the optimization of the local average focal power, and the calculation equations for different surface heights. In contrast, how to obtain reasonable focal power profile distributions on the lenses has rarely been reported. In addition, a conic parametric equation can be changed into an equation satisfying the conditions of the focal power profile distribution along the meridian. Therefore, this paper proposes a method based on a conic parametric equation to reasonably distribute the focal power profile on the entire lens, achieve the design of PALs by the direct method, and ultimately reduce peripheral astigmatism.
On the basis of the principles of geometry and the direct method, the law of curvature change along the meridian of the lens is determined to satisfy the trigonometric function in this study, and the surface height equation is calculated as a spherical equation. Specifically, the function of the focal power profile distribution is solved by the circular parametric equation and also by the hyperbolic, parabolic, and elliptic equations. Then, the four sets of surface height data are used to simulate the focal power and astigmatism of the lenses in the simulation software. The designed lenses are processed and tested by the free-form surface machining machine, and the experimental results are verified. Finally, the influences of different conic parametric equations, i.e., hyperbolic, parabolic, elliptic, and circular equations, are analyzed for the optical properties, such as the focal power and astigmatism, of the lenses.
Theoretical analysis, actual processing, detection, and comparison reveal that the method of solving the focal power profiles of lenses by conic parametric equations is feasible (Fig. 7). The actual focal power in the distance area and ADD of the four groups of lenses meet the national standard (GB 10810.1—2005). The conic parametric equations mainly include the hyperbolic, parabolic, elliptic, and circular equations, and different equations can be used to design the focal power profile on the whole lens. Moreover, the width of the distance and near areas can be set as required, and the distribution of peripheral astigmatism can be adjusted. With the same parameter (Table 1), the maximum peripheral astigmatism of the lens obtained by solving the hyperbolic equation is 1.36 times the ADD, and the visual effect is relatively poor (Table 2); the distortion of the lens on the periphery of its area of the fixed focal power calculated by the elliptic equation is the smallest. The maximum peripheral astigmatism of the lens obtained by solving the parabolic equation is the smallest, and the corresponding ratio of the maximum peripheral astigmatism of the lens to the ADD is also the smallest. The area with peripheral astigmatism larger than 1.75 D on the lens obtained by solving the elliptic equation is relatively small (Fig. 8), and the width of the actual visible area at the fixed focal power point in the distance area is the largest. Therefore, the elliptic equation can be used as the basis for further optimization design in the future.
In this paper, the focal power profile distributions obtained by four different conic equations are proposed to design PALs, and the four groups of lenses are simulated, evaluated, and processed. The results show that the focal power profile distributions obtained by different conic equations have an impact on the design of PALs. With the design parameters, the peripheral astigmatism of the lens obtained by solving the hyperbolic equation is large and thus highly likely to cause severe vertigo when people wear such lenses to look around. In contrast, the peripheral astigmatism of the lenses calculated by the elliptic, circular, and parabolic equations is all smaller than that calculated by the hyperbolic equation. On this basis, variables are added to control the size of the distance and near areas so that the visible area at the fixed focal power point can be adjusted. However, a larger area of the fixed focal power corresponds to larger distortion and dispersion of the spherical lens. Consequently, the actual width at the fixed focal power point will be smaller than the theoretical value. When the area of the fixed focal power is small, the distortion of the PAL designed on the basis of the circular equation on the periphery of its area of the fixed focal power is the smallest. In future research, the inner surface of PALs can be transformed from a spherical design to an aspherical design on the basis of this design method to further study the optimal design of PALs, reduce the tangential error, and obtain more accurate actual results.
1 引言
渐进多焦点镜片(PAL)子午线上的光焦度具有连续变化的特点,既解决了老年人由于视远和视近需要不同光焦度的问题,又克服了双光镜片两个校正区域之间的像跳。因此,渐进多焦点镜片的设计具有良好的发展前景[1-2]。
目前渐进多焦点镜片设计方法主要有Winthrop法(直接法)和间接法。间接法设计方便,但其光焦度变化时产生的像散较大。使用直接法设计渐进多焦点镜片存在周边最大像散超过1倍加光度(ADD)的缺点,但该方法具有相对较好的远用和近用区域优势[3]。1992年,Winthrop[4]使用柱面与多个球面相交的方法得到整个渐进表面的光焦度分布;2011年,唐运海等[5]利用平均曲率流对初始设计的渐进多焦点镜片进行局部优化,以减小指定区域的像散;2012年,秦琳玲等[6]也通过对补偿平均曲率来降低周边像散;2014年,唐运海等[7]提出运用遗传算法来寻找渐进多焦点眼镜片最优子午线的设计方案;2015年,Spratt等[8]根据眼睛波前测量得到的信息,修改镜片的初始设计;2017年,张皓等[9]使用分离变量法和傅里叶变换法求解满足光焦度轮廓线分布的拉普拉斯方程,从求解方法上优化镜片设计;2020年,Moon等[10]从瞳孔中心之间的距离获得指数曲线,从而确定通道长度;2022年,张海平等[11]将内表面矢高表达式从球面公式改为非球面公式。
综上,国内外研究人员主要从子午线上的光焦度变化、局部平均光焦度优化和不同矢高计算方程等方面对直接法进行优化,而对于如何得到镜片上合理的光焦度轮廓分布的研究较少,因此找到一种合适的光焦度分布轮廓函数来实现渐进镜片光学性能的优化十分重要。本文在已有研究[4,12-13]的基础上,首先设置子午线上曲率变化规律满足三角函数。其次,将不同圆锥曲面与圆柱面相交引入圆锥曲线方程,重新设计镜片光焦度轮廓分布。通过对镜片光焦度轮廓进行定义,控制远近视区域大小,将光焦度轮廓线函数代入矢高方程得到整个面型。然后,仿真加工了4块镜片,并进行对比。最后,通过仿真软件进行镜片光焦度仿真,并利用自由曲面加工机床对设计镜片进行加工和检测,对实验结果进行验证。
2 基本原理
采用内渐进球面设计方法[4]。如
为了确定渐进多焦点镜片的内表面矢高
式中:
如
式中:
通过
3 镜片光焦度轮廓设计
3.1 光焦度轮廓原理
由函数
对于光焦度轮廓,在设计的镜片左右对称的情况下,当
式中:a为斜率;b为函数
只要满足
式中:
根据
图 4. 不同圆锥曲线方程的平面分布图。(a)双曲线;(b)抛物线;(c)椭圆;(d)圆
Fig. 4. Plane distribution of different conic equations. (a) Hyperbola; (b) parabola; (c) ellipse; (d) circle
3.2 光焦度轮廓设计
根据
当
式中:
将
为保证移动后通道长度不变,
假设当
当输入
4 设计实例及分析
为了分析不同光焦度轮廓设计对光学性能[15-17]的影响,设计实例选取远视区光焦度(SPH)、ADD(ADD)、折射率、远视区像散(CYL)、镜片中心厚度(CT)等作为镜片参数,它们的取值如
将
表 1. 4组渐进多焦点镜片的设计参数
Table 1. Design parameters of four sets of progressive addition lenses
|
图 6. 基于不同圆锥曲线方程求解得到的u(x,y)等高线图。(a)双曲线;(b)抛物线;(c)椭圆;(d)圆
Fig. 6. u(x,y) contour maps obtained by solving different conic curve equations. (a) Hyperbola; (b) parabola; (c) ellipse; (d) circle
表 2. 4块渐进多焦点镜片的实际测量结果
Table 2. Actual measurement results of four progressive addition lenses
|
使用FFV软件对得到的镜片矢高矩阵进行仿真,得到对应的光焦度分布图和像散分布图,分别如
图 7. 4种光焦度轮廓分布的FFV软件仿真结果。(a)双曲线;(b)抛物线;(c)椭圆;(d)圆
Fig. 7. FFV software simulation results of four focal power distributions. (a) Hyperbola; (b) parabola; (c) ellipse; (d) circle
图 8. 4种像散分布的FFV软件仿真结果。(a)双曲线;(b)抛物线;(c)椭圆;(d)圆
Fig. 8. FFV software simulation results of four different astigmatism distributions. (a) Hyperbola; (b) parabola; (c) ellipse; (d) circle
使用自由曲面加工机床对所设计的镜片进行加工,并使用VM2000自由曲面检测仪器对镜片进行测量[19],得到4块镜片的光焦度和像散分布图,如
图 9. 4种光焦度轮廓分布的实际测量结果。(a)双曲线;(b)抛物线;(c)椭圆;(d)圆
Fig. 9. Actual measurement results of four focal power distributions. (a) Hyperbola; (b) parabola; (c) ellipse; (d) circle
图 10. 4种光散像分布的实际测量结果。(a)双曲线;(b)抛物线;(c)椭圆;(d)圆
Fig. 10. Actual measurement results of four optical astigmatism distributions. (a) Hyperbola; (b) parabola; (c) ellipse; (d) circle
使用NIDEK的LM-1800P焦度计测量4块镜片的定焦点光焦度、周边像散最大值、ADD、远视区角度、近视区角度、
综合
5 结论
利用4种圆锥曲线方程的光焦度轮廓分布来设计渐进多焦点镜片,并对获得的4块镜片进行仿真评价与加工检测,结果表明,由不同圆锥曲线方程求解得到的光焦度轮廓分布对渐进镜片设计的影响不同。基于渐进多焦点镜片的设计参数,采用双曲线方程设计得到的镜片周边像散为ADD的1.36倍,人佩戴该镜片往四周看物体时,容易产生强烈的眩晕,而采用椭圆方程、圆和抛物线方程计算得到的镜片周边像散较小。在此基础上加入控制变量,实现远近视区定焦点处可视区域的调整。但由于定焦区域越大,球面镜片畸变和像散越大,因此实际定焦点处的宽度会小于理论值。当定焦区较大时,基于椭圆方程设计的渐进自由曲面镜片定焦区周边畸变最小;当定焦区较小时,基于圆方程设计的渐进自由曲面镜片定焦区周边畸变最小。未来可在该设计方法的基础上,将渐进多焦点镜片的内表面从球面设计转变为非球面设计,从而进一步研究渐进镜片的优化设计方案,减小切向误差,使得实际结果更精确。
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Article Outline
詹小蝶, 项华中, 王亚琼, 张云进, 张欣, 丁琦慧, 郑泽希, 王成, 张大伟, 陈家璧, 庄松林. 基于圆锥曲线参数方程的渐进多焦点镜片设计[J]. 光学学报, 2023, 43(7): 0722001. Xiaodie Zhan, Huazhong Xiang, Yaqiong Wang, Yunjin Zhang, Xin Zhang, Qihui Ding, Zexi Zheng, Cheng Wang, Dawei Zhang, Jiabi Chen, Songlin Zhuang. Design of Progressive Addition Lenses Based on Conic Parametric Equations[J]. Acta Optica Sinica, 2023, 43(7): 0722001.