Slow tool servo diamond turning of optical freeform surface for astigmatic contact lens

Chen, Chun‐Chieh; Cheng, Yung‐Chen; Hsu, Wei-Yao; Chou, Hsiao-Yu; Wang, Pei-Jen; Tsai, Din Ping

doi:10.1117/12.892447

Cited by 13 publications

(9 citation statements)

References 6 publications

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“…3 By measuring the ogive form error of the sample after machining, it is possible to directly assess the tool offset error using the following equation:…”

Section: In a 2-axis Configurationmentioning

confidence: 99%

Tool offset optimisation for the machining of free-form optics with a non-zero gradient at the centre

Bourgenot

Robertson

2015

SPIE Proceedings

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Free form surfaces are now commonly used components in optics applications and can be widely found in fields such as ophthalmics, car illumination and head-up display systems and laser optics. The machining of free form optics on a 3-axis diamond turning machines is made possible with the use of tool servo machining which synchronises either or both the axial and radial motions of the tool and surface positions (X & Z axes) to the angular position of the spindle (C axis). However, the machining of surfaces with non-zero gradient at the surface centre is particularly troublesome because the tool is still subject to a relatively large amplitude motion when reaching the central area of the surface. As a result, a small tool offset in either X (radial) or Y (height) creates a particular central signature that can be readily identified, measured and subsequently corrected by the machine operator. In this paper, we report on a method to optimise the tool offset (X axis) in the particular case of non-zero central gradient and illustrate our discussion with simulation and measurement results.

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“…3 By measuring the ogive form error of the sample after machining, it is possible to directly assess the tool offset error using the following equation:…”

Section: In a 2-axis Configurationmentioning

confidence: 99%

Tool offset optimisation for the machining of free-form optics with a non-zero gradient at the centre

Bourgenot

Robertson

2015

SPIE Proceedings

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“…Parameters range of LS-SVM was set as [2 −8 , 2 11 ] for the regularization parameter γ and [2 −10 , 2 8 ] for kernel parameter σ 2 . In CPSO, both learning factors were set to 2.0, linearly varying inertia weight was varying form 0.9 at the beginning of the search to 0.4 at the end, the population size was 20, the maximum number of iterations was 1,000, and the stopping criterion for CLS was 50.…”

Section: Ls-svm Modelingmentioning

confidence: 99%

“…Toric and progressive addition lenses (PAL) are a kind of opthalmic lenses with freeform surface, and their application is limited for a long time by the difficulty to design and manufacture. At present, freeform surfaces can be machined by fast tool servo [1][2][3][4], micro-milling [5][6][7], fly-cutting or raster milling [8,9], and slow tool servo (STS) [10][11][12][13][14] etc. Among these technologies, with the advantages of high surface accuracy and high machining efficiency, STS is gradually applied to machine freeform surface.…”

Section: Introductionmentioning

confidence: 99%

“…One of such improvements can be made to STS turning by developing predictive models for surface roughness. There were a few papers discussing fabrication of freeform surface using STS [10][11][12][13][14], and path planning and error compensation [10,15,16] were also reported. However, little literature dealt with the prediction of surface topography using STS.…”

Section: Introductionmentioning

confidence: 99%

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Predictive modeling of surface roughness in lenses precision turning using regression and support vector machines

Wang

Kang

et al. 2013

Int J Adv Manuf Technol

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Slow tool servo (STS) turning is superior in machining precision and in complicated surface. However, STS turning is a complex process in which many variables can affect the desired results. This paper focuses on surface roughness prediction in lenses STS turning. An exponential model, based on the five main cutting parameters including tool nose radius, feed rate, depth of cut, C-axis speed, and discretization angle, for surface roughness prediction of lenses is developed by means of orthogonal experiment regression analysis. Meanwhile, a prediction model of surface roughness based on least squares support vector machines (LS-SVM) with radial basis function is constructed. Orthogonal experiment swatches are studied, and chaotic particle swarm optimization and leaveone-out cross-validation are applied to determine the model parameters. The comparison of LS-SVM model and exponential model is also carried out. Predictive LS-SVM model is found to be capable of better predictions for surface roughness and has absolute fraction of variance R 2 of 0.99887, the mean absolute percent error e M of 8.96 %, and the root mean square error e R of 10.68 %. The experimental results and prediction of LS-SVM model show that effects of tool nose radius and feed rate are more significant than that of depth of cut on surface roughness of lenses turning.

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“…This extra degree of freedom enables 3-D fabrication of non-rotationally symmetric objects like lens arrays. Although fast and fully automated, the edge slopes of lenses fabricated by STS and FTS are limited by the diamond tool's relief angle [8][9][10][11]. STS/FTS tools with a 40° relief angle have recently become available [12], but it is impossible to achieve a 90° relief angle.…”

Section: Introductionmentioning

confidence: 99%

Rapid fabrication of miniature lens arrays by four-axis single point diamond machining

McCall¹,

Tkaczyk²

2013

Opt. Express

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A novel method for fabricating lens arrays and other nonrotationally symmetric free-form optics is presented. This is a diamond machining technique using 4 controlled axes of motion -X, Y, Z, and C. As in 3-axis diamond micro-milling, a diamond ball endmill is mounted to the work spindle of a 4-axis ultra-precision computer numerical control (CNC) machine. Unlike 3-axis micro-milling, the C-axis is used to hold the cutting edge of the tool in contact with the lens surface for the entire cut. This allows the feed rates to be doubled compared to the current state of the art of micro-milling while producing an optically smooth surface with very low surface form error and exceptionally low radius error.

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Slow tool servo diamond turning of optical freeform surface for astigmatic contact lens

Cited by 13 publications

References 6 publications

Tool offset optimisation for the machining of free-form optics with a non-zero gradient at the centre

Tool offset optimisation for the machining of free-form optics with a non-zero gradient at the centre

Predictive modeling of surface roughness in lenses precision turning using regression and support vector machines

Rapid fabrication of miniature lens arrays by four-axis single point diamond machining

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