1、 ISO 2017 Ophthalmic optics and instruments Free form technology Spectacle lenses and measurement Optique et instruments ophtalmiques Technologie free form Verres de lunettes et mesurage TECHNICAL REPORT ISO/TR 18476 Reference number ISO/TR 18476:2017(E) First edition 2017-06 ISO/TR 18476:2017(E)ii
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4、2 749 09 47 copyrightiso.org www.iso.org ISO/TR 18476:2017(E)Foreword iv 1 Scope . 1 2 Normative references 1 3 T erms and definitions . 1 4 Technical introduction . 1 4.1 Preliminaries 1 4.2 What is free form? 1 4.3 Does free form equal better vision? 2 4.4 Classification . 2 5 Manufacturing . 3 5.
5、1 General . 3 5.2 Conventional surfacing 4 5.3 Free form surfacing . 5 5.4 Comparison of conventional and free form manufacturing . 6 6 P ot ential benefits of fr ee form lens calculation . 7 6.1 Oblique astigmatism 7 6.2 Limitations of conventional lenses 9 6.3 Potential benefit of free form lens d
6、esign .10 6.4 Optimization for prescription .11 6.5 Customization for the as-worn position 12 6.5.1 Explaining the as-worn position .12 6.5.2 As-worn position and verification power .13 6.6 Customization for the frame size .14 6.7 Personalization of the lens design 15 7 Measurement and quality contr
7、ol .16 7.1 Lens performance 16 7.2 Conformity with standards .16 7.3 Design integrity and process control 17 7.3.1 General.17 7.3.2 Surface shape measurement .17 7.3.3 Through power measurement 17 7.4 Measuring the as-worn position .18 7.5 Inspection gates of the manufacturing process .21 Annex A (i
8、nformative) T ypical dispensing flo w chart .22 Annex B (informative) Measurement technology 23 Annex C (informative) Glossary of terms and their descriptions 28 Bibliography .30 ISO 2017 All rights reserved iii Contents Page ISO/TR 18476:2017(E)Foreword ISO (the International Organization for Stand
9、ardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right
10、to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. The procedures u
11、sed to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types of ISO documents should be noted. This document was drafted in accordance with the editorial rules
12、 of the ISO/IEC Directives, Part 2 (see www. iso. org/ directives). Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent rights iden
13、tified during the development of the document will be in the Introduction and/or on the ISO list of patent declarations received (see www. iso. org/ patents). Any trade name used in this document is information given for the convenience of users and does not constitute an endorsement. For an explana
14、tion on the voluntary nature of standards, the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISOs adherence to the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following URL: www .iso. org/ i
15、so/ foreword. html. This document was prepared by Technical Committee ISO/TC 172, Optics and photonics, Subcommittee SC 7, Ophthalmic optics and instruments. iv ISO 2017 All rights reserved TECHNICAL REPORT ISO/TR 18476:2017(E) Ophthalmic optics and instruments Free form technology Spectacle lenses
16、and measurement 1 Scope This document outlines all the steps from refraction to dispensing of spectacles, with particular attention to the benefits added by using free form technology, and provides a collection of relevant terms and descriptions. This document does not contain the proprietary featur
17、es of lens designs provided by suppliers. 2 Normative references There are no normative references in this document. 3 T erms a nd definiti ons No terms and definitions are listed in this document. ISO and IEC maintain terminological databases for use in standardization at the following addresses: I
18、EC Electropedia: available at h t t p :/ www .electropedia .org/ ISO Online browsing platform: available at h t t p :/ www .iso .org/ obp 4 Technical introduction 4.1 Preliminaries 4.1.1 There are various ways of spelling the term “free form”. This document uses two separate words. 4.1.2 There are v
19、arious terms explaining spectacle lens optical power design which are commonly used such as “optical function”, “optical characteristics”, “optical properties”, or “design property”. For purpose of simplicity, this document uses the word “characteristics”. The phrase “optical properties” is used sim
20、ply to describe the optical results of the geometry of the lens, but not an intended design or characteristic. 4.1.3 A typical flowchart including refraction, dispensing and manufacturing is shown in Figure A.1 (see Annex A). 4.1.4 A glossary of terms and their descriptions is provided in Annex C. 4
21、.2 What is free form? In ophthalmic optics, the term “free form surfacing” refers to a spectacle lens surfacing process that is capable of producing continuous, smooth, non-symmetrical lens surfaces that lack point, axial or plane symmetry and are described by three-dimensional coordinates created b
22、y mathematical formulation. This design and surfacing process enables optimization of the lens performance. Conventional lens surfacing technology which smooths and polishes using hard lap tools can produce only simple spherical or toroidal lens surfaces. ISO 2017 All rights reserved 1 ISO/TR 18476:
23、2017(E) Modern free form lens surfacing methods are now capable of generating surfaces that are much more complex than simple spherical and toroidal surfaces, allowing local optical laboratories to manufacture progressive-power and other lens designs directly onto the lens blank with the required pr
24、escription curves. In order to produce these complex surface shapes, free form surfacing utilizes precise, computer- driven control of the cutter with three or more axes of movement. Often, the surface is machined using single-point diamond turning and then polished using flexible lap tools. A “free
25、 form process” can thus be summarized as a lens surfacing process using Computer Numeric Control (CNC) devices capable of producing a free form surface with optical characteristics on either or both side(s) of the lens. It should be noted that when simpler surfaces that can be manufactured by conven
26、tional methods are produced by free form processing, these simpler surfaces should not be termed free form surfaces nor the resulting lenses free form lenses. 4.3 Does free form equal better vision? As an enabling technology, free form surfacing makes possible the application of optical characterist
27、ics, using information specific to the individual wearer, immediately prior to lens manufacture. The use of free form surfacing as a manufacturing method does not guarantee any visual benefit to the wearer. It is true that the soft lap tool polishing process used during free form surfacing is not su
28、bject to the rounding errors of conventional lens surfacing. Conversely, it can maintain an accurately generated free form surface. Hence, soft lap polishing actually relies on more extensive process engineering and quality control in order to achieve high quality lens surfaces. Free form surfacing
29、provides a powerful vehicle for overcoming the limitations of conventional semi- finished lens manufacturing when utilized in conjunction with sufficiently advanced optical design software by delivering lenses custom-designed for the specific visual requirements of the individual wearer. It becomes
30、possible to optimize the optical design of the lens individually (i.e. upon the exact prescription power and orientation of the fitted lens) before the lens is actually manufactured, in order to preserve the intended optical lens characteristics for each and every wearer. In addition to preserving t
31、he intended optical lens characteristics for any combination of prescription power or as-worn position, it is also possible to customize other features of the lens design for the individual wearer. The lens can be adapted further in order to modify the corridor length for the fitting height in small
32、 increments, optimize the viewing zones for occupational demands, and adjust peripheral power gradients for the head-eye movement behaviour, and so on. It is important to note, however, that only custom-designed free form lenses will offer this level of sophistication and design properties for the w
33、earer. Nevertheless, without the application of real-time optical design to optimize the lens design for the individual wearer, the potential visual advantages of using free form surfacing are relatively small. 4.4 Classification With free form surfacing, an optical laboratory can surface a variety
34、of lens designs directly onto a semi-finished lens blank in addition to the prescription curves that are normally applied. With two separate surfaces to work with, the optical characteristics, addition power, if any, and prescription components of a free form lens can be applied to the lens blank in
35、 a variety of possible lens surface configurations. Each type of free form lens represents a particular combination of factory-moulded and directly-surfaced lens curves. The lens surfaces involved range in complexity from simple spherical surfaces to individually-optimized progressive power surfaces
36、 that simultaneously fulfil all of the prescription requirements of the wearer.2 ISO 2017 All rights reserved ISO/TR 18476:2017(E) When free form surfacing is used to transfer the optical characteristics onto the lens blank, free form progressive-power lenses may be classified by the distribution of
37、 the optical characteristics between the front and back surfaces (see Figure 1). a) Front surface free form lenses (A in Figure 1) employ a directly-surfaced progressive surface with the full addition power on the front and conventionally-surfaced prescription curves on the back. The progressive opt
38、ics are surfaced directly onto the lens. While less common, this configuration may, for instance, be utilized to achieve broader prescription ranges. b) Dual-surface free form lenses (B in Figure 1) employ a factory-moulded (or, in some cases, a directly- surfaced) progressive-like surface with a co
39、mponent of the total addition power on the front and a digitally-surfaced progressive surface with, for instance, the remaining addition power that has been combined with the prescription curves on the back. The progressive-power optics are distributed between both lens surfaces. c) Back-surface fre
40、e form lenses (C in Figure 1) employ a factory-moulded spherical surface on the front and a directly-surfaced progressive surface that has been combined with the prescription curves on the back. The progressive lens design may be a standard (fixed) design or an optically- optimized design. For the p
41、urpose of simplicity, the rest of this document will refer only to full back surface lenses (C in Figure 1). NOTE Image by Darryl Meister. Reproduced with permission from Carl Zeiss Vision GmbH, USA. F i g u r e 1 C l a s s i f i c a t i o n o f f r e e f o r m p r o g r e s s i v e - p o w e r l e
42、n s e s b y t h e d i s t r i b u t i o n o f t h e addition power between the front and back surfaces 5 Manufacturing 5.1 General Whatever the process used to manufacture the lens, the lens manufacturing cycle is the same. The general lens manufacturing flow is described in Figure 2. F i g u r e 2
43、G e n e r a l l e n s m a n u f a c t u r i n g f l o w w i t h s e m i - f i n i sh e d l e n s b l a n k s a n d s u r f a c i n g ISO 2017 All rights reserved 3 ISO/TR 18476:2017(E) 5.2 Conventional surfacing Conventional surfacing is a four-step process for finishing the unfinished back surface
44、of a semi- finished lens blank with the required prescription curves (see Figure 3). Semi-finished lens blanks have an optical-quality front surface that has been moulded by a manufacturer. In the first step termed “blocking”, the semi-finished lens blank is mounted by its finished surface on a supp
45、ort to hold it for the next three steps. In the second step, the unfinished surface of the lens is machined by a generator to approximately the required shape using a grinding, turning or milling process. In the third step, known as fining or smoothing, the worked surface is ground to the precise su
46、rface shape by a toroidal smoothing/polishing machine that rapidly moves the lens surface in a cyclical motion over a hard lap tool fitted with abrasive pads that matches the intended curvature of lens surface. This brings the lens surface to a quality suitable for polishing. In the fourth and final
47、 manufacturing step, known as polishing, the abrasive pad is replaced by a polishing pad. The lens surface is once again cycled over the hard lap tool in a toroidal smoothing/polishing machine, while the pad is soaked with polishing slurry. The lens is then “de-blocked”. See Figure 3 a) and b). In F
48、igure 3 b) the hard lap tool copies the fixed two principal meridians curvatures to the lenss concave surface. a) Scheme of conventional surfacing process b) Fining process used in conventional surfacing Figure 3 Conventional surfacing process The simplest generators are two-axis machines that utili
49、ze a diamond-impregnated grinding wheel to generate a spherical or toroidal lens surface. The emphasis of a conventional generating process is on throughput and rapid removal of lens material. Any inaccuracy in the shape of the generated lens surface is ultimately corrected during the fining process by the hard lap tool. In particular, the fining process with hard lap tools exploits the rotational or meridional circular symmetry of spherical or toroidal lens surfaces, since these surfaces can be cycled over the hard lap tool using a unif
