HRP920919A2

HRP920919A2 - Dual grooved fresnel lens for overhead projectors

Info

Publication number: HRP920919A2
Application number: HR920919A
Authority: HR
Inventors: Dennis F Vanderwerf
Original assignee: Minnesota Mining & Mfg
Priority date: 1988-12-16
Filing date: 1992-10-02
Publication date: 1995-06-30
Also published as: HRP920919B1

Description

Prikazani izum se općenito odnosi na epidijaskope, a posebno na kondenzatorske leće za takve projektore. The presented invention generally relates to epidiascopes, and in particular to condenser lenses for such projectors.

Konvencionalne Fresnelove leće koje se koriste kao kondenzatori, koncentratori i veće leće u okularima ili objektivima, obično su u vidu jednog elementa sa prizmatičnim kružnim žljebovima na jednoj strani i ravnom površinom na drugoj strani. Kada je potrebna velika svjetlosna popustljivost pri malim f brojevima, dvije takve leće se koriste zajedno i sljepljuju se zajedno po vanjskim rubovima. Kako se ove leće obično nalaze blizu ravnine slike ili ploče projektora, na projektiranoj slici mogu se pojaviti tzv. Svilaste interferencijske šare ukoliko se središta kružnih struktura žljebova ne poklapaju unutar jedne određene tolerancije. Conventional Fresnel lenses, used as condensers, concentrators, and larger lenses in eyepieces or objectives, are usually a single element with prismatic circular grooves on one side and a flat surface on the other. When high light tolerance is required at small f-numbers, two such lenses are used together and glued together at the outer edges. As these lenses are usually located close to the image plane or projector panel, so-called Silky interference patterns if the centers of the circular groove structures do not match within a certain tolerance.

Fresnelova leća sa jednim elementom, koja ima identičnu strukturu žljebova sa obje strane, opisana je u japanskom patentu 57-109618. U tom patentu izvedena su dva identična kalupa od iste strukture žljebova i veoma su precizno poravnana u jednom alatu koji koristi stupove za vođenje. Leća se izrađuje sipanjem jedne termoplastične smole između kalupa poslije čega se primjenjuju toplina i tlak. A single-element Fresnel lens, which has an identical groove structure on both sides, is described in Japanese patent 57-109618. In that patent, two identical molds are made of the same groove structure and are very precisely aligned in one tool that uses guide posts. The lens is made by pouring a single thermoplastic resin between molds, after which heat and pressure are applied.

Takva dvo-elementna leća ima ekonomske prednosti u odnosu na konvencionalnu konstrukciju sa dvije leće, budući je potreban samo jedan list materijala za leću. Nažalost, zahtjev da središta ožljebljenih površina budu poravnana u uskim tolerancijama, povećava cijenu upotrebljive dvoelementarne leće, pa joj to u izvjesnoj mjeri smanjuje prednosti. Such a two-element lens has economic advantages over conventional two-lens construction, since only one sheet of lens material is required. Unfortunately, the requirement that the centers of the grooved surfaces be aligned within tight tolerances increases the cost of a usable two-element lens, so this reduces its advantages to a certain extent.

Ako se želi smanjiti cijena izrade jedne upotrebljive dvoelementarne leće izostavljanjem ili ublažavanjem zahtjeva za vrlo točno poravnavanje središta ožljebljenih elemenata za obje strane leće. If it is desired to reduce the cost of making a usable two-element lens by omitting or relaxing the requirement for very accurate center alignment of the grooved elements for both sides of the lens.

Prikazani izum daje jedno elementnu, dvostrano ožljebljenu Fresnelovu leću sa neidentičnim strukturama žljebova, koristeći konvencionalnu tehniku lijevanja u kalupima pod tlakom. Kutovi žljebova su projektirani da ostvare maksimalnu propustljivost za svjetlost, pri čemu su frekvencije žljebova obje površine pažljivo kontrolirane da bi se smanjila potreba za precizno poravnavanje središta, kako bi se otklonila spomenuta svilenasta šara. The presented invention provides a single-element, double-sided grooved Fresnel lens with non-identical groove structures, using a conventional pressure die casting technique. The angles of the grooves are engineered to achieve maximum light transmission, with the groove frequencies of both surfaces carefully controlled to minimize the need for precise center alignment to eliminate the aforementioned silk pattern.

Ovaj se izum sastoji od veoma provodljive, jednoelementne, dvostrano ožljebljene Fresnelove leće malog f-broja. Naspramne strukture žljebova su projektirane za veliku svjetlosnu propustljivost, a odnos frekvencija žljebova između dvije površine izabran je da svede na minimum pojavu svilenaste šare, čak i kada kalupi za lijevanje nisu precizno centrirani za vrijeme lijevanja leće. This invention consists of a highly conductive, single-element, double-sided grooved Fresnel lens with a small f-number. Opposite groove structures are designed for high light transmission, and the groove frequency ratio between the two surfaces is chosen to minimize the appearance of a silk pattern, even when the casting molds are not precisely centered during lens casting.

Točnije, izum je jedna poboljšana dvostrano ožljebljena Fresnelova leća kod koje jedan jedini list materijala leće sadrži ožljebljene Fresnelove elemente na obje velike površine ove leće, a frekvencija žljebova na jednoj velikoj površini ove leće je najmanje četiri puta veća od frekvencije žljebova na drugoj velikoj površini, a nije cijeli umnožak frekvencije žljebova na drugoj velikoj površini, čime se smanjuje tzv. Svilenasta interferencija. More specifically, the invention is an improved double-sided grooved Fresnel lens in which a single sheet of lens material contains grooved Fresnel elements on both large surfaces of this lens, and the frequency of grooves on one large surface of this lens is at least four times greater than the frequency of grooves on the other large surface, and is not the whole multiple of the frequency of the grooves on the second large surface, which reduces the so-called Silky interference.

Kod preporučljivog izvođenja izuma, frekvencija žljebova na spomenutim Fresnelovim elementima na jednoj glavnoj površini iznosi oko 7,45 puta frekvenciju žljebova Fresnelovih elemenata na drugoj velikoj površini. In the recommended embodiment of the invention, the frequency of the grooves on the mentioned Fresnel elements on one main surface is about 7.45 times the frequency of the grooves of the Fresnel elements on the other large surface.

Prikazani izum bit će detaljnije opisan sa pozivom na priloženi crtež gdje se isti brojevi odnose na iste dijelove u nekoliko projekcija, pri čemu: The presented invention will be described in more detail with reference to the attached drawing where the same numbers refer to the same parts in several projections, whereby:

- slika 1 prikazuje presjek dvostruko ožljebljene Fresnelove leće prema prikazanom izumu. - figure 1 shows a section of a double grooved Fresnel lens according to the presented invention.

Slika 1 prikazuje dvostrano ožljebljenu Fresnelovu leću, uobičajeno označeno sa 10, prema prikazanom izumu. Pojam “dvostrano” odnosi se na činjenicu da je leća 10 izlivena od jednog jedinog lista materijala sa kružnim Fresnelovim elementima 12 i 14 ulivenim u svaku od velikih površina tog lista. Kod konvencionalnih dvostrano ožljebljenih leća važno je za otklanjanje ili za smanjenje svilenaste interferencije da središta 16 i 18 kružnih Fresnelovih elemenata budu poravnana u uskim tolerancijama. Ovo poravnanje je posebno kritično kada su frekvencije žljebova ovih dviju površina identične, ili skoro identične. Figure 1 shows a double-sided grooved Fresnel lens, commonly designated 10, according to the disclosed invention. The term "double sided" refers to the fact that the lens 10 is cast from a single sheet of material with circular Fresnel elements 12 and 14 molded into each of the large surfaces of that sheet. With conventional double-sided grooved lenses, it is important to eliminate or reduce silk interference that the centers 16 and 18 of the circular Fresnel elements are aligned within tight tolerances. This alignment is especially critical when the groove frequencies of these two surfaces are identical, or nearly identical.

U praksi je, međutim, teško poravnati dva kalupa u konvencionalnoj operaciji lijevanja pod tlakom. Da bi se održalo ravnanje središta potrebno je da se otkloni svilenasta interferencija. Utvrđeno je, međutim, da se reguliranjem odnosa frekvencije žljebova ova dva elementa svilenasta šara može svesti na zanemarljiv intenzitet, čak i kada središta nisu poravnana. Točnije, utvrđeno je da se ovo dešava kada je frekvencija žljebova jedne od ožljebljenih površina najmanje četiri puta veća od druge, a nije cijeli umnožak iste. Ovaj odnos frekvencija žljebova može se zadovoljiti bilo konstantnom, bilo promjenjivom širinom žljebova za svaku od površina. In practice, however, it is difficult to align the two molds in a conventional die casting operation. In order to maintain the alignment of the center, it is necessary to remove the silk interference. It was found, however, that by regulating the frequency ratio of the grooves of these two elements, the silk pattern can be reduced to negligible intensity, even when the centers are not aligned. More precisely, it was determined that this happens when the frequency of the grooves of one of the grooved surfaces is at least four times higher than the other, and is not a whole multiple of the same. This ratio of groove frequencies can be satisfied by either a constant or a variable groove width for each of the surfaces.

Jedan specifičan primjer je dan za dvostrano ožljebljenu leću 10 koja se koristi u epidijaskopu. Kutovi žljebova Fresnelovih elemenata 12 i 14 koncizno su opisani slijedećom formulom, koja je izvedena iz formule ugiba jedne općenite asferične površine: One specific example is given for a double-sided grooved lens 10 used in an epidiascope. The angles of the grooves of the Fresnel elements 12 and 14 are concisely described by the following formula, which is derived from the formula of the deflection of a general aspheric surface:

[image] [image]

Y = rastojanje od središta leće do središta žlijeba Y = distance from the center of the lens to the center of the groove

a = kut pojedinačnog žlijeba u odnosu na ravninu leće a = angle of the individual groove in relation to the plane of the lens

C = krivina vrha C = tip curvature

K = konusna konstanta K = conic constant

d, e, f, g = koeficijenti asferičke deformacije d, e, f, g = aspheric deformation coefficients

Dvostrano ožljebljena Fresnelova leća 10, koja se koristi za projektiranje epidijaskopom, ima stvarnu žarišnu daljinu od 182,5 mm i čist otvor zaslona od 350 mm. Frekvencija žljebova svake od ove dvije površine je između dva i osam žljebova po milimetru, a materijal Fresnelove leće je često optička akrilna plastična masa. Da bi se svela na minimum svilenasta interferencijska šara, odnos frekvencija žljebova između Fresnelovih elemenata 12 i 14 dvaju ožljebljenih površina treba se održavati tako, daje jedna bar četiri puta veća od druge, a da nije cijeli broj umnožaka iste. U praksi se pokazalo da je odnos frekvencija žljebova od oko 4,74 efikasan. Ako svaka od površina ima promjenjivu širinu žljebova, tada se ovaj odnos mora održati za svaki od parova gornje i donje površine. The double-sided grooved Fresnel lens 10, used for epidiascope projection, has an actual focal length of 182.5 mm and a clear screen aperture of 350 mm. The groove frequency of each of these two surfaces is between two and eight grooves per millimeter, and the Fresnel lens material is often an optical acrylic plastic mass. In order to minimize the silky interference pattern, the groove frequency ratio between the Fresnel elements 12 and 14 of the two grooved surfaces should be maintained so that one is at least four times larger than the other, without being an integer multiple of the same. In practice, it has been shown that the groove frequency ratio of about 4.74 is efficient. If each of the surfaces has a variable groove width, then this relationship must hold for each pair of upper and lower surfaces.

Parametri profila žljebova za površinu 12 su: The parameters of the groove profile for surface 12 are:

C = 0,00521682 mm-1 C = 0.00521682 mm-1

K=-1,87385 K=-1.87385

d=-2,87E-9 d=-2.87E-9

e=2,59E-14 e=2.59E-14

F=-1,53E-19 F=-1.53E-19

g=4,40E-25 g=4.40E-25

Parametri profila žljebova za površinu 14 su: The parameters of the groove profile for surface 14 are:

C=0,00598319 mm-1 C=0.00598319 mm-1

K=-1,344788 K=-1.344788

d=-4,56E-9 d=-4.56E-9

e=3,47E-14 e=3.47E-14

f=--2,18E-19 f=--2.18E-19

g=8,40E-25 g=8.40E-25

Materijal leće je optička akrilna plastična masa, koja ima indeks prelamanja, nd, jednak 1,491 za žuto svijetlo. The lens material is an optical acrylic plastic mass, which has a refractive index, nd, equal to 1.491 for yellow light.

Claims

1. An improved double-sided grooved Fresnel lens 10 in which one sheet of lens material comprises grooved Fresnel elements 12, 14 on each of the large surfaces, characterized in that the frequency of the Fresnel elements (12) on one of the large surfaces of the lens ( 10) is at least four times higher than the frequency of the Fresnel elements (14) on the second large surface of the lens (10) and is not a whole multiple of the frequency of the grooves of the Fresnel elements (14) on the second large surface, thus avoiding the silk rings.

2. Improved double-sided grooved Fresnel lens 10 according to claim 1, characterized in that the frequency of the grooves of the Fresnel elements (12) of the first large surface is about 4.74 times higher than the frequency of the Fresnel elements (14) on the second large surface.

3. Improved double-sided grooved Fresnel lens 10 according to claim 1, characterized in that the width of the groove of the Fresnel elements (12, 13) on each of the large surfaces of this lens is variable.