SG180059A1

SG180059A1 - Flash unit having a micro fresnel lens

Info

Publication number: SG180059A1
Application number: SG2010080893A
Authority: SG
Inventors: Jianghong Zhou
Original assignee: Xenon Technologies Pte Ltd
Priority date: 2010-11-03
Filing date: 2010-11-03
Publication date: 2012-05-30
Also published as: WO2012060777A4; SG190115A1; WO2012060777A3; WO2012060777A2

Abstract

FLASH UNIT HAVING A MICRO FRESNEL LENSThe present application discloses a flash unit having a micro Fresnel lens with smallerequivalent radius than that of a known Fresnel lens. It also provides a flash unit having a micro Fresnel lens with equivalent aspherical profile which has convex portion at the center and concave portion at both ends. It further mentions a flash unit having a micro Fresnel lens with equivalent aspherical surface which has concaveportion at the center and convex portion at both ends. A portable electronic device that comprises the flash unit is made known too.The present application provides a fabrication method using plastic injection molding technique. The present application further provides a fabrication method of the inserts for the tooling of injection molding using diamond turning method.[Figure 2]

Description

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FLASH UNIT HAVING A MICRO FRESNEL LENS

: [0001] This application relates to a flash unit having a micro Fresnel lens. The present application also relates to a method of making the micro Fresnel lens.

[0002] A flash unit comprises a xenon lamp with a light output distribution angle over a broad angular range. Typically, a reflector is introduced to reflect and direct light rays towards the target of interest for photographing. The reflector is usually a combination of a few quadratic surfaces. Effectiveness of the reflector needs to be improved by using an additional lens covering the reflector to further bend light rays towards the target of interest, especially in the longitudinal direction of the flash unit in which the reflector is hard to manage light travelling direction, due to the long length of the lamp.

[0003] Usually the additional lens has a spherical surface of big radius with gentie oo curvature because of space limitation of the flash unit. It thus is collapsed into the known Fresnel lens by breaking the lens into a series Fresnel zones with equivalent radius of the original lens, making the original lens slimmer and lighter. This Fresnel lens usually has Fresnel zones on the inner surface only facing the reflector and lamp.

The other surface exposing to user of the flash unit is usually flat in order not to be worn easily and deteriorate optical performance if it were Fresnel zones as weil. - However, the housing thickness of the flash unit where the additional lens is formed is very thin, usually 0.4-tmm, therefore the equivalent radius of the Fresnel lens is limited in order not to remove too much material of the housing to maintain its strength. The Fresnel zone usually has Fresnel pattern of constant pitch, say 1mm, and maximum height 0.1mm so that the cover has sufficient strength to protect the flash unit from external impact. Consequently the light bending capability of traditional

Fresnel lens is insufficient to achieve higher guide number or uniform distribution for illuminating an objection of photographing.

[0004] The present application aims to provide some new and useful devices and } “methods.

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[0005] According to a first aspect of the application, there is provided a flash unit having a micro Fresnel lens with smaller equivalent radius than that of a known

Fresnel lens. :

[0006] According to a second aspect of the application, there is provided a flash unit having a micro Fresnel lens with equivalent aspherical profile which has convex portion at the center and concave portion at both ends.

[0007] According to a third aspect of the application, there is provided a flash unit having a micro Fresnel lens with equivalent aspherical surface which has concave : portion at the center and convex portion at both ends.

[0008] According to a fourth aspect of the application, there is provided a portable

Co electronic device comprising the flash unit according to any of the preceding claims.

The portable electronic device can be in the form of a camera, a mobile phone, an electronic gaming device and the like.

[0009] According to a fourth aspect of the application, there is provided a fabrication method using plastic injection molding technique. - [0010] According to a fifth aspect of the application, there is provided a fabrication method of the inserts for the tooling of injection molding using diamond turning method for making the micro Fresnel lens.

[0011] The Fresnel lens with a high compressed structure can be manufactured using plastic injection molding method. Compared with known Fresnel lens, micro Fresnel lens has more optical power. It is easier to design the optics in flash unit to achieve desirable guide number and distribution on illumination target by implementing the ~ micro Fresnel lens which is more powerful to manipulate light rays emitted from the lamp. : [0012] Some of the accompanying figures illustrate embodiments of disclosed : inventions and serve to explain principles of the disclosed embodiments. It is to be

9-2010-00321 understood, however, that these drawings are presented for purposes of illustration only, and not for defining limits of the disclosed inventions.

[0013] Figure 1 illustrates a cross-section view of a known Fresnel lens for showing

Fresnel “teeth”.

[0014] Figure 2 illustrates a cross-section view of a first embodiment of the micro

Fresnel lens.

[0015] Figure 3 illustrates a cross-section view of a second embodiment of the micro :

Fresnel lens that has an equivalent aspheric surface with high order polynomial coefficients.

[0016] Figure 4 shows a third embodiment of the micro Fresnel lens that has an equivalent aspheric surface with high order polynomial coefficients to achieve guide number very close to that using the known Fresnel lens by moving the joint location of the concave and convex portion nearer to the center of the lens as compared to embodiment of Figure 3.

[0017] Figure 5 illustrates a fourth embodiment of the micro Fresnel lens that has a negative equivalent aspheric surface with high order polynomial coefficients compared to embodiment of Figure 4,

[0018] Figure 6 illustrates a micro Fresnel lens with a further reduced convex portion such that an equivalent profile of the micro Fresnel lens comprises of a concave : : portion only.

[0019] Figure 7 illustrates relative illuminance on illumination targets versus flash coverage angle by using a known Fresnel lens and micro Fresnel lenses of three embodiments respectively.

[0020] Figure 8 illustrates a fifth embodiment of the micro Fresnel lens with a new appearance.

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[0021] Figure 9 illustrates a sixth embodiment of the micro Fresnel lens with another new appearance.

[0022] Figure 10 illustrates a micro Fresnel lens with a known appearance.

[0023] Figure 11 illustrates a micro Fresnel lens with another known appearance.

[0024] Figure 12 shows two teeth of the tooling insert of the mold of a micro Fresnel lens that is being cut by a diamond cutter. :

[0025] Exemplary, non-limiting embodiments of the present application will now be - described with references to the above-mentioned figures.

[0026] Figure 1 is the cross-section view of a known Fresnel lens 20 showing Fresnel “teeth” 22. This Fresnel lens 20 has an equivalent radius 24 of 20mm, which is shown above the cross-section view. The pitch 26 is 0.5mm. The last two Fresnel “teeth” 22 on both edges have the steepest slope which results in maximum material removal : approximately 0.056mm from the lens 20.

[0027] Figure 2 is the cross-section view of a first embodiment of micro Fresnel lens 28. This micro Fresnel lens 28 has an equivalent radius 30 of 5mm as shown. The . pitch 32 is preferably 0.02-0.2mm and it is 0.1mm in this example. The maximum material removal is 0.07mm approximately at the ends of the micro Fresnel lens 28. In most cases 0.07mm material removal from a typical thickness of 0.5mm of the micro

Fresnel lens 28 will not significantly reduce the strength of the micro Fresnel lens 28.

But to be comparable with the known Fresnel lens 20 shown in Figure 1, it is possible : to remove less material by decreasing the pitch of the Fresnel teeth and maintain the equivalent radius 30 of 5mm and thus maintain the same optical power. For example, if the pitch 32 is 0.07mm, the maximum material removal is 0.05mm at the ends of the micro Fresnel lens 28.

[0028] In this embodiment, since the equivalent radius 30 of the micro Fresnel lens 28 is smaller, the convergent capability is stronger than that of the known Fresnel lens 20. As such, either travelling directly to the Fresnel lens 28 or being re-directed by the

9-2010-00321 reflector to the Fresnel lens 28, more light rays emitted from the lamp will be bended towards the center illumination area of interest. [luminance at the center is increased by 8-20%. llluminance rays received by the entire illumination area of interest are also increased, thereby light usage efficiency is improved.

[0029] Figure 3 is the cross-section view of the second embodiment of micro Fresnel lens 34, namely example one for easier description. This Fresnel lens 34 has an equivalent profile 36 of aspheric surface with high order polynomial coefficients. The : center portion of this lens 34 is convex while it changes to concave at the edge of the : 10 lens 34, While the convex portion at the center of the micro Fresnel lens 34 {ends to bend the light rays hitting the convex surface towards the illumination center area, the . concave portion of the lens tends to divert rays hitting the concave surface to the edge of the illumination area.

[0030] By changing the radius, conic value, and the high order polynomial coefficients : of the equivalent aspheric profile of surface 36, the joint location of the convex and concave portions can be shifted towards either the center or the edge of the lens 34.

The position of joint location is determinative to achieve higher or lower guide number.

To have a more uniform distribution on the illumination target, it is preferable to have the joint location closer to the lens center. This is due io the reason that the area of concave portion of the lens 34 is bigger, and therefore more light will be re-directed towards the edges of the illumination area. Using this idea in micro Fresnel design it is convenient to have a flash unit design which has desirable guide number in between the cases using the micro Fresnel lens 28 shown in Figure 2 and the known Fresnel lens 20 shown in Figure 1.

[0031] Figure 4 shows another example (example two) of this embodiment in order to . have a guide number very close to that using the known Fresnel lens 20 by moving the joint location nearer to the center of the lens compared to example one 34 shown in Figure 3. In this case illuminance distribution on the illumination target will be also very close to that using the known Fresnel lens 20. An equivalent profile 42 of the micro Fresnel lens is indicated by a curvature with two valleys.

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[0032] The third embodiment of the micro Fresnel lens is shown in Figure 5, where the Fresnel lens 44 has an equivalent aspheric profile 46 with high order polynomial coefficients too. However the equivalent aspheric profile 46 differs from the embodiments shown in Figure 3 and Figure 4 in the way that its equivalent profile 46 has concave portion at the center and convex portion at the both ends of the iens 44. - The convex portion can be further reduced so that the equivalent profile of a micro

Fresnel lens 48 comprises of a concave portion only, as shown in Figure 6. This embodiment further distributes more light rays towards the edges of the illumination target, causing a more uniform distribution on the illumination target.

[0033] Figure 7 shows the illuminance on illumination target against the flash coverage angle, using the known Fresnel lens, the first, the second and the third embodiment of the micro Fresnel lens respectively. The illuminance is measured from the horizontal central line across the illumination target. The illuminance at the center using the known Fresnel lens is normalized to be 1.00. We can see the first embodiment shown in Figure 2 achieves the highest illuminance at the center, which can be as big as 1.2, while the illuminance at the edges are lower, since more light rays are directed to the illumination center, contributing to its highest illuminance at the center. Compared to the first embodiment, Examples one and two of the second ~~ 20 embodiment shown in Figure 3 and Figure 4 achieve higher illuminance at the edges of the target by sacrificing illuminance at the center. The third embodiment shown in oo Figure 5 tends to create a more uniform distribution curve than the case using the known Fresnel lens 20.

[0034] It is to be understood that while above embodiments show only the micro

Fresnel fens with vertical linear Fresnel pattern, micro Fresnel lens can be also made with circular Fresnel pattern whose equivalent radius or profile is identical to the : above respective embodiments. The center of the circular Fresnel pattern will be the center of the micro Fresnel lens. Using circular Fresnel pattern for the micro Fresnel lens, the curves of llluminance on illumination target against the flash coverage angle for the known Fresnel lens, the first, the second and the third embodiment of the micro Fresnel lens respectively will not be significantly different from those shown in

So Figure 7. llluminance at the center of the first embodiment shown in Figure 2 is the oo highest, followed by the example one of the second embodiment shown in Figure 3,

9-2010-00321 followed by the known Fresnel lens, followed by the example two of the second embodiment shown in Figure 4, followed by the third embodiment shown in Figure 5.

[0035] An average human being's naked eye is able to resolve a slit of about 0.07mm placed at the point of most distinct vision. If the micro Fresnel lens has a series of parallel linear Fresnel teeth or concentric circular Fresnel teeth of pitch about 0.07mm, - one is unable to look through this micro Fresnel lens onto the lamp and reflector.

Thus this micro Fresnel lens offers a method preventing the lamp and reflector clearly visible to the human eyes as in the case of using the known Fresnel fens 20. Such feature of the micro Fresnel lens is of particular interest to many manufacturers of portable electronic device using flash unit. .

[0036] Maintaining the equivalent radius or profile of the micro Fresnel lens 28, 34, 40, 44, 48, appearance of a micro Fresnel pattern can be changed to give end user a different and new feeling of the flash unit as shown in Figure 8 and Figure 9, for example, compared to Figure 10 and Figure 11 which use known Fresnel lenses of vertical and circular Fresnel zones whose pitch is 0.5mm respectively. Design in

Figure 8 comprises of a circular micro Fresnel zone on the inner surface of the center portion of the flash unit housing, and vertical Fresnel zone on the inner surface at both left and right portions of the flash unit housing. These Fresnel patterns have constant depth, 0.03-0.05mm for example, and variable pitch ranging from 0.5mm at the center to 0.04mm at the edge of each zone. Design in Figure 9 comprises of four quadrants, where each two symmetrical quadrants are identical but in opposite locations. The Fresnel patterns have constant pitch of 0.07mm and the depths are changing from 0.001 to 0.05mm. For decoration only each of the four quadrants has two Fresnel teeth having pitch of 1mm and depth 0.1mm.

[0037] The micro Fresnel lens is mass producible using plastic injection molding technique. Optical plastic materials such as polymethyl methacrylate (PMMA), polystyrene, polycarbonate (PC), etc., can be used for micro Fresnel lens molding.

Diamond turing is a practical method to fabricate accurately the tooling insert of mold of this micro Fresnel lens. It can be used to cut with high precision directly on either soft metal such as copper or hard metal such as stainless steel. Choosing a soft or hard metal as the insert for molding of micro Fresnel lens usually depends on

9-2010-00321 the quantity requirement of production. An insert for the micro Fresnel lens made of copper may sustain 200 thousands molding cycles, while stainless steel insert is able to produce 1 million parts before the teeth of micro Fresnel lens on the insert needs to : : be re-sharpened. Figure 12 schematically shows two teeth of a micro Fresnel pattern 9 of the insert and the diamond cutter who has a radius R at the tip. Preliminarily fed with the designed profile to be cut, the cutter of the diamond turning machine takes the radius R into consideration and follows this profile to remove material of the insert to leave an accurate approximation of this profile. Instead of being perfectly sharp, the

Fresnel teeth valley of the insert where points B and E locate are rounded with radius

R due to the physical size limitation of diamond turning cutter. This causes a round : : Fresnel teeth peak of radius R of the molded part. Experiences show that radius R of 1-5 microns and horizontal feeding step of 1 micron are preferable for a good balance of cuiting cost, cutting efficiency, and final finish quality which is related to optical performance. Experiences also show that the segments AB and DE of the Fresnel teeth representing the profile to be cut can be approximated by straight lines for a good balance of cutting cost, cutting efficiency, and final finish quality as well. The optical inactive segments BD and EF usually are not perpendicular to the horizontal line HH’, which represents top surface of the insert to be cut for reference only, but have an angle a, which is usually termed as draft angle, for easy ejection of molded part after cooling down in molding process without damaging the teeth of the Fresnel : pattern. The draft angle a can be 0 to 10 degree but preferably 3-4 degree. The optical material's refraction index, approximation of straight lines AB and CD, round peak of micro Fresnel lens, and the draft angle a should be taken into consideration during design phase of the micro Fresnel lens. - [0038] In the application, unless specified otherwise, the terms “comprising”, "comprise", and grammatical variants thereof, intended to represent "open" or “inclusive” language such that they include recited elements but also permit inclusion of additional, non-explicitly recited elements.

[0039] As used herein, the term "about", in the context of concentrations of components of the formulations, typically means +/- 5% of the stated value, more : typically +/- 4% of the stated value, more typically +/- 3% of the stated value, more

9-2010-00321 typically, +/- 2% of the stated value, even more typically +/- 1% of the stated value, and even more typically +/- 0.5% of the stated value.

[0040] Throughout this disclosure, certain embodiments may be disclosed in a range format. The description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, . : - from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

[0041] It will be apparent that various other modifications and adaptations of the application will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the application and it is : intended that all such modifications and adaptations come within the scope of the appended claims.

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Reference Numerals 20 micro Fresnel lens 22 Fresnel “teeth” 5b 24 equivalent radius 26 pitch 28 micro Fresnel lens 30 equivalent radius : 32 pitch 34 micro Fresnel lens : 36. equivalent radius oo 38 micro Fresnel lens 40 equivalent radius 42 micro Fresnel lens 44 equivalent radius 46 micro Fresnel lens 48 equivalent radius

Claims

9-2010-00321 Claims

1. Flash unit having a micro Fresnel lens with smaller equivalent radius than that fo : of a known Fresnel lens.

2. Flash unit having a micro Fresnel lens with equivalent aspherical profile which has convex portion at the center and concave portion at both ends.

:

3. Flash unit having a micro Fresnel lens with equivalent aspherical surface which has concave portion at the center and convex portion at both ends.

4, Portable electronic device comprising the flash unit according to any of the preceding claims.

5. Fabrication method using plastic injection molding technique.

6. Fabrication method of the inserts for the tooling of injection molding using diamond turning method.