Optical: systems and elements – Lens – Fluid
Reexamination Certificate
2001-01-19
2003-09-09
Spector, David N. (Department: 2873)
Optical: systems and elements
Lens
Fluid
C359S665000
Reexamination Certificate
active
06618208
ABSTRACT:
This application is a 371 of PCT/GB99/00747 filed Mar. 18, 1999.
The present invention relates to improvements in the field of variable focus optical devices, in particular variable focus lenses, for example of the type in which the optical power of the lens is variable by varying the volume and/or pressure of a transparent fluid within a transparent envelope.
Variable focus lenses are known and have been described for example in GB 2183059, GB 2184562 and WO96/38744. However, to date, despite the many examples of variable focus lenses described in the prior art, none have achieved widespread commercial acceptance as an alternative to fixed-focus ground glass or plastic lenses.
It is believed that the failure of known variable focus lenses to gain commercial acceptance is due to a number of factors. For example, many known such lenses suffer from leakage of the fluid from the envelope in use. Furthermore, many known such lenses suffer from poor optical quality due to the mounting arrangement of the flexible membrane and/or the material chosen for the membrane. A further contributor to the poor optical quality of known lenses has been the fluid selected to fill the envelope, which has had a less than optimal transparency or homogeneity of refractive index. An additional reason for the non-acceptance of known lenses has been their complex and bulky configuration which has lead to a poor aesthetic effect, for example when the known lenses have been mounted in spectacles, and has also increased the cost of such spectacles to a level which is not competitive with traditional fixed-focus lenses.
The present invention seeks to provide a variable focus lens and a method of making a variable focus lens, embodiments of which overcome at least some of the problems of known variable focus lenses, whereby a more commercially attractive product can be achieved. It also seeks to provide eyewear incorporating variable focus lenses.
According to an invention disclosed herein, there is provided a variable focus lens comprising a transparent envelope at least partially defined by a flexible, transparent membrane and containing a transparent fluid, a frame member engaging one face of the flexible membrane and a ring member engaging an opposite face of the flexible membrane, the ring member and the frame member being urged towards each other by retaining means, wherein the respective surfaces of the frame member and the ring member that engage the flexible membrane are substantially complementary and profiled so as to cause a peripheral region of the flexible membrane to change direction more than once.
It has been realised by the applicant that, in order to obtain a high optical quality of the membrane, the membrane should be held under tension at all times. Furthermore, it has been found by the applicant that the membrane, when under tension, and particularly when formed of preferred materials such as Mylar tends to form its own seal against the frame member or ring member.
The profiles of the engaging surfaces of the frame member and the ring member allow the flexible membrane to be retained under tension on the frame member simply by the action of the engaging surfaces. In this way the construction of the variable focus lens is considerably simplified in comparison to known such lenses.
The profiles of the engaging surfaces may be stepped or comprise one or more projections and complementary recess(es). The portions of the engaging surfaces substantially perpendicular to the plane of the unstretched membrane will tend to frictionally engage the membrane as the ring member is urged towards the frame member by the retaining means. Such frictional engagement will tend to stretch the membrane on the frame member, ensuring that the membrane is under tension.
In a particularly advantageous arrangement, the engaging surfaces comprise at least one oblique surface which increases in radial extent towards the frame member. In this way, as the ring member is urged towards the frame member by the retaining means, friction between the oblique surface of the ring member and the flexible membrane tends to urge the periphery of the membrane radially outwardly, thereby increasing the tension in the membrane, i.e. stretching the membrane.
The ring member and frame member may be of a material or materials which is/are sufficiently rigid to positively interengage with each other and to ensure that the ring member and frame member can maintain the flexible membrane under tension. The material of the ring member and frame member is preferably also lightweight to facilitate the incorporation of lenses described herein in spectacles. Thus, the ring member and frame member may be made, for example, of a high impact resistant plastics material, or of aluminium, or of titanium.
It is generally advantageous to maximise the friction between the engaging surfaces and the membrane, not only to maximise the stretching effect described above, but also to ensure that the membrane is securely held by the ring member and the frame in the assembled lens. Preferably therefore, at least one of the surfaces is a high friction surface.
This in itself is believed to be new and thus according to an invention disclosed herein there is provided a variable focus lens comprising a transparent envelope at least partially defined by a flexible, transparent membrane and containing a transparent fluid, a frame member engaging one face of the flexible membrane and a ring member engaging an opposite face of the flexible membrane, the ring member and the frame member being urged towards each other by retaining means, wherein the respective surfaces of the frame member and the ring member that engage the flexible membrane are substantially complementary and at least one of the surfaces is a high friction surface.
For example, one or more of the frame member and the ring member may be made of a material having a high coefficient of friction at its surface. Alternatively, at least one of the engaging surfaces may have been roughened or expanded to increase its surface friction.
In a preferred arrangement, however, at least one of the engaging surfaces is provided with a coating of high friction material. A particularly preferred material for this coating is rubber or a synthetic elastomer, as this has been found by the applicant to engage well with the preferred materials for the membrane, such as Mylar.
A further advantage of providing at least one of the engaging surfaces with a coating of rubber or synthetic elastomer is that the rubber or elastomer tends to form a high integrity fluid seal at the interface between the engaging surface and the membrane.
Thus, according to an invention defined herein there is provided a variable focus lens comprising a transparent envelope at least partially defined by a flexible, transparent membrane and containing a transparent fluid, a frame member engaging one face of the flexible membrane and a ring member engaging an opposite face of the flexible membrane, the ring member and the frame member being urged towards each other by retaining means, wherein at least one of the engaging surfaces is provided with a coating of rubber or synthetic elastomer.
It has been found by the applicant that the coating need only be thin, in order to achieve an advantageous effect. For example, the coating may have thickness of less than 100 &mgr;m, or less than 50 &mgr;m, or less than 20 &mgr;m or even less than 10 &mgr;m.
Preferably, the coating is provided on the engaging surface that engages the face of the membrane which also forms an inner surface of the envelope, so that the sealing interface aids in the containment of the fluid. This surface will generally be provided on the frame member. Of course, both engaging surfaces may be provided with a coating.
The peripheral shape of the ring member, and also of the frame member, may be chosen as required. For example, the members may have a circular, oval, elliptical, or other closed curve, peripheral shape.
The frame member may comprise a rigid transparent window forming a wa
Spector David N.
Sughrue & Mion, PLLC
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