Rimless or semi-rimless safety eyeglasses

Details Rimless or semi-rimless safety eyeglasses Rimless or semi-rimless safety eyeglasses

2000-05-17

2001-04-17

Dang, Hung Xuan (Department: 2873)

Optics: eye examining, vision testing and correcting

Spectacles and eyeglasses

Brace arm or semi-rimless mounting

C351S103000, C351S110000

Reexamination Certificate

active

06217169

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to an improved rimless or semi-rimless safety eyeglass frame, and more particularly to an improved endpiece and a cushioning ring for such a frame.
SUMMARY OF THE INVENTION
The invention relates to improvements in a rimless or semi-rimless safety eyeglass frame.
The corner of the eyeglass frame, where the screws are located for attaching the frame to the temple, is called the endpiece. Relative movement between the endpiece and the lens at the corners of the endpiece can cause chipping of certain types of plastic lenses. This chipping occurs most often when an optician needs to adjust the endpieces inwardly, to fit a person whose head is more narrow than the standard fit for which the eyeglass frame was built. This adjustment is accomplished by bending each endpiece inward, toward the user's head, with pliers, thereby narrowing the angle defined by the temples and the front of the eyeglass frame. It is during this inward bending that pressure is exerted on the plastic lens, and often causes the lens to chip or crack. Chipping can also occur when the optician must bend the endpieces outward, to accommodate a wearer with a wide head.
This problem is more acute in a rimless or semi-rimless frame in which the lens is secured with a metal wire as opposed to a nylon filament, and particularly, when the lens is made of plastic. The problem is especially acute with extremely thin lenses, and with plastic safety lenses, which are required to be relatively thick according to current safety standards, i.e., not less than 3 millimeters thick. The thickness can be even greater if needed for a particular prescription.
For present purposes, “safety” eyeglasses are defined as protective eyewear that conforms to the American National Standard Institute's (ANSI) Z-87 “Practice for Occupational and Educational Eye and Face Protection.” The present standard is designated as ANSI Z-
87.1-1989
. The present standard requires prescription lenses to be 3 mm thick for most prescriptions (2.5 mm is allowed for a limited number of prescriptive powers). It is believed that an upcoming revision of the ANSI standard may be based not on this “design” requirement but rather on a “performance” requirement, and may allow 2 mm lenses.
This problem of damage to the lenses of safety eyeglasses has not been solved up to now. In particular, it has been believed impossible to provide plastic rimless or semi-rimless prescription safety eyeglass frames, because it has been impossible to meet the stringent impact requirements necessary to meet government standards for safety eyewear. Only recently have the present applicants developed an effective semi-rimless safety eyeglass frame, disclosed in Ser. No. 09/425,120 filed Oct. 22, 1999 now U.S. Pat. No. 6,099,119, incorporated by reference.
With the greater use of polycarbonate (available from General Electric under the trademark Lexan) and CR-39 plastic for ophthalmic lenses, rimless eyewear has become more popular. Plastic lenses, regardless of the material, can be easily cut to accommodate the rimless-type bevel. However, a problem with CR-39 plastic is that it can chip or flake under certain types of stress. Though it is shatter-resistant, it readily breaks and can chip as well. The endpiece (corner) area of the frame is a primary area where stress is likely to be induced due to the flitting adjustments performed by the optician. If the endpiece is bent beyond a very limited range, and if the endpiece is not chamfered, the endpiece can contact the edge of the CR-39 plastic lens and chip it, making it unusable.
The inventors have observed that this chipping or flaking of plastic safety lenses can be avoided by providing the endpiece, particularly on the interior side but also advantageously on the exterior side, with a chamfer defining a relief angle between the endpiece and the lens. The relief angle may be varied according to the nature of the particular lens and endpiece and their specifications. The chamfer provides enough relief so that the endpiece will not exert pressure on the edge of a prescription lens, causing sufficient stress to chip or flake the plastic lens material, when the eyeglass temples are bent inward to be fitted to the user's head. Instead the endpiece will twist inward without bearing upon and damaging the lens.
The range of the rear edge chamfer angle is about 8° to 50°, for example about 40° as shown in the drawings. The range of the front edge chamfer angle is about 8° to 65°, for example about 12° as shown in the drawings. A front edge chamfer angle of up to 65° may be useful, for example, for a wearer with a large head. The rear edge chamfer angle probably does not have to be so large, unless the wearer has an exceptionally narrow head.
The specific chamfer angles can be chosen by those having the ordinary degree of skill in this art, depending on the design of the frame, for example the configurations of the front and back surfaces of the frame. The illustrated angles have been found to be useful average values for the general marketplace. However, with other frame configurations than those illustrated, the 40° and 12° angles may not be optimal.
Other chamfer angles, even those not within the combination of ranges described above, may be appropriate for a frame with an unusual configuration. It is sufficient for the purposes of the invention if the chamfer angles chosen are effective to reduce lens chipping when the frame is adjusted to fit the wearer's head.
Although the above invention has general applicability to other types of eyeglasses, the invention finds specific utility in prescriptive safety eyewear utilizing plastic lenses because of the requirements mandated by government standards, and the difficulties associated with rimless or semi-rimless eyeglass frames. It is probably for these reasons that no rimless or semi-rimless frames exist on the prescription side of the safety eyewear market.
A second problem of known safety eyeglasses concerns the potential stresses on the lens that can be caused by the movement of the lens in a different direction from the reverse groove in the metal eyewire. This too can cause chipping of certain types of plastic lenses.
In addition, all eyeglass frames are bent to a common base curve (known as a 6-Base lens curve). However, there are many prescription lenses that must be made for either a flatter or more curved base curve—and consequently, the frame must be bent to match the lens curvatures.
To overcome the potential chipping (or flaking) of some types of plastic lenses, a cushioning ring of an elastic material is inserted so as to prevent the metal frame from exerting stress on the plastic lens. By adding an elastic ring or band (which may be made for example of silicone material or synthetic rubber), an air space is created between the plastic lens and the metal eyerim. This air space prevents the metal eyerim from having direct contact with the plastic lens. Further, it provides more space for the angling of the endpiece during adjustment to help keep the stress off the lens itself.
Furthermore, it does this around the entire circumference of the lens. Some areas of the lens are more apt to be stress-sensitive (namely, any corner area and the endpiece area). The cushioning ring by nesting inside the lens groove enables the lens to avoid stresses anywhere there is contact between the lens and the eyerim or rimless wires.
Another benefit of the cushioning ring is to effectively allow for greater tolerance when grooving the lens. If a rimless lens is grooved too deep, then it will be too loose to fit properly inside the frame. The cushioning ring allows the optical laboratory to have greater latitude in the cutting of the groove. This can be helpful as grooving cutters wear and settings are changed. As lenses are expensive, it enables the laboratory to reduce their spoilage.
The cushioning ring can be made of any stretchable or compressible material. For example, it can be rubber, synthetic rubber, silicone, or any simil

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