GB2289546A

GB2289546A - Variable power mirror with vent

Info

Publication number: GB2289546A
Application number: GB9408858A
Authority: GB
Inventors: Joshua David Silver; Paul Alfred Ellsmore
Original assignee: OXFORD LENSATS Ltd
Current assignee: OXFORD LENSATS Ltd
Priority date: 1994-05-04
Filing date: 1994-05-04
Publication date: 1995-11-22
Also published as: WO1995030920A2; AU2349695A; GB9408858D0; WO1995030920A3

Abstract

A mirror of variable power comprises a housing 16, 19 containing a medium-filled space 11 delimited in part by a flexible reflective membrane 10, means 14, 15, 17 to vary the pressure of the medium in the space and thereby alter the radius of curvature of the membrane 10 to vary the power of the mirror, and means to vent medium from the space 11 eg. a spring-urged air valve or plug of resilient material. Spigot 14a may be in threaded engagement with cup 15 captive in the centre of plate 16 but turnable relative thereto by lever arm 17. <IMAGE>

Description

IMPROVED MIRROR OF VARIABLE POWER This invention relates to a flexible membrane mirror comprising a housing containing a closed space delimited in part by a tensioned reflective flexible membrane and means to vary the pressure in the closed space and thereby alter the radius of curvature of the membrane to vary the power of the mirror.

Part spherical mirrors based upon a reflective flexible member whose radius of curvature can be adjusted in some way are well known. Some such mirrors use mechanical means to stress edge regions of a disc of flexible reflective material, means being provided to alter the forces applied to the edge regions to vary the shape of the mirror surface and thus vary the power of the mirror.

This invention, however, is concerned with that type of flexible membrane mirror which uses variations in the pressure of a medium contained in a closed space delimited in part by the membrane to provide the required changes in the shape of the membrane and thus in the power of the mirror.

According to one aspect of the present invention a mirror of variable power comprises a housing containing a mediumfilled space delimited in part by a flexible reflective membrane and means to vary the pressure of the medium in the space and thereby alter the radius of curvature of the membrane to vary the power of the mirror and is characterised in that means is provided to vent medium from the space.

Suitably the medium filling the space is air and the venting means is an air valve. Conveniently the venting means is operable independently of the means for varying the pressure of the medium in the space. Desirably the housing has a cover for protecting the membrane when the mirror is not in use and the action of moving the cover into a protective position (e.g. where it closes the housing) actuates the vent means (e.g. an air valve) to open the space to atmosphere.

Preferably the reflective membrane is backed by the space (e.g. the mirror surface is not viewed through the space) so that intrusion of dust and/or moisture into the space through the vent means has no effect on the clarity of the image reflected by the mirror surface.

It is expected that mirrors in accordance with this invention will have many uses, but one early use is expected to be a vanity mirror for use in the application of cosmetics to the face.

Preferably the flexible membrane is mounted between opposed O-rings in the manner described in our GB-B-2183059, GB-B72184562 or EP-B-0291596.

Some embodiments of mirror in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figures la to Ic show, in schematic section, the housing of a mirror with the reflective surface shown plane in Figures la, convex in Figure 1b and concave in Figure lc, Figure 2 is a view of the back of the housing shown in Figure la showing a turnable adjusting lever for varying mirror power, and Figures 3a and 3b show sectional views through an alternative construction using a rotatable camshaft in place of a turnable lever for varying mirror power.

The mirror surface shown in Figures la to ic is a flexible plastics membrane 10 defining the upper (as shown in Figure la) boundary of an air-filled space 11 defined peripherally by a pair of O-ring retainers 12a, 12b, and by a flexible lower seal 13 secured to a movable actuator 14.

The membrane 10 can have its metallised surface protected by an anti-scratch layer and thus does not need a protective glass or rigid plastics "window" between it and the user.

The annular retainers 12a, 12b are rigid rings grooved to receive confronting O-rings 15a, 15b (e.g. of elastomeric material) which squeeze the membrane between them thereby tensioning the membrane in a radial direction as described in the patent specifications mentioned above. Because the 0rings 15a, 15b form an air-tight seal to the membrane 10 and the lower seal 13 also forms an air-tight seal to the lower ring retainer 12b, the space 11 is closed off from atmosphere whereby any movement of the seal 13 towards the membrane 10 will increase the pressure of air in the space 11 causing the membrane to become convex as shown in Figure 1b whereas any movement of the seal 13 away from the membrane 10 will reduce the pressure in the space 11 causing the membrane to adopt the concave shape shown in Figure lc.

These movements of the seal 13 are effected using the plate-like actuator 14 which has a spigot 14a in threaded engagement with a cup 15 captive in the centre of a rear plate 16 of the mirror housing but turnable relative thereto by means of a lever arm 17.

Figure 2 shows the lever arm 17 in its mid-position (corresponding to Figure la) although it can traverse over an arc (shown as being of almost 700) to left and right of the central position.

Shown schematically by the arrow 20 in Figure la is a venting means which allows the pressure in the space 11 to be made equal to atmospheric pressure, irrespective of the position of the lever arm 17 around its available arc of travel. The venting means can be a simple spring-urged air valve, a plug of resilient material movable into and out of blocking relationship with an air duct through the ring retainers 12a, 12b or some other arrangement for controllably allowing air to flow into or out of the space 11. The demands on the valve of the venting means are not great since the pressure difference across it is unlikely to exceed a few tenths of an atmosphere and some leakage of air past the valve can be tolerated in view of the short period in which the mirror is likely to be used on a given power setting and the ease with which resetting of the pressure in the space 11 can be achieved. The air valve can be manually actuated directly or via a closing movement of a protective cover for the mirror housing. Such a cover is shown dotted at 19 in Figure Ib and may be hinged to the rear plate 16 and/or to either or both ring retainers 12a, 12b.

Figures 1b and lc show how the movement of the actuator 14 causes the mirror membrane 10 to become either convex or concave. This actuator movement is achieved by the action of the screw thread which joins the actuator 14 to the lever arm 17. The lever arm 17 must be attached to the rear plate 16 in such a way as to allow the lever arm to rotate with respect to the plate 16 but not to move away from it. In addition, the flexible seal 13 must have enough torsional stiffness to prevent the actuator 14 from rotating. In practice, both these conditions are easy to arrange.

The lever arm 17 is designed so that the user can sweep this lever back and forth through its operating arc as required using a finger or thumb. In practice, it has been found possible to work the mirror shown in Figures 1 and 2 using just one hand, that is to hold the housing in one hand and use a finger or thumb of the same hand to operate the lever arm 17 while holding the housing.

The mechanism for varying the power of the mirror should be designed so that it is not possible to excessively stretch and permanently distort the membrane 10. The simple vent 20 may allow dust and condensation into the "sealed" space 11 but this would not be visible to the user, since this "sealed" volume is behind the mirror membrane 10.

One design of vent has a small hole in the lower 0-ring retainer 12b communicating between the "sealed" space 11 and the outside world. This vent hole would normally be sealed up by a spring-loaded seal of some sort. On the front face of the upper O-ring retainer 12a is a small button which, when pressed, opens the seal and allows the pressure between the mirror membrane 10 and the flexible seal 13 to become equal to ambient. This button can be pressed by the user, but is also sited in such a way that when the cover 19 is closed the vent is automatically operated. Thus, when stored (in a handbag or suitcase) the space behind the mirror is always vented and so the membrane 10 is protected from even the most extreme changes in atmospheric pressure.

This provision of the vent means also has one other useful attribute - it halves the angle of rotation of the lever arm 17 that would otherwise be necessary to go from a fully concave configuration to a fully convex configuration.

The operation is as follows: With the lever arm 17 in one or other extreme position, the vent 20 is operated and the mirror membrane 10 is allowed to become flat. Moving the lever arm through its full arc of travel to its other extreme now gives the maximum curvature (either concave or convex). To change the "sense" of the mirror, the vent 20 is now operated again, causing the mirror to again become flat. Moving the lever arm 17 back through its full operating arc will now cause the mirror membrane 10 to curve to the maximum extent in the opposite sense.

Figures 3a and 3b show a modified actuating mechanism in which the thread between the cup 15 and the actuator 14 is dispensed with and an offset cam arrangement is used. The lever 17 now becomes a cam shaft 17a rotatable about its own axis by a knob or crank arm (not shown).

Claims

1. A mirror of variable power comprising a housing containing a medium-filled space delimited in part by a flexible reflective membrane and means to vary the pressure of the medium in the space and thereby alter the radius of curvature of the membrane to vary the power of the mirror, characterised- in- that means is provided to vent medium from the space.

2. A mirror according to claim 1, characterised-in- that the medium filling the space is air and the venting means is an air valve.

3. A mirror according to claim 2, characterised-i--that the air valve is a spring-urged member located in one of a pair of O-ring retainers between which the membrane is clamped.

4. A mirror according to any preceding claim, characterised- in- that the venting means is operable independently of the means for varying the pressure of the medium in the space.

5. A mirror according to claim 2 or any preceding claim dependent on claim 2, characterised-in-that the housing has a cover for protecting the membrane when the mirror is not in use and the action of moving the cover into a position where it closes the housing actuates the vent means to open the space to atmosphere.

6. A mirror according to any preceding claim, characterised-i--that the reflective membrane is backed by the space so that intrusion of dust and/or moisture into the space through the vent means has no effect on the clarity of the image reflected by the mirror surface.

7. A mirror according to any preceding claim, characterised-in-that the means to vary the pressure of the medium in the space is a lever arm traversable over an arc to left and right of a central position and moving an actuator plate within the housing away from a median position of the membrane in one direction of movement of the arm from the central position and towards said median position in the other direction of movement of the arm from said central position.

8. A mirror according to claim 7, characterised-in-that the actuator has a spigot in threaded engagement with a cup, the cup being captive in the housing but turnable relative thereto by the lever arm.

9. A mirror as claimed in claim 7 or claim 8, characterised-in-that the vent means can be actuated when the lever arm is in either extreme left or right positioS relative to the central position to permit either varying degrees of convexity or concavity to be obtained in the membrane on movement of the lever arm away from the respective extreme position.

10. A variable power mirror substantially as herein described with reference to the accompanying drawings