GB2361026A

GB2361026A - Method and apparatus for mounting a lens for machining

Info

Publication number: GB2361026A
Application number: GB0007498A
Authority: GB
Inventors: Michael O'neill
Original assignee: CAMWRITE Ltd
Current assignee: CAMWRITE Ltd
Priority date: 2000-03-29
Filing date: 2000-03-29
Publication date: 2001-10-10
Also published as: GB0007498D0

Abstract

An apparatus for and method of holding a lens for machining, comprising clamping a lens mounting block (fig 1) to substantially prevent relative movement between the clamping means 12,14 and the mounting block (fig 1). The mounting block (fig 1) is preferably located on one side of the lens to leave the other side of the lens fully accessible for drilling etc. The clamping device may employ a pair of jaws which are movable relative to each other to substantially prevent relative movement between the clamping means and the mounting block.

Description

2361026 METHOD AND APPARATUS The present invention relates to a method and

apparatus for holding spectacle lenses, notably lenses for rimless 5 spectacles, for machining with a drill or milling tool.

Spectacle lenses are typically cut to a required shape (profile) by releasably securing a mounting block to the centre of one side of a standard sized lens using adhesive. The lens is then cut using an edging machine or similar device to cut the profile shape while the lens is turned. In cutting the shape, the chuck of a grinding machine engages with a slot or other feature at the free end of the mounting block, and a stop member is urged against the other side of the lens to hold the lens and the mounting block in compression between the stop and the chuck while the lens is being turned.

After the lens has been cut, it is released from the chuck and the mounting block is removed. If the lens is to be used in the assembly of rimless spectacles, a rimless frame must be fixed to the lens by means of fixings (for example, screws) through the lens itself. In order to attach the lens to the frame or frame pieces, the lens must contain apertures (for example holes and/or slots) to accept the fixings. To provide the apertures the lens is held in the hand and offered up to a manually operated bench drill or similar device, to drill the apertures in the lens.

Using this process, it can be difficult to position the drill accurately. It is an object of the present invention to reduce the above problem.

According to an aspect of the present invention there is provided a method of holding a lens for machining, comprising clamping a mounting block by clamping means so as substantially to prevent relative movement between the clamping means and the mounting block, the lens to be machined having the mounting block releasably secured to one side thereof and the clamping means being located on only the said one side of the lens so as to leave the other side of the lens fully accessible.

By clamping the mounting block using clamping means on only one side of the lens, the other side of the lens is completely accessible to a drill without inhibiting motion of the drill across the surface of the lens.

The mounting block may conveniently be the same mounting block which has previously been used to mount the lens on the chuck of a grinding machine. However, it would also be possible to secure a different mounting block to the lens. The mounting block may be adhered to the lens either before or after the block is clamped.

In a preferred embodiment, a pair of lenses which are to f orm a pair of spectacles are held side by side so that both may be machined. This permits greater accuracy in locating the appropriate apertures for a particular frame.

It would be possible to clamp the mounting block by means such as magnetism or adhesive. However, the clamping operation is preferably carried out by means of a clamping device which applies lateral restraint or pressure to the mounting block.

Accordingly, another aspect of the invention provides a clamping device for clamping a lens mounting block comprising a lens receiving surface and a mounting body having a predetermined side profile, the device comprising a pair of jaws which are relatively movable towards and away from each other and at least one of which jaws is shaped to mate with at least some of the side profile of the mounting body, the clamping device having means for substantially preventing relative movement between the jaws and the mounting body when the jaws are fully closed around the mounting body.

If the mounting block has a slot or other locating feature at its free end, this is pref erably engaged by a corresponding feature on the clamping device to inhibit or prevent turning of the mounting block and to orient the lens correctly. The mounting block could alternatively have a side profile which is radially unsymmetrical, for example of a square cross section, so that rotation relative to the mating surface is prevented.

The jaws may each be independently movable, or one jaw may be fixed.

In a preferred embodiment, the clamping device has two pairs of jaws for clamping two lenses that will be made into a pair of spectacles. Clamping may be effected by both pairs of jaws by operation of a single can locking member which has surfaces that bear against a movable jaw from each pair.

The invention will now be further described, by way of example, with reference to the following drawings in which:

Figure 1 is a perspective view of a known mounting block f or securing to a lens; Figure 2 is a plan view of an assembled clamping device in accordance with one aspect of the present invention; Figure 3 is an enlarged view of the clamping mechanism shown in Figure 2; Figure 4 is a plan view of the base plate of the clamping device of Figure 2; Figure 5 is a plan view of the fixed clamp plate of the clamping device of Figure 2; Figure 6 is a plan view of the left hand movable clamp plate of the clamping device of Figure 2; Figure 7 is an end elevational view of the movable clamp plate of Figure 6; Figure 8 is a sectional view along the line A-A of Figure 6; Figure 9 is plan view of the cam locking member of the clamping device of Figure 2; and Figure 10 is a sectional view along the line B-B of Figure 9.

The known mounting block shown in Figure 1 comprises a body 4, in this example made f rom brass, with a head 2, in this example made from rubber. The head 2 has an adhesive coating on its upper surface which permits the mounting block to be releasably adhered to a lens. An alignment slot 6 is f ormed in the bottom of the body 4. When used in a known lens-cutting operation, a lens is secured to the head 2 and the lens and mounting block are mounted between the chuck of a grinding machine (which engages with the location slot 6) and a stop member which is urged against the free side of the lens. This arrangement is not suitable for further machining operations such as drilling and engraving because the stop member prevents or inhibits motion of a drill or engraving instrument over the surf ace of at least some of the lens.

The clamping device shown in Figure 2 comprises a base plate 8, a fixed clamp plate 12, movable clamp plates 14, and a cam locking member 16. The base plate 8 has holes 10 to enable it to be mounted on a movable support, for example an x-y table, which may be operated under computer control. Referring now to Figure 4, the base plate has a pair of upstanding lugs 22, each for engaging with the alignment slot 6 of a mounting block. A spindle 24 is provided on the base plate for mounting the can locking member 16. The lugs 22, holes 18 and spindle 24 are located in a recess 26 which is the same shape as the fixed clamp plate 12. The base plate has holes 18 for securing it to the fixed clamp plate 12 and to a top plate (not shown). The top plate is fitted over the assembly shown in Figure 3 to hold the assembly together.

The clamping assembly is shown in more detail in Figure 3. The fixed clamp plate 12 has slots 38 that co-operate with slots 32 in the movable clamp plates 14 to house springs 20 that urge the jaws 30 of the movable clamp plates away from corresponding jaws 28 on the fixed clamp plate. The jaws of the clamp plates are profiled to match the external profile of the mounting block, as best shown in Figures 6 to 8. When a mounting block is correctly located between the jaws, with the lug 22 located in the locating slot 6 of the block, the mounting block is held securely when the cam locking member 16 is turned to a locking orientation at which it urges the jaws 30 of the movable clamp plate 14 towards the jaws 28 of the fixed clamp plate 12. The mounting block is waisted so that clamping around the waist is sufficient to prevent translational movement. However, it is desirable to support most or all of the side of the block while a lens is being machined so as to restrict tilting of the lens.

Different shaped mounting blocks may be used. In a preferred embodiment, a plurality of fixed and/or movable clamp plates are provided each of which is profiled to match a specified mounting block and each of which may be interchanged with a corresponding part to enable secure clamping of any of the different mounting blocks. Alternatively, the profile of either or both jaws could be adjustable.

The can locking member 16 has an elliptical shape in plan view. It has a cruciform slot 34 in its upper surface and an aperture 36 in its lower surface which is rotatably mounted on the spindle 24 of the base plate 8. To turn the cam locking member 16, a suitably shaped key (for example a cross- head screwdriver) is inserted into the cruciform, slot and turned.

To use the clamping device, a lens, attached to a mounting block, is inserted between the jaws of the fixed and movable clamp plates. The movable clamp plates 14 are held apart from the jaws of the fixed clamp plate at this stage by the springs 20. With the lug 22 located in the locating slot 6, the clamp plates are then closed around the mounting block by turning the cam locking member so that its long axis aligns with the centre of the mounting block, securely holding the lens in place. The lens can then be machined, for example by drilling or engraving. Because the lens is held securely from below, leaving the top surface completely open, a machining tool can access all of the lens and fixings may be attached anywhere around the lens.

Claims

1. A method of holding a lens f or machining, comprising clamping a mounting block by clamping means so as substantially to prevent relative movement between the clamping means and the mounting block, the lens to be machined having the mounting block releasably secured to one side thereof and the clamping means being located on only the said one side of the lens so as to leave the other side of the lens fully accessible.

2. A method of holding a lens as claimed in claim 1, wherein a second lens is held adjacent to the first lens while the f irst lens is held.

3. A method of holding a lens as claimed in claim 1 or claim 2, wherein the lens is secured to the mounting block 15 before the mounting block is clamped.

4. A method of holding a lens as claimed in any one of the preceding claims, wherein the mounting block has a locating feature at one end and a corresponding feature associated with the clamping means engages in the locating 20 feature to prevent rotation of the mounting block.

5. A method of machining a lens, comprising clamping a mounting block by clamping means so as substantially to prevent relative movement between the clamping means and the mounting block, the lens to be machined having the mounting block releasably secured to one side thereof and the clamping means being located on only the said one side of the lens so as to leave the other side of the lens fully accessible, and then performing a machining operation on the lens.

6. A clamping device for clamping a lens mounting block comprising a lens receiving surface and a mounting body having a predetermined side profile, the device comprising a pair of jaws which are relatively movable towards and away from each other and at least one of which j aws is shaped to mate with at least some of the side prof ile of the mounting body, the clamping device having means f or substantially preventing relative movement between the jaws and the mounting body when the jaws are fully closed around the mounting body.

7. A clamping device as claimed in claim 6, wherein the mounting body has a locating feature, and the clamping device is provided with a corresponding feature for engagement with the locating feature so as to prevent turning of the mounting block when the features are interengaged.

8. A clamping device as claimed in claim 6 or claim 7, further comprises a second pair of jaws spaced apart from and of similar construction to the first pair of jaws.

9. A clamping device as claimed in claim 8, wherein a rotatable cam locking member is provided between the first pair of jaws and the second pair of jaws, the arrangement being such that rotation of the cam locking member moves it between a locking orientation where the locking member urges at least one jaw of each pair towards the other jaw so as to close the jaws, and an unlocked orientation where the locking member permits or causes each of the pairs of j aws to open.

10. A clamping device as claimed in any one of claims 6 to 9, wherein each jaw of a pair is urged away from the other jaw by spring means.

11. A clamping device as claimed in any one of claims 6 to 10, wherein each jaw is shaped to mate with substantially all of the side profile of the mounting body of the mounting block.

12. Apparatus for holding a lens for machining, comprising:

a lens mounting block comprising a lens receiving surface and a mounting body; and a clamping device comprising a pair of jaws which are relatively movable towards and away from each other and at least one of which jaws is shaped to mate with at least some of the side profile of the mounting body, the clamping device having means for substantially preventing relative movement between the jaws and the mounting body when the jaws are fully closed around the mounting body.

13. A clamping device substantially as herein described with reference to or as shown in Figures 2 to 10 of the drawings.

14. A method of holding a lens f or machining, substantially as herein described with reference to drawings.