GB2230487A

GB2230487A - Optical-lens tool

Info

Publication number: GB2230487A
Application number: GB9008745A
Authority: GB
Inventors: Stephen Jack Wylde; Timothy Noakes
Original assignee: J&S Wylde Ltd
Current assignee: J&S Wylde Ltd
Priority date: 1989-04-21
Filing date: 1990-04-18
Publication date: 1990-10-24
Also published as: GB8909060D0; GB9008745D0

Abstract

A rotary tool for optical lens production has grinding points or edges (65) which are distributed over a boundary which is curved in any and every axial-sectional plane of the tool, and which is bisected by a plane which is orthogonal to the rotary axis of the tool. The tool boundary may be spherical or part-spherical and may consist of a working surface encrusted with diamond particles. The tool boundary may alternatively be defined by the edges of the cutters spaced apart around the tool. The tool may be mounted in a copy form unit for grinding lenses or lens tools. <IMAGE>

Description

O#tical-lens tool The present invention relates to an optical-lens tool for generating a lens, and possibly also for generating a different lens tool.

Earlier forms of lens generator have comprised angled cup grinding wheels and variable length radius arms to generate compound forms or toric lenses having more than one radius of curvature. Such machines suffer the drawbacks (a) that there is always some upper limit to the radius of curvature that can be generated (b) that the lower limit is relatively high and (c) that elliptical error occurs when the tool is traversed at different radii.

In our prior British Patent Specification No.

2,185,917, we describe a lens generator that is less subject to one or more of the foregoing drawbacks. Thus, in that specification we describe a copy form unit comprising a lens master mount, a lens blank or lens tool blank mount, and a copy form unit having a lens master feeler and a lens or lens tool grinder, miller cutter or other machining tool, in which the feeler and the machining tool have the same relative positioning as a lens master and a lens or lens tool blank when these are inserted in the generator, and in which the machining tool is coupled to the feeler to execute the same movement as the feeler as the latter is moved across a face of a lens master mounted in the lens master mount. The machining tool is in the form of a circular plate.

It will be appreciated that the generator may generate further lens tools as well as lenses themselves.

A disadvantage encountered by such a generator arises from the use of a circular plate grinder, which tests have shown to limit the strength of lens which can be ground satisfactorily. In fact, it is very difficult with such a grinder to grind a lens of greater strength than 11 dioptres accurately without failure of the grinder.

The present invention seeks to provide a remedy.

Accordingly, the present invention is directed to a rotary optical-lens tool having cutting or grinding points or edges which are distributed over a boundary which is curved in any and every axial-sectional plane of the tool, and which is bisected by a plane which is orthogonal to the rotary axis of the tool.

The said boundary may comprise a real working surface, which may be encrusted with cutting or grinding particles such as diamond particles, or it may be a notional two-dimensional configuration defined by curved edges of cutters or grinders spaced apart around the tool. It has been found that the latter is preferable because of the voids provided between successive cutters or grinders which assist the flow of swarf and also the flow of water or slurry applied to the working area.

Advantageously, the curvature of the said boundary in any and every axial-sectional plane follows a part conic section, preferably part of a circle.

It is desirable to have the radius of curvature of the said boundary in any and every axial-sectional plane nowhere less than a quarter of the distance between the said boundary in the orthogonal plane and the rotary axis of the tool. Advantageously, the radius of curvature is everywhere equal to the said distance, so that the said boundary lies on a sphere centred on the mid-point of the axis of the tool.

A tool made in accordance with the present invention is particularly effective in a generator having the construction set out in the fifth sentence of the present specification, the tool being what is referred to as the machining tool in that sentence.

One or more of the following further advantages are obtainable with such a generator: 1. The range of powers of lenses which can be made is increased from a maximum of 200 to a minimuum 58mm radius when using an 86 P.C.D. cup wheel on existing machines, to a maximum of infinity radius and a minimum of 30mm radius when using a copy form machine.

2. Substantially no elliptical error is generated by the copy form generator, as it is able to copy the original master form exactly, the master form having been cut by a single point tool, following true arcs. The angled wheel of existing generators when traversed at different radius, will form an elliptical curve.

3. An automatic generator at lower cost, with a greater range, and more accurate powers, is therefore possible with the copy form principle. This is true because an existing engineering technology is used for the body of the copy form machine, in the use of a standard centre lathe, for example, while one of several makes of hydraulic copying machines can be used to actuate a grinding or milling tool mounted upon the lathe.

An example of a tool made in accordance with the present invention, and an example of a generator having such a tool, are illustrated in the accompanying diagrammatic drawings, in which: Figure 1 is an elevational side view of such a generator; Figure 2 shows, on a larger scale, a side view of such a tool; Figure 3 shows a front view of the tool viewing it in the direction III shown in Figure 2; Figure 4 shows a side view of a modified form of tool; Figure 5 shows a front view of the tool shown in Figure 4, viewing it in the direction V; Figure 6 shows an axial sectional view of a further modified form of tool; and Figure 7 shows a front view of the tool shown in Figure 6, viewing in the direction VII.

The generator shown in Figure 1 comprises a 165 centre lathe 8 on a mounting block 10 of a horizontal slide 12 of which is mounted an hydraulically operated copy form unit 14 via mutually perpendicular horizontal fine adjustment slides 16 and 18. The mounting block 10 of the slide 18 has a rotary adjustment wheel 22 by which the position of the block 10 can be adjusted along the slide 18, for example by means of a rack and pinion engagement or a screwthread (not shown). Similarly, the fine adjustment slides 16 and 18 are provided with rotary adjustment wheels 24 and 26.

The copy form unit 14, apart from a ball-shaped grinder 28, with belt drive motor 30 drivingly coupled thereto, mounted in the tool position of the unit, is a well-known piece of equipment so that it will not be described in detail. It will suffice to state here that it has a rotary stylus 32 which constitutes the feeler and which is mounted at the end of an arm 34 at a position directly above the grinder 28. The stylus 32 has the same dimensions as the grinder 28. The arm 34 is provided with a screwthreaded adjustment, operable by a rotary adjustment wheel 35, to enable the length of the arm 34 to be adjusted.The copy form unit has means (not shown) to urge the stylus 32 resiliently against the master form which is to be copied, screw-threaded drive means normally provided as part of the cross slide 16 of the lathe to traverse the stylus across the form automatically and simultaneously the grinder 28 across the lens blank or tool blank (in this case in a vertical plane), means (not shown) to provide a measure of the longitudinal position of the stylus 32 as it rides over the form, and a hydraulic servo mechanism to move the grinder 28 so that it constantly adopts the same longitudinal position as the stylus 32, and hence copies the movement of the sylus 32.

Connecting lines are labelled 31 and 33.

The lathe 8 is provided with a first rotary chuck 36 mounted on the lathe with its axis of rotation horizontal and at a position directly opposite the grinder 28, so that the chuck 36 faces the grinder 28 and a lens blank or tool blank held therein is presented to the grinder 28. The lathe 8 has a second rotary chuck 38 mounted directly above the first chuck 36, with the same spacing as that between the stylus 32 and the grinder 28.

The chuck 38 also has its axis of rotation horizontal, parallel to that of the chuck 36, and is positioned directly opposite the stylus 32, so that the chuck 38 faces the stylus 32 and a lens master form held therein is presented to the stylus 32.

The rotary chucks 36 and 38 are mounted at respective ends of two shafts 40 and 42. These shafts are simultaneously driven by means of a timing drive 44. The latter includes a motor 46 by means of which both chucks can be rotated about their axes at a speed in the range from 60 to 600 rpm in synchronisation with one another.

The machining tool constituted by the grinder 28, and embodying the present invention by way of example only, is shown in greater detail in Figures 2 and 3. It comprises a die cast metal or hard synthetic plastics ball 48 having a near complete spherical surface 50 which is diamond encrusted. A shaft 52 extends through a bearing 54 fixed to the ball 48, the shaft 52 having its elongate axis coincident with the rotary axis of the grinder 28.

The shaft 54 is fixed to the bearing 54 and is cantilevered from a rotary mount 56 (shown in Figure 1) on the copy form unit 14. The shaft 52 is engaged by the belt drive 30 to rotate the grinder 28 about its rotary axis.

It will be appreciated that the region of greatest wear on the surface of the grinder shown in Figures 2 and 3 is in the region 56 between the parallel broken lines shown in Figure 3. Therefore, it would be possible to modify the grinder by making it thinner, eliminating those parts of the ball 48 which offer substantially unused surface areas. The resulting construction is shown in Figures 4 and 5.

An improved form of construction of the grinder is shown in Figures 6 and 7, comprising a high speed steel body 60 having a series of teeth 62 spaced apart around the periphery of the grinder. Each tooth has a tungsten carbide tip 64 providing a cutting or grinding edge 65.

Each edge 65 is curved, and the edges 65 of all the teeth 62 together define a boundary having the same twodimensional configuration as the working surface of the grinder shown in Figures 4 and 5. The face 56 of the body 60 which is further from the shaft 52 may be recessed to reduce the weight of the body. Each tooth 62 slants away from an intended sense of rotation of the grinder to increase its resistance to the forces acting upon it during grinding.

The construction of grinder shown in Figures 6 and 7 has an advantage over the constructions shown in Figures 2 and 3, and Figures 4 and 5, in that voids 68 are provided between successive teeth 62, which voids assist the flow of swarf and cooling water or slurry which may be trained on the working area during cutting or grinding.

The operation of the generator is as follows.

The selected lens master form is clamped in the upper chuck 38 and the lens or tool blank is clamped in the lower chuck 36. Any necessary adjustments are made to the position of the copy form unit 14 by means of the adjustment wheels 22, 24, 26 and 35. Adjustment to the wheel 35 moves the stylus 32 relative to the grinder 28 to allow for different intended thicknesses of the finished product relative to the tool. The generator is now switched on and performs a pre-programmed operation automatically in which the stylus 32 moves from the centre of the tool to the periphery thereof and the grinder 28 follows the movement of the stylus to copy the surface of the master form onto the lens blank or tool blank.

Simultaneously, both chucks 36 and 38 are rotated at a speed in the range from 60 to 600 rpm in synchronisation with one another, and the grinder 28 is rotated at several thousand rpm. If the master form has a toric face which is being copied, the stylus 32 and therefore the grinder 28 will reciprocate towards and away from the chucks 36 and 38 accordingly as the latter are rotated in synchronisation with one another and as the stylus traces a spiral path on the master form surface.

Many modifications and variations to the illustrated examples will occur to the reader without taking the resulting construction outside the scope of the present invention. For example, although for clarity the stylus 32 and the grinder 28 are shown in Figure 1 as having horizontal axes of rotation, it would be preferable for them to have vertical axes of rotation. Whilst a belt drive has been illustrated in Figure 1, a gear box drive for rotation of the grinder 28 is preferred. The grinder 28 which is shown in the Figures as being cantilevered may alternatively be supported in rotary bearings at both ends of the shaft 52, the latter passing right the way through the ball 48 or other member which provides the working surface. Instead of a shaft 52 passing right the way through the ball 48, one or two shaft positions may be fixed to opposite sides thereof. The positions of the master form mount and the lens or lens tool blank mount may be swapped, in which case the positions of the stylus and the grinder on the copy form unit would also be swapped.

Claims

1. A rotary optical-lens tool having cutting or grinding points or edges which are distributed over a boundary which is curved in any and every axial-sectional plane of the tool, and which is bisected by a plane which is orthogonal to the rotary axis of the tool.

2. A tool according to claim 1, in which the said boundary comprises a working surface.

3. A tool according to claim 2, in which the working surface is encrusted with cutting or grinding particles.

4. A tool according to claim 3, in which the cutting or grinding particles comprise diamond particles.

5. A tool according to claim 1, in which the said boundary is a notional two-dimensional configuration defined by curved edges of cutters or grinders spaced apart around the tool.

6. A tool according to any preceding claim, in which the curvature of the said boundary in any and every axial-sectional plane follows a part conic section, preferably part of a circle.

7. A tool according to any preceding claim, in which the radius of curvature of the said boundary in any and every axial-sectional plane is nowhere less than a quarter of the distance between the said boundary in the orthogonal plane and the rotary axis of the tool.

8. A tool according to claim 7, in which the said radius of curvature is everywhere equal to the said distance, so that the said boundary lies on a sphere centred on the mid-point of the axis of the tool.

9. A rotary optical-lens tool substantially as described herein with reference to Figures 2 and 3, Figures 4 and 5, or to Figures 6 and 7 of the accompanying drawings.

10. A lens generator comprising a lens master mount, a lens blank or lens tool blank mount, and a copy form unit having a lens master feeler and a rotary optical-lens tool as claimed in any preceding claim, in which the feeler and the optical-lens tool have the same relative positioning as a lens master and a lens or lens tool blank when these are inserted in the generator, and in which the optical-lens tool is coupled to the feeler to execute the same movement as the feeler as the latter is moved across a face of a lens master mounted in the lens master mount.

11. A lens generator substantially as described herein with reference to Figure 1 in combination with Figures 2 and 3, or in combination with Figures 4 and 5, or in combination with Figures 6 and 7 of the accompanying drawings.