GB2168276A - Automatic device for locating the ideal position of a diamond or gem during the cutting thereof - Google Patents

Abstract

A device for locating automatically the ideal position of a diamond 9 during cutting the facets thereof comprises in combination with a grindstone 10, means for measuring for each orientation wherealong a facet is cut, the amount diamond being stripped during a specific time interval, and means for comparing said amounts. The diamond 9 is carried by a bridge 5 vertically slidable on a column 2 and a follower 7 on the bridge co-operates with an eccentric disc 14 rotated by a motor-gear unit 16. An electric circuit which is closed when the disc 14 contacts the follower 7 controls operation of the motor-gear unit 16, and a pulse generator-sensor 22 passes to an electronic computer 18 signals which accurately represent the rate at which material is removed from the diamond. <IMAGE>

Description

SPECIFICATION Device for automatically locating the ideal position of a diamond or gem during the cutting thereof This invention relates to a device for automatically locating the ideal position of a diamond or gem during the cutting thereof.

Diamond is comprised of pure crystallized carbon.

By means of radio-crystallography, the "cubic, centered-side" structure of the diamond the elementary mesh of which is comprised of eighteen carbon atoms, has been determined. The links between said atoms are covalent and extremely strong, which explains the high hardness of diamond. The arrangement of the eighteen atoms in the elementary mesh of the structure explains the various properties of said gem, particularly the welldefined planes for cleaning, sawing, polishing, as well as the shapes of the rough crystals.

The energy which joins the molecules together may be considered as maximum in some plane sides and minimum in the cleaving planes. The most usual crystal shapes are the octahedron, the hexahedron, the dodecahedron and the cube. It often happens that two crystals or more enter one another or else be intimately associated by one side of the octahedron. Such diamonds with different orientations are very difficult to cut.

It is possible to cut and polish a diamond but after determining for each crystal side or face, the direction with the lowest hardness. The stone to be cut or polished, will then be arranged along such direction on a metal table, coated with diamond powder and rotating with a speed about 3000 RPM.

The diamond side will be cut or polished but when it is laid along the accurate direction on the table. In all other directions, the diamond will cause a more or less fast wear of said table.

The direction wherealong the diamond may be polished is dependent on the stong crystallographic structure.

The invention has thus for object to design a device fitting in a machine allowing to polish the diamond faces by means of a new method for determining the optimum direction wherealong that diamond facet to be polished should be arranged relative to the table.

Various methods and machines have already been proposed to determine the ideal direction wherealong the diamond side to be polished should be engaged.

According to Belgian Patent 748,183, it has already been proposed to sense the so-called "softest" direction, and this by using an oscillation sensor. The friction between the diamond and grindstone does indeed generate varying oscillations which can be measured and compared relative to one another.

According to said Belgian Patent, there is provided in a control device for cutting monocrystals, a stone-holder supported on the end of a vertical shaft, which is rotatable about the geometrical axis thereof, and means are provided to rotate the stone at right angle to the axis thereof relative to the polishing grindstone.

Measuring oscillations and particularly converting same into comparison values, raises extremely intricate technical problems, in such a way that it is to be granted that the final result is not always reliable.

According to another working method disclosed in the description of a machine for polishing precious stones according to Belgian Patent 880,678 in the name of Bonas Machine Company Ltd., the resistance between the stone to be polished and the grindstone is measured, and a signal is provided which is dependent on the poishing rate to allow so directing the shaft following the "grain", so as to insure a so-called "efficient" polishing.

According to said Patent, the force being provided to obtain a "feeding rate" is being measured, actually the slowing-down. The determination of the resistance to polishing implies the use of an extremely sophisticated apparatus, requiring many adjustments which may be assumed as requiring an extremely sensitive and costly working way.

Finally in another Belgian Patent mentioned here as part of the previous art (n 856,692), use is also made of a device for holding the diamond which is mounted at right angle to a grindstone and is rotatably adjustable over 3600 to be continously brought in the ideal cutting position thereof according to the friction factor as measured in kg/m or KG/calories. The Patent also refers to German Patent 293,160 wherein the same object is searched for by monitoring the backing-off at various speeds of the stone-holding device against the grindstone and this for various angular positions thereof.

Actually when summing-up the statements of the previous Applicants, it is noted that they have accessorily observed the amount diamond being removed and the computations have thus been directed according to other parameters such as the slowing-down being caused by the diamond applied with the various sides thereof against the grindstone, the heating caused by polishing, the strain noted during the polishing, as well as the oscillations involved by such polishing.

All such investigations have not allowed discovering a method nor a device allowing the fast estimating (a few seconds) of the diamond material loss during the polishing of each side thereof along directions distributed over 3600. As long as simple and reliable means have not been proposed to measure extremely rapidly the amount diamond being stripped by the grindstone during the polishing under various tested angles, any method based on such verification is useless because any extended contact of a diamond with the grindstone under an unsuitable angle, will rapidly cause wear thereof.

The invention has thus for object to provide a device for automatically locating the ideal position of a diamond or a gem during the cutting thereof.

For this purpose in such a device comprising in combination with a grindstone: - aheight-adjustable shaft which is slidable along a vertical column which is partof the machine structure; - astone-holder so mounted as to be directable according to the polishing angle (+ 40O) on the lowermost end of a vertical arm secured through a bridge to said slidable shaft, said vertical arm bearing the stone-holder, being directable over 3600 about the vertical axis thereof in such a way as to present each diamond side along a number of directions relative to the grindstone;; said automatic device comprises a follower arm bearing in a starting position on a disk eccentrically secured to a horizontal shaft rotated by a motorgearing unit, the disk eccentricity being so designed as to have when the diamond engages the grindstone, the contact between said slidable arm and eccentric disk be broken after a minute disk rotation, means being provided to stop rotating that shaft said eccentric disk is secured to when the contact between the disk and follower arm is broken, the shaft being rotated anew when the grindstone has removed a diamond layer, which causes lowering the follower arm and the vertical arm on the end of which the stone-holder is mounted, and resuming of the engagement between the eccentric disk and follower arm, means being finally provided to record the pulses counted between the breaking and resuming of said contacts.

Other details and features of the invention will stand out from the following description given by way of non limitative example and with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic view of the device according to the invention as associated to a grindstone-table.

Figures 2 to 7 diagrammatically show various preferential directions wherealong the tables and collets from three different stones may be worked.

Before describing in detail the device according to this Patent Application and with reference to figures 2 to 7, it will be recalled that those stones having the table thereof in parallel relationship with a cubic side, are called "Four-points" and will be cut according to the diagram in figures 2 and 3. Those stones the table of which lies parallel to an octahedron side, are called "Three-points" and will be cut according to the diagram in figures 4 and 5.

Those stones the table of which lies parallel to a rhombohedron side, are called "Two-points" and will be cut according to the diagram in figures 6 and 7.

The stones which include a plurality of crystallographic types are called "macles" and do not have a specific diagram. There should thus be formed for each facet of this kind of stones, the most suitable polishing direction. All the sides of a diamond are cut on a turntable along one from eight directions extending over 3600.

To determine for each facet of a diamond the ideal direction wherealong such facet should be cut or polished, there is provided a device according to the invention which allows to measure for every direction the cutting or polishing is made along, the amount of material which is being abraded. The device according to the invention does not only enable such measuring, but same is obtained for every direction wherealong the facet is engaged by the grindstone, within an extremely short time. This is essential when it is desired to compare with one another the various results and deduce therefrom the most favourable direction, which is in turn deduced from the maximum amount diamond being stripped and this due to storing the data being obtained for each direction and comparing same with one another.

The device according to the invention comprises a structure 1 wherewith a column 2 is integral, wherealong a height-adjustable shaft 4 is mounted through linear ball-bearings 3. Said shaft is connected to a bridge 5 wherewith the vertical arm 6 and follower arm 7 are also integral.

The stone-holder 8 is secured to the lowermost part of vertical arm 6. The stone 9 may be oriented relative to the grindstonetable 10 by means of a micromotor 11, to present to the grindstone-table 10 rotated by a motor 12, succeedingly each stone facet. The vertical arm 6 may in turn be rotated about the geometric axis thereof by means of a micromotor 13.

As regards follower arm 7 the function' of which is essential, it bears with the base thereof on a disk 14 which is eccentrically secured to a shaft 15 which is rotated by a motor-gearing unit 16.

To said shaft 15 there is fastened for example an electric pulse generator-sensor 22. The electric signals shown diagrammatically in 17 are received by an electronic computer 18 which is notably so programmed as to compare with one anotherthe signals being received, as explained hereinafter with reference to the description of the operation of the device according to the invention.

With reference to figure 1, there will further be noted that in a possible embodiment, the follower arm 7 is provided inwardly with a channel 19, a microswitch 20 and a diaphragm flow-meter 21 the air pressure inside channel 19 remaining at a specific value as long as the base of said channel 19, that is follower arm 7 remains engaged with the revolution surface of eccentric disk 14. In another embodiment not shown, a leaf which forms an electro-mechanical contact with disk 14, is provided at the bottom of follower arm 7. The contact between said leaf and disk 14, and the contact breaking comprise two conditions which will be described hereinafter.

The operation of the device according to the invention is as follows: The stone 9 being secured to the stone-holder 8 on the lowermost part of vertical arm 6, the device is started, the grindstone-table rotating with the usual speed thereof. The vertical arm goes down and stone 9 comes to bear on the grindstone-table 10.

The facet, called facet 1, engages the grindstonetable 10. The friction required for polishing is obtained. Afew seconds contact or friction are enough to determine whether the direction wherealong the stone has been laid on contact with the grindstone-table is correct, that is whether this direction is suitable for polishing, or else if said direction is to be considered as ideal. A few seconds friction are enough to use a minute amount diamond.For each facet, eight polishing directions distributed over 360 will be used and the amounts diamond being stripped from the facet along each direction will be compared to one anotherthe measurings and the comparison thereof will be explained hereinafter: When the eccentric disk 14 driven by motorgearing unit 16 rotates, it has a tendency to bring the smallest axis thereof in engagement with follower arm 7. Said disk 14 directly engages the bottom of follower arm 7. An electric contact is made between both said components.

As soon as the diamond engages the grindstonetable, the eccentric disk keeps on rotating due to driving by the motor-gearing unit 16. As soon as the contact between said eccentric disk and the follower arm 7 is broken, the power to motor-gearing unit 16 is cut-off. The diamond then bears directly and without support on the grindstone-table due only to the weight of vertical arm 6. The eccentric disk is stopped.

As soon as some wear, as minute as it may be, of the diamond occurs, the bottom of follower arm 7 engages again eccentric disk 14, which closes again the electric contact. This starts again the motorgearing unit 16, while the revolution surface of eccentric disk 14 moves away from follower arm 7.

This is when considering the revolution direction of eccentric disk 14 and due to noting the radius thereof becoming smaller during the rotation. As soon as diamond 9 is laid again 6n grindstone-table 10, the contact eccentric disk 14-follower arm 7 is broken again, which causes the motor-gearing unit 16 to stop.

There is thus obtained the stopping, followed by the starting, followed again by the stopping of the motor-gearing unit 16. The accurate wear of the diamond corresponds to this very accurate course.

To measure such course, use is made of an electric pulse generator-sensor 22. Said sensor may be an electro-optic angular sensor as shown in diagrammatic figure 1, fastened to the extension of horizontal shaft 15. Use may also be made of a capacitive sensor or a differential-transformer sensor, or any other rotating or linear device which can generate electric pulses in relation with the short path of disk 14 and thus also of motor-gearing unit 16.

There has thus been obtained an electric pulse value which is accurately proportional to the diamond wear. Said electric pulses are coupled to an electronic computer 18 which will store the pulse number. Said computer insures the automatic control of the device.

The abovedescribed test will be performed within a very short time (for example a few seconds). The vertical arm 6 will be raised automatically under command of computer 18 which is programmed therefor. The diamond will be oriented along the vertical axis of the stone-holder in the following position or position n0 2, and this still on the same facet. The same process is thus reproduced eight times, as explained above. The process thus comprises lowering the vertical arm 6, followed by engaging diamond 9 with the grindstone-table 10, breaking the contact between eccentric disk 14 and follower arm 7 due to rotating of motor-gearing unit 16 until a new contact is made between said components due to the diamond wear.

In the following step, there occurs the raising of said arm and repeating said operation in 6 to 8 positions (which number anyway vary). The electronic computer 18 will thus have recorded the pulse number as well as the corresponding diamond position relative to the position of grindstone-table 10. Said position will be kept and thus stored according to a preferential sequence depending on the collected pulse number and in decreasing order. The electronic computer is so programmed as to know at every moment, due to comparing of the obtained results in the various positions, which is the position or direction which causes the most diamond wear during the shortest time period. Said direction may be considered as the most favourable direction for the cutting and polishing, and does correspond to the softest direction relative to the grindstone abrading.After locating automatically the second facet, the arm will repeat the same operations for each position relative to the axis at right angle to the grindstonetable. The 8, 16 or 24 facets a brilliant or gem should comprise are thus tested.

At the end of the complete process, the device will be ready to begin the cutting work proper. The device is then operated again to cut automatically according to the stored data, all the diamond facets and this under the best possible working conditions.

The device starts with the cutting or polishing of the first facet. The device vertical arm 6 automatically assumes the best position as computed by the microprocessor or electronic computer. The arm will be lowered to engage the diamond with the grindstone-table 10. When the first facet has been completed, that is when it has the required size, the arm is raised. Rotating of the stone-holder will locate the second facet facing the turntable and this in the best position as given by the electronic computer for the second facet.

The vertical arm 6 will be lowered again and the cutting of the diamond on all the facets thereof will thus be pursued.

From the description of the working process as well as the device for the working thereof, it is immediately clear that the device electronic computer may calculate with the data coupled thereto, whether the wear process is not fast enough. It will then command the stone-holder to move to the second-best position resulting from the comparison in the electronic computer. It may indeed occur when some diamond amount has been worn, that crystallographic irregularities will appear on the surface. Such irregularities sometimes require another location of the stone holder to be removed. This is the reason why the electronic computer keeps on analyzing permanently the wear process, which will enable cutting the stone completely within a minimum time interval and this completely automatically.

The analysis of the diamond wear magnitude before and during the cutting or polishing process lets the automatic device cut all crystailographic types of diamond, as well as all the hard or precious stones wherein the cut is dependent on the crystallographic orientation.

As regards counting the electric pulses between that moment where the contact between eccentric disk 14 and the bottom of follower arm 7 is broken, and the moment said contact is made again, this may occur with any means known to the man of the art.

Claims (8)

1. Device for automatically locating the ideal position of a diamond or gem during cutting thereof, comprising in combination with a grindstone: - aheight-adjustable shaft which is slidable along a vertical column which is part of the machine structure; - astone-holder so mounted as to be directable according to the polishing angle (+ .00) on the lowermost end of a vertical arm which is secured by means of a bridge, to said slidable shaft, said vertical arm bearing the stone-holder being orientable over 360 about the vertical axis thereof, in such a way as to present each diamond side along a number of directions relative to the grindstone, which device comprises a follower arm bearing in the starting position, on a disk eccentrically secured to a horizontal shaft rotated by a motor-gearing unit, the eccentricity of said disk being so designed as to have when the diamond engages the grindstone, the engagement between said slidable arm and eccentric disk be broken after a minute rotation of said disk, means being provided to stop rotating that shaft the eccentric disk is secured to when the contact between said disk and follower arm is broken, the shaft being rotated again when the grindstone has removed a diamond layer, which causes lowering of said eccentric disk and follower arm, means being finally provided to generate and record pulses which are counted during the disk rotation and this between the stopping and resuming of said contacts, the pulse number providing a electric magnitude which is accurately proportional to the amount diamond being worn.

2. Device as defined in claim 1, in which said means for generating and recording said pulses are comprised of an electro-optic angular which is mounted on said shaft.

3. Device as defined in claim 1, in which said means for generating and recording said pulses are comprised of a capacitive sensor.

4. Device as defined in claim 1, in which said means for generating and recording said pulses are comprised of a differential-transformer sensor.

5. Device as defined in claim 1, in which said means for generating and recording said pulses are comprised of a rotating or linear-movement device which can generate electric pulses due to rotating of said horizontal shaft.

6. Device as defined in any one of claims 1--5, in which a pressurized air channel is provided inside said follower arm, which channel is normally closed due to the engagement between the base of said follower arm and said eccentric disk, while means are provided to cut-off the electric power to the motor-gearing unit when the contact is broken between the follower arm base and said eccentric disk, thus causing the air pressure inside said channel to drop.

7. Device as defined in any one of claims 1-5, in which said follower arm base is provided with a leaf which normally engages the revolution surface of said eccentric disk to let an electric current flow in such a way that when the contact between said leaf and eccentric disk is broken, the electric power to the motor-gearing unit is cut-off.

8. A device for automatically locating the ideal position of a diamond or gem during cutting thereof, substantially as hereinbefore described with reference to and as shown in the accompanying drawings.