Abrasion apparatus and method

Abstract

Apparatus for abrading a diamond element, comprising: an element support for supporting a diamond element; an abrasion means for abrading a surface of the element in an abrasion direction; an actuation system for controlling the relative orientation of the element support and the abrasion means; a sensor configured to sense a measured abrasion parameter, the measured abrasion parameter relating to an abrasion distance defined as the perpendicular depth of material that has been removed from the surface during abrasion; and a control system. The control system is configured to: a) receive information relating to i) a soft direction of a first facet to be abraded and ii) a target abrasion distance of the first facet; b) send a control signal to the actuation system to cause a change in relative orientation between the abrasion means and the element support to align the abrasion direction with the soft direction; c) receive information from the sensor relating to the measured abrasion parameter as the first facet is abraded; d) determine, based at least on the measured abrasion parameter, whether the abrasion distance is equal to the target abrasion distance; and e) halt abrasion of the first facet when the abrasion distance is equal to the target abrasion distance.

Description

[0001] Abrasion Apparatus and Method

[0002] The invention relates to an abrasion apparatus and method, in particular for grinding and / or polishing elements. While the apparatus and method may be used to grind or polish any suitable element, including for example a faceted element made of glass, ceramic glass-ceramic, plastics material, precious or-semi precious stone, it is particularly suitable for grinding and / or polishing faceted elements made of materials having an ordered crystal structure, and especially where the ordered crystal structure results in a directional-preference for polishing or grinding (so-called ‘soft’ and ‘hard’ directions). It is therefore particularly appropriate for grinding and polishing diamond elements.

[0003] Diamond cutting and polishing is a highly precise process. To produce a finished diamond, a rough diamond is first cut into a pre-form by a process of laser-cutting, followed by coning, blocking and bruting. The resulting pre-form 10 is shown in Figure 2b. The conical surface of the pre-form is then ground at appropriate locations and angles by hand to remove material and produce the facets of the diamond geometry. The ground facets are then polished to a mirror finish in a hand-polishing process.

[0004] Both the grinding and polishing stages are abrasion processes during which material is removed. In the grinding process, a larger amount of material is removed, to obtain the desired geometry of the facets. This process typically uses a relatively large grit size to remove material efficiently. In the polishing process, a smaller amount of material is removed. The geometry is essentially unchanged, but the facet is polished to a mirror finish.

[0005] Because of the underlying crystal structure, each facet has one or more ‘soft’ polishing directions, while the other directions are ‘hard’ polishing directions. The ‘soft’ direction is the direction with lowest atomic density along that direction, while the ‘hard’ direction is the direction with highest atomic density along that direction. It will be appreciated that the hard and soft directions apply equally to grinding and polishing.

[0006] Figure 1 illustrates soft and hard directions for different crystal planes of the diamond structure. Because the different facets of a pre-form are formed along a different crystallographic plane, the soft and hard directions will be different for different facets.

[0007] When a facet is abraded by movement in the soft direction, abrasion is relatively easy - i.e. material can be removed relatively easily to grind or polish the surface. When the facet is abraded by movement in the hard direction, abrasion is nearly impossible, and the surface cannot be ground or polished. The friction coefficient is typically ten times larger in the soft direction than in the hard direction.

[0008] Figure 2a illustrates the geometry of a diamond 10a having facets 12a, 12b corresponding to a brilliant cut. Each facet can be defined by geometric parameters that include a shape of the facet, and azimuth angle A of the facet relative to the azimuth axis A0, and a slope angle B of the facet, defined by an angle between the azimuth axis A0 and the axis B0 that is perpendicular to the facet surface.

[0009] Each facet can be abraded in different abrasion directions or polishing directions, which are in the plane of the facet. A particular polishing direction can be defined by an angle X about the axis B0 that is perpendicular to the facet surface. Throughout this description, the rotational position of a pre-form about this axis B0 is referred to as the “orientation” of the pre-form.

[0010] A first facet 12a has a soft polishing direction Sa and a hard polishing direction Ha. A second facet 12b, which is at a different azimuth angle A and slope angle B to Facet 12a and hence a different crystallographic plane, has a different soft polishing direction Sb and a different hard polishing direction Hb. To grind or polish each facet 12a, 12b of the diamond 10a from the pre-form 10, the cutter will find an orientation corresponding to the soft direction Sa, Sb of each individual facet through trial and error. During an initial abrasion phase, they will move the stone 10 to a location and inclination corresponding to a desired facet 12a, and will rotate the stone in different orientations so as to abrade the facet 12a in different abrasion directions, and feel the friction coefficient of different directions. If they believe they have located a direction with a high friction coefficient, they will abrade in that direction for a test period, and inspect the stone 10 to see if it has been abraded: if so, the soft direction Sa has been located, and the facet 12a can be abraded in that direction.

[0011] Once that facet 12a is abraded as needed, the cutter moves to the next facet 12b, and repeats the process to find the soft direction Sb for that facet. This is a time-consuming process, which must be carried out for every facet in turn. It also requires a high level of skill and experience from the cutter. A typical one carat diamond will take around 8 hours to grind and polish using this process.

[0012] It is against this background that the invention has been devised.

[0013] Summary of the invention

[0014] Against this background, the invention resides in apparatus for abrading a diamond element, the apparatus comprising: an element support for supporting a diamond element; an abrasion means for abrading a surface of the element in an abrasion direction; an actuation system for controlling the relative orientation of the element support and the abrasion means; a sensor configured to sense a measured abrasion parameter, the measured abrasion parameter relating to an abrasion distance defined as the perpendicular depth of material that has been removed from the surface during abrasion; and a control system. The control system is configured to: a) receive information relating to i) a soft direction of a first facet to be abraded and ii) a target abrasion distance of the first facet; b) send a control signal to the actuation system to cause a change in relative orientation between the abrasion means and the element support to align the abrasion direction with the soft direction; c) receive information from the sensor relating to the measured abrasion parameter as the first facet is abraded; d) determine, based at least on the measured abrasion parameter, whether the abrasion distance is equal to the target abrasion distance; and e) halt abrasion of the first facet when the abrasion distance is equal to the target abrasion distance.

[0015] The abrasion means may be an abrasion wheel that is rotatable about a rotation axis. The control system may be configured to cause relative movement between the abrasion wheel and the test facet in an x-y plane perpendicular to the rotation axis to vary the abrasion direction. The control system may be configured to move the abrasion wheel in the x-y plane to cause relative movement between the abrasion wheel and the test facet.

[0016] The abrasion process may be a grinding process ora polishing process. The abrasion means preferably comprises a first or grinding abrasion region and a second or polishing abrasion region, the first abrasion region comprising a first abrasion material and the second abrasion region comprising a second abrasion material, the first abrasion material being larger than the second abrasion material. Where the abrasion means is an abrasion wheel, the first abrasion region is preferably arranged radially outwardly of the second abrasion region.

[0017] The apparatus may comprise an element support configured to support the element, and one or more support arms that support the element support, the or each support arm being moveable to move the element support towards the abrasion means to keep the facet surface in contact with the abrasion means as material is removed from the facet surface during abrasion, the sensor being configured to sense the position of a reference part of the or each support arm, wherein a measured position of the support arm defines the measured abrasion parameter. The position may be a linear position or an angular position. The sensor may be configured to provide information to the control system related to a rate of movement of the or each support arm.

[0018] The reference part of the support arm may be defined by an end of the support arm that is opposite the element support.

[0019] The support arm may be supported on a pivot, the element support being arranged at a forward side of the pivot. The apparatus may be configured to permit rotation of the support arm about the pivot during abrasion, to keep the element support in contact with the abrasion means.

[0020] The apparatus may comprise a force applicator for applying a force to the support arm to control the force with which the facet surface is applied to the abrasion means.

[0021] Where the support arm is supported by a pivot with the element support at the forward side of the pivot, the force applicator may be configured to apply a force on a rearward side of the pivot.

[0022] The force applicator may comprise a feed actuator that is coupled to the support arm. The control system may be configured to control the feed actuator to vary the force applied by the force applicator. The actuator may be coupled to the support arm via a spring.

[0023] The element support may be configured to receive one or more element holders. The apparatus may be configured to cause rotation of the or each element holder in the element support about an azimuth axis that is parallel to a longitudinal axis of a element held in the or each holder. The apparatus may comprise an azimuth actuator configured to rotate the or each element holder. The control system may be configured to control the azimuth actuator. The azimuth actuator may comprise a servo motor.

[0024] The element support may be connected to the support arm by a pivot for rotation of the element support about an axis that is perpendicular to the azimuth axis. The apparatus may comprise a slope actuator configured to rotate the element support about the axis. The control system may be configured to control slope actuator. The slope actuator may comprise a servo motor.

[0025] The controller may be configured to determine, based on the measured abrasion parameter and one or more calibration parameters, whether the abrasion distance is equal to the target abrasion distance. The controller may be configured to determine an updated target abrasion distance based on the target abrasion distance and the one or more calibration parameters, and to determine an updated target abrasion parameter based on the target abrasion distance. The controller may be configured to determine that when the measured abrasion parameter is equal to the updated target abrasion parameter, the abrasion distance is equal to the target abrasion distance.

[0026] The control system may be configured to determine the updated target abrasion distance and / or updated target abrasion parameter at a rate of at least 50 updates per second, preferably at least 100 updates per second.

[0027] The control system may be configured to store x-y calibration information relating to the deviation of the height of the abrasion wheel along its axis of rotation within the x-y plane. The stored x-y calibration information may define a first calibration parameter. The control system may be configured to determine, based at least on the measured abrasion parameter and the information relating to the stored x-y calibration information, whether the abrasion distance is equal to the target abrasion distance.

[0028] The apparatus may comprise a reference surface, and the control system may be configured to determine the calibration information relating to the deviation of the height of the abrasion wheel along its axis of rotation within the x-y plane by: i) causing the reference surface to be brought into contact with the abrasion wheel; ii) moving the abrasion wheel in the x-y plane and determining the height of the reference surface along the axis of rotation of the abrasion wheel to produce a height deviation map; iii) storing the information relating to the height deviation map as the calibration information.

[0029] The apparatus may comprise an element position sensor configured to sense a position of the element in a direction parallel to a longitudinal axis of the element, and send information relating to the element position to the control system. The stored position of the element may define a second calibration parameter. The control system may be configured to determine, based at least on the measured abrasion parameter and information relating to the element position, whether the abrasion distance is equal to the target abrasion distance.

[0030] During the abrasion process, the friction between the element and the abrasion wheel causes the element to heat up. The surrounding components such as the holder and element support also heat up. This causes thermal expansion of the components, which alters the position of the element in the feed direction. The sensor senses this change of position and the control system uses the information as a calibration parameter.

[0031] The control system may be further configured to generate the information relating to the soft direction of the first facet of the element by: i) causing relative movement between the abrasion means and the element support to bring the first facet into contact with the abrasion means to abrade the first facet in a first abrasion direction; ii) receiving information from the sensor relating to the abrasion speed of the first facet surface during abrasion in the first abrasion direction; iii) causing relative movement between the abrasion means and the first facet to change the abrasion direction to a plurality of different abrasion directions; iv) receiving information from the sensor relating to the abrasion speed of the first facet surface during abrasion for each of the different abrasion directions; and determining an abrasion direction that corresponds to a highest abrasion speed of the first facet surface, and identifying that abrasion direction as a soft direction for the first facet.

[0032] Where the abrasion means is an abrasion wheel that is rotatable about a rotation axis, the actuation system may be configured to cause relative movement between the abrasion wheel and the element support in the x-y axis to vary the abrasion direction.

[0033] The control system may be configured to move the abrasion wheel continuously in the x-y plane so as to vary the abrasion direction continuously.

[0034] The control system may be configured to calculate a predicted soft direction for a further facet, based on: i) the crystal structure of diamond; ii) the geometry and determined soft direction of each test facet; and iii) the geometry of the further facet.

[0035] The control system may be configured to determine the soft direction for each of three test facets, and to calculate a predicted soft direction for a fourth facet.

[0036] The element support may be configured to support an element holder that holds the element. The control system may be configured to store element holder information relating to the relative position and / or orientation of the element in the element holder. The control system may be configured to calculate the predicted soft direction for the further facet, based on: i) the crystal structure of diamond; ii) the geometry and determined soft direction of each test facet; iii) the geometry of the further face; and iv) the stored element holder information. The control system may be configured to move the element support to a configuration in which the element is presented to the abrasion means at an azimuth angle and slope angle corresponding to the further facet, and to cause the abrasion means to abrade the surface in the predicted soft direction for the further facet.

[0037] The control system may be configured to receive information relating to the abrasion speed of the further facet during abrasion in the predicted soft direction, to determine if the abrasion speed is greater than a target speed, and if the abrasion speed is not greater than the target speed the control system is further configured to: determine that the predicted soft direction for the further facet is not the true soft direction: determine the true soft direction of the further facet by: causing relative movement between the abrasion means and the test facet to change the abrasion direction to a plurality of different abrasion directions; receiving information from the sensor relating to the abrasion speed of the facet surface during abrasion for each of the different abrasion directions; and determining an abrasion direction that corresponds to a highest abrasion speed of the facet surface, and identifying that abrasion direction as the true soft direction for the further facet; and calculate a predicted soft direction for a next further facet, based on: i) the crystal structure of diamond; ii) the geometry and determined soft direction of each test facet and the further facet; and iii) the geometry of the next further facet.

[0038] The control system may be configured to determine an angular displacement a, p, y between each axis of an axis system X, Y, Z of the diamond cut geometry and each respective axis X’, Y, Z’ of an axis system of the diamond crystal structure, and to calculate the predicted soft directions of the further facet based on the angular displacements and the geometry of the further facet.

[0039] If the abrasion speed is greater than the target speed, the control system may be further configured to optimise the determined soft direction by i) causing relative movement between the abrasion means and the further facet to change the abrasion direction to a plurality of different abrasion directions that vary from the predicted soft direction in a deviation of no more than + / - 10 degrees, preferably no more than + / - 5 degrees ii) receiving information from the sensor relating to the abrasion speed of the further facet surface during abrasion for each of the different abrasion directions; and determining an abrasion direction that corresponds to a highest abrasion speed of the facet surface, and identifying that abrasion direction as the optimised soft direction for that further facet.

[0040] The invention also extends to apparatus for abrading a diamond, the apparatus comprising: an abrasion means for abrading facets of a diamond pre-form; a sensor for providing information related to an abrasion speed of a facet surface during abrasion; a pre-form support for supporting the pre-form; a control system configured to cause relative movement between the abrasion means and the pre-form support, to receive information relating to the abrasion speed of the facet surface, and to determine a soft direction of each of a plurality of test facets of a pre-form by: causing relative movement between the abrasion means and the element support to bring the test facet into contact with the abrasion wheel to abrade the test facet in a first abrasion direction; receiving information from the sensor relating to the abrasion speed of the facet surface during abrasion in the first abrasion direction; causing relative movement between the abrasion means and the test facet to change the abrasion direction to a plurality of different abrasion directions; receiving information from the sensor relating to the abrasion speed of the facet surface during abrasion for each of the different abrasion directions; and determining an abrasion direction that corresponds to a highest abrasion speed of the facet surface, and identifying that abrasion direction as a soft direction for that test facet. The invention also resides in a method of grinding a diamond element to shape facets of a diamond geometry, the method comprising: a) providing a diamond element having a diamond crystal structure with a crystallographic axis system X’, Y’, Z’; b) providing information relating to a desired diamond cut geometry having a plurality of facets, the diamond cut geometry having a geometry axis system X, Y, Z; c) determining an angular displacement a, p, y, between each axis of the crystallographic axis system and each respective axis of the geometry axis system; d) determining the soft direction of each of the facets of the diamond cut geometry, based i) the crystallographic axis system of the diamond structure ii) the desired diamond cut geometry and iii) the angular displacement between each axis of the crystallographic axis system and each respective axis of the geometry axis system; e) providing an abrasion means; f) causing relative movement between the element and the abrasion means to move each facet directly to a position in which the abrasion means is arranged to grind the respective facet in its determined soft direction; g) abrading each facet in its respective determined soft direction.

[0041] The step of determining the angular displacement between each axis of the crystallographic axis system and each respective axis of the geometry axis system may comprise: a) determining the soft direction of a plurality of test facets by: abrading each test facet in a first abrasion direction with an abrasion means; sensing the abrasion rate of the facet surface during abrasion in the first abrasion direction; causing relative movement between the abrasion means and the test facet to change the abrasion direction to a plurality of different abrasion directions; sensing the abrasion rate of the facet surface during abrasion for each of the different abrasion directions; and determining an abrasion direction that corresponds to a highest abrasion rate of the facet surface, and identifying that abrasion direction as a soft direction for that test facet;c) calculating the angular displacement based on: i) the crystal structure of diamond; ii) the position and angle of each test facet relative to the geometry axis system; and iii) the determined soft direction of each test facet.

[0042] The invention also resides in a method of grinding a diamond element to shape facets of a diamond geometry, the method comprising: a) providing a diamond element; b) determining the soft direction of a plurality of test facets by: grinding each test facet in a first abrasion direction; sensing the abrasion speed of the facet surface during abrasion in the first abrasion direction; causing relative movement between the abrasion means and the test facet to change the abrasion direction to a plurality of different abrasion directions; sensing the abrasion speed of the facet surface during abrasion for each of the different abrasion directions; and determining an abrasion direction that corresponds to a highest abrasion speed of the facet surface, and identifying that abrasion direction as a soft direction for that test facet; c) calculating a predicted soft direction for each of a plurality of further facets based on: i) the crystal structure of diamond; ii) the geometry and determined soft direction of each test facet; and iii) the geometry of the further facet; and d) grinding each test facet in its respective determined soft direction and grinding each further facet in its respective predicted soft direction, to form the diamond having the diamond geometry.

[0043] The method may further comprise polishing each test facet in its respective determined soft direction and polishing each further facet in its respective predicted soft direction.

[0044] The method may comprise setting a target abrasion distance for each test facet and each further facet, and, during abrasion, measuring an abrasion parameter that is related to the abrasion distance. The method may comprise determining, based at least on the measured abrasion parameter, whether the abrasion distance is equal to the target abrasion distance. The abrasion means may be an abrasion wheel, and the method may comprise rotating the abrasion wheel about a rotation axis. The method may comprise causing relative movement between the abrasion wheel and the test facet in an x-y plane perpendicular to the rotation axis to vary the abrasion direction.

[0045] The method may comprise moving the abrasion wheel in the x-y plane to cause relative movement between the abrasion wheel and the test facet. The method may comprise moving the abrasion wheel continuously in the x-y plane so as to vary the abrasion direction continuously.

[0046] The method may comprise determining the soft direction for each of three test facets, and calculating a predicted soft direction for a fourth facet.

[0047] The method may comprise arranging the element in an element holder, retrieving information relating to the relative position and / or orientation of the element in the element holder, and calculating the predicted soft direction forthe furtherfacet, based on: i) the crystal structure of diamond; ii) the geometry and determined soft direction of each test facet; iii) the geometry of the further face; and iv) the element holder information.

[0048] The method may comprise moving the element support to a configuration in which the element is presented to the abrasion means at an azimuth angle and slope angle corresponding to the further facet, and causing the abrasion means to abrade the surface in the predicted soft direction for the further facet.

[0049] The method may comprising monitoring the abrasion speed of the further facet during abrasion in the predicted soft direction, to determine if the abrasion speed is greater than a target speed, and if the abrasion speed is not greater than the target speed: determining that the predicted soft direction for the further facet is not the true soft direction: determining the true soft direction of the further facet by: causing relative movement between the abrasion means and the test facet to change the abrasion direction to a plurality of different abrasion directions; monitoring the abrasion speed of the facet surface during abrasion for each of the different abrasion directions; and determining an abrasion direction that corresponds to a highest abrasion speed of the facet surface, and identifying that abrasion direction as the true soft direction for the further facet; and calculating a predicted soft direction for a next further facet, based on: i) the crystal structure of diamond; ii) the geometry and determined soft direction of each test facet and the further facet; and iii) the geometry of the next further facet.

[0050] The method may comprise determining an angular displacement between each axis of an axis system of the pre-form and each respective axis of an axis system of the diamond crystal structure, and calculating the predicted soft directions of the furtherfacet based on the angular displacements and the geometry of the further facet.

[0051] If the abrasion speed is greater than the target speed, the method may comprise optimising the determined soft direction by i) causing relative movement between the abrasion means and the further facet to change the abrasion direction to a plurality of different abrasion directions that vary from the predicted soft direction in a deviation of no more than + / - 10 degrees, preferably no more than + / - 5 degrees ii) monitoring the abrasion speed of the further facet surface during abrasion for each of the different abrasion directions; and determining an abrasion direction that corresponds to a highest abrasion speed of the facet surface, and identifying that abrasion direction as the optimised soft direction for that further facet.

[0052] The method may comprise setting a target abrasion distance for an abrasion process associated with the further facet, measuring the abrasion distance via the sensor, and causing the facet surface to remain in contact with the element until the abrasion distance is equal to the target abrasion distance.

[0053] The method may comprise moving the facet surface away from the abrasion means when the target abrasion distance has been reached.

[0054] The abrasion process may be a grinding process ora polishing process. The abrasion means preferably comprises a first or grinding abrasion region and a second or polishing abrasion region, the first abrasion region comprising a first abrasion material and the second abrasion region comprising a second abrasion material, the first abrasion material being larger than the second abrasion material. Where the abrasion means is an abrasion wheel, the first abrasion region is preferably arranged radially outwardly of the second abrasion region.

[0055] The method may comprise supporting the element in an element support, and supporting the element support on one or more support arms. The method may comprise moving the or each support arm to move the element support towards the abrasion means to keep the facet surface in contact with the abrasion means as material is removed from the facet surface during abrasion. The method may comprise monitoring the position of a reference part of the or each support arm. A rate of movement of the or each support arm may provide the information relating to the rate of abrasion of the facet surface.

[0056] The method may comprise measuring an abrasion parameter that is related to the abrasion distance (defined as the perpendicular depth of material that has been removed from the surface during abrasion) and determining, based on the measured abrasion parameter and one or more calibration parameters, whether the abrasion distance is equal to a target abrasion distance for the facet.

[0057] The method may comprise determining an updated target abrasion distance based on the target abrasion distance and the one or more calibration parameters, and determining an updated target abrasion parameter based on the target abrasion distance. The method may comprise determining that when the measured abrasion parameter is equal to the updated target abrasion parameter, the abrasion distance is equal to the target abrasion distance.

[0058] The method may comprise determining the updated target abrasion distance and / or updated target abrasion parameter at a rate of at least 50 updates per second, preferably at least 100 updates per second.

[0059] The method may comprise storing x-y calibration information relating to the deviation of the height of the abrasion wheel along its axis of rotation within the x-y plane. The stored x-y calibration information may define a first calibration parameter. The method may comprise determining, based at least on the measured abrasion parameter and the information relating to the stored x-y calibration information, whether the abrasion distance is equal to the target abrasion distance.

[0060] The method may comprise determining the calibration information relating to the deviation of the height of the abrasion wheel along its axis of rotation within the x-y plane by: causing a reference surface to be brought into contact with the abrasion wheel; moving the abrasion wheel in the x-y plane and determining the height of the reference surface along the axis of rotation of the abrasion wheel to produce a height deviation map; and storing the information relating to the height deviation map as the calibration information. The method may comprise monitoring a position of the pre-form in a direction parallel to a longitudinal axis of the element. The position of the pre-form may define a second calibration parameter. The method may comprise determining, based at least on the measured abrasion parameter and the information relating to the element position, whether the abrasion distance is equal to the target abrasion distance.

[0061] Any of the methods described above may be computer-implemented methods. In such methods, any ‘determining’ steps or ‘monitoring’ steps may be performed by a computer processor. Any movement or control of any component (e.g. the abrasion means or the diamond element) may be effected by the computer processor.

[0062] The invention thereby extends to a computer-implemented method of grinding a diamond element to shape facets of a diamond geometry. The method comprises: a) providing a diamond element having a diamond crystal structure with a crystallographic axis system X’, Y’, Z’; b) providing information relating to a desired diamond cut geometry having a plurality of facets, the diamond cut geometry having a geometry axis system X, Y, Z; c) determining an angular displacement a, p, y, between each axis of the crystallographic axis system and each respective axis of the geometry axis system; d) calculating the soft direction of each of the facets of the diamond cut geometry, based on i) the crystallographic axis system of the diamond structure ii) the desired diamond cut geometry and iii) the angular displacement between each axis of the crystallographic axis system and each respective axis of the geometry axis system; e) providing an abrasion means; g) causing relative movement between the element and the abrasion means to move each facet directly to a position in which the abrasion means is arranged to grind the respective facet in its determined soft direction; and g) abrading each facet in its respective determined soft direction.

[0063] The step of determining the angular displacement between each axis of the crystallographic axis system and each respective axis of the geometry axis system may comprise: a) determining the soft direction of a plurality of test facets by: abrading each test facet in a first abrasion direction with an abrasion means; sensing the abrasion speed of the facet surface during abrasion in the first abrasion direction; causing relative movement between the abrasion means and the test facet to change the abrasion direction to a plurality of different abrasion directions; sensing the abrasion speed of the facet surface during abrasion for each of the different abrasion directions; and determining an abrasion direction that corresponds to a highest abrasion speed of the facet surface, and identifying that abrasion direction as a soft direction for that test facet; c) calculating by means of a computer processor, the angular displacement based on: i) the crystal structure of diamond; ii) the position and angle of each test facet relative to the geometry axis system; and iii) the calculated soft direction of each test facet.

[0064] The method may comprise arranging the diamond element in an element support and controlling movement of the element support, and hence the diamond, by a computer-implemented controller.

[0065] The invention also extends to a computer-readable medium carrying instructions for carrying out any of the above methods. Optional features of any aspect of the invention may be used alone, or in appropriate combination, with other aspects of the invention also.

[0066] It will be appreciated that when abrading a diamond element such as a pre-form to produce a finished diamond having a selected diamond cut geometry, material must be gradually abraded away from the surface of the pre-form. For each facet that is to be ground, material is gradually abraded away from the preform in a plane that is parallel to the facet, until the required amount of material has been removed. Throughout this document, ‘abrading a facet’ therefore means removing material in a plane parallel to the chosen facet until sufficient material has been removed.

[0067] Brief Description of the Drawings

[0068] Figure 1 illustrates multiple crystallographic planes of the diamond structure and indicates soft and hard directions of each plane;

[0069] Figure 2a is a perspective view of a diamond having a diamond cut geometry corresponding to a brilliant cut;

[0070] Figure 2b is a perspective view of a diamond element in the form of a pre-form for the brilliant cut diamond of Figure 2a;

[0071] Figure 2c is a perspective view of the diamond cut geometry of Figure 2a, showing an axis system of the diamond cut geometry having axes X, Y, Z, and an axis system of the underlying diamond crystal structure having axes X’, Y’, Z’, with an angular displacement a, p, y between each respective axis of the axis system X, Y, Z and each respective axis of the axis system X’, Y, Z’;

[0072] Figure 2d is a schematic cross-section showing a target abrasion distance TAD, defined as the perpendicular depth of material to be abraded away from a touch point on the surface of the pre-form of Figure 2b to form a respective facet of the diamond geometry if Figure 2a;

[0073] Figure 3 is a perspective view of apparatus for abrading a diamond element;

[0074] Figure 4 is a perspective view of a lower body forming part of the abrasion apparatus of Figure 3, and comprising an abrasion means;

[0075] Figure 5 is a partial perspective view of the apparatus of Figure 3, showing an upper body that comprises an element support system;

[0076] Figure 6 is a schematic side view of the element support system of Figure 5,

[0077] Figures 7 and 8 are schematic cross-sectional views of an element holder for use in conjunction with the apparatus of Figure 3;

[0078] Figures 9a to 9c are schematic cross-sectional views of the element holders of Figures 7 and 8, illustrating displacements of a diamond element relative to the element holder;

[0079] Figure 10 is a schematic diagram illustrating inputs and outputs to a controller that forms part of the apparatus of Figure 3;

[0080] Figures 11a to 11d illustrate stages in grinding a diamond element in the form of the pre-form of Figure 2b to form a facet of the diamond geometry of Figure 2a; Figure 12 is a schematic top-down view of an element being abraded by the abrasion means forming part of the apparatus of Figure 3, illustrating different relative positions of the element and the abrasion means, wherein in each relative position the abrasion direction is in a different orientation;

[0081] Figure 13 is a map of abrasion speed against abrasion direction for each of a plurality of facets;

[0082] Figure 14 is a schematic flow diagrams showing steps in a process of determining a soft direction of a test facet;

[0083] Figure 15 is a schematic flow diagrams showing steps in a process of determining the soft directions of further facets, and polishing the further facets in their determined soft directions;

[0084] Figure 16 is a map showing Z-axis deviations in the height of an abrasion means forming part of the apparatus of Figure 3, at different positions in an X-Y plane;

[0085] Figure 17 is a graph indicating detected changes in the position of a diamond element when the element undergoes abrasion in the apparatus of Figure 3; and

[0086] Figure 18 is a perspective view of an alternative element support, configured to hold multiple element holders.

[0087] Detailed description of Embodiments of the invention

[0088] Figure 3 illustrates a diamond abrasion apparatus 20 that is used to grind and / or polish the facets 12 of a diamond element. The diamond element may be any component that is made of diamond, for example a diamond rough, diamond pre-form, or any other diamond component.

[0089] In the following description the diamond element takes the form of a diamond pre-form 10, such as that shown in Figure 2b. The ‘pre-form’ is a diamond component that will be ground and polished to take the form of a diamond jewellery stone, having a particular diamond cut geometry, such as that shown in Figure 2a. The diamond cut geometry has its own reference axes X, Y, Z, illustrated in Figure 2a, and also in Figure 2c, where the Z axis defines a longitudinal axis of the cut geometry. The diamond cut geometry may also have a pre-defined reference point R.

[0090] The pre-form initially comprises substantially conical surfaces, as shown in the pre-form of Figure 2b. The pre-form can define the same X, Y, Z axis system as the diamond cut geometry, with the Z axis similarly defining a longitudinal axis of the cut geometry. To align the diamond cut geometry exactly as required with the pre-form geometry, relative rotation around the Z axis must be set. The reference point R can be used to set this desired rotation. Once the diamond cut geometry has been set relative to the pre-form geometry the pre-form undergoes a first abrasion process in the form of grinding to reveal facets of the desired diamond structure, and a second abrasion process in the form of polishing to polish the facets to a mirror finish.

[0091] To grind the pre-form to produce the finished diamond, the apparatus abrades material from the surface of the pre-form at an appropriate slope and azimuth angle to produce a desired diamond cut geometry, such as that shown in Figure 2a. To polish the facets 12, the apparatus removes a small amount of material from the pre-ground facets to produce a mirror finish.

[0092] The diamond pre-form comprises diamond material having a diamond crystal structure that is defined by a crystallographic axis system having axes X’, Y’, Z’. The relative orientations of the crystallographic axis system X’, Y’, Z’ and the axis system X, Y, Z of the diamond cut geometry determines the different crystallographic planes that define each different facet of the diamond cut. For example, one facet may be defined by an (011) plane, and another by a (001) plane, etc. Each crystallographic plane will have its own soft direction.

[0093] In some situations, the positions and orientations of the crystallographic axis system X’, Y’, Z’ of the diamond element relative to the axis system X, Y, Z of the diamond cut geometry that is to be ground from the pre-form may be known or partially known. For example, as shown in Figure 2c, angular displacements a, p, y between each respective pair of axes X-X’, Y-Y’, Z-Z’ may be known. In this case, the apparatus may be supplied with information relating to the relative displacements (for example it may be supplied with the angular displacements a, p, y, or other related information). The apparatus has the capability to use this information to determine the soft directions of each of the facets of the diamond cut geometry, and to grind and / or polish the facets only in the determined soft direction.

[0094] Alternatively, if the relative positions and orientations of the crystallographic axis system are unknown, the apparatus 20 has the capability to determine automatically the soft directions of the facets 12 of the pre-form 10, before grinding and / or polishing the facets 12 in those soft directions.

[0095] The apparatus 20 comprises an abrasion wheel 30 and an element support system, embodied here as a pre-form support system 60 that is configured to support the pre-form (not visible in Figure 3) and move it relative to the abrasion wheel 30. The apparatus 20 is also configured such that the abrasion wheel 30 is moveable relative to the pre-form support system 60. A control system 200 (see Figure 9) is configured to control the movement of the pre-form support 60, and the abrasion wheel 30 through an actuation system that comprises a plurality of actuators. By movement of the pre-form support system 60, a pre-form can be presented to the abrasion wheel 30 in a desired slope and azimuth angle, and brought into contact with the abrasion wheel 30 for grinding and polishing of facets 12.

[0096] The apparatus 20 is configured to grind and polish a pre-form 10 using the soft directions S for each facet 12 of a particular diamond cut geometry in an automated process.

[0097] In one variant of the process, where the relative positions and orientations of the crystallographic axis system and the axis system of the pre-form are known, the apparatus 20 is configured to receive this information together with information relating to the diamond cut geometry, to determine the soft direction of the facets of the diamond cut geometry, and to grind and / or polish the facets in the soft direction.

[0098] In another variant of the process, in which the relative positions and orientations of the crystallographic axis system and the axis system of the pre-form are not known, in a first stage of the automated process, the apparatus 20 is configured to determine the soft direction S for a plurality of facets 12 automatically and empirically, and to grind and polish those facets in the soft direction. Once the soft direction S has been determined for a small number of facets, in a second stage of the process, the apparatus 20 is configured to calculate a predicted soft direction for subsequent facets, to test that prediction empirically, and to adjust its prediction if necessary according to the results of the test to produce a final prediction model. In a third stage of the process, with its prediction model finalised, the apparatus is configured to determine the soft direction of subsequent facets and to grind and polish those facets in the soft direction.

[0099] Considering the apparatus 20 in more detail, the apparatus 20 comprises a lower body 22 that houses and supports the abrasion wheel 30, and an upper body 24 that defines the pre-form support system 60. The upper body 24 is mounted onto the lower body 22.

[0100] The lower body 22 is shown in detail in Figure 4. The lower body houses the abrasion wheel 30, which configured to rotate about an axis A to effect grinding of a facet. A wheel drive 31 (not shown in Figure 4, but shown schematically in Figure 10) is configured to effect rotation of the abrasion wheel 30 according to signals received from a control system 200.

[0101] In the example shown, the abrasion wheel 30 is suitable for both grinding and polishing of facets. To this end, the abrasion wheel 30 has a grinding region 30a, in which the grit size of the abrasion wheel 30 is relatively large (for example a mean average particle diameter of 10 microns), and hence suitable for grinding, and a polishing region 30b, in which the grit size of the abrasion wheel 30 is relatively small (for example a mean average particle diameter of 1 micron), and hence suitable for polishing. The polishing region 30b is defined by a circular region at the centre of the abrasion wheel 30, and the grinding region 30a is defined by annular region that surrounds the polishing region 30b.

[0102] The abrasion wheel 30 is mounted on an abrasion wheel support in the form of a platform 32. The platform 32 is slidably mounted on a pair of first or Y-axis rails 34, to allow movement of the platform 32, and hence the abrasion wheel 30, in a first direction parallel to a Y axis. A first grinding wheel actuator 36 in the form of a servo motor (not shown in Figure 4, but shown schematically in Figure 10) is configured to cause movement of the platform 32 along the Y axis, in response to signals from the control system 200.

[0103] The first rail 34 and first grinding wheel actuator 36 are mounted on a carriage 38. The carriage 38 is in turn slidably mounted on a pair of second or X-axis rails 40, to allow movement of the carriage 38, and hence the abrasion wheel 30, in a second direction orthogonal to the Y axis and parallel to an X axis. A second grinding wheel actuator 42 in the form of a servo motor is configured to cause movement of the carriage 38 along the X axis, in response to signals from the control system 200.

[0104] The X-axis rails are mounted to a machine bed 46 that defines a vibration-absorbing body. The machinebed 46 may be made for example from granite, or another material that is suitably dense and capable of absorbing vibrations. Because the abrasion wheel 30 is supported on the machine bed 46, the abrasion wheel 30 is thereby protected from vibrations.

[0105] The machine bed 46 also supports a further platform 44, which in this case defines a static platform. The further platform 44 defines a horizontal support surface 48. As will be described in more detail later, the further platform 44 supports the pre-form support system 60. In this example, the further platform 44 is raised away from the machine bed 46 by pillars 49, so that the level of the horizontal support surface 48 is above the level of the abrasion wheel 30.

[0106] As best seen in Figure 3, the lower body 22 comprises a cover 43 that is arranged to cover the components of the lower body 22, leaving the abrasion wheel 30 exposed for polishing. The cover 43 may comprise multiple cover components, for example multiple panels, including vertical panels and one or more horizontal panels.

[0107] Figures 5 to 7 illustrate the pre-form support system 60.

[0108] The pre-form support system 60 is configured to receive a standard holder 50 that holds a diamond preform 10 or other element with a portion of the pre-form 10 exposed for polishing. Examples of such holders 50a, 50b are illustrated in Figures 8a and 8b.

[0109] Each holder 50a, 50b comprises a body 52 that has a generally conical shape, defining an elongate axis E. In end region of the body 52, a slot divides the body 52 into first and second prongs or parts 52a, 52b that are joined together at their base. In this way, the prongs 52a, 52b can be moved together and apart in a controlled manner) to clamp a stone 10 therebetween. An end region of the body 52 defines a contact surface 54a, 54b against which the stone 10 rests securely when the stone 10 is clamped in place. The contact surface 54a, 54b is configured according to the surface of the stone 10 that is to be supported. For example, the holder 50a of Figure 8a is configured to support a stone 20 for polishing a pavilion 14 of the stone 10. The pavilion 14 must be exposed for polishing, so the crown 16 of the stone 10 must rest against the contact surface 54a, and the contact surface 54a is therefore horizontal, i.e. it defines a plane that is perpendicular to axis E. The holder 50b of Figure 8b is configured to support a stone 20 for polishing a crown 16 of the stone 10. The crown 16 must be exposed for polishing, so the pavilion 14 of the stone 10 must rest against the contact surface 54b, and the contact surface 54b is therefore angled, and slopes towards axis E moving away from the end of the body 52.

[0110] As will be described in more detail below, the holder 50, with the pre-form 10, is fitted to the pre-form support system 60, where it can be moved to present different parts of the pre-form to the abrasion wheel 30 at different azimuth and slope angles, for grinding and polishing.

[0111] The pre-form support system 60 will now be described in detail with reference to Figures 5 to 7. Referring to Figures 5 and 6, the pre-form support system 60 defines a front region 60a, which is the region that supports the holder 50 and hence the pre-form 10 for grinding, and which faces towards the abrasion wheel 30, and a rear region 60b, which is opposite to the front region 60a.

[0112] The pre-form support system 60 is fixed to the further platform 44 by means of a support structure 62. In this example, the support structure 62 comprises a base portion 63 that is fixed to the further platform 44, a vertical wall 64 that projects upwardly from the base portion 63. A rear column 65 projects upwardly from a rear of the base portion 63, and joins a rear edge of the vertical wall 64. At an upper edge of the vertical wall an upper panel 66 projects away from the vertical wall 64. The vertical wall 64 is wedge- shaped, tapering towards the rear of the wall, so that the upper edge of the vertical wall is slanted towards the rear. The upper panel 66 is therefore correspondingly slanted, and slopes downwardly as it extends from its front to its rear.

[0113] In this way, the base 63, vertical wall 64, rear column 65 and upper panel 66 define four sides of a casing having a slanted upper wall, with the front and one side of the casing being open.

[0114] A pre-form manipulation system 68 is supported on the support structure 62, which is configured to move the holder 50, and hence the pre-form, so that all the facets of the pre-form can be presented to the abrasion wheel 30.

[0115] Starting at the front region 60a, the manipulation system 68 comprises a holder support 70 having a cavity for receiving the holder 50 with the attached pre-form 10. The cavity is of substantially the same size and shape as the holder 50, so that the holder 50 can be fitted into the cavity and held in place by friction. A spring-loaded locking mechanism (not shown) is also provided to lock the holder in place.

[0116] The holder support 70 is configured to rotate about an azimuth axis A (see Figure 6), so as to rotate the pre-form about its corresponding azimuth axis A (see Figure 2a). Rotation about this axis is controlled by an azimuth actuator 71 in the form of an azimuth servo motor, which is controlled by the control system 200.

[0117] The holder support 70 is mounted on a first carriage 74. The first carriage 74 is mounted between two parallel support arms 75, 76 (both visible in Figure 5, while Figure 6 shows only one of the arms 75). The first carriage 74 is mounted to the support arms 75, 76 via a first pivot 77, visible in Figure 6. The first pivot 77 takes the form of a first rotary bearing. By virtue of the first pivot 77, the first carriage 74 can be rotated in slope direction B, around an axis that runs through the pivot and is perpendicular to the azimuth axis A. Rotation in the slope direction B rotates the pre-form about its corresponding slope direction B (see Figure 2a). Movement of the first carriage 74 in the direction B is controlled by a slope actuator in the form of a slope servo motor 72, which is controlled by the control system 200.

[0118] In this way, the apparatus is configured to rotate the pre-form to different azimuth angles A, and to different slope angles B, so that the pre-form 10 can be presented to the grinding wheel at an azimuth angle and slope angle that corresponds to the azimuth angle and slope angle of any given facet.

[0119] Each support arm 75, 76 is mounted to a base piece 79 via a second pivot 78. Each base piece 79 is mounted to the further platform 74. The base pieces 79 are obscured from view in Figures 5 and 6, but are shown schematically in Figure 7.

[0120] The second pivot 78 takes the form of a second rotary bearing. By virtue of the second pivot 78, each support arm 75, 76 can be rotated relative to further platform (and hence relative to the abrasion wheel 30) in direction C, around an axis that runs through the second pivot 78 and is perpendicular to the azimuth axis A. Rotation in the feed direction C has the effect of moving the pre-form 10 towards or away from the abrasion wheel 30.

[0121] Each support arm 75, 76 is generally L-shaped, with the pivot 78 arranged at the junction or elbow of the arm. A first or forward portion 75a, 76a of the support arm 75, 76 extends from the pivot 78 towards the front of the apparatus. A second or rearward portion 75b, 76b extends from the pivot 78 at an obtuse angle to the first or forward portion 75a, 76a, towards the rear of the apparatus.

[0122] A front region of the first portion 75a, 76a of each support arm 75, 76 supports the first pivot 77 that in turn supports the first carriage 74. In this way, the carriage 74 is mounted between the front portions 75a, 76a of the support arm. The support arms 75, 76 can pivot such that the front portions 75a, 76a move downwardly, bringing the pre-form 10 towards the abrasion wheel 30, or upwardly bringing the pre-form 10 away from the abrasion wheel 30. Pivoting of the support arms 75, 76 about the pivot 78 thereby ‘feeds’ the pre-form 10 towards the abrasion wheel 30 by rotation in a ‘feed’ direction C.

[0123] A force applicator 91 controls the pivoting of the arms 75, 76 and hence controls the overall force F with which the pre-form 10 is applied to the abrasion wheel 30. The force applicator 91 applies a force F’ to the rear portion 75b, 76b of the support arms 75, 76 to control the corresponding force on the front portion 75a, 76a of each support arm, and hence the force on the pre-form.

[0124] In the embodiment described, this force applicator takes the form of a spring mechanism 94 that is connected to the rear ends 75b, 76b of the support arms 75, 76, which is illustrated schematically in Figure 7.

[0125] A rear end of the second portion 75b, 76b of each arm 75, 76 is mounted to a second carriage 80. The carriage 80 is slidably received in a housing 82, which is mounted to the support structure 62.

[0126] The second carriage 80 is configured for sliding movement within the housing 82 in a direction S, so that the second carriage 80 and hence the rear ends 75b, 76b of the support arms 75, 76 pre-form can move back and forth in the Direction S. Because of the support arm pivot 78, movement of the rear ends 75b, 76b of the support arms 75, 76 causes opposite movement of the front ends 75a, 76a of the support arms 75, 76, which moves the first carriage 74, holder 50 and hence the pre-form.

[0127] The second carriage 80 defines a hollow body having a first or upper end that is connected to the support arm 75, 76, and a second or lower end that is partially closed by a wall. The wall defines an inward-facing bracing surface 95. A plunger 96 is housed in the hollow body of the second carriage 80, with a plunger head 96a being contained in the hollow body, and a stem 96b extending out of the lower end of the second carriage. An elastic element in the form of a spring 97 is coiled around the stem 96b and is accommodated between the plunger head 96a and the bracing surface 95. In this way. Movement of the plunger 96a downwardly in direction S compresses the spring, which causes the spring to exert a downward force F against the bracing surface 95 of the second carriage 80. Because of the spring 97, the magnitude of the force F can be carefully controlled by movement of the plunger 97, thereby controlling a net application force with which the pre-form is applied to the abrasion wheel 30. The application force can be increased or decreased by correspondingly decreasing or increasing the force F by moving the plunger 96.

[0128] If desired, the plunger 96 can be moved to such an extent that the force F is opposite to and greater than the weight W, which causes the support arms 75, 76 to pivot about the support arm pivot 78, thereby lifting the first carriage and hence the pre-form upwardly, away from the abrasion wheel 30.

[0129] As seen in Figure 6, movement of the plunger 96 is controlled by an appropriate actuator or motor 73. In the example shown, the stem 96b of the plunger 96 ends in a toothed protrusion 84, and the toothed protrusion 84 is configured to interact with a toothed gear wheel 86. A feed actuator in the form of a feed servo motor 73 drives rotation of the toothed gear wheel to drive movement of the plunger 96 and hence movement of the second carriage 80. The feed servo motor 73 is controlled by the control system 200.

[0130] The manipulation system 68 comprises sensors 88, 90 for sensing certain movements within the system 68. A support arm position sensor 88 is provided for sensing a position of the support arms 75, 76, and in particular for sensing movement in the S Direction. As will be described in more detail below, the position of the support arm as sensed by the sensor is an ‘abrasion parameter’ that is used to monitor the progress of abrasion towards the target abrasion distance. The support arm sensor 88 is mounted to the upper panel 66 of the support structure 62, and is arranged to protrude beyond the upper panel 66.

[0131] A pre-form position sensor 90 is provided for sensing a position of the pre-form 10. The pre-form position sensor 90 is mounted to the first carriage 74, and is configured to detect a position of the pre-form 10.

[0132] For each of the support arm sensor 88 and pre-form position sensor 90, any suitable sensor may be used. For example each sensor 88, 90 may be an optical sensor or any other appropriate device.

[0133] The manipulation system 68 also comprises a calibration protrusion 92, which in this example is mounted on the first portion 76a of one of the support arms 76. The calibration protrusion 92 is arranged on an exterior of the support arm 76, and can be brought into contact with the abrasion wheel as part of a calibration process, as will be described in detail later.

[0134] Use of the apparatus 20 in grinding and polishing a diamond pre-form 10 of the type shown in Figure 2b will now be described.

[0135] In a first embodiment now described, the apparatus is used to determine the soft directions of the facets of the desired diamond geometry, as will now be described.

[0136] Before using the abrasion apparatus 20, the diamond pre-form 10 is prepared in a conventional manner. A rough diamond is first provided, and assessed to determine how to cut the stone for the best yield. One or more pre-forms 10 are then cut from the rough stone, for example as illustrated in Figure 2b. Each pre-form 10 is intended to create a diamond with a specific and pre-determined diamond geometry, for example the geometry shown in Figure 2a, with associated geometric data. For example, the geometric data will include parameters of the overall stone (stone height, stone width, girdle height etc), as well as parameters associated with each individual facet 12a, 12b (facet shape and size, the azimuthal position of the individual facet relative to other facets of the pre-form, and the angle of inclination of the facet compared to the table), as well as the axis system of the geometric cut.

[0137] The geometric data also includes information about the amount of material that must be abraded away from a surface 10a of the pre-form 10 to reveal each facet 12. With reference to Figure 2d, this information may be provided, for example, as a preliminary target abrasion distance TAD that is associated with each facet 12, where the preliminary target abrasion distance TAD indicates the depth of material that is to be abraded from a touch point 11 on the surface 10a of the pre-form 10, in a perpendicular direction, to reveal that facet surface.

[0138] Once the pre-form 10 has been prepared, the pre-form 10 is ready for further geometric assessment and polishing.

[0139] First, the pre-form 10 is arranged in a holder 50a as shown in Figure 8a, with the pavilion 14 exposed for grinding and polishing.

[0140] The holder 50 and pre-form 10 undergo an assessment process to determine particular geometric parameters relating to the position of the pre-form 10 in the holder 50. The geometric parameters are shown in Figures 9a to 9c.

[0141] Figure 9a illustrates the ‘tilt’ of the pre-form 10 in the holder 50: this is the angle between the longitudinal axis LP of the pre-form (i.e. the axis perpendicular to the table 14), and the longitudinal axis LH of the holder. The tilt is measured by a laser measuring machine, in a known manner.

[0142] Figure 9b illustrates the ‘shift’ of the pre-form 10 in the holder 50: this is the lateral shift between the longitudinal axis LP of the pre-form (i.e. the axis perpendicular to the table 14), and the longitudinal axis LH of the holder. The shift is measured by a silhouette projector, in a known manner.

[0143] Figure 9c illustrates the ‘twist’ of the pre-form 10 in the holder 50: this is the azimuthal position of the facet pattern relative to the holder. The twist is measured by a silhouette projector, in a known manner.

[0144] Referring to Figure 10, information 100 relating to the pre-determined geometric parameters of the preform diamond geometry is provided to the control system 200 of the apparatus 20. Information 102 relating to the tilt, shift and twist of the pre-form relative to the holder 50 is also provided the control system 200. The control system 200 also has access to information 104 relating to the diamond crystal structure.

[0145] The holder 50 and attached pre-form 10 is then attached to the holder support 70 ready for a pavilion polishing stage, in which each facet of the pavilion 16 of the pre-form 10 is ground and then polished to a mirror finish.

[0146] The process is illustrated schematically in Figures 14 and 15.

[0147] A first facet 12a of the pavilion 16 is selected for a first facet testing step, in which the soft direction of the first facet 12a is determined empirically.

[0148] From the information 100 relating to the pre-determined geometric parameters of the pre-form geometric cut, and the information 102 relating to the tilt, shift and twist of the pre-form relative to the holder 50, the control system 200 can determine the precise location and inclination at which the pre-form 12 must be held so that the first facet 12a will be parallel to the abrasion wheel 30. (i.e. so that abrading the conical surface of the pre-form 10 at that particular azimuth angle and slope angle will reveal the first facet 12a). The control system 200 causes the actuators 71 , 72, 73 of the actuation system to move the holder 50 and hence the pre-form 10 in the directions A, B, C and S so that the pre-form is presented to the abrasion wheel 30 at an azimuth angle and slope angle corresponding to the first facet 12a.

[0149] The control system 200 causes the abrasion wheel actuator 31 to rotate of the abrasion wheel 30 at an appropriate speed, and then brings the pre-form 10 into contact with the abrasion wheel 30, as shown in Figures 11 a and 11 b, so that a touch point 11 on the pre-form surface 10a touches the abrasion wheel 10.

[0150] The size of the pre-form 10 is significantly smaller than the diameter of the abrasion wheel 30. As a result, abrasions that are formed on the facet 12a by the abrasion wheel 30 are essentially linear, with a single abrasion direction. As illustrated in Figure 12, the orientation of the abrasion direction will depend on the circumferential location of the pre-form 10 on the abrasion wheel 30, as well as the direction of rotation R of the wheel.

[0151] In Figure 12, line O defines a reference line from which a circumferential location can be measured. Pre-form 10a is located on the reference line O, with an abrasion direction perpendicular to the reference line (i.e. horizontal and to the right as shown in Figure 10). Pre-forms 10b, 10c and 10d are located at is located at angular displacements of C1 , C2 and C3 respectively from reference line O, and the abrasion directions at these locations are correspondingly rotated.

[0152] During the first facet testing step, the soft direction Sa of the first facet 12a is determined by testing the abrasion speed of the first facet 12a when the facet 12a is abraded in different abrasion directions.

[0153] The pre-form 10 is brought into contact with the abrasion wheel 30 at a known location relative to the wheel 30, for example a location along reference axis O. The control system 200 records the abrasion direction for that location.

[0154] The apparatus 20 is configured to measure the rate at which the material of the pre-form 10 is abraded during this test process. As the surface of the pre-form 10 is abraded, the pre-form support 50 moves towards the abrasion wheel 30 in a direction perpendicular to the facet 12, with a defined force. This movement causes the support arms 75, 76 to pivot slightly about the pivot point 78. The perpendicular depth of material removed from the touch point (i.e. the measured abrasion distance and the rate of change of that abrasion distance (i.e. the abrasion rate) can therefore be monitored by measuring the respective movement and rate of movement of the support arms 75, 76, using the support arm position sensor 88. In this example, the movement of the rearward portions 75b, 76b is measured, and forms an abrasion parameter that is related to the depth of material that has been abraded. The measured abrasion parameter and the abrasion rate is provided to the control system 200, where it is stored, associated with the particular abrasion direction.

[0155] During the test process, the abrasion direction is changed, and the abrasion rate monitored, to build up a map of abrasion rates for different abrasion directions. The abrasion direction is changed by continuously altering the relative position of the pre-form 10 and the abrasion wheel 30. To alter the relative position, the control system 200 controls the first and second actuators of the abrasion wheel 30, to move the abrasion wheel 30 relative to the pre-form support system 60, so that the pre-form 10 is moved to different circumferential locations relative to the abrasion wheel 30.

[0156] The abrasion wheel 30 is moved continuously at an appropriate speed, for example between 3 degrees per second and 20 degrees per second. As the grinding wheel 30 moves, the apparatus continuously measures the abrasion rate in the manner described above. The abrasion rate is stored, associated with the respective grinding direction, thereby building up a data set or map of abrasion speed compared to abrasion direction for that particular facet. An example of such a map is illustrated in Figure 13. Different lines on the map correspond to different test facets. For each test facet, the direction with the highest rate of abrasion corresponds to the soft direction Sa. As can be seen in Figure 13, for each facet, the rate of abrasion is significantly higher in one particular direction than in other directions: this direction corresponds to the soft direction for that facet.

[0157] The control system 200 assesses the stored data to determine the soft direction Sa for the facet 12a. The control system 200 stores the determined soft direction Sa associated with the first facet 12a. The control system 200 then moves the abrasion wheel 30 to a location relative to the pre-form 10 in which the abrasion direction aligns with the soft direction Sa, and in which the pre-form is located in the grinding region 30a of the wheel 30 and grinds the pre-form 10 in the soft direction Sa. As shown in Figures 11 c and 11d, grinding continues until the apparatus 20 determines that the pre-form 10 has been sufficiently ground to reveal the facet 12a (see later for more information on how the apparatus determines this).

[0158] In this example, the controller 200 is configured such that after grinding is complete, a polishing process takes place immediately to polish the facet to a mirror finish. To this end, the controller is configured to move the abrasion wheel 30 such that the pre-form is located in the polishing region 30b of the wheel 30, with the abrasion direction still aligned with the soft direction Sa, and to hold the wheel 30 and preform in that position until the apparatus 20 determines that the facet 12a has been polished to a mirror finish (see later for more information on how the apparatus determines this).

[0159] The test process is then repeated in the same way in respective of the second facet 12b in a second facet testing step, to determine the soft direction Sb of the second facet. The control system 200 stores the determined soft direction Sb associated with the first facet 12b. The second facet 12b is then ground and polished.

[0160] The test process is then repeated in the same way in respective of the third facet 12c in a third facet testing step, to determine the soft direction Sb of the third facet 12c. The control system 200 stores the determined soft direction Sb associated with the third facet 12c. The second facet 12b is then ground and polished.

[0161] After the third facet testing step, the control system 200 calculates a provisional model that determines a likely soft direction of all the facets. The model is calculated based on the determined soft directions Sa, Sb, Sc of the first second and third facets 12a, 12b, 12c, data relating to the geometry of the preform, and data relating to the diamond crystal structure.

[0162] A typical model is shown in Figure 3, in which the diamond cut geometry has an allocated pre-form axis system X, Y, Z, where Z corresponds to the Longitudinal axis of the cut, or the Azimuth axis A. The determined soft directions of the three facets are used to determine a likely orientation of the axis system of the underlying diamond crystal structure X’, Y’, Z’. The angular displacement a, p, y between each axis pair X-X’, Y-Y’, Z-Z’ of the diamond geometry and the underlying diamond crystal structure are calculated to determine a relative orientation of the diamond crystal structure axis system compared to the pre-form axis system. From the angular displacements a, p, y, and the geometry of the facets, the crystallographic plane of each facet can be determined. The corresponding soft direction for each crystallographic plane can be calculated based on the crystal structure, and hence the soft direction for each facet can be determined.

[0163] With the provisional model determined, an expected soft direction Sx of each facet 12x can be calculated by the controller. For each facet, the angular displacements a, p, y can be used to determine the crystallographic plane of the facet, and the soft direction for that plane can be determined according to the direction in which the atomic density is the lowest.

[0164] The next step is a verification step, in which the apparatus 20 is configured to verify whether the expected soft direction Sd of a fourth facet 12d, according to the provisional model, is correct. To carry out this verification step, the control system 200 moves the pre-form 10 so that the fourth facet 12d is presented to the abrasion wheel 30, and moves the abrasion wheel 30 so that the polishing direction aligns with the expected soft direction Sd, calculated by the controller according to the provisional model. The control system 200 moves the pre-form 10 into contact with the abrasion wheel 30 to grind the fourth facet 12d in the expected soft direction Sd. The abrasion distance and abrasion rate is measured in the manner described above.

[0165] If the abrasion rate is higher than a pre-determined threshold, the expected soft direction Sd is deemed to be correct, and the provisional model is confirmed. Grinding continues until sufficient material has been removed, and the fourth facet is subsequently polished until the fourth facet 12d is polished to the appropriate mirror finish.

[0166] If the abrasion rate is lower than the pre-determined threshold, the expected soft direction Sd is deemed to be incorrect. The apparatus 20 then carries out a fourth facet testing step on the fourth facet, in the same manner as the first to third testing steps, to determine the true soft direction Sd of the fourth facet 12d. The fourth facet is then ground and polished in the true soft direction Sd. The control system 200 calculates a corrected model that determines a likely soft direction of all the facets. The model is calculated based on the determined soft directions Sa, Sb, Sc, Sd of the first to fourth facets 12a, 12b, 12c, 12d, data relating to the geometry of the pre-form, and data relating to the diamond crystal structure.

[0167] The verification step is then repeated for a fifth facet. If the abrasion rate is higher than the predetermined threshold, the expected soft direction Sd is deemed to be correct, and the corrected model is confirmed. If the abrasion rate is lower than the pre-determined threshold, the expected soft direction Sd is deemed to be incorrect, the true soft direction is determined for the fifth facet, the model is corrected again, and the verification step is repeated. The verification step may be repeated as many times as necessary until the model is confirmed as correct.

[0168] Once the model is confirmed as correct, all subsequent facets 12x of the pavilion are ground and polished in a final step. The confirmed model provides the soft direction Sx for each facet 12x, so that for each facet 12x the abrasion wheel 30 can be moved directly to the appropriate location to align with the confirmed soft direction Sx, and grinding and polishing can commence immediately, without the need for any further empirical testing.

[0169] The controller may optionally be configured to carry out an additional optimisation process for the soft direction of each facet after it has been predicted based on a confirmed model. In this process, the controller is configured to move the abrasion wheel 30 to vary the abrasion direction away from the predicted soft direction by a small amount: for example + / - 5 degrees, or + / - 10 degrees, to check if the soft direction can be further optimised. The controller is configured to cause the apparatus to monitor the abrasion speed during this optimisation process in the manner already described above, to determine the abrasion direction that corresponds to the peak abrasion speed, and to adjust the soft direction to correspond to the direction of peak abrasion speed, before grinding and polishing the facet in the optimised soft direction.

[0170] In some cases, it may be difficult to determine the soft direction of a particular facet. This may occur, for example, if the facet is at certain unfavourable orientations with respect to the crystal structure. The controller may be configured such that if a soft direction cannot be identified for any of the test facets (for example if no peak abrasion speed can be found for any abrasion direction), the controller will select a new test facet, and will carry out the test procedure on the new test facet. Once the model is confirmed, the controller will cause the machine to return to the test facet, and carry out an optimisation process around the predicted soft direction, to determine the true optimised soft direction before grinding and polishing in that direction.

[0171] During the grinding process, the progress of abrasion is carefully monitored.

[0172] As described above with reference to Figure 2d, because the geometry of the conical pre-form and the geometry of the desired diamond cut are known precisely, each facet has a known ‘target’ abrasion distance corresponding to the depth of material that needs to be abraded to reveal the facet. For each facet, as abrasion takes place, the progress of abrasion is monitored, and grinding continues until the target abrasion distance TAD has been reached. A typical target abrasion distance is, for example, 100 - 200 microns. The grinding process may take, for example, between 5 seconds and 1 ,000 seconds, depending on the crystallographic orientation of the facet.

[0173] As described above, as the surface is abraded during grinding, the pre-form support 70 and hence the support arms 75, 76 move towards the abrasion wheel 30. The abrasion distance that has been achieved so far can therefore be monitored by monitoring movement of the support arms 75, 76 via the position sensor 88. Grinding is deemed to be complete when the controller determines that the correct amount of material has been abraded away, i.e. the depth of material removed is equal to the target abrasion distance.

[0174] The position of the support arms 75, 76 is monitored continuously by the support arm position sensor 88, and this information provides an ‘abrasion parameter’ that is sent to the control system 200. The position may be a linear position or an angular position. The measured abrasion parameter is related to the abrasion distance (i.e. the actual depth of material that has been removed from the surface) by a mathematical relationship that is known to the controller. The mathematical relationship may be a geometric relationship, and / or it may also be based on one or more calibration parameters.

[0175] The control system uses the information relating to the abrasion parameter to determine if the abrasion distance is equal to the target abrasion distance. When the control system 200 determines that the abrasion distance is equal to the target abrasion distance, the control system 200 stops the grinding process, and begins the polishing process.

[0176] The polishing process is substantially the same as the grinding process, except that the pre-form is located in the polishing region 10b of the wheel 30 instead of the grinding region 30a. During the polishing process, a relatively small amount of material is removed from the facet surface - for example between 1 and 5 microns. A particular target abrasion distance is set for a polishing process in the manner described above, though the target distance will be smaller for a polishing process than for a grinding process. Progress of abrasion during polishing is monitored in the manner described above, i.e. by monitoring the position of the support arms 88 via the sensor. When a target distance of the facet surface has been reached (i.e. when a pre-determined amount of material has been abraded away during the polishing process), the control system 200 stops the polishing process, and moves to the next facet to grind a polish that facet.

[0177] When every facet of the pavilion has been ground and polished, the holder 50 is removed from the apparatus, and the pre-form 10 is removed from the holder. The pre-form is re-arranged in a holder 50b so that the crown is exposed for polishing. The alignment tests of Figures 8a, 8b and 8c are repeated, and the holder 50b is placed in the apparatus once again. The process described above is then repeated in respect of the crown facets, with the same testing, verification and final grinding / polishing steps.

[0178] Once the crown facets have been ground polished, the pre-form 10 is removed, and the girdle is polished by hand to produce the finished, polished diamond.

[0179] The apparatus therefore provides an efficient and effective means for automatically grinding and polishing the facets of a diamond. After an initial testing and verification stage using a small number of facets (typically between 3 and 5 facets), the apparatus can predict the soft directions of all subsequent facets, and can automatically align each facet in turn for grinding and polishing in the soft direction. The apparatus requires very little human input to grind and polish a diamond from a pre-form. Because it can accurately predict the soft directions of most of the facets of the diamond without the need for empirical testing, many of the time-consuming testing steps that are required in a hand- grinding / polishing process can be omitted, resulting in significant time saving.

[0180] It will be appreciated that a high level of accuracy is desirable in the apparatus 20. In particular, it is desirable that any assessment of the amount of material abraded away from the facet surface during polishing is highly accurate, so that the shape of the diamond is accurate. During abrasion, a typical abrasion rate is measured in terms of 100s of nm / second (for example 800 nm / second might be a typical abrasion rate in a soft direction). To ensure accurate assessment of the abrasion speed, and accurate monitoring of polishing progress, it is therefore desirable to be accurate on a nm scale when assessing the movement of the facet surface as it is abraded.

[0181] As described above, the control system is configured to monitor a position of the support arms, which provides a measured abrasion parameter that is related to the abrasion distance. The control system therefore makes the determination as to whether the abrasion distance is equal to the target abrasion distance based on at least the measured abrasion parameter. However, there are situations where additional factors need to be taken into account to ensure an accurate assessment. The control system may therefore also be configured to make the determination as to whether the abrasion distance is equal to the target abrasion distance based on the measured abrasion parameter and additionally one or more calibration parameters.

[0182] Two examples of calibration parameters are described below: i) X-Y calibration

[0183] As noted above, the abrasion wheel 30 is moveable in the X and Y axes by virtue of the sliding rail arrangement described. As the wheel is moved in the X and Y axes, some deviation of the wheel 30 in the Z axis may occur. Movements in the Z-direction would bring the wheel 30 closer to and further away from the pre-form, which would change the z-position of the pre-form, and cause movement of the support arms 75, 76. As described above, the position of the support arm 75, 76 as measured by the support arm position sensor 88 is an important parameter used to determine the abrasion rate, and to determine the abrasion parameter. Movement of the support arms 75, 76 as they accommodate Z-axis deviation of the abrasion wheel 30 could therefore impact the measure abrasion parameter. This would lead, for example, to over-polishing or under-polishing of the facets, and hence an imperfect diamond geometry.

[0184] The apparatus 20 is configured to compensate for such z-axis movements of the abrasion wheel 30, by calculating and storing a map of z-axis deviations, and using the stored information as a first calibration parameter. In a first calibration stage, the control system moves the manipulation system 68 until the calibration protrusion 68 is in contact with the abrasion wheel at a known location, and them moves the abrasion wheel systematically across the X-Y space. As the wheel moves, any deviations in the z-axis position cause the calibration protrusion to move in the z direction, which causes the support arms 75, 76 to move. The controller monitors the position of the support arms 75, 76 to measure the Z-axis deviation of the wheel at each position within the X-Y space thereby producing a calibration map.

[0185] An example of the z-axis deviation map is shown in Figure 16. This information is stored in the control system 200. When the abrasion wheel 30 is moved to a particular X-Y co-ordinate, the control system determines the Z-axis deviation associated with that co-ordinate from the stored data. The Z-axis deviation can be used as a first calibration parameter. ii) Temperature calibration

[0186] During polishing, friction between the abrasion wheel and facet surface generates heat, which causes the pre-form and the surrounding components to heat up. The pre-form holder may be especially prone to heating. Heating causes expansion, which results in movement of the components and hence movement of the pre-form, especially in a direction parallel to the feed direction.

[0187] This movement can be monitored using the pre-form position sensor 90, which is configured to sense the position of the pre-form by direct measurement. Changes in position that occur as a result of temperature changes can thereby be determined directly. Information from the pre-form position sensor 90 relating to pre-form position is sent to the controller, where it is used as a second calibration parameter.

[0188] An example of the pre-form movement monitored over time during the polishing process is shown in Figure 17.

[0189] In a particularly preferred example, the x-y calibration information is used as a first calibration parameter, and the temperature calibration information is used as a second calibration parameters.

[0190] When the calibration parameters are used, the control system is configured to make the determination as to whether the abrasion distance is equal to the target abrasion distance based on the measured abrasion parameter and the one or more calibration parameters.

[0191] As an example: the controller may be configured to update the target abrasion distance to an “updated target distance” based on the calibration parameters. For example:

[0192] Updated target abrasion distance = target abrasion distance - calibration parameters

[0193] The updated target distance may then be used to calculate a target abrasion parameter that takes account of the calibration parameters. For example, if the abrasion parameter is an angular position of the support arm about the pivot, the target abrasion parameter will correspond to a target angular position of the support arm.

[0194] When the measured abrasion parameter is equal to the updated target abrasion parameter, the abrasion distance (corresponding to the actual depth of material abraded) is known to be equal to the target abrasion distance. The controller therefore causes abrasion to stop.

[0195] Examples are envisaged in which only one calibration parameter is necessary. Examples are also envisaged in which further calibration parameters are used. Where calibration parameters are used, the controller may be configured to calculate an updated target distance and / or updated target abrasion parameters at regular intervals, for example 128 times per second. The relevant calibration information may be obtained at the same rate - for example the z-axis deviation may be updated at the same rate, and the sensor 90 may be configured to determine the position of the pre-form at the same rate.

[0196] The described controller 200 may be in the form of any suitable computing device, for instance one or more functional units or modules implemented on one or more computer processors. Such functional units may be provided by suitable software running on any suitable computing substrate using conventional or custom processors and memory. The one or more functional units may use a common computing substrate (for example, they may run on the same server) or separate substrates, or one or both may themselves be distributed between multiple computing devices. A computer memory may store instructions for performing the methods performed by the controller, and the processor(s) may execute the stored instructions to perform the method.

[0197] Referring to Figure 10, the controller 200 is configured to receive internal input signals from the described sensors 80, 90 of the apparatus, and to receive external input signals from sources external to the apparatus as appropriate. For example, the controller 200 may be configured to receive user- initiated input signals which may be input, for example, through a user interface. The controller 200 may also be configured to receive appropriate input signals from other apparatus: for example through wireless signals. As an example, the information 102 relating to holder calibrations may be provided as a user-initiated input, or it may be sent to the controller automatically from the appropriate testing apparatus. Information 100 relating to the desired cut geometry may similarly be provided by a user, or may be provided by external apparatus. Information 104 relating to the diamond crystal structure may be stored within the controller, for example in the computer memory.

[0198] The controller 200 is configured to generate output signals that control components of the apparatus, and in particular to generate output signals to control the actuators 31 , 36, 42 that control the rotation and position of the abrasion wheel 30, and the actuation system 71 , 72, 73 that controls the orientation of the pre-form support 70.

[0199] In the embodiment described above, the apparatus is used to determine the relative angular displacement a, p, y between each axis pairX-X’, Y-Y’, Z-Z’ of the diamond geometry and the underlying diamond crystal structure, which can then be used to calculate the soft direction of each facet.

[0200] However, embodiments are also envisaged in which the apparatus is not used or configured to make this determination, and instead the angular displacements a, p, y, are provided from another source: for example, the information may be calculated or decided elsewhere, or provided by the supplier of the diamond element, or a combination of both. In this case, the controller is configured to receive this information from another source (for example it may be supplied manually by a user) and to calculate the corresponding soft direction for each facet in the same manner. Embodiments are also envisaged in which some of the information relating to the angular displacements is provided elsewhere, and some is determined by the apparatus. In these examples, the apparatus may calculate the soft directions of all facets before the abrasion process begins, and the apparatus may proceed immediately to abrading all facets in their respective soft direction. The element may be moved in the same manner already described above, and all other aspects of the abrasion process may be the same.

[0201] Figure 18 illustrates an alternative first carriage 174 of the holder support system 60, which can replace the first carriage 74 described above. The alternative first carriage 174 comprises multiple holder supports 170, arranged in close proximity to each other, each with a cavity that is configured to receive a holder 50 with an attached pre-form 10, in the manner already described above. In this way, the alternative first carriage can support multiple pre-forms 10. Each holder support 170 is configured to rotate about its own azimuth axis A, so as to rotate the preform about its corresponding azimuth axis A. Rotation about this axis is controlled by an azimuth actuator 171 in the form of an azimuth servo motor, which is controlled by the control system 200. The same azimuth actuator may control the rotation of all the holder supports 170, so that holder support 170, and hence each pre-form 10, is always rotated by the same azimuth angle as the others.

[0202] The alternative first carriage 174 is incorporated into the apparatus in the same way as the first carriage 74 described above i.e. it is supported between the support arms 75, 76 for movement around the slope axis B and the feed axis C in the same way. This alternative first carriage 174 allows multiple pre-forms 10 to be arranged in place in the apparatus, so that each pre-form 10 can be arranged at the same azimuth angle, slope angle and feed angle. In this way, multiple pre-forms can be abraded simultaneously, using the same angles. This arrangement is particularly desirable if the relative displacements a, p, y between the crystallographic axis system X’, Y’, Z’ and the axis system X, Y, Z of the diamond cut geometry are pre-known: in that case, each pre-form 10 can be arranged in the first carriage 174 with respective reference points R at the same orientation around the Z axis, and each pre-form can be moved by simultaneously by identical angles to grind and polish each pre-form identically and simultaneously.

[0203] Further embodiments are envisaged in which some, but not all, information relating to the relative displacements a, p, y between the crystallographic axis system X’, Y’, Z’ and the axis system X, Y, Z of the diamond cut geometry are pre-known. For example, the crystallographic plane of the table of a preform may be known, but no other information. In this case, the angular displacements p and y are known, but angular displacement a is unknown. The soft direction of one or more test facets may be determined by the apparatus in the manner described above, and this information can be combined with the already-known angular displacements p and y, the diamond crystal structure and the diamond cut geometry to determine the angular displacement a. In this case, fewer test facets may be required because some information is already known.

[0204] In all the embodiments of the apparatus described above, the abrasion direction is changed by moving the abrasion wheel in an X-Y plane. However, the apparatus may be configured to change the abrasion direction by other means. For example, the apparatus may be configured to cause translation of the pre-form support in the X-Y plane to change the relative position of the pre-form and the abrasion wheel. The apparatus may also be configured to rotate the pre-form about an axis perpendicular to the plane of the facet to change the abrasion direction.

[0205] In the embodiments described, the front and rear parts of the support arms meet at an obtuse angle to define an angled shape. This need not be the case and the support arms may take any suitable shape. Other components of the support structure may take any suitable form or shape. The force control mechanism may take any suitable form that is capable of controlling the force applied to the support arm.

[0206] In the process described above, after a soft direction is found for each test facet, the facet is immediately ground and polished, but this need not be the case: the model may be calculated and verified before the facets are ground and polished. In the method described, polishing of each facet takes place immediately after grinding, though this need not be the case: for example all facets may be ground, and subsequently all facets may be polished.

[0207] The pre-form may be any suitable shape and the diamond cut may be of any suitable geometry.

[0208] It will be appreciated that many other variations and modification of the above apparatus and method are envisaged within the scope of the appended claims.

Claims

Claims1 . Apparatus for abrading a diamond element, the apparatus comprising: an element support for supporting a diamond element; an abrasion means for abrading a surface of the element in an abrasion direction; an actuation system for controlling the relative orientation of the element support and the abrasion means; a sensor configured to sense a measured abrasion parameter, the measured abrasion parameter relating to an abrasion distance defined as the perpendicular depth of material that has been removed from the surface during abrasion; and a control system configured to: receive information relating to i) a soft direction of a first diamond facet to be abraded and ii) a target abrasion distance of the first facet; send a control signal to the actuation system to cause a change in relative orientation between the abrasion means and the element support to align the abrasion direction with the soft direction to allow abrasion of the first facet surface in the soft direction; receive information from the sensor relating to the measured abrasion parameter, as the first facet is abraded; determine, based at least on the measured abrasion parameter, whether the abrasion distance is equal to the target abrasion distance; and halt abrasion of the first facet when the abrasion distance is equal to the target abrasion distance.

2. The apparatus of Claim 1 , wherein the abrasion means is an abrasion wheel that is rotatable about a rotation axis, and wherein the actuation system is configured to cause relative movement between the abrasion wheel and the element support in the x-y axis to align the abrasion direction with the soft direction.

3. The apparatus of Claim 1 or Claim 2, wherein the apparatus comprises one or more support arms that support the element support, the or each support arm being moveable to move the element support towards the abrasion means to keep the first facet surface in contact with the abrasion means as material is removed from the first facet surface during abrasion, the sensor being configured to sense the position of a reference part of the or each support arm, and provide information to the control system related to a position and / or rate of movement of the or each support arm.

4. The apparatus of Claim 3, wherein the support arm is supported on a pivot, the element support being arranged at a forward side of the pivot, and wherein the apparatus is configured to permit rotation of the support arm about the pivot during abrasion, to keep the first facet surface of the element in contact with the abrasion means.

5. The apparatus of Claim 3 or Claim 4, comprising a force applicator for applying a force to the support arm to control the force with which the first facet surface is applied to the abrasion means.

6. The apparatus of Claim 5, wherein the force applicator comprises a feed actuator that is coupled to the support arm via a spring.

7. The apparatus of Claim 2, or any claim dependent thereon, wherein the control system is configured to store x-y calibration information relating to the deviation of the height of the abrasion wheel along its axis of rotation within the x-y plane, and wherein the controller is configured to determine, based at least on the measured abrasion parameter and the x-y calibration information, whether the abrasion distance is equal to the target abrasion distance.

8. The apparatus of any preceding claim, comprising an element position sensor configured to sense a position of the element in a direction parallel to a longitudinal axis of the element, and send information relating to the element position to the control system, wherein the controller is configured to determine, based at least on the measured abrasion parameter and information relating to the element position, whether the abrasion distance is equal to the target abrasion distance.

9. The apparatus of any preceding claim wherein the control system is further configured to generate the information relating to the soft direction of the first facet of the element by: i) sending a control signal to the actuation system to align the abrasion means and element support such that the abrasion means abrades the first facet in a first abrasion direction; ii) receiving information from the sensor relating to the abrasion speed of the first facet surface during abrasion in the first abrasion direction; iii) causing relative movement between the abrasion means and the first facet to change the abrasion direction to a plurality of different abrasion directions; iv) receiving information from the sensor relating to the abrasion speed of the first facet surface during abrasion for each of the different abrasion directions; and v) determining an abrasion direction that corresponds to a highest abrasion speed of the first facet surface, and identifying that abrasion direction as a soft direction for the first facet.

10. The apparatus of Claim 9, wherein the controller is configured to determine the soft direction for each of a plurality of test facets, one of the test facets being defined by the first facet, by: i) sending a control signal to the actuation system to align the abrasion means and element support such that the abrasion means abrades the test facet in a first abrasion direction; ii) receiving information from the sensor relating to the abrasion speed of the facet surface during abrasion in the first abrasion direction; iii) causing relative movement between the abrasion means and the test facet to change the abrasion direction to a plurality of different abrasion directions; iv) receiving information from the sensor relating to the abrasion speed of the facet surface during abrasion for each of the different abrasion directions; and v) determining an abrasion direction that corresponds to a highest abrasion speed of the facet surface, and identifying that abrasion direction as a soft direction for that test facet.11 . The apparatus of Claim 10, wherein the control system is configured to calculate a predicted soft direction for a further facet, based on: i) the crystal structure of diamond; ii) the geometry and determined soft direction of each test facet; and iii) the geometry of the further facet.

12. The apparatus of Claim 11 , wherein the element support is configured to support a element holder that holds the element, and wherein the control system is configured to store element holder information relating to the relative position and / or orientation of the element in the element holder and to calculate the predicted soft direction for the further facet, based on: i) the crystal structure of diamond; ii) the geometry and determined soft direction of each test facet; iii) the geometry of the further facet; and iv) the stored element holder information.

13. The apparatus of Claim 11 or Claim 12, wherein the control system is configured to receive information relating to the abrasion speed of the further facet during abrasion in the predicted softdirection, to determine if the abrasion speed is greater than a target speed, and if the abrasion speed is not greater than the target speed the control system is further configured to: determine that the predicted soft direction for the further facet is not the true soft direction: determine the true soft direction of the further facet by: i) causing relative movement between the abrasion means and the test facet to change the abrasion direction to a plurality of different abrasion directions; ii) receiving information from the sensor relating to the abrasion speed of the facet surface during abrasion for each of the different abrasion directions; and iii) determining an abrasion direction that corresponds to a highest abrasion speed of the facet surface, and identifying that abrasion direction as the true soft direction for the further facet; and calculate a predicted soft direction for a next further facet, based on: i) the crystal structure of diamond; ii) the geometry and determined soft direction of each test facet and the further facet; and iii) the geometry of the next further facet.

14. A method of grinding a diamond element to shape facets of a diamond geometry, the method comprising: a) providing a diamond element having a diamond crystal structure with a crystallographic axis system X’, Y’, Z’; b) providing information relating to a desired diamond cut geometry having a plurality of facets, the diamond cut geometry having a geometry axis system X, Y, Z; c) determining an angular displacement a, p, y, between each axis of the crystallographic axis system and each respective axis of the geometry axis system; d) determining the soft direction of each of the facets of the diamond cut geometry, based on i) the crystallographic axis system of the diamond structure ii) the desired diamond cut geometry and iii) the angular displacement between each axis of the crystallographic axis system and each respective axis of the geometry axis system; e) providing an abrasion means; f) causing relative movement between the element and the abrasion means to move each facet directly to a position in which the abrasion means is arranged to grind the respective facet in its determined soft direction; g) abrading each facet in its respective determined soft direction.

15. The method of Claim 14, wherein the step of determining the angular displacement between each axis of the crystallographic axis system and each respective axis of the geometry axis system comprises: a) determining the soft direction of a plurality of test facets by: abrading each test facet in a first abrasion direction with an abrasion means; sensing the abrasion speed of the facet surface during abrasion in the first abrasion direction; causing relative movement between the abrasion means and the test facet to change the abrasion direction to a plurality of different abrasion directions; sensing the abrasion speed of the facet surface during abrasion for each of the different abrasion directions; and determining an abrasion direction that corresponds to a highest abrasion speed of the facet surface, and identifying that abrasion direction as a soft direction for that test facet; c) calculating the angular displacement based on: i) the crystal structure of diamond; ii) the position and angle of each test facet relative to the geometry axis system; and iii) the determined soft direction of each test facet.

16. A computer-implemented method of grinding a diamond element to shape facets of a diamond geometry, the method comprising: a) providing a diamond element having a diamond crystal structure with a crystallographic axis system X’, Y’, Z’; b) providing information relating to a desired diamond cut geometry having a plurality of facets, the diamond cut geometry having a geometry axis system X, Y, Z; c) determining an angular displacement a, p, y, between each axis of the crystallographic axis system and each respective axis of the geometry axis system; d) determining the soft direction of each of the facets of the diamond cut geometry, based on i) the crystallographic axis system of the diamond structure ii) the desired diamond cut geometry and iii) the angular displacement between each axis of the crystallographic axis system and each respective axis of the geometry axis system; e) providing an abrasion means; f) causing relative movement between the element and the abrasion means to move each facet directly to a position in which the abrasion means is arranged to grind the respective facet in its determined soft direction; g) abrading each facet in its respective determined soft direction.

17. The computer-implemented method of Claim 16, wherein the step of determining the angular displacement between each axis of the crystallographic axis system and each respective axis of the geometry axis system comprises: a) determining the soft direction of a plurality of test facets by: abrading each test facet in a first abrasion direction with an abrasion means; sensing the abrasion speed of the facet surface during abrasion in the first abrasion direction; causing relative movement between the abrasion means and the test facet to change the abrasion direction to a plurality of different abrasion directions; sensing the abrasion speed of the facet surface during abrasion for each of the different abrasion directions; and an abrasion direction that corresponds to a highest abrasion speed of the facet surface, and identifying that abrasion direction as a soft direction for that test facet; c) calculating the angular displacement based on: i) the crystal structure of diamond; ii) the position and angle of each test facet relative to the geometry axis system; and iii) the determined soft direction of each test facet.

18. A computer-readable medium carrying instructions for implementing the method of Claim 16 or Claim 17.

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