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Title:
MEASUREMENT OF ROUGH GEMSTONES
Document Type and Number:
WIPO Patent Application WO/2020/254059
Kind Code:
A1
Abstract:
A method of obtaining multiple measurements of a rough gemstone comprises feeding a rough stone into a measurement system using a feed system; detecting that a single rough stone has been fed into the measurement system and halting the feed system; dispensing the stone to a first measurement location, and carrying out an optical 5 measurement of the stone to generate a 3D model of the stone; dispensing the stone to a second measurement location, and obtaining a weight measurement of the stone.

Inventors:
PORTSMOUTH ANDREW JOHN (GB)
HARRIS PHILLIP (GB)
BODHINAYAKE SUDATTA (GB)
HONG QI HE (GB)
HARRIES TREVOR ANTHONY (GB)
POWELL DR GRAHAM RALPH (GB)
Application Number:
PCT/EP2020/064227
Publication Date:
December 24, 2020
Filing Date:
May 21, 2020
Export Citation:
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Assignee:
DE BEERS UK LTD (GB)
International Classes:
A44C17/00; B07C5/16; B07C5/342; B28D5/00; B65G47/74; G01B11/24; G01G21/22; G01G21/28; G01N21/87
Domestic Patent References:
WO2011054822A12011-05-12
WO2009068354A12009-06-04
WO2017035324A12017-03-02
Foreign References:
CN109389351A2019-02-26
Attorney, Agent or Firm:
BRANDERHORST, Matthijs (GB)
Download PDF:
Claims:
CLAIMS:

1 . A method of obtaining multiple measurements of a rough gemstone, the method comprising:

feeding a rough stone into a measurement system using a feed system;

detecting that a single rough stone has been fed into the measurement system and halting the feed system;

dispensing the stone to a first measurement location, and carrying out an optical measurement of the stone to generate a 3D model of the stone;

dispensing the stone to a second measurement location, and obtaining a weight measurement of the stone.

2. The method of claim 1 , wherein dispensing the stone to a first measurement location comprises:

receiving the stone into a cone formed by a retractable set of stabilizing elements in a first receiving position;

stabilizing the stone in a central position on a platform using the set of stabilizing elements; and

applying a vacuum to the platform to retain the stone in the central position while retracting the set of stabilizing elements away from one another into a second retracted position.

3. The method of claim 2, wherein carrying out an optical measurement of the stone to generate a 3D model of the stone comprises:

rotating the platform while capturing a series of 2D silhouette images of the stone at discrete rotational positions; and

processing the series of captured images to form the 3D model of the stone.

4. The method of any preceding claim, wherein obtaining a weight measurement of the stone comprises dispensing the stone into a weigh pan and enclosing an area around the weigh pan prior to carrying out the weight measurement using a weigh cell.

5. An apparatus for obtaining multiple measurements of a rough gemstone, the apparatus comprising: a feed system configured to feed a rough stone into a measurement system, and to be halted once the rough stone has been fed into the measurement system;

a detection system configured to detect that a single rough stone has been fed into the measurement system;

a first dispense system for dispensing the stone to a first measurement location; an optical measurement system for carrying out an optical measurement of the stone at the first measurement location;

a processor configured to generate a 3D model of the stone, based upon the optical measurement;

a second dispense system for dispensing the stone to a second measurement location, and

a weigh cell configured to weigh the stone at the second measurement location.

6. The apparatus of claim 5, further comprising:

a retractable set of stabilizing elements configured to receive and stabilize the stone at the first measurement location;

a vacuum supply for selectively applying vacuum to the first measurement location to retain the stone in a central position at the first measurement location.

7. The apparatus of claim 6, wherein the optical measurement system comprises: an illumination device configured to illuminate the stone;

an image capture device configured to obtain a series of 2D silhouette images of the illuminated stone at discrete rotational positions;

wherein the processor is configured to process the series of captured 2D images to generate the 3D model of the stone.

8. The apparatus of any one of claims 5 to 7, wherein the first measurement location comprises a rotatable platform.

9. The apparatus of any one of claims 5 to 8, wherein the second measurement location is a weigh pan and wherein an area around the weigh cell is enclosable.

10. A measurement system configured to weigh discrete objects, comprising an automatic weighing device, and a feeder for feeding the discrete objects into the system, wherein the feeder is stopped during weighing of the discrete objects. 1 1 . A measurement system configured to measure discrete objects, the system comprising:

a set of stabilizing elements configured to receive a discrete object in freefall and to stabilize the discrete object in a central position on a measurement platform;

a vacuum system configured to be selectively applied to the measurement platform to retain the discrete object in the central position;

wherein the set of stabilizing elements form a cone shape for receiving the discrete object when in a first receiving position, and are configured to be retracted away from one another into a second retracted position once the discrete object is stabilized and retained by the vacuum system.

12. A measurement system configured to weigh discrete objects, the system comprising:

a weigh pan for receiving a discrete object to be weighed; and

a weigh cell configured to weigh a discrete object in the weigh pan;

wherein the weigh pan is configured to be closed by a flap after receiving the discrete object, such that the weigh pan is enclosed while the discrete object is weighed.

Description:
MEASUREMENT OF ROUGH GEMSTONES

Technical Field

The present invention relates to a method and an apparatus for measuring multiple properties of a rough gemstone. In particular, although not exclusively, the invention relates to a method and an apparatus for measuring properties of rough diamonds.

Background

Rough (i.e. uncut) gemstones, such as diamonds, may be used for many purposes. For example, a gemstone-quality rough diamond may be faceted for use in jewellery, such as rings or watches. Alternatively, an industry-quality stone may be cut for use in drilling, grinding or polishing, or may be ground into an abrasive powder.

In order to establish the future use of a gemstone it is usually necessary to obtain a series of measurements, for example of the stone’s weight, shape and composition, and/or images of the stone, which can be used in constructing 3D models that enable the cutting of a stone to be planned.

Obtaining multiple properties of a rough stone can be time consuming and may require the use of more than one piece of equipment. It would therefore be desirable to automate the measurement of multiple properties of a rough stone.

Summary

In one aspect of the present invention there is provided a method of obtaining multiple measurements of a rough gemstone, the method comprising: feeding a rough stone into a measurement system using a feed system; detecting that a single rough stone has been fed into the measurement system and halting the feed system; dispensing the stone to a first measurement location, and carrying out an optical measurement of the stone to generate a 3D model of the stone; dispensing the stone to a second measurement location, and obtaining a weight measurement of the stone. In a further aspect of the present invention there is provided an apparatus for obtaining multiple measurements of a rough gemstone. The apparatus comprises a feed system configured to feed a rough stone into a measurement system, and to be halted once the rough stone has been fed into the measurement system; a detection system configured to detect that a single rough stone has been fed into the measurement system; a first dispense system for dispensing the stone to a first measurement location; an optical measurement system for carrying out an optical measurement of the stone at the first measurement location; a processor configured to generate a 3D model of the stone, based upon the optical measurement; a second dispense system for dispensing the stone to a second measurement location, and a weigh cell configured to weigh the stone at the second measurement location.

In a still further aspect of the present invention there is provided a measurement system configured to weigh discrete objects, comprising an automatic weighing device, and a feeder for feeding the discrete objects into the system, wherein the feeder is stopped during weighing of the discrete objects.

In a yet further aspect of the present invention there is provided a measurement system configured to measure discrete objects, the system comprising: a set of stabilizing elements configured to receive a discrete object in freefall and to stabilize the discrete object in a central position on a measurement platform; a vacuum system configured to be selectively applied to the measurement platform to retain the discrete object in the central position; wherein the set of stabilizing elements form a cone shape for receiving the discrete object when in a first receiving position, and are configured to be retracted away from one another into a second retracted position once the discrete object is stabilized and retained by the vacuum system.

In a further aspect of the present invention there is provided a measurement system configured to weigh discrete objects, the system comprising: a weigh pan for receiving a discrete object to be weighed; and a weigh cell configured to weigh a discrete object in the weigh pan; wherein the weigh pan is configured to be closed by a flap after receiving the discrete object, such that the weigh pan is enclosed while the discrete object is weighed. Brief Description of the Drawings

Figure 1 is a cross-sectional view of an exemplary apparatus for obtaining measurements of a rough stone;

Figure 2 is a front view of an imaging assembly of the apparatus of Figure 1 ;

Figure 3 is a cross-sectional view of a rotatable stage and set of jaws, for use in the apparatus of Figure 1 , in a first position;

Figure 4 is a cross-sectional view of the rotatable stage and set of jaws in a second, retracted position;

Figure 5 is a cross-sectional view of the rotatable stage and one of the set of jaws in a third position;

Figure 6 is a cross-sectional view of the imaging assembly and a weigh cell for use in the apparatus of Figure 1 ; and

Figure 7 illustrates a method of obtaining multiple measurements of a rough gemstone.

Detailed Description

Disclosed herein with reference to Figures 1 to 7 is a method of measuring multiple properties of a rough gemstone. Also disclosed is an exemplary apparatus 100 for carrying out at least some of the steps of the afore-mentioned method.

Figure 1 illustrates the exemplary apparatus 100, or measurement system, configured to obtain multiple measurements of a rough stone. In this example, the measurements comprise the shape of the stone and the weight of the stone. The shape of the stone is determined by capturing a plurality of 2D silhouette images of the stone which are then combined to form a 3D model of the rough stone.

As shown in Figure 1 , the exemplary apparatus 100 comprises a feed system 1 10, a double feed detection assembly 120, 125, an imaging assembly 170, a set of stabilising elements ( e.g . jaws) 150, 155, a rotatable platform and a weigh cell 140.

Rough stones are introduced, for example, from a parcel of stones, into the feed system. In this example, the feed system comprises a vibrating bowl 1 10, which provides single stone feeding along a spiral path into the measurement section of the apparatus 100. The vibrating bowl 1 10 is driven until a stone falls, substantially vertically, off the edge of the bowl 1 10. This event is detected by a first laser light curtain (not shown here) at the exit of the bowl 1 10. Detection of a stone leaving the bowl 1 10 by the first laser light curtain is used to signal that vibration of the bowl 1 10 should be stopped. Due to the accuracy required for the measurements of the stone, the vibrating bowl 1 10 is preferably not driven (i.e. vibrated) whilst the measurements are taken.

Optionally, a second laser light curtain (not shown here) may be located just before the end of the bowl 1 10. The second laser light curtain is used to‘prime’ the bowl 1 10 to ensure that, where possible, a further stone is located near the exit of the bowl 1 10. This minimises the time it takes to feed each stone.

Once a stone exits the bowl 1 10 it free falls through a double feed detection assembly 120, 125. In this example, the double feed detection assembly 120, 125 comprises a first 120 and a second 125 level of double feed detection (DFD). In this example, the two double feed detectors (DFD) 120, 125 are mounted one on top of the other with a separation between the two of about 50 mm. The lower DFD 125 is offset horizontally from the upper DFD 120 by about 30 mm.

Each DFD 120, 125 defines an aperture (not shown) through which the stone falls. These apertures are linked by an enclosed chute or ramp which, owing to the horizontal and vertical offsets of the upper 120 and lower 125 DFDs, is angled at about 45 degrees. This angle leads to stones falling through the aperture of the upper DFD 120 hitting a lower face of the chute. The stone is guided by the chute to the aperture of the lower DFD 125.

It is possible that a multiple feed (i.e. more than one stone) may not be detected by the upper DFD 120, as the stones may appear as a single object. Flowever, any double feed stones that have travelled together through the upper DFD 120 are spatially and temporally separated (i.e. split from one another) by impacting on the lower face of the chute after falling through the upper DFD 120 aperture. This separation leads to an increased likelihood of the double feed being correctly detected by the lower double feed detector 125. Two DFDs 120, 125 are preferable since it is equally possible that multiple feeds might appear separate in the upper DFD 120 but together in the lower DFD 125. Only if both DFDs 120, 125 report the presence of a single stone is the feed deemed to be successful. If either DFD 120, 125 reports more than one stone detected, then a multiple feed is assumed.

In this example, the DFD levels 120, 125 include imaging systems that each comprise two orthogonal axes of light that are broken when a stone passes through them. A processor (not shown here) linked to the double feed detection assembly 120, 125 runs software that completes boundary tracking of the stone(s) and is therefore able to differentiate between single and multiple feeds. In other words, each of the DFD levels 120, 125 distinguish between the presence of a single stone or more than one stone.

After passing through the two levels of the double feed detection assembly 120, 125 the stone is collected into an upper hold gate (UFIG) 130. The UFIG 130 is a single entry, double exit hold gate that forms a first dispense system that is used for two purposes.

Firstly, the UFIG 130 is used to separate multiple feeds from single feeds. Multiple feeds (i.e. where more than one stone is present) are ejected from the UFIG 130 from a first exit port (not shown here) and are subsequently fed down a tube directly into a reject dispense bin (not shown here). Single feeds are fed through a second exit port (not shown here) of the UFIG 130 and into a loading system of the imaging assembly 170.

The second function of the UFIG 130 is to act as a‘hold gate’ in which a stone is held ready to be measured as close to a first measurement position as possible. This means that when the measurement system below the UFIG 130 becomes free the next stone can be loaded with minimal delay. Once the loading is complete, the hold gate 130 is ready to accept the next stone. This allows the machine 100 to operate with fewer delays and, therefore, faster.

The UFIG 130 comprises a rotational bucket that rotates in one direction to dispense the stone to the first exit port and rotates in the opposite direction to dispense the stone to the second exit port. At both the entry and the exits to the UFIG 130 there are fibre optic light curtains which are used to detect that stones have correctly entered or exited the UHG 130 (i.e. that a stone has not become stuck in the entry or one of the exit ports).

An exemplary imaging assembly 170 is illustrated in Figure 2. The imaging assembly comprises an optical measurement system, including an image capture device, e.g. a camera 174 fitted with a telecentric lens 175, back lit illumination 178 (e.g. one or more LEDs, located opposite to the camera 174) with a telecentric lens 179, and a rotational stage, or platform 172. The captured images obtained by the camera 174 are 2D silhouette images that include the outline/shape of the rough stone.

The stone freefalls from the second exit port of the UHG 130 and is received into the loading system of the imaging assembly 170, at a first measurement location. The stone is then positioned in the centre of the rotatable stage 172 and a number of images of the stone are captured using the camera 174 at multiple discrete rotational positions as the stage 172 completes a single full 360° revolution. The captured images are subsequently processed by a processor (not shown here) and combined to create a 3D model of the stone. Various methods of processing 2D images to form a 3D model are known in the art. The 2D images obtained by the camera 174 and/or the generated 3D model of the rough stone may be stored at a storage device or database.

The number of captured images is configurable but the greater the number of images taken the more accurate the 3D model created, albeit with a time penalty of more images having to be captured and processed. Nominally, around 21 images may be taken. It will be appreciated however that fewer or additional images of the stone may be captured.

As previously discussed, during image capture at the imaging assembly 170 the vibratory bowl 1 10 is preferably not driven.

The imaging assembly 170 requires the rough stone to be positioned centrally on the rotational stage 172. The stone must not move on the stage 172 whilst the stage 172 rotates. Once a single stone is released from the UHG 130 (i.e. from the second exit port) it drops into a set of retractable jaws 150, 155. The jaws 150, 155 are independently operated using a front jaw drive mechanism 156 for operating the front jaw 155, and a rear jaw drive mechanism 151 for operating the rear jaw 150.

As illustrated in Figure 3, an exemplary set of stabilizing elements comprising jaws 150, 155 when brought together in a first position form a conical cup shape C. The cup shape C defines a hole H through its middle of approximately 4 mm when positioned to receive a stone, i.e. when the jaws 150, 155 are together.

In the first, receive position shown in Figure 3, both jaws 150, 155 are positioned directly above the centre of the rotational stage 172 and the hole FI in the bottom of the jaws 150, 155 aligns with a hole FT of approximately 3 mm in the rotational stage 172.

A switchable vacuum 176 is applied through the hole FT in the centre of the rotational stage 172. The vacuum is used to both pull the stone down onto the stage 172 as the jaws retract away from one another into a second, retracted position and then to hold the stone precisely in place whilst the stage 172 rotates and the images of the stone are taken by the camera 174.

As illustrated in Figure 4, once the vacuum 176 has been applied and the stone is held firmly in place on the stage 172 (i.e. the first measurement location), the jaws 150, 155 retract away from the stone and completely out of the field of view of the optical system (camera 174 and illumination 178, not shown here). Once the jaws 150, 155 have retracted the optical measurement or imaging (i.e. the image capture and 3D model creation) is carried out.

As illustrated in Figure 5, once all images have been captured, the vacuum supply 176 through the rotational stage 172 is shut off using a vacuum solenoid (not shown here) and the rear jaw 150 sweeps across the stage 172 into a third, dispensing position, pushing the stone off the stage 172. It will be appreciated that in an alternative configuration the front jaw 155 could be used for this purpose.

Referring now to Figure 6, surrounding the stage 172 is a slope 173 that feeds down into a flap hold gate (FFHG) 180, which forms a second dispense system. As the stone enters the FFIG 180 it passes through a fibre optic light curtain (not shown here) which is used to detect that the stone has entered the FFIG 180. The FFIG 180 holds the stone above the second measurement point, the weigh cell 140. In one example, the weigh cell 140 is a Wipotec weigh cell. The slope 173 forms a feed system between the imaging assembly 170 in which the first measurement of the stone is obtained (the shape measurement) and the weigh cell 140 from which the second measurement of the stone (the weight measurement) is obtained.

Once the weigh cell 140 is ready to receive a stone, the flap hold gate (FHG) 180, which is driven by a rotational solenoid (not shown), opens allowing the stone to drop into a weigh pan 190 mounted on top of the weigh cell 140. The weigh pan 190 forms the second measurement location. Optionally, the FHG 180 may be fitted with a rotary encoder to allow more controlled opening and closing of the flap 180 to minimise air disturbances and mechanical impact effects which would affect the weigh cell. Once the stone has dropped into the weigh pan 190, the FHG 180 then closes to enclose the area around the weigh cell 140 to ensure no draughts or air movements affect the weight measurement. This may be particularly important where smaller stones are being measured. The weigh cell 140 then weighs the stone. The weight measurement is of high accuracy and may determine the weight of the rough stone to 3 decimal places of a carat.

Once the weight measurement has been completed, the stone is ejected from the weigh cell 140 using a motor and linkage system (not shown) to open the weigh pan 190. The stone then falls under gravity out of the weigh pan 190 into a lower hold gate (LHG) 135. In this example, the LHG 135 is of substantially the same design as the UHG 130 and is provided with a single entry, and double exit ports. The stone can be dispensed through either of the LHG 135 exit ports.

If all measurements have been collected correctly, the stone is dispensed into a pass bin (not shown). However, if either measurement (i.e. the shape measurement or the weight measurement) has been compromised in any way the stone is instead dispensed into a reject dispense bin. For example, a feedback mechanism between the processor that processes the 2D silhouette images into a 3D model may indicate that the 3D model creation has been unsuccessful. Similarly, the weigh cell may be linked to a processor that may indicate that the weight measurement has been unsuccessful or is anomalous. The reject dispense bin may be the same dispense way that the rejected stones are fed into out of the UHG 130. Stones dispensed into the reject dispense bin may ultimately be fed back into the measurement system via the feed system 1 10.

The above-described exemplary apparatus provides measurement of multiple properties of rough stones of around 2 grains to 10 carats in weight. All shapes of rough stone can be accommodated by the apparatus, and the quality of the rough stones is not important. The apparatus may achieve a throughput of approximately 5 stones per minute.

In one example, a number of stones may be processed through different stages of the apparatus at the same time. For instance, simultaneously there may be one stone in the UHG 130, one stone being optically imaged at the first measurement location (one the platform 172), one stone in the FHG 180, one stone being weighed at the second measurement location (the weigh pan 190) and one stone in the LHG 135. In this case, the feeder is not driven during measurement of the stones (i.e. during the optical imaging measurement or the weight measurement, or both).

For example, the vibratory bowl 1 10 may be stopped when a first stone leaves the bowl 1 10, then restarted once the first stone arrives at the first measurement location, such that a second stone is delivered to the UHG 130. Driving of the vibratory bowl may then be stopped during optical imaging of the first stone. Alternatively, driving of the bowl may not restart until after the optical measurement of the first stone is complete and the first stone is being dispensed by the rear jaw 150 sweeping across the stage 172 into a third, dispensing position, and pushing the first stone off the stage 172. Feeding of the second stone into the UHG 130 using the vibratory bowl may take place during removal of the first stone from the stage 172. In one example, halting of the vibratory bowl (or other feeder) may be synchronised with optical imaging of a first stone at the first measurement location and weighing of a second stone at the second measurement location. The various light curtains described above may signal to a motor driving the bowl when to stop and start.

Alternatively, each feed or single stone may be completely processed through the apparatus before a further stone is fed into the system by the vibratory bowl. In this case, the vibratory bowl (or other feeder) would not be driven from the point at which a first stone leaves the bowl to a point at which the stone is either dispensed into a reject bin or is dispensed into a pass bin. In other words, driving of the vibratory bowl would re-commence once the first stone is dispensed into a bin.

As described above, once passed through the double feed detection assembly, the rough stone is received into the cup, or cone, shape formed by a set of jaws. The jaws act to stabilize the stone in a central position on the rotatable stage, and once stabilized the stone is held in position by a vacuum applied through a hole in the stage. The orientation of the rough stone in the cup is not relevant for the purposes of shape measurement. Preferably, the stone is held perfectly still while multiple images are captured. This enables a highly accurate 3D model of the stone to be generated. This 3D model may be used to plan cutting and/or faceting of the rough stone. The captured images may also be used to generate an identifier for the stone that may be used for re-identification purposes.

Once the image capture process is complete, the stone is fed into the weigh pan. As discussed, the pan is enclosed by a flap, minimising any disturbance to the stone caused by air turbulence, for example. Again, this enables a highly accurate weight measurement of the rough stone to be obtained. The weight measurement of a stone may be especially important in determining its potential value and the yield of any “target” (i.e. faceted) gemstone to be cut from the rough stone.

Illustrated in Figure 7 is an exemplary method of obtaining multiple measurements of a rough stone. The method comprises the following steps:

Step 1 : feeding a rough stone into a measurement system using a feed system;

Step 2: detecting that a single rough stone has been fed into the measurement system and halting the feed system;

Step 3: dispensing the stone to a first measurement location, and carrying out an optical measurement of the stone to generate a 3D model of the stone;

Step 4: dispensing the stone to a second measurement location, and obtaining a weight measurement of the stone.

In one example, dispensing the stone to a first measurement location comprises receiving the stone into a cone formed by a retractable set of stabilizing elements in a first receiving position; stabilizing the stone in a central position on a platform using the set of stabilizing elements; and applying a vacuum to the platform to retain the stone in the central position while retracting the set of stabilizing elements away from one another into a second retracted position.

In one example, carrying out an optical measurement of the stone to generate a 3D model of the stone comprises rotating the platform while capturing a series of 2D silhouette images of the stone at discrete rotational positions; and processing the series of captured images to form the 3D model of the stone.

In one example, obtaining a weight measurement of the stone comprises dispensing the stone into a weigh pan and enclosing an area around the weigh pan prior to carrying out the weight measurement using a weigh cell.

As discussed above, the method may further include one or more of: checking for and removing multiple feeds using a double feed detection layer or layers, rejecting multiple feeds via an upper hold gate, using the set of jaws to dispense the stone from the platform after image capture onto a ramp, which feeds the stone to a further hold gate; dispensing the stone into the weigh pan by opening a flap on the hold gate and closing the flap to enclose the area around the pan; dispensing the weighed stone from the pan to a pass or reject bin via a lower hold gate. Various light curtains or other sensors may be used to determine the location of the stone within the system.

The properties of the stone obtained by the various measurements described herein may be combined and stored for future use.

It will be appreciated by the person skilled in the art that various modifications may be made to the above-described embodiment, without departing from the scope of the present invention.

For example, the stage or platform may not be rotatable, and instead a plurality of image capture devices, such as cameras, may be provided at discrete circumferential positions around the platform, to capture a series of 2D images of a stone on the platform. Optionally, for each image capture device an illumination device may be positioned circumferentially opposed to the respective image capture device. It will further be appreciated that while the aforementioned apparatus and method have been described with reference to, and are particularly suited for, rough gemstones, both could be applied to the measurement of properties of other small, discrete objects.