Abstract:
A diamond marking attachment comprising a laser, for a 3D diamond mapping apparatus, and a method of laser marking on a diamond surface, via a material that is capable of interacting with a laser beam either in a way that this material is permanently changed and turns into a char mark that adheres to the diamond surface, or in a way that a permanent mark is etched through the material into the diamond surface.

Description:
FIELD OF THE INVENTION 
     The present invention is in the field of laser marking on diamonds. 
     BACKGROUND OF THE INVENTION 
     Marking on diamonds is required for such purposes as their sawing or indicia stamping (identification and quality marks, etc). 
     For marking various indicia on a diamond surface, different laser marking techniques are known to be employed as suggested, for example, in U.S. Pat. Nos. 5,410,125, 5,573,684 and EP 0 054 840. 
     In order to obtain durable marking with the known laser marking techniques, a high level of laser energy density is used, which may adversely affect the value of the diamond by heating and vaporizing a portion of its body and/or causing microcracks. The required graphics of the indicia is achieved through the employment of various means including complex optical axis tilting, numerous X-Y tables, partial masking, etc. 
     For sawing purposes, predetermined ‘sawing lines’ are marked on diamond surfaces and actual sawing is performed in accordance with these lines. The marks are nowadays drawn manually, with ink dots representing the lines. Positions of the dots are chosen by eye judgment either alone, or aided by various CAM devices such as the DiaExpert 2000 by Sarin Technologies Ltd. in Israel. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, there is provided an attachment to 3D diamond mapping apparatus, for diamond laser marking. The 3D mapping apparatus is capable of mapping a diamond whose surface is to be marked with a marking pattern, and of determining a succession of points representing said pattern. The attachment comprises a laser source with its associated focusing optics for emitting a focused laser beam along an optical path which extends between said source and a marking position on said surface of the diamond and a beam orientation system to move said path relative to the diamond and to thereby bring it to said marking position. The mapping apparatus and the attachment constitute, at least in operation, an integral mapping and marking system whose computer means calculates coordinates of each point of the marking pattern and manipulates said beam orientation system to direct the laser beam successively to said points. 
     In accordance with another aspect of the present invention, there is provided a method of permanent laser marking allowing the use of lower laser power by means of coating the diamond prior to its marking and performing the marking through or on the coating. 
     The present invention, in accordance with both aspects thereof, can be used for performing any marking on any diamonds, but it is particularly advantageous for diamond CAM laser marking of ‘sawing lines’. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     In order to understand the invention and to see how it may be carried out in practice, a preferred embodiment will now be described, by way of non-limiting example only, with reference to the following drawings of which: 
     FIG. 1 is an illustration of a system for 3D mapping and laser marking of diamonds, according to the present invention; 
     FIG. 2 is a schematic illustration of the optical set-up of the marking attachment of the system of FIG. 1; and 
     FIG. 3 is an illustration of the mechanical design of the marking attachment of FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     FIG. 1 shows a system for 3D mapping and marking of a diamond A, according to the present invention. The system comprises a mapping apparatus  1  and a marking attachment  2  integrally assembled with each other, and a computer (not shown) to control the operation of the apparatus and the attachment. 
     The mapping apparatus  1  is preferably of the kind as the DiaExpert 2000 manufactured by Sarin Technologies Ltd., Israel. The marking apparatus comprises a turntable  4  with a central axis X of rotation and a top surface  6  having means for the fixation thereon of the diamond A, and illumination, imaging and image processing means (not shown) mounted in a housing  7  of the apparatus, for generating a map of the diamond A and for determining a succession of marking points representing a pattern to be marked thereon. The pattern may be a ‘sawing line’ or indicia of any kind such as identification barcodes, quality marks, arbitrary inscriptions, etc. As shown schematically in FIG. 2, in the system of the present invention, each marking point P of the pattern is considered to have coordinates defined by an angle θ to which the diamond A needs to be rotated by the turntable  4  to bring the point P into its marking position, by a distance D between the marking point P and the central axis X, and by a height H of the point P relative to the top surface  6 . 
     FIG. 2 schematically illustrates an optical set-up of the marking attachment  2 , comprising a laser source  10  for emitting a focused laser beam along an optical path O which extends between the laser source  10  and the marking point P of the diamond on its surface to be marked, and a beam orientation system generally designated as  12  for the orientation of the optical path in such a manner as to bring the laser beam to the point P. The beam orientation system is designed to ensure that the laser beam is focused at a location spaced from the central axis X by the distance D and spaced from the top surface  6  of the turntable  4  by the distance H, with the point P being brought in its marking position by the rotation of the turntable  4 . 
     As shown in FIG. 2, the beam orientation system divides the optical path O into a leading section L, a trailing section T and an intermediate section I therebetween. The leading section L lies in a first horizontal plane parallel to the top surface  6  of the turntable  4  and located under it, and is oriented in the direction in which the laser  10  emits its focused beam. The trailing section T lies in a second horizontal plane parallel to the top surface  6  and located above it, and is oriented perpendicular to and passing through the central axis X. The intermediate section I is comprised of two mutually perpendicular sub-sections I′ and I″, the sub-section I′ lying in the first horizontal plane and the sub-section I″ lying in a vertical plane that is perpendicular to the first and second horizontal planes and passes through the central axis X. 
     The above optical set-up of the beam orientation system is obtained by the system comprising a laser displacement device schematically shown as  20 , first, second and third laser beam diverting optics schematically shown as  22 ,  24  and  26 , respectively, and by a diverting optics displacement device schematically designated as  28 . 
     FIG. 3 shows a mechanical design of the marking attachment  2  (without the optical components of the attachment shown in FIG.  2 ), which is in the form of a base  30  with an elongated frame  32  having supporting surfaces  34  for mounting thereon the mapping apparatus  1  (shown in FIG. 1) and a hollow area  38  between the supporting surfaces. The hollow area  38  accommodates the laser displacement device  20  adjacent one end  40  of the hollow area, for carrying thereon the laser  10  with its focusing optics, and the first laser beam diverting optics  22  adjacent the other end  42  thereof. The base  30  is further formed with a compartment  44  for accommodating therein second and third laser beam diverting optics  24  and  26  and the diverting optics displacement device  28  for the diverting optics  26 . 
     As seen in FIG. 3, the laser displacement device  20  comprises guides  50  and a cartridge  52  displaceable along the guides and capable of carrying thereon the laser  10  with its focusing optics, so as to ensure that the leading section L of the optical path (FIG. 2) extends within the hollow area  24  in the second plane. 
     The diverting optics displacement device  28  may be of any appropriate kind, e.g. may be similar to the laser displacement device, to enable moving the diverting optics  26  parallel to the central axis X. 
     The computer is provided with an appropriate software to manipulate the motions of the turntable  4 , the laser displacement device  20  and the diverting optics displacement device  28  in accordance with the marking pattern and, possibly, to trigger the laser source  10  to irradiate the diamond surface at the succession of its marking points corresponding to the pattern. Preferably, the computer is also capable of generating appropriate corrections when the diamond surface to be marked is not perpendicular to the trailing section T of the optical path at each of the points. 
     In operation, a diamond A is fixed at the center of the turntable  6  and the mapping apparatus creates its 3D model, based on which its marking pattern, such as for example a sawing plan, is defined manually or automatically by using optimization programs stored in the system&#39;s software, and coordinates of the marking points of the pattern are calculated. Similarly, any data or graphics that need to be imprinted anywhere on the diamond&#39;s surface can be translated to the coordinates. 
     The laser source  10  may be any laser with the power suitable to create a permanent mark at each of the marking points. Preferably, the laser source is a low power laser source. For example, the laser source may have an average power of 34.5 mW, at wavelength of 1064 nm, pulse energy approximately 8 μJoul and pulse repetition of approximately 3.8 KHz. 
     To enable the use of the above low power laser source in general and, particularly with the marking system of the present invention, it is suggested to coat the diamond that is to be marked with a solution of a co-polymer in a hydrocarbon solvent such as styrene-butadiene co-polymer (K-Resin made by Philips) in cyclohexane, tinted with white pigment, such as a commercial concentrate of titanium dioxide in a paraffin solution. Typical solution is made of 3% K-Resin and 5% titanium dioxide in cyclohexane. 
     With the coated diamond to be marked being irradiated by the lower power laser, the coating reacts on the laser radiation in a way that a permanent mark is imprinted on the surface of the aforesaid diamond. This happens due to the optical breakdown and plasma formation at the irradiated region of the coating, which plasma is responsible for the chemical attack on the surface of the diamond and the etching thereof. The laser power needed for the plasma formation of the coating material is lower than that which is necessary to directly etch the diamond itself. In particular, an average laser power less than 50 mW would be sufficient versus 500 mW to 5 kW which is required for direct diamond marking. 
     Alternatively, the diamond to be marked may be coated with a material which, when irradiated by a lower power laser beam, is carbonized and thus produces char that adheres permanently onto the diamond surface, at much lower laser power than the power that would have been required for achieving such marking directly on the diamond surface without the coating. Such material may, for example, be chosen from a silver compound in the form of a suspension prepared from silver carbonate. However, since the density of silver carbonate is higher than that of ordinary solvents used in the preparation of the suspension, various additives have to be added thereto, such as resins, silica, etc. One example of such suspension is a suspension prepared by grinding and suspending the following components (expressed in % weight percent): 60 parts 10% K-Resin (Philips Chemicals, a polystyrene copolymer) in 60/40 hexane/dichloromethane; 35 parts cyclohexane, 3.6 parts silver carbonate; 0.5 parts 10% calcium/barium petronate dispersant; 0.5 parts silica flatting agent, OK-500 by Degussa; and 0.36 parts fumed silica, Cab-O-Sil 720 by Cabot. The suspension should be stirred before its application to a diamond, to prevent settling of its solid components.