Laser marking apparatus and methods

Abstract

A laser marking apparatus for marking a moving workpiece such as a wire or cable directs a substantially constant rapidly pulsed beam of laser radiation in the U.V. band towards a low inertia, low mass rotatable mask with character apertures disposed around its periphery. The mask is driven asynchronously and slaved to the laser to present successive character apertures in the beam at each pulse. The drive system has a prestored drive profile for each possible angular increment to ensure that mask is very rapidly indexed between characters. Also disclosed is an optical transformation scheme for optionally transforming the mask characters to reduce the mask size, and a solid state spatial light modulator for obviating the need for a rotatable mask.

1 . Laser marking apparatus for making a mark or succession thereof on a laser markable surface of a workpiece, said apparatus comprising: 
 a source of laser radiation for generating in use a pulsed beam of radiation capable of marking said laser markable surface;    an addressable spatial light modulator for receiving and modulating said beam of radiation, and    an image compositor for controlling the spatial light modulator to modulate said beam of radiation to create a modulated beam, whereby a corresponding character or code symbol is formed in use on the surface of said workpiece in an exposure, such that said character or code symbol is formed on said workpiece in a single exposure.    
     
     
         2 . Laser marking apparatus according to    claim 1   , wherein said image compositor composes a respective individual character or code symbol in a single exposure.  
     
     
         3 . Laser marking apparatus according to    claim 1   , wherein said image compositor composes a respective group of characters or code symbols for marking said workpiece with said group of characters or code symbols in a single exposure.  
     
     
         4 . Laser marking apparatus according to    claim 1   , wherein said apparatus further includes a drive for advancing the workpiece between exposures.  
     
     
         5 . Laser marking apparatus according to    claim 1   , wherein said addressable spatial light modulator comprises an addressable mirror device.  
     
     
         6 . Laser marking apparatus according to    claim 5   , wherein said addressable mirror device comprises a digital micromirror device made up of an array of individually addressable pixels.  
     
     
         7 . Laser marking apparatus according to    claim 6   , wherein the switching time of each pixel is approximately 10 μs.  
     
     
         8 . Laser marking apparatus according to    claim 1   , wherein said source of laser radiation is a solid state laser.  
     
     
         9 . Laser marking apparatus according to    claim 8   , wherein said laser is a Nd:YAG laser.  
     
     
         10 . Laser marking apparatus according to    claim 8   , wherein said laser is a flash lamp pumped laser.  
     
     
         11 . Laser marking apparatus according to    claim 1   , which includes a drive for advancing the workpiece during and between successive exposures, and said image compositor applies a further modulator to the beam to deflect the image written by said modulator during an exposure to compensate for movement of the workpiece relative to the apparatus.  
     
     
         12 . Laser marking apparatus according to    claim 1   , wherein said workpiece is an elongate flexible workpiece.  
     
     
         13 . Laser marking apparatus according to    claim 12   , wherein said elongate flexible workpiece is a cable.  
     
     
         14 . Laser marking apparatus according to    claim 12   , wherein said elongate flexible workpiece is a wire.  
     
     
         15 . A method for making a mark or succession thereof on a laser markable surface of an elongate flexible workpiece, which comprises providing a pulsed beam of radiation capable of marking said laser markable surface, passing said beam of laser radiation to a spatial light modulator to be modulated thereby with the modulated beam passing to said laser markable surface, and composing on said spatial light modulator a pattern comprising at least one character or code symbol, thereby to mark a corresponding character or code symbol on the laser markable surface, in a single exposure.  
     
     
         16 . A method according to    claim 15   , wherein said pattern comprises a plurality of characters or code symbols, thereby to mark a corresponding plurality of characters or code symbols in each radiation exposure.