Abstract:
An apparatus for processing a work-piece ( 80 ) includes a laser source ( 102 ) and a first lens assembly ( 108 ). The laser source is configured for emitting laser beams. The first lens assembly is configured for adjustably focusing the laser beams onto the work-piece. The first lens assembly is disposed in optical alignment with the laser source and includes a first lens set having a positive refractive power and a second lens set having a negative refractive power. Because of the first lens assembly, the laser beams emitted from the laser source can be focused accurately onto the work-piece, and then the apparatus for processing the work-piece has accurately focused laser beams as a result.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is related to commonly-assigned copending applications entitled, “laser system and method for patterning mold inserts using same”, filed Jul. 28, 2009 Ser. No. 11/309,343, and “laser welding system for welding workpiece”, filed on Jun. 23, 2006 (U.S. application Ser. No. 11/473,965). Disclosures of the above identified applications are incorporated herein by reference. 
   FIELD OF THE INVENTION 
   The present invention relates to processing apparatuses and, more particularly, to an apparatus for processing a work-piece. 
   DESCRIPTION OF RELATED ART 
   Lasers have been used for marking and machining of materials since shortly after their invention. Established techniques include laser cutting, laser drilling, and laser welding. These techniques have been applied to a wide range of materials including metals, ceramics, polymers, and natural products such as cotton and paper. 
   When using lasers to machine a work-piece, the laser beam from a laser source is focused onto the work-piece with a lens assembly. Typically, it is at the focal point of the lens, where the laser beam is the smallest and hence the most concentrated, that the work-piece is machined. The distance between the lens and its focal point is fixed by the dimensions and specification of the lens, and is constant for any given lens and any given laser beam. 
   During the machining process, the work-piece is moved under the fixed laser beam such that the features are machined according to the wanted design. Alternatively, the work-piece can be stationary and the laser focus can move. Of critical importance for the best possible machining parameters is to have the work-piece at a constant distance from the lens to keep its surface within the working focal range. In most cases, laser machining is performed on flat work-pieces. 
   If the work-piece has deformations along the laser beam axis, the laser will be caused to go out of focus on the work-piece, such that the laser will not properly machine in that area. Even if the work-piece is fastened to a holder or substrate, deformations due to the heat damage of the laser or preexisting deformations may result in that region of the work-piece being unmachinable. Similarly, it becomes difficult to machine work-pieces with curved surfaces. 
   What is needed, therefore, is a laser machining apparatus capable of accurately focusing laser beams and controlling the laser source. 
   SUMMARY OF THE INVENTION 
   In a preferred embodiment of the present invention, An apparatus for processing a work-piece includes a laser source and a first lens assembly. The laser source is configured for emitting laser beams. The first lens assembly is configured for adjustably focusing the laser beams onto the work-piece. The first lens assembly is disposed in optical alignment with the laser source and includes a first lens set having a positive refractive power and a second lens set having a negative refractive power. A distance between the lens sets of the first lens assembly satisfy the following equation:
 
 d 12=( k 1 +k 2 −k 12)/( k 1 ×k 2).
 
Wherein k1 represents an index of refraction of the first lens set, k2 represents an index of refraction of the second lens set, k12 represents an index of refraction of the first lens assembly, and an effective focal length f1 of the first lens assembly satisfies the following equation:
 
 f 1=1 /k 12.
 
A back focal length f2 of the first lens assembly satisfies the following equation:
 
 f 2=(1 −d 12 ×k 1)/ k 12 =f 1×(1 −d 12 ×k 1).
 
   Because of the first lens assembly, the laser beams emitted from the laser source can be focused accurately onto the work-piece, and then the apparatus for processing the work-piece can maintain accurate focusing of the laser beams. 
   Advantages and novel features will become more apparent from the following detailed description of the present laser machining system and laser machining method, when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Many aspects of the apparatus for processing a work-piece can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present laser machining system. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
       FIG. 1  is a schematic, perspective view of an apparatus for processing a work-piece in accordance with a preferred embodiment; and 
       FIG. 2  is a schematic flow chart of method for processing a work-piece in accordance with a second preferred embodiment. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Reference will now be made to the drawings to describe preferred embodiments of the apparatus for processing work-pieces. 
     FIG. 1  illustrates an apparatus for processing the work-piece  100  in accordance with a preferred embodiment. The apparatus for processing a work-piece  100  is used for machining a work-piece  80 . The apparatus for processing a work-piece  100  includes a laser source module  10 , a feedback module  20  and a laser-controlling module  40 . 
   The laser source module  10  includes a laser source  102 , a shutter  104  and a lens module  106 . The laser source  102  emits laser beams toward a surface of the work-piece  80 . The laser source  102  can be selected from a group consisting of gas lasers, excimer lasers and solid-state lasers depending on composition of the work-piece  80 . If the material of the work-piece  80  is, for example, glass or porcelain, a gas laser is preferable. If the material of the work-piece  80  is, for example, metal or plastic, a solid-state laser is preferable. In this preferred embodiment, the laser source  102  is a solid-state laser such as, for example, a neodymium-doped yttrium-aluminium garnet (Nd:YAG) laser source with a wavelength of 800 nanometers, a ytterbium-doped yttrium-aluminium garnet (Yd:YAG) laser source with a wavelength of 940 nanometers or a neodymium-doped vanadate (Nd:Vanadate) laser source with a wavelength in a range from 1047 nanometers to 1064 nanometers. Additionally, in order to keep the laser source  102  working stably, a laser-cooling device  1022  is connected with the laser source  102  for cooling the laser source  102 . 
   The laser beams emitted from the laser source  102  are transmitted to the shutter  104 . The shutter  104  controls an intensity of the laser beams. For example, if the shutter  104  is completely opened, the laser beams completely pass through the shutter  104 , and the intensity of the laser beams can be said to be at a maximum. If the shutter  104  is completely closed, the laser beams can not pass through the shutter  104 , and, the intensity of the laser beams can be said to be at a minimum. The shutter  104  is controlled depending on the fineness required for working on the surface of the work-piece  80 . 
   The lens module  106  is used for focusing the laser beams from the shutter  104  to the work-piece  80 . The lens module  106  includes a first lens assembly  108  and a lens barrel  110 . The first lens assembly  108  includes a first lens set  1082  having a positive refractive power adjacent to the laser source  102  and a second lens set  1084  having a negative refractive power adjacent to the work-piece  80  along a transmission direction of the laser beams. The first lens set  1082  and the second lens set  1084  are coaxial and are contained in the lens barrel  110 . A relative distance between the first lens set  1082  and the second lens set  1084  is changeable in the lens barrel  110  based on a focus controlling unit  50  connected with the lens barrel  110  so as to adjust a focus of the lens module  106 . The index of refraction of the first lens set  1082  and the index of refraction of the second lens set  1084  are respectively represented by k1 and k2, the distance between the first lens set  1082  and the second lens set  1084  is represented by d12, and the index of refraction of the first lens assembly  108  is represented by k12. Wherein, k1, k2, k12 and d12 are related by the following formula:
 
 d 12=( k 1 +k 2 −k 12)/( k 1 ×k 2)   (1)
 
An effective focal length f1 of the lens module  106  satisfies the following equation:
 
 f 1=1 /k 12   (2)
 
A back focal length f2 of the lens module  106  satisfies the following equation:
 
 f 2=(1 −d 12 ×k 1)/ k 12 =f 1×(1 −d 12 ×k 1)   (3)
 
Therefore, the effective focal length f1 and the back focal length f2 can be changed by changing the distance d12 so as to change a position of a focal point of the lens module  106  on the surface of the work-piece  80 . Alternatively, the first lens assembly  108  may include three, four or more lenses.
 
   The laser beams from the laser source module  10  are guided onto the surface of the work-piece  80  to machine the work-piece  80 . The work-piece  80  can be disposed on a worktable  60 . The worktable  60  can be moved horizontally and vertically, and it also can tilt and rotate. In order to avoid the temperature of the work-piece  80  becoming too high, which is disadvantageous to machining, a work-piece cooler  70  can be positioned between the worktable  60  and the work-piece  80  for cooling the work-piece  80 . In this preferred embodiment, the work-piece cooler  70  can be, for example, a thermal electric cooler. 
   The feedback module  20  includes a laser monitoring assembly  200  and a processing unit  30 . The laser monitoring assembly  200  receives the reference laser beams that are reflected by the work-piece  80  as an optical signal and transforms the optical signal into an electronic signal. The laser monitoring assembly  200  includes a second lens assembly  202  and an optical detector  204 . The second lens assembly  202  includes a third lens set  2022  having a negative refractive power and a fourth lens set  2024  having a positive refractive power being coaxial and positioned in turn from the work-piece  80  to the optical detector  204  along a transmission direction of the reference laser beams. The third lens set  2022  diverges the reference laser beams and the fourth lens set  2024  converges the diverged reference laser beams to project onto the optical detector  204 . The optical detector  204  receives the projected reference laser beams as the optical signal and transforms the optical signal into an electronic signal and further transmits the electronic signal to the processing unit  30 . 
   The laser-controlling module  40  is used for controlling the parameters of the laser source, for example, the pulse energy, the pulse durations, the pulse repetition rate etc. The processing unit  30  receives the electronic signal from the optical detector  204 , and then processes the electronic signal. After the processing the electronic signal, feedback signal of the position being machined of the work-piece  80 , for example, the distance between the position being machined of the work-piece  80  and the laser source module  10  etc. is acquired. The processing unit  30  transmits the feedback signal processed to the laser-controlling module  40  and the focus controlling unit  50 . The laser-controlling module  40  can optimize the working parameters of the laser source  102 , for example, the intensity of the laser beams, according to the feedback signal receiving from the processing unit  30 . The focus controlling unit  50  can control the lens barrel  110  to adjust the focal length of the lens module  106 , and thus focusing the laser beams on the surface of the work-piece  80 . 
   In this preferred embodiment, the first lens assembly  108  including the first lens set  1082  and the second lens set  1084  is used in the apparatus for processing a work-piece  100  to adjust the focal length of the lens module  106 . Moreover, the feedback module  20  is used for receiving and processing the information for machining the work-piece  80 . The laser-controlling module  40  and focus controlling unit  50  confirm and optimize the working parameters of the laser source module  10  so that smoothness of the work-piece is enhanced. 
   Referring to  FIGS. 1 and 2 , a method for machining using the apparatus  100  of the first embodiment is described below: 
   In step  902 , the work-piece  80  is disposed on the work-piece cooler  70 , which is connected with the worktable  60 . The work-piece cooler  70  is used for cooling the work-piece  80  to avoid overheating of the work-piece  80 . 
   In step  904 , the laser source  102  emits laser beams using the preset working parameters based on the laser-controlling module  40  and transmits the laser beams to the shutter  104 . The laser source  102  is controlled by the laser-controlling module  40  and generates laser beams for machining the work-piece  80 . The laser-controlling module  40  presets working parameters of the laser source  102 . The working parameters include, for example, the pulse energy, the pulse duration, the repetition rate etc. In this preferred embodiment, the pulse energy is preset in the range from 30 micro-joules to 300 micro-joules, the pulse duration is preset in the range from 30 microseconds to 3000 microseconds and the range from 100 microseconds to 500 microsecond is preferable, and the repetition rate is preset in the range from 1 kilo-Hz to 10 kilo-Hz. 
   In step  906 , the shutter  104  adjusts an intensity of the laser beams based on the machining precision to the work-piece  80  required and the laser beams is transmitted to the lens barrel  110 . 
   In step  908 , the lens barrel  110  of the lens module  106  changes a relative position between the first lens set  1082  and the second lens set  1084  so as to focus the laser beams on the surface of the work-piece  80 , and thus the surface of the work-piece  80  is machined by the laser beams. The laser beams can be focused to a focal spot with a range of size from 1 micrometer to 1000 micrometer and the range from 10 micrometer to 100 micrometer is preferable. 
   In step  910 , the feedback module  20  receives the laser beams reflected by the surface of the work-piece  80 , transforms the optical signal of the laser beams to an electrical signal, processes the electrical signal to achieve feedback signal of the position of the surface being machined of the work-piece  80 , and then the surface of the work-piece  80 . The feedback signal includes the distance between the position being machined of the work-piece  80  and the laser source module  10  etc. 
   In step  912 , the laser-controlling module  40  optimizes the working parameters of the laser source  102 , for example, the intensity of the laser beams, according to the feedback signal receiving from the feedback module  30 . The focus controlling unit  50  controls the lens barrel  110  to adjust the focal length of the lens module  106 , thus focusing the laser beams onto the surface of the work-piece  80  and thus machining the work-piece  80 . 
   It is to be understood that the above-described embodiment is intended to illustrate rather than limit the invention. Variations may be made to the embodiment without departing from the spirit of the invention as claimed. The above-described embodiments are intended to illustrate the scope of the invention and not restrict the scope of the invention.