Abstract:
The present invention provides methods, apparatus, and systems for a wrist assembly including a housing having a cap and a bottom, at least one pivot at least partially enclosed in the housing and adapted to be coupled to a robot arm, and a belt coupled to the pivot and adapted to rotate the pivot about a bearing. The bottom of the housing is adapted to reflect heat away from the at least one pivot and the bearing.

Description:
The present application claims priority to U.S. Provisional Patent Application Ser. No. 60/822,200, filed Aug. 11, 2006, which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to electronic device manufacturing robots, and, more specifically, to a wrist assembly for use with such manufacturing robots. 
     BACKGROUND 
     Robots used in electronic device manufacturing may be exposed to significant environmental stresses (e.g., high temperatures) that may affect the performance and/or lifespan of the robots. Thus, what is needed are methods and apparatus to improve the performance and/or lifespan of such robots. 
     SUMMARY OF THE INVENTION 
     In some aspects, the present invention provides a wrist assembly including a housing having a cap and a bottom; at least one pivot at least partially enclosed in the housing and adapted to be coupled to a robot arm; and a belt coupled to the pivot and adapted to rotate the pivot about a bearing. The bottom of the housing is adapted to reflect heat away from the at least one pivot and the bearing. 
     In other aspects, the present invention provides a method of extending a life of a wrist assembly which includes attaching a reflective shield to a bottom of the wrist assembly; constructing a housing of the wrist assembly from a material having a low thermal conductivity relative to a pivot of the wrist assembly; and forming at least one heat choke in the housing. 
     In yet other aspects, the present invention provides a robot for electronic device manufacturing that includes a wrist assembly that includes a housing having a cap and a bottom; at least one pivot at least partially enclosed in the housing and adapted to be coupled to a robot arm; and a belt coupled to the pivot and adapted to rotate the pivot about a bearing. The bottom of the housing is adapted to reflect heat away from the at least one pivot and the bearing. 
     Other features and aspects of the present invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top schematic view of an example robot wrist assembly according to some embodiments of the present invention. 
         FIGS. 2A and 2B  illustrate bottom schematic views of a wrist assembly with a radiation shield secured ( 2 A) and removed ( 2 B), respectively. 
         FIG. 3  is a close up bottom schematic view of an example wrist assembly according to some embodiments of the present invention. 
         FIG. 4  is an exploded schematic view of an example bearing assembly for use in some embodiments of the present invention. 
         FIG. 5  is a side cut-away schematic view of a portion of a wrist assembly. 
         FIG. 6  is a top schematic view of a dual robot including two wrist assemblies according to embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Semiconductor wafer processing robots may experience premature failure at the robot wrist assembly. Failures may be caused by build-up of particles, chemical breakdown of lubricants, overheating, and/or other causes. The present invention provides a robot wrist assembly which reduces and/or eliminates various failure modes, including reducing robot wrist temperature. 
     The present invention improves upon the prior art through temperature reduction, the elimination of problem moving parts, improved bearing performance, and/or improved particle containment and/or heat transfer, among other things. In some embodiments, the improved wrist assembly provides superior cross-section and material selection; thus, the heat flow is improved and/or optimized to restrict conductive and radiated heat flow into the assembly while improving and/or maximizing the heat flow out of the assembly. For example, in some embodiments, the base material, e.g., used for the enclosure, may be titanium, which has a significantly lower thermal conductivity than aluminum in conventional wrist assemblies (e.g., about 1/10 of the thermal conductivity of aluminum). Additionally, the cross-sectional area of contact surface between the blade and wrist may be significantly reduced by thermal chokes. Both measures reduce heat flow into the assembly. Similarly, by making pivots out of aluminum or the like, heat flow out of the wrist is increased. The larger cross section of these pivots may also increase heat flow out of the wrist. 
     A radiation shield may be added to the bottom surface of the assembly to reflect radiation from any heating element within a chamber that employs the assembly. The shield may include a simple low cost, sheet metal cover, for example. In some embodiments, the shield may be polished to a mirror finish (e.g., on one side only). Also, inverting the mounting of the bearings from the bottom surface (the conventional position) to the top surface (e.g., a titanium top cap) of the enclosure may reduce the heat transfer from radiation of process chamber heaters as the wrist assembly passes over these heat sources. In some embodiments, the result is a 50% reduction in wrist temperature, which significantly increases lubricant life. It is estimated that lowering the temperature alone will more than double the life of the assembly. 
     Further protection of the semiconductor wafer from particle contamination in the event of a bearing failure may be created by a labyrinth designed into the base/housing, pivots, and preload rings. Additionally, the opening between the wrist and the blade seen in prior wrist assemblies may be sealed off. 
       FIG. 1  is a top schematic view of a robot wrist assembly  100  according to some embodiments of the present invention. The robot wrist assembly  100  may be coupled to a robot (e.g., to one or more robot arms) (not shown) by pivots  102   a - b . The robot wrist assembly  100  may have a top cap  104  (e.g., a housing or other enclosure). Adjacent and/or coupled to the top cap  104  may be one or more thermal chokes  106 . Also adjacent and/or coupled to the top cap  104  may be a cut-away region  108  and a wrist closure  110 . 
     In some embodiments, the pivots  102   a - b  may be constructed of aluminum. The thermal conductivity of aluminum pivots  102   a - b  may increase outflow of heat away from the wrist assembly  100 . Other materials may be used (e.g., aluminum alloys, and/or other conductive materials). The pivots  102   a - b  may have an increased cross section so as to transfer heat to the arms (not shown) more quickly. For example, in at least one embodiment, the pivots  102   a - b  may have an increased cross sectional area by increasing a height of the pivots (e.g., by doubling the height of the pivots while maintaining about the same pivot width). In one particular embodiment, the pivots may have a cross section of about ⅜″ by ½″, although other dimensions may be used. 
     In the same or alternative embodiments, the top cap  104  may be constructed of titanium or other similar materials. By using titanium, with a significantly lower thermal conductivity than aluminum, the top cap  104  may assist in preventing excessive heat transfer to the remainder of the wrist assembly  100 . 
     Heat may be restricted further via thermal chokes  106  (e.g., projections from the top cap  104 ), which may serve to prevent heat from being passed conductively (or otherwise) from a blade (not shown) to the wrist assembly  100  by reducing contact area. Similarly, the cut-away region  108  may minimize contact between the blade (not shown) and the wrist assembly. In some embodiments, the combination of the thermal chokes  106  and the cut-away region  108  may reduce contact area between the blade and the wrist assembly by about 90% over prior wrist assemblies. The thermal chokes  106  may be constructed of a metal, such as titanium, an insulating material, such as ceramic, or any other suitable material. 
     Wrist closure  110  may be formed as part of top cap  104 , or may be a separate piece. In some embodiments, the wrist closure  110  may be constructed of titanium. The wrist closure  104  may reduce and/or eliminate contact between the blade (not shown) and the internal area (shown in  FIGS. 2 and 3 ) of the wrist assembly  100 . This may reduce or prevent heat transfer and/or prevent particles from accumulating inside the wrist assembly  100 . 
       FIGS. 2A and 2B  illustrate bottom schematic views of the wrist assembly  100  with a radiation shield  112  secured in place and removed, respectively. The radiation shield  112  may be mounted to the wrist assembly  100  with fasteners  114  (e.g., screws, bolts, or other suitable fasteners). The radiation shield  112  may enclose, along with other portions of the wrist assembly  100  and top cap  104  described above with respect to  FIG. 1 , the internal area of the wrist assembly  100 . This internal area will be described in further detail below with respect to  FIG. 3 . 
     The radiation shield  112  may be a sheet metal cover, such as a steel plate, or other similar material. In some embodiments, the radiation shield  112  may be polished to a mirror finish on a side facing away from the internal area of the wrist assembly  100 . In this way, the radiation shield  112  may reflect radiation heat away from the wrist assembly  100 . Similarly, the radiation shield  112  may be coated and/or plated (e.g., gold plated) to produce a reflective finish. Other materials and/or finishes may be used. 
       FIG. 3  is a close up bottom schematic view of the wrist assembly  100  according to some embodiments of the present invention. Pivots  102   a - b  may be secured to the inside of top cap  104  around bearings  116   a - b . Pivots  102   a - b  may be actuated by drive belts  118   a - b . Drive belts  118   a - b  may be secured to the pivots  102   a - b  by tensioners  120   a - b.    
     Securing the pivots  102   a - b  to top cap  104  may reduce heat transfer from radiation of process chamber heaters (not shown) as the wrist assembly  100  passes over these heat sources in operation (e.g., because the bearings/pivots are spacially/thermally isolated from the shield  112  which faces the heat sources). 
     The net effect of the above described features is to concurrently decrease the amount of heat that may enter the wrist assembly (e.g., from the blade and/or a substrate on the blade) and increase the amount of heat that may dissipate out of the wrist (e.g., to the robot arms). Thus, Q out  from the wrist assembly is much larger than Q in  to the wrist assembly where Q represents heat flow. 
       FIG. 4  is an exploded schematic view of bearing assembly  500 , which may be similar to bearings  116   a - b , for use in some embodiments of the present invention. Bearing assembly  500  may include a one or more bearings  502   a - b . Bearings  502   a - b  may comprise inner races  504   a - b  and outer races  506   a - b  which may hold spacer balls  508  and/or load balls  510 . 
     In some embodiments, inner races  504   a - b  and outer races  506   a - b  may be constructed of stainless steel  440 C or a similar material. Other grade stainless steels and/or other materials may be used. Similarly, spacer balls  508  may be constructed of stainless steel  440 C or a similar material. Other grade stainless steels and/or other materials may be used. Load balls  510  may be constructed of ceramic or other appropriate materials. In some embodiments, at least one or more of the load balls  510  may be replaced with a ball made of an electrically conductive material (e.g., stainless steel) that maintains electrical contact between the bearings&#39;  502   a - b  inner races  504   a - b  and outer races  506   a - b . The conductive replacement ball may be slightly smaller than the non-conductive (e.g., ceramic) load balls  510  so as to be non-load bearing (or to bear less weight than the non-conductive load balls  510 ) while still maintaining contact between the bearings&#39;  502   a - b  inner races  504   a - b  and outer races  506   a - b.  This contact prevents static electricity from building up in the wrist assembly  100  by allowing a path for the discharge/dissipation of static electricity. 
       FIG. 5  is a side cut-away schematic view of a portion of the wrist assembly  100 . Specifically,  FIG. 5  illustrates one side of the wrist assembly  100  which includes bearings  502   a - b  and an exemplary path that a particle would have to travel to exit the wrist assembly  100 . In the example of  FIG. 5 , particles  602  leaving the bearings  502   a - b  must travel through a labyrinth  604  designed into the top cap  104  and/or pivot  102 , among other things. In the event of a bearing failure, wafers handled by the robot to which the robot wrist assembly  100  is attached are protected from particles  602  dispersed therefrom as the particles  602  would have to travel through the difficult labyrinth  604  path to exit the wrist assembly  100 . 
     Turning to  FIG. 6 , a top schematic view of a dual robot  600  including two wrist assemblies  702  is depicted. Each of the wrist assemblies  702  are coupled to robot arms  704  and a blade  706  adapted to carry a substrate. Note that the example wrist assemblies described and depicted in the present application are for “frog-leg” type robots. However, the principles and features of the present invention may be applied to the wrist assemblies of any type of robot including Selective Compliant Articulated Robot Arms (SCARA) and other types of robots. 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.