Abstract:
A substrate processing apparatus comprising a frame, a drive section, an articulated arm, and at least one pair of end effectors. The drive section is connected to the frame. The articulated arm is connected to the drive section. The articulated arm has a shoulder and a wrist. The arm is pivotally mounted to the drive section at the shoulder. The drive section is adapted to rotate the articulated arm relative to the frame about an axis of rotation at the shoulder, and to displace the wrist relative the shoulder. The pair of end effectors is connected to the articulated arm. The pair of end effectors is pivotally jointed to the wrist of the articulated arm to rotate relative to the articulated arm about a common axis of rotation at the wrist. Each end effector is independently pivotable relative to each other about the common axis of rotation at the wrist. At least one end effector is independently pivotable about the common axis of rotation of the wrist relative to the articulated arm.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit of U.S. Provisional Application No. 60/305,052, filed Jul. 13, 2001, which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a substrate processing apparatus and, more particularly, to a substrate processing apparatus with a transport apparatus having multiple independent end effectors. 
     2. Prior Art 
     The throughput of a substrate processing apparatus is a significant concern of manufacturers of semi-conducting substrates (e.g. manufacturers of semi-conducting wafers or of flat panel displays). The throughput of a given substrate processing apparatus has a direct impact on the cost of the processed substrate and hence on the final cost of any electronic devices which employ the substrates either in part on in their entirety. The higher the throughput, the lower the fabrication costs of the substrates and hence the lower the costs of the final product. The throughput of a substrate processing apparatus is dependent at least in part on the efficiency and speed with which substrates are transported from the storage cassettes, such as the commonly used front opening universal pods (FOUP), through the processing apparatus and returned to the FOUPs. There are conventional substrate processing apparatus, which employ substrate transport apparatus with one or more end effectors for carrying one of more substrates which may allow for faster swapping of substrates for example. Some of the end effectors on these conventional substrate transport apparatus may be independently operable. The drives driving these end effectors are located on the end of the transport arm, proximate the end effector. This increases the mass moment of the arm, with a corresponding impact on the speed and control of the transport arm during movement of the substrates. Substrate transport apparatus having the end effector drive at the end of the transport arm also has a large space envelope. It is desired to maintain the space envelope of the substrate transport arm as small as possible in order to minimize the size of the processing apparatus thereby allowing a larger number of processing apparatus to be employed within a given manufacturing facility. The present invention overcomes the problems of conventional substrate process apparatus as will be described in greater detail below. 
     SUMMARY OF THE INVENTION 
     In accordance with a first embodiment of the present invention, a substrate processing apparatus is provided. The apparatus comprises a frame, a drive section, an articulated arm, and at least one pair of end effectors. The drive section is connected to the frame. The articulated arm is connected to the drive section. The articulated arm has a shoulder and a wrist. The articulated arm is pivotally mounted to the drive section at the shoulder. The drive section is adapted to rotate the articulated arm relative to the frame about an axis of rotation at the shoulder, and to displace the wrist relative to the shoulder. The pair of end effectors is connected to the articulated arm. The pair of end effectors is pivotally jointed to the wrist of the articulated arm to rotate relative to the articulated arm about a common axis of rotation at the wrist. Each end effector is independently pivotable relative to each other about the common axis of rotation at the wrist and at least one of the end effectors is independently pivotable about the common axis of rotation of the wrist relative to the articulated arm. 
     In accordance with another embodiment of the present invention, a substrate transport apparatus is provided. The apparatus comprises a drive section, an upper arm, a forearm, and at least one pair of end effectors. The upper arm is connected to the drive section. The forearm is movably connected to the upper arm. The pair of end effectors is movably connected to the forearm so that the pair of end effectors is movable relative to the forearm. The pair of end effectors are located on the forearm. The pair of end effectors are operably connected to the drive section for moving the pair of end effectors relative to the forearm. Each end effector of the pair of end effectors is independently movable relative to each other. 
     In accordance with another embodiment of the present invention, a substrate transport apparatus is provided. The apparatus comprises a drive section, an articulated arm, at least one pair of end effectors, and another drive section. The drive section has a coaxial shaft assembly. The articulated arm is operably connected to the coaxial shaft assembly at a shoulder of the arm for rotating the arm about the shoulder and extending or retracting the arm relative to the shoulder. The pair of end effectors is movably connected to the articulated arm so that each end effector of the pair is independently pivotable relative to the articulated arm about a common axis of rotation. The other drive section is operably connected to the pair of end effectors for moving the end effectors relative to the arm. The other drive section has at least one motor mounted on the arm proximate the shoulder. 
     In accordance with another embodiment of the present invention, a substrate transport apparatus is provided. The apparatus comprises a drive section, an upper arm, a forearm, and at least one pair of end effectors. The upper arm is connected to the drive section. The forearm is movably connected to the upper arm. The pair of end effectors is movably connected to the forearm. The forearm has a support member fixed thereto. The pair of end effectors is movably mounted to support member to allow each end effector of the pair of end effectors to rotate independently relative to the forearm. The drive section is operably connected to each end effector so that each end effector is moved independently by the drive section. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing aspects and other features of the present invention are explained in the following description, taken in connection with the accompanying drawings, wherein: 
     FIG. 1 is a schematic top plan view of a substrate processing apparatus incorporating features of the present invention; 
     FIG. 2 is a perspective view of a substrate transport apparatus of the substrate processing apparatus in FIG. 1; 
     FIG. 3 is a cross-sectional view of a drive section of the substrate transport apparatus in FIG. 2; 
     FIG. 4 is a schematic elevation view of the articulated arm in FIG. 4; 
     FIG. 4A is another schematic elevation view of the articulated arm showing the arm in another position; 
     FIG. 5 is a schematic bottom view of the articulated arm of the substrate transport apparatus in FIG. 2; and 
     FIG. 6 is a cross-sectional view of an end effector drive of the articulated arm taken through line  6 — 6  in FIG.  2 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1, there is shown an exploded perspective view of a substrate processing apparatus  10  incorporating features of the present invention. Although the present invention will be described with reference to the single embodiment shown in the drawings, it should be understood that the present invention can be embodied in many alternate forms of embodiments. In addition, any suitable size, shape or type of elements or materials could be used. 
     The substrate processing apparatus  10  may comprise a front or atmospheric section  12 , and an adjoining back or vacuum section  14 . The arrangement of the processing apparatus  10  shown in FIG. 1 is exemplary, and in alternate embodiments, the substrate processing apparatus may have any suitable arrangement or configuration. In the embodiment shown in FIG. 1, the front section  12  generally has a frame  16 , substrate holding cassettes  22 , and a substrate transport apparatus  24 . The back section  14  generally has a main section  18 , processing modules  36 , and a vacuum substrate transport apparatus  34 . The frame  16  of the front section  12  may be adjacent of the back section  14  of the substrate processing apparatus  10 . The front section frame  16  generally supports a number (only two are shown in FIG. 1 for example purposes) of the substrate holding cassettes  22  which hold a number of substrates S therein. The substrates may be for example, semiconductor wafers, flat panel displays substrates, or any other suitable type of substrates. The frame  16  of the front section  12  is open to atmosphere. The atmospheric substrate transport apparatus  24  is mounted to the frame  16  for transporting substrates between the holding cassettes  22  and the vacuum back section  14  of the apparatus  10 . The main section  18  of the back section  14  includes a central chamber  26 , and intermediate chambers  28 ,  30 . Processing modules  36  are disposed generally around the main section  18  and communicate with the central chamber  26  through openings in the exterior of the main section. The intermediate chambers  28  communicate with the central chamber  26  through internal openings in the main section. The main section  18  also has outer openings allowing the intermediate chambers  28 ,  30  to communicate with the adjoining atmospheric front section  12 . The vacuum substrate transport apparatus  34  is mounted in the main section for transporting substrates through the central chamber  26  between the intermediate chambers  28  and the processing modules  36 . The processing modules  36  include one or more chambers with appropriate systems to perform processes such as for example, sputtering, coating, etching, soaking, or any other suitable process on substrates deposited in the chambers. The central chamber  26  of the back section  14  is maintained substantially in a vacuum to prevent contamination of substrates when being transported between the intermediate chambers  28 ,  30  and processing modules  36 . Outer openings  32  of the back section may be closed to isolate the central chamber  26  from the processing modules  36 . Internal openings  38  may be closed to isolate the central chamber  26  from intermediate chambers  28 ,  30  and outer openings  40  of main section  18  may be closed to isolate the intermediate chambers from atmospheric conditions outside the chambers. The substrate processing apparatus  10  further includes a controller  400  which controls the operation of the apparatus  10 . In accordance with commands from the controller  400 , the atmospheric transport apparatus  24  transports new substrates from cassettes  22  to intermediate chambers  28 ,  30  and returns processed substrates from the intermediate chambers to the cassettes  22 . The atmospheric transport apparatus  24  may have multiple independent end effectors to rapidly swap substrates in and out of cassettes  22  as will be described in greater detail below. One or both of the intermediate chambers  28 ,  30  may be configured as a load lock. The controller  400  cycles the load lock and operates the vacuum substrate transport apparatus  34  to transport substrates from intermediate chambers  28 ,  30  through the central chamber to processing modules  36 . The vacuum transport apparatus  34  may have multiple independent end effectors to rapidly swap substrates in and out of the load locks or processing modules as will be described in greater detail below. The substrates are then processed and returned through the intermediate chambers to cassettes  22 . 
     Still referring to FIG. 1, in the embodiment shown, the frame  16  of the front section  12  supports two cassettes  22  from the front end  20  of the frame. The cassettes  22  are held in a generally side by side configuration. The cassettes may be front opening uniform pods (FOUP) which in the preferred embodiment are capable of holding about 26, 200/300 mm semiconductor substrates. In alternate embodiments, the front section frame may support any desired number of substrate holding cassettes. The cassettes may be of any suitable type and be capable of holding any desired number of substrates. The cassettes may be capable of holding any desired type of substrates including substrates used in manufacturing flat panel displays. In other alternate embodiments, the substrate holding cassettes may be also located on the sides of the front section frame as well as the front. Each cassette  22  has a front face  22 F facing the frame  16  of the front section  12 . The front face  22 F has an opening (not shown) through which substrates S are removed and inserted into the respective cassette  22 . As seen in FIG. 1, the atmospheric substrate transport apparatus  24  is mounted to frame  16  between the cassettes  22  and the back section  14  of the apparatus  10 . In the preferred embodiment, the substrate transport apparatus  24  comprises a drive section  42  which moves a movable arm  44 . 
     Still referring to FIG. 1, the vacuum section  14  is shown in an exemplary configuration, and in alternate embodiments the vacuum section may have any suitable arrangement. In the embodiment shown in FIG. 1, the main section  18  has a general rectangular shape. The processing modules  36  are shown located along three sides of the main section  18 , though in alternate embodiments processing modules may be located on one or two sides. Also, in this embodiment two processing modules  36  may be located on each side of the main section  18 . As seen in FIG. 1, the processing modules  36  on each side of the main section are offset radially from the vacuum substrate transport apparatus  34 . The intermediate chambers  28 ,  30 , located as noted before on a side of the main section  18  adjacent the atmospheric module  12 , may be oriented to be radially aligned with the substrate transport apparatus  34 . The substrate transport apparatus  34  may be substantially centered in the central chamber  26  of the main section  18 . The vacuum substrate transport apparatus  34  may be substantially similar to the atmospheric transport apparatus  24  with a drive section  42 A and an articulated arm assembly  44 A. As noted before, the vacuum transport apparatus  34  has multiple independent end effectors on the arm assembly. 
     The atmospheric transport apparatus  24  and vacuum transport apparatus  34  in this embodiment are substantially similar. Hence, the atmospheric apparatus  24  and vacuum apparatus will be described in greater detail below with specific reference to the atmospheric apparatus  24 . As seen in FIG. 2, the movable arm  44  has four sections including upper arm  60 , forearm  62 , and two end effectors  64 ,  66 . The upper arm  60  and forearm  62  are connected in series. The forearm  66  supports the two end effectors  64 ,  66  that are stacked one over the other at one end of the forearm. The upper arm is connected to the drive section  42  as will be described in greater detail below. In this embodiment, the drive section  42  of the transport apparatus  24  may be fixedly mounted to the frame  16  with the center of the transport apparatus being between the side by side cassettes  22  (see FIG.  1 ). In alternate embodiments the drive section may be mounted on a car capable of movement in the horizontal plane relative to the frame of the apparatus. The drive section  42  is a three-axis drive section capable of moving the movable arm  44  along three axes. The drive section  42  includes suitable drives (not shown) for vertically raising and lowering (i.e. movement along the “Z” axis) the movable arm  44 . For example, the drive section may include a housing  46  (see also FIG. 2) from which the movable arm  44  is supported. The vertical drives may include a motor and ball screw arrangement (not shown) connected to the housing which when operated raise and lower the housing (in the direction indicated by arrow Z in FIG. 2) along the ball screw. In alternate embodiments, the vertical drive may be any suitable type of linear drive. The vacuum transport apparatus (see FIG. 1) may not have a vertical drive. Referring now also to FIGS. 2 and 3, the housing preferably includes a co-axial drive  48  for moving the movable arm  44  about the rotation axis θ (i.e. θ movement) and for extending or retracting the arm along the radial axis T (i.e. T movement). In the embodiment shown the co-axial drive  48  of drive section  42  is a co-axial drive such as shown in U.S. Pat. No. 5,899,658, which is incorporated by reference herein in its entirety. In alternate embodiments, the co-axial drive may be any other suitable drive capable of moving the movable arm to generate both θ movement and T movement. 
     As seen in FIG. 3, the housing  46  has a flange with a central aperture through which two concentric output shafts extend. The outer shaft is designated  4 , and the inner shaft is designated  5 . At the extremities of the output shafts a pilot bearing  6  separates the shafts and supports them upon each other. The two shafts are independently rotatable about rotation axis θ. The motion of the shafts may be one in which they rotate together, and another in which they rotate in opposite directions. The former motion serves to rotate the arm  44 , and the latter motion serves to extend and retract the arm. The inner shaft is longer than the outer shaft, and the extremity of the inner shaft outside the housing  46  extends beyond the corresponding extremity of the outer shaft. The extremity of the inner shaft  5  is connected to a drive pulley  71  of transmission system  70 . The extremity of the outer shaft is directly fastened to the upper arm  60 . Accordingly when the outer shaft  4  is rotated, the upper arm rotates with the shaft about axis θ. A rotor  7  is supported on the outer surface of the outer shaft  4 , and a corresponding stator  8  is supported outside the rotor  7 . Similarly, a rotor  9  is supported on the outer surface of the inner shaft  5 , and a corresponding stator  11  is supported outside the rotor  9 . Each stator is part of a drive which rotates the corresponding shaft. Each rotor-stator pair  7 ,  8  and  9 ,  10  may form part of a conventional brushless DC motor such as the M &amp; K Series manufactured by Technology Inc., 200 Thirteenth Avenue, Ronkonkoma, N.Y. 11779. In alternate embodiments, the drive section may include any other suitable type of motors, such as for example brushless AC motors, stepper motors, conventional (brushed) AC or DC motors, to effect rotation of the inner and outer shafts. Each shaft  4 ,  5  may have a corresponding encoder mechanism  13 ,  15  suitable for measuring the rotation of the shaft. The encoders  13 ,  15  are connected to controller  400  (See FIG. 1) and signal the shaft rotation and position to the controller. 
     Referring now to FIGS. 4 and 5, there is shown respectively a schematic cross sectional elevation and a schematic top plan view of arm assembly  44  (the end effectors  64 ,  66  are not shown in FIG. 5 for clarity) As noted before, arm assembly  44  includes upper arm  60 , forearm  62 , and in this embodiment, two end effectors  64 ,  66 , though in alternate embodiments the arm may have any desired number of end effectors. For example, the arm may have but one end effector mounted on the forearm. The arm assembly  44  also includes transmission system  70  for rotating the forearm  62  and two end effector drive systems  78 ,  80  for independently rotating the end effectors  64 ,  66 . The upper arm  60  has an outer casing  61 , or other suitable structural frame which is shown schematically in FIGS. 4 and 5. As noted before, the outer casing  61  of the upper arm  60  (which may be made from any suitable material) is fastened directly to the outer shaft  4  of the co-axial drive. The joint between the upper arm casing  61  and outer drive shaft  4  defines the shoulder  72  of the arm assembly  44 . The outer casing  61  also pivotally supports the forearm  62  as shown in FIG. 4 thereby defining the elbow joint  74  of the arm assembly. As can be realized from FIGS. 2 and 4, rotation of the outer shaft  4 , rotates the upper arm casing  61 , and hence the entire arm, about axis θ which extends through the shoulder  72 . As shown in FIGS. 4 and 5, the outer casing  61  of the upper arm holds transmission system  70 , and part of end effector drive systems  78 ,  80 . Transmission system  70  generally comprises a drive pulley  71 , idler pulley  73  and belt  70 . As noted before, drive pulley  71  is mounted on the inner shaft  5  of the co-axial drive unit at the shoulder  72  of the arm. The idler pulley  73  is mounted on outer shaft  92  of the co-axial shaft assembly  90  at the elbow  74  of the arm assembly  44 . The belt  70  connects the drive pulley  71  to the idler pulley  73  so that rotation of the drive pulley  71  (caused by rotation of the inner shaft  5 ) imparts rotation of the  73  and hence of shaft  92 . 
     The coaxial shaft assembly  90  at the elbow  24  preferably comprises three concentric shafts  92 ,  94 ,  96 . The outer shaft  92 , intermediate shaft  94  and inner shaft  96  are rotatably supported from the outer casing  61  by a suitable combination of thrust and roller or ball bearings (not shown) so that the shafts may rotate independently about axis y 1  at the elbow  74  of the arm. The outer shaft  92  is shortest, with the intermediate shaft  94  and inner shaft  96  extending serially both above and below the outer shaft (as seen in FIG.  4 ). The outer shaft  92  is fastened at one end to the forearm  62 , and the idler pulley  73  is fixedly mounted onto the outer shaft  92 . Accordingly, when the transmission system  70  rotates the idler pulley  73 , the forearm  62  is rotated about axis Y 1  at the wrist. 
     The part of the end effector drive systems housed in the outer casing  61  of the upper arm include motors  82 ,  84  and transmission segments  79 ,  81 . The outer casing  61  has an extended portion  63  which depends from inner portion  61 I of the casing (see FIG.  4 ). Inner portion  61 I extends between the shoulder  72  and the elbow  74 . As shown in FIG. 4 the extended portion  63  is located on the opposite side of the shoulders (i.e. axis of rotation θ) from the inner portion  61 I of the outer casing. The extended portion  63  may be enlarged relative to the rest of the outer casing  61 . The extended portion has an inner wall  63 W located sufficiently back from the shoulder to allow the forearm to rotate freely 360° about axis Y 1  at the elbow without interference with the extended portion  63  of the upper arm  60 . As seen in FIG. 4A, the extended portion  63  and inner portion  61 I define a step or recess  61 R in the upper arm in which the forearm  62  is located. Accordingly, this arrangement having the forearm  62  located in a recess  63 R of the upper arm  60  allows the overall stack height (i.e. between uppermost surface  66 T and lowermost surface  66 B) of the arm assembly (indicated at H in FIG. 4A) to be smaller in comparison to conventional arm assemblies. Also, in having the extended portion  63  of the upper arm  60  offset from the shoulder, the height of the extended portion  63  may be sized as desired to house motors  82 ,  84  for the end effector drive system without increasing the stack height of the arm assembly or interfering with forearm motion. In this embodiment, the extended portion  63  houses two motors  82 ,  84  of the end effector drive system. In this embodiment, the motors  82 ,  84  are housed side by side as will be described in greater detail below (see FIG.  6 ). Accordingly, as seen in FIG. 2, the outer casing  61  has a generally tapered shape that is narrow at the elbow  74  and widens towards the extended portion  63 . In alternate embodiments however, the outer casing of the upper arm may have any suitable shape to accommodate the motors and transmissions of the end effector drive system as well as the transmission system moving the forearm. 
     Referring now also to FIG. 6, there is shown a schematic cross-section taken through line  6 — 6  in FIG. 2 of the extended portion  63  of the upper arm outer casing  61 . As seen in FIG. 6, in this embodiment the two motors  82 ,  84  are mounted in a side by side arrangement. In alternate embodiments, as has been noted before, the arm assembly may have any suitable number or motors for independently rotating the end effectors, and the motors may be arranged in any desired configuration in the upper arm. For example, in an alternate embodiment in which the arm assembly has one end effector, only one motor for moving the end effector would be located in the extended portion of the upper arm. In other alternate embodiments, the motors in the upper arm may be arranged in any other suitable manner, such as for example, an asymmetric arrangement, or an inline arrangement aligned with the rotation axis at the shoulder of the arm. Motors  82 ,  84  may be brushless DC motors such as available from Kollmorgan though any other suitable motors may be used. This is particularly advantageous in the vacuum transport apparatus  34  (see FIG.  1 ), because brushless motors minimize contact between moving parts thereby avoiding generation of contamination in the vacuum section of the apparatus. The motors  82 ,  84  are substantially similar, except as otherwise noted and will be described below with reference to motor  82 . Motor  82  may have a housing  82 H which holds shaft  82 S. The housing  82 H may be supported from the top  63 T of the extended portion  63 . The shaft  82 S is rotatably held in the housing by suitable radial and axial bearings. The shaft  82 S has a rotor  82 R of the DC motor mounted thereon. The stator  82 T is mounted on the housing  82 H. The shaft  82 R is also provided with a suitable encoder (not shown), which is connected to the controller  400  (see FIG. 1) to signal the rotation/position of shaft  82 S to the controller. When motor  82  is energized, the motor drives end effector drive system  78  which rotates the end effector  64  (See FIG.  4 ). Accordingly, one end of shaft  82 S is connected to drive pulley  101  of transmission segment  79 . Motor  84  is used to power drive system  80  which rotates end effector  66 . Shaft  84 S is connected to drive pulley  103  of transmission segment  81 . The end of shaft  84 S is located such that pulley  103  is located below pulley  101  on shaft  82 S. The end of shaft  82 S is located such that pulley  101  is below pulley  71  (see FIG.  4 ). Transmission segment  79  (located in the upper arm  60 ) of drive system  78  includes drive pulley  101  as well as idler  104  and belt  102 . The idler  104  and drive pulley  101  may be sized to provide for example a 4:1 pulley reduction, though any other desired pulley reduction may be used. In alternate embodiments, the transmission segment in the upper arm may have any other desired drive to idler pulley ratio. Idler  104  is mounted on intermediate shaft  94  of co-axial shaft assembly  90  at the elbow  74  (see FIG.  4 ). Belt  102  connects the drive pulley  101  and idler  104 . Transmission segment  81  (in the upper arm  60 ) of the second end effector drive system  80  includes drive pulley  103  as well as idler  106  and belt  105 . Idler  106  is mounted on inner shaft  96  of co-axial shaft assembly  90  at the elbow  74 . Belt  105  connects the drive pulley  103  and idler  106 . As shown in FIG. 4, transmission segments  79 ,  81  are located one over the other in the upper arm, with segment  81  below segment  79 . Both transmission segments  79 ,  81  are below transmission system  70  for operating the forearm. FIG. 5 shows a schematic bottom view illustrating the arrangement of transmission system  70 , and end effector drive systems  78 ,  80  inside the arm assembly  44 . As seen in FIG. 5, tension members  70 T,  79 T,  80 T, such as spring loaded bearings, may be provided in the arm assembly to prevent slack on the belts  70 ,  102 ,  105 , and to restrain the belts away from pulleys of adjoining drive systems. 
     As seen in FIGS. 4,  5 , and  6 , the end effector drive systems  78 ,  80  each include a second transmission segment  83 ,  85  which are housed in the forearm  62 . Transmission segment  85  transmits torque from inner shaft  96  (which is powered by segment  81 ) to rotate end effector  66 . Transmission segment  83  transmits torque from intermediate shaft  94  (powered by segment  79 ) to rotate end effector  64 . Transmission segment  85  includes pulley  110 , idler  114  and belt  112 . Pulley  110  is mounted on the upper end of inner shaft  96  so that the pulley and shaft rotate together about axis Y 1  at elbow  74 . Idler  114  is fixedly mounted to shaft  120  of co-axial shaft assembly  118  located at the wrist end  62 W of the forearm. Co-axial shaft assembly  118  includes preferably outer shaft  120  and inner shaft  122 . The outer and inner shafts  120 ,  122  are supported by suitable radial and thrust bearings allowing the shafts to rotate independently about axis of rotation Y 2  at the wrist  76 . The outer shaft  120  is fixedly connected to end effector  64 . Thus, when torque is transferred by belt  112  to idler  114 , the outer shaft  120  rotates end effector  64  about axis Y 2 . Transmission segment  83  includes pulley  116 , idler  119 , and belt  118 . Pulley  116  is mounted on the upper end of intermediate shaft  94 . The idler  119  is mounted fixedly onto inner shaft  122  so that the idler and shaft rotate as a unit about axis Y 2 . The inner shaft  122  is also fixedly mounted at the other end to end effector  66 . Accordingly, when torque is transferred by belt  118  from pulley  116  (on shaft  94 ) to idler  119 , the inner shaft  122  rotates end effector  66  about axis Y 2  at the wrist. In this manner, the end effectors may be rotated independently about axis Y 2  at the wrist. This may be used in an advantageous manner when transporting substrates, by rapidly swapping substrates into and out of a given chamber. By way of example, one end effector  64  may be extended into a chamber to pick up a substrate therein, while the other end effector  66  (which holds a replacement) is turned slightly away, for example no more than about 90°, to prevent interference with the chamber. The arm  44  is then moved to withdraw the substrate from the chamber and to orient the other end effector  66  with that chamber. The first end effector  64  is then turned away and the arm is moved to place the second end effector  66  in the chamber. As can be realized, the end effector drive systems  78 ,  80  allow each end effector  64 ,  66  to be continuously and independently rotated about axis Y 2  at the wrist relative to the other end effector  64 ,  66  and relative to the arm itself. 
     This invention allows for fast wafer/substrate swaps using a transport apparatus  24 ,  34  with a two-link arm  44  with two independent articulated end effectors  64 ,  66 . The present invention couples an arm  44  with two motors  82 ,  84  mounted in the upper arm to a three-axis robot. The two motors  82 ,  84  in the upper arm  60  are offset beyond the robot center (as identified by axis of rotation θ in FIG. 2) but inside the arm swept diameter. The tapered or wedge shape of the upper arm  60  allows for the motor assemblies that drive the articulated end effector/wrist modules to share the height of the upper arm and forearm. This reduces the overall height of the arm. In contrast, conventional three-axis transport apparatus have the motors powering motion of the upper arm, forearm, and end effectors located along a co-axial shaft assembly at the shoulder. The motors are vertically stacked along the shaft assembly so that each motor may be connected to a corresponding shaft. The stacking of the motors in the conventional apparatus causes the overall height of the drive section at the arm shoulder to increase with a resultant increase in the space envelope used for the transport apparatus. Moreover, the articulated arm assembly which is mounted to the top of drive section at the shoulder is elevated higher with respect to a base of the processing apparatus. This may prevent the uppermost end effector from reaching the substrates held in the lowermost storage positions of the storage areas or processing modules. It is desired to minimize this height in order to reach the lowest substrate with the top end effector  66 . The instant embodiment achieves this by placing the drive motors moving the end effectors in the upper arm and in effect having the drive motors shape the height of the upper arm and forearm. The motors are coupled to a tri-axial elbow assembly  90  via timing belts and a pulley reduction. The pulley reduction may be 4:1, as previously described, though any other pulley reduction may be used. From the elbow to the wrist the motors are again coupled with timing belts to a co-axial wrist joint to which the end effectors are mounted. The center of gravity of the upper arm is also moved closer to the center of the robot. One motor can be removed from the upper arm, and the arm can be utilized as a 4-axis design. In this case the arm has but one end effector mounted on the forearm. Existing solutions typically have motors located at the wrist joint. The proposed design has the motors in the upperarm which drastically reduces the forearm inertia and will improve the robot arm controllability. Moreover as noted before, the end effector, or end effectors are each capable of continuous and independent rotation about the wrist with respect to the forearm and with respect to each other (in the case the arm has two or more end effectors as shown in FIG.  1 ). This allows the use of simpler controller architecture for controlling the movement of the arm between substrate storage/processing stations. A further advantage of this degree of freedom provided the end effector(s) is that the arm may employ shorter moves when moving between storage/processing stations and teaching the arm the desired motion is simplified. 
     It should be understood that the foregoing description is only illustrative of the invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.