Abstract:
A substrate handling robot having a robot body and a robot arm with an end effector is configured to exhibit angular (θ), radial (R) and Z motion. A pair of coaxial shafts link the robot arm to respective motors dedicated to angular (θ) and radial (R) motions. The motors are stationarily mounted with respect to the robot body. The shafts are rotatably supported by a floating platform which is motivated in the Z direction by a third motor also stationarily mounted with respect to the robot body. The third motor is coupled to the platform by a Z motion linkage. The first and second motors are coupled to the coaxial shafts by angular and radial motion linkages each of which includes primary and secondary timing belts whose relative motions are synchronized with the Z motion linkage to achieve controllable independent angular (θ), radial (R) and Z motions in a simple, light-weight package.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    (Not applicable) 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to robots used for substrate transport in semiconductor processing. 
         [0004]    2. Description of the Related Art 
         [0005]    Robots are commonly used in semiconductor processing environments, in order to transport substrates such as wafers to and from storage locations or various processing stations. The highly repetitive nature of the motions involved and the speeds required for high throughput make robots ideal candidates for these tasks. The types of motions of which these types of robots are capable vary. Typically, a robot having a robot body and robot arm extending from the robot body will exhibit angular (θ), radial (R) and Z motions in a cylindrical coordinate system. Angular motion refers to rotation of the robot arm about a primary axis at which it is pivotably coupled to the robot body. Radial motion is extension/retraction motion of the robot arm to and from the primary axis. Z motion is elevation of the robot arm (up-down) with respect to the robot body. Details of operation of such robots are described in U.S. Pat. No. 5,789,890, entitled “ROBOT HAVING MULTIPLE DEGREES OF FREEDOM (Genov et al.), incorporated herein by reference in its entirety. 
         [0006]    Issues that are of concern in these types of robots include weight, size, complexity, and range. The present invention seeks to address one or more of these issues, to thereby improve factors such as robot performance, reliability, and throughput, and to increase longevity and reduce costs of robot manufacture and maintenance. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    In accordance with one aspect of the invention, there is provided a robot that includes a robot arm and a robot body. Also included is a floating Z platform mounted for motion in a Z direction in the robot body, a shaft coupled to the robot arm and to the floating Z platform, the shaft being rotatable about a primary axis and movable with the floating Z platform, a first motor configured to impart Z motion to the floating Z platform and to the shaft, a primary timing belt stationarily mounted in the robot body, a second motor configured to rotate the primary timing belt, and a secondary timing belt coupled to the primary timing belt and to the shaft to thereby transfer motion of the primary timing belt to the robot arm by way of said shaft. 
         [0008]    In accordance with a further aspect of the invention, there is provided an assembly for providing a robot having a robot arm and a robot body with Z motion and at least one of R and θ motions. The assembly includes a floating platform configured for translation relative to the robot body in a first direction, a shaft coupled to the robot arm and supported by the floating platform, the shaft being translatable with the floating platform in the first direction and being axially rotatable about a primary axis extending in the first direction, a first motor mounted stationarily relative to the robot body such that translation of the floating platform and shaft occurs relative to the first motor, a second motor mounted stationarily relative to the body such that translation of the floating platform and shaft occurs relative to the second motor, a first linkage coupling the first motor to the floating platform such that the first motor is capable of motivating the translation of the floating platform and the shaft, and a second linkage coupling the second motor to the shaft such that the second motor is capable of motivating the axial rotation of the shaft. The second linkage includes a primary timing belt stationarily mounted relative to the robot body, and a motion conversion assembly translatable with the floating platform and the shaft, the motion conversion assembly including a secondary timing belt coupled to the primary timing belt. 
         [0009]    In accordance with a further aspect of the invention, there is provided a method for enabling a robot having a robot arm and a robot body to undergo Z motion and at least one of radial (R) and angular (θ) motions. The method includes coupling motion of a first motor that is stationarily mounted with respect to the robot body to the robot arm by way of a shaft that is mounted for axial translation along a primary axis in response to the first motor motion, and coupling motion of a second motor that is stationarily mounted with respect to the robot body to the robot arm by way of the shaft, the shaft being mounted for rotation about the primary axis in response to the second motor motion. The coupling of motion of a second motor includes, in response to rotation of the second motor, rotating a primary timing belt that is stationarily mounted with respect to the robot body, and converting the rotation of the primary timing belt to the rotation of the shaft about the primary axis using a motion conversion assembly that is configured to translate axially with the shaft. 
         [0010]    In accordance with a further aspect of the invention, there is provided an apparatus for enabling a robot having a robot arm and a robot body to undergo Z motion and at least one of radial (R) and angular (θ) motions. The apparatus includes means for coupling motion of a first motor that is stationarily mounted with respect to the robot body to the robot arm by way of a shaft that is mounted for axial translation along a primary axis in response to said the motor motion, and means for coupling motion of a second motor that is stationarily mounted with respect to the robot body to the robot arm by way of the shaft, the shaft being mounted for rotation about the primary axis in response to the second motor motion. The means for coupling motion of a second motor is operative to, in response to rotation of the second motor, rotate a primary timing belt that is stationarily mounted with respect to the robot body, and convert the rotation of the primary timing belt to the rotation of the shaft about the primary axis using a motion conversion assembly that is configured to translate axially with the shaft. 
         [0011]    In accordance with a further aspect of the invention, there is provided a method for providing motion to a robot arm in a robot having a Z motion linkage capable of imparting Z motion to a robot arm, a robot body angular (θ) motion linkage capable of imparting angular motion to the robot arm, and a robot body radial (R) motion linkage capable of imparting radial motion to the robot arm. The method includes actuating a first motor coupled to the robot arm by way of the Z motion linkage, actuating a second motor coupled to the robot arm by way of the robot body angular (θ) motion linkage, actuating a third motor coupled to the robot arm by way of the robot body radial (R) motion linkage, and synchronizing the first, second and third motors such that the robot arm undergoes Z motion while maintaining fixed angular (θ) and radial (R) positions. 
         [0012]    In accordance with a further aspect of the invention, there is provided a computer readable medium containing a program that causes a robot having a Z motion linkage capable of imparting Z motion to a robot arm, a robot body angular (θ) motion linkage capable of imparting angular motion to the robot arm, and a robot body radial (R) motion linkage capable of imparting radial motion to the robot arm, to undergo motion based on a procedure that includes actuation of a first motor coupled to the robot arm by way of the Z motion linkage, actuation of a second motor coupled to the robot arm by way of the robot body angular (θ) motion linkage, actuation of a third motor coupled to the robot arm by way of the robot body radial (R) motion linkage, and synchronization of the first, second and third motors such that the robot arm undergoes Z motion while maintaining fixed angular (θ) and radial (R) positions. 
         [0013]    Advantages provided by some or all of the invention aspects disclosed herein include light weight due to the types and arrangement of linkages and components. This minimizes robot weight and reduces component inertia, thereby allowing for greater operational speeds, and reduced wear. Another advantage is the ability to achieve angular rotation of the robot arm that is “endless”—that is, greater than 360 degrees, without the hinderance of cables or the like that would twist and limit rotation. Other advantages will become evident from a reading of the description below. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0014]    Many advantages of the present invention will be apparent to those skilled in the art with a reading of this specification in conjunction with the attached drawings, wherein like reference numerals are applied to like elements, and wherein: 
           [0015]      FIG. 1  is a top plan view of a semiconductor processing environment including a robot; 
           [0016]      FIG. 2  is a schematic view of the robot of  FIG. 1   
           [0017]      FIG. 3  is a schematic view detailing the motions of the robot arm of the robot of  FIG. 2 ; 
           [0018]      FIGS. 4-9B  are perspective views showing details of the interior of the robot of  FIG. 2 ; 
           [0019]      FIG. 9C  is a schematic view showing the connection of the coaxial shafts to the respective large pulleys driven by the secondary timing belts; 
           [0020]      FIG. 10  is a schematic view of an alterative Z motion linkage using a threaded rod and engaged threaded nut; 
           [0021]      FIG. 11  is a schematic view of an alterative Z motion linkage using a rack and pinion arrangement; and 
           [0022]      FIG. 12  is a block diagram showing the controller and related components for controlling the robot of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    Embodiments of the present invention are described herein in the context of robots used for substrate transport in semiconductor processing. Those of ordinary skill in the art will realize that the following detailed description of the present invention is illustrative only and is not intended to be in any way limiting. Other embodiments of the present invention will readily suggest themselves to such skilled persons having the benefit of this disclosure. Reference will now be made in detail to implementations of the present invention as illustrated in the accompanying drawings. The same reference indicators will be used throughout the drawings and the following detailed description to refer to the same or like parts. 
         [0024]    In the interest of clarity, not all of the routine features of the implementations described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made in order to achieve the developer&#39;s specific goals, such as compliance with application- and business-related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill in the art having the benefit of this disclosure. 
         [0025]      FIG. 1  is a top plan view of a semiconductor processing environment  100 , typically exhibiting clean room conditions. A robot  200  having a robot body  201  and a robot arm  202  is disposed between two rows of stations  106 . The robot arm  202  is configured to carry a semiconductor wafer  108 , for example a standard 300 mm wafer, between the stations  106 . Other substrates may also be similarly transported, for example 200 mm wafers, flat panel displays, and so forth. The stations  106  include for example one or more storage cassettes  110  in which the substrates—that is, the 300 mm wafers in this example—are stacked. Additional stations, such as CVD (chemical vapor deposition) stations  112 , may be provided, in which various fabrication procedures take place. Also included is a prealignment station  114  at which the wafer  108  may be deposited such that its orientation can be determined and/or adjusted. Alignment may also be conducted by the robot arm itself if suitably equipped. 
         [0026]      FIG. 2  is a more detailed view of robot  200  of  FIG. 1 . Arm  202  comprises a plurality of links  204 ,  206  and  208 , the distalmost of which,  208 , engages the substrate to be transported and is herein referred to as the end effector. Robot  200  exhibits R, θ and Z motion as defined in a polar coordinate system, with the R motion being generally radial motion of the distamost link (that is, end effector  208 ) from primary axis A of the robot  200 . θ motion is rotation of arm  202  about the primary axis A. Z motion is motion of arm  202  along primary axis A (that is, “up-down” motion). In addition, end effector  208  may exhibit yaw (Y) motion, which is defined as rotation about an end effector or yaw axis B which is substantially parallel to primary axis A. While not detailed herein, additional motions, such roll and pitch of the end effector  208 , and tilting of the robot  200  relative to the Z axis, are also contemplated. 
         [0027]      FIG. 3  is a schematic diagram illustrating details of the manner in which R and θ motions of robot arm  202  are effected. Links  204 ,  206  and  208  (end effector) are pivotably coupled to one another. Taking primary axis A as the point of reference, a first, outer driving shaft  310  is rigidly connected to the proximalmost portion of proximalmost link  204 . Driving shaft  310  is centered about primary axis A and is mounted for rotation axially around said axis. Rotation of outer driving shaft  310  provides angular rotation—that is, the θ motion—of link  204  and robot arm  202 . Rotation takes place bidirectionally—that is, clockwise and counter-clockwise—and is, “endless”, meaning that it is not limited to a full circle but can take the form of multiple, or an “infinite” number of revolutions. 
         [0028]    An arm radial (R) motion linkage is provided to effect radial (R) motion of the robot arm  202 . The arm radial motion linkage includes a plurality of belts and pulleys coupled to the links  204 - 208 . Motion of the plurality of belts and pulleys, including belts  312  and  314  and pulleys  316 ,  318  and  320 , is motivated by inner driving shaft  322  and is coordinated such that rotation of the inner driving shaft causes retraction or extension of arm  202  in radial (R) direction. Details of radial® motion implementation are provided in the aforementioned U.S. Pat. No. 5,789,890. 
         [0029]    During maneuvering of the robot arm  202 , the θ and R motions are synchronized in a controlled manner for optimum performance. Synchronization takes place by controlling the rotational motions of outer driving shaft  310  and inner driving shaft  322 , which can be moved independently of one another. Control and synchronization of arm  202  are effected in the spatial, velocity and acceleration and planes such that multi-segment smooth trajectories including non-radial straight line motion of the end effector  308  can be achieved. The term “non-radial” is with reference to primary axis A and means that the end effector  208  is movable in a straight line that does not pass through said primary axis. During this and other motions, the orientation of the end effector  208  can be preserved or controllably altered as desired. One manner of providing this feature is through the use of independent yaw motion of the end effector  208 . It will be appreciated that the arrangement described herein is exemplary only and that other arrangements for effecting θ, R and Y motions are contemplated, including those that use different numbers of pulleys and belts, different gearing ratios, and so forth. It will also be appreciated that while the discussion herein is directed to robot arms having three links, the same principles are applicable to greater or lesser number of links and the concepts described herein are equally applicable to such devices. Further details of the manner in which θ, R and Y motions are achieved and synchronized in a robot arm such as arm  202  can be found for example in the aforementioned U.S. Pat. No. 5,789,890, entitled “ROBOT HAVING MULTIPLE DEGREES OF FREEDOM (Genov et al.). 
         [0030]      FIG. 4-9B  are various views showing inner details of robot body  201 . A portion of arm  202  excluding end effector  208  is also shown, in a first elevation in  FIG. 4  and in a higher elevation in  FIG. 5 . Inner ( 322 ) and outer driving ( 310 ) shafts are shown in their lowest position in  FIG. 4 . They are also shown in a raised position in  FIG. 5 , such that robot arm  202  is at its lowest height or Z position in  FIG. 4 , and is at a higher elevation or Z position in  FIG. 5 . 
         [0031]    As seen from the drawings, a frame structure is comprised of a top plate  402  and base plate  404 . These are mounted substantially parallel to one another and supported by a side plate  406  and a pair of vertical supports  408  and  410 . Base plate  404  may be raised above a bottom flange  412 , with sufficient clearance to accommodate circuit boards or other components (not shown) if desired. 
         [0032]    Disposed between top plate  402  and base plate  404  are three motors,  414 ,  416  and  418  dedicated respectively to the θ, R and Z motions exhibited by the robot  200 . The motors are mounted horizontally—that is, each of their drive shafts lies substantially in a horizontal plane which is parallel to base plate  404  on which the motors are preferably mounted, and is disposed substantially perpendicularly to the primary axis A about which the inner ( 322 ) and outer ( 310 ) driving shafts are disposed. A robot body angular (θ) motion linkage, of which outer driving shaft  310  is part, transfers rotational motion of drive shaft  420  of motor  414  to proximalmost link  204  of robot arm  202  such that angular (θ) motion of the robot arm is achieved. A robot body radial (R) motion linkage, of which inner driving shaft  322  is part, transfers rotational motion of drive shaft  422  of motor  416  to the arm radial motion linkage such that radial (R) motion of robot arm  202  is achieved. A Z motion linkage transfers rotational motion of drive shaft  424  of motor  418  to axial motion of inner ( 322 ) and outer ( 310 ) driving shafts such that Z motion of arm  202  attached thereto is achieved. 
         [0033]    The Z motion linkage includes a first drive pulley  426  coupled for rotation with drive shaft  424  of motor  418 . Either direct drive or a geared drive of pulley  426  by drive shaft  424  is contemplated. Drive pulley  426  is geared, or toothed, and engages with and rotates timing belt  428  which extends between drive pulley  426  and driven idler pulley (also toothed or geared)  430  mounted to the bottom-facing portion of top plate  402 . Timing belt  428  is thus stationarily mounted in robot body  201 , meaning that even though it rotates, its position in the robot body does not change. Timing belt  428  is provided with teeth on the interior face thereof, said teeth engaging the teeth of drive pulley  426  and the teeth of driven idler pulley  430  to minimize relative slippage between the timing belt and the pulleys. As an alternative to a belt, which is preferably made of Kevlar™ or other minimal stretch material, a stainless steel band having suitable slots or holes for engaging appropriately-configured teeth on drive pulley  426  and idler pulley  430  can be used. Timing belt  428  is kept in tension to minimize slack. To provide adjustment of this tension, vertical adjustment of the position of drive pulley  426  and/or of idler pulley  430  can be provided, using a suitable adjustment mechanism, such as set screws (not shown) or the like. Moving one or both the drive pulley  426  and/or of idler pulley  430  pulleys apart increases the tension of belt  428 , and moving them closer together reduces tension. In the preferred direct drive case, moving drive pulley  426  may entail moving the motor  418  and shaft  424  on which the drive pulley is mounted. This can be accomplished in a simple manner using set screws (not shown) or the like for instance. 
         [0034]    A floating Z platform  432  supporting coaxial or nested driving shafts  310  and  322  is provided. Floating Z platform  432  is movable vertically (up-down) and is guided in said motion by a linear guide  434  provided on support plate  406 . The guide serves to limit motion of floating Z platform  432  to a single direction—the Z direction. Motion of Z platform  432  is tied to that of timing belt  428 . This is accomplished by providing a clamp  435  or similar connection mechanism which is rigidly attached to Z platform  432  and which is clamped to timing belt  428  such that it is immovable relative to the belt. It will be appreciated that clamp  435  should be clamped to a portion of timing belt  428  that exhibits Z (up-down) motion, but that the configuration of the timing belt can be different from that shown. In other words, timing belt  428  can have more than the two legs ( 428   a ,  428   b ) shown ( FIG. 9A ), and these legs do not all have to extend vertically or even be in the same plane, so long as at least a portion of one leg extends vertically, to which portion the clamp  435  should be coupled. When motor  418  is actuated, it rotates drive pulley  426 , which moves timing belt  428 , thereby vertically moving Z platform  432  clamped thereto. This causes shafts  310  and  322  to move vertically, and, commensurately, arm  202  coupled to the upper portions of the shafts. Because the motors  414 ,  416  and  418  are disposed at the bottom of the interior region of robot body  201  and are preferably side by side and arranged such that they are parallel to and close to the base plate  404 , they provide clearance for Z platform  432 , allowing its descent unimpeded towards the bottom of the robot body  201 . This allows for a vertically more compact robot body and/or more Z travel for robot arm  202 . 
         [0035]    It will be appreciated that in other embodiments the Z motion linkage can be a means for motivating the Z platform in the Z direction other than timing belt  432  and clamp  435 . Instead, a screw-type mechanism can be used, as shown in  FIG. 10 , in which a motor  418 ′ rotates a vertically mounted threaded rod  419  which engages threaded nut  421  rigidly mounted to the floating Z platform  432 ′. Alternatively, a rack-and-pinion arrangement as shown in  FIG. 11  can be used, wherein a motor  418 ″ mounted in floating Z platform  432 ″ rotates a pinion  423  which engages a toothed rack  425 , imparting Z motion to the floating Z platform on which the motor and pinion are mounted. 
         [0036]    The robot body angular (θ) motion linkage includes a first drive pulley  436  coupled for rotation with drive shaft  420  of motor  414 . Again, either direct drive or a geared drive is contemplated. Drive pulley  436  is geared, or toothed, and serves to rotate a primary timing belt  438  which extends between drive pulley  436  and driven idler pulley (also toothed or geared)  440  mounted to the bottom-facing portion of top plate  402 . Priming timing belt  438  is thus stationarily mounted in robot body  201 , meaning that even though it rotates, its position in the robot body does not change. Primary timing belt  438  is provided with teeth on the interior face thereof, these teeth engaging the teeth of drive pulley  436  and driven idler pulley  440  to minimize relative slippage of the timing belt and pulleys. As an alternative to a belt, which is preferably made of Kevlar™ or other minimal-stretch material, a stainless steel band having suitable slots or holes for engaging appropriately-configured teeth on drive pulley  436  and idler pulley  440  can be used. Primary timing belt  438  is kept in tension to minimize slack. To provide adjustment of this tension, the position of drive pulley  436  and/or of idler pulley  440  can be adjusted vertically. Moving one or both of these pulleys apart increases the tension of belt  438 , and moving them towards one another reduces the tension. Of course, in the preferred direct drive case, moving drive pulley  436  entails moving the motor  414  and shaft  420  on which the drive pulley is mounted. This can be accomplished in a simple manner using set screws (not shown) for instance. 
         [0037]    An angular (θ) motion conversion assembly is mounted to floating Z platform  432  and coupled to primary timing belt  438 . The angular (θ) motion conversion assembly includes a driving ( 442 ) and a driven ( 444 ) pulley ( FIG. 9A ) that are axially coupled to one another such that rotation of driving pulley  442  causes rotation of driven pulley  444 . The pulleys  442  and  444  are toothed, with the teeth of driving pulley  442  engaging the teeth of primary timing belt  438 . Guiding wheels  446  and  448  provided on either side of driving pulley  442  serve to bias the driving pulley against primary timing belt  438  for proper engagement therewith. The teeth of driven pulley  444  engage the teeth of a secondary timing belt  450  which is coupled to outer driving shaft  310  by way of a large, toothed pulley  452  mounted axially to the base of the driving shaft ( FIG. 9C ). As an alternative to a belt, which is preferably made of Kevlar™ or other minimal stretch material, a stainless steel band having suitable slots or holes for engaging appropriately-configured teeth on driven pulley  444  and large pulley  452  can be used. Secondary timing belt  450  has a 90-degree “folded” configuration such that rotation of pulleys  442  and  444  in a first (horizontal) axis is converted to rotation of outer driving shaft  310  in a second (vertical) axis. Folding is effected using an arrangement of freely rotating pins or wheels  454 , optionally in combination with toothed pulleys  456 , around which the secondary timing belt  450  is directed to achieve the desired directional changes. Large pulley  452  is rotationally mounted in floating Z platform  432  and is rigidly connected to the base of outer driving shaft  310  such that its rotational motion caused by secondary timing belt. (See  FIG. 9C ). Shaft  310  (and shaft  322 ) passes through top plate  402  and is free to rotate and slide axially (up-down) therein. A bearing  458  in top plate  402  facilitates this. Axial (up-down) motion of outer shaft  310  is coupled to axial motion of inner shaft  322  disposed therein such that the two shafts move axially (Z motion) together along the robot primary axis. However, rotational motion of the two shafts is independent—that is, the two shafts may simultaneously or alternately rotate in the same direction at the same or different rates, or they may rotate in opposite directions at the same or different rates. Suitable bearings (not shown) are provided to ensure this. The two shafts  310  and  322  are therefore rotationally independent of one another. It will be appreciated that driving pulley  442  of the angular (θ) motion conversion assembly should couple to a portion of primary timing belt  438  that extends in the Z (up-down) direction commensurately with the travel of the floating Z platform  432  to which the angular (θ) motion conversion assembly is mounted, but that the configuration of the primary timing belt can be different from that shown. In other words, the primary timing belt  438  can have more than the two legs ( 438   a ,  438   b ) shown ( FIG. 9A ), and these legs do not all have to extend vertically or even be in the same plane, so long as at least a portion of one leg extends vertically to the same extent as the travel of the floating Z platform  432 . 
         [0038]    The robot body radial (R) motion linkage includes a first drive pulley  460  coupled for rotation with drive shaft  422  of motor  416 . Again, either direct drive or a geared drive is contemplated. Drive pulley  460  is geared, or toothed, and serves to rotate a primary timing belt  462  which extends between drive pulley  460  and driven idler pulley (also toothed or geared)  464  mounted to the bottom-facing portion of top plate  402 . Priming timing belt  462  is thus stationarily mounted in robot body  201 , meaning that even though it rotates, its position in the robot body does not change. Primary timing belt  462  is provided with teeth on the interior face thereof, these teeth engaging the teeth of drive pulley  460  and driven idler pulley  464  to minimize relative slippage of the timing belt and pulleys. As an alternative to a belt, which is preferably made of Kevlar™ or other minimal-stretch material, a stainless steel band having suitable slots or holes for engaging appropriately-configured teeth on drive pulley  460  and idler pulley  464  can be used. Primary timing belt  462  is kept in tension to minimize slack. To provide adjustment of this tension, the position of drive pulley  460  and/or of idler pulley  464  can be adjusted vertically. Moving one or both of these pulleys apart increases the tension of belt  462 , and moving them towards one another reduces the tension. Of course, in the preferred direct drive case, moving drive pulley  460  entails moving the motor  416  and shaft  422  on which the drive pulley is mounted. This can be accomplished in a simple manner using set screws (not shown) for instance. 
         [0039]    A radial (R) motion conversion assembly is mounted to floating Z platform  432  and coupled to primary timing belt  462 , as detailed in  FIG. 9B . The radial (R) motion conversion assembly includes a driving ( 466 ) and a driven ( 468 ) pulley that are axially coupled to one another such that rotation of driving pulley  466  causes rotation of driven pulley  468 . The pulleys  466  and  468  are toothed, with the teeth of driving pulley  466  engaging the teeth of primary timing belt  462 . Guiding wheels  470  and  472  provided on either side of driving pulley  466  serve to bias the driving pulley against primary timing belt  462  for proper engagement therewith. The teeth of driven pulley  468  engage the teeth of a secondary timing belt  474  which is coupled to inner driving shaft  322  by way of a large, toothed pulley  476  attached axially to the base of the driving shaft ( FIG. 9C ). As an alternative to a belt, which is preferably made of Kevlar™ or other minimal stretch material, a stainless steel band having suitable slots or holes for engaging appropriately-configured teeth on driven pulley  468  and large pulley  476  can be used. Secondary timing belt  474  has a 90-degree “folded” configuration such that rotation of pulleys  466  and  468  in a first (horizontal) axis is converted to rotation of inner driving shaft  322  in a second (vertical) axis. Folding is effected using an arrangement of freely rotating pins or wheels  478 , optionally in combination with toothed pulleys  480 , around which the secondary timing belt  474  is directed to achieve the desired directional changes. Large pulley  476  is rotationally mounted in floating Z platform  432  below and coaxially with large toothed pulley  452  and is rigidly connected to the base of inner driving shaft  322  such that its rotational motion caused by secondary timing belt  474  is transferred to rotation of the inner shaft. Inner shaft  322  is nested in outer shaft  310 , both of which pass through top plate  402  and are free to rotate and slide axially (up-down) therein. A bearing  458  in top plate  402  between the plate and outer driving shaft  310  facilitates this, along with a bearing between the shaft to facilitate their rotation independently of one another. As stated above, independent rotational motion of the shafts means that the two shafts may simultaneously or alternately rotate in the same direction at the same or different rates, or they may rotate in opposite directions at the same or different rates. It will be appreciated that driving pulley  466  of the radial (R) motion conversion assembly should couple to a portion ( 462   a ,  462   b ) of primary timing belt  462  that extends in the Z (up-down) direction commensurately with the travel of the floating Z platform  432  to which the radial (R) motion conversion assembly is mounted, but that the configuration of the primary timing belt  462  can be different from that shown. In other words, the primary timing belt  462  can have more than the two legs  462   a ,  462   b  shown, and these legs do not all have to extend vertically or even be in the same plane, so long as at least a portion of one leg extends vertically to the same extent as the travel of the floating Z platform  432 . 
         [0040]    The arrangement detailed above provides the robot  200  with motion along three axes—R, θ and Z. That is, robot  200  is thus provided with three degrees of freedom. Moreover, angular (θ) motion is unrestricted, meaning that an “endless” number of revolutions of robot arm  202  is possible, with no cables or other mechanical encumbrances preventing rotations of greater than 360 degrees. In addition, other degrees of freedom, including yaw (Y), pitch and roll of the end effector  208  are possible, in accordance with principles described in the aforementioned U.S. Pat. No. 5,789,890, entitled “ROBOT HAVING MULTIPLE DEGREES OF FREEDOM (Genov et al.) 
         [0041]    It will be appreciated that because of the manner in which the robot body angular (θ) motion linkage and the robot body radial (R) motion linkage are coupled to the Z motion linkage, Z motion must be synchronized with angular (θ) and radial (R) motions. For instance, consider the case in which only Z motion is desired, and the angular (θ) and radial (R) positions of the robot arm  202  are to remain unchanged—that is, no angular (θ) or radial (R) motions are to occur. As floating Z platform  432  is raised or lowered by action of motor  418  and timing belt  428 , motors  414  and  416  must also be actuated so that no relative motion between primary timing belt  438  and driving pulley  442  of the angular (θ) motion conversion assembly takes place, and also so that no relative motion between primary timing belt  462  and driving pulley  466  of the radial (R) motion conversion assembly takes place, because such relative motions would cause angular (θ) or radial (R) displacement of robot arm  202 . In the case of the floating Z platform  432  being raised, motors  414  and  416  would need to be actuated in a first direction, and in the case of floating Z platform  432  being lowered, motors  414  and  416  would need to be actuated in a second, opposite direction. Consider also the case in which only angular (θ) motion is desired. This would require activation of motor  414  only. Similarly, if only radial (R) motion is desired, only motor  416  need be activated. 
         [0042]    It will be noted that in practice, during translation of floating Z platform  432  in the Z direction, relative motion between primary timing belt  438  and driving pulley  442  of the angular (θ) motion conversion assembly, along with relative motion between primary timing belt  462  and driving pulley  466  of the radial (R) motion conversion assembly, may in fact be desired, so that motion of the robot arm  202  can take place in multiple degrees of freedom simultaneously, in order shorten or optimize trajectories and travel times and thereby increase robot speed and performance. The relative motions can take place at different rates and in opposite directions depending on the desired trajectory, and actuation of motors  414 ,  416  and  418  can be controlled accordingly. Of course all motor actuation is provided by a controller which is programmable such that it causes actuation of the motors in any fashion necessary to achieve the desired trajectories of robot arm  202 . This is illustrated in  FIG. 12 , which shows that the controller  482  provides actuation signals to the motors  414 ,  416 , and  418 . The controller operates at least in part based on sensor signals from sensor group  484 . The sensor signals derive from one or more sensors (not shown) which determine for example the positions of various robot components using devices such as encoders and so forth. In this manner controller  482  is provided with feedback according to which it issues the actuation signals to the motors. The controller  482  may be external to the robot  200  or internal thereto, or it may be partially external such that some components thereof are external, and partially internal such that other components thereof are internal. 
         [0043]    The above are exemplary modes of carrying out the invention and are not intended to be limiting. It will be apparent to those of ordinary skill in the art that modifications thereto can be made without departure from the spirit and scope of the invention as set forth in the following claims.