Abstract:
An apparatus and method for picking and placing an object is disclosed. The apparatus includes an elongated frame, first and second carriages slidingly engaged with the frame, first and second connecting rods pivotally engaged with the first carriage at one end and at least a third connecting rod pivotally engaged with the second carriage at one end, and a gripper pivotally and operatively attached to the connecting rods at their other ends. The method of operation includes moving the gripper in a first direction (upwardly) by sliding the first and second carriages away from each other along the frame, moving the gripper in a second direction (laterally), perpendicular to the first direction, by sliding the first and second carriages together along the frame in the same direction, and moving, the gripper in a third direction (downwardly), opposite to the first direction, by sliding the first and second carriages toward each other along the frame.

Description:
FIELD OF THE INVENTION 
     This invention relates to a device for picking-up a part from a first manufacturing station and thereafter placing and releasing the part in a second station. Such devices are typically used in robotics and automatic manufacturing applications and are commonly referred to as “pick and place” devices or “transfer mechanisms”. 
     BACKGROUND OF THE INVENTION 
     Pick and place devices known in the art typically incorporate two axes of motion configured perpendicular to each other. For example, two independently operated pneumatic slide carriages can be mounted on axes perpendicular to each other, wherein the first carriage supports the second carriage. The two carriages can be driven either by linear servo motors or by ball screws and rotary servo motors. An example of such a two-axes, two-carriage device is illustrated in U.S. Pat. No. 5,086,559 to Akatsuchi. 
     The disadvantage of such prior art devices is that the first carriage axis carries the second carriage axis. Therefore, the first axis must robust enough to carry the weight of the part being moved in addition to the weight of the second axis, and the driving force propelling the first axis must be large enough to accelerate and decelerate the part in addition to the second axis. Another disadvantage is that the accuracy of the motion of the second axis depends on the accuracy of the mounting that attaches the second axis to the first axis. If the two axes are not mounted exactly perpendicular to each other, the motion will not have the desired accuracy. Moreover, the mounting is often fixed during manufacturing and cannot be adjusted in the field. 
     Instead of using two independently powered carriages on two perpendicular axes, some pick and place devices utilize a barrel cam driven by an electric motor, or a pneumatic cylinder moving the carriages in a cam slot. Pick and place devices utilizing U-shaped cam slots are illustrated in U.S. Pat. No. 5,564,888 to Doan, and U.S. Pat. No. 4,740,134 to Dixon. A pick and place machine utilizing a generally Y-shaped cam slot is illustrated in U.S. Pat. No. 4,451,196 to Harada et al. 
     A primary disadvantage of these cam-type prior art devices is that they provide little, if any, provision for adjustment of the device motion ranges. Typically, the motion of the device is fixed, thereby requiring that the parts handling system be built around the dimensions of the pick and place device. If the pick and place device does not have the exact range of motion specified by the manufacturer, the parts handling system must subsequently be redesigned. 
     Using another type of transfer apparatus, U.S. Pat. No. 3,065,861 to Cruciani discloses a rope crane having substantially parallel carrying ropes with a pair of blocks connected to one another. By winding the rope of one capstan and paying out the rope of another capstan, the pair of blocks can be carried to any desired point located between two predetermined locations. The main disadvantage of this rope crane is that, since it relies on gravity, it can only exert a positive force in the upward direction (i.e., a “pull force”), and cannot exert a positive force in the downward direction (i.e., a “push force”). The inability to provide a positive pushing force prohibits the device from operating effectively as a pick and place device, particularly if the device is inverted (e.g., located under the automation system). 
     U.S. Pat. No. 4,687,400 to Lichti discloses another type of device for moving objects in a closed container. This complex device has four degrees of freedom (i.e., up-and-down, back-and-forth, opening and closing the fingers, and rotation around a horizontal axis) but requires manipulation of four arms to obtain the desired motion. Linear horizontal motion is complicated as it requires a combination of vertical and rotational motion. Therefore, it is too complex and expensive for cost-effective use in an application requiring only two degrees of freedom (i.e., up and down, side-to-side). 
     U.S. Pat. No. 4,190,912 to Nilsson discloses a device for lifting and transferring a hospital patient. Rotation of a lever, pivotally attached to a connecting rod at a predetermined angle, raises, translates, and then lowers a patient in and out of bed. However, due to its design, the range of vertical movement is fixed through the entire lift and transfer cycle (i.e., the mechanism must place at the same level it picks). Thus, this mechanism can-only move from a first predetermined location to another predetermined spot at approximately the same height as the first location, and has limited flexibility. 
     A need, therefore, exists for a two-axis pick and place device that is simple in construction, highly accurate, programmably adjustable, robust in operation, and yet cost effective. 
     OBJECTS AND SUMMARY OF THE INVENTION 
     Accordingly, it is a primary object of the present invention to provide a pick and place device which overcomes the disadvantages previously described. 
     It is another object of the present invention to provide a pick and place device that can be programmed to move in accordance with the computer instructions of many different manufacturing operations. 
     It is still another object of the present invention to provide a pick and place device that has carriages which move along two parallel axes instead of two perpendicular axes, to increase the accuracy of movement. 
     In accordance with one aspect of the present invention, there is provided a pick and place device comprising a single elongate frame extending in a longitudinal direction, first and second carriages slidingly engaged on the frame, first and second motors which drive each of the first and second carriages to slide along the frame, a gripper for gripping an object to be relocated, a first linking arrangement including at least two connecting rods pivotally attached to the first carriage at one end and pivotally attached to the gripper at the other end, and a second linking arrangement including at least one connecting rod pivotally attached to the second carriage at one end and pivotally attached to the gripper at the other end. 
     In accordance with the present invention, the method of picking and placing an object includes the steps of sliding the first and second carriages away from each other along the frame substantially simultaneously in opposite directions which moves the gripper in an upward direction, sliding the first and second carriages along the frame substantially simultaneously in the same direction which moves the gripper in a lateral direction, and sliding the first and second carriages toward each other along the frame substantially simultaneously in opposite directions which moves the gripper in a downward direction. 
     In accordance with another aspect of the present invention, there is provided a pick and place device including carriages slidingly engaged with a frame, a platform with an attached gripper, and at least four connecting rods extending between the platform and the carriages, the platform having a first range of motion in a first direction and a second range of motion in a second direction that is substantially perpendicular to the first direction. The first range of motion depends on the length of the frame and the length of the connecting rods. The second range of motion depends on the length of the frame only. 
     In accordance with still another aspect of the present invention, there is provided a pick and place device comprising an elongate frame extending in a longitudinal direction, a first carriage assembly slidingly engaged with the frame and including at least two pivotally mounted connecting rods, a second carriage assembly, operatively independent from the first carriage assembly, slidingly engaged with the frame and including at least two pivotally mounted connecting rods, a platform pivotally connected to the connecting rods of the first and second carriage assemblies, and a motor which drives each of the first and second carriage assemblies to slide along the frame. Sliding the carriage assemblies along the frame away from each other exerts a force to move the platform in a first direction. Sliding the carriage assemblies along the frame in the same direction exerts a force to move the platform in a second direction which is substantially perpendicular to the first direction. Sliding the first and second carriage assemblies along the frame toward each other exerts a force to move the platform in a third direction, substantially opposite to the first direction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention itself, however, together with further objects and advantages thereof, may best be understood by reference to the following description when taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a side view of a first embodiment of a pick and place device according to the present invention; 
     FIG. 2 is a cross-sectional view of the first embodiment of the pick and place device, taken along line II—II of FIG. 1; 
     FIGS. 3A-3D are perspective views that schematically illustrate different embodiments of the mounting configuration for the platform of FIG. 1; 
     FIGS. 4A-4F are side views illustrating various positions during the operation of the pick and place device in accordance with the present invention; 
     FIG. 5 is a side view of a second embodiment of a pick and place device of the present invention; 
     FIG. 6 is a cross-sectional view of the second embodiment of the pick and place device, taken along line VI—VI of FIG. 5; 
     FIGS. 7A and 7B are perspective and top views, respectively, that schematically illustrate the mounting configuration for the platform of FIG. 5; and 
     FIG. 8 is a cross-sectional view of another embodiment of the pick and place device of the present invention, illustrating an angle frame configuration for mounting to an adjacent structure. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a side view of a first embodiment of a pick and place device  10  according to the present invention, while FIG. 2 shows a cross-sectional view taken across lines II—II of FIG.  1 . In this embodiment, support frame  12  is mounted to an overhead structure  14  using fasteners  16 , illustrated here as mounting bolts. The fasteners may alternatively include screws, rivets, or welding. 
     In FIG. 1, the support frame  12 , extends overhead in a longitudinal direction and provides at least one single axis bearing rail  18  on which two independent carriages  20   a  and  20   b  slide. Bearing rail  18  extends outwardly from support frame  12 , and each carriage  20  includes at least one bearing  19  which engages the bearing rail  18  for smooth sliding of carriages  20  along the rail. 
     A motor  22  is contained within and drives each of the carriages  20 . In a preferred embodiment, the motor is a linear servo motor, but may include other suitable drive means such as a ball screw and rotary servo motor, or timing belt drive and rotary servo motor. The motors  22  driving the two independent carriages  20  may be controlled using a computer numerical control (CNC) controller  24  or any other two-axis controller. CNC controller Model No. 8000 available from Giddings &amp; Lewis, Inc. of Fond du Lac, Wis., may be used to control motors  22 . The power connection to the motors  22  are made to carriages  20  by cable carriers  26  which allow carriages  20  to slide along bearing rail  18  without tangling or breaking of the wires. Cables are connected at one end to the controller  24  and at the other end to the motor  22  of each carriage  20 . The cable carriers  26  are attached to support frame  12  by cable carrier fasteners  28 , illustrated here as mounting bolts. The fasteners may alternatively include screws, rivets, or other suitable attachments. Carriages  20  are driven by the motors  22  back and forth along a single axis in the longitudinal direction of support frame  12 . Therefore, carriages  20  each have one degree of freedom, i.e., side-to-side in FIG.  1 . 
     The pick and place device  10  of the present invention also includes a plurality of connecting rods  30 . One end  31  of each of the connecting rods  30  is pivotally connected to one of the carriages  20  by mounting to a flange  32  of the carriage  20 , using a pivot joint  34 . Each pivot joint  34  preferably includes a bearing  36 , e.g., a ball bearing or a block bearing, for smooth pivoting, and may also include bearing fasteners  38 , e.g., set screws, hex nuts, or bolts. In the embodiment of FIG. 1, each carriage  20  has four flanges  32 , arranged in two rows each having two adjacent aligned flanges as shown. Flanges  32  of each carriage  20  are preferably formed integrally with the carriage, either as a monoblock structure or by welding a flange member to the carriage. 
     The other end  39  of each of the connecting rods  30  is pivotally mounted to a platform  40 . In the embodiment shown in FIG. 1, platform  40  has six flanges  42 , arranged in two rows each having three adjacent aligned flanges as shown. Connecting rods  30  are mounted to flanges  42  using a pivot joint  44 , preferably including a bearing  46 , e.g., a ball bearing or a block bearing, and may also include bearing fasteners  48 , e.g., set screws, hex nuts, or bolts. Flanges  42  of platform  40  are also formed integrally with the platform, either as a monoblock structure or by welding. 
     At least three connecting rods  30  are required to control the parallelism of the platform to the support frame. More connecting rods  30  may be used to increase stability of the platform  40  and/or allow transfer of heavier loads. It is important to note that all of the connecting rods should not be in a single line (i.e., linear alignment), but instead should be mounted to platform  40  such that they provide a stable transfer force that does not allow undesirable twisting forces across the plane of platform  40 . 
     In the embodiment shown in FIGS. 1 and 2, four connecting rods  30   a,    30   b,    30   d  (located directly behind  30   a  in FIG.  1 ), and  30   e  (located directly behind  30   b ), are pivotally mounted to the first carriage  20   a  and to platform  40 . Two additional connecting rods  30   c,    30   f  (located directly behind  30   c ), are pivotally mounted to the second carriage  20   b  and to the platform  40 . 
     FIGS. 3A-3F show perspective views of the platform  40 , indicating schematically how the connecting rods  30  are configured on the flanges of platform  40 . In FIG. 3A, the six connecting rods  30   a-f  are configured as shown in FIGS. 1 and 2, i.e., arranged along the perimeter of the platform  40  in two rows each having three connecting rods. Four connecting rods  30   a,    30   b,    30   d,    30   e  are connected to the first carriage  20   a  in order to keep platform  40  level with respect to the support frame  12 , while only two connecting rods  30   c,    30   f  are required to be connected to the second carriage  20   b.  Note that less than six connecting rods can be used. Since three points define a plane, using only connecting rods  30   a,    30   c,  and  30   e  would represent one example of the minimum number of rods needed to keep the platform  40  level. Note that using connecting rods  30   a,    30   c,  and  30   d  would not keep the platform level, since rods  30   a  and  30   d  are connected along a centerline that is perpendicular to the axis of motion (+/−X direction). With only three connecting rods, the two rods from the same carriage cannot be mounted along such a perpendicular centerline. 
     FIG. 3B illustrates a second embodiment for the mounting configuration of the connecting rods  30  to a different platform  52 . In this embodiment, only four connecting rods  54   a,    54   b,    54   c,  and  54   d  are used to support platform  52  as shown. Note that this four-point support, arranged in three rows of one-two-one rods each, still serves to keep the platform  52  level because the two connecting rods  54   a,    54   d  are mounted at opposite edges of the platform and configured to straddle the perpendicular centerline of the other two connecting rods  54   b,    54   c  as shown. If either connecting rod  54   b  or  54   c  from carriage  20   b  were removed, the platform  52  could tilt around the centerline. If, however, either one of connecting rods  54   a  or  54   d  from carriage  20   a  were removed, the platform would not tilt because the connecting rods  54   b  and  54   c  from the same carriage  20   b  would prevent it. For heavier loads, a three-point mounting configuration using connecting rods  54   a,    54   b,  and  54   c  would tend to twist the platform, since rod  54   a  is moving along a different parallel axis than rods  54   b  and  54   c.  Hence, a four-point mounting configuration is used to minimize twisting forces. 
     FIG. 3C illustrates a third embodiment of the connecting rod mounting configuration. In this embodiment, four connecting rods  56   a,    56   b,    56   c,  and  56   d  are used to support platform  57  and arranged as three rows of one-two-one connecting rods each as shown. Note that at least one of two connecting rods from the same carriage are not mounted on the centerline between the other two connecting rods, i.e., rod  56   c  is not mounted in line with rods  56   a,    56   b,  and  56   d.  This configuration keeps the platform  57  from tilting around the centerline. If either connecting rod  56   b  or  56   c  were removed, the platform would tilt. 
     FIG. 3D illustrates a fourth embodiment for the platform mounting configuration. In this embodiment, the four connecting rods  58   a,    58   b,    58   c,  and  58   d  are used to support platform  59 . Again note that at least one of the two connecting rods from the same carriage are mounted off of the perpendicular centerline in order to counteract the tilting forces applied to the platform by the other connecting rods. 
     Again referring to FIGS. 1 and 2, a mounting plate  60  is fastened to the bottom surface of the platform  40 , preferably by welding. An adapter plate  62  is fastened to the mounting plate  60  by fasteners  64 , illustrated as mounting bolts. In the embodiment shown here, a pneumatic gripper  66  is mounted to adapter plate  62 . The use of adapter plate  62  increases the versatility of the pick and place device  10  of the present invention by allowing a number of different grippers  66 , including mechanical, pneumatic, and magnetic grippers, to be used with the pick and place device as desired. One example of a mechanical gripper which could be used with the pick and place device  10  is Model No. RPL-3 available from Robohand, Inc. of Monroe, Conn. 
     In the embodiment of FIG. 1, a linear servo motor  70  is used on each carriage  20 . As can best be seen in FIG. 2, the magnets of a motor stator  72  extend along the longitudinal axis between support frame  12  and a motor coil or windings  74  attached to each carriage. The motor stator  72  is fastened to the support frame  12  by adhesive. Hence, using a linear servo motor, the stator  72  is fixed to the support frame and the motor coil  74  propels the carriage along the frame. One example of a linear servo motor which could be used with the present invention is The MegaThrust Series “Y” linear motor available from NSK Corporation of Ann Arbor, Mich. 
     FIGS. 4A through 4F illustrate the movement of the pick and place device  10  of the present invention during its operation. In FIG. 4A, the pick and place device is shown in an initial position wherein the platform  40  is raised above an object  80  to be moved. In the example shown in FIGS. 4A-4F, the object  80  is being moved from one station, such as a first conveyor belt  82 , to another station, such as a work fixture  84 . 
     In a first step, the two independent carriages  20  are moved along the longitudinal axis of the support frame  12  (X axis) toward each other such that the platform  40  is lowered, along the axis perpendicular (Z axis) to the axis of the support frame, to the position shown in FIG.  4 B. 
     The gripper  66  is then activated to “pick” the desired object  80 . 
     In a second step the two independent carriages  20  are moved along the longitudinal axis of the support frame  12  away from each other such that the platform  40  is raised to the position shown in FIG. 4C to raise the object. The gripper  66  remains activated. The range of motion of the platform  40  as it is raised and lowered is limited by the length of the support frame  12  and the length of the connecting rods  30 . 
     Preferably, in the first and second steps, the two independent carriages  20  move along the longitudinal axis of the support frame  12  at substantially the same speed. However, if the two independent carriages do not move at the same speed, the platform will be displaced along the longitudinal axis of the support frame (i.e., horizontally) instead of only being displaced perpendicular to the longitudinal axis of the support frame (i.e., vertically). Although it is generally desirable that the platform be displaced solely along the vertical axis during the raising and lowering of the platform to “pick” the load (since it is easier to program and control), it may be determined that some horizontal motion may be advantageous in some applications. 
     In a third step, the two independent carriages  20  move along the support frame in the same direction at substantially the same speed such that the load is transferred along the longitudinal direction of the support frame  12  to a desired position as shown in FIG.  4 D. The range of motion of the platform along this longitudinal axis is limited only by the length of the support frame. As before, if the two independent carriages do not move along the longitudinal axis of the support frame (i.e., horizontally) at the same speed, the platform will be displaced in a direction perpendicular to the longitudinal axis of the support frame (i.e., vertically) as it is moved along the longitudinal axis. Again, although it is generally desirable that the platform be displaced solely along the longitudinal axis of the support frame during transfer of the load, some applications may require simultaneous movement along both the vertical axis and the horizontal axis. In such a case, the path of the platform (and object) would be diagonal or curved instead of coincident with the X and Z axes. 
     In a fourth step, the two independent carriages  20  are again moved toward each other along the longitudinal axis of the support frame  12  to again lower the platform to the position as shown in FIG.  4 E. The gripper is then deactivated to “place” the desired object in a particular location. 
     In a fifth step, after placing the load, the two independent carriages  20  are again moved away from each other along the longitudinal axis of the support frame to again raise the platform to the position as shown in FIG.  4 F. The gripper remains deactivated. Preferably, in the fourth and fifth steps, the two independent carriages move along the longitudinal axis of the support frame at the same speed, unless otherwise required for particular applications. 
     In a sixth step, the two independent carriages  20  are moved along the support frame in the same direction such that the platform is returned to its starting position as shown in FIG.  4 A. Following return of the pick and place device to its starting position, the operation illustrated in FIGS. 4A-F is repeated for each object to be transferred. 
     FIG. 5 is a side view of a second embodiment of a pick and place device  110  of the present invention, and FIG. 6 is a cross-sectional view thereof taken across lines VI—VI of FIG.  5 . Support frame  112  is mounted to a mounting structure  114  using fasteners  116 , again illustrated here as mounting bolts. The fasteners may alternatively include screws, rivets, or welding. As shown above in FIGS. 1 and 2, the support frame  112  extends overhead in a longitudinal direction and provides a bearing rail  118  on which two independent carriages  120  are mounted. In this embodiment, the bearing rail  1   18  extends laterally from the support frame  112 , and each carriage  120  includes at least one bearing  119  which engages the bearing rail  118  for smooth sliding of carriages  120  along the rail. A front cover  121  is fastened to the support frame  112 . 
     A motor  122  is again operatively connected to and drives each of the carriages  120 . The motors  122  are controlled through cable carriers  126  which allow carriages  120  to slide along the bearing rail  118 . In this embodiment, each cable carrier  126  is connected at one end to a controller (not shown) and at another end to the motor  122  of each carriage  120 . The carriers  126  are mounted to support frame  112  by a mounting bracket  127 . 
     The pick and place device  110  also includes at least three connecting rods  130 . One end  131  of each of the connecting rods  130  is pivotally connected to one of the carriages  120  by mounting to a flange  132 , using a pivot joint  134 , preferably including a bearing  136  (e.g., a ball bearing or a block bearing) for smooth pivoting. Each carriage  120  has two flanges  132 . Flanges  132  of each carriage  120  are formed integrally with the carriage, either as a monoblock structure or by welding. The other end  139  of each connecting rod  130  is pivotally mounted to a platform  140 . 
     In the embodiment shown in FIGS. 7A and 7B, platform  140  has four flanges  142 . Connecting rods  130  are mounted to flanges  142  using a pivot joint  144 , preferably including a bearing  146  (e.g., a ball bearing or a block bearing) for smooth pivoting. Flanges  142  of platform  140  are formed integrally with the platform, either as a monoblock structure or by welding. An adapter plate (not shown) may also be used, if desired. A gripper  166  is mounted to a bottom surface of platform  140  by fasteners  164 , illustrated as mounting bolts. The fasteners may alternatively include screws, rivets, or welding. 
     As stated above, at least three connecting rods are required. More connecting rods may be used to increase stability of the device and/or allow transportation of heavier loads. It is important that all of the connecting rods are mounted to platform  140  such that they provide a stable lifting force which does not allow undesirable twisting forces across the plane of the platform. Hence, FIG. 7B shows a top view of platform  140 , indicating how the four connecting rods  130   a-d  are mounted on flanges  142  of platform  140 . Accordingly, two X-axis aligned connecting rods  130   a,    130   c,  are pivotally mounted to the first carriage  120   a  and to platform  140 . Two additional Y-axis aligned connecting rods  130   b,    130   d,  are pivotally mounted to the second carriage  120   b  and to platform  140 . This symmetrical connecting rod arrangement provides the proper lifting forces without exerting undesired twisting forces on the platform. 
     In the embodiment of FIG. 5, an encoder scale  172  extends along substantially the entire length of the support frame  112  and is used, with encoders  174  located on each of the carriages  120 , to track the position of each carriage along the support frame  112 . The motors  122  driving independent carriages  120  may be controlled using computer numerical control (CNC) or any other two-axis control devices. Therefore, the location of each carriage  120  along the support frame  112  is communicated to the control device by the respective encoder  174 . Encoder Model No. RGH 22, available from Renishaw, Ltd., U.K., may be used to provide this function. 
     FIG. 8 illustrates a cross-sectional side view of a third embodiment  210  of the pick and place device of the present invention, which uses an angle frame  212  mounted to an adjacent structure  214  using fasteners  216 , illustrated as mounting bolts. The fasteners may alternatively include screws or rivets. A front cover  217  is also mounted to the angle frame  212 . At least one bearing rail  218  is mounted to the angle frame  112  to provide sliding support for the carriage  220  as shown. 
     In this embodiment, a linear motor  222  is used to move each carriage  220 . A motor magnet  221  is mounted to angle frame  212  using fasteners  223 , illustrated as mounting bolts. A spacer  224  is provided between motor magnet  221  and angle frame  212 . A motor coil  225  extends from each carriage  220  into motor magnet  221 . Each carriage  220  includes a bearing  219 , illustrated as a block bearing, which engages a bearing guide for smooth sliding of carriages  220  along bearing rail  218 . Cable carriers  260  are mounted to an angle bracket  262  using fasteners  263 . A plate support  264  is mounted to front cover  217  by fasteners  265 . Cable carriers  260  are also mounted to support plate  264 . 
     As before, connecting rods  230  are pivotally mounted at one end  231  to the carriage  220  using pivot joints  234 , and at the other end  239  to platform  240  using pivot joints  244 . A gripper  266  is mounted either to an adapter plate (not shown) or to the bottom surface of platform  240  using fasteners  265 , illustrated as mounting bolts. 
     In review, it can now be seen that the present invention provides an improved two-axis pick and place device that is more efficient in construction and operation than previous designs. The present invention provides a highly accurate, programmably adjustable, robust machine that can easily be controlled using conventional two-axis controllers. It is the interconnecting linkage between the two independent carriages and the gripper that translates motion along a longitudinal axis, such as the horizontal axis, into motion perpendicular to that axis, such as the vertical axis. 
     While specific embodiments of the present invention have been shown and described herein, further modifications and improvements may be made by those skilled in the art. In particular, it should be noted that more than three connecting rods can be used to provide additional load-handling capabilities and machine stiffness. Also note that most any type of pick and place gripper and/or platform could be substituted for those shown in the figures. Furthermore, while the invention has been described using an individual motor to control each independent carriage, it should be recognized that a single motor in conjunction with various types of linkages and drives could control two carriages. Numerous other hardware and software modifications may also be made to customize the present invention for various other applications. All such modifications which retain the underlying principles disclosed and claimed herein are within the scope of the invention.