Abstract:
An industrial robot includes a parallel kinematics mechanism that provides three degrees of freedom to a ring structure while maintaining the ring structure substantially in a fixed orientation relative to a reference plane established by a stationary base plate. A pivot sleeve is suspended within the stationary base plate and may pivot on two perpendicular axes of an intermediate gimbal. An elongate boom is mounted within the pivot sleeve and extends from an upper end through the pivot sleeve to a lower end. An end effector is mounted at the lower end of the elongate boom and is arranged for carrying a work element. Gimbal rings are located at the upper and lower ends of the elongate boom and are interconnected by a control linkage to maintain the end effector substantially parallel to the ring structure during movement of the end effector through a three-dimensional work envelope.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     “Not Applicable” 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     “Not Applicable” 
     INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISK 
     “Not Applicable” 
     FIELD OF THE INVENTION 
     This invention relates to robotic technologies, and more particularly to a robot for use in industrial processes including pick-and-place operations having the advantages of mechanical amplification, stability, load-bearability, and improved dynamic characteristics. 
     BACKGROUND OF THE INVENTION 
     The use of industrial robots for the flexible automation of industrial processes has become increasingly common for replacing time consuming, monotonous and difficult work. Such work can, for example, be transferring confectionary products such as chocolate or similar fragile or small objects from a conveyor belt to places in predetermined locations in, for example, boxes, with high speed and precision where the object is moving on a separate conveyor belt. The ability to be able to handle small and delicate objects effectively with great speed and precision is much sought after in the automation of industrial processes. 
     Delta type robots (also known as parallel robots) have applications in diverse industries, for example in the food industry and the pharmaceutical industry. The delta robot was first developed in 1985 by R. Clavel and is described in U.S. Pat. No. 4,976,582 (Clavel). Delta robots have proven their worth in particular for packaging lightweight foods, since they permit extremely high speed and high accuracy for performing pick-and-place applications, such as may be effectively used in the packaging machine industry, for picking products from a conveyor belt and placing them in cartons. Delta robots are typically parallel robots with three degrees of freedom (3 DoF), and with simpler, more compact structure and favorable dynamic characteristics. 
     The delta robot is a parallel robot, i.e. it consists of multiple kinematic chains, e.g., middle-jointed arms connecting a base with the end-effector. The key concept of the delta robot is the use of parallelograms which restrict the movement of the platform on which the end-effector is mounted to pure translation, i.e. only movement in the X, Y or Z direction with no rotation. The robot&#39;s base is mounted above the workspace. A plurality of actuators, e.g., three motors, are mounted equidistantly to the base. From the base, three middle-jointed arms extend. The ends of these arms are connected to a small platform. Actuation of the middle-jointed arms will move the platform along the X, Y or Z direction. Actuation can be done with linear or rotational actuators, with or without reductions (direct drive). Since the actuators are all located in the base, the middle-jointed arms can be made of a light composite material. As a result of this, the moving parts of the delta robot have a small inertia. This allows for very high speed and high accelerations. Having all the arms connected together to the end-effector increases the robot stiffness, but reduces its working volume. Each middle-jointed arm is comprised of an upper arm and a pivotally attached lower arm. Each lower arm is formed of two parallel rods that form a parallelogram. Because the lower arm consists of two parallel rods, the end effector always moves, parallel to the base plate located thereabove. This is also known as parallelogram-based control, or parallel kinematics. Note that at least three sets of the arms are necessary to provide generally translation-only motion of the end effector through three dimensions. 
     In use, a delta robot may be suspended over a conveyor type system to grasp and move small objects rapidly and with a high rate of precision. The end effector is arranged to support a tool or other device for carrying out a particular function or task. By a swivelling of the actuators, the end effector can be maneuvered in three-dimensional space formed by the X, Y, and Z axes to any desired position of the available work space. In addition, the end effector of the delta robot is usually equipped with visual guidance capability so that objects moving along a conveyor may be identified for picking and placing into cartons, cases, etc. 
     A fast movement over a relatively great distance, namely the width of the conveyor belt, requires a fast movement of several arms. This is possible in practice only if the robot arms have a low mass inertia, which in the case of delta robots is achieved through the use of light-weight materials, so that the mass inertia of the delta robot is minimized. However, the use of light-weight materials in the construction of the delta robot considerably restricts the load to which the delta robot can be subjected, which means that the delta robot can be used only for gripping light objects with a light gripper. For this reason, its useability and practical application is limited. Use of more robust parts and components would provide capability for gripping heavier objects, however such a benefit comes at the cost of a reduction in speed due to higher mass inertia. Also, light-weight materials used in the construction of delta robots tend to be less robust and cannot provide continuous production cycle times, e.g., 24-hour cycle times. Also, many light-weight materials cannot provide the benefits of low maintenance and infrequent repair as more robust parts and components that are utilized in other types of industrial machinery. 
     Generally, in the foodstuffs industry or in pharmaceutical applications, it is important that components of the delta robots be capable of being cleaned easily. For example, delta robots may include many parts, e.g., arms, located in proximity to the foodstuffs such as raw chicken parts being conveyed. During operation, these parts cannot be shielded from the chicken parts, making wash-down and clean-up of a delta robot a time consuming and expensive task. It would be an improvement within the art to provide an industrial robot where parts and components can be shielded from the foods or other materials that are being picked and placed to reduce or eliminate such wash-down and clean-up requirements. 
     Also, in many industrial processes, such as in pick-and-place operations, it is important for robots to exhibit superior range of motion in all directions. Because of its overall design, the end effector of a traditional delta robot has a limited range of motion, in that the end effector does not benefit from any mechanical amplification of movement. Further, superior range of motion in the Z-axis direction is critical for picking products from a conveyor belt and placing them into deep cartons or cases for shipping. As a result of the design of the pivotable arms of the delta robot which extend laterally as they move through their range of motion, often the laterally-extending arms will interfere with placement of products into cartons or cases to such depths. Also, with the delta robot, to obtain incremental increases in range of motion in the Z-axis direction, it is necessary to increase the length of the arms considerably, which adds weight and reduces production cycle time. 
     For the foregoing reasons, there is room for improvement within the art. 
     SUMMARY OF THE INVENTION 
     An industrial robot includes a parallel kinematics mechanism that provides three degrees of freedom to a ring structure while maintaining the ring structure substantially in a fixed orientation relative to a reference plane established by a stationary base plate. A pivot sleeve is suspended within the stationary base plate and may pivot on two perpendicular axes of an intermediate gimbal. An elongate boom is mounted within the pivot sleeve and extends from an upper end through the pivot sleeve to a lower end. An end effector is mounted at the lower end of the elongate boom and is arranged for carrying a work element. Gimbal rings are located at the upper and lower ends of the elongate boom and are interconnected by a control linkage to maintain the end effector substantially parallel to the ring structure during movement of the end effector through a three-dimensional work envelope. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an embodiment of the industrial robot of the present invention positioned over a conveyor illustrated in phantom; 
         FIG. 2  is a perspective view of the industrial robot of the present invention illustrating the boom in a lowered position; 
         FIG. 3  is a perspective view of the industrial robot of the present invention illustrating the boom in an articulated position; 
         FIG. 4  is an enlarged perspective view of a top portion of the preferred embodiment of the industrial robot of the present invention; 
         FIG. 5  is an enlarged sectional view taken along line  5 - 5  of  FIG. 4 ; 
         FIG. 6  is an enlarged sectional view taken along line  6 - 6  of  FIG. 1 ; 
         FIG. 7  is a perspective view of the preferred embodiment of the industrial robot of the present invention in another articulated position; 
         FIG. 8  is a schematic view illustrating the internal linkages that hold the end effector in a fixed orientation; 
         FIG. 9  is an enlarged sectional view taken along line  9 - 9  of  FIG. 1 ; 
         FIG. 10  is an enlarged perspective view of the end effector portion of the preferred embodiment of the industrial robot of the present invention; and, 
         FIG. 11  is an enlarged perspective view of the end effector portion of the preferred embodiment of the industrial robot of the present invention when the robot is in an articulated position. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now in greater detail to the drawings in which like numerals represent like components throughout the several views, there is shown in  FIGS. 1 through 7  an embodiment of the industrial robot of the present invention which is broadly designated by the numeral  20 . In this application, the robot  20  is shown positioned in proximity to a conveyor belt  24  and in this application pick objects (oriented or disoriented) from the belt  24  and places them onto trays or into cartons (not shown) for shipping. It should be understood that use of the industrial robot  20  in this high-speed pick-and-place application is merely exemplary and the robot  20  of the present invention could be utilized for other highs-speed applications such as assembly, and pharmaceutical and medical applications. As best shown in  FIGS. 1-7 , the industrial robot  20  includes a stationary base plate  28  that includes a plurality of through holes  32  for mounting, e.g., bolting, the base plate  28  to a suitable surface (not shown) within a production facility. 
     As best shown in  FIGS. 1, 5 and 6 , the base plate  28  is generally rectangular in shape and includes a central opening  36  through which a boom  40  extends. A parallel kinematics structure is mounted to the base plate  28  to surround the central opening  36 . The parallel kinematics structure includes actuators  44  mounted to the base plate  28  and control arms  48  extending upwardly from the actuators  44 . The control arms  48  include parallelogram shaped links  76  to restrict movement of an upper outer ring  52  to pure translation, i.e. only movement in the X, Y or Z direction with no rotation. The parallel kinematics structure may be similar in construction to a delta robot. However, the invention contemplates parallel kinematics structures of other constructions. 
     As best shown in  FIG. 6 , the base plate  28  includes a plurality of upstanding flanges  56   a ,  56   b , and  56   c  bolted or welded thereto which together form a triangle-shaped structure  60  having welded reinforcement segments  64   a ,  64   b , and  64   c  situated over the central opening  36 . Extending radially from the triangular structure  60  is a plurality of mounting flanges  68  which are attached to the base plate  28  by any suitable means, e.g., welding. The plurality of actuators  44  are mounted to the mounting flanges  68 , the mounting flanges  68  utilizing any suitable hardware, e.g., bolts. Each actuator  44  serves as a drive source for a control arm  48  linked thereto. As best shown in  FIG. 1 , each control arm  48  includes a drive link  72  pivotably linked to a parallelogram link  76 . In particular, each actuator  44  includes a crank that is rotated for changing the position of the drive link  72  connected to the crank. By this rotation, the tip end  72   a  of the drive link  72  moves upward and can move downward through one of a plurality of T-shaped clearance openings  80  located in the base plate  28 . In the description below, the “drive link  72  rotates upward” indicates that the drive link  72  rotates so that the tip end  72   a  moves upward, and the “drive link  72  rotates downward” indicates that the drive link  72  rotates so that the tip end  72   a  moves downward. 
     As best shown in  FIG. 1 , at the tip end  76  of each drive link  72 , through holes are provided in which a rotatable swivel rod  78  having flattened ends is located. Each drive link  72  is pivotally connected, e.g., bolted, to a corresponding parallelogram link  76 , which is a link driven by the drive link. Referring now to  FIGS. 1 and 4 , each parallelogram link  76  includes two bar-shaped members  88  that extend substantially vertically and parallel to each other between the drive link  72  and an upper outer ring  52 . As best shown in  FIG. 4 , the upper outer ring  52  includes a plurality of housings  96 , each housing  96  provided to house a swivel rod  78  therein, the swivel rod  78  including flattened ends rotatably mounted therein. The housings  96 , e.g., three housings, are connected to each other by bolting or other suitable means through connector elements  100 . Together, the housings  96  and connector segments  100  form the upper outer ring  52 , which is generally hexagonal in shape. Paddle-shaped connectors  104  are fastened to the upper and lower ends of each bar shaped member  88 , by any suitable means, e.g., bolting. With the paddle-shaped connectors fastened at opposite ends of each bar member  88 , at their upper ends, the bar members  88  may be fastened, e.g., bolted, to the swivel rod  78  located within each housing  96 . At their lower ends, the bar members  88  may be fastened, e.g., bolted, to the swivel rod  78  located at the tip end  76  of each drive link  72 . Together, the substantially parallel bar members  88  and substantially parallel swivel rods  78  form the parallelogram shape of the parallelogram links  76 . By connecting the upper ends of at least two of the parallelogram links  76  to the upper outer ring  52 , movement of the upper outer ring  52  is restricted to purely translational movement (movement only with 3 degrees of freedom; translation in the X, Y or Z direction). In this manner, the upper outer ring  52  remains in a fixed orientation, whatever the motion of the control arms  48  may be. The plurality of control arms  48  are movable in different positions between a fully raised position and a fully lowered position relative to the base plate  28  and relative to each other to move the upper outer ring  52  to different elevational and horizontal positions within three-dimensional space while maintaining the upper outer ring  52  substantially in a fixed orientation. 
     Referring now to  FIGS. 4, 5 and 8 , the upper outer ring  52  includes two axle segments  108  and  112  located on opposite ends of the upper outer ring&#39;s periphery. The axles  108  and  112  are attached to the upper outer ring  52  by any suitable means, e.g., bolts  108   a  in  FIG. 4 . The axle segments  108  and  112  are coaxial and extend inwardly from the periphery of the upper outer ring  52  to form a first upper axis  110 . As best shown in  FIGS. 4 and 5 , the axle  108  passes through a slot  42   a  in the housing  42 . An upper gimbal ring  116  is rotatably mounted on these axle segments  108  and  112 . As shown in  FIG. 5 , the upper gimbal ring  116  is octagonal in shape, however, other shapes could be utilized within the scope of the invention. Likewise, the upper gimbal ring  116  includes two axle segments  120  and  124  located on opposite ends of the upper gimbal ring&#39;s outer periphery. The axle segments  120  and  124  lie along a second upper axis  122  and extend inwardly from the periphery of the upper gimbal ring  116 . The axle segments of the upper gimbal ring  116  are oriented at 90 degrees with respect to the axle segments  108  and  112  of the upper outer ring  52 . At its upper end, the boom  40  includes an octagonal-shaped housing  42  (best shown in  FIGS. 4 and 5 ). This housing  42  of the boom  40  is mounted on the axle segments  120  and  124  of the upper gimbal ring  116 . In this manner, movement of the boom  40  remains independent of translational movement of the upper outer ring  52  in the X, Y and Z directions. 
     As best shown in  FIGS. 1 and 4 , an actuator  44  is attached to the boom  40  above the housing  42 . Attached at the bottom of the housing  42 , the boom  40  includes a generally cylindrical portion  126  that extends downwardly and below the upper gimbal ring  116 . Thereafter, the cylindrical portion  126  extends through the central opening  36  in the base plate  28  to a distal end  40   b  where an end effector  128  is located. As best shown in  FIG. 6 , a rotation shaft  132  extends centrally within the boom  40  to connect the actuator  44  attached above thehousing  42  with a tool (not shown) mounted to the end effector  128 . The rotation shaft  132  provides unlimited rotational capability to a tool (not shown) mounted to the end effector  128 . 
     Referring now to  FIGS. 1, 5, 6, and 8 , the central opening  36  of the base plate  28  acts as a middle pivot point for pivotal movement of the boom  40  therein. Specifically, an axle segment  136  is provided approximately midway along the length of upstanding flange  56   c  and an opposing axle segment  140  is provide approximately midway along the length of the bolted reinforcement section  64   c . The opposing axle segments  136  and  140  may be secured to the upstanding flange  56   c  and to the attached reinforcement section  64   c  utilizing any suitable hardware, e.g., bolts  142 . The axle segments  136  and  140  are coaxial to form a first central axis  138  ( FIG. 8 ). The axle segments extend inwardly from their respective mounting surfaces. A center gimbal ring  144  is provided with mounting holes (not shown) to enable it to be rotatably mounted on the axle segments  136  and  140  within the central opening  36  of the base plate  28 . The central opening  36  is sufficiently large to permit rotational movement of the central gimbal ring  144  therein. In this manner, the center gimbal ring  144  is free to rotate about the first central axis  138  formed by axle segments  136  and  140 . Likewise, the center gimbal ring  144  is provided with axle segments  148  and  152  mounted in a similar manner thereto. The axle segments  148  and  152  are mounted to the center gimbal ring  144  using any suitable hardware and are located on opposite sides of the periphery of the center gimbal ring  144  and extend inwardly. The axle segments  148  and  152  are oriented at 90 degrees with respect to the axle segments  136  and  140  and define a second central axis  150  ( FIG. 8 ) which is perpendicular to the first central axis  138 . The intersection of the first and second central axes defines a mid-pivot point  156  ( FIG. 8 ). A pivot sleeve  160  is mounted to the axle segments  148  and  152  of the center gimbal ring  144  and extends through the center gimbal ring  144 . In this manner, the mid-pivot point  156  is located centrally within the pivot sleeve  160  enabling the pivot sleeve  160  to pivot in any direction about the mid-pivot point  156 . As best shown in  FIG. 6 , the boom  40  extends through the pivot sleeve  160 . In this manner, the boom  40  is able to pivot about the mid-pivot point  156  in all directions within the central opening  36  of the base plate  28 . In addition, the boom  40  is free to slide up and down within the pivot sleeve  160  based upon movement of the control arms  48  from the fully raised to the fully lowered positions. 
     Referring now to  FIGS. 2, 3, and 7 , the industrial robot  20  of the present invention has a range of motion covering Cartesian X, Y and Z directions such that the end effector  128  located at the distal end  40   b  of the boom  40  may move transversely and longitudinally within a range of motion defined by a truncated cone indicated at  164 . Referring now to  FIG. 2 , the industrial robot  20  is illustrated therein with each of the control arms  48  in its fully lowered positions, thus causing the end effector  128  to be lowered to its lowest position in the Z direction within the range of motion  164 . In particular, the T-shaped clearance openings  80  are provided on the base plate  28  to accept entry of the drive links  72  therein, thus enabling movement of the control arms to a lower position in the Z direction that otherwise would be possible in the absence of the clearance openings  80 . Referring now to  FIGS. 3 and 7 , by moving the control arms  48  to different positions with respect to each other between fully raised and fully lowered, the boom  40  can be maneuvered, e.g., pivoted, in three-dimensional space to any desired articulated position within the available range of motion  164 . As illustrated in  FIGS. 3 and 7 , because each control arm  48  consists of a parallelogram link, the upper outer ring  52  always moves substantially in a fixed orientation relative to the base plate  28  located therebelow. This is also known as parallelogram-based control, or parallel kinematics. The three control arms  48  provide generally translation-only motion to the upper outer ring  52  through three dimensions. It is also shown in  FIGS. 1, 3 and 7  that regardless of the position of the upper outer ring  52  in three-dimensional space, the end effector  128 , to which a tool (not shown) is mounted, will also exhibit translation-only motion through three dimensions, and remain substantially parallel to the upper outer ring  52 . Such translation-only movement of the end effector is critical to use of the industrial robot  20  in the applications discussed above, e.g., pick and place, etc. 
     Referring now to  FIG. 8 , there is shown a simplified representation of a portion of the industrial robot  20  of the present invention. The simplified representation includes like numerals to represent like components, where applicable. At this juncture, it is important to mention that the appearance of many components in  FIG. 8  may be different than in other figures in that they are simplified and representational only.  FIG. 8  is provided to illustrate the manner in which the end effector  128  exhibits translation-only motion through three dimensions, and remains substantially parallel to the upper outer ring  52  regardless of the pivotal movement of the boom  40 . 
     As shown in  FIG. 8 , and as previously discussed in connection with other figures, the upper end of the boom  40  is rotatably mounted on opposing axle segments  120  and  124  of the upper gimbal ring  116 . The upper gimbal ring  116  is rotatably mounted on opposing axle segments  108  and  112  of the upper outer ring  52  which form a first upper axis  110 . The opposing axle segments  120  and  124  of the upper gimbal ring  116  are oriented at 90 degrees with respect to the opposing axle segments  108  and  112  of the upper outer ring  52  and form a second upper axis  122 . In this manner, movement of the boom  40  remains independent of translational movement of the upper outer ring  52  in the X, Y, and Z directions. The cylindrical boom  40  extends downwardly and through the pivot sleeve  160 . As previously discussed, the pivot sleeve  160  is rotatably mounted on opposing axle segments  148  and  152  of the center gimbal ring  144 . The center gimbal ring  144  is rotatably mounted to opposing axle segments  136  (not shown in  FIG. 8 ) and  140  which are mounted to the structure represented at  60 . First and second central axes are defined at  138  and  150 , respectively, in  FIG. 8 . Thereafter, the boom  40  extends to its distal end  40   b  where the end effector  128  is located. 
     Referring again to  FIG. 8 , a lower gimbal ring  172  is rotatably mounted at the distal end  40   b  of the boom. In particular, the lower gimbal ring  172  includes opposing axle segments  176  and  180  that extend through openings located at the distal end  40   b  of the boom  40 . An end effector  128  is rotatably mounted to the lower gimbal ring  172 . In particular, the end effector  128  includes opposing axle segments  188  and  192  which define a first lower axis  190 . Axle segments  188  and  192  are arranged to pass through openings in the lower gimbal ring  172  to enable the end effector  128  to rotate about the first lower axis  190  that is substantially perpendicular to a second lower axis  177  defined by opposed axle segments  176  and  180  of the lower gimbal ring  172 . The lower gimbal ring  172  includes an arcuate arm  208  extending arcuately approximately ninety degrees with an attachment point lying on the first lower axis  190 . The end effector  128  also includes an arcuate arm  204  that extends arcuately approximately ninety degrees and includes an attachment point lying in the second lower axis  177 . 
     Similarly, the upper outer ring  52  is provided with an arcuate arm  196  that extends to an attachment point lying in the second upper axis  122  and the upper gimbal ring  116  is provided with an arcuate arm  200  that extends to an attachment point lying in the first upper axis  110 . A first rigid connecting rod  212  connects at its upper end to the attachment point of the arcuate arm  196  and at its lower end connects with the attachment point of arcuate arm  204 . A second rigid connecting rod  216  connects at its upper end to the attachment point of the arcuate arm  200  and at its lower end connects with the arcuate arm  208 . The rigid connecting rods  212  and  216  are approximately equal in length. Together, through their connection to the arcuate arms of the upper outer ring  52  and the upper gimbal ring  116 , the connecting rods  212  and  216  serve to limit motion of the end effector  128  to translation-only motion through three dimensions. In this manner, the end effector  128  will remain substantially parallel to the upper outer ring  52  regardless of the pivoting motion of the boom  40  to which the end effector  128  is connected. 
     For example, as best shown in  FIG. 8 , as the lower end of the boom  40  swings along axis  177  to the right, the boom lower end  40   b  will pivot out of a plane parallel to the upper outer ring  52 . However, because the end effector  128  is pivotally mounted to the lower gimbal ring  172 , and connected to the upper outer ring  52  through the rigid connecting rod  212 , the end effector  128  will remain parallel to the upper outer ring  52  through this movement. 
     The actual components forming the upper arcuate arms  196  and  200  can be seen in  FIG. 5 . The arcuate arm  196  is shown as bending at an angle that is less than 90 degrees and the arcuate arm  200  is shown as including two 45 degree bends. As best shown in  FIG. 5 , the top end of the rigid connecting rod  212  is housed within a stirrup  214  which is connected to upper arcuate arm  196 . The top end of the rigid connecting rod  216  may include a circular eyelet (not shown) including a central opening through which the upper arcuate arm  200  may extend to connect these components. 
     Referring now to  FIGS. 9-11 , the actual components relating to operation of the end effector  128  are illustrated. In particular, the end effector  128  includes a housing  184  which attaches at the distal end  40   b  of the boom ( FIG. 1 ). A lower gimbal ring  172  has an outer surface that is generally octagonal in shape. The lower gimbal ring  172  includes opposing axle segments  176  and  180  that extend outwardly. The lower gimbal ring  172  is shown as rotatably mounted within the housing  184  by the axle segments  176  and  180  extending through openings (not shown) in the housing  184 . The opposing axle segments  176  and  180  define the second lower axis  177 . The end effector  128  includes a cylindrical tube  128   a  in which a central axle segment  186  is disposed. The central axle segment  186  is mounted within the lower gimbal ring  172  by any suitable means, e.g., bolts  186   a  extending through a bolt plate  186   b . The central axle segment  186  may be non-rotational with respect to the lower gimbal ring  172 , however, the cylindrical tube  128   a , and thus the end effector, are rotatable about the central axle segment  186 . The central axle segment  186  defines the first lower axis  190  which is substantially perpendicular to the second lower axis  177 . 
     As best shown in  FIG. 10 , two L-shaped stand-off brackets  224  are shown attached, e.g., bolted, to the end effector  128  in two places. The L-shaped brackets extend under the central axle segment  186  and are shown attached to a square-shaped receptacle  220 . The rigid connecting rod  212  is shown rotatably mounted within the receptacle  220  and retained therein by a pin  225  extending through the receptacle  220  and the L-shaped stand-off brackets  224  located on opposite sides of the receptacle  220 . Likewise, the rigid connecting rod  216 , which includes a trapezoidal head  216   a , is shown rotatably mounted over the axle segment  186 . As mentioned previously, at its upper end, the connecting rod  212  is connected to the upper outer ring  52 , and at its upper end, the connecting rod  216  is connected to the upper gimbal ring  116 . As best shown when comparing  FIG. 10  and  FIG. 11 , as the boom  40  articulates, the connecting rod  212  will rotate. Through its connection to the upper outer ring  52 , the connecting rod  212  will cause the end effector  128  to rotate about the axle segment  186  so as to maintain the end effector  128  substantially parallel to the upper outer ring  52 .