Abstract:
A precision positioning device, such as a robot, decouples the different axes of motion by utilizing a modular motion unit for each different axis of motion. Each modular motion unit includes a base structure, a linear guide, a carriage, a drive motor, and a cable to convert the torque of the drive motor into useful, controlled carriage movement. The parts and sub-assemblies of each modular motion unit are interchangeable without concern about the ultimate orientation of the unit. To assemble the units into a robot, the modular motion units are attached to an underlying frame structure to provide computer-controlled movement over a designated physical work space. Re-tensioning of a drive cable within the modular motion unit is accomplished without requiring the operator to have special training or tools. One end of the drive cable is attached to a tensioner that is releasably locked into place. When the tensioner is released, a spring operates to move the tensioner, and the cable, to a properly tensioned position.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/504,584, filed Sep. 19, 2003, the disclosure of which is hereby incorporated by reference herein in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates generally to precision positioners and, more particularly, to computer controlled positioning tables.  
       BACKGROUND OF THE INVENTION  
       [0003]     Robots that move in the X, Y and Z axes are used in many technological fields to automate repetitive tasks, like those encountered on a production line. One particular type of robot, or precision positioning unit, of this nature involves a carriage that moves in a linear fashion over a range of positions under control of a computer. Conventionally, these robots include, for each axis of motion, a linear guide on a base structure that is interconnected with base structures for the other axes. A respective drive unit, such as a chain, belt, gear, ball screw or lead screw moves the carriage along the linear guide in a particular axis of motion. The connections between the base structures for each axis of motion can range from rails that connect to, or physically support, one another to even the sharing of drive components such as belts, cables and gears. These robots typically include a tool that is attached to perform a production-line function such as welding, soldering, gluing, heating, or dispensing material.  
         [0004]     Because the base structures are integrated with one another, the design and operation of one base structure (e.g., the X-axis) is dependent on the size and other physical characteristics of the other base structures (e.g., the Y-axis). Accordingly, even though the linear guides, the base structures, and other parts serve similar functions for each axis of motion, they are not interchangeable. This can increase design complexity and costs. Additionally, it can be very difficult to change the robot&#39;s range of motion and range of travel without redesigning and rebuilding the entire robot.  
       SUMMARY OF THE INVENTION  
       [0005]     Embodiments of the present invention address these and other problems of the prior art by providing a modular motion unit that can be readily designed and built without concern about its intended axis-of-movement direction.  
         [0006]     One aspect of the present invention relates to a cable-drive modular motion unit for one axis of motion in a positioning device which includes a base structure and a linear guide attached with the base structure, wherein the linear guide has a major axis aligned with the one axis of motion. Also included is a carriage arranged on the linear guide such that motion of the carriage is limited to being along the major axis. The cable-drive is effected by a drive motor attached to the base structure, and a cable attached to the carriage and the drive motor such that rotation of the drive motor causes movement of the carriage, but, during operation of the positioning device, the cable is not connected to any portion of the positioning device that moves in another axis of motion.  
         [0007]     Another aspect of the invention relates to a modular motion unit usable along any axis of motion in a positioning device that includes a base structure; a linear guide attached to the base structure and having a major axis; and a carriage arranged on the linear guide such that motion of the carriage is limited to being along the major axis. Also included are a drive motor attached to the base structure and a cable attached to the carriage and the drive motor such that rotation of the drive motor causes movement of the carriage. During operation of the positioning device, the modular motion unit is attached to a frame member of the positioning device such that the major axis is aligned with an intended axis of motion.  
         [0008]     A further aspect of the invention relates to a positioning device that includes a first and a second modular motion unit that include, respectively, a base structure and a linear guide attached to the base structure having a major axis aligned with one axis of motion. The positioning device further includes a carriage arranged on the linear guide such that motion of the carriage is limited to being along the major axis. Also, a drive motor is attached to the base structure and a cable is attached to the carriage and the drive motor such that rotation of the drive motor causes movement of the carriage. During operation of the positioning device, the first and second modular motion units are unconnected to one another. As a result, the modular motion units described above may be aligned along any desired axis of motion independent of other modular motion units. This allows parts and pieces of the modular motion units to be generic to any axis of motion. Therefore, manufacturing processes may be uniform for all motion units without regard for their intend use and the amount of different parts in inventory may be reduced. Additionally, re-sizing of a robot incorporating multiple modular motion units is simplified. Instead of re-engineering a complex two-dimensional motion unit, the present modular motion unit need only be re-sized in one dimension to change the range of motion for a robot.  
         [0009]     Yet another aspect of the present invention relates to a tensioning device for a cable of a cable drive system. According to this aspect, the tensioning device includes a linear channel along which a tensioner plate can move, wherein the tensioner plate is attached with one end of the cable and movement of the tensioner plate in a first direction increases tension on the cable and movement of the tensioner plate in a second direction decreases tension on the cable. Also, a spring is included having a first fixed end and a second end operationally coupled with the tensioner plate; in particular, the spring is compressed so as to exert a force in the first direction. A releasable lock is attached to the tensioner plate and configured, in a first position, to prevent the tensioner plate from moving and, in a second position, permit the tensioner plate to move; whereby when the releasable lock is in the second position, the spring effects movement of the tensioner plate in the first direction. Accordingly, a conventional (rather than a specialized) tool may be employed to retention the cable and such an operation would not require a technician have specialized training.  
         [0010]     Various additional advantages and features of the invention will become more apparent upon review of the following detailed description of the preferred embodiments of the invention taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a perspective view of a precision positioner having three modular motion units.  
         [0012]      FIG. 2  is a perspective view of the three modular motion units of  FIG. 1  without depicting the framework of the positioner.  
         [0013]      FIG. 3  is a top perspective view of an exemplary modular motion unit.  
         [0014]      FIG. 4  is a bottom perspective view of an exemplary modular motion unit.  
         [0015]      FIG. 5  is a perspective view of a tensioner according to the present invention.  
         [0016]      FIG. 6  top perspective view of another exemplary modular motion unit.  
         [0017]      FIG. 7  is a bottom perspective view of another exemplary modular motion unit. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]      FIG. 1  illustrates a positioner unit, or robot, that includes three modular motion units assembled on a frame.  FIG. 2  illustrates the same arrangement of the modular motion units without the frame structure being depicted. While precision positioner units of various sizes and capabilities are contemplated by the present invention, one exemplary positioner unit operates at acceleration forces of approximately ¼ g, provides positional accuracy to about 5 mils and positional repeatability of about 2 mils.  
         [0019]     Referring to  FIGS. 1 and 2 , the positioner unit  101  includes a base  100 , that in this instance houses the computer control assemblies and other electronic circuitry of the robot. With respect to the modular motion units, the base  100  provides a place to mount one of the modular motion units. Although obscured by the base  100  and the splash guard  105 , in this drawing, the modular motion unit is oriented so as to extend from the front of the base  100  to its rear and allows the carriage  102  to move along the Y-axis. A pair of upright legs  104 ,  108  are attached to the rear of the base  100  and support a horizontal beam  106 .  
         [0020]     Along the front of the horizontal beam  106  another modular motion unit  103  is attached and oriented such that its carriage (not shown in  FIG. 1 ) travels between the two upright legs  104 ,  108 . This axis of motion is orthogonal to the Y-axis and is considered the X-axis. Mounted on the carriage of the modular motion unit  103  is a support base  112  for the third modular motion unit  114 . While the support base  112  travels along the X-axis, the modular motion unit  114  is oriented vertically, so that its carriage  116  travels along the Z-axis.  
         [0021]     In operation, a work surface, such as a circuit board (not shown), is attached to the carriage  102  thereby being positioned within the robot, or positioner unit,  101 . A tool (not shown), such as a solder dispenser, is mounted on the carriage  116  of the modular motion unit  114 . Under supervision of a computer controlled-algorithm, for example, the work surface (e.g., the circuit board) and the tool (e.g., the solder dispenser) are moved using the three modular motion units so that solder can be applied at appropriate locations on the circuit board. In addition to solder dispensing, the positioner unit  101  may be used in a variety of manners, such as, for example, epoxy dispensing, flux dispensing, and other tools in addition to dispensing tools.  
         [0022]     Computer control of robots and programming tool-control routines in automated equipment are well understood by one of ordinary skill in this field. The provision of appropriate computers, controllers, motors, encoders and their interconnection to accomplish accurate and repeatable motor control can be accomplished according to conventional techniques and procedures.  
         [0023]      FIG. 2  depicts the three modular motion units without the presence of the frame legs  104 ,  108 , splash guard  105 , and base  100 . The extruded frame  203  of the Y-axis unit  202  is shown with its carriage  102 , a linear guide  204 , and a motor  206 . Similarly, the X-axis unit  103  and the Z-axis unit  114  are depicted as well. The X-axis unit  103  has its own linear guide  214  and motor  216  attached to its frame  215  as well. Similarly, the Z-axis unit  114  includes a separate motor  226 , linear guide  224  and carriage  116 .  
         [0024]     In particular,  FIG. 2  illustrates that the modular motion unit  202 , for example, is designed such that it is not directly connected to another modular motion unit  103 ,  114 . Thus, a drive cable of the modular motion unit  202  is not directly connected to any portion of the positioner device  101  that moves in one of the other axes of motion. Similarly, the respective drive cables of the other modular motion units  103 ,  114  also are not directly connected with some other portion of the positioner device  101  that moves along a different axis of motion.  
         [0025]      FIGS. 3 and 4  depict a more detailed view of any of the modular motion units ( 103 ,  114 ,  202 ) according to one embodiment of the present invention. For convenience,  FIG. 3  will be described as a top view and  FIG. 4  as a bottom view. However, in practice, each modular motion unit can be oriented in any manner and the terms “top” and “bottom” or other terms of spatial orientation used herein should not be viewed as limiting.  
         [0026]     In  FIG. 3 , an extruded metal frame  301  is shown which provides the underlying base structure, or framework, for the modular motion unit  300 . On this base structure, a motor  302  is attached that is under computer control to effect motion of the carriage  312 . The carriage  312  rides along a linear guide  304  that is also attached to the underlying extruded frame  301 . In general, linear guides and carriages are known and one of ordinary skill will readily appreciate that through the use of appropriate devices such as, for example, ball-bearings and guide tracks, motion of the carriage  312  can be limited to linear motion along the major axis of the linear guide  304 .  
         [0027]     Along each end of the linear guide  304 , there is a bumper  308 ,  310  to stop and/or cushion the travel of the carriage  312 . A “home switch”  306  is shown near the bumper  308 ; the switch  306  interacts with the flange  330  to detect when the carriage  312  is positioned in a known or “home” position. A number of pulleys  314 ,  316 ,  318 ,  326  and  324  define the travel path of a drive cable  404  which moves the carriage  312 . A tensioner unit  322 , described in more detail later, and a cable tie-off  320  define the starting and endpoints of the drive cable  404 . The tensioner  322  operationally engages the channel  340  which, in this exemplary embodiment, is C-shaped.  
         [0028]     The drive cable  404 , which may advantageously be a nylon-coated, multi-strand steel cable, has a ball  329  at one end that engages a hole  328  of the tensioner  322 . The cable  404  is held in position by the ball  329  and travels to and around the pulley  316  and then back towards the pulley  326 . From underneath the unit  300 , the cable  404  re-emerges at the pulley  318  and travels towards and around the pulley  314 . The cable  404  ends at the tie-off area  320  that can be two screws over which the cable  404  is arranged as a figure-eight and the screws tightened.  
         [0029]     From the bottom view of  FIG. 4 , the path of the cable  404  can be seen to start at the pulley  326 , travel to the pulley  402 , return towards the pulley  324 , and then wrap around the motor-driven spool  406 . The cable  404  leaves the spool  406  and then travels to the pulley  318 . The number of wraps  408  around the spool  406  depends on the amount of travel permitted by the modular motion unit  300 . For example, a wrap  408  of eleven turns would be sufficient to allow motion unit  300  to have a carriage  312  that travels approximately seventeen inches, assuming that a {fraction (1/16)} inch cable  404  is used to wrap around a one inch spool  406  in which there is a 2:1 drive ratio such that one inch of cable  404  leaving the spool  406  causes the carriage  312  to move ½ inch. A skilled artisan would readily recognize that other cable sizes, spool sizes, number of turns, and drive ratios may be selected to provide a variety of different modular motion units without departing from the scope of the present invention.  
         [0030]     The pulleys and pulley paths are arranged to minimize wear on the cable  404 . For example, if a cable  404  having a {fraction (1/16)} inch diameter is used, then a pulley (e.g.  402 ) having a diameter of approximately fifteen times this size or more will decrease the bend angle on the cable  404  as it travels around the pulley  402  and, thereby, reduce stress on the cable  404 . Also, maximizing the distance between pulleys, such as between pulleys  402 ,  324 , and  326  (see  FIG. 4 ) reduces stress on the cable  404  as well. The greater the distance between pulleys, the less the cable  404  must flex when entering or leaving a pulley. Additionally, when appropriate, pulleys are arranged so that the cable  404  travels in a single plane. For example, the pulleys  314  and  318 , and  316  and  326  are positioned such that the cable  404  travels substantially in a horizontal plane.  
         [0031]     Even when the path of the cable  404  is controlled as described above, the stress and forces on the cable  404  can cause its tension to change over time. Because the programmed routines of the computerized controls of the positioner unit  101  assume the cable  404  of a motion unit (e.g.,  300 ) is under a particular tension, routine maintenance on the cable  404  is typically performed to adjust its tension. Historically, re-tensioning a cable has required special tools and training to ensure proper adjustment. In contrast, embodiments of the present invention include a tensioner  322  arranged within the cable path that can be used to re-tension the cable  404  without special tools or training.  
         [0032]      FIG. 5  depicts a more detailed view of the tensioner  322 . The tensioner  322  includes a flange  503  having a hole that engages the ball-end  329  of the cable  404  (as shown in  FIG. 3 ). As previously mentioned, the tensioner  322  rides in the channel  340  that has roughly a C-shaped cross-sectional profile. If the tensioner  322  moves away from the motor  302  in  FIG. 3 , then the drive cable  404  gets tighter and, conversely, if the tensioner  322  moves towards the motor  302 , then the cable  404  becomes more slack. The exemplary tensioner  322  of  FIG. 5  is constructed of two pieces that sandwich the two upper flanges  341 ,  342  of the channel  340 . In operation the top piece  513  of the tensioner  322  sits above the channel  340  and the bottom piece  511  of the tensioner  322  sits within the channel  340 . By way of the two screws  504 ,  506  the two pieces  511 ,  513  of the tensioner  322  are tightened together (or loosened). When the screws  504 ,  506  are tightened, the tensioner  322  pinches the upper flanges  341 ,  342  such that the tensioner  322  cannot move. By loosening the screws  504 ,  506 , the tensioner  322  is free to move along the channel  340 . To assist in this movement, and to keep the tensioner  322  from becoming cocked, or angled, within the channel  340 , one or more ball bearings  510  can be attached to the bottom piece  511  of the tensioner  322  to act as a guide and to reduce friction.  
         [0033]     A spring  512  is attached to the tensioner  322  such that the spring  512  is under compression and imparts a force on the tensioner  322 . This spring  512  has one end  514  that cannot move relative to the drive cable and another end  516  that is in contact with the tensioner  322 . For example, the spring  512  is positioned within the channel  340  with a stop  513  that prevents the end  514  from moving. The other end  516  engages the tensioner  322  simply by contacting the tensioner  322  or by being fixedly attached to the tensioner  322 . When the screws  504 ,  506  are loose, the spring  512  acts to move the tensioner  322  away from the end  514 , thereby tensioning the drive cable  404 . Once the tensioner  322  no longer moves, the screws  504 ,  506  are tightened to hold the tensioner  322  in place. Thus, an untrained operator can accurately re-tension the drive cable  404  without special tools or training.  
         [0034]     The nylon-coated, steel cables often used in motor-driven motion units in accordance with embodiments of the present invention are typically operated at approximately 10 pounds of tension which correlates to moving a slack cable  404  of this type approximately {fraction (1/10)} inch. A 5 to 8 inch spring  512  having a spring rate of approximately 1.5 pounds/inch will readily accomplish uniform tensioning of the cable  404  for the expected mechanical lifetime of the modular motion unit  300 .  
         [0035]     While some embodiments of the present invention may use various drive mechanisms to move a carriage (e.g.,  312 ), using a cable drive has a number of advantages. Instead of requiring a specific length ball screw, lead screw, rack and pinion, or belt for a given travel length, cable can be bought in bulk and cut to size. Additionally, cable has advantages over traditional drive elements such a ball and lead screws that have high inertia which requires a bigger motor and power source to move the same loads as a cable. Also, rack and pinion and both types of screws are difficult to align; belts are typically made of highly elastic materials that creep in time and slide on their drive sprockets thus being inaccurate both statically and dynamically.  
         [0036]      FIGS. 3 and 4  illustrate an exemplary modular motion unit  300 ; however, the location of the linear guide  304 , the motor  302  and the various pulleys can be modified without departing from the scope of the present invention. For example,  FIGS. 6 and 7  depict a top and bottom view of a modular motion unit  600  having the motor  602  located opposite the carriage  604 . Because the extruded base structure  606  of a modular motion unit  600  is used to attach the unit to an underlying robot framework, it is beneficial to have alternative motor and carriage arrangements to address potential space limitations that might be encountered at a particular work area.  
         [0037]     Similar numbers in  FIGS. 6 and 7  reference similar elements in earlier figures. Other than the motor placement, the modular motion unit  600  of  FIGS. 6 and 7  is substantially similar in structure to earlier described embodiment. In particular, there is an extruded base structure  606  having a linear guide  304  over which the carriage  604  travels between the bumpers  308 ,  310 . Because of the different location of the motor  602  and spool  704 , the pulleys  610 ,  614 ,  616  are arranged differently to provide an appropriate path for the drive cable  702 . In this alternative configuration the path for the drive cable  702  is designed while accounting for the concerns expressed earlier relating to cable maintenance and longevity. Similarly, the tensioner unit  322  may also be present in order to provide a way for an untrained operator to properly retention the drive cable  702 .  
         [0038]     While the invention has been illustrated by the description of certain embodiments and while these embodiments have been described in considerable detail, there is no intention to restrict nor in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those Who are skilled in the art.  
         [0039]     Therefore, the invention in its broadest aspects is not limited to the specific details shown and described. Consequently, departures may be made from the details described herein without departing from the spirit and scope of the claims which follow.