Abstract:
A drive system for a robot includes a track including opposed sidewalls, an electrified rail positioned between the sidewalls, a shoe mounted on the robot for contacting the electrified rail providing power to the robot, a drive motor mounted on the robot, a rotating drive member, the drive member engaging the track to drive the robot when the drive motor is actuated, means for coupling the drive member to the drive motor and means for increasing the friction between the drive system and the track at selected locations along the track.

Description:
TECHNICAL FIELD  
       [0001]     The invention relates to track mounted trolleys such as delivery robots and in particular to an electrically powered, belt-type drive for a track mounted delivery robot.  
       BACKGROUND OF THE INVENTION  
       [0002]     Track mounted trolley systems are employed in a wide variety of applications including automated sorting and delivery systems in which delivery robots are utilized to receive and sort items to a variety of locations. One such system employing a plurality of track mounted robots in a sorting and delivery system is described in commonly assigned U.S. patent application Ser. No. 10/142,348 for an Apparatus and Method for Mail Sorting, filed Feb. 27, 2003, the disclosure which is incorporated herein by reference for all purposes. Various means of driving such track mounted units are known, including chain drives, belt drives and friction type traction drives where a wheel or pulley is rotated against the track to drive the unit. In many cases, these drive systems suffer from a number of drawbacks including excessive noise, inability to precisely position the trolley for loading or unloading, and excessive component wear. These drawbacks tend to be compounded when the unit being driven is heavy, requiring more force to accelerate, decelerate and precisely position the unit. The invention described herein addresses these shortcomings.  
       SUMMARY OF THE INVENTION  
       [0003]     In accordance with the invention, a drive unit for a track mounted delivery robot includes a drive motor mounted on the robot coupled to at least one drive wheel through a motor pulley and a resilient drive belt formed from a relative soft material so as to have a high coefficient of friction. The drive wheel is positioned to engage the track to drive the robot and configured to match the profile of the track. The drive wheel and resilient belt are configured such that the belt does not substantially engage the track as the drive wheel engages the track to drive the robot. As used herein, the phrase “does not substantially engage” means that the belt does not normally contact the track, however, it does not exclude incidental contact resulting from variations in clearances and manufacturing tolerances. In order to facilitate rapid acceleration, deceleration and precise positioning of the robot, one or more track extensions are mounted on the track at selected locations. The extensions are mounted on the side of the track in locations where the resilient belt will engage the extension to provide additional driving or braking force, thereby enhancing the ability of the system to rapidly start, stop and precisely position the robot.  
         [0004]     A track mounted robot according to the invention includes a frame, a drive motor mounted on the frame, and at least one drive wheel coupled to the drive motor and mounted on the frame to engage the track and drive the robot when rotated. The robot further includes means for increasing the friction between the drive system and the track in selected locations along the track. In one variation, the robot includes a motor pulley coupled to the drive motor and a drive belt extending around the motor pulley and the drive wheel, the drive wheel and belt being configured such that the drive belt does not substantially engage the track as the robot travels along the track.  
         [0005]     The drive wheel includes a belt groove extending circumferentially around the drive wheel such that the drive belt drives the drive wheel without substantial contact with the track. The robot also includes one or more shoes or brushes mounted on the frame, the shoe(s) being configured to contact an electrified rail positioned between opposed sides of the track to provide electric power to the robot. Preferably, the robot is provided with an onboard power supply such as a battery or, capacitor having electrical storage capacity sufficient to provide power to drive the robot along the track. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a partial perspective view of a drive system for a track mounted robot in accordance with one aspect of the invention;  
         [0007]      FIG. 2  is an enlarged view of the electrified rail and shoes of the system of  FIG. 1 ;  
         [0008]      FIG. 3  is a partial side view of a robot equipped with the system of  FIG. 1 ;  
         [0009]      FIGS. 4 and 5  are partial cross-sections of the track, drive wheels and idler wheels of the system of  FIG. 1 ;  
         [0010]      FIG. 6  is a partial perspective view of an alternative drive system according to the invention;  
         [0011]      FIG. 7  is a partial front view of the drive system of  FIG. 6 ;  
         [0012]      FIG. 8  is a partial cross-section of the drive system of  FIG. 6 ;  
         [0013]      FIG. 9  is a schematic representation of a timing belt utilized in the system of the invention; and  
         [0014]      FIG. 10  is a partial side view of a track and extension according to the invention.  
         [0015]      FIG. 11  is a perspective view of another alternative drive system according to the invention; and  
         [0016]      FIG. 12  is a partial front view of the drive system of  FIG. 11 . 
     
    
     DETAILED DESCRIPTION  
       [0017]     Referring to  FIGS. 1-4 , a delivery robot  10  configured to receive and transport articles to one of a number of selected destinations includes a frame  12  and a plurality of guide wheels  14  along the lower edge of frame  12  for supporting the robot on a shelf or similar structure (not shown) positioned below the robot as the robot travels along a track  16 . Track  16  includes a flat top wall  20  and a pair of trough shaped sidewalls  22  that form a downwardly opening channel  18 . One or more electrified rails  24  mounted on the inside surface of top wall  20  extend downwardly into channel  18  to provide power to robot  10 . As shown, robot  10  is equipped with a plurality of shoes or brushes  26 , each configured to contact an electrified rail  24  to provide power to robot  10 .  
         [0018]     Robot  10  is equipped with a drive unit  15  which includes an electric motor  28  mounted on frame  12  with a motor pulley  30 , a drive belt  34  that extends around motor pulley  30  and a pair of drive wheels  36  that engage track  16  to drive robot  10  when motor  28  is actuated. Belt  34  is preferably formed from a resilient, relatively soft material such as a synthetic rubber so that at least the outside surface of the belt has a high coefficient of friction. An adjustable idler pulley  32  provides means for setting and adjusting the tension on belt  34 . As best illustrated in  FIG. 4 , each of drive wheels  36  are mounted on an axle  37  and formed with a face  38  and relieved (sloped) corners or shoulders  40  such that face  38  substantially matches the profile of trough-shaped sidewall  22  of track  16 . A belt groove  42  formed in face  38  is sufficiently recessed to allow belt  34  to drive wheels  36  with little or no contact between belt  34  and track  16  during normal operations.  
         [0019]     In order to maintain drive wheels  36  firmly in contact with track  16 , a pair of idler wheels  44  mounted on frame  12  are positioned to contact sidewall  22  of track  16  opposite drive wheels  36 . Idler wheels  44 , similar to drive wheels  36 , are each formed with a circumferential face  48  and shoulders  50  that are configured to match the right-hand profile of trough-shaped sidewall  22  of track  16 . Each of idler wheels  44  is mounted on an axle  45  which in turn is mounted in a C-shaped bracket  43 . As illustrated, a pair of springs  46  are held in compression against bracket  43  to bias idler wheels  44  against track  16  with sufficient force to hold drive wheels  36  firmly in contact with track  16 .  
         [0020]     Motor  28  is preferably a variable speed, DC motor equipped with an encoder that registers the revolutions turned by the motor and transmits a signal to an onboard microprocessor  31  which uses the encoder signal to measure movement of the robot  10  along track  16 . Microprocessor  31  controls the operation of robot  10 , including motor  28  which is powered directly from electrified rails  24  or from an onboard rechargeable storage device  33  such as a battery or a high power capacitor commonly known as an ultra capacitor. Capacitive power supplies are disclosed in U.S. Pat. No. 5,528,121 issued Jun. 18, 1996 and U.S. Pat. No. 5,532,572 issued Jul., 2, 1996 for a “Storage Capacitor Power Supply,” U.S. Pat. No. 5,604,426 issued Feb. 18, 1997 for an “Electric Apparatus with a Power Supply Including an Electric Double Layer Capacitor” and U.S. Pat. No. 5,783,928 issued Jul. 21, 1998 for a “Storage Capacitor Power Supply” the contents of which are incorporated herein by reference.  
         [0021]     In many applications, it is desirable to minimize the length and number of electrified rails  24  required to operate the system. Thus, in a preferred embodiment, the onboard rechargeable storage device  33  is charged as robot  10  travels along selected, relatively short segments of the total length of track  16  that are equipped with a length of electrified rail  24 . Ideally, the onboard rechargeable storage device  33  has sufficient capacity to enable robot  10  to complete a delivery cycle without recharging, thereby reducing the length of electrified rail  24  required to operate the system.  
         [0022]     During operation, robot  10  is required to accelerate and decelerate quickly at various locations along track  16 . For example, robot  10  is required to stop rapidly and precisely to deliver objects or articles at a selected destination. Robot  10  may also be required to accelerate to move rapidly along long stretches where track  16  in order to reduce cycle time. Turning to  FIG. 5 , in order to enhance the capability of robot  10  to rapidly accelerate or decelerate at selected locations along track  16 , track extensions  52  are mounted on track  16  at such locations. As illustrated, track extension  52  comprises a shim-like strip mounted in the trough portion of sidewall  22  of track  16 .  
         [0023]     Extensions  52  may be constructed from a suitable plastic, metal or a synthetic rubber. When robot  10  travels though a section of track  16  where an extension  52  has been installed, belt  34  contacts the extension, creating additional frictional force between track  16  and drive unit  15 . The additional frictional force enhances the capability of robot  10  to accelerate or decelerate quickly in selected areas of track  16  where extensions  52  have been installed. Preferably, extensions  52  are provided with ends that taper in a width wise direction to facilitate engagement of belt  34  with the extension. Preferably, the thickness of extension  52  is selected to provide sufficient contact between belt  34  and extension  52  such that belt  34  and wheels  36  simultaneously contact track  16  to drive robot  10 .  
         [0024]     The use of extensions  52  in combination with drive unit  15  provides a number of advantages. Since belt  34  is formed from a resilient, relatively soft material,.continuous contact with track  16  would result in excessive wear of the belt. Thus, the use of extensions  52  only where additional friction between drive unit  15  and track  16  is required to enhance the ability of robot  10  to accelerate and decelerate rapidly increases the useable life of belt  34  while simultaneously enhancing the travel capability of robot  10 . This is particularly advantageous in applications where robot  10  is heavy, in which case a substantial amount of force is required to abruptly change the velocity of the robot or negotiate a curved section of track. Further, since belt  34  is formed from a relatively soft material, noise levels are significantly reduced during operation.  
         [0025]     Referring now to  FIGS. 6-8 , in another embodiment, robot  60  employs a modified drive unit  62  configured to provide additional clearance between the robot and a track  64 . As shown, track  64  is substantially identical to track  16  of  FIGS. 1-4 . Modified drive unit  62  includes an electric motor  66 , motor pulley  68  and a first drive belt  65  that extends around motor pulley  68  to drive a pair of intermediate pulleys  70  mounted on axles  72 . As shown, a pair of drive wheels  74  mounted on the upper ends of axles  72  are positioned to engage track  64  to drive robot  60 . A second, resilient drive belt  78 , formed from a relatively soft material extends around drive wheels  74  engaging a belt groove  76  in each of drive wheels  74 . Drive wheels  74  and drive belt  78  function in substantially the same manner as described in connection with drive belt  34  and drive wheels  36  described above. In particular, resilient drive belt  78  engages extensions  52  in the same manner as drive belt  34 . Likewise, a pair of idler wheels  80 , mounted on axles  82  are biased against track  64  with springs  84  to function in the same manner as idler wheels  44 , described above, to hold drive wheels  74  and/or belt  78  in contact with track  64 .  
         [0026]     Referring now to  FIGS. 9 and 10 , a double-sided timing belt  90  having a plurality of teeth or ridges  92  separated by grooves  94  may be substituted for belt  34  or belt  78 . In this embodiment, a rack-shaped shim or extension  96  having a plurality of teeth and grooves  98  and  100 , respectively, is substituted for extension  52 . Similar to belts  34  and  78 , double sided timing belt  90  is formed from a resilient, relatively soft material in order to minimize noise during operation and to aid in indexing teeth  92  to the corresponding grooves  100  of extension  96 . To further aid in indexing double-sided timing belt  90  to extension  96 , the length of teeth  98  of extension  96  is progressively reduced adjacent the ends of the extension. The combination of double-sided timing belt  90  and track extension  96  functions in substantially the same manner as belt  34  and extension  52  to aid in accelerating and positioning robot  10 . Thus, as in the case of extension  52 , extensions  96  are mounted on track  102  at locations where robot  10  may be required to accelerate or decelerate rapidly and/or where precise positioning of robot  10  is required.  
         [0027]     Turning to  FIGS. 11 and 12 , in yet another embodiment, a drive unit  110  includes a pinion gear  118  configured to engage rack-like track extensions  128  at selected locations on track  126 . As illustrated drive unit  110  includes one or more drive wheels  112  mounted on a shaft  114  along with a drive gear  116  and pinion gear  118 . An electric motor  120  drives shaft  114 , drive wheels  112  and pinion gear  118  with a timing belt  122  that passes around motor pulley  121  and drive gear  116 . One or more opposed idler wheels  124  are biased against track  126  to hold drive wheels  112  in contact with the rail. As illustrated, pinion gear  118  is mounted on shaft  114  above drive gear  116  and configured to engage the teeth  130  of rack-like track extensions  128  mounted on track  126  in those areas where robot  10  is required to rapidly accelerate and decelerate. In order to facilitate indexing of pinion gear  118  with teeth  130  of extension  128 , the length of teeth  130  may be progressively reduced adjacent the ends of the extension in the manner illustrated in  FIG. 10 .  
         [0028]     While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. Thus, while the invention has been described in connection with an automated delivery robot, the drive system described herein may be used in connection with a variety of track mounted trolleys. All such variations and additions are specifically contemplated to be with the scope of the invention. It is, therefore, intended that the appended claims encompass any such modifications or embodiments.