Patent Publication Number: US-2020290501-A1

Title: Compact Payload Stopper for Mobile Robot Comprising Conveyor

Description:
SUMMARY 
     Embodiments of the invention relate in general to a payload stopper for a mobile robot. More specifically, embodiments of the invention relate to a compact payload stopper for a mobile robot. Even more specifically, embodiments of the invention relate to a payload stopper on a mobile robot. Even more specifically, embodiments of the invention relate to a compact payload stopper for a conveyor on an autonomous mobile robot. 
     A compact payload stopper configured to stop a payload from moving from a position on a conveyor on a mobile robot includes: an interface assembly that serves as a main structural member of the payload stopper, the interface assembly attaching the payload stopper to the mobile robot, the payload stopper configured to stop the payload from moving off the mobile robot; a stopper blade assembly connected to the interface assembly so as to allow the stopper blade assembly to pivot about an axis of the interface assembly, the stopper blade assembly comprising a stopper blade configured to regulate movement of the payload, the stopper blade assembly configured to have a disengaged position that allows for one or more of moving a payload onto the robot and moving a payload off the robot, the stopper blade assembly further configured to have an engaged position that stops the payload from moving off the robot; and a motor assembly comprising a motor, the motor assembly connected to the interface assembly, the motor assembly configured to apply a force to the stopper blade assembly, causing the stopper blade assembly to rotate into a desired position of the engaged position and the disengaged position. 
     A compact payload stopper configured to stop a payload from moving from a position on a conveyor on a mobile robot, includes: an interface assembly that serves as a main structural member of the payload stopper, the interface assembly attaching the payload stopper to the mobile robot, the payload stopper configured to stop the payload from moving off the mobile robot; a stopper blade assembly connected to the interface assembly so as to allow the stopper blade assembly to pivot about an axis of the interface assembly, the stopper blade assembly configured to have a disengaged position that allows for one or more of moving a payload onto the robot and moving a payload off the robot, the stopper blade assembly further configured to have an engaged position that stops the payload from moving off the robot, the stopper blade assembly further comprising a plurality of stopper shoulder screws configured to fasten the stopper blade assembly through a plurality of slots in the interface assembly, the stopper shoulder screws configured to resist rotation of the stopper blade assembly when the payload impacts the stopper blade; a linkage configured to actuate the stopper blade assembly between the engaged position and the disengaged position by converting rotational output of the motor into rotation of the stopper blade assembly; and a motor assembly comprising a motor, the motor assembly connected to the interface assembly, the motor assembly configured to apply a force through the linkage to the stopper blade assembly, causing the stopper blade assembly to rotate into a desired position of the engaged position and the disengaged position. 
     A compact payload stopper configured to stop a payload from moving from a position on a conveyor on a mobile robot includes: an interface assembly that serves as a main structural member of the payload stopper, the interface assembly attaching the payload stopper to the mobile robot, the payload stopper configured to stop the payload from moving off the mobile robot; a stopper blade assembly connected to the interface assembly so as to allow the stopper blade assembly to pivot about an axis of the interface assembly, the stopper blade assembly configured to have a disengaged position that allows for one or more of moving a payload onto the robot and moving a payload off the robot, wherein the disengaged position folds the stopper blade assembly down beneath the height of the conveyor, the stopper blade assembly further configured to have an engaged position that stops the payload from moving off the robot, wherein the payload stopper is configured to provide feedback when the payload stopper is in the engaged position that it is safe for the robot to move, wherein the payload stopper is further configured to provide feedback when it is in the disengaged position that it is not safe to move; a linkage configured to actuate the stopper blade assembly between the engaged position and the disengaged position by converting rotational output of the motor into rotation of the stopper blade assembly; and a motor assembly comprising a motor, the motor assembly connected to the interface assembly, the motor assembly configured to apply a force through the linkage to the stopper blade assembly, causing the stopper blade assembly to rotate into a desired position of the engaged position and the disengaged position, wherein the payload stopper is installed on one or more of a front side and a back side of the robot. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings provide visual representations which will be used to more fully describe various representative embodiments and can be used by those skilled in the art to better understand the representative embodiments disclosed herein and their inherent advantages. In these drawings, like reference numerals identify corresponding elements. 
         FIG. 1A  is an exploded drawing in perspective view of a payload transport system for a mobile robot comprising a payload stopper. 
         FIG. 1B  is a drawing in perspective view of a fully assembled payload transport system for a mobile robot comprising a payload stopper. 
         FIG. 2  is an exploded view depicting principal components of a payload stopper for a mobile robot. 
         FIG. 3A  is an exploded view depicting individual components of a payload stopper for a mobile robot. 
         FIG. 3B  is a drawing of a fully assembled payload stopper for a mobile robot. 
         FIG. 4  is a drawing in cross-section view of a payload transport system comprising a payload stopper for a mobile robot. 
         FIG. 5A  is a cross-section detail view showing a stopper blade assembly of a payload stopper in an engaged position to stop the payload from moving. 
         FIG. 5B  is a cross-section detail view showing a stopper blade assembly of a payload stopper in a disengaged position to allow the payload to move. 
         FIG. 5C  is a detail view of the payload stopper for a mobile robot showing an aligned orientation of the receiving safety switch relative to the transmitting safety switch when the stopper blade assembly is in the engaged position. 
         FIG. 5D  is a detail view of the payload stopper for a mobile robot showing the orientation of the receiving safety switch relative to the transmitting safety switch when the stopper blade assembly is in the disengaged position. 
         FIG. 6  is an exploded view of a stopper blade assembly of a payload stopper for a mobile robot. 
         FIG. 7  is an exploded view of a motor assembly of the payload stopper for a mobile robot. 
         FIG. 8  is an exploded view of the interface assembly of the payload stopper for a mobile robot. 
     
    
    
     DETAILED DESCRIPTION 
     While the present invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail one or more specific embodiments, with the understanding that the present disclosure is to be considered as exemplary of the principles of the invention and not intended to limit the invention to the specific embodiments shown and described. In the following description and in the several figures of the drawings, like reference numerals are used to describe the same, similar or corresponding parts in the several views of the drawings. 
     This invention relates to the transport of a payload by mobile robots in an industrial setting, and entails industrial control and automation, industrial safety, industrial conveyor systems. “Conveyor” as it is referred to in this context includes but is not limited to one or more of a roller style conveyor system and a belt conveyor system. Preferably, although not necessarily, the conveyor comprises a roller style conveyor system. 
     The payload stopper for a mobile robot comprises a stopper blade assembly, the stopper blade assembly configured to have a disengaged position that allows for a payload to be transported from the accessory onto other equipment without interference, the stopper blade assembly further configured to have an engaged position that stops the payload from moving off the robot. 
     The stopper blade assembly rotates up when the mobile robot is navigating so as to contact the payload and hold it in place when the mobile robot is braking. Conversely, the stopper blade assembly folds down beneath the height of the conveyor during one or more of moving a payload onto the robot and moving a payload off the robot. The payload stopper also comprises components configured to actuate its structure. The payload stopper further includes components configured to sense a position of the payload stopper, providing positional feedback to one or more of safety system of the mobile robot and electronics that control actuation of a stopper blade assembly. 
     A payload stopper is installed on one or more of a front side and a back side of the robot relative to a conveyor onto which the payload is being moved. When engaged, the payload stopper is configured to do one or more of stop unloading of a payload by the conveyor and stop the payload from falling off of the moving robot. 
     The payload stopper for a mobile robot is configured to stop a payload from moving from a position on a conveyor on top of a mobile robot. The payload stopper for a mobile robot is further configured to enable the autonomous mobile robot to maintain control of the payload while the robot does one or more of slow down and stop. The payload stopper for a mobile robot is further configured to enable the autonomous mobile robot to maintain control of the payload upon braking. 
       FIG. 1A  is an exploded drawing in perspective view of a payload transport system comprising a payload stopper for a mobile robot. 
     A payload transport system  100  comprises a mobile robot  105 . For example, the mobile robot  105  comprises a Freight1500 mobile robot, manufactured by Fetch Robotics of San Jose, Calif. (www.fetchrobotics.com). For example, the mobile robot  105  comprises a Freight500 mobile robot, manufactured by Fetch Robotics of San Jose, Calif. (www.fetchrobotics.com). For example, the mobile robot  105  comprises one or more wheels  110 . For example, as depicted, the mobile robot  105  comprises six wheels  110 . (Three of the six wheels  110  are omitted from the figure because they are hidden from view.) For example, the mobile robot  105  comprises mobility hardware other than wheels (not shown). 
     The payload transport system  100  further comprises a conveyor  115  that is attached to the mobile robot  105 . Typically, the conveyor  115  is physically attached to the mobile robot  105 . Typically, and as depicted, the conveyor  115  sits on top of the mobile robot  105 . The conveyor  115  comprises a pallet  120 . The pallet  120  comprises a payload  125 . For example, the payload  125  comprises one or more items obtained to fulfill an order by a customer. For example, the payload  125  comprises one or more items received from a supplier. For example, the payload  125  comprises one or more items returned by a customer. 
     The conveyor  115  further comprises one or more of a left frame member  130  and a right frame member  135 . As illustrated, the conveyor  115  comprises both the left frame member  130  and the right frame member  135 . The conveyor  115  further comprises a plurality of rollers  140 . The rollers  140  are mounted to one or more of the left frame member  130  and the right frame member  135 . Preferably, but not necessarily, the plurality of rollers  140  are mounted to both the left frame member  130  and the right frame member  135 . Preferably, but not necessarily, the rollers  140  span between the left frame member  130  and the right frame member  135 . One or more of the left frame member  130  and the right frame member  135  serve as structural supports for the rollers  140 . The rollers  140  work together to support one or more of the pallet  120  and the payload  125 . When desired, when the payload transport system  100  is stationary, the conveyor  115  can cause the payload  125  to be one or more of unloaded off the pallet  120  and loaded onto the pallet  120 . For example, the conveyor  115  can cause the payload  125  to be unloaded off the pallet  120  in a controlled unloading operation. Typically, although not necessarily, the conveyor  115  does this (causing of the payload  125  to be one or more of unloaded and loaded) using the rollers  140 . The rollers  140  are powered to spin, thereby causing the payload  125  to be one or more of unloaded from the robot  105  in a controlled unloading operation and loaded onto the robot  105 . For example, the payload is one or more of unloaded off the pallet  120  in a controlled unloading operation and loaded onto the pallet  120 . For example, a pallet  120  sitting on the robot  105  is unloaded when the rollers  140  spin. Alternatively, a pallet  120  sitting on an adjacent stationary conveyor is loaded onto the robot  105  when the rollers  140  spin. 
     As depicted, the payload  125  sits on top of the pallet  120 . When the mobile robot  105  moves, the conveyor  115  moves, and thus the pallet  120  moves and thus the payload  125  moves. 
     The conveyor  115  further comprises a payload stopper  145  configured to stop the pallet  120  from moving off the conveyor  115 , thereby preventing the payload  125  from moving off the conveyor  115 . The payload stopper is installed on one or more of a front side  117  and a back side  118  of the robot  105 . 
     The payload stopper  145  comprises a stopper blade  150  that runs along the width of the rollers (not shown in this figure). The stopper blade  150  regulates movement of the payload  125 . 
       FIG. 2  is an exploded drawing depicting principal components of a payload stopper  145  for a mobile robot (not shown in this figure). The payload stopper  145  comprises an interface assembly  202  that serves as a main structural member of the payload stopper  145 . The payload stopper  145  further comprises a stopper blade assembly  205 . The stopper blade assembly  205  is free to pivot about an axis  207 . The stopper blade assembly  205  is fastened to the interface assembly  202  using one or more of stopper shoulder screws  210 , stopper washers  215 , and stopper lock-nuts  220 . The three stopper shoulder screws  210  fasten the stopper blade assembly  205  through three slots  230 A,  230 B, and  230 C in the interface assembly  202 . The stopper shoulder screws  210  are configured to resist rotation of the stopper blade assembly  205  when the payload  120  impacts the stopper edge 
     A motor assembly  235  comprises a motor  237 . The motor assembly  235  mounts to the interface assembly  202  using motor assembly fasteners  240 . A linkage  245  connects to the stopper blade assembly  205  using a linkage shoulder screw  250  and using a washer  255 . For example, the linkage  245  comprises a mechanical linkage  245 . Using the linkage  245 , the motor assembly  235  rotates and applies a force to the stopper blade assembly  205 , causing it to rotate about the pivot axis  207  into a desired position, the desired position comprising one of an engaged position (not shown in this figure, visible in  FIGS. 5A-5B ) and a disengaged position (not shown in this figure, visible in  FIGS. 5A-5B ). 
       FIG. 3A  is an exploded drawing showing components of a payload stopper  145  for a mobile robot (not shown in this figure). An aspect of the invention and of the operation of the payload stopper  145  is the method by which the stopper blade assembly  205  is actuated between the upwardly rotated or engaged position (position  505  in  FIG. 5  below) and a downwardly rotated or disengaged position (position  510  in  FIG. 5  below). The interface assembly  202  comprises the interface weldment  301 . The interface weldment  301  attaches the payload stopper  145  to the mobile robot (not shown in this figure). The payload stopper  145  again comprises the interface assembly  202  that serves as a main structural member of the payload stopper  145 . 
     The interface assembly  202  further comprises a plurality of stopper ribs  302 ,  304 ,  306 . The stopper ribs  302 ,  304 ,  306  structurally connect the stopper blade assembly  205  to the interface assembly  202 . The stopper ribs  302 ,  304 ,  306  serve a purpose of transferring an impact of one or more of the pallet  120  and the payload  125  from the stopper blade  150  through the stopper shoulder screws  210  to the interface assembly  202 . As depicted, the interface assembly  202  further comprises a left stopper rib  302 , a middle stopper rib  304 , and a right stopper rib  306 . One or more of the left stopper rib  302 , the middle stopper rib  304 , and the right stopper rib  306  attach to the interface weldment  301  using a plurality of rib fasteners  308 . A plurality of pivot bushings  310  are press-fit into each of the left stopper rib  302 , the middle stopper rib  304 , and the right stopper rib  306 . As depicted, two pivot bushings  310  are press-fit into each of the left stopper rib  302 , the middle stopper rib  304 , and the right stopper rib  306 . 
     The stopper blade assembly  205  comprises the stopper blade  150  that runs along the width of the rollers (not shown in this figure). The stopper blade  150  regulates movement of the payload (not shown in this figure). The stopper blade assembly  205  further comprises a left pivot arm  313 A, a middle pivot arm  313 B, and a right pivot arm  313 C. The pivot arms  313 A- 313 C attaches to the interface assembly  202  so as to allow the stopper blade assembly  205  to pivot about the axis  207 . 
     At least one pivot arm  313 A- 313 C is attached to at least one stopper rib  302 . Preferably, but not necessarily, each pivot arm  313 A- 313 C is attached to each stopper rib  302 . The stopper shoulder screws  210 , the stopper washers  215 , and the stopper lock-nuts  220  fasten the left pivot arm  313 A to the left stopper rib  302  through a left pivot point  314 A and a left curved slot  230 A. Similarly, the stopper shoulder screws  210 , the stopper washers  215 , and the stopper lock-nuts  220  fasten the middle pivot arm  313 B to the middle stopper rib  304  through a middle pivot point  314 B and a middle curved slot  230 B. In a like manner, the stopper shoulder screws  210 , the stopper washers  215 , and the stopper lock-nuts  220  fasten the right pivot arm  313 C to the right stopper rib  306  through a right pivot point  314 C and a right curved slot  230 C. A purpose of the stopper washers  215  is to distribute the pressure of the stopper lock-nuts  220  over the surface of each pivot arm  313 A- 313 C and to minimize loosening of the stopper lock-nuts  220  over time. During a braking scenario when the payload impacts the payload stopper  145 , these stopper shoulder screws  210  are used to transfer the load from where the payload contacts the stopper blade  150  through the three pivot arms  313 A- 313 C to the interface weldment  301 . 
     The pivot arms  313 A- 313 C are attached to the stopper blade  150  using a plurality of pivot arm fasteners  315 . The stopper blade assembly  205  further comprises a linkage mount  316  attached to the stopper blade  150 . The linkage mount  316  attaches to the stopper blade  150  using a plurality of linkage mount fasteners  317 . The stopper blade assembly  205  further comprises a transmitting safety switch  318 . For example, the transmitting safety switch  318  comprises a non-contact safety switch actuator, manufactured by Sick of Waldkirch, Germany (www.sick.com). The transmitting safety switch  318  is held in place by a transmitting safety switch holder  319 . Since the transmitting safety switch holder  319  is also attached to the stopper blade  150 , the transmitting safety switch holder  319  causes the transmitting safety switch  318  to move with the stopper blade  150  when the transmitting safety switch holder  319  is actuated up or down. The transmitting safety switch holder  319  is attached to the stopper blade  150  using a plurality of transmitter holder fasteners  324 . Pressed into the transmitting safety switch holder  319  are a plurality of transmitter threaded inserts  326 . The transmitter threaded inserts  326  are attached to the transmitting safety switch holder  319  by press-fitting. The transmitter threaded inserts  326  use a plurality of transmitter fasteners  330  to mate the transmitting safety switch holder  319  with the transmitting safety switch  318 . 
     The linkage  245  comprises a crank link  332  that on one end is attached to the output shaft  333  of motor  237  with a crank fastener  336  and on the other end is attached to a rocker link  338 . The crank link  332  mates to the rocker link  338  with the use of a linkage shoulder screw  250 , linkage washer  255  and a linkage bushing  340  inserted into the rocker link  338 . For example, the linkage bushing  340  comprises a sleeve bearing with flange, manufactured by Igus of Cologne, Germany (www.igus.com). The linkage bushing  340 , linkage shoulder screws  250 , and linkage washer  255  ensure smooth articulation of the linkage by reducing friction between contact surfaces. The other end of the rocker link  338  attaches to the stopper blade assembly  205  through the linkage mount  316  with a linkage shoulder screw  250 , linkage washer  255  and a linkage bushing  340  that is inserted into the rocker link  338 . The purpose of the linkage mount  316  is to attach the rocker link  338  to the stopper blade assembly  205 . The purpose of the crank link  332  and the rocker link  338  is to actuate the stopper blade assembly  205  between the engaged position  505  and the disengaged position  510  by converting rotational output of the motor  237  into rotation of the stopper blade assembly  205 . For example, the motor  237  comprises a gear motor, manufactured by Source Engineering, Inc. of Santa Clara, Calif. (www.sei-automation.com). Thus the purpose of the motor  237  is to provide an initial source of actuation by converting electrical energy to rotational (mechanical) energy. 
     The payload stopper  145  further comprises a receiving safety switch  342 . The position of the stopper blade assembly  205  relative to the interface weldment  301  is detected through the use of the transmitting safety switch  318  in combination with the receiving safety switch  342 . For example, the receiving safety switch  342  comprises a non-contact safety switch sensor manufactured by Sick of Waldkirch, Germany (www.sick.com). The receiving safety switch  342  is mounted to the interface weldment  301  using a receiving safety switch holder  344 , receiver holder fasteners  346  and receiver fasteners  348  that thread into the receiver threaded inserts  350  of the receiving safety switch holder  344 . The receiving safety switch  342  interfaces electrically with a safety system controller (not shown in this figure) on the mobile robot (not shown in this figure) to ensure that the mobile robot (not shown in this figure) will only be able to drive when the stopper blade assembly  205  is rotated into the engaged position (not shown in this figure). As shown in more detail in  FIGS. 9A-9B  below, the receiving safety switch  342  and transmitting safety switch  318  are mounted relative to each other such that the receiving safety switch  342  will only transmit a signal to a safety controller if the stopper blade assembly  205  is rotated into the engaged position (not shown in this figure). This ensures that the mobile robot payload transport system  100  maintains control of the pallet  120  and payload  125  when the mobile robot payload transport system  100  is navigating in a customer&#39;s facility. 
       FIG. 3B  is a drawing of a fully assembled payload stopper  145  for a mobile robot (not shown in this figure). The payload stopper  145  comprises the stopper blade  150 , the interface assembly  202 , the stopper shoulder screws  210 , the stopper washers  215  (not visible in the upper part of the figure but visible in the middle and lower part of the figure), the stopper lock-nuts  220  the three slots  230 A,  230 B, and  230 C, and the motor assembly  235 , and the linkage  245 . 
       FIG. 4  is a drawing in cross-section view of a payload transport system  100  comprising a payload stopper  145  for a mobile robot  105 . 
     The payload transport system  100  again comprises a mobile robot  105 , the mobile robot  105  again comprising wheels  110 . The mobile robot payload transport system  100  again further comprises a conveyor  115  that is attached to the mobile robot  105 . The conveyor  115  again comprises a pallet  120 . The pallet  120  again comprises a payload  125 . The conveyor  115  again further comprises a payload stopper  145  configured to stop the pallet  120  from moving off the conveyor  115 , thereby preventing the payload  125  from moving off the conveyor  115 . 
       FIG. 5A  is a cross-section detail view  500  of a stopper blade assembly  205  of a payload stopper (not shown in this figure) for a mobile robot (not shown in this figure) in an engaged position  505  to stop the pallet  120  from moving to the right. Also shown are the rollers  140  and the interface assembly  202 . When the stopper blade assembly  205  is in the engaged position  505 , the stopper shoulder screws  210  that sit at a top of the slot  230 A (and sit at tops of slots  230 B and  230 C, not visible in this figure) prevent the stopper blade assembly  205  from continuing to rotate when the pallet  120  impacts the stopper blade  150 . Thus each of the left stopper rib  302 , middle stopper rib  304 , and right stopper rib  306  serve the purpose of absorbing the load from the pallet  120  impacting the stopper blade assembly  205 . The motor assembly (not shown in this figure) does not absorb the impact of the pallet  120  comprising the payload  125 , enabling the motor assembly (not shown in this figure) to fulfill its function of actuating the stopper blade assembly  205  between the engaged position  505  and the disengaged position  510 . 
       FIG. 5B  is a cross-section detail view  550  of a stopper blade assembly  205  of a payload stopper (not shown in this figure) for a mobile robot (not shown in this figure) in the disengaged position  510  in order to allow the payload  125  to be one or more of one or more of unloaded off the pallet  120  in a controlled unloading operation and loaded onto the pallet  120 . 
     Height window  555  comprises a distance between a bottom face  560  of the interface assembly  202  and a top face  570  of the rollers  140 . When in the disengaged position  510 , the payload stopper  145 , or more specifically, the stopper blade assembly  205  of the payload stopper  145 , fits within dimension  555 . As depicted, the height window  555  equals approximately four inches. With the stopper blade assembly  205  below the top of the rollers  140 , when the pallet transport system (not shown) is stationary, the pallet  120  and thus the payload  125  are allowed to be one or more of unloaded off the pallet  120  in a controlled unloading operation and loaded onto the pallet  120 . For example, during the one or more of loading and unloading, the pallet  120  moves over the payload stopper  145 , with the payload stopper  145  supporting the payload  120  as it passes over the payload stopper  145 . For example, the payload stopper  145  acts as a skid plate for the payload  120  as it passed over the payload stopper  145 . 
       FIG. 5C  is a detail view  580  of the payload stopper (not shown in full in this figure) for the mobile robot  105  showing an aligned orientation of the receiving safety switch  342  relative to the transmitting safety switch  318  when the stopper blade assembly  205  is in the engaged position (as shown in  FIG. 5A ). The mobile robot  105  comprises a safety system controller  585 . For example, the safety system controller  585  comprises electronics controlling actuation of the stopper blade assembly (not shown in this figure). The alignment of the receiving safety switch  342  and the transmitting safety switch  318  in the engaged position (as shown in  FIG. 5A ) results in generation of a signal from the receiving safety switch  342  over wire  587  to the safety system controller  585 . The signal indicates that the robot  105  is safe to move. 
       FIG. 5D  is a detail view  590  of the payload stopper (not shown in full in this figure) for the mobile robot  105  showing a non-aligned orientation of the receiving safety switch  342  relative to the transmitting safety switch  318  when the stopper blade assembly  205  is in the disengaged position (as shown in  FIG. 5B ). The non-alignment of the receiving safety switch  342  and the transmitting safety switch  318  in the disengaged position (as shown in  FIG. 5B ) results in non-generation of a signal over the wire  587  to the safety controller  585 . This enables a known-truth signaling in that the robot  105  can be instructed not to move if it does not receive an appropriate signal over the wire  587  from the receiving safety switch  342 . 
       FIG. 6  is an exploded view of the stopper blade assembly  205  of a payload stopper (not shown in this figure) for a mobile robot (not shown in this figure). 
     The stopper blade assembly  205  again comprises the stopper blade  150  that runs along the width of the rollers (not shown in this figure), the pivot arms  313 A- 313 C, the pivot arm fasteners  315 , the linkage mount  316 , the linkage mount fasteners  317 , the transmitting safety switch  318 , the transmitting safety switch holder  319 , the transmitter holder fasteners  324 , the transmitter threaded inserts  326 , and the transmitter fasteners  330 . The purpose of the stopper blade  150  is to contact the side of the pallet (not shown in this figure) when the stopper blade assembly  205  is rotated in the engaged position (not shown in this figure). The stopper blade assembly  205  stops the pallet (not shown in this figure) when the stopper blade assembly  205  is rotated into the engaged position (not shown in this figure) and allows the pallet (not shown in this figure) to pass when the stopper blade assembly  205  is rotated into the disengaged position (not shown in this figure). 
       FIG. 7  is an exploded view of a motor assembly  235  of a payload stopper (not shown in this figure) for a mobile robot (not shown in this figure). Output and input magnets  701 A and  701 B are respectively fastened to output and input magnet holders  702  A and  702 B. Output and input magnet holders  702 A and  702 B are respectively bonded to output and input shafts  704 A and  704 B on each end of the motor  237 . The motor  237  mounts to a motor holder  710  with motor fasteners  715 . The motor holder  710  attaches the motor  237  to the interface weldment  301 . The motor holder  710  supports the output shaft  333  of the motor  237 , providing a second support so that the output shaft  333  is not cantilevered. Output encoder fasteners  720  attach an output encoder board  725  to the motor holder  710 . Input encoder fasteners  730  affix an input encoder board  732  to a backside of the motor  237  through the use of an encoder holder  735  as a spacer. When the motor  237  spins, the output magnet  701 A and the input magnet  701 B spin. The output encoder board  725  reads a position of the output magnet  701 A. The input encoder board  732  reads a position of the input magnet  701 B. The output encoder board  725  and the input encoder board  732  use the respective positions of the output magnet  701 A and of the input magnet  701 B to control a position of the motor  237  and to thereby control a position of the stopper blade assembly  205 . 
       FIG. 8  is an exploded view of the interface assembly  202  of a payload stopper (not shown in this figure) for a mobile robot (not shown in this figure). The interface assembly  202  again comprises the left stopper rib  302 , the middle stopper rib  304 , the right stopper rib  306 , the rib fasteners  308 , and the pivot bushings  310 . For example, the pivot bushing  310  comprises a sleeve bearing with flange, manufactured by igus of Cologne, Germany (www.igus.com). 
     Advantages of the invention include the ability of embodiments of the invention to ensure that very heavy payloads can be retained on top of the moving robot. In case the mobile robot is not in motion, safety is increased by having a mechanism which is able to sense its own state (either a safe engaged position or an unsafe disengaged position), and communicate to the other mobile robots whether it is safe for the robot to move. Another advantage is the ability of embodiments of the invention to handle a high impact force produced from the inertia of the payload when a mobile robot brakes suddenly. Another advantage is permitting higher speeds of the mobile robot due to the enhanced safety. For example, the speeds range between approximately 1 meter per second to approximately 2 meters per second. Another advantage is that payloads are thereby maintained in better condition. A further advantage of embodiments of the invention is that they allow for faster deceleration than a coefficient of friction between the rollers and the payload would allow on its own. 
     Another advantage of embodiments of the invention is that they allow for a payload to be transported from a mobile robot onto other equipment without interference. A still further advantage of embodiments of the invention is that the payload stopper provides to users working in the same areas as the mobile robot a visual signal of a workflow state of the robot. For example, if the payload stoppers are in the downward or disengaged position, one can tell that the robot will not move (and likely is either waiting to be loaded or is ready to transfer a payload). 
     Another advantage of embodiments of the invention is that the compact design allows for the robot to be positioned as closely as possible to an existing conveyor. A still further advantage of embodiments of the invention is that during payload transfer, this mechanism also acts as a skid plate for the payload, supporting the payload as it passes over the mechanism. 
     Another advantage of embodiments of the invention is that the way the stopper is attached to the robot chassis transfers the load from the components of the payload stopper to the robot base. Another advantage is that the stress point is not on the motor that moves the mechanism but on the base itself. 
     Advantages of the payload stopper for a mobile robot include preventing a payload from sliding on a mobile robot conveyor and falling off when the mobile robot comes to an abrupt stop. A further advantage of the payload stopper for a mobile robot is its ability to handle heavy payloads of up to approximately 3,000 pounds. A still further advantage of the payload stopper for a mobile robot is its ability to prevent an uncontrolled discharge of a payload of up to approximately 3,000 pounds. A yet further advantage of the payload stopper for a mobile robot is the invention&#39;s prevention of one or more of bodily injury and fatality even in scenarios when the mobile robot itself is able to sufficiently come to a stop. 
     Another advantage of the payload stopper for a mobile robot is that it is both robust enough to handle the high impact forces involved in stopping a heavy payload while also being compact enough to fold down and out of the way when the payload is conveyed across the mobile robot conveyor. For example, the high impact forces range between approximately 20 kiloNewtons (kN) and 40 kN. Another advantage is that the payload stopper is compact enough, when in the disengaged position, to fit in an approximately 4-inch height window to allow payloads to be conveyed across the mobile robot&#39;s conveyor during one or more of on-loading and off-loading. 
     The payload stopper for a mobile robot includes a plurality of components such as one or more of electronic components, hardware components, and computer software components. A number of such components can be combined or divided in the system. An example component of the system includes a set and/or series of computer instructions written in or implemented with any of a number of programming languages, as will be appreciated by those skilled in the art. 
     The system in one example employs one or more computer-readable signal-bearing media. The computer-readable signal bearing media store software, firmware and/or assembly language for performing one or more portions of one or more implementations of the invention. The computer-readable signal-bearing medium for the system in one example comprises one or more of a magnetic, electrical, optical, biological, and atomic data storage medium. For example, the computer-readable signal-bearing medium comprises floppy disks, magnetic tapes, CD-ROMs, DVD-ROMs, hard disk drives, downloadable files, files executable “in the cloud,” and electronic memory. 
     For example, it will be understood by those skilled in the art that software used by the payload stopper for a mobile robot may be located in any location in which it may be accessed by the system. It will be further understood by those of skill in the art that the number of variations of the network, location of the software, and the like are virtually limitless. It is intended, therefore, that the subject matter in the above description shall be interpreted as illustrative and shall not be interpreted in a limiting sense. 
     While the above representative embodiments have been described with certain components in exemplary configurations, it will be understood by one of ordinary skill in the art that other representative embodiments can be implemented using different configurations and/or different components. 
     For example, it will be understood by one of ordinary skill in the art that the order of certain steps and certain components can be altered without substantially impairing the functioning of the invention. For example, the motor moves in a way not involving rotation. For example, the function of the motor is instead performed by an actuator. For example, the actuator moves in a way not involving rotation. For example, one or more of the motor and the actuator comprises one or more of a pneumatic piston and a hydraulic piston. In these cases, the linkage converts the non-rotational output of the motor into movement of the stopper blade assembly. 
     The representative embodiments and disclosed subject matter, which have been described in detail herein, have been presented by way of example and illustration and not by way of limitation. It will be understood by those skilled in the art that various changes may be made in the form and details of the described embodiments resulting in equivalent embodiments that remain within the scope of the invention. It is intended, therefore, that the subject matter in the above description shall be interpreted as illustrative and shall not be interpreted in a limiting sense.