Patent Publication Number: US-2022218171-A1

Title: Cleaning roller for cleaning robots

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of and claims priority to U.S. application Ser. No. 16/725,107, now U.S. Pat. No. 11,284,769, filed on Dec. 23, 2019, which is a continuation of and claims priority to U.S. application Ser. No. 15/380,530, now U.S. Pat. No. 10,512,384, filed on Dec. 15, 2016, the entire contents of which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This specification relates to cleaning rollers, in particular, for cleaning robots. 
     BACKGROUND 
     An autonomous cleaning robot can navigate across a floor surface and avoid obstacles while vacuuming the floor surface to ingest debris from the floor surface. The cleaning robot can include rollers to pick up the debris from the floor surface. As the cleaning robot moves across the floor surface, the robot can rotate the rollers, which guide the debris toward a vacuum airflow generated by the cleaning robot. In this regard, the rollers and the vacuum airflow can cooperate to allow the robot to ingest debris. During its rotation, the roller can engage debris that includes hair and other filaments. The filament debris can become wrapped around the rollers. 
     SUMMARY 
     In one aspect, a cleaning roller mountable to a cleaning robot includes an elongate shaft extending from a first end portion to a second end portion along an axis of rotation. The first and second end portions are mountable to the cleaning robot for rotating about the axis of rotation. The cleaning roller further includes a core affixed around the shaft and having outer end portions positioned along the elongate shaft and proximate the first and second end portions. The core tapers from proximate the first end portion of the shaft toward a center of the shaft and tapers from proximate the second end portion of the shaft toward the center of the shaft. The cleaning roller further includes a sheath affixed to the core and extending beyond the outer end portions of the core. The sheath includes a first half and a second half each tapering toward the center of the shaft. The cleaning roller further includes collection wells defined by the outer end portions of the core and the sheath. 
     In another aspect, an autonomous cleaning robot includes a body, a drive operable to move the body across a floor surface, and a cleaning assembly. The cleaning assembly includes a roller. The roller is, for example, a first cleaning roller mounted to the body and rotatable about a first axis, and the cleaning assembly further includes a second cleaning roller mounted to the body and rotatable about a second axis parallel to the first axis. A shell of the first cleaning roller and the second cleaning roller define a separation therebetween, the separation extending along the first axis and increasing toward a center of a length of the first cleaning roller. 
     In some implementations, a length of the cleaning roller is between 20 cm and 30 cm. The sheath is, for example, affixed to the elongate shaft along 75% to 90% of a length of the sheath. 
     In some implementations, the elongate shaft is configured to be driven by a motor of the cleaning robot. 
     In some implementations, the core includes a plurality of discontinuous sections positioned around the shaft and within the sheath. In some cases, the sheath is fixed to the core between the discontinuous sections. In some cases, the sheath is bonded to the shaft at a location between the discontinuous sections of the core. 
     In some implementations, the core includes a plurality of posts extending away from the axis of rotation toward the sheath. The posts engage the sheath to couple the sheath to the core. 
     In some implementations, a minimum diameter of the core is at the center of the shaft. 
     In some implementations, each of the first half and the second half of the sheath includes an outer surface. The outer surface, for example, forms an angle between 5 and 20 degrees with the axis of rotation. 
     In some implementations, the first half of the sheath tapers from proximate the first end portion to the center of the shaft, and the second half of the sheath tapers from proximate the second end portion of the shaft toward the center of the shaft. 
     In some implementations, the sheath includes a shell surrounding and affixed to the core. The shell includes frustoconical halves. 
     In some implementations, the sheath includes a shell surrounding and affixed to the core. The sheath includes, for example, a vane extending radially outwardly from the shell. A height of the vane proximate the first end portion of the shaft is, for example, less than a height of the vane proximate the center of the shaft. In some cases, the vane follows a V-shaped path along an outer surface of the sheath. In some cases, the height of the vane proximate the first end portion is between 1 and 5 millimeters, and the height of the vane proximate the center of the shaft is between 10 and 30 millimeters. 
     In some implementations, a length of one of the collection wells is 5% to 15% of the length of the cleaning roller. 
     In some implementations, tubular portions of the sheath define the collection wells. 
     In some implementations, the sheath further includes a shell surrounding and affixed to the core, a maximum width of the shell being 80% and 95% of an overall diameter of the sheath. 
     In some implementations, the shell of the first cleaning roller and a shell of the second cleaning roller define the separation. 
     In some implementations, the separation is between 5 and 30 millimeters at the center of the length of the first cleaning roller. 
     In some implementations, the length of the first cleaning roller is between 20 and 30 centimeters. In some cases, the length of the first cleaning roller is greater than a length of the second cleaning roller. In some cases, the length of the first cleaning roller is equal to a length of the second cleaning roller. 
     In some implementations, a forward portion of the body has a substantially rectangular shape. The first and second cleaning rollers are, for example, mounted to an underside of the forward portion of the body. 
     In some implementations, the first cleaning roller and the second cleaning roller define an air gap therebetween at the center of the length of the first cleaning roller. The air gap, for example, varies in width as the first cleaning roller and the second cleaning roller are rotated. 
     Advantages of the foregoing may include, but are not limited to, those described below and herein elsewhere. The cleaning roller can improve pickup of debris from a floor surface. Torque can be more easily transferred from a drive shaft to an outer surface of the cleaning roller along an entire length of the cleaning roller. The improve torque transfer enables the outer surface of the cleaning roller to more easily move the debris upon engaging the debris. Compared to other cleaning rollers that do not have the features described herein that enable improved torque transfer, the cleaning roller can pick up more debris when driven with a given amount of torque. 
     The cleaning roller can have an increased length without reducing the ability of the cleaning roller to pick up debris from the floor surface. In particular, the cleaning roller, when longer, can require a greater amount of drive torque. However, because of the improved torque transfer of the cleaning roller, a smaller amount of torque can be used to drive the cleaning roller to achieve debris pickup capability similar to the debris pickup capability of other cleaning rollers. If the cleaning roller is mounted to a cleaning robot, the cleaning roller can have a length that extends closer to lateral sides of the cleaning robot so that the cleaning roller can reach debris over a larger range. 
     In other examples, the cleaning roller can be configured to collect filament debris in a manner that does not impede the cleaning performance of the cleaning roller. The filament debris, when collected, can be easily removable. In particular, as the cleaning roller engages with filament debris from a floor surface, the cleaning roller can cause the filament debris to be guided toward outer ends of the cleaning roller where collection wells for filament debris are located. The collection wells can be easily accessible to the user when the rollers are dismounted from the robot so that the user can easily dispose of the filament debris. In addition to preventing damage to the cleaning roller, the improved collection of filament debris can reduce the likelihood that filament debris will impede the debris pickup ability of the cleaning roller, e.g., by wrapping around the outer surface of the cleaning roller. 
     In further examples, the cleaning roller can cooperate with another cleaning roller to define a separation therebetween that improves characteristics of airflow generated by a vacuum assembly. The separation, by being larger toward a center of the cleaning rollers, can concentrate the airflow toward the center of the cleaning rollers. While filament debris can tend to collect toward the ends of the cleaning rollers, other debris can be more easily ingested through the center of the cleaning rollers where the airflow rate is highest. 
     The details of one or more implementations of the subject matter described in this specification are set forth in the accompanying drawings and the description below. Other potential features, aspects, and advantages will become apparent from the description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a bottom view of a cleaning head during a cleaning operation of a cleaning robot. 
         FIG. 1B  is a cross-sectional side view of a cleaning robot and the cleaning head of  FIG. 1A  during the cleaning operation. 
         FIG. 2A  is a bottom view of the cleaning robot of  FIG. 1B . 
         FIG. 2B  is a side perspective exploded view of the cleaning robot of  FIG. 2A . 
         FIG. 3A  is a front perspective view of a cleaning roller. 
         FIG. 3B  is a front perspective exploded view of the cleaning roller of  FIG. 3A . 
         FIG. 3C  is a front view of the cleaning roller of  FIG. 3A . 
         FIG. 3D  is a front cutaway view of the cleaning roller of  FIG. 3A  with portions of a sheath and a support structure of the cleaning roller removed to reveal collection wells of the cleaning roller. 
         FIG. 3E  is a cross-sectional view of the sheath of the cleaning roller of  FIG. 3A  taken along section  3 E- 3 E shown in  FIG. 3C . 
         FIG. 4A  is a perspective view of a support structure of the cleaning roller of  FIG. 3A . 
         FIG. 4B  is a front view of the support structure of  FIG. 4A . 
         FIG. 4C  is a cross sectional view of an end portion of the support structure of  FIG. 4B  taken along section  4 C- 4 C shown in  FIG. 4B . 
         FIG. 4D  is a zoomed in perspective view of an inset  4 D marked in  FIG. 4A  depicting an end portion of the subassembly of  FIG. 4A . 
         FIG. 5A  is a zoomed in view of an inset  5 A marked in  FIG. 3C  depicting a central portion of the cleaning roller of  FIG. 3C . 
         FIG. 5B  is a cross-sectional view of an end portion of the cleaning roller of  FIG. 3C  taken along section  5 B- 5 B shown in  FIG. 3C . 
         FIG. 6  is a schematic diagram of the cleaning roller of  FIG. 3A  with free portions of a sheath of the cleaning roller removed. 
     
    
    
     Like reference numbers and designations in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1A and 1B , a cleaning head  100  for a cleaning robot  102  includes cleaning rollers  104   a ,  104   b  that are positioned to engage debris  106  on a floor surface  10 .  FIG. 1A  depicts the cleaning head  100  during a cleaning operation, with the cleaning head  100  isolated from the cleaning robot  102  to which the cleaning head  100  is mounted. The cleaning robot  102  moves about the floor surface  10  while ingesting the debris  106  from the floor surface  10 .  FIG. 1B  depicts the cleaning robot  102 , with the cleaning head  100  mounted to the cleaning robot  102 , as the cleaning robot  102  traverses the floor surface  10  and rotates the rollers  104   a ,  104   b  to ingest the debris  106  from the floor surface  10  during the cleaning operation. During the cleaning operation, the cleaning rollers  104   a ,  104   b  are rotatable to lift the debris  106  from the floor surface  10  into the cleaning robot  102 . Outer surfaces of the cleaning rollers  104   a ,  104   b  engage the debris  106  and agitate the debris  106 . The rotation of the cleaning rollers  104   a ,  104   b  facilitates movement of the debris  106  toward an interior of the cleaning robot  102 . 
     In some implementations, as described herein, the cleaning rollers  104   a ,  104   b  are elastomeric rollers featuring a pattern of chevron-shaped vanes  224   a ,  224   b  (shown in  FIG. 1A ) distributed along an exterior surface of the cleaning rollers  104   a ,  104   b . The vanes  224   a ,  224   b  of at least one of the cleaning rollers  104   a ,  104 , e.g., the cleaning roller  104   a , make contact with the floor surface  10  along the length of the cleaning rollers  104   a ,  104   b  and experience a consistently applied friction force during rotation that is not present with brushes having pliable bristles. Furthermore, like cleaning rollers having distinct bristles extending radially from a shaft, the cleaning rollers  104   a ,  104   b  have vanes  224   a ,  224   b  that extend radially outward. The vanes  224   a ,  224   b , however, also extend continuously along the outer surface of the cleaning rollers  104   a ,  104   b  in longitudinal directions. The vanes  224   a ,  224   b  also extend along circumferential directions along the outer surface of the cleaning rollers  104   a ,  104   b , thereby defining V-shaped paths along the outer surface of the cleaning rollers  104   a ,  104   b  as described herein. Other suitable configurations, however, are also contemplated. For example, in some implementations, at least one of the rear and front rollers  104   a ,  104   b  may include bristles and/or elongated pliable flaps for agitating the floor surface in addition or as an alternative to the vanes  224   a ,  224   b.    
     As shown in  FIG. 1A , a separation  108  and an air gap  109  are defined between the cleaning roller  104   a  and the cleaning roller  104   b . The separation  108  and the air gap  109  both extend from a first outer end portion  110   a  of the cleaning roller  104   a  to a second outer end portion  112   a  of the cleaning roller  104   a . As described herein, the separation  108  corresponds a distance between the cleaning rollers  104   a ,  104   b  absent the vanes on the cleaning rollers  104   a ,  104   b , while the air gap  109  corresponds to the distance between the cleaning rollers  104   a ,  104   b  including the vanes on the cleaning rollers  104   a ,  104   b . The air gap  109  is sized to accommodate debris  106  moved by the rollers  104   a ,  104   b  as the rollers  104   a ,  104   b  rotate and to enable airflow to be drawn into the cleaning robot  102  and change in width as the cleaning rollers  104   a ,  104   b  rotate. While the air gap  109  can vary in width during rotation of the rollers  104   a ,  104   b , the separation  108  has a constant width during rotation of the rollers  104   a ,  104   b . The separation  108  facilitates movement of the debris  106  caused by the rollers  104   a ,  104   b  upward toward the interior of the robot  102  so that the debris can be ingested by the robot  102 . As described herein, the separation  108  increases in size toward a center  114  of a length L 1  of the cleaning roller  104   a , e.g., a center of the cleaning roller  114   a  along a longitudinal axis  126   a  of the cleaning roller  114   a . The separation  108  decreases in width toward the end portions  110   a ,  112   a  of the cleaning roller  104   a . Such a configuration of the separation  108  can improve debris pickup capabilities of the rollers  104   a ,  104   b  while reducing likelihood that filament debris picked up by the rollers  104   a ,  104   b  impedes operations of the rollers  104   a ,  104   b.    
     Example Cleaning Robots 
     The cleaning robot  102  is an autonomous cleaning robot that autonomously traverses the floor surface  10  while ingesting the debris  106  from different parts of the floor surface  10 . In the example depicted in  FIGS. 1B and 2A , the robot  102  includes a body  200  movable across the floor surface  10 . The body  200  includes, in some cases, multiple connected structures to which movable components of the cleaning robot  102  are mounted. The connected structures include, for example, an outer housing to cover internal components of the cleaning robot  102 , a chassis to which drive wheels  210   a ,  210   b  and the rollers  104   a ,  104   b  are mounted, a bumper mounted to the outer housing, etc. As shown in  FIG. 2A , in some implementations, the body  200  includes a front portion  202   a  that has a substantially rectangular shape and a rear portion  202   b  that has a substantially semicircular shape. The front portion  202   a  is, for example, a front one-third to front one-half of the cleaning robot  102 , and the rear portion  202   b  is a rear one-half to two-thirds of the cleaning robot  102 . The front portion  202   a  includes, for example, two lateral sides  204   a ,  204   b  that are substantially perpendicular to a front side  206  of the front portion  202   a.    
     As shown in  FIG. 2A , the robot  102  includes a drive system including actuators  208   a ,  208   b , e.g., motors, operable with drive wheels  210   a ,  210   b . The actuators  208   a ,  208   b  are mounted in the body  200  and are operably connected to the drive wheels  210   a ,  210   b , which are rotatably mounted to the body  200 . The drive wheels  210   a ,  210   b  support the body  200  above the floor surface  10 . The actuators  208   a ,  208   b , when driven, rotate the drive wheels  210   a ,  210   b  to enable the robot  102  to autonomously move across the floor surface  10 . 
     The robot  102  includes a controller  212  that operates the actuators  208   a ,  208   b  to autonomously navigate the robot  102  about the floor surface  10  during a cleaning operation. The actuators  208   a ,  208   b  are operable to drive the robot  102  in a forward drive direction  116  (shown in  FIG. 1B ) and to turn the robot  102 . In some implementations, the robot  102  includes a caster wheel  211  that supports the body  200  above the floor surface  10 . The caster wheel  211 , for example, supports the rear portion  202   b  of the body  200  above the floor surface  10 , and the drive wheels  210   a ,  210   b  support the front portion  202   a  of the body  200  above the floor surface  10 . 
     As shown in  FIGS. 1B and 2A , a vacuum assembly  118  is carried within the body  200  of the robot  102 , e.g., in the rear portion  202   b  of the body  200 . The controller  212  operates the vacuum assembly  118  to generate an airflow  120  that flows through the air gap  109  near the rollers  104   a ,  104   b , through the body  200 , and out of the body  200 . The vacuum assembly  118  includes, for example, an impeller that generates the airflow  120  when rotated. The airflow  120  and the rollers  104   a ,  104   b , when rotated, cooperate to ingest debris  106  into the robot  102 . A cleaning bin  122  mounted in the body  200  contains the debris  106  ingested by the robot  102 , and a filter  123  in the body  200  separates the debris  106  from the airflow  120  before the airflow  120  enters the vacuum assembly  118  and is exhausted out of the body  200 . In this regard, the debris  106  is captured in both the cleaning bin  122  and the filter  123  before the airflow  120  is exhausted from the body  200 . 
     As shown in  FIGS. 1A and 2A , the cleaning head  100  and the rollers  104   a ,  104   b  are positioned in the front portion  202   a  of the body  200  between the lateral sides  204   a ,  204   b . The rollers  104   a ,  104   b  are operably connected to actuators  214   a ,  214   b , e.g., motors. The cleaning head  100  and the rollers  104   a ,  104   b  are positioned forward of the cleaning bin  122 , which is positioned forward of the vacuum assembly  118 . In the example of the robot  102  described with respect to  FIGS. 2A, 2B , the substantially rectangular shape of the front portion  202   a  of the body  200  enables the rollers  104   a ,  104   b  to be longer than rollers for cleaning robots with, for example, a circularly shaped body. 
     The rollers  104   a ,  104   b  are mounted to a housing  124  of the cleaning head  100  and mounted, e.g., indirectly or directly, to the body  200  of the robot  102 . In particular, the rollers  104   a ,  104   b  are mounted to an underside of the front portion  202   a  of the body  200  so that the rollers  104   a ,  104   b  engage debris  106  on the floor surface  10  during the cleaning operation when the underside faces the floor surface  10 . 
     In some implementations, the housing  124  of the cleaning head  100  is mounted to the body  200  of the robot  102 . In this regard, the rollers  104   a ,  104   b  are also mounted to the body  200  of the robot  102 , e.g., indirectly mounted to the body  200  through the housing  124 . Alternatively or additionally, the cleaning head  100  is a removable assembly of the robot  102  in which the housing  124  with the rollers  104   a ,  104   b  mounted therein is removably mounted to the body  200  of the robot  102 . The housing  124  and the rollers  104   a ,  104   b  are removable from the body  200  as a unit so that the cleaning head  100  is easily interchangeable with a replacement cleaning head. 
     In some implementations, rather than being removably mounted to the body  200 , the housing  124  of the cleaning head  100  is not a component separate from the body  200 , but rather, corresponds to an integral portion of the body  200  of the robot  102 . The rollers  104   a ,  104   b  are mounted to the body  200  of the robot  102 , e.g., directly mounted to the integral portion of the body  200 . The rollers  104   a ,  104   b  are each independently removable from the housing  124  of the cleaning head  100  and/or from the body  200  of the robot  102  so that the rollers  104   a ,  104   b  can be easily cleaned or be replaced with replacement rollers. As described herein, the rollers  104   a ,  104   b  can include collection wells for filament debris that can be easily accessed and cleaned by a user when the rollers  104   a ,  104   b  are dismounted from the housing  124 . 
     The rollers  104   a ,  104   b  are rotatable relative to the housing  124  of the cleaning head  100  and relative to the body  200  of the robot  102 . As shown in  FIGS. 1B and 2A , the rollers  104   a ,  104   b  are rotatable about longitudinal axes  126   a ,  126   b  parallel to the floor surface  10 . The axes  126   a ,  126   b  are parallel to one another and correspond to longitudinal axes of the cleaning rollers  104   a ,  104   b , respectively. In some cases, the axes  126   a ,  126   b  are perpendicular to the forward drive direction  116  of the robot  102 . The center  114  of the cleaning roller  104   a  is positioned along the longitudinal axis  126   a  and corresponds to a midpoint of the length L 1  of the cleaning roller  104   a . The center  114 , in this regard, is positioned along the axis of rotation of the cleaning roller  104   a.    
     In some implementations, referring to the exploded view of the cleaning head  100  shown in  FIG. 2B , the rollers  104   a ,  104   b  each include a sheath  220   a ,  220   b  including a shell  222   a ,  222   b  and vanes  224   a ,  224   b . The rollers  104   a ,  104   b  also each include a support structure  226   a ,  226   b , and a shaft  228   a ,  228   b . The sheath  220   a ,  220   b  is, in some cases, a single molded piece formed from an elastomeric material. In this regard, the shell  222   a ,  222   b  and its corresponding vanes  224   a ,  224   b  are part of the single molded piece. The sheath  220   a ,  220   b  extends inward from its outer surface toward the shaft  228   a ,  228   b  such that the amount of material of the sheath  220   a ,  220   b  inhibits the sheath  220   a ,  220   b  from deflecting in response to contact with objects, e.g., the floor surface  10 . The high surface friction of the sheath  220   a ,  220   b  enables the sheath  220   a ,  220   b  to engage the debris  106  and guide the debris  106  toward the interior of the cleaning robot  102 , e.g., toward an air conduit  128  within the cleaning robot  102 . 
     The shafts  228   a ,  228   b  and, in some cases, the support structure  226   a ,  226   b , are operably connected to the actuators  214   a ,  214   b  (shown schematically in  FIG. 2A ) when the rollers  104   a ,  104   b  are mounted to the body  200  of the robot  102 . When the rollers  104   a ,  104   b  are mounted to the body  200 , mounting devices  216   a ,  216   b  on the second end portions  232   a ,  232   b  of the shafts  228   a ,  228   b  couple the shafts  228   a ,  228   b  to the actuators  214   a ,  214   b . The first end portions  230   a ,  230   b  of the shafts  228   a ,  228   b  are rotatably mounted to mounting devices  218   a ,  218   b  on the housing  124  of the cleaning head  100  or the body  200  of the robot  102 . The mounting devices  218   a ,  218   b  are fixed relative to the housing  124  or the body  200 . In some cases, as described herein, portions of the support structure  226   a ,  226   b  cooperate with the shafts  228   a ,  228   b  to rotationally couple the cleaning rollers  104   a ,  104   b  to the actuators  214   a ,  214   b  and to rotatably mount the cleaning rollers  104   a ,  104   b  to the mounting devices  218   a ,  218   b.    
     As shown in  FIG. 1A , the roller  104   a  and the roller  104   b  are spaced from another such that the longitudinal axis  126   a  of the roller  104   a  and the longitudinal axis  126   b  of the roller  104   b  define a spacing S 1 . The spacing S 1  is, for example, between 2 and 6 cm, e.g., between 2 and 4 cm, 4 and 6 cm, etc. 
     The roller  104   a  and the roller  104   b  are mounted such that the shell  222   a  of the roller  104   a  and the shell  222   b  of the roller  104   b  define the separation  108 . The separation  108  is between the shell  222   a  and the shell  222   b  and extends longitudinally between the shells  222   a ,  222   b . In particular, the outer surface of the shell  222   b  of the roller  104   b  and the outer surface of the shell  222   a  of the roller are separated by the separation  108 , which varies in width along the longitudinal axes  126   a ,  126   b  of the rollers  104   a ,  104   b . The separation  108  tapers toward the center  114  of the cleaning roller  104   a , e.g., toward a plane passing through centers of the both of the cleaning rollers  104   a ,  104   b  and perpendicular to the longitudinal axes  126   a ,  126   b . The separation  108  decreases in width toward the center  114 . 
     The separation  108  is measured as a width between the outer surface of the shell  222   a  and the outer surface of the shell  222   b . In some cases, the width of the separation  108  is measured as the closest distance between the shell  222   a  and the shell  222   b  at various points along the longitudinal axis  126   a . The width of the separation  108  is measured along a plane through both of the longitudinal axes  126   a ,  126   b . In this regard, the width varies such that the distance S 3  between the rollers  104   a ,  104   b  at their centers is greater than the distance S 2  at their ends. 
     Referring to inset  132   a  in  FIG. 1A , a length S 2  of the separation  108  proximate the first end portion  110   a  of the roller  104   a  is between 2 and 10 mm, e.g., between 2 mm and 6 mm, 4 mm and 8 mm, 6 mm and 10 mm, etc. The length S 2  of the separation  108 , for example, corresponds to a minimum length of the separation  108  along the length L 1  of the roller  104   a . Referring to inset  132   b  in  FIG. 1A , a length S 3  of the separation  108  proximate the center  114  of the cleaning roller  104   a  is between, for example, 5 mm and 30 mm, e.g., between 5 mm and 20 mm, 10 mm and 25 mm, 15 mm and 30 mm, etc. The length S 3  is, for example, 3 to 15 times greater than the length S 2 , e.g., 3 to 5 times, 5 to 10 times, 10 to 15 times, etc., greater than the length S 2 . The length S 3  of the separation  108 , for example, corresponds to a maximum length of the separation  108  along the length L 1  of the roller  104   a . In some cases, the separation  108  linearly increases from the center  114  of the cleaning roller  104  toward the end portions  110   a ,  110   b.    
     The air gap  109  between the rollers  104   a ,  104   b  is defined as the distance between free tips of the vanes  224   a ,  224   b  on opposing rollers  104   a ,  104   b . In some examples, the distance varies depending on how the vanes  224   a ,  224   b  align during rotation. The air gap  109  between the sheaths  220   a ,  220   b  of the rollers  104   a ,  104   b  varies along the longitudinal axes  126   a ,  126   b  of the rollers  104   a ,  104   b . In particular, the width of the air gap  109  varies in size depending on relative positions of the vanes  224   a ,  224   b  of the rollers  104   a ,  104   b . The width of the air gap  109  is defined by the distance between the outer circumferences of the sheath  220   a ,  220   b , e.g., defined by the vanes  224   a ,  224   b , when the vanes  224   a ,  224   b  face one another during rotation of the rollers  104   a ,  104   b . The width of the air gap  109  is defined by the distance between the outer circumferences of the shells  222   a ,  222   b  when the vanes  224   a ,  224   b  of both rollers  104   a ,  104   b  do not face the other roller. In this regard, while the outer circumference of the rollers  104   a ,  104   b  is consistent along the lengths of the rollers  104   a ,  104   b  as described herein, the air gap  109  between the rollers  104   a ,  104   b  varies in width as the rollers  104   a ,  104   b  rotate. In particular, while the separation  108  has a constant length during rotation of the opposing rollers  104   a ,  104   b , the distance defining the air gap  109  changes during the rotation of the rollers  104   a ,  104   b  due to relative motion of the vanes  224   a ,  224   b  of the rollers  104   a ,  104   b . The air gap  109  will vary in width from a minimum width of 1 mm to 10 mm when the vanes  224   a ,  224   b  face one another to a maximum width of 5 mm to 30 mm when the vanes  224   a ,  224   b  are not aligned. The maximum width corresponds to, for example, the length S 3  of the separation  108  at the centers of the cleaning rollers  104   a ,  104   b , and the minimum width corresponds to the length of this separation  108  minus the heights of the vanes  224   a ,  224   b  at the centers of the cleaning rollers  104   a ,  104   b.    
     Referring to  FIG. 2A , in some implementations, to sweep debris  106  toward the rollers  104   a ,  104   b , the robot  102  includes a brush  233  that rotates about a non-horizontal axis, e.g., an axis forming an angle between 75 degrees and 90 degrees with the floor surface  10 . The non-horizontal axis, for example, forms an angle between 75 degrees and 90 degrees with the longitudinal axes  126   a ,  126   b  of the cleaning rollers  104   a ,  104   b . The robot  102  includes an actuator  234  operably connected to the brush  233 . The brush  233  extends beyond a perimeter of the body  200  such that the brush  233  is capable of engaging debris  106  on portions of the floor surface  10  that the rollers  104   a ,  104   b  typically cannot reach. 
     During the cleaning operation shown in  FIG. 1B , as the controller  212  operates the actuators  208   a ,  208   b  to navigate the robot  102  across the floor surface  10 , if the brush  233  is present, the controller  212  operates the actuator  234  to rotate the brush  233  about the non-horizontal axis to engage debris  106  that the rollers  104   a ,  104   b  cannot reach. In particular, the brush  233  is capable of engaging debris  106  near walls of the environment and brushing the debris  106  toward the rollers  104   a ,  104   b . The brush  233  sweeps the debris  106  toward the rollers  104   a ,  104   b  so that the debris  106  can be ingested through the separation  108  between the rollers  104   a ,  104   b.    
     The controller  212  operates the actuators  214   a ,  214   b  to rotate the rollers  104   a ,  104   b  about the axes  126   a ,  126   b . The rollers  104   a ,  104   b , when rotated, engage the debris  106  on the floor surface  10  and move the debris  106  toward the air conduit  128 . As shown in  FIG. 1B , the rollers  104   a ,  104   b , for example, counter rotate relative to one another to cooperate in moving debris  106  through the separation  108  and toward the air conduit  128 , e.g., the roller  104   a  rotates in a clockwise direction  130   a  while the roller  104   b  rotates in a counterclockwise direction  130   b.    
     The controller  212  also operates the vacuum assembly  118  to generate the airflow  120 . The vacuum assembly  118  is operated to generate the airflow  120  through the separation  108  such that the airflow  120  can move the debris  106  retrieved by the rollers  104   a ,  104   b . The airflow  120  carries the debris  106  into the cleaning bin  122  that collects the debris  106  delivered by the airflow  120 . In this regard, both the vacuum assembly  118  and the rollers  104   a ,  104   b  facilitate ingestion of the debris  106  from the floor surface  10 . The air conduit  128  receives the airflow  120  containing the debris  106  and guides the airflow  120  into the cleaning bin  122 . The debris  106  is deposited in the cleaning bin  122 . During rotation of the rollers  104   a ,  104   b , the rollers  104   a ,  104   b  apply a force to the floor surface  10  to agitate any debris on the floor surface  10 . The agitation of the debris  106  can cause the debris  106  to be dislodged from the floor surface  10  so that the rollers  104   a ,  104   b  can more contact the debris  106  and so that the airflow  120  generated by the vacuum assembly  118  can more easily carry the debris  106  toward the interior of the robot  102 . As described herein, the improved torque transfer from the actuators  214   a ,  214   b  toward the outer surfaces of the rollers  104   a ,  104   b  enables the rollers  104   a ,  104   b  to apply more force. As a result, the rollers  104   a ,  104   b  can better agitate the debris  106  on the floor surface  10  compared to rollers and brushes with reduced torque transfer or rollers and brushes that readily deform in response to contact with the floor surface  10  or with the debris  106 . 
     Example Cleaning Rollers 
     The example of the rollers  104   a ,  104   b  described with respect to  FIG. 2B  can include additional configurations as described with respect to  FIGS. 3A-3E, 4A-4D, and 5A-5G . As shown in  FIG. 3B , an example of a roller  300  includes a sheath  302 , a support structure  303 , and a shaft  306 . The roller  300 , for example, corresponds to the rear roller  104   a  described with respect to  FIGS. 1A, 1B, 2A, and 2B . The sheath  302 , the support structure  303 , and the shaft  306  are similar to the sheath  220   a , the support structure  226   a , and the shaft  228   a  described with respect to  FIG. 2B . In some implementations, the sheath  220   a , the support structure  226   a , and the shaft  228   a  are the sheath  302 , the support structure  303 , and the shaft  306 , respectively. As shown in  FIG. 3C , an overall length L 2  of the roller  300  is similar to the overall length L 1  described with respect to the rollers  104   a ,  104   b.    
     Like the cleaning roller  104   a , the cleaning roller  300  can be mounted to the cleaning robot  102 . Absolute and relative dimensions associated with the cleaning robot  102 , the cleaning roller  300 , and their components are described herein. Some of these dimensions are indicated in the figures by reference characters such as, for example, W 1 , S 1 -S 3 , L 1 -L 10 , D 1 -D 7 , M 1 , and M 2 . Example values for these dimensions in implementations are described herein, for example, in the section “Example Dimensions of Cleaning Robots and Cleaning Rollers.” 
     Referring to  FIGS. 3B and 3C , the shaft  306  is an elongate member having a first outer end portion  308  and a second outer end portion  310 . The shaft  306  extends from the first end portion  308  to the second end portion  310  along a longitudinal axis  312 , e.g., the axis  126   a  about which the roller  104   a  is rotated. The shaft  306  is, for example, a drive shaft formed from a metal material. 
     The first end portion  308  and the second end portion  310  of the shaft  306  are configured to be mounted to a cleaning robot, e.g., the robot  102 . The second end portion  310  is configured to be mounted to a mounting device, e.g., the mounting device  216   a . The mounting device couples the shaft  306  to an actuator of the cleaning robot, e.g., the actuator  214   a  described with respect to  FIG. 2A . The first end portion  308  rotatably mounts the shaft  306  to a mounting device, e.g., the mounting device  218   a . The second end portion  310  is driven by the actuator of the cleaning robot. 
     Referring to  FIG. 3B , the support structure  303  is positioned around the shaft  306  and is rotationally coupled to the shaft  306 . The support structure  303  includes a core  304  affixed to the shaft  306 . As described herein, the core  304  and the shaft  306  are affixed to one another, in some implementations, through an insert molding process during which the core  304  is bonded to the shaft  306 . Referring to  FIGS. 3D and 3E , the core  304  includes a first outer end portion  314  and a second outer end portion  316 , each of which is positioned along the shaft  306 . The first end portion  314  of the core  304  is positioned proximate the first end portion  308  of the shaft  306 . The second end portion  316  of the core  304  is positioned proximate the second end portion  310  of the shaft  306 . The core  304  extends along the longitudinal axis  312  and encloses portions of the shaft  306 . 
     Referring to  FIGS. 3D and 4A , in some cases, the support structure  303  further includes an elongate portion  305   a  extending from the first end portion  314  of the core  304  toward the first end portion  308  of the shaft  306  along the longitudinal axis  312  of the roller  300 . The elongate portion  305   a  has, for example, a cylindrical shape. The elongate portion  305   a  of the support structure  303  and the first end portion  308  of the shaft  306 , for example, are configured to be rotatably mounted to the mounting device, e.g., the mounting device  218   a . The mounting device  218   a ,  218   b , for example, functions as a bearing surface to enable the elongate portion  305   a , and hence the roller  300 , to rotate about its longitudinal axis  312  with relatively little frictional forces caused by contact between the elongate portion  305   a  and the mounting device. 
     In some cases, the support structure  303  includes an elongate portion  305   b  extending from the second end portion  314  of the core  304  toward the second end portion  310  of the shaft  306  along the longitudinal axis  312  of the roller  300 . The elongate portion  305   b  of the support structure  303  and the second end portion  314  of the core  304 , for example, are coupled to the mounting device, e.g., the mounting device  216   a . The mounting device  216   a  enables the roller  300  to be mounted to the actuator of the cleaning robot, e.g., rotationally coupled to a motor shaft of the actuator. The elongate portion  305   b  has, for example, a prismatic shape having a non-circular cross-section, such as a square, hexagonal, or other polygonal shape, that rotationally couples the support structure  303  to a rotatable mounting device, e.g., the mounting device  216   a . The elongate portion  305   b  engages with the mounting device  216   a  to rotationally couple the support structure  303  to the mounting device  216   a.    
     The mounting device  216   a  rotationally couples both the shaft  306  and the support structure  303  to the actuator of the cleaning robot, thereby improving torque transfer from the actuator to the shaft  306  and the support structure  303 . The shaft  306  can be attached to the support structure  303  and the sheath  302  in a manner that improves torque transfer from the shaft  306  to the support structure  303  and the sheath  302 . Referring to  FIGS. 3C and 3E , the sheath  302  is affixed to the core  304  of the support structure  303 . As described herein, the support structure  303  and the sheath  302  are affixed to one another to rotationally couple the sheath  302  to the support structure  303 , particularly in a manner that improves torque transfer from the support structure  303  to the sheath  302  along the entire length of the interface between the sheath  302  and the support structure  303 . The sheath  302  is affixed to the core  304 , for example, through an overmold or insert molding process in which the core  304  and the sheath  302  are directly bonded to one another. In addition, in some implementations, the sheath  302  and the core  304  include interlocking geometry that ensures that rotational movement of the core  304  drives rotational movement of the sheath  302 . 
     The sheath  302  includes a first half  322  and a second half  324 . The first half  322  corresponds to the portion of the sheath  302  on one side of a central plane  327  passing through a center  326  of the roller  300  and perpendicular to the longitudinal axis  312  of the roller  300 . The second half  324  corresponds to the other portion of the sheath  302  on the other side of the central plane  327 . The central plane  327  is, for example, a bisecting plane that divides the roller  300  into two symmetric halves. In this regard, the fixed portion  331  is centered on the bisecting plane. 
     The sheath  302  includes a first outer end portion  318  on the first half  322  of the sheath  302  and a second outer end portion  320  on the second half  324  of the sheath  302 . The sheath  302  extends beyond the core  304  of the support structure  303  along the longitudinal axis  312  of the roller  300 , in particular, beyond the first end portion  314  and the second end portion  316  of the core  304 . In some cases, the sheath  302  extends beyond the elongate portion  305   a  along the longitudinal axis  312  of the roller  300 , and the elongate portion  305   b  extends beyond the second end portion  320  of the sheath  302  along the longitudinal axis  312  of the roller  300 . 
     In some cases, a fixed portion  331   a  of the sheath  302  extending along the length of the core  304  is affixed to the support structure  303 , while free portions  331   b ,  331   c  of the sheath  302  extending beyond the length of the core  304  are not affixed to the support structure  303 . The fixed portion  331   a  extends from the central plane  327  along both directions of the longitudinal axis  312 , e.g., such that the fixed portion  331   a  is symmetric about the central plane  327 . The free portion  331   b  is fixed to one end of the fixed portion  331   a , and the free portion  331   c  is fixed to the other end of the fixed portion  331   a.    
     In some implementations, the fixed portion  331   a  tends to deform relatively less than the free portions  331   b ,  331   c  when the sheath  302  of the roller  300  contacts objects, such as the floor surface  10  and debris on the floor surface  10 . In some cases, the free portions  331   b ,  331   c  of the sheath  302  deflect in response to contact with the floor surface  10 , while the fixed portions  331   b ,  331   c  are radially compressed. The amount of radially compression of the fixed portions  331   b ,  331   c  is less than the amount of radial deflection of the free portions  331   b ,  331   c  because the fixed portions  331   b ,  331   c  include material that extends radially toward the shaft  306 . As described herein, in some cases, the material forming the fixed portions  331   b ,  331   c  contacts the shaft  306  and the core  304 . 
       FIG. 3D  depicts a cutaway view of the roller  300  with portions of the sheath  302  removed. Referring to  FIGS. 3A, 3D, and 3E , the roller  300  includes a first collection well  328  and a second collection well  330 . The collection wells  328 ,  330  correspond to volumes on ends of the roller  300  where filament debris engaged by the roller  300  tend to collect. In particular, as the roller  300  engages filament debris on the floor surface  10  during a cleaning operation, the filament debris moves over the end portions  318 ,  320  of the sheath  302 , wraps around the shaft  306 , and then collects within the collection wells  328 ,  330 . The filament debris wraps around the elongate portions  305   a ,  305   b  of the support structure  303  and can be easily removed from the elongate portions  305   a ,  305   b  by the user. In this regard, the elongate portions  305   a ,  305   b  are positioned within the collection wells  328 ,  330 . The collection wells  328 ,  330  are defined by the sheath  302 , the core  304 , and the shaft  306 . The collection wells  328 ,  330  are defined by the free portions of the sheath  302  that extend beyond the end portions  314  and  316  of the core  304 . 
     The first collection well  328  is positioned within the first half  322  of the sheath  302 . The first collection well  328  is, for example, defined by the first end portion  314  of the core  304 , the elongate portion  305   a  of the support structure  303 , the free portion  331   b  of the sheath  302 , and the shaft  306 . The first end portion  314  of the core  304  and the free portion  331   b  of the sheath  302  define a length L 5  of the first collection well  328 . 
     The second collection well  330  is positioned within the second half  324  of the sheath  302 . The second collection well  330  is, for example, defined by the second end portion  316  of the core  304 , the free portion  331   c  of the sheath  302 , and the shaft  306 . The second end portion  316  of the core  304  and the free portion  331   c  of the sheath  302  define a length L 5  of the second collection well  330 . 
     Referring to  FIG. 3E , the sheath  302  tapers along the longitudinal axis  312  of the roller  300  toward the center  326 , e.g., toward the central plane  327 . Both the first half  322  and the second half  324  of the sheath  302  taper along the longitudinal axis  312  toward the center  326 , e.g., toward the central plane  327 , over at least a portion of the first half  322  and the second half  324 , respectively. The first half  322  tapers from proximate the first outer end portion  308  of the shaft  306  to the center  326 , and the second half  324  tapers from proximate the second outer end portion  310  of the shaft  306  to the center  326 . In some implementations, the first half  322  tapers from the first outer end portion  318  to the center  326 , and the second half  324  tapers from the second outer end portion  320  to the center  326 . In some implementations, rather than tapering toward the center  326  along an entire length of the sheath  302 , the sheath  302  tapers toward the center  326  along the fixed portion  331   a  of the sheath  302 , and the free portions  331   b ,  331   c  of the sheath  302  are not tapered. The degree of tapering of the sheath  302  varies between implementations. Examples of dimensions defining the degree of tapering are described herein elsewhere. 
     Similarly, to enable the sheath  302  to taper toward the center  326  of the roller  300 , the support structure  303  includes tapered portions. The core  304  of the support structure  303 , for example, includes portions that taper toward the center  326  of the roller  300 .  FIGS. 4A-4D  depict an example configuration of the core  304 . Referring to  FIGS. 4A and 4B , the core  304  includes a first half  400  including the first end portion  314  and a second half  402  including the second end portion  316 . The first half  400  and the second half  402  of the core  304  are symmetric about the central plane  327 . 
     The first half  400  tapers along the longitudinal axis  312  toward the center  326  of the roller  300 , and the second half  402  tapers toward the center  326  of the roller  300 , e.g., toward the central plane  327 . In some implementations, the first half  400  of the core  304  tapers from the first end portion  314  toward the center  326 , and the second half  402  of the core  304  tapers along the longitudinal axis  312  from the second end portion  316  toward the center  326 . In some cases, the core  304  tapers toward the center  326  along an entire length L 3  of the core  304 . In some cases, an outer diameter D 1  of the core  304  near or at the center  326  of the roller  300  is smaller than outer diameters D 2 , D 3  of the core  304  near or the first and second end portions  314 ,  316  of the core  304 . The outer diameters of the core  304 , for example, linearly decreases along the longitudinal axis  312  of the roller  300 , e.g., from positions along the longitudinal axis  312  at both of the end portions  314 ,  316  to the center  326 . 
     In some implementations, the core  304  of the support structure  303  tapers from the first end portion  314  and the second end portion  316  toward the center  326  of the roller  300 , and the elongate portions  305   a ,  305   b  are integral to the core  304 . The core  304  is affixed to the shaft  306  along the entire length L 3  of the core  304 . By being affixed to the core  304  along the entire length L 3  of the core  304 , torque applied to the core  304  and/or the shaft  306  can transfer more evenly along the entire length L 3  of the core  304 . 
     In some implementations, the support structure  303  is a single monolithic component in which the core  304  extends along the entire length of the support structure  303  without any discontinuities. The core  304  is integral to the first end portion  314  and the second end portion  316 . Alternatively, referring to  FIG. 4B , the core  304  includes multiple discontinuous sections that are positioned around the shaft  306 , positioned within the sheath  302 , and affixed to the sheath  302 . The first half  400  of the core  304  includes, for example, multiple sections  402   a ,  402   b ,  402   c . The sections  402   a ,  402   b ,  402   c  are discontinuous with one another such that the core  304  includes gaps  403  between the sections  402   a ,  402   b  and the sections  402   b ,  402   c . Each of the multiple sections  402   a ,  402   b ,  402   c  is affixed to the shaft  306  so as to improve torque transfer from the shaft  306  to the core  304  and the support structure  303 . In this regard, the shaft  306  mechanically couples each of the multiple sections  402   a ,  402   b ,  402   c  to one another such that the sections  402   a ,  402   b ,  402   c  jointly rotate with the shaft  306 . Each of the multiple sections  402   a ,  402   b ,  402   c  is tapered toward the center  326  of the roller  300 . The multiple sections  402   a ,  402   b ,  402   c , for example, each taper away from the first end portion  314  of the core  304  and taper toward the center  326 . The elongate portion  305   a  of the support structure  303  is fixed to the section  402   a  of the core  304 , e.g., integral to the section  402   a  of the core  304 . 
     Similarly, the second half  402  of the core  304  includes, for example, multiple sections  404   a ,  404   b ,  404   c  discontinuous with one another such that the core  304  includes gaps  403  between the sections  404   a ,  404   b  and the sections  404   b ,  404   c . Each of the multiple sections  404   a ,  404   b ,  404   c  is affixed to the shaft  306 . In this regard, the shaft  306  mechanically couples each of the multiple sections  404   a ,  404   b ,  404   c  to one another such that the sections  404   a ,  404   b ,  404   c  jointly rotate with the shaft  306 . The second half  402  of the core  304  accordingly rotates jointly with the first half  400  of the core  304 . Each of the multiple sections  404   a ,  404   b ,  404   c  is tapered toward the center  326  of the roller  300 . The multiple sections  404   a ,  404   b ,  404   c , for example, each taper away from the second end portion  314  of the core  304  and taper toward the center  326 . The elongate portion  305   b  of the support structure  303  is fixed to the section  404   a  of the core  304 , e.g., integral to the section  404   a  of the core  304 . 
     In some cases, the section  402   c  of the first half  400  closest to the center  326  and the section  404   c  of the second half  402  closest to the center  326  are continuous with one another. The section  402   c  of the first half  400  and the section  404   c  of the second half  402  form a continuous section  406  that extends from the center  326  outwardly toward both the first end portion  314  and the second end portion  316  of the core  304 . In such examples, the core  304  includes five distinct, discontinuous sections  402   a ,  402   b ,  406 ,  404   a ,  404   b . Similarly, the support structure  303  includes five distinct, discontinuous portions. The first of these portions includes the elongate portion  305   a  and the section  402   a  of the core  304 . The second of these portions corresponds to the section  402   b  of the core  304 . The third of these portions corresponds to the continuous section  406  of the core  304 . The fourth of these portions corresponds to the section  404   b  of the core  304 . The fifth of these portions includes the elongate portion  305   b  and the section  404   a  of the core  304 . While the core  304  and the support structure  303  are described as including five distinct and discontinuous portions, in some implementations, the core  304  and the support structure  303  include fewer or additional discontinuous portions. 
     Referring to both  FIGS. 4C and 4D , the first end portion  314  of the core  304  includes alternating ribs  408 ,  410 . The ribs  408 ,  410  each extend radially outwardly away from the longitudinal axis  312  of the roller  300 . The ribs  408 ,  410  are continuous with one another and form the section  402   a.    
     The transverse rib  408  extends transversely relative to the longitudinal axis  312 . The transverse rib  408  includes a ring portion  412  fixed to the shaft  306  and lobes  414   a - 414   d  extending radially outwardly from the ring portion  412 . In some implementations, the lobes  414   a - 414   d  are axisymmetric about the ring portion  412 , e.g., axisymmetric about the longitudinal axis  312  of the roller  300 . 
     The longitudinal rib  410  extends longitudinal along the longitudinal axis  312 . The rib  410  includes a ring portion  416  fixed to the shaft  306  and lobes  418   a - 418   d  extending radially outwardly from the ring portion  416 . The lobes  418   a - 418   d  are axisymmetric about the ring portion  416 , e.g., axisymmetric about the longitudinal axis  312  of the roller  300 . 
     The ring portion  412  of the rib  408  has a wall thickness greater than a wall thickness of the ring portion  416  of the rib  410 . The lobes  414   a - 414   d  of the rib  408  have wall thicknesses greater than wall thicknesses of the lobes  418   a - 418   d  of the rib  410 . 
     Free ends  415   a - 415   d  of the lobes  414   a - 414   d  define outer diameters of the ribs  408 , and free ends  419   a - 419   d  of the lobes  418   a - 418   d  define outer diameters of the ribs  410 . A distance between the free ends  415   a - 415   d ,  419   a - 419   d  and the longitudinal axis  312  define widths of the ribs  408 ,  410 . In some cases, the widths are outer diameters of the ribs  408 ,  410 . The free ends  415   a - 415   d ,  419   a - 419   d  are arcs coincident with circles centered along the longitudinal axis  312 , e.g., are portions of the circumferences of these circles. The circles are concentric with one another and with the ring portions  412 ,  416 . In some cases, an outer diameter of ribs  408 ,  410  closer to the center  326  is greater than an outer diameter of ribs  408 ,  410  farther from the center  326 . The outer diameters of the ribs  408 ,  410  decrease linearly from the first end portion  314  to the center  326 , e.g., to the central plane  327 . In particular, as shown in  FIG. 4D , the ribs  408 ,  410  form a continuous longitudinal rib  411  that extends along a length of the section  402   a . The rib extends radially outwardly from the longitudinal axis  312 . The height of the rib  411  relative to the longitudinal axis  312  decreases toward the center  327 . The height of the rib  411 , for example, linearly decreases toward the center  327 . 
     In some implementations, referring also to  FIG. 4B , the core  304  of the support structure  303  includes posts  420  extending away from the longitudinal axis  312  of the roller  300 . The posts  420  extend, for example, from a plane extending parallel to and extending through the longitudinal axis  312  of the roller  300 . As described herein, the posts  420  can improve torque transfer between the sheath  302  and the support structure  303 . The posts  420  extend into the sheath  302  to improve the torque transfer as well as to improve bond strength between the sheath  302  the support structure  303 . The posts  420  can stabilize and mitigate vibration in the roller  300  by balancing mass distribution throughout the roller  300 . 
     In some implementations, the posts  420  extend perpendicular to a rib of the core  304 , e.g., perpendicular to the lobes  418   a ,  418   c . The lobes  418   a ,  418   c , for example, extend perpendicularly away from the longitudinal axis  312  of the roller  300 , and the posts  420  extend from the lobe  418   a ,  418   c  and are perpendicular to the lobes  418   a ,  418   c . The posts  420  have a length L 6 , for example, between 0.5 and 4 mm, e.g., 0.5 to 2 mm, 1 mm to 3 mm, 1.5 mm to 3 mm, 2 mm to 4 mm, etc. 
     In some implementations, the core  304  includes multiple posts  420   a ,  420   b  at multiple positions along the longitudinal axis  312  of the roller  300 . The core  304  includes, for example, multiple posts  420   a ,  420   c  extending from a single transverse plane perpendicular to the longitudinal axis  312  of the roller  300 . The posts  420   a ,  420   c  are, for instance, symmetric to one another along a longitudinal plane extending parallel to and extending through the longitudinal axis  312  of the roller  300 . The longitudinal plane is distinct from and perpendicular to the transverse plane from which the posts  420   a ,  420   c  extend. In some implementations, the posts  420   a ,  420   c  at the transverse plane are axisymmetrically arranged about the longitudinal axis  312  of the roller  300 . 
     While four lobes are depicted for each of the ribs  408 ,  410 , in some implementations, the ribs  408 ,  410  include fewer or additional lobes. While  FIGS. 4C and 4D  are described with respect to the first end portion  314  and the section  402   a  of the core  304 , the configurations of the second end portion  316  and the other sections  402   b ,  402   c , and  404   a - 404   c  of the core  304  may be similar to the configurations described with respect to the examples in  FIGS. 4C and 4D . The first half  400  of the core  304  is, for example, symmetric to the second half  402  about the central plane  327 . 
     The sheath  302  positioned around the core  304  has a number of appropriate configurations.  FIGS. 3A-3E  depict one example configuration. The sheath  302  includes a shell  336  surrounding and affixed to the core  304 . The shell  336  include a first half  338  and a second half  340  symmetric about the central plane  327 . The first half  322  of the sheath  302  includes the first half  338  of the shell  336 , and the second half  324  of the sheath  302  includes the second half  340  of the shell  336 . 
     In some implementations, the first half  338  and the second half  340  of the shell  336  include frustoconical portions  341   a ,  341   b  and cylindrical portions  343   a ,  343   b . Central axes of the frustoconical portions  341   a ,  341   b  and cylindrical portions  343   a ,  343   b  each extend parallel to and through the longitudinal axis  312  of the roller  300 . 
     The free portions  331   b ,  331   c  of the sheath  302  include the cylindrical portions  343   a ,  343   b . In this regard, the cylindrical portions  343   a ,  343   b  extend beyond the end portions  314 ,  316  of the core  304 . The cylindrical portions  343   a ,  343   b  are tubular portions having inner surfaces and outer surfaces. The collection wells  328 ,  330  are defined by inner surfaces of the cylindrical portions  343   a ,  343   b.    
     The fixed portion  331   a  of the sheath  302  includes the frustoconical portions  341   a ,  341   b  of the shell  336 . The frustoconical portions  341   a ,  341   b  extend from the central plane  327  along the longitudinal axis  312  toward the end portions  318 ,  320  of the sheath  302 . The frustoconical portions  341   a ,  341   b  are arranged on the core  304  of the support structure  303  such that an outer diameter of the shell  336  decreases toward the center  326  of the roller  300 , e.g., toward the central plane  327 . An outer diameter D 4  of the shell  336  at the central plane  327  is, for example, less than outer diameters D 5 , D 6  of the shell  336  at the outer end portions  318 ,  320  of the sheath  302 . Whereas the inner surfaces of the cylindrical portions  343   a ,  343   b  are free, inner surfaces of the frustoconical portions  341   a ,  341   b  are fixed to the core  304 . In some cases, the outer diameter of the shell  336  linearly decreases toward the center  326 . 
     While the sheath  302  is described as having cylindrical portions  343   a ,  343   b , in some implementations, the portions  343   a ,  343   b  are part of the frustoconical portions  341   a ,  341   b  and are also tapered. The frustoconical portions  341   a ,  341   b  extend along the entire length of the sheath  302 . In this regard, the collection wells  328 ,  330  are defined by inner surfaces of the frustoconical portions  341   a ,  341   b.    
     Referring to  FIG. 3D , the shell  336  includes core securing portions  350  affixed to the lobes of the core  304 , e.g., the lobes  414   a - 414   d ,  418   a - 418   d . In particular, the core securing portions  350  fix the frustoconical portions  341   a ,  341   b  to the core  304 . Each core securing portion  350  extends radially inwardly from the outer surface of the shell  336  and is affixed to the lobes of the core  304 . For example, the core securing portions  350  interlock with the core  304  to enable even torque transfer from the core  304  to the frustoconical portions  341   a ,  341   b . In particular, the core securing portions  350  are positioned between the lobes  414   a - 414   d ,  418   a - 418   d  of the core  304  such that the core  304  can more easily drive the shell  336  and hence the sheath  302  as the core  304  is rotated. The core securing portions  350  are, for example, wedge-shaped portions that extend circumferentially between adjacent lobes  414   a - 414   d ,  418   a - 418   d  of the core  304  and extend radially inwardly toward the ring portions  412 ,  416  of the core  304 . 
     Referring to  FIG. 3E , the shell  336  further includes a shaft securing portion  352  that extends radially inwardly from the outer surface of the shell  336  toward the shaft  306 . The shaft securing portion  352  fixes the frustoconical portions  341   a ,  341   b  to the shaft  306 . In particular, the shaft securing portion  352  extends between the discontinuous sections  402   a ,  402   b ,  402   c  inwardly to the shaft  306 , enabling the shaft securing portion  352  to fix the sheath  302  to the shaft  306 . In this regard, the sheath  302  is affixed to the support structure  303  through the core  304 , and the sheath  302  is affixed to the shaft  306  through the gaps  403  (shown in  FIG. 4B ) between the discontinuous sections of the core  304  that enable direct contact between the sheath  302  and the shaft  306 . In some cases, as described herein, the shaft securing portion  352  directly bonds to the shaft  306  during the overmold process to form the sheath  302 . 
     Because the shaft  306  is affixed to both the core  304  and the shaft  306 , torque delivered to the shaft  306  can be easily transferred to the sheath  302 . The increased torque transfer can improve the ability of the sheath  302  to pick up debris from the floor surface  10 . The torque transfer can be constant along the length of the roller  300  because of the interlocking interface between the sheath  302  and the core  304 . In particular, the core securing portions  350  of the shell  336  interlock with the core  304 . The outer surface of the shell  336  can rotate at the same or at a similar rate as the shaft  306  along the entire length of the interface between the shell  336  and the core  304 . 
     In some implementations, the sheath  302  of the roller  300  is a monolithic component including the shell  336  and cantilevered vanes extending substantially radially from the outer surface of the shell  336 . Each vane has one end fixed to the outer surface of the shell  336  and another end that is free. The height of each vane is defined as the distance from the fixed end at the shell  336 , e.g., the point of attachment to the shell  336 , to the free end. The free end sweeps an outer circumference of the sheath  302  during rotation of the roller  300 . The outer circumference is consistent along the length of the roller  300 . Because the radius from the axis  312  to the outer surface of the shell  336  decreases from the ends  318 ,  320  of the sheath  302  to the center  327 , the height of each vane increases from the ends  318 ,  320  of the sheath  302  to the center  327  so that the outer circumference of the roller  300  is consistent across the length of the roller  300 . In some implementations, the vanes are chevron shaped such that each of the two legs of each vane start at opposing ends  318 ,  320  of the sheath  302 , and the two legs meet at an angle at the center  327  of the roller  300  to form a “V” shape. The tip of the V precedes the legs in the direction of rotation. 
       FIGS. 5A and 5B  depict one example of the sheath  302  including one or more vanes on an outer surface of the shell  336 . Referring to  FIG. 3C , while a single vane  342  is described herein, the roller  300  includes multiple vanes in some implementations, with each of the multiple vanes being similar to the vane  342  but arranged at different locations along the outer surface of the shell  336 . The vane  342  is a deflectable portion of the sheath  302  that, in some cases, engages with the floor surface  10  when the roller  300  is rotated during a cleaning operation. The vane  342  extends along outer surface of the cylindrical portions  343   a ,  343   b  and the frustoconical portions  341   a ,  341   b  of the shell  336 . The vane  342  extends radially outwardly from the sheath  302  and away from the longitudinal axis  312  of the roller  300 . The vane  342  deflects when it contacts the floor surface  300  as the roller  300  rotates. 
     Referring to  FIG. 5B , the vane  342  extends from a first end  500  fixed to the shell  336  and a second free end  502 . A height of the vane  342  corresponds to, for example, a height H 1  measured from the first end  500  to the second end  502 , e.g., a height of the vane  342  measured from the outer surface of the shell  336 . The height H 1  of the vane  342  proximate the center  326  of the roller  300  is greater than the height H 1  of the vane  342  proximate the first end portion  308  and the second portion  310  of the shaft  306 . The height H 1  of the vane  342  proximate the center of the roller  300  is, in some cases, a maximum height of the vane  342 . In some cases, the height H 1  of the vane  342  linearly decreases from the center  326  of the roller  300  toward the first end portion  308  of the shaft  306 . In some cases, the height H 1  of the vane  342  is uniform across the cylindrical portions  343   a ,  343   b  of the shell  336 , and linearly decreases in height along the frustoconical portions  341   a ,  341   b  of the shell  336 . In some implementations, the vane  342  is angled rearwardly relative to a direction of rotation  503  of the roller  300  such that the vane  342  more readily deflects in response to contact with the floor surface  10 . 
     Referring to  FIG. 5A , the vane  342  follows, for example, a V-shaped path  504  along the outer surface of the shell  336 . The V-shaped path  504  includes a first leg  506  and a second leg  508  that each extend from the central plane  327  toward the first end portion  318  and the second end portion  320  of the sheath  302 , respectively. The first and second legs  506 ,  508  extend circumferentially along the outer surface of the shell  336 , in particular, in the direction of rotation  503  of the roller  300 . The height H 1  of the vane  342  decreases along the first leg  506  of the path  504  from the central plane  327  toward the first end portion  318 , and the height H 1  of the vane  342  decreases along the second leg  508  of the path  504  from the central plane  327  toward the second end portion  320 . In some cases, the height of the vanes  342  decreases linearly from the central plane  327  toward the second portion  320  and decreases linearly from the central plane  327  toward the first end portion  318 . 
     In some cases, an outer diameter D 7  of the sheath  302  corresponds to a distance between free ends  502   a ,  502   b  of vanes  342   a ,  342   b  arranged on opposite sides of a plane through the longitudinal axis  312  of the roller  300 . The outer diameter D 7  of the sheath  302  is, in some cases, uniform across the entire length of the sheath  302 . In this regard, despite the taper of the frustoconical portions  341   a ,  341   b  of the shell  336 , the outer diameter of the sheath  302  is uniform across the length of the sheath  302  because of the varying height of the vanes  342   a ,  342   b  of the sheath  302 . 
     When the roller  300  is paired with another roller, e.g., the roller  104   b , the outer surface of the shell  336  of the roller  300  and the outer surface of the shell  336  of the other roller defines a separation therebetween, e.g., the separation  108  described herein. The rollers define an air gap therebetween, e.g., the air gap  109  described herein. Because of the taper of the frustoconical portions  341   a ,  341   b , the separation increases in size toward the center  326  of the roller  300 . The frustoconical portions  341   a ,  341   b , by being tapered inward toward the center  326  of the roller  300 , facilitate movement of filament debris picked up by the roller  300  toward the end portions  318 ,  320  of the sheath  302 . The filament debris can then be collected into the collection wells  328 ,  330  such that a user can easily remove the filament debris from the roller  300 . In some examples, the user dismounts the roller  300  from the cleaning robot to enable the filament debris collected within the collection wells  328 ,  330  to be removed. 
     In some cases, the air gap varies in size because of the taper of the frustoconical portions  341   a ,  341   b . In particular, the width of the air gap depends on whether the vanes  342   a ,  342  of the roller  300  faces the vanes of the other roller. While the width of the air gap between the sheath  302  of the roller  300  and the sheath between the other roller varies along the longitudinal axis  312  of the roller  300 , the outer circumferences of the rollers are consistent. As described with respect to the roller  300 , the free ends  502   a ,  502   b  of the vanes  342   a ,  342   b  define the outer circumference of the roller  300 . Similarly, free ends of the vanes of the other roller define the outer circumference of the other roller. If the vanes  342   a ,  342   b  face the vanes of the other roller, the width of the air gap corresponds to a minimum width between the roller  300  and the other roller, e.g., a distance between the outer circumference of the shell  336  of the roller  300  and the outer circumference of the shell of the other roller. If the vanes  342   a ,  342   b  of the roller and the vanes of the other roller are positioned such that the air gap is defined by the distance between the shells of the rollers, the width of the air gap corresponds to a maximum width between the rollers, e.g., between the free ends  502   a ,  502   b  of the vanes  342   a ,  342   b  of the roller  300  and the free ends of the vanes of the other roller. 
     Example Dimensions of Cleaning Robots and Cleaning Rollers 
     Dimensions of the cleaning robot  102 , the roller  300 , and their components vary between implementations. Referring to  FIG. 3E  and  FIG. 6 , in some examples, the length L 2  of the roller  300  corresponds to the length between the outer end portions  308 ,  310  of the shaft  306 . In this regard, a length of the shaft  306  corresponds to the overall length L 2  of the roller  300 . The length L 2  is between, for example, 10 cm and 50 cm, e.g., between 10 cm and 30 cm, 20 cm and 40 cm, 30 cm and 50 cm. The length L 2  of the roller  300  is, for example, between 70% and 90% of an overall width W 1  of the robot  102  (shown in  FIG. 2A ), e.g., between 70% and 80%, 75% and 85%, and 80% and 90%, etc., of the overall width W 1  of the robot  102 . The width W 1  of the robot  102  is, for instance, between 20 cm and 60 cm, e.g., between 20 cm and 40 cm, 30 cm and 50 cm, 40 cm and 60 cm, etc. 
     Referring to  FIG. 3E , the length L 3  of the core  304  is between 8 cm and 40 cm, e.g., between 8 cm and 20 cm, 20 cm and 30 cm, 15 cm and 35 cm, 25 cm and 40 cm, etc. The length L 3  of the core  304  corresponds to, for example, the combined length of the frustoconical portions  341   a ,  341   b  of the shell  336  and the length of the fixed portion  331   a  of the sheath  302 . The length L 3  of the core  304  is between 70% and 90% the length L 2  of the roller  300 , e.g., between 70% and 80%, 70% and 85%, 75% and 90%, etc., of the length L 2  of the roller  300 . A length L 4  of the sheath  302  is between 9.5 cm and 47.5 cm, e.g., between 9.5 cm and 30 cm, 15 cm and 30 cm, 20 cm and 40 cm, 20 cm and 47.5 cm, etc. The length L 4  of the sheath  302  is between 80% and 99% of the length L 2  of the roller  300 , e.g., between 85% and 99%, 90% and 99%, etc., of the length L 2  of the roller  300 . 
     Referring to  FIG. 4B , a length L 8  of one of the elongate portions  305   a ,  305   b  of the support structure  303  is, for example, between 1 cm and 5 cm, e.g., between 1 and 3 cm, 2 and 4 cm, 3 and 5 cm, etc. The elongate portions  305   a ,  306   b  have a combined length that is, for example, between 10 and 30% of an overall length L 9  of the support structure  303 , e.g., between 10% and 20%, 15% and 25%, 20% and 30%, etc., of the overall length L 9 . In some examples, the length of the elongate portion  305   a  differs from the length of the elongate portion  305   b . The length of the elongate portion  305   a  is, for example, 50% to 90%, e.g., 50% to 70%, 70% to 90%, the length of the elongate portion  305   b.    
     The length L 3  of the core  304  is, for example, between 70% and 90% of the overall length L 9 , e.g., between 70% and 80%, 75% and 85%, 80% and 90%, etc., of the overall length L 9 . The overall length L 9  is, for example, between 85% and 99% of the overall length L 2  of the roller  300 , e.g., between 90% and 99%, 95% and 99%, etc., of the overall length L 2  of the roller  300 . The shaft  306  extends beyond the elongate portion  305   a  by a length L 10  of, for example, 0.3 mm to 2 mm, e.g., between 0.3 mm and 1 mm, 0.3 mm and 1.5 mm, etc. As described herein, in some cases, the overall length L 2  of the roller  300  corresponds to the overall length of the shaft  306 , which extends beyond the length L 9  of the support structure  303 . 
     Referring to  FIG. 3E , in some implementations, a length L 5  of one of the collection wells  328 ,  330  is, for example, between 1.5 cm and 10 cm, e.g., between 1.5 cm and 7.5 cm, 5 cm and 10 cm, etc. The length L 5 , for example, corresponds to the length of the cylindrical portions  343   a ,  343   b  of the shell  336  and the length of the free portions  331   b ,  331   c  of the sheath  302 . The length L 5  of one of the collection wells  328 ,  330  is, for example, 2.5% to 15% of the length L 2  of the roller  300 , e.g., between 2.5% and 10%, 5% and 10%, 7.5% and 12.5%, 10% and 15% of the length L 2  of the roller  300 . An overall combined length of the collection wells  328 ,  330  is, for example, between 3 cm and 15 cm, e.g., between 3 and 10 cm, 10 and 15 cm, etc. This overall combined length corresponds to an overall combined length of the free portions  331   b ,  331   c  of the sheath  302  and an overall combined length of the cylindrical portions  343   a ,  343   b  of the shell  336 . The overall combined length of the collection wells  328 ,  330  is, for example, between 5% and 30% of the length L 2  of the roller  300 , e.g., between 5% and 15%, 5% and 20%, 10% and 25%, 15% and 30%, etc., of the length L 2  of the roller  300 . In some examples, the combined length of the collection wells  328 ,  330  is between 5% and 40% of the length L 3  of the core  304 , e.g., between 5% and 20%, 20% and 30%, and 30% and 40%, etc. of the length L 3  of the core  304 . 
     In some implementations, as shown in  FIG. 6 , a width or diameter of the roller  300  between the end portion  318  and the end portion  320  of the sheath  302  corresponds to the diameter D 7  of the sheath  302 . The diameter D 7  is, in some cases, uniform from the end portion  318  to the end portion  320  of the sheath  302 . The diameter D 7  of the roller  300  at different positions along the longitudinal axis  312  of the roller  300  between the position of the end portion  318  and the position of the end portion  320  is equal. The diameter D 7  is between, for example, 20 mm and 60 mm, e.g., between 20 mm and 40 mm, 30 mm and 50 mm, 40 mm and 60 mm, etc. 
     Referring to  FIG. 5B , the height H 1  of the vane  342  is, for example, between 0.5 mm and 25 mm, e.g., between 0.5 and 2 mm, 5 and 15 mm, 5 and 20 mm, 5 and 25 mm, etc. The height H 1  of the vane  342  at the central plane  327  is between, for example, 2.5 and 25 mm, e.g., between 2.5 and 12.5 mm, 7.5 and 17.5 mm, 12.5 and 25 mm, etc. The height H 1  of the vane  342  at the end portions  318 ,  320  of the sheath  302  is between, for example, 0.5 and 5 mm, e.g., between 0.5 and 1.5 mm, 0.5 and 2.5 mm, etc. The height H 1  of the vane  342  at the central plane  327  is, for example, 1.5 to 50 times greater than the height H 1  of the vane  342  at the end portions  318 ,  320  of the sheath  302 , e.g., 1.5 to 5, 5 to 10, 10 to 20, 10 to 50, etc., times greater than the height H 1  of the vane  342  at the end portions  318 ,  320 . The height H 1  of the vane  342  at the central plane  327 , for example, corresponds to the maximum height of the vane  342 , and the height H 1  of the vane  342  at the end portions  318 ,  320  of the sheath  302  corresponds to the minimum height of the vane  342 . In some implementations, the maximum height of the vane  342  is 5% to 45% of the diameter D 7  of the sheath  302 , e.g., 5% to 15%, 15% to 30%, 30% to 45%, etc., of the diameter D 7  of the sheath  302 . 
     While the diameter D 7  may be uniform between the end portions  318 ,  320  of the sheath  302 , the diameter of the core  304  may vary at different points along the length of the roller  300 . The diameter D 1  of the core  304  along the central plane  327  is between, for example, 5 mm and 20 mm, e.g., between 5 and 10 mm, 10 and 15 mm, 15 and 20 mm etc. The diameters D 2 , D 3  of the core  304  near or at the first and second end portions  314 ,  316  of the core  304  is between, for example, 10 mm and 50 mm, e.g., between 10 and 20 mm, 15 and 25 mm, 20 and 30 mm, 20 and 50 mm. The diameters D 2 , D 3  are, for example the maximum diameters of the core  304 , while the diameter D 1  is the minimum diameter of the core  304 . The diameters D 2 , D 3  are, for example, 5 to 20 mm less than the diameter D 7  of the sheath  302 , e.g., 5 to 10 mm, 5 to 15 mm, 10 to 20 mm, etc., less than the diameter D 7 . In some implementations, the diameters D 2 , D 3  are 10% to 90% of the diameter D 7  of the sheath  302 , e.g., 10% to 30%, 30% to 60%, 60% to 90%, etc., of the diameter D 7  of the sheath  302 . The diameter D 1  is, for example, 10 to 25 mm less than the diameter D 7  of the sheath  302 , e.g., between 10 and 15 mm, 10 and 20 mm, 15 and 25 mm, etc., less than the diameter D 7  of the sheath  302 . In some implementations, the diameter D 1  is 5% to 80% of the diameter D 7  of the sheath  302 , e.g., 5% to 30%, 30% to 55%, 55% to 80%, etc., of the diameter D 7  of the sheath  302 . 
     Similarly, while the outer diameter of the sheath  302  defined by the free ends  502   a ,  502   b  of the vanes  342   a ,  342   b  may be uniform, the diameter of the shell  336  of the sheath  302  may vary at different points along the length of the shell  336 . The diameter D 4  of the shell  336  along the central plane  327  is between, for example, 7 mm and 22 mm, e.g., between 7 and 17 mm, 12 and 22 mm, etc. The diameter D 4  of the shell  336  along the central plane  327  is, for example, defined by a wall thickness of the shell  336 . The diameters D 5 , D 6  of the shell  336  at the outer end portions  318 ,  320  of the sheath  302  are, for example, between 15 mm and 55 mm, e.g., between 15 and 40 mm, 20 and 45 mm, 30 mm and 55 mm, etc. In some cases, the diameters D 4 , D 5 , and D 6  are 1 to 5 mm greater than the diameters D 1 , D 2 , and D 3  of the core  304  along the central plane  327 , e.g., between 1 and 3 mm, 2 and 4 mm, 3 and 5 mm, etc., greater than the diameter D 1 . The diameter D 4  of the shell  336  is, for example, between 10% and 50% of the diameter D 7  of the sheath  302 , e.g., between 10% and 20%, 15% and 25%, 30% and 50%, etc., of the diameter D 7 . The diameters D 5 , D 6  of the shell  336  is, for example, between 80% and 95% of the diameter D 7  of the sheath  302 , e.g., between 80% and 90%, 85% and 95%, 90% and 95%, etc., of the diameter D 7  of the sheath  302 . 
     In some implementations, the diameter D 4  corresponds to the minimum diameter of the shell  336  along the length of the shell  336 , and the diameters D 5 , D 6  correspond to the maximum diameter of the shell  336  along the length of the shell  336 . The diameters D 5 , D 6  correspond to, for example, the diameters of the cylindrical portions  343   a ,  343   b  of the shell  336  and the maximum diameters of the frustroconical portions  341   a ,  341   b  of the shell  336 . In the example depicted in  FIG. 1A , the length S 2  of the separation  108  is defined by the maximum diameters of the shells of the cleaning rollers  104   a ,  104   b . The length S 3  of the separation S 3  of the separation  108  is defined by the minimum diameters of the shells of the cleaning rollers  104   a ,  104   b.    
     In some implementations, the diameter of the core  304  varies linearly along the length of the core  304 . From the minimum diameter to the maximum diameter over the length of the core  304 , the diameter of the core  304  increases with a slope M 1  between, for example, 0.01 to 0.4 mm/mm, e.g., between 0.01 to 0.3 mm/mm, 0.05 mm to 0.35 mm/mm, etc. In this regard, the angle between the slope M 1  defined by the outer surface of the core  304  and the longitudinal axis  312  is between, for example, 0.5 degrees and 20 degrees, e.g., between 1 and 10 degrees, 5 and 20 degrees, 5 and 15 degrees, 10 and 20 degrees, etc. 
     Referring to  FIG. 3E , similarly, the diameter of the shell  336  also varies linearly along the length of the shell  336  in some examples. From the minimum diameter to the maximum diameter along the length of the shell  336 , the diameter of the core  304  increases with a slope M 2  similar to the slope described with respect to the diameter of the core  304 . The slope M 2  is between, for example, 0.01 to 0.4 mm/mm, e.g., between 0.01 to 0.3 mm/mm, 0.05 mm to 0.35 mm/mm, etc. The angle between the slope M 2  defined by the outer surface of the shell  336  and the longitudinal axis is similar to the slope M 1  of the core  304 . The angle between the slope M 2  and the longitudinal axis  312  is between, for example, 0.5 degrees and 20 degrees, e.g., between 1 and 10 degrees, 5 and 20 degrees, 5 and 15 degrees, 10 and 20 degrees, etc. In particular, the slope M 2  corresponds to the slope of the frustoconical portions  341   a ,  341   b  of the shell  336 . 
     Example Fabrication Processes for Cleaning Rollers 
     The specific configurations of the sheath  302 , the support structure  303 , and the shaft  306  of the roller  300  can be fabricated using one of a number of appropriate processes. The shaft  306  is, for example, a monolithic component formed from a metal fabrication process, such as machining, metal injection molding, etc. To affix the support structure  303  to the shaft  306 , the support structure  303  is formed from, for example, a plastic material in an injection molding process in which molten plastic material is injected into a mold for the support structure  303 . In some implementations, in an insert injection molding process, the shaft  306  is inserted into the mold for the support structure  303  before the molten plastic material is injected into the mold. The molten plastic material, upon cooling, bonds with the shaft  306  and forms the support structure  303  within the mold. As a result, the support structure  303  is affixed to the shaft  306 . If the core  304  of the support structure  303  includes the discontinuous sections  402   a ,  402   b ,  402   c ,  404   a ,  404   b ,  404   c , the surfaces of the mold engages the shaft  306  at the gaps  403  between the discontinuous sections  402   a ,  402   b ,  402   c ,  404   a ,  404   b ,  404   c  to inhibit the support structure  303  from forming at the gaps  403 . 
     In some cases, the sheath  302  is formed from an insert injection molding process in which the shaft  306  with the support structure  303  affixed to the shaft  306  is inserted into a mold for the sheath  302  before molten plastic material forming the sheath  302  is injected into the mold. The molten plastic material, upon cooling, bonds with the core  304  of the support structure  303  and forms the sheath  302  within the mold. By bonding with the core  304  during the injection molding process, the sheath  302  is affixed to the support structure  303  through the core  304 . In some implementations, the mold for the sheath  302  is designed so that the frustoconical portions  341   a ,  341   b  are bonded to the core  304 , while the cylindrical portions  343   a ,  343   b  are not bonded to the core  304 . Rather, the cylindrical portions  343   a ,  343   b  are unattached and extend freely beyond the end portions  314 ,  316  of the core  304  to define the collection wells  328 ,  330 . 
     In some implementations, to improve bond strength between the sheath  302  and the core  304 , the core  304  includes structural features that increase a bonding area between the sheath  302  and the core  304  when the molten plastic material for the sheath  302  cools. In some implementations, the lobes of the core  304 , e.g., the lobes  414   a - 414   d ,  418   a - 418   d , increase the bonding area between the sheath  302  and the core  304 . The core securing portion  350  and the lobes of the core  304  have increased bonding area compared to other examples in which the core  304  has, for example, a uniform cylindrical or uniform prismatic shape. In a further example, the posts  420  extend into sheath  302 , thereby further increasing the bonding area between the core securing portion  350  and the sheath  302 . The posts  420  engage the sheath  302  to rotationally couple the sheath  302  to the core  304 . In some implementations, the gaps  403  between the discontinuous sections  402   a ,  402   b ,  402   c ,  404   a ,  404   b ,  404   c  enable the plastic material forming the sheath  302  extend radially inwardly toward the shaft  306  such that a portion of the sheath  302  is positioned between the discontinuous sections  402   a ,  402   b ,  402   c ,  404   a ,  404   b ,  404   c  within the gaps  403 . In some cases, the shaft securing portion  352  contacts the shaft  306  and is directly bonded to the shaft  306  during the insert molding process described herein. 
     This example fabrication process can further facilitate even torque transfer from the shaft  306 , to the support structure  303 , and to the sheath  302 . The enhanced bonding between these structures can reduce the likelihood that torque does not get transferred from the drive axis, e.g., the longitudinal axis  312  of the roller  300  outward toward the outer surface of the sheath  302 . Because torque is efficiently transferred to the outer surface, debris pickup can be enhanced because a greater portion of the outer surface of the roller  300  exerts a greater amount of torque to move debris on the floor surface. 
     Furthermore, because the sheath  302  extends inwardly toward the core  304  and interlocks with the core  304 , the shell  336  of the sheath  302  can maintain a round shape in response to contact with the floor surface. While the vanes  342   a ,  342   b  can deflect in response to contact with the floor surface and/or contact with debris, the shell  336  can deflect relatively less, thereby enabling the shell  336  to apply a greater amount of force to debris that it contacts. This increased force applied to the debris can increase the amount of agitation of the debris such that the roller  300  can more easily ingest the debris. Furthermore, increased agitation of the debris can assist the airflow  120  generated by the vacuum assembly  118  to carry the debris into the cleaning robot  102 . In this regard, rather than deflecting in response to contact with the floor surface, the roller  300  can retains its shape and more easily transfer force to the debris. 
     ALTERNATIVE IMPLEMENTATIONS 
     A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. 
     While some of the foregoing examples are described with respect to a single roller  300  or the roller  104   a , the roller  300  is similar to the front roller  104   b  with the exception that the arrangement of vanes  342  of the roller  300  differ from the arrangement of the vanes  224   b  of the front roller  104   b , as described herein. In particular, because the roller  104   b  is a front roller and the roller  104   a  is a rear roller, the V-shaped path for a vane  224   a  of the roller  104   a  is symmetric to the V-shaped path for a vane  224   b  of the roller  104   b , e.g., about a vertical plane equidistant to the longitudinal axes  126   a ,  126   b  of the rollers  104   a ,  104   b . The legs for the V-shaped path for the vane  224   b  extend in the counterclockwise direction  130   b  along the outer surface of the shell  222   b  of the roller  104   b , while the legs for the V-shaped path for the vane  224   a  extend in the clockwise direction  130   a  along the outer surface of the shell  222   a  of the roller  104   a.    
     In some implementations, the roller  104   a  and the roller  104   b  have different lengths. The roller  104   b  is, for example, shorter than the roller  104   a . The length of the roller  104   b  is, for example, 50% to 90% the length of the roller  104   a , e.g., 50% to 70%, 60% to 80%, 70% to 90% of the length of the roller  104   a . If the lengths of the rollers  104   a ,  104   b  are different, the rollers  104   a ,  104   b  are, in some cases, configured such that the minimum diameter of the shells  222   a ,  222   b  of the rollers  104   a ,  104   b  are along the same plane perpendicular to both the longitudinal axes  126   a ,  126   b  of the rollers  104   a ,  104   b . As a result, the separation between the shells  222   a ,  222   b  is defined by the shells  222   a ,  222   b  at this plane. 
     Accordingly, other implementations are within the scope of the claims.