Abstract:
A robot cleaning system includes a debris collection volume, a vacuum airway configured to deliver debris to the debris collection volume, and a cleaning head in pneumatic communication with the vacuum airway. The cleaning head includes two shape-changing resilient tubes separated by an air gap opposing the vacuum airway. The cleaning head is operable in a first configuration, where the two shape-changing resilient tubes rotate against a cleaning surface engaged by the cleaning head to agitate debris on the cleaning surface to pass through the air gap and into the vacuum airway, and a second configuration, where both shape changing resilient tubes deform opposite one another to roll an object larger than the air gap to pass into the vacuum airway.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This U.S. patent application is a continuation of, and claims priority under 35 U.S.C. §120 from, U.S. patent application Ser. No. 13/460,261, filed on Apr. 30, 2012, which claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application 61/481,147, filed Apr. 29, 2011. The disclosures of these prior applications are considered part of the disclosure of this application and are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to a cleaning head for a robotic vacuum, such as a cleaning head for a robotic vacuum having improved cleaning ability. 
     BACKGROUND 
     Concerns for robotic vacuum designers and manufacturers include, among other things, maximizing the effectiveness of the cleaning head and increasing the volume of the dust bin, minimizing the overall size of the robotic vacuum and production cost, providing adequate cleaning power, and preventing hair and other debris from interrupting or degrading performance of the robotic vacuum. 
     A dust bin collects hair, dirt and debris that has been vacuumed and/or swept from a floor. A larger dust bin volume can allow the robotic vacuum to remove more debris from an environment before requiring that the user remove and empty the dust bin, which can increase user satisfaction. 
     Robotic vacuums typically remove debris from the floor primarily using one or more rotating brushes and/or a vacuum stream that pulls the debris into the cleaning head and generally toward the dust bin. 
     It is known that hair and similar debris such as string and thread can become entangled, and stall the robotic vacuum and/or degrade cleaning ability. 
     In many robotic vacuums, impellers can be located in a robotic vacuum dust bin to pull air carrying swept dirt, hair, and debris into the dust bin. 
     SUMMARY 
     The present teachings provide an improved cleaning head for a robotic vacuum. In some implementations, a compressible, resilient roller rotatably engaged with an autonomous coverage robot includes a resilient tubular member having one or more vanes extending outwardly from an outer surface thereon. The resilient tubular member has integrally formed therein a plurality of resilient curvilinear spokes extending between an inner surface of the flexible tubular member and a hub disposed along the longitudinal axis of the tubular member. The hub has one or more engagement elements formed therein for engaging securely with a rigid drive shaft. In one embodiment, engagement elements are a pair of receptacles formed into the circumference of the hub for receiving raised key elements formed along the outer surface of the rigid drive shaft. The engagement elements enable the transfer of torque from the drive shaft to the resilient tubular member via the resilient curvilinear spokes. 
     In some implementations, the curvilinear spokes extend within about 5% to about 50% of the longitudinal length of the flexible tubular member, or more specifically about 10% to about 30% of the longitudinal length of the flexible tubular member, or more specifically about 10% to about 20% of the longitudinal length of the flexible tubular member 
     In some implementations, the compressible roller further includes a resilient compressible material disposed between the flexible tubular tube and the rigid drive shaft. The resilient compressible material may be, for example, Thermoplastic Polyurethane (TPU) foam, Ethyl Vinyl Acetate (EVA), or polypropylene foam, and in some implementations, the resilient compressible material may be affixed permanently to the rigid shaft to resist shear forces that would otherwise dislodge the resilient compressible material. In one implementation, the curvilinear spokes are serpentine shaped in cross section and therefore automatically spring back to their full extension upon removal of external (e.g., a radial) force. The curvilinear spokes and hub may be located along the entire longitudinal length of the tubular member, but need only occupy a portion of the longitudinal length. For example, in one implementation, the curvilinear spokes and hub may occupy only about 10% to about 20% of the length of the resilient tubular member and may be centered about a central portion of the tubular member along the longitudinal axis of the tubular member, leaving 80% or more of unobstructed length along which compressible resilient material may be disposed. 
     In one aspect, the one or more vanes are integrally formed with the resilient tubular member and define V-shaped chevrons extending from one end of the resilient tubular member to the other end. In one embodiment, the one or more vanes are equidistantly spaced around the circumference of the resilient tube member. In one embodiment, the vanes are aligned such that the ends of one chevron are coplanar with a central tip of an adjacent chevron. This arrangement provides constant contact between the vanes and a contact surface with which the compressible roller engages. Such uninterrupted contact eliminates noise otherwise created by varying between contact and non-contact conditions. In one implementation, the one or more vanes extend from the outer surface of the tubular roller at an angle α between 30° and 60° relative to a radial axis and inclined toward the direction of rotation (see  FIG. 20 ). In one embodiment the angle α of the vanes is 45° to the radial axis. Angling the vanes in the direction of rotation can reduce stress at the root of the vane, thereby reducing or eliminating the likelihood of a vane tearing away from the resilient tubular member. The one or more vanes contact debris on a cleaning surface and direct the debris in the direction of rotation of the compressible, resilient roller. 
     In some implementations, the vanes are V-shaped chevrons and the legs of the V are at a 5° to 10° angle θ relative a linear path traced on the surface of the tubular member and extending from one end of the resilient tubular member to the other end (see  FIG. 22 ). In one embodiment, the two legs of the V-shaped chevron are at an angle θ of 7°. By limiting the angle θ to less than 10°, the compressible roller is more easily manufacturable by molding processes. Angles steeper than 10° can create failures in manufacturability for elastomers having a durometer harder than 80 A. In one embodiment, the tubular member and curvilinear spokes and hub are injection molded from a resilient material of a durometer ranging from and including 60 A to 80 A. A softer durometer material than this range may exhibit premature wear and catastrophic rupture and a resilient material of harder durometer will create substantial drag (i.e. resistance to rotation) and will result in fatigue and stress fracture. In some implementations, the resilient tubular member is manufactured from TPU and the wall of the resilient tubular member has a thickness of about 1 mm. In some examples, the inner diameter of the resilient tubular member is about 23 mm and the outer diameter is about 25 mm. In one embodiment of the resilient tubular member having a plurality of vanes, the diameter of the outside circumference swept by the tips of the plurality of vanes is 30 mm. 
     Because the one or more vanes extend from the outer surface of the resilient tubular member by a height that is, in one embodiment, at least 10% of the diameter of the resilient tubular roller, they can prevent cord-like elements from directly wrapping around the outer surface of the resilient tubular member. The one or more vanes therefore prevent hair or other string-like debris from wrapping tightly around the core of the compressible roller and reducing efficacy of cleaning. Defining the vanes as V-shaped chevrons further assists with directing hair and other debris from the ends of a roller toward the center of the roller, where the point of the V-shaped chevron is located. In one embodiment, the V-shaped chevron point is located directly in line with the center of a vacuum inlet of the autonomous coverage robot. 
     These structural elements of the compressible roller enable contact with objects passing by the compressible roller into the vacuum airway, while minimizing clearance spaces. Tight clearances (e.g., 1 mm gaps) between the compressible roller and the cleaning head module concentrate the vacuum airflow from the vacuum airway at the cleaning surface, thereby maintaining airflow rate. The compressibility of the roller enables objects larger than those narrow clearance gaps to be directed by the one or more vanes into the vacuum airway. The compressible roller resiliently expands and regains full structural extension once the object passes by the compressible roller into the vacuum airway, thereby removing the contact force. 
     In some implementations, the frame or cage of the cleaning head surrounds the cleaning head and facilitates attachment of the cleaning head to the robotic vacuum chassis. The four-bar linkage discuss hereinabove facilitates movement (i.e., “floating”) of the cleaning head within its frame. When a robotic vacuum having a cleaning head in accordance with the present teachings is operating, it is preferable that a bottom surface of the cleaning head remain substantially parallel to the floor, and in some embodiments, it is preferable that the front roller be positioned slightly higher than the rear roller during operation to prevent the front roller from digging into the cleaning surface, especially during transition from a firm surface (e.g., hardwood or tile) to a compressible surface (e.g., carpet). The cleaning head moves vertically during operation, for example to accommodate floor irregularities like thresholds, vents, or moving from a vinyl floor to carpet. The illustrated four-bar linkage provides a simple mechanism to support the cleaning head within the frame and allow the cleaning head to move relative to the frame so that the cleaning head can adjust vertically during operation of the robotic vacuum without pivoting in a manner that will cause the cleaning head to lose its parallel position with respect to the floor. 
     The frame is intended to remain fixed relative to the robotic vacuum chassis as the cleaning head components illustrated herein move relative to the frame and the chassis. 
     In another implementation, an autonomous coverage robot has a chassis having forward and rearward portions. A drive system is mounted to the chassis and configured to maneuver the robot over a cleaning surface. A cleaning assembly is mounted on the forward portion of the chassis and at has two counter-rotating rollers mounted therein for retrieving debris from the cleaning surface, the longitudinal axis of the forward roller lying in a first horizontal plane positioned above a second horizontal plane on which the longitudinal axis of the rearward roller lies. The cleaning assembly is movably mounted to the chassis by a linkage affixed at a forward end to the chassis and at a rearward end to the cleaning assembly. When the robot transitions from a firm surface to a compressible surface, the linkage lifts the cleaning assembly from the cleaning surface. The linkage lifts the cleaning assembly substantially parallel to the cleaning surface but such that the front roller lifts at a faster rate than the rearward roller. 
     The robot has an enclosed dust bin module mounted on the rearward portion of the chassis, and the enclosed dust bin module defines a collection volume in communication with the two counter rotating rollers via a sealed vacuum plenum (which can include an air inlet). The sealed vacuum plenum has a first opening positioned above the two counter-rotating rollers and a second opening positioned adjacent an entry port to the collection volume. The plenum comprises a substantially horizontal elastomeric or hinged portion leading into the collection volume. The substantially horizontal portion flexes or pivots to create a downward slope when the linkage lifts the cleaning assembly to accommodate height differentials in cleaning surfaces. In one embodiment, the substantially horizontal elastomeric portion flexes in a vertical dimension at least 5 mm such that debris lifted from the cleaning surface by the rollers travels up into the plenum and is directed down into the enclosed dust bin. 
     In certain embodiments, the elastomeric portion flexes in a range of about 1 mm to about 10 mm, or more specifically from about 2 mm to about 8 mm, or more specifically from about 4 mm to about 6 mm (e.g., 5 mm) 
     In one embodiment, the linkage lifts at a variable rate (the front roller lifting at a faster rate than the rearward roller) such that maximum lift angle from resting state is less than 10°. 
     The forward roller is positioned higher than the rearward roller such that, on a firm cleaning surface, such as hardwood, the forward roller suspends above the surface and only the rearward roller makes contact. As the robot transitions from a firm cleaning surface to a thick, compressible surface, such as a carpet, the linkage raises the entire cleaning assembly, including the two counter rotating rollers, upward and substantially parallel to the cleaning surface. Additionally, the linkage lifts the front of the cleaning assembly at a faster rate than the rear of the cleaning assembly such that the forward roller lifts faster than the rearward roller. This uneven lift rate accommodates for a transition, for example, between hardwood flooring and carpet while reducing current draw. The current draw would spike if the forward wheel, which rotates in the same direction as the drive wheels of the robot, were to dig into the carpet. 
     In some implementations, the cleaning assembly has a cleaning head frame and a roller housing, and the cleaning head frame defines the portion of the chassis to which the roller housing is movably linked. In another implementation, an autonomous mobile robot includes a chassis having a drive system mounted therein in communication with a control system. The chassis has a vacuum airway disposed therethrough for delivering debris from a cleaning assembly mounted to the chassis to a debris collection bin mounted to the chassis. The vacuum airway extends between the cleaning assembly and debris collection bin and is in fluid communication at with an impeller member disposed within the debris collection bin. A cleaning head module connected to the chassis has, rotatably engaged therewith, a front roller and a rear roller positioned adjacent one another and beneath an inlet to the vacuum airway. In one embodiment, the front roller and rear roller are in parallel longitudinal alignment with the inlet. In one implementation both the front roller and rear roller are compressible. In another implementation, one of the front and rear rollers is a compressible roller. 
     In some implementations, the cleaning head assembly further includes at least two raised prows positioned adjacent the front roller directly above a cleaning surface on which the autonomous mobile robot moves. Each prow is separated from an adjacent prow by a distance equal to or less than the shortest cross sectional dimension within the vacuum airway. Additionally, the maximum distance formable between the front roller and rear roller, at least one of which is compressible, is equal to or shorter than the shortest cross sectional dimension of the vacuum airway. Any debris larger than the shortest cross-sectional airway dimension therefore will be pushed away from the vacuum airway by the at least two prows such that no objects lodge in the vacuum airway. In one implementation, the at least two prows are a plurality of prows distributed evenly across the cleaning head along the length of the front roller. In another aspect, the cleaning head assembly includes a pair of “norkers,” or protrusions, disposed substantially horizontally to the cleaning surface and positioned between the cleaning surface and the front and rear rollers. Each of the protrusions extends inward along the non-collapsible ends of the rollers, thereby preventing objects from lodging between the ends of the rollers. For example, the protrusions will prevent electrical cords from migrating between the front roller and rear roller and arresting a drive motor. 
     In one implementation, a compressible roller rotatably engaged with the cleaning head module includes a resilient tubular member having one or more vanes extending outwardly from an outer surface thereon. The resilient tubular member has integrally formed therein a plurality of resilient curvilinear spokes extending between an inner surface of the flexible tubular member and a hub disposed along the longitudinal axis of the tubular member. The hub has one or more engagement elements formed therein for engaging securely with a rigid drive shaft. In one embodiment, engagement elements are a pair of receptacles formed into the circumference of the hub for receiving raised key elements formed along the outer surface of the rigid drive shaft. The engagement elements enable the transfer of torque from the drive shaft to the resilient tubular member via the resilient curvilinear spokes. 
     In one embodiment, the compressible roller further includes a resilient compressible material disposed between the flexible tubular member and the rigid drive shaft. The resilient compressible material may be, for example, TPU foam, EVA foam, or polypropylene foam, and in some implementations, the resilient compressible material may be affixed permanently to the rigid shaft to resist shear forces that would otherwise dislodge the resilient compressible material. In other implementations, the resilient compressible material may be affixed permanently to the inner surface of the flexible tubular member to resist shear forces that would otherwise dislodge the resilient compressible material. In one implementation, the curvilinear spokes are serpentine shaped in cross section and therefore automatically spring back to their full extension upon removal of external (e.g., radial) force. The curvilinear spokes and hub may be located along the entire longitudinal length of the tubular member but need only occupy a portion of the longitudinal length. For example, in one implementation, the curvilinear spokes and hub may occupy only about 10% to 20% of the length of the resilient tubular member and may be centered about a central point along the longitudinal axis of the tubular member, leaving 80% or more of unobstructed length along which compressible resilient material may be disposed. 
     In one aspect, the one or more vanes are integrally formed with the resilient tubular member and define V-shaped chevrons extending from one end of the resilient tubular member to the other end. In one embodiment, the one or more vanes are equidistantly spaced around the circumference of the resilient tubular member. In one embodiment, the vanes are aligned such that the ends of one chevron are coplanar with a central tip of an adjacent chevron. This arrangement provides constant contact between the vanes and a contact surface with which the compressible roller engages. Such uninterrupted contact eliminates noise otherwise created by varying between contact and no contact conditions. In one implementation, the one or more vanes extend from the outer surface of the tubular roller at an angle α between 30° and 60° relative to a radial axis and inclined toward the direction of rotation. In one embodiment the angle α of the vanes is 45° to the radial axis. Angling the vanes in the direction of rotation reduces stress at the root of the vane, thereby reducing or eliminating the likelihood of the vanes tearing away from the resilient tubular member. The one or more vanes contact debris on a cleaning surface and direct the debris in the direction of rotation of the compressible roller. 
     In some implementations, the vanes are V-shaped chevrons and the legs of Cthe V are at a 50 to 10° angle θ relative a linear path traced on the surface of the tubular member and extending from one end of the resilient tubular member to the other end. In one embodiment, the two legs of the V-shaped chevron are at an angle θ of 7°. In one embodiment, the tubular member and curvilinear spokes and hub are injection molded from a resilient material of a durometer in a range of 60 A to 80 A. A soft durometer material than this range may exhibit premature wear and catastrophic rupture and a resilient material of harder durometer will create substantial drag (i.e. resistance to rotation) and will result in fatigue and stress fracture. In one embodiment, the resilient tubular member is manufactured from TPU and the wall of the resilient tubular member has a thickness of about 1 mm. In one embodiment, the inner diameter of the resilient tubular member is about 23 mm and the outer diameter is about 25 mm. In one embodiment of the resilient tubular member having a plurality of vanes, the diameter of the outside circumference swept by the tips of the plurality of vanes is 30 mm. 
     Because the one or more vanes extend from the outer surface of the resilient tubular member by a height that is, in one embodiment, at least 10% of the diameter of the resilient tubular roller, they prevent cord like elements from directly wrapping around the outer surface of the resilient tubular member. The one or more vanes therefore prevent hair or other string like debris from wrapping tightly around the core of the compressible roller and reducing efficacy of cleaning. Defining the vanes as V-shaped chevrons further assists with directing hair and other debris from the ends of a roller toward the center of the roller, where the point of the V-shaped chevron is located. In one embodiment the V-shaped chevron point is located directly in line with the center of a vacuum inlet of the autonomous coverage robot. 
     These structural elements of the compressible roller enable contact with objects passing by the compressible roller into the vacuum airway, while minimizing clearance spaces. Tight clearances (e.g., 1 mm gaps) between the compressible roller and the cleaning head module concentrate the vacuum airflow from the vacuum airway at the cleaning surface, thereby maintaining airflow rate. The compressibility of the roller enables objects larger than those narrow clearance gaps to be directed by the one or more vanes into the vacuum airway. The compressible roller resiliently expands and regains full structural extension once the object passes by the compressible roller into the vacuum airway, thereby removing the contact force. 
     In an embodiment having two compressible rollers, objects twice as large may pass between the two compressible rollers into the vacuum airway, as compared to an embodiment having a single compressible roller. For example, in one embodiment having two collapsible rollers facing one another and each having a plurality of vanes, the outer surfaces of the resilient tubular members are spaced apart by a distance of 7 mm. The vanes on each compressible roller extend a distance of 3 mm from the outer surface of the resilient tubular member, and the vanes on each roller are spaced apart by 1 mm at their closest contact point. In this embodiment, objects as large as 14 mm may compress the compressible rollers on their way to a vacuum plenum that has a shortest dimension of no less than 14 mm. Although the spacing between the outer surfaces of the resilient tubular members is controlled, the gap between the vanes of the compressible rollers will vary because the timing of the position of each of the one or more vanes need not be coordinated. 
     In certain embodiments, the gap between the rollers is about 7 mm, the vanes come within 1 mm of one another and each vane has a height of about 3 mm. due to the compressibility of the rollers, such an embodiment is configured to allow an item as large as about 14 mm, and for example, items ranging in size from about 7 mm to about 21 mm, to pass between the rollers and into the vacuum inlet and central plenum for deposit within the dust bin. In certain embodiments, the space between the roller can range from 5 mm to 10 mm, or more specifically from 6 mm to 8 mm (e.g., 7 mm). The height of the vanes can range, for example, from 1 mm to 5 mm, or preferably from 2 mm to 4 mm (e.g., 3 mm). The spacing between the vanes of adjacent rollers can range from, for example, ½/mm to 5 mm, or more specifically ½ mm to 2 mm (e.g., 1 mm). 
     In certain embodiments, the rollers, with vanes, can have a diameter of about 30 mm to 31 mm, and can have diameter of the tube, without vanes, of about 25 mm., in such an embodiment, the central axes of adjacent rollers are about 33 mm apart. The outer diameter of the roller tube without vanes can be, for example, about 15 mm to about 50 mm, or more specifically about 20 mm to about 40 mm, or more specifically about 25 mm to about 30 mm. 
     In certain embodiments, the collapsible, resilient, shape-changing rollers can co-deform or bend in, such that each roller shape changes to permit debris of greater than ⅓ of the roller diameter to pass between the rollers, or preferably greater than ½ of the roller diameter to pass through the rollers. 
     In certain embodiments of the present teachings, the height of the vanes makes up less than ⅔ of the full separation between the rollers, and preferably less than ½ of the full separation of the roller, and further preferably more than about 1 cm of the full separation. 
     In one implementation, a roller rotatably engaged with an autonomous coverage robot includes a resilient tubular member having therein a plurality of resilient curvilinear spokes extending between an inner surface of the flexible tubular member and a hub disposed along the longitudinal axis of the tubular member. The hub has one or more engagement elements formed therein for engaging securely with a rigid drive shaft. In one embodiment, the engagement elements are a pair of receptacles formed into the circumference of the hub for receiving raised key elements formed along the outer surface of the rigid drive shaft. The engagement elements enable the transfer of torque form the drive shaft to the resilient tubular member via the resilient curvilinear spokes. 
     In one embodiment, the compressible roller further includes a resilient compressible material disposed between the flexible tubular sheet and the rigid drive shaft. The resilient compressible material may be TPU foam, EVA foam, or polypropylene foam, and in some implementations, the resilient compressible material may be affixed permanently to the rigid shaft to resist shear forces that would otherwise dislodge the resilient compressible material. In one implementation, the curvilinear spokes are serpentine shaped in cross section and therefore automatically spring back to their full extension upon removal of external (e.g., radial) force. The curvilinear spokes and hub may be located along the entire longitudinal length of the tubular member but need only occupy a portion of the longitudinal length. For example, in one implementation, the curvilinear spokes and hub may occupy only about 10% to 20% of the length of the resilient tubular member and may be centered about the central point along the longitudinal axis of the tubular member, leaving 80% or more of unobstructed length along which compressible resilient material may be disposed. 
     In one aspect, the resilient compressible material extends along the length of the drive shaft a from the hub to a location inward from one or both ends of the drive shaft, the resilient tubular member thereby leaving at least one hollow pocket at either or both ends of the roller. In one embodiment, each end of the roller has therein a first hollow pocket and a second hollow pocket. The first hollow pocked is a substantially cylindrical volume bounded by the resilient tubular member and a first guard member (or flange) extending radially outward from the drive shaft at a distance shorter than the inner radius of the resilient tubular member and substantially in parallel alignment with the end of the resilient tubular member. The first guard member therefore is separated from the inner surface of the resilient tubular member by gap large enough to accommodate strands of hair migrating into the hollow pocket. In one implementation, the roller further includes an end cap having one or more concentric walls, or shrouds, inserted into the ends of the resilient tubular member and concentrically aligned with the longitudinal axis of the drive shaft. In one embodiment, the outer shroud member is longer than the inner shroud member. The outer shroud member of the cap fits into, but does not fully occlude the gap between the shroud and the resilient tubular member such that hair migrates into the first hollow pocket. Hair migrating into the first hollow pocket then may migrate further into a second hollow pocket bounded by the inner and outer shroud members, the first guard member a second guard member extending radially from the drive shaft and positioned on the end of the drive shaft in alignment with the end of the inner shroud member. 
     The first hollow pocket and second hollow pocket collect hair so as to prevent the hair from interfering with rotational drive elements, for example, gears. Once the first and second hollow pockets are filled with hair, additional hair will be rejected and prevented from migrating toward rotational drive elements. The hair collected within the first and second hollow pockets additionally will build up a static charge that repels additional hair attempting to migrate into the roller. Both the drive end and non-driven end of the roller have similarly constructed first and second hollow pockets for collecting hair and preventing interference with rotational elements. 
     In another implementation, an autonomous mobile robot includes a chassis having a drive system mounted therein in communication with a control system. The chassis has a vacuum airway disposed therethrough for delivering debris from a cleaning head assembly mounted to the chassis to a debris collection bin mounted to the chassis. The vacuum airway extends between the cleaning assembly and debris collection bin and is in fluid communication with an impeller member disposed within the debris collection bin. A cleaning head module connected to the chassis has, rotatably engaged therewith, a tubular front roller and a tubular rear roller positioned adjacent one another and beneath an inlet to the vacuum airway. The longitudinal axis of the front roller lies in a first horizontal plane positioned above a second horizontal plane on which the longitudinal axis of the rear roller lies, and the rear roller extends beneath a lower cage of the cleaning head assembly to make contact with the cleaning surface. The front roller and rear roller are separated by a narrow air gap such that the vacuum draw directed from the vacuum airway is concentrated at a point on a cleaning surface directly beneath the gap. In one embodiment, the narrow gap spans a distance at or between about 1 mm and about 2 mm. In one aspect, the cross sectional area of the gap between the front and rear rollers is substantially equal to or less than the cross sectional area of the vacuum inlet. This further maintains vacuum concentration at the cleaning surface directly beneath the gap between the front and rear rollers. In one embodiment, the ratio of the area of the gap to the area of a planar cross section taken across the vacuum airway inlet positioned above the front and rear rollers is 1:1 and may range to as much as 10:1. In one embodiment, the ratio of the area of the gap to the area of a planar cross section taken across the vacuum airway inlet positioned above the front and rear rollers is 4:1. 
     Additionally, in some embodiments, a lower surface of the lower cage is positioned above the cleaning surface at a distance no greater than 1 mm, thereby further maintaining a concentrated vacuum beneath the cleaning head assembly, beneath the front roller (which floats above the cleaning surface), and up through the gap between the front and rear rollers. 
     In one embodiment, the vacuum airway has a substantially constant non-angular cross section from a vacuum inlet positioned above the rollers to an airway outlet positioned adjacent the debris collection bin. In another embodiment, the vacuum inlet flares outward along the longitudinal axis of the front and rear rollers to capture debris entering along the entire length of the rollers. The vacuum inlet is angled toward, and redirects the debris into, the smaller cross sectional volume of the vacuum airway extending from the vacuum inlet. Similarly, the airway outlet may be flared to distribute debris throughout the entire width of the debris collection bin rather than ejecting debris in a single mound directly adjacent the airway outlet. By maintaining a narrower constriction throughout the majority of the vacuum airway and flaring only the vacuum inlet and airway outlet, the airflow velocity is maximized through the vacuum airway, including at a throat, or bend, in the vacuum airway. Maintaining high air velocity throughout the vacuum airway enables debris to pass through the throat of the vacuum airway rather than settling there and obstructing airflow. 
     In one embodiment, the front roller and the rear roller are in parallel longitudinal alignment with the vacuum airway inlet and both rollers have one or more vanes extending outwardly from an outer surface thereof. In one embodiment, the one or more vanes extend from the outer surface of the roller by a height that is, in one embodiment, at least 10% of the diameter of the resilient tubular roller, and the vanes on the front roller are spaced apart from the vanes on the rear roller by a distance of 1 mm. Maintaining a gap between the vanes allows airflow to pass between the front and rear rollers, and minimizing that gap maintains airflow velocity at the cleaning surface directly beneath and between the front and rear rollers. 
     The one or more vanes prevent cord-like elements, such as hair or string, from directly wrapping around the outer surface of the roller and reducing efficacy of cleaning. In one embodiment, the one or more vanes are V-shaped chevrons. Defining the vanes as V-shaped chevrons further assists with directing hair and other debris from the ends of the roller toward the center of the roller, where the point of the V-shaped chevron is located. In one embodiment, the V-shaped chevron point is located directly in line with the center of the vacuum airway inlet of the autonomous coverage robot. 
     In another implementation, an autonomous mobile robot includes a chassis having a drive system mounted therein in communication with a control system. The chassis has a vacuum airway disposed therethrough for delivering debris from a cleaning head assembly mounted to the chassis to a debris collection bin mounted to the chassis. The vacuum airway extends between the cleaning head assembly and debris collection bin and is in fluid communication at with an impeller member disposed within the debris collection bin. A cleaning head module connected to the chassis has rotatably engaged therewith a tubular front roller and a tubular rear roller positioned adjacent one another and beneath an inlet to the vacuum airway. The longitudinal axis of the front roller lies in a first horizontal plane positioned above a second horizontal plane on which the longitudinal axis of the rear roller lies, and the rear roller extends beneath a lower cage of the cleaning head assembly to make contact with the cleaning surface. The front roller and rear roller are separated by an air gap such that the vacuum draw directed from the vacuum airway is concentrated at a point on a cleaning surface directly beneath the air gap. In one embodiment, the air gap spans a distance at or between 1 mm and 2 mm. The cleaning head module envelopes between 125° and 175° of the outer circumference of each roller at a spacing of 1 mm or less between an inner surface of the cleaning head module and the outer surfaces of the front and rear rollers. In one embodiment, the cleaning head module envelopes 150° of the outer circumferential surface of each roller at distance of 1 mm or less. Vacuum airflow is therefore directed substantially between the rollers, and debris lifted by the rollers from the cleaning surface will flow into the vacuum airway through the air gap between the rollers rather than lodging between the rollers the cleaning head module. 
     Additionally, in some implementations, a lower surface of the lower cage of the cleaning head is positioned above the cleaning surface at a distance no greater than 1 mm, thereby further maintaining a concentrated vacuum beneath the cleaning head assembly, beneath the front roller (which floats above the cleaning surface), and up through the gap between the front and rear rollers. 
     In one aspect, the cross-sectional area of the gap between the front and rear rollers is substantially equal to or less than the cross-sectional area of the vacuum inlet. This further maintains vacuum concentration at the cleaning surface directly beneath the gap between the front and rear rollers. In one embodiment, the ratio of the area of the gap to the area of a planar cross section taken across the vacuum airway inlet positioned above the front and rear rollers is 1:1 and may range to as much as 10:1. In one embodiment, the ratio of the area of the gap to the area of a planar cross section taken across the vacuum airway inlet positioned above the front and rear rollers is 4:1. 
     In some implementations, the front roller and rear roller are in parallel longitudinal alignment with the vacuum airway inlet and both rollers have one or more vanes extending outwardly from an outer roller surface. In one embodiment, the one or more vanes extend from the outer surface of the roller by a height that is, in one embodiment, at least 10% of the diameter of the resilient tubular roller, and the vanes on the front roller are spaced apart from the vanes on the rear roller by a distance of 1 mm. Maintaining a gap between the vanes allows airflow to pass between the front and rear rollers, and minimizing that gap maintains airflow velocity at the cleaning surface directly beneath and between the front and rear rollers. 
     In some implementations, the vanes are V-shaped chevrons and the legs of the V are at a 5° to 10° angle θ relative a linear path traced on the surface of each roller and extending from one end of a roller to the other end. The one or more vanes prevent cord-like elements, such as hair or string, from directly wrapping around the outer surface of the roller and reducing efficacy of cleaning. In one embodiment, the one or more vanes are V-shaped chevrons. Defining the vanes as V-shaped chevrons further assists with directing hair and other debris from the ends of the roller toward the center of the roller, where the point of the V-shaped chevron is located. In one embodiment the V-shaped chevron point is located directly in line with the center of the vacuum airway inlet of the autonomous coverage robot. 
     In another implementation, an autonomous mobile robot includes a chassis having a drive system mounted therein in communication with a control system. The chassis has a vacuum airway disposed therethrough for delivering debris from a cleaning head assembly mounted to the chassis to a debris collection bin mounted to the chassis. The vacuum airway extends between the cleaning head assembly and debris collection bin and is in fluid communication with an impeller member disposed within the debris collection bin. A cleaning head module connected to the chassis has rotatably engaged therewith a tubular front roller and a tubular rear roller positioned adjacent one another and beneath an inlet to the vacuum airway. The longitudinal axis of the front roller lies in a first horizontal plane positioned above a second horizontal plane on which the longitudinal axis of the rear roller lies, and the rear roller extends beneath a lower cage of the cleaning head assembly to make contact with the cleaning surface. The front roller and rear roller are separated by a gap equal to or less than 1 mm such that the vacuum draw directed from the vacuum airway is concentrated at a point on a cleaning surface directly beneath the gap. The cleaning head module envelopes between 125° and 175° of the outer circumference of each roller at a distance of 1 mm or less between an inner surface of the cleaning head module and the outer surfaces of the front and rear rollers. In one embodiment, the cleaning head module envelopes 150° of the outer circumferential surface of each roller at spacing of 1 mm or less. Vacuum airflow is therefore directed substantially between the rollers, and debris lifted by the rollers from the cleaning surface will flow into the vacuum airway through the air gap between the rollers rather than lodging between the rollers the cleaning head module. 
     Additionally, in some implementations, a lower surface of the lower cage of the cleaning head is positioned above the cleaning surface at a distance no greater than 1 mm, thereby further maintaining a concentrated vacuum beneath the cleaning head assembly, beneath the front roller (which floats above the cleaning surface), and up through the gap between the front and rear rollers. 
     In one embodiment, the robot further includes an air filter disposed between the debris collection bin, and an axial intake of the impeller such that the axial intake of the impeller and the longitudinal axis of the air filter are substantially coplanar. Additionally, in embodiments, a removable air filter lid encapsulates the air filter and impeller intake. The volume defined beneath the removable air filter lid and the air filter has a transverse cross-sectional area equal to the cross-sectional area of the impeller intake such that airflow remains continuous and free of airflow contraction and/or constriction throughout the volume and into the debris collection bin. 
     In some implementations, the front roller and rear roller are in parallel longitudinal alignment with the vacuum airway inlet and both rollers have one or more vanes extending outwardly from an outer roller surface. In one embodiment, the one or more vanes extend from the outer surface of the roller by a height that is, in one embodiment, at least 10% of the diameter of the resilient tubular roller and the vanes on the front roller are spaced apart from the vanes on the rear roller by a distance of 1 mm. Maintaining a gap between the vanes allows airflow to pass between the front and rear rollers, and minimizing that gap maintains airflow velocity at the cleaning surface directly beneath and between the front and rear rollers. 
     In some implementations, the vanes are V-shaped chevrons, and the legs of the V are at a 50 to 10° angle θ relative a linear path traced on the surface of each roller, extending from one end of a roller to the other end. The one or more vanes prevent cord-like elements, such as hair or string, from directly wrapping around the outer surface of the roller and reducing efficacy of cleaning. In one embodiment, the one or more vanes are V-shaped chevrons. Defining the vanes as V-shaped chevrons further assists with directing hair and other debris from the ends of the roller toward the center of the roller, where the point of the V-shaped chevron is located. In one embodiment the V-shaped chevron point is located directly in line with the center of the vacuum airway inlet of the autonomous coverage robot. 
     In another implementation, an autonomous mobile robot includes a chassis having a drive system mounted therein in communication with a control system. The chassis has a vacuum airway disposed therethrough for delivering debris from a cleaning head assembly mounted to the chassis to a debris collection bin mounted to the chassis. The vacuum airway extends between the cleaning head assembly and debris collection bin and is in fluid communication with an impeller member disposed within the debris collection bin. A cleaning head module connected to the chassis has rotatably engaged therewith a tubular front roller and a tubular rear roller positioned adjacent one another and beneath an inlet to the vacuum airway such that a fluid airflow travels upward from a vacuum airway inlet positioned above the rollers through a front portion of the vacuum airway and into a rear portion of the vacuum airway mated to the debris collection bin. 
     In embodiments, the front portion extending from the vacuum airway (e.g., the vacuum inlet  392  shown in  FIG. 3 ) is sloped such that a top inner surface redirects debris, particularly heavy debris, into the rear portion of the vacuum airway. The longitudinal axis of the front portion is sloped at less than 90° and preferably around 45° relative to a vertical axis. 
     In embodiments, the front portion extending from the vacuum airway inlet is curved toward the rear portion. The front portion may form a partial parabola for instance, having a variable radius. The apex of the parabola may be located above the rear roller, behind a vertical axis aligned with vacuum inlet. The inner wall of the upper surface of the curved vacuum airway will deflect debris into the rear portion of the vacuum airway. 
     The front portion and rear portion of the vacuum airway may be formed as a unitary, monolithic component, but in some embodiments the rear portion is an elastomeric member adjoined to a rigid front portion at a sealed joint. In one embodiment, the sealed joined is a compression fit wherein the rigid front portion is inserted into an elastomeric rear portion and affixed by radial compression forces. In another embodiment the sealed joint is an elastomeric overmold. The sealed joint forms a sealed vacuum path that prevents vacuum loses. In embodiments, the rear portion terminates in a flange abutting an opening to the debris collection bin in a sealed configuration. The vacuum airway therefore enables a smooth, sealed vacuum airflow. In one embodiment, the elastomeric rear portion is manufactured from a thermoplastic material such as Mediprene™ or a thermoplastic vulcanizate (TPV) such as Santoprene™. In one embodiment, the rigid from portion is manufactured from a plastic material such as acrylonitrile butadiene styrene (ABS) or Nylon, which materials have anti-static properties and resist the accumulation of hair. 
     The longitudinal axis of the front roller lies a first horizontal plane positioned above a second horizontal plane on which the longitudinal axis of the rear roller lies, and the rear roller extends beneath a lower cage of the cleaning head assembly to make contact with the cleaning surface. In some embodiments, a lower surface of the lower cage is positioned above the cleaning surface at a distance no greater than 1 mm, thereby further maintaining a concentrated vacuum beneath the cleaning head assembly, beneath the front roller (which floats above the cleaning surface), and up through the gap between the front and rear rollers. 
     In one embodiment, the front roller and rear roller are in parallel longitudinal alignment with the vacuum airway inlet and both rollers have one or more vanes extending outwardly from an outer roller surface. In one embodiment, the one or more vanes extend from the outer surface of the roller by a height that is, in one embodiment, at least 10% of the diameter of the resilient tubular roller and the vanes on the front roller are spaced apart from the vanes on the rear roller by a distance of 1 mm. Maintaining a gap between the vanes allows airflow to pass between the front and rear rollers, and minimizing that gap maintains airflow velocity at the cleaning surface directly beneath and between the front and rear rollers. 
     Objects and advantages of the present teachings will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present teachings. The objects and advantages of the teachings will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. 
     The foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present teachings, as claimed. 
     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present teachings and, together with the description, serve to explain the principles of the teachings. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a top perspective view of an exemplary cleaning robot. 
         FIG. 2A  is a cross sectional view of an exemplary robotic vacuum cleaning head. 
         FIG. 2B  is a cross sectional view of another exemplary robotic vacuum cleaning head. 
         FIG. 3  is a cross sectional view of the cleaning head depicted in  FIG. 2A , in combination with a corresponding removable dust bin. 
         FIG. 4  is an exploded rear perspective view of the cleaning head and dust bin embodiment of  FIGS. 2A and 3 . 
         FIG. 5  is a side rear perspective view of the cleaning head and dust bin embodiment of  FIG. 2B . 
         FIG. 6  is a partial side perspective cross-sectional view of the cleaning head embodiment of  FIGS. 2A ,  3 , and  4 . 
         FIG. 7  is a side perspective view of an exemplary motor and cleaning head gear box for the cleaning head shown in  FIG. 2B . 
         FIG. 8  is a side perspective view of an exemplary impeller assembly, for use in a cleaning head such as that shown in  FIG. 2B . 
         FIG. 9  is a cross-sectional view of the cleaning head embodiment of  FIG. 5 , taken through the impeller shown in  FIG. 8 . 
         FIG. 10  is a cross-sectional view the cleaning head in accordance with  FIG. 2B . 
         FIG. 11  is a side view of the cleaning head embodiment of  FIG. 3 , showing two arms of a four-bar linkage. 
         FIG. 12  is another side view of the cleaning head embodiment of  FIG. 3 , showing two other arms of the four-bar linkage. 
         FIG. 13  is a perspective view of an exemplary arm for a four-bar linkage suspension. 
         FIG. 14  is a perspective view of another exemplary arm for a four-bar linkage suspension. 
         FIG. 15  is bottom perspective view of the embodiment of  FIG. 3 . 
         FIG. 16  is bottom perspective view of a portion of the cleaning head embodiment of  FIG. 3  with a roller frame opened to expose the rollers. 
         FIG. 17  illustrates, schematically, passage of large debris through exemplary collapsible resilient rollers. 
         FIG. 18  is a partial cross-sectional view of an exemplary driven end of a roller. 
         FIG. 19  is a partial cross-sectional view of an exemplary non-driven end of a roller. 
         FIG. 20  is a side perspective view of exemplary resilient rollers. 
         FIG. 21  is an exploded side perspective view of an exemplary resilient roller. 
         FIG. 22  is a cross-sectional view of an exemplary roller having a spoked resilient support. 
         FIG. 23  is a front perspective view of an exemplary dust bin having a front bin door open. 
         FIG. 24  is a top perspective view of the dust bin of  FIG. 23 , having a filter access door open. 
         FIG. 25  is a top perspective view of the dust bin of  FIG. 23 , having the bin top and filter removed. 
         FIG. 26  is a cross sectional view of the dust bin of  FIG. 23 , taken through the impeller housing. 
         FIGS. 27A to 27C  schematically illustrate three positions for an exemplary cleaning assembly suspension. 
         FIGS. 28A and 28B  are section views of exemplary robotic vacuum cleaning heads. 
         FIG. 29  is a bottom view of an exemplary cleaning robot. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     In accordance with certain embodiments, the present teachings contemplate a cleaning head or cleaning head assembly utilizing at least one, and for example two, rollers having collapsible but resilient cores. Embodiments of the collapsible but resilient roller include an outer tubular surface having vanes extending there from. The outer tubular surface can be supported underneath with a resilient support system including, for example, one or more of a foam material and a flexible spoke. The flexible spokes and foam can be designed to have a curvature, size, and composition suitable to obtain a desired roller flexibility and resiliency. While it may be desirable, in certain embodiments, for the flexibility and resiliency of the roller to be consistent along an entire length of the roller, the present teachings contemplate embodiments wherein the flexibility and resiliency of the roller varying along its length. 
     In certain embodiments, the foam support can simply be glued to a vane tubular outer tube of the flexible, resilient roller, and can be provided along the entire length of the roller. Alternatively, the roller can be molded to have resilient spokes supporting the tubular tube along the entire length of the roller. In certain embodiments, the tubular tube can be provided by both resilient spokes and foam, for example utilizing resilient spokes in a center portion of the roller and foam at its outer edges, or vice versa. The tubular tube can be keyed to a drive shaft to transfer torque from the drive shaft to the tubular tube to turn the roller appropriately in the cleaning head. 
     In various embodiments of the present teachings, vanes extending from an outer surface of the tubular tube, from one of the roller to the other end of the roller, can have a generally chevron-type shape. The chevron-type shape can facilitate movement of debris swept by the roller toward a center of the roller (i.e., toward a point of the chevron) so that debris such as hair does not get caught in the ends of the rollers where it can interfere with operation of the roller and thus the cleaning head. To reduce noise caused by interaction of the roller vanes with the floor, the point of one vane chevron can be tangent with the apex of an adjacent vane. 
     In certain embodiments of the present teachings, a trailing (rear) roller can be set lower that a leading (front) roller. Embodiments of the present teachings can also employ a linkage within the cleaning head attaching the rollers to the cleaning head frame that allows the cleaning head to float the cleaning head leading edge higher than a the cleaning head trailing edge. Keeping the leading roller elevated can prevent the leading roller, which typically rotates in the same direction as the wheels of the robotic vacuum during its forward motion, from digging into carpeting during operation of the vacuum. The trailing roller typically rotates in a the opposite direction from the wheels of the robotic vacuum during its forward motion, and therefore tends to not run the risk of digging into carpeting as it encounters and/or moves across carpeting. The front roller can be aligned, for example, with a bottom portion of the cleanings head, structure, so as to not protrude beyond it. 
     In certain embodiments of the cleaning head, one collapsible, resilient roller can be aligned parallel to and “face” another roller. The other roller can similarly be collapsible and resilient. “Facing” the other roller can mean that the chevron shapes of the roller vanes mirror each other as the rollers are installed in the cleaning head to be parallel with one another. The present teachings can also pair a resilient collapsible roller as disclosed herein with a conventional robotic vacuum cleaning head roller or brush. 
     A cleaning head in accordance with certain embodiment of the present teachings can provide a high velocity air system, maximizing air flow velocity by situating the cleaning head rollers close together (with minimal spacing between them) so that the vanes thereon are close together, having an air intake tube of the cleaning head situated directly above the minimal space between the rollers. In addition, a roller frame and a lower housing of the cleaning head can be shaped to minimize the space between the rollers and the portions of the cleaning head housing surrounding the rollers, to again minimize the area of vacuum flow to maximize its speed. The roller frame and a lower housing of the cleaning head should be close enough to the rollers to maximize airflow or obtain a predetermined level of air flow, but should also be spaced from the rollers such that debris does not get wedged therein. 
     In various embodiments of the present teachings, airflow goes straight up from the rollers into a vacuum inlet having a surface that can act as a deflecting surface (e.g., it is angled or curved) to bounce denser/heavier debris swept upward by the rollers toward a plenum that leads to the dust bin. Bouncing denser debris toward the plenum and dust bin is better facilitated by an angled vacuum inlet, and such bouncing can assist the vacuum in moving denser/heavier debris to the dust bin. In certain embodiments of the present teachings, the vacuum inlet can have a parabolic shape or a constant radius of curvature, although a parabolic shape is preferred. The vacuum inlet need not have a constant radius. The vacuum inlet can be shaped to help guide larger debris toward the center of the plenum, where the air velocity is highest. The vacuum inlet directs air into the plenum and can comprises a more rigid material for better wear resistance and to better bounce debris toward the dust bin. In embodiments of the teachings employing a floating cleaning head, the plenum can comprise a more flexible material that allows the cleaning head to float. Various embodiments contemplate that the junction of the vacuum inlet and the plenum is overmolded to provide a smooth surface over which incoming air flows. 
     In certain embodiments of the present teachings, during operation with the removable dust bin properly installed, airflow from the cleaning head through to the vacuum impeller is substantially scaled to prevent leaks from lowering vacuum strength. Various embodiments of the present teachings employ a sealed filter within the removable dust bin. The filter is located along the path of the air flow between the cleaning head and the vacuum impeller to prevent dust from migrating to the impeller. The filter is preferably removable but sealed when installed to prevent airflow leakage. Certain embodiments of the present teachings include a “filter presence” indicator tab within a filter cavity. The filter presence indicator tab can prevent operation of the vacuum when the filter is not properly installed, for example by preventing a filter access door from closing such that the removable dust bin cannot be installed in the robotic vacuum. 
     A robotic vacuum having a cleaning head and dust bin in accordance with the present teachings has improved fluid dynamics due to one or more of the following: impeller design, impeller enclosure design, minimizing turns in the air path from the rollers to the vacuum impeller, minimizing the length of the path from the rollers to the vacuum impeller, minimizing any eddy-producing protrusions along the path from the rollers to the vacuum impeller. The improved fluid dynamics can, for example, allow a lower-powered vacuum impeller (drawing less battery power) to provide a suitable amount of airflow for the robotic vacuum. 
     In certain embodiments, air flow velocity can additionally or alternatively be maximized by maintaining a substantially constant cross sectional area of air flow across the filter and into the impeller. 
     Reference will now be made in detail to embodiments of the present teachings, examples of which are illustrated in the accompanying drawings. The cleaning head rollers/brushes disclosed and illustrated herein may include, for example, brushes as disclosed in U.S. patent application Ser. No. 13/028,996, filed Feb. 16, 2011, titled Vacuum Brush, the disclosure of which is incorporated by reference herein in its entirety. 
     As used herein, “climb rotation” shall mean a rotation of a roller that opposes the direction of forward movement of the robot, i.e., that is opposite to the rotation of the drive wheels as the robot moves in a forward direction. “Roll rotation” shall mean the opposite direction, i.e., a rotation of the roller that is in the same direction as the rotation of the drive wheels in a forward direction. Such rotation need not be at the same speed as the drive wheels, and the directional description is for reference purposes, i.e., a roller may rotate in “climb rotation” even if the robot is stationary or moves backward. “Tube”, as used herein, means “covering tube” and need not have a terminal or sealed end. “Linkage” has its ordinary meaning, and is considered to encompass planar linkages, four-bar linkages, slider-crank linkages, and arrangements of link members with pivots, springs, wires, strings, cords, cams, and/or grooves. 
       FIG. 1  is a top perspective view of an embodiment of a cleaning robot in accordance with the present teachings. 
       FIGS. 2A and 2B  are cross sectional views of different embodiments of a similar portion of a robotic vacuum, each depicting an embodiment of a cleaning head  300 ,  100  in accordance with the present teachings. In general, the following description shall describe common features of different embodiments; as well as pairs of matching features within one embodiment, using reference numerals separated by a comma. 
     With respect to both embodiments, the cleaning head includes a front roller  310 ,  110  and a rear roller  320 , 120 , each roller having an axle  330 , 130  that is preferably substantially rigid and not collapsible and a collapsible, resilient core  340 , 140  surrounding the axle  330 ,  130 . The collapsible, resilient core  340 ,  140  can comprise, for example, a foam material, or other resilient material such as curvilinear spokes, discussed in further detail below. “Collapsible roller” as used herein means a roller with a substantially contiguous tubular outer surface. Upon material external pressure, the tubular outer surface bends or deforms, and upon relief of such pressure, resiliently returns to its former shape, like a balloon, ball, or “run-flat” tire. 
     The rollers  310 ,  320 ,  110 ,  120  preferably have a circular cross section. The collapsible, resilient core  340 ,  140  can be surrounded by a tube  350 , 150  having chevron vanes  360 ,  160 . In accordance with certain embodiments of the present teachings, the chevron vanes  360 ,  160  are chevron-shaped and, for example, spaced at equal intervals  170  around the tube  350 ,  150 , although the present teachings contemplate a variety of vane spacing intervals and shapes. The chevron vanes  360 ,  160  may be arranged as 5, 6, 7, 8, or 9 regularly spaced chevron vanes, and are integral with the collapsible tube  350 ,  150  (preferably injection molded as a complete part) and deform together with the collapsible tube  350 ,  150 . In certain embodiments of the present teachings, the height H (see  FIG. 2 ) of the chevron vanes  360 ,  160  can be selected to bridge a preselected amount of a gap G between the front roller  310 ,  110  and the rear roller  320 ,  120 , for example at least about half of the gap G between the front roller  310 ,  110  and the rear roller  320 ,  120 . In an exemplary embodiment of the present teachings, the gap G between the front roller  310 ,  110  and the rear roller  320 ,  120  is about 7 mm, and the height H of the vanes  360 ,  160  is about 3 mm, making the gap g between the vanes  360 ,  160  about 1 mm. 
     A roller frame  380 ,  180  and the lower housing  390 ,  190  of the cleaning head  300 ,  100 , can be shaped to complement the outer shape of rollers  310 ,  320 ,  110 ,  120  such that the roller frame  380 ,  180  and lower housing  390 ,  190  are close enough to the rollers to maximize airflow in the gap G between the rollers  310 , 320 ,  110 ,  120 , but should also be spaced from the rollers such that debris does not get wedged therein. Proximity of the roller frame  380 ,  180  and the lower housing  390 ,  190  to the rollers  310 ,  320 ,  110 ,  120  resists air from being pulled from an outboard gap OG, so that the vacuum pull will be stronger within the gap G between the rollers  310 ,  320 ,  110 ,  120 . In certain embodiments of the present teachings, the clearance between the chevron vanes  360 ,  160  (or other outermost portion of the rollers  310 ,  320 ,  110 ,  120 ) and the surrounding portions of the roller frame  380 ,  180  and the lower housing  390 , 190  can be about 1 mm. 
     In various embodiments of the present teachings, air can be pulled through the air gap G between the front roller  310 ,  110  and the rear roller  320 ,  120 , for example by an impeller housed within or adjacent to the cleaning head. The impeller can pull air into the cleaning head from the environment below the cleaning head, and the resulting vacuum suction can assist the rollers  310 ,  320 ,  110 ,  120  in pulling dirt and debris from the environment below the cleaning head  300 ,  100  into a dust bin of the robotic vacuum. In the illustrated embodiment of  FIGS. 2A and 2B , the vacuum impeller pulls air (airflow being indicated by the arrows) through a vacuum inlet  392 ,  200  to a central plenum  394 ,  210  that can extend between the vacuum inlet  392 ,  200  and the dust bin (not shown in  FIG. 1 ). 
       FIG. 3  is a cross sectional view of, with reference to the embodiment of  FIG. 2A , a portion of a robotic vacuum having an embodiment of a cleaning head  300  and an embodiment of a removable dust bin  400  in accordance with the present teachings. Air can be pulled through the air gap between the front roller  310  and the rear roller  320 , for example by a vacuum impeller housed within or adjacent to the cleaning head  300 . The impeller can pull air into the cleaning head from the environment below the cleaning head, and the resulting vacuum suction can assist the rollers  310 ,  320  in pulling dirt and debris from the environment below the cleaning head  300  into the dust bin  400  of the robotic vacuum. In the illustrated embodiment of  FIG. 3 , the vacuum impeller (shown in  FIGS. 26 ,  30 , and  32 ) is housed within the dust bin and pulls air through a vacuum inlet  392  to a central plenum  394  that can extend between the vacuum inlet  392  and the dust bin  400 . In the illustrated embodiment, the vacuum inlet  392  has an angled surface that can act as a deflecting surface such that debris swept upward by the rollers and pulled upward by the vacuum suction can strike the angled wall of the vacuum inlet  392  and bounce toward the central plenum  394  and the dust bin  400 . Bouncing denser debris toward the central plenum  394  and dust bin  400  is better facilitated by an angled vacuum inlet, for example having an angle of inclination with respect to the horizontal of from about 30° to about 60°. The vacuum inlet  392  directs air into the central plenum  394 . The vacuum inlet  392  can comprise a more rigid material for better wear resistance and to better bounce debris toward the dust bin  400 . In embodiments of the teachings employing a floating cleaning head  300 , the central plenum  394  can comprise a more flexible material that allows the cleaning head  300  to “float” with respect to cleaning head frame  398  and the dust bin  400 . In such a case, the central plenum  394  is made of an elastomer approximately half the thickness or thinner than the relatively rigid plastic of the introductory plenum  392 . Various embodiments contemplate that the junction of the vacuum inlet  392  and the central plenum  394  is overmolded or otherwise smoothed at joint  396  to provide a smooth surface over which incoming air flows. 
     In certain embodiment of the present teachings, a seal (not shown) can be provided to reduce friction, provide wear resistance, and serve as a face seal between the cleaning head  300  and the dust bin  400 . Seals within the cleaning head and the dust bin may be subject to a combination of rotation and translation forces along their surfaces as the cleaning head moves up and down within the robotic vacuum chassis. In such cases, sealed surfaces may be forced or biased toward one another with mechanical engagements that accommodate such rotation and translation (such as, e.g., elastomer to elastomer butt joints and/or interlocking joints). 
     The illustrated exemplary removable dust bin  400  includes a release mechanism  410  that can be, for example, spring-loaded, a cavity  420  for debris collection, a removable filter  430 , and a filter door  440  that, in the illustrated embodiment, provides an air flow cavity  445  that allows air to flow from the filter to a vacuum impeller housed within the dust bin. The cavity  420  has a collection volume. The exemplary dust bin is described in greater detail below. 
       FIG. 4  is an exploded rear perspective view of the cleaning head  300  and the dust bin  400  embodiments of  FIG. 3 . As shown, the dust bin  400  includes a release mechanism  410  and a filter door  440 . In certain embodiments, the vacuum impeller would be housed within the dust bin under the portion  450  depicted in  FIG. 5 . Indeed, the portion  450  of FIG. can be a removable panel allowing access to the vacuum impeller. A chassis lies above the cleaning head frame  398 . Within the cleaning head  300 , a roller motor  610  is illustrated at a front of the cleaning head  300 , and a gear box  620  is shown that performs gear reduction so that the roller motor  610  can drive the rollers that are positioned under the roller housing  390 . The central plenum  394  and vacuum inlet  392  are also shown. As shown in  FIG. 4 , the exhaust vent for exhaust air exiting the bin is directed through a series of parallel slats angled upward, so as to direct airflow away from the floor. This prevents exhaust air from blowing dust and fluff on the floor as the robot passes. 
     The cleaning head  300  is supported by a ‘four bar linkage’, ‘slider-crank linkage’, or equivalent mechanism permitting the front of the cleaning head  300  to move upward at a slightly faster rate than the rear. The very front of the cleaning head  300 , integral with the floating link, is synthesized to lift at a higher rate than the very rear (e.g., 100% to 120% rate). Alternatively, the cleaning head  300 , integral with the floating link is synthesized to lift to start with a small angle lift (e.g., 0% to 5%) and end with a higher angle lift (e.g., 1% to 10%). Alternatively, the cleaning head  300 , integral with the floating link, is synthesized to translate upwards by a fixed amount and to simultaneously, or later in the synthesis, rotate up by a small angle (0% to 10%). Synthesis of the linkage through three positions or two positions, function generation, path generation, or motion generation, as is known in the art, determines the links&#39; lengths and pivot locations. 
     Most depictions of the cleaning head  300 ,  100  in the present description show the cleaning head  300 ,  100  in a suspended position, e.g., in a position where gravity would pull the cleaning head  300 ,  100  when the robot is lifted, or alternatively, the full downward extension permitted by the linkage stops within the chassis assembly as the robot chassis moves over various terrain. The three positions schematically shown in  FIGS. 27A to 27C  show a suspended position; a hard floor operating position, and a position as the robot and cleaning head encounter a carpet or rug. 
     A first link  630  and a second link  640  (grounded links) of a four-bar linkage are shown on a right side of the  FIG. 4  depiction of the cleaning head  300 , and are substantially similar to the two linkages  530 ,  560  of the four-bar linkage of  FIG. 5  (described below). The cleaning head forms a floating link between the joints connecting the two grounded links  630 ,  640 , and the chassis supports the fixed link. The links  630 ,  640  extend adjacent to the roller gearbox  620  and connect to roller gearbox  620  to the frame  398  so that the roller gearbox  620  (and thus the rollers connected thereto) can “float” with respect to the frame  398 . Another second link  650  of a second, parallel four-bar linkage is shown on the opposite side of the cleaning head  300 . Another first link  660  of the second, parallel four-bar linkage can also be seen located under the second link  650 . The links  640 ,  650 , and  660  are substantially straight. The first link  630  of the illustrated four-bar linkage has a bent, somewhat shallow V-shape. 
       FIG. 5  is a front perspective view of the second embodiment of a cleaning head in accordance with the present teachings, such as the cleaning head illustrated in  FIG. 2B . In this configuration, the impeller is positioned within the robot body rather than within the cleaning bin, and vacuum airflow is drawn through the bin via vacuum inlet  200 . In  FIG. 5 , a central plenum  210  and vacuum inlet  200  can be seen, as well as an air input  520  to a vacuum impeller  500 . The vacuum impeller  500 , a motor  510 , and a roller gearbox  530  can also be seen in  FIG. 5 . In contrast to the first embodiment described with reference to  FIG. 4 , the second (grounded) link  570  of the far-side (in  FIG. 5 ) four-bar linkage comprises an exemplary L-shaped wire connecting the cage  540  to an impeller housing, which is illustrated in more detail below. A wire is used as the second link  570  to provide more room in the cleaning head  100  for the impeller  500 , in embodiments of the present teachings accommodating the vacuum impeller within the cleaning head. Advantages of housing the impeller within the cleaning head can include facilitating a larger dust bin cavity and allowing the same motor to power the impeller and the rollers. 
       FIG. 6  is a partial side perspective cross-sectional view of the cleaning head embodiment of  FIGS. 2A and 4 . The relationship of the front roller  310 , rear roller  320 , vacuum inlet  392 , central plenum  394 , roller motor  610 , and roller gearbox  620  can be seen. The roller motor  610  drives both the front roller  310  and the rear roller  320  via the gear box  620  in a known manner. In certain embodiments of the present teachings, the roller motor  610  rotates the front roller  310  in a roll rotation direction to sweep debris from the floor at an angle toward the rear roller  320 , and the roller motor  610  rotates the rear roller  320  in a climb rotation direction to catch the debris launched by the front roller  310  (and other debris) and sweep that debris further upward at an angle toward the vacuum inlet and the suction provided by a vacuum impeller. The debris can bounce off of the rigid, angled surface of the vacuum inlet  392  through the central plenum  394  and into the dust bin  400 . The illustrated roller axles  330  are preferably not collapsible and are capable of transferring torque, via key features  335 , from the gearbox  620  through to the rollers  310 ,  320 . The illustrated axles  330  can be solid or hollow, and can be keyed at  335  to facilitate rotating torque transfer to the rollers  310 ,  320 . Also shown are curved spokes  340  to provide collapsible but resilient support to the roller tube  350 . 
     Another embodiment of a cleaning head drive system, complementary to the cleaning head arrangement of  FIGS. 2B and 5 , is illustrated in  FIGS. 7 ,  8 ,  9 ,  10 A, and  10 B. The illustrated exemplary drive system can be used with the cleaning head of  FIG. 5 , and in contrast to the embodiment of  FIGS. 2A ,  4 , and  6 , includes a motor  510  that can drive both a vacuum impeller and two cleaning head rollers. A vacuum impeller, such as impeller  500  shown in  FIG. 4 , can be driven by an output shaft  700 , a front roller (e.g., front roller  110  in  FIG. 1 ) can be driven by a front roller drive shaft  710 , and a rear roller (e.g., rear roller  120  in  FIG. 1 ) can be driven by a rear roller drive shaft  720 . A cleaning head gear box of  730  contains gears that allow the motor, having a given rotational speed sufficient to drive a vacuum impeller, to drive the front roller at a desired rotational speed in a roll rotation direction and the rear roller at a desired rotational speed in a climb rotation direction. 
     The illustrated exemplary cleaning head gear box  730  includes a gearbox housing  740  being illustrated as transparent so that the gears can be seen. In the illustrated embodiment, roller drive shafts  720 ,  710  are shown extending from a first gear  750  and a fourth gear  758 , the roller drive shafts  710 ,  720  being used to drive the front and rear cleaning head rollers  110 ,  110 , respectively.  FIG. 7  also shows the motor output shaft  700  for connection to a vacuum impeller drive shaft (see  FIG. 8 ), the motor output shaft  700  extending directly from a first end of the motor  510 . Another output shaft of the motor  510  extends from an opposite end of the motor into the cleaning head gearbox  730  to drive the rollers. 
     The rotational velocity of the front roller and the rear roller can be different than the rotational velocity of the motor output, and can be different than the rotational velocity of the impeller. The rotational velocity of the impeller can be different than the rotational velocity of the motor. In use, the rotational velocity of the front and rear rollers, the motor, and the impeller can remain substantially constant. 
       FIG. 8  is a side perspective view of an exemplary embodiment of a vacuum impeller assembly  800  in accordance with the present teachings, to be used together with the assembly of  FIG. 7 . The illustrated impeller assembly  800  can be used in a cleaning head such as the cleaning head  100  shown in  FIG. 4 . The assembly  800  includes an impeller  500 , a coupler  810  that can be coupled to the motor output shaft  700  shown in  FIG. 7 , an impeller drive shaft  820 , an impeller housing  830  including an outer portion  832  and an inner portion  834 , the inner portion  834  of the impeller housing  830  including an air outlet  840  that directs air exiting the impeller  500  back into the environment. A gearbox cover  850  is shown to run along the outer portion of the impeller housing  830 , the gearbox cover protecting gears (not shown) that provide a gear reduction from the drive shaft  820  to the impeller  500 . 
     In certain embodiments of the impeller assembly  800 , the drive shaft  820  is a 2 mm steel shaft and bushings support the drive shaft on either end. In various embodiments, ribs on the impeller housing  830  can stiffen the housing to prevent deformation under loading and to limit vibration for sound reduction. The illustrated impeller housing  830  includes a connection point  860  for the link  570  shown in  FIG. 5 , such that the link  570  can connect the impeller housing  830  to the cage  540  to facilitate “floating” of the rollers within the chassis. 
       FIG. 9  is a cross-sectional view of an embodiment of the robotic vacuum cleaning head  100  of  FIG. 5 , taken through the impeller  500  and a portion of the air inlet  520 . The front roller  110  can also be seen, with a portion of the vacuum inlet  200  above it. A portion of the air inlet  520  to the impeller  500  is shown, the air inlet conduit mating with in inner portion  900  of the impeller housing as shown. The impeller  500  is enclosed by the inner portion  900  of the impeller housing and an outer portion  910  of the impeller housing. A gear  920  of the impeller gearbox is shown along with bushings  930  on each side thereof, which are housed between the outer portion  910  of the impeller housing and the gearbox cover  850 . The illustrated impeller  500  includes an inner portion  940  and an outer portion  950  that can, for example, be snapped together, fastened, adhered, or integrally molded. In use, air is pulled by the impeller  500  from the dust bin through the air inlet. 
       FIGS. 10A and 10B  are is a cross-sectional views of the cleaning head of  FIGS. 2B and 5 , showing respectively the plenum  210  in cutaway and the impeller air inlet conduit  520  in cutaway. As shown in  FIG. 10A , in the embodiment of a cleaning head depicted in  FIG. 2B  the central plenum  210  is a low-friction plenum comprising, for example, a polyoxymethylene (e.g, Delrin®), which is an engineering thermoplastic used in precision parts that require high stiffness, low friction and excellent dimensional stability. In certain embodiment of the present teachings, a felt seal  220  can be provided to reduce friction, provide excellent wear resistance, and serve as a face seal between the cleaning head  100  and the dust bin (not shown). All seals within the cleaning head and between the cleaning head and the dust bin will be subject to a combination of rotation and translation forces along their surfaces as the cleaning head moves up and down within the robotic vacuum chassis. 
       FIG. 2  is a partial cross sectional view of the robotic vacuum cleaning head environment of  FIG. 1 , illustrating an exemplary embodiment of an annular seal  230  that can be employed between the vacuum conduit  200  and the central plenum  210 . The illustrated annular seal  230  can be mounted to a protrusion  240  extending from an end of the vacuum conduit  200 , the annular seal  230  facilitating a substantially airtight mating between the vacuum conduit  200  and an opening  250  of the central plenum  210 . The illustrated exemplary annular seal  230  includes a rubber lip  260  configured to maintain an airtight seal between the vacuum conduit  200  and the central plenum  210 , while allowing the vacuum conduit  200  and central plenum  210  to move relative to each other during operation of the robotic vacuum. The vacuum conduit  200  and the central plenum  210  may move relative to each other as the cleaning head moves relative to the robotic vacuum chassis. In the illustrated embodiment, the central plenum opening  250  has an increased radius to accommodate the vacuum conduit  200  and the annular seal  230 , and provide room for relative movement of the vacuum conduit  200  and the central plenum  210 . 
     The impeller inlet conduit  520  is shown to include two portions, a front portion  1010  and a rear portion  1020 . The rear portion  1020  extends from the dust bin to the front portion  1010 . The front portion  1010  extends from the rear portion  1020  to the impeller  500 . A rotating and sliding seal arrangement  1030  is shown to mate the front portion  1010  of the air inlet conduit  520  with the rear portion  1020  of the air inlet conduit  520 . Like the seal  230  between the vacuum conduit  200  and the central plenum  210  discussed with respect to  FIG. 2B , the sliding seal arrangement  1030  between the front portion  1010  and the rear portion  1020  of the air inlet conduit  520  includes lips/protrusions (two are shown in the illustrated embodiment) that maintain an airtight seal between the air inlet and the air input duct, while allowing the air inlet and the air input duct to move relative to each other during operation of the robotic vacuum, and particularly while portions of the cleaning head “float” using the four-bar linkage described herein. 
       FIG. 11  shows a left side view of a cleaning head of  FIG. 4 , wherein the frame  398  is shown, along with the attached link  650  and link  660  of one side&#39;s four-bar linkage that allows portions of the cleaning head  300  to move with respect to the frame  398  and thus the robotic vacuum chassis; and  FIG. 12  shows a right side view of the cleaning head of  FIG. 4 , wherein the frame  398  is shown, along with the attached link  630  and fourth link  640  of the opposite side&#39;s four-bar linkage that allows portions of the cleaning head  300  to move with respect to the frame  398  and thus the robotic vacuum chassis. 
     In various embodiments of the present teachings, the four-bar linkage(s) operates to lift the front roller a slightly faster rate than the rear roller. In the illustrated embodiments, the four-bar linkage is “floating” the cleaning head, and the linkages have slightly different lengths (e.g., only millimeters different) and the points of attachment to the frame, cage, or cleaning head do not form a rectangle or a parallelogram. 
       FIGS. 13 and 14  are perspective views of an exemplary links for a four-bar linkage suspension in accordance with the present teachings, for example the link  550  of the embodiment of  FIG. 4  or the link  640  of the embodiment of  FIG. 12 .  FIG. 13  depicts a substantially straight link;  FIG. 14  depicts one having a bent, somewhat shallow V-shape. In various embodiments of the present teachings, the arms can comprise, for example, PEI, PC, Acetal, Nylon 6, PBT, PC/PET, ABS, PET, or a combination thereof. 
       FIG. 15  is a bottom perspective view of the cleaning head  300  and dust bin  400  embodiment of  FIG. 5 , with the dust bin  400  removably engaged with the cleaning head  300 . The rollers  310 ,  320  are shown, along with the roller frame  380  in a closed position. In embodiments of the present teachings including a removable roller frame  380  allowing access to the roller  310 ,  320  for, for example, removal or cleaning of the rollers  310 ,  320 . The roller frame  380  can be releasably and hingedly attached to the gearbox  620  or the lower housing  390 , for example via hinges  1525  and tabs  1520  of a known sort. The tabs  1520  can be pressed toward a front of the cleaning head to release the rear side of the roller frame  380  and the roller frame  380  can pivot open to provide access to the rollers  310 ,  320 . The illustrated exemplary roller frame  380  shown in  FIG. 15  includes multiple prows  1500  on a forward edge. The prows can be provided to support the cleaning head as it floats across the surface to be cleaned, and also limit the size of debris that can enter the cleaning head to the size of the vacuum conduit. The illustrated exemplary roller frame  380  also includes “norkers”  1510  that can be used to prevent cords and other long, thin material from getting pulled between the rollers  310 ,  320 . In the context of this specification, a “norker” is a short, V-shaped trough as depicted. The “norkers”  1510  are located at very end of the rollers  310 ,  320 , and can additionally prevent larger debris from entering between the rollers  310 ,  320  at the end of the rollers  310  where the rollers may not be as compressible. In some embodiments, the tubular outer shell of the roller, which itself can deform substantially, abuts a hard cylindrical core at the end of the roller. The purpose of the “norker” is to prevent captured objects larger than a certain size (e.g., larger than the gap G) from jamming between the rollers at the very ends, where the rollers may not deform because of the hard cylindrical core at the roller end. 
       FIG. 16  is a bottom perspective view of the cleaning head of  FIG. 15 , with the roller frame  380  open to expose the rollers  310 ,  320 . As can be seen, some of the roller area covered by the norkers  1510  may not be the compressible, resilient tubing  350  of the rollers. The tabs  1520  that allow the roller frame  380  to release from the lower housing  390  can releasably engage latching mechanisms  1535  of the lower housing  390  to close the roller housing  380 . The non-driven ends  1600  of the rollers  310 ,  320  are shown in  FIG. 16  and an exemplary embodiment thereof is shown in  FIG. 19  and described below. 
       FIG. 17  schematically illustrates a large piece of debris D being accommodated by the rollers  310 ,  320 , the rollers being collapsible to allow the debris D to pass through a center of the rollers  310 ,  320 , despite the size of the debris D being larger than the gap between the rollers. After the debris D has passed through the roller  310 ,  320 , the rollers will retain (rebound to) their circular cross section due to their resiliency and the debris will move upward toward a dust bin conduit in a direction VB. As shown, the front roller  310  rotates in a roll rotation direction CC and the rear roller  320  rotates in a climb rotation direction C. 
       FIG. 18  is a cross sectional view of an exemplary driven end of an embodiment of a cleaning head roller (e.g., rollers  110 ,  120 ,  310 ,  320 ) in accordance with the present teachings. The roller drive gear  1800  is shown in the gearbox housing  1810 , along with a roller drive shaft  1820  and two bushings  1822 ,  1824 . The roller drive shaft  1820  can have, for example, a square cross section or a hexagonal cross section as would be appreciate by those skilled in the art. A shroud  1830  is shown to extend from the within the roller tube  350  to contact the gearbox housing  1810  and the bearing  1824  and can prevent hair and debris from reaching the gear  1800 . The axle  330  of the roller engages the roller drive shaft  1820 . In the illustrated embodiment, the area of the axle  330  surrounding the drive shaft  1800  includes a larger flange or guard  1840  and a smaller flange or guard  1850  spaced outwardly therefrom. The flanges/guards  1840 ,  1850  cooperate with the shroud  1830  to prevent hair and other debris from migrating toward the gear  1800 . An exemplary tube overlap region  1860  is shown, where the tube  350  overlaps the shroud  1830 . The flanges and overlapping portions of the drive end shown in  FIG. 18  can create a labyrinth-type seal to prevent movement of hair and debris toward the gear. In certain embodiments, hair and debris that manages to enter the roller despite the shroud overlap region  1860  can gather within a hair well or hollow pocket  1870  that can collect hair and debris in a manner that substantially prevents the hair and debris from interfering with operation of the cleaning head. Another hair well or hollow pocket can be defined by the larger flange  1840  and the shroud  1830 . In certain embodiments, the axle and a surrounding collapsible core preferably extend from a hair well on this driven end of the roller to a hair well or other shroud-type structure on the other non-driven end of the roller. In other embodiments, curvilinear spokes replace all or a portion of the foam supporting the tube  350 . 
       FIG. 19  is a cross sectional view of an exemplary non-driven end of an embodiment of a cleaning head roller (e.g., rollers  110 ,  120 ,  310 ,  320 ) in accordance with the present teachings. A pin  1900  and bushing  1910  of the non-driven end of the roller are shown seated in the cleaning head lower housing  390 . A shroud extends from the bushing housing  1920  into the roller tube  350 , for example with legs  1922 , to surround the pin  1900  and bushing  1910 , as well as an axle insert  1930  having a smaller flange or guard  1932  and a larger flange or guard  1934 , the larger flange  1934  extending outwardly to almost contact an inner surface of the shroud  1920 . An exemplary tube overlap region  1960  is shown, where the tube  350  overlaps the shroud  1920 . The flanges/guards and overlapping portions of the drive end shown in  FIG. 19  can create a labyrinth-type seal to prevent movement of hair and debris toward the gear. The shroud is preferably shaped to prevent entry of hair into an interior of the roller and migration of hair to an area of the pin. In certain embodiments, hair and debris that manages to enter the roller despite the shroud overlap region  1960  can gather within a hair well or hollow pocket  1970  that can collect hair and debris in a manner that substantially prevents the hair and debris from interfering with operation of the cleaning head. Another hair well or hollow pocket can be defined by the larger flange  1934  and the shroud  1920 . 
       FIG. 20  illustrates exemplary facing, spaced chevron vane rollers such as the front roller  310  and rear roller  320  of  FIG. 3 . The flanges  1840  and  1850  of the axle  330  can be seen, as can the foam  140  supporting the tubular tube  350 . The rollers  310 ,  320  face each other, which means that, in the illustrated embodiment, the chevron-shaped vanes  360  are mirror images. Each chevron-shaped vane of the illustrated exemplary rollers include a central point  365  and two sides or legs  367  extending downwardly therefrom on the front roller  310  and upwardly therefrom on the rear roller  320 . The chevron shape of the vane  360  can draw hair and debris away from the sides of the rollers and toward a center of the rollers to further prevent hair and debris from migrating toward the roller ends where they can interfere with operation of the robotic vacuum. 
       FIG. 21  illustrates a side perspective exploded view of an exemplary embodiment of a roller, such as roller  310  of  FIG. 20 . The axle  330  is shown, along with the flanges  1840  and  1850  of its driven end. The axle insert  1930  and flange  1934  of the non-driven end are also shown, along with the shroud  1920  of the non-driven end. Two foam inserts  140  are shown, which fit into the tubular tube  350  to provide a collapsible, resilient core for the tube. In certain embodiments, the foam inserts can be replaced by curvilinear spokes (e.g., spokes  340  shown in  FIG. 6 , or can be combined with curvilinear spokes. The curvilinear spokes can support the central portion of the roller  310 , between the two foam inserts  140  and can, for example, be integrally molded with the roller tube  350  and chevron vane  360 . 
       FIG. 22  illustrates a cross sectional view of an exemplary roller having curvilinear spokes  340  supporting the chevron vane tube  350 . As shown, the curvilinear spokes can have a first (inner) portion  342  curvilinear in a first direction, and a second (outer) portion  344  that is either lacks curvature or curves in an opposite direction. The relative lengths of the portions can vary and can be selected based on such factors as molding requirements and desired firmness/collapsibility/resiliency. A central hub  2200  of the roller can be sized and shaped to mate with the axle that drives the roller (e.g., axle  330  of  FIG. 21 ). To transfer rotational torque from the axle to the roller, the illustrated roller includes two recesses or engagement elements/receptacles  2210  that are configured to receive protrusions or keys  335  (see  FIG. 6 ) of the axle. One skilled in the art will understand that other methods exist for mating the axle and the roller that will transfer rotational torque from the axle to the roller. 
       FIG. 23  is a front perspective view of an exemplary embodiment of a dust bin  400  in accordance with the present teachings. The dust bin includes, on its top surface a release mechanism  410  and a filter door  440 . In certain embodiments, the vacuum impeller would be housed within the dust bin under the portion  450  of the top surface of the bin. Indeed, the portion  450  of the top surface can be a removable panel allowing access to the vacuum impeller. The embodiment of  FIG. 23  also illustrates a filter door release mechanism  2300  that, as shown in  FIG. 24 , can include a resilient tab  2400  and a recess  2410  that the tab engages in a known manner. A door  2310  of the dust bin  400  is shown in a open position, exposing hinges  2330  and the cavity  420  for debris collection. The door  2310  includes an opening  2320  that preferably matches up in size and location with, for example, the central plenum  394  of the cleaning head  300  shown in  FIGS. 5 and 6 . An impeller housing  2340  is located within the housing. In the illustrated embodiment, the impeller housing  2340  is located toward a side of the dust bin cavity  420 . 
       FIG. 24  is a top perspective view of the dust bin  400  of  FIG. 23 , showing the filter door  440  in an open position that exposes the filter  430  and the walls  442 ,  444 ,  446  that partially define the air flow cavity  445  that allows air to flow from the filter  430  to a vacuum impeller housed within the dust bin cavity  420 . In the illustrated embodiment, air flows from the central plenum (e.g., central plenum  394  of  FIG. 5 ) through the opening  2320  in the filter door  2310 , through the filter  430 , and through the air flow cavity  445  in the direction of the arrow of  FIG. 24  to reach the vacuum impeller. The filter  430  is preferably releasable and includes a tab  430 T that allows a user to remove the filter  430  from the dust bin, for example for cleaning and/or replacement. The exemplary embodiment of  FIG. 24  includes an optional a “filter presence” indicator tab  2430  within a filter cavity. The filter presence indicator tab  2430  can, for example, prevent operation of the robotic vacuum when the filter  430  is not properly installed, for example by moving to a position that prevents the filter door  440  from closing, which in turn prevents the removable dust bin  400  from being installed in the robotic vacuum. In a preferred embodiment of the present teachings, the filter is sealed within the surrounding portion of the dust bin. The seal can be employed on the filter, on the dust bin, or on both the filter and the dust bin. 
       FIG. 25  is a top perspective view of a portion of the dust bin  400  of  FIGS. 23 and 24 , with a top portion of the dust bin and the filter  430  removed. In the exemplary embodiment, a multiple bars  2510  are used to retain the filter  430  within the dust bin. One skilled in the art will appreciate that other arrangements can be used to support and retain the filter within the dust bin. In certain embodiments of the present teachings, a transverse cross sectional area of the air flow cavity  445  (e.g. a cross section taken transverse to the longitudinal axis) equals the cross sectional area of the impeller opening  2500  such that airflow remains constant and free of airflow contraction and/or constriction throughout the volume and into the debris collection bin. 
       FIG. 26  is a cross sectional view of the dust bin of  FIGS. 23-25 , taken through the impeller housing  2340 , the impeller motor  2610 , and the impeller  2620 . The pathway from the air flow cavity  445  to the impeller  2500  can be seen. 
     Other embodiments of the present teachings will be apparent to those skilled in the art from consideration of the specification and practice of the teachings disclosed herein, some exemplary embodiments of which are set forth in the details and descriptions below. 
     In certain embodiments of the present teachings, the one or more vanes are integrally formed with the resilient tubular member and define V-shaped chevrons extending from one end of the resilient tubular member to the other end. In one embodiment, the one or more chevron vanes are equidistantly spaced around the circumference of the resilient tube member. In one embodiment, the vanes are aligned such that the ends of one chevron are coplanar with a central tip of an adjacent chevron. This arrangement provides constant contact between the chevron vanes and a contact surface with which the compressible roller engages. Such uninterrupted contact eliminates noise otherwise created by varying between contact and no contact conditions. In one implementation, the one or more chevron vanes extend from the outer surface of the tubular roller at an angle α between 30° and 60° relative to a radial axis and inclined toward the direction of rotation (see  FIG. 20 ). In one embodiment the angle α of the chevron vanes is 45° to the radial axis. Angling the chevron vanes in the direction of rotation reduces stress at the root of the vane, thereby reducing or eliminating the likelihood of vane tearing away from the resilient tubular member. The one or more chevron vanes contact debris on a cleaning surface and direct the debris in the direction of rotation of the compressible roller. 
     In one implementation, the vanes are V-shaped chevrons and the legs of the V are at a 5° to 10° angle θ relative a linear path traced on the surface of the tubular member and extending from one end of the resilient tubular member to the other end (see  FIG. 22 ). In one embodiment, the two legs of the V-shaped chevron are at an angle θ of 7°. By limiting the angle θ to less than 10° the compressible roller is manufacturable by molding processes. Angles steeper than 10° create failures in manufacturability for elastomers having a durometer harder than 80 A. In one embodiment, the tubular member and curvilinear spokes and hub are injection molded from a resilient material of a durometer between 60 and 80 A. A soft durometer material than this range may exhibit premature wear and catastrophic rupture and a resilient material of harder durometer will create substantial drag (i.e. resistance to rotation) and will result in fatigue and stress fracture. In one embodiment, the resilient tubular member is manufactured from TPU and the wall of the resilient tubular member has a thickness of about 1 mm. In one embodiment, the inner diameter of the resilient tubular member is about 23 mm and the outer diameter is about 25 mm. In one embodiment of the resilient tubular member having a plurality of chevron vanes, the diameter of the outside circumference swept by the tips of the plurality of vanes is 30 mm. 
     Because the one or more chevron vanes extend from the outer surface of the resilient tubular member by a height that is, in one embodiment, at least 10% of the diameter of the resilient tubular roller, they prevent cord like elements from directly wrapping around the outer surface of the resilient tubular member. The one or more vanes therefore prevent hair or other string like debris from wrapping tightly around the core of the compressible roller and reducing efficacy of cleaning. Defining the vanes as V-shaped chevrons further assists with directing hair and other debris from the ends of a roller toward the center of the roller, where the point of the V-shaped chevron is located. In one embodiment the V-shaped chevron point is located directly in line with the center of a vacuum inlet of the autonomous coverage robot. 
     The four-bar linkage embodiments discussed hereinabove facilitate movement (“floating”) of the cleaning head within its frame. When a robotic vacuum having a cleaning head in accordance with the present teachings is operating, it is preferable that a bottom surface of the cleaning head remain substantially parallel to the floor, and in some embodiments, it is preferable that the front roller  110 ,  310  be positioned slightly higher than the rear roller  120 ,  320  during operation. However, the cleaning head should be able to move vertically during operation, for example to accommodate floor irregularities like thresholds, vents, or moving from a vinyl floor to carpet. The illustrated four-bar linkage provides a simple mechanism to support the cleaning head within the frame and allow the cleaning head to move relative to the frame so that the cleaning head can adjust vertically during operation of the robotic vacuum without pivoting in a manner that will cause the cleaning head to lose its parallel position with respect to the floor. As shown, in the illustrated exemplary embodiment, both the top and bottom links can be snap fit to the cleaning head assembly. The top link connects the frame to the outer portion of the impeller housing. The bottom link also connects the frame to the outer portion of the impeller housing. The frame is intended to remain fixed relative to the robotic vacuum chassis as the cleaning head components illustrated herein move relative to the frame and the chassis. As shown in the illustrated exemplary embodiment, the frame can be cutaway to allow full visual and physical access to linkages. 
     The frame is intended to remain fixed relative to the robotic vacuum chassis as the cleaning head components illustrated herein move relative to the frame and the chassis. 
     In certain embodiments, the linkage lifts at a variable rate (the front wheel lifting at a faster rate than the rearward wheel) such that maximum lift angle from resting state is less than 10°. In one embodiment, the linkage is a four bar linkage symmetrically placed about the cleaning assembly such that the forward end of each bar linkage attaches adjacent a forward edge of the cleaning assembly. 
     In another implementation an autonomous coverage robot has a chassis having forward and rearward portions. A drive system is mounted to the chassis and configured to maneuver the robot over a cleaning surface. A cleaning assembly is mounted on the forward portion of the chassis and at has two counter rotating rollers mounted therein for retrieving debris from the cleaning surface, the longitudinal axis of the forward roller lying in a first horizontal plane positioned above a second horizontal plane on which the longitudinal axis of the rearward roller lies. The cleaning assembly is movably mounted to the chassis by a linkage affixed at a forward end to the chassis and at a rearward end to the cleaning assembly. When the robot transitions from a firm surface to a compressible surface, the linkage lifts the cleaning assembly from the cleaning surface. The linkage lifts the cleaning assembly substantially parallel to the cleaning surface but such that the front roller lifts at a faster rate than the rearward roller. 
     In certain embodiments of the present teachings, the central plenum comprises a substantially horizontal elastomeric portion leading into the collection volume. The substantially horizontal elastomeric portion flexes to create a downward slope when the linkage lifts the cleaning assembly to accommodate height differentials in cleaning surfaces. In one embodiment, the substantially horizontal elastomeric portion flexes in a vertical dimension at least 5 mm such that debris lifted from the cleaning surface by the rollers travels up into the plenum and is directed down into the enclosed dust bin. 
       FIGS. 28A and 28B  illustrate flexure of the central plenum  394  to create a downward slope as the linkage lifts the cleaning assembly when the robotic vacuum is placed on a cleaning surface, for example prior to or during operation of the robotic vacuum. 
     The front portion and rear portion of the vacuum airway may be formed as a unitary, monolithic component, but in some embodiments the rear portion is an elastomeric member adjoined to a rigid front portion at sealed joint. In one embodiment, the sealed joined is a compression fit wherein the rigid front portion is inserted into an elastomeric rear portion and affixed by radial compression forces. In another embodiment the sealed joint is an elastomeric overmold. The sealed joint forms a sealed vacuum path that prevents vacuum loses. In embodiments, the rear portion terminates in a flange abutting an opening to the debris collection bin in a sealed configuration. The vacuum airway therefore enables a smooth, sealed vacuum airflow. In one embodiment, the elastomeric rear portion is manufactured from a thermoplastic material such as Mediprene™ or a thermoplastic vulcanizate (TPV) such as Santoprene™. In one embodiment, the rigid from portion is manufactured from a plastic material such as acrylonitrile butadiene styrene (ABS) or Nylon, which materials have anti-static properties and resist the accumulation of hair. 
       FIG. 29  is a bottom view of an embodiment of a cleaning robot in accordance with the present teachings. 
     A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.