Agitator element for a vacuum cleaner

Abstract

A cleaner head for a vacuum cleaner comprises an agitator rotatably mounted within a housing, the agitator being arranged transversely within the housing such that it is perpendicular to the direction

Description

TECHNICAL FIELD The present invention relates to an agitator element for a cleaner head of a vacuum cleaner, as well as to a cleaner head comprising such an agitator element, and to a vacuum cleaner comprising such a cleaner head. BACKGROUND A vacuum cleaner typically comprises a cleaner head having a housing defining a suction chamber. The housing is configured to be moved over a floor or other surface that needs to be cleaned while air is drawn into the suction chamber together with dust, hair, and other dirt that is thereby removed from the surface. An outlet of the housing is coupled to a motor via a wand or hose. The motor provides for the suction needed to generate the airflow through the suction chamber. In many modern vacuum cleaners, the cleaner head comprises one or more brush bars or other types of agitator elements that rotate while the housing moves over the surface to be cleaned. The agitator elements serve to detach dirt from the surface and to increase the chance that it is picked up, thereby improving the cleaning performance of the vacuum cleaner. Typically, vacuum cleaner heads experience some degree of hair ingress during use, which means that hair can ingress into or between parts of the cleaner head. Hair can also become wound around the agitator elements which can damage the agitator elements and which can also reduce their ability to detach dirt and hair from the floor, especially if a thick layer of hair becomes wrapped around the agitator elements. It is against this background that the present invention has been developed. SUMMARY In an aspect according to the present invention, described is a cleaner head for a vacuum cleaner, the cleaner head having an agitator rotatably mounted within a housing, the agitator being arranged transversely within the housing such that it is perpendicular to the direction of travel of the cleaner head during use, the agitator being conical in shape, such that a first end has a larger diameter than a second end and a suction cavity comprising an opening through which debris enters the cleaner head, and an outlet. In other aspects according to the present invention, the agitator has a main body with an outer conical surface and the lowermost portion of the conical surface is parallel with a flat supporting surface when the cleaner head is in use. The axis of rotation of the agitator is inclined with respect to a flat supporting surface on which the cleaner head is supported during use. In alternative aspects, the cleaner head also has an agitator engaging member for pressing against the agitator any debris which has become wrapped around the agitator. The agitator engaging member extends substantially the entire length of the agitator, and can be biased towards the agitator. The agitator engaging member can also have a resilient member which is biased towards the agitator. The resilient member can be in the form of a strip of resilient material and it can have a substantially uniform width. In other aspects according to the invention, the suction cavity is defined by a substantially conical housing of the cleaner head, and wherein the agitator engaging member is mounted on the housing. In further aspects, the core of the agitator comprises upstanding helical ridges, and the agitator comprises a row of bristles located between the helical ridges. The agitator engaging member can be arranged to press wrapped debris against at least the bristles of the agitator. In alternative aspects, the cleaner head can also have a drive for driving rotation of the agitator, and wherein the agitator is connected to the drive at or towards the first end of the agitator. In another embodiment, the present invention provides an agitator element for a vacuum cleaner, wherein the agitator element has an axis of rotation which extends from a first end of the agitator element towards a second end of the agitator element and a shape which tapers from the first end of the agitator element towards the second end of the agitator element, wherein the second end of the agitator element includes a chamfered edge and the second end of the agitator defines an alcove with a wall of the housing, wherein the alcove is configured to releasably retain a debris strand ball formed during use of the agitator element in a vacuum cleaner. The present invention is advantageous as the alcove provides room for the debris ball to form against the wall of the housing before it is released from the brush bar to be removed to a bin by the vacuum. The chamfered edge of the agitator element helps to encourage the debris strand ball to migrate out of the alcove while ensuring there is no friction overload in the vacuum cleaner. In one example, the alcove has a distance of between 0.5mm to 10mm when measured between the second send of the agitator element and the wall of the housing. This allows the debris strand ball sufficient time and space to form and migrate out of the alcove. Optionally a strip is located along the agitator element from the first end of the agitator element towards the second end of the agitator element. This is advantageous as the strip interrupts the alcove so that the formed strand ball is more readily disturbed and less likely to reside in the alcove. The strip optionally has the form of at least a portion of a spiral curve. The rotational sense of the spiral curve when viewed from the second end of the agitator element may correspond to the direction of rotation of the agitator element in use to help gather the strands together to form the debris strand ball. Alternatively, the rotational sense of the spiral curve when viewed from the second end of the agitator element may be opposite to the direction of rotation of the agitator element in use to help eject the debris hair ball from the alcove. In one example, the agitator element may comprise an outer surface which is continuous from the first end of the agitator element to the second end of the agitator element. In a further aspect, the present invention provides vacuum cleaner head comprising: a housing which defines a vacuum chamber having an outlet, wherein the housing comprises a cover portion and wall portions which extend away from the cover portion; and an agitator element as described above mounted for rotation within the vacuum chamber, wherein the second end of the agitator element is located opposite to, and spaced from, a wall portion of the housing. Optionally the agitator element is arranged within the vacuum chamber such that, in use, a first end of the axis of rotation located at the first end of the agitator element is located further from a floor surface to be cleaned than a second end of the axis of rotation located at the second end of the agitator element wherein the second end of the agitator element includes a chamfered edge and the second end of the agitator defines an alcove with a wall of the housing, wherein the alcove is configured to releasably retain a debris strand ball formed during use of the agitator element in a vacuum cleaner. The inner surface of the wall portion located opposite the second end of the agitator element may define a first plane which may be optionally orientated at an acute angle with respect to a second plane which is orthogonal to the axis of rotation of the agitator element located at the second end of the agitator element. The inner surface of the wall portion located opposite the second end of the agitator element may comprise a textured surface. In one example the agitator element is cantilevered from a hub located at the first end of the agitator element. Optionally the vacuum cleaner head may comprise two agitator heads mounted for rotation within the vacuum chamber. In yet another aspect, the present invention describes an agitator element for a vacuum cleaner, wherein the agitator element has an axis of rotation which extends from a first end of the agitator element towards a second end of the agitator element and a shape which tapers from the first end of the agitator element towards the second end of the agitator element, wherein the second end of the agitator element comprises a recess, wherein the recess is configured to releasably retain a debris strand ball formed during use of the agitator element in a vacuum cleaner. The recess may extend in a direction away from the second end of the agitator element towards the first end of the agitator element. The present invention is advantageous as the recess provides room for the debris ball to form before it is released from the brush bar or agitator to be removed to a bin by the vacuum. Optionally the recess is open on a first side of the recess, and closed on a second side of the recess, wherein the first side of the recess is opposed to the second side of the recess. This is advantageous as it helps to encourage the debris strand ball to migrate out of the recess. The closed side of the recess is optionally bounded by a wall which terminates in a crescent shaped surface located at the second end of the agitator element, wherein a first portion of the wall located proximate a first end of the crescent shaped end surface flares outwardly away from the axis of rotation of the agitator element. The flared surface is advantageous as it helps to encourage strands and other debris to enter the recess when the brush bar is rotated in a direction with the flared surface leading. If the brush bar is rotated in the opposite sense, the flared surface help the strand ball to migrate out of the recess. A second portion of the wall located proximate a second end of the crescent shaped end surface may flare outwardly away from the axis of rotation of the agitator element, wherein the profile of the outward flare of the second portion of the wall is different to the profile of the outward flare of the first portion of the wall. In this example, the brush bar rotates in use such that the surface with the greater extent of flare leads and the surface with the lesser extent of flare follows. This arrangement helps to encourage strands and other debris to be swept into the recess at the side of the recess with the greater flare, and to be released from the recess at the side with the lesser flare. In one example the recess may be located between a pair of prongs located on opposite sides of the agitator element. Optionally the prongs are asymmetric about a plane located midway between the prongs. In particular, the inner facing surfaces of the prongs may be asymmetric about the said plane. The recess may also optionally be asymmetric about a plane located midway between the prongs. In one example the prongs may be of different lengths. The innermost surface of one or both prongs may flare outwardly away from the axis of rotation of the agitator element proximate one or both side edges of the prongs. The flared surfaces are advantageous as they help to encourage strands and other debris to enter the recess when the brush bar is rotated in a direction with the flared surface leading. If the brush bar is rotated in the opposite sense, the flared surfaces help the strand ball to migrate out of the recess. In one example the extent of outward flare may increase towards the second end of the agitator element of at least one side edge of at least one prong. Optionally the extent of outward flare on a first side edge of a first one of the prongs is greater than the extent of outward flare on the opposite side edge of the opposite prong. In this example, the brush bar rotates in use such that the surfaces with the greater extent of flare lead and the surfaces with the lesser extent of flare follow. This arrangement helps to encourage strands and other debris to be swept into the recess at the side of the recess with the greater flare, and to be released from the recess at the side with the lesser flare. The recess optionally comprises a step configured such that a first portion of the recess on a first side is shallower than a second portion of the recess. This is advantageous as the step interrupts the recess so that the formed strand ball is more readily disturbed and less likely to reside in the recess. The step may extend in a direction between the first prong and the second prong. Optionally a projection is located in the recess, wherein the projection extends towards the second end of the agitator element. This is advantageous as the projection interrupts the recess so that the formed strand ball is more readily disturbed and less likely to reside in the recess. The projection optionally has the form of at least a portion of a spiral curve. The rotational sense of the spiral curve when viewed from the second end of the agitator element may correspond to the direction of rotation of the agitator element in use to help gather the strands together to form the debris strand ball. Alternatively, the rotational sense of the spiral curve when viewed from the second end of the agitator element may be opposite to the direction of rotation of the agitator element in use to help eject the debris hair ball from the recess. In one example, the agitator element may comprise an outer surface which is continuous from the first end of the agitator element to the second end of the agitator element. In a second aspect, the present invention provides vacuum cleaner head comprising: a housing which defines a vacuum chamber having an outlet, wherein the housing comprises a cover portion and wall portions which extend away from the cover portion; and an agitator element as described above mounted for rotation within the vacuum chamber, wherein the second end of the agitator element is located opposite to, and spaced from, a wall portion of the housing. Optionally the agitator element is arranged within the vacuum chamber such that, in use, a first end of the axis of rotation located at the first end of the agitator element is located further from a floor surface to be cleaned than a second end of the axis of rotation located at the second end of the agitator element. The inner surface of the wall portion located opposite the second end of the agitator element may define a first plane which may be optionally orientated at an acute angle with respect to a second plane which is orthogonal to the axis of rotation of the agitator element located at the second end of the agitator element. The inner surface of the wall portion located opposite the second end of the agitator element may comprise a textured surface. In one example the agitator element is cantilevered from a hub located at the first end of the agitator element. Optionally the vacuum cleaner head may comprise two agitator heads mounted for rotation within the vacuum chamber. Features described above in connection with the first aspect of the invention are equally applicable to the second and third aspects of the invention, and vice versa. During the use of the cleaner head, any debris which has become wrapped around the agitator is encouraged by the conical shape of the agitator to migrate along the agitator towards the free end, where it can become released from the agitator. In order to minimise the risk of this released debris becoming re-wrapped around the agitator before it is conveyed away from the agitator within an airflow which is passing through the suction cavity, the suction cavity comprises a second air outlet located adjacent the free end of the agitator. A first part of the airflow passing through the suction cavity leaves the suction cavity through the first air outlet, and a second part of this airflow leaves the suction cavity through the second air outlet. The first part of the airflow, generally containing dust and other detritus which has been agitated from a floor surface by the agitator, passes along a first airflow path extending from the first air outlet to an outlet of the cleaner head. The second part of the airflow, into which debris which has been released from the agitator generally becomes entrained, passes along a second airflow path extending from the second air outlet towards the first airflow path so as to merge with the first part of the airflow between the first air outlet and the outlet of the cleaner head, and thus before any part of the airflow is emitted from the cleaner head. In yet a further aspect, there is provided a cleaning head comprising a suction chamber having a suction aperture; a brush bar arranged in the suction chamber; and a comb having a plurality of teeth, each tooth extending into the suction chamber so that at least a distal end of said tooth is arranged to contact a portion of the brush bar; wherein a contact face of each tooth is arranged to contact a radially extending portion of the brush bar. Here, at least one corner between the contact face and a side face of the angled tooth includes a first notch. In some embodiments, said at least one comer between the contact face and a side face of the angled tooth includes a second notch. Optionally, both first and second corners between the contact face and respective side faces of the angled tooth include first and optionally second notches. In the embodiments wherein both corners comprise first and optionally second notches, the contact face may comprise corresponding notch channels. For instance, notch channels may run across the contact face between the comer notches. Here, the notch channels across the front face may be parallel to each other. Additionally, or alternatively, at least one of the notch channels or both notch channels may be parallel to the longitudinal axis. Advantageously, the corner notches and the notch channels help break hair and other debris that might be wound on the brush bar, and assists in entraining the hair or debris in the airflow through the suction aperture. According to an embodiment, at least one angled tooth is arranged at an oblique angle relative to a radial direction of the brush bar and so as to extend at least partially in a longitudinal direction of a longitudinal axis of the brush bar and towards the suction port. The at least one angled tooth contacts the brush bar and assists in urging hair to migrate in the longitudinal direction of the brush bar that the angled tooth extends. Advantageously, by arranging the angled tooth to extend at least partially in the longitudinal direction and towards a suction aperture, the hair can be urged to migrate towards the suction aperture. Since the suction is generally highest adjacent the suction aperture, using the angled tooth to urge hair towards the suction aperture increases the likelihood of the hair being entrained in the airflow. In the embodiments, the cleaning head suitably comprises a comb having a plurality of teeth. Here, each tooth extends into a suction chamber of the cleaning head and so as to contact a portion of the brush bar. In some embodiments, any tooth in the plurality of teeth that is angled at an oblique angle relative to the radial direction of the brush bar and so as to extend at least partially in the longitudinal direction of the longitudinal axis can be considered an angled tooth. However, in some embodiments, the oblique angle that the angle tooth extends relative to the radial direction and so as to extend in the longitudinal direction is preferably at least 8° . Here, it has been found that an oblique angle of at least 8° is particularly suitable for encouraging the migration of the hair. In these embodiments wherein the comb has a plurality of teeth, only the teeth in the plurality of teeth arranged at an oblique angle of at least 8° are considered angled teeth. Thus, if the comb has one or more teeth arranged at an oblique angle of at least 8°, these teeth are considered angled teeth. If the comb also has one or more teeth arranged at an angle of less than 8°, these teeth are not considered angled teeth in these preferable embodiments, wherein the oblique angle is preferably at least 8°. In some embodiments, the oblique angle that the angled tooth extends relative to the radial direction and so as to extend in the longitudinal direction is preferably less than 30°, or less than 20°, or less than 15°, or less than 12°. Thus, in some embodiments, the preferred range of the oblique angle is between 8° and 30°, or between 8°, and 20°, or between 8° and 15° or, between 8° and 12°. Again, in these embodiments, the comb may have one or more teeth arranged at an angle outside of the preferred range, in which case teeth that are arranged at an oblique angle within the range are considered angled teeth, and teeth that are arranged at an angle outside the range are not considered angle teeth. In another embodiment, the oblique angle that the angled tooth extends relative to the radial direction and so as to extend in the longitudinal direction is around 10°. In these embodiments, teeth arranged at an oblique angle of around 10° are considered angled teeth. If the comb includes one or more teeth arranged at an angle relative to the radial direction and so as to extend in the longitudinal direction but not at an angle of around 10°, these teeth are not considered angled teeth. A combination of the oblique angle that the angled tooth extends relative to the radial direction and so as to extend in the longitudinal direction, and the spacing and angle of adjacent teeth, along with a length and a width of the teeth define a coverage area. The coverage area is an area of the brush bar contacted by the angled tooth. Preferably, the angled tooth and said adjacent teeth are configured so that the coverage area covers a substantial width of the brush bar between an axial extent of one tooth and an axial extent of the adjacent tooth. Here, the axial extent of the teeth is relative to a base of each tooth. That is, the axial extent of the angled tooth is a radial line through the base of the angled tooth. And the axial extent of said adjacent tooth is a radial line through the base of the adjacent tooth. Whilst the coverage area is preferably at least 100% of the distance between the axial extents, the coverage area may be at least 90% or at least 70% or at least 50% or at least 40% of the width of the brush bar from an axial extent of one tooth to an axial extent of the adjacent tooth. In embodiments having a comb with a plurality of teeth, the plurality of teeth suitably comprise a first set of two or more of said angled teeth. Here, the plurality of angled teeth of said first set are spaced from one another along a first region of the brush bar. In suitable embodiments, the first region of the brush bar is a first end region of the brush bar. The plurality of angled teeth in said first set may be arranged at a common first oblique angle. The first set of angled teeth may be arranged to extend in a longitudinal direction of the brush bar aligned with a mechanical pump direction of the brush bar. In this instance, the angled teeth act to slow migration of hair along the brush bar’s longitudinal axis. That is, although the angled teeth act to urge the hair in the longitudinal direction aligned with the mechanical pump direction, the presence of angled teeth slows the migration compared to a brush bar operating without angled teeth. However, the common first oblique angle preferably acts to move the hair against a mechanical pump direction of the brush bar. That is, the brush bar may comprise a supporting body with a helical brush that acts as a mechanical pump to move debris along the brush bar in a mechanical pump direction, and the angled teeth of the first region are arranged to extend counter to the mechanical pump direction. As explained, in particularly suitable embodiments, the oblique angle that the angled teeth are arranged is at least 8°. In these embodiments, the first region can be spaced from the suction aperture. Here, the comb may preferably comprise a set of transition teeth, where the transition teeth are arranged between the first region and the suction aperture. In embodiments having a comb with a plurality of teeth, including a first set of two or more of said angled teeth, the plurality of teeth may further comprise a second set of two or more of said angled teeth. Again, the plurality of angled teeth of said second set are spaced from one another along a second region of the brush bar. Suitably, additionally to the first region of the brush bar being a first end region, the second region of the brush bar may be a second end region of the brush bar. The plurality of angled teeth in said second set may be inclined towards the angled teeth of said first set. As explained, in particularly suitable embodiments the oblique angle at which the angled teeth are arranged is at least 8°. Here, the comb preferably comprises a set of transition teeth, where the transition teeth are arranged between the first region and the suction aperture. In the embodiments having a first set of angled teeth and a second set of angled teeth, the first region and the second region are suitably separated by the suction aperture. Thus, the angled teeth in the first region extend in a first longitudinal direction, and the angled teeth in the second region extend in a second longitudinal direction, where the first longitudinal direction is opposed to the second longitudinal direction. In the exemplary embodiments wherein the angled teeth of the first region are arranged to extend counter to a mechanical pump direction of the brush bar, the angled teeth in the second region may be arranged to extend in the mechanical pump direction. That is, the brush bar may comprise a supporting body with a constant helical brush along a longitudinal length of the supporting body and that acts as a mechanical pump to move debris along the brush bar in a mechanical pump direction, and the angled teeth in the second region are arranged to extend in a longitudinal direction aligned with the mechanical pump direction, whereas the angled teeth in the first region are arranged to extend in a longitudinal direction counter to the mechanical pump direction. As explained, in some embodiments, one or more transition teeth are arranged between the suction aperture and the first region and the suction aperture and the second region. In embodiments having transition teeth, each transition tooth is arranged so as to extend at least partially in said longitudinal direction, wherein the transition teeth are not parallel to the angled teeth. Preferably, the transition teeth therefore transition from an angle of around 8° and to around 0°. In the embodiments, the cleaning head suitably comprises a suction chamber. The suction chamber has an inlet generally arranged to be adjacent a surface being treated. The suction chamber defines an enclosure within which the brush bar is arranged. Suitably, the cleaning head comprises a casing assembly. Here, the casing assembly at least partially defines the suction chamber and the suction aperture. The suction aperture is formed adjacent the brush bar and is an opening aperture through the casing from the suction chamber. Thus, the suction aperture is a part of a suction port formed in the casing assembly. For instance, the suction port may include a connection to a hose or the like. The suction port therefore also includes a channel through the casing assembly from the suction aperture to the connection. The channel is suitably approximately orthogonal to the longitudinal axis of the brush bar. In the embodiments wherein the cleaning head comprises a casing assembly, the at least one angled tooth may be included in a comb having a plurality of teeth, wherein the comb extends from the casing assembly, for instance from the casing assembly and into the suction chamber. That is, the comb, and in particular the plurality of teeth, project from the casing assembly and into the suction chamber. Suitably, the comb is formed integrally to the casing assembly. In the embodiments, suitably the brush bar is arranged in the suction chamber to rotate about its longitudinal axis. In the embodiments including a casing assembly, the brush bar is preferably rotatably mounted to the casing assembly. Consequently, according to an exemplary aspect, there is provided a cleaning head for a surface treating appliance, the cleaning head comprising: a suction chamber having a suction aperture; a brush bar arranged in the suction chamber to rotate about a longitudinal axis; and a comb having a plurality of teeth, each tooth extending into the suction chamber so that at least a distal end of said tooth is arranged to contact a portion of the brush bar; wherein at least one of the plurality of teeth comprises an angled tooth that is arranged at an oblique angle relative to a radial direction of the brush bar and so as to extend at least partially in a longitudinal direction of the longitudinal axis and towards the suction aperture. The brush bar may be an assembly including a supporting body and bristles. The bristles are attached to the supporting body and extend generally radially therefrom. In an alternative embodiment, a set of bristles may extend from the supporting body such that the bristles form an acute angle (a) with the surface normal of the supporting body, forming a set of slanted bristles. The bristles can be generally arranged in one or more helical brush patterns. When the brush bar, and specifically the supporting body is rotated, the helical brush patterns act to move debris along the longitudinal axis of the brush bar. For instance, the helical brush patterns are arranged to act as a mechanical pump to move debris. The plurality of teeth of the comb extend into contact with the brush bar. Suitably, the portion of the brush bar which the plurality of teeth extend into contact with is a portion of the bristles. Here, the teeth may extend a depth into the bristles. That is, the teeth extend from the tips of the bristles towards the supporting body. Suitably, the bristles have a height from the supporting body, and the teeth may extend a depth at least 30% of the height or at least 50% of the height or at least 80% of the height. Accordingly, there is always a gap in between the comb and the surface of the supporting body in order to avoid rubbing and damaging the supporting body surface. When the tangled hair wraps tighter onto the supporting body surface as the brush bar rotates, it may lose possible contact with the comb and hence may not be picked up. In order to move the hair out from the supporting body surface so it can come in contact with the comb, the hair may need to be migrated from one bristle filament to an adjacent bristle filament. As such a migration effect can be created when the slanted bristles are combined with the one or more helical brush patterns. With the migration effect, tangled hair may be forced away from the supporting body surface and the hair removal efficiency may be further improved. In some embodiments, the acute angle (a) that the slanted bristles form with the surface normal of the supporting body is preferably less than 90°, or less than 60°, or less than 45°, or less than 35°. Thus, in some embodiments, the preferred range of the oblique angle is between 25° and 90°, or between 25°, and 60°, or between 25° and 45° or, between 25° and 35°. Again, in these embodiments, the bristles may be arranged such that a subset of the bristles extend substantially parallel to the surface normal of the supporting body, in which case the bristles that are arranged at an acute angle within the range are considered slanted bristles, and the bristles that are arranged to extend substantially parallel to the surface normal of the supporting body are considered straight bristles. The cleaning head preferably comprises a first set of two or more of said angled teeth, wherein the angled teeth of said first set are spaced from one another along a first region of the brush bar and wherein the angled teeth of said first set are arranged at a common first oblique angle. When the cleaning head has a first set of said angled teeth, the cleaning head may further comprise a second set of two or more of said angled teeth, wherein the angled teeth of said second set are spaced from one another along a second region of the brush bar and wherein the angled teeth of said second set are arranged at a common second oblique angle. Here, suitably, the first region of the brush bar is a first end region of the brush bar and the second region of the brush bar is a second end region of the brush bar or agitator. When the cleaning head has a first set of said angled teeth, the cleaning head may comprise a third set of the plurality of teeth. Here, the third set is preferably arranged between the suction aperture and said first region, the third set of the plurality of teeth comprising transition teeth. Each transition tooth of the third set is arranged so as to extend at least partially in said longitudinal direction, wherein the transition teeth are not parallel to the angled teeth. Here, the angle of transition teeth is less than the oblique angle of the angled teeth. When the cleaning head has a second set of said angled teeth, the cleaning head may comprise a fourth set of the plurality of teeth arranged between the suction aperture and said second region, the fourth set of the plurality of teeth comprising transition teeth. Here, each transition tooth of the fourth set is angled relative to the radial direction of the brush bar and so as to extend at least partially in said longitudinal direction, wherein the angle of adjacent said transition teeth reduces as a spacing from said second region increases. Here, the angle of transition teeth is less than the oblique angle of the angled teeth. In the embodiments including a first region, suitably the first region extends at least 5% of a longitudinal length of the brush bar. Additionally, or alternatively, in the exemplary embodiments including a second region, suitably the second region extends at least 5% of the longitudinal length of the brush bar. Optionally the first region, and additionally or alternatively the second region, extend at least 15% or at least 20% of the longitudinal length of the brush bar. The first region, and additionally or alternatively the second region, may extend less than 50% of the longitudinal length of the brush. The first region, and additionally or alternatively the second region, may extend less than 40% or less than 25% of the longitudinal length of the brush bar. Thus, the first region, and additionally or alternatively the second region, may extend between 5% and 50% or between 15% and 40% or between 20% and 30% of the longitudinal length of the brush bar. In a particularly suitable example, the first region, and additionally or alternatively the second region, extends around 25% of the longitudinal length of the brush bar. The plurality of teeth of the comb may be symmetrical about a mid-point of the brush bar along the longitudinal axis. Suitably, the suction aperture is arranged about the midpoint of the brush bar. Thus, the plurality of teeth to one side of the suction aperture may be arranged at an angle to a radial direction of the brush bar and so as to extend at least partially in one longitudinal direction of the longitudinal axis towards the suction port, for instance a positive angle. The plurality of teeth to the other side of the suction aperture may be arranged at an angle to a radial direction of the brush bar and so as to extend at least partially in a second longitudinal direction of the longitudinal axis towards the suction port, for instance a negative angle. Here, teeth which are equidistant from the mid-point have the same angle, but the angle is a positive angle to one side of the suction aperture and a negative angle to the other side of the suction aperture. In the embodiments including a first set of angled teeth, suitably, the brush bar is configured so that when it is rotated, the brush bar or agitator forms a mechanical pump to move debris along a first direction of the longitudinal axis, and wherein the angled teeth of said first set are arranged to extend at least partially in a second direction of the longitudinal axis, wherein the second direction is opposed to the first direction. Advantageously, the angled tooth assists in urging the hair to migrate against the mechanical pump direction and therefore reduce build-up of hair at an end of the brush bar. Preferably, the cleaning head having at least one angled tooth, has a first tooth that is configured to extend towards a centre of the brush bar in the longitudinal axis, and said first angled tooth is arranged in an end region of the brush bar. Suitably, the brush bar is configured so that when it is rotated, the brush bar forms a mechanical pump to move debris along a first direction of the longitudinal axis, and wherein said first angled tooth is arranged to extend at least partially in a second direction of the longitudinal axis, wherein the second direction is opposed to the first direction. Advantageously, the angled tooth assists in urging the hair to migrate against the mechanical pump direction and therefore reduce build-up of hair at an end of the brush bar. In embodiments of the cleaning head, a contact face of each said angled tooth is arranged to contact a radially extending portion of the brush bar. Here, at least one comer between the contact face and a side face of the angled tooth includes a first notch. According to a further aspect, there is further provided a method of treating a surface with a cleaning head. The method comprises applying a suction to a suction aperture of a suction cavity; causing a brush bar to rotate about a longitudinal axis within the suction chamber; using a comb having a plurality of teeth, each tooth extending into the suction chamber so that at least a distal end of each said tooth is arranged to contact the brush bar, wherein at least one tooth of the plurality of teeth is an angled tooth arranged at an oblique angle relative to a radial direction of the brush bar and so as to extend at least partially in a longitudinal direction of the longitudinal axis. Advantageously, the method comprises using the at least one angled tooth to guide debris to move along the brush bar in said longitudinal direction. In the method, the brush bar acts as a mechanical pump to move debris along the brush bar in a first longitudinal direction of the longitudinal axis, and the method comprises rotating the brush bar and using the at least one angled tooth to move at least some of the debris along the brush bar in a second longitudinal direction of the longitudinal axis, the second direction being opposed to the first direction. In an alternative aspect, there is provided a cleaner head comprising: a body defining a suction cavity; and a rotatable agitator located in the suction cavity; wherein the agitator comprises a core having a first, free end, and a second end opposite the free end that is rotatably connected to the body; wherein the agitator comprises a row of bristles extending between the free end and the second end of the core; and wherein the row of bristles includes a first group of bristles located next to the free end of the core, and a second group of bristles located between the first group of bristles and the second end of the core, the first group of bristles being shorter than the second group of bristles. The inventors have found that debris (such as hair or threads) can have a tendency to get tangled with bristles at the free end of the core, thus preventing it from being removed from the cleaner head by an air flow through the cleaner head. Providing shorter bristles next to the free end of the core reduces a likelihood of debris becoming tangled at the free end of the core, thus improving an efficiency with which dust and debris can be aspirated through the cleaner head. Thus, the shorter first group of bristles may act to agitate dust and / or debris on the floor surface near the first end of the core, whilst reducing a risk of tangling with debris. Furthermore, debris such as hair may become wrapped around the core in use. Providing the shorter first group of bristles next to the free end of the core may encourage debris wrapped around the core to fall off the free end of the core, further improving efficiency of debris removal via the cleaner head. The second group of bristles, which is located away from the free of the core, may provide more effective agitation of dust and / or debris on the floor surface compared to the first group of bristles, due to the greater bristle length in the second group. Thus, providing two groups of bristles with different lengths may allow for effective agitation with bristles along a majority of a length of the core, whilst reducing debris tangling at the free end of the core. The cleaner head may be adapted for use with any suitable vacuum cleaner. The body corresponds to a structure (e.g. a housing) in which the suction cavity is defined. For example, the suction cavity may correspond to a hollow space in the body. The rotatable agitator is located in the suction cavity, such that the rotatable agitator is located within the body. The suction cavity may comprise an opening (inlet) arranged to face towards a floor surface, and through which debris may enter the cleaner head in use. The suction cavity may further comprise an air outlet, through which air may be drawn from the cleaner head. An air flow path is defined through the suction cavity in the cleaner head, between the opening and the air outlet, such that air can be drawn along the air flow path in use. For example, in use, the air outlet may be connected to a main body of a vacuum cleaner, which generates suction so as to cause a (dirt-bearing) air flow to enter the cleaner head via the opening, and exit the cleaner head via the air outlet. The agitator may also be referred to as a brush bar. The agitator core is located in the suction cavity, and is rotatably connected to the body via a suitable rotatable coupling. In particular, the second end of the core is rotatably connected to the body, whilst the first end of core is free. In other words, the first end of the core is not connected to the body. For example, there may be a gap between the free end of the core and the body. The core may be rotatable relative to the body about a longitudinal axis of the core. A cross-section of the core may be substantially circular in a direction normal to the longitudinal axis of the core. The longitudinal axis of the core may be oriented such that an outer surface of the core is substantially parallel to a plane including the opening of the suction cavity, such that the outer surface of the core may be parallel to the floor surface in use. The core acts as a support for the row of bristles. Thus, the row of bristles may protrude from the outer surface of the core. The row of bristles extends between the free end and the second of the core. Thus, the row of bristles may extend along a length of the core. In some cases, the row of bristles may be a helical row of bristles, which extends in a helical manner around the core from the first end to the second end. The bristles may be made of a flexible (resilient) material, so that they have sufficient strength to agitate dust and debris located upon a surface to be cleaned in use, whilst having sufficient flexibility to resiliently deform (bend) relative to the core. For example, the bristles may be formed of strands of nylon and / or carbon fibre. The row of bristles may be arranged such that at least a portion of the row of bristles protrudes through the opening of the suction cavity. For example, the second group of bristles may be arranged to protrude through the opening of the suction cavity. In this manner, the row of bristles may come into contact with the floor surface in use, to agitate dust and / or debris on the floor surface. The first group of bristles is located next to (e.g. adjacent to) the free end of the core. Thus, the first group of bristles corresponds to a portion of the row of bristles which is closest to the free end. The second group of bristles is located between the first group of bristles and the second end of the core. Thus, the second group of bristles is further from the free end compared to the first group of bristles. The first group of bristles is shorter than the second group of bristles. In other words, the bristles in the first group of bristles are shorter than the bristles in the second group of bristles. Thus, a length of the bristles in the first group protruding from the surface of the core is shorter than a length of the bristles in the second group protruding from the surface of the core. As noted above, the shorter bristles of the first group serves to reduce a likelihood of debris becoming tangled with the bristles at the free end of the core, and / or to encourage debris to fall off the free end of the core. A length of the bristles in the first group of bristles may decrease towards the free end. Decreasing bristle length towards the free (first) end of the core may serve to reduce a likelihood of debris becoming tangled with the bristles towards the free end, whilst improving agitation performance of the bristles away from the free end. This may therefore serve to reduce an impact on agitation performance caused by the shorter bristles in the first group. The reduction in bristle length towards the free end may also encourage debris wrapped around the core to fall off the free end of the core. The length of the bristles in the first group of bristles may decrease gradually towards the free end. For example, the length of the bristles in the first group may decrease in a continuous manner towards the free end. In line with the above, this may provide a gradual improvement in agitation performance of the bristles in the first group away from the free end, thus reducing an impact on agitation performance of the bristles near the free end. The length of the bristles in the first group may decrease linearly towards the free end. In other words, tips of the bristles in the first group may follow a substantially straight line, such that the length of the bristles decreases linearly towards the free end. Such a linear decrease in bristle height towards the free end may serve to provide a balance between reduced risk of tangling with bristles at the free end, and improved agitation performance of the bristles away from the free end. Tips of the bristles in the first group follow a line which is inclined relative to an outer surface of the core at an angle between 30° and 60°. Such an incline may provide an effective balance between reduced risk of tangling with bristles at the free end, and improved agitation performance of the bristles away from the free end. In particular, this may avoid too steep an incline of the decrease, which could result in increased risk of debris tangling at the free end, whilst avoiding too shallow an incline of the decrease, which could result in reduced agitation performance of the bristles along a larger portion of the core. The first group of bristles may comprise a first portion of bristles and a second portion of bristles, the first portion being located nearer the free end, and the first portion of bristle being shorter than the second portion. For example, there may be a step change in bristle height between the first portion and the second portion of the first group of bristles. In this manner, the shorter first portion of bristles may serve to reduce a risk of debris tangling at the free end of the core. The longer second portion of bristles may serve to improve agitation performance of the bristles away from the free end of the core. The second portion of the first group of bristles may be shorter than the second group of bristles. In some cases, the first group of bristles may comprise a plurality of portions of bristles, each portion having a different bristle height, wherein the plurality of portions of bristles are arranged in order of decreasing bristle height towards the free end of the core. The second group of bristles may comprise a portion of the row of bristles extending between the first group of bristles and the second end of the core, and a length of bristles in the second group of bristles may be substantially constant along the row of bristles. In other words, the bristles in the row of bristles may have a substantially constant length outside the first group of bristles. In this manner, the bristles may only be shorter next to the free end of the core. Thus, the bristles in the second group of bristles may provide a substantially uniform agitation performance along a portion of the core. As only the bristles in the first group are shorter, any reduction in agitation performance due to the shorter bristles may be localised to a small region at the end of the core, so as to minimally impact performance of the agitator. The second group of bristles may extend along a majority of a length of the core. For example, the second group of bristles may extend along 85% or more of a length of the core. Thus, the first group of bristles may be located next to the free end of the core and extend along only 5% or less of the length of the core. Thus, the row of bristles may include only a relatively short region with shorter bristles, providing a balance between agitation performance of the bristles and reduced risk of tangling with debris at the free end. Here, a length of the core may correspond to a length along its longitudinal axis, i.e. from the free end to the second end of the core. Bristles in the row of bristles may be inclined towards the free end of the core. In other words, each bristle may be inclined (angled) such that a tip of the bristle is closer to the free end of the core than a base of the bristle. This can reduce the risk of any wrapped debris becoming lodged between adjacent bristles, and can further promote the migration of wrapped debris towards the free end of the agitator. As an example, the bristles may be inclined towards the free end of the core at an angle between 40° and 80° relative to an outer surface of the core. Bristles in the row of bristles may be arranged in tufts. In other words, the row of bristles may comprise a plurality of discrete bristle tufts arranged in a row. Alternatively, the row of bristles may comprise a continuous row of bristles. The core may have a shape that tapers towards the free end, such that the free end of the core has a smaller cross-sectional area than the second end of the core. Such a tapered shape of the core may serve to encourage debris (such as hair or threads) wrapped around the core to migrate towards the free end of the core when the core is rotated in use, so that the debris may fall off the free end of the core and be carried out of the cleaner head with the air flow. Due to the shorter bristles at the free end, a risk of the debris tangling with the bristles at the free end is reduced. Here, the cross-sectional area of the core may refer to a cross-sectional area in a direction normal to the longitudinal axis (i.e. axis of rotation) of the core. As an example, the core may have a conical (including frustoconical) shape. In some cases, the agitator may comprise multiple (e.g. two or more) rows of bristles extending between the free end and the second end of the core. Each row of bristles may be as described above, i.e. with a respective first group and second group of bristles. In some cases, the cleaner may comprise more than one rotatable agitator in the suction cavity. For example, the cleaner head may comprise a first agitator and a second agitator, both of which are arranged as described above in relation to the rotatable agitator. Preferential features of aspects of the present invention may be applied equally to other aspects of the present invention, where appropriate. In an alternative aspect, the present invention provides a vacuum cleaner comprising a vacuum cleaner head as described above. BRIEF DESCRIPTION OF THE DRAWINGS Figure lisa perspective view of an example embodiment of a vacuum cleaner; Figure 2A shows an explanatory cleaning head having a brush bar and comb according to an example arrangement; Figure 2B shows a schematic representation of the migration of hair along the brush bar according to the example arrangement of Figure 2A; Figure 3 shows a schematic view of a portion of the comb of exemplary embodiments; Figure 4 shows a top plan view of the exemplary cleaning head; Figure 5 shows a bottom plan view of the exemplary cleaning head; Figure 6 shows a schematic side view of an agitator for a cleaner head. Figures 7A, 7B, and 7C show schematic side views of rows of bristles for an agitator. Figure 8 is a partial cross-sectional view of the cleaner head of the vacuum cleaner of Figure 1; Figure 9 is a partial perspective view of an end of the agitator element of Figure 8; DETAILED DESCRIPTION Figure 1 shows a hand-held vacuum cleaner 2 comprising a main body 4, a wand 6 and a cleaner head 20. The main body 4 comprises a separating system 10, in the form of a cyclonic separator, a motor and impeller (not visible) arranged to draw air through the separating system 10, and a power supply 12, in the form of a battery, for powering the motor. The main body 4 has a handle 14 which is gripped by a user, and a clean air outlet 16 through which air that has passed through the separating system 10 is discharged. The wand 6 is attached at one end to the main body 4 and at the other end to the cleaner head 20. The wand 6 provides fluid communication between the cleaner head 20 and the separating system 10 and supports the cleaner head 20 during use. Referring to Figures 2A and 2B, an example arrangement of a cleaning head 10 is shown. In the example arrangement, the cleaning head 10 comprises a brush bar 20 rotatably assembled to a casing assembly 30. The casing assembly defines a suction chamber having a suction aperture 34. The suction aperture forms a portion of a suction port 32. The suction port 32 is an area generally defining a channel through the casing assembly. The channel extends between the suction aperture 34 and a connector with a suction outlet. The connector connects the suction outlet to a negative air pressure. The brush bar 20 comprises a supporting body 23. The supporting body may be a supporting tube housing a turbine, but embodiments without a turbine are envisaged. In any event, the supporting body has a generally circular outer surface. The supporting body 23 is rotationally mounted to the casing assembly 30 within the suction chamber and so that the brush bar can rotate about a rotational axis. As will be appreciated, the longitudinal axis of the brush bar is generally coincident with a centre of the circular outer surface. In Figures 2A and 2B, the brush bar comprises the supporting body 23 and bristles 24. The bristles extend radially from the supporting body. Alternatively, the set of bristles extending from the supporting body 23 can be such that the bristles form an acute angle (a) with the surface normal of the supporting body 23, to form a set of slanted bristles. The bristles are arranged in a strip or pattern forming a helical brush. The helical brush wraps around the supporting body. In Figures 2A and 2B, the bristles are shown as forming two helical brushes, but one helical brush or further helical brushes are envisaged as is known in the art. The helical brushes are arranged to act as a mechanical pump as the brush bar is rotated. The brush bar therefore has a mechanical pump direction. Here the mechanical pump direction is a direction along the longitudinal axis in which the bristles urge dirt and the like to migrate. In Figures 2A and 2B, the mechanical pump direction is shown as acting in the longitudinal direction of the longitudinal axis from left to right. In Figures 2A and 2B, the cleaning head 10 further comprises a comb 40. The comb 40 includes a plurality of teeth 42. The plurality of teeth 42 are shown as extending across a longitudinal extent of the brush bar. Each tooth of the plurality of teeth is spaced from an adjacent tooth to form the comb. Each tooth 42 of the plurality of teeth extend into the suction chamber so that a distal end of the tooth contacts the bristles 24 of the brush bar. When the brush bar rotates, the plurality of teeth forming the comb penetrate the helical brush and part the bristles 24. In the example arrangement shown in Figures 2A and 2B, the plurality of teeth forming the comb are arranged to extend radially relative to the brush bar. As shown in Figure 2B, hair 12a contacted by the bristles 24 on the left-hand end of the brush bar 20 is urged to migrate in the mechanical pump direction of the brush bar. However, as the plurality of teeth forming the comb penetrate the helical brushes, they act to part the bristles and contact the hair. It has been found that the plurality of teeth forming the comb acting on the hair assist in slowing the migration of the hair along the brush bar. In turn, by slowing the migration of hair, the hair 12a is encouraged to be entrained in the airflow which therefore reduces the likelihood of hair wrapping tightly around the supporting body at the suction aperture. Thus, the example arrangement of Figure 2B requires less manual cleaning of the hair from the brush bar. However, whilst the comb acts on hair 12b contacted by bristles to the right hand side of the suction aperture to also slow migration of the hair in the mechanical pump direction, which increases the entraining of the hair 12b in the airflow, it has been found that hair 12b can still amass at the end of the brush bar in the mechanical pump direction. The teeth 42 of the comb 40 can be angled teeth, and the angled teeth can be arranged at an oblique angle relative to a radial direction of the brush bar 20 so that to extend at least partially in a longitudinal direction of the longitudinal axis of the brush bar and towards the suction aperture. The angled teeth 44 to the left-hand side of the suction aperture 34 can be arranged to extend in the longitudinal direction corresponding to the mechanical pump direction. The angled teeth 44 can act to slow the migration of hair 12a along the brush bar, thereby increasing the likelihood of the hair 12a being entrained in the airflow and therefore removed from the brush bar. Whilst the angled teeth 44 encourage the hair to migrate in the direction in which they extend (i.e. with the angled teeth on the left-hand side to migrate in the mechanical pump direction), the angled teeth still act to reduce the speed at which the hair 12a migrates as compared to the acknowledged art. . In relation to the angled teeth 44 arranged to the right-hand side of the suction aperture 34, the angled teeth 44 extend in a second direction along the longitudinal axis. The second direction is opposed to the mechanical pump direction. Here, the angled teeth act to urge the hair to migrate against the mechanical pump direction and move back towards the suction aperture 34. . It is believed that the higher level of suction at the suction aperture 34 increases the entraining of the hair in the airflow and therefore removal of the hair 12b from the brush bar. Consequently, the manual cleaning of the brush bar 20 is reduced. Figure 3 provides a comparison of the angled teeth 44 of the exemplary embodiment described earlier and the (non-angled) teeth of the example arrangement. As shown in the upper image, where the teeth 42 are not angled to the radial direction, each tooth 42 contacts an area of the brush bar spanning a width of the brush bar in the longitudinal axis which is equal to a thickness of the tooth. In contrast, the angled teeth 44 shown in the lower image have an increased coverage area. That is each angled tooth 44 extends from a base 45 to a tip 46 that penetrates the bristles. A radial extent of one angled tooth 44 is indicated by line B drawn through the base 45 of the angled tooth 44. A distal extent of an adjacent tooth 44 is also indicated by line C drawn through the base of the adjacent tooth. Here, the distal extent of the angled tooth 44 and the adjacent tooth span a width Z, being a portion of the brush bar. As can be seen, the tip 46 of the adjacent tooth extends substantially the full width Z of the axial extent of the angled tooth 44 and the axial extent of the adjacent tooth. Figures 4 and 5 show the exemplary casing assembly 30 without the brush bar fitted. The casing assembly 30 forms the suction chamber (indicated generally at 36) and the suction aperture (indicated generally at 34). The comb 40 is shown as extending across the suction chamber 36. Each tooth of the plurality of teeth of the comb extends from the casing assembly into the suction chamber. Suitably, each tooth is connectedly fixed to the casing assembly 30 at a base and extends in the longitudinal direction to the tip 46. As explained, the teeth are arranged to both sides of the suction aperture 34. Preferably, the teeth are symmetrical about a mid-point along the casing assembly (i.e. a mid point along the brush bar), with the suction aperture 34 centred on the mid-point. Apart from the central tooth 48 that is not arranged at an angle to the radial direction, all of the teeth of the plurality of teeth are arranged at an angle to the radial direction and so as to extend at least partially in either one longitudinal direction (i.e. in the mechanical pump direction to the left-hand side of the suction aperture) or in the other longitudinal direction (i.e. against the mechanical pump direction to the right-hand side of the suction aperture). Thus, other than the central tooth 48, all of the teeth of the plurality of teeth forming the comb 40 can be considered angled teeth. However, it has been found that to provide good action on the hair to move the hair against the mechanical pump direction, an oblique angle of the angled tooth of at least 8° is preferred. As shown in Figure 8, the teeth of the plurality of angled teeth extending at an oblique angle of at least 8° are shown as a first set of teeth 40a to the right-hand end region of the casing assembly (i.e. to the right-hand end region of the brush bar) and a second set of teeth 40b to the left-hand end region of the casing assembly (i.e. to the left-hand end region of the brush bar). Thus, all of the plurality of teeth in the first set and the second set are arranged at an oblique angle of at least 8° and preferably between 8° and 30°. As shown, the teeth in the first set are arranged parallel to each other and at a first oblique angle of around 10°. Also, the teeth in the second set are arranged parallel to each other and at a second oblique angle of around 10°, where the second oblique angle might be considered an angle of -10°. Here, third and fourth sets 40c, 40d of the plurality of teeth are formed between the mid-point and the respective first and second set 40a, 40b. The teeth in the third and fourth sets 40c, 40d are angled to the radial direction at an angle of less than the oblique angle of the angled teeth. That is, the teeth in the third and fourth sets are arranged at an angle of less than 8° to the radial direction and so as to extend in a longitudinal direction of the brush bar. Here, the teeth in the third and fourth sets 40c, 40d are termed transition teeth 49. In the exemplary embodiment wherein the angled teeth have an oblique angle of at least 8°, the transition teeth are arranged at varying angles. For instance, in the third set 40c, the transition tooth adjacent the first set 40a forms an angle of around 7°, and adjacent teeth towards the mid-point reduce the angle so that a tooth of the third set adjacent the midpoint is angled around 1°. Like the third set 40c, the fourth set 40d of teeth also comprise transition teeth arranged between the second set 40b and the mid-point. A side view of the first agitator 116a is shown in Fig. 6. The agitator 116a includes a core (or body) 120, which may be formed of a relatively rigid material, e.g. a plastic material such as acrylonitrile butadiene styrene (ABS) or similar. The core 120 includes a first, free end 122, and a second end 124 opposite the free end 122. The second end 124 of the core 120 is rotatably connected to a support member of the body, via a rotatable coupling. The free end 122 of the core is not connected to the body, such that a gap 126 is formed between the free end 122 and a sidewall of the body of the cleaner head 20. In the example shown, the core 120 has a shape that tapers towards the free end 122, such that the core has a smaller cross-sectional area towards the free end 122 and a larger cross-sectional area towards the second end 124. For instance, as shown, the core 120 may have an approximately conical (or frustoconical) shape, with one or more helical ridges 128 arranged on an outer surface of the core 120. The agitator 116a can also have a row of bristles 130 which extends between the free end 122 and the second end 124 of the core 120. As shown in Figures 6, 7A-C, the row of bristles 130 can extend between the free end 122 and the second end 124 in a helical (curved) manner, such that it extends at least partly around the outer surface of the core 120. The row of bristles 130 comprises a plurality of bristles arranged in a row, and which protrude from the outer surface of the core 120. In some cases, a channel may be formed in the outer surface of the core 120, the channel extending in a helical manner between the free end 122 the second end 124. Then, the row of bristles 130 may be mounted in the channel, so as to protrude from the channel beyond the outer surface of the core 120. In use, the bristles 130 come into contact with a surface to be cleaned to agitate dust, dirt and / or debris on the surface. The bristles may thus be formed of a flexible material so that they have sufficient strength to agitate dust and debris located upon a surface to be cleaned in use, whilst having sufficient flexibility to resiliently deform (bend) relative to the core 120. For example, the bristles may be formed of strands of nylon and / or carbon fibre. The row of bristles 130 includes bristles with different heights, as illustrated in more detail in Figs. 7A, 7B, and 7C. In particular, the row of bristles 130 includes a first group of bristles 132 which is arranged next to the free end 122 of the core 120, the first group of bristles 132 being shorter than the bristles in the remainder of the row of bristles 130. As shown, the agitator 116a may further comprise a strip 131 made of felt or some similar material, which extends in a helical manner between the free end 122 and the second end 124 of the core 120. Helical ridges 128 may be arranged between the row of bristles 130 and the strip 131. Fig. 7A shows a side view along a length of the row of bristles 130, according to a first example. For illustration purposes, only an outline (profile) of the row of bristles 130 is shown and it does not depict individual bristles. The row of bristles 130 includes a first group of bristles 132, which is located next to (adjacent to) the free end 122 of the core 120, and a second group of bristles 134 which extends between the first group of bristles 132 and the second end of the core 124. The bristles of the first group of bristles 132 are shorter than the second group of bristles 134. Thus, a length of the bristles protruding from the core 120 is shorter in the first group 132 next to the free end 122 of the core 120. The bristles in the second group 134 may have a substantially constant length along the row of bristles 130. Thus, starting at the second end of the core 124 and moving along the row of bristles 130, the bristles may have a substantially constant length, until the second group 132 is reached near the free end 122 of the core, in which the bristles are shorter. In the example of Fig. 7A, a length of the bristles in the first group of bristles 132 decreases gradually towards the free end 122 of the core 120. In particular, the length of the bristles in the first group 132 decreases in a linear manner, such that tips of the bristles in the first group 132 follow a (substantially straight) line 136 which is inclined relative to the outer surface of the core 120 from which the bristles protrude. For example, the line 136 may be inclined relative to the outer surface of the core at an angle 138, which may be between 30° and 60°. Fig. 7B shows a side view along a length of the row of bristles 130, according to a second example. For illustration purposes, Fig. 7B only shows an outline (profile) of the row of bristles 130 and does not depict individual bristles. Similarly to the example of Fig. 7A, the example of Fig. 7B includes first group of bristles 132 located next to the free end 122 of the core 120 and which is shorter than a remaining second group of bristles 134. In the example of Fig. 7B, the length of the bristles in the first group of bristles 132 decreases progressively in a stepped manner towards the free end 122 of the core 120. In particular, the first group of bristles 132 includes a first portion 142 and a second portion 144, the first portion 142 being located nearer the free end 122 of the core. The first portion 142 of bristles is shorter than the second portion 144 of bristles. Fig. 7C shows a side view along a length of the row of bristles 130, and is similar to the above examples except that, the bristles are arranged in discrete tufts (bristle groups) which are regularly spaced along the row of bristles 130. As shown, the tufts of bristles in the first group of bristles 132 may decrease linearly in height towards the free end 122 of the core 120, in a similar manner to that described previously. Alternatively, the tufts of bristles in the first group of bristles 132 may decrease in height in a stepped manner towards the free end 122 of the core 120, similarly to the example of Fig. 7B. In the examples described above, the bristles in the row of bristles 130 may be inclined towards the free end 122 of the core 120. In other words, each bristle may be inclined (angled) such that a tip of the bristle is closer to the free end 122 of the core 120 than a base of the bristle. For example, the bristles may be inclined towards the free end of the core at an angle between 20° and 60° relative to an outer surface of the core. The row of bristles 130 may further comprise a bristle carrier 140, on which the bristles are held and from which the bristles protrude. For example, the bristles may be woven into the bristle carrier 140 so as to protrude from the bristle carrier 140. The bristle carrier 140 can then be fixed to the outer surface of the core 120. The bristle carrier 140 may be made of any suitable flexible material. Where the bristles are mounted in a channel on the outer surface of the core 120, as mentioned above, the bristle carrier 140 may be mounted in the channel so that the bristles protrude from the channel. During the use of the cleaner head, any debris which has become wrapped around the agitator is encouraged by the conical shape of the agitator to migrate along the agitator towards the free end, where it can become released from the agitator. In order to minimise the risk of this released debris becoming re-wrapped around the agitator before it is conveyed away from the agitator within an airflow which is passing through the suction cavity, the suction cavity comprises a second air outlet located adjacent the free end of the agitator. A first part of the airflow passing through the suction cavity leaves the suction cavity through the first air outlet, and a second part of this airflow leaves the suction cavity through the second air outlet. The first part of the airflow, generally containing dust and other detritus which has been agitated from a floor surface by the agitator, passes along a first airflow path extending from the first air outlet to an outlet of the cleaner head. The second part of the airflow, into which debris which has been released from the agitator generally becomes entrained, passes along a second airflow path extending from the second air outlet towards the first airflow path so as to merge with the first part of the airflow between the first air outlet and the outlet of the cleaner head, and thus before any part of the airflow is emitted from the cleaner head. As used herein, the term “conical shape” includes both conical and frustoconical shapes. The cone angle of a conical shape is the angle subtended between the longitudinal axis of the conical shape and the external conical surface of the conical shape. In some embodiments, the cone angle can vary between 5 to 15°, and in other embodiments, the cone angle is 7°. As used herein the term “debris” refers to strands which have the potential to wrap around the agitator during operation of the cleaner head. For example, debris may be considered to comprise strands having a length which is greater than the maximum circumference of the agitator. Examples of debris include hairs, threads and other relatively long fibres and strands. The suction cavity is preferably defined by a conical housing of the cleaner head. The housing preferably has substantially the same shape as the agitator. The agitator preferably comprises a conical core having helical ridges upstanding from an external conical surface of the core, and a row of bristles located between the helical ridges. The bristles may be mounted on a flexible bristle base which is inserted between the upstanding ridges of the core. The bristles may be arranged so as to bend freely, for example, against the upper surfaces of the helical ridges, as debris becomes wrapped around the agitator. This can further encourage the migration of the debris towards the free end of the agitator. For example, the bristles may be formed from relatively thin strands of nylon or carbon fibre. As measured in a direction perpendicular to the longitudinal axis of the core, the height of the upstanding ridges is preferably at least 50% of the height of the bristles. This can prevent the debris from sinking between the bristles towards the bristle base upon which the bristles are mounted, and so becoming trapped within the row of bristles. The cleaner head preferably comprises a bottom surface, or sole plate, in which the opening is formed. The longitudinal axis of the agitator is preferably inclined at an acute angle to a plane containing the opening of the cleaner head. In a preferred embodiment the cone angle is 7°. In use, the lowermost portion of the external surface of the core is preferably parallel to the plane containing the opening so that the lowermost portion of the external surface of the core is evenly spaced along its length from this plane. The opening is preferably trapezoidal in shape. The opening may be defined by a relatively long leading edge, and relatively long trailing edge, and two side edges each extending between the leading edge and the trailing edge. The leading edge may be perpendicular to the side edges, or, as in a preferred embodiment, it may be inclined relative to the side edges so that it subtends an acute angle with one side edge and an obtuse angle with the other side edge. Each of the first air outlet and the second air outlet is preferably located rearwardly of the agitator. The second air outlet is preferably located directly behind the free end of the agitator, whereas the first air outlet is preferably located midway between the free end and the second end of the agitator. Where the agitator comprises a helical row of bristles, we have found that these locations of the first and second air outlets, and thus the directions in which air passes through the suction cavity, can encourage debris to wrap around the agitator in a direction which is generally orthogonal to the longitudinal axis of the agitator, as opposed to a direction extending generally along or alongside the helical row of bristles. This can promote the migration of debris along the agitator and its subsequent release from the agitator. The first air outlet and the second air outlet are preferably spaced in a direction extending parallel to the longitudinal axis of the agitator. The first airflow path is preferably defined, at least in part, by a neck for conveying air from the first air outlet to the outlet of the cleaner head. The neck preferably comprises a connector for connecting the cleaner head to a vacuum cleaner. The first part of the airflow and the second part of the airflow preferably merge within the neck. The second airflow path is preferably defined, at least in part, by a duct for conveying air from the second air outlet to an air inlet port formed in the neck and from which the second part of the airflow enters the first part of the airflow. The air inlet port is located between the first air outlet and the outlet of the cleaner head. The second airflow path thus extends away from the suction cavity in parallel to the portion of the first airflow path located upstream from the air inlet port. The duct, and thus the second airflow path, preferably extends externally of the housing from the second air outlet to the neck. To minimise turbulence, the duct is preferably curved, and preferably curves through 90° between the second air outlet and the air inlet port. The duct may have a constant or a varying radius of curvature along its length. To facilitate manufacture, the duct is preferably integral with at least part of the neck and / or at least part of the housing. The cleaner head preferably comprises a single conical agitator which has a free end located adjacent to, but spaced from a side wall of the suction cavity, and a second end, located opposite to free end, which has a larger diameter than the free end. The agitator is preferably mounted, at or towards the second end of the agitator, to a drive for driving the rotation of the agitator relative to the suction cavity. The drive preferably comprises a motor located externally of the agitator, and a belt connecting the agitator to the motor. Alternatively, the motor may be located within the agitator. To maximise cleaning performance by preventing released debris from becoming trapped between the free end of the agitator and the side wall of the housing, the spacing between the free end of the agitator and the side wall is preferably in the range from 2 to 10 mm, more preferably in the range from 3 to 5 mm. As the cleaner head is manoeuvred over a carpeted floor surface, a portion of the carpet can become raised and drawn into the suction cavity through the opening, in view of the relatively low air pressure generated within the suction cavity by the vacuum cleaner. This can cause the raised portion of the carpet to contact the agitator, in particular the bristles and the helical ridges upstanding from the external surface of the core. When debris has become wrapped around the agitator, the action of the carpet pressing upon the agitator can encourage this debris to become more tightly wrapped around the agitator. We have observed that tightly wrapping the debris around the agitator can promote its migration towards the free end of the agitator. So as not to be reliant upon the movement of carpet into the suction cavity to urge debris against the agitator, to promote migration of the wrapped debris along the agitator the cleaner head preferably comprises an agitator engaging member for pressing against the agitator any debris which has become wrapped around the agitator. The engaging member preferably extends substantially the entire length of the agitator. With rotation of the agitator within the suction cavity, this enables the engaging member to press against substantially the entire length of the row of bristles and the ridges of the core. The engaging member preferably extends in a direction which is inclined at the cone angle to the longitudinal axis of the agitator. This can allow the engaging member to be aligned relative to the agitator so that it lies substantially parallel to a portion, preferably an upper portion of the external surface of the core of the agitator. This can enable the engaging member to apply a substantially uniform force to the agitator along its length. The engaging member is preferably biased towards the agitator. The engaging member may comprise a plate or bar which is biased towards the agitator by one or more springs or other resilient members. Alternatively, the engaging member may be in the form of a resilient member which is biased internally towards the agitator. The resilient member may comprise a strip of resilient material, which preferably has a substantially uniform width. The width of the engaging member is selected such that the engaging member presses wrapped debris against at least the bristles of the agitator, and preferably against also the helical ridges of the core. In an embodiment, the width of the strip of resilient material is in the range from 2 to 5 mm. The engaging member may be mounted on any surface of the cleaner head so as to engage the agitator. The engaging member is preferably located opposite to the opening through which debris enters the cleaner head so that it is located opposite to any raised carpet which is also pressing against the agitator. This can enable the forces being applied to the agitator by the carpet and the engaging member to be balanced. In a preferred embodiment, the engaging member is mounted on the housing which defines the suction cavity. As mentioned above, the bristles may be arranged so as to bend freely as debris becomes wrapped around the agitator so as to further encourage the migration of the debris towards the free end of the agitator. These bristles may be mounted on the bristle base so as to extend substantially perpendicular to the bristle base. As debris becomes wrapped around the agitator, the bristles flex towards an upper end of an upstanding ridge of the core, and / or so as to at least partially overlie adjacent bristles. As an alternative, the bristles may be inclined relative to the bristle base, and thus relative to the external surface of the core, in a direction extending towards the free end of the core. This can reduce the risk of any wrapped debris becoming lodged between adjacent bristles and not migrating towards the bristle base, and so can further promote the migration of wrapped threads towards the free end of the agitator. The row of bristles extends in a row direction, and the bristles are preferably inclined at an acute angle to, and towards, the row direction. The row of bristles may be formed by securing the bristles to the flexible bristle base, and using a hot rolling technique to angle the bristles towards the bristle base. The row of bristles is then inserted between the ridges of the core so that the row of bristles adopts a helical shape which extends towards the free end of the core in a helical direction, and so that the bristles are inclined towards the free end of the core at an acute angle to the helical direction. The acute angle is preferably in the range from 20 to 60°, more preferably in the range from 30 to 50°. The row of bristles may comprise a continuous row of bristles, or it may comprise a plurality of discrete bristle tufts. Figure 8 shows a partial cross-sectional view of a cleaner head 220 of the vacuum cleaner 2. The cleaner head 220 has a housing 232, which defines a suction chamber 234 comprising an outlet for expulsion of air and debris towards the vacuum cleaner 2. The cleaner head 220 comprises a pair of agitator elements 222, 224 mounted for rotation about their respective axes. The agitator elements 222, 224 are each cantilevered from opposing sides of a hub portion 230 of the cleaner head 220 such that the side of the agitator elements in contact with the surface to be cleaned is flat against this surface. In the illustrated embodiment, the hub portion 230 is at a laterally central position with respect to the overall cleaner head 220, although this may not always be the case. For example, if the agitator elements 222, 224 have different lengths, then the hub portion 230 could be offset laterally relative to the laterally central part of the cleaner head 220. The hub portion 230 serves to rotatably support the first ends 226, 229 of the agitator elements 222, 224 and may comprise a drive housing holding a drive mechanism for rotating the agitator elements 222, 224. In an alternative embodiment, the agitator elements 222, 224 may be cantilevered from separate hubs located at the first ends 226, 229 of the agitator elements 222, 224 respectively. The housing 232 comprises a cover portion 233 and wall portions 235 which extend away from the cover portion 233 towards a floor surface to be cleaned in use. The cover portion 233 generally extends over the agitator elements 222, 224, and the wall portions 235 generally surround the agitator elements 222, 224, and this can be in the manner of a skirt. The cross-section of only one of the agitator elements 222 is shown in its entirety in Figure 9, and the description below is given in the context of the agitator element 222. It will be understood that the agitator element 224, and the portion of the housing 232 not shown in Figure 8, is the same as described below in respect of agitator element 222. The agitator element 222 comprises a first end 226 and a second free end 228. In this embodiment, the agitator element 222 has a frustoconical shape which tapers from the first end 226 towards the second end 228 in a direction along the axis of rotation RI. The cross-sectional area of the first end 226 of the brush bar 222 in a direction orthogonal to the axis of rotation RI is consequently larger than the cross-sectional area of the second end 228 in a direction orthogonal to the axis of rotation RI. It should be appreciated that a portion of the agitator element 222 may not be tapered. For example, the agitator element 222 may consist of a cylindrical portion combined with a frustoconical portion. In other embodiments, the agitator element 222 may be fully cylindrical. Referring additionally to Figure 9, the second end 228 of the agitator element 222 comprises a chamfered cut 223 on one edge, with an identical chamfered cut made on the opposite edge of the second end 228 (not shown). This chamfered cut 223 can assist in diverting away debris while ensuring there is no unintentional friction from rubbing against the housing, particularly with a heavy load of debris. The chamfer cut 223 can be designed to begin from the center of the second end 228 and end in line with the bristle for handover of debris, particularly hair. The angle of the chamfer can range between 20 to 50 degrees. The agitator element 222 also comprises helically wound strip, which extend along the agitator element 222 from the first end 226 to the second end 228. This strip 221 can be made of microfiber, nylon bristles that are upstanding and stiff, or any other relevant material used for cleaning surfaces. The upstanding bristles may be angled towards the second end 228 of the agitator element 222. In alternative embodiments, one or both of the helical strips 221 may be augmented with, or replaced by, a flexible rubber blade or microfiber strips or similar. In the example shown in Figure 8, the second end 228 of the agitator element is located opposite to, and spaced from, an end wall portion 235 of the housing 220 and this defines an alcove 240. The end wall portion 235 is flat and configured so that it extends downwardly, in use, from the cover portion 233 towards the floor surface to be cleaned. The alcove as defined from the end of the agitator element to the wall of the housing can be between 1mm to 10mm, depending on the type of debris that needs to be cleared by the cleaning appliance. The agitator element 222 is arranged within the vacuum chamber 234 such that, in use, a first end of the axis of rotation RI located at the first end 226 of the agitator element 222 is located further from the floor surface to be cleaned than a second end of the axis of rotation RI located at the second end 228 of the agitator element 222. The inner surface of the end wall portion 235 can be smooth or it can comprise a textured surface which may be provided by an applied surface covering or coating, or which may be formed in the material of the end wall portions 236. The textured surface may be a rough surface or surface covering, and / or may comprise regular or irregular projections with the same or different forms. Example forms for the projections include, but are not limited to, demi-spherical, cylindrical, spiral, and pyramidal. In use, the cleaner head 20, 220 is moved over a surface to be cleaned and a vacuum is created in the vacuum chamber 234 by the motor located in the main body 4. At the same time, the agitator elements 222, 224 are rotated about their respective axes by the agitator element drive mechanism. Typically, the agitator elements 222, 224 rotate in a direction towards a primary direction of use. For example, referring to Figure 8, if the primary direction of use of the cleaner head 220 is out of the page, then the agitator elements 222, 224 rotate in a clockwise direction about their respective axes of rotation when viewed along the axes of rotation from the first to the second end of the agitator elements. When the cleaner head 220 passes over hair or other long strands of debris, the strands tend to become wrapped around the agitator elements 222, 224. The tapered configuration of the agitator elements 222, 224 tends to cause the wrapped strands to migrate along the agitator elements towards the second, or smaller, ends 227, 228 where they can be removed by way of the vacuum chamber 234. The strands which have migrated off the agitator elements 222, 224 tend to form debris strand balls which reside in the alcove until they are of a sufficient size to be sucked from the alcove 240 by the vacuum in the vacuum chamber 234. The inner surface of the end wall 235 can also help to cause debris strand balls to be pulled from the alcove 240 once they have reached a sufficient size. Also shown in Figure 8 is a front bumper 250 and its various embodiments is described in Figures 10A and 10B. The front bumper 250 can have openings 251 to allow larger debris to enter and allow the debris to be swept by the agitator 222 into the vacuum chamber 234. In Figure 10A, we can see that the opening 251 is flanked by surfaces 252, 254 that guide debris into the opening 251. The suction air flow provided by the vacuum cleaner 2 assists in moving the debris into the opening, and it was found that the air flow takes over much closer to the opening compared to further away. An alternative bumper 250 is shown in Figure 10B where the surfaces 262, 264 flanking the opening 251 are curved. The steeper gradient of the surface 262, 264 further from the opening can assist debris in moving towards the opening at a faster pace. This also reduces the chance of larger debris bouncing off the surfaces 262, 264, 266, 268. Any of the agitator elements described above may be used alone or in matched or unmatched pairs in the cleaner head 20.

Claims

1. A cleaner head for a vacuum cleaner, the cleaner head comprising:an agitator rotatably mounted within a housing, the agitator being arranged transversely within the housing such that it is perpendicular to the direction of travel of the cleaner head during use, the agitator being conical in shape, such that a first end has a larger diameter than a second end anda suction cavity comprising an opening through which debris enters the cleaner head, and an outlet.

2. A cleaner head according to claim 1, wherein the agitator has a main body with an outer conical surface, and the lowermost portion of the conical surface is parallel with a flat supporting surface when the cleaner head is in use.

3. A cleaner head according to claim 1 or 2, wherein the axis of rotation of the agitator is inclined with respect to a flat supporting surface on which the cleaner head is supported during use.

4. A cleaner head according to claim 1, wherein the cleaner head further comprises an agitator engaging member for pressing against the agitator any debris which has become wrapped around the agitator.

5. A cleaner head according to claim 4, wherein the agitator engaging member extends substantially the entire length of the agitator.

6. A cleaner head according to claim 4, wherein the agitator engaging member is biased towards the agitator.

7. A cleaner head according to claim 4, wherein the agitator engaging member comprises a resilient member which is biased towards the agitator.

8. A cleaner head as claimed in claim 7, wherein the resilient member is in the form of a strip of resilient material.

9. A cleaner head as claimed in claim 8, wherein the strip of resilient member has a substantially uniform width.

10. A cleaner head as claimed in any preceding claim, wherein the suction cavity is defined by a substantially conical housing of the cleaner head, and wherein the agitator engaging member is mounted on the housing.

11. A cleaner head as claimed in any preceding claim, wherein the core of the agitator comprises upstanding helical ridges, and the agitator comprises a row of bristles located between the helical ridges.

12. A cleaner head as claimed in claim 11, wherein the agitator engaging member is arranged to press wrapped debris against at least the bristles of the agitator.

13. A cleaner head as claimed in any preceding claim, comprising a drive for driving rotation of the agitator, and wherein the agitator is connected to the drive at or towards the first end of the agitator.

14. A cleaner head according to claim 1, wherein the agitator has a shape which tapers from the first end of the agitator towards the second end of the agitator, wherein the second end of the agitator includes a chamfered edge and the second end of the agitator defines an alcove with a wall of the housing, wherein the alcove is configured to releasably retain a debris strand ball formed during use of the agitator in a vacuum cleaner.

15. A cleaner head according to claim 14, wherein the agitator further comprises a strip along the agitator from the first end of the agitator towards the second end of the agitator element.

16. A cleaner head according to claim 15, wherein the strip has the form of at least a portion of a spiral curve.

17. A cleaner head according to claim 16, wherein the rotational sense of the spiral curve when viewed from the second end of the agitator element corresponds to the direction of rotation of the agitator in use.

18. A cleaner head according to claim 16, wherein the rotational sense of the spiral curve when viewed from the second end of the agitator element is opposite to the direction of rotation of the agitator in use.

19. A cleaner head according to any preceding claim, wherein the agitator comprises an outer surface which is continuous from the first end of the agitator to the second end of the agitator.

20. A cleaner head according to any one of claims 14 to 19, wherein the agitator is cantilevered from a hub located at the first end of the agitator.

21. A cleaner head according to claim 1, further comprising a comb having a plurality of teeth, each tooth extending into the suction chamber so that at least a distal end of said tooth is arranged to contact a portion of the agitator; and wherein a contact face of each tooth is arranged to contact a radially extending portion of the agitator.

22. A cleaner head according to claim 21, wherein at least one of the plurality of teeth comprises an angled tooth that is arranged so as to extend at least partially in a longitudinal direction of the longitudinal axis of the agitator and towards the suction chamber.

23. A cleaner head according to claim 22, further comprising a first set of two or more of said angled teeth, wherein the angled teeth of said first set are spaced from one another along a first region of the agitator.

24. A cleaner head according to claim 23, further comprising a second set of two or more of said angled teeth, wherein the angled teeth of said second set are spaced from one another along a second region of the agitator and wherein the angled teeth of said second set are inclined towards the angled teeth of said first set.

25. A cleaner head according to any one of claims 23 to 25, wherein a third set of the plurality of teeth are arranged between the suction chamber and said first region, the third set of the plurality of teeth comprising transition teeth, wherein each transition tooth of the third set is arranged so as to extend at least partially in said longitudinal direction wherein the transition teeth are not parallel to the angled teeth.

26. A cleaner head comprising:a body defining a suction cavity; anda rotatable agitator located in the suction cavity;wherein the agitator comprises a core having a first, free end, and a second end opposite the free end that is rotatably connected to the body;wherein the agitator comprises a row of bristles extending between the free end and the second end of the core; andwherein the row of bristles includes a first group of bristles located next to the free end of the core, and a second group of bristles located between the first group of bristles and the second end of the core, the first group of bristles being shorter than the second group of bristles.

27. A cleaner head according to claim 26, wherein a length of the bristles in the first group of bristles decreases towards the free end.

28. A cleaner head according to claim 27, wherein the length of the bristles in the first group of bristles decreases gradually towards the free end.

29. A cleaner head according to claim 27 or 28, wherein the length of the bristles in the first group decreases linearly towards the free end.

30. A cleaner head according to claim 29, wherein tips of the bristles in the first group follow a line which is inclined relative to an outer surface of the core at an angle between 30° and 60°.

31. A cleaner head according to claim 27 or 28, wherein the first group of bristles comprises a first portion of bristles and a second portion of bristles, the first portion being located nearer the free end, and wherein the first portion of bristles is shorter than the second portion.

32. A cleaner head according to claim 26, wherein the second group of bristles comprises a portion of the row of bristles extending between the first group of bristles and the second end of the core, and wherein a length of bristles in the second group of bristles is substantially constant along the row of bristles.

33. A cleaner head according to claim 26, wherein bristles in the row of bristles are inclined towards the free end of the core.

34. A cleaner head according to claim 26, wherein bristles in the row of bristles are arranged in tufts.

35. A cleaner head according to claim 26, wherein the core has a shape that tapers towards the free end, such that the free end of the core has a smaller cross-sectional area than the second end of the core.

36. A cleaner head according to any preceding claim, further comprising a front bumper with an opening for debris to be swept into the suction chamber by the agitator.

37. A cleaner head according to claim 36, wherein said opening is flanked by a pair of walls that guide debris into the opening.

38. A cleaner head according to claim 37, wherein said pair of walls are straight.

39. A cleaner head according to claim 37, wherein said pair of walls are curved.

40. A cleaner head according to claim 39, wherein said pair of walls are curved with a gradient that is greater the further away from the opening.

41. A vacuum cleaner head comprising:a housing which defines a vacuum chamber having an outlet, wherein the housing comprises a cover portion and wall portions which extend away from the cover portion; andan agitator element according to any preceding claim mounted for rotation within the vacuum chamber,wherein the second end of the agitator element is located opposite to, and spaced from, a wall portion of the housing.

42. A vacuum cleaner head according to claim 41, wherein the agitator element is arranged within the vacuum chamber such that, in use, a first end of the axis of rotation located at the first end of the agitator element is located further from a floor surface to be cleaned than a second end of the axis of rotation located at the second end of the agitator element.

43. A vacuum cleaner head according to claim 42, wherein the inner surface of the wall portion located opposite the second end of the agitator element defines a first plane which is orientated at an acute angle with respect to a second plane which is orthogonalto the axis of rotation of the agitator element located at the second end of the agitator element.

44. A vacuum cleaner head according to any one of claims 41 to 43, wherein the inner surface of the wall portion located opposite the second end of the agitator element comprises a textured surface.

45. A vacuum cleaner head according to any one of claims 41 to 44, wherein the agitator element is cantilevered from a hub located at the first end of the agitator element.

46. A vacuum cleaner head according to any one of claims 41 to 45, comprising two agitators according to any one of the preceding claims 1 mounted for rotation within the vacuum chamber.

47. A vacuum cleaner comprising a vacuum cleaner head according to any one of the proceeding claims.

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