Field of the Invention

The present invention concerns a web-cleaning apparatus. More particularly, but not exclusively, this invention concerns a web cleaning apparatus comprising a roller brush for cleaning a moving web and an associated method.

Background of the Invention

Web-processing machines are used in industry to perform an operation on a web, which may be in the form of a roll of sheet material, for example paper, plastic, or the like. Operations can include but are not limited to cleaning web, printing onto web and applying treatments to web. Examples of web processing machines include a printing machine, a laminating machine, a machine which provides coatings to web and/or a machine involved in the production of batteries, where web is prepared.

Web-cleaning devices are used in industry to prepare the surface of a web and may form part or, or be used in conjunction with, a web-processing machine. Webcleaning devices can be non-contact web cleaning systems, such as the Meech CyClean™-R Non-Contact Web Cleaning System, or can be contact web cleaning systems such as the Meech VacClean™ Contact Web Cleaning System, or Meech RoClean™-C Contact web cleaner. Contact web cleaning systems typically comprise a roller brush and/or positive and/or vacuum airflow. RoClean-C cleans web surface through the use of a bristle roller brush. The roller brush rotates to sweep clean the surface of the web. The contamination is then immediately vacuumed into an air handling unit filtration unit to avoid recontamination of the surface.

In ultra-clean applications, such as battery film processing, where the acceptable levels of contamination are low (in the region of 10 microns), the RoClean-C Contact Web Cleaner is used, with a roller brush having suitable bristle media.

A problem that arises with the use of roller brushes to clean contaminants, is that contaminant particles can attach to the bristles of the roller brush, reducing the cleaning effectiveness of the roller brush. Over time, the build-up of contaminants on the roller brush bristles reduces the cleaning efficiency to such an extent that the roller brush has to be replaced, as it cannot meet the required standards of cleanliness in its application. This is especially problematic in ultra-clean applications where the acceptable remaining particle size (after cleaning by the cleaner head) must be below 25 microns (or in some applications down to less than 10 microns).

Contaminants on bristles are especially troublesome in battery film processing (which requires an ultra-clean environment). It is particularly important to have low levels of cross-contamination in battery film processing, because anode film and cathode film can be processed consecutively by the same web-cleaning apparatus, and the contaminants from the anode can affect the performance of the cathode (and vice versa).

The present invention seeks to mitigate one or more of the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved web-cleaning apparatus and/or an improved method of cleaning a web.

Summary of the Invention

The present invention provides, according to a first aspect, a web cleaning apparatus comprising a cleaning head which comprises a roller brush for cleaning a moving web, wherein the web cleaning apparatus is configured and/or provided with extra apparatus to facilitate cleaning of the roller brush, preferably while the roller brush remains in situ. In one embodiment, the cleaning head is moveable from a first position, in which the web cleaning apparatus is in a web cleaning configuration, to a second position in which the web cleaning apparatus is in a roller brush cleaning configuration enabling the roller brush to undergo a roller brush cleaning cycle. Arranging the cleaning head to be moveable away from its web cleaning configuration to the roller brush cleaning configuration, enables the brush to be cleaned in situ with the consequent saving of time and/or reduction of down-time of the web cleaning apparatus. It may also facilitate more frequent cleaning of the roller brush, thus reducing the risk of contaminant build-up on the brush and/or assisting in web cleaning efficiency.

The roller brush is mounted for rotation about a rotation axis, for example by means of a shaft. The diameter of the shaft may be at least 20mm (and may be less than 100mm). In use, the roller brush is driven about its rotation axis at high speed when cleaning the moving web. The brush, when cleaning the moving web, is preferably rotated in a direction opposite to the movement of the web, so that the bristles closest to the moving web are moving in one direction while the web is moving in an opposite direction. The speed of rotation of the roller brush, when cleaning the web, may be of the order of at least lOOrpm (preferably at least 200rpm), for example between lOOrpm and lOOOrpm. The diameter of the roller brush (including the bristles of the brush) may be at least 20mm, for example 30mm or more (and may be less than 200mm, and possibly less than 100mm). The bristles of the brush may each have a diameter (thickness) of between 0.05mm and 1mm, and for ultra clean environments this may be between 0.05mm and 0.5mm, and possibly between 0.1mm and 0.2mm. While movement of the cleaning head relative to the rest of the web cleaning apparatus could be achieved by holding the cleaning head static and moving other parts of the machine, it is preferred that the cleaning head moves together with the roller brush away from other parts of the web cleaning apparatus, which may remain static as between the transition from the web cleaning configuration to the roller brush cleaning configuration.

The web cleaning apparatus may include an elongate brush cleaning member for cleaning the roller brush. The elongate brush cleaning member may be arranged, when the web cleaning apparatus is in the roller brush cleaning configuration, to dislodge contaminant particles from bristles of the roller brush by contacting the bristles as the roller brush is rotated during the roller brush cleaning cycle. The elongate brush cleaning member may be arranged, when the web cleaning apparatus is in the web cleaning configuration to be spaced apart from the bristles of the roller brush. It may be that the elongate brush cleaning member needs to be moved during the transition from the web cleaning configuration to the roller brush cleaning configuration. When cleaning the roller brush, it is preferred that the elongate brush cleaning member remains in the same position, while the roller brush is rotated. While the elongate brush cleaning member may have moving parts, or flexing parts, which assist in the cleaning of the roller brush, it is preferred that the part(s) of the elongate brush cleaning member which are for cleaning the roller brush remain static when cleaning the roller brush.

The web cleaning apparatus may comprise an elongate plate for assisting with cleaning the roller brush. The elongate plate may for example be moveable from a first position in which the web cleaning apparatus is in its web cleaning configuration, to a second position in which the web cleaning apparatus is in its roller brush cleaning configuration and in which the plate assists in the roller brush cleaning cycle. During use of the web cleaning apparatus, there may be a step of inserting the elongate plate into the web cleaning apparatus, for example, optionally by a step of sliding the plate longitudinally (in a direction along its length) into the apparatus (the web cleaning apparatus preferably comprising support surfaces provided to facilitate this step). The web cleaning apparatus and plate may be configured so that the plate is removed from the web cleaning apparatus when the web cleaning apparatus is in its web cleaning configuration. The web cleaning apparatus may include one or more parts to enable the fixing, or holding in position, of the plate when in its second position. The length of the elongate plate may be sufficient to extend across the entire roller brush length (the dimension parallel to the rotation axis). The elongate plate may be formed in one or more sections. The elongate plate may be formed as a one-piece part. If the elongate plate is formed as a multi-part structure, it is preferred if at least one part extends across the entire length of the roller brush.

During use, the plate may be so arranged that rotation of the roller brush causes bristles of the roller brush to contact a part of the plate and therefore cause contaminant particles to be dislodged from the roller brush. It is preferred that the aforementioned elongate brush cleaning member forms part of the plate, preferably being integrally formed as a part thereof. For example, the removable plate may have a ridge extending along its length, the ridge performing the function of a brush cleaning member. The ridge may extend into the brush, so that it is located between the bristles of the roller brush as the roller brush rotates when being cleaned. The plate may be arranged such that during cleaning the bristles are deflected by at least 30 degrees, preferably between 40 and 80 degrees (in comparison with the radial direction which the bristles extend from the brush core). It may be that, in use, the bristles flick back into the radial direction which the bristles extend from the brush core once they have passed the plate, causing contaminants to be released from the bristles. Additionally, or alternatively, the elongate brush cleaning member may itself comprise bristles for cleaning the roller brush (e.g. bristles that are stiffer than the bristles of the roller brush). Additionally, or alternatively, the elongate brush cleaning member may be so shaped that it is in the form of a nub extending outwardly from the plate, when viewed in cross-section (the section being taken on a plane that is perpendicular to the roller brush axis of rotation). The nub, when viewed in a perspective view, may have the general shape of a ridge. The nub may have a rounded shape (i.e. with no sharp edges that might otherwise damage the bristles of the roller brush). The upper surface of the nub may have a shape that is generally semi-circular in form. The plate and/or the elongate brush cleaning member may have a constant cross-section along the majority, preferably substantially the entirety (i.e. at least 90%) of its length. The removable plate may improve the efficiency of the brush cleaning process. The removable plate may improve the level to which the brush can be cleaned.

The plate may comprise a well (i.e. a concave region when viewed in crosssection) which is arranged to accommodate the roller brush, when the web cleaning apparatus is in its roller brush cleaning configuration. The radius of curvature of the well may be equal to the radius of the roller brush +/- 50% (preferably within +/- 20%). The well may be interrupted by the aforementioned nub. More generally, it is preferred that the elongate brush cleaning member is positioned in the well. This geometry has been found to facilitate efficient cleaning of the roller brush, particularly when air flow considerations are taken into account. As will now be described, air flows may be used when cleaning the web and/or when cleaning the roller brush.

The web cleaning apparatus may arranged to receive air from an air supply unit both when the web cleaning apparatus is in its web cleaning configuration and when the web cleaning apparatus is in its roller brush cleaning configuration. The web cleaning apparatus may be arranged to supply air to an air filtration unit both when the web cleaning apparatus is in its web cleaning configuration and when the web cleaning apparatus is in its roller brush cleaning configuration. It is preferred for the function of the aforementioned air supply unit to be performed by the same unit as performs the function of the air filtration unit. Such a unit may be referred to as an air handling unit. Thus, it may be that the web cleaning apparatus is arranged to receive air from, and to supply air to, an air handling unit both when the web cleaning apparatus is in its web cleaning configuration and when the web cleaning apparatus is in its roller brush cleaning configuration. Air may therefore be provided on one side of the brush roller as a positive airflow supply and on the other side as negative airflow (e.g. vacuum/suction). The air handling unit may include an air filter system. The web cleaning apparatus may so arranged that the airflow, when the web cleaning apparatus is in its roller brush cleaning configuration, is entrained along a path such that the majority of the air passes through the roller brush. The entrainment of such airflow as between the web cleaning configuration and the roller brush cleaning configuration may be modified. It is preferred that plenty of air flows around the bristles of the roller brush during the cleaning of the brush to assist with dislodging of particulate matter from the roller brush. It may be that the airflow is entrained along a path such that air flows to the roller brush via an inlet gap formed between a front edge of the plate and the periphery of the roller brush and via an outlet gap formed between a rear edge of the plate and the periphery of the roller brush. Thus, the removable plate may increase the effectiveness of the air supplies in passing air through the bristles and removing contaminants.

It may be that when the elongate plate is in its second position it acts as a barrier between the roller brush and the web, or the position where the web would be if present. This may assist in preventing the passage of the particulate matter removed from the roller brush contaminating the web when the apparatus is next used for web cleaning in its web cleaning configuration.

The web cleaning apparatus will typically be operated as part of a larger system, for example a web-processing machine. The web-processing machine may for example be configured for producing thin layer films for forming the various layers (e.g. anode layer, cathode layer etc) in an energy cell, as part of a battery manufacturing process. The webs of such machines can be less than 1mm in thickness. The layers of material that form the cathode and/or anode in the finished battery may be of the order of microns. In some applications, the thickness of the base web may be less than 50 microns, optionally less than 10 microns. The web may have a width of at least 300mm. A web-processing machine will typically include several large rollers for transporting web from one part of the machine for performing a process on the web to another. The web cleaning apparatus of the present invention may be provided as part of such a machine and associated with a roller on which web is carried as it moves through the machine, and possibly with a single roller provided for the purpose of facilitating cleaning of the web.

According to a second aspect of the invention there is also provided a method of cleaning a brush roller, the brush roller being used as part of a web cleaning system. Such a method may include a step of operating a web cleaning apparatus in an operational mode in which a roller brush rotates about a rotation axis and cleans a moving web. Such a method may include a step of operating the web cleaning apparatus in a self-clean mode in which particulate matter is removed from the roller brush as it rotates. This step may include using a barrier between the roller brush and the web, or the position where the web would be if present, to prevent the passage of the particulate matter removed from the roller brush contaminating the web when next operating the web cleaning apparatus in the operational mode. The barrier (for example in the form of an elongate plate) may be moved from a first position when the web cleaning apparatus is in its operational mode to a second position when the web cleaning apparatus is in its self-clean mode. There may be a step of moving the roller brush from a first position when the web cleaning apparatus is in its operational mode to a second position when the web cleaning apparatus is in its self-clean mode. The method may include rotating the roller brush such that a cleaning member dislodges the particulate matter from the roller brush. The roller brush may remain in situ (i.e. remain as part of the cleaning head) during both web-cleaning (operational mode) and brush-cleaning (self-cleaning mode).

The method may comprise a step of arranging the roller brush and a cleaning member so that the cleaning member is in contact with the bristles of the roller brush. It will be understood that the roller brush and cleaning member would not normally be in contact when the roller brush is used to clean the web, it being preferred for the cleaning member to be moved out of contact, and away, from the roller brush and the web when the roller brush is used to clean the web. The method may comprise a step of rotating the roller brush about a rotation axis, preferably while in situ in the machine, such that the bristles impact the cleaning member to dislodge particulate matter from the bristles. Such particulate matter so dislodged from the machine may then be removed, preferably via an airflow.

The method may comprise a step of moving the roller brush to the position in which the particulate matter is removed from the roller brush, for example by a movement that is transverse (for example perpendicular) to the rotation axis. The method may comprise a step of moving the roller brush to the position in which it cleans a web in use. The method may comprise a step of moving (e.g. inserting) a removable plate into the cleaner head, to a position in which at least part of the plate is in contact with the roller brush. At least part of the plate may be directly adjacent to (and for example following the shape of), but either not in direct contact with the roller brush or if in direct contact with the roller brush not to an extent that significantly bends the bristles as they pass (e.g. less than 10 degree flexing compared with non-contact shape). During cleaning, the roller brush may be rotated in a first direction and then in a second opposite direction. Such a reciprocating motion may assist in dislodging contaminant particles from the roller brush.

During performance of the method, when the roller brush is used to clean a web it is rotated such that it reaches a first maximum rotation speed. When the roller brush is itself being cleaned it is rotated and reaches a second maximum rotation speed. The second maximum rotation speed may be greater than the first maximum rotation speed, preferably at least 50% greater. The second maximum rotation speed is preferably greater than 600 rpm, possibly 1000 rpm or more. The roller brush may, for example, be rotated at between 200 and 600 rpm during the web-cleaning mode to be fast enough to clean the web, but not so fast as to risk damage to the web. The roller brush may be rotated at a faster speed (e.g. between 600 and 1800 rpm) during brush cleaning, in order to assist with cleaning the brush.

The cleaning cycle (cleaning of the brush roller) may be completed within 5 minutes, preferably less than 100 seconds.

According to a third aspect of the invention there is also provided a plate as described or claimed herein. The plate may be in the form of a removable elongate ridged plate, configured for dislodging particulate matter from a rotating roller brush used for cleaning a web in a web-processing machine. The plate may be provided together with the brush roller with which it is associated, as a kit of parts.

It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:

Figure 1 shows a cross-sectional view of a web cleaning apparatus according to a first embodiment of the invention;

Figure 2 shows a cross-sectional view of a web cleaning apparatus according to a first embodiment of the invention; Figure 3 shows a cross-sectional view of a web cleaning apparatus according to a first embodiment of the invention;

Figure 4 shows a cross sectional view of a removable plate;

Figure 5 shows a perspective view of a removable plate;

Figure 6 shows a perspective view of a web cleaning apparatus with a removable plate in-situ, and

Figure 7 shows a flow diagram of a method of operating a web cleaning apparatus.

Detailed Description

According to a first embodiment of the invention, there is provided a cleaning head suitable for cleaning a web. In normal use (i.e. a production mode or operational mode) the cleaning head has a roller brush configured to rotate against, and therefore clean, a moving web. After a set period of time, or after the bristles of the roller brush become laden with contaminants, or during a change of webbing (“webbing up”), the roller brush body is moved relative to the cleaning head and away from the web (e.g. away from a web cleaning configuration), into a retracted position (i.e. into a roller brush cleaning configuration, in which the roller brush can undergo a cleaning cycle). A cleaning plate can then be inserted into the cleaning head, arranged against the bristles of the roller brush. The cleaning plate has an elongate ridge against which the bristles are driven by rotating the roller brush. As a result, the bristles are flicked as they pass the ridge, causing contaminants to be shed from the bristles. The bristles can deflect by up to about 60 degrees when they pass over the ridge. There is a positive air supply and a vacuum air supply in the cleaning head which work in tandem to blow air into the bristles on one side of the cleaning plate, and suck air with contaminants from the other side of the cleaning plate.

Figure 1 shows a cleaning head 10 positioned above a web 20 and a web roller 22. The cleaning head 10 is shown in its production mode, wherein a roller brush 30 is positioned such that its bristles 31 are in contact with the web 20. The roller brush 30 has a core 32 attached to the cleaning head 10, and there is a motor (not shown) which rotates the core 32. The bristles 31 are connected to the core 32 and are therefore rotated by movement of the motor. The roller brush 30 is a removable component. The web may pass through a cloud of positive and negative ions in order to which neutralise any static charges on the web before being cleaned by the roller brush 30. Partially surrounding the roller brush 30 is a shroud 35. There is a positive air supply 16 arranged on one side of the roller brush 30 and a vacuum 15 drawing air (and contaminants) on the other side of the roller brush 30. The positive air supply 16 and the vacuum 15 are separated by a central column 14 and the shroud 35. Air passes from the positive air supply 16 to the vacuum 15 by travelling between the shroud 35 and the positive air baffle 42 and thereafter through the bristles 31 and/or between the web 20 and the bristles 31 and over the surface of the web 20. Air is then drawn between the vacuum baffle 41 and the shroud 35 and into the vacuum 15. The roller brush 30 rotates, in the opposite direction of, and against the web 20 to dislodge contaminants on the web 20, which are blown/sucked into the vacuum 15. The roller brush physically disturbs the boundary layer on the web whilst simultaneously loosening the contaminants, which are then extracted by the vacuum air. The contaminants are subsequently trapped in a filter located in the air handling unit (not shown separately) which provides the vacuum and positive air supplies. Sometimes, in production mode, contaminants stick to the bristles 31 of the roller brush 30 instead of being dislodged from the web 20 and leaving in the airflow to the vacuum 15.

When it is desired to clean the bristles 31 of the roller brush 30, the cleaning head 10 undergoes an internal cam movement to withdraw the roller brush 30 and the rest of the internal structure up within the cleaning head 10 and away from the web 20. This is the position shown in Figure 2. The cleaner head 10 has a cleaner head body 11 and a movable internal structure 12. The movable internal structure 12 is movable in relation to the cleaner head body 11. The cleaner head body 11 does not move in relation to the web roller 22.

To clean the bristles 31, the movable internal structure 12 is moved to be in its retracted position shown in Figure 2, thus moving the structure 12 and roller brush 30 away from the web roller 22. A cleaning plate 50 is then inserted into the cleaner head 10, in the cleaner head body 11. The cleaning plate in-situ in the cleaning head 10 is shown in cross-section in Figure 3, with the internal movable structure 12 in its retracted position. It will be seen from the view shown in Figure 3, that the removable plate 50 has a well 52 around the position of the bristles 31, and a nub 51 in the well 52. The nub 51 (as seen only in cross section in Figure 3) is the elongate ridge mentioned above (as would be clear when the plate is seen in a perspective view). During cleaning, the roller brush 30 is rotated so that the bristles 31 spin against the nub 51. This causes the bristles 31 to be flicked, which dislodges contaminants from the bristles 31 of the roller brush 30. The positive air supply 16 and the vacuum 15 work in tandem to drive contaminants into the vacuum and remove contaminants from the bristle area. The removable plate 50 forms a barrier between the roller brush 30 and the web roller 22, and therefore the cleaning process is conducted in an environment with a degree of separation from the web 20 and web roller 22 which prevents contaminants from the bristles 31 contaminating the web 20 and/or the web roller 22.

Figure 4 shows a cross-sectional view of the removable plate, mid-way along the length of the plate. The removable plate 50 has a nub 51, in the most recessed portion of the well 52 in the centre of the removable plate 50. Locating pins 55 are also shown in Figure 4. Figure 5 shows a perspective view of the removable plate 50, and shows the well 52 formed in a central portion of the removable plate, with the ridge/nub 51 at the centre of the well. As can be seen in Figure 5, the ridge/nub 51 of the removable plate 50 is elongate and performs the function of an elongate brush cleaning member in use. The removable plate 50 also features guiding protrusions 58, a low friction track 59 on each side of the well 52, locating pins 55 and holes 56.

Figure 6 shows a view of the cleaning head 10 with the removable plate 50 in- situ. The removable plate has two locating pins 55 which help to locate the removable plate within the cleaning head 10 (i.e. they prevent it being inserted too far). The removable plate also has two holes 56, which are for aiding insertion and removal of the plate.

Figure 7 shows a flow diagram representing a method 100 of operating a web cleaning apparatus. The initial step is operating 101 the web cleaning apparatus in a production mode, where a roller brush is in contact with a web and the web is cleaned by the roller brush of the web cleaning apparatus. The method also comprises the step of retracting 103 the roller brush to a position within the cleaner head (away from the web). The method further comprises the step of inserting 105 a removable plate into the cleaner head. The method further comprises the step of cleaning 107 the roller brush by rotating the bristles of the roller brush against the removable plate (i.e. a roller brush cleaning mode or self-cleaning mode). The method can include the step of rotating the brush in a first direction and then in a second opposite direction, to assist with dislodging contaminants. The direction of rotation of the roller brush may be reversed several times during the roller brush cleaning mode. The method can include that the roller brush is rotated at a first speed (e.g. 400 rpm) in the operating 101 step, and a second, faster speed during the cleaning 107 step, for example the cleaning 107 step may be at least 50% faster the speed of the operation 101 step. In this example, the second speed is 800 rpm. The method can further comprise the step of providing positive airflow 109 towards the bristles and removable plate. The method can further comprise the step of providing a vacuum 111 to the bristles and removable plate. When the roller brush is rotated against the removable plate, contaminants present on the bristles are subjected to a force which is not present during normal cleaning of a web during the production step 101, and so the contaminants are more likely to be dislodged from the bristles. The method may also include the steps of removing 113 the removable plate from the cleaner head, extending 115 the roller brush towards the web and web roller, and then entering a production mode 117 wherein web is cleaned by the roller brush. The method may include a step of changing the web, between the steps of retracting 103 the roller brush and extending 115 the roller brush.

The method involves the production step 101 wherein the roller brush is in contact with the web. This is an open environment, in that the bristles (and any contaminants attached thereto) are able to contact the web. The method further comprises the step of retracting 103 the roller brush from the web and inserting 105 a removable plate into the cleaner head. Once the removable plate is inserted into the cleaner head, there is a physical barrier between the roller brush and the web or web roller. This means that when the cleaning step 107 is performed, the contaminants released from the bristles are unlikely to contaminate the web or web roller, or the production zone which the cleaner head is expected to clean during the production step. This is therefore, by contrast, a substantially “closed” environment. This environment can be described as the environment wherein the cleaner head is in its self-clean mode. There is an additional benefit to the removable plate: when it is in place and there is positive airflow being supplied towards the roller brush bristles/removable plate, and/or a vacuum airflow supplied to extract airflow from the roller brush bristles/removable plate, then the removable plate helps to direct the airflow so that it passes through the bristles. Without the removable plate, there would be less force acting on the bristles by way of air passing through them, and so the plate provides an extra cleaning benefit in addition to the nub/ridge 51 enabling the bristles to be flicked. The method can include returning the cleaner head to the cleaning position it occupies in the production step 101.

The method can include using the web cleaning apparatus as described above in relation to the other Figures.

Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

In the Figures, the cleaning head 10 is shown above the web 20 and web roller 22, however the orientation does not necessarily have to be that way. For example, the cleaning head can be arranged below the web and web roller, or slightly/wholly to the side of the web and web roller.

The bristle and roller brush types may vary, as can the shape and size of the cleaning head, web, and/or web roller.

Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.