Patent Publication Number: US-11376375-B2

Title: Aerosol generator

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application claims the priority benefit under 35 U.S.C. § 371 of international patent application no. PCT/EP2017/051453, filed Jan. 25, 2017, which claims the benefit of European Patent Application No. 16154653.6, filed on Feb. 8, 2016, the contents of which are herein incorporated by reference. 
     FIELD OF THE INVENTION 
     Aspects of the present invention relate to an aerosol generator for generating liquid droplets by nebulization, to a nebulizer, and to a method of manufacturing an aerosol generator. 
     BACKGROUND OF THE INVENTION 
     Aerosol generators for generating liquid droplets are used in various industries. An exemplary use is in nebulizers, to deliver pharmaceuticals in a droplet form, for inhalation by a patient. Maintaining good hygiene is one design consideration when designing nebulizer parts. Typically, a patient spends a considerable amount of time cleaning, and disinfecting a nebulizer. A typical disinfection procedure involves boiling the nebulizer for about ten minutes. A typical nebulizer needs to withstand a large number of boiling treatments. 
     A general type of nebulizer is the vibrating mesh nebulizer  20 .  FIG. 1  shows a schematic diagram of a typical vibrating mesh nebulizer. A vibratory element comprising a piezoelectric element  12  (typically ring-shaped) atop a metal washer  14  (also typically ring-shaped) supports a mesh  10 . A liquid reservoir  23  is provided underneath the mesh  10 . The mesh may be brought into vibration by the action of the piezoelectric element  12  through the metal washer  14 . A drop of liquid  21  is introduced (for example, by gravity) when the mesh  10  is vibrating, and an aerosol mist is produced. Residue is collected by the open top of the liquid reservoir  23 . If the vibratory element is located in proximity to an air stream, the aerosol so produced will be entrained in the airstream. Typically, the vibratory element is encapsulated in an encapsulation element  16  (typically an over-moulding), and a protective encapsulation  18  may be provided. 
     A typical piezoelectric element  12  is made out of ceramic. If water molecules penetrate the ceramic, the piezoelectric element  12  will typically lose functionality. The encapsulation element  16 , and the encapsulation  18  provide an imperfect seal, and water ingress into the piezoelectric element  12  in the presence of repeated, harsh boiling procedures may still present a problem. 
     WO 2015/091564 discusses a water-resistant nebulizer of the general type discussed above. Such nebulizers of this general type may, however, be further improved. 
     SUMMARY OF THE INVENTION 
     It would be advantageous to have an improved technique for sealing the vibratory element of an aerosol generator against water ingress. 
     Towards this end, a first aspect of the invention provides an aerosol generator for generating liquid droplets by nebulization, comprising:
         an aperture member comprising a plurality of apertures to provide the liquid droplets;   a vibratory element arranged to generate a vibration of the aperture member; and   an encapsulation element arranged to encapsulate a portion of the vibratory element.       

     An interface region is provided between the vibratory element and the encapsulation element, wherein the interface region comprises a sealing portion comprising a liquid resisting seal, provided as a first discontinuity formed on a face of the vibratory element and/or the encapsulation element. 
     Therefore, an aerosol generator is provided with improved resistance to fluid ingress. This is because, traditionally, over moulded elastomers in contact with metal aerosol generator parts do not usually bond with the metal with chemical bonds, but only via a mechanical “locking” to granules of metal. Thus, there is a gap between the metal and the elastomer that enables fluid creepage. 
     According to an aerosol generator meeting the definition of the aerosol generator the first aspect, the first discontinuity formed on the face of the vibratory element acts as a barrier geometry, and functions to arrest the progress of the meniscus of an advancing fluid. In this way, the advancing fluid is stopped before it makes contact with the vibratory element. The first discontinuity causes an advancing liquid contact line to experience increased surface forces caused by the increase in surface area of the liquid contact line at the discontinuity. 
     In addition, the aerosol generator is actively vibrated by a vibratory element. The interface between the metal part and an over moulded elastomer causes stress at the interface, during vibration. This can cause the over moulded component to peel away from the metal as a result of the vibration, creating capillary spaces that can fill with fluid. 
     According to an aerosol generator meeting the definition of the aerosol generator the first aspect, the discontinuity also functions to increase the “lock-in” effect in the adhesion to the parts of the aerosol generator (for example, made of metal). 
     According to an embodiment of the first aspect, an aerosol generator is provided which further comprises an adhesive layer provided in the interface region. 
     According to this embodiment, the adhesive layer is also provided with discontinuities which present a liquid barrier to an advancing fluid. 
     According to an embodiment of the first aspect, an aerosol generator according to the first aspect is provided, wherein the vibratory element further comprises a piezo-electric element arranged in mechanical contact with an aperture member support structure, the aperture member support structure is configured to support the aperture member; and wherein the interface region is provided on a portion of the aperture member support structure. 
     According to this embodiment, a piezo-electric element may be protected from fluid ingress when attached to an aperture member support structure. 
     According to an embodiment of the first aspect, an aerosol generator according to the first aspect is provided, wherein the vibratory element has a first side and a second side, and the sealing portion comprises a first sealing portion and a second sealing portion disposed on the first and the second sides of the vibratory element, respectively. 
     According to this embodiment, fluid ingress may be prevented from affecting the operation of the vibratory element from several different directions. 
     According to an embodiment of the first aspect, an aerosol generator according to the first aspect is provided, wherein the first discontinuity has a depth in the range of 10 to 50 microns. 
     According to this embodiment, a preferred range of discontinuity depths having good fluid blocking performance is provided. 
     According to an embodiment of the first aspect, an aerosol generator according to the first aspect is provided, wherein the first discontinuity is provided as a groove, or a plurality of grooves. 
     According to this embodiment, the first discontinuity has at least two parallel edges, enabling improved fluid blocking performance. 
     According to an embodiment of the first aspect, an aerosol generator according to the first aspect is provided, wherein the groove, or grooves of the plurality of grooves, have an aspect ratio of 1. 
     According to this embodiment, the first discontinuity has proportions which make manufacturing of a fluid seal more practical. 
     According to an embodiment of the first aspect, an aerosol generator is provided wherein the plurality of grooves is disposed on first and second opposite sides of the vibratory element, and the grooves of the first opposite side are offset in relation to the grooves of the second opposite side. 
     According to this embodiment, a fluid seal having improved fluid resistance is provided. 
     According to an embodiment of the first aspect, an aerosol generator is provided wherein the encapsulation element further comprises a second discontinuity configured to form a complementary interlock structure with the first discontinuity of the vibratory element at the sealing portion. 
     According to this embodiment, a fluid seal preventing fluid ingress between an adhesive layer and the encapsulation element is provided, because the encapsulation element itself has discontinuities which cause a resistance to an advancing fluid by the mechanism of capillary action. 
     According to a second aspect of the invention, there is provided a nebulizer, comprising:
         an aerosol generator according to the first aspect, or one of the embodiments of the first aspect.       

     Therefore, a more reliable nebulizer can be provided. An aerosol generator as described above will have a much lower risk of failure owing to the improved sealing properties of the vibratory element and encapsulation element. 
     According to a third aspect of the invention, there is provided a method of manufacturing an aerosol generator. The method comprises the steps of: 
     a) providing ( 60 ) a vibratory element arranged, in use of the component, to generate a vibration of an aperture member; 
     b) forming ( 62 ) a first discontinuity in a face of the vibratory element: 
     c) providing ( 64 ) an encapsulation element arranged to contact and encapsulate a portion of the vibratory element, to form an interface region incorporating a sealing portion with a liquid resisting seal provided by the first discontinuity. 
     Therefore, an aerosol element with more effective fluid resistance between the vibratory element and the encapsulation element can be manufactured, owing to the capillary action of the discontinuity against fluid droplets. 
     According to an embodiment of the third aspect, the method of manufacturing, further comprises: 
     b1) providing an adhesive on the interface region of a face of a vibratory element. 
     According to an embodiment of the third aspect, the method of manufacturing, further comprises: 
     b2) providing on a face of the encapsulation element a complementary second discontinuity arranged to interlock with the first discontinuity of the vibratory element at the sealing portion. 
     According to this embodiment, a fluid seal preventing fluid ingress between an adhesive layer and the encapsulation element is provided, because the encapsulation element itself has discontinuities which cause a resistance to an advancing fluid by the mechanism of capillary action. 
     According to an embodiment of the third aspect, the method of manufacturing, further comprises forming the first and/or second discontinuities on the respective vibratory element or encapsulation element using a laser engraving technique. 
     Accordingly, a discontinuity may be provided on the vibratory element, and/or the encapsulation element, in a simple way. Additionally, a laser engraving technique provides additional roughness in the area of the discontinuity, enhancing the “lock-in” effect of an interference fit, or of the effect of an adhesive. 
     In the following description, it is to be understood that the term “liquid droplets” includes liquid droplets having diameters in a range which makes them suitable for oral inhalation by a patient. Preferably, the droplets are provided in the order of microns. 
     In the following description, it is to be understood that the term “aperture member” includes a mesh which may be brought into vibratory action by a vibratory element. The mesh has holes which are suitable for producing liquid droplets on the order of microns, for example. As the aperture member vibrates against a droplet from a gravity feeding arrangement, or against a liquid surface, small droplets are created. 
     Therefore, it can be seen as a basic idea of the invention to add a barrier geometry to an aerosol generator. The barrier geometry prevents fluid ingress, which can damage piezoelectric components. The barrier geometry exploits the capillary effect present when a fluid droplet experiences a discontinuity. 
     These, and other aspects of the invention, will become apparent from, and are elucidated with reference to, the embodiments described hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a side-view of an aerosol generator as known in the prior art. 
         FIG. 2  shows an enlarged side-view of an aerosol generator as known in the prior art. 
         FIG. 3  shows a side-view of  FIG. 3  shows an aerosol generator according to the first aspect. 
         FIGS. 4 a   ) and  4   b ) show side views of a portion of an aerosol generator according to embodiment, and a variant embodiment, of the first aspect. 
         FIGS. 5 a   ) and  5   b ) show side views of a portion of an aerosol generator according to an embodiment, and a variant embodiment, of the first aspect. 
         FIG. 6  shows a side view of a portion of an aerosol generator according to an embodiment of the first aspect. 
         FIG. 7  shows side views of various embodiments of discontinuities, according to embodiments of the first aspect. 
         FIG. 8  shows a nebulizer according to the second aspect. 
         FIG. 9  shows a method of manufacturing an aerosol generator according to a third aspect. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     As noted above,  FIG. 1  shows a side view of a known configuration of a vibrating mesh aerosol generator. An aperture member  10 , such as a mesh, is vibrated by a vibratory element, which in  FIG. 1  is a piezoelectric element  12  which may, for example, be annular. The aperture member  10  is vibrated against the surface of a liquid, or has liquid droplets dropped onto it whilst the mesh vibrates, and an aerosol mist comprising fluid droplets is generated. The aerosol mist can be entrained in an airflow, enabling the delivery of pharmaceuticals to the lungs of a patient. The typical construction, discussed above, involves the piezoelectric element  12  being supported on a washer  14 . The washer is usually metal. The piezoelectric element  12  and the washer  14  are embedded in an encapsulation element  16 , typically with an adhesive layer  18  (such as an epoxy adhesive) between the washer  14 , piezoelectric element  12 , and the encapsulation element  16 . The epoxy adhesive is intended to act as a first fluid barrier, and as a primer layer for a second barrier, which is the encapsulation element  16 . As will be discussed below, it is, alternatively, possible to embed the piezoelectric element  12  and the washer  14 , or analogous components, in the encapsulation element  16  without an adhesive layer  18 . In this case, the surface of the encapsulation element  16  may optionally be activated using a solvent primer. 
     As discussed above, the encapsulation element  16  is typically intended to isolate the vibrations of the piezoelectric element  12  and washer  14 , and to provide a mounting. In addition, sterilization of aerosol-generating elements is typically performed by holding the active end of the nebulizer, including the aerosol-generating element, in boiling water. Thus, the encapsulation element  16  and the adhesive layer  18  are also intended to provide a seal which is fluid-tight to a limited extent. 
     Experience has shown that water ingress into the piezoelectric element  12  is still a major failure mode of the prior-art aerosol generators discussed above. It takes considerable effort to make the encapsulation element  16  water-tight. Aerosol-generators which fail frequently, thus require a more frequent replacement of the aerosol-generating element, or possibly replacement of the entire nebulizer unit, if the aerosol generating element is integrated, and not removable. 
     The water ingress occurs at the boundary of the washer  14 , adhesive layer  18 , and boundary of the encapsulation element  16 . 
       FIG. 2  illustrates the view of  FIG. 1 , with an enlarged area showing the relevant boundary areas. The boundary of the washer  14 , adhesive layer  18 , and boundary of the encapsulation element  16  is shown enlarged on a top side and a bottom side of the vibratory element. Water ingress due to boiling occurs via the path shown by arrows  22  and  24 . The cause of the fluid ingress lies principally in the fact of the adhesion between the epoxy adhesive of the adhesive layer  18 , and the (typically metal) surface of the washer  14 . Metal granules of the washer  14  promote adhesion to the epoxy of the adhesive layer  18  via a mechanism of mechanical “locking-in” of adhesive around the metal granules, rather than by forming chemical bonds to the washer  14 . This means that fluid may propagate through the spaces between the metal granules, advancing progressively with each boiling of the fluid. Eventually, the fluid will migrate as far as the piezoelectric element  12 , and cause damage to it. 
     According to a first aspect of the invention, an aerosol generator for generating liquid droplets by nebulization is provided. The aerosol generator comprises:
         an aperture member comprising a plurality of apertures to provide the liquid droplets;   a vibratory element arranged to generate a vibration of the aperture member; and   an encapsulation element arranged to encapsulate a portion of the vibratory element.       

     An interface region is provided between the vibratory element and the encapsulation element, wherein the interface region comprises a sealing portion comprising a liquid resisting seal, provided as a first discontinuity formed on a face of the vibratory element and/or the encapsulation element. 
     Therefore, an aerosol generator is provided with improved resistance to fluid ingress. The first discontinuity formed on the face of the vibratory element acts as a barrier geometry, and functions to arrest the progress of the meniscus of an advancing fluid. In this way, the advancing fluid is stopped before it makes contact with the vibratory element. The first discontinuity causes an advancing liquid contact line to experience increased surface forces caused by the increase in surface area of the liquid contact line at the first discontinuity. 
       FIG. 3  illustrates a side-view of a basic embodiment of an aerosol generator according to the first aspect. It will be appreciated that this view shows a side view of a cut-through of a “washer” type aerosol generator, although many other types and shapes of aerosol generator are relevant. 
     In  FIG. 3 , an encapsulation element  26  (typically an over moulded silicon rubber, or equivalent) encloses a vibratory element  28 . A portion of the vibratory element  28  protrudes from the encapsulation element  26 , and an aperture member  30  is attached to the protruding portion. In the illustration of  FIG. 3 , the interface region is considered to be any part of the vibratory element  28  which is in contact with the encapsulation element  26 . The interface region may comprise an adhesive layer, as will be discussed subsequently. Alternatively, the interface region may be an “interference fit” in which the vibratory element  28  is attached to the encapsulation element  26  through the effects of a very tight contact. A first discontinuity  32  is provided in the surface of the vibratory element  28 . The location where the first discontinuity is provided in the vibratory element is a sealing portion of the aerosol generator. 
     The first discontinuity may take many forms. The purpose of the first discontinuity is to provide a barrier geometry to impede, or stop, the propagation of fluid droplets along the interface region. It will be appreciated that the first discontinuity extends along a plane of the interface region to seal the entire interface region from water ingress. 
     In  FIG. 3 , the first discontinuity is provided as a single rectangular “step” feature extending along an annular path around the circumference of a top surface of the vibratory element  28 . A fluid droplet propagating along the interface region will, upon reaching the first discontinuity  32 , encounter a straight angle that interrupts the capillary forces pulling the fluid droplet along the interface region. Thus, the fluid droplet cannot propagate further along the interface region. Different forms, and specific details of the first discontinuity, will be provided subsequently. 
     Optionally, the aerosol generator is provided with an adhesive layer provided in the interface region. 
     Optionally, a portion of the vibratory element  28  is made from metal. 
     Optionally, a portion of the vibratory element  28  is a metal washer which holds a piezoelectric element. 
     Optionally, the interface region between the vibratory element  28  and the encapsulation element  26  encloses a flexible sealing member. The sealing member may comprise a pad of open-cell foam, or closed cell foam, for example. The presence of a discontinuity in the interface region stops the migration of fluid when a sealing member is present, because the flexible sealing member assumes the shape of the discontinuity when the vibratory element  28  and the interface element  26  are fixed together. 
       FIG. 4 a   ) shows a portion of an aerosol generator according to an embodiment of the first aspect. An adhesive layer  34  separates the encapsulation element  26  from the vibratory element  28  at the interface region. Part of the vibratory element  28  (such as the side of a washer) comprises a plurality of discontinuities  36  in a trench-like arrangement, although it will be appreciated that many types of discontinuity providing a barrier geometry to an advancing fluid may be provided, as will be discussed subsequently. The adhesive layer  34  fills in the gaps between the discontinuities in the interface region. 
     In the case that fluid ingress occurs mainly between the surface of the vibratory element  28  (such as a section of an annular metal washer holding a piezoelectric element) and the adhesive layer  34  (see arrow  38 ), the discontinuity  36  in the vibratory element  28  will prevent migration of the fluid droplet, owing to the barrier geometry presented by the discontinuity. 
       FIG. 4 b   ) illustrates a variant embodiment of the first aspect in which the interface region is provided as an “interference fit”. In other words, in the embodiment of  FIG. 4 b   ), the surface of the vibratory element  28  directly contact the encapsulation element  26  with no adhesive. A discontinuity is provided in the interface region. The discontinuity may be a step, a groove, or a wide range of discontinuities). 
     In the alternative, or additional, case that fluid ingress occurs between the encapsulation element and the adhesive layer, a discontinuity may be provided in the encapsulation element. 
       FIG. 5 a   ) shows another fluid-ingress prevention arrangement for an aerosol generator. In this case, the encapsulation element  40  further comprises a second discontinuity  42  configured to form a complementary interlock structure with the first discontinuity of the vibratory element  44  at the sealing portion. In other words, the encapsulation element  40  is, itself provided with a discontinuity  42  which performs as a barrier geometry for fluid droplets propagating along the interface between the adhesive layer  41 . The vibratory element  44  has a first discontinuity, as discussed above. Therefore, the structure illustrated in  FIG. 5  can protect against fluid migration (i) between the vibratory element  44  and the adhesive layer  41 , and (ii) between the adhesive layer  41  and the encapsulation element  40 . 
       FIG. 6  shows a variation of the fluid-ingress prevention arrangement for an aerosol generator. In this case, an encapsulation element  45  encapsulates a portion of a vibratory element  48 . The vibratory element has no discontinuities. The encapsulation element  45  is provided with discontinuities in the interface region, into which the adhesive layer  46  is formed. Therefore, the variation of  FIG. 6  is also applicable when fluid ingress occurs mainly between the adhesive layer  46  and the encapsulation element  45 . 
     According to an embodiment of the first aspect, the vibratory element further comprises a piezo-electric element arranged in mechanical contact with an aperture member support structure. The aperture member support structure is configured to support the aperture member, and the interface region is provided on a portion of the aperture member support structure. 
     In other words, according to this embodiment, the vibratory element  28  is provided as a composite element. 
     Optionally, the vibratory element  28  is an annular member comprising an annular piezo element and an annular washer. 
     According to an embodiment of the first aspect, the vibratory element has a first side and a second side, and the sealing portion comprises a first sealing portion and a second sealing portion disposed on the first and the second sides of the vibratory element, respectively. 
     Accordingly, the vibratory element is protected from fluid ingress from two directions. For example,  FIG. 4  illustrates a vibratory element having a first side and a second side. Because a first set of discontinuities is provided on the top side of the vibratory element, and a second set of discontinuities provided on the bottom side of the vibratory element, it is not possible for fluid to migrate under the bottom of the vibratory element  28 . 
     According to an embodiment of the first aspect, the first discontinuity has a depth in the range of 1 to 500 microns, 10 to 500 microns, 10 to 100 microns, 10 to 80 microns, 10 to 60 microns, or preferably 10 to 50 microns. 
     According to an embodiment of the first aspect, the first discontinuity and/or second discontinuity is provided as a step discontinuity, having a depth in the range of 10 to 500 microns, 10 to 100 microns, 10 to 80 microns, 10 to 60 microns, or preferably 10 to 50 microns. 
     According to an embodiment of the first aspect, the first discontinuity and/or second discontinuity is provided as a groove, or a plurality of grooves. 
     According to an embodiment of the first aspect, the first discontinuity and/or second discontinuity is provided as a flat-bottomed trench, a pointed-trench, or an inverse trapezoidal shape trench. 
     It will be appreciated that the path of the discontinuity may take many different forms, to suit the form-factor of a particular aerosol generator. A washer-type aerosol generator has an annular shape, and therefore an annular discontinuity would be relevant in that case. However, many different paths for the continuity could be used (a “squiggle” pattern, for example) provided a complete seal around the area containing the piezo-electric element is provided. 
       FIG. 7 a   ) shows a discontinuity provided as a step discontinuity with a depth d, and a width w.  FIG. 7 b   ) shows a discontinuity in the form of a flat-bottomed trench, or two step-discontinuities facing each other.  FIG. 7 c   ) shows a plurality of flat-bottomed groove discontinuities.  FIG. 7 d   ) shows the discontinuity provided as a pointed-trench.  FIG. 7 e   ) shows the discontinuity provided as a inverse trapezoidal shape trench. 
     According to an embodiment of the first aspect, an aerosol generator is provided wherein the plurality of grooves is disposed on first and second opposite sides of the vibratory element, and the grooves of the first opposite side are offset in relation to the grooves of the second opposite side. 
     According to a second aspect of the invention, there is provided a nebulizer, comprising:
         an aerosol generator according to the first aspect, or its above-described embodiments.       

       FIG. 8  illustrates a nebulizer according to the second aspect. The nebulizer comprises a lower section  56  which may be configured to hold an aerosol generator and/or a mixing chamber to enable generated aerosols to mix with an air stream. A mouthpiece  52  is in a fluid connection with the mixing chamber held in the lower section  56 , enabling a generated aerosol to be entrained in an air stream generated by the inhalation of a patient. The upper section  54  of the nebulizer  50  may contain a fluid reservoir, and an aerosol generator for providing an aerosol to the mixing chamber. It will be appreciated that the preceding description refers to an exemplary nebulizer, but the aerosol generator according to the first aspect is suitable for use in a wide range of nebulizers. 
     According to a third aspect of the invention, there is provided a method of manufacturing an aerosol generator. The method comprises the steps of: 
     a) providing ( 60 ) a vibratory element arranged, in use of the component, to generate a vibration of an aperture member; 
     b) forming ( 62 ) a first discontinuity in a face of the vibratory element: 
     c) providing ( 64 ) an encapsulation element arranged to contact and encapsulate a portion of the vibratory element, to form an interface region incorporating a sealing portion with a liquid resisting seal provided by the first discontinuity. 
       FIG. 9  illustrates the method according to the third aspect. 
     According to an embodiment of the third aspect, the method further comprises the step b1): 
     b1) providing an adhesive on the interface region of a face of a vibratory element. 
     According to an embodiment of the third aspect, the method further comprises the step b2): 
     b2) providing on a face of the encapsulation element a complementary second discontinuity arranged to interlock with the first discontinuity of the vibratory element at the sealing portion. 
     According to an embodiment of the third aspect the first and/or second discontinuities are formed on the respective vibratory element or encapsulation element using a laser engraving technique. 
     It should to be noted that embodiments of the invention are described with reference to different subject-matters. In particular, some embodiments are described with reference to method-type claims, whereas other embodiments are described with reference to the device-type claims. However, a person skilled in the art will gather from the above, and the following description, that unless otherwise notified, in addition to any combination of features belonging to one type of subject-matter, also any other combination between features relating to different subject-matters is considered to be disclosed with this application. 
     All features can be combined to provide a synergetic effect that is more than the simple summation of the features. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary, and not restrictive. The invention is not limited to the disclosed embodiments. 
     Other variations to the disclosed embodiments can be understood, and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the dependent claims. 
     In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single processor, or other unit, may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.