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CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. application Ser. No. 14/200,909, filed on Mar. 7, 2014, which claims the benefit of Provisional Application No. 61/774,749 filed on Mar. 8, 2013. The disclosure of each of U.S. application Ser. No. 14/200,909 and Provisional Application No. 61/774,749 is hereby incorporated by reference herein in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to a building panel such as a floor panel, a wall panel, a ceiling panel, a furniture component or the like, which is provided with a mechanical locking system comprising a displaceable tongue. 
       TECHNICAL BACKGROUND 
       [0003]    Building panels provided with a mechanical locking system comprising a displaceable tongue cooperating with a tongue groove for vertical locking is known and disclosed in, e.g., FR 2 975 717. The mechanical locking system in FR 2 975 717 has a displaceable tongue comprising an outer element which is pushed by a wedge part of a removable inner part of the tongue into a tongue groove, for vertical locking of adjacent edges of two floorboards. A drawback with this known system is that the locking strength is rather low. 
         [0004]    The above description of various known aspects and drawback is the Applicant&#39;s characterization of such, and is not an admission that any of the above description is considered as prior art. 
         [0005]    Although the description in the present disclosure relates to a floor panel, the description of techniques and problems thereof is applicable to other applications as well. For example, the description is also applicable to panels for other purposes, such as wall panels, ceiling panels, furniture panels and components, etc. 
       SUMMARY 
       [0006]    It is an object of embodiments of the present disclosure to provide an improvement over the above described conventional techniques. 
         [0007]    A further object of embodiments of the present disclosure is to provide building panels, such as floorboards, provided with a locking system that comprises a tongue that improves the vertical locking of the floorboards. 
         [0008]    Another object of embodiments of the present disclosure is to provide a more efficient production method, which requires less complicated production equipment. 
         [0009]    At least some of these and other objects and advantages that will be apparent from the present disclosure have been achieved by certain embodiments of the building panels described herein. The building panels, such as floorboards, are provided with a locking system that comprises a displacement groove at a first edge of a first floorboard and a tongue groove at a second edge of a second floorboard. A tongue is arranged in the displacement groove and is configured to cooperate, in a second position, with the tongue groove for vertical locking of the first edge and the second edge. The tongue comprises, in a first position, an inner element and an outer element. the inner element is removable along the displacement groove, and is configured to cooperate with the outer element to obtain a displacement of the outer element towards the tongue groove and thereby obtain the second position. The inner element and the outer element are preferably configured to vertically overlap each other in the first position to obtain an increased contact surface between a surface of the displacement groove and the outer element of the tongue in the second position. The inner element and the outer element are arranged such that the increased contact surface takes up a moment of force that arises on the tongue when a load is applied on the first or the second floorboard. The inner element in the first position may be arranged above or below the outer element. 
         [0010]    The inner element in the first position may also be arranged partly above partly behind the outer element, or may be arranged partly below the outer element and partly behind the outer element. 
         [0011]    The entire outer element is in the first position preferably arranged within the displacement groove. 
         [0012]    The outer element maybe provided with a guiding groove at either an inner and upper edge of the outer element or at an inner and lower edge of the outer element, wherein at least a part of the inner element in the first position is arranged in said guiding groove. The outer element may be provided with a guiding groove at an inner surface of the outer element, between an upper surface and lower surface of the outer element, wherein at least a part of the inner element is arranged in said guiding groove in the first position. The guiding groove facilitates the removal of the inner element by guiding the inner element in a controlled manner and provides a groove without obstructions and desired friction. The guiding groove preferably extends essentially along the whole longitudinal length of the outer element. This embodiment of the outer element provides for a simple production of the outer element for example by plastic profile extrusion and cutting of the profile in the desired length. 
         [0013]    The inner element preferably comprises a first protruding part configured to cooperate with the guiding groove, to obtain said displacement of the outer element. 
         [0014]    The first protruding part in the first position is preferably arranged outside of the outer element and/or in a recess of the outer element. When the inner element is removed by a displacement along the displacement groove and preferably in the guiding groove, the outer element is gradually pushed into the tongue groove to obtain the second position. 
         [0015]    The first protruding part may be wedge shaped or of an essentially spherical shape. Such shapes facilitate the displacement of the inner element. The outer element may also be provided with guiding surfaces at the location of the first protruding part in the first position. The first protruding part is preferably elastic, to make it easier to displace the first protruding part over irregularities in the displacement groove. The first protruding part may comprise an elastic material and may be provided with a recess to increase the elasticity. 
         [0016]    The inner element is preferably provided with a second protruding part, preferably configured such that the second protruding part is easy to grasp by an installer of the floorboards. The second protruding part may also be configured such that the inner element is secured in the correct position. 
         [0017]    The cross section of the inner element may be L-shaped or rectangular or of an essentially circular shape. 
         [0018]    The inner element may comprise plastic and may be produced by injection molding or extrusion. An extruded inner element of plastic may be provided with the first and or the second protruding part by heating and compressing a part of the extruded profile in a press tool. 
         [0019]    The inner and outer element may be produced in one piece by injection molding of plastic and connected together by a connection configured to break when the inner element is displaced or when the tongue is inserted into the displacement groove. 
         [0020]    The building panels may comprise a wood-based core, preferably made of at least one of MDF, HDF, OSB, WPC (Wood Powder Composite), and particleboard, or of plastic, such as vinyl or PVC. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    The present disclosure will by way of example be described in more detail with reference to the appended schematic drawings, which illustrate several embodiments. 
           [0022]      FIGS. 1-3  show a known locking system with a tongue comprising an inner and an outer element. 
           [0023]      FIGS. 4-7  show a tongue comprising a guiding groove at an inner edge, according to embodiments of the present disclosure. 
           [0024]      FIGS. 8 and 9  each shows a tongue from a top view, according to embodiments of the present disclosure. 
           [0025]      FIGS. 10 and 11  show cross-sections of a tongue comprising an L-shaped inner element, according to embodiments of the present disclosure. 
           [0026]      FIGS. 12-15  show tongues comprising a guiding groove at an inner surface, according to embodiments of the present disclosure. 
           [0027]      FIGS. 16-18  show a method for producing an inner element of a tongue, according to embodiments of the present disclosure. 
           [0028]      FIG. 19  shows an embodiment of an inner element of a tongue, according to an embodiment of the present disclosure. 
           [0029]      FIGS. 20 and 21  show a tongue with an inner element having a circular cross-section, according to an embodiment of the present disclosure. 
           [0030]      FIGS. 22-24  show a displacement groove provided with recess, according to an embodiment of the present disclosure. 
           [0031]      FIG. 25  shows a tongue from a top view, according to an embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0032]      FIGS. 1-3  show floorboards provided with a known locking system which comprises a tongue  20  having an inner element  21  and an outer element  22 . The tongue  20  is arranged in a displacement groove  24  at a first edge  1   b  of a first floorboard.  FIG. 1  shows a position during assembling of the first floorboard. The first floorboard is arranged in a second row and is connected at a third edge to a fourth edge of a third floorboard in first row. A second floorboard is arranged in an angled position with a third edge adjacent the fourth edge of the third floorboard and a second edge  1   c  of the second floorboard is arranged adjacent the first edge  1   b  of the first floorboard. 
         [0033]      FIG. 2  shows a cross-section of the first edge  1   b  and the second edge  1   c  after the second floorboard is angled down and connected to the third floorboard in the first row. The first edge  1   b  and the second edge  1   c  are in  FIG. 2  locked together in the horizontal direction, and the inner element  21  and the outer element  22  of the tongue  20  are arranged in a first position. The first edge  1   b  and the second edge  1   c  are in the first position vertically un-locked. To lock the first edge  1   b  and the second edge  1   c  in the vertical direction, the inner element  21  is displaced and removed along the first edge  1   b . The inner element  21  is provided with a protruding part. The protruding part pushes the outer element  22  of the tongue  20  into a tongue groove  23  at the second edge  1   c  of the second floorboard when the inner element  21  is displaced and removed. 
         [0034]      FIG. 3  shows a cross-section of the first edge  1   b  and the second edge  1   c  in a second position. The inner element  21  of the tongue  20  is in the second position displaced and removed. The outer element  22  of the tongue  20  cooperates with the tongue groove  23  at the second edge  1   c  of the second floorboard for vertical locking of the first edge  1   b  and the second edge  1   c.    
         [0035]    An embodiment of the present disclosure is shown in  FIG. 4  and  FIG. 5 , with an inner and outer element  31 ,  30  of the tongue  10  arranged in a displacement groove  32  at a first edge  1   b  of a first floorboard.  FIGS. 4 and 5  illustrate the first position and the second position, respectively, of the inner and outer elements  31 ,  30 . The outer element  30  of the tongue  10  extends below the inner element  31  of the tongue  10 , such that the inner element  31  vertically overlaps the outer element  30 . The inner element  31  is in this embodiment arranged in a guiding groove  60  at an inner and upper edge of the outer element  30 . The width x of a first contact surface between a lower surface of the outer element  30  of the tongue  10  and the displacement groove  32  is increased, as compared to the known locking system shown in  FIG. 3 , in order to improve the strength of the locking system and minimize the offset in height between the first edge  1   b  and the second edge  1   c  when a load is applied, in the second position, on the first floorboard. 
         [0036]    The second position in which the outer element  30  is pushed into the tongue groove  33  at the second edge  1   c  is shown in  FIG. 5 . The outer element  30  is pushed into tongue groove  33  by a first protruding part  36  (see  FIGS. 8 and 9 ) arranged on the inner element  31 , when the inner element  31  is removed and displaced along the first edge  1   b . A load applied on the first edge  1   b  will be taken up by a second contact surface, between an upper surface of the outer element  30  of the tongue  10  and the displacement groove  32 , and a third contact surface between a lower surface of the outer element  30  of the tongue and the tongue groove  33 . Since the second contact surface and the third contact surface are displaced, the load applied will result in a moment of force, which is taken up by the first contact surface. In order to increase the strength of the locking system, the width x of the first contact surface is preferably larger than the width y of the third contact surface, and preferably the width x is about twice ore more the width y. For the purpose of reducing the momentum that arises when a load is applied on the first edge  1   b , the horizontal distance between the second and the third contact surfaces should be as small as possible, preferably less than about 1 mm and more preferably less than about 0.5 mm. This applies also to the embodiments described below. 
         [0037]    The locking system additionally comprises in this embodiment a locking strip  6 , which protrudes horizontally from the first edge  1   b . The locking strip  6  is provided with a locking element  8  which cooperates with a locking groove  14  provided at the second edge  1   c  for horizontal locking of the first edge  1   b  and the second edge  1   c . A load applied on the second edge  1   c  is preferably taken up by a strip contact surface between an upper surface of the locking strip  6  and a lower surface of the second edge  1   c.    
         [0038]    In order to push the first edge  1   b  and the second edge  1   c  vertically against each other, a lower surface of the tongue groove  33  at the third contact surface is preferably arranged with an angle β1 in relation to the horizontal plane of the floorboards. The angle β1 may be in the range of about 5° to about 20°, and preferably about 15°. 
         [0039]    In the embodiment shown in  FIGS. 6 and 7 , the tongue  10  is arranged in a displacement groove  32  at the second edge  1   c . The inner element  31  of the tongue  10  is for this embodiment preferably arranged in a guiding groove  60  at an inner and lower edge of the outer element  30  of the tongue  10  to obtain an increased first contact surface between an upper surface of the outer element  30  of the tongue  10  and the displacement groove  32 . Also, in this embodiment the first contact surface takes up a momentum force resulting from a load applied at the first edge  1   b , in a similar way as described for the embodiment shown in  FIGS. 4 and 5 . In order to push the first edge  1   b  and the second edge  1   c  vertically against each other, an upper surface of the tongue groove is preferably arranged with an angle β2 in relation to the horizontal plane of the floorboards. The angle β2 may be in the range of about 5° to about 20°, and preferably about 15°. 
         [0040]      FIGS. 8 and 9  show top view embodiments of an elongated tongue  10 , to be arranged in a displacement groove  32  at a first edge  1   b  of a first floorboard. The elongated tongue comprises an inner element  31 , and an outer element  30 . The inner element  31  is arranged in a guiding groove  60  at an inner edge of the outer element  30 . 
         [0041]    The inner element  31  is preferably a bar element of an elongated shape and is provided at a first short edge with a first protruding part in the form of a wedge shaped element  36 . The wedge shaped element is in a preferred embodiment guided by the guiding groove during the displacement of the inner element. The wedge shaped element  36  is configured to push the outer element  30  into a tongue groove  33  of an adjacent second edge  1   c  of a second floorboard when the inner element  31  is removed and displaced along the first edge  1   b . The wedge shaped element  36  is, before the displacement, preferably arranged adjacent and at least partly outside a first short edge of the outer element  30  as shown in  FIG. 8 . A second edge of the inner element  31  is preferably provided with a gripping part  37  that facilitates the displacement of the inner element  31 . 
         [0042]      FIG. 9  shows that the first short edge of the outer element  30  may be provided with first chamfer  38  that guides the wedge shaped element  36  into the guiding groove  60 . The gripping part  37  is, before displacement of the inner element  31 , preferably arranged adjacent a second short edge of the outer element  30  and preferably outside the second edge. As shown in  FIG. 9  the inner element  31  may be provided with a second protruding part  40 , for a correct positioning of the inner element  31 , that before displacement of the inner element is preferably arranged in a notch or in a second chamfer  39  provided at the second short edge of the outer element  30 . The outer element  30  may have a uniform cross-section from the first short edge to the second short edge. A uniform cross-section makes it possible to produce the outer element  30  at low cost, by e.g., extrusion of plastic. Also the inner element  31  may have uniform cross-section with the exception of the protruding part (wedge shaped element)  36  at the first edge. For the purpose of obtaining a correct position of the inner element  31 , a preferred embodiment of the present disclosure comprises the first chamfer  38  and the second chamfer  39 , which cooperate with the first protruding part  36  and the second protruding part  40 , respectively. 
         [0043]      FIGS. 10 and 11  show an embodiment of the tongue  10  comprising an L-shaped inner element  31  arranged in a corresponding guiding groove at an inner edge of the outer element  30 . 
         [0044]      FIGS. 12-15  show an embodiment of the tongue  10  comprising inner element  31  arranged in a guiding groove  60  at an inner surface of the outer element  30 .  FIG. 13  shows that outer edges  42 ,  43  of the outer element  30  may be chamfered in order to guide the outer element  30  into the tongue groove  33 .  FIG. 14  shows a cross section of the tongue  10  and that the guiding groove  60  may be provided with chamfered edges  41 .  FIG. 15  shows a cross section of the tongue  10  in a plane indicated by AA in  FIG. 14 . The inner element  31  in this embodiment is provided with friction elements  44  that avert that the inner element  31  from falling out before the floorboards are installed. The first protruding part  36  is provided with a recess  45  that makes its most protruding part  46  more resilient. The most protruding part  46  may be, during the displacement of the inner element  31 , compressed during, e.g., entrance of the inner element  21  into the guiding groove  60 , or at any irregularities in the displacement groove  32 . Also the other embodiments of the tongue  10  may be provided with a friction element  44  on the inner element  31  and/or on the outer element  30 , and/or a recess  45  in the first protruding part  36 . 
         [0045]    A method for producing the first protruding part  36  and/or the second protruding part  40  of the inner element  31  is illustrated in  FIGS. 16-18 . A plastic blank  50  of an elongated shape is displaced into a press tool comprising a first part  55  and a second part  56 . The first part  55  and the second part  56  are displaced against each other and a protruding part  35  at a first short edge of the plastic blank  50  is formed under heat and pressure. The process may be repeated for a second short edge of the plastic blank  50 . 
         [0046]    The method may also comprise the step of forming the second protruding part  35  simultaneously and essentially in the same manner as the first protruding part  35 . The produced first and/or second protruding part  35  may be of, for example, an essentially spherical shape or wedge shaped.  FIG. 19  shows an inner element  31  that may be produced according to the method illustrated in  FIGS. 16-18 . The inner element  31  preferably has an essentially circular cross-section and preferably comprises protruding parts  35  of an essentially spherical shape. 
         [0047]      FIGS. 20 and 21  show that an inner element  31  with a circular cross section may be combined with a displacement groove  32  having an inner surface  62 , which is smaller than the opening of the displacement groove  32 . The inner surface  62  may be provided with a round shaped bottom that facilitates the displacement of the inner element  31 . 
         [0048]    An upper or lower surface of the displacement groove  32  may be provided with a recess  34  having an angled surface at an angle β3 to the horizontal plane. The angle β3 may be in the range of about 3° to about 10°. An embodiment of the recess  34  is shown in 
         [0049]      FIGS. 22-24 . The recess  34  and the angled surface has the effect that the outer element  30  of the tongue  10  tilts and the outer element  30  is restrained from being displaced back into the displacement groove  32  after the outer element  30  is pushed into the tongue groove  33  by the inner element  31 . Such a recess  34  may be provided in locking systems comprising any type of the disclosed displaceable tongue. 
         [0050]    A preferred embodiment of the tongue  10  is shown in  FIG. 25 . The inner element  31  and the outer element  30  are produced in one piece by injection moulding of plastic. The inner element  31  and the outer element  30  are connected together by a connection  47  configured to break when the inner element is displaced or when the tongue is inserted into the displacement groove.

Summary:
Building panels, such as floorboards, provided with a mechanical locking system. The mechanical locking system includes a displacement groove at a first edge of a first floorboard and a tongue groove at a second edge of a second floorboard A tongue is arranged in the displacement groove and is configured to cooperate, in a second position, with the tongue groove for vertical locking of the first and the second edge. The tongue includes, in a first position, an inner element and an outer element. The inner element is removable along the displacement groove, and is configured to cooperate with the outer element to obtain a displacement of the outer element towards the tongue groove and thereby obtain the second position. Said inner element and said outer element vertically overlap each other.