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CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a Divisional application of U.S. patent application Ser. No. 12/064,945 filed Mar. 10, 2008 which was a National Stage Entry of International Application No. PCT/EP2006/011684 filed Dec. 6, 2006, which claimed the priority of DE 10 2006 002 027.8 filed Jan. 13, 2006, DE 10 2006 002 028.6 filed Jan. 13, 2006, and DE 10 2006 011 887.1 filed Mar. 15, 2006, the priorities of these applications are claimed and these applications are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention concerns a locking element, panel with separate locking element for locking panels, method of installing a panel covering comprising panels with locking elements and a method and apparatus for pre-mounting one or more locking elements to a panel. 
         [0003]    The invention concerns a locking element for a fixing system for quadrangular plate-shaped panels wherein the locking element is provided with an insertion portion for insertion of the locking element into a locking groove, provided in the longitudinal direction of an edge of the panels, of a first panel in an insertion position, and a locking portion for engagement into a latching recess of an undercut configuration, which is provided in a laid configuration of the panels in an opposite edge of a second panel and extending in the longitudinal direction of said edge and in opposite relationship to the locking groove, wherein the locking portion includes a resilient latching tongue which during assembly of the two panels is automatically latchable into the latching recess. 
         [0004]    The locking groove of the edge of the panel is also referred to hereinafter as the holding gap. 
         [0005]    It primarily concerns a panel which can be connected to a similar panel by a substantially vertical movement of a fresh panel, namely, perpendicularly to its plane, with similar panels, wherein the above-mentioned resilient locking element is used. 
         [0006]    It further concerns a method of automatically mounting a resilient locking element to an edge of a panel, wherein the panels are for example those such as wall, floor and ceiling panels which are used for the fitment to rooms. 
         [0007]    A general state of the art of a locking element is known from WO 00/47481. A locking element of the general kind set forth is known from WO 03/016654. 
         [0008]    The locking element of WO 03/016654, prior to the panels being laid, is inserted with its insertion portion into the locking groove in a panel. During the mounting operation the latching tongue of the locking element latches automatically in a latching recess in an adjoining panel. For that purpose, to produce a spring energy, the latching tongue will be applied against the spring force of the latching tongue as far as possible in a direction towards the insertion portion, which detrimentally requires a correspondingly high level of application force. In addition, the locking element can disadvantageously slip due to the handling procedure involved when laying the panels, whereby proper laying of the panels with the latching engagement into the latching recess is at least rendered more difficult. 
       SUMMARY OF THE INVENTION 
       [0009]    The object of the invention is to provide a latching element, also referred to as a locking element, of the kind set forth in the opening part of this specification, which effectively counteracts the above-indicated disadvantages, and aims to afford a panel which can be easily installed, with an additional locking element, which can be inexpensively produced by machine, more specifically by means of a method and an apparatus for automatically pre-mounting the locking element to an edge of the panel, in which respect industrial mounting is to be possible. 
         [0010]    In accordance with the invention the specified object is attained in that the locking element has anchoring means and the locking element can be captively anchored by the anchoring means with its insertion portion in the locking groove. 
         [0011]    That arrangement provides that the locking element is held in its insertion position and cannot slip due to the handling procedure involved when laying the panels. 
         [0012]    Preferably the locking element is made in one piece. Further preferably the locking element comprises plastic material. Preferably the locking element is produced by extrusion. 
         [0013]    In an embodiment the anchoring means can provide that the locking element can be inserted in the locking groove, producing a mechanical prestressing effect. For that purpose the locking element can be inserted remaining loose with its insertion portion in the locking groove. The mechanical prestressing action causes the insertion portion to be braced in the locking groove, insofar as it is supported in the insertion position against inner side surfaces of the locking groove so that it is only with the application of an elevated level of force that it can be moved against the prestressing force in the locking groove out of its insertion position. 
         [0014]    For that purpose the insertion portion, at least at a location of its cross-section, can have an oversize in relation to the width of the locking groove provided for insertion of the locking element. In that way, the insertion portion in the insertion position can be deformed at that location of its cross-section, with elastic or plastic-elastic deformation of the locking element, and can press against the inner side surfaces of the groove, whereby material delimiting the locking groove can be elastically and/or plastically-elastically deformed. As a consequence, a corresponding anchoring force can be achieved for anchoring the locking element in the insertion position and thus for affording a force-locking connection between the insertion position and the locking groove. In addition at the location of its oversize the insertion portion can dig fast, hook or bore into the inside walls of the locking groove, whereby a positively locking connection can be afforded between the insertion portion and the locking groove. As a further advantage, compensation in respect of dimensional inaccuracies between the insertion portion and the locking groove can be implemented by way of the oversize portion. It will be appreciated that a plurality of locations or one or more portions or points on the insertion portion can also be provided with an oversize and, with insertion of the insertion portion into the locking groove, can result in a force-locking and/or positively locking connection between the insertion portion and the locking groove. 
         [0015]    To provide the oversize, at least one projection can be provided at least at a larger side surface of the insertion portion, which side surface is towards the inner side surfaces of the locking groove in the insertion position. In that case the projection can project beyond the larger side surface to provide the location having the oversize portion. In that way the projection, in the insertion position of the locking element, can bear at the end against the inner side surface of the locking groove, which is towards the larger side surface, and, by virtue of its oversize, can produce a corresponding bracing effect for the insertion portion in the locking groove. In regard to a uniform bracing effect and in regard to production of the locking element which should preferably be extruded from plastic material, it is proposed that the projection is to extend at least over a lengthwise portion of the locking element, preferably over the entire lengthwise extent of the locking element. To provide for mechanically more stable support for the locking element in the locking groove, the arrangement preferably has a plurality of projections which are in parallel mutually spaced relationship on at least one of the two larger side surfaces, which can be applied at the end against the inner side surface, that is towards the larger side surface, of the locking groove with the oversize, and thus can produce corresponding bracing for the insertion portion in the locking groove. Projections or the like can also be provided on both larger side surfaces to afford a locally limited oversize. 
         [0016]    The projection can be of a configuration which decreases towards its end face. By virtue of that configuration its cross-section can be trapezoidal. In that case, only one longitudinal side surface of the projection can be inclined towards the centre line of the projection while the other longitudinal side surface is perpendicular to the insertion portion. The trapezium of the cross-section can also be of an equilateral configuration. The longitudinal side surfaces of the projection can also be of a curve configuration perpendicularly to the longitudinal extent thereof. Preferably the cross-section is of a part-spherical shape. 
         [0017]    In a preferred development of the projection the two longitudinal side surfaces of the projection converge in a wedge shape. In that case the cross-section can be of a triangular configuration, preferably an isosceles or right-angled triangle, the longitudinal side surfaces being flat while the free tip of the respective triangle preferably includes an acute angle. 
         [0018]    Preferably the longitudinal side surface remote from the free end of the insertion portion can extend perpendicularly to the longitudinal extent of the insertion portion or in a directional component away from the free end from the larger side surface. Accordingly, with the two longitudinal side surfaces converging to afford a wedge configuration, in cross-section this can form a right-angled triangle or a sawtooth-like triangle or, with curved longitudinal side surfaces, a shark&#39;s fin-like triangle each with a respective longer side. That permits the insertion portion to be easily pressed into the locking groove in an insertion direction over the longer side in the direction towards the free end of the insertion portion or towards the base of the locking groove and permits the projection to dig fast or hook into the inside walls of the locking groove upon release of the insertion portion in opposite relationship to the insertion direction. 
         [0019]    The longitudinal side surfaces can also converge in a curved configuration and in cross-section can define a tip with a preferably over-acute angle, whereby plastic-elastic deformation of the tip is facilitated with insertion of the locking element into the locking groove to compensate for inaccuracies in respect of shape and for simultaneously clamping the locking element fast in the locking groove. 
         [0020]    The insertion portion can be of a curved configuration towards its free end. In other words, in its larger side surfaces the insertion portion can be of a curved configuration. That curvature causes the insertion portion to be preferably elastically braced in the locking groove. Preferably, in cross-section the sides formed by larger side surfaces are simply curved and curvature of the larger side surfaces is in approximately the same direction, wherein the radius of curvature preferably extends approximately in the direction of the section straight lines formed by the cross-sectional plane and the longitudinal sectional plane or perpendicularly to the larger side surfaces of the insertion portion. 
         [0021]    In an alternative configuration the free end of the insertion portion can additionally or alone be of a hook-shaped configuration. In that case the free end can be braced in the insertion position in the locking groove. 
         [0022]    Furthermore the free end can additionally or alone have a slot which is provided from the end of the insertion portion and approximately parallel to the lengthwise extent of the insertion portion or towards the locking portion. Furthermore at least one of the sides which delimit the slot at the free end of the slot can extend in a curved configuration away from the slot. Preferably the slot is V-shaped, wherein, at the location at which the sides of the slot converge, there can preferably be provided an enlargement which for easier insertion of the insertion portion into the locking groove makes it easier for the sides of the slot to be pressed or brought together. For insertion purposes the sides of the slot can preferably be compressed by way of a guide which is provided, and in the insertion position they can be supported against and braced against the inner side surfaces of the locking groove. 
         [0023]    The locking element can be at least in part over its lengthwise extent of a curved shape, the radius of curvature of which extends approximately in the direction of the section straight lines formed by the cross-sectional plane and the longitudinal sectional plane. With insertion into the locking groove which is of a linear configuration, the locking element is straightened in opposite relationship to its curvature and thus in the insertion position bears in a stressed condition against the inner side surfaces of the locking groove. 
         [0024]    For easier insertion of the locking element into the locking groove, the locking element can have an introduction aid, particularly when it has an oversize portion as described hereinbefore. For that purpose the cross-section of the free end of the insertion portion can be of a decreasing configuration, preferably of a taperingly decreasing configuration, at least from one of its larger side surfaces which in the insertion position faces towards the inner side surfaces of the locking groove. For the purposes of more secure fixing in the locking groove, the bottom of the locking groove can have an opening which is adapted to the free end for receiving the free end with the introduction aid. 
         [0025]    In a preferred development the locking portion can be of an approximately V-shaped cross-section with a first and a second limb, wherein the latching tongue is formed by the first limb and the second limb is laterally connected to the insertion portion. In that respect attention is directed to the V-shaped locking element also described in WO 03/016654 and the disclosure of WO 03/016654 in respect of the V-shaped locking element is hereby incorporated into the present disclosure. 
         [0026]    In the latching position the first limb can bear at its end against a contact surface provided in the latching recess. With insertion of the locking element into the insertion position and latching of the locking tongue in the latching recess, the end contact against the contact surface provides that, as is described in greater detail hereinafter, the second panel can be lifted off the first panel in opposite relationship to its assembly direction so that locking of the two panels can be achieved by the end contact of that arrangement. That procedure is also described in WO 03/016654 and clearly illustrated therein for example in  FIGS. 18 and 19 , the disclosure of WO 03/016654 in regard to laying the panel also being incorporated herein. 
         [0027]    In a development of possible embodiments, the locking portion can have two or more latching tongues which extend in mutually spaced relationship from the second limb and which in the latching position can be supported against a provided contact surface or against a respective contact surface. In that way the two latching tongues, with the second limb, can form a double V-profile with two first limbs. 
         [0028]    Preferably, an application aid can be provided on the locking element for elastically applying the two limbs, the first and the second limb, against each other upon assembly of the panels. The latching tongue is prestressed by way of the elastic application procedure and stores a specific spring energy. In the assembly procedure described hereinafter, which involves locking to a panel disposed in a first row a new panel in a second row, elastic application is effected by the new panel firstly being attached to the lying panel in an inclined position relative to the lying panel and then pivoted downwardly into the plane of the lying panel. For that purpose the new panel has the locking element which in the insertion position is positioned in the locking groove arranged in the edge which is towards the lying panel but which has not yet been completely lowered, in which case the V-shaped profile of the locking portion faces with its tip towards the lying panel. When the mutually facing edges of the two panels move past each other, the first limb is pressed with the latching tongue against the second limb, producing a spring stressing force, and is preferably caused to bear against the second limb. When the new panel is moved downwardly, the locking tongue at least partly relaxes into the latching recess in the lying panel. For that purpose the end of the latching tongue, for locking purposes, can bear against its contact surface associated therewith. 
         [0029]    In that respect it can be provided that the latching tongue engages directly on the insertion portion and in the relaxed condition includes an angle of greater than 90° with the insertion portion. In that case, in the same manner as described hereinbefore in relation to the V-shaped profile, the latching tongue with its attachment to the insertion portion, can first be moved past the lying panel and braced at an angle relative to the insertion portion, which is preferably somewhat greater than 90°, equal to 90° or somewhat less than 90°. 
         [0030]    The fact of the two limbs bearing against each other at the location at which the mutually facing inner side surfaces of the two limbs are fed onto each other can lead to deformation which causes difficulty in applying the two limbs against each other. It can therefore be provided that at that location the locking element has an application aid in the form of an enlargement in the intermediate space between the limbs. The enlargement can be in the form of a round bore. 
         [0031]    In addition or alone, for the application aid, the second limb can be of a configuration in respect of its cross-section such as to enlarge conically towards its end connected to the first limb. That means that it is possible to enlarge the intermediate space between the limbs, which facilitates application of the limbs for laying the panels in the usual fashion. Preferably the latching tongue should be pivotable towards the second limb to such an extent that it is perpendicular to the surface on which the panels are to be laid. 
         [0032]    Preferably the latching tongue in the relaxed position can be at an angle relative to the second limb which is greater than that in the latching position of the latching limb. In that way the latching tongue in its latching position can bear in a prestressed condition laterally against a side surface of the latching recess. That can provide that the first limb or the latching tongue can still be supported at the end against a contact surface provided in the latching recess, even upon slight movement away from each other of two panels connected by way of the locking element, insofar as, in that slight movement away from each other of the panels, the resilient latching tongue, by virtue of further relaxation, remains laterally against the side surface of the latching recess and thus at the end against the contact surface. 
         [0033]    To increase its potential spring force and to afford a greater degree of safeguard against kinking, the latching tongue or the first limb can be of a curved shape with a curvature which faces away from the second limb. 
         [0034]    To strengthen and increase the stability of the V-shaped profile, the portion of the V-shaped profile, which is formed by both limbs jointly, is large in comparison with the height of the limbs. in that respect that portion can be up to a half of the total height of the V-shaped profile. That is also a way of adjusting the potential spring force of the latching tongue. 
         [0035]    It will be appreciated that the above-described features of the locking element when combined together can also lead to advantageous configurations of the locking element. 
         [0036]    To attain the object of the invention, there can be provided a fixing system for quadrangular plate-shaped panels with holding profiles which are arranged at the edges of the panels and of which holding profiles arranged in mutually opposite relationship fit to each other in such a way that similar panels can be connected together, in particular for floor panels, with mutually oppositely disposed first holding profiles which are of such a configuration that it is possible to lock to a panel disposed in a first row in a second row a new panel by a procedure whereby the new panel is firstly attached to the lying panel in an inclined position relative to the lying panel and is then pivoted downwardly into the plane of the lying panel, and mutually oppositely disposed second holding profiles which have corresponding hooks, wherein a hook connection can be made with one of the hooks of the new panel and a hook of a panel which is already lying in the second row, by the downward pivotal movement of the new panel, and associated with each hook connection is an additional locking element which, prior to the hooking of two panels, can be inserted into a locking groove of one of the hooks of a first panel into an insertion position such that in the hooked condition of two panels it prevents release of the hook connection in a direction perpendicularly to the plane of the laid panels, wherein the locking element and the locking groove are provided at a surface of the hook which in the laid condition of the panels is oriented approximately perpendicularly to the plane of the panels, which plane is in the form of the laying plane, and wherein the locking element can be of one of the above-described configurations. In other respects in regard to the configuration of the fixing system and here in particular regarding the configuration and function of the hook connections attention is directed to the disclosure of WO 03/16654 which is also incorporated into the disclosure of the present invention. 
         [0037]    As already described hereinbefore the latching tongue can bear under a spring prestressing against an inner side surface of the latching recess. 
         [0038]    It is further provided that the inner side surfaces of the locking groove are arranged in mutually parallel relationship, for conformity with the above-described embodiments of the insertion portion, so that the insertion portion can engage into the locking groove without any problem. 
         [0039]    For anchoring thereof or in addition to the above-described anchoring options, the locking element can also be glued in the locking groove. 
         [0040]    Furthermore there are provided panels in particular floor panels, of a quadrangular, plate-shaped configuration, wherein a panel lying in a first row is lockable to a new panel for a second row, by a procedure whereby the new panel is firstly attached to the lying panel in an inclined position relative to the lying panel and subsequently pivoted downwardly into the plane of the lying panel, wherein the two panels can be connected together by a fixing system according to one of the above-described embodiments with a locking element according to one of the above-described embodiments. 
         [0041]    A further embodiment by way of example for a locking element stands out from the known locking element by virtue of its substantially simpler structure. The locking element is made from material which is in strip form or in the form of an elongate line, and is of a for example flat straight cross-section. In order to mount it to a panel, a part of the cross-section of the locking element is inserted into a holding gap provided for same in an edge of a panel while the other part of the cross-section projects freely from the edge of the panel. The projecting part acts as a resilient latching tongue. The latching tongue is bent over, in the assembled condition of two panels. The latching tongue then extends into a latching recess which must be provided on a coupled adjacent panel. That blocks the return movement, that is to say the panels are prevented from moving away from each other in a direction perpendicularly to the plane of the panels. 
         [0042]    In order to simplify insertion and automatic latching engagement, the locking element, instead of a straight flat cross-section, can alternatively involve a cross-section with a bend or kink. In that case the latching tongue already faces, in the neutral position, in that direction in which it is further bent during the joining movement, before it springs back by a short distance into the latching recess and comes into latching engagement. 
         [0043]    Each of the above-described locking elements can either be provided on a lying panel and can come into latching engagement in a latching recess in a panel which is moved vertically thereto, or can be provided on that panel which is moved vertically to a panel which is in a lying position, depending on which panel has the holding gap for anchoring the locking element. Panels can also be latched with two locking elements if both the edge of a panel in a lying position and also the edge of a panel which is moved vertically thereto have a holding gap, in which a respective locking element is anchored. 
         [0044]    A further embodiment of a locking element is in the form of a resilient locking clasp. For use, that locking clasp is fitted into a holding gap in a panel edge. The locking clasp can spring back into that holding gap when the locking clasp is pressed flat due to an external action thereon. A concept of that kind is known from WO 2005/054599. Preferably the locking clasp according to the invention however is in the form of an extruded plastic member. If the extrusion process produces an elongate straight profile, the profile, preferably when it has issued from the extruder and is still in a warm-deformable condition, is shaped with an additional device to form a curved clasp which cools and sets in that form. The extruded profile can be cut up into separate locking clasps prior to or after the operation for shaping the clasp. 
         [0045]    As mentioned in the opening part of this specification the invention relates predominantly to a panel which can be joined to similar panels by a substantially vertical movement of a new panel, more specifically perpendicularly to the plane thereof, with similar panels. 
         [0046]    Panels can be made up from wood or wood materials such as chipboard, MDF (medium density fiberboard), HDF (high density fiberboard) or other standard wood panel materials and at the top side and underside can have coatings which have decorative functions and which in addition, at least on the top side, form a resistant duty surface. The panels are produced by means of usual production installations. The production installations effect in particular profiling of the panel edges because the panel edges generally have complementary edge profiles so that similar panels can be joined together. Usual thicknesses for the panels are in the range of 3 mm to 20 mm. 
         [0047]    A panel of the general kind set forth of quadrangular shape, with a top side, underside, peripherally extending edges and with holding profiles at the edges is known from DE 299 24 454 U1. This involves a panel whose holding profiles of two edges adjacent to a corner form an upper hook which has an opening directed towards the top side and whose holding profiles of the other edges adjacent a corner are respectively in the form of a counterpart portion in relation to the oppositely disposed upper hook, as a corresponding lower hook which has an opening directed towards the underside, wherein, as mentioned above, a new panel can be connected to similar panels by a vertical movement, namely perpendicularly to its plane, and wherein an additional automatically latching locking element is provided or mounted on the panel for arresting the connection to prevent it from coming loose. 
         [0048]    The structure of a locking element as known from DE 299 24 454 U1 is inexpedient. It requires a great deal of structural space. In addition the structural shape of the sole embodiment of the additional locking element, which is disclosed in DE 299 24 454 U1, is considered to be disadvantageous. It is disadvantageous for example when the situation involves fitting the locking element to a panel edge by machine and automatically during operation of a panel production installation. 
         [0049]    As discussed in the opening part of this specification the invention aims to provide a panel which is simple to install, with an additional locking element which can be inexpensively produced by machine. 
         [0050]    In accordance with the invention that object is attained in that the edge of the panel is provided with a holding gap, also referred to as a locking groove, that the locking element has at least one anchoring tongue, also referred to as an insertion portion/insertion tongue, and that the anchoring tongue has a pressing surface which is pressed by a pressing-in tool and by way of which a force was applied for pressing the anchoring tongue of the locking element into the holding gap of the panel. 
         [0051]    Another important development of the solution to the technical problem involved provides that at least one edge of the panel has at least one locking element strip which is brought into connection with the edge of the panel by way of a zip fastener movement. 
         [0052]    It appears to be an important innovation for a panel to be developed in such a way that automatic fitment of a locking element, as synchronously as possible, becomes a possibility. Synchronous means that the feed and attachment of the locking element takes place synchronously with the conveyor movement of the panels in a production installation. 
         [0053]    That is achieved because the components involved can be processed, on the basis of the zip fastener principle. In accordance with the invention that means that a locking element strip is moved to the edge of a panel in such a way as occurs in principle with a zip fastener edge which is moved towards a second zip fastener edge and deflected and connected by a slider of the zip fastener. The locking element is of such a configuration that it can be moved in a similar manner towards the edge of a panel and deflected with suitable means. In that case however anchorage of the locking element to the edge of the panel is effected easily without being based on the principle of zip fastener hooks which are meshingly dovetailed together. 
         [0054]    As the panel is intended preferably to be connected to father panels by a pure vertical movement, resilient locking elements are arranged at least at two edges. It is desirable if required to provide different resilient locking elements depending on the respective loading at the edges. 
         [0055]    It is also desirable if at least one locking element is in the form of a clip with clip portions arranged in a V-shape or U-shape, wherein the anchoring tongue is arranged transversely at one of the clip portions. 
         [0056]    At least one other locking element is in the form of an extruded curved locking clasp, the locking clasp is accommodated resiliently movably in the holding gap, wherein provided over the length of the locking clasp is at least one region which forms the anchoring tongue. 
         [0057]    The invention concerns a method of installing a floor comprising panels having locking elements. Methods are separately set forth, which relate exclusively to locking a first row of panels because, for laying a first row of panels, depending on the respective installation situation involved, it is possible to apply different laying steps which are not possible in a following row. 
         [0058]    The basic starting point adopted is that of locking quadrangular panels which have a top side, an underside and peripherally extending edges with holding profiles arranged thereat, with the proviso that at least two oppositely disposed holding profiles of each panel are in the form of complementary hook profiles so that hook profiles of adjacent panels can be fitted one into the other in a vertical direction, wherein at least one of the hook profiles is provided with an additional locking element with a resilient latching tongue which can be latchingly engaged into a latching recess in an adjacent panel. 
         [0059]    In that situation the first row of panels can be locked without involving a vertical movement for coupling purposes and without latching engagement, more specifically as an alternative by inserting the complementary hook profiles into each other in mutually aligned relationship. 
         [0060]    It is possible to dispense with a vertical movement for coupling purposes and for latching engagement purposes, only for locking the first row of panels. The hook profile with locking element is laid in aligned relationship behind the complementary hook profile of an adjacent panel and the hook profiles are then pushed one into each other. For the beginning of the pushing movement, the locking element can be somewhat deformed resiliently so that it fits into the latching recess in the adjacent panel. 
         [0061]    Alternatively the first row of panels is locked by a procedure whereby the hook profiles to be coupled are firstly laid loosely one upon the other and then the edges of the panels are pushed towards each other until the latching tongue of the resilient locking element is pushed resiliently inwardly by contact with the adjacent panel and the panel with the locking element is thereafter moved vertically, namely perpendicularly to the plane of the panel, into the hook profile of the adjacent panel until the resiliently inwardly moved latching tongue of the locking element automatically moves resiliently out into the latching recess of the adjacent panel and arrests the hook connection in a vertical direction. 
         [0062]    The hook profiles to be locked are desirably in the form of an upper hook and a lower hook, with the upper hook being laid loosely on the lower hook. The locking element can be arranged either on the upper hook or the lower hook. As soon as the edges of the panel are pushed towards each other by a substantially horizontal movement and the latching tongue of the locking element is moved resiliently inwardly, the upper hook is hooked into the lower hook by a substantially vertical movement. In that situation the inwardly moved latching tongue of the locking element automatically moves resiliently outwardly in the latching recess of the adjacent panel and arrests the hook connection. 
         [0063]    The way in which panels in following rows are laid depends on what kind of holding profiles is provided on those edges with which the panels of different rows of panels are connected together. A first general kind of holding profiles for connecting rows of panels is designed for a joining movement in a vertical direction, namely perpendicularly to the plane of the panel. That situation preferably involves using a hook profile provided with one of the resilient locking elements according to the invention. In a poorer design configuration, it is also possible to use one of the known locking elements. At any event a new navel is attached from above to panels which have already been installed. The new panel can be moved downwardly either in a parallel position in relation to the panels which have already been installed or it is first moved downwardly somewhat more deeply at one corner until the hook profiles partially engage into each other and it is then progressively brought into hooking engagement on the basis of the zip fastener process. Panels which are flexible and can be bent and twisted favor the zip fastener process. In that way panels which for hooking engagement require a substantially vertical motion component can be particularly easily connected. 
         [0064]    Another general kind of holding profiles is of such a nature that a positively locking connection is made by inclinedly attaching a new panel to panels, which are in a lying condition, in a front row, and then pivoting the new panel downwardly into the plane of the panels which are in the lying position. Modified tongue-and-groove profiles are provided for that purpose at the edges for connection to a front row. 
         [0065]    The invention concerns a method of automatically mounting a locking element to an edge of a panel. The panels are for example wall, floor or ceiling panels which are intended for fitting in rooms. 
         [0066]    Panels which are suitable for locking with a locking element comprise for example wood or wood materials such as chipboard, MDF (medium density fiberboard), HDF (high density fiberboard) or other standard wood panel materials. The panels are produced by means of conventional production installations. The production installations implement in particular profiling of the panel edges because the panel edges generally have complementary edge profiles so that similar panels can be joined together. 
         [0067]    An example for an automatic locking element is known from WO 00/016654 (EP 1 415 056 B1), the disclosure of which in respect of the configuration of the loose locking element is incorporated herein by the foregoing reference. 
         [0068]    The known locking element serves for arresting two panels. It is of a V-shaped cross-section, wherein provided at one end of the V-shaped cross-section is a laterally projecting insertion tongue which can be fitted into a groove in an edge of a panel in order to join the locking element to the panel. 
         [0069]    The object of the present invention is to propose a method and an apparatus for mounting the known locking element automatically to an edge of the panel, in which respect industrial mounting is to be a possibility. 
         [0070]    According to the invention that object is attained in that the locking element in the form of an endless cable-like locking element line is taken from a storage means and passed into a guide passage and fed to a separating station which separates the locking element line into individual locking elements, and wherein each individual locking element is moved in synchronous movement in relation to a panel continuously transported by the panel production installation to an edge of said panel and pressed by a pressing device into a receiving region of the edge of the panel. 
         [0071]    The new method can be integrated without any problem into conventional production installations for wall, floor and ceiling panels because it requires a small amount of space for it to be carried into effect. Because those production installations usually transport panels at high speed in a continuous movement, each locking element is respectively moved to the panel edge at the same speed as that at which the production installation is operated at that time. 
         [0072]    Desirably, the locking element is formed from plastic material and for example extruded. In that case it is processed in the form of an endless line of locking elements. 
         [0073]    As the locking element is so small that it fits within a connecting location of wail, floor and ceiling panels, it is of a relatively small cross-section. It is desirable if the heightwise dimension of the locking element is no greater than half the thickness of the panel. Embodiments with a larger locking element have a detrimental effect because the strength of the edge of the panel is worsened because of portions which are milled away to receive the locking element, and the panel edges become susceptible to breakage. 
         [0074]    Because of the small cross-section of the locking element, special precautions must be taken for applying a transport movement to the locking element line. A tensile loading on the locking element line is possible without any problem. Applying pressing forces for the purposes of transmitting movement by a pushing action however is difficult because the locking element line is susceptible to kinking or buckling. 
         [0075]    In order to prevent a buckling effect, there is provided a guide passage for the locking element line, which prevents lateral outward buckling of the locking element line. The guide passage is of a cross-sectional shape which also prevents unwanted rotation of the locking element line. 
         [0076]    In order to obtain individual locking elements, the locking element line is guided to a separating station which separates the locking element line into individual locking elements. 
         [0077]    The individual locking elements are advantageously moved to the edge in question of the panel at an acute angle of about 10.degree. and are pressed into the receiving region of the edge of the panel by the above-mentioned pressing device. The receiving region of the panel edge has the receiving groove into which the insertion tongue of the locking element is pressed and preferably anchored in frictionally locking relationship. 
         [0078]    A variant of the method provides a pushing advance device which pushes the locking elements or the locking element line through the guide passage in the direction of the pressing device. 
         [0079]    In accordance with a development of the method the locking element line is separated into individual locking elements by a separating station which is arranged upstream of the advance device in the direction of through movement of the locking element line. The separated locking elements are then pushed in a row by the advance device successively through the guide passage to the pressing device. The advantage of this method is that transmission of a transport movement from the advance device to the row of locking elements occurs continuously. 
         [0080]    A preferred method transposes the working steps in such a way that the locking element line is separated into individual locking elements by a separating station which in the through-travel direction is arranged downstream of the advance device. That involves a change in the transmission of movement. The locking element line is transported in a pushing mode by the advance device into the guide passage. As soon as the locking element is cut off however, it is transported out of the guide passage by a pulling force applied by the pressing device. The locking element is therefore cut off near the location at which the locking element is fed to the edge of the panel. The separating operation takes place at a time when the locking element is already in contact with the pressing device. For that reason the separating operation takes place so close to the panel edge that the front end of the locking element is already forced in between the pressing device and the panel edge because then the transport movement for the locking element can be transmitted from the pressing device into the locking element. That case involves a pulling force which is applied to the locking element by the pressing device. 
         [0081]    Desirably, the transport movement of the locking element line is braked at the separating location, the braking action being produced by the engagement of the separating station, for example with a cutting blade, into the locking element line, because the cutting blade closes the guide passage. That ensures that the separating operation is not impeded by any transport movement and the cutting edge can precisely cut during the stoppage phase of the locking element line. 
         [0082]    Furthermore, it is desirable in terms of a high production speed if the advance device conveys further locking element line during the braking of the transport movement without stopping. With the high production speed intended, constantly decelerating and accelerating the advance device in order thereby to implement a cyclic stopping action for the separating operation would be problematical. 
         [0083]    The length of the locking element line which is conveyed during the separating operation must be put into intermediate storage. A buffer region is provided for that purpose. The arrangement dispenses with a rigid narrow guide passage in the buffer region. Instead, there is provided space in which the supplied length of the locking element line can move out of its regular travel path by a buckling movement. 
         [0084]    In a simpler fashion a storage spring provided in the buffer region is actuated by the outward buckling movement of the locking element line. In that way a stress is imparted to the storage spring and spring energy is stored. That stored spring energy is automatically liberated after termination of the separating operation of the separating station, in which case the length of the locking element line which has been stored by virtue of the outward buckling thereof is advanced with a jerk. 
         [0085]    Desirably the storage spring operates automatically in the buffer region so that there is no need for a particular control for buffer storage of the locking element line. 
         [0086]    Another desirable development of the method provides that a given length of the locking element line is retained in a stock supply region between the storage means and the advance device. 
         [0087]    The removal device, acting on the same principle as the advance device, can transmit a transport movement to the locking element line, in which case the locking element line is retained in the storage means in such a way that it is to be removed in as twist-free condition as possible. If removal is to be implemented from time to time at a reduced removal speed in order to keep the locking element line twist-free, the downward loop-forming part of the locking element line forms a supply zone in which a sufficient length of the locking element line is retained in order to process same at the required advance speed and to feed it to the separating station and the pressing device. 
         [0088]    An apparatus is provided for carrying out the method. The apparatus serves for automatic mounting of a locking element to an edge of a panel, in particular a floor panel, wherein the locking element is in the form of an endless bucklable line which can be fed from a storage means, wherein there are provided a guide passage, an advance device, a separating station and a pressing device, and wherein the locking element line can be separated into individual locking elements by means of the separating station and pressed into a receiving region of the edge of the panel by means of the pressing device in synchronous movement with a panel continuously transported by the panel production installation. 
         [0089]    In order to guarantee reliable guidance of the locking element line the guide passage is of a free cross-section which is almost coincident with the cross-section of the locking element line. Therefore the guide passage has a V-shaped cross-sectional region and a laterally projecting cross-sectional region, wherein the laterally projecting cross-sectional region adjoins an end of the V-shaped cross-sectional region. 
         [0090]    Desirably the advance device has at least one advance roller with which a rotary movement can be transmitted to the locking element line by way of a frictional contact. In order to guarantee good transmission of movement, the advance roller is provided with a contour which forms a negative of that side of the locking element line, with which the advance roller is in frictional contact. The advance device is particularly reliable if there are provided two mutually opposite advance rollers which are driven in opposite directions and between which the locking element line is engaged. 
         [0091]    The pressing device can have at least one pressing roller, by means of which a pressing force can be produced in perpendicularly relationship to the edge of a panel, and wherein with the pressing roller, if necessary, the rotary movement thereof can be converted by frictional contact into a transport movement of the locking element. 
         [0092]    Preferably servomotors can be used for all driven rollers of the entire apparatus, servomotors being advantageous because of their positionally accurate controllability. 
         [0093]    Desirably the separating station for the locking element line is arranged downstream of the advance device in the through-travel direction. That design configuration guarantees problem-free feed of the locking element line through the guide device and provides that the separating operation is effected only just before the position at which the locking element is fitted to the edge of the panel. In this embodiment the separating operation is effected only when the front portion of the locking element is already in frictional contact with the pressing device. That is because the transport movement for the locking element, after being cut away from the locking element, can only still be transmitted by the pressing device pulling the locking element. In this embodiment of the apparatus therefore there must be a change in the transport mode, namely from pushing transport by the advance device into pulling transport by the pressing device. 
         [0094]    Desirably there is provided a buffer region for the locking element line, which is further conveyed thereto, while the separating station is in an engagement condition. 
         [0095]    In a simpler fashion the buffer region has an elastically deformable storage element and spring energy can be stored in the elastically deformable storage element by virtue of outward buckling of the locking element line, in which case the spring energy can be delivered or liberated by the elastically deformable storage element. The spring energy is liberated as soon as the separating operation at the separating station is concluded and the conveyor cross-section of the guide passage which the separating station closed off during the separating operation is opened again. The spring energy then causes a jerk advance movement of that part of the locking element line which was fed to the buffer region during the separating operation and which brought about mechanical stressing of the storage element with spring energy. 
         [0096]    A simple construction of a buffer region with a storage element has a conveyor passage which is elastically deformable and in particular variable in length. By virtue of its elastic deformability such a conveyor passage stores on the one hand spring energy and on the other hand stores a length of the locking element line, insofar as the conveyor passage is elastically increased in length by virtue of the outward buckling effect of the locking element line. 
         [0097]    Desirably the conveyor passage is formed from a helical cylindrical spring. The helical cylindrical spring can be connected between the advance device and the pressing device. 
         [0098]    Desirably the conveyor passage is arranged in a neutral position in an arc, whereby the locking element line is deflected. The deflection effect promotes the buckling action and also allows the entire apparatus to be of a construction which saves on space. In that way the apparatus can be integrated in a very small space into conventional production installations for wall, floor and ceiling panels. 
         [0099]    A further helpful measure is found in the fact that there is provided at least one means for synchronization of the transport movement of the locking elements with the transport movement of the panels in the production installation. 
         [0100]    The means for synchronization of the transport movement can have a movement pickup. The movement pickup detects the transport movement of the panels in the production installation, wherein the information for synchronization can be transmitted from the movement pickup to a control means with which the transport movement of the locking elements is controllable. 
         [0101]    If a panel is to be provided at one or more further edges with a locking element or a plurality of locking elements, by way of example an additional apparatus as described hereinbefore can be integrated into the production installation for each further edge. The panels are transported in the usual manner for processing in a longitudinal direction and the transport direction is altered for processing in a transverse direction, for example being deflected through 90°. The speeds can vary. They depend substantially on the ratio of the edge lengths. If the panel is a square panel the edges in the longitudinal and transverse directions are of the same length. The transport speeds are preferably the same. If in contrast a panel has oppositely disposed long and short edges, then the transport speed is appropriately adapted to the ratio of the different edge lengths. The transport speed in a direction parallel to the long edges is usually higher than in a direction parallel to the short edges of a panel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0102]    The present invention is described in greater detail hereinafter by means of a number of embodiments illustrated in a drawing. In the drawing: 
           [0103]      FIG. 1  shows a part of a sectional view of two panels which are laid together, with a fixing system with a locking element; 
           [0104]      FIG. 2  shows a cross-sectional view of a locking operation for the two panels in first step; 
           [0105]      FIG. 3  shows a cross-sectional view of the two panels in the locking operation in a second step; 
           [0106]      FIG. 4  shows a cross-sectional view of the locking element  5  in the relaxed position; 
           [0107]      FIGS. 5   a  and  b  show a perspective plan view of the locking element of  FIG. 1 , but prior to insertion thereof into the fixing system; 
           [0108]      FIG. 6  shows a perspective plan view of the locking element in a second embodiment; 
           [0109]      FIGS. 7   a  and  b  show a perspective plan view of the locking element in a third embodiment.; 
           [0110]      FIGS. 8   a - i  show cross-sectional views of the locking element in a further embodiment; 
           [0111]      FIGS. 9   a - c  show cross-sectional views of the locking element in fundamentally different embodiments; 
           [0112]      FIGS. 10   a - d  show cross-sectional views of the locking element in further fundamentally different embodiments; 
           [0113]      FIG. 11  shows a diagrammatic view from three sides of a panel with hook profiles at all edges; 
           [0114]      FIGS. 12-14  show cross-sections through panels with a lower hook and an upper hook provided with a locking element, wherein the upper hook is shown in different joining positions in relation to the panel with the lower hook; 
           [0115]      FIG. 15  shows a cross-section through an alternative panel with locking element in the upper hook-arrested condition; 
           [0116]      FIGS. 16-18  show cross-sections through panels with an upper hook and a lower hook provided with a locking element, wherein the lower hook is shown in different joining positions in relation to the panel with the upper hook; 
           [0117]      FIG. 19  shows a cross-section through an alternative panel with locking element in the lower hook-arrested condition; 
           [0118]      FIG. 20  shows a cross-section through panels with two locking elements prior to the locking action; 
           [0119]      FIG. 21  shows a cross-section through panels as shown in  FIG. 20 , after the locking action; 
           [0120]      FIGS. 22-25  show cross-sections through panels with a simplified locking element at a lower hook, wherein an upper hook is shown in different joining positions relative to the panel with the lower hook; 
           [0121]      FIGS. 26-29  show cross-sections through panels with a simplified locking element on an upper hook, wherein the upper hook is shown in different joining positions relative to the panel with the lower hook; 
           [0122]      FIG. 30  shows a cross-section through panels with two locking elements, prior to the locking action; 
           [0123]      FIG. 31  shows a cross-section through panels as shown in  FIG. 30 , after the locking action; 
           [0124]      FIGS. 32-35  show cross-sections through panels with a locking element on a lower hook, wherein a panel with an upper hook is shown in different joining positions relative to the panel with the lower hook; 
           [0125]      FIG. 36  shows a plan view of a panel edge as indicated at XXXVI in  FIG. 32 ; 
           [0126]      FIG. 37  shows a plan view of a panel edge as indicated at XXXVII in  FIG. 34 ; 
           [0127]      FIGS. 38-41  show cross-sections through panels with a locking element at an upper hook, wherein the panel with the upper hook is shown in different joining positions relative to a panel with a lower hook; 
           [0128]      FIG. 42  shows a cross-section through panels with a lower hook and with an upper hook provided with a locking element; 
           [0129]      FIG. 43  shows a locking element; 
           [0130]      FIG. 44  shows a perspective view with hook profiles of a first row of panels which are pushed into each other in aligned relationship; 
           [0131]      FIG. 45  is a perspective view in relation to the method of installing panels with hook profiles which are hooked vertically with a locking element; 
           [0132]      FIG. 46  shows a panel for carrying out the method shown in  FIG. 45 ; 
           [0133]      FIG. 53  is a diagrammatic view of an apparatus for automatically mounting a locking element to an edge of a panel; 
           [0134]      FIG. 54  is a view onto a transfer passage in accordance with in  FIG. 1 ; 
           [0135]      FIG. 55  is a view onto two advance rollers in accordance with in  FIG. 1 ; 
           [0136]      FIG. 56  is a plan view of the advance rollers of  FIG. 3 ; 
           [0137]      FIG. 57  is a view of a guide passage in accordance with V-V in  FIG. 1 ; 
           [0138]      FIG. 58  is a view of a separating station in accordance with VI-VI in  FIG. 1 ; 
           [0139]      FIG. 59  is a view of the apparatus shown in  FIG. 1  with a reel storage means for a locking element line; 
           [0140]      FIG. 60  is a side view of the apparatus of  FIG. 7 ; and 
           [0141]      FIG. 61  is a diagrammatic view of an alternative embodiment of an apparatus for automatically mounting a locking element to an edge of a panel. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0142]      FIG. 1  shows a part of a cross-sectional view of two panels  1 ,  2  of a quadrangular, plate-shaped configuration, wherein the illustrated part reproduces a fixing system  3  having a locking element  5 , by way of which the two panels  1 ,  2  are connected together and locked together at their edges or narrow sides by means of a hook connection  4  and a locking element  5  according to the invention. The hook connection  4  has two hooks  4 . 1 ,  4 . 2  which in the locking position are hooked into each other in such a way that the panels  1 ,  2  cannot be displaced horizontally relative to each other in the position which here is horizontal. 
         [0143]    The locking element  5  is inserted with a portion in the form of an insertion portion  6  in a locking groove  7  which extends in the longitudinal direction of the edges of the panel  2 , which edges extend in the plane of the drawing. The locking element  5  also has a portion in the form of a locking portion  8  with a resilient latching tongue  9  which is latched into a latching recess  10  and which with its end  11  bears against a contact surface  12  in the latching recess  10 . As will be described in greater detail hereinafter, the latching tongue  9  is elastically pivotable about its attachment  13  to the rest of the locking portion  8  about an axis parallel to its longitudinal extent and in the position shown here bears under a spring bias against the contact surface  12 . So that the latching tongue  9  finds its appropriate contact point against the contact surface  12  with its pivotal movement into the latching recess  10 , the contact surface  12  is inclined out of the horizontal. That makes it possible for the latching tongue  9  to reliably bear against the contact surface  12 , in spite of slight changes in the dimensions within given tolerance ranges. Even in the event of the two panels  1 ,  2  moving slightly away from each other within a given tolerance range, the latching tongue  9  can still remain against the contact surface  12 , by virtue of the prestressing of the latching tongue  9 , insofar as the latching tongue  9  is further pivoted by virtue of its end  11  sliding down against the inclined plane formed by the contact surface  12 . That arrangement prevents the two panels from being able to come loose from each other, perpendicularly to the surface V on which they are laid. The inclination of the contact surface  12  is substantially determined by the pivot radius of the latching tongue  9  about its attachment  13  and the force against which the latching tongue  9  bears against the contact surface  12 . The depth of the latching recess  10 , which is shown here, is only to be viewed as being by way of example and, in order to satisfy larger tolerance fluctuations in the dimensions of the panels  1 ,  2 , it can also be made deeper into the narrow side or edge of the panel  1 . The contact surface  12  which in the embodiment illustrated here opens straight into the edge of the panel  1  can additionally have a projection which is provided at the mouth opening and which does not project laterally beyond the narrow side of the panel  1  and which can serve as an abutment for the latching tongue  9  to ensure that the latching tongue  9  cannot slip out of the latching recess  10  under particularly high forces in opposite relationship to the force P for locking the panels and in perpendicular relationship to the laying surface. 
         [0144]      FIGS. 2 and 3  each show a cross-sectional view illustrating the assembly of the two panels  1 ,  2  in two steps, wherein here the hook  4 . 1  is of a somewhat different design configuration from  FIG. 1 , which however is not of crucial significance in terms of the mode of operation of the locking element  5  according to the invention. Assembly of the two panels  1 ,  2  is also described in greater detail in WO 03/016654 to which reference is explicitly directed here and the disclosure of which in regard to the assembly of the two panels  1 ,  2  is expressly also incorporated here. 
         [0145]    In order to lock a panel  1  which is lying in a first row to a new panel  2  for a second row, then, as described in greater detail and illustrated in WO 03/016654, firstly the new panel  2  is attached to the lying panel  1  in an inclined position relative to the lying panel  1  and subsequently pivoted downwardly into the plane of the lying panel  1  in the direction of the force P. In that situation the locking element has already been inserted with its insertion portion  6  into the locking groove  7 , prior to the locking procedure  5 . When the new panel  2  is pivoted downwardly into the plane of the lying panel  1 , the edges with the fixing system  3  slide past each other over their length and brace the locking element  5 . 
         [0146]    In the structure shown in  FIGS. 1 to 3 , the locking portion  8  is of an approximately V-shaped cross-section with a first limb  14  and a second limb  15 , wherein the latching tongue  9  is formed by the first limb  14  and the second limb  15  is laterally connected to the insertion portion  6 . When the new panel  2  is pivoted downwardly and the two edges of the panels  1 ,  2  slide down against each other, the latching tongue  9  is pressed out of the relaxed condition shown in  FIG. 4 , a cross-sectional view of the latching element  5  in the relaxed condition, against the second limb  15  and in that case is prestressed like a leaf spring with a specific spring energy. When the locking position of the two panels  1 ,  2  is reached, which is shown in  FIGS. 1 and 3 , the hooks  4 . 1  and  4 . 2  engage into each other to afford the hook connection  4 . At the same time the latching tongue  9  is partially relaxed into the latching recess  10 : in a latching position the latching tongue  9  comes to bear with its end  11  against the contact surface  12  and bears against it in a prestressed condition. 
         [0147]    In that situation the surface regions of the panels  1 ,  2 , which surface regions are away from the laying surface V, are of a convergent configuration at the edges in such a way that they completely close the gap  16  between the two panels  1 ,  2  upwardly. For that purpose the hook  4 . 1  engages over the locking portion  8  in the position shown in  FIG. 2  in which the two limbs  14 ,  15  bear against each other, almost completely from above, so that the two edges can slide as tightly against each other as possible for locking the two panels  1 ,  2 , upon pivotal movement of the new panel  2 . 
         [0148]    In the locking operation the hooks  4 . 1 ,  4 . 2  slide against each other at inclined surfaces  17  and thereby draw the edges of the two panels  1 ,  2  towards each other, as is also described in greater detail in WO 03/016654, to which reference is made. In that way the two panels  1 ,  2  which are connected together by way of the fixing system  3  cannot be unlocked in the plane of the drawing without destroying parts of the panels  1 ,  2  or the fixing system  3 . 
         [0149]    The locking element  5  additionally has anchoring means  18  by which it can be captively anchored with its insertion portion  6  in the locking groove  7 . The anchoring means  18  thus hold the locking element  5  in the locking groove  7  so that the locking element  5  cannot be unintentionally and undesirably displaced in the locking groove  7  prior to and during the locking operation. 
         [0150]    In terms of the production procedure the anchoring means  18  should satisfy the condition that the locking element  5  can be anchored in the locking groove  7  without any problem. For that purpose, as is not further shown here, the locking element  5  can be glued with its insertion portion  6  into the locking groove  7 . Hereinafter however further different solutions in regard to the configuration of the anchoring means  18  will be described in greater detail with reference to  FIGS. 5 to 10 . 
         [0151]      FIGS. 5 to 7  each show a perspective view of the locking element  5  in different embodiments. In this case the locking element  5  which is shown loose is still in the latching position shown in  FIGS. 1 to 3 , in which the locking element is not yet completely relaxed, as is shown in  FIG. 4 . For the sake of enhanced clarity the locking element  5  is shown as being transparent in  FIGS. 5 to 7 . That corresponds at the same time to a possible embodiment in which the locking element  5  is extruded from a transparent plastic material. The locking element  5  shown in  FIG. 5   a  corresponds to the locking element  5  shown in  FIG. 1 . 
         [0152]    To provide an oversize, three projections  19  are provided at a larger side surface of the insertion portion  6 , being the side surface which in the insertion position of the locking element  5  faces towards the inner side surfaces of the locking groove  7 , in other words, in the embodiments of the locking element  5  which are shown in  FIGS. 5   a+b , the three projections  19  are provided at the top side of the insertion portion  6 . The projections  19  extend over the entire lengthwise extent of the locking element  5 . The longitudinal side surfaces  20  of the projections  19  are arranged inclinedly relative to each other. As a result the projections  19  which are arranged towards the free end of the insertion portion  6  converge in a wedge configuration to provide a tip  21 . In that respect it is provided in accordance with the invention that the height h of the insertion portion  6  is somewhat greater than the width by of the locking groove  7  ( FIG. 1 ) so that the tips  21  are elastically or plastically-elastically deformed upon insertion of the locking element  5  into the locking groove  7  and by way thereof clamp the locking element  5  fixedly in the locking groove  7  and dig fixedly into the inner side surfaces of the locking groove  7 . 
         [0153]      FIG. 5   b  shows a modification of the configuration of the locking element  5  shown in  FIG. 5   a , which is distinguished in that over its longitudinal extent the locking element  5  is of a curved shape, the radius of curvature r of which extends approximately in the direction of the section line formed by the cross-sectional plane and the longitudinal sectional plane, that is to say in the embodiment illustrated here, the locking element  5  is curved downwardly. 
         [0154]    When now the curved locking element  5  is inserted into the locking groove  7  which is of a linear configuration, the locking element  5  is straightened in opposite relationship to its bend and bears in an elastically prestressed condition against the inner side surfaces of the locking groove  7 , thereby providing for additional anchorage of the locking element  5  in the locking groove  7 . 
         [0155]    In a configuration which is not shown here, the insertion portion  6  can also be designed without an oversize in respect of its height h relative to the width by of the locking groove  7  so that the locking element  5  is anchored in the locking groove  7  solely by virtue of its elastic prestressing as a consequence of its previous curvature (as described above). 
         [0156]    In both the embodiments illustrated in  FIGS. 5   a  and  5   b , there is provided an introduction aid  22  for easier introduction of the locking element  5  into the locking groove  7 , which is here formed by the longitudinal side surface  20  of the projection  19 , which is closest to the free end of the locking portion  8 . In this case the longitudinal side surface  20  serves as an inclined plane, over which the insertion portion  6  can be easily pushed into the locking groove  7 , in spite of its oversize. An introduction aid can be provided in the same manner on the other embodiments still to be described. 
         [0157]    Referring to  FIG. 6  an insertion portion  6  is of a curved configuration towards its free end so that a hook  23  is formed at the free end, the hook elastically bracing the insertion portion  6  upon the insertion thereof into the locking groove  7 , thereby achieving an anchoring effect for the locking element  5  in the locking groove  7 . It will be appreciated that in this case also the locking element  5  can be curved as described above. 
         [0158]    The embodiment of the locking element  5  shown in  FIGS. 7   a  and  b  has a slot  24  which extends from the end of the insertion portion and in the direction of the locking portion  8 , the sides  25  delimiting the slot  24  being curved away from the slot  24 . The end of the insertion portion  6  is beveled towards the slot  24  to form the introduction aid  22  and thus, as in the embodiments of  FIGS. 5 and 6 , forms inclined planes for easier introduction of the insertion portion  6  into the locking groove  7 . Upon introduction of the insertion portion  6  into the locking groove  7  the two slot sides  25  are moved towards each other whereby the insertion portion  6  is elastically braced in the locking groove. 
         [0159]    Further possible embodiments of the locking element  5  are shown in following  FIGS. 8 to 10 , showing however only a cross-sectional view of the respective locking element  5 . In this case, in  FIGS. 8 and 10 , the latching tongue  9  is shown in a completely relaxed position (broken lines) and in the latching position (solid lines) in a partially stressed condition. 
         [0160]    In  FIGS. 8   a  to  e  the locking portion  8  of the respective locking element  5  is still in the V-shaped form already described above. The individual embodiments differ however in various details which are now to be described. 
         [0161]    In  FIG. 8   a  the insertion portion  6  has three projections  19  each with a respective asymmetrical tip  21 , in which the longitudinal side surface  20  of the projection  19 , which is remote from the free end of the insertion portion  6 , extends perpendicularly to the lengthwise extent of the locking portion  8 , that is to say perpendicularly in the Figure here. As a consequence of that arrangement, the respective other longitudinal side surfaces  2 G of the projections  19  form an inclined plane which is operative upon introduction of the insertion portion  6  so that the insertion portion  6  can be easily pushed into the locking groove  7 . In an opposite movement in relation thereto however, that is to say in the event of a movement of the insertion portion  6  out of the locking groove  7 , the tips  21  of the projections  19  dig into the inner side surfaces of the locking groove  7  by virtue of the oversize of the insertion portion  6  and the direction of the tips  21 , and thereby hold the locking element  5  fast in the locking groove  7 . In  FIG. 8   b  the hooks are disposed at the underside of the insertion portion  6 , whereby they are better protected prior to insertion into the locking groove  7 , than those in  FIG. 8   a . In  FIG. 8   c  the projections  19  are disposed on both sides of the insertion portion  6 , in which case for example the projections  19  here have symmetrical tips  21 . 
         [0162]    The embodiments of the insertion portion  6 , which are shown in  FIGS. 8   f  to  i , are of a curved shape, whereby the insertion portion  6  is elastically braced in the locking groove  7  when it is inserted thereinto. In addition, the embodiment of  FIGS. 8   h  and  8   i  has projections  19  which impart an oversize to the insertion portion  6  and by way thereof, upon insertion of the insertion portion  6  into the locking groove  7 , provide that the insertion portion  6  digs fast into the inner side surfaces of the locking groove  7 . In this arrangement the projection shown in  FIG. 8   i  is of a design such as to face in a direction away from the free end of the insertion portion  6 , whereby the projection  19  acts like a barb which, when the insertion portion  6  is being pulled out of the locking groove  7 , hooks into the inner side surface of the locking groove  7 . 
         [0163]    Crucial aspects in regard to the effectiveness of the locking element  5  are inter alia the spring energy which can be stored when the first limb  14  or the latching tongue  9  bears against the second limb  15  and the possible spring travel which is available due to complete relaxation of the locking element  5 . Both parameters can be generally adjusted by way of the configuration of the profile of the locking portion  8  and the locking element  5  respectively, so that, depending on its purpose of use, the locking element  5  can be designed with a suitable potential spring energy. More specifically, for example in  FIGS. 8   a  and  b , the two limbs  14 ,  15  converge at different heights h 1  of the locking portion  8  so that the latching tongue  9  in  FIG. 8   a  can be more easily caused to bear against the second limb, than the latching tongue  9  in  FIG. 8   b.    
         [0164]    In  FIGS. 8   d  and  e , a respective additional enlargement  26  is provided in the form of a round bore  27  which, in comparison with an acute-angled V-shaped profile, in the pivotal movement of the two limbs  14 ,  15  towards each other, prevents an accumulation of material at that location, so that here the latching tongues can be more easily caused to bear against the second limb  15 , in comparison with the acute-angle V-shaped profile. A similar but attenuated effect is achieved by the profiles shown in the other embodiments of  FIG. 8 , by means of a rounded configuration  28 . 
         [0165]    In  FIGS. 9   a  to  c , the embodiments of the locking element  5  have an additional latching tongue  9  which is also intended to bear against a contact surface provided for same in the latching recess, in the latching position of the locking element  5 . 
         [0166]      FIGS. 10   a  to  d  show four further fundamentally different embodiments of the locking element  5  which differ from the other embodiments of the locking element  5  which have been described by way of example, in particular in regard to the configuration of their locking portion  8 . In this case the latching tongue  9  is connected directly to the insertion portion  6 . For locking the two panels  1 ,  2  together, the latching tongue is pressed against the edge of the panel  2  carrying it and thus prestressed and, as in the other embodiments of the locking element  5 , when the latching recess  10  is reached, it can relax into the intended latching position into the latching recess  10 , in which respect it is also provided here that in the latching position the latching tongue  9  bears in a prestressed condition against the contact surface  12  associated therewith. 
         [0167]    All embodiments of the locking element  5  which are described herein are integrally produced from plastic material by extrusion. 
         [0168]      FIG. 11  shows a diagrammatic view of a panel  30  of rectangular shape. The panel  30  has hook profiles  31  and  32  at all four edges. The panel  30  can be connected to similar panels by means of the hook profiles  31  and  32 . Two of the hook profiles which come together in an L-shape at a first corner have a lower hook  31  while the other two hook profiles which are also arranged in an L-shape relative to each other each have a respective upper hook  32 . That hook profile which, when a panel  30  is lying flat on a surface, has an upwardly directed hook end  31   a  and a hook opening  31   b  is identified as the lower hook  31 . The upper hook  32  forms a co-operating portion for the lower hook  31  and has a hook opening  32   b  which, when the panel  30  is in the lying condition, is directed downwardly, more specifically faces towards a laying surface. At least one of the hook profiles is provided with an additional locking element which has been omitted in the diagrammatic view in  FIG. 11  for the sake of simplicity. 
         [0169]    In order to fit two edges together in a vertical direction or with a motion component in perpendicular relationship to the plane of the panels and to secure them against movement in the reverse direction by means of an additional locking element  33 , a number of embodiments of panels with locking elements  33  are set forth with reference to  FIGS. 12 to 42 . In this respect different locking elements  33  are provided, as well as special hook profiles which co-operate with the locking elements  33 . In addition embodiments of locking elements as shown in  FIGS. 1 to 10   d  can be used. 
         [0170]    The Figures generally show a connecting location between two panels  30   a  and  30   b  so that the complementary hook profiles and the function thereof can be clearly seen. The rest of the panels is not illustrated. Provided at the respectively omitted end of each panel  30   a  and  30   b  respectively there is always a complementary hook profile. One of the oppositely disposed edges of a panel is in the form of an upper hook and the other is in the form of a lower hook. The two panel portions  30   a  and  30   b  when fitted together give a complete panel  30 . 
         [0171]    An embodiment of a panel with a locking element  33  on the upper hook  32  will now be described with reference to  FIGS. 12 to 14 . 
         [0172]    That panel  30   b  with the lower hook  31 , as shown in  FIG. 12 , is disposed on a support surface U. The lower hook  31  has an upwardly facing hook end  31   a  and an upwardly directed opening  31   b , that is to say which is facing away from the surface U. The upper hook  32  provided with the locking element  33  has a downwardly facing hook end  32   a  and a downwardly directed opening  32   b . The hook ends  31   a / 32   a  and openings  31   b / 32   b  are of such a configuration that a hook end  32   a  of the upper hook  32  of the one panel  30   a  can always be inserted into the opening  31   b  of the lower hook  31  of the other panel  30   b . The lower hook  31  has a latching recess  31   c  for the locking element  33 . The cross-section of the locking element  33  is of a V-shaped configuration in the manner of a clip. It has two clip portions  33   a  and  33   b . The clip portion  33   a  forms a resilient latching tongue  33   a . The other clip portion  33   b  is provided with an anchoring tongue  33   c  which has anchoring means and which is inserted into a holding gap  32   d  provided for same in the upper hook  32 . The latching tongue  33   a  of the locking element  33  projects from the edge of the panel  30   a  in the neutral condition, without spring stressing. 
         [0173]    The two panels  30   a  and  30   b  are arranged in mutually superposed relationship or overlap each other in  FIG. 12 . The panel  30   a  with the upper hook  32  is arranged higher than the panel  30   b  prior to the locking involvement. 
         [0174]    The two hook ends  31   a  and  32   a  of the panels  30   a  and  30   b  have inclinedly arranged undercut surfaces H 1  and H 2  which, in the locked condition of the panels  30   a  and  30   b , prevent the panels  30   a  and  30   b  from moving away from each other in the plane thereof and perpendicularly to the edges. 
         [0175]      FIG. 13  shows an intermediate position during the connection of the hook profiles. The upper hook  32  is arranged over the lower hook  31  in such a way that edge surfaces  31   e  and  32   e  which form a join at the top side of the panels are in contact in a vertical plane. The downward movement of the upper hook  32  causes the resilient latching tongue  33   a  of the locking element  33  to be automatically folded together. The latching tongue  33   a  is resiliently stressed by virtue of the contact of the latching tongue  33   a  with the edge surface  31   e  of the lower hook  31 . The edge surface  31   e  of the lower hook  31  thus acts as a clamping surface  31   e  for the latching tongue  33   a.    
         [0176]    Upon a continuation of the joining movement the latching tongue  33   a  slides completely past the clamping surface  31   e  until the end of the latching tongue  33   a  becomes free and automatically moves resiliently outwardly into the latching recess  31   c  of the lower hook  31 . The latching recess  31   c  has a latching surface R along which the latching tongue  33   a  slides. The latching surface R is arranged inclinedly to such a degree as to limit the spring travel of the latching tongue  33   a  before the latching tongue  33   a  is completely displaced resiliently outwardly. Latching engagement of the latching tongue  33   a  can already start before the end position of the hook profiles  31  and  32  as shown in  FIG. 14  is reached. 
         [0177]    In the end position the latching tongue  33   a  preferably still has a residual portion of the spring stressing and as a result provides for resilient contact with the latching recess  31   c . The clip portions  33   a  and  33   b  of the locking element  33  are therefore closer together in  FIG. 15  than in the neutral position shown in  FIG. 12 . 
         [0178]    The undercut surface H 1  of the lower hook  31  is in contact with the undercut surface H 2  of the upper hook  32 . The inclined positioning of the undercut surfaces H 1 /H 2  provides, during the joining process, a motion component in a horizontal direction, namely, parallel to the plane of the panels  30   a  and  30   b . In that way the edge surface  31   e  of the panel  30   a  is moved against the edge surface  32   e  of the panel  30   b . Depending on the respective nature of the production tolerances for the individual dimensions of the hook ends  31   a / 32   a , the edge surface  31   e / 32   e  can either be caused to bear exactly snugly against each other, have a gap, or be pressed against each other with a certain pressure under elastic biasing by the hook profiles  31 / 32 . 
         [0179]    As shown in  FIG. 14  the hook end  31   a  of the lower hook  31  is in contact with a bottom  32   f  of the opening  32   b  of the upper hook  32 . In that way, a loading on the surface of the panel  30   a  can be absorbed in the thinnest region of the upper hook  32  and is stably supported by surface contact with the hook end  31   a  of the lower hook  31 . 
         [0180]    The hook end  32   a  of the upper hook  32  in contrast does not extend as far as a bottom  31   f  of the opening  31   b  of the lower hook  31 . Instead, there is a gap S here. That assists with manufacture as only the opening  32   b  and the associated hook end  31   a  have to be produced with a high level of dimensional accuracy. The high level of dimensional accuracy ensures a smooth surface for connected panels  30   a  and  30   b  without a heightwise displacement at the join  34 . In addition any dust which may be present or other particles can be received in the gap S so that precise positioning of the hook profiles is not adversely affected by foreign bodies which are clamped therein. 
         [0181]    In addition a dust chamber M is formed in  FIG. 14 . It is disposed between the bottom  32   f  of the opening  32   b  of the upper hook  32  and the hook end  31   a  of the lower hook  31 . Any dust which may be present is displaced thereinto and in that way does not prevent contact between the hook end  31   a  and the bottom  31   f  of the opening  32   b  of the upper hook  31 . 
         [0182]      FIG. 15  shows an alternative structure which has only one modification in relation to  FIG. 14 . The modification is that the contact location between the opening and the hook end is interchanged. In  FIG. 15  it is not the hook end  31   a  of the lower hook  31  but the hook end  32   a  of the upper hook  32  which is in contact, namely against the bottom  31   f  of an opening  31   b  of the lower hook  31 . The hook end  31   a  of the lower hook  31  does not involve any contact with the bottom  32   f  of the opening  32   b  of the upper hook  32 . In that way a loading on the upper hook  32  near the join  34  of two panels  30   a  and  30   b  is particularly well supported because the hook end  32   a  of the upper hook  32  is supported in flat surface contact in the opening  31   b  of the lower hook  31 . 
         [0183]    In addition a dust chamber M is formed in  FIG. 15 . It is disposed between the bottom  31   f  of the opening  31   b  of the lower hook  31  and the hook end  32   a  of the upper hook  32 . Any dust which may be present trickles thereinto and in that way does not impede contact between the hook end  32   a  and the bottom  31   f  of the opening  31   b  of the lower hook  31 . In contrast the opening  32   b  of the upper hook  32  does not involve any contact at its bottom  32   f  with the hook end  31   a  of the lower hook  31 . Instead a gap S is provided here. The depth of the opening  31   b  of the lower hook  31  and the corresponding dimension of the hook end  32   a  are also the sole important functional dimensions which are important for ensuring a common floor surface and for avoiding a heightwise displacement at a join  34 . 
         [0184]    Another panel, namely with a locking element  33  at a lower hook  31 , is described with reference to  FIG. 16  which shows two panels  30   a  and  30   b  laid one upon the other with some heightwise displacement, as in  FIG. 12 . A panel  30   b  is disposed on a support surface U. That panel  30   b  has a hook profile with a lower hook  31 . The lower hook  31  has an upwardly directed opening  31   b , that is to say which faces away from the support surface U. The hook profile of the second panel  30   a  has an upper hook  32  provided with a downwardly directed opening  32   b . Both hook profiles have hook ends  31   a  and  32   a  which respectively fit into the opening  31   b  and  32   b  respectively of the associated hook profile co-operating portion. 
         [0185]    At its free end the lower hook  31  is provided with an additional locking element  33  which has a resilient latching tongue  33   a . The latching tongue  33   a  projects from the edge of the panel  30   b . The upper hook  32  of the adjacent panel  30   a  is provided with a latching recess  32   c  with a latching surface R co-operating with the latching tongue  33   a  of the locking element  33 . 
         [0186]    The locking element  33  is the same as in  FIG. 12 . Its cross-section is of a V-shaped configuration in the manner of a clip. It has two clip portions  33   a  and  33   b  which are visible at the outside edge of the hook profile  31  and which are resilient in the bend of the V-shape. Provided at one of the clip portions  33   b  is an anchoring tongue  33   c  with anchoring means which is fitted into a holding gap  31   d  of the lower hook  31 . The locking element  33  is captively connected to the lower hook  31 . 
         [0187]      FIG. 17  shows an intermediate position during the connection of the hook profiles. The upper hook  32  is arranged over the lower hook  31  in such a way that edge surfaces  31   e  and  32   e  which form a join  34  at the top side of the panels  30   a / 30   b  are in contact in a vertical plane. The resilient latching tongue  33   a  is automatically folded together by the movement of the upper hook  32  towards the locking element  33 . In that case the latching tongue  33   a  is in contact with a surface of the upper hook  32 , which acts as a clamping surface  32   g  for the latching tongue  33   a.    
         [0188]    As soon as the clamping surface  32   g  has slid completely past the latching tongue  33   a  upon a continuation of the joining movement and the end of the latching tongue  33   a  becomes free, it automatically springs into the latching recess  32   c  of the upper hook  32 . That process can already take place before the definitive position of the hook profiles as shown in  FIG. 18  is reached. 
         [0189]    In the end position the latching tongue  33   a  is preferably still in a spring-stressed condition and as a result causes secure contact and latching in the latching recess  32   c . The clip portions  33   a  and  33   b  of the locking element  33  are therefore closer together in  FIG. 18  than in the neutral position shown in  FIG. 16 . 
         [0190]    The two hook ends  31   a  and  32   a  of the panels  30   a  and  30   b  have inclinedly arranged undercut surfaces H 1  and H 2  which, in the locked condition of the panels  30   a  and  30   b , prevent the panels  30   a  and  30   b  from moving away from each other in their plane and perpendicularly to the edges, as in the embodiment in  FIG. 14 . 
         [0191]    As shown in  FIG. 18  the hook end  32   a  of the upper hook  32  is in contact with a bottom  311  of the opening  31   b  of the lower hook  31 . In that way a loading on the surface of the panel  30   a  in the region of the hook end  32   a  of the upper hook  32  can be absorbed by surface contact in the opening  31   b  of the lower hook  31 . The opening  32   b  of the upper hook  32  in contrast does not involve any contact at its bottom  32   f  with the hook end  31   a  of the lower hook  31 . Instead there is a gap S here. The depth of the opening  31   b  of the lower hook  31  and the corresponding dimension of the hook end  321  are in addition the sole important functional dimensions which are important for ensuring a common floor surface and for avoiding a heightwise displacement at the join  34 . 
         [0192]    A dust chamber M is also formed in  FIG. 18 . It is between the bottom  32   f  of the opening  32   b  of the upper hook  32  and the hook end  31   a  of the lower hook  31 . Any dust which may be present is displaced thereinto and accordingly does not impede contact between the hook end  32   a  and the bottom  31   f  of the opening  31   b  of the lower hook  31 . 
         [0193]      FIG. 19  shows an alternative structure of a panel which has only one modification in relation to  FIG. 18 . The modification is that the contact location between the opening and the hook end is interchanged. In  FIG. 19  the hook end  31   a  of the lower hook  31  bears against a bottom  32   f  of the opening  32   b  of the upper hook  32  whereas the hook end  32   a  of the upper hook  32  does not involve any contact with the bottom  311  of the opening  31   b  of the lower hook  31 . Instead there is a gap S there. Providing contact precisely at that location affords the advantage that that region of the upper hook  32 , which is of the thinnest cross-section, is always supported by the hook end  31   a  of the lower hook  31  when a loading occurs on the floor surface at that location. In addition any dust which may be present or other particles can be received in the gap S so that precise positioning of the hook profiles is not adversely influenced by foreign bodies which are jammed therein. 
         [0194]    A dust chamber is also formed in  FIG. 19 . It is disposed between the bottom  32   f  of the opening  32   b  of the upper hook  32  and the hook end  31   a  of the lower hook  31 . Any dust which may be present is displaced thereinto and accordingly does not interfere with contact between the hook end  31   a  and the bottom  32   f  of the opening  32   b  of the upper hook  31 . 
         [0195]    A particular embodiment of a panel is described with reference to  FIGS. 20 and 21 .  FIG. 20  shows the connecting location of two panels  30   a  and  30   b . The panels  30   a  and  30   b  have hook profiles. Each complete panel has the complementary hook profiles which are shown in  FIG. 20 , at opposite edges. Furthermore each of the opposite hook profiles is provided with a locking element  33 . In that way two panels  30   a  and  30   b  are always arrested at a join  34  by means of two locking elements  33 . The locking elements  33  used are of a cross-section which has clip portions  33   a  and  33   b  which are of a V-shaped configuration in the manner of a clip and of which one is provided with an anchoring tongue  33   c  with anchoring means. A first one of the locking elements  33  is anchored to a lower hook  31  of a panel  30   b . The second locking element is arranged at an upper hook  32  of the adjacent panel  30   a . Automatic latching of the locking elements  33  takes place automatically. Latching engagement of the locking element  33  on the upper hook  32  substantially corresponds to the process described with reference to  FIGS. 12 to 14 . Latching of the locking element  33  on the lower hook  31  corresponds to the process described with reference to  FIGS. 16 to 18 . 
         [0196]    An alternative embodiment of a panel with another locking element  33  is described with reference to  FIGS. 22 to 25 .  FIG. 22  shows panels  30   a  and  30   b  with hook profiles, namely a lower hook  31  and an upper hook  32 , wherein the lower hook  31  is provided with the locking element  33  which can be resiliently bent. As  FIG. 22  shows the locking element  33  is of a narrow rectangular cross-section. It is anchored with an end  33   b  in a holding gap  31   d  of the lower hook  31 . The other end of the locking element  33  projects freely and forms a resilient latching tongue  33   a . For latching engagement the latching tongue  33   a  is automatically bent over by a joining movement of the upper hook  32 . The panel  30   b  with the lower hook  31  lies on a support surface U. The lower hook  31  is provided with an upwardly facing hook end  31   a  and with an upwardly directed opening  31   b , that is to say which faces away from the support surface. 
         [0197]    As shown in  FIG. 22  the upper hook  32  has a latching recess  32   c  co-operating with the latching tongue  33   a  of the locking element  33  when the panels  30   a  and  30   b  are locked. 
         [0198]    Furthermore  FIG. 22  indicates an alternative configuration of a locking element  33 ′ in broken line. The broken-line locking element  33 ′, in the neutral condition, is already of a bent or curved shape. That facilitates the assembly procedure and can improve stability and durability of the locking element  33 ′ in relation to the locking element  33  because the locking element  33 ′ has to be bent less than the straight locking element  33 . 
         [0199]      FIG. 23  shows the embodiment of  FIG. 22  in a first intermediate position in which the upper hook  32  is in contact with the latching tongue  33   a  of the locking element  33  and urges it in the direction of the opening  31   b  of the lower hook  31 . In that situation the locking element  33  stores elastic spring energy. 
         [0200]    A further intermediate step in the joining movement is shown in  FIG. 24 . In that position edge surfaces  31   e  and  32   e  have come into contact, more specifically in the region of a join  34  which occurs at the surface of the panels  30   a  and  30   b . In addition the latching tongue  33   a  of the locking element  33  bears against a clamping surface  32   g  of the upper hook  32 . The latching tongue  33   a  of the locking element  33  involves its maximum spring stressing in that position. After the clamping surface  32   g  of the upper hook  32  has slid completely past the latching tongue  33   a  the latching tongue  33   a  of the locking element  33  automatically snaps into the latching recess  32   c  of the upper hook  32  by virtue of the effect of the spring stressing of the latching tongue. The structure is preferably so designed that, in the latched end position, there still remains a residual portion of the spring stressing in the locking element  33  so that, in the  FIG. 25  position, contact is always ensured between the latching tongue  33   a  of the locking element  33  and the latching recess  32   c.    
         [0201]    The two hook ends  31   a  and  32   a  of the panels  30   a  and  30   b  have inclinedly arranged undercut surfaces H 1  and H 2  which, in the locked condition of the panels  30   a  and  30   b , prevent the panels  30   a  and  30   b  from moving away from each other in their plane and perpendicularly to the edges, as in the embodiment of  FIG. 14 . 
         [0202]    It can further be seen from  FIG. 25  that the hook end  32   a  of the upper hook  32  is in contact with a bottom  31   f  of the opening  31   b  of the lower hook  31 . That guarantees load transmission from the hook end  32   a  of the upper book  32  into the lower hook  31 . The hook end  31   a  of the lower hook  31  in contrast does not involve any contact with a bottom  32   f  of the opening  32   b  of the upper hook  32 . At this juncture attention is to be directed to an alternative which is not shown and in which the contact location in respect of the opening/hook end between the upper hook  32  and the lower hook  31  can be interchanged so that the hook end  31   a  of the lower hook  31  bears against the bottom of the opening of the upper hook  32  and conversely the hook end  32   a  of the upper hook is not in contact against the bottom  31   f  of the opening  31   b  of the lower hook  31 . Instead, there is a gap S. The advantages and disadvantages of such a configuration are as described hereinbefore with reference to  FIG. 19 . 
         [0203]    A further embodiment of a panel with hook profiles at opposite edges is described with reference to  FIGS. 26 to 29 . This again involves a panel with lower hook  31  at one edge and upper hook  32  at the opposite edges. In this case the upper hook  32  is that which is provided with an additional locking element  33 . 
         [0204]    The locking element  33  corresponds to the locking element  33  of  FIG. 22 . It is of a narrow rectangular cross-section. The rectangular cross-section has a part which serves as an anchoring tongue  33   b  and which is anchored in a holding gap  32   d . The other part  33   a  of the locking element projects out of the holding gap, in the form of a resilient bendable latching tongue  33   a.    
         [0205]    A dust chamber M is also formed in  FIG. 25 . It is between the bottom  31   f  of the opening  31   b  of the lower hook  31  and the hook end  32   a  of the upper hook  32 . Any dust which may be present is displaced thereinto and accordingly does not impede contact between the hook end  32   a  and the bottom  31   f  of the opening  31   b  of the lower hook  32 . 
         [0206]      FIG. 26  also indicates an alternative embodiment of a locking element  33 ′, shown more specifically in broken line. This involves a locking element  33 ′ which, in its neutral position, is of a curved or bent form. The curve/bend points in the direction in which the locking element  33 ′ has to be bent for latching engagement. 
         [0207]    In  FIG. 26  the panel  30   b  illustrated with the lower hook  31  rests on a support surface U. The upper hook  32  of an adjacent panel  30   a  is disposed above the support surface U. There is not yet any contact between the panels  30   a  and  30   b.    
         [0208]    In  FIG. 27  the upper hook  32  has been moved downwardly by a distance so that the locking element  33  has come into contact with the hook end  31   a  of the lower hook  31  and the latching tongue  33   a  is bent. Upon further downward movement of the upper hook  32  the bending of the latching tongue  33   a  of the locking element  33  increases until it slides along a clamping surface  31   g  of the lower hook  31 . The bending of the latching tongue  33   a  of the locking element  33  is at its greatest when its free end is in contact with the damping surface  31   g  of the lower hook  31 . Insofar as the clamping surface  31   g  is arranged in parallel relationship with the direction of movement, the prestressing of the locking element  33  remains constant during the joining movement, and that applies moreover in regard to all embodiments. It will be appreciated that the prestressing can also be of a variable nature insofar as a suitable shape and arrangement is imparted to the clamping surface  31   g , which afford a change in the spring travel of the latching tongue  33   a  while the joining movement is taking place. 
         [0209]    In the present case the prestressing effect changes when the latching tongue  33   a  of the locking element  33  has slid down as far as the end of the clamping surface  31   g  automatically. That is because the latching tongue  33   a  then springs out into a latching recess  31   c  in the lower hook  31 . In that situation the level of spring energy decreases. Desirably however the structure is so designed that a residual portion of the spring energy always remains stored in the locking element. That thus ensures that the latching tongue  33   a  of the locking element  33  always exerts a certain spring pressure against the latching recess  31   c  and ensures a secure latching effect. 
         [0210]    It can be further be seen from  FIG. 28  that the two panels  30   a  and  30   b  come into contact in the region of a join  34  which is at the surface of the panels. Upon a further downward movement of the upper hook  32  edge surfaces  31   e  and  32   e  slide past each other in the region of the join  34 . 
         [0211]    The two hook ends  31   a  and  32   a  of the panels  30   a  and  30   b  have inclinedly arranged undercut surfaces H 1  and H 2  which, in the locked condition of the panels  30   a  and  30   b , prevent the panels  30   a  and  30   b  from moving away from each other in their plane and perpendicularly to the edges, as in the  FIG. 14  embodiment. 
         [0212]    The end position of the hook profiles is shown in  FIG. 29  in which the locking element  33  is in latching engagement. The hook end  31   a  of the lower hook  31  is in contact with a bottom  32   f  of the opening  32   b  of the upper hook  32  whereas the hook end  32   a  of the upper hook  32  does not involve any contact with a bottom  31   f  of the opening  31   b  of the lower hook  31 . Here there is a gap S. As is already the case with the above-described embodiments, however, that can be interchanged. The possibility of the two hook ends and bottoms of the openings being so-to-speak brought into contact with each other is also proposed because this involves a particularly stable configuration if there is no gap at all. This configuration (not shown) presupposes a high level of manufacturing quality. 
         [0213]    A dust chamber M is also formed in  FIG. 29 . It is between the bottom  32   f  of the opening  32   b  of the upper hook  32  and the hook end  31   a  of the lower hook  31 . Any dust which may be present is displaced thereinto and accordingly does not prevent contact between the hook end  31   a  and the bottom  32   f  of the opening  32   b  of the upper hook  31 . 
         [0214]    A further embodiment of a panel is described with reference to  FIGS. 30 and 31 .  FIG. 30  shows two panels  30   a  and  30   b  which have hook profiles at opposite sides. The panel  30   b  is provided with a lower hook  31  to which an additional locking element  33  is anchored. The panel  30   a  is provided with an upper hook  32  to which an additional locking element  33  is also anchored. At the edges which are not shown, the panels  30   a  and  30   b  are each provided with the respective complementary hook profile. As a panel is provided with a locking element at each of the opposite edges, two locking elements  33  are always involved at a connecting location between two panels  30   a  and  30   b.    
         [0215]    The two hook ends  31   a  and  32   a  of the panels  30   a  and  30   b  have inclinedly arranged undercut surfaces H 1  and H 2  which, in the locked condition of the panels  30   a  and  30   b , prevent the panels  30   a  and  30   b  from moving away from each other in their plane and perpendicularly to the edges, as in the embodiment of  FIG. 14 . 
         [0216]    Latching engagement of the locking element  33  provided on the lower hook  31  corresponds to the process which is described with reference to  FIGS. 22 to 25 . Latching engagement of the locking element  33  provided on the upper hook  32  substantially corresponds to the process described with reference to  FIGS. 26 to 29 . 
         [0217]    In the intermediate position shown in  FIG. 30  the locking elements  33  involve maximum spring stressing. Latching engagement of the two locking elements occurs automatically and, with the symmetrical structure by way of example in respect of the hook profiles, almost simultaneously. 
         [0218]    A further embodiment of a panel is shown in  FIGS. 32 to 37 . This is a panel with hook profiles at opposite edges. As shown in  FIG. 32  a panel  30   b  is provided with a lower hook  31  and a panel  30   a  is provided with an upper hook  32 . The lower hook  31  has an additional locking element  33  in the form of a locking clasp  33 . 
         [0219]    The locking clasp  33  has anchoring tongues  33   c  with which it is anchored in a holding gap  31   d  of the lower hook  31 . In order to clearly show the configuration of the locking clasp  33 , attention is directed to  FIGS. 36 and 37 .  FIG. 36  shows a plan view on to the edge of the panel  30   b . The curved shape of the locking clasp  33  is shown in broken line. It is possible to see the anchoring tongues  33   c  which are inserted deeply into the holding gap  31   d  to the bottom thereof. As shown in  FIG. 36  the locking clasp  33  is in a neutral condition without spring stressing. The locking clasp  33  has a latching tongue  33   a  which projects out of the holding gap  31   d  as shown in  FIG. 36 . The neutral initial position of the locking clasp  33  shown in  FIG. 36  is the same as the position shown in  FIG. 32 . 
         [0220]    In  FIG. 33  the upper hook  32  has been moved downwardly by a distance and as a result has pressed against the latching tongue  33   a  of the locking clasp  33 . As a result the latching tongue is deflected back a distance into the holding gap  31   d . Upon a continuation of the joining movement of the upper hook  32  the latching tongue  33   a  is further pressed into the holding gap  31   d  and clears the way for the upper hook  32 . 
         [0221]    The two hook ends  31   a  and  32   a  of the panels  30   a  and  30   b  have inclinedly arranged undercut surfaces H 1  and H 2  which, in the locked condition of the panels  30   a  and  30   b , prevent the panels  30   a  and  30   b  from moving away from each other in their plane and perpendicularly to the edges, as in the  FIG. 14  embodiment. 
         [0222]    When the locking clasp  33  assumes the position shown in  FIG. 34 , the maximum level of spring stressing is reached, which can be imparted to the locking clasp  33  in the present structure. A plan view of that position of the locking clasp  33  is shown in  FIG. 37 . The latching tongue  33   a  of the locking clasp  33  is pushed back into the holding gap  31   d  as far as the edge thereof. 
         [0223]    In a further joining movement the latching tongue  33   a  moves automatically out of the holding gap  31   d  again by virtue of the spring energy stored in the locking clasp  33  and engages into a latching recess  32   c  in the upper hook  32 . 
         [0224]    The definitive position of the hook profiles  31 / 32  is shown in  FIG. 35  in which the latching tongue  33   a  of the locking clasp  33  presses with a residual portion of the spring stressing against the latching recess  32   c  in the upper hook  32  and securely arrests the hook profiles. 
         [0225]    A dust chamber M is also formed in  FIG. 35 . It is between a bottom  311  of an opening  31   b  of the lower hook  31  and a hook end  32   a  of the upper hook  32 . Any dust which may be present or other particles trickle thereinto and accordingly do not impede contact between the hook end  32   a  and the bottom  31   f  of the opening  31   b  of the lower hook  31 . 
         [0226]    In contrast an opening  32   b  of the upper hook  32  does not have any contact at a bottom  32   f  with a hook end  31   a  of the lower hook  31 . Instead, there is a gap S here. The depth of the opening  31   b  of the lower hook  31  and the corresponding dimension of the lower hook  32   a  are also the sole important functional dimensions which are important for ensuring a common floor surface and for avoiding a heightwise displacement at a join  34 . 
         [0227]    A further embodiment of a panel is shown in  FIGS. 38 to 41 . This involves a panel with hook profiles at opposite edges. As shown in  FIG. 38  a panel  30   b  is provided with a lower hook  31  and a panel  30   a  is provided with an upper hook  32 . The upper hook  32  has an additional locking element  33  in the form of a locking clasp  33 . 
         [0228]    The locking clasp  33  has anchoring tongues  33   c  with which it is anchored in a holding gap  32   d  of the upper hook  32 . In order to clearly show the configuration of the locking clasp  33  attention is directed to  FIGS. 36 and 37 .  FIG. 36  shows the principle of the locking clasp  33  based on the viewing direction XXXVI as shown in  FIG. 38 , namely a view from below on to the edge of the panel  30   a .  FIG. 37  shows the principle of the locking clasp  33  based on the viewing direction XXXVII as shown in  FIG. 40 , namely also a view from below on to the edge of the panel  30   a . The locking clasp  33  has anchoring tongues  33   c  which are inserted into a holding gap  32  deeply as far as the bottom thereof. The locking clasp  33  again has a latching tongue  33   a  which, as shown in  FIG. 38 , projects out of the holding gap  32 . 
         [0229]    The upper hook  32  has been moved downwardly by a distance in  FIG. 39 . The latching tongue  33   a  of the locking clasp  33  has been pressed against a hook end  31   a  of the lower hook  31  and deflected back into the holding gap  32   d  by a distance. Upon a continuation of the joining movement of the upper hook  32  the latching tongue  33   a  is further pressed into the holding gap  32   d  and clears the way for the upper hook  32  to be introduced completely into the lower hook  31 . 
         [0230]    When the locking clasp  33  assumes the position shown in  FIG. 40  the maximum level of spring stressing is reached, which can be imparted to the locking clasp  33  in the present construction. A view of that position of the locking clasp  33  from below corresponds to the view in  FIG. 37 . The latching tongue  33   a  of the locking clasp  33  is pushed back into the holding gap  32   d  as far as the edge thereof. 
         [0231]    The two hook ends  31   a  and  32   a  of the panels  30   a  and  30   b  have inclinedly arranged undercut surfaces H 1  and H 2  which, in the locked condition of the panels  30   a  and  30   b , prevent the panels  30   a  and  30   b  from moving away from each other in their plane and perpendicularly to the edges, as in the embodiment of  FIG. 14 . 
         [0232]    In a further joining movement the latching tongue  33   a  automatically moves out of the holding gap  32   d  again by virtue of the spring energy stored in the locking clasp  33  and engages into a latching recess  31   c  provided on the lower hook  31 . 
         [0233]    The definitive position of the hook profiles  31 / 32  is shown in  FIG. 41 , in which the latching tongue  33   a  of the locking clasp  33  presses with a residual portion of the spring stressing against the latching recess  31   c  of the lower hook  31  and securely arrests the hook profiles. 
         [0234]    A dust chamber M is also formed in  FIG. 41 . It is between the bottom  32   f  of an opening  32   b  of the upper hook  31  and a hook end  31   a  of the lower hook  31 . Any dust which may be present or other particles trickles thereinto and accordingly does not impede contact between the hook end  31   a  and the bottom  32   f  of the opening  32   b  of the lower hook  32 . 
         [0235]    In contrast an opening  31   b  of the lower hook  31  does not involve contact at a bottom  31   f  with a hook end  32   a  of the upper hook  32 . Instead, there is a gap S here. The depth of the opening  32   b  of the upper hook  32  and the corresponding dimension of the hook end  31   a  of the lower hook  31  are also the sole important functional dimensions which are important for ensuring a common floor surface and for avoiding a heightwise displacement at a join  34 . 
         [0236]      FIG. 42  shows an intermediate position during the operation of connecting two panels  30   a  and  30   b  having hook profiles. An upper hook  32  is arranged over a lower hook  31  in such a way that edge surfaces  31   e  and  32   e  which form a join at the top side of the panels are in contact in a vertical plane. A resilient latching tongue  33   a  of a locking element  33  has been automatically folded together by a relative movement of the hook  32  towards the panel  30   b . The latching tongue  33   a  is resiliently stressed by virtue of the contact of the latching tongue  33   a  with the edge surface  31   e  of the lower hook  31 . The edge surface  31   e  of the lower hook  31  thus acts as a clamping surface  31   e  for the latching tongue  33   a.    
         [0237]    Upon a continuation of the joining movement the latching tongue  33   a  slides completely past the clamping surface  31   e  until the end of the latching tongue  33   a  becomes free and automatically springs out into a latching recess  31   c  in the lower hook  31 . The latching recess  31   c  has a latching surface R along which the latching tongue  33   a  slides. The latching surface R is arranged inclinedly at an extent which limits the spring travel of the latching tongue  33   a  before the latching tongue  33   a  has moved completely outwardly resiliently. The neutral relaxed position of the latching tongue  33   a  of the locking element  33  is shown in broken line. 
         [0238]    The locking element in  FIG. 42  is shown in cross-section in  FIG. 43 . The locking element is in a neutral relaxed condition. Its cross-section is of a V-shaped or U-shaped configuration in the manner of a clip. It has two clip portions  33   a  and  33   b . The clip portion  33   a  forms a resilient latching tongue  33   a . The other clip portion  33   b  is provided with an anchoring tongue  33   c . A curved clip portion  33   d  is provided between the clip portions  33   a  and  33   b . The curved clip portion  33   d  is thinner than the clip portions  33   a  and  33   b  in order to assist with spring mobility. The anchoring tongue  33   c  is shaped in the manner of a harpoon leg. It has two prongs  33   e  as anchoring means. The prongs  33   e  provide a good anchoring effect on the part of the locking element when it is fitted into a holding gap  32   d  provided for same in the upper hook  32 , as in  FIG. 42 . The anchoring tongue  33   c  has a pressing surface which is pressed by a pressing-in tool and by way of which a force is applied for pressing the anchoring tongue of the locking element into a holding gap of a panel. The pressing surface is intended and designed to receive a pressing force from the pressing-in tool E and to transmit it into the anchoring tongue  33   c . The pressing-in surface is provided on the clip portion  33   b  in the embodiment of the locking element shown in  FIG. 42 . The clip portion  33   b  has the property of being able to carry a pressing force without being bent by that pressing force. For that purpose, the material and the material thickness of the clip portion  33   b  are so selected that the desired function of transmitting the force is performed without the clip portion  33   b  being put at risk of breaking off or thus bending. 
         [0239]    In general terms locking elements  5  or  200  which are of a different shape can also have a pressing surface. The pressing surface has to be provided at a region of the locking element  5  or  200 , whose quality and thickness of material are adapted to permit transmission of a force which is applied to the locking element by a pressing-in tool E. 
         [0240]    A pressure roller is diagrammatically illustrated in  FIG. 43  as the pressing-in tool E. That corresponds in principle to the pressing roller  600   a  shown in  FIGS. 53 and 61 . 
         [0241]    The pressing surface can be provided with means which promote force transmission in frictionally locking relationship, for example a structured surface. For example that can prevent slip between a pressing roller E which transmits a pressing-in force to the locking element  33  by means of a rotary movement. 
         [0242]    All locking elements  33  shown in  FIGS. 12 to 42  are preferably provided only for locking the panels  30   a  and  30   b  in a direction substantially perpendicular to the plane of the panels. 
         [0243]    Other means are provided for affording a locking action to prevent connected panels  30   a  and  30   b  from moving away from each other in a direction parallel to the plane of the panels  30   a  and  30   b , namely substantially horizontally. Preferably the undercut surfaces H 1 /H 2  which are common to all hook profiles themselves form the means for horizontal locking, which in the locked condition prevent the panels from moving away from each other. 
         [0244]    The hook profiles can be produced in such a way that contact surfaces of an undercut configuration which are effective to provide for horizontal locking are either forced against each other with elastic deformation of the panel material or a gap is present between the contact surfaces of the undercut configuration. A gap affords a connection which involves play in a horizontal direction. Otherwise, if undercut surfaces of the hook profiles can be assembled with pressure and with elastic deformation thereof, the result achieved is a connection in which there is no play at the join between two panels, but there is an elastic prestressing action between the connected panels. 
         [0245]    Alternatively it is possible to provide between undercut surfaces an additional element which for example in turn forces the edges of the panels  30   a  and  30   b  against each other by an elastic action, so that a join  34  at the surface of a panel covering is closed as much as possible. 
         [0246]      FIG. 44  shows perspective views of parts of two panels  30   a  and  30   b  with different locking elements. There is also a diagrammatic view which shows the arrangement of the panels  30   a  and  30   b  as a whole within a row of panels P 1 . The foremost panel of the row P 1  is shown in broken line. Besides the top side and the underside, the panels  30   a  and  30   b  have peripherally extending edges on which holding profiles are disposed. The oppositely disposed holding profiles of each panel are formed as complementary hook profiles in paired relationship, for the purposes of a vertical component in the joining movement. 
         [0247]      FIG. 45  diagrammatically shows a plurality of panels  35 ,  36 ,  37 ,  38  and  39  arranged in two rows P 1  and P 2  of panels. The panels  35 ,  36 ,  37 ,  38 ,  39  are already locked with locking elements which are not shown in the simplified diagrammatic view. A new panel  40  has to be locked as shown in  FIG. 45  at two edges which are arranged at an angle relative to each other, namely both with the edge  40   a  to panels  37  and  38  of the row P 1  and also with the edge  40   b  to a panel  39  in the same row P 2 . 
         [0248]    As shown in  FIG. 44 , a new panel  30   b  is connected to a panel  30   a  of the first row P 1 . There is no row of panels disposed in front of the row P 1  of panels. The new panel  40  is locked with one of its edges only to a panel  30   a  in the same row P 1 . For that purpose the panel  30   b  is moved in aligned relationship as indicated by F with the panel edges. The panels  30   a  and  30   b  lie in that case on a support surface. 
         [0249]    The panel  30   a  has hook profiles which are arranged at an angle to each other, namely an upper hook  32  and a lower hook  31 . The upper hook  32  has a holding gap  32   d . A locking element  33  with a resilient latching tongue  33   a  is anchored in the holding gap  32   d . The lower hook has a holding gap  31   d . A locking clip  33  is anchored in the holding gap  31   d . A resilient latching tongue  33   a  of the locking clip  33  projects out of the holding gap  31   d . Respective complementary hook profiles are provided at the opposite edges (not shown) of the lower hook  31  and the upper hook  32 . 
         [0250]    The panel  30   b  also has hook profiles arranged at an angle to each other. Of those, the two upper hooks  32  and  35  are to be seen in the part shown in  FIG. 44 . The upper hook  32  of the panel  30   b  corresponds to the upper hook  32  of the panel  30   a . The panel  30   b  thus also has a holding gap  32   d  in which a locking element  33  is anchored. A resilient latching tongue  33   a  of the locking element  33  projects from the edge of the panel  30   b . The shape of the upper hook  35  of the panel  30   b  is the complementary counterpart of the lower hook  31  and vice-versa. The respective complementary hook profiles as referred to above are provided at the opposite edges (not shown) of the upper hook  32  and the lower hook  35 . 
         [0251]    For the purpose of locking the panels  30   a  and  30   b  of the first row of panels, the panel  30   b  is pushed in a flat movement with its upper hook  32  from the side into the complementary lower hook of the panel  30   a . At the beginning of that movement the upper hook  32  of the panel  30   b  should be moved towards the edge of the panel  30   a  in such a way that the latching tongue  33   a  of the locking element  33  is moved resiliently inwardly by the contact with the panel  30   a . The inward resilient movement of the latching tongue  33   a  provides that the cross-section of the locking element  33  assumes a position which fits into the internal cross-section of the latching recess of the complementary lower hook of the panel  30   a . As soon as the panel  30   b  has been fitted in that way the panels  30   a  and  30   b  are connected by a simple pushing movement until the upper hook of the panel  30   b  is connected over the entire length of the corresponding edge to the lower hook of the panel  30   a . In that situation the latching tongue  33   a  is progressively automatically resiliently displaced into the latching recess at the location of entry. 
         [0252]    The process for locking the first row of panels is obviously not limited to those locking elements which are shown in  FIG. 44 . Alternatively it is possible to use at least each locking element as shown in  FIGS. 12 to 42  as well as the hook profile configuration specified therein. 
         [0253]    A process which uses the steps of  FIGS. 12 to 14  and  FIGS. 16 to 18  respectively is equally simple. In that case firstly a substantially horizontal component of movement is used to feed the resilient latching tongue of a locking element not from above but from the side, to bring it into contact with the adjacent panel. That can be easily performed because the upper hook  32  of the panel  30   a , as shown in  FIGS. 12 and 16 , can be laid loosely on the lower hook  31  of the panel  30   b  and thereafter the panel  30   a  can be pushed against the edge surface  31   e  of the panel  30   b , whereby the latching tongue  33   a  moves resiliently inwardly and bears tightly against the hook profile. 
         [0254]    It is only when the latching tongue  33   a  has been displaced resiliently inwardly that the panel  30   a  with its upper hook  32  is moved vertically downwardly, namely hookingly engaged into the lower hook of the adjacent panel  30   b  perpendicularly to the plane of the panel, until the inwardly displaced latching tongue  33   a  of the locking element  33  automatically springs out against a latching surface R of a latching recess of the respective adjacent panel and arrests the hook connection. 
         [0255]    A process for locking a panel having hook profiles at opposite edges and a locking element with a resilient latching tongue, wherein a fresh panel  40  has to be connected both to panels of a first row P 1  and also to a panel  39  of the same row P 2 , is shown with reference to diagrammatic  FIG. 45 .  FIG. 46  shows a plan view and a side view of the panel  40  shown in  FIG. 45 . The edges  40   a  and  40   b  are in the form of upper hooks while the two edges  40   c  and  40   d  are in the form of lower hooks. Basically it is possible to use any hook profile configuration as shown in  FIGS. 12 to 42  for the hook profiles in  FIG. 46 . In the present case the lower hooks  40   c  and  40   d  correspond to the embodiment of  FIGS. 32 to 35 . 
         [0256]    As shown in  FIG. 45  a new panel is locked by a procedure whereby it is laid with a corner, here the corner of the upper hooks  40   a / 40   b , on lower hooks of the row P 1  of panels and a lower hook of the panel  39  of the same row P 2  respectively. The upper hook  40   b  is then inserted on the basis of the zip fastener principle, over the entire length thereof. The insertion operation can be simplified if the panel  40  is flexed somewhat. As can be seen from  FIG. 45  a curvature has been imparted to the edge  40   b . In that way it is possible for the upper hook  40   b  to be connected to the lower hooks of the panels  37  and  38  of the row P 1  in the manner of a zip fastener, because a progressing point of the upper hook always engages into a lower hook. If the panel  40  were not actively flexed, a pivotal movement of the straight edge  40   b  would provide that the upper hook comes simultaneously into contact over the entire length with the lower hook of the row P 1 . In that case a slight lateral displacement can easily make it difficult to fit the components one into the other in a scissor-like configuration because the upper hook and the lower hook at the end of the scissor movement still have to be adjusted and brought into exact overlap with each other. That adjustment problem is countered with the zip fastener process applied to the laying procedure, with active flexing of the panel  40 . 
         [0257]    The same applies to the edge with the upper hook  40   a , in which case the zip fastener process is of greater significance for a long edge than for a short edge. 
         [0258]    It will be appreciated that the zip fastener process can also be applied for the edge  40   b  in the opposite direction, namely beginning at the edge  40   c  in the direction of the edge  40   a , in which case however there is no installation assistance for correct positioning of the panel  40  and it is therefore more difficult for the zip fastener process to be caused to end exactly at the panel  39 . It can happen that a gap remains in relation to the panel  39  or that the panel  39  is overlapped by the panel  40 . 
         [0259]    During insertion of the upper hooks  40   a  and  40   b  into the lower hooks of the panels  37 ,  38  and  39  latching engagement of the locking clasps  33  takes place automatically, as in  FIGS. 32 to 35 . 
         [0260]      FIG. 47  shows alternative panels  46 ,  47 ,  48 ,  49  and  50  as well as a laying process intended for same. The panels form a part of a panel covering. They have two kinds of holding profiles. The interlocked panels  46 ,  47  and  48  are shown in a front row V 1  of the panel covering. Shown in a following row V 2  is a panel  49  which is preferably positively lockingly connected to the panels  46  and  47  of the front row. A new panel  50  is inclinedly attached with an edge  50   c  to the panels  47  and  48  of the front row V 1 . The new panel  50  still has to be pivoted downwardly into the plane of the lying panels  46 ,  47 ,  48  and  49 . 
         [0261]    Those edges of the panels  46 ,  47 ,  48 ,  49  and  50  which are provided for connecting the rows V 1  and V 2  of panels to each other must have a holding profile which is suitable for inclined attachment and subsequent locking by downward pivotal movement into the plane of the lying panels. Such a holding profile is known from WO 00/63510 A1. The disclosure thereof in respect of those panel edges which serve for connecting different rows of panels is hereby incorporated as an embodiment. WO 00/63510 A1 discloses in that respect a special hook profile which connects a new panel to panels of a front row, by a pivotal movement. In either respects hook profiles are also provided for locking the panels of the same row. More specifically those hook profiles are fitted into each other by a scissor-like pivotal movement and thus automatically come into hooking engagement in one movement. 
         [0262]    In addition  FIGS. 48 to 52  show suitable holding profiles which are suitable for locking by inclined attachment and subsequent downward pivotal movement into the plane of lying panels. These examples involve modified tongue-and-groove profiles. The groove  61  has at least one undercut surface  62 . The same applies for the tongue  63  which is provided with an undercut surface  64 . In regard to  FIG. 49  attention is directed to WO 97/47834. In regard to  FIG. 52  attention is directed to DE 79 28 703 U1. The holding profiles with a tongue-and-groove profile desirably provide for a positively locking connection which locks the panels both perpendicularly to their plane and also within their plane and also perpendicularly to a groove edge or tongue edge respectively. 
         [0263]    During the downward pivotal movement of the panel  50  from the inclined position shown in  FIG. 47  the edge  50   a  of the panel  50  is moved scissor-like towards the edge  49   b  of the panel  49 . The edges  50   a  and  49   b  involve complementary hook profiles which are secured with at least one locking element according to the invention, namely to prevent them from moving away from each other perpendicularly to the plane of the panels. The edge  49   b  has a lower hook and the edge  50   a  has an upper hook as a counterpart portion. 
         [0264]    The hook profiles  50   a / 49   b  are secured against coming loose perpendicularly to the plane of the panels by means of a locking element with a resilient latching tongue. 
         [0265]    Structural configurations which are known from the state of the art can be used. Structural configurations which have been found to be expedient are those which provide for resilient locking only in regard to the panels moving away from each other perpendicularly to the plane of the panels but which do not have a resilient action in relation to the panels moving away from each other parallel to their plane. It will be appreciated that any locking element according to the invention can be used, which has been mentioned in the present description, as well as the respective hook profile configuration suited thereto. 
         [0266]    Locking of the edges  49   b  and  50   a  takes place simultaneously with the scissor-like pivotal movement of the panel  50 . Prior to or during the pivotal movement, a translatory motion component can take place, with which exact overlap of the upper hook of the edge  50   a  of the panel  50  with the lower hook of the edge  49   b  of the panel  49  is achieved. That translatory movement takes place along the edge of the front row of panels, in which the edge  50   b  of the panel  50  is inclinedly inserted. The translatory movement can be influenced for example by the hook profiles of the edges  49   b  and  50   a . That can be when surfaces slide against each other, which for example are arranged inclinedly and thereby produce a component of motion parallel to the edge  50   b , while they come into contact in a scissor-like manner. 
         [0267]    The upper hook of the edge  50   a  is moved with a substantially vertical component of motion, on to the complementary lower hook of the edge  49   b  of the panel  49 . An integral component part of the resulting hook connection is a locking element with a resilient latching tongue in accordance with one of the described embodiments. The locking element will not be set forth at this juncture. 
         [0268]      FIG. 53  shows a substantial part of an apparatus  1  for mounting a locking element  200  to panels, on the basis of which the method according to the invention is also described. 
         [0269]    The apparatus  100  is intended for retro-fitment to a conventional production installation A for wall, floor or ceiling panels.  FIG. 53  shows portions of three panels  300   a ,  300   b  and  300   c . The through-travel direction T of the panels  300   a ,  300   b  and  300   c  in the production installation A is indicated by an arrow. 
         [0270]    A locking element is firstly supplied in the form of an endless locking element line  400 .  FIG. 53  does not show a storage means from which the locking element line  400  is removed. An example of a storage means is described hereinafter with regard to  FIGS. 59 and 60 . 
         [0271]      FIG. 53  shows a locking element line  400  which is firstly moved in perpendicular relationship to the through-travel direction T of the panels  300   a ,  300   b  and  300   c  to the panels  300   a ,  300   b  and  300   c  and, shortly before reaching the panels  300   a ,  300   b  and  300   c , is deflected in an arcuate configuration so that the locking element line  400  is brought up to an edge  500  of a panel  300   a , at a preferably acute angle α. 
         [0272]    There is provided a pressing device  600  having a pressing roller  600   a  which presses the front end of the locking element line  4  against the panel edge  500  of the panel  300   a . The panel edge  500  is provided with a receiving region N co-operating with a locking element  200 , as is known from the disclosure of WO 00/016654 (EP 1 415 056 B1), incorporated herein by reference. In the phase in which the pressing device  600  presses the locking element  200  against the panel edge  500 , a front part of the locking element line  400  is cut off and affords the separated locking element  200 . The diagrammatically illustrated separating station  700  is provided for that purpose. From the moment in time at which the locking element  200  is cut off the locking element line  400 , further transport of the locking element  200  is effected by frictional contact with the pressing roller  600   a . The pressing roller  600   a  is driven in such a way that its peripheral speed is synchronized with the transport speed of the panel  300   a  in the production installation A. 
         [0273]    In order to transport the locking element line  400  to the panel  300   a , the apparatus has an advance device  800  with advance rollers  800   a ,  800   b ,  800   c  and  800   d , which by way of frictional contact convert a rotational movement into a rectilinear transport movement of the locking element line  400 . The illustrated embodiment has two pairs of advance rollers, namely the advance roller pair  800   a / 800   b  and the advance roller pair  800   c / 800   d . All advance rollers  800   a ,  800   b ,  800   c  and  800   d  are driven by way of a pulling means  900 . The pulling means  900  is passed around the advance rollers  800   a ,  800   b ,  800   c  and  800   d  in such a way that the advance roller pair  800   a / 800   b  rotate in mutually opposite relationship. The same applies to the advance roller pair  800   c / 800   d . Each of the advance rollers  800   a ,  800   b ,  800   c  and  800   d  has substantially two regions, namely a region with a running surface  1000  for the pulling means  900  and a region with a friction surface  1100  for the transmission of movement to the locking element line  400 . The other two rollers of the advance device  800  involve a drive roller  1200  which is driven by a motor M 1  and a tensioning roller  1300  with which the desired tensile stress can be produced in the pulling means  900 . 
         [0274]    Provided in the region of the advance device  800  is a guide passage  1400  with which the locking element line  400  is held in a straight transport path. Particularly downstream of the advance device  800  in the direction of transport of the locking element line, it is necessary for the locking element line  400  to be stabilized with a guide because the locking element line  400  already buckles at low levels of pressure forces, because of its small cross-section. The locking element line  400  which is preferably made from plastic material, because of its small cross-section, can admittedly carry high tensile forces but, in comparison therewith, only low pressure forces, without a change in its shape. The locking element line  400  behaves mechanically like a tensile bar because it can carry high levels of tensile forces. It is unsuited as a compression bar because just low pressure forces already result in buckling or kinking thereof. 
         [0275]    Downstream of the advance device  800  in the transport direction, the locking element line  400  is guided in a conveyor passage  1500  arranged in an arcuate configuration. The conveyor passage  1500  opens into a further portion of conveyor passage which is to be referred as the transfer passage  1600 . The transfer passage  1600  has a gap  1600   c . The separating station  700  extends into that gap  1600   c . The separating station  700  cuts off a respective advanced front portion of the locking element line  400  as soon as the front portion is in contact with the pressing roller  600   a . That ensures that, after the separating operation, the transport movement is transmitted from the pressing roller  600   a  to the locking element  200  which has been cut off. 
         [0276]    When the separating station  700  carries out the separating operation and is in engagement with the locking element line  400 , the front portion of the locking element line  400  is braked by the engagement of the separating station  700  and can come to a complete halt. The separating station  700  is provided in the present embodiment with a cutting blade  700   a  which is arranged on a rotatable blade carrier  700   b . The engagement of the cutting blade  700   a  into the locking element line  400  provides that the transport movement of the locking element line  400  is braked in the region of the transfer passage  1600 . An exact separating cut is performed in that way. 
         [0277]    Subsequent separating operations thus take place cyclically. 
         [0278]    Although the separating station  700  operates cyclically the present embodiment does not provide that the advance device  800  is controlled in such a way that it produces a cyclic transport movement of the locking element line  400 . In terms of designing the apparatus  100 , it was assumed that the through-travel speed of the panels  300   a ,  300   b  and  300   c  in the production installation A is so high that, with the drive technology which is usual nowadays and which could be used for the advance device, it is not possible, or it is possible only at a high level of complication and expenditure, to implement a cyclic transport movement of the locking element line  400  at a suitably high cycle frequency. For that reason the advance device  800  of the present embodiment continuously drives the locking element line  400 . That is even during the period of time in which the separating station  700  is carrying out the separating operation and is braking the transport movement of the locking element line  400  in the transfer passage  1600 . 
         [0279]    The length of the locking element line  400  which is delivered by the advance device  800  during the separating operation passes into the conveyor passage  1500  which is disposed between the advance device  800  and the transfer passage  1600 . The conveyor passage  1500  is in the form of a buffer region P in which the delivered length of the locking element line  400  is put into intermediate storage during the separating operation. The buffer region P is provided with a storage spring  1700 . The storage spring  1700  is actuated by an outward buckling movement of the locking element line  400  in the buffer region P. In that way spring energy is stored in the storage spring  1700 . The spring energy progressively rises with increasing buckling and increasing length of the locking element line  400  which is in intermediate storage. The absorption of spring energy ends as soon as the separating operation is concluded and the separating station  700  opens the transfer passage  1600  again. At that moment the storage spring  1700  abruptly unleashes its spring energy and moves back into its arcuate initial position F 1 . In that situation the length of the conveyor passage is reduced because the outwardly buckled position F 2  of the conveyor passage  1500  is longer than the neutral arcuate initial position F 1  of the conveyor passage  1500 . The difference between the outwardly buckled length and the initial length of the conveyor passage corresponds to the length in intermediate storage, of the locking element line  400 , that length being transported with a jerk into the transfer passage  1600  by virtue of the unleashing of the spring energy of the storage spring  1700 . 
         [0280]    As shown in  FIG. 53  the storage spring  1700  is a cylindrical coil spring which is so arranged that the cylindrical interior of the coil spring forms a free conveyor cross-section  1500   a  of the conveyor passage. The storage spring  1700  is shown both in its initial position F 1  and also in an outwardly buckled position F 2 , in  FIG. 53 . 
         [0281]      FIG. 53  also shows a movement pickup D with which the travel speed of the panels  300   a ,  300   b  and  300   c  in the production installation A is detected. The movement pickup D detects any change in the travel speed and transmits that information to a control C. The control C is in turn connected to a drive motor M 1  for the advance device  800 , a drive motor M 2  for the pressing device  600  and the drive motor M 3  for the separating station. All those drives M 1  to M 3  are in that way automatically synchronized with the panel production installation. That provides that the apparatus can advantageously be operated without intervention in the installation control of the production installation A. In spite of the fact of being independent of the production installation the apparatus implants any change which occurs in the travel speed of the production installation A. The motors are servomotors which are desirable because of their positionally accurate controllability. It will be appreciated that alternatively other precise drives can be used. 
         [0282]      FIG. 54  shows the cross-section of the transfer passage  1600  in accordance with II-II in  FIG. 53 . The transfer passage  1600  is formed from three passage elements U 1 , U 2  and U 3  which are releasably connected together. It has a free cross-section which is almost coincident with the cross-section of the locking element line  400 . More specifically the transfer passage  1600  has a V-shaped cross-sectional region  1600   a , wherein an apex point  1600   b  of the V-shape is provided with a rounding. The transfer passage  1600  is arranged on a table  1800 . The rounding of the V-shaped cross-sectional region is on the side of the transfer passage  1600 , which is remote from the table  1800 . Provided at an end of the V-shaped cross-sectional region  1600   a  is a laterally projecting cross-sectional region  1600   d  into which an insertion tongue  400   a  of the locking element line  400  projects. In the present embodiment the insertion tongue  400   a  has two claw prongs  400   b , for which reason the projecting cross-sectional region  1600   d  of the transfer passage  1600  is provided with pointed spaces  1600   c  for the claw prongs  400   b  of the locking element line  400 . 
         [0283]    The position of the locking element line  400  shown in  FIG. 54  corresponds to that position in which the locking element  200  is pressed by the pressing device  600  against the edge  500  of the panel  300   a . In the present embodiment it is assumed that the panel production installation A transports the panels  300   a ,  300   b  and  300   c  with their rear side upwardly. In other words, the surface of the panels  300   a ,  300   b  and  300   c  which is shown in  FIG. 53  is the rear side of each of the panels. An oppositely disposed front side of the panels is usually provided with a decoration and is directed downwardly, that is to say towards the table  1800 , in the views in  FIGS. 53 and 54 . 
         [0284]    In order to clearly show how the pressing roller  600   a  of the pressing device  600  operates,  FIG. 54  diagrammatically indicates by a dash-dotted line the position in which the pressing roller  600   a  reaches the locking element  200  at the end of the transfer passage  1600  and causes a transport movement of the locking element  200  in frictionally locking relationship. 
         [0285]      FIG. 55  is a view in accordance with III-III in  FIG. 53 , namely showing a pair of advance rollers  800   a / 800   b . Each advance roller  800   a  and  800   b  has two regions, namely a running surface  1000  for a pulling means  900  and a friction surface  1100  for transmitting the transport movement to a locking element line  400 . The cross-section of the locking element line  400  is shown on an enlarged scale beneath the advance rollers  800   a  and  800   b  in order to clearly show the position in which the locking element line  400  is forced in between the two advance rollers  800   a  and  800   b . The insertion tongue  400   a  of the locking element line  400  is arranged in that position in parallel relationship with the axes of rotation a and b of the advance rollers  800   a  and  800   b  respectively. The overall width r of the locking element line  400 , which is to be measured between the two advance rollers  800   a  and  800   b , is less in the illustrated enlarged position than the overall height h of the locking element line  400 , which is to be measured in parallel relationship with the axis of the advance rollers  800   a  and  800   b . That position is desirable because the friction surfaces  1100  of the advance rollers  800   a  and  800   b  have regions which are of radii of different sizes from the respective axis of rotation a and b respectively of the advance rollers. The differing radii result in different peripheral speeds at different regions of a friction surface  1100 . That leads to a slippage between the friction surface  1100  and the locking element line  400  and thus wear of the advance rollers  800   a  and  800   b . In order to minimize the slippage, the locking element line  400  is arranged in that position between the advance rollers  800   a  and  800   b , in which the locking element line  400  is of the smallest dimension (r 1 &lt;h 1 ) in order thereby to minimize differences in the peripheral speed of the friction surface  1100  of a respective advance roller  800   a  and  800   b  respectively. 
         [0286]    In order to improve the frictionally locking transmission of the movement from the advance roller  800   a ,  800   b ,  800   c ,  800   d  to the locking element line  400 , it can be provided that at least one of the advance rollers of a pair thereof is provided with a roughened or microprofiled surface. 
         [0287]      FIG. 56  shows a plan view of the advance rollers  800   a  and  800   b  shown in  FIG. 55 . It will be seen that the running surfaces  1000  for the pulling means  900  are provided with a toothed configuration  1900 . The pulling means  900  of the present embodiment is therefore a toothed belt. The toothed belt is provided with teeth  900   a  and  900   b  on both sides, so that drive in opposite relationship of the advance rollers of a pair  800   a / 800   b  and  800   c / 800   d  respectively is possible by the belt passing around the advance rollers  800   a ,  800   b ,  800   c  and  800   d  in the manner shown in  FIG. 53 . 
         [0288]      FIG. 57  shows the cross-section through a guide passage  1400  in accordance with V-V in  FIG. 53 . The guide passage is formed from three passage elements K 1 , K 2  and K 3  which are releasably connected together. It will be clear that the locking element line  400  is enclosed in the guide passage  1400  in a position which is rotated through 90° with respect to the position of the locking element line  400  within the transfer passage  1600 . The  FIG. 57  position corresponds to the position in which the locking element line  400  passes through the advance device. As soon as the locking element line  400  has passed the guide passage  1400  and moves into the resilient conveyor passage  1500  shown in  FIG. 53 , the locking element line  400  is gradually twisted through an angle of 90° and passed into the transfer passage  1600 . 
         [0289]    The transfer passage  1600  is shown in  FIG. 58  in the same position on a table  1800 , as in  FIG. 54 . In addition  FIG. 58  shows a side view of the separating station  700 . The separating station  700  has a blade carrier  700   b , to which a single cutting blade  700   a  is mounted. In the present embodiment this involves a rotatable blade with which severing cuts are implemented to cut the locking element  200  off the locking element line  400 . 
         [0290]    A further part of the apparatus is shown in  FIGS. 59 and 60 .  FIG. 59  shows a plan view of the entire apparatus  100 . The Figure also indicates a transport path of the production installation A, by reference to the panels  300   a ,  300   b  and  300   c  which are transported in the through-passage direction T. A panel  300   a  has reached the pressing device  600  and is just being fitted with a locking element  200 . In addition the Figure indicates the advance device  800  and the guide passage  1400 .  FIG. 59  also shows a storage means  2000  for the locking element line  400 . In the preferred embodiment this involves a reel storage means  2000  in which a very long locking element line  400  is wound up. 
         [0291]    In the full state of the reel storage means  2000  it is of a high mass. It would therefore be inappropriate to use the advance device  800  to remove the locking element line  400  from the heavy reel storage means  2000  because in that situation the locking element line  400  could easily tear away. For that reason it is provided that the reel storage means  2000  itself is driven. A drive motor M 4  is provided for that purpose. The motor M 4  is desirably an exactly controllable servomotor. As can best be seen from  FIG. 60 , the locking element line  400  is not fed directly to the advance device  800  but is firstly guided into a loop-forming supply region  2100  in which the locking element line  400  forms at least one loop in the manner of a block-and-tackle arrangement. The illustrated embodiment involves three mutually juxtaposed loops  2200 ,  2300  and  2400 . In order to lay the locking element line  400  in three loops  2200 ,  2300  and  2400 , arranged on an upper fixed spindle  2500  are four storage rollers  2600  while arranged on a lower loose spindle  2700  are three storage rollers  2800 . The loose spindle can be moved up and down in a defined adjustment region  2900 , whereby the length of the loops  2200 ,  2300  and  2400  of the locking element line  400  is changed. A minimum value and a maximum value are predetermined for the loop length. Detectors Q are provided which detect the minimum and the maximum loop length and control the drive for the reel storage means  2000  in dependence on the loop length. When the minimum loop length is reached, the stored length of the locking element line  400  is excessively short and the reel storage means  2000  is set in operation in order to provide a make-up supply of locking element line. As soon as the maximum loop length is reached the drive of the reel storage means  2000  is automatically stopped. 
         [0292]    From the supply region  2100  the locking element line  400  is fed to the advance device  800 . As a result, in operation of the apparatus, the advance device  800  can always pull locking element line  400  out of the supply region  2100  and transport it to the pressing device  600 . 
         [0293]    Reference will also be made to  FIG. 59  to explain how panels are firstly conveyed through the production installation in their longitudinal direction L and are then transported displaced through an angle of 90° in a transverse direction to the pressing device  600 , namely in the passage direction T. The preceding conveying movement in the longitudinal direction L is effected at a given speed G 1 . If the production installation were operated in the passage direction T at a speed G 2 =G 1 , there would be large intermediate spaces between the panels  300   a ,  300   b  and  300   c . The speed G 2  in the passage direction T is therefore reduced so that the panels  300   a ,  300   b  and  300   c  are transported with a smaller spacing therebetween. The reduced speed G 2  is favorable in terms of applying the locking element  200  by machine. It will be appreciated that the problem arises only when the situation involves rectangular panels of different edge lengths in the longitudinal and transverse directions. The speeds and intermediate spacings in contrast do not differ if the panels are of a square shape. 
         [0294]    An alternative embodiment of an apparatus for mounting a locking element  200  to panels is shown in  FIG. 61 . It is first to be noted that the apparatus shown in  FIG. 61  is preferably provided with the reel storage means  2000  described with reference to  FIGS. 59 and 60 . 
         [0295]    The difference between the apparatus of  FIG. 53  and the apparatus of  FIG. 61  is that the separating station  700  which separates the locking element line  400  into individual locking elements  200  is arranged upstream of the advance device  800  in the transport direction of the locking element line  400 . The advance device in other respects does not differ from the advance device  800  shown in  FIG. 53 , the design configuration of which is thus incorporated into the embodiment shown in  FIG. 61 . There is provided a guide passage  1400  which guides the locking element line in the region of the advance device  800 . The guide passage  800  has a curve and merges into a transfer passage  1600  which leads to a pressing device  600 . It is provided that the position of the locking element in the region of the transfer passage  1600  corresponds to the position shown in  FIG. 54 . In the region of the advance device  800  the position of the locking element is rotated through 90° and corresponds to the position shown in  FIG. 57 . Provided between the guide passage  1400  and the transfer passage  1600  is a region in which the locking element line  400  experiences a twist. 
         [0296]    As shown in  FIG. 61  the guide passage  1400  or the transfer passage  1600  is filled with a row of locking elements  200  which have already been cut up. The transport movement of the locking elements  200  is guaranteed because a locking element  200  pushes forward the respective next locking element  200  within the narrow guide passage  1400 . 
         [0297]    It is advantageous in this embodiment that a separate transport operating in cyclic fashion can be provided for the separating station  700  and therefore it is possible to dispense with a buffer region between the advance device  800  and the pressing device  600 , with which intermediate storage of additional locking element line  400  has to be implemented, as in the embodiment shown in  FIG. 53 . 
       LIST OF REFERENCE CHARACTERS 
       [0000]    
       
           1  panel 
           2  panels 
           3  fixing system 
           4  hook connection 
           4 . 1  hook 
           4 . 2  hook 
           5  locking element 
           6  insertion portion 
           7  locking groove 
           8  locking portion 
           9  latching tongue 
           10  latching recess 
           11  end 
           12  contact surface 
           13  attachment 
           14  first limb 
           15  second limb 
           16  gap 
           17  inclined surface 
           18  anchoring means 
           19  projection 
           20  longitudinal side surface 
           21  tip 
           22  introduction aid 
           23  hook 
           24  slot 
           25  slot side 
           26  enlargement 
           27  bore 
           28  rounded portion 
         V/U laying surface 
         P force 
         h height 
         h 1  height 
         b width 
         r radius of curvature 
           30  panel 
           30   a  panel 
           30   b  panel 
           31  lower hook 
           31   a  hook end 
           31   b  opening 
           31   c  latching recess 
           31   d  holding gap 
           31   e  edge surface 
           31   f  bottom 
           31   g  clamping surface 
           32  upper hook 
           32   a  hook end 
           32   b  opening 
           32   c  latching recess 
           32   d  holding gap 
           32   e  edge surface 
           32   f  bottom 
           32   g  clamping surface 
           33  locking element 
           33   a  resilient latching tongue 
           33   b  clip portion 
           33   c  clamp portion/anchoring tongue 
           34  join 
           35  upper hook 
           36  panel 
           37  panel 
           38  panel 
           39  panel 
           40  panel 
           40   a  edge 
           40   b  edge 
           46  panel 
           47  panel 
           48  panel 
           49  panel 
           49   b  edge 
           50  panel 
           50   a  edge 
           50   b  edge 
           50   c  edge 
         E pressing-in tool 
         H 1  undercut surface 
         H 2  undercut surface 
         M dust chamber 
         P 1  first row of panels 
         P 2  second row of panels 
         R latching surface 
         S gap 
         U/V support surface 
         V 1  front row 
         V 2  following row 
           100  apparatus 
           200  locking element 
           200   a  front part 
           300   a  panel 
           300   b  panel 
           300   c  panel 
           400  locking element line 
           400   a  insertion tongue 
           400   b  claw prong 
           500  edge 
           600  pressing device 
           600   a  pressing roller 
           700  separating station 
           700   a  cutting blade 
           700   b  blade carrier 
           800  advance device 
           800   a  advance roller 
           800   b  advance roller 
           800   c  advance roller 
           800   d  advance roller 
           900  pulling means/toothed belt  900   a  tooth 
           900   b  tooth 
           1000  running surface 
           1100  friction surface 
           1200  drive roller 
           1300  tensioning roller 
           1400  guide passage 
           1500  conveyor passage 
           1500   a  conveyor cross-section 
           1600  transfer passage 
           1600   a  V-shaped cross-sectional region 
           1600   b  apex point 
           1600   c  gap 
           1600   d  projecting cross-sectional region 
           1700  storage spring 
           1800  table 
           1900  tooth configuration 
           2000  reel storage means 
           2100  supply region 
           2200  loop 
           2300  loop 
           2400  loop 
           2500  fixed spindle 
           2600  storage roller 
           2700  loose spindle 
           2800  storage roller 
           2900  adjustment region 
         α angle 
         A production installation 
         a axis of rotation 
         b axis of rotation 
         T through-travel direction 
         P buffer region 
         D movement pickup 
         C control 
         G 1  speed 
         G 2  speed 
         L longitudinal direction 
         M 1  drive motor 
         M 2  drive motor 
         M 3  drive motor 
         M 4  drive motor 
         N receiving region 
         r 1  overall width 
         h 1  overall height 
         Q detector 
         K 1  passage element 
         K 2  passage element 
         K 3  passage element 
         U 1  passage element 
         U 2  passage element 
         U 3  passage element

Summary:
The apparatus mounts a locking element into a groove in an edge of a panel. An advance device feeds a stream of locking elements to a pressing device which mounts the locking elements into the groove on the edge of the panel. The locking elements are fed from a line of locking elements stored on a reel. A separating device cuts the line of locking elements into individual locking elements. The separating device is positioned either upstream of the advancing device or immediately upstream of the pressing device. When the separating device is immediately upstream of the pressing device, a spring is used to flex the stream during the short stoppage when the separating device separates individual locking elements from the line of locking elements.