Abstract:
A method and apparatus for producing and/or machining panels. The apparatus includes a transport device for transporting a panel along a transport path and a machining device for machining the panel as it moves via the transport device. The transport device includes a plurality of positioning devices arranged one behind the other and spaced apart by a distance along the transport path. Each positioning device includes upper and lower abutment mechanisms arranged opposite one another and on opposite sides of a panel plane, and being spaced apart by a distance. An adjusting device is used for setting the distance between the upper and lower abutment mechanisms. An actuating arrangement is structured and arranged to actuate the adjusting device of at least two of the plurality of positioning devices. An arrangement is used for independently adjusting each of the upper and lower abutment mechanisms of at least one of the plurality of positioning devices.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a U.S. National Stage of International Patent Application No. PCT/EP2007/006732 filed Jul. 30, 2007 which published as WO 2008/014963 on Feb. 7, 2008, and claims priority of German Patent Application No. 10 2006 035 648.9 filed Jul. 31, 2006. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an apparatus for the production and/or machining of panels, comprising a transport device for transporting a panel along a transport device. The transport device has a plurality of positioning devices, which are arranged one behind the other at a distance apart along the transport path and which respectively comprise: an upper and a lower abutment mechanism, which lie opposite one another at a distance apart on both sides of a panel plane, and an adjusting device, with which the distance between the abutment mechanism can be set. 
         [0004]    2. Discussion of Background Information 
         [0005]    Apparatuses of this type are known in the field of the production or machining of panels and generally comprise an upper and a lower revolving continuous belt, the transporting strands of which are guided in parallel at a distance apart. Between the transporting strands of the continuous belts, panels to be transported are received in frictional engagement and moved on in the transport direction. Along the transport path of the continuous belts, machining devices are usually arranged, which subject the lateral edges of the panels to a machine cutting operation. As machining devices, various types of milling tools in particular can be used here, which on a longitudinal side or a transverse side of the panel form a groove and on the opposite longitudinal side a corresponding tongue. Panels of this type can be joined together in known tongue and groove connection to form, for example, a floor surface of a room. 
         [0006]    In order for the panels to be machined with constant quality, it is necessary to ensure a best possible relative positioning between the machining device and the panel to be machined. Thus, particularly where the machining device on the longitudinal side or transverse side of the panel is intended to mill a tongue or a groove, crucial importance is attached to the height position of the tongue or groove beneath the visible surface of the panels, in order to allow a total visible surface of the joined-together panels which is as even as possible. The known apparatuses of the type stated in the introduction therefore comprise said positioning devices having an upper and a lower abutment means and having the adjusting device for setting the distance between the abutment means. Depending on the number of machining devices and the length of the panels to be machined, a correspondingly large number of positioning devices along the transport device is necessary. In order to set the distance between the abutment means in accordance with a specific panel type, all positioning devices of the transport device must be individually adjusted. The traditional panel apparatuses which are used for different panel types with varying plate thickness in the range between about 6 and 12 mm, when the panel type to be machined is changed, thus require a big adjustment effort by the operator, combined with corresponding down times of the apparatus. 
       SUMMARY OF THE INVENTION 
       [0007]    The invention provides an apparatus of the type stated in the introduction, which reduces the adjustment effort, associated with a change of panel type to be machined, on the apparatus, and increases the economy of the apparatus. 
         [0008]    The invention also provides an apparatus of the type stated in the introduction, in which the adjusting devices of at least two positioning devices can be actuated simultaneously by way of a common actuating arrangement. 
         [0009]    With the measures according to the invention, it is possible, by a single adjusting operation, to simultaneously set a plurality of positioning devices to a desired set distance between their respective abutment mechanism. Where the panel type to be machined is changed to a panel type of larger or smaller plate thickness, the apparatus according to the invention thus allows a marked reduction in the working time needed by an operator for setting the apparatus and a reduction in the downtime of the apparatus which is necessary due to the setting operation. In the final analysis, a more economic overall operation of the apparatus is achieved. 
         [0010]    Where in the present description and the associated claims general position terms or phrases such as, say, “top”, “bottom”, “lateral” or “one behind the other”, etc., are used, then these relate to the design and the structure of an apparatus in which the panels are usually transported horizontally, i.e., in such a way that their visible surfaces lie mainly in a horizontal plane. Of course, the subject of the invention also embraces apparatuses in which panels are transported in a different orientation, in which case the above-stated position terms or phrases then relate to the visible surface of the panels to be transported as the imaginary horizontal plane. 
         [0011]    In a preferred embodiment of the invention, the actuating arrangement comprises a connecting rod arrangement. Such a connecting rod arrangement offers the possibility of a constructively simple, yet reliable mechanical motional coupling of the adjusting motions of the individual associated positioning devices. Particularly advantageously, it is then possible to interconnect all adjusting devices assigned to the actuating arrangement via a common connecting rod, so that then, for a plurality of positioning devices, only a single connecting rod is necessary. In this case, each of the adjusting devices preferably has a connecting rod coupling for the coupling to the common connecting rod. 
         [0012]    In an advantageous refinement of the embodiment using the connecting rod arrangement, it can be provided that the connecting rod is a threaded rod, which, at least in portions assigned to the adjusting devices, has a thread, and that the connecting rod couplings have mating threads, which are in engagement with the threaded rod. Through the use of a threaded rod in interaction with a mating thread of the connecting rod couplings, a rotary adjusting motion of the threaded rod, which can be performed in a simple manner by an operator or an actuator, can be converted into a translatory adjusting motion of the associated adjusting devices. In this case, the step-down effect of the thread engagement, in particular, can be utilized to reduce the amount of effort necessary for the adjustment and to carry out an adjustment of the distance between the abutment mechanism with great precision. The pitch of the used threads can be chosen in accordance with such requirements. 
         [0013]    In order also to be able along the transport path of the transport device to bridge a greater distance by the connecting rod arrangement, or to be able to connect a desired number of positioning devices to a common connecting rod in a constructively simple manner, in a further embodiment of the invention it is also proposed that the connecting rod runs substantially parallel to the transport path and that each of the adjusting devices assigned to the actuating arrangement has a motion converting device, which converts the adjusting motion of the connecting rod coupling, which is substantially parallel to the transport path, into an adjusting motion orthogonal to the panel plane in order to displace at least one of the abutment mechanism. 
         [0014]    In a further embodiment of the invention, it can be provided that, in at least one of the adjusting devices assigned to the actuating arrangement, each of the two abutment mechanism has an own adjusting mechanism, the two adjusting mechanism being able to be actuated independently of each other. In an apparatus of this design, not only can the distance between the abutment mechanism be tailored to the plate thickness of a specific panel type, but also the absolute height of the panel positioned by the positioning devices, i.e. the vertical position of the panel in relation to the machining device, can be altered per se. 
         [0015]    If each of the two abutment mechanism has its own adjusting mechanism, then it can be provided that only one of the two adjusting mechanism can be actuated via the common connecting rod. Thus, the common actuating arrangement can be used, for instance, to adjust the position of the upper abutment mechanism so as to adapt to a desired panel type of specific plate thickness, while the lower abutment mechanism can be set for the less frequently required alteration of the vertical position of the panel individually on each positioning device. Alternatively, however, just the lower adjusting mechanism, can also be adjustable by the common actuating arrangement, or the common actuating arrangement is configured to move both abutment mechanism simultaneously. 
         [0016]    In an advantageous refinement, each of the above-stated embodiments can be designed such that at least one of the adjusting devices assigned to the actuating arrangement also has a single-adjustment device, with which the distance between the abutment mechanism of this adjusting device is adjustable independently of the distances between the abutment mechanism of other adjusting devices. In this way, differences between the positioning devices assigned to the common actuating arrangement device, which arise due to production tolerances or due to wear, can be compensated accordingly. In addition, certain differences between the operating characteristics of the respective motion converting devices of the positioning devices and between the individual connecting rod couplings of the positioning devices cannot be precluded, so that said single-adjustment device, in this case also, can be advantageously used for improving the positioning accuracy of the apparatus. 
         [0017]    The aforementioned single-adjustment devices can be configured in a constructively simple yet very reliable manner such that at least one of the adjusting devices assigned to the actuating arrangement has a first slide, which is movable substantially orthogonally to the panel plane and is connected to the motion converting device, and a second slide, which is movable substantially orthogonally to the panel plane and to or on which at least one of the abutment mechanism is coupled or formed, a distance between the first slide and the second slide in the direction orthogonal to the panel plane being adjustable by the single-adjustment device. 
         [0018]    In a further embodiment of the invention, it is proposed that at least one of the adjusting devices assigned to the actuating arrangement also has a pretensioning device, in particular a spring arrangement, by way of which the upper and/or the lower abutment mechanism can be elastically pretensioned with a specific pretensioning force in the direction of a diminution of the distance between the abutment mechanism, in which case the pretensioning force can then be adjustable by a pretensioning adjusting device of the adjusting device. In this embodiment, a panel to be transported and positioned can be secured with a defined pretensioning force in frictional engagement between the abutment mechanism, the pretensioning force being able to be adapted, where appropriate, to different panel types or to a desired positioning accuracy. 
         [0019]    Regarding the technical realization of the above-described embodiments, it is particularly envisaged that the motion converting device and/or, where appropriate, the single-adjustment device and/or, where appropriate, the pretensioning adjusting device comprise(s) a control cam mechanism, in particular a sliding wedge mechanism or a link mechanism. Such control cam mechanisms work particularly reliably and can be designed and produced in a problem-free manner according to the stated requirements with regard to force transmission and motional direction. 
         [0020]    The invention also provides for an apparatus for producing and/or machining panels, which comprises a transport device for transporting a panel along a transport path, a machining device for machining the panel as it moves via the transport device, the transport device comprising a plurality of positioning devices arranged one behind the other and spaced apart by a distance along the transport path, each positioning device comprising upper and lower abutment mechanisms arranged opposite one another and on opposite sides of a panel plane, and being spaced apart by a distance and an adjusting device for setting the distance between the upper and lower abutment mechanisms, an actuating arrangement structured and arranged to actuate the adjusting device of at least two of the plurality of positioning devices, and an arrangement for independently adjusting each of the upper and lower abutment mechanisms of at least one of the plurality of positioning devices. 
         [0021]    The at least one positioning device having the arrangement for independently adjusting each of the upper and lower abutment mechanisms may be one of coupled to the actuating arrangement and activatable by the actuating arrangement. The arrangement for independently adjusting each of the upper and lower abutment mechanisms may comprise a first device for independently adjusting a position of the upper abutment mechanism and a second device for independently adjusting a position of the lower abutment mechanism. The actuating arrangement may comprise a connecting rod arrangement. The connecting rod arrangement may comprise a threaded rod. Each of the adjusting devices may be one of coupled to the actuating arrangement and activatable by the actuating arrangement. 
         [0022]    The apparatus may further comprise a coupling connecting each of the adjusting devices to the actuating arrangement. Each of the plurality of positioning devices may be one of coupled to the actuating arrangement and activatable by the actuating arrangement. 
         [0023]    The actuating arrangement may be coupled to at least two of the adjusting devices of the plurality of positioning devices via a common connecting rod. The actuating arrangement may be coupled to each of the adjusting devices of the plurality of positioning devices via a common connecting rod. The actuating arrangement may be coupled to at least two of the adjusting devices of the plurality of positioning devices via a threaded connecting rod and threaded couplings. 
         [0024]    The actuating arrangement may run substantially parallel to the transport path. The apparatus may further comprise at least one motion converting device adapted to cause at least one of the upper and lower abutment mechanisms to move orthogonal to the panel plane upon actuation of the actuating arrangement. 
         [0025]    One of each of the plurality of positioning devices further comprises at least one motion converting device adapted to cause at least one of the upper and lower abutment mechanisms to move orthogonal to the panel plane upon actuation of the actuating arrangement and each of the plurality of positioning devices further comprises an arrangement adapted to cause at least one of the upper and lower abutment mechanisms to move orthogonal to the panel plane upon actuation of the actuating arrangement. 
         [0026]    The apparatus may further comprises one of a single-adjustment device adapted to adjust a distance between at least one of the upper and lower abutment mechanisms and the adjusting device, wherein the distance is adjustable independently of the distance between another of the at least one of the upper and lower abutment mechanisms and another adjusting device and an arrangement adapted to adjust a distance between at least one of the upper and lower abutment mechanisms and the adjusting device of one of the plurality of positioning devices, wherein the distance is adjustable independently of the distance between at least one of the upper and lower abutment mechanisms and the adjusting device of another of the plurality of positioning devices and a first slide movable substantially orthogonally to the panel plane, a second slide movable substantially orthogonally to the panel plane and coupled to at least one of the upper and lower abutment mechanisms, and at least one motion converting device connected to the first slide and being adapted to cause at least one of the upper and lower abutment mechanisms to move orthogonal to the panel plane upon actuation of the actuating arrangement, and a first slide movable substantially orthogonally to the panel plane, at least one motion converting device connected to the first slide and being adapted to cause at least one of the upper and lower abutment mechanisms to move orthogonal to the panel plane upon actuation of the actuating arrangement, a second slide movable substantially orthogonally to the panel plane, and a single-adjustment device coupled to the second slide and being adapted to adjust a distance between at least one of the upper and lower abutment mechanisms and the adjusting device, wherein the distance is adjustable. 
         [0027]    The apparatus may further comprise at least one pretensioning device adapted to elastically pretension at least one of the upper and lower abutment mechanisms, whereby one of the upper and lower abutment mechanisms is biased towards another of the upper and lower abutment mechanisms. A biasing force may be adjustable via a pretensioning adjusting device. The apparatus may further comprise a control cam mechanism arranged on at least one of at least one motion converting device, a single-adjustment device, and a pretensioning adjusting device. The control cam mechanism may be one of a sliding wedge mechanism and a link mechanism. 
         [0028]    The invention also provides for an apparatus for producing and/or machining panels, comprising a transport device for transporting a panel along a transport path, a machining device for machining the panel as it moves via the transport device, the transport device comprising a plurality of positioning devices arranged one behind the other and spaced apart by a distance along the transport path, each positioning device comprising upper and lower abutment mechanisms arranged opposite one another and on opposite sides of a panel plane, and being spaced apart by a distance and an adjusting device for setting the distance between the upper and lower abutment mechanisms, an actuating arrangement structured and arranged to actuate each of the adjusting devices of the plurality of positioning devices, and an arrangement for independently adjusting the upper and lower abutment mechanisms of each of the plurality of positioning devices. 
         [0029]    The invention also provides for a method of using an apparatus for producing and/or machining panels, comprising transporting via a transport device a panel along a transport path, wherein the transport device comprises a plurality of positioning devices arranged one behind the other and spaced apart by a distance along a transport path, machining the panel via a machining device as it moves via the transport device, setting a distance via an adjusting device between upper and lower abutment mechanism of at least one the plurality of positioning devices, wherein the upper and lower abutment mechanisms are arranged opposite one another and on opposite sides of a panel plane, and are spaced apart by the distance, actuating via an actuating arrangement each of the adjusting devices of the plurality of positioning devices, and independently adjusting the upper and lower abutment mechanisms of each of the plurality of positioning devices. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0030]    The present invention is explained in greater detail below with reference to a preferred embodiment, with reference to the appended drawings. 
           [0031]      FIG. 1  is a basic representation of an inventive apparatus according to a first embodiment, in side view. 
           [0032]      FIG. 2  shows a front view of a positioning device of the transport device shown in  FIG. 1 . 
           [0033]      FIG. 3  shows a rear view of the positioning device represented in  FIG. 2 . 
           [0034]      FIG. 4  shows a side view of the positioning device represented in  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0035]    In  FIG. 1 , an apparatus for the machining of panels is illustrated in general terms by  10 . As machining devices, the apparatus  10  comprises three milling tools  12 , which, in  FIG. 1 , are shown purely schematically as rectangles. By way of the milling tools  12 , the panels are intended to be machined such that on their one longitudinal side a groove and on their opposite longitudinal side a tongue, corresponding to the geometry of the groove, is formed. 
         [0036]    In order to feed the panels to be machined to the milling tools  12 , the apparatus  10  has a transport apparatus having an upper conveyor belt  14  and a lower conveyor belt  16 . Both conveyor belts  14  and  16  respectively have a continuous belt  18 , which respectively revolve around deflection pulleys  20  disposed at the ends of the conveyor belts  14  and  16 . Via mountings  22 , the deflection pulleys  20  are each attached rotatably to a frame  24 , the two frames  24  of the upper and the lower conveyor belt  14  and  16  being fastened to a common support structure  26 , which supports the apparatus  10  fixedly on the ground B. 
         [0037]    As a result of the support structure  26 , the two conveyor belts  14  and  16  are held in a fixed relative position to one another, in which they run substantially parallel to each other, to be precise such that a conveyor strand  28  formed by a lower strand  28  of the upper conveyor belt  14  bears against a conveyor strand  30  formed by an upper strand  30  of the lower conveyor belt  16 , or has from this latter conveyor strand a uniform distance roughly corresponding to the plate thickness of a panel, or less. 
         [0038]    The upper conveyor belt  14  and the lower conveyor belt  16  thus lie opposite one another on both sides of a horizontal panel plane P and can thus receive a panel between the conveyor strand  28  of the upper conveyor belt  14  and the conveyor strand  30  of the lower conveyor belt  16  and transport it in a transport direction T, the panel remaining aligned substantially in the panel plane P throughout its entire transport through the apparatus  10 . 
         [0039]    Although a certain positioning of the transported panels already takes place as a result of the above-described reception of the panels between the upper conveyor belt  14  and the lower conveyor belt  16 , for the machining of the panels at the milling tools  12  a more accurate positioning of the panels, particularly in the vertical direction, is still necessary. In the embodiment shown in  FIG. 1 , this vertical positioning is taken care of by three positioning devices  32  arranged one behind the other along the transport direction T, which in  FIG. 1  are likewise represented purely schematically. The positioning devices  32  each have an upper abutment mechanism  34  and a lower abutment mechanism  36 , which are arranged at a distance apart in order to receive a panel between them. 
         [0040]    In order to be able to use the apparatus  10  for use with panel types of different plate thickness, the distance between the upper and lower abutment mechanisms  34 ,  36  is adjustable via an adjusting device  38 , which in  FIG. 1  is likewise only indicated. 
         [0041]    Above the positioning devices  32 , a threaded rod  40  runs parallel to the transport direction T and extends over the regions of all positioning devices  32  along a large part of the length of the upper conveyor belt  14 . At its ends, the threaded rod  40  is respectively mounted in a rotatable, yet axially non-displaceable manner, in bearing portions  42  fastened to the frame  24  of the upper conveyor belt  14 . The threaded rod  40  is also acted upon by an actuating device  44  for the rotary actuation of the threaded shaft  40 , which in  FIG. 1  is illustrated schematically by a crank  44  attached to one end of the threaded rod  14 . 
         [0042]    As can be seen in  FIG. 1 , the adjusting devices  38  of all three positioning devices  32  are each motionally coupled to the threaded rod  40 , so that a rotary motion of the threaded rod  40  is converted by the actuating device  44  in each of the positioning devices  32  into an adjusting motion of the adjusting devices  38 , which adjusting motion will be described below. 
         [0043]      FIGS. 2 ,  3  and  4  show detailed views of one of the three positioning devices  32 . A segment of the threaded rod  40  is indicated with dashed lines, the rotary motion of which is converted into an adjusting motion of the adjusting device  38  for altering a distance “h” between the upper abutment mechanism  34  and the lower abutment mechanism  36 . In the embodiment shown, the adjusting device  38  converts the rotary motion of the threaded rod  40  into a vertical displacement motion of the upper abutment mechanism  34 . 
         [0044]    To this end, the threaded rod  40  has mounted on it a threaded block  46 , which has an internal thread corresponding to the external thread of the threaded rod  40 , so that, upon a rotation of the threaded rod  40  mounted non-displaceably in the axial direction, it realizes a displacement in the transport direction T or in a direction opposite thereto. 
         [0045]    A pin  48  of the threaded block  46  is inserted displaceably into an elongated recess  52  of a rocker  50 , which is mounted rotatably on a fixed frame  54  of the positioning device  32 . The rocker  50  has at its opposite end a second elongated recess  56 , in which a pin  58  of a slide bar  60  is inserted. The slide bar  60  is mounted on the frame  54  on two displacement bearings  61  such that it can only move to and fro parallel to the transport direction T. 
         [0046]    Configured on or fastened to the slide bar  60  are two further pins  62 , which engage in slots  64 , inclined relative to the horizontal plane, of a first slide  66 . The first slide  66  is guided on the frame  54  such that it can be displaced only upward or downward in the vertical direction. Upon a displacement of the slide bar  60  parallel to the transport direction T, the pins  62  of the slide bar  60  accordingly run along the oblique slots  64  and thus displace the first slide  66  in the vertical direction. 
         [0047]    In a recess  68  of the first slide  66  in the lower region of the first slide  66 , a second slide  70  is guided in a vertically displaceable manner. A distance between the first slide  66  and the second slide  70  in the vertical direction is fixed by an adjusting wedge  72 , which is disposed in the vertical direction between the first and the second slide  66  and  70 . The adjusting wedge  72  has on its bottom side wedge surfaces  74 , which run obliquely to the horizontal plane and bear against corresponding wedge surfaces  76  on the top side of the second slide  70 . An adjusting screw  78  mounted on the frame  54  moves the adjusting wedge  72  to or fro parallel to the transport direction T, so that the wedge surfaces  74 ,  76  slide one against the other, whereby the distance between the first slide  66  and the second slide  70  is adjusted. 
         [0048]    Similarly to the first slide  66 , the second slide  70  also has a recess  80  in its lower region, the recess  80  having at its lower end an inwardly projecting flange  82 . Against this inner flange  82  can rest an outer flange  84  of an approximately T-shaped coupling portion  86 , which is integrally connected to the upper abutment mechanism  34 . A contact between the outer flange  84  of the coupling portion  86  and the inner flange  82  of the second slide  70  defines a maximum distance between the second slide  70  and the upper abutment mechanism  34  held in a vertically displaceable manner thereon. 
         [0049]    The vertical displacement of the coupling portion  86  of the upper abutment mechanism  34  in the second slide  70  is subject to a pretensioning by a tensioning device  88 , which in  FIG. 2  is symbolized by two springs  88 . The tensioning device  88  is supported, on the one hand, against the coupling portion  86  and, on the other hand, against a third slide  90  and pretensions the coupling portion  86  in the direction of a contact between the outer flange  84  of the coupling portion  86  and the inner flange  82  of the second slide  70 . 
         [0050]    The third slide  90  is likewise guided in a vertically displaceable manner in the recess  80  of the second slide bar  70  so as to be able to alter the pretensioning of the tensioning device  88 . For this pretensioning adjusting motion, between the third slide  90  and the second slide  70  there is arranged a pretensioning adjusting wedge  92 , which, similarly to the working principle of the above-described adjusting wedge  72 , is displaceable parallel to the transport direction T and, by way of oblique wedge surfaces, sliding one against the other, on the top side of the third slide  90  and the bottom side of the pretensioning adjusting wedge  92 , makes the vertical distance between the second slide  70  and the third slide  90  adjustable. 
         [0051]    The motion of the pretensioning adjusting wedge  92  which is necessary for the pretensioning adjustment is effected with the use of a pretensioning setscrew  94  mounted on the frame  54 . 
         [0052]    In addition to the adjustment of the height or pretensioning force of the upper abutment mechanism, the positioning device shown in  FIG. 2  additionally offers the possibility of adjusting the vertical position of the lower abutment mechanism  36  and of thereby adjusting the absolute vertical position of a panel positioned in the positioning device  32 . For this purpose, the lower abutment mechanism  36  is guided in a vertically displaceable manner on the frame  54 , a vertical distance between the second abutment mechanism  36  and a lower portion  55  of the frame  54  being determined by an adjusting wedge  96 . The adjusting wedge  96  is disposed between the lower abutment mechanism  36  and the lower portion  55  of the frame  54  and has on its top side wedge surfaces  98 , which run obliquely to the horizontal plane and bear against corresponding oblique wedge surfaces  100  on the bottom side of the lower abutment mechanism  36 . Upon a displacement of the adjusting wedge  96  by a setscrew  102  in a direction parallel to the transport direction T, the wedge surfaces  98 ,  100  slide one against the other and correspondingly displace the lower abutment mechanism  36  in the vertical direction. 
         [0053]    The working method of the apparatus  10  is discussed briefly below. In order to prepare the apparatus  10  for the machining of panels of a specific plate thickness, the actuating device  44  is started up and rotates the threaded rod  40  by a specific amount. As an example, the hypothesis is adopted that the apparatus  10  is due to be adjusted from the machining of a thicker panel type to the machining of a thinner panel type. In dependence on the pitch of the thread of the threaded rod  40 , the threaded rod  40  is then rotated such that the threaded block  46  shifts a specific distance to the right in  FIG. 2 . The rightward motion of the threaded block  46  is converted by the rocker  50  into a leftward displacement of the slide bar  60 , and the resultant leftward displacement of the pins  62  causes a downward motion of the slots  64  and thus of the first slide  66 . This downward motion of the slide  66  is then transmitted via the second slide  70 , the third slide  90 , the tensioning device  88  and the coupling portion  86  finally to the upper abutment mechanism  34 , which is then likewise displaced downward by the desired amount. 
         [0054]    It is here assumed that the upper abutment mechanism  34  is in the unloaded state, i.e. there is no panel inserted between the abutment mechanism  34 ,  36 , so that the tensioning device  88  holds the outer flange  84  of the coupling portion  86  in contact with the inner flange  82  of the second slide  70 . The distance “h” between the upper and lower abutment mechanisms  34 ,  36 , which is thereby adjusted in the unloaded state, is in practice set slightly smaller than the plate thickness of the panels to be positioned, so that the tensioning device  88  can generate a predetermined contact pressure with which the upper abutment mechanism  34  is pressed against the panel. 
         [0055]    In the manner described, the adjusting devices  38  of all positioning devices  32  of the apparatus  10  can be simultaneously adjusted, by rotation of the common threaded rod  40 , to a new panel type of smaller plate thickness. The correspondingly reverse adjustment by rotation of the threaded rod  40  in the opposite direction can be realized if the apparatus  10  is due to be prepared for the machining of thicker panels. 
         [0056]    If, between the individual positioning devices  32 , variances in the respective distance “h” should arise as a result of production tolerances, temperature differences, wear or the like, each of the adjusting devices can also from time to time be individually readjusted by the adjusting screw  78  in the manner described. Similarly, for each positioning device  32 , the pretensioning force of the tensioning device  88  can be tuned by adjustment of the pretensioning setscrew  94 , for example to particular requirements of the machining device  12  disposed in this region. 
         [0057]    The facility to adjust the pretensioning of the tensioning device  88  also offers the advantage that, in the event of wear to the continuous belt  18  of the upper conveyor belt  14 , the positioning device  32  can be adapted to this wear by adjustment of the pretensioning force, without an ensuing adjustment of the first slide  66  or second slide  70 , and thus an adjustment of the distance “h” between the upper and lower abutment mechanisms  34 ,  36  in the unloaded state. The drawback which arises in traditional apparatuses, namely that, if the apparatus is adapted to the wear on the upper belt, the setting of the distance “h” also changes, resulting in a change of pressure exerted upon the material by the upper abutment mechanism  34 , which in these apparatuses of the prior art can lead to scratching or damaging of the panels, can thus be avoided.