Patent Publication Number: US-10786887-B2

Title: Holding apparatus for holding a pipe in a rotatable manner to be machined

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the National Stage of PCT/DE2015/100259 filed on Jun. 26, 2015, which claims priority under 35 U.S.C. § 119 of German Application No. 10 2014 109 150.7 filed on Jun. 30, 2014, the disclosures of which are incorporated by reference. The international application under PCT article 21(2) was not published in English. 
     BACKGROUND 
     The invention relates to a holding apparatus for holding a work piece to be machined, having a round and/or tubular cross-section, in such a manner that in the held state, the work piece can be rotated relative to the holding apparatus. 
     Such a holding apparatus can be used, for example, as a constituent of a circular saw for pipes. The pipe to be machined is fixed in place in such a manner that a rotational movement of the pipe relative to the holding apparatus is permitted for machining. Cutting through the pipe is carried out in that a saw unit having a saw blade is pressed against the outer circumference of the pipe, and then the entire circular saw for pipes is moved around the pipe, wherein the saw unit remains in active contact with the pipe. 
     SUMMARY 
     The holding apparatus usually has two clamping arms that are held on a base part so as to pivot, for gripping the pipe to be machined, which arms engage around at least part of the outside circumference of the pipe and exert a clamping force on the pipe. An adjustment mechanism is usually provided for moving the clamping arms in the direction toward the pipe. 
     An embodiment of the invention is based on the task of technically optimizing a holding apparatus having the characteristics stated initially. In particular, a holding apparatus having the characteristics stated initially is supposed to be made available, which apparatus allows fast release of the clamping arms out of clamping engagement on the work piece to be machined. In particular, a holding apparatus having the characteristics mentioned initially is supposed to be made available, the adjustment mechanism of which apparatus has a compact construction with regard to the clamping arms, and requires relatively little space for performing possible clamping movements. 
     This task is accomplished with a holding apparatus that has the characteristics of claim  1 . Furthermore, the task is accomplished with holding apparatus that has the characteristics of claim  3 . Advantageous embodiments of the invention are evident from the dependent claims, the following description, and the figures. 
     A holding apparatus for holding a work piece to be machined, the work piece having a round and/or tubular cross-section, in such a manner that in the held state, the work piece can be rotated relative to the holding apparatus, has at least two clamping arms mounted on a base part, by means of which arms a clamping force can be exerted on the work piece. In particular, at least part of the outside circumference surface of the work piece can be grasped by the clamping arms. In particular, the clamping force acts on the work piece as a holding force. 
     The holding apparatus furthermore has an adjustment mechanism for the clamping arms, the mechanism having a threaded spindle that can be manually activated and/or activated by means of an auxiliary force, which spindle is releasably in threaded engagement with a threaded part, such as a spindle nut, for example, wherein the threaded part is held on a component of the holding apparatus, particularly on the base part, so as to be fixed in place or fixed on the housing with reference to the base part, in the axial direction of the threaded spindle. In particular, the threaded spindle and the threaded part are releasably in threaded engagement with one another in the radial direction with reference to the threaded spindle. 
     In this way, a spindle drive is implemented for activation of the adjustment mechanism, which drive allows quick adjustment of the threaded spindle relative to the threaded part, in the axial direction. For this purpose, the threaded spindle is releasably held in threaded engagement with the threaded part. This is because the function of the spindle drive, as a screw gear mechanism, is put out of force by release of the threaded part from the threaded engagement with the threaded spindle, and the threaded spindle can be freely moved relative to the threaded part, in the axial direction. In this respect, this measure allows overly rapid release of the clamping arms from the clamping engagement on the work piece to be machined. 
     Supplementally or alternatively to this, the adjustment mechanism can have at least two drivers guided in straight manner. These drivers can drive clamping arms wherein, by means of the movements of these drivers, the clamping arms can be pivoted or are pivoted toward one another, if applicable by way of at least one intermediate element, such as, for example, an intermediate brace. Viewed in the direction transverse to the movement direction of the drivers, the drivers are disposed to lie one behind the other. 
     In this way, the adjustment mechanism of the holding apparatus is implemented in a technically simple manner. This is because adjustment of the clamping arms is brought about by means of a simple straight-line movement of the drivers. The drivers are preferably guided in a straight line by means of a corresponding guide, in order to guarantee that the drivers remain on their intended movement path. 
     Furthermore, the adjustment mechanism is configured to have a compact construction. This is because the expanse of the adjustment mechanism in the movement direction of the drivers is less, since the drivers lie one behind the other in the direction transverse to their movement direction, than if the drivers were to lie on a common line in the direction transverse to their movement direction. Also, the space requirement of the adjustment mechanism for performing the adjustment movement of the clamping arms is relatively slight. This is because in order to achieve a maximal adjustment, the drivers do not have to be pushed as far apart from one another than if the drivers were to lie on a common line in the direction transverse to their movement direction. 
     It can be provided that the drivers are mounted to be movable in the direction of the movement of the clamping arms, particularly that they are mounted to be essentially translationally movable. This measure also aims at configuring the adjustment mechanism so as to have a compact construction. This is because in this way, the drivers essentially move in the plane spanned by the movement of the clamping arms. For example, the drivers can be movable in such a manner that the movement of the drivers essentially takes place transverse to the axis of rotation of the clamping arms. 
     It is possible for the drivers, viewed transverse to their movement direction, to be arranged offset from one another. In this way, the drivers span a further distance in their movement direction, without the respective driver itself having a length over this distance. By means of the offset arrangement of the drivers, it is therefore possible, in simple manner and with a relatively small length expanse of the respective driver, to achieve a relatively great longitudinal expanse as a whole, by means of which coupling to the clamping arms, which are disposed at a distance from one another, is facilitated. This is because the distance between the coupling points of the respective clamping arm and driver is preferably dimensioned in such a manner that the work piece can be accommodated between them. 
     Of course, the drivers can also be disposed so as to essentially align with one another, viewed transverse to their movement direction. 
     It is possible that the drivers overlap, viewed in their movement direction. In this way, the drivers can be movement-coupled with one another in a technically simple manner, so that, for example, in the case of a movement of the one driver, movement of the other driver is also brought about at the same time. For example, the overlapping region can be utilized by a gear mechanism, in order to act both on the one driver and also on the other driver. 
     A possible embodiment of the invention consists in that the drivers are movement-coupled with one another by way of a reversal gear mechanism. In this way, it is guaranteed that the drivers can be moved both in the one direction and also in the other direction, in their movement guided in a straight line, and that one and the same gear mechanism, namely the reversal gear mechanism, is used for this purpose. By means of the reversal gear mechanism, it can be provided that the drivers can be moved toward one another and can also be moved away from one another. 
     According to a further embodiment of the invention, it is provided that the drivers each have gear-tooth systems, and, between them, a gear wheel that meshes with the gear-tooth systems, particularly a rotatable gear wheel, is provided. In particular, the gear wheel is held to be fixed in place or fixed on the housing with reference to the base part. In this way, movement coupling of the drivers with one another is implemented in a technically simple manner. 
     Alternatively to the gear wheel, a friction wheel can also be provided, which is disposed between the drivers and stands in active contact with a counter-friction surface of one of the drivers, in each instance. In particular, the friction wheel is fixed in place or fixed on the housing, with reference to the base part. 
     It can be provided that the gear-tooth systems or counter-friction surfaces are disposed laterally on the drivers and that the axis of rotation of the gear wheel or friction wheel lies essentially transverse to the movement direction of the drivers. In this way, movement coupling of the drivers can be implemented in a technically simple manner, by means of the gear wheel or friction wheel, if the drivers are disposed to lie one behind the other, viewed transverse to their movement direction, and lie in the region of the base part, so that the gear wheel or friction wheel can be mounted on the base part. 
     For example, it can be provided that at least one of the drivers has a gear rack or is configured as a gear rack. This measure is also aimed at implementing the movement coupling of the drivers in as technically simple a manner as possible. 
     According to a further embodiment of the invention, it is provided that the threaded spindle is connected to act with one of the drivers, in the axial direction, particularly that it engages on one of the drivers and/or is mounted on it, particularly mounted on it so as to rotate. In this way, transfer of the adjustment movement predetermined by the threaded spindle to the clamping arms is made possible in a technically simple manner. For this purpose, all that is required is coupling of the threaded spindle, in the direction of its longitudinal axis, with one of the drivers, if necessary by way of an intermediate element. 
     It is possible that the threaded part can be displaced in the radial direction with reference to the threaded spindle, particularly that is can be displaced in a compulsorily guided manner, and can be brought out of threaded engagement by means of displacement in the radial direction. In this way, the threaded part can be brought out of engagement with the threaded spindle in technical simple manner. Releasing the threaded part from the threaded engagement with the threaded spindle, and also bringing the threaded part into threaded engagement with the threaded spindle, can be carried out in a operationally reliable and easily handled manner, in that the threaded part is compulsorily guided. 
     In simple manner, the threaded part can be brought out of engagement with the threaded spindle if the threaded part engages around the threaded spindle over a circumference section that extends at most over half the circumference of the threaded spindle. Then, the threaded part is present only in a small section, particularly a circular section, and can be released from the threaded spindle by means of radial displacement. 
     According to a further embodiment of the invention, an activation element that can be manually activated and/or activated by means of an auxiliary force is provided. This activation element through the auxiliary force, can bring the threaded part out of threaded engagement with the threaded spindle, counter to the force of a spring element, for example. In this way, the threaded part can be released from the threaded engagement with the threaded spindle, in an easy to handle manner. 
     If a spring element is provided, counter to the force of which the activation element is activated to bring the threaded part out of threaded engagement with the threaded spindle, the threaded part is automatically brought back into the threaded engagement by means of the reset force of the spring element when activation of the activation element has ended. For example, the activation element can be configured as a pressure element, particularly a push button, which brings the threaded part out of threaded engagement with the threaded spindle, counter to the force of a spring element, by means of a pressure force exerted by a user. 
     It is possible that the activation element is firmly connected with the threaded part by way of at least one connection element; in particular, the connection element should be displaceably guided on the component on which it is fixed in place, or on the base part. In this way, reliable and permanent functioning of the activation mechanism is guaranteed, in order to bring the threaded part out of engagement with the threaded spindle and also to guide it reliably back into threaded engagement. 
     Furthermore, the invention comprises an apparatus for machining a work piece that has a round and/or tubular cross-section, having a holding apparatus of the type described above. 
     In particular, the apparatus has a machining unit that is held on the base part of the holding apparatus so as to pivot, and can be brought in the direction toward a work piece held in the holding apparatus by means of pivoting. 
     The apparatus can be configured for processing of the work piece by machine. The processing unit is then configured as a machine unit. 
     It can be provided that the machining unit is configured for cutting the work piece and/or chamfering or beveling an end of the work piece. For example, the machining unit can have a circular saw or be configured as a circular saw, for example having at least one blade or saw blade. 
     Furthermore, it is possible that the apparatus is configured as a hand tool. 
     Further goals, advantages, characteristics, and application possibilities of the present invention are evident from the following description of an exemplary embodiment, using the drawings. In this regard, all the characteristics described and/or shown in the figures form the object of the present invention, by themselves or in any desired practical combination, also independent of how they are combined in the claims or their antecedents. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects and features of the present invention will become apparent from the following detailed description considered in connection with the accompanying drawings which disclose at least one embodiment of the present invention. It should be understood, however, that the drawings are designed for the purpose of illustration only and not as a definition of the limits of the invention. 
       In the drawings, wherein similar reference characters denote similar elements throughout the several views: 
         FIG. 1  a possible embodiment of a holding apparatus for rotatable holding of a work piece to be machined, having a round and/or tubular cross-section, in a perspective representation from below, 
         FIG. 2  an enlarged detail from  FIG. 1  in the region of an adjustment mechanism of the holding apparatus according to  FIG. 1 , 
         FIG. 3  a region of the adjustment mechanism of the holding apparatus according to  FIG. 1 , seen as a view from above, 
         FIG. 4  the holding apparatus according to  FIG. 1  in the region of an activation device for the adjustment mechanism and a quick-adjustment unit, 
         FIG. 5  an enlarged detail of the activation device according to  FIG. 4  in the region of the quick-adjustment unit, as a sectional representation, 
         FIG. 6 a    the activation device according to  FIG. 4  in an open position of the quick-adjustment unit, 
         FIG. 6 b    the activation device according to  FIG. 4  in a closed position of the quick-adjustment unit, 
         FIG. 7  an enlarged detail from  FIG. 1  in the region of a transition from the adjustment mechanism to one of the clamping arms for holding the work piece, in a perspective representation, 
         FIG. 8  a further possible embodiment of a holding apparatus for rotatable holding of a work piece to be machined, having a round and/or tubular cross-section, in a detail view from below, onto a region of an adjustment mechanism, 
         FIG. 9  a top view of a hand-held circular saw having a holding apparatus according to  FIG. 1 , and 
         FIG. 10  a hand-held circular saw according to  FIG. 9  in a sectional representation. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows—in a schematic representation—a possible embodiment of a holding apparatus  1  for holding a work piece to be machined, having a round and/or tubular cross-section, in such a manner that in the held state, the work piece can be rotated relative to the holding apparatus  1 . In other words, the holding apparatus  1  can be attached to a round and/or tubular work piece that is to be machined (not shown in  FIG. 1 ), such as a pipe, for example, so as to rotate around it. Rotation proceeds in such a manner that the holding apparatus  1  remains stationary in the axial direction of the work piece. 
     Preferably, the holding apparatus  1  has multiple roller bodies  7 ,  8 ,  9 , and  10 , which are mounted so as to rotate, for example. The roller bodies  7 ,  8 ,  9 , and  10  act in supporting manner, so that the holding apparatus  1  can be rotated in a plane perpendicular to the center axis of the work piece when they are pressed against the outer surface of the work piece. The roller bodies  7 ,  8 ,  9 , and  10  can be provided in the axial direction of the work piece, at least in pairs. 
     The holding apparatus  1  comprises a base part  2  and at least two clamping arms  3 ,  4 , which proceed from there. Preferably, the clamping arms  3 ,  4  are held on the base part  2  so that they can pivot in the direction toward one another, for example in that the pivot arms  3 ,  4  are articulated onto the base part  2  with one end. The base part  2  can be formed by a frame profile, housing or the like. Preferably, the base part  2  has a base plate  11 , so that a machining unit for machining the work piece can be disposed on top of or on the side of the plate. 
     The clamping arms  3  and  4  are configured in such a manner and disposed on the base part  2  in such a manner that at least a part of the outside circumference surface of the work piece can be encompassed. Preferably, for this purpose the clamping arms  3  and  4  can be rotated about a related axis of rotation  5  and  6 , respectively, in each instance, wherein the axes of rotation  5 ,  6  are disposed at a distance from one another, preferably run essentially parallel to one another, and preferably lie essentially parallel to the center axis of the work piece. 
     The clamping arms  3  and  4  are designed for exerting a holding force, preferably a clamping force on the work piece, wherein the rotatability of the work piece relative to the holding apparatus  1  is maintained. For this purpose, at least one of the roller bodies  7 ,  8 ,  9 ,  10  is disposed on each of the clamping arms  3 ,  4 , which body can be provided in the region of the free end of the clamping arms  3 ,  4 , for example. Preferably, further roller bodies  7 ,  8 ,  9 ,  10  are disposed on the base part  2  in the region between the clamping arms  3 ,  4 . 
     The holding apparatus  1  has an adjustment mechanism  20  for the clamping arms  3 ,  4 . The adjustment mechanism  20  comprises two drivers  21  and  22 , and the clamping arms  3  and  4  can be pivoted toward one another by the movement of the drivers. Preferably, the drivers  21  and  22  are movement-coupled with the related clamping arm  3  or  4  by way of an intermediate element  23  or  24 , respectively, for this purpose, for example in that the respective driver  21  or  22  is articulated onto the related intermediate element  23  or  24 , the respective intermediate element  23  or  24  in turn is articulated onto the related clamping arm  3  or  4 , and preferably, the respective intermediate element  23  or  24  is disposed at an angle relative to the related driver  21  or  22 . The intermediate elements  23  and  24  can be configured in the manner of an elongated or ridge-like connection part or a strut, in each instance, or can have such a part. 
       FIG. 2 , in an enlarged detail, shows the region of the holding apparatus  1  having the adjustment mechanism  20 . The adjustment mechanism  20  is configured in such a manner that in order to adjust the clamping arms  3  and  4 , the drivers  21  and  22  perform an essentially straight-line adjustment movement (straight line adjustment movements  25  and  26 ), in each instance. Preferably, in this connection the drivers  21  and  22  move on a respective movement path, which paths lie essentially parallel to one another. Viewed in the direction transverse to the movement direction of the adjustment movement (straight line adjustment movements  25 ,  26 ) of the drivers  21  and  22 , the drivers  21  and  22  are disposed to lie one behind the other and offset from one another, wherein the drivers  21  and  22  overlap over a section. This overlap section is used to provide a movement element  27  in between, by way of which element the drivers  21  and  22  are movement-coupled with one another. The movement element  27  is fixed in place on a component of the holding apparatus  1 , with reference to the base part  2 , so as to rotate about itself; in particular, it is mounted on the base part  2  so as to rotate. 
     The movement coupling of the drivers  21  and  22  can be implemented in such a manner that the drivers  21  and  22  each have gear-tooth systems  28 ,  29 , and that a gear wheel  30  that meshes with the gear-tooth systems  28  and  29  is provided in between, which gear wheel forms the movement element  27 . In this way, a reversal gear mechanism is formed, by means of which the drivers  21  and  22  can be moved in the direction toward one another and also in the direction away from one another, so that the clamping arms  3  and  4  can be moved both in the direction toward a work piece to be machined and also in the direction away from the work piece to be machined, without additional measures, by means of this reversal gear mechanism. 
     For this purpose, the drivers  21  and  22  can each be configured as a gear rack or can have a gear rack. Also, it can be provided that the drivers  21  and  22  have depressions, notches or passage openings, for example are configured as a hollow structure, so that the drivers  21  and  22  are relatively light, in terms of weight. 
     Preferably, the drivers  21  and  22  are guided in terms of their movement, particularly compulsorily guided. For this purpose, a guide  45  or  46  or one single guide, in each instance, can be provided, as is evident from  FIG. 3 . There, the holding apparatus  1  is shown as a detail in the region of the adjustment mechanism  20 , in a view from above onto the holding apparatus  1 , wherein the base part  2  has been left out for the sake of simplicity. 
     The guide  45  for the driver  21  and the guide  46  for the driver  22  can be formed by a guide element  47 ,  48 , in each instance, on which the driver  21  or  22  slides during the course of its adjustment movement, guided in a straight line in the movement direction  60 . For example, the respective guide element  47 ,  48  can be configured as a rod, over which the related driver  21  or  22  is pushed. For this purpose, the related driver  21  or  22  can have a passage channel, a passage opening or the like, through which the rod projects, so that the driver  21  or  22  is guided so as to be displaceable by means of the related rod. Preferably, the respective guide element  47  or  48  is disposed on a component of the holding apparatus  1 , fixed in place or fixed on the housing with reference to the base part  2 , particularly attached to the base part  2 . 
     A threaded spindle  31  is provided for adjusting the drivers  21  and  22 , as is evident from  FIG. 1 , for example. The threaded spindle  31  can be configured for manual activation by way of an activation element  33 , such as a rotary button, for example. Also, the threaded spindle  31  can be configured so that it can be activated by means of an auxiliary force. 
     Preferably, the threaded spindle  31  is movement-coupled with one of the drivers  21 ,  22 . For this purpose, an intermediate element  49  can be provided, on which the threaded spindle  31  engages, particularly is mounted so as to rotate, wherein the intermediate element  49  is firmly connected with the driver  21  ( FIG. 3 ). For example, the threaded spindle  31  is disposed between the drivers  21  and  22  in the longitudinal direction. The intermediate element  49  then serves to bridge the transverse offset of the threaded spindle  31  relative to the driver  21 , with which the threaded spindle  31  is movement-coupled with regard to the adjustment movement. 
       FIG. 4 , in a sectional representation, shows the holding apparatus  1  in the region of the threaded spindle  31 . As is evident from this, the threaded spindle  31 , with its thread, is in threaded engagement with a threaded part  32 , which has a counter-thread. The threaded part  32  is fixed on a component of the holding apparatus  1 , so as to be fixed in place with regard to the base part  2 , in the axial direction of the threaded spindle  31 , for example fixed on the base part  2  itself. 
     An advancing movement of the threaded spindle  31  in the axial direction and thereby an adjustment movement of the driver  21  coupled with it comes about by means of rotating the threaded spindle  31  relative to the threaded part  32 . The adjustment movement initiated by the threaded spindle  31  is transferred to both clamping arms  3  and  4  by means of the movement coupling of the driver  21  with the driver  22 , by way of the movement element  27 , so that in this way, the clamping arms  3  and  4  can be brought into a closed position with regard to a work piece to be machined, by means of the threaded spindle  31 , or, by means of opposite activation of the threaded spindle  31 , the clamping arms  3  and  4  can be brought into an open position with regard to the work piece to be machined. 
     In order to accelerate opening and closing by means of the threaded spindle  31 , the holding apparatus  1  has a quick-adjustment unit. The quick-adjustment unit is formed in that the threaded part  32  can be brought out of threaded engagement relative to the threaded spindle  31  by means of radial displacement. Preferably, the counter-thread of the threaded part  32  is merely configured over a circumference section for this purpose, in order to allow the radial displacement of the threaded part  32  relative to the threaded spindle  31 . In that the threaded part  32  comes out of engagement with the threaded spindle  31 , displacement of the threaded spindle  31  relative to the fixed-in-place threaded part  32  and thereby adjustment of the drivers  21 ,  22  can be carried out, without the threaded spindle  31  having to be rotated for this purpose. 
       FIG. 5 , in a detail, shows the method of activation for bringing the threaded part  32  out of engagement with the threaded spindle  31 . As is evident from this and, in particular, from  FIG. 4 , the threaded part  32  is held in threaded engagement with the threaded spindle  31  by means of the bias force of a spring element  34 . In the case of radial displacement of the threaded part  32  relative to the threaded spindle  31 , the threaded part  32  is brought out of threaded engagement counter to the force of the spring element  34 , so that the threaded part  32  moves back into threaded engagement with the threaded spindle  31 , by means of the reset force of the spring element  34 , if, for example, the activation force for releasing the threaded part  32  has been cancelled out. 
     In order to displace the threaded part  32  in the radial direction and to bring it out of threaded engagement, an activation element  35  can be provided, which is a pressure element that can be manually activated, for example, so that the threaded part  32  is brought out of threaded engagement with the threaded spindle  31  by means of pressing the activation element  35 . For this purpose, the threaded part  32  is firmly connected with the activation element  35 , preferably by way of at least one or at least two connection elements  36  and  37 , and guided in the axial displacement movement on a component provided in a fixed location relative to the base part  2 . 
     For example, the guide can be formed by a section of the base part  2  itself, wherein the spring element  34  is situated between the activation element  35  and the section of the base part  2 . In order to accelerate opening of the holding apparatus  1 , it can furthermore be provided that the clamping arms  3  and  4  are automatically moved to their open position by means of the force of a further spring element  38  when the threaded part  32  is brought out of threaded engagement with the threaded spindle  31 . The further spring element  38  can be configured as a torsion spring, which is disposed, for example, in the region of the respective axis of rotation  5  or  6  of the clamping arm  3  or  4 , respectively. 
       FIGS. 6 a  and 6 b    show the holding apparatus  1  in the region of the threaded spindle  31  and of the quick-adjustment unit, as a sectional representation, in each instance, once in the open position A ( FIG. 6 a   ) and once in a closed position ( FIG. 6 b   ). The open position A is achieved by means of the quick-adjustment unit, in that a pressure force F is exerted on the activation element  35 , and thereby the threaded part  32  comes out of engagement with the threaded spindle  31 . Opening of the clamping arms  3  and  4  and thereby a movement of the drivers  21  and  22  away from one another automatically comes about by means of the force of the further spring elements  38  ( FIG. 4 ). 
     The clamping arms  3  and  4  are moved in a direction toward one another and thereby the closed position B relative to a work piece to be held is achieved, if, according to  FIG. 6 b   , the threaded part  32  is present in threaded engagement with the threaded spindle  31 , in other words the pressure force F has been taken away from the activation element  35 . The threaded spindle  31  can then be rotated while in threaded engagement with the threaded part  32 , and pushes the driver  21  and, by way of the movement element  27 , also the driver  22  in the direction toward one another. 
       FIG. 7  shows a possible embodiment of at least one of the intermediate elements  23  and  24 , by means of which elements the drivers  21  and  22  are movement-coupled with the related clamping arm  3  or  4 , respectively, using the example of the intermediate element  24  for the clamping arm  4 . 
     The intermediate element  24  has two length sections  41  and  42 , between which at least one, preferably two setting devices  40  are provided, in order to be able to change the distance of the length sections  41  and  42  relative to one another. In this way, the length of the intermediate element  24  between the articulation point  43  relative to the driver  22  and the articulation point  44  relative to the clamping arm  4  can be changed. By means of the length change of the intermediate element  24 , precise adjustment of the position of the drivers  21  and  22  relative to the position of the clamping arms  3  and  4  can be carried out. The setting device  40  can be formed by a screw, for example, which is screwed into a thread, for example on a nut disposed on one of the length sections  41  or  42 , to a greater or lesser extent. One or more counter-nuts can also be provided there for locking. 
       FIG. 8  shows a further possible embodiment of a holding apparatus  1 ′ for rotatable holding of a work piece to be machined, having a round and/or tubular cross-section. There, the holding apparatus  1 ′ is shown in a detail view from below of a region of the adjustment mechanism  20 . Components of the holding apparatus  1 ′ according to  FIG. 8 , which are identical to or functionally equivalent with components of the holding apparatus  1  according to the previous figures, are provided with the same reference symbols; in this respect, reference is made to the description of the holding apparatus  1 . 
     The holding apparatus  1 ′ according to  FIG. 8  differs from the holding apparatus  1 , among other things, in that counter-holders  50 ,  51  or thrust bearings for the drivers  21 ,  22  are provided, by means of which a movement of the drivers  21 ,  22  transverse to the movement direction  60  of the adjustment movement and thereby slip between the drivers  21 ,  22  and the gear wheel  30  are prevented. Viewed transverse to the movement direction  60  of the drivers  21 ,  22 , the counter-holders  50 ,  51  are preferably disposed in the region of the gear wheel  30 . For example, the driver  21  is situated between the counter-holder  50  and the gear wheel  30 , and the driver  22  is situated between the counter-holder  51  and the gear wheel  30 . 
     The counter-holders  50 ,  51  can be formed by a rotationally movable rolling part  55  or a torque-proof sliding part, which is mounted on a part  54  that is fixed on the housing, for example the bearing part for the rollers  9  and  10 . Supplementally, further counter-holders or thrust bearings can be provided, which serve as a stop or restriction for the drivers  21 ,  22  on the side having the gear-tooth system  28  or  29 . For example, the further counter-holders are formed by a common material projection  56  on a component fixed on the housing, particularly the base part  2 . There, a contact surface  57  that serves as a counter-holder or thrust bearing can provided, in each instance. 
       FIGS. 9 and 10  show a possible application of the holding apparatus  1  according to  FIG. 1 . There, the holding apparatus  1  is a constituent of an apparatus  100  for machining of work pieces having a round and/or tubular cross-section, such as pipes, for example.  FIG. 9  shows the apparatus  100  in a view from above.  FIG. 10  shows the apparatus  100  in a sectional representation. Alternatively to the holding apparatus  1 , the apparatus  100  can also have the holding apparatus  1 ′ according to  FIG. 8 . 
     The apparatus  100  has a machining unit  110 , which can be covered by a housing  120 , at least in part, toward the outside. Preferably, the machining unit  110  is mounted on the base part  2  or the base plate  11  of the holding apparatus  1  so as to pivot about an axis of rotation  130 , in order to move the machining unit  110  to or away from the work piece to be machined, which is held in the holding apparatus  1  for machining. 
     The machining unit  110  can be configured as a processing unit that is part of a machine, Pivoting of the machining unit  110  toward the work piece or away from the work piece can be performed manually. For example, the machining unit  110  is configured as a circular saw for cutting the work piece to be machined to length. 
     The apparatus  100  preferably functions as follows: The holding apparatus  1 , together with the machining unit  110 , is fitted around the work piece to be machined, at a desired machining point, and the holding apparatus  1  is attached in this position by means of the threaded spindle  31 . The drivers  21  and  22  perform a setting movement by means of the rotation of the threaded spindle  31 , thereby moving the clamping arms  3  and  4  toward the work piece to be machined and bringing them into a clamping position relative to the work piece. 
     When the holding apparatus  1  is attached to the work piece, the machining unit  110  can be pivoted toward the work piece about the axis of rotation  130 , so that the machining unit  110  can begin or does begin with machining of the work piece. Then, rotation of the holding apparatus  1 , together with the machining unit  110 , around the work piece, in the direction of the rolling path established by the clamping arms  3  and  4  and the roller bodies  7 ,  8 ,  9 , and  10  follows. 
     After machining of the work piece, the machining unit  110  is pivoted away from the work piece, and the work piece is released from the holding apparatus  1 . For this purpose, the quick-adjustment unit can be activated, for one thing, in that the activation element  35  is pressed and the threaded part  32  comes out of engagement with the threaded spindle  31 , and thereby the clamping arms  3  and  4  are automatically moved into the open position A, by means of the spring force of further spring elements  38 . Alternatively, it is also possible that the threaded spindle  31  is rotated during threaded engagement of the threaded part  32 , and thereby the clamping arms  3  and  4  are moved apart from one another by way of the drivers  21  and  22 . 
     REFERENCE SYMBOL LIST 
     
         
           1  holding apparatus 
           2  base part 
           3  clamping arm 
           4  clamping arm 
           5  axis of rotation 
           6  axis of rotation 
           7  roller body 
           8  roller body 
           9  roller body 
           10  roller body 
           11  base plate 
           20  adjustment mechanism 
           21  driver 
           22  driver 
           23  intermediate element 
           24  intermediate element 
           25  straight line adjustment movement 
           26  straight line adjustment movement 
           27  movement element 
           28  gear-tooth system 
           29  gear-tooth system 
           30  gear wheel 
           31  threaded spindle 
           32  threaded part 
           33  activation element 
           34  spring element 
           35  activation element 
           36  connection element 
           37  connection element 
           38  further spring element 
           40  setting device 
           41  length section 
           42  length section 
           43  articulation point 
           44  articulation point 
           45  guide 
           46  guide 
           47  guide element 
           48  guide element 
           49  intermediate element 
           50  counter-holder 
           51  counter-holder 
           54  part fixed in place on housing 
           55  rolling part 
           56  material projection 
           57  contact surface 
           60  movement direction 
           100  apparatus 
           110  machining unit 
           120  housing 
           130  axis of rotation A open position B closed position