Patent Publication Number: US-10328475-B2

Title: Method and device for bending of strand-shaped workpieces

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to a method and device for bending strand-shaped workpieces, in particular pipelines. 
     Description of Related Art 
     Various types of bending machines are known for bending e.g., fuel, brake or hydraulic lines. 
     DE 203 01 138 U1 describes a bending machine with a fixed clamping unit for fixing a pipe to be bent and a bending unit that can move relative thereto with a bending head to which a bending tool is attached at the end of an extension arm. The bending tool comprises a counter roller and a sliding block that can be pivoted around the counter roller. The bending tool is positioned by moving the bending head at a bending point so that the bending of the pipe is effectuated by pivoting the sliding block around the counter roller. 
     In EP 1 591 174, a bending device is described for rod-shaped and tubular workpieces that has a bending head with a bending mandrel and a clamping apparatus for pressing the workpiece to be bent against a shaped groove in the bending mandrel. The bending mandrel can be rotated by means of a rotary drive, and the clamping apparatus can be pivoted concentrically to the rotary axis of the bending mandrel. The bending head is connected to rotary drives that are independent of each other. To transmit the drive from the three rotary drives to the bending mandrel, conversion gears and the clamping apparatus, three rotary shafts arranged concentrically with each other are provided, each of which is connected to one of the rotary drives. 
     BRIEF SUMMARY OF THE INVENTION 
     It can be considered an object to provide a method and device for bending strand-shaped workpieces in which a wide range of bends is enabled by a particularly flexible ability to control a bending tool. 
     The object is achieved by a device according to claim  1  and a method according to claim  15 . Dependent claims refer to advantageous embodiments of the invention. 
     A device according to the invention comprises a holder for a strand-shaped workpiece. A strand-shaped workpiece is understood to be an elongated, preferably at least substantially cylindrical workpiece such as a rod or a pipe. The workpiece can be consistently homogeneous, i.e., for example an unchanging material, preferably metal, and can have a consistent diameter. It is likewise also possible for the workpiece to have different sections, such as connections or thicker regions in the middle or at the ends, sections with different diameters, flexible sections, etc. It is generally preferable for the workpiece to be straight at the start of processing. Since the currently preferred embodiments of the invention were developed with regard to the processing of pipes, the workpiece will also be occasionally termed a pipe in the following to simplify the description. This however should not be understood as a restriction, a person skilled in the art will discern that the device according to the invention and the method according to the invention can be likewise applied to other strand-shaped workpieces. 
     The holder according to the invention for the workpiece secures the workpiece at least sectionally and temporarily within the device so that processing by a bending tool is possible. In preferred embodiments, the holder comprises at least one clamping device for clamping the workpiece. Moreover, a bushing can be provided for the workpiece. The clamping device preferably serves to clamp an unbent section of the workpiece, preferably a pipe end. 
     According to the invention, the device moreover comprises a bending tool by means of which a bend in the workpiece can be created at a desired bending point. Generally, the bending tool comprises at least one radius part and one bending part that preferably can be placed on opposite sides of the bending tool. A bend can accordingly be created by swinging the bending part about the radius part. The radius part and/or the bending part can preferably be each designed as rollers. 
     According to the invention, a tool driveshaft is provided to drive the bending tool. The tool driveshaft serves to transmit a rotary movement to elements of the bending tool, in particular preferably to the radius part and/or bending part. On the one hand, this can provide the necessary force to create the bend; on the other hand, the bending movement can be precisely controlled in order for example to achieve a desired bend angle. 
     To create a desired bend geometry, the bending tool can preferably be variably positioned relative to the workpiece. Preferably, the bending tool and/or the workpiece can be moved in its longitudinal direction; more preferably, the workpiece and bending tool can also pivot about the longitudinal direction relative to each other. It is particularly preferable to fixedly arrange the workpiece and suitably position the bending tool relative to the fixed workpiece, for example by rotating, displacing or moving. 
     According to the invention, a positioning device is provided in order to position the bending tool relative to the workpiece so that the bending tool and the tool driveshaft connected thereto can also be displaced in a transverse direction. The transverse direction is transverse, i.e., at least substantially perpendicular to the longitudinal direction of the workpiece driveshaft. The positioning device allows a displacement in at least one direction transverse to the longitudinal direction, preferably in different transverse directions. 
     To drive the tool driveshaft, a drive wheel is provided that is coupled to the tool driveshaft by a transmission device. The drive wheel can rotate about an axis that is fixed relative to the workpiece. As is discernible in the preferred embodiments described below, the drive wheel is preferably rotatably arranged about the longitudinal axis of the workpiece. A drive device such as a motor drive can preferably be provided to drive the drive wheel. 
     According to the invention, the transmission device has at least one coupling element that is movable transversely to the axis of the drive wheel. For example, the position of the coupling element can be adjustable in a transverse direction. Given its mobility in a transverse direction, the coupling element can enable a transmission of the drive movement from the drive wheel to the workpiece driveshaft. The coupling element can be any type of one or more parts suitable for transmitting a rotary movement, such as belts, chains, shafts, gears, etc. Preferably, it is a single gear that can be displaced transverse to its rotary axis. 
     With the assistance of the coupling element that can be moved in a transverse direction, the rotary movement can nonetheless be continuously transmitted from the fixed drive wheel to the workpiece driveshaft, and hence to the bending tool, despite the displacement of the bending tool and the tool driveshaft in a transverse direction. Accordingly, a very flexible positioning is enabled while the bending tool can still be precisely driven. Highly variable different bends and bending geometries can be achieved by the accordingly very flexible positioning of the bending tool relative to the workpiece. 
     Displacing the bending tool in a transverse direction, i.e., for example as a lift in the vertical direction or an offset in the horizontal direction (relative to a horizontally arranged workpiece) enables highly flexible bending positions and movements to be controlled. For example, a lift can be used to bring different pipe sections specifically into contact with different sections of the elements of the bending tool, for example in that grooves of different sizes in the radius part, or respectively in the bending part, are specifically brought into contact with the workpiece by adjusting the lift. An offset of the bending tool relative to the workpiece can in particular be used to change the contact side of the radius part and bending part, i.e., enable bending to the right, or respectively to the left. By a combined lift/offset movement, the bending tool that was previously positioned on one side of the workpiece can for example pass under the workpiece and be positioned thereupon on the other side. 
     By driving the bending tool with the tool driveshaft, different movable elements of the bending tool can preferably be specifically moved and thus be brought into desired positions. Primarily, this relates to a pivoting movement of the bending part about the radius part in order to create a bend of the workpiece by a desired bending angle. Moreover, the radius part, preferably designed as a radius roller, can also for example be rotated about its own axis so that both bending by rolling and drawing are enabled. Moreover, at least one additional movable element can be provided on the bending tool, for example a counter holder that is pivotable, or respectively movable, in order to be placed on the side of the workpiece during bending. For each drive of one of the aforementioned movable elements of the bending tool, a separate tool driveshaft can be provided, wherein the shafts are preferably arranged parallel, and particularly preferably coaxial, i.e., at least partially as hollow shafts. 
     For a plurality of tool driveshafts, preferably a plurality of coupling elements and a plurality of drive wheels are provided. Preferably, the drive wheels and coupling elements can each be arranged axially next to each other and coaxially driveable. 
     In all of the movements enabled by displacing the tool driveshaft, coupling with the fixed drive wheel can always be retained so that drivable elements of the bending tool can still be precisely positioned. 
     According to one preferred embodiment of the invention, the holder is designed so that the workpiece is aligned in a longitudinal direction, i.e., the tool driveshaft establishing the longitudinal direction is aligned parallel to the longitudinal direction of the workpiece. Such an arrangement is particularly preferred to achieve a minimal “interfering edge”. The parts attached to the bending tool constitute a restriction to the achievable bending geometries, i.e., the bends that can still be achieved without striking the bent end of the pipeline. A small interfering edge is of decisive importance, for example with complicated bend geometries, in particular with larger bending angles. The arrangement of the tool driveshaft parallel to the longitudinal axis of the still unbent workpiece can significantly reduce the disturbing edge. 
     According to a further embodiment of the invention, the positioning device comprises at least one slide that can be displaced in a transverse direction (i.e., transversely to the longitudinal direction established by the progression of the tool driveshaft, preferably also transversely to the longitudinal axis of the workpiece). Such a slide is preferably guided in the transverse direction. The guide can for example be designed as a sliding guide, and preferably is a rail guide. To move the slide, at least one slide drive device can be provided, preferably with an advancing element to convert a rotational movement into a linear movement. Such an advancing element can for example be formed by a worm drive; preferably, a toothed rack engaged with a pinion is used. The slide is preferably coupled to the tool driveshaft to be able to move it in the transverse direction. In particular, the slide can enclose the tool driveshaft and thereby laterally guide it in at least one direction to realize positioning in the transverse direction with simultaneous free rotatability. 
     To achieve positionability that is as free as possible, a first and second slide can be provided according to a preferred embodiment. The first slide is movably guided in a first transverse direction, and the second slide is movably guided in a second transverse direction that runs at an angle, preferably a right angle to the first transverse traction. Accordingly, desired movements can be achieved such as a lift or offset. This makes it possible for the second slide to be movably guided on the first slide. It is likewise possible for the guides of the slides to be arranged separate from each other, wherein the slides then form side guides for the element arranged thereupon, preferably the tool driveshaft. 
     In one preferred embodiment, the positioning device enables the bending tool to rotate around the longitudinal direction of the tool driveshaft, and preferably also around the longitudinal direction of the workpiece. Accordingly, the bending direction can be set by correspondingly rotating the bending tool, preferably relative to a fixed workpiece. To achieve the rotation, a support for the tool drive shaft can be rotatably arranged around a rotary axis aligned in the longitudinal direction. It is preferable that also the transmission device and/or guides, and possibly drives for displacing in a transverse direction are arranged on the rotatable carrier, for example the above-described slides. 
     For the transmission device, it is preferable for the drive wheel to be designed as a drive gear, and for a drive pinion to be provided on the tool driveshaft. Particularly preferably, the coupling element can be designed as a coupling gear which is engaged with the drive pinion and the drive wheel. For example, the coupling gear can be connected in each case to the tool driveshaft and the drive gear by at least one spacing element such as a tab so that the distance remains constant, and the coupling gear always remains engaged with the drive pinion and the drive gear even when the drive pinion moves in the transverse direction. An example of such an arrangement will be further explained below in the preferred embodiment. 
     The arrangement of a coupling gear always allows the transmission of a desired rotary movement from the drive gear to the drive pinion, and via the tool driveshaft to the bending tool, even when the tool driveshaft is displaced in a transverse direction, i.e., in a lift or offset. Accordingly, coupling can always be sustained, and the position of drivable elements of the bending tool can always be appropriately established independent of lift and offset. 
     In one preferred embodiment, the drive wheel is coupled to at least one motor drive, such as via a gearing, shaft, chain, belt drive, etc. The motor drive comprises a motor such as an electric motor and can moreover comprise further elements such as a rotary position sensor, gearing, etc. 
     Preferably, an activation device is provided for activating the motor drive. It is particularly preferable for the activation device to specify an activation of the motor drive depending on the displacing of the bending tool in the transverse direction. Because, by means of the coupling element, a displacement in the transverse direction can accordingly bring about a relative rotation, for example of a drive pinion of the tool driveshaft relative to the drive wheel. This can change in the rotary angle relationship between the drive wheel and the drive pinion depending on the displacement. By taking into account the rotary angle relationship depending on the displacement, incorrect activation can be avoided, or respectively in an ideal case, any influence of the displacement on the rotary position can be avoided. 
     It is particularly preferable to use a compensating rotation of the drive wheel when a displacement is executed in the transverse direction. The activation device stipulates a compensating rotation of the drive wheel in a manner such that a change in the rotary angle relationship caused by the displacement between the drive wheel and the drive pinion is compensated by the compensating rotation. Accordingly, the rotary position of the drive pinion can be retained during displacement despite ongoing coupling. 
     According to one preferred embodiment of the invention, the drive wheel can be coupled to a drive disk via a transmission shaft, wherein the drive disk can be driven directly or indirectly by a motor drive. It is particularly preferable to provide not just one drive wheel, but rather to rotatably arrange at least one or preferably a plurality of additional drive wheels around the same rotary axis as the first drive wheel, preferably axially adjacent to each other. In one preferred embodiment, the drive wheels are coupled via coaxial hollow shafts respectively to associated drive disks that also can be axially arranged adjacent to each other. In this context, it has proven to be particularly useful to provide a bushing for the workpiece within the hollow shafts. This allows drive power to be transferred from one or preferably a plurality of motor drives via the drive disks and hollow shafts to one or preferably a plurality of drive wheels. Given the workpiece bushing, the entire arrangement can be rotated about the longitudinal axis of the workpiece. 
     The aforementioned additional drive wheels can be provided for various functions. For example, at least one drive wheel can serve to drive the displacement of the bending tool in a transverse direction. Preferably, two drive wheels are used for this in order to enable lift and offset. Moreover, at least one drive wheel can serve to rotate the bending tool about the longitudinal direction of the tool driveshaft (or about the longitudinal axis of the workpiece). 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       In the following, embodiments of the invention will be further described with reference to the drawings. In the drawings: 
         FIG. 1 a -1 c    show side views of a pipe bending machine with a bending tower in different positions. 
         FIG. 2  shows a perspective view of the bending tower of the bending machine from  FIG. 1  with a bending head. 
         FIG. 3  shows a side view of the bending tower and bending head from  FIG. 2  with a partially removed housing. 
         FIG. 4  shows a perspective view of a tool holder of the bending head from  FIG. 2, 3 . 
         FIG. 5  shows a plan view of the bending tool from  FIG. 4 . 
         FIG. 6  shows a view of the tool holder from  FIG. 4  in a longitudinal section; 
         FIG. 7  shows a perspective view of the bending head from  FIG. 2  without a housing; 
         FIG. 8  shows a plan view of the bending head from  FIG. 7  without a housing. 
         FIG. 9  shows a representation in a longitudinal section of hollow shafts with drive wheels of the bending head. 
         FIG. 10  shows a front view of the bending tool from  FIG. 7, 8  with elements of a coupling device. 
         FIG. 11  shows a perspective view of elements of the coupling device. 
         FIG. 12 a -12 c    show front views of elements of the coupling device in different positions. 
         FIG. 13  shows a schematic representation of an activation device for different motor drives. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1 a -1 c    show a pipe bending machine  10  with a fixed clamping unit  12 , relative to which a bending tower  14  in a machine bed  16  can be moved in a longitudinal direction L. 
     The bending tower  14  bears a bending head  22  to which a bending tool  26  is attached by a tool holder  24 . The bending head  22  can rotate about a longitudinal axis L. Controllable drives  13   a  (not shown in  FIG. 1 ) and  13   b - g  are provided for moving the bending tower  14  and rotating the bending head  22 . The individual functions of the drives  13   a - g  will be explained in greater detail below. 
     In  FIG. 1 a   , an unbent pipeline  20  is securely clamped in a clamping head  18  of the clamping device  12  so that the pipe  20  is aligned in the longitudinal direction of the axis L. The clamped pipe end remains consistently stationary during the bending process and is not moved or rotated. The bending head  22  has an opening  28  of an axially running passage through which the pipe  20  is inserted. The bending tool  26  is positioned on the pipe  20 . 
     While the pipe bending machine  10  is operating, the pipe  20  is shaped into a desired bend geometry by the bending tool  26  by applying successive bends as can be seen from the sequence in  FIG. 1 a  to 1 c   . First the bending point at the furthest distance from the clamped end of the pipe  20  is approached, and the bending tool  26  is positioned there. By means of a rotating mechanism which will be explained further below, the bending head  22  can be rotated about the longitudinal axis L of the pipe  20  so that the bending tool  26  also rotates conjointly and can be activated to create a bend about a bending axis running transverse to the longitudinal axis L. 
     The elements of the bending tool  26  can be seen more precisely in  FIG. 4, 5 . As movable, driven elements, the bending tool  26  comprises a radius roller  30  that can rotate about a bending axis B, a sliding block  32  that can pivot about the bending axis B, and a counter holder  34  that can pivot about a pivot axis S. 
     As can be seen in  FIG. 4  and also in  FIG. 5 , the radius roller  30  comprises a plurality of bending grooves  36  at a distance from each other in the longitudinal direction of the radius roller  30  that each extend around a part of the circumference of the radius roller  30 . The sliding block  32  comprises associated bending grooves  38  at the same spacing which are arranged on the side of the bending roller  32  facing the radius roller  30 . 
     To create a bend in the pipeline  20 , it is accommodated between the radius roller  30  and the sliding block  32  in one of the radial grooves  36  and one of the bending grooves  38 . The different radial grooves  36  and associated bending grooves  38  are provided to accommodate pipelines of different outer diameters. 
     By pivoting the sliding block  32  about the bending axis B, a bend of the pipe  20  is generated in a bending plane perpendicular to the bending axis B while simultaneously rotating the radius roller  30 . 
     The sliding block  32  is pivotably arranged around the radius roller  30 . The radius roller  30  is rotatable. Bending by rolling as well as drawing is accordingly possible with the bending tool  26 . The sliding block  32  can be pivoted about the radius roller  30  within a pivoting range of at least 180°. Depending on the actuation of the radius roller  30  and sliding block  32  in the bending plane, a bend both to the right and left is possible. 
     If required by the respective bend which in particular can be the case when bending pipelines with flexible sections, the pivotable counter holder  34  can be placed on the side of the pipe  20 . As a lever, the counter holder  34  can pivot about the pivot axis S that runs parallel from the bending axis B at a distance. The counter holder  34  can be moved into the suitable pivot position for each bend. Various grooves to be placed against the side of the pipe  20  are provided one above the other in the counter holder  34  as well. 
     In order to shape the initially unbent pipe  20  into a desired bending geometry, a plurality of bends are made sequentially in the above-described manner, wherein the bending tool  26  is relatively positioned at the next bending point by moving the bending tower  14  (see  FIG. 1 a -1 c   ) along the longitudinal direction L toward the clamping device  12 , then, by rotating the bending head  22 , the bending tool  26  is positioned about the pipe axis L in the desired bending plane, and subsequently the radius roller  30 , sliding block  32 , and if applicable counter roller  34  are actuated to create the desired bend. 
       FIG. 1 a   - FIG. 1 c    sequentially show how the bending tower  14  gradually approaches the clamping device  12  when creating the sequential bends. In so doing, the clamping head  18  arranged on an extension  42  of the clamping device  12  is guided through the opening  28  and passage in the bending head  22  until the last bend is performed. The bent pipe can then be removed. 
     As shown in  FIG. 1 a   - FIG. 1 c    and as can be seen in greater detail in  FIG. 2, 4 , only the bending tool  26 , from which extends only the elongated, relatively thin tool holder  24 , is arranged directly on the pipe  20 . Since the tool holder  24  is aligned in the longitudinal direction L and extends toward the clamping device  18 , a design is achieved in which, proceeding from the bending point, there is only a very small interfering edge, i.e., fixed parts of the bending tool  26 , or of its attachment (tool holder  24 ), which the pipeline can strike when bending, in particular at large bending angles. 
     In this process the tubular tool holder  24  serves not only to hold and position the bending tool  26 , but also to drive the movable elements  30 ,  32 ,  34  of the bending tool  26 . 
     As can be seen from the longitudinal section in  FIG. 6 , the tool holder  24  is a hollow pipe that is fastened at one end to the bending tool  26  and at the other end to the bending head.  FIG. 6  does not show the entire length of the tool holder  24 ; in fact, the tool holder is about six times as long as it is wide as, for example, can be seen in  FIG. 2, 4 . 
     Three shafts are coaxially arranged within the interior of the tool holder  24 . A solid inner shaft serves as a radius driveshaft  44 . A hollow shaft arranged around the radius driveshaft  44  serves as a bending driveshaft  46 . Also arranged around the bending driveshaft  46  coaxial thereto is another hollow shaft as a counter holder driveshaft  48 . 
     As can be seen in  FIG. 4  and  FIG. 6 , three drive pinions  50   a ,  50   b ,  50   c  that are arranged axially next to each other are provided on the inner end of the tool holder  24 . As can be seen in  FIG. 6 , the radial inner radius driveshaft  44  is coupled to the rear-most drive pinion  50   a , the bending driveshaft  46  is coupled to the middle pinion  50   b , and the outer counter holder driveshaft  48  is coupled to the front pinion  50   c.    
     As shown in  FIG. 6 , the rotary movement of the three tool drive shafts  44 ,  46 ,  48  is transmitted by corner gears to the radius roller  30 , sliding block  32  and counter holder  34 . 
     For this purpose, corner gears are always provided on the outer end of each of the tool drive shafts  44 ,  46 ,  48  by means of which the rotary movement is deflected by bevel gears at an angle of 90° in the depicted example. A first corner gear  52   a  is formed between a first bevel gear  54   a  formed on the end of the radius driveshaft  44  and a second bevel gear  56   a  coupled to the radius roller  30 . A second corner gear  52   b  is formed between a first bevel gear  54   b  formed on the end of the bending driveshaft  46  and a second bevel gear  56   b  coupled to the bending roller  32 . The bevel gears  54   a ,  56   a  of the first corner gear  52   a  are designed solid, whereas the bevel gears  54   b ,  56   b  of the second corner gear  52   b  are designed hollow and are arranged coaxial to the bevel gears  54   a ,  56   a  of the first corner gear  52   a . In this manner, rotary movements of the drive pinions  50   a ,  50   b  are transmitted via the coaxial tool drive shafts  44 ,  46  and converted into coaxial rotations of the radius roller  30  and sliding block  32 . 
     A third corner gear  52   c  is formed on the bending tool  26  at a distance from the first and second corner gear  52   a ,  52   b . For this purpose, the counter holder driveshaft  48  is designed somewhat shorter than the two other tool driveshafts  44 ,  46 . A first bevel gear  54   c  is arranged on its end and engages with a second bevel gear  56   c  which is arranged around the pivot axis S of the counter holder  34 . In this manner, a rotary movement of the drive pinion  50   c  can be transmitted by the counter holder driveshaft  48  and corner gear  52   c  to the counter holder  34 . 
     Accordingly, the movable elements  30 ,  32 ,  34  on the bending tool  26  can be rotatably driven independently and separate from each other in order to execute desired rotary, or respectively pivoting movements to create desired bends. In doing so the achievable movements are not thereby restricted, so that bends to the right/left are also enabled as well as rolling/draw bending as desired. 
     In this process the tool holder  24  makes it possible for the bending tool  26  to be suitably positioned by the bending head  22  in each case, wherein at the same time a drive of the elements  30 ,  32 ,  34  of the bending tool  26  is achieved in an extremely compact arrangement with a small interfering edge. 
     To position the bending tool  26 , the bending head  22  is rotatably arranged about the longitudinal axis L of the pipe  20  as indicated by an arrow in  FIG. 2 . The bending head  22  has a housing  40  in which a positioning device  62  for the tool holder  24  is arranged on a head plate  60 . The housing  40  can be rotated about the longitudinal axis L of the pipe  20  so that the positioning device  62  arranged therein also rotates about the longitudinal axis L with the tool holder  24  and the bending tool  26 . 
     As can be seen in particular in  FIG. 10 , the positioning device  62  comprises a first slide  64  and a second slide  66 . The slides  64 ,  66  are each guided in associated rail guides  65 , 67  on both sides so that the first slide  64  can be displaced to execute an offset movement in a first transverse direction X (in  FIG. 10 ), and the second slide  66  can be displaced to execute a lifting movement in a second transverse direction Y at a right angle thereto. In doing so the slides  64 ,  66  are driven by the engagement of drive gears in toothed racks  68 ,  69 . 
     The first slide  64  forms a side guide by two side frame elements  70  for the tool holder  24  in the X direction, whereas the second slide  66  forms a guide in the Y direction for the tool holder  24 . The tool holder  24  can accordingly be displaced in a plane parallel to the head plate  60  into a desired X/Y position so that the bending tool  26  attached thereto executes the desired lift/offset movement. 
     In order to ensure that the drive shafts  44 ,  46 ,  48  held in the tool holder  24  are consistently driven despite the displaceability of the tool holder  24 , a transmission device  72  is provided on the bending head  22 . For each of the three tool driveshafts  44 ,  46 ,  48 , this comprises the associated pinion ( FIG. 6 )  50   a ,  50   b ,  50   c , a drive wheel  74   a ,  74   b ,  74   c  each of which being fixedly arranged to the bending head  22 , and a coupling gear  76   a ,  76   b ,  76   c  each of which being engaged with the respective pinion  50   a ,  50   b ,  50   c  and drive wheel  74   a ,  74   b ,  74   c.    
     The transmission device  72  is depicted in  FIG. 11  once again without housing elements and without the slides  64 ,  66 . The drive wheels  74   a ,  74   b ,  74   c  are connected by first spacing tabs  78  to the coupling gears  76   a ,  76   b ,  76   c , and these are connected via second spacing tabs  80  to the drive pinions  50   a ,  50   b ,  50   c  on the tool holder  24 . A consistent distance and hence continuous engagement between the gears is ensured by the tabs  78 ,  80 . 
       FIG. 12 a  to 12 c    shows an example of the transmission device  72  with reference to the second drive pinion  50   b , the associated coupling gear  76   b  and the second drive wheel  74   b  provided therefor. This depiction equally applies to all three drive wheels  74   a ,  74   b ,  74   c , coupling gears  76   a ,  76   b ,  76   c , and drive pinions  50   a ,  50   b ,  50   c.    
     Here the drive wheels  74   a ,  74   b ,  74   c  are arranged on a rotary axis fixed to a bending head  22 , i.e., around the pipe penetration  28 . By positioning the tool holder  24 , the drive pinions  50   a ,  50   b ,  50   c  are moved by means of the slides  64 ,  66  (not shown in  FIG. 12 a -12 c   ) in the X and Y direction. By means of the space tabs  78 ,  80  (also not shown in  FIG. 12 a -12 c   ), the distances L 1 , L 2  between the gears remain unchanged. Consequently as shown in  FIG. 12 a  to 12 c   , the drive pinion  50   b  can be variably positioned in the X and Y direction relative to the fixed drive wheel  74   b , wherein the coupling gear  76   b  then assumes in each case an appropriate intermediate position so that engagement is consistently ensured. 
     Independent of the X/Y position of the drive pinion  50   b , coupling is always retained so that a rotating drive by the drive wheel  74   b , and correspondingly the precise establishment of the rotary position of the drive pinion  50   b , remain ensured in each position. 
     However, an altered angular relationship of the two gears relative to each other results by displacing the drive pinion  50   b  relative to the drive wheel  74   b . This depends on the angle α between the axes in each case formed by the coupling gear  76   b  with the drive wheel  74   b  and the drive pinion  50   b . Based on the design parameters of the gears, i.e., their respective radius and number of teeth, a correction, or respectively compensation angle β, can accordingly be calculated or determined by experiments for each X/Y displacement of the drive pinion  50   b  by which the drive wheel  74   b  can be rotated in order to achieve a fixed rotary position of the drive pinion  50   b  despite the displacement. The respective correction, or respectively compensation angle β can be considered a term to be subtracted in the activation, i.e., if rotation is desired in the displacement and not a fixed rotary position of the drive pinion  50   b , the compensation angle can be subtracted from the rotary angle to be specified. 
     The activation and hence the precise positioning and movement of the bending tool  26  relative to the pipe  20  is effectuated by the motor drives  13   a - 13   g  already mentioned. These are always position-controlled electric motors which are activated by a central control device  82  as schematically portrayed in  FIG. 13 . 
     A first motor drive  13   a  serves to move the bending tower  14  in the longitudinal direction, such as by a worm drive or rack and pinion drive (not shown). 
     As can be seen in particular in  FIG. 3 , the motor drives  13   b  to  13   g  are arranged on the rear of the bending tower  14 . They are each coupled by belts to a number of drive disks  84  arranged axially adjacent to each other. 
     As can be seen in  FIGS. 9 and 11 , the drive disks  84  are rotatably arranged about the pipe penetration  28  and hence the longitudinal axis L of a pipe  20  accommodated therein. As can be seen in  FIG. 9 , each of the individual drive disks  84  coupled to the motor drives  13   b  to  13   g  is coupled to associated drive wheels  74  of the positioning device  62  by one hollow shaft  86  penetrating the head plate  60 . In this manner, the controllable motor drives  13   b  to  13   g  can drive and specify the rotary position to the drive wheels  74 . 
     In so doing, the head plate  60  of the bending head  22  is directly coupled to a first drive disk to thereby enable a controlled rotation of the head plate  60  and the entire positioning device  62  fastened thereto with the housing  40  about the longitudinal axis L. The second motor drive  13   b  schematically portrayed in  FIG. 13  accordingly causes the entire bending head  22 , and hence also the bending tool  26  arranged on the tool holder  25 , to rotate by the coupling that is also only schematically portrayed in  FIG. 13 . 
     With the third and fourth motor drive  13   c ,  13   d , the lift and offset movements of the slides  64 ,  66  of the positioning device  62  are controlled by rack and pinion drives as already explained in association with  FIG. 10 . Accordingly, the X/Y position of the bending tool  26  can be specified. 
     With the fifth, sixth and seventh motor drive  13   e  to  13   g , three drive gears  74   a ,  74   b ,  74   c  of the positioning device  62  are activated by a belt coupling, drive disks  84  and hollow shafts  83  as described. These are coupled by the coupling device  72  to the three drive pinions  50   a ,  50   b ,  50   c  at the end of the tool holder  24  as explained in association with  FIG. 12 a    bis  12   c . Accordingly the rotary movement of the radius roller  30  can be specified by the fifth motor drive  13   e , the pivot movement of the sliding block  32  can be specified by the sixth motor drive  13   f , and the pivot movement of the counter holder  34  can be specified by the seventh motor drive  13   g.    
     Accordingly, by activating the motor drives  13   a  to  13   g , the control device  82  can control all the movements of the bending tower  14 , bending head  22  and bending tool  26  to assume a respective desired bending position, to position the bending tool  26  there in the desired alignment relative to the pipe  20  and finally to generate the desired bend by activating the bending tool  26 . 
     The lift and offset movements that can be specified by activating the drives  13   c  and  13   d  can on the one hand serve to position the bending tool  26  relative to the pipe  20  so that an appropriate pair of the various grooves  36 ,  38  of the bending tool is brought into contact with the pipe  20 . On the other hand by specifying a path of travel in the X/Y direction, a change of the contact side of the radius roller  30 , sliding block  32  and counter holder  34  can be achieved to switch the bending direction to, for example, switch from bending to the right to bending to the left. An activation sequence that is suitable for this could for example first specify a lift in the negative Y direction to remove the bending tool  26  from the pipe  20 , then a displacement movement in the X direction to bring the bending tool  26  to the other side of the pipe, and finally a lifting movement in the positive Y direction in order to move the bending tool on the opposite side up to the pipe  20 . At the same time, it is always useful to position the sliding block  32  and counter holder  34  in neutral positions during these movements so that the bending tool  26  can be freely positioned on the pipe  20 . When specifying the activations for the motor drives  13   e  to  13   g , the control device  82  takes into account the compensation angle to be calculated from the X/Y displacement position. 
     The described design of the pipe bending machine  10  depicted in the drawings with the embodiment of the bending tower  14 , clamping device  12 , bending head  22 , positioning device  62  and bending tool  26  shown in the drawings and described above, is accordingly suitable for generating highly complex bending geometries, even for pipelines that for example have sections with different diameters, flexible hose sections, connecting pieces and other special features. 
     Changes are also possible in comparison to the depicted and described embodiments. In particular, the bending tool  26  can also have more or fewer movable elements instead of three movable parts (counter holder  34 , sliding block  32 , radius roller  30 ). The number of tool drive shafts in the tool holder  24  would then also need to be adapted as well as the number of coupling devices  72  and drive devices therefor. Likewise, the positioning device  62  could be simplified when only one displacement in a single direction is needed instead of the movement in the X and Y directions. 
     Moreover, the arrangement of the motor drives  13   b - g  on the rear of the bending tower  14  and the transmission of the drive movement via drive disks  84  and hollow shafts  86  are preferred; nonetheless, this can also be achieved differently in alternative embodiments.