Patent Publication Number: US-6701596-B2

Title: Clamping and spreading device for the relative movement of two workpieces

Description:
The present disclosure relates to the subject matter disclosed in German Application No. 101 41 153.7 of Aug. 17, 2001, which is incorporated herein by reference in its entirety and for all purposes. 
     BACKGROUND OF THE INVENTION 
     The invention relates to a clamping and spreading device for the relative movement of two workpieces which have surfaces lying essentially parallel to a common plane, comprising a first holder, on which the first workpiece can be fixed, and a second holder, on which the second workpiece can be fixed, wherein the two holders are movable relative to one another. 
     Such a device is sold, for example, under the name VERIFIX by the Josef Bohle Stiftung &amp; Co. KG, Haan, Germany. Furthermore, such a device is known by the name “Rigid Seaming Vacuum Pads” from Pinske Edge, Plato, Minn., USA. 
     The object underlying the invention is to improve a clamping and spreading device specified at the outset in such a manner that this can be used in a simple manner comfortable for the operator. 
     SUMMARY OF THE INVENTION 
     This object is accomplished in accordance with the invention in that the first holder and the second holder are connected to one another via a guiding device so as to be displaceable and that the guiding device comprises an actuating element which is not only mounted on the first holder so as to be movable but is also mounted on the second holder so as to be movable and via which a relative movement of the two holders can be actuated. 
     Due to the fact that the two holders are connected to one another via the guiding device and, in addition, via the actuating element of the guiding device which is, in particular, of a rigid design, a relative movement between the two holders and, therefore, between respective fixed workpieces may be carried out in a concerted and simple manner in order to bring about, in particular, a clamping movement or a spreading movement. A good stability and rigidity of the device is achieved by the coupling of the two holders via the guiding device so that, in particular, any tilting of the two workpieces relative to one another can be prevented to a large extent. 
     A large path of displacement of the two holders relative to one another may be brought about via the movable mounting of the actuating element not only on the first holder but also on the second holder without the outer dimensions needing to be increased significantly as a result. 
     In this respect, it is provided, in particular, for the actuating element to be mounted on the first holder so as to be rotatable or rotatably displaceable relative to it. A corresponding moment may be exerted as a result of rotation in order to be able to act on the two holders with a force relative to one another in order to be able to carry out a clamping procedure or a spreading procedure as a result. 
     Furthermore, it is provided for the actuating element to be mounted on the second holder so as to be rotatably displaceable relative to it. The second holder is then displaced relative to the actuating element via a rotation of the actuating element and, therefore, the two holders may be displaced relative to one another. If the actuating element is also held on the first holder so as to be rotatably displaceable, a translational movement not only of the first holder but also of the second holder takes place during a rotation of the actuating element. If the actuating element is mounted so as to only be rotatable with respect to the first holder, no translational movement takes place in relation to it. 
     As a result of rotary actuation of the actuating element, the second holder may be favorably moved towards the first holder or away from the first holder depending on the direction of rotation. In this respect, it may also be provided for the first holder to itself move in a translational manner with respect to the actuating element. 
     It is particularly advantageous when the distance between the two holders can be adjusted infinitely via the actuating element in order to thus be able to set any optional distance and in order to facilitate constant action with a force during a clamping movement or spreading movement. 
     Furthermore, it is favorable when a specific distance between the two holders is determined via a specific position of the actuating element. As a result, a specific position need not be maintained by the actuating element being acted upon from outside with a force but rather a set distance between the two holders also remains fixed without any external action with a force. 
     In one embodiment which can be used in a simple manner, the actuating element comprises a spindle which is, in particular, of a rigid design and extends between the two holders. 
     In this respect, the spindle is, in particular, rotatably mounted so as to be non-translational with respect to the first holder. It is then sufficient to provide only one rotary sliding bearing, for example, via threads engaging in one another and, in particular, no oppositely directed threads need be provided in order to bring about a relative movement of the two holders via a rotation of the spindle. 
     In an alternative embodiment, the actuating element comprises a sleeve which is arranged so as to be rotatable on one holder or between the two holders and in relation to which at least one holder is displaceable. Such a sleeve may also be arranged between the holders in order to obtain a particularly space-saving design. As for the rest, such a device may also be designed with great symmetry, i.e. the actuating element may be arranged in a plane of symmetry in order to minimize any tilting moment of the entire device. 
     In this respect, it is particularly provided for the holder or holders, with respect to which the sleeve is arranged so as to be rotatable, to have a respective, non-rotatable spindle for engaging the sleeve. A relative displacement of the holders towards one another or away from one another may then be achieved via actuation and, in particular, rotation of the sleeve as a result of the combination spindle/sleeve and with formation of a rotary sliding bearing, in particular, via threads engaging in one another. 
     The actuating element is advantageously provided with at least one threaded section which engages in a corresponding threaded section of an associated holder for the displaceable guidance of this holder. As a result, a rotary sliding bearing may be formed in a technically simple manner and so a rotary movement of the actuating element can be converted into a translational movement, wherein a clamping force or spreading force can be exerted on workpieces via torque on the actuating element. 
     In this respect, at least the second holder is favorably provided with an internal thread for engaging in an external thread of the actuating element in order to be able to displace the second holder in relation to the first holder by forming a corresponding rotary sliding bearing. In this respect, it may be provided for the first holder to also be provided with a rotary sliding bearing in order to be able to displace not only the first holder but also the second holder in relation to it in a translational manner during rotation of the actuating element. 
     It is particularly advantageous when the actuating element is provided with a handle. Such a handle, such as, for example, a wooden handle which sits well in the hand, may be grasped by an operator with one hand so that the operator can get a good grip on it and thus can exert a high torque on the actuating element and, therefore, can exert a correspondingly high clamping force or spreading force on workpieces. 
     In a variation of one embodiment, the handle is arranged at one end of the actuating element outside an intermediate area between the two holders so that unhindered engagement on the handle is possible. 
     In an alternative embodiment, the handle is arranged in the intermediate area between the two holders. As a result, the outer dimensions of the device are minimized and, in addition, a symmetric construction may be achieved, by means of which tilting moments of the device are, for example, minimized in relation to workpieces. 
     It is provided, in particular, for a first threaded section of the first holder or the actuating element and a second threaded section of the second holder or the actuating element to be designed such that the two holders are displaceable relative to one another during rotation of the actuating element. During a rotary actuation of the actuating element, not only the first holder but also the second holder are moved in a translational manner, namely towards one another in order to generate, for example, a clamping force or away from one another in order to generate, for example, a spreading force. A corresponding threaded design may be achieved by way of oppositely directed threaded sections or ones with different pitches. 
     It is particularly advantageous when the guiding device comprises at least two spaced guide rails, via which the two holders are guided for displacement relative to one another. As a result, a high stability of the device is achieved since the two holders are coupled to one another several times, namely via the actuating element and the two guide rails. As a result, a levering moment, with which the device engages on workpieces, is minimized. Furthermore, an operator can exert a force on two workpieces in a simple and secure manner, for example, a clamping force and a spreading force, namely in a largely symmetric manner in order to keep troublesome tilting moments of the device in relation to the workpieces small. 
     In this respect, a guide rail is advantageously provided with an end stop in order to prevent any detachment of a holder from the device. 
     An inventive device may be produced in a simple and inexpensive way when the first holder and the second holder each have a guide bracket, on which the guide rails are guided or fixed. As a result, the guidance of the two holders may be designed separately from the holding function of the two holders. For example, the holders may be magnetic holders, vacuum suction means or holders which can be fixed on a workpiece in a form-locking, frictional or adhesive manner. In order to form a guiding device, these holders do not have to be substantially modified and, in particular, their holding function is not affected by the design of a guiding device. In addition, certain dimensions which are advantageous for the functioning of the device may be modified as a result of a separate formation of guide brackets. For example, the guide rails may be “lowered” via the guide brackets in order to, in particular, keep the lever arm of the guide rails and thus of the entire device slight in relation to workpieces. 
     In this respect, the guide brackets of the two holders are advantageously of essentially the same design in order to keep the production costs low. 
     Furthermore, it is advantageous when a guide bracket is designed with respect to its outer configuration to be essentially symmetric to a longitudinal axis of the device. As a result, tilting moments of the device are minimized in relation to a workpiece. 
     Furthermore, it is advantageous when a guide bracket is designed such that the guide rails are located beneath the actuating element with respect to a holding plane facing the workpiece surface. In this way, the lever arm of the device, which is present in relation to a workpiece surface, is reduced. 
     In a particularly advantageous variation of one embodiment, a spindle is mounted as actuating element on the first guide bracket of the first holder and the second guide bracket of the second holder. The spindle is, in particular, mounted on the first guide bracket so as to be rotatable and mounted on the second guide bracket so as to be rotatably displaceable. 
     With such an embodiment, it is, in addition, favorable when the guide rails are fixed on the first holder so that during a rotary actuation of the spindle only the second holder is displaced in relation to the spindle via the guide bracket. 
     In order to be able to minimize the lever arm of the device in relation to workpieces, the spaced guide rails are favorably arranged in the area of a transverse end of a guide bracket. 
     Furthermore, it is favorable when the actuating element is mounted between the guide rails parallel to them in order to, on the one hand, reduce the production costs and, on the other hand, achieve a good and stable coupling between the two holders. 
     In a variation of one embodiment, a lever for compensating for differences in the levels of the workpieces is guided for displacement on a guide rail. When two workpieces, for example, two plates are clamped to one another by means of the inventive device, it is possible that in the area of the join small differences in levels are present, i.e. the plates do not lie exactly flush in this area. Such small differences in levels may be compensated at the join transition with such a lever which presses on the plates in the area where they join. 
     For this purpose, the lever is, in particular, pivotable with a contact surface in the direction of the surface of the workpieces so that a slight tilting of the two workpieces relative to one another can be brought about as required via the contact surface in order to obtain a flush transition via a join. 
     Furthermore, it is favorable when the contact surface is essentially located on a plane defined by the two holders in a compensation position of the lever in order to obtain a flush adjustment. 
     It is, furthermore, favorable when the lever has a free space on its contact surface. This free space can accommodate glue when the two workpieces are intended to be adhered or glued via the join. Furthermore, it is possible via this free space to supply adhesive material or glue to the join, for example, from above without the lever needing to be released. 
     It may be favorable when the guiding device is biased to reduce the guidance play, for example, in that the guide rails are bent. This has functional advantages since the corresponding bearings need to be of a less exact design and, nevertheless, a high clamping force or spreading force can be achieved. 
     With the inventive device, the most varied of holders can be used. In the case of magnetic materials, magnetic holders can, for example, be used. It may also be provided for the holder to comprise a block which is screwed, for example, to a workpiece. Particularly for plate-like components with a smooth surface, it is advantageous when the holder comprises a vacuum suction device which can adhere securely to a workpiece via underpressure. 
     The following description of preferred embodiments serves to explain the invention in greater detail in conjunction with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a plan view of a first embodiment of an inventive clamping and spreading device; 
     FIG. 2 shows a side view of the device according to FIG. 1, wherein a first holder and a second holder of the device hold respective workpieces; 
     FIG. 3 shows a side view similar to FIG. 2, wherein the two workpieces have been pushed towards one another by means of the inventive device; 
     FIG. 4 shows an enlarged view of section A in FIG. 3; 
     FIG. 5 shows a plan view of a second embodiment of an inventive clamping and spreading device; 
     FIG. 6 shows a schematic sectional view along line  6 — 6  according to FIG.  5  and 
     FIG. 7 shows a schematic sectional view similar to FIG. 6 of a third embodiment of an inventive clamping and spreading device. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An inventive clamping and spreading device, of which a first embodiment is shown in FIGS. 1 to  4  and designated in these Figures as a whole as  10 , comprises a first holder  12  and a second holder  14 , wherein a holder  12 ,  14  may be fixed on a respective workpiece  16 ,  18  (FIGS. 2 to  4 ) and may be fixed, in particular, on a surface of the respective workpiece  16 ,  18 . A corresponding holding surface  20  of the first holder  12  facing the workpiece  16  is thereby located essentially in the same plane as the corresponding holding surface  22  of the second holder  14 . 
     The holders  12 ,  14 , which are, in particular, of the same constructional design, can, for example, be magnetic holders when magnetic workpieces  16 ,  18  are intended to be processed. 
     In the embodiment shown, the holders  12 ,  14  are designed as vacuum suction means, with the aid of which workpieces  16 ,  18  with smooth surfaces may also be clamped or spread relative to one another. Such a vacuum suction means, which is known per se, has a bowl  24  with a cavity. This cavity is covered opposite a workpiece  16  by a disk  26  consisting of an elastic material, wherein this disk  26  can be drawn at least partially into the cavity but leaves the edges of the disk  26  covered in an air-tight manner opposite the workpiece  16 . A lever  28  is provided for drawing the disk  26  into the cavity and is pivotable, in particular, about a pivot shaft  30 . 
     In order to fix a vacuum suction means to a workpiece  16 , the bowl  24  is placed in position with the disk  26  with a lever  28  open (FIG.  2 ). Only a very slight space filled with air then remains between the disk  26  and the surface of the workpiece  16 . If the lever  28  is now shifted (shown in FIG. 2 with the reference numeral  32  in broken lines) and, as a result, the disk  26  is moved in the direction of the cavity, wherein the disk  26 , which has a greater diameter than the bowl  24  at the contact area of the disk  26 , seals the area between the workpiece  16  and an edge of the disk  26  essentially in an air-tight manner, the volume of the space between the disk  26  and the workpiece  16  between the edges mentioned is increased, whereby the pressure decreases. This is therefore less than the air pressure and the bowl  24  with the disk  26  adheres to the workpiece surface by way of suction as a result. 
     A first guide bracket  34  is seated on the first holder  12  and this is, for example, produced from a cold-drawn, profiled aluminum section. This first guide bracket  34  is rigidly connected to the first holder  12 , for example, via a screw connection  36 . A transverse dimension of the first guide bracket  34  transversely to a longitudinal axis  38  of the clamping and spreading device  10  is thereby greater than a corresponding transverse dimension of the first holder  12 . In relation to this longitudinal axis  38 , the first guide bracket  34  is essentially of a symmetric design. 
     The first guide bracket  34  is designed such that a central area  40 , via which the first guide bracket  34  is fixed on the first holder  12 , is located higher, in relation to the holding surface  20 , than an outer area  42  and, in particular, a (preferably rounded) transverse edge  44 . 
     A rotary bearing  46  for a spindle  48  as actuating element for a relative displacement of the two holders  12  and  14  is arranged in the first guide bracket  34 . In order not to hinder any pivoting movement of the levers  28  of the vacuum suction means as holders  12 ,  14 , the rotary bearing  46  is placed off-center, i.e. is offset in relation to the longitudinal axis  38 . The spindle  48  can be rotated on the first holder  12  about an axis of rotation  49  parallel to the longitudinal axis. 
     A first guide rail  50  and a second guide rail  52  are arranged on the first guide bracket  34  parallel to the longitudinal axis  38  in the respective area of the left and right transverse edges  44 . Such a guide rail is secured on the first guide bracket  34 , for example, by means of a holding pin  55  so as to be non-rotatable and non-displaceable. A guide rail  50 ,  52  is designed, in particular, in the form of a round bar which is, for example, produced by cold drawing. 
     A plane formed by the two guide rails  50  and  52  is essentially parallel to the holding surface  20  and  22 , respectively, of the two holders  12  and  14 . The distance from the guide rails  50 ,  52  to the holding surfaces  20 ,  22  is less than the distance from the spindle  48  in order to thus ensure a small lever arm during the clamping or spreading of two workpieces  16 ,  18  relative to one another; the first guide bracket is, to a certain extent, lowered in the area where the guide rails  50 ,  52  are fixed in position. 
     In order to guide the second holder  14  relative to the first holder  12 , a guiding device designated as a whole as  54  comprises, in addition, a second guide bracket  56  which is, in principle, of the same design as the first guide bracket  34 , wherein the second guide bracket  56  is fixed in relation to the second holder  14 . In this respect, the second guide bracket  56  is, in particular, aligned essentially flush with the first guide bracket  34 . 
     The second guide bracket  56  has for the first guide rail  50  and for the second guide rail  52  respective sliding bearings  58  and  60 , via which the second holder  14  can be displaced towards the first holder  12  or away from it in a direction of displacement  62  parallel to the longitudinal axis  38 . Such a sliding bearing is formed, in particular, by a corresponding recess (in the case of a cylindrical guide rail  50 ,  52  a cylindrical recess). 
     A guide rail  50 ,  52  is provided with an end stop  64  which is formed, for example, by a pin projecting above a surface of the guide rail  50 ,  52  in order to prevent the second guide bracket  56  from separating from the guide rails  50  and  52  during a displacement of the second holder  14  away from the first holder  12 . 
     Furthermore, a rotary sliding bearing  66  is formed in the second guide bracket  56 , aligned flush with the rotary bearing  46 , and this accommodates the spindle  48 . The spindle  48  extends continuously from the first holder  12  via its first guide bracket  34  to the second holder  14  via its second guide bracket  56  and, as a result, connects the two holders  12  and  14 . The spindle  48  is mounted on the first holder  12  so as to be movable, namely rotatable, via the rotary bearing  46  and is held on the second holder  14  so as to likewise be movable but rotatably displaceable in relation to it. Since the spindle  48  is, therefore, held so as to be non-displaceable in relation to the first holder  12 , a relative movement of the second holder  14  in relation to the first holder  12  may be generated via the rotary sliding bearing  66 . 
     For this purpose, the spindle  48  is provided with an external thread  68 , for example, with a trapezoidal thread which is produced rolled and cold-worked and is, in particular, wear-resistant. The rotary sliding bearing  66  is formed by a corresponding internal thread  70  which is arranged in the second guide bracket  56  and in which the spindle  48  engages with its external thread  68 . By turning the spindle  48 , the second guide bracket  56  and with it the second holder  14  are displaced as a result, wherein the direction of displacement  62  is determined depending on the direction of rotation. 
     As a result of the external thread  68  engaging in the internal thread  70 , any distance between the first holder  12  and the second holder  14  can be adjusted infinitely, wherein a specific distance is ensured, i.e. is set securely at a specific rotary position of the spindle  48  and can only be altered due to rotation of the spindle  48  itself. 
     In order to exert torque, the spindle  48  is provided with a handle  72  which can be grasped, in particular, by a grip hand. For example, a wooden handle which sits well in the hand is provided and this is riveted to the spindle  48 . 
     The handle  72  is arranged in the first embodiment  10  at an end of the spindle  48  which is located opposite the internal thread  70  so that the handle  72  is seated outside the intermediate space between the two guide brackets  34  and  56  and, therefore, the displacement of the second holder  14  relative to the first holder  12  can be actuated from outside and is thus easily accessible. 
     The first guide bracket  34  is arranged on the first holder  12  such that the grippability and the rotatability of the handle  12  are essentially not hindered by it. 
     A respective lever  74  is seated on the guide rails  50  and  52  and serves to compensate for differences in the levels of the workpieces  16  and  18 . The lever  74  is displaceable relative to the first holder  12  in a direction of displacement  76  parallel to the direction of displacement  62  and so it can be displaced, in principle, into any optional position on the associated guide rail (for example, guide rail  50 ). The lever  74  is mounted on the associated guide rail  50 ,  52  so as to be rotatable (indicated in FIG. 2 by the reference numeral  75 ), i.e. the guide rail  50 ,  52  represents a rotary shaft for the lever  74 . 
     The lever  74  is provided with a contact element  78  (FIGS. 3,  4 ) which has a contact surface  80 , with which the contact element  78  can be abutted on a workpiece surface of the workpiece  16  and  18 . The contact surface  80  can be pivoted towards the workpieces  16 ,  18  due to pivoting of the lever  74  on the associated guide rail  50  and  52 , respectively, so that the contact surface  80  can be abutted on one workpiece  16  or  18  or on both workpieces  16  and  18 . If the contact surface  80  is thereby placed over a join  82  of the two workpieces  16  and  18 , a level compensation may be carried out, i.e. the flush connection of the workpiece surfaces in the area of the join  82  can be improved. Workpieces may also be moved somewhat during the pivoting movement of the lever  74  via its lever action. 
     The contact element  78  has in the area of its contact surface  80  a free space  84  which is formed between a first arm  86  and a second arm  88  of the contact element  78 , wherein an end face  90  of the first arm  86  and an end face  92  of the second arm  88  form the contact surface  80 . 
     This free space  84  can accommodate, for example, adhesive remains or glue residues which are pressed through in the direction of the contact element  78  during adhesion of the two workpieces  16  and  18  at the join  82  or the join  82  may be acted upon with, for example, adhesive or glue from the upper side of the workpieces  16  and  18  via the free space  84 . 
     The inventive clamping and spreading device operates as follows: 
     It is placed on the workpieces  16  and  18  in that the first holder  12  is placed on the workpiece  16  and the second holder  14  on the workpiece  18 . By shifting the lever through 90° into the position  32  (FIG. 2) the two vacuum suction means  12  and  14  adhere firmly to the respective workpieces  16  and  18  by way of suction. As a result of rotation of the spindle  48  the second holder  14  may be displaced relative to the first holder  12 , wherein the direction of displacement  62  is determined by the rotational direction of the rotation which is conveyed via the handle  72 . When the second holder  14  is moved away from the first holder  12 , the workpiece  18  is moved away from the workpiece  16 , i.e. a spreading movement is carried out. If the second holder  14  is moved towards the first holder  12 , a clamping movement is carried out. The directions of movement of the workpieces  16  and  18  are indicated in FIG. 2 by the reference numeral  89 . 
     Any differences in levels at a join  82  between the two workpieces  16  and  18  may be compensated via the lever  74  in order to bring about a better flush connection of the two workpieces  16  and  18  which are, in particular, plate-like workpieces. 
     Due to the fact that the guide rails  50  and  52  have a smaller vertical distance from the workpieces  16  and  18  than the spindle  48 , the lever arm of the clamping and spreading device  10  is minimized in relation to the workpieces  16  and  18  in the case of a simple rotatability of the spindle  48 , i.e. simple actuatability of the relative displacement of the two holders  12  and  14 . Such a “lowering” of the guide rails  50  and  52  (and, therefore, the point of gravity of the device, as well) improves the flush alignments of the workpieces  16  and  18  at a join  82 . Moreover, an additional level compensation may be achieved. 
     The largest possible distance which can be achieved between the two holders  12  and  14  is determined by the fact that the second guide bracket  56  butts against the end stops  64  of the guide rails  50  and  52 . The smallest distance between the two holders  12  and  14  is determined by the fact that the disks  26  of the two holders  12  and  14  abut on one another. 
     To reduce the production costs by saving on material, it is therefore advantageous when the two guide brackets  34  and  56  are arranged on facing areas of the two holders  12  and  14 . In the case of the arrangement shown in FIG. 1, the first guide bracket  34  is, however, arranged such that the handle  72  is easily accessible without needing to substantially increase the height of the guide brackets  34  and  56  in relation to the holding surfaces  20 ,  22 . 
     It may be provided in accordance with the invention for the guiding device  54  to be biased in such a manner that the bearing clearance is reduced. As a result, the precision, in particular, of the sliding bearings  58  and  60  and also of the rotary sliding bearing  66  may be reduced and thus the production costs kept lower. Such a biasing is achieved, for example, in that the guide rails  50  and  52  are slightly bent, namely away from the holding surfaces  20  and  22 , in particular. 
     In a second embodiment of an inventive clamping and spreading device, which is shown in FIGS. 5 and 6 and designated as a whole as  94 , a first holder  96  and a second holder  98  are likewise provided and these are, in principle, of the same design as the holders  12  and  14  described above and also operate in the same way. A first guide bracket  100  is securely arranged on the first holder  96  and a second guide bracket  102  on the second holder  98 . The two holders  96  and  98  are connected to a first guide rail  104  and a second guide rail  106  via the guide brackets  100  and  102  in a similar way to the first embodiment  10 . The second guide bracket  102  has sliding bearings  108  and  110  for the guide rails  104  and  106  so that the second holder  98  is displaceable with the second guide bracket  102  relative to these guide rails  104  and  106 , namely in a direction of displacement  112 . 
     The first guide bracket  100  is of an identical design to the second guide bracket  102  and comprises, in particular, sliding bearings  114  and  116  for the guide rails  104  and  106  so that the first holder  96  is guided on the guide rails  104 ,  106  for displacement along them in a direction of displacement  118  which coincides with the direction of displacement  112 . 
     A spindle  120  is non-rotatably arranged on the first guide bracket  100  facing the other guide bracket  102 . This spindle  120  is provided with an external thread  122 . 
     Symmetrically thereto, a spindle  124 , which is likewise provided with an external thread  126  and is aligned flush with the spindle  120 , is non-rotatably arranged on the second guide bracket  102  facing the other guide bracket  100 . 
     A rotatable sleeve  128  is seated as actuating element between the two spindles  120  and  124  and this sleeve connects the two spindles  120  and  124  and, therefore, the two holders  96  and  98  to one another. The sleeve  128  has an internal thread  130  for engaging in the external thread  122  and an additional internal thread  132  for engaging in the external thread  126  of the spindle  124 , wherein the pairs of threads  122 ,  130  and  126 ,  132  are designed such that during rotation in one direction an oppositely directed translational movement of the associated spindles  120  and  124  takes place, i.e. these are moved either towards one another or away from one another depending on the rotational movement. 
     In a variation of one embodiment it is provided for the sleeve  128  to be mounted on one holder so as to be rotatable but non-displaceable whereas it is mounted on the other holder, as described, so as to be rotatably displaceable. 
     The sleeve  128  is advantageously designed as a handle or provided with one so that a rotation of it is possible in a simple manner. 
     If the sleeve  128  is turned in one direction, this causes the two holders  96  and  98  to either be moved towards one another or be moved away from one another on account of the rotatably displaceable mounting of the spindles  120  and  124  in the sleeve  128 , wherein both holders are moved, i.e. both carry out a relative translational movement with respect to the sleeve  128 . In the case of a correspondingly symmetric configuration of the pairs of threads  122 ,  130  and  126 ,  132 , the movement towards one another or the movement away from one another is likewise symmetric. 
     As for the rest, the clamping and spreading device  94  operates like the clamping and spreading device  10 . 
     In a third embodiment, which is shown in FIG.  7  and designated as a whole as  134 , a first guide bracket  138  is again fixed on a first holder  136  and a second guide bracket  142  on a second holder  140 . Corresponding guide rails are designed and arranged as explained on the basis of the second embodiment  94 . 
     The two holders  136  and  140  are connected to one another by means of the guide brackets  138  and  142  via a rigid continuous spindle  144 , wherein this spindle  144  is mounted on the first guide bracket  138  so as to be rotatably displaceable and is mounted on the second guide bracket  142  so as to be rotatably displaceable. For this purpose, the two guide brackets  138  and  142  have respective internal threads  146 ,  148 , in which a two-part external thread  150  of the spindle  144  engages with a first threaded section  151  and a second threaded section  153 . The spindle  144  is rotatably mounted on the guide brackets  138  and  142 . The pairs of threads  146 ,  151  and  148 ,  153  are designed such that when the spindle  144  is turned an oppositely directed displacement movement is brought about, i.e. the two holders  136  and  140  are moved towards one another or are moved away from one another. In the case of a symmetric configuration of the pairs of threads  146 ,  151  and  148 ,  153  the relative movement is, in particular, symmetric. 
     In this respect, it may be provided for the spindle  144  to have an extension towards the outside, on which a handle  152  is arranged, in order to be able to cause the spindle  144  to rotate in a simple manner. 
     As for the rest, the clamping and spreading device operates in accordance with the third embodiment  134  as described above.