Abstract:
A pneumatic-hydraulic blind riveting device has a device housing and a pulling device arranged in the device housing. The pulling device has a chuck housing and chuck jaws arranged in the chuck housing. The pulling device has a pulling piston connected to the chuck housing and also has a return piston. The pulling device has a pressure bushing arrangement resting against the chuck jaws and interacting with the return piston. A pressure chamber is defined between the return piston and the pulling piston. A control device is designed to load the pressure chamber with a controlled pressure.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a pneumatic-hydraulic blind riveting device with a pulling device arranged in a device housing and comprising a chuck housing that is connected with a hydraulic pulling piston and surrounds chuck jaws against which a pressure bushing arrangement rests which cooperates with a return piston.  
           [0003]    2. Description of the Related Art  
           [0004]    Such a blind riveting device is known from German patent DE 31 53 057 C2. The energy required for the riveting action of a blind riveting device is provided by means of compressed air which is available in many manufacturing facilities at a standard pressure of 6 bar. This compressed air actuates a pneumatic piston. This pneumatic piston is rigidly connected to a hydraulic piston which has a considerably smaller active surface. The hydraulic piston generates accordingly a relatively high pressure in a hydraulic liquid. This hydraulic liquid acts then onto the pulling piston. The pulling piston has a pulling force-transmitting connection with the chuck housing. The chuck housing has at its inner side a conically extending contact surface for the chuck jaws which rest in a ready position of the riveting device on a mouth and can thus be inserted into the chuck housing so that they open and a riveting drift of a blind rivet can be inserted. The movement of the chuck housing caused by the pulling piston has two effects. On the one hand, the chuck jaws are pressed together radially inwardly when the chuck housing is moved in the pulling direction across the chuck jaws. When the chuck jaws then secure the drift of the rivet, a further pulling movement of the chuck housing causes the chuck jaws to entrain the drift of the rivet so that the drift initially deforms the hollow rivet in a manner known in the art and subsequently is broken off.  
           [0005]    After the drift has broken off, the pneumatic cylinder is relieved so that the hydraulic pressure on the pulling piston decreases. Pressure, for example, resulting from compressed air, now acts on the return piston. The return piston moves the pulling piston and thus also the chuck housing again into the initial position. The pressure bushing arrangement comprises for this purpose at its center a pressure spring so that the return piston can move the chuck housing farther by a small distance when the chuck jaws rests against a mouth of the housing. Accordingly, the chuck jaws become free of the chuck housing and can open. The broken-off riveting drift can then be removed or can be sucked out to the rear of the blind riveting device. A new blind rivet can then be inserted with its riveting drift. In the end, during opening of the chuck jaws the spring, which is responsible for the closing force of the chuck jaws onto the riveting drift during the next riveting process of the blind rivet, is pretensioned.  
           [0006]    Such an embodiment of a blind riveting device has basically proven successful in practice. However, after riveting a certain number of blind rivets it was found that the chuck jaws no longer are secured with the desired reliability on the riveting drift. Increasingly, the chuck jaws slide on the riveting drift so that the formation of the rivet connection to be formed with the blind rivet no longer provides the desired reliability. This is so increasingly when the teeth of the chuck jaws are already slightly dull as a result of wear. Accordingly, gripping of the riveting drift is no longer possible or is at least made significantly more difficult; this can result in failure of the device. The chuck jaws then have to be replaced.  
         SUMMARY OF THE INVENTION  
         [0007]    It is an object of the present invention to control the riveting process with blind rivets in a reliable fashion.  
           [0008]    In accordance with the present invention, this is achieved in that between the return piston and the pulling piston a pressure chamber is arranged which is loadable by means of a control device with a controlled pressure.  
           [0009]    With such a configuration it is possible to affect the closing forces acting on the chuck jaws in a more directed way. Primarily, it is possible to effect by means of the controlled pressure an opening of the chuck jaws upon return of the pulling device as well as an application of a closing force which, in general, is greater than the closing force provided by a spring. When the pressure chamber is loaded with pressure, the pulling piston and thus also the chuck housing are moved by the pressure into the front-most position in which the chuck jaws come free of the chuck housing. The chuck jaws, because they rests against the mouth, cannot be moved farther to the front. When however the pressure in the pressure chamber is lowered and at the same time, or at a later point in time, the pulling piston is loaded with hydraulic pressure, the chuck housing-is moved to the rear against the chuck jaws, i.e., away from the mouth, with a force which is as large as the force which secures the return piston in the return piston position. Accordingly, substantially greater forces are transmitted onto the chuck jaws which results in a safe gripping of the riveting drift with a substantially increased service life of the gripping jaws. This primarily reduces the wear of the gripping jaws. At the same time, it can be ensured over a longer period of time that the riveting process for the rivets is carried out with the desired reliability.  
           [0010]    Preferably, the pressure bushing arrangement is of a rigid configuration between the return piston and the chuck jaws in the pressure direction. Accordingly, there is no pressure spring arranged between the return piston and the chuck jaws; instead, the return piston can be forced permanently from behind against the chuck jaws. Accordingly, the pressure with which the return piston presses via the pressure bushing arrangement onto the chuck jaws is a measure for the closing force with which the chuck housing can press the chuck jaws together. The closing force, which in the past was supplied by a pressure spring, is thus replaced by a closing force which is controlled by pressures.  
           [0011]    Preferably, the pressure bushing arrangement has a pressure bushing which is divided in the transverse direction whose end facing the chuck jaws is embodied as a hollow cylinder with a smooth mantle surface. This part is also a wear member which, if needed, can be easily exchanged. When closing the chuck jaws, there is always a small movement with a corresponding wear at the contact location between the pressure bushing and the chuck jaws because this movement is partially carried out under a relatively high pressure. When now the end of the wear member facing the chuck jaws is formed as an exchangeable part, it is no longer required to exchange the entire pressure bushing arrangement.  
           [0012]    Preferably, the control device lowers the pressure in the pressure chamber when it loads the pulling piston in the pulling direction with hydraulic pressure. The change of the two pressures can be carried out simultaneously or at least within a narrow temporal time frame. It is possible in this way to effect the control of the two pressures with a single movement of the hand or finger of the operator. When the pressure in the pressure chamber is lowered, the movement of the pulling piston no longer is counteracted by a direct resistance so that the movement of the pulling piston can be immediately converted into a closing movement with subsequent pulling movement.  
           [0013]    Preferably, on both sides of the return piston the same pressure is adjustable, wherein the return piston on a side facing away from the pulling piston has a larger active surface than on a side facing the pulling piston. The adjustment of the same pressures is a relatively simple measure. Required is only a single pressure source. By arranging active surfaces of different sizes at the front side (facing the pulling piston) and the backside of the return piston, it is then possible, also in a very simple way, to apply different forces onto the return piston. These forces are oriented such that the return piston is always loaded in the direction toward the mouth. When the chuck jaws rests against the mouth, only the difference of the two forces acts onto the mouth so that the configuration of the housing must not be excessively greatly dimensioned.  
           [0014]    In this connection it is especially preferred that the return piston is connected to a return pipe which projects into a connecting pipe. With the aid of the pulling piston pipe it is now possible in a simple way to reduce the size of the active surface.  
           [0015]    Preferably, the side of the return piston facing away from the pulling piston is loaded with a constant pressure. This pressure can be a pressure with which the blind riveting devices operate, for example, compressed air at  6  bar. Since the side of the pulling piston facing away from the return piston must no longer be pressure-controlled, its configuration is very simple. This pressure on the backside of the return piston must only be able to push the pulling device again back into its initial position.  
           [0016]    Preferably, the return piston is guided in an ejector pipe. This embodiment has several advantages. On the one hand, on the side of the return piston facing away from the pulling piston a pressure chamber can be formed which is closed to the exterior and at the same time provides a disposal path for broken-off riveting drifts. On the other hand, with an additional guiding of the return piston it is ensured that lateral movements of the return piston are substantially completely excluded so that sealing problems are minimized. It is possible with simple measures to seal the return piston relative to the housing.  
           [0017]    In this respect, it is particularly preferred that the ejector pipe comprises a lock which can be actuated by the riveting drift collecting container. The lock has a lock surface which is matched such to the cross-section of the ejector pipe that a gap remains which allows an effective flowing of air but prevents ejection of the blind riveting drifts. This lock is a safety feature. In many blind riveting devices, the broken-off riveting drifts are removed by vacuum or by means of compressed air and are collected in a collecting container. A collecting container not only collects the riveting drifts over a certain period of time. It also prevents that operating personnel is endangered by riveting drifts which, in the truest sense of the word, can be shot out of the pulling mechanism during vacuuming of the device. It is possible to prevent that the riveting drifts are shot out to the rear from the ejector pipe by simply closing off the ejector pipe. However, in this situation, a pressure is generated which in the end leads to the riveting drifts to be shot out toward the front, i.e., through the mouth. These two possibilities are excluded when the lock is now configured such that the air can flow out but the gap between lock and ejector pipe is so small that the riveting drifts can no longer pass through the opening. The riveting drifts remain thus in the ejector pipe as long as the lock is in its locking position. Such a situation occurs, for example, when the operator has removed the collecting container in order to empty it.  
           [0018]    In this connection, it is particularly preferred to form the lock by a finger on a plate which is pivotable about an axis which extends parallel to the axis of the ejector pipe. This considerably reduces the construction length of the device. The lock requires practically no space in the axial or pulling direction but can close off reliably the path extending through the ejector pipe.  
           [0019]    This is true in particular when the finger can be inserted substantially radially into the ejector pipe. In this case, the movement of the lock requires practically no additional construction space.  
           [0020]    Preferably, the chuck jaws are guided in the chuck housing in grooves whose groove bottoms have a constant cross-section across a predetermined length, wherein the chuck jaws are matched to their cross-section, respectively. In this case, the chuck jaws are secured in the chuck housing always by a defined pressing surface, independent of the axial position, i.e., the position in the direction of pulling. With this measure, the surface pressing onto the chuck jaws can be maintained identical independent of the position of the chuck jaws. Impermissibly high pressing forces are thus prevented.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0021]    In the drawing:  
         [0022]    [0022]FIG. 1 is a schematic sectional view of a blind riveting device;  
         [0023]    [0023]FIG. 2 is an enlarged representation of a portion of the blind riveting device;  
         [0024]    [0024]FIG. 3 is a schematic illustration of a lock in the closed state; and  
         [0025]    [0025]FIG. 4 is a schematic illustration of the lock in the open state.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0026]    [0026]FIG. 1 shows a pneumatic-hydraulic blind riveting device  1  with a compressed air connector  2  via which compressed air is supplied to the blind riveting device  1  at a pressure of, for example, 6 bar. A sliding valve  3 , known in the art, controls the supply of compressed air to the individual components of the blind riveting device  1 , in particular, under the effect of a push-button switch or pressure switch  4  which is arranged in the grip area  5  on the grip  6  of the blind riveting device  1  such that it can be actuated, for example, by the index finger of an operator.  
         [0027]    The basic function of such a blind riveting device is known. When the push-button switch  4  is suppressed, the sliding valve  3  is controlled such that the compressed air is guided to a location underneath a pneumatic piston  7  and moves it in the upward direction (relative to the illustration of FIG. 1). By means of a piston rod  8  a hydraulic piston  9  is rigidly connected with the pneumatic piston  7  and, upon movement of the pneumatic piston  7 , is also moved in the upward direction and thus pressurizes the hydraulic liquid in a hydraulic cylinder  10  and conveys it via a channel  11  into a working chamber  12 . The working chamber  12  is fillable via a closure plug  13  with hydraulic liquid. The working chamber  12  is delimited inter alia by a movable pulling piston  14  which is pressurized by the hydraulic liquid flowing in through the channel  11  and is moved thereby. When the push-button switch  4  is released and moved into the position illustrated in FIG. 1, the sliding valve  3  is switched and relieves the area below the pneumatic piston  7  so that the pulling piston  14  is returned to thereby displace the hydraulic liquid into the hydraulic cylinder  10 .  
         [0028]    In a manner known in the art, the air is displaced through a pipe  15  into the chamber above the pneumatic piston  7  and is then available at a later point in time for blowing out or vacuuming out a broken-off riveting drift.  
         [0029]    The compressed air of connector  2  is also permanently available at the housing chamber  16  and flows from there via a channel  17  into a return chamber  18 . Here a constant pressure is provided which matches the supply pressure of the blind riveting device  1 .  
         [0030]    [0030]FIG. 2 shows on a slightly enlarged scale the head  19  of the blind riveting device. This head  19  has a housing  20  into which a front part  21  with a mouth  22  is screwed. The mouth  22  has an opening  23  through which, in a manner known in the art, the riveting drift of a blind rivet (not shown) is introduced. The mouth  22  projects with a cone-shaped projection  24  slightly into the housing  20  or its front part  21 .  
         [0031]    In the device housing  20  a pulling device is arranged which, projecting from the pulling piston  14 , comprises a connecting pipe  25 . A chuck housing  26  is screwed onto the connecting pipe  25  at its front end where the chuck jaws  27  are arranged.  
         [0032]    The chuck housing  26  has a groove  28  for each chuck jaw  27 , and in the grooves the chuck jaws  27  can be moved parallel to the pulling direction illustrated by the arrow  29 . The groove bottom of the groove  28  is substantially semi-circular in shape. The back of the chuck jaw  27  has a matching semi-circular rounded shape. In other respects, the walls of the groove  28  extend parallel to radial-beams so that the chuck jaws  27  are always guided in the groove  28 , but at the same time, independent of their position parallel to the pulling direction  29 , rest against the chuck housing  26  always with the same contact surface.  
         [0033]    The chuck jaws  27  are forced by a pressure bushing in the direction toward the mouth  22 , wherein the pressure bushing has a first bushing portion in the form of a front part  30  and a second bushing portion in the form of a rear part  31  which rest against one another. The front part  30  and the rear part  31  can be lifted off one another. However, when pressure is applied counter to the pulling direction  29  onto the rear part  31 , the front part  30  is pressed against the chuck jaws  27 . The front part  30  is formed as a simple tubular portion, i.e., it is a hollow cylinder. It has a conical front side  32  by which the chuck jaws  27  can be slightly spread apart when the chuck housing allows such a spreading movement. The chuck jaws  27  are correspondingly slanted in the opposite direction.  
         [0034]    The rear part  31  projects into an ejector pipe  33  and is guided therein in a telescopic fashion. A return piston  34  is sealingly guided in the housing  20 . The return piston  34  forms a movable boundary for the return chamber  18 . It is loaded by pressure in the return chamber  18 .  
         [0035]    The return piston  34  is connected via a return pipe  35  with the rear part  31  wherein it is sufficient when this connection can transmit pressure forces. For this purpose, the rear part  31  has a circumferential projection  36  on which a reduced diameter portion  37  of the return pipe  35  rests. Of course, the return pipe  35  can also be screwed together with the rear part  31  of the pressure bushing. The connecting tube  25  is received in a support pipe  38  wherein between the connecting pipe  25  and the support pipe  38  a gap-shaped channel  39  remains by which a channel  40  is connected with an opening  41  in the connecting pipe  25 . The opening  41 , on the other hand, opens into an annular chamber  42  between the return pipe  35  and the connecting pipe  25 . This annular chamber  42  is sealed in the forward direction by the return pipe  35  which for this purpose has an outer circumferential projection  43 . To the rear, this annular chamber  42  opens into a pressure chamber  44  which is delimited by the pulling piston  14  and the return piston  34 .  
         [0036]    The blind riveting device  1  operates as follows:  
         [0037]    In the rest or ready position illustrated in FIG. 2, the push-button switch  4  is not actuated and the valve  45  controlled by it is thus closed. In the return chamber  18  the pressure of the compressed air supply is present, for example, 6 bar. The same pressure reaches via the sliding valve  3  the channel  56 , the channel  40 , the channel  39 , the opening  41 , and the annular chamber  42  opening into the pressure chamber  44 . The working chamber  12  is not loaded. The active pressure attack surface of the return piston  34  which delimits the pressure chamber  44  is smaller than the active surface which delimits the return chamber  18 . This results from the return pipe  35  having a greater diameter than the ejector pipe  33 . Accordingly, the return piston, for identical pressures, is pre-tensioned in the direction toward the mouth  22  and presses the chuck jaws  27  against the mouth  22 , more precisely, against its projection  24 . The force which acts in this connection onto the chuck jaws  27  results from the pressure difference between the two sides of the return piston  34 .  
         [0038]    The pressure in the pressure chamber  44  acts also on the pulling piston  14  and forces it also in the direction toward the mouth  22 . Since the chuck jaws  27  cannot move farther, the chuck housing  26  is moved past the chuck jaws  27 . This movement has the result that the chuck housing  26  frees the chuck jaws  27  and the chuck jaws  27  can open radially outwardly. In this state, a riveting drift of a blind rivet can be inserted easily through the opening  23 .  
         [0039]    The surfaces of the return piston  34  can be selected, for example, such that for a compressed air pressure of 6 bar a force of a magnitude of 600 N will act in the direction toward the mouth  22  will act while a force in the magnitude of 570 N will act in the opposite direction. Accordingly, only a force of 30 N will act on the mouth  22 .  
         [0040]    When a blind rivet is now inserted, the push-button switch  4  is actuated after insertion of the blind rivet into the mouth  22 . It now vents the pressure chamber  44  via the annular chamber  42 , the opening  41 , and the channel  39  as well as the channel  40 . Accordingly, the pressure in the pressure chamber  44  will collapse more or less suddenly. At the same time, via the sliding valve  3  the pneumatic piston  7  is loaded with pressure so that the hydraulic pressure, which is now quickly generated, reaches the working chamber  12  and moves the pulling system to the rear, i.e., to the right in FIG. 2.  
         [0041]    On the return system  34  the forces caused by the pressure in the return chamber  18  act now on one side, in particular, in the direction toward the mouthpiece  22 . In the described embodiment this is, for example, 600 N. With the 600 N the chuck jaws  27  are forced into the chuck housing  26 . This force is significantly higher than a force that can be generated by most springs. A very high closing force results so that the riveting drift can be safely gripped by the chuck jaws  27 . When because of the riveting drift a further inward movement of the chuck jaws  27  is no longer possible, the pulling piston  14  moves the riveting drift, secured in the chuck jaws  27 , via the chuck housing  26  farther to the right so that the rivet head is formed and the riveting drift is broken off later on. In doing so, the pulling piston  14  must work against the pressure in the return chamber  18  wherein it transmits the corresponding forces via the chuck housing and the chuck jaws onto the return piston  34 . This pressure in the return chamber  18  is however comparatively minimal so that it does not interfere with the riveting process in a disruptive way.  
         [0042]    When the riveting process is completed, which the operator can hear and feel as a result of the riveting drift breaking off, the operator will release the push-button switch  4 . The hydraulic pressure in the working chamber  12  drops because the compressed air pressure under the pneumatic piston is lowered by the control valve  3  and the pneumatic piston  7  is returned together with the hydraulic piston  9  into the initial position. At the same time, the pressure in the pressure chamber  44  is built up. Since the pressure in the pressure chamber  44  is of the same magnitude as the pressure in the return chamber  18 , but the surfaces of the return piston  34  are different, the pressure in the return chamber  18  moves the return piston  34  therefore in the direction toward the mouth  22  until the chuck jaws  27  rest on the mouth  22 . The pressure in the pressure chamber  44  moves the chuck housing  26  slightly farther in the direction toward the mouth  22  so that the chuck jaws  27  come free and the riveting drift is released.  
         [0043]    The now released riveting drift is then transported by means of a principally known vacuum removal device through the front part  30  and the rear part  31  as well as the ejector pipe  33  to a container  46 , only schematically illustrated, which is fastened to the rear on the head  19 . This container  46  has two tasks. On the one hand, it collects the broken-off riveting drifts; on the other hand, it prevents that the riveting drifts will shoot freely out of the device during ejection from the head.  
         [0044]    In order to prevent that such a danger is present when the container  46  is removed, a lock  47  is provided, which is illustrated in more detail in FIGS. 3 and 4. The lock  47  cooperates with the ejector pipe  33 . The lock  47  comprises a plate  48  with a finger  49  wherein the plate  48  is pivotable about the pivot point  50 . The pivot axis of the plate  48  is parallel to the axis of the ejector pipe  33 . The ejector pipe  33  has an opening  51  through which the finger  49  can be introduced. A spring  52  secures the plate  48  in the position illustrated in FIG. 3 when the container  46  is not mounted. The container  46  can be connected by means of a bayonet closure to the head, for example, a rotation by approximately 45° is sufficient for fastening. As this rotation is carried out, the container engages of projection  53  on the plate  48  and moves it into the position illustrated in FIG. 4.  
         [0045]    In the position illustrated in FIG. 3 the finger  49  does not close completely the free cross-section of the ejector pipe  33 . A gap  54  remains instead which is selected to be so large that the air required for removing the riveting drifts can flow out freely, so that no pressure is built up in the ejector pipe  33 , but to be so small that the broken-off riveting drifts cannot pass the finger  49 .  
         [0046]    This lock can also be used independent of the described configuration of the pulling device.  
         [0047]    While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.