Abstract:
A pressing tool for connecting pipe-shaped work pieces wherein the pressing tool has a fork-shaped receiver and a clamping tool interchangeably held in the receiver by a connecting bolt. The pressing tool has two clamping jaws which can be moved toward each other. A drive motor operates the clamping tool. The connecting bolt can be pushed through bores in the fork-shaped receiver and in the clamping tool, for maintaining the clamping tool in an exchangeable position within the fork-shaped receiver. A contactless electronic tracing device is arranged in the fork-shaped receiver, which determines a relative position of the clamping jaws in relation to the fork-shaped receiver. The contactless electronic tracing device also passes a signal to either an optical warning device or an acoustical warning device.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a pressing tool for connecting pipe-shaped workpieces, having a fork-shaped receiver, a clamping tool, which is interchangeably held in this receiver by a connecting bolt and has two clamping jaws, which can be moved toward each other, and of a drive motor for operating the clamping tool. A connecting bolt can be pushed through bores in the fork-shaped receiver and in the clamping tool for interchangeably maintaining the clamping tool in the fork-shaped receiver. 
     2. Description of Prior Art 
     Pressing tools are known, which have pipe-shaped workpieces that are pressed together and two elements that are connected with each other in this way. Known cylinder-shaped workpieces are, for example, press sleeves, press fittings or connecting sleeves, as well as pipe sections, which can be pushed into each other and pressed together. These pressing tools are mostly constructed in a pistol shape and have a clamping tool. The clamping tool encloses a workpiece to be pressed. When the pressing tool is activated, the clamping jaws of the clamping tool are pressed together. So that various diameters of workpieces, such as coupling elements, can be processed by the same pressing tool if designed in such a way that appropriately dimensioned clamping tools can be simply exchanged. 
     The pressing tool has a fork-shaped receiver, in which the clamping tool is interchangeably held by a connecting bolt. The fork-shaped receiver and the clamping tool have bores for this purpose, through which passes the connecting bolt. 
     However, such pressing tools are tools with an increased accident risk. Several work accidents have already occurred, wherein the clamping tool was ejected in an uncontrolled manner and the fork-shaped receiver was bent open and deformed. Moreover, these pressing tools preform an increased number of incorrect pressings. Damages occur with both electro-mechanically and electro-hydraulically operated pressing tools. 
     In accordance with European Patent Reference EP-A-0 712 696, a monitoring element monitors the connecting bolt in its completely pushed-in position and is connected with the drive motor via a switch element. 
     Even if the clamping tool is correctly held in the pressing tool, this alone does not assure precise pressing of the pipe-shaped workpieces. The reasons for qualitatively unsatisfactory pressings can be of a wide variety. Besides functional reasons of the pressing tool, there are reasons which are connected with unsatisfactory processing. For example, the tool, or respectively the clamping jaws, can be dirty, so that sufficient closing of the clamping tool cannot be achieved, or the size of the pipe connector or pressing sleeve does not correspond to the size for which the corresponding tool is provided. 
     For these reasons a pressing tool was proposed in accordance with European Patent Reference EP-A-0 858 850, in which the length of the stroke of the drive which acts on the clamping tool is monitored. The appropriate length of the stroke for completely closing the clamping tool is known. This length of the stroke can also be indirectly determined, for example by a volumetric measurement of the hydraulic fluid in the case where the pressing tool is hydraulically operated. However, to monitor correctly, the pressing tool must determine which clamping tool is in use. Such a clamping tool determination requires an electronic data exchange between the clamping tool and the pressing tool, as well as appropriate electronic logic means, by which the information can be evaluated for appropriate signals that indicate a correct or an incorrect pressing operation. Such electronic monitoring devices then can be combined without problems with further electronic information, which also indicates the correct operation and the perfect state of the pressing tool. 
     Since these pressing tools are often employed at building sites, soiling, in particular of the clamping tool, can hardly be avoided. Such soiling then often leads to interruptions in the electronic transmission, and therefore to erroneous information. 
     A pressing tool is also described in German Patent Reference DE-A-19 631 019 wherein the final press position of the clamping jaws is monitored. Accordingly, the clamping tool can detect this final press position and pass it on to a display device. One problem with transmitting information from the clamping tool to the pressing tool remains. Appropriate electronics must be integrated into the clamping jaws in addition to elements which are also mechanically intricate. Here, the functional ability of the checking means is often hard to determine, and the user can also not see whether their functioning is still assured. Accordingly, the device continuously provides the information that the pressing process is unsatisfactory, while in actuality the pressing process is satisfactory, but there is an error in monitoring. 
     SUMMARY OF THE INVENTION 
     It is one object of this invention to provide a pressing tool that has two clamping jaws that move toward each other, which permits monitoring without an electronic data transmission from the clamping tool to the pressing tool, and which is as inexpensive as possible and allows the user to easily determine that the monitoring process is operational. 
     This object is achieved by a pressing tool discussed in this specification and in the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred exemplary embodiment of this invention is shown in the drawings, wherein:. 
     FIG. 1 shows a perspective view of a first pressing tool with a clamping tool; 
     FIG. 2 is an exploded perspective view of another embodiment of a corresponding representation of a second pressing tool with a clamping tool; 
     FIG. 3 shows a horizontal section taken through a fork-shaped receiver with a connecting bolt inserted, without a clamping tool; 
     FIG. 4 is an exploded perspective view of another preferred embodiment of a clamping tool; 
     FIG. 5 shows a top view of a clamping tool in an assembled state with a bearing plate on a top omitted. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     A pressing tool for pipe-shaped workpieces is shown in a perspective view in each of FIGS. 1 and 2. The pressing tool comprises an electromechanical or electro-hydraulic device, which is designed in the shape of a pistol. The device, or respectively the pressing tool, has a housing  2  with a grip  1 . The pistol-shaped housing  2  terminates in a fork-shaped receiver  3  at an end remote from the grip  1 . An interchangeable clamping tool  4  with two clamping jaws  40  is releasably fastened in the fork-shaped receiver  3 . Together, the clamping jaws  40  form a circular opening  41  corresponding to a diameter of the workpiece to be pressed. The clamping tool  4  has two clamping jaws  40 , which are securely seated between bearing plates  42 , shown in detail in FIG. 4. A bore  43 , extending vertically with respect to the longitudinal direction of the housing  2 , extends through the bearing plates  42 . In the assembled state, the bearing plates  42  are enclosed by the fork-shaped receiver  3 . The fork-shaped receiver  3  has two lateral jaws  31 , through each of which the bore  30  extends. When the clamping tool is assembled, the two bores  30  are aligned with the bores  43  in the bearing plates  42 . A connecting bolt  5  can be pushed or passed through the bores  30  and thus can fix the clamping tool  4  in the fork-shaped receiver  3 . A drive device, seated in the housing  2  and not shown, acts via a piston rod or a spindle on the clamping tool  4  and thus moves the two clamping jaws  40  in relation toward each other, so that a pressing process can be performed. 
     The correct insertion of the connecting bolt  5  is checked here by means of a monitoring element  6 , shown in FIG.  3 . The pressing tool can only be operated when the connecting bolt  5  is in a completely inserted position. 
     The fork-shaped receiver  3  is schematically represented in FIG.  3 . Besides the bearing bore  30 , which extends in an aligned manner through the two jaws  31 , the connecting bolt  5  also guides. In the embodiment shown, a receiving space  36  is milled into one of the two jaws  31  of the receiver  3 . The receiving space  36  is covered by a cover plate  33 . A printed circuit board  35  is arranged in the receiving space  36 . A bore, which is used as a sensor receptacle  32 , leads from the receiving space  36  into the space  37  between the two jaws  31 . A sensor  34  is arranged in the sensor receptacle  32 . The sensor  34  is connected at least electrically with the printed circuit board  35 . 
     If the fork-shaped receiver  3 , or respectively the jaws  31 , do not provide sufficient space for attaching the receiving space  36 , it is also possible for only a single sensor receptacle bore  32  to be provided, in which a sensor  34  is housed, while the printed circuit board  35  with the appropriate electronic devices for signal processing can be housed in the housing  2 . 
     The sensor  34  is an electronic element. The sensor  34  can in principle be a transmitting as well as a receiving unit. However, it is also easily possible to only provide a transmitter, while the receiver can be housed in the oppositely located jaw  31  and can be brought into a communicating connection with the transmitter. In this case monitoring can be provided by a photoelectric or acoustical barrier. 
     If, however, as in the example shown here, the sensor  34  is only arranged in one jaw  31  of the fork-shaped receiver  3 , then the sensor  34  is designed as a transmitting-receiving unit and detects whether a transmitted signal is reflected at all, or is reflected with a predetermined quality. In this case the sensor  34  is employed as a reflection barrier. The reflection barrier can also be operated optically, acoustically or even electro-magnetically. Such means are sufficiently known and their exact design need not be addressed here. 
     The clamping tool  4 , which is specially designed for a particular embodiment, is shown in FIGS. 4 and 5. The clamping tool  4  has two clamping jaws  40 , the same as the clamping tools in accordance with the prior art. Each one of the clamping jaws  40  has half an opening, which together define an opening  41 . Grooves or flutes are cut into the half-openings  41 ″, in which the material of the pipe-shaped workpieces, which can be plastically deformed, is received. The two clamping jaws  40  are held between two bearing plates  42 . The bearing plates  42  correspondingly have two bearing bores  45 ″ which, in the assembled state of the clamping tool  4 , are aligned with each other and with the appropriate bearing bore  47  between the clamping jaws  40 . Respectively one bearing bolt  45 , which is secured on both ends by retaining rings  46 , passes through the bearing bores  45 ″ as well as the bearing bore  47  of the clamping tool  40 . A compression spring  7 , which is used as a restoring spring, is arranged between the two clamping jaws  40 . The compression spring  7  is seated in appropriate blind bores in the two clamping jaws  40 . Each clamping jaw  40  has a pressure, or respectively striking surface  48 . In the closed state of the clamping tool  4 , these two surfaces rest on each other, or at least approximately on each other. In addition, each clamping jaw  40  has a recess  49  which provides space for a pivot lever  50 . A pivot shaft  51  accordingly projects from the clamping jaw  40  into the area of the recess  49 . 
     The special shape of the pivot lever  50  is shown in FIG. 5, in particular. With respect to the pivot shaft  41 , the pivot lever  50  is two-armed. The two lever arms  52  and  54  extend approximately at right angles with respect to each other. The considerably shorter lever arm  52  has a tracing end  53  which, in the closed state of the clamping tool  4 , rests on the pressure surface  48 . If the clamping tool is opened, the lever  50  can be pivoted into the position represented by dashed lines. A torsion spring, not shown, which can be arranged around the pivot shaft  51 , for example, pushes the pivot lever  50  into a position drawn in dashed lines as long as the clamping tool  4  is opened. In place of a torsion spring it is also possible for another type of spring, for example a relatively small arched spring plate, to provide this function of the restoration of the pivot lever  50 . 
     The pivot lever  50  is designed in such a way that the ratio of length of the two lever arms  52  and  54  is approximately 1:10. This is necessary, because the pivot movement of the clamping jaws  40  during the actual pressing process is relatively small. Accordingly it is necessary to greatly multiply the path, so that it is possible to obtain dependable information despite small movements. When the two clamping jaws  40  are closed toward each other, the tracing end  53  rests on the pressure surface  48 , as already mentioned, and the lever arm  54  is pivoted into the position shown in FIG.  5 . This can only take place sensibly if the clamping tool  4  is mounted in the fork-shaped receiver  3 . In this case the clamping tool  4  projects with the two bearing plates  42 , in which the bores  43  are arranged, into the fork-shaped receiver  3 , and the connecting bolt  5  extends through the bearing bores  30  in the jaws  31  of the receiver  3 , as well as through the two bores  43  of the bearing plates  42 . Here, the bearing plates  42  are designed to have a tongue  44 , in which the bore  43  is arranged. Thus, the tongue  44  projects into the fork-shaped receiver  3 . In principle the tongue  44  covers the sensor receptacle  32  and blocks the signal path of the sensor  34 . The bearing plates  42  accordingly have bores  56 , through which the sensor signal can pass. The pivot lever  50  pivots suddenly in front of the bores  56  only after the tool  4  is closed. Only when the tool  4  is completely closed does the transmitted signal of the sensors meet a reflector  55 , which can be attached in the end area of the lever arm  54 . The signal reflected by the reflector  55  then is detected by the receiving unit of the sensor  34 , which emits a signal to the control unit, not shown in the drawings. As already previously mentioned, the control unit can be arranged on the printed circuit board  35 , or in an area of the housing  2  which is not visible. 
     Although the embodiments described in this specification are preferred embodiments, they are not the only preferred embodiments. For example, with differently designed clamping tools, other movements can also occur which, however, can also be monitored by a sensor which is housed in the fork-shaped receiver  3 . This can also occur indirectly, so that in principle not the clamping jaws, but the piston rod, which acts on the clamping jaws, is detected. However, this can also take place in a completely analogous manner. 
     This invention is of particular interest because it functions completely independently of the size of the opening  41 , or respectively of the size of the clamping tool. For monitoring, it is thus not necessary to provide information regarding the clamping tool used to the logic device. Accordingly, information need not flow from the clamping tool to the pressing tool. Therefore no electrical connection is required between the two units. If the clamping tool is not employed, it is normally closed and the pivot levers  50  are maintained in the extracted position. In this position they are completely protected and covered by the bearing plates  42 . Practically no soiling or mechanical wear can occur. The actual tool itself, to which the sensor device is attached, is handled more carefully anyway. Accordingly, soiling occurs here also much more rarely. But the sensor device is completely protected in the jaws  31  of the fork-shaped receiver  3 .