Abstract:
In an integrated cutting and tapping tool, a part in the form of a strip is held on a strip support with a hole facing a tap carried by a tapping tool. The bottom dead center point of the tap is detected by a feeler associated with a multiplier lever pivoting about a transverse shaft and pulling on a transmission cable whose free end is detected by position detection means. In this way the position detection means may be moved out of the tool platen, so that the plunger and the multiplier lever constitute an assembly that is easy to integrate under the tapping area. The machining of defective tappings is detected in this way.

Description:
TECHNICAL FIELD OF THE INVENTION 
   The present invention relates to press tapping devices, in which a part such as a strip to be cut and tapped is held in a tool for forming and cutting the strip, which tool is also provided with at least one tapping tool. 
   These cutting and tapping tools are generally adapted to produce parts at a high throughput from continuous strip. 
   When tapping on a press, it is generally desirable to limit the travel of the taps to exactly that needed to obtain a thread of the correct size. Limiting the tapping stroke limits machining time, and increases throughput. A sensor may be used for this purpose that detects the end of the tapping operation, as suggested in U.S. Pat. No. 5,615,471 A. 
   The document DE 197 29 263 A1 discloses a press tapping unit comprising three sensors: a first sensor for detecting possible retrograde movement of the tap and its support; a second sensor for detecting displacement of the tap carrier spindle; a third sensor for detecting if the tapped hole is free or blocked by a broken tap. 
   However, it sometimes happens that the tapping is not completely performed: the tap does not pass completely through the material, and so the tapping is incomplete. 
   It has been found that these defects occur at random in a batch of parts, and that they are relatively difficult to detect. 
   Current requirements are oriented towards machining that is 100% reliable, i.e. machining that produces batches of tapped parts that are 100% satisfactory, meaning there is a total absence of defective parts in the batch. 
   This necessitates detecting the presence of a defective part as soon as it is machined, in order to prevent it ending up in the batch, which will then contain only correct parts. The devices described in U.S. Pat. No. 5,615,471 A and in the document DE 197 29 263 A1 do not provide this reliable detection of defective parts. 
   Until now, correct tapping has been detected, in each cycle, by verifying the lowermost position of the tap, to be sure that the tap has performed a stroke of sufficient length for it to be certain that it has passed through the part. 
   Thus a tap position detector is placed directly under the tapping tool, entirely within the platen of the tool, the detector sending electrical signals over a line to a control device. 
   A serious defect of these prior art detection devices is that in each case an appropriate device must be fitted under the tapping tool, and must conform to the normal stroke of the tap. Because the detector is not accessible, it is difficult or even impossible to adjust the stroke. 
   Another drawback is that the detection devices are bulky, i.e. they occupy a non-negligible space below the tapping tool, with the result that detectors may not be placed very close together when a plurality of parallel holes are to be tapped in the same product. Because of the necessary overall size of the detection device placed in the press support, it is impossible to execute closely spaced tappings. 
   Also, prior art devices are sensitive to the presence of tapping swarf, which affects the reliability of detection. 
   SUMMARY OF THE INVENTION 
   The problem addressed by the present invention is to design a new tap position sensor structure for tapping on a press, enabling use over a wide range of tapping options, and enabling adjustment of the detectors according to the required final position of the tap. 
   Another object of the invention is to provide a tap position sensor structure that is particularly reliable, and accurate, in order to detect defective parts with certainty and to reject them from the batch as soon as they are fabricated. 
   Another object of the invention is to provide a tap position sensor that is particularly compact, and easy to integrate into a tool platen under the tapping tool, to enable the execution of closely spaced tappings. 
   To achieve the above and other objects, the invention provides a tap position sensor for tapping on a press, comprising:
         a feeler adapted to be integrated into a platen of a cutting tool and to be loaded by the end of the tap at the end of tapping,   a displacement multiplier device, loaded by the feeler and adapted to amplify the displacement of the feeler,   a transmission cable, coupled by a first end to the displacement multiplier device, and whose second end is offset away from the feeler,   position detection means, adapted to detect the position of the second end of the transmission cable.       

   Thanks to the transmission cable, the above combination of features enables the position detection means to be moved out of the area occupied by the tap, avoiding possible measurement and detection errors that might be introduced by the necessary clearances of the mechanical transmission from the tap to the position detection means, and considerably facilitating the integration of the device into the tool platen area under the tapping tool. 
   The invention therefore proposes a solution of relatively low cost, using a detector having one portion that is placed in the lower cavity under the tap in the platen of the tool, to come into contact with the tap in order to identify accurately its bottom dead center position, and to transmit this information remotely to the exterior of the tool support in a manner that frees up the maximum space under the tap, enabling integration of a plurality of closely spaced taps and adjustment of the detectors. 
   The transmission cable may be bare, provided that it works in traction, remains taut, and slides between two end supports fastened to the frame of the device. 
   The transmission cable preferably slides in a sheath itself fastened to the frame of the device. 
   In one advantageous embodiment of the invention, the displacement multiplier device comprises a multiplier lever having an upstream arm shorter than the downstream arm. 
   The multiplier lever is preferably cranked and has a waiting position in which its upstream arm is in a horizontal orientation appropriate to detecting vertical movement of a tap and at least a portion of its downstream arm is in a vertical orientation appropriate to horizontal departure of the transmission cable. This facilitates integration of the device into the press support under the area occupied by the tapping tool. 
   In one embodiment, the feeler comprises a plunger adapted to move in vertical translation and functionally connected to the upstream arm of the multiplier lever by a transverse pin engaged with and adapted to move in longitudinal translation along the upstream arm of the multiplier lever. 
   In another embodiment, the feeler comprises a generally horizontal reversing lever pivoting about a horizontal median shaft and whose upstream end is loaded by the tap at the end of the tapping stroke and whose downstream end is coupled to the multiplier lever. 
   In a third embodiment the feeler comprises a vertical plunger fastened to the upstream arm which is substantially horizontal, and in line with the trajectory of the tap to be detected. 
   The multiplier lever is preferably spring-loaded into a waiting position by a spring. The spring constitutes the means for returning the feeler, the transmission cable and the position detection means to the waiting position. 
   A position sensor of the kind defined above may be integrated into an integrated cutting and tapping tool. In this kind of embodiment, the integrated cutting and tapping tool comprises two platens, a strip support for supporting a strip to be cut, tools for cutting the strip, and at least one tapping tool carrying a tap. The tool comprises at least one position sensor comprising a remote detector as defined hereinabove, with the feeler and the displacement multiplier device integrated into the bottom platen of the tool in the area below the tapping tool. 
   The transmission cable is preferably adapted to pass through the bottom platen of the tool from the area below the tapping tool to the exterior of the bottom platen of the tool, and the position detection means are placed outside the bottom platen of the tool where they are therefore directly accessible by the user. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and advantages of the present invention will emerge from the following description of particular embodiments, which is given with reference to the appended drawings, in which: 
       FIG. 1  is a diagrammatic side view in section of an integrated cutting and tapping tool provided with a tap position sensor conforming to a first embodiment of the invention, with the tool in a waiting position; 
       FIG. 2  is a diagrammatic plan view of the tap position sensor system from  FIG. 1 , showing the section line A—A used for the side views; 
       FIG. 3  is a side view in section of the integrated cutting and tapping tool from  FIG. 1 , with the tool in a tap bottom dead center point detection position; 
       FIG. 4  is a side view in section of an integrated cutting and tapping tool provided with a tap position sensor conforming to a second embodiment of the present invention, with the tool in a waiting position; 
       FIG. 5  shows the cutting tool from  FIG. 4  in a tap bottom dead center point detection position; 
       FIG. 6  is a side view in section of an integrated cutting and tapping tool provided with a tap position sensor conforming to a third embodiment of the present invention, with the tool in a waiting position; and 
       FIG. 7  is a side view in section of the tool from  FIG. 6  in a tap bottom dead center point detection position. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the embodiments shown in the figures, the tap position sensor of the invention is shown in its position of use within an integrated cutting and tapping tool. 
   The integrated cutting and tapping tool comprises a bottom platen  1  and a top platen  8  supporting all of the other components. 
   The integrated cutting and tapping tool comprises a plurality of stations comprising cutting and shaping tools, not shown, and a station comprising the tapping tool  11 , shown in  FIGS. 1 ,  3 ,  4 ,  5 ,  6  and  7 . 
   The material worked by this tool takes the form of a strip  6  fed horizontally under the tool on a strip support  4  which comprises guides  5  for holding it. The strip  6  has at least one hole  7  through it which is to be tapped. The hole may have been formed at a preceding station of the tool, for example. 
   This tool is mounted on a press. The bottom platen  1  rests on the table of the press and the top platen  8  is fixed to the slide of the press, which moves it vertically. 
   At the tapping station, this vertical movement is converted to a rotation movement by a screw/nut device  9 . The resulting rotation movement is transmitted to the tapping tool  11 , which in turn transmits a helicoidal movement to a tap carrier spindle  12 . The tap carrier spindle  12  is conformed to carry a tap  14  placed opposite the hole  7  to be tapped. 
   In the waiting position shown in  FIG. 1 , the top platen  8  is raised and the tap  14  is away from the strip  6 . 
   At the bottom dead center point of the tap, shown in  FIG. 3 , the top platen  8  is lowered, and the tap carrier spindle  12  has performed a helicoidal movement, entraining in said movement the tap  14  which has passed through the hole  7  in the part  6 . The distal end of the tap  14  projects slightly below the strip  6 . 
   In certain tools, the strip support  4  may also be reciprocated in vertical translation to accompany the cutting and forming operations effected at the other stations of the tool. The tapping station is then adapted to this movement of the strip support  4 . Thus, in the  FIG. 1  waiting position, the strip support  4  is raised away from the bottom platen  1  whereas at the  FIG. 3  bottom dead center point the strip support  4  is lowered and therefore closer to the bottom platen  1 . This vertical movement of the strip support  4  does not affect the detection of the bottom dead center point of the tap  14  by the detection means of the invention. 
   In all embodiments, the tap position sensor essentially comprises a feeler  15 , a displacement multiplier device  16 , a transmission cable  17 , and position detection means  18 . 
   Also, in all the embodiments shown in the figures, the displacement multiplier device  16  comprises a multiplier lever  19  having an upstream arm  20  shorter than its downstream arm  21 , and mounted to pivot about an intermediate horizontal transverse shaft  22  at the junction between the upstream arm  20  and the downstream arm  21 . However, it may be assumed that multiplier lever structures articulated at one end may be used instead. 
   In the embodiment shown in  FIGS. 1 to 3 , the multiplier lever  19  is cranked and, in the waiting position shown in  FIG. 1 , its upstream arm  20  is horizontal and its downstream arm  21  is vertical. A spring  19   a  spring-loads the multiplier lever  19  toward its  FIG. 1  waiting position, with the downstream arm  21  vertical and the upstream arm  20  horizontal. In this embodiment, the feeler  15  comprises a vertical plunger  23  fastened to the upstream arm  20  and in line with the trajectory of the tap  14  to be detected. 
   The feeler  15 , integrated into the bottom platen  1  of the tool and into the strip support  4 , is adapted to be loaded by the distal end of the tap  14  at the end of tapping. 
   The displacement multiplier device  16  is loaded by the feeler or vertical plunger  23  so that it pivots about the intermediate horizontal transverse shaft  22 , and so that the different lengths of the upstream arm  20  and the downstream arm  21  amplify the displacement of the feeler or vertical plunger  23 . 
   A first end  17   a  of the transmission cable  17  is connected to the displacement multiplier device  16 . In practice, the first end  17   a  of the transmission cable  17  is fixed to the distal end of the downstream arm  21 . Its second end  17   b , which is away from the feeler  15 , is detected by the position detection means  18 . 
   The multiplier lever  19  and its spring  19   a  are mounted in a feeler body  24  fixed into the bottom platen  1  of the tool. 
   The transmission cable  17  allows the position detection means  18  to be offset outwards, away from the area of the tap  14 , and the detection means  18  are fastened to a detector body  25  which is itself fixed to the bottom platen  1  of the tool. 
   The transmission cable  17  advantageously slides in a sheath  26  that is fixed relative to the bottom platen  1  of the tool. 
   For example, the position detection means  18  may comprise a proximity detector, responsive to the position of an end-piece  27  which slides in the detector body  25  and which constitutes the second end  17   b  of the transmission cable  17 . 
   At the end of the tapping stroke, the tap  14  passes through the hole  7  and its end loads the vertical plunger  23  which tilts the multiplier lever  19  toward the inclined position shown in  FIG. 3 ; the multiplier lever  19  pulls on the transmission cable  17 , whose second end  17   b  is then detected by the position detection means  18 , which confirms the presence of the tap  14  at the dead center point, thus confirming that the tapping that has been effected is of good quality. 
   The embodiment shown in  FIGS. 4 and 5  comprises the same essential components as the integrated cutting and tapping tool from  FIGS. 1 to 3 , and these essential components are identified by the same reference numbers. 
   It also comprises the essential means of the tap position sensor, and in particular the feeler  15 , the displacement multiplier device  16 , the transmission cable  17 , and the position detection means  18 . 
   In this second embodiment, only the feeler  15  and the displacement multiplier device  16  are modified. 
   In this embodiment, there is also a feeler body  24  supporting a vertical plunger  23  constituting the feeler itself and associated with a multiplier lever  19  mounted to pivot about an intermediate horizontal transverse shaft  22 , the multiplier lever  19  having two perpendicular levers, comprising a generally horizontal upstream arm  20  and a generally vertical downstream arm  21 . 
   The vertical plunger  23  slides vertically in alignment with the vertical stroke of the tap  14 , and is functionally connected to the upstream arm  20  by a transverse pin  23   a  on the vertical plunger  23 , the transverse pin  23   a  being engaged in a horizontal oblong slot  20   a  in the upstream arm  20 . This converts vertical translation movement of the vertical plunger  23  into rotation of the multiplier lever  19 , which then loads in translation the transmission cable  17 , movement of which is detected by the position detection means  18 .  FIGS. 4 and 5  respectively show the waiting position and the bottom dead center point position of the tap  14 . 
   It should be noted that in this embodiment the spring  19   a  spring-loading the detector into the waiting position is mounted on the vertical plunger  23 . 
   The embodiment shown in  FIGS. 6 to 7  also includes the essential means of the previous embodiments, and in particular the feeler body  24  carrying the feeler  15 , the multiplier lever  19 , and the return spring  19   a , as well as a transmission cable  17  and position detection means  18 . 
   In this embodiment, the feeler  15  comprises a generally horizontal reversing lever  28  pivoting about a horizontal median shaft  29 . The upstream end  28   a  is loaded by the tap  14  at the end of the tapping stroke, and its downstream end  28   b  is coupled to the upstream end region of the upstream arm  20  of the multiplier lever  19 . The position of the multiplier lever  19  is reversed compared to the position shown in  FIGS. 1 to 4 . 
   As may be seen in  FIG. 2 , the feeler body  24 , that contains the feeler  15  and the displacement multiplier device  16 , occupies a small width L under the tapping area  14 . The width L is small because the multiplier lever pivots about a horizontal shaft  22  and is itself narrow. Likewise the reversing lever  28 . It is therefore possible to place feeler bodies  24  close together to detect the position of taps that are themselves close together. 
   Also, because of the facility to move the other units such as the position detection means  18  away from the bottom platen  1 , it is easy to integrate the subassembly comprising the feeler body  24  and the components that it contains into the bottom platen  1  of the tool. 
   Thanks to the structure according to the invention, it is possible to monitor efficiently the correct execution of each tapping operation. As a result, in the event of detection of an incomplete tapping, it is possible to reject the part at the fabrication stage, with the result that the batch of parts contains only satisfactory parts. 
   The present invention is not limited to the embodiments explicitly described and encompasses variants and generalizations thereof within the scope of the following claims.