Positive-feed machine tool permitting a clearing operation

Abstract

This tool comprises: a casing ( 3 ), a tool-holder spindle ( 5 ) extending along an axis (A), a drive mechanism ( 9 ) for the tool-holder spindle, the mechanism comprising: a first member ( 21 ) for driving the spindle ( 5 ) in rotation about its axis, a second member ( 35 ) for driving the spindle in translation along its axis, the second drive member being screwed onto a threaded portion of the spindle ( 5 ) so that the spindle ( 5 ) advances or returns along the axis (A) as a function of the relative rate of rotation of the drive members ( 21, 35 ). The tool comprises means ( 37 ) for displacing the second drive member ( 35 ) relative to the casing ( 3 ) along the axis (A) between an advanced position and a returned position. Application, for example, to pneumatic drilling tools.

2 . A machine tool of the type comprising: 
 a casing,    a tool-holder spindle extending along an axis,    a mechanism for driving the tool-holder spindle, the mechanism comprising:    a first member for driving the spindle in rotation about its axis relative to the casing,    a second member for driving the spindle in translation along its axis relative to the casing, the second drive member being screwed onto a threaded portion of the spindle so that the spindle advances or returns along the axis as a function of the relative rate of rotation of the drive members,    and further comprising means for displacing the second drive member relative to the casing along the axis between an advanced position and a returned position.    
   
   
       2 . A tool according to claim  1 , wherein the first drive member is a gear wheel which is coaxial with and connected in rotation to the spindle, the spindle being able to slide along its axis relative to the first drive member, in that the drive mechanism comprises a first gear wheel/positive clutch meshing with the first drive member, a second gear wheel/positive clutch connected to the second drive member in order to be able to drive it in rotation, and in that the second gear wheel/positive clutch is mobile between an advance position of the spindle, in which it is form-fitted to the first gear wheel/positive clutch, and a return position of the spindle in which it is disengaged from the first gear wheel/positive clutch.  
   
   
       3 . A tool according to  claim 2 , wherein, in its returned position, the second drive member is not connected in rotation to the second gear wheel/positive clutch.  
   
   
       4 . A tool according to  claim 3 , wherein the drive mechanism comprises a second gear wheel which is coaxial with the spindle and which meshes with the second gear wheel/positive clutch, and a rotary positive clutch which is fixed for rotation with the second gear wheel, and in that the second drive member is a dog/positive clutch which is form-fitted to the positive clutch when the dog/positive clutch is in the advanced position, and which is freed from the positive clutch when the dog/positive clutch is in the returned position.  
   
   
       5 . A tool according to  claim 2 , wherein the drive mechanism comprises a fixed positive clutch which is form-fitted to the second gear wheel/positive clutch when it is in the advance position of the spindle.  
   
   
       6 . A tool according to  claim 3 , wherein the drive mechanism comprises a fixed positive clutch which is form-fitted to the second gear wheel/positive clutch when it is in the advance position of the spindle.  
   
   
       7 . A tool according to  claim 4 , wherein the drive mechanism comprises a fixed positive clutch which is form-fitted to the second gear wheel/positive clutch when it is in the advance position of the spindle.  
   
   
       8 . A tool according to claim  1  and further comprising a device for controlling the displacement means as a function of the torque provided by the drive motor of the spindle.  
   
   
       9 . A tool according to  claim 8 , wherein the control device ( 59 ) comprises means for comparing a quantity representative of the torque provided by the motor with a predetermined value beyond which a clearing operation must be triggered.  
   
   
       10 . A tool according to claim  1  and further comprising a device for controlling the displacement means as a function of the thrust exerted by the tool on a workpiece to be machined.  
   
   
       11 . A tool according to claim  1  and further comprising a device for controlling the displacement means at regular time intervals.  
   
   
       12 . A tool according to  claim 11 , wherein the displacement means comprise a pneumatic jack, and the control device comprises a generator of pneumatic pulses for producing regularly over time pneumatic pulses for controlling the jack.  
   
   
       13 . A tool according to claim  1 , wherein the displacement means comprise a jack which is substantially coaxial with the tool-holder spindle.  
   
   
       14 . A tool according to claim  1  and further comprising additional elements for retaining the second drive member against displacement towards its returned position.  
   
   
       15 . A tool according to claim  1  and further comprising members for braking the rotation of the second drive member relative to the tool-holder spindle during a displacement of the second drive member from its advanced position to its returned position.