Tonnage monitor for a mechanically driven press

Abstract

The upper platen of a press is driven by a ballscrew that is rotated by an electric motor. The ballscrew is suspended from the crown of the press, and the force on the ballscrew shaft when the upper platen is driven into the workpiece causes the crown to flex upward. The flexure of the crown is sensed by a position transducer mounted on a cantilever support. The position transducer generates a signal that can be used to determine the tonnage force developed by the press.

We claim:  
     
         1 . A mechanically driven press having a tonnage monitor, the press comprising: 
 a base having a lower platen for supporting a workpiece;    a pair of vertical columns attached to the base and a crown supported by the columns;    a platen driving member suspended from the crown and coupled to the upper platen;    a drive source for causing the platen driving member to press the upper platen against the workpiece; and,    a displacement measuring instrument for measuring the distortion of the crown caused by the platen driving member pressing the upper platen against the workpiece.    
     
     
         2 . The mechanically driven press of  claim 1  further comprising: 
 a ballscrew comprising the platen driving member; and,  
 an electric motor driving the ballscrew comprising the drive source.  
 
     
     
         3 . The mechanically driven press of  claim 2  further comprising: 
 a body and a movable probe comprising the displacement measuring instrument; and,  
 a cantilever support for the displacement measuring instrument for measuring the distortion of the crown, whereby the cantilever support isolates the body of the displacement measuring instrument from the distortion of the press crown.  
 
     
     
         4 . The mechanically driven press of  claim 3  further comprising: 
 a displacement transducer comprising the displacement measuring instrument.  
 
     
     
         5 . The mechanically driven press of  claim 4  further comprising: 
 a linear variable differential transformer (LVDT) comprising the displacement transducer.  
 
     
     
         6 . The mechanically driven press of  claim 5  further comprising: 
 a mount for mounting the body of the LVDT to the cantilever support; and,  
 a probe extending from the body of the LVDT, whereby the end of the probe is in contact with the crown of the press, and whereby movement of the crown of the press relative to the cantilever support causes the probe to move relative to the body of the LVDT.  
 
     
     
         7 . The mechanically driven press of  claim 6  further comprising: 
 A block for mounting the cantilever support to the crown of the press, the block being attached to the crown of the press at the middle of the crown, midway between the pair of vertical columns.  
 
     
     
         8 . A press comprising an upper platen and a lower platen and having a tonnage monitor for monitoring the force exerted by the upper platen against the lower platen, the press comprising: 
 a base for supporting the lower platen;    a pair of vertical columns attached to the base and a crown supported by the columns;    a platen driving member suspended from the crown and coupled to the upper platen;    a drive source for causing the platen driving member to press the upper platen against the lower platen;    guide posts for maintaining the upper platen in alignment with the lower platen; and,    an instrument for measuring the distortion of the crown caused by the platen driving member pressing the upper platen against the lower platen.    
     
     
         9 . The press of  claim 8  further comprising: 
 An electric motor comprising the drive source;  
 a ballscrew comprising the platen driving member;  
 a thrust shaft mounted for rotation in the crown of the press, the thrust shaft being coupled to one end of the ballscrew; and,  
 bearings for mounting the thrust shaft in the crown of the press, whereby force developed by the press is transferred by the ballscrew to the crown of the press and the resulting distortion of the crown is measured by the instrument for measuring the distortion of the crown.  
 
     
     
         10 . The mechanically driven press of  claim 9  further comprising: 
 a linear variable differential transformer (LVDT) having a motion following probe extending from the body of the LVDT in contact with the crown of the press, the LVDT comprising the instrument for measuring the distortion of the crown; and,  
 a cantilever support for the LVDT, whereby the distortion of the crown of the press is isolated from the body of the LVDT and the probe of the LVDT is able to follow the distortion of the crown.  
 
     
     
         11 . The mechanically driven press of  claim 10  further comprising: 
 A block for mounting the fixed end of the cantilever support to the crown, the block being located in the middle of the crown.  
 
     
     
         12 . The mechanically driven press of  claim 11  wherein the force developed by the press is at least 150,000 pounds.  
     
     
         13 . The mechanically driven press of  claim 12  wherein the distortion of the crown of the press that is measured by the LVDT is less than 0.25 inches.  
     
     
         14 . A press comprising an upper platen and a lower platen and having a tonnage monitor for monitoring the force exerted by the upper platen against the lower platen, the press comprising: 
 a base for supporting the lower platen;    a pair of vertical columns attached to the base and a crown supported by the columns;    a ballscrew shaft suspended from the crown and coupled to the upper platen;    a rotary electric motor coupled to the ballscrew shaft for causing the platen driving member to press the upper platen against the lower platen;    guide posts for maintaining the upper platen in alignment with the lower platen;    an instrument for measuring the distortion of the crown caused by the platen driving member pressing the upper platen against the lower platen; and,    a cantilever support supporting the instrument over the top of the crown, the cantilever support being mounted on a support block, the support block being located in the center of the crown, whereby the instrument measures the increase in height of the center of the crown relative to the ends of the crown.