Abstract:
A mechanical press having a press deflection controller. The press includes press members which have work surfaces, such as a slide and a bed. The press deflection controller includes a tie rod which is encased in a tube. The tie rod is connected to the press member and is maintained in tension while the tube is maintained in compression. Adjusting the tension in the tie rod during press operation works to adjust deflection in the press member.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and apparatus for controlling deflections in the work surfaces of a mechanical press. The method and apparatus of the current invention may be used to alter the deflection in the work surface of, for example, the slide or the bed of a mechanical press. The method and apparatus of the current invention may be employed to alter deflections prior or not prior to machining the work surface of a press member and/or during press operation. 
     2. Description of the Related Art 
     Mechanical presses, for example, stamping presses and drawing presses, comprise a frame having a crown and a bed with a slide supported within the frame for motion toward and away from the bed. Such mechanical presses are widely used for stamping and drawing operations and vary substantially in size and available tonnage depending upon the intended use. 
     Conventional press machines employ a tooling apparatus in the form of a die assembly to shape a workpiece, such as in a stamping or drawing operation. The die assembly particularly includes a lower die attached to the work surface of a non-moveable bed or bolster and an upper die or punch attached to the work surface of a reciprocating slide. The upper and lower dies, which are installed in opposing spaced apart relation to one another, cooperate during press machine operation to mutually engage the workpiece at respective sides thereof to thereby effect the desired forming activity. 
     Repeated stamping operations of a mechanical press cause deflections in portions of the press. For example, press operation causes deflections in the bed and the slide of the mechanical press. Bed and slide deflections are typically within the range of 0.002″ per foot to 0.005″ per foot of slide or bed width. In some production environments, such deflections will cause scrapping of stamped product which leads to increased cost and production time. 
     The working surfaces of the slide and the bed are typically machined to produce substantially uniform work surfaces. Having to re-machine these work surfaces is undesirable due to the necessary press down time and the wear to the work surfaces caused by additional machining. Replacing deflected work surfaces is undesirable due to the necessary press down time and substantial expense. 
     What is needed in the art is an apparatus and method to minimize the deflection experienced by portions of the mechanical press during press operation. What is additionally needed in the art is an apparatus and a method to monitor deflections experienced during press operation and to provide a means for automatically adjusting deflections during press operation. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method and apparatus which works to eliminate deflection experienced in members of a mechanical press. 
     The present invention places members of a mechanical press in a prestressed condition to minimize deflection in the work surface of the press member. Further, the present invention can be utilized to monitor deflections experienced during press operation and to automatically adjust deflection during press operation. 
     The invention, in one form thereof, comprises a mechanical press including a press member which has a work surface that experiences deflection during press operation. A deflection controller is provided and controls the deflection of the work surface of the press member. The press member can be, for example, a slide or a bed. 
     The invention, in another form thereof, includes a deflection controller which comprises a tie rod that is connected to a press member and is maintained in tension. In one form of the current invention, the tie rod is connected to the work surface of the press member. 
     In one form of the current invention, the deflection controller comprises a tie rod which is connected by a pair of tie rod nuts to a press member. The tie rod nuts are threadedly connected to the tie rod and are selectively actuatable. When actuated the tie rod nuts increase the tension in the tie rod which correspondingly alters the deflection in the press member. 
     The invention, in another form thereof, comprises a deflection controller for controlling the deflection in the work surface of a press member which includes a tie rod connected to the press member and which is maintained in tension. A pair of tie rod nuts are threadedly connected to the tie rod so that when actuated the tie rod nuts increase the tension in the tie rod and correspondingly alter the deflection in the press member. A deflection measuring means which can be, for example, a strain gage or a non-contacting optical or electrical sensing means measures the deflection of the press member. A display device is provided and is communicatively connected to the deflection measuring means and displays the deflection measured by the deflection measuring means. The display device may also display a predetermined desired deflection. In this way, the deflection experienced in a press member may be compared to a predetermined desired deflection so that the tie rod nuts may be actuated when the measured deflection deviates from the predetermined desired deflection. In this way, the deflection experienced during press operation may be altered. 
     The invention, in another form thereof, comprises a deflection controller for controlling the deflection of the work surface of a mechanical press member. In this form, the deflection controller comprises a tie rod connected to the press member by a pair of pressure activated tie rod nut assemblies such that the tie rod is in tension. When the tie rod nut assemblies are activated, they increase the tension in the tie rod and correspondingly alter the deflection in the press member. A feedback means is connected to a deflection measuring means and to the tie rod nut assemblies for comparing a predetermined desired deflection to a measured deflection. The feedback means activates the tie rod nut assemblies when the measured deflection deviates from the predetermined desired deflection. 
     The invention, in another form thereof, includes pressure activated tie rod nuts. The pressure activated tie rod nuts each include a cylinder block which has a cylinder bore fit about a tie rod. A piston is threadedly engaged about the tie rod and slidingly disposed within the cylinder bore thereby forming an inner chamber. A plurality of seals are operatively located between the piston and the cylinder block to seal the inner chamber. A tie rod nut is threadedly engaged about the tie rod, engaging the piston, so that when the inner chamber is pressurized with a liquid, the increase in pressure forces the piston and tie rod nut away from the cylinder block and thereby increases the tension in the tie rod. In one form of the current invention, a tube encases the tie rod and is in compression. 
     The invention, in another form thereof, includes a feedback means which activates the pressure activated tie rod nut assemblies by altering the pressure within the inner chamber. The feedback means comprises: pressurizing means connected to the pressure activated tie rod nut assemblies and a comparator. The pressurizing means is activated by a control signal and changes the pressure of liquid communicated to the tie rod nut assemblies in response to the control signal. The pressurizing means can be, for example, a pump, a hydraulic cylinder, or a hydraulic power unit. The comparator has input lines for a measured deflection from a deflection measuring means and for a predetermined desired deflection. The comparator further includes an output line connected to the pump. The comparator causes a control signal to be formed on the output line on the basis of a comparison between a measured deflection and a predetermined desired deflection. 
     The invention, in another form thereof, comprises a press in which a crown and bed are connected together by a frame. A slide is connected within the frame for reciprocating movement in opposed relation to the bed. Both the bed and the slide have work surfaces and opposing sides which are substantially parallel to each other and perpendicular to their respective work surfaces. A first tie rod which has a first and a second end is connected to either the opposing sides of the bed or the opposing sides of the slide. In one form of the current invention, a second tie rod which has a first and a second end may be connected to the other of the opposing sides of the bed or the opposing sides of the slide. Both the first and the second tie rod may further include a tube which encases the tie rod and is in compression. 
     The invention, in another form thereof, comprises a method for controlling the deflection in the work surfaces of a mechanical press. This method comprises the steps of: connecting a first tie rod to one of the slide or the bed of the press and placing the first tie rod in tension. 
     The invention, in another form thereof, comprises a method for controlling the deflection in the work surfaces of a mechanical press. This method comprises the steps of: connecting a first tie rod to one of the slide or the bed of the press, placing the first tie rod in tension, encasing the first tie rod within a first tube, placing the first tube in compression, monitoring the deflection in the work surface of the press member to which the first tie rod is connected and altering the tension in the first tie rod and thereby correspondingly altering the compression in the first tube based upon the monitored deflection in the work surface of the press member to which the first tie rod is connected. 
     The invention, in another form thereof, comprises a method for controlling the deflection in the work surfaces of a mechanical press. This method comprises the steps of: connecting a first tie rod to one of the slide or the bed of the press; connecting a second tie rod to the other of the slide or the bed of the press; placing the both the first tie rod and the second tie rod in tension; encasing the both the first tie rod and the second tie rod within a first tube and a second tube, respectively; placing the first tube and the second tube in compression; monitoring the deflection in the work surfaces of the press members to which the first and second tie rods are connected and altering the tension in the first tie rod and/or the second tie rod and thereby correspondingly altering the compression in the first tube and/or the second tube based upon the monitored deflection in the work surface of the press member to which the first tie rod and/or the second tie rod is connected. 
     The invention, in another form thereof, comprises an apparatus for placing an object in a prestressed condition. This apparatus includes a tie rod and a tube encasing the tie rod. The tie rod and the tube encasing the tie rod are connected to the object which is to be placed in a prestressed condition such that the tie rod is in tension and the tube is in compression. 
     An advantage of the present invention is that the work surface of a mechanical press member may be placed in a prestressed condition prior to the machining of the work surface so that deflections experienced by the work surface may be minimized. 
     Another advantage of the present invention is that deflections experienced by a member of a mechanical press during press operation may be adjusted without having to re-machine the work surface or disassemble the mechanical press. 
     Yet another advantage of the present invention is that deflections may be automatically sensed and eliminated during press operation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a front elevational view of a mechanical press incorporating the deflection controller of the present invention; 
     FIG. 2 is a cross sectional view taken along lines A-A′ in FIG. 1 to illustrate the tie rod/tube combination in accordance with an embodiment of the present invention; 
     FIG. 3 is an enlarged sectional view of a pressure activated tie rod nut assembly of the present invention; 
     FIG. 4 is a schematic of the feedback means of the present invention; and 
     FIG. 5 is a schematic of the display means of the present invention. 
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIG. 1, mechanical press  10  comprises a crown  12 , a bed  14  having a bolster  16  connected thereto and uprights  18  connecting crown  12  with bed  14 . Uprights  18  are connected to or integral with the underside of crown  12  and the upper side of bed  14 . Tie rods (not shown) extend through crown  12 , uprights  18  and bed  14  and are attached on each end with tie rod nuts (not shown). Leg members  22  are formed as an extension of bed  14  and are generally mounted on the shop floor  24  by means of shock absorbing pads  26 . 
     A drive mechanism, such as a press drive motor  28 , is attached to crown  12  of the press and connected by a clutch/brake mechanism (not shown) to a crankshaft (also not shown) to which connecting rods  32  are attached. A slide  34  is operatively connected to connecting rods  32 . During operation, drive motor  28  rotates the crankshaft which operates eccentrically connected connecting rods  32  to cause slide  20  to reciprocate in rectilinear fashion toward and away from bed  14 . 
     FIG. 2 illustrates a cross section of first tie rod  42  and first tube  46 . Referring to FIG. 1, first tie rod  42  is connected to bed  14  by pressure activated tie rod nuts  40 . First tube  46  encases first tie rod  42 . Second tie rod  44  is connected to slide  34  by tie rod nuts (not shown). Second tube  48  encases second tie rod  44 . 
     Press deflection is controlled by first measuring the deflection of a press member, such as bed  14 . Deflection measuring means  20 , for example, a non-contacting optical or electrical sensing means, or a strain gage is utilized to measure deflection of bed  14  during press operation. Deflection may similarly be measured in slide  34 . 
     FIG. 3 illustrates a pressure activated tie rod nut  40  of the present invention. Pressure activated tie rod nut  40  comprises an annular cylinder  36  mounted upon bed  14  and about first tie rod  42 . Annular cylinder  36  includes an annular bore  38  about first tie rod  42  into which an annular piston  50  is slidingly interfit. Annular piston  50  includes an annular threaded bore  52  which is threadedly engaged on threads  54  of first tie rod  42 . Annular piston  50  sealingly interfits within annular bore  38  by means of seals  56 . Seals  56  seal between annular piston  50  and annular cylinder  36  defining a chamber  58 . Chamber  58  is connected to an oil inlet  60  that is constructed through annular cylinder  36 . Annular piston  50  slides within annular cylinder  36  based on the pressure of oil injected through oil inlet  60 . 
     On annular piston  50  and first tie rod  42  is threaded a tie rod nut  62 . Tie rod nut  62  includes an annular bore having threads  64  that engage threads  54  of first tie rod  42 . The bottom surface  66  of tie rod nut  62  engages the top surface  68  of annular piston  50 . 
     As illustrated in FIG. 4, automatic control of deflection is maintained by control feedback means  70 . The press operator may choose differing values for preselected deflection  76  including values corresponding to a bowed configuration of the press member. Preselected deflection  76  is communicated along communication line  72  to comparator  74 . Comparator  74  can be, for example, a microprocessor. Alternatively, comparator  74  may be constructed from a programmable logic controller as is known in the art. Comparator  74  receives input signals and provides output or control signals as a function of its input. 
     Deflection measuring means  20  (FIG. 1) transmits an actual deflection measurement  78  (FIG. 4) through communication line  80  to comparator  74  during press operation. Comparator  74  compares input preselected deflection  76  to actual deflection measurement  78  and forms a control signal based upon this comparison. The control signal is communicated along communication line  82  to a pressurizing means such as pump  84 . A hydraulic pump or a hydraulic power unit may also be utilized as the pressurizing means. Pump  84  communicates pressurized fluid along fluid line  86  to pressure activated tie rod nut  40 . The result of the comparison between preselected deflection  76  and actual deflection measurement  78  causes comparator  74  to vary the control signal on communication line  82  to pump  84  which then alters the pressure to the pressure activated tie rod nut(s)  40 . Tension in first tie rod  42  (FIG. 1) is thus controlled by altering the pressure within chamber  58  in one or both of pressure activated tie rod nut(s)  40 . 
     FIG. 5 illustrates an alternate embodiment of the present invention which utilizes display device  88 . Display device  88  is communicatively connected to deflection measuring means  20 . Actual deflection measurement  78  is communicated along communication line  90  to display device  88 . Input preselected deflection  76  is communicated along communication line  92  to display device  88 . During press operation, a press operator can monitor display device  88  to determine if actual deflection measurement  80  is outside an acceptable range, or deviates from input preselected deflection  76  by an unacceptable amount. The press operator may then manually actuate the tie rod nuts, or signal the pressurizing means to actuate the press activated tie rod nut assemblies depending upon which type of tie rod nut is utilized. 
     Alternatively, the tie rod may terminate in conventional (one piece) tie rod nuts. In this case, the tie rod may be placed into tension and thereby prestressed prior to press operation or slide or bed surface milling. The work surface may thereby be bowed by the prestressed, thereby being prepared for possible deflection during press operation. 
     In the embodiment illustrated in FIG. 4, preselected deflection  76  is communicated along communication line  72  to comparator  74 . During press operation, deflection measuring means  20  continually monitors the deflection in a press member, for example, the deflection (d) in the bed. Deflection measuring means  20  communicates actual deflection measurement  78  along communication line  80  to comparator  74 . Comparator  74  varies the control signal on communication line  82  to pump  84  which then alters the pressure in the pressure activated tie rod nut(s)  40 . As the pressure in the pressure activated tie rod nuts  40  is increased, the tension in first tie rod  42  increases and adjusts deflection (d). In this way, deflections experienced during press operation are constantly monitored and adjustments resulting in the minimization of deflection are constantly made. 
     While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.