Patent Publication Number: US-4653311-A

Title: Short stroke press with automated feed mechanism

Description:
FIELD OF INVENTION 
     The present invention relates generally to power presses and is particularly useful in transfer presses having servo-driven feed mechanisms. 
     Power presses are typically designed with the stroke of the press long enough to allow adequate time for the feed mechanism to execute its transfer cycle while the dies of the press are open, i.e., while the press slide is far enough above the workpieces to permit them to be accessed by the feed mechanism. As the stroke of the press is lengthened, the cost of the press increases not only because of the larger press size required for the longer stroke, but also because the increased torque demand of the longer stroke requires larger and higher-powered clutches and brakes. This also results in an undesirably high impact velocity which, in turn, produces high noise levels and increased die wear rates. 
     This problem exists not only in transfer presses, which have multiple work stations within a single press, but also in single-station presses operating alone or in a synchronized line of such presses. Each single-station press normally has both a loading mechanism and an unloading mechanism associated with it, and the cycle time of these mechanisms can be even longer than that of the feed mechanism in a transfer press, thereby requiring even longer press strokes. 
     SUMMARY OF THE INVENTION 
     It is a primary object of the present invention to provide an improved power press which reduces the size and cost of the press while at the same time providing a very low impact velocity and allowing adequate time for the feed mechanism, or the loading and unloading mechanisms, to operate during the &#34;open&#34; portion of the press cycle. In this connection, a related object of the invention is to provide such an improved press which permits the use of relatively small and less expensive clutches and brakes which consume less power than the clutches and brakes used in comparable presses today. 
     It is another important object of this invention to provide such an improved press which reduces the noise levels and die wear rates by reducing the impact velocity. 
     A further object of this invention is to provide such an improved press which offers relatively low overall energy consumption rates for any given amount of work. 
     Still another object of this invention is to provide such an improved press which has a relatively short stroke length, e.g., a stroke length only half as long as the stroke of presses currently used for the same purposes. 
     A still further object of the invention is to provide an improved method of operating power presses, which can be implemented by retrofitting presses already in the field. 
     Other objects and advantages of the invention will be apparent from the following detailed description and the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a perspective view of a transfer press with a servo-driven feed mechanism; 
     FIG. 2 is a diagrammatic illustration of the movement paths of the main press drive shaft and crank and the press slide; 
     FIG. 3 is a diagrammatic illustration of the path of movement of the transfer feed mechanism; 
     FIG. 4 is a fragmented perspective view of a transfer feed mechanism for use in the press of FIG. 1, and FIGS. 4A, 4B, and 4C are enlargements of the three fragments of the transfer feed mechanism shown in FIG. 4; 
     FIG. 5 is a section taken generally along line 5--5 in FIG. 4, on an enlarged scale; 
     FIG. 6 is a side elevation taken generally along line 6--6 in FIG. 5; 
     FIG. 7 is a section taken generally along line 7--7 in FIG. 5, on an enlarged scale; 
     FIG. 8 is a section taken generally along line 8--8 in FIG. 6, on an enlarged scale; and 
     FIG. 9 is a side elevation of a synchronized line of single-station presses each of which has a loading mechanism and an unloading mechanism associated therewith. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed, but, on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     Turning now to the drawings and referring first to FIG. 1, there is shown a power press 10 having a vertically movable slide 11 which is supported by a plurality of columns 12. In operation, the slide 11 carries an upper die 13, and is reciprocated vertically such that the upper die 13 and a stationary lower die 14 are alternately brought into and out of contact with a workpiece positioned between the two dies. The lower half of the die 14 is supported by a bolster 15 which can be moved transversely in and out of the press slide region. 
     The press 10 is powered from a large motor-driven flywheel on the crown 16. A clutch and brake interlock mechanism is mounted axially on the flywheel and is adapted to arrest the movement of the slide 11. The flywheel delivers power through a differential drive arrangement to each of the four corners of the slide 11 via a pitman 17. The shaft on which the eccentric is located normally has a rotary transducer positioned on one end to monitor the angular motion of the eccentric and hence the pitman and transduces it into an analog signal which is directly proportional to the angular position of the eccentric at any given point during the stroke. 
     A pair of transfer rails 21 and 21&#39; extends longitudinally through the press 10 for transporting workpieces through successive workstations in the press. To accomplish this workpiece movement, the transfer rails 21, 21&#39; can be moved longitudinally (the &#34;X axis&#34;), transversely (the &#34;Y axis&#34;), and vertically (the &#34;Z axis&#34;) by a tri-axial transfer drive. Conventional finger units (see FIGS. 4-8) are rigidly attached to the transfer rails 21, 21&#39; for gripping the workpieces. 
     FIGS. 2 and 3 illustrate one complete operating cycle of a hypothetical press for performing a drawing operation. The top portion of FIG. 2 represents the 360° rotation of the main press drive shaft and crank; the lower portion of FIG. 2 represents the corresponding vertical stroke of the press slide; and FIG. 3 represents the tri-axial movement of the feed mechanism. As indicated by the legends at the top of FIG. 2, the &#34;open&#34; portion of the press cycle begins at the point at which the slide has been raised far enough above its bottom-dead-center (BDC) position to admit the feed mechanism between the dies, and ends at the point at which the upper die (carried on the slide) engages the workpiece. In the illustrative example of FIG. 2, this &#34;open&#34; portion of the press cycle begins at a crank angle of 110° and ends at 274°. The &#34;closed&#34; portion of the press cycle is the remainder of the cycle, and in the illustrative example extends from the crank angle of 110° to 274°. 
     During the &#34;closed&#34; portion of the cycle, the press slide performs the desired work on the workpiece and then moves upwardly to an elevation sufficiently high to admit the feed mechanism between the workpiece and the die carried on the slide. In the illustrative example, the slide traverses the final 28% of its downstroke and about 55% of its upstroke during this &#34;closed&#34; portion of the cycle. During the final 28% of the downstroke, a relatively deep draw is produced in the workpiece; during the initial 28% of the upstroke the die carried by the press slide is withdrawn from the workpiece; and during the next 27% of the upstroke, the slide is raised far enough above the workpiece to admit the feed mechanism which transfers the workpieces between successive stations. 
     During the &#34;open&#34; portion of the cycle, the press slide traverses the final 45% of its upstroke and the initial 72% of its downstroke. It is during this interval that the feed mechanism picks up the workpieces and transfers them to the succeeding stations. 
     Before describing the physical structure of the feed mechanism, it will be helpful to refer to FIG. 3 which diagrammatically illustrates a typical transfer cycle. At the end of the &#34;closed&#34; portion of each press cycle, the feed mechanism moves the transfer finger units into the space between the open dies so as to bring the finger units into engagement with the respective workpieces. The feed mechanism dwells at this position, which is identified as position A in FIG. 3, for a brief interval to allow the finger units to securely grip the workpieces. The feed mechanism is then elevated from position A to position B to lift the workpieces off the lower dies, after which the mechanism is moved both vertically and longitudinally from position B to position C, and then longitudinally to transport the workpieces to the next stations. At position D the feed mechanism begins to descend toward the lower dies, continuing its longitudinal movement until it reaches position E, and then moving straight down to position F to lower the workpieces onto their respective succeeding lower dies. The feed mechanism again dwells at position F for a brief interval to allow the finger units to be disengaged from the workpieces, after which the mechanism is retracted transversely from position F to position G and then returned longitudinally through positions H and I to its original position J, ready for the next transfer cycle. 
     The diagrammatic illustration in FIG. 3 does not include a turnover step, but if the finger units are adapted to turn one or more workpieces while they are being transferred from one workstation to the next, the turnover step is carried out during the longitudinal movement from position C to position D. 
     Turning now to FIGS. 4-8, there is shown a feed mechanism for transferring workpieces sequentially along multiple workstations in the transfer press 10. In order to transfer the various workpieces to the desired positions and with the desired orientations at each of the multiple stations, the feed mechanism can be moved along any or all of the three different axes referred to as the longitudinal or X axis, the transverse or X axis, and the vertical or Z axis. As will be apparent from the ensuing description, the movement of the feed mechanism along each of these three axes is controlled by one or more independently controllable servo motors. 
     As can be seen most clearly in FIG. 4, the feed mechanism includes the aforementioned transfer rails 21 and 21&#39; which extend along opposite sides of the multiple workstations. Each of these rails 21 and 21&#39; carries a set of finger units 22a, 22b . . . 22n and 22&#39;a, 22&#39;b . . . 22&#39;n, respectively, for gripping the workpieces at the respective workstations and transferring them to the next successive workstations. It will be appreciated that a press using a feed mechanism of this type normally has separate loading and unloading mechanisms situated at opposite ends of the press for supplying workpieces to the first pair of finger units 22a, 22&#39;a and removing the finished workpieces from the final pair of finger units 22n, 22&#39;n. 
     Because the entire mechanism associated with one of the transfer rails 21 and 21&#39; is identical to the mechanism associated with the other rail, the detailed description to follow will be directed only to the mechanism associated with one of the rails, and corresponding parts associated with the two rails will be identified by identical reference numerals with the addition of a distinguishing prime for those parts associated with the rail 21&#39;. 
     The illustrative feed mechanism supports the rail 21 on a pair of vertically movable columns 23a and 23b. For vertical movement of the rail 21, a pair of Z-axis servo motors 30a and 30b drive elongated shafts 31a and 31b via successive bevel gear pairs 32a, 33a and 32b, 33b, respectively. The two shafts 31a and 31b carry respective pinions 34a and 34b which mesh with cooperating vertical racks 35a and 35b fastened to the columns 23a and 23b, respectively. As can be seen most clearly in FIG. 4B, the ends of the shafts 31a and 31b are journaled in stationary bearing blocks 36a, 37a and 36b, 37b on the base of the feed mechanism. 
     Each of the columns 23a and 23b is mounted for vertical sliding movement within two sets of six roller bearings 40a, 41a and 40b, 41b (see FIGS. 5 and 6) mounted on housings 42a and 42b, respectively. The roller bearings 40a, 41a and 40b, 41b ride on hardened steel tracks on the vertical side walls of the columns 23a and 23b, thereby guiding the columns along straight vertical paths for lifting and lowering the rail 21. The vertical position of the rail 21 at any given time, of course, is determined by the positions of the racks 35a and 35b as controlled by the Z-axis drive motors 30a and 30b. The two Z-axis drive motors 30a and 30b are driven in synchronism with each other so that the rail 21 is always maintained in a perfectly horizontal position. 
     Transverse movement of the rails 21 and 21&#39; is effected and controlled by a pair of Y-axis servo motors 50a and 50b mounted on the stationary base of the feed mechanism. These two drive motors 50a and 50b drive corresponding pinions 51a and 51b via respective pairs of bevel gears 52a and 52b, and the pinions 51a and 51b in turn mesh with parallel pairs of cooperating horizontal racks 53a, 54a and 53b, 54b attached to the respective housings 42a, 42&#39;a and 42b, 42&#39;b. Thus, reciprocating movement of the racks 53a and 53b moves the housings 42a and 42b, and thus the columns 23a and 23b and the rail 21 mounted thereon, back and forth in the transverse (Y-axis) direction. To accommodate this Y-axis movement, each of the housings 42a, 42b is supported and guided by four roller bearing triplets, 55a and 55b respectively, riding on two pairs of stationary transverse rails 56a, 57a and 56b, 57b (see FIGS. 4B, 4C, 5 and 6). 
     During the traversing movement of the housings 42a and 42b along the transverse rails 56a, 57a and 56b, 57b, the vertical columns 23a, 23b and the racks 35a, 35b mounted thereon, as well as the pinions 34a, 34b meshing therewith, are carried along with the two housings. This traversing movement of the pinions 34a and 34b is effected by respective pairs of bosses 58a and 58b projecting from the housings 42a and 42b on opposite sides of the pinions. To accommodate this Y-axis movement of the Z-axis drive pinions 34a, 34b, the end portions of the shafts 31a and 31b are splined so that the pinions 34a, 34b can slide back and forth along the splined portions of the shafts 31a, 31b while being simultaneously driven by those shafts. The shafts themselves remain stationary except for their rotational movement, and the bevel gears 33a,  33b which drive the shafts are located between the splined portions of the shafts so that they do not interfere with the Y-axis movement of the Z-axis drive pinions 34a, 34b. 
     For longitudinal movement of the transfer rail 21, an X-axis servo motor 60 (see FIG. 4A) drives a transverse shaft 61 carrying a pinion 62 meshing with a stationary rack 63 formed on the bottom of a rail 64 fastened to the base of the feed mechanism. The drive motor 60 is fastened to the bottom of a transverse beam 65 supported for smooth sliding X-axis movement by a pair of linear bearings 66 and 66&#39; sliding on the top and side surfaces of the rails 64 and 64&#39;. The beam 65 is also attached to the ends of the two rails 21 and 21&#39; by a pair of slide blocks 67 and 67&#39; captured in a pair of transverse gibs 68 and 68&#39;. These slide blocks 67, 67&#39; and gibs 68, 68&#39; permit the rails 21, 21&#39; to be moved transversely (in the Y-axis direction) along the beam 65 simultaneously with longitudinal (X-axis) movement of the rails and the beam 65. Vertical movement of the rails 21 and 21&#39; is also permitted by pivoting links 69 and 69&#39; between the respective slide blocks 67, 67&#39; and the rails 21, 21&#39;. 
     To permit the rail 21 to move longitudinally relative to the columns 23a and 23b, even while the columns are moving the rails vertically and/or laterally, the rails 21, 21&#39; ride on parallel sets of roller bearings 70a and 70b carried on the tops of the respective columns 23a and 23b. To hold the rails 21, 21&#39; captive on the columns 23a and 23b for vertical and/or lateral movement therewith, the underside of each rail forms a longitudinal channel 71 which receives a set of canted roller bearings 72a and 72b which are also carried on the tops of the respective columns 23a and 23b. These roller bearings 72a and 72b ride on beveled surfaces within the channel 71, thereby holding the rail 21 captive on the columns while permitting longitudinal movement of the rail relative to the columns. 
     To permit the workpieces to be turned over while they are being transferred from one work station to the next, each of the finger units 22a . . . 22n and 22&#39;a . . . 22&#39;n has the construction illustrated in FIGS. 7 and 8 for the finger unit 22&#39;b. Thus, the grippers 80 of the finger unit are mounted on a shaft 81 carrying a pinion 82 which meshes with a rack 83. The rack 83 can be driven back and forth in the X-axis direction by means of an air cylinder 84, thereby rotating the gripping fingers 80 about the Y-axis to turn over the workpiece carried by the fingers. 
     In accordance with one important aspect of the present invention, the press drive shaft is driven at a first, relatively fast angular velocity during the &#34;closed&#34; portion of each cycle of reciprocating movement of the press slide, and is then driven at a second angular velocity slower than the first angular velocity, during the &#34;open&#34; portion of each cycle of reciprocating movement of the press slide; the second angular velocity is sufficiently slow to allow the automatic feed mechanism to execute its transfer cycle during the &#34;open&#34; portion of each cycle. 
     In the method of this invention, the press drive shaft is decelerated at the beginning of the &#34;open&#34;  portion of the press cycle, preferably as soon as the press slide has been raised to an elevation that permits the feed mechanism to enter the space between the upper and lower dies to remove the workpieces from that space. The drive shaft then continues to be driven at the reduced velocity throughout the &#34;open&#34; portion of the cycle, i.e., until the upper die is about to impact the next workpiece. Thus, the press can have a short stroke with a low impact velocity while at the same time allowing adequate time for the transfer cycle of even the most complex feed mechanism. For example, in the example to be described below, the press stroke is only half as long as the stroke used in current presses for performing the same work (20 inches instead of 40 inches). In general, each inch of stroke length requires an additional three inches of press height, so a 20-inch reduction in stroke length permits a 60 inch reduction in the height of the press. 
     Furthermore, the impact velocity can be reduced below the lowest levels that are feasible in current long-stroke presses, and this lower impact velocity translates into reduced noise levels, reduced die wear rates, and improved part quality. The clutch and brake can be smaller as a result of the improved mechanical advantage of the shorter stroke, which means they have a lower cost, require less space, and generally present fewer maintenance problems. The lower inertia of the smaller clutch also provides the benefit of reduced energy consumption in comparison to the alternative long stroke system when that system incorporates a &#34;slow down&#34; to reduce the inherent high impact velocity. 
     Moreover, the relatively slow velocity of the press during the entire &#34;open&#34; portion of the cycle is a safer mode of operation because the press can be stopped more quickly, and with less damage, in the event of a fault. Most faults occur during the &#34;open&#34; portion of the press cycle when the dies are open so that obstructions, such as a misaligned workpiece or a faulty feed mechanism, can become lodged between the dies. When the dies are closed or in the process of opening, there is little that can go wrong; and these are the only times when the press drive shaft is driven at the higher velocity in the method of this invention. 
     The following specific example will illustrate how to practice this invention using a conventional eddy current press drive system in a 3200-ton transfer press having the following characteristics: 
     
         ______________________________________                                    
CRANK RADIUS:          9.00    IN.                                        
PITTMAN LENGTH:        130.00  IN.                                        
BELT RATIO:            4.000   to 1                                       
(MOTOR TO CLUTCH)                                                         
GEAR RATIO:            20.000  to 1                                       
(OUTPUT SHAFT TO CRANK)                                                   
SLIDE WEIGHT:          200     TONS                                       
MIN. COUNTERBALANCE FORCE:                                                
                       178.9   TONS                                       
MAX. COUNTERBALANCE FORCE:                                                
                       221.1   TONS                                       
ROTATING PARTS INERTIA 2500    LB-FT.sup.2                                
REFL. TO DRIVE SHAFT:                                                     
FRICTION TORQUE INERTIA                                                   
                       0       LB-FT                                      
REFL. TO DRIVE SHAFT:                                                     
AIR BRAKE TORQUE INERTIA                                                  
                       0       LB-FT                                      
REFL. TO DRIVE SHAFT:                                                     
PRESS IS GEARED FOR:   22.50   SPM                                        
______________________________________                                    
 
    
     Operation of this press was simulated for the following loads: 
     
         ______________________________________                                    
X (IN. FROM BDC) LOAD (TONS)                                              
______________________________________                                    
18.000             0                                                      
5.100              0                                                      
5.000             200                                                     
4.000             300                                                     
3.000             400                                                     
2.000             500                                                     
1.000            2000                                                     
0.500            3200                                                     
0.010            3200                                                     
0.000              0                                                      
______________________________________                                    
 
    
     using an &#34;eddy current&#34; adjustable speed press drive system with the following characteristics: 
     
         ______________________________________                                    
&#34;DYNAMATIC&#34; PRESS DRIVE MODEL:                                            
                         49-63 RUN                                        
PARAMETERS:                                                               
CLUTCH DESCR.:  CES 49-63    STRKL: 5                                     
MAX. CLUTCH TORQUE:                                                       
                95,000  LBS-FT   ICOND: 0.000                             
MAX. BRAKE TORQUE:                                                        
                475,000 LBS-FT.sup.2                                      
                                 HPLL: 16.000                             
INPUT INERTIA:  140,000 LBS-FT.sup.2                                      
                                 DELT: 0.010                              
OUTPUT:         10,000  LBS-FT   PRINTV: 0.050                            
MOTOR ID:                                                                 
         NEMA D                                                           
HP:      800                                                              
RPM:     1800                                                             
SLIP:    8%                                                               
INERTIA: 350 LBS-FT.sup.2                                                 
______________________________________                                    
 
    
     The simulated set points for the crank velocity were 12.5 SPM for 0° to 100°; 20.0 SPM from 110° to 274°; and 12.5 SPM from 274° to 360°. 
     a computer-simulated operation of the above press under the above conditions yielded the following results: 
     
         __________________________________________________________________________
                FLY CLUTCH      BRAKE                                     
TIME                                                                      
    MOTOR       WHL         DISS     DISS                                 
SEC RPM TQ  HP  RPM RPM TQ  HP  TQ   HP                                   
__________________________________________________________________________
CONTROL MODE - CRANK VELOCITY                                             
DRIVE TYPE - TOP                                                          
OPERATING MODE - CONTINUOUS STROKING                                      
0.000                                                                     
    1693                                                                  
        2095                                                              
            676 423 247 60  2        0                                    
0.050                                                                     
    1697                                                                  
        2038                                                              
            659 424 248 20  1        0                                    
0.100                                                                     
    1700                                                                  
        1982                                                              
            642 425 248 7   0        0                                    
0.150                                                                     
    1704                                                                  
        1926                                                              
            625 426 248 2   0        0                                    
0.200                                                                     
    1707                                                                  
        1872                                                              
            609 427 248 1   0        0                                    
0.250                                                                     
    1710                                                                  
        1818                                                              
            592 427 248     0        0                                    
0.300                                                                     
    1713                                                                  
        1766                                                              
            576 428 249     0        0                                    
0.350                                                                     
    1716                                                                  
        1714                                                              
            560 429 249     0        0                                    
0.400                                                                     
    1719                                                                  
        1663                                                              
            545 430 250     0        0                                    
0.450                                                                     
    1722                                                                  
        1614                                                              
            529 430 250     0        0                                    
0.500                                                                     
    1724                                                                  
        1565                                                              
            514 431 251     0        0                                    
0.550                                                                     
    1727                                                                  
        1518                                                              
            499 432 251     0        0                                    
0.600                                                                     
    1729                                                                  
        1471                                                              
            485 432 252     0        0                                    
0.650                                                                     
    1732                                                                  
        1426                                                              
            470 433 252     0        0                                    
0.700                                                                     
    1734                                                                  
        1382                                                              
            456 434 253     0   -554 -26                                  
0.750                                                                     
    1737                                                                  
        1338                                                              
            443 434 253     0   -494 -23                                  
0.800                                                                     
    1739                                                                  
        1296                                                              
            429 435 253     0   -401 -18                                  
0.850                                                                     
    1741                                                                  
        1255                                                              
            416 435 253     0   -410 -19                                  
0.900                                                                     
    1743                                                                  
        1214                                                              
            403 436 253     0   -364 -17                                  
0.950                                                                     
    1745                                                                  
        1175                                                              
            391 436 253     0   -317 -14                                  
1.000                                                                     
    1747                                                                  
        1137                                                              
            378 437 253     0   -269 -12                                  
1.050                                                                     
    1749                                                                  
        1099                                                              
            366 437 253     0   -213 -9                                   
1.100                                                                     
    1751                                                                  
        1063                                                              
            355 438 253     0   -154 -6                                   
1.150                                                                     
    1753                                                                  
        1028                                                              
            343 438 253     0   -92  -3                                   
1.200                                                                     
    1754                                                                  
        994 332 439 252     0   -34  -1                                   
1.250                                                                     
    1756                                                                  
        960 321 439 252     0   -11  0                                    
1.300                                                                     
    1758                                                                  
        928 311 439 252     0   -3   0                                    
1.350                                                                     
    1759                                                                  
        896 300 440 252     0        0                                    
1.400                                                                     
    1761                                                                  
        866 290 440 252     0        0                                    
1.450                                                                     
    1762                                                                  
        836 281 441 252     0        0                                    
1.500                                                                     
    1763                                                                  
        812 273 441 252 3707                                              
                            433      0                                    
1.550                                                                     
    1758                                                                  
        912 306 440 269 38692                                             
                            1254     0                                    
LOAD ZONE ENTERED - START FINE PRINT INTERVAL                             
1.570                                                                     
    1752                                                                  
        1045                                                              
            349 438 290 53484                                             
                            1510     0                                    
1.580                                                                     
    1748                                                                  
        1127                                                              
            375 437 301 58775                                             
                            1521     0                                    
1.590                                                                     
    1743                                                                  
        1217                                                              
            404 436 311 61925                                             
                            1465     0                                    
1.600                                                                     
    1738                                                                  
        1309                                                              
            433 435 323 63609                                             
                            1356     0                                    
1.610                                                                     
    1733                                                                  
        1402                                                              
            463 433 334 64322                                             
                            1217     0                                    
1.620                                                                     
    1728                                                                  
        1494                                                              
            492 432 345 62000                                             
                            1024     0                                    
1.630                                                                     
    1723                                                                  
        1580                                                              
            519 431 356 57867                                             
                            826      0                                    
1.640                                                                     
    1719                                                                  
        1658                                                              
            543 430 365 52741                                             
                            647      0                                    
1.650                                                                     
    1715                                                                  
        1727                                                              
            564 429 373 46654                                             
                            492      0                                    
1.660                                                                     
    1712                                                                  
        1785                                                              
            582 428 380 40133                                             
                            368      0                                    
1.670                                                                     
    1709                                                                  
        1833                                                              
            597 427 385 33144                                             
                            269      0                                    
1.680                                                                     
    1707                                                                  
        1871                                                              
            608 427 388 27063                                             
                            202      0                                    
1.690                                                                     
    1705                                                                  
        1899                                                              
            617 426 389 22283                                             
                            159      0                                    
1.700                                                                     
    1704                                                                  
        1920                                                              
            623 426 389 18311                                             
                            129      0                                    
1.710                                                                     
    1703                                                                  
        1935                                                              
            628 426 388 15907                                             
                            114      0                                    
1.720                                                                     
    1702                                                                  
        1946                                                              
            631 426 386 14786                                             
                            111      0                                    
1.730                                                                     
    1702                                                                  
        1956                                                              
            634 425 384 14750                                             
                            115      0                                    
1.740                                                                     
    1701                                                                  
        1966                                                              
            637 425 382 15560                                             
                            128      0                                    
1.760                                                                     
    1700                                                                  
        1990                                                              
            644 425 379 18668                                             
                            165      0                                    
1.770                                                                     
    1699                                                                  
        2005                                                              
            649 425 377 20456                                             
                            185      0                                    
1.780                                                                     
    1698                                                                  
        2022                                                              
            654 424 376 22125                                             
                            202      0                                    
1.790                                                                     
    1697                                                                  
        2042                                                              
            660 424 376 23531                                             
                            216      0                                    
1.800                                                                     
    1695                                                                  
        2063                                                              
            666 424 376 24586                                             
                            225      0                                    
1.810                                                                     
    1694                                                                  
        2085                                                              
            673 423 375 26135                                             
                            242      0                                    
1.820                                                                     
    1692                                                                  
        2110                                                              
            680 423 373 28483                                             
                            273      0                                    
1.830                                                                     
    1691                                                                  
        2137                                                              
            688 423 370 31927                                             
                            322      0                                    
1.840                                                                     
    1689                                                                  
        2169                                                              
            698 422 366 36412                                             
                            390      0                                    
1.850                                                                     
    1686                                                                  
        2206                                                              
            709 422 362 40890                                             
                            463      0                                    
1.860                                                                     
    1684                                                                  
        2249                                                              
            721 421 358 45520                                             
                            544      0                                    
1.870                                                                     
    1681                                                                  
        2297                                                              
            735 420 354 49170                                             
                            615      0                                    
1.880                                                                     
    1677                                                                  
        2350                                                              
            751 419 351 52750                                             
                            688      0                                    
1.890                                                                     
    1674                                                                  
        2406                                                              
            767 418 347 55656                                             
                            753      0                                    
1.900                                                                     
    1670                                                                  
        2464                                                              
            784 417 344 58358                                             
                            816      0                                    
1.910                                                                     
    1666                                                                  
        2525                                                              
            801 416 341 60883                                             
                            876      0                                    
1.920                                                                     
    1661                                                                  
        2588                                                              
            819 415 337 63613                                             
                            943      0                                    
1.930                                                                     
    1657                                                                  
        2653                                                              
            837 414 334 65606                                             
                            1001     0                                    
1.940                                                                     
    1652                                                                  
        2719                                                              
            856 413 331 66232                                             
                            1040     0                                    
1.950                                                                     
    1647                                                                  
        2784                                                              
            874 412 327 66913                                             
                            1083     0                                    
1.960                                                                     
    1643                                                                  
        2849                                                              
            891 411 323 67604                                             
                            1126     0                                    
1.970                                                                     
    1638                                                                  
        2913                                                              
            909 409 320 68266                                             
                            1169     0                                    
1.980                                                                     
    1633                                                                  
        2977                                                              
            926 408 316 68866                                             
                            1208     0                                    
1.990                                                                     
    1628                                                                  
        3040                                                              
            943 407 313 69329                                             
                            1239     0                                    
2.000                                                                     
    1624                                                                  
        3102                                                              
            959 406 311 69495                                             
                            1250     0                                    
2.010                                                                     
    1619                                                                  
        3163                                                              
            975 405 311 69387                                             
                            1242     0                                    
2.020                                                                     
    1614                                                                  
        3223                                                              
            991 403 311 69021                                             
                            1218     0                                    
2.030                                                                     
    1609                                                                  
        3281                                                              
            1006                                                          
                402 312 68417                                             
                            1178     0                                    
2.040                                                                     
    1604                                                                  
        3337                                                              
            1020                                                          
                401 314 67588                                             
                            1124     0                                    
2.050                                                                     
    1600                                                                  
        3391                                                              
            1033                                                          
                400 316 66550                                             
                            1058     0                                    
2.060                                                                     
    1595                                                                  
        3443                                                              
            1046                                                          
                399 320 65226                                             
                            981      0                                    
2.070                                                                     
    1591                                                                  
        3493                                                              
            1059                                                          
                398 324 63365                                             
                            890      0                                    
2.080                                                                     
    1587                                                                  
        3541                                                              
            1070                                                          
                397 329 61312                                             
                            793      0                                    
2.090                                                                     
    1583                                                                  
        3585                                                              
            1081                                                          
                396 334 59079                                             
                            694      0                                    
2.100                                                                     
    1579                                                                  
        3627                                                              
            1091                                                          
                395 340 55853                                             
                            584      0                                    
2.110                                                                     
    1576                                                                  
        3665                                                              
            1100                                                          
                394 346 52233                                             
                            477      0                                    
2.120                                                                     
    1572                                                                  
        3699                                                              
            1108                                                          
                393 352 48109                                             
                            374      0                                    
2.130                                                                     
    1570                                                                  
        3729                                                              
            1115                                                          
                392 359 43662                                             
                            280      0                                    
2.140                                                                     
    1567                                                                  
        3754                                                              
            1121                                                          
                392 365 38349                                             
                            194      0                                    
2.150                                                                     
    1565                                                                  
        3775                                                              
            1125                                                          
                391 372 31342                                             
                            117      0                                    
2.160                                                                     
    1564                                                                  
        3789                                                              
            1129                                                          
                391 379 22850                                             
                            53       0                                    
LOAD ZONE COMPLETE - RESUME COARSE PRINT INTERVAL                         
2.200                                                                     
    1565                                                                  
        3776                                                              
            1126                                                          
                391 390 1909                                              
                            1        0                                    
2.250                                                                     
    1571                                                                  
        3714                                                              
            1111                                                          
                393 391 724 0        0                                    
2.300                                                                     
    1577                                                                  
        3650                                                              
            1096                                                          
                394 392 573 0        0                                    
2.350                                                                     
    1583                                                                  
        3586                                                              
            1081                                                          
                396 393 491 0        0                                    
2.400                                                                     
    1589                                                                  
        3521                                                              
            1065                                                          
                397 393 465 0        0                                    
2.450                                                                     
    1594                                                                  
        3456                                                              
            1049                                                          
                399 394 484 0        0                                    
2.500                                                                     
    1600                                                                  
        3390                                                              
            1033                                                          
                400 395 470 0        0                                    
2.550                                                                     
    1605                                                                  
        3325                                                              
            1017                                                          
                401 395 432 1        0                                    
2.600                                                                     
    1611                                                                  
        3260                                                              
            1000                                                          
                403 396 383 1        0                                    
2.650                                                                     
    1616                                                                  
        3194                                                              
            983 404 396 328 0        0                                    
2.700                                                                     
    1621                                                                  
        3129                                                              
            966 405 396 268 0        0                                    
2.750                                                                     
    1627                                                                  
        3063                                                              
            949 407 397 208 0        0                                    
2.800                                                                     
    1632                                                                  
        2997                                                              
            932 408 397 145 0        0                                    
2.850                                                                     
    1637                                                                  
        2932                                                              
            914 409 397 92  0        0                                    
2.900                                                                     
    1641                                                                  
        2866                                                              
            896 410 397 51  0        0                                    
2.950                                                                     
    1646                                                                  
        2801                                                              
            878 412 397 21  0        0                                    
3.000                                                                     
    1651                                                                  
        2735                                                              
            860 413 378 11  0   -75326                                    
                                     -5421                                
3.050                                                                     
    1655                                                                  
        2672                                                              
            842 414 211 2034                                              
                            78  -99850                                    
                                     -4016                                
3.100                                                                     
    1656                                                                  
        2668                                                              
            841 414 160 30606                                             
                            1479                                          
                                -16021                                    
                                     -487                                 
3.150                                                                     
    1640                                                                  
        2893                                                              
            903 410 206 65867                                             
                            2562                                          
                                -5534                                     
                                     -216                                 
3.200                                                                     
    1624                                                                  
        3094                                                              
            957 406 257 18529                                             
                            525 -8473                                     
                                     -414                                 
3.350                                                                     
    1634                                                                  
        2970                                                              
            924 408 245 1818                                              
                            57  -1164                                     
                                     -53                                  
3.400                                                                     
    1638                                                                  
        2914                                                              
            909 409 245 1742                                              
                            54  -381 -17                                  
3.450                                                                     
    1642                                                                  
        2857                                                              
            894 411 246 1212                                              
                            38  -124 -5                                   
3.500                                                                     
    1647                                                                  
        2797                                                              
            877 412 247 724 23  -40  -1                                   
3.550                                                                     
    1651                                                                  
        2735                                                              
            860 413 247 476 15  -12  0                                    
3.600                                                                     
    1655                                                                  
        2673                                                              
            843 414 247 417 13  -3   0                                    
3.650                                                                     
    1660                                                                  
        2612                                                              
            826 415 247 433 14       0                                    
3.700                                                                     
    1664                                                                  
        2551                                                              
            808 416 247 447 14       0                                    
3.750                                                                     
    1668                                                                  
        2490                                                              
            791 417 247 436 14       0                                    
3.800                                                                     
    1672                                                                  
        2430                                                              
            774 418 247 403 13       0                                    
3.850                                                                     
    1676                                                                  
        2371                                                              
            757 419 247 358 12       0                                    
3.900                                                                     
    1680                                                                  
        2312                                                              
            740 420 247 308 10       0                                    
3.950                                                                     
    1683                                                                  
        2254                                                              
            723 421 247 254 8        0                                    
4.000                                                                     
    1687                                                                  
        2196                                                              
            706 422 247 198 7        0                                    
4.050                                                                     
    1691                                                                  
        2138                                                              
            689 423 247 139 5        0                                    
4.100                                                                     
    1694                                                                  
        2081                                                              
            672 424 247 78  3        0                                    
__________________________________________________________________________
PRESS                          LOAD                                       
TIME REF  ACT. SLIDE                                                      
                    SLIDE                                                 
                         CRANK                                            
SEC  SPM  SPM  VEL  POSIT                                                 
                         ANGLE TONS                                       
                                   TQ                                     
__________________________________________________________________________
CONTROL MODE - CRANK VELOCITY                                             
DRIVE TYPE - TOP                                                          
OPERATING MODE - CONTINUOUS STROKING                                      
0.000                                                                     
     12   12.4 0.0  18.00                                                 
                         0     0                                          
0.050                                                                     
     12   12.4 3.5  17.99                                                 
                         4     0   62                                     
0.100                                                                     
     12   12.4 7.0  17.93                                                 
                         7     0   124                                    
0.150                                                                     
     12   12.4 10.5 17.85                                                 
                         11    0   183                                    
0.200                                                                     
     12   12.4 14.0 17.72                                                 
                         15    0   239                                    
0.250                                                                     
     12   12.4 17.4 17.57                                                 
                         19    0   290                                    
0.300                                                                     
     12   12.4 20.8 17.38                                                 
                         22    0   337                                    
0.350                                                                     
     12   12.5 24.2 17.15                                                 
                         26    0   377                                    
0.400                                                                     
     12   12.5 27.5 16.89                                                 
                         30    0   411                                    
0.450                                                                     
     12   12.5 30.7 16.60                                                 
                         34    0   438                                    
0.500                                                                     
     12   12.5 33.8 16.28                                                 
                         37    0   457                                    
0.550                                                                     
     12   12.6 36.8 15.93                                                 
                         41    0   468                                    
0.600                                                                     
     12   12.6 39.8 15.54                                                 
                         45    0   471                                    
0.650                                                                     
     12   12.6 42.6 15.13                                                 
                         49    0   466                                    
0.700                                                                     
     12   12.6 45.2 14.69                                                 
                         52    0   468                                    
0.750                                                                     
     12   12.6 41.5 14.23                                                 
                         56    0   448                                    
0.800                                                                     
     12   12.6 49.7 13.74                                                 
                         60    0   420                                    
0.850                                                                     
     12   12.6 51.7 13.23                                                 
                         64    0   387                                    
0.900                                                                     
     12   12.6 53.5 12.71                                                 
                         68    0   346                                    
0.950                                                                     
     12   12.6 55.1 12.16                                                 
                         71    0   300                                    
1.000                                                                     
     12   12.6 56.5 11.60                                                 
                         75    0   248                                    
1.050                                                                     
     12   12.6 57.6 11.03                                                 
                         79    0   191                                    
1.100                                                                     
     12   12.6 58.5 10.45                                                 
                         83    0   131                                    
1.150                                                                     
     12   12.6 59.1 9.87 87    0   68                                     
1.200                                                                     
     12   12.6 59.5 9.27 90    0   4                                      
1.250                                                                     
     12   12.6 59.6 8.68 94    0   -57                                    
1.300                                                                     
     12   12.6 59.5 8.08 98    0   -118                                   
1.350                                                                     
     12   12.6 59.0 7.49 102   0   -177                                   
1.400                                                                     
     12   12.6 58.3 6.90 105   0   -234                                   
1.450                                                                     
     12   12.6 57.3 6.32 109   0   -286                                   
1.500                                                                     
     20   12.6 56.3 5.76 113   0   -479                                   
1.550                                                                     
     20   13.5 60.4 5.19 117   0   -1778                                  
LOAD ZONE ENTERED - START FINE PRINT INTERVAL                             
1.570                                                                     
     20   14.5 64.3 4.94 119   206 -16082                                 
1.580                                                                     
     20   15.0 66.1 4.81 119   219 -16670                                 
1.590                                                                     
     20   15.6 67.8 4.68 120   232 -17473                                 
1.600                                                                     
     20   16.1 69.6 4.55 121   246 -18205                                 
1.610                                                                     
     20   16.7 71.3 4.41 122   260 -18895                                 
1.620                                                                     
     20   17.3 72.7 4.27 123   274 -19470                                 
1.630                                                                     
     20   17.8 73.7 4.12 124   288 -19976                                 
1.640                                                                     
     20   18.3 74.4 3.98 126   303 -20436                                 
1.650                                                                     
     20   18.7 74.7 3.83 127   318 -20850                                 
1.660                                                                     
     20   19.0 74.6 3.68 128   333 -21231                                 
1.670                                                                     
     20   19.2 74.1 3.53 129   347 -21574                                 
1.680                                                                     
     20   19.4 73.2 3.38 130   362 -21917                                 
1.690                                                                     
     20   19.4 72.0 3.24 131   377 -22262                                 
1.700                                                                     
     20   19.4 70.6 3.10 132   391 -22590                                 
1.710                                                                     
     20   19.4 69.0 2.96 134   405 -22916                                 
1.720                                                                     
     20   19.3 67.4 2.82 135   419 -23227                                 
1.730                                                                     
     20   19.2 65.7 2.69 136   432 -23512                                 
1.740                                                                     
     20   19.1 64.1 2.56 137   445 -23763                                 
1.760                                                                     
     20   18.9 60.9 2.31 139   470 -24131                                 
1.770                                                                     
     20   18.9 59.4 2.18 141   482 -24235                                 
1.780                                                                     
     20   18.8 57.9 2.07 142   494 -24281                                 
1.790                                                                     
     20   18.8 56.5 1.95 143   578 -27771                                 
1.800                                                                     
     20   18.8 55.0 1.84 144   746 -34836                                 
1.810                                                                     
     20   18.7 53.2 1.73 145   908 -41222                                 
1.820                                                                     
     20   18.6 51.3 1.63 146   1066                                       
                                   -46998                                 
1.830                                                                     
     20   18.5 49.4 1.53 147   1218                                       
                                   -52162                                 
1.840                                                                     
     20   18.3 47.4 1.43 148   1364                                       
                                   -56723                                 
1.850                                                                     
     20   18.1 45.5 1.34 149   1504                                       
                                   -60681                                 
1.860                                                                     
     20   17.9 43.6 1.25 151   1638                                       
                                   -64063                                 
1.870                                                                     
     20   17.7 41.7 1.16 152   1767                                       
                                   -66879                                 
1.880                                                                     
     20   17.5 39.9 1.08 153   1890                                       
                                   -69167                                 
1.890                                                                     
     20   17.4 38.2 1.00 154   2012                                       
                                   -71100                                 
1.900                                                                     
     20   17.2 36.5 0.93 155   2192                                       
                                   -74688                                 
1.910                                                                     
     20   17.0 34.8 0.85 156   2364                                       
                                   -77526                                 
1.920                                                                     
     20   16.9 33.1 0.79 157   2527                                       
                                   -79678                                 
1.930                                                                     
     20   16.7 31.4 0.72 158   2683                                       
                                   -81173                                 
1.940                                                                     
     20   16.5 29.7 0.66 159   2830                                       
                                   -82042                                 
1.950                                                                     
     20   16.3 28.1 0.60 160   2970                                       
                                   -82334                                 
1.960                                                                     
     20   16.2 26.5 0.55 161   3102                                       
                                   -82085                                 
1.970                                                                     
     20   16.0 25.0 0.49 162   3200                                       
                                   -80676                                 
1.980                                                                     
     20   15.8 23.5 0.45 163   3200                                       
                                   -76686                                 
1.990                                                                     
     20   15.7 22.2 0.40 164   3200                                       
                                   -72716                                 
2.000                                                                     
     20   15.6 20.9 0.36 164   3200                                       
                                   -68737                                 
2.010                                                                     
     20   15.5 19.7 0.32 165   3200                                       
                                   -64741                                 
2.020                                                                     
     20   15.5 18.5 0.28 166   3200                                       
                                   -60716                                 
2.030                                                                     
     20   15.6 17.4 0.24 167   3200                                       
                                   -56654                                 
2.040                                                                     
     20   15.7 16.3 0.21 168   3200                                       
                                   -52546                                 
2.050                                                                     
     20   15.8 15.2 0.18 169   3200                                       
                                   -48382                                 
2.060                                                                     
     20   16.0 14.0 0.15 170   3200                                       
                                   -44154                                 
2.070                                                                     
     20   16.2 12.8 0.12 171   3200                                       
                                   -39855                                 
2.080                                                                     
     20   16.4 11.6 0.10 172   3200                                       
                                   -35479                                 
2.090                                                                     
     20   16.7 10.3 0.08 173   3200                                       
                                   -31019                                 
2.100                                                                     
     20   17.0 9.0  0.06 174   3200                                       
                                   -26471                                 
2.110                                                                     
     20   17.3 7.5  0.04 175   3200                                       
                                   -21832                                 
2.120                                                                     
     20   17.6 6.0  0.03 176   3200                                       
                                   -17102                                 
2.130                                                                     
     20   17.9 4.4  0.02 177   3200                                       
                                   -12280                                 
2.140                                                                     
     20   18.3 2.7  0.01 178   1267                                       
                                   -2921                                  
2.150                                                                     
     20   18.6 0.9  0.01 179   128 -96                                    
2.160                                                                     
     20   18.9 1.0  0.01 181   0   17                                     
LOAD ZONE COMPLETE - RESUME COARSE PRINT INTERVAL                         
2.200                                                                     
     20   19.5 9.0  0.05 185   0   2                                      
2.250                                                                     
     20   19.6 19.0 0.19 191   0   2                                      
2.300                                                                     
     20   19.6 28.8 0.42 197   0   1                                      
2.350                                                                     
     20   19.6 38.3 0.76 203   0   1                                      
2.400                                                                     
     20   19.7 47.3 1.19 209   0   1                                      
2.450                                                                     
     20   19.7 55.8 1.71 215   0   1                                      
2.500                                                                     
     20   19.7 63.7 2.30 221   0   3                                      
2.550                                                                     
     20   19.8 70.8 2.98 227   0   7                                      
2.600                                                                     
     20   19.8 77.0 3.72 232   0   12                                     
2.650                                                                     
     20   19.8 82.4 4.51 238   0   18                                     
2.700                                                                     
     20   19.8 86.7 5.36 244   0   24                                     
2.750                                                                     
     20   19.8 90.1 6.25 250   0   30                                     
2.800                                                                     
     20   19.9 92.4 7.16 256   0   34                                     
2.850                                                                     
     20   19.9 93.6 8.09 262   0   35                                     
2.900                                                                     
     20   19.9 93.8 9.03 268   0   33                                     
2.950                                                                     
     20   19.9 92.9 9.96 274   0   26                                     
3.000                                                                     
     12   18.9 82.5 10.87                                                 
                         280   0   3114                                   
3.050                                                                     
     12   10.6 42.3 11.52                                                 
                         284   0   3480                                   
3.100                                                                     
     12   8.0  36.1 11.90                                                 
                         287   0   -957                                   
3.150                                                                     
     12   10.3 47.6 12.30                                                 
                         290   0   -2591                                  
3.200                                                                     
     12   12.9 54.6 12.81                                                 
                         293   0   -673                                   
3.350                                                                     
     12   12.2 45.7 14.31                                                 
                         304   0   -477                                   
3.400                                                                     
     12   12.3 43.6 14.76                                                 
                         308   0   -509                                   
3.450                                                                     
     12   12.3 41.3 15.18                                                 
                         312   0   -507                                   
3.500                                                                     
     12   12.3 38.8 15.58                                                 
                         316   0   -497                                   
3.550                                                                     
     12   12.4 36.0 15.95                                                 
                         319   0   -486                                   
3.600                                                                     
     12   12.3 33.1 16.30                                                 
                         323   0   -471                                   
3.650                                                                     
     12   12.3 30.1 16.62                                                 
                         327   0   -449                                   
3.700                                                                     
     12   12.3 27.1 16.90                                                 
                         330   0   -420                                   
3.750                                                                     
     12   12.3 23.9 17.16                                                 
                         334   0   -383                                   
3.800                                                                     
     12   12.4 20.6 17.38                                                 
                         338   0   -340                                   
3.850                                                                     
     12   12.4 17.3 17.57                                                 
                         341   0   -292                                   
3.900                                                                     
     12   12.4 13.9 17.73                                                 
                         345   0   -239                                   
3.950                                                                     
     12   12.4 10.5 17.85                                                 
                         349   0   -182                                   
4.000                                                                     
     12   12.4 7.0  17.93                                                 
                         353   0   -123                                   
4.050                                                                     
     12   12.4 3.5  17.99                                                 
                         356   0   -61                                    
4.100                                                                     
     12   12.4 0.0  18.00                                                 
                         360   0                                          
__________________________________________________________________________
 SUMMARY OF STROKE 3                                                      
 AVE. STROKING RATE 14.63 SPM                                             
 RMS MOTOR HP. 755.7                                                      
 AVE. MOTOR HP. 712.0                                                     
 AVE. CLUTCH DISS. HP. 172.2                                              
 AVE. BRAKE DISS. HP. -162.8                                              
 AVE. WORK HP. 383.9                                                      
 AVE. FLYWHEEL HP. LOSS -3.5                                              
 RELATIVE STABILITY HAS BEEN REACHED                                      
 ANALYSIS COMPLETE                                                        
 
    
     It can be seen from the above data that the &#34;reference SPM&#34; of the system was set at 12 for the &#34;open&#34; portion of the press cycle, and at 22 for the &#34;closed&#34; portion of the cycle. During a portion of the press downstroke in the &#34;open&#34; portion of the cycle, i.e., within the crank angle range of 52° to 98°, the eddy current brake was energized to maintain the press at the commanded slow speed. When the commanded speed was increased by changing the &#34;reference SPM&#34; to 20, just before the load zone was entered, the eddy current clutch was energized to supply the necessary power to both increase the speed of the press drive and perform the desired work. The &#34;reference SPM&#34; was maintained at 20 through the balance of the downstroke and 89° of the upstroke, and then reduced to 12 again. It can be seen that the brake was again energized, to reduce the press speed, as soon as the &#34;reference SPM&#34;  was reduced. With this system, the stroke length was only 18 inches, and yet ample time (2.55 sec.) was allowed for the feed mechanism to access the workstations during the &#34;open&#34; portion of the cycle. 
     As mentioned previously, the present invention is useful not only in transfer presses, which have multiple workstations within a single press, but also in single-station presses operating alone or in a synchronized line of such presses. An exemplary line of single-station presses is illustrated in FIG. 9, which is similar to the synchronized press lines described in Danly U.S. Pat. Nos. 3,199,439 and 3,199,443. As described in those patents, such a press line performs successive operations upon a workpiece W, and may be extended to include any desired number of presses. Each individual press includes a base 100 extending below the floor level 101, and an upperly extending frame 102 topped by a crown 103. Recriprocatingly mounted in the press frame is a slide 104 carrying a die 105 for cooperating with a lower die 106 with the slide being driven by a motor 107. 
     Each of the three presses A, B and C is provided with a loading mechanism 110 for loading workpieces into the working area of the press, and an unloading mechanism 111 for removing workpieces from the work area. These loading and unloading mechanisms are cantilevered from opposite sides of the main frame of the press. Depending from each loading and unloading mechanism 110 and 111 is a transfer arm 112 having a gripper 113 for gripping the workpieces while they are being transferred. The details of these loading and unloading mechanisms are well known in the art and, therefore, need not be described in detail here. The details of how to synchronize such a line of multiple presses are also well known in the art, and one version thereof is described in the aforementioned Danly U.S. Pat. No. 3,199,439. 
     The reason for describing the synchronized press line here is to illustrate one of the most useful applications of the present invention. It will be appreciated that in a line of multiple presses, each having its own loading and unloading mechanism, a considerable amount of time is required in each cycle to allow the loading and unloading mechanisms to move the workpieces in and out of the workstations of the respective presses. In the past, the necessary cycle time for these operations has been provided by increasing the strokes of all the presses to allow adequate time for the press having the maximum cycle time. In certain situations this has required excessive vertical space or the re-design of the top portions of the presses in order to reduce their overall height. By applying the present invention to such a press line, however, adequate cycle time can be provided while at the same time reducing the size and cost of each individual press, along with all the other advantages of the invention described above. The resultant overall savings in a multi-press line of the type illustrated in FIG. 9 are quite significant. 
     The method of this invention can be implemented by retrofitting presses already in the field, particularly those presses equipped with inching drives. An inching drive provides a means to operate the press at a speed much slower than its normal cycle rate, typically providing full tonnage at a speed of one stroke per minute. Inching drives are well known and typically use an inching motor geared to a brake housing mounted on bearings so that the complete brake can be rotated. The housing is connected to an auxiliary brake which keeps the housing in a fixed position during normal operation of the press. For inching, the clutch is deenergized, the main brake is engaged, and the inching motor drives the press (at a reduced speed) through the main brake. 
     To inplement the present invention via an inching drive, a variable speed drive motor can be substituted for the conventional fixed speed inching drive motor.