Work following apparatus and method for press working

A work following device for controlling the movement of the free portion of a work during a press working process such as a bending press working process to prevent the free portion of the work from warping due to the inertia thereof in the final stage of the press working process and for restoring the work to its initial position after the same has been pressed. The work following device having a base plate mounted with the components, a drum case fixedly disposed on the base plate and rotatably housing a drum, an electromagnet which holds to the free portion of a work during the press working process, an electromagnet holding member, a positioning block which positions the electromagnet holding member at a predetermined seating position at the start of the work following operation, an elongate spring plate having one end fixed to the drum and the other end fixed to the electromagnet holding member, and wound on the drum, a clutch connecting the drum to and disconnecting the drum from a reduction gear which is driven by a motor, and a control unit for controlling the operation of the components in accordance with a control program.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to press working techniques and, 
more specifically, to a work following device and method for automatically 
following a work being pressed on a press such as a press brake. 
2. Description of the Prior Art 
In pressing a work, for example, a thin plate, on a press such as a press 
brake, the work needs to be positioned on the press accurately and the 
work needs to be held properly during the press working so that the work 
will not be deformed. 
FIG. 18 illustrates a conventional press brake 1 in operation. The bending 
press 1 has a ram 2 which is lowered for press working, and a bed 5 
provided with dovetail grooves 11. A movable bending die 3 is secured to 
the ram 2 with bolts 4, and a fixed bending die 6 is fixed in place on the 
bed 5 by means of holding bars 7, fulcrums 8, bolts 9 and nuts 10 using 
the dovetail grooves 11 of the bed 5. 
In press working, a work 13 such as a flat plate is positioned accurately 
relative to the fixed bending die 6, and then a foot switch 14 is pressed 
to lower the ram 2, so that the work 13 is bent in a predetermined size 
between the movable bending die 3 and the fixed bending die 6. Then, the 
foot switch 14 is pressed again to raise the ram 2 to separate the movable 
bending die 3 from the fixed bending die 6. Then, the pressed work 13 is 
transferred from the bending press 1 to a delivery table, not shown. This 
press working cycle is repeated to bend works successively. 
Problem occurs in bending the work 13 when the same is a comparatively 
large thin plate. Referring to FIG. 19, when such a comparatively large 
work 13 is pressed on the bending press 1 to bend one longitudinal side 
portion of the work 13, the opposite longitudinal side portion 13a of the 
same moves as indicated by an arrow as the work 13 is bent between the 
movable bending die 3 and the fixed bending die 6, in which the 
longitudinal side portion 13a is liable to move excessively by inertia to 
a position C beyond a normal position B and stops with a residual warp. To 
suppress such an undesirable movement of the longitudinal side portion 
13a, the operator 12 is required to hold the longitudinal side portion 13a 
by hand to follow the movement of the longitudinal side portion 13a during 
the press working as illustrated in FIG. 18. Such a work is very dangerous 
to the operator 12. 
To facilitate a press working and to eliminate such a dangerous manual 
work, in advanced press mills, an industrial robot for feeding a work to 
and removing a pressed work from a bending press, and a numerically 
controlled hydraulic work following apparatus which holds the work 
following the movement of the work during press working are employed in 
combination with a bending press. The work following apparatus positions a 
work fed by the industrial robot to the bending press accurately for press 
working, prevents the undesirable deformation of the work during press 
working and positions the pressed work accurately for removal by the 
industrial robot. However, the known work following apparatus requires a 
large floor space for installation in addition to a floor space for 
installing the bending press and has a complicated construction, which is 
disadvantageous in practical application of the work following apparatus. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a work 
following apparatus of a simple and compact construction capable of being 
installed on the bed of a press. 
It is another object of the present invention to provide a work following 
apparatus capable of firmly holding a work during press working and of 
steadily following the work throughout the press working. 
It is a further object of the present invention to provide a work following 
method for enabling a work following apparatus to operate and follow a 
work automatically throughout press working from the start of the press 
working. 
According to one aspect of the present invention, a work following 
apparatus comprises; a work holding element such as an electromagnet which 
holds to a work; a work holding element holder holding the work holding 
element; a positioning block for positioning the work holding element 
holder; an elongate elastic member attached at one end thereof to the work 
holding element holder; a drum on which the elongate elastic member is 
wound with the other end thereof fixed to the drum; a drum case rotatably 
accommodating the drum; a clutch; a motor for driving the drum for 
rotation through a reduction gear an the clutch; a sensor for detecting 
the correct seating of the work holding element holder on the positioning 
block; and a base mounted with those components. 
According to another aspect of the present invention, the free rotation of 
the drum is controlled by internal annular protrusions formed in the inner 
surface of the drum case so that the elongate elastic member wound on the 
drum will be unwound properly when the work holding element holding to the 
work rises together with the work and so that the work holding element 
holder is held in place on the positioning block after the same has been 
seated correctly on the positioning block by fully winding the elongate 
elastic member on the drum. 
According to a further aspect of the present invention, the work holding 
element is held by means of a floating member on the work holding element 
holder so that the work holding element is able to hold to a work even if 
the work fed to the press is warped slightly. 
The above and other objects features and advantages of the present 
invention will become apparent from the following description taken in 
conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The preferred embodiments of the present invention will be described 
hereinafter as applied to a press brake with reference to the accompanying 
drawings. 
First Embodiment 
Referring to FIG. 1, a work following apparatus 102, in a first embodiment, 
according to the present invention is installed on the bed 107 of a press 
brake 101 below the ram 103 of the press brake 101. A movable bending die 
104 is secured to the ram 103, and a fixed bending die 105 is fixed to the 
bed 107 so as to mate with the movable bending die 104 when the ram 103 is 
lowered for press working. The fixed bending die 105 is supported on a 
spacing block 106 to provide a clearance for the work following apparatus 
102. A work supporting table 109 is provided in front of the fixed bending 
die 105 to support a work 124 (FIG. 2), for example, a flat plate, fed to 
the press brake 101, for example, by an industrial robot 100 (FIG. 5). 
Positioning pins 110 are provided fixedly on the work supporting table 109 
to position the work 124 placed thereon. 
Referring to FIGS. 2 and 5, the work following apparatus 102 has an 
electromagnet 111, namely, a work holding means, which attracts and holds 
to the work 124, an electromagnet holder 112, namely, a work holding means 
holding member, holding the electromagnet 111, and a positioning block 113 
for positioning the electromagnet holder 112 at a seating position. An 
elongate spring plate 114, namely, an elongate elastic member, has one end 
fixed to the electromagnet holder 112 and the other end fixed to a drum 
115. The spring plate 114 is wound on and unwound from the drum 115. The 
drum 115 is supported rotatably within a drum case 116 fixed to a base 
plate 122. A first shaft 117 concentrically fixed to the drum 115 is 
connected to a first safety coupling 126 connected to the output shaft of 
a clutch 118 fixed to the base plate 122. The input shaft of the clutch 
118 is connected through a second safety coupling 126 to an output shaft 
reduction gear 120. An input shaft of the reduction gear is connected to a 
motor 119 for driving the drum 115. The motor 119 and the reduction gear 
120 are supported fixedly on a bracket 121 which in turn is fixed to the 
base plate 122. The correct seating of the electromagnet holder 112 on the 
positioning block 113 is confirmed through the detection of a lug 127 
attached to the electromagnet holder 112 by a reflective photoelectric 
sensor 123. 
Referring to FIG. 5, a control unit 160 for controlling the work following 
operation of the work following apparatus comprises a microcomputer 162 
which processes input data according to predetermined control programs to 
control the respective operations of the press brake 101 and the work 
following apparatus 102, and an interface 164 connected to the 
microcomputer 162. The interface receives detection signals from the 
sensor 123, a work sensor 166 provided on the work supporting table 109 to 
detect the correct positioning of the work 124 on the work supporting 
table 109, a top dead center sensor 168 for detecting the arrival of the 
movable bending die 104 at the top dead center, and a bottom dead center 
sensor 170 for detecting the arrival of the movable bending die 104 at the 
bottom dead center, and then gives signals corresponding to the detection 
signals to the microcomputer 162. Then, the microcomputer 162 gives 
command signals to the electromagnet 111, the clutch 118, the industrial 
robot 100 and the press brake 101 according to the predetermined control 
programs to control the respective operations of the press brake 101, the 
work following apparatus 102 and the industrial robot 100. 
The manner of operation of the work following apparatus thus constituted 
will be described hereinafter with reference to FIGS. 2, 3, 4 and 6 
showing a state in which the work 124 is set in place on the press brake 
101 with the electromagnet 111 holding to the work 124, a state in which 
the work 124 has been bent and the spring plate 114 is pulled out from the 
drum case 116, a state in which the movable bending die 104 is raised, the 
spring plate 114 is retracted into the drum case 116 and the work 124 is 
returned to the initial position after the bending press working has been 
completed, and a time chart of the respective operations of the motor 119, 
the industrial robot 100, the press brake 101, the electromagnet 111 and 
the clutch 118, respectively. 
First, the motor 119 of the work following apparatus 102, the press brake 
101 and the industrial robot 100 are connected to a power source at time 
T.sub.1, consequently, the motor 119 is actuated and the press brake 101 
and the industrial robot 100 are ready to operate upon the reception of 
command signals from the control unit 160. Then, the operating means of 
the control unit 160, such as a keyboard, is operated to give a program 
start command to the microcomputer 162 at time T.sub.2. Then, industrial 
robot 100 starts operating from the home position at time T.sub.3 to 
position the work 124 on the work supporting table 109 so as to receive 
the positioning pins 110 in positioning holes formed in the work 124, 
respectively. Then, the work sensor 166 gives a detection signal 
indicating the correct reception of the work 124 on the work supporting 
table 109 to the microcomputer 162. Then, the control unit 160 magnetizes 
the electromagnet 111 at time T.sub.4 to attract the work 124 to the 
electromagnet 111. Upon the detection of the return of the industrial 
robot 100 to the home position, the control unit 160 gives a command 
signal at time T.sub.5 to actuate the ram of the press brake 101 and 
thereby the movable bending die 104 is lowered to bend the work 124. The 
free longitudinal side portion of the work 124 rises as the opposite 
longitudinal side position of the work 124 is bent, and hence the 
electromagnet 111 rises together with the free longitudinal side portion 
of the work 124 pulling out the spring plate 114 from the drum case 116. 
During the bending process, the clutch 118 is kept disengaged to time 
T.sub.8 and hence the drum 115 is free to rotate. Accordingly, only a 
frictional resistance of the drum case 116 acts on the spring plate 114 
when the spring plate 114 is pulled out. 
The movable bending die 104 arrives at the bottom dead center at time 
T.sub.6 and held there for a predetermined time to time T.sub.7. When the 
movable bending die 104 is raised after the completion of bending press 
working, the control unit engages the clutch 118 at time T.sub.8 to 
connect the drum 115 to the motor 119 to start winding the spring plate 
114 on the drum 115 to return the electromagnet holder 112 to the seating 
position on the positioning block 114. Thus, the electromagnet holder 112 
is seated again on the positioning block 113 at the seating position and, 
at the same time, the work 124 is positioned again on the work supporting 
table 109 with the positioning holes receiving the positioning pins 110 
therein, respectively. Upon the detection of the arrival of the 
electromagnet holder 112 at the correct seating position on the 
positioning block 113 by the sensor 123 at time T.sub.9, the electromagnet 
111 is demagnetized, the clutch 118 is disengaged and the industrial robot 
100 is actuated again to transfer the pressed work 124 from the press 
brake 101 to a predetermined position. Then, the industrial robot 100 is 
returned to the home position at time T.sub.10. 
In case the electromagnet holder 112 failed to return to the correct 
seating position on the positioning block 113 for some trouble and the 
sensor 123 is unable to detect the lug 127 within a predetermined time, an 
alarm lamp, not shown, is lighted up, an alarm information is displayed, 
the clutch 118 is disengaged and the motor 119 is stopped. 
The safety couplings 126, for example, helical couplings, are overload 
protectors, which break to protect the components of the work following 
apparatus 102 from overloading, when an excessive torque is applied 
thereto. 
Although this embodiment employs the industrial robot 100 for automatically 
feed and position the work 124 on the work supporting table 109 and for 
automatically removing the pressed work 124 from the press brake 101, 
controls the operation of the press brake 101 and the work following 
apparatus 102 by the control unit on the basis of the detection signals 
provided by the sensors, such work need not necessarily be carried out 
automatically; the work 124 may be fed and positioned on the work 
supporting table 109, the pressed work 124 may be removed from the press 
brake 1 and the operation of the press brake 101 and the work following 
apparatus 102 may be controlled by means of manual switches (not shown) by 
an operator. 
Furthermore, the electromagnet 111 may be substituted by a pneumatic or 
mechanical clamping means. 
Still further, although the first embodiment has been described as 
employing a single electromagnet as a work holding means to simplify the 
explanation, a plurality of assemblies each of the electromagnet 111, the 
electromagnet holder 112, the positioning block 113, the spring plate 114, 
the drum 115 and the drum case 116 may be arranged on the first shaft 117 
depending on the size and shape of the work to be pressed. 
Although the first embodiment of the present invention has been described 
as applied to a press brake, naturally, the present invention is 
applicable to other presses. 
Second Embodiment 
The second embodiment is substantially the same as the first embodiment in 
constitution and function, and hence only parts and functions of the 
second embodiment different from those of the first embodiment will be 
described herein to avoid duplication. 
Referring to FIGS. 7 and 8, the second embodiment is provided with a 
clutch-brake unit 228, which corresponds to the clutch 118 of the first 
embodiment, and a sensor monitor for monitoring the detection signal of 
the sensor 223, and is capable of detecting and correcting the dislocation 
of the electromagnet holder 212 from the seating position on the 
positioning block 213 at the start of the work following operation. The 
clutch system and brake system of the clutch-brake unit 228 do not 
function simultaneously; while one of the systems is operative, the other 
remains inoperative. 
In some cases, the electromagnet holder 212 is moved away from the correct 
seating position on the positioning block 213 by the resilience of the 
spring plate 214 urging the spring plate 214 to recoil against the 
frictional resistance of the drum case 216, after the electromagnet holder 
212 has been seated on the positioning block 213 at the seating position. 
If the electromagnet holder 212 is not positioned correctly at the seating 
position, the work following apparatus 202 is unable to start 
automatically. 
In the second embodiment, when the dislocation of the electromagnet holder 
212 from the correct seating position is detected by the sensor 223 before 
starting the work following operation, the motor 219 is actuated 
automatically and operates for a predetermined time to wind the spring 
plate 214 further on the drum 215 so that the electromagnet holder 212 is 
seated correctly on the positioning block 213 at the seating position, and 
then the motor 219 is stopped and the brake system of the clutch-brake 
unit 228 is actuated simultaneously to check the rotation of the drum 215 
in the unwinding direction. 
The manner of work following operation of the second embodiment will be 
described hereinafter with reference to FIG. 8. 
At the start of the work following operation, a decision is made, on the 
basis of the mode of the sensor 223, whether or not the electromagnet 
holder 212 is seated correctly on the positioning block 213 at the seating 
position in step 232. When the electromagnet holder 212 is seated 
correctly on the positioning block 213, the sensor 223 provides a 
detection signal. When the electromagnet holder 212 is seated correctly on 
the positioning block 213, the brake system of the clutch-brake unit 228 
is applied to start the work following operation in step 234. 
When the sensor 223 does not provide any detection signal, namely, when the 
electromagnet holder 212 is not seated correctly on the positioning block 
213, the clutch system of the clutch-brake unit 228 is selected in step 
236, and then the clutch system is engaged in step 238. Then, 
simultaneously, the motor 219 is started in step 240 and the sensor 
monitor is actuated in step 242. Consequently, the torque of the motor 219 
is transmitted to the drum 215 to start winding the spring plate 214 on 
the drum 215. A decision is made in step 244 whether or not the sensor 223 
has provided a detection signal within a predetermined monitoring period 
(in this embodiment, 1 sec) after the start of the motor 219. When the 
decision in step 244 is "Yes", namely, when the sensor 223 is ON and the 
detection signal is given, the sensor monitor is reset in step 246, and 
then the motor 219 is stopped in step 248. At the same time, the brake 
system of the clutch-brake unit 228 is selected in step 250 and the brake 
system is applied in step 234. Thus, the steps of the control operation 
from step 248 to stop the motor 219 to step 234 to apply the brake system 
of the clutch-brake unit 228 are executed successively, and hence there is 
no time for the spring plate 214 to rotate the drum 215 in the reverse 
direction. Consequently, the electromagnet holder 212 thus seated 
correctly on the positioning block 213 is held in place to permit the work 
following apparatus to start the normal work following operation. 
In step 252, a decision is made whether or not time monitor error detector 
is on. When the decision in step 252 is "Yes", namely, when the sensor 223 
does not provide any detection signal within the predetermined monitoring 
period, the sensor monitor is turned off in step 254, the motor 219 is 
stopped in step 256 and the clutch system of the clutch-brake unit 228 is 
disengaged in step 258 successively. Then, the alarm lamp is lighted up 
and an alarm information is displayed in step 260. After the causes of the 
abnormal condition have been removed, the foregoing control procedures are 
started again. 
Thus, in the second embodiment, the dislocation of the electromagnet holder 
212 from the correct seating position of the positioning block 213 is 
corrected automatically to enable the work following apparatus to start 
the work following operation automatically without requiring any manual 
work for correcting the dislocation of the electromagnet holder 212 from 
the correct seating position at the start of the work following operation, 
so that operator's work is reduced remarkably and perfectly automatic 
press working is possible. 
Third Embodiment 
The third embodiment is substantially the same in constitution and function 
as the first and second embodiments, except that further improvements in 
construction and components are incorporated therein. 
As shown in FIG. 17, a work 118 placed on the work supporting table is 
tilted, in some cases, relative to the attracting surface of the core 103 
of the work holding assembly with a gap C diminishing the effective 
attraction of the electromagnet exerted on the work. Furthermore, the 
frictional resistance of the drum case against the unwinding movement of 
the spring plate possibly separates the work holding assembly from the 
work when the work holding assembly moves upward together with the work. 
The third embodiment incorporates further improvements to obviate such 
undesirable conditions. 
Referring to FIG. 9, mounted on and fixed with bolts 325 to a base plate 
321 are the main block 323 of a work following mechanism 320, an 
electromagnetic clutch 309 a bracket 324. A motor 310 and a reduction gear 
311 are fastened to the bracket 324 with bolts 326A shaft 327 extending 
between the reduction gear 311 and the electromagnetic clutch 309 has one 
end connected to the electromagnetic clutch 309 and the other end 
connected to the output shaft of the reduction gear 311. A work holding 
assembly positioning unit 328 and a work following unit 330 are mounted on 
the main block 323 of the work following mechanism 320. A work holding 
assembly 329 is received in the work holding assembly positioning unit 
328. A spring plate 331, namely, a work following member, extends between 
the work holding assembly 329 and the work following unit 330. 
Referring to FIG. 11, the work holding assembly positioning unit 328 has 
positioning blocks 332 and 333 secured to the main block 323 with bolts 
334 inserted in holes 323c formed in the main block 323. Guide members 360 
for guiding the spring plate 331 are driven into holes 323e formed in the 
side wall of the main block 323. The work following unit 330 includes a 
drum case 341 having a side wall provided with a central hole 341a, 
threaded holes 341b distributed in point symmetry with respect to the 
central hole 341a, and a boss 341c (FIG. 13), and a circumferential wall 
provided with annular protrusions in the inside surface thereof (FIG. 13) 
and a recess 341e (FIG. 12) for passing the spring plate 331 therethrough. 
As shown in FIG. 13, the drum case 341 is fastened to the main block 323 
with the boss 341c fitted in a hole 323a formed in the main block 323 with 
bolts 334 inserted through bolt holes 323d and screwed in the threaded 
holes 341b of the drum case 341. As shown in FIGS. 11, 12 and 13, a drum 
342 has a boss 342a provided with a central bore 342c, and a recess 342d 
(FIG. 13) for reducing the weight. A spiral groove 342e of H in width and 
a depth slightly greater than the width of the spring plate 331 is formed 
in the drum 342 so as to extend from a point separated from the center of 
the drum 342 by a distance E along a diameter and by a distance F along 
another diameter perpendicular to the former and to merge into the 
circumference of the drum 342. On end 331a of the spring plate 331 and a 
plate 345 are inserted in the bottom of the spiral groove 342e and are 
fastened to the drum 342 with bolts 344. The work holding assembly 329 
includes an electromagnet 335 and a floating stem 339 screwed in the 
electromagnet 335. The floating stem 339 is inserted from the under side 
of a holding member 336 through a hole 336a formed in the holding member 
336, and then screwed in the electromagnet 335 to join the electromagnet 
to the holding member 336. Slide blocks 337 and 338 are fixed to the 
holding member 336 with bolts 340. The other end 331b of the spring plate 
331 and a plate 346 are fixed to the lower end of the slide block 337 with 
bolts 347. One end 343b of a shaft 343 is inserted in the central bore 
342c of the drum 342 and the central hole 341a of the drum case 341. The 
other end of the shaft 343 is inserted in a hole 349b formed in a cover 
plate 349. The drum 342 is fixed to the shaft 343 with a bolt 351 inserted 
through a hole 342b formed in the boss 342a thereof and screwed in a 
threaded hole 343a formed in the end 343b of the shaft 343. The spring 
plate 331 is wound on the drum 342 to seat the work holding assembly 329 
on the work holding assembly positioning unit 328. The shaft 343 is 
coupled at the other end thereof with the output shaft of the 
electromagnetic clutch 309. Spacing bars 348 are fixed to the main block 
323 by screwing the respective threaded ends 348a thereof in threaded 
holes 323b formed in the main block 323, and then the cover plate 349 is 
fixed to the spacing bars 348 by screwing bolts 350 in threaded holes 348b 
formed in the free ends of the spacing bars 348, respectively, through 
holes 349a formed in the cover plate 349. 
Referring to FIG. 14 showing the essential portion of the work holding 
assembly 329, the electromagnet 335 is formed by placing a coil 353 and a 
core 354 in a case 352, fixing the core 354 to the case 352 by screwing 
the threaded position of the floating stem 339 in a threaded hole 354a 
formed in the core 354, and filling the case 352 with a molding material 
355. After the molding material 355 has solidified, the floating stem 339 
is removed from the electromagnet 335, and then the floating stem 339 is 
passed through the central hole 336a of the holding member 336 to be 
screwed in the core 354 again to join the work holding assembly 329 to the 
holding member 336. The diameter of the hole 336a of the holding member 
336 is greater than the outside diameter of the stem portion of the 
floating stem 339 and is smaller than the outside diameter of the head of 
the floating stem 339, and the thickness I of the wall of the holding 
member 336 having the hole 336a is slightly greater than the length J of a 
portion of the floating stem 339 projecting from the outer surface of the 
bottom wall of the case 352. A counterbore 336b is formed in the holding 
member 336 concentrically with the hole 336a to allow the free movement of 
the head 339c of the floating stem 339. Thus, the work holding assembly 
329 is able to move relative to the holding member 336 within a limited 
range. 
The manner of operation of the third embodiment will be described 
hereinafter with reference to FIGS. 9, 10, 12, 13 and 14. 
As shown in FIG. 10, the work following apparatus 319 is fixedly mounted on 
the bed of a bending press 301 having a movable bending die 317 fixed to 
the ram, a fixed bending die 313 fixedly mounted on a die holder, and a 
work supporting table 314. A work 318 such as a flat plate is positioned 
on the work supporting table 314. If the work 318 is tilted relative to 
the attracting surface of the electromagnet 335 of the work holding 
assembly 329, the electromagnet 335 is able to hold to the work 318, 
because the floating stem 339 is movable relative to the holding member 
336. After the electromagnet 335 has held to the work 318, the movable 
bending die 317 is lowered to bend the work 318. Then, the work holding 
assembly 329 rises together with the free side of the work 318 as the work 
318 is bent. A frictional resistance of the drum case 341 acting on the 
spring plate 331 against the upward movement of the work holding assembly 
329 tends to separate the electromagnet 335 from the work 318. 
However, since the annular protrusions 341d formed in the inside surface of 
the circumferential wall of the drum case 341 as shown in FIG. 13 and the 
spring plate 331 is drawn out from the drum case 341 tangentially as shown 
in FIG. 12, the frictional resistance of the drum case 341 is unvariable 
and is limited to a moderate level high enough to apply a sufficient 
resistance to the spring plate 331 to prevent the work 318 from warping in 
the final stage of the bending press working. Although the weight of the 
work 318 tends to cause the spring plate 331 flex outward after the 
movable bending die 317 has been raised, the guide members 360 prevent the 
spring plate 331 from bending outward, so that the work holding assembly 
329 moves downward together with the work 318 until the work 318 is 
restored to the correct position on the work supporting table 314 defined 
by the positioning pins 315. 
Fourth Embodiment 
The fourth embodiment is different from the third embodiment only in the 
construction of the work holding assembly 329. As shown in FIG. 15, the 
work holding assembly 435 of the fourth embodiment further comprises a 
compression spring 456. The rest of the components and the construction of 
the work holding assembly 429 of the fourth embodiment are the same as 
those of the third embodiment. 
Referring to FIG. 15, the work holding assembly 429 comprises a core 454, a 
coil 453 mounted on the core 454, a case 452 accommodating the core 454 
and the coil 453, a molding material 455 filled in the case 452, a 
floating stem 439, and the compression spring 456. The compression spring 
456 is interposed between the bottom wall of the case 452 and a holding 
member 436. The compression spring 456 prevents the collision of the work 
holding assembly 429 against the holding member 436 when the work holding 
assembly 429 is in a free state. 
Fifth Embodiment 
The fifth embodiment, as shown in FIG. 16, is different from the third 
embodiment only in the construction of the work holding assembly 329. The 
work holding assembly 529 of the fifth embodiment comprises a core 554, a 
coil 553 mounted on the core 554, a case 552 accommodating the core 554 
and the coil 553, a molding material 555 filled in the case 552, and a 
stem 558 having a spherical head 558a and a threaded end screwed in the 
threaded hole 554a of the core 554. A holding member 557 has a central 
spherical hole to receive the spherical head 558a of the stem 558, and a 
member 559 having a spherical recess in the central portion thereof and 
fitted in a counterbore 557a formed in the holding member 557 so as to 
support the spherical head 558a of the stem 558. The spherical head 558a 
of the stem 558, the spherical hole of the holding member 557 and the 
member 559 form a ball-and-socket joint allowing the rotary motion of the 
stem 558 in every direction within certain limits. The function of the 
work holding assembly 529 of the fifth embodiment is the same as those of 
the work holding assemblies of the third and fourth embodiments, and hence 
the description thereof will be omitted. 
As apparent from the foregoing description, according to the present 
invention, the work holding assembly of the work following apparatus holds 
surely to the work and follows the movement of the work throughout the 
bending press working, so that the work is held satisfactorily, whereby 
the undesirable warping of the work in the final stage of the bending 
process is prevented. 
Although the invention has been described in its preferred forms with a 
certain degree of particularity, as many apparently widely different 
embodiments of the present invention may be made without departing from 
the spirit and scope thereof, it is to be understood that the invention is 
not limited to the specific embodiments thereof except as defined in the 
appended claims.