Wire electrode pull-up mechanism in wire-cut electric discharge machine

A wire electrode pull-up mechanism in a wire-cut electric discharge machine having an energized wire electrode stretched between upper and lower guides for machining a workpiece wherein the wire electrode pull-up mechanism pulls up a wire electrode which has been passed through a bore in the workpiece until the upper end of the wire electrode protrudes from the upper side of the workpiece, and includes a gripping member for gripping the wire electrode. The gripping member includes an arm having a bearing wall at the distal end thereof; a clamping member pivotally provided on the arm and having a cam body and a restraining portion for abutting against the bearing wall of the arm; a spring member for urging the clamping member in such a manner that the restraining portion thereof abuts against the bearing wall; and an operating member pivotally provided on the arm and having a cam operating portion abutting against the cam body of the clamping member for pivoting the clamping member, the operating member being pivoted owing to pressured contact with the upper surface of the workpiece. The clamping member is pivoted as the operating member abuts against the workpiece, in such a manner that the clamping member causes a gap to be formed between the restraining portion and the bearing wall, and the operating member separates from the workpiece when the arm is raised.

BACKGROUND OF THE INVENTION 
This invention relates to a wire electrode pull-up mechanism in a wire-cut 
electric discharge machine and, more particularly, to a wire electrode 
pull-up mechanism for gripping and pulling up a wire electrode. 
A so-called wire-cut electric discharge machine, namely an electric 
discharge machine which uses a wire electrode as a cutter, operates by 
impressing a pulsed voltage between a wire electrode and a workpiece to 
produce an electrical discharge or spark across the intervening space for 
the purpose of eroding the workpiece where the spark occurs. By 
simultaneously moving the workpiece relative to the wire electrode on the 
basis of machining command data, the workpiece may be cut into any desired 
contour. There are occasions where the wire electrode breaks within the 
workpiece during the cutting operation if such machining cutting 
conditions as the wire electrode feed speed and tension are improper. In 
the event of such breakage, it is required that this fact be sensed by 
circuitry within the discharge machine and that the wire electrode be 
restored automatically without delay. 
An apparatus for restoring a wire electrode has already been proposed by 
the Inventors in, for example, Japanese Patent Application No. 54-075227. 
With this previously disclosed apparatus, a limit switch for sensing 
breakage of the wire electrode is operable to suspend an electric 
discharge cutting operation immediately upon sensing breakage of the 
electrode during the passage thereof through the workpiece. At the same 
time, a clamping mechanism located below the workpiece is activated to 
clamp the wire electrode and prevent it from falling on the supply side. 
The used wire electrode, namely the wire electrode passed through the 
workpiece and located on the take-up side, is then pulled up by feed 
rollers and fed into a wire electrode disposal mechanism where the wire 
may be cut up into small pieces, by way of example. Next, the remaining 
portion of the wire electrode which has broken off in the workpiece is 
pulled downwardly until the upper end of the broken wire is extracted from 
the workpiece. Thereafter, with the aid of a guiding device such as a 
nozzle, said end of the wire electrode is again fed into the slit formed 
in the workpiece by the electric discharge until the wire end emerges a 
predetermined distance from the top side of the workpiece. Now, a wire 
electrode pull-up mechanism located on the take-up side of the workpiece 
grips the protruding end of the wire electrode, pulls the wire electrode 
upwardly and feeds it into the feed rollers which then grasp the electrode 
between them, thereby completing the restoration of the wire electrode. 
In the prior-art apparatus described above, the wire electrode pull-up 
mechanism is provided with a wire electrode gripping device having a 
construction which will now be described with reference to FIGS. 1(a), 
1(b) and 1(c). 
FIG. 1(a) is a perspective view and FIGS. 1(b) and 1(c) are sectional views 
illustrating the gripping device of the conventional wire electrode 
pull-up mechanism. In FIGS. 1(a) and 1(b), the gripping device has an arm 
AR at the distal end formed to include a downwardly tapered hole BH and a 
downwardly flared guide hole CH communicating therewith. The tapered hole 
BH receives a rotatable clamping roller DB movable freely up and down 
within the hole. In restoring a wire electrode 2 which has broken, the arm 
AR is lowered until it abuts against the top surface of the workpiece 12, 
as shown in FIG. 1(b). This is followed by passing the end of the broken 
wire electrode 2 upwardly through the workpiece 12 and into the guiding 
hole CH and tapered hole BH of the arm AR until the wire end pushes up the 
clamping roller DB and emerges from the arm on the upper side thereof, as 
illustrated in FIG. 1(c). Thenceforth, the arm AR is raised in the 
direction of the arrow shown in FIG. 1(c), whereupon the clamping roller 
DB slides downwardly under its own weight along the wall of the tapered 
hole BH. Owing to the oblique wall of the hole BH, the roller DB wedges 
the wire electrode 2 against the opposing surface to clamp the wire in 
place. Raising the arm AR therefore causes the wire electrode 2 to be 
pulled upwardly as the arm ascends. 
A problem encountered in a wire-cut electric discharge machine having a 
gripping device of the above-described type involves the matter of wire 
diameter. Specifically, for reasons of cutting precision and the like, it 
is preferred to make use of a wire electrode which is as slender as 
possible. However, owing to the construction of the gripping device which 
requires that the end of the wire electrode push up the clamping roller, 
the wire must have sufficient rigidity and, hence, there is a limitation 
on how slender the wire may be. Accordingly, there is need of a wire 
electrode pull-up mechanism capable of clamping and pulling up even a very 
slender wire electrode. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide a wire 
electrode pull-up mechanism which is capable of clamping and pulling up a 
slender wire electrode. 
Another object of the present invention is to provide a wire electrode 
pull-up mechanism which is capable of clamping a slender wire electrode in 
a reliable manner. 
Still another object of the present invention is to provide a wire 
electrode pull-up mechanism in which a wire electrode meets little 
resistance in being passed through the mechanism, and in which the wire 
electrode can be clamped rigidly in place thereafter. 
Yet another object of the present invention is to provide a wire electrode 
pull-up mechanism which is capable of clamping a wire electrode through 
utilizing the force applied by a gripping member as said member is raised 
with respect to the workpiece. 
A further object of the present invention is to provide a wire electrode 
pull-up mechanism which is capable of improving the cutting precision of a 
wire-cut electric discharge machine by utilizing a very slender wire 
electrode. 
According to the present invention, these and other objects are attained by 
providing, in an electric discharge machine of the type having an 
energized wire electrode stretched between upper and lower guides for 
cutting a workpiece moved against the wire electrode, a mechanism for 
pulling up the wire electrode from a bore in the workpiece after the wire 
electrode has been re-inserted through the bore following breakage. The 
pull-up mechanism comprises a gripping member for gripping the wire 
electrode. The gripping member includes an arm having a bearing wall at 
the distal end thereof; a clamping member pivotally provided on the arm 
and having a cam body and a restraining portion for abutting against the 
bearing wall of the arm; a coiled spring for urging the clamping member in 
such a manner that the restraining portion thereof abuts against the 
bearing wall; and an operating rod pivotally provided on the arm and 
having a cam operating portion abutting against the cam body of the 
clamping member for pivoting the clamping member, the operating rod being 
pivoted owing to pressured contact with the upper surface of the workpiece 
when the gripping member is lowered into abutting contact with the upper 
surface of the workpiece by the drive member. The clamping member is 
pivoted by the cam operating portion as the operating rod abuts against 
the workpiece, in such a manner that the clamping member causes a gap to 
be formed between the restraining portion and the bearing wall, and the 
operating rod separates from the workpiece when the arm is raised, whereby 
the clamping member is pivoted by the coiled spring so that the upper end 
of the wire electrode, inserted into the gap, is retained between the 
restraining portion of the clamping member and the bearing wall of the 
arm. 
Other features and advantages of the invention will be apparent from the 
following description taken in connection with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The overall construction of a wire-cut electric discharge machine to which 
the present invention can be applied is illustrated in FIG. 2. The machine 
includes a column 1, a wire electrode 2 for cutting a workpiece 12, a wire 
electrode supply reel 3, a wire electrode tension brake 4, guide rollers 
5, 6 for guiding the wire electrode 2, a lower guide 7 for the wire 
electrode, a wire electrode clamping mechanism 8, a wire electrode feed 
mechanism 9, a wire electrode position detecting mechanism 10, a nozzle 11 
located directly below the cutting position, and a wire electrode pull-up 
mechanism 13 provided at one end with a wire electrode gripping device 30 
having a gripping member 110 at the distal end thereof. The machine 
further comprises an upper guide 14 for the wire electrode 2, a conduction 
pin 15 for supplying the wire electrode 2 with electric current, feed 
rollers 16 for feeding the wire electrode, a unit 17 for disposing the 
wire electrode, an encoder 18 for sensing the rotational position of the 
guide roller 5, a table mechanism 19 for supporting the workpiece 12, 
workpiece feed motors MX, MY for transporting the table mechanism 19, 
namely the workpiece 12, in X and Y directions, respectively, a drive 
motor 20 for driving the wire electrode pull-up mechanism 13, a limit 
switch L1 for sensing breakage of the wire electrode 2, a limit switch L2 
which senses when lowering of the wire electrode pull-up mechanism 13 has 
been completed, and a limit switch L3 which senses when elevation of the 
pull-up mechanism has been completed. 
In operation, the wire electrode is guided substantially vertically from 
the lower guide 7 to the upper guide 14 and is pulled and fed upwardly by 
the feed roller 16 longitudinally so as to travel by the part of the 
machine where the workpiece 12 is cut. A prescribed voltage is impressed 
across the wire electrode 2 and the workpiece 12, and the latter is moved 
in a horizontal plane by the feed motors MX, MY in a predetermined manner 
so as to be cut along a desired path by the electric discharge. 
According to the embodiment of the invention, the clamping mechanism 8 is 
provided on the supply side of the wire electrode 2 and is adapted to 
clamp a portion of the wire electrode 2 instantaneously upon breakage, 
thereby preventing it from falling under its own weight. Meanwhile, the 
nozzle 11 and the wire electrode feed mechanism 9 provided on the supply 
side for grasping and feeding the above-mentioned portion of the electrode 
cooperate to position the upper end of the electrode at a predetermined 
point. This enables the portion of the broken wire electrode 2 remaining 
on the supply side to be re-threaded through a slit or bore 21 located in 
the workpiece and then delivered to the upper guide 14 and feed roller 16, 
which then proceeds to feed the wire electrode to the disposing unit 17. 
Thus, when the wire electrode breaks, restoration of the wire can take 
place in a fully automatic manner. 
The construction of the clamping mechanism 8 for clamping the wire 
electrode 2 can be best understood from FIGS. 3 through 5. The clamping 
mechanism 8 includes a pair or knurled rollers 85 set into a block 84 
having a slit 81 to permit the passage of the wire electrode 2 
therethrough, a pair of inclined walls 83 defining an inwardly tapered 
surface, and a bottom surface 82. The rollers 85 are loosely mounted on 
corresponding shafts 86 that are caused to occupy the positions shown in 
FIG. 4 by activating a plunger magnet 87, or the positions shown in FIG. 3 
by deactivating the plunger magnet 87. 
The plunger magnet 87 is deactivated during the course of a normally 
proceeding discharge machining operation, so that the rollers 85 are 
positioned as shown in FIG. 3. The rollers 85 rotate freely in the 
directions indicated by the arrows B as the wire electrode 2 is fed 
upwardly in the direction shown by arrow A, and therefore permit the 
upward passage of the wire through the block 84. When the wire breaks in 
the vicinity of the workpiece 12, the portion of the wire electrode above 
the rollers 85 is no longer tensioned and the wire tends to be pulled 
downward under its own weight. However, the pair of rollers 85, owing to 
their knurled surfaces and in cooperation with the inwardly inclined walls 
83, function to grasp and clamp the wire electrode immediately upon 
breakage. The plunger magnet 87 is then activated to move the shafts 86 to 
the positions shown in FIG. 4, thereby disengaging the rollers 85 from the 
inwardly inclined walls 83 so that the rollers can now rotate in the 
directions of the arrows D when the wire electrode 2 moves in the 
direction of the arrow C. Thus, the rollers 85 when positioned as shown in 
FIG. 4 permit the downward passage of the wire electrode 2, but are still 
free to rotate in the directions B, allowing the wire electrode to be 
moved upwardly through the block 84, that is, in the direction A, as will 
be required in a later step. 
Referring now to FIGS. 6 through 9 for a detailed description of the 
construction and operation of the wire feed mechanism 9, the feed 
mechanism includes a pair of drive rollers 91, 92 coupled to a motor 99 
through respective shafts 93, 94 and gear mechanisms 95, 96, 97, 98. The 
shafts 93, 94 are journalled in bearings 100, 101 attached to one end of 
respective leaf springs 102, 103, and a plunger magnet 109 is connected to 
the bearings 100, 101 through a lever mechanism comprising lever elements 
104, 105, 106, 107 and 108. 
The magnet 109 of the wire feed mechanism 9 is deactivated during the 
course of the machining operation, so that the drive rollers 91, 92 are 
spaced from each other and do not contact the wire electrode 2, as 
illustrated in FIGS. 6 and 8. The magnet 109 is activated only when the 
electrode breaks. When such is the case, the magnet 109 depresses the 
lever 108 in the direction of the arrow in FIG. 7, thereby pivoting the 
lever element 107 clockwised and causing the lever elements 106, 105, 104 
to cooperate in moving the shafts 93, 94 toward each other against the 
biasing force of the leaf springs 102, 103 so as to bring the bearings 
100, 101 and, hence, the drive rollers 91, 92, closer together, the latter 
clamping the wire electrode 2 between them, as shown in FIGS. 7 and 9. 
Accordingly, when the motor 99 coupled to the drive rollers 91, 92 via the 
gear mechanism and shafts 93, 94 is rotated in one direction, the drive 
rollers 91, 92 pull the wire electrode 2 upwardly and, when rotated in the 
other direction, the drive rollers 91, 92 pull the wire electrode 2 
downwardly, as shown in FIG. 9. 
The detector 10 shown in FIG. 2 ordinarily is in contact with the wire 
electrode 2. When the wire electrode breaks and is pulled downward by the 
wire electrode feed mechanism 9 after being clamped by the clamping 
mechanism 8, the detector 10 is operable to detect the end of the broken 
wire as it passes by, and to deliver a signal indicative of this fact to 
the motor 99. The signal halts the motor 99 so that the drive rollers 91, 
92 which are pulling the broken wire down are stopped before the end of 
the wire reaches them. The broken end of the wire electrode 2 is now 
located below the workpiece and remains there until the arrival of a 
signal csuses the wire electrode feed mechanism 9 to feed the wire 
upwardly by a prescribed amount through a hole in the workpiece. 
The wire electrode pull-up mechanism 13 shown in FIG. 2 is depicted in 
greater detail in FIGS. 10 through 14. Referring first to FIGS. 10 and 11, 
the mechanism includes a wire electrode gripping member 110, a sliding 
member 111 coupled to the gripping member, and a tube 112 whose periphery 
has a longitudinally extending coulisse 114. The sliding member 111 is 
provided with a pin 113 engaging with the coulisse 114, and is capable of 
sliding up and down along the tube 112. Thus, the sliding portion 111, in 
moving along the tube 112, is constrained to turn in a particular manner 
which is decided by the shape of the coulisse 114. The sliding portion 111 
is turned in order that the pull-up mechanism 13 will not interfere with 
the upper guide 14 at the stage where the wire electrode 2 is set between 
the feed rollers 16 shown in FIG. 2. 
Referring to FIGS. 12 and 13, the gripping member 110 comprises a mounting 
portion 110a and an arm portion 110b which meets the mounting portion 110a 
at right angles. The arm portion 110b has a cavity for accommodating a 
clamping member 110c and an operating rod 110d which are pivotally 
supported by shafts 110e, 110f, respectively. The clamping member 110c 
includes a restraining portion 110g and a cam body 110h. A coiled spring 
110i is wound on the pivot shaft 110e and, as shown in FIG. 12, urges the 
clamping member 110c in the clockwise direction, thereby bringing the 
restraining portion 110g thereof into abutting pressing contact with a 
wall 110j for bearing the applied pressure. The wall 110j, constituting a 
portion of the arm 110b, will be referred to as a bearing wall 
hereinafter. As shown in FIG. 14, one end of the operating rod 110d 
pivoted at the support shaft 110f is formed to include a cone-shaped 
nozzle 110k, and a slit 110l from which the wire electrode 2, which has 
been passed through the nozzle 110k, is released. Further, as shown in 
FIG. 12, the operating rod 110d is provided with a position adjusting 
screw 110m, a position adjusting screw 110n which serves also as a member 
for pushing up the clamping member 110c, and a cam operating surface 110p. 
The distal end of the gripping portion 110 as seen from above is shown in 
FIG. 15. 
Described next will be the manner in which the pull-up mechanism pulls up a 
broken wire electrode. 
The gripping member 110 is lowered via a cord 22 (FIG. 2) by rotating the 
motor 20. The cord 22 slackens when the gripping member 110 comes to rest 
upon the upper surface of the workpiece 12, and the limit switch L2 opens 
upon sensing the slack in the cord, thereby deactivating the motor 20. As 
the foregoing takes place, the gripping member 110 operates in the 
following manner. As shown in (a) of FIG. 16, the end of the operating rod 
110d is the first part of the gripping member 110 to abut against the 
upper surface of the workpiece 12 as the gripping member is lowered. As 
the gripping member 110 continues to be lowered, the operating rod 110d 
pivots in the counter-clockwise direction about the pivot shaft 110f, 
causing the upper end of the position adjusting screw 110n to abut against 
the clamping member 110c. With further descent of the gripping member 110, 
as shown in (b) of FIG. 16, the position adjusting screw 110n rotates the 
clamping member 110c counter-clockwise so that the cam body 110h of the 
clamping member is situated above the cam operating portion 110p of the 
operating rod 110d. As the gripping member 110 continues to be lowered, 
the cam operating portion 110b presses up on the cam body 110h, thereby 
amplifying the effect of the operating rod 110d to swing the clamping 
member 110c through a large angle in the counter-clockwise direction. As a 
result, the clamping member 110c is rotated through an angle of about 90 
degrees from the position shown in FIG. 16(a). The coiled spring 110i, it 
should be noted, is twisted and tightly compressed by the clamping member 
110c as it is rotated. When the lower surface of the operating rod 110 
finally comes into surface-to-surface abutting contact with the upper 
surface of the workpiece 12, cord 22 slackens, limit switch L2 opens, and 
motor 20 is stopped to halt the descent of the gripping member 110. This 
is the condition shown in (c) of FIG. 16, in which the operating rod 110 
is shown flush against the upper surface of the workpiece, with the nozzle 
110k in alignment with the hole 21 in the workpiece. 
Next, the wire electrode feed mechanism 9 is actuated to feed the wire 
electrode 2 upwardly, whereupon the upper end of the broken wire electrode 
2 is threaded through the bore 21 in the workpiece 12 and passed directly 
through the nozzle 110k of the operating rod 110d. The wire then passes 
the inner side of the bearing wall 110j at the end of the arm 110b and 
emerges from the upper side of the arm, as shown in (c) of FIG. 16. Thus 
the wire electrode 2 may pass completely through and emerge from the 
gripping member 110 without meeting any substantial resistance. This is 
followed by running the motor 20 in the reverse direction, whereby the 
gripping member 110 is raised. Now the operating rod 110d is rotated in 
the clockwise direction about the pivot shaft 110f owing to the 
restoration force of the coiled spring 110i. As the operating rod 110d is 
rotated in this manner, the effect of the relaxing spring 110i and of the 
engaging cam operating portion 110p and cam body 110h causes the clamping 
member 110c to rotate through a large angle in the clockwise direction. As 
the clamping member 110 continues to be raised, the restraining portion 
110g comes into contact with the wire electrode 2 and presses it against 
the bearing wall 110j, applying a clamping force to the wire electrode to 
hold it firmly in place as the gripping member 110 continues to rise. 
Owing to the wedge effect of the restraining portion 110g, any attempt by 
the wire electrode 2 to fall under its own weight is fully counteracted by 
a stronger clamping force, assuring that the wire electrode 2 will not 
fall. The gripping member 110 thus is raised while carrying the clamped 
wire electrode 2 along with it. At the end of the elevating operation, 
limit switch L3 (FIG. 2) is closed to suspend the rotation of the motor 
20. At this time the upper end of the wire electrode 2 has been pulled up 
to a position high enough to permit it to be engaged by the feed rollers 
16, as shown in FIG. 11, the latter then being driven to feed and pull up 
the wire electrode 2 grasped between them, whereby the end of the wire is 
introduced into wire electrode disposing unit 17. 
The gripping member 110 is at rest when the wire electrode 2 is pulled up 
by the feed rollers 16. Owing to the upward movement of the wire electrode 
under the action of the feed rollers at such time, the clamping member 
110c pivots slightly in the counter-clockwise direction so that the 
restraining portion 110g thereof exerts less force upon the bearing wall 
110j. The wire electrode 2 may therefore pass through the gripping member 
110 with facility as it is being fed into the disposing unit 17. After 
this latter step has been accomplished, the gripping member 110 is turned 
about the longitudinal axis of the mounting portion 110a thereof while 
being lowered slightly, whereupon the wire electrode 2 slips out from 
between the restraining portion 110g and bearing wall 110j and exits from 
the gripping member 110 completely via the slit 110l. This establishes the 
condition for a resumption of the electric discharge machining operation. 
In pulling up the wire electrode 2 by means of the pull-up mechanism 13 and 
feeding the end of the wire into the roller mechanism 16, the conduction 
pin 15 is retracted to permit proper delivery of the wire electrode to the 
upper guide 14. This is accomplished by the conduction pin retracting 
mechanism illustrated in FIG. 17. 
With reference to FIG. 17, the conduction pin 15 is mounted on a lever 141 
which is capable of being pivoted about a pivot point 140 by a piston rod 
143 connected at one end to the lever 141 and at the other end to a piston 
146 within a cylinder 142. Opening a valve 144 communicates the interior 
of the cylinder 142 with the atmosphere and allows a spring 145 to urge 
the piston 146, and hence the piston rod 143, to the extreme left as shown 
in FIG. 17. This causes the lever 114 to rotate counter-clockwise about 
the pivot point 140 so that the conduction pin 15 is swung into the 
retracted position away from the path 2' along which the wire electrode 
will travel. This facilitates the threading of the wire electrode into the 
upper guide 14. 
On the other hand, closing the valve 144 sends a pressurizing fluid into 
the cylinder 142 so that the piston 146 and its piston rod 143 are driven 
as far to the right as possible, thereby rotating the lever 141 clockwise. 
This swings the conduction pin 15 back into the operating position shown 
in FIG. 2, so that the pin may contact the wire electrode. Numeral 147 in 
FIG. 17 designates a cable for connecting the conduction pin to a power 
supply. 
It should be noted that a nozzle for supplying a machining liquid, or 
dielectric, can also be mounted on the above retraction mechanism together 
with the conduction pin so that the nozzle can also be swung away from the 
wire electrode. Furthermore, the machining liquid can be employed as the 
pressurizing fluid delivered to the cylinder 142. 
In accordance with the present invention as described and illustrated 
hereinabove, the gripping member 110 for gripping the end of the wire 
electrode 2 is provided with the pivoted clamping member 110c and 
operating rod 110d. When the gripping member 110 abuts against the 
workpiece and grips the wire electrode, the cam operating portion 110p of 
the operating rod 110d operates on the cam body 110h of the clamping 
member 110c. As a result, the clamping member 110c is shifted by an amount 
comparatively large in comparison with the amount of operating rod 
movement, so that the portion of the clamping member for restraining the 
wire electrode is swung through a wide arc to permit passage of the wire 
electrode through the gripping member without obstruction. When the 
gripping member 110 is separated from the workpiece surface to clamp the 
wire electrode, the action of the cam operating portion on the cam body 
causes the clamping member 110c to pivot more quickly, with the coiled 
spring 110i assisting in the pivoting operation. In consequence, the 
clamping member 110c is pivoted in the electrode clamping direction 
rapidly and reliably. In accordance with the invention, therefore, a wire 
electrode, regardless of how slender, may be passed through the gripping 
member without any resistance. Moreover, since the wire electrode is 
clamped positively between the restraining portion and the bearing wall 
owing to the force applied by the coiled spring when the gripping member 
is raised, the invention assures that the wire electrode will be gripped 
and pulled up in a very reliable manner. 
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.