Piezo-electric actuator operated press

A piezo-electric actuator operated press in which piezo-electric actuators are employed as punch driving sources, and, with a workpiece held between an upper and lower die set, the punches are driven by the piezo-electric actuators to punch the workpiece; the punches and the piezo-electric actuators are built in the respective die sets, and the movable one of the die sets is coupled to a die shifting mechanism, so that it is driven to a die opening position or a die closing position, whereby the workpiece can be smoothly fed in and taken out of the press.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a punch press; and more particularly to one in 
which utilizes piezo-electric actuators as punch driving sources to punch 
a workpiece, such as a metal foil. 
2. Discussion of the Related Art 
A punching press for shearing a workpiece, such as a thin metal foil 
(several tens of micrometers) with high accuracy, namely, a press with 
lamination type piezo-electric actuators as punch driving sources is 
disclosed Japanese Patent Application (OPI) No. 127997/1990 (the term 
"OPI" as used herein means an "unexamined published application"). 
FIG. 10 shows the arrangement of the aforementioned press. As shown in FIG. 
10, a frame 1 incorporates a variety of components such as a die unit 
comprising an upper die set 2, lower die set 3, movable stripper 4, upper 
die 5, lower die 6, upper punch 7 and lower punch 8, and piezo-electric 
actuators 9 for operating the stripper 4. Two actuator casings 12 are 
disposed on the top and bottom of the frame 1, respectively. The actuator 
casings 12 include piezo-electric actuators 10 provided as drive sources 
for the upper punch 7 and the lower punch 8 in combination with movable 
pieces 11, which are rod members for transmitting the amount of 
displacement of the respective piezo-electric actuators 10 to the punches. 
Further in FIG. 10, reference numeral 13 designates tightening screws for 
fixedly securing the die sets 2 and 3 inside the frame; springs 14 for 
urging the movable stripper 4; springs 15 for returning the punches 7 and 
8; and pre-loaded springs 16 mounted on the movable pieces 11 so as to 
maintain pressure on the piezo-electric actuators at all times, the 
springs 16 being incorporated in the casings 12 together with the movable 
pieces 11. 
In order to punch a belt-shaped workpiece or a metal foil 17, the press 
thus constructed operates as follows: 
First, the piezo-electric actuators 9 are operated to move the movable 
stripper 4 upwardly. Under this condition, the workpiece 17 is fed into 
the space between the upper die 5 and the lower die 6. Thereafter, the 
piezo-electric actuators 9 are restored so that the-workpiece 17 is held 
between the upper die 5 and the lower die 6 with the aid of the elastic 
forces of the urging springs 14. Under this condition, the upper punch 7 
and the lower punch 8 are driven alternately with the piezo-electric 
actuators 10, to punch the workpiece 17 by so-called "vertical two-way 
punching". Thereafter, the piezo-electric actuators 9 are operated again 
to move the stripper 4 thereby to release the workpiece. The workpiece 17 
thus released is shifted a predetermined distance. 
The above-described press is impractical. As described above, in the press 
of FIG. 10, the piezo-electric actuators 10 are fixedly mounted on the top 
and the bottom of the frame 1, respectively, and the piezo-electric 
actuators 9 are driven to move the movable stripper 4 adapted to hold the 
workpiece 17. In general, the amount of displacement provided by a 
lamination type piezo-electric actuator, which is formed by stacking a 
number of piezo-electric elements, is no more than several tens of microns 
(.mu.m). Therefore, when the movable stripper 4 is moved upwardly as was 
described above, the space formed between the upper and lower dies of the 
press is such that the metal foil workpiece 17 can be barely inserted into 
it; that is, the space is not quite large enough. 
For example, if the workpiece is bent during pressing, or burrs are formed 
at the cut edges during shearing, the workpiece may be caught in the 
press. In such event, sometimes, it is at times impossible to feed the 
workpiece. If this occurs, no emergency measure can be taken; that is, it 
is impossible to release the workpiece, for instance, with a jig or tool 
inserted from outside, because the space between the upper and lower dies 
is considerably narrow, of the order of several tenths of microns. 
Therefore, the die unit must be disassembled to remove the workpiece 
caught in the press, which is a troublesome operation. 
SUMMARY OF THE INVENTION 
Accordingly, an object of this invention is to eliminate the 
above-described difficulties accompanying a conventional piezo-electric 
actuator operated press. 
More specifically, an object of the invention is to provide a 
piezo-electric actuator operated press in which punch driving 
piezo-electric actuators and a die unit are improved in arrangement so 
that, when the die unit is opened, a sufficiently large space is formed 
between the top and bottom parts thereof, whereby the workpiece can be 
smoothly fed into and moved out of the press without interfering with the 
die unit, and even if the workpiece is caught in the press, it can be 
externally corrected with ease. 
The foregoing object and other objects of the invention have been achieved 
in a first aspect by punches and punch driving piezo-electric actuators 
being built in die sets; and whereby one of the die sets, which is 
movable, is coupled to a die tightening or shifting mechanism, so that it 
is moved to a die opening position or a die closing position. 
The first aspect is preferably embodied technically as follows: 
A piezo-electric actuator together with a movable piece and a pre-loaded 
spring for transmitting the displacement of the piezo-electric actuator to 
the punch is accommodated in an actuator casing in such a manner that it 
is subjected to pressure. The actuator casing is built in the die set. A 
position adjusting mechanism is provided for the piezo-electric actuator, 
in such a manner that it is positioned between the actuator casing 
accommodating the piezo-electric actuator and the die set, to set the 
initial position of the punch. 
The position adjusting mechanism comprises: a wedge mechanism inserted 
between the rear surface of the piezo-electric actuator and the die set; 
and pressure means for pushing the casing against the wedge mechanism. The 
wedge mechanism comprises: a wedge piece inserted between the rear surface 
of the actuator casing and the die set; and an adjusting bolt for moving 
the wedge piece back and forth, and one end portion of the wedge piece is 
loosely engaged with the shank of the adjusting bolt. 
The pressure means includes a compression spring interposed between the 
front surface of the casing and the die set, or it includes: a rod built 
in the actuator casing in such a manner that the end portion of the rod 
protrudes from the front surface of the actuator casing; and a compression 
spring for urging the rod towards the die set. 
The punch driven by the piezo-electric actuator may be contouring punch 
with a piercing punch built in the contouring punch, so that a workpiece 
is contour-punched and pierce-punched at the same time. A spring seat is 
formed in the outer wall of the rear end portion of the contouring punch, 
and return springs are connected between the spring seat and the die set, 
to urge the punch rearwardly. 
In a second aspect, an upper die set and a lower die set are set between a 
stationary die plate and a movable die plate coupled to a mechanical die 
shifting mechanism, and punch driving piezo-electric actuators are mounted 
on the die plates in such a manner as to oppose the punches built in 
respective die sets. 
The technical concept of the second problem solving means described above 
can be embodied as follows: 
A plurality of punches are built in each of the die sets, a movable plate 
is interposed between the die set and the piezo-electric actuator in such 
a manner as to cover the plurality of punches, and those punches are 
driven simultaneously through the movable plate by the piezo-electric 
actuator. The movable plates are built in the die plates or die sets in 
such a manner that the movable plates are supported in a respective guide 
mode. 
A plurality of piezo-electric actuators are provided on each die plate in 
such a manner as to oppose the corresponding movable plate, and the 
plurality of piezo-electric actuators thus provided are synchronously 
energized to drive the movable plate. 
Basically, according to the first and second aspects of the invention, the 
movable one of the upper and lower dies which are arranged on both sides 
of the workpiece conveying path is coupled to the mechanical die shifting 
mechanism made up of an air cylinder or hydraulic cylinder so that it is 
moved to the die opening position or the die closing position. The punch 
driving piezo-electric actuators are built in the die sets in combination 
with the punches, respectively, or mounted on the die plates to which the 
die sets including the punches are connected. Therefore, each of the 
piezo-electric actuators is moved to the die opening position or the die 
closing position in association with the die set. Hence, it is unnecessary 
to adjust the die opening and closing stroke of the die tightening 
mechanism to the stroke of displacement of the punch. The mechanical die 
shifting mechanism provides much larger die opening and closing strokes 
than the piezo-electric actuator. Therefore, the workpiece can be fed in 
and taken out of the press without interference with the die unit. Even if 
the workpiece is caught inside the press during punching, emergency 
measures can be taken; that is, it may be corrected inside the press or 
removed from it with a suitable jig, because the die can be opened wide 
enough by operating the die shifting mechanism. 
Furthermore, in the various embodiments described herein, the punches can 
be positioned in place with ease. In addition, a plurality of piercing 
punches and contouring punches are built in the die. Therefore, when it is 
necessary to punch a workpiece with a contouring punch and a piercing 
punch, those punching operations can be carried out simultaneously or 
successively on only one press. 
The nature, utility and principle of the invention will be more clearly 
understood from the following detailed description and the appended claims 
when read in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Preferred embodiments of this invention will be described with reference to 
the accompanying drawings, in which parts corresponding functionally to 
those which have been described with reference to FIG. 10 (the prior art) 
are therefore designated by the same reference numerals or characters. 
An example of a vertical press with a one-way punching system wherein 
punches and punch driving piezo-electric actuators or built in the sets, 
and one of the die sets, which is movable, is coupled to a die tightening 
or shifting mechanism so that it is moved to a die opening or die closing 
position according to a first embodiment of the invention, will be 
described with reference to FIG. 1. 
In the first embodiment, upper die set 2 forms an assembly with punch 7, 
piezo-electric actuator 10 for driving the punch 7, and a position 
adjusting mechanism 18 (hereinafter described) provided for piezo-electric 
actuator 10. This assembly is coupled to a ram 19a of a die shifting 
mechanism 19 mounted on the top of frame 1. The mechanism 19 comprises an 
air cylinder or hydraulic cylinder. The lower die set 3, opposing upper 
die set 2, is fixedly mounted on frame 1. The die set 3 also includes die 
6 which is used in combination with the punch 7. The press further 
comprises guide pins 20 in engagement with the upper die set 2, and a 
punch guide 21. 
The piezo-electric actuator 10, the movable piece 11 and the pre-loaded 
spring 16 are accommodated in the actuator casing 12, which is set inside 
the die set 2 in such a manner that the piezo-electric actuator 10 is 
vertically slidable. The aforementioned position adjusting mechanism 18 is 
provided above the casing 12 accommodating the piezo-electric actuator 10, 
and a compression spring 22 for urging the casing 12 towards the position 
adjusting mechanism 18 is provided below the piezo-electric actuator 10. 
The position adjusting mechanism is a kind of wedge mechanism which 
comprises: a wedge piece 18a inserted into the rear surface of the casing 
12 accommodating the piezo-electric actuator 10 a wedge or tapered groove 
formed in the die set 2; and an adjusting bolt 18b and a compression 
spring 18c arranged on both sides of the wedge piece 18a. The position 
adjusting mechanism 18 is a fine adjusting means for initially positioning 
the punch 7 in place before the start of the press. That is, when the 
wedge piece 18a is moved to the left-hand side as viewed in FIG. 1, by 
turning the adjusting bolt 18b clockwise, the piezo-electric actuator 10 
is moved downwardly against the compression spring 22; and when the 
adjusting bolt 18b is turned counterclockwise, the wedge piece 18a is 
moved to the right-hand side, as viewed in the drawing so that the 
piezo-electric actuator 10 is moved upwardly being urged by the 
compression spring 22. Thus, the initial position of the punch 7 can be 
set correctly with the variations in dimension of the related components 
compensated. Instead of the above-described position adjusting mechanism 
18, an adjusting screw may be employed which is screwed into the die set 2 
from above to abut against the end face of the casing 12 accommodating the 
piezo-electric actuator 10. However, the adjusting screw tends to 
interfere with the frame 1 when operated. On the other hand, with the 
above-described wedge mechanism, the position adjustment of the punch can 
be freely achieved without interfering with the frame 1. 
The operation of the press thus constructed will be described with 
reference to the situation where a workpiece 17 is punched on it. 
First, the die shifting mechanism 19 is operated to move the upper die set 
2 upwardly. Under this condition, the die unit is opened to provide a 
sufficiently wide space between the upper die set 2 and the lower die set 
3. Thereafter, the workpiece 17 is fed to the work position, and then the 
die shifting mechanism 19 is operated to move the die set 2 downwardly to 
a closed position, so as to hold the workpiece 17 between the die 6 and 
the die set 2. Under this condition, voltage is applied to the 
piezo-electric actuator 10 to move the punch 7 downwardly, as a result of 
which the workpiece 17 is punched. Thereafter, the application of voltage 
to the piezo-electric actuator 10 is suspended, while the die tightening 
mechanism is operated to open the die unit to release the workpiece 17. 
The workpiece 17 thus released is shifted a predetermined distance. 
Thereafter, the above-described operations are repeatedly carried out, to 
continuously punch the workpiece 17. 
FIG. 2 shows the arrangement of one example of a vertical press with a 
two-way punching system which constitutes a second embodiment of the 
present invention. 
Similar to the press shown in FIG. 10, the upper die set 2 incorporates the 
punch 7 and the piezo-electric actuator 10, while the lower dies set 3 
incorporates the punch 8 and the piezo-electric actuator 10. The die set 2 
is coupled to a die shifting mechanism 19 similarly as in the press shown 
in FIG. 1 (the first embodiment). Furthermore, similar to the first 
embodiment described above, each of the die sets 2 and 3 has the position 
adjusting mechanism 18 on one side of the casing 12, and pressure means 
for pushing the casing 12 towards the position adjusting mechanism 18 on 
the other side of the casing 12. The pressure means in the upper die set 2 
is a compression spring 16 which is similar to the one in the first 
embodiment (FIG. 1). The pressure means in the lower die set 3 is designed 
as follows: The pressure means comprises a rod 23 whose end portion 
protrudes through a hole formed in a front wall of the casing 12; and a 
compression spring 24 urges the rod 23 from behind. The pressure means is 
built in the casing 12 in such a manner that the compression spring pushes 
the rod 23 against the die set 3 so that the reaction of it pushes the 
casing 12 against the position adjusting mechanism 18. 
FIGS. 3 and 4 shows one modification of the wedge mechanism, or the 
position adjusting mechanism 18, for the piezo-electric actuator 10 in the 
above-described first or second embodiment. One end portion of the wedge 
piece 18 is bent like the character "L", and a U-shaped grove 18d is 
formed in the end portion thus bent. On the other hand, a pair of flanges 
18e are formed on the adjusting bolt 18 near the head. The adjusting bolt 
18b is loosely engaged with the U-shaped groove 18d with the pair of 
flanges 18e set on both sides of the end portion where the U-shaped groove 
18d is formed. With the position adjusting mechanism thus designed, the 
wedge piece 18a is moved back and forth as the adjusting bolt 18b is 
turned. Therefore, the modification dispenses with the compression spring 
18c employed in the above-described first and second embodiment, and can 
adjust the position more positively. 
FIG. 5 shows one example of a press for forming an article 25 which, as 
shown in FIG. 6, is in the form of an elongated rectangle with two holes, 
which constitutes a third embodiment of the invention. In the third 
embodiment, the upper die set 2 and the lower die set 3 have contouring 
punches 7 and 8 corresponding to the contour of the article 25, and 
piercing stationary punches 26 and 27 built in the punches 7 and 8 to form 
the holes 25a in the article 25, respectively. The contouring punches 7 
and 8 are fitted in the dies 5 and 6, respectively. The contouring punches 
7 and 8 thus fitted are driven by the corresponding movable piece 11 which 
in turn is drawn by the piezo-electric actuator 10, similar to the 
above-described first and second embodiments. The piercing stationary 
punches 26 and 27 are fixedly secured through respective punch holders 28 
to the die sets 2 and 3. In order to push the punches 7 and 8 against the 
movable pieces 11 for moving the latter in a reciprocation mode, returning 
springs 15 are employed. More specifically, grooves are formed in the 
outer walls of the rear end portions of the punches 7 and 8, respectively, 
and spring seats 29 are fitted in the corresponding grooves. The return 
springs 15 are each inserted between one of the spring seats 29 and the 
corresponding die 5 and 6. With this structure, the returning springs 15 
will never interfere with the stationary punches. This structure can be 
employed even when the contouring punches 7 and 8 are intricate in 
configuration. 
The press thus designed operates as follows: When the die unit is closed 
with the workpiece 17 fed therein, the workpiece 17 is held between the 
upper and lower dies 5 and 6 and accordingly between the piercing punches 
26 and 27, while the piercing punches 26 and 27 go in the workpiece 17 to 
form the holes 25a. Thereafter, with the die unit held closed, the 
contouring punches 7 and 8 are moved towards and retracted from the 
workpiece alternately by the respective piezo-electric actuators 10. That 
is, the workpiece is contour-punched by "vertical two-way punching", so 
that the article 25 as shown in FIG. 6 is formed. 
The piercing punches 26 and 27 are so set that their ends are flush with 
the end faces of the dies 5 and 6, respectively. In the case where the 
piercing punches are thin, they may be broken when the workpiece is held 
between the upper and lower dies. That is, when the die unit is closed to 
hold the workpiece, an excessively large load may be applied to the 
piercing punches to break the latter. In order to eliminate this 
difficulty, a liner 30 corresponding in thickness to a workpiece 17 to be 
handled is provided for the lower die 6 as shown in FIG. 5. When the die 
unit is closed, the upper surface of the liner 30 serves as a stopper, to 
prevent the application of an excessively large load to the piercing 
punches 26 and 27. 
In the previously described first embodiment, the punching operation is 
carried out according to the vertical one-way punching system; and in the 
second and third embodiments, the punching operation is carried out 
according to the vertical two-way punching system. The second or third 
embodiment, which has the punches in the upper and lower parts of the die 
unit, may employ a punching method in which the workpiece is held between 
the upper punch and the lower punch; and then the piezo-electric actuators 
are driven to vibrate those punches repeatedly. The present inventors have 
confirmed that, according to the punching method, even a metal foil of 
thin stainless steel, such as several tens of micrometers thin (.mu.m), 
for example, can be accurately punched without formation of burrs. 
A fourth embodiment of a two-way punching system press according to the 
second aspect of the invention wherein an upper die set and a lower die 
set are set between a stationary die plate and a movable die plate coupled 
to a mechanical die shifting mechanism, and punch driving piezo-electric 
actuators are mounted on the die plates in such a manner as to oppose the 
punches built in respective die sets will be described with reference to 
FIG. 7. The press, as shown in FIG. 7, is constructed as follows: The 
punches 7 and 8 are built in the upper and lower parts of the die unit, 
respectively. The lower die set 3 is mounted through a stationary die or 
fixing plate 31 on a table 1 mounted to frame 1. A sliding member 33 is 
coupled to a mechanical die shifting mechanism 19, which is made up of a 
hydraulic cylinder 34, a cylinder rod 34a, and a swing lever 35 pivotably 
connected between the cylinder rod and the slider 33. The slider 33 is 
moved vertically along the frame 1 by the hydraulic cylinder 34, so that 
the upper part of the die unit, being guided by guide posts 20, is moved 
away from and towards the lower part of the die unit; that is, it is moved 
to a die opening position or a die closing position. The piezo-electric 
actuators 10, which are adapted to drive the corresponding punches 7 and 8 
are built in the actuator casings 12 and are similar in structure to those 
of the first embodiment. These actuators 10 are fitted in the stationary 
and movable die plates 31 and 32, respectively, in such a manner that the 
end faces of the movable pieces 11 are confronted with the rear end faces 
of the punches 7 and 8, respectively. 
The operation of the press of FIG. 7 will be described in connection with 
the punching of a workpiece 17. First, the die shifting mechanism 19 is 
operated to open the die unit. With the die unit opened, the workpiece 17 
is fed into the space between the upper die set 2 and the lower die set 3; 
and then the die shifting mechanism 19 is operated to close the die unit; 
that is, the workpiece 17 is fixedly held between the upper and lower 
parts of the die unit. Under this condition, voltage is applied to the 
piezo-electric actuators alternately which are coupled to the stationary 
die plate 31 and the movable die plate 32, to punch the workpiece 17 by 
two-way punching. After the workpiece 17 has been punched in this way, the 
die tightening mechanism 19 is operated to open the die unit to release 
the workpiece 17. The workpiece thus released is then moved to a 
subsequent processing station. 
In the fourth embodiment, similar to the above-described first through 
third embodiments, the workpiece can be smoothly fed into the press. 
Furthermore, in the fourth embodiment, the piezo-electric actuators 10 are 
separated from the die sets 2 and 3, and instead they are coupled to the 
die plates 31 and 32. This arrangement is beneficial in that the die can 
be replaced with ease. In addition, the piezo-electric actuators can be 
readily removed; and therefore, when it is necessary to inspect or replace 
the piezo-electric actuators, it is unnecessary to disassemble the die 
unit. 
FIG. 8 shows a fifth embodiment of a press with a two-way punching system, 
in which a plurality of punches are built in the die; and the workpiece is 
moved successively in the die unit. The fifth embodiment is different from 
the fourth embodiment as follows: A plurality of punches 7 and a plurality 
of dies 5 are built in the upper die set 2. Similarly, a plurality of 
punches 8 and a plurality of dies 6 are built in the lower die set 3. A 
movable plate 36 is interposed between the piezo-electric actuators 10 
coupled to the stationary die plate 31 and the punches 8 in such manner 
that it covers the punches 8. Similarly, another movable plate 36 is 
interposed between the piezo-electric actuators 10 coupled to the movable 
die plate 31 and the punches 7 in such a manner that it covers the punches 
7. The movable die plates 36 are built in the stationary and movable die 
plates 31 and 32, respectively, in such a manner that they are vertically 
movable. 
The piezo-electric actuators are mounted on the die plates 31 and 33 in 
such a manner that two piezo-electric actuator 10 are provided on the rear 
side of each of the movable plates 36 at predetermined intervals. The 
movable plates 36 are urged towards the piezo-electric actuators 10 by 
springs 37. The displacement of the movable plate 36 is monitored by a 
displacement gauge 38. A movable stripper 14 is provided between the upper 
die set 2 and the lower die set 3. 
In the fifth embodiment, the die tightening mechanism 19 is of so-called 
"toggle type". The output shaft of a driving servo motor 39 is connected 
to a feed screw mechanism 40 which is coupled to a toggle link mechanism 
41. A coupling bar 43 is connected through an adjusting screw 42 to the 
link mechanism 41 at the bottom dead point. The coupling bar 43 thus 
connected is coupled through slide shafts 44 to the above-described 
movable die plate 32. 
In the fifth embodiment, the workpiece pressing operation is fundamentally 
similar to those in the above-described first through fourth embodiments. 
The piezo-electric actuators 10, two for each of the stationary and 
movable die plates 31 and 32, are synchronously energized, so that the 
plurality of punches built in the upper and lower die sets 2 and 3 are 
driven through the movable plates 36 simultaneously. Thus, by moving the 
workpiece in the press successively, one article can be formed with a 
plurality of punches. In the fifth embodiment, two piezo-electric 
actuators 10 are provided for each movable plate 36 as was described 
above; and therefore, the movable plate 36 can be moved uniformly. In this 
embodiment, in addition to the punches 7 and 8 being driven by the 
piezo-electric actuators 10, a stationary punch 27 may also be provided. 
FIG. 9 shows a sixth embodiment which is a modification of the fifth 
embodiment. In the previously described embodiment of FIG. 8, the movable 
plates 36 are built in the die plates 31 and 32, that is, each die plate 
is partially changed in wall thickness, which decreases the mechanical 
strength. In order to overcome this difficulty, in the fifth embodiment 
the movable plates 36 are built in the die sets 2 and 3 instead of the die 
plates 31 and 32 respectively. 
As was described above, in the piezo-electric actuator operated press 
according to the invention, the punch driving actuators are built in the 
die set together with the punches, or mounted on the die plates coupled to 
the die sets; and the movable die set is coupled to the mechanical die 
shifting mechanism so that it is moved to the die opening position or the 
die closing position together with the piezo-electric actuator or 
actuators. Hence, in the press of the invention, the die unit can be 
opened wide enough with the die shifting mechanism. Thus, the workpiece 
can be fed into and taken out of the press without interference with the 
die unit. Even if the workpiece is caught in the press during the punching 
operation, emergency measures can be taken; that is, it may be corrected 
inside the press or removed from it with a suitable jig. That is, the 
press according to the invention can be handled with ease. 
While there has been described preferred embodiments of this invention, it 
will be obvious to those skilled in the art that various changes and 
modifications may be made therein without departing from the invention, 
and it is intended, therefore, to cover in the appended claims all such 
changes and modifications as fall within the true spirit and scope of the 
invention.