Presses – Reciprocating press construction – With mechanical force multiplier
Reexamination Certificate
2002-05-23
2004-01-20
Ostrager, Allen (Department: 3725)
Presses
Reciprocating press construction
With mechanical force multiplier
C100S230000, C100S289000, C100S257000
Reexamination Certificate
active
06679164
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to a press machine for use in sheet metal working, for example, and more particularly to a press machine having a simple construction and capable of fixed-stroke press operation requiring precise positional control.
BACKGROUND ART
Fluid pressure cylinders have heretofore been widely used as means for driving a ram that comes into contact with a workpiece in a press machine. As such fluid pressure cylinders, hydraulic (or oil pressure) cylinders have been commonly used. When a fixed-stroke press operation, that is, a press operation in a state where the distance between the ram and the table is kept constant, is carried out in such a press machine driven by a hydraulic cylinder, a press operation called the “Do-zuki press operation” is usually needed.
FIG. 6
is a diagram of assistance in explaining the conventional “Do-zuki press operation.” In
FIG. 6
, numeral
31
refers to a table, on which a ram
32
of a press machine is operated vertically with a hydraulic cylinder to press a workpiece
33
.
In order to precisely press the workpiece
33
to a thickness t in this arrangement, a projection
35
equal to the thickness t is provided on the lower end of the ram
32
downward from the working surface
34
.
When the ram
32
is operated downward with the aforementioned construction, the working surface
34
can perform a desired work on the workpiece
33
, and the thickness t of the workpiece
33
can be maintained with precision since the projection
35
of the ram
32
comes in contact with the table
31
, resulting in a press operation without dimensional variations. This leads to an improved working accuracy.
The press operation as shown in
FIG. 6
above has the following problems, though press working accuracy can be improved with the fixed-stroke press operation. That is, not only the ram
32
violently hits against the workpiece
33
, but also the projection
35
of the ram
32
also violently hits against the table
31
, generating impact noises. Particularly greater noises are generated during high-speed press operations involving high frequencies of ram reciprocation.
Fixed-stroke press operation with electrically operated press machines has heretofore been commonly used, which has recently been enjoying popularity due to its advantage in effectively preventing noises generated in the so-called Do-zuki press operation with hydraulic press machines.
FIG. 7
is a longitudinal sectional view of a typical electric-powered press machine of a conventional type, as disclosed in Japanese Published Unexamined Patent Application No. Hei-6(1994)-218591.
In
FIG. 7
, numeral
41
refers to pressure generating means that is housed in a top frame member
44
provided on a column
43
integrally formed with a table
42
.
Numeral
45
refers to a cylindrical body provided in the top frame member
44
and having a bearing
46
on the upper end thereof. Numeral
47
refers to a screw shaft formed in a suspended state with the top end thereof supported by the bearing
46
.
Next, numeral
48
refers to a ram shaft formed into a hollow cylindrical shape, with a nut
49
engaging with the screw shaft
47
fixedly fitted to the upper end thereof, and provided vertically movably in the cylindrical body
45
. Numeral
50
refers to a pushing member provided detachably on the lower end of the ram shaft
48
. The screw shaft
47
and the nut
49
form a ball screw engagement.
Next, numeral
51
refers to an anti-vibration device comprising a guide
52
provided in the top frame member
44
, an anti-vibration bar
53
vertically movably provided in the guide
52
, and a connecting plate
54
provided on the lower ends of the ram shaft
48
and the anti-vibration bar
53
. Numeral
55
refers to a drive motor provided in the top frame member
44
to drive the screw shaft
47
in forward and backward rotations via a pulley
56
and a belt
57
provided on the upper end of the screw shaft
47
.
Furthermore, measuring means, central processing unit (not shown), etc. are provided so as to control the settings of the initial start position and the fixed stop position of the pushing member
50
, as well as the rotational speed and the forward/backward rotation of the drive motor
55
.
With the aforementioned construction, when the drive motor
55
is operated to cause the screw shaft
47
to rotate via the belt
57
and the pulley
56
, the ram shaft
48
to the upper end of which the nut
49
is fixedly fitted is lowered, bringing the pushing member
50
into contact with the workpiece W at a predetermined position as shown by chain double-dashed lines in the figure and with a predetermined pushing force to carry out a predetermined press operation.
Upon completion of the press operation, the drive motor
55
is rotated in the reverse direction to lift the ram shaft
48
and the pushing member
50
back to the initial position. By repeating the above operations, predetermined fixed-stroke press operations can be performed sequentially on a plurality of the workpieces W.
With an electric-powered press machine having the aforementioned construction, fixed-stroke press operation can be accomplished without generating harsh noises. The conventional types of electric-powered press machines, however, have the following problems. That is, the height h of the lower end surface of the pushing member
50
from the table
42
in
FIG. 7
is controlled to be kept constant at any time, as needed in fixed-stroke press operation, and therefore a predetermined pushing force is applied to the workpiece W via the pushing member
50
at that position. In other words, a reaction force equal to the abovementioned pushing force is exerted onto the screw shaft
47
and the nut
49
always at the same relative positions.
The screw shaft
47
and the nut
49
, on the other hand, constitutes a ball screw engagement to ensure high-precision positional control of the ram shaft
48
and the pushing member
50
, in which balls and ball grooves constituting a ball screw engage with each other in line or point contact. For this reason, when the aforementioned reaction force acts on both the balls and the ball grooves many times at the same relative position, the balls and/or the ball grooves could be locally worn out, leading to lowered working accuracy and reduced service life. Even in cases where the aforementioned screw shaft
47
and the nut
49
constitute a normal screw engagement, the aforementioned local wear problem may persist.
To solve the aforementioned problem, the present applicant has already filed a patent application (Japanese Unexamined Published Patent Application No. Hei-11(1999)-23483) for an invention comprising a base formed into a flat plate shape, a guide bar provided on the base in such a manner that an end of the guide bar orthogonally intersects the base, a support plate formed into a flat plate shape provided at the other end of the guide bar in such a manner as to orthogonally intersect the guide bar, a screw shaft supported by the guide bar in parallel with the guide bar in such a manner as to be rotatable in forward and backward directions, a movable body axially movably engaged with the guide bar, a nut member formed into a hollow cylindrical shape, having a differential male thread on the outer surface thereof, in such a manner as to engage with the screw shaft, a differential member formed into a hollow cylindrical shape, having a differential female thread for engaging with the differential male thread, and formed rotatably in the movable body, and a worm wheel fixedly fitted to the differential member for engaging a worm.
FIG. 4
is a longitudinal sectional front view illustrating essential parts of a typical improved invention, and
FIG. 5
is a cross-sectional view taken along line A—A in FIG.
4
.
In
FIGS. 4 and 5
, numeral
1
refers to a base formed into a shape of a rectangular flat plate, for example, on the four corners of which provided upright are columnar guide bars
2
. To the upper ends of the guide bars
2
fixedly fitted v
Futamura Shoji
Kaneko Hiromitsu
Institute of Technology Precision Electrical Discharge Work&apos
McGlew and Tuttle , P.C.
Self Shelley M
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