Pressurizer

Details Pressurizer Pressurizer

2001-12-03

2004-09-21

Jones, David B. (Department: 3725)

Metal deforming

With means to drive tool

Including pneumatic- or fluid-actuated tool support

C072S453020, C100S270000

Reexamination Certificate

active

06792788

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pressure device, such as a pressing machine used, for example, in sheet metal working and, more particularly, to a pressure device which is capable of pressing operation requiring accurate position control and which, at the same time, involves a large pressing force and yet small driving energy.
2. Description of the Related Art
In a conventional type of press working machine, a hydraulic cylinder is widely used as a means of driving a ram that comes in contact with a workpiece and, in particular, an oil hydraulic cylinder is frequently used. In this type of hydraulic cylinder-operated pressing machine, it is necessary to perform press working as shown in
FIG. 6
, that is, working is conducted with the distance between a ram and a table kept constant.
FIG. 6
is an explanatory drawing of conventional working. In
FIG. 6
, numeral
31
indicates a table. With respect to this table
31
, a ram
32
of a pressing machine moves up and down by use of an oil hydraulic cylinder, for example, to perform the press working of a workpiece
33
. In order to accurately work the workpiece
33
to a thickness dimension t with this arrangement, the bottom end of the ram
32
is provided with projections
35
that have a height equal to the workpiece thickness t and protrude downward from a working surface
34
.
With this arrangement, when the ram
32
is operated downward, the working surface
34
can perform prescribed working of the workpiece
33
. Keeping the projections
35
of the ram
32
abutting against the table
31
allows the thickness dimension t of the workpiece
33
to be accurately maintained, free from dimensional variations. Thus, the working accuracy of the workpiece
33
can be improved.
The working method shown in
FIG. 6
, however, poses the following problem although the working accuracy can be improved by this method. That is, impact noises are inevitably generated because the ram
23
hits against the workpiece
33
in an impacting manner and because the projections
35
of the ram
32
also violently hit against the table
31
. In particular, in the case of high-speed working where the working frequency of the ram
32
per unit time is high, noises become so great that they impair the working environment.
On the other hand, working by use of an electrically-driven press has so far been practiced, and it is known that this working method is favorable for preventing the generation of noises caused by the working as shown in
FIG. 6
by the above hydraulic press, etc.
FIG. 7
is a longitudinal sectional view of essential portions of an example of the conventional electrically-driven press. This drawing is contained in Japanese Published Unexamined Patent Application No. Hei-6(1994)-218591, for example. In
FIG. 7
, reference numeral
41
indicates a pressing force generating means. The pressing force generating means
41
is housed within a head frame
44
installed on a column
43
, which is formed integrally with a table
42
.
Numeral
45
indicates a tubular body. The tubular body
45
is installed within the head frame
44
and is provided with a bearing part
46
at the top end thereof. Numeral
47
indicates a screw shaft. The top end of the screw shaft
47
is supported by the bearing part
46
in a suspended state. Numeral
48
indicates a ram shaft, which is formed in a hollow cylindrical shape. A nut
49
, which engages with the screw shaft
47
, is fixed to the top end of the ram shaft
48
. The ram shaft
48
is installed so that it can move vertically within the tubular body
45
. Numeral
50
indicates a pressing element detachably installed in the bottom end portion of the ram shaft
48
. The screw shaft
47
and nut
49
are in ball-screw engagement.
Next, numeral
51
indicates a sliding guide post. The sliding guide post
51
comprises a guide portion
52
installed within the head frame
44
, a sliding rod
53
, and a connecting plate
54
installed between the ram shaft
48
and the bottom end of the sliding rod
53
. Numeral
55
indicates a drive motor. The drive motor
55
is installed within the head frame
44
and drives the screw shaft
47
in both forward and reverse directions via a pulley
56
and a belt
57
, which are installed in the top end portion of the screw shaft
47
.
Note that measuring means, central processing unit, etc., which are not shown in the drawing, set the start and stop positions of the pressing element
50
and the rotational speed of the drive motor
55
, give the drive motor
55
instructions for rotation in the forward and reverse directions, etc.
With the above construction of the electrically-operated press, as the screw shaft
47
is rotated by the operation of the drive motor
55
via the belt
57
and the pulley
56
, the ram shaft
48
having the nut
49
fixed to the upper end thereof descends and the pressing element
50
abuts against a workpiece W with a pressing force in a preset position as shown by chain lines to perform the prescribed press working. After the completion of press working, the ram shaft
48
and pressing element
50
ascend by the reverse rotation of the drive motor
55
and return to the initial positions. By repeating the above operation, the prescribed press working can be accomplished on a plurality of workpieces W.
When an electrically-driven press as mentioned above is used, it is possible to perform working without generating noises. However, a conventional electrically-driven press poses problems as described below. Because the pressing force applied to the workpiece W is determined by the capacity of the drive motor
55
, large-capacity pressing machines require the drive motor
55
having a large capacity. Furthermore, in a large-capacity and large-size pressing machine, moving parts including the ram shaft
48
and pressing element
50
also become large both in size and weight. As a result, the driving energy necessary for the repeated vertical movements of the moving parts also becomes large, adding momentum to the undesirable trend toward larger size design and larger capacity design of drive motor
55
.
Furthermore, it is difficult to precisely position the pressing element
50
in a prescribed position (height h), for example, above the table
42
, and positioning errors frequently occur. Since the pressing element
50
is caused to move vertically by the movement of the nut
49
engaging with the screw shaft
47
as the screw shaft
47
is rotated, it is necessary to increase the number of revolutions and/or the screw pitch of the screw shaft
47
in order to shorten the working cycle time. This results in a decrease in the positioning accuracy of the pressing body
50
. On the other hand, reducing the number of revolutions and/or the screw pitch of the screw shaft
47
in order to improve the locating accuracy of the pressing element
50
could increase the time required for the vertical movement of the pressing element
50
and therefore the working cycle time accordingly, resulting in a decrease in working efficiency.
Although there can be another arrangement where the vertical movement of the pressing element
50
is accomplished by use of a plurality of drive means, this requires a complicated structure and a large-sized unit, and it is difficult to smoothly perform the control of a plurality of drive means. Therefore, this method has not been put to practical use.
SUMMARY OF THE INVENTION
This invention is intended to overcome the aforementioned problems inherent in the prior art, and it is therefore an object of the present invention to provide a pressure device for press working having high working accuracy and a large pressing force and requiring small driving energy.
To solve the above problems, the present invention adopts a technical means that comprises: a base plate; a support plate spaced at a predetermined distance from the base plate; a first slider and a second slider, both being formed so that they can move between the base plate and the support plate in a directi

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