Presses – Safety device – Means to disable or to forestall power to the press
Reexamination Certificate
1999-12-20
2001-09-11
Vo, Peter (Department: 3721)
Presses
Safety device
Means to disable or to forestall power to the press
Reexamination Certificate
active
06286420
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to an overload protector for a mechanical press.
2. Description of the Prior Art
There is a conventional device which is recited in Japanese Patent Publication No. 5-20629 the present inventor proposed earlier, as an example of the overload protector of this type.
The conventional device comprises an overload absorbing hydraulic chamber formed within a slide of a mechanical press and an overload protecting valve connected to this overload absorbing hydraulic chamber. The overload protecting valve has an interior area provided with a relief member and a valve closing spring of a pressure compensating valve. The relief member is adapted to act for valve closing through an urging force of the valve closing spring.
The above-mentioned pressure compensating valve serves to relieve pressurized oil within the hydraulic chamber by an amount corresponding to pressure increase when the pressurized oil has increased its pressure at a very slow speed from a set charging pressure during the press working. Therefore, it is necessary to set a relief pressure (hereafter referred to as ‘set compensating pressure’) of the pressure compensating valve at a value a little higher than the set charging pressure.
Consequently, in the case of enhancing the set charging pressure depending on the capacity and usage of the mechanical press, the set compensating pressure had to be increased accordingly. Similarly, in the case of decreasing the set charging pressure, the set compensating pressure had to be reduced.
The conventional technique is excellent in that it houses the pressure compensating valve within the overload protecting valve and therefore can be made compact. However, when changing the set compensating pressure, it was required to vary the urging force of the valve closing spring arranged within the overload protecting valve. This entailed a disadvantage that it took quite a labor to vary the urging force of the valve closing spring and effect a confirmation test after having varied it.
SUMMARY OF THE INVENTION
The present invention aims at making it possible to easily vary the set compensating pressure of the pressure compensating valve in correspondence with the change of the set charging pressure to the overload absorbing hydraulic chamber.
In order to accomplish the foregoing aim, an invention as set forth in claim
1
has constructed an overload protector for a mechanical press in the following manner, for example, as shown in
FIGS. 1 and 2
.
The overload protector is provided with a pneumatic hydraulic booster pump
5
which supplies pressurized oil under a set charging pressure to an overload absorbing hydraulic chamber
3
within a slide
2
of a mechanical press
1
. And it is provided with an overload protecting valve
10
which performs a relief operation when a pressure of the hydraulic chamber
3
has exceeded a set overload pressure. It is also provided with a pressure compensating valve
14
which performs a relief operation when the pressure of the hydraulic chamber
3
increases at a very slow speed and as a result has exceeded a set compensating pressure. The pressure compensating valve
14
comprises a restricting passage
60
and a relief valve
61
connected to each other in series. The relief valve
61
comprises a valve closing piston
71
hermetically inserted into a cylinder hole
70
so as to push a relief member
72
in a direction for valve closing, a valve closing actuation chamber
73
which opposes to the valve closing piston
71
and communicates with a compressed air supply passage
30
of the booster pump
5
, and a resilient means
74
for retaining residual pressure which urges the relief member
72
in the direction for valve closing.
The invention of claim
1
produces the following function and effect.
The booster pump discharges pressurized oil having its pressure increased in accordance with a sectional area ratio between a pneumatic piston and a hydraulic piston (or a hydraulic plunger). Thus when enhancing the set charging pressure to the overload absorbing hydraulic chamber, it is sufficient to increase air pressure to be supplied to the booster pump. Then this simultaneously increases air pressure to be supplied from the compressed air supply passage of the booster pump to the valve closing actuation chamber of the pressure compensating valve to result in enlarging a pushing force for valve closing of the relief valve and therefore enhancing the set compensating pressure of the pressure compensating valve.
Similarly, when decreasing the set charging pressure to the hydraulic chamber, it is enough to reduce the air pressure to be supplied to the booster pump. Then this simultaneously reduces the air pressure to be supplied to the valve closing actuation chamber to result in decreasing the pushing force for valve closing of the relief valve and therefore reducing the set compensating pressure of the pressure compensating valve.
Consequently, it is possible to automatically vary the set compensating pressure of the pressure compensating valve in correspondence with the change of the set charging pressure to the overload absorbing hydraulic chamber with ease and assuredness.
Further, even if the compressed air supply passage has lost its pressure because the press stops working or for the like reason, the relief member can be closed through an urging force of the resilient means, which leads to a possibility of leaving pressurized oil of a predetermined pressure in the overload absorbing hydraulic chamber. Thus it is possible to smoothly and promptly recharge the pressurized oil to the hydraulic chamber.
It is preferable to attach at least one of the booster pump
5
and the overload protecting valve
10
as well as the pressure compensating valve
14
to a common block
16
as an invention of claim
2
indicates.
According to the invention of claim
2
, it is possible to omit piping between at least one of the booster pump and the overload protecting valve, and the pressure compensating valve, which invites a possibility of making the device compact and besides lessening the labor for assembling the device.
Further, as indicated by an invention of claim
3
, the valve closing piston
71
is integrally formed with the relief member
72
. The resilient means
74
is composed of a compression spring. The resilient means
74
of the compression spring has one end connected to an end wall of the valve closing actuation chamber
73
and has the other end connected to the valve closing piston
71
. In this case, the pressure compensating valve can be downsized to make the device compact.
Moreover, as indicated by an invention of claim
4
, in the event the overload protecting valve
10
has a pushing force for valve closing which is an urging force of a valve closing spring
50
, even if the air pressure to be supplied to the booster pump is changed, it is possible to retain the pushing force for valve closing of the overload protecting valve at an initial value and therefore prevent the set overload pressure of the overload protecting valve from varying by mistake.
REFERENCES:
patent: 4085669 (1978-04-01), Yonezawa
patent: 4166415 (1979-09-01), Spanke et al.
patent: 4593547 (1986-06-01), Heiberger
patent: 4760781 (1988-08-01), Moriyama
patent: 4827839 (1989-05-01), Yonezawa et al.
patent: 5216959 (1993-06-01), Hayashie
patent: 5620024 (1997-04-01), Yonezawa
patent: 5638748 (1997-06-01), Daniel
patent: 5-20629 (1993-03-01), None
Bacon & Thomas PLLC
Huynh Louis K.
Kabushiki Kaisha KOSMEK
Vo Peter
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