Hydraulic actuator

A hydraulic actuator including a single cylinder body which defined therein a pressure chamber in which a first piston with a piston rod and a second piston with a piston rod are independently movably inserted, a first working member secured to the first piston rod, a second working member secured to the second piston rod, and pressurized fluid inlet and outlet ports provided in the cylinder body to be connected to the pressure chamber.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a hydraulic actuator, and more precisely, 
it relates to a two-stage hydraulic actuator having a cylinder device in 
which two pistons are inserted. 
2. Description of Related Art 
In a conventional hydraulic actuator, a single piston is reciprocally moved 
in a cylinder. A multi-stage cylinder device is also known in which a main 
piston and an auxiliary piston are provided in a cylinder. 
To continuously carry out a series of operations, it is usually necessary 
to provide a cylinder device array consisting of a plurality of cylinder 
devices which are successively actuated, thus resulting in a complex and 
expensive equipment. 
The primary object of the present invention is to provide a hydraulic 
actuator including a single cylinder device which can perform a plurality 
of successive operations. 
Another object of the present invention is to provide a simple hydraulic 
actuator in which no eccentric load is produced during the operation. 
SUMMARY OF THE INVENTION 
According to the present invention, there is provided a hydraulic actuator 
comprising a single cylinder body which defined therein a pressure chamber 
in which a first piston with a piston rod and a second piston with a 
piston rod are independently movably inserted, a first working member 
secured to the first piston rod, a second working member secured to the 
second piston rod, and pressurized fluid inlet and outlet ports provided 
in the cylinder body to be connected to the pressure chamber. 
Preferably, the pressure chamber comprises first, second and third separate 
pressure chambers, so that the first and second pressure chambers are 
separated by the first piston, and the second and third pressure chambers 
are separated by the second piston. 
Provision is also made to a fluid pipe which extends through the first 
piston to be connected to the second pressure chamber. 
The pressure chamber can be either annular or circular in cross section. 
Preferably, each of the first and second piston rods is comprised of a 
plurality of rod elements. 
These rod elements can be circumferentially spaced at an equiangular 
distance. 
According to another aspect of the present invention, there is provided a 
press machine comprising a hydraulic actuator which includes a single 
cylinder body which defined therein a pressure chamber in which a first 
piston wish a piston rod and a second piston with a piston rod are 
independently movably inserted, a first working member secured to the 
first piston rod, a second working member secured to the second piston 
rod, and pressurized fluid inlet and outlet ports provided in the cylinder 
body to be connected to the pressure chamber, and a knock-out cylinder 
device which includes a knock-out on which a workpiece to be pressed is 
located, and an auxiliary hydraulic cylinder having a piston which is 
slidably inserted therein, so that the knock out is connected to the 
auxiliary hydraulic cylinder.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIGS. 1 through 6 show a first embodiment of the present invention in which 
a hydraulic actuator is applied to a hydraulic press machine 20. 
The press machine 20 includes a circular cylinder body 21, in which first 
and second pistons 30 and 40 are inserted. The first piston 30 has a 
piston rod 31 consisting of a plurality of rod elements concentrically 
arranged along a first imaginary circle. The piston rod 31 is provided on 
the front end (lower end) thereof with a punch 32 as a first working 
member. The first piston 30 is reciprocally moved in the cylinder body 21 
in the axial direction thereof by a pressurized oil which is introduced in 
and discharged from the cylinder body 21 through first and second oil 
ports 23a and 24a formed in upper and lower end plates 23 and 24 of the 
cylinder body 21. 
The second piston 40 has a piston rod 41 consisting of a plurality of rod 
elements concentrically arranged along a second imaginary circle larger 
than the first imaginary circle. The piston rod 41 is provided on the 
front end (lower end) thereof with a pressure pad (die cushion) 42 as a 
second working member. The second piston 40 is reciprocally moved in the 
cylinder body 21 in the axial direction thereof by a pressurized oil which 
is introduced in and discharged from the cylinder body 21 through an oil 
passage 35 which extends through the first piston 30 and the second oil 
port 24a of the end plate 24. 
The oil passage 35 movably extends through the upper end plate 23 and is 
secured to the first piston 30 so as to move together with the first 
piston 30. 
In the first embodiment illustrated in FIGS. 1 through 6, the cylinder body 
21 is provided with a center column 22, so that first, second and third 
annular pressure chambers 26, 27 and 28 are defined in the cylinder body 
21. The first and second pressure chambers 26 and 27 are separated by the 
first piston 30, and the second and third pressure chambers 27 and 28 are 
separated by the second piston 40. 
Below the cylinder body 21 is provided a lower knock-out 50 which is 
slidably inserted in a housing (die) 5B and is connected to a piston rod 
52 of a piston 54 which is slidably inserted in a knock-out cylinder 
(auxiliary hydraulic cylinder) 51. 
As mentioned above, a plurality of (e.g., four) rod elements of the first 
piston rod 31 of the first annular piston 30 are surrounded by a plurality 
of (e.g., four) rod elements of the second piston rod 41 of the second 
annular piston 40, as can be seen in FIG. 5. In a preferred arrangement, 
the rod elements R of the first piston rod 31 and/or the rod elements R of 
the second piston rod 41 are spaced from one another at an equiangular 
distance, as shown in FIG. 6, so that even an irregular shape of press die 
M which tends to receive an eccentric load can be substantially uniformly 
pressed for example at the peripheral edge thereof. 
In the illustrated embodiment, the second working member (cushion pad) 42 
is annular, so that the first working member (punch) 32 is slidably fitted 
in the second working member. 
The hydraulic actuator as constructed above, according to the present 
invention operates as follows (particularly see FIGS. 1 through 43. 
FIG. 1 shows a press contact position in which the second piston 40 is 
advanced (moved downward in FIG. 1) to bring the cushion pad 42 into press 
contact with a workpiece W located on the housing 53 and the knock-out 50 
whose upper surface is flush with the upper surface of the housing 53 in 
the initial position. 
In the press contact position shown in FIG. 1, a predetermined amount of 
pressurized fluid (e.g., pressurized oil) is introduced in advance in the 
second pressure chamber 27 through the oil passage (pipe) 35, and 
thereafter, a valve (not shown) provided in the oil passage 35 is closed. 
Thereafter, the pressurized fluid (e.g., pressurized oil) is introduced in 
the first pressure chamber 26 through the oil port 23a. As a result, both 
the first and second pistons 30 and 40 are advanced (moved downward in 
FIG. 1) while maintaining a constant distance between the first and second 
pistons 30 and 40 owing to the pressurized oil enclosed in the second 
pressure chamber 27. Namely, the pressurized oil enclosed in the second 
pressure chamber 27 serves as a rigid connector (fluid connector) to 
transmit the movement of the first piston 30 to the second piston 40. 
The advance of the first and second pistons 30 and 40 causes the 
pressurized oil in the third pressure chamber 28 to be discharged 
therefrom through the oil port 24a formed in the lower end plate 24. 
FIG. 2 shows a press (working) position in which the punch 32 is protruded 
by the first piston 30 to press (deform) the workpiece W into a desired 
shape. 
To advance the first piston 30, the pressurized oil is introduced in the 
first pressure chamber 26 through the oil port 23a and the pressurized oil 
contained in the second pressure chamber 27 is gradually discharged 
therefrom through the oil passage (pipe) 35 while retaining a 
predetermined fluid pressure (i.e., adjustment of back pressure). 
The adjustment of the back pressure during the discharge of the oil from 
the second pressure chamber 27 through the oil passage 35 while adjusting 
ensures a die cushion effect. 
The workpiece W is pressed into a desired shape by the advance of the punch 
32 caused by the movement of the first piston 30. To this end, the lower 
knock-out 50 is retracted (moved downward in FIG. 2). 
FIG. 3 shows a workpiece expelling position in which the valve (not shown) 
of the oil passage 35 is closed, so that the pressurized oil is enclosed 
in the second pressure chamber 27 to serve as a rigid connector, as 
mentioned above, and the pressurized oil is introduced in the third 
pressure chamber 28 through the oil port 24a to retract the second piston 
40 together with the first piston 30. At the same time, the knock-out 
cylinder 51 is actuated to protrude the knock-out piston 54, and 
accordingly, the piston rod 52 thereof. Consequently, the pressed 
workpiece W is expelled by the knock-out 50 from the housing 53. 
During the retraction (i.e., upward displacement) of the first piston 30, 
the pressurized oil in the first chamber 26 is discharged from the oil 
port 23a. 
FIG. 4 shows a workpiece removing position in which the pressed workpiece W 
is removed from the punch 32. In FIG. 4, a valve (not shown) provided in 
an oil passage connected to the third pressure chamber 28 through the oil 
port 24a is closed, and thereafter, the pressurized oil is introduced in 
the second pressure chamber 27 through the oil passage 35. As a result, 
the introduction of the pressurized oil in the second pressure chamber 27 
causes only the first piston 30 to move upward in FIG. 4 without moving 
the second piston 40 since the pressure in the third pressure chamber 28 
is kept constant by the closure of the valve. 
During the upward movement of the first piston 30, the pressurized oil in 
the first pressure chamber 26 is discharged therefrom through the oil port 
23a. 
Consequently, the pressed workpiece W is removed from the punch 32 by the 
upward movement of the first piston 30. 
FIGS. 7 through 11 show a second embodiment of the present invention. 
The press machine 60 shown in FIGS. 7 through 11 has a cylinder body 61 
having therein a circular pressure chamber consisting of first, second and 
third pressure chambers 66, 67 and 68. The second embodiment illustrated 
in FIGS. 7 through 11 is different from the first embodiment illustrated 
in FIGS. 1 through 6 only in the shape of the pressure chamber which is 
annular in the first embodiment and circular in the second embodiment, 
respectively. Namely, the cylinder body 61 has no center column 22 as 
shown in FIGS. 1 through 4. 
The operation of the second embodiment is substantially identical to that 
of the first embodiment. Namely, the first piston 70 has a piston rod 71 
secured thereto, which is provided on the front (lower) end thereof with a 
punch 72 serving as a first working member. The first piston 70 is 
reciprocally moved in the cylinder body 61 in the axial direction by the 
pressurized fluid (e.g., pressurized oil) introduced in and discharged 
from the pressure chamber through the oil ports 63a and 64a formed in the 
end plates 63 and 64, respectively. 
The second piston 80 has a piston rod 81 secured thereto, which is 
provided, on the front (lower) end thereof with, a pressure pad 82 for die 
cushion as a second working member. The second piston 80 is reciprocally 
moved in the cylinder body 61 in the axial direction by the pressurized 
fluid (e.g., pressurized oil) introduced in and discharged from the second 
pressure chamber 67 through the oil passage (pipe) 75 which extends 
through the first piston 70 and the upper end plate 63. 
Numeral 90 designates the lower knock-out, 91 the knock-out cylinder, 92 
the piston rod, 93 the housing (die), 94 the piston, corresponding to 
those in the first embodiment shown in FIGS. 1 through 4, respectively. 
FIG. 7 shows the press contact position corresponding to FIG. 1, in which 
the second piston 80 is advanced (moved downward), so that the cushion pad 
82 comes into press contact with the workpiece X. Similarly to FIG. 1, in 
the press contact position shown in FIG. 7, a predetermined amount of 
pressurized fluid (e.g., pressurized oil) is introduced in advance in the 
second pressure chamber 67 through the oil passage (pipe) 75, and 
thereafter, a valve (not shown) provided in the oil passage 75 is closed. 
Thereafter, the pressurized fluid (e.g., pressurized oil) is introduced in 
the first pressure chamber 66 through the oil port 63a. As a result, both 
the first and second pistons 70 and 80 are advanced (moved downward in 
FIG. 7). 
FIG. 8 shows a working position corresponding to FIG. 1, in which the punch 
82 is protruded by the first piston 70 to press (deform) the workpiece X 
into a desired shape. 
To advance the first piston 70, the pressurized oil is introduced in the 
first pressure chamber 66 through the oil port 63a and the pressurized oil 
contained in the second pressure chamber 67 is gradually discharged 
therefrom through the oil passage (pipe) 75 while retaining a 
predetermined fluid pressure (i.e., adjustment of back pressure). 
Thus, the workpiece X is pressed into a desired shape by the advance of the 
punch 32 caused by the movement of the first piston 70. To this end, the 
lower knock-out 90 is retracted (moved downward in FIG. 8). 
FIG. 9 shows a workpiece expelling position corresponding to FIG. 3, in 
which the valve (not shown) of the oil passage 75 is closed, so that the 
pressurized oil is enclosed in the second pressure chamber 67 to serve as 
a rigid connector, as mentioned above, and the pressurized oil is 
introduced in the third pressure chamber 68 through the oil port 64a to 
retract the second piston 80 together with the first piston 70. At the 
same time, the knock-out cylinder 91 is actuated to protrude the knock-out 
piston 94, and accordingly, the piston rod 92 thereof. Consequently, the 
pressed workpiece X is expelled by the knock-out 90 from the die 93. 
During the retraction (i.e., upward displacement) of the first piston 70, 
the pressurized oil in the first chamber 66 is discharged from the oil 
port 63a. 
FIG. 10 shows a workpiece removing position in which the pressed workpiece 
X is removed from the punch 82. In FIG. 10, a valve (not shown) provided 
in an oil passage connected to the third pressure chamber 68 through the 
oil port 64a is closed, and thereafter, the pressurized oil is introduced 
in the second pressure chamber 67 through the oil passage 75. As a result, 
the introduction of the pressurized oil in the second pressure chamber 67 
causes only the first piston 70 to move upward in FIG. 10 without moving 
the second piston 80 since the pressure in the third pressure chamber 68 
is kept constant by the closure of the valve. 
During the upward movement of the first piston 70, the pressurized oil in 
the first pressure chamber 66 is discharged therefrom through the oil port 
63a. 
Consequently, the pressed workpiece X is removed from the punch 82 by the 
upward movement of the first piston 70. 
As can be seen from the foregoing, according to the present invention, 
since a plurality of successive operations can be carried out by a simple 
single actuator, the actuator not only requires a reduced installation 
space and a less energy consumption, but also makes it possible to realize 
an automated simple manufacturing line including an automatic conveyance 
of the workpieces. 
Furthermore, the provision of a plurality of piston rods prevents 
occurrence of an eccentric load applied to the die and accordingly the 
workpiece, thus resulting in a high precision pressing.