Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF THE INVENTION
A PRESS MACHINE
This is a division of Canadian Patent Application
Serial No. 461,503, filed August 22, 1984.
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to a press machine, more
specifically, to a press maçhine such as a press brake used
for bending sheet-like wor~pieces.
Description of the Prior Art
As is well-known, a bending press or press machine such
as a press brake for bending sheet-like workpieces such as
sheet metals is provided with a pair of upper and lower
bending tools one of which is so arranged as to be vertically
moved by a ram ~oward and away from the other to bend a
workpiece. Usually, the lower bending tool is fixed and the
upper tool is mounted on the ram to be vertically moved toward
and away from the lower bending tool, but, in some bending
presses, the upper bending tool is fixed and the lower bending
tool is movably held by the ram. Anyway, the workpiece to be
bent is placed or held on the lower bending tool so that it
may be bent when either of the upper and lower bending tools,
which is movable, is vertically moved toward the other which
is fixed. Also, the ram carrying the movable bending tool, in
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many bending presses, is hydraulically operated by a hydraulic
means to vertically move the movable bending tool toward and
away from the fixed bending tool.
In such a bending press, the bending angle to which the
workpiece is to be bent is determined by the travelling limit
of the ram to which the ram is vertically moved to move the
movable bending tool toward the fixed bending tool to bend the
workpiece. Accordingly, it is necessary to accurately set the
travelling limit of the ram or the movable bending tool so as
to accurately bend the workpiece to a desired angleO In order
to accurately control the position to which the ram is raised
or lowered, in the case of a hydraulic press a control valve
is installed in the hydraulic circuit to raise or lower the
ram. In addition, the press machine or bending press has a
position determining member which controls the position to
~hich the ram is raised or lowered by controlling the
above-mentioned control valve, and the ram has an operation
member which causes the valve to open when it is con~acted by
the position determinin~ member. That is, when an operation
member on the ram contacts the position determining member,
the vertical movement of the ram is stopped to control its
position.
It is desirable for the position determination to be
done near the center of the ram. If it is done at one end,
the equilibrium of the ram can be upset resulting in large
position error.
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The above-mentioned position determining member
consists of a rotating link located on the frame side at the
center of the ram along the length of the ram so that it is
free to rotate up and down. ~he operation member on the ram
is designed to contact the tip of the rotating link. The
position of the ram is determined by setting the angle of the
above-- mentioned rotating link. Consequently, the operation
member, which moves up and down, contacts the rotating link
the tip of which describes a circular arc. Since there is no
relation of proportionality between the position at which the
rotating link angle is set and ~he position at which the ram
is set to stop, it is very difficult to accurately set the
~osition at which the ram stops in the vertical direction.
The position of the above-mentioned position
determining member can be set either manually or
automatically. Manual setting, which is done by rotating a
handle provided on the side of the press machlne, is difficult
to accurately operate. Automatic setting, which is done by
ON/OFF operation of a pushbutton switch on a control box, is
also hard to accurately operate.
Control of the speed of vertically moving ram in the
press machine or bending press is accomplished by opening and
closing an unload valve in the hydraulic circuit that drives
the ram vertically. The above-mentioned unload valve is
opened and closed by stepping on a link-type foot pedal on the
front of the press machine. This makes it impossible to
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operate the press machine from a remote location, which is a
problem from the point of view of safety improvement.
There is another type of press machine or bending press
in which there is a hydraulic fluid - filled cylinder under
the foot pedal, and the pressure on the foot pedal is
transmitted through the fluid to operate the unload valve.
However, this method also has problems: the hydraulic hose
connected to the foot pedal is large in diameter and rigid,
which makes operation difficult; and, when the machine is
moved or transported, the foot pedal must be removed from the
press machine allowing some of the hydraulic fluid to leak out
and get on the floor and other nearby objects.
Still another problem with existing press machines or
bending presses is that there is no detection device to
directly detect the position of the ram which moves
vertically.
SUMMARY OF THE INVENTION
The main objective of the invention defined in the
present divisional case is to provide a press machine or
bending press in which the speed of the vertically moving
ram can be easily controlled.
To achieve this objective, an electromagnetic
proportional valve is installed in the hydraulic circuit
which drives the ram up and down. The system is designed so
that the speed of the vertically moving ram can be controlled
by the control of this electromagnetic proportional valve
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corresponding ~o operation of a speed control device.
Accordingly, the invention in one aspect provides a
press machine comprising a generally vertically
movable ram for supporting an upper or lower bending tool;
means including a hydraulic circuit for driving the ram up
and down, an electromagnetic proportional valve installed in
the hydraulic circuit which drives said ram up and down for
controlling the speed of vertical movement of said ram; a
speed control device for controlling the electromagnetic
proportional valve wherein the speed of vertical movement of
said ram can be controlled in cor~espondence with the control
setting of said speed control device.
Other and further features and advantages of the
present invention will be apparent from-the following
description and accompanying drawings which, by way of
illustration, show preferred embodim~nts of the present
invention and the principles thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a perspective view of a press machine
incorporating this invention.
Figure 2 is an enlarged cross-sectional view taken
along the line II - II in Figure 1.
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Figure 3 is a view seen in the direction of the arrows
III-III in Figure 2.
Figure 4 is a cross - sectional view taken along the
line IV - IV in Figure 3.
Figure 5 is a partly broken and partly cross-sectional
view of another embodiment of the present invention.
Figure 6 is an enlarged front view of the control panel
shown in Figure 1.
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Figure 7 is a block diagram of the pulse motor control
system.
Figure 8 is an enlarged cross-sectional view taken
along the line VIII - VIII in Figure 1.
Figure 9 is a view seen in the direction of the arrows
IX - IX in Fiyure 8.
Figure 10 is an enlarged cross-sectional view taken
along the line X - X in Figure 1.
Figure 11 is a partially cut-away side view of the
section shown in Figure 10.
Figure 12 is a cross-sectional view taken along the
line XII - XII in Figure 11.
Figure 13 is a hydraulic circuit diagram.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to Figure 1, a press machine or bending press
1 such as a press brake has right and left C-shaped side
frames 3R and 3L, upper and lower frames S and 7 supported on
both sides by the right and left frames 3R and 3L, and a ram 9
installed inside the lower frame 7 in an opposing relationship
with the upper frame 5. An upper bending tool 11 used for
bending sheet-like workpieces W is attached to the bottom of
the above-mentioned upper frame 5 so that it can be removed
and replaced. A lower bending tool 13 is attached to the top
of the ram 9 opposite to the upper bending tool 11 so that it
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can be removed and replaced.
As will be explained in more detail below, the ram 9 is
driven up and down by a hydraulic cylinder 15 for ~ertical
operation installed inside the lower frame 7. The upward
movement of the ram 9 pushes the lower bending tool 13 up
~gainst the upper bending tool 11, thereby bending the work
piece W which is clamped between the upper and lower bending
tools 11 and 13. That is, in this embodiment, in order to
bend the work piece W the ram 9 moves upward, but the
applicability of this invention is not limited to this
embodiment; this invention can also be applied in a press
machine or bending press in which the ram is installed in the
upper frames and moves downward to push one bending tool
against the other.
Referring to Figures 2 through 4, the hydraulic
cylinder 15 which drives the up-and-down movement of the
above-mentioned ram 9 is built in to the lower part of the
lower ~rame 7 having front and rear frames 7a and 7b. In this
emkodiment, an operation member 19 which is attached to the
ram 9 operates a position determining device 17 to determine
the position at which the upward movement of the ram is
stopped. More specifically, the stop position determining
device 17 is attached to the lower rear frame 7b, which is
located to the rear of the ram 9, through a bracket 21. The
operation member 19 is located so that its tip sticks through
the opening of the lower rear frame 7b to within the range of
movement of a position determining member 23, which is part of
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the position determining device 17 and is installed so that
its position can be adjusted. The system is designed so that
the upward movement of the ram 9 will stop when this operation
member 19 contacts the position determining member 23.
Consequently, the stop position of the ram 9 in the vertical
operation can be controlled by adjusting the position of the
stop position determining member 23.
As can be seen from Figures 2 through 4, the position
determining member 23 is designed so that its position is
adjusted by linear up-and-down motion. That is to say, two
opposing guide rails 25 are mounted on the above-mentioned
bracket 21; these guide rails 25 support the position
determining member 23 while allowing it to move up and down.
The position determining member 23 is screwed into a threaded
bolt 27 which is parallel to the guide rails 25; this threaded
bolt 27 is coupled to a pulse motor PM which i5 mounted on the
bracket 21. Consequently, by turning the threaded bolt 27 by
the pulse motor PM, the position determining member 23 can be
moved up and down along the guide rails 25.
In more detail, the pulse motor PM has a pulse encoder
PE which detects the actual amount of rotation of the pulse
motor PM; and a rotating shaft 29 of the pulse motor PM and
the lower end of the above-mentioned threaded bolt 27 are
spline-coupled. In addition, the upper end of the threaded
bolt 27 is rotatably supported by a bearing block 31, which is
supported so that it is free to move up and down along the
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above-mentioned guide rails 25. That is, when the upward
motion of the above-mentioned ram 9 pushes the operation
member 19 up against the position determining member 23, the
position determining member ~3 and the threaded bolt 27 can
move upward together as a single unit.
In order to detect the contact of the operation member
19 with the position determining member 23 and stop the upward
motion of the ram 9, the stop position determining device 17
has a switching valve 33 which opens and closes the hydraulic
circuit to the above- mentioned hydraulic cylinder 15. This
switching valve 33 having a slidable spool 33S allows part of
the hydraulic fluid in the above-mentioned hydraulic circuit
to return to a tank when the spool 33S is pushed. One end of
the spool 33S is in contact with Dne end 35a of a lever 35.
The lever 35 is connected to the bracket 21 through a sha~t 37
so that it is free to swing. The other end 35b of the lever
35 is in contact with the above-mentioned bearing block 31.
The above-mentioned lever 35b is always held at the other end
thereoE in contact with the bearing block 31 by the action o~
an elastic body 39' such as a torsion spring or a compression
spring.
As can be understood from the mechanism described
above, as mentioned above when the operation member 19
contacts the position determining member 23, the lever 35 is
rotated against the resistance of the elastic body 39', and
the spool 33S of the switching valve 33 is pushed against one
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25~;3~i~
end 35a of the lever 35, causing the switching valve 33 to
operate, stopping the upward motion of the ram 9.
When the above-mentioned pulse motor PM is operated to
raise or lower the above-mentioned position determining member
23, in order to detect whether or not the position determining
member 23 is in contact with the operation member 19, as is
most clearly shown in Figure 3, an auxiliary lever 39 is
attached to the above-mentioned lever 35 at the center thereof
and extending in an up-down direction. Dogs 41a and 41b are
attached to both sides of the tip of this auxiliary lever 39
so that they can be adjusted. The dog 41a is opposite a first
limit switch LSl which is attached to a mounting plate 43
which is fixed to the bracket 21. The other dog 41b is
opposite a second limit switch LS2 which is also attached to
the mounting plate 43. That is to say, the tip of the
auxiliary lever 39 is located between the limit switches LSl
and LS2. ~~
In the above configuration, as has already been
discussed when the operation member 19 contacts the position
determining member 23, the lever 35 rotates causing the
normally closed contact of the ~econd limit switch LS2 to
open; thus the contact of the operation member 19 with the
position determining member 23 is detected.
When an instruction to the pulse motor PM starts the
pulse motor PM rotating in such a direction as to turn the
threaded bolt 27 in a direction that drives the position
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determining member 23 downward, the position determining
member 23 contacts the operation member 19. In addition, when
the threaded rod 27 rotates in such a direction as to advance
downward, the bearing block 31 rises and the lever 35 rotates
pushing the spool 33S of the swtiching valve 33. If the spool
33S of the switching valve 33 is pushed farther than
necessary, the first limit switch LSl switches ON and the
rotation commands to the pulse motor PM stop. In this way the
rotation of the threaded bolt 27 shows that the position
determining member 23 cannot go down any farther.
A third limit switch LS3 is attached to the bracket to
detect when the position determining meber 23 has reached its
upper limit. A dog 45 is attached to the position determining
member ~3 so that it can be freely adjusted, in order to
operate the third limit switch LS3. Consequently, when the
third limit switch LS3 has been operated, it is known that the
position determininy member 23 cannot be moved up any fartherO
Figure S shows another embodiment in which the threaded
bolt 27 operates the switching valve 33 directly. In this
embodiment, a driven pulley 49 is rotatably supported by a
bearing block 47, which is attached to the switching valve 33.
The upper tip of the threaded bolt 27 is spline-coupled to
this driven pulley 49. In addition, the threaded bolt 27 is
connected to the spool 33S of the switching valve 33 through a
sliding pin 51. A belt 53 connects the driven pulley 49 to a
driving pulley 55 which is in turn driven by the pulse motor
PM.
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- Since this embodiment operates in a similar manner to
the ~mbodiment discussed abover like members having similar
functions are designated by like numbers, and the detailed
explanation is omitted here.
It should be noted that this invention can be used in a
number of different embodiments. For example, the position
determining member 23 could have a slanted surface which the
operation member 19 would contact, and a component of the
force would move the position determining member 23. A
configuration in which the position determining member 23 is
adjusted by horizontal movement is also possible.
Referring again to Figure 1, the press machine 1 has a
control panel 57 which controls the press machine 1 and the
pulse motor PM. More specifically, a control box 59 is
mounted on either one of the above-mentioned riyht and left
side frames 3R and 3L as appropriate. Mounted on this control
box 59 is a supporting column 61 which sticks straight up and
is free to rotate. This supporting column 61 in turn supports
at the upper portion thereof the base of an arm 63 which can
be adjusted by expansion and contraction. Rotatably depending
rom the tip of this arm 63 is a support bar 65, at the lower
end of which is supported the control panel 57. Thusl the
position of the control panel 57 can be adjusted arbitrarily
through a fairly wide range.
As shown in detail in Figure 6, the control panel 57
has a manual pulse generator 67 for operating the
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above-mentioned pulse motor PM and a position indicator 69
which receives the pulse signals from the above--mentioned
pulse encoder PE and indicates the position of the position
determining member 23. The control panel 57 also has an
origin setting button 71 which sets as the origin the position
to which the ram 9 has risen when the above-mentioned upper
bending tool 11 and lower bending tool 13 are in direct
contact to generate a predetermined pressure between them, a
lower limit position setting switch 73 which can set the lower
limit position of the ram 9 to any desired value, and a speed
conversion position setting switch 75 which automatically
changes the rising speed of the ram 9 at an arbitrarily
selected position. The above-mentioned lower limit position
setting switch 73 and speed conversion position setting switch
75 are digital switches, and their settings can be changed
arbitrarily.
The above-mentioned manual pulse generator 67 might,
for example, be a pulse encoder. When a knob 67N is turned,
pulses corresponding to the speed are generated. As shown in
Figure 7, this manual pulse generator 67 is connected to a
motor driver 77, which drives the above-mentioned pulse motor
PM, through a rotation direction discrimination circuit 79.
Connected to the motor driver 77 are an auxiliary switch 81,
which overrides input from the manual pulse generator 67, even
when rotated, and prevents the pulse motor PM from turning,
and the limit switches LSl and LS3 which detect when the
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position determining mèmber 23 has reached its moving limits.
Consequently, when the auxiliary switch 81 and the
limit switches LSl and LS3 are all closed, turning the knob
67N of the manual pulse generator 67 in the forward or reverse
direction causes the pulse motor PM to turn in the forward or
reverse direction at a rate corresponding to the speed. In
this way the position of the above-mentioned position
determining member 23 is adjusted.
The turning of the above-mentioned pulse motor PM is
detected by the pulse encoder PE. This pulse encoder PE is
connected to a counter 83 which counts the pulses from it.
The value of the count is used by the position indicator 69 to
give a digital indication of the position of the
above-mentioned position determining member 23. The counter
83 is cleared by the origin switch SW when the origin of the
ram is to be set.
Consequently, by operating the manual pulse generator
67 while watching the position indicator 69, the position of
the position determining member 23 can be set accurately,
which also means that the position at which the ram 9 will
stop rising is determined accurately. Since the actual
rotation of the pulse motor PM during the rotation of pulse
motor is detected by the pulse encoder PE, the position of the
position determining member 23 is always indicated accurately
even if a step out problem occurs, for example if the knob 67N
of the manual pulse generator 67 is turned too fast and the
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pulse motor PM can't ~èep up, or there are large load
fluctuations beyond the capability of the pulse motor PM to
follow. The pulse motor PM can be operated in either the
~orward ~r reverse direction automatically, without using the
manual pulse generator 67, by connecting it to another
suitable pulse generator.
Referring to Figures 8 and 9, the press machine l has a
position detecting system 85 to detect the vertical position
to which the above-mentioned ram 9 has been raised or lowered.
More specifically, the position detecting system 85 comprises
a position detector 87, such as a linear encoder, which is
mounted on the lower rear frame 76, and a detection member 89
which is mounted on this position detector 87 so as to be able
to move up and down freely. The upper tip of this detection
member 89 is coupled to a coupling block 93, which is attached
to the ram 9, through a suitable elastic body 91. In this
embodiment the elastic body 91 is a plate-spring with a 90
twist. A lower limit dog 95 is fixed to the above-mentioned
coupling block 93 so that its position can be adjusted up and
down freely. Mounted on the lower rear frame 76 is a forth
limit switch LS4, which is operated by the lower limit dog 95
when the ram 9 has been lowered to its lower limit position.
In the configuration described above, the detection
member 89 and the ram 9, which are coupled, move up and down
together, and pulses corresponding to the amount of vertical
motion of the ram 9 are generated by the position detector 87.
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Consequently, by counting the above-mentioned pulses, the
position to which the ram 9 has been raised or lowered can be
detected and the necessary switching performed at the
positions set by the lower limit position setting switch 73
and the speed conversion position setting switch 75.
When the ram 9, lowering from its raised position,
reaches the position which has been set by the lower limit
position setting switch 73, its lowering movement stops. When
the ram 9, rising from its lowerPd position, reaches the
position which has been set by the speed conversion position
setting switch 75, the rising speed of the ram g is switched
from fast to slow.
When the ram 9 moves up or down and its position is
detected by the above-mentioned position detector 87 as
discussed above, if errors occur in the positions of the
surfaces of the coupling block 93 connected to the elastlc
body 91 and to the detector 87, or if the ram 9 is deformed
when the workpiece W is bent, the error can be absorved by
deformation of the elastic body 91. That is to sayl in the
~onfiguration described above the position to which the ram 9
is raised or lowered can be detected accurately.
Referring again to Figure 1, the above-mentioned
control box 59 is connected to a foot pedal unit 99 through a
cable 97. The foot pedal unit 99 can be positioned anywhere
within a fairly wide range with respect to the above-mentioned
control panel 57. The foot pedal unit 99 controls the speed
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of the above-mentioned vertically moving ram 9. It has a
pedal 101U for upward movement and a pedal 101L for downward
movement.
As is shown best in Figures 10 through 12, the foot
pedal unit 99 is contained in a box 105 which has an opening
103 on one side for inserting toes. This box 105 is made in
one piece with a casing 109 which has a handle 107 on the top
thereof. Inside this casing 109 are a pair of vertically
moving rods 113U and 113L supported by a side bracket 111,
inside the box 105, so that they can move up and down freely,
and in addition a potentiometer 115 is mounted in a vertical
position.
A disc-shaped stop member 117 is integrally mounted to
an operation rod 115R of the above-mentioned potentiometer
115. The operation rod 115R is always pushed upward by the
action of a spring 119 compressed between this stop member 117
and the bracket 111. Operation pieces 121U and 121L, which
are free to contact the upper surface of the above-mentioned
stop member 117, are attached to the above-mentioned
vertically moving rods 113U and 113L. In addition, these
vertically moving rods 113U and 113L are always biased upward
by the action of springs 123U and 123L.
The diameters of the vertically moving rods 113U and
113L are reduced at their lower tips. Limit switches LSU and
LSL are mounted in positions corresponding to these narrowed
tips. In addition, rollers 125U and 125L are attached to the
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lower tips of the vertically moving rods 113U and 113L.
Levers 127U and 127L, which are connected to the
above-mentioned pedals lOlU and lOlL, are in contact with the
tops of the rollers 125U and 125L. The pedals lOlU and lOlL
are pivotally attached to the inside of the box 105 through a
shaft 129 which is rotatably supported by the bracket which is
connected to the lower frame of the above-mentioned box 105.
In addition, a cover member 133, which has an opening and
closing lever 131, is attached to the opening 103 of the box
105 so that it is free to open and close through a shaft 135,
which is rotatably supported by the upper frame body of the
box 105.
As has already become clear, in the configuration
described above when the pedal lOlU for upward movement or the
pedal lOlL for downward movement is stepped on, one of the
vertically moving rods 113U, 131L is lowered and the
corresponding limit switch LSU or LSL operates, and, at the
same time, the operation rod 115R of the potentiometer 115 is
lowered. Thus, the action of the limit switch LSU or LSL
tells whether the ram 9 is being raised or lowered, while an
output signal corresponding to the amount of motion of the
operation rod 115R is obtained from the potentiometer 115. By
controlling an electro- magnetic proportional valve to be
described later, corresponding to the output signal from this
potentiometer 115, the rising or lowering speed of the ram 9
is controlled corresponding to the amount of foot pressure on
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the pedal 101U or 101L.
~ eferring to Figure 13, a 4-port 3-position solenoid
valve 137 is connected to a first hydraulic fluid path Ll
which in turn is connected to a hydraulic pump P. At the same
time a relief valve 139 and an electromagnetic valve 141 are
branch-connected. The electromagnetic proportional valve 141
is supposed to control the flow rate of hydraulic fluid which
is recirculated to the tank T in either direct or inverse
proportion to the voltage applied to a solenoid SOL.
The above-mentioned solenoid SOL of the electromagnetic
proportional valve 141 is controlled by a controller 143. The
controller 143 receives input feed back signals for position
detection of the spool of the electromagnetic proportional
valve 141. The controller 143 is also connected to the above-
mentioned potentiometer 115 and to the above-mentioned limit
switches LSU and LSL. Consequently the controller 143 can
receive signals from the limit switches ~SU and LSL and judge
~he directionality, and control the degree of opening of the
electromagnetic proportional valve 141 corresponding to the
output signal from the potentiometer 115.
The above-mentioned solenoid valve 137 is connected to
a second hydraulic fluid path ~2 which in turn is connected to
a first chamber 15F of the above-mentioned cylinder 15 used
for the vertical movement of the ram. This second hydraulic
fluid path L2 is provided with a check valve 145 and a
counterbalance valve 147 in parallel. In addition the
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above-mentioned switching valve 33 is connected to a branch of
the hydraulic system.
In addition, a third hydraulic fluid path L3 is
connected as a branch of the second hydraulic fluid path.
speed conversion valve 149 is installed in this third
hydraulic fluid path L3. A regulator 151 is branch-connected
to the above-mentioned third hydraulic fluid path L3; and a
manometer 153 is also branch-connected through a cutoff valve
155.
A forth hydraulic fluid path L4, which is connected to
the above-mentioned speed switching valve 149, is connected to
a second chamber 15S of the hydraulic cylinder 15, and to an
auxiliary cylinder 157; and, at the same time, it is connected
to the tank T through a check valve 159 and a pilot - operated
check valve 161.
In addition, a fifth hydraulic path L5, which is
connected to the above-mentioned solenoid valve 137, is
connected to a third chamber 15T of the hydraulic cylinder 15.
In the configuration described above, stepping on the
pedal lOlU for upward movement of the foot pedal unit 99 cuts
off the connection to the electromagnet~c proportional valve
141; in addition, when the solenoid valve 137 is switched to
connect the first hydraulic fluid path Ll to the second
hydraulic fluid path L2, hydraulic fluid is supplied from the
hydraulic fluid pump P to the first chamber 15F of the
hydraulic cylinder 15, driving the ram 9 upward. At this time
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the rising speed of the ram 9 can be controlled by controlling
the degree of opening of the electromagnetic proportional
valve 141, which is done by adjusting the foot pressure on the
pedal lOlU in the foot pedal unit 99.
When the ram 9 is driven upward as described above, the
position to which the ram 9 has risen is detected by the
position detector 87. When the ram 9 rises to the posi~ion
which has been set in advance by the speed conversion position
setting switch 75, the speed switching valve 149 is operated,
hydraulic fluid is also supplied to the second chamber 15S of
the cylinder 15 and to the auxiliary cylinder 157, and the
rising speed of the ram 9 is switched from fast to slow; and
the workpiece W between the upper bending tool 11 and the
lower bending tool 13 is bent.
When, as discussed above, the ram 9 is raised, and, as
also discussed above, the operation member 19 attached to the
ram 9 contacts the position determining member 23, the
switching valve 33 switches and part of the hydraulic fluid
drains back to the tank T, so the rising of the ram 9 stops.
After thatt when the solenoid valve 137 switches, hydraulic
fluid is supplied to the third chamber 15T of the cylinder 15,
and, at the same time, the pilot operated check valve 161 is
opened causing the ram 9 to be lowered. At this time, the
speed of lowering of the ram 9 can be controlled by adjusting
the foot pressure on the pedal lOlL in the foot pedal unit 99.
When the ram 9 is lowered as discussed above, and the
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position of the ram 9 as detected by the position detector 87
reaches the position which has been set in advance by the
lower limit position setting switch 73, the lowering of the
ram 9 stops.
As can be understood from the explanation above, the
positions where the rising and lowering of a ram in a press
machine stop can be set accurately. In addition, the speed of
the vertically moving ram can be controlled accurately, and
the position of the ram can be accurately detected.
While preferred embodiments of this invention have been
shown and described, it will be appreciated that other
embodiments will become apparent to those skilled in the art
upon be limited by the disclosed embodiments.
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