U.S. patent number 3,554,067 [Application Number 04/802,346] was granted by the patent office on 1971-01-12 for fail-safe double-action safety guard.
Invention is credited to Joseph Scutella.
United States Patent |
3,554,067 |
Scutella |
January 12, 1971 |
FAIL-SAFE DOUBLE-ACTION SAFETY GUARD
Abstract
A fail-safe, double-action safety guard having two separate and
distinct protective circuits, shown installed on a treadle operated
punch press, the primary circuit being both pneumatically and
electrically operated, while the secondary or followup circuit is
hydraulically operated. Actuation of the foot treadle will open the
pneumatic circuit to a preset flow control circuit and also to an
air solenoid valve. From the flow control circuit, air pressure
passes through and operates a pneumatic drive cylinder which in
turn drives a guard-actuating device or butterfly flipper having a
guard shield attached thereto. The butterfly flipper is rotated a
preset amount to drive the guard shield in front of the work area.
Only when the guard shield is completely in front of the work area,
an electrical off/on switch is operated which in turn actuates an
air solenoid and releases line air pressure to the clutch trip
cylinder which trips the press. To operate the followup hydraulic
circuit, a preset cam throw is mounted on the crankshaft of the
press. When the press is tripped and the ram starts its downward
stroke, the cam positively drives a hydraulic cylinder. This
cylinder is connected via hydraulic lines to a second hydraulic
cylinder which is mounted next to the guard-actuating device or
butterfly flipper diagonally opposite the pneumatic drive cylinder,
the length of the stroke of the second hydraulic cylinder and the
pneumatic drive cylinder being equal. Before the ram has completed
a minor fraction of its downward stroke, the second hydraulic
cylinder is completely activated against the butterfly flipper. In
normal operation, the hydraulic cylinder merely follows the
pneumatic cylinder and butterfly flipper action. It is a positive
drive but only drives the guard shield in any emergency operation
such as a double tripping of the press, or a clutch, air pressure,
spring, electrical or air solenoid valve failure. The positive
hydraulic drive exerts a large force that may be as great as the
punch press, however, and in both normal and unexpected operations,
this force cannot easily be overcome by the operator. When the
stroke of the second hydraulic cylinder is fully extended to the
butterfly flipper, it holds the guard shield in front of the work
area until the ram has completed its downward stroke and has
started its upward stroke. Meanwhile, the pneumatic drive cylinder
retracts and is ready for the next cycle. Desirably the guard
shield is opened by means of a return spring and the work area is
cleared and made ready for the next cycle of the press.
Inventors: |
Scutella; Joseph (Olean,
NY) |
Family
ID: |
25183455 |
Appl.
No.: |
04/802,346 |
Filed: |
February 26, 1969 |
Current U.S.
Class: |
83/397;
192/134 |
Current CPC
Class: |
F16P
3/02 (20130101); F16P 1/04 (20130101); Y10T
83/606 (20150401) |
Current International
Class: |
F16P
3/02 (20060101); F16P 1/04 (20060101); F16P
3/00 (20060101); F16P 1/00 (20060101); B26d
005/00 () |
Field of
Search: |
;83/397 ;74/616 ;100/53
;192/133,134 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Juhasz; Andrew R.
Assistant Examiner: Coan; James F.
Claims
I claim:
1. A fail-safe double-action safety guard mechanism for a punch
press having a reciprocable ram and a treadle for effecting the
operation of said ram, said mechanism comprising a guard mechanism,
a flow control circuit, a first pneumatic actuator for moving said
guard to a guarding position and a second hydraulic actuator for
positively driving said guard to said guarding position, said
treadle means including a control valve interconnecting a source of
fluid under pressure to said first actuator and to said flow
control circuit, said flow control circuit comprising a control
valve having resilient means for actuating said control valve to a
first position for directing fluid into said first actuator to
effect the movement of said guard to said guarding position, said
resilient means being operable to move said control valve to a
second position to exhaust fluid and effect the movement of said
first actuator to its retracted position.
2. The guard mechanism of claim 1 wherein said flow control circuit
includes first and second regulating valves interconnecting said
control valve, first actuator and said source of fluid, said first
and said second valves being normally open to effect the actuation
of said control valve to said first and second positions responsive
to said treadle and independently of the movement of said ram.
3. The guard mechanism of claim 2 wherein said first valve
comprises a housing having a spring-biased diaphragm member for
regulating flowing fluid by reducing the pressure thereof, said
first valve being adapted to supply fluid at reduced pressure to
said control valve.
4. The guard mechanism of claim 2 wherein said second valve
comprises a housing having a flow pressure-regulating needle valve
and a flow direction-regulating spring biased ball valve for
restricting and delaying the flow of fluid to said control valve,
responsive to fluid flow from said first valve.
5. The guard mechanism of claim 1 wherein said control valve
comprises a housing having a reduced fluid pressure inlet port, a
delayed fluid pressure inlet port, a first actuator fluid pressure
outlet port, an exhaust port and an internal chamber for receiving
an an internal valve means, said internal chamber including opposed
chamfered sealing surfaces within said housing, said internal valve
means having opposed chamfered portions thereon for coacting with
said chamfered sealing surfaces, and a resilient means biasing said
internal valve means, said internal valve means normally permitting
reduced fluid pressure to pass therethrough and to said first
pneumatic actuator, the flow of delayed fluid pressure to said
internal valve means gradually overcoming the resistance of said
resilient biasing means to thereby close said internal valve means
and permit fluid to exhaust therethrough.
6. The guard mechanism of claim 1 wherein said guard mechanism is
rotatably mounted and is provided with upper and lower pressure
faces for actuation of said guard member responsive to said first
and second actuators, respectively.
7. The guard mechanism of claim 1 including an electrical switch
means, and a pneumatic solenoid means, said first actuator being
adapted to actuate said electrical switch means, said electrical
switch in turn being adapted to actuate said pneumatic solenoid for
operating said punch press.
8. The guard mechanism of claim 1 wherein said second hydraulic
actuator comprises a first ram driven hydraulic cylinder and a
second hydraulic driving cylinder operatively connected to said
first hydraulic cylinder responsive to the movement thereof, the
movement of said ram driving said first and second hydraulic
cylinders to thereby positively drive said guard mechanism.
Description
This invention relates to guard devices for machine tools and more
particularly to a highly improved fail-safe, double-action guard
mechanism especially useful for clutch operated machine tools such
as a punch press or the like wherein a clutch or equivalent device
is engaged and disengaged in response to a manual or automatic
signal to produce intermittent or continuous work strokes upon an
object being operated upon by the machine. A specific application
of this invention relates to great improvements in guard devices
for the protection of the operator of a punch press under adverse
as well as normal operating conditions wherein an added feature of
this invention is the possible prevention of costly damage to the
mechanical dies.
With the usual punch press, the press operator is required to
sequentially and continuously place metal parts into the die with
his hands. The operator then removes his hands from the die area
and usually trips the press operating treadle with his foot,
independently of his hand movements. This tripping of the press,
acting through the clutch mechanism, releases the ram of the press
to do work on the metal parts. If the operator fails to remove his
hands, an accident causing serious personal injury could result. If
the metal part is placed incorrectly on the die, and the press is
tripped, costly damage to the die as well as personal injury to the
operator could result.
Safety devices to protect the press operator, and/or guard against
damage to the press and dies, are known, but such devices have not
been entirely satisfactory, and more importantly, such devices have
not been "fail-safe" in practice. By the term "fail-safe," it is
meant that the guard device should perform the dual function of
protecting the operator during normal operation, as well as during
any unexpected operation of the press, such as those press
operations caused by mechanical failures, "repeats" (that is, more
than one press cycle caused by prolonged depression of the
operating treadle), or any other possible and unexpected tripping
of the press. Thus, known guard devices, which may protect the
operator during normal press operation, have not performed the
desired guarding function when it is most needed, such as during
any unexpected press operations, and during any press operation
wherein the guard device may fail to function due to power failure
or a mechanical failure therein.
In the device described and claimed in the Knoth U.S. Pat. No.
2,724,287, dated Nov. 22, 1955, there is an air operated sweep
guard which "sweeps" in front of the work area. If there is any
restriction to the movement of this guard, such an obstruction by
the operator's hand being in the work area, this guard is supposed
to prevent operation of the press. In normal operation, this guard
is actuated by a foot treadle that applies air at supply line
pressure (normally 80 p.s.i.) to a three-way valve but the foot
treadle is also directly connected to the clutch-tripping rod of
the press. Thus, failure of this valve would prevent pneumatic
operation of the sweep guard but would not prevent tripping of the
press, which is controlled through direct linkage of the foot
treadle to the clutch. As an example, when the foot treadle is
actuated, the compressed spring in the three way valve is released
and the valve goes to an open position. While spring operated
valves are known and even desirable in the present invention for
purposes of economy, a broken valve spring in the Knoth device
would give rise to a serious failure because the three-way valve
would not move to the open position and allow air at line pressure
to operate the guard mechanism. This, or any other malfunction of
the valve would be a failure of the primary guard operation and
once the guard mechanism is actuated and the press is tripped,
there can be no restriction to the movement of the press because
the guard would not "sense" any obstruction, including the
operator's head, hands or his tools. Also in this device, there is
a short time delay between actuation of the foot treadle and
operation of the guard. The length of time of this delay is equal
to the time it takes for the air to travel from the three-way valve
to and through a guard actuator control valve which opens a
pneumatic line to the guard-operating cylinder which controls the
guard sweep. If the air line supply is lost, for example through
compressor failure, the foot treadle will trip the press but not
operate the guard and in this case, the work area would again be
unprotected.
A further objection to this device occurs in the secondary or
emergency operation of the Knoth guard mechanism wherein, when the
press is tripped, the press crankshaft on its downward stroke opens
a second three-way valve which then becomes part of the air supply
line and performs the same functions that were performed by the
opening of the first three-way valve. Since there is only 80
-p.s.i. line pressure in this emergency operation, the guard
movement is not a positive sweep as it does not take a very large
external force to obstruct 80 p.s.i. acting in a small cylinder
against leverage afforded to the external force and thereby leave
the work area unprotected. This commonly occurs in practice where
an experienced press operator, working on a piece basis and being
rushed for time, can become accustomed to overcoming the force of
air operated guard mechanisms in order to perform almost split
second movements, and thus endanger himself and the machine. Also,
a loss of the line supply pressure, as noted above, would render
this emergency feature of the Knoth device completely inoperable
with the press on its downward stroke, and again the work area
would be unprotected, and in a highly accident prone condition. The
Knoth guard also finds disadvantage with the press ram adjustment
which varies with the type and height of the job and the dies to be
used whenever there is a job change or change of operation to be
performed in the press. This means there will be a different
distance of ram travel for each job and the ram must be adjusted to
fit the job. If this adjustment is neglected, it is possible that
the ram head could reach the bottom of the stroke before the
emergency three-way valve opens, completely eliminating the
secondary feature of the Knoth guard.
Apparently in an attempt to overcome objections to completely air
operated devices such as in the Knoth patent, the guard device
described and claimed in the Madden U.S. Pat. No. 2,888,123 dated
May 26, 1959, is lowered and raised by a cam action. Actuation of
the punch press foot treadle in this patent opens a valve and the
valve in turn opens high line pressure (usually 80 p.s.i.) to a
guard-operating cylinder directly connected to the cam which in
turn is connected to the guard. When the guard-operating cylinder
is actuated by air pressure against the resistance of an internal
spring, the guard-operating cam rotates in a counterclockwise
direction and lowers the guard, and the guard is locked in place by
the expanding force of a spring in a pin-actuating cylinder which
slides a suitable pin into a pin-receiving detent in the
guard-operating cam. The press is mechanically tripped by the
expanding action of this compression spring in the pin-actuating
cylinder, almost simultaneously with the movement of the pin. The
Madden device thus employs a completely mechanical-locking and
press-actuating operation while the guard operates on line
pressure, but there is no automatic retraction of the guard in case
of an obstruction, such as by the operator's hand, or misaligned
dies and tools, and the foot treadle must be released before the
guard will return to its original open position.
After the Madden press is tripped, an eccentric cam on press
crankshaft operates a control valve which opens line pressure to
the pin-actuating actuating cylinder. Line pressure then overcomes
the resistance of the compression spring in the pin-actuating
cylinder to disengage the pin from the cam detent in the
guard-operating cam to disengage the flywheel and allow this cam to
rotate in a clockwise direction and raise the guard. Thus, if the
Madden press should have a "repeat" or double trip, there would be
no protection with this guard, as there is no completely positive
emergency feature. Moreover, if the operator's foot should remain
on the treadle at the time the press reaches the bottom of its
downward stroke, the momentary opening of the control valve by the
eccentric cam on the crankshaft will cause the pin to be lifted
from the guard-operating cam, but the air pressure in the
guard-operating cylinder will remain therein and the internal
spring in such cylinder thus will not rotate the guard-operating
cam such that this action is controlled by the chance at best and
is subject to failure. Also, the springs and air lines of the
Madden device are subject to the same mechanical failures as the
Knoth device, such that press operation can continue after a
mechanical or air pressure failure, as long as the mechanical
press-operating features are in position to permit continued press
operation.
Accordingly, the art is still desirous of a fully reliable guard
for machine tools such as the punch press wherein the guard will
function, not only during normal operation, but also in a fail-safe
manner to provide a safeguarding function during unexpected press
operations and during mechanical and power failures that may occur
during press and guard operations.
It is therefore a principal object of this invention to provide a
double-action, fail-safe safety guard for machine tools.
It is another object of this invention to provide an improved guard
mechanism that will actuate a safety guard on a punch press during
both normal and unexpected press operations.
It is a further object of this invention to provide an improved and
fail-safe mechanism for controlling the actuation of a safety guard
on a punch press to insure the movement of the guard to its
operative position prior to the movement of the ram of the
press.
It is still another object of this invention to provide a fail-safe
safety guard for punch presses which will perform the dual function
of protecting the operator during normal operation, and during any
unexpected operation of the press caused by repeats, mechanical
failures or other accidental trippings of the press.
Other and further objects of this invention, together with a better
appreciation for the advantages thereof, will become more apparent
as this description proceeds.
Broadly described, the objects of this invention are accomplished
by providing a fail-safe, double-action safety guard having two
separate and distinct protective circuits, the primary circuit
being both pneumatically and electrically operated, while the
secondary or follow up circuit is hydraulically operated. As an
illustration of a manner in which the objects of the invention are
accomplished, these two circuits may be combined on a suitable
known punch press wherein the operator of the press may actuate a
foot treadle so that his hands are free at all times for production
purposes. According to the invention, actuation of the foot treadle
will open the pneumatic circuit to a preset flow control circuit
and also to an air solenoid valve. From the flow control circuit,
air pressure passes through and operates a pneumatic drive cylinder
which in turn drives a guard-actuating device or butterfly flipper
having a guard shield attached thereto. The butterfly flipper is
rotated a preset amount to drive the guard shield in front of the
work area. Only when the guard shield is completely in front of the
work area, an electrical off/on switch is operated which in turn
actuates an air solenoid and releases line air pressure to the
clutch trip cylinder which trips the press.
To operate the follow up hydraulic circuit, a preset cam throw is
mounted on the crankshaft of the press. When the press is tripped
and the ram starts its downward stroke, the cam positively drives a
hydraulic cylinder. This cylinder is connected via hydraulic lines
to a second hydraulic cylinder which is mounted next to the guard
actuating device or butterfly flipper diagonally opposite the
pneumatic drive cylinder, the length of the stroke of the second
hydraulic cylinder and the pneumatic drive cylinder being equal.
Before the ram has completed a minor fraction of its downward
stroke, the second hydraulic cylinder is completely activated
against the butterfly flipper. In normal operation, the hydraulic
cylinder merely follows the pneumatic cylinder and butterfly
flipper action. It is a positive drive but only drives the guard
shield in any emergency operation such as a double tripping of the
press, or a clutch, air pressure, spring, electrical, or air
solenoid valve failure. The positive hydraulic drive exerts a large
force that may be as great as the punch press however, and in both
normal and unexpected operations, this force cannot easily be
overcome by the operator. When the stroke of the second hydraulic
cylinder is fully extended to the butterfly flipper, it holds the
guard shield in front of the work area until the ram has completed
its downward stroke and has started its upward stroke. Meanwhile,
the pneumatic drive cylinder retracts and is ready for the next
cycle. Desirably, the guard shield is opened by means of a return
spring and the work area is cleared and made ready for the next
cycle of the press. A return spring is preferred according to the
present invention, although such springs are subject to failure,
since any positive drive for returning the guard shield could
possibly operate in a manner similar to the objectionable known
devices and open the work area during a "repeat" or during a
failure of the primary secondary circuit. Direct and positive
drives obviously can be used with the invention however, but
preferably in instances where a positive guard return drive is
desired, it can take the form of a line pressure operated pneumatic
cylinder which may be actuated by release of the holding action of
the secondary circuit herein.
Turning now to the drawings:
FIG. 1 is a front view of a suitable punch press having the
fail-safe safety guard of the invention mounted thereon;
FIG. 2 is a side view of the punch press in FIG. 1 with the fly
wheel indicated in phantom lines to show details of the flow
control portion of the primary circuit;
FIG. 3 is a diagrammatic view in cross section and greatly
enlarged, to show details of the flow control circuit shown in FIG.
2; and
FIG. 4 is a diagrammatic view of a portion of the primary
protective circuit.
Referring now to FIG. 1 of the drawings, there is provided a punch
press of known design and indicated generally by the reference
numeral 10, having a work area indicated by the reference numeral
11 and the usual foot treadle for operating the press, indicated by
the reference numeral 12. The punch press, work area and foot
treadle are not shown in elaborate detail as their designs are
known in the art and do not form a part of this invention.
According to this invention, the foot treadle directly operates a
three-way air valve 14 shown in diagrammatic form in FIG. 3, and
having an exhaust port 15, a primary circuit port 16 and a line
supply port 17 for receiving the air line supply conduit 18, having
a line pressure in the order of 80 p.s.i. The air valve 14 is
connected via port 16 to the primary circuit air line 21 leading to
a tee 22 to provide a flow regulator circuit supply line 26 and an
air solenoid supply line 24 which continues to the top of the press
to the air solenoid valve to be described hereinafter. The line 26
leads from tee 22 to a flow control circuit generally indicated by
the reference numeral 30.
In the flow control circuit 30 shown in more detail in FIG. 3,
there is an air regulator valve generally indicated by the
reference numeral 40, a restrictor valve generally indicated by the
reference numeral 60 and a "quick dump" type control valve
generally indicated by the reference numeral 80.
The air regulator valve 40 of the flow control circuit is comprised
of an upper body portion 41 and a lower body portion 42 provided
with intake port 46 and regulated outlet port 44. The regulator
valve 40 regulates the air pressure in a manner known in the art by
means of a suitable diaphragm 51, the pressure on which may be
controlled in part by the lower needle control 45, while the
overall tension on the diaphragm 51 is controlled by the upper
needle control 50 acting on the spring 53. Valve 40 is connected to
the restrictor valve 60 by air lines 31 and 33 connected at tee 32,
which tee also provides connection to the "quick dump" control
valve 80 by means of the line 34, the valve 80 being in turn
connected to the valve 60 by means of the line 35. The restrictor
valve 60 comprises a body portion 61, a regulated air intake port
63 and a "quick dump" valve port 65. Air flow through the
restrictor valve may be controlled by the needle control 62, while
the direction of flow is controlled by the spring-biased ball 66,
the bias spring 67 thereof being controlled by a suitable threaded
nut 64. The "quick dump" valve 80 is comprised of a body portion 81
and valve ports 84, 85 and 88 for connection with the lines 34, 35
and 28 respectively, valve port 82 being a simple exhaust port. The
direction of flow and the regulation of flow in the "quick dump"
valve is controlled by the spring 89 and threaded thumb screw
member 83 having chamfered portions 86 and 87 thereon which are
connected by means of the rod 91 and are adapted to sealingly
engage suitable upper and lower internal chamfered portions 96 and
97 of the valve body.
An air line 38 containing air under regulated pressure leads from
the "quick dump" valve to the primary electrical-pneumatic circuit
indicated at 100 and having a pneumatic drive cylinder 103 having
associated therewith a piston rod 105 and an electrical on-off
switch 106 which controls an air solenoid valve 107 through the
electrical circuit indicated at 104. The air solenoid valve 107
controls the clutch trip cylinder 108 mounted on the side of the
press by a suitable mounting bracket generally indicated at 111,
which cylinder in turn actuates the clutch cylinder clevis
connecting rod 113 known per se in the art and, accordingly, not
forming a part of this invention. The crankshaft and flywheel
assembly of the press, indicated at 13 and actuated by means of the
clutch cylinder and clevis connecting rod, drives a cam 131, which
is connected by means of the connecting piston rod 135 to a
hydraulic cylinder 142 of the secondary or hydraulic circuit
indicated at 140. Hydraulic cylinder 140 preferably mounted on the
cam side of the press by the mounting bracket generally indicated
at 141, forces hydraulic fluid through the line 144 to the
hydraulic drive cylinder 143 having piston rod 145.
The guard assembly 150 comprising guard shield 153 is mounted via
bracket 154, arm 152 and the butterfly flipper 160 to a suitable
area of the punch press by means of the mounting bracket 151. The
actuator or flipper assembly 160 having upper and lower faces 162
and 163 is connected via axis 164 to a mounting bushing 161 on the
bracket 151. The pneumatic drive cylinder 103 acting through piston
rod 105 drives the upper face 162 of the butterfly flipper 160 and
the guard member, the butterfly flipper and guard assembly relying
on the action of return spring 166 to return it to its raised
position. When the guard assembly is in the lowered or safety
position, the piston rod 145 of hydraulic drive cylinders 143 will
act against the lower flipper face 163 to lock the guard assembly
in the safety position in a manner to be described in more detail
hereinafter. However, during unexpected operation of the press or
during a repeated trip operation, or due to failure of the
pneumatic line, the hydraulic drive cylinder will act with
substantially the entire force of the press to positively drive the
butterfly flipper into the guard position before the press will
complete about one quarter of its drive stroke.
As for spring 166, one end is fastened to the guard mounting frame
151. The other end is fastened to the upper face 162 of the
butterfly flipper. Spring 166 is a tension spring that is in
tension when the guard is operated, the sole purposes of this
spring being to return the shield 153 to its nonoperated position.
During press operation however, drive cylinder 102 and then
hydraulic cylinder 143 overcome the tension of spring 166 and drive
the shield over the work area 11.
The fail-safe double action safety guard performs the dual function
of protecting the operator during normal operation of a machine
tool such as a punch press and during unexpected operation thereof
caused by repeats, mechanical failures or any other possible
tripping of the machine tool. Accordingly, the ensuing description
is offered as an illustration of the operation of this invention
and should not be considered as limiting on the advantages or
utility thereof.
An examination of FIG. 1 shows that there are two separate and
distinct protective circuits, the primary circuit 100 being
pneumatically and electrically operated and the follow up circuit
140 being hydraulically operated. As is known in the art, when the
operator of the punch press actuates the foot treadle 15 his hands
are free at all times for production purposes. Operating the
three-way valve 14 by means of the foot treadle 15 opens the 80
-p.s.i. air supply to line 21, the line pressure being fed directly
to the valve 107 via line 24 and 80-p.s.i. line pressure is
maintained whenever the foot treadle is operated. Actuating the
foot treadle 15 thus opens the pneumatic circuit to the preset flow
control circuit 30 and also to the air solenoid valve 107 via line
24.
The operation of the flow control circuit will be more fully
appreciated when reference is had to FIG. 3 of the drawings. From
line 21 through a standard tee 22, 80-p.s.i. line pressure is also
fed to the air regulator valve 40 which regulates the air supply to
line 38 and maintains this at a constant pressure which may be 55
p.s.i. as an example. This 55-p.s.i. regulated line pressure passes
through the valve 80 and also through a standard tee 32 to a
restrictor valve 60. The restrictor valve 60 feeds air pressure to
the port 85 of valve 80 until it overcomes the tension of spring 89
of valve 80. When this happens, the exhaust port 82 is opened and
the air in line 38 quick exhausts and releases cylinder 103 to its
nonoperative position. Release of the foot treadle 12 quick
exhausts lines 26 and 24 through valve 14.
Sequentially, the operation of the flow control circuit involves
first depressing the foot treadle to open valve 14 and feed
80-p.s.i. line pressure to valves 40 and 107. Valve 40 regulates
and maintains 55-p.s.i. pressure for valves 60 and 80, valve 60
restricting flow of air through line 35. There is a steady build up
of 55-p.s.i. air pressure in line 35 until spring tension in valve
80 is overcome. Before spring tension in valve 80 is overcome,
55-p.s.i. pressure is maintained on cylinder 103. After the spring
tension is overcome, the inlet port 84 is closed by chamfered
surfaces 87 and 97 so that the exhaust port 82 opens in valve 80.
Air from cylinder 103 exhausts through exhaust port causing
cylinder 103 to release. Release of foot treadle 12 then quick
exhausts lines 24 and 26 through valve 14.
From the flow control circuit the air pressure goes through line 38
and operates the pneumatic drive cylinder 103 which in turn drives
the butterfly flipper 150 having the guard assembly 150 and shield
attached thereto. The butterfly flipper is rotated a preset amount
by piston rod 105 and this in turn drives the guard shield 153 in
front of the work area 11. When, and only when, the guard shield is
completely in front of the work area, the electrical off/on switch
106 is operated through a suitable connection to the piston rod
105. With this switch on, the electrical circuit 104 to the air
solenoid 107 is closed to actuate the air solenoid and releases
line air pressure to the clutch trip cylinder 108 which trips the
press.
In the sequence of operation, air under pressure is released to the
flow control circuit and to the air solenoid valve. The air
solenoid valve holds this line pressure until the solenoid is
activated. Thereafter, the regulated air pressure from the flow
control circuit goes into the pneumatic drive cylinder, so that the
guard shield is driven in front of the work area. If the guard
shield is obstructed in any way, it will return to its original
upper or open position and the press will not trip and the foot
treadle would have to be reactivated to start a new cycle of
operation. When the guard shield completely covers the work area,
the electrical off/on switch is activated. Operating the off/on
switch closes the electrical circuit and actuates the solenoid so
that line air pressure is released to the clutch trip cylinder. The
clutch trip cylinder is actuated and trips the press but if the
guard shield is not completely closed, the electrical switch cannot
be actuated and the press cannot be tripped.
The cylinder 103 is an air cylinder with built in electrical
contacts 106, as shown in FIG. 4. When the cylinder 103 is not
pressurized, there is no possible chance of activating solenoid
valve 107, a dormant circuit. When cylinder 103 is activated with
air pressure, its piston and rod are driven the length of the
cylinder stroke and the electrical contacts 106 are closed at the
end of the cylinder travel. At this time, the circuit with air
solenoid valve 107 is completed.
As the cylinder 103 is air activated, simultaneously, the guard
sweep and shield 153 are being driven across the die area 11. When
the guard sweep and shield 153 reach the closure point, the
cylinder 103 is fully extended and at this point electrical
contacts 106 complete the circuit with air solenoid valve 107. As
air solenoid valve 107 is electrically activated, it opens up its
airport to line pressure through air line 24. The line pressure
operates the clutch cylinder 108, which pulls the clutch of the
punch press as the air activates it; thus, the press is tripped
while the guard is closed (done pneumatically the same time as the
one electrical circuit.) It is important to note that if the
electrical circuit should fail, it would be a safe failure because
the press cannot trip without closing of the electrical
circuit.
The secondary or follow up circuit 140 is hydraulically operated.
The preset cam throw 131 mounted on the crankshaft of the press
drives the hydraulic cylinder 142 when the press is tripped and the
ram starts its downward stroke. Cylinder 142 is connected to a
second hydraulic cylinder 143 which is mounted next to the
butterfly flipper diagonally opposite the pneumatic drive cylinder,
the length of the stroke of the second hydraulic cylinder and the
pneumatic drive cylinder being equal. Before the ram has completed
one-fourth of its downward stroke, the second hydraulic cylinder is
completely activated against the butterfly flipper 160. In normal
operation, the hydraulic cylinder merely follows the butterfly
flipper action. It is a positive drive but only drives the guard
shield in any emergency operation such as a double tripping of the
press or a clutch failure. After the stroke of the second hydraulic
cylinder is fully extended to the butterfly flipper, it holds the
guard shield in front of the work area until the ram has completed
its downward stroke and has started its upward stroke, the upward
stroke of the press retracting the piston rod 145 by raising the
rod 135 of cylinder 142. Meanwhile, the pneumatic drive cylinder
retracts and is ready for the next cycle, and the guard shield is
then raised by the spring 166 so that the work area is cleared and
made ready for the next cycle of the press.
It is to be understood that the above-described arrangements are
simply illustrative of the application of the principles of this
invention. Numerous other arrangements may be readily devised by
those skilled in the art which will embody the principles of the
invention and fall within the spirit thereof. For example, the
present device may be modified for mounting on other machine tools,
such as drill presses, stamping machines, molding machines and the
like. Accordingly, this invention should only be limited to the
scope of the following claims.
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