US3554067A

US3554067A - Fail-safe double-action safety guard

Info

Publication number: US3554067A
Authority: US
Inventors: Joseph Scutella
Original assignee: Individual
Current assignee: Individual
Priority date: 1969-02-26
Filing date: 1969-02-26
Publication date: 1971-01-12
Anticipated expiration: 1988-01-12

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.

Description

United States Patent Joseph Scutella [72] Inventor 886 N. 4th St., Olean, N.Y. 14760 [2] Appl. No. 802,346 [22] Filed Feb. 26, 1969 [45] Patented Jan. 12, 197 1 [54] FAILS/\FE DOUBLE-ACTION SAFETY GUARD 8 Claims, 4 Drawing Figs.

PrimaryExaminer-Andrew R. .luhasz Assistant Examiner-James F. Coan Attorney-Cushman, Darby & Cushman 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 ofi'lon 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.

PATENTED m1 219?: 554- SHEET 1 BF 3 INVENTOR JOSEPH Sc 0 7-54 9 ATTORNEYS INVENTOR ,Josepfl ,S'Zwram VWL/ Q\ \M \\\\\\\\\K //4 SHEET 3 BF 3 PATENTED JAN 1 2197| ATTORNEYS This invention relates to guard devices for machine tools and more particularly to a highly improved fail-safe, doubleaction 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 amanual or automatic signalto produce intermittent or continuous work strokes upon an object being operated upon by the machinefA specific application of this invention relates. to great improvementsin guard devices .for the protection of the'operator of a punch press under adverse as well as normal operating conditions wherein an added feature ofthis invention isfthe possible prevention of costly damage to the mechanical dies. u With the usual punch press, the press operator is required to e l sequentially and continuously place metal 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 clutchme'chanism, releases the 7 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'pl aced incorrectly on the die, and the'press is tripped, costly damage to the die'as well as personal injury tothe operator could result.

Safety devices to protect the pressoperator, and/or guard against damage to the press and dies, areknown, 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 these press operations caused by mecln'mical' failures, repeats"(that is, more one press cycle caused by prolongeddep'ression of the operating trea- I die); 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 40 the desired guarding function when it is most needed, such as e 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.

guard is supposed to prevent'operation of thep'ress. In normal operation, guard is actuated by a foot treadle that applies air at supply line pressure (normally 80 psi.) to a three-way "valve but the foot treadle is also directly connected to the clutch-tripping rodof the press. Thus, failure of this valve I would prevent pneumatic operation of the sweep guard but would not prevent tripping of the press, which iscontrolled i 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 inthe 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 linepressure to operate the guard mechanism. This, or anyother malfunction of the valve would be a failure of the primary guard operationand once the-guard mechanism is actuatedland 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 7Q 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 thethree-way valve to and throu'gh a guard actuator control valve which opens a pneumatic line to the guard-operating the crankshaft will call-5a lnthe device described .andclaimed in the Knoth Pat. 45

cylinder which controls the guard sweep. If the air line supply is lost, forexample 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 -p.s.i. line pressure in this emergency operation, the guard movement is not a posiperienced 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,

5 completely eliminating the secondary feature of the Knoth guard.

Apparently in an attempt to overcome objections to completely air operated devices such ah the Knoth patent, the guard device described and claimed in the Madden US. Pat. No. 2,888,123 dated May 26, 1959, is loweredand 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 hne 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 guardoperating 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 mechanicallocking 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 operators 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 trapped, an eccentric cam on press crankshaft operates a control valve which opens line pressure to the pin-actuating actuating cylinder. l ine 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 operators foot should remain on the treadle at the time the press reaches the bottom of itsl dolwnmard stroltte, tziemmgl;

' in of the contro va ve y e eccen nc memary open 8 he pin to be lifted from the guardoperating 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 pressduring 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 failsafe 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 a guard-actuating device or butterfly flipper having a guard shield attached thereto. The butterfly flipper is rotated a prwet 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. I 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. I 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 II 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 I4 shown in diagrammatic form in FIG. 3, and having an exhaust port IS, a primary circuit port 16 and a line supply port I7 for receiving the air line supply conduit I8, having a line pressure in the order of 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,

spring being to return theshield 153 to its nonoperated position. During press operation however, drive cylinder 102 and the direction of flow is controlled by the spring-biased bal ,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 land 88 for connection with the

lines

34,35 and 28 respectively, valve port 82 beings 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 charnf'ered portions 86 and 87 thereon which are connected byjrneans 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 cyl'nder103 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 actuatesgithe clutch cylinder clevis connecting rod113 known per se in the art and, accordingly, not forming a part of this invention; The crankshaft and flywheel assembly of the press, 'indieated at 13 and actuated by means of the clutch cylinder and tfil'evis connecting rod, drives a cam 131, which is connected by means of the connecting piston rod 135 to a hydrau- Iiccylinder 142 of the secondary or hydraulic circuit indicated at 3140. Hydraulic cylinder 140 preferably mountedon the cam side of the press by the r'nountingbracket generally indica'teti at'141, forces hydraulic fluidthrough the line 144 to the hydraulic drive cylinder 143 having piston rod 145.

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 mou r 'ting bracket 151. The actuator or flipper assembly 160 haviiig 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 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. Whenthe guard assembly is in the lowered or safety pdsition, the piston rod 145 of hydraulic, drive cylinders 143 willafct against the lower flipper face 163 to lock the guard asseinbly in the safety position in a manner to be described in moredetail hereinafter. However, during unexpected operation of the press or during a repeated trip operation, or due to H failure of the pneumatic line, the hydraulic drive cylinder will with substantially the entire force of the press' to positively drive the butterfly flipper into the guard. position before the twill complete about one quarter of its drive stroke.

for spring 166, one end is fastened to the guard mounting frame 151. The other end is fastened to the upper face 162 of t e butterfly flipper. Spring 166 is a tension spring, that is in on when the guard is operated, the sole purposes of this then hydraulic cylinder 143 overcome the tensionof spring 166 and drive the shield over the work area 1 1.

;.j'-;F he 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 failyres or any other possible tripping of the machine tool. Ac-

.coi'dingly, the ensuing description is offered as an illustration ofgthe operation of this invention and should not be considered as limiting on the advantages or utility thereof.v

s'An examination of FIG. I shows that there are two separate and distinct protective circuits, theprimary circuit 100 being prieumatically and electrically operated and the follow up cirdid-140 being hydraulically operated. Asis known in the art,

' when the operator of the punch press actuates the foot treadle The operation of the flow control circuit will be more fully i appreciated when referenceis 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 restn'cror valve feeds air pressure to the pori 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. 1 t

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. airpressurein 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 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 onefourth 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.

1 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 mechanrsm of claim 2 wherern 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 rarn 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.

Claims

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.

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.