US3054314A

US3054314A - Presses for cutting blanks from sheet material having safety means to protect the operator

Info

Publication number: US3054314A
Authority: US
Inventors: George O Anderson; Robert W Bradley
Original assignee: United Shoe Machinery Corp
Current assignee: United Shoe Machinery Corp
Priority date: 1959-01-15
Filing date: 1959-01-15
Publication date: 1962-09-18
Anticipated expiration: 1979-09-18
Also published as: GB937666A; FR1245298A

Description

Sept. 18, 1962; G. o. ANDERSON ETAL 3,054,314

PRESSES FOR CUTTING BLANKS FROM SHEET MATERIAL HAVING SAFETY MEANS TO PROTECT THE OPERATOR Filed Jan. 15, 1959 In veniors G'eor ye 0. An der-son Robert Wfir'adley 94 K15 0 96 By i/zezr Attorney United States Patent Ofifice 3,054,314 Patented Sept. 18, 1962 PRESSES FOR CUTTING BLANKS FROM SHEET MATERIAL HAVING SAFETY MEANS T PRO- TECT THE OPERATOR George 0. Anderson, Scituate, and Robert W. Bradley,

Marblehead, Mass, assignors to United Shoe Machinery Corporation, Flemington, N.J., a corporation of New Jersey Filed Jan. 15, 1959, Ser. No. 786,976 6 Claims. (Cl. 83-68) This invention relates to cutting presses and more particularly to improvements in cutting presses of the type employing dies for cutting blanks from sheet material such as leather or fabric.

In the shoemaking industry, use has long been made of presses comprising a flat work support, on which leather or fabric to be cut is laid with a cutting die positioned thereon, and a flat-bottomed beam or platen mounted to be swung over the die. Upon actuation of a trip handle by the operator, the platen is arranged to be moved by power means toward the work support for driving the die through the work.

In some older types of presses, the power means comprises a flywheel linked mechanically through a one-revolution clutch to the platen to move it toward and away from the work support in a fixed stroke the height of which is adjustable by a hand wheel to accommodate dies of different heights. Obviously such presses present a personal injury hazard to the operator.

More recently, there have been employed presses with hydraulic motor power means and an electric stroke terminating control operating automatically to interrupt the stroke in response to the formation of an electric path from the platen to a conductive surface on the work support by the cutting die penetrating through the work and engaging the conductive surface of the support. To allow the die to complete the cut around its periphery after the initial breakthrough, the stroke terminating control relay circuit includes a variable delay means adjustable in steps by the operator through a suitable range of delay values for accommodating a variety of materials. A machine of this type is discolsed in United States Letters Patent No. 2,783,838, issued March 5, 1957 on an application filed in the names of Roy G. Ericson and Frank E. Stratton.

The electric stroke terminating control described affords an opportunity to provide enhanced safety of operation for presses. Thus in the machine of the cited patent, the cutting stroke will be terminated by the control in response to the formation of an electric path by body conductivity if the platen touches the operator while he is holding the starting switch handle, even if the body portion touched, for example a finger, is insulated by the work from direct contact with the work support as it would be if it were resting on the die at the time the stroke was initiated.

While the operation of the stroke terminating control means disclosed in Patent No. 2,783,838 has been very effective in avoiding serious injury, it will be appreciated that the operation of the delay means in providing an incremental downward movement necessary to the cutting function may allow more or less pressure to be brought to bear on an intervening body portion before the platen stops its downward movement, particularly where the operator has set the delay means at its maximum value. Thus although serious injury is obviated, it is still possible in the most extreme circumstances for a painful cut to be inflicted on the operator.

I It is accordingly an object of the present invention to provide an improved organization for presses of the type described which will provide enhanced protection to the operator in normal operation while permitting a greater flexibility of choice with regard to the nature of the cutting surface.

To this end and in accordance with a feature of the invention, a press organization is provided comprising a work support, a power operated platen, manually operable means for initiating a cut-ting stroke, said means embodying an electrode adapted to be connected to the operator in the normal course of operation of the press and insulated from the striking surface of the platen, nondelayed relay means, responsive to the formation by body conductivity of an electric path between said electrode and the conductive surface of the platen, and connected for controlling the power means to interrupt movement of the platen toward the work support in an emergency and relay means, controlled by switch means in response to movement of the platen to a predetermined position, and connected to said power means for controlling it to interrupt movement of the platen toward the work support in normal operation. We have thus found that by providing in the organization for separate performance of the two functions, namely safety stroke termination and cutting stroke termination, we have been able to provide a press organization in which both functions are handled to better advantage. For example, by relieving the safety relay of the task of cutting termination, no delay therein is necessary and the control will function to interrupt the cutting stroke in the event the platen touches the operator before any injury can occur. It is no longer possible for the operator to delay the operation of this control to his own misfortune. At the same time greater flexibility in regard to the cutting function is obtained. Thus the choice of the cutting surface is not restricted to conductive materials, but may include, for example, wood cutting blocks or cutting pads of non-conductive rubber.

The convenience of operation is enhanced through the provision of manual means for adjusting the platen position at which the switch means is actuated to interrupt the stroke. Thus by rotation of a readily accessible knob adjacent the front of the work support, the operator may adjust the stroke to accommodate dies of different heights.

Further features and advantages of the invention will best be understood by the following description taken in connection with the accompanying drawings, in which:

FIG. 1 is a side elevation, partly in sect-ion, of a portion of a press embodying the present invention and includes a diagrammatic View showing a hydraulic motor and control mechanism therefor; and

FIG. 2 is a schematic of apparatus embodying the present invention.

Referring to the drawings, FIG. 1 represents the essential elements of a hydraulic press comprising a bed 10, constituting part of the machine frame, and a work support member 12, constituting one of a pair of presser members, mounted on the frame 10. For clarity, only that portion of the frame 10 which supports the member 12 is shown, but it will be understood that the other elements of the press are also mounted on the frame. Thus a platen 14 constituting the other presser member is carried by a post 16 journaled in bearings in the frame 10 so that the platen 14 is mounted to be swung horizontally about the post 16 by an operator grasping a handle 18, and is mounted for vertical movement toward and away from the member 12.

Motor means are provided for moving the platen 14 toward and away from the work support. For this purpose a hydraulic cylinder 20 is mounted on the frame while a piston 22 fitting the bore of the cylinder is attached to the post 16 by a spindle 24. The cylinder 24} is connected to fluid pressure supply means (indicated generally by the numeral 26) which includes a valve 28 having a solenoid-operated spool 30. The supply means 26 is connected and arranged to admit fluid under pressure from a pump 31 to a lower port 32 of the cylinder when the solenoid S of the valve 28 is not energized, the spool 30 being then in the position shown, and to an upper port 34 when the solenoid S is energized to move the spool 30 to a lower position. A spring 36 normally supports the spool 30 in its upper position so that the platen 14 is normally held by fluid pressure in spaced relation to the member 12. Thus energization of the solenoid S effects a cutting stroke of the platen by admitting pressure fluid to the upper side of the piston 22 while deenergization of the solenoid effects termination of the stroke.

Included in the fluid pressure supply means 26 is a pressure switch 38. This switch has a spring-biased movable element communicating with a fluid pressure supply passage between the valve 28 and the pump. The pressure switch 38 also includes contacts PS which are normally open but which are closed by upward movement of the element 40 in the event the fluid pressure at the valve should build up beyond a predetermined value. As hereinafter described, this switch provides a means of effecting termination of the cutting stroke in the event of mechanical stoppage of the platen during a cutting stroke. The fluid pressure supply means also include a high pressure relief valve 44, a low pressure relief valve 46 and a one-way restricting valve 48. For a more complete description of the elements of the fluid pressure supply means and of the cutting press generally, reference may be had to United States Letters Patent No. 2,818,922, issued January 7, 1958 on an application filed in the names of Frank E. Stratton and Fred T. MacKenzie.

Switch means are provided on the machine arranged to be actuated in response to downward movement of the platen to a predetermined position. For this purpose, normally open switch contacts LS are mounted on the frame of the machine in cooperative relation with variable actuating means connected to the platen. The actuating means comprise a link 52 slidably mounted for height- Wise movement, through a vertical hole in the cylinder 20, the lower end of the link 52 having integral therewith a laterally extending finger portion 54. The upper surface of the distal portion of the finger 54 bears against a reduced portion 56 of the piston 22, which reduced portion extends through a bore in a cap 57 closing the lower part of the cylinder. The upper end of the link 52 carries 4 integral therewith a bracket portion 58 having formed therein an internally threaded hole 60 alined verticaly with a nonthreaded hole in a bracket 62 extending from the cylinder 20. Extending through these two holes is a a rod 64 the upper portion of which is threaded to cooperate with the threads in the hole 60, the lower portion of which is smooth for vertical sliding through the hole in the bracket portion 62. Intermediate of the holes, the rod 64 has an enlarged portion 66 against which bears one end of a spring 68 the other end of which bears against the bracket portion 62, the spring being thus arranged to urge the rod 64 upwardly. The switch contacts LS are so disposed in relation to the rod 64 that downward movement of the rod carries the enlarged portion 66 into actuating relation with the contacts LS to effect closure thereof. The heightwise position of the platen at which this closure takes place may be varied by rotation of the rod 64 which varies the heightwise disposition of the enlarged portion 66 in relation to the finger portion 54 and hence in relation to the platen.

Manual means are provided for adjusting the aforesaid heightwise relationship to accommodate dies of different heights. For this purpose a knob 70 is rotatably mounted on the bed 10 adjacent the front edge of the work support 12 in a position for convenient manipulation by the operator and is connected by means of a flexible cable 72 to the rod 64 whereby rotation of the knob 70 effects rotation of the rod 64.

Turning now to the safety stroke terminating control system, the bottom portion of the platen 14 comprises a metallic striking plate 74 which may either be grounded or attached in electrically insulated relation to the platen 14 by means comprising a layer of insulation 76. The handle 18 has a conductive surface and is connected to a rod 78 journaled for vertical movement in a bushing 80 of insulating material mounted in the platen 14. Fastened to the rod 78 is a cam element 82 having sloping shoulders. Normally open contacts TS are mounted on the platen in cooperative relation with the cam element 80 so that downward movement of the handle 18 effects closure of the contacts TS. The conductive surface of the handle 18 which the operator must grasp to initiate a cutting stroke constitutes an electrode to which the operator is connected in the normal course of operation of the machine. The handle 18 and the striking plate 74 are connected in an electric circuit, hereinafter described, for terminating a cutting stroke initiated by closure of the contacts TS should the operator engage the striking plate with the other hand.

The schematic shown in FIG. 2 discloses the control cir cuit for the machine. In this schematic, the main leads and 91 are supplied with alternating current at a suitable voltage, for example volts, from an appropriate power source not shown. Suitably, the supply voltage may be derived via a transformer from a three-phase circuit supplying an electric motor to drive the pump 31.

The control circuit shown in FIG. 2 comprises five electromagnetic relays having coils K1, K2, K3, K4 and K5 (the symbols also identifying the relays themselves), a cold cathode thyratron 92 and a DC. power supply therefor comprising a rectifier 94 and a capacitor 96 connected in series across the leads 90, 91 for charging the capacitor from the AC. power supply. Suitably, the thyratron may be a 5823 requiring a positive grid bias of about 70 volts for firing at an anode voltage of approximately volts DC. as provided by 110 volts A.C. across the leads 90, 91. The thyratron grid 98 is connected to the cathode 99 by a grid resistor 100 shunted by a transient-eliminating filter capacitor 102 of small value, and to the handle 18 through a K ohm current limiting resistor 104. The cathode 99 is connected to the negative terminal of the capacitor 96 through the lead 91. The anode 106 of the thyratron is connected to the positive terminal of the capacitor 96 through relay coil K3 and the shunt combination of the normally closed contacts KID of relay K1 and the normally open contacts KSC of relay K5. The striking plate 74 is connected to the junction of coil K3 and said contacts through current limiting resistors 108 partially shunted by a pulse transmitting capacitor 110 of low value which provides a momentary low impedance to facilitate the firing of the thyratron by body conductivity. The striking plate 74 is connected to the handle 18 through normally closed contacts K1C of relay K1 to apply a large positive bias to the grid 98. Accordingly, in normal operation with AC. power supplied to the leads 90, 91 the thyratron 92 is fired energizing K3 if K1 is not energized or if contacts KSC are closed by energization of K5 and the striking plate 74 and handle 18 are bridged (symbol Br) as by a body portion of the operator. Accordingly, in terms of Boolean algebra,

The relay coil K1 is in circuit with the contacts TS of the trip switch across the leads 90, 91, the circuit comprising the contacts TS (shunted by a holding circuit comprising the n.c. contacts K3A and no contacts KSA), the n.c. contacts K2A, the n.c. contacts K4A, and the coil K1. In normal operation with the relay K1 not energized by closure of the trip switch, contacts K1C and KID are closed and the thyratron 92 is fired in a pretest condition with K3 energized if the thyratron circuit is prepared to exercise its safety function.

Closure of the contacts TS energizes K1, and, after a time delay (symbol TD), K5. Energization of K1 resets the thyratron circuit to a condition for performing its safety function by opening contacts K and KID, respectively to disconnect the handle 18 from the striking plate 74 and to remove the B+ voltage from the thyratron to extinguish it. The relay K5 has its coil connected in a circuit from the junction of K1 and contacts K4A to lead 91 through contacts KIA, a resistor 112, a diode 114 and a capacitor 116, whereby K5 is energized a little later than K1. Closure of its contacts K50 restores the B+ voltage to the thyratron after this time delay.

The solenoid S is connected across the leads 90, 91 in series with the n.c. contacts K3B, n.c. contacts KZC and n.c. contacts K'SB. Accordingly, in the absence of energization of relays K2 and K3, the energization of relay K5 is effective by closure of contacts K5B to energize the solenoid S to initiate a cutting stroke.

Thereafter should the handle 18 and the striking plate 74 be electrically bridged, the thyratron 92 will be fired, energizing K3 and opening, by means of contacts KSB, the energizing circuit of the solenoid S. If, during the cutting stroke, the switch contacts LS or the pressure switch contacts PS should be closed energizing relay K2, contacts K2C will perform a similar function. Once energized, K2 will remain energized if contacts TS are closed, and, if TS is not closed, until K5 is de-ener'gized.

The operation of the circuit may also conveniently be understood from the following Boolean equations:

In operation with fluid pressure being supplied by the pump 31 and AC. voltage being supplied to the leads 90-, 91, the platen is supported by fluid pressure spaced above the cutting pad 12 and the control circuit is in its pretest condition with the thyratron 92 fired and K3 energized (Eq. 3). If the thyratron 92 is not fired, the relay K4, in circuit across leads 9f), 91 with n.c. contacts K3B, n.c. contacts K20 and n.c. contacts KlB, opens the contacts K4A to prevent energization of relays K1 and K5 (Eq. 4) to inhibit the start of a cutting stroke (per Eq. 1). The operator will, if all is well, proceed to dispose a work piece W on the cutting pad 12 with a die D disposed thereon where he wishes to cut out a blank, and will then swing the platen 14 over the :die. If he has not already done so, the operator will then adjust the position of the switch actuator 66 by rotating the knob 70 until the switch will be actuated at the appropriate heightwise position of the platen 14 wherein the die will have cut completely through the work but will not have been pressed deeply into the cutting pad 12.

By moving the handle 18 downwardly, the operator effects closure of the trip switch contacts TS to initiate a cutting stroke (Eqs. 5 and 6) which will thereafter be terminated automatically by the control as hereinbefore described.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent of the United States is:

1. In a cutting press, in combination, a frame, a work support mounted on said frame, a platen having a conductive striking surface, said platen being mounted in said frame for movement toward and away from the work support, power means for moving said platen toward and away from the work support, manually operable means for controlling said power means for initiating a cutting stroke, an electrode embodied in said manually operable means and adapted to be connected to the operator in the normal course of operation of the press, said electrode being insulated fromrthe striking surface of the platen, nondelayed fixed time response relay means responsive to the formation by body conductivity of an electric path between said electrode and the conductive surface of the platen for controlling the power means to interrupt movement of the platen toward the work support, switch means arranged for actuation by closing movement of said platen at a predetermined position thereof, and relay means controlled by said switch means and operative in response to such actuation to cause said power means to interrupt movement of the platen toward the Work support in normal operation.

2. In a press, in combination, a frame, a pair of presser members mounted on the frame, one of said members being movable toward and away from the other, one of said members having a conductive surface subject to being touched by the operator during movement of the movable presser member, motor means for effecting said movement of said presser member, a conductive surfaced handle movably mounted on one of said pressure members and insulated from the conductive surface of said one member, control means operable by movement of said handle to cause said motor means to effect movement of said member toward the other, a switch arranged for actuation by said movement at a predetermined spacing of the members and controlling said motor means for terminating said movement upon such actuation, and an electric stroke terminating control comprising a nondelayed fixed time response relay electrically connected to said handle and to said conductive surface of one member and connected to said motor means for controlling it to interrupt the movement of the movable presser member toward the other in response to the reduction in resistance beween said handle and said conductive surface afforded by the conductivity of a human body portion connecting said handle and said surface.

3. In a press, in combination, a frame, a pair of presser members mounted on the frame, one of said members being movable toward and away from the other, one of said members having a conductive surface subject to being touched by the operator during said movement of the movable presser member, motor means for effecting movement of said movable presser member, manually operable starting control means for causing said motor means to effect movement of said movable member to-. ward the other, a switch mechanically connected between the members for actuation at a predetermined spacing thereof and electrically connected to said motor means to efifect termination of the movement of the movable member toward the other in response to actuation, manual means mounted in readily accessible disposition adjacent one of said members for varying the mechanical connection of the switch to adjust the spacing of the members at which the switch is actuated, an electrode embodied in the starting control means and adapted to be connected to the operator in the normal course of operation of the press, at least one of the electrodes and the conductive surface being insulated from the frame, and an electric stroke terminating control electrically connected to said electrode and to said conductive surface and operably connected to said motor means for controlling it to interrupt the movement of the movable presser member toward the other member in response to the operators touching said conductive surface while connected to said electrode, said stroke terminating control comprising a fixed time nondelayed sensitive relay.

4. In a cutting press, in combination, a frame, a work support mounted on said frame, a platen having a conductive striking surface, said platen being mounted in said frame for movement toward and away from the work support, power means for moving said platen, manually operable means for controlling said power means for initiating a cutting stroke, an electrode embodied in said manually operable means and adapted to be connected to the operator in the normal course of operation of the press, said electrode being insulated from the striking surface of the platen, nondelayed fixed time response relay means responsive to the formation by body conductivity of an electric path between said electrode and the conductive surface of the platen for controlling the power means to interrupt movement of the platen toward the work support, switch means arranged for actuation by closing movement of the platen at a predetermined position thereof, relay means controlled by said switch means and operative in response to such actuation to cause said power means to interrupt movement of the platen toward the work support in normal operation, and manual means comprising a knob mounted for rotation on the frame adjacent the front of the work support and connected to said switch means for adjusting the position of the platen at which movement thereof toward the work support is terminated by operation of said switch means.

5. In a cutting press having two presser members one of which is movable toward and away from the other, said movable member having a conductive work engaging surface, a solenoid valve, fluid pressure power means controlled by said solenoid valve, and a manual stroke initiating control adjacent one of said members and actuatable for causing said power means to effect movement of the movable presser member in a cutting stroke, in combination therewith, an electrode embodied in said manual stroke initiating control, a switch arranged to be actuated by a closing movement of the movable member at a predetermined point of closure of the presser members and connected to the power means for control thereof to terminate such movement in response to such actuation, manual means for adjusting the point of closure at which said switch will be operated, and an electrically operated relay responsive to the formation by body conductivity of an electric path between the conductive work engaging surface of the movable presser member and the electrode embodied in said manual stroke initiating control for causing said power means to terminate movement of the movable presser member to.- ward the other member, said electrical means comprising a thyratron having a grid and having in its anode-cathode circuit the coil of a relay for controlling said solenoid valve for terminating said stroke, a grid bias circuit for normally biasing said thyratron non-conductive, and means for applying a firing potential to said grid immediately upon the formation by body conductivity of an electric path between said conductive surface and said electrode.

6. In a cutting press, in combination, a frame, a work support mounted on said frame, a platen having a conductive striking surface, said platen being mounted in said frame for movement toward and away from the work support, power means for moving said platen toward and away from the work support, manually operable means for controlling said power means for initiating a cutting stroke, an electrode embodied in said manually operable means and adapted to be connected to the operator in the normal course of operation of the press, said electrode being insulated from the striking surface of the platen, nondelayed fixed time response relay means responsive to the formation by body conductivity of an electric path between said electrode and the conductive surface of the platen for controlling the power means to interrupt movement of the platen toward the work support, and switch means arranged for actuation by closing movement of the platen at a predetermined position thereof, and relay means controlled by said switch means for normally controlling the downward movement of the platen.

References Cited in the file of this patent UNITED STATES PATENTS 1,727,013 Johnson et al Sept. 3, 1929 2,693,235 Kenworthy et al. Nov. 2, 1954 2,783,838 Erieson et a1 Mar. 5, 1957