US2250705A - Automatic press control system - Google Patents

Description

Patented July 2 9, 1941 AUTOMATIC PRESS QONTROL SYSTEM Walter Ernst, Mount .Gilead, Ohio, assignor to The Hydraulic Development Corp. Inc., Wilmington, Del., a corporation of Delaware Application August 31, 1939, Serial No. 292,932

2 Claims.

This invention relates to presses, and in particular, to control systems for hydraulic presses.

a One object of this invention is to provide an automatic. press control system, wherein the press ram-is. halted at the end of its working strokeand held in its halted position for a predetermined period of time beforebeing automatically reversed and retracted. I

Another object is to provide an automatic press control system, wherein the press ram is halted at a predetermined point on its forward stroke by tripping a limit switch which sets in motion a time delay device adapted to alter the energization of the electrical press control circuit at the end of the period of time for which the device is adjusted, thereby reversing and retracting the press ram.

Another object is to provide an electrical press control system,- wherein the press ram is halted and held under a predetermined pressure at a predetermined position on its forward stroke for a predetermined period of time as controlled by a time delay device, after which the pressure is-automatically released and pressure fluid admitted to the push-back cylinders to retract the press ram.

The drawing shows one embodiment of a press having an automatic control system according to the invention, arranged in a diagrammatic circuit partly in section.

In general, the automatic press control system of this invention consists of a limit switch adapted to be shifted by the press ram at a position corresponding to the end'of its working stroke, but reversal is delayed by the action of a time delay device. at the end of the working stroke, pressure is During the dwell thus providedthe invention, in brief, includes a pressurere sponsive switch actuated by the control rod of v the press at the limit of the working stroke, with a time delay device to provide a dwell and to prevent premature backing off of the press ram, a pressure-holding servomotor being provided with a reversible variabledelivery pump to prevent a continuing rise of pressure during the time delay period. The particular arrangement shown in the drawing also utilizes a closed hydraulic circuit interconnecting the pump and press.

Referring to the drawing in detail, there is shown a press III, a reversible variable delivery main pump ll of the pressure-holding servomoa fluid tank l3, a pilot pump l4, a control valve I5,,a time delay device IS, a solenoid H for. ac-

gization of the solenoid H, a press-reversing maintained upon the workpiece at a predeterdelivery position, causing pressure fluid to. be

supplied to the push-back cylinders and withdrawn from the main cylinder, thereby retracting the press ram. When the press ram reaches the end of its return or retraction stroke, an arm attached to the ram actuates mechanism which places the pump flow-control member or shift ring in its neutral position and thus holds the press ram in its retracted location.

Thus the automatic press control system of bed 2!.

arm 29 for engaging a stop collar 30 upon the limit switch l9 for initiating the operation of the time delay device [6 and a push-button switch 20 for initiating the operation of the entire circuit.

The push-button switch 20 is provided as the simplest form of starting arrangement to furnish semi-automatic operation. -It will be evident that the circuit may beenlarged to provide full automatic operation by circuits known to those skilled in the art.

The press i0 is shown diagrammatically for the sake of simplicity, and consists of a. bed 2| connected by strain rods 22 to a head 23. Mounted on the head 23 is a main cylinder 24 containing a main plunger 25, to which is attached the press ram or platen 26. Also secured to the latter are push-back plungers Z'l reciprocating in push-back cylinders 28 mounted upon .the press The press ram 26 is provided with an press control rod 3!, the latter being reclprocably supported by the arm 32 mounted upon the press bed 2|. The control rod 3! is urged upwardly by the compression spring 33, mounted between the collar 30 and the end of the arm 32..

The control rod 3| also carries anannular cam 36 near its lower end for closing the normally open reversing limit switch IS. The latter is provided with a switch arm 35 and contacts 36 and 31, maintained in a normally open condition by the coil spring 38. The control rod 3| also carries a collar or head 39 at its upper end,

beneath which is a coil spring 40 providing a a cushioning stop for the platen arm 29. Separable from the control rod 3| but in contacting engagement therewith is the valve-lifting rod 4| of the valve I5. The latter serves to lift the valve plunger 42 when the platen arm engages the coil spring 40 and lifts the control rod 3| and valve-lifting rod 4| into the position shown in the drawing. A coil spring 43 urges the valve plunger 42 downwardly toward its seat 44 between the inlet chamber 45 and exhaust chamber 45. The latter is connected by the exhaust conduit 41 to the tank I3, whereas the former is connected by the by-pass conduit 48 with the pilot pump I4.

' The valve I also contains a pressure relief plunger 49, urged downwardly by a coil spring 50 to close the passageway 5| leading from the conduit 48 to the chamber 52. The latter is connected by the passageway 53 to the exhaust chamber. Thus when pressure in the conduit 48 exceeds a predetermined maximum, it raises the pressure relief valve plunger 49 and escapes through the chamber 52, the passageway 53, the exhaust chamber 45 and the exhaust conduit 41, back to the tank I3. The valve-lifting rod 4| is provided with spaced collars 54 engaged by the yoked end of a lever 55, pivotally mounted upon the shaft 56 and pivotally connected to the armature 51 of the solenoid I1. The armature 51 is urged upwardly by the compression spring The main cylinder 24 is supplied with pressure fluid from the main pump H by way of the conduit 59, having a branch 65 communicating with a chamber 5| surrounding the pump centering piston area 62 upon the pump flow-control rod 63. The latter is connected to the shift ring of the reversible variable delivery pump II, the

conduit 18 to the conduit 59, whereas the opposite end chamber 11 is connected by the conduit 19 with the conduit 12.

In addition to the press reversing limit switch I9 and the solenoid I1, the electrical circuit contains the time delay device I6 and the contactor I8, all of which are energized from the power lines 80 and 8|. The power lines 80 and 8| are connected to the lines 82 and 83 leading to the solenoid winding 84 when the contactor coil 85 is energized so as to pull its armature 86 to the left and with it the switch blades 81, 88 and 89 into engagement with their respective contacts. The coil spring 90 holds the armature B5 and switch blades 81, 88. and 89 in a normally open condition when the contactor coil 85 is deenergized.

' The switch blade 59 provides a holding circuit for maintaining the energization of the contactor coil 85 by way of the power line 8|, the lines 9|,92, 93 and 94, the contacts 95 and 96 of the time delay device I5, and the line 91 leading to the power line Bil. This holding circuit is main- 1 tained after the circuit between the lines 98 and the circuit in operation. The press-reversing opposite side of which is connected to the rod I 64, threaded as at 65, to receive a hand wheel 55 for adjusting the thrust of a coil spring 51 mounted within the cylindrical spring casing 58. The spring 61 urges the shift ring of the pump in one direction in opposition to the pressure of the pressure fluid against the centering piston area 62. When the pressure in the main cylinder 24 rises to a sufiicient height to overcome the thrust of the spring 61, it pulls the shift ring of the pump II to its neutral or no-delivery position. The pump II is of the radial piston type, well known to those skilled in the art.

The pump flow-control rod 63 beyond the centering piston area 62 is provided with an enlarged piston head 69, reciprocable within 3. cylinder 1B supplied with pressure fluid on its left hand side by the conduit 1| connected to the pilot pump pressure conduit 48. When pressure limit switch I9 is connected to the time delay device Is by the line 99, and to the power line 8| by the line I00. The time delay device I6 is provided with a motor IIlI which opens the contacts 95 and 95 a predetermined period of time after the energization of the motor IIlI, in a manner well known to those skilled in the art.

In the operation of the press control system of this invention, to start the press in operation the operator momentarily depresses the push-button switch 29. This action energizes the coil 85 of the contactor I8, causing the armature 86 to move to the left so that the switch blades 81, 88 and 89 engage their respective contacts. The energization is maintained through the holding circuit established by the switch blade 89, in the manner previously described. The consequent energization of the winding 84 of the solenoid I1 pulls the armature 51 downward, and rocks the lever so as to push the valve-lifting rod 4| fluid of a sufliciently high pressure is admitted through the conduit 1| to the inner end of the cylinder 10, it shifts the piston head 69 and pump flow-control rod 53 to the right, placing the shift ring of the pump in its reverse position so' that pressure fluid is thenceforth discharged through the conduit 12 leading to the push-back cylinders 28. At the same time, in its reversed condition the pump II withdraws fluid from the main cylinder 24, through the conduit 59, as hereinafter described in connection with the operation of the circuit. The tank I3 is connected by a conduit 13 with the middle chamber 14 of the make-up valve I2, the valve member 15 of -which is shifted to and fro by pressure existing in the conduit 12 or the conduit 59 so as to upwards Assuming that the main pump II and pilot pump I4 are running, the unseating of the valve plunger 42 by this operation causes the discharge of the pilot pump I4 to be by-passed through the line 48, the chambers 45 and 46 and the conduit 41, to the tank I3. Thus no pressure is permitted to stand in the left-hand end of the pumpreversing cylinder 10, and the spring 61 consequently urges the rod 64 and pump shift ring to the left, placing the pump II upon stroke in a forward delivery position. When this occurs the pump I I delivers pressure fluid through the conduit 59 to the main cylinder, 24. forcing the main plunger 25 and press ram or platen 25 downwardly. At the same time fluid is withdrawn A from the pull-back cylinders 28 through the con- The ram 25 descends until it reaches while, the pressure built up in the main cylinder by the resistance of the workpiece backs up in the conduits 59 and 60 and chamber Bl, where it acts against the centering piston area 82 to overcome the thrust of the coil spring 61 and pull the pump flow-control rod 63 and shiitring to their neutral position. The pump H then holds the pressure upon the main plunger 25 at a predetermined maximum, depending upon the thrust of the spring 61 as adjusted by the hand wheel 66.

When the timing motor Hil has run the course for which it has been set, it separates the contacts 95 and 96, breaking the circuit between the lines 91 and 94 and deenergizing the coil 85 of the contactor IS. The latter then opens, deenergizing the winding 84 of the solenoid ii.

The coil spring 43, which has been compressed,

by the energization of the solenoid l'i, now pushes the valve plunger 42 downward into engagement with its seat, closing of! communication between the chambers 46 and 45 and ending the by-passing of the pilot pump l4 through the' conduits 4B and 41. The pilot pump It then delivers pressure fluid through the line 1| into the left-hand end of the pump-reversing cylin- .1

der HI, causing the large piston head 69 to overcome the thrust of the coil spring 61 and shift the pump flow-control rod 63 and shift ring past their neutral positions into their reversed positions. The pump ll, thus reversed, discharges pressure fluid into the conduit 12 and push-back cylinders 28, forcing the push-back plungers 21,

main ram 28 and main plunger 25 upward upon their retraction or return strokes. At the same time the pump ll withdraws fluid from the main cylinder 24 by way-of the conduit 59.

When the main ram or platen 26 nears the end of its return or retraction stroke the arm 29 engages the coil spring 40 and lifts the control rod 3| by means of its head 39. This forces the valve-lifting plunger 4| upward a short distance so that it lifts the valve plunger 42 slightly on its seat 54. This action permits the pressure in the conduit H to be relieved-slightly by a slight by-passing through the conduits 48 and 41, thus permitting the pump flow-control rod 63 and shift ring to return to their neutral or no-delivery positions. When the platen 26 tends to descend, however, the platen arm 2! releases the coil 'spring 40 and permits the control rod 3i, valvelifting plunger 4| and valve plunger 42 to descend,

ending the by-passing' action and permitting the pressure to be raised by the pilot pump l4 inthe conduit "II and reversing cylinder 10. In this manner the shift ring of the pump H is mainthe end of its retraction stroke, and the main ram 26 is held in its raised position and prevented from coasting downwardly.

It will be understood that I desire to comprehend within my invention such modifications as come within the scope of the claims and the invention.

Having thus fully described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A hydraulic press control system comprising in combination, a liquid operable and reciprocable main plunger, a reversible pump for supplying pressure fluid to actuate said main plunger in opposite directions, a. pilot pump feeding a hydraulic circuit for reversing said reversible pump, valve means controlling the supply of liquid from said pilot pump to said reversing circuit, means normally biasing said valve meansinto one position, a press control element comprising two axially aligned unconnected parts mounted for movement parallel to said main plunger, an electric operator having means connecting the same to the first of said parts whereby .energization of said electric operator will operate said first part, said valve being connected to the first of said parts and adapted to be actuated thereby against said biasing means, means on said second part whereby the same may be actuated by said main plunger during part of its movement in one direction, bothof said parts being actuated in the same direction by said main plunger and said electrical operator, additional means on said second part whereby actuation by said secondpart, when the same is moved by said additional means, and means actuated by said switch for de-energizing said electric operator whereby said biasing means moves said valve means to reverse said reversible pump and cause the retraction of said main plunger.

2. The combination as claimed in claim 1 including a timing device adapted to be energized by the operation of said electric switch for delaying de-energization of said electric operator for a predetermined period of time.

WALTER ERNST.

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