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Publication numberUS2241556 A
Publication typeGrant
Publication dateMay 13, 1941
Filing dateJun 20, 1938
Priority dateJun 20, 1938
Publication numberUS 2241556 A, US 2241556A, US-A-2241556, US2241556 A, US2241556A
InventorsHoward F Macmillin, Thoreson Reider
Original AssigneeHydraulic Dev Corp Inc
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Photoelectrically controlled press
US 2241556 A
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Description  (OCR text may contain errors)

y 1941- H. F. M MlLLlN ETA;- 2,241,556

PHOTOELECTRIGALLY CONTROLLED PRESS Filed June; 20, 1938 3 Sheets-Sheet 1 ljl.

Jmoubon HOWARD EMAcM/LLIN. REIDER THORESON,

May 13, 1941. H. F. M MlLLlN EI'AL 2,241,556

PHOTOELECTRICALLY CONTROLLED PRESS Filed JuneQgZO, 19 38 3 Sheets-Sheet 3 .T uwu.

HOWARD F. MncMILLIN, REIDER THORESON,

QS JAW 1; SW

Patented May 13, 1941 2,241,556 PHOTOELECTRICALLY CONTROLLED mmss Howard F. MacMillin, Mount Gilead, Ohio, and

Reider Thoreson, Birmingham, Mich., assignors to The Hydraulic Development Corp. Inc., Wilmington, Del., a corporation of Delaware Application June 20, 1938, Serial No. 214,852

Claims.

This invention relates to press control systems, and in particular, to electrical systems for controlling presses.

One object of this invention is to provide a photoelectric circuit for controlling the plunger movements of a hydraulic press in such a manner that the press plunger remains inoperative if the light beam for actuating the photoelectric circuit becomes broken.

Another object is to provide a photoelectric press control system, wherein the press control circuit is arranged selectively for full automatic or semi-automatic operation, but under the control of a photoelectric circuit having a light beam extending across a portion of the press in position for interruption by the hands or body of the operator, so that the light beam must be uninterrupted if the circuit is to be energized.

Another object is to provide a press control system arranged for full automatic or semi-automatic control of the press, this system including a photoelectric circuit having a light beam which when uninterrupted actuates a relay to complete the energization of the press control circuit but which, when interrupted, as by the hands or body of the operator, deenergizes the relay and accordingly deenergizes the press control circuit, thereby making it temporarily impossible to operate the press and endanger the operator.

In the drawings:

Figure 1 is a diagrammatic front elevation of a press partly broken away, and showing the installation of the photoelectric system in a typical press installation.

Figure 2 is a horizontal section through the press shown in Figure 1, taken along the line 2-2 therein.

Figure 3 is a horizonta1 section similar to Figure 2, but showing a modification.

Figure 4 is a horizontal section similar to Figures 2 and 3, but showing a further modification.

Figure 5 is a wiring diagram of the photoelectrically controlled press circuit of this invention.

General arrangement In general, the photoelectrically controlled press circuit of this invention consists of an electrical circuit having electrical means for operating the contro1 rod for controlling the distribution of pressure fluid to the press. This electrical operating means is energized by a circuit in such a manner as to provide for semi-automatic or full automatic operation of the press. Semi-automatic operation occurs when the ram executes a pressing stroke, halts, returns to its retracted position and again halts until the circuit is again energized by the operator. Full automatic operation occurs when the press ram immediately reverses upon returning to its retracted position and executes another pressing stroke, without the intervention of the operator, thereby repeating an indefinite number of pressing and retraction strokes until halted by the operator. Arranged to be intercepted by the arms or body of the operator is a light beam for operating a photoelectric circuit disposed in such a manner that the light beam will be broken or interrupted when the operator is loading or unloading the press. The photoelectric circuit is so arranged that a relay controlling the energization of the press control circuit is energized and closed as long as the light beam remains unbroken, but is deenergized and opened when the light beam is broken, as by the'hands or body of the operator.

Referring to the drawings in detail, Figure 1 shows diagrammatically a press equipped with the photoelectric control system of the invention. This press consists of a bed I0 andhead II, interconnected by side members l2 and held together by strain rods l3 with nuts l4 threaded upon their opposite ends. The press side members I2 contain guideways l5, which are engaged by the guide plates l6 secured to the press platen W for guiding the latter in its reciprocation. The platen H is secured to the main plunger 1 8, which 'reciprocates in the main cylinder lB mounted in the press head ll.

Above the main cylinder 89 is mounted the surge tank 20 for containing the operating fluid, such as oil.

Also mounted upon the press head I l is an electric motor 2 I, arranged to drive a pump 22, preferably of the reversible variable delivery type. The pump 22 .is provided with junctions 23 and 24 for the connection of pipes 25 and 26 for delivering pressure fluid fromthe pump 22 to the remainder of the hydraulic circuit. The details of the hydraulic circuit and pump control circuit in themselves form no part of the present invention and may be of any suitable type. A typical pump control circuit is disclosed and claimed in the Ernst Patent No. 2,038,272 of April 21, 1936. The reversible variable delivery pump 22 is preferably of the radial piston type having a servomotor for shifting the flow-control member or shift ring thereof under the direction of a servomotor control valve operated by a valve rod, as set forth in the above-mentioned patent.

The servomotor valve rod of the pump 22 is connected, through suitable linkage (not shown),

to a final link 21 (Figure 5) attached to one arm of a bellcrank 28 pivoted upon the shaft 28. The

other arm of this bellcrank 28 is connected to the platen II to move downwardly. When the solenoid 3| is deenergized, however, the pressure fluid from the pump 22 is redirected to cause the main plunger I8 and platen II to move upwardly. The servomotor valve rod of the pump 22 is also mechanically connected to the control rod 33 of the press in such a manner as to be actuated manually. For this purpose the control rod 33 is mounted in brackets'34 and 35, attached respectively to the head I I and bed I8 of the press. The platen I1 is also provided with an arm 36, which serves to actuate the control rod 33 to shift the pump servomotor valve when the platen arm 36 reaches either of the collars 31 or 38 upon the control rod 33. The control rod 33 may also be moved manually by means of the yoke bellcrank lever 33 engaging the control rod 33 between the spaced collars- 48, and having a hand lever M for actuating this mechanism. The bellcrank lever 39 is mounted upon a jack shaft 42, supported upon the bed I8 of the press.

Mounted upon one side of the press is a light source and photocell unit 43, cooperating with a mirror unit 44 upon the opposite side of the press. The unit 43 contains a pair of electric light bulbs 45 and a pair of photoelectric cells 46 connected electrically, as shown in Figure 5, in a manner subsequently to be described. The light coming from the light bulbs 45 is rendered parallel by the lenses 41, and passes in beams 48 of parallel rays to the mirrors 49 and 58, where it is reflected and returned to lenses 5| focused upon the light sensitive elements in the photoelectric cells 46. Thus, if any object intercepts any of the light beams 48, the light reaching the photocells 46 is cut oil? and the control circuit is actuated in a manner to prevent the occurrence of the forward stroke of the main plunger I8 and-platen I1, as described below.

Electrical system Referring to Figure 5, the electrical system for controlling the press is energized by-a pair of power lines 52 and 53. The electrical system consists of a number of difierent units, each containing a number of electrical elements. The arrangement of the photocell and light source unit 43 has already been described. This unit,

however, also contains a transformer 54 for eneranode and the cathode, and the electron flow takes place from the cathode to the anode, and in this manner carries an electric current. The value of this current is determined by the amount of light falling upon the cathode.

The circuit is also provided with a photo! electric relay unit, generally designated 55. This unit includes a. so-called pliotron tube 56, an adjusting potentiometer 51, a sensitive relay 58 under the control of the pliotron tube 56, a heavyduty relay 59 under the control of the sensitive relay 58, a photocell transformer 68 for applying the voltage betweenythe anode and cathode of the photocells 46, a transformer 6| for supplying current to energize the filament 62 of the pliotron tube 56, and a transformer 63 for supplying current to the photoelectric relay unit 55. Condensers 64 and 65 and a high impedance 66 are also included in the photoelectric relay unit 55.

The electrical control system is provided with a push-button switch unit 61 containing a pair of forward push-button switches 68 and 68, a reverse push-button switch I8, a signal light II and a resistor I2. Also provided is a hand automatic switch I3, which when opened, enables the circuit to be operated only by hand, and when closed permits the full automatic or semi-automatic energization of the circuit. The photoelectric system is energized whenever the automatic selector switch I3 is closed in the manner shown in Figure 5. The selection of the type of automatic control is determined by the automatic selector switch I4, which when open, permits only semi-automatic operation of the circult, but which when closed, permits full operation with an indefinitely repeated number of pressing and retraction strokes of the press.

Elsewhere on the press is mounted a normally closed forward limit switch I5 for limiting the forward stroke of the press. This forward limit switch I5 may be either pressure-responsive or position-responsive. If pressure-responsive the switch I5 is opened when the pressure within the press circuit reaches a predetermined amount. If, however, the switch I5 is position-responsive, it is opened by the platen or mechanism connected thereto when the platen reaches a predetermined position on its forward stroke. The switch I5, for example, may be operated by the control rod 33 (Figure i) when the platen arm 36 reaches the collar 38. Whatever the manner of actuating the forward limit switch I5,how-

ever, its actuation, causes the reversal of the press operating circuit to reverse the travel of the main plunger l8 and platen II. Also mounted elsewherein the press is the normally open retraction limit switch I6. This switch is arranged to be closed when the press platen II reaches its upper or retracted position, such as when the platen arm 36 (Figure 1) engages the collar 31 upon the control rod 33.

Arranged to be controlled by the current from these various elements is a contactor switch unit 11 (Figure 5) having an operating coil I8 and normally open switch bars I9, 88 and 8| mounted upon the armature rod 82. The switch bars 88 and BI serve directly to energize the solenoid winding 32 when the contactor operating coll I8 is energized, whereas the switch bar I3 serves to maintain a holding circuit for the energization of the operating coil I8. The press control sys-- tem is so arranged that when the solenoid winding 32 is energized the platen I1 and main plunger l8 will move downwardly upon a pressing stroke, whereas when the solenoid winding 32 is deenergized they will move upwardly upon a retraction stroke.

The pliotron tube 56 contains the filament 62, previously described, and also an anode 83 and a grid 84. When the pliotron tube 56 is energized from the transformer M a stream of electrons flows from the cathode or filament 62 to the anode 83. The grid 84, however, regulates the flow of electrons, depending upon the amount of positive charge on the grid 84. By passing the photocell current through the high imped-, ance 66-and applying the resulting voltage to the pliotron grid 84', the pliotron current is placed under the control of the current from the photocells 46 and hence is controlled by the amount of light falling upon the cathodes of the photocells 46. This pliotron current flowing from the anode 83 is of suflicient strength to actuate the sensitive relay 58, closing the switch bar 85 thereof, and consequently energizing the relay 59 to close its switch bar 86. By adjusting the potentiometer 51 the current can be controlled in such a manner that the sensitive relay 58 is energized sufficiently to close its switch bar 85 when precisely the desired amount of light strikes either of the photocells 46 from the light sources 45.

Operation Assuming that the operator has closed the 20.

switch I3 is kept open and the press can then;

only be operated by manually moving the control rod 33, as by the hand lever 4I. If it is desired to operate the press automatically; however, the hand automatic switch 64 is closed. When th1s switch is closed the press will operate in either a semi-automatic or automatic cycle, depending upon the setting of the automatic selector switch I4. If the switch I4 is kept open, semi-automatic operation occurs so that the operator must start each new pressing cycle of the press by closing the forward switches 68 and 69. If the switch I4 is closed, however, full automatic operation occurs so that once the operator has closed the forward switches 68 and 69, the press plunger I8 and platen I1 continue to execute an indefinite number of pressing and retraction strokes as long as the circuit is energized, unless it is temporarily deenergized by opening the reverse switch 18 or by interrupting the light beam 48 to deenergize theheavy-duty relay 59.

When the hand automatic switch I3 is closed, the photoelectric cell unit 43 and photoelectric relay unit 55 are energized by current flowing from the power line 53, through th line 81, the

hand automatic switch 13, the lines 88, 89 and 98, the primary winding of the transformer 63 and th lines 9I and 92 leading to the power line 53. The same energization of the line 98 also energizes the primary windings of the transformers 68 and 6| by way of the lines 93 and 94, arranged to bridge the lines 98 and 9I. The transformer 68, when energized, produces a voltage between the anode and cathode of the photocells 46, through the lines 95, 96 and 91 and the condenser 64. The light sources 45 are energized, through the lines 98, 99, I88 and I8I, by the energization of the transformer 54, the primary of which is energized through the lines 92 and I82 bridging the power line 83 and the line 5 89, the energization of which has been previously described.

The energization of the primary winding of the pliotron transformer 6I supplies current through the lines I83 and I84 to energize the filament or cathode 62 of the pliotron tube 56. The midpoint of the secondary winding of the pliotron transformer 6I is connected to the line I85 leading from the secondary winding of the transformer 63 to the movable contact or slider I86 of the potentiometer 61. The opposite end of the secondary winding of the transformer 63 is connected by the line IN to the sensitive relay 68, the opposite side of which is connected by the line I88 to the anode 83 of the pliotron tube 56. The line 98 terminates at the contact I89 opposite the relay switch bar 85, from which the line I I8 runs to the heavy-duty relay 59, the opposite side of which is connected to the line 9|. With the hand automatic switch 13 and automatic selector switch I4 closed, the entir photoelectric circuit is thus energized and the signal light II is illuminated through the resistor I2 and the lines III and H2 leading respectively to the lines 89 and H3, the latter leading to the line II4 which is connected to the power line 53.

To start the press in full automatic operation so that it will execute an indefinitely repeated number of pressing and retraction strokes, the operator now depresses both of the forward switches 68 and 69. By supplying two switches the operator is obliged to use both hands in starting the press, hence, cannot get his hands in the path of the platen, with possible danger of injury. When the push-button forward switches 68 and 69 are closed, the operating coil I8 of the contactor switch I1 is energized. This takes place by current passing from the power line '53, through the lines H4 and H3, the now closed forward push-button switch 69, the line II5, the now closed forward push-button switch.68, the lines H6 and N1, the heavy-duty relay switch bar 86, which is now closed upon its contacts by the energization of the photocell circuit, the line I I8 leading to the operating coil I8, the lines 89 and 88, the hand automatic switch I3 and the line 8! leading to the power line 52. The

energization of the operating coil I8 closes the contact switch bars 88 and BI upon their contacts, energizing the winding 32 of the solenoid 8i.

Thesame operation closes the switch bar 19' upon its contacts, and thereby energizes a hold ing circuit for the operating coil I8 when the forward push-button switches 68 and 69 are released by the operator. This holding circuit runs from the power line 53, through the line II4, the now closed contactor switch bar I9, the line I28, the forward limit switch I5, the line I2I, the normally closed reverse switch I8, the line I22, the line 1, the now closed switch bar 86 of the heavy-duty relay 59, the line II8, the contactor switch operating coil I8, the lin 89, the hand automatic switch I3 and the line 81 leading to the power line 52. I

Thus, the solenoid 3| remains energized when the forward push-button switches 68 and 69 are released, thereby drawing down the solenoid armature 38 and shifting the belldrank 28 and the rod 2! to set the servomotor control valve of the pump 22 in a position to cause the pump 22 to deliver pressure fluid to the main cylinder I9 to force the main plunger I8 and platen II downwardly upon a forward or pressing stroke. Assumlng that nothing is interposed in the light beams 48 to break the path thereof, the heavyduty relay 59 remains closed with its normally open switch bar 86 engaging its contacts, and the press platen I"I moves downwardly upon a pressing stroke until the forward limit switch I5 is opened. If 15 is a pressure-responsive switch it will be actuated in response to the building up i of a predetermined pressure against the platen I'I, whereas if it is a position-responsive switch it will be actuated when the platen II reaches a predetermined position, as heretofore described. In either case, the opening of the forward limit switch 15 breaks the holding circuit for the operating coil 18 of the contactor switch 11, deenergizing it and consequently opening its switch,bars I8, 88 and 8| and deenerg'izing the solenoid winding 32.

When this occurs the pump servomotor control valve of the pump 22 is shifted, as by a spring, so as to reverse thedelivery of fluid from the pump 22 and to cause the platen I1 and main plunger I8 to execute a retraction stroke. The platen I1 moves upwardly until its arm 36 engages the collar 31, raising the control rod 33 and shifting the pump control into a neutral delivery position so that the delivery of pressure fluid is terminated, either to or from the main cylinder I8. In this position, therefore, the main plunger I8 and platen I1 would come to a halt if the automatic selector switch I8 were open, hence, a semiautomatic pressing cycle will have been accom- V plished. To start the platen H on another forward stroke with the automatic selector switch I4 open, it is necessary for the operator to again depress the forward push-button switches 88 and 69.

In the present description of the operation, however, it has been assumed that the operator has closed the automatic selector switch I4 in order to bring about full automatic operation so as to cause the press platen II to execute an indefinite number of pressing and retraction strokes. As the platen arm 36 moves upwardly to engage the collar 31 and lift the control rod 33, the upward motion of the latter lifts the cam collar I23 and closes the normally open retraction limit switch I6 (Figures 1 and before the control rod 33 has risen a suflicient distance to place the pump control in a neutral or no delivery position. The closing of the retraction limit switch I8 completes an energization circuit, which bridges around the now open forward push-button switches 68 and 68. This bridging circuit runs from the line II3 (which is already connected through the line I I4 to the power line 53), through the now closed switch bar of the retraction limit switch I8, the line I24, the now closed automatic selector switch I4, the line II, the now closed switch bar 86 of the heavy-duty relay 58, the line II8, the contactor switch operating coil I8, the lines 83 and 88, the hand automatic switch 13 and the line 81 leading to the power line 52.

The energization of the contactor switch operating coil I8 again closes its switch bars I8, 88 and 8|, energizes the holding circuit through the switch bar I8 and also energizes the solenoid coil 32 through the switch bars 88 and 8I. The energization of the solenoid 3| again draws downwardly its armature 38 and again shifts the control' of the pump 22 to its forward delivery position. The plunger I8 and platen I1,.therefore, start downwardly upon another pressing. stroke, after halting only momentarily at the top of the retraction stroke. therefore be executed in the foregoing manner, and retraction will occur when the forward limit switch 15 is opened, either by pressure or by the platen reaching a predetermined position, as

' heretofore described, and the press platen I1 will execute an indefinite number of'uninterrupted pressing and retraction strokes.

If, however, the operator has not completed his unloading or loading of the press, or for any reason is not clear of the press at the time the Another pressing stroke will,65

platen I'I starts downwardly upon another pressing stroke, his hands or body or the article being worked upon will obstruct the light beam 48. When the light beam 48 is thus interrupted the light no longer falls in sufficient quantity upon the photocells 48, and hence, an insuflicient amount of current reaches the pliotron grid 84 through the line 86 and resistor 68 sufllcient to supply enough current from the pliotron anode 83, through the line I88, to keep the sensitive relay 58 energized. As a consequence, the sensitive relay switch bar 86 flies open, thereby deenergizing the operating coil of the heavy-duty relay 58, the switch bar 88 of which also flies open. When this occurs the circuit between the lines Ill and H8 is broken, thereby deenergizing the contactor switch operating coil I8, consequently deenergizing the solenoid 32 and placing the pump control in a reverse delivery position to bring about a retraction stroke of the platen I! and plunger I8, in the manner previously described. Thus, the operator will be protected, and the main platen II will be prevented from moving downwardly until the operator removes his hands or finishes his unloading or loading operation.

Moreover, reversal of the pump control to bring about a retraction stroke of the platen will also automatically take place in the same manner if the operator interposes his hands or any opaque object in the path of the light beam after the platen has-already commenced its downward or forward stroke.

When this has been finished and as soon as the light beam 48 is no longer obstructed, the current in sufficient quantities again flows along the line 86 to the pliotron grid 84, causing sufficient current to flow along the line I88 from the anode 83 to reenergize the sensitive relay 68 and thereby again closing the previously broken circuit between the lines I I1 and I I8, and permitting the operating coil 18 of the contactor switch 'II to be reenergized. Thus, the solenoid winding 32 will be reenergized and the pump control placed in a forward delivery position to cause the press platen H to move downwardly upon a forward stroke as soon as the interruption of the light beam 48 is terminated and the light beam again strikes the photoelectric cells 46. In this manner the operator is completely protected against injury if he is delayed in removing his hands from the press before the platen starts downwardly. This photoelectric press control system, therefore, removes a serious hazard which has previously endangered the operator in the operation of a press under a full automatic system of operation.

Modified arrangements The modified arrangement shown in Figure 3 employs mirrors I38, I3I and I32, placed at three corners of the press so that the light beam 48 will pass completely around the four sides of the press from the light source 45 to the photocell 46. The arrangement shown in Figure 3, therefore,

protects not only the front and back of the press,

relay 59 and the consequent deenergization of the .contactor operating coil 18 with the subsequent in principle to that shown in Figure 3 in that it protects all four sides of the press by photoelectric light beams instead of merely the front and back of the press. The arrangement shown in Figure 4 differs from that shown in Figure 3 in that no mirrors are employed, but in their stead four complete sets of photocell units, comprising the light-source 45 and photocell 4B, are used, each photocell unit protecting a single side of the press. The operation, however, and the result are similar to those obtained in Figure 3, but a more positive operation is insured because the intensity of the light beam will not be retarded by the deterioration or dust coating of the mirrors I30.

It will be understood that we desire to comprehend within our invention such modifications as come within the scope of theclaims and the invention.

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

1. In a press control system for a hydraulic press, a reciprocable platen, a hydraulic motor for moving said platen in the forward and reverse directions, a reversible variable delivery pump having a pump flow-controller therein, an electrical control circuit for controlling the actuation of said platen-moving means and including electromagnetic means connected to said flowcontroller for automatically shifting said flowcontroller to control the motion of said hydraulic motor and platen in response to the attainment of predetermined conditions during the power driven working and power driven return strokes of said platen for effecting completely automatic operation of said platen, a photoelectric circuit having its light beam extending across an access opening to said platen, and means responsive to the interception of said light beam for altering the electrical condition of said electrical control circuit instantaneously to reverse the power driven motion of said hydraulic motor upon the occurrence of said interception during forward motion of the platen.

2. In a press control system for a hydraulic press, a reciprocable platen, a hydraulic motor for moving said platen in the forward and reverse directions, a reversible variable delivery pump having a pump flow-controller therein, an electrical control circuit for controlling the actuation of said platen-moving means and including electromagnetic means connected to said flow-controller for automatically shifting said flow-controller to control the motion of said hydraulic motor and platen in response to the attainment of a predetermined condition during the power driven working and power driven return strokes of said platen for effecting completely automatic operation of said platen, a photoelectric circuit having its light beam extending across an access opening to said platen, and relay means having a circuit interrupter disposed in said electrical circuit, said relay means being responsive to the interception of said light beam for shifting said circuit interrupter to alter the electrical condition of said electrical control circuit instantaneously to reverse the power driven motion of said bydraulic motor upon the occurrence of said interception during forward motion of the platen.

3. In a press control system for a hydraulic press, a reciprocable platen, a hydraulic motor for moving said platen in the forward and reverse directions, a reversible variable delivery pump havinga pump flow-controller therein, an electrical control circuit for controlling the actuation of said platen-moving means and including electromagnetic means connected to said flow-controller for automatically shifting said flow-controller to control the motion of said hydraulic motor and platen in response to the attainment of a predetermined condition during the power driven working and power driven return strokes of said platen for effecting completely automatic operation of said platen, a photoelectric circuit having its light beam extending across an access opening to said platen, and relay means having a circuit interrupter disposed in said electrical circuit, said relay means being responsive to the interception of said light beam to release said circuit interrupter and open said electrical control circuit instantaneously to reverse the power driven motion of said hydraulic motor upon the occurrence of said interception during forward motion of the platen.

4. In a press control system for a hydraulic press, a reciprocable ram, a hydraulic motor connected thereto, a reversible variable delivery pump having a flow-controller therein for reversing the delivery of pressure fluid from said pump to said hydraulic motor to operate said ram upon the power driven working and power driven return strokes, electrically-actuated means for shifting said flow-controller, an electrical circuit for controlling the energization of said electrically-actuated shifting means, a photoelectric circuit power driven motion of said hydraulic motor upon the occurrence of said interception during forward motion of the platen.

5. In a press control system for a hydraulic press, a reciprocable ram, a hydraulic motor connected thereto, a reversible variable delivery pump having a flow-controller therein for reversing the delivery of pressure fluid from said pump to said hydraulic motor to operate said ram upon the power driven working and power driven return strokes, electrically-actuated means for shifting said flow-controller, an electrical circuit for controlling the energization of said electrically-actuated shifting means, a photoelectric circuit having its light beam extending across an access opening to said ram, and an electrical relay means having a circuit interrupter disposed in said electrical circuit, said relay means being responsive to the interception of said light beam for altering the electrical condition of said electrical circuit to alter the energization of said electrically-actuated shifting means, and instantaneously reverse the power driven vmotion of said hydraulic motor upon the occurrence of said interception during forward motion of the platen.

HOWARD F. mom-1m. REIDER 'IHOREBON.

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Classifications
U.S. Classification192/130, 83/DIG.100, 60/911
International ClassificationF16P3/14
Cooperative ClassificationF16P3/14, Y10S60/911, Y10S83/01
European ClassificationF16P3/14