US2353389A - Apparatus for controlling the slide movement in long-bed hydraulic presses - Google Patents

Description

y 9 4- E. CANNON 2,353,389

APPARATUS FOR CONTROLLING THE SLIDE MOVEMENT IN LONG-BED HYDRAULIC PRESSES Filed March 16, 1943 3 Sheets-Sheet 1 lNVENTOR 562?! daw/van BY AT ORNEYS July 11, 1944. E. CANNON APPARATUS FOR CONTROLLING THE SLIDE MOVEMENT IN LONG-BED HYDRAULIC PRESSES Filed March 16, 1943 5 Sheets-Sheet 2 1062 108 c s /a63/ INVENTOR 47,9?! Chm MGM BY 2 d, w P

AT ORNEYS Patented July 11, 1944 APPARATUS FOR CONTROLLING THE SLIDE MOVEMENT LONG-BED HYDRAULIC PRESSES Earl Cannon, Rockville Centre, N. Y., assignor to E. W. Bliss Company, Brooklyn, N. Y., a. corporation of Delaware Application March 16, 1943, Serial No. 479,308

23 Claims.

This invention relates to improvements in apparatus for controlling the slide movement in long-bed hydraulic presses, and more particularly relates to improved means for maintaining the slide of such a press substantially in parallelism with the press bed during the advance or downward movement of said slide despite any die or blank irregularity which might tend to induce tilting of the slide.

Any reference in the following specification and claims to parallelism or"non-parallelis is intended to relateto the attitude of the slide of a press relatively to the bed of the press. Any reference herein to long-bed" presses is, intended to refer to any hydraulic press wherein the present invention may be employed advantageously to-maintain, substantially, the mentioned parallelism of the slide and bed of the press.

An important object of the present invention is the provision of improved means for automatically effecting compensating variations in the delivery of liquid to plural rams located at various points along the slide of a long-bed press whereby to substantially compensate for initial inequalities in such delivery caused by unequal resistance offered to the advance of the press slide at various points thereon, as, for example, unequal resistance which might be offered by a die of irregular shape. r

A further object of the invention is the provision of improved means for electrically con.- trolling apparatus adapted to effect compensating variations in the delivery of liquid to such plural rams. The invention disclosed herein comprises improved means for accomplishing the foregoing and other objects which should be apparent from this specification and the accompanying drawings.

The present invention is a further embodiment of certain features disclosed in my copending applications filed September 26, 1942, and October 28, 1942, under Serial Nos. 459,854 and 463,604, respectively, and, in certain respects, constitutes improvements thereover. Said application Serial No. 459,854 has been issued as Patent 2,328,258, dated Aug. 31, 1943. The details of various component parts of the structure described herein are fully set forth in said co-pending applications and therefore the description in the present application is limited to such details as are necessary to an understanding of the improvements illustrated and claimed herein. The means disclosed in said co-pending Patent 2,328,258, are chiefly mechanical means which are employed to effect compensatory transfer of liquid from a liquid supply for a ram or rams toward one end of the press slide to a liquid supply for a ram or rams toward the opposite end of the slide. The improvements disclosed in said co-pending application, Serial No. 463,604, reside principally in certain electrical or pneumatic apparatus and circuits which are employed to derive a response from non-parallelism and to control such a compensatory transfer of liquid.

The improvements of the present invention are directed toward the provision of improved electrical, pneumatic and mechanical apparatus and combinations thereof, adapted to function to maintain substantial parallelism. and being of a character which yields a highly sensitive compensation to non-parallelism and obviates the use of certain sliding electrical contacts employed in the structure disclosed in said application No. 463,604.

For the purpose of illustrating the present invention and without limiting the invention thereto, a preferred embodiment thereof is shown in the accompanying drawings, in which:

Figure 1 is a perspective View illustrating the application of the present invention to a longbed press;

Fig. 2 is a horizontal sectional view taken substantially on the line 2-2 of Fig. 1 and on the line 22 of Fig. 3.

Fig. 3 is a vertical sectional view taken substantially on the line 33 of Fig. 2;

Fig. 4 is a. flattened semi-circular sectional view taken on the line 4-4 of Fig. 3; and

Fig. 5 is a diagram illustrating the various component parts of the present embodiment of the invention and the interconnection of said parts.

Referring first to Fig. 1, the press with which the invention is illustrated may comprise a long-bed ll provided in a base l2 suitably tied at its opposite ends to a crown l3 by tie-rods I 4 extending through slide housings I5 which serve at least partially, to guide a verticallyreciprocating slide l6 and to suitably space apart the said crown and bed and to maintain the two latter members fixedly in their proper relationship. Tie-rod nuts ll preferably are provided at the upper and lower ends (the latter are not visible in the drawings) of the said tierods.

The slide I6 is reciprocated in a well understood ,manner by rams Illa and l8b, fixed symmetrically upon the slide toward opposite ends thereof. These rams, as best understood from Fig. 5, may be enlarged at their upper ends to form ram pistons 19a, [9b and may be urged downwardly on their advance strokes by liquid introduced into advance chambers 20a, 20b and upwardly on their return strokes by liquid introduced into return chambers Zia, 2lb. The said chambers of the general character indicated in Fig. may, of course, be suitably formed within the crown [3 of the press.

Separate substantially identical pumping systems are provided for handling the supply of liquid for operating each of the rams I 8a and Nb. Describing in detail only the said pumping system which is related toram l8a, it comprises a continuously-acting pump 22a suitably driven as by an electric motor (not shown). The said pump receives liquid from a supply tank 23 through pipe 24a and pumps said liquid through pipe 25a into a distributing slide valve 26a, which, depending upon the position of a piston 21a therewithin, directs the liquid either through a pipe 28a to the ram advance chamber 20a to move the ram I811 downwardly or through a pipe 29a to the ram return chamber 2la to move the said ram upwardly, or through a pipe 30a back to the tank 23 when it is desired that the ram remain substantially at rest. The mentioned liquid distribution yielding the said ram movements is controlled largely by the provision on the piston 21a of three enlarged portions or spools 31a, 32a. and 33a and intervening neck portions 34a and 35a.

When it is desired to advance the ram l8a (i. e., move it downwardly) to advance the slide l6 toward the bed I I and a die and blank thereon, the piston ZIa'is shifted, by any suitable means, to its extreme left position as shown in Fig. 5, whereupon liquid entering the valve 26a, through pipe 25a, passes around neck portion 34a, of the said piston, into pipe 28a, and thence to the ram advance chamber 20a, thereby forcing the ram l8a downwardly while liquid is exhausted from the ram return chamber Ila through pipe 29a into the valve 26a, wherein the exhaust liquid passes around neck 35a of said piston to pipe 30a which carries it to the tank 23. By shifting the piston 21a, to its extreme right position, the flow of liquid is reversed with respect to the said ram chambers thereby causing the ram l8a to pursue its upward or return movement.

When it is desired to arrest the movement of the ram la, the piston 21a, may be moved to its mid-position, in which the several mentioned spools on said piston close off all liquid communication between the pump 22a and the ram chambers 20a and 21a. However, the liquid, continuing to be discharged by the pump 22a passes from pipe 25a into interior lateral passage 36a in the spool 32a, thence through longitudinal passage 3la into lateral passages 38a, 39a, in the spools 3 la and 33a, whence said liquid passes into pipe 30a which carries it to the tank 23.

In view of the similarity of the pumping systems for actuating the two rams, the foregoing description is intended to suffice for both. For this reason, the similar parts of the pumping systems are given reference characters, in the drawings and hereinafter in the specification, differing only in their sumxes, the suffix a being applied to parts of the pumping system related to ram I81: and the sumx b being applied to parts of the pumping system related to ram l8b. Both valves 26a and 261) function alike and may be constrained to function in unison by having their respective pistons tied together by extension rods 40a and 40b which preferably are adjustably coupled by a turnbuckle 4 I. The said plstonsmay be hifted within their respective valves by any suitable means to control the reciprocation of th press slide. Such means, for example, may be operated manually, electrically, by compressed air, or by hydraulic pressure.

As illustrated in the accompanying drawings, an electric solenoid 42 may suitably be connected as by a pin 43 to an end extension 44 of the piston 21a. The said solenoid is adapted, when energized, to move the pistons 21a and 21b to their left'po'sitions, as shown in the drawings, to cause downward movement of the press slide I6 Another solenoid 45 may be similarly connected tothe piston 21b for moving both pistons to their right positions to cause upward movement of the press slide. The two said solenoids, of course, are connected in suitable electric circuits for controlling the operation of the press.

The pistons 21a, 2117 may be held yieldably in their mid-positions by any suitable means which, for example, may employ springs or air or hydraulic pressure. As illustrated in the accompanying drawings, a spring-centering device is employed comprising a coil-spring 46 which is positioned about the extension rod 401) and is compressed between washers 41 which, normally, are held against the end of said spring by collars 48 formed on or fixed on the rod 40b. A cagelike frame 49 is fixed upon some fixed part of the press or other suitable fixed support in such position, adjacent the rod 40b, that the latter passes through holes 50 in the ends of said frame, large enough to freely pass the said collars 48 but small enough to confine the washers 41 within the said frame. Thus, when the pistons 21a and 21b are held in their left positions, as illustrated in the drawings, by the energized solenoid 42, the spring 46 is exerting compression upon the right washer 4'! and the right collar 48 which, when the said solenoid is de-energized, will cause the said pistons to move to their mid-positions. A similar, but opposite action of the centering device results when the said pistons are held in their right position by the solenoid 45 and the latter is then de-energized.

Although the pumping systems for operating the ram [8a ad MD, as thus far described in detail, may be substantially identical in design, it will be appreciated that, where resistance to the advance of the slide is not uniformly distributed thereover, the different slippages in the two pumps, slight leakages, and possibly other factors, would cause the side or end of the press slide encountering the least resistance to advance ahead of the other side thereof and this uneven advance or cocking of the slide, in manw instances, would become more pronounced as the slide progressed toward the end of its advance stroke. This highly undesirable functioning of the press may be substantially obviated by compensating means now to be described in detail.

An important feature of this invention is the provision of quick acting automatic means for substantialy equalizing the supply of liquid to the which carries the liquid supply to ram advance chamber 20a and connected by a pipe 53 to the pipe 28b which carries the liquid supply to ram advance chamber 201:.

. herein described in detail.

The compensator pump may be a continuously-acting reversible pump suitably driven as by an electric motor (not shown) The said compensator pump further is preferably provided with a pumping mechanism which is adjustable, by movable means which extend to the exterior of the pump itself, for reversing the flow of liquid through the pump and for controlling the volume of such flow. Although various types of pumps having. pumping mechanisms conforming to these preferred characteristics may be used, a pump of the so-called "Hele-Shaw type such as is illustrated and described in my said co-pending application, Serial No. 459,854, is well suited to the purpose of the present invention.

As the particular control mechanism employed in the compensator pump is not an essential part of the present invention, the said pump is not It is sufficient to observe for present purposes that the flow of liquid through the pump 5i may 'be reversed and the volume thereof controlled by a reciprocating control member 54which extends from the interior mechanism of said pump to the exterior thereof and is operatively connected to an extension 56 of a piston 51 of an air motor 58, by a lever 55 which is *pivotally supported at a fulcrum point 55a. The said motor, as hereinafter explained, is automatically operated in such manner as to regulate the direction and volume of flow of liquid through the compensator pump 5| in order to derive a transfer of a'suitable volume of liquid from the liquid supply of one of the mentioned rams to the liquid supply of the other of said rams whereby to substantially restore and maintain parallelism of the press slide during its advance movement. a

The supply of air, as a driving medium, to the air motor 58, is preferably controlled by means of an air distributing valve 59 and an air release valve 60. In carrying out the present invention it is preferable to provide electrical means for operating the valves 59 and '60, which electrical means may conveniently be arranged to respond to non-parallelism of the press slide and to control the operation of the air motor 58- so that the latter may operate the control means of the pump 5| to give to the latter its desired compensating effect.

The piston 51 of the air motor 59 has two spools or piston heads 6i! and Mr integrally formed therewith or fixedly secured thereupon and is arranged to reciprocate within a bore in an elongated casing 62. The said bore is of different diameters at various points therealong to form a central air chamber 63 and certain oppositelyacting air chambers located toward opposite ends of said casing, namely, balancing chambers 641 and 641', driving chambers 65!, 65r, and drain chambers 66! and 661'. All the mentioned chambers in the air motor 59, as shown in Fig. 5, are

provided with suitable ports which. in the case of the drain chambers 661, '661 afford communication between said chambers and the free exterior air, and in the cases of the other mentioned chambers afford means of connecting the latter to a compressed air line and to the air valves 59 and 50.

Similar oppositely-acting centering sleeves -6ll,

611' are accurately fitted to slide upon the piston 51 outwardly of the spools 6| 1, 6H and are accurately fitted to slide within annular webs 60!, 681* which separate thesaid balancing and driving chambers at opposite ends of the air motor. The

said centering sleeves have annular flanges 61 at their outer ends for limiting the sliding movement of said sleeves.

Another pair of similar oppositely-acting sleeves 691, -69r are accurately fitted to slide upon the piston 5'! at points between the spools 6|! and Mr. These sleeves have similar annular flanges 69! on their inner ends, the said flanges being :granged to work within the central air chamber The air distributing valve 59 is very similar to the hydraulic distributing valves 26a and 26b. It comprises a piston 10, having three spools H, l2, 13 formed on or fixed thereon, and accurately fitted to slide within a bore 14 in a casing I5. The said spools define neck portions 16 and 11 on said piston. The valve 59, as shown in Fig. 5, is provided with suitable ports, which may be covered and uncovered by the spools ll, 12, 13, when the piston 10 is moved to various longitudinal positions, and which afford means for connecting the interior of the valve 59 with the free air and with various ports of the relief valve 69 and the air motor 58. The valve 59 may be provided with a centering spring 18 which operates to center the piston 10 in the same manner as the spring 46 functions to center the pistons of the hydraulic valves 26a and 26b. The piston I0 is connected to oppositely-acting solenoids I9, 80, which are connected in circuits, hereinafter described.

The air release valve 60 comprises a piston 8| having two spools 82, 83, accuratel fitted to reciprocate within a bore 84 of a casing 85. The said spools define a neck portion 8 la therebetwe'en. The casing 85, as shown in Fig. 5, is provided with several ports affording means for connecting the interior of the bore 84 to free air and to pipes leading to the air motor 58 and the valve 59. The piston is normally urged toward the right by a compression spring 96 and is movable toward the left against the compression of said spring by means of a solenoid 81 which is suitably connected to said piston. The said solenoid is connected in electric circuits, hereinafter described.

In order to mechanically detect any non-parallelism of the press slide IS, a pair of verticallydisposed racks 08 (see Fig. 1) are secured at their lower ends to slide l6 toward opposite ends thereof. The said racks may be guided within suitable guides 89 fixed upon the crown l3 and are the said racks and shafts at opp site ends of the press slide is of similar step-up characteristics so that if the press slide remains in parallelism as it descends, the shafts 901 and 90rrotate to similar degrees; if the slide tilts as itdescends, one of said shafts rotates to a greater degree than the other. The two mentioned shafts are supported within brackets 94 fixed upon the crown l3.

A differential mechanism 95 is employed between the shafts 901 and 901' as may best be understood from Fig. 1. The said mechanism may be of a conventional type, as shown in Fig. 2. It comprises bevel gears 961 and 961', keyed respectively upon the inner ends of shafts 901 and 901' and meshing with bevel. differential gears 91 which are mounted within a cage 99 upon studs 99. The cage 99 preferably is freely mounted upon shafts 901 and 90r and is confined between a pair of said brackets 94, the mounting being such that the said cage is capable of rotation relatively to said shafts.

It should be apparent that if theparallelism.

of thepress slide I6 is maintained as it descends,

the shafts 901 and 901' move in similar degrees but in opposite directions, so that the rotation passage of light rays from the several incandescent lamps to the several photoelectric cells.

imparted to the differential gears 91 by the bevel gear 961, tending to turn the cage 99 in one direction, is exactly counteracted by the rotation imparted by the bevel gear 991 to said differential gears, tending to turn said cage in its opposite direction. It, hen'ce, results that while the slide I6 moves downwardly in parallelism with the bed I I, the cage 99 remains at rest.

0n the other hand, if the slide I9 does not maintain its parallelism as it moves downwardly, one of the shafts 901 or 901' turns to a greater degree than the other, thus, through the differential gears 91, imparting a. rotative movement to the cage 98 in a direction and to an extent which depends upon the direction and extent of tilting of the press slide. The mentioned movement of the differential cage is employed, in the present invention, to control various electric circuits which, on their part, control apparatus adapted to operate the flow-controlling mechanism ofthe compensator pump ii to substantialy maintain parallelism of the press slide. The movement of said differential cage also functions,

in a manner hereinafter explained, to stop the press if tilting of the press slide should go beyond certain predetermined limits which may be considered dangerous or detrimental to the press. The manner in which the mentioned differential cage movement controls these functions is now It is preferred to provide, within the casing I02, a pair of similar opaque partitions I09 which, as best seen in Figs. 1 and 2, are disposed parallel to and closely adjacent the opposite faces of the disc I00. These partitions preferably are U shaped and extend from the crown l9 into intimate engagement with the casing I02, to which they may be welded, and also extend substantially about the differential cage 99. A second pair of U shaped partitions I04 may be welded or otherwise fixed to the inner edges of the partitions I03 and extend outwardly therefrom, normally to the latter, into intimate engagement with covers I05 which may be secured, as by bolts I06 to the casing I02 and to the crown I3 of the press.

The fixed partitions I03 and the disc I00 are suitably apertured in a manner hereinafter described and function together as a shutter mechanism. On one side of said mechanism, a plurality of light sources, which are disclosed herein as four incandescent lamps I01, I09, I09, H0,

The disposition of the said apertures may best be understood from Figs. 3 and 4. Apertures in the form of radial slots I0'I:1:, I08a:, I09a:, H03: are located similarly in the partitions I03 in alignment respectively with the lamps and cells I0'|-I0Ic, I09-I080, I09--I09c, and IIO--I0c. The disc I00 is provided with a plurality of radial apertures in the form of slots I0'Iy, I091], I09y, I092, IIOy and H02, which are located on said discsubstantially as shown in full lines in Fig. 3, which figure also clearly shows the relationship of said apertures to the apertures I012, I09zc, I090: and 0.1:, which are'indicated therein in broken lines.

The location and relationship of the various mentioned apertures is also made clear in Fig. 4 which also shows clearlythe relationship of said slots to the several pairs of incandescent lamps and photoelectric cells. The latter' figure, it should be remembered, is a flattened semi-circular sectional view taken on the line 4-4 of Fig. 3, and, hence, counterclockwis movement of the disc I00 as viewed in Fig. 3 appears as upward movement thereof in Fig. 4, while the clockwise movement of said disc appears as downward movement thereof in Fig. 4.

In Fig. 4, the disc I00 is shown in the position in which it is set and remains while the press slide I9 is parallel to the press bed II. If in the operation of th press the left side of the slide I9, during its down stroke, moves ahead of the right side thereof, the disc I 00 will turn to some extent in a clockwise direction as viewed in Fig. 3. or downwardly as viewed in Fig. 4.

Even a relatively slight non-parallelism of the particular character just mentioned will cause aperture I09y to move at least partially into alignment with apertures I09:1:, thus permitting light rays from lamp I09 to pass to cell I09c and cause the latter to function in an electric circuit in a manner hereinafter described. If such non-parallelism becomes more pronounced, aperture I09y will move into at least partial alignment with apertures I09:c, thus permitting light rays from lamp I09 to pass to cell I090. If such non-parallelism becomes still more pronounced and is of such magnitude as to be dangerous or otherwise objectionable, aperture H011 moves into at least partial alignment with aperture 0.1:, permitting light rays from lamp H0 to pass to cell IIOc.

If, in the downward movement .of the press slide the right side' thereof moves ahead of the left side thereof, movement of the disc I00 would occur in the opposite direction, i. e., counterclockwise as viewed in Fig. 3, and upwardly as viewed in Fig. 4. The latter character of nonparallelism would result, first in alignment of aperture I0'ly with apertures I0'I:c to permit passage of light rays from lamp I01 to cell IIIlc; then if such non-parallelism were to become more pronounced, aperture I092 would move into alignment with apertures I091: to permit passage of cell I I00.

The embodiment of the present invention disclosed herein includes other electric apparatus and electric and hydraulic circuits which may be understood from the following explanation of the operation of the apparatus.

In practice, the 'parts of the described apparatus are so assembled that, when the slide I6 and the bed I I are perfectly parallel, the apertures in partitions I03 and in the disc I are in the relative positions shown in Fig. 4 so that no light rays may pass to any of the photoelectric cells, and the pistons of the air valves 59 and 60 and of the air motor 58 are all in the positions indicated in Fig. 5 of the'drawings.

If the press is open and it is desired to cause the press slide I6 to move downwardly to perform a pressing operation, th operator sets switch I I4 to its "down position, as shown in Fig. 5, thereby closing a circuit from main lead H5 (indicated as a negative lead), through switch H4, wire H6, the coil of solenoid 42, wire H1, normally-closed contactors I42a, of relay I42, and wire H8, to main lead I2I which is indicated as a positive lead. Automatic or semiautomatic means may be and usually are provided for controlling the circuits through solenoids 42 and 45, but such means are not described herein as they constitute no part of the present invention.

Upon the closing of the mentioned circuit through solenoid 42, the latter is energized and draws the pistons of the hydraulic valves 26a, 26b to their left positions as shown in Fig.5, whereupon liquid from the pumps 22a, 22b passes through said valves and through pipe lines 28a, 28b to ram advance chambers 20a, 20b, respectively, thus causing rams I61: and I8b to descend with the slide I6, the liquid from return chambers 2Ia, 2Ib, meanwhile, being exhausted through pipes 29a, 29b to the valves 26a, 26b and thence through pipes 30a, 30b to the tank 23.

The closing of switch H4 to its down position also establishes two circuits through the several incandescent lamps. The first of said circuits extends from main lead H5 through switch H4, wires H6, H9, lamp H0, and wire I20 to main lead I2); thus lamp H0 is lighted at all times when switch I4 is in down position. The second of said circuits extends from main lead H5 through switch H4, wires H6, H9, I22, normally closed contactor I42b of relay I42, wire I23, lamps I01, I08, I09, and wire I20 to main'lead I2I; thus lamps I01, I08, I09 which are connected in parallel in this circuit, are lighted at all times when switch I I4 is in down" position, except when relay I42 is energized in a manner hereinafter described. v

For present purposes it may be supposed that the press contains a die or dies of such irregular vertical dimensions. or that the blank is of such a character, that th slide I6, in its downward movement, meets a greater resistance to such movement toward its right and thus inducing, in the pump 22b, a greater slippage than is present in the pump 22a, with the result that the latter pump passes a somewhat greater volume of liquid into ram advance chamber 20a than is passed into ram advance chamber 20b by the pump 22b with the result that the left side of the slide I6 tends to move downwardly ahead of the right side thereof, thus giving the slide an objectionable tilting attitude which may impair the precision of the pressing operation as aifecting the blank and which, in any event, introduces very objectional friction and consequent wear in the slide guides of the press.

However, immediately upon the inception of such uneven descent and before the tilting of the press slide becomes objectionable in any practical sense, the shaft 901 rotates somewhat more than the shaft 901', thus imparting to the disc I00, of the shutter mechanism, a clockwise motion as viewed in Fig. 3 (downward motion as viewed in Fig. 4), causing the aperture I081; to move into alignment with apertures I 082:, thus permitting light rays from lamp I08 to pass to cell I080 thus activating the latter to complete, in a well understood manner, circuits from said cell through wires I24, I25 to a suitable amplifier I26 and from the latter, by suitable wiring, through the coil of relay I21.

The mentioned circuit through. the coil of relay I21 energizes the said coil and causes the contactor I21a of said relay to move from its normally open position to closed position, thus completing a circuit from main lead I I5, through wire I28, the coil of solenoid 19, wire I29, contactor H111 and wire I30 to main lead I2I. Upon the closing of the said circuit through solenoid 19, the latter is energized and draws the piston of air distributing valve 59 toward the left against the tension of spring 18 to a position in which compressed air from air line I3I may freely enter the valve 59 through pipe I34 and pass along and around neck portion 11 of the piston 10, whence it may pass out of the valve 59 through pipe I32 into driving chamber 651' of the air motor 68.

As will be seen from Fig. 5, the balancing chambers 641, Mr are directly connected to air line I3I, hence the air pressure in said balancin'g chambers functions normally to maintain the piston 51 of the air motor in its mid position, as shown in the drawings, by air pressure exerted on the outer ends of the sleeves 6", 611', which press at their inner ends against the spools 6Il, 6Ir, respectively. However, when the compressed air at the same pressure is introduced into driving chamber-651, in the manner just described, the force of said pressure exerted upon the right side of the spool 6I1', is greater than the difierence between the forces of the pressure on the left and right sides of the flange 61f of the sleeve 61!, hence the piston 51 is driven toward the left until the spool 6Ir engages the right end of the sleeve 691' but proceeds no further inasmuch as the force of the air pressure within the central air chamber 63, which is normally connected to air line I3I through pipe I33 and valve 60, exerts a greater force upon sleeve 691' than the difference in the forces applied to the spool 6Ir in the chamber 651' and to ,"t'he sleeve 611 in the chamber 641.

The mentioned limited shifting of the piston 51 to the left in themanner just explained causes the lever 55 to turn about its fulcrum 55a and move the control member 54 of the reciprocating pump 5| to the right, and the connection of the said control member to the said pump is such that the latter pumps liquid through pipes 53 and 52 from the primary liquid supply of ram 'I8a to the primary liquid supply of ram I8b.

This pumping action of the pump 5|, resulting from the limited shifting of the piston 51 of the air motor 58 and the consequent limited control change in the compensator pump may transfer sumo-lent liquid from one side of the press to the other to fully compensate for the pre-existing inequalities in the volumes of liquid supplied to the opposite side of the press, with the result that the slide I5 of the press is restored to parallelism with the press bed II. While such restoration is taking place, there occurs a counterclockwise movement of the disc I00, asa result of which aperture I081 moves out of alignment with apertures I08r, thus cutting off the light beam to cell I080. This causes the latter to become deactivated, thus opening the mentioned circuits through the amplifier I26, the coil of relay I21, and the solenoid I9, thereby deenergizing the latter and permitting the piston 10 of the air distributing valve 50 to be restored to its mid-position shown in Fig. 5 by the centering spring I8.

In the said mid-position of the position 10, the spool I2 closes oil pipe I34 while driving chamber 551' of the air motor is connected to exhaust port I35 of the air valve 59 through air pipe I32 and through the interior of valve 59 wherein the exhaust air from chamber 551' may pass around neck portion 1'! to said exhaust port I35 and pass through the latter to free air. Upon chamber 551' of the air motor being connected to free air in the manner just described, the air pressure in the balancing chamber 54! functions to move sleeve 6" to the right, carrying the piston 51 with it back to the latters mid-position, as shown in the drawings. The said movement of the mentioned piston, of course, restores the control member 54 of the compensator pump 5I to its normal position in which the pumping mechanism of said pump, although being driven by its motor, is nevertheless not passing any liquid.

If, after the discontinuance of the pumping action of the compensator pump 5|, the irregularity of the die or blank causes the left side of the press slide I6 again to move ahead of the right side thereof, the described apparatus again functions in a. similar manner to bring the compensator pump into play to again restore the parallelism of the press slide. This compensat- 'ing action may conceivably take place a number of times during theadvance of the press slide so that, during said advance, the press slide pursues an almost imperceptible rocking action. The latter action, of course, is restrained within permissible limits so that, in so far as any material considerations are concerned, th press slide is maintained in parallelism with the bed of the press during its entire advance movement.

If the irregularity of the die or blank is such as to cause the right side of the press slide Hi to advance slightly ahead of the left side thereof, the compensator pump and the controls thereof function in a manner similar to that just described but various parts are actuated in opposite directions to achieve the desired opposite compensation. When non-parallelism of the latter character occurs the disc I00 turns to some extent in a counterclockwise direction so that aperture I0Iy registers with aperture I013: to permit light rays from lamp I01 to pass to and activate cell I010. Th latter cell is connected through amplifier I35 and relay I31 to solenoid 80 similarly to the previously recited connections of cell I080 to solenoid I9, hence, when cell I0'lc i activated as a result of the mentioned counterclockwise rotation of disc I00, solenoid 00 is energized causing the piston of the air distributing valve 59 to be moved to the right instead of to the left, so that compressed air is introduced into chamber 651 of the air motor 58 instead of into chamber 551- thereof, thereby causing the piston of said air motor to move toward the right. This latter movement causes the reciprocating control member 54 of the compensating pump to move to the left whereby to cause the pumping mechanism of said pump to transfer liquid from the primary liquid supply of ram l8b to the primary liquid supply of ram I8'a, thus restoring the parallelism of the press slide.

It may occur in practice that die or blank irregularities or other conditions may be such as to cause a more pronounced or objectionable tilting of the press slide than the permissible tilting which the compensating means thus far described is adapted to compensate. Such objectionable tilting may be of such magnitude that, if we assume the left side of the press slide to be moving in advance of the right side thereof, not only would cell I 080 be activated by the clockwise rotation of the disc I00, but such rotation would be suflicient to also bring aperture I09y into alignment with apertures I09: to permit light rays from lamp I09 to pass to and activate cell I090 which, as may be seen from Fig. 5, is connected through amplifier I38 and relay I39 with the coil of solenoid 81. Thus, in the event of such excessive tilting of the press slide, the solenoid 81 is energized and moves piston 8| of air release valve 60 toward the left against the compression of spring 85, causing spool 83 to close ofl air line I3I from communication with the interior of said valve and at the same time affording a passage permitting air from central air chamber 63 of the air motor 58 to exhaust through pipe I33 into release valve 60, whence said exhaust air passes around and along the neck portion of the piston BI and escapes to free air through exhaust port I40.

Upon the opening of central air chamber 53 of the air motor 58 to exhaust, the sleeve 59r which theretofore functioned as a stop, limiting the sliding movement of the piston 51 to the left, becomes free to move to the left within chamber 53 thus permitting a further movement of the piston 51 to the left, in addition to the limited sliding movement previously pursued by said piston, in response to air introduced into chamber 551'. This further movement of the piston 51 to the left causes a corresponding further movement of the reciprocating control member 54 of the compensator pump, toward the right, thus increasing the compensating flow of liquid through the pump 5| to yield sumcient additional compensation to overcome the excessive tilting of the press slide and restore it to parallelism. It will be observed from Figs. 3, 4 and 5 that the aperture I081; is of suflicient width that cell I080 remains activated to maintain air pressure in chamber 551 of the air motor 58 while cell I09c is activated in the manner and for the purposes just described whereby to yield the mentioned additional sliding movement of the piston 51 when pressure in the chamber 53 is released. Aperture I0'Iy similarly is of sufficient width to yield a like additional sliding movement of the piston 51 to the right if the compensation desired is opposite to that just described.

side thereof, the disc I turns in a counterclockwise direction and brings aperture I092 instead of aperture I09y into alignment with apertures I09x; thus, regardless of which side of the press slide is moving ahead when excessive tilting is present, the solenoid 01 is energized to shift the piston ill of the air release valve 60 toward the left, in the manner already described, to exhaust the air and relieve the pressure from central air chamber 53 of the air motor 58. Such release of pressure in said chamber permits sleeve 501 to move toward the right when the piston 51 is being urged toward the right, thereby permitting said piston to move beyond said initial limited movement, causing a corresponding increase in the movement of the reciprocating control member 54 of the compensator pump to the left so that the flow of liquid through said pump, in the proper direction, is increased sufficiently to yield the desired increased compensating effect.

Under some conditions it may be feasible to dispense with the air release valve 60. If this is done, the apparatus employed would be so designed and adjusted that the compensator pump 5|, under any anticipated operating conditions, would fully yield the compensating effect necessary to restore the parallelism of the press slide as the result of a single shift of the control member 54. However, if the compensating capacity of the compensator pump 5| is stepped up sufliciently to cause adequate compensation in all instances, in response to the activation of only one of the cells I0'Ic or I080, compensation would occur very rapidly and consequently the mentioned rocking of the press slide, under some circumstances, might be objectionably rapid, and

during a single advance stroke of the slide might occur so frequently as to be objectionable.

The air release valve is advantageous in that, by its use, a complete stroke of the piston 51 of the air motor 58 and consequent extreme adjustment of the control member 54 of the compensator pump, is accomplished in two distinct steps rather than in one step. If excessive tilting of the press slide occurs, the mentioned two step adjustments yield the maximum compensating effect necessary to restore the press slide to para lelism; However, the tilting of the press slide, in many cases, may be effected before becoming excessive, by the efiect of only one step of compensator pump adjustment. It follows that when only the lower compensating effect. of a single step of compensator pump adjustment, is brought into play, the rocking action of the press slide is much slower and not frequent enough to be objectionable.

It may be understood from the foregoing explanation of the effects of too rapid compensation that it is important to so correlate the movement of the piston 51 of the air motor 58 to the movement of the reciprocating control element of the compensator pump that only the proper degree of compensation is obtained. In order to readily permit correlation of these movements it is preferable to provide a variable fulcrum point for the lever 55. A suitable variable fulcrum arrangement is fully disclosed and described in my mentioned co-pending application Serial No. 463,604.

Ordinarily, compensation takes place through the activation of either cell I0Ic or I08c, and where additional compensation is necessary it is ordinarily derived from the activation of cell I090; However, if some part of the system were to fail, with the consequent failure of the compensating mechanism, or if for any other reason compensation should not take place and the tilting of the press slide were to progress sufflcientiy IIOz into alignment with apertures IIOrc, thus permitting light rays from lamp IIO to'pass to cell 00. The light thus activates said cell and causes it, through amplifier I ll and relay I42 to move the contactors I42a and I421) of said relay from their normally closed to open positions.

The opening of contactor I42a breaks the electric circuit through solenoid 42, whereupon the pistons of the several hydraulic distributing valves assume their mid-positions, thus stopping the movement of the press slide. The opening of cont-actor I42bbreaks the electric circuit through the lamps I01, I 08, I09, thus deactivating cells I0jIc, I080 and I09c, assuring that the solenoids 00, I9 and B1, controlled respectively by said cells, permit the pistons of air valves 50 and 60 to move to the positions shown in Fig. 5 so that the compensator pump adjustment is shifted back to neutral or non-pumping position. Thus the cell Ili c fuctions as a safety device to stop the operation of the press.

It is well known by those familiar with the art relating to hydraulic ,pr'esses, that suitable means in the form of drain or bypass ducts or clearances must be provided in certain portions of the various valves and the air motor to prevent locking thereof. Such means, however,'are not essential features of the present invention and, therefore, have not been fully illustrated in the drawings.

It should be understood. of course, that the invention may be employed in presses using more than two rams and that the use of a compensator pump or pumps may be avoided in some installations, by adapting the electric or pneumatic ap paratus, or both, to function directly with the pumps provided for supplying liquid to the several ram chambers, whereby to effect compensation directly in said pumps. The invention may be practiced in these and many other ways without, however, departing from the substance of the invention as defined in the accompanying claims.

What I claim is: I

1. Apparatus for substantially maintaining parallelism of two relatively movable pressing members in a press, said apparatus comprising an electrical system, means controlled by said system for moving said pressing members into parallelism, photoelectric means associated with said e ectrical. system, and an operating member, adapted to move operatively in either of opposite directions relatively to paths of light to said photoelectric means, in response to departure of said pressing members from parallelism, whereby to oppositely modify the operation of said-photoelectric means and electrical system. and thereby to move said pressing members into parallelism.

2. Apparatus for maintaining parallelism of a s ide member and a bed member relatively to each other in a long-bed press during the closing there of, the said apparatus comprising compensating means coacting with one of said members for varying the attitude thereof relatively to the other of said members, and an electric control system adapted to control the operation of said compensating means, thesaid system including photo electric means and a member, for operatingthe latter means, adapted to respond operatively to non-parallelism in either of opposite directions whereby to cause said compensating means substantially to remedy such non-parallelism.

3. Apparatus for maintaining parallelism of a slide member and a bed member relatively to each other in a long-bed press during the closing thereof, the said apparatus comprising compensating means coacting with opposite sides of one of said members for varying the attitude thereof relatively to the other of said members, and an electric control system adapted to control the operation of said compensating means, the said system including photoelectric means and a member, for operating the latter means, adapted to respond operatively to non-parallelism in either of opposite directions whereby to cause said compensating means substantially to remedy such nonparallelism.

4. Apparatus for controlling the slide movement in a long-bed press having a plurality of slide-actuating means, the said apparatus comprising compensating means for efiecting compensating variations in the operation of said actuating means during the advance movement of the press slide, and an electric control system adapted to control the operation of said compensating means, the said system including photoelectric means and a member, for operating the latter means, adapted to respond operatively to non-parallelism of the press slide in either of opposite directions whereby to cause said compensating means to eifect compensation in the operation of said actuating means, substantially to remedy such non-parallelism,

5. Apparatus for controlling the slide movement in a long-bed hydraulic press having a plurality of symmetrically-disposed slide-actuating rains and related ram advance chambers, the said apparatus comprising a separate pumping system for each of said chambers adapted to pump liquid thereto, compensating means for eii'ecting compensating variations, during the advance movement of the press slide, in the volume of liquid pumped into said chambers, and an electric control system adapted to control the operation of said compensating means, the said system including photoelectric means and a member, for operating the latter means, adapted to respond operatively to non-parallelism of the press slide in either of opposite directions whereby to cause said compensating means to efiect compensation in the volume of liquid pumped into said chambers substantially to remedy such non-parallelism.

6. Apparatus according to" claim 5, further characterized in that it includes a pair of movable members coacting with the press slide at opposite sides thereof and with said operating member to operate said photoelectric means whereby to control the operation of said electric system and, through the latter, to control said compensating means.

7. Apparatus according to claim 5, further characterized in that the said compensating means comprise a movable member adapted to control the said compensating variations, and in having driving means coacting with and adapted to actuate said movable member, the said electric control system being adapted to control the said driving means, and, through control of the latter, to control the said compensating means to remedy non-parallelism of the press slide.

8. Apparatus for controlling the movement of a press slide comprising actuating means for actuating said slide, an electric circuit adapted to control said actuating means, photoelectric means in said circuit and adapted to control the latter, an operating member, operatively responsive tonon-parallelism of said slide in any one of plural directions and adapted to operate said photoelectric means and, through the latter, to control said actuating means whereby to stop the movement of said slide when non-parallelism of the latter goes beyond a predetermined degree.

9. Apparatus for controlling the attitude of a slide of a press relatively to a bed thereof, comprising compensating means coacting with said slide for effecting compensating variations in such atttitude, a photoelectric cell adapted to control said means, and a shutter member adapted to be moved, operatively, in response to changes in such attitude in anyone of plural directions whereby to so control the passage of light to said cell as to cause said compensating means substantially to maintain parallelism of the press slide and bed.

10. Apparatus according to claim 9, further characterized in that said shutter member has an open space and coacts with the press slide to move, with the departure of the latter from parallelism, between registering and non-registering positions of said open space with reference to a path of light to said cell.

11. Apparatus for controlling the slide movement in a long-bed hydraulic press having a plurality of symmetrically-disposed slide-actuating rams and related'ram advance chambers, the said apparatus comprising a separate pumping system for each of said chambers adapted to pump liquid thereto, compensating means for effecting compensating variations, during the advance movement of the press slide, in the volume of liquid pumped into said chambers, and an electric control system adapted to control the operation of said compensating means, the said system including photoelectric means adapted to respond to non-parallelism of I the press slide whereby to cause said compensating means to effect compensation in the volume of liquid pumped into said chambers substantially to remedy such non-parallelism, the said apparatus being further characterized in that the said photoelectric means comprise a shutter member coacting with opposite sides of the press slide and adapted to move in response to differences in the movements. of said opposite sides whereby to so control the passage of light in said photoelectricmeans as to cause said electric control system and slide-actuating means to remedy nonparallelism.

12. Apparatus for controlling the slide movement in a long-bed hydraulic press having a plurality of symmetrically-disposed slide-actuating rams and related ram advance chambers, the said apparatus comprising a separate pumping system for each of said chambers adapted to pump liquid thereto, compensating means for effecting compensating variations, during the advance movement of the press slide, in the volume of liqui pumped into said chambers, and an electric control system adapted to control the operation of said compensating means, the said system including photoelectric means adapted to respond to non-parallelism of the press slide whereby to cause said compensating means to effect compensation in the volume of liquid pumped into said chambers substantially to remedy such non-parallelism, the said apparatus being further characterized in that it includes a pair of rotatable shafts, driving means at each or opposite sides of the press slide controlled by the movement of the latter and adapted to coact with and separately rotate said shafts, during the advance movement of the slide, to degrees which correspond r difier in accordance with the parallelism or non-parallelism of the slide, a movable member operably connected to both said shafts and adapted to be moved by the latter in either of two dirctions depending upon the differences in degrees of rotation of said shafts, and in that the said photoelectric means comprise a shutter member constrained to move with said movable member whereby to control the passage of light in said photoelectric means, and, through the latter, to control the said compensating means; a I

13. Apparatus for controlling the slide movement in a long-bed hydraulic press having a plurality of symmetrically-disposed slide-actuating rams and related ram advance chambers, the said apparatus comprisinga separate pumping system for each of'said chambers adapted to pump liq-, uid thereto, compensating means for effecting compensating variations, during the advance movement of the press slide, in the volume of liquid pumped into said chambers, and an electric control system adapted to control the operation of said compensating means, the said system including photoelectric means adapted to respond to non-parallelism of the press slide whereby to cause said compensating means to effect compensation in the volume of liquid pumped into said chambers substantially to remedy such nonparallelism, the said apparatus being further characterized in that'it includes a pair of rotatable shafts coacting with and driven by opposite sides of the press slide, and a differential mechanism connected operably between said shafts, and in that the said photoelectric means comprise a shutter member adapted to be rotated by said diflferential mechanism in a direction and to an extentcorresponding to the differential direction and extent of rotation of said mechanism whereby to control the passage of light in said photoelectric means.

14. Apparatus for controlling the slide movement in a long-bed hydraulic press having a plurality of symmetrically-disposed slide-actuating rams and related ram advance chambers, the said apparatus comprising a separate pumping system for each of said chambers adapted to pumpliquid thereto, compensating means for'efiecting compensating variations, during the advance movement of the press slide, in the volume of liquid pumped into said chambers, and an electric control system adapted to control the operation of said compensating means, the said system including photoelectirc means adapted to respond to non-parallelism of the press slide whereby to cause said compensating means to efiectcompensation in the volume of liquid pumped into said chambers substantially to remedy such nonparallelism, the said apparatus being further characterized in that the said compensating means comprise a movable member adapted to control the said compensating variations, and in having a'fiuid-actuated motor coacting with and adapted to actuate said" movable member, the said electric control system being'adapted to control the said motor, and, through control of the latter, to control the said compensating means to remedy non-parallelism of the press slide.

15. Apparatus for controlling the slide movement in a long-bed hydraulic press having a plurality of symmetrically-disposed slide-actuating rams and related ram advance chambers, the said apparatus comprising a separate pumping system for each of said chambers adapted to pump liquid thereto, compensating means for etfecting compensating variations, during the advance movement of the press slide, in the volume of liquid pumped into said chambers, and an electric control system adapted to control the operation of said compensating means, the said system including photoelectric means adapted to respond to non-parallelism of the press slide whereby to cause saidcompensating means to effect compensation in the volume of liquid pumped into said chambers substantially, to remedy such non-parallelism, the said apparatus being further characterized in thatthe said coin-, pensating means comprise a movable member adapted to control said compensating variations to a degree corresponding substantially to the degree of movement of said movable member, and in having driving means for moving said movable member, the said driving means having plural, separately controllable stages of operation, and the said photoelectric means including plural photoelectric cells, each responsive to different degrees of non-parallelism of the press slide and adapted to control the said separate stages of operation of said driving means.

16. Apparatus for controlling the slide movement in a long-bed hydraulic press having a plurality of symmetrically-disposed slide-actuating rams and related ram advance chambers, the said apparatus comprising a separate pumping system for each of said chambers adapted to pump liquid thereto, compensating means for effecting compensating variations, during the advance movement'of the press slide, in the volume of liquid pumped into said chambers, and an electric control system adapted to control the operation of said compensating means, the said system including photoelectric means adapted to respond to non-parallelism of the press slide whereby to cause said compensating means to efiect compensation in the volume of liquid pumped into said chambers substantially to remedy such non-parallelism, the said apparatus being further characterized in that the said compensating means comprise a movable member adapted to control said compensating variations to a degree corresponding substantially to the degree of movement of said movable member, and in'having driving means for-moving said movable member, the said driving means comprising a fluid-actuated motor including a casing, and a piston adapted to reciprocate within said casing, the casing having separate chambers for fluid for causing plural stages of movement of said piston in one direction, and the said photoelectric means including plural photoelectric cells, each responsive to difierent degrees of nonparallelism of the press slide and adapted to control the supply of fluid to said separate chambers, in accordance with the degree of nonparallelism of the press slide,

17. Apparatus for controlling the slide movement in a long-bed hydraulic press having a plurality of symmetrically-disposed slide-actuating rams and related ram advance chambers, the said apparatus comprising a separate pumping system for each of said chambers adapted to pump liquid thereto, compensating means for effecting compensating variations, during the advance movement of the press slide, in the volume of liquid pumped into said chambers, and an electric control system adapted to control the operation of said compensating means, the said system including photoelectric means adapted to respond to non-parallelism of the press slide whereby to cause said compensating means to'eflect compensation in the volume oi! liquid pumped into said chambers substantially to remedy such non-parallelism, the said ,apparatus .being further characterized in that the said compensating means comprise a movable member adapted to control said compensating variations to a degree corresponding substantially to the degree of move-. ment of said movable member, and in having driving means for moving said movable member, the said drivingmeans comprising a fluid-actuated motor including a casing, and a piston adapted to reciprocate within said casing, the casing having separate chambers for fluid for causing plural stages of movement of said piston in each direction, and the said photoelectric means including plural-photoelectric cells, each responsive to diiierent direction and degrees of non-parallelism or the press slide and adapted to control the supply of iiuid to said separate chambers in accordance with the direction and degree of non-parallelism of thepress slide.

18. Apparatus for controlling the slide movement in a long-bed hydraulic press having a plurality of symmetrically-disposed slide-actuating rams and related ram advance chambers, the

said apparatus comprising a separate pumping system for each.- of said chambers adapted to pump liquid thereto, compensating means for efiecting compensating variations, during the advance movement of the press slide, in the volume of liquid pumped into said chambers, and an electric control system adapted to control the operation of said compensating means, the said system including photoelectric means adapted to respond to non-parallelism of the press slide whereby to cause said compensating means to efiectcompensation in the volume of liquid pumped into said chambers ubstantially to remedy such non-parallelism, the said apparatus being further characterized in that the said compensating means comprise a reversible pump connected between ram advance chambers at of liquid pumped into said chambers, and an electric control system adapted to control the operation of said compensating means, the said system including photoelectric means adapted to respond to non-parallelism of the press slide whereby to cause said compensating means to effect compensation in the volume of liquid pumped into said chambers substantially to remedy such non-paralelism, the said apparatus being further characterized in that the said electric control system includes a compensation-con trol circuit having a first photoelectric cell therein and being adapted to control said compensating means, and a safety circuit having asecond photoelectric cell therein and being adapted to control the advance movement of the press slide, the said first cell being adapted to respond to a to cause said compensating means to eilect compensation, and the said second cell beingadapted to respond to non-parallelism beyond a predeattitude, a photoelectric cell adapted to control,"

said means, and a shutter member adapted to be moved in response to changes in such attitude whereby to so control the passage or light to said cell as to cause said compensating means substantially to maintain parallelism of the press slide and bed, the said apparatus being further characterized in comprising a plurality of such cells, a first one of said cells being adapted to control a first stage of compens'ationin such attitude, and a second one of said cells being adapted 'to control a second stage of such compensation, and characterized further in that the said shutter member has at least one open space related to each of said cells and coacts with the press slide, upon its departure from parallelism, to cause a space in said shutter member, related to said first cell, to move between registering and nonregistering positions with reference to a path of light to said first cell to cause a first stage of compensation, and coacts with the press slide,

upon a greater departure thereof from parallelism, to cause a space in said shutter member, related to said second cell, to move between registering and non-registering positions with referenceto a path oi. light to said second cell to cause a second stage of compensation.

21. Apparatus for controlling the attitude of a slide of a press relatively to a bed thereof, comprising compensating means coacting with said slide for eflecting compensating variations in such attitude, a photoelectric cell adapted to control said means, and a shutter member adapted to be moved in response to changes in such attitude whereby to so control the passage of light to said cell as to cause said compensating means substantially to maintain parallelism of the press slide and bed, the said apparatus being further characterized in having, actuating means for actuating said press slide and in having, a second photoelectric cell adapted to control said actuating means, and further characterized in that the said shutter member has at least one open space related to each of said cells and coacts with the press slide, upon its departure from parallelism, to cause a shutter space, related to the cell adapted to control the said compensating means, to move between registering and non-registering positions with reference to apath of light to the last-mentioned cell to cause compensation of the press slide, and coacts with the press slide, upon a greater departure thereof from parallelism, to cause a space in said shutter member, related to said second cell, to move between registering and non-registering positions with reference to a path of light to said second cell to render the slideactuating means inoperative in order to stop the movement of the press slide.

22. Apparatus for controlling the attitude of a slide of a press relatively to a bed thereof, coniprising compensating means coacting with said slide for effecting compensating variations in such attitude, a photoelectric 'cell adapted to conpredetermined degree of non-parallelism whereby trol said means, and a shutter member adapted to be moved in response to changes in such attitude whereby to so control the passage of light to said cell as to cause said compensating means substantially to maintain parallelism of the press slide and bed, the said apparatus being further characterized in having actuating means for actuating said press slide and in having a first cell for controlling the compensating means to yield compensation in one direction, a second cell for controlling the compensating means to yield compensation in the opposite direction, and a third cell for controlling said actuating means, and further characterized in that the said shutter member has at least one open space related to each of said cells and coacts with the press slide, upon its departure from parallelism in one direction, to cause a shutter space, related to said first cell, to move between registering and non-registering positions with reference to a path of light to said first cell to cause compensation tending to restore parallelism, and coacts with the press slide, upon its departure from parallelism in the opposite direction, to cause a shutter space, related to said second cell, to move between registering and non-registering positions with reference to a path of light to said second cell to cause compensation tending'to restore parallelism, and coacts with the press slide, upon. a greater departure thereof from parallelism in either of said directions, to cause a shutter space, related to said third cell, to move between registering and nonregistering positions with reference to a path of light to said third cell, to render the slide-actuating means inoperative in order to stop the movement of the press slide.

23. Apparatus for controlling the attitude of a slide of a press relatively to a bed thereof, comprising compensating means coacting with said slide for eflecting compensating variations in such attitude, a photoelectric cell adapted to control said means, and a shutter member adapted to be moved in response to changes in such attitude whereby to so control the passage of light to said cell as to cause said compensating means substantially to maintain parallelism of the press slide and bed, the said apparatus being further characterized in having a pair of shafts coacting with opposite sides of the press slide to derive rotation in opposite directions, a differential mechanism operatively connected between and driven by said shafts, a difierential member in said mechanism adapted to rotate in accordance with the difierential of the rotation of said shafts and in that the shutter member is disc-like and is "constrained to rotate with said differential member and has at least one open space adapted to move between registering and non-registering positions with reference to a path of light to said cell.

EARL CANNON.

. CE'RTIFICATE OF CORRECTION. Patent No. 2,555,589. July 11, 19141;.

EARL CANNON.

It is hereby certified. that error appears in the printed specification of the above,numbered patent requiring correction as follows: Page 2, sec- 0nd column, line '50, for "ad" read and--; line 59, for ."manw" read -many--; page 5, first column, lines 15 and 114., for "application, Serial No. 159,35lu' read --Patent No.-2,528,258; page 1;, second column, line 1 for "10" read --ll0c--; page 6, first column, line 22, for "position 70" read piston TO--; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

si ned and sealed this 29th day of August, A. D. 19%.

Leslie Frazer (Seal) Acting Commissioner of Patents.

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