US2906096A

US2906096A - Precision control system for press brakes or the like

Info

Publication number: US2906096A
Application number: US398080A
Authority: US
Inventors: Rolland A Richardson
Original assignee: Pacific Industrial Manufacturing Co
Current assignee: Pacific Industrial Manufacturing Co
Priority date: 1953-12-14
Filing date: 1953-12-14
Publication date: 1959-09-29
Anticipated expiration: 1976-09-29

Description

p 1959 R. A. RICHARDSON 2,906,096

PRECISION CONTROL SYSTEM FOR PRESS BRAKES OR THE LIKE Filed Dec. 14, 1953 2 Sheets$hee t 1 IN V EN TOR.

ROLLA/VD A RICHARDSON HIS ATTORNEYS Sept. 29, 1959 2,906,096

R. A. RICHARDSON PRECISION CONTROL SYSTEM FOR PRESS BRAKES OR THE LIKE Filed Dec. 14, 1953 2 Sheets-Sheet 2 /7/ J IN V EN TOR.

HOL LAND 4 RICHARDSON 157. 2. By

HIS Arm/PM);

United States PRECISION CONTROL SYSTEM FOR PRESS BRAKES OR THE LIKE My invention relates to machines such as press brakes or the like in which a forming or like tool engages work and deforms the same or otherwise performs work thereon, and more particularly relates to hydraulically powered machines and a precision control system for such machines.

Among the objects of my invention are:

(1) To provide a novel and improved control system for press brakes or like machines;

(2) To provide a novel and improved control system for press brakes or the like, wherein the ram or blade executes a rapid approach to within A; inch of completion of the work stroke and then completes its operation at slow speed and under precision control;

(3) To provide a novel and improved control system for press brakes or the like, wherein the ram or blade may be arbitrarily stopped at any point in both its work stroke and return stroke;

(4) To provide a novel and improved control system for press brakes or the like wherein the ram or blade may be urged at slow precision controlled speed against the work; and

(5) To provide a novel and improved control system for press brakes or the like embodying all of the foregoing objects.

Additional objects of my invention will be brought ou in the following description of a preferred embodiment of the same taken in conjunction with the accompanying drawings wherein:

Figures 1 and 2, together, embody a disclosure of a complete system constituting the subject of the present invention; and

Figure 3 is a view depicting a switch arrangement in said system.

Referring to these drawings for details of the invention in its preferred form, the system is depicted as applied to a press brake 1, shown from the rear in outline, to bring out the relationship to the press brake, of certain of the components of my system which in an actual installation are mounted on the machine.

The press brake comprises in general a pair of side plates 3 and 5 across the lower front edges of which is a stationary bed or lower fixed blade 7. Slidably mounted on suitable guides along the upper front edges of these side plates, is a moving ram or upper moving blade 9.

This blade is supported at each end from a piston 11, working in a cylinder 13 which is mounted above the blade at the upper end of the side plates. Each of these atent cylinders is of the double acting type, that is, the operating fluid can be forced into the upper end of the cylinder to drive the blade downward, or it can be forced into the lower end of the cylinder to lift the blade.

The operation of the press brake depends on each of these cylinders being supplied with the same volume of hydraulic fluid such as oil, and toward this end, each cylinder is included in its own hydraulic system, with the pump 15, of the one system matching that of the other system, and driven from the same prime mover, which,

in practically every instance, will be an electric motor.

In addition to the pump, each such hydraulic system includes a tank 17, symbolically represented in the drawing and which may be common to both systems. A discharge line 19 from each pump connects back to the tank when the brake is not functioning, and connects to the upper end of its assigned cylinder for a down stroke of the ram or blade, while for the up stroke, the discharge line is shifted over to the lower end of the other cylinder through a check valve 20.

These functions are accomplished through the utilization of a main operating valve 21 which is depicted sym bolically in accordance with Joint Industry Conference standards. Each half of the valve represents the equivalent of a separate valve for one of the main hydraulic systems, and is depicted as capable of three adjustable positions with respect to a discharge line from one of the pumps. With such valve in its central or neutral position as depicted in the drawings, the discharge line is shown symbolically as discharging back to the tank 17 with no hydraulic pressure being applied to the cylinders. A shift to the left, will place the discharge line 19 from the right hand pump, as viewed in the drawing, in communication with the upper right cylinder, while the dis charge line from the left pump will be similarly placed in communication with the upper end of the left cylinder. Each of the cylinders will then discharge from its lower end back to the tank through a resistance check valve 23, the resistance of which will be suflicient to support its end of the blade in the absence of pressure applied to the upper end of the cylinder.

A shift of the main operating valve to the right from the position indicated in Figure 2 will place the discharge line 19 of the right hand pump in communication with the lower end of the left cylinder through associated check valve 20, while placing the discharge line of the left pump in communication with the lower end of the right cylinder through its associated check valve 20, and the resulting discharge from the upper end of each of the cylinders will be directed into the tank via its associated resistance check valve 23. Under these conditions, the blade will be lifted upwardly.

Shifting of the main operating valve to the left is accomplished by electrical energization of an end solenoid 24, while a shift in the reverse direction is realized through energization of a solenoid 26 at the opposite end of the valve.

The hydraulic pressure applied to the cylinders is equalized through the inclusion of-a blocking valve 27 in the discharge line from each of the pumps. This blocking valve has a discharge opening which is adjustable through shifting movement of a spring biased spool. This is symbolically represented by the hinged arrow 29 and the associated spring 31.

Hydraulic fluid at pump pressure is applied against one end of the spool as symbolically represented by the by-pass line 33, such pressure being in a direction to expose the discharge opening. Opposing this is a connection 35 from a point in the discharge line of the other system located beyond the blocking valve in said system. Pressure at this point in the other system is lower than the pump pressure by an amount equal to the pressure drop across the blocking valve and will thus permit of sufficient opening of the discharge passage in the blocking valve to permit of proper functioning of the machine. Inasmuch as the pressures in both hydraulic systems are thus interrelated to one another, the pressures in both systems will thereby be equalized.

Protecting each pump against sudden increase in pressure or against surges, is a relief valve 37 adjusted to open and place the pump in communication with the tank when the pressure reaches a value at which such protection is desired.

valve, will serve to level the moving blade of the machine,

should it tend to depart from such position while moving. Each level control valve is electrically operated by means of a solenoid 41 and is capable of occupying either of two positions, a normally closed position when not energized, and an open position when energized. Either valve will be actuated when one end of the ram tends to lead the other end, and a re-establishment of the ram to a level position is accomplished by passing a slight amount of oil through such valve from the leading to the lagging system. Such flow of oil occurs by reason of the pressure differential across the associated blocking valve.

Any excessive tilting of the ram is taken care of by what may be termed a maximum out-of-level control valve 43 associated with each of the hydraulic systems. Such valve is a two positional valve actuated by a solenoid 45 as in the case of the level control valves previously described, and is coupled to the relief valve in its associated system by a pipe connection 47 to vent and dump the same, thus causing the proximate pump to discharge directly back into the tank and remove the hydraulic power from that side of the machine.

The foregoing level control valves and maximum outof-level control valves are under immediate control of associated micro-switches, which in turn are made responsive to any tilting of the ram or blade during operation of the machine. The micro-switch associated with the right level control valve involves a contact 49 in normal open relationship to an actuable armature 51, while a similar micro-switch having a normally open contact 53 and associated armature 55 is associated with the left level control valve, but disposed in opposing relationship to the other switch.

A bar 57 pivotally disposed at an intermediate point, with its upper end lying between the actuable armatures 51 and 55 of the level control valve switches, is adapted to close one or the other of these switches when swung in one direction or the other on its pivot axis.

To one side of this pivoted bar below its pivot axis, is mounted a micro-switch involving a contact 59in normally closed relationship to an actuable armature 61, while on the other side of the pivoted bar is a similar switch having a normally closed contact 63 and associated armature 65, this switch being mounted in opposed relationship whereby pivotal movement of the bar will open one or the other of these latter two switches depending upon direction of swing of the bar.

One of these switches is associated with the left maximum-out-of-level control valve, while the other is associated with the right maximum-out-of-level control valve. While the spacing between the pivoted bar and the level control switches is quite close, the spacing between the bar and the maximum-out-of-level control switches, is sufficiently great to preclude opening of such switches until the ram or blade has tilted to a predetermined extreme position. Below the maximum-out-oflevel switches are mounted a similar pair of normally closed but opposing switches 67 and 69, which from their function in the system may be designated emergency switches, the purpose of these switches being to open the electrical power supply to the machine and to cause a cessation of all operations.

To convert the tilt of the blade to appropriate swing of the pivoted bar, a level 71 extending from the pivoted bar has its free end coupled to one end of a cable 73 which runs downwardly under a pulley 75 mounted on the back of the blade just below the lever, such cable then extending across the 'back of the blade and over another pulley 77 mounted on the back of the blade at 4 the opposite end thereof. The cable is then anchored to a bracket 79 mounted on the side adjacent that end of the blade. Tension on 'the cable is maintained by a spring 80.

With the blade level and the cable length such that the pivoted bar occupies a mid-position between the actuablearmatures of the switches to either side thereof, it will be apparent that as the blade moves downward, the pulley 75 will tend to tighten up on the cable while the pulley 77 at the opposite end of the blade will proportionately slack up on the cable so long as the blade maintains its horizontal position. Under these conditions, the pivoted bar will maintain its intermediate position and not engage any of the switches associated therewith. Any slight tilting of the blade during its movement however, will upset such proportionality and cause the pivoted arm to swing in one direction or the other depending on the direction of tilt of the blade, and thereby actuate the appropriate switch.

While the tilting of the blade is under control of the pivoted arm and its associated switches, the length of stroke of the blade and its upper and lower limits of travel are under control of switch means located at each end of the blade.

At one end of the machine, there is supported from the side plate a pair of

switches

83 and 85, one above the other. The upper switch 83 is ,a two-wayswitch having an upper contact 87 and lower contact 89 with an intermediate actuable armature 91 normally engaging the upper contact of this switch but adapted to establish engagement with the lower contact when the armature is actuated in that direction. This switch 83 may be designated a depth switch, in that its function is to determine the lower extreme position reached by the proximate end of the blade in its downward travel. A similar switch 93 is mounted on the other side plate of the machine. This switch likewise involves an upper contact '95, a lower contact 97, and an intermediate actuable armature '99 normally engaging the upper contact.

The lower switch is similar in'construction to the switch above it, but is reversed as to direction and utilizes in its operation only .a lower contact 101. The armature 103 of this switch will normally maintain engagement with this lower contact and is therefore a normally closed switch, which opens only in response to pressure against the actuable armature.

Mounted along side these switches but afiixed to the end of the blade is a scale 105. On this scale is adjustably mounted a stop 107 in line with the depth switcl183 so as to engage and actuate the same during downward movement of the ram, and inasmuch as it is mounted at the left end of the blade as viewed in the drawings, it will control the depth of stroke of this end of the blade. To assure microscopic accuracy asto such depth of stroke, the stop incorporates a micrometer adjustment 109 whereby such accuracy of adjustment may be .obtained.

Likewise at the far end of the machine, a similar stop 111 is affixed to that end of the blade in position to engage the depth limit switch 93 controlling the right end of the blade. The mounting of this stop, however, is preferably made adjustable on the blade by affixing it to a slotted strip 113 which is mounted for vertical adjustment on that end of the blade and adapted to be fixed in any such adjustment. The left depth stop 83 is connected to the lower end of the mounting strip of the right depth stop 111 by a cable 115 which is threaded under and over a pair of pulleys 117, 119 respectively, mounted at the left end of the blade and then extending across the blade and over a 'third pulley 121, and thence down to the lower end of the mounting strip 113. The adjustment of one stop, namely the left depth stop, will thereby determine the corresponding adjustment of the right depth stop, and when once both stops are adjusted and locked to "the ram the micrometer adjustments may thereafter be'made to assure the precision desired.

On the scale at a point below the upper limit switch 85 is adjustably mounted another stop 123, such stop being adapted to open the upper limit switch when the blade has reached a desired upper limit of travel. Inasmuch as the upper limit of blade movement is not critical, this latter stop need not include any micrometer adjustment.

Of extreme importance to the present invention is the provision of means which cooperates with the aforementioned hydraulic systems and associated switches to create operating characteristics in the machine which permit of extreme precision control and corresponding results in the nature of the Work accomplished by this machine. Extreme accuracy in the work output of the machine is the result of precision control in the operation of such machine, and such precision is realized in the functioning of the present invention by slowing up the movement of the ram during a critical period in its work stroke and more particularly just prior to the blade reaching the lower extremity of such stroke, and then exercising extremely close supervision and control of the ram during this period.

In terms of the overall length of the work stroke, the change in speed to the reduced value may be adjusted to occur when the blade is within A; of an inch of the lower extremity of its work stroke. To accomplish such change in speed, and to realize extreme precision and accuracy during such slow speed completion of the work stroke, a unique electrically controlled hydraulic system is provided which is cooperatively tied in with the previously described systems and associated switches whereby the changeover from the one to the other will occur automatically and at the proper point in the work stroke of the blade.

This unique hydraulic system includes a pair of relatively low capacity

flow control valves

127, 129 connected to receive operating fluid from the pump line of one of the main hydraulic systems and at a point in such line at pump pressure. One of these flow control valves 127 is connected by a pipe line 128, through a check valve 131 to the upper end of the left cylinder, while the other of said flow control valves 129 is connected by a pipe line 132 through a check valve 133 to the upper end of the right cylinder.

The flow in the line to the left cylinder is normally blocked by a normally closed valve 135 adapted to be opened in response to electrical energization of a solenoid 137 associated with such valve. In like manner, the flow to the upper end of the right cylinder is normally blocked by a normally closed valve 139 similarly actuable by an associated solenoid 141 when energized.

This low fiow capacity system is maintained unbalanced by utilizing fiow control valves which are of slightly different capacities, that associated with the left cylinder being preferably of slightly higher capacity than that of the other, whereby when passing liquid to their respective cylinders, the piston in the left cylinder will tend to always lead the piston in the right cylinder and in the absence of any correcting factors will always tend to cause the left end of the ram to lead the right end.

Such tendency to lead is compensated for by a third flow control valve 142 designated a precision level valve from its function in the system. This valve is connected across the lower capacity control valve 129 through a three gallons per minute and the right fiow -control valve, a capacity of 2.75 gallons per minute, then the precision level valve will have a capacity of about /2 gallon per minute.

When the capacity of the precision level valve is added to the flow through the right flow control valve, the combined output will exceed that of the left control valve, and when the precision level valve is closed, the output of the right flow control valve alone, will be less than that of the left control valve. By reason of their low capacities, these flow control valves, when they go into operation will necessarily reduce the speed of the blade from what it was when such blade was actuated by the fluid in the main hydraulic systems.

Hydraulic switching from the main hydraulic systems to the slow speed drive system including the flow control valves is accomplished in part by the inclusion of a valve 151 in the pressure equalizer line 35 to the blocking valve 29 of the main hydraulic system from which the slow speed drive system derives its hydraulic fluid. This valve is a solenoid controlled valve which is normally closed when its solenoid 152 is not energized. In the operation of the machine when the main hydraulic systems are doing the driving, the solenoid is electrically energized and thus holds the valve in its open position, ready to close upon being de-energized.

Cooperating with this valve in the hydraulic switching from the main hydraulic systems to the slow speed system, is a pipe connection 153, 155 respectively, from each of the flow

control valve lines

128 and 132 through its own check valve 157, 159 respectively, to the pressure equalizer line. Thus as the slow speed hydraulic system goes into operation, a portion of the fluid in the flow control valve lines will be discharged into the aforementioned pressure equalizer line. The closing of the precision control valve 151, forces this fluid to flow toward the blocking valve to oppose the pump pressure which tends to hold this blocking valve open. However, since this opposing pressure is approximately equal to the pump pressure, the opposing force exerted thereby will be sufiicient to close the blocking valve and completely divert the hydraulic fluid from the main hydraulic system to the slow speed precision hydraulic system.

The point in the work stroke at which the change in speed is afiected is automatically determined :by the location of a speed change switch 163 in the path of movement of the left depth stop 107. This switch involves an upper contact 165 and a lower contact 167 between which is disposed, an actuable armature 169 normally in contact with the upper contact and adapted to be depressed and held in engagement with the lower contact by pressure applied to a lever =17'1 pivotally mounted in contact with the armature.

Having described the various hydraulic systems and the various switches involved in the operation of the invention, one is now in position to consider the electrical control circuits which involve such switches and control the functioning of various hydraulic systems and valves therein.

The down or work stroke of the machine is initiated by electrical energization of the down solenoid 24 of the main operating valve. This solenoid is connectable across a power line 181 through the normally open contacts 183 of a starting relay 185 whose winding is connected at one end through the upper cont-act 165 of the speed change switch to a contact 187 ofa double pole double throw switch 189, and thence to the lower contact 191 of a two-way foot switch 193. The foot pedal :95 of this switch is connected to one side of the power From the other end of the relay, the circuit is completed to the other side of the power line through a pair of fast acting normally closed contacts 197 associated with a time delay relay 199, such circuit further including the emergency stop switches 67, 69 in series.

The starting relay .185, in addition to the first mentioned contacts, also includes a second pair of normally open contacts 201, which when closed in response to energization of the relay, will condition the level control circuits by connecting one side of the line to the armatures 51 and 55 of the level switches, the normally open contact 49 and 53 respectively of said switches being connected to the other side of the line through the solenoid 41 of an associated level control valve 39.

Of the two level control circuits, the left one includes in addition, the normally closed contacts 205 of a control relay -207, which remains unenergized until the speed change switch 163 is actuated.

When such actuation occurs, the armature of the speed change switch is depressed into engagement with the lower contact, thus breaking the circuit at the upper contact and making circuit with the lower one. Breaking of the .circuit at .the upper contact serves to deen er gize the starting relay 185, causing its contacts to fallout. This results in the main operating valve 21 being de-energized and forced to return to its neutral position, and the circuit to the level controls being opened. With the main operating valve in its neutral position, power to the machine from the main hydraulic systems is cut 05.

When the lower contact of the speed change switch is engaged, however, a number of things happen. The left cylinder precision valve 135 for one thing, is opened for flow of hydraulic fluid through the associated flow control valve 127 to the upper end of the left cylinder. This is accomplished by completing the circuit from the foot switch through the lower contact 167 of the speed change switch, thence to the upper contact 87 of the left depth switch and through the solenoid 137 of the valve to the other side of the line by way of the normally closed contacts 197 of the time delay relay and the emergency stop switches 67, 69.

The right cylinder precision valve 139 is likewise opened for flow to the upper end of the right cylinder by a circuit from the lower contact -167 of the speed change switch through the solenoid 141 of that valve and thence to the other side of the line by way ,of the right depth limit switch 93, the normally closed contact-s 197 of the time delay relayand the emergency stop switches 67, 69.

Along with the above, the control relay 207 is con nected in circuit through the same norm-ally .closed contacts of the time delay relay and the emergency stop switches, and is thereby energized to open its normally closed contacts 205 and thus disconnect the left level switch. At the same time, however, it closes two pairs 209, 21-1 of associated normally opened contacts. The closing of these two pairs of contacts conditions the left level switch for operation by transferring it to the solenoid 145 of the precision level valve '143.

Following actuation of the speed change switch, the ram or blade of the machine is under control of the slow speed precision hydraulic system. The movement of the ram at the slow speed continues for about one eighth of an inch to complete the down or work stroke thereof, as determined by engagement of the left and right depth stops with their associated switches. During this slow moving portion of the cycle, the speedchange switch is held in its actuated or down position.

To assure that the speed change shall take effect before either lower limit switch is actuated, it is within the purview of my invention to include a speed change switch at each end of the ram.

When the left depth switch is engaged, the upper contact 87 is opened which serves to de-energize the left cylinder precision valve 135 and thereby cut off hydraulic power to the left cylinder. Likewise, breaking of the circuit at the upper contact of the right depth switch will result in de-energizing the right precision valve and thereby cut off hydraulic power to the right cylinder. Inasmuch as the left cylinder precision valve and'the right cylinder precision valve are de-energized independently of each other, it becomes apparent that should one end of the blade lag slightly behind the other, the lagging end will necessarily have to complete its full stroke before power is removed from its associated cylinder. The ram or blade will therefore have to end up in accurate relationship to the work. As will be seen, a very minute lag is deliberately introduced during the slow moving portion of the cycle, by the functioning of the flow control valves '127, 129 and the precision level valve '143.

The

lower contacts

89 and 97 of the depth switches, are connected in series in a circuit which includes a relay 215, the normally closed contacts 197 of the delay relay, and the emergency stop switches 67, 69. This relay 215 therefore cannot become energized until both the right and left depth switches have closed at their lower contacts, and when energized, the relay will close a pair of normally opened contacts 217 associated therewith.

These contacts when closed, complete an energizing circuit through the time delay relay 199 by way of the lower contact 101 of the upper limit switch, which contact is automatically engaged by its associated armature 103 as soon as the ram begins its down stroke.

When the time delay relay is thus energized, its normally closed contacts 197 open immediately, which de-energizes the relay 215 and opens the time delay relay energizing circuit at the contacts 217. The time delay relay, however, is prevented from becoming de-energized at this time by the simultaneous closing of a pair of associated fast acting normally open contacts 219 associated with this relay which establish a holding-circuit by shunting the now open contacts 217.

After a slight delay, the closing of a pair of slow acting contacts 221, associated with the time delay relay, completes a circuit to a relay 223 having associated there.- with, two pairs 225 and 227 of normally open contacts, which close upon energization of such relay. The one pair 225 of such contacts, closes a circuit through the up solenoid 26 associated with the main operating valve 21 and thus restores hydraulic power to the machine to initiate an up stroke of the ram or blade.

Simultaneous therewith the closing of the second pair 227 of contacts restores the level control system for cooperation with the main hydraulic systems to keep the blade level during such up stroke. The ram or blade thus proceeds upwardly until the upper limit switch is opened by engagement of the stop 123 with the armature 103 of that switch, whereupon the circuit through the time delay relay is broken, which in turn results in deenergiz ing of-the-relay 223 and restoration of the main operating valve to its neutral position. The operating cycle is thus completed and the machine is ready for a subsequent .cycle which will follow automatically so long as the foot pedal is held in its down position. Should the foot pedal be released at the termination of a work stroke, the blade will return to its up position and stop. The circuit controlling this operation involves the up contact 195 of the foot switch, a second contact 229 on the switch 189, the lower contact 101 of the upper limit switch 85, all of which completes a circuit through the time delay relay 197 and starts the upward travel of the blade. Such upward travel comes to a stop when the upper limit switch is opened by the stop 123 engaging the same.

The time delay is introduced prior to energization of the relay 223, to afford the blocking valve 27 an opportunity to reestablish itself in preparation for the up stroke of the ram.

When operating in accordance with the cycle described above, the blade travels at a relatively fast rate and with substantial accuracy to within about one-eighth of an inch of the lower extremity of its work stroke. By this time it will have engaged the work and performed the better portion of its operation on such work. Within the short space of travel remaining for completing of the work stroke, the machine functions with exacting precision to complete its operation with microscopically accurate results in spite of the heavy character of the work performed. This is attributed to the functioning of the flow control valves and associated precision level valve.

The normal unbalance in the slow speed drive system brought on by the slight difference in capacity between the two flow control valves, will in the absence of any compensating force, produce a tilt of the ram sufficient to close the left level switch. This in turn will energize the precision level valve 143 to reverse the unbalance, for that brief moment required to level the ram and separate the left level switch contacts ever so slightly, whereupon the normal unbalance in the system will be restored and the leveling cycle repeated. The net result will be to cause the switch armature to hug the switch contact and microscopically hover about the make-and-break point of switch operation. This means that the ram will be microscopically controlled throughout the slow movement portion of its operation and this coupled with the independent halting of each end of the ram permits of accuracies within a thousandth of an inch.

Quite frequently, the nature of the Work is such as to make it desirable to place the operator in control of the blade position at any point in its down or up stroke. This will enable the operator to approach the work in steps, giving him an opportunity to make whatever adjustments are necessary in the position of the work as well as to affect adjustments of the blade stroke.

Such control may be realized merely through a flip of the double pole, double throw switch 189, which for convenience sake may be of the toggle type. In this position, only one contact 231 is utilized, and it is connected (l) to the armature 91 of the left stop switch to energize the left cylinder precision valve 135, (2) to the solenoid 141 to energize the right cylinder precision valve 139, and (3) to the solenoid of the precision control valve 151 to energize it, thus fulfilling the conditions for slow speed movement of the blade, the operator, however, maintaining control through the foot switch, whereby the blade may be stopped at any moment, thus permit ting intermittent movement at the slow speed. This is referred to as inching? When operating in this manner, the depth stops remain functional.

From the foregoing description of the entire system in its preferred form, it will be apparent that the same fulfills the objects of my invention. The system, however, is subject to alteration and modification without departing from the fundamental principles involved, and I accordingly do not desire to be limited in my protection to the specific details illustrated and described except as may be necessitated by the appended claims.

I claim:

1. A control system for press brakes or the like in which a ram approaches the work to perform an operation thereon and then has it direction of movement reversed, said control system comprising means for moving said ram toward said work, and means for automatically halting each end of said ram independently of the other end at the end of its work stroke to complete such operation with precision prior to such reversal of its direction of movement.

2. A control system for press brakes or the like in which a ram approaches the work to perform an operation thereon and then has its direction of movement reversed, said control system comprising means for moving said ram toward said work at a relatively rapid ,speed, means for substantially reducing said speed before completion of the work stroke, and means for automatically halting each end of said ram independently of the other end at the end of its work stroke to complete such operation with precision prior to such reversal of its direction of movement.

3. A control system for press brakes or the like in which a ram approaches the work to perform an operation thereon, said control system comprising means for .T10 moving said ram toward said work at a relatively rapid speed, means for substantially reducing said speed after engagement of said work by said ram and before completion of the work stroke, and means for microscopically halting each end of said ram independently of the other end in completing the work stroke.

4. A precision control system for press brakes or the like in which a ram approaches the work to perform an operation thereon, said control system comprising a hydraulic system of low flow capacity, said low flow capacity hydraulic system including a pair of low capacity fiow control valves, a drive cylinder at each end of said ram, a flow connection from one of said flow control valves to one of said drive cylinders, a flow connection from the other of said flow control valves to the other of said drive cylinders; a level switch; means in said low capacity hydraulic system for causing said ram during movement thereof, and in the absence of any correcting force, to effect a slightly greater rate of movement at one end than at the other end, said means involving a slightly greater flow capacity in one of said flow control valves than in the other, sufficient to unbalance the system and actuate said level switch; and means responsive to actuation of said level switch for reversing the unbalance of said system for a brief moment sufficient only to restore said switch and said system to their previous condition whereby said switch will be caused to hover about its make-and-break point of operation.

5. A precision control system for press brakes or the like in which a ram approaches the work to perform an operation thereon, said control system comprising a hydraulic system of low flow capacity, said low flow capacity hydraulic system including a pair of low capacity flow control valves, a drive cylinder at each end of said ram, a flow connection from one of said flow control valves to one of said drive cylinders, said connection including a normally closed valve, a flow connection from the other of said flow control valves to the other of said drive cylinders, said latter flow connection including a normally closed valve; a level switch; means in said low capacity hydraulic system for causing said ram during movement thereof, and in the absence of any correcting force, to eflect a slightly greater rate of movement at one end than at the other end, said means involving a slightly greater flow capacity in one of said flow control valves than in the other, sufiicient to unbalance the system and actuate said level switch; and means responsive to actuation of said level switch for reversing the unbalance of said system for a brief moment sufficient only to restore said switch and said system to their previous condition whereby said switch will be caused to hover about its makeand-break point of operation, said last means including a precision level valve connected across the flow control valve of lower capacity and having a capacity which when added to the capacity of said lower capacity valve will exceed the capacity of the larger capacity flow control valve, and a normally closed valve blocking flow through said precision level valve and adapted to open in response to actuation of said level switch.

6. A precision control system for press brakes or the like in which a ram approaches the work to perform an operation thereon, said control system comprising a hydraulic system of low flow capacity, said low flow capacity hydraulic system including a pair of low capacity flow control valves, a drive cylinder at each end of said ram, a flow connection from one of said flow control valves to one of said drive cylinders, said connection including a normally closed valve, a flow connection from the other of said flow control valves to the other of said drive cylinders, said latter flow connection including a normally closed valve; a level switch; means in said low capacity hydraulic system for causing said ram during movement thereof, and in the absence of any correcting force, to effect aslightly greater rate of movement at one end than at the other end, said means involving a slightly greater flow capacity ;in one of said flow control valves than in the other, suflicient to unbalance the system and actuate said level switch; means responsive to actuation of said level switch for reversing the unbalance of said system for a brief moment sutficient only to restore said switch and said system to their previous condition, whereby said switch will be caused to hover about its make and-break point of operation, said last means including a precision level valve connected across the flow control valve of lower capacity and having a capacity which when added to the capacity of said lower capacity valve will exceed the capacity of the larger capacity flow control valve, and a normally closed valve blocking flow through said precision level valve and adapted to open in response-to actuation of said level switch; and means for microscopically halting each end of said ram independently of the other end in completing the work stroke of said ram.

7. A precision control system for press brakes or the like .in which a ram approaches the work to perform an operation thereon, said control system comprising means for moving said 'ram toward such work at a relatively rapid speed, said ram moving means involving apair of main hydraulic systems each including a pump and a drive cylinder, with the drive cylinder of one hydraulic system in drive relationship to said ram at one end thereof and the drive cylinder of the other system in drive relationship to said ram at the other end thereof; means for substantially reducing the speed of said min before completion of the work stroke, said means involving a hydraulic system of substantially lower flow capacity than either of said main hydraulic systems, said low flow capacity hydraulic system including a pair of low capacity flow control valves, a flow connection from one of said flow control valves toone of said drive cylinders, said connection including a normally closed valve, a flow connection from the other of said flow control valves to the other of said drive cylinders, said latter flow connection including a normally closed valve, and means responsive to the arrival of the ram to the point of desired speed change switching thepower to said ram from said main hydraulic systems .to said low flow capacity'system; means in said 'low capacity hydraulic system for causing said ram during such reduced speed travel and in the absence of any'correcting force, to eifect a slightly greater rate of movement at one .end than at the other end; means responsive to such slightly greater rate of movement of one end of said ram for counteracting such difference in rate of movement between the ends of said ram; and means for microscopically halting each end of said ram independently of the other ,end in completing the work stroke of said ram.

8. A precision control system for pressbrakes or the like in which a ram approaches the work to perform an operation thereon, said control system comprising means for moving said ram toward such work at a relatively rapid speed, said ram moving means involving a pair of main hydraulic systems each including ,a pump and .a drive cylinder, with the drive cylinder of one hydraulic system in drive relationship to said ram at one ,endthereof and the drive cylinder of other system in drive relationship to said ram at the other end thereof; means for substantially reducing the speed of said ram after engagement with the work, but before completion of to one of said drive cylinders, said connection including a normally closed valve, a how connection from the other of said flow control valves to the other of said drive cylinders, said latter flow connection including a normally closed valve, and means responsive to the arrival of the ram to the point of desired speed change for switching the power to said ram from said main hydraulic systems to said low flow capacity system; and means for microscopically halting each end of said ram independently of the other end in completing the work strike of said ram.

9. A precision control system for press brakes or the like in which a ram approaches the work to perform an operation thereon, said control system comprising means for moving said ram toward such work at a relatively rapid speed, said ram moving means involving a pair of main hydraulic systems each including a pump and a drive cylinder, with the drive cylinder of one hydraulic system in drive relationship to said ram at one end thereof and the drive cylinder of the other system in drive relationship to said ram at the other end thereof; means for substantially reducing the speed of said ram after engagement with the work, but before completion of the work stroke, said means involving a hydraulic system of substantially lower flow capacity than either of said main hydraulic systems, said low fiow capacity hydraulic system being connected to the pump of one of said main hydraulic systems for its supply of fluid, and including a pair of low capacity flow control valves, a flow connection from one of said flow control valves to one of said drive cylinders, said connection including a normally closed valve, a flow connection from the other of said flow control valves to the other of said drive cylinders, said latter flow connection including a normally closed valve, and means responsive to the arrival of the ram to the point of desired speed change for switching the power to said ram from said main hydraulic systems to said low flow capacity system; a level switch; means in said low capacity hydraulic system for causing said ram during such reduced speed travel and in the absence of any correcting force, to eifect a slightly greater rate of movement at one end than at the other end, sufiicient to actuate said level switch; means responsive to actuation of said level switch for restoring said switch and said system to their previous condition whereby said switch will be caused to hover about its make-and-break point of operation; and means for microscopically halting each end of said ram independently of the other end in completing the Work stroke of said ram.

10. A precision control system for press brakes or the like in which a ram approaches the work to perform an operation thereon, said control system comprising means for moving said ram toward such work at a relatively rapid speed, said ram moving means involving a pair of main hydraulic systems each including a pump and a drive cylinder, with the drive cylinder of one hydraulic system in drive relationship to said ram at one end thereof and the drive cylinder of the other system in drive relationship to said ram at the other end thereof; means for substantially reducing the speed of said ram after engagement with the work, but before completion of the work stroke, said means involving a hydraulic system of substantially lower flow capacity than either of said main hydraulic systems, said low flow capacity hydraulic system being connected to the pump of one of said main hydraulic systems for its supply of fluid, and including a pair of low capacity flow control valves, a flow connection from one of said flow control valves to one of said drive cylinders, said connection includinga normally closed valve, a flow connection from the other of said flow control valves to the other of said drive cylinders, said latter flow connection including a normally closed valve, and means responsive to the arrival of .the ram to the point of desired speed change for switching the power to said ram from said main hydraulic systems to said low flow capacity system; a level switch; means in said low capacity hydraulic system for causing said ram during such reduced speed travel and in the absence of any ment at one end than at the other end, said means involving a slightly greater flow capacity in one of said flow control valves than in the other, suificient to unbalance the system and actuate said level switch; means responsive to actuation of said level switch for reversing the unbalance of said system for a brief moment suflicient only to restore said switch and said system to their previous condition whereby said switch will be caused to hover about its make-and-break point of operation, said means including a precision level valve of the flow control type connected across the flow control valve of lower capacity and having a capacity which when added to the capacity of said lower capacity valve will exceed the capacity of the larger capacity flow control valve, and a normally closed valve blocking flow through said precision level valve and adapted to open in response to actuation of said level switch.

11. A precision control system for press brakes or the like in which a ram approaches the work to perform an operation thereon, said control system comprising means for moving said ram toward such work at a relatively rapid speed, said ram moving means involving a pair of main hydraulic systems each including a pump and a drive cylinder, with the drive cylinder of one hydraulic system in drive relationship to said ram at one end thereof and the drive cylinder of the other system in drive relationship to said ram at the other end thereof; means for equalizing the travel of each end of said ram with respect to the other end, said means including a pair of level switches, each responsive to movement of one end of the ram in advance of the other end to effect a correction; means for substantially reducing the speed of said ram after engagement with the work, but before completion of the work stroke, said means involving a hydraulic system of substantially lower flow capacity than either of said main hydraulic systems, said low flow capacity hydraulic system being connected to the pump of one of said main hydraulic systems for its supply of fluid, and including a pair of low capacity flow control valves, a flow connection from one of said flow control valves to one of said drive cylinders, said connection including a normally closed valve, a flow connection from the other of said flow control valves to the other of said drive cylinders, said latter flow connection including a normally closed valve, and means responsive to the 14 arrival of the ram to the point of desired speed change for hydraulically switching the power to said ram from said main hydraulic systems to said low flow capacity system; means for simultaneously coupling said level switches to said low flow capacity system; means in said low capacity hydraulic system for causing said ram during such reduced speed travel and in the absence of any correcting force, to eifect a slightly greater rate of movement at one end than at the other end, said means involving a slightly greater flow capacity in one of said flow control valves than in the other, suflicient to unbalance the system and actuate one only of said level switches; means responsive to actuation of said level switch for reversing the unbalance of said system for a brief moment sufiicient only to restore said switch and said system to their previous condition whereby said switch will be caused to hover about its make-and-break point of operation, said means including a precision level valve of the flow control type connected across the flow control valve of lower capacity and having a capacity which when added to the capacity of said lower capacity valve will exceed the capacity of the larger capacity flow control valve, and a normally closed valve blocking flow through said precision level valve and adapted to open in response to actuation of said level switch; and means for microscopically halting each end of said ram independently of the other end in completing the work stroke of said ram.

References Cited in the file of this patent UNITED STATES PATENTS 1,999,834 Ernst Apr. 30, 1935 2,169,113 Sheppard Aug. 8, 1939 2,317,563 Tucker Apr. 27, 1943 2,343,167 Bench Feb. 29, 1944 2,462,580 Watson Feb. 22, 1949 2,558,071 Castle et al. June 26, 1951 2,565,639 Waldie Aug. 23, 1951 2,578,546 Havener Dec. 11, 1951 2,603,145 Dreis July 15, 1952 2,708,344 Greer May 17, 1955 FOREIGN PATENTS 894,596 France Mar. 20, 1944