US3749005A

US3749005A - Electrical control system for a power press

Info

Publication number: US3749005A
Application number: US00185186A
Authority: US
Inventors: M Einecker; K Mahorney
Original assignee: Danly Machine Corp
Current assignee: Wabash Alloys Inc; Avondale Industries Inc
Priority date: 1971-09-30
Filing date: 1971-09-30
Publication date: 1973-07-31
Anticipated expiration: 1990-07-31

Abstract

An electrical control system for a power press having three different modes of operation known as ''''inch,'''' ''''single stroke, '''' and ''''continuous.'''' The control system incorporates numerous safety features, one of which is that two ''''run'''' buttons must be held depressed at all times during the ''''inch'''' mode, and during the major portion of the downstroke in the ''''single stroke'''' mode so as to avoid the possibility of attempted single-handed operation by the operator, which would leave one hand free to enter the path of the ram. In the ''''single stroke'''' mode, a malfunction of the relay which stops the press ram at the end of each cycle renders the reset circuit inoperative so that the malfunction must be corrected before press operation can be resumed. In the absence of a malfunction, the resetting is performed automatically. In the ''''continuous'''' mode, the ''''run'''' buttons must be held down during a major portion of the downstroke of the ram, and an additional button must be depressed during the first stroke of the ram in order to put the press into the ''''continuous'''' mode of operation. If the mode selector switch is turned from one mode position to another, the system must be reset so that any malfunctions will be detected, thereby preventing the operator from switching from one mode to another to circumvent the effect of a malfunction. Various other fail safe features, redundancies, and double redundancies are also included.

Description

United States Patent [1 1 Eine'cker et al.

[451 July 31,1973

1 1 ELECTRICAL CONTROL SYSTEM FOR A POWER PRESS [75] Inventors: Mathew F.'Einecker, Hoffman Estates; Kenneth R. Mahorney, Bartlett, both of 111.

[73] Assignee: Danly Machine Corporation,

Chicago, 111.

[22] Filed: Sept. 30, 1971 [21] Appl. No.: 185,186

[52] US. Cl. 100/53, 192/131 R Primary Examiner-Billy .l. Wilhite Assistant Examiner-Philip R. Coe

Attorney-C. Frederick Leydig, Stephen G. Rudisill et al.

[5 7 ABSTRACT An electrical control system for a power press having three different modes of operation known as inch," single stroke, and continuous. The control system incorporates numerous safety features, one of which is that two run buttons must be held depressed at all times during the inch mode, and during the major portion of the downstroke in the single stroke mode so as 'to-avpid the possibility of attempted singlehanded operation by the operator, which would leave one hand free to enter the path of the ram. In the single stroke mode, a malfunction of the relay which stops the press ram at the end of each cycle renders the reset circuit inoperative so that the malfunction must be corrected before press operation can be resumed. 1n the absence of a malfunction, the resetting is performed automatically. 1n the continuous mode, the run buttons must be held down during a major portion of the downstroke of the ram, and an additional button must be depressed during the first stroke of the ram in order to put the press into the continuous mode of operation. If the mode selector switch is turned from one mode position to another, the system must be reset so that any malfunctions will be detected, thereby preventing the operator from switching from one mode to another to circumvent the effect of a malfunction. Various other fail safe features, redundancies, and double redundancies are also included.

13 Claims, 4 Drawing Figures PAIENTED mm mm sum 1 BF 2 ELECTRICAL CONTROL SYSTEM FOR A POWER PRESS DESCRIPTION OF THE INVENTION The present invention relates generally to power presses and, more particularly, to an improved control system for a power press.

Efforts have been made over the years to improve the safety and reliability of control circuitry for power presses and in particular to prevent spurious or accidental cycling which is a hazard to both the operator and the equipment. For example, where a certain safety function has been performed by a particular component, alternate or redundant means have been provided to insure that the function was performed. However, where the function has been performed by the alternate means, the press has continued to be operable even though there is evidence that a failure has occurred. Thus it has been necessary to rely upon periodic inspection procedures to being to light component failures in the system. While it has been known to employ warning signals to indicate failure of a safety component, this has not provided adequate protection because of the tendency of some operators to ignore warning signals in order to continue production, and because of the loss of a warning when the warning device itself fails to function.

Another problem with previous press control systems is that in the case of operation of the press in the continuous or automatically repeating mode, operation of the press, once initiated, has continued indefinitely and reliance, particularly where foot switch controls have been used has been placed upon use of point of operation guards to block access to the working area and upon the use of an emergency stop button. Unfortunately, in shops where formal safety procedures are lacking, such guards are often dispensed with. Similarly, in the conventional inching control which is intended primarily for use by skilled setup personnel in jogging the slide through small increments of movement it has been possible to complete a working cycle, and accidents have occurred when the press operator has resorted to inching control to do production work.

A further difficulty with previous press control systems is that the stroke selector switch which is employed to establish a desired mode of operation can generally be switched from one mode to another while the press is in operation and while this does not stop movement of the slide, operation of the press can then be reinitiated by use of the operating means alone. This may create a hazard, particularly if the setting of the selector is changed accidentally or without knowledge of the operator.

In general, while efforts have been made to incorporate fail safe" techniques in controls for power presses, prior press control systems have not employed such techniques fully to the point of cylical testing of the elements which are relied upon to insure that any failure occurs in a mode which is safe to both the operator and the equipment.

It is, accordingly, an object of the present invention to provide a control system for a power press which is inherently safer and more foolproof than systems which have been available in the past, and in which failure of a component serves to bring the press to a safe stop and minimizes the opportunities provided to the press operator to re-establish the system in operation by manipulation of the controls. It is specifically an object of the invention to provide a press control system which guards against the effect of sticking relays and which prevents the operator of the press from counteracting the sticking of relays by the expedient of manipulating the operating means.

It is another object of the invention to provide a press control system which prevents the carrying out of production work on the press by resort to the inch" mode, with any loss of the normal safety features of inch mode, in the event that regular operation in the run mode becomes impossible by reasons of circuit malfunction.

It is still another object of the present invention to provide increased safety when the press is operated in the continuous mode and which insures that the press will not be operated continuously except as a result of predetermined and essential action on the part of the operator. Thus it is an object to provide a press control system which enables the press to be more safely operated in the continuous mode.

It is a general object of the invention to provide a press control system which provides additional safety in all modes of operation, even where a foot switch is employed instead of the usual palm-operated run buttons.

It is another object of the present invention to provide a press control system which employs a mode selector switch but in which any attempt to change the mode during the course of a cycle results in shut-down of the press and requires resetting before operation may be resumed with the normal operating means.

It is yet another object of the invention to provide a press control system which makes increased use of failsafe techniques and in which failure of a component not only results in a safe condition of shut-down but in which redundant circuit elements, provided in the interest of safety, are automatically and continuously checked either during or after each press operation.

Then, too, it is an object of the invention to provide a control system for a power press which is conveniently switchable to provide the various modes of operation, which provides a high level of flexibility, and which is easily operated and highly economical as well as being easily and quickly serviced in the event that servicing becomes necessary.

Other objects and advantages of the invention will become apparent upon reading the attached detailed description and upon reference to the drawings in which:

FIG. 1 is a perspective view of a power press controlled by a control system embodying this invention;

FIG. 2 is an elevation of one of the control panels on the front of the press of FIG. 1;

FIG. 3 is an elevation of the other control panel on the front of the press of FIG. I; and

FIG. 4 is a schematic diagram of the control system associated with the control panels of FIGS. 2 and 3 for controlling the press of FIG. 1.

While the invention will be described in connection with certain preferred embodiments, it will be understood that it is not intended to limit the invention to these particular embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalent arrangements as may be included within the spirit and scope of the invention.

Turning now to the drawings and referring first to FIG. 1, there is shown a power press having a conventional type ram mounted for vertical reciprocating movement. As the ram is lowered, it strikes a workpiece positioned on the worktable l0, and then the ram is raised for the next operating cycle. A stroke selector switch SS is provided on one of the control panels (see FIG. 3) on the front of the press to permit selection of three different modes of operation, namely the inch mode, the single stroke" mode, and the continuous mode. The press can be stopped at any time by turning the selector switch SS to the "off" position or by pressing a stop button 12 on the second control panel (see FIG. 2) on the front of the press. The second control panel 13 represents the operators control station, and includes two palm-sized run-

inch buttons

14 and 15, a ready light 16, a reset button 17, a continuous button 18, and a top stop button 19.

When the selector switch SS is set to the inch" mode position, the operator depresses and releases the reset" button 17, after which the ready light 16 is illuminated. The operator then depresses and releases both run-inch palm-buttons l4 and 15 as desired to inch the ram through its stroke. As will be explained in more detail below, both buttons must be concurrently released whenever either button is released before the inch" mode of operation can be repeated.

When the selector switch SS is set to the single stroke" position, the operator again initiates press operation by depressing and releasing the reset" button 17, after which the ready light 16 is illuminated. The operator then depresses both run-inch" palm-buttons and holds them depressed through the major portion of the downstroke of the press ram. The rarn will then continue in motion stopping at the top of its stroke. If either

button

14 or 15 is released during the downstroke of the press ram, both buttons must be concurrently released and re-depressed before the ram motion can be re-initiated. The ram will stop at the top of its stroke regardless of whether either or both buttons are held depressed through the end of the stroke.

When the selector switch SS is set to the continuous" mode position, the operator again initiates operation of the press by depressing and releasing the reset pushbutton 17, after which the ready light 16 is illuminated. The operator then depresses both run-inch" palm-buttons l4 and 15 and holds them depressed through the major portion of the downstroke, and in addition he depresses the continuous pushbutton l8 sometime during the first stroke. The press will then continue to run. To interrupt the continuous operation and stop the ram at the top of a stroke, the operator momentarily depresses the "top stop" pushbutton 19.

Turning next to FIG. 4 for a more detailed description of the internal control system which responds to the various manually initiated operator commands described above, it should first be noted that all switches and contacts are shown in their normal positions prior to actuation of any of the manual controls, with all relays de-energized, and with all cams in their positions. All the cams are connected for rotation in synchronism with movement of the press ram, with each cam completing one revolution for each complete cycle of reciprocating movement of the ram; that is, each cam rotates 180 during each downstroke of the ram, and another 180 during each up stroke of the ram, or 360 for each complete stroke cycle of the ram,

with the 0 position normally being at the top of the stroke. All relay coils are identified by the designator CR with sequential prefix numbers, e.g., lCR; all relay contacts are identified by the designator of their controlling coil followed by the number of the line (see left side of FIG. 4) of the circuit diagram in which the respective contacts appear in FIG. 4, and further followed by suffix letters if two or more contacts controlled by the same coil appear in the same line, e.g., 2CR5a, 2CR5b; all switch-controlling cams are identified by the designator CLS with sequential prefix numbers, e.g., lCLS"; all cam-controlled switches are identified by the designator of their controlling cam followed by the number of the line of the circuit diagram in which the respective switches appear in FIG. 4, e.g., ICLS3"; all pushbutton-operated switches are identified by the designator PB followed by the number of the line of the circuit diagram in which the respective switches appear in FIG. 4, and further followed by suffix letters if two or more pushbuttonoperated switches appear in the same line, e.g., PB5a," PBSb; all air pressure operated switches are identified by the designator PS" followed by the number of the line of the circuit diagram in which the switch appears and all contacts controlled by the selector switch SS are identified by the designator SS followed by the number of the line of the circuit diagram in which the respective contacts appear in FIG. 4 and further followed by suffix letters if two or more contacts controlled by the selector switch appear in the same line, e.g., SS9a," SS9b."

The main power supply to the circuit illustrated in FIG. 4 is applied across lines L1 and L2. The primary outputs of the circuit are represented by solenoids S1 and S2 which control an air valve unit 40 of the type described in more detail in the assignees copending application Ser. No. 122,008, Filed Mar. 8, 1971, entitled Safety Valve Assembly for Controlling Clutch and Brake in Power Press or the Like," and invented by Kenneth R. Mahorney. As indicated by the title of the copending application, the air valve unit 40 controls the clutch and brake in the main press drive, in response to energization and de-energization of the two solenoids S1 and S2. More particularly, concurrent energization of both solenoids S1 and S2 engages the clutch of the drive unit, and releases the brake of the drive unit, whereas de-energization of either solenoid S1 or S2 disengages the clutch and engages the brake as described in more detail in the aforementioned copending application. In addition to controlling the clutch and brake, the air valve unit 40 mechanically actuates two pairs of limit switches .86, 11.812 (corresponding to limit switch 61 in the copending application) and 21.86, 2LS12 (corresponding to limit switch 62 in the copending application). When the solenoids S1 and S2 are de-energized, the limit switches 1LS6 and 2LS6 are closed and limit switches 11.812 and 21.812 are open. As indicated schematically in FIG. 4, the valve operated by solenoid 81 controls switches lLS6 and lLSl2 while the valve operated by solenoid S2 controls switches 2LS6 and 2LS12. Since the limit switches are mechanically actuated by the valves, of course, they provide a means of determining any malfunction of the valves.

When the press ram is at the top of its stroke, the control circuit is in the state illustrated in FIG. 4, with the brake engaged and the clutch disengaged. To insure that the air supply 41 for the air valve unit 40 is sufficient for proper operation of the clutch and brake, this air supply controls a switch PS1, closing the switch PS1 when the air pressure is above a prescribed minimum pressure. If the switch PS1 is open due to insufficient air pressure at the source, power is cut off from the entire control system so that the press is inoperative until the requisite air pressure is provided.

The stop pushbutton 12 on the press control panel 13 controls a switch PBl connected in serieswith the switch PS1 and is normally closed. If the operator presses the stop pushbutton 12, the switch P81 is opened to cut off the power supply from the entire control system, with the same effect as opening of the switch PS1. Turning now to the single stroke mode of operation of the control system shown in FIG. 4, when the selector switch SS on the press control panel 11 is set to the single stroke position, it closes selector switch contacts SS3 and SS9b, the function of which will be apparent from the ensuing description. Next the operator depresses the reset pushbutton 17 on the control panel 13, thereby opening switch Pl36a to prevent an anti-repeat" relay ICR from energizing before the reset button 17 is released. Next, the reset button 17 closes switch PB2 to energize a checking relay coil 3CR via normally closed contact 1CR3. The relay coil ICR which controls contact 1CR3 is an antirepeat relay which automatically stops the press ram at the end of each up stroke in the single stroke mode, as will be described in more detail below. If this relay coil lCR becomes stuck in its energized position due to a malfunction, the contact 1CR3 remains open and the checking relay coil 3CR cannot be energized when the reset button is depressed. Thus, the contact 1CR3 represents a safety feature which prevents operation of the press in the event of a malfunction of the anti-repeat relay coil lCR. It can be seen that it is important to open switch PB6a before closing switch P82 because otherwise relay coil lCR could energize and open contact 1CR3 to de-energize coil 3CR before it locked itself in (the locking in of 3CR will be described below).

If the contact 1CR3 is in its normally closed position, thereby energizing the relay coil 3CR upon closing of the reset switch PB2, contact 3CR4 closes to bypass the reset switch P82 and switches 1CLS3 and 3CLS3 to lock in the relay coil 3CR through switch SS3 and a normally closed cam-operated switch 2CLS3. Consequently, if the selector switch SS is moved to a different position, the relay coil 3CR is de-energized to deactuate the press drive by opening contact 3CR6 and thereby de-energizing solenoids S1 and S2. This is an important safety feature of the present control system because press operators sometimes attempt to overcome a press shutdown effected by a safety feature, while the press is in the single stroke mode, by switching the selector switch SS to a different position. With the control system of the present invention, however, switching the selector switch SS to a different position immediately de-energizes the relay coil 3CR so that it is necessary for the operator to again depress the reset pushbutton, thereby initiating all of the automatic checks effected by the closing of the reset switch PR2.

Energization of relay coil SCR also opens contact 3CR7 so as to prevent a short circuit to ground after the reset button is released to close switch PB6a. The relay coil 3CR also closes contact 3CR8 to enable sub sequent energization of relay coil 2CR via switches to I be described below.

In addition to the contact operation mentioned above, energization of the checking relay coil 3CR closes contacts BCRIl and 3CR5 and opens contact 3CRll2, all for purposes to be discussed in detail below.

When the operator releases the reset button 1?, switch PBZ returns to its normal open position and switch PB6a returns to its normal closed position. As mentioned previously, the opening of switch P132 does not result in de-energization of the relay coil 3ClR since this relay is locked in through its own contacts 3CR4. The closing of switch PBtfia energizes the anti-repeat relay coil llCR via switches SS3, 1CLS6, 4CR6, 3CR6, 11.86, 2LS6, PBfia, PBhb, PBfic, ZCRSb, PBSa, PBSb, and 2CR4. If the run relay coil ZCR remains energized due to a malfunction during the previous cycle, contacts 2CR5b and 2CR4 remain open so that relay coil lCR cannot be energized, thereby providing a safety check on the run relay ZCR.

Itwill be appreciated that the anti-repeat relay llCR provides a safety check on all the switches included in its energization circuit. More specifically, if the relay lCR is not energized, its contact 1CR8 remains in the open position, thereby making it impossible to energize the solenoids S11 and S2 so that the press drive cannot be actuated, and preventing illumination of the ready light. Thus, the relay KCR provides a safety check on the two run-inch" buttons 14 and 15 which control switches PBSa and PBSb (this is an important safety check because thepress operators sometimes attempt to effect permanent actuation of the run-inch" palm-buttons which control switches PBSa and PBSb by wedging or taping the buttons in their depressed positions, so that the operator can control the press by single handed operation of only one of the pushbuttons; such single handed operation is an inherently dangerous situation due to the fact that the operator would have one hand free to manipulate the workpiece within the closing travel path of the press ram); the top-stop pushbutton i9 controlling switch lPBtic; the continuous pushbutton i8 which controls switch PBtSb; the reset" pushbutton 117 which controls switch PBoa; the air valves that control switches liLSb and 21486; relay coil ECR which controls contact SCRb (which is open if the relay coil SCR is not locked in through its own contacts); relay coil AlClR which controls contact sons (if this relay 4CR is stuck in its energized position, contact 4CR6 remains open); cam llCLS as well as the ram position reflected by the cam (if the ram has not completed a full cycle in its previous stroke, and thus is not properly positioned to begin a new stroke, so that the ram is between its 320 and 340 positions, the cam llCLS holds the switch iCLStS open); and the selector switch SS which controls switch 883..

When the relay ilCR is energized, it closes a contact 1CR4 so as to bypass switches ZCRSb, PB5a, PBSb, and ZCRi, so that the relay llClR remains energized independently of these four switches. The relay llCR also closes contact HCRS which prevents energization of the press drive unit in the event of a failure of the relay ICR to energize. The closing of contact ICR also energizes the ready" light 16 on the control panel 113 of the press, so as to indicate to the operator that the press is ready for operation in the selected mode.

After the ready" light s is energized, the operator must depress both run-inch pushbuttons M and 15 to initiate a stroke of the press ram, and these buttons must be held depressed until the ram has traversed at least 150 of its complete stroke cycle, i.e., until the ram is near the bottom of the down stroke. Depression of the

pushbuttons

14 and 15 opens switches PBSa and PBSb, but this does not affect the energization of relay lCR since the closing of contact 1CR4 bypassed the two switches PBSa and PBSb. The

same pushbuttons

14 and 15 close switches PBSa and PB8b, thereby energizing the run relay 2CR which closes contacts 2CR9 and 2CR10 to concurrently energize the solenoids S1 and S2 and thereby acutate the press drive. As the press drive is acutated, the opening of the air valves within the air valve unit 40 closes switches lLSl2 and 2LS12 for a purpose to be described below. The same air valves also open switches lLS6 and 2LS6 thereby opening the orginal energizing circuit to relay lCR. However, the energization of relay 2CR closes 2CR8 so that the relay lCR remains energized through a circuit extending from switch lCLS6 through 2CR8 and switch PB6c. This places energization of the relay lCR under the control of relay ZCR, since de-energization of relay 2CR opens the contact 2CR8 and thereby deenergizes relay lCR. This is an important safety feature because it means that if the operator releases either of the "run-

inch pushbuttons

14 or 15 during the down stroke of the ram, he must release both pushbuttons l4 and 15 before operation can be resumed. For example, assume that switch PB8a is opened by release of the corresponding pushbutton, but switch PB8b remains closed because the operator has taped or wedged the corresponding pushbutton in its depressed position. In this situation, the relay 2CR is de-energized by the opening of switch PBBa, thereby stopping the press. In addition, however, relay contact 2CR8 opens, thereby de-energizing the anti-repeat relay ICR. At this point the only way to resume press operation is to re-energize relay lCR, since contact 1CR8 must be closed to energize the run relay 2CR and re-start the press. However, relay lCR cannot be re-energized unless both switches PBSa and PBSb are closed, and thus the operator must release both of the run-inch pushbuttons. Consequently, in order to re-start the press, the operator must release both run-inch pushbuttons so as to allow them to return to their normal positions.

When the ram traverses 95 of its stroke cycle, the cam 3CLS closes a switch 3CLS10 so as to bypass the contact 3CR8, thereby enabling an alternate energizing circuit for the run relay ZCR after the checking relay 3CR is de-energized. The cam 3CLS also opens a switch 3CLS3 for a purpose to be described below.

When the ram traverses 150 of its stroke cycle, the cam 2CLS opens a switch 2CLS3 so as to de-energize the checking relay 3CR. This returns all of the contacts associated with relay 3CR to their normal positions. The closing of contact 3CR7 has no effect in normal operation of the press since contacts ZCRSb and 2CR4 are open. However, if a ground exists in the switches PB5a or PB5b or their wiring, for example, the closed contact 3CR7 shorts out the line to this ground via contact 2CR8, switch lCLS6 and switch SS3, thereby blowing the main circuit fuses. This is an exceptional safety feature, in that it blows the main fuses and shuts down the entire press, but it averts an exceptionally dangerous position in that it prevents the operator from attaining single handed operation by permanently depressing a shorted switch.

Returning to the effect of the de-energization of checking relay 3CR, an alternate energizing path for the run relay 2CR is provided by the opening of contact 3CR8 and the closing of contact 3CR12. More particularly, the original energizing circuit through contact 3CR8 is opened, and the new energizing circuit is through 2CR11, 3CR12, 2LS12, 1Lsl2, SS9b, 3CLS10, 1CR8, 2CR8, lCLS6, and SS3. (It should be noted that if switch 3CLS10 was not closed at the takeover sub-mode is not achieved, so that both switches 3CLS10 and 2CLS3 are necessary parts of the takeover system.) At this point the control system is in a take-over sub-mode in which the run-

inch pushbuttons

14 and 15 may be released and the control system automatically takes over to continue completion of the ram stroke cycle in progress. More specifically, the ram cycle is continued since relay 2CR is energized via contact 3CR12 rather than via contact 3CR8 and switches PB8a and PB8b. It will be appreciated that this take-over sub-mode is not attained until the ram is into its stroke cycle, i.e., until the relay CR3 is deenergized. At this point in the stroke cycle, the ram has nearly completed its down stroke, and there is little or no danger to the operators hands. In the event of a malfunction of the relay 3CR or the cam 2CLS or its switch 2CLS3, the press will stop when the operator releases either one or both of the run-inch"

pushbuttons

14 or 15, thereby providing the operator with an indication of the malfunction.

When the press ram traverses 320 of its stroke cycle, cam lCLS opens a switch 1CLS6 to de-energize the relay 2CR, relay lCR, and solenoids S1 and S2, thereby disengaging the clutch and applying the brake as previously described and returning all the contacts associated with 1CR and 2CR to their normal positions until initiation of the next operating cycle. Consequently, the ram movement is stopped at the end of its stroke regardless of what the press operator does. The resultant closing of the air valves in the air valve unit 40 opens switches 1LS12 and 2LS12 and closes switches 1LS6 and 2LS6 thereby resetting these switches for the next cycle of operation.

Although the press drive is de-energized when the ram reaches 320 of its stroke cycle, the inertia of the ram carries it on to its 360 point. When the ram traverses 325 of its stroke cycle, the cam 3CLS opens the switch 3CLS10 to provide a redundancy for the switch lCLS6. Thus, if the switch 1CLS6 should fail to open at the 320 point, the relay 2CR is still de-energized along with solenoids S1 and S2 at the 325 point by the opening of switch 3CLS10. The de-energization of relay 2CR in turn de-energizes lCR by opening contact 2CR8. [n the event of a malfunction in the cam lCLS, the press will still be stopped by the redundant switch 3CLS10, but the cam switch ICLSS will remain open, thereby resulting in a loss of the automatic reset feature to be described below, providing the operator with an indication of the malfunction.

At the 325 point, the cam 3CLS also closes a switch 3CLS3 to initiate an automatic resetting of the control system. That is, the closing of the switch 3CLS3 has the same effect as the closing of the reset switch PB2, since switches SS3, 2CLS3, and 1CLS3 are all closed in series with switch 3CLS3. Switch 1CLS3 was previously closed at 320 by cam lCLS when it opened switch lCLS6, and switch 2CLS3 was previously closed at 270 by cam ZCLS. However, in the event of a failure of the relay lCR to drop out, so that it remains energized, the contact 1CR3 is open so that the automatic reset cannot occur. Furthermore, the system cannot be manually reset by closing the switch PBZ because the contact 1CR3 is located between swtich H32 and relay 3CR. Nor will holding the run-inch palm-buttons l4 and depressed during the entire preceding stroke cycle be effective to continue operation of the machine. Thus, it can be seen that if the anti-repeat relay lCR is not de-energized at the end of a stroke cycle, the control system cannot be reset until the malfunction is corrected.

When the press ram traverses 340 of its stroke cycle, the cam lCLS closes switch lCLS6 to automatically re-energize the anti-repeat relay lCR via SS3, lCLS6, 4CR6, 3CR6, lLS6, 2LS6, PB6a, PB6b, PB6c, 2CR5b, PBSa, PBSb and 2CR4. At this point the control system has been automatically reset and the ready light 16 is illuminated to indicate that the press is in condition for another cycle of operation in the single stroke mode. It should be noted that this automatic resetting of the control system does not bypass any of the safety checks effected by the manual reset in response to closing of the switch PB2 as described above. This automatic resetting of the control system provides a convenience for the operator in that it enables him to initiate successive single strokes by merely depressing the two run-inch" palm-buttons l4 and 15 without manually pressing the reset" pushbutton 17 between successive strokes.

Turning next to the inch" mode of operation of the illustrative system, this mode of operation is selected by turning the selector switch SS on panel 11 to the inch" position, thereby opening switch SS3 and closing switch 88%. This inch mode of operation enables the operator to run the press ram through its stroke in small, sequential increments, with a pause after each incremental movement of the ram. Before operation of the press can be commenced in this mode, the control system must be reset by depressing the reset pushbutton 17, as in the single stroke" mode. One difference in the reset operation is that the relay 3CR is locked in through its contact 3CR1 and switch SS1 which is closed in response to setting of the selector switch SS to the inch position. Consequently, if the selector switch SS is moved to a different position, the switch SS1 opens to prevent lock-in of the relay coil 3CR so that a manual reset is required to resume operation of the press. Also, the closing of contacts 3CR4 and 3CR5 in response to energization of the relay 3CR serves no functional purpose in this mode, since the switch 88% is also closed. The opening of contact 3CR12 is also idle since both switches 88% and 8811 are open in this mode.

When the anti-repeat relay coil ICR is energized in the inch mode, in response to release of the reset" pushbutton 17, the energization path is the same as that described above for the single stroke mode except that switch SS9a replaces switches SS3 and 1CLS6 in the energization circuit for the relay coil lCR. The cam-operated switch lCLS6 is the "top stop switch which is not used in the inch mode and therefore need not be checked by including it in the energization path for relay coil lCR.

After the reset operation is completed, the operator initiates inching, incremental motion of the press ram by simultaneously depressing both of the run-inch" W palm-buttons l4 and 15. To interrupt the inching process, the operator releases either or both of the two run-inch palm-buttons. To resume operation, the operator must release both run-inch" palm buttons and then concurrently re-depress them.

When the run-inch pushbuttons are depressed so as to open switches PBSa and PBSb and close switches PB8a and PB8b, the operation is similar to that described above in the single stroke" mode except that the checking relay 3CR is never de-energized due to the closure of switch SS1. Thus, the switches controlled by the cams lCLS, 2CLS and 3CLS are all bypassed, either by switch SS1 or switch SS9a, so that there is no take-over sub-mode and, therefore, no end-of-cycle operation. Consequently, energization and deenergization of the solenoids S1 and S2 is controlled manually by the run-inch switches PB8a and PB8b.

If the operator releases either of the run-inch palm buttons, the opening of the corresponding switch PBBa or PB8b de-energizes the relay ZCR and the solenoids S1 and S2. The resultant closing of the two valves in the air valve unit 40 closes the two limit switches 1LS6 and 2LS6 to enable a re-energizing circuit to the coil lCR. It will be recalled that energization of the anti-repeat relay coil lCR is under the control of relay coil 2CR via contact 2CR8 so that the coil ICR is de-energized each time the coil 2CR is de-energized. To complete the reenergization path to coil ICR, contacts 2CR5b and 2CR4 are also closed. In order to re-start the press, the operator must release both run-inch" palm-buttons M and 15 to close both switches PBSa and PBSb to energize the relay lCR. Energization of relay coil lCR then closes contact 1CR4 to lock in the coil lCR via contact 1CR4, bypassing switches 2CR5b, PBSa, PBSb, and 2CR4. Contact 1CR8 also closes, thereby enabling the energizing circuit to relay coil 2CR so that the press is started again when the operator concurrently depresses both run-inch palm-buttons to concurrently close the two switches PB8a and PB8b.

In the inch mode, the press does not stop at the top of each stroke, since the top-stop switches llCLS6 and 3CLS10 are idle. However, since both of the operator's hands must be on the run-inch palm-buttons for the press to run, i.e., there is no take-over" sub-mode, there is no danger of single handed operation by the operator. When the operator wishes to stop the press as the ram inches toward the top of its stroke, he merely releases either or both of the run-inch palm-buttons. The circuit then automatically returns to its original reset configuration, ready for the operator to resume the inching process. If, however, the operator changes the position of the selector switch SS, the relay coil 3CR drops out due to the opening of switch SS1, and then coil lCR drops out due to the opening of 889a and the reset configuration of the circuit is lost.

To operate the press in the continuous mode, the operator switches the selector switch SS on panel 11 to the continuous" position, thereby closing switches SS5, SS7, and SS1 1. In this mode, the operator initiates press operation in the same manner asin the single stroke" mode, then depresses an additional continuous pushbutton 18 so that the control system automatically recycles the press until it is stopped. When the operator depresses and releases the reset" pushbutton 17, and then depresses the two run-

inch palmbuttons

14 and 15 to initiate press operation, the operation of the control system illustrated in FIG. 4 is the same as described above for the single stroke mode, except that switch SS takes the place of switch SS3. All the safety features which are operative during the single stroke mode are also operative during the downstroke of the initial cycle of the continuous mode.

During the downstroke of the initial cycle, when the press ram reaches the 150 point, the control system operates in the take-over" sub-mode. At this point, the operator can remove both hands from the runinch" palm-buttons and, if the operator does nothing more, the press will continue to operate precisely as in the single stroke mode, even though the selector switch SS is in the continuous position. However, if the operator depresses the continuous pushbutton during the initial cycle, the control system takes over operation of the press and causes it to operate in a continuous, recycling fashion with no stopping at the top of each stroke, until the operator depresses the top stop" pushbutton 19. The requirement that the operator depress the continuous pushbutton in order to achieve the continuous mode of operation is an important safety feature, in that it prevents the operator from inadvertently depressing both run-inch palm-buttons thinking he is in the single stroke mode, when in fact he is in the continous mode, and having the press continue in operation when in fact the operator would expect it to stop at the completion of a single stroke cycle. Thus, unintentional continuous operation is avoided by the requirement that the operator both set the selector switch SS in the continuous" position and additionally depress the continuous pushbutton 18 at some time during the initial cycle of operation.

Returning now to FIG. 4, when the operator depresses the continuous pushbutton 18, a switch PB6b is opened and P813 closes. The closing of switch P813 energizes a relay coil 4CR via P813, S813, 3CLS10, (or 3CR8 if the continuous" pushbutton is depressed before 150 of the first cycle is completed, i.e., when relay coil 3CR is still energized), 1CR8, 2CR8, lCLS6, and SS5. It will be noted that this energizing path provides a number of safety features, namely: the coil 4CR cannot be energized unless the selector switch SS is in the continuous" position, so that depressing the continuous" pushbutton 18 in either the single stroke or inch" mode cannot energize coil 4CR to produce accidental continuous operation; coil 4CR cannot be energized if the continuous" pushbutton is depressed before the ram stroke is initiated (even if coil 4CR is energized due to a malfunction, the open contact 4CR6 prevents coil lCR from energizing so as to prevent stroke initiation); if the continuous" pushbutton is depressed during the first 150 of the initial downstroke of the press ram, the coil 4CR is energized but the operator must still keep both hands on the run-inch palmbuttons until the coil 3CR drops out at the 150 point, thereby closing contact 3CR12, and keeping coil 2CR energized in the continuous mode.

Energization of the relay coil 4CR closes contact 4CR7 to bypass the top stop switch 1CLS6 via 1CR7 and SS7 to eliminate the top stop feature of the single stroke" mode of operation. Finally, energization of coil 4CR closes contacts 4CR14 and 4CR15 to lock in the coil 4CR via 4CR14, 4CR15, 2CR8, 4CR7, lCR7, and SS7, thereby bypassing the top stop backup switch 3CLS10 and lCR8.-

When the operator releases the continuous pushbutton, switch PB6b closes and switch PB13 opens, but the relay coil 4CR remains energized due to its lock-in energizing circuit as described above. The control system is now in the continuous mode of operation, with relay coils 4CR, 2CR, and lCR all energized, independently of the switches controlled by cams CLS], CLS2, and CLS3. Consequently, the press continues in operation until the operator depresses the top stop" pushbutton 19.

When the operator depresses the top stop pushbutton l9, switch PB6c is opened, thereby de-energizing relay coil ICR. When relay coil lCR is de-energized, contact 1CR7 opens, but the press continues to run since coils 2CR and 4CR remained locked in via contacts 4CR14, 4CR15, and 2CR8, and switches lCLS6 and SS5. The opening of the contact 1CR7 puts the relay coils 2CR and 4CR under control of the top stop switch 1CLS6, since both coils 2CR and 4CR are now energized via switch 1CLS6. Consequently, when the press ram passes the 320 point in its stroke cycle, the resultant opening of switch 1CLS6 de-energizes both coils 2CR and 4CR and solenoids S1 and S2 so that the press stops at the top of the ram stroke as in the single stroke mode.

When the press ram reaches the end of its stroke cycle, the switch lCLS6 closes again so that the circuit is ready for the nest cycle operation. In the event that the switch 1CLS6 were to fail to close due to a malfunc tion, no further operation of the press is possible except in the inch" mode. Another safety feature is that if the relay coil 4CR does not drop out, due to a malfunction, contact 4CR6 remains open, so that no further operation of the press is possible.

As can be seen from the foregoing detailed description, the control system provided by this invention is inherently safer and more foolproof than systems that have been available in the past, in that it serves to bring the press to a stop at the end of a cycle while minimizing the opportunities provided to the press operator to maintain the system in operation by manipulation of the controls. The present control system guards against sticking of relays and prevents the operator of the press from counteracting the sticking of relays by the by the expedient of holding down run buttons. The system also prevents switching from one mode to the other in the event of a malfunction in the first mode, and provides increased safety when the press is operated in the continuous mode, insuring that the press will not be operated continuously except as a result of predetermined and essential action on the part of the operator. This control system makes increased use of fail safe techniques in that failure of a component not only results in a safe condition of shutdown, but also redundant circuit elements are automatically and continuously checked either during or after each press operation. All of these safety features are provided in a control system which is also conveniently switchable to provide the various modes of operation, which provides a high level of flexibility, and which is easily and highly economical as well as being easily and quickly serviced.

We claim as our invention:

1. An automatic control system for a power press having a vertically reciprocating ram, said control system comprising the combination of a selector switch having an inoperative position and a first operative position for enabling movement of the press ram through one cycle of reciprocating movement, a second operative position for enabling movement of the press ram through successive increments of its reciprocating cycle according to manually initiated command signals, and a third operative position for enabling movement of the press ram continuously through repetitive cycles of reciprocating movement, reset means operatively connected to said selector switch and including a manually operated actuator for enabling movement of the press ram when said selector switch is in any one of its three operative positions, a pair of spaced apart, manually operated press actuators operatively connected to said selector switch and to said reset means and having operative positions for initiating movement of the press ram when said selector switch is in any one of its three operative positions and when said reset means is actuated, and means responsive to the switching of said selector switch from one of its operative positions to another for stopping movement of the press ram and rendering said press actuators inoperative until said reset means is acutated again.

2. An automatic control system as set forth in claim 1 which includes single stroke mode control means responsive to movement of the press ram and operatively connected to said selector switch for automatically stopping the press ram at the end of one cycle of reciprocating movement when said selector switch is in said first operative position regardless of whether said press actuators are operated at the end of said cycle.

3. An automatic control system as set forth in claim 2 which includes automatic resetting means responsive to movement of the press ram for automatically acutating said reset means at the end of each ram cycle so that successive single strokes of the ram can be effected by operating said press actuators without manually actuating said reset means between successive ram strokes.

4. An automatic control system as set forth in claim 3 which includes second single stroke mode control means responsive to movement of the press ram and operatively connected to said selector switch for automatically stopping the press ram at the end of one cycle of ram movement when said selector switch is in said first operative position regardless of whether said press actuators are in their operative positions at the end of said cycle, said second single stroke mode control means also being responsive to a malfunction of said first single stroke mode control means for rendering said reset means ineffective so that further movement of the press ram is prevented until the malfunction of said first single stroke mode control means is corrected.

5. An automatic control system as set forth in claim 4 which includes a third single stroke mode control means for rendering said press actuators inoperative in response to a malfunction of said second single stroke mode control means so that further movement of the press ram is prevented until the malfunction of the second single stroke mode control means is corrected.

6. An automatic control system as set forth in claim 2, which includes control means responsive to movement of either of said press actuators away from its operative position for stopping ram movement and rendering both press actuators inoperative until both of said press actuators are concurrently moved away from their operative positions and then concurrently returned to their operative positions.

7. An automatic control system as set forth in claim 1 which includes control'means responsive to movement of either of said press actuators away from its operative position for stopping ram movement and rendering both press actuators inoperative until both of said press actuators are concurrently moved away from their operative positions and then concurrently returned to their operative positions.

8. An automatic control system as set forth in claim 7 which includes a continuous mode control means responsive to movement of the press ram and including a manual actuator for automatically repeating successive cycles of ram movement only when said manual actuator is moved to an operative position, when the press ram has traversed a selected initial portion of the first half cycle of ram movement, and when said selector switch is in said third operative position.

9. An automatic control system as set forth in claim 1 in which said press acutators initiate movement of the press ram, via press operating control means, and which includes means for rendering said press actuators inoperative in response to a malfunction of said press operating control means so that further movement of the press ram is prevented until the malfunction of the press operating control means is corrected.

10. An automatic control system as set forth in claim 1 which includes means responsive to movement of the press ram and operatively connected to said press actuators for automatically stopping ram movement in response to movement of either of said press actuators away from their operative positions during a selected initial portion of the first half cycle of ram movement, and means operatively connected to said selector switch and responsive to movement of the press ram for automatically continuing movement of the press ram through the remaining portion of the ram cycle regardless of the position of said press acutators, when said selector switch is in said first operative position.

- 11. An automatic control system as set forth in claim 1 which includes means for de-energizing the entire control system in response to a grounding of one of said press actuators or the wiring associated thereto.

12. An automatic control system as set forth in claim 1 which includes a continuous mode control means responsive to movement of the press ram and including a manual actuator for automatically repeating successiv'e cycles of ram movement only when said manual actuator is moved to an operative position, when the press ram has traversed a selected initial portion of the first half cycle of ram movement, and when said selector switch is in said third operative position.

13. An automatic control system as set forth in claim 12 which includes a top stop control means having a manual acutator for automatically stopping the press ram at the end of a cycle in response to movement of said actuator to an operative position at any time during said cycle.

f 10 "o" i

Claims

7. An automatic control system as set forth in claim 1 which includes control means responsive to movement of either of said press actuators away from its operative position for stopping ram movement and rendering both press actuators inoperative until both of said press actuators are concurrently moved away from their operative positions and then concurrently returned to their operative positions.

11. An automatic control system as set forth in claim 1 which includes means for de-energizing the entire control system in response to a grounding of one of said press actuators or the wiring associated thereto.

12. An automatic control system as set forth in claim 1 which includes a continuous mode control means responsive to movement of the press ram and including a manual actuator for automatically repeating successive cycles of ram movement only when said manual actuator is moved to an operative position, when the press ram has Traversed a selected initial portion of the first half cycle of ram movement, and when said selector switch is in said third operative position.