US 3911344 A
A control system for presses and the like of the type having a path for insertion and removal of work pieces includes a motor operated protective shutter insertable into the work piece insertion and removal path and a photocell system defining a light controlled area arranged transversely across such path and on the operator's side of the shutter. Circuitry responsive to the condition of the photocell device controls operation of the shutter motor. Press releasing circuitry, actuable to permit initiation of a press cycle, is controlled by contacts actuable by the shutter and by timing circuitry. Operation of the timing circuitry is initiated when the light controlled area, or light curtain, becomes unoccupied, the timing circuitry operating for a short time within which the shutter initiates and completes its closing movement. Then, the press is released for initiating a press cycle, in response to the contacts sensing the closed position of the shutter and in cooperation with the timing circuitry.
Description (OCR text may contain errors)
[ Oct. 7, 1975 United States Patent Svensson  CONTROLLING SYSTEM IN PROTECTIVE Primary Examiner-Bcnjamin Dobeck DEVICES OF PHOTOCELL TYPE FOR PRESSES AND THE LIKE Attorney, Agent, or FirmWoodhams, Blanchard & Flynn  lnventor: Lars Erik Svensson, Tullinge,
Sweden  ABSTRACT A control system for presses and the like of the type  Assignee: Safer Marketing Aktiebolag,
Stockholm, Sweden having a path for insertion and removal of work pieces includes a motor operated protective shutter insert Dec. 18, 1973  Filed: able into the work piece insertion and removal path [21 1 and a photocell system defining a light controlled area Appl. No.: 425,913
arranged transversely across such path and on the operators side of the shutter. Circuitry responsive to the  Forelgn Apphcauon Pnonty Data condition of the photocell device controls operation of 1972 16833/72 the shutter motor. Press releasing circuitry, actuable to permit initiation of a press cycle, is controlled by contacts actuable by the shutter and by timing cir-  US. Cl. 318/480; 318/484; 317/124 Int.
GOZF HOZH cuitry. Operation of the timing circuitry is initiated Field of when the light controlled area, or light curtain, be-
125 comes unoccupied, the timing circuitry operating for a short time within which the shutter initiates and com- References Cited pletes its closing movement. Then, the press is re- UNITED STATES PATENTS lU/l97l leased for initiating a press cycle, in response to the 3 612 884 Linardosm"Hmnmmmu" 7/124 X contacts sensing the closed position of the shutter and in cooperation with the timing circuitry.
11 Claims, 5 Drawing Figures US. Patent Oct. 7,1975 Sheet 2 of 5 3,911,344
[BEE-l U.S. Patent Oct. 7,1975 Sheet 3 of5 3,911,344
U.S. atent Oct. 7,1975 Sheet 4 of5 3,911,344
mm m 4m Q Arm Q NU m 1 4 Ni m m H m n L m ,2 a llllllllllllllllll l i um m m L T n 51' n w i m 1 v u L m u "I 1 1 l. m k m B a rlllfilllallh Y Pi CONTROLLING SYSTEM IN PROTECTIVE DEVICES OF PI-IOTOCELL TYPE FOR PRESSES AND THE LIKE The present invention refers to a controlling system in protective devices of photocell type for presses and the like.
It has previously been proposed to arrange protective devices for presses and the like comprising a so-called light curtain, i.e. a photocell arrangement comprising a plurality of light tracks in front of the place where the working pieces are to be inserted and taken out from the press during work, as well as a protective shutter adapted to close said path of introduction and removal while the press is performing its working stroke. In order to increase the safety in systems of the type here in question it is necessary to automatize to the utmost extent the operation of the press so that the operator will not unnecessarily be concerned with a plurality of controlling steps for every working stroke to be performed by the press. By reducing the number of working operations for every working stroke an automatic increase in safety is obtained and the operator will be able to concentrate on the working step itself, i.e. to cause the working pieces in question to arrive at the proper place and in correct position in the press and the pressing operation to be correctly performed. In an arrangement according to the present invention the operator only needs to introduce and remove the working pieces to be worked into and from the press along the prescribed paths of insertion and removal, the protective device automatically operating the press in such a way that when the path in question is free from foreign objects and hands the press will be automatically started. In order to provide absolute safety in such a device, however, a system comprising mutually cooperating devices is required.
The characterizing features of the present invention appear from the attached claims. The invention will be more closely described by reference to an embodiment shown in the attached drawings in a simplified sche matic way. The various FIGS. 1 to show the system in various positions of operation, wherein:
FIG. 1 diagrammatically discloses the system embodying the invention in an initial operational state, wherein the protective shutter S is lifted to free the path through the light curtain L for insertion or removal of a work piece therethrough and wherein the press is in its starting position.
FIG. 2 is a view similar to FIG. 1 but showing the system in a subsequent state resulting from insertion of an object into the light curtain L.
FIG. 3 is a view similar to FIG. 2 but showing the system in a subsequent state, following removal of such object and the resultant closure of the shutter S and starting of the press.
FIG. 4 is a view similar to FIG. 3 but showing the system in a subsequent state wherein an object has again been inserted into the light curtain L, resulting in stopping of the press.
FIG. 5 is a view similar to FIG. 3 but showing the system in a subsequent state near the end of the press cycle and wherein the control circuit to the press is broken to cause the press to stop.
In all the drawings the press itself is only represented by a cam disc P driven by the press and adapted, during the operation of the press, to rotate in the direction of the arrow P. The cam disc P is adapted to operate two contact means to be described later. The protective device proper is represented by a light curtain device L with light beams indicated by broken lines. The light curtain is provided at the path for inserting and removing work pieces in the press. Immediately behind the path seen from the operator there is provided a protective shutter S which is movable up and down for respectively exposing and closing the said path for insertion and removal of work pieces into and from the press. The protective shutter S is adapted to be driven by a linear motor having the general designation M. The protective shutter S is guided in guides SG provided with cams N1, N2 and N3 adapted to cooperate with contact means G1, G2, G3 respectively. The lastmentioned contact means comprise a plurality of break and make contacts and for identification of these contacts in the surrounding schematic representation, in all the Figures the first contact of for example contact means G1 is designated as G11, its second contact as G12 and its third contact as G13 and in correspondence thereto the first contact of contact means G2 as G21, the second contact as G22 etc. This system of identifying the contacts is used throughout the specification also as far as contact groups belonging to relays areconcerned. Two contact means G4 and G5, the contact groups of which in an analogous way can be traced in the schematic representation, cooperate with cam disc P.
Between the poles, here designated as O and of an alternating current mains there is connected a circuit for controlling the linear motor M adapted to drive the protective shutter 1 up and down. The phase contacts of the motor are designated X, Y, Z and provided within the broken-line rectangle on the left side of the Figures. The motor is such that it can operate in opposed working directions depending on the connection of its phase capacitor FC to the contacts X or Y. To cut-in the motor in different driving directions a contact B3 is provided in a contact group belonging to a relay B to be described later on, that contact providing insertion of the phase capacitor FC between one pole of the mains and the pole clamp X while at the same time the pole clamp Y is in direct connection with the last-mentioned mains pole or vice versa. Contact Z is continuously connected to the other mains pole O. In the position shown in FIG. 1 shutter S is in its upper position, i.e. the linear motor pulls the shutter upwardly and the opening through the light curtain L is exposed. In order to reverse the driving direction of motor M it is only necessary to reverse contact B3 whereby the pole clamp X of the motor will be directly connected to the one pole of the alternating current mains via a contact K1 to be described later on, the capacitor FC being connected between said alternating current pole and the pole contact Y on the motor. Three other contacts are also provided in the motor circuit viz. contacts C2 and D2 belonging to contact groups in relays C and D and a contact K2 belonging to a manual corrective button K as well as a contact G51.
Also connected to the alternating current mains is a transformer the secondary of which feeds a rectifier circuit to form together a net unit, or dc. current supply, designated as DC. Said net unit feeds relay circuits and electronic circuits with current. The minus pole of net unit DC is connected to so-called protective earth, or groundT-Ewhereas the positive pole is connected to the current supply for the relay circuits. Within a broken-line rectangle to the right of net unit DC there is shown a photocell amplifier circuit F which is in direct connection with the light curtain L and the contact function of which is symbolically indicated by a contact Fl. In connection with the net unit there are provided relays A, B, C and D with their contact groups designated A1, A2, A3, B1, B2 etc. Moreover, there are provided in said circuits current limiting resistors R1, R2, R3, R4, R5 and capacitors E1, E2, E3, E4 as well diodes HI and H2. The various relays aswell as the connection of the contacts and their mutual cooperation will be most simply described by describing the functional processes occurring during different states of operation. In order to facilitate the study of the Figures those conductors which in an illustrated state of operation do not conduct current have been shown in broken lines.
FIG. 1 shows a state of operation of the protective device in which the protective shutter S is lifted and the passage through the light curtain L is thus free to insert or remove one work piece therethrough. The press is in the starting position as indicated by the cam disc P which is directly connected to the press. Here, it will be seen that control circuits for linear motor M are in such a contact position that the protective shutter 1 is held D3, resistor R3, contact A2 and contact A3. It is to be.
noted that all relays in the actual condition are inactive. In this position the press still cannot be started, because contacts Cl and D1 are in their. inoperative positions and thus only close the supervising circuit T. Also, the
I protective shutter S cannot be lowered to closed posiin the lifted position. Contact member G5 contributes thereto by its cooperation with cam P" whereby the contact thereof G51 is held in closed position and forms, as previously mentioned, a link in the motor circuit to the protective shutter. In respect to the fact that the light curtain L is unbroken the photocells thereof (not shown) are actuated, the electrical signals derived therefrom being amplified in thc photocell amplifier F, thereby to obtain such a contact function that a closure is obtained through F1, whereby the circuit of relay A is closed and relay A is actuated. The circuit connected to relay A comprises resistor R2 and capacitor E2 which are connected in series between plus and minus in the conductors coming from DC. When contact function F1 is broken, capacitor E2 will be charged to full direct voltage through resistor R2. When contact function F] is closed there will be full voltage supply through capacitor E2 over the relay coil belonging to A. Thereby E2 will be discharged through the relay coil causing the relay to operate. Resistor R2 is so chosen as to adequately supply relay A with holding current but not to be able to cause the relay to operate. The state as described causes all the relevant contacts Al, A2 and A3 to be in their actuated positions. In the state shown in FIG. 1, the circuits to all relay coils B, C and D are broken thereby causing the respective contacts C1 and D1 to be in their inactive positions, a supervising circuit T being connected indicating that no operation can be performed. The control circuit U for the press machine is fully disconnected.
Thus, in this position the press cannot start because both relays C and D are inactive. Both these relays must be actuated to enable the control circuit U to be closed by means of contacts C1, D1.
If a hand HA, FIG. 2, is now inserted into the light curtain L the outgoing signals from the photocell device will be changed immediately, the photocell amplifier reacting in such a way that the closing of the contact at F1 ceases thereby disabling relay A. The consequence thereof is that the capacitor El will be charged via resistor R1 and contact A2. Also capacitor E3 will be charged via contacts G52, G12, G22, C3,
tion because the driving direction of motor M is such as to hold shutter S in the elevated position.
If now hand HA is removed from the light curtain L as in FIG. 3, the following actions will take place. Due to the fact that the photocells now again are fed by the full light curtain flow such signals are obtained to the photocell amplifier F that the contact function Fl again is closed whereby relay A is actuated. This has the consequence that a state of contact actuation similar to FIG. 1 is obtained. However, during the time under which the hand has been within the light curtain the capacitor El has been charged and due to the actuated position of contact A2, discharge current now flows from capacitor E1 through the coil of relay B via contact G41 to ground. Hereby relay B will be actuated and holding current will be supplied to the relay via its contact Bl,compare FIG. 3. By its transition to the actuated position contact B2, initially, will not bring about any change in current flow whereas the reversal of contact B3 reverses the direction of rotation of the linear motor M so that the protective shutter S will be lowered. This lowering of the protective shutter has several consequences. Contact members G1 and G2 will cooperate with cams N1 and N2, the contact groups comprised by these contact members thereby changing position. Contact member G3 will be brought out of engagement with cam N3 so that also its contacts will change position. The immediate consequence thereof will be that the previously charged capacitor E3 will discharge its discharge current through contact A3, diode H2 and the now series-connected closed contacts G21 and G11 to the parallel-connected coils of relays C and D. After actuation of these relays a holding current chain for the relays is prepared comprising contacts A1, G43, B2, D3, C3 and contacts G11, G21. However, no holding current is obtained prior to the press being started and rotation of cam disc P to such an extent that cam P" is disengaged from contact G5 whereby contact G53 thereof will close the holding current circuit for C and D. By closing relays C and D also contacts Cl and D1 are closed whereby the control circuit U of the press is closed and the press starts. As soon as cam P" on cam disc P comes out of engagement with contact member G5, contact G51 will be broken which means that if for some reason the press would stop in the position illustrated in FIG. 3 the protective shutter S cannot be caused to open even if relay B for some reason should be released so that contact B3 would be reversed. Normally, in the state illustrated in FIG. 3 the protective shutter S is held by motor torque in the closed position because relay B all the time is actuated. In the state illustrated in FIG. 3 all relays are actuated. Capacitor E2 is connected in parallel over relay coil A via current limiting resistor R2 but does not receive any substantial charging voltage.
If for some reason hand HA is introduced into the light curtain L in the state illustrated in FIG. 3 in a way as shown in FIG. 4 the following actionswill take place. The photocells cooperating with the light curtain L will not emit any'control signals to the photocell amplifier F, thus breaking the contact function F1 and causing the relay A to drop. Hereby, contact AI will drop causing the holding current to relays C and D to cease and the relays to drop. When relays C and D drop contacts Cl and D1 will interrupt the control circuit U of the press and close the supervising circuit T causing the press to stop. Relay 8 is still actuated which means that via contact B3 the linear motor M is fed so that shutter S is maintained in the closed position. Thereby, the operator is prevented from inserting the hands into the region about the work piece without specific measures while in such a case the working stroke of the press has been interrupted. As appears from the circuit diagram in FIG. 4 capacitor E2 will be charged in this state to its full voltage by the current limiting resistor R2. Moreover, capacitor E1 will be charged via current limiting resistor R1 and contact A2. In contrast, capacitor E3 will be discharged through the circuit formed by contacts A3, resistor R3, contact D3, C3, resistor R5, contact D3, C3, resistor R5 and contact G31 to ground. This is a safety measure taken because the press shall not be operable again from its interrupted position without specific measures when the hand is removed from the light curtain. As appears from the circuit diagram, upon removal of hand HA from the light curtain relay A will again be actuated whereby contact A3 connects capacitor E3 with the coils of relays C and D.
In order to get, in this position, access to and to adjust the work piece that may have come into a faulty position, the protective shutter S must be elevated to permit free passage through the light curtain. Such an operation can be performed by pressing the so-called corrective button K while simultaneously the hand HA is within the light curtain. The contacts K1, K2 and K3 of the corrective button K are hereby reversed causing contact Kl to break the current to linear motor M holding the protective shutter in closed position whereas a contact K2 via the dropped relay contacts C2 and D2 connects the linear motor M to the mains in such a way that shutter S is lifted. As soon as protective shutter S started its upward movement contact members G1 and G2 will be disengaged from cams N1 and N2 and subsequently contact member G3 will start cooperation with cams N3. Due to this contact reversal contacts G11 and G2] will break the connection to relays C and D thus eliminating any possibility to start the press (contacts C l and D1 connected to the supervising circuit T). The reversal of contacts G12 and G22 means no change in the current flows. However, G31 breaks the discharge current path for capacitor E3. This capacitor, however, is fully discharged under the present conditions. Contact K3 now causes a current path to be established through contact A1 so that capacitor E4 is charged through current limiting resistor R4. The contact positions just described are designated by dotted marks both concerning contacts and current paths. The operator now can freely handle the work piece without risk of press operation and personal injury caused thereby.
After having performed the adjustment the operator only needs to withdraw the hand from the light curtain and to release the corrective button to cause the press to start again. During this last-mentioned operation the following coupling sequence will take place. By removal of the hand from the light curtain the photocell device will emit signals and causes the contact function F1 to be closed so that relay A is actuated by a current impulse received from capacitor E2 in this phase, however, the actuation of relay A does not entail any immediate change in current flows. However, the reversal of contacts K1 and K2 entails a reversed connection of linear motor M causing protective shutter S immediately to be shifted down to closing position. Hereby, contact members G1 and G2 will come into cooperation with cams N1 and N2 causing, among others, contacts G11 and G21 D close. Due to the charge brought about during closing of contacts K3 in capacitor E4, there is now a direct discharge current path via diode H1 and contacts G21 and G1] to relays C and D which will be actuated and, in a way described above, cause the press to start (contacts C1 and D1 close the control circuit U of the press).
After the above described operation the press will continue its working stroke while simultaneously the cam disc P will rotate in the direction of the arrow P.
When the press movement has continued so far that cam P" comes into cooperation with contact member G4 the following action takes place. Contact G4] interrupts the holding current path through relay B which is released. Thereby, also the holding current paths to relays C and D are interrupted due to the fact that contact B2 is transferred to its disengaged position. Already before relay B drop's, the holding current path to relays C and D has been broken by contact G43. Hereby, also relays C and cl will be disengaged and contact group C1, D1 breaks the control circuit to the press which is stopped. As a safety measure capacitor E3 is connected by contact A3 to ground via contact G42 in the state as described. During the lastmentioned action the brake mechanisms of the press are actuated to bring the press to a correct stopping position and starting position after some additional movement corresponding to a rotation of cam disc P so that cam P" again comes into contact with contact element G5. Hereby, a starting position as shown in FIG. 1 is obtained. It is to be noted that when relay B is disengaged and drops contact B3 breaks the connection between the linear motor M and the mains. The protective shutter, however, remains in its closed position due to gravity. This brief moment in the final phase of the working stroke of the press is considered as undangerous from the safety point of view so that the current to the linear motor in this case can be disconnected during the period in question. As soon as the cam P comes into engagement with contact element G5 contact G51 is again closed connecting the linear motor so to the mains that the protective shutter S is lifted whereby the starting position according to FIG. 1 is again reached.
As will clearly appear from the above description a particularly efficient protective system is obtained by the arrangement according to the present invention also permitting an extremely simple control of the press by the operator. The construction offers, among others, the following advantages which efficiently contribute to the safety obtained with the device in question. In order to initiate a press movement the operator only has to pull out his hand from contact with the light curtain L whereafter the press performs a complete working stroke without further measures. If during the working stroke of the press the operator introduces his hand into the light curtain the press will be stopped but the protective shutter will remain blocked against mechanical opening due to the fact that the linear motor is connected to the mains with such a driving direction that the protective shutter S is held closed. Only after depression of the corrective button K while the hand simultaneously is maintained within the light curtain the protective shutter S can be brought to open position for any necessary adjustment of the work piece. During this action the press is fully locked against unintentional start because the control releasing relays C and D cannot supply any operating current due to the fact that among others the series-connected contacts G11 and G21 both are open. As soon as the operator removes his hand from the light curtain and releases the corrective button K the press will start immediately and continue its working stroke without additional measures taken by the operator. It is to be noted that if the press has been stopped by insertion of the hand HA in the light curtain as shown in FIG. 4 no new starting impulse can be obtained unless both the corrective button K has been actuated and the hand HA has been removed from the light curtain L. A new starting pulse in the position illustrated in FIG. 4 can be obtained only by the charging voltage received by capacitor E4 during depression of contact K3 of the corrective button. A current path which in a conventional way can charge capacitor E3 for normal start does not exist in this case.
Also a safeguard against inter circuit faults is enclosed in the system. If for some reason relays C and D will not be actuated within a certain prescribed interval of time the actuating current pulse will cease because capacitor E3 is so dimensioned that its energy content at a given charging voltage is exactly sufficient for a normal actuation of said relays C and D. This requirement is also valid for the rest of the capacitors E1, E2 and E4 because if for some reason the relays to be actuated by these capacitors do not operate immediately there shall be no actuating current on these relays which thereby are prevented from being actuated accidentally at times when they could cause the press to start under faulty conditions. By such an arrangement of capacitors for obtaining actuating pulses for relays an indirect supervision of the correctness of the relay function is obtained whereby the actuating times are held within tolerance limits. Moreover, such safety is also obtained in that the protective shutter must be in the closed position in order to enable the operating relays C and D of the press to be actuated, which means that contacts G1 and G2] must be closed simultaneously. Moreover, the press will not start if, for example, only relay C would be actuated because then only contact Cl would be in the closed position, leaving the control circuit U still open. Moreover, the holding current circuit for relays C and D comprises seriesconnected contacts C3, D3 from the respective relay contact groups.
Finally, in case of a current interruption in the circuit shown in the Figures, the press cannot be started even if there is current present at the press control means, because the control circuit U of the press is interrupted as long as relays C and D are disabled due to the respective contacts Cl and D1. It is also not possible to inadvertently start the press if there is current charge on all control circuits but not on the driving motor of the press, which means that even if the circuits should reach the starting condition by removal of the hand HA in FIG. 2, a subsequent supply of driving current to the press would not cause the press to start because the actuating pulse time for relays C and D then has expired already a long time ago without a movement of cam disc P and without closure of the holding current circuit for the respective relays C and D by, among others, contact G53.
In the specification and claims it is stated that a socalled light curtain is to be used in connection with the system described. However, other equivalent arrangements such as capacitive feeling devices can be used. Moreover, reference has been made throughout to relays. However, this term is intended to comprise equivalent means such as electronic switches and the like.
What I claim is:
l. A control system for operating presses and the like of the type having a path for insertion and removal of work pieces, comprising:
a motor operated protective shutter moveable into and out of said work piece insertion and removal a light curtain incorporating a photocell device and defining alight controlled area transversely in said path and on the operators side of said shutter;
shutter circuit means connected to and controlled by said photocell device for initiating operation of the shutter motor to close said shutter;
shutter contact means actuable by said shutter upon such closure thereof;
press releasing circuit means responsive to said actuation of said shutter contact means for starting said press;
timing means in circuit with said shutter circuit means and actuable upon said removal of an interrupting object from said light curtain for timing a short period of time during which closure of said shutter must be initiated;
and further timing means in circuit with said press releasing circuit means for timing a period during which press operation must be initiated.
2. Control system as claimed in claim 1, in which said timing means comprises capacitors, and including relay means coupled to said photocell device and (1) disabled thereby when the light curtain is broken for causing said capacitors to be charged and (2) actuated thereby when the light curtain becomes unbroken for permitting discharge of said capacitors to said circuit shutter means so as to close the shutter, and then to said press releasing circuit means so as to start said press, said time periods being the discharge times of said capacitors.
3. A control system for operating presses and the like of the type having a path along which work pieces are insertable and removable by an operator, comprising:
a motor operated protective shutter moveable for blocking and unblocking the work piece insertion and removal path;
light curtain means disposed transversely of said path and on the operators side of said shutter and including photocell means responsive to objects inserted through the light curtain; I
contact means actuable by said shutter upon opening and closing of the shutter;
start pulse circuit means actuable for initiating a press starting sequence in response to at least partial interruption of said light curtain by an object and responsive to a subsequent removal of the interrupting object from the light curtain for changing state, said start pulse circuit means being coupled to and actuated by said photocell means;
shutter control circuit means actuable in response to said change of state of said start pulse circuit means for initiating closing said shutter;
press releasing circuit means coupled to said start pulse circuit means and contact means and responsive to closing of said shutter for simultaneously initiating the press stroke;
timing means coupled to said shutter control circuit means and press releasing circuit means. respectively, for timing limited time intervals within which said control circuit means and press release circuit means must carry out said initiations 4. Control system as claimed in claim 3 in which said start pulse circuit means include a relay coupled to said photocell means and actuable thereby when the light curtain is unbroken and disabled thereby when the light curtain is broken, said timing means comprising capacitors, said control circuit means and press releasing circuit means including paths coupling respective said capacitors to said relay l for charging of said capacitors when said relay is disabled and, upon a subsequent actuation of said relay, (2) for enabling discharge of current from said capacitors to time said limited intervals, said shutter control circuit means and press releasing circuit means including portions coupled to respective said capacitors for actuation by the discharge current therefrom.
5. Control system as claimed in claim 3 in which said press releasing circuit means includes a pair of relays with coils connected in parallel, said relays having contacts, a contact of one said relay being connected in series with a contact of the other said relay, the press having a press control circuit containing said series contacts and responsive to closure of both said contacts for operating said press.
6. Control system as claimed in claim 5 in which said contact means actuable by said shutter include a series pair of shutter contacts closeable and openable with said shutter, said control circuit means including a current path in which said series shutter contacts are in series with said parallel relay coils, whereby closure of both said shutter contacts is required for actuation of said relay coils.
7. Control system claimed in claim 6 in which said start pulse circuit means includes a relay actuable by said photocell means and having contacts, said pair of relays of said press releasing circuit means having respective further contacts in series, said press releasing circuit means further including a holding current path for said pair of relays which includes said series further contacts thereof and further includes a contact of said photocell actuable relay, said control circuit means including a further relay responsive to said photocell actuable relay for operating said shutter, means moveable in synchronism with the working stroke of the press and press stroke contacts associated therewith for completing said holding current path upon initiation of the working stroke of the press.
8. Control system as claimed in claim 7 in which said means moveable in synchronism with the working stroke of the press include a further contact, said control circuit including a current path to the shutter motor and containing said last mentioned contact for deenergizing said shutter motor upon initiation of said working stroke of said press.
9. Control system as claimed in claim 7 including means coupling a contact of said photocell actuable relay in series in said holding current path of said pair of press releasing circuit means relays for breaking said holding current path upon interruption of the light curtain following starting of the press, whereby to deenergize said pair of press releasing circuit means relays and stop said press.
10. Control system as claimed in claim 9 including a corrective contact member manually actuable after said stopping of said press and means coupling contacts of said corrective contact member in said shutter control circuit means, means defining a charging current path including a further contact of said manually actuable corrective contact member, said charging current path defining an additional start pulse circuit means responsive to deactuation of said manually actuable corrective contact member and elimination of said light curtain interruption for, simultaneously with a subsequent closing of said shutter, once again applying operating current through said series pair of shutter contacts to said parallel press releasing circuit means relays to restart the press after an interruption of press operation by an interruption of the light curtain.
11. Control system as claimed in claim 10 in which said press releasing circuit means includes a normal press starting pulse path including a contact of said photocell responsive relay, contacts of said pair of relays of said press releasing circuit means, and a contact of said shutter actuable contact means, said normal starting pulse path being coupled to the timing means capacitor associated with said press releasing circuit means for discharging said capacitor therethrough.