US2705297A - Relay-operated control circuit - Google Patents

Description

March 29, 1955 R, OC 2,705,297

RELAY-OPERATED CONTROL CIRCUIT Filed March 10 1951 0 LINE J0 MT 4/ 4 LINE 3 3,6 a2 43 J 4/ 2 LOAD 53 I LINE LOAD o 46 47 J7 35 I lflvenfor ymem M W United States Patent M apolis-Honeywell Regulator Company, Minneapolis,

Minn., a corporation of Delaware Application March 10, 1951, Serial No. 214,953

3 Claims. (Cl. 317-135) This invention relates to electrical control circuits, and particularly to a control circuit for a power operated machine, such as a punch press.

An important aspect of the invention is concerned with the prevention of unwanted second strokes of a punch press or other power operated machine. Today some punch presses have single stroke features in the clutch mechanism, but many punch presses now in use have no such provision for limiting it to a single stroke during its operating cycle. The present invention is adapted to add the single stroke control feature to all such machines, of any size and operating at any speed, without altering the construction thereof. Therefore, it is an object of this invention to provide a control circuit for a punch press which prevents undesired second strokes thereof during an operating cycle.

Another object of this invention is to operated single stroke control circuit.

Another object of this invention is to provide a control circuit in which either single stroke or continuous operation may be had, with either hand or foot operated controls.

In carrying out single stroke control over a punch press or the like, it is not satisfactory to employ a control circuit which is responsive only to elapsed time. This is so because of the undeterminable time which elapses before the clutch pin is pulled. This time varies from stroke to stroke, and on some presses this time variation may be quite appreciable, sometimes amounting to almost as much time as is consumed by the operating cycle of the press. Consequently, a control which operates solely on a time basis is undesirable since it might prevent the first stroke or it might permit unwanted second strokes because of the tolerance of the combination. Therefore, it isalso an object of this invention to provide a control which terminates the energization of the device responsive to completion of a certain portion of the operating cycle thereof. 1

A still further object of this invention is to provide a control circuit operable to disconnect an electrical load from its power supply when only one of a pair of switches is actuated within a predetermined time interval. In accordance with this object, the invention is adapted for a two hand safety device which requires the operator to provide a relayuse two hands concurrently, or within a brief time interval,

in order to operate a punch press or the like, and to prevent operation if one of the hand switches is tied down or otherwise held in the operating position.

Other and further objects of the invention will be apparent from a consideration of the following description of preferred embodiments of the invention.

In the drawings:

Figure 1 is a circuit diagram showing one form of the present invention selectively providing for single or multiple stroke operation and either foot or hand control;

Fig. 2 is a circuit diagram of another form of single stroke control circuit;

Fig. 3 is a circuit diagram of a third form of single stroke control circuit according to the present invention;

Fig. 4 is a circuit diagram of a fourth embodiment of single stroke control circuit, and

Fig. 5 is a circuit diagram of a selective foot or hand control circuit differing from that shown in Figure 1.

As shown in Figure 1, the control is connected between the line and the load. A conductor 1 from the line is in series with the normally open hand switch 2, conductor 2,705,297 Patented Mar. 29, 1955 3, one side of the double throw switch 4, which forms one pole of the double pole, double throw selector switch 5, and conductor 6 leading to the load. Conductor 7, connected to the other side of the line, is in series with normally closed hot wire operated switch 8, a conductor 9, the normally open hand switch 10, conductor 11, one side of the double throw switch 12, which is the other pole of the double pole, double throw selector switch 5, conductor 13, normally closed contacts of the double throw relay contacts 14, and conductor 15 leading to the load. A shunt 16 is connected between conductor 1 and the other side of switch 4. A normally open foot switch 17 joins conductor 7 to the other side of switch 12.

An autotransformer 18 between conductors 1 and 9 has a mid-tap 19. A potentiometer 20, and hot wire 21 controlling switch 8 are connected in series between mid-tap 19 and the center tap 22 of resistor 23, which is connected between conductors 3 and 11.

A relay coil 24 which controls relay contacts 14 is connected between conductors 6 and 13 through conductor 25, the normally open cycle control switch 26 and selector switch 27. A conductor 28 joins the normally open contact of the relay contacts 14 with conductor 25.

The load may be any type of electrical apparatus such as a piece of machinery, a lamp, or a heater; or it may be an electrical control device such as a relay or solenoid. The line may be any source of electric power. If a trans former is employed, alternating current must be used, but a mid-tapped resistor could be substituted for the transformer.

In operation the double pole, double throw selector switch 5 is thrown to one side or the other depending upon whether two hand or foot control is to be used. If two hand control is to be used switch 5 is thrown to the left and circuits are closed from conductor 3 through switch 4 to conductor 6 and from conductor 11 through switch 12 to conductor 13. With the switch in this position it is necessary to close both hand switches 2 and 10 to complete the circuit to the load. When the hand switch 2 is closed, it completes a circuit from the line to the load through conductor 1, hand switch 2, conductor 3, switch 4, and conductor 6. When hand switch 10 is closed, it completes a circuit from the line to the load through conductor 7, hot wire switch 8, conductor 9, hand switch 10, conductor 11, switch 12, conductor 13, relay contacts 14, and conductor 15. Since the tap 19 is at the midpoint of autotransformer 18 with the hand switches 2 and 10 closed the potential between conductor 1 and the mid-tap 19 is equal to the potential between mid-tap 19 and conductor 9. In like manner, since the' tap 22 is at the center of resistor 23, the voltage between conductor 3 and the center tap 22 is equal to the voltage between center tap 22 and conductor 11. Under this circumstance the taps 19 and 22 are at the same potential so that no current will flow through potentiometer 20 and hot wire 21. If, however, the hand switch 2 is open while hand switch 10 is closed, that portion of the resistor 23 between center tap 22 and conductor 11 with potentiometer 20 and hot wire 21 constitutes a load on the autotransformer 18, so that current will flow through the hot wire 21." This current flowing through the hot wire 21 causes it to heat up and open the switch 8, breaking the circuit. The length of time required for the switch to be opened is dependent upon the current flowing through the hot wire 21. The magnitude of this current is determined by the setting of the potentiometer 20. The switch 8 is of the manual reset type so that it will not reclose when the wire 21 cools. The operator must, therefore, manually reclose the switch 8, which is so located that he must move away from the hand switches 2 and 10. In the same manner the switch 8 is opened if the hand switch 2 is closed while the hand switch 10 is open. It is thus assured that the operator will be unable to tie down or otherwise hold closed one of the hand switches and operate the machine with the other. The device described thus far would permit the load to be energized for as long a time as the hand switches 2 and 10 were held closed. This would permit multiple operations, which are frequently undesirable.

When the relay, incorporating contacts 14 and coil 24, is connected as shown it can prevent more than one operation. If only a single operation is desired, the selector switch 27 is closed. When the hand switches 2 and 10 are subsequently closed completing the circuit to the load a potential exists between conductors 6 and 13. At a predetermined time during the operating cycle the normally open cycle control switch 26 is automatically closed briefly, completing the circuit through the relay coil 24 to energize the same and cause the relay contacts 14 to break the circuit to the load and complete a circuit from conductor 13 through relay contacts 14, conductor 28 and relay coil 24 to conductor 6, so that the load circuit is held open as long as both hand switches are held closed. When one or both of the hand switches 2 or- 10 is opened the circuit through the relay coil 24 is broken permitting the relay contacts 14 to again set up the circuit to the load. If only one of the hand switches 2 or 10 is opened the hot wire switch 8 will be opened as previously described to prevent further operation of the device. When both hand switches 2 and 10 are open the control is ready for the second operation.

If it is desired that continuous operation be permitted, it is only necessary to open the selector switch 27 which brakes the circuit through the relay coil 24 and so prevents the relay contacts 14 from opening the circuit between conductors 13 and 15.

If foot switch control is desired, the double pole, double throw selector switch is thrown to the right so that the switch 4 closes the circuit between conductors 16 and 6 and the switch 12 closes the circuit between foot switch 17 and conductor 13. Under these conditions the hand switches 2, are ineffective to control the load. One circuit from the line to the load is completed through conductors 1 and 16, switch 4 and conductor 6. Another circuit from the line to the load is set up through conductor 7, foot switch 17, switch 12, conductor 13, contacts 14 and conductor 15. The circuit is completed by closing foot switch 17. The single stroke control is still effective and operates as previously described to prevent a second operation.

In the single stroke control circuit of Fig. 2, one of the double throw switches 29 has its common terminal connected to line, while the common terminal of the other double throw switch 30 is connected to the other side of the line. Normally open relay contacts 31, 32 are connected to opposite sides of the line before double throw switches 29, 30 through conductors 33, 34 respectively. In one position of the double throw switches 29, 30 the conductors 35, 36 are connected to the line through the double throw switches. A series combination of normally closed cycle control switch 37 and relay coil 38 is connected across conductors 35, 36. In the other position of double throw switches 29, 30 the conductors 39, 40 are connected to line and are adapted to connect the line to the load when normally open relay contacts 41, 42 are closed. All the relay contacts 31, 32, 41, 42 are under the control of relay coil 38, such that energization of this relay coil effects closure of all the relay contacts.

In the operation of this system, with the double throw switches 29, 30 in the position connecting conductors 35 and 36 to the line, relay coil 38 is energized by the line through the normally closed cycle control switch 37. Energization of the relay coil causes closure of all the relay contacts 31, 32, 41, 42. In this condition of the circuit the load is still not connected to the line because the position of double throw switches 29, 30 disconnects conductors 39, 40 from the line. Also, in this position of the double throw switches, closure of relay contacts 31, 32 effects energization of the relay coil 38 independently of the position of double throw switches 29, 30, because the circuit to the relay coil is completed from one side of the line through conductor 33, closed relay contacts 31, conductor 35, normally closed switch 37, relay 38, conductor 36, closed relay contacts 32 and conductor 34 to the other side of the line.

When double throw switches 29, 30 are moved to their other alternate positions conductors 39, 40 are connected to opposite sides of the line to connect the load to the line through closed relay contacts 41, 42. This energization of the load continues as long as double throw switches 29, 30 remain in this position and relay contacts 4 1,42 remain closed. De-energization of relay coil 38 can be effected by disconnecting it from the line, and such de-energization of the relay coil will result in release of relay contacts 41, 42 to their normal open positions, to disconnect the load from the line. Opening of cycle control switch 37 effects this re-energization of relay coil 38 to disconnect the load from the line.

Switch 37 is automatically opened briefly during the operating cycle initiated by energization of the load, and the resulting de-energization of relay coil 38 causes relay contacts 31, 32, 41, 42 to open. This action disconnects the load from the line, and in addition, makes energization of relay coil 38 dependent upon the position of double throw switches 29, 30 because relay contacts 31, 32 are now open, and will remain so until relay coil 38 is again energized. Thus, even after cycle switch 37 closes, relay coil 38 can be energized again only if double throw switches 29, 30 are returned to the initial position connecting conductors 35 and 36 to the line. The load cannot be re-connected to the line (by closure of relay contacts 41, 42) until relay coil 38 is again energized in this way and the double throw switches 29, 30 are moved to connect conductors 39, 40 to the line. When the double throw switches 29 are returned to this initial position, the entire sequence of operation of the control circuit is repeated. Obviously, either of movable relay contacts 41 or 42, connected respectively to opposite sides of the load, could be fixedly connected to the corresponding conductor 39 or 40, free from the control of relay coil 38 without affecting the operation of the system.

It will be apparent that the conrtol circuit of Fig. 2 is well adapted for the previously mentioned application to a two hand safety control. Double throw switches 29, 30 would be the hand switches in such a system. Even if one of the hand switches 29, 30 could be held operated (i. e., in the position connecting conductor 35 or 36 and the line) it would be impossible to obtain more than one operation by so doing. Therefore, the operator of the machine would not be tempted to try this procedure.

In the event that it is desired to use the circuit of Fig. 2 with a single operator-controlled switch 29 or 30, this can also be accomplished readily by slightly modifying the described circuit. To do this conductors 36 and 40 could be conductively joined at the switch 30 so that both would be continuously connected to the line through the conductor formed by the no-longer-movable contact of switch 30. Also relay contacts 32, connected directly to the same side of the line as switch 30, would be permanently closed, free from the control of relay coil 38. In effect, such modification of the system of Fig. 2 would mean the elimination of switch 30 and movable relay contacts 32, while switch 29 and the other movable relay contacts 31 remain as before. Obviously, the same result could be accomplished by eliminating double throw switch 29 and the corresponding movable relay contacts 31 in shunt therewith in the same manner, while double throw switch 30 and relay contacts 32 remain movable as in Fig. 2. Along with this, even further simplification of the control circuit could be obtained by making either of movable contacts 41 or 42 fixedly connected to the corresponding conductor 39 or 40. With the circuit of Fig. 2 modified in this manner, the single operator-controlled double throw switch 29 or 30 could advantageously be foot operated, and the cyclic operation of switch 37, under the control of the punch press, would insure single stroke operation thereof.

In the single stroke control circuit of Fig. 3, the common terminals of double throw switches 43, 44 are respectively connected to opposite sides of the line. Relay coil 49a is connected through conductors 45, 46 to one set of alternate contacts of the double throw switches 43, 44 to be connected across the line in one position of those switches. Relay contact 47 is connected by conductor 48 to one side of the line before double throw switch 44, and is connected through normally closed cyclic switch 43a, relay coil 49b and conductor 50 to the other side of the line before double throw switch 43. The load is adapted to be connected to one side of the line through conductor 51 in the other alternate position of double throw switch 44. The other side of the load is adapted to be connected to the other side of the line through normally open relay contacts 52 and conductor 53 in the other alternate position of double throw switch 43. Both sets of relay contacts 47, 52 are adapted to be closed in response to energization of either relay coil 49a or 49b, which act in the same direction.

With the double throw switches 43, 44 in the position shown, relay coil 49a is connected across the line and is energized thereby. This causes normally open relay contacts 47 and 52 to close. Closing of contacts 47 effects energization of the other relay coil 49b as long as cyclic switch 43a remains closed, and relay coil 49b is thus energized independent of the position of double throw switches 43 and 44.

Thereafter, when the double throw switches are thrown to the other position, relay coil 49a will be de-energized but relay coil 49b will remain energized to maintain relay contacts 47 and 52 closed. In this position of the double throw switches the load will be connected across the line through switch 43, conductor 53, closed relay contacts 52, and switch 44 and conductor 51. At a predetermined point in the operation of the device at the load side of the control circuit, the cycle control switch 43a is briefly opened automatically, thus breaking the circuit to relay coil 49b to de-energize the same. De-energization of relay coil 49b results in relay contacts 52 returning to the normally open position to disconnect the load from the line, and in the return of relay contacts 47 to the open position.

A second operation of the device can be obtained only by returning the double throw switches to the original position, after which the operating sequence of the control system repeats.

It will be readily apparent that the described system of Fig. 3 lends itself readily to the two hand safety control, since both double throw switches must be thrown to the lower position to connect the load to the line, and both double throw switches must be thereafter thrown to the upper position to again energize relay coil 49a for the next operating cycle.

In the event that one desires to control the system of Fig. 3 by a single operator-controlled switch, this can be readily accomplished. Switch 43 can be eliminated by conductively joining conductors 45 and 53, and then connecting the pair to one side of the line. Alternatively, switch 44 can be eliminated by conductively joining conductors 51 and 46, and then connecting both to the corresponding side of the line. In either modification, the circuit would operate as a single stroke control as described in connection with Fig. 3, except that there would be only one switch 43 or 44 under control of the machine operator.

In the single stroke control circuit of Fig. 4, relay closing coil 54 is adapted to be connected across the line in one position of hand switches 55, 56 from hand switch 55, through conductor 57, relay coil 54, normally closed relay contacts 58, conductor 59, and the other hand switch 56. The load is adapted to be connected to the line on one side through double throw switch 55 in the other position thereof, and on the other side through double throw switch 56 in its other position, conductor 60, and normally open relay contacts 61. Both sets of relay contacts 58 and 61 are movable in response to energization of relay closing coil 54 such that relay contacts 58 open and relay contacts 61 close upon such energization. The relay associated with coil 54 is of the latch type, electrically reset, in which a latch 62 engages and holds armature 63, which has been moved into position for such engagement by energization of coil 54. Armature 63 determines the positions of relay contacts 58 and 61. Relay opening coil 64 and normally open cycle control switch 65 are connected in series with each other across conductors 66 and 67 leading to the load. When coil 64 is energized it causes latch 62 to release armature 63 to permit movement of relay contacts 58 and 61 back to their normal closed and open positions, respectively.

In operation, with the double throw switches in the upper position of Fig. 4, relay closing coil 54 becomes energized from the line through double throw switch 55, conductor 57, coil 54, normally closed relay contacts 58, conductor 59, and double throw switch 56. Energization of relay closing coil 54 draws armature 63 into position to open contacts 58 and close contacts 61 and to be engaged by latch 62. The opening of contacts 58 breaks the circuit to relay closing coil 54, which becomes deenergized.

When the double throw switches are next thrown to the opposite lower position in Fig. 4, the load is connected to the line on one side through double throw switch 55 and conductor 66 and on the other side through double throw switch 56, conductor 60, relay contacts 61 (which until either double throw switch is moved to the'other position or relay contacts 61 open. Cyclic switch 65 closes briefly under the automatic control of the load device at a predetermined time during the operating cycle and this causes relay opening coil 64 to be energized to cause latch 62 to release armature 63. Release of armature 63 results in opening of relay contacts 61 to de-energize the load and closure of relay contacts 58. Thus, the system is ready to repeat this sequence upon movement of the double throw switches 55, 56 to the original (upper) position.

With the described pair of double throw switches 55, 56, it will be seen that the control circuit of Fig. 4 is readily susceptible to the two hand safety control application.

To apply this system to single stroke control using only a single operator-controlled switch, either of the double throw switches or 56 can be eliminated by connecting its alternate fixed contacts together and directly to the corresponding side of the line.

If it is desired to use the two hand safety control of Figure 1 in combination with the single stroke circuit of either of Figs. 2, 3 or 4, in order to positively prevent even a single operation of the machine when one of the hand switches is held operated, this can be effected by connecting center-tapped resistor 23 of Figure 1 across conductors 39 and 40 in Fig. 2, or across conductors 53 and 51 in Fig. 3, or across conductors 66 and in Fig. 4, and adding to the system of either Fig. 2, 3 or 4 the circuit of Figure 1 to the left of resistor 23.

Fig. 5 shows a circuit by which alternate foot switch control can be obtained. It may be used in combination with any of the species shown in Figs. 2, 3 and 4. In it, the common terminals of double throw hand switch 68 and 69 are connected to opposite sides of the line. The normally closed terminal of switch 68 is connected to one of the alternate terminals of the double throw switch 70, which is one pole of a three pole, double throw selector switch 71. The common terminal of switch 70 is connected by conductor 72 into the circuits of Figs. 2, 3 or 4 the same as the respective conductor 35, 45 or 57 therein. The normally closed terminal of hand switch 69 is connected by conductor 73 into the circuits of Figs. 2, 3 or 4 in the same manner as the respective conductor 36, 46 or 59 therein. The normally open terminal of hand switch 68 is joined to one of the alternate terminals of switch 74, which is the second pole of the three pole switch 71. The common terminal of switch 74 is connected by conductor 75 into the circuits of Figs. 2, 3 or 4 the same as the respective conductor 39, 53 or 66 therein. One of the alternate terminals of switch 76 is connected to the normally open terminal of hand switch 69. The switch 76 is the third pole of the three pole switch 71. The common terminal of switch 76 is connected by conductor 77 into any of the circuits shown in Figs. 2, 3 or 4 in the same manner as the respective conductor 40, 51 or 60 therein. The common terminal of the double throw foot switch 78 is connected to the common terminal of hand switch 68. The normally closed terminal of switch 78 is joined to the other terminal of switch 74. A conductor 79 connects the common terminal of hand switch 69 with the other terminal of switch 76.

When it is desired to use two hand control, the selector switch 71 is thrown to the left, as shown, so that when the line is energized a circuit is established from the line through hand switch 68, switch 70 and conductor 72 at the same time that another circuit is established from the line through hand switch 69 and conductor 73. When the hand switch 68 is operated, a circuit is set up from the line through hand switch 68, switch 74 and conductor 75. When hand switch 69 is operated, a circuit is set up from the line through hand switch 69, switch 76 and con ductor 77.

If foot switch control is desired, the selector switch 71 is thrown to the right, so that when the line is energized, a circuit is established from the line through foot switch 78, switch 70 and conductor 72. Other circuits are established from the line through hand switch 69, and conductor 73 and from the line through conductor 79, switch 76 and conductor 77. When the foot switch 78 is operated, the circuit through conductor 72 is broken and a circuit is completed from the line through foot switch 78, switch 74 and conductor 75. The fact that circuits are continuously set up from the line through conductors 73 and 77 makes no difference since circuits are only completed by connecting 72 or '75 therein, under control of the foot switch 78. It will thus be seen that the same operation results whether two hand control or foot switch control is employed.

In this specification double throw switches have occasionally been referred to as having normally closed and normally open terminals. By this is meant that these switches are of a type in which the switch blade is biased into engagement with one of the contacts which would be referrednto' as the normally closed contact, while the terminal associated with it would be referred to as the normally closed terminal. In like manner the normally open terminal is associated with the normally open contact, that is to say, the one toward which the blade is not biased. It is to be understood, however, that this type of double throw switch need not be used, although, it is probably most convenient. Reference has also been made to foot switches and hand switches. It must be understood that control is not limited to use of foot and hand switches. It may be accomplished by limit switches or any type of circuit making and breaking device.

I claim:

1. In a single cycle two hand safety control to be connected between a power line and a load, a transformer connected across the line, a resistor connected across the load side of the transformer, a normally open hand switch -on each side of the resistor between said transformer and said'resistor, a hot wire connected between mid-taps on said transformer and resistor, a normally closed manually reset switch between said transformer and said line adapted to he opened by said hot wire, a relay coil and a normally open automatically operated switch' in parallel with said resistor at the load side thereof, and double throw relay contacts operable by said coil to break the circuit between said line and said load and to shunt said automatically operatedswitch upon operation of the latter, said hot wire heatingto open said reset switch when only one hand switch is closed.

2. In a control device inserted between line and load,.

the combination of a single-pole operator-controlled switch in series between the line and the load operative to control the energization of the load from the line, a relay in series between the line and the load operative to control the energization of the load from the line, relay operating means operative to actuate said relay between a closed condition interconnecting the line and load and an open condition disconnecting the load from the lie, said relay operating means being in series with said operator-con trolled switch to be de-energized to maintain the relay closed when said operator-controlled switch is open, and means in circuit between the line and said relay operating means operated automatically in timed relation with the cycle of operation of the load operative to complete a circuit from the line to said relay operating means to energize said relay operating means for actuating said relay to its open condition, said operator-controlled switch upon being closed completing the circuit through the closed relay from the line to the load to initiate a cycle of operation of the load, said automatically operated means at a predetermined time after the initiation of said cycle of operation of the load completing a circuit from the line to said relay operating means to energize the relay operating means to open said relay to disconnect the load from the line while said operator-controlled switch is closed, said operator-controlled switch while closed after the opening of said relay completing a circuit from the line to said relay operating means to maintain said relay operating means energized to hold the relay open, said relay operating means being de-energized to close the relay in response to the re-opening of said operatorcontrolled switch.

3. In a control device inserted between line and load, a single-pole operator-controlled switch in series between the line and the load and operable when closed to complete a circuit from the line to the load to energize the load and initiate a cycle of operation of the load, relay contacts in series between said operator-controlled switch and said load and operable in open position to break said circuit, an automatically operated switch and a relay coil which controls said relay contacts connected in series with said automatically operated switch across the line, said automatically operated switch and said relay coil forming a series circuit connected across the line after said oper' ator-controlled switch and in parallel with the circuit formed by said relay contacts and the load, said automatically-operated switch being operable in timed relation with the aforementioned cycle of operation to control the energization of said relay coil to open said relay contacts to break the circuit between the line and the load, the energization of said relay coil being controlled responsive to the opening of the operator-controlled switch to close said relay contacts to permit said circuit between the line and the load to be made again upon reclosing of the operator-controlled switch.

References Cited in the file of this patent UNITED STATES PATENTS 2,052,795 Rapisarda Sept. 1, 1936 2,302,838 Bundy Nov. 24, 1942 2,404,980 Munschauer July 30, 1946 2,491,363 Dehn Dec. 13, 1949 2,541,577 Dornbos Feb. 13, 1951 2,543,620 Anderson Feb. 27, 1951 2,545,549 Guill Mar. 20, 1951 2,579,595 McLane Dec. 25, 1951 FOREIGN PATENTS 418,577 Great Britain Oct. 23, 1924

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