US3579049A

US3579049A - Safety control system for actuating electrically controlled mechanical device

Info

Publication number: US3579049A
Authority: US
Inventors: Donald D Kikta
Original assignee: Grayhill Inc
Current assignee: Grayhill Inc
Priority date: 1969-11-28
Filing date: 1969-11-28
Publication date: 1971-05-18
Anticipated expiration: 1988-05-18

Abstract

A control system for an electrically controlled device for applying energy thereto including first and second hand-operated switches positioned to be actuated by the two hands of an operator, and a relay actuated by simultaneous operation of the switches including a contact for controlling the output circuit which energizes the device. A second relay having normally closed contacts connected in series with contacts of the first relay provides a holding circuit for the first relay which is released only when both hand switches are released. The output circuit may include a third relay for applying power to the controlled device, and which actuates a timer which holds the third relay operated for a predetermined time interval.

Description

United States Patent inventor Donald D. Kikta Downers Grove, Ill. Appl. No 880,657 Filed Nov. 28, 1969 Patented May 18, 1971 Assignee Grayhill, Inc.

La Grange, Ill.

SAFETY CONTROL SYSTEM FOR ACTUATING ELECTRICALLY CONTROLLED MECHANICAL DEVICE 115V AC [56] References Cited UNlTED STATES PATENTS 2,541,577 2/1951 Dornbos et al. 317/135 2,680,216 6/1954 Schmidt 317/135 Primary E.taminerLee T. Hix Attorney-Mueller, Aichele & Rauner ABSTRACT: A control system for an electrically controlled device for applying energy thereto including first and second hand-operated switches positioned to be actuated by the two hands of an operator, and a relay actuated by simultaneous operation of the switches including a contact for controlling the output circuit which energizes the device. A second relay having normally closed contacts connected in series with contacts of the first relay provides a holding circuit for the first relay which is released only when both hand switches are released. The output circuit may include a third relay for applying power to the controlled device, and which actuates a timer which holds the third relay operated for a predetermined time interval.

COUNTER Patentd j May 18, 1971 @KIT? INVENTOR DONALD D. KIKTA BY fleLA KW ATTYS v 1 I SAFETY CONTROL SYS'IEM FOR ACTUA'IING ELECTRICALLY CONTROLLED MECHANICAL DEVICE BACKGROUND or THE mvsn'nolv In order to prevent injury to an operator of an eleqtricallyoperated mechanical device, such as a press, it is known to provide a pair of hand switches which must both be operated before energy is applied to the press to cause relative movement between the'parts thereof. The operators hands, therefore, must both be on the switches so that they cannot be in the path of movement of the parts to be injured thereby. The systems which have been provided have not been entirely satisfactory for a number of reasons. Some systems have used mechanical latching relays whichremain in a particular position when operated and require a second operation to ielease the same. However, the mechanical latch used may be unintentionally released by vibrations which may be present in a shop havinga number of presses which cause substantial shocks when they open and close.

Another problem is that certain systems, while requiring both hands on the switches for operation, will releasewhen only one switch is released, and this may cause undesired recycling of the machine. Various other problems have been encountered in connection with known safety control circuits.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved control system for an electrically controlled mechanical device which has two hand-operated switches, and which will operate only when both switches are simultaneously closed, and which will remain in operated condition until both switches are released.

Another object of the invention is to provide a safety control system including a plurality of relays, which is arranged so that failure of one of the relays does not cause a dangerous condition.

A further object of the invention is to provide a control system for an electrically operated mechanical device which is operated by first and second hand-actuated switches, and which causes operation of the device for a predetermined time period.

A feature of the invention is the provision of a safety control system including a pair of relays, with the first being energized by the simultaneous actuation of two hand switches and held energized through aholding circuit including normally closed contacts of the second relay, with the holding circuit being released when both hand switches are released to operate the second relay. 1

A further feature of the invention is the provision of a control system including a firstrelay actuated by hand switches, a second relay for releasing the first relay when both hand switches are released, and a third relay for applying energy to the operated device. A timer maybe coupled to the third relay for holding the same operated for a predetermined time period.

ln practicing the invention, a control system isprovided for an electrically controlled mechanical device having mechanically moving parts, such as a press. The device may be directly actuated by electrical power, or may be actuated pneumatically or hydraulically through action of an electrical control.

' The system includes first and second hand-operated switches each having a normally open contact and a normally closed contact, and the device is operated only when the hand switches are simultaneously closed. A first relay is energized by simultaneous operation of the two switches through the normally open contacts thereof. A second relay is provided having a pair of normally closed contacts, each connected in series with a contact of the firstrelay in parallel aeross'the normally open contacts of one'of the switches, to provide a holding circuit for the first relay. The-second relay is energized through the nonnally closed contacts of the switches and through a contactof thefirstrelay-so'that when'both switches are released, the second relay is actuated to open its normally cloud contacts and release the first relay. An output circuit is actuated through an additional'contact of the first relay and includes a third relay with contacts for supplying electrical energy to the controlled device. The third relay may have a further contact tfr actpating a timer which is connected to the third relay for h lding the same operated for a predetermined time period. A counter may also be operated by the output circuit to indicate the number of operations. Electrical energy for the system is supplied through a circuit including a lamp which indicates an improper connection of the system to the electrical supply.

The control system of. the invention is illustrated in the single FIGURE of the drawing, which is a schematic diagram of the control circuit.

Referring now to the drawing, the device to be controlled is indicated at 10, and this may be any electrically operated device which has a moving part, and wherein there is a possibility that the operator can be injured by movement of such part when the device operates. The device can be energized from the standard alternating current power supply, or alternatively can be operated by a hydraulic or pneumatic actuator which is electricallycontrolled. The equipment illustrated includes

conductors

12 and 14 between which alternating current potential is applied. Thesupply also includes a ground terminal 15, as is now common practice, and a connection is made thereto through switch 17. One of the

conductors

12 and 14 is also normally at a ground potential, and in the circuit shown this is the conductor 14. Connected between the conductors 14 and15 is a neon lamp 16 in series with resistor 18. In the event that the conductor 14 is not a ground potential there will be a potential between conductors 14 and 15 and the neon lamp 16 will light to show this. Also, if the conductor 15 is not connected to ground,jthe potential between conductors-12 and 14 will be applied across the circuit including lamp l6 and resistors 18 and 19. The lamp 16 will, therefore, light to show that there is a failure of ground. The switch 17 can be operated to break the ground connection to test the lamp 16 to see that it is not burned out. In the event that the connections of the

conductors

12 and 14 to the supply is reversed, lamp 16 and resistor 18 will connected between the high potential conductor and ground, and again the lamp 16 will light. The circuit including the lamp 16 therefore indicates when the system is not properly connected to the volt pp y- Considering now the control circuit proper, switches 20 and 22 are positioned adjacent the press or other electromechanical device to be controlled, so that the operator can operate each switch with one of his hands. This will insure that the operators two hands are positioned at the switches. The switches are positioned away from the moving .parts of the press so that there is no danger of the operators hands being injured by moving parts of the device. The switch 20 includes a normally closed contact 24 and a normally open contact 25. Similarly the switch 22 includes a normally closed contact 26 and a normally open contact 27L Relay 30 has its energizing coil connected to switch

contact

25 and 27, and when the switches 20 and 22 are closed these contacts are connected to conductors l2 and 14 so that current is applied to the relay 30. This causes relay 30 to operate to close its

contacts

31, 32, 33 and 34. A second relay 36 is provided having normally closed

contacts

38 and 39. Contact 38 is in series with contact 31 of relay 30, and complete'a holding circuit across'the normally open contact 25 of switch 20. Accordingly, when relay 30 is actuated and contact 31 closes, aholding circuit is connected across the contact 25 to complete the circuit from connector 12 to relay 30, even when the switch 20 is released. Normally closed contact 39 of relay 36 is similarly connected in series with contact 34 of relay 30 across normally open contact '27 of switch 22. This circuit likewise connects relay 30 to the conductor 12, even when switch 22 is released, so that relay 30 is held operated after it has been initially When both switches 20 and 22 are released, a circuit is established to the relay 36 through normally closed contact 24 of relay 20, contact 32 of relay 30 which is operated and normally closed contact 26 of switch 22. Relay 36 therefore operates and opens its normally closed

contacts

38 and 39 to release the holding circuit to relay 30, so that this relay drops out. It is pointed out however, that release of either one of the switches 20 and 22 will not cause the relay 30 to release, and this relay is not released until both hand switches 20 and 22 are simultaneously released.

The control system has an output circuit portion including relay 40 and timer 45 which cooperates with relay 40 to energize the controlled device for a predetermined time period. Contact 33 of relay 30 connects conductor 12 to timer 45, and the circuit continues through contacts 46 of the timer to the winding of relay 40. The relay 40 is permanently connected to conductor 14 so that contact 33 of relay 30 is effective to energize relay 40. Contact 41 of relay 40 is connected in parallel with contact 33 of relay 30 so that when relay 40 is once operated, it is held operated even after relay 30 releases.

Contacts

42 and 43 of the relay 40 connect the controlled device 10 to the

power supply conductors

12 and 14, and this connection is maintained for the period of time that the relay 40 is operated.

The timer 45 may be of known construction, such as the solid state timer manufactured by Telex/AEMCO. The timer 45 is actuated when a potential is applied to

tenninals

47 and 48 thereof. As has been stated, operation of relay 30 closes contact 33 to provide a potential'to terminal 48, and terminal 47 is permanently connected to conductor 14. The timer 45 will, therefore, initiate a timing cycle, and at the end of the cycle will open contacts 46 thereof and close contacts 49. Opening of contacts 46 will deenergize relay 40 so that the energizing connection to the controlled device 10 is broken. Closing of contacts 49 of the timer will energize the counter 50 which counts the number of operations of the device. The counter 50 may be connected through switch 51, so that the counter can be disconnected in the event that the device is operated through cycles which are not to be counted, such as during testing.

It will be apparent that the control system insures that the equipment doesnot operate until both hand switches 20 and 22 are simultaneously closed. This prevents accidents resulthands of an operator, each of said switches having a normally closed contact and a normally open contact, first relay means having a plurality of normally open electrical circuit portions, an actuating circuit coupled to said first relay means and including said normally open contacts of said first and second switches for actuating said first relay means to complete the circuits through said circuit portions of said first relay means in response to simultaneous operation of said first and second switches, second relay means having at least one normally closed circuit portion,

a holding circuit coupled to said first relay means extending through a first circuit portion of said first relay means and said normally closed circuit portion of said second relay means,

an actuating circuit coupled to said second relay means and including said normally closed contacts of said first and second switches and a second circuit portion of said first relay means and responsive to release of said first and second switches to actuate said second relay means to open said circuit portion thereof and release the holding circuit for said first relay means, and

an output circuit adapted to be coupled to the electrically controlled device and connected to a third circuit portion of said first relay means to operate the device in response to operation of said first relay means.

2. The control system of claim 1 wherein said output circuit includes third relay means having circuit portions completed in response to operation of said first relay means for applying current to the electrically controlled device.

3. The control system of claim 2 further including timer means connected to said third relay means for holding the same operated for a predetermined time period.

4. The control system of claim 1 wherein said first relay means includes a fourth circuit portion, and said second relay means includes first and second normally closed circuit portions, said first circuit portion of said first relay means and said ing from the operators hand being in the path of movement of 5 the controlled device. Further, the system does not release the output circuit until both hand switches have been released. This prevents undesired recycling of the equipment. To further prevent improper operation of the system, the switches 20 and 22 can be snap action switches which snap into both the open and closed positions. It a switch fails, the system will not operate. The relays may be computer grade relays which provide highly reliable operation. Failure of relay 30 will prevent operation of the system and this will not create a dangerous condition. Inasmuch as the holding circuit is completed through relay 36 when it is deenergized, failure of this relay will prevent the resetting for a new cycle.

The control system described is advantageous in that it provides the desired control with a high degree of safety for the operator. The system is quite simple and inexpensive, and provides reliable operation with a minimum of maintenance.

I claim:

1. A manually operable electrical control system for an electrically controlled device including in combination,

fast and second manually operated electrical control switches positioned to be actuated respectively by the two first circuit portion of said second relay means being connected in series with each other and in parallel across said normally open contacts of said first switch, and said fourth circuit portion of said first relay means and said second circuit portion of said second relay means being connected in series with each other and in parallel across said normally open contacts of said second switch. l

5. The control system oi claim 1 wherein said first relay means includes a first electromechanical relay having an energizing winding and nonnally open contacts which are closed in response to energization of said winding, and said second relay means includes a second electromechanical relay having an energizing winding and normally closed contacts which are opened in response to energization of said winding of said second relay means.

6. The control system of claim 5 wherein said output circuit includes a third electromechanical relay having an energizing winding and a plurality of normally open contacts, and wherein said winding is energized in response to operation of said first electromechanical relay to close at least one of said contacts for operating the electrically controlled device.

7. The control system of claim 6 further including timer means connected to said third relay for holding the winding thereof energized for a predetermined time period.

8. The control system of claim 7 further including a counter connected to said timer for indicating the number of times the device is operated.

Claims

1. A manually operable electrical control system for an electrically controlled device including in combination, first and second manually operated electrical control switches positioned to be actuated respectively by the two hands of an operator, each of said switches having a normally closed contact and a normally open contact, first relay means having a plurality of normally open electrical circuit portions, an actuating circuit coupled to said first relay means and including said normally open contacts of said first and second switches for actuating said first relay means to complete the circuits through said circuit portions of said first relay means in response to simultaneous operation of said first and second switches, second relay means having at least one normally closed circuit portion, a holding circuit coupled to said first relay means extending through a first circuit portion of said first relay means and said normally closed circuit portion of said second relay means, an actuating circuit coupled to said second relay means and including said normally closed contacts of said first and second switches and a second circuit portion of said first relay means and responsive to release of said first and second switches to actuate said second relay means to open said circuit portion thereof and release the holding circuit for said first relay means, and an output circuit adapted to be coupled to the electrically controlled device and connected to a third circuit portion of said first relay means to operate the device in response to operation of said first relay means.

4. The control system of claim 1 wherein said first relay means includes a fourth circuit portion, and said second relay means includes first and second normally closed circuit portions, said first circuit portion of said first relay means and said first circuit portion of said second relay means being connected in series with each other and in parallel across said normally open contacts of said first switch, and said fourth circuit portion of said first relay means and said second circuit portion of said second relay means being connected in series with each other and in parallel across said normally open contacts of said second switch.

5. The control system of claim 1 wherein said first relay means includes a first electromechanical relay having an energizing winding and normally open contacts which are closed in response to energization of said winding, and said second relay means includes a second electromechanical relay having an energizing winding and normally closed contacts which are opened in response to energization of said winding of said second relay means.