US3147421A - Limit switch motor braking control for hoists - Google Patents

Description

Sept. 1, 1964 D. E. CHILDS. 3,147,421

LIMIT swrrcn MOTOR BRAKING cou'rRoL FOR HOISTS Filed Nov. 13, 1961 \5 g I \9 HOISTFLOWER 1/ LII-l XVR as I m F/g.

2 INVENTOR.

DAVID e. CHILDS ATTORNEY United States Patent Ohio Filed Nov. 13, 1961, Ser. No. 151,850 8 Claims. (Cl. 318-266) This invention relates to electric control systems and more particularly to a system for controlling an electric motor when used to hoist and lower a load.

Heretofore, electric control systems of this type did not rapidly stop and hold the load after it was hoisted through the overhoist limit switch when the drum controller was left in one of the hoist positions. The contacts of the overhoist limit switch, when tripped, disconnect the motor from the source of power and reconnect it in a dynamic braking circuit to assist in stopping the upward movement of the load. Once this upward movement is stopped, the load was allowed to lower out of the overhoist limit switch due to its own weight and because the overhoist limit switch contacts did not disconnect the winding of the friction brake from the source of power. As soon as the load lowered out of the overhoist limit switch, the overhoist limit switch reset and its contacts operated to reconnect the motor to the source; and since the drum controller remained in one of the hoist positions, the load would again hoist through the overhoist limit switch. This cycling of the load in and out of the overhoist limit switch was dangerous and, in addition, caused undue wear on the equipment.

It is therefore an object of this invention to provide a hoist control system which prevents the cycling of the load through the overhoist limit switch.

It is another object of this invention to provide a hoist control system with a protective system that is more sensitive to the operation of the motor in the hoist direction after going through the overhoist limit switch than it is to the operation of the motor in the other conditions.

It is another object of this invention to provide a hoist system which prevents the speed of lowering out of the overhoist limit switch from becoming excessive.

It is still another object of this invention to prevent the motor from running away should the overhoist limit switch fail to reset during the lowering of the load through it.

The embodiment of this invention utilizes a voltage relay that is connected to be energized by the voltage drop across the series field winding when the overhoist limit switch is in its normal untripped condition, and that is connected to be energized by the voltage drop across the dynamic braking resistor when the overhoist limit switch is tripped. The voltage relay has contacts in the hoist control circuit and when it is operated, it causes the motor and brake to be disconnected from the source of power whereby the brake sets to stop and hold the load.

The voltage relay is polarized in that it is operated by a lower voltage after the tripping of the overhoist limit switch due to a load being hoisted therethrough than the voltage required to operate the relay under the other operating conditions of hoisting and lowering. This is very desirable and increases the stability of the hoist operation because it allows the voltage to operate the relay 3,147,42l Patented Sept. 1, 1964 after the overhoist limit switch has been tripped to be very small, and it is in this instance, that it is desirable to have the relay operate as soon as possible. In the other operating condition, the relay is required to operate only when excessive conditions exist, and under these conditions a much larger voltage signal is present. Also, aids in reducing the possibility of relay operation due to transients.

It is also desirable to utilize a relay which has a slight time delay between its energization and the operation of its contacts as is described in the co-pending application of Harry M. Cook and Christian Chermely, filed on or about July 10, 1961, bearing Serial Number 122,817, and having the same assignee as the instant application.

Operation of the relay requires that the control circuit be reset by moving the drum controller to the OH position and thereby re-establish the energizing circuit for the control circuit.

Other objects and advantages of this invention will become apparent to those skilled in the art when the following description is read in conjunction with the drawings in which:

FIGURE 1 is an across-the-line type of diagram of the power and control circuits for a hoist system; and

FIGURE 2 is another embodiment of this invention illustrating the method of connecting the relay.

Referring to the drawings, there is shown at it) in FIG- URE 1 an armature of a DC. motor having a series field winding 11.

Armature 10 is connected to be energized from a source of DC. power represented by lines 12 and 13 through contacts of various contactors. When contactors M and H are operated to close contacts M1 and H1, armature It is energized to rotate in the hoisting direction. When contactors M and L are operated to close contacts M1 and L1, armature 10 is energized to rotate in the lowering direction.

Armature 10 is connected by a drive shaft 14 to a hoist drum 15 which has a cable 16 wound thereon. At the free end of cable 16 is a load hook 17 which serves as the means of engaging the load to be hoisted or lowered. Hook 17 has an arm 18 which serves to engage and operate an overhoist limit switch when hook 1'7 is hoisted too high. The overhoist limit switch is diagrammatically represented at 19 and has normally open contacts 20 and 21 and normally closed contacts 22 and 23.

Armature 1th is also connected to a normally set friction brake (not shown) of known construction, having an electromagnetic winding 24 for releasing the friction brake when energized. When winding 24 is not energized, the friction brake sets to stop rotation of armature 10 and drum 15.

At 25 generally is a drum type controller which, in the diagrammatic illustration thereof, comprises movable con tacts 26 to 36. Contacts 27 through 36 are all connected together as shown and connected to contact UVl and wire 37 to wire 12. Contact 26 is connected directly to wire 37 to wire 12 and will only conduct current when drum controller 25 is in its off position.

These contacts, as will be understood by those skilled in the art, are all movable in unison from the illustrated off position towards the right to five successive lowering points, La to Le, or towards the left to five successive hoisting points, Ha to He, indicated by the vertical lines below the legends Lowering and Hoisting.

On the several lowering points, movable contacts 27 and 28 and 311 to 36 are engageable with bar contacts 38 to 46; and on the several hoisting points, movable contacts 27 to 29 and 32 to 36 are engageable with bar contacts 47 to 54.

Drum controller 25, on the various described points, operates or restores electromagnetic contactors as follows.

A contactor UV having a winding 55 and normally open contacts UV1 and UV2.

A contactor M having a winding 56 and a normally open contact M1.

A contactor A having a winding 57 and a normally open contact 5A1 and a normally closed contact 5A2.

A contactor H having a winding 58 and normally open contacts H1 and H2 and a normally closed contact H3.

A contactor L having a winding 59 and normally open contacts L1 and L2 and a normally closed contact L3.

A contactor 1A having a winding 60 and a normally open contact 1A1 and a normally closed contact 1A2.

A contactor S having a winding 61 and normally open contacts S1 to S3 and a normally closed contact S4.

A contactor CR having a winding 62 and a normally open contact CR1 and normally closed contacts CR2 and CR3.

A contactor DB having a winding 63 and a normally open contact DB1 and normally closed contacts DB2 and DB3.

A contactor 2A having a winding 64 and normally open contacts 2A1 and 2A2 and a normally closed contact 2A3.

A timing contactor 2T having a winding 65 and a normally closed contact 2T1.

A timing contactor 1T having a winding 66 and a normally open contact 1T1 and a normally closed contact 1T2.

A timing contactor 3T having a winding 67 and normally open contacts 3T1 and 3T2.

A contactor 3A having a winding 68 and normally open contacts 3A1 and 3A2 and a normally closed contact 3A3.

A contactor 4A having a winding 69 and normally open contacts 4A1 and 4A2 and a normally closed contact 4A3.

Timing contactors 1T, 2T and ST are of the known type that have means delaying their contact operation until a time interval has elapsed after the energization of their windings.

The contactors and timing contactors are all illustrated in normally de-energized or restored condition. The said contacts of these contactors and timing contactors are shown without connection thereto, but are reproduced elsewhere in the drawing, with their connections, to there'- by avoid the complexity in the drawings.

The windings of the contactors are shown in an acrossthe-line type of diagram comprising horizontal lines 70 to 80, with their left ends connected to the various bar contacts of drum controller 25. The right end of wire 70 is connected to wire 13. The right end of wires 71 to 76 are connected to a wire 81. The right end of wires 77 to 36 are connected to a wire 82.

In the illustrated 01f position of drum controller 25, contactor UV is operated by current through controller contact 26, cross Wire 70, winding 55 of contactor UV and contact XVR1 to wire 13. Contactor UV operates to close contact UV1 which connects wire 12 via wire 37 directly to contacts 27 through 36. Contact UV2 closes to connect wire 81 to wire 13. The control circuit is now connected to the source of power and ready for operation.

On the first point of hoisting Ha, contactor M is operated by current through contact 27, bar contact 47, cross wire 71, winding 56, wire 81 and contact UV2 to wire 13. Contactor M operates to close contact M1.

At the same time, contactor H is operated by current from contact 29, through bar contact 49, cross wire 73, contact S4, winding 58 of contactor H, wire 81 and contact UV2 to wire 13. Contactor H operates to close contacts H1 and H2 and open contact H3.

The operation of contactors M and H connect the motor so that it is energized by current flowing from wire 12 through contact H1, contact 22, armature 10, contact 23, series field 11, winding 24, resistor sections R1, R2, R3 and R4, and contact M1 to wire 13. Resistor sections R5 and R6 and contact DB2 are connected in parallel with contact 22, armature 10, contact 23 and series field 11.

The current flowing through winding 24 of the friction brake releases the brake, allowing the motor to rotate. Armature 10 is energized with current in a direction to cause the motor to rotate in the hoisting direction, but at a low hoisting speed due to the series connected resistors R1 to R4 and the armature shunt circuit of resistors R5 and R6.

On going to the second point of hoisting Hb, the operating conditions described for the first point hoisting remain the same; and additionally, contactor 5A operates to short out resistance section R2 and contactor DB operates to open the armature shunt circuit as follows.

Current flows through controller contact 28, bar contact 48, cross wire 72, contact 2T2, winding 57 of contactor 5A, wire 81 and contact UV2 to wire 13. Contactor 5A opeartes to close contact 5A1 which shorts out resistance section R2, and contact 5A2 opens.

Controller contact 32 engages with bar contact 50 and current flows therethrough and through contact H2, cross wire 76, winding 63 of contactor DB, contact DB3, wire 81 and contact UV2 to wire 13. Contactor DB operates to close contact DB1 and open contacts DB2 and DB3. The opening of contact DB2 disconnects the armature shunt circuit consisting of resistors R5 and R6. The opening of contact DB3 inserts resistor R7 in the energizing circuit of winding 63. The closing of contact DB1 connects wire 82 to wire 13.

The motor is now energized by current from wire 12 through contact H1, contact 22, armature 10, contact 23, series field 11, winding 24, resistor R1, resistor R3, resistor R4- and contact M to wire 13. Armature It is now energized with a higher current and is caused to hoist the load at a faster speed.

On going to the third point of hoisting He, the operating conditions described for the second hoisting point remain the same; and additionally, contactor A2 operates to connect resistors R8, R9 and R10 in parallel with resistors R1 and R3 which is accomplished as follows.

Controller contact 33 engages with bar contact 51 and current flows therethrough and through cross wire 77, contact L3, winding 64 of contactor 2A, wire 82 and contact DB1 to wire 13. Contactor 2A operates to close contacts 2A1 and 2A2 and open contact 2A3. The closing of contact 2A1 connects resistors R8, R9 and R10 in parallel with resistors R1 and R3.

The closing of contact 2A2 allows current to flow from controller contact 34 through bar contact 52, contact 2A2, cross wire 78, winding 66 of timing contactor 1T, wire 82 and contact DB1 to wire 13. After the elapse of a time interval, contactor 1T operates to close contact 1T1 and open contact 1T2.

The motor is now energized by current from wire 12 through contact H1, contact 22, armature 10, contact 23, series field 11, winding 24, the parallel connected resistors R1 and R3, and R8, R9 and R10, resistor R4, and contact M1 to wire 13. The armature is now eners gized with increased currents so the motor hoist the load at a higher speed.

On going to the fourth point of hoisting Hd, the operating conditions described for the third hoisting point remain the same; and additionally, contactor 3A operates to short out resistor R10 and connects resistors operates to i R1, R3 and R4 in parallel wtih resistors R8 and R9 as follows.

Controller contact 35 engages with bar contact 53 and current flows therethrough and through cross wire 79, contact 1A2, contact 1T1, winding 68 of contactor 3A, wire 82 and contact DB1 to wire 13. It is to be noted, that winding 68 cannot be energized until after the expiration of the time interval of timing contactor 1T. After this expires, contactor 3A is operated to close contacts 3A1 and 3A2 and open contact 3A3. The closing of contact 3A1 shorts out resistor R10 to connect resistor R1, R3 and R4 in parallel with resistors R8 and R9.

The closing of contact 3A2 allows winding 67 of timing contactor 3T to be energized through the circuit consisting of controller contact 34, bar contact 52, cross wire 78, contact 3A2, winding 67, wire 82 and contact DB1 to wire 13. After the expiration of its time interval, contacts 3T1 and 3T2 operate to close.

Current now flows through the motor from wire 12 to contact H1, contact 22, armature 10, contact 23, series field 11, winding 24, the parallel circuit of resistors R1, R3, R4 and contact M1, and resistors R8 and R9 to wire 13. The motor is energized with a still higher current to cause it to hoist the load faster.

On going to the fifth point of hoisting He, the operating conditions described for the fourth hoisting point remain the same; and additionally, contactor 4A operates to remove all of the resistance from the armature circuit as follows.

Controller contact 36 engages with bar contact 54 and current flows therethrough and through cross wire 80, contact 3T2, winding 69 of contactor 4A, wire 82 and contact DB1 to wire 13. Contactor 4A cannot operate until after the elapse of the time interval for timing contactor 3T, after the expiration of which, contactor 4A operates to close contacts 4A1 and 4A2 and open contact 4A3. The closing of contact 4A1 shorts out all the remainder resistor sections from the motor circuit.

The motor is now energized by current flowing from wire 12 through contact H1, contact 22, armature 10, contact 23, series field 11, winding 24, contact 2A1 and contact 4A1 to wire 13. The motor is now energized with its maximum current and will therefore hoist the load at the maximum speed.

On going to the first point of lowering La, contactors M, L and 5A are operated as follows.

Controller contact 27 engages with bar contact 38 and current flows therethrough and through cross wire 71, winding 56 of contactor M, wire 81 and contact UV2 to wire 13. Contactor M operates to close contact M1.

Controller contact 28 engages with bar contact 39 and current flows therethrough and through cross wire 72, contact 2T1, winding 57 of contactor 5A, wire 81 and contact'UV2 to wire 13. Contactor 5A operates to close contact 5A1 and open contact 5A2.

Controller contact 30 engages with bar contact 40 and current flows therethrough and through cross wire 74, contact 2A3, winding 59 of contactor L, wire 81 and contact UV2 to wire 13. Contactor L operates to close contacts L1 and L2 and open contact L3.

Also, current flows from controller contact 30 through bar contact 40, cross wire 74, contact 2A3, contact 1T2, winding 60 of contactor 1A, wire 81 and contact UV2 to wire 13. Contactor 1A operates to close contact 1A1 and open contact 1A2.

The motor is now connected to be energized as a shunt motor by current flowing from wire 12 through contact L1, the circuit of armature 10, contact 22, resistors R5 and R6, and contact DB2, connected in parallel with contact 23 and series field 11, and thence through winding 24 and resistor R1, and parallel connected resistor R3 with resistors R9 and R10, resistor R4 and contact M1 to wire 13.

On going to the second point of lowering Lb, the operating conditions described for the first lowering point remain the same; and additionally, contactors S and DB are energized to continue to operate the motor as a shunt motor as follows.

Controller contact 31 engages bar contact 41 and current flows therethrough and through cross wire 75, contact H3, winding 61 of contactor S, wire 81 and contact UV2 to wire 13. Contactor S operates to close contacts S1 to S3 and open contact S4.

Controller contact 32 engages with bar contact 42 and after contact S2 closes, current flows from contact 32 through bar contact 42, contact S2, cross wire 76, winding 63 of contactor DB, contact DB3, wire 81 and contact UV2 to wire 13. Contactor DB operates to close contact DB1 and open contacts DB2 and DB3. Even though contact DB3 opens, winding 63 is maintained energized through resistor R7.

Current now flows through to energize the motor from wire 12 through contact L, the circuit of armature 10, contact 22, resistor R5, contact S1 and resistor R8, all connected in parallel with the circuit of contact 23, series field 11, winding 24, resistor R1 and contact 1A1, and thence through resistors R9 and R18 connected in parallel with resistor R3, and through resistor R4 and contact M1 to wire 13.. This increases the current flowing through armature 10 to increase this motor speed so it lowers the load faster.

On going to the third point of lowering Lc, the operating conditions described for the second lowering point remain the same, except that contactors 3A, 4A, and CR and timing contactors IT and ST become energized and contactor 1A becomes tie-energized.

Controller contact 34 engages bar contact 44 and current flows therethrough and through contact L2, cross wire 78, winding 66 of timing contactor 1T, wire 82 and contact DB1 to wire 13. After the expiration of its time interval, timing contactor 1T operates to close contact 1T and open contact 1T2. The opening of contact 1T2 de-energizes winding 60 and contactor 1A restores to open contact 1A1 and close contact 1A2.

The closing of contacts 1A2 and 1T1 allows current to flow from controller contact 35 through bar contact 45, cross wire 79, contact 1A2, contact 1T1, winding 68 of contactor 3A, wire 82, and contact DB1 to wire 13. Contactor 3A operates to close contacts 3A1 and 3A2 and to open contact 3A3.

The closing of contact 3A2 allows current to flow from controller contact 34, through bar contact 44, contact 3A2, winding 67 of timing contactor 3T, wire 82, and cont-act DB1 to wire 13. After the expiration of its time interval, timing contactor 3T operates to close its contacts 3T1 and 3T2.

The closing of contact 3T2 allows current to flow from controller contact 36, through ba-r contact 46, cross wire 88, contact 3T2, winding 69 of contactor 4A, wire 82 and contact DB1 to wire 13. Contactor 4A operates to close contacts 4A1 and 4A2 and to open contact 4A3.

The closing of contact 4A2 allows current to flow from controller contact 31, through bar contact 41, cross wire 75, contact H3, contact 4A2, winding 62 of contactor CR, wire 81 and contact UV2 to wire 13. Contractor CR is operated to close contact CR1 and open contacts SR2 and CR3.

Current now flows to energize the motor from wire 12 through contact L1 and the circuit of armature 10, contact 22, resistor R5, contact S1, contact 4A1 to wire 13 which is connected in parallel with the circuit of contact 23, series field 11, Winding 24, resistors R1, R3 and R4,

and contact M1 to wire 13. This increases the current allowed to flow through armature 10 to still further increase the motor speed and allows the lowering speed of the load to be increased.

On going to the fourth point of lowering Ld, the operating conditions described for the third lowering point remain the same, eXcept that contactors M and 3A become de energized as follows.

vWinding 46 becomes de-energized and contactor M restores when controller contact 27 leaves bar contact 38. Winding 68 becomes tie-energized and contactor 3A restores when controller contact 35 leaves bar contact 45.

Current now flows through to energize the motor from wire 12 through contact L1, the circuit of armature 16, contact 22, resistor R5, contact S1 and the parallel cirquit of contact 23, series field 11, winding 24, resistors R1, R3, R10, R9 and R8, and thence through contact 4A1 to wire 13. This further increases the current through armature 10 to increase the speed at which the motor drives the load downward.

On going to the fifth point of lowering Le, the operating conditions described for the fourth lowering point remain the same, except that contactor 5A is de-energized as follows. 7

Controller contact 33 engages with bar contact 43 and current flows therethrough and through cross wire 77, contact CR1, winding 65 of timing contactor 2T, wire 82 and contact DB1 to wire 13. After the elapse of its time interval, timing contacto-r 2T operates to open its contact 2T1.

The opening of contact 2T1 opens the circuit energizing winding 57 and it becomes de-energized to restore contactor 5A which opens contact 5A1 and closes contact 5A2. Current now flows toenergize the motor from wire 12 through contact L1, the circuit of armature 10, contact 22, resistor R5, contact S1 and the parallel connected circuit of contact 23, series field 11, winding 24, resistors R1 R2, R3, R4, R10, R9 and R8, and thence through contact 4A1 to wire 13. This increases the current flowing through armature 10 to its maximum whereby the lowering speed of the load is increased to its maximum. 7 A

When hook 17 is hoisted too high, arm 18 engages overhoist limit switch 19 causing contacts 22 and 23 to open and contacts 20 and 21 to close.

The openings of contacts 22 and 23 disconnect armature 10 and series field 11 from the source of power. It also interrupts the power to brake winding 24 unless drum controller 25 is in the first point hoisting, Ha. The closing of contacts 20 and 21 reconnect armature 16 and series field 11 in a dynamic braking circuit which has connected in series a dynamic braking resistor R11. Current now flows from armature 10 through contact 21, series field 11, resistor R11, contact 20 back to armature 10. This flow of current produces dynamic braking torque and will assist in rapidly stopping the motor.

V, Relay XVR has two windings 83A and 83B wound in the same direction oh its core. Bothv windings are connected in parallel with resistor R11 when contact 20 is closed. Winding 83 has a rectifier 85 connected in series with it in a manner to permit the flow of the current through winding 83A only after overhoist limit switch 19 has been tripped and a dynamic braking current is flowing. Therefore, after overhoist limit switch 19 has been tripped both windings 83A and 83B will be energized by the voltage drop across resistor R11 to operate relay XVR.

When relay XVR is operated, it opens its contacts XVR1. Contact XVR1 is connected in series with winding 55 of contactor UV. Winding 55 then becomes deenergized to restore contactor UV and open its contact UV1 which disconnects the power from the entire control circuit. All of the contactor-s and timing contactors in the control circuit are thus dc-energized and their contacts are restored to their unoperated condition. This disconnects the power source from armature 10 by the opening of contacts H1, L1, and M1. Armature 10 remains connected by limit switch contacts in the dynamic braking circuit of contact 22, resistors R5 and R6, contact DB2, series field 11 and contact 23. The power source is also disconnected from winding 24 of the friction brakeso its sets to stop and hold the load by the opening of the same contacts.

As soon as the voltage across resistor R11 has been reduced to a low value, windings 83A and 83B are deenergized and relay XVR restores to reclose its contact XVR1.

a Drum controller 25 then must be moved to the off position to reset the control circuit. As described for the off position, Winding 55 is energized through contact XVR1 to operate contactor UV and close its contacts UVI and UV2.

The operator may now lower the load out of the overhoist limit switch 19 by moving drum controller 25 to any of the lowering positions, La through Le, it being preferred that lowering point La be used.

The motor is now energized by current flowing from wire 12 through contact L1, armature 10, contact 21, series field 11, to friction brake winding 24. Current also flows from wire 12 through contact L1, contact 20, res'istor R11 to friction brake winding 24. The current then flows through winding 24 and the various resistor sections R1 through R10 depending upon the position of drum controller 25. The friction brake is thus released and the motor starts rotating to lower the load.

It is noted that relay XVR is again eneriz'ed by the voltage drop across resistor R11, but in this instant the voltage drop is of the reverse polarity. Therefore, current can only flow through winding 83B and cannot flow through winding 83A because of the blocking action of rectifier 85.

Should the lowering speed of the load become too great, the voltage drop across resistor R11 would reach the value at which Winding 83B will alone operate relay XVR. Relay XVR will operate to stop further downward movement of the load by deenergizing the control circuit and setting the friction brake in the same manner as previously described.

Thus, it is seen that relay XVR not only prevents the objectional cycling of the load in and out of the overhoist limit switch, but also prevents the load from being lowered too fast out of the limit switch, and provides this function at two different sensitivities.

As" the load is lowered through the overhoist limit switch, contacts 20 and 21 re-open and contacts 22 and 23 reclose. This connects the motor as a shunt motor for normal lowering. The reconnection of the motor by the contacts of the overhoist limit switch could, if the load were being lowered at a very fast speed, cause a terrific jar to the crane and to the load itself.

It is seen that relay XVR is connected across series field 11 and contact 23 during the normal hoisting and lowering operation of the hoist. Therefore, it is sensitive to any excessively high voltage conditions that may exist across the series field. However, in these instances only winding 833 will be energized as winding 83A cannot be because of the blocking action of rectifier 85. This makes relay XVR quite insensitive to normal transient condi tion and yet allows it to operate when the overhoist limit switch is tripped at very low voltages.

It is to be noted that when the load was hoisted through overhoist limit switch 19 in the hoisting direction, both windings were energized to operate relay XVR. When lowering the load out of the limit switch and after it has been reset, and when hoisting before tripping the limit switch only winding 83B was energized. Therefore, it is obvious that in the former case a much smaller voltage will operate relay XVR than would be required in the latter case. It therefore may be said that relay XVR is polarized to the hoisting direction of operation and nonpolarized to the other operating conditions.

It has been found that the operation of the circuit is improved and many safety features are added when the relay XVR is of the time delay type as described in the co-pending application of Harry M. Cook and Christian Chermely filed on July 10, 1961, hearing Serial Number 122,817 and having the same assignee as the instant application. FIGURE 2 illustrates the manner in which the relay of that application may be connected so that it may be polarized to provide the same advantages set forth in this application.

FIGURE 2 shows an XVR relay having a single wind ing 83. Connected in series with it is a parallel connected resistor 87 and a rectifier 86. Rectifier 86 is poled so it only connects current when dynamic braking current is flowing in the dynamic braking circuit. In all other instances, the current will flow in the reverse direction through winding 83 and because of the blocking action of rectifier 86, it must flow through resistor 87. Therefore, a. high voltage is required to operate relay XVR when the energizing current flows through the resistor than when the energizing current flows through rectifier 86 because of the voltage drop across resistor 87. Thus, it may be stated that relay XVR is polarized to the one condition and non-polarized to the other condition.

Although I have described my invention with a certain degree of particularity, it is understood that the above disclosure has been made only by way of example, as is required by law, and that many changes in the arrangement of the circuit may be resorted to without departing from the spirit and the scope of my invention as hereinafter claimed.

I claim as my invention:

1. In a control system for hoists and the like having a driving motor provided with a series field; a brake for said motor having an operating winding in series with said motor; a reversing type drum controller connected in a series circuit to a source by normally closed contacts of a relay, and having operable contacts and circuits controlled thereby for selectively connecting said motor to a source for rotation in either direction; a limit switch mechanism having normally closed contacts in the connections from the motor to the source and normally open contacts; a dynamic braking circuit including a resistor having the normally open limit switch contacts in the said circuit connections to the armature and the series field; a relay for operating said normally closed relay contacts and connected to be energized by the voltage drop across said resistor when the normally open limit switch contacts are closed and by the voltage drop across said series field when the normally closed limit switch contacts are closed; said relay capable of being energized in a polarized manner and responsive to a selected voltage when energized by the voltage drop across the resistor and in a non-polarized manner and responsive to selected greater voltage when energized by the voltage drop across the field; said limit switch responsive to a predetermined limit of operation of the motor in one direction for opening the normally closed limit switch contacts to disconnect the motor from the source and for closing said normally open limit switch contacts to complete the dynamic braking circuit whereby said relay is energized in the polarized manner by the voltage drop across said resistor and it operates to open said normally closed contacts which disconnects the drum controller from the source to deenergize the brake winding, and the brake sets to assist in stopping and to hold the load.

2. In a control system for hoists and the like as described in claim 1 wherein said relay has two energizing windings connected in parallel, a rectifier connected in series with one of said windings and in a direction whereby said winding can only be energized by the voltage drop across said resistor when dynamic braking current is flowing through said resistor.

3. In a control system for hoists and the like as described in claim 1 wherein a parallel connected resistor and rectifier are connected in series with the energizing winding for said relay, and said rectifier connected in a manner to allow current to flow therethrough to energize said winding of said relay only when dynamic braking current is flowing through said resistor.

4. In a control system for hoists and the like having a driving motor provided with a series field; a brake for said motor having an operating winding in series with said motor; a reversing type drum controller connected to a source by a normally closed contact of a relay and having operable contacts and circuits controlled thereby for selectively connecting said motor to a source for rotation in either direction; a limit switch mechanism having normally closed contacts in the connections from the motor to the source and normally open contacts; a dynamic braking circuit including a resistor and having the normally open limit switch contacts in the connections to the armature and the series field; a relay for operating said normally closed contacts and connected to be energized by the voltage drop across said resistor when the normally open limit switch contacts are closed and by the voltage drop across said series field when the normally closed limit switch contacts are closed; said relay capable of being energized in a polarized manner and in a nonpolarized manner; said limit switch responsive to a predetermined limit of operation of the motor in one direction for opening the normally closed limit switch contacts and disconnecting the motor from the source, and for closing said normally open limit switch contacts to complete the dynamic braking circuit; control circuits responsive to operation of said drum controller for connecting said motor to said source for rotation in the reverse direction; and should the speed of said motor in the reverse direction become too fast, said relay is energized in a non-polarized manner by the voltage drop across said series field and it operates to open said normally closed contact which disconnects the drum controller from the source to de-energize the brake winding, and the brake sets to stop and hold the motor.

5. In a control system for hoists and the like as described in claim 1 wherein additional control circuits are responsive to operation of the drum controller for connecting said motor to said source for rotation in the reverse direction after said limit switch has been tripped, whereby should the speed of the motor in the reverse direction become too great before resetting said limit switch in the reverse direction, said relay is energized in a non-polarized manner by the voltage drop across said resistor and said relay operates to open the normally closed contacts which disconnect the drum controller from the source to de-energize the motor and the brake, and the brake sets to stop and hold the motor.

6. In a control system for hoists and the like having a driving motor provided with a series field; a brake for said motor having an operating winding in series with said motor; a reversing type drum controller connected to a source by normally closed contacts of a relay, and having operable contacts and circuits controlled thereby for selectively connecting said motor to a source for rotation in either direction; a limit switch mechanism having normally closed contacts in the connection from the motor to the source and normally open contacts; a dynamic braking circuit including a resistor and having the normally open limit switch contacts in the said circuit connections to the armature and the series field; said limit switch responsive at a predetermined limit of operation of the motor in one direction for opening the normally closed limit switch contacts to disconnect the motor from the source and for closing said normally open limit switch contacts to complete the dynamic braking circuit; a relay for operating said normally closed contacts and capable of being energized in a polarized and non-polarized manner, said relay connected to be energized in the nonpolarized manner by the voltage drop across said series field when said limit switch is in its normal unoperated condition and only connected to be energized in the polarized manner by the voltage drop across said resistor due to the flow of dynamic braking current immediately after said limit switch has been operated.

7. In a control system for hoists and the like as described in claim 6 wherein additional circuits are responsive to the operation of the drum controller for connecting said motor to said source for rotation in the reverse direction after said limit switch has been operated whereby said relay is energized by the voltage drop across said resistor in the non-polarized manner, and after said limit switch has been reset to its normal unoperated condition said relay is energized by the voltage drop across said series field in the non-polarized manner.

8. In a control system for hoists and the like as described in claim 7 wherein said relay has two energizing windings connected in parallel, a rectifier connected in series with one of said windings and in a direction to allow the flow of current therethrough when dynamic braking current is flowing through said resistor.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. IN A CONTROL SYSTEM FOR HOISTS AND THE LIKE HAVING A DRIVING MOTOR PROVIDED WITH A SERIES FIELD; A BRAKE FOR SAID MOTOR HAVING AN OPERATING WINDING IN SERIES WITH SAID MOTOR; A REVERSING TYPE DRUM CONTROLLER CONNECTED IN A SERIES CIRCUIT TO A SOURCE BY NORMALLY CLOSED CONTACTS OF A RELAY, AND HAVING OPERABLE CONTACTS AND CIRCUITS CONTROLLED THEREBY FOR SELECTIVELY CONNECTING SAID MOTOR TO A SOURCE FOR ROTATION IN EITHER DIRECTION; A LIMIT SWITCH MECHANISM HAVING NORMALLY CLOSED CONTACTS IN THE CONNECTIONS FROM THE MOTOR TO THE SOURCE AND NORMALLY OPEN CONTACTS; A DYNAMIC BRAKING CIRCUIT INCLUDING A RESISTOR HAVING THE NORMALLY OPEN LIMIT SWITCH CONTACTS IN THE SAID CIRCUIT CONNECTIONS TO THE ARMATURE AND THE SERIES FIELD; A RELAY FOR OPERATING SAID NORMALLY CLOSED RELAY CONTACTS AND CONNECTED TO BE ENERGIZED BY THE VOLTAGE DROP ACROSS SAID RESISTOR WHEN THE NORMALLY OPEN LIMIT SWITCH CONTACTS ARE CLOSED AND BY THE VOLTAGE DROP ACROSS SAID SERIES FIELD WHEN THE NORMALLY CLOSED LIMIT SWITCH CONTACTS ARE CLOSED; SAID RELAY CAPABLE OF BEING ENERGIZED IN A POLARIZED MANNER AND RESPONSIVE TO A SELECTED VOLTAGE WHEN ENERGIZED BY THE VOLTAGE DROP ACROSS THE RESISTOR AND IN A NON-POLARIZED MANNER AND RESPONSIVE TO SELECTED GREATER VOLTAGE WHEN ENERGIZED BY THE VOLTAGE DROP ACROSS THE FIELD; SAID LIMIT SWITCH RESPONSIVE TO A PREDETERMINED LIMIT OF OPERATION OF THE MOTOR IN ONE DIRECTION FOR OPENING THE NORMALLY CLOSED LIMIT SWITCH CONTACTS TO DISCONNECT THE MOTOR FROM THE SOURCE AND FOR CLOSING SAID NORMALLY OPEN LIMIT SWITCH CONTACTS TO COMPLETE THE DYNAMIC BRAKING CIRCUIT WHEREBY SAID RELAY IS ENERGIZED IN THE POLARIZED MANNER BY THE VOLTAGE DROP ACROSS SAID RESISTOR AND IT OPERATES TO OPEN SAID NORMALLY CLOSED CONTACTS WHICH DISCONNECTS THE DRUM CONTROLLER FROM THE SOURCE TO DEENERGIZE THE BRAKE WINDING, AND THE BRAKE SETS TO ASSIST IN STOPPING AND TO HOLD THE LOAD.

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