US2968754A - Adjustable voltage control system - Google Patents

Description

Jan. 17, 1961 c. c. GOULD ETAL 2,963,754

ADJUSTABLE VOLTAGE CONTROL SYSTEM Filed NOV. 29, 1957 (HA/H55 (OZ [LL GOULD GER/204907 H P/ffff ()3 By Q 0 51f ATTOR/VEVJ.

United States Patent C ADJUSTABLE VOLTAGE CONTROL SYSTEM t'lharles tIovell Gould, Solon, and Gerhardt H. Piethe, South Russell, Ohio, assignors to Square D Company, Detroit, Mich, a corporation of Michigan Filed Nov. 29, 1957, Ser. No. 699,611

3 Claims. (Cl. 318-151) This invention relates to an adjustable voltage crane hoist control system, and more particularly to an adjustable voltage crane hoist control system including a power circuit limit switch which is rendered operative upon over-hoisting of a hook block to complete a dynamic braking circuit for the motor which drives the hoist mechanism and to cause setting of a spring-set, electro-magnetically-released, friction brake for the hoist mechanism.

One of the principal advantages of a constant potential or rheostatic dynamic lowering crane hoist control system is that it can be provided easily with a power circuit limit switch which, upon over-hoisting, operates or trips to complete a dynamic braking circuit for the motor and to cause setting of a friction brake. The circuit arrange ment of the usual constant potential system is such that, although further hoisting operations are impossible while the limit switch is tripped, the motor can be caused to operate in the lowering direction to reset the limit switch merely by moving a master switch into a lowering position.

It has long been desired to provide similar over-hoist protection in adjustable voltage crane hoist control systems by providing a limit switch of the type that has become standardized for use in constant potential systems and arranging the circuit so that the limit switch, upon tripping, completes a dynamic braking circuit for the motor and causes setting of the friction brake, and so that, while the limit switch is tripped, operation of the motor in the lowering direction is easily efiected although further operation in the hoisting direction is impossible.

Heretofore, an adjustable voltage hoist control system including this over-hoist protection has not been available because of the difficulty of providing both a dynamic braking circuit and a lowering-out circuit. Furthermore, a shunt brake, which must be used with adjustable voltage systems, does not lend itself to coordinated operation with the limit switch.

it is an object of this invention to provide an improved adjustable voltage control system adapted for a hoist mechanism and the like.

Another object is to provide an adjustable voltage motor control system in which a limit switch is rendered operative upon over-travel in one direction to complete a dynamic braking circuit for the motor and in which means are provided to permit operation of the motor in the other direction while the dynamic braking circuit is completed.

Another object is to provide an adjustable voltage crane hoist control system in which a limit switch is rendered operative upon over-hoisting to complete a dynamic braking circuit for the motor driving the hoist and to cause setting of a friction brake.

Another object is to provide an adjustable voltage crane hoist control system in which, after the motor driving the hoist has been stopped by dynamic braking as a result of operation of an over-hoist limit switch, move ment of a master switch into a lowering position causes the motor to operate in the lowering direction.

Briefly, in accordance with this invention as applied to a crane hoist, an over-hoist limit switch is arranged to be rendered operative, upon tripping by a hook block driven by a motor supplied from an individual generator, to connect the motor and the generator in a dynamic braking loop circuit including a blocking rectifier. An additional contact of the limit switch opens upon tripping to cause setting of a friction brake for the motor. Upon movement of a master switch into any one of its lowering positions while the limit switch is tripped, current is caused to flow to the motor through the blocking rectifier and a closed contact of the limit switch in a by-pass circuit around an open contact of the limit switch, thereby to cause operation of the motor in the lowering direction. A circuit through the master switch which is effective only in the lowering positions bypasses the additional limit switch contact to cause release of the brake while lowering with the limit switch tripped.

Other objects and advantages of this invention will become apparent from the following description wherein reference is made to the drawings, in which:

Fig. l is a wiring diagram of an adjustable voltage hoist control system incorporating the invention, and

Fig. 2 is a fragmentary wiring diagram illustrating a modification.

Referring to Figure l in which the invention is shown as applied in an otherwise conventional adjustable voltage hoist control system, a multi-position, reversing master switch 10 having contacts 10a through 10 is arranged to control the polarity and strength of a shunt field 11 of a generator 11 having its armature winding 11a connected through brushes 11b and in a closed loop circuit with an armature winding 12a of a shunt motor 12 having a shunt field 12 Any suitable means (not shown) may be used for driving the generator 11. The armature 12a is provided with brushes 12b and 12c and is mechanically coupled to a suitable electro-magnetically-re1eased friction brake 16 having an operating winding 16w and to a hoist drum 13 from which is suspended a hook block 19 and associated hook so arranged that, near the upper limit of travel, the hook block 19 engages a trip lever 20 of a conventional power circuit over-hoist limit switch 21 having normally closed contacts 21:2 and 21b and normally open contacts 21c. A conventional over-hoist limit switch has a second set of normally open contacts which are not used in the embodiment of Figure 1 and thus are not shown in the drawing.

For delaying the rate of change of current in the generator shunt field 11 a relatively small motor 24 driving a flywheel 25 and having its armature winding 24a connected in series with a resistor 26 in a parallel circuit with the generator field 11 may be used. The motor 24 has a shunt field winding 24f permanently connected across a direct current power source, indicated by supply conductors 27 and 28, which also supplies power for the armature 24a, the shunt fields 11 and 12 and the brake 16. Preferably the conductor 27 is positive and the conductor 28 is negative.

The master switch It) is illustrated as having five hoisting and five lowering speed positions. Each of the contacts, itia through filly, is open in the Oil. position and in other positions, except as its closure is indicated by crosses horizontally aligned therewith. For example, the contacts 10g are open in the first two of the hoisting and lowering positions and are closed in the last three of the hoisting and lowering positions.

The connection of the shunt field winding 11, of the generator 11 to the source 27-28 is controlled by an electromagnetic contactor 30 having an operating Winding 39w and normally open contacts 30a. A circuit for the brake winding 16w and a self-excited or suicide connection for the generator field 11 are controlled by an electromagnetic contactor 31 having an operating winding 31w, normally open contacts 31a, and normally closed contacts 31b. The contacts 311 while closed connect the armature 11a in a closed circuit with the field winding 11 through a resistor 32.

The master switch It), the contactors 3t) and 31 and the generator 11 are arranged to be mounted on a structure movable with respect to the structure on which the hoist motor 12, the brake 16, and the limit switch 21 are mounted. To this end a plurality of trolley bar and collector mechanisms 34a through 34g are provided. Hereinatter, these mechanisms are referred to as collectors.

In accordance with this invention, the normally closed contacts 21a of the limit switch 21 are interposed in the circuit between the collector 34d and the armature brush 12c, and, in parallel with the contacts 21a, is a circuit including a blocking rectifier 35, the normally open contacts 21c, and a resistor 36. The limit switch contacts 2117 are interposed in a circuit between the positive supply conductor 27 and the windings 30w and 31w which circuit is also controlled by the master switch contacts itli and 1th.

As will become apparent, the normally closed contacts 21a when closed complete the usual armature loop circuit for the motor 12. and the generator 11, the normally closed contacts 21b when closed complete an energizing circuit for the generator field winding 11 which can be bypassed only when lowering, and the normally-open contacts 210 when closed complete a generator-motor loop circuit operable for dynamic braking and for lowerin Considering first the operation of the system When the limit switch 21 is in its normal or untripped position shown in the drawing, with power available at the supply conductors 27 and 28, the motor field windings 12 and 2 5- are energized. The circuit for the field winding 12 is through the collectors 34a and 34b, whereas the field winding 24 is connected directly across the supply conductors 27 2i Assuming the master switch 11'? to be in its Off position, the generator field 11 and the brake winding 1" are de-energized. It is assumed that the generator is being driven at a constant speed.

Upon movement of the master switch 18 into the lowering positions, an energizing circuit is completed for the windings 3dr.) and 31w from the positive supply conduc tor 2'7 through the now closed contacts 101' and the windings 39w and 31w in series to the negative supply conductor 23. The contactor 30, upon energization of its winding 313w, close its contacts 3tla to complete a circuit from the positive supply conductor 27 through the collector 34g, the contacts 21b, the collector 34 the contacts Pitta, at least a portion of a resistor 38, the now closed contacts b, the generator field 11 from right to left, and the now closed contacts 10a to the negative supply conductor 28. Upon energization of the winding 31w, the contacts 31a close to complete an energizing circuit for the brake winding 16w andthe contacts 31b open to disconnect the armature 11a from the field winding 11f. The brake 16 releases upon energization of its winding 16w and its release is substantially concurrent with the energization of the field winding 11 With the right hand terminal of the field winding 11 positive, the brush 11c of the generator armature 11a may be considered positive, and current flows from the brush through the collector 34d, the contacts 21a, the motor armature 12:: from the brush 12c to the brush 12b, and the collector 34c to the brush 11b of the generator armature 11a. (lurrent flowing through the motor armature 12a from brush 120 to 12b with the brake 16 released causes the motor 12 to drive the drum 18 in a direction to lower the hook block 19. The counter- Elv .F. of the motor armature 12 is in the direction from the brush 12b to the brush 120. If the load on the hook block 19 is overhauling, the voltage at the motor armature 12a rises above the voltage at the generator armature 11a and the current in the generator-motor loop circuit reverses. Irrespective of the direction of current in the generator-motor loop circuit, movement of the master switch into the lowering speed positions beyond the first causes an increase in speed of the motor 12 because of a reduction of the effective resistance of the resistor 38 caused by sequential closing of the contacts 10c through 1 h, the motor 24 with its flywheel 25 acting to prevent too sudden a change in the strength of the field winding 11f during acceleration as well as deceleration.

Upon return of the master switch 10 to the Off position from the lowering positions, the contactor 31 is deenergized and the contacts 31a open to permit the brake 16 to set and the contacts 311; close to connect the generator field 11 in a suicide connection across the generator armature 11a through the resistor 32. The contactor 30 is also tie-energized at this time so that the contacts 30a open to disconnect the field winding 11 from the source 2728. The circuit to the field winding 11] is also opened at the contacts 10a and 10b. The motor 12 thus stops quickly.

Upon movement of the master switch 14} into the hoisting positions, an energizing circuit is completed for the windings 36w and 31w from the positive conductor 27 through the collector 34g, the limit switch contacts 21b, the collector 34 the master switch contact 1th, and the windings 30w and 31w to the negative supply conductor 2$. The contactor 30, upon energization of its winding 30w, closes its contacts 3% to complete a circuit from the now positive collector 34f through at least a portion of the resistor 33, the contacts 10d, the generator field winding 11 from left to right, and the contacts to the negative supply conductor 28. The contactor 31, upon energization of its winding 31w, closes its contacts 31a to complete the previously traced circuit for the brake winding 16w, and opens its contacts 31b to interrupt the suicide connection between the motor armature 11a and the generator field winding 11.

The left-hand terminal of the field winding 11 is now positive causing the brush 11b of the generator 11 to be positive instead of the brush as during lowering. Current now flows from the brush 11b through the collector 34c, the motor armature 12a from the brush 12b to the brush 12c, the limit switch contact 210, and the collector 34d to the brush 11c. Current fiowing through the armature from the brush 12b to the brush causes the motor 12 to drive the drum 18 in a direction to raise the hook block 19. The counter-EMF. of the motor armature 12 is in the direction from the brush 12c to the brush 12b.

Movement of the master switch 10 into the hoisting speed positions beyond the first causes a step-by-step reduction in the effective resistance of the resistor 38 by sequential closing of the contacts 1% through 1011, there by causing an increase voltage of the generator 11 and an increase in the speed of the motor 12. Upon return of the master switch 30 to the Off position from the hoisting positions, the contactors 3t) and 31 are de-energized and the field winding 11f is connected in a suicide connection as described hereinbefore for return of the master switch 10 to the Oh position from the lowering posltion.

Should the motor 12 drive the drum 1% in the hoisting direction to an extent causing the book block 19 to strike the limit switch trip lever 20, the limit switch 21 operates to close its contacts 210 and open its contacts 21a and 21b. Opening of the contacts 21b causes de-energization of the contactors 30 and 31 and disconnects the generator field winding 11] from the source irrespective of the position of the master switch 10. De-energization of the contactor 31 causes opening of the contacts 31a thereby to permit the brake 16 to set and closure of the contacts 31b to complete the suicide connection for the field winding 11]. Opening of the contacts 21a interrupts the generator-motor loop for flow of current from a brush 12b to the brush 12c through the motor armature 12a.

Since the voltage at the generator armature 11 drops quickly as soon as the field winding 11 is disconnected from the source and connected across the armature 11a through the contacts 31b, closure of the contacts 21c permits a dynamic braking or regenerative braking current to flow from the brush 12b of the armature 12a through the collector 34c, the armature 11a from the brush 11b to the brush 110, the collector 34d, the rectifier 35, the contacts 21c, and the resistor 36 to the brush 12c. Closure of the contacts 210 thus completes a dynamic braking circuit for the motor 12 through the armature winding 11a of the generator 11. Completion of this dynamic braking circuit and setting of the friction brake 16 brings the hook block 19 to a stop quickly.

With the limit switch tripped, movement of the master switch into the lowering positions completes the previously traced energizing circuit for the brake winding 16w and for the generator field 11 which permit the motor 12 to operate in the lowering direction to cause the hook block 19 to be lowered. With the master switch in the lowering positions, the generator field 11f is energized to cause the brush 11c to be positive. Current then flows from the brush 110 through the collector 34d, the rectifier 35, the now closed contacts 21c, the resistor 36, the armature 12a from the brush 120 to the brush 12b, and the collector 342 to the brush 11b. This causes the motor 12 to operate in the lowering direction.

When the hook block 19 releases the trip lever 20, the contacts 21a and 21b re-c1ose and the contacts 21c reopen. Closure of the contacts 21a completes the normal loop circuit including the armature 11a and the armature 12a and opening of the contacts 21c interrupts the circuit through the rectifier 35. The motor 12 can now continue to operate in the lowering direction or, upon movement of the master switch into the hoisting positions, to operate in the hoisting direction.

From the foregoing, it is seen that there has been provided a control arrangement for an adjustable voltage hoist control system which permits the use of a convention over-hoist limit switch to complete a dynamic braking circuit upon over-hoisting and to complete a lowering circuit which is effective for causing the motor to operate only in the lowering direction while the limit switch is tripped.

In the modification of Figure 2, a compound motor 50 having an armature 50a, a shunt field winding 50sh, and a cumulative series field winding 50 has its armature 5011 connected in a loop circuit with an armature 51a of a shunt generator 51 having a shunt field winding 51 The generator 51 may be the same as the generator 11 of Figure 1 and its field winding 51 may be controlled as in Figure l to cause the left-hand terminal of its armature 51a to be positive during lowering operations and negative during hoisting operations.

With the left-hand terminal of the generator armature 51a positive, current flows through a rectifier 52 around the motor series field 50) when the motor 50 is operating to lower a non-overhauling load and flows from the lefthand terminal of the motor armature 50a through the series field 50] when the motor 50 is overhauled by a load. During hoisting operations, the right-hand terminal of the generator armature 51a is positive, and current flows through the motor armature 50a from right to left and through the series field 50]. The rectifier 52 thus serves during operation with the limit switch in its normal position to insure that the series field 50 is ineffective when the motor 50 is operating as a motor in the lowering direction since, under these conditions, the field 50f would be differential.

Upon over-hoisting in the modification of Figure 2, the limit switch contacts 21 open to interrupt the only possible circuit that could cause operation of the motor 50 in the hoisting direction. Dynamic braking current flows from the motor 50 through the generator armature 51a and the rectifier 52 as described in connection with Figure 1. Also, the rectifier 52 is so poled that, with the limit switch 21 tripped, the motor 50 can be caused to operate as a motor in the lowering direction by current flowing through the rectifier 52 but cannot be caused to operate in the hoisting direction.

Having thus described our invention, we claim:

1. A control system comprising a motor having a motor armature, a generator having a generator armature connected in a loop circuit with the motor annature, said generator having a field winding, means including a source of field current for energizing the field winding and for controlling the polarity of the generator, thereby to determine the direction of rotation of the motor armature, a switch having first and second sets of normally closed contacts, and adapted to be tripped to open the first and second sets of contacts, said first set of contacts being interposed in said loop circuit between the motor and generator armatures, said second set of contacts being interposed in series with said generator field and between the generator field and the source of field current to deenergize said generator field when said switch is tripped and said second set of contacts are thus opened, rectifier means connected in shunt with said first set of contacts with the rectifier poled to permit dynamic braking current to flow from said motor armature through said generator armature when said switch is tripped and said first set of contacts are thus opened, and means in cooperation with the field of the generator to control the reduction of strength of the generator field and thereby the magnitude of the braking current.

2. A control system combination in accordance with claim 1 characterized in that said motor also has a series field and said series field is connected in series with said normally closed contact and in parallel with said rectifier.

3. The control system as set forth in claim 1 additionally including the feature of a third set of normally open contacts on said switch and interposed in series with said rectifier means.

References Cited in the file of this patent UNITED STATES PATENTS 2,298,188 Wright Oct. 16, 1942 2,397,557 McCoy Apr. 2, 1946 2,666,176 Fath Jan. 12, 1954 2,830,248 Posselt Apr. 8, 1958

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