US2208401A - Crane hoist control - Google Patents

Description

July 16, 1940. Q E STQLTZ 2,208,401

CRANE HOIST CONTROL Filed May 16, 1939 2 Sheets-Sheet l lo Q u i LQ L3 9 in m Q u l 5?, fb n) l u I ,p U sa l u I a in u.. ll Q51ml! Q' 4? w m N P N \D Ik Q x im N ATTORNEY July 16, 1940- G. E. sToLTz CRANE HOIST CONTROL Filed May 16, 1939 2 vSheetS-Sheet M/ZZ Cun/e151 /00 80 6o 40 zo 0 Za 4o 60 490 wlTNEssEs:

INVENTOR /enn 50/ IZ- ATTORNEY O O O O O Patented July 16, 1940 UNITED STATES PATENT OFFC CRANE HOIST CONTROL East ittsburgh, Pa.,

Sylvania a corporation ot Penn- Application May 16, 1939, Serial No. 273,851

9 Claims.

My invention relates to a control system for an electric motor and is particularly applicable to a motor utilized for operating load hoisting or elevating devices "or load lowering devices such 5 as cranes and the like.

An object of my invention is to provide a system or control that embodies a minimum number of units and which is simple and reliable in operation, and is inexpensive to manufacture.

l0 Another object of my invention is to provide a control system which has substantially ideal or most desirable speed torque curves for a hoist motor when operating in the lowering direction.

A more specific object of my invention is to 13 provide a motor-generator set used as a booster to boost the eld strength of the main motor when the main motor is regenerating current due to an overhauling load in the lowering direction and, in effect, is acting as a generator and which motor generator is inoperative when the main or hoist motor is acting as a motor either in the lowering or hoisting operation. l

Other objects and advantages will become more apparent from a study of the following specification when considered in conjunction with the accompanying drawings, in which:v

Figure 1 is a diagrammatic showing of a complete system of control embodying my invention;

Fig. 2 shows the motor circuit for the fifth controller position of hoisting;

Fig. 3 shows the motor circuit for the th controller position during the lowering operation;

Fig. 4 shows a series of samples of speed torque curves for control systems conventional in the art for all the controller positions of the motor when the motor is operating in the lowering direction; and

Fig. 5 is a sequence chart shownig the sequence n circuits both for the hoisting and the lowering operation.

In a crane hoist control it lls desirable to obtain as high a speed as possiblefor the crane hook when lowering empty, and at the same time not obtain an excessive speed when lowering with a heavy load. Referring to the speed torque curves in Fig. 4, which are illustrative of control systems when the load is overhauling, the hoist motor is used to develop a braking torque, the figure showing that with 63% field current the increase in speed with load is appreciable but not dangerous. The figure also shows the performance of the motor in one instance with 37% field current and another with 24% iield 22 of the booster generator G.

of operation in the various switches in the motor field current, where with less than full load on the hook, the hoist motor would run away.

In accordance with my invention the above mentioned runaway condition will be eliminated and the speed torque curves for low values of f. field current will be substantially ilattened, very much like those illustrating 44% and 63% field current.

Referring more particularly to Figure i of the drawings, M designates a hoist motor (of the series type), which is to be controlled and B and F, respectively, designate the brake winding and field winding. M' and G' designate the units oi the motor-generator set, which set is used as a booster. Associated with the motor of the i5 motor-generator set is a field coil 253 and a conventional control rheostat 2|. The generator G of the motor-generator set has a field winding 22, a conventional control rheostat 23 and a rectler unit, preferably of the copper oxide type, 26, all of which are connected in shunt across a resistance R, which resistance is permanently in series with the armature or motor .lr/i. Since it will be logical to place the motor-generator set used as a booster on or near the crane cab with the control, resistance R is installed in the lead of the armature of the hoist motor, from which will be shunted current to excite the The voltage of the generator should then be proportional to the loads taken by the armature up to the point where the field of the booster saturates. it not essential that the booster voltage be dire1 proportional to the armature current of the hoist motor, but it will be necessary to design booster so that it does not saturate at too low load. The rectier unit 2c is placed in the circuit of the booster generator so thatrcurr it will flow in the iielol of the booster generator only f when the load is heavy enough to cause the hoist armature to regenerate and, in eiect, act as generator. When the hoist armature is heilig accelerated or when the ioad is so low that the hoist motor operating as a motor, the flow of current wili 'se in the opposite direction the rectifier unit 2li will prevent current nos.' in the elcl 22 of the booster so that the l: will have no modifying eiiect on the field oi Sie main motor when the latter is acting as a moto in the lowering direction.

Since this booster eiiect of the crane motor Viele is only wanted in the lowering direction, t

armature of the booster will be connected in th held circuit of the hoist motor in such a manner 35 that it will be in the circuit only during the lowering direction.

A control system is illustrated for the motor and is shown in the deenergized position. A controller C which may be of any desirable type such as the drum type and has a plurality of Contact segments for varying the circuit connections for different positions in the hoisting or lowering direction. Five positions are shown in the hoisting direction and five positions are also shown in the lowering direction for giving various values of speed and torque to the motor in these directions. Contact members I to II, inclusive, and I6 (and Ic) are operable by relays IA to IIA, inclusive, and ISA respectively to secure various circuit combinations in the hoisting and lowering directions. Contact members I2 and I2C, I3, I and Ib, inclusive, are operable by time limit relays IZA to IA, inclusive, respectively. The time limit relays I2A to ISA, inclusive, have main coils I2M to lM, inclusive, and neutralizing coils l2N to I5N, inclusive, respectively. Each of these relays is biased in one direction by a spring as shown. A relay rheostat 26 is provided for adjusting a time constant of the relays. It will be noted that the springs associated with each of the relays is also adjustable thereby providing additional adjusta bility of the time constant of the relays. The operation of these time limit relays forms no part of my invention, but to briefly describe their operai tion it may be generally\ stated that relay I2A holds one of its associated contact members I2 closed in the lowering operation, due to the time delay of coil l2N, long enough to insure release of the brake by maintaining relay 5A energized to close contact members 5, and prevents closing of contact members I8 in the lowering direction until contact members I2 are open. Time limit relay I3A picks up on the fourth point lowering and holds its contact members I3 closed thereby completing a circuit to energize coil 6A and close contact members Iii to insure energization or' relay l IA which closes contact members I I to provide a regular braking circuit, and to open contact members tto prevent application of the emergency braln'ng circuit for a fraction of a second if the master switch is returned suddenly to the off position.

By referring to Fig. 5, which is a sequence chart showing the sequence of operation of the various switches in the motor circuits for both hoisting and lowering operations, the particular circuit for any oi the five positions of hoisting or lowering can be identified. Inasmuch as my invention is not concerned with the successive steps or positions in the operation of the motor either in the hoisting or in the lowering direction, it is deemed that a detailed explanation of each successive position in hoisting or lowering is unnecessary. Furthermore, the control system illustrated in the iigures together with the sequence chart in Fig. 5 will readily disclose to those familiar with the art what the various circuit in each successive position in hoisting or lowering consists of.

operative since it is omitted from the circuit and all of the field coils together with the braking field coil are connected in series with the inf coming power line, hence the motor operates as a series motor. Fig. 2 shows the fth position of hoisting and is illustrative of this series connection. 0n the other hand, on all five positions of lowering, the motor generator set M', G', together with its associated parts, is included in the circuit. Furthermore, on all ve positions of lowering, the field coil F and the brake coil B are connected in parallel with the motor armature M so that the motor is now acting as a shunt motor. Fig. 3 which shows the fifth position of lowering is illustrative of the shunt connection. In the hoisting operation the full value of starting resistance is connected in series with the various field coils, brake coil and motor armature and, in general, in going through the ve successive steps, the starting resistance is gradually shunted out. by successive increments until finally, as shown in Fig. 2 representing the fth hoisting position, the starting resistance is completely shunted out and the motor with its various I'ield coils and brake coil is connected directly across the line. On the other hand, in the lower operation in going from the first tothe fth position, resistance is gradually inserted in series withthe shunt field in successively greater amounts until finally, as will be noted from Fig. 3 illustrating the fifth lowering position, the full value of resistance is inserted in series with the shunt field. As it will be obvious to those skilled in the electrical art, as the resistance is gradually decreased in going from the first to the fifth position in the hoisting operation of a constant load when the motor M is connected as a series motor, the speed and torque thereof will gradually increase. On the other hand, in the lowering operation, as the resistance in series with the shunt ield is gradually increased so as'to gradually weaken the shunt eld, the speed of the motor gradually 1ncreases and the torque decreases.

My invention is specically directed to the use of a booster motor-*generator set in the lowering operation of the main hoist motor. When light loads are lowered and the main motor is acting as a motor, no shunt current will traverse the field coil Y22, because of the blocking action of rectifier 25j However, on heavier loads in the lowering direction, which are sufficient to cause the motor to overhaul and regenerate current in the opposite direction of the normal motor current, a shunt current will flow through the generator field coil 22 in an opposite direction and will no longer be arrested by rectifier 26, and this boosting current will strengthen the main eld F to such an extent as to cause the speed to increase less rapidly with increasing loads, or to remain substantially constant or even decrease, depending on the ampere turns of field coil 22.

These characteristics will become more apparent in tracing the circuit. When light loads are lowered and the main motor M is acting as a motor, the main circuit may be traced, in Figs. 1 and 3, from the terminal marked (-l) through bridged contact members 2, motor M, resistor R, bridged contact members l, 9 and 8, respectively, to the negative terminal marked Connected in parallel toresistor R, is another circuit including rheostat 23, field coil 22 (of generator G of the booster motor-generator set) and rectier 24. However, inasmuch as the flow of current is of from left to right through resistor R, the recticr 24 will arrest current fiow through Y the parallel path. However, if a load is being lowered that is sufficiently heavy so as to cause motor M to overhaul, then current will be regenerated by motor M in the above traced main circuit but in an opposite direction dueto the fact that the motor M is now acting, in effect, as a generator. Inasmuch as this regenerated current may be greater than the normal flow of supply current (previously traced) but opposite in direction, the resultant current will flow through resistance R in a direction from right to left. Now current will flow through the paralle] path including rectifier 24, booster generator field coil 22 and rheostat 23 due to the manner in which rectifier 24 is connected, as the result of which generator G' will start to generate a voltage in the direction indicated by the arrow. A main shunt path may now be traced from the terminal marked through bridged contact members 2, field coil F, brake coil B, resistors R2 and Re, the armature of generator G', bridged contact members IBc, II, 9 and 8 successively to the negative terminal It will thus be seen that as the current regenerated by motor M increases, the current through field winding 22 increases and the voltage developed across the armature of generator increases therefore boosting the current flow through the main shunt path (i. e., through field coil F) hence tending to decrease the speed of motor M. It will be noted that the main shunt path is the same during lowering light loads during which motor M is acting as a motor, that is, it includes the armatureof generator G', however, since no voltage is developed across'this armature (since no current is flowing through the field coil 22 due to the arresting action of rectiiier 24) no additional current Will be sent through the main shunt circuit through field coil F, hence there will be no modifying or boosting action on While I have described the motor generator set as being in the circuit in all positions or lowering, it will be obvioous that it is also possible, instead, to have the motor-generator set in circult only in a few of the ultimate positions of lowering, say for example, in the fourth and fifth positions only of lowering. In other words, it is recognized that the most important use of the booster is in the latter positions or the last position of lowering. The necessary change in the circuit connections for accomplishing this will be obvious to those skilled in the art. Also, if the booster is put in other than the fifth point such as the fourth or third, its effect can be decreased. This will be partially automatic as the motor field approaches saturation. this alternate arrangement is recognized, it is felt that the preferable and most simple circuit connection would be that as previously described, since a minimum number of contactors is used, that is, the arrangement by which the motorgenerator is kept in circuit throughout the entire lowering operation.

On cranes it is desirable only to prevent the load and motor from running away under heavy loads, the value of the booster can be selected to keep the speed torque curves flat, approximately as shown in Fig. 4 for 63% and 44% ield amperes. On other applications where it may be desirable to have a lower speed load condition than with empty hook, the value of the booster can be increased so that the speed torque curves drop oir with increased loads.

My control system is a substantial improvement over the well known control systems employing relays and the like wherein abrupt changes are secured for the purpose of checking excessively high speed but which abrupt changes of: (fri are detrimental to safe operation ci a crane hoist. Obviously any sudden change in the speed of the crane either in the raising or lowering position might cause a shaking off of the load dangerous and at the of the crane would be very confusing and difficult.

Many protective features usually embodied in control systems of this kind such as an overload and undervoltage protection have been omitted for the sake of simplicity, but it is understood, of course, that these features may be incorporated in the above described control system.

I am, of course, aware that others, particularly after having had the benet of the teachings of my invention, may devise other devices embodying my invention, and I, therefore, do not wish to be limited to the specilic showings made in the drawings and the descriptive disclosure hereinbefore made,

prior art that may be pertinent.

I claim as my invention: l. A control system for a hoist motor comprising, in combination, a hoist motor, circuit means :for a hoist motor compriscontinuously and directly boosting the iield ,f

strength of said motor in accordance with the load oi said motor to eiect slowing down of said motor.

3. A control system for a hoist motor comprising, in combination, a hoist motor, circuit means for energizing said motor to ei'l'ect a hoisting or lowering operation, said motor, having a field coil which is connected in shunt therewith during lowering operation of the motor, a booster generator which is effective during the lowering operation only, of' said motor for boosting the eld strength thereof and for effecting slowing down of said motor.

4. A control system for a hoist motor for a crane or the like comprising, in combination,

hoist motor including a iield coil, circuit means for energizing said motor to effect either a hoisting or lowering operation, a booster generator having a leldrcoil which is effective to compensate said motor field relation `with the armature of said motor so that the voltage impressed on said booster generator neld coil is proportional to the load current flowing through the armature of said hoist motor.

5. A control system for a hoist motor for a crane or the like comprising i combination, a hoist motor, including a iield coil circuit means for energizing said motor to either a hoisting or lowering operation, a booster generator having a field coil which durinf at least a part of the lowering operation, of said motor is in circuit relation with the armature ci said mctor so that the voltage impressed on said booster generator eld coil is proportional to the load current flowing through the hoist motor, circuit means coil and which is in circuit a:

armature of said t hoist motor, rectier meins in circuit relation with said field coil which allows current flow only in the direction of flow of regenerated current developed in said armature due to an overhauling load, and which-is not conductive to current flowing through said armature when said motor is operating as a motor. Y

6. A control system for a hoistA motor for a crane or the like comprising, in combination, a hoist motor including a field coll, circuit means for energizing said motor to eiect either` a holsting or lowering operation, a. booster generator having a field coil which during the entire lowering operation, only, of said motor is in circuit relation with the armature of said motor so that the voltage impressed on said booster generator iield coil is proportional to the load current owing through Ythe armature of said hoist motor, rectifier means in series with said eld coil which allows current flow only in the direction of flow of regenerated current developed as the result of generator action ofV said motor during an overhauling load, and which is not conductive to current flow through said armature when said.

motor is operating as a motor.

7. A control system for a holst motor for a crane or the like comprising, in combination, a

hoit motorV including a eld'coil, circuit means for energizing said motor, to effect either a hoisting or lowering operation, a resistor, whichl may be a series winding or lead of the hoist motor armature in series with the amature of said motor, a motor-generator booster set having a generatoriield, rectifier means connected in series relationship with said booster generator field and said rectier means and booster generator field being connected in shunt with said resistor, said motor-generator boster set being operable to compensate the eld coil of said hoist motor only during lowering operation of said motor, said rectifier means allowing flow of current deveioped by regeneration of said motor due to its generator action during overhauling loads and impeding the flow of motor current in said armature when said motor is acting as a motor.

8. A control system for a hoist motor for a crane. derrick or the like comprising, in combination, a hoistmotor including a field coil, circuit means for energizing said motor, to eect either a hoisting or lowering operation, a resistor in series with the armature of said motor, a motor-generator booster set having a generator eld, rectier means connected in series relationship with said booster generator eld, and said rectifier means and booster generator iield being connected in shunt with said resistor, said motorgenerator booster set being operable to compenvsate the iield coil of said hoist motor only during lowering operation of said motor and during at least a part of said lowering operation, said rectifier means allowing flow of current developed by regeneration of said motor due to its generator action during overhauling loads in the lowering direction and impeding the flow of motor current in said armature when said motor is acting as a motor.

9. A control system for a hoist motor for a crane or the like comprising, in combination, a

hoist motor including a eld coil, circuit means for energizing said motor, to eiect either a hoisting or lowering operation, a resistor in series withV the armature of said motor, a motor-generator booster set having a generator field, rectifier means connected in series relationship with said booster generator field, and said rectier means and booster generator field being connected in shunt with said resistor, said motor-generator booster set being operable to compensate the ield coil of said hoist motor only during lowering operation of said motor, saidrectier means allow- Ving fiow of current developed by regeneration of said motor due to its generator action during overhauling loads and impeding the iiow of current in the booster eld when said motor is acting as a motor, said hoist motor including a ileld Y coil which is connected in series relation with said booster armature thereof during lowering operation, said booster generator being effective during lowering operation with an overhauling load to increase the field strength of said hoist motor field thereby slowing down said motor.

, GLENN E. STOLTZ.

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