US2208409A - Crane hoist control - Google Patents

Description

July' l5, 1940. G.l A. CALDWELL CRANE HOST CONTROL Filed May 5, 1959 2 Sheets-Sheet l ATTORNEY July 16 1940 G. A. CALDWELL CRANE HOIST CONTROL Filed May 5, 1939 2 Sheets-Sheet 2 Speed 7rque fur ves For L over/'ng No tor/'ng L aad No or 7' orgue 74E/'ak ing Parque l* L, o Y md m E/ R Va .O mC FU nn. A n E Mm G ,M 50 0000.000 f4@ OOOO o .w30 O OO o H020 o o o /O O O Ong.l OO O 00000 oo r2 OOO O OO ma o o O o OO /0 4 OO o O OO 5 O OOOOOO conL/zmnmaa4 gnessss; i l Xl/M Patented July 16, 194i) APATENT oFFlcE CRANE nols'r coN'raol.

Glenn A. Caldwell, Edgewood, Pa., assigner to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa.. a corporation of Pennsylvania Application May 5, 1939, Serial No. 271.979

2 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 as cranes and the like. y

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

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

A more specific object of my invention is to provide a split series field winding for the hoisting motor comprising, a main portion and an auxiliary portion, and which is so arranged that the auxiliary portion will provide a cumulative u iield when the motor is operating in the lowering direction with an overhauling load, that is, when the motor `is providing regenerative current and,

in eilect, is acting as a generator.

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:

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

Fig. 2 shows the motor circuit -for the ilfth controller position oi.' hoisting;

Fig. 3 shows the motor circuit for the fifth controller position during the lowering operation:

Fig. 4 showsy 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 showing the sequence of operation in the various switches in the motor circuits both for the hoisting and the lowering operation.

In a crane hoist control it is desirable to obtain as high a speed as possible for 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 lcurves in Fig. 4, which are illustrative of control formance of the motor i one instance with 37%` iield current and another with 24% eld current,

(ci. 11a-.179)

and the speed torque curves for low .values of 6 iield current will be substantially flattened, very much llkethose illustrating 44% and 63%- field current.v

Referring more vparticularly to Fig. l o! the drawings, M designates the-hoisting motor to be 10 controlled and B and C refer, respectively, to the brake winding and the commutating field winding for the motor. F and F' refer to a split series iield winding in which F is the main portion and F' is an auxiliary portion. A control 15 system is illustrated for the motor and is shown in the deenergized position. A controller |00 may be of any desirable type, such as the drum type having a plurality of contact segments for varying the circuit connections for different positions in 20 inclusive, and neutralizing coils I2N to I5N inclusive, respectively. Each .of these relays is biased in one direction by a spring as shown. A 35 relay rheostat I6 is provided for adjusting the time constant of the relay. It will be noted that the springs associated with each of the relays is also adjustable, therebyproviding additional adjustability of the time constant of the relays. 40 The operation of these time limit relays forms no part of my invention, but to preferably describe their operation it may be generally stated that relay IZA holds one of its associated contacts closed in the lowering operation long enough to insure release of the brake, and prevents closing of contact members 8 in the lowering'rdirection 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 of the five positions of hoisting or lowering lcan 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 controlsystem illustrated in the figures together with'. the sequence chart in Fig. 5 will readily disclose to those familiar with the art what is included in the various circuits is each successive position for both hoisting and lowering. It is felt `that a detailed explanation o'f each step would be not only superfluous, but would tend to confuse the reader as to the essence of the invention. However, to .briefly summarize the suc-` cessive operations in both hoisting and vlowering operation, it `may be stated that in all five positions of hoisting, all ofthe field coils (see F and F) together with the braking eld coil, are connected in series with the incoming power line, hence the motor operates as a series motor. Fig. 2, which shows the fifth position of hoisting, is illustrative of this series connection. On the other hand, on all five positions of lowering, the main field coil F together with the commutating field coil C and the braking fleld coil B, are connected in parallel with motor M, whereas the auxiliary field coil F still remains in series in motor M; hence motor M operates as a shuntmo-l tor. Fig. 3 is an illustrative showing of the fifth position of lowering. In the hoisting operation, the full value of starting resistance is connected in series with the various field coils, brake coil and motor and, ingeneral, by going through the five successive steps, the starting -resistance is gradually shunted out by successive increments untilfinally, as shown in Fig. 2, representing the fifth hoisting position, the startingresistancel is completely shunted out and the motor with its various field coils and brake coil is connected directly across the line. Onvthe other hand, vin the .lower operation in going from the first to the fifth position, resistance is gradually'inserted in' series with the shunt field in successively greater amounts until finally, as will be noted from Fig. \3 illustrating the fth lowering position, the full value of resistance Vvis inserted in series with the shunt iield. 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 oper'- ation 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 field is gradually in-A creased so as to gradually weaken theshunt field,

' the speed of the motor and the torque thereof gradually increases.

My invention is specifically directed to the .split eld series winding F and F' in which the auxiliary portion F is preferably 10% or lessv of the field strength of the main portion F. As will be noted from Figs. 2 and 3, the auxiliary portion F' is always connectedin series with the motor M in both hoisting and lowering operations. However, the main portion F is connected in series with motor M in all five positions of hoisting (as illustrated in Fig. 2) but is connected in parallel with motor M in all ve positions of lowering (illustrated in Fig. 3). When motor M acts as a motor, for example, in all five hoisting positions and under certain conditions of lowering, field F' willbuck the main field F. This, however. will not be objectionable as long as the auxiliary field F' is not over 10% of the field strength of the main eld F. When lowering a very heavy load, that is, an overhauling load, a regenerative current is obtained and motor M will, in eect, act as a generator and willgene'rate current in a direction opposite the motor current. Hence the auxiliary field F' and the main field F will be cumulative and will decrease the speed and tend to keep speed torque substantially fiat. In this manner, when a heavy overhauling load is being lowered, a dangerously high speed will be` avoided. Furthermore, inasmuch as the split field coils are permanently in the circuit, a gradual braking action will be secured which'is a substantial improvement over the well-known control systems employing relays and the like whereinabrupt changes `are secured for the purpose of checking excessively high speed, but which abrupt changes are detrimental to safe operation of 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, which would be highly dangerous, and at the same time, the control of the crane would be very confusing and difficult.

Manyprotective features usually embodied in control systems of this kind such as Voverload and undervoltage protection, have been omitted for the sake of simplicity, but itA 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 benefit of the teachings of my invention, may devise other devices embodying my invention, and I, therefore, do not wish to be limited to the specific showings made in the drawings and the descriptive disclosure hereinbefore made, but. wish to be limited only by the scope of the appended claims and such prior art that may be pertinent.

I claim as my invention:

` 1A control system for a hoist motor for operatinga crane or the like, comprising, in combination, a hoist motor having an armature windtion being permanently connected in series with# said armature winding, said portions being wound so that their eld strengths are cumulative during lowering operation when said motor is acting as a generator due to regenerative current developed as the result of an overhauling load, thereby slowing down said motor and which field strengths are in bucking relationshipwhen said motor is acting as a motor, thereby speeding up' said motor, and a commutating winding also permanently connected in series with said armature Winding and said main portion of said split field winding.

2. A control system for a hoist motor for a crane or the like comprising,in combination, a hoist motor having an armature winding and having a split eld winding including a main portion and an auxiliary portion, circuit means for connecting said main portion in series with the armature winding of said motor during hoisting operation and in parallel circuit relation with said armature winding during lowering operation, control means for controlling said circuit means, said auxiliary portion being permanently concted in series with said armature winding, said portions of said split eld winding being wound so that theirlfield strengths are cumulative during lowering operation when said motor is acting as a generator due to regenerative current developed as a result of an overhauling load,

thereby decreasing the speed of said motor and which tleld strengths are in bucking relationship when said motor is acting as a motor, thereby increasing the speed of said motor, said auxiliary portion being operable to develop a eld strength which is normally less than 10% of the field strength of said main portion and a commutatingwinding permanently connected in series with said armature winding and main portion of said split field winding.

GLENN A. CALDWELL.

Images