US2175037A - Electric hoist - Google Patents

Description

R. E. SMITH ELECTRIC HOIST Filed Sept. 6, 1938 2 Shuts-Sheet 1 h 5 w a 277/ (ATTO NEIJS Oct. 3, 1939.

R. E. SMITH ELECTRIC HOIST 1 Filed Sept. 6, 1958 l s i 01111101111111,

2 Shuts-Sheet 2 ma WM.

(ATTOQNEjKS Patented Oct. 3, 12159 UNITED STATES ELECTRIC nors'r Ralph E. Smith, Muskegon Heights, Mich., as-

signor to Manning, Maxwell & Moore,*lnc., Muskegon, Mich, a corporation of New Jersey r Application September 6, 1938, Serial No.:228,510 5 Claims. (01. 192 2) The invention relates to electric hoists and more particularly to such hoists of the type embodying an electric driving motor together with a brake for holding the associated motor driven 5 hoist member against rotation when the driving motor is stopped.

In hoists of the type noted above, it has heretofore been proposed to utilize a single manually operated actuator for both the motor reversinglu controller and the brake mechanism. In general, the actuator has a central or neutralposition' and may be shifted in opposite directions from this neutral position for hoisting and lowering respectively. When the actuator is in its neu- I 1.3 tral position the brake is set but is subsequently released whenever the actuator is moved from neutral to either hoisting or lowering ositions. One serious danger likely to arise with such a system is that there will be a substantial time 20 interval, upon moving from neutral position, be-

tween the release of the brake and the closure of the controller contacts to energize the motor.

It will be understood that this cannot be readily overcome by arranging the motor contacts to be closed substantially before the release of the brake since in that case the motor would be overloaded by being started with the brake applied. On the other hand, it is 'difiicult to synchronize exactly the release of the brake and 30 closure of the controller contacts, and even if they are exactly synchronized during the initial adjustment of the hoist, subsequent wear of the brake parts and the like is likely to throw them out of synchronization.

35 Another factor to be considered is the prevalent tendency of hoist operators to move the manual control cords or levers of the hoist with a very slow movement when it is desired to inch'the hoist along very slowly. If the brake 4o is released before the controller contacts are closed. then such slow operation by the operator will of course greatly increase the actual time interval between the release of the brake and closure of the contacts. During such an inter- 45 val, if the hoist is loaded, the load is free to descend by gravity and thereby very quickly accelerates the deenergized driving motor with consequent danger of injury to the motor and associatedhoist parts. This danger is particularly aggravated in the event that the driving motor is of the single phase alternating current, type with a speed responsive switch-controlled starting winding such as is disclosed in the copending application of Preston- W. Whitcomb and Ralph 55 E. Smith, Serial No. 228,509, filed September 6,

1938. If a motor of the type noted is accelerated by a freely falling load attached to the hoist, the speed responsive switch on the starting winding is opened and may in many cases be actually torn apart by the centrifugal force resulting from 5 the undue acceleration of the motor. Even if the speed responsive switch is only opened, rather than broken, the motor is rendered incapable of hoisting the load until it has first been stopped since it is a characteristic of such motors that they will'continue to rotate, in the direction in which they have previously been started, upon application of a voltage to them unless the starting winding is in circuit. These considerations make it amply apparent that .a motor driven I5 hoist, and particularly one embodying a motor of the type described, is likely to be rendered altogether inoperative ii there is any appreciable time interval between the release of the brake mechanism and the energization of the driving motor.

The general object of the present invention is to provide an electric hoist in which the dimculties described above are overcome by the provision of a snap-acting mechanism for positively insuring a rapid and complete throw of the brake and motor control devices from their respective neutral positions to their full hoisting or lowering positions despite any misguided or inadvertent attempt on the part of the operator to move them slowly. By virtue of this improved arrangement, the motor and brake controller devices snap into position so quickly that even if the are not exactly synchronized, the time interval between the release of the brake and energization of the motor will be so short that any load attached to the hoist cannot descend an appreciable distance due to gravity.

The invention also resides in certain structural improvements and combinations of parts em- 0 bodied in the control mechanism for the hoist.

Further objects and advantages of the invention will become apparent as the following description proceeds taken in connection with the following drawings, in which:

Figure 1 is a general perspective view of an electric hoist embodying the invention.

Fig. 2 is an enlarged endelevation of the brake end of the'hoist shown in Fig. 1.

Fig. 3 is a detail end elevation partly in section of the snap-action control device included in the hoist.

Fig. 4 1s an enlarged detail end elevation of a modified form of cam adapted to be embodied in the mechanism of Fig. 3. 5

Figs. 5 and 6 are respectively enlarged detail end and side elevations of a further modified form of snap-action c'ontrol mechanism adapted to be used with the hoist of Fig. l.

Fig. 7 is a wiring diagram of the motor con trol circuits for the hoist.

For purposes of illustration of its various novel features, the invention has been shown herein (Fig. l) as embodied in a small hoist of what may be designated as the portable type. -t will be understood, however, that the invention is, in many of its aspects, also applicable to other types of hoists. The particular hoist selected for illustration of the invention embodies in general an electric driving motor l (l mounted on one end face of a gear case M and supported as a unitary structure therewith by a suitable hook 02. The motor ill drives a revolvable hoisting member such as a chain pinion (not shown) located below the motor it], through the medium of a speed reduction gearing enclosed by the gear casing M. The chain pinion is disposed below the motor ill in general vertical alinement with the supporting hook i2, and a suitable hoist line such as a roller chain i l is reeved over the pinion with one end of the chain made fast to the gear case i l and with the other end hanging free for hoisting a load hook l5 being attached to its lower end, A brake mechanism, designated generally by the numeral. Elli, for holding the motor iii and driven chain pinion against rotation when the motor is stopped, is mounted on the outboard end of the motor (Fig. 2). Alsoa reversing controller ll, operated for example through the medium of a pair of control cords it and i9, is secured to the lower side of the motor. It will be understood that the particular location or arrangement of the parts of the hoist as described above forms no part of the present invention and may be varied as necessity or expediency require.

Turning now to a more detailed consideration of the parts of the hoist illustrated, the driving motor iii may be of the single phase alternating current type and embody a main field winding Ell as well as a starting winding 2!! (Fig. 7) cooperating with a rotor Ell A control arrangement adapting such a motor for use in an electric hoist is disclosed in the Whitcomb et al. application referred to above. Although the present invention is applicable to hoists embodying other types of motors it does find particular utility with the type of motor noted and accordingly such type of motor has been illustrated and described herein. The motor starting winding 20 is, in order to reduce the cost of the motor, made of such small current carrying capacity that it must be out out of circuit after the motor has started. For this purpose a speed responsive switch 22, which may be of the conventional centrifugal type and binlt into the motor itself in the usual manner, is utilized to open circuit the starting winding 2 l whenever the motor ill is operating at a speed in excess of a predetermined value.

The reversing controller ill for the motor has been shown in developed or schematic form in Fig. '7. As illustrated it embodies two rows of fixed contacts and 25 and 26, 271, and 23 as well as cooperating movable contacts 2t], 3t, 3 ll, 32, 33 and 3t. ried by an oscillatable rotor, actuated by rock shaft 35 (Fig. 2) Current is supplied to the motor ill from suitable alternating current supv ply lines L1-Lz. Vfhen the controller l? is in its central or neutral position, with the movable These movable contacts are car- I air/ace? contacts disposed with their center line at N (Fig. 7 the motor id is open circuited and hence deenergized. Upon shifting the controller contacts to the left to hoisting position H, the hoisting movement of the motor is initiated with the main winding. Bil energized (through a circuit L1-3li 23-S@2 l37l 2d 38 2i t i 2839Lz) and the starting winding H is also energized (through a circuit L13623-30 ill-43 |l2li l l-Z l l222 l3-25- 33 -M 3/J2339L2). It will be noted that the speed responsive switch 22 is included in the starting winding circuit and as soon as the motor attains a predetermined speed for which the switch is set, the switch 22 opens thereby deenergizing the starting winding. Upon a subsequent deenergization of the motor, the switch 22 again falls closed as the motor decelerates although usually at a somewhat lower speed than that at which it opens, due to the inherent sluggishness of such switches. In a similar manner, when the movable contacts of the controller it are shifted so that their center line occupies the position located at L, a reverse or lowering motion of the motor .is initiated, the main winding Ell being energized with the voltage reversed as compared to that for hoisting (through a circuit L1-3B2 9-' ll3@-2l7382 il3 l- 2t, -32 l 3328-89-Lz) and the starting winding 2i is energized in the same voltage sense as before (through a circuit L1362329 lil3tl 2G- l l 2 l-dE-Q 2-t3-2 5-32-M-- 33 -28- 39L2). As before, the speed responsive switch 22 is included in the starting winding circuit and is automatically opened after the motor comes up to speed.

The brake mechanism 66 is utilized for holding the motor iii and the connected hoist pinion 113 against rotation when the motor is deenergized. The brake mechanism has been shown to be of the friction shoe type although other types or forms of brake mechanisms may be used if desired. In the particular construction shown (Fig. 2), the brake mechanism embodies a brake drum 1-5 keyed to the outboard end of shaft 16 of motor ill and a cooperating pair of brake shoes 4?. The brake shoes are pivotally mounted on'the end of the motor casing as indicated at 48, and each brake shoe includes an integral laterally extending actuator arm ll. The brake shoes all are yieldably urged into engagement with the drum it by a pair of compression springs 56! encircling a pin 5! and interposed between the outer faces of the arms 69 and nuts 52 threaded on the pin iii. The lower ends of the brake arms embrace a generally diamond shaped cam 35 fixed on the outer end of the controller rock shaft 35. Abutments 5'17, adjustably mounted on the opposed ends of the brake arms are disposed to contact the cam and cause the brake arms to be pushed apart and release the brake whenever the controller is shifted from its central-neutral position to either hoisting or lowering positions. When the controller is in its neutral position (indicated by the clot dash line N in Fig. 2) the brake arms are pressed toward each other by the springs Ell so that the brake is set to hold the motor ll] against rotation.

One difficulty with the arrangement so far described is that the brake i6 is likely to be released before, rather than substantially in synchronism With, the closure of the contacts of controller [[1 for hoisting or lowering. It will be apparent that even though the parts are nicely adjusted at the factory when the hoist is assembled, that after continued use the friction brake or other parts may become worn or misadjusted. In the event that the brake isreleased even slightly before the closure of the controller contacts, there is danger that the operator will move the actuating mechanism so slowly that an appreciable time interval will elapse during which the brake is released and the motor deenergized. In this interval any load attached to the hoist falls freely by gravity and very quickly accelerates the driving motor Ill. There seems to be an almost inirradicable impression on the part of most hoist operators that the speed of operation of the hoist bears a direct ratio to the speed with which the control mechanism is moved. In other words, there is, for obvious psychological reasons, a strong tendency to pull gingerly or slowly on the control cords |8l9 when it is desired to inch the hoist line along slowly. Of course, the speed of motor operation actually bears no relation whatever to the speed of operation of the controller, and as a matter of fact, a very dangerous operating condition is likely to result from such attempted slow operation. With a split phase alternating current motor of the type described, the danger. is particularly aggravated. 4 For example, if a load is suspended by the hoist in stopped position and the operator moves the controller rock shaft 35 slowly toward hoisting position, the brake may be released before the controller contacts close to energize the motor. In such case, the motor is rapidly accelerated by the load which falls under the influence of gravity, and the speed responsive/switch 22 is opened. After this switch has once opened, then even if the operator subsequently closes the controller contacts in the manner which would normally energize the motor for hoisting, the motor will not, in fact, be energized for such movement, but will, on the other hand, continue to rotate in the lowering direction. This latter result is due .to the inherent characteristic of motors of the type noted that when once rotation has been'initiated, any reversing of the voltage on the main winding alone will not serve to reverse the direction of rotation, but on the other hand, such reversal of rotation can only be obtained when the starting winding is in circuit. Even though some other type of driving motor be used, the sudden acceleration due to release of the load is likely to strain or break the motor parts due to the extreme centrifugal forces encountered.

In accordance with the present invention a mechanism of the snap-acting type has been provided for positively insuring a quick throw of the brake and motor controller mechanisms from their neutral positions to either their hoisting or lowering position, no matter how slowly the operator applies force to the control cords l8--l9, or other manual actuating devices In the particular construction illustrated in Figs." 1, 2 and 3, the controller rock shaft 35 is provided with a cross bar 53 fixed thereon and carrying the control cords l8 l9 at its outer ends. The cord I8 may be used, for example, to shift the controller to hoisting position and the cord l9 to shift it to lowering position. A peripheral cam 54 isfixed on the inner end of the rock shaft 35. This cam 54 includes (Fig. 3) a high pointor nose 55 and a rounded butt end portion 56. .In order to accommodate the cam 54 for snap-acting motion, notches 58 are fashioned in the opposite side edges of the cam and are positioned to receive a cam follower roller or stop member 59 carried by a I plunger which is mounted for axial sliding movement in a bracket H. The cam follower roller 59 is yieldably urged into engagement with the cam by a helical compression spring 62.

When the controller rock shaft 35 is in its neutral position, the cam follower roller 59 is pressed against the nose 55 of the cam. Then as soon as the operator shifts the rock shaft 35 slightly to the right or left for hoisting or lowering, the spring 62 pushes the cam around so that the roller 59 finally moves into the'corresponding one of the notches 58 with a rapid or snap action. The controller shaft 35 is thus movedwith such rapidity into its full hoisting or lowering position that the brake is released and the controller contacts closed substantially instantaneously. Consequently, there is no appreciable time interval for the load on the hoist to gain momentum by falling even though the brake and controller mechanisms are not exactly synchronized. In this manner, the operator, no matter how misguided, is powerless to move the controller rock shaft slowly with the consequent danger of faulty operation described above.

Too rapid shifting of the controller from hoisting to lowering position or vice versa is prevented by the engagement of the cam nose 55 with the spring pressed roller 59 as it passes neutral position. This engagement of the cam by the roller circuit.

A modified form of control cam 54 has been illustrated in Fig. 4. This cam is substantially identical with the cam 54 except that a notch 63 is formed in the nose 55 to receive the cam follower roller 59 when the cam is in its central or neutral position. Otherwise, the cam 54 is shaped like the cam 54 previously described and includes peripheral edge notches 58 for receiving the cam follower when the cam is in its hoisting or lowering positions, respectively. The additional notch 63 serves two purposes. First, it acts to center and positively hold the cam in its neutral position. Second, it cooperates with the cam follower roller 53 to resist movement of the cam from its neutral position and as a result a comparatively large force must be exerted on the rock shaft 35 before the cam 54 can be moved from its neutral position. This strong initial force on the rock shaft helps to carry it through its complete movement to hoisting or lowering position with the required rapidity.

To further insure snap action of the controller rock shaft 35 a spring or similar energy storing means may be interposed between the manual operating device and the rock shaft. For example, as shown in Figs. 5 and 6, a manual operat ing cross arm 53Amay be loosely .iournaled on fixed thereto, as in the case of the arm 53 in Fig. 2. A cam 54 is fixed to the rock shaft 35 and is identical in construction with the cam 54 of Fig. 4, being provided with a cam follower mechanism also identical with that previously described. A helical torsion spring 64 is interposed between the cross arm 53 and the cam 54. This spring may surround the rock shaft and have two opposite ends fixed to the cam and to the cross arm. With such an arrangement, when the operator pulls down on either of the control cords |8l 9 the cross arm 53" is oscilated about the rock shaft and tension built up in the torsion spring ti l. Subsequently, when the force stored up in the spring reaches a predetermined amount, the cam- 55 is pulled sharply controller for controlling the energization of said motor including a control member oscillatable froma central neutral position in which said motor is deenergized to either a hoisting or low- 5 by the spring to either. its full hoisting or lowerering position displaced on respective opposite 5 ing position, as the case may be. By this means sides of said neutral position and in which said. a full snap-acting type of operation for the motor energizing circu t is completed with cormotor and brake controls is achieved and there is respondingly reversed voltage for hoistng or lowno possibility of a time lag between release 01 ering, means including a brake for releasably w the brake and energization of the driving motor. holding said motor and hoisting member against n rotation, brake actuating means for setting said brake when said control member is in neutral position and for releasing said brake in response to movement of said control member to either hoisting or lowering position, manually operable 15 means for oscillating said control. member, and a peripheral cam carried by said control menihesaid cam having peripheral notches on opposite sides of a -orojeet 1' nose portion, and means i Although certain particular embodiments of the inventionhave been described in some detail for purposes of explanation of the invention, there is no intention to limit the invention thereby to such embodiments but, on the other hand, the appended claims are intended to cover all modifications and alternative constructions Within the spirit and scope of the invention.

1' claim as my invention:

{in An electric hoist comprising, in combination, cluding a resilient cam Bowe e a 29 a '"evolvable hoist member, an electric motor p r phery of s id am f r m n said control 0 ectcd in en relation with said hoist memm neutral position to ei h r h i in energizing circuit, a reversing g position W. a c snap action .tl'olnng the energizatien of said 5 uhe speed with which force is Lg fjfj control membe" oscillatabie ma ual means. 25 wh ch eie a1 osition or in "or reieasaloly hol member to movement n auxiliary a speed re-- I I i St 11g no-tor is ..otating at a speed in "lined Value ersing conn lve setting said bra in neutral posi ion e in response to 101 i Toer to either hoistualiy operable m 01 member, l member from 'ng or lowering pos t osition in opposite ting and lo ens, a releasable brake lor holding said inotor against rotation, means responsive to in movement of said control member for setting said brake when said control in nber is in its neutral position and fOl leasing said brake when said control member is in either hoisting or ion/e position, i named means ineluding a peripheral cam connected to said control member and having an elongated nose portion thereon with a notch in' the end thereof, and means including a cam follower yieldably urged into engagement with'said cam and engageable with the notch therein when said control member is in neutral position for slowing up the movement of said control member in passing from hoisting to lowering position and vice versa to thereby increase the period during which said brake is set in the course of such reversing operation, whereby said motor is slowed down to eflect actuation of said speed responsive switch during the reversing operation.

'1. An electric hoist comprising, in combination, an electric hoisting motor, a controller for reversing and deenergizing said motor, said controller including a shaft rockable from a central neutral position in one direction or the other ing positions, an actuator respectively to hoisting and lowering positions, a peripheral cam shaft on said shaft, said cam having peripheral notches therein corresponding to the neutral position as well as the hoisting and loweringpositions of said shaft, stop means yieldably pressed into engagement with the notched portion of said camior releasably holding the same in any one of its several correspondnaled on said shaft, manual means for moving said actuator, and means including a helical torsion spring anchored at its opposite ends to said cam and to said actuator member for operatively connecting the same to store up force upon oscillation of said actuator and thereby move said cam from one position to another with a rapid snap action.

I RALPH E. SMITH.

member loosely jour-

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