US1117588A - Electric hoist. - Google Patents

Description

G. K. MITCHELL.

ELECTRIC HOIST.

APPLICATION FILED MAR. 13. 1912.

Patented Nov. 17, 1914.

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3 SHEETS SHEET 2 G. K. MITCHELL.

ELECTRIC HOIST.

APPLICATION FILED MAR. 13 1912- sz l z za Zz G. K. MITCHELL.

ELECTRIC HOIST.

APPLICATION FILED MAR.13. 1912.

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GUY K. MITCHELL, OF BALTIMORE, MARYLAND.

ELECTRIC I-IOIST.

Specification of Letters Patent.

Patented Nov. 17, 1914.

Application filed March 13, 1912. Serial No. 683,576.

To all wk am it may concern:

Be it known that I, GUY K. MITCHELL, a citizen of the United States, residing at Baltimore, in the State of Maryland, have invented certain new and useful Improvements in Electric Hoists, of which the following is a specification.

This invention relates to power driven hoists or elevators and more particularly to electrically operated elevators of the type commonly known as dumb waiters.

One object of the invention is to provide a silent and eilicient drive for such machines and to so arrange the gearing that the speed ratio between the motor and cable sheave may be varied as desired.

Another object is to provide an improved arrangement of manual control for starting, stopping and reversing the machine.

A still further object is to provide means for automatically shutting off the power from the motor as the car approaches the limits of its movement, such means being designed especially to prevent over-throwing of the control Wheel in machines where the car travels at comparatively high speed.

lVith the above and other objects in view, and to improve generally the details ofconstruction of such machines, the invention consists in the arrangement hereafter described and claimed, and shown in the accompanying drawings, in which,-

Figure 1 is a plan View of my improved dumb waiter machine complete; Fig. 2 is a sectional detail showing a modified constructions; Fig. 3 is a front elevation of the brake, the cam shaft being shown in section; Fig. 1 is a transverse section of the machine substantially on the line as of Fig. 1; Fig. 5 is an end elevation of the machine as shown in Fig. 1; Fig. 6 is a diagram of thecircuit connections employed; and, Fig. 7 is a diagram showing the improved arrangement of control ropes.

Referring to the drawings in detail, 1

designates a suitable frame constituting a base or support on which the mechanism is carried. An electric motor 2, preferably of the shunt type, is mounted on one end of the frame, with the commutator housing 2 on the outside. On the inner end of the shaft 3 of the motor is secured a friction disk 4, the face of which is adapted to be engaged by the periphery of a friction wheel 5, which is secured to a drive shaft 6 by means of a key or feather 7. By adjusting the position of the wheel 5 along the shaft 6, it may be caused to engage the face of the disk 4-. at points more or less removed from the center thereof, and by this means the speed ratio between the motor shaft and drive shaft may be varied as desired. The shaft 6 is mounted in journals 8 which slide in Ways 9, and are urged toward the motor as by means of springs 10. The friction wheel is thus caused to firmly contact with the disk 1. Rigidly mounted upon the shaft (3 is the @able sheave 11 over which passes the driving rope to which the car and counterweight are attached. As shown, the shaft 6 is at right angles to the motor shaft 3, but by using specially beveled friction wheels the angle may be aried as desired.

J ournalcd in bearings 13 is a controlling shaft 12. This is preferably in the form of a cam shaft consisting of a solid cylindrical bar having segments 14- cut or milled out as clearly shown in Fig. 1, such segments being arranged alternately on opposite sides of the bar for the purpose hereinafter described. Near one end the shaft has two segments cut from opposite sides of the ba at the same point as indicated at 15, and adjacent this end also is a similar flattened portion 16 (see Fig. 3) in which the cut out portions are arranged at right angles to those indicated at 15. adapted to be engaged by a pair of arms 17 projecting from a hand brake 1S, hinged at 19 to the frame 1 and adapted to embrace the periphery of the friction disk 1. The arms 17 are normally urged together so as to apply the brake by means of a compres sion spring 20, which encircles a bolt 21 which passes through the arms 17, the spring being arranged between one arm and a nut on the end of a bolt.

The direction of rotation of the motor and the starting and stopping thereof is controlled by means of a set of reversing switches 22. A field switch 23 is also provided for controlling the circuit of the shunt field, as will be hereinafter described.

Each of the switches consists of a pivoted arm carrying at one end a contact surface adapted to engage a fixed contact 2 1. Each of the switch arms is pivoted at to a bracket, such brackets, as well as the contacts 24, being mounted upon a slab 28 of slate or other insulating material. Under each arm on the side of the pivot remote from the contact 24;, is arranged a compression The flattened portion 16 is,

spring 26, which tends to move the arm so as to bring the contacts into engagement and close the switch. Each of the switches is provided at its end opposite the contact with a roll 27 which engages the lower surface of the cam. shaft 12, as clearly shown in Fig. 4. As long as the roller 2? is in engagement with the cylindrical portion of the shaft, the switch is held open, but when such roller enters the segment shaped cut out portions 14 or 15 the spring 26 is permitted to move the switch arm. to closed position.

In order to prevent the possible flashing of sparks from the contacts 24 and to reduce fire risks, the supporting slab 23 and the switches and contacts carried thereby are all inclcsed within a fire proof tray or pan 29, as clearly shown in 4. This pan is preferably made of sheet metal.

30 designates an automatic starting device of any well known type, which is placed in the armature circuit to limit the rush of current therein at the moment of starting, or if the load becomes excessive. This starter is also preferably inclosed in a fire proof tray or pan 31, similar to that shown at 29.

On the end of the cam shaft 12 is mounted a control wheel 32 over which passes "the manual control rope by means of which the cam shaft is operated and the movements of the motor and car controlled.

As shown in the drawing, the cam shaft is illustrated in its neutral or stop position. In this position it will be observed that all of the rollers 27 engage with cylindrical portions of the cam shaft, and consequently all of the switches 22 and 23 are opened. Means are provided for yieldingly maintaining the wheel 32 in this position and for preventing over-throwing thereof by the hand rope. As shown, such means consists in the provision of a notch 33 in the periphery of the wheel 32, which notch is adapted to be engaged by a roller 34 carried by a lever 35, pivoted at one end 36 to a suitable support 38, and provided at the other end with either a spring (not shown) or a weight 37.

While the apparatus, as shown in Fig. 1, is suitable for some purposes, I prefer to use, where space permits, the arrangement shown in Fig. 2. In this arrangement the bearings 8, Fig. 1, are made fixed, the springs 10 being omitted. The motor shaft, however, is extended beyond the commutator.

housing 2 as indicated at 3, and at such extended end is formed an anti-friction thrust bearing 41 which preferably consists of a pair of disks having a raceway and antifriction balls between them. A compression spring 42 bears upon. the outer of these disks and the degree of pressure can be regulated by meansof a set screw 43, which is carried by a casing 40 inclosing the thrust bearing. It will be observed therefore that the spring 42 constitutes "means for urging the motor shaft and disk 4 toward the friction wheel 5. This construction is more compact and simpler than the provision of sliding bean the switches in the position they will assume when the rope wheel 32 is turned 90 degrees to ard the righ from the position shown in F l and The cut out portions 14 of the cam shaft pe nit the switches a and c to close, while of thecut "out portions 15 permits the switcl'i to close simultaneously. Current flows from the conductor j to switch 0, thence from contact c over the connection 9, (indicated in dotted lines, and being made on the back of the slab 28) to contact 6, thence through conductor it, to armature 2' of the motor,- thence through conductor y' to contact a, switch a, connection. 70, conductor Z, through the auto matic starter 30, conductor in, andback to the other side of the line at a. Current also simultaneously passes from conductor f through the connection "0, switch 6, Contact 0, conductor p, shunt field winding q to the other side of the line at at. The motor then runs in such a direction as to (say) raise the car. When it is desired "to stop the car the hand rope is moved so as to turn the wheel back to the position shown in Fig. 1. When it is desired to lower the car the rope is moved so as to turn the wheel 32 90 degrees to the left, from the position shown in Fig. 1. This permits switches Z) and (Z to close, as well as the switch 23, and the motor then runs in the rei e'r's'e direction. It will be seen therefore that the field switch 23 is closed when the cam shaft is moved in either direction from the stop position, and that two of the switches 22"ar'e closed for one direction of rotation, and the other two for the other direction.

In Fig. 7, 44 designates the usual hand rope which passes over the wheel 32 at one end, and over an idler 45 at the other end of the shaft. Ordinarily, as heretofore constructed, it has been common to provide knocker balls on the rope 44 so arranged as to be engaged the car as it approaches the limits of its travel so as to automatically bring the wheel 32 back to neutral position and thus shut off the power. car operates at high speed, however, great difliculty has been found in ractice on account of the over thro'wi'n'g of such wheel past the stop position. It is with a view to overcoming this difiiculty that I have provided the arrangement shown in Fig. 7.

Where the 5 the other end around a wheel 49. Secured to the wheel 49 is a small sprocket wheel 48 which is geared by means of a chain 47 or other suitable gearing to a larger sprocket wheel 46, rigidly connected with the shaft 12 or wheel 32. Knocker balls 52 and 53 are secured to the rope and are adapted to be engaged by a projection 54 carried by the car 55.

By virtue of the reduced speed gearing between the wheel 49 and the wheel 32 it will be seen that the rope 50 will have a much greater travel than the rope 44. Suppose, for example, that the ratio between the wheels 48 and 46 is one to three. This would mean that after engaging the knocker ball, the car could move say six feet without moving the control rope 44 more than two feet. In other words, by the employment of such reduction gearing, the car is given a much greater distance in which to come to rest after striking the knocker ball than would be possible where the knocker balls are mounted directly upon the manual control rope 44. Therefore, with my improved arrangement it is no more difficult to automatically stop a high speed car than it is to automatically stop a low speed car with the old arrangement. I regard this as one of the important features of my invention.

From the foregoing it will be seen that I have provided an improved dumb waiter machine having an adjustable silent drive and having improved controlling means whereby current is entirely cut oil from the motor when the machine is idle, and it is thought that the many advantages of my invention will be readily appreciated by those familiarwith the requirements of such apparatus.

What I claim is 1. In an electric hoist, a motor, a drive shaft, gearing therebetween, a cable sheave on said drive shaft, a car, controlling switches for said motor, a rotary cam shaft for operating said switches, a rope wheel secured to sald cam shaft, and means whereby the rope wheel is turned by said car as the latter approaches its limiting positions, said rope wheel having a notch in its periphery, and a lever having a projection adapted to engage said notch, whereby overthrowing of said rope wheel pastthe stop position is prevented.

2. In an electric hoist, a motor, a driving disk secured to the end of the motor shaft, a cable sheave adapted to be driven by such disk, a brake engaging the periphery of said disk, and comprlsing a pair of pivotallyconnected arms controlling switches for said motor, and a rotary cam shaft for operating said switches, said cam shaft comprising a straight cylindrical bar having a segment cut out adjacent each switch, said bar being also cut out adjacent said brake, and extending between the arms thereof to control the same.

3. In an electric hoist, the combination with the motor and cable sheaf and car, of a plurality of switch elements controlling said motors, a brake acting directly on the motor armature, a rotary cam shaft to simultaneously actuate said switches and brake, a rope wheel secured to said cam shaft, said wheel having a notch in its pe-' riphery, a lever pivoted at one end and weighted at the other, and having intermediate its ends a projection adapted to engage said notch and thus arrest said rope wheel and cam shaft in stop position, and

means whereby the rope wheel is turned by said car as the latter approaches its limitin positions.

In testimony whereof I afiix my signature, in presence of two witnesses.

GUY K. MITCHELL.

\Vitnesses:

KATHARINE H. Roonns, NonL L. BURNS.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents,

Washington, D. C.

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