US2578006A - Load limit control - Google Patents

Description

9 1951 J. F. GREEN EMWW LOAD LIMIT CONTROL Original Filed Feb. 21, 1946 2 SHEETS-SHEET 1 291/ (72/ 52 9 F/"f ,231.66 fif 62%571.

Dec, H, 1951 J. F. GREEN LOAD LIMIT CONTROL 2 SHEETS-SHEET 2 Original Filed Feb. 21, 1946 Patented Dec. 11, 1951 UNITED STATES PATENT OFFICE Illinois Continuation of application Serial No. 649,283, February 21, 1946. This application January 31, 1950, Serial No. 141,535

5 Claims. 1

This invention relates to improvements in load limit controls in elevating systems, and more particularly to an improved load-operated switch and an actuating system therefor.

This application is a continuation of my copending application entitled Load Limit Control filed February 21, 1946, as Serial No. 649,283, now abandoned.

One feature of this invention is that it pro-'- vides an improved load limit control system; another feature of this invention is that it provides a load limit control system which is direct and positive in action; a further feature of this invention is that it provides a load limit control system which can be installed and utilized in elevating 1 systems already built and in use; an additional feature of the invention is that it includes a motion-multiplying arrangement whereby great accuracy of operation is obtained; yet another feature of the invention is that it includes means to adjust the system to operate over a wide range of loads, thus permitting adjustment for operation at any desired maximum load in any particular elevating system wherein my invention is installed; and still a further feature of the inveninvention Fig. 2 is a top view of a portion of the invention shown near the upper right of Fig. 1;

Fig. 3 is a side elevation, partly in cross section, of the same portion of the invention as shown in Fig. 2;

Fig. 4 is an enlarged fragmentary view, partly in cross section of a portion of the invention shown near the upper left of Fig. 1.

The problem of load limit control in elevator systems has been, in the past, perplexing to elevator manufacturers and operators. In ordinary passenger elevators such as are found in stores and office buildings, the problem, it is true, is not serious because the load capacity and the square foot area of the platform are functions of each other, and the elevator may be designed and built so that it cannot be overloaded with more than its rated capacity so long as it carries human beings. However, in the case of freight elevators, the capacity and the square foot area of the platform are not functions of each other. and the problem of overload becomes serious. Since such elevators are often of large platform area so they may accommodate light, bulky materials, they are susceptible to being overloaded by placing on them loads of small volume, but of great weight, such as iron bars, rails, or sheets, etc. A converse aspect of the problem is seen in the case of hospital elevators, which must necessarily be of large platform area, but which are not heavily loaded in operation. Because of the large platform area, code requirements force manufacturers to build these elevator systems with a large load capacity, such as 3,500 pounds, including large machine units and unnecessarily heavy equipment, for in operation these elevators are seldom loaded in excess of 1,000 or 1,200 pounds.

One difficulty with many existing load limit control systems is that they require suspension of the elevator cage from a toggle or a spring, or in some other way disrupt the conventional suspension arrangement wherein the hoisting cables are rigidly secured to the crosshead of the car, or the lifting beam, and thus they find cliificulty in meeting governmental codes and the requirements of underwriters and other inspection organizations.

I have devised and am here disclosing and claiming a load limit control system in which the conventional suspension construction is not disr'upted, the hoisting cables being rigidly fastened to the crosshead of the car, or the lifting beam. It has been found that the crosshead 0r lifting beam will be deformed or bowed slightly in proportion to the load it carries, and the indication of overload in my invention is initiated in the movement which occurs in this crosshead when it is slightly deformed under load conditions. My load limit control can thus be readily installed in existing elevating systems or utilized in new elevating systems without in either case changing the approved method of suspension.

Referring now to the drawings which illustrate one embodiment of my invention, in Fig. 1 a conventional elevator car is shown at H), which car contains a platform or bottom II and side members 12. A conventional crosshead or lifting beam is shown at l3 with conventional hoisting cables [4 rigidly secured to the center of the crosshead by a hitch plate in the conventional manner, as at I5. The cables lead to a conventional pulley or drum driven by a conventional motor, neither being shown since they form no part of this invention.

Lever I6 is pivotally secured near one of its ends, as shown in greater detail in Fig. 4, in spaced relation to the crosshead by means of the bolt [1 carried by the L-shaped bracket i8, the bolt passing through a ball bearing in the lever, the bracket being immovably secured to the crosshead near the end thereof by means of the bolt I9. At '20 is shown a fulcrum which may be of any appropriate size and material and supports the lever at such a height above the crosshead that when no load is on the cage the lever it rests preferably substantially parallel to the crosshead. The fulcrum may be fastened to the lever or the crosshead, and is preferably located near the center of the crosshead, though it may be located at any point between the pivot point i? and the center of the crosshead. It will be seen that if a load is placed on the car so that the crosshead is deformed or bowed, the downward movement of the end of the crosshead shown at the left in Fig. 1 will be transmitted to the lever at the pivot point l1. Since the lever is fulcrumed at 20', the free (or right) end of the lever will move upward. The extent of this upward movement will depend upon the ratio of the distance between the point of applied force I! and the fulcrum 20 on the one -hand, and the distance between the fulcrum and the free end of the lever on the other hand, in accordance with the ordinary laws of physics.

.In the embodiment of the invention shown in the drawing, this ratio is approximately 1 to l, so that if the left end of the crosshead were deformed downwardly to the extent of one thirtysecond of an inch, pulling the pivoted end of the lever downwardly one thirty-second of an inch, the free end of the lever would move upwardly one thirty-second of an inch.

I The free end of the lever l6 projects into the open end of a box 2| which is mounted on the crosshead by bolts 22, and is spaced from said crosshead by plate 23 in an amount sufficient to receive the free end of lever l6, leaving adequate space between the top of said lever and the top of the box to allow for movement of the lever when the system is operating.

Referring now more particularly to Figures 2 and 3, a second lever 24 is pivotally joined to the free end of lever 16 by the bolt 25 passing through a ball bearing 26a in bracket 26, which bracket is carried by lever l6. Lever 24 is fulfcrumed by the bolt 21 mounted in ball bearing 21a and supported above the crosshead by bracket 28. Thus, if the free end of lever It moves upward, it will carry with it the adjoining right hand end of lever 24, and since lever 24 is fulcrumed atIZ'I, the left end of lever 24 will move downward. The amount of downward movement of the left end of lever 24 will be approximately tance between the point of applied force 25 and the fulcrum. So it will be seen that an upward movement of, for example, one thirty-second of an inch at point 25 will appear as a downward 'movement of approximately one-sixth of an inch at the left end of lever 24.

A conventional Micro-Switch 29 is so located Qas'to be operated by downward movement of an adjustable bolt 30 which is threaded through bracket 3|, said bracket being immovably joined to the left end of lever 24. The levers l6 and 24 are held in proper vertical track by means of guide pins 32 as shown, so that the bolt 30 is always in vertical alignment with the arm 35, of Micro-Switch 29. The Micro-Switch 29 is of a conventional snap-acting type, and is movable between two positions. It is biased to one position by a spring or other conventional means, and is so connected that upon movement to the position as a result of downward movement of the adjustable bolt 30 for a predetermined distance, the motor circuit is broken, an overload signal is given, or operation of the elevating system is in some other manner forestalled. A preferred method of connecting the Micro-Switch to forestall operation of the elevating system is disclosed in Matthews Patent 2,506,805, which issued May 9, 1950. When pressure of the bolt 30 on switch arm 35 is released, the Micro-Switch returns to its first position. The bolt 30 may be adjusted so that various amounts of movement of the left end of lever 24 will cause the bolt to operate the Micro-Switch, and since the amount of movement of the left end of the lever 24 is a direct function of the load on the crosshead, the amount of load necessary to actuate the load control system maybe adjusted over a wide range.

Operation of the system is as follows:

Assume that the elevating system in which my invention is installed is designed to carry a maximum load of 4,000 pounds, and that adjustment of the bolt 30 has been made accordingly. As the elevator is loaded, the crosshead it will be deformed or bowed slightly in proportion to the increasing load. This deformation will pull the ends of the crosshead down with respect to the center thereof, and this downward movement will be transmitted to the left end of lever it through the bracket i8 and the bolt H, and lever 16 will pivot upon its fulcrum 20. As the right end of lever 16 moves upward, this movement will be transmitted to the right end of lever 24 and multiplied as explained above, and the left end of lever 24, carrying the bolt 30, will move downward toward the switch arm 35. This movement will be aided and increased by the downward deformation of the right end of the crosshead, carrying with it the bracket 28 and the fulcrum 21 of lever 24. When a load of 4,000 pounds is reached, where that is the adjustment which has been made, the movement will be sufficient to operate the Micro-Switch 29, and operation of the elevating system will be forestalled as noted above.

While I have shown and described a certain embodiment of my invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the appended claims.

I claim:

1. In an elevator system including a cage, a hoisting cable affixed thereto, and drive means therefor, a load limit control system including: switch means movable between two positions; and motion-multiplying control means for operating said switch means in accordance with load conditions on said cage, said control means having a portion afilxed to said cage and a portion adapted to be actuated by movement of said cage in accordance with load conditions thereon.

2. In an elevator system including a cage, a hoisting cable affixed thereto, and drive means therefor, a load limit control system including: switch means movable between two positions;

switch means movable between two positions, and

adapted while in one position to forestall operation of the drive means; motion-multiplying lever means for varying the position of the switch means to forestall operation of the drive means upon loading of the cage over a predetermined maximum, said lever means having a portion pivotally mounted on said cage and a portion adapted to be actuated by movement of said cage in accordance with load conditions thereon; and apparatus for adjusting the load point at which the switch means is moved to forestalling position, said adjusting apparatus being carried by the lever system near the point of greatest motion to provide minimum sensitivity of the adjusting apparatus.

4. In an elevator system including a cage, a hoisting cable aifixed thereto, and drive'means therefor, a load limit control system including: switch means movable between two positions, and adapted while in one position to forestall operation of the drive means; a motion-multiplying lever for varying the position of the switch means to forestall operation of the drive means upon loading of the cage over a predetermined maximum; means providing a pivotal mounting for said lever; means on said lever for actuating said switch; and means adapted to engage said lever to move said lever about said pivot in accordance with and in a degree proportional to the load on said cage, the distance between the pivotal mounting and last mentioned means being less than the distance between said pivotal. mounting and said actuating means.

5. In an elevator system including a cage, a hoisting cable aflixed thereto, and drive means therefor, a load limit control system, including: a crosshead comprising the lifting beam of the cage; a motion-multiplying lever pivotally affixed in spaced relation to said crosshead;-means on said cage for moving said lever about said pivot in accordance with and in a degree proportional to the load on said cage; switch means movable between two positions, and adapted while in one position to forestall operation of the drive means, the position of said switch means being varied through action of the lever to forestall operation of the drive means upon loading of the cage over a predetermined maximum; and apparatus for adjusting the load point at which the switch means is moved to forestalling position, said adjusting apparatus comprising a movable switch actuating member carried by the lever adjacent the point of greatest motion to provide minimum adjustment sensitivity, the means for moving the lever being adapted to engage said lever at a point closer to said point of pivotal mounting than the distance between said point of pivotal mounting and said actuator.

JOSEPH F. GREEN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 170,467 Boomer Nov. 30, 1875 1,758,605 Jackson May 13, 1930 2,404,415 Turner July 23, 1946

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