US3095979A - Overload device - Google Patents

Description

July 2, 1963 M. E. SILBERGER OVERLOAD DEVICE Filed April 8, 1960 FIG. 4

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Filed Apr. 8, 1960, Ser. No. 20,975 3 Claims. (Cl. 212-134) This invention relates to load measuring devices, and has particular reference to the automatic limitation of loads attempted to be moved by material handling devices.

For the purpose of illustration and explanation, the device is shown as part of an electric hoist utilizing a cable as the lifting element but, as will appear, the invention is by no means limited to such structure. Any load handling devce, such as a lift truck, jib crane, portal or other types of cranes, can utilize the invention with only trifling modifications.

The desirability of load limiting devices has long been recongized, in particular, in connection with hoists and cranes. Because competitive conditions require that a hoist be relatively inexpensive, and, at the same time, give long service under adverse conditions, the designers are limited in the safety factors which can be built into their products. In fact, users frequently overload hoists depending upon the safety factors to prevent breakage. The resulting wear under such conditions is excessive and the hazard to life and property very high. Another source of trouble is running the hoist with slack in the sling chains and jerking the load upward, which, if the load is near the capacity of the hoist, unduly strains many parts of the mechanism.

As a hoist in many installations is available to anyone on the floor who wishes to use it, and many who have only occasional need for it are ignorant or indifferent to the limitations on its use, it would seem desirable to arrange a hoist so that it cannot be abused by overloads engendered by attempts to lift large weights or by various faulty practices which produce excessive and unsafe impact stresses on the hoist. Because acceleration stresses are indetectable until they have occurred, one method of prevention or discouraging practices generating them is to penalize the operator if the hoist is so operated. As a general proposition, a great deal of the abuse of a hoist is a result of any attempt to hurry up a task, and a hoist which requires an additional time to perform a certain duty, if incorrectly used, is soon treated with caution.

With the above in mind, it is a primary object of the present invention to prevent as far as possible, the imposition of impact and acceleration loads on the hoist, by rendering such action non-profitable to the operator.

It is a further object of the present invention to provide a hoist with a device to prevent it from lifting any but a predetermined load.

It is a further object of the present invention to provide a device for a hoist which can be readily adjusted for a required load.

It is a further object of the present invention to provide a hoist with a safety device which prevents overloading the hoist but interferes with the normal operation of the hoist as little as possible.

Referring now to the drawings, which illustrate a preferred form of device embodying the present invention:

FIG. 1 is a pictorial representation, partly in section, showing one type of hoist to which the present invention is adapted;

FIG. 2 is a top view of the actuating device;

FIG. 3 is a section taken on line -33 of FIG. 2; and,

FIG. 4 is a section taken on line 44 of FIG. 3.

3,095,979 Patented July 2, 1963 ice Briefly, the present invention contemplates a load responsive unit which controls an electrical circuit which, in turn, controls the operation of the hoist and/ or various signal devices. In the particular example selected for illustration, the hoist is electrical, but the same device may be readily adapted to hydraulic devices, if necessary, by the use of suitable solenoid valves or the like. As shown in FIG. 1, the hoist used for illustrative purposes employs cable 10 as the lifting agency, which cable is secured at one end, passing around a traveling block 1 1 and wound on an electrically driven drum. In the usual arrangement, the :dead end of the cable is secured to some part of the hoist frame. In the present device, the cable 10 is supplied with a ball fitting 13 which is received within a suitable terminal 14, forming part of the mechanism with which this invention is chiefly concerned. The terminal comprises a pair of semi-cylindrical sleeves 15, suitably bored to receive and retain the ball fitting 13 and a somewhat similar ending .16 on a reciprocable member 17. The two half cylinders are held together by an outer sleeve 18, which is retained in place by a spring ring 19. This particular ending is selected to permit ready replacement of the cable without the necessity of hammering or heating or other rough treatment on the member 17.

In order to support the entire device, trunnions 20 are provided, forming part of a platform 21 and capable of transmitting the entire load from the wire rope end to the hoist frame. The member 17 has an enlarged portion 22 extending through an opening in the platform, and a head 23, too large to pass through said opening. Between the head 23 and the upper surface of the platform 21 are one or more Bellville springs 24. These springs, a common article of commerce, are essentially conical washers of spring material, which flatten under load. It is the flattening of these springs which gives the mo tion necessary to operate the electrical part of the device.

By way of example, a pair of these springs are shown, with their concave surfaces toward each other. It will be appreciated that for a given load, the flattening of the springs will result in twice the movement of the member 17 which would result if but a single spring were used. Conversely, if the springs both faced in the same direction, the motion would be one-half of that which results from the arrangement shown, and the load which can be can ried -by the latter arrangement is twice that which can be carried by the first-mentioned arrangement. 'It therefore can be appreciated that any number of springs can be piled, either all facing the same way, facing alternately up and down, or any combination of them, to give the proper load bearing ability and deflection sufficient to operate the part of the device now to be described.

To form a housing, a suitable cover 25 is provided, secured to the platform 21 as by screws at 26 or the like. On its inner surf-ace, the cover 25 carries a pair of projections 27, arranged to limit the upward motion of the head 23. It is intended that the Bellville springs be lightly compressed by the projections 27, but the main reason for the projections is to protect the mechanism in the event a hook slips off the load, or other sudden release of the load occurs, which would cause the member 17 to be suddenly projected upward. Also, the projections 27 prevent oscillation of the load on the springs 24 beyond a slight oscillation possible before the member 23 engages the projections 27.

A switch 28 is provided in the housing 25 which controls the proper circuit for stopping the hoist upon over load. The particular type of switch depends upon the way it is supposed to control the hoist, but the simplest would be a normally open switch which closes upon proper travel upward of the button 29. If such a switch were in the up control circuit, in series with the up button or its equivalent, it can be seen that the boss 39 must be in contact with the switch element 29 to close the switch and to permit the hoist to raise at all.

It is obvious that if the switch 28 were rigidly mounted, the device could be made to work to prevent lifting of overloads, provided the switch was capable of suificient travel or the Bellville springs were held under sufficient compression by the projections 27 to limit travel of the boss 30 to which the switch plunger 29 can follow. However, such a mechanism will give no indication whatever of other improper treatment mentioned in the beginning.

For the purpose of making the device sensitive to impact overloads, the switch is resiliently mounted, a threaded .stud 31 secured to the switch passing through an opening in the cover, and tree to slide therethrough. A spring 32 between the housing and the switch urges the switch downward, and a pair of locknuts 33 on the stud serves to limit such movement. For the purpose of preventing tampering, a cover 34 may be secured in any convenient way to render removal readily detectable.

It can be seen that the location of the locknuts 33 on the studs can be varied to set the overload at which the switch opens, which it will do when the lower nut touches the housing and the boss 30 loses contact with the button 29.

The spring 32 is selected to be of such compressive strength relative to the internal spring of the switch so that once the switch is opened, it cannot close until subwith a force suflicient to cause actuation of the switch.

In the case of an overload caused by impact, the switch acts exactly the same way and it will be necessary to remove the load hy lowering the load until it is supported on the floor, before the load can be raised. It has been found that this behavior of the hoist. soon forces the user to handle the hoist and loads with needed care and within safe bounds, to avoid the necessity of this additional operation.

It can be readily seen that the particular mechanism described can have its externals modified to adapt it to any instrumentality exerting a force, where it is desired to limit the force or signal that the force is about to be, or has been, exceeded. A typical application is in an elevator or lift, on a fork truck or the like, or on a jib or other type of crane to prevent a load from being raised which would be suflicient to overturn or overload it. Such applications are contemplated without the exercise of invention over the structure described.

I claim:

1. In a device for lifting indeterminate weights, means for causing operation of the device in a weight-lifting direction, an electrical circuit for controlling such operation, spring means operatively connected to said device and defiecta'ble in response to the weight imposed on said device, switch means in said circuit operative in response to deflection of said spring means by a weight greater than a predetermined maximum to prevent operation of the lifting device in a weight-lifting direction, and means maintaining said switch in operation-preventing condition until reduction of the deflection of the spring means corresponding to reduction of the imposed weight to a predetermined value below the predetermined maximum.

2. In a weight-lifting device, an electrical circuit controlling the operation of the device in a weight-lifting direction, means including a spring causing relative movement of a pair of elements in response to imposition of a weight on the device, a spring normally open switch in said circuit, a resilient mount for said switch on one of said elements, the other of said elements bearing on the switch operation means, the resilient means being related to the switch spring to require reduction in the weight lifted to below a predetermined maximum upon operation of the switch by a weight greater than a second, larger predetermined maximum.

3. A safety device for a weight-lifting device to require removal of at least part of the weight being lifted in response to momentary acceleration of the weight-producing forces greater than a predetermined maximum comprising, an electrical circuit controlling the operation of the weight-lifting device in a weightlifting direction, a switch in said circuit having a spring holding it normally open, a pair of elements mounted on the weight-lifting de- References Cited in the file of this patent FOREIGN PATENTS 814,642 Great Britain June 10, 1959

Claims (1)

1. IN A DEVICE FOR LIFTING INDETERMINATE WEIGHTS, MEANS FOR CAUSING OPERATION OF THE DEVICE IN A WEIGHT-LIFTING DIRECTION, AN ELECTRICAL CIRCUIT FOR CONTROLLING SUCH OPERATION, SPRING MEANS, OPERATIVELY CONNECTED TO SAID DEVICE AND DEFLECTABLE IN RESPONSE TO THE WEIGHT IMPOSED ON SAID DEVICE, SWITCH MEANS IN SAID CIRCUIT OPERATIVE IN RESPONSE TO DEFLECTION OF SAID SPRING MEANS BY A WEIGHT GREATER THAN A PREDETERMINED MAXIMUM TO PREVENT OPERATION OF THE LIFTING DEVICE IN A WEIGHT-LIFTING DIRECTION, AND MEANS MAINTAINING SAID SWITCH IN OPERATION-PREVENTING CONDITION UNTIL REDUCTION OF THE DEFLECTION OF THE SPRING MEANS CORRESPONDING TO REDUCTION OF THE IMPOSED WEIGHT TO A PREDETERMINED VALUE BELOW THE PREDETERMINED MAXIMUM.

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