US3208729A

US3208729A - Limit switch apparatus

Info

Publication number: US3208729A
Application number: US158270A
Authority: US
Inventors: Townsen Eugene Alexander
Original assignee: Lockheed Aircraft Corp
Current assignee: Lockheed Corp
Priority date: 1961-12-11
Filing date: 1961-12-11
Publication date: 1965-09-28
Anticipated expiration: 1982-09-28

Description

Sept. 28, 1965 E. A. TOWNSEN 3,208,729

LIMIT SWITCH APPARATUS Filed Dec. 11, 1961 2 Sheets-Sheet 1 Agent Sept. 28, 1965 A. TOWNSEN 3,208,729

LIMIT SWITCH APPARATUS Filed Dec. 11, 1961 2 Sheets-Sheet 2 FlG.5

IN VEN TOR.

EUGENE ALEXANDER TOWNSEN 2 Agent United States Patent 3,208,729 LIMIT SWITCH APPARATUS Eugene Alexander Townsen, Burbank, 'Calif., assignor to Lockheed Aircraft Corporation, Los Angeles, Calif. Filed Dec. 11, 1961, Ser. No. 158,270 3 Claims. (Cl. 254173) The present invention relates to limit switches and, more particularly, to a limit switch apparatus for preventing the overlap of a cable on a crane and hoist apparatus.

As is well-known, crane and hoist apparatus usually utilize a drum upon which a cable is spirally wound and unwound, such drum being powered by an engine or electric motor; The peripheral surface of the drum may he provided with circumferentially spiraled grooves into which the cable will fall when the cable is wound upon the drum so that the cable will be spirally wound without crossing or climbing or otherwise overlapping upon itself. Severe problems occur if the cable accidentally over-laps during the lifting operation. For example, such overlapping may cause the cable to break thus dropping the load or, during continued winding or subsequent unwinding, the overlapped portion of the cable may suddenly sli into its proper position on the drum, such slip causing a severe shock to the load which may either damage the load or cause the cable to break. Obviously, the breaking of a cable presents a serious hazard to both the load itself and any personnel who may be working in the area adjacent therebelow.

Therefore, it is one of the objects of the present invention to provide a limit switch for automatically stopping the drive means on a cable, crane and hoist apparatus when the cable is in an overlapping condition.

Another object of the present invention is to provide limit switch apparatus for automatically sensing a cable overlap condition for causing stopping of the cable drive means;

A further object of the present invention is the provision of apparatus .and method for automatically sensing a radial projection anywhere along the peripheral length of a relatively long cylindrical device.

According to the present invention, limit switch apparatus is provided for axially fixed disposition adjacent the peripheral surface of a cable drum along the length thereof and comprises a sensing bar member parallel to the drum axis and located a distance less than the diameter of the cable from the peripheral surface of the drum, such periphery being defined for the purposes hereof as the normal maximum radially outer location of the cable, a pair of rod members each having one end elfectively connect-ed to respective opposite ends of such sensing bar member and extending therefrom in a direction radial to the drum, and switch means coupled to the other ends of such rod members for actuation thereby, such switch means being connected into the control device for the drive means of the cable drum. In operation, overlapping of the cable upon itself at any point along the peripheral length of the cable drum will cause the overlapping portion of the cable to contact the sensing bar member and move either or both of the bar member ends in a radially outward direction, thus causing one or more of the rod members to be moved for I ctuating the switch means. If the overlapped condition occurs near the middle of the length of the sensing bar member, the rod members may be displaced substantially 3,208,729 Patented Sept. 28, 1965 equal amounts; if the overlapping occurs closer to one of the sensing bar member ends than the other, the corresponding rod member will be displaced a relatively greater amount but in any event, .at least one of the rod members will be displaced a distance at least equal to the abnormal projection distance of the cable, and such displacement of either or both of the rod members will cause actuation of the switch means.

In a preferred embodiment of the present invention, the switch means comprises a pair of switches of the microswitch type which are mechanically separate from each other but in electrical series, each switch having .a finger member pivoted at one end thereof and coupled to the corresponding rod member at the other end thereof, with a switch contact 'button located in abutment with the middle of such finger member for actuation by movement thereof.

The features of the present invention which are [believed to be novel are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings, in which:

FIGURE 1 is a perspective view of the cable drum portion of a crane and hoist apparatus showing a preferred embodiment of the present invention mounted thereon;

FIGURE 2 is an enlarged iiragmentary elevation View, partly in section, of the apparatus illustrated in FIGURE 1; and

FIGURE 3 is a further enlarged fragmentary elevation view showing the position of the apparatus when the cable is in an overlap position.

Referring to the drawings, a cable drum 10 is provided with a drum shield 111 having a cutaway bottom opening 12 to permit the cable 16 to move freely around the drum 10. In the embodiment illustrated, the drum 10 is provided with a spiral groove l1-4 for guiding the cable '13 in spiral progression from the left end '15 to the right end 16 of the cable-bearing portion of the drum 10. The groove I14 is divided along its spiral length by a ridge 17 of finite thickness to permit separation of each coil of the cable '13 along the drum surface. A pair of switches '18 and 19 are mounted on the exterior surface '20 of the drum shield 1 1 [by means of respective mounting blocks 21 and :22 which, in turn, are secured to the drum shield l1i1 by respective brackets 23 and Q4 which are welded or otherwise secured to the drum shield 11. Mounting blocks 21 and .2-2 have respective bores Q5 and 26 which are radial to the axis of the drum 10 and receive

respective rod members

27 and 28 there-through in freely slidabl-e relationship with sufficient clearance to permit a slight amount of lateral movement of the rods 27 and 2-8, as will be explained more fully herein-after. The drum shield 11 similarly is provided with

bore holes

29 and 30. The rod members .27 and .28 are provided with respective threaded ends 31 and 6'2 by which they are threadvably secured to

pivotal blocks

33 and 34, respectively.

Blocks

33 and 34 are disposed within respective apertures 35 and '36 near the

opposite ends

37 and 38 of a sensing bar member 3-9 which has a length at least equal to the cable-bearing axial length of the cable drum 10. The

blocks

33 and 34 are mounted to the sensing bar member 39 by

respective pivot pins

40 and 41 so as to rotate about axes tangential to the drum 10. The threaded

ends

31 and 32 of the rod members 27 and :28 are secured to the blocks I33 and 34 in a position eccentric to the pivot pins 40 and 441 so that tilt-ing of the sensing bar member 39 at an angle to the drum axis will cause the blocks 33 and '34 to rotate on their

respective pivot pins

40 and 41 to prevent undue lateral stress on the

rod members

27 and 28. The

rod members

27 and 28 are each provided with a plurality of stop means comprising lock nuts which will be described only in connection with rod member 28, as particularly seen in FIGURE 3, because of the symmetry of the apparatus.

Referring to FIGURE 3, the rod member 28 may be threaded over its entire length or, at least, from both of its ends a suflicient distance for the appropriate disposition of the various lock nuts which will be herein designated in pairs. Lock nuts 42 are secured to the rod member 28 so as to normally rest upon the mounting block 22 and provide an adjustment for the distance between the sensing bar member 39 and the cable drum 10. A spring 44 serves to provide shock absorption as well as to urge the sensing bar member 39 downwardly in opposition to the action of a spring 46 which is compressed between lock nuts 47 and a finger member 48 of the switch 19. Lock nuts 47 are tightened against spring 46 until the finger member 48 has depressed the push button 49 of the switch 19 to cause contact between the inner contacts (not shown) of the switch 19, the construction and the operation of the latter being well-known in the art. Then the lock nuts 50 are secured to the rod member 28 in a position of abutment against the finger member 48 so that, upon upward movement of the rod member 28 in response to sensing action of the sensing bar member 39, the lock nuts 50 will push the finger member 48 upwardly about its pivot pin 51 to release the push button 49 for opening the contacts of the switch 19.

The proximal edge or surface 52 of the sensing bar member 39 is adjusted by means of the lock nuts 42 on both of the

rod members

27 and 28 so as to be parallel to the plane of the radially outer extremities 53 of the cable 13, which plane constitutes the effective peripheral surface of the cable-drum apparatus, and spaced a distance therefrom less than any abnormal projection of the cable 13 y from thecable-drum 10, such projection being caused by series-connected

switches

18 and 19 is connected into the electricalcontrol system for the cable winding operation in any convenient and well-known manner so that, upon actuation of the cable overlap sensing mechanism to open either or both of the switches, the cable winding operation will immediately cease. Thus, as the cable 13 is wound upon the drum 10, the occurrence of an abnormal projection of a portion of the cable 13, such as is shown in FIGURE 3, will cause either or both of the ends of the sensing bar member 39 to be forcibly moved by such cable portion in a radially outward direction from the cable-drum to move either or both of the

rod members

27 and 28 upwardly whereby the lock nuts 50 will release the engagement of the finger member 48 from the push button 49 to open the contacts of the corresponding switch. Since the sensing bar member 39 is of a length at least equal to the cable-bearing length of the drum 10,

the sensing bar member 39 will be responsive to such abnormal projection of the cable 13 anywhere along such length. The maximum deflection of the push button 49 by the finger member 48 is chosen to be less than the minimum possible displacement of either of the

rod members

27 and 28 in response to any sensed abnormal projection of the cable 13.

If the sensed projection occurs nearer one rod member than the other, the sensing bar member 39 will be moved into a tilted position instead of perfectly parallel to its original position, and accordingly, the

blocks

33 and 34 will pivot about their

respective pivot pins

40 and 41 to permit the

rod members

27 and 28 to remain in their substantially vertical positions illustrated. However, the

rod members

27 and 28 may shift laterally a very slight amount without affecting the operation of the device, which shift amount is accommodated by the large clearance of the respective bores for the

rod members

27 and 28.

While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

What is claimed is:

1. Limit switch apparatus mountable adjacent and substantially parallel to the periphery of a cable accepting apparatus for sensing cable projections beyond the surface comprising: a sensing bar member including a longitudinal axis positioned adjacent the apparatus surface and such that projections from the peripheral surface cause movement of at least one end of said sensing bar in a direction substantially normal to the surface; a separate rod member connected to each end of said sensing bar member; pivotal mounting means being mounted on the bar member at right angles to the bar member longitudinal axis and coupled to one end of each rod member and thereby permitting pivotal movement of the rod member in a plane passing through the sensing bar member longitudinal axis facilitating such connection such that movement of one end of said sensing bar member and said rod member connected thereto results in substantially no misalignment of said rod members; and motion responsive means mechanically coupled to the other ends of said rod members for actuation thereby in response to said radial motion.

2. Limit switch apparatus, mountable adjacent the peripheral of a cylindrical apparatus which is rotatable about its longitudinal axis, for sensing a radial projection from such cylindrical apparatus anywhere along 'such peripheral length, such cylindrical apparatus being rotat ably driven by motor means, comprising: a sensing bar member positioned adjacent the peripheral surface of such cylindrical apparatus and parallel to the longitudinal axis thereof whereby the occurrence of a radial projection from such peripheral surface anywhere along the length thereof causes movement of at least one end of said sensing bar member in a direction radially outward from such cylindrical apparatus; a pair of rod members each having one end connected to respective opposite ends of said sensing bar member and oriented radially with respect to said longitudinal axis of such cylindrical apparatus whereby such radial movement of said at least one end of said sensing bar member causes a corresponding said rod member to move in a radial direction; and switch means mechanically coupled to the other ends of said rod members for actuation thereby in response to said radial motion, said switch means being in control relationship to said motor means for causing stopping thereof.

3. Limit switch apparatus, mountable adjacent the effective peripheral surface of a cable as it is wound upon a cylindrical drum which is rotatable about its longitudinal axis, for sensing a radial projection of such cable from its normal such peripheral surface anywhere along the length of the drum, such drum being rotatably driven by motor means, comprising: a sensing bar member positioned adjacent such pripheral surface and parallel thereto whereby the occurrence of a radial projection of such cable from such peripheral surface anywhere along the length thereof causes movement of at least one end of said sensing bar member in a direction radially outward from such cylindrical drum; a pivot member rotatably connected to respective opposite ends of said sensing bar member, a pair of rod members each having one end connected to one of said pivot members for movement independent of the other of said rod members and oriented radially with respect to said longitudinal axis of such cylindrical drum whereby such radial movement of said at least one end of said sensing bar member causes a corresponding said rod member to move in a radial direction with a minimum of stress being introduced into the said rod members; and separate switch means mechanically coupled to the other ends of each of said rod members for actuation thereby in response to said radial motion, said switch means being in control relationship to said motor means for causing stopping thereof.

References Cited by the Examiner UNITED STATES PATENTS SAMUEL F. COLEMAN, Primary Examiner.

5 HARRISON R. MOSELEY, Examiner.

Claims

1. LIMIT SWITCH APPARATUS MOUNTABLE ADJACENT AND SUBSTANTIALLY PARALLEL TO THE PERIPHERY OF A CABLE ACCEPTING APPARATUS FOR SENSING CABLE PROJECTIONS BEYOND THE SURFACE COMPRISING: A SENSING BAR MEMBER INCLUDING A LONGITUDINAL AXIS POSITIONED ADJACENT THE APPARATUS SURFACE AND SUCH THAT PROJECTIONS FROM THE PERIPHERAL SURFACE CAUSE MOVEMENT OF AT LEAST ONE SAID SENSING BAR IN A DIRECTION SUBTANTIALLY NORMAL TO THE SURFACE; A SEPARATE ROD MEMBER CONNECTED TO EACH END OF SAID SENSING BAR MEMBER; PIVOTAL MOUNTING MEANS BEING MOUNTED ON THE BAR MEMBER T RIGHT ANGLES TO THE BAR MEMBER LONGITUDINAL AXIS AND COUPLED TO ONE END OF EACH ROD MEMBER AND THEREBY PERMITTING PIVOTAL MOVEMENT OF THE MEMBER IN A PLANE PASSING THROUGH THE SENSING BAR MEMBER LONGITUDINAL AXIS FACILITATING SUCH CONNECTION SUCH THTAT MOVEMENT OF ONE END OF SAID SENSING BAR MEMBER AND SAID ROD MEMBER CONNECTED THERETO RESULTS IN SUBSTANTIALLY NO MISALIGNMENT OF SAID ROD MEMBERS; AND MOTION RESPONSIVE MEANS MECHANICALLY COUPLED TO THE OTHER ENDS OF SAID ROD MEMBERS FOR ACTUATION THEREBY IN RESPONSE TO SAID RADIAL MOTION.