US2727953A

US2727953A - Safety switch

Info

Publication number: US2727953A
Application number: US403898A
Authority: US
Inventors: Albert R Wilhelm
Original assignee: Individual
Current assignee: Individual
Priority date: 1954-01-13
Filing date: 1954-01-13
Publication date: 1955-12-20
Anticipated expiration: 1972-12-20

Description

Dec. 20, 1955 A. R. WILHELM 2,727,953

SAFETY SWITCH Filed Jan. 13, 1954 2 Sheets-Sheet 1 ZJYFM.

ATTORNEYS Dec. 2o, 1955 A. R. WILHELM 2,727,953

SAFETY SWITCH Filed Jan. 13, 1954 2 Sheets-Sheet 2 YIIIIIIIIIIIIIIIIIIII'III' L :@11. f -QI:

, v HHHHUWI INVENTOR ALBERT R. WTLHEIM ATTORNEYS United States Patent O SAFETY SWITCH Albert R. Wilhelm, Louisville, Ky. Application January 13, 1954, Serial No. 403,898 6 Claims. (Cl. 200-50) 'Ihis invention relates to safety devices particularly adapted for use in association with dual operation hoists of the type operable either electrically or manually at the option of the operator. It is an improvement over the structure disclosed in my prior Patent 2,404,153.

It is extremely important in the operation of the hoists commonly used in raising and lowering life boats that when the hoist is to be operated manually that it be irnpossible for the electrical system to be accidentally put into operation. As the hoists are manually operated by means of large heavy cranks which the operator must turn by using both hands, the accidental application of the electrical system will cause the crank to rotate at high speed, with the possibility of killing or seriously injuring the operator.

In the prior patent mentioned above, a safety device was disclosed which in one position blocked the end of the crank shaft so that the crank could not be applied and, at the same time, closed the electrical circuit. When the bar was moved from shaft blocking position, the electrical circuit was opened.

The present invention contemplates the provision of a similar safety device but of improved structure.

One of the objects of the invention is to provide a safety device of this character with improved means for operating they switch member upon movement of the hoist crank shaft locking bar arm.

Another object is the provision of such a device in which the switch member is biased toward closed position and positively opened whenever the locking bar arm is moved from hoist shaft blocking position.

A still further object is to provide a safety device in which the switch arm is cam actuated to permit quick action in making and breaking the circuit to prevent arcmg.

Other objects of the invention will become apparent from the following description of one practical embodiment thereof when taken in conjunction with the drawings which accompany, and form a part of, this specification.

In the drawings:

Figure l is a side elevation of a safety device embodying the principles of the present invention;

Figure 2 is a longitudinal horizontal section through the device taken on the line 2-2 of Figure l;

Figure 3 is an end elevation;

Figure 4 is a top plan view with the major portion of the switch housing cover plate broken away to show the interior mechanism; and,

Figure is a transverse of Figure 4.

Referring to the drawings in detail, the safety device comprises a switch housing 1, within which is mounted a switch 2, and to which is pivotally connected a locking bar arm 3 movable to and from a position adjacent the end of a crank shaft 4 of a hoist of the type which may be operated either electrically or manually as desired. Means are provided to open and close the switch upon movement of the locking bar arm to its various positions.

section taken on the line 5 5 The switch housing is a box-like member, which may be cast or formed in any other suitable manner, and is mounted upon a base 5 of channel shape bolted to the housing by the bolts 6 passing through openings in the base and in ears 7 projecting from the ends of the housing 1. The housing is closed by a cover plate 8 which is held in place by bolts 9 which pass through openings in matching ears projecting from the edges of the housing and cover plate.

Locking bar arm 3 is mounted upon a shaft 10 which extends transversely across the housing and is journalled in the side walls. One end of the shaft projects beyond the housing and the arm is securely fastened to it so as to rotate therewith. The arm 3 is shown as an elongated channel member having a pair of opposed openings in its side walls near one end to receive shaft 10. A U bolt 11 encircles the shaft and binds the arm tightly upon it. The locking bar arm is thus mounted for pivotal movement in a plane parallel to the side wall of the switch housing. Near its free end arm 3 carries a locking bar 12. This bar is in the form of a plate mounted against the open side of the channel forming the locking bar arm and is clamped to the arm by means of a U bolt 13. The locking bar is fixed to the arm so that it will project across the switch housing when the bar and arm are in inoperative position. By reason of this construction the switch housing may be mounted to one side of the hoist shaft in the horizontal plane of the shaft and when the bar and arm are in operative position the bar will extend across the end of the hoist shaft.

Positioned upon the shaft 16 centrally of the housing is a switch-actuating cam 14. The cam is fixed to the shaft by means of a set screw. The cam has a concentric portion 1S of reduced radius with respect to the balance of the cam terminating in outwardly extending shoulders, or faces 16 and 17, forming in effect a notch. T he shoulders cooperate alternately with a projection 18 which extends inwardly from the housing to limit the rotative movement of the shaft 10 and, consequently, determine the two extreme positions of the locking bar arm 3. The cam is positioned on the shaft so that one position of the locking bar arm will be perpendicular to the cover plate of the housing. It is in this position that the locking bar extends in front of the hoist crank shaft. The cam is provided with a second concentric portion 19 which rises from an eccentric portion 20. The shoulder formed between the

portions

19 and 20 serves to actuate the switch 2 to open and close the electric circuit to the hoist upon operation of the locking bar arm.

The switch is mounted upon an insulating base 21 screwed, or otherwise fastened against the base wall of the housing. Fixed contacts 22 are fastened upon the base and a pivoted switch arm 23 carries the contacts 24. The switch arm is pivotally mounted between the upstanding legs of a U bracket 25. The U bracket is screwed or bolted to the insulating base. The contacts 24 are mounted upon a metallic carrier 26 which is positioned transversely across the end of switch arm 23 and extends beyond the sides thereof. The contacts are made yieldable by mounting them upon the carrier with their stud ends extending through openings in the carrier plate. Springs 27 surround the shanks of the contacts between the carrier plate and the Contact heads and a pin, or cotter key, 28 is passed through the shank of the contact below the carrier plate to limit the outward movement of the contacts under the infiuence of the springs. This arrangement permits the contacts 24 to bear solidly upon the contacts 22 and compensate for any inequalities as to contact height. The switch arm is biased toward contact closing position by means of a coiled spring 29. The spring has one end anchored in the insulating base and the opposite end fastened to the switch arm between the contactsV and the pivotal point of the arm'. The spring may be fastened in any desired manner, but is shown as having its ends passed through openings in the insulating base and the switch arm and locked in position by pins which project through the end loops of the spring and bear upon the base and switch arm respectively. This permits easy assembly and quick repair when necessary. The end of the switch arm opposite the contacts bears upon the switch actuating cam 14. When the end of the switch arm contacts the high concentric portion of the cam the arm is rocked to separate the switch contacts and open the circuit controlling the electric system for the hoist. When the cam is rotated in a counterclockwise direction, as viewed in Figure 2, the end of the switch arm will move off of the high portion of the cam on to the shoulder between the high portion and the eccentric portion 2G. As the cam continues to rotate, the outer end of the switch arm can move with this shoulder, and spring 29 will draw the movable contacts against the Xed ones. Firm conv tact between 'the switch elements will be made when the shoulder 17 ot the cam is in contact with the projection 18. Reverse movement of the cam will cause the switch arm to move-on to the high portion of the cam and open the circuit. lt will be noted that due to the position of the shoulder 30 radial to the shaft 10 the entire movement of the switch arm is accomplished within a very small are of movement of the shaft and cam. This will cause the switch to open and close quickly and thus reduce arcing. 1

It will be noted that when the locking bar arm is in the position shown in full lines in Figure 2 that the switch will beV open. At this ltime the locking bar will be removed from blocking relation with respect to the hoist shaft. A crank may be readily placed upon the shaft of the hoist and the hoist operated by hand without danger of accidentally closing the electrical circuit. When the locking bar arm is moved to the dotted line position shown in Figure 2 it will block the hoist shaft so that the crank cannot be placed upon it. When the locking bar arm is in this position the switch is closed so that the hoist lmay be operated electrically.

In order to make the switch housing water-tight, a gasket 31 may be interposed between the housing and cover plate and the opening in the housing through which the shaft 10 projects may be sealed by a gasket 32 which encircles the shaft and bears against the side of the switch housing. A gasket bearing plate 33 may be placed against the gasket and held firmly in place by a spring 34 mounted'on the shaft 10 between the cam 14 andthe bearing plate 33.

It is desirable that the locking bar arm be xed in its two positions so as to be immovable. For this purpose ears 35 are provided on the housing cover plate and a locking plate 36 is welded or otherwiseksecured to the locking bar arm 3. The locking plate is provided with openings 37 which are arcuately spaced apart a distance equal to the arc of movement of the locking bar arm so that one of the openings will be in alignment with the openings in the ears 35 when the locking bar arm is in either of its two positions. A locking pin 38 may be inserted through the ears 35 and the selected opening 37 in the locking plate to hold the locking bar arm in desired position.

It will be noted that the construction disclosed herein is very simple and the various parts may be readily assembled. The arrangement shown provides for positive opening of the switch whenever the locking bar arm is i moved away from the hoist shaft. This is highly desirable, for with this construction there can be no possibility of the switch sticking in closed position.

While in the above one practical embodiment of the invention has been disclosed, it will be understood that the details of construction shown and described are merely by way of example and that changes may be made from the precise structure disclosed within the scope of the appended claims.

What is claimed is:

1. In a safety switch for a dual operation hoist having a crank-shaft for manual operation and an electric circuit including a motor for electrical operation, a housing for mounting adjacent said crank-shaft, a switch in said housing and connected in said circuit, said switch having a iixed contact and a movable Contact, a switch arm carrying said movable contact at one end and pivoted for swinging movement, means to bias said switch arm toward contact-closing position, a shaft journalled in said housing and projecting beyond said housing, a switch cam fixed on said shaft and in contact with said switch arm, said camV having a dwell to permit said switch contacts to close when said cam is rotated in one direction, and a rise to separate said contacts when said cam is rotated in an opposite direction, and a locking 4bar arm Xed on the projecting portion of said shaft and movable to and from a position blocking the end of said crank-shaft, said cam and locking bar arm being mounted upon saiclv shaft so that when said locking bar arm is in crank-shaft blocking position said switch arm will be in contact with the dwell of said cam and said switch will be closed. j

2. In a safety switch as claimed in claim 1, said cam having a recess terminating in shoulders at the ends and a stop pin projecting from said housing to contact said shoulders alternately to limit the rotation of said cam to position said locking bar arm in crank-shaft blocking position when the cam is rotated in one direction and to open said switch when the cam is rotated in an opposite direction.

3. In a safety switch as claimed in claim 1, one of said contacts having a resilient mounting to ensure solid contact between them.

4, In a safety switch as claimed in claim 1, said shaft being positioned normal to the plane of swinging movement of said switch cam, and said cam lying and rotating in said plane.

5. In a safety switch as claimed in claim 1, said shaftl v being positioned normal to the plane of swinging movement of said switch arm, said cam lyingV and rotating in said plane, companion means carried by said housing and said locking bar arm to permit locking said bar in its two positions.

6. In a safety switch as claimed in claim 1, a cover for said housing, a gasket between said housing and cover, a sealing gasket about said shaft within said housing adjacent the side of said housing through which said shaft projects, and a spring about said shaft bearing against said cam and said sealing gasket to press the sealing gasket into sealing relation with said side of the housing.

References Cited in the le of this patent UNITED STATES PATENTS 2,197,251 De Chime Apr. 16, 1940 2,404,153 Wilhelm `Iuly 16, 1946 2,423,361 Wood July 1, 1947 2,644,047 Leonard June 30, 1953