US3768594A

US3768594A - Gravity lock for extension ladders

Info

Publication number: US3768594A
Application number: US00270514A
Authority: US
Inventors: H Kramer
Original assignee: KRAMER ENTERPRISE Inc
Current assignee: KRAMER ENTERPRISE Inc
Priority date: 1972-07-10
Filing date: 1972-07-10
Publication date: 1973-10-30
Anticipated expiration: 1990-10-30

Abstract

A gravity lock for extension ladders, said gravity lock comprising a pair of side struts and a cross-bar which are interconnected to form an A-frame, the lower ends of said side struts being bent inwardly toward each other to form rungengageable hook elements. Where necessary, a flipper is attached to one of said hook elements. By changing the dimensions of the side struts and cross-bar and the angle between them, the gravity lock may be applied in different ways to different kinds and sizes of extension ladders. In one form of the invention, there is a single cross-bar and it is attached to the side struts; in another form of the invention, there are two cross-bars and each is integral with one of the side struts.

Description

Kramer Oct. 30, 1973 GRAVITY LOCK FOR EXTENSION LADDERS Primary Examiner-Reinaldo P Machado Att0rneySamuel J. Stoll et al.

[57] ABSTRACT A gravity lock for extension ladders, said gravity lock comprising a pair of side struts and a cross-bar which are interconnected to form an A-frame, the lower ends of said side struts being'bent inwardly toward each other to form rung-engageable hook elements. Where necessary. a flipper is attached to one of said hook elements. By changing the dimensions of the side struts and cross-bar and the angle between them, the gravity lock may be applied in different ways to different kinds and sizes of extension ladders. In one form of the invention, there is a single cross-bar and it is attached to the side struts; in another form of the invention, there are two cross-bars and each is integral with one of the side struts.

4 Claims, 13 Drawing Figures PAIENTEDUBIBO I973 13. 768,594

SHEET 10F 3 GRAVITY LOCK FOR EXTENSION LADDERS BACKGROUND OF THE INVENTION 1. Field of the Invention Extension ladders comprising ground and fly sections and gravity locks which support the fly sections in extended positions on the ground sections.

2. Description of the Prior Art The closest art known to applicant is applicants own U.S. Pat. No. 3,556,253, issued Jan. 19, 1971. However, the gravity lock disclosed and claimed therein does not have the capacity for adjustment to the requirements of extension ladders of different kinds and dimensions.

SUMMARY OF THE INVENTION The present invention provides a gravity lock for extension ladders, wherein the gravity lock comprises a pair of side struts and a cross-bar which interengages the struts to form an A-frame, the lower ends of the struts below the cross-bar being bent inwardly toward each other to form rung-engageable hooks. A flipper may be pivotally connected to one of said hooks for swingable movement into engagement with the other of the said hooks.

It will be understood that the gravity lock may be pivotally mounted on the fly section of the extension ladder for supporting engagement with the tread portion of the rungs of the ground section of the ladder or, alternatively, it may be pivotally mounted on the ground section of the ladder for supporting engagement with the undersides of the rungs of the fly section. In the former case, the A-frame is right-side up; in the latter case, it is upside down. Also, the cross-bar may be lengthened to span the width of two rungs (of both the fly and ground sections of the ladder) or it may be shortened to engage only a single rung (of either the fly or ground sections of the ladder). By the same token, the cross-bar may be lengthened or shortened, depending upon the width of the rungs of.the ladder. The angle between the side struts will be adjusted accordingly.

It will also be understood that the present gravity lock is adjustable in other respects. Thus, either strut (or both struts).may be lengthened r shortened, depending upon the requirements of individual types and sizes of extension ladders. The cross-bar may be tilted in either direction relativeto the side struts, thereby changing the base angles accordingly (the angles be tween the struts and the cross-bar). This form of adjustment may be required for mounting the gravity lock on the ground section, rather than the fly section (or vice versa) of the ladder, and depending on the location of the mounting connections relative to the rungs of the ladder.

The foregoing remarks apply to all forms of the present invention, including the form in which there are two cross-bars and each is integral with one'of the side struts. In the latter case, the two cross-bars are interconnected to form the effective structural and functional equivalent of a single cross-bar. There are substantial advantages in the design in which the cross-bars are integral with the side struts, for example, in enhanced structural strength, smoother performance, lessened abrasive effect upon the rungs of the ladder, and simpler, less costly construction. However, as in the case of all other forms of the invention, this design (in which the cross-bars and struts are integrally connected) provides the various adjustment features above described. Its struts may be lengthened or shortened, its cross-bars may be lengthened or shortened, and the angles between the struts, and between the struts and the cross-bars, may be varied as required by each individual application.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a front view of a ladder embodying a gravity lock made in accordance with one form of the invention, said gravity lock being shown mounted on the fly section of an extension ladder, which fly section is slidably disposed on the back of the ground section of the ladder.

FIG. 2 is a longitudinal section therethrough on the line 22 of FIG. 1.

FIG. 3 is an enlarged perspective view of said gravity lock.

FIG. 4 is an enlarged fragmentary transverse section on the line 44 of FIG. 1.

FIG. 5 is a fragmentary view showing a detail of the gravity lock.

FIG. 6 is a fragmentary longitudinal section showing a gravity lock made in accordance with a second form of this invention, mounted on the fly section ofa differ ent kind of extension ladder wherein the fly section is slidably disposed in front of the ground section.

FIG. 7 is an enlarged fragmentary sectional view showing the fly section of the ladder being raised and the gravity lock sliding against one of the rungs of the ground section of the ladder.

FIG. 8 is a view similar to that of FIG. 7, but showing the fly section being lowered and showing the flipper of the gravity lock in closed position to enable the gravity lock to slip past the rungs of the ground section of the ladder.

FIG. 9 is an enlarged fragmentary section showing the bracket support for the gravity lock on the ladder.

FIG. 10 is an enlarged fragmentary section showing the details of the flipper.

FIG. 11 is an enlarged fragmentary transverse section showing a gravity lock made in accordance with a third form of the invention, said gravity lock being mounted on the fly section of a ladder corresponding to the ladder shown. in FIG. 6.

FIG. 12 is a vertical section on the line l2-l2 of FIG. 11.

FIG. 13 is an exploded perspective view showing the component parts of the gravity lock of FIGS. 11 and 12.

DESCRIPTION OF PREFERRED FORMS OF THE INVENTION FIGQ 1 of the drawing illustrates a representative extension ladder 10 of conventional aluminum construction, but it will be clearly understood that the invention is not limited to application to ladders made of aluminum or to the particular ladder design shown in the drawing. It is applicable to all forms of extension ladders, whether made of aluminum, magnesium, wood or any other conventional ladder material.

Extension ladder 10 comprises a ground section 12 (sometimes called base section), a movable fly section 14 which is slidably mounted on the ground section, and a pair of gravity-actuated

locks

16 and 18 which interengage the two ladder sections to support the fly section in extended position on and relative to the ground section. As is conventional, ground section 12 consists of a pair of left and

right side rails

12a and 12b, respectively, and a plurality of rungs supported thereby. Similarly, fly section 14 consists of a complementary pair of left and right side rails 14a and 14b, respectively, and a plurality of rungs 22 supported thereby.

Referring now to gravity lock 16, it will be noted that it comprises a pair of supporting

struts

30 and 32, and a cross-bar 34 which interconnects said struts. In this particular design, a flipper 36 is pivotally connected to strut 32.

More specifically, strut 30 comprises a generally straight shank 30a, a bent or-curved portion 30b at its lower end, and a widened (press-formed) upper end portion 30c having a hole formed therein to receive a fastener such as bolt 38. Strut 32 also consists ofa gen erally straight shank 32a, a bent or curved portion 32b at its lower end, and a widened (press-formed) upper end portion 320 having a hole formed therein to receive said bolt 38. When a flipper is used, lower end 32b will have a hole formed therein to receive a second fastener such as rivet 40.

Bolt 38 interconnects upper portions 30c and 320 of the two struts and it also pivotally attaches said struts (together with the other elements of the gravity lock) to rail 14a of fly section 14 of the ladder. A bracket 39 helps secure said bolt to said rail and support it in perpendicular relation thereto. If desired, a bushing or spacer 39a may be placed on bolt 38 between bracket 39 and rail 14a. It will be observed that

struts

30 and 32 are pivotally supported by bolts 38 (and bushing or spacer 39a, if used) and a washer or spacer 3912 may be used to enable said struts to clear the adjacent flanges of said rail 14a.

In the preferred form of the invention,

struts

30 and 32 are round rods made of aluminum or other suitable material, such as steel or iron. Bracket 39 is also made, preferably, of aluminum, but it may be made of other materials such as steel or iron.

In the preferred form of the invention, cross-bar 34 is a flat aluminum bar (but it may be made of other suitable material such as steel or iron) with a pair of double-ended keyhole-shaped holes 34a and 34b formed therein adjacent its ends to receive

struts

30 and 32. It will now be observed that

struts

30 and 32 are pinched above and below cross-bar 34 to form

embossments

30d and 32d thereon.-These embossments prevent the struts and cross-bar from shifting relative to each other. Holes 34a and 34b in said cross-bar are shaped like double-ended keyholes to enable the struts to thread through them despite the presence of said embossments. After the struts are threaded through said holes, the' struts are turned 90 and the embossments are thereby moved out of phase or registration with the keyhole extensions of the holes. The struts are now locked to the cross-bar.

It will now be evident that the cross-bar functions as a tie between the struts,- and when their upper ends are held togetherby .bolts 38, the entire assembly defines an A-frame wherein the struts are its sides and the cross-bar is its cross-piece. The lower ends 30b and 32b of said struts are bent or curved inwardly toward each other to form a pair of hook-shaped elements adapted to engage

rungs

20 and 22 of the two sections of the ladder between them.

Referring now to flipper 36, it will be understood that it may take many forms and that the form shown in the drawing is merely illustrative. Thus, flipper 36 is made of flat sheet (strip) material folded over to define a channel section 36a and remaining unfolded at its lower end to define a generally flat, preferably curved end piece 36b. The upper end of the channel section provides a shoulder 36c which engages the bent or curved portion 32b of strut 32 and positions the flipper relative to the rungs of the ladder.

Thus far, the invention has been described in terms of the extension ladder shown in FIG. 1 of the drawing. In that Figure, the ground section of the ladder is shown in front of the fly section, that is, the fly section is situated between the ground section and the building or other support against which the ladder rests when in use. In such case, when gravity lock 16 is in locked position to support the fly section in extended position relative to the ground section, cross-bar 34 bears against a pair of

rungs

20 and 22 of the two ladder sections (mainly against rung 20). The load of the fly section and of a person standing thereon is thereby supported on rung 20 of the ground section, being transmitted thereto through bolt 38 and the gravity lock. Inwardly bent end portions 30b and 32b of the struts function as hooks around

rungs

20 and 22 and prevent displacement of the gravity lock from said rungs.

In the following description of the operation of the first form of the invention, a torsion spring 46 around bolt 38 urges the gravity lock forwardly, that is, in the direction away from the wall or other vertical surface against which the ladder is inclined. This spring bias brings strut 30 of the gravity lock into engagement with rungs 20 of the ground section, as will shortly be described.

In the operation of this device, the ladder is placed on the ground or other horizontal support 50 in inclined position against the side wall of a building or other support 52 and pull rope 54 is pulled to raise fly section 14. If necessary, the ladder is tilted slightly away from the building to facilitate extension of said fly section. As the fly section rises, struts 30 of the gravity locks will engage successive rungs 20 of the ground section of the ladder, under the bias of springs 46, and the gravity locks will thereby be cammed rearwardly (toward wall 52) against the spring action. As each rung 20 is passed, the gravity locks are swung forwardly (away from wall 52) under the action of springs 46 and into overlapping or overriding position relative to the rung.

When the desired extension has been achieved, that is, when the gravity locks are elevated above the particular ground section rung 20 on which they are to be supported, the fly section is permitted to drop sufficiently to seat cross-bars 34 of the two gravity locks upon'said rung. The fly section will now be securely supported by the ground section in extended position.

When it is desired to lower the fly section, it is temporarily raised to disengage the gravity locks from the rung 20 on which they rested. The ladder is then tilted forwardly (toward the vertical) to a slightly smaller angle of inclination relative to wall 52 and the flippers thereupon swing forwardly to a position wherein they 1 will engage rungs 20. The fly section of the ladder is now lowered, and as each rung 20 is engaged by the flippers they are swung upwardly into engagement with curved end portions 30b of struts 30 of the two gravity locks. The flippers now function as earns (or cam followers) with respect to said rung 20, and the two gravity locks are thereby cammed rearwardly to by-pass the said rung and they will then intermittently engage and bypass all successive rungs 20 as the fly section continues its downward movement. When the fly section reaches its desired level, the ladder is again tilted back to its original angle of inclination relative to wall 52. This will cause the flippers to swing out of range of rungs 20 and further downward movement of-the fly section relative to the ground section will be blocked by engagement of the gravity locks with the'next rung 20 to be reached. A

In the second illustrated form of the invention, gravity locks 100 are shown appliedto an extension ladder 102 wherein the fly section 104 is forward of the ground section 106. As shown in the drawing, ground section 106 supports the ladder on the ground 108 and said ground section is disposed between the fly section and the vertical wall 1 or other support against which the ladder is inclined.

In this form of the invention there is no need of spring bias to properly position the gravity locks relative to rungs 112 of the-ground section. Gravity locks 100 are 'pivotally mounted on side rails 104a of the fly section by means of bolts 114 and brackets 116. As is the case with the gravity lock first above described, gravity locks 100 comprise a pair of

struts

100a and 100b, said struts having inwardly bent or curved lower end portions 100C and 100d, respectively, a cross-bar 100e and a flipper 100f.

It will be noted that the struts and cross-bar define an A-frame of somewhat different shape from the A-frame of the gravity lock 16 first above described. The reason is that whereas gravity locks 16 are mounted on the rearwardly disposed fly section of extension ladder 10, gravity locks 100 are mounted on the forwardly disposed fly section of extension ladder 102. In the case of gravity locks 16, a spring is used to urge them forwardly into engagement with rungs of the forwardly disposed ground section. In the case of gravity locks 100, gravity alone swings them rearwardly into engagement with rungs 112 of the rearwardly disposed ground section.

Gravity locks 16 and 100 illustrate the versatility and adaptability of the present invention. Its struts may be lengthened or shortened, as required by each individual ladder design. So may the cross-bar. By the same token, the angle between the struts, and between the struts and the cross'ban may be varied to adapt the gravity lock design to the manner of its application to the ladder (e.g., whether mounted on the forward or rearward section) and to other factors.

Other variations are encompassed within the scope of the present invention. For example, it would be sufficient if the cross-bar were shortened to engage the rungs of the ground section alone. Also, the gravity locks may be mounted on the ground section, instead of the fly section, of the ladder. In such case, the gravity locks would be inverted so that their cross-bar would engage the underside of the ladder rungs (mainly the rungs of the fly section) to support the fly section in elevated position relative to the ground section.

Referring now to the form of the invention wherein there are two cross-bars and they are integral with the side struts (FIGS. 11-13 of the drawing), it will be seen that gravity lock 150 comprises a pair of side struts 152 and 154, a cross-bar 152a which is integral with strut 152, an inwardly bent or curved hook element 152b which is integral with cross-bar 152a, a second crossbar 154a which is integral with strut 154 and a second hook element 154b which is integral with said second cross-bar 154a. A flipper 156 may be pivotally connected to hook element 154b.

It is evident from the foregoing that, apart from flipper 156, gravity lock consists of only two parts, one comprising strut 152, cross-bar 152a and hook 152b, and the other comprising strut 154, cross-bar 154a and hook 154b. However, these two parts define an A- frame of substantially the same configuration as the three-part designs previously described.

The two parts of the embodiment of the invention now under discussion may be assembled in any conventional way. One method is to swage the upper end and cross-bar sections of each component so that the combined thicknesses of these sections will approximate the'unswaged thickness of each part. The result will be that, although the two parts are secured in side-by-side relationship at their upper end and cross-bar sections, the over-all thickness of the entire gravity lock assembly will not substantially exceed, if at all, the single thickness of the rod material from which the parts are made.

It will be understood from the foregoing that a gravity lock 150 made, for example, of% inch round rod, will be swaged down to 3/16 inch thickness at the upper end and cross-bar sections. Consequently, when upper end portions152c and 1546 of

struts

152 and 154 are swaged, punched, and joined by means of bolt 158, their combined thickness is inch. So, too, when cross-bar portions 152a and 154a are swaged and joined (by rivets 160 or staples or otherwise), their combined thickness is also inch.

Gravity lock 150 may be attached to the fly section of an extension ladder, whether the fly section is mounted in front of or behind'the ground section, and it may be attached to the ground section, also regardless of whether itis disposed in front of or behind the fly section. In short, this is a versatile gravity lock; since it may be adapted to the individual requirements of any kind or size of extension ladder by lengthening or shortening either or both of its struts, lengthening or shortening its cross-bar members, and enlarging or narrowing the angles which define the triangular top of the A- frame.

I claim:

1. A gravity lock comprising:v

a. a two-piece A-frame consisting of:

b. a first load-bearing strut, cross-bar element and rung-engageable hook,

c. one end of said strut being integral with one end of the cross-bar element, and the rung-engageable hook being integral with the opposite end of the cross-bar element, and

d. a second'load-bearing strut, cross-bar element and rung-engageable hook,

e. one end of said second strut being integral with one end of the second cross-bar element, and the second rung-engageable hook being integral with the opposite end of the second cross-bar element,

f. the opposite ends of said first and second struts being interconnected to form the sides of the A- frame, and

g. said first and second cross-bar elements being interconnected in side-by-side:relationship to form the cross-piece of the A-frame.

2. A gravity lock in accordance with claim 1,

wherein: I

a. the first mentioned ends of the two load-bearing struts which are integral with their respective crossbar elements are the lower ends of said struts, and

b. the opposite ends of said load-bearing struts which are interconnected to form the sides of the A-frame are the upper ends of said struts.

3. A gravity lock in accordance with claim 1,

wherein:

a. a flipper is pivotally connected to one of said rungengageable hooks for swingable movement into engagement with the other of said rung-engageable hooks,

b. whereby the space between the two hooks is bridged to prevent entry of a ladder rung,

c. the outer surface of said flipper defining a cam surface which is engageable with the rungs on the other of said ladder sections to cam the A-frame away from them during descent of the fly section relative to the ground section 4. A gravity lock in accordance with claim 3, wherein the flipper comprises:

a. a one-piece stamped and formed element;

b. one end of said element being bent longitudinally of the element to form a generally U-shaped configuration in cross-section to wrap partially around the hook to which it is attached;

c. the opposite end of said element comprising a curved tongue adapted to provide a cam surface engageable with the rungs of said other section of the extension ladder.

Claims

1. A gravity lock comprising: a. a two-piece A-frame consisting of: b. a first load-bearing strut, cross-bar element and rungengageable hook, c. one end of said strut being integral with one end of the cross-bar element, and the rung-engageable hook being integral with the opposite end of the cross-bar element, and d. a second load-bearing strut, cross-bar element and rungengageable hook, e. one end of said second strut being integral with one end of the second cross-bar element, and the second rung-engageable hook being integral with the opposite end of the second crossbar element, f. the opposite ends of said first and second struts being interconnected to form the sides of the A-frame, and g. said first and second cross-bar elements being interconnected in side-by-side relationship to form the cross-piece of the Aframe.

2. A gravity lock in accordance with claim 1, wherein: a. the first mentioned ends of the two load-bearing struts which are integral with their respective cross-bar elements are the lower ends of said struts, and b. the opposite ends of said load-bearing struts which are interconnected to form the sides of the A-frame are the upper ends of said struts.

3. A gravity lock in accordance with claim 1, wherein: a. a flipper is pivotally connected to one of said rung-engageable hooks for swingable movement into engagement with the other of said rung-engageable hooks, b. whereby the space between the two hooks is bridged to prevent entry of a ladder rung, c. the outer surface of said flipper defining a cam surface which is engageable with the rungs on the other of said ladder sections to cam the A-frame away from them during descent of the fly section relative to the ground section.

4. A gravity lock in accordance with claim 3, wherein the flipper comprises: a. a one-piece stamped and formed element; b. one end of said element being bent longitudinally of the element to form a generally U-shaped configuration in cross-section to wrap partially around the hook to which it is attached; c. the opposite end of said element comprising a curved tongue adapted to provide a cam surface engageable with the rungs of said other section of the extension ladder.