BACKGROUND OF THE INVENTION

The present invention relates to fastener- driving tools, also known as

power nailers, which are typically powered by combustion, pneumatics,

electricity, are powder-activated or otherwise powered. In such tools, a plurality

of fasteners are sequentially arranged in a magazine and are urged by a biased

follower toward a driving end of the magazine where the fasteners are each pushed

into a nosepiece. Once in the nosepiece, the fasteners are driven into a workpiece

by a reciprocating driver blade.

A design criterion of most such tools is that the tool should be

disabled when the magazine is empty of fasteners. So-called "dry firing" or

"blank firing" generates significant stresses in the tool and can damage the

workpiece or the tool itself. Indicator mechanisms are known in such tools to

indicate to the user when the magazine is empty or almost empty, so that the

magazine can be refilled prior to a dry firing condition. In some of these known

mechanisms, once a magazine follower reaches a preset point where a relatively

few fasteners remain in the magazine, the tool is disabled by locking a workpiece

contact element to prevent dry firing.

While the prevention of dry firing is common to many types of

fastener-driving tools, it is particularly challenging when the fasteners are finish

nails, which typically are provided in stamped strips. The problems associated

with driving such fasteners are described in commonly assigned U.S. Patent No.

6,176,412 which is incorporated by reference. Each fastener is relatively thin, and

this reduced thickness results in a relatively small increment of movement of the

follower upon the driving of each fastener. Thus, it is difficult to design a tool

using such fasteners to effectively alert the user when the magazine needs

refilling.

A related design problem is that visual indicator systems for

preventing dry firing require attention by the operator for effectiveness. If the user

is understandably preoccupied with driving fasteners, the status of the magazine

may be overlooked, resulting in a dry firing situation due to an empty magazine.

In some cases, audible warning systems may also be overlooked when the user is

concentrating on fastener application.

A related design issue is that in some cases, leftover fastener strip

segments are prone to "tumble" or become misaligned within the magazine. Such

segments can cause the tool to jam, especially in applications where the nail

follower or pusher in the magazine fails to strongly urge the fasteners toward the

nosepiece. This problem is especially severe when plastic collated fasteners are

used. Since the plastic collation media is relatively brittle, the tendency is for the

fasteners to become detached from the media and tumble around inside the

magazine.

Thus, there is a need for providing a power nail feeding mechanism

for a fastener-driving tool which prevents the tumbling or misalignment of

fastener strip segments within the magazine. There is also a need for providing a

power nail feeding mechanism for such a tool which prevents jams in either the

magazine or the nosepiece due to stray or misaligned fastener strip segments.

There is also a need for a more effective system for preventing dry firing in fastener-driving tools .

BRIEF SUMMARY OF THE INVENTION

The above-listed objects are met or exceeded by the magazine

follower for a fastener-driving tool, wherein the follower is configured to block

downward movement of the driver blade after the driving of the last fastener in a

strip or in the magazine. By completely emptying the magazine before blocking

tool operation, the problems created by stray or misaligned fastener strip segments

and associated collating strip material are reduced.

More specifically, in a fastener- driving tool with a magazine, a

nosepiece, and a driver blade slidably reciprocating relative to the nosepiece for

driving fasteners, a mechanism for preventing jamming includes a follower

slidably disposed inside the magazine for urging fasteners toward the nosepiece,

and having a formation for engaging the driver blade and preventing driver blade

reciprocation after the last fastener in the magazine has been driven.

In another embodiment, a fastener-driving tool includes a magazine

having a first end for receiving fasteners, a second end for delivering fasteners for

driving, and a guide channel. A nosepiece defines a fastener passage slot in

communication with the magazine for receiving fasteners from the second end,

and a driver blade path in communication with the slot. A driver blade slidably

reciprocates in said driver blade path for driving fasteners. A follower is slidably

disposed inside the magazine and has a first portion for urging fasteners toward

the nosepiece and a second portion for engaging the driver blade and preventing

driver blade reciprocation after the last fastener in a fastener strip has been driven.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a rear perspective elevation of a fastener-driving tool of the

type which is suitable for use with the present invention;

FIG. 2 is an enlarged, fragmentary side elevation of the tool shown

in FIG. 1 with portions omitted for clarity; and

FIG. 3 is an enlarged fragmentary front perspective of the tool of

FIG. 1 , with portions omitted for clarity.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGs. 1 and 2, a fastener-driving tool suitable for

use with the present lockout mechanism is generally designated 10. While the tool

10 is depicted as a pneumatic tool, it is contemplated that the present mechanism

may also be utilized with combustion-powered, powder, electric-powered, or any

other power sources for fastener tools, provided they employ a magazine for

sequentially feeding fasteners to a nosepiece or equivalent structure where they are

impacted by a driver blade for driving action into a workpiece. The tool 10

includes a housing 12 enclosing a fastener driving portion 14 which includes a

reciprocating driver blade 16 traveling in a driver blade path 18 in a nosepiece 20

for driving fasteners into a workpiece as is known in the art.

A magazine 22 is associated with the housing 12 and has a first or

feed end 24 and a second or driving end 26, the latter closer to, and connected to

the nosepiece 20 for feeding fasteners (not shown) contained within the magazine

toward the driver blade path 18. As is known in the art, the fasteners are

preferably provided in strips, with adjacent fasteners temporarily secured to each

other with chemical adhesives, tape or plastic collator strips. A disadvantage of

conventional tools is that the last few remaining fasteners in a strip, and/or collator

strips or other adhesive materials often become jammed in the magazine 22 and/or

the nosepiece 20.

The fasteners are inserted into the magazine 22 at the feed end 24

through a slot 28 as is well known in the art. In some tools, the slot 28 is provided

in an endcap which in turn is secured to a main magazine body. A handle 30 is

connected to the housing 12 between the fastener-driving portion 14 and the feed

end 24 of the magazine 22. In some embodiments, the handle 30, the magazine 22

and the fastener- driving portion 14 of the housing 12 are integrally formed. It is

also contemplated to have the handle 30 and the fastener-driving portion 14

integrally formed, with the magazine 22 a separate component.

Referring again to the magazine 22, a fastener track 32 is defined for

enabling the passage of the fasteners toward the nosepiece 20. In a preferred

embodiment, the fastener track 32 is partially defined by opposing halves 34, 36 of

the magazine 22. Unitary magazines are also contemplated. An interior of an

upper portion 38 the magazine 22 appears generally 'T'-shaped in cross section,

with a generally vertical leg 39 formed by the fastener track 32, and a generally

horizontal leg 40 formed at an upper end of the fastener track, the leg 40 also

referred to as a guide channel. The guide channel 40 is in communication with the

vertical leg 39 and is used to slidably receive heads of the fasteners for guiding

them towards the second or driving end 26 of the magazine 22. Elongate shank

portions of the fasteners slide in the vertical leg 39.

Referring now to FIGs. 2 and 3, the nosepiece 20 includes a shear

block 42 defining a fastener passage slot 44 which is in communication with the

fastener track 32 of the magazine 22, and is also in communication with the driver

blade path 18. Depending on the configuration of the particular tool, the

nos-epiece__2D-_and._the_ she_ar_ block__44_ may beja single component, or may be

separate pieces. Thus, fasteners are fed from the magazine 22, through the

passage slot 44 into the driver blade path 18, where they are impacted by the

driver blade 16, which sequentially separates each fastener from the strip as it is

driven.

A follower 46 is slidably disposed in the magazine 22 and is subject

to a biasing force provided by a spring 48 (shown hidden) or the like, so that the

follower urges the fasteners towards the nosepiece 20, and more specifically,

toward the passage slot 44. As is well known in the art, one end of the spring 48 is

connected to the magazine 22.

The follower 46 includes a first or front edge portion 50 for

engaging the fastener strip, and a second portion 52 for slidably engaging the

guide channel 40. The second portion 52 laterally expands past the first portion

for stabilizing the sliding travel of the follower 46 in the magazine 22. As such,

the follower 46 is generally ^ς 'T"-shaped when viewed from the front.

A follower handle 54 is provided to the follower 46 for facilitating

the pulling of the follower 46 against the force of the spring 48 toward the feed

end 24. As is known in the art, a shoulder or step (not shown) is formed in the

fastener track 32 for holding the follower 46 in place while fasteners are inserted

into the fastener track. Other equivalent devices known in the art are

contemplated for temporarily securing the follower 46 in position in the fastener

track 32.

An important feature of the present mechanism for preventing

jamming is that the second portion 52 of the follower 46 is also configured for

engaging the driver blade 16, thus preventing driver blade reciprocation after the

last fastener in a fastener strip, or the last fastener in the magazine, has been

driven. In addition, the follower 46 is constructed and arranged so that the front or

leading edge 50 enters the passage slot 44 when the last fastener is driven.

Referring now to FIGs. 2 and 3, it will be seen that the driver blade

16 has a lower end 56. Once the driver blade 16 returns to a pre- firing position,

and upon the driving of the last fastener in the magazine, the leading edge 50 of

the follower 46 projects or extends into the nosepiece 20, specifically into the

fastener passage slot 44, and the second portion 52 is disposed in close proximity

to the driver blade's lower end 56. More specifically, the lower end 56 of the

driver blade 16 is preferably disposed approximately 0.025 to 0.10 inch from an

upper surface 58 of the second portion 52, and most preferably 0.05 inch from the

lower end, however other spacing is contemplated depending on the situation. By

providing a relatively short distance between the lower end 56 and the second

portion 52, in the event the tool 10 is fired after the last fastener in the magazine

has been driven, the energy of impact of the driver blade against the second

portion is insignificant, and does not damage the follower 46.

The second portion 52 is slidably retained in the guide channel 40.

To support the follower 46 against the impact force of the driver blade 16, the

shear block 42 has_anjrrjper edge_6JL^nd_a lower edge_62 of ^" the _secondj)o_rtion 52

slidably engages the upper edge once the last fastener is driven. This engagement

provides a back-up support for the second portion 52 against the momentum of the

driver blade 16.

It will be seen that a front edge 64 of the second portion 52 extends

farther into the driver blade path 18 than the first portion or leading edge 50 of the

follower 46. Also, both the first and second portions 50, 52 extend into the driver

blade path 18 after the last fastener in the magazine has been driven.

In operation, the follower 46 urges fasteners toward the shear block

42, where they are sequentially driven by the driver blade 16. Once the last

fastener has been driven, the leading edge 50 and the second portion 52 of the

follower 46 extend into the driver blade path 18, such that the second portion is in

close proximity to the lower end 56 of the driver blade 16. In the event the user

triggers a tool firing after the magazine 22 is empty, the lower end 56 of the driver

blade 16 will impact the second portion 52, and will be prevented from further

reciprocal movement. The user will then be alerted to the need for additional

fasteners in the magazine 22. Once the follower 46 is retracted in the course of

reloading the magazine 22, the tool 10 will be restored to normal operating

conditions.

While specific embodiments of the of the present power nailer with

driver blade blocking mechanism in a magazine have been shown and described, it

will be appreciated by those skilled in the art that changes and modifications may

be made thereto without departing from the invention in its broader aspects and as

set forth in the following claims.