Patent Description:
<CIT> relates to a driving tool. <CIT> relates to a dryfire lockout with a bypass for a fastener driving device. <CIT> relates to a nail-driving device with safety unit. <CIT>, being relevant under Article <NUM>(<NUM>) EPC, discloses a safety device for tackers. When the tacker is used to staple an object, a safety slide is pushed against the object and drives a rod to be retracted into the body of the tool. The rod moves backward and an ignition spring is movable with the rod and activates a contact plate of a safety switch.

Fastening tools, such as concrete nailers, staplers, and other nailers, are normally provided with fastener magazines. Typically, fasteners loaded in the magazine are biased toward a drive track of the fastening tool, so that the fastening tool drive system can drive a fastener into a work surface. However, if the supply of fasteners in the magazine becomes exhausted or "dry" when the fastening tool is fired, the driver of the drive system encounters no resistance as the driver is fired along the drive track, until the driver ultimately engages some other portion of the fastening tool, or even the work surface via the contact trip. This condition is called a "dry-fire", and is highly destructive to fastening tool mechanisms.

To date, conventional attempts to solve the problem have been unsatisfactory for several reasons. One reason is that many conventional dry-fire avoidance systems freeze a lower contact trip so that the lower contact trip is unable to move even if the lower contact trip is thrust against a work surface, an event which places additional stresses on the contact trip system.

Another reason is that conventional dry-fire avoidance systems often position the contact trip off-center from the fastening tool drive axis, which creates a moment arm with the contact trip. Consequently, when an operator slams the contact trip against a work surface, or drops the fastening tool, nose first, onto an unyielding surface, like concrete, the shock is amplified and transmitted throughout the entire contact trip system.

Conventional contact trip systems include three major elements: a contact trip, a dry-fire avoidance system, and a fastener drive system arming device. The fastener drive system arming device is linked to the contact trip so that, when the contact trip moves to a firing position after having engaged the work surface, the fastener drive system arming device assumes a firing condition enabling the fastener drive system, which is now armed, to drive a fastener. Then, when an operator pulls a trigger switch on the fastening tool, the fastening tool can fire a fastener. However, the vulnerability of conventional contact trip systems to being slammed or dropped significantly reduces the lifetimes of conventional arming devices.

Still another reason why conventional dry-fire avoidance systems have proven unsatisfactory is that, in electrically-driven fastening tools, the fastener drive system arming device often includes a relatively fragile contact trip switch, which is closed by a linkage actuated by the contact trip when the contact trip moves to the firing position. The contact trip switch is electrically connected to the fastener drive system so that, when the contact trip closes the contact trip switch, the fastener drive system arming device assumes the firing condition, and an operator can fire the fastening tool. However, conventional fastening tools include no systems for limiting the force exerted upon the contact trip switch when the contact trip is shoved against a work surface, even during normal operating conditions when the magazine is loaded with fasteners.

The problems enumerated above still exist in fastener drive system arming devices connected mechanically or otherwise to other types of fastener-driving systems, such as pneumatic, explosive-gas, or hydraulic. Impact forces exerted upon the lower portion of a contact trip assembly are still directly transmitted to the fastener drive system arming device.

Consequently, existing fastening tools are vulnerable both to dry-fire conditions and to shocks caused by the operator slamming the tool against a work surface, or dropping the tool nose-first onto an unyielding surface, like concrete. What is needed, therefore, is a fastening tool that both handles dry-fire conditions, and insulates an arming device from the forces exerted upon the arming device by a contact trip.

According to aspects of the present invention there are provided a method according to claim <NUM> and a fastening tool according to claim <NUM>.

In one embodiment of a fastening tool according to the present disclosure, the contact trip is moved to bypass a fastener drive system arming device. A biasing agent, such as a coil spring, is placed between the upper portion of the contact trip and the fastener drive system arming device. The coil spring allows the contact trip to move the entire distance the contact trip normally travels to reach the firing position, while taking up or absorbing the force that the contact trip would normally expend on the arming device. This arrangement yields several benefits.

One benefit of moving the contact trip to bypass the fastener drive system arming device is that the amount of force which is ultimately applied to an element of the fastener drive system arming device, namely a contact trip switch, can be limited by configuring the coil spring to be, in effect, a force take-up member. For example, in an electrically-driven fastening tool of the present disclosure, it is desirable that the contact trip switch survive hundreds of thousands of connections during the lifetime of the fastening tool. By configuring the coil spring to limit the force ultimately applied to the contact trip switch to two pounds or less, the contact trip switch will survive hundreds of thousands of connections, no matter how hard the operator slams the contact trip against a work surface, and no matter how many times the fastening tool is dropped.

Another benefit of moving the contact trip to bypass the fastener drive system arming device is that the coil spring acts as a distance take-up member, causing the contact trip to bypass direct engagement with the contact trip switch in response to a "bypass event". Such an event can include, for example, the fastener magazine reaching a dry-fire condition, in which the coil spring can be compressed to take up or absorb the entire distance that the contact trip travels to reach the firing position, without the contact trip engaging the arming device.

Yet another benefit of the bypass system of the present disclosure is that the system permits the contact trip to be disposed in the fastening tool housing coaxially with the fastening tool drive axis. Therefore, a lower portion of the fastening tool housing can now act as a "hard stop" against which a toe of the contact trip is driven if the contact trip is ever slammed against the concrete, or the fastening tool is dropped nose-first. Thus the inherently rugged fastening tool housing itself takes the shock, rather than the more fragile elements of the contact trip switch, which are simultaneously protected by the force-limiting action of the coil spring. The hard stop eliminates the shock-amplifying arrangement of conventional dry-fire avoidance systems that position the contact trip off-center from the drive axis.

The bypass system of the present disclosure is implemented by disposing the coil spring in a biasing agent housing between a plate or appendage connected for joint movement with an upper part of the contact trip, and an upper inner surface, or roof, of the biasing agent housing. The coil spring also normally biases the biasing agent housing in a direction to engage the fastener drive system arming device. Thus, as the contact trip moves upwardly in response to having engaged a work surface, it carries with it the appendage, which in turn pushes the coil spring upwardly in the biasing agent housing, thereby pushing the biasing agent housing upwardly as well. When the contact trip reaches the uppermost point in its travel (its firing position), the biasing agent housing engages a switch lever, which pivots to close the contact trip switch. The switch lever and contact trip switch collectively form the fastener drive system arming device.

On the other hand, if a dry-fire condition were to occur in the fastener magazine, a fastener pusher probe disposed in the fastener magazine blocks the biasing agent housing from moving upwardly. If an operator nevertheless were to cause the contact trip to engage a work surface, the contact trip will still move upwardly toward the firing position. As the contact trip moves upwardly, the contact trip again carries the appendage, which in turn pushes the coil spring upwardly. However, (inasmuch as the biasing agent housing is configured to permit relative movement between the biasing agent housing and the appendage, and inasmuch as upward movement of the biasing agent housing has been blocked), the upward movement of the contact trip will not close the contact trip switch. Instead, continued joint upward movement of the contact trip - appendage combination results in the coil spring being compressed inside the biasing agent housing, which still remains stationary. Thus, the coil spring takes up or absorbs the distance that the contact trip would normally travel to reach the firing position, thereby causing the upward movement of the contact trip to bypass the contact trip switch, but allowing the contact trip to move the entire distance the contact trip needs to travel to reach the firing position.

In another embodiment, the magazine fastener pusher probe pushes the biasing agent housing laterally away from the line of vertical movement the biasing agent housing would normally take to engage the switch lever, in response to the quantity of fasteners in the magazine having reached a minimum. When the magazine is fully loaded, the pusher is retracted and a return spring returns the biasing agent housing to a position in which the biasing agent housing is engageable with the switch lever. If desired, a force take-up member, such as another coil spring, may be operatively disposed between the biasing agent housing and the appendage to limit the force applied by the biasing agent housing against the switch lever.

Embodiments of the invention will now be described by way of non-limiting example with reference to the accompanying drawings, in which:.

Referring now to the Drawings and particularly to <FIG>, a fastening tool <NUM> in accordance with an embodiment of the present invention includes a housing <NUM> and a fastener drive system <NUM> disposed in the housing (<FIG>). The fastener drive system <NUM> includes a driver <NUM> for driving fasteners <NUM> along a drive track <NUM> and a drive axis <NUM>, and into a work surface <NUM>. The fastener drive system <NUM> also includes a motor <NUM> powered by a battery <NUM> and operatively associated with the driver <NUM> to drive the fasteners <NUM>. A contact trip switch <NUM> and a trigger switch <NUM> are electrically connected to the fastener drive system <NUM>. Both the contact trip switch <NUM> and the trigger switch <NUM> must be closed before the fastening tool <NUM> fires. The contact trip switch <NUM>, which is normally open, is closed in response to movement of a switch lever <NUM>, which is pivotably mounted in the fastening tool housing <NUM> about a pivot <NUM>. The contact trip switch <NUM> and switch lever <NUM> constitute an arming device <NUM>. The arming device <NUM> is actuated in response to upward movement of a contact trip <NUM> when the contact trip is pressed against a work surface <NUM>. When the contact trip switch <NUM> is closed by movement of the contact trip <NUM>, the contact trip switch assumes a firing condition, thereby causing the fastener drive system <NUM> to be armed. The fastening tool <NUM> can now drive a fastener <NUM> when an operator presses the trigger switch <NUM>. If the contact trip <NUM> does not engage the work surface <NUM>, the contact trip switch <NUM> remains in a no-fire condition, and pressing the trigger switch <NUM> will not fire the fastening tool <NUM>.

At this point, it should be noted that, although the embodiments of the fastening tool depicted in the drawings are shown as concrete nailers, it will be appreciated that aspects and embodiments of the present invention can be incorporated in any fastening tool, including, without limitation, staplers and other nailers. Furthermore, although the embodiments of the dry-fire bypass system are shown being used in connection with a fastening tool having an electric-powered drive system, it will again be appreciated that the dry-fire bypass system may also be employed in fastening tools using pneumatic, hydraulic, and gas/explosive drive systems, among others.

The main elements of the dry-fire bypass system include a contact trip assembly <NUM>, a biasing agent housing assembly <NUM> and a magazine <NUM>.

Referring now to <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>, the contact trip assembly <NUM> includes the contact trip <NUM>, having a contact trip toe <NUM>, which engages the work surface <NUM>. The contact trip <NUM> is movably disposed within a lower housing member <NUM>, which in turn defines a lower portion <NUM>, against which the contact trip toe <NUM> abuts when the contact trip reaches a firing position <NUM>, as shown in <FIG>, <FIG>, <FIG>, <FIG>, <FIG> and <FIG>.

Referring to <FIG>, the contact trip <NUM> moves upwardly within lower housing member <NUM> from a position where the contact trip is not fully engaged, as shown in <FIG>, to the contact trip firing position <NUM>, shown in <FIG>. A plate or appendage <NUM> is attached to the contact trip <NUM> for joint movement with the contact trip.

Returning to <FIG>, a main coil spring <NUM>, grounded at an upper end of the coil spring to the fastening tool housing <NUM>, is connected to the appendage <NUM>. Thus, the main coil spring <NUM> normally biases the contact trip <NUM> toward engagement with a work surface <NUM>. It has been discovered that configuring the main coil spring <NUM> to exert of force of about <NUM> times the weight of the fastening tool <NUM> achieves the best results. That means a ten-pound fastening tool would require a main coil spring <NUM> capable of exerting <NUM> pounds of force against the appendage <NUM> and contact trip <NUM> combination. Still referring to <FIG>, the appendage <NUM> is threaded onto a bushing <NUM>, which slides along a bushing rod <NUM>. Thus the appendage <NUM>, main coil spring <NUM>, bushing <NUM> and bushing rod <NUM> complete the contact trip assembly <NUM>.

The biasing agent housing assembly <NUM> is shown, for example, in <FIG>, and includes a biasing agent housing <NUM>, a lever-engaging member <NUM> extending from the biasing agent housing and engageable with the switch lever <NUM>, a blocking member <NUM>, and a biasing agent <NUM>. The biasing agent <NUM> is disposed in the biasing agent housing <NUM> between the appendage <NUM> and an upper surface <NUM> of the biasing agent housing (see <FIG>). The appendage <NUM> is movable independently of the biasing agent housing <NUM> within a slot (not shown) formed on one side of the biasing agent housing. When the appendage <NUM> moves upwardly in response to movement of the contact trip <NUM>, the appendage pushes the biasing agent <NUM> upwardly, as well. This in turn pushes the biasing agent housing <NUM> toward engagement with the switch lever <NUM>, unless movement of the biasing agent housing is blocked. In the embodiment shown in the Drawings, the biasing agent <NUM> is depicted as a coil spring. However it will be appreciated that the biasing agent <NUM> may take on other forms and include multiple elements, all of which will work satisfactorily provided they bias the biasing agent housing <NUM> in the direction of the switch lever <NUM>.

As will be later described in more detail, the biasing agent <NUM> also takes on the function of a force-limiting or force take-up member, being configured to limit the force that the lever-engaging member <NUM> exerts upon the switch <NUM> to two pounds or less, even when an operator slams the contact trip <NUM> against an unyielding surface like concrete, or when the fastening tool <NUM> is dropped, nose-first, onto a hard surface.

Moving now to the magazine <NUM>, and again referring to <FIG>, the magazine contains a supply of fasteners such as nails <NUM>. A fastener pusher <NUM> is biased to push the nails <NUM> toward the drive track <NUM>, along which a nail can be driven into a work surface <NUM> when the fastening tool <NUM> is fired. As shown in <FIG>, when the supply of nails <NUM> reaches a dry-fire condition, for example, when the supply of nails reaches a predetermined minimum quantity, a pusher probe <NUM> extending from the fastener pusher <NUM> in the direction of the biasing agent housing <NUM> engages the blocking member <NUM>, thereby blocking movement of the biasing agent housing <NUM> toward the lever <NUM>, and thus preventing the fastening tool <NUM> from firing. The cooperation of the pusher probe <NUM> and the blocking member <NUM> can be adjusted so that the movement of the biasing agent housing <NUM> can be blocked when the remaining quantity of nails in the magazine <NUM> reaches any desired minimum, for example, from one to three nails. Blocking the movement of the biasing agent housing <NUM> constitutes a "bypass event", as will be discussed below.

The operation of the dry-fire bypass system will be described with reference to <FIG> and <FIG>. As shown in <FIG>, the contact trip <NUM> has touched the work surface <NUM>, but no downward force has been exerted on the fastening tool <NUM> to fully depress the contact trip. Consequently, the toe <NUM> of the contact trip <NUM> remains spaced a distance D1 below the lower portion <NUM> of lower housing member <NUM>. The distance D1 is precisely the amount of distance that the contact trip <NUM> travels when it moves from the position shown in <FIG> to the firing position <NUM>, shown in <FIG>. The dry-fire bypass system will take up or absorb the entire distance D1, so that the effect of an upward movement of the contact trip will not be expended upon the contact trip switch <NUM>. At the stage shown in <FIG>, the appendage <NUM> is located at its lowermost position, as is the biasing agent housing <NUM>, inasmuch as the appendage <NUM> has yet to move the coil spring <NUM> upwardly against the upper surface <NUM> of the biasing agent housing.

As shown in <FIG> and <FIG>, the contact trip <NUM> has moved upwardly (see arrows in <FIG>), causing the appendage <NUM> to move the coil spring <NUM> upwardly, which in turn has caused the biasing agent housing <NUM> to move upwardly by the same amount, so that the lever-engaging member <NUM> is almost touching the lever <NUM>. At this point, the contact trip toe <NUM> is only a small distance D2 from the lower portion <NUM> of the lower housing member <NUM>. However, when the contact trip <NUM> reaches the firing position <NUM> shown in <FIG>, the incremental amount of upward movement D2 by the contact trip (and therefore the appendage <NUM>) to the <FIG> position now causes the biasing agent housing <NUM> to engage lever <NUM> to close the contact trip switch <NUM>. The contact trip switch <NUM> has thus assumed the firing condition, and the fastener drive system <NUM> is now armed.

<FIG> and <FIG> show that, simultaneously with the upward movement of the contact trip <NUM>, the appendage <NUM> moves upwardly by the same incremental amount D2, thereby slightly compressing the coil spring <NUM> within the biasing agent housing <NUM>. The coil spring <NUM> has therefore taken up or absorbed the incremental amount of distance traveled by the contact trip <NUM> in ultimately reaching the firing position <NUM>. In so doing, the coil spring <NUM> has assumed the role of a distance take-up member, responding to another type of bypass event, namely, the incremental movement of the contact trip <NUM> beyond a predetermined distance, which movement would otherwise exert a force greater than two pounds on the contact trip switch <NUM>. Thus, the coil spring <NUM> has also acted to limit or take up the force exerted by the lever-engaging member <NUM> upon the fastener drive system arming device (switch lever <NUM> and contact trip switch <NUM>). As can now be appreciated, the force-limiting action is consequently not limited to a dry-fire condition, but protects the arming device <NUM> even when the magazine <NUM> is loaded with fasteners <NUM>.

The bypass arrangement, in contrast to conventional dry-fire avoidance systems, allows the contact trip <NUM> to be disposed coaxially with the drive axis <NUM>, thereby enabling a hard stop for the contact trip <NUM> to be located right at the lower portion <NUM> or base of the lower housing member <NUM>. Accordingly, in the event the contact trip <NUM> is slammed against an unyielding surface, the hard stop dissipates the shock of the impact of the contact trip toe <NUM> throughout the inherently rugged housing <NUM> of the fastening tool <NUM>, simultaneously with the coil spring <NUM> limiting the force which is ultimately applied to the contact trip switch <NUM>.

After the fastening tool <NUM> has been lifted from the work surface <NUM>, and in the absence of a dry-fire condition, the coil spring <NUM> returns to a relaxed condition, inasmuch as the contact trip <NUM> is biased by the main spring <NUM> normally to extend outwardly or downwardly from the fastening tool housing <NUM>, thereby returning the appendage <NUM> to the position shown in <FIG>.

An example of the bypass action (or distance and force take-up) of the coil spring <NUM> is exhibited in the case of a dry-fire bypass event. In response to the quantity of remaining fasteners <NUM> in the magazine <NUM> having reached a minimum, the magazine pusher probe <NUM> cooperates with the blocking member <NUM> to block upward movement of the biasing agent housing <NUM>, as shown in <FIG> and <FIG>. Here, although the biasing agent housing <NUM> has been rendered immobile, the contact trip <NUM> is still allowed to travel all of the way to the firing position <NUM>. That is because the appendage <NUM>, being movable independently of the biasing agent housing <NUM>, is able to compress the coil spring <NUM> within the biasing agent housing <NUM> by an amount D3 to the position shown in <FIG> and <FIG>. The coil spring <NUM> thus takes up or absorbs all of the distance traveled by contact trip <NUM> in reaching the firing position <NUM>. Consequently, movement of the contact trip <NUM> during the bypass event has effectively bypassed contact trip switch <NUM>, which remains in the no-fire condition.

Another embodiment of the present invention <NUM> is shown in <FIG> and <FIG>. In this embodiment, a fastening tool <NUM> is disclosed. All of the elements of the fastening tool <NUM> remain the same, except for a biasing agent housing <NUM>, which is disposed on the appendage <NUM> for movement generally transverse to the direction of the movement of the appendage (which still moves vertically with the movement of the contact trip <NUM>). The biasing agent housing <NUM> includes a vertical arm <NUM>, which is aligned with the switch lever <NUM> so that upward movement of the biasing agent housing <NUM> will cause the vertical arm <NUM> to engage the switch lever. A biasing agent housing return spring <NUM> connected between the appendage <NUM> and the biasing agent housing <NUM> normally biases the biasing agent housing to the position shown in <FIG>. If desired, a force take-up member or coil spring <NUM> (shown in phantom in <FIG> and <FIG>) may be operatively disposed between the biasing agent housing <NUM> and the appendage <NUM> to limit the force applied to the contact trip switch <NUM> to two pounds or less, as is similarly performed by the coil spring <NUM> in the first embodiment of the fastening tool <NUM>. In operation, as shown in <FIG>, when the contact trip <NUM> reaches the firing position <NUM>, the appendage <NUM> moves the biasing agent housing <NUM> upwardly (as shown by the arrow) so that the biasing agent housing directly engages the lever <NUM> to close the contact trip switch <NUM>, thereby placing the contact trip switch in the firing condition.

When a dry-fire bypass event occurs, as shown in <FIG>, the pusher probe <NUM> pushes the vertical arm <NUM> of the biasing agent housing <NUM> horizontally away from alignment with the switch lever <NUM>, as indicated by the arrows. Consequently, even if the contact trip <NUM> is pushed to the firing position <NUM>, thereby moving the appendage <NUM> vertically a distance that would normally engage the switch lever <NUM> and close the contact trip switch <NUM>, the vertical arm <NUM> of the biasing agent housing <NUM> completely misses or bypasses the switch lever <NUM>, and the contact trip switch remains in the no-fire condition.

It can now be seen that the two embodiments of the fastening tool <NUM>, <NUM> provide a method both for bypassing the fastener drive system arming device <NUM> during a dry-fire condition, and for limiting the force applied to the contact trip switch <NUM> as the contact trip <NUM> reaches the firing position <NUM>, even when the magazine <NUM> is loaded with fasteners <NUM>.

Claim 1:
A method of limiting the force applied to a contact trip switch (<NUM>) by a contact trip (<NUM>) of a fastening tool (<NUM>) having a fastening tool housing (<NUM>) as the contact trip (<NUM>) moves toward a firing position closing the switch, comprising:
transmitting force between the contact trip (<NUM>) and the contact trip switch (<NUM>) via a biasing agent (<NUM>), wherein the biasing agent (<NUM>) is disposed in a biasing agent housing (<NUM>).