Patent Description:
The present invention relates to a fastener driving device and particularly, but not exclusively, to a fastener driving device including a pressure chamber and a positive air return system.

Combustion powered fastening devices use the expansion of gases generated during an explosion within a combustion chamber to drive a piston. Alternatively, a separate source of pressurised gas can be used to drive the piston. The piston then drives a fastener (for example a nail) from the device into an external object (for example a wall). The piston must return to its original position in order for a second fastener to be loaded and driven. <CIT> discloses a fastener according to the preamble of claim <NUM>.

Incomplete piston return can result in a blank fire or misfire. The device may then have to be manually reset in order to fire again. A blank or misfire can therefore cause delays in firing fasteners. Additionally, the need for a manual reset can expose the user to risk, in the event of uncontrolled firing of a fastener.

It is an aim of certain examples of the present invention to solve, mitigate or obviate, at least partly, at least one of the problems and/or disadvantages associated with the prior art. Certain examples aim to provide at least one of the advantages described below.

According to the present invention there is provided a fastener driving device comprising: a pressure chamber; a first piston coupled to the pressure chamber such that pressurized gas in the pressure chamber causes the piston to slide from a first position to a second position; a fastener channel configured to receive a fastener, wherein when moving from the first position to the second position the first piston is configured to engage the fastener and drive it from the device; and a second piston slidable within a sleeve and arranged such that when the first piston slides from the first position to the second position the first piston drives the second piston and compresses gas within the sleeve; wherein compressed gas in the sleeve biases the first piston towards the first position.

The pressure chamber may further comprise an exhaust configured to release pressurized gas after a fastener has been driven from the device.

When the force of the compressed gas in the sleeve acting upon the second piston exceeds the force of the gas in the pressure chamber acting upon the first piston, the second piston may act against the first piston to slide the first piston towards the first position.

The fastener driving device may further comprise an additional chamber fluidically linked to the sleeve, the additional chamber being configured to house compressed gas from the sleeve.

The additional chamber may be parallel to or surround the sleeve.

Gas within the sleeve or additional chamber may be pressurised above atmospheric pressure when the first piston is in the second position.

The second piston and sleeve may be positioned on a nose portion of the fastener device.

The second piston and sleeve may be mounted on or parallel to the fastener channel.

The sleeve may further comprise a rebalancing hole, wherein the first piston may be configured to occlude the rebalancing hole when in the second position, the rebalancing hole being open when the first piston is in the first position to couple the sleeve to the outside of the device.

The pressure chamber may be coupled to a pressurised gas reservoir configured to selectively pressurise the pressure chamber to drive the first piston from the first position to the second position.

The fastener driving device may be a combustion fastener driving device, and combustion gas expansion within the pressure chamber may drive the first piston from the first position to the second position.

The pressure chamber may be coupled to the sleeve such that expanded combustion gas is supplied to the sleeve to increase the gas pressure in the sleeve.

The pressure chamber may be coupled to the sleeve via a one-way valve.

Examples of the invention are further described hereinafter with reference to the accompanying drawings, in which:.

Referring now to <FIG> a fastener driving device <NUM> according to the prior art is shown. <FIG> show the process of driving a fastener <NUM> (for instance, a nail) from the fastener driving device <NUM>.

The fastener driving device <NUM> may include an exterior housing <NUM>. The exterior housing <NUM> encloses at least some of the components of the fastener driving device <NUM>. The fastener driving device may also include a trigger <NUM>. In some examples the trigger <NUM> may be attached to a chamber lockout <NUM>, the purpose of which is explained below in connection with <FIG>.

The fastener driving device <NUM> includes a combustion chamber <NUM> defined by a combustion chamber housing <NUM>. The combustion chamber housing <NUM> is slidable within the fastener driving device <NUM>. For example, the combustion chamber housing <NUM> can slide in a direction towards a combustion mechanism <NUM> and in a direction away from the combustion mechanism <NUM>. The movement of the combustion chamber housing <NUM> may also be aligned with the direction in which a fastener is driven from the device <NUM>. In this example the combustion mechanism <NUM> includes a fuel injector <NUM> and a spark plug <NUM>. The fastener driving device <NUM> further includes a fan <NUM> which is configured to disperse fuel injected by the fuel injector <NUM>.

As shown in <FIG> the fastener driving device <NUM> includes a nose portion <NUM>. The nose portion <NUM> includes a fastener channel <NUM> and a probe <NUM>. A fastener <NUM> can be received in the fastener channel <NUM>. The nose portion <NUM> includes a work contact element <NUM> to direct the fastener <NUM> (that is, to allow the user to determine where the fastener <NUM> is to be driven into an external surface <NUM>). The work contact element <NUM> may be integral with the probe <NUM> such that they move together. Furthermore, only when the work contact element <NUM> is pressed against an external surface <NUM> can the fastener driving device <NUM> be fired. The work contact element <NUM> being pressed against the external surface <NUM> may trigger a switch (not shown) to allow the fastener driving device <NUM> to fire, for example. As will be explained below, when the work contact element <NUM> is pressed against the external surface <NUM> it is depressed into nose portion <NUM>, which activates the firing mechanism and is a necessary condition for a fastener <NUM> to be discharged. Accordingly, the work contact element <NUM> also serves as a safety mechanism by preventing a fastener <NUM> from being fired other than directly into an external surface <NUM>.

The probe <NUM> may extend toward the combustion chamber housing <NUM>. In this way the probe <NUM> is integral with or coupled to the combustion chamber housing <NUM>. The probe <NUM> may form part of the walls of the combustion chamber <NUM>.

As shown in <FIG> when the work contact element <NUM> is pushed against an external surface <NUM> the work contact element <NUM> moves into the nose portion <NUM>. The probe <NUM> in turn pushes against the combustion chamber housing <NUM>, such that the combustion chamber <NUM> slides back away from the work contact element <NUM>. The combustion chamber housing <NUM> then forms a sealed combustion chamber (sealed with O-rings or other forms of seal) with the combustion mechanism <NUM>, shown in <FIG>. The fastener driving device <NUM> will not fire until the combustion chamber housing <NUM> has been slid such that combustion chamber <NUM> is sealed. Owing to the coupling between the probe <NUM> and the combustion chamber housing <NUM>, pressing the work contact element <NUM> against the external surface <NUM> directly closes the combustion chamber <NUM>, thus only permitting the device <NUM> to be fired when in a safe firing position. The pulling of the trigger <NUM> when the combustion chamber <NUM> has moved into the sealed position allows the chamber lockout <NUM> to engage with the combustion chamber housing <NUM>. This prevents return of the combustion chamber <NUM> during firing. Also, until the work contact element <NUM> has been depressed and the combustion chamber housing <NUM> has slid back, the chamber lockout <NUM> will not be able to move back when the trigger <NUM> is pulled (this being evident by comparison of <FIG>). Accordingly, until the device <NUM> is in a safe firing position, the trigger <NUM> cannot be fully pulled to activate the firing mechanism.

In this example the combustion chamber housing <NUM> contacts a sealing element <NUM> on a wall <NUM> of the combustion mechanism <NUM>. This then triggers the fan <NUM> to start and fuel is injected into the combustion chamber <NUM> and dispersed by the fan <NUM>. When the trigger <NUM> is subsequently pulled the spark plug <NUM> ignites the fuel. By injecting fuel as soon as the combustion chamber <NUM> is closed, rather than waiting until the trigger <NUM> is pulled, firing delay is minimised.

The combustion of the fuel results in a temperature increase, which increases the volume and therefore the pressure of gas within the sealed combustion chamber <NUM>. The expansion of the combustion gases within the combustion chamber <NUM> acts upon a face of piston <NUM> which faces into the combustion chamber <NUM>. Gas pressure in the combustion chamber <NUM> drives the piston <NUM> from a first position (shown in <FIG>) toward the second position (shown in <FIG> shows piston <NUM> in an intermediary position. The gases may do this by exerting force on a plate <NUM>. The plate <NUM> can be sized to contact the interior walls of a sleeve <NUM> so as to form a seal between the sleeve <NUM> and the combustion chamber <NUM>. As the piston <NUM> moves within the sleeve <NUM> gases contained within the sleeve <NUM> escape via a vent <NUM> and an exhaust <NUM> (illustrated by the arrows in <FIG>). In some examples, the sleeve <NUM> may include a plurality of vents <NUM> and/or exhausts <NUM> around the perimeter of the sleeve <NUM>. The exhaust <NUM> may not be present in every example.

The sleeve <NUM> may include a bumper <NUM> or other resilient device or in some cases a plurality of bumpers <NUM>. The bumpers <NUM> are positioned in the sleeve <NUM> so that the bumpers <NUM> are impacted upon when the piston <NUM> moves to the second position. In this way the bumpers <NUM> are at an end of the sleeve <NUM> and provide protection from any impact forces of the piston <NUM> to that end of the sleeve <NUM>. The bumpers <NUM> further serve to encourage the return of piston <NUM> towards the first position as they rebound.

The piston <NUM> includes a drive blade <NUM> extending from the plate <NUM> towards a fastener <NUM> located in a fastener channel <NUM> defined within the nose portion <NUM>. The drive blade <NUM> sits partially within the fastener channel <NUM> and therefore slides within it. During firing, the plate <NUM> pushes the drive blade <NUM>, which then contacts the fastener <NUM> and pushes it from the fastener driving device <NUM>, through the fastener channel <NUM>.

The drive blade <NUM> may pass through the base of the sleeve <NUM> into the fastener channel <NUM>. In this example a sealing O-ring is positioned at the end of the sleeve around the drive blade <NUM> to prevent gases escaping the sleeve <NUM> around the drive blade <NUM>.

The exhaust <NUM> is spaced apart from the vent <NUM>. In this example, the exhaust <NUM> is positioned on the sleeve <NUM> closer to the combustion mechanism <NUM> than the vent <NUM>. The exhaust <NUM> may include a one-way valve <NUM>. The one-way valve <NUM> covering the exhaust <NUM> is orientated such that gas can move out of the sleeve <NUM> or combustion chamber <NUM> (dependent on the position of the piston <NUM>) but not enter either the combustion chamber <NUM> or the sleeve <NUM>.

Before the piston <NUM> reaches the second position, the plate <NUM> of the piston <NUM> moves past the exhaust <NUM>. This allows the combustion gases to escape from the combustion chamber <NUM> via the exhaust <NUM>, which partially reduces the gas pressure in the combustion chamber <NUM>. At this time the piston <NUM> has already been fully accelerated and will continue to move towards the second position even under the reduced gas pressure.

When the piston <NUM> is in the second position the plate <NUM> impacts upon the bumpers <NUM>. In some examples the plate <NUM> may then rebound from the bumpers <NUM> and then impact the bumpers <NUM> a second time, as is shown in <FIG>. A piston rebound is an undesired event. For example, piston rebound can lead to double drive blade impact on the external surface, which may be unsightly or against building regulations. In some cases a large rebound can lead to double fastener fire by engagement of a further fastener in the channel. Furthermore, piston rebound can affect the exhaust efficiency of the burned combustion gases because the piston <NUM> moves towards the first position during the rebound and so moves past the exhaust <NUM>. In this way no combustion gases can be exhausted from the combustion chamber <NUM> during at least a portion of the piston rebound. Moreover a piston rebound increases the return piston time which decreases shot-to-shot speed.

<FIG> shows the piston <NUM> in the second position. The second position may be where the plate <NUM> is in contact with the bumpers <NUM>, for example. In the combustion chamber <NUM>, once the fuel has been combusted, the gases in the combustion chamber <NUM> cool, which creates a vacuum. The exhaust <NUM> having a one-way valve <NUM> prevents gases retuning to the combustion chamber <NUM>. The vacuum therefore encourages piston <NUM> to slide towards the first position. As vent <NUM> does not include a one-way valve, gas can re-enter the sleeve <NUM> via the vent <NUM> as shown by the arrow in <FIG>. In the figures the probe <NUM> is extending around the sleeve <NUM>. However, probe <NUM> may not be continuous around the circumference of sleeve <NUM>: it may include gaps or comprise only a think element coupling the work contact element <NUM> with the combustion chamber wall <NUM>. Accordingly, vent <NUM> and exhaust <NUM> effectively communicate with the ambient environment outside of the device <NUM>.

As shown in <FIG>, the fastener driving device may also include a chamber spring <NUM>. The chamber spring <NUM> may be attached to the combustion chamber housing <NUM> so as to provide a biasing force against the sliding motion of the combustion chamber <NUM>. That is, when the combustion chamber <NUM> is moved by the probe <NUM>, such that the combustion chamber <NUM> is sealed, the spring <NUM> is compressed. After the fastener <NUM> is fired the device <NUM> may be moved away from the external surface <NUM> by the user. When the trigger <NUM> is released by the user (releasing lockout <NUM>) spring <NUM> acts to move the combustion chamber <NUM> into its initial position as indicated by the arrow. This opens the combustion chamber <NUM> by the wall <NUM> separating from seal <NUM> about the combustion mechanism <NUM> to allow for air scavenging (that is, fresh air replenishing the combustion chamber <NUM>). A second fastener 102b is drawn into nose <NUM> and aligned for firing the next shot shown in <FIG>. The mechanism for supplying fasteners <NUM> may be entirely conventional and so will not be further described.

Movement of the combustion chamber wall <NUM> may also open the combustion chamber <NUM> about the outside of sleeve <NUM> (the side of the combustion chamber <NUM> opposite to the combustion mechanism <NUM>). When the work contact element <NUM> is depressed, this side of the combustion chamber wall <NUM> is also sealed by an O-ring about the sleeve <NUM>.

The cycle for firing a fastener <NUM> requires a period of driving the fan <NUM>, plus additional time to spark and ignite the fuel. To allow for piston <NUM> to move to the second position and return to the first position the trigger <NUM> is disabled to prevent an attempt at a further shot. The trigger <NUM> may be electronically disabled, that is a switch detection may be ignored when the trigger <NUM> is disabled. Once the combustion chamber <NUM> is opened a period of scavenging time is required. The cycle duration from the pressing of the work contact element <NUM> against the external surface to the fastener driving device <NUM> being ready for the next shot is therefore typically between <NUM> and <NUM>.

Alternatively, a fastener driving device <NUM> may be a pneumatically operated as shown in <FIG>. The fastener driving device <NUM> includes a chamber <NUM> and a piston <NUM> configured to drive a fastener (not shown). The piston <NUM> slides between a first position (not shown) and a second position shown in <FIG>. In this example the piston <NUM> includes a plate <NUM> and a drive blade <NUM> similar to drive blade <NUM> as described above.

Before firing, the piston <NUM> is in the first position. When the trigger is pulled the chamber <NUM> is filled with pressurised gas from a pressurised source connected to the fastener driving device <NUM> via an intake channel <NUM>. This pushes the piston <NUM> into the second position thereby firing the fastener from the device <NUM>. The chamber <NUM> is fed until a user release the trigger. A valve then closes the intake channel so pressurised gas is no longer fed into the chamber <NUM> and opens an exhaust <NUM>.

The chamber <NUM> is therefore depressurised via the exhaust <NUM>. The piston <NUM> may be returned to its initial position using a conventional mechanism, for instance a positive air return chamber (not shown) that acts when the pressure in the return chamber exceeds the pressure of chamber <NUM> to move the piston back to the first position. However this conventional approach requires a relatively long time between shots.

Turning now to <FIG>, a fastener driving device <NUM> according to an example of the present invention includes a pneumatic spring <NUM> to speed up the piston return. <FIG> illustrates an example of the present invention for a combustion powered fastener driving device. However, in accordance with another example of the present invention the pneumatic spring <NUM> may be incorporated into a pneumatically powered fastener driving device. The pneumatic spring <NUM> includes a sleeve <NUM> and a second piston <NUM>.

In this example, the pneumatic spring is arranged on the nose portion <NUM> of the fastener driving device <NUM>. The second piston <NUM> is arranged relative to the first piston <NUM>, such that as shown in <FIG>, when the first piston <NUM> is in the first position the second piston <NUM> is extended towards the first piston <NUM> to give a maximum volume of sleeve space <NUM> within the second sleeve <NUM>.

<FIG> shows the combustion chamber <NUM> in the open position. <FIG> shows the work contact element <NUM> pushed against an external surface <NUM>. The work contact element <NUM> being pushed into the nose portion <NUM> moves the probe <NUM> which also pushes the combustion chamber <NUM> backwards. In this way, the combustion housing <NUM> contacts a seal ring <NUM> around the periphery of the sleeve <NUM> and forms a sealed combustion chamber <NUM>.

Expansion of the combustion gases drive the first piston <NUM> to the second position, shown in <FIG>. Gases within the sleeve <NUM> escape through a vent <NUM>, such that there is minimal gas compression within the sleeve <NUM> of the first piston <NUM>. The movement of the first piston <NUM> to the second position allows the first piston <NUM> to engage with the second piston <NUM> to move the second piston <NUM> to a second position. For example, a drive blade <NUM> of the second piston <NUM> may engage with the plate <NUM> of the first piston <NUM>. The movement of the plate <NUM> pushes against the drive blade <NUM> of the second piston <NUM>, which then moves a plate <NUM> (of the second piston <NUM>). The plate <NUM> is attached to the drive blade <NUM> at an end opposed the end of the drive blade <NUM> which contacts the first piston <NUM>. The plate <NUM> of the second piston <NUM> may have a sealing ring <NUM> around the periphery so as to contact the interior walls of the sleeve <NUM>. Further in some examples the second sleeve <NUM> may include a bumper (not shown) for the second piston to impact upon in the second position.

In this example when the second piston <NUM> is in the second position the sleeve space <NUM> volume is reduced to a minimum. In this way, the movement of the second piston <NUM> from the first position into the second position compresses the gas within the second sleeve <NUM>. This compression of gases within the sleeve space <NUM> provides a force biasing the second piston <NUM> (and thereby the first piston <NUM>) toward the first position.

In some examples the gas within the second sleeve <NUM> may be pressurised above atmospheric pressure to give a higher biasing force on the second piston <NUM>. For example the pressure in the second sleeve may be <NUM> BarA. During firing, the pressure from the expanding combustion gases within the combustion chamber <NUM> overcomes this biasing force, driving the fastener <NUM> from the fastener driving device <NUM>.

As shown in <FIG> once combustion has occurred and the gases within the combustion chamber <NUM> cool the pressure in the sleeve space <NUM> acting upon the second piston <NUM> can generate a force that exceeds the force upon the first piston <NUM> exerted by the residual pressure in the combustion chamber <NUM>. The pressure in the sleeve space <NUM> therefore acts to slide the second piston <NUM> to the first position. The sliding of the second piston <NUM> to the first position acts to also slide the first piston <NUM> back to the first position.

Once the first piston <NUM> is in the first position and the work contact element <NUM> is no longer pressed against the external surface the chamber spring <NUM> acts to reopen the combustion chamber <NUM> by sliding it towards the work contact element <NUM>.

In other examples, the combustion chamber <NUM> may be opened by the recoil of the fastener driving device <NUM>. That is, as the fastener driving device <NUM> moves away from the external surface <NUM>, the work contact element <NUM> is pushed out of the nose portion by the spring <NUM>. This opens the combustion chamber <NUM> via the probe <NUM>. The second piston <NUM> then biases the first piston <NUM> back to the first position.

<FIG> shows a fastener driving device <NUM> according to a further example of the present invention, where the pneumatic spring <NUM> includes an additional chamber <NUM> which is configured to extend the second sleeve. In this way when the second piston <NUM> moves to the second position the compressed gas is at least partially contained by the additional chamber <NUM>. In this example the additional chamber <NUM> forms part of the sleeve space <NUM> to give the same volume of space <NUM> as described with reference to <FIG>. The additional chamber <NUM> may be linked to the second sleeve <NUM> via a vent <NUM>, with gas able to flow between the two as indicated by the arrow. The vent <NUM> may be behind the plate <NUM> of the second piston. The gas within the sleeve <NUM> and the additional chamber <NUM> is pressurised by movement of the second piston <NUM> into the second position. In some examples the additional chamber <NUM> (and the sleeve space <NUM>) may be pressurised above atmospheric pressure. By having the additional chamber <NUM> the length of the second sleeve can be reduced compared to the example of <FIG> to d. This allows the user a better line of sight to the work contact element <NUM>.

<FIG> illustrates a yet further example of the fastener driving device <NUM> further including a channel <NUM> from the combustion chamber <NUM> to the second sleeve <NUM>. The channel <NUM> may include a one-way valve <NUM>, such as a reed valve, to prevent return flow of gases from the additional chamber <NUM> to the combustion chamber <NUM>.

In this example, combustion gases from the combustion chamber <NUM> enter the additional chamber <NUM> and further pressurise the sleeve <NUM> while the pistons <NUM>, <NUM> move from the first position to the second position. The force biasing the second piston <NUM> towards the first position is therefore increased (or alternatively the capacity of the sleeve <NUM> may be reduced). Once combustion has concluded, the return to the first position for both the first and second pistons is therefore sped up due to the high biasing force of the pressurized second sleeve <NUM>.

In this example the pneumatic spring <NUM> further includes a depressurisation hole <NUM> to the fastener channel <NUM>. When the second piston <NUM> is sliding form the first position to the second position or in the second position the plate <NUM> of the second piston <NUM> seals the depressurisation hole <NUM> from the additional chamber <NUM>.

The depressurisation hole <NUM> is configured to be uncovered when the second piston <NUM> is in the first position. That is the depressurisation hole <NUM> allows the second sleeve <NUM> to be fluidically linked to the fastener channel <NUM> and thereby the exterior of the fastener driving device. The depressurisation hole <NUM> therefore allows the pressure within the second sleeve <NUM> and the additional chamber <NUM> to rebalance after a shot is fired while allowing the pressure within the second sleeve <NUM> to increase during the shot.

In the examples described above the pneumatic spring <NUM> is shown on a combustion driven fastener device, however the pneumatic spring <NUM> could equally be applied to the pneumatic fastener driving device <NUM> as shown in <FIG>. Accordingly, after the chamber <NUM> has been pressurised by the pressure reservoir the piston <NUM> compresses a secondary piston in the manner described above. Similarly the secondary piston then biases the first piston <NUM> back to the first position once the chamber <NUM> pressure is exhausted.

The above-described embodiments provide the advantage of improving piston return time. This can therefore reduce time between firings. The need for a chamber lockout is also eliminated, thereby allowing for even less time between successive shots.

Further a pneumatic spring may be more resilient to the high speeds and pressures exerted upon it than a mechanical spring.

Compared with a positive air return system the energy loss from a pneumatic spring is significantly lower and the sleeve space required is less than a return chamber of positive air return systems, thus allowing for a better line of sight.

Claim 1:
A fastener driving device (<NUM>) comprising:
a pressure chamber (<NUM>);
a first piston (<NUM>) coupled to the pressure chamber such that pressurized gas in the pressure chamber causes the first piston to slide from a first position to a second position;
a fastener channel (<NUM>) configured to receive a fastener (<NUM>), wherein when moving from the first position to the second position the first piston is configured to engage a fastener and drive it from the device; and characterised by
a second piston (<NUM>) slidable within a sleeve (<NUM>) and arranged such that when the first piston slides from the first position to the second position the first piston drives the second piston and compresses gas within the sleeve;
wherein compressed gas in the sleeve biases the first piston towards the first position.