Patent Description:
The present disclosure relates to a return mechanism for a cordless nailer.

Fastening tools, such as power nailers have become relatively common place in the construction industry. Pneumatically-powered nailers, which are connected to an air compressor via an air hose, and powder nailers, which employ a powder fuel source that is rapidly combusted to produce a volume of pressurized gas, initially dominated the market. Both products, however, suffer from several drawbacks.

Pneumatically powered nailers require a relatively expensive air compressor that can be relatively cumbersome to transport. Additionally, it can be inconvenient to operate the nailer while it is tethered (via the air hose) to the air compressor. Many of the nailers powered by a powder fuel source are of the "single shot" variety and require significant effort to reload. Additionally, nailers employing a powder fuel source can be relatively noisy and can produce unpleasant odors during their operation.

Despite these limitations, pneumatic and powder-powered nailers continue to predominate for those construction applications, such as steel framing and concrete construction, which employ fasteners requiring a high degree of power to install the fasteners. Hence, while cordless electric nailers have become very successful for use in conventional wood construction (i.e., framing and trimming), cordless electric power nailers of this type are presently not suitable for use in steel framing or concrete construction applications.

Cordless electric powered nailers typically use springs to return the nail driver of the tool to its home position. A cordless electric powered nailer that is capable of installing concrete fasteners, including the installation of hardened fasteners through steel framing into concrete, must impart a significant amount of energy to the concrete fastener. Such driver return springs are prone to failure when subjected to the energy required to drive concrete fasteners. Accordingly, a much more robust and capable driver return mechanism is desired to improve the reliability of cordless electric powered nailers, including those capable of installing concrete fasteners.

<CIT> relates to magnetic profile lifter. <CIT> relates to a gas spring fastener driving tool with improved lifter and latch mechanisms. <CIT> relates to an activation system having multi-angled arm and stall release mechanism.

<CIT> relates to a nailer driver blade stop for a fastening tool.

According to the invention there is provided a cordless electric nailer of claim <NUM>. Optional features thereof are defined in dependent claims <NUM> to <NUM>.

In addition, any feature or combination of features included in this general summary is not necessarily critical or particularly important to the disclosure.

In accordance with an aspect of the disclosure, a cordless electric nailer can include a power take-off assembly positioned and operable to selectively engage a pinch roller against a nail driver having a home position to pinch the nail driver against a battery-powered electric motor driven flywheel and fire the nail driver. A return rack can be fixedly coupled to and positioned along a longitudinal length of the nail driver. A driver return assembly can be positioned to engage and return the nail driver to the home position. The driver return assembly can include a return motor operably coupled to a return pawl to alternating drive the return pawl in a homeward direction while the return pawl is in a raised position relative to the nail driver in which the return pawl is engageable with the return rack, and in a driven direction while the return pawl is in a lowered position relative to the nail driver in which the return pawl is not engageable with the return rack. In accordance with another aspect of the disclosure, a cordless electric concrete nailer can include a power take-off assembly positioned and operable to selectively engage a pinch roller against a concrete nail driver having a home position to pinch the concrete nail driver against a battery-powered electric motor driven flywheel and fire the concrete nail driver. A return rack is fixedly coupled to and positioned along a longitudinal length of the concrete nail driver. A driver return assembly is positioned to return the concrete nail driver to the home position. The driver return assembly includes a solenoid driving a plunger in a reciprocating motion in a homeward direction and a driven direction. A return pawl is coupled to the plunger and pivotable into a pawl raised position relative to the plunger in which the pawl is engageable with the return rack during movement of the plunger in the homeward direction, and pivotable into a pawl lowered position relative to the plunger in which the pawl is not engageable with the return rack during movement of the plunger in the driven direction.

With reference to <FIG> and <FIG> of the drawings, a cordless nailer constructed in accordance with the teachings of the present disclosure is generally indicated by reference numeral <NUM>. The driving tool <NUM> can include a housing <NUM>, a frame <NUM>, a drive motor assembly <NUM>, a driver return mechanism or assembly <NUM>, a control unit <NUM>, a nosepiece assembly <NUM>, a magazine assembly <NUM> and a battery pack <NUM>. The nosepiece assembly <NUM>, the magazine assembly <NUM> and the battery pack <NUM> can be constructed in a conventional manner and as such, need not be described in detail herein. The control unit <NUM> can include various switches, such as a trigger switch <NUM>, which is responsive to a state of a trigger <NUM>, and a contact trip switch <NUM>, which is responsive to a state of a contact trip <NUM> associated with the nosepiece assembly <NUM>, various sensors, such as a motor speed sensor (not shown), and a controller <NUM> that can receive signals from the various switches and sensors and responsively operate the drive motor assembly <NUM> and the driver return assembly <NUM>.

The housing <NUM> can be of a clam-shell construction that can be employed to cover various components of the nailer <NUM>, such as the drive motor assembly <NUM>, the driver return assembly <NUM> and the control unit <NUM>. The housing <NUM> can form a handle <NUM> that can be grasped by the operator of the nailer <NUM> to operate the nailer <NUM>, and a battery pack mount <NUM> to which the battery pack <NUM> can be fixedly but removably coupled.

The frame <NUM> can formed of one or more frame components and is the structure to which the drive motor assembly <NUM>, the driver return assembly <NUM> and the nosepiece assembly <NUM> can be fixedly coupled. In the particular example provided, the frame <NUM> comprises a motor mount <NUM> and a return mechanism mount <NUM> that are fixedly coupled to one another via a plurality of threaded fasteners (not specifically shown).

With reference to <FIG> and <FIG>, the drive motor assembly <NUM> can comprise an electric motor <NUM>, a flywheel <NUM>, a driver <NUM> and a power take-off unit (PTU) or power take-off assembly <NUM>. The electric motor <NUM> can be an inside-out motor having a stator <NUM>, which is fixedly coupled to the motor mount <NUM> (<FIG>), and a rotor <NUM> that can be disposed about (i.e., radially outwardly of) the stator <NUM>. The flywheel <NUM> can be disposed about (i.e., radially outwardly of) and fixedly coupled to the rotor <NUM> such that the rotor <NUM> and the flywheel <NUM> are rotatable about a common rotational axis <NUM>. As best shown in <FIG>, the flywheel <NUM> can have a flywheel profile <NUM> on its outer circumferential surface.

With reference to <FIG>, the driver <NUM> can include a driver body <NUM> and a driver blade <NUM>. The driver body <NUM> can have a driver profile <NUM> on a first surface, and a cam profile <NUM> on a second surface that is opposite the first surface. The driver profile <NUM> is configured to meshingly engage the flywheel profile <NUM> on the flywheel <NUM>. The flywheel profile <NUM> and driver profile <NUM> can cooperate to provide increased surface area over which the flywheel <NUM> and the driver <NUM> contact one another (relative to a configuration that employs a cylindrically-shaped surface on the flywheel <NUM> and a flat surface on the driver <NUM>) and/or can provide a configuration that maintains a desired level of contact between the flywheel <NUM> and the driver <NUM> despite the occurrence of wear on one or both of the flywheel <NUM> and the driver <NUM>. in the example provided, resistance to wear is created through the use of V-shaped grooves <NUM> in the flywheel profile <NUM> and mating V-shaped ribs <NUM> on the driver profile <NUM>. The driver blade <NUM> can be integrally and unitarily formed with the driver body <NUM> from an appropriate material, such as ISI <NUM> steel. The cam profile <NUM> is configured to be contacted by a pinch roller <NUM> of the PTU <NUM>. The cam profile <NUM> cooperates with the PTU <NUM> to coordinate the generation of a clamping force that is transmitted between the driver profile <NUM> and the flywheel profile <NUM>. In the example provided, the cam profile <NUM> includes a pair of contoured rails <NUM>, each of which having a first rest portion <NUM>, a loading ramp <NUM>, a sustained load portion <NUM>, an unloading ramp <NUM> and a second rest portion <NUM>. The first and second rest portions <NUM> and <NUM> are generally flat and are sized so that no or relatively little clamp load is generated when the pinch roller <NUM> is disposed on either of those portions. The sustained load portion <NUM> is configured to cooperate with the PTU <NUM> to generate a clamping force that is within a predetermined load range. The loading ramp <NUM> tapers from the first rest portion <NUM> to the sustained load portion <NUM>, while the unloading ramp <NUM> tapers from the sustained load portion <NUM> to the second rest portion <NUM>.

With reference to <FIG>, the PTU <NUM> can include an activation arm <NUM>, a yoke axle <NUM>, a pinch roller yoke <NUM>, the pinch roller <NUM>, a spring mount <NUM>, a spring <NUM>, a plunger <NUM>, a PTU solenoid <NUM> and a solenoid spring <NUM>. The activation arm <NUM> can be fixedly coupled to the motor mount <NUM> (<FIG>) and can include a pair of arm members <NUM>, each of which defining a spring slot <NUM>, which can be disposed generally parallel to a longitudinal driver axis <NUM> along which the driver <NUM> can translate, and an axle slot <NUM> that can be disposed generally perpendicular to the driver axis <NUM>. The yoke axle <NUM> can be received into the axle slots <NUM> in the arm members <NUM> so that the yoke axle <NUM> can rotate about its axis within the axle slots <NUM> and can move generally perpendicular to the driver axis <NUM> relative to the activation arm <NUM>. The pinch roller yoke <NUM> can be pivotably mounted on the yoke axle <NUM>. The pinch roller <NUM> can be rotatably mounted to the pinch roller yoke <NUM> at a location that is offset from the yoke axle <NUM>. The spring mount <NUM> can include a spring seat <NUM> and a spring arm <NUM>. The spring <NUM> can be received in the spring mount <NUM> such that a first end of the spring <NUM> abuts the spring seat <NUM> and a second, opposite end of the spring <NUM> abuts an end of the spring arm <NUM>. The spring mount <NUM> can include a pair of tabs <NUM>, each of which being received in a corresponding one of the spring slots <NUM>. The spring arm <NUM> defines an axle cam <NUM> that contacts the yoke axle <NUM>. The plunger <NUM> is coupled to an end of the spring arm <NUM> that is opposite the spring <NUM> and the spring mount <NUM>. The solenoid spring <NUM> is configured to bias the plunger <NUM> away from the PTU solenoid <NUM> and toward the spring seat <NUM>. The PTU solenoid <NUM> is configured to selectively generate a magnetic field that draws the plunger <NUM> in a direction that is parallel to the driver axis <NUM> into the PTU solenoid <NUM> against the bias of the solenoid spring <NUM>. Movement of the plunger <NUM> toward the PTU solenoid <NUM> causes corresponding motion of the spring arm <NUM>, and therefore corresponding translation of the axle cam <NUM> across the yoke axle <NUM>, which causes the axle cam <NUM> to drive the yoke axle <NUM> (and therefore the pinch roller yoke <NUM> and the pinch roller <NUM>) in a direction generally perpendicular to the driver axis <NUM> and toward the flywheel <NUM>.

Operation of the PTU solenoid <NUM> when the flywheel <NUM> is rotated within a predetermined speed range will cause the plunger <NUM> to move the spring mount <NUM> toward the PTU solenoid <NUM> so that the axle cam <NUM> drives the yoke axle <NUM>, and therefore the pinch roller <NUM>, toward the flywheel <NUM>. Initial contact between the pinch roller <NUM> and the first rest portion <NUM> of the cam profile <NUM> drives the driver profile <NUM> into contact with the (rotating) flywheel profile <NUM> so that the rotational energy of the flywheel <NUM> begins to drive the driver <NUM> along the driver axis <NUM> from a driver returned position or driver "home" position to a driver extended position or driver "driven" position. Movement of the driver <NUM> along the driver axis <NUM> toward the driver extended or driven position causes the pinch roller <NUM> to ride up the loading ramp <NUM> and onto the sustained load portion <NUM>, which drives the yoke axle <NUM> away from the flywheel <NUM>. Movement of the yoke axle <NUM> away from the flywheel <NUM> correspondingly moves the spring arm <NUM> so that the spring <NUM> is compressed between the spring seat <NUM> and the end of the spring arm <NUM>. A corresponding reaction force is applied through the yoke axle <NUM>, the pinch roller yoke <NUM>, and the pinch roller <NUM> to the driver <NUM> to provide the clamping force that drives the driver profile <NUM> into the flywheel profile <NUM> so that the rotational energy of the flywheel <NUM> can be rapidly transmitted to the driver <NUM> to rapidly accelerate the driver <NUM> along the driver axis <NUM>. Compression of the spring <NUM> is released as the unloading ramp <NUM> travels over pinch roller <NUM>. Additionally, the pinch roller yoke <NUM> pivots about the yoke axle <NUM> so that the pinch roller <NUM> pivots toward the PTU solenoid <NUM> when the pinch roller <NUM> is disposed over the second rest portion <NUM>. Thereafter, the driver return assembly <NUM> can be selectively operated by the controller <NUM> to return the driver <NUM> from the driver extended or driven position to the driver returned or home position.

With reference to <FIG>, the driver return assembly <NUM> comprises a return mount <NUM>, a return motor <NUM>, a return pawl <NUM>, and a return rack <NUM>. As illustrated, both the power take-off assembly <NUM> and the driver return assembly <NUM> can be positioned on the same side of the driver <NUM>. The return mount <NUM> can include a first girder <NUM>, a second girder <NUM> and a link <NUM> that is coupled to the first and second girders <NUM> and <NUM>. The first and second girders <NUM> and <NUM> can be formed of sheet steel and can be fixedly coupled to the return mechanism mount <NUM> (<FIG>) below the driver <NUM>. Each of the first and second girders <NUM> and <NUM> can have a side wall <NUM> that can define a pivot pin slot <NUM> that can be arranged generally parallel to the driver axis <NUM>. The link <NUM> can be formed of any suitable material, such as a plastic material and can be coupled to the first and second girders <NUM> and <NUM> in any desired manner. In the particular example provided, the link <NUM> rests on side walls <NUM> of the first and second girders <NUM> and <NUM>, a pin <NUM> is disposed through holes in the side walls <NUM> and the link <NUM>, and the link <NUM> abuts a pair of girder tabs <NUM>. Each of the girder tabs <NUM> can extend generally perpendicular from the side wall <NUM> of the associated one of the first and second girders <NUM> and <NUM> toward the other one of the girder tabs <NUM>.

The return motor <NUM> can comprise a solenoid <NUM>, a plunger <NUM>, a return spring <NUM>, and a bumper <NUM>. The solenoid <NUM> can include a solenoid housing <NUM>, which can be fixedly coupled to and span between the first and second girders <NUM> and <NUM>, and an electromagnetic coil <NUM> that can be received in the solenoid housing <NUM>. The solenoid housing <NUM> can define a plunger aperture <NUM>. The plunger <NUM> can have a plunger body <NUM> and a plunger flange <NUM>. A proximal end <NUM> of the plunger body <NUM> can be cylindrically shaped and can be received into the plunger aperture <NUM> in the solenoid housing <NUM>. A first pin bore <NUM> can be formed into a distal end <NUM> of the plunger body <NUM>. The plunger flange <NUM> can extend radially outwardly from the plunger body <NUM> proximate the distal end <NUM>. The return spring <NUM> can be a compression spring that can be received about the plunger body <NUM> between the plunger flange <NUM> and the solenoid housing <NUM>. in the example provided, the return spring <NUM> is wound in a conical manner so that a larger diameter end of the return spring <NUM> is abutted against the solenoid housing <NUM>, while a smaller diameter end of the return spring <NUM> is abutted against the plunger flange <NUM>. The return spring <NUM> can bias the plunger <NUM> into an extended position (shown in <FIG>) in which the first pin bore <NUM> is disposed a first distance away from the solenoid housing <NUM>. The bumper <NUM> can be a foam bumper and the plunger <NUM> can engage against the foam bumper <NUM> to absorb some momentum of the plunger <NUM> to stop the plunger <NUM> as it moves into its fully retracted position. This can help reduce some of the forces that the solenoid return spring <NUM> absorbs, which can significantly extend the life of the return spring <NUM> and the overall reliability of the nailer <NUM>. The bumper <NUM> can also facilitate immediate or essentially instantaneous reversal in movement of the plunger <NUM> from movement toward the retracted position to movement toward the extended position. The resulting forces on the plunger <NUM> can facilitate or speed pivotal movement of the return pawl <NUM> from its raised position to its lowered position, which positions are illustrated in, e.g., <FIG>, respectively, and described below. The electromagnetic coil <NUM> can be operated to generate a magnetic field that can move the plunger <NUM> toward the solenoid housing <NUM>/electromagnetic coil <NUM> so that the first pin bore <NUM> is disposed a second, smaller distance away from the solenoid housing <NUM>.

The return pawl <NUM> can comprise a pawl body <NUM>, a pawl tooth <NUM>, a return stop <NUM> and an extend stop <NUM>. The pawl body <NUM> can be a yoke-shaped structure that can be disposed about the plunger body <NUM> and can define a second pin bore <NUM> that can be aligned to the first pin bore <NUM>. A pivot pin <NUM> can be received through the first and second pin bores <NUM> and <NUM> to thereby pivotably couple the pawl body <NUM> to the distal end <NUM> of the plunger body <NUM>. The pivot pin <NUM> can be received in the pivot pin slots <NUM> and can extend through the first and second girders <NUM> and <NUM>. It will be appreciated that the pivot pin <NUM> can cooperate with the first and second girders <NUM> and <NUM> to inhibit rotation of the plunger <NUM> and the return pawl <NUM> about a longitudinal axis of the plunger <NUM>. The pawl tooth <NUM> can be fixedly coupled to the pawl body <NUM> and can be configured to engage the return rack <NUM>. The return stop <NUM> and the extend stop <NUM> can be fixedly coupled to the pawl body <NUM> on opposite sides of the second pin bore <NUM>. The return pawl <NUM> can pivot about the pivot pin <NUM> relative to the plunger <NUM> between a pawl returned or lowered position (shown in <FIG>), in which the return stop <NUM> is abutted against the plunger flange <NUM> and the pawl tooth <NUM> is in a lowered position, and a pawl extended or raised position in which the extend stop <NUM> is abutted against the plunger flange <NUM> and the pawl tooth <NUM> is in a raised position. Thus, the return pawl <NUM> can be coupled to a component, e.g., plunger <NUM>, of the return motor via a pivot pin <NUM>, and the return pawl <NUM> can be pivotable about the pivot pin <NUM> away from the return motor component <NUM> into the raised positon, and pivotable about the pivot pin <NUM> toward the return motor component <NUM> into the lowered positon.

As in the illustrated example, the return rack <NUM> can be positioned along a longitudinal length of the nail driver <NUM> and at an upper end of the nail driver <NUM> that is opposite its driving end. The return rack <NUM> can comprise a plurality of rack teeth <NUM> that can be fixedly coupled to (e.g., unitarily and integrally formed with) the driver <NUM>. The rack teeth <NUM> can be disposed on a lower side of the driver <NUM> in an area that is opposite the driver profile <NUM> (on the driver <NUM>) that is configured to engage the flywheel profile <NUM> (on the flywheel <NUM>). Each of the rack teeth <NUM> can have a tooth engagement face <NUM>, which is disposed generally perpendicular to a longitudinal axis of the driver <NUM>, and a relief face <NUM> that tapers from the distal end of the tooth engagement face <NUM> toward the upper side of the driver <NUM> and terminates at the tooth engagement face <NUM> of an adjacent one of the rack teeth <NUM>.

As described above, the controller <NUM> can control the operation of the electric motor <NUM> (<FIG>) and the PTU solenoid <NUM> (<FIG>) to cause the driver <NUM> to be rapidly propelled along the driver axis <NUM> to the driver extended or driven position. Thereafter, the controller <NUM> (<FIG>) can deactivate the PTU solenoid <NUM> (<FIG>). When a predetermined amount of time has elapsed after the PTU solenoid <NUM> (<FIG>) has been deactivated, the return motor <NUM> can be operated to cause the driver return assembly <NUM> to drive the driver <NUM> to the driver return or home position. <FIG> depict the driver return assembly <NUM> through one complete cycle in the operation of the return motor <NUM>.

With reference to <FIG>, the plunger <NUM> is in the plunger extended position and the return pawl <NUM> is disposed in the pawl returned position so that the pawl tooth <NUM> is in its lowered position and spaced apart from the rack teeth <NUM>.

With reference to <FIG>, electric power can be provided to the electromagnetic coil <NUM> to generate a magnetic field that draws the plunger body <NUM> into the electromagnetic coil <NUM>. It will be appreciated that translation of the plunger body <NUM> into the electromagnetic coil <NUM> causes the pivot pin <NUM> to correspondingly translate with the plunger body <NUM>. It is desirable that the return pawl <NUM> pivot about the pivot pin <NUM> in a relatively rapid manner as the plunger <NUM> is moved from the extended position toward the retracted position to cause the pawl tooth <NUM> to move from the lowered position to the raised position. It will be appreciated the return pawl <NUM> can be rotated about the pivot pin <NUM> by any desired means, such as a torsion spring (not shown). In the particular example provided, however, a magnet assembly <NUM> includes link <NUM>, a permanent magnet <NUM> and a pin <NUM>. The permanent magnet <NUM> (<FIG>) is mounted to the link <NUM> (<FIG>) and the magnet assembly <NUM>, via the permanent magnet <NUM>, the link <NUM>, the pin <NUM>, or any combination thereof, can include a surface <NUM> that is arranged to contact the return pawl <NUM> when the plunger <NUM> is disposed in the extended position. Contact between the surface <NUM> of the permanent magnet assembly <NUM> (<FIG>) and the return pawl <NUM> when the plunger <NUM> is moved from the retracted position to the extended position can aid in rotating the return pawl <NUM> about the pivot pin <NUM> to move the pawl tooth <NUM> from the raised position to the lowered position and retain it there while the plunger <NUM> is in the extended position. When the plunger <NUM> is moved from the extended position toward the retracted position, the magnetic field of the permanent magnet <NUM> (<FIG>) can cooperate with the ferro-magnetic material of the return pawl <NUM> to bias or draw the pawl tooth <NUM> toward the permanent magnet <NUM> (<FIG>) as the pivot pin <NUM> is moved in an opposite direction toward the electromagnetic coil <NUM>, which can correspond to a driven direction. The moment that is applied to the return pawl <NUM> (i.e., by the biasing magnetic force and the force of the plunger <NUM>) can cause the return pawl <NUM> to pivot about the pivot pin <NUM> as the plunger <NUM> is moved toward the retracted positon so that the pawl tooth <NUM> moves from the lowered position into the raised position such that the pawl tooth <NUM> is disposed between an adjacent pair of the rack teeth <NUM> as shown in <FIG>.

Further motion of the plunger <NUM> toward the retracted position can engage the pawl tooth <NUM> to the tooth engagement face <NUM> of one of the rack teeth <NUM> and thereafter, the driver <NUM> can move with the plunger <NUM> at <NUM>:<NUM> rate. <FIG> depicts the driver return assembly <NUM> and the driver <NUM> during this portion of the return cycle. Thus, as in the illustrated embodiment, this movement of the plunger <NUM> toward its retracted position can correspond to movement of the return pawl <NUM> in a driver homeward direction while the return pawl <NUM> is in a raised position relative to the nail driver in which the return pawl <NUM> is engageable with the return rack <NUM>.

Electric power to the electromagnetic coil <NUM> can be halted during the return cycle based on any desired criteria. In the particular example provided, the controller <NUM> (<FIG>) halts the supply of electric power to the electromagnetic coil <NUM> after a predetermined amount of time irrespective of whether or not the plunger <NUM> was actually moved to the retracted position. Alternatively, a sensor (not shown) could be employed to sense a position of the plunger <NUM> or the return pawl <NUM> and generate a sensor signal in response thereto that could be received and employed by the controller <NUM> (<FIG>) to control the timing at which the supply of electric power to the electromagnetic coil <NUM> is halted. Once electric power to the electromagnetic coil <NUM> is halted, the return spring <NUM> can urge the plunger <NUM> toward the extended position. Contact between pawl tooth <NUM> and any of the rack teeth <NUM> while the plunger <NUM> is in the retracted position (<FIG>) or as the plunger <NUM> is moved toward the extended position (<FIG>) can cause the return pawl <NUM> to pivot about the pivot pin <NUM> so that the pawl tooth <NUM> moves toward the lowered position. This permits the plunger <NUM> to be moved to the extended position as depicted in <FIG> without causing corresponding movement of the driver <NUM> toward the driver extended or driven position. Thus, as in the illustrated embodiment, this movement of the plunger <NUM> toward its extended position can correspond to movement of the return pawl <NUM> in a driver driven direction while the return pawl <NUM> is in a lowered position relative to the nail driver <NUM> in which the return pawl <NUM> is not engageable with the return rack <NUM>. Also as in the illustrated example, each of the homeward direction and the driven direction along which the return pawl <NUM> travels can comprise a linearly extending direction. Contact between the return pawl <NUM> and the link <NUM> (<FIG>) when the plunger <NUM> is in the extended position can drive the return pawl <NUM> about the pivot pin <NUM> so that the pawl tooth <NUM> is moved into and maintained in the lowered position. The return motor <NUM> can alternate between driving the plunger <NUM> and/or return pawl <NUM> in a homeward direction and in a driven direction. In addition, this can include driving or moving the plunger <NUM> and/or the return pawl <NUM> in a reciprocating motion.

As noted above, the controller <NUM> can control operation of the solenoid return motor. The controller <NUM> can include a circuit <NUM> that controls the electrical energization and de-energization of the return solenoid <NUM>. For example, the circuit <NUM> can include a discrete timing chip <NUM>, a series of logic gates <NUM>, a counter <NUM>, and input/output terminals <NUM> that are linked to a solenoid driver <NUM> for the solenoid <NUM>. As another example, the circuit <NUM> can analogously include a CPU <NUM>, memory <NUM>, a clock <NUM>, and an input/output <NUM> that is linked to a solenoid driver <NUM> for the solenoid <NUM>. In the CPU example, the CPU <NUM> can be programmed to energize and de-energize the return solenoid <NUM>. One example of such CPU programming can include: (<NUM>) sending a signal to the solenoid driver <NUM> to energize the solenoid <NUM> at a predetermined initiation period of time after the CPU initiates firing or driving of the driver <NUM>; then (<NUM>) at a predetermined period of energized time after the CPU sends the signal to energize the solenoid <NUM>, the CPU sends a signal to the solenoid driver <NUM> to de-energize the solenoid <NUM>; next, (<NUM>) the CPU increments a cycle register by <NUM> and compares that to a predetermined number of cycles; and: (4a) if the number in the cycle register is less than a than the predetermined number of cycles, then at a predetermined period of de-energized time after the CPU sends the signal to energize the solenoid, the CPU send a signal to the solenoid driver <NUM> to again energize the solenoid <NUM> and return to step (<NUM>); or (4b) if the number in the cycle register is equal to the predetermined number of cycles, then the CPU resets the cycle register to zero and stops this solenoid energization/de-energization loop.

It will be appreciated that depending on various factors, including the length of the stroke of the plunger <NUM>, the distance between the driver extended position and the driver return position, and the efficiency with which motion of the plunger <NUM> is converted into motion of the driver <NUM>, the return motor <NUM> may have to be operated through several full cycles to completely drive the driver <NUM> to the driver return position. In the particular example provided, the return motor <NUM> is cycled through five cycles, corresponding to the predetermined number of cycles, each time that the driver <NUM> is to be moved to the returned position, with a short dwell of approximately or about <NUM> seconds between the halting of one cycle and the starting of another cycle, corresponding to the predetermined period of de-energized time. It will also be appreciated that during one or more of the cycles, it may not be possible for the plunger <NUM> to move fully into the retracted position.

<FIG> are exemplary time-based plots depicting force and distance, respectively, as a function of time during the operation of the return motor <NUM>. in <FIG>, each cycle <NUM> of the return motor includes a first section <NUM>, in which force is applied by the plunger to engage the return pawl to the rack teeth, a second portion <NUM> in which movement of the plunger causes initial movement of the driver, and a third portion <NUM> in which the amount of force to move the driver falls off somewhat due to the inertia/momentum of the (moving) driver. In <FIG>, corresponding movement of the driver is shown, with segments <NUM> being the intervals at which the driver is moved.

<FIG> depicts two plots that demonstrate the relationships between the length of stroke of the plunger that is required to move the pawl tooth to the raised position and either the pawl angle (shown in solid line) or the force applied to the rack teeth along the driver axis (shown in broken line). The pawl angle is the angle at which the pawl tooth and the rack teeth are inclined relative to the driver axis. As will be appreciated from the figure, selection of a pawl angle for use on the pawl tooth and the rack teeth involves a trade-off between the amount of the stroke of the plunger that is employed to move the pawl tooth from the lowered position to the raised position, and the amount of force that is required to move the pawl tooth to the raised position. In the illustrated embodiment, the length of stroke of the plunger <NUM> is about <NUM> and the pawl angle through which the return pawl <NUM> pivots between the lowered and raised positions is about <NUM> degrees, and the length of the return pawl <NUM> from the pivot axis of pivot pin <NUM> to the distal end of the pivot pawl <NUM> is about <NUM>.

Claim 1:
A cordless electric nailer (<NUM>) comprising:
a power take-off assembly (<NUM>) positioned and operable to selectively engage a pinch roller (<NUM>) against a nail driver (<NUM>) having a home position to pinch the nail driver against a battery-powered electric motor driven flywheel (<NUM>) and fire the nail driver, characterised by;
a return rack (<NUM>) fixedly coupled to and positioned along a longitudinal length of the nail driver; and
a driver return assembly (<NUM>) positioned to return the nail driver to the home position, the driver return assembly including:
a solenoid (<NUM>) driving a plunger (<NUM>) in a reciprocating motion in a homeward direction and a driven direction;
a return pawl (<NUM>) coupled to the plunger and pivotable into a pawl raised position relative to the plunger in which the pawl is engageable with the return rack during movement of the plunger in the homeward direction, and pivotable into a pawl lowered position relative to the plunger in which the pawl is not engageable with the return rack during movement of the plunger in the driven direction.