Patent Description:
Flywheel driven fastening tools typically include a rotating flywheel that engages a driver to impart energy to the driver, causing the driver to move and drive or deform the fastener. Thus, a drive motor assembly can include an electric motor coupled to the flywheel to rotate the flywheel without engaging the driver. When activated, the drive motor assembly causes the rotating flywheel and driver to engage each other to propel the driver from the returned position to the extended position. In a cordless electric nailer, for example, fasteners, such as nails, are driven into a workpiece by a driver blade or driver through a process known as a "drive" or "drive cycle". Generally, a drive cycle involves the driver striking a fastener head during a drive stroke to an extended position and returning to a home or returned position during a return stroke. The structure of the drive motor assembly can result in changes in the attack angle or other changes that affect the efficiency with which the energy is transferred from the flywheel to the driver as the driver wears over the life of the tool.

Flywheel driven fastening tools can include a pinch roller positioned on the opposite side of the driver from the flywheel. The driver is sandwiched or pinched between the pinch roller and the flywheel to the transfer of energy from the flywheel to the driver. The pinch roller can permit flexing of the drive blade of the driver, resulting in detrimental oscillation of the fastener engaging end of the drive blade, as the driver moves along the drive path.

Flywheel driven fastening tools can include a driver return assembly. Typically, such driver return mechanisms include compression return springs mounted on guide rails along which the driver moves. These compression return springs are compressed during the drive stroke and operate to return the driver during the return stroke. Such compression return springs experience extremely high dynamic loading forces as the profile is accelerated and decelerated in driving a nail. For example, in some cases a driver profile can accelerate from zero to <NUM> meters per second in about <NUM> milliseconds. As a result, return springs of such a driver profile generate problematic surge velocity waves which are highly detrimental to a desired long fatigue life of the springs. In addition, the room that is required along the drive rails to accommodate the compressed spring at the end of the drive stroke, can limit the ability to shorten the length of the tool in the direction of the diver axis.

Accordingly, there remains a need to improve flywheel driven fastening tools to address the problems identified above or to address other problems of the drive motor assembly, the pinch roller, and the driver return assembly.

<CIT> relates to a nail driving machine provided with a tool main body, a fly wheel, a driver, a pressing mechanism, and a return mechanism. The pressing mechanism comprises a spring mechanism and a pressing roller. The pressing roller can rotate around a rotation axis and is supported so as to be movable in the left-right direction. During a driving process in which the driver moves from an initial position to a driving position, the press roller presses the driver toward the fly wheel by means of a biasing force of the spring mechanism, thereby enabling the transfer of rotational energy to the driver. The pressing mechanism is configured such that the position of the pressing roller with respect to the driver changes in the left-right direction during the driving process and a returning process, thus making it impossible for the driver to be pressed by the pressing roller during the returning process.

In accordance with some aspects of the present disclosure a flywheel driven fastening tool can include a fastener driver drivable along a driver axis and a flywheel driven by an electric motor. The flywheel can be mounted on a flywheel carriage, and the flywheel carriage can include a pair of axles. A tool frame can include two pairs of guide slots with opposite ends of each of the pair of axles positioned within the two pairs of guide slots. The flywheel carriage can be movable along the two pairs of guide slots between a disengaged position in which the flywheel is spaced from the fastener driver, and an engaged position in which the flywheel is engaged with the fastener driver to drive the fastener driver along a driver axis.

At least engagement ends of the two pairs of guide slots can extend linearly, and can be aligned with each other in a common plane. The two pairs of guide slots can extend linearly and can be aligned with each other in a common plane to guide each of the pair of axles of the flywheel carriage along the common plane as the flywheel carriage moves between the engaged position and the disengaged position. The common plane can extend at an acute angle relative to the driver axis that is between <NUM> and <NUM> degrees.

A bearing can be mounted on the opposite ends of each of the pair of axles. The bearing can rotate as the flywheel carriage moves along the two pairs of guide slots between the engaged position and the disengaged position.

The flywheel drive fastening tool can include a nosepiece assembly having a fastener discharge opening. The flywheel can be positioned closer to a fastener discharge opening of the nosepiece assembly and can be spaced from the fastener driver in the disengaged position. The flywheel can be positioned farther from the fastener discharge opening and in contact with the fastener driver in the engaged position.

The flywheel carriage can carry a permanent magnet that is operable to retain the flywheel carriage in the disengaged position. An electromagnetic actuator can be operable to move the flywheel carriage along the two pairs of guide slots between the engaged position and the disengaged position. The electromagnetic actuator can include a permanent magnet mounted on the flywheel carriage and an electromagnet. The electromagnet can have an activated state in which the permanent magnet is repelled by the electromagnet to move the flywheel carriage from the disengaged position to the engaged position along the two pairs of guide slots. The electromagnet can have an inactive state in which the permanent magnet is attracted to a core of the electromagnet to retain the flywheel carriage in the disengaged position along the two pairs of guide slots.

Both the flywheel and the electric motor can be mounted on the flywheel carriage. The flywheel and electric motor can be provided as a flywheel engine in which the flywheel and electric motor are integrated together into a single unit that is mounted on the flywheel carriage. The flywheel engine can include a brushless motor with an outer rotor, and the outer rotor of the brushless motor can include the flywheel.

In accordance with some aspects of the present disclosure a flywheel driven fastening tool can include a fastener driver drivable along a driver axis. The fastener driver can include a driver profile and a driver blade. A flywheel can be coupled to a tool frame and driven by an electric motor. The flywheel can be engageable with a flywheel side of the driver profile along a longitudinal flywheel engagement length. A pair of pinch rollers can be coupled to the tool frame and can be engageable with a pinch roller side of the driver profile that is opposite the flywheel side along a longitudinal roller engagement length of the pinch roller side of the driver profile. A plane aligned with an axis of rotation of the flywheel and oriented perpendicular to the driver axis can be located between an axis of rotation of each of the pair of pinch rollers throughout engagement of the flywheel with the fastener driver along the longitudinal flywheel engagement length.

The axes of rotation of the pair of pinch rollers can be spaced a longitudinal distance from each other that is <NUM>% or less of the longitudinal flywheel engagement length of the driver profile.

The flywheel side of the driver profile can have a flywheel engaging surface profile that is uniform along the longitudinal flywheel engagement length. The pinch roller side of the driver profile can have a roller engaging surface profile that is uniform along the longitudinal roller engagement length. The axis of rotation of each of the pair of pinch rollers can be fixedly positioned with respect to the tool frame. The pair of pinch rollers are mounted on a roller carriage that is coupled to the tool frame. The roller carriage can be fixedly positioned relative to the tool frame.

In accordance with some aspects of the present disclosure, the flywheel driven fastening tool can have a driver return assembly that can include a pivoting linkage that is pivotably coupled to the tool frame at a first end of the pivoting linkage. The pivoting linkage can be coupled to the fastener driver at a second end of the pivoting linkage. The second end is opposite the first end of the pivoting linkage. A spring can have a fixed spring end couipled to the tool frame and a moving spring end coupled to the pivoting linkage.

The spring can be a torsion spring. The torsion spring can be positioned around a spring axis, and the pivoting linkage can be coupled to the tool frame to pivot at the spring axis. The spring can be an expansion spring.

The pivoting linkage can include a first link arm pivotably coupled to a second link arm. The first end of the pivoting linkage can be a proximal end of the first link arm, and the second end of the pivoting linkage can be a distal end of the second link arm.

The second end of the pivoting linkage can include an elongated slot. A pin of the fastener driver can extend into the elongated slot to couple the second end of the pivoting linkage to the fastener driver. The pivoting linkage can include a single pivot arm having both the first end and the second end of the pivoting linkage.

In accordance with some aspects of the present disclosure, the flywheel driven fastening tool can be an electric cordless fastening tool. including a battery that can be mounted to a tool housing of the flywheel driven fastening tool and electrically coupled to the electric motor. The electric cordless fastening tool can be an electric cordless nailer, and the fastener driver can be a nail driver.

Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings, including when the corresponding parts are not identical.

With reference to <FIG>, one example of a flywheel driven fastening tool <NUM> in the form of a cordless nailer in accordance with the present disclosure is illustrated and described. The cordless nailer <NUM> can include a housing assembly <NUM>, a frame <NUM>, a control unit <NUM>, a drive motor assembly <NUM>, a nosepiece assembly <NUM>, a magazine assembly <NUM>, and a battery pack <NUM>. The housing assembly <NUM> can shroud all or portions of the frame <NUM>. The frame <NUM> can serve as a structure or foundation to which various components can be mounted. The housing assembly <NUM>, the control unit <NUM>, the nosepiece assembly <NUM>, the magazine assembly <NUM>, and the battery pack <NUM> can be constructed and operated to drive a fastener, such as a nail.

The drive motor assembly <NUM> can include a drive source <NUM>, which includes a motor <NUM> and a flywheel <NUM>. As in the illustrated example, the drive source <NUM> can comprise the motor <NUM> and the flywheel <NUM> being integrated together into a single unit to form a flywheel engine <NUM>. In an example flywheel engine <NUM>, the motor <NUM> can be an outer rotor brushless motor <NUM> with the flywheel <NUM> being an integral part of the outer rotor of the motor <NUM>. Alternatively, the drive source <NUM> can comprise separate motor <NUM> and flywheel <NUM> units, for example, where the motor <NUM> drives the flywheel <NUM> via a transmission (not shown) between the two separate units <NUM>, <NUM>. The drive motor assembly <NUM> can additionally include an electromagnetic actuator <NUM>.

In operation, fasteners, such as nails, are stored in the magazine assembly <NUM>, which sequentially feeds the fasteners into the nosepiece assembly <NUM>. The drive motor assembly <NUM> is operable to drive a driver <NUM> along a driver axis <NUM> aligned in a longitudinal direction of the driver <NUM>. The drive motor assembly <NUM> can be actuated by the control unit <NUM> to cause the driver <NUM> to translate along the driver axis <NUM> and impact a fastener in the nosepiece assembly <NUM>. The nosepiece assembly <NUM> guides the fastener as it is driven from the fastening tool <NUM> through a fastener discharge opening <NUM> of the nosepiece assembly <NUM> and into a workpiece.

The drive source <NUM> and an electromagnetic actuator <NUM> including an electromagnet <NUM> of the drive motor assembly <NUM> can be electrically driven. For example, electrical energy supplied from the battery pack <NUM> can be used to operate the motor <NUM> and the electromagnetic actuator <NUM>. The motor <NUM> is employed to drive the flywheel <NUM> so that energy may be transferred from the flywheel <NUM> to the driver <NUM> upon actuation of the electromagnetic actuator <NUM> to cause the driver <NUM> to translate along the driver axis <NUM> from a home or returned position (e.g., <FIG>) to an home or returned position (e.g., <FIG>).

The flywheel <NUM>, such as one provided by a flywheel engine <NUM>, can be mounted to a sliding flywheel carriage <NUM>. The flywheel <NUM> or flywheel engine <NUM> can be mounted between a pair of parallel axles <NUM> that form a portion of the sliding flywheel carriage <NUM>. Opposite ends of the axles <NUM> can include at least one bearing <NUM> or wheel. For example, opposite ends of each of the axles <NUM> can have a bearing or wheel <NUM> mounted thereon.

The fastening tool <NUM> includes a frame <NUM> and the frame can include a plurality of carriage guide slots <NUM>. As in the illustrated example, the guide slots <NUM> can extend through portions of the frame <NUM>. Alternatively, the carriage guide slots <NUM> can be provided by the frame <NUM> without extending completely through relevant portions of the frame <NUM>. As in the illustrated example, the frame <NUM> can include two pairs of guide slots <NUM> with opposite ends of the each of the pair of axles <NUM> received in one of the pair of guide slots <NUM>.

The guide slots <NUM> can have a disengaged end <NUM> and an engaged end <NUM>. When the axles <NUM> of the flywheel carriage <NUM> are positioned along the guide slots <NUM> at the disengaged end <NUM>, the carriage <NUM> and the flywheel <NUM> can be in a disengaged position in which the flywheel is spaced from the driver <NUM>. When the axles <NUM> of flywheel carriage <NUM> are positioned along the guide slots <NUM> at the engaged end <NUM>, the flywheel carriage <NUM> and the flywheel <NUM> can be in an engaged position in which the flywheel <NUM> is engaged with the driver <NUM>. The engaged end <NUM> of the guide slots <NUM>, and the flywheel carriage <NUM> and the flywheel <NUM> in the engaged position, can be positioned further from the fastener discharge opening <NUM> of the nosepiece assembly <NUM> than the disengaged end <NUM> of the guide slots <NUM>, and the flywheel carriage <NUM> and flywheel <NUM> in the engaged position and vice versa.

As in the illustrated example, the carriage guide slots <NUM> can extend linearly and can be aligned with each other. In alternative examples, the guide slots <NUM> can have an arcuate shape, can be misaligned with each other, or both. In some cases where the guide slots <NUM> have an arcuate shape, the engaged end <NUM> of the guide slots <NUM> can extend linearly and can be aligned with each other. The flywheel carriage <NUM> can slide along the guide slots <NUM> between an engaged position (e.g., <FIG>) toward the engaged end <NUM> of the guide slots <NUM> in which the flywheel <NUM> is engaged with the driver <NUM>, and a disengaged position (e.g., <FIG>) toward the disengaged end <NUM> of the guide slots <NUM> in which the flywheel <NUM> or flywheel engine <NUM> is disengaged, or spaced from the driver <NUM>. This engaged position arrangement results in the action of the spinning flywheel <NUM> engaging against the driver <NUM> generating a force that acts on the flywheel carriage <NUM> in the direction of the engaged end <NUM> of the guide slots <NUM>.

The guide slots <NUM> can operate as ramps that enable the flywheel <NUM> to be wedged against the driver <NUM> when the flywheel carriage <NUM> is slid to the engaged position along the guide slots <NUM>. The engaged end <NUM> or the entirety of the guide slots <NUM> can extend at an acute angle relative to the driver axis <NUM>. In some cases, this acute angle can be between <NUM> degrees and <NUM> degrees. In some cases, this acute angle can be between <NUM> degrees and <NUM> degrees; and in some cases, this acute angle can be <NUM> degrees. This angle can also be referred to as the attack angle at which the flywheel <NUM> engages the driver <NUM>.

The electromagnetic actuator <NUM> of the drive motor assembly <NUM> can operate to move the flywheel carriage <NUM> and flywheel <NUM> along the guide slots <NUM> between their respective engaged positions and disengaged positions. As in the illustrated embodiment, the electromagnetic actuator <NUM> can include a permanent magnet <NUM> carried by the flywheel carriage <NUM>. When the electromagnetic actuator <NUM> is not energized the permanent magnet <NUM> is in an inactive state, and the permanent magnet <NUM> can be attracted to the coil of the electromagnet <NUM> of the electromagnetic actuator <NUM> to retain the flywheel carriage <NUM> and flywheel <NUM> in their respective disengaged positions along the guide slots <NUM>. When the electromagnetic actuator <NUM> is energized the electromagnet <NUM> is in an activated state, and the electromagnet <NUM> of the electromagnetic actuator <NUM> can repel the permanent magnet <NUM> to drive the carriage <NUM> and the flywheel <NUM> into their respective engaged positions along the guide slots <NUM>.

Alternatively, the electromagnetic actuator <NUM> of the drive motor assembly <NUM> can include a reciprocating rod (not shown), such as a solenoid that is coupled to the flywheel carriage <NUM> to move the flywheel carriage <NUM> and flywheel <NUM> between their respective engaged and disengaged positions along the guide slots <NUM>.

Generally, in response to appropriate signals, the control unit <NUM> can be configured to energize the motor <NUM>, causing the flywheel <NUM> to rotate, and when the flywheel <NUM> is rotating at its firing speed, to energize the electromagnetic actuator <NUM> to drive the carriage <NUM> and flywheel <NUM>, such as provided by a flywheel engine <NUM>, from their respective disengaged to engaged positions along the guide slots <NUM>. In these engaged positions, the flywheel <NUM> engages the driver <NUM> to drive the driver <NUM> along the driver axis <NUM> and causing the driver <NUM> to engage and drive a fastener from the tool <NUM> through the discharge opening <NUM> and into a workpiece (not shown).

The driver <NUM> can include a driver profile <NUM> and a driver blade <NUM>. The flywheel <NUM> can engage the driver <NUM> along a flywheel side of the driver profile <NUM>. The flywheel <NUM>, such as one provided by a flywheel engine <NUM>, can have outer circumferential grooves <NUM> that mate with cooperating axial or longitudinal grooves <NUM> along the flywheel side of the driver profile <NUM>. The cooperating or longitudinal grooves of the flywheel side of the driver profile <NUM> define a flywheel engaging surface profile that is uniform along the longitudinal flywheel engagement length of the driver <NUM>. For example, the flywheel engaging surface profile does not vary or ramp up and down along the longitudinal flywheel engagement length of the driver <NUM>. These cooperating grooves <NUM>, <NUM> increase the frictional contact area between the flywheel <NUM> and the driver <NUM>. The driver blade <NUM> engages and drives the fastener, such as a nail, from the tool <NUM> as the driver <NUM> moves along the driver axis <NUM> toward the discharge opening <NUM>.

As in this example, the flywheel driven fastening tool <NUM> can include a pair of pinch rollers <NUM> coupled to the frame <NUM>. The pinch rollers <NUM> can be part of a roller assembly <NUM> that includes a roller bracket or carriage <NUM>, which can be coupled to the frame <NUM>. The pinch rollers <NUM>, roller carriage <NUM>, and the roller assembly <NUM> can be coupled to the frame <NUM> in a fixed position relative to the frame <NUM>. Alternatively, the pinch rollers <NUM> can be pivotable or slidable relative to the frame <NUM> toward and away from the driver <NUM>.

The pinch rollers <NUM> can be positioned on a pinch roller side of the driver profile <NUM>, which pinch roller side is opposite the flywheel side of the driver profile <NUM>. As a result, the driver profile <NUM> of the driver <NUM> can be disposed or sandwiched between the flywheel <NUM> and the pair of pinch rollers <NUM>. As the carriage <NUM> and flywheel <NUM> move from their disengaged position to their engaged position, the flywheel <NUM> engages the driver profile <NUM> and pinches it between the flywheel <NUM> and the pinch rollers <NUM>. Alternatively, the pinch rollers <NUM> can move relative to the frame <NUM> to an engaged position to pinch the driver profile <NUM> of the driver <NUM> against the flywheel <NUM>, with or without movement of the flywheel <NUM> relative to the frame <NUM>. The pinching action provided by the flywheel <NUM> and pinch rollers <NUM> facilitates efficient transfer of energy from the flywheel <NUM> to the driver <NUM>.

The pinch roller side of the driver profile <NUM>, can have a pinch roller engaging surface profile that is uniform along a longitudinal pinch roller engagement length thereof. For example, the flywheel engaging surface profile does not vary or ramp up and down along the longitudinal roller engagement length of the driver <NUM>.

The pair of pinch rollers <NUM> each have a roller axis <NUM> about which each rotates and the flywheel <NUM> has a flywheel axis <NUM> about which it rotates. A plane <NUM> that extends along the flywheel axis <NUM> and that extends perpendicular to the driver axis <NUM> can be located between the roller axis <NUM> of each of the pair of pinch rollers <NUM> as shown in <FIG>. In addition, the plane <NUM> can be located between and parallel to the pair of roller axes <NUM> of the pair of pinch rollers <NUM> throughout engagement of the flywheel <NUM> and the pinch rollers <NUM> with the driver <NUM>. As a result of each roller axis of rotation <NUM> being on opposite sides of the plane <NUM> and of the flywheel axis <NUM>, the pair of pinch rollers <NUM> operate to keep the driver <NUM> aligned with the driver axis <NUM> during its engagement with the flywheel <NUM> and pinch rollers <NUM>, which in turn helps minimize unwanted flexing of the driver blade <NUM> of the driver <NUM>.

In some cases, a distance between the pair of roller axes <NUM> can be <NUM>% or less than a longitudinal engagement length of the driver profile <NUM>. In some cases, the distance between the pair of roller axes <NUM> can be <NUM>% or less than the longitudinal engagement length of the driver profile <NUM>. In some cases, the distance between the pair of roller axes <NUM> can be <NUM>% or less than the longitudinal engagement length of the driver profile <NUM>. As used herein, the longitudinal engagement length of the driver profile <NUM> means the overall longitudinal length along which the flywheel <NUM> contacts the driver profile <NUM> during operation of the tool.

As in this example, the flywheel driven fastening tool <NUM> can include a driver return assembly <NUM> coupled to the frame <NUM>. The driver return assembly <NUM> can include a spring <NUM> and a pivoting linkage <NUM> providing a coupling between the spring <NUM> and a trailing end of the driver <NUM>. The driver <NUM> can be guided along the driver axis <NUM> by a pair of guide rails <NUM> as the driver <NUM> moves between an extended position (e.g., <FIG>) and a return or home position (e.g., <FIG>).

As in this example the spring <NUM> can be a torsion spring, and the pivoting linkage <NUM> can include two link arms <NUM>, <NUM>. For example, first link arm <NUM> can be pivotable about an axis <NUM> of the torsion spring <NUM> and can be coupled between the torsion spring <NUM> and a second link arm <NUM>. The second link arm <NUM> can be pivotably coupled to and between the first link arm <NUM> and a trailing end of the driver profile <NUM> of the driver <NUM>. A fixed spring end <NUM> can be fixedly coupled to the frame <NUM> and a moving spring end <NUM> can be coupled to the first link arm <NUM> to bias the pivoting linkage <NUM> and the driver <NUM> into their respective return or home positions. The first link arm <NUM> can have an L-shape or hockey stick shape, for example.

As in the example illustrated in <FIG>, the pivoting linkage <NUM> can be a single link arm <NUM> that includes a slot <NUM> at one end through which a protruding pin <NUM> of the trailing end of the driver <NUM> is disposed. The single link arm <NUM> of the pivoting linkage <NUM> can be pivotable about an axis <NUM> of the torsion spring <NUM> with the moving spring end <NUM> coupled thereto. The slot <NUM> enables the pivoting motion of the single link arm <NUM> of the pivoting linkage <NUM> to be converted to the linear motion of the driver <NUM> along the guide rails <NUM> as the single link arm <NUM> of the pivoting linkage <NUM> pivots and the driver <NUM> moves along the driver axis <NUM>.

As in the example illustrated in <FIG>, the spring <NUM> can be an expansion spring. The expansion spring <NUM> can be coupled between the single link arm <NUM> of the pivoting linkage <NUM> and the frame <NUM>.

As in the examples of <FIG>, and <FIG>, the flywheel carriage <NUM> can be a pivoting carriage <NUM>, which pivots about a pivot axis <NUM>. The actuator <NUM> can operate to pivot the carriage <NUM> clockwise (as oriented in <FIG>, and <FIG>) to bring the flywheel <NUM> into contact with the driver profile <NUM> of the driver <NUM>.

With respect to an X, Y, Z three dimensional coordinate system and the example embodiments illustrated and described herein, the driver axis <NUM> and longitudinal direction of the driver <NUM> are each oriented or extend in the X direction. Each of the flywheel axis <NUM> of rotation, the roller axes <NUM> of rotation, the axis of rotation or central axis of the axles <NUM>, the axis of rotation of the wheels or bearings <NUM>, the axis <NUM> of the torsion spring <NUM>, and a pivot axis <NUM> of the pivoting flywheel carriage <NUM> are oriented or extend in the Z direction, and the plane <NUM> is oriented or extends in the Z and Y directions.

As used herein, a "single pivot arm" means one and only one pivot arm. Although the single pivot arm can be made up of multiple parts, a single pivot arm does not include multiple arms or sections between its coupling ends that pivot relative to each other.

While the fastening tool is illustrated as being electrically powered by a suitable power supply or energy storage device, such as the battery pack, those skilled in the art will appreciate that the disclosure, in its broader aspects, may be constructed somewhat differently and that aspects of the present disclosure may have applicability to pneumatically powered fastening tools. Furthermore, while aspects of the present disclosure are described herein and illustrated in the accompanying drawings in the context of a fastening tool, those of ordinary skill in the art will appreciate that the disclosure, in its broadest aspects, has further applicability. For example, the drive motor assembly may also be employed in various other mechanisms that use reciprocating motion, including rotary hammers, hole forming tools, such as punches, and riveting tools, such as those that install deformation rivets.

Claim 1:
A flywheel driven fastening tool comprising:
a fastener driver drivable along a driver axis, and the fastener driver including a driver profile and a driver blade;
a flywheel coupled to a tool frame and driven by an electric motor, and the flywheel being engageable with a flywheel side of the driver profile along a longitudinal flywheel engagement length; and
a pair of pinch rollers coupled to the tool frame and being engageable with a pinch roller side of the driver profile that is opposite the flywheel side along a longitudinal roller engagement length of the pinch roller side of the driver profile;
wherein a plane aligned with an axis of rotation of the flywheel and oriented perpendicular to the driver axis is located between an axis of rotation of each of the pair of pinch rollers throughout engagement of the flywheel with the fastener driver along the longitudinal flywheel engagement length.