Patent Description:
The present disclosure relates generally to surgical instruments and use thereof. More specifically, the present disclosure relates to a bi-spring surgical impact tool and methods of use thereof.

Orthopedic surgeons commonly utilize tools for cutting or carving bone that require a hammer or mallet to transmit an impaction force to the tool. An example is a broach tool used to prepare the proximal end of a femur to receive the stem of a hip implant. Such broaches can be used with a hammer wielded by the physician or with a pneumatic "jackhammer"' like tool. However, striking a broach tool with a hammer can be tiresome and can cause high stresses on the physician's own joints, such as the shoulder joint. Furthermore, pneumatic impact tools require connection to an air hose, which can be inconvenient and can potentially limit the physician's ability to orient the tool in the desired manner. <CIT> discloses a motor-driven orthopedic impacting tool provided for orthopedic impacting in the hips, knees, shoulders and the like. The tool comprises a housing defining a cavity; a shuttle located within the cavity and defining a plurality of indentations, a pinion located proximate the shuttle and having a plurality of protrusions sized to mesh with the plurality of indentations during rotation of the pinion; two spring mechanically coupling the housing to the shuttle; wherein rotation of the pinion translates the shuttle in a linear direction.

The present invention provides a bi-spring surgical impact tool as defined in claim <NUM>.

Optionally the pinion carriage comprises a pinion plate defining a plurality of spokes, each of the plurality of bearings connected to a respective spoke of the pinion plate.

Optionally the pinion carriage comprises first and second pinion plates defining a plurality of spokes, each of the plurality of bearings located in between respective spokes of the first and second pinion plates.

Optionally the bi-spring impact tool includes a drive rod oriented along an axis of the housing extending from the first end of the housing to the second end of the housing, the shuttle translatable along the drive rod, the shuttle and drive rod movable in the first and second linear directions along the axis of the housing. Optionally the first and second springs are located axially along a longitudinal axis of the drive rod. Optionally the bi-spring impact tool further includes a drive rod collar affixed to the drive rod; and an insert coupled to the first spring and arranged to impact the drive rod collar upon disengagement of the plurality of protrusions from the plurality of the indentations.

Optionally the bi-spring surgical impact tool includes a motor; a switch; and a sensor arranged to detect a position of the shuttle and in electrical communication with the switch, wherein when the shuttle is out of position to allow the plurality of indentations of the shuttle to mesh with the plurality of the protrusions of the pinion, the switch severs electrical communication of the motor to a power supply.

Optionally, the sensor is a Hall effect sensor.

Optionally the bi-spring impact tool includes a chuck mechanically coupled to the shuttle.

Further described herein is a bi-spring surgical impact tool comprising: a housing defining a cavity having a housing axis that extends from a first end of the housing to a second end of the housing; a drive rod having a drive rod axis oriented parallel to the housing axis; a drive rod collar connected to the drive rod; a shuttle translatable along the drive rod and having a plurality of shuttle teeth; a pinion located proximate the shuttle and having a plurality of pinion teeth sized to mesh with the plurality of shuttle teeth; a first spring mechanically coupling the first end of the housing to the first end of the shuttle, the first spring located coaxially with the drive rod; and a second spring mechanically coupling the second end of the housing to the second end of the shuttle, the second spring located coaxially with the drive rod, wherein rotation of the pinion in a first rotational direction translates the shuttle in a first direction towards the first end of the housing and rotation of the pinion in a second rotational direction translates the shuttle in a second direction towards the second end of the housing, wherein when the shuttle is out of position to allow the plurality of shuttle teeth to mesh with the plurality of pinion teeth, the shuttle is movable by the first and second springs.

The pinion comprises: a pinion carriage; and a plurality of bearings that may form the teeth.

Optionally, the pinion carriage comprises a pinion plate defining a plurality of spokes, each of the plurality of bearings connected to a respective spoke of the pinion plate.

Optionally, the pinion carriage comprises first and second pinion plates defining a plurality of spokes, each of the plurality of bearings located in between respective spokes of the first and second pinion plates.

Optionally, the bi-spring surgical impact tool includes a motor; a switch; and a sensor arranged to detect a position of the shuttle and in electrical communication with the switch, wherein when the shuttle is out of position to allow the plurality of shuttle teeth to mesh with the plurality of pinion teeth, the switch severs electrical communication of the motor to a power supply.

Further described herein is a bi-spring surgical impact tool comprising: a housing defining a cavity having a housing axis that extends from a first end of the housing to a second end of the housing; a drive rod having a drive rod axis oriented parallel to the housing axis; a drive rod collar connected to the drive rod; a shuttle translatable along the drive rod and having a plurality of shuttle teeth; a pinion located proximate the shuttle and having a plurality of pinion teeth sized to mesh with the plurality of shuttle teeth; a first spring mechanically coupled to the first end of the housing, the first spring located coaxially with the drive rod; a first insert coupled to the shuttle and the first spring, the first insert defining a first insert shoulder arranged to contact the drive rod collar and drive the drive rod in a first linear direction under a first force generated by the first spring; a second spring mechanically coupled to the second end of the housing, the second spring located coaxially with the drive rod; and a second insert coupled to the shuttle and the second spring, the second insert defining a second insert shoulder arranged to contact the drive rod collar and drive the drive rod in a second linear direction under a second force generated by the second spring, wherein rotation of the pinion in a first rotational direction translates the shuttle in the second linear direction and rotation of the pinion in a second rotational direction translates the shuttle in the first linear direction, wherein when the shuttle is out of position to allow the plurality of shuttle teeth to mesh with the plurality of pinion teeth, the shuttle is movable by the first and second springs in the first and second directions.

Optionally, the pinion comprises: a pinion carriage; and a plurality of bearings that form the plurality of pinion teeth.

In the drawings, which are not necessarily drawn to scale, like numerals can describe similar components in different views. Like numerals having different letter suffixes can represent different instances of similar components.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate exemplary embodiments of the disclosure, and such exemplifications are not to be construed as limiting the scope of the disclosure in any manner.

As an alternative to a pneumatic piston driven system, disclosed herein are spring driven systems. Specifically, the surgical impact tools disclosed herein can include a bi-spring design. The surgical impact tools disclosed herein can include a housing that defines a cavity having a first end and a second end. A shuttle located within the cavity can define a plurality of indentations. As disclosed herein, a pinion located proximate the shuttle can have a plurality of protrusions sized to mesh with the plurality of indentations during rotation of the pinion. First and second springs can mechanically couple the housing to the shuttle. Rotation of the pinion in a first direction can translate the shuttle in a first direction towards the first end of the housing and rotation of the pinion in a second direction can translate the shuttle in a second direction towards the second end of the housing.

During use, when the protrusions and the indentations are no longer in a meshing engagement, the springs can cause the shuttle to move about a drive rod. The drive rod can be oriented along an axis of the housing and can extend from the first end of the housing to the second end of the housing. A drive rod collar can be affixed to the drive rod. An insert can be coupled to the first spring and arranged to impact the drive rod collar upon disengagement of the plurality of protrusions from the plurality of the indentations. The impact of the shuttle hitting the drive rod collar can cause the drive rod to transfer an impact force to a tool, such as a rasp, broach, etc., attached to a chuck of the surgical impact tool.

The pinion can include a pinion carriage and a plurality of bearings. The bearings can form the plurality of protrusions. The pinion carriage can include one or more pinion plates that define a plurality of spokes. Each of the plurality of bearings can be connected to a respective spoke of the pinion plate. When the pinion includes two pinion plates, each of the plurality of bearings can be located in between respective spokes of first and second pinion plates.

The surgical impact tool can include a motor that causes the pinion to rotate and move the shuttle. A switch can be electrically coupled to the motor and a sensor. The sensor can be arranged to detect a position of the shuttle. When the shuttle is out of position to allow the plurality of indentations of the shuttle to mesh with the plurality of the protrusions of the pinion, the switch can sever electrical communication of the motor to a power supply. The sensor can be a Hall effect sensor.

The above discussion is intended to provide an overview of subject matter of the present patent application. The description below is included to provide further information about the present patent application.

Turning now to the figures, <FIG> shows an embodiment of a bi-spring power impact tool <NUM> according to various principles of the present disclosure. <FIG> shows an isometric cutaway view of the bi-spring power impact tool <NUM> in the neutral position, waiting to be activated. <FIG> shows a close up of the region around a motor mounting block (MMB) <NUM>. The bi-spring power impact tool <NUM> can have a handle <NUM> with grip <NUM> and trigger <NUM> in an upper handle portion <NUM>. A base <NUM> of the handle can contain a control circuit and can receive a removable and rechargeable battery <NUM>, such as commonly used with cordless power tools. The top of the handle <NUM> can connect to the motor mounting block <NUM>. The motor mounting block <NUM> can contain a mount for the gearmotor <NUM> (see <FIG>) and the spring and shuttle tube (SST) <NUM>.

As shown in <FIG>, the spring and shuttle tube <NUM> can include an outer tube <NUM> that contains a distal spring 160D and a proximal spring 160P, a shuttle <NUM> and a driver <NUM>. The distal end of the spring and shuttle tube <NUM> can include an end cap 112B connected to a distal end of the outer tube <NUM>, with a cover cap 112A connected to the end cap 112B. An end cap <NUM> can be provided at the proximal end of the outer tube <NUM>. The end cap <NUM> can include an aperture with a proximal end of the driver <NUM> extending through the aperture. A tool holder <NUM> can be attached to the proximal end of the driver <NUM>. The driver <NUM> can include an elongated drive rod <NUM>. A stop collar <NUM> can be attached on the distal end of the rod <NUM>. The stop collar <NUM> can be attached by a clamp-on, screw-on, clip-on or other connection method. An impact flange <NUM> can be disposed on a central region of the rod <NUM>. The impact flange <NUM> can be formed integral with the rod <NUM> for structural integrity. The tool holder <NUM> can be attached to the proximal end of the drive rod <NUM> by threading, for example, so it can be easily changed if needed.

A soft blow clip (SBC) <NUM> can be snapped onto the drive rod <NUM>. The soft blow clip <NUM> can alternatively slide onto the end cap 112B that could even allow for several different displacement settings by clicking into place to provide different settings for intensity of impact desired. A similar clip can be used at the distal end of the drive rod.

In another embodiment a rotary sleeve can be disposed between end cap <NUM> and tool holder <NUM> and can include an internal shelf disposed only on a portion of the rotary sleeve and the shelf can rotate to engage with a mating and similarly restricted shelf disposed on the proximal face of the end cap <NUM>. Helical ramps adjacent to the shelves can allow the user to access the functionality of the soft blow clip <NUM> by rotation of the sleeve, providing similar displacement(s).

In the neutral state, the distal die spring 160D and proximal die spring 160P can be compressed (preloaded) to approximately half of their maximum deflection state (typically about <NUM>% of their free length). The ends of the springs 160D and 160P can reside in counter bores 171D and 171P in the shuttle <NUM> respectively for the distal and proximal spring ends respectively that press on the shuttle <NUM> to maintain their coaxial alignment with the shuttle <NUM> and the drive rod <NUM>.

The spring 160D, 160P can be die springs because the "coils" are made from rectangular cross section material so they tend to provide lateral rigidity to the spring so it is less likely to buckle sideways which could lead to rubbing (energy loss and especially when heavily compressed). Another design detail of efficient robust (low-wear) mechanisms is that helical (coil) springs can rotate slightly when they are compressed. Thus, when two springs are preloaded against the shuttle <NUM>, one of the springs 160D, 160P can be made with a clockwise helix and the other of the springs 160D, 160P be made with a counterclockwise helix to counteract the rotation of one another and minimize rubbing induced energy losses and wear. Additionally, thrust washer can be used to allow for low friction rotation of the springs and shuttle mechanisms.

Referring to <FIG>, the shuttle <NUM> can have integral annular gear rack drive teeth <NUM> (<NUM> teeth are shown with a <NUM> pitch) which are offset with respect to the central plane of the shuttle <NUM> to enable proper fore and aft position for forward and reverse impact. A partial tooth pinion <NUM> can drivingly engage the shuttle <NUM>. Three annular teeth <NUM> (the drive teeth 175P (proximal), <NUM> (middle) and 175D (distal)) of the shuttle <NUM> can be used for driving the shuttle <NUM> forward and three annular teeth (the retract teeth 175RP, 175RM and <NUM> RD) can be used for retracting the shuttle <NUM> forward. When the distal drive tooth 175D is offset from the center of shuttle <NUM> by a distance of P/<NUM>, the distal drive tooth 175D is positioned for initial engagement of the tooth 302C of the partial tooth pinion <NUM> at the start of the process for moving the shuttle <NUM> to displace the springs <NUM>. However, because only a partial tooth pinion <NUM> is used, as tooth 302a comes around to re-engage the rack, an additional offset of about P/<NUM> (plus about <NUM> for the <NUM> pitch gear as discussed below) is needed to ensure it does not collide with the drive tooth <NUM> (the middle drive tooth).

The springs 160D, 160P can be mounted on either side of the shuttle <NUM> with integral "annular" gear rack drive teeth <NUM> (the pitch diameter is infinite so the flanks of the teeth <NUM> need not be involutes but rather straight). The annular teeth <NUM> can wrap around the circumference of the shuttle <NUM> because when a coil spring is compressed, it can rotate slightly, and if a conventional section of a gear rack (straight across and not wrapped annular) were machined into the shuttle <NUM> (or mounted), as the shuttle <NUM> compresses the springs (e.g. 160P and 160D), its rotation can cause straight-across teeth <NUM> to rotate and edge load the drive gear <NUM> resulting in high contact stresses and early tooth wear. The shuttle <NUM> can include an inner cavity <NUM> that can be sized as shown in <FIG>.

The shuttle <NUM> can be held concentric to the drive rod <NUM> with distal and proximal sliding contact flanged bearings 174D and 174P, respectively. Flanged bearings 174D and 174P can prevent rotation of the drive rod and therefore tool holder <NUM>. Once installed and the springs are preloaded to the shuttle <NUM>, the ends of springs 160D and 160P can keep the bearings 174D and 174P in place. The bearing can be manufactured from PEEK so as to allow for sliding contact and is steam sterilizable. Bearings 174DD and 174PP can center the drive rod <NUM> in the housing end caps 112b and <NUM>, respectively. Bearings 174D and 174P can center the shuttle <NUM> on the drive rod <NUM> during cocking and can keep it centered while the shuttle <NUM> is moving fast to impact the driver <NUM>'s center impact flange <NUM>.

As disclosed herein, the elements can be collinear, and this can result in the drive rod <NUM> being slender in order to fit down the center of the springs <NUM> and the shuttle <NUM>. From a mass perspective, this can be beneficial because the mass of the drive rod <NUM>, plus the mass of the tool holder <NUM> and the tool held therein can all be considered the system mass being driven by the impact force from the shuttle <NUM>. However, as disclosed herein, the drive rod <NUM> can also support the shuttle <NUM> while it is being cocked, and if the gear tooth separation forces push radially too hard on the drive rod <NUM> for its size, it can deflect and cause the gear teeth to skip.

In the neutral state, such as just after the driver <NUM>'s impact flange <NUM> has been impacted on its distal side by shuttle <NUM>'s distal flange <NUM>, the springs <NUM> can have oscillated for a few cycles after impact but have come to rest, typically is <NUM>-<NUM> cycles which will take a on the order of <NUM>-<NUM> milliseconds as the natural frequency of the shuttle <NUM> can be about <NUM>. The impact can be a mix of elastic and inelastic and while one might think that a heavier shuttle <NUM> may be better for energy transfer, too heavy and the speed will be slow including the time to come to rest because the natural frequency will be low. The blows per second required by the surgeon, typically in the range of <NUM>-<NUM>, can be selected by the surgeon and controlled by the control circuits in the base <NUM>), which are governed by the rotation of the partial tooth pinion (PTP) <NUM> by the gearmotor <NUM>. The gearmotor <NUM> can revolve at a constant rate during the period of use for a set rate of impacts as this allows the gearmotor <NUM>'s reflected rotational inertia at the PTP <NUM>, which is considerable, to contribute to the effort to cock the shuttle170 for another strike, thereby helping with overall system efficiency and increased battery life.

To rotate at a constant speed for a set impact rate, once the last tooth 302A has cleared the shuttle proximal drive tooth 175P, the shuttle <NUM> can be propelled forward by the stored energy in the springs 160D and 160P. As disclosed herein, the two opposed compression springs each of stiffness k can both contribute to the forward energy of the system, because they are preloaded against each other. They act as one with bidirectional stiffness <NUM> as long as they are preloaded against each other. Meanwhile, as the shuttle <NUM> is accelerating forward increasing its kinetic energy as it is transferred to the shuttle <NUM> from the stored potential energy in the springs 160D and 160P, the PTP <NUM> continues to rotate. The shuttle <NUM> impacts the drive rod <NUM> and settles down in time for PTP tooth 302C to have come around and make contact with the shuttle distal drive tooth 175D as shown in the system neutral position in <FIG> and <FIG>.

For full strength forward impact, the user can push the bi-spring powered impact tool <NUM> forward such that the soft blow clip (SBC) <NUM> (or another spacer embodiment) can be pressed against the proximal surface of the end cap <NUM>, which can displace the drive rod <NUM>'s impact flange <NUM> backwards. The impact flange <NUM>'s distal face can then be pressed against the proximal face of the shuttle <NUM>'s impact flange <NUM>. At this point the PTP tooth 302C can have engaged the shuttle distal drive tooth 175D and turned counterclockwise as shown will move the shuttle <NUM> back to the ready-to-fire position shown in <FIG> and <FIG>. <FIG> shows the progression of steps from initial making of tooth contact (a), to the end of rolling contact between the involute teeth (b), to the final displaced position where the tooth 302A breaks contact with the shuttle proximal drive tooth 175P.

Rotation of the PTP <NUM> from initial contact to final moment of rolling can cause linear motion of the rack as shown in <FIG>. The tooth 302A can break contact with the shuttle drive tooth 175P and the shuttle <NUM> is thus released and accelerates towards the driver <NUM>'s impact flange <NUM>. During this period of motion, there can be sliding contact between tooth 302A and 175P. If finer resolution of motion is desired, a finer pitch can be used but then the teeth may be smaller and weaker.

The gear teeth base material (e.g., <NUM> and <NUM>) can be hardened (RC50 or more), ground with tips rounded and coated with a wear resistant coating, such as tungsten carbide applied by physical vapor deposition. As the teeth are not large with respect to depth of contact stresses, they can be through hardened. A dry laminar solid lubricant can also be applied during the coating process, one such as tungsten disulfide WS<NUM>, a soft lamellar material similar to graphite/MoS<NUM>. Also note that since the coating has a much higher modulus of elasticity and strength than the base steel of the gear the contact stress can be limited by that of the steel, for if the steel should yield below the coating layer thickness, the coating would peel off. In a gear with full circumference of teeth engaging another gear with full circumference of teeth, the tooth tip edge does not make high stress contact and thus is generally not rounded over; yet here the last tooth's tip does make high force contact with the rack teeth just before firing. This tooth tip edge to edge contact is like the edges of a trigger system, and thus care can be needed to prevent unacceptable wear.

Driver <NUM>'s impact flange <NUM> can be impacted on its distal face to produce force in the forward (proximal) direction for driving a tool into an object (e.g., a femur) by distal drive flange <NUM>'s proximal face. The distal drive flange <NUM> can be integrally made with the shuttle <NUM> as it can be subject to the highest stresses. The distal spring 160D can be coaxial with the driver <NUM> and the flange <NUM> and thus force can be applied directly to the opposite side of the flange that impacts the driver flange <NUM> thereby making a very robust design.

For retraction of the driver <NUM>, as shown in <FIG> and <FIG> (and see <FIG> and <FIG> for the shuttle's <NUM> components), the flange insert <NUM>, which can be seated against counterbore face <NUM> in the shuttle <NUM>'s proximal end, can be held in place with internal snap ring <NUM>. In the retract mode the force does not have to be as high. This can be adjusted at assembly by making the driver <NUM>'s end clamp on stop collar <NUM> (see <FIG>). A snap ring can take the load, but it may be somewhat more dissipative (i.e., less efficient) than the integral flange <NUM>.

For rearward impact to extract a tool, the user can pull the bi-spring impact tool <NUM> backwards such that stop end collar <NUM> is pressed against the counterbore in end cap 112B and the proximal surface of the driver <NUM>'s impact flange <NUM> faces the distal surface of the shuttle's flange insert <NUM>. Selecting reverse (e.g., by a reverse button on the handle180) and activating the gearmotor <NUM> (e.g., with the switch <NUM> on the handle <NUM>), the PTP <NUM> can rotate in the opposite direction for forward impact, and now the PTP tooth 302A can engage the shuttle <NUM>'s proximal retract tooth 175RP and turning clockwise as shown, can move the shuttle <NUM> forward to the ready-to-fire position, shown in <FIG>, until the tooth 302C breaks contact with the shuttle <NUM>'s distal retract tooth 175RD at which point the springs <NUM> move the shuttle <NUM> rearward at high speed until the driver's impact flange <NUM> proximal surface is impacted by the distal surface of the shuttle's flange insert <NUM>. The shuttle <NUM> can have three teeth for retraction, 175RP, 175RM, and 175RD (i.e., proximal, middle, distal retract teeth respectively), each in this embodiment that can be engaged by the three teeth on the PTP <NUM>.

The shuttle <NUM>'s circular gear rack drive teeth <NUM> can be driven by the teeth <NUM> on the partial tooth pinion <NUM> (see <FIG>) which can have a D-shape bore <NUM> to slidingly fit onto the gear motor's D-shaped output shaft <NUM>. In <FIG> the front flange of the gearmotor <NUM> can be seen, but one of the bolts <NUM> that hold it in place is hidden behind partial tooth pinion <NUM>. A fastener, such as a flat tip setscrew <NUM>, can hold partial tooth pinion <NUM> in place although as will be discussed, the PTP <NUM> is axially constrained but the gearmotor shaft and outrigger support bearings (see <FIG>). For the illustrated embodiment, three teeth, 302A, 302B, and 302C as determined by the gear pitch and pitch diameter are needed to drive the rack the desired distance in either direction.

The rear collar <NUM> on the rod <NUM> is shown as a fixed clamp collar, but to adjust the retraction force, it could easily be a threaded collar on the shaft so the surgeon can rotate the collar and adjust its axial position with respect to the flange <NUM>. In this case, the rear cap 112A could be removable or the threaded collar have a protrusion through it for dialing the position.

In forward and reverse impacts, the energy can be changed by changing the distance the shuttle travels (accelerates) before it impacts the flange <NUM>. Thus, the spring stiffness (spring size) can be fixed to the maximum of what may ever be needed, and with great sensitivity the energy achieved per blow is easily adjusted by changing the position of the flange <NUM> inside the shuttle cavity <NUM>. This can enable great robustness of design, as it is not a slip clutch or other energy robbing element.

Motor gearbox combinations ("gearmotor"'), particularly those with high ratios, can output very high torques. Often this torque can be transmitted to another shaft with a coupling. Sometimes a gear or pulley can be directly attached to the gearmotor output shaft. However, in this case, especially since there may be a shock load of the load on the drive gear (PTP <NUM>) suddenly being released, it may be found that the equivalent radial load of the torque transmitted divided by the pitch radius of the gear exceeds the allowable radial load on the gearmotor <NUM> output shaft <NUM>. It can be possible to position the gear teeth (e.g., teeth <NUM>) tight against the face of the motor with the gear hub on the outside, here this is not shown because the shuttle <NUM>'s circular rack teeth <NUM> would contact the face of gearmotor <NUM>.

As shown in <FIG>, a gearmotor's front faces can have a precision round locating boss which can be concentric with their inner bearings that supports the output shaft <NUM>. Hence, they can be mounted such that the boss can be a sliding fit in a precision bore <NUM>, which can extend across the region in which the shuttle <NUM> passes to the other side of the MMB <NUM> where precision outrigger support bearing(s) <NUM> can be placed. The bore diameter for the locating boss can be the same as the bore <NUM> required for the outrigger bearing <NUM>, so a straight through line bore operation can be made and the hole reamed to exact tolerances.

In the center region of the structure into which the precision bore <NUM> has been made, a cavity can be made which contains the partial tooth pinion (PTP) <NUM> on an integrally formed gear shaft structure <NUM>. On this gear shaft structure <NUM>, on the gear end (PTP <NUM>), the diameter can be big enough for a precision bore to mate with the gearmotor shaft <NUM>, including a shaft feature such as a flat, keyway or spline so excellent torque transmission can be obtained without the need for a coupling. The other end of shaft structure <NUM> can have a shaft <NUM> that fits into the outrigger bearing(s) <NUM>. Two bearings <NUM> can be used to give some additional moment support and stiffness. The effect can be a simply supported shaft (structure <NUM>) with a gear (PTP <NUM>) essentially in the middle and the radial load from the gear teeth (302B) tangential force, as well as gear tooth separation forces, is shared by the gearmotor shaft support bearings and the outrigger bearings <NUM>. However, the precision fits and alignment obtained by this arrangement can be made possible by the monolithic structure of the motor mounting block.

As shown in <FIG>, since the gear tooth tangential and separation forces always essentially add to have a net upwards direction, the outrigger bearings' bore <NUM> can have its lower quadrant relieved to form a fan-shaped access <NUM> enabling the partial tooth gear <NUM> to be slid into place. A snap ring groove <NUM> in the bore <NUM> can hold a snap ring <NUM> that can axially retain the bearings in the bore <NUM>, which can be covered in the fully assembled device by the cap <NUM> (see <FIG>). A top access port <NUM> can allow access to tighten bolts <NUM> to hold the gearmotor <NUM>'s gearhead <NUM> securely to the housing <NUM>. This access port can be covered in the fully assembled device by the cap <NUM> (see <FIG>). The bore <NUM> can be collinear and the same diameter as bore <NUM> so they can be line-bored for high precision. The gearmotor front boss <NUM> can be precisely held concentric as discussed above. By selecting outrigger bearings 280A and 280B to have the same outside diameter as the boss <NUM>, the PTP shaft <NUM> can fit in the bearings' <NUM> bores, and the PTP D-shape bore <NUM> can slide over the gearmotor shaft <NUM>, the bearings in the gearmotor <NUM> will not be over constrained by the outrigger bearings 280A and 280B, which can seat against shaft <NUM>'s shoulder <NUM>. As a result, high radial loads due to tangential and gear tooth separation forces on the gear teeth <NUM>, can be shared by the bearings in the gearmotor <NUM> and the outrigger bearings <NUM>.

In the case of the circular gear rack teeth <NUM> shown herein, the crown of the gear rack tooth can operate to hinder misalignment. Note that this crowning can result in higher contact stresses than a conventional flat flank gear rack tooth engaging with a drive gear would experience, but this can be engineered as shown here with advanced analysis of the system that includes not only calculation of the gear tooth strength but also of the contact stress of the drive gear teeth <NUM> with the circular gear rack teeth <NUM>.

The rear face of the tool holder <NUM>, which can be attached to the end of drive rod <NUM>, can come into contact with the front of the system's outer tube <NUM> front end cap <NUM>. The center impact flange <NUM> of the drive rod <NUM> can be positioned within the system such that as when the shuttle <NUM> is cocked, its proximal flange (nearest the tool holder <NUM>) inner face is just in contact, or a tolerance clearance of about one mm to prevent an over constraint condition where the drive gear <NUM> has just a little bit more to go before it can release and fire the shuttle <NUM>, but the drive rod <NUM> impact flange <NUM> is already in contact with the shuttle <NUM>'s proximal flange inner surface (see <FIG> and <FIG>).

In a second embodiment shown in <FIG>, a monolithic spring shuttle structure (SSS) <NUM> can include the two springs 560P and 560D and the shuttle section <NUM> with integral gear teeth. The springs can be machined with 560P being CW and 560D being CCW. It can be made integral by machining the springs from a steel rod or tube. The circular rack teeth <NUM> can still be machined into shuttle section <NUM>. The forward impact surface for driving the tool forward can be monolithic with the shuttle <NUM>, but if desired a high force capacity snap ring could be used. Using a custom machined spring, the advantage is a larger diameter somewhat shorter spring can be used which also incorporates the end caps needed to mate with the spring and shuttle tube (SST) <NUM>. In this case, one spring <NUM> is clockwise and one is machined counterclockwise, so there is no net appreciable torque on the ends that attach to the outer tube <NUM>, thus sliding or wear are avoided. Preload can be obtained when the system's outer tube <NUM> would be placed over SSS <NUM> and then the proximal end of the tube seats against flange <NUM>. SSS <NUM> would be gripped from the inside (e.g., with an expansion tool) and pulled in tension until a snap ring would be fitted into groove <NUM>. The SSS <NUM> can be kept centered in the outer housing tube <NUM> by end bosses <NUM> and <NUM> that would be typically about <NUM>-<NUM> larger in diameter than the outside diameter of the circular rack gears 175P, <NUM>, 175D and 175RP, 175RM and 175RD for forward (drive) and rearward (retract) impact actuation of the shuttle section <NUM>.

<FIG> shows a bi-spring surgical impact tool <NUM> consistent with at least one example of this disclosure. <FIG> shows a section view of the bi-spring surgical impact tool <NUM> consistent with at least one example of this disclosure. The impact tool <NUM> can include a chuck <NUM>, a chuck shroud <NUM>, a housing <NUM>, an end cap <NUM>, a trigger group <NUM>, and a battery <NUM>. The chuck shroud <NUM> can allow the chuck <NUM> to move as indicated by arrow <NUM> without exposing a drive rod <NUM> as disclosed herein. During use, a surgeon may press a first trigger <NUM> to drive a tool or a second trigger <NUM> to extract a tool as disclosed herein. For example, to drive a broach the surgeon may press the first trigger <NUM> and to remove the broach from a bone the surgeon may press the second trigger <NUM>.

Housing <NUM> can define a cavity <NUM> a first end <NUM> and a second end <NUM>. A shuttle <NUM> can be located within the cavity <NUM> and define a plurality of indentations <NUM>, sometimes called shuttle teeth. The shuttle <NUM> can have a first end <NUM> and a second end <NUM>. The shuttle <NUM> can define a through hole <NUM>. The drive rod <NUM> can pass through the through hole <NUM> and the shuttle <NUM> can translate in a first direction and a second direction along the drive rod <NUM> as disclosed herein to generate impact and extraction forces. For example, a pinion <NUM> can be located proximate shuttle <NUM> and have a plurality of protrusions <NUM>, sometimes referred to as pinion teeth, sized to mesh with indentations <NUM> during rotation of the pinion <NUM> as disclosed herein.

A first spring <NUM> can mechanically couple the first end <NUM> of the housing <NUM> to the first end <NUM> of the shuttle <NUM>. For example, the first spring <NUM> can encircle a portion of an insert <NUM> and a plug <NUM>. The plug <NUM> can be a portion of the end cap <NUM> or be a separate component that is connected to the end cap <NUM>. As shown in <FIG>, the insert <NUM> can define a shoulder that allows the first spring <NUM> to exert a force on the shuttle <NUM> to cause linear motion of the shuttle <NUM> as disclosed herein. The plug <NUM> or the end cap <NUM> also can define a shoulder <NUM> to allow the first spring <NUM> to rest on a stationary surface.

A second spring <NUM> can mechanically couple the second end <NUM> of the housing <NUM> to the second end <NUM> of the shuttle <NUM>. For example, the second spring <NUM> can encircle a portion of an insert <NUM> and a portion <NUM> of a front end cap <NUM>. As shown in <FIG>, the insert <NUM> can define a shoulder <NUM> that allows the second spring <NUM> to exert a force on the shuttle <NUM> to cause linear motion of the shuttle <NUM> as disclosed herein. The front end cap <NUM> also can define a shoulder <NUM> to allow the second spring <NUM> to rest on a stationary surface.

The plug <NUM> and the front end cap <NUM> can each define an annular cavity <NUM> and <NUM>, respectively. The first and second springs <NUM> and <NUM> can be located axially along a longitudinal axis of the drive rod <NUM>. The cavities <NUM> and <NUM> can allow the first spring <NUM> and second spring <NUM> to compress without deflection in a radial direction. By constraining the first spring <NUM> and the second spring <NUM> to compress in only an axial direction, energy stored in the first spring <NUM> and the second spring <NUM> when compressed can be released in a more efficient matter since energy is not wasted by spring movement in radial directions.

As disclosed herein, rotation of the pinion <NUM> in a first direction as indicated by arrow <NUM> can cause the shuttle <NUM> to translate in a first direction as indicated by arrow <NUM> towards the first end <NUM> of the housing <NUM>. Rotation of the pinion <NUM> in a second direction as indicated by arrow <NUM> can cause the shuttle <NUM> to translate the shuttle <NUM> in a second direction as indicated by arrow <NUM> towards the second end <NUM> of the housing <NUM>. As disclosed herein, the shuttle <NUM> can move in a linear fashion. When the shuttle <NUM> is out of position so that the pinion <NUM> does not mesh with the indentations <NUM> of the shuttle <NUM>, the shuttle <NUM> is freely movable by the first and second springs <NUM> and <NUM>.

A drive rod collar <NUM> can be affixed to the drive rod <NUM>. For example, one or more roll pins <NUM> can be used to affix the drive rod collar <NUM> to the drive rod <NUM> as shown in <FIG>. Other attachment mechanisms such as set screws, welding, epoxies, etc. may be used to affix the drive rod collar <NUM> to the drive rod <NUM>. As disclosed herein, when the shuttle <NUM> travels in the first direction indicated by arrow <NUM> and the pinion <NUM> no longer engages the shuttle <NUM>, the first spring <NUM> can cause the shuttle <NUM> to travel in second direction as indicated by arrow <NUM> and the insert <NUM> can contact the drive rod collar <NUM> to generate an impact force. The impact force can be transmitted via the drive rod <NUM> to the chuck <NUM> and a tool, such as a rasp. To generate an extraction force, the opposite can occur. For instance, the shuttle <NUM> can be moved in a second direction as indicated by arrow <NUM> and when the pinion <NUM> no longer engages the shuttle <NUM>, the second spring <NUM> can cause the insert <NUM> to impact the drive rod collar <NUM> to generate a retraction force. The retraction force can be transmitted via the drive rod <NUM> to the chuck <NUM> and the tool.

<FIG>, <FIG>, and <FIG> each shows a motor pinion assembly <NUM> of the bi-spring surgical impact tool <NUM> of <FIG> consistent with at least one example of this disclosure. Motor pinion assembly <NUM> can include a motor <NUM> having a shaft <NUM> with the pinion <NUM> mounted thereto. One or more wires <NUM> can be used to electrically couple the motor <NUM> to the battery <NUM>, the trigger group <NUM>, a switch <NUM>, and a sensor <NUM>.

As shown in <FIG>, the pinion <NUM> can include a pinion carriage <NUM>. The pinion carriage <NUM> can include a first pinion plate <NUM> and a second pinion plate <NUM>. One or more bearings <NUM> can be located in between the first and second pinion plates <NUM> and <NUM>. The bearings <NUM> can form a plurality of protrusions that mesh with the indentations <NUM>. Non-limiting examples of the bearings <NUM> include roller bearings, journal bearings, etc. The bearings <NUM> can be sized to mesh with the indentations <NUM> as shown in <FIG> so as to minimize play in between the bearings <NUM> and surfaces forming the indentations <NUM>. Because surfaces of the bearings <NUM> roll across surfaces of the indentations <NUM>, wear of contacting surfaces of the indentations <NUM> and the bearings <NUM> can be minimized without the need for grease, oil, other lubrications. A bearing sleeve can be used to allow for even radial loading on the bearing surface.

The first and second pinion plates <NUM> and <NUM> can each define a plurality of spokes <NUM>. Each of the bearings <NUM> can be connected to a respective spoke <NUM>. While <FIG> shows two pinion plates, embodiments disclosed herein may use one or two pinion plates. For example, a single pinion plate, such as the first pinion plate <NUM> may be used and the bearings <NUM> secured to the first pinion plate <NUM> via a bolt or other fastener. Also, while <FIG> shown the bearings <NUM> attached to the pinion plates <NUM> and <NUM>, the bearings <NUM> can be attached to the shuttle <NUM> and the pinion <NUM> can define the indentations that mesh with the bearings <NUM> attached to the shuttle <NUM>.

The motor <NUM> can be in electrical communication with the switch <NUM>. The sensor <NUM> can be arranged to detect a position of the shuttle <NUM>. For example, the sensor <NUM> can be a Hall effect sensor that measures change in magnetic flux due to the movement of the drive rod <NUM>, which can be ferrous metal or any other material whose movement can cause a change in a magnetic field or flux. The sensor <NUM> can also be in electrical communication with the switch <NUM>. When sensor <NUM> detects that shuttle <NUM> is out of position to allow indentations <NUM> to mesh with the bearings <NUM>, or any protrusions of the pinion <NUM>, the switch <NUM> can sever electrical communication of the motor <NUM> with a power supply (i.e., battery <NUM>). For example, to prevent binding or other mismatching of the pinion <NUM> and the shuttle <NUM>, the sensor <NUM> can detect a position of the shuttle <NUM> and halt rotation of motor the <NUM> when the shuttle <NUM> is not in a position to allow the spokes <NUM> to mesh with the indentations <NUM>.

The end cap <NUM> can be rotated to axially translate a barrel cam <NUM> to continuously adjust the position of the drive rod <NUM> and coupled drive rod collar <NUM> to allow for variable magnitude impacts. As shown in <FIG>, the barrel cam <NUM> can include slots <NUM> and pins <NUM> (only one pin is visible in <FIG>). The barrel cam <NUM> can be rotated, such as by rotating the end cap <NUM> or by using a wrench, socket, etc. Rotation of the barrel cam <NUM> can cause the pins <NUM> to move within the slots <NUM>. The movement of the pins <NUM> can cause the drive rod <NUM> to be repositioned in a continuous manner.

<FIG>, and <FIG> shows the bearings <NUM> (labeled individually as bearings 1916A and 1916B) and shuttle <NUM> consistent with at least one example of this disclosure. As disclosed herein, the bearings <NUM> and the shuttle <NUM> can allow for greater forces and torque generation. The bearings <NUM> and the shuttle <NUM> can also reduce energy loses due to bending loads and sliding contact stresses at the point of release that may be experience in traditional rack and pinion systems. Since rolling contact between the teeth can occur even at the very last moment just before contact is lost and so there is no sliding wear.

As a non-limiting example, the bearings <NUM> can have a <NUM> OD and installed on a pinion plate <NUM>, which can have a diameter of <NUM>. The bearings <NUM> can be spaced <NUM>° apart. The shuttle <NUM> can include trapezoidal teeth <NUM> (labeled individually as tooth 2006A and 2006B), which can include rounded tops <NUM>. For the bearing sizes stated above, the teeth <NUM> can be spaced <NUM> apart. The initial location of the tooth center can enable in forward motion having <NUM> J of energy, and about <NUM> J for retraction. This also only requires the user to push forward <NUM> or pull back <NUM> to position the drive rod <NUM> and chuck <NUM> for impact in either direction.

As shown in <FIG>, and <FIG>, as the pinion plate <NUM> rotates in the first rotational direction as indicated by arrow <NUM>, bearing 1918A can contact tooth 2006A (<FIG>). Continued rotation of the pinion plate <NUM> can cause tooth 1916B to contact tooth 2006B before bearing 1918A breaks contact with tooth 2006A, thereby reducing jerkiness and/or slippage. Continued rotation of the pinion plate <NUM> will eventually cause teeth <NUM> to break contact from teeth <NUM> and allow the shuttle <NUM> to move under the power of the first and second springs <NUM> and <NUM>.

While <FIG>, and <FIG> show two teeth, any number of teeth may be present. For example, <FIG> shows the shuttle <NUM> having three teeth. As disclosed herein, the third tooth can be a "reverse tooth" that can be shorter than the two primary teeth. The shorter tooth can allow for a motor capable of <NUM> N-m of torque to achieve <NUM> J of forward energy and <NUM> J of retract energy.

To generate a traction or extraction force, the pinion plate <NUM> can be rotated in the second direction as indicated by arrow <NUM>. Rotation in the second direction can cause the bearings <NUM> to contact the teeth <NUM> in the reverse order as described above.

Claim 1:
A bi-spring surgical impact tool (<NUM>) comprising:
a housing (<NUM>) defining a cavity (<NUM>) having a first end (<NUM>) and a second end (<NUM>);
a shuttle (<NUM>) located within the cavity (<NUM>) and defining a plurality of indentations (<NUM>), the shuttle (<NUM>) having a first end (<NUM>) and a second end (<NUM>);
a pinion (<NUM>) comprising a pinion carriage (<NUM>) and a plurality of bearings (<NUM>) that form a plurality of protrusions, the pinion (<NUM>) located proximate the shuttle (<NUM>) and the plurality of protrusions sized to mesh with the plurality of indentations (<NUM>) during rotation of the pinion (<NUM>);
a first spring (<NUM>) mechanically coupling the first end (<NUM>) of the housing (<NUM>) to the first end (<NUM>) of the shuttle (<NUM>); and
a second spring (<NUM>) mechanically coupling the second end (<NUM>) of the housing (<NUM>) to the second end (<NUM>) of the shuttle (<NUM>),
wherein rotation of the pinion (<NUM>) in a first rotational direction translates the shuttle (<NUM>) in a first linear direction towards the first end (<NUM>) of the housing (<NUM>) and rotation of the pinion (<NUM>) in a second rotational direction translates the shuttle (<NUM>) in a second linear direction towards the second end (<NUM>) of the housing (<NUM>).