Surgical impactor with linear electromagnetic motor

Abstract

A surgical impactor comprising an anvil configured to impart an impact to an object and a linear motor. The linear motor comprises a striker comprising one or more magnets, wherein the striker is configured to be driven to move linearly along a path of movement within the linear motor to strike the anvil and a stator. The stator comprises: a magnetic core, coils and one or more wires. The magnetic core has: a channel passing through the magnetic core from a first end of the magnetic core to a second end of the magnetic core, the second end being opposite to the first end, the channel being configured to receive the striker and defining the path of movement for the striker; and a break in the magnetic core running from the first end to the second end of the magnetic core and extending between an outside of the magnetic core to the channel across its length to reduce eddy currents within the magnetic core. The coils surround the path of movement and are positioned in order down the length of the channel for driving the striker to move along the channel. The one or more wires are configured to provide current to the coils. The one or more wires are located within the break of the magnetic core.

Description

[0001] Surgical Impactor with Linear Electromagnetic Motor

[0002] TECHNICAL FIELD

[0003] The application relates to surgical impactors with linear electromagnetic motors, and in particular, to an improved design of linear electromagnetic motor for a surgical impactor with a compact form and reduced eddy currents.

[0004] BACKGROUND

[0005] When performing surgery, particularly hip replacement surgery, it is sometimes necessary to provide an impact force. This can be through the use of a surgical mallet and hip hammer.

[0006] For instance, in total hip replacement surgery, a surgeon may utilise a broaching tool to remove less dense (cancellous) bone from a femoral canal without damaging the hard cortical bone surrounding it. This broaching may require multiple strikes, both in the forward and reverse direction. Thereafter, the surgeon may seat an implant in the prebroached femur and seat a head on the implant.

[0007] Similarly, when seating an acetabular cup, the acetabular may be reamed using a reamer before an acetabular cup is inserted. The acetabular cup may be held in place by a press-fit. Seating the acetabular cup may require a number of impactions (e.g. 8- 10 impactions) to ensure a secure fit.

[0008] Surgical impactors can be driven in a variety of ways, for instance, pneumatic drive. Pneumatic drives can be bulky and can provide limited control over impact power. Pneumatic drives can also require connection to a gas supply, which can limit movement and make the impactors more difficult to use.

[0009] SUMMARY

[0010] In general, the application relates to surgical impactors that are powered through linear electromagnetic motors. In particular embodiments, a linear electromagnetic motor is provided that has a reduced size relative to conventional motors. This makes the surgical impactor more manoeuvrable, making it easier for the surgeon to position and orient the device correctly during surgery. This is particularly important for surgical impactors, as access to the surgical site can be restricted during surgery.

[0011] Particular embodiments locate wiring and / or sensor(s) within a break in the magnetic core of the stator (e.g. within an air gap of the magnetic circuit). This achieves the dual function of reducing the size of the motor, whilst providing an air gap in the magnetic circuit that reduces or prevents eddy currents within the magnetic core. Eddy currents can cause a magnetic field that opposes (e.g. resists) the drive of the motor. By reducing or preventing eddy currents, the resistance to the drive of the impactor is reduced, thereby improving the efficiency and effectiveness of the impactor.

[0012] According to a first aspect there is provided a surgical impactor comprising an anvil configured to impart an impact to an object and a linear motor. The linear motor comprises a striker comprising one or more magnets, wherein the striker is configured to be driven to move linearly along a path of movement within the linear motor to strike the anvil and a stator. The stator comprises: a magnetic core, coils and one or more wires. The magnetic core has: a channel passing through the magnetic core from a first end of the magnetic core to a second end of the magnetic core, the second end being opposite to the first end, the channel being configured to receive the striker and defining the path of movement for the striker; and a break in the magnetic core running from the first end to the second end of the magnetic core and extending between an outside of the magnetic core to the channel across its length to reduce eddy currents within the magnetic core. The coils surround the path of movement and are positioned in order down the length of the channel for driving the striker to move along the channel. The one or more wires are configured to provide current to the coils. The one or more wires are located within the break of the magnetic core.

[0013] According to an embodiment the break forms a further channel within the magnetic core, wherein the channel is defined between opposing side walls of the channel, wherein the one or more wires are located between the opposing side walls of the channel.

[0014] According to an embodiment the one or more wires comprise a plurality of subsets of one or more wires, wherein each subset of one or more wires is connected to a corresponding subset of the coils. According to an embodiment one or more of the wires are insulated to prevent connection to one or more coils other than the corresponding subset of coils.

[0015] According to an embodiment each subset of the coils comprises plurality of coils, and the winding direction of the coils alternates within each subset of the coils.

[0016] According to an embodiment the surgical impactor further comprises one or more sensors for sensing a position of the striker along the path of movement, the one or more sensors being located within the break of the magnetic core.

[0017] The one or more sensors may comprise a first set of one or more sensors located in a first region between the coils and the first end of the magnetic core and a second set of one or more sensors located in a second region between the coils and the second end of the magnetic core. The one or more sensors may be magnetic field sensors (e.g. Hall effect sensors) for sensing the magnetic field from the magnets of the striker.

[0018] According to an embodiment the magnetic core comprises one or both of: a first extension portion that extends beyond the coils to the first end; and a second extension portion that extends beyond the coils to the second end.

[0019] According to an embodiment the one or more sensors comprise a first set of one or more sensors located within the break within the first extension portion and a second set of one or more sensors located within the break within the second extension portion.

[0020] According to an embodiment the surgical impactor further comprises a bearing sleeve within the channel, the bearing having a bearing surface for supporting the striker as it moves within the channel. According to an embodiment, the surgical impactor comprises a corresponding bearing sleeve located within the each extension portion,

[0021] According to an embodiment, the (or each) bearing sleeve may be formed of a non- conductive material (e.g. ceramic).

[0022] According to an embodiment each coil comprises a plurality of turns, wherein each turn has a cross-sectional shape with an elongated width. Each turn may be a single portion of the coil that wraps around the coil a single time. The width may be taken along a direction parallel to a central axis of the coil (e.g. a longitudinal axis of the surgical impactor). Each winding may extend across the full width of the coil (e.g. along the direction parallel to the central axis of the coil).

[0023] According to an embodiment each coil comprises a plurality of turns, wherein one or more of the turns has a reduced thickness at a location that aligns with one or both of an input wire to the coil and an output wire from the coil. The thickness may be measured in a radial direction (e.g. in a direction perpendicular to the central axis of the coil).

[0024] According to an embodiment, each coil is formed of solid metal eroded or cut into shape.

[0025] According to an embodiment each coil is contained within a corresponding coil cavity within the magnetic core, wherein each coil cavity extends radially outwards from the channel and opens into the break.

[0026] According to an embodiment the surgical impactor further comprises, for each coil, a pair of insulating spacers on opposite sides of the coil to separate and insulate the coil from the magnetic core.

[0027] According to an embodiment one or more of the insulating spacers comprise one or more holes that open onto the coils for allowing potting compound to be supplied between turns of the coils.

[0028] According to an embodiment each coil is positioned within a corresponding coil cavity within the magnetic core, between opposing side walls of the coil cavity, and wherein one or more of the side walls comprises one or more channels passing through the side wall for allowing potting compound to be supplied between turns of the coils. The surgical impactor may further comprises potting compound that encapsulates the coils (e.g. following supply of the potting compound during manufacture).

[0029] According to a further aspect there is provided a surgical impactor comprising an anvil configured to impart an impact to an object and a linear. The linear motor comprises: a striker comprising one or more magnets and configured to be driven to move linearly along a path of movement within the linear motor to strike the anvil; and a stator. The stator comprises: a magnetic core having: a channel passing through the magnetic core from a first end of the magnetic core to a second end of the magnetic core, the second end being opposite to the first end, the channel being configured to receive the striker and defining the path of movement for the striker; and a break in the magnetic core running from the first end to the second end of the magnetic core and extending between an outside of the magnetic core to the channel across its length to reduce eddy currents within the magnetic core. The stator further comprises: coils surrounding the path of movement and positioned in order down the length of the channel for driving the striker to move along the channel; and one or more sensors for sensing a position of the striker along the path of movement, the one or more sensors being located within the break of the magnetic core.

[0030] According to a further aspect there is provided a surgical impactor comprising: an anvil configured to impart an impact to an object; and a linear motor. The linear motor comprises: a striker comprising one or more magnets and configured to be driven to move linearly along a path of movement within the linear motor to strike the anvil; and a stator. The stator comprises a magnetic core having a channel passing through the magnetic core from a first end of the magnetic core to a second end of the magnetic core, the second end being opposite to the first end, the channel being configured to receive the striker and defining the path of movement for the striker. The stator further comprises coils surrounding the path of movement and positioned in order down the length of the channel for driving the striker to move along the channel. The magnetic core comprises one or both of: a first extension portion that extends beyond the coils to the first end; and a second extension portion that extends beyond the coils to the second end.

[0031] According to an embodiment the coils are arranged sequentially over a first distance; and each extension portion has a length that is: greater than or equal to half of the first distance; or greater than or equal to three quarters of the first distance.

[0032] BRIEF DISCRIPTION OF THE DRAWINGS

[0033] Arrangements of the present invention will be understood and appreciated more fully from the following detailed description, made by way of example only and taken in conjunction with drawings in which: FIG. 1 A shows a surgical impactor fitted with a broaching tool according to an embodiment;

[0034] FIG. 1 B shows a surgical impactor fitted with an acetabular cup implant according to an embodiment;

[0035] FIG. 2 shows a cross-section of a surgical impactor according to an embodiment;

[0036] FIG. 3 shows a zoomed in cross-section of the motor according to an embodiment;

[0037] FIG. 4 shows a perspective view of a stator assembly according to an embodiment;

[0038] FIG. 5 shows a side view of a first end of the stator assembly according to an embodiment;

[0039] FIG. 6 shows a perspective view of a magnetic core according to an embodiment;

[0040] FIG. 7 shows a perspective view of an underside of the stator assembly according to an embodiment;

[0041] FIG. 8 shows a plan view of the underside of the stator assembly according to an embodiment;

[0042] FIG. 9 is a circuit diagram showing a connection arrangement between coils according to an embodiment;

[0043] FIG. 10 shows a transverse cross-section of a stator assembly according to an embodiment along a plane passing through a coil;

[0044] FIG. 11 shows a cross-section of a coil according to an embodiment;

[0045] FIGs. 12A and 12B show transverse cross-sections of a stator assembly according to an embodiment along respective planes passing through first and second insulating spacers.

[0046] DETAILED DESCRIPTION

[0047] Embodiments provide a surgical impactor with an improved motor design that reduces or prevents eddy currents and that is able to be manufactured in a more compact form. Further embodiments include a stator with an extended magnetic core that extends magnetic flux beyond coils of the motor and along a path of movement of a striker to provide a driving force over a wider range of motion. Further embodiments include a striker with a magnetisable core that provides reduced friction during use. FIG. 1A shows a surgical impactor 10 fitted with a broaching tool 150 according to an embodiment. FIG. 1B shows a surgical impactor 10 fitted with an acetabular cup 160 according to an embodiment.

[0048] The surgical impactor 10 comprises a handle 110, a body 120 and an attachment coupling 130. The body 120 and handle 110 may collectively form a housing for the surgical impactor 10. The body 120 houses an anvil 170 and a motor comprising a striker 180 and a stator 200 (see FIG. 2). The stator 200 is configured to drive the striker 180 to impact the anvil 170. The anvil 170 is connected to the attachment coupling 130 such that impact force is transmitted from the anvil 170 to the attachment coupling 130. The attachment coupling 130 is configured to receive and secure an attachment. For instance, as shown in FIG. 1A, a broaching tool 150 may be attached to an adaptor 155 which may be received and secured within the attachment coupling 130. Similarly, as shown in FIG. 1 B, an acetabular cup 160 may be attached to an adaptor 165 which may be received and secured within the attachment coupling 130. When the anvil 170 is impacted, the impact force is transmitted to the attachment via the attachment coupling 130. The attachment is therefore driven to provide an impact force (e.g. to bone).

[0049] The broaching tool 150 comprises an elongate body having teeth. The teeth may be in the form of ridges running around the circumference of the elongate body. The broaching tool 150 may be mounted onto an adaptor 155 which may be secured within the attachment coupling 130. The broaching tool 150 may be used for broaching (e.g. broaching a femoral canal). When driven to reciprocate forwards and backwards, the teeth cut into the cavity being broached (e.g. into the bone) and then pull loose material out of the cavity being broached. Alternately broaches may be configured to compact the soft cancellous bone, in which case these tend to be driven predominantly in the forward direction.

[0050] The acetabular cup 160 comprises an external curved (e.g. hemi-spherical) surface. The external curved surface may be convex. The external curved surface may be roughened. A socket on an opposite side to the curved external surface may be configured to receive a femoral implant consisting of a stem and a head. The acetabular cup 160 may be mounted to an adaptor 165 which may be secured in the attachment coupling 130. The acetabular cup 160 may be seated within an acetabulum through repeated impacts, driven by the impactor 100. After seating, the adaptor 165 is removed from the acetabular cup 160 to allow the femoral implant to be fitted within the acetabular cup 160.

[0051] As noted above, the impactor 10 may also be fitted with various adaptors. The adaptors may act as a means of mounting different attachments (e.g. broaches, acetabular cups, etc.) to the impactor 10. Different adaptors may be used depending on the surgical approach and type of attachment being connected to it. They can also be used on their own (connected to the attachment coupling 130) for impacting other components (e.g. the femoral implant, femoral head, acetabular liner, etc.) and for revision surgery.

[0052] The surgical impactor 10 may be provided with one or more of a trigger 140, a mode selector 145, and a power selector 147. The trigger 140, mode selector 145 and power selector 147 are all input devices, allowing the user to adjust operating parameters, instruct the device to operate and change operating mode. The operation of the surgical impactor may be controlled by a processor (not shown).

[0053] The trigger 140 is configured to, in response to being depressed, provides an input to a processor to instruct the surgical impactor to drive the striker 180 to impact the anvil 170. The trigger 140 may be configured to output a varying signal depending on the extent that the trigger is depressed. The processor may be configured to adjust the impact force and / or impact frequency based on the extent that the trigger 140 is depressed (e.g. increase impact force and / or impact frequency with greater depression and decrease impact force and / or impact frequency with lesser depression).

[0054] The mode selector 145 may be configured to input a mode signal to the processor.

[0055] The mode signal may define an operating mode of the impactor 10. The mode may be selected from forward mode, backward mode, and reciprocating mode. In one embodiment, the mode selector 145 is a sliding switch, with different positions of the sliding switch defining different modes. For instance, a forward position may define forward mode, a middle position may define reciprocating mode, and a backward position may define reverse mode. In forward mode, the striker 180 may be driven to impart a primary force in a first direction (defined herein as a forward direction). The forward direction may be a direction in which the attachment coupling 130 (and by extension, an attachment or adaptor secured in the attachment coupling 130) moves away from the body 120 (e.g. along a longitudinal axis of the body 120).

[0056] In reverse mode the striker 180 may be driven to impact a primary force in a second direction opposite to the first direction (defined herein as a reverse direction). The reverse direction may be a direction in which the attachment coupling 130 (and by extension, an attachment or adaptor secured in the attachment coupling 130) moves towards the body 120 (e.g. along the longitudinal axis of the body 120).

[0057] In reciprocating mode, the striker 180 is driven to alternately drive the striker 180 in the forward direction and in the reverse direction to alternately impact the anvil 170 to impart a first primary force in the forward direction and to impact the anvil 170 to impart a second primary force in the reverse direction.

[0058] Whilst the forward and reverse modes of operation drive the striker 180 to impart primary forces in the forward and reverse directions respectively, they also may drive the striker 180 to move opposite to these directions (e.g. to prepare to be driven). When preparing to be driven, the striker 180 may impart a secondary force to the anvil 170 in an opposite direction to the primary force in that mode of operation. This secondary force may be smaller (e.g. may have a smaller magnitude) than the primary force.

[0059] The power selector 147 may be configured to input a power signal to the processor to control an impact force or energy. In the present description, the terms “power”, “force” and “energy” may be used interchangeably when discussing the force of impact. It will be appreciated that these terms are related to each other, such that a larger impact force will impart a larger amount of kinetic energy and that, more powerful impacts (e.g. through driving the striker 180 more powerfully) will impart more force.

[0060] The power selector 147 may be in the form of a rotating dial, although alternative forms of input device may be used. The power selector 147 may have varying positions related to specific power modes. For instance, one or more power modes may relate to respective levels of impact force. A safety mode may stop the impactor 10 from being driven (e.g. by disabling the driving of the impactor 10 and / or locking the trigger 147). An automatic mode may allow the operating parameters (e.g. impact force) to be adjusted automatically by the processor. The automatic mode may allow the operating parameters to be adjusted by an external device.

[0061] FIG. 2 shows a cross-section of a surgical impactor 10 according to an embodiment. The surgical impactor 10 comprises an anvil 170 and a linear motor comprising a striker 180 and a stator 200.

[0062] The anvil 170 (otherwise known as an anvil system) includes a front anvil 172, a rear anvil 174 and a connector 176. The front anvil 170 is connected to (e.g. integrated with) the attachment coupling 130, such that movement of the anvil 170 causes the attachment coupling 130 (otherwise known as a tool holder) to also move. Any attachment or adaptor held within the attachment coupling 130 is therefore driven. For instance, a broaching tool or acetabular cup may be driven via a corresponding adaptor secured within the attachment coupling 130. The front anvil 172 and the rear anvil 174 are positioned on either side of the striker 180. The connector 176 connects the front anvil 172 to the rear anvil 174 such that the anvil 170 forms a single unit. In the present embodiment, the connector 176 is in the form of a shaft that runs along a longitudinal axis of the impactor 10.

[0063] The striker 180 is mounted within the body 120 such that it may slide forwards and backwards within a channel within the body 120, between the front anvil 172 and the rear anvil 174. The striker 180 may include bearings (e.g. linear bearings) which are configured to assist the striker 180 in moving longitudinally. The bearings may act on an internal wall within the impactor 10. The internal wall may define a longitudinal channel (or cavity) within which the striker 180 is housed. The longitudinal channel may be cylindrical.

[0064] In one embodiment, the striker 180 is configured to move along the connector 176. For instance, a shaft may pass through the striker 180 through which the connector 176 passes. For instance, the shaft may be centrally located (e.g. along a central longitudinal axis of the striker 180). The striker 180 may be cylindrical. Having said this, alternative arrangements are possible, which have a variety of different shapes of striker 180. Similarly, alternative arrangements are possible which may have a different shaped connectors 176 and / or different numbers of connectors 174.

[0065] The striker 180 is configured to be driven by the stator 200 to impact the anvil 170 to impart a force to the coupling attachment 130. The stator 200 is an electromagnetic driving mechanism.

[0066] The striker 180 includes magnets 182 (referred to herein as “striker magnets”) configured to be driven by the stator 200. The striker magnets 182 may be annular (ring shaped). The magnets 182 may be magnetised along a direction parallel to the longitudinal axis of the impactor 10 (e.g. parallel to the direction of movement of the striker 180). The polarity of the magnets 182 may alternate down the length of the striker 180. By alternating the polarity, the strength of the magnetic field generated by the magnets 182 is increased. The stator 200 may comprise a number of electromagnets. The stator 200 may form part of a rectilinear motor configured to drive the striker 180 forwards and rearwards along the longitudinal axis. A driving force may be provided by the stator 200 through adjusting the current passing through each electromagnet to provide a moving magnetic field. The force provided by the stator 200 may be controlled by adjusting the magnitude and rate of change of the currents. The arrangement of the stator 200 and striker 180 shall be described in more detail below.

[0067] Processing circuitry (not shown) is configured to control the stator 200. The processing circuitry is configured to control the stator 200 to drive the striker 180 in response to an input from the user through the trigger 140.

[0068] When the striker 180 is driven in a forward direction, it impacts the front anvil 172 and imparts a force in the forward direction. When the striker 180 is driven in a reverse direction, it impacts the rear anvil 174 and imparts a force in the reverse direction. The forward and reverse directions are opposite to each other and are both parallel to the longitudinal axis.

[0069] The terms “forward”, “reverse”, “backward” and “rearward” are intended to be relative terms (i.e. relative to the structure of the impactor 10) and are not intended to relate to any orientation of the impactor 10 in use. A centring system may be provided to provide biasing forces to centre the anvil 170 after it has been displaced. The centring system may comprise a number of resilient members (e.g. springs, dampers, etc.). The centring system may be configured to bias the anvil system 170 towards a resting position. For instance, after the anvil system 170 has been driven forward within the body 120, the centring system may be configured to bias the anvil system 170 rearwards, towards the resting position of the anvil system 170. Similarly, after the anvil system 170 has been driven backwards within the body 120, the centring system may be configured to bias the anvil system 170 forwards, towards the resting position of the anvil system.

[0070] The stator 200 can be controlled to drive the striker 180 to provide a single impact, or a sequence of impacts. Once the user engages the trigger 140, the striker 180 is driven to impact the anvil 170. If the user continues to engage (hold down) the trigger 140, then the processing circuitry controls the stator 200 to reciprocate the striker 180 to provide a continuous sequence of impacts. At the point that the user releases the trigger 140, then the stator 200 disengages and the striker 180 is returned to a resting position.

[0071] The processing circuitry may be configured to control the stator 200 according to one of three selectable modes of operation: forward mode, reverse mode, and reciprocating mode. The processing circuitry may be configured to switch between these modes of operation based on an input from the user through the mode selector 145.

[0072] In forward mode, the impactor 10 is configured to provide a primary force in the forward direction. In reverse mode, the impactor 10 is configured to provide a primary force in the rearward direction. In reciprocating mode, the impactor 10 is configured to alternately provide forward and backward primary forces. The strength of the primary force(s) imparted by the impactor 10 can be set through input from the user via the power selector 147.

[0073] When driven (e.g. in response to an input via the trigger 140), the stator 200 may initiate the striker 180 by moving the striker 180 to an initiation position. In forward mode, the initiation position may be rearward of the resting position of the striker 180. In reverse mode, the initiation position may be forwards of the resting position of the striker 180. In reciprocating mode, the initiation position may depend on whether the first primary impact is to be a forward or rearward impact. In certain embodiments, the first primary impact in reciprocating mode is a forwards impact. Positioning the striker 180 at the initiation position provides the striker 180 with an increased distance over which it can be accelerated towards the anvil 170.

[0074] The initiation movement may result in the striker 180 contacting the anvil 170. In addition, this initiation movement may result in the striker 180 moving the anvil 170. For instance, when initiating ahead of a forward drive (e.g. in forward mode) the striker 180 may contact the rear anvil 174. When initiating ahead of a rearward drive (e.g. in reverse mode) the striker 180 may contact the front anvil 172. Whilst this initiation movement may provide a force (e.g. a secondary force) on the anvil system (that is opposite to the primary force), this secondary force is less than the primary force that is imparted when the striker 180 is driven. Accordingly, in forward mode, a secondary force may be imparted rearwards before the striker 180 is driven forwards to provide a primary force forwards. Similarly, in reverse mode, a secondary force may be imparted forwards before the striker 180 is driven rearwards to provide a primary force rearwards.

[0075] After initiation, the striker 180 is driven to impact the anvil 170 to impart the primary force (e.g. via a tool secured in the attachment coupling 130). In forward mode the striker 180 is driven forwards to impact the front anvil 172 and impart a primary force in the forward direction. In reverse mode the striker 180 is driven rearwards to impact the rear anvil 174 and impart a primary force in the rearward direction. After being driven, the stator 200 may return the striker to a resting position.

[0076] If the striker 180 is being driven again (e.g. if the user continues to engage the trigger 140) during forward mode or reverse mode, then the stator 200 may move the striker 180 back to the initiation position before driving the striker 400 to impact the anvil 170 again.

[0077] In reciprocating mode, the striker 180 may be moved to the initiation position ahead of the first impact in a similar manner to forward or reverse mode (depending on the direction of the first impact), but after this point the driving process may differ. Instead of using the stator 200 to move the striker 180 to the initiation position, the striker 180 may instead be driven in the opposite direction to produce an impact with a primary force in the opposite direction. For instance, after a forward impact, the striker 180 may be driven to impact the rear anvil 174 to provide a rearward impact. Similarly, after a rearward impact, the striker 180 may be driven to impact the front anvil 172 to provide a forward impact. In this manner, the anvil system may be reciprocated to provide alternating forward and rearward impact forces. As the range of motion of the striker 180 is greater than the distance between the front anvil 172 and rear anvil 174, the striker 180 may be reciprocated to alternately impact the front anvil 172 and rear anvil 174. This process can continue until the user releases the trigger 140.

[0078] Reciprocating mode can be useful when performing broaching. In a broaching process, a broaching tool (a broach) is driven into a channel and then is pulled out of the channel. As the tool is pulled out of the channel, debris that has been built up within the channel is pulled out of the channel. This frees up space in the channel for the broach to be further inserted into the channel. By removing debris from the channel, radial forces against the walls of the channel are reduced, thereby reducing the chance of breakage of the material being broached. Broaching may be used to increase the size of a channel or cavity within a bone. For instance, in femoral broaching (e.g. in total hip arthroplasty) a channel is formed in the medullary canal to receiving a femoral stem portion of a hip implant. By reciprocating the broaching tool, debris is cleared from the channel, thereby reducing the risk of radial splitting of the femur during the broaching process.

[0079] Forward mode can be used to hammer an object. For instance, an implant (e.g. an acetabular cup) may be hammered into a channel or fitting through the use of an adaptor. Reverse mode can be used to pull an object. For instance, a pulling attachment may be connected to, secured to, engaged with, or grip an object, and the reverse mode can be used to pull the object (e.g. pull the object out of another object). For instance, reverse mode can be used to pull (or extract) an implant from a channel or fitting in which the implant is fitted. In addition, reverse mode can be used to help pull a tool or attachment out of an object (e.g. when the tool or attachment becomes lodged or stuck within a cavity).

[0080] The above description refers to a “resting position” of the anvil 170. It will be appreciated that as the front anvil 172 and the rear anvil 174 are separated from each other, they may have different respective resting positions. The use of the term “resting position” this generally refers to a position particular component (e.g. the anvil 170) when not receiving any external forces. It should be noted that position of the anvil 170 may move depending on external forces being applied to the anvil 170. For instance, if the impactor 10 is being pushed against an object, a rearward force may be applied to the anvil 170. This may move the anvil 170 rearwards within the body 120. Similarly, if the impactor 10 is being pulled away from an object (e.g. through the use of a pulling tool), a forward force may be applied to the anvil 170. This may move the anvil 170 forwards within the body 120. Moving the position of the anvil 170 through the application of external forces (e.g. pushing / pulling the impactor 10) can alter the forces applied by the impactor 10, by adjusting the relative positions of the anvil 170, striker 180 and centring system.

[0081] The impactor 10 may be powered via a battery (e.g. a removable battery) (not shown). The battery may be aseptic or sterile. The battery may be connected to the base of the impactor 10 (e.g. a bottom of the handle 110) and communication between the battery and controller may be enabled through a hard wire connection.

[0082] The battery may contain a wireless transmitter / receiver, which can enable the impactor 10 to communicate with external devices. Alternatively, the impactor 10 may comprise a wireless transmitter / receiver. The external device could be a battery charger or a user interface such as a tablet, touchscreen, navigation system, robotic system or smart device. These devices could be used to provide real time information about the impactor 10 and anatomical patient data.

[0083] FIG. 3 shows a zoomed in cross-section of the motor according to an embodiment. FIG. 4 shows a perspective view of a stator assembly according to an embodiment. FIG. 5 shows a side view of a first end of the stator assembly according to an embodiment. FIG. 6 shows a perspective view of a magnetic core 210 according to an embodiment. FIG. 7 shows a perspective view of an underside of the stator assembly according to an embodiment. FIG. 8 shows a plan view of the underside of the stator assembly according to an embodiment.

[0084] Referring to FIG. 3, the stator 200 comprises a magnetic core 210, wires 230, sensors

[0085] 240 and coils 250. The magnetic core 210 forms a magnetic circuit. The magnetic core

[0086] 210 may be a magnetically soft material (e.g. a soft ferromagnetic material, such as magnetically soft iron or magnetically soft steel). The magnetic core 210 may therefore be magnetisable, but may not maintain magnetisation over a prolonged period, once the external magnetic field has been removed.

[0087] The magnetic core 210 comprises a central region within which the coils 250 are located. The magnetic core 210 may also comprise a first magnetic extension portion 220 and a second magnetic extension portion 225 that extend from opposite ends of the central portion, and act to conduct magnetic flux along the path of motion of the striker 180, beyond the extent of the coils 250. This improves the range of motion of the striker 180 over which the striker 180 is effectively driven.

[0088] FIGs. 3-6, the magnetic core 210 has a channel (or cavity) running down its length. The channel defines the path of motion for the striker 180. In the present embodiment, the channel is cylindrical (has a circular cross-section); however, alternative shapes are possible (e.g. square or rectangular cross-section). The central region of the magnetic core 210 comprises coil cavities. A coil 250 is located within each coil cavity.

[0089] Accordingly, whilst the term “magnetic core” is used, the magnetic core 210 may surround the coils 250 (e.g. may extend along side surfaces and an external surface of each coil 250). The magnetic core 210 therefore need not be centrally located within the coils 250.

[0090] The central portion of the magnetic core 210 may comprise a set of rings that are secured around the coils 250. Each ring may comprise an external wall that extends around the channel, and may comprise or be connected to at least one side wall that protrudes towards the centre of the channel. A coil cavity may be formed between each adjacent pair of side walls.

[0091] Referring to FIG. 3 and FIG. 6, one or more holes 208 may be provided in the magnetic core 210 between each adjacent pair of coil cavities (within sidewalls of the coil cavities). One or more holes 208 may also be provided between an external surface of the magnetic core 210 to one or more of the coil cavities. The one or more holes 208 may provide injection channels for allowing potting compound (e.g. epoxy resin) to be injected into the stator during manufacture to pot the motor. In this process, potting compound (e.g. an insulator) surrounds and insulates the coil turns from each other and from the magnetic core 210. During manufacture, the potting compound may be hardened (e.g. cured) to secure and insulate the coils 250 within the motor.

[0092] A bearing sleeve 205 is located within the magnetic core 210, and may act as a bearing along which the striker 180 may slide. A single bearing sleeve 205 may extend along the whole length of the channel, or multiple bearing sleeves 205 may be located along the channel. For instance, a bearing sleeve 205 may be located within each of the first extension region 220 and the second extension region 225. An internal surface of each bearing sleeve 205 may define a bearing surface along which the striker 180 may slide. Where the bearing sleeve(s) 250 do not extend into the centre of the coils 250, the internal surface of potting compound used to insulate the coils 250 may align with the internal surface of each bearing sleeve to define the channel through which the striker 180 travels. Each bearing sleeve 205 may be formed of a non-conductive material, such as a non-metallic material (e.g. a ceramic) to prevent eddy currents being produced within the bearing sleeve 205 which could oppose the driving force of the motor.

[0093] The striker 180 comprises a series of magnets 182 located down its length. Each magnet 180 may encircle a core 188 of the striker 180. The polarity of the magnets may alternate down the length of the striker 180. Each magnet 180 may be ring shaped (e.g. toroidal). Spacers 184 may be located between adjacent magnets 182. The core 188 and the spacers 182 may be made of steel (e.g. stainless steel). A cover may be provided over the magnets 182 to protect the magnets during use. One or more bearings 186 (e.g. linear bearings) may be located on an external surface of the striker 180 to slide along the bearing sleeve(s) 205. The one or more bearings 186 may be made of a non-conductive material, such as a non-metallic material (e.g. a polymer or ceramic), and may act as an electrical isolator. Alternatively, the one or more bearings 186 may be metallic (e.g. formed of steel).

[0094] Referring to FIGs. 4-8, a break 214 is provided along the length of the magnetic core 210 (e.g. down the length of each of the first extension region 220, the second extension region 225, and the central portion). The break 214 may be in the form of a channel that runs from a first end (e.g. a front) of the magnetic core 210 to a second end (e.g. a rear) of the magnetic core 210 (e.g. may run longitudinally along a direction parallel to the path of motion of the striker 180). The channel may also run from an outside surface of the magnetic core 210 to an inside surface of the magnetic core 210 (e.g. may run radially along a direction perpendicular to the path of motion of the striker 180). In this manner, the break 210 may form an air gap within the magnetic circuit, which reduces or prevents eddy currents being generated within the magnetic core 210. The air gap may break the magnetic material to prevent the magnetic material forming a complete loop around the longitudinal axis of the device (the path of motion of the striker 180). The term “air gap” refers to a break in the magnetic material (e.g. a region in which magnetic material is not located) within a magnetic circuit (e.g. along a closed loop path through which magnetic flux passes during use); however, the air gap need not be filled with air (e.g. the air gap may contain other components, such as wires and / or sensors, as discussed below).

[0095] Without the inclusion of the break 214 the motion of the magnets 182 in the striker 180 as the striker 180 is driven can generate eddy currents within the magnetic core 210. Without the break 214, these eddy currents can run circumferentially around the magnetic core 210, producing a force that resists the motion of the striker 180. Due to the fast response time of the impactor, this resistive force can affect the output of the device. By forming a break in the magnetic circuit around a circumference of the magnetic core 210, there is no continuous path within the magnetic core 210 that fully encircles the channel within which the striker 180 moves. This therefore helps prevent eddy currents generating forces that resist the motion of the striker 180, thereby enabling the striker 180 to be driven more efficiently, to provide a higher impact force.

[0096] To help reduce the overall size of the motor, wiring 230 to the coils 250 may be provided within the break 214. In addition, or alternatively, one or more sensors 240 may be located within the break 214 for sensing the position of the striker 180 within the channel. In the present embodiment, both the wiring 230 and the one or more sensors 240 are located within the break 214, although it will be appreciated that only one of these need be located within the break 214 in order to achieve a reduction in the size of the motor.

[0097] Referring to FIGs. 3, 7 and 8, the wiring 230 runs along a length of the motor (e.g. along a direction parallel to the direction of motion of the striker 180). The wiring 230 includes a plurality of wires 230. One set of wires 230 is provided for each phase of the motor. In the present case, the motor is a three phase motor, meaning that three sets of wires 230 are provided. Each set of wires 230 connects to a different subset of the coils 250, to allow each subset of the coils 250 to be driven differently. This enables the different phases of the motor to be driven to generate magnetic fields of different polarities. This enables a linear force to be generated to drive the striker 180 along the path of motion.

[0098] For instance, in the present embodiment, nine coils 250 are utilized, in three sets of three. One set of wires 230 is provided for each of the three coils within the set. Each set of wires 230 connects a different subset of coils 250 in series to form a chain of coils 250. Every third coil 250 is connected. Each coil 250 may be driven in either a first direction (e.g. clockwise) or a second direction (e.g. anticlockwise). At each time point within the driving cycle, one set of wires 230 may be driven to provide a clockwise current to its respective subset of coils 250, one set of wires may be driven to provide an anticlockwise current to its respective subset of coils 250, and one set of wires 230 may not be driven (e.g. may be grounded or may be floating). As the striker 180 moves along the stator, the polarities of the coils 250 may be switched (commuted) to continue to drive the striker 180. The driving and switching of the coils may be controlled by electronic circuitry within the impactor 10.

[0099] Each set of wires 230 is insulated from the coils 250 that they are not connected to (e.g. through sheath(s) of insulation). Within each set of coils 250, the winding direction of the coils 250 may be alternated, and the input and output end of the coils 250 may be alternated. For instance, a first coil 250 may have an input at an outer end of the coil 250, and an output at the inner end of the coil 250 and may be wound in a first direction (e.g. clockwise). The next coil 250 in the chain (e.g. a fourth coil 250) may have an input at the inner end of the next coil 250 that is connected to the output (the inner end) of the first coil 250. An output of this next coil 250 may be located at an outer end 250 and this next coil 250 may be wound in a second direction (e.g. anticlockwise). In this manner, the length of the wires 230 between coils 250 may be minimized, whilst ensuring that all coils 250 in the chain are driven to provide a current in the same direction (e.g. clockwise or anticlockwise).

[0100] FIG. 9 is a circuit diagram showing a connection arrangement between coils 250 according to an embodiment. Nine coils 250 are connected, in three sets of three. Each set includes a plurality of coils connected in series. The winding direction alternates down the set. In addition, the location of the input and output terminals of the coils alternates down the set.

[0101] The first, fourth and seventh coils are connected in series in a first set. The second, fifth and eight coils are connected in series in a second set. The third, sixth and ninth coils are connected in series in a third set.

[0102] Each of the first, second and third sets are wound and connected in a similar manner. Accordingly, only the winding and connections in the first set are described below, although it will be appreciated that this description applies equally to the second and third sets.

[0103] The first set comprises the first, fourth and seventh coils. The fourth coil has an opposite winding direction to the first and seventh coils. The first coil has an input at an inner end of the first coil and an output at the outer end of the first coil. The outer end of the first coil is connected to the outer end of the fourth coil. The fourth coil has an input at the outer end of the fourth coil and an output at the inner end of the fourth coil. The inner end of the fourth coil is connected to the inner end of the seventh coil. The seventh coil has an input at an inner end of the seventh coil and an output at the outer end of the seventh coil. The output of the seventh coil is the output of the first set.

[0104] The outputs of each set of coils is connected to the outputs of the other sets of coils. Accordingly, depending on how the coils are driven, a positive current can pass through one set of coils and a negative current can pass back through another set of coils. The final set of coils may be switched off to prevent current passing through the third set. By selectively switching the coils, the magnetic field can be varied within the channel to drive the striker 180.

[0105] Referring to FIGs. 3, 5 and 7, one or more sensors 240 may be provided within the break 214. The one or more sensors 240 may be configured to measure a position of the striker 180 within the channel. The one or more sensors 240 may be magnetic sensors (e.g. Hall effect sensors) configured to measure a magnetic field provided by the magnets 182 in the striker 180. In one embodiment, two sets of one or more sensors are provided on opposite sides of the coils 250. By providing sets of sensors 240 on each side of the coils 250 the length of the striker 180 may be reduced relative to its range of motion whilst still allowing continuous sensing of the striker 180 position. By locating the sensors 240 outside of the coils 250, the size of the coils 250 can be reduced, and the sensors 240 are affected less by the magnetic field produced by the coils 250.

[0106] In one embodiment, each set of sensors 240 comprises two or more sensors 240. Each set of two or more sensors 240 may have a spacing between adjacent sensors that is substantially equal to half the magnet 182 spacing on the striker 180. This provides a sensor reading from each sensor that is 90° out of phase from the adjacent sensor(s), enabling the position of the striker 180 within the channel to be determined effectively.

[0107] FIG. 10 shows a transverse cross-section of a stator assembly according to an embodiment along a plane passing through a coil 250. FIG. 11 shows a cross-section of a coil 250 according to an embodiment. Each coil 250 is positioned within a coil cavity within the magnetic core 210. Each coil 250 comprises a series of turns from an outer circumference, decreasing in radius towards an inner circumference (winding around a central axis of the coil). The coil 250 may be formed of a conductor. The coil 250 may be formed of a metal, such as copper. Each turn has a width (e.g. in a direction parallel to a central axis of coil) that extends across the whole width of the coil 250 (in the direction parallel to the central axis of the coil). That is, for each coil, only a single turn is provided at each radial position away from the centre of the coil 250. The cross section of each turn is therefore elongated in this width direction. For instance, as shown in FIG. 2, each turn may have a rectangular cross-section, although other cross-sectional shapes are possible.

[0108] The coils 250 may be formed of solid metal (e.g. as opposed to strands of flexible wire). The coils 250 can be formed by cutting or eroding the coil 250 from a solid block of metal. For instance, the block may be cut or eroded into shape through electrical discharge machining, laser cutting, waterjet cutting, or any other cutting or erosion method. Alternatively, the block may be moulded (e.g. through casting or metal injection moulding). It is possible to determine the method of manufacture from the finished coil. For instance, where erosion has been used, one or more parting pips may be present after the coil has been cut off the rest of the material it has been formed from. Forming the coils 250 in this manner provides a greater design freedom. In addition, it allows each turn to be a single, continuous extent of metal that extends across the full width of the coil 250. This is in contrast to coils 250 formed of wires, in which multiple turns may be required at each radius to cover the full width of the coil 250. By forming each turn so that it extends across the full width of the coil 250, the resistance within the coil 250 is reduced by increasing the cross-section of the turns and reducing the length of the conduction path through the coil 250 (e.g. relative to wire windings). This improves the power performance of the system (e.g. improving battery performance), by allowing a relatively high current to be drawn without a significant drop in voltage.

[0109] The greater flexibility in the geometry of the coils 250 also allows the thickness of the turns in the coils to be varied around their length to further help reduce the size of the motor. For instance, the thickness of the turns is reduced at an angular position around the turn that aligns with the wire connections into and out of the coil 250 (e.g. that aligns with at least a portion of the break 214). That is, the thickness (e.g. in the radial direction) of the turn is smaller at an angular position around the turn that aligns with the wire connections than at other positions around the turn. This allows the wires 230 to be located partially within the diameter of the coil 250, thereby further helping to reduce the size of the motor.

[0110] The reduced thickness of the turns also allows the input and output wires for the coil 250 to overlap without negatively affecting the size of the motor (see arrangement of FIG. 10). By overlapping the input and output wires, the width the break can be reduced, thereby increasing the amount of magnetic material in the magnetic core, and therefore increasing the magnetic field generated by the motor.

[0111] In addition, for certain coils, the inner end will extend to an angle beyond the angle of the outer end, or vice versa (see arrangement of FIG. 11). This may be necessary when the input and output wires do not directly overlap. For instance, for the coil 250 shown in FIG. 11 , at the outer end, an extension portion that overlaps the inner end has a reduced thickness. By reducing a portion of at least one of the turns within the break 214, an additional turn portion may be included to allow greater flexibility in the wiring arrangement without greatly impacting the size of the motor. FIGs. 12A and 12B show transverse cross-sections of a stator assembly according to an embodiment along respective planes passing through first 260 and second 265 insulating spacers. For each coil 250, a first insulating spacer 260 and a second insulating spacer 265 is located on either side of the coil 250. These insulating spacers 260 and 265 separate and insulate the coil 250 from the side walls of the coil cavities of the magnetic core 210. The insulating spacers 260 and 265 are made of an insulating material, such as polyimide (e.g. Kapton™) or polyether ether ketone (PEEK).

[0112] The insulating spacers 260 and 266 have equivalent shapes. The insulating spacers 260 and 265 have substantially toroidal shapes, to match a cross-section of the coils 250; however, the insulating spacers 260 and 265 also have cut outs spaced around their internal circumference. These cut outs allow potting compound to be injected into the coils and to flow through the motor during manufacture. One or more of the cut outs align with the one or more holes 208 in the magnetic core 210 to allow potting to pass through the one or more holes 208. Cut outs also align with the wiring 230 to allow the wiring 230 to pass through the insulating spacers 260 and 265.

[0113] Given the above, embodiments provide a surgical impactor 10 having a linear electromagnetic motor that can be manufactured in a more compact form. The motor can be made smaller without compromising the impact force generated by the impactor 10. This is achieved by placing components (e.g. wiring 230 and / or sensors 240) within a break 214 in the magnetic core 210 that is provided to prevent eddy currents. In addition, the magnetic core 210 includes extension regions 220 and 225 that extend beyond the coils 250 to extend magnetic flux along a greater distance. Furthermore, the striker 180 is provided with a core 188 that is magnetisable which helps reduces radial forces thereby reducing the friction of the striker 180 within the impactor 10.

[0114] While certain arrangements have been described, the arrangements have been presented by way of example only, and are not intended to limit the scope of protection. The inventive concepts described herein may be implemented in a variety of other forms. In addition, various omissions, substitutions and changes to the specific implementations described herein may be made without departing from the scope of protection defined in the following claims.

Claims

CLAIMS:1 . A surgical impactor comprising: an anvil configured to impart an impact to an object; and a linear motor comprising: a striker comprising one or more magnets, wherein the striker is configured to be driven to move linearly along a path of movement within the linear motor to strike the anvil; a stator comprising: a magnetic core having: a channel passing through the magnetic core from a first end of the magnetic core to a second end of the magnetic core, the second end being opposite to the first end, the channel being configured to receive the striker and defining the path of movement for the striker; and a break in the magnetic core running from the first end to the second end of the magnetic core and extending between an outside of the magnetic core to the channel across its length to reduce eddy currents within the magnetic core; coils surrounding the path of movement and positioned in order down the length of the channel for driving the striker to move along the channel; and one or more wires configured to provide current to the coils, wherein the one or more wires are located within the break of the magnetic core.

2. The surgical impactor of claim 1 wherein the break forms a further channel within the magnetic core, wherein the channel is defined between opposing side walls of the channel, wherein the one or more wires are located between the opposing side walls of the channel.

3. The surgical impactor of claim 1 or claim 2 wherein the one or more wires comprise a plurality of subsets of one or more wires, wherein each subset of one or more wires is connected to a corresponding subset of the coils.

4. The surgical impactor of claim 3 wherein each subset of the coils comprises plurality of coils, and wherein the winding direction of the coils alternates within each subset of the coils.

5. The surgical impactor of any preceding claim further comprising: one or more sensors for sensing a position of the striker along the path of movement, the one or more sensors being located within the break of the magnetic core.

6. The surgical impactor of any preceding claim wherein the magnetic core comprises one or both of: a first extension portion that extends beyond the coils to the first end; and a second extension portion that extends beyond the coils to the second end.

7. The surgical impactor of claim 6, when dependent on claim 5, wherein the one or more sensors comprise a first set of one or more sensors located within the break within the first extension portion and a second set of one or more sensors located within the break within the second extension portion.

8. The surgical impactor of any preceding claim further comprising a bearing sleeve within the channel for supporting the striker as it moves within the channel.

9. The surgical impactor of claim 8 wherein the bearing sleeve is formed of a non- conductive material.

10. The surgical impactor of any preceding claim wherein each coil comprises a plurality of turns, wherein each turn has a cross-sectional shape with an elongated width.11 . The surgical impactor of any preceding claim wherein each coil comprises a plurality of turns, wherein one or more of the turns has a reduced thickness at a location that aligns with one or both of an input wire to the coil and an output wire from the coil.

12. The surgical impactor of any preceding claim wherein each coil is formed of solid metal eroded or cut into shape.

13. The surgical impactor of any preceding claim wherein each coil is contained within a corresponding coil cavity within the magnetic core, wherein each coil cavity extends radially outwards from the channel and opens into the break.

14. The surgical impactor of any preceding claim further comprising, for each coil, a pair of insulating spacers on opposite sides of the coil to separate and insulate the coil from the magnetic core.

15. The surgical impactor of claim 15 wherein one or more of the insulating spacers comprise one or more holes that open onto the coils for allowing potting compound to be supplied between turns of the coils.

16. The surgical impactor of any preceding claim wherein each coil is positioned within a corresponding coil cavity within the magnetic core, between opposing side walls of the coil cavity, and wherein one or more of the side walls comprises one or more channels passing through the side wall for allowing potting compound to be supplied between turns of the coils.

17. A surgical impactor comprising: an anvil configured to impart an impact to an object; and a linear motor comprising: a striker comprising one or more magnets and configured to be driven to move linearly along a path of movement within the linear motor to strike the anvil; a stator comprising: a magnetic core having: a channel passing through the magnetic core from a first end of the magnetic core to a second end of the magnetic core, the second end being opposite to the first end, the channel being configured to receive the striker and defining the path of movement for the striker; and a break in the magnetic core running from the first end to the second end of the magnetic core and extending between an outside of the magnetic core to the channel across its length to reduce eddy currents within the magnetic core; coils surrounding the path of movement and positioned in order down the length of the channel for driving the striker to move along the channel; and one or more sensors for sensing a position of the striker along the path of movement, the one or more sensors being located within the break of the magnetic core.

18. A surgical impactor comprising:an anvil configured to impart an impact to an object; and a linear motor comprising: a striker comprising one or more magnets and configured to be driven to move linearly along a path of movement within the linear motor to strike the anvil; and a stator comprising: a magnetic core having a channel passing through the magnetic core from a first end of the magnetic core to a second end of the magnetic core, the second end being opposite to the first end, the channel being configured to receive the striker and defining the path of movement for the striker; and coils surrounding the path of movement and positioned in order down the length of the channel for driving the striker to move along the channel, wherein the magnetic core comprises one or both of: a first extension portion that extends beyond the coils to the first end; and a second extension portion that extends beyond the coils to the second end.

19. The surgical impactor of claim 18 wherein: the coils are arranged sequentially over a first distance; and each extension portion has a length that is: greater than or equal to half of the first distance; or greater than or equal to three quarters of the first distance.

Images