WO2008080007A1

WO2008080007A1 - Surgical tool with user-selected torque / speed map

Info

Publication number: WO2008080007A1
Application number: PCT/US2007/088429
Authority: WO
Inventors: Ricky Colby Wilson Ii
Original assignee: Stryker Corporation
Priority date: 2006-12-22
Filing date: 2007-12-20
Publication date: 2008-07-03

Abstract

A surgical tool system including a handpiece with an electric motor and a control circuit for applying energization signals to the motor. The control circuit applies energization signals to the motor based on a maximum torque-at-speed map. The control circuit allows the user to custom define the maximum torque-at-speed map so that when the handpiece is exposed to different loads it responds based on the preferences of the surgeon using the handpiece.

Description

SURGICAL TOOL WITH USER-SELECTED TORQUE / SPEED MAP

Field of the Invention

[0001] This invention relates generally to powered surgical tools that include a handpiece with an electric motor. More particularly, this invention relates to powered surgical tool with a motorized handpiece wherein motor operation is based on a torque/speed map that is user determined.

Background of the Invention

[0002] In modern surgery, powered surgical tools are some of the most important instruments medical personnel have available for performing certain surgical procedures. Many surgical tools take the form of some type of motorized handpiece to which a cutting accessory like a drill bit, a bur or a saw blade is attached. These tools are used to selectively remove small sections of hard or soft tissue or to separate sections of tissue. The ability to use powered surgical tools on a patient lessens the physical strain of physicians and other personnel when performing surgical procedures on a patient. Moreover, most surgical procedures can be performed more quickly and more accurately with powered surgical tools than with the manual equivalents that preceded them.

[0003] Generally a powered surgical tool includes a handpiece. A powered surgical handpiece usually includes one of two different types of motor, electrical or pneumatic. The function of the motor is convert energy from in a first form, electrical or fluid under pressure (pneumatic) into mechanical energy. The mechanical energy is output as rotational force, torque, from the motor shaft. The torque is what overcomes the resistive load of the tissue against which the accessory is pressed so that the accessory cuts the tissue.

[0004] Many surgical handpieces provided with electrical motors have a brushless DC motor. One reason for this is that a DC motor can, immediately after start-up output a relatively large amount of torque. Moreover, when exposed to a sudden rise in load (mechanically resistive force) a DC motor can quickly output a large amount of torque. Further, it has proven possible to provide DC motors that are compact in size. This has made it possible to provide similar compact handpieces, (outer diameter < 3 cm and/or length < 15 cm. )

[0005] The power a motor outputs is a function of both the speed at which its shaft is rotating and the torque being output. Generally, the power any motor can output is limited in part by the physical construction of the motor, factors including the internal resistance and torque constant of the motor. The power is also limited by the device supplying power to the motor. In a DC motor, the above relationship means that that motor, absent other constraints, has a torque/speed map that has a linear profile. This map starts at a first point, a maximum speed at which the motor shaft will rotate when not subject to any load (no torque being output) ω_n. The map extends to a second point, the point wherein, just before the motor speed falls to zero, the motor stalls out, the maximum torque, τ_s, (torque at stall) is being produced. What this plot means is that generally, as the load to which a motor is exposed is increased and therefore, the torque the motor is required to output also increases, the speed of the motor will drop. This torque increase/speed drop increases until the motor longer turns, <X>_ACIUAL = 0. Here the torque produced is considered the torque at stall, τ_s.

[0006] The power to drive a handpiece with an electric motor typically comes from one of two sources. Some handpieces are corded. The power to drive this type of handpiece comes from the control console to which the handpiece is connected. Alternatively, the handpiece is battery driven, cordless. The power to drive this type of handpiece comes from a battery that is typically attached to the handpiece. The power to drive a pneumatic handpiece comes from the pressurized gas supplied to the handpiece. This gas is supplied from a source remote to the handpiece and connected to it by a gas line motor. [0007] The Applicant's Assignee's U.S. Patent No. 6,017,354, issued 25 January 2000, the contents of which are incorporated herein by reference, discloses a surgical tool system comprising a handpiece that is removably connected to a complementary control console. The handpiece contains a memory with torque speed map data specific to that handpiece. The control console, based on these map data, supplies an energization signal to the motor so it operates in accordance to the custom map.

[0008] One possible custom map is presented in Figure 1. Here, starting at the highest speed/lowest torque position, the motor operates at a maximum speed that is less than the free speed of the motor. Motor free speed is the speed the motor could attain at the maximum voltage supplied to the motor. The map at this point is vertical, segment 10. This means that when the surgeon first runs the motor at its maximum speed and applies it to tissue so that motor is exposed to a small load, the speed remains constant. Then, as represented by segment 12 of the map, as the load to which the motor is exposed slowly increases, there is a small drop off in motor speed. In a third state, represented by map segment 14, an increase in motor load results in a more noticeable drop in maximum speed. In a fourth segment, segment 16, as the amount of torque the motor produces increases, the drop off in speed with increase in torque is slightly less than that of segment 14. Map segment 18 is the segment that extends from the highest torque/slowest maximum speed terminal point of segment 16 to the torque at stall terminal point of the map. Segment 18 occupies the lowest 15% and often the lowest 10% speed range for the motor. In this segment of the map, the drop off in motor speed as the amount of torque produced is relatively small. However, prior to the motor operating within the state of terminal segment 18 the motor had previously cycled through the rapid speed drop offs of segments 14 and 16. The gradual drop of speed through these initial segments provides tactile and audible feedback to the surgeon, that the motor will soon be operating close to the stall state. The ability of the motor to continue to operate, produce a large amount of torque, as the speed finally slows to stall, provides the surgeon with a final opportunity to perform the desired procedure while, as the speed continues to drop, receive notice that the motor is even closer to stalling. [0009] Thus, the above system makes it possible to operate a motorized surgical tool in accordance with torque and speed characteristics that, while limited by the physical constructs of the tool and the power supply, can be defined independently of these constraints. As indicated by the example above, this makes it possible to define the operating characteristics of the handpiece to provide notice regarding how close the motor is operating near the stall state .

[00010] The Applicant's Assignee's U.S. Patent Publication No. US 2006/0074405 Al, published 6 April 2006 further describes a surgical tool system wherein that allows the surgeon to adjust the maximum torque τ_s the motor is able to produce.

[00011] Some surgeons find it useful to operate a handpiece in accordance with the above described torque/speed map. Other surgeons prefer operating a handpiece that operates in accordance with a more conventional, substantially linear torque/speed map. Further there are some instances in which how the surgeon may want to operate the handpiece is a function of the particular procedure for which the handpiece is to be used. Thus, for one procedure, the surgeon may want the handpiece to, when producing a large amount of torque, produce the torque at the highest possible speed at which that torque can be produced. The surgeon may, for another procedure, want to operate the handpiece so that, when a large amount of torque is output, the motor runs at a speed below the actual maximum speed for that maximum amount of torque supplied to the motor.

[00012] To date, the means by which it is possible to provide the "same" instrument that operates according to these different torque/speed maps to provide plural instruments, each identical save for its own torque/speed map .

Summary of the Invention

[00013] This invention relates to a new and useful surgical tool system with a handpiece that includes an electric motor. The tool system of this invention includes plural torque/speed boundary maps for the motor internal to the handpiece. This system of this invention allows the surgeon to select under which torque/speed map the motor will operate.

[00014] This surgical tool system of this invention thus allows the surgeon to custom configure the operation of the handpiece to the preference of the surgeon. Brief Description of the Drawings

[00015] The invention is pointed out with particularity in the claims. The above and further features and benefits of this invention may be better understood by the Detailed Description below taken in conjunction with the accompanying drawings in which:

[00016] Figure 1 depicts the single torque/speed map under which prior art motorized surgical handpieces are able to operate.

[00017] Figure 2 is a view of the basic components of a powered surgical tool system of this invention; [00018] Figure 3 is a block diagram of the components of the system that regulate the operation of the handpiece motor;

[00019] Figure 4 illustrates boundary torque/speed maps as well as intermediate torque/speed maps that may be generated based on the boundary maps;

[00020] Figure 5 depicts the contents of a memory of this system that stores data for defining the boundary torque/speed maps;

[00021] Figure 6 is a flow chart of the process steps executed by the system of this invention to generate a user- selected torque/speed map;

[00022] Figure 7 illustrates the image presented on the control console touch screen that allows the user to select the torque map under which the handpiece is to operate [00023] Figure 8 illustrates an alternative pair of boundary torque/speed maps.

Detailed Description

[00024] Figure 2 illustrates the basic components of a surgical tool system 30 constructed in accordance with this invention. System 30 includes a powered surgical handpiece 32. Internal to handpiece 32 is an electric brushless DC motor 34, shown as phantom block in Figure 2 and symbolically in Figure 3. Handpiece motor 34 drives a cutting accessory 38 that extends forward from the handpiece 32. In Figure 2, the illustrated cutting accessory is a bur. This is understood to be only for purposes of illustration and not limiting. Often, the cutting accessory 38 is removably attached to both the handpiece 32 and the motor 34. In Figure 2, a ring 39 at the proximal end, the front end, of the handpiece 32 represents the coupling assembly that removably holds the cutting accessory to the other components of the handpiece 32. The exact structure of the coupling assembly is not relevant to the structure of this invention. It should also be realized that often internal to the handpiece there is a gear assembly (not illustrated) . This gear assembly transfers the rotational moment of the motor rotor shaft to the cutting accessory 38.

[00025] A control console 42, also part of system 30, generates the energization signals that actuate the motor 34. Handpiece 32 is removably connected to console by a cable 44. Console 42 has a control circuit that, as described, below selectively applies DC voltage to the individual windings 40 of the rotor internal to the motor 34 (Figure 3) . These signals are output to the handpiece 32 over cable 44. Console 42 has a touch screen display 46. Data both in alphanumeric and graphic/image form are presented to the user on display 46. By pressing images of buttons presented on the display 46, the user configures system 30 so that the handpiece motor 34 operates in a manner preferred by the user.

[00026] Shown in Figure 2 but not understood to be part of this invention is an irrigation tube 48 that extends from control console 42 to handpiece 32. Irrigation tube 48 supplies irrigation fluid so it can be discharged through the handpiece 32 or discharged from a tube separate from or attached to the handpiece.

[00027] Figure 3 illustrates the components of system 30 that provide energization signals to handpiece motor 34. Some of these components, such as the power supply 52 are implemented in hardware. Other components, such as the torque map generator 74, are implemented in software and executed by a processor internal to the control console (processor not illustrated.) Other components, such as the high and low side drive circuit 54 (DRIVERS 54 in Figure 3) comprise a combination of hardware components and software instructions .

[00028] The power supply 52 converts the available AC power into a DC voltage that can be applied to the motor windings 40. The high and low driver circuit 54 selectively ties the motor windings 40 to the DC voltage, ground or high impedance (open state) . Specifically, the high and low driver circuit 54 determines across which pair of windings the drive signal should be applied, the commutation of the windings. The high and low driver circuit 54 also regulates the driving of the motor. That is, the high and low driver circuit 54 also determines the duty cycle at which the energization signal should be applied to the pair of windings selected for commutation.

[00029] For the purposes of this invention, high and low driver circuit 54 is considered to have three (3) pairs of series connected FETs (not illustrated.) A separate one of the windings 40 is connected to the junction of each pair of FETs. In each pair of FETs, the high side FET, is turned on to connect the associated winding to the DC power signal. The second winding of each pair of FETs, the low side FET, is turned on to selectively tie the winding to ground. [00030] High and low driver circuit 54 selectively ties each winding to the DC voltage, ground or open based on input signals from three sources. A first source is the commutation state detector 56. Commutation state detector 56 monitors the back electromotive forces, (BEMF, ) the voltage produced across each motor winding 40 when the winding is not being commutated. Based on these signals, commutation state detector 56 determines the position of the motor rotor. The position of the motor rotor determines which pair of motor windings 40 should next be subjected to commutation. In Figure 3, for purposes of simplicity, only the connection of a single one of the motor windings 40 to the commutation state detector 56 is shown. [00031] A second input signal into the high and low driver circuit 54 comes from a speed detector and controller 58. Speed detector and controller 58 generates control signals based on two inputs. A first input is a user selected speed signal, sometimes called a user speed set point signal. The user may enter this signal by one of any number of means. This signal may be generated as the consequence of the actuation of a handswitch attached to the handpiece 32 (handswitch not illustrated) . Alternatively, this signal is based on the depression of a footswitch 47 of the depression of one or more buttons on console touch screen 46. In Figure 3, this signal is represented as USER_SPD_SELECT input to the speed detector and controller 58.

[00032] The second input to speed detector and controller 58 is a measure of the actual speed of the motor rotor. This measurement is based on the integration of the BEMF signals. The integration of the BEMF signal reaching a threshold triggers a commutation event. Speed is determined as a function of the frequency of the commutation events. In Figure 3, a connection is shown between the commutation state detector 56 and speed detector and controller 58. This connection represents that the commutation state detector provides the speed detector and controller 58 with the BEMF signals that are subjected to integration. It should be realized this is only one means by which BEMF signals can be used to determine motor speed. Some motors, for example, rely on Hall sensors that sense rotor position, this does not require the sensing of BEMF signals. [00033] When the handpiece is actuated, speed detector and controller 58 compares the actual motor speed to the user-selected set point speed. Based on the extent to which these two speeds match, speed detector and controller 58 generates signals that regulate the driving of the windings being commutated.

[00034] A torque controller 60 is the third circuit internal to the control console 42 that supplies a control signal to the high and low driver circuit 54. Torque controller 60 receives as one input a measure of motor current, the current being drawn by the motor 36. In Figure 3 the signal representative of the motor current is supplied to the torque controller from a motor current processor 62. Motor current processor 62 determines the motor current by measuring the voltages across three resistors 63, 64 and 65. Each of these resistors 63, 64, and 65 is connected between the source of a separate one of the low side FETs of the high and low driver circuit and ground. Thus, when each low side FET is turned on to tie its associated winding 40 to ground, the voltage across the associated resistor 63, 64 or 65 is forwarded to the motor current processor 62. [00035] Motor current processor 62 selectively amplifies the received voltage measurements and forwards them to the torque controller 60. It is understood that these voltage measurements are proportional to the motor current, I_Mc- There is a direct, generally linear relationship between the current drawn by the motor and the torque being instantly output . [00036] Torque controller 60 ensures that, for the torque being output by the motor 34, the motor runs at or below an appropriate speed. Thus, a second input signal into the torque controller is the motor speed. In Figure 3, a connection is shown between the speed detector and controller 58. This connection represents the speed detector and controller 58 supplying a signal to the torque controller 60 a signal representative of motor speed. [00037] The torque controller 60 determines whether or not the motor is running below the specified maximum speed by first initially determining, for the instantaneous torque being produced by the motor, the maximum speed. This determination is made based on a torque/speed map. Data representative of this map are contained in a memory internal to control console 42 as torque map 70. [00038] When the handpiece is actuated, motor current processor 62, based on the voltages across resistors 63, 64 and 65, generates a signal representative of motor current. This signal is converted by the torque controller 60 into a signal representative of instantaneous torque produced by the motor. By reference to the torque map 70, torque controller 60 determines the maximum speed at which the motor should be running for the given amount of torque being produced. The actual speed of the motor is compared to this torque based maximum. If the motor is running at or below the maximum speed for the torque being produced, torque controller 60 asserts signals to the high and low driver circuit 54 that cause the circuit 54 to assert driver signals based on the signals asserted by the speed detector and controller 58.

[00039] There are times when the instantaneous torque produced by the motor will be in excess of what it should be for the present operating speed of the motor 34. In an instance of this type, torque controller 60 asserts signals to high and low side drive circuit 54 that prevent or reduce the extent to which drive signals are applied to the windings 40 being commutated. The reduction, the modulation, of these drive signals reduces the current and, as a consequence, the torque supplied to the motor. If the torque applied to the motor rotor through the cutting accessory exceeds the torque supplied by as a consequence of the application of the drive current, the motor speed falls to an equilibrium speed. This equilibrium speed is the speed where the allowed supplied torque, as dictated by the map, equals the torque applied through the cutting accessory.

[00040] A more detailed understanding of the above circuit can be found in the above-mentioned, incorporated by reference U.S. Patent Pub. No. US 2006/0074405 Al. [00041] The torque/speed data contained in the torque map 70 is produced by the torque map generator 74. This torque map generator 74 contains as one input two boundary torque maps, represented in Figure 4 as being contained in module 76. Figure 4 graphically depicts the boundary torque maps, maps 80 and 120. Map 80 the lower of the two maps, is substantially linear. Map 120, the upper of the two maps comprises a number of line segments with different slopes. [00042] Each map 80 and 120 can be considered to be formed with a number of different segments. Maps 80 and 120 have a common initial no load maximum speed point, point 76, for their initial segments. Maps 80 and 120 of Figure 4 are further shown as having a shared zero speed/torque at stall point, point 78. As discussed below this is exemplary. Other boundary maps, wherein either one or both of the no load maximum speed and the torque at stall points are different, are possible.

[00043] Between the end points, inflection points define the beginnings and ends of each one of the map defining segments. Map 80 is defined by a first vertical segment 81 and four diagonal segments 83, 85, 87 and 89. Diagonal segments 83, 85, 87 and 89 are for map 80 co-linear. Point 82 is the inflection point where segment 83 angles away from segment 81. Point 84 is the inflection point between segments 83 and 85. Point 86 is the inflection point between segments 85 and 87. Point 88 is the inflection point between segments 87 and 89. As, mentioned above segments 83, 85, 87 and 89 of map 80 are collinear. Therefore, inflection points 84, 86 and 88 of map 80 are not points around which there are actual geometric inflections of the segment-defining maps.

[00044] Map 120 is similarly formed from a first vertical segment, segment 121 and four diagonal segments 123, 125, 127 and 129. Segment 121 of map 120 includes segment 81 of map 80. Diagonal segments 123, 125, 127 and 129 have different slopes. For example the decrease is maximum speed with increase in torque is less over segment 129 of map 120 than over adjacent segment 127. Point 122 is the inflection point between vertical segment 121 and diagonal segment 123. Point 124 is the inflection point between segments 123 and 125. Point 126 is the inflection point between segments 125 and 127 Point 128 is the inflection point between segments 127 and 129. Points 122, 124, 126 and 128 are thus each points around which there is an actual geometric inflection of the associated map-defining segments. [00045] The data defining boundary torque maps can come from one of a number of sources. The data may be stored in the console memory at manufacture. Thus, boundary torque curves 76 can, in some versions of the invention, be considered part of the data stored in the control console memory. Alternatively, the data may be stored in a memory integral with the handpiece 32. As described in the incorporated by reference U.S. Patent No. 6,017,354, this memory stores other data used to regulate the operation of the handpiece. This memory may be in the housing comprising the handpiece. Alternatively, this handpiece-unique memory may be in one of the proximal end plug of handpiece cable 44. In Figure 2 phantom circle 33 in the handpiece represents this memory.

[00046] Figure 5 is a diagrammatic illustration of the memory 140 (either in the handpiece or control console) the contents of which contains the data used to define both boundary torque maps 80 and 120. Memory 140 includes, for the first boundary map, here, lower boundary map 80, a max speed field 142. The data in field 142 represents for map 80 the no-load maximum speed point for the map. Also for this first map, there are four torque/speed set point fields, 144, 146, 148 and 150. The data in each one of fields 144-150 represent a specific inflection point for map 80. The remaining field specific to the first boundary map 80 is a torque at stall field 152. Field 152 contains data indicating the maximum amount of torque the motor should produce upon stalling.

[00047] Memory fields 156, 158, 160, 162, 164, 166 contain data for upper boundary map 120 similar to that used to define lower boundary map 80. Specifically, field 156 contains data indicating the no load maximum speed. There are four torque/speed set point fields 158, 160, 162 and 164. The data in fields 158-164 are for map 120 equivalent to the data in fields 144-150 for map 80. The torque at stall point for map 120 is defined by the data in field 166. [00048] Lower and upper boundary torque maps 80 and 120, respectively, of Figure 4 have identical no load speed and torque at stall terminal points. Therefore, the data in max speed fields 144 and 156 are identical. Similarly the data in torque at stall fields 152 and 166 are identical. It should be understood that these field pairs not always contain duplicate data. What is important for the purposes of generating user-selected torque speed maps between the boundary maps, using the equations set forth below, is that there be data defining the same number of map inflection points for each boundary map.

[00049] Also shown in memory 140 is a current/torque coefficient field 170. Field 170 contains a coefficient that is supplied to the torque controller 70. Specifically using this coefficient, β, torque controller 70 determines the instantaneous torque produced, by the motor according to the formula:

Here, T_MTR is the torque produced by the motor at any given instant .

[00050] The torque map generator 74, another processing module executed by the processor internal to the control console 42, based on the boundary torque maps, generates the actual torque map loaded into memory 70. Torque map generator 74 presents an image on the console display 46 that allows the user to select which of the boundary torques he/she wants loaded into memory 70 for controlling the handpiece motor 36. Torque map generator 74 can also generate a user-specified toque map for loading into memory 70 that is between the two boundary torque maps 80 and 120.

[00051] The process by which the torque map generator 74 creates and loads a torque map into memory 70 is now explained by reference to the flow chart of Figure 6. Step 184 that represents the loading of the boundary torque maps 80 and 120 into boundary map memory 74. Step 184 is an optional step that is performed if the data in memory 140 is not previously stored in the control console. Step 184 is performed if memory 140 is contained in a separate unit such as the memory integrally associated with the handpiece 32. [00052] In a step 186, torque map generator invites the user to designate which torque map he/she wants to use as the controlling torque map for the particular procedure. This invitation appears as an image on the display 46. As seen in Figure 7, this image includes buttons 188 and 192 labeled with data identifying characteristics associated with the boundary torque/speed maps 80 and 120. The image also contains an indication 190 of the relationship of the selected torque map is close to the boundary torque maps. In one version of the invention, this relationship is a percent where 0% means the selected map is the actual lower boundary torque torque/speed map 80, the map represented by button 188. In this version of the invention, 100% is the actual upper boundary torque/speed map 120, the map represented by button 192. Shown integral with numeric indication 190 is an arrow that indicates to which of the boundary torque/speed maps 80 or 120, the user-selected torque map is closest.

[00053] Button 194 is depressed to enter the user selected torque map. In the flow chart of Figure 6, step 198 represents the entry of the user selected torque map .

[00054] In response to the selection of a torque map by the user, torque map generator, in step 202 calculates the terminal and inflection points for the selected torque/speed map. The no-load speed, s^_ECTED, for the selected torque map is calculated according to the following formula

MAX _ , , MAX _ MAX ^>. ^ / 1 0 CH 4- ^MΑX I ? "\

UPPER BNDRY ¹^ LOWER BNDRY ' ' -^■- " " ^{/ 1}^ LOWER BNDRY

Here, s _{σppER BNDRY} is the no load maximum speed for the upper boundary torque map; s^_{ER BNDRY} is the no load maximum speed for the lower boundary torque map. Variable m is the user designated percent. [00055] The inflection set points are set based on the following additional torque and speed determinations:

N _ N

SELECTED ^~ ( ( τ UPPER BOUND 'ARY - τ N LOWER BOUND ARY ) m/100 )

+ τ N

LOWER BOUNDARY !3)

N _ N N

SELECTED ^~ ( ( s UPPER BOUND 'ARY - s LOWER BOUND ARY ) m/100 )

N

+ S LOWER BOUNDARY (4)

Here the superscripts mean that the input variable is the torque or speed point for the inflection point N. The subscript indicates that, for the inflection point N the variable is from either the upper or lower boundary torque plot. In the illustrated embodiment of the invention, each torque speed map has four (4) inflection points. Accordingly, in step 202, Equations 3 and 4 are executed four (4) times to generate the four inflection points for the user-selected torque map.

[00056] In Figure 4, the "X" points represent the inflection points that define user-selected torque/speed map 90. Map 90 it is observed has the characteristic of being closer to boundary map 80 than boundary map 120. Map 90, between the inflection points, is illustrated by a dot-and-dashed line. The "o" points in Figure 3 are the inflection points that define user-selected torque/speed map 110. Map 110 has a profile that is closer to boundary map 120 than boundary map 80 than boundary map 80. Map 110, between the inflection points, is illustrated by a dashed line .

[00057] Mathematically and from Figure 4, it will be appreciated that, for a intermediate torque/speed map, each inflection point defines the adjacent terminuses of adjacent segments of the map.

[00058] The user-selected torque at stall is calculated according the following formula: ^ SELECTED ' ' ^ UPPER _ BOUNDARY ^ LOWER _ BOUNDARY ' ^' -L U U j

N

BOUNDARY :5)

[00059] Based on the generation of these six (6) points, no-load speed, the four inflection points and the torque at stall point, torque map generator 180 interpolates between the adjacent points to generate the user-specified torque/speed map, step 204. Torque map generator 180 then loads the data defining this map into torque map 70, step 206.

[00060] Then, during the actuation of the handpiece 32, torque controller 60, as described above, references the data in torque map 70 to determine whether or not, for the torque being produced by the handpiece motor 34, the motor is operating at a below the maximum designated speed. If the motor 34 is running above the designated speed, torque controller 70 takes the steps needed to bring the motor speed down to within the acceptable limits. [00061] System 30 of this invention thus allows the surgeon to configure the handpiece 32 for more than such factors as maximum speed and maximum torque. System 30 further allows the surgeon to configure the handpiece 32 for different responses to the different loads to which the handpiece is exposed.

[00062] For example, the memory 140 associated with a particular handpiece 32 can be loaded with the boundary maps 80 and 120 of Figure 3. Here boundary map 80 represents how a pneumatic motor responds to increases in load. This is represented by the label associated with button 188. In other words, a pneumatic motor typically response to increases in loads with speed that decreases substantially linearly along the length of the map. Here "substantially linearly" can be considered to be that for at least 50% of the map from the no load speed to the torque at stall speed, the Δtorque/Δ speed profile is a constant first order relationship. Boundary map 120 represents how a handpiece with an electric motor responds to increases in loads, represented by the label associated with button 192. With this type of motor, increases in load resistance in the medium operating range of the motor result in a slower decrease in speed than increases in either initial or final load resistance.

[00063] Accordingly, by providing system 30, the surgeon can select to operate the handpiece as if it actually has an electric motor; operate the motor based on the torque/speed map of boundary map 120. Alternatively, by selecting to operate the motor based on the torque/speed map of boundary map 80, can configure to operate the handpiece so it emulates a handpiece with a pneumatic motor. Still further, system 30 allows the surgeon to operate the handpiece so that the motor responds based on a surgeon-selected torque/speed map that is intermediate to the torque/speed boundary maps 80 and 120.

[00064] Memory 140 may alternatively be loaded with alternative torque/speed boundary maps such as boundary maps 180 and 210 of Figure 8. Torque/speed boundary map 180 is similar to boundary map 120, it is a profile to the responsiveness to load of a standard handpiece. Map 210, which is rectangular is shape, has the profile of a torque- limiting wrench. That is, for all speeds, from the no-load speed to the stall speed, the handpiece is configured so that the motor is able to produce up to the set maximum amount of torque.

[00065] Thus, when torque controller 60 is operating the handpiece motor in accordance with map 210 and it is determined the motor 36 is outputting the maximum torque or trying to operate above the maximum speed, torque controller 60 inhibits the driving of the motor to prevent the motor from outputting more than the maximum designated torque .

[00066] In Figure 8, inflection points 182, 184, 186 and 188 define the line segments that collectively form boundary map 180. Inflection points 212, 214, 216 and 218 define the line segments that form boundary map 210. Since boundary map 210 is for a motor that emulates a torque limiting wrench, inflection points 212, 214, define the slight offset from the horizontal portion of the torque limiting wrench map when, as a load is applied to a motor there is a slight drop off from the maximum speed. Inflection points 214, 216 and 218 as well as the torque at stall point for the map collectively define a set of line segments that are linear and along a line of constant torque .

[00067] Thus, when a boundary torque maps 180 and 210 are loaded in system 30, the surgeon is able to custom configure the handpiece so it can respond as: a conventional motorized handpiece or as a torque limiting wrench. Alternatively, by using the custom setting feature, the surgeon can configure the handpiece so that, in response to changes in loads, it responds based on a torque/speed map intermediate to that between a conventional handpiece and a torque limiting wrench.

[00068] It should likewise be appreciated that as part of system 30 of this invention, the surgeon may be given the option of adjusting the no-load speed and/or torque at stall of either of the boundary maps or the custom user-specified map. In many but not all versions of the invention, this is an adjustment downward, from a maximum no-load speed or a maximum torque.

[00069] It should be appreciated that the above is directed to one specific version of this invention and that other versions of the invention may have features different from what has been described.

[00070] Thus, there is no requirement that all versions of the invention employ the described control circuit for regulating both the commutation and driving of the handpiece motor 34.

[00071] Likewise, not all versions of the invention may provide the surgeon all the described map definition option. In some versions of the invention, the surgeon may only be allowed to operate the handpiece based on either of the boundary torque/speed maps.

[00072] Alternatively, instead of the memory associated with the handpiece storing data defining two boundary torque/speed maps, the memory may contain data describing intermediate maps. In these versions of the invention, torque map generator may allow the surgeon to select under which one of the three or more torque speed map he/she can operate the handpiece. The data defining the selected torque/speed map is located in torque map memory 70. Alternatively, in these versions of the invention, the surgeon, after selecting two of torque/speed map uses the process described with respect to Figure 5 to generate a custom torque/speed map with a profile intermediate the selected, defined maps.

[00073] The methods of regulating the torque supplied to the motor and/or motor speed are understood to be exemplary and not limiting. Thus, in some versions of the invention, torque controller may limit the energization signal applied to the motor when it is determined that motor produces excessive torque for the given speed. Similarly, some motors employ either magnet or optical sensors for determining motor rotor position. Control consoles used to regulate these motors include circuits different than what has been disclosed to determine rotor position and rotor speed.

[00074] Similarly, the actual format for storing the user-selected torque/speed map is not limited to the disclosed method. In some versions of the invention, the torque map memory 70 may actually just store the no-load speed, torque/speed inflection points at torque-at-stall points for the user-selected torque map. Then, as part of the process of torque regulating the actuation of the motor 34, torque controller 60 determines the torque/speed set point for the instantaneous current speed (or torque currently being produced) for the motor. This set point is based on the above-described data.

[00075] Likewise, there is no requirement that in all versions of the invention, either the boundary or user- selected torque speed maps/maps be linear. In some versions of the invention, the map segments between defining terminal and inflection points may actually be mapped. In these versions of the invention, map-defining algorithms define the map points between the terminal and inflection points. Thus these collection of points can define some map segments that are curved and some map segments that are linear. [00076] Alternatively, the system may allow the user to select between map defining points whether or not the map section is linear or mapped, and the radius of the curvature .

[00077] In some versions of the invention, the boundary maps or base torque/speed maps upon which the user selected torque maps are based may come from a remote server to which the control console is attached. Alternatively, the data defining these maps may come from removable memory modules. [00078] Also, in some versions of the invention, the boundary maps may intersect. This may be the situation for a handpiece that can selectively be operated as a conventional handpiece or as a torque limiting wrench. In the latter configuration, to avoid mechanical damage to the motor at high speeds, the set constant torque level may be less than what the motor could otherwise produce when operating near the stall speed.

[00079] Likewise the algorithm by which the user- selected, the user-determined, torque/speed map may be different from what has been described. Thus, in an alternative version of the invention, the system may present a basic torque/speed map on display 46. The user is then invited to reset the inflection points. The user's selections are allowed provided they are within an envelop established by a set of boundary torque/speed maps. Alternatively, the borders of the envelop are established by set ranges relative to the inflection points of single center torque/speed map. These ranges may be different for each inflection point. These ranges thus implicitly define boundary torque maps. Alternatively, the single torque map from which the envelop of acceptable torque/speed maps is defined may be one of the boundary torque maps. Thus, in this version of the invention, the range data associated with each inflection point could, for example indicate the range of torques that extend up (or down) from the inflection point. Thus, when other algorithms are used to generate the user-selected torque/speed map, data different from that described above with respect to Figure 5 may be provided.

[00080] It should likewise be appreciated that the "cutting accessory" driven by the handpiece is not limited devices that actual shape tissue such as a bur, a drill bit a shaver, a rasp, a saw blade, gouge dermabrade or a reamer. A cutting accessory can be any device applied to a surgical site that applies torque to either the tissue or another component at or adjacent the surgical site. For example a screw or other fastener drivers or a wrench used to fasten a guide or a plate to bone are understood to be cutting accessories that are driven by the system of this invention. Wire drivers chucking devices are likewise understood to be cutting accessories.

[00081] Further, while described system 30 includes a corded handpiece, this is likewise understood to be exemplary, not limiting. In alternative versions of the invention, the handpiece may be a cordless battery powered unit. In these versions of the invention the torque map generator and associated components may be in a static unit that is separate from the handpiece. Prior to the start of the procedure, the surgeon selects his/her torque map. The generator than loads the selected or generated torque map into the torque map memory integral with the handpiece. Alternatively, by depressing switches or otherwise entering commands into the handpiece the surgeon selects or generates the torque map upon which the motor is to be controlled. [00082] Therefore it is object of the appended claims to cover all such modifications and variations that come within the true spirit and scope of this invention.

Claims

1. A surgical tool assembly including: a handpiece (32) including a variable speed electric motor (34) and a cutting accessory (38) for application to a surgical site that is connected to the motor for actuation by the motor; a control circuit (54, 56, 58, 60) for supplying energization signals to the handpiece motor, the control circuit configured to: monitor the speed of the motor; monitor the torque produced by said motor; by reference to the motor speed and a torque map (70), determine if the torque produced is above the maximum torque for that speed; and, if the torque produced is above the maximum torque for that speed, modulate the application of energization signals to reduce the torque supplied to the motor; characterized in that: the controller includes a torque map generator (74) that allows a user to select from between two boundary torque maps (80, 120) for the electric motor which torque map should be used as the torque map upon which the maximum speed-at-torque comparison is based.

2. The surgical tool assembly of Claim 1, wherein said torque map generator further allows the user to select an intermediate torque map that is between the two boundary torque maps as the torque map upon which the maximum speed- at-torque comparison is based.

3. The surgical tool assembly of Claim 2, wherein: each said boundary torque map is defined by at least one torque produced/maximum speed inflection point; and when the user selects an intermediate torque map, said torque map generator is configured to interpolate between the torque produced/maximum speed inflection points of the boundary torque maps to produce at least one intermediate torque produced/maximum speed inflection point between the boundary torque maps (202) and to generate the intermediate torque map at least partially based on the at least one intermediate torque produced/maximum speed inflection point (204) .

4. The surgical tool assembly of Claims 2 or 3, wherein : each said boundary torque map is defined at one end by a no load/maximum speed point (ω_n) and at a second end by a torque at stall point (τ_s) , wherein at least of one of the load/maximum speed points or torque-at-stall points of said boundary torque maps are different from each other; when the user selects an intermediate torque map, said torque map generator is configured to interpolate between the different no load/maximum speed set points or the different torque-at-stall points to produce an intermediate no load/maximum speed set point or an intermediate torque- at-stall point that is between the boundary torque maps (202) and to generate the intermediate torque map at least partially based on the intermediate no load/maximum speed set point or the intermediate torque-at-stall point (204).

5. The surgical tool assembly of Claims 1, 2, 3 or 4 wherein: each said boundary torque map is defined at one end by a no load/maximum speed point (ω_n) and at a second end by a torque-at-stall point (τ_s) ; and at least one of the boundary torque maps has, between the no load/maximum speed point and the torque-at-stall point, a relationship between the maximum speed for the torque being produced that is linear along at least 50% of the map (83, 85, 87, 89) .

6. The surgical tool assembly of Claims 1, 2, 3, 4, or 5, wherein each said boundary torque map is defined at one end by a no load/maximum speed point (ω_n) and at a second end by a torque at stall point (τ_s) ; and at least one of the boundary torque map has, between the no load/maximum speed point and the torque at stall point, a segment (210) wherein, for a particular speed range, there is a single maximum torque the motor should produce.

7. The surgical tool assembly of Claims 1, 2, 3, 4, 5 or 6, wherein at least one of boundary torque maps consists of a plurality of maximum speed for torque produced relationships that emulates the maximum speed for torque produced relationship if the motor in the handpiece is a pneumatic motor.

8. The surgical tool assembly of Claims 1, 2, 3, 4, 5, 6 or 7, wherein said control console is configured to: based on the torque being produced and reference to the torque map, determine the maximum speed at which the motor should be operating; compare the speed at which the motor is operating to the determined maximum speed; and if the motor is operating at a speed in excess of the determined maximum speed, modulate the application of energization signals to the motor to reduce the motor speed.

9. The surgical tool assembly of Claims 1, 2, 3, 4, 5, 6 or 7, wherein said control console is configured to: based on the speed at which the motor is operating and reference to the torque map, determine for that speed the maximum torque the motor should be producing; compare the torque being produced to the maximum torque at speed; and, if the motor is producing more torque than the maximum torque for that speed, modulate the application of energization signal to the motor.

10. The surgical tool assembly of Claims 1, 2, 3,

4, 5, 6, 7, 8 or 9, wherein: a memory (33) is integrally associated with the handpiece and said memory includes data defining the boundary torque maps; and said control console is further configured to read from the memory associated the handpiece the data defining the boundary torque maps and to use as the boundary torque maps (184) .

11. The surgical tool assembly of Claims 1, 2, 3, 4,

5, 6, 7 8 or 9 wherein said control console includes a memory (140) in which data defining the boundary torque maps are stored.

12. The surgical tool assembly of Claims 1, 2, 3,4,5,

6, 7, 8, 9, 10 or 11, wherein the control circuit is contained in a console (42) separate from the handpiece and said handpiece is removably connected to said console.