Abstract:
A surgical instrument is provided. The surgical instrument includes: a handle assembly; a jaw assembly comprising a staple cartridge containing a plurality of staples and an anvil to form the plurality of staples upon firing; a drive assembly at least partially located within the handle and connected to the jaw assembly and the lockout mechanism; a motor disposed within the handle assembly and operatively coupled to the drive assembly; and a controller operatively coupled to the motor, the controller configured to control supply of electrical current to the motor and to monitor a current draw of the motor, wherein the controller is further configured to terminate the supply of electrical current to the motor in response to a rate of change of the current draw indicative of a mechanical limit of at least one of the jaw assembly, the drive assembly, or the motor.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims the benefit of and priority to a U.S. Provisional Patent Application Ser. No. 61/879,445, filed on Sep. 18, 2013, the entire contents of which are incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The present disclosure relates to surgical apparatuses, devices and/or systems for performing endoscopic surgical procedures and methods of use thereof. More specifically, the present disclosure relates to electromechanical, hand-held surgical apparatus, devices and/or systems configured for use with removable disposable end effectors and/or single use end effectors for clamping, cutting and/or stapling tissue. 
         [0004]    2. Background of the Related Art 
         [0005]    A number of surgical device manufacturers have developed product lines with proprietary drive systems for operating and/or manipulating electromechanical surgical devices. In many instances the electromechanical surgical devices include a reusable handle assembly, and disposable or single use end effectors. The end effectors are selectively connected to the handle assembly prior to use and then disconnected from the handle assembly following use in order to be disposed of or in some instances sterilized for re-use. 
         [0006]    Many of these electromechanical surgical devices include complex drive components that utilize a variety of user interfaces that accept user inputs (e.g., controls) for controlling the devices as well as provide feedback to the user. To prevent actuation of drive mechanisms beyond mechanical limits, various switches and sensors are used to detect operational state of the surgical devices. Inclusion of multiple switches and/or sensors in the devices as well as end effectors presents various problems. In addition, cost or other considerations prevent the use of such devices. Accordingly, there is a need for systems and apparatuses having safety mechanisms that can detect mechanical limits without relying on multiple mechanical limit sensors and/or switches disposed throughout the surgical device. 
       SUMMARY 
       [0007]    According to one embodiment of the present disclosure a surgical instrument is provided. The surgical instrument includes: a handle assembly; a jaw assembly including a staple cartridge containing a plurality of staples and an anvil to form the plurality of staples upon firing; a drive assembly at least partially located within the handle and connected to the jaw assembly and the lockout mechanism; a motor disposed within the handle assembly and operatively coupled to the drive assembly; and a controller operatively coupled to the motor, the controller configured to control supply of electrical current to the motor and to monitor a current draw of the motor, wherein the controller is further configured to terminate the supply of electrical current to the motor in response to a rate of change of the current draw indicative of a mechanical limit of at least one of the jaw assembly, the drive assembly, or the motor. 
         [0008]    According to one aspect of the above embodiment, the controller is further configured to determine if motor current is unstable by determining whether the rate of change of the current draw is outside a first range. 
         [0009]    According to one aspect of the above embodiment, the controller is further configured to determine if motor current is stable by determining whether the rate of change of the current draw is within a second range, wherein the second range is within the first range. 
         [0010]    According to one aspect of the above embodiment, the controller is further configured to store a stability counter of current draw samples within the second range. 
         [0011]    According to one aspect of the above embodiment, the controller determines whether motor current is stable if the stability counter is above a predetermined stability threshold. 
         [0012]    According to one aspect of the above embodiment, the controller is further configured to determine if the motor reached the mechanical limit by determining whether the motor current is stable and the rate of change of the current draw is within a third range. 
         [0013]    According to one aspect of the above embodiment, the third range is within the first range and is higher than the second range. 
         [0014]    According to one aspect of the above embodiment, the controller is further configured to store an event counter of current draw samples within the third range. 
         [0015]    According to one aspect of the above embodiment, the controller determines whether the motor reached the mechanical limit if the event counter is above a predetermined event threshold. 
         [0016]    According to another embodiment of the present disclosure a surgical instrument is provided. The surgical instrument includes: a handle assembly; a jaw assembly including a staple cartridge containing a plurality of staples and an anvil to form the plurality of staples upon firing; a drive assembly at least partially located within the handle and connected to the jaw assembly and the lockout mechanism; a motor disposed within the handle assembly and operatively coupled to the drive assembly; and a controller operatively coupled to the motor, the controller to determine whether the motor has reached a mechanical limit based on a rate of change of a current draw by the motor indicative of the mechanical limit. 
         [0017]    According to one aspect of the above embodiment, the controller is further configured to determine whether motor current is unstable by determining whether the rate of change of the current draw is outside a first range. 
         [0018]    According to one aspect of the above embodiment, the controller is further configured to determine whether motor current is stable by determining whether a plurality of samples of the rate of change of the current draw are within a second range. 
         [0019]    According to one aspect of the above embodiment, the controller is further configured to store a stability counter of current draw samples within the second range. 
         [0020]    According to one aspect of the above embodiment, the controller determines whether motor current is stable if the stability counter is above a predetermined stability threshold. 
         [0021]    According to one aspect of the above embodiment, the controller is further configured to determine whether the motor reached the mechanical limit by determining whether the motor current is stable and a plurality of samples of the rate of change of the current draw are within a third range. 
         [0022]    According to one aspect of the above embodiment, the second and third ranges are within the first range and the third range is higher than the second range. 
         [0023]    According to one aspect of the above embodiment, the controller is further configured to store an event counter of current draw samples within the third range. 
         [0024]    According to one aspect of the above embodiment, the controller determines whether the motor reached the mechanical limit if the event counter is above a predetermined event threshold. 
         [0025]    According to a further embodiment of the present disclosure a method for controlling a surgical instrument is provided. The method includes: monitoring a current draw of a motor coupled to a drive assembly for actuating a jaw assembly; calculating a rate of change of the current draw; and determining whether the motor has reached a mechanical limit based on the rate of change of the current draw by the motor. 
         [0026]    According to one aspect of the above embodiment, the method further includes determining whether the rate of change of the current draw is outside a first range to determine whether motor current is unstable. 
         [0027]    According to one aspect of the above embodiment, the method further includes determining whether a plurality of samples of the rate of change of the current draw are within a second range to determine whether motor current is stable. 
         [0028]    According to one aspect of the above embodiment, the method further includes: storing a stability counter of current draw samples within the second range; and determining whether motor current is stable if the stability counter is above a predetermined stability threshold. 
         [0029]    According to one aspect of the above embodiment, the method further includes: whether the motor current is stable and a plurality of samples of the rate of change of the current draw are within a third range to determine whether the motor reached the mechanical limit by. 
         [0030]    According to one aspect of the above embodiment, the second and third ranges are within the first range and the third range is higher than the second range. 
         [0031]    According to one aspect of the above embodiment, the method further includes: storing an event counter of current draw samples within the third range; and determining whether the motor reached the mechanical limit if the event counter is above a predetermined event threshold. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0032]    Embodiments of the present disclosure are described herein with reference to the accompanying drawings, wherein: 
           [0033]      FIG. 1  is a perspective, disassembled view of an electromechanical surgical system including a surgical instrument, an adapter, and an end effector, according to the present disclosure; 
           [0034]      FIG. 2  is a perspective view of the surgical instrument of  FIG. 1 , according to the present disclosure; 
           [0035]      FIG. 3  is perspective, exploded view of the surgical instrument of  FIG. 1 , according to the present disclosure; 
           [0036]      FIG. 4  is a perspective view of a battery of the surgical instrument of  FIG. 1 , according to the present disclosure; 
           [0037]      FIG. 5  is a top, partially-disassembled view of the surgical instrument of  FIG. 1 , according to the present disclosure; 
           [0038]      FIG. 6  is a front, perspective view of the surgical instrument of  FIG. 1  with the adapter separated therefrom, according to the present disclosure; 
           [0039]      FIG. 7  is a side, cross-sectional view of the surgical instrument of  FIG. 1 , as taken through 7-7 of  FIG. 2 , according to the present disclosure; 
           [0040]      FIG. 8  is a top, cross-sectional view of the surgical instrument of  FIG. 1 , as taken through 8-8 of  FIG. 2 , according to the present disclosure; 
           [0041]      FIG. 9  is a perspective, exploded view of a end effector of  FIG. 1 , according to the present disclosure; 
           [0042]      FIG. 10  is a schematic diagram of the surgical instrument of  FIG. 1  according to the present disclosure; 
           [0043]      FIG. 11  is a schematic diagram of motor current values stored in memory of the surgical instrument of  FIG. 1  according to the present disclosure; 
           [0044]      FIG. 12  is a flow chart of a method for controlling the surgical instrument of  FIG. 1  according to the present disclosure; 
           [0045]      FIGS. 13-15  are plots of motor current of the surgical instrument as controlled by the method of the present disclosure; and 
           [0046]      FIG. 16  is a flow chart of a method for controlling the surgical instrument of  FIG. 1  according to another embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0047]    A surgical system, in accordance with an embodiment of the present disclosure, is generally designated as  10 , and is in the form of a powered hand held electromechanical instrument configured for selective attachment thereto of a plurality of different end effectors that are each configured for actuation and manipulation by the powered hand held electromechanical surgical instrument. 
         [0048]    As illustrated in  FIG. 1 , surgical instrument  100  is configured for selective connection with an adapter  200 , and, in turn, adapter  200  is configured for selective connection with an end effector or single use loading unit  300 . 
         [0049]    As illustrated in  FIGS. 1-3 , surgical instrument  100  includes a handle housing  102  having a lower housing portion  104 , an intermediate housing portion  106  extending from and/or supported on lower housing portion  104 , and an upper housing portion  108  extending from and/or supported on intermediate housing portion  106 . Intermediate housing portion  106  and upper housing portion  108  are separated into a distal half-section  110   a  that is integrally formed with and extending from the lower portion  104 , and a proximal half-section  110   b  connectable to distal half-section  110   a  by a plurality of fasteners. When joined, distal and proximal half-sections  110   a ,  110   b  define a handle housing  102  having a cavity  102   a  therein in which a circuit board  150  and a drive mechanism  160  is situated. 
         [0050]    Distal and proximal half-sections  110   a ,  110   b  are divided along a plane that traverses a longitudinal axis “X” of upper housing portion  108 , as seen in  FIGS. 2 and 3 . Handle housing  102  includes a gasket  112  extending completely around a rim of distal half-section and/or proximal half-section  110   a ,  110   b  and being interposed between distal half-section  110   a  and proximal half-section  110   b . Gasket  112  seals the perimeter of distal half-section  110   a  and proximal half-section  110   b . Gasket  112  functions to establish an air-tight seal between distal half-section  110   a  and proximal half-section  110   b  such that circuit board  150  and drive mechanism  160  are protected from sterilization and/or cleaning procedures. 
         [0051]    In this manner, the cavity  102   a  of handle housing  102  is sealed along the perimeter of distal half-section  110   a  and proximal half-section  110   b  yet is configured to enable easier, more efficient assembly of circuit board  150  and a drive mechanism  160  in handle housing  102 . 
         [0052]    Intermediate housing portion  106  of handle housing  102  provides a housing in which circuit board  150  is situated. Circuit board  150  is configured to control the various operations of surgical instrument  100 , as will be set forth in additional detail below. 
         [0053]    Lower housing portion  104  of surgical instrument  100  defines an aperture (not shown) formed in an upper surface thereof and which is located beneath or within intermediate housing portion  106 . The aperture of lower housing portion  104  provides a passage through which wires  152  pass to electrically interconnect electrical components (a battery  156 , as illustrated in  FIG. 4 , a circuit board  154 , as illustrated in  FIG. 3 , etc.) situated in lower housing portion  104  with electrical components (circuit board  150 , drive mechanism  160 , etc.) situated in intermediate housing portion  106  and/or upper housing portion  108 . 
         [0054]    Handle housing  102  includes a gasket  103  disposed within the aperture of lower housing portion  104  (not shown) thereby plugging or sealing the aperture of lower housing portion  104  while allowing wires  152  to pass therethrough. Gasket  103  functions to establish an air-tight seal between lower housing portion  106  and intermediate housing portion  108  such that circuit board  150  and drive mechanism  160  are protected from sterilization and/or cleaning procedures. 
         [0055]    As shown, lower housing portion  104  of handle housing  102  provides a housing in which a rechargeable battery  156 , is removably situated. Battery  156  is configured to supply power to any of the electrical components of surgical instrument  100 . Lower housing portion  104  defines a cavity (not shown) into which battery  156  is inserted. Lower housing portion  104  includes a door  105  pivotally connected thereto for closing cavity of lower housing portion  104  and retaining battery  156  therein. 
         [0056]    With reference to  FIGS. 3 and 5 , distal half-section  110   a  of upper housing portion  108  defines a nose or connecting portion  108   a . A nose cone  114  is supported on nose portion  108   a  of upper housing portion  108 . Nose cone  114  is fabricated from a transparent material. An illumination member  116  is disposed within nose cone  114  such that illumination member  116  is visible therethrough. Illumination member  116  is may be a light emitting diode printed circuit board (LED PCB). Illumination member  116  is configured to illuminate multiple colors with a specific color pattern being associated with a unique discrete event. 
         [0057]    Upper housing portion  108  of handle housing  102  provides a housing in which drive mechanism  160  is situated. As illustrated in  FIG. 5 , drive mechanism  160  is configured to drive shafts and/or gear components in order to perform the various operations of surgical instrument  100 . In particular, drive mechanism  160  is configured to drive shafts and/or gear components in order to selectively move tool assembly  304  of end effector  300  (see  FIGS. 1 and 9 ) relative to proximal body portion  302  of end effector  300 , to rotate end effector  300  about a longitudinal axis “X” (see  FIG. 2 ) relative to handle housing  102 , to move anvil assembly  306  relative to cartridge assembly  308  of end effector  300 , and/or to fire a stapling and cutting cartridge within cartridge assembly  308  of end effector  300 . 
         [0058]    The drive mechanism  160  includes a selector gearbox assembly  162  that is located immediately proximal relative to adapter  200 . Proximal to the selector gearbox assembly  162  is a function selection module  163  having a first motor  164  that functions to selectively move gear elements within the selector gearbox assembly  162  into engagement with an input drive component  165  having a second motor  166 . 
         [0059]    As illustrated in  FIGS. 1-4 , and as mentioned above, distal half-section  110   a  of upper housing portion  108  defines a connecting portion  108   a  configured to accept a corresponding drive coupling assembly  210  of adapter  200 . 
         [0060]    As illustrated in  FIGS. 6-8 , connecting portion  108   a  of surgical instrument  100  has a cylindrical recess  108   b  that receives a drive coupling assembly  210  of adapter  200  when adapter  200  is mated to surgical instrument  100 . Connecting portion  108   a  houses three rotatable drive connectors  118 ,  120 ,  122 . 
         [0061]    When adapter  200  is mated to surgical instrument  100 , each of rotatable drive connectors  118 ,  120 ,  122  of surgical instrument  100  couples with a corresponding rotatable connector sleeve  218 ,  220 ,  222  of adapter  200  as shown in  FIG. 6 . In this regard, the interface between corresponding first drive connector  118  and first connector sleeve  218 , the interface between corresponding second drive connector  120  and second connector sleeve  220 , and the interface between corresponding third drive connector  122  and third connector sleeve  222  are keyed such that rotation of each of drive connectors  118 ,  120 ,  122  of surgical instrument  100  causes a corresponding rotation of the corresponding connector sleeve  218 ,  220 ,  222  of adapter  200 . 
         [0062]    The mating of drive connectors  118 ,  120 ,  122  of surgical instrument  100  with connector sleeves  218 ,  220 ,  222  of adapter  200  allows rotational forces to be independently transmitted via each of the three respective connector interfaces. The drive connectors  118 ,  120 ,  122  of surgical instrument  100  are configured to be independently rotated by drive mechanism  160 . In this regard, the function selection module  163  of drive mechanism  160  selects which drive connector or connectors  118 ,  120 ,  122  of surgical instrument  100  is to be driven by the input drive component  165  of drive mechanism  160 . 
         [0063]    Since each of drive connectors  118 ,  120 ,  122  of surgical instrument  100  has a keyed and/or substantially non-rotatable interface with respective connector sleeves  218 ,  220 ,  222  of adapter  200 , when adapter  200  is coupled to surgical instrument  100 , rotational force(s) are selectively transferred from drive mechanism  160  of surgical instrument  100  to adapter  200 . 
         [0064]    The selective rotation of drive connector(s)  118 ,  120  and/or  122  of surgical instrument  100  allows surgical instrument  100  to selectively actuate different functions of end effector  300 . As will be discussed in greater detail below, selective and independent rotation of first drive connector  118  of surgical instrument  100  corresponds to the selective and independent opening and closing of tool assembly  304  of end effector  300 , and driving of a stapling/cutting component of tool assembly  304  of end effector  300 . Also, the selective and independent rotation of second drive connector  120  of surgical instrument  100  corresponds to the selective and independent articulation of tool assembly  304  of end effector  300  transverse to longitudinal axis “X” (see  FIG. 2 ). Additionally, the selective and independent rotation of third drive connector  122  of surgical instrument  100  corresponds to the selective and independent rotation of end effector  300  about longitudinal axis “X” (see  FIG. 2 ) relative to handle housing  102  of surgical instrument  100 . 
         [0065]    As mentioned above and as illustrated in  FIGS. 5 and 8 , drive mechanism  160  includes a selector gearbox assembly  162 ; and a function selection module  163 , located proximal to the selector gearbox assembly  162 , that functions to selectively move gear elements within the selector gearbox assembly  162  into engagement with second motor  166 . Thus, drive mechanism  160  selectively drives one of drive connectors  118 ,  120 ,  122  of surgical instrument  100  at a given time. 
         [0066]    As illustrated in  FIGS. 1-3 , handle housing  102  supports a control assembly  107  on a distal surface or side of intermediate housing portion  108 . The control assembly  107  is a fully-functional mechanical subassembly that can be assembled and tested separately from the rest of the instrument  100  prior to coupling thereto. 
         [0067]    Control assembly  107 , in cooperation with intermediate housing portion  108 , supports a pair of finger-actuated control buttons  124 ,  126  and a pair rocker devices  128 ,  130  within a housing  107   a . The control buttons  124 ,  126  are coupled to extension shafts  125 ,  127  respectively. In particular, control assembly  107  defines an upper aperture  124   a  for slidably receiving the extension shaft  125 , and a lower aperture  126   a  for slidably receiving the extension shaft  127 . 
         [0068]    Reference may be made to a commonly-owned U.S. patent application Ser. No. 13/331,047, the entire contents of which are incorporated by reference herein, for a detailed discussion of the construction and operation of the surgical instrument  100 . 
         [0069]    Referring to  FIG. 9 , drive assembly  360  of end effector  300  includes a flexible drive shaft  364  having a distal end which is secured to a dynamic drive beam  365 , and a proximal engagement section  368 . Engagement section  368  includes a stepped portion defining a shoulder  370 . A proximal end of engagement section  368  includes diametrically opposed inwardly extending fingers  372 . Fingers  372  engage a hollow drive member  374  to fixedly secure drive member  374  to the proximal end of shaft  364 . Drive member  374  defines a proximal porthole which receives a connection member of drive tube  246  ( FIG. 1 ) of adapter  200  when end effector  300  is attached to distal coupling  230  of adapter  200 . 
         [0070]    When drive assembly  360  is advanced distally within tool assembly  304 , an upper beam of drive beam  365  moves within a channel defined between anvil plate  312  and anvil cover  310  and a lower beam moves within a channel of the staple cartridge  305  and over the exterior surface of carrier  316  to close tool assembly  304  and fire staples therefrom. 
         [0071]    Proximal body portion  302  of end effector  300  includes a sheath or outer tube  301  enclosing an upper housing portion  301   a  and a lower housing portion  301   b . The housing portions  301   a  and  301   b  enclose an articulation link  366  having a hooked proximal end  366   a  which extends from a proximal end of end effector  300 . Hooked proximal end  366   a  of articulation link  366  engages a coupling hook (not shown) of adapter  200  when end effector  300  is secured to distal housing  232  of adapter  200 . When drive bar (not shown) of adapter  200  is advanced or retracted as described above, articulation link  366  of end effector  300  is advanced or retracted within end effector  300  to pivot tool assembly  304  in relation to a distal end of proximal body portion  302 . 
         [0072]    As illustrated in  FIG. 9  above, cartridge assembly  308  of tool assembly  304  includes a staple cartridge  305  supportable in carrier  316 . Staple cartridge  305  defines a central longitudinal slot  305   a , and three linear rows of staple retention slots  305   b  positioned on each side of longitudinal slot  305   a . Each of staple retention slots  305   b  receives a single staple  307  and a portion of a staple pusher  309 . During operation of instrument  100 , drive assembly  360  abuts an actuation sled  350  and pushes actuation sled  350  through cartridge  305 . As the actuation sled moves through cartridge  305 , cam wedges of the actuation sled  350  sequentially engage staple pushers  309  to move staple pushers  309  vertically within staple retention slots  305   b  and sequentially eject a single staple  307  therefrom for formation against anvil plate  312 . 
         [0073]    The end effector  300  may also include one or more mechanical lockout mechanisms, such as those described in commonly-owned U.S. Pat. Nos. 5,071,052, 5,397,046, 5413,267, 5,415,335, 5,715,988, 5,718,359, 6,109,500, the entire contents of all of which are incorporated by reference herein. 
         [0074]    Another embodiment of the instrument  100  is shown in  FIG. 10 . The instrument  100  includes the motor  164 . The motor  164  may be any electrical motor configured to actuate one or more drives (e.g., rotatable drive connectors  118 ,  120 ,  122  of  FIG. 6 ). The motor  164  is coupled to the battery  156 , which may be a DC battery (e.g., rechargeable lead-based, nickel-based, lithium-ion based, battery etc.), an AC/DC transformer, or any other power source suitable for providing electrical energy to the motor  164 . 
         [0075]    The battery  156  and the motor  164  are coupled to a motor driver circuit  404  disposed on the circuit board  154  which controls the operation of the motor  164  including the flow of electrical energy from the battery  156  to the motor  164 . The driver circuit  404  includes a plurality of sensors  408   a ,  408   b , . . .  408   n  configured to measure operational states of the motor  164  and the battery  156 . The sensors  408   a - n  may include voltage sensors, current sensors, temperature sensors, telemetry sensors, optical sensors, and combinations thereof. The sensors  408   a - 408   n  may measure voltage, current, and other electrical properties of the electrical energy supplied by the battery  156 . The sensors  408   a - 408   n  may also measure rotational speed as revolutions per minute (RPM), torque, temperature, current draw, and other operational properties of the motor  164 . RPM may be determined by measuring the rotation of the motor  164 . Position of various drive shafts (e.g., rotatable drive connectors  118 ,  120 ,  122  of  FIG. 6 ) may be determined by using various linear sensors disposed in or in proximity to the shafts or extrapolated from the RPM measurements. In embodiments, torque may be calculated based on the regulated current draw of the motor  164  at a constant RPM. In further embodiments, the driver circuit  404  and/or the controller  406  may measure time and process the above-described values as a function thereof, including integration and/or differentiation, e.g., to determine the change in the measured values and the like. 
         [0076]    The driver circuit  404  is also coupled to a controller  406 , which may be any suitable logic control circuit adapted to perform the calculations and/or operate according to a set of instructions described in further detail below. The controller  406  may include a central processing unit operably connected to a memory which may include transitory type memory (e.g., RAM) and/or non-transitory type memory (e.g., flash media, disk media, etc.). The controller  406  includes a plurality of inputs and outputs for interfacing with the driver circuit  404 . In particular, the controller  406  receives measured sensor signals from the driver circuit  404  regarding operational status of the motor  164  and the battery  156  and, in turn, outputs control signals to the driver circuit  404  to control the operation of the motor  164  based on the sensor readings and specific algorithm instructions, which are discussed in more detail below. The controller  406  is also configured to accept a plurality of user inputs from a user interface (e.g., switches, buttons, touch screen, etc. of the control assembly  107  coupled to the controller  406 ). 
         [0077]    The present disclosure provides for an apparatus and method for controlling the instrument  100  or any other powered surgical instrument, including, but not limited to, linear powered staplers, circular or arcuate powered staplers, graspers, electrosurgical sealing forceps, rotary tissue blending devices, and the like. In particular, torque, RPM, position, and acceleration of drive shafts of the instrument  100  can be correlated to motor characteristics (e.g., current draw). Current drawn by the motor  164  may be used for detecting mechanical limits since the current drawn by the motor  164  changes with the load and speed of the motor  164 . Thus, analysis of the amount of change (e.g., rate of change) of current draw allows for distinguishing between different types of load conditions, e.g., load exerted by tissue versus load exerted by a mechanical stop. 
         [0078]    During normal operation of the motor  164  the current draw generally does not fall outside a predetermined range (e.g., first range). During clamping and stapling, the load exerted on the motor  164  by the tissue varies within a second range, encompassed by the first range. In particular, as the motor  164  encounters an increased load due to the tissue being clamped by the anvil and cartridge assemblies  306 ,  308  the current draw increases and is within the second range for a second period of time (e.g., increase in the current draw occurs for a predetermined period of time). If the motor  164  encounters a mechanical limit there is also a corresponding increase in current draw in a relatively short time that is larger than the current draw associated with tissue clamping. In particular, the current draw due to a mechanical stop is within a third range that is higher than the second range for a third period of time. In comparison, startup of the motor  164  draws more current than either clamping/fastening or the mechanical stop and the duration of the increased current draw is the shortest of the two current draws described above. 
         [0079]    In embodiments, mechanical stops may be detected by comparing motor current with a predetermined threshold since the current drawn by the motor  164  upon encountering a mechanical stop is usually much higher than the normal operating current. The controller  406  may use the satisfaction of this condition to shut off the motor  164 . 
         [0080]    This approach presents some challenges when the motor  164  encounters high momentary loads during normal operation (e.g., clamping tissue). The current draw associated with tissue clamping can reach the threshold, thus causing the controller  406  to shut off the motor  164  prematurely. In embodiments, the premature shutoff may be prevented by analyzing normal current draw of the motor  164  and construct a normal motor load profile. The controller  406  may then be programmed to adjust the shutoff threshold in accordance with that profile. This configuration is well-suited to motors  164  having little variation in the load profile. However, large variations can produce false positives if the load profile deviates from the current draw associated with normal use. 
         [0081]    Efficiency of the motor  164  and drive mechanism also have an effect in calculating the motor current limit. Since mechanical efficiencies can vary from one instrument to another, each instrument needs to be individually calibrated during assembly. Further, mechanical efficiencies change with wear and tear of the instrument and can also affect performance of the software. 
         [0082]    The algorithm according to the present disclosure overcomes the issues of using single-threshold or profile-based algorithms. An advantage of the algorithm according to the present disclosure is that the algorithm utilizes rate of change/current over time rather than comparing amplitude of the motor current to a predetermined threshold. The rate of change of the motor current associated with different loads, e.g., normal load, heavy loads, mechanical stops, load spikes, etc. may be classified into different ranges, in which each range is associated with a specific load. The classification into ranges may then be used to identify distinct loads on the motor  164  and filtering out spikes caused by starting and stopping of the motor  164 . Since the identification of the mechanical loads is based on the rate of change in motor current rather than its amplitude, deviation from the load profiles do not affect load identification. In addition, mechanical efficiencies do not affect load identification based on rate of change in motor current. Less efficient instruments draw more current to attain the same speed, however, the slopes (e.g., rate of change in current draw) for reaching those speeds remains similar to those of more efficient systems. This eliminates the need for load profiling and calibration operation during assembly of the instrument  100 . 
         [0083]    Another advantage of the algorithm according to the present disclosure is the low computational overhead. The algorithm relies on calculating the rate of change of the motor current and as such can be determined by taking the difference between two values, allowing for implementation of the algorithm in an 8-bit microcontroller. 
         [0084]    The change in motor current can be measured by sampling current periodically. In embodiments, the sampling rate may be from about 100 per second to about 10,000 per second, in embodiments from about 500 per second to about 1,000 per second. The samples may then be used by the controller  406  to calculate the change in the motor current (e.g., current draw). The controller  406  may then use the change in motor current to determine the operating condition of the instrument  100  and take appropriate action. 
         [0085]    The present disclosure also provides a feedback system and method for controlling the instrument  100  based on external operating conditions such as firing difficulty encountered by the instrument  100  due to tissue thickness and/or mechanical stop (e.g., the drive beam  365  reaching the distal end of the channel defined in the anvil plate  312  and the staple cartridge  305 . In addition, the present disclosure provides for modeling of different usages of the instrument  100  in response to the external operating conditions (e.g., specific failures) to derive internal system feedback. The sensor information from the sensors  408   a - n  is used by the controller  406  to alter operating characteristics of the instrument  100  and/or notify users of specific operational conditions. In embodiments, the controller  406  controls (e.g., limits) the current supplied to the motor  164 . 
         [0086]    The controller  406  includes a computer-readable memory  406   a  and/or non-transitory medium for storing software instructions (e.g., algorithm) for detecting mechanical limits of the instrument  100  based on the measured current draw. As used herein, the term “mechanical limit” denotes any of the electromechanical components reaching end-of-travel positions including, but not limited to, e.g., the drive beam  365  reaching the distal end of the channel defined in the anvil plate  312  and the staple cartridge  305 , actuation of mechanical safety lockout mechanisms preventing travel of the shaft  364 , articulation link  366  reaching articulation limits of the end effector  300 , and the like. 
         [0087]    The change in motor current associated with the onset of certain load conditions (e.g., tissue clamping or mechanical limits) falls within predefined ranges and persists for a certain duration. These conditions are used by the algorithm to identify operating properties of the motor  164  and react accordingly in response thereto. 
         [0088]    With reference to  FIG. 11 , the memory  406   a  stores a plurality of current draw values. The memory  406   a  includes look-up table  500  or any other suitable data structure having values “I-V.” The first value I and the fifth value “V” define a first range encompassing a stable current draw signal indicative of normal (e.g., load-bearing) operation of the motor  164 . The second and third values “II” and “III” define a second range corresponding to the current draw associated with current draw of the motor  164  during tissue clamping and fourth and fifth values “IV” and “V” defining a third range corresponding to the current draw associated with a mechanical stop. In embodiments, the first value “I” may be the same as the second value “II.” 
         [0089]    The controller  406  also includes a condition-of-interest counter which counts the number of samples during which the slope (e.g., rate of change) of the motor current lies within the desired range (e.g., either first, second or third ranges). The controller  406  also includes a signal stability counter, which counts the number of samples for which the slope lies within the second range. The controller  406  determines if the measured rate of change current draw signal is stable using the values of the table  500 . The signal is considered to be unstable if a predetermined number of current draw samples are outside the first range and stable if a predetermined number of samples are within the second range. 
         [0090]      FIG. 12  shows a method according to the present disclosure for determining if the motor  164  encounters a mechanical stop. The method may be implemented as software instructions (e.g., algorithm) stored in the controller  406  as described above. Initially, the controller  406  calculates a moving average of the measured motor current (e.g., current draw). As used herein, the term “moving average” denotes an average of a predetermined subset of samples that is updated every time a new sample is obtained. The moving average may include from about 2 plurality of samples to about 256 plurality of samples, and in embodiments, from about plurality of samples  16  about plurality of samples  64 , depending on the sampling rate described above. The controller  406  stores the first moving average and calculates the second moving average for the subsequent sample set. The controller  406  then determines the difference between the moving averages to calculate the sample-to-sample change. 
         [0091]    As shown in  FIGS. 12-13 , the moving average of the samples may be graphed as plots  700 ,  800 ,  900 , with the sample-to-sample change being represented as the slope of the plots  700 ,  800 ,  900 . The plots  700 ,  800 ,  900  may be generated and outputted on a display allowing the user to view the current draw of the motor  164 . In embodiments, the plots  700 ,  800 ,  900  may be stored in the memory  406   a  as a series of values, without reproducing the sample values as a plot. 
         [0092]    The change in the monitored motor current, also defined as the slope is used to differentiate between different types of loads encountered by motor  164 . The controller  406  initially determines if the signal is stable by determining whether the calculated slope/change is outside the first range (e.g., the slope is larger than fifth value “V” or less than first value “I”). If the slope lies outside the first range for a predefined number of samples, the controller  406  initializes or resets the condition-of-interest and signal stability counters by setting them to zero, 0. In addition, the controller  406  also sets the signal status as “unstable.” 
         [0093]    With reference to  FIGS. 14 and 15 , the samples below first value “I,” as shown in  FIG. 14 , and above the fifth value “V,” as shown in  FIG. 15 , are filtered out since they represent abnormal negative and positive spikes in current draw. These spikes may be caused by starting and stopping of the motor  164  and may result false positives in threshold-based decision making algorithms. 
         [0094]    After determining if the slope is outside the first range, the controller  406  determines if the slope is within the second range (value II≦slope≦value III). If so, the stability counter is incremented. The controller  406  checks if the stability counter has reached a predetermined threshold before changing the signal status to “stable.” This ensures that the sample has been within the second range for a sufficient period of time. Any deviation, e.g., the slope being outside the first range, resets the condition-of-interest and signal stability counters and sets the signal status as “unstable” as described above. 
         [0095]    With reference to  FIGS. 13-15 , the signal is considered to be stable if the slope is within the second range, irrelevant of the actual amplitude of the motor current samples. Thus, the higher amplitude of the samples within the second range of  FIG. 15  and lower amplitude of the samples within the second range of  FIGS. 13 and 14  is treated similarly by the algorithm of the present disclosure as the attribute of interest is the rate of change of slope of the motor current samples. 
         [0096]    The controller  406  also determines if the sample is within the third range. For each sample within the third range, while the signal is deemed stable, the condition-of-interest counter is incremented. Every time the sample falls below second value “II,” the condition-of-interest counter is decremented. The condition-of-interest counter is used to identify a mechanical stop, as described in further detail below. If the condition-of-interest counter is above a predetermined threshold, then the controller  406  determines that a mechanical stop has been reached. With reference to  FIG. 13 , a plurality of samples have a slope that falls within the third range, this increments the condition-of-interest counter and upon reaching the predetermined count triggers the indication that the mechanical stop has been reached. Once the controller  406  determines that the mechanical limit has been reached the supply of current to the motor  164  may be terminated to prevent further operation of the instrument  100  and/or the instrument  100  may issue an alarm. 
         [0097]      FIG. 16  shows a method according another embodiment of to the present disclosure for determining if the motor  164  encounters a mechanical stop. 
         [0098]    The controller  406  includes the stability and condition-of-interest counters, as described above. The controller  406  further includes a positive spike counter and a negative spike counter. These counters maintain a number of times a current (e.g., slope) has spiked outside the first range. More specifically, the positive spike counter is incremented when the motor current is above the value “V” and the negative spike counter is incremented when the motor current is below the value “I.” The controller  406  determines if the measured rate of change current draw signal is stable using the values of the table  500 . The signal is considered to be unstable if a predetermined number of current draw samples are outside the first range (e.g., is the number of positive and negative spikes is above a predetermined positive and negative spike threshold) and stable if a predetermined number of samples are within the second range. 
         [0099]    The method of  FIG. 16  may also be implemented as software instructions (e.g., algorithm) stored in the controller  406  as described above. Initially, the controller  406  calculates a moving average of the measured motor current (e.g., current draw). As used herein, the term “moving average” denotes an average of a predetermined subset of samples that is updated every time a new sample is obtained. The moving average may include from about 2 samples to about 256 samples, and in embodiments, from about 16 to about 64 samples, depending on the sampling rate described above. The controller  406  stores the first moving average and calculates the second moving average for the subsequent sample set. The controller  406  then determines the difference between the moving averages to calculate the sample-to-sample change (e.g., slope). 
         [0100]    The change in the monitored motor current, also defined as the slope, is used to differentiate between different types of loads encountered by motor  164 . The controller  406  initially determines if the slope is larger than fifth value “V” and updated the previous moving average to the presently calculated moving average. If the slope is above the fifth value “V,” the positive spike counter is incremented while the negative spike counter is decremented. In addition, the controller  406  verifies if the positive spike counter is above a predetermined positive spike counter threshold. If so, the controller  406  initializes or resets the condition-of-interest and signal stability counters by setting them to zero, 0. In addition, the controller  406  also sets the signal status as “unstable.” If the positive spike counter is below the predetermined positive spike counter threshold, the stability counter is decremented. 
         [0101]    After determining if the slope is above the fifth value “V,” the controller  406  determines if the sample falls below second value “II,” the condition-of-interest counter is decremented. 
         [0102]    The controller  406  also determines if the slope is smaller than the first value “I” and updated the previous moving average to the presently calculated moving average. If the slope is above the first value “I,” the negative spike counter is incremented while the positive spike counter is decremented. In addition, the controller  406  verifies if the negative spike counter is above a predetermined negative spike counter threshold. If so, the controller  406  initializes or resets the condition-of-interest and signal stability counters by setting them to zero, 0. In addition, the controller  406  also sets the signal status as “unstable.” If the negative spike counter is below the predetermined negative spike counter threshold, the stability counter is decremented. 
         [0103]    With reference to  FIGS. 14 and 15 , the samples below first value “I,” as shown in  FIG. 14 , and above the fifth value “V,” as shown in  FIG. 15 , are filtered out since they represent abnormal negative and positive spikes in current draw. These spikes may be caused by starting and stopping of the motor  164  and may result false positives in threshold-based decision making algorithms. 
         [0104]    The controller  406  also determines if the slope is within the second range (e.g., value “II”≦slope≦value “III”). If so, the stability counter is incremented. The controller  406  also checks if the stability counter has reached a predetermined threshold before changing the signal status to “stable.” This ensures that the sample has been within the second range for a sufficient period of time. In addition, the controller  406  initializes or resets the positive and negative spike counters by setting them to zero, 0. Regardless whether the stability counter is below or above the predetermined threshold, the previous moving average is updated to the presently calculated moving average. Any deviation, e.g., the slope being outside the first range, also resets the condition-of-interest and signal stability counters and sets the signal status as “unstable” as described above. 
         [0105]    The controller  406  also determines if the sample is within the third range. For each sample within the third range, while the signal is deemed stable, the condition-of-interest counter is incremented. The condition-of-interest counter is used to identify a mechanical stop, as described in further detail below. If the condition-of-interest counter is above a predetermined threshold, then the controller  406  determines that a mechanical stop has been reached. With reference to  FIG. 13 , a plurality of samples have a slope that falls within the third range, this increments the condition-of-interest counter and upon reaching the predetermined count triggers the indication that the mechanical stop has been reached. Once the controller  406  determines that the mechanical limit has been reached the supply of current to the motor  164  may be terminated to prevent further operation of the instrument  100  and/or the instrument  100  may issue an alarm. 
         [0106]    In addition to basic feedback about device performance the present disclosure also provides a method for powered devices to detect and discern other external factors, e.g., thicker tissue, which previously were difficult to detect. As a result, improved cutoffs and values for limits can be implemented, greatly improving the safety of powered devices in use. Using the feedback mechanisms discussed above, users may make intelligent decisions about what settings and techniques should be used when operating the instrument  100 . This intelligence can range from choosing a different reload to fire with a linear stapler, deciding to fire at a different articulation angle, to choosing to use a completely different surgical technique. 
         [0107]    It should be understood that the foregoing description is only illustrative of the present disclosure. Various alternatives and modifications can be devised by those skilled in the art without departing from the disclosure. Accordingly, the present disclosure is intended to embrace all such alternatives, modifications and variances. The embodiments described with reference to the attached drawing figures are presented only to demonstrate certain examples of the disclosure. Other elements, steps, methods and techniques that are insubstantially different from those described above and/or in the appended claims are also intended to be within the scope of the disclosure.