Patent Publication Number: US-10765429-B2

Title: Systems and methods for providing alerts according to the operational state of a surgical instrument

Description:
TECHNICAL FIELD 
     The present disclosure relates to surgical instruments and, in various circumstances, to surgical stapling and cutting instruments that are designed to cut and staple tissue. 
     BACKGROUND 
     In a surgical stapling and cutting instrument it may be useful to control the display and other components of the instrument to provide alerts to the clinician using the instrument, power down the instrument, and take other such actions according to the operational state of the surgical instrument. The operational state of the surgical instrument (i.e., whether the instrument is cutting, stapling, clamping, articulating, or taking other such actions) can be detected by one or more sensors, which can be communicably coupled to a control circuit configured to execute various processes according to the states of the instrument detected by the sensors. In some situations, it may be useful to provide alerts to the clinician in order to alert the clinician as to errors experienced by the surgical instrument. In other situations, it may be useful to power down the instrument when the instrument has completed its surgical stapling and cutting operations. In still other situations, it may be useful to display the position of the knife during the course of a firing stroke thereof in order to allow a clinician to view the cutting progress. 
     SUMMARY 
     In one aspect, a surgical instrument comprising: a displacement member movable between a first position and a second position; a sensor configured to detect a position of the displacement member and provide a signal indicative thereof; and a control circuit coupled to the sensor, the control circuit configured to: determine a velocity of the displacement member; and upon the velocity being equal to zero: determine an operational state of the surgical instrument; determine a relative position of the displacement member according to the position of the displacement member compared to at least one of the first position or the second position; and provide an alert according to the operational state of the surgical instrument and the relative position of the displacement member. 
     In another aspect, a surgical instrument comprising: a displacement member movable between a first position and a second position; a sensor configured to detect a position of the displacement member and provide a signal indicative thereof; and a control circuit coupled to the sensor, the control circuit configured to: determine a velocity of the displacement member; and upon the displacement member not moving: determine an operational state of the surgical instrument; determine a zone between the first position and the second position in which the displacement member is positioned; and provide an alert according to the operational state of the surgical instrument and the zone in which the displacement member is positioned. 
     In yet another aspect, a method of operating a surgical instrument comprising a displacement member movable between a first position and a second position, a motor coupled to the displacement member, the motor configured to drive the displacement member between the first position and the second position, and a sensor configured to detect a position of the displacement member and provide a signal indicative thereof, the method comprising: determining a velocity of the displacement member; and upon determining that the velocity of the displacement member equals zero: determining an operational state of the surgical instrument; determining a zone in which the displacement member is positioned; and providing an alert according to the operational state of the surgical instrument and the zone in which the displacement member is positioned. 
    
    
     
       FIGURES 
       The novel features of the aspects described herein are set forth with particularity in the appended claims. These aspects, however, both as to organization and methods of operation may be better understood by reference to the following description, taken in conjunction with the accompanying drawings. 
         FIG. 1  is a perspective view of a surgical instrument that has an interchangeable shaft assembly operably coupled thereto according to one aspect of this disclosure. 
         FIG. 2  is an exploded assembly view of a portion of the surgical instrument of  FIG. 1  according to one aspect of this disclosure. 
         FIG. 3  is an exploded assembly view of portions of the interchangeable shaft assembly according to one aspect of this disclosure. 
         FIG. 4  is an exploded view of an end effector of the surgical instrument of  FIG. 1  according to one aspect of this disclosure. 
         FIGS. 5A-5B  is a block diagram of a control circuit of the surgical instrument of  FIG. 1  spanning two drawing sheets according to one aspect of this disclosure. 
         FIG. 6  is a block diagram of the control circuit of the surgical instrument of  FIG. 1  illustrating interfaces between the handle assembly, the power assembly, and the handle assembly and the interchangeable shaft assembly according to one aspect of this disclosure. 
         FIG. 7  illustrates a control circuit configured to control aspects of the surgical instrument of  FIG. 1  according to one aspect of this disclosure. 
         FIG. 8  illustrates a combinational logic circuit configured to control aspects of the surgical instrument of  FIG. 1  according to one aspect of this disclosure. 
         FIG. 9  illustrates a sequential logic circuit configured to control aspects of the surgical instrument of  FIG. 1  according to one aspect of this disclosure. 
         FIG. 10  is a diagram of an absolute positioning system of the surgical instrument of  FIG. 1  where the absolute positioning system comprises a controlled motor drive circuit arrangement comprising a sensor arrangement according to one aspect of this disclosure. 
         FIG. 11  is an exploded perspective view of the sensor arrangement for an absolute positioning system showing a control circuit board assembly and the relative alignment of the elements of the sensor arrangement according to one aspect of this disclosure. 
         FIG. 12  is a diagram of a position sensor comprising a magnetic rotary absolute positioning system according to one aspect of this disclosure. 
         FIG. 13  is a section view of an end effector of the surgical instrument of  FIG. 1  showing a firing member stroke relative to tissue grasped within the end effector according to one aspect of this disclosure. 
         FIG. 14  illustrates a block diagram of a surgical instrument programmed to control distal translation of a displacement member according to one aspect of this disclosure. 
         FIG. 15  illustrates a diagram plotting two example displacement member strokes executed according to one aspect of this disclosure. 
         FIG. 16  is a partial perspective view of a portion of an end effector of a surgical instrument showing an elongate shaft assembly in an unarticulated orientation with portions thereof omitted for clarity, according to one aspect of this disclosure. 
         FIG. 17  is another perspective view of the end effector of  FIG. 16  showing the elongate shaft assembly an unarticulated orientation, according to one aspect of this disclosure. 
         FIG. 18  is an exploded assembly perspective view of the end effector of  FIG. 16  showing the elongate shaft assembly aspect, according to one aspect of this disclosure. 
         FIG. 19  is a top view of the end effector of  FIG. 16  showing the elongate shaft assembly in an unarticulated orientation, according to one aspect of this disclosure. 
         FIG. 20  is another top view of the end effector of  FIG. 16  showing the elongate shaft assembly in a first articulated orientation, according to one aspect of this disclosure. 
         FIG. 21  is another top view of the end effector of  FIG. 16  showing the elongate shaft assembly in a second articulated orientation  16   n , according to one aspect of this disclosure. 
         FIG. 22  is a perspective view of a surgical system including a handle assembly coupled to an interchangeable surgical tool assembly that is configured to be used in connection with conventional surgical staple/fastener cartridges and radio frequency (RF) cartridges according to one aspect of this disclosure. 
         FIG. 23  is an exploded perspective assembly view of the surgical system of  FIG. 22  according to one aspect of this disclosure. 
         FIG. 24  is a top cross-sectional view of a portion of the interchangeable surgical tool assembly of  FIG. 22  with the end effector thereof in an articulated position according to one aspect of this disclosure. 
         FIG. 25  is a perspective view of an onboard circuit board arrangement and RF generator plus configuration according to one aspect of this disclosure. 
         FIG. 26  illustrates a logic flow diagram of a process of monitoring for lack of articulation and firing movement of the surgical instrument according to one aspect of this disclosure. 
         FIG. 27  illustrates a front view of a display screen or portion thereof showing an image indicating that the articulation of the end effector is blocked according to one aspect of this disclosure. 
         FIG. 28  illustrates a front view of a display screen or portion thereof showing an image indicating that the articulation of the end effector is blocked according to one aspect of this disclosure. 
         FIG. 29  illustrates a front view of a display screen or portion thereof showing an image indicating that the end effector is at maximum articulation according to one aspect of this disclosure. 
         FIG. 30  illustrates a front view of a display screen or portion thereof showing an image indicating that the end effector is at maximum articulation according to one aspect of this disclosure. 
         FIG. 31  illustrates a front view of a display screen or portion thereof showing an image indicating that the surgical instrument is stalled according to one aspect of this disclosure. 
         FIG. 32  illustrates a front view of a display screen or portion thereof showing an image indicating that there is no cartridge in the surgical instrument according to one aspect of this disclosure. 
         FIGS. 33A-C  illustrate line diagrams of various displacement member strokes according to one aspect of this disclosure. 
     
    
    
     DESCRIPTION 
     Applicant of the present application owns the following patent applications filed concurrently herewith Sep. 29, 2017 and which are each herein incorporated by reference in their respective entireties: 
     U.S. patent application Ser. No. 15/720,811, entitled SYSTEMS AND METHODS OF DISPLAYING A KNIFE POSITION FOR A SURGICAL INSTRUMENT, by inventors Richard L. Leimbach et al., filed Sep. 29, 2017. 
     U.S. patent application Ser. No. 15/720,829, entitled SYSTEMS AND METHODS OF INITIATING A POWER SHUTDOWN MODE FOR A SURGICAL INSTRUMENT, by inventors Richard L. Leimbach et al., filed Sep. 29, 2017. 
     U.S. patent application Ser. No. 15/720,838, entitled SYSTEMS AND METHODS FOR LANGUAGE SELECTION OF A SURGICAL INSTRUMENT, by inventors Richard L. Leimbach et al., filed Sep. 29, 2017. 
     U.S. patent application Ser. No. 29/619,596, entitled DISPLAY SCREEN OR PORTION THEREOF WITH ANIMATED GRAPHICAL USER INTERFACE, by inventors Tony C. Siebel et al., filed Sep. 29, 2017. 
     U.S. patent application Ser. No. 29/619,600, entitled DISPLAY SCREEN OR PORTION THEREOF WITH ANIMATED GRAPHICAL USER INTERFACE, by inventors Tony C. Siebel et al., filed Sep. 29, 2017. 
     U.S. patent application Ser. No. 29/619,609, entitled DISPLAY SCREEN OR PORTION THEREOF WITH ANIMATED GRAPHICAL USER INTERFACE, by inventors Tony C. Siebel et al., filed Sep. 29, 2017. 
     U.S. patent application Ser. No. 29/619,624, entitled DISPLAY SCREEN OR PORTION THEREOF WITH ANIMATED GRAPHICAL USER INTERFACE, by inventors Tony C. Siebel et al., filed Sep. 29, 2017. 
     U.S. patent application Ser. No. 15/720,852, entitled SYSTEM AND METHODS FOR CONTROLLING A DISPLAY OF A SURGICAL INSTRUMENT, by inventors Richard L. Leimbach et al., filed Sep. 29, 2017. 
     Certain aspects are shown and described to provide an understanding of the structure, function, manufacture, and use of the disclosed devices and methods. Features shown or described in one example may be combined with features of other examples and modifications and variations are within the scope of this disclosure. 
     The terms “proximal” and “distal” are relative to a clinician manipulating the handle of the surgical instrument where “proximal” refers to the portion closer to the clinician and “distal” refers to the portion located further from the clinician. For expediency, spatial terms “vertical,” “horizontal,” “up,” and “down” used with respect to the drawings are not intended to be limiting and/or absolute, because surgical instruments can used in many orientations and positions. 
     Example devices and methods are provided for performing laparoscopic and minimally invasive surgical procedures. Such devices and methods, however, can be used in other surgical procedures and applications including open surgical procedures, for example. The surgical instruments can be inserted into a through a natural orifice or through an incision or puncture hole formed in tissue. The working portions or end effector portions of the instruments can be inserted directly into the body or through an access device that has a working channel through which the end effector and elongated shaft of the surgical instrument can be advanced. 
     In some aspects, surgical instruments can include devices capable of performing cutting (as in, e.g.,  FIGS. 1 and 22 ), stapling (as in, e.g.,  FIG. 1 ), electrosurgical (as in, e.g.,  FIG. 22 ), and/or ultrasonic operations, as described in further detail below. Further detail regarding ultrasonic surgical instruments can be found in U.S. Pat. No. 6,283,981, entitled METHOD OF BALANCING ASYMMETRIC ULTRASONIC SURGICAL BLADES; U.S. Pat. No. 6,309,400, entitled CURVED ULTRASONIC WAVEGUIDE HAVING A TRAPEZOIDAL CROSS SECTION; and U.S. Pat. No. 6,436,115, entitled BALANCED ULTRASONIC WAVEGUIDE INCLUDING A PLURALITY OF BALANCE ASYMMETRIES, the entire disclosures of which are hereby incorporated herein by reference. 
       FIGS. 1-4  depict a motor-driven surgical instrument  10  for cutting and fastening that may or may not be reused. In the illustrated examples, the surgical instrument  10  includes a housing  12  that comprises a handle assembly  14  that is configured to be grasped, manipulated, and actuated by the clinician. The housing  12  is configured for operable attachment to an interchangeable shaft assembly  200  that has an end effector  300  operably coupled thereto that is configured to perform one or more surgical tasks or procedures. In accordance with the present disclosure, various forms of interchangeable shaft assemblies may be effectively employed in connection with robotically controlled surgical systems. The term “housing” may encompass a housing or similar portion of a robotic system that houses or otherwise operably supports at least one drive system configured to generate and apply at least one control motion that could be used to actuate interchangeable shaft assemblies. The term “frame” may refer to a portion of a handheld surgical instrument. The term “frame” also may represent a portion of a robotically controlled surgical instrument and/or a portion of the robotic system that may be used to operably control a surgical instrument. Interchangeable shaft assemblies may be employed with various robotic systems, instruments, components, and methods disclosed in U.S. Pat. No. 9,072,535, entitled SURGICAL STAPLING INSTRUMENTS WITH ROTATABLE STAPLE DEPLOYMENT ARRANGEMENTS, which is hereby incorporated herein by reference in its entirety. 
       FIG. 1  is a perspective view of a surgical instrument  10  that has an interchangeable shaft assembly  200  operably coupled thereto according to one aspect of this disclosure. The housing  12  includes an end effector  300  that comprises a surgical cutting and fastening device configured to operably support a surgical staple cartridge  304  therein. The housing  12  may be configured for use in connection with interchangeable shaft assemblies that include end effectors that are adapted to support different sizes and types of staple cartridges, have different shaft lengths, sizes, and types. The housing  12  may be employed with a variety of interchangeable shaft assemblies, including assemblies configured to apply other motions and forms of energy such as, radio frequency (RF) energy, ultrasonic energy, and/or motion to end effector arrangements adapted for use in connection with various surgical applications and procedures. The end effectors, shaft assemblies, handles, surgical instruments, and/or surgical instrument systems can utilize any suitable fastener, or fasteners, to fasten tissue. For instance, a fastener cartridge comprising a plurality of fasteners removably stored therein can be removably inserted into and/or attached to the end effector of a shaft assembly. 
     The handle assembly  14  may comprise a pair of interconnectable handle housing segments  16 ,  18  interconnected by screws, snap features, adhesive, etc. The handle housing segments  16 ,  18  cooperate to form a pistol grip portion  19  that can be gripped and manipulated by the clinician. The handle assembly  14  operably supports a plurality of drive systems configured to generate and apply control motions to corresponding portions of the interchangeable shaft assembly that is operably attached thereto. A display may be provided below a cover  45 . 
       FIG. 2  is an exploded assembly view of a portion of the surgical instrument  10  of  FIG. 1  according to one aspect of this disclosure. The handle assembly  14  may include a frame  20  that operably supports a plurality of drive systems. The frame  20  can operably support a closure drive system  30 , which can apply closing and opening motions to the interchangeable shaft assembly  200 . The closure drive system  30  may include an actuator such as a closure trigger  32  pivotally supported by the frame  20 . The closure trigger  32  is pivotally coupled to the handle assembly  14  by a pivot pin  33  to enable the closure trigger  32  to be manipulated by a clinician. When the clinician grips the pistol grip portion  19  of the handle assembly  14 , the closure trigger  32  can pivot from a starting or “unactuated” position to an “actuated” position and more particularly to a fully compressed or fully actuated position. 
     The handle assembly  14  and the frame  20  may operably support a firing drive system  80  configured to apply firing motions to corresponding portions of the interchangeable shaft assembly attached thereto. The firing drive system  80  may employ an electric motor  82  located in the pistol grip portion  19  of the handle assembly  14 . The electric motor  82  may be a DC brushed motor having a maximum rotational speed of approximately 25,000 RPM, for example. In other arrangements, the motor may include a brushless motor, a cordless motor, a synchronous motor, a stepper motor, or any other suitable electric motor. The electric motor  82  may be powered by a power source  90  that may comprise a removable power pack  92 . The removable power pack  92  may comprise a proximal housing portion  94  configured to attach to a distal housing portion  96 . The proximal housing portion  94  and the distal housing portion  96  are configured to operably support a plurality of batteries  98  therein. Batteries  98  may each comprise, for example, a Lithium Ion (LI) or other suitable battery. The distal housing portion  96  is configured for removable operable attachment to a control circuit board  100 , which is operably coupled to the electric motor  82 . Several batteries  98  connected in series may power the surgical instrument  10 . The power source  90  may be replaceable and/or rechargeable. A display  43 , which is located below the cover  45 , is electrically coupled to the control circuit board  100 . The cover  45  may be removed to expose the display  43 . 
     The electric motor  82  can include a rotatable shaft (not shown) that operably interfaces with a gear reducer assembly  84  mounted in meshing engagement with a with a set, or rack, of drive teeth  122  on a longitudinally movable drive member  120 . The longitudinally movable drive member  120  has a rack of drive teeth  122  formed thereon for meshing engagement with a corresponding drive gear  86  of the gear reducer assembly  84 . 
     In use, a voltage polarity provided by the power source  90  can operate the electric motor  82  in a clockwise direction wherein the voltage polarity applied to the electric motor by the battery can be reversed in order to operate the electric motor  82  in a counter-clockwise direction. When the electric motor  82  is rotated in one direction, the longitudinally movable drive member  120  will be axially driven in the distal direction “DD.” When the electric motor  82  is driven in the opposite rotary direction, the longitudinally movable drive member  120  will be axially driven in a proximal direction “PD.” The handle assembly  14  can include a switch that can be configured to reverse the polarity applied to the electric motor  82  by the power source  90 . The handle assembly  14  may include a sensor configured to detect the position of the longitudinally movable drive member  120  and/or the direction in which the longitudinally movable drive member  120  is being moved. 
     Actuation of the electric motor  82  can be controlled by a firing trigger  130  that is pivotally supported on the handle assembly  14 . The firing trigger  130  may be pivoted between an unactuated position and an actuated position. 
     Turning back to  FIG. 1 , the interchangeable shaft assembly  200  includes an end effector  300  comprising an elongated channel  302  configured to operably support a surgical staple cartridge  304  therein. The end effector  300  may include an anvil  306  that is pivotally supported relative to the elongated channel  302 . The interchangeable shaft assembly  200  may include an articulation joint  270 . Construction and operation of the end effector  300  and the articulation joint  270  are set forth in U.S. Patent Application Publication No. 2014/0263541, entitled ARTICULATABLE SURGICAL INSTRUMENT COMPRISING AN ARTICULATION LOCK, which is hereby incorporated herein by reference in its entirety. The interchangeable shaft assembly  200  may include a proximal housing or nozzle  201  comprised of nozzle portions  202 ,  203 . The interchangeable shaft assembly  200  may include a closure tube  260  extending along a shaft axis SA that can be utilized to close and/or open the anvil  306  of the end effector  300 . 
     Turning back to  FIG. 1 , the closure tube  260  is translated distally (direction “DD”) to close the anvil  306 , for example, in response to the actuation of the closure trigger  32  in the manner described in the aforementioned reference U.S. Patent Application Publication No. 2014/0263541. The anvil  306  is opened by proximally translating the closure tube  260 . In the anvil-open position, the closure tube  260  is moved to its proximal position. 
       FIG. 3  is another exploded assembly view of portions of the interchangeable shaft assembly  200  according to one aspect of this disclosure. The interchangeable shaft assembly  200  may include a firing member  220  supported for axial travel within the spine  210 . The firing member  220  includes an intermediate firing shaft  222  configured to attach to a distal cutting portion or knife bar  280 . The intermediate firing shaft  222  may include a longitudinal slot  223  in a distal end configured to receive a tab  284  on the proximal end  282  of the knife bar  280 . The longitudinal slot  223  and the proximal end  282  may be configured to permit relative movement there between and can comprise a slip joint  286 . The slip joint  286  can permit the intermediate firing shaft  222  of the firing member  220  to articulate the end effector  300  about the articulation joint  270  without moving, or at least substantially moving, the knife bar  280 . Once the end effector  300  has been suitably oriented, the intermediate firing shaft  222  can be advanced distally until a proximal sidewall of the longitudinal slot  223  contacts the tab  284  to advance the knife bar  280  and fire the staple cartridge positioned within the elongated channel  302 . The spine  210  has an elongated opening or window  213  therein to facilitate assembly and insertion of the intermediate firing shaft  222  into the spine  210 . Once the intermediate firing shaft  222  has been inserted therein, a top frame segment  215  may be engaged with the shaft frame  212  to enclose the intermediate firing shaft  222  and knife bar  280  therein. Operation of the firing member  220  may be found in U.S. Patent Application Publication No. 2014/0263541. A spine  210  can be configured to slidably support a firing member  220  and the closure tube  260  that extends around the spine  210 . The spine  210  may slidably support an articulation driver  230 . 
     The interchangeable shaft assembly  200  can include a clutch assembly  400  configured to selectively and releasably couple the articulation driver  230  to the firing member  220 . The clutch assembly  400  includes a lock collar, or lock sleeve  402 , positioned around the firing member  220  wherein the lock sleeve  402  can be rotated between an engaged position in which the lock sleeve  402  couples the articulation driver  230  to the firing member  220  and a disengaged position in which the articulation driver  230  is not operably coupled to the firing member  220 . When the lock sleeve  402  is in the engaged position, distal movement of the firing member  220  can move the articulation driver  230  distally and, correspondingly, proximal movement of the firing member  220  can move the articulation driver  230  proximally. When the lock sleeve  402  is in the disengaged position, movement of the firing member  220  is not transmitted to the articulation driver  230  and, as a result, the firing member  220  can move independently of the articulation driver  230 . The nozzle  201  may be employed to operably engage and disengage the articulation drive system with the firing drive system in the various manners described in U.S. Patent Application Publication No. 2014/0263541. 
     The interchangeable shaft assembly  200  can comprise a slip ring assembly  600  which can be configured to conduct electrical power to and/or from the end effector  300  and/or communicate signals to and/or from the end effector  300 , for example. The slip ring assembly  600  can comprise a proximal connector flange  604  and a distal connector flange  601  positioned within a slot defined in the nozzle portions  202 ,  203 . The proximal connector flange  604  can comprise a first face and the distal connector flange  601  can comprise a second face positioned adjacent to and movable relative to the first face. The distal connector flange  601  can rotate relative to the proximal connector flange  604  about the shaft axis SA-SA ( FIG. 1 ). The proximal connector flange  604  can comprise a plurality of concentric, or at least substantially concentric, conductors  602  defined in the first face thereof. A connector  607  can be mounted on the proximal side of the distal connector flange  601  and may have a plurality of contacts wherein each contact corresponds to and is in electrical contact with one of the conductors  602 . Such an arrangement permits relative rotation between the proximal connector flange  604  and the distal connector flange  601  while maintaining electrical contact there between. The proximal connector flange  604  can include an electrical connector  606  that can place the conductors  602  in signal communication with a shaft circuit board, for example. In at least one instance, a wiring harness comprising a plurality of conductors can extend between the electrical connector  606  and the shaft circuit board. The electrical connector  606  may extend proximally through a connector opening defined in the chassis mounting flange. Further details regarding slip ring assembly  600  may be found in U.S. Patent Application Publication No. 2014/0263541. 
     The interchangeable shaft assembly  200  can include a proximal portion fixably mounted to the handle assembly  14  and a distal portion that is rotatable about a longitudinal axis. The rotatable distal shaft portion can be rotated relative to the proximal portion about the slip ring assembly  600 . The distal connector flange  601  of the slip ring assembly  600  can be positioned within the rotatable distal shaft portion. 
       FIG. 4  is an exploded view of one aspect of an end effector  300  of the surgical instrument  10  of  FIG. 1  according to one aspect of this disclosure. The end effector  300  may include the anvil  306  and the surgical staple cartridge  304 . The anvil  306  may be coupled to an elongated channel  302 . Apertures  199  can be defined in the elongated channel  302  to receive pins  152  extending from the anvil  306  to allow the anvil  306  to pivot from an open position to a closed position relative to the elongated channel  302  and surgical staple cartridge  304 . A firing bar  172  is configured to longitudinally translate into the end effector  300 . The firing bar  172  may be constructed from one solid section, or may include a laminate material comprising a stack of steel plates. The firing bar  172  comprises an I-beam  178  and a cutting edge  182  at a distal end thereof. A distally projecting end of the firing bar  172  can be attached to the I-beam  178  to assist in spacing the anvil  306  from a surgical staple cartridge  304  positioned in the elongated channel  302  when the anvil  306  is in a closed position. The I-beam  178  may include a sharpened cutting edge  182  to sever tissue as the I-beam  178  is advanced distally by the firing bar  172 . In operation, the I-beam  178  may, or fire, the surgical staple cartridge  304 . The surgical staple cartridge  304  can include a molded cartridge body  194  that holds a plurality of staples  191  resting upon staple drivers  192  within respective upwardly open staple cavities  195 . A wedge sled  190  is driven distally by the I-beam  178 , sliding upon a cartridge tray  196  of the surgical staple cartridge  304 . The wedge sled  190  upwardly cams the staple drivers  192  to force out the staples  191  into deforming contact with the anvil  306  while the cutting edge  182  of the I-beam  178  severs clamped tissue. 
     The I-beam  178  can include upper pins  180  that engage the anvil  306  during firing. The I-beam  178  may include middle pins  184  and a bottom foot  186  to engage portions of the cartridge body  194 , cartridge tray  196 , and elongated channel  302 . When a surgical staple cartridge  304  is positioned within the elongated channel  302 , a slot  193  defined in the cartridge body  194  can be aligned with a longitudinal slot  197  defined in the cartridge tray  196  and a slot  189  defined in the elongated channel  302 . In use, the I-beam  178  can slide through the aligned longitudinal slots  193 ,  197 , and  189  wherein, as indicated in  FIG. 4 , the bottom foot  186  of the I-beam  178  can engage a groove running along the bottom surface of elongated channel  302  along the length of slot  189 , the middle pins  184  can engage the top surfaces of cartridge tray  196  along the length of longitudinal slot  197 , and the upper pins  180  can engage the anvil  306 . The I-beam  178  can space, or limit the relative movement between, the anvil  306  and the surgical staple cartridge  304  as the firing bar  172  is advanced distally to fire the staples from the surgical staple cartridge  304  and/or incise the tissue captured between the anvil  306  and the surgical staple cartridge  304 . The firing bar  172  and the I-beam  178  can be retracted proximally allowing the anvil  306  to be opened to release the two stapled and severed tissue portions. 
       FIGS. 5A-5B  is a block diagram of a control circuit  700  of the surgical instrument  10  of  FIG. 1  spanning two drawing sheets according to one aspect of this disclosure. Referring primarily to  FIGS. 5A-5B , a handle assembly  702  may include a motor  714  which can be controlled by a motor driver  715  and can be employed by the firing system of the surgical instrument  10 . In various forms, the motor  714  may be a DC brushed driving motor having a maximum rotational speed of approximately 25,000 RPM. In other arrangements, the motor  714  may include a brushless motor, a cordless motor, a synchronous motor, a stepper motor, or any other suitable electric motor. The motor driver  715  may comprise an H-bridge driver comprising field-effect transistors (FETs)  719 , for example. The motor  714  can be powered by the power assembly  706  releasably mounted to the handle assembly  14  for supplying control power to the surgical instrument  10 . The power assembly  706  may comprise a battery which may include a number of battery cells connected in series that can be used as the power source to power the surgical instrument  10 . In certain circumstances, the battery cells of the power assembly  706  may be replaceable and/or rechargeable. In at least one example, the battery cells can be Lithium-Ion batteries which can be separably couplable to the power assembly  706 . 
     The shaft assembly  704  may include a shaft assembly controller  722  which can communicate with a safety controller and power management controller  716  through an interface while the shaft assembly  704  and the power assembly  706  are coupled to the handle assembly  702 . For example, the interface may comprise a first interface portion  725  which may include one or more electric connectors for coupling engagement with corresponding shaft assembly electric connectors and a second interface portion  727  which may include one or more electric connectors for coupling engagement with corresponding power assembly electric connectors to permit electrical communication between the shaft assembly controller  722  and the power management controller  716  while the shaft assembly  704  and the power assembly  706  are coupled to the handle assembly  702 . One or more communication signals can be transmitted through the interface to communicate one or more of the power requirements of the attached interchangeable shaft assembly  704  to the power management controller  716 . In response, the power management controller may modulate the power output of the battery of the power assembly  706 , as described below in greater detail, in accordance with the power requirements of the attached shaft assembly  704 . The connectors may comprise switches which can be activated after mechanical coupling engagement of the handle assembly  702  to the shaft assembly  704  and/or to the power assembly  706  to allow electrical communication between the shaft assembly controller  722  and the power management controller  716 . 
     The interface can facilitate transmission of the one or more communication signals between the power management controller  716  and the shaft assembly controller  722  by routing such communication signals through a main controller  717  residing in the handle assembly  702 , for example. In other circumstances, the interface can facilitate a direct line of communication between the power management controller  716  and the shaft assembly controller  722  through the handle assembly  702  while the shaft assembly  704  and the power assembly  706  are coupled to the handle assembly  702 . 
     The main controller  717  may be any single core or multicore processor such as those known under the trade name ARM Cortex by Texas Instruments. In one aspect, the main controller  717  may be an LM4F230H5QR ARM Cortex-M4F Processor Core, available from Texas Instruments, for example, comprising on-chip memory of 256 KB single-cycle flash memory, or other non-volatile memory, up to 40 MHz, a prefetch buffer to improve performance above 40 MHz, a 32 KB single-cycle serial random access memory (SRAM), internal read-only memory (ROM) loaded with StellarisWare® software, 2 KB electrically erasable programmable read-only memory (EEPROM), one or more pulse width modulation (PWM) modules, one or more quadrature encoder inputs (QEI) analog, one or more 12-bit Analog-to-Digital Converters (ADC) with 12 analog input channels, details of which are available for the product datasheet. 
     The safety controller may be a safety controller platform comprising two controller-based families such as TMS570 and RM4x known under the trade name Hercules ARM Cortex R4, also by Texas Instruments. The safety controller may be configured specifically for IEC 61508 and ISO 26262 safety critical applications, among others, to provide advanced integrated safety features while delivering scalable performance, connectivity, and memory options. 
     The power assembly  706  may include a power management circuit which may comprise the power management controller  716 , a power modulator  738 , and a current sense circuit  736 . The power management circuit can be configured to modulate power output of the battery based on the power requirements of the shaft assembly  704  while the shaft assembly  704  and the power assembly  706  are coupled to the handle assembly  702 . The power management controller  716  can be programmed to control the power modulator  738  of the power output of the power assembly  706  and the current sense circuit  736  can be employed to monitor power output of the power assembly  706  to provide feedback to the power management controller  716  about the power output of the battery so that the power management controller  716  may adjust the power output of the power assembly  706  to maintain a desired output. The power management controller  716  and/or the shaft assembly controller  722  each may comprise one or more processors and/or memory units which may store a number of software modules. 
     The surgical instrument  10  ( FIGS. 1-4 ) may comprise an output device  742  which may include devices for providing a sensory feedback to a user. Such devices may comprise, for example, visual feedback devices (e.g., an LCD display screen, LED indicators), audio feedback devices (e.g., a speaker, a buzzer) or tactile feedback devices (e.g., haptic actuators). In certain circumstances, the output device  742  may comprise a display  743  which may be included in the handle assembly  702 . The shaft assembly controller  722  and/or the power management controller  716  can provide feedback to a user of the surgical instrument  10  through the output device  742 . The interface can be configured to connect the shaft assembly controller  722  and/or the power management controller  716  to the output device  742 . The output device  742  can instead be integrated with the power assembly  706 . In such circumstances, communication between the output device  742  and the shaft assembly controller  722  may be accomplished through the interface while the shaft assembly  704  is coupled to the handle assembly  702 . 
     The control circuit  700  comprises circuit segments configured to control operations of the powered surgical instrument  10 . A safety controller segment (Segment  1 ) comprises a safety controller and the main controller  717  segment (Segment  2 ). The safety controller and/or the main controller  717  are configured to interact with one or more additional circuit segments such as an acceleration segment, a display segment, a shaft segment, an encoder segment, a motor segment, and a power segment. Each of the circuit segments may be coupled to the safety controller and/or the main controller  717 . The main controller  717  is also coupled to a flash memory. The main controller  717  also comprises a serial communication interface. The main controller  717  comprises a plurality of inputs coupled to, for example, one or more circuit segments, a battery, and/or a plurality of switches. The segmented circuit may be implemented by any suitable circuit, such as, for example, a printed circuit board assembly (PCBA) within the powered surgical instrument  10 . It should be understood that the term processor as used herein includes any microprocessor, processors, controller, controllers, or other basic computing device that incorporates the functions of a computer&#39;s central processing unit (CPU) on an integrated circuit or at most a few integrated circuits. The main controller  717  is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and provides results as output. It is an example of sequential digital logic, as it has internal memory. The control circuit  700  can be configured to implement one or more of the processes described herein. 
     The acceleration segment (Segment  3 ) comprises an accelerometer. The accelerometer is configured to detect movement or acceleration of the powered surgical instrument  10 . Input from the accelerometer may be used to transition to and from a sleep mode, identify an orientation of the powered surgical instrument, and/or identify when the surgical instrument has been dropped. In some examples, the acceleration segment is coupled to the safety controller and/or the main controller  717 . 
     The display segment (Segment  4 ) comprises a display connector coupled to the main controller  717 . The display connector couples the main controller  717  to a display through one or more integrated circuit drivers of the display. The integrated circuit drivers of the display may be integrated with the display and/or may be located separately from the display. The display may comprise any suitable display, such as, for example, an organic light-emitting diode (OLED) display, a liquid-crystal display (LCD), and/or any other suitable display. In some examples, the display segment is coupled to the safety controller. 
     The shaft segment (Segment  5 ) comprises controls for an interchangeable shaft assembly  200  ( FIGS. 1 and 3 ) coupled to the surgical instrument  10  ( FIGS. 1-4 ) and/or one or more controls for an end effector  300  coupled to the interchangeable shaft assembly  200 . The shaft segment comprises a shaft connector configured to couple the main controller  717  to a shaft PCBA. The shaft PCBA comprises a low-power microcontroller with a ferroelectric random access memory (FRAM), an articulation switch, a shaft release Hall effect switch, and a shaft PCBA EEPROM. The shaft PCBA EEPROM comprises one or more parameters, routines, and/or programs specific to the interchangeable shaft assembly  200  and/or the shaft PCBA. The shaft PCBA may be coupled to the interchangeable shaft assembly  200  and/or integral with the surgical instrument  10 . In some examples, the shaft segment comprises a second shaft EEPROM. The second shaft EEPROM comprises a plurality of algorithms, routines, parameters, and/or other data corresponding to one or more shaft assemblies  200  and/or end effectors  300  that may be interfaced with the powered surgical instrument  10 . 
     The position encoder segment (Segment  6 ) comprises one or more magnetic angle rotary position encoders. The one or more magnetic angle rotary position encoders are configured to identify the rotational position of the motor  714 , an interchangeable shaft assembly  200  ( FIGS. 1 and 3 ), and/or an end effector  300  of the surgical instrument  10  ( FIGS. 1-4 ). In some examples, the magnetic angle rotary position encoders may be coupled to the safety controller and/or the main controller  717 . 
     The motor circuit segment (Segment  7 ) comprises a motor  714  configured to control movements of the powered surgical instrument  10  ( FIGS. 1-4 ). The motor  714  is coupled to the main controller  717  by an H-bridge driver comprising one or more H-bridge field-effect transistors (FETs) and a motor controller. The H-bridge driver is also coupled to the safety controller. A motor current sensor is coupled in series with the motor to measure the current draw of the motor. The motor current sensor is in signal communication with the main controller  717  and/or the safety controller. In some examples, the motor  714  is coupled to a motor electromagnetic interference (EMI) filter. 
     The motor controller controls a first motor flag and a second motor flag to indicate the status and position of the motor  714  to the main controller  717 . The main controller  717  provides a pulse-width modulation (PWM) high signal, a PWM low signal, a direction signal, a synchronize signal, and a motor reset signal to the motor controller through a buffer. The power segment is configured to provide a segment voltage to each of the circuit segments. 
     The power segment (Segment  8 ) comprises a battery coupled to the safety controller, the main controller  717 , and additional circuit segments. The battery is coupled to the segmented circuit by a battery connector and a current sensor. The current sensor is configured to measure the total current draw of the segmented circuit. In some examples, one or more voltage converters are configured to provide predetermined voltage values to one or more circuit segments. For example, in some examples, the segmented circuit may comprise 3.3V voltage converters and/or 5V voltage converters. A boost converter is configured to provide a boost voltage up to a predetermined amount, such as, for example, up to 13V. The boost converter is configured to provide additional voltage and/or current during power intensive operations and prevent brownout or low-power conditions. 
     A plurality of switches are coupled to the safety controller and/or the main controller  717 . The switches may be configured to control operations of the surgical instrument  10  ( FIGS. 1-4 ), of the segmented circuit, and/or indicate a status of the surgical instrument  10 . A bail-out door switch and Hall effect switch for bailout are configured to indicate the status of a bail-out door. A plurality of articulation switches, such as, for example, a left side articulation left switch, a left side articulation right switch, a left side articulation center switch, a right side articulation left switch, a right side articulation right switch, and a right side articulation center switch are configured to control articulation of an interchangeable shaft assembly  200  ( FIGS. 1 and 3 ) and/or the end effector  300  ( FIGS. 1 and 4 ). A left side reverse switch and a right side reverse switch are coupled to the main controller  717 . The left side switches comprising the left side articulation left switch, the left side articulation right switch, the left side articulation center switch, and the left side reverse switch are coupled to the main controller  717  by a left flex connector. The right side switches comprising the right side articulation left switch, the right side articulation right switch, the right side articulation center switch, and the right side reverse switch are coupled to the main controller  717  by a right flex connector. A firing switch, a clamp release switch, and a shaft engaged switch are coupled to the main controller  717 . 
     Any suitable mechanical, electromechanical, or solid state switches may be employed to implement the plurality of switches, in any combination. For example, the switches may be limit switches operated by the motion of components associated with the surgical instrument  10  ( FIGS. 1-4 ) or the presence of an object. Such switches may be employed to control various functions associated with the surgical instrument  10 . A limit switch is an electromechanical device that consists of an actuator mechanically linked to a set of contacts. When an object comes into contact with the actuator, the device operates the contacts to make or break an electrical connection. Limit switches are used in a variety of applications and environments because of their ruggedness, ease of installation, and reliability of operation. They can determine the presence or absence, passing, positioning, and end of travel of an object. In other implementations, the switches may be solid state switches that operate under the influence of a magnetic field such as Hall-effect devices, magneto-resistive (MR) devices, giant magneto-resistive (GMR) devices, magnetometers, among others. In other implementations, the switches may be solid state switches that operate under the influence of light, such as optical sensors, infrared sensors, ultraviolet sensors, among others. Still, the switches may be solid state devices such as transistors (e.g., FET, Junction-FET, metal-oxide semiconductor-FET (MOSFET), bipolar, and the like). Other switches may include wireless switches, ultrasonic switches, accelerometers, inertial sensors, among others. 
       FIG. 6  is another block diagram of the control circuit  700  of the surgical instrument of  FIG. 1  illustrating interfaces between the handle assembly  702  and the power assembly  706  and between the handle assembly  702  and the interchangeable shaft assembly  704  according to one aspect of this disclosure. The handle assembly  702  may comprise a main controller  717 , a shaft assembly connector  726  and a power assembly connector  730 . The power assembly  706  may include a power assembly connector  732 , a power management circuit  734  that may comprise the power management controller  716 , a power modulator  738 , and a current sense circuit  736 . The power assembly connectors  730 ,  732  form an interface  727 . The power management circuit  734  can be configured to modulate power output of the battery  707  based on the power requirements of the interchangeable shaft assembly  704  while the interchangeable shaft assembly  704  and the power assembly  706  are coupled to the handle assembly  702 . The power management controller  716  can be programmed to control the power modulator  738  of the power output of the power assembly  706  and the current sense circuit  736  can be employed to monitor power output of the power assembly  706  to provide feedback to the power management controller  716  about the power output of the battery  707  so that the power management controller  716  may adjust the power output of the power assembly  706  to maintain a desired output. The shaft assembly  704  comprises a shaft assembly controller  722  coupled to a non-volatile memory  721  and shaft assembly connector  728  to electrically couple the shaft assembly  704  to the handle assembly  702 . The shaft assembly connectors  726 ,  728  form interface  725 . The main controller  717 , the shaft assembly controller  722 , and/or the power management controller  716  can be configured to implement one or more of the processes described herein. 
     The surgical instrument  10  ( FIGS. 1-4 ) may comprise an output device  742  to a sensory feedback to a user. Such devices may comprise visual feedback devices (e.g., an LCD display screen, LED indicators), audio feedback devices (e.g., a speaker, a buzzer), or tactile feedback devices (e.g., haptic actuators). In certain circumstances, the output device  742  may comprise a display  743  that may be included in the handle assembly  702 . The shaft assembly controller  722  and/or the power management controller  716  can provide feedback to a user of the surgical instrument  10  through the output device  742 . The interface  727  can be configured to connect the shaft assembly controller  722  and/or the power management controller  716  to the output device  742 . The output device  742  can be integrated with the power assembly  706 . Communication between the output device  742  and the shaft assembly controller  722  may be accomplished through the interface  725  while the interchangeable shaft assembly  704  is coupled to the handle assembly  702 . Having described a control circuit  700  ( FIGS. 5A-5B and 6 ) for controlling the operation of the surgical instrument  10  ( FIGS. 1-4 ), the disclosure now turns to various configurations of the surgical instrument  10  ( FIGS. 1-4 ) and control circuit  700 . 
       FIG. 7  illustrates a control circuit  800  configured to control aspects of the surgical instrument  10  ( FIGS. 1-4 ) according to one aspect of this disclosure. The control circuit  800  can be configured to implement various processes described herein. The control circuit  800  may comprise a controller comprising one or more processors  802  (e.g., microprocessor, microcontroller) coupled to at least one memory circuit  804 . The memory circuit  804  stores machine executable instructions that when executed by the processor  802 , cause the processor  802  to execute machine instructions to implement various processes described herein. The processor  802  may be any one of a number of single or multi-core processors known in the art. The memory circuit  804  may comprise volatile and non-volatile storage media. The processor  802  may include an instruction processing unit  806  and an arithmetic unit  808 . The instruction processing unit may be configured to receive instructions from the memory circuit  804 . 
       FIG. 8  illustrates a combinational logic circuit  810  configured to control aspects of the surgical instrument  10  ( FIGS. 1-4 ) according to one aspect of this disclosure. The combinational logic circuit  810  can be configured to implement various processes described herein. The circuit  810  may comprise a finite state machine comprising a combinational logic circuit  812  configured to receive data associated with the surgical instrument  10  at an input  814 , process the data by the combinational logic  812 , and provide an output  816 . 
       FIG. 9  illustrates a sequential logic circuit  820  configured to control aspects of the surgical instrument  10  ( FIGS. 1-4 ) according to one aspect of this disclosure. The sequential logic circuit  820  or the combinational logic circuit  822  can be configured to implement various processes described herein. The circuit  820  may comprise a finite state machine. The sequential logic circuit  820  may comprise a combinational logic circuit  822 , at least one memory circuit  824 , and a clock  829 , for example. The at least one memory circuit  820  can store a current state of the finite state machine. In certain instances, the sequential logic circuit  820  may be synchronous or asynchronous. The combinational logic circuit  822  is configured to receive data associated with the surgical instrument  10  an input  826 , process the data by the combinational logic circuit  822 , and provide an output  828 . In other aspects, the circuit may comprise a combination of the processor  802  and the finite state machine to implement various processes herein. In other aspects, the finite state machine may comprise a combination of the combinational logic circuit  810  and the sequential logic circuit  820 . 
     Aspects may be implemented as an article of manufacture. The article of manufacture may include a computer readable storage medium arranged to store logic, instructions, and/or data for performing various operations of one or more aspects. For example, the article of manufacture may comprise a magnetic disk, optical disk, flash memory, or firmware containing computer program instructions suitable for execution by a general purpose processor or application specific processor. 
       FIG. 10  is a diagram of an absolute positioning system  1100  of the surgical instrument  10  ( FIGS. 1-4 ) where the absolute positioning system  1100  comprises a controlled motor drive circuit arrangement comprising a sensor arrangement  1102  according to one aspect of this disclosure. The sensor arrangement  1102  for an absolute positioning system  1100  provides a unique position signal corresponding to the location of a displacement member  1111 . Turning briefly to  FIGS. 2-4 , in one aspect the displacement member  1111  represents the longitudinally movable drive member  120  ( FIG. 2 ) comprising a rack of drive teeth  122  for meshing engagement with a corresponding drive gear  86  of the gear reducer assembly  84 . In other aspects, the displacement member  1111  represents the firing member  220  ( FIG. 3 ), which could be adapted and configured to include a rack of drive teeth. In yet another aspect, the displacement member  1111  represents the firing bar  172  ( FIG. 4 ) or the I-beam  178  ( FIG. 4 ), each of which can be adapted and configured to include a rack of drive teeth. Accordingly, as used herein, the term displacement member is used generically to refer to any movable member of the surgical instrument  10  such as the drive member  120 , the firing member  220 , the firing bar  172 , the I-beam  178 , or any element that can be displaced. In one aspect, the longitudinally movable drive member  120  is coupled to the firing member  220 , the firing bar  172 , and the I-beam  178 . Accordingly, the absolute positioning system  1100  can, in effect, track the linear displacement of the I-beam  178  by tracking the linear displacement of the longitudinally movable drive member  120 . In various other aspects, the displacement member  1111  may be coupled to any sensor suitable for measuring linear displacement. Thus, the longitudinally movable drive member  120 , the firing member  220 , the firing bar  172 , or the I-beam  178 , or combinations, may be coupled to any suitable linear displacement sensor. Linear displacement sensors may include contact or non-contact displacement sensors. Linear displacement sensors may comprise linear variable differential transformers (LVDT), differential variable reluctance transducers (DVRT), a slide potentiometer, a magnetic sensing system comprising a movable magnet and a series of linearly arranged Hall effect sensors, a magnetic sensing system comprising a fixed magnet and a series of movable linearly arranged Hall effect sensors, an optical sensing system comprising a movable light source and a series of linearly arranged photo diodes or photo detectors, or an optical sensing system comprising a fixed light source and a series of movable linearly arranged photo diodes or photo detectors, or any combination thereof. 
     An electric motor  1120  can include a rotatable shaft  1116  that operably interfaces with a gear assembly  1114  that is mounted in meshing engagement with a set, or rack, of drive teeth on the displacement member  1111 . A sensor element  1126  may be operably coupled to a gear assembly  1114  such that a single revolution of the sensor element  1126  corresponds to some linear longitudinal translation of the displacement member  1111 . An arrangement of gearing and sensors can be connected to the linear actuator via a rack and pinion arrangement or a rotary actuator via a spur gear or other connection. A power source  1129  supplies power to the absolute positioning system  1100  and an output indicator  1128  may display the output of the absolute positioning system  1100 . In  FIG. 2 , the displacement member  1111  represents the longitudinally movable drive member  120  comprising a rack of drive teeth  122  formed thereon for meshing engagement with a corresponding drive gear  86  of the gear reducer assembly  84 . The displacement member  1111  represents the longitudinally movable firing member  220 , firing bar  172 , I-beam  178 , or combinations thereof. 
     A single revolution of the sensor element  1126  associated with the position sensor  1112  is equivalent to a longitudinal linear displacement d 1  of the of the displacement member  1111 , where d 1  is the longitudinal linear distance that the displacement member  1111  moves from point “a” to point “b” after a single revolution of the sensor element  1126  coupled to the displacement member  1111 . The sensor arrangement  1102  may be connected via a gear reduction that results in the position sensor  1112  completing one or more revolutions for the full stroke of the displacement member  1111 . The position sensor  1112  may complete multiple revolutions for the full stroke of the displacement member  1111 . 
     A series of switches  1122   a - 1122   n , where n is an integer greater than one, may be employed alone or in combination with gear reduction to provide a unique position signal for more than one revolution of the position sensor  1112 . The state of the switches  1122   a - 1122   n  are fed back to a controller  1104  that applies logic to determine a unique position signal corresponding to the longitudinal linear displacement d 1 +d 2 + . . . dn of the displacement member  1111 . The output  1124  of the position sensor  1112  is provided to the controller  1104 . The position sensor  1112  of the sensor arrangement  1102  may comprise a magnetic sensor, an analog rotary sensor like a potentiometer, an array of analog Hall-effect elements, which output a unique combination of position signals or values. 
     The absolute positioning system  1100  provides an absolute position of the displacement member  1111  upon power up of the instrument without retracting or advancing the displacement member  1111  to a reset (zero or home) position as may be required with conventional rotary encoders that merely count the number of steps forwards or backwards that the motor  1120  has taken to infer the position of a device actuator, drive bar, knife, and the like. 
     The controller  1104  may be programmed to perform various functions such as precise control over the speed and position of the knife and articulation systems. In one aspect, the controller  1104  includes a processor  1108  and a memory  1106 . The electric motor  1120  may be a brushed DC motor with a gearbox and mechanical links to an articulation or knife system. In one aspect, a motor driver  1110  may be an A3941 available from Allegro Microsystems, Inc. Other motor drivers may be readily substituted for use in the absolute positioning system  1100 . A more detailed description of the absolute positioning system  1100  is described in U.S. patent application Ser. No. 15/130,590, entitled SYSTEMS AND METHODS FOR CONTROLLING A SURGICAL STAPLING AND CUTTING INSTRUMENT, the entire disclosure of which is hereby incorporated herein by reference. 
     The controller  1104  may be programmed to provide precise control over the speed and position of the displacement member  1111  and articulation systems. The controller  1104  may be configured to compute a response in the software of the controller  1104 . The computed response is compared to a measured response of the actual system to obtain an “observed” response, which is used for actual feedback decisions. The observed response is a favorable, tuned, value that balances the smooth, continuous nature of the simulated response with the measured response, which can detect outside influences on the system. 
     The absolute positioning system  1100  may comprise and/or be programmed to implement a feedback controller, such as a PID, state feedback, and adaptive controller. A power source  1129  converts the signal from the feedback controller into a physical input to the system, in this case voltage. Other examples include pulse width modulation (PWM) of the voltage, current, and force. Other sensor(s)  1118  may be provided to measure physical parameters of the physical system in addition to position measured by the position sensor  1112 . In some aspects, the other sensor(s)  1118  can include sensor arrangements such as those described in U.S. Pat. No. 9,345,481, entitled STAPLE CARTRIDGE TISSUE THICKNESS SENSOR SYSTEM, which is hereby incorporated herein by reference in its entirety; U.S. Patent Application Publication No. 2014/0263552, entitled STAPLE CARTRIDGE TISSUE THICKNESS SENSOR SYSTEM, which is hereby incorporated herein by reference in its entirety; and U.S. patent application Ser. No. 15/628,175, entitled TECHNIQUES FOR ADAPTIVE CONTROL OF MOTOR VELOCITY OF A SURGICAL STAPLING AND CUTTING INSTRUMENT, which is hereby incorporated herein by reference in its entirety. In a digital signal processing system, absolute positioning system  1100  is coupled to a digital data acquisition system where the output of the absolute positioning system  1100  will have finite resolution and sampling frequency. The absolute positioning system  1100  may comprise a compare and combine circuit to combine a computed response with a measured response using algorithms such as weighted average and theoretical control loop that drives the computed response towards the measured response. The computed response of the physical system takes into account properties like mass, inertial, viscous friction, inductance resistance, etc., to predict what the states and outputs of the physical system will be by knowing the input. The controller  1104  may be a control circuit  700  ( FIGS. 5A-5B ). 
     The motor driver  1110  may be an A3941 available from Allegro Microsystems, Inc. The A3941 driver  1110  is a full-bridge controller for use with external N-channel power metal oxide semiconductor field effect transistors (MOSFETs) specifically designed for inductive loads, such as brush DC motors. The driver  1110  comprises a unique charge pump regulator provides full (&gt;10 V) gate drive for battery voltages down to 7 V and allows the A3941 to operate with a reduced gate drive, down to 5.5 V. A bootstrap capacitor may be employed to provide the above-battery supply voltage required for N-channel MOSFETs. An internal charge pump for the high-side drive allows DC (100% duty cycle) operation. The full bridge can be driven in fast or slow decay modes using diode or synchronous rectification. In the slow decay mode, current recirculation can be through the high-side or the lowside FETs. The power FETs are protected from shoot-through by resistor adjustable dead time. Integrated diagnostics provide indication of undervoltage, overtemperature, and power bridge faults, and can be configured to protect the power MOSFETs under most short circuit conditions. Other motor drivers may be readily substituted for use in the absolute positioning system  1100 . 
     Having described a general architecture for implementing aspects of an absolute positioning system  1100  for a sensor arrangement  1102 , the disclosure now turns to  FIGS. 11 and 12  for a description of one aspect of a sensor arrangement  1102  for the absolute positioning system  1100 .  FIG. 11  is an exploded perspective view of the sensor arrangement  1102  for the absolute positioning system  1100  showing a circuit  1205  and the relative alignment of the elements of the sensor arrangement  1102 , according to one aspect. The sensor arrangement  1102  for an absolute positioning system  1100  comprises a position sensor  1200 , a magnet  1202  sensor element, a magnet holder  1204  that turns once every full stroke of the displacement member  1111 , and a gear assembly  1206  to provide a gear reduction. With reference briefly to  FIG. 2 , the displacement member  1111  may represent the longitudinally movable drive member  120  comprising a rack of drive teeth  122  for meshing engagement with a corresponding drive gear  86  of the gear reducer assembly  84 . Returning to  FIG. 11 , a structural element such as bracket  1216  is provided to support the gear assembly  1206 , the magnet holder  1204 , and the magnet  1202 . The position sensor  1200  comprises magnetic sensing elements such as Hall elements and is placed in proximity to the magnet  1202 . As the magnet  1202  rotates, the magnetic sensing elements of the position sensor  1200  determine the absolute angular position of the magnet  1202  over one revolution. 
     The sensor arrangement  1102  may comprise any number of magnetic sensing elements, such as, for example, magnetic sensors classified according to whether they measure the total magnetic field or the vector components of the magnetic field. The techniques used to produce both types of magnetic sensors encompass many aspects of physics and electronics. The technologies used for magnetic field sensing include search coil, fluxgate, optically pumped, nuclear precession, SQUID, Hall-effect, anisotropic magnetoresistance, giant magnetoresistance, magnetic tunnel junctions, giant magnetoimpedance, magnetostrictive/piezoelectric composites, magnetodiode, magnetotransistor, fiber optic, magnetooptic, and microelectromechanical systems-based magnetic sensors, among others. 
     A gear assembly comprises a first gear  1208  and a second gear  1210  in meshing engagement to provide a 3:1 gear ratio connection. A third gear  1212  rotates about a shaft  1214 . The third gear  1212  is in meshing engagement with the displacement member  1111  (or  120  as shown in  FIG. 2 ) and rotates in a first direction as the displacement member  1111  advances in a distal direction D and rotates in a second direction as the displacement member  1111  retracts in a proximal direction P. The second gear  1210  also rotates about the shaft  1214  and, therefore, rotation of the second gear  1210  about the shaft  1214  corresponds to the longitudinal translation of the displacement member  1111 . Thus, one full stroke of the displacement member  1111  in either the distal or proximal directions D, P corresponds to three rotations of the second gear  1210  and a single rotation of the first gear  1208 . Since the magnet holder  1204  is coupled to the first gear  1208 , the magnet holder  1204  makes one full rotation with each full stroke of the displacement member  1111 . 
     The position sensor  1200  is supported by a position sensor holder  1218  defining an aperture  1220  suitable to contain the position sensor  1200  in precise alignment with a magnet  1202  rotating below within the magnet holder  1204 . The fixture is coupled to the bracket  1216  and to the circuit  1205  and remains stationary while the magnet  1202  rotates with the magnet holder  1204 . A hub  1222  is provided to mate with the first gear  1208  and the magnet holder  1204 . The second gear  1210  and third gear  1212  coupled to shaft  1214  also are shown. 
       FIG. 12  is a diagram of a position sensor  1200  for an absolute positioning system  1100  comprising a magnetic rotary absolute positioning system according to one aspect of this disclosure. The position sensor  1200  may be implemented as an AS5055EQFT single-chip magnetic rotary position sensor available from Austria Microsystems, AG. The position sensor  1200  is interfaced with the controller  1104  to provide an absolute positioning system  1100 . The position sensor  1200  is a low-voltage and low-power component and includes four Hall-effect elements  1228 A,  1228 B,  1228 C,  1228 D in an area  1230  of the position sensor  1200  that is located above the magnet  1202  ( FIGS. 15 and 16 ). A high resolution ADC  1232  and a smart power management controller  1238  are also provided on the chip. A CORDIC processor  1236  (for Coordinate Rotation Digital Computer), also known as the digit-by-digit method and Volder&#39;s algorithm, is provided to implement a simple and efficient algorithm to calculate hyperbolic and trigonometric functions that require only addition, subtraction, bitshift, and table lookup operations. The angle position, alarm bits, and magnetic field information are transmitted over a standard serial communication interface such as an SPI interface  1234  to the controller  1104 . The position sensor  1200  provides 12 or 14 bits of resolution. The position sensor  1200  may be an AS5055 chip provided in a small QFN 16-pin 4×4×0.85 mm package. 
     The Hall-effect elements  1228 A,  1228 B,  1228 C,  1228 D are located directly above the rotating magnet  1202  ( FIG. 11 ). The Hall-effect is a well-known effect and for expediency will not be described in detail herein, however, generally, the Hall-effect produces a voltage difference (the Hall voltage) across an electrical conductor transverse to an electric current in the conductor and a magnetic field perpendicular to the current. A Hall coefficient is defined as the ratio of the induced electric field to the product of the current density and the applied magnetic field. It is a characteristic of the material from which the conductor is made, since its value depends on the type, number, and properties of the charge carriers that constitute the current. In the AS5055 position sensor  1200 , the Hall-effect elements  1228 A,  1228 B,  1228 C,  1228 D are capable producing a voltage signal that is indicative of the absolute position of the magnet  1202  in terms of the angle over a single revolution of the magnet  1202 . This value of the angle, which is unique position signal, is calculated by the CORDIC processor  1236  is stored onboard the AS5055 position sensor  1200  in a register or memory. The value of the angle that is indicative of the position of the magnet  1202  over one revolution is provided to the controller  1104  in a variety of techniques, e.g., upon power up or upon request by the controller  1104 . 
     The AS5055 position sensor  1200  requires only a few external components to operate when connected to the controller  1104 . Six wires are needed for a simple application using a single power supply: two wires for power and four wires  1240  for the SPI interface  1234  with the controller  1104 . A seventh connection can be added in order to send an interrupt to the controller  1104  to inform that a new valid angle can be read. Upon power-up, the AS5055 position sensor  1200  performs a full power-up sequence including one angle measurement. The completion of this cycle is indicated as an INT output  1242 , and the angle value is stored in an internal register. Once this output is set, the AS5055 position sensor  1200  suspends to sleep mode. The controller  1104  can respond to the INT request at the INT output  1242  by reading the angle value from the AS5055 position sensor  1200  over the SPI interface  1234 . Once the angle value is read by the controller  1104 , the INT output  1242  is cleared again. Sending a “read angle” command by the SPI interface  1234  by the controller  1104  to the position sensor  1200  also automatically powers up the chip and starts another angle measurement. As soon as the controller  1104  has completed reading of the angle value, the INT output  1242  is cleared and a new result is stored in the angle register. The completion of the angle measurement is again indicated by setting the INT output  1242  and a corresponding flag in the status register. 
     Due to the measurement principle of the AS5055 position sensor  1200 , only a single angle measurement is performed in very short time (˜600 μs) after each power-up sequence. As soon as the measurement of one angle is completed, the AS5055 position sensor  1200  suspends to power-down state. An on-chip filtering of the angle value by digital averaging is not implemented, as this would require more than one angle measurement and, consequently, a longer power-up time that is not desired in low-power applications. The angle jitter can be reduced by averaging of several angle samples in the controller  1104 . For example, an averaging of four samples reduces the jitter by 6 dB (50%). 
       FIG. 13  is a section view of an end effector  2502  of the surgical instrument  10  ( FIGS. 1-4 ) showing an I-beam  2514  firing stroke relative to tissue  2526  grasped within the end effector  2502  according to one aspect of this disclosure. The end effector  2502  is configured to operate with the surgical instrument  10  shown in  FIGS. 1-4 . The end effector  2502  comprises an anvil  2516  and an elongated channel  2503  with a staple cartridge  2518  positioned in the elongated channel  2503 . A firing bar  2520  is translatable distally and proximally along a longitudinal axis  2515  of the end effector  2502 . When the end effector  2502  is not articulated, the end effector  2502  is in line with the shaft of the instrument. An I-beam  2514  comprising a cutting edge  2509  is illustrated at a distal portion of the firing bar  2520 . A wedge sled  2513  is positioned in the staple cartridge  2518 . As the I-beam  2514  translates distally, the cutting edge  2509  contacts and may cut tissue  2526  positioned between the anvil  2516  and the staple cartridge  2518 . Also, the I-beam  2514  contacts the wedge sled  2513  and pushes it distally, causing the wedge sled  2513  to contact staple drivers  2511 . The staple drivers  2511  may be driven up into staples  2505 , causing the staples  2505  to advance through tissue and into pockets  2507  defined in the anvil  2516 , which shape the staples  2505 . 
     An example I-beam  2514  firing stroke is illustrated by a chart  2529  aligned with the end effector  2502 . Example tissue  2526  is also shown aligned with the end effector  2502 . The firing member stroke may comprise a stroke begin position  2527  and a stroke end position  2528 . During an I-beam  2514  firing stroke, the I-beam  2514  may be advanced distally from the stroke begin position  2527  to the stroke end position  2528 . The I-beam  2514  is shown at one example location of a stroke begin position  2527 . The I-beam  2514  firing member stroke chart  2529  illustrates five firing member stroke regions  2517 ,  2519 ,  2521 ,  2523 ,  2525 . In a first firing stroke region  2517 , the I-beam  2514  may begin to advance distally. In the first firing stroke region  2517 , the I-beam  2514  may contact the wedge sled  2513  and begin to move it distally. While in the first region, however, the cutting edge  2509  may not contact tissue and the wedge sled  2513  may not contact a staple driver  2511 . After static friction is overcome, the force to drive the I-beam  2514  in the first region  2517  may be substantially constant. 
     In the second firing member stroke region  2519 , the cutting edge  2509  may begin to contact and cut tissue  2526 . Also, the wedge sled  2513  may begin to contact staple drivers  2511  to drive staples  2505 . Force to drive the I-beam  2514  may begin to ramp up. As shown, tissue encountered initially may be compressed and/or thinner because of the way that the anvil  2516  pivots relative to the staple cartridge  2518 . In the third firing member stroke region  2521 , the cutting edge  2509  may continuously contact and cut tissue  2526  and the wedge sled  2513  may repeatedly contact staple drivers  2511 . Force to drive the I-beam  2514  may plateau in the third region  2521 . By the fourth firing stroke region  2523 , force to drive the I-beam  2514  may begin to decline. For example, tissue in the portion of the end effector  2502  corresponding to the fourth firing region  2523  may be less compressed than tissue closer to the pivot point of the anvil  2516 , requiring less force to cut. Also, the cutting edge  2509  and wedge sled  2513  may reach the end of the tissue  2526  while in the fourth region  2523 . When the I-beam  2514  reaches the fifth region  2525 , the tissue  2526  may be completely severed. The wedge sled  2513  may contact one or more staple drivers  2511  at or near the end of the tissue. Force to advance the I-beam  2514  through the fifth region  2525  may be reduced and, in some examples, may be similar to the force to drive the I-beam  2514  in the first region  2517 . At the conclusion of the firing member stroke, the I-beam  2514  may reach the stroke end position  2528 . The positioning of firing member stroke regions  2517 ,  2519 ,  2521 ,  2523 ,  2525  in  FIG. 18  is just one example. In some examples, different regions may begin at different positions along the end effector longitudinal axis  2515 , for example, based on the positioning of tissue between the anvil  2516  and the staple cartridge  2518 . 
     As discussed above and with reference now to  FIGS. 10-13 , the electric motor  1122  positioned within the handle assembly of the surgical instrument  10  ( FIGS. 1-4 ) can be utilized to advance and/or retract the firing system of the shaft assembly, including the I-beam  2514 , relative to the end effector  2502  of the shaft assembly in order to staple and/or incise tissue captured within the end effector  2502 . The I-beam  2514  may be advanced or retracted at a desired speed, or within a range of desired speeds. The controller  1104  may be configured to control the speed of the I-beam  2514 . The controller  1104  may be configured to predict the speed of the I-beam  2514  based on various parameters of the power supplied to the electric motor  1122 , such as voltage and/or current, for example, and/or other operating parameters of the electric motor  1122  or external influences. The controller  1104  may be configured to predict the current speed of the I-beam  2514  based on the previous values of the current and/or voltage supplied to the electric motor  1122 , and/or previous states of the system like velocity, acceleration, and/or position. The controller  1104  may be configured to sense the speed of the I-beam  2514  utilizing the absolute positioning sensor system described herein. The controller can be configured to compare the predicted speed of the I-beam  2514  and the sensed speed of the I-beam  2514  to determine whether the power to the electric motor  1122  should be increased in order to increase the speed of the I-beam  2514  and/or decreased in order to decrease the speed of the I-beam  2514 . Further regarding surgical instruments  10  driven by an electric motor  1122  may be found in U.S. Pat. No. 8,210,411, entitled MOTOR-DRIVEN SURGICAL CUTTING INSTRUMENT, which is hereby incorporated herein by reference in its entirety. Further detail regarding surgical instruments  10  including sensor arrangements may be found in U.S. Pat. No. 7,845,537, entitled SURGICAL INSTRUMENT HAVING RECORDING CAPABILITIES, which is hereby incorporated herein by reference in its entirety. 
     Force acting on the I-beam  2514  may be determined using various techniques. The I-beam  2514  force may be determined by measuring the motor  2504  current, where the motor  2504  current is based on the load experienced by the I-beam  2514  as it advances distally. The I-beam  2514  force may be determined by positioning a strain gauge on the drive member  120  ( FIG. 2 ), the firing member  220  ( FIG. 2 ), I-beam  2514  (I-beam  178 ,  FIG. 20 ), the firing bar  172  ( FIG. 2 ), and/or on a proximal end of the cutting edge  2509 . The I-beam  2514  force may be determined by monitoring the actual position of the I-beam  2514  moving at an expected velocity based on the current set velocity of the motor  2504  after a predetermined elapsed period T 1  and comparing the actual position of the I-beam  2514  relative to the expected position of the I-beam  2514  based on the current set velocity of the motor  2504  at the end of the period T 1 . Thus, if the actual position of the I-beam  2514  is less than the expected position of the I-beam  2514 , the force on the I-beam  2514  is greater than a nominal force. Conversely, if the actual position of the I-beam  2514  is greater than the expected position of the I-beam  2514 , the force on the I-beam  2514  is less than the nominal force. The difference between the actual and expected positions of the I-beam  2514  is proportional to the deviation of the force on the I-beam  2514  from the nominal force. Such techniques are described in U.S. patent application Ser. No. 15/628,075, entitled SYSTEMS AND METHODS FOR CONTROLLING MOTOR VELOCITY OF A SURGICAL STAPLING AND CUTTING INSTRUMENT, which is hereby incorporated herein by reference in its entirety. 
       FIG. 14  illustrates a block diagram of a surgical instrument  2500  programmed to control distal translation of a displacement member according to one aspect of this disclosure. In one aspect, the surgical instrument  2500  is programmed to control distal translation of a displacement member  1111  such as the I-beam  2514 . The surgical instrument  2500  comprises an end effector  2502  that may comprise an anvil  2516 , an I-beam  2514  (including a sharp cutting edge  2509 ), and a removable staple cartridge  2518 . The end effector  2502 , anvil  2516 , I-beam  2514 , and staple cartridge  2518  may be configured as described herein, for example, with respect to  FIGS. 1-13 . 
     The position, movement, displacement, and/or translation of a liner displacement member  1111 , such as the I-beam  2514 , can be measured by the absolute positioning system  1100 , sensor arrangement  1102 , and position sensor  1200  as shown in  FIGS. 10-12  and represented as position sensor  2534  in  FIG. 14 . Because the I-beam  2514  is coupled to the longitudinally movable drive member  120 , the position of the I-beam  2514  can be determined by measuring the position of the longitudinally movable drive member  120  employing the position sensor  2534 . Accordingly, in the following description, the position, displacement, and/or translation of the I-beam  2514  can be achieved by the position sensor  2534  as described herein. A control circuit  2510 , such as the control circuit  700  described in  FIGS. 5A and 5B , may be programmed to control the translation of the displacement member  1111 , such as the I-beam  2514 , as described in connection with  FIGS. 10-12 . The control circuit  2510 , in some examples, may comprise one or more microcontrollers, microprocessors, or other suitable processors for executing instructions that cause the processor or processors to control the displacement member, e.g., the I-beam  2514 , in the manner described. In one aspect, a timer/counter circuit  2531  provides an output signal, such as elapsed time or a digital count, to the control circuit  2510  to correlate the position of the I-beam  2514  as determined by the position sensor  2534  with the output of the timer/counter circuit  2531  such that the control circuit  2510  can determine the position of the I-beam  2514  at a specific time (t) relative to a starting position. The timer/counter circuit  2531  may be configured to measure elapsed time, count external evens, or time external events. 
     The control circuit  2510  may generate a motor set point signal  2522 . The motor set point signal  2522  may be provided to a motor controller  2508 . The motor controller  2508  may comprise one or more circuits configured to provide a motor drive signal  2524  to the motor  2504  to drive the motor  2504  as described herein. In some examples, the motor  2504  may be a brushed DC electric motor, such as the motor  82 ,  714 ,  1120  shown in  FIGS. 1, 5B, 10 . For example, the velocity of the motor  2504  may be proportional to the motor drive signal  2524 . In some examples, the motor  2504  may be a brushless direct current (DC) electric motor and the motor drive signal  2524  may comprise a pulse-width-modulated (PWM) signal provided to one or more stator windings of the motor  2504 . Also, in some examples, the motor controller  2508  may be omitted and the control circuit  2510  may generate the motor drive signal  2524  directly. 
     The motor  2504  may receive power from an energy source  2512 . The energy source  2512  may be or include a battery, a super capacitor, or any other suitable energy source  2512 . The motor  2504  may be mechanically coupled to the I-beam  2514  via a transmission  2506 . The transmission  2506  may include one or more gears or other linkage components to couple the motor  2504  to the I-beam  2514 . A position sensor  2534  may sense a position of the I-beam  2514 . The position sensor  2534  may be or include any type of sensor that is capable of generating position data that indicates a position of the I-beam  2514 . In some examples, the position sensor  2534  may include an encoder configured to provide a series of pulses to the control circuit  2510  as the I-beam  2514  translates distally and proximally. The control circuit  2510  may track the pulses to determine the position of the I-beam  2514 . Other suitable position sensor may be used, including, for example, a proximity sensor. Other types of position sensors may provide other signals indicating motion of the I-beam  2514 . Also, in some examples, the position sensor  2534  may be omitted. Where the motor  2504  is a stepper motor, the control circuit  2510  may track the position of the I-beam  2514  by aggregating the number and direction of steps that the motor  2504  has been instructed to execute. The position sensor  2534  may be located in the end effector  2502  or at any other portion of the instrument. 
     The control circuit  2510  may be in communication with one or more sensors  2538 . The sensors  2538  may be positioned on the end effector  2502  and adapted to operate with the surgical instrument  2500  to measure the various derived parameters such as gap distance versus time, tissue compression versus time, and anvil strain versus time. The sensors  2538  may comprise a magnetic sensor, a magnetic field sensor, a strain gauge, a pressure sensor, a force sensor, an inductive sensor such as an eddy current sensor, a resistive sensor, a capacitive sensor, an optical sensor, and/or any other suitable sensor for measuring one or more parameters of the end effector  2502 . The sensors  2538  may include one or more sensors. 
     The one or more sensors  2538  may comprise a strain gauge, such as a micro-strain gauge, configured to measure the magnitude of the strain in the anvil  2516  during a clamped condition. The strain gauge provides an electrical signal whose amplitude varies with the magnitude of the strain. The sensors  2538  may comprise a pressure sensor configured to detect a pressure generated by the presence of compressed tissue between the anvil  2516  and the staple cartridge  2518 . The sensors  2538  may be configured to detect impedance of a tissue section located between the anvil  2516  and the staple cartridge  2518  that is indicative of the thickness and/or fullness of tissue located therebetween. 
     The sensors  2538  may be is configured to measure forces exerted on the anvil  2516  by the closure drive system  30 . For example, one or more sensors  2538  can be at an interaction point between the closure tube  260  ( FIG. 3 ) and the anvil  2516  to detect the closure forces applied by the closure tube  260  to the anvil  2516 . The forces exerted on the anvil  2516  can be representative of the tissue compression experienced by the tissue section captured between the anvil  2516  and the staple cartridge  2518 . The one or more sensors  2538  can be positioned at various interaction points along the closure drive system  30  ( FIG. 2 ) to detect the closure forces applied to the anvil  2516  by the closure drive system  30 . The one or more sensors  2538  may be sampled in real time during a clamping operation by a processor as described in  FIGS. 5A-5B . The control circuit  2510  receives real-time sample measurements to provide analyze time based information and assess, in real time, closure forces applied to the anvil  2516 . 
     A current sensor  2536  can be employed to measure the current drawn by the motor  2504 . The force required to advance the I-beam  2514  corresponds to the current drawn by the motor  2504 . The force is converted to a digital signal and provided to the control circuit  2510 . 
     Using the physical properties of the instruments disclosed herein in connection with  FIGS. 1-13 , and with reference to  FIG. 14 , the control circuit  2510  can be configured to simulate the response of the actual system of the instrument in the software of the controller. A displacement member can be actuated to move an I-beam  2514  in the end effector  2502  at or near a target velocity. The surgical instrument  2500  can include a feedback controller, which can be one of any feedback controllers, including, but not limited to a PID, a State Feedback, LQR, and/or an Adaptive controller, for example. The surgical instrument  2500  can include a power source to convert the signal from the feedback controller into a physical input such as case voltage, pulse width modulated (PWM) voltage, frequency modulated voltage, current, torque, and/or force, for example. 
     The actual drive system of the surgical instrument  2500  is configured to drive the displacement member, cutting member, or I-beam  2514 , by a brushed DC motor with gearbox and mechanical links to an articulation and/or knife system. Another example is the electric motor  2504  that operates the displacement member and the articulation driver, for example, of an interchangeable shaft assembly. An outside influence is an unmeasured, unpredictable influence of things like tissue, surrounding bodies and friction on the physical system. Such outside influence can be referred to as drag which acts in opposition to the electric motor  2504 . The outside influence, such as drag, may cause the operation of the physical system to deviate from a desired operation of the physical system. 
     Before explaining aspects of the surgical instrument  2500  in detail, it should be noted that the example aspects are not limited in application or use to the details of construction and arrangement of parts illustrated in the accompanying drawings and description. The example aspects may be implemented or incorporated in other aspects, variations and modifications, and may be practiced or carried out in various ways. Further, unless otherwise indicated, the terms and expressions employed herein have been chosen for the purpose of describing the example aspects for the convenience of the reader and are not for the purpose of limitation thereof. Also, it will be appreciated that one or more of the following-described aspects, expressions of aspects and/or examples, can be combined with any one or more of the other following-described aspects, expressions of aspects and/or examples. 
     Various example aspects are directed to a surgical instrument  2500  comprising an end effector  2502  with motor-driven surgical stapling and cutting implements. For example, a motor  2504  may drive a displacement member distally and proximally along a longitudinal axis of the end effector  2502 . The end effector  2502  may comprise a pivotable anvil  2516  and, when configured for use, a staple cartridge  2518  positioned opposite the anvil  2516 . A clinician may grasp tissue between the anvil  2516  and the staple cartridge  2518 , as described herein. When ready to use the instrument  2500 , the clinician may provide a firing signal, for example by depressing a trigger of the instrument  2500 . In response to the firing signal, the motor  2504  may drive the displacement member distally along the longitudinal axis of the end effector  2502  from a proximal stroke begin position to a stroke end position distal of the stroke begin position. As the displacement member translates distally, an I-beam  2514  with a cutting element positioned at a distal end, may cut the tissue between the staple cartridge  2518  and the anvil  2516 . 
     In various examples, the surgical instrument  2500  may comprise a control circuit  2510  programmed to control the distal translation of the displacement member, such as the I-beam  2514 , for example, based on one or more tissue conditions. The control circuit  2510  may be programmed to sense tissue conditions, such as thickness, either directly or indirectly, as described herein. The control circuit  2510  may be programmed to select a firing control program based on tissue conditions. A firing control program may describe the distal motion of the displacement member. Different firing control programs may be selected to better treat different tissue conditions. For example, when thicker tissue is present, the control circuit  2510  may be programmed to translate the displacement member at a lower velocity and/or with lower power. When thinner tissue is present, the control circuit  2510  may be programmed to translate the displacement member at a higher velocity and/or with higher power. 
     In some examples, the control circuit  2510  may initially operate the motor  2504  in an open loop configuration for a first open loop portion of a stroke of the displacement member. Based on a response of the instrument  2500  during the open loop portion of the stroke, the control circuit  2510  may select a firing control program. The response of the instrument may include, a translation distance of the displacement member during the open loop portion, a time elapsed during the open loop portion, energy provided to the motor  2504  during the open loop portion, a sum of pulse widths of a motor drive signal, etc. After the open loop portion, the control circuit  2510  may implement the selected firing control program for a second portion of the displacement member stroke. For example, during the closed loop portion of the stroke, the control circuit  2510  may modulate the motor  2504  based on translation data describing a position of the displacement member in a closed loop manner to translate the displacement member at a constant velocity. 
       FIG. 15  illustrates a diagram  2580  plotting two example displacement member strokes executed according to one aspect of this disclosure. The diagram  2580  comprises two axes. A horizontal axis  2584  indicates elapsed time. A vertical axis  2582  indicates the position of the I-beam  2514  between a stroke begin position  2586  and a stroke end position  2588 . On the horizontal axis  2584 , the control circuit  2510  may receive the firing signal and begin providing the initial motor setting at t 0 . The open loop portion of the displacement member stroke is an initial time period that may elapse between t 0  and t 1 . 
     A first example  2592  shows a response of the surgical instrument  2500  when thick tissue is positioned between the anvil  2516  and the staple cartridge  2518 . During the open loop portion of the displacement member stroke, e.g., the initial time period between t 0  and t 1 , the I-beam  2514  may traverse from the stroke begin position  2586  to position  2594 . The control circuit  2510  may determine that position  2594  corresponds to a firing control program that advances the I-beam  2514  at a selected constant velocity (V slow ), indicated by the slope of the example  2592  after t 1  (e.g., in the closed loop portion). The control circuit  2510  may drive I-beam  2514  to the velocity V slow  by monitoring the position of I-beam  2514  and modulating the motor set point signal  2522  and/or motor drive signal  2524  to maintain V slow . 
     A second example  2590  shows a response of the surgical instrument  2500  when thin tissue is positioned between the anvil  2516  and the staple cartridge  2518 . During the initial time period (e.g., the open loop period) between t 0  and t 1 , the I-beam  2514  may traverse from the stroke begin position  2586  to position  2596 . The control circuit may determine that position  2596  corresponds to a firing control program that advances the displacement member at a selected constant velocity (V fast ). Because the tissue in example  2590  is thinner than the tissue in example  2592 , it may provide less resistance to the motion of the I-beam  2514 . As a result, the I-beam  2514  may traverse a larger portion of the stroke during the initial time period. Also, in some examples, thinner tissue (e.g., a larger portion of the displacement member stroke traversed during the initial time period) may correspond to higher displacement member velocities after the initial time period. 
       FIGS. 16-21  illustrate an end effector  2300  of a surgical instrument  2010  showing how the end effector  2300  may be articulated relative to the elongate shaft assembly  2200  about an articulation joint  2270  according to one aspect of this disclosure.  FIG. 16  is a partial perspective view of a portion of the end effector  2300  showing an elongate shaft assembly  2200  in an unarticulated orientation with portions thereof omitted for clarity.  FIG. 17  is a perspective view of the end effector  2300  of  FIG. 16  showing the elongate shaft assembly  2200  in an unarticulated orientation.  FIG. 18  is an exploded assembly perspective view of the end effector  2300  of  FIG. 16  showing the elongate shaft assembly  2200 .  FIG. 19  is a top view of the end effector  2300  of  FIG. 16  showing the elongate shaft assembly  2200  in an unarticulated orientation.  FIG. 20  is a top view of the end effector  2300  of  FIG. 16  showing the elongate shaft assembly  2200  in a first articulated orientation.  FIG. 21  is a top view of the end effector  2300  of  FIG. 16  showing the elongate shaft assembly  2200  in a second articulated orientation. 
     With reference now to  FIGS. 16-21 , the end effector  2300  is adapted to cut and staple tissue and includes a first jaw in the form of an elongated channel  2302  that is configured to operably support a surgical staple cartridge  2304  therein. The end effector  2300  further includes a second jaw in the form of an anvil  2310  that is supported on the elongated channel  2302  for movement relative thereto. The elongate shaft assembly  2200  includes an articulation system  2800  that employs an articulation lock  2810 . The articulation lock  2810  can be configured and operated to selectively lock the surgical end effector  2300  in various articulated positions. Such arrangement enables the surgical end effector  2300  to be rotated, or articulated, relative to the shaft closure tube  260  when the articulation lock  2810  is in its unlocked state. Referring specifically to  FIG. 18 , the elongate shaft assembly  2200  includes a spine  210  that is configured to (1) slidably support a firing member  220  therein and, (2) slidably support the closure tube  260  ( FIG. 16 ), which extends around the spine  210 . The shaft closure tube  260  is attached to an end effector closure sleeve  272  that is pivotally attached to the closure tube  260  by a double pivot closure sleeve assembly  271 . 
     The spine  210  also slidably supports a proximal articulation driver  230 . The proximal articulation driver  230  has a distal end  231  that is configured to operably engage the articulation lock  2810 . The articulation lock  2810  further comprises a shaft frame  2812  that is attached to the spine  210  in the various manners disclosed herein. The shaft frame  2812  is configured to movably support a proximal portion  2821  of a distal articulation driver  2820  therein. The distal articulation driver  2820  is movably supported within the elongate shaft assembly  2200  for selective longitudinal travel in a distal direction DD and a proximal direction PD along an articulation actuation axis AAA that is laterally offset and parallel to the shaft axis SA-SA in response to articulation control motions applied thereto. 
     In  FIGS. 17 and 18 , the shaft frame  2812  includes a distal end portion  2814  that has a pivot pin  2818  formed thereon. The pivot pin  2818  is adapted to be pivotally received within a pivot hole  2397  formed in pivot base portion  2395  of an end effector mounting assembly  2390 . The end effector mounting assembly  2390  is attached to the proximal end  2303  of the elongated channel  2302  by a spring pin  2393  or equivalent. The pivot pin  2818  defines an articulation axis B-B transverse to the shaft axis SA-SA to facilitate pivotal travel (i.e., articulation) of the end effector  2300  about the articulation axis B-B relative to the shaft frame  2812 . 
     As shown in  FIG. 18 , a link pin  2825  is formed on a distal end  2823  of the distal articulation driver  2820  and is configured to be received within a hole  2904  in a proximal end  2902  of a cross link  2900 . The cross link  2900  extends transversely across the shaft axis SA-SA and includes a distal end portion  2906 . A distal link hole  2908  is provided through the distal end portion  2906  of the cross link  2900  and is configured to pivotally receive therein a base pin  2398  extending from the bottom of the pivot base portion  2395  of the end effector mounting assembly  2390 . The base pin  2398  defines a link axis LA that is parallel to the articulation axis B-B.  FIGS. 17 and 20  illustrate the surgical end effector  2300  in an unarticulated position. The end effector axis EA is defined by the elongated channel  2302  is aligned with the shaft axis SA-SA. The term “aligned with” may mean “coaxially aligned” with the shaft axis SA-SA or parallel with the shaft axis SA-SA. Movement of the distal articulation driver  2820  in the proximal direction PD will cause the cross link  2900  to draw the surgical end effector  2300  in a clockwise CW direction about the articulation axis B-B as shown in  FIG. 19 . Movement of the distal articulation driver  2820  in the distal direction DD will cause the cross link  2900  to move the surgical end effector  2300  in the counterclockwise CCW direction about the articulation axis B-B as shown in  FIG. 21 . As shown in  FIG. 21 , the cross link  2900  has a curved shape that permits the cross link  2900  to curve around the pivot pin  2818  when the surgical end effector  2300  is articulated in that direction. When the surgical end effector  2300  is in a fully articulated position on either side of the shaft axis SA-SA, the articulation angle  2700  between the end effector axis EA and the shaft axis SA-SA is approximately sixty-five degrees (65°). Thus, the range of articulation on either said of the shaft axis is from one degree (1°) to sixty-five degrees) (65°). 
       FIG. 19  shows the articulation joint  2270  in a straight position, i.e., at a zero angle θ 0  relative to the longitudinal direction depicted as shaft axis SA, according to one aspect.  FIG. 20  shows the articulation joint  2270  of  FIG. 19  articulated in one direction at a first angle θ 1  defined between the shaft axis SA and the end effector axis EA, according to one aspect.  FIG. 21  illustrates the articulation joint  2270  of  FIG. 19  articulated in another direction at a second angle θ 2  defined between the shaft axis SA and the end effector axis EA. 
     The surgical end effector  2300  in  FIGS. 16-21  comprises a surgical cutting and stapling device that employs a firing member  220  of the various types and configurations described herein. However, the surgical end effector  2300  may comprise other forms of surgical end effectors that do not cut and/or staple tissue. A middle support member  2950  is pivotally and slidably supported relative to the spine  210 . In  FIG. 18 , the middle support member  2950  includes a slot  2952  that is adapted to receive therein a pin  2954  that protrudes from the spine  210 . This enables the middle support member  2950  to pivot and translate relative to the pin  2954  when the surgical end effector  2300  is articulated. A pivot pin  2958  protrudes from the underside of the middle support member  2950  to be pivotally received within a corresponding pivot hole  2399  provided in the base portion  2395  of the end effector mounting assembly  2390 . The middle support member  2950  further includes a slot  2960  for receiving a firing member  220  there through. The middle support member  2950  serves to provide lateral support to the firing member  220  as it flexes to accommodate articulation of the surgical end effector  2300 . 
     The surgical instrument can additionally be configured to determine the angle at which the end effector  2300  is oriented. In various aspects, the position sensor  1112  of the sensor arrangement  1102  may comprise one or more magnetic sensors, analog rotary sensors (such as potentiometers), arrays of analog Hall effect sensors, which output a unique combination of position signals or values, among others, for example. In one aspect, the articulation joint  2270  of the aspect illustrated in  FIGS. 16-21  can additionally comprise an articulation sensor arrangement that is configured to determine the angular position, i.e., articulation angle, of the end effector  2300  and provide a unique position signal corresponding thereto. 
     The articulation sensor arrangement can be similar to the sensor arrangement  1102  described above and illustrated in  FIGS. 10-12 . In this aspect, the articulation sensor arrangement can comprise a position sensor and a magnet that is operatively coupled to the articulation joint  2270  such that it rotates in a manner consistent with the rotation of the articulation joint  2270 . The magnet can, for example, be coupled to the pivot pin  2818 . The position sensor comprises one or more magnetic sensing elements, such as Hall effect sensors, and is placed in proximity to the magnet, either within or adjacent to the articulation joint  2270 . Accordingly, as the magnet rotates, the magnetic sensing elements of the position sensor determine the magnet&#39;s absolute angular position. As the magnet is coupled to the articulation joint  2270 , the angular position of the magnet with respect to the position sensor corresponds to the angular position of the end effector  2300 . Therefore, the articulation sensor arrangement is able to determine the angular position of the end effector as the end effector articulates. 
     In another aspect, the surgical instrument is configured to determine the angle at which the end effector  2300  is positioned in an indirect manner by monitoring the absolute position of the articulation driver  230  ( FIG. 3 ). As the position of the articulation driver  230  corresponds to the angle at which the end effector  2300  is oriented in a known manner, the absolute position of the articulation driver  230  can be tracked and then translated to the angular position of the end effector  2300 . In this aspect, the surgical instrument comprises an articulation sensor arrangement that is configured to determine the absolute linear position of the articulation driver  230  and provide a unique position signal corresponding thereto. In some aspects, the articulation sensor arrangement or the controller operably coupled to the articulation sensor arrangement is configured additionally to translate or calculate the angular position of the end effector  2300  from the unique position signal. 
     The articulation sensor arrangement in this aspect can likewise be similar to the sensor arrangement  1102  described above and illustrated in  FIGS. 10-12 . In one aspect similar to the aspect illustrated in  FIG. 10  with respect to the displacement member  1111 , the articulation sensor arrangement comprises a position sensor and a magnet that turns once every full stroke of the longitudinally-movable articulation driver  230 . The position sensor comprises one or more magnetic sensing elements, such as Hall effect sensors, and is placed in proximity to the magnet. Accordingly, as the magnet rotates, the magnetic sensing elements of the position sensor determine the absolute angular position of the magnet over one revolution. 
     In one aspect, a single revolution of a sensor element associated with the position sensor is equivalent to a longitudinal linear displacement d 1  of the of the longitudinally-movable articulation driver  230 . In other words, d 1  is the longitudinal linear distance that the longitudinally-movable articulation driver  230  moves from point “a” to point “b” after a single revolution of a sensor element coupled to the longitudinally-movable articulation driver  230 . The articulation sensor arrangement may be connected via a gear reduction that results in the position sensor completing only one revolution for the full stroke of the longitudinally-movable articulation driver  230 . In other words, d 1  can be equal to the full stroke of the articulation driver  230 . The position sensor is configured to then transmit a unique position signal corresponding to the absolute position of the articulation driver  230  to the controller  1104 , such as in those aspects depicted in  FIG. 10  Upon receiving the unique position signal, the controller  1104  is then configured execute a logic to determine the angular position of the end effector corresponding to the linear position of the articulation driver  230  by, for example, querying a lookup table that returns the value of the pre-calculated angular position of the end effector  2300 , calculating via an algorithm the angular position of the end effector  2300  utilizing the linear position of the articulation driver  230  as the input, or performing any other such method as is known in the field. 
     In various aspects, any number of magnetic sensing elements may be employed on the articulation sensor arrangement, such as, for example, magnetic sensors classified according to whether they measure the total magnetic field or the vector components of the magnetic field. The number of magnetic sensing elements utilized corresponds to the desired resolution to be sensed by the articulation sensor arrangement. In other words, the larger number of magnetic sensing elements used, the finer degree of articulation that can be sensed by the articulation sensor arrangement. The techniques used to produce both types of magnetic sensors encompass many aspects of physics and electronics. The technologies used for magnetic field sensing include search coil, fluxgate, optically pumped, nuclear precession, SQUID, Hall-effect, anisotropic magnetoresistance, giant magnetoresistance, magnetic tunnel junctions, giant magnetoimpedance, magnetostrictive/piezoelectric composites, magnetodiode, magnetotransistor, fiber optic, magnetooptic, and microelectromechanical systems-based magnetic sensors, among others. 
     In one aspect, the position sensor of the various aspects of the articulation sensor arrangement may be implemented in a manner similar to the positioning system illustrated in  FIG. 12  for tracking the position of the displacement member  1111 . In one such aspect, the articulation sensor arrangement may be implemented as an AS5055EQFT single-chip magnetic rotary position sensor available from Austria Microsystems, AG. The position sensor is interfaced with the controller to provide an absolute positioning system for determining the absolute angular position of the end effector  2300 , either directly or indirectly. The position sensor is a low voltage and low power component and includes four Hall-effect elements  1228 A,  1228 B,  1228 C,  1228 D in an area  1230  of the position sensor  1200  that is located above the magnet  1202  ( FIG. 11 ). A high resolution ADC  1232  and a smart power management controller  1238  are also provided on the chip. A CORDIC processor  1236  (for Coordinate Rotation Digital Computer), also known as the digit-by-digit method and Volder&#39;s algorithm, is provided to implement a simple and efficient algorithm to calculate hyperbolic and trigonometric functions that require only addition, subtraction, bitshift, and table lookup operations. The angle position, alarm bits and magnetic field information are transmitted over a standard serial communication interface such as an SPI interface  1234  to the controller  1104 . The position sensor  1200  provides 12 or 14 bits of resolution. The position sensor  1200  may be an AS5055 chip provided in a small QFN 16-pin 4×4×0.85 mm package. 
     With reference to  FIGS. 1-4 and 10-12 , the position of the articulation joint  2270  and the position of the I-beam  178  ( FIG. 4 ) can be determined with the absolute position feedback signal/value from the absolute positioning system  1100 . In one aspect, the articulation angle can be determined based on the drive member  120  of the surgical instrument  10 . As described above, the movement of the longitudinally movable drive member  120  ( FIG. 2 ) can be tracked by the absolute positioning system  1100  wherein, when the articulation drive is operably coupled to the firing member  220  ( FIG. 3 ) by the clutch assembly  400  ( FIG. 3 ), for example, the absolute positioning system  1100  can, in effect, track the movement of the articulation system via the drive member  120 . As a result of tracking the movement of the articulation system, the controller of the surgical instrument can track the articulation angle θ of the end effector  2300 . In various circumstances, as a result, the articulation angle θ can be determined as a function of longitudinal displacement of the drive member  120 . Since the longitudinal displacement of the drive member  120  can be precisely determined based on the absolute position signal/value provided by the absolute positioning system  1100 , the articulation angle θ can be determined as a function of longitudinal displacement. 
     In another aspect, the articulation angle θ can be determined by locating sensors at the articulation joint  2270 . The sensors can be configured to sense rotation of the articulation joint  2270  using the absolute positioning system  1100  in a manner adapted to measure absolute rotation of the articulation joint  2270 , rather than the longitudinal displacement of the drive member  120 , as described above. For example, the sensor arrangement  1102  comprises a position sensor  1200 , a magnet  1202 , and a magnet holder  1204  adapted to sense rotation of the articulation joint  2270 . The position sensor  1200  comprises one or more than one magnetic sensing elements such as Hall elements and is placed in proximity to the magnet  1202 . The position sensor  1200  described in  FIG. 12  can be adapted to measure the rotation angle of the articulation joint  2270 . Accordingly, as the magnet  1202  rotates, the magnetic sensing elements of the position sensor  1200  determine the absolute angular position of the magnet  1202  located on the articulation joint  2270 . This information is provided to the controller  1104  to calculate the articulation angle of the articulation joint  2270 . Accordingly, the articulation angle of the end effector  2300  can be determined by the absolute positioning system  1100  adapted to measure absolute rotation of the articulation joint  2270 . 
     In one aspect, the firing rate or velocity of the I-beam  178  may be varied as a function of end effector  2300  articulation angle to lower the force-to-fire on the firing drive system  80  and, in particular, the force-to-fire of the I-beam  178 , among other components of the firing drive system  80  discussed herein. To adapt to the variable firing force of the I-beam  178  as a function of end effector  2300  articulation angle, a variable motor control voltage can be applied to the motor  82  to control the velocity of the motor  82 . The velocity of the motor  82  may be controlled by comparing the I-beam  178  firing force to different maximum thresholds based on articulation angle of the end effector  2300 . The velocity of the electric motor  82  can be varied by adjusting the voltage, current, pulse width modulation (PWM), or duty cycle (0-100%) applied to the motor  82 , for example. 
       FIGS. 22 and 23  depict a motor-driven surgical instrument  10  that may be used to perform a variety of different surgical procedures. The surgical instrument  10  can comprise an end effector  3602 , which can comprise one or more electrodes. The end effector  3602  can be positioned against tissue such that electrical current may be introduced into the tissue. The surgical instrument  10  can be configured for monopolar or bipolar operation. During monopolar operation, current may be introduced into the tissue by an active (or source) electrode on the end effector  3602  and returned through a return electrode. The return electrode may be a grounding pad and separately located on a patient&#39;s body. During bipolar operation, current may be introduced into and returned from the tissue by the active and return electrodes, respectively, of the end effector. 
     The end effector  3602  can comprise a first jaw  3604  and a second jaw member  3608 . At least one of the jaw members  3604 ,  3608  may have at least one electrode. At least one of the jaw members  3604 ,  3608  may be moveable from a position spaced apart from the opposing jaw for receiving tissues to a position in which the space between the jaw members  3604 ,  3608  is less than that of the first position. This movement of the moveable jaw may compress the tissue held between. Heat generated by the current flow through the tissue in combination with the compression achieved by the jaw&#39;s movement may form hemostatic seals within the tissue and/or between tissues and, thus, may be particularly useful for sealing blood vessels, for example. The surgical instrument  10  may comprise a knife member  3628  that is extendable through the end effector  3602 . The knife member  3628  may be movable relative to the tissue and the electrodes to transect the tissue. 
     The surgical instrument  10  may include mechanisms to clamp tissue together, such as a stapling device, and/or mechanisms to sever tissue, such as a tissue knife. The electrosurgical instrument  10  may include a shaft for placing the end effector  3602  proximate to tissue undergoing treatment. The shaft may be straight or curved, bendable or non-bendable. In an electrosurgical instrument  10  including a straight and bendable shaft, the shaft may have one or more articulation joints to permit controlled bending of the shaft. Such joints may permit a user of the electrosurgical instrument  10  to place the end effector in contact with tissue at an angle to the shaft when the tissue being treated is not readily accessible using an electrosurgical device having a straight, non-bending shaft. 
     Electrical energy applied by electrosurgical devices can be transmitted to the instrument by a generator  3400  in communication with the handle assembly  3500 . The electrical energy may be in the form of radio frequency (“RF”) energy. RF energy is a form of electrical energy that may be in the frequency range of 200 kilohertz (kHz) to 1 megahertz (MHz). In application, an electrosurgical instrument can transmit low frequency RF energy through tissue, which causes ionic agitation, or friction, in effect resistive heating, thereby increasing the temperature of the tissue. Because a sharp boundary is created between the affected tissue and the surrounding tissue, surgeons can operate with a high level of precision and control, without sacrificing un-targeted adjacent tissue. The low operating temperatures of RF energy is useful for removing, shrinking, or sculpting soft tissue while simultaneously sealing blood vessels. RF energy works particularly well on connective tissue, which is primarily comprised of collagen and shrinks when contacted by heat. 
     The RF energy may be in a frequency range described in EN 60601-2-2:2009+A11:2011, Definition 201.3.218—HIGH FREQUENCY. For example, the frequency in monopolar RF applications may be typically restricted to less than 5 MHz. However, in bipolar RF applications, the frequency can be almost anything. Frequencies above 200 kHz can be typically used for monopolar applications in order to avoid the unwanted stimulation of nerves and muscles that would result from the use of low frequency current. Lower frequencies may be used for bipolar applications if the risk analysis shows the possibility of neuromuscular stimulation has been mitigated to an acceptable level. Normally, frequencies above 5 MHz are not used in order to minimize the problems associated with high frequency leakage currents. Higher frequencies may, however, be used in the case of bipolar applications. It is generally recognized that 10 mA is the lower threshold of thermal effects on tissue. 
     In the illustrated arrangement, the surgical instrument  10  comprises an interchangeable surgical tool assembly  3600  that is operably coupled to a handle assembly  3500 . In another surgical system aspect, the interchangeable surgical tool assembly  3600  may also be effectively employed with a tool drive assembly of a robotically controlled or automated surgical system. For example, the surgical tool assembly  3600  disclosed herein may be employed with various robotic systems, instruments, components and methods such as, but not limited to, those disclosed in U.S. Pat. No. 9,072,535, entitled SURGICAL STAPLING INSTRUMENTS WITH ROTATABLE STAPLE DEPLOYMENT ARRANGEMENTS, which is hereby incorporated herein by reference in its entirety. 
     In the illustrated aspect, the handle assembly  3500  may comprise a handle housing  3502  that includes a pistol grip portion that can be gripped and manipulated by the clinician. As will be briefly discussed below, the handle assembly  3500  operably supports a plurality of drive systems that are configured to generate and apply various control motions to corresponding portions of the interchangeable surgical tool assembly  3600 . As shown in  FIG. 22 , the handle assembly  3500  may further include a handle frame  3506  that operably supports the plurality of drive systems. For example, the handle frame  3506  can operably support a “first” or closure drive system, generally designated as  3510 , which may be employed to apply closing and opening motions to the interchangeable surgical tool assembly  3600 . In at least one form, the closure drive system  3510  may include an actuator in the form of a closure trigger  3512  that is pivotally supported by the handle frame  3506 . Such arrangement enables the closure trigger  3512  to be manipulated by a clinician such that when the clinician grips the pistol grip portion  504  of the handle assembly  3500 , the closure trigger  3512  may be easily pivoted from a starting or “unactuated” position to an “actuated” position and more particularly to a fully compressed or fully actuated position. In use, to actuate the closure drive system  3510 , the clinician depresses the closure trigger  3512  towards the pistol grip portion. As described in further detail in U.S. Patent Application Publication No. 2015/0272575, entitled SURGICAL INSTRUMENT COMPRISING A SENSOR SYSTEM, which is hereby incorporated herein by reference in its entirety, when the clinician fully depresses the closure trigger  3512  to attain the full closure stroke, the closure drive system  3510  is configured to lock the closure trigger  3512  into the fully depressed or fully actuated position. When the clinician desires to unlock the closure trigger  3512  to permit it to be biased to the unactuated position, the clinician simply activates a closure release button assembly  3518  which enables the closure trigger to return to unactuated position. The closure release button assembly  3518  may also be configured to interact with various sensors that communicate with a microcontroller in the handle assembly  3500  for tracking the position of the closure trigger  3512 . Further details concerning the configuration and operation of the closure release button assembly  3518  may be found in U.S. Patent Application Publication No. 2015/0272575. 
     In at least one form, the handle assembly  3500  and the handle frame  3506  may operably support another drive system referred to herein as a firing drive system  3530  that is configured to apply firing motions to corresponding portions of the interchangeable surgical tool assembly that is attached thereto. As was described in detail in U.S. Patent Application Publication No. 2015/0272575, the firing drive system  3530  may employ an electric motor  3505  that is located in the pistol grip portion of the handle assembly  3500 . In various forms, the motor  3505  may be a DC brushed driving motor having a maximum rotation of, approximately, 25,000 RPM, for example. In other arrangements, the motor  3505  may include a brushless motor, a cordless motor, a synchronous motor, a stepper motor, or any other suitable electric motor. The motor  3505  may be powered by a power source  3522  that in one form may comprise a removable power pack. The power pack may support a plurality of Lithium Ion (“LI”) or other suitable batteries therein. A number of batteries may be connected in series may be used as the power source  3522  for the surgical instrument  10 . In addition, the power source  3522  may be replaceable and/or rechargeable. 
     The electric motor  3505  is configured to axially drive a longitudinally movable drive member  3540  in a distal and proximal directions depending upon the polarity of the motor. For example, when the motor  3505  is driven in one rotary direction, the longitudinally movable drive member will be axially driven in a distal direction “DD.” When the motor  3505  is driven in the opposite rotary direction, the longitudinally movable drive member  3540  will be axially driven in a proximal direction “PD.” The handle assembly  3500  can include a switch  3513  which can be configured to reverse the polarity applied to the electric motor  3505  by the power source  3522  or otherwise control the motor  3505 . The handle assembly  3500  can also include a sensor or sensors (not shown) that is configured to detect the position of the drive member and/or the direction in which the drive member is being moved. Actuation of the motor  3505  can be controlled by a firing trigger (not shown) that is adjacent to the closure trigger  3512  and pivotally supported on the handle assembly  3500 . The firing trigger may be pivoted between an unactuated position and an actuated position. The firing trigger may be biased into the unactuated position by a spring or other biasing arrangement such that when the clinician releases the firing trigger, it may be pivoted or otherwise returned to the unactuated position by the spring or biasing arrangement. In at least one form, the firing trigger can be positioned “outboard” of the closure trigger  3512 . As discussed in U.S. Patent Application Publication No. 2015/0272575, the handle assembly  3500  may be equipped with a firing trigger safety button (not shown) to prevent inadvertent actuation of the firing trigger. When the closure trigger  3512  is in the unactuated position, the safety button is contained in the handle assembly  3500  where the clinician cannot readily access it and move it between a safety position preventing actuation of the firing trigger and a firing position wherein the firing trigger may be fired. As the clinician depresses the closure trigger, the safety button and the firing trigger pivot down wherein they can then be manipulated by the clinician. 
     In at least one form, the longitudinally movable drive member  3540  may have a rack of teeth formed thereon for meshing engagement with a corresponding drive gear arrangement (not shown) that interfaces with the motor. Further details regarding those features may be found in U.S. Patent Application Publication No. 2015/0272575. In at least one arrangement, however, the longitudinally movable drive member is insulated to protect it from inadvertent RF energy. At least one form also includes a manually-actuatable “bailout” assembly that is configured to enable the clinician to manually retract the longitudinally movable drive member should the motor  3505  become disabled. The bailout assembly may include a lever or bailout handle assembly that is stored within the handle assembly  3500  under a releasable door  3550 . The lever may be configured to be manually pivoted into ratcheting engagement with the teeth in the drive member. Thus, the clinician can manually retract the drive member  3540  by using the bailout handle assembly to ratchet the drive member in the proximal direction “PD.” U.S. Pat. No. 8,608,045, entitled POWERED SURGICAL CUTTING AND STAPLING APPARATUS WITH MANUALLY RETRACTABLE FIRING SYSTEM, the entire disclosure of which is hereby incorporated herein by reference, discloses bailout arrangements and other components, arrangements and systems that may also be employed with any one of the various interchangeable surgical tool assemblies disclosed herein. 
     As shown in  FIG. 22 , in at least one arrangement, the interchangeable surgical tool assembly  3600  includes a tool frame assembly  3610  that comprises a tool chassis that operably supports a nozzle assembly  3612  thereon. As further discussed in detail in U.S. patent application Ser. No. 15/635,631, entitled SURGICAL INSTRUMENT WITH AXIALLY MOVABLE CLOSURE MEMBER, which is hereby incorporated herein by reference in its entirety, the tool chassis and nozzle assembly  3612  facilitate rotation of the surgical end effector  3602  about a shaft axis SA relative to the tool chassis. Such rotational travel is represented by arrow R in  FIG. 22 . The interchangeable surgical tool assembly  3600  includes a spine assembly  3630  (see  FIGS. 3 and 24 ) that operably supports the proximal closure tube  3622  and is coupled to the surgical end effector  3602 . In various circumstances, for ease of assembly, the spine assembly  3630  may be fabricated from an upper spine segment and a lower spine segment that are interconnected together by snap features, adhesive, welding, etc. In assembled form, the spine assembly  3630  includes a proximal end that is rotatably supported in the tool chassis. In one arrangement, for example, the proximal end of the spine assembly  3630  is attached to a spine bearing (not shown) that is configured to be supported within the tool chassis. Such arrangement facilitates rotatable attachment of the spine assembly  3630  to the tool chassis such that the spine assembly may be selectively rotated about a shaft axis SA relative to the tool chassis. 
     In the illustrated aspect, the interchangeable surgical tool assembly  3600  includes a surgical end effector  3602  that comprises a first jaw  3604  and a second jaw  3608 . In one arrangement, the first jaw comprises an elongated channel  3614  that is configured to operably support a conventional (mechanical) surgical staple/fastener cartridge  304  ( FIG. 4 ) or a radio frequency (RF) cartridge  3606  ( FIGS. 22 and 23 ) therein. The second jaw  3608  comprises an anvil  3616  that is pivotally supported relative to the elongated channel  3614 . The anvil  3616  may be selectively moved toward and away from a surgical cartridge supported in the elongated channel  3614  between open and closed positions by actuating the closure drive system  3510 . In the illustrated arrangement, the anvil  3616  is pivotally supported on a proximal end portion of the elongated channel  3614  for selective pivotal travel about a pivot axis that is transverse to the shaft axis SA. Actuation of the closure drive system  3510  may result in the distal axial movement of a proximal closure member or proximal closure tube  3622  that is attached to an articulation connector  3618 . Actuation of the proximal closure tube  3622  will result in the distal travel of the distal closure tube segment  3620  to ultimately apply a closing motion to the anvil  3616 . 
     In at least one arrangement, RF energy is supplied to the surgical tool assembly  3600  by a conventional RF generator  3400  through a supply lead  3402 . In at least one arrangement, the supply lead  3402  includes a male plug assembly  3406  that is configured to be plugged into corresponding female connectors  3410  that are attached to a segmented RF circuit  3656  on the an onboard circuit board  3654 . See  FIG. 25 . Such arrangement facilitates rotational travel of the shaft and end effector  3602  about the shaft axis SA relative to the tool chassis by rotating the nozzle assembly  3612  without winding up the supply lead  3402  from the generator  3400 . An onboard on/off power switch  3420  is supported on the latch assembly  3624  and tool chassis for turning the RF generator on and off. When the tool assembly  3600  is operably coupled to the handle assembly  3500  or robotic system, the onboard segmented RF circuit  3656  communicates with the microprocessor  3560  through the connectors  3668  and, in some arrangements, a housing connector (not shown). As shown in  FIG. 22 , the handle assembly  3500  may also include a display screen  3430  for viewing information about the progress of sealing, stapling, knife location, status of the cartridge, tissue, temperature, etc. As can also be seen  FIG. 25 , the slip ring assembly  3652  includes a proximal connector  3666  that interfaces with a distal connector  3658  that includes a flexible shaft circuit strip or assembly  3646  that may include a plurality of narrow electrical conductors  3662  for stapling related activities and wider electrical conductors  3664  used for RF purposes. As shown in  FIGS. 24 and 25 , the flexible shaft circuit strip  3646  is centrally supported between the laminated plates or bars  3636  that form the knife bar  3626 . Such arrangement facilitates sufficient flexing of the knife bar  3626  and flexible shaft circuit strip  3646  during articulation of the end effector  3602  while remaining sufficiently stiff so as to enable the knife member  3628  to be distally advanced through the clamped tissue. 
     In at least one arrangement, the elongated channel  3614  includes a channel circuit  3642  supported in a recess that extends from the proximal end of the elongated channel  3614  to a distal location in the bottom portion of the elongated channel  3614 . The channel circuit  3642  includes a proximal contact portion that contacts a distal contact portion  3644  of the flexible shaft circuit strip  3646  for electrical contact therewith. In at least one arrangement, the distal end of the channel circuit  3642  is received within a corresponding wall recess formed in one of the walls of the elongated channel  3614  and is folded over and attached to an upper edge of the elongated channel  3614  wall. A series of corresponding exposed contacts are provided in the distal end of the channel circuit  3642 . Correspondingly, the cartridge  3606  can include a flexible cartridge circuit that is attached to a distal micro-chip and is affixed to the distal end portion of the body of the cartridge  3606 . An end of the flexible cartridge circuit can be folded over the edge of the deck surface of the cartridge  3606  and includes exposed contacts configured to make electrical contact with the exposed contacts of the channel circuit  3642 . Thus, when the RF cartridge  3606  is installed in the elongated channel  3614 , the electrodes as well as the distal micro-chip of the RF cartridge  3606  are powered and communicate with the onboard circuit board  3654  through contact between the flexible cartridge circuit, the flexible channel circuit  3642 , the flexible shaft circuit  3646 , and the slip ring assembly  3652 . Further details regarding the RF cartridges  3606  and the corresponding circuitry and sensor arrangements of the surgical instrument  10  that communicate and/or interact with the RF cartridges  3606  can be found in U.S. patent application Ser. No. 15/636,096, entitled SURGICAL SYSTEM COUPLABLE WITH STAPLE CARTRIDGE AND RADIO FREQUENCY CARTRIDGE, AND METHOD OF USING SAME, which is hereby incorporated herein by reference in its entirety. 
       FIG. 26  illustrates a logic flow diagram of a process  4000  of monitoring for lack of articulation and firing movement of the surgical instrument  10  ( FIGS. 1, 22 ) as executed by the controller  1104  ( FIG. 10 ) according to one aspect of this disclosure. During use, the surgical instrument  10  can encounter various situations where the movement of the surgical instrument  10  is halted. Such situations can include when the articulation of the end effector  2300  is blocked, the end effector  2300  is at an end of its articulation range, the surgical instrument  10  has stalled, or a cartridge has not been inserted into the end effector  2300 . It can be desirable for the surgical instrument  10  to execute processes, such as process  4000 , to monitor for the occurrence of these situations so that the surgical instrument  10  can alert the clinician or otherwise take corrective action. In the following description of the process  4000 , reference should also be made to  FIGS. 3, 10, and 16-23 . In the following described aspects, the displacement member  1111  depicted in  FIG. 10  can represent the longitudinally movable drive member  3540 . The longitudinally movable drive member  3540  alternatively drives the knife bar  280  or the articulation driver  230 , according to whether the clutch assembly  400  is in the engaged position (in which the lock sleeve  402  couples the articulation driver  230  to the firing member  220 ) or the disengaged position. As the longitudinally movable drive member  3540  drives both the knife bar  280  and the articulation driver  230 , tracking the movement of the longitudinally movable drive member  3540  alone can be utilized as a proxy for tracking the movement of both the firing system (referring collectively to the knife bar  280  or firing bar  172 , I-beam  178 , and/or wedge sled  190 ) and the articulation system  2800 . 
     In alternative aspects, the absolute positioning system  1100  depicted in  FIG. 10  can be configured to independently track the movement of the firing system and the articulation system  2800  instead of, or in addition to, tracking the movement of the longitudinally movable drive member  3540 . In these aspects, the absolute positioning system  1100  can be configured to determine the position of multiple displacement members, rather than a single displacement member  1111  as depicted in  FIG. 10 . For example, the absolute positioning system  1100  can determine the position of a first displacement member representing the articulation driver  230 , the distal articulation driver  2820 , or any other component of the articulation system  2800  that is movable between a first position and a second position to articulate of the end effector  2300 . Further, the absolute positioning system  1100  can determine the position of a second displacement member representing the firing member  220 , the firing bar  172  ( FIG. 4 ), the I-beam  178  ( FIG. 4 ), or any other component of the firing system that is movable between a first position and a second position to cause the clamping, cutting, and/or stapling operations at the end effector  2300 . The process  4000  will be discussed from this point forward in terms of tracking a single displacement member  1111  driving both the firing system and the articulation system  2800  (i.e., the longitudinally movable drive member  3540 ); however, the teachings herein are likewise applicable to surgical instruments  10  wherein the firing system and the articulation system  2800  are tracked independently from each other. 
     Accordingly, the controller  1104  determines  4002  whether the velocity of the longitudinally movable drive member  3540  is equal (or nearly equal) to zero (i.e., whether the longitudinally movable drive member  3540  is not moving). The controller  1104  can calculate the velocity of the longitudinally movable drive member  3540  via a combination of the output from the position sensor  1112  and the timer/counter circuit  2531  ( FIG. 14 ) to track the position of the longitudinally movable drive member  3540  over time. In various aspects, the controller  1104  can track the velocity of the longitudinally movable drive member  3540  as, e.g., a rolling average, by sampling the output of the position sensor  1112 , sampling the output of the timer/counter circuit  2531 , determining a distance that the longitudinally movable drive member  3540  translated between the current instance and an nth prior instance, determining an elapsed time over the n instances, and then determining a velocity of the longitudinally movable drive member  3540  according to the distance translated and the elapsed time. In some aspects, the process  4000  determines  4002  that the velocity of the longitudinally movable drive member  3540  is zero when the longitudinally movable drive member  3540  stops at any particular moment. In other aspects, the process  4000  determines  4002  that the velocity of the longitudinally movable drive member  3540  is zero when the rolling average of the longitudinally movable drive member  3540  reaches zero. 
     If the velocity of the longitudinally movable drive member  3540  is not equal to zero, then the process  4000  continues along the NO branch and loops to continue monitoring the velocity of the longitudinally movable drive member  3540 . In other aspects, if the process  4000  continues along the NO branch, the process  4000  simply ends and the controller  1104  executes the next procedure-appropriate process or algorithm. If the velocity of the longitudinally movable drive member  3540  is equal to zero, then the process  4000  continues along the YES branch and next determines  4004  the operational state of the surgical instrument  10 . The operational state of the surgical instrument  10  is defined as which operation is currently being carried out by the surgical instrument  10 , which includes articulating, clamping, stapling, applying RF energy, applying ultrasonic energy, and/or cutting. In one aspect, the process  4000  determines  4004  whether the end effector  2300  is in a clamped and firing operational state, as opposed to an articulating operational state. Knowing which operational state that the surgical instrument  10  is in allows one to determine whether the lack of movement of the longitudinally movable drive member  3540  is indicative of an issue with the firing system or the articulation system  2800 . Stated explicitly, if the surgical instrument  10  is in the clamped and firing operational state, then the longitudinally movable drive member  3540  is driving the firing system and the lack of velocity of the longitudinally movable drive member  3540  is thus indicative of a potential issue with the firing system. Conversely, if the surgical instrument  10  is not in the clamped and firing operational state, then the longitudinally movable drive member  3540  is driving the articulation system  2800  and the lack of velocity of the longitudinally movable drive member  3540  is thus indicative of a potential issue with the articulation system  2800 . 
     The process  4000  can determine  4004  whether the end effector  2300  is clamped and firing via one or more sensors associated with the controls of the surgical instrument  10 , the closure drive system  3510 , the jaws  3604 ,  3608  (or the anvil  3616  and the cartridge  3606 ) of the end effector  2300 , the firing drive system  3530 , the firing member  220 , the knife bar  280 , the articulation system  2800 , and/or combinations thereof. For example, the other sensor(s)  1118  can include a closure trigger sensor configured to determine when the closure trigger  3512  has been actuated. As the closure trigger  3512  causes the closure drive system  3510  to be activated, detecting whether the closure trigger  3512  has been actuated thus serves as a proxy for determining whether the end effector  2300  is in a clamped or unclamped position. The closure trigger sensor can include, e.g., a position sensor configured to detect the position of the closure trigger  3512  relative to the handle assembly  3500 . Other aspects can include a firing trigger sensor or a firing button sensor for detecting the actuation of the firing controls. The other sensor(s)  1118  can further include a closure drive system sensor configured to detect the activation of the closure drive system  3510 . For example, the other sensor(s)  1118  can include a sensor configured to measure forces exerted on the anvil  3616  by the closure tube  3620  or a sensor configured to measure the relative position of the closure tube  3620  or another movable component of the closure drive system that translates between a first position and a second position to effect the closure of the end effector  2300 . The other sensor(s)  1118  can further include a jaw sensor configured to determine whether the jaws  3604 ,  3608  of the end effector  2300  are in a clamped or unclamped position. For example, the other sensor(s)  1118  can include a sensor configured to detect a distance between the first jaw  3604  and the second jaw  3608 , a pressure sensor disposed on at least one of the first jaw  3604  and/or the second jaw  3608  that is configured to detect when the end effector  2300  is clamped on an object (e.g., tissue), or an impedance sensor configured to detect impedance of tissue located between the first jaw  3604  and the second jaw  3608 . The other sensor(s)  1118  can further include a firing drive system sensor configured to determine when the firing drive system  3530  has been activated. For example, the other sensor(s)  1118  can include a current sensor  2536  ( FIG. 14 ) configured to measure a current draw by the motor  2504  ( FIG. 14 ) or a sensor arrangement configured to measure the relative position of a displacement member  1111  that is a component of, or is driven by, the firing drive system  3530  (e.g., I-beam  2514 , articulation driver  230 , knife bar  280 , longitudinally movable drive member  3540 , firing member  220 ). Further information regarding various sensor arrangements can be found in U.S. patent application Ser. No. 15/628,175, entitled TECHNIQUES FOR ADAPTIVE CONTROL OF MOTOR VELOCITY OF A SURGICAL STAPLING AND CUTTING INSTRUMENT, which is hereby incorporated herein by reference in its entirety. 
     The surgical instrument  10  can include various combinations of the sensors described above, such that the sum total of the outputs of the various sensors and sensor arrangements can be received by the controller  1104  and then utilized by the controller  1104  to determine  4004  whether the surgical instrument  10  is in a clamped and firing state or an articulating state. As one specific example, the surgical instrument  10  can include a closure trigger sensor and a firing button or trigger sensor to detect when the respective systems have been activated. As another specific example, the surgical instrument  10  can include a jaw sensor configured to detect when the jaws  3604 ,  3608  are clamped and a current sensor ( FIG. 14 ) to detect when the motor  2504  is drawing a current from the energy source  2512 . As yet another specific example, the surgical instrument  10  can include a sensor configured to measure forces exerted on the anvil  3616  by the closure tube  3620 , a firing button or trigger sensor, and an articulation sensor arrangement configured to measure the angular position of the end effector  2300 . 
     If the surgical instrument  10  is not clamped and firing, then the surgical instrument  10  is in an articulating operational state and the process  4000  continues along the NO branch and next determines whether the end effector  2300  is at the end of its articulation range. In one aspect, the process  4000  determines the relative articulation position of the end effector  2300  by determining  4006  whether the longitudinally movable drive member  3540  is positioned in a zone corresponding to the section(s) of its stroke at or near a first or proximal position and/or a second or distal position. The proximal and distal positions can correspond to, e.g., the furthest proximal position (i.e., proximal limit) and the furthest distal position (i.e., distal limit) between which the longitudinally movable drive member  3540  is translated. Because the articulation of the end effector  2300  is driven by the longitudinally movable drive member  3540 , the limits of the translation range of the longitudinally movable drive member  3540  correspond to the limits of the articulation range of the end effector  2300 . Thus, the proximal position of the longitudinally movable drive member  3540  corresponds to a first limit of the articulation range of the end effector  2300  and, accordingly, the distal position of the longitudinally movable drive member  3540  corresponds to a second limit of the articulation range of the end effector  2300 . Therefore, the process  4000  executed by the controller  1104  can determine the position of the end effector  2300  relative to the limits of its articulation range by determining  4006  the position of the longitudinally movable drive member  3540  relative to the limits of its own translation range. The proximal and distal positions of the longitudinally movable drive member  3540  can be, e.g., stored in the memory  1106  and retrieved by the controller  1104  to calculate the relative angular position of the end effector  2300 . 
     In another aspect, the process  4000  determines the relative articulation position of the end effector  2300  by determining the position of the articulation driver  230  (or another movable component in the articulation system  2800 ) relative to the proximal and distal limits between which the articulation driver  230  is translated, as described above with respect to the longitudinally movable drive member  3540 . In another aspect, the process  4000  determines the relative articulation position of the end effector  2300  by directly detecting the angle at which the articulation joint  2270  and/or end effector  2300  is oriented by, e.g., an articulation sensor arrangement. The detected articulation angle of the end effector  2300  can be compared to the limits of its articulation range, which can be, e.g., stored in the memory  1106  and retrieved by the controller  1104 , to calculate the relative position of the end effector  2300 . 
     In some aspects, the process  4000  determines  4006  that the longitudinally movable drive member  3540  is at a limit of its articulation range when the position of the longitudinally movable drive member  3540  is coincident with one of the limits of its stroke. In other aspects, the process  4000  determines  4006  that the longitudinally movable drive member  3540  is at a limit of its articulation range when the position of the longitudinally movable drive member  3540  is within a threshold of one of the limits of its stroke. 
     If the longitudinally movable drive member  3540  is not stopped at an end of its stroke, the process  4000  continues along the NO branch and thereby determines  4008  that the articulation of the end effector  2300  is blocked. The determination that the articulation is blocked is based on the fact that the end effector  2300  is not clamped and firing and is also not articulating, despite not being positioned at or near the limits of its articulation range. The articulation of the end effector  2300  can be blocked when the surgical instrument  10  is in use for a variety of reasons, such as if the end effector  2300  is making contact with the sidewalls of the access device through which the surgical tool assembly  3600  is inserted during surgical operations. When the process  4000  determines that the articulation of the end effector  2300  is blocked, the controller  1104  can initiate an alert to notify the clinician as such. The alert can include, e.g., audible feedback, haptic feedback, or visual feedback. In one aspect depicted in  FIGS. 27-28 , the controller  1104  causes the display  4050  (or a portion thereof) to display an image  4052  depicting an end effector  4054  contacting an access device  4056 . The image  4052  can additionally include animations or other icons to further indicate that an error is occurring. The position at which the image of the end effector  4054  is depicted in the image  4052  can correspond to the relative position of the end effector  4054  as determined by the articulation sensor arrangement. 
     If the longitudinally movable drive member  3540  is stopped at an end of its stroke, the process  4000  continues along the YES branch and thereby determines  4010  that the end effector  2300  is at a limit of its articulation range. When the process  4000  determines that the end effector  2300  is at a limit of its articulation range, the controller  1104  can initiate an alert to notify the clinician as such. The alert can include, e.g., audible feedback, haptic feedback, or visual feedback. In one aspect depicted in  FIGS. 29-30 , the controller  1104  causes the display  4050  (or a portion thereof) to display an image  4058  depicting an end effector  4060  positioned at an articulation limit. In one aspect, the end effector  4060  is depicted in the image  4058  at either a first articulation limit  4062  or a second articulation limit  4064  corresponding to the limit at which it is actually positioned. 
     In some aspects, after determining that the end effector  2300  is blocked o at its articulation limit, the process  4000  includes an additional step of allowing the clinician to attempt to re-articulate the end effector  2300  prior to providing the alert. In other words, the alert is only triggered if the process  4000  determines  4010  that the end effector  2300  is repeatedly blocked or repeatedly being articulated to its articulation limit. In other aspects, the process  4000  includes a time component to determining  4008  that the end effector  2300  is blocked and/or determining  4010  that the end effector  2300  is at its articulation limit, such that the process  4000  only triggers the alert if the end effector  2300  is blocked or at its articulation limit for a period of time exceeding a threshold. These aspects limit providing the alert to situations where the end effector  2300  is repeatedly blocked or repeatedly articulated to the articulation limit, or where the end effector  2300  is held in a blocked position or held at the articulation limit for a certain period of time, so that the surgical instrument  10  provides the alert to the clinician only when the clinician appears to be having difficult using the surgical instrument  10 . 
     Returning to the step of the process  4000  of determining  4004  the operational state of the surgical instrument  10 , if the process  4000  determines  4004  that the surgical instrument  10  is clamped and firing, then the process  4000  continues along the YES branch and next determines  4012  whether the longitudinally movable drive member  3540  has advanced beyond a threshold position in its firing stroke. Stated differently, the process  4000  determines  4012  whether the longitudinally movable drive member  3540  is positioned in a zone corresponding to the section(s) of its firing stroke extending beyond a particular threshold position, which may or may not be located more proximally than distally. The process  4000  can determine  4012  the position of the longitudinally movable drive member  3540  via the absolute positioning system  1100 , as discussed above. In some aspects, the threshold position against which the advancement (or lack thereof) of the longitudinally movable drive member  3540  is compared is the initial position of the longitudinally movable drive member  3540 . In other aspects, the threshold position against which the advancement (or lack thereof) of the longitudinally movable drive member  3540  is compared can correspond to a proximal portion of the initial zone of a firing stroke. The first or initial zone of the firing stroke can correspond to the closed loop period from t 0  to t 1 , as depicted in  FIG. 15 . In certain aspects, this initial zone of the firing stroke may also be referred to as a lockout zone. In the lockout zone, the surgical instrument  10  may be triggered to enter a lockout state if certain conditions occur, such as if a cartridge  3606  has not been inserted into the elongated channel  3614  of the end effector  2300 . The lockout state can be initiated by, e.g., a current spike being triggered during the lockout zone. 
     In various aspects, the surgical instrument  10  can include mechanical or electronic firing lockout systems to prevent the knife bar  280  from advancing if a cartridge  3606  is not present in the end effector  2300 . If the knife bar  280  is prevented from advancing, then the longitudinally movable drive member  3540  driving the knife bar  280  is likewise prevented from advancing beyond a particular threshold position due to the mechanical linkage between the components. The firing lockout systems prevent the knife bar  280  from transecting tissue if there would be no corresponding sealing of the tissue via staples or RF energy from the cartridge  3606 . The firing lockout system can initiate a lockout state by triggering a motor current spike if the knife bar  280  or longitudinally movable drive member  3540  is locked or otherwise unable to advance when in the lockout zone. In one aspect, the surgical instrument  10  is configured with an electronic firing lockout system. In this aspect, the controller  1104  will initiate a lockout state if the channel circuit  3642  ( FIG. 24 ) has not made contact with the distal contact portion  3644  of the flexible shaft circuit strip  3646  to establish electrical contact therebetween. In another aspect, the surgical instrument  10  is configured with a mechanical firing lockout system (not shown) that includes openings on each side of the elongated channel  3614 , which are configured to receive a channel engagement feature or foot  186  ( FIG. 4 ) of the firing bar  172  ( FIG. 4 ) or knife bar  280  when the knife bar  280  is in a starting position. When the foot  186  of the knife bar  280  is engaged with the openings of the elongated channel  3614 , the knife bar  280  is maintained in a locked position and cannot be advanced. In these aspects, the cartridge  3606  further includes pads that are received within and occupy the openings of the elongated channel  3614  when the cartridge  3606  is installed properly, which prevents the foot  186  of the knife bar  280  from engaging the openings and thereby allows the knife bar  280  to be advanced. Further description regarding the lockout mechanisms U.S. patent application Ser. No. 15/636,096, entitled SURGICAL SYSTEM COUPLABLE WITH STAPLE CARTRIDGE AND RADIO FREQUENCY CARTRIDGE, AND METHOD OF USING SAME, which is hereby incorporated herein by reference in its entirety. 
     If the longitudinally movable drive member  3540  is not located at its starting portion or has otherwise advanced to or beyond the threshold position in its firing stroke, the process  4000  continues along the YES branch and thereby determines  4014  that the surgical instrument  10  has stalled. The determination that the surgical instrument  10  is stalled is based on the fact that the longitudinally movable drive member  3540  has advanced beyond the threshold position (which means that the lack of a cartridge  3606  or another such condition causing the lockout state to be triggered has not occurred), but is not currently advancing despite the clamping and firing operations of the surgical instrument  10  having been initiated. The surgical instrument  10  can stall due to a number of different reasons, including the knife bar  280  encountering unexpectedly thick or tough tissue, a motor  1120  error, or a mechanical error in the firing drive system  3530 . When the process  4000  determines  4014  that the surgical instrument  10  has stalled, the controller  1104  can initiate an alert to notify the clinician as such. The alert can include, e.g., audible feedback, haptic feedback, or visual feedback. In one aspect depicted in  FIG. 31 , the controller  1104  causes the display  4050  (or a portion thereof) to display an image  4066  depicting a caution or error symbol  4068  that can be, e.g., overlaid on the screen that is displayed during transection. 
     If the longitudinally movable drive member  3540  is located at its starting portion or has otherwise not advanced to or beyond a threshold position in its firing stroke, the process  4000  continues along the NO branch and thereby determines  4016  that a cartridge  3606  is not present in the end effector  2300  (or has been improperly loaded into the end effector  2300 ). The determination that a cartridge  3606  is not present or is improperly loaded is based on the fact that the longitudinally movable drive member  3540  is not advancing beyond its starting position, despite the clamping and firing operations of the surgical instrument  10  having been initiated. When the process  4000  determines  4016  that no cartridge  3606  is present, the controller  1104  can initiate an alert to notify the clinician as such. The alert can include, e.g., audible feedback, haptic feedback, or visual feedback. In one aspect depicted in  FIG. 32 , the controller  1104  causes the display  4050  (or a portion thereof) to display an image or an icon  4070  providing a visual cue indicating that there is an error with the end effector  4072  (e.g., an “X” overlying the end effector  4072 ). 
     In order to further illustrate the principles discussed herein, the description will now turn to  FIGS. 33A-C , which illustrate line diagrams  4100 ,  4200 ,  4300  of various exemplary displacement member strokes according to one aspect of this disclosure. In the following description of  FIGS. 33A-C , reference should also be made to  FIG. 26 . The displacement member of the exemplary strokes depicted in  FIGS. 33A-C  can include, e.g., longitudinally movable drive member  3540 . Each of the line diagrams  4100 ,  4200 ,  4300  depicts in representative format an exemplary displacement member stroke including a stop position  4106  at which the displacement member has stopped (i.e., where its velocity equals zero) between a first position or first end  4102  and a second position or second end  4104  of the stroke. The first end  4102  and the second end  4104  can correspond to the proximal end and the distal end, respectively, of the displacement member stroke. The stop position  4106  of the displacement member, which varies in each of the line diagrams  4100 ,  4200 ,  4300 , corresponds to the displacement member position determined by the process  4000  described in connection with  FIG. 26  when the displacement member velocity is equal to zero. Further, the displacement member stroke can be divided into multiple zones by one or more thresholds. The zone or zones in which the displacement member is located determine, in combination with the operation state of the surgical instrument  10  determined  4004  by the process  4000 , what actions the process  4000  takes. 
     The stop position  4106  of the longitudinally movable drive member  3540  is depicted in each of the line diagrams  4100 ,  4200 ,  4300  in relation to a first threshold  4108  and a second threshold  4110 . The stop position  4106  of the displacement member is compared against the first and second thresholds  4108 ,  4110  when the surgical instrument is in an articulating operational state. The first and second thresholds  4108 ,  4110  can demarcate the positional limits at which the displacement member is consider to be “at” or “near” the first end  4102  or the second end  4104 , respectively. The first and second thresholds  4108 ,  4110  define a first zone and a second zone. The first zone corresponds to the aggregation of the sections of the displacement member stroke between the first threshold  4108  and the first end  4102  and between the second threshold  4110  and the second end  4104 . The second zone corresponds to the section of the displacement member stroke between the first threshold  4108  and the second threshold  4110 . If the stop position  4106  of the displacement member is in the first zone, then the displacement member is considered to be positioned at the respective end  4102 ,  4104  of the stroke. In operation, if the stop position  4106  of the displacement member is in the first zone when the instrument is not clamped and firing, then the process  4000  determines  4010  that the end effector  2300  is at its articulation limit. Conversely, if the stop position  4106  of the displacement member is in the second zone when the instrument is not clamped and firing, then the process  4000  determines  4008  that the articulation of the end effector  2300  is blocked. 
     The stop position  4106  of the longitudinally movable drive member  3540  is depicted in each of the line diagrams  4100 ,  4200 ,  4300  in further relation to a third threshold  4112 . The stop position  4106  of the displacement member is compared against the third threshold  4112  when the surgical instrument is in a clamped and firing operational state. The third threshold  4112  can demarcate the positional limit beyond which the displacement member cannot advance if a cartridge  3606  is not present in the end effector  2300 . The third threshold  4112  defines a third zone and a fourth zone. The third zone corresponds to the section of the displacement member stroke between the first end  4102  (i.e., the proximal end of the firing stroke) and the third threshold  4112 . The fourth zone corresponds to the section of the displacement member stroke between the third threshold  4112  and the second end  4104  (i.e., the distal end of the firing stroke). In operation, if the stop position  4106  of the displacement member is in the third zone when the instrument is clamped and firing, then the process  4000  determines  4016  that no cartridge is present in the end effector  2300  because the displacement member has not advanced beyond the lockout zone in its firing stroke delineated by the third threshold  4112 . Conversely, if the stop position  4106  of the displacement member is in the fourth zone when the instrument is clamped and firing, then the process  4000  determines  4014  that surgical instrument  10  has stalled. 
     To now address each of the line diagrams  4100 ,  4200 ,  4300  individually, the first line diagram  4100  depicts the stop position  4106  of the displacement member in the first zone and the fourth zone. It should be noted that the different sets of zones demarcated by the different sets of thresholds can overlap with each other. The particular set of zones against which the stop position  4106  is compared depends upon the operational state of the surgical instrument  10  because the different thresholds are associated with the different operational states. When the displacement member is in this position, the process  4000  will either determine  4010  that the end effector  2300  is at its articulation limit or determine  4014  that the surgical instrument  10  is stalled, depending upon the operational state of the surgical instrument  10 . The second line diagram  4200  depicts the stop position  4106  of the displacement member in the second zone and the fourth zone. When the displacement member is in this position, the process  4000  will either determine  4008  that the articulation of the end effector  2300  is blocked or determine  4014  that the surgical instrument  10  has stalled, depending upon the operational state of the surgical instrument  10 . The third line diagram  4300  depicts the stop position  4106  of the displacement member in the second zone and the third zone. When the displacement member is in this position, the process  4000  will either determine  4008  that the articulation of the end effector  2300  is blocked or determine  4016  that no cartridge is present in the surgical instrument  10 , depending upon the operational state of the surgical instrument  10 . The actions taken by the process  4000  according to the surgical instrument&#39;s operational state for other stop positions  4106  of the displacement member should be apparent from the above description. 
     The functions or processes of providing alerts according to the operational state of the surgical instrument described herein may be executed by any of the processing circuits described herein, such as the control circuit  700  described in connection with  FIGS. 5A-6 , the circuits  800 ,  810 ,  820  described in  FIGS. 7-9 , the controller  1104  described in connection with  FIGS. 10 and 12 , and/or the control circuit  2510  described in  FIG. 14 . 
     Aspects of the motorized surgical instrument may be practiced without the specific details disclosed herein. Some aspects have been shown as block diagrams rather than detail. Parts of this disclosure may be presented in terms of instructions that operate on data stored in a computer memory. An algorithm refers to a self-consistent sequence of steps leading to a desired result, where a “step” refers to a manipulation of physical quantities which may take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. These signals may be referred to as bits, values, elements, symbols, characters, terms, numbers. These and similar terms may be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. 
     Generally, aspects described herein which can be implemented, individually and/or collectively, by a wide range of hardware, software, firmware, or any combination thereof can be viewed as being composed of various types of “electrical circuitry.” Consequently, “electrical circuitry” includes electrical circuitry having at least one discrete electrical circuit, electrical circuitry having at least one integrated circuit, electrical circuitry having at least one application specific integrated circuit, electrical circuitry forming a general purpose computing device configured by a computer program (e.g., a general purpose computer or processor configured by a computer program which at least partially carries out processes and/or devices described herein, electrical circuitry forming a memory device (e.g., forms of random access memory), and/or electrical circuitry forming a communications device (e.g., a modem, communications switch, or optical-electrical equipment). These aspects may be implemented in analog or digital form, or combinations thereof. 
     The foregoing description has set forth aspects of devices and/or processes via the use of block diagrams, flowcharts, and/or examples, which may contain one or more functions and/or operations. Each function and/or operation within such block diagrams, flowcharts, or examples can be implemented, individually and/or collectively, by a wide range of hardware, software, firmware, or virtually any combination thereof. In one aspect, several portions of the subject matter described herein may be implemented via Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), digital signal processors (DSPs), Programmable Logic Devices (PLDs), circuits, registers and/or software components, e.g., programs, subroutines, logic and/or combinations of hardware and software components. logic gates, or other integrated formats. Some aspects disclosed herein, in whole or in part, can be equivalently implemented in integrated circuits, as one or more computer programs running on one or more computers (e.g., as one or more programs running on one or more computer systems), as one or more programs running on one or more processors (e.g., as one or more programs running on one or more microprocessors), as firmware, or as virtually any combination thereof, and that designing the circuitry and/or writing the code for the software and or firmware would be well within the skill of one of skill in the art in light of this disclosure. 
     The mechanisms of the disclosed subject matter are capable of being distributed as a program product in a variety of forms, and that an illustrative aspect of the subject matter described herein applies regardless of the particular type of signal bearing medium used to actually carry out the distribution. Examples of a signal bearing medium include the following: a recordable type medium such as a floppy disk, a hard disk drive, a Compact Disc (CD), a Digital Video Disk (DVD), a digital tape, a computer memory, etc.; and a transmission type medium such as a digital and/or an analog communication medium (e.g., a fiber optic cable, a waveguide, a wired communications link, a wireless communication link (e.g., transmitter, receiver, transmission logic, reception logic, etc.). 
     The foregoing description of these aspects has been presented for purposes of illustration and description. It is not intended to be exhaustive or limiting to the precise form disclosed. Modifications or variations are possible in light of the above teachings. These aspects were chosen and described in order to illustrate principles and practical application to thereby enable one of ordinary skill in the art to utilize the aspects and with modifications as are suited to the particular use contemplated. It is intended that the claims submitted herewith define the overall scope. 
     Various aspects of the subject matter described herein are set out in the following numbered examples: 
     Example 1. A surgical instrument comprising: a displacement member movable between a first position and a second position; a sensor configured to detect a position of the displacement member and provide a signal indicative thereof; and a control circuit coupled to the sensor, the control circuit configured to: determine a velocity of the displacement member; and upon the velocity being equal to zero: determine an operational state of the surgical instrument; determine a relative position of the displacement member according to the position of the displacement member compared to at least one of the first position or the second position; and provide an alert according to the operational state of the surgical instrument and the relative position of the displacement member. 
     Example 2. The surgical instrument of Example 1, wherein the alert comprises an image. 
     Example 3. The surgical instrument of Example 2, further comprising a display, wherein the control circuit is configured to cause the display to display the image. 
     Example 4. The surgical instrument of Example 2 or Example 3, wherein the image indicates that articulation of the surgical instrument is blocked or at its limit according to the position of the displacement member. 
     Example 5. The surgical instrument of one or more of Example 2 or Example 3, wherein the image indicates that the surgical instrument is in a lockout state according to the position of the displacement member. 
     Example 6. The surgical instrument of one or more of Example 2 or Example 3, wherein the image indicates that the surgical instrument has stalled according to the position of the displacement member. 
     Example 7. The surgical instrument of one or more of Examples 1 through Example 6, further comprising: an end effector comprising: jaws movable between a clamped position and an unclamped position; and a knife bar drivable by the displacement member between a retracted position and an extended position through the end effector; wherein the operational state corresponds to whether the jaws are clamped and the knife bar is being driven to the extended position. 
     Example 8. A surgical instrument comprising: a displacement member movable between a first position and a second position; a sensor configured to detect a position of the displacement member and provide a signal indicative thereof; and a control circuit coupled to the sensor, the control circuit configured to: determine a velocity of the displacement member; and upon the displacement member not moving: determine an operational state of the surgical instrument; determine a zone between the first position and the second position in which the displacement member is positioned; and provide an alert according to the operational state of the surgical instrument and the zone in which the displacement member is positioned. 
     Example 9. The surgical instrument of Example 8, wherein the alert comprises an image. 
     Example 10. The surgical instrument of Example 9, further comprising a display, wherein the control circuit is configured to cause the display to display the image. 
     Example 11. The surgical instrument of Example 9 or Example 10, wherein the image indicates that articulation of the surgical instrument is blocked or at its limit according to the position of the displacement member. 
     Example 12. The surgical instrument of one or more of Example 9 or Example 10, wherein the image indicates that the surgical instrument is in a lockout state according to the position of the displacement member. 
     Example 13. The surgical instrument of one or more of Example 9 or Example 10, wherein the image indicates that the surgical instrument has stalled according to the position of the displacement member. 
     Example 14. The surgical instrument of one or more of Example 8 through Example 13, further comprising: an end effector comprising: jaws movable between a clamped position and an unclamped position; and a knife bar drivable by the displacement member between a retracted position and an extended position through the end effector; wherein the operational state corresponds to whether the jaws are clamped and the knife bar is being driven to the extended position. 
     Example 15. A method of operating a surgical instrument comprising a displacement member movable between a first position and a second position, a motor coupled to the displacement member, the motor configured to drive the displacement member between the first position and the second position, and a sensor configured to detect a position of the displacement member and provide a signal indicative thereof, the method comprising: determining a velocity of the displacement member; and upon determining that the velocity of the displacement member equals zero: determining an operational state of the surgical instrument; determining a zone in which the displacement member is positioned; and providing an alert according to the operational state of the surgical instrument and the zone in which the displacement member is positioned. 
     Example 16. The method of Example 15, wherein the alert comprises an image. 
     Example 17. The method of Example 15, wherein the image indicates that articulation of the surgical instrument is blocked or at its limit according to the position of the displacement member. 
     Example 18. The method of Example 15, wherein the image indicates that the surgical instrument is in a lockout state according to the position of the displacement member. 
     Example 19. The method of one or more of Example 15 through Example 18, wherein the image indicates that the surgical instrument has stalled according to the position of the displacement member.