Patent Publication Number: US-11382638-B2

Title: Closed loop feedback control of motor velocity of a surgical stapling and cutting instrument based on measured time over a specified displacement distance

Description:
TECHNICAL FIELD 
     The present disclosure relates to surgical instruments and, in various circumstances, to surgical stapling and cutting instruments and staple cartridges therefor that are designed to staple and cut tissue. 
     BACKGROUND 
     In a motorized surgical stapling and cutting instrument it may be useful to control the velocity of a cutting member or to control the articulation velocity of an end effector. Velocity of a displacement member may be determined by measuring elapsed time at predetermined position intervals of the displacement member or measuring the position of the displacement member at predetermined time intervals. The control may be open loop or closed loop. Such measurements may be useful to evaluate tissue conditions such as tissue thickness and adjust the velocity of the cutting member during a firing stroke to account for the tissue conditions. Tissue thickness may be determined by comparing expected velocity of the cutting member to the actual velocity of the cutting member. In some situations, it may be useful to articulate the end effector at a constant articulation velocity. In other situations, it may be useful to drive the end effector at a different articulation velocity than a default articulation velocity at one or more regions within a sweep range of the end effector. 
     During use of a motorized surgical stapling and cutting instrument it is possible that the velocity of the cutting member or the firing member may need to be measured and adjusted to compensate for tissue conditions. In thick tissue the velocity may be decreased to lower the force to fire experienced by the cutting member or firing member if the force to fire experienced by the cutting member or firing member is greater than a threshold force. In thin tissue the velocity may be increased if the force to fire experienced by the cutting member or firing member is less than a threshold. Therefore, it may be desirable to provide a closed loop feedback system that measures and adjusts the velocity of the cutting member or the firing member based on a measurement of time over a specified distance. It may be desirable to measure the velocity of the cutting member by measuring time at fixed set displacement intervals. 
     SUMMARY 
     In one aspect, the present disclosure provides a surgical instrument. The surgical instrument, comprising: a displacement member configured to translate within the surgical instrument over a plurality of predefined zones; a motor coupled to the displacement member to translate the displacement member; a control circuit coupled to the motor; a position sensor coupled to the control circuit, the position sensor configured to monitor the position of the displacement member; a timer circuit coupled to the control circuit, the timer/counter circuit configured to measure elapsed time; wherein the control circuit is configured to: receive, from the position sensor, a position of the displacement member in a current zone defined by a set displacement interval; measure time at a set position of the displacement interval, wherein the measured time is defined as the time taken by the displacement member to traverse the displacement interval; and set a command velocity of the displacement member for a subsequent zone based on the measured time in the current predefined zone. 
     In another aspect, the surgical comprises a displacement member configured to translate within the surgical instrument over a plurality of predefined zones; a motor coupled to the displacement member to translate the displacement member; a control circuit coupled to the motor; a position sensor coupled to the control circuit, the position sensor configured to monitor the position of the displacement member; a timer circuit coupled to the control circuit, the timer/counter circuit configured to measure elapsed time; wherein the control circuit is configured to: receive, from the position sensor, a position of the displacement member in a current zone defined by a predetermined displacement interval; measure time as the displacement member moves from a parked position to a target position; and set a command velocity of the displacement member for a first dynamic zone based on the measured time. 
     In another aspect, the present disclosure provides a method of controlling motor velocity in a surgical instrument, the surgical instrument comprising a displacement member configured to translate within the surgical instrument over a plurality of predefined zones, a motor coupled to the displacement member to translate the displacement member, a control circuit coupled to the motor, a position sensor coupled to the control circuit, the position sensor configured to monitor the position of the displacement member, a timer circuit coupled to the control circuit, the timer/counter circuit configured to measure elapsed time, the method comprising: receiving, from a position sensor, a position of a displacement member within a current zone defined by a set displacement interval; measuring, by a timer circuit, a time at a set position of the displacement member, wherein the time is defined by the time taken by the displacement member to traverse the displacement interval; and setting, by the control circuit, a command velocity of the displacement member for a subsequent zone based on the measured time in the current zone. 
    
    
     
       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. 16A  illustrates an end effector comprising a firing member coupled to an I-beam comprising a cutting edge according to one aspect of this disclosure. 
         FIG. 16B  illustrates an end effector where the I-beam is located in a target position at the top of a ramp with the top pin engaged in the T-slot according to one aspect of this disclosure. 
         FIG. 17  illustrates the I-beam firing stroke is illustrated by a chart aligned with the end effector according to one aspect of this disclosure. 
         FIG. 18  is a graphical depiction comparing I-beam stroke displacement as a function of time (top graph) and expected force-to-fire as a function of time (bottom graph) according to one aspect of this disclosure. 
         FIG. 19  is a graphical depiction comparing tissue thickness as a function of set displacement interval of I-beam stroke (top graph), force to fire as a function of set displacement interval of I-beam stroke (second graph from the top), dynamic time checks as a function of set displacement interval of I-beam stroke (third graph from the top), and set velocity of I-beam as a function of set displacement interval of I-beam stroke (bottom graph) according to one aspect of this disclosure. 
         FIG. 20  is a graphical depiction of force to fire as a function of time comparing slow, medium and fast I-beam displacement velocities according to one aspect of this disclosure. 
         FIG. 21  is a logic flow diagram of a process depicting a control program or logic configuration for controlling command velocity in an initial firing stage according to one aspect of this disclosure. 
         FIG. 22  is a logic flow diagram of a process depicting a control program or logic configuration for controlling command velocity in a dynamic firing stage according to one aspect of this disclosure. 
     
    
    
     DESCRIPTION 
     Applicant of the present application owns the following patent applications filed on Jun. 20, 2017 and which are each herein incorporated by reference in their respective entireties: 
     U.S. patent application Ser. No. 15/627,998, titled CONTROL OF MOTOR VELOCITY OF A SURGICAL STAPLING AND CUTTING INSTRUMENT BASED ON ANGLE OF ARTICULATION, by inventors Frederick E. Shelton, IV et al., filed Jun. 20, 2017, now U.S. Pat. No. 10,390,841. 
     U.S. patent application Ser. No. 15/628,019, titled SURGICAL INSTRUMENT WITH VARIABLE DURATION TRIGGER ARRANGEMENT, by inventors Frederick E. Shelton, IV et al., filed Jun. 20, 2017, now U.S. Pat. No. 10,881,396. 
     U.S. patent application Ser. No. 15/628,036, titled SYSTEMS AND METHODS FOR CONTROLLING DISPLACEMENT MEMBER MOTION OF A SURGICAL STAPLING AND CUTTING INSTRUMENT, by inventors Frederick E. Shelton, IV et al., filed Jun. 20, 2017, now U.S. Pat. No. 11,090,046. 
     U.S. patent application Ser. No. 15/628,050, titled SYSTEMS AND METHODS FOR CONTROLLING MOTOR VELOCITY OF A SURGICAL STAPLING AND CUTTING INSTRUMENT ACCORDING TO ARTICULATION ANGLE OF END EFFECTOR, by inventors Frederick E. Shelton, IV et al., filed Jun. 20, 2017, now U.S. Patent Application Publication Ser. No. 2018/0360446. 
     U.S. patent application Ser. No. 15/628,075, titled SYSTEMS AND METHODS FOR CONTROLLING MOTOR VELOCITY OF A SURGICAL STAPLING AND CUTTING INSTRUMENT, by inventors Frederick E. Shelton, IV et al., filed Jun. 20, 2017, now U.S. Pat. No. 10,624,633. 
     U.S. patent application Ser. No. 15/628,154, titled SURGICAL INSTRUMENT HAVING CONTROLLABLE ARTICULATION VELOCITY, by inventors Frederick E. Shelton, IV et al., filed Jun. 20, 2017, now U.S. Patent Application Publication Ser. No. 2018/0360456. 
     U.S. patent application Ser. No. 15/628,158, titled SYSTEMS AND METHODS FOR CONTROLLING VELOCITY OF A DISPLACEMENT MEMBER OF A SURGICAL STAPLING AND CUTTING INSTRUMENT, by inventors Frederick E. Shelton, IV et al., filed Jun. 20, 2017, now U.S. Pat. No. 10,888,321. 
     U.S. patent application Ser. No. 15/628,162, titled SYSTEMS AND METHODS FOR CONTROLLING DISPLACEMENT MEMBER VELOCITY FOR A SURGICAL INSTRUMENT, by inventors Frederick E. Shelton, IV et al., filed Jun. 20, 2017, now U.S. Pat. No. 10,646,220. 
     U.S. patent application Ser. No. 15/628,168, titled CONTROL OF MOTOR VELOCITY OF A SURGICAL STAPLING AND CUTTING INSTRUMENT BASED ON ANGLE OF ARTICULATION, by inventors Frederick E. Shelton, IV et al., filed Jun. 20, 2017, now U.S. Pat. No. 10,327,767. 
     U.S. patent application Ser. No. 15/628,175, titled TECHNIQUES FOR ADAPTIVE CONTROL OF MOTOR VELOCITY OF A SURGICAL STAPLING AND CUTTING INSTRUMENT, by inventors Frederick E. Shelton, IV et al., filed Jun. 20, 2017, now U.S. Pat. No. 10,881,399. 
     U.S. patent application Ser. No. 15/628,045, titled TECHNIQUES FOR CLOSED LOOP CONTROL OF MOTOR VELOCITY OF A SURGICAL STAPLING AND CUTTING INSTRUMENT, by inventors Raymond E. Parfett et al., filed Jun. 20, 2017, now U.S. Pat. No. 10,307,170. 
     U.S. patent application Ser. No. 15/628,053, titled CLOSED LOOP FEEDBACK CONTROL OF MOTOR VELOCITY OF A SURGICAL STAPLING AND CUTTING INSTRUMENT BASED ON MAGNITUDE OF VELOCITY ERROR MEASUREMENTS, by inventors Raymond E. Parfett et al., filed Jun. 20, 2017, now U.S. Pat. No. 11,071,554. 
     U.S. patent application Ser. No. 15/628,067, titled CLOSED LOOP FEEDBACK CONTROL OF MOTOR VELOCITY OF A SURGICAL STAPLING AND CUTTING INSTRUMENT BASED ON MEASURED DISPLACEMENT DISTANCE TRAVELED OVER A SPECIFIED TIME INTERVAL, by inventors Frederick E. Shelton, IV et al., filed Jun. 20, 2017, now U.S. Patent Application Publication No. 2018/0360473. 
     U.S. Patent Application Publication Ser. No. 15/628,072, titled CLOSED LOOP FEEDBACK CONTROL OF MOTOR VELOCITY OF A SURGICAL STAPLING AND CUTTING INSTRUMENT BASED ON MEASURED TIME OVER A SPECIFIED NUMBER OF SHAFT ROTATIONS, by inventors Frederick E. Shelton, IV et al., filed Jun. 20, 2017, now U.S. Pat. No. 10,980,537. 
     U.S. patent application Ser. No. 15/628,029, titled SYSTEMS AND METHODS FOR CONTROLLING DISPLAYING MOTOR VELOCITY FOR A SURGICAL INSTRUMENT, by inventors Jason L. Harris et al., filed Jun. 20, 2017, now U.S. Pat. No. 10,368,864. 
     U.S. patent application Ser. No. 15/628,077, titled SYSTEMS AND METHODS FOR CONTROLLING MOTOR SPEED ACCORDING TO USER INPUT FOR A SURGICAL INSTRUMENT, by inventors Jason L. Harris et al., filed Jun. 20, 2017, now U.S. Pat. No. 10,779,820. 
     U.S. patent application Ser. No. 15/628,115, titled CLOSED LOOP FEEDBACK CONTROL OF MOTOR VELOCITY OF A SURGICAL STAPLING AND CUTTING INSTRUMENT BASED ON SYSTEM CONDITIONS, by inventors Frederick E. Shelton, IV et al., filed Jun. 20, 2017, now U.S. Pat. No. 10,813,639. 
     Applicant of the present application owns the following U.S. Design patent applications filed on Jun. 20, 2017 and which are each herein incorporated by reference in their respective entireties: 
     U.S. Design patent application Ser. No. 29/608,238, titled GRAPHICAL USER INTERFACE FOR A DISPLAY OR PORTION THEREOF, by inventors Jason L. Harris et al., filed Jun. 20, 2017, now U.S. Design Pat. No. D879,809. 
     U.S. Design patent application Ser. No. 29/608,231, titled GRAPHICAL USER INTERFACE FOR A DISPLAY OR PORTION THEREOF, by inventors Jason L. Harris et al., filed Jun. 20, 2017, now U.S. Design Pat. No. D879,808. 
     U.S. Design patent application Ser. No. 29/608,246, titled GRAPHICAL USER INTERFACE FOR A DISPLAY OR PORTION THEREOF, by inventors Frederick E. Shelton, IV et al., filed Jun. 20, 2017, now U.S. Design Pat. No. D890,784. 
     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. 
       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 herein incorporated 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 “first” or 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 herein incorporated 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 firing member  220  may be referred to as a “second shaft” or a “second shaft assembly”. 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 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. U.S. Patent Application Publication No. 2014/0263551, entitled STAPLE CARTRIDGE TISSUE THICKNESS SENSOR SYSTEM, is incorporated herein by reference in its entirety. U.S. Patent Application Publication No. 2014/0263552, entitled STAPLE CARTRIDGE TISSUE THICKNESS SENSOR SYSTEM, is incorporated by reference in its entirety. 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  200  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 microcontroller processor  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 shaft 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 processor  719  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 processor  719 , 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  1118  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, filed on Apr. 15, 2016, the entire disclosure of which is herein incorporated 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 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 comprises 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 . U.S. Pat. No. 8,210,411, entitled MOTOR-DRIVEN SURGICAL CUTTING INSTRUMENT, which is incorporated herein by reference in its entirety. U.S. Pat. No. 7,845,537, entitled SURGICAL INSTRUMENT HAVING RECORDING CAPABILITIES, which is 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. Pat. No. 10,624,633, which is 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. 1-14 , 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 (Vslow), 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 Vslow by monitoring the position of I-beam  2514  and modulating the motor set point  2522  and/or motor drive signal  2524  to maintain Vslow. 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 (Vfast). 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. 
     The disclosure now turns to a closed loop feedback system to provide velocity control of a displacement member. The closed loop feedback system adjusts the velocity of the displacement member based on a measurement of actual time over a specified distance or displacement interval of the displacement member. In one aspect, the closed loop feedback system comprises two phases. A start phase defined as the start of a firing stroke followed by a dynamic firing phase while the I-beam  2514  advances distally during the firing stroke.  FIGS. 16A and 16B  show the I-beam  2514  positioned at the start phase of the firing stroke.  FIG. 16A  illustrates an end effector  2502  comprising a firing member  2520  coupled to an I-beam  2514  comprising a cutting edge  2509 . The anvil  2516  is in the closed position and the I-beam  2514  is located in a proximal or parked position  9002  at the bottom of the closure ramp  9006 . The parked position  9002  is the position of the I-beam  2514  prior to traveling up the anvil  2516  closure ramp  9006  to the top of the ramp  9006  to the T-slot  9008 . A top pin  9080  is configured to engage a T-slot  9008  and a lockout pin  9082  is configured to engage a latch feature  9084 . 
     In  FIG. 16B  the I-beam  2514  is located in a target position  9004  at the top of the ramp  9006  with the top pin  2580  engaged in the T-slot  9008 . As shown in  FIGS. 16A-16B , in traveling from the parked position  9002  to the target position  9004 , the I-beam  2514  travels a distance indicated as X o  in the horizontal distal direction. During the start phase, the velocity of the I-beam  2514  is set to a predetermined initial velocity V o . A control circuit  2510  measures the actual time t o  that it takes the I-beam  2514  to travel up the ramp  9006  from the parked position  9002  to the target position  9004  at the initial velocity V o . In one aspect, the horizontal distance is 4.1 mm and the initial velocity V o  is 12 mm/s. As described in more detail below, the actual time z o  is used to set the command velocity of the I-beam  2514  to slow, medium, or fast in the subsequent staple cartridge zone Z as the I-beam  2514  advances distally. The number of zones may depend on the length/size of the staple cartridge (e.g., 35 mm, 40 mm, 45 mm, 50 mm, 55 mm, 60 mm, &gt;60 mm). The command velocity or set velocity is the velocity of the motor  2504  that is applied to the motor  2504  by the control circuit  2510  and motor control  2508  in order effect a desired velocity of the I-beam  2514 . The actual velocity of the I-beam  2514  is determined by the control circuit  2510  by measuring the actual time t o  with the timer/counter  2531  circuit that it takes the I-beam  2514  to traverse a specified or fixed distance provided by the position sensor  2534 . In accordance with one aspect of the present disclosure, the closed loop feedback control system of the surgical instrument measures the actual time t n  it takes the I-beam  2514 , or a displacement member, to travel a predetermined fixed distance or displacement interval X n . A predetermined fixed distance or displacement interval X n  is defined for each zone (e.g., Z 1 , Z 2 , Z 3  . . . Z n ). 
       FIG. 17  illustrates the I-beam  2514  firing stroke is illustrated by a chart  9009  aligned with the end effector  2502  according to one aspect of this disclosure. As shown, the initial zone (Z o ), or base zone, is defined as the distance traveled by the I-beam  2514  from the parked position  9002  to the target position  9004 . The measured time T o  is the time it takes the I-beam  2514  to travel up the closure ramp  9006  to the target position  9004  at an initial set velocity V o . The measured times T 1 -T 5  are reference periods of time for traversing the corresponding zones Z 1 -Z 5 , respectively. The displacement of the I-beam  2514  in zone Z o  is X o . The period T o , the time it takes for the I-beam  2514  to travel over a distance X o , is used to set the command velocity in the subsequent zone Z 1 . 
     With reference now to  FIGS. 14-17 , at the start phase, e.g., at the beginning of a firing stroke, the control circuit  2510  is configured to initiate firing the displacement member, such as the I-beam  2514 , at a predetermined velocity V o  (e.g., 12 mm/s). During the start phase, the control circuit  2510  is configured to monitor the position of the I-beam  2514  and measure the time t o  (sec) it takes for the I-beam  2514  to travel from the I-beam  2514  parked position  9002  to the I-beam  2514  target position  9004 , either to the top of the anvil  2516  closure ramp  9006 , or at the end of a low power mode of operation. Time t o  in the initial zone  9010  is used by the control circuit  2510  to determine the firing velocity of the I-beam  2514  through the first zone Z 1 . For example, in one aspect, if time t o  is &lt;0.9 sec the velocity V 1  may be set to fast and if time t o≥ 0.9 sec the velocity may be set to medium. Faster or slower times may be selected based on the length of the staple cartridge  2518 . The actual time t 1 -t 5  that it takes the I-beam  2514  to traverse a corresponding zone Z 1  to Z 5  is measured at a corresponding set displacement δ 1 -δ 5  and is compared to a corresponding reference time period T 1 -T 5 . In various aspects, if a lockout condition is encountered, the motor  2504  will stall before the I-beam  2514  reaches the target position  9004 . When this condition occurs, the surgical instrument display indicates the instrument status and may issue a stall warning. The display also may indicate a speed selection. 
     During the dynamic firing phase, the surgical instrument enters the dynamic firing phase, where the control circuit  2510  is configured to monitor the displacement interval δ n  of the I-beam  2514  and measure the time t n  that it takes the I-beam  2514  to travel from the beginning of a zone to the end of a zone (e.g., a total distance of 5 mm or 10 mm). In  FIG. 17 , the reference time T 1  is the time taken by the I-beam  2514  to travel from the beginning of zone Z 1  to the end of zone Z 1  at a set velocity V 1 . Likewise, the reference time T 2  is the time it takes the I-beam  2514  to travel from the beginning of zone Z 2  to the end of zone Z 2  at a set velocity V 2 , and so on. Table 1 shows zones that may be defined for staple cartridges  2518  of various sizes. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Defined Zones For Staple Cartridges Of Various Sizes 
               
            
           
           
               
               
            
               
                   
                 Zones 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 Staple Cartridge 
                 Z 1   
                 Z 2   
                 Z 3   
                 Z 4   
                 Z 5   
                 Z 6   
               
               
                   
               
               
                   35 mm 
                 0-5 mm 
                 5-15 mm 
                 15-25 mm 
                   &gt;25 mm 
                 N/A 
                 N/A 
               
               
                 40-45 mm 
                 0-5 mm 
                 5-15 mm 
                 15-25 mm 
                 25-35 mm 
                   &gt;35 mm 
                 N/A 
               
               
                 55-60 mm 
                 0-5 mm 
                 5-15 mm 
                 15-25 mm 
                 25-35 mm 
                 35-45 mm 
                 &gt;45 mm 
               
               
                   
               
            
           
         
       
     
     For staple cartridges  2518  over 60 mm, the pattern continues, but the last 10-15 mm continues at a command or indicated velocity of the previous zone pending other interventions for end of stroke, among others. At the end of each zone, the actual time t n  it took the I-beam  2514  to pass through the zone is compared to the values in other tables (e.g., Tables 2-5 below) to determine how to set the command velocity for the next zone. The command velocity is updated for the next zone and the process continues. Whenever the command velocity is updated, the next zone will not be evaluated. The end of stroke is handled in accordance with a predetermined protocol/algorithm of the surgical instrument including limit switches, controlled deceleration, etc. At the end of stroke, the I-beam  2514  is returned to the initial I-beam park position  9002  at the fast speed. End of return stroke (returning to the parked position  9002 ) is handled in accordance with the protocol/algorithm of the surgical instrument. Other zones may be defined without limitation. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Time To Travel Through Zones At Specified Command Velocity For  
               
               
                 Various Dynamic Firing Zones 
               
            
           
           
               
               
            
               
                   
                 Time (sec) to Travel Through  
               
               
                   
                 Zone at Specified  
               
               
                 Dynamic Firing Zone 
                 Command Velocity 
               
            
           
           
               
               
               
               
            
               
                 (mm) 
                 Fast 
                 Medium 
                 Slow 
               
               
                   
               
               
                 First Zone (X 1 mm long) 
                 t &lt; t 1   
                 t 1  &lt; t &lt; t 2   
                 t &gt; t 2   
               
               
                 Intermediate Zones (X 2 mm long) 
                 t &lt; t 3   
                 t 3  &lt; t &lt; t 4   
                 t &gt; t 4   
               
               
                 Last Measured Zone (X 3 mm long) 
                 t &lt; t 5   
                 t 5  &lt; t &lt; t 6   
                 t &gt; t 6   
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Non-limiting Examples Of Time To Travel Through Zones At  
               
               
                 Specified Command Velocity For Various Dynamic Firing Zones 
               
            
           
           
               
               
            
               
                   
                 Time (sec) to Travel Through  
               
               
                   
                 Zone at Specified  
               
               
                 Dynamic Firing Zone 
                 Command Velocity 
               
            
           
           
               
               
               
               
            
               
                 (mm) 
                 Fast 
                 Medium 
                 Slow 
               
               
                   
               
               
                 First Zone (5 mm long) 
                 t &lt; 0.5 
                 0.5 &lt; t &lt; 0.6 
                 t &gt; 0.6 
               
               
                 Intermediate Zones (10 mm long) 
                 t &lt; 0.9 
                 0.9 &lt; t &lt; 1.1 
                 t &gt; 1.1 
               
               
                 Last Measured Zone (10 mm long) 
                 t &lt; 1.0 
                 1.0 &lt; t &lt; 1.3 
                 t &gt; 1.3 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Algorithm To Set Velocity Based On Time To Travel Up Ramp 
               
            
           
           
               
               
               
            
               
                 Algorithm 
                 t a  (sec) 
                 t b  (sec) 
               
               
                   
               
               
                 If time t (sec) for I-beam to travel up ramp is . . .  
                 t 1  &lt; t &lt; t 2   
                 t &gt; t 2  to t 3   
               
               
                 Then initial velocity V of I-beam in T-slot is . . .  
                 V 1    
                 V 2    
               
               
                   
                 (mm/sec) 
                 (mm/sec) 
               
               
                 And automatic velocity is set at . . .  
                 FAST 
                 MEDIUM 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Non-limiting Example Of Algorithm To Set Velocity Based On  
               
               
                 Time To Travel Up Ramp 
               
            
           
           
               
               
               
            
               
                 Algorithm 
                 t a  (sec) 
                 t b  (sec) 
               
               
                   
               
               
                 If time t (sec) for I-beam to travel up  
                 0.0 &lt; t &lt; 0.9 
                 t &gt; 0.9 to 1.8 
               
               
                 ramp is . . . 
                   
                   
               
               
                 Then initial velocity of I-beam in T-slot  
                 30 mm/sec 
                 12 mm/sec 
               
               
                 is . . . 
                   
                   
               
               
                 And automatic velocity is set at . . .  
                 FAST 
                 MEDIUM 
               
               
                   
               
            
           
         
       
     
     In one aspect, Tables 1-5 may be stored in memory of the surgical instrument. The Tables 1-5 may be stored in memory in the form of a look-up table (LUT) such that the control circuit  2510  can retrieve the values and control the command velocity of the I-beam  2514  in each zone based on the values stored in the LUT. 
       FIG. 18  is a graphical depiction  9100  comparing the I-beam  2514  stroke displacement interval δ n  as a function of time  9102  (top graph) and expected force-to-fire the I-beam  2514  as a function of time  9104  (bottom graph) according to one aspect of this disclosure. Referring to the top graph  9102 , the horizontal axis  9106  represents time (t) in seconds (sec) from 0-1.00X, where X is a scaling factor. For example, in one aspect, X=6 and the horizontal axis  9106  represents time from 0-6 sec. The vertical axis  9108  represents displacement (δ) of the I-beam  2514  in millimeters (mm). The displacement interval δ 1  represents the I-beam  2615  stroke  9114  or displacement at the top of the ramp  9006  ( FIGS. 16A, 16B ) for thin tissue and medium thick tissue. The time for the I-beam  2514  to reach the top of ramp stroke  9114  for thin tissue is t 1  and the time for the I-beam  2514  to reach the top of ramp stroke  9114  for medium thick tissue is t 2 . As shown, t 1 &lt;t 2 , such that it takes less time for the I-beam  2514  to reach the top of the ramp stroke  9114  for thin tissue as it takes for medium or thick tissue. In one example, the top of ramp stroke  9114  displacement interval δ 1  is about 4.1 mm (01.60 inches) and the time t 1  is less than 0.9 sec (t 1 &lt;0.9 sec) and the time t 2  is greater than 0.9 sec but less than 1.8 sec (0.9&lt;t 2 &lt;1.8 sec). Accordingly, with reference also to Table 5, the velocity to reach the top of ramp stroke  9114  is fast for thin tissue and medium for medium thick tissue. 
     Turning now to the bottom graph  9104 , the horizontal axis  9110  represents time (t) in seconds (sec) and has the same scale of the horizontal axis  9106  of the top graph  9102 . The vertical axis  9112 , however, represents expected force to fire (F) the I-beam  2514  in newtons (N) for thin tissue force to fire graph  9116  and medium thick tissue force to fire graph  9118 . The thin tissue force to fire graph  9116  is lower than medium thick tissue force to fire graph  9118 . The peak force F 1  for the thin tissue force to fire graph  9116  is lower than the peak force F 2  for the medium thick tissue to fire graph  9118 . Also, with reference to the top and bottom graphs  9102 ,  9104 , the initial velocity of the I-beam  2514  in zone Z o  can be determined based on estimated tissue thickness. As shown by the thin tissue force to fire graph  9116 , the I-beam  2514  reaches the peak force F 1  top of ramp stroke  9114  at a fast initial velocity (e.g., 30 mm/sec) and as shown by the medium thick tissue force to fire graph  9118 , the I-beam  2514  reaches the peak force F 2  top of ramp stroke  9114  at a medium initial velocity (e.g., 12 mm/sec). Once the initial velocity in zone Z o  is determined, the control circuit  2510  can set the estimated velocity of the I-beam  2514  in zone Z 1 , and so on. 
       FIG. 19  is a graphical depiction  9200  comparing tissue thickness as a function of set displacement interval of I-beam stroke  9202  (top graph), force to fire as a function of set displacement interval of I-beam stroke  9204  (second graph from the top), dynamic time checks as a function of set displacement interval of I-beam stroke  9206  (third graph from the top), and set velocity of I-beam as a function of set displacement interval of I-beam stroke  9208  (bottom graph) according to one aspect of this disclosure. The horizontal axis  9210  for each of the graphs  9202 ,  9204 ,  9206 ,  9208  represents set displacement interval of an I-beam  2514  stroke for a 60 mm staple cartridge, for example. With reference also to Table 1, the horizontal axis  9210  has been marked to identify the defined zones Z 1 -Z 6  for a 60 mm staple cartridge. As indicated in Table 1, the defined zones may be marked for staple cartridges of various sizes. With reference also to  FIG. 14 , in accordance with the present disclosure, the control circuit  2510  samples or measures the elapsed time from the timer/counter circuit  2531  at set I-beam  2514 , or other displacement member, displacement intervals along the staple cartridge  2518  during the firing stroke. At set displacement intervals δ n  received from the position sensor  2534 , the control circuit  2510  samples or measures the elapsed time t n  it took the I-beam  2514  to travel the fixed displacement intervals δ n . In this manner, the control circuit  2510  can determine the actual velocity of the I-beam  2514  and compare the actual velocity to the estimated velocity and make any necessary adjustments to the motor  2504  velocity. 
     The tissue thickness graph  9202  shows a tissue thickness profile  9220  along the staple cartridge  2518  and an indicated thickness  9221  as shown by the horizontal dashed line. The force to fire graph  9204  shows the force to fire profile  9228  along the staple cartridge  2518 . The force to fire  9230  remains relatively constant while the tissue thickness  9222  remains below the indicated thickness  9221  as the I-beam  2514  traverse zones Z 1  and Z 2 . As the I-beam  2514  enters zone Z 3 , the tissue thickness  9224  increases and the force to fire also increase while the I-beam  2514  traverses the thicker tissue in zones Z 3 , Z 4 , and Z 5 . As the I-beam  2514  exits zone Z 5  and enters zone Z 6 , the tissue thickness  9226  decrease and the force to fire  9234  also decreases. 
     With reference now to  FIGS. 14, 17-19  and Tables 2-3, the velocity V 1  in zone Z 1  is set to the command velocity V o  determined by the control circuit  2510  in zone Z o , which is based on the time it takes the I-beam  2514  to travel to the top of the ramp  9006  in zone Z o  as discussed in reference to  FIGS. 16A, 16B, and 18 . Turning also to the graphs  9206 ,  9208  in  FIG. 19 , the initial set velocity V o  was set to Medium and thus the set velocity V 1  in zone Z 1  is set to Medium such that V 1 =V o . 
     At set displacement position δ 1  (e.g., 5 mm for a 60 mm staple cartridge), as the I-beam  2514  exits zone Z 1  and enters zone Z 2 , the control circuit  2510  measures the actual time t 1  that it takes the I-beam  2514  to traverse the set displacement interval X 1  (5 mm long) and determines the actual velocity of the I-beam  2514 . With reference to graphs  9206  and  9208  in  FIG. 19 , at set displacement position δ 1 , the actual time t 1  it takes the I-beam  2514  to travel the set displacement interval X 1  is t 1 =0.55 sec. According to Table 3, an actual travel time t 1 =0.55 sec in zone Z 1  requires the command or set velocity V 2  in zone Z 2  to be set to Medium. Accordingly, the control circuit  2510  does not reset the command velocity for zone Z 2  and maintains it at Medium. 
     At set displacement position δ 2  (e.g., 15 mm for a 60 mm staple cartridge), as the I-beam  2514  exits zone Z 2  and enters zone Z 3 , the control circuit  2510  measures the actual time t 2  it takes the I-beam  2514  to traverse the set displacement interval X 2  (10 mm long) and determines the actual velocity of the I-beam  2514 . With reference to graphs  9606  and  9608  in  FIG. 19 , at set displacement position δ 2 , the actual time t 2  it takes the I-beam  2514  to travel the set displacement interval X 2  is t 2 =0.95 sec. According to Table 3, an actual travel time t 2 =0.95 sec in zone Z 2  requires the command or set velocity V 3  in zone Z 3  to be set to Medium. Accordingly, the control circuit  2510  does not reset the command velocity for zone Z 3  and maintains it at Medium. 
     At set displacement position δ 3  (e.g., 25 mm for a 60 mm staple cartridge), as the I-beam  2514  exits zone Z 3  and enters zone Z 4 , the control circuit  2510  measures the actual time t 3  it takes the I-beam  2514  to traverse the set displacement interval X 3  (10 mm long) and determines the actual velocity of the I-beam  2514 . With reference to graphs  9606  and  9608  in  FIG. 19 , at set displacement position δ 3 , the actual time t 3  it takes the I-beam  2514  to travel the set displacement interval X 3  is t 3 =1.30 sec. According to Table 3, an actual travel time t 3 =1.30 sec in zone Z 3  requires the command or set velocity V 4  in zone Z 4  to be set to Slow. This is because the actual travel time of 1.3 sec is greater than 1.10 sec and is outside the previous range. Accordingly, the control circuit  2510  determines that the actual I-beam  2514  velocity in zone Z 3  was slower than expected due to external influences such as thicker tissue than expected as shown in tissue region  9224  in graph  9202 . Accordingly, the control circuit  2510  resets the command velocity V 4  in zone Z 4  from Medium to Slow. 
     In one aspect, the control circuit  2510  may be configured to disable velocity reset in a zone following a zone in which the velocity was reset. Stated otherwise, whenever the velocity is updated in a present zone the subsequent zone will not be evaluated. Since the velocity was updated in zone Z 4 , the time it takes the I-beam  2514  to traverse zone Z 4  will not be measured at the end of zone Z 4  at the set displacement distance δ 4  (e.g., 35 mm for a 60 mm staple cartridge). Accordingly, the velocity in zone Z 5  will remain the same as the velocity in zone Z 4  and dynamic time measurements resume at set displacement position δ 5  (e.g., 45 mm for a 60 mm staple cartridge). 
     At set displacement position δ 5  (e.g., 45 mm for a 60 mm staple cartridge) as the I-beam  2514  exits zone Z 5  and enters zone Z 6 , the control circuit  2510  measures the actual time t 5  it takes the I-beam  2514  to traverse the set displacement interval X 5  (10 mm long) and determines the actual velocity of the I-beam  2514 . With reference to graphs  9606  and  9608  in  FIG. 19 , at set displacement position δ 5 , the actual time t 5  it takes the I-beam  2514  to traverse the set displacement interval X 5  is t 5 =0.95 sec. According to Table 3, an actual travel time of t 5 =0.95 sec in zone Z 5  requires the command or set velocity V 6  in zone Z 6  to be set to High. This is because the actual travel time of 0.95 sec is less than 1.00 sec is outside the previous range. Accordingly, the control circuit  2510  determines that the actual velocity of the I-beam  2514  in zone Z 5  was faster than expected due to external influences such as thinner tissue than expected as shown in tissue region  9626  in graph  9602 . Accordingly, the control circuit  2510  resets the command velocity V 6  in zone Z 6  from Slow to High. 
       FIG. 20  is a graphical depiction  9300  of force to fire as a function of time comparing slow, medium and fast I-beam  2514  displacement velocities according to one aspect of this disclosure. The horizontal axis  9302  represents time t (sec) that it takes an I-beam to traverse a staple cartridge. The vertical axis  9304  represents force to fire F (N). The graphical depiction shows three separate force to fire curves versus time. A first force to fire curve  9312  represents an I-beam  2514  ( FIG. 14 ) traversing through thin tissue  9306  at a fast velocity and reaching a maximum force to fire F 1  at the top of the ramp  9006  ( FIG. 16B ) at t 1 . In one example, a fast traverse velocity for the I-beam  2514  is ˜30 mm/sec. A second force to fire curve  9314  represents an I-beam  2514  traversing through medium tissue  9308  at a medium velocity and reaching a maximum force to fire F 2  at the top of the ramp  9006  at t 2 , which is greater than t 1 . In one example, a medium traverse velocity for the I-beam  2514  is ˜12 mm/sec. A third force to fire curve  9316  represents an I-beam  2514  traversing through thick tissue  9310  at a slow velocity and reaching a maximum force to fire F 3  at the top of the ramp  9006  at t 3 , which is greater than t 2 . In one example, a slow traverse velocity for the I-beam  2514  is ˜9 mm/sec. 
       FIG. 21  is a logic flow diagram of a process  9400  depicting a control program or logic configuration for controlling command velocity in an initial firing stage according to one aspect of this disclosure. With reference also to  FIGS. 14 and 16-20 , the control circuit  2510  determines  9402  the reference position of the displacement member, such as the I-beam  2514 , for example, based on position information provided by the position sensor  2534 . In the I-beam  2514  example, the reference position is the proximal or parked position  9002  at the bottom of the closure ramp  9006  as shown in  FIG. 16B . Once the reference position is determined  9402 , the control circuit  2510  and motor control  2508  set the command velocity of the motor  2504  to a predetermined command velocity V o  and initiates  9404  firing the displacement member (e.g., I-beam  2514 ) at the predetermined command velocity V o  for the initial or base zone Z o . In one example, the initial predetermined command velocity V o  is ˜12 mm/sec, however, other initial predetermined command velocity V o  may be employed. The control circuit  2510  monitors  9406  the position of the displacement member with position information received from the position sensor  2534  until the I-beam  2514  reaches a target position at the top of the ramp  9006  as shown in  FIG. 16B . The predetermined displacement period T o  is the expected displacement period of the displacement member traveling at the current set command velocity V o . The deviation between actual displacement period T n  and the predetermined displacement period T o  is due at least in part to external influences acting on the displacement member such as tissue thickness acting on the cutting edge  2509  of the I-beam  2514 . 
     With timing information received from the timer/counter circuit  2531  and position information received from the position sensor  2534 , the control circuit  2510  measures  9408  the time t o  it takes the displacement member to travel from the reference position  9002  to the target position  9004 . The control circuit  210  sets  9410  the command velocity V 1  for the first zone Z 1  based on the measured time t o . As indicated in Table 1, various defined zones may be defined for staple cartridges of various sizes. Other zones, however, may be defined. The control circuit  2510  sets  9410  the command velocity V 1  for the first zone Z 1  by comparing  9412  the measured time t o  to values stored in memory, such as, for example, stored in a lookup table (LUT). In one example, as indicated in Table 4 generally and in Table 5 by way of specific example, if the time t o  it takes the I-beam  2514  to travel up the ramp  9006  from the reference position  9002  to the target position  9004  is between 0.0 and 0.9 sec (0.0 sec&lt;t o &lt;0.9 sec), then the command velocity for the first zone Z 1  is set  9414  to FAST (e.g., 30 mm/sec). Otherwise, if the time t o  (sec) for the I-beam  2514  to travel up the ramp  9006  from the reference position  9002  to the target position  9004  is greater than 0.9 sec to 1.8 sec (t o &gt;0.9 sec to 1.8 sec), then the command velocity for the first zone Z 1  is set  9416  to MEDIUM (e.g., 12 mm/sec). Subsequently, the control circuit  2510  checks  9418  for lockout and stops  9420  the motor  2504  if there is a lockout condition. Otherwise, the control circuit enters  9422  the dynamic firing phase as described below in reference to process  9450  in  FIG. 22 . 
       FIG. 22  is a logic flow diagram of a process  9450  depicting a control program or logic configuration for controlling command velocity in a dynamic firing stage according to one aspect of this disclosure. With reference also to  FIGS. 14 and 16-20 , the control circuit  2510  sets  9452  the initial command velocity of the motor  2504  for the first zone Z 1  based on the initial time t o , as described in reference to the process  9400  in  FIG. 21 . As the displacement member traverses the staple cartridge  2518 , the control circuit  2510  receives the position of the displacement member from the position sensor  2534  and timing information from the timer/counter  2531  circuit and monitors  9454  the position of the displacement member over the predefined zone Z n . At the end of the zone Z n , the control circuit  2510  measures  9456  the actual time t n  the displacement member took to travel from the beginning of the zone Z n  to the end of the zone Z n  and compares  9458  the actual time t n  to a predetermined time for a particular zone as shown generally in Table 2 and by way of specific example in Table 3. The predetermined displacement period T n  is the expected displacement period of the displacement member traveling at the current set command velocity V n . The deviation between actual displacement period t n  and the predetermined displacement period T n  is due at least in part to external influences acting on the displacement member such as tissue thickness acting on the cutting edge  2509  of the I-beam  2514 . 
     For example, with reference to Table 3 the time to travel through a zone at specified command velocity is provided for various dynamic firing zones. For example, if the dynamic firing zone is the zone Z 1  (5 mm long) and t n &lt;0.5 sec, the command velocity for the next zone Z 2  is set to FAST; if 0.5&lt;t n &lt;0.6 sec, the command velocity for the next zone Z 2  is set to MEDIUM; and if t n &gt;0.6 sec, the command velocity for the next zone Z 2  is set to SLOW. 
     If, however, the dynamic firing zone is an intermediate zone Z 2 -Z 5  (10 mm long), for example, located between the first zone Z 1  and the last zone Z 6  and if t n &lt;0.9 sec, the command velocity for the next zone Z 2  is set to FAST; if 0.9&lt;t n &lt;1.1 sec, the command velocity for the next zone Z 3 -Z 5  is set to MEDIUM; and if t n &gt;1.1 sec, the command velocity for the next zone Z 3 -Z 5  is set to SLOW. 
     Finally, if the dynamic firing zone is the last measured zone Z 5  (10 mm long) and t n &lt;1.0 sec, the command velocity for the final zone Z 6  is set to FAST; if 1.0&lt;t n &lt;1.3 sec, the command velocity for the final zone Z 6  is set to MEDIUM; and if t n &gt;1.3 sec, the command velocity for the final zone Z 6  is set to SLOW. Other parameters may be employed not only to define the dynamic firing zones but also to define the time to travel through a zone at specified command velocity for various dynamic firing zones. 
     Based on the results of the comparison  9458  algorithm, the control circuit  2510  will continue the process  9450 . For example, if the results of the comparison  9458  indicate that the actual velocity (FAST, MEDIUM, SLOW) in the previous zone Z n  is the same as the previous command velocity V 1  (FAST, MEDIUM, SLOW), the control circuit  2510  maintains  9460  the command velocity V 1  for the next zone Z n+1  the same as the as the previous command velocity V 1 . The process  9450  continues to monitor  9454  the position of the displacement member over the next predefined zone Z n+1 . At the end of the next zone Z n+1 , the control circuit  2510  measures  9456  the time t n+1  the displacement member took to travel from the beginning of the next zone Z n+1  to the end of the next zone Z n1  and compares  9458  the actual time t n+1  to a predetermined time for a particular zone as shown generally in Table 2 and by way of specific example in Table 3. If there are no changes required to the command velocity, the process  9450  until the displacement member, e.g., the I-beam  2514 , reaches the end of stroke  9466  and returns  9468  the displacement member to the reference position  9002 . 
     If the results of the comparison  9458  indicate that the actual velocity (FAST, MEDIUM, SLOW) in the previous zone Z n  is different as the previous command velocity V 1  (FAST, MEDIUM, SLOW), the control circuit  2510  resets  9462  or updates the command velocity to V new  for the next zone Z n+1  according to the algorithm summarized in Tables 2 and 3. If the command velocity is reset  9462  or updated, the control circuit  2510  maintains  9464  the command velocity V new  for an additional zone Z n+2 . In other words, at the end of the next zone Z n+1 , the control circuit  2510  does not evaluate or measure the time. The process  9450  continues to monitor  9454  the position of the displacement member over the next predefined zone Z n+1  until the displacement member, e.g., the I-beam  2514 , reaches the end of stroke  9466  and returns  9468  the displacement member to the reference position  9002 . 
     The functions or processes  9400 ,  9450  described herein may be executed by any of the processing circuits described herein, such as the control circuit  700  described in connection with  FIGS. 5-6 , the circuits  800 ,  810 ,  820  described in  FIGS. 7-9 , the microcontroller  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 operation. 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 configured to translate within the surgical instrument over a plurality of predefined zones; a motor coupled to the displacement member to translate the displacement member; a control circuit coupled to the motor; a position sensor coupled to the control circuit, the position sensor configured to monitor the position of the displacement member; a timer circuit coupled to the control circuit, the timer/counter circuit configured to measure elapsed time; wherein the control circuit is configured to: receive, from the position sensor, a position of the displacement member in a current zone defined by a set displacement interval; measure time at a set position of the displacement interval, wherein the measured time is defined as the time taken by the displacement member to traverse the displacement interval; and set a command velocity of the displacement member for a subsequent zone based on the measured time in the current predefined zone. 
     Example 2 
     The surgical instrument of Example 1, wherein the control circuit is configured to: determine the set displacement interval in which the displacement member is located, wherein the set displacement interval is defined by a beginning position and an ending position; and measure the time when the displacement member reaches the ending position of the displacement interval. 
     Example 3 
     The surgical instrument of Example 1 through Example 2, wherein the control circuit is configured to: compare the measured time to a predetermined time stored in a memory coupled to the control circuit; and determine whether to adjust or maintain the command velocity based on the comparison. 
     Example 4 
     The surgical instrument of Example 3, wherein the control circuit is configured to maintain the command velocity for the subsequent zone the same as the command velocity of the current zone when the measured time is within a range of predetermined times. 
     Example 5 
     The surgical instrument of Example 3 through Example 4, wherein the control circuit is configured to set the command velocity for the subsequent zone different from the command velocity of the current zone when the measured time is outside a range of predetermined times. 
     Example 6 
     The surgical instrument of Example 5, wherein the control circuit is configured to skip a time measurement for a subsequent zone when the command velocity is adjusted. 
     Example 7 
     The surgical instrument of Example 1 through Example 6, wherein multiple zones are defined for a staple cartridge configured to operate with the surgical instrument. 
     Example 8 
     The surgical instrument of Example 7, wherein at least two zones have a different length. 
     Example 9 
     A surgical instrument, comprising: a displacement member configured to translate within the surgical instrument over a plurality of predefined zones; a motor coupled to the displacement member to translate the displacement member; a control circuit coupled to the motor; a position sensor coupled to the control circuit, the position sensor configured to monitor the position of the displacement member; a timer circuit coupled to the control circuit, the timer/counter circuit configured to measure elapsed time; wherein the control circuit is configured to: receive, from the position sensor, a position of the displacement member in a current zone defined by a predetermined displacement interval; measure time as the displacement member moves from a parked position to a target position; and set a command velocity of the displacement member for a first dynamic zone based on the measured time. 
     Example 10 
     The surgical instrument of Example 9, wherein the control circuit is configured to compare the measured time to a predetermined time stored in a memory coupled to the control circuit. 
     Example 11 
     The surgical instrument of Example 10, wherein the control circuit is configured to set the command velocity for the initial zone to a first velocity when the measured time is within a first range of times and set the command velocity for the initial zone to a second velocity when the measured time is within a second range of times. 
     Example 12 
     The surgical instrument of Example 9 through Example 11, wherein the control circuit is configured to determine a lockout condition and stop the motor. 
     Example 13 
     A method of controlling motor velocity in a surgical instrument, the surgical instrument comprising a displacement member configured to translate within the surgical instrument over a plurality of predefined zones, a motor coupled to the displacement member to translate the displacement member, a control circuit coupled to the motor, a position sensor coupled to the control circuit, the position sensor configured to monitor the position of the displacement member, a timer circuit coupled to the control circuit, the timer/counter circuit configured to measure elapsed time, the method comprising: receiving, from a position sensor, a position of a displacement member within a current zone defined by a set displacement interval; measuring, by a timer circuit, a time at a set position of the displacement member, wherein the time is defined by the time taken by the displacement member to traverse the displacement interval; and setting, by the control circuit, a command velocity of the displacement member for a subsequent zone based on the measured time in the current zone. 
     Example 14 
     The method of Example 13, further comprising: determining, by the control circuit and the timer circuit, the set displacement interval in which the displacement member is located, wherein the set displacement interval is defined by a beginning position and an ending position; and measuring, by the control circuit, the time when the displacement member reaches the ending position of the displacement interval. 
     Example 15 
     The method of Example 13 through Example 14, further comprising: comparing, by the control circuit, the measured time to a predetermined time stored in a memory coupled to the control circuit; and determining, by the control circuit, whether to adjust or maintain the command velocity based on the comparison. 
     Example 16 
     The method of Example 15, further comprising maintaining, by the control circuit, the command velocity for the subsequent zone the same as the command velocity of the current zone when the measured time is within a range of predetermined times. 
     Example 17 
     The method of Example 15 through Example 16, further comprising setting, by the control circuit, the command velocity for the subsequent zone different from the command velocity of the current zone when the measured time is outside a range of predetermined times. 
     Example 18 
     The method of Example 17, further comprising skipping, by the control circuit, a time measurement for a subsequent zone when the command velocity is adjusted. 
     Example 19 
     The method of Example 13 through Example 18, further comprising defining, by the control circuit, multiple zones are defined for a staple cartridge configured to operate with the surgical instrument. 
     Example 20 
     The method of Example 19, further comprising defining, by the control circuit, at least two zones having a different length.