Patent Publication Number: US-10760932-B2

Title: Methods to shorten calibration times for powered devices

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/683,407, filed Apr. 10, 2015, which is a continuation-in-part of U.S. patent application Ser. No. 12/895,897, filed on Oct. 1, 2010, (now U.S. Pat. No. 9,113,880), which claims priority to U.S. Provisional Patent Application Ser. No. 61/248,971, filed on Oct. 6, 2009, and to U.S. Provisional Patent Application Ser. No. 61/248,504, filed on Oct. 5, 2009. U.S. patent application Ser. No. 12/895,897, filed on Oct. 1, 2010, is a continuation-in-part, (now abandoned), of U.S. patent application Ser. No. 12/189,834, filed on Aug. 8, 2008, which claims priority to U.S. Provisional Patent Application Ser. No. 60/997,854, filed on Oct. 5, 2007. The entire contents of the above-mentioned applications are hereby incorporated by reference herein. 
    
    
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a surgical stapler for implanting mechanical surgical fasteners into the tissue of a patient, and, in particular, to a surgical stapler which is powered by a motor for firing surgical fasteners into tissue and a controller for determining one or more conditions related to the firing of the surgical fasteners and controlling the stapler in response to one or more sensed feedback signals. 
     2. Background of Related Art 
     Motor-powered surgical staplers include motors which translate components that are used to clamp tissue and activate a staple firing mechanism. Pre-stapling calibration identifies the current position of the translating components. This calibration can be time consuming, requiring full strokes of the translating components to their full proximal and distal stop positions. Additionally, precise calibration may be difficult where tolerances between mating components and/or gear meshes have some gap or slip associated to enable assembly of the motor-powered surgical stapler. Thus, there is a need for new and improved powered surgical staplers that precisely determine the position of the translating components to calibrate the powered surgical staplers. 
     SUMMARY 
     In an aspect of the present disclosure, a hand-held surgical instrument is provided. The hand-held surgical instrument includes a drive motor, a firing rod controlled by the drive motor and having at least one indicator, and a sensor configured to detect the indicator. The hand-held surgical instrument also includes a microcontroller having a pulse modulation algorithm stored therein to control the drive motor. The microcontroller executes a calibration algorithm to adjust a program coefficient in the pulse modulation algorithm. 
     The indicator may be a bump, groove, indentation, magnet, notch, or at least one thread on the firing rod. The sensor may be a linear displacement sensor. 
     In some aspects, the instrument also includes a position calculator configured to determine a time between when the firing rod begins translation and when the sensor detects the indicator. The microcontroller receives the determined time from the position calculator and compares the determined time to a stored predetermined time. The microcontroller adjusts a program coefficient based on the comparison between the determined time and the stored predetermined time. 
     In other aspects, the sensor also determines the linear speed of the firing rod and selects the stored predetermined time based on the linear speed. 
     In another aspect of the present disclosure, a method for calibrating a hand-held surgical instrument having a drive motor, a firing rod, a sensor, a microcontroller, and a memory having a pulse modulation algorithm stored therein is provided. The method includes initiating translation of the firing rod, detecting at least one indicator on the firing rod, and determining a time between when translation of the firing rod is initiated and when the indicator is detected. The method also includes comparing the determined time with a stored predetermined time and adjusting at least one program coefficient in the pulse modulation algorithm based on the comparison between the determined time and the stored predetermined time. 
     In some aspects, if the determined time is less than the predetermined time, a program coefficient is adjusted so that the firing rod is translated a relatively shorter distance. 
     In other aspects, if the time is greater than the predetermined time, the program coefficient is adjusted so that the firing rod is translated a relatively longer distance. 
     In aspects, the linear speed of the firing rod is determined, and the stored predetermined time is selected based on the determined linear speed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments of the subject instrument are described herein with reference to the drawings wherein: 
         FIG. 1  is a perspective view of a powered surgical instrument according to an exemplary embodiment of the present disclosure; 
         FIG. 2  is a partial enlarged perspective view of the powered surgical instrument of  FIG. 1 ; 
         FIG. 2A  is a partial enlarged perspective view of a variant of the powered surgical instrument of  FIGS. 1 and 2 ; 
         FIG. 2B  is a proximal end view of the variant of the powered surgical instrument of  FIG. 2A ; 
         FIG. 3  is a partial enlarged plan view of the powered surgical instrument of  FIG. 1 ; 
         FIG. 4  is a partial sectional view of internal components of the powered surgical instrument of  FIG. 1 ; 
         FIG. 4A  is a partial view of internal components of the variant of the powered surgical instrument of  FIG. 4 ; 
         FIG. 5  is a perspective view of an articulation mechanism with parts separated of the powered surgical instrument of  FIG. 1 ; 
         FIG. 6  is a partial cross-sectional view showing internal components of the powered surgical instrument of  FIG. 1  disposed in a first position; 
         FIG. 7  is a partial cross-sectional view showing internal components of the powered surgical instrument of  FIG. 1  disposed in a second position; 
         FIG. 8  is a perspective view of the mounting assembly and the proximal body portion of a loading unit with parts separated of the powered surgical instrument of  FIG. 1 ; 
         FIG. 9  is a side cross-sectional view of an end effector of the powered surgical instrument of  FIG. 1 ; 
         FIG. 10  is a partial enlarged side view showing internal components of the powered surgical instrument of  FIG. 1 ; 
         FIG. 10A  is a partial enlarged cross-sectional view of the internal components of the variant of the powered surgical instrument of  FIG. 4A ; 
         FIG. 11  is a perspective view of a unidirectional clutch plate of the powered surgical instrument of  FIG. 1 ; 
         FIG. 12  is a partial enlarged side view showing internal components of the powered surgical instrument of  FIG. 1 ; 
         FIG. 13  is a schematic diagram of a power source of the powered surgical instrument of  FIG. 1 ; 
         FIG. 14  is a flow chart diagram illustrating a method for authenticating the power source of the powered surgical instrument of  FIG. 1 ; 
         FIGS. 15A-B  are partial perspective rear views of a loading unit of the powered surgical instrument of  FIG. 1 ; 
         FIG. 16  is a flow chart diagram illustrating a method for authenticating the loading unit of the powered surgical instrument of  FIG. 1 ; 
         FIG. 17  is a perspective view of the loading unit of the powered surgical instrument of  FIG. 1 ; 
         FIG. 18  is a side cross-sectional view of the end effector of the powered surgical instrument of  FIG. 1 ; 
         FIG. 19  is a side cross-sectional view of the powered surgical instrument of  FIG. 1 ; 
         FIG. 20  is a schematic diagram of a control system of the powered surgical instrument of  FIG. 1 ; 
         FIG. 21  is a schematic diagram of a feedback control system according to an exemplary embodiment of the present disclosure; 
         FIGS. 22A-B  are perspective front and rear views of a feedback controller of the feedback control system according to an exemplary embodiment of the present disclosure; 
         FIG. 23  is a schematic diagram of the feedback controller according to an exemplary embodiment of the present disclosure; 
         FIG. 24  is a partial sectional view of internal components of a powered surgical instrument in accordance with an embodiment of the present disclosure; 
         FIG. 25  is a partial perspective sectional view of internal components of the powered surgical instrument in accordance with an embodiment of the present disclosure; 
         FIG. 26  is a partial perspective view of a nose assembly of the powered surgical instrument in accordance with an embodiment of the present disclosure; 
         FIG. 27  is a partial perspective view of a retraction lever of the powered surgical instrument in accordance with an embodiment of the present disclosure; 
         FIG. 28  is a partial perspective view of the powered surgical instrument in accordance with an embodiment of the present disclosure; 
         FIG. 29  is a perspective view of a lever in accordance with an embodiment of the present disclosure; 
         FIG. 30  is a perspective view of a modular retraction assembly of the powered surgical instrument in accordance with an embodiment of the present disclosure; 
         FIG. 31  is an enlarged partial sectional view of internal components of a powered surgical instrument in accordance with an embodiment of the present disclosure; and 
         FIG. 32  is an enlarged partial sectional view of internal components of a powered surgical instrument in accordance with an embodiment of the present disclosure. 
         FIG. 33  is a perspective view of a powered surgical instrument having one or more sealing members around a power head of the instrument according to an embodiment of the present disclosure; 
         FIG. 34  is a partial cross-sectional view of the power head of  FIG. 33  illustrating the internal components of the power head and the one or more sealing members; 
         FIG. 35  is a perspective view illustrating a battery pack or power supply pack for the power head of  FIGS. 33 and 34  according to one embodiment of the present disclosure; 
         FIG. 36  is a perspective view of a battery pack or power supply pack having a sealing member according to one embodiment of the present disclosure; 
         FIG. 37  is a perspective view of the exterior of the housing of the power head of the surgical instrument according to the present disclosure; 
         FIG. 38  is a partial cross-sectional view of the power head of  FIG. 37  illustrating a set of operating components mounted on a structural member or chassis according to one embodiment of the present disclosure; 
         FIG. 39  is a view of one side of the structural member or chassis showing the features for mounting the operating components according to one embodiment of the present disclosure; 
         FIG. 40  is an exploded perspective view of the power head of  FIG. 36  showing the housing portions and a set of operating components mounted on the structural member or chassis according to the present disclosure; 
         FIG. 41  is another exploded perspective view of the power head of  FIG. 36  showing the housing portions and a set of operating components mounted on the structural member or chassis according to the present disclosure; 
         FIG. 42  is a view of the side of the structural member or chassis as illustrated in  FIG. 39  and illustrating a set of operating components mounted on the structural member or chassis; 
         FIG. 43  is a view of another side of the structural member or chassis and illustrating a set of operating components mounted on the structural member or chassis; and 
         FIG. 44  is a flow chart depicting a method for calibrating a powered surgical instrument according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the presently disclosed powered surgical instrument are now described in detail with reference to the drawings, in which like reference numerals designate identical or corresponding elements in each of the several views. As used herein the term “distal” refers to that portion of the powered surgical instrument, or component thereof, farther from the user while the term “proximal” refers to that portion of the powered surgical instrument or component thereof, closer to the user. 
     Additionally, in the drawings and in the description that follows, terms such as “front”, “rear”, “upper”, “lower”, “top”, “bottom” and the like are used simply for convenience of description and are not intended to limit the disclosure thereto. 
     A powered surgical instrument, e.g., a surgical stapler, in accordance with the present disclosure is referred to in the figures as reference numeral  10 . Referring initially to  FIG. 1 , powered surgical instrument  10  includes a housing  110 , an endoscopic portion  140  defining a first longitudinal axis A-A extending therethrough, and an end effector  160 , defining a second longitudinal axis B-B extending therethrough. Endoscopic portion  140  extends distally from housing  110  and the end effector  160  is disposed adjacent a distal portion of endoscopic portion  140 . In an embodiment, the components of the housing  110  are sealed against infiltration of particulate and/or fluid contamination and help prevent damage of the component by the sterilization process. 
     According to an embodiment of the present disclosure, end effector  160  includes a first jaw member having one or more surgical fasteners (e.g., cartridge assembly  164 ) and a second opposing jaw member including an anvil portion for deploying and forming the surgical fasteners (e.g., an anvil assembly  162 ). In certain embodiments, the staples are housed in cartridge assembly  164  to apply linear rows of staples to body tissue either in simultaneous or sequential manner. Either one or both of the anvil assembly  162  and the cartridge assembly  164  are movable in relation to one another between an open position in which the anvil assembly  162  is spaced from cartridge assembly  164  and an approximated or clamped position in which the anvil assembly  162  is in juxtaposed alignment with cartridge assembly  164 . 
     It is further envisioned that end effector  160  is attached to a mounting portion  166 , which is pivotably attached to a body portion  168 . Body portion  168  may be integral with endoscopic portion  140  of powered surgical instrument  10 , or may be removably attached to the instrument  10  to provide a replaceable, disposable loading unit (DLU) or single use loading unit (SULU) (e.g., loading unit  169 ). In certain embodiments, the reusable portion may be configured for sterilization and re-use in a subsequent surgical procedure. 
     The loading unit  169  may be connectable to endoscopic portion  140  through a bayonet connection. It is envisioned that the loading unit  169  has an articulation link connected to mounting portion  166  of the loading unit  169  and the articulation link is connected to a linkage rod so that the end effector  160  is articulated as the linkage rod is translated in the distal-proximal direction along first longitudinal axis A-A. Other means of connecting end effector  160  to endoscopic portion  140  to allow articulation may be used, such as a flexible tube or a tube comprising a plurality of pivotable members. 
     The loading unit  169  may incorporate or be configured to incorporate various end effectors, such as vessel sealing devices, linear stapling devices, circular stapling devices, cutters, etc. Such end effectors may be coupled to endoscopic portion  140  of powered surgical instrument  10 . The loading unit  169  may include a linear stapling end effector that does not articulate. An intermediate flexible shaft may be included between handle portion  112  and loading unit. It is envisioned that the incorporation of a flexible shaft may facilitate access to and/or within certain areas of a patient&#39;s body. 
     With reference to  FIG. 2 , an enlarged view of the housing  110  is illustrated according to an embodiment of the present disclosure. In the illustrated embodiment, housing  110  includes a handle portion  112  having a main drive switch  114  disposed thereon. The switch  114  may include first and second switches  114   a  and  114   b  formed together as a toggle switch. The handle portion  112 , which defines a handle axis H-H, is configured to be grasped by fingers of a user. The handle portion  112  has an ergonomic shape providing ample palm grip leverage which helps prevent the handle portion  112  from being squeezed out of the user&#39;s hand during operation. Each switch  114   a  and  114   b  is shown as being disposed at a suitable location on handle portion  112  to facilitate its depression by a user&#39;s finger or fingers. In another embodiment, the instrument  10  includes two separates switches  114   a  and  114   b  separated by a rib feature. 
     Additionally, and with reference to  FIGS. 1 and 2 , switches  114   a ,  114   b  may be used for starting and/or stopping movement of drive motor  200  ( FIG. 4 ). In one embodiment, the switch  114   a  is configured to activate the drive motor  200  in a first direction to advance firing rod  220  ( FIG. 6 ) in a distal direction thereby clamping the anvil and the cartridge assemblies  162  and  164 . Conversely, the switch  114   b  may be configured to retract the firing rod  220  to open the anvil and cartridge assemblies  162  and  164  by activating the drive motor  200  in a reverse direction. Once the stapling and cutting mode has been initiated, during the retraction mode, a mechanical lock out (not shown) is actuated, preventing further progression of stapling and cutting by the loading unit  169 . The lockout is redundantly backed up with software to prevent the cutting of tissue after the staples have been previously deployed. The toggle has a first position for activating switch  114   a , a second position for activating switch  114   b , and a neutral position between the first and second positions. The details of operation of the drive components of the instrument  10  are discussed in more detail below. 
     The housing  110 , in particular the handle portion  112 , includes switch shields  117   a  and  117   b . The switch shields  117   a  and  117   b  may have a rib-like shape surrounding the bottom portion of the switch  114   a  and the top portion of the switch  114   b , respectively. The switch shield  117   a  and  117   b  prevent accidental activation of the switch  114 . Further, the switches  114   a  and  114   b  have high tactile feedback requiring increased pressure for activation. 
     In one embodiment, the switches  114   a  and  114   b  are configured as multi-speed (e.g., two or more), incremental or variable speed switches which control the speed of the drive motor  200  and the firing rod  220  in a non-linear manner. For example, switches  114   a, b  can be pressure-sensitive. This type of control interface allows for gradual increase in the rate of speed of the drive components from a slower and more precise mode to a faster operation. To prevent accidental activation of retraction, the switch  114   b  may be disconnected electronically until a fail safe switch is pressed. In addition a third switch  114   c  may also be used for this purpose. Additionally or alternatively, the fail safe can be overcome by pressing and holding the switch  114   b  for a predetermined period of time from about 100 ms to about 2 seconds. The firing rod  220  then automatically retracts to its initial position unless the switches  114   a  and  114   b  are activated (e.g., pressed and released) during the retraction mode to stop the retraction. Subsequent pressing of the switch  114   b  after the release thereof resumes the retraction. Alternatively, the retraction of the firing rod  220  can continue to full retraction even if the switch  114   b  is released, in other embodiments. Other embodiments include an auto retract mode of the firing rod  220  that fully retracts the firing rod  220  even if switch  114   b  is released. The mode may be interrupted at any time if one of the switches  114   a  or  114   b  is actuated. 
     The switches  114   a  and  114   b  are coupled to a non-linear speed control circuit  115  which can be implemented as a voltage regulation circuit, a variable resistance circuit, or a microelectronic pulse width modulation circuit. The switches  114   a  and  144   b  may interface with the control circuit  115  by displacing or actuating variable control devices, such as rheostatic devices, multiple position switch circuit, linear and/or rotary variable displacement transducers, linear and/or rotary potentiometers, optical encoders, ferromagnetic sensors, and Hall Effect sensors. This allows the switches  114   a  and  114   b  to operate the drive motor  200  in multiple speed modes, such as gradually increasing the speed of the drive motor  200  either incrementally or gradually depending on the type of the control circuit  115  being used, based on the depression of the switches  114   a  and  114   b.    
     In a particular embodiment, the switch  114   c  may also be included ( FIGS. 1, 2 and 4 ), wherein depression thereof may mechanically and/or electrically change the mode of operation from clamping to firing. The switch  114   c  is recessed within the housing  110  and has high tactile feedback to prevent false actuations. Providing a separate control switch to initialize the firing mode allows the jaws of the end effector to be repeatedly opened and closed, so that the instrument  10  is used as a grasper until the switch  114   c  is pressed, thus activating the stapling and/or cutting mode. The switch  114  may include one or more microelectronic switches, for example. For example, a microelectronic membrane switch provides a tactile feel, small package size, ergonomic size and shape, low profile, the ability to include molded letters on the switch, symbols, depictions and/or indications, and a low material cost. Additionally, switches  114  (such as microelectronic membrane switches) may be sealed to help facilitate sterilization of the instrument  10 , as well as helping to prevent particle and/or fluid contamination. 
     As an alternative to, or in addition to switches  114 , other input devices may include voice input technology, which may include hardware and/or software incorporated in a control system  501  ( FIG. 20 ), or a separate digital module connected thereto. The voice input technology may include voice recognition, voice activation, voice rectification, and/or embedded speech. The user may be able to control the operation of the instrument in whole or in part through voice commands, thus freeing one or both of the user&#39;s hands for operating other instruments. Voice or other audible output may also be used to provide the user with feedback. 
     Prior to continuing the description of surgical instrument  10 ,  FIGS. 2A and 2B  illustrate a variant of surgical instrument  10 . More particularly, surgical instrument  10 ′ includes a housing  110 ′ that is configured with a handle  112 ′ having a partial hour-glass shape. Surgical instrument  10 ′ provides an alternative ergonomic configuration to surgical instrument  10 . 
     Returning again to the description of surgical instrument  10  and referring to  FIG. 3 , a proximal area  118  of housing  110  having a user interface  120  is shown. The user interface  120  includes a screen  122  and a plurality of switches  124 . The user interface  120  may display various types of operational parameters of the instrument  10  which may be based on the information reported by sensors disposed in the instrument  10  and communicated to user interface  120 . Illustrative operational parameters include “mode” (e.g., rotation, articulation or actuation), “status” (e.g., angle of articulation, speed of rotation, or type of actuation), and “feedback,” such as whether staples have been fired. Error and other codes (e.g., improper loading, replace battery, battery level, the estimated number of firings remaining, or any non-functioning sub systems) may also be displayed on user interface  120 . 
     The screen  122  may be an LCD screen, a plasma screen, an electroluminescent screen or the like. In one embodiment the screen  122  may be a touch screen, obviating the need for the switches  124 . The touch screen may incorporate resistive, surface wave, capacitive, infrared, strain gauge, optical, dispersive signal or acoustic pulse recognition touch screen technologies. The touch screen may be used to allow the user to provide input while viewing operational feedback. This approach allows sealed screen components to help sterilize the instrument  10 , as well as preventing particle and/or fluid contamination. In certain embodiments, the screen  122  is pivotably or rotatably mounted to the instrument  10  for flexibility in viewing screen during use or preparation (e.g., via a hinge or ball-and-socket mount). 
     The switches  124  may be used for starting and/or stopping movement of the instrument  10  as well as selecting the type of single use loading unit (SULU) or disposable loading unit (DLU), the pivot direction, speed and/or torque. It is also envisioned that at least one switch  124  can be used for selecting an emergency mode that overrides various settings. The switches  124  may also be used for selecting various options on the screen  122 , such as responding to prompts while navigating user interface menus and selecting various settings, allowing a user input different tissue types, and various sizes and lengths of staple cartridges. 
     The switches  124  may be formed from a micro-electronic tactile or non-tactile membrane, a polyester membrane, elastomer, plastic, or metal keys of various shapes and sizes. Additionally, switches may be positioned at different heights from one another and/or may include raised indicia or other textural features (e.g., concavity or convexity) to allow a user to depress an appropriate switch without the need to look at user interface  120 . 
     In addition to the screen  124 , the user interface  120  may include one or more visual outputs  123  which may include one or more colored visible lights or light emitting diodes (“LED”) to relay feedback to the user. The visual outputs  123  may include corresponding indicators of various shapes, sizes and colors having numbers and/or text which identify the visual outputs  123 . The visual outputs  123  are disposed on top of the housing  110  such that the outputs  123  are raised and protrude in relation to the housing  110  providing for better visibility thereof. 
     The multiple lights display in a certain combination to illustrate a specific operational mode to the user. In one embodiment, the visual outputs  123  include a first light (e.g., yellow)  123   a , a second light (e.g., green)  123   b  and a third light (e.g., red)  123   c . The lights are operated in a particular combination associated with a particular operational mode as listed in Table 1 below. 
     
       
         
           
               
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Light Combination 
                   
               
            
           
           
               
               
               
            
               
                 Light 
                 Status 
                 Operational Mode 
               
               
                   
               
               
                 First Light 
                 Off 
                 No loading unit 169 or staple cartridge is 
               
               
                 Second Light 
                 Off 
                 loaded. 
               
               
                 Third Light 
                 Off 
                   
               
               
                 First Light 
                 On 
                 The loading unit 169 and/or staple cartridge is 
               
               
                 Second Light 
                 Off 
                 properly loaded and power is activated, 
               
               
                 Third Light 
                 Off 
                 allowing the end effector 160 to clamp as a 
               
               
                   
                   
                 grasper and articulate. 
               
               
                 First Light 
                 Flashing 
                 A used loading unit 169 or staple cartridge is 
               
               
                 Second Light 
                 Off 
                 loaded. 
               
               
                 Third Light 
                 Off 
                   
               
               
                 First Light 
                 N/A 
                 Instrument 10 is deactivated and prevented 
               
               
                 Second Light 
                 Off 
                 from firing staples or cutting. 
               
               
                 Third Light 
                 N/A 
                   
               
               
                 First Light 
                 On 
                 A new loading unit 169 is loaded, the end 
               
               
                 Second Light 
                 On 
                 effector 160 is fully clamped and the instru- 
               
               
                 Third Light 
                 Off 
                 ment 10 is in firing staple and cutting modes. 
               
               
                 First Light 
                 On 
                 Due to high stapling forces a “thick tissue” 
               
               
                 Second Light 
                 Flashing 
                 mode is in effect, providing for a pulsed or 
               
               
                 Third Light 
                 Off 
                 progression time delay during which tissue is 
               
               
                   
                   
                 compressed. 
               
               
                 First Light 
                 N/A 
                 No system errors detected. 
               
               
                 Second Light 
                 N/A 
                   
               
               
                 Third Light 
                 Off 
                   
               
               
                 First Light 
                 On 
                 Tissue thickness and/or firing load is too high, 
               
               
                 Second Light 
                 On 
                 this warning can be overridden. 
               
               
                 Third Light 
                 On 
                   
               
               
                 First Light 
                 N/A 
                 Functional system error is detected, instrument 
               
               
                 Second Light 
                 N/A 
                 10 should be replaced. 
               
               
                 Third Light 
                 Flashing 
                   
               
               
                 First light 
                 N/A 
                 Replace the battery pack or the power source 
               
               
                 Second light 
                 N/A 
                 is not properly connected. 
               
               
                 Third light 
                 ON 
               
               
                   
               
            
           
         
       
     
     In another embodiment, the visual output  123  may include a single multi-colored LED which display a particular color associated with the operational modes as discussed above with respect to the first, second and third lights in Table 1. 
     The user interface  120  also includes audio outputs  125  (e.g., tones, bells, buzzers, integrated speaker, etc.) to communicate various status changes to the user such as lower battery, empty cartridge, etc. The audible feedback can be used in conjunction with or in lieu of the visual outputs  123 . The audible feedback may be provided in the forms of clicks, snaps, beeps, rings and buzzers in single or multiple pulse sequences. In one embodiment, a simulated mechanical sound may be prerecorded which replicates the click and/or snap sounds generated by mechanical lockouts and mechanisms of conventional non-powered instruments. This eliminates the need to generate such mechanical sounds through the actual components of the instrument  10  and also avoids the use of beeps and other electronic sounds which are usually associated with other operating room equipment, thereby preventing confusion from extraneous audible feedback. The instrument  10  may include one or more microphones or other voice input devices which can be used to determine the background noise levels and adjust the audible feedback volumes accordingly for clear feedback recognition. 
     The instrument  10  may also provide for haptic or vibratory feedback through a haptic mechanism (not explicitly shown) within the housing  110 . The haptic feedback may be used in conjunction with the auditory and visual feedback or in lieu thereof to avoid confusion with the operating room equipment which relies on audio and visual feedback. The haptic mechanism may be an asynchronous motor that vibrates in a pulsating manner. In one embodiment, the vibrations are at a frequency of about 20 Hz or above, in embodiments from about 20 Hz to about 60 Hz, and providing a displacement having an amplitude of 2 mm or lower, in embodiments from about 0.25 mm to about 2 mm, to limit the vibratory effects from reaching the loading unit  169 . 
     It is also envisioned that user interface  120  may include different colors and/or intensities of text on the screen and/or on the switches for further differentiation between the displayed items. The visual, auditory or haptic feedback can be increased or decreased in intensity. For example, the intensity of the feedback may be used to indicate that the forces on the instrument are becoming excessive. 
       FIGS. 2, 3 and 4  illustrate an articulation mechanism  170 , including an articulation housing  172 , a powered articulation switch  174 , an articulation motor  132  and a manual articulation knob  176 . The articulation switch  174  may be a rocker and/or a slide switch having an arm  174   a  and  174   b  on each side of the housing  110  allowing for either right or left hand usage thereof. Translation of the powered articulation switch  174  activates the articulation motor  132 . Pivoting of the manual articulation knob  176  will actuate the articulation gear  233  of the articulation mechanism  170  as shown in  FIG. 5 . Actuation of articulation mechanism  170 , by either switch  174  or knob  176 , causes the end effector  160  to move from its first position, where longitudinal axis B-B is substantially aligned with longitudinal axis A-A, towards a position in which longitudinal axis B-B is disposed at an angle to longitudinal axis A-A. Preferably, a plurality of articulated positions is achieved. The powered articulation switch  174  may also incorporate similar non-linear speed controls as the clamping mechanism as controlled by the switches  114   a  and  114   b.    
     Further, the housing  110  includes switch shields  117   c  and  117   d  having a wing-like shape and extending from the top surface of the housing  110  over the switch  174 . The switch shields  117   c  or  117   d  prevent accidental activation of the switch  174  when the instrument  10  is placed down or from physical obstructions during use and require the user to reach below the shield  169  in order to activate the articulation mechanism  170 . 
     Rotation of a rotation knob  182  about first longitudinal axis A-A causes housing assembly  180  as well as articulation housing  172  and manual articulation knob  176  to rotate about first longitudinal axis A-A, and thus causes corresponding rotation of distal portion  224  of firing rod  220  and end effector  160  about first longitudinal axis A-A. The articulation mechanism  170  is electro-mechanically coupled to first and second conductive rings  157  and  159  which are disposed on housing nose assembly  155  as shown in  FIGS. 4 and 26 . The conductive rings  157  and  159  may be soldered, glued, press fit, snap fit or crimped onto the nose assembly  155  and are in electrical contact with the power source  400  thereby providing electrical power to the articulation mechanism  170 . The nose assembly  155  may be modular (e.g., separate from the housing  110 ) and may be attached to the housing  110  during assembly to facilitate the aforementioned methods of mounting the rings. The articulation mechanism  170  includes one or more brush and/or spring loaded contacts in contact with the conductive rings  157  and  159  such that as the housing assembly  180  is rotated along with the articulation housing  172  the articulation mechanism  170  is in continuous contact with the conductive rings  157  and  159  thereby receiving electrical power from the power source  400 . 
     Further details of articulation housing  172 , powered articulation switch  174 , manual articulation knob  176  and providing articulation to end effector  160  are described in detail in U.S. Pat. No. 7,431,188, the contents of which are hereby incorporated by reference in their entirety. It is envisioned that any combinations of limit switches, proximity sensors (e.g., optical and/or ferromagnetic), linear variable displacement transducers or shaft encoders which may be disposed within housing  110 , may be utilized to control and/or record an articulation angle of end effector  160  and/or position of the firing rod  220 . 
       FIGS. 4, 5-10 and 11-12  illustrate various internal components of the instrument  10 , including a drive motor  200 , an internally threaded drive tube  210 , and a firing rod  220  having a proximal portion  222  and a distal portion  224 . The drive tube  210  is rotatable about drive tube axis C-C extending therethrough. Drive motor  200  is disposed in mechanical cooperation with drive tube  210  and is configured to rotate the drive tube  210  about drive gear axis C-C. In one embodiment, the drive motor  200  may be an electrical motor or a gear motor, which may include gearing incorporated within its housing. 
     The housing  110  may be formed from two halves  110   a  and  110   b  as illustrated in  FIG. 3 . The two housing portion halves  110   a  and  110   b  may be attached to each other using screws at boss locators  111  which align the housing portions  110   a  and  110   b . In one embodiment, ultrasonic welding directors may be used to attach halves  110   a  and  110   b  to seal the housing from external contamination. In addition, the housing  110  may be formed from plastic and may include rubber support members applied to the internal surface of the housing  110  via a two-shot molding process. The rubber support members may isolate the vibration of the drive components (e.g., drive motor  200 ) from the rest of the instrument  10 . 
     The housing halves  110   a  and  110   b  may be attached to each other via a thin section of plastic (e.g., a living hinge) that interconnects the halves  110   a  and  110   b  allowing the housing  110  to be opened by breaking away the halves  110   a  and  110   b.    
     In one embodiment, the drive components (e.g., including drive motor  200 , drive tube  210 , and firing rod  220 , etc.) may be mounted on a support plate allowing the drive components to be removed from the housing  110  after the instrument  10  has been used. The support plate mounting in conjunction with the hinged housing halves  110   a  and  110   b  provide for reusability and recyclability of specific internal components while limiting contamination thereof. 
     More particularly, by providing as the support plate a separate, internal, structural member or chassis for the surgical instrument or device, a stronger and higher precision assembly can be produced that is easier to assemble, service, reprocess, reuse or recycle. 
     Generally, such a structural member or chassis can be much smaller and therefore more accurate dimensionally than an all inclusive handle set cover, e.g., the housing  110  with at least the first and second housing portions  110   a  and  110   b , when produced with similar manufacturing processes. Additional datum planes and locating features can also be designed into the structural member or chassis because of its geometry that is substantially independent of the exterior surface design of the housing  110 . The exterior surface geometry of the housing  110  can hinder many aspects of strength and limit numerous aspects of “net shape” molded features. 
     Higher precision manufacturing methods or processes can also be applied to the structural member or chassis to increase accuracy and decrease required tolerances as compared to the handle set cover. The structural member or chassis may be formed of higher strength/performance materials and/or additional structure as compared to the handle set cover, thereby improving the robustness and fatigue life of at least the operating components contained within the housing  110 . That is, the additional precision, alignment and strength can benefit the mechanisms, bearings, gears, clutches, and/or couplings of the surgical instrument  10  or  10 ′, particularly for instruments that are driven and/or powered by electromechanical or pneumatic subsystems that operate under higher linear and/or rotation speeds/loads. Added structure from the structural member or chassis can support extreme or repetitive fatigue loads preventing deformation which can result in misalignment and/or mechanical failures. 
     Integrating fastener mounting points and/or features into sides of the structural member or chassis allows the housing portions  110   a  and  110   b  to be easily removed or replaced while maintaining all of the functional assembly alignments. Components may be assembled from multiple planes of access thereby simplifying the overall assembling, servicing, reprocessing, reusing and recycling of the surgical instrument. 
       FIG. 4A  illustrates the internal components of the variant surgical instrument  10 ′.  FIG. 4A  is provided for a general comparison with respect to  FIG. 4  and will not be discussed in detail herein. 
     Returning again to the description of surgical instrument  10  and with reference to  FIGS. 4, 5, 6 and 7 , a firing rod coupling  190  is illustrated. Firing rod coupling  190  provides a link between the proximal portion  222  and the distal portion  224  of the firing rod  220 . Specifically, the firing rod coupling  190  enables rotation of the distal portion  224  of the firing rod  220  with respect to proximal portion  222  of firing rod  220 . Thus, firing rod coupling  190  enables proximal portion  222  of firing rod  220  to remain non-rotatable, as discussed below with reference to an alignment plate  350 , while allowing rotation of distal portion  224  of firing rod  220  (e.g., upon rotation of rotation knob  182 ). 
     With reference to  FIGS. 6 and 7 , the proximal portion  222  of firing rod  220  includes a threaded portion  226 , which extends through an internally-threaded portion  212  of drive tube  210 . This relationship between firing rod  220  and drive tube  210  causes firing rod  220  to move distally and/or proximally, in the directions of arrows D and E, along threaded portion  212  of drive tube  210  upon rotation of drive tube  210  in response to the rotation of the drive motor  200 . As the drive tube  210  rotates in a first direction (e.g., clockwise), firing rod  220  moves proximally. As illustrated in  FIG. 6 , the firing rod  220  is disposed at its proximal-most position. As the drive tube  210  rotates in a second direction (e.g., counter-clockwise), firing rod  220  moves distally. As illustrated in  FIG. 6 , the firing rod  220  is disposed at its distal-most position. 
     The firing rod  220  is distally and proximally translatable within particular limits. Specifically, a first end  222   a  of proximal portion  222  of firing rod  220  acts as a mechanical stop in combination with alignment plate  350 . That is, upon retraction when firing rod  220  is translated proximally, first end  222   a  contacts a distal surface  351  of alignment plate  350 , thus preventing continued proximal translation of firing rod  220  as shown in  FIG. 6 . Additionally, threaded portion  226  of the proximal portion  222  acts as a mechanical stop in combination with alignment plate  350 . That is, when firing rod  220  is translated distally, the threaded portion  226  contacts a proximal surface  353  of the alignment plate  350 , thus preventing further distal translation of firing rod  220  as shown  FIG. 7 . The alignment plate  350  includes an aperture therethrough, which has a non-round cross-section. The non-round cross-section of the aperture prevents rotation of proximal portion  222  of firing rod  220 , thus limiting proximal portion  222  of firing rod  220  to axial translation therethrough. Further, a proximal bearing  354  and a distal bearing  356  are disposed at least partially around drive tube  210  for facilitation of rotation of drive tube  210 , while helping align drive tube  210  within housing  110 . The drive tube  210  includes a distal radial flange  210   a  and a proximal radial flange  210   b  on each end of the drive tube  210  which retain the drive tube  210  between the distal bearing  356  and the proximal bearing  354 , respectively. 
     Rotation of drive tube  210  in a first direction (e.g., counter-clockwise) corresponds with distal translation of the firing rod  220  which actuates jaw member  162  or  164  (e.g., anvil and cartridge assemblies  162 ,  164 ) of the end effector  160  to grasp or clamp tissue held therebetween. Additional distal translation of firing rod  220  ejects surgical fasteners from the end effector  160  to fasten tissue by actuating cam bars and/or an actuation sled  74  ( FIG. 9 ). Further, the firing rod  220  may also be configured to actuate a knife (not explicitly shown) to sever tissue. Proximal translation of firing rod  220  corresponding with rotation of the drive tube  210  in a second direction (e.g., clockwise) actuates the anvil and cartridge assemblies  162 ,  164  and/or knife to retract or return to corresponding pre-fired positions. Further details of firing and otherwise actuating end effector  160  are described in detail in U.S. Pat. No. 6,953,139, the disclosure of which is hereby incorporated by reference herein. 
       FIG. 8  shows a partial exploded view of the loading unit  169 . The end effector  160  may be actuated by an axial drive assembly  213  having a drive beam or drive member  266 . The distal end of the drive beam  213  may include a knife blade. In addition, the drive beam  213  includes a retention flange  40  having a pair of cam members  40   a  which engage the anvil and the cartridge assembly  162  and  164  during advancement of the drive beam  213  longitudinally. The drive beam  213  advances an actuation sled  74  longitudinally through the staple cartridge  164 . As shown in  FIG. 9 , the sled  74  has cam wedges for engaging pushers  68  disposed in slots of the cartridge assembly  164 , as the sled  74  is advanced. Staples  66  disposed in the slots are driven through tissue and against the anvil assembly  162  by the pushers  66 . 
     With reference to  FIG. 10 , a drive motor shaft  202  is shown extending from a transmission  204  that is attached to drive motor  200 . Drive motor shaft  202  is in mechanical cooperation with clutch  300 . Drive motor shaft  202  is rotated by the drive motor  200 , thus resulting in rotation of clutch  300 . Clutch  300  includes a clutch plate  302  and a spring  304  and is shown having wedged portions  306  disposed on clutch plate  302 , which are configured to mate with an interface (e.g., wedges  214 ) disposed on a proximal face  216  of drive tube  210 . 
     Spring  304  is illustrated between transmission  204  and drive tube  210 . Specifically, and in accordance with the embodiment illustrated in  FIG. 10 , spring  304  is illustrated between clutch face  302  and a clutch washer  308 . Additionally, drive motor  200  and transmission  204  are mounted on a motor mount  310 . As illustrated in  FIG. 8 , motor mount  310  is adjustable proximally and distally with respect to housing  110  via slots  312  disposed in motor mount  310  and protrusions  314  disposed on housing  110 . 
     In an embodiment of the disclosure, the clutch  300  is implemented as a slip bi-directional clutch to limit torque and high inertia loads on the drive components. Wedged portions  306  of clutch  300  are configured and arranged to slip with respect to wedges  214  of proximal face  216  of drive tube  210  unless a threshold force is applied to clutch plate  302  via clutch spring  304 . Further, when spring  304  applies the threshold force needed for wedged portions  306  and wedges  214  to engage without slipping, drive tube  210  will rotate upon rotation of drive motor  200 . It is envisioned that wedged portions  306  and/or wedges  214  are configured to slip in one and/or both directions (i.e., clockwise and/or counter-clockwise) with respect to one another when a firing force is attained on the firing rod  220 . 
       FIG. 10A  illustrates a partial enlarged view of the internal components of surgical instrument  10 ′ as described above with respect to  FIGS. 2A, 2B and 4A . Again, in a similar manner,  FIG. 10A  is provided for a general comparison with respect to  FIG. 10  and will not be discussed in detail herein. Some of the components that are common with surgical instrument  10  have been identified with the corresponding identification numerals pertaining to surgical instrument  10 . 
     Returning again to the description of surgical instrument  10  and with reference to  FIGS. 11 and 12 , the clutch  300  is shown with a unidirectional clutch plate  700 . The clutch plate  700  includes a plurality of wedged portions  702  each having a slip face  704  and a grip face  706 . The slip face  704  has a curved edge which engages the wedges  214  of the drive tube  210  up to a predetermined load. The grip face  706  has a flat edge which fully engages the drive tube  210  and prevents slippage. When the clutch plate  700  is rotated in a reverse direction (e.g., counter-clockwise), the grip face  706  of the wedged portions  702  engage the wedges  214  without slipping, providing for full torque from the drive motor  200 . This feature helps to assure that jaws  162 ,  164  will open under retraction during extreme load scenarios. When the clutch plate  700  is rotated in a forward direction (e.g., clockwise), the slip faces  704  of the wedged portions  702  engage the wedges  214  and limit the torque being transferred to the drive tube  210 . Thus, if the load being applied to a slip face  704  is over the limit, the clutch  300  slips and the drive tube  210  is not rotated. This can prevent high load damage to the end effector  160  or tissue from the motor and drive components. More specifically, the drive mechanism of the instrument  10  can drive the firing rod  220  in a forward direction with less torque than in reverse. In addition, an electronic clutch may also be used to increase or decrease the motor potential (e.g., driving the drive rod  220  in forward or reverse along with the drive motor  200 , drive tube  210 , clutch assembly  300 , alignment plate  350 , and any portion of the firing rod  220 ) as discussed in more detail below. 
     It is further envisioned that drive motor shaft  202  includes a D-shaped or non-round cross-section  708 , which includes a substantially flat portion  710  and a rounded portion  712 . Thus, while drive motor shaft  202  is translatable with respect to clutch plate  700 , drive motor shaft  202  will not “slip” with respect to clutch plate  700  upon rotation of drive motor shaft  202 . That is, rotation of drive motor shaft  202  will result in a slip-less rotation of clutch plate  700 . 
     The loading unit, in certain embodiments according to the present disclosure, includes an axial drive assembly that cooperates with firing rod  220  to approximate anvil assembly  162  and cartridge assembly  164  of end effector  160 , and fire staples from the staple cartridge. The axial drive assembly may include a beam that travels distally through the staple cartridge and may be retracted after the staples have been fired, as discussed above and as disclosed in certain embodiments of U.S. Pat. No. 6,953,139. 
     With reference to  FIG. 4 , the instrument  10  includes a power source  400  which may be a rechargeable battery (e.g., lead-based, nickel-based, lithium-ion based, etc.). It is also envisioned that the power source  400  includes at least one disposable battery. The disposable battery may be between about 9 volts and about 30 volts. 
     The power source  400  includes one or more battery cells  401  depending on the energy and voltage potential needs of the instrument  10 . Further, the power source  400  may include one or more ultracapacitors  402  which act as supplemental power storage due to their much higher energy density than conventional capacitors. Ultracapacitors  402  can be used in conjunction with the cells  401  during high energy draw. The ultracapacitors  402  can be used for a burst of power when energy is desired/required more quickly than can be provided solely by the cells  401  (e.g., when clamping thick tissue, rapid firing, clamping, etc.), as cells  401  are typically slow-drain devices from which current cannot be quickly drawn. This configuration can reduce the current load on the cells thereby reducing the number of cells  401 . Ultracapacitors  402  can also regulate the system voltage, providing more consistent speed of motor  200  and firing rod  220 . It is envisioned that cells  401  can be connected to the ultracapacitors  402  to charge the capacitors. 
     The power source  400  may be removable along with the drive motor  200  to provide for recycling of these components and reuse of the instrument  10 . In another embodiment, the power source  400  may be an external battery pack which is worn on a belt and/or harness by the user and wired to the instrument  10  during use. 
     The power source  400  is enclosed within an insulating shield  404  which may be formed from an absorbent, flame resistant and retardant material. The shield  404  electrically and thermally isolates components of the instrument  10  from the power source  400 . More specifically, the shield  400  prevents heat generated by the power source  400  from heating other components of the instrument  10 . In addition, the shield  404  may also be configured to absorb any chemicals or fluids which may leak from the cells  402  during heavy use and/or damage. 
     The power source  400  may be coupled to a power adapter  406  which is configured to connect to an external power source (e.g., a DC transformer). The external power source may be used to recharge the power source  400  or provide for additional power requirements. The power adapter  406  may also be configured to interface with electrosurgical generators which can then supply power to the instrument  10 . In this configuration, the instrument  10  also includes an AC-to-DC power source which converts RF energy from the electrosurgical generators and powers the instrument  10 . 
     In another embodiment the power source  400  is recharged using an inductive charging interface. The power source  400  is coupled to an inductive coil (not explicitly shown) disposed within the proximal portion of the housing  110 . Upon being placed within an electromagnetic field, the inductive coil converts the energy into electrical current that is then used to charge the power source  400 . The electromagnetic field may be produced by a base station (not explicitly shown) which is configured to interface with the proximal portion of the housing  110 , such that the inductive coil is enveloped by the electromagnetic field. This configuration eliminates the need for external contacts and allows for the proximal portion of the housing  110  to seal the power source  400  and the inductive coil within a water-proof environment which prevents exposure to fluids and contamination. 
     With reference to  FIG. 6 , the instrument  10  also includes one or more safety circuits such as a discharge circuit  410  and a motor and battery operating module  412 . For clarity, wires and other circuit elements interconnecting various electronic components of the instrument  10  are not shown, but such electromechanical connections wires are contemplated by the present disclosure. Certain components of the instrument  10  may communicate wirelessly. 
     The discharge circuit  410  is coupled to a switch  414  and a resistive load  417  which are in turn coupled to the power source  400 . The switch  414  may be a user activated or an automatic (e.g., timer, counter) switch which is activated when the power source  400  needs to be fully discharged for a safe and low temperature disposal (e.g., at the end of surgical procedure). Once the switch  414  is activated, the load  417  is electrically connected to the power source  400  such that the potential of the power source  400  is directed to the load  417 . The automatic switch may be a timer or a counter which is automatically activated after a predetermined operational time period or number of uses to discharge the power source  400 . The load  417  has a predetermined resistance sufficient to fully and safely discharge all of the cells  401 . 
     The motor and battery operating module  412  is coupled to one or more thermal sensors  413  which determine the temperature within the drive motor  200  and the power source  400  to ensure safe operation of the instrument  10 . The sensors may be an ammeter for determining the current draw within the power source  400 , a thermistor, a thermopile, a thermocouple, a thermal infrared sensor or the like. Monitoring temperature of these components allows for a determination of the load being placed thereon. The increase in the current flowing through these components causes an increase in temperature therein. The temperature and/or current draw data may then be used to control the power consumption in an efficient manner or assure safe levels of operation. 
     In order to ensure safe and reliable operation of the instrument  10 , it is desirable to ensure that the power source  400  is authentic and/or valid (e.g., conforms to strict quality and safety standards) and operating within a predetermined temperature range. Authentication that the power source  400  is valid minimizes risk of injury to the patient and/or the user due to poor quality. 
     With reference to  FIG. 13 , the power source  400  is shown having one or more battery cells  401 , the thermal sensor  413  and an embedded microcontroller  405  coupled thereto. The microcontroller  405  is coupled through wired and/or wireless communication protocols to microcontroller  500  ( FIGS. 6, 13 and 20 ) of the instrument  10  to authenticate the power source  400 . In one embodiment, the thermal sensor  413  can be coupled directly to the microcontroller  500  instead of being coupled to the embedded microcontroller  405 . The thermal sensor  413  may be a thermistor, a thermopile, a thermocouple, a thermal infrared sensor, a resistance temperature detector, linear active thermistor, temperature-responsive color changing strips, bimetallic contact switches, or the like. The thermal sensor  413  reports the measured temperature to the microcontroller  405  and/or microcontroller  500 . 
     The embedded microcontroller  405  executes a so-called challenge-response authentication algorithm with the microcontroller  500  which is illustrated in  FIG. 13 . In step  630 , the power source  400  is connected to the instrument  10  and the instrument  10  is switched on. The microcontroller  500  sends a challenge request to the embedded microcontroller  405 . In addition the microcontroller  500  may request the battery temperature from microcontroller  405  which receives it from thermal sensor  413 . In step  632 , the microcontroller  405  interprets the challenge request and generates a response as a reply to the request. The response may include an identifier, such as a unique serial number stored in a radio frequency identification tag or in memory of the microcontroller  405 , a unique electrical measurable value of the power source  400  (e.g., resistance, capacitance, inductance, etc.). In addition, the response includes the temperature measured by the thermal sensor  413 . 
     In step  634 , the microcontroller  500  decodes the response to obtain the identifier and the measured temperature. In step  636 , the microcontroller  500  determines if the power source  400  is authentic based on the identifier, by comparing the identifier against a pre-approved list of authentic identifiers. If the identifier is not valid, the instrument  10  is not going to operate and displays an error code or a “failure to authenticate battery” message via the user interface  120 . If the identifier is valid, the process proceeds to step  640  where the measured temperature is analyzed to determine if the measurement is within a predetermined operating range. If the temperature is outside the limit, the instrument  10  also displays an error message. Thus, if the temperature is within the predetermined limit and the identifier is valid, in step  642 , the instrument commences operation, which may include providing a “battery authenticated” message to the user. 
     Referring back to  FIGS. 4 and 6  a plurality of sensors for providing feedback information relating to the function of the instrument  10  are illustrated. Any combination of sensors may be disposed within the instrument  10  to determine its operating stage, such as, staple cartridge load detection as well as status thereof, articulation, clamping, rotation, stapling, cutting and retracting, or the like. The sensors can be actuated by rotational encoders, proximity, displacement or contact of various internal components of the instrument  10  (e.g., firing rod  220 , drive motor  200 , etc.). 
     In the illustrated embodiments, the sensors can be rheostats (e.g., variable resistance devices), current monitors, conductive sensors, capacitive sensors, inductive sensors, thermal-based sensors, limit actuated switches, multiple position switch circuits, pressure transducers, linear and/or rotary variable displacement transducers, linear and/or rotary potentiometers, optical encoders, ferromagnetic sensors, Hall Effect sensors, or proximity switches. The sensors measure rotation, velocity, acceleration, deceleration, linear and/or angular displacement, detection of mechanical limits (e.g., stops), etc. This is attained by implementing multiple indicators arranged in either linear or rotational arrays on the mechanical drive components of the instrument  10 . The sensors then transmit the measurements to the microcontroller  500  which determines the operating status of the instrument  10 . In addition, the microcontroller  500  also adjusts the motor speed or torque of the instrument  10  based on the measured feedback. 
     In embodiments where the clutch  300  is implemented as a slip clutch as shown in  FIGS. 11 and 12 , linear displacement sensors (e.g., linear displacement sensor  237  in  FIG. 4 ) are positioned distally of the clutch  300  to provide accurate measurements. In this configuration, slippage of the clutch  300  does not affect the position, velocity and acceleration measurements recorded by the sensors. 
     With reference to  FIG. 4 , a load switch  230  is disposed within the housing nose assembly  155 . The switch  230  is connected in series with the power source  400 , preventing activation of the microcontroller  500  and instrument  10  unless the loading unit  169  is properly loaded into the instrument  10 . If the loading unit  169  is not loaded into the instrument  10 , the connection to the power source  400  is open, thereby preventing use of any electronic or electric components of the instrument  10 . This prevents any possible current draw from the power source  400  allowing the power source  400  to maintain a maximum potential over its specified shelf life. 
     Thus, the switch  230  acts as a so-called “power-on” switch which prevents false activation of the instrument  10  since the switch is inaccessible to external manipulation and can only be activated by the insertion of the loading unit  169 . In  FIGS. 18 and 19 , the switch  230  is activated by displacement of sensor plate  360  to the sensor tube  362  which displaces the sensor cap  364  as the loading unit  169  is inserted into the endoscopic portion  140 . Once the switch  230  is activated, the power from the power source  400  is supplied to the electronic components (e.g., sensors, microcontroller  500 , etc.) of the instrument  10  providing the user with access to the user interface  120  and other inputs/outputs. This also activates the visual outputs  123  to light up according to the light combination indicative of a properly loaded loading unit  169  wherein all the lights are off as described in Table 1. 
     More specifically, as shown in  FIGS. 18 and 19 , the endoscopic portion  140  includes a sensor plate  360  therein which is in mechanical contact with a sensor tube also disposed within the endoscopic portion  140  and around the distal portion  224  of firing rod  220 . The distal portion  224  of the firing rod  220  passes through an opening  368  at a distal end of a sensor cap  364 . The sensor cap  364  includes a spring and abuts the switch  230 . This allows the sensor cap  364  to be biased against the sensor tube  362  which rests on the distal end of the sensor cap  364  without passing through the opening  368 . Biasing of the sensor tube  362  then pushes out the sensor plate  360  accordingly. 
     When the loading unit  169  is loaded into the endoscopic portion  140 , the proximal portion  171  abuts the sensor plate  360  and displaces the plate  360  in a proximal direction. The sensor plate  360  then pushes the sensor tube  362  in the proximal direction which then applies pressure on the sensor cap  364  thereby compressing the spring  366  and activating the switch  230  denoting that the loading unit  169  has been properly inserted. 
     Once the loading unit  169  is inserted into the endoscopic portion, the switch  230  also determines whether the loading unit  169  is loaded correctly based on the position thereof. If the loading unit  169  is improperly loaded, no switches are activated and an error code is relayed to the user via the user interface  120  (e.g., all the lights are off as described in Table 1). If the loading unit  169  has already been fired, any mechanical lockouts have been previously activated or the staple cartridge has been used, the instrument  10  relays the error via the user interface  120 , e.g., the first light  123   a  is flashing. 
     In one embodiment, a second lock-out switch (not shown) coupled to the microcontroller  500  (see  FIG. 6 ) may be implemented in the instrument  10  as a bioimpedance, capacitance or pressure sensor disposed on the top surface of, or within, the handle portion  112  configured to be activated when the user grasps the instrument  10 . Thus, unless the instrument  10  is grasped properly, all switches are disabled. 
     In one embodiment, with reference to  FIG. 6 , the instrument  10  includes a position calculator  416  for determining and outputting current linear position of the firing rod  220 . The position calculator  416  is electrically connected to a linear displacement sensor  237  and a rotation speed detecting apparatus  418  is coupled to the drive motor  200 . The apparatus  418  includes an encoder  420  coupled to the motor for producing two or more encoder pulse signals in response to the rotation of the drive motor  200 . The encoder  420  transmits the pulse signals to the apparatus  418  which then determines the rotational speed of the drive motor  200 . The position calculator  416  thereafter determines the linear speed and position of the firing rod based on the rotational speed of the drive motor  200  since the rotation speed is directly proportional to the linear speed of the firing rod  220 . The position calculator  416  and the speed calculator  422  are coupled to the microcontroller  500  which controls the drive motor  200  in response to the sensed feedback form the calculators  416  and  422 . This configuration is discussed in more detail below with respect to  FIG. 20 . 
     The instrument  10  includes first and second indicators  320   a ,  320   b  disposed on the firing rod  220 , which determine the limits of firing rod  220 . The linear displacement sensor  237  determines the location of firing rod  220  with respect to drive tube  210  and/or housing  110 . For instance, a limit switch may be activated (e.g., shaft start position sensor  231  and clamp position sensor  232 ) by sensing first and second indicators  320   a  and/or  320   b  (e.g., bumps, grooves, indentations, etc.) passing thereby to determine the limits of firing rod  220  and mode of the instrument  10  (e.g., clamping, grasping, firing, sealing, cutting, retracting, etc.). Further, the feedback received from first and second indicators  320   a ,  320   b  may be used to determine when firing rod  220  should stop its axial movement (e.g., when drive motor  200  should cease) depending on the size of the particular loading unit attached thereto. The first indicator  320   a  may also be used to calibrate the instrument  10  as will be described below with reference to  FIG. 44 . 
     More specifically, as the firing rod  220  is moved in the distal direction from its resting (e.g., initial) position, the first actuation of the position sensor  231  is activated by the first indicator  320   a  which denotes that operation of the instrument  10  has commenced. As the operation continues, the firing rod  220  is moved further distally to initiate clamping, which moves first indicator  320   a  to interface with clamp position sensor  232 . Further advancement of the firing rod  220  moves the second indicator  320   b  to interface with the position sensor  232  which indicates that the instrument  10  has been fired. 
     As discussed above, the position calculator  416  is coupled to a linear displacement sensor  237  disposed adjacent to the firing rod  220 . In one embodiment, the linear displacement sensor  237  may be a magnetic sensor. The firing rod  220  may include magnets or magnetic features. The magnetic sensor may be a ferromagnetic sensor or a Hall Effect sensor which is configured to detect changes in a magnetic field. As the firing rod  220  is translated linearly due to the rotation of the drive motor  200 , the change in the magnetic field in response to the translation motion is registered by the magnetic sensor. The magnetic sensor transmits data relating to the changes in the magnetic field to the position calculator  416  which then determines the position of the firing rod  220  as a function of the magnetic field data. 
     In one embodiment, a select portion of the firing rod  220  may be a magnetic material, such as the threads of the internally-threaded portion  212  or other notches (e.g., indicators  320   a  and/or  320   b ) disposed on the firing rod  220  may include or be made from a magnetic material. This allows for correlation of the cyclical variations in the magnetic field with each discrete translation of the threads as the magnetized portions of the firing rod  220  are linearly translated. The position calculator  416  thereafter determines the distance and the position of the firing rod  220  by summing the number of cyclical changes in the magnetic field and multiplies the sum by a predetermined distance between the threads and/or notches. 
     In one embodiment, the linear displacement sensor  237  may be a potentiometer or a rheostat. The firing rod  220  includes a contact (e.g., wiper terminal) disposed in electromechanical contact with the linear displacement sensor  237 . The contact slides along the surface of the linear displacement sensor  237  as the firing rod  220  is moved in the distal direction by the drive motor  200 . As the contact slides across the potentiometer and/or the rheostat, the voltage of the potentiometer and the resistance of the rheostat vary accordingly. Thus, the variation in voltage and resistance is transmitted to the position calculator  416  which then extrapolates the distance traveled by the firing rod  220  and/or the firing rod coupling  190  and the position thereof. 
     In one embodiment, the position calculator  416  is coupled to one or more switches  421  which are actuated by the threads of the internally-threaded portion  212  or the indicators  320   a  and/or  320   b  as the firing rod  220  and the firing rod coupling  190  are moved in the distal direction. The position calculator  416  counts the number of threads which activated the switch  421  and then multiplies the number by a predetermined distance between the threads or the indicators  320   a  and/or  320   b.    
     The instrument  10  also includes a speed calculator  422  which determines the current speed of a linearly moving firing rod  220  and/or the torque being provided by the drive motor  200 . The speed calculator  422  is connected to the linear displacement sensor  237  which allows the speed calculator  422  to determine the speed of the firing rod  220  based on the rate of change of the displacement thereof. 
     The speed calculator  422  is coupled to the rotation speed detecting apparatus  424  which includes the encoder  426 . The encoder  426  transmits the pulses correlating to the rotation of the drive motor  200  which the speed calculator  422  then uses to calculate the linear speed of the firing rod  220 . In another embodiment, the speed calculator  422  is coupled to a rotational sensor  239  which detects the rotation of the drive tube  210 , thus measuring the rate of rotation of the drive tube  210  which allows for determination of the linear velocity of the firing rod  220 . 
     The speed calculator  422  is also coupled to a voltage sensor  428  which measures the back electromotive force (“EMF”) induced in the drive motor  200 . The back EMF voltage of the drive motor  200  is directly proportional to the rotational speed of the drive motor  200  which, as discussed above, is used to determine the linear speed of the firing rod  220 . 
     Monitoring of the speed of the drive motor  200  can also be accomplished by measuring the voltage across the terminals thereof under constant current conditions. An increase in a load of the drive motor  200  yields a decrease in the voltage applied at the motor terminals, which is directly related to the decrease in the speed of the motor. Thus, measuring the voltage across the drive motor  200  provides for determining the load being placed thereon. In addition, by monitoring the change of the voltage over time (dV/dt), the microprocessor  500  can detect a quick drop in voltage which correlates to a large change in the load or an increase in temperature of the drive motor  200  and/or the power source  400 . 
     In a further embodiment, the speed calculator  422  is coupled to a current sensor  430  (e.g., an ammeter). The current sensor  430  is in electrical communication with a shunt resistor  432  which is coupled to the drive motor  200 . The current sensor  430  measures the current being drawn by the drive motor  200  by measuring the voltage drop across the resistor  432 . Since the voltage applied to power the drive motor  200  is proportional to the rotational speed of the drive motor  200  and, hence, the linear speed of the firing rod  220 , the speed calculator  422  determines the speed of the firing rod  220  based on the voltage potential of the drive motor  200 . 
     The current sensor  430  may also be coupled to the power source  400  to determine the current draw thereof which allows for analysis of the load on the end effector  160 . This may be indicative of the tissue type being stapled since various tissue have different tensile properties which affect the load being exerted on the instrument  10  and the power source  400  and/or the motor  200 . 
     The speed calculator  422  may also be coupled to a second voltage sensor (not explicitly shown) for determining the voltage within the power source  400  thereby calculating the power draw directly from the source. In addition, the change in current over time (dI/dt) can be monitored to detect quick spikes in the measurements which correspond to a large increase in applied torque by the drive motor  200 . Thus, the current sensor  430  may be used to determine the torque and the load of the drive motor  200 . 
     In addition, the velocity of the firing rod  220  as measured by the speed calculator  422  may be then compared to the current draw of the drive motor  200  to determine whether the drive motor  200  is operating properly. Namely, if the current draw is not commensurate (e.g., large) with the velocity (e.g., low) of the firing rod  220  then the motor  200  is malfunctioning (e.g., locked, stalled, etc.). If a stall situation is detected, or the current draw exceeds predetermined limits, the position calculator  416  then determines whether the firing rod  220  is at a mechanical stop. If this is the case, then the microcontroller  500  can shut down the drive motor  200  or enters a pulse and/or pause mode (e.g., discontinuous supply of power to the drive motor  200 ) to prevent damage to the motor  200 , battery or power source  400 , and microcontroller  500 , to unlock the instrument  10  and to retract the firing rod  220 . 
     In one embodiment, the speed calculator  422  compares the rotation speed of the drive tube  210  as detected by the rotation sensor  239  and that of the drive motor  200  based on the measurements from and the rotation speed detecting apparatus  424 . This comparison allows the speed calculator  422  to determine whether there is clutch activation problem (e.g., slippage) if there is a discrepancy between the rotation of the clutch  300  and that of the drive tube  210 . If slippage is detected, the position calculator  416  then determines whether the firing rod  220  is at a mechanical stop. If this is the case, then the microcontroller  500  can shut down the instrument  10  or enter a pulse and/or pause mode (e.g., discontinuous supply of power to the drive motor  200 ), or retract the firing rod  220 . 
     In addition to linear and/or rotational displacement of the firing rod  220  and other drive components, the instrument  10  also includes sensors adapted to detect articulation of the end effector  160 . With reference to  FIG. 4 , the instrument  10  includes a rotation sensor  241  adapted to indicate the start position, the rotational direction and the angular displacement of the rotating housing assembly  180  at the start of the procedure as detected by the shaft start position sensor  231 . The rotation sensor  241  operates by counting the number of indicators disposed on the inner surface of the rotation knob  182  by which the rotation knob  182  has been rotated. The count is then transmitted to the microcontroller  500  which then determines the rotational position of the endoscopic portion  142 . This can be communicated wirelessly or through an electrical connection on the endoscopic portion and wires to the microcontroller  500 . 
     The instrument  10  also includes an articulation sensor  235  which determines articulation of the end effector  160 . The articulation sensor  235  counts the number of features  263  disposed on the articulation gear  233  by which the articulation knob  176  has been rotated from its 0° position, namely the center position of the articulation knob  176  and, hence, of the end effector  160  as shown in  FIG. 5 . The 0° position and can be designated by a central unique indicator  265  also disposed on the articulation gear  233  which corresponds with the first position of the end effector  160 , where longitudinal axis B-B is substantially aligned with longitudinal axis A-A. The count is then transmitted to the microcontroller  500  which then determines the articulation position of the end effector  160  and reports the articulation angle via the interface  120 . The features can include protrusions, magnetic material, transmitters, etc. 
     In addition, the articulation angle can be used for the so-called “auto stop” mode. During this operational mode, the instrument  10  automatically stops the articulation of the end effector  160  when the end effector  160  is at its central first position. Namely, as the end effector  160  is articulated from a position in which longitudinal axis B-B is disposed at an angle to longitudinal axis A-A towards the first position, the articulation is stopped when the longitudinal axis B-B is substantially aligned with longitudinal axis A-A. This position is detected by the articulation sensor  235  based on the central indicator. This mode allows the endoscopic portion  140  to be extracted without the user having to manually align the end effector  160 . 
     With reference to  FIG. 1 , the present disclosure provides a loading unit identification system  440  which allows the instrument  10  to identify the loading unit  169  and to determine operational status thereof. The identification system  440  provides information to the instrument  10  on staple size, cartridge length, type of the loading unit  169 , status of cartridge, proper engagement, and the like. This information allows the instrument to adjust clamping forces, speed of clamping and firing and end of stroke for various length staple cartridges. 
     The loading unit identification system  440  may also be adapted to determine and communicate to the instrument  10  (e.g., a control system  501  shown in  FIG. 20 ) various information, including the speed, power, torque, clamping, travel length and/or strength limitations for operating the particular end effector  160 . The control system  501  may also determine the operational mode and adjust the voltage, clutch spring loading and stop points for travel of the components. More specifically, the identification system may include a component (e.g., a microchip, emitter or transmitter) disposed in the end effector  160  that communicates (e.g., wirelessly, via infrared signals, etc.) with the control system  501 , or a receiver therein. It is also envisioned that a signal may be sent via firing rod  220 , such that firing rod  220  functions as a conduit for communications between the control system  501  and end effector  160 . In another embodiment, the signals can be sent through an intermediate interface, such as a feedback controller  603  ( FIGS. 21-23 ). 
     By way of example, the sensors discussed above may be used to determine if the staples have been fired from the staple cartridge, whether they have been fully fired, whether and the extent to which the beam has been retracted proximally through the staple cartridge, and other information regarding the operation of the loading unit. In certain embodiments of the present disclosure, the loading unit incorporates components for identifying the type of loading unit, and/or staple cartridge loaded on the instrument  10 , including magnetic, optical, infra-red, cellular, radio frequency or conductive identification chips. The type of loading unit and/or staple cartridge may be received by an associated receiver within the control system  501 , or an external device in the operating room for providing feedback, control and/or inventory analysis. 
     Information can be transmitted to the instrument  10  via a variety of communication protocols (e.g., wired or wireless) between the loading unit  169  and the instrument  10 . The information can be stored within the loading unit  169  in a microcontroller, microprocessor, non-volatile memory, radio frequency identification tags, and identifiers of various types such as optical, color, displacement, magnetic, electrical, binary and/or gray coding (e.g., conductance, resistance, capacitance, impedance). 
     In one embodiment, the loading unit  169  and the instrument  10  include corresponding wireless transceivers, an identifier  442  and an interrogator  444 , respectively. The identifier  442  includes memory or may be coupled to a microcontroller for storing various identification and status information regarding the loading unit  169 . Once the loading unit  169  is coupled to the instrument  10 , the instrument  10  interrogates the identifier  442  via the interrogator  444  for an identifying code. In response to the interrogatory, the identifier  442  replies with the identifying code corresponding to the loading unit  169 . During operation, once identification has occurred, the identifier  442  is configured to provide the instrument  10  with updates as to the status of the loading unit  169  (e.g., mechanical and/or electrical malfunction, position, articulation, etc.). 
     The identifier  442  and the interrogator  444  are configured to communicate with each other using one or more communication protocols, such as Bluetooth®, ANT3®, KNX®, ZWave®, X10® Wireless USB®, IrDA®, Nanonet®, Tiny OS®, ZigBee®, 802.11 IEEE, and other radio, infrared, UHF, VHF communications or the like. In one embodiment, the transceiver  400  may be a radio frequency identification (RFID) tag, either active or passive, depending on the interrogator capabilities of the transceiver  402 . 
       FIGS. 15A and 15B  illustrate additional embodiments of the loading unit  169  having various types of identification devices. With reference to  FIG. 15A , a proximal end  171  of the loading unit  169  having an electrical identifier  173  is shown. The identifier  173  may include one or more resistors, capacitors, or inductors and is coupled with a corresponding electrical contact  181  disposed on the distal end of the endoscopic portion  140 . The contact may include slip rings, brushes and/or fixed contacts disposed in the endoscopic portion. The identifier  173  may be disposed on any location of the loading unit  168  and may be formed on a flexible or fixed circuit or may be traced directly on the surface of the loading unit  169 . 
     When the loading unit  169  is coupled with the endoscopic portion  140 , the contact applies a small current through the electrical identifier  173 . The interrogator contact also includes a corresponding electrical sensor which measures the resistance, impedance, capacitance, and/or impedance of the identifier  173 . The identifier  173  has a unique electrical property (e.g., frequency, wave patterns, etc.) which corresponds to the identifying code of the loading unit  169 . Thus, when the electrical property thereof is determined, the instrument  10  determines the identity of the loading unit  169  based on the measured property. 
     In one embodiment, the identifier  173  may be a magnetic identifier such as gray coded magnets and/or ferrous nodes incorporating predetermined unique magnetic patterns identifying the loading unit  169  by the identifying code. The magnetic identifier is read via a magnetic sensor (e.g., ferromagnetic sensor, Hall Effect sensor, etc.) disposed at the distal end of the endoscopic portion  140 . The magnetic sensor transmits the magnetic data to the instrument  10  which then determines the identity of the loading unit  169 . It can also be envisioned that the contacts  181  behave as a non-contact antenna of a conductive ink or flex circuit in which the contacts  181  excite identifier  173  to emit a frequency identification signal. 
       FIG. 15B  illustrates the proximal end  171  of the loading unit  169  having one or more protrusions  175 . The protrusions  175  can be of any shape, such as divots, bumps, strips, etc., of various dimensions. The protrusions  175  interface with corresponding displacement sensors  183  disposed within the proximal segment of the endoscopic portion  140 . The sensors are displaced when the protrusions  175  are inserted into the endoscopic portion. The amount of the displacement is analyzed by the sensors and converted into identification data, allowing the instrument  10  to determine staple size, cartridge length, type of the loading unit  169 , proper engagement, or the like. The displacement sensors can be switches, contacts, magnetic sensors, optical sensors, variable resistors, linear and rotary variable displacement transducers which can be spring loaded. The switches are configured to transmit binary code to the instrument  10  based on their activation status. More specifically, some protrusions  175  extend a distance sufficient to selectively activate some of the switches, thereby generating a unique code based on the combination of the protrusions  175 . 
     In another embodiment, the protrusion  175  can be color coded. The displacement sensors  183  include a color sensor configured to determine the color of the protrusion  175  to measure one or more properties of the loading unit  169  based on the color and transmits the information to the instrument  10 . 
       FIG. 16  shows a method for identifying the loading unit  169  and providing status information concerning the loading unit  169  to the instrument  10 . In step  650  it is determined whether the loading unit  169  is properly loaded into the instrument  10 . This may be determined by detecting whether contact has been made with the identifier  173  and/or protrusions  175 . If the loading unit  169  is properly loaded, in step  652 , the loading unit  169  communicates to the instrument  10  a ready status (e.g., turning on the first light of the visual outputs  123 ). 
     In step  654 , the instrument  10  verifies whether the loading unit  169  has been previously fired. This may be accomplished by providing one or more fired sensors  900  disposed in the cartridge assembly  164  ( FIG. 9 ) which determine whether any of the staples  66  have been fired. The fired sensor  900  may be a switch or a fuse which is triggered when the sled  74  is advanced in the distal direction which is indicative of the end effector  160  being used. The fired sensor  900  may be coupled to the identifier  442  which then stores a value indicative of the previously fired status. A second fired sensor  900  may be placed distal of the last row of staples  66  such that when the sensor  900  is triggered, it is indicated that firing of the cartridge assembly  164  is complete. 
     If the loading unit  169  was fired, in step  656 , the instrument  10  provides an error response (e.g., flashing the first light of the visual outputs  123 ). If the loading unit  169  has not been fired, in step  658  the loading unit  169  provides identification and status information (e.g., first light is turned on) to the instrument  10  via the identification system  440 . The determination whether the loading unit  169  has been fired is made based on the saved “previously fired” signal saved in the memory of the identifier  442  as discussed in more detail below with respect to step  664 . In step  660 , the instrument  10  adjusts its operating parameters in response to the information received from the loading unit  169 . 
     The user performs a surgical procedure via the instrument  10  in step  662 . Once the procedure is complete and the loading unit  169  has been fired, the instrument  10  transmits a “previously fired” signal to the loading unit  169 . In step  664 , the loading unit  169  saves the “previously fired” signal in the memory of the identifier  442  for future interrogations by the instrument  10  as discussed with respect to step  654 . 
     With reference to  FIG. 17 , the loading unit  169  includes one or more tissue sensors disposed within the end effector  160  for detecting the type of object being grasped, such as recognizing non-tissue objects or the tissue type of the object. The sensors can also be configured to determine amount of blood flow being passed between the jaw members of the end effector  160 . More specifically, a first tissue sensor  177  is disposed at a distal portion of the anvil assembly  162  and a second tissue sensor  179  is disposed at a distal portion of the cartridge assembly  164 . The sensors  177  and  179  are coupled to the identifier  442  allowing for transmission of sensor data to the microcontroller  500  of the instrument  10 . 
     The sensors  177  and  179  are adapted to generate a field and/or waves in one or more arrays or frequencies therebetween. The sensors  177  and  179  may be acoustic, ultrasonic, ferromagnetic, Hall Effect sensors, laser, infrared, radio frequency, or piezoelectric devices. The sensors  177  and  179  are calibrated for ignoring commonly occurring material, such as air, bodily fluids and various types of human tissue and for categorizing specific tissue types (e.g., scar tissue, lung, stomach, sphincter, etc.) or detecting certain types of foreign matter. The foreign matter may be bone, tendons, cartilage, nerves, major arteries and non-tissue matter, such as ceramic, metal, plastic, etc. 
     The sensors  177  and  179  detect the foreign material passing between the anvil and cartridge assemblies  162  and  164  based on the absorption, reflection and/or filtering of the field signals generated by the sensors. If the material reduces or reflects a signal, such that the material is outside the calibration range and is, therefore, foreign, the sensors  177  and  179  transmit the interference information to the microcontroller  500  which then determines the type of the material being grasped by the end effector  160 . The determination may be made by comparing the interference signals with a look up table listing various types of materials and their associated interference ranges. The microcontroller  500  then alerts the user of the foreign material being grasped as well as the identity thereof. This allows the user to prevent clamping, cutting, or stapling through areas containing foreign matter or the control system  501  can alter the performance of the drive motor  200  for specific tissue scenarios. 
       FIG. 20  illustrates a control system  501  including the microcontroller  500  which is coupled to the position and speed calculators  416  and  422 , the loading unit identification system  440 , the user interface  120 , the drive motor  200 , and a data storage module  502 . In addition the microcontroller  500  may be directly coupled to various sensors (e.g., first and second tissue sensors  177  and  179 , the load switch  230 , shaft start position sensor  231 , clamp position sensor  232 , articulation sensor  235 , linear displacement sensor  237 , rotational sensor  239 , firing rod rotation sensor  241 , motor and battery operating module  412 , rotation speed detecting apparatus  418 , switches  421 , voltage sensor  428 , current sensor  430 , the interrogator  444 , etc.). 
     The microcontroller  500  includes internal memory which stores one or more software applications (e.g., firmware) for controlling the operation and functionality of the instrument  10 . The microcontroller  500  processes input data from the user interface  120  and adjusts the operation of the instrument  10  in response to the inputs. The adjustments to the instrument  10  may include, for example, powering the instrument  10  on or off, controlling speed by means of voltage regulation or voltage pulse width modulation, limiting torque by reducing duty cycle, or pulsing the voltage on and off to limit average current delivery during a predetermined period of time. 
     The microcontroller  500  is coupled to the user interface  120  via a user feedback module  504  which is configured to inform the user of operational parameters of the instrument  10 . The user feedback module  504  instructs the user interface  120  to output operational data on the screen  122 . In particular, the outputs from the sensors are transmitted to the microcontroller  500  which then sends feedback to the user instructing the user to select a specific mode, speed or function for the instrument  10  in response thereto. 
     The loading unit identification system  440  instructs the microcontroller  500  which type of end effector is on the loading unit. In an embodiment, the control system  501  is capable of storing information relating to the force applied to firing rod  220  and/or end effector  160 , such that when the loading unit  169  is identified, the microcontroller  500  automatically selects the operating parameters for the instrument  10 . This allows for control of the force being applied to the firing rod  220  so that firing rod  220  can drive the particular end effector  160  that is on the loading unit in use at the time. 
     In one embodiment, the microcontroller  500  also analyzes the calculations from the position and speed calculators  416  and  422  and other sensors to determine the actual position and/or speed of the firing rod  220  and operating status of components of the instrument  10 . The analysis may include interpretation of the sensed feedback signal from the calculators  416  and  422  to control the movement of the firing rod  220  and other components of the instrument  10  in response to the sensed signal. The microcontroller  500  is configured to limit the travel of the firing rod  220  once the firing rod  220  has moved beyond a predetermined point as reported by the position calculator  416 . Additional parameters which may be used by the microcontroller  500  to control the instrument  10  include motor and/or battery temperature, number of cycles remaining and used, remaining battery life, tissue thickness, current status of the end effector, transmission and reception, external device connection status, etc. 
     In one embodiment, the instrument  10  includes various sensors configured to measure current (e.g., ammeter), voltage (e.g., voltmeter), proximity (e.g., optical sensors), temperature (e.g., thermocouples, thermistors, etc.), and force (e.g., strain gauges, load cells, etc.) to determine for loading conditions on the loading unit  169 . During operation of the instrument  10  it is desirable to know the forces being exerted by the instrument  10  on the target tissue during the approximation process and during the firing process. Detection of abnormal loads (e.g., outside a predetermined load range) indicates a problem with the instrument  10  and/or clamped tissue which is communicated to the user. 
     Monitoring of load conditions may be performed by one or more of the following methods: monitoring speed of the drive motor  200 , monitoring torque being applied by the motor, monitoring proximity of jaw members  162  and  164 , monitoring temperature of components of the instrument  10 , or measuring the load on the firing rod  220  via a strain sensor  185  ( FIG. 4 ) and/or other load bearing components of the instrument  10 . Speed and torque monitoring is discussed above with respect to  FIG. 6  and the speed calculator  422 . 
     Measuring the distance between the jaw members  162  and  164  can also be indicative of load conditions on the end effector  160  and/or the instrument  10 . When large amounts of force are imparted on the jaw members  162  and  164 , the jaw members are deflected outwards. The jaw members  162  and  164  are parallel to each other during normal operation, however, during deformation, the jaw members are at an angle relative to each other. Thus, measuring the angle between the jaw members  162  and  164  allows for a determination of the deformation of the jaw members due to the load being exerted thereon. The jaw members may include strain gauges  187  and  189  as shown in  FIG. 17  to directly measure the load being exerted thereon. Alternatively, one or more proximity sensors  191  and  193  can be disposed at the distal tips of the jaw members  162  and  164  to measure the angle therebetween. These measurements are then transmitted to the microcontroller  500  which analyzes the angle and/or strain measurements and alerts the user of the stress on the end effector  160 . 
     In another embodiment, the firing rod  220  or other load-bearing components include one or more strain gauges and/or load sensors disposed thereon. Under high strain conditions, the pressure exerted on the instrument  10  and/or the end effector  160  is translated to the firing rod  220  causing the firing rod  220  to deflect, leading to increased strain thereon. The strain gauges then report the stress measurements to the microcontroller  500 . In another embodiment, a position, strain or force sensor may be disposed on the clutch plate  302 . 
     During the approximation process, as the end effector  160  is clamped about tissue, the sensors disposed in the instrument  10  and/or the end effector  160  indicate to the microprocessor  500  that the end effector  160  is deployed about abnormal tissue (e.g., low or high load conditions). Low load conditions are indicative of a small amount of tissue being grasped by the end effector  160  and high load conditions denote that too much tissue and/or a foreign object (e.g., tube, staple line, clips, etc.) is being grasped. The microprocessor  500  thereafter indicates to the user via the user interface  120  that a more appropriate loading unit  169  and/or instrument  10  should be chosen. 
     During the firing process, the sensors can alert the user of a variety of errors. Sensors may communicate to the microcontroller  500  that a staple cartridge or a portion of the instrument  10  is faulty. In addition, the sensors can detect sudden spikes in the force exerted on the knife, which is indicative of encountering a foreign body. Monitoring of force spikes could also be used to detect the end of the firing stroke, such as when the firing rod  220  encounters the end of the stapling cartridge and runs into a hard stop. This hard stop creates a force spike which is relatively larger than those observed during normal operation of the instrument  10  and could be used to indicate to the microcontroller that the firing rod  220  has reached the end of loading unit  169 . Measuring of the force spikes can be combined with positional feedback measurements (e.g., from an encoder, linear variable displacement transducer, linear potentiometer, etc.) as discussed with respect to position and speed calculators  416  and  422 . This allows for use of various types of staple cartridges (e.g., multiple lengths) with the instrument  10  without modifying the end effector  160 . 
     When force spikes are encountered, the instrument  10  notifies the user of the condition and takes preventative measures by entering a so-called “pulse”, or pulse width modulation (PWM) or an electronic clutching mode, which is discussed in more detail below. During this mode the drive motor  200  is controlled to run only in short bursts to allow for the pressure between the grasped tissue and the end effector  160  to equalize. The electronic clutching limits the torque exerted by the drive motor  200  and prevents situations where high amounts of current are drawn from the power source  400 . This, in turn, prevents damage to electronic and mechanical components due to overheating which accompanies overloading and high current draw situations. 
     The microcontroller  500  controls the drive motor  200  through a motor driver via a pulse width modulated control signal. The motor driver is configured to adjust the speed of the drive motor  200  either in clockwise or counter-clockwise direction. The motor driver is also configured to switch between a plurality of operational modes which include an electronic motor braking mode, a constant speed mode, an electronic clutching mode, and a controlled current activation mode. In electronic braking mode, two terminals of the drive motor  200  are shorted and the generated back EMF counteracts the rotation of the drive motor  200  allowing for faster stopping and greater positional precision in adjusting the linear position of the firing rod  220 . 
     In the constant speed mode, the speed calculator  422  in conjunction with the microcontroller  500  and/or the motor driver adjust the rotational speed of the drive motor  200  to ensure constant linear speed of the firing rod  220 . The electronic clutching mode involves repeat engagement and/or disengagement of the clutch  300  from the drive motor  200  in response to sensed feedback signals from the position and speed calculators  416  and  422 . In controlled current activation mode, the current is either ramped up or down to prevent damaging current and torque spikes when transitioning between static to dynamic mode to provide for so-called “soft start” and “soft stop.” 
     The data storage module  502  records the data from the sensors coupled to the microcontroller  500 . In addition, the data storage module  502  records the identifying code of the loading unit  169 , the status of the end effector  100 , number of stapling cycles during the procedure, etc. The data storage module  502  is also configured to connect to an external device such as a personal computer, a PDA, a smartphone, a storage device (e.g., Secure Digital® card, Compact Flash® card, MemoryStick®, etc.) through a wireless or wired data port  503 . This allows the data storage module  502  to transmit performance data to the external device for subsequent analysis and/or storage. The data port  503  also allows for so-called “in the field” upgrades of firmware of the microcontroller  500 . 
     A feedback control system  601  is shown in  FIGS. 21-23 . The system includes a feedback controller  603  which is shown in  FIGS. 22A-B . The instrument  10  is connected to the feedback controller  603  via the data port  502  which may be either wired (e.g., Firewire®, USB®, Serial RS232®, Serial R5485®, USART®, Ethernet®, etc.) or wireless (e.g., Bluetooth®, ANT3®, KNX®, ZWave®, X10® Wireless USB®, IrDA®, Nanonet®, Tiny OS®, ZigBee®, 802.11 IEEE, and other radio, infrared, UHF, VHF communications or the like). 
     With reference to  FIG. 21 , the feedback controller  603  is configured to store the data transmitted thereto by the instrument  10  as well as process and analyze the data. The feedback controller  603  is also connected to other devices, such as a video display  604 , a video processor  605  and a computing device  606  (e.g., a personal computer, a PDA, a smartphone, a storage device, etc.). The video processor  605  is used for processing output data generated by the feedback controller  603  for output on the video display  604 . The computing device  606  is used for additional processing of the feedback data. In one embodiment, the results of the sensor feedback analysis performed by the microcontroller  600  may be stored internally for later retrieval by the computing device  606 . 
     The feedback controller  603  includes a data port  607  ( FIG. 22B ) coupled to the microcontroller  600  which allows the feedback controller  603  to be connected to the computing device  606 . The data port  607  may provide for wired and/or wireless communication with the computing device  606  providing for an interface between the computing device  606  and the feedback controller  603  for retrieval of stored feedback data, configuration of operating parameters of the feedback controller  603  and upgrade of firmware and/or other software of the feedback controller  603 . 
     The feedback controller  603  is further illustrated in  FIGS. 22A-B . The feedback controller  603  includes a housing  610  and a plurality of input and output ports, such as a video input  614 , a video output  616 , a heads-up (“HUD”) display output  618 . The feedback controller  603  also includes a screen  620  for displaying status information concerning the feedback controller  603 . 
     Components of the feedback controller  603  are shown in  FIG. 23 . The feedback controller  603  includes a microcontroller  600  and a data storage module  602 . The microcontroller  600  and the data storage module  602  provide a similar functionality as the microcontroller  500  and the data storage module  502  of the instrument  10 . Providing these components in a stand-alone module, in the form of the feedback controller  603 , alleviates the need to have these components within the instrument  10 . 
     The data storage module  602  may include one or more internal and/or external storage devices, such as magnetic hard drives or flash memory (e.g., Secure Digital® card, Compact Flash® card, MemoryStick®, etc.). The data storage module  602  is used by the feedback controller  603  to store feedback data from the instrument  10  for later analysis of the data by the computing device  606 . The feedback data includes information supplied by the sensors disposed within the instrument  10  and the like. 
     The microcontroller  600  is configured to supplant and/or supplement the control circuitry, if present, of the instrument  10 . The microcontroller  600  includes internal memory which stores one or more software application (e.g., firmware) for controlling the operation and functionality of the instrument  10 . The microcontroller  600  processes input data from the user interface  120  and adjusts the operation of the instrument  10  in response to the inputs. The microcontroller  600  is coupled to the user interface  120  via a user feedback module  504  which is configured to inform the user of operational parameters of the instrument  10 . More specifically, the instrument  10  is configured to connect to the feedback controller  603  wirelessly or through a wired connection via a data port  407  ( FIG. 6 ). 
     In a disclosed embodiment, the microcontroller  600  is connected to the drive motor  200  and is configured and arranged to monitor the battery impedance, voltage, temperature and/or current draw and to control the operation of the instrument  10 . The load or loads on battery  400 , transmission, drive motor  200  and drive components of the instrument  10  are determined to control a motor speed if the load or loads indicate a damaging limitation is reached or approached. For example, the energy remaining in battery  400 , the number of firings remaining, whether battery  400  must be replaced or charged, and/or approaching the potential loading limits of the instrument  10  may be determined. The microcontroller  600  may also be connected to one or more of the sensors of the instrument  10  discussed above. 
     The microcontroller  600  is also configured to control the operation of drive motor  200  in response to the monitored information. Pulse modulation control schemes, which may include an electronic clutch, may be used in controlling the instrument  10 . For example, the microcontroller  600  can regulate the voltage supply of the drive motor  200  or supply a pulse modulated signal thereto to adjust the power and/or torque output to prevent system damage or optimize energy usage. 
     In one embodiment, an electric braking circuit may be used for controlling drive motor  200 , which uses the existing back electromotive force of rotating drive motor  200  to counteract and substantially reduce the momentum of drive tube  210 . The electric braking circuit improves the control of drive motor  200  and/or drive tube  210  for stopping accuracy and/or shift location of powered surgical instrument  10 . Sensors for monitoring components of powered surgical instrument  10  and to help prevent overloading of powered surgical instrument  10  may include thermal-type sensors, such as thermal sensors, thermistors, thermopiles, thermocouples and/or thermal infrared imaging and provide feedback to the microcontroller  600 . The microcontroller  600  may control the components of powered surgical instrument  10  in the event that limits are reached or approached and such control can include cutting off the power from the power source  400 , temporarily interrupting the power or going into a pause mode and/or pulse modulation to limit the energy used. The microcontroller  600  can also monitor the temperature of components to determine when operation can be resumed. The above functions of the microcontroller  600  may be used independently of, or factored with current, voltage, temperature and/or impedance measurements. 
     The result of the analysis and processing of the data by the microcontroller  600  is output on video display  604  and/or the HUD display  622 . The video display  604  may be any type of display such as an LCD screen, a plasma screen, electroluminescent screen and the like. In one embodiment, the video display  604  may include a touch screen and may incorporate resistive, surface wave, capacitive, infrared, strain gauge, optical, dispersive signal or acoustic pulse recognition touch screen technologies. The touch screen may be used to allow the user to provide input while viewing operational feedback. The HUD display  622  may be projected onto any surface visible to the user during surgical procedures, such as lenses of a pair of glasses and/or goggles, a face shield, and the like. This allows the user to visualize vital feedback information from the feedback controller  603  without losing focus on the procedure. 
     The feedback controller  603  includes an on-screen display module  624  and a HUD module  626 . The modules  626  process the output of the microcontroller  600  for display on the respective displays  604  and  622 . More specifically, the OSD module  624  overlays text and/or graphical information from the feedback controller  603  over other video images received from the surgical site via cameras disposed therein. The modified video signal having overlaid text is transmitted to the video display  604  allowing the user to visualize useful feedback information from the instrument  10  and/or feedback controller  603  while still observing the surgical site. 
       FIGS. 24-25  illustrate another embodiment of the instrument  10 ′. The instrument  10 ′ includes a power source  400 ′ having a plurality of cells  401  arranged in a straight series configuration. The power source  400 ′ is inserted vertically into a vertical battery chamber  800  within the handle portion  112 . The battery chamber  800  includes spring contacts  802  within the top portion thereof to push downward the power source  400 ′. In one embodiment, the spring contacts  802  may include contacts to electrically couple with the power source  400 ′. The power source  400 ′ is held within the battery chamber  800  via a battery cap  804  which is configured to slide in a distal direction to lock in place. The cap  804  and the handle  112  may include tongue and groove couplings to keep the cap  804  from sliding out. The power source  400 ′ is biased against the cap  804  due to the downward force of the spring contacts  802 . As the cap  804  is slid in a proximal direction, the power source  400 ′ is ejected from the battery chamber  800  by the spring contacts  802 . 
       FIG. 25  shows another embodiment of the rotational sensor  239  which detects the rotation of the drive tube  210 , thus, measuring the rate of rotation of the drive tube  210  which allows for determination of the linear velocity of the firing rod  220 . The rotational sensor  239  includes an encoder wheel  810  mounted to drive tube  210  and an optical reader  812  (e.g., photo interrupter). The optical reader  812  is configured to determine the number of interruptions in a light beam which is continuously provided between two opposing edges  814  and  816  thereof. The wheel  810  rotates with the drive tube  210  and includes a plurality of slits  811  therethrough. 
     The outer edge of the wheel  810  is disposed between the opposing edges of the optical reader  812  such that the light being transmitted between the edges  814  and  816  shines through the slits  811 . The light beam between the edges  814  and  816  is interrupted by the wheel  810  as the drive tube  210  is rotated. The optical reader  812  measures the number of interruptions in the light beam and rate of occurrences thereof and transmits these measurements to the speed calculator  422  which then determines the speed of the drive rod  220  as discussed above. 
       FIGS. 27-32  show the instrument  10 ′ having a retraction assembly  820  for retracting the firing rod  220  from a fired position. The retraction assembly  820  provides for a manually driven mechanical interface with the drive tube  210  allowing for manual retraction of the firing rod  220  via ratcheting action of the retraction assembly  820 . This may be useful in certain situations to give the user of the instrument manual control over the position of the firing rod  220  (e.g., electrical malfunction, stuck end effector  160 , etc.). The retraction assembly  820  may be configured as a modular assembly which can be inserted into the instrument  10 ′. 
     With reference to  FIG. 30 , the retraction assembly  820  includes a retraction chassis  822  having a top portion  823  and a bottom portion  825 . The retraction assembly  820  interfaces mechanically with the drive tube  210  via a drive gear  826  and a retraction gear  824 . First spur gear  830  is rigidly attached to the retraction gear  824 . The drive gear  826  is attached to the drive tube  210  and is translated in response to the rotation of the drive tube  210 . Conversely, rotation of the drive gear  826  imparts rotation on the drive tube  210 . The drive gear  826  and the retraction gear  824  may be bevel gears allowing the gears  824  and  826  to interface in an orthogonal manner. 
     The retraction gear  824  is coupled to a first spindle  828  which is disposed in a substantially orthogonal manner between the top and bottom portions  823  and  825  of the retraction chassis  822 . The first spindle  828  is rotatable around a longitudinal axis defined thereby. The first spindle  828  further includes first spur gear  830  attached thereto and to the retraction gear  824 . The first spur gear  830  interfaces with a second spur gear  832  disposed on a second spindle  834  which is also is disposed in a substantially perpendicular manner between the top and bottom portions  823  and  825  of the retraction chassis  822  and is rotatable around a longitudinal axis defined thereby. 
     The second spur gear  832  interfaces mechanically with a third spur gear  836  which is disposed on the first spindle  828 . The third spur gear  836  is attached to a first clutch portion  838  of a unidirectional clutch assembly  840 . The clutch assembly  840  further includes a second clutch portion  840  rotatably disposed on the first spindle  828  above the first clutch portion  838  with a spring  843  disposed between the first and second clutch portions  838  and  842  thereby biasing the first and second clutch portions  838  and  842  toward a raised non-interlocking configuration (e.g., first configuration) as shown in  FIG. 31 . 
     Rotation of the drive tube  210  and/or the drive gear  826  imparts rotation on the retraction gear  824  and the first, second and third spur gears  830 ,  832  and  836  along with the first portion  838  and the respective spindles  828  and  834 . Since, the second clutch portion  842  can rotate about the spindle  828  and is separated from the first clutch portion  838  by the spring  843 , the rotation of the first portion  838  is not translated thereto. 
     The first and second clutch portions  838  and  842  include a plurality of interlocking teeth  844  having a flat interlocking surface  846  and a sloping slip surface  848 . (See  FIG. 30 .) The retraction assembly  820  is actuated by a retraction lever  845 . As shown in  FIG. 32 , the second clutch portion  842  is pushed downwards by the retraction lever  845  thereby interfacing the teeth  844 . The slip surfaces  848  allow for the interlocking surfaces  846  to come in contact with each other thereby allowing rotation of the second clutch portion  842  to rotate the first clutch portion  838  and all of the interfacing gears. 
     The retraction lever  845  includes a camming portion  847  and a handle  849  attached thereto. The camming portion  847  includes an opening  853  which houses a unidirectional needle clutch  855  which is in mechanical cooperation with a fitting  856  which is operatively coupled to the first spindle  828  thereby allowing the retraction lever  845  to rotate about the first spindle  828 . 
     With reference to  FIG. 29 , the lever  845  includes a one or more camming members  850  each having a camming surface  852 . In the first configuration, the lever  845  is disposed along a lever pocket  860  of the housing  110  as shown in  FIG. 27 . By nesting the lever  845  into the housing  110 , a longer lever can be utilized which gives the user a much greater mechanical advantage over other manual retraction systems. The lever  845  is pushed up by the spring  843  against the top portion  823  and the camming members  850  are disposed within corresponding cam pockets  858 . The lever  845  is also maintained in the first configuration by a return extension spring  862  mounted between the top portion  823  and the camming portion  847 . The camming members  850  and the lever pocket  860  limit the rotational range of the lever  845 . 
     As the lever  845  is pulled out of the lever pocket  860 , the camming members  850  interface with the corresponding cam pockets  823  and push the camming portion  847  of the lever  845  in a downward direction. The downward movement compresses the spring  843  and pushes the first and second clutch portions  838  and  842  together interlocking the teeth  844  thereby engaging the portions  838  and  842  in a second configuration. Rotation of the camming portion  847  in a counterclockwise direction actuates the needle clutch  855  which interfaces with the fitting  856  and is axially coupled to the first spindle  828 . Continual rotation of the lever  845  rotates the clutch assembly  840  which in turn rotates the fitting  856  which is keyed to the upper clutch  842 , which is now mated to the lower clutch  838 . This lower clutch  838  is fastened to the third spur gear  836  which then drives the spur gears  836 ,  832  and  830  and the retraction and drive gears  824  and  826 . This in turn rotates drive tube  210  and retracts the drive rod  220 . 
     The lever  845  can be rotated until the handle  849  abuts the housing  110  as shown in  FIG. 28 . Thereafter, the lever  845  is brought back to its first configuration by the return extension spring  862  which rides in the radial groove  854 . This raises the camming portion  847  allowing the second clutch portion  842  to also move upward and disengage the first clutch portion  838 . The needle clutch  855  releases the fitting  856  allowing the lever  845  to return to the first configuration without affecting the movement of the drive tube  210 . Once the lever  845  is returned to the first configuration, the lever  845  may be retracted once again to continue to ratchet the driving rod  220 . Thus, the assembly can be configured for one or more movements of the lever  845  to partially or fully retract the firing rod  220 . 
     With respect to other aspects of the present disclosure, to advance the state of the art of minimizing medical waste, it is contemplated that a sealed battery pack compartment, and/or a sealed instrument housing and/or a sealed handle assembly can be configured as part of a surgical apparatus according to the present disclosure to prevent contamination of batteries of battery-powered surgical apparatuses. Thus, the perimeter at which sealing of the battery pack occurs can be extended, in one embodiment, from the battery pack to the handle assembly and in yet another embodiment to the instrument housing. 
     More particularly, referring to  FIGS. 33-36 , surgical instrument  10 ″ is illustrated. Surgical instrument  10 ″ is substantially identical to surgical instrument  10 ′ except that surgical instrument  10 ″ includes at least one battery-retaining structure such as battery chamber or compartment  800 ′ that differs from battery chamber or compartment  800 . In addition, although surgical instrument  10 ′ also includes a power head, surgical instrument  10 ″ includes a power head  900 ′ that is configured to include the battery chamber or compartment  800 ′. As defined herein, the power head  900 ′ is the portion of the surgical instrument  10 ″ extending from proximal portion  118  of the housing  110  to a distal portion  118 ′ of the housing portion  110 . Power head  900 ′ includes, as defined below with respect to  FIG. 38  and  FIGS. 4-12 , a set of operating components that provide power and operate the surgical instrument  10 ″ and that are mounted within or adjacent the housing  110 . For reference purposes, the battery chamber  800 ′ includes an upper end  800 ′ a  and a lower end  800 ′ b . As illustrated in  FIGS. 35 and 36 , at least one battery  451 ′ or a plurality of the cells or batteries  451 ′ forming a battery pack  451  may be oriented either in a side-by-side configuration  451   a  as illustrated in  FIG. 35  or in an end-to-end configuration  451   b  as illustrated in  FIG. 36 . As defined herein, a battery may include, in addition to battery cells  451 ′, a capacitor or an induction coil each storing electrical charge or a fuel cell or other suitable power supply mechanism. The battery cells  451 ′ in configurations  451   a  and  451   b  provide a cell alignment/shape/configuration that facilitates ejection of the cell or battery pack  451 ′ from the battery chamber  800 ′ so as to avoid medical contamination of the individual battery cells  451 ′ or of the battery pack  451  either during or after the ejection process. The battery packs in the side-by-side configuration  451   a  include terminal connector strips  902  that alternately extend between and connect positive and negative polarized terminals of the battery cells  451 ′. In configuration  451   a , the battery pack  451  includes an upper end  452   a ′ and a lower end  452   a″.    
     The battery packs in the end-to-end configuration  451   b  include terminal connector strips  902  that are disposed only at the longitudinal ends of the battery cells  451 ′. In configuration  451   b , the battery pack  451  includes an upper end  452   b ′ and a lower end  452   b ″. Alignment posts and/or keys  920  may be disposed on the perimeter or exterior of the battery pack  451  to ensure correct orientation during mating/loading into the battery chamber  800 ′. Correct orientation also ensures proper battery terminal polarity within the battery chamber  800 ′ or housing of the device. 
     Electrical contacts  906  may be disposed at the upper end  800 ′ a  of the battery chamber  800 ′ to mate with the corresponding polarized terminals on the particular battery pack  451  and are in electrical communication with power circuitry (not shown). The contacts  906  may serve at least two functions. 
     In one embodiment, referring to  FIG. 34 , the contacts  906  may be spring loaded positive and negative electrical connections  802 . During loading of the battery pack  451  into the battery chamber  800 ′ through battery chamber port  910 , the upper ends  452   a ′,  452   b ′ of either battery pack configuration  451   a  or  451   b , respectively, are inserted through the chamber port  910  so that the alignment keys  920  can align properly within the chamber  800 ′ via receptacles (not shown) until contact is made with the contacts  906  that are spring loaded and that are located at the upper end  800 ′ a  of the chamber  800 ′. The battery chamber  800 ′ includes ribbing  904  in the instrument housing  110  to captivate, isolate and easily eject the battery pack  451 . The ribbing  904  assists in containing and aligning the battery pack  451  and defines a battery ejection path within the battery chamber  800 ′ that forms at least one battery-retaining structure of the power head  900 ′. 
     When compressed by contact with the battery pack  451 , the contacts  906  create a compression force that tends to eject the battery pack  451  in a direction, as shown by arrow A, towards the lower end  800 ′ b  of the battery chamber  800 ′ back through the chamber port  910 , thus further defining the battery-ejection path through the chamber port  910 . 
     A battery chamber access door  912  is configured to sealingly interface with chamber port  910  at the lower end  800 ′ b  of the chamber  800 ′. The access door  912  is rotatably mounted on the handle portion  112  via an offset hinge or pivot connection  914  that is disposed to enable the access door  912  to rotatably swing downwardly or upwardly, as shown by arrow B, either away from the chamber port  910  or towards the chamber port  910 , respectively, to either expose or seal the chamber port  910 , respectively. The hinge or pivot connection  914  may include a spring (not shown) to leverage an additional closure force, as explained below. The access door  912  includes a free end  912   a  that rotatably swings downwardly and upwardly as shown by arrow B and a fixed end  912   b  that is mounted at the offset hinge or pivot connection  914 . The free end  912   a  is configured as a receiving end  916  to engage with, and receive, a barb on a latch, as discussed below. In one embodiment, the hinge or pivot connection  914  is mounted on a distal side  112   b  of the handle portion  112 , as illustrated in  FIG. 34 . 
     As mentioned above, a latch  930 , having an upper arm  930   a  with an end  930   a ′ and a lower arm  930   b  with a lower end  930   b ′, is movably mounted within the handle portion  112  in the vicinity of a proximal side  112   a  via a pivot connection  932  that is disposed to enable the latch  930  to rotatably swing around the pivot connection  932  such that the ends  930   a  and  930   b  of the latch  930  rock alternately to and from the proximal side  112   a . The lower arm  930   b  of the latch  930  is configured as an engaging end or barb  934  that engages with or meshes with the receiving end  916  of the access door  912 , thereby engaging the end or barb  934  of the latch  930 . 
     In one embodiment, an energy storage mechanism  936 , e.g., a compression spring, may also be disposed in the interior of the handle portion  112  on the proximal side  112   a  so as to limit motion of the upper arm  930   a  of the latch  930  in the proximal direction towards proximal side  112   a  and to bias motion of the upper arm  930   a  towards the distal side  112   b.    
     A battery chamber access actuation mechanism  940 , e.g., an elongated push button as shown, may be disposed in a recessed aperture  942  on the proximal side  112   a  of the handle portion  112 . The battery chamber access mechanism  940  is configured to be actuated by a user of the surgical instrument  10 ″. The recessed aperture  942  penetrates through the proximal side  112   a  and enables contact between the access actuation mechanism  940  and the lower arm  930   b  of the latch  930 . 
     When the battery chamber access actuation mechanism  940  is depressed in the distal direction towards distal side  112   b , the battery chamber access actuation mechanism  940  urges the lower arm  930   b  in the distal direction, thereby forcing the latch  930  to rotatably swing around the pivot connection  932 , against the compression force of the spring  936 , and causing disengagement of the engaging end or barb  934  of the latch  930  from the receiving end  916  of the access door  912 . The disengagement of the engaging end or barb  934  of the latch  930  from the receiving end  916  of the access door  912  enables the access door  912  to rotatably swing or rotate downwardly in the direction of arrow B by pivoting around the hinge or pivot connection  914 , thereby transferring the access door  912  from a closed position, as shown, to an open position (not shown) and at least partially exposing the chamber port  910 . Disposal of the battery chamber access actuation mechanism  940  in the recessed aperture  942  reduces the probability of inadvertent actuation of the battery pack  451  during a surgical procedure. An interlock feature (not shown), e.g., a mechanical feature such as a cap, may be provided to lock the battery chamber access actuation mechanism  940  during the surgical procedure. If the battery pack  451  does not perform adequately during the surgical procedure, the power head  900 ′ may be removed from the operating area to perform the ejection of the battery pack  451 . 
     The rotating or swinging of the access door  912  is further enabled by the compression force, created by the contacts  906 , that, as described above, tend to eject the battery pack  451  in a direction, as shown by arrow A, towards the lower end  800 ′ b  of the battery chamber back through the chamber port  910 . The combination of the rotating or swinging of the access door  912 , together with the compression force, and the assistance of gravity, enables the battery pack  451  to overcome constraining frictional forces and to be ejected in a direction that may include the direction of gravity into a sterile environment or container for charging, non-hazardous waste disposal, or recycling. The streamlined configuration of the battery pack  451 , together with the provision of the ribbing  904  in the battery chamber  800 ′, facilitates both loading and ejection of the battery pack  451  from the battery chamber  800 ′. Thus, surgical apparatus  10 ″ is configured to enable ejection of the at least one battery cell  451 ′ of the battery pack  451  by one hand of a user without medical contamination thereof. The access actuation mechanism  940  thus provides access to the battery chamber  800 ′ by opening the access door  912 . In effect, the access door  912  serves as a hinged housing cover for the power head  900 ′. More particularly, since the battery chamber  800 ′ forms at least one battery-retaining structure of the power head  900 ′, the battery-retaining structure further includes the hinged cover or access door  912 . When the hinged cover or access door  912  is in a closed position, the hinged cover or access door  912  prevents access to the at least one battery  451 ′ and when the hinged cover or access door  912  is in an open position, the hinged cover or access door  912  enables ejection of the at least one battery  451 ′ from the at least one battery-retaining structure along the battery ejection path. 
     Additionally, the spring loaded positive and negative electrical connections  802  of contacts  906  provide structure that breaks or interrupts the electrical connection or electrical communication from the battery pack  451  to all external contacts, including to at least one electrical component, within the power head  900 ′ to assist in handling and disposability of the battery pack  451 . As defined herein, an electrical component includes an electronic component. 
     It is contemplated that structure that breaks or interrupts the electrical connection or electrical communication from the battery pack  451  may further include a breakable foil or wire bridge. It is also contemplated that a slow discharge resistor or circuit may be incorporated into the power head  900 ′ to slowly drain the battery at a safe, low temperature rate to further assist in handling and disposability. 
     In a separate embodiment, the button can be a switch to activate one or more solenoids that translate output shafts to unlatch the battery door and/or release a spring force to eject the battery. For example, the energy storage mechanism  936 , e.g., the compression spring, that may also be disposed in the interior of the handle portion  112  on the proximal side  112   a  so as to limit motion of the upper arm  930   a  of the latch  930  in the proximal direction towards proximal side  112   a  and to bias motion of the upper arm  930   a  towards the distal side  112   b , may be replaced by a solenoid (not shown) that is activated by the battery chamber access actuation mechanism  940 . 
     All or part of the spring ejection forces for the battery pack  451  can be restrained or isolated from the pack with a pin or latch so that the battery pack  451  does not normally experience the compression force from the spring  802  during routine operation. The resulting potential energy from the spring  802  can then be released by a separate mechanism (not shown) activated when the battery ejection button is depressed. 
     In one embodiment, as illustrated in  FIGS. 33-34 , the power head  900 ′ of the surgical apparatus or instrument  10 ″ further includes at least one sealing member  950  that extends around the one or more battery-retaining structures, e.g., battery chamber  800 ′, such that the sealing member  950  is configured to enable ejection of at least one battery cell  451 ′ of the battery pack  451 , or of the entire battery pack  451 , from the one or more battery-retaining structures, e.g., the battery chamber  800 ′, along the battery-ejection path as described above without medical contamination of the battery cell(s)  451 ′ or the battery pack  451 . The sealing member  950  may incorporate an O-ring or gasket  960  that forms a perimeter on the sealing member  950 , that may extend from a position  960   a  on the proximal side  112   a  of handle  112  to a position  960   b  on the distal side  112   b  of handle  112 , to enable the access door  912  to open during ejection of the battery cell(s)  451 ′ or the battery pack  451 . 
     In one embodiment, the power head  900 ′ of the surgical apparatus or instrument  10 ″ includes a handle assembly, e.g., handle portion  112 , wherein the handle assembly or handle portion  112  includes the one or more battery-retaining structures, e.g., battery chamber  800 ′, and wherein at least one sealing member  952  extends around the handle assembly or handle portion  112  or the one or more battery-retaining structures such as battery chamber  800 ′ such that the one or more sealing members  952  are configured to enable ejection of at least one battery cell  451 ′, or the entire battery pack  451 , from the one or more battery-retaining structures, e.g., battery chamber  800 ′, along the battery-ejection path as described above without medical contamination of the battery cell(s)  451 ′ or the battery pack  451 . In a similar manner as with respect to sealing member  950 , sealing member  952  may incorporate O-ring or gasket  960 , that may extend from a position  960   a  on the proximal side  112   a  of handle  112  to a position  960   b  on the distal side  112   b  of handle  112 , to enable the access door  912  to open during ejection of the battery cell(s)  451 ′ or the battery pack  451 . 
     In one embodiment, the power head  900 ′ of the surgical apparatus or instrument  10 ″ includes an instrument housing, e.g., instrument housing  110 , wherein the instrument housing  110  includes the one or more battery-retaining structures, e.g., battery compartment  800 ′, wherein sealing member  954  extends around the instrument housing  110  or the one or more battery-retaining structures such as battery chamber  800 ′ such that the one or more sealing members  954  are configured to enable ejection of at least one battery cell  451 ′, or the entire battery pack  451 , from the one or more battery-retaining structures, e.g., battery chamber  800 ′, without medical contamination of the battery cell(s)  451 ′ or the battery pack  451 . Again, as with respect to sealing members  950  and  952 , sealing member  954  may incorporate O-ring or gasket  960 , that may extend from a position  960   a  on the proximal side  112   a  of handle  112  to a position  960   b  on the distal side  112   b  of handle  112 , to enable the access door  912  to open during ejection of the battery cell(s)  451 ′ or the battery pack  451 . 
     As can be appreciated from the foregoing description of the sealing members  950 ,  952  and  954  of the power head  900 ′, the sealing members  950 ,  952  and  954  provide an integral or separate seal or gasket or adhesive system between the battery pack  451  and other housing components, while allowing electrical communication between the battery pack  451  and the contacts  906  that may be spring loaded positive and negative electrical connections  802 . 
     As can also be appreciated from the foregoing description, the present disclosure relates also to the power head  900 ′ having at least one battery-retaining retaining structure, e.g., battery chamber  800 ′, that is configured to retain at least one battery cell  451 ′. The one or more battery-retaining structures are configured to enable ejection of the battery cell(s)  451 ′ without medical contamination thereof, e.g., by ejection along a battery ejection path defined by the ribbing  904  within the battery chamber  800 ′. 
     In one embodiment, the at least one battery-retaining structure, e.g., battery chamber  800 ′, is configured to enable ejection of the battery cell(s)  451 ′ by one hand of a user. The ejection of the battery cell(s)  451 ′ occurs without medical contamination thereof, e.g., by ejection along a battery ejection path defined by the ribbing  904  within the battery chamber  800 ′. 
     In one embodiment, as illustrated in  FIG. 34 , the power head  900 ′ includes at least one energy storage mechanism, e.g., spring  802 , that is operatively coupled to the one or more battery-retaining structures, e.g., battery chamber  800 ′, wherein actuation of the one or more energy storage mechanisms, e.g., spring  802 , enables ejection of the battery cell(s)  451 ′ without medical contamination thereof, e.g., by ejection along a battery ejection path defined by the ribbing  904  within the battery chamber  800 ′. 
     In a similar manner as described above with respect to energy storage mechanism  936 , the spring  802  may be replaced by a solenoid (not shown) that is activated by battery chamber access actuation mechanism  940 . 
     In one embodiment, as also illustrated in  FIG. 34 , the power head  900 ′ includes at least one energy storage mechanism, e.g., spring  802 , that is operatively coupled to the one or more battery-retaining structures, e.g., battery chamber  800 ′, and is configured wherein actuation of the one or more energy storage mechanisms, e.g., spring  802  via actuation of the battery chamber access actuation mechanism  940 , enables ejection of the battery cell(s)  451 ′ by one hand of a user and is configured wherein the ejection of the battery cell(s)  451 ′ by the one hand of a user enables ejection of the battery cell(s)  451 ′ without medical contamination thereof, e.g., by ejection along a battery ejection path defined by the ribbing  904  within the battery chamber  800 ′. 
     Returning again to  FIGS. 4-12 , as described previously,  FIGS. 4-12  illustrate various internal components of the instrument  10 , including a drive motor  200 , a drive tube  210  and a firing rod  220  having a proximal portion  222  and a distal portion  224 . The drive tube  210  is rotatable about drive tube axis C-C extending therethrough. Drive motor  200  is disposed in mechanical cooperation with drive tube  210  and is configured to rotate the drive tube  210  about drive gear axis C-C. In one embodiment, the drive motor  200  may be an electrical motor or a gear motor, which may include gearing incorporated within its housing. 
     Referring now to  FIGS. 37-43 , power head  900 ′ of surgical instrument  10 ″ includes the first housing portion  110   a  and the second housing portion  110   b  defining the plurality of ports or boss locators  111 , which as described above with respect to  FIG. 3 , align the two housing halves or portions  110   a  and  110   b  to each other and are disposed within the second housing portion  110   b  to enable joining of the first housing portion  110   a  and the second housing portion  110   b.    
     Referring particularly to  FIGS. 37-38 , in one embodiment according to the present disclosure, power head  900 ′ of surgical instrument  10 ″ includes a structural member or chassis  1001  for mounting a set of operating components  1000  of the power head  900 ′ and/or surgical instrument  10 ″. The housing  110 , being formed of the first housing portion  110   a  and the second housing portion  110   b , enables access to an interior volume  1002  of the power head  900 ′ of surgical instrument  10 ′″ that is encompassed by the housing  110 . As described above with respect to  FIGS. 4-12 , a set of operating components are mounted in the interior volume  1002 . More particularly, the set of operating components  1000  includes, among others, drive motor  200  (and associated gear assembly), proximal bearing  354  and distal bearing  356 , drive tube  210 , powered articulation switch  174 , and portions of switch  114 , that may include first and second switches  114   a  and  114   b  formed together as a toggle switch external to the interior volume  1002  and having an internal interface  114 ′ that is substantially disposed within the interior volume  1002 , and position and limit switches (e.g., shaft start position sensor  231  and clamp position sensor  232 ) that are disposed within the interior volume  1002 . 
     As described above, the boss locators  111  align the two housing halves  110   a  and  110   b  to join together as housing  110 . In addition, since the set of operating components  1000  have a proper configuration for alignment when mounted within the interior volume  1002  encompassed by the housing  110 , the boss locators  111  also enable the proper configuration for alignment of the set of operating components  1000 . 
     In one embodiment according to the present disclosure, the set of operating components  1000  may be mounted on the chassis  1001  rather than directly on the housing halve or portion  110   a  as applicable to power head  900 ′ of surgical instrument  10  (see  FIG. 4 ). 
     As illustrated in  FIG. 39 , the chassis  1001  includes boss locator ports  111 ′ that are configured to align with the boss locators  111  of the housing halves or portions  110   a  and  110   b  (see  FIG. 38 ). The chassis  1001  is configured with a proximal portion  1010   a , a central portion  1010   b , and a distal portion  1010   c , wherein the proximal portion  1010   a , the central portion  1010   b  and the distal portion  1010   c  are operatively connected therebetween or integrally formed therebetween to yield the chassis  1001 . The proximal portion  1010   a  is configured with a first recess  1012  and a second recess  1014 , both recesses being formed within the chassis  1001  to receive particular components of the set of operating components  1000 . The second recess  1014  is distal to the first recess  1012 . More particularly, first recess  1012  is configured to receive and align the drive motor  200  (and associated gear assembly) while the second recess  1014  is configured to receive and align the proximal bearing  354  (see  FIG. 38 ). In the exemplary embodiment illustrated in  FIG. 38 , the proximal portion  1010   a  has a proximal portion  1011  with a partially oval-shaped cross section and is adjacent to a distal portion  1013  that has a trapezoidal-shaped cross section. The first recess  1012  is formed in the proximal portion  1011  that has a partially oval-shaped cross section while the second recess  1014  is formed within the distal portion  1013  that has a trapezoidal-shaped cross section. 
     The central portion  1010   b , which may be semi-cylindrically shaped with a corresponding rectangular-shaped cross section, is configured with a recess  1016  formed within the chassis  1001 . The recess  1016  is configured to receive and align the drive tube  210 . 
     In the exemplary embodiment illustrated in  FIG. 39 , in conjunction with  FIG. 38 , the distal portion  1010   c  has a trapezoidal-shaped cross section with a recess  1017  formed therein that is configured to receive and align the distal bearing  356 . The distal portion  1010   c  has a generally T-shaped aperture  1020  that is distal to the recess  1017 . The aperture  1020  is configured to enable receipt, retention and alignment of the position and limit switches, e.g., shaft start position sensor  231  and clamp position sensor  232 . The distal portion  1010   c  further includes a slot  1022  formed therein and disposed between the recess  1017  and the aperture  1020 . The slot  1022  serves as a datum for alignment of the set  1000  of operating components and is configured and disposed to retain and align the alignment plate  350  which locates the firing rod  220  concentrically, as previously described with respect to  FIGS. 6 and 7 . Again, the alignment plate  350  includes an aperture  355  therethrough, which has a non-round cross-section (see  FIG. 7 ). The non-round cross-section of the aperture  355  prevents rotation of proximal portion  222  of firing rod  220 , thus limiting proximal portion  222  of firing rod  220  to axial translation therethrough. The alignment plate  350  also functions as a bearing support and mechanical stop. The distal surface  351  of the alignment plate  350  is also used as a mounting face and datum for the start position sensor  231  and the clamp position sensor  232 . 
     The distal portion  1010   c  further includes a downwardly directed protrusion or extension  1024  in which is formed a recess  1026  that is configured to receive and align the internal interface  114 ′ of the toggle switch  114 , and that is substantially disposed within the interior volume  1002 . 
     As can be appreciated from the foregoing description, the chassis  1001  is configured to provide the proper configuration for alignment for the set of operating components  1000  mounted on the chassis  1001  if the chassis  1001  and set of operating components  1000  are mounted within the interior volume  1002  of the housing  110 . Though not explicitly illustrated in  FIGS. 37-43 , the chassis  1001  is configured to provide the proper configuration for alignment for a replacement set of operating components (not explicitly shown) of the surgical instrument  10 ′″ mounted on the chassis  1001  if the chassis  1001  and replacement set of operating components are mounted within the interior volume  1002  of the housing  110 . Thus the chassis  1001  is configured to provide the proper configuration for alignment for the set of operating components  1000  and/or the replacement set of operating components including either the set of operating components  1000  or the replacement set of operating components. Those skilled in the art will recognize that although the replacement set of operating components is generally identical to an original set of operating components  1000  that would be first provided by the manufacturer with the power head  900 ″ of surgical instrument  10 ′″, the replacement set of operating components need only be identical to the original set of operating components  1000  to the extent necessary to maintain alignment, fit and suitable operability of the surgical instrument  10 ′″ when inserted within the interior volume  1002 . 
     Referring to  FIG. 37 , and as described above with respect to  FIGS. 4-12 , the housing  110  includes at least first housing portion  110   a  and second housing portion  110   b . At least the first housing portion  110   a  is removable to expose at least a portion of the interior volume  1002  of the surgical instrument  10 ′. The first housing portion  110   a  defines a plurality of ports  111  and the second housing portion  110   b  defines a plurality of ports  1010  that are disposed to enable the proper configuration for alignment of the set of operating components  1000  and of a replacement set of operating components (not explicitly shown) if the first housing portion  110   a  and the second housing portion  110   b  are joined together. 
     In addition, as illustrated in  FIG. 39 , the chassis  1001  defines a plurality of ports  111 ′ that are disposed to enable the proper configuration for alignment of the set of operating components  1000  and of a replacement set of operating components (not explicitly shown) if or wherein the first housing portion  110   a  and the second housing portion  110   b  are joined together and if or wherein the chassis  1001  and the set of operating components  1000  or replacement set of operating components are mounted within the interior volume  1002  of the housing  110 . 
     It is contemplated that clips, buckles, snaps, quick turn fasteners or other suitable connectors make be incorporated at appropriate locations on the first and second housing portions  110   a  and  110   b , respectively, and/or on the chassis  1001  to provide ease of disassembly. 
     The chassis  1001  can be made from ferrous, conductive or magnetic metals to shield electronic components, e.g., the control switch  114  or shaft start position sensor  231  and clamp position sensor  232 , from radio frequency (RF) noise and electro-magnetic interference (EMI). The structural member/chassis  1001  can also be operatively coupled or operatively connected to such components, including the drive motor  200 , as a common ground for direct current (DC) applications. 
       FIGS. 40-41  illustrate exploded views of the surgical instrument  10 ′″ showing first and second housing portions  110   a  and  110   b  and, as described above with respect to  FIGS. 37-39 , the set of operating components  1000  mounted on the chassis  1001 . 
     The electrosurgical instrument  10 ′″ includes a rotating front end interchange assembly  1050  that is operatively coupled to the power head  900 ″ to enable the power head  10 ″ to drive and operate the firing rod  220  (see  FIG. 6 ). The rotating front end interchange assembly  1050  includes an interface connection  1052  to enable interchanging of front end  1054  of firing rod  220 . A Tyco Healthcare Model EGIA front end  1054  is shown. The interchange assembly  1050  is configured to receive and operate other front ends  1054 , e.g., Tyco Healthcare Model EEA having a circular cross-section, Model EEA having a circular cross-section, Model TA having a right angle cross-section, or a cutter, a cautery, an RF energy, or a clamp or a grasper front end. 
       FIG. 42  is a view of an open side  1001   a  of the chassis  1001  showing the set of operating components  1000  as mounted on the chassis  1001  with the open side  1001   a  facing the viewer.  FIG. 43  is a view of a closed side  1001   b  of the chassis  1001  showing the set of operating components  1000  as mounted on the chassis  1001  with the closed side  1001   b  facing the viewer. 
     In one embodiment, the chassis  1001  is formed from metal and the housing  110  is formed from a polymer. The set of operating components  1000  or the replacement set of operating components (not shown) includes at least one electrical component, e.g., battery cell(s)  451 ′ (see  FIGS. 40-41 ), and the chassis  1001  is configured to enable electrical grounding of the electrical component. 
     Thus, as can be appreciated from the above disclosure, a power head  900 ′ of a surgical instrument such as surgical instrument  10 ″, wherein the power head  900 ′ includes the chassis  1001  improves reusability or reprocessing of costly components by enabling easier removal/disposal of a contaminated housing or cover while enabling maintaining all or many critical component assembly alignments and positions. In addition, chassis  1001  provides the following advantages:
         a. enables additional durability, strength and structural support for the surgical instrument  10 ″;   b. enables utilization or deployment as a chassis platform for mounting components, fasteners and removable housing covers;   c. enables easier multi-plane accessibility for assembling or repairing parts versus a single plane housing cover assembly configuration;   d. enables greater endurance of multiple cycles of installing and removing fasteners for multiple reprocess, service and/or repair cycles vs. standard plastic housing fastener bosses;   e. enables higher tolerance datum positioning for accurate bearing and mechanism alignment as compared to net molded housing assembly methods;   f. enables utilization or deployment as an electrical ground platform for all components within a DC or microelectronic device; and   g. creates Radio Frequency (RF) and Electromagnetic Interference (EMI) shielding for electronic components within the device.       

       FIG. 44  is a flowchart depicting a calibration algorithm stored in the microcontroller  500  for calibrating the instrument  10 . The microcontroller  500  stores a pulse modulation algorithm that is used to control the drive motor  200 . The calibration algorithm of microcontroller  500  is used to adjust program coefficients in the pulse modulation algorithm to calibrate the instrument  10 . As shown in  FIG. 44 , instrument  10  is started and the firing rod  220  is translated while the linear displacement sensor  237  is placed in an active state in order to detect the first indicator  320   a . Upon detection of the first indicator  320   a , by the linear displacement sensor  237  in step  1102   a , the position calculator  416  determines, in step  1104   a , a time “T” that elapsed between when the firing rod  220  started translating and when the linear displacement sensor  237  detected the first indicator  320   a . The position calculator also determines the linear speed of the firing rod  220  based on a rotational speed of the drive motor  200  in step  1102   b . The position calculator  416  provides the time “T” and the linear speed to the microcontroller  500 , which compares the time “T” to a stored predetermined time “T P ”. The stored predetermined time “T P ” is selected by the microprocessor  500  based on the received linear speed in step  1104   b . In step  1106 , if the microcontroller  500  determines that the time “T” is equal to the predetermined time “T P ”, the calibration algorithm is ended and the drive motor  200  translates the firing rod its predetermined distance. If the times “T” and “T P ” are not equal, the algorithm proceeds to step  1108  where the microcontroller  500  determines whether time “T” is less than the predetermined time “T P ”. If time “T” is less than the predetermined time “T P ”, the algorithm proceeds to step  1110  where the microcontroller  500  adjusts a program coefficient in the pulse modulation algorithm to control the drive motor  200  to advance the firing rod  220  for a distance shorter than the predetermined distance. If time “T” is greater than the predetermined time “T P ”, the calibration algorithm proceeds to step  1112  where the microcontroller  500  adjusts the program coefficient in the pulse modulation algorithm to control the drive motor  200  to advance the firing rod  220  for a distance longer than the predetermined distance. 
     It will be understood that various modifications may be made to the embodiments shown herein. Therefore, the above description should not be construed as limiting, but merely as exemplifications of preferred embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.