Abstract:
A cordless drive assembly for driving various orthopedic surgical instruments is described. The drive assembly is battery powered and includes tracks in the handle portion of its housing for receiving the battery. A latch locks the battery to the housing.A combination of a rechargeable, detachable battery system and a power tool. The battery slides onto the power tool through a complementary groove and flange structure.

Description:
ThisThis patent application is a reissue continuation of U.S. patent application Ser. No.  09 / 637 , 339 , filed Aug.  11 ,  2000 , now abandoned, which is an application for reissue of U.S. patent application Ser. No.  08 / 692 , 886 , filed Jul.  24 ,  1996 , now U.S. Pat. No.  5 , 792 , 573 , issued Aug.  11 ,  1998 , which application is a divisional of U.S. patent application Ser. No. 08/258,338, filed Jun. 10, 1994, now U.S. Pat. No. 5,553,675, issued Sep. 10, 1996. 
     Notice: More than one reissue application has been filed for the reissue of U.S. Pat. No.  5 , 792 , 573 . This reissue applications are application Ser. Nos.  09 / 954 , 536  ( the present application ) ,  09 / 637 , 339 , and  11 / 129 , 760 . U.S. patent application Ser. No.  11 / 129 , 760 , filed May  16 ,  2005 , is a continuation of this reissue application.   
    
    
     TECHNICAL FIELD 
     The present invention is directed to cordless rechargeable battery powered drive assemblies for driving orthopedic surgical instruments. 
     BACKGROUND 
     Orthopedic drive assemblies are well known in the art. Such drive assemblies may be adapted for various orthopedic procedures such as drilling, screwing, reaming, wire driving, pinning and sawing (both reciprocating and sagittal). Typically a drive assembly is powered by either a rechargeable battery system (e.g. a cordless system) or by a pneumatic system which utilizes compressed fluid to power the device. 
     The art is replete with cordless rechargeable battery powered drive assemblies for driving orthopedic surgical instruments. Typically, such instruments comprise generally pistol-shaped devices having elongate handle and drive portions. Examples of such drive assemblies comprise: (1) the Orthopower 90 cordless instruments available from Stryker of Kalamazoo. Mich.; (2) the Cordless 200 Reamer, Cordless 800 Wire Driver, Cordless Sagittal Saw or Cordless 450 Orthopedic Drill available from Dyonics of Andover Md., (3) the Maxion™ orthopedic drive device, previously sold by the Minnesota Mining and Manufacturing Co. (3M) of St. Paul, Minnesota; (4) the Hall Versipower orthopedic instruments available from Hall Surgical of Carpinerina California (associated with Zimmer); and (5) the product known as the 200 Reamer, previously sold by Black &amp; Decker. Cordless battery powered drive assemblies for driving orthopedic surgical instruments are described in U.S. Pat. Nos. 3,734,207; 4,050,528; 4,091,880; 4,441,563; 4,641,076; 4,728,876 and 5,080,983. 
     Because the batteries in an orthopedic drive device are preferably rechargeable, releasable attachment means are provided in some prior art devices for releasably attaching a battery pack to the rest of the device. Typically, a battery pack is attached to and removed from the handle portion of the device in a direction that is substantially parallel to the axis of elongation of the handle portion. Individual batteries are placed in a housing creating the battery pack which is then attached to the device by being slid in a direction generally parallel to the elongate axis of the handle portion of the device. The battery pack typically includes electrical circuit connection means for connecting the battery pack to electronic circuitry in the device. A device typically secures the battery pack to the rest of the device. 
     While such releasable attachment means are generally acceptable, they leave room for improvement. One drawback of such a releasable attachment means is that gravity tends to continuously operate on the battery pack to urge it out of the device. Another drawback for some prior devices is that, because of the significant vibration forces encountered during use of the orthopedic drive assembly (particularly during sagittal sawing), the electrical circuit connection means tend to corrode. This type of corrosion is known as fretting corrosion. As used herein, the phrase “fretting corrosion” means surface degradation occurring at the interface of mating electrical contacts which results in the reduction or even loss of electrical continuity. 
     Fretting corrosion is found in components forming contacts which are allowed to move independently with respect to each other during current flow. This independent movement is believed to cause mechanical abrasion which will wear the surfaces. Gaping between the electrical contacts during electrical flow may result in electrical arcing with attendant generated heat potentially sufficient to melt the surface of the contacts. Pitting, welding and burning may also result. Also, a physical change in the material forming the contacts may occur. Plating for enhanced electrical contact may be lost and carbon deposits may accumulate resulting in reduced electrical continuity. 
     Because orthopedic drive assemblies are used in surgical procedures which require delicate yet physically demanding tasks, the balance and maneuverability of an orthopedic drive device is also important to surgeons. Hand fatigue is a problem associated with many existing drive assemblies as well as a general difficulty in maneuvering the device during some surgical procedures. Weight distribution and size considerations are believed to contribute to these problems, as the typical cordless rechargeable battery powered drive assembly may be cumbersome to hold and use, particularly during a delicate orthopedic procedure where only the highest quality is tolerated. Size and weight considerations involved in the placement of elements such as the batteries, transmission, electronic control circuitry and motor typically render an existing device difficult to maneuver. 
     Other prior art drive assemblies are excessively large. Oversized drive assemblies may be difficult to maneuver, particularly during a surgical procedure at a cramped or remote location. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to the present invention there is provided a drive assembly for driving orthopedic surgical instruments which (1) affords excellent balance and maneuverability for a user which offers enhanced handling characteristics and convenience during use, (2) affords attachment and removal of a battery pack in a direction other than the direction of elongation of the handle portion of the device, (3) includes a connection between the battery pack and the electronic circuitry of the device which resists fretting corrosion, (4) includes an ergonomically designed handgrip shape that fits a surgeon&#39;s hand comfortably, and (5) is sized for convenient maneuvering during an orthopedic surgical procedure. 
     According to the present invention, there is provided a drive assembly for driving various orthopedic surgical instruments, such as, but not limited to, drills, screws, reamers, wires, pins and saws (both reciprocating and sagittal). The drive assembly comprises a housing having elongate drive and handle portions with the handle portion projecting from the drive portion. A drive is present comprising an motor preferably mounted within the drive portion. The motor has a motor shaft, and the drive includes a transmission for transmitting power of the motor shaft to the surgical instrument. The transmission includes a drive member. Preferably the drive portion has surfaces defining a wire receiving chamber adapted to receive an orthopedic wire adapted to be driven during an orthopedic surgical procedure. 
     The drive assembly also includes a trigger assembly movable relative to the handle portion; and electrical circuit means operatively associated with the trigger assembly for controlling the motor. 
     The handle portion comprises a releasably attachable battery having at least one cell (preferably eight), a battery housing, and a pair of battery contacts. The handle portion also has a battery receiving portion having battery terminals adapted to engage the battery contacts; and releasable attachment means for releasably attaching the battery to the battery receiving portion in a direction other than the direction of elongation of the handle portion. Preferably, the direction is a direction substantially parallel to the axis of the drive portion. 
     In the preferred embodiment, the releasable attachment means comprises a) the handle portion having a pair of tracks defining flanges that are elongate in a direction substantially parallel to the longitudinal axis of the drive portion, b) the battery having a pair of grooves adapted to receive the flanges of the tracks, and a pair of flexible, resilient cantilever members, and c) the battery receiving portion having surfaces defining a cantilever member cavity for receiving the pair of flexible, resilient cantilever members in an interference fit so that the battery is frictionally held in place relative to the battery receiving portion. A latch for releasably securing the battery to the battery receiving portion is also preferably present. 
     The drive assembly also includes a novel floating battery terminal assembly comprising biasing means for biasing the battery terminals toward a rest position, and mounting means for mounting the battery terminals for deflection from the rest position. In one embodiment, each of the battery terminals comprises a substantially flat plate member having opposite side surfaces, and each of the battery contacts comprise a pair of flexible, resilient arcuate members which are adapted to engage opposite side surfaces of a battery terminal. 
     Also preferably, the handle portion comprises a handgrip portion having outer surfaces that are sized and shaped to be grasped by a user without touching the battery, and inner surfaces defining a handgrip cavity. The handgrip cavity is free of the transmission, the motor and any cells of the battery when the battery is received in the battery receiving portion. Preferably, the cells of the battery are spaced on an opposite end of the handgrip portion than the motor and transmission. 
     Alternatively, the present invention may be described as a rechargeable battery adapted to be repeatably and releasably attached to an orthopedic drive assembly. In this aspect of the invention, the orthopedic drive assembly has elongate drive and handle portions, a battery receiving portion having a pair of tracks defining flanges, a pair of battery terminals, and surfaces defining a cantilever member receiving cavity. 
     The battery comprises an autoclavable battery housing having opposite top and bottom portions, at least one cell within the battery housing and a pair of battery contacts mounted adjacent the top portion of the housing and adapted to engage the battery terminals of the orthopedic drive assembly. Releasable attachment means are present for releasably attaching the battery to the battery receiving portion in a direction other than the direction of elongation of the handle portion. The releasable attachment means and battery terminals comprise the preferred versions as discussed above. 
     In this aspect of the invention, the battery contacts each include a first end fixedly attached to the top portion of the battery housing and a second end adapted to abut a support shoulder of the top portion of the battery housing. The battery housing comprises opposite, substantially flat front and rear walls constructed from a material suitable for protecting the cell(s) during an autoclave procedure. The battery comprises eight substantially cylindrical cells having longitudinal axes. The eight cylindrical cells are arranged in: a) a front row of three cells substantially adjacent a front wall of the battery housing, b) a rear row substantially adjacent a rear wall of the battery housing, and c) a middle row of two cells between the front and rear rows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be further described with reference to the accompanying drawing wherein like reference numerals refer to like parts in the several views, and wherein: 
         FIG. 1  is a perspective view of a drive assembly for driving orthopedic surgical instruments according to the present invention; 
         FIG. 2  is an enlarged sectional view of the drive assembly of  FIG. 1 , illustrating a battery pack of the device removed from the device in solid lines, and illustrating the position of the battery pack when attached to the drive assembly in phantom lines; 
         FIG. 3  is an enlarged perspective view of the battery pack for use in the drive assembly of  FIG. 1 ; 
         FIG. 4  is an enlarged rear view of the drive assembly of  FIG. 1 ; 
         FIG. 5  is a top view of the battery pack of  FIG. 3 ; 
         FIG. 6  is a sectional view of the battery pack of  FIG. 3 ; 
         FIG. 6A  is a bottom view of portions of the drive assembly of  FIG. 2  with the battery pack removed which illustrates battery terminals that are adapted to be connected to the battery contacts of the battery pack of  FIG. 3 ; 
         FIG. 7  is an enlarged side view of the drive assembly of  FIG. 1 ; 
         FIG. 8  is a top view of the orthopedic drive assembly of  FIG. 7 ; 
         FIG. 9  is a front view of the drive assembly of  FIG. 7 ; 
         FIG. 10  is a side view of the battery pack of  FIG. 3 ; 
         FIG. 11  is an enlarged bottom view of a handle portion of a drive assembly with the battery pack removed to illustrate details of a second embodiment of battery terminals according to the present invention and with portions of a battery pack receiving cavity illustrated with dashed lines; 
         FIG. 12  is a partial sectional view of a battery receiving portion of the drive assembly and cantilever arms of the battery pack showing the position of the cantilever arms when the battery pack is attached to the rest of the orthopedic drive assembly; 
         FIG. 13  is a top view of one of a pair of preferred battery contacts for a battery pack according to the present invention, which battery pack is adapted to be connected to a drive assembly having the battery terminals of  FIG. 11 ; 
         FIG. 14  is a side view of the battery contact of  FIG. 13 ; 
         FIG. 15  is an enlarged bottom view of portions of the handle portion of the drive assembly of  FIG. 11  which illustrates details of a pair of floating battery terminal assemblies including a battery terminal of one of the assemblies shown offset relative to the axis of the drive portion of the housing of the device; 
         FIG. 16  is a sectional view of a floating battery terminal assembly of  FIG. 15  which illustrates details of a battery terminal in a rest position; 
         FIG. 17  is a sectional view of portions of the drive assembly of  FIG. 16  taken approximately along lines  17 — 17  of  FIG. 16  except that one battery terminal and connector are removed to illustrate details of a hole for receiving the battery terminal; 
         FIG. 18  is a sectional view similar to  FIG. 16  except that the floating battery terminal assembly is slightly offset from its rest position, as may occur during vibration of the orthopedic drive device; 
         FIG. 19  is a sectional view of the floating battery terminal of  FIG. 17  with the battery terminal offset laterally with respect to its longitudinal axis in a rest position and with other portions omitted to illustrate details; 
         FIG. 20  is a sectional view of the floating battery terminal assembly of  FIG. 17  with the battery terminal illustrated in a rest position and with other portions omitted to illustrate details; 
         FIG. 21  is a schematic illustration of a switch mechanism for use in the drive assembly according to the present invention; 
         FIG. 22  is a top view of another embodiment of battery contact for use with a drive assembly having the battery terminals of  FIG. 11 ; 
         FIG. 23  is a side view of the battery contact of  FIG. 22 ; and 
         FIG. 24  is a perspective view of a battery with the battery contacts of FIGS.  13  and  14 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIGS. 1 through 10  of the drawing there is shown an embodiment of a cordless rechargeable battery powered drive assembly for driving orthopedic surgical instruments according to the present invention, generally designated by reference character  10 . The drive assembly  10  includes a housing comprising elongate drive  4  and handle  6  portions defining drive D and handle H portion longitudinal axes. The drive portion  4  and a significant portion of the handle portion  6  are constructed by assembling two large housing pieces (see  FIG. 7 ) to afford convenient disassembly of the device for repair. 
     Referring now to  FIG. 2 , the drive assembly  10  includes a motor assembly having a D.C. electric powered motor  12  including a rotor  14  and a motor shaft  16 . A drive is also present comprising a transmission for transmitting the power of the motor shaft  16  to the surgical instrument. The illustrated transmission includes a drive member or spindle  18 , a ring gear  19 , and a gear pin and planetary gear assembly  21 . 
     Preferably, the motor  12  is mounted within the drive portion  4 . As used in this application, when it is said that the motor is within the drive portion  4 , it is meant that the rotor  14  and motor shaft  16  are substantially completely located within the structure of the housing defining the drive portion  4 , as opposed, for example, to one of the rotor or motor shaft being located in the handle portion  6  or a substantial portion of the motor being located in the handle portion  6 , of course some wires and electronic circuitry associated with the motor may be present outside the drive portion  4 , and yet the motor will nevertheless be within the drive portion  4  as understood in the present invention. Also preferably, the transmission (e.g.  18 ,  19  and  21 ) is mounted within the drive portion  4 . 
     A connector is provided for attaching a chuck or other such holder or instrument that may be driven by the drive assembly  10 . The connector comprises a nose insert  26  having a socket into which a cylindrical portion of the surgical instrument can project with a splined central rotatable driven collar engaged with mating splines  17  on the inner surface of the drive member  18 , and with pins (not shown) projecting radially of the cylindrical portion engaged in longitudinally extending slots  15  opening through the end of the housing. A helix pin/collar assembly  25  is rotatable about the axis D of the drive portion and is biased by torsion spring  27  so that circumferentially projecting hooks near slots  15  on the collar  25  can engage the pins on the surgical instrument to maintain the pins within the slots  15  and thereby the surgical instrument in driven engagement with the drive assembly  10 . 
     The surgical instrument may comprise any instrument suitable for use in an orthopedic surgical procedure, including but not limited to, drills, screws, reamers, pins and saws (both reciprocating and sagittal) or a suitably designed chuck or adapter for use with any of the previously mentioned instruments. 
     As a particular example, the surgical instrument may comprise the chuck described in U.S. Pat. No. 4,728,876, the entire contents of which are herein expressly incorporated by reference. Alternatively, for example, an appropriate wire driving attachment adapter may be attached to the drive assembly  10  so that it may be used as an orthopedic wire driver, optionally, but not preferably, engagement between the orthopedic wire and the spindle  18  may afford operation of the device  10  as a wire driver. 
     A stationary member  22  extends from a proximal end  1  of the housing toward its distal end  3 . Preferably, the stationary member  22  includes a through chamber so that a surgical wire may be passed through the stationary member  22  from the proximal end  1  of the device  10  toward the distal end  3 . The through chamber in the stationary member  22  forms a portion of a wire receiving chamber in the drive portion  4  between the proximal end  1  and the distal end  3 . Threading a surgical wire through the wire receiving chamber affords use of the device  10  as a wire driver. 
     O-rings  64  and  65  restrict internal contamination of the drive assembly  10  from ambient contaminants. O-ring  66  is compressed against member  22  to restrict the member  22  from rotating relative to the handle  6  and drive  4  portions of the housing. 
     The drive assembly  10  also includes a rechargeable battery or battery pack  30  that is adapted to provide a rechargeable source of power for the motor  12 . Unique mounting means (described in greater detail below) attach the battery  30  to the rest of the assembly  10 . 
     A trigger assembly  40  is movable relative to the handle portion  6 . The trigger assembly includes a button member  45  adapted to be engaged by a user&#39;s digits, a trigger shaft  46 , an O-ring seat  41  for fixedly connecting the button member  45  to the trigger shaft  46 , a coil spring  42  and magnet  44  that is rigidly attached to the trigger shaft  46 . The trigger assembly  40  is movable between a released or extended position ( FIG. 2 ) and a depressed or inner position relative to the handle portion  6 . 
     The drive assembly  10  also includes electrical circuit means operatively associated with the trigger assembly  40  for controlling the motor  12 . The illustrated electrical circuit means comprises an on/off hall sensor  52  and a speed control hall sensor  54 . 
     The on/off hall sensor  52  is a digital hall sensor having an output signal with two levels corresponding to an on state and an off state. The on/off hall sensor  52  senses the presence of a magnetic field from the magnet  44  on the trigger assembly  40 . When the trigger assembly  40  is released, the magnet  44  is positioned directly over the on/off hall sensor  52  (FIG.  2 ). The magnetic field of the magnet  44  causes the on/off hall sensor  52  to produce an output signal corresponding to an off state. As the trigger assembly  40  is depressed, the magnet  44  moves away from the on/off hall sensor  52 . The on/off hall sensor  52 , no longer sensing the presence of a magnetic field, produces an output signal corresponding to an on state. 
     The output signal from the on/off hall sensor  52  is conditioned by electrical circuitry which provides a standby signal when the on/off hall sensor  52  produces an off signal. The standby signal disables motor drive circuitry and the speed control hall sensor  54 . The standby signal therefore ensures that the motor  12  is off whenever the trigger assembly  40  is in a released position (FIG.  2 ). An added benefit of disabling the motor drive circuitry and the speed control hall sensor  54  is that the electrical power required by the device  10  is significantly reduced during periods when the trigger assembly  40  is not depressed. This current reduction during a standby mode improves energy efficiency of the device  10 . In this manner, the device  10  may optionally include a battery saver feature. 
     The speed control hall sensor  54  is a linear hall sensor which provides a speed control signal having a range of levels based upon the strenth of the magnetic field that the variable speed hall sensor  54  detects. As the strength of the magnetic field increases, the speed control hall sensor  54  produces a speed control signal with a higher level. As the trigger assembly  40  is depressed, the magnet  44  moves towards the speed control hall sensor  54  and increases the magnetic field across it. The speed control signal from the speed control hall sensor  54  is conditioned and drives the motor control circuit to provide motor speeds proportional to the speed control signal. Therefore, as the trigger assembly  40  is further depressed, the motor control circuitry increases the motor speed of the drive assembly  10 . In this manner, the drive assembly  10  may optionally comprise a variable speed device. 
     The circuit has a 25 amp current limit to protect the batteries, motor and electronics. The electrical circuit means may optionally include directional drive circuitry which is discussed in greater detail below. 
     As best seen in  FIGS. 2 and 6A , the device  10  also comprises battery terminals  39 . Each of the battery terminals  39  have three generally flat surfaces including two end surfaces situated at an angle relative to a middle surface. The function of the battery terminals  39  will be described in greater detail below. 
     The battery terminals  39  may be constructed from any suitable material appropriate for use to construct orthopedic surgical tools. For example, the battery terminals may be constructed from copper, brass, bronze, beryllium copper, stainless steel, steel and aluminum. One or more platings may be present to enhance the electrical conducting and corrosion resisting properties of the battery terminals  39 . Examples of such platings include, but are not limited to copper, nickel, gold, silver, tin, electroless nickel, rhodium, sulfamate, nickel, cadmium and zinc. 
     The handle portion  6  of the device  10  projects (downwardly in  FIG. 2 ) from the drive portion  4  of the device  10 . The handle portion  6  of the housing comprises the battery  30  and a handgrip portion  5 . The handgrip portion  5  has manually engageable or graspable surfaces and top T and bottom B ends (see FIG.  2 ). Preferably, the handgrip portion  5  is sized and shaped so that, during use of the device  10 , the user does not need to grasp any portion of the battery  30 . For example, the handgrip portion  5  may have a height from its bottommost point to the bottom of the drive portion  4  of less than approximately 6 inches (preferably about 4.5 inches), a width of its neck portion of less than about 2.8 inches (preferably about 1.1 inches), and a length of its neck portion of less than about 2.5 inches (preferably about 1.3 inches). 
     The handgrip portion  5  includes specially shaped surfaces that result in a handle that is comfortably held in the hand of a surgeon. A middle part of the handgrip  5  includes an curved front surfaces to form a conveniently held handle. A lip portion  51  is situated adjacent the button member  45  to restrict the chance that a surgeon&#39;s glove may be caught between the handle portion  6  and the button  45  when the button  45  is depressed. 
     As shown in the figures, the width and length of the handgrip portion  5  vary along its height to afford convenient grasping of the device  10 . The bottom of the handgrip portion  5  includes a battery receiving portion  48  having the battery terminals  39  adapted to engage battery contacts  33  (described in greater detail below) when the battery  30  is attached to the battery receiving portion  48 . 
     A battery housing  31  ( FIGS. 2 and 3 ) preferably comprises opposite, substantially flat front  201  and rear  203  walls constructed from an autoclavable material. An autoclavable material is a material suitable for protecting battery cell(s) during repeated autoclave procedures. Examples of suitable materials are described below. 
     The battery  30  comprises at least one rechargeable cell  32  and preferably eight substantially cylindrical cells  32  as shown in FIG.  2 . Because the cells  32  are located in a position below or remote from where a user is expected to grasp the drive assembly  10 , the handgrip portion is free to be used for mounting other electrical and/or mechanical components such as an electronic printed circuit board forming a portion of the electrical circuit means discussed above. 
     The battery  30  preferably comprises eight substantially cylindrical cells  32  having longitudinal axes. The axes of the cells are preferably substantially parallel to the front and rear walls  201  and  203 . The eight cylindrical cells  32  are arranged in a front row F of three cells substantially adjacent the front wall  201 , a rear row R of three cells substantially adjacent the rear wall  203 , and a middle row M of two cells between the front and rear rows  201  and  203 . All of the rows F, M and R are enclosed within the battery housing  31  so that the cells are protected during an autoclave or other sterilization procedure. 
     The weight distribution of the device  10  is substantially balanced about the handgrip portion  5  as the relatively heavier elements such as the battery cells and the motor/transmission assemblies of the device  10  are spaced on opposite ends (top T and bottom B) of the handgrip  5 . A handgrip cavity  53  is formed within the inner portions the handgrip  5 . As opposed to prior art devices which include a battery or motor within the portion of its housing that is designed to be manually grasped, the cavity  53  is free of batteries or motors or transmission or gear assemblies. Since battery cells  30  (described in greater detail below) are situated below the battery receiving portion of the handle portion  6 , some of the electronic control circuitry mentioned above may be placed in the handgrip cavity  53  of the handle portion  6 . This is believed to further contribute to the beneficial balance and handling characteristics of the device  10 . 
     The cells  32  are preferably stacked in the manner shown in  FIG. 2 , with a distal row of three cells placed at the front of the battery  30 , a proximal row three cells at the rear of the battery  30 , and a middle row of two cells placed between the front and rear cells. The axes of the cells are perpendicular to the axis D of the drive portion of the housing. The cells  32  may comprise, for example, nickel-cadmium secondary (rechargeable) sub “C” size cells with a 22 mm diameter and a 34 mm length in a nickel-plated steel case. Such cells are expected to provide a capacity of about 1.4 amp hours at 9.6 volts, D.C. Suitable cells may be obtained from Saft of Valdosta. Ga.; Panasonic of Japan; Sanyo Electric Co. Ltd. of Sumoto-City, Hyogo Japan or Gates available from DC Battery Products of St. Paul. Minn. 
     The cells  32  are enclosed in an autoclave proof (saturated steam @ 280 degrees Fahrenheit, @ 30 pounds per square inch, and vacuum @ 26 inches of mercury) housing or casing  31 . The casing  31  preferably is designed to withstand other sterilization techniques and remain suitable to protect the battery cells  32 . The casing  31  includes a poppet or umbrella valve  8  (e.g. the #VL2491-102 Vernay valve generally available from Vernay of Calif.) to relieve any pressure, such as pressure generated by the cells  32 . Optionally, the battery housing  31  may include a power terminal (not shown) for a power cord so that the drive assembly  10  may be powered without discharging the cells  32 . 
     The particular material used to construct the casing  31  may comprise any suitable material for use in an orthopedic device. Specific examples include, but are not limited to, poly-ether-imide (PEI) including Ultem (e.g. GE grades 1000 Black #7101, 1000 Black #1000, 2100 muddled natural #1000 10% glass fill, 2200 muddled natural 20% glass fill, 3452 muddled natural #1000 45% short glass and mineral, or 6200 muddled natural #1000 20% glass fill high temperature); poly-phenyl-sul-fone (PPSU) (e.g. Amoco Radel R, grades R5100 Black #935 or #937, or R 5000, natural); polysulfone (PSU) (e.g. Amoco Udel P, grade P 1700, natural #11); polyaryletherketone (PAEK) (e.g. BASF Ultrapek, grade KR4176, natural); liquid crystal polymer (LCP) (e.g. Vectra grades A950 natural, A530 muddled natural moderately mineral filled, or A130 muddled natural 30% glass fill); and polyketone (PEK) (e.g. Amoco Kadel E grade 1000 natural). 
     The motor  12  of the drive assembly  10  is designed to: (1) operate between about 9.6 volts and a reduced voltage which is the output range the battery will produce under load, and (2) have very low internal resistance to restrict internal losses when handling the high current flow by which it is powered. Since the motor  12  and transmission are relatively heavy elements of the device  10  (e.g. the motor may weight about 0.82 pounds), the motor  12  and transmission are preferably located within the drive portion  4  of the housing. Locating the motor  12  and transmission in a position spaced from the handgrip cavity  53  frees the handgrip cavity  53  for use to store the electronic circuitry of the device  10 . The location of the motor  12  and transmission also contribute to the beneficial balance and weight distribution of the device  10  and improves its handling characteristics. These improvements are believed to reduce hand fatigue for some users. 
     The battery  30  shown in  FIGS. 1-7 ,  9  and  10  comprises the battery housing or casing  31 , and a pair of battery contacts  33 , one of which is an electrically positive terminal, the other of which is an electrically negative terminal. The battery contacts  33  comprise thin, arcuate contact members. The arcuate contact members  33  are connected at one end to the housing  31  and are in electrical communication with the cells  32  (which are connected in series by electrically conductive strips). The other end of the contact members  33  is free to float along the top of the casing  31 . Preferably, the contacts  33  are constructed from a flexible, resilient electrically conductive material, such as a material selected from the group comprising copper, brass, bronze, beryllium copper, nickel, stainless steel, aluminum or steel. Optionally, one or more materials may be plated to the contacts to enhance their performance and corrosion resistance. Plating materials include, but are not limited to gold, copper, nickel, silver, tin, electroless nickel rhodium, sulfamate nickel, cadmium and/or zinc. The shape of the arcuate contact/members  33  afford their resilient deflection in a direction substantially parallel to the axis H of the handle portion  6  of the housing upon abutment with the battery terminals  39 . 
     Referring now to  FIGS. 11 ,  13 - 14 ,  15 - 16 ,  18 - 20  and  24  of the drawings, there is shown a second embodiment of cooperable battery terminals and battery contacts according to the present invention with the battery contacts designated with reference character  33 A and the battery terminals designated by reference character  39 A. 
     As best seen in  FIG. 16 , handgrip  5  has a portion constructed from an electrically insulating material  106 . The battery terminals  39 A are each attached to the insulating material  106  by screw  87 . A crimp-on connector  107  is situated between the screw  87  and the battery terminal  39 A. The crimp-on connector  107  places the battery terminal  39 A in electrical communication with the rest of the electrical circuit means by virtue of insulated wire  108 . 
     The battery terminals  39 A are mounted on the manually graspable portion  5  of the housing to float relative to the rest of the housing (including the insulating portion  106 ). This feature is particularly useful when the device  10  generates vibration as the floating battery terminals  39 A tend to retain electrical communication between the battery  30  and the rest of the electronics of the device  10 . 
     The battery terminal  39 A is placed in an oblong hole  88  in the handgrip portion  5  of the housing. The oblong hole  88  preferably affords side to side float (movement in a direction that is substantially perpendicular to both axes H and D) of the battery terminal  39 A (see FIG.  19 ), but restricts float of the battery terminal  39 A in a direction substantially parallel to the axis D so that the battery terminal  39 A is not unduly deflected upon insertion and removal of the battery  30  from the device  10 . 
     A coil spring  89  is provided to afford float of the battery terminal  39 A and to bias the battery terminal  39 A toward a rest position (see FIGS.  16  and  20 ). The coil spring  89  has a pair of ends, one of which abuts the crimp-on connector  107 , and the other of which abuts the insulating portion  106  of the housing. A rest position of battery terminal  39 A is shown in FIG.  16 . When the battery terminal  39 A is deflected from its rest position (such as when the device  10  vibrates during an orthopedic surgical procedure), the spring  89  deflects in compression from its rest position and biases the battery terminal  39  toward its rest position. Alternatively, the spring  89  may be designed to deflect in tension from its rest position to bias the battery terminal  39  toward its rest position. 
     The screw  87 , crimp-on connector  107 , coil spring  89  and portions of the battery terminals  39 A are situated within cavity  109  in the handgrip  5 . The cavity  109  has a diameter at least slightly larger than the diameter of the screw  87  to afford float of the battery terminals  39 A. Unlike the battery terminals  39 , the battery terminals  39 A comprise a substantially flat, rectangular contact member having a pair of opposite sides  91  and  92  for contacting the battery contacts  33 A. 
     Battery contact  33 A for use with the battery terminals  39 A is shown in  FIGS. 13 ,  14  and  24 . Each of the battery contacts  33 A include a pair of flexible, resilient deflecting members  81  and  82 . The flexible, resilient deflecting members  81  and  82  each have a first end rigidly affixed to the battery housing  31 , and a second end, opposite the first end. The second end of the members  81  and  82  is free to slide along the top of the casing  31  when the members  81  and  82  are deflected. A support shoulder surface  115  of the top portion of the battery housing  31  receives the second end of the members  81  and  82  and affords sliding movement of the second ends of the members  81  and  82 . 
     The battery terminal  39 A is designed to be sandwiched between the flexible, resilient deflecting members  81  and  82  and to deflect the members  81  and  82  in a direction that is substantially perpendicular to both of the axes H and D during vibration of the battery terminals  39 A. Preferably, side  91  of the battery contact  33 A is in electrical communication with deflecting member  81 , and side  92  of the battery contact is in electrical communication with deflecting member  82 . 
     The battery contacts  33 A are constructed from a flexible, resilient, electrically conductive material. Any of the materials and platings mentioned above for use in constructing the battery contacts  33  may be used to construct the battery contacts  33 A. Particular examples include beryllium copper, Brush Wellman alloy 25, 0.0159 (26 Ga) thick, ¼ H temper, or equivalent UNS No. C17200, (ASTM temper TD01) heat treated 2 hours @ 600 degrees fahrenheit (ASTM TH01), R/C 38-43. As an example not intended to be limiting, the contacts  33 A may have an overall height in  FIG. 14  of about 0.17 inches, a overall length ( FIG. 13 ) of about 1.44 inches and an overall width of approximately 0.32 inches. 
       FIGS. 22 and 23  illustrate another embodiment of battery contact  33 B for use with a drive assembly having the battery terminals of FIG.  11 . The battery contact  33 B is similar to the battery contact  33 A except in that the contact  33 B has a slightly different shape when viewed in the top view. 
     The handle portion  6  of the housing has a releasable attachment means for releasably attaching the battery  30  to the battery receiving portion  48  in a direction other than the direction of elongation of the handle portion  6 . In the illustrated embodiment, that means comprises surfaces on the battery receiving portion  48  defining track portions  49  with flanges that are elongate in a direction substantially parallel to the longitudinal axis D of the drive portion. The battery  30  has a pair of opposite mounting grooves  35  adapted to cooperably receive the flanges of the track portions  49  (see FIGS.  4  and  6 ). 
     The battery pack  30  also has a pair of flexible, resilient cantilever members  37  having opposite ends. Each of the cantilever members  37  has a first end attached to the battery housing  31  and an enlarged distal end  38 . The cantilever members  37  project from the structure defining the grooves  35  in a direction other than direction of elongation of the handle portion  6  (preferably in a direction substantially parallel with the top of the battery and the drive portion axis D). Referring now to  FIG. 11 , the battery receiving portion  48  of the housing includes a cantilever member receiving cavity  77  formed in part by a relatively thin shelf. The cantilever member receiving cavity  77  includes radiused side walls  75  (see FIG.  12 ). 
     The flexible, resilient cantilever members  37  are shown mounted in the cantilever member receiving cavity  77  in FIG.  12 . When the battery  30  is mounted on the battery receiving portion  48 , the flexible, resilient cantilever members  37  interfere with the surfaces defining the cantilever member receiving cavity  77  to resist movement of the battery  30  relative to the rest of the device  10 , particularly movement in the D axis direction. The flanges of the track  49  cooperably engage the grooves  35  and prevent the battery  30  from separating from the rest of the device  10 . 
     The distal ends  38  of the flexible, resilient cantilever members  37  have a bevel  78  to allow them to ramp onto the shelf forming the cavity  77 . The engagement between the bevel  78  and the shelf forming the cavity  77  forces the flexible, resilient cantilever members  37  upward in the H axis direction (in  FIG. 2 ) when the battery  30  is mounted in the battery receiving portion  48 . Consequently, the battery  30  is forced into abutment with the manually grasping portion  5 . When the battery  30  is fully mounted in the battery receiving portion  48 : (1) portion  71  (see  FIG. 3 ) of the battery housing  31  is preferably in contact with the bottom side of the shelf forming the cavity  77 , and (2) the flexible, resilient cantilever members  37  are in engagement with the side surfaces forming the cavity  77  which results in a pinching interference fit that tends to resist transmission of vibration to the contacts  33  or  33 A. The pinching interference holds the flanges of the track portions  49  in engagement with the grooves  35  of the battery housing  31  to retain the battery  30  attached to the handgrip  5 . 
     The enlarged distal ends  38  of the flexible, resilient cantilever members  37  have an outward biased radius  28 . When the battery  30  is inserted into the receiving portion  48  of the handle portion  6 , the outward biased radius  28  contacts the radiused side wall  75  (FIG.  12 ). The width between the outermost portions of the two distal end outward biased radiuses  28  is greater than the width of the radiused side walls  75 . With this difference in widths, the flexible, resilient cantilever members  37  are forced inward when the battery  30  is received in the battery receiving portion  48  thereby generating a resistance to movement. For example, the interference is preferably less than about 0.1 inches and is more preferably less than about 0.02 inches. This slight interference causes the resilient members  37  to deflect and to provide excellent frictional contact with the cavity  77  in the battery receiving portion  48 . In the manner described above, the cantilever members  37  stabilize the front end of the battery  30 . This is especially effective in resisting movement when using the instrument is used for oscillating sawing where side to side forces (perpendicular to the axis H) are generated. 
     Preferably, the flexible, resilient cantilever members  37  comprise a single, unitary, integral monolithic piece with the battery housing  31 . Thus, the material for the battery housing  31  should be sufficiently durable for forming a battery housing (e.g. it should be able to withstand autoclaving procedures), and yet resiliently flexible to accomplish the repeated interference fit of the flexible, resilient cantilever members  37  and cavity  77 . Any suitable materials may be used including the materials discussed above as suitable for use to construct the casing  31 . Alternatively, the flexible, resilient cantilever members  37  may be constructed from a material different than the material used to construct the casing  31 . 
     When the drive assembly  10  is held in the position referenced in  FIG. 2 , the mounting grooves  35  and flanges of the track portions  49  are cooperable to resist the effect of gravity on the device  10  which, in prior art devices, tends to urge the battery away from contact with the rest of the device. A latch  56  is provided for releasably securing the battery  30  to the battery receiving portion  48 , and for retaining the electrical contact between contacts  33  of the battery  30  and the battery terminals  39  (or the terminals  39 A with the contacts  33 A) of the battery receiving portion  48 . The latch  56  comprises a blocking member  57  mounted on the lower portion of the housing  6  for movement between a latched ( FIG. 4 ) and a release position. A coil spring  58  biases the blocking member  57  toward the latched position. The latch  56  also includes the battery housing  31  having surfaces defining slot  34  for receiving a chamfered end  55  of the blocking member  57 . 
     In the latched position, (1) the mounting grooves  35  of the battery  30  are received in the track portions  49  (see  FIG. 4 ) in the battery receiving portion  48 , and (2) the chamfered end  55  of the blocking member  57  is biased into engagement with the slot  34  of the battery  30  to lock the battery  30  to the battery receiving portion  48  of the housing. Indicia  59  may be present to provide user information such as how to unlatch the battery  30 . 
     The latch  56  also includes means for automatically moving the blocking member  57  from the latched toward the release position as the battery  30  is mounted to the battery receiving portion  48 . That means comprises the battery housing  31  having a ramp surface  36  adapted to engage the chamfered end  55  on the blocking member  57 . 
     Referring to  FIG. 2 , as the battery  30  is slid into the track portions  49  of the battery receiving portion  48 , the ramp surface  36  engages the chamfered end  55  on the blocking member  57  and cams the blocking member  57  toward the release position, thereby enabling the flanges of the track portions  49  to be slid into the corresponding, cooperable grooves  35  of the battery housing  31 . Once the battery  30  is fully mounted on the battery receiving portion  48 , the chamfered end  55  of the blocking member  57  is biased into engagement with the slot  34  of the battery housing  31  as described above. The side of the blocking member  57  opposite chamfered end  55  is not chamfered to resist inadvertent release of the battery  30 . 
     As a portion of the electrical circuit means mentioned above, the drive assembly  10  also includes a convenient rotary switch means, operated by ribbed member  72  on the proximal end  1  of the drive housing  4  opposite drive member  18 , for causing the motor  12  to rotate the drive member  18  either in forward or reverse (clockwise or counterclockwise) directions, or to prevent any rotation by the motor  12  even when the trigger  40  is moved to its inner position. Indicia  73  indicate when the device is in the forward, reverse or stop modes. 
       FIG. 21  is a schematic illustration of the switch means. The motor control switch with forward, off and reverse positions is preferably mounted behind the motor. The motor control switch includes a rotatable knob  72  with an attached magnet  62  and a detent mechanism  63  with three positions that correspond to the forward, off and reverse positions. When the knob is rotated fully clockwise, the magnet  62  by its magnetic field, activates one of two hall sensors  61  to run the motor counter-clockwise when facing the output shaft. When the knob is rotated fully counter-clockwise, it will reverse the motor. A center, neutral (off) position is also included. 
     The present invention has now been described with reference to several embodiments thereof. It will be apparent to those skilled in the art that many changes or additions can be made in the embodiments described without departing from the scope of the present invention. Thus, the scope of the present invention should not be limited to the structures described in this application, but only by structures described by the language of the claims and the equivalents of those structures.