Abstract:
A power tool including a power tool base unit with a motor surrounded by a motor housing a first coupler operably connected to the motor and a ledge. An attachment head is removably attached to the base unit, the attachment head including a second coupler, the first and second couplers being coupled together to transfer rotational motion from the motor to the attachment head. An angle between a longitudinal axis of the handle and a longitudinal axis of the motor is between 50 and 120 degrees. The ledge extends outwardly from the power tool base in a direction towards the attachment head in a direction substantially parallel to the longitudinal axis of the motor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/610,268 filed Mar. 13, 2012, and U.S. Patent Application No. 61/508,962 filed Jul. 18, 2011. This application is related to power tools including interchangeable heads, such as those described in commonly owned U.S. Pat. Nos. 6,153,838; 6,286,611; 6,176,322; 6,641,467; 6,263,980; 6,675,911; 6,634,439; 6,553,642; 6,170,579; and 6,206,107; U.S. Patent Application No. 61/610,268 (filed Mar. 13, 2012) and U.S. Patent Application No. 61/508,962 (filed Jul. 18, 2011) each of which are incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    In order to increase the ease of use and flexibility, some handheld power tools have allowed interchangeability of tool heads. Permitting interchangeability of the tool heads, while keeping the same tool body, allows for the same tool body to operate as a variety of different tools—such as a drill, drill/driver, circular saw, sander a jigsaw, etc. 
         [0003]    There have been various attempts made to make such power tools with interchangeable heads. Such previous attempts have met with varying amounts of success. 
         [0004]    In general, different tools have different shapes for ergonomic and other reasons. Accordingly, one challenge when making a power tool with interchangeable heads is to make one tool body ergonomic for use with a variety of different tools. This may be particularly important when contemplating the design of the tool when it is being used as a drill, since a drill is a well known and widely used power tool. When a user is using a drill head and using the power tool as a drill, the user wants the look, feel and comfort of a stand-alone drill. Additionally, when the drill head is removed and a sander head, for example, is attached to the power tool body such that the power tool is now intended to operate as a sander, the user wants the sander to operate comfortably and ergonomically. 
         [0005]    Furthermore, because the tool head is removable, there are challenges with supporting the tool head. In some power tools with removable heads, the tool head has been provided with extra support by having a dual or D-shaped handle. In other prior attempts, the power tool may be shaped as an in-line power tool. In that instance, the motor is perpendicular to the output of the drill head spindle, making the drill a right-angle drill. In addition to the challenges mentioned above, a tool of this type does not provide for a traditional power drill configuration of a motor being substantially perpendicular to the handle. 
         [0006]    In those previous attempts, the tool handle and trigger are far back from where the tool head is attached to the tool body and the work surface when a pistol grip is employed. When the trigger is far back from the work surface, it is difficult for a user to control the tool. Particularly, the user&#39;s hand in these cases is far from the work surface. That makes it difficult for a user to judge where the tool will hit the work surface. 
         [0007]    Additionally, much of the weight in the previous attempts is forward of the connection between the tool base unit and tool head. This tends to cause the tool to tend to rotate out of a users hand/grip. 
         [0008]    It is therefore beneficial to provide an improved power tool system with interchangeable tool heads. 
       SUMMARY OF THE INVENTION 
       [0009]    According to one aspect, an exemplary embodiment includes a kit comprising a first tool body having a first motor housing and a first handle, the first handle disposed substantially mid-way between a front end and a rear end of the first motor housing, a DC motor having a first output shaft disposed within the motor housing, the first output shaft extending along a first output shaft axis; a second tool body having a second motor housing and a second handle, the second handle disposed substantially mid-way between a front end and a rear end of the second motor housing; an AC motor having a second output shaft disposed within the second motor housing, the second output shaft extending along a second output shaft axis; a drill tool head removably attachable to both the first tool body and the second tool body, the drill tool head including a drill tool head driven shaft in driving engagement with the first output shaft when the drill tool head is attached to the first tool body and in driving engagement with the second output shaft when the drill tool head is attached to the second tool body, the drill tool head driven shaft in driving engagement with a drill tool head output spindle, the drill tool head output spindle extending along an axis which is substantially parallel to the first output shaft axis when the drill tool head is attached to the first tool body and along an axis which is substantially parallel to the second output shaft axis when the drill tool head is attached to the second tool body; and a sander tool head removably attachable to both the first tool body and the second tool body, the sander tool head including a sander tool head driven shaft in driving engagement with the first output shaft when the sander tool head is attached to the first tool body and with the second output shaft when the sander tool head is attached to the second tool body, the sander tool head driven shaft in driving engagement with a sander platen, the sander platen having a sanding surface which extends substantially parallel to the first output shaft axis when the sander tool head is attached to the first tool body and to the second output shaft axis when the sander tool head is attached to the second tool body. 
         [0010]    When the sander tool head is attached to either the first tool body or the second tool body to form a power sander, and the power sander is set down with the sander platen resting on a work surface, the power sander may rest stably on the work surface. 
         [0011]    When the sander tool head is attached to the second tool body at a forward surface of the second motor housing as defined relative to a region where the second handle extends from the second motor housing to thereby form a power sander, the percentage of the total combined weight of the second motor housing and the sander tool head which is disposed rearwardly of a rearwardmost location of the region may be in the range of 10-50%. 
         [0012]    When the sander tool head is attached to the second tool body at a forward surface of the second motor housing as defined relative to a region where the second handle extends from the second motor housing to thereby form a power sander, the percentage of the total combined weight of the second motor housing and the sander tool head which is disposed rearwardly of a forwardmost location of the region may be in the range of 25-75%. 
         [0013]    When the drill tool head is attached to the second tool body at a forward surface of the second motor housing as defined relative to a region where the second handle extends from the second motor housing to thereby form a power drill, the percentage of the total combined weight of the second motor housing and the drill tool head which is disposed rearwardly of a rearwardmost location of the region may be in the range of 10-50%. 
         [0014]    When the drill tool head is attached to the second tool body at a forward surface of the second motor housing as defined relative to a region where the second handle extends from the second motor housing to thereby form a power drill, the percentage of the total combined weight of the second motor housing and the drill tool head which is disposed rearwardly of a forwardmost location of the region may be in the range of 25-75%. 
         [0015]    When the sander tool head is attached to the first tool body at a forward surface of the first motor housing as defined relative to a region where the first handle extends from the first motor housing to thereby form a power sander, the percentage of the total combined weight of the first motor housing and the sander tool head which is disposed rearwardly of a rearwardmost location of the region may be in the range of 10-50%. 
         [0016]    According to another aspect, an exemplary embodiment includes a sander tool head for a kit, the kit including: 
         [0017]    a first tool body having a first motor housing and a first handle, the first handle disposed substantially mid-way between a front end and a rear end of the first motor housing, a DC motor having a first output shaft disposed within the motor housing, the first output shaft extending along a first output shaft axis; 
         [0018]    a second tool body having a second motor housing and a second handle, the second handle disposed substantially mid-way between a front end and a rear end of the second motor housing; an AC motor having a second output shaft disposed within the second motor housing, the second output shaft extending along a second output shaft axis, and 
         [0019]    a drill tool head removably attachable to both the first tool body and the second tool body, the drill tool head including a drill tool head driven shaft in driving engagement with the first output shaft when the drill tool head is attached to the first tool body and with the second output shaft when the drill tool head is attached to the second tool body, the drill tool head driven shaft in driving engagement with a drill head output spindle, the drill head output spindle extending along an axis which is substantially parallel to the first output shaft axis when the drill tool head is attached to the first tool body and along an axis which is substantially parallel to the second output shaft axis when the drill tool head is attached to the second tool body; wherein, 
         [0020]    the sander tool head is removably attachable to both the first tool body and the second tool body, the sander tool head including a sander tool head driven shaft in driving engagement with the first output shaft when the sander tool head is attached to the first tool body and with the second output shaft when the sander tool head is attached to the second tool body, the sander platen having a sanding surface which extends substantially parallel to the first output shaft axis when the sander tool head is attached to the first tool body and to the second output shaft axis when the sander tool head is attached to the second tool body. 
         [0021]    According to another aspect, there is an embodiment of a kit comprising: 
         [0022]    a first tool body having a first motor housing and a first handle, the first handle disposed substantially mid-way between a front end and a rear end of the first motor housing, a DC motor having a first output shaft disposed within the motor housing, the first output shaft extending along a first output shaft axis; 
         [0023]    a second tool body having a second motor housing and a second handle, the second handle disposed substantially mid-way between a front end and a rear end of the second motor housing; an AC motor having a second output shaft disposed within the second motor housing, the second output shaft extending along a second output shaft axis; 
         [0024]    a drill tool head removably attachable to both the first tool body and the second tool body, the drill tool head including a drill tool head driven shaft in driving engagement with the first output shaft when the drill tool head is attached to the first tool body and in driving engagement with the second output shaft when the drill tool head is attached to the second tool body, the drill tool head driven shaft in driving engagement with a drill tool head output spindle, the drill tool head output spindle extending along an axis which is substantially parallel to the first output shaft axis when the drill tool head is attached to the first tool body and along an axis which is substantially parallel to the second output shaft axis when the drill tool head is attached to the second tool body; and 
         [0025]    saw tool head removably attachable to both the first tool body and the second tool body, the saw tool head including a saw tool head driven shaft in driving engagement with the first output shaft when the saw tool head is attached to the first tool body and with the second output shaft when the saw tool head is attached to the second tool body, the saw tool head driven shaft in driving engagement with a saw output shaft which is driven in reciprocating motion along an axis which is substantially parallel to the first output shaft axis when the saw head is attached to the first tool body and along an axis which is substantially parallel to the second output shaft axis when the saw head is attached to the second tool body. 
         [0026]    According to another aspect, an embodiment includes a power tool comprising: 
         [0027]    a power tool body, the power tool body including a motor surrounded by a motor housing, a trigger for activating the motor, a foot, a single handle disposed between the motor housing and the foot and a ledge where the handle meet; 
         [0028]    an attachment head removably attached to the power tool body; 
         [0029]    the angle between a longitudinal axis of the handle and a longitudinal axis of the motor being between 65 and 115 degrees 
         [0030]    wherein the ledge is substantially parallel to the longitudinal axis of the motor and the attachment head is at least partially supported by the ledge. 
         [0031]    The attachment head may be a sander head and a distance from an action point of the trigger to a work surface may be less than 110 mm. 
         [0032]    There may be at least two attachment heads which may be selectively attached and removed from the base unit and wherein when each of the at least two attachment heads is attached to the base unit, a distance from an action point of the trigger to a work surface is less than 150 mm. 
         [0033]    The at least two attachment heads may include a drill head and a sander head. 
         [0034]    The at least two attachment heads may include a drill head a sander head and a saw head. 
         [0035]    At least two attachment heads which may be selectively attached and removed from the base unit and wherein when each of the at least two attachment heads is attached to the base unit, a distance from an action point of the trigger to a work surface may be less than 110 mm. 
         [0036]    The at least two attachment heads may include a drill head and a sander head. 
         [0037]    A center of gravity of the tool when either of the two tool heads is connected to the base unit may be less than 30 mm forward of an interface where the base unit and the tool heads meet. 
         [0038]    A center of gravity of the tool when either of the two tool heads may be connected to the base unit is less than 20 mm forward of an interface where the base unit and the tool heads meet. 
         [0039]    According to another aspect, an embodiment includes a power tool with a power tool body, the power tool body including a motor surrounded by a motor housing, a trigger for activating the motor, a foot, a single handle disposed between the motor housing and the foot, the angle between a longitudinal axis of the handle and a longitudinal axis of the motor being between 65 and 115 degrees; 
         [0040]    an attachment head removably attached to the power tool body; 
         [0041]    wherein the power tool body and the power tool head define an interface surface where the power tool body and the power tool head meet; and 
         [0042]    where in the trigger lies on a line that runs along the interface surface. 
         [0043]    At least two attachment heads may be selectively attached and removed from the base unit and wherein when each of the at least two attachment heads is attached to the base unit and a distance from an action point of the trigger to a work surface may less than 150 mm. 
         [0044]    The base unit may include a first coupler and the tool head comprises a second coupler, the first and second couplers being coupled together to transfer rotational motion from the motor to the tool head and a motor mount may be attached to the motor and a plate is attached to a rear face of the tool head and the motor mount and the plate have complementary alignment features which align the first and second couplers. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0045]      FIG. 1  is a side view of a power tool according to an exemplary embodiment of the invention with a drill head attached; 
           [0046]      FIG. 2  illustrates the power tool with the tool head detached; 
           [0047]      FIG. 3  illustrates a drill head tool head attachment; 
           [0048]      FIG. 4  is a perspective view of a coupling portion of the power tool base unit; 
           [0049]      FIG. 5  is a perspective view of a coupling portion of the tool head; 
           [0050]      FIG. 6  is a cut-away view showing the internals of the base unit with the drill tool head attached; 
           [0051]      FIG. 7  is a cut-away view showing the internals of the base unit with the drill tool head dettached; 
           [0052]      FIG. 8  is a perspective view of a corded base unit; 
           [0053]      FIG. 9  is a perspective view of a cordless base unit which receives a 3-cell battery pack; 
           [0054]      FIG. 10  is a side view of a power tool according to an exemplary embodiment of the invention with a jig saw head attached; 
           [0055]      FIG. 11  is a side view of a power tool according to an exemplary embodiment of the invention with a sander head attached; 
           [0056]      FIG. 12  is a side view of a power tool according to an exemplary embodiment of the invention with an impact driver head attached; 
           [0057]      FIG. 13  is a side view of a power tool according to an exemplary embodiment of the invention with a two speed hammer drill head attached; 
           [0058]      FIG. 14  is a side view of a power tool according to an exemplary embodiment of the invention with a oscillating tool head attached; 
           [0059]      FIG. 15  is a side view of a power tool according to an exemplary embodiment of the invention with a router tool head attached; 
           [0060]      FIG. 16  is a side view of a power tool according to an exemplary embodiment of the invention with a trim saw head attached; 
           [0061]      FIG. 17  is a side view of a power tool according to an exemplary embodiment of the invention with an inflator tool head attached; 
           [0062]      FIG. 18  is a close-up side view of the power tool of  FIG. 1  showing the center of gravity; 
           [0063]      FIG. 19  is a close-up side view of the power tool of  FIG. 11  showing the center of gravity; 
           [0064]      FIG. 20  is a close-up side view of the power tool of  FIG. 16  showing the center of gravity; 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0065]      FIGS. 1-3  show an exemplary embodiment of a power tool according to the present application.  FIG. 1  illustrates a cordless power tool base unit (tool body) with a drill as the power tool head.  FIG. 2  shows the base unit alone and  FIG. 3  shows the drill tool head alone. 
         [0066]    As shown in  FIGS. 1-3 , the tool comprises a tool base unit  100  and a removably attached tool head  200 . In this case the tool head  200  is a drill head. The tool base unit  100  includes a motor housing portion  101  a handle  102  extending from the motor housing portion and a foot  103  at the far end of the handle  102 . The tool base unit  100  further includes a ledge  104  that helps to support the drill head  200 . A trigger  120  is used to activate the motor  400 . 
         [0067]    As shown in  FIG. 1 , the motor housing has a longitudinal axis A. The longitudinal axis A is co-incident with the longitudinal axis of the motor housed in the motor housing  101 . Additionally, the handle  102  has a longitudinal axis B. According to the exemplary embodiment, the handle  102  is located substantially mid-way between a front end and a rear end of the motor housing  101  and is substantially perpendicular to the motor housing  101 . According to exemplary embodiments of the application, the angle θ between the longitudinal axis of the handle B and the longitudinal axis A of the motor housing  101  may be between 50 and 120 degrees. In  FIG. 1 , the handle  102  is substantially perpendicular to the motor housing  101  and it is contemplated that exemplary embodiments of the tool which have an angle θ between 65 and 115 degrees, and particularly between 70 and 110 degrees, provide good ergonomics for at least the drill tool head  200 . 
         [0068]    Typical power tools have only a single configuration and any tool head is not readily removable and interchangeable with other tool heads. Because the tool heads in such typical power tools are simply integrated into the power tool, the tool head is firmly and securely supported and held in place by such integral construction. In a power tool system with removable and interchangeable heads, the tool head must be supported, but, must also be removable. Thus, the tool head cannot be attached in the permanent manner of stand alone power tools. In prior power tool systems with interchangeable tool heads, the tool head has been supported by various means to address this. For example, in U.S. Pat. No. 6,634,439, the power tool uses a D-handle to provide extra support. In other attempts, the power tool is constructed as an in-line tool (the tool motor and handle are substantially in-line with one another) such that the tool head sits entirely on the base unit. In still other prior tools, no particular support has been provided, such as U.S. Pat. No. 5,033,552. In contrast to these previous attempts, the present power tool system has a base unit with a ledge  104  which is substantially parallel to an axis of the motor  400  and/or the longitudinal axis A of the motor housing. The tool ledge  104  allows the tool to have a single mid-handle  102  that is angled with respect to the longitudinal axis A of the motor housing, while sufficiently supporting the tool head. Having a ledge  104  of this type also allows for a good portion of the tool head to be exposed so that controls can be exposed for the user on another side of the tool head (see, for example, the two speed hammer drill head  262  having a gear change shifter  272  as shown in  FIG. 13 ). The design also allows for tool shapes such as the trim saw shown in  FIG. 16  without unnecessarily increasing the distance between the power tool trigger and the work surface. 
         [0069]    The drill head  200  and the tool base unit  100  meet at an interface C. The ledge  104  extends forward from this interface C and a line running through the interface intersects the trigger  120 . 
         [0070]      FIGS. 4 and 5  illustrate the coupling features of the tool base unit  100  and the tool head  200 , respectively, in more detail. As shown in  FIG. 4 , the tool base unit  100  has a front face  105  of the motor housing  101 . The front face  105  of the motor housing abuts against the rear face  230  of the drill head  200 . The plane in which the front face  105  and the rear face  230  meet forms the interface C of  FIG. 1 . 
         [0071]    As seen in  FIG. 4 , the base unit  100  has a generally circular opening  150  into which a coupling portion of the tool head  200  can be fit. Inside the circular opening  150 , there is also a motor mount opening  160  which exposes the motor mount  161 . A male coupler  110  which is coupled to the motor and spins with the motor shaft is at a center of the motor mount  161 . The male coupler  110  transfers mechanical power from the tool base unit  100  to the tool head  200 . Adjacent to the motor mount opening  160  is a first recessed face  151 . The first recessed face  151  has several features for mating with the tool head  200 , including slots  152 , ribs  153  and cutout  154 . There is a second recessed face  155  in a direction towards the tool head  200  and a plurality of ribs  106  at corners of the first recessed face  151 . 
         [0072]    Furthermore, as can be seen in  FIG. 4 , the ledge  104  has an opening  107  for receiving a contact plate  420  of the tool head  200 . The contact plate  420  contacts a plate member  430  and together they serve as a lock-out as described in further detail in U.S. Patent Application 61/508,962, which has been incorporated by reference (the same reference numbers are not used in application 61/508,962 as in the present application). 
         [0073]    The coupling portion of the tool head  200  is shown in  FIG. 5 . As shown in  FIG. 5 , the tool head  200  has a rear face  230  that abuts the front face  105  of the tool head when the tool head  200  is coupled to the tool base unit  100 . Additionally, the tool head has a plate  201  that is screwed onto the rear face  230  with screws  202 . A first protrusion  210  protrudes from the plate  201  towards the tool base unit  100 . There are four receiving corners or slots  211  which receive the ribs  106  of the tool base unit  100 . 
         [0074]    The tool head  200  coupling portion further includes a second protrusion portion  220  which extends from the first protrusion  210 . The second protrusion portion  220  is generally cyrlindrical in shape. It includes slots  221  and ribs  222  and  223 . It further includes a recess  224  which receives a spring  425  (see  FIG. 6 ). When coupled to the tool base unit  100 , the slots  221  receive the ribs  153 , the protrusions  222  fit in the slots  152  and the ribs  223  slide into the cutout  154 . Furthermore, the tool head  200  includes a female coupler  250  which engages the male coupler  110  of the tool base unit. Additionally, the spring  425  sets into the recess  224  to axially lock the tool head  200  in place. The spring  425  and recess  224  of the present application operate similarly to the spring and recess combination shown in U.S. Pat. No. 6,634,439, which is incorporated by reference. While this exemplary embodiment shows the base unit coupler  110  being male and the tool head coupler  250  being female, these could be reversed. Similarly, the other various mating features could be reversed. 
         [0075]    As shown in the exemplary embodiment, the features of the plate  201  directly mate with those of the motor mount  161 . As can be appreciated, in a tool system with interchangeable heads according to an exemplary embodiment of the present application, the male coupler  160  has to be aligned with the female coupler  250  in order to transfer drive from the motor  400  to the tool head  200  and the output of the tool head  200 . In the present exemplary embodiment, the motor  400  is clamped tightly into the motor housing  101  and the male coupler  160  and female coupler  250  have to be closely aligned. By making the tolerance alignment features on the plate  201  and the motor mount  161 , as described above, unnecessary tolerance stack-up (as may be seen if the outside of the motor housing  101  were used for tolerance alignment) is avoided. That is, at least some of the features on the plate  201  and the motor mount  161  are used as alignment features. If features on the outside of housing of the drill head  200  were used in conjunction with features on the motor housing  101  to align the tool head  200  and the tool base unit  100 , there can be a much more significant tolerance stack-up, because of the number of assembled parts between the alignment features and the male and female couples  110 ,  250 , which ultimately must be aligned. 
         [0076]      FIGS. 6 and 7  show internals of the base unit  100  (the base units  100 ′ of FIGS.  8  and  100 ″ of  FIG. 9  includes similar internal features). As shown in these figures, the base unit  100  of the tool has a motor  400  (in the exemplary embodiment of  FIG. 1  a DC motor; in the exemplary embodiment of  FIG. 8  an AC motor). The motor  400  has a motor fan  401  at its front end for dissipating heat. The exemplary motor additionally has a brush ring  402  and a commutator  403 . An output shaft  404  extends from the motor and provides drive to the male coupler  110 . At its rear end, the motor  400  is supported by a shaft  410  which is partially covered by insulation  411 . The shaft  410  may be integral and continuous with shaft  404  or may be a separate second shaft. At the rear end of the shaft  410 , there is a bearing  411  supported in the housing. The motor  400  is activated by the variable speed trigger  120  and provides power to the base unit coupler  110 . 
         [0077]    As shown in  FIG. 7 , the trigger  120  is attached to a switch  130 . Pulling the trigger  120  activates the switch  130  which in turn causes power to be provided to the motor. Ion this embodiment, the switch  130  and trigger  120  are variable speed, such that the speed of the motor  400  can be varied by pulling the trigger  120  more or less. 
         [0078]    As shown in  FIGS. 8 and 9 , more than one type of tool base unit is contemplated.  FIG. 1  shows a power tool base unit  100  which receives a slide-type battery pack  300 .  FIG. 8 , on the other hand, is a corded base unit  100 ′ and receives AC power and has an AC motor. For the corded base unit  100 ′ shown in  FIG. 8 , the area at the bottom of the handle near where the cord is located is considered a foot. There may also be base units with different types of battery packs. For example,  FIG. 9  shows a base unit  100 ″ which receives a 3-cell type battery pack. Other battery packs, such as a tower pack, are also contemplated. The battery packs may differ both in the mechanical interface and power/voltage. Additionally, the same tool head may fit into each of the different base units  100 ,  100 ′ and  100 ″. For example, the drill head  200  may fit into the base unit  100 , as shown in  FIG. 1 , and alternatively into the base unit of  FIG. 8  or  FIG. 9 . Likewise, when the sander head operates as the tool head, as shown in  FIG. 11 , it may fit into a base unit with a sliding battery pack as shown in  FIGS. 1 and 11 . It may also fit with the base units of  FIGS. 8 and 9 . This allows a user to have both a cordless and a corded system using the same tool heads. 
         [0079]      FIGS. 10-17  illustrate the power tool system with a variety of different tool heads. Particularly,  FIG. 10  illustrates a jig saw head  266   FIG. 11  shows a sander head  260 ;  FIG. 12  illustrates an impact driver  261 ;  FIG. 13  illustrates a two speed hammer drill  262 ;  FIG. 14  shows an oscillating tool  267 ;  FIG. 15  illustrates a router  263 ;  FIG. 16  illustrates a trim saw  264  and  FIG. 17  illustrates an inflator  265 . Each of these tool heads  260 - 267  have a coupling section as shown in  FIG. 5  for the drill head  200 . That allows each of the tool heads  260 - 267  to similarly fit with a base unit with a sliding battery pack as shown in  FIGS. 10-17  or one of the other base units as shown in  FIGS. 8 and 9 . Particularly,  FIG. 10  illustrates a jig saw head  266   FIG. 11  shows a sander head  260 ;  FIG. 12  illustrates an impact driver  261 ;  FIG. 13  illustrates a two speed hammer drill  262 ; FIG.  14  shows an oscillating tool  267 ;  FIG. 15  illustrates a router  263 ;  FIG. 16  illustrates a trim saw  264  and  FIG. 17  illustrates an inflator  265 . Each of these tool heads  260 - 267  have a coupling section as shown in  FIG. 5  for the drill head  200 . That allows each of the tool heads  260 - 267  to similarly fit with a base unit with a sliding battery pack as shown in  FIGS. 10-17  or one of the other base units as shown in  FIGS. 8 and 9 . 
         [0080]    As discussed above, the design of the exemplary embodiment of the power tool system shown in the present application allows for the work surface to be spaced an efficient distance from the tool trigger. As shown in the figures, the drill driver  200 , impact driver  261 , sander  260 , router  264 , trim saw  265  and oscillating  267  tool heads each have distances from the action point of the trigger  120  to the work surfaces which are less than 110 mm. The two speed hammer drill  262  is has a trigger to work surface distance that is somewhat longer due to the additional gears needed to provide a hammer mode and a gear change. However, it still has a trigger to work surface distance of less than 150 mm. 
         [0081]    Furthermore, the configuration of the power tool system allows a center of gravity of the assembled power tool to be well placed for at least some of the most commonly used tool heads.  FIG. 18  shows the center of gravity (CG) when the drill tool head  200  is attached. As shown in  FIG. 18 , when the drill tool head  200  is attached, the center of gravity of the power tool is located slightly above a top surface of the ledge (4.8 mm) and forward of the interface C (by 14.5 mm). This location is also slightly forward of the actuation point of the trigger.  FIG. 19  shows the center of gravity (CG) when the sander tool head  260  is attached. As shown in  FIG. 19 , when the sander tool head  260  is attached, the center of gravity (CG) of the power tool is again located slightly above a top surface of the ledge  104  (2.9 mm) and forward of the interface C (by 14 mm). As with when the drill tool head is attached, the CG location is also slightly forward of the actuation point of the trigger.  FIG. 20  shows the center of gravity (CG) when the trim saw tool head  265  is attached. As shown in  FIG. 20 , when the trim saw tool head  265  is attached, the center of gravity (CG) of the power tool is located slightly above a top surface of the ledge  104  (3 mm) and forward of the interface C (by 14 mm). As with when the drill tool head  200  and the sander head  260  are attached, the CG location is also slightly forward of the actuation point of the trigger. 
         [0082]    A center of gravity location is beneficial for a number of reasons. Initially, by being located above the ledge  140 , the center of gravity location allows for the tool heads to be well supported by the ledge and helps to facilitate the single, mid-handle design. Additionally, by having the CG less than 30 mm forward of the interface C, the ledge  140  does not have to be made unnecessarily long to support the CG. Additionally, that provides a CG near the actuation point of the trigger. 
         [0083]    According to another aspect of the present application, the weight of the power tool with respect to a region where the handle extend from the motor housing is designed for ergonomic usage of different tool heads. As discussed above, exemplary embodiments of the present application improve the ergonomics of a power tool system with interchangeable heads. Therefore, according to one aspect of the present application, the percentage of weight when the sander tool head  200  is attached to the base unit  100  shown in  FIG. 1  or the base unit  100 ′ shown in  FIG. 8 , at a forward surface of the motor housing as defined relative to a region where the handle extends from the motor housing to thereby form a power sander, the percentage of the total combined weight of the motor housing and the sander tool head which is disposed rearwardly of a rearwardmost location of said region is in the range of 10-50%. The ergonomics can be further improved when the percentage is in the range of 20-40% and yet further improved as the weight is in the range of 25-35%. When measured from the forwardmost location of the region, the percentage is in the range of 25-75%, ergonomics are improved when the range is in 35-65% and further improved if the percentage is within the range of 45-55%. When a drill tool head  200  is used, the percentage of weight of the exemplary embodiment is in the same range, thus providing a consistent experience for the user for two of the most widely used handheld power tools. 
         [0084]    Numerous modifications may be made to the exemplary implementations described above.