Direct plug-in cordless screwdriver
This is a continuation of application Ser. No. 08/219,832, filed Mar. 30, 1994, which was abandoned upon the filing hereof. 
    
    
     BACKGROUND OF THE INVENTION 
     a) Field of the Invention 
     The invention concerns a cordless electric appliance. In particular, the present invention concerns a cordless electric screwdriver which includes provisions for plugging the screwdriver directly into a standard electrical power socket. 
     b) Description of Related Art 
     Conventional electric screwdrivers are either of the &#34;corded&#34; or the &#34;cordless&#34; variety. Corded electric screwdrivers are electrically linked to a power source socket by finite length wire conductors. By convention, the electrical contact tangs of a male plug-in connector are associated with an electrical appliance, and each tang is respectively received in a female electrical contact of a power source socket. Also by convention, the electrical contact tangs and female electrical contacts are arranged in a standardized pattern to facilitate mating between the plug and socket. A disadvantage of corded screwdrivers is the range of operation is limited to the finite length of the wire conductors from the power source socket. Another disadvantage is the added bulk and inconvenience a cord causes in tight spaces. 
     Conventional cordless electric screwdrivers include an internal power reserve. The internal power reserve may be provided by standard, non-rechargeable batteries, however the most common power reserve is one or more rechargeable batteries. During periods of screwdriver inactivity, the rechargeable batteries may be linked to a power source socket through a recharging unit. 
     Known recharging units for cordless electric screwdrivers generally consist of either a rectifying transformer unit which is simultaneously &#34;plugged-in&#34; between both a standard electrical power source socket and an input receptacle on the screwdriver, or a support bracket which cradles the screwdriver and concurrently establishes electrical links between the bracket and the screwdriver. Consequently, it is necessary to have either the rectifying transformer unit or the support bracket to recharge the screwdriver. 
     Inasmuch as it is not always convenient to carry an additional rectifying transformer unit or support bracket for recharging the cordless electric screwdriver, having a separate, secondary element becomes a disadvantage. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an electrical appliance from which male electrical contact tangs are arranged to directly project. In particular, it is an object of the present invention to provide a cordless, rechargeable screwdriver having male electrical contact tangs extended directly from the housing for the rechargeable screwdriver. In a further embodiment of the present invention, the projection of the tangs is along a line which passes through the center of gravity for the appliance. 
     Another object of the present invention is to provide retractable male electrical contact tangs mounted on a common support. Specifically, it is an object of the present invention to commonly mount a pair of electrical contact tangs on a carriage supported for relative motion with respect to the screwdriver housing. Motion of the carriage with respect to the housing causes the tangs to be retracted within, or extended from the housing. According to yet a further object of the invention, movement of the carriage concomitantly changes the electrical connections within the electrical appliance. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a screwdriver according to the present invention. 
     FIG. 2 is a left side view of a screwdriver according to the present invention. 
     FIG. 3 is a right side view of a screwdriver according to the present invention. 
     FIG. 4 is a longitudinal section view of a screwdriver according to the present invention. 
     FIG. 5 is a first end view of a screwdriver according to the present invention, with the tangs extended. 
     FIG. 6 is a second end view of a screwdriver according to the present invention, with the tangs extended. 
     FIG. 7 is an enlarged detail view of a carriage control element according to the present invention. 
     FIG. 8 is a transverse section view, taken along line 8--8 in FIG. 4, showing a carriage according to the present invention. 
     FIG. 9 is a transverse section view, taken along line 9--9 in FIG. 2, showing a switch according to the present invention. 
     FIG. 10 is a transverse section view, taken along line 10--10 in FIG. 3, showing ergonomic contours according to the present invention. 
     FIG. 11 is a transverse section view, taken along line 11--11 in FIG. 3, showing ergonomic contours according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     According to the present invention, an electric appliance such as a cordless screwdriver 10, comprises a tool such as a direct current motor 12. In a preferred embodiment of the invention, the direct current motor 12 rotates a collet 14 via a reduction gear assembly 16. 
     An electric storage cell 18 such as one or more batteries provide a source of direct current to the motor 12. In a preferred embodiment of the present invention, the cell 18 is recharged from a conventional, household alternating current voltage source. Specifically, an electrical converter 20 transforms and rectifies the alternating current voltage into the direct current voltage which is stored in the cell 18. 
     A switch 22 selects operating characteristics of the motor 12 such as clockwise rotation, no rotation, or counter-clockwise rotation. In a preferred embodiment, the switch 22 is a DPDT switch which selectively establishes the electrical connections between the motor 12 and the cell 18, in a conventional manner. It is also possible that the switch 22 could be used to operate a speed control circuit (not shown) and thereby select the rate of rotation, as well as the direction of rotation. 
     Tangs 30 establish the physical connection with respective female electrical contacts of a standard, household wall socket. Tangs 30A, 30B are communally mounted on a carriage 32 which is itself relatively movably supported by a housing 40. It is within the scope of this invention that the movement of the carriage 32 can be to translate, pivot, or some combination thereof, with respect to the housing 40. The essence of the motion is to extend the tangs 30 to a first position wherein they are adapted to engage a standard, household wall socket, and to retract the tangs 30 to a second position within a recess 42 in the housing 40. The tangs 30 extend through a first aperture(s) 44 out of the recess 42, while a control element 34 associated with carriage 32 can extend through a second aperture 46 out of the recess 42. The control element 34 is engaged by an individual&#39;s digit for the purpose of moving the carriage 32 with respect to the housing 40, and consequently extending or retracting the tangs 30. The illustrated preferred embodiment of FIG. 8 shows carriage 32 relatively translatable with respect to the housing 40. FIG. 8 also shows an interlock mechanism 36 which requires overcoming the opposing force of a spring loaded catch before the carriage 32 can be moved out of the first or second positions. 
     Another important aspect of the present invention is the location of the extended tangs 30 with respect to the center of gravity for the electric appliance 10. Specifically, the projection of the tangs 30, while in the first position, is centered on a line which passes through the center of gravity for the appliance 10. This location for the tangs 30 minimizes stress on the tangs 30, carriage 32 and housing 40 during recharging (likely to be long periods of support by virtue of being &#34;plugged-in&#34; to a household wall socket). Yet another aspect of the present invention is the potential safety feature obtained by movement of the carriage 32 that concomitantly electrically disconnects the tangs 30 from the converter 20. That is to say, the motion of carriage 32 with respect to housing 40 can act like a switch to electrically isolate the tangs 30 in the second position, or when not in the first position. 
     The housing 40 supports the direct current motor 12, collet 14, reduction gear assembly 16, electric storage cell 18, electrical converter 20, switch 22, tangs 30, carriage 32, control element 34 and interlock mechanism 36. However, another important aspect of present invention is the configuration of the housing 40. In order to provide improved ergonomics to the appliance 10, several features have been incorporated into the design of the housing 40. A plurality of adjacent ridges 50A and valleys 50B comprise a textured section 50 of the housing 40 which only partially circumscribes the longitudinal axis of the housing. As best shown in FIG. 5, the textured section 50 is generally located diametrically opposite to the circumferential position of the switch 22. Additional facets of the housing 40 include a constricted portion 52, as well as distinct cross-sectional profiles illustrated in the preferred embodiments shown in FIGS. 9-11. As a consequence of the constricted portion 52, the cross-section illustrated in FIG. 9 has the distinctively flattened profile. Additionally, an intermediate portion 54 of the housing interposed between the constricted portion 52 and an end portion 56, has the relatively expanded cross-section illustrated in Figure 11 as compared with the cross-section of the end portion 56 illustrated in FIG. 10. The textured section 50 and the constricted portion 52, as well as the relative sizing and shape of the intermediate and end portions 54,56, each contribute to the overall ergonomics improvement provided by the present invention. 
     In an alternate embodiment to the present invention, access 41 (FIG. 4) is provided through the housing 40 for the purpose of separating the electric storage cell 18 from the appliance 10. That is to say, a plurality of interchangeable cells 18 could be maintained and sequentially connected to the appliance 10 as preceding cells 18 are exhausted.