Abstract:
A power tool, in particular a cordless power tool, having a housing from which a tool emerges, with which tool a lighting device for a work field is associated, is made convenient to use because an LED serves as a light source, downstream of which is an optical light guide system, particularly with curved end faces, that collects the light from the LED and conducts it and aims it at a work field, and the LED and the light guide system are located in a light tube on the housing.

Description:
CROSS-REFERENCE TO A RELATED APPLICATION  
       [0001]     The invention described and claimed hereinbelow is also described in German patent application DE 1.02005 021383.9 filed on May 4, 2005. This German patent application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.SC. 119(a)-(d).  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention is based on a power tool.  
         [0003]     Power tools that have simple work field illumination that is either fixedly set or complicatedly adjustable are known. One disadvantage of fixedly set work field illumination systems is that the beam of the lighting means is aimed only relatively imprecisely at the working tip of the tool.  
       SUMMARY OF THE INVENTION  
       [0004]     It is therefore an object of the present invention to provide a power tool with a work field illumination, which is a further improvement of the existing power tools.  
         [0005]     According to the invention, the power tool does not have multiple optical lenses but instead a one-piece compact light guide system, which is simple to manufacture and which in conjunction with an LED with a high light yield assures that the focused beam is projected toward the front lens and onward toward the work field.  
         [0006]     The light guide system is convex on its rearward end, where it forms a rear lens. The thickness of the convex rear lens is markedly greater than its diameter, so that it forms an elongated cylinder. This cylinder merges at its front end with a convex front lens of larger diameter. Over the length of the cylinder, the rear lens conducts the light, focused parallel, to the front lens, which protrudes in mushroomlike fashion radially past the cylinder. A compact, sturdy and economical optical system is thus created, with which precise illumination of the work field with a target-seeking function is possible, so that the drill tip or screwdriver bit tip can be brought especially quickly and precisely to the working point of the drilled hole or the screwdriving location.  
         [0007]     The larger diameter of the oval front lens is approximately twice that of the circular rear lens, so that the illumination of the work field is therefore accomplished with an especially clearly contoured, concentrated beam of light.  
         [0008]     The light guide system with its rear lens—jointly with an LED serving as a light source—is located so as to be protected from the outside against impacts or jarring, in an extremely compact arrangement in the interior of a light tube in the housing of the power tool.  
         [0009]     The light tube, extending parallel to the axis of the driven shaft on the gearbox, is distinguishable on the outside thereof as a tubular contour and serves to reinforce the gearbox. The gearbox can be manufactured inexpensively, since as a cast part it can easily be unmolded from the casting mold jointly with the integrated light tube.  
         [0010]     The rear lens, located at a defined spacing from the LED, collects virtually all the light emitted by the LED and carries it, inside the cylindrical part, known as a light conduit, of the light guide system, parallel as far as the convex, large-area front lens that is inclined toward the front. As a result, the light yield in the light guide system is especially high.  
         [0011]     Because of the inclination of the front lens toward the front, the light emerges from the front lens aimed in a defined way obliquely upward and outward toward the work field and assures an especially sharply concentrated, bright beam of light.  
         [0012]     A plastic piece holds the LED and, as a spacer or base, keeps it at the calculated spacing from the rear lens in the light tube positionally correctly and in a self-clamping way, and in particular fixed against relative rotation, so that no further fastening elements are needed for the LED.  
         [0013]     The light tube extends parallel to and below the work spindle of the power tool. It protrudes past the front lens at the front and guards the front lens with its edge against damage from striking things as the power tool is manipulated and worked with.  
         [0014]     The shape and dimensions of the light guide system, and especially the front lens, determine the projection length and the direction of the beam of light, and the light emerging from the front lens assures uniform-quality illumination of the work field over a relatively wide, variable range of spacing from the work field—that is, regardless of the length of the screwdriving or drill bit.  
         [0015]     The focal point is located approximately 12 to 13 mm in front of the face end of the gearbox, for the sake of brilliant illumination of the work field, which is typically located approximately 30 to 100 mm in front of the end of the driven shaft. Because of this position of the focal point, the beam of light is “constricted” and is maximally deflected upward, without intersecting the contour of the gearbox.  
         [0016]     The LED base can be fixed in the interior of the light tube in the manner of a stopper or by force-locking, so that the position of the LED in the light tube relative to the light guide system can be defined precisely.  
         [0017]     The inner diameter of the light tube tapers conically over its length—in the self-inhibition region—and as a result fixes the base with the LED and the light guide system especially securely. These elements can also be positionally secured in the light tube by adhesive or by form-locking securing.  
         [0018]     Because the light guide system is in one piece of glass-clear plastic with a scratchproof rear lens and front lens, its length being approximately 8 mm, the diameter of the cylinder being approximately 4 mm, and the larger diameter of the front lens being approximately 6 to 7 mm, and extends in the perpendicular center plane of the power tool, a highly effective, easily manufactured and easily installed optical system for improved illumination of the work field is created.  
         [0019]     The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]      FIG. 1  shows a side view of the power tool of the invention;  
         [0021]      FIG. 2  shows a side view of the gearbox of the power tool of the invention;  
         [0022]      FIG. 3  is a three-dimensional side view of the gearbox, with the lighting device of the power tool of the invention shown in exploded form;  
         [0023]      FIG. 4  is an X-ray view of the power tool of the invention;  
         [0024]      FIG. 5  is an enlarged detail of the lighting device of  FIG. 4 ;  
         [0025]      FIG. 6  is a schematic illustration of the lighting device;  
         [0026]      FIG. 7  is a side view of the optical light guide system with the beam path; and  
         [0027]      FIG. 8  is an enlarged side view of the light guide system of  FIG. 7 .  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0028]     The power tool  10  shown in  FIG. 1  is a cordless screwdriver, whose housing  12  has a pistol-type grip  14 . Located in the interior of the grip  14  are a rechargeable battery  15  ( FIG. 4 ) and an outward-protruding pushbutton  16 , which serves to switch the motor  17  ( FIG. 4 ) on and off. The motor  17  drives a driven shaft  20 , which is supported in the gearbox  18  and protrudes from it toward the front side  22 . The metal gearbox  18  is flanged, on the right in the viewing direction, to a plastic motor housing  19 . In exemplary embodiments of the invention that are not shown, the gearbox may be of plastic.  
         [0029]     An integrated light tube  26  is located on the underside  24  of the gearbox  18  and receives a lighting device  31 ; it is visible from outside as a semicylindrical contour parallel to the motor shaft  20 , and it has a front opening  28 , beveled toward the front, for a focused beam of light  22  to emerge from. Adjoining the light tube  26 , a tubular transition piece  30  extends on the motor housing  19 , and a power cord  35  for supplying power to a lighting device is guided in it for the sake of connection to the battery  15 .  
         [0030]      FIG. 2  shows a side view of the gearbox  18  as a detail, in which the light tube  26  can be seen on the underside  24 , with the lighting device  31  drawn in dashed lines in the internal contour of the light tube. The lighting device comprises a light-emitting diode (LED)  32 , which is seated on a base  34  that serves as an axial spacer and as a fitting piece for inserting and locking the LED  32  in the light tube  26 . A one-piece light guide system  36 , which corresponds to an elongated cylindrical biconvex lens is located at a defined axial spacing in front of the LED  32  in the light tube  26 .  
         [0031]      FIG. 3  shows a three-dimensional side view of the gearbox  18  and driven shaft  20  and with the lighting device  31  shown in exploded form. The design of the LED  32  and of the one-piece light guide system  36  with the rear lens and front lens  38 ,  40  ( FIGS. 5, 6 ) is clearly apparent along with the front opening  28  of the light tube  26 . It can also be seen that the driven shaft  20  is provided with a hexagonal socket  21 , which serves to receive screwdriving or drill bits  48 ,  50  that have a hexonagonal shank.  
         [0032]     The X-ray view of the power tool  10  shown in  FIG. 4  shows, besides the details which have already been explained in conjunction with the previous drawings and will not be mentioned again here, a focused beam of light  52 , which converges at the focal point  54  just in front of the front opening  28  or the front lens  40  and, diverging at that point, is projected obliquely upward and frontward onto the screwdriving or drill bits  48 ,  50  and onward onto a work field  58 . The outlines of the screwdriving or drill bits  48 ,  50  are projected in the form of shadows  56 ,  57  onto the work field  58 . The shadows  56 ,  57  are more sharply contoured and are projected closer to the axis  60  of the driven shaft  20 , the closer the screwdriving or drill bit  48 ,  50  comes to the work field  58 . These shadows  56 ,  57  act like mirror images of the tip of the screwdriving or drill bit  48 ,  50  and together with it act like a crosshair, which finally closes at the point where the tip meets the work field, since the tip of each bit  48 ,  50  touches the tip of the shadow  56 ,  57 .  
         [0033]     The shadow  56  of the screwdriving bit  48  located farther away from the work field  58  is projected onto the work field markedly farther above the axis  60  than the shadow  57  of the drill bit  50  located closer to the work field  58 . Thus the closer the particular bit  48 ,  50 , with its tip, approaches the work field, the closer to the axis  60  where the tip of the bit  48 ,  50  be projected.  
         [0034]      FIG. 5  shows an enlarged detail of the region of the power tool  10  having the lighting device  31 . Its individual parts are clearly recognizable by their shape and location relative to one another; besides the base  34 , the LED  32  and the light guide system  36 , one can see the power cord  35  and the embodiment of the cylinder  42  between the rear lens and front lens  38 ,  40 , with the eccentric cylinder  44  located above the lenses for improving the light transfer from the rear lens  38  to the front lens  40 , as well as the front opening  28 , protruding past the front lens  40 , of the light tube  26 .  
         [0035]      FIG. 6  shows the detail of the lighting device  31  of  FIG. 4  schematically, with the LED  32  and the base  34  and the cord  35 , along with the light guide system  36 .  
         [0036]      FIG. 7  shows a side view of the optical light guide system  36  with the beam path of the focused beam  52 ; the focal point  54  is located approximately 12 mm in front of the front lens  40 , and the work field  58  is located approximately 100 mm in front of the front lens.  
         [0037]      FIG. 8  shows an enlarged side view of the light guide system  36  of  FIG. 7 ; the details of the rear lens  38 , front lens  40 , cylinder  42 , and eccentric cylinder  44  are visible, along with longitudinally extending ribs  46 , on both sides of the cylinder  44 , for fitting the light guide system  36  into the light tube  26  and firmly holding it there.  
         [0038]     It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the types described above.  
         [0039]     While the invention has been illustrated and described as embodied in a power tool with a work field illuminator, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.  
         [0040]     Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.