Abstract:
A power belt sander ( 10 ) with a housing ( 11 ), which contains means for driving a sanding belt ( 24 ) which can be continuously guided by means of a drive roller ( 23 ), preferably also by means of a deflection roller ( 22 ), is less costly, lighter in weight, and more efficient due to the fact that the sanding belt ( 24 ) is supported by a toothed sanding belt ( 21 ), wherein the toothed sanding belt ( 21 ) is oriented with its toothed side ( 25 ) toward the drive roller ( 23 ), preferably the guide roller ( 22 ).

Description:
BACKGROUNG OF THE INVENTION 
     The invention relates to a power belt sander. 
     A power belt sander of this generic type has been disclosed by GB 2 293 122, in which the power of a motor is transmitted by means of a drive roller to a sanding belt, which travels over a deflection roller spaced apart from and parallel to the drive roller. At the same time, there is frictional adhesion between the inside of the sanding belt and the deflection and drive rollers. 
     In order to assure the frictional adhesion between the sanding belt and the drive roller, the sanding belt traveling over the drive roller must be prestressed in relation to it with a minimum force. This is achieved by virtue of the fact that the deflection roller is supported so that it can be elastically displaced and is supported so that it is prestressed against the inside of the sanding belt. Tension elements are required for this, which attempt to press the deflection roller elastically away from the drive roller. 
     The slippage required for the power transmission between the drive roller and the sanding belt causes a relatively intense wear on the drive roller friction cover, which is usually made rubber. In addition, the sanding belt and the drive roller are heated relatively intensely by the slippage. This increases the tendency of the sanding agent layer to clog up and the tendency of the work piece surface to become lubricated, for example with paint residue or lacquer, which are already intensely heated anyway during the sanding. In the extreme case, surface regions of the work piece can become heat blackened. 
     Due to the heating and the slippage, the inside of the sanding belt becomes continuously smoother so that the service life of the sanding belt and the service the drive roller are reduced. 
     In addition, with the known power belt sanders, the continuous sanding belt, which is guided by frictional adhesion, must be kept in a central running position in relation to the drive roller and the guide roller by means of a complex adjusting device in order to prevent it from coming off the side of the drive roller and the deflection roller. 
     SUMMARY OF THE INVENTION 
     The power belt sander according to the Invention can be produced at a lower cost, is lighter in weight, and can be smaller in design than the known machines because the adjusting and tensioning means are no longer necessary. Moreover, the positive engagement between the drive roller and the sanding belt permits a quasi slip-free transmission of power to the sanding belt and results in an extended service life of the sanding belt and greater sanding abrasion. 
     Since a toothed sanding belt, as a support for the sanding belt, is guided on matched denticulations of the drive roller and deflection roller, the sanding belt does not have to be centered or elastically prestressed because even with the relatively low tension of the toothed sanding belt, the positive engagement between the drive roller and the uniform revolution of the toothed sanding belt are assured. 
     The slippage between the toothed sanding belt and the sanding belt can be minimized by virtue of the fact that on its back side, the toothed sanding belt supports the sanding belt so that it is secured against relative movement, e.g. by means of an adhesive connection or a hook-and-loop fastener. 
     Because the sanding belt is open, i.e. has two ends and does not constitute a closed ring, it is cheaper to produce and is easier to mount in abutting fashion on the power belt sander or on the toothed sanding belt. 
     For the case in which the toothed sanding belt has a sanding agent layer glued, vulcanized, or injection molded in place on its back side, the toothed sanding belt, with a particularly long service life, performs the function of the sanding belt, whose initial cost and installation are then rendered superfluous. 
     A clogging of the abutting point between the ends of the sanding belt with sanding dust is counteracted by virtue of the fact that one end of the sanding belt is thicker than the other and is disposed before the thinner end in the rotation direction of the sanding belt. 
     The fact that the ends of the sanding belt extend parallel to each other, diagonal to the travel direction effectively further counteracts the clogging of the impact point. 
     By virtue of the fact that instead of the toothed sanding belt, a V-belt or flat belt are used and instead of the drive roller and deflection roller, V-belt wheels or flat belt wheels are used, the above-mentioned advantages can be achieved in a manner similar that of a toothed sanding belt. 
     Because the toothed sanding belt, flat belt, or V-belt has recesses on its back side for the insertion of sanding segments, separate sanding segments can be disposed overlapping one another and can be individually replaced when they become worn. 
     By virtue of the fact that the tooth points of the toothed sanding belt are provided with a low-friction cover, in particular a textile cover, the toothed belt can be guided via a sliding shearing force and during sanding, is supported against this sliding shearing force so that it is possible for the sanding belt to exert a uniform distribution of force on the work piece. 
     The above-mentioned advantage that over its entire width or over its entire lower surface area oriented toward a work piece to be machined, the sanding belt is supported uniformly on the work piece, is improved by virtue of the fact that the sanding shoe which serves to support the sanding belt in relation to a work piece, is recessed in groove fashion in the vicinity of the toothed sanding belt so that its distance from the back side of the sanding belt and the back side of the toothed sanding belt is approximately equally small. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The current invention will be described in detail below in an exemplary embodiment in conjunction with accompanying drawings. 
     FIG. 1 shows the side view of a power belt sander according to the invention, 
     FIG. 2 is a three-dimensional oblique rear view of the power belt sander according to FIG. 1, without the side casing, 
     FIG. 3 shows a side view of a another exemplary embodiment of a power belt sander, 
     FIG. 4 shows a cross section through the power belt sander according to FIG. 3, 
     FIG. 5 shows a schematic representation of the drive roller and deflection roller with the toothed sanding belt and the sanding belt, 
     FIG. 6 shows a cross section through the drive roller and deflection roller with the toothed sanding belt and the sanding belt, and 
     FIG. 7 is an enlarged depiction of the engagement region between the deflection roller and drive roller and the toothed belt. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The side view of a power belt sander  10  in FIG. 10 shows its housing  11 , which has a rear handle  12  with a switch button  14  and has a front auxiliary handle  13 . The toothed belt deflection gear  22  and toothed belt drive gear  23  that are located at the bottom of the power belt sander  10  can also be seen, which continuously carry a toothed sanding belt  21  along with them. 
     On its side remote from the teeth  21 , the toothed sanding belt  21  has hook-and-loop hooks  31  which engage with a velour layer  32  (FIG. 7) on the back side of the sanding belt  24 , i.e. on the side opposite from its sanding agent layer  30 . The hook/velour system  31 ,  32  attaches the sanding belt  24  to the toothed sanding belt  21  so that it is secured against relative movement. When its teeth  210  engage in the complementary denticulation  230  of the toothed belt deflection gear  22  and the toothed belt drive gear  23 , this toothed sanding belt  21  is carried along in a positively engaging fashion and therefore experiences only minimal slippage. 
     The sanding belt  24  and the toothed sanding belt  21  are supported with their back sides against a sanding shoe  33  so that for sanding, the sanding belt  24  can be placed against a work piece with pressure distributed evenly over its surface area. This assures a uniform removal of material from the work piece over the entire contacting surface area or over the sanding agent layer  30  of the sanding belt  24  (FIGS. 5 to  7 ). 
     FIG. 2 is a three-dimensional depiction of the power belt sander  10  from the left rear, without a casing that covers the main handle  12  and without an auxiliary handle according to FIG.  1 . The main handle  12  has a switch button  14  for a switch that is not shown in detail. 
     In the vicinity of the main handle  12 , electrical lines  15  are shown which are used to supply energy to the motor  16  (FIG.  4 ). A drive shaft protruding from the left side of the housing  11  supports a toothed belt drive pinion  18 . This drive pinion is associated with a toothed belt driven pinion  19 , which is disposed axially parallel to the drive pinion, lower down in the housing  11  and is affixed in a rotationally secure fashion to the toothed belt drive gear  23  of the power belt sander  10 . The two pinions  18 ,  19  are engaged from the outside by a toothed drive belt  20  so that the motor rotation is transmitted to the toothed belt drive gear  23 . 
     In the front, lower region of the housing  11 , the toothed belt deflection gear  22  is shown, which together with the toothed belt drive gear  23 , is encompassed by the toothed sanding belt  21 ; the sanding belt  24 , not shown, can be fastened to the back side of the toothed sanding belt  21  by means of a hook-and-loop fastening system. The drawing also shows the teeth  210  of the toothed sanding belt  21  and the counterpart denticulation  230  of the toothed belt drive gear  23  and the toothed belt driven gear  22 . 
     FIG. 3 shows a side view of another exemplary embodiment of a particular type of power belt sander  210 , having a housing  211  with a handle  212  that has a switch button  214  for switching the drive motor  216  on and off (FIG. 4) in order to operate the power belt sander  210 . In the front region of the housing  211 , there is an auxiliary handle  213  for securely guiding the power belt sander  210  with both hands. In the upper region of the housing  211 , the toothed sanding belt  221  is guided around a toothed belt deflection gear  222 . 
     The exceptional feature of the power belt sander  210  is comprised in that the sanding belt  224  protrudes through a slot-like opening  312  on the machine sole  311  in a design similar to a plane, only in the circumference region of the toothed belt drive gear  223  and can therefore be placed on a work piece and is comprised in that as a result, the power belt sander  210  constitutes a modified roll sander. 
     FIG. 4 shows the power belt sander  210  in a longitudinal section through the toothed belt drive gear  223 , which simultaneously supports and guides the sanding belt  224  along its non-toothed circumference and with this sanding belt  224 , is provided to be placed on a work piece to be machined so that the sanding belt  224  can be brought into contact with a work piece only along a line. 
     The motor  216  is disposed in the lower region of the housing  211 , with a drive shaft  217  which supports a toothed belt drive pinion  218 . A toothed drive belt  220  is guided around this toothed belt drive pinion  218  and around a toothed belt driven pinion  219  that is axially parallel to and spaced apart from the drive pinion  218 . 
     The toothed belt driven pinion  219  is supported in a non-rotatable fashion on a drive shaft  2190  which also supports a pinion  2191 , which meshes with a gear  2192 . This gear is non-rotatably supported on a drive shaft  2231  which in turn supports a toothed belt drive gear  223  which is used to drive a sanding belt  224  with its sanding agent layer  330 . To that end, the toothed belt drive gear  223  is provided with a denticulation  2230  that is disposed in the center and is recessed in a groove-like fashion, which the toothed sanding belt  221  engages in with its teeth  2210 . The groove-like recessed denticulation  2230  is dimensioned so that the toothed sanding belt  221  that meshes with it fits into it in a flush manner. As a result, the contour of the back of the toothed sanding belt  221  is flush with the smooth contour of the non-toothed region of the toothed belt drive gear  223  on both sides of the denticulation  2230 . 
     The toothed belt drive gear  223  simultaneously serves as a first deflection roller of the sanding belt  224  and also absorbs the support force when the power belt sander  210  is placed on a work piece and/or during machining of the work piece. In this connection, the sanding belt  224  is supported with its inside against the toothed belt drive gear  223  and is coupled to the toothed sanding belt  221  in a driven fashion only by means of a central velour strip (FIG. 7) and with its region protruding laterally beyond the toothed sanding belt  221 , is guided in a deflecting manner with a slight support force against the smooth, non-toothed circumference of the toothed belt drive gear  223 . 
     The toothed belt deflection gear  222  disposed in the upper region of the housing  211  is embodied similarly to the toothed belt drive gear  223  and simultaneously serves as a second deflection roller for the toothed sanding belt  221  and the sanding belt  224 . With its lateral velour strip-free regions, this sanding belt  224  is also guided there in a deflecting fashion, with a slight support force against the lateral, non-toothed circumference regions of the toothed belt deflection gear  222 . The central denticulation  230  of the toothed belt deflection gear  222  is also dimensioned so that the toothed sanding belt  221  that meshes with it rests with its back side flush with the non-toothed, respective lateral regions and the sanding belt  24  can be guided with its velour strip-free region continuously supported against this toothed sanding belt  221 . 
     FIG. 5 is a schematic representation of the toothed belt drive gear  23  and the toothed belt driven gear  22  in the vicinity of their denticulation  230 , which the teeth  210  of the toothed sanding belt  21  positively engage in and can be guided to rotate in a non-slip fashion. 
     The toothed sanding belt  21  is oriented with its toothed side  25  toward a sanding shoe  33  affixed to the housing so that when the flat region of the sanding belt  24  disposed between the toothed belt drive gear  23  and the toothed belt driven gear  22  is pressed against a work piece, the tooth points  211  of the teeth  210  of the toothed sanding belt  21  can slide along against the sanding shoe  33 . As a result, the sanding shoe  33  can be used to uniformly distribute the pressure against the region of the sanding belt  24  disposed underneath it and from there onto a work piece. In order to reduce wear, the tooth points  211  are provided with a sliding cover  34  comprised of textile fibers or the like (FIG.  7 ). 
     The sanding belt  24  is connected to the back side of the toothed sanding belt  21  so as to be secured against relative movement, by means of a hook-and-velour system  31 ,  32 . The ends of the sanding belt  24  form a butt joint  27  or a gap. The toothed sanding belt  21  is narrower than the sanding belt  24  so that only its central region is provided with a velour strip  32 . This is why the sanding shoe  33 , in the vicinity of the tooth points  211  of the sanding belt  24 , is recessed in a groove-like fashion so that the tooth points  211  are spaced slightly apart from the corresponding region of the sanding shoe  33 . Likewise, the distance of the lateral velour strip-free regions of the sanding belt  24  from the sanding shoe  33  is slight in order to be able to be supported against it over the entire surface. 
     The directional arrow  341  indicates the movement direction of the sanding belt  24 , the toothed sanding belt  21 , and the gears  22 ,  23 . The one end  261  of the sanding belt  24  is designed to be slightly higher than the other end  26  so that dust is prevented from collecting between the two ends  261 ,  26 , at the bottom of the step-like height difference  35  between them, i.e. in the vicinity of the butt joint or gap  27  between the ends  26  of the sanding belt  24 , and so that the dust is prevented from falling out by itself during sanding. 
     FIG. 6 shows a cross section of the toothed belt drive gear  23  and the toothed belt deflection gear  22  with the counterpart denticulation  230  according to FIG.  5 . The teeth  210  of the toothed sanding belt  21  continuously engage in a slip-free fashion in the counterpart denticulation  230 . 
     On its back side, the toothed sanding belt  21  has hook-and-loop hooks  31  which engage in the velour layer  32  disposed on the back side of the sanding belt  24 . With the back side of its velour  32  covered region, the sanding belt  24  is supported on the sanding shoe  33  and with a uniformly distributed pressure, can produce a uniform removal of material on a work piece to be machined. 
     FIG. 7 gives an enlarged view of the disposition of the sanding belt  24 , with its outwardly pointing sanding surface  30  and the velour cover  32  on its back side. The FIG. also shows the sanding shoe  33 , the hook-and-loop hooks  31  of the toothed sanding belt  21 , the teeth  210  of the toothed sanding belt  21  with the sliding cover  34  disposed in the vicinity of its tooth points  211 . These permit a sliding support of the continuous toothed sanding belt  21  with its back side against the sanding shoe  33  so that the inner region of the sanding belt  24  that is coupled to the toothed sanding belt  21  can also be placed against a work piece with the same pressure as at the side or in the edge region of the sanding belt  24 .