Abstract:
An electric power tool comprises one or more optical waveguides which are combined with a shaped body so as to form a support element having a stable shape. The light guides may be part of optical switches or sensors. The support element ensures protection of the optical waveguides from vibrations, dust and so on, whereby a high level of operational reliability is ensured.

Description:
RELATED APPLICATIONS  
       [0001]     This application is a continuation application of copending International Patent Application PCT/EP2003/011098 filed Apr. 29, 2004 and claiming priority of German patent application DE 102 48 924.6 filed Oct. 17, 2002 which is fully incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to an electric tool with an electric motor adapted to drive a tool.  
         [0003]     An electric tool of that kind has been known, for example, from U.S. Pat. No. 5,038,481. The known electric tool is a compass saw provided with a light source for observation of the cutting area. The light source may be connected via an optical waveguide.  
         [0004]     Further, German patent application DE 197 14 248 A1 discloses a low-power motor unit for an electric tool which is particularly well-suited for dental applications, as drive for tooth drills, polishing, grinding, milling tools, screwing tools, or the like. In order to guarantee especially good handling properties, a supply unit for the low-power motor is connected with the low-power motor in rotating contactless fashion, for which purpose a plug-in connection and rotation-limiting means are preferably provided. The plug-in connection can be adapted to provide the connection of both the electric system and the fluid lines. Further, a lamp adapted to be coupled with the low-power motor via an optical waveguide can be provided in the working area of the electric tool.  
         [0005]     More recently, there have been proposed by applicant electric tools that are controlled by means of optical switches each of which comprises two optical waveguides between which the transmission of light signals can be influenced via a control element. Depending on the signal received, the switch output is then controlled by an electronic evaluation unit.  
         [0006]     Optical switches of that kind are known from U.S. patent application Ser. No. 10/214,844 which is fully incorporated by reference herewith.  
         [0007]     In cases where optical waveguides are used in implementing optical switches or sensors of electric tools, this is done with the predominant aim to achieve high reliability as well as simple and low-cost assembly.  
       SUMMARY OF THE INVENTION  
       [0008]     It is a first object of the invention to provide an electric tool having at least one optical waveguide received within the electric tool in a reliable and safe manner.  
         [0009]     It is a second object of the invention to disclose an electric tool comprising one or more optical control elements, such as optical sensors or switches, that are safely received within the electric tool and are protected against environmental influences such as dust and the like.  
         [0010]     It is a third object of the invention to disclose an electric tool having a high reliability in operation.  
         [0011]     These and other objects of the invention are achieved by an electric tool with an electric motor adapted to drive a tool having at least one optical waveguide, which is combined with a support element serving as support to form a dimensionally stable unit.  
         [0012]     The object of the invention is perfectly achieved in this way.  
         [0013]     Each optical waveguide is sufficiently protected in this way from vibration, environmental influences and the like. Precise alignment of mutually associated optical waveguides and the fact that the optical waveguides are largely shielded from contact with dust, and the like, guarantee a favorable signal-to-noise ratio. In addition, the assembly operation is simplified by the fact that each optical waveguide is combined with a support element so that work is limited to mounting an already completed support element. It is thus no longer necessary to assemble separate, non-stabilized and unprotected optical waveguides.  
         [0014]     The support element so formed is an element separate from the housing which serves to receive, to correctly position and to protect the optical waveguide connected or integrated with it. After integration of the optical waveguides and, if necessary, of other elements connected with them, the unit is then connected with the housing of the tool in suitable fashion.  
         [0015]     According to a further development of the invention, the support element comprises a shaped body in which recesses are provided for locating the optical waveguides.  
         [0016]     That embodiment therefore allows optical waveguides to be positioned and fixed in the locating recesses.  
         [0017]     The optical waveguides may be rigid or flexible optical waveguides, made from a plastic material. In addition, it is of course also possible to use glass-fiber optical waveguides, preferably in the form of sheathed glass-fiber bundles.  
         [0018]     The optical waveguides can be produced as rigid optical waveguides, for example as injection-molded elements, and can then be fitted in the respective recesses. However, there is also the possibility to use flexible optical waveguides that are fixed on the support element in a suitable way.  
         [0019]     The support element may be a pre-shaped element, for example an injection-molded plastic element in which the completed optical waveguides are fitted or on which they are fixed in some other way.  
         [0020]     An especially efficient and intimate connection, and especially good protection of the optical waveguides from environmental influences is, however, achieved when the one or more optical waveguides are connected with a shaped body in form-fitting fashion, preferably when they are completely embedded in it.  
         [0021]     In this case, the optical waveguides and the shaped body may be combined, if desired, using the so-called 2-K technology. In this case, a first part, for example the shaped body, is first molded in an injection mold whereafter the remaining parts, such as the optical waveguides, are injection-molded into corresponding cavities left for this purpose. Due to the fact that different plastic materials are used for this purpose, especially intimate bonding is achieved in this case between the different components. It is understood that it is of course also possible in this case to first mold the optical waveguides and to then mold the shaped body around them.  
         [0022]     Basically, the optical waveguides can be configured as completely sheathed optical waveguides, with the sheathing, consisting of an optically thinner medium, guaranteeing the necessary total reflection. This then also provides an especially good signal-to-noise ratio.  
         [0023]     However, when the optical waveguides are completely coated with the material of the shaped body, it is of course also imaginable to configure the boundary surfaces between the optical waveguides and the coating in a manner to provide total reflection. In order to obtain reliable total reflection, it is then necessary to give the optical waveguide a higher refractive index and the plastic material of the surrounding shaped body, which then is optically transparent, a correspondingly lower refractive index.  
         [0024]     There is also the possibility in this case, if necessary, to fill the cavities of the hollow body with fluid in such a way that total reflection will be achieved again at the boundary surfaces to the surrounding shaped body. This may result in improved mechanical damping properties of the support element so produced.  
         [0025]     Further, the shaped body may comprise mounting points for transmitter or receiver elements associated to the optical waveguides, or for switching elements adapted to influence radiation transmitted by the optical waveguides.  
         [0026]     Further, the shaped body may comprise positioning points for LEDs.  
         [0027]     It is thus possible to mount on the support elements not only the optical waveguides but also the associated transmitter or receiver elements, together with the associated switching elements, which generally allows both the structure and the assembly operation to be simplified.  
         [0028]     Moreover, it is preferred to have the shaped body cooperate with the housing of the electric tool for sealing the optical waveguides fitted in the shaped body, and/or the transmitter or receiver elements or switching element coupled with them, so as to protect them from contamination by dust or the like.  
         [0029]     This leads to higher operating safety, the support element serving to shield the optical waveguides from dust or the like. This is of particular importance in connection with tools where high amounts of dust are expected to occur, as is the case for example with grinding tools.  
         [0030]     According to an additional further improvement of the invention, the shaped body consists of a vibration-damping and/or acoustically damping material.  
         [0031]     This also leads to improved operating safety and, in addition, to an ergonomically improved design.  
         [0032]     The shaped body may, for example, be configured as a three-dimensionally shaped plate and may take the form of a compression-molded plastic part or of an injection-molded plastic part.  
         [0033]     This permits low-cost production and adaptation to the most different shapes to be guaranteed.  
         [0034]     The shaped body may additionally comprise recesses and/or projections intended to receive parts of the electric tool or for connection of parts of the electric tool.  
         [0035]     This allows the flat support element to be fitted in the electric tool in a favorable way.  
         [0036]     It is understood that the features of the invention mentioned above and those yet to be explained below can be used not only in the respective combinations indicated, but also in other combinations or in isolation, without leaving the scope of the present invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0037]     Further features and advantages of the invention will be apparent from the description that follows of certain preferred embodiments, with reference to the drawing in which:  
         [0038]      FIG. 1  shows a view, seen obliquely from the top, of an electric tool according to the invention in the form of an angle grinder shown in partly assembled condition and with a rod-shaped housing;  
         [0039]      FIG. 2  shows a side view of the electric tool illustrated in  FIG. 1 ;  
         [0040]      FIG. 3  shows an enlarged representation of the electric tool illustrated in  FIG. 1 , i.e. of the area between the tool head and the stator;  
         [0041]      FIG. 4  shows a view of the support element according to  FIG. 1 ;  
         [0042]      FIG. 5  shows a view of the optical waveguide bundle intended to be inserted into the support element according to  FIG. 4 ; and  
         [0043]      FIG. 6  shows a cross-section through an alternative embodiment of a support element having three optical waveguides in a shaped body applied around them by injection-molding. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0044]      FIG. 1  shows a top view of an electric tool according to the invention indicated generally by reference numeral  10 .  
         [0045]     The tool shown is an angle grinder with a rod-shaped housing which latter is indicated in  FIG. 1  by broken lines only, and is indicated by reference numeral  12 .  
         [0046]     The electric tool  10  comprises an electric motor with a self-supporting stator  18 , whose two ends are provided with a first carrying element  20  and a second carrying element  22 , respectively.  
         [0047]     The two carrying elements  20 ,  22  are screwed together through the stator  18  of the electric tool  16 , to form a strong unit on which further parts of the electric tool are mounted. The first carrying element  20  supports, for example, a tool head  14  with its gearing. And the optical switches  52 ,  73  are likewise mounted on that carrying element. The second carrying element carries further optical switches, one of which is indicated by reference numeral  90 . In addition, the motor shaft with the armature (not shown) is likewise supported on the carrying elements  20 ,  22  or the tool head  14 , respectively. Finally, an electronic control unit (not shown) adapted to control the electric tool  10  is mounted on the second carrying element  22 . The housing  12  of the electric tool is likewise mounted on the two carrying elements  20 ,  22 .  
         [0048]     The switches are configured as optical switches with optical waveguides, between which the transmitted signals can be influenced via controlling elements, the optical waveguides having associated to them transmitter and receiver elements of the kind basically known from German Patent Application 101 41 161.8, which however has not been published yet and the disclosure of which is included herein by reference.  
         [0049]     Mounted on the first carrying element  20 , in opposite arrangement on the upper face of the electric tool  10 , and offset by 180° also on the lower face, are respective brush holders  54  with a brush (carbon brush)  56  received in them, respectively. Pressure is applied on each of the brushes  56  by a brush spring  58 , which is indicated diagrammatically only in  FIG. 3 .  
         [0050]     There can be further seen in  FIGS. 1 and 2  the mounting holes  13  for a clamping lever positioned on the tool head  14  and intended for loading and unloading the tool (for example a grinding wheel). Given the fact that the electric tool  10  should be operated only with the clamping lever in closed condition, the clamping lever cooperates with a sensor which continuously checks that the clamping lever occupies its closed position. The upper end of the tool head  14  is provided for this purpose with a light-optical switch  52  that can be operated via a switching element  53  adapted for being displaced by the clamping lever. In the closed position of the clamping lever, the switching element  53  is displaced with the result that a light beam is released and transmitted via optical waveguides, a circumstance which is evaluated by associated evaluation logics.  
         [0051]     As can be seen in  FIGS. 1 and 2 , there is further provided on the upper surfaces of the first and the second carrying elements a support element  60  on which a plurality of optical waveguides are mounted that are part of the optical switches  52 ,  73 ,  90 .  
         [0052]     In  FIG. 3 , the structure of the optical switches  52 ,  73 ,  90  used in the electric tool  10  can be seen in more detail. Each optical switch comprises two optical waveguides, one of them being configured as a transmitter pipe coupled with an LED, the other one being configured as a receiver pipe connected with an associated evaluation unit. In the illustrated case, every two associated optical waveguides end at a certain distance one from the other, in the form of prisms, so that light can cross over between them. If no object is present between the two prisms light will cross over from the transmitter pipe to the receiver pipe, a circumstance that will be detected by the evaluation logics.  
         [0053]      FIG. 3  now shows a total of six optical waveguides  63 ,  64 ,  66 ,  67 ,  71 ,  72 , each received in recesses  62  configured as groves in a shaped body  61 . The shaped body  61  is part of the support element  60  whose shape can be seen more clearly in  FIG. 4 . The shaped body  61  consists substantially of a plate made from a suitable plastic material, which is suitably curved in the direction of extension of the optical waveguides  63  to  72  received in it. The plastic material of the shaped body  61  preferably has mechanically and, if necessary, acoustically damping properties so that vibration can be damped more efficiently. Given the fact that the optical waveguides  63  to  72  are fitted in associated recesses  62  in the form of grooves, they are especially well protected from external environmental influences so that reliable operation is guaranteed. Moreover, a favorable signal-to-noise ratio is guaranteed, and the path of the optical waveguides is fixed by the spacing defined by the recesses  62 . This can be achieved, preferably, by the use of rigid optical waveguides that are curved three-dimensionally to provide the desired shape.  
         [0054]     In the illustrated case, an oblong recess  65  or  68  or  70 , which extends from the two ends in the area of the prisms toward the outside, is associated to each pair of mutually associated optical waveguides  63 ,  64  or  66 ,  67  or  71 ,  72 . That recess  65 ,  68 ,  70  can be engaged by an associated switching element for interrupting the light crossing over between the two ends.  
         [0055]     In  FIG. 3 , the recess  68  between the two optical waveguides  66 ,  67  cooperates with a slide  55  that can be moved by the switching element  53  into the area between the two prism ends for preventing the light from crossing over. The switch  73 , which cooperates with the two optical waveguides  71 ,  72 , is provided in the area of the recess  70  with a switching element  74  which is pivotally mounted on the first carrying element  20  and which is provided with a switching tongue  76  adapted to be moved into the area of the recess  70  between the two prism ends of the optical waveguides  71 ,  72 .  
         [0056]     The shaped body  61  is further provided with a suitable recess for mounting the brush holder  54  with the brush  56  and the brush spring  58  of the electric motor  16 . A corresponding mounting screw  79  can be seen in  FIG. 3 .  
         [0057]      FIG. 4  shows an overall view of the support element  60  together with the optical waveguides  63  to  72 .  
         [0058]      FIG. 5  illustrates a way of combining the respective optical waveguides  63  to  72 , being preferably rigid and held together by a common support  86 , to a pre-fabricated optical waveguide bundle  84 . The support comprises recesses for connection of LEDs for associated transmitter diodes, and connections for receiver elements. In  FIG. 5 , a single LED  87  is indicated by way of example.  
         [0059]      FIGS. 1 and 2  further illustrate the way in which the support element  60 , with the optical waveguides received in it, has been placed on the upper face of the two carrying elements  20 ,  22  and has been inserted directly adjacent the tool head  14 . When the housing is then fitted, it preferably assumes a sealing relationship relative to the edges of the support element  60 . Thus, the support element  60  occupies a position adjacent the fitted housing, with the optical waveguides received in it safely protected from dirt or the like that may penetrate into the housing.  
         [0060]     There can be further seen in  FIG. 2  the slightly angled shape of the support element  60  in the area of the support  86  on which the transmitter LEDs and the receiver elements are arranged. There can be further seen in  FIG. 2  the switching elements  74  and  91 , which cooperate with the switches  73  and  90 , for interrupting the transmission of light between associated optical waveguides.  
         [0061]     An alternative embodiment of the support element according to the invention is illustrated in  FIG. 6 , and is indicated generally by reference numeral  100 .  
         [0062]     Three optical waveguides  102 , made from a plastic material, are fully enclosed in this case by a plastic shaped body  101 . This can be effected, for example, by coating the optical waveguides with plastic material in a suitable injection mold. The optical waveguides as such may be provided in this case with a suitable sheathing to guarantee light-piping by total reflection. However, it is likewise imaginable to ensure total reflection by a corresponding configuration of the boundary surfaces  103  between the optical waveguides and the surrounding plastic material of the shaped body  101 . In the latter case, the shaped body  101  consists of a suitable transparent plastic material of lower optical density (a lower refractive index) than the embedded optical waveguides  102  so that reliable total reflection is obtained.  
         [0063]     It is understood that instead of proceeding in the way described above, it is of course also possible to coat glass optical waveguides or plastic optical waveguides, which as such are sheathed in a suitable way, with a plastic material in the conventional way. The shaped body may then be made from a considerably softer material with clearly approved mechanical and acoustic damping properties. This in turn may result in improved vibration damping and noise damping and may guarantee especially reliable long-time operation.