Abstract:
A machine tool with a generator for generating electrical power is disclosed. The generator has a rotor and a stator. A coil and a magnet are arranged on the stator. The rotor is capable of moving relative to the stator and has a first region and a second region. The rotor is configured in such a way that, during a movement of the rotor relative to the stator, a magnetic flux in the coil is changed due to differences between the first and second regions in terms of their magnetic permeability and/or in terms of their geometric configuration, and an electrical voltage is induced.

Description:
This application claims priority under 35 U.S.C. §119 to German patent application no. 10 2010 002 182.2, filed Feb. 22, 2010, the disclosure of which is incorporated herein by reference in its entirety. 
     Cross Reference is made to copending U.S. patent application Ser. No. 13/031,483, entitled “Machine Tool with an Active Electrical Generator for Power Generation,” filed on Feb. 21, 2011. 
     The present disclosure relates to a machine tool with an electrical generator for passive power generation. 
     BACKGROUND 
     When working with electric tools, auxiliary means are often required for optimizing the performance of work. For example, illumination of the working area by means of light-emitting means may be useful. 
     DE 10 2006 045 157 A1, for example, has disclosed tools in which the light-emitting means are integrated in the tool. However, the supply of energy to the light-emitting means can pose a problem. 
     SUMMARY 
     An object of the present disclosure can therefore be considered that of providing an improved machine tool which enables a supply of energy to additional elements. 
     This object can be achieved by the subject matter of the present disclosure. Advantageous embodiments of the present disclosure are described herein. 
     Features, details and possible advantages of an apparatus in accordance with the embodiments of the disclosure will be discussed in detail below. 
     In accordance with a first aspect of the present disclosure, a machine tool, such as a handheld machine tool, for example, with a generator which generates electrical energy or power is described. The generator has a stator and a rotor which is capable of moving in relation thereto. At least one coil, for example an induction coil, and at least one magnet, for example a permanent magnet or an electromagnet, are arranged on the stator. The rotor has at least one first and at least one second region. The first region has a first magnetic permeability and a first geometric configuration. The second region has a second magnetic permeability and a second geometric configuration. The first permeability and the second permeability are in this case different and/or the first geometric configuration and the second geometric configuration are different. Depending on whether the first or second region of the rotor is located closer to the stator, the magnetic lines of force emanating from the magnet can propagate differently. During a movement of the rotor relative to the stator, the position of the first and second regions of the rotor with respect to the stator changes continuously. As a result, the magnetic flux changes and a voltage in the coil of the stator is induced. 
     The first and second regions of the rotor can be configured, for example, as a profile in the rotor. That is to say that the first region can correspond to elevations and the second region can correspond to cutouts in the rotor. Optionally, different materials, in particular with different magnetic permeability, can be used for the different regions. 
     With the aid of the generator according to the disclosure, it is possible to provide voltage or electrical energy for machine tool-internal components, such as light sources for illuminating the working area, for example. This electrical energy is advantageously independent of a mains or battery voltage of the machine tool. Therefore, no additional elements for rectification and transformation of the mains current need to be installed in the machine tool. This may be advantageous in particular in the case of handheld machine tools since a weight saving can also be made. In addition, the electrical circuit of the generator according to the disclosure can be designed for operation on a low voltage (for example less than 50 V) and is therefore not subject to the requirements for mains-operated machines, such as the maintenance of insulation gaps, for example. This provides greater freedom in terms of the structural design of the machine tool. 
     In addition, the generator according to the disclosure is preferably designed without any movable magnets. During operation of the machine tool, only the rotor moves, while both the coil and the magnet are arranged immovably on the stator. This makes it possible for already existing machine tools to be subsequently modified in a simple manner. In addition, this enables simple, space-saving and inexpensive implementation of an energy source for machine-internal components of newly produced machine tools, such as light sources, for example. 
     In accordance with one exemplary embodiment of the disclosure, the stator and the rotor comprise ferromagnetic materials. That is to say the relative permeability μ of the materials is equal to, greater than or preferably substantially greater than 1 (μ&gt;&gt;1). Such materials can be, for example, steel, iron, cobalt, nickel and combinations thereof. The stator and the rotor can for the most part or completely consist of these materials. 
     In accordance with one exemplary embodiment, the rotor can be coupled to the output drive, for example to an output shaft, of the machine tool mechanically in a force-fitting, form-fitting and/or frictionally engaged manner or can be formed as part of the output drive or integrated therein. This can take place, for example, by the change of existing parts of the output drive and can thus be implemented in a cost-saving manner. The rotor can also be connected to the output drive cohesively, such as by means of an adhesive, for example. The output drive can be part of the machine which outputs power and can be, for example, a spindle, a ring gear, an accommodating flange or a tool receptacle, a motor shaft or the protrusion thereof. 
     In accordance with a further exemplary embodiment, the generator can have a second circuit which is electrically isolated from or independent of the first circuit of the machine. The first circuit is connected, for example, to a mains supply or a rechargeable battery supply. The second circuit can generate a voltage which is different from the first circuit by the operation of the generator. As a result, for example, a machine-internal light source, for example, can be supplied with energy without a mains voltage needing to be transformed and rectified. It is thus possible to dispense with additional components and therefore to save installation space and considerable additional costs. 
     In accordance with further exemplary embodiments, the machine tool can have one or more light sources. The light source is supplied with energy by the generator according to the disclosure and is connected thereto, for example directly or via an electrical transducer. In addition, the light source can be integrated directly into the machine or arranged thereon and can be a light source which enables possibly continuous illumination of a working area during operation of the machine. An additional light source can output a light signal, for example by means of changing color or by means of a change in intensity and therefore indicate a present rotation speed of the rotor. For example, the signal can be a blinking signal. It is thus possible to signal that specific rotation speeds are being passed through, exceeded and/or undershot, for example in the event of an overload, and an overtravel of the rotor or the motor even once the machine has been disconnected. In addition, for example, an additional light source can be configured as a laser light source for labeling the working area and guiding the machine. 
     In accordance with a further exemplary embodiment, the machine tool has an electrical energy store, such as a capacitor and/or a rechargeable battery, for example. By virtue of the electrical energy store, it is possible, for example, for the persistence time and intensity of the light source to be improved. The electrical energy store can be integrated, for example, in electronics of the machine. In the electronics, the electrical voltage generated can be matched to the requirements of the light source. 
     In accordance with a further exemplary embodiment, the coil or a plurality of coils of the stator is or are arranged at or on a yoke which intensifies the magnetic flux. The yoke can connect the magnet(s) to one another and/or to the coil(s). The yoke can have a higher magnetic permeability than the material of the stator housing, for example, and can contribute to targeted guidance of the magnetic lines of force and intensify the magnetic flux. Owing to this intensification of the flux, a sufficient voltage, for example for operation of light sources, can also be generated at low operating speeds. 
     In accordance with a further exemplary embodiment, the rotor can perform a rotary or linearly oscillating movement. The machine tool can therefore be configured as, for example, an angle grinder or straight grinder, screwdriver, drill, circular saw or in the form of a saw, for example a jigsaw, a saber saw, a crosscut saw or precision saw. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features and advantages of the present disclosure will become apparent to a person skilled in the art from the description below relating to exemplary embodiments, which should not, however, be interpreted as being restrictive to the disclosure, with reference to the attached drawings. 
         FIG. 1  shows a cross section through an angle grinder; 
         FIGS. 2A ,  2 B show, schematically, the mode of operation of the generator of the machine tool; 
         FIGS. 3A ,  3 B,  3 C,  3 D show a generator with an accommodating flange as rotor; 
         FIGS. 4A ,  4 B,  4 C show possible embodiments of the stator from  FIGS. 3A-3D ; 
         FIGS. 5A ,  5 B show a generator with a ring gear as rotor; 
         FIGS. 6A ,  6 B show possible configurations of the rotor; 
         FIGS. 7A ,  7 B,  7 C show a configuration of the stator with magnet coils; 
         FIG. 8  shows a cross section through a jigsaw; 
         FIGS. 9A ,  9 B,  9 C show a generator with a linearly oscillating rotor; and 
         FIGS. 10A ,  10 B,  10 C,  10 D,  10 E show an alternative embodiment of the generator from  FIG. 9 . 
     
    
    
     All of the figures are merely schematic illustrations of devices according to the disclosure or parts thereof. In particular, distances and size relationships have not been reproduced true to scale in the figures. Corresponding elements have been provided with the same reference numerals in the various figures. 
     DETAILED DESCRIPTION 
       FIGS. 1 to 7  illustrate the machine tool with a rotating rotor using the exemplary embodiment of an angle grinder, and  FIGS. 8 to 10  illustrate the machine tool with a linearly oscillating rotor using the example of a jigsaw. 
       FIG. 1  shows a schematic illustration of a cross section through an angle grinder  1 . The angle grinder  1  has the conventional components such as motor housing  25 , motor  27 , fan  29 , pinion  31 , gear housing  33 , protective cover  35 , two-hole nut  37 , spindle  39 , ring gear  41 , bearing flange  43  and accommodating flange  47 . A light source  15  can illuminate a working region  45  or the working area  45 . The light source  15  can be integrated, for example, in the bearing flange  43 . In the case of the angle grinder  1 , the ring gear  41 , the accommodating flange  47  or the spindle  39  can be used as the rotor  7 . 
       FIGS. 2A and 2B  represent the mode of operation of the generator  3  of the machine tool  1 . In this case,  FIGS. 2A and 2B  show cross sections through the generator  3  in different movement phases of the rotor  7 . A coil  11  and two magnets  13  with different polarity are arranged on the stator  5 . The magnets  13  and the coil  11  are arranged on a yoke  23  for intensifying the magnetic flux. 
     Owing to the movement  63  (indicated by the arrow) of the rotor  7  with respect to the stator  5 , the magnetic field in which the coil  11  is located changes. As a result, a voltage is induced in the coil  11 , it being possible for the voltage to be passed on to a light source  15 , for example via the electronics  21 , which can comprise an electrical energy store  19 . A change in the magnetic field can be achieved, for example, by the change in the resistance (also referred to as reluctance) of the magnetic circuit. 
     In  FIG. 2A , a first region  51  of the rotor  7  is located opposite the coil  11  of the stator  5 . Second regions  53  of the rotor  7  are located opposite the magnets  13  of the stator  5 . In the exemplary embodiment, the first region  51  and the second region  53  have different geometric configurations. The first region  51  has an elevation in the direction of the stator  5 . The second region  53 , on the other hand, is set back with respect to the stator  5  in comparison with the first region  51 , with the result that the air gap  9  between the stator  5  and the rotor  7  in the second region  53  is greater than in the first region  51 . 
     During a movement  63  of the rotor  7 , the magnetic flux emanating from the permanent magnet  13  changes. The magnetic lines of force  17  therefore change as illustrated in  FIG. 2  and a voltage  11  is induced in the coil. 
     The regions  51 ,  53  of the rotor  7  can comprise different materials with different magnetic permeability given the same or different geometric configuration. In this case, the rotor  7  can be realized by virtue of changes to existing parts of the output drive  49  of the machine tool  1 . For example, the rotor  7  can be provided with grooves. During a movement of the rotor  7 , the reluctance changes as follows: in a position of the grooves  51  with respect to the magnets  13 , a high reluctance is brought about by the large air gap  9 ; in a position of webs  51  with respect to the magnets, a low reluctance is brought about. 
       FIGS. 3A ,  3 B,  3 C,  3 D illustrate a generator  3  with an accommodating flange  47  as the rotor  7 .  FIGS. 3A and 3B  show different perspectives of the generator  3 .  FIGS. 3C and 3D  illustrate cross sections through the generator  3 . Webs  51  and grooves  53  are arranged in the accommodating flange  47 . When the magnets  13  are positioned with respect to webs  51  of the flange  47 , the magnetic flux can develop both tangentially ( FIG. 3C ) and radially ( FIG. 3D ) thanks to the low reluctance. This is indicated by the magnetic lines of force  17  in  FIGS. 3C and 3D . 
     As shown in  FIG. 3B , additional grooves  55  can be arranged, for example, on that side of the flange  47  which faces the spindle  39 . As a result, the fluctuation in the magnetic flux can be increased in the different positions of the rotor  7 . As a result, higher voltages can be induced in the coil  11  of the stator  5 . In this case, the stator can be integrated in the bearing flange  43 . 
       FIGS. 4A ,  4 B,  4 C illustrate possible embodiments of the stator shown in  FIGS. 3A-3D . As is shown in  FIG. 4A , the stator  5  can be in the form of a ring and have a plurality of magnets  13  and coils  11  connected by a yoke  23 . Alternatively, for example if there is not sufficient installation space or the induced voltage is sufficient, the stator  5  can consist of a yoke section and a coil  11 , as shown in  FIGS. 4B and 4C . In this case, the yoke  23  can consist of solid material or of strips of sheet metal. An embodiment of the stator with only one magnet  13  is also possible. This is shown in  FIG. 4C . 
       FIGS. 5A and 5B  illustrate different perspectives of a generator  3  with a ring gear  41  as the rotor  7 . The lower side of the ring gear can be provided with teeth in order to realize the different regions  51 ,  53  of the rotor  7 . 
       FIGS. 6A ,  6 B illustrate possible configurations of the rotor  7 .  FIG. 6A  shows an intensifying yoke  50  with a high relative permeability in comparison with the materials of the rotor. The intensifying yoke  50  can reduce the reluctance. When seen individually, it can be used as the rotor  7 , as shown in  FIG. 6A . Alternatively, the intensifying yoke  50  can be integrated in other parts of the output drive  49  such as the ring gear  41  or the accommodating flange  47 , as shown in  FIG. 6B , and make the desired reluctance profile possible. In addition, it is possible to integrate the desired material properties directly in the parts of the output drive  49 . For example, this can be performed by the simultaneous or successive processing of a plurality of materials during the production of the components in a sintering process. 
       FIGS. 7A ,  7 B,  7 C illustrate the configuration of the stator  5  with magnet coils  57 .  FIG. 7A  shows a magnet coil  57  with a permanent magnet  13  and a coil  11  wound around the core  59 . As is shown in cross section through the generator  3  in  FIG. 7C , the magnet coil  57  is aligned axially and perpendicular to the ring gear  41  and the accommodating flange  47 , respectively. The magnetic lines of force  17  are closed via the rotor  7  (in this case: ring gear  41 ) and the core  59  of the magnet coil  57 . 
     As is shown in  FIG. 7B , the magnet coils  57  can be integrated in the bearing flange  43 . The magnet coils  57  can also be integrated in an additional element, such as the magnet coil former  61 . The coils  11  or the magnet coils  57  can be connected in series, for example, in such a way that the output power is maximized. The number and position of the magnet coils  57  can be selected differently. For example, they can be arranged rotationally symmetrically. 
       FIG. 8  shows a schematic illustration of a cross section through a machine tool  1 , in the form of a jigsaw. The jigsaw  1  has a lifting rod  65 , which can move linearly up and down. The stator  5  is arranged around the lifting rod  65 . The light source  15  illuminates a working area  45  during operation of the rotor  7 . The lifting rod  65  and the saw blade  67  arranged thereon perform a linearly oscillating movement  63  (indicated by an arrow). 
       FIGS. 9A ,  9 B,  9 C illustrate embodiments of the generator  3  with a linearly oscillating rotor  7 .  FIG. 9A  shows a plan view of the generator  3 .  FIGS. 9B and 9C  show the generator  3  in cross section in different positions of the rotor  7 . The stator  5  with the coil  11  and the magnet  13  surrounds the lifting rod  65  in the form of a ring. In addition, a magnetic return disk  69  with a relative magnetic permeability which is preferably high is arranged on the stator. The rotor  7  consists of the lifting rod  65  and a magnetic return yoke  71 , which is in the form of a disk and is moved along with the lifting rod  65 . The magnetic return yoke  71  remains below the stator  5  in the exemplary embodiment shown in  FIG. 9 . 
     In  FIG. 9B , the rotor  7  is located in a lower position, with the result that the magnetic return yoke  71  of the rotor  7  is so far removed from the stator  5  that the magnetic lines of force  17  (indicated by dashed lines) do not pass through the yoke  71  and are relatively weak. In  FIG. 9C , the rotor  7  is in an upper position, with the result that the magnetic lines of force  17  run via the magnetic return yoke  71  of the rotor  7  and the magnetic lines of force  17  are more pronounced. In this case, the magnetic return yoke  71  can be considered to be a first region  51  of the rotor  7  with a high permeability. The remaining regions of the lifting rod  65  can be considered to be a second region  53  with a low permeability. 
       FIGS. 10A ,  10 B,  10 C,  10 D,  10 E illustrate alternative embodiments of the generator  3  shown in  FIGS. 9A ,  9 B,  9 C.  FIG. 10A  shows a plan view of the generator  3 .  FIG. 10B  illustrates an enlarged detail of  FIG. 10A ;  FIGS. 10C ,  10 D and  10 E illustrate cross sections of the generator in different movement phases of the rotor  7 . The stator  5  in  FIGS. 10A-10E  is formed with one magnetic return disk  69  above the magnet  13  and one below the magnet. The rotor  7  with the magnetic return yoke  71  can move completely through the stator  5  in the exemplary embodiment in  FIGS. 10A-10E . In comparison with the exemplary embodiment in  FIG. 9 , this has the advantage that a movement of the lifting rod  59  is not impaired and that higher voltages can be induced in the coil  11 , as a result of a higher possible frequency of the fluctuation of the magnetic lines of force  17 . As is shown in  FIGS. 10A-10E , a cylindrical configuration of the components of the rotor  7  and the stator  5  can be advantageous. 
     By virtue of the magnetic return yoke  71 , it is possible to realize the regions  51 ,  53  of different geometric configuration or different magnetic permeability on the rotor  7 . The magnetic return yoke  71  can consist of a material with a high magnetic permeability. In addition, the magnetic return yoke  71  can be realized as part of the lifting rod  59 . By virtue of the movement  63  of the alternately tapered magnetic return yoke  71 , the reluctance of the magnetic circuit changes. As a result, the magnetic flux varies and a voltage is induced in the coil  11 . The rotor  7  can be considered to be a “magnetic valve”, which can inhibit the development paths of the magnetic flux in the manner of a bar. 
     By way of conclusion it should be noted that expressions such as “having” or the like are not intended to rule out the possibility of further elements or steps being provided. Furthermore, the use of “one” or “a” is not intended to rule out a greater number. In addition, features described in connection with the various embodiments can be combined with one another as desired.