Abstract:
The invention relates to an electrical machine tool, particularly a hand machine tool, having a contrast detection device, an analysis unit, and at least one sensor provided for capturing a surface of a work piece. According to the invention, the analysis unit is provided for detecting a differentiation of the surface from an at least partially automatic guide using data captured by a sensor.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a 35 USC 371 application of PCT/EP2009/054755 filed on Apr. 21, 2009. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     An electric power tool with a device for detecting a surface of a work piece is already known. 
     The invention relates to an electrical machine tool, particularly a hand machine tool. 
     DESCRIPTION OF THE PRIOR ART 
     Advantages and Summary of the Invention 
     The present invention proposes an electric power tool, in particular a hand-held power tool, equipped with a contrast detection device that has an evaluation unit and at least one sensing device that is provided for detecting a surface, in particular of a work piece; the evaluation unit is provided to detect a differentiation of the surface based on data detected by the sensing means for an at least partially automatic guidance. In this context, “provided” should be understood to mean specially designed and/or specially embodied and/or specially programmed. In addition, an “evaluation unit” should in particular be understood to be a unit that can be composed of a control unit, a processing unit, a control device, and/or a regulating unit; the evaluation unit can be composed of a processor and/or a microcontroller alone and can also be composed of a processor and/or a microcontroller as well as other electronic components such as a storage means. In addition, a “differentiation of a surface” should in particular be understood to be a distinguishing between at least two regions of the surface based on a contrast and/or a wavelength difference so as to recognize light and dark regions or different-colored regions of the surface. In this context, a “contrast” should in particular be understood to be a distinguishing feature for a brightness gradient and/or color gradient of an image or between two pixels, in particular image signals or pixels of the image detected by the sensing device; preferably, the contrast or a difference in the brightness gradient can be detected for the evaluation unit. The embodiment according to the invention can be advantageously used to detect a line provided on a surface of a work piece to be machined—preferably a line that is of a different color than the surface such as a light or white line on a dark or black surface, etc.—through differentiation of the surface of the work piece. In addition, this can be used in a particularly advantageous fashion to achieve an at least partially automatic line tracking of the electric power tool, namely in that the electric power tool, preferably controlled by a guide unit, automatically follows a curve of the line detected by the contrast detection device. 
     The electric power tool with the contrast detection device can basically be embodied in the form of any electric power tool deemed suitable by the person skilled in the art, in which an at least partial contrast detection of a work piece surface and/or an at least partially automatic tracking of a line is advantageous. It is particularly advantageous, though, for the electric power tool to be a hand-held power tool—in particular a hand-held power tool provided for sawing and/or cutting and/or grinding such as a jigsaw, a hand-held circular saw, etc.—in which it is desirable for the hand-held power tool to be guided along a line, in particular along a line provided on a surface of the work piece. 
     According to another proposal, the contrast detection device for a contrast measurement is provided before at least one operating mode of a motor and/or tool. In this context, “before” should in particular be understood to mean that particularly in an individual work procedure, a first action, in particular a contrast measurement, occurs chronologically before a second action, in particular an operating mode of the motor and/or tool. Preferably, in at least one sequence, a successful contrast measurement can be a requirement for an operating mode of the motor and/or tool, i.e. in particular, only after a successful contrast measurement can the motor be started and/or a machining procedure of the work piece with the tool be carried out. A contrast measurement can advantageously take place before the start of work with the electrical appliance and it is possible to effectively measure a contrast while avoiding interference influences such as work remnants and/or dust, and thus to advantageously prevent undesirable malfunctions in the contrast measurement, for example during a work procedure. 
     According to another proposal, the contrast detection device has at least one illumination device provided for illuminating a measurement region. The illumination device here can enhance a differentiation of the surface or augment a contrast of a line, thus facilitating a contrast detection in the contrast detection unit and in the evaluation unit. This also makes it possible to advantageously minimize undesirable external influences, e.g. a disadvantageous casting of shadow by external lighting, during the contrast measurement. The illumination device is preferably embodied in the form of a spectral illumination device such as an infrared light emitting diode and/or another illumination means deemed suitable by the person skilled in the art. 
     A structurally simple, particularly cost-saving contrast measurement can be achieved if the sensing device is at least partially composed of a camera. A “camera” should in particular be understood here to be a sensing device that is provided for sensing or detecting static and/or moving images, in particular of the surface of the work piece. Basically, however, it is also possible for the sensing device to be composed of another device that the person skilled in the art deems suitable for performing a contrast measurement. 
     A structurally simple, particularly cost-saving contrast measurement can be achieved if the sensing means is at least partially composed of a camera. A “camera” should in particular be understood here to be a sensing means that is provided for sensing or detecting static and/or moving images, in particular of the surface of the work piece. Basically, however, it is also possible for the sensing means to be composed of another means that the person skilled in the art deems suitable for performing a contrast measurement. 
     According to another proposal, the contrast detection device has at least one filter element for selecting at least one measurement signal, thus making it possible in particular for a sensitivity to a measurement signal for the contrast measurement to be limited to a specified spectral range. In addition, this can advantageously separate the measurement signal out from undesired interference signals. In this context, a “filter element” should in particular be understood to be an optical filter element that is preferably permeable only for a limited spectral range. 
     According to another proposal, the evaluation unit has at least one differentiation device for detecting a contrast, by means of which a contrast change in the sensed surface can be detected or ascertained in a particularly simple way, structurally, namely in that the differentiation device differentiates the sensed measurement signal by producing a differential quotient, thus making it possible to detect changes in the signal waveform in a particularly simple and reliable way. In this context, a “differentiation device” should in particular be understood to be an electronic, preferably analog, component in which an input signal is converted through differentiation, in particular in order to detect fluctuations and/or changes in the input signal or contrast signal as a function of a differentiation parameter. The differentiation device here can be composed of an operational amplifier, an analog processor of a microcontroller, and/or other analog components and/or software program components deemed suitable by the person skilled in the art. 
     According to another proposal, the contrast detection device has at least one adjusting device that is provided for an adjustment to a threshold value for at least one contrast parameter. This makes it advantageously possible to adapt a contrast detection to a color gradient and/or brightness gradient of the surface. The adjusting means in this case can be composed of a manual adjusting device for a manual adjustment of the threshold value by the operator and/or composed of an adjusting device for an at least partially automatic adjustment, preferably controlled by the evaluation unit. The adjusting device in this case can be composed of a digital/analog converter and/or other components deemed suitable by the person skilled in the art. 
     In another proposed embodiment of the invention, a contrast detection device for an electric power tool, in particular a hand-held power tool, is equipped with a contrast detection device that is provided to carry out a contrast measurement for an at least partially automatic guidance of the electric power tool; in at least one contrast detection mode, a contrast measurement of a surface of a work piece is carried out. This can be a detection of a line provided on a surface of a work piece to be machined—for example a light or white line on a dark or black surface, etc.—in the contrast detection mode of the contrast detection device. A “contrast detection mode” should in particular be understood here to be an operating mode of the contrast detection device for carrying out a contrast measurement. 
     In a particularly advantageous embodiment, in the contrast detection procedure, the contrast detection mode of the contrast detection device takes place before at least one operating mode of a motor and/or tool of the electric power tool. It is thus advantageously possible to carry out a contrast measurement before beginning work with the electrical appliance and to effectively measure a contrast while avoiding interference influences such as work remnants and/or dust. 
     According to another proposal, an illumination parameter, in particular a spectral illumination parameter, is adjusted in the contrast detection mode, making it possible to augment a contrast of a line, thus facilitating a contrast measurement or contrast detection. It is also possible to advantageously minimize undesirable external influences, e.g. a disadvantageous casting of shadow by external lighting, during the contrast measurement. 
     According to another proposal, at least one contrast parameter is determined by producing a differential quotient of at least one sensed measurement signal, making it possible in a particularly simple way, structurally, to detect or ascertain a contrast change in the sensed surface in that the differentiation device differentiates the sensed measurement signal by producing a differential quotient, thus making it possible to detect changes in the signal waveform in a particularly simple and reliable way. In this connection, a “contrast parameter” should in particular be understood to be a parameter that reproduces a contrast gradient or a change in the brightness gradient of an image. 
     An advantageous contrast detection that is adapted to a color gradient and/or brightness gradient of the surface can be achieved by adjusting a threshold value for a contrast measurement. 
     In a particularly advantageous fashion, in at least one contrast detection mode, the curve of a line on the surface of a work piece is detected for an at least partially automatic guidance of the electric power tool, in particular making it possible to achieve an at least partially automatic guidance of the electric power tool and thus a high degree of operating convenience for an operator. 
     According to another proposal, a contrast parameter of the contrast measurement is used to adjust the sensing device, in particular the camera, making it possible to achieve an advantageous adaptation and/or adjustment of the sensing device, in particular for adapting and/or adjusting a sensor parameter, in order to detect the contrast before and/or during a contrast measurement. Preferably, the adaptation and/or adjustment of the sensor parameter of the sensing device adjusts and/or adapts in particular an amplification factor such as a gain factor and/or white balance of the sensing device. In a particularly advantageous fashion, the adaptation and/or adjustment of the sensing device occurs in an automated fashion, preferably controlled by the evaluation unit. 
     According to another proposal, at least one information parameter of the contrast measurement is output to an operator. In this context, an “information parameter” should in particular be understood to be a parameter that contains information, in particular a current status, about a contrast operating mode and/or a contrast measurement of the contrast detection device. For this purpose, the contrast detection device or the electric power tool is advantageously equipped with an output unit for outputting the information parameter. This embodiment permits an operator to advantageously access a current status of a contrast measurement. Moreover, if the contrast ratios are insufficient for a differentiation of the surface of the work piece to be machined, the operator of the electrical appliance can be informed of this before starting work. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages ensue from the following description of the drawings. The drawings show an exemplary embodiment of the invention. The drawings, the description, and the claims contain numerous features in combination. The person skilled in the art will also suitably consider the features individually and unite them in other meaningful combinations. 
         FIG. 1  is a schematic view of an electric power tool that is embodied in the form of a jigsaw and equipped with a contrast detection device, 
         FIG. 2  is a schematic depiction of the contrast detection device, 
         FIG. 3  is a schematic depiction of a process sequence of a contrast measurement, 
         FIG. 4  is a partial view of a subregion of a surface of the work piece provided for a contrast measurement, 
         FIG. 5  shows a measurement signal detected by a sensor unit of the contrast detection device, and 
         FIG. 6  shows a signal that a differentiation means has converted in order to determine a contrast. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       FIG. 1  shows an electric power tool  10  according to the invention, depicted in the form of a hand-held power tool  12 . The hand-held power tool  12  is embodied in the form of a jigsaw. Basically, the hand-held power tool  12  could also be embodied in the form of another hand-held power tool  12  or electric power tool  10  deemed suitable by the person skilled in the art, such as a hand-held circular saw, etc. The hand-held power tool  12  has a housing  36  with a handle region  38  and a switch element  40  for switching the hand-held power tool  12  on and off. The housing  36  of the hand-held power tool  12  contains a motor unit  42  that drives a tool  44  via a motor shaft, not shown in detail, and a transmission, not shown in detail. The hand-held power tool  12  also has a contrast detection device  14  with an evaluation unit  16  and a sensing means  18 , which is provided to detect a surface  20  of a work piece  22  to be machined. The evaluation unit  16  in this case is provided to detect a differentiation of the surface  20  in the form of a contrast and/or a wavelength difference based on data detected by the sensing means  18  for an at least partially automatic guidance of the hand-held power tool  12 . In this case, a contrast measurement of the surface  20  of the work piece  22  is carried out in at least one contrast detection mode KM 1 . 
       FIG. 2  is a schematic depiction of the contrast detection device  14 . In addition to the evaluation unit  16  and the sensing means  18  embodied in the form of a camera  28 , the contrast detection device  14  also has an illumination means  24  and a filter element  30 . The illumination means  24  is provided for illuminating a measurement region  26  in a contrast detection mode and the filter element  30  is provided for selecting a measurement signal. To this end, the filter element  30  is situated in front of the sensing means  18  along a signal path leading into the sensing means  18 . In addition, the contrast detection device  14  contains a differentiation means  32 , which is for detecting a contrast and is contained in the evaluation unit  16 , and a microcontroller  46  and contained in the evaluation unit  16 . To detect the surface  20  of the work piece  22 , in the contrast detection device  14 , a contrast measurement of an initial contrast detection mode KM 1  is performed before an operating mode B 1 , B 2  of an initial operation of the motor unit  42  and/or the tool  44  of the hand-held power tool  12  ( FIG. 3 ) so that before work begins, a contrast measurement can be carried out to detect a guide line  48  provided on the surface  20 . 
     In this case, after a switching-on procedure E of the hand-held power tool  12 , a contrast measurement takes place in the first contrast detection mode KM 1  in that the sensing means  18 , activated by the evaluation unit  16 , senses the surface  20  of the work piece  22  or the measurement region  26  of its surface  20  ( FIGS. 1 and 4 ). Then the sensed data are analyzed in the evaluation unit  16 . The data sensed by the sensing means  18  are conveyed via an internal data line, not shown in detail, to the evaluation unit  16  and are processed there by the differentiation means  32 . In the differentiation means  32 , a measurement signal  50  of the sensing means  18  is used to produce a differential quotient. Then the measurement signal  50  of the differentiation means  32  is evaluated in the microcontroller  46 . 
     In order to achieve an effective contrast measurement, the illumination means  24 , which is embodied in the form of a spectral illumination means and is controlled by the evaluation unit  16 , illuminates the measurement region  26  of the surface  20  of the work piece  22 , thus increasing the contrast sharpness of the surface  20  or the contrast sharpness of the guide line  48  provided on the surface  20  in relation to the surface  20 . The illumination means  24  is embodied in the form of an infrared light emitting diode. The evaluation unit  16  controls the illumination of the measurement region  26  by the illumination means  24 . In so doing, the evaluation unit  16  adapts an illumination parameter of the illumination means  24  to a contrast gradient or brightness gradient of the measurement region  26  of the surface  20  detected by means of the sensing means  18  and the differentiation means  32 . Also controlled by the evaluation unit  16 , a contrast parameter determined during the contrast measurement is used to adjust the sensor unit, in particular to adjust a sensor parameter such as an amplification factor and/or white balance, thus adapting the sensed measurement signal  50  of the sensing means  18  or the camera  28  to a contrast gradient of the measurement region  26 . 
     If a contrast detection by means of the contrast detection device  14  is unsuccessful, then the operator of the hand-held power tool  12  is provided with a first output A 1  of an information parameter and the operator can start a normal operating mode B 1  of the hand-held power tool  12  with a manual guidance. If a contrast detection by means of the contrast detection device  14  is successful, then the operator is notified of this by means of an output A 2  of an information parameter, also enabling an operating mode B 2  of the hand-held power tool  12  with a guidance mode F that provides an at least partially automatic guidance along the guide line  48 . The successful contrast measurement is a requirement for the guidance mode F. Furthermore, at the same time as the operating mode B 2  of the hand-held power tool  12 , a second contrast detection mode KM 2  carries out a continuous detection of the guide line  48 . 
     The hand-held power tool  12  is equipped with an output unit  72  for outputting the information parameter of the contrast measurement. The output unit  72  includes an optical output means and an acoustic output means; the optical output means can output a guide line  48 , which is detected by the contrast detection device  14 , for the operator of the hand-held power tool  12  and the acoustic output means can output an error message if necessary. This is particularly important for the case in which the detection of the guide line  48  provided on the surface  20  is unsuccessful due to the presence of foreign matter and/or other interfering external influences, permitting this to be communicated to an operator before the work begins. 
       FIG. 5  depicts a sensed measurement signal  50  of the sensing means  18  embodied in the form of a video camera. In this case, a first downward-sloped signal region  54  is composed of a start signal for the differentiation means  32 . The start signal is produced by a separate component that is not shown in detail. Different regions  60 ,  62 ,  64  with different brightness stages in the measurement region  26  on the surface  20  of the work piece  22  are described by different signal levels in the measurement signal  50  of the video camera. In the signal waveform shown in  FIG. 5 , a first region  60  with a light surface  20  of the work piece  22  from  FIG. 4  is described by a high level  56  in the measurement signal  50 . A second, dark region  62  composed of the provided guide line  48  (depicted with cross-hatching in  FIG. 4 ) is described by a low level  58  in the measurement signal  50 . A subsequent third, light region  64  of the surface  20  is once again described by a high level  56  in the measurement signal  50  of the video camera, analogous to the one from the first region  60 . The measurement signal  50  of the video camera is supplied to the evaluation unit  16  and differentiated by the differentiation means  32 , thus yielding a differential quotient of the measurement signal  50 . 
       FIG. 6  depicts a differentiated signal  52  of the differentiation means  32  or an output signal of the differentiation means  32 . A change in the measurement signal  50  of the video camera results in a jump  66  in the curve of the differential quotient or of the differentiated signal  52 ; this jump  66  is due to an abrupt transition from the light region  60 ,  64  to the adjacent dark or black region  62  ( FIG. 4 ). The curve of the signal  52  in the region of the jump  66  is produced by an unsteady function. A value of the differential quotient of the differentiated signal  52  is constituted by a contrast parameter. 
     An evaluation of the differentiated data from the differentiation means  32  is performed in the microcontroller  46  of the evaluation unit  16 . To detect a clear contrast within the evaluation unit  16 , a value of the differential quotient or of the contrast parameter must lie above an established threshold value  68 . The contrast detection device  14  also has an adjusting means  70  that is provided for adjusting a threshold value  68  for at least one contrast parameter. The adjusting means  70  is contained in the evaluation unit  16 . In addition, the adjusting means  70  is composed of an adjusting means  70  provided for a manual adjustment so that an operator can carry out an adaptation of the contrast detection during operation of the hand-held power tool  12 . In another embodiment of the invention, it is essentially possible at any time for the adjusting means  70  to be controlled automatically by the evaluation unit  16 . In this case, in the event of insufficient contrast ratios, an operator can use the adjusting means  70  to vary the threshold value  68  so that it is once again possible to carry out a contrast detection in the evaluation unit  16 , e.g. in the case of a gray surface  20  with a guide line  48  that is a few gray levels darker or in the event of a slow transition occurring in gray stages from the surface  20  to the guide line  48 ; in this case, a signal change can be detected in the differentiation means  32  by a slight slope in the signal waveform. During such a variation, the threshold value  68  of the adjusting means  70  must always lie above an established minimum threshold. 
     The contrast measurement or a contrast detection process of the contrast detection device  14  is thus used to detect the guide line  48  along which the hand-held power tool  12  is to be guided during operation. To this end, the hand-held power tool  12  has a guidance unit, not shown in detail, which, during operation of the hand-held power tool  12 , provides an at least partially automatic guidance of the hand-held power tool  12  along the guide line  48  on the surface  20  of the work piece  22  detected by means of the contrast detection device  14 . 
     The foregoing relates to the preferred exemplary embodiment of the invention, it being understood that other variants and embodiments thereof are possible within the spirit and scope of the invention, the latter being defined by the appended claims.