Abstract:
The disclosure relates to a mechanical hand tool device, in particular a fret and/or a reciprocating saw device, including a locating unit having at least one antenna. The locating unit is configured to detect objects outside a workpiece and to detect objects inside the workpiece.

Description:
This application is a 35 U.S.C. §371 National Stage Application of PCT/EP2011/063426, filed on Aug. 4, 2011, which claims the benefit of priority to Serial No. DE 10 2010 041 726.2, filed on Sep. 30, 2010 in Germany, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     The disclosure is based on a handheld machine tool apparatus as described herein. 
     A handheld machine tool apparatus has already been proposed for a handheld circular saw apparatus, having a locating unit which has a capacitive antenna and which is provided for the purpose of detecting the hand of a user outside the workpiece. 
     SUMMARY 
     The disclosure is based on a handheld machine tool apparatus, particularly a jigsaw and/or reciprocating saw apparatus, having a locating unit which has at least one antenna and which is provided for the purpose of detecting objects outside a workpiece. 
     It is proposed that the locating unit is provided for the purpose of detecting objects inside the workpiece. A “locating unit” is intended to be understood to mean particularly a unit which is provided for the purpose of ascertaining at least one piece of information about an object that is different than a workpiece. Advantageously, the locating unit ascertains at least a presence of the object in a locating space, particularly in a direction region of one of the antennas. Particularly advantageously, the locating unit ascertains at least one piece of information about a position of the object in the locating space. In particular, “provided” is intended to be understood to mean specifically programmed, designed and/or equipped. 
     In particular, the term “antenna” is intended to be understood to mean a unit which is provided for the purpose of sending and/or receiving a signal. Preferably, the signal is in the form of a magnetic field, in the form of an electrical field, in the form of another signal which appears meaningful to a person skilled in the art and/or preferably in the form of an electromagnetic field. In addition, the locating unit could have an ultrasound sensor and/or an optical sensor, particularly for locating between the sensor and the workpiece. Advantageously, the antenna comprises at least one element. Preferably, two or more antennas have the same element, that is to say that the antennas are at least to some extent of integral design. Advantageously, the locating unit has antennas for different fields and/or signals, as a result of which it is possible to achieve a particularly high level of reliability. Preferably, the locating unit could have an inductive antenna for live lines. In particular, an “element” is intended to be understood to mean an element of the antenna which radiates a power particularly for the purpose of locating. An “object inside a workpiece” is intended to be understood to mean particularly an object which is of separate design from the workpiece and is at least partially surrounded thereby. In particular, “objects outside the workpiece” are intended to be understood to mean objects which are arranged in front of or advantageously behind the workpiece. Preferably, objects outside the workpiece are not surrounded thereby. The locating unit is provided for the purpose of detecting objects which are arranged at an interval of more than 1 mm, advantageously more than 5 mm, from the workpiece. A “workpiece” is intended to be understood to mean particularly a unit which can be processed by an insertion tool, such as particularly a board made of plastic and/or advantageously wood. “At an interval” is intended to be understood to mean particularly that every point of the object is at a distance of greater than 1 mm from every point of the workpiece. The inventive refinement of the handheld tool apparatus allows particularly comprehensive and reliable protection to be achieved by means of a particularly simple design. 
     Furthermore, it is proposed that the handheld machine tool apparatus comprises a workpiece guide means having a workpiece support level, wherein the locating unit has a locating space which penetrates the workpiece support level, which allows particularly comprehensive protection to be achieved for an advantageous tool design. Preferably, the locating space is arranged at least to some extent behind the workpiece guide means as seen in a main working direction, specifically advantageously on a straight line that is parallel to the main working direction and that intersects the locating space and the workpiece guide means. Alternatively or in addition, the workpiece guide means could be designed to be able to be penetrated by the locating signal. Advantageously, at least one of the antennas emits a penetration signal. A “penetration signal” is intended to be understood to mean particularly a signal which is provided for the purpose of penetrating a workpiece which is mostly used with the handheld machine tool, particularly a wooden board, at least to some extent from one outer side to another outer side. Preferably, the penetration signal is provided for the purpose of penetrating at least one workpiece having a permittivity of between 1.5 and 4 and having a thickness of between 0.5 mm and 50 mm, advantageously between 2 mm and 25 mm, for locating purposes. A “workpiece guide means” is intended to be understood to mean particularly a means which is provided for the purpose of supporting at least one insertion tool mount on the workpiece so as to be able to move relative to the workpiece, specifically advantageously with a force in a direction which is oriented parallel to a motor-driven movement by the insertion tool mount. In particular, the term “workpiece support level” is intended to be understood to mean a level which is generated by a workpiece support face on the handheld tool, that is to say passes through it and is oriented parallel to it. Preferably, the workpiece support face touches the workpiece during a work operation. Preferably, the workpiece support level is oriented parallel to the main working direction. Advantageously, the workpiece support level is oriented perpendicular to a motor-driven work movement by the insertion tool mount. A “locating space” is intended to be understood to mean particularly a space in which the locating apparatus performs locating. Preferably, the locating space is determined by an orientation and configuration of the antennas, by a power of the emitted signal and by signal processing of the received signal. Advantageously, the locating space extends in a direction perpendicular to the workpiece support level beyond the workpiece support level, specifically advantageously at least on a side of the workpiece support level which is remote from the antenna. In particular, the locating space extends more than 1 cm, advantageously more than 2 cm, particularly advantageously more than 5 cm, beyond the workpiece support level. 
     It is also proposed that the locating space of the locating unit has, on a side of the workpiece support level which faces the antenna, an extent of greater than 1 cm, advantageously greater than 2 cm, particularly advantageously greater than 5 cm, perpendicular to the workpiece support level, as a result of which it is possible to achieve advantageous protection, particularly for a user. Preferably, the extent of the locating space that faces the antenna adjoins the workpiece support level at least to some extent. Alternatively or in addition, the extent of the locating space that faces the antenna could adjoin the workpiece guide means at least to some extent. Preferably, the locating space stretches in a direction perpendicular to the workpiece support level at least as far as a lower dead point of a lower end of a machining region of the insertion tool of the handheld tool. Preferably, the locating space stretches in a direction perpendicular to the workpiece support level at least as far as an upper dead point for an upper end of the machining region of the insertion tool. 
     In addition, it is proposed that the antenna is arranged behind an insertion tool mount as seen in the main working direction, as a result of which it is a particularly simple matter to monitor a region on which the insertion tool acts next. Alternatively or in addition, a direction region of the antenna could be oriented to a region in front of the insertion tool. A “main working direction” is intended to be understood to mean particularly a direction in which the insertion tool makes working progress. Advantageously, a user moves at least the locating unit in the main working direction at least in one work operation. “Behind . . . as seen in the main working direction” is intended to be understood to mean particularly that first the insertion tool and then the antenna are arranged in the main working direction, particularly on levels that are oriented perpendicular to the main working direction. 
     In a further refinement, it is proposed that at least the antenna is of planar design. Preferably, at least the first and second antennas, advantageously at least four antennas, are of planar design. Advantageously, the antennas are at least to some extent of integral design, specifically the antennas particularly advantageously have a common ground plane and/or preferably a dielectric of integral design. An “antenna of planar design” is intended to be understood to mean particularly an antenna which has at least one element which, in particular, at least essentially comprises a flat conductive layer. Advantageously, the layer has a thickness of less than 2 mm, preferably less than 0.5 mm, particularly preferably less than 0.1 mm. Preferably, a ratio between the maximum extent of the element and the thickness of the layer is greater than 5, advantageously greater than 10, particularly advantageously greater than 10. Advantageously, the element has a surface area on one level which is greater than 100 mm 2 , advantageously greater than 250 mm 2 . Preferably, the antenna has two conductive layers, at least one of which forms the element. Preferably, the layers extend along different, in particular parallel, levels. Advantageously, the layers are arranged at intervals of less than one quarter wavelength, advantageously less than one tenth wavelength, of the transmission signal from one another. Preferably, the planar antenna has a dielectric which is arranged particularly between the layers. Advantageously, the dielectric connects the layers permanently to one another. Preferably, the antenna of planar design is at least to some extent formed by an, in particular, etched printed circuit board. Alternatively or in addition, an insulator, for example a housing portion, can be coated with a conductive face. For this, various methods which appear meaningful to a person skilled in the art are conceivable, such as PVD coating, CVD coating, lacquering, rotation coating, gas-dynamic powder coating and/or cathode sputtering coating. The conductive face is advantageously formed from a metal, but could also be formed from another organic or inorganic substance, such as indium tin oxide. The planar structure means that the antenna is of particularly space-saving and inexpensive design. In addition, an advantageous directional effect can be attained with a little effort. 
     Furthermore, it is proposed that at least the antenna is fed in a balanced form, which means that it is possible to achieve low crosstalk and, in particular, an advantageous direction region in a simple manner in design terms. An “antenna fed in a balanced form” is intended to be understood to mean particularly an antenna which is provided for the purpose of radiating and/or receiving the signal when fed with two signal elements of the same amplitude and opposite phases, particularly relative to a ground plane. Preferably, the antenna has a balun which is provided for the purpose of adjusting the antennas. Preferably, the balun is in the form of a microstrip component. Alternatively, the antennas could be fed in an unbalanced form. Preferably, at least the first and second antennas are fed in a balanced form. 
     In addition, it is proposed that at least the antenna is provided for the purpose of sending and/or receiving on a narrowband basis, as a result of which it is possible to achieve signal generation and signal processing which are particularly simple in terms of design, and, in particular, low legal licensing requirements. In particular, the term “narrowband” is intended to be understood to mean having a bandwidth, particularly a 3 dB bandwidth, of less than 10%, advantageously less than 5%, particularly advantageously less than 1%, of a center frequency. Preferably, at least the first and second antennas are provided for the purpose of sending and/or receiving on a narrowband basis. Advantageously, the locating unit has a signal generator which, during operation, produces a particularly narrowband signal. Preferably, a center frequency for the signal is in an ISM band (Industrial, Scientific and Medical Band; ITU-R Regulations 5.138 and 5.150). Particularly preferably, the center frequency is between 2.400 GHz and 2.500 GHz. Alternatively, the antenna could be provided for the purpose of sending and/or receiving on a wideband basis and/or on a plurality of frequencies on a narrowband basis. 
     In addition, it is proposed that the locating unit has not only the first antenna but also a second antenna, which is provided for the purpose of receiving the signal in a second polarization, which is different than the first polarization of the first antenna, which means that the change of polarization in a reflected signal as a result of an object can be detected particularly easily in design terms. A “polarization” is intended to be understood to mean particularly an orientation of an electrical field component of an electromagnetic field from an antenna, particularly relative to an orientation of an electromagnetic field from another antenna, during operation. Preferably, the first antenna and the second antenna have linear polarization. Alternatively, the antennas could have circular polarization. In particular, “different polarization” is intended to be understood to mean polarizations in which the electrical field components during operation are at an angle relative to one another that is particularly greater than 30 degrees, advantageously greater than 60 degrees, particularly advantageously at least essentially 90 degrees. 
     Furthermore, it is proposed that the locating unit has at least one compensating means which, during operation, at least partially compensates for crosstalk by a signal from the first antenna on the second antenna, as a result of which it is possible to achieve particularly simple and reliable evaluation of a received signal in design terms. A “compensating means” is intended to be understood to mean particularly a means which combines at least one piece of information from the crosstalk with a signal received particularly from the second antenna. Advantageously, the compensating means combines on an analog basis. Alternatively or in addition, the compensating means could combine on a digital and, in particular, complex basis. Preferably, the compensating means subtracts a value for the crosstalk from the received signal. Preferably, the compensating means compensates not only for the crosstalk from the antenna but also for further crosstalk, such as in lines and/or in baluns. The phrase “during operation” is intended to be understood to mean particularly while the first antenna is sending a signal and particularly while the second antenna is receiving a signal. Preferably, the second antenna receives a reflection, advantageously a reflection with only phase alteration, of the signal sent by the first antenna from a located object and/or particularly from a workpiece. “Crosstalk from the first antenna on the second antenna” is intended to be understood to mean particularly a signal profile via a signal path on the first antenna to the second antenna within at least one portion of the locating unit and advantageously within the antenna. Preferably, the crosstalk is a portion of a power which is output by a signal generator and picked up by a receiver, said portion being independent of the workpiece and/or the located object. A “signal” is intended to be understood to mean particularly a power that is used for locating. In particular, the term “compensate” is intended to be understood to mean that the compensating means particularly substantially reduces an influence by at least the crosstalk on a signal arriving on a receiver. 
     In addition, it is proposed that the locating unit has at least three antennas, advantageously at least four antennas, with different polarizations, as a result of which particularly reliable detection of an object by virtue of a change of polarization in a reflected signal is a simple manner in design terms. Preferably, an angle between two polarizations that are adjacent in the angle is at least essentially 45 degrees. Advantageously, the locating unit has antennas with a 0-degree, a 45-degree, a 90-degree and a 135-degree polarization. Advantageously, there is an angle of at least essentially 90 degrees between an antenna which is sending in at least one mode of operation and a simultaneously received antenna. 
     In one advantageous form of the disclosure, it is proposed that the handheld tool apparatus has a computation unit, wherein the antennas have different direction regions and the computation unit is provided for the purpose of ascertaining at least one piece of information about a position of an object from, in particular, received signals from the antennas and parameters of the direction regions, as a result of which it is a simple matter to find the position of an object with particularly little effort. A “computation unit” is intended to be understood to mean particularly a controller having a processor, a memory unit, and/or an operating, control and/or calculation program stored in the memory unit. Preferably, the computation unit is in the form of a digital signal processor. Alternatively or in addition, the computation unit could be in the form of an RISC controller. Preferably, the computation unit is at least to some extent of integral design with a computation unit which controls a drive motor in a handheld machine tool, particularly the jigsaw and/or reciprocating saw. Alternatively, the computation units could be of separate design and, in particular, communicate with one another in at least one mode of operation, particularly by means of analog signals, by means of binary signals and/or advantageously by means of a data bus. A “direction region” is intended to be understood to mean particularly a region to which at least one antenna sends during operation and/or from which at least one antenna receives during operation. Preferably, the direction region is in the form of a space arranged inside a 3 dB beam angle of the antenna. A “parameter of a direction region” is intended to be understood to mean particularly a piece of information which describes a physical arrangement of the direction region, such as an antenna arrangement and/or an antenna orientation. A “piece of information about a position of an object” is intended to be understood to mean at least one piece of information which describes an at least partial arrangement of the object in a region of intersection between two direction regions. An “object” is intended to be understood to mean particularly an object that is different than a workpiece and is intended to be protected from a machining operation, such as a body part, an electrical line, a water line, a bar arranged behind the workpiece and/or other objects which appear meaningful to a person skilled in the art. Preferably, the object has different physical properties than the workpiece. 
     Furthermore, it is proposed that the locating unit is provided for the purpose of evaluating only a change in a received signal at least during workpiece machining, as a result of which particularly simple evaluation and a particularly simple design for the locating unit are possible. Preferably, the computation unit evaluates the change in the received signal. The phrase “during workpiece machining” is intended to be understood to mean particularly during a movement sequence which causes the workpiece to be cut. Advantageously, the user moves at least the antennas relative to the workpiece during workpiece machining. In particular, the phrase “evaluate a change in a received signal” is intended to be understood to mean that the locating unit merely calculates a difference between the currently received signal and a previously received signal and evaluates the difference. Preferably, the locating unit compares the difference with at least one threshold value. In particular, the locating unit does not detect absolute propagation times for a received signal, for example for the purpose of determining a distance. 
     In addition, it is proposed that the locating unit defines two different reaction regions, as a result of which a particularly convenient and nevertheless effective reaction to a situation is possible. A “reaction region” is intended to be understood to mean particularly a space in which an object, upon entry, causes a reaction at least from the locating unit. Advantageously, a reaction region is defined as a warning region. Preferably, an object entering this reaction region prompts a, in particular, visual, audible and/or tactile warning to the user, for example by virtue of a main grip vibrating. Advantageously, a reaction region is defined as a protection region. Preferably, an object entering this reaction region prompts a protective measure, such as an insertion tool being stopped and/or other protection that appears meaningful to a person skilled in the art. 
     The disclosure is also based on a handheld tool, particularly machine tool, having a handheld tool apparatus according to the disclosure, as a result of which a, in particular, safe handheld tool can be achieved particularly easily in design terms. A “handheld tool” is intended to be understood to mean particularly a manually guided unit which is provided for the purpose of interacting with a workpiece, particularly for gauging and/or machining. In particular, the term “handheld machine tool” is intended to be understood to mean a manually guided, motor-operated tool. Preferably, the handheld tool is in the form of a jigsaw and/or reciprocating saw. A “jigsaw and/or reciprocating saw” is intended to be understood to mean particularly a saw which is provided for the purpose of puncturing a workpiece. Advantageously, the jigsaw and/or reciprocating saw has a drive motor and the insertion tool mount. Advantageously, the insertion tool mount mounts the insertion tool on one side during operation. Preferably, the insertion tool is provided for the purpose of sawing curves. Alternatively, the handheld tool could be in the form of another handheld machine tool which appears meaningful to a person skilled in the art, such as particularly a drill, a hammer drill, a saw, a plane, a screwdriver, a milling machine, a grinder, an angle grinder, a garden tool and/or a multifunction tool. Preferably, the handheld tool apparatus is integrated in the handheld tool. Alternatively, the handheld tool apparatus could have a connecting means which is provided for the purpose of making an operative connection for the handheld tool which can be broken by a user. Hence, the handheld tool apparatus could be in the form of an attachment and/or accessory. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further advantages emerge from the description of the drawing which follows. The drawing shows six exemplary embodiments of the disclosure. The drawing, the description and the claims contain numerous features in combination. A person skilled in the art will expediently also consider the features individually and combine them into meaningful further combinations. 
       In the drawing: 
         FIG. 1  shows a handheld machine tool according to the disclosure, which is in the form of a jigsaw, having a handheld tool apparatus which has two antennas, 
         FIG. 2  shows a schematic illustration of the antennas, a signal generator, a receiver and a compensating means of the handheld tool apparatus from  FIG. 1 , 
         FIG. 3  shows a plan view of the antennas of the handheld tool apparatus from  FIG. 1 , 
         FIG. 4  shows a side view of the antennas of the handheld tool apparatus from  FIG. 1 , 
         FIG. 5  shows a handheld machine tool according to the disclosure, which is in the form of a reciprocating saw, 
         FIG. 6  shows a further exemplary embodiment of the antennas from  FIG. 1 , which are in the form of a dipole of cruciform design with a bracket, 
         FIG. 7  shows the antenna from  FIG. 6  without the bracket, 
         FIG. 8  shows four antennas fed in an unbalanced form with a common round element, 
         FIG. 9  shows two antennas fed in an unbalanced form with one element each, 
         FIG. 10  shows four antennas fed in an unbalanced form with a common round element, and 
         FIG. 11  shows eight antennas fed in an unbalanced form with four elements. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a handheld tool  10   a , specifically a handheld machine tool. The handheld tool  10   a  is in the form of a jigsaw. The handheld tool  10   a  has a drive motor  12   a , an insertion tool mount  14   a , a workpiece guide means  16   a  having a workpiece support face  17   a  and a main grip  18   a . During a work process, the drive motor  12   a  drives the insertion tool mount  14   a , specifically in oscillating fashion. In addition, the drive motor  12   a  drives an insertion tool  20   a  back and forth during operation. In a ready state, the insertion tool mount  14   a  mounts the insertion tool  20   a . The insertion tool  20   a  is in the form of a jigsaw blade. During a work process, when moved by a user, the handheld tool  10   a  slides over a workpiece  22   a  on the workpiece support face  17   a . The main grip  18   a  is arranged on a side of the handheld tool  10   a  which is remote from the workpiece guide means  16   a.    
     In addition, the handheld tool  10   a  has a handheld tool apparatus  24   a , shown schematically in  FIG. 2 . The handheld tool apparatus  24   a  comprises a locating unit  26   a  having a first antenna  28   a , a second antenna  30   a , a compensating means  32   a , a signal generator  34   a , a receiver  36   a , a computation unit  38   a , a splitter  40   a  and a combiner  42   a . Filters, impedance converters, baluns, amplifiers, a power supply and other units of the locating unit  26   a  which appear meaningful to a person skilled in the art are not shown in more detail. 
     As shown in  FIG. 1 , in particular, the locating unit  26   a  has a locating space  41   a  which penetrates a workpiece support level  43   a . To this end, the signal generator  34   a  produces a narrowband, radio-frequency signal, specifically at 2.4 GHz. The antennas  28   a ,  30   a  emit the signal directionally into the locating space  41   a . The computation unit  38   a  regulates an amplitude of the signal. In addition, the computation unit  38   a  matches a transmission period to a movement by the insertion tool mount  14   a , as a result of which it is possible for interference by the insertion tool to be minimized. On a side of the workpiece support level  43   a  which faces the antennas  28   a ,  30   a , the locating space  41   a  has an extent of greater than 5 cm perpendicular to the workpiece support level. The antennas  28   a ,  30   a  are arranged at an interval from the workpiece support level  43   a  in a locating direction. 
     The computation unit  38   a  is of integral design with a computation unit which controls and/or regulates the drive motor  12   a . During operation, the handheld tool apparatus  24   a  obtains operating energy from an energy source—not shown in more detail—for the drive motor  12   a . Alternatively, the handheld tool apparatus  24   a  could have an independent energy source, particularly a storage battery and/or a battery. 
     As  FIGS. 3 and 4  show, the antennas  28   a ,  30   a  have a common element  44   a . The element  44   a  is in the form of a square, electrically conductive face. The antennas  28   a ,  30   a  each have two contact points  45   a  which make contact with the element  44   a . The contact points  45   a  are each arranged on opposite sides of the element  44   a . They are in the form of plated-through holes and are linked by means of striplines. The antennas  28   a  feed the element  44   a  in a balanced form. To this end, each antenna  28   a ,  30   a  has a balun—not shown in more detail. The second antenna  30   a  has a polarization that is different than the polarization of the first antenna  28   a , specifically the polarization differs by 90 degrees. The element  44   a  has crosstalk  46   a  between the first antenna  28   a  and the second antenna  30   a . The element  44   a  is oriented such that the polarizations of the antennas  28   a ,  30   a  are at an angle of 45 degrees to a main working direction  54   a.    
     During a locating process between the signal generator  34   a  and the first antenna  28   a , the splitter  40   a  decouples a compensating portion from a signal from the signal generator  34   a . The compensating portion is smaller than the signal sent, but could also be of equal magnitude or larger. The compensating portion passes through the compensating means  32   a . During a locating process, the combiner  42   a  between the second antenna  30   a  and the receiver  36   a  combines a received signal and the compensating portion. The received signal has the crosstalk  46   a  in this case. 
     The compensating means  32   a  has an amplitude control element  48   a  and a phase control element  50   a . The amplitude control element  48   a  and the phase control element  50   a  are of adjustable design. The amplitude control element  48   a  is in the form of an attenuation element. It could alternatively also be in the form of an amplifier. During calibration, the amplitude control element  48   a  is adjusted such that an amplitude of the compensating portion and an amplitude of the crosstalk  46   a  are of equal magnitude in the receiver  36   a . In addition, during calibration, the phase control element  50   a  is adjusted such that a phase of the compensating portion and a phase of the crosstalk  46   a  differ by 180 degrees in the receiver  36   a . The phase control element  50   a  is in the form of a delay line. An amplitude control element and a phase control element could be of integral design, for example in the form of a vector modulator. 
     The compensating portion largely cancels out the crosstalk  46   a  in the received signal before the latter reaches the receiver. The calibration of the compensating means  32   a  takes place during production. Alternatively or in addition, calibration could, in particular, take place shortly before, during or after a work process and/or when initiated by a user, for example by means of feedback. Hence, the compensating means  32   a  compensates for the crosstalk  46   a  by the signal from the first antenna  28   a  on the second antenna  30   a.    
     The first antenna  28   a  emits the signal in a direction region  52   a . During the work process, the user moves the handheld tool  10   a  in the main working direction  54   a . The field from the first antenna  28   a  penetrates the workpiece  22   a  in the direction region  52   a , which is situated behind—as seen in the main working direction  54   a —the insertion tool mount  14   a . In addition, the antennas  28   a ,  30   a  are arranged behind—as seen in the main working direction  54   a —the insertion tool mount  14   a . Hence, during locating the locating unit  26   a  captures objects inside the workpiece  22   a  and objects outside the workpiece  22   a.    
     The second antenna  30   a  receives reflections of the sent signal that have an altered polarization. The receiver  36   a  is in the form of an analog-digital converter. The computation unit  38   a  evaluates the received signal. To this end, the receiver  36   a  determines an amplitude for the received signal. Alternatively, the computation unit  38   a  could evaluate a received signal in terms of absolute value and phase. To this end, the receiver could be in the form of a complex receiver, for example in the form of an IQ receiver. In this case, the computation unit  38   a  could have a compensating means in the form of a computation routine. 
     The computation unit  38   a  has a computation routine which, during a work process, specifically during a movement at least by the antenna relative to a workpiece, evaluates a change in the received signal. The evaluation begins when the computation unit  38   a  recognizes that a work process is beginning. To this end, the computation unit  38   a  evaluates a power draw by the drive motor  12   a . At that time, calibration could take place. The computation unit  38   a  subsequently compares an earlier value of the received signal with a current value of the received signal. Alternatively, the computation unit  38   a  could compare a current value of the received signal with an average and/or filtered value of the signal. 
     If a difference between the values exceeds a threshold value, the computation unit  38   a  triggers a reaction. In this exemplary embodiment, the handheld tool  10   a  warns the user visually. To this end, the computation unit  38   a  switches on a red light-emitting diode—not shown in more detail—which illuminates a region behind—as seen in the main working direction  54   a —the insertion tool  20   a . The computation unit  38   a  switches the warning off when the difference between the values falls back below the threshold value. Alternatively or in addition to the warning, the computation unit  38   a  could stop the insertion tool mount  14   a , particularly after a warning. By way of example, the computation unit  38   a  could switch off the drive motor  12   a , open a coupling between the drive motor  12   a  and the insertion tool mount  14   a , switch off a back-and-forth stroke, actively stop the insertion tool mount  14   a  by means of the drive motor  12   a  and/or trigger a braking and/or blocking function. When a user operates an operator control means  56   a  on the handheld tool  10   a , the computation unit  38   a  could enable the work process to be continued. In this case, a main operator control means could be operated again or the handheld tool  10   a  could have a separate operator control means for the enabling. Alternatively, the computation unit  38   a  could enable a machining process after the handheld tool  10   a  is lifted. 
       FIGS. 3 and 4  show the two antennas  28   a ,  30   a . The antennas  28   a ,  30   a  are of planar design. To this end, the element  44   a  is formed by a conductive face on an outer side of a printed circuit board  58   a . Arranged on another side of the printed circuit board  58   a  is a ground plane  60   a . Between the element  44   a  and the ground plane  60   a , the printed circuit board  58   a  has a dielectric  62   a . The dielectric  62   a  connects the element  44   a  and the ground plane  60   a  mechanically. Alternatively, the element  44   a  and the ground plane  60   a  can have a louver arranged between them. The element  44   a  has a square shape. As a result, the element  44   a  has a narrowband frequency profile. Hence, the antennas  28   a ,  30   a  send and/or receive on a narrowband basis. Alternatively, the element  44   a  could have a rectangular or other shape which appears meaningful to a person skilled in the art. 
       FIGS. 5 to 11  show further exemplary embodiments particularly of portions of the disclosure. The descriptions and the drawings which follow are essentially limited to the differences between the exemplary embodiments, and reference can also be made, in principle, to the drawings and/or the description of the other exemplary embodiments, particularly in  FIGS. 1 to 4 , for components having the same designation, particularly for components having the same reference symbols. In order to distinguish between the exemplary embodiments, the letter a is suffixed to the reference symbols of the exemplary embodiment of  FIGS. 1 to 4 . In the exemplary embodiments in  FIGS. 5 to 11 , the letter a has been replaced by the letters b to g. 
       FIG. 5  shows a handheld tool  10   b  which is in the form of a reciprocating saw. The handheld tool  10   b  has a handheld tool apparatus  24   b  having a locating unit  26   b . The locating unit  26   b  comprises two antennas  28   b ,  30   b , which are described in the exemplary embodiment in  FIGS. 1 to 4 . A direction region  52   b  of the antennas  28   b ,  30   b  is arranged behind an insertion tool mount  14   b  in the main working direction  54   b  in this case too. The handheld tool  10   b  has a main extent, which is oriented perpendicular to the main working direction  54   b.    
       FIGS. 6 and 7  show two alternative antennas  28   c ,  30   c , each of which is in the form of a dipole antenna. Each antenna  28   c ,  30   c  has elements  44   c . Each element  44   c  has two poles  64   c  in a parallel orientation. Together, the antennas  28   c ,  30   c  form a cruciform dipole. A ground plane  60   c  of the antennas  28   c ,  30   c  causes a directional effect, specifically in a direction that points from the ground plane  60   c  to the elements  44   c .  FIG. 5  shows a bracket  66   c  for the antennas  28   c ,  30   c . The bracket is partly in the form of a printed circuit board  58   c , specifically the elements  44   c  are arranged on a printed circuit board. The bracket  66   c  is formed from a dielectric material. It mounts the elements  44   c  in an insulating fashion. A length of the elements  44   c , a width of the elements  44   c , a shape of the elements  44   c  and an interval between the elements  44   c  and the ground plane  60   c  are dependent on a frequency and a bandwidth of a signal that is sent during operation. The antennas  28   c ,  30   c  are fed in a balanced form. 
       FIG. 8  shows four alternative antennas  28   d ,  30   d ,  68   d ,  70   d  with a common element  44   d . The element  44   d  is in the form of a circular conductive face. The antennas  28   d ,  30   d ,  68   d ,  70   d  each have a contact point  45   a . The contact points  45   d  are each arranged at an angle of 45 degrees to the next contact point  45   d . The antennas  28   d ,  30   d ,  68   d ,  70   d  are fed in an unbalanced form. This results in two antenna pairs with two antennas  28   d ,  30   d ;  68   d ,  70   d  each, which each have an angle of 90 degrees between their polarizations. The antenna pairs have an angle of 45 degrees between their polarizations. Hence, a locating unit has four antennas  28   d ,  30   d ,  68   d ,  70   d  with different polarizations. 
     Each one of the antennas  28   d ,  68   d  in an antenna pair is connected to a signal generator. Each one of the antennas  30   d ,  70   d  in an antenna pair is connected to a receiver. The antennas  28   d ,  68   d  alternately emit a signal. In this case, the respective antenna  30   d ,  70   d , which is at an angle of 90 degrees to the sending antenna  28   d ,  68   d , is receiving. This design and this operation also allow objects to be located which have an orientation and/or shape which do not alter a polarization of a reflecting signal in the case of one of the sending antennas. 
       FIG. 9  shows two antennas  28   e ,  30   e  which are fed in an unbalanced form by means of a respective contact point  45   e . The antennas  28   e ,  30   e  have elements  44   e  in separate form. One of the antennas  28   e  is connected to a signal generator. One of the antennas  30   e  is connected to a receiver. The antennas  28   e ,  30   e  can locate only objects which are arranged in a direction region for both antennas  28   e ,  30   e , as a result of which a locating space can advantageously be arranged, particularly at an interval from the antennas. 
       FIG. 10  shows eight antennas  28   f ,  30   f ,  68 - 78   f . Two antennas  28   f ,  30   f ;  68   f ,  70   f ;  72   f ,  74   f ;  76   f ,  78   f  in each case have a common element  44   f  and a polarization difference of 90 degrees. The antennas  28   f ,  30   f ,  68 - 78   f  are fed in an unbalanced form by means of a contact point  45   f  (provided with a reference symbol only once). Four of the antennas  28   f ,  30   f ,  68   f - 78   f  in each case have the same polarization. The antennas  28   f ,  68   f ,  72   f ,  76   f  with the same polarization send during operation and the other antennas  30   f ,  70   f ,  74   f ,  78   f  with the same polarization receive during operation. The antennas  28   f ,  30   f ,  68   f - 78   f  are contact-connected in phase. As a result, a particularly narrow beam angle is obtained for a common direction region for the antennas  28   f ,  30   f ,  68   f - 78   f . Alternatively, the antennas could be contact-connected out of phase, particularly in adjustable form, as a result of which it is possible to achieve different angles and/or orientations for a direction region. In addition, this principle would alternatively be possible with two or more antennas. 
     The antennas  30   f ,  70   f ,  74   f ,  78   f  which receive during operation are each connected to a receiver—not shown in more detail. As a result, as shown particularly in  FIG. 11 , it is possible to determine information about a position of an object easily in design terms.  FIG. 1  schematically shows a side view of two elements  44   f  and direction regions  52   f  associated with the elements  44   f . The elements  44   f  and hence the antennas  28   f ,  30   f ,  68   f - 78   f  have different direction regions  52   f . The direction regions  52   f  overlap in an overlap region  80   f . Alternatively, the antennas  30   f ,  70   f ,  74   f ,  78   f  which receive during operation could be connected to a common receiver, as a result of which a directional effect of the four antennas can be used easily in design terms. 
     When a reflected signal from an element  44   f  has changes, an object is entering the direction regions  52   f  for said element, as a result of the antennas  28   f ,  30   f ,  68   f - 78   f  being moved relative to the object. When a reflected signal from another element  44   f  has changes, the object is entering the direction regions  52   f  for said element. When signals reflected by the object from the two elements  44   f  have been altered, the object is arranged in the overlap region  80   f . As a result of individual sending antennas  28   f ,  68   f ,  72   f ,  76   f  being switched on and off, further position finding is possible. A computation unit which is described in the first exemplary embodiment has a computation routine which takes the signals from the antennas and parameters of the direction regions  52   f  for the antennas  28   f ,  30   f ,  68   f - 78   f  and ascertains information about a position of an object. This principle would alternatively be possible with two antennas or more antennas. 
     The computation unit defines two different reaction regions  82   f ,  84   f . The reaction regions  82   f ,  84   f  are arranged behind an insertion tool mount  14   f , behind one another as seen in the main working direction  54   f . The computation unit warns the user when an object is arranged in the reaction regions  82   f  and is at a greater interval from the insertion tool mount  14   f . The computation unit stops the insertion tool mount  14   f  when an object is arranged in the reaction regions  82   f  and is facing the insertion tool mount  14   f . The overlap region  80   f  could be associated with one of the reaction regions  82   f ,  84   f  or with an independent reaction region, for example with a further warning level.