Abstract:
A method to control a power tool including the method steps:
       specifying the rotational speed of the drive at a first value,   measuring a first amplitude of a signal,   filtering the signal within a frequency range,   measuring a second amplitude of the filtered signal,   reducing the rotational speed of the drive to a second value if the first amplitude exceeds a first quantity and if the second amplitude exceeds a second quantity, and   incrementally increasing the rotational speed of the drive to the first value, whereby each incremental increase of the rotational speed only takes place once the first amplitude remains below the first quantity for a time interval, and the second amplitude remains below the second quantity.       
 
     A power tool that uses this method, includes:
       a drive,   an acceleration sensor   a filter, and   a control unit.

Description:
[0001]    The present invention relates to a method to control a power tool comprising a drive to drive a tool and a control unit for when a workpiece is being worked. 
         [0002]    The invention also relates to a power tool that uses this method. 
         [0003]    The power tool can be, for instance, a core drilling machine used for core drilling. 
       BACKGROUND 
       [0004]    A core drilling machine uses a cylindrical diamond-tipped drill bit to cut a ring-shaped groove into a workpiece that is to be worked in order to create a cylindrical drill core there which can then be removed in its entirety from the drilled hole. The material can be, for example, concrete, masonry, stone or the like. 
         [0005]    Numerous technical problems can arise during the individual phases of a core drilling procedure. Particularly during the so-called spot-drilling phase, that is to say, the phase when the drill bit is placed onto the workpiece that is to be worked and the core drilling procedure is started, undesired oscillations or vibrations can be exerted onto the drill bit and onto the core drilling machine. These oscillations or vibrations can often also lead to resonances in the drill bit and in the core drilling machine, thereby greatly impairing the drilling procedure. 
         [0006]    These oscillations or vibrations and ultimately also the resonances usually arise in that, during the early phase of the core drilling procedure (spot-drilling phase), the drill bit has not yet penetrated deep enough into the material that is to be worked and therefore, the rotating drill bit is not yet being sufficiently guided in the hole that is being drilled. However, it can also be the case that, during later phases of the core drilling procedure, when the drill bit apparently already has sufficient guidance in the hole being drilled, undesired oscillations or vibrations and consequently also resonances might occur. Even during these later drilling phases, these oscillations, vibrations and resonances lead to insufficient operation. 
         [0007]    Generally speaking, oscillations, vibrations and resonances should be avoided during a core drilling procedure since they exert severe mechanical and dynamic loads on the drilling tools which, in turn, can give cause damage to the drill bit, to the drilling machine and/or to the drill stand. Moreover, this can translate into poor drilling results in the form of crooked drilled holes that do not run at the prescribed angle (e.g. 90°) relative to the surface of the material that is to be worked. 
         [0008]    Furthermore, these oscillations, vibrations and resonances also entail certain safety risks. A user could be tempted to try to provisionally reduce the vibrations, that is to say, by placing auxiliary means onto the drill bit, for example, the user&#39;s own foot. This, however, might cause injury to the user and/or cause damage to the core drilling machine. 
         [0009]    As a measure aimed at avoiding the undesired oscillations and vibrations, the rotational speed of the drill drive and thus the drilling speed are usually reduced, as a result of which the drill advances altogether more slowly. As a consequence, the core drilling procedure is prolonged, thus rendering the drilling procedure altogether inefficient. 
       SUMMARY OF THE INVENTION 
       [0010]    It is an object of the present invention to provide a method to control a power tool comprising a drive to drive a tool and a control unit for when a workpiece is being worked. Moreover, it is the an objective of the present invention to also put forward a system device that uses this method. Due to the method according to the invention as well as the system device according to the invention, the above-mentioned drawbacks are overcome and the working of the material transpires more efficiently. 
         [0011]    The present invention provides a method to control a power tool comprising a drive to drive a tool and a control unit for when a workpiece is being worked, encompassing the following method steps:
       specifying the rotational speed of the drive at a first value,   measuring a first amplitude of a signal,   filtering the signal within a prescribed frequency range,   measuring a second amplitude of the filtered signal,   reducing the rotational speed of the drive to a second value if the first amplitude exceeds a first prescribed quantity and if the second amplitude exceeds a second prescribed quantity, and   incrementally increasing the rotational speed to the first value, whereby each incremental increase of the rotational speed only takes place once the first amplitude remains below the first prescribed quantity for a prescribed time interval, and the second amplitude remains below the second prescribed quantity.       
 
         [0018]    Moreover, a power tool is provided that uses this method and it comprises:
       a drive to drive a tool,   an acceleration sensor to measure a first amplitude and a second amplitude of a signal,   a filter to filter the signal within a prescribed frequency range, and   a control unit to control at least the rotational speed of the drive.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The invention will be explained in greater detail on the basis of advantageous embodiments, whereby the following is shown: 
           [0024]      FIG. 1 : a power tool according to the invention, having a tool on a tool stand, for core drilling into a horizontally oriented material; 
           [0025]      FIG. 2 : the power tool according to the invention, having the tool on the tool stand, for core drilling into a vertically oriented material; 
           [0026]      FIG. 3 : a flow chart of the control method according to the invention; 
           [0027]      FIG. 4 : a flow chart of a resonance check as an integral part of the method according to the invention; and 
           [0028]      FIG. 5 : a graph about the time-related adaptation of the motor rotational speed during the drilling procedure. 
       
    
    
     DETAILED DESCRIPTION 
       [0029]      FIGS. 1 and 2  show a power tool for working a material such as, for example, concrete, stone, masonry or the like. 
         [0030]    The power tool  1  is configured in the form of a core drilling machine and it comprises a drive  10 , a drive shaft  20 , a tool  30  in the form of a drill bit, an acceleration sensor  40 , a control unit  50  and a filter  60 . 
         [0031]    As likewise shown in  FIG. 1 , the power tool  1  can be detachably fastened to a tool stand  13  by means of a feed mechanism  12 . The feed mechanism  12  serves to automatically move the power tool  1  relative to the tool stand  13  reversibly along the direction of arrows D and E by means of a drive. The tool stand  13  has a guide means  14 , a foot element  15 , a position and distance sensor  16  as well as a vacuum pump  17 . The guide means  14  has an elongated guide element  18  on which the feed mechanism  12  can be held and reversibly moved along the direction of arrows D and E. The power tool  1 , in turn, is detachably attached to the feed mechanism  12 . The feed mechanism  12  and the guide means  14  can move the power tool  1  in a controlled manner towards and away from a material W that is to be worked. The foot element  15  has a fastening element  19  that is connected to the vacuum pump  17  via a hose  11 . The vacuum pump  17  can be used to generate a vacuum in the fastening element  19 , as a result of which the tool stand  13  and the power tool  1  attached thereto can be held against a substrate or against the material W that is to be worked. The vacuum pump  17  is connected to the control unit  50  via a data line  51 . The vacuum pump  17  can be controlled and regulated by means of the control unit  50 , as a result of which the contact force of the fastening element  19  in the foot element  15  can be controlled and regulated. As shown in  FIG. 2 , the tool stand  13  with the power tool  1  can also be fastened on a vertical wall or to a vertical material W in order to carry out horizontal core drilling into the material W. 
         [0032]    The position and distance sensor  16  is situated between the elongated guide element  18  of the guide means  14  and the feed mechanism  12 , and it is connected to the control unit  50  as well as to the feed mechanism  12 . By means of the control unit  50 , the measured data and parameters of the position and distance sensor  16  can be stored, processed and made available for other work procedures. The position and distance sensor  16  serves, on the one hand, to ascertain the position of the feed mechanism  12  relative to the elongated guide element  18  or to a prescribed starting position, and, on the other hand, to measure the distance traveled by the feed mechanism  12  on the elongated guide element  18 . On the basis of the position and path measurements, it is always possible to ascertain the position of the power tool  1  or of the tool  30  relative to the material W as well as the distance already traveled by the power tool  1  or by the tool  30  in the material W, that is to say, in the drilled hole B. This makes it possible to ascertain, for instance, the depth of the drilled hole or the remaining time or distance to be traveled until the desired drilling depth is reached. Moreover, the position and distance measurement also allows the determination that a material W such as, for example, a wall, has been drilled through if the thickness of the material W that is to be worked is known. On the basis of the transmission of the information to the control unit  50  indicating that the material W has been drilled through, the control unit  50  can either reduce the rotational speed of the rive  10  to a minimum or else completely stop the drive  10 , for instance, in order to save energy. 
         [0033]    The drive  10  is configured in the form of an electric motor although it is also possible to use any other suitable motor or drive modality. 
         [0034]    The drive shaft  20  is connected to the drill bit  30  and it transmits the torque generated by the drive  10  to the drill bit  30 . Owing to the generated torque and to a corresponding contact pressure that is exerted onto the drill bit  30 , the drill bit  30  serves to drill a hole B into the material W. 
         [0035]    The control unit  50  is positioned in the power tool  1  and connected to the drive  10 , the position and distance sensor  16 , the acceleration sensor  40 , the vacuum pump  17  and the filter  60 . The control unit  50  serves primarily to control as well as regulate the parameters and especially the rotational speed of the drive  10 . As already described above, the control unit  50  also controls and regulates the vacuum pump  17  and it collects as well as processes data form the position and distance sensor  16 , from the filter  60  and from the acceleration sensor  40 . 
         [0036]    The acceleration sensor  40 , which can also be referred to as an acceleration measuring device, an accelerometer, an A-sensor or a G-sensor is connected to the control unit  50  and serves to measure acceleration values. The measurement of the acceleration values makes it possible to detect vibrations or oscillations on the power tool  1 , on the tool  30 , on the tool stand  13  as well as on the foot element  15 . The detection of vibrations and oscillations in the foot element  15  especially serves to ascertain whether critical threshold values pertaining to the vibrations and oscillations have been exceeded, which could cause the foot element  15  of the tool stand  13  to be detached from the substrate or from the material that is to be worked. If critical threshold values pertaining to the vibrations and oscillations have been exceeded, the control unit  50  can be used to raise the output of the vacuum pump  17 , so that the contact force is likewise raised correspondingly, in order to prevent the foot element  15  from being detached from the material that is to be worked due to the vibrations and oscillations. 
         [0037]    If the tool stand  13  is used without the foot element  15  with a connected vacuum pump  17  but, instead, a tool stand  13  with a foot element  15  that is attached by means of a number of bolts or screws to the material W that is to be worked, then the acceleration sensor  40  likewise serves to detect vibrations and oscillations in the foot element  15  that might indicate a possible detachment of the bolts or screws. 
         [0038]    Moreover, the acceleration sensor  40  also serves to ascertain the position or orientation the power tool  1 , that is to say, based on the force of gravity, the acceleration sensor  40  can determine whether the power tool  1  with the tool stand  13  is secured to the horizontally oriented material W (on the floor in  FIG. 1 ) or else to a vertically oriented material W (on a wall in  FIG. 2 ). As will be described in detail below, this orientation or position of the power tool  1  is particularly important when it comes to ending the core drilling procedure. 
         [0039]    The filter  60  is likewise connected to the control unit  50  and its function is to filter certain frequencies of a measured signal so that only certain frequencies or a certain frequency range is filtered out and made available. The measured signal in the present case is the acceleration value that is generated by the oscillations and vibrations on the power tool  1  and on the tool  30 . 
         [0040]    During the core drilling procedure, the drive  10  of the power tool  1  transmits a torque via the drive shaft  20  to the tool  30  configured as a drill bit, thus imparting said tool  30  with a rotational movement around the axis C in the direction of arrow A or B. In this context, the rotational speed of the drive  10  and of the drill bit  30  corresponds to a relatively low value, that is to say, to a spot-drilling rotational speed or velocity. The drill bit  30  operated at the spot-drilling speed is then moved downwards in the direction of arrow D onto the material W. The tool stand  13  described above serves to ensure that the power tool  1  and the drill bit  30  can be moved in a controlled manner. 
         [0041]    After completion of the core drilling procedure, the drill bit  30  is pulled in the direction of arrow E out of the hole B that was drilled into the material W. However, in this process, the drill bit  30  is not pulled completely out of the drilled hole B in one motion. Particularly in those cases in which the drilled hole B is to be made into a vertically oriented material W (see  FIG. 2 ), for safety reasons, at least a minimum length of the drill bit  30  should stay in the drilled hole B after the drilling procedure has ended. As already described above, the acceleration sensor  40  can be used to ascertain whether the power tool  1  and the tool stand  13  are attached to a horizontally oriented material W (on the floor in  FIG. 1 ) or else to a vertically oriented material W (on a wall in  FIG. 2 ). Once the drilling procedure has ended, the drill core (not shown here) is inside the drill bit  30 , as a result of which a relatively high additional weight is exerted on the drill bit  30 . This additional weight of the drill core could cause the tool stand  13  with the power tool  1  to become detached from the vertically oriented material W, that is to say, from the wall (see  FIG. 1 ), and to fall. In view of the fact that at least a minimum length of the drill bit  30  remains inside the drilled hole B, it can be ensured that the drill bit  30  is still being supported in the drilled hole B and that the full weight of the drill bit  30  and of the drill core are not exerted on the attachment of the tool stand  13  on the vertically oriented material W, that is to say, on the wall (see  FIG. 1 ). As already mentioned above, the position and distance sensor  16  as well as the control unit  50  serve to detect the position of the drill bit  30  in the drilled hole B, as a result of which the procedure of pulling the drill bit  30  out of the drilled hole B can be properly stopped if at least a minimum length of the drill bit  30  is still inside the drilled hole B. This minimum length can be, for example, half the length of the drill bit  30  or else just a few centimeters. The minimum length depends on a number of parameters such as, for instance, the diameter of the drill bit, the length of the drill bit, the type of attachment of the tool stand  13  to the material W and on the material W itself, and it can be preset by the control unit  50 . 
         [0042]    The control method for the power tool  1  in the case of a resonance generated by oscillations and vibrations on the power tool  1  and especially on the tool  30  will be described below making reference to  FIGS. 3, 4 and 5 . 
         [0043]    As shown in  FIG. 3 , the operation of the power tool  1  to carry out a drilling procedure begins with step S 1  when the drive  10  of the power tool  1  is started. In this process, in step S 2 , the rotational speed DZ of the drive  10  is set to a value  4  (see  FIG. 5 ). In step S 3 , the resonance is checked, that is to say, it is checked whether a resonance has been triggered on the power tool  1  by oscillations and vibrations. The resonance check is presented in detail in  FIG. 4 . During the resonance check, the acceleration sensor  40  is employed in step R 1  in order to measure a first amplitude of a signal in the form of an oscillation or of vibrations. Moreover, in step R 2 , the filter  60  filters this signal in such a way that only a certain frequency range of the oscillation or vibration signal is present. A second amplitude of this oscillation or vibration signal, which is filtered within a certain frequency range, is then measured in step R 3  by means of the acceleration sensor  40 . 
         [0044]    In step R 4 , the control unit  50  checks whether the first amplitude of the oscillation or vibration signal exceeds a first prescribed quantity. By the same token, in step R 5 , the control unit  50  checks whether the second amplitude of the oscillation or vibration signal exceeds a second prescribed quantity. 
         [0045]    If the first amplitude does not exceed the first quantity and/or the second amplitude does not exceed the second quantity, the control unit in step R 6  determines that there is no resonance. The resonance check is thus ended in step R 7 . Therefore, in step S 4 , the determination is made that there is no resonance and the rotational speed of the drive  10  remains at a value  4  (see  FIG. 5 ). 
         [0046]    However, if the first amplitude exceeds the first quantity and if the second amplitude exceeds the second quantity, the control unit  50  makes the determination in step R 8  that there is a resonance triggered by the oscillations or vibrations. The resonance check is thus ended in step R 9  (see  FIG. 4 ). Therefore, in step S 4 , the determination is made that there is a resonance, as a result of which the control unit  50  reduces the rotational speed of the drive  10  from the value  4  to the value  1  in order to eliminate the resonance in this manner (see  FIG. 5 ). In this context, the value  1  for the rotational speed is selected in such a way that there is no resonance at this value  1  at any point in time. In step S 6 , the drive remains at the value  1  until the end of a prescribed time interval t 1 . After the end of this time interval t 1 , the rotational speed of the drive  10  is increased from value  1  to value  2  in step S 7  (see  FIG. 5 ). In this context, the value  3  for the rotational speed of the drive  10  is greater than the value  2  but lower than the value  1 . If the time interval t 1  has not yet ended after the resonance check S 3  has been completed, then another resonance check S 3  is carried out. 
         [0047]    In step S 8 , another resonance check is carried out. This resonance check in Step S 8  corresponds to the resonance check described above in step S 3  according to  FIG. 4 . If there is a resonance, the rotational speed of the drive  10  is reduced from value  2  back to value  1  in step S 9  since, at the value  1  for the rotational speed, there is definitely no resonance. However, if it is ascertained by the control unit  50  in step S 9  and after the end of a time interval t 2  in step S 10  that there is no resonance, then, in step S 11 , the rotational speed of the drive  10  is raised to a value  3 , see  FIG. 3 . In this context, the value  3  for the rotational speed of the drive  10  is greater than the value  2  and greater than the value  1  but smaller than the value  4 . If the time interval t 2  has not yet ended after the resonance check S 8  has been completed, then another resonance check S 8  is carried out. 
         [0048]    In step S 12 , another resonance check is carried out. This resonance check in Step S 12  again corresponds to the resonance check described above in step S 3  or in step S 8  according to  FIG. 4 , see  FIG. 5 . If there is a resonance, the rotational speed of the drive  10  is reduced from value  3  back to value  1  in step S 13  since, at the value  1  for the rotational speed, there is definitely no resonance. However if it is ascertained by the control unit  50  in step S 14  and after the end of a time interval t 3  that there is no resonance, then the rotational speed of the drive  10  is raised to a value  1 , see  FIG. 5 . If the time interval t 3  has not yet ended after the resonance check S 12  has been completed, then another resonance check S 12  is carried out. 
         [0049]    The method described above with the steps S 1  to S 14  together with the steps R 1  to R 9  are repeated during a drilling procedure.