Machine tool having a tool and method of operating a machine tool

Abstract

The present invention relates to a machine tool having a tool connectable to the machine tool using a tool receiving area, the machine tool having a motor for generating torque, the torque being transmittable to the tool receiving area by a drive train of the machine tool. The drive train is provided with play, and a target current for the machine tool motor can be specified with a regularly changing sign, the sign of the motor target current varying at a frequency ranging from 7 Hz to 60 Hz. A second aspect of the present invention relates to a method for operating a machine tool, wherein a motor target current can be specified with a frequency ranging from 7 Hz to 60 Hz, such that torque in different rotational directions is transmitted from the motor to the tool receiving area of ​​the machine tool, and a fixed tool can be released from a borehole.

Description

[Technical Field]

[0001] The present invention relates to a machine tool having a tool connectable to the machine tool with the aid of a tool mount, the machine tool having a motor for generating torque, the torque being transmittable to the tool mount with the aid of a drive train of the machine tool. The drive train is provided with play, and the setpoint current of the machine tool's motor can be specified with a regularly alternating sign, and the frequency for the change of sign of the motor setpoint current is in the range of 7 to 60 Hz. In a second aspect, the present invention relates to a method for operating a machine tool, in which the motor setpoint current is predetermined at a frequency in the range of 7 to 60 Hz, so that torque is transmitted from the motor to the tool mount of the machine tool in different rotational directions, thereby releasing a stuck tool from a borehole. For example, the present invention can be used to release a stuck drill core from a drill bit. [Background technology]

[0002] Core drilling devices capable of cutting a cylindrical drill core from a solid substrate such as concrete, masonry, or stone are known in the prior art. The core drilling device has a substantially cylindrical drill bit as a tool, which is hollow inside to accommodate the drill core. Users of core drilling devices know from experience that removing the drill core from the drill bit once drilling has been successfully completed and the drill bit has been released from the substrate can be a challenge. In addition, it can be difficult to remove a stuck drill bit from a borehole. In many cases, problems are encountered in which the release of the drill core from the drill bit or the removal of the drill bit from the borehole takes longer than the actual core drilling process itself.

[0003] In the prior art, it is known to remove a drill core from a drill bit or a drill bit from a borehole, for example, by mechanical means. To do this, for example, the drill bit is separated from a core drilling device, and the drill core is released from the drill bit by shaking or hammering, in an attempt to remove the drill core from inside the drill bit. This procedure can sometimes be very laborious and time-consuming. Furthermore, the drill bit can be damaged by the hammer blows, which can shorten its useful life.

[0004] To carry out such a process of swinging the drill core off the drill bit, machine tools often use mechanical slip clutches. The mechanical slip clutches can generate assist forces and torque peaks that can swing the drill core off the drill bit. Alternatively, these assist forces and torque peaks can be used to swing a stuck or jammed drill bit free from the borehole. Once the drill bit has been swung free, drilling can either continue or the drill bit can simply be withdrawn from the borehole.

[0005] However, in the course of technological improvements in the field of machine tools, there is a trend toward no longer providing mechanical solutions for individual applications, but instead using electronic and / or mechatronic solutions to swing the drill bit free. For example, electronic slip clutch solutions are known in the prior art, as are solutions for adjusting torque in machine tools. However, these electronic and / or mechatronic solutions are unable to limit or effectively utilize peak torques in the power train, which often occur for very short periods of time. In addition, incorporating a slip clutch into the power train of a machine tool can be complex, and as a result, experts would welcome the elimination of this additional component.

[0006] For example, DE 102018216702 A1 describes a method for controlling or adjusting a handheld machine tool, which allows two different torques to be applied to a threaded fastening means of the machine tool, and EP 4082703 A1 discloses a method for releasing a drill core from a drill bit of a core drill device. Summary of the Invention [Problem to be solved by the invention]

[0007] The object underlying the present invention is to overcome the above-mentioned drawbacks of the prior art and to specify a method for operating a core drilling device which allows for improved release of stuck drill bits from boreholes. Furthermore, experts would be pleased if the method could be used to simplify removal of the drill core from the drill bit, eliminating the need for a mechanical slip clutch. Furthermore, the machine tool to be provided should be configured to be particularly lightweight and compact, so that it is easier to handle and the user can work with the machine tool for an extended period of time. Furthermore, removal of the drill core from the drill bit or removal of the machine tool from the borehole should be quicker than with conventional machine tools known from the prior art. A further aspect of the present invention is that a machine tool, in particular a core drilling device, is provided for carrying out the method. [Means for solving the problem]

[0008] This object is achieved by the subject matter of the independent claims. Advantageous embodiments of the subject matter of the independent claims can be found in the dependent claims.

[0009] According to the present invention, a machine tool is provided having a tool, the tool being connectable to the machine tool via a tool mount. The machine tool has a motor for generating torque, which can be transmitted to the tool mount with the help of a drive train of the machine tool, and the drive train of the machine tool is provided with a play. The setpoint current of the machine tool motor can be specified with a regularly alternating sign, and the frequency for the sign change of the motor setpoint current is in the range of 7 to 60 Hz. The play is in the range of 2 to 10 degrees. By providing the play and specifying the motor setpoint current with a different sign, particularly high torque, especially torque peaks, can be transmitted from the machine tool motor toward the tool mount. This generates a rocking motion in the tool mount, which can be used to release a stuck tool from a borehole. The proposed machine tool advantageously does not require a mechanical slip clutch, thereby providing a particularly compact and lightweight machine tool that ensures easy operation and handling. It has been shown that the proposed machine tool can be used both to facilitate the release of stuck tools from boreholes and to simplify and significantly speed up the release of drill cores from tools designed as drill bits. This is because, if the drill bit becomes stuck in a borehole, the rocking motion caused by the motor setpoint current settings with alternating signs can be used to rock the drill bit free from the borehole. On the other hand, the rocking motion can be used to release the drill core, which has been released from the substrate, from the interior of the drill bit after the drilling process is completed so that a new drilling process can be started with an "empty" drill bit. The present invention therefore advantageously fulfills several objectives and improves various functions of the proposed machine tool.

[0010] For the purposes of the present invention, the expression "regularly alternating signs" preferably encompasses situations in which the direction of rotation of the motor changes from one direction of rotation to the other. Such a change in direction of rotation can be achieved in the context of the present invention by the motor setpoint current changing its sign from "positive" to "negative" or from "negative" to "positive" at regular intervals. However, the expression "regularly alternating signs" preferably also encompasses situations in which the motor of the machine tool does not completely change its direction of rotation, but for example, when a motor setpoint current setting with a positive sign becomes "zero" and therefore has no sign, or when a motor setpoint current setting with a negative sign becomes "zero". Therefore, the scope of protection of the present invention preferably also encompasses situations in which a motor setpoint current setting other than "zero" returns to "zero" and therefore to a neutral value. Preferably, the following sign sequences are included in the scope of protection of the present invention: (+ / - / + / - / +), (+ / 0 / + / 0 / +), (- / 0 / - / 0 / -) or (+ / 0 / - / 0 / + / 0 / -).

[0011] In the sense of the present invention, the power transmission system of the machine tool comprises a motor, a transmission mechanism, and a pinion, the pinion being arranged to drive a larger gear wheel, which is preferably arranged on an output shaft, and the output shaft driving the tool of the machine tool. The tool of the machine tool is preferably driven by transmitting torque from the motor of the machine tool to the tool, the torque being transmitted first, in particular to the tool mount of the machine tool. The pinion is preferably a first gear wheel arranged to drive a second gear wheel, the first gear wheel being slightly smaller than the second gear wheel. The gear wheels belong together in the sense that the first gear wheel drives the second gear wheel. In the context of the present invention, the second, i.e., larger, gear wheel can also preferably be called a "big wheel."

[0012] For the purposes of the present invention, the larger gear wheel and the output shaft are preferably referred to as drive train components, even though, strictly speaking, they form the power train of the machine tool (see FIG. 2). For the purposes of the present invention, the term "drive train" refers in general terms to both the power train and the power train of the machine tool. Therefore, for the purposes of the present invention, the drive train preferably comprises both the motor, transmission mechanism and pinion of the machine tool on one side (drive side) and the larger gear wheel and output shaft on the other side (output side). Consequently, pairs of components from these two subgroups that are adjacent to each other can be considered "adjacent components of the drive train" within the meaning of the present invention.

[0013] For the purposes of the present invention, it is preferred that play be provided between adjacent components in the drive train of the machine tool. However, for the purposes of the present invention, it may also be preferred that play be obtained within a component of the drive train of the machine tool.

[0014] In the sense of the present invention, the larger gear wheel and the output shaft particularly preferably represent "adjacent components of the drive train" within the meaning of the present invention. For the purposes of the present invention, torque coupling preferably occurs between the larger wheel and the output shaft. For the purposes of the present invention, this preferably means that torque is transmitted from the drive shaft of the machine tool to the output shaft with the help of the larger wheel. In the sense of the present invention, torque coupling between adjacent components of the drive train of the machine tool, preferably the larger wheel and the output shaft, preferably makes it possible to incorporate abrupt changes in stiffness and / or play into the drive train. Abrupt changes in stiffness can be made possible, for example, by providing one or more torsion springs.

[0015] For purposes of the present invention, the term "abrupt change in stiffness" preferably means that two components of a powertrain have different stiffnesses. This results in a large stiffness difference between these components of the powertrain, referred to in the context of the present invention as an "abrupt change in stiffness." For example, the stiffness of the powertrain may be in the range of 1,000 to 100,000 Nm / rad, while the stiffness of the motor shaft on the drive side of the powertrain may be in the range of more than 50 Nm / rad. The abbreviation "Nm" represents the unit "Newton-meter," which is a unit of torque or mechanical work or energy. The abbreviation "wheel" represents the unit "radian," which is an angle or radian. For purposes of the present invention, the stiffness of the powertrain is preferably dominated by the stiffness of the output shaft, which, as explained above, is preferably considered a powertrain component in the context of the present invention. For purposes of the present invention, the motor shaft of a machine tool may also be referred to as the rotor shaft or drive shaft. For purposes of the present invention, the rotor shaft is preferably significantly thinner than the output shaft of the machine tool.

[0016] For purposes of the present invention, the drive shaft and / or output shaft in the drive train are preferably characterized by a specific stiffness, the shaft stiffness preferably being specified in units of Nm / rad. Preferably, the overall stiffness of the drive train is less than the smallest individual stiffness of the components in the drive train. This is due to the fact that the overall stiffness of the drive train can be determined by a virtual series connection of torsion springs. For purposes of the present invention, the sudden change in stiffness is preferably caused by play created when the direction of rotation of the motor is changed in combination with a rotation stop. For purposes of the present invention, this preferably means that the sudden change in stiffness can be achieved by providing a rotation stop. Rapidly changing the direction of rotation of the motor can lead to loading and unloading of the drive train components.

[0017] For the purposes of the present invention, the general term "play" refers to two different situations. On the one hand, it refers to play in the conventional sense of the word, where two adjacent components of the drive train can move at an angle of several degrees relative to each other. A particularly preferred play angle in the context of the present invention can be approximately 6 degrees. Such conventional play can exist, for example, between the output shaft and the motor shaft or in the region of the gear wheels of the drive train. On the other hand, the general term "play" can refer to an abrupt change in stiffness or stiffness difference between the stiffness of two adjacent components of the drive train. Such an abrupt change in stiffness can occur, for example, between the stiffness of the output shaft (large diameter, high stiffness) and the stiffness of the motor shaft (small diameter, low stiffness). For the purposes of the present invention, the term "stiffness" preferably refers to torsional stiffness. Therefore, the present invention relates to a machine tool having a drive train that, due to the design of the drive train, allows for rapid changes in the direction of the motor current setting without causing damage. It has been shown that a drive train with play is particularly suitable for achieving this goal.

[0018] For the purposes of the present invention, the play is preferably a rotational play in the power transmission line of the machine tool. For the purposes of the present invention, it is very particularly preferred that the rotational play occurs on the output shaft of the power transmission line of the machine tool. For the purposes of the present invention, this preferably means that the rotor shaft can rotate through a play angle without rotating the output shaft. This play angle preferably corresponds to the product of the play and the transmission ratio of the machine tool. The play angle can be, for example, 5 to 10 degrees, such as 6, 7, 8, 9 degrees, or any intermediate value. If the rotor shaft hits the aforementioned rotation stop during rotation, the play can be advantageously utilized by reversing the direction of rotation. For the purposes of the present invention, it is very particularly preferred that the play is provided between the output shaft and its gear wheel.

[0019] According to the present invention, it is provided that the clearance is in the range of 2 to 10 degrees. The clearance can be preferably in the range of 3 to 9 degrees, particularly preferably in the range of 5 to 7 degrees, and most preferably 6 degrees. A value of 6 degrees has been found to be particularly advantageous for enabling a particularly uncomplicated release of stuck tools, such as drill bits, having various diameters. For example, drill bits used in the context of the present invention can have diameters in the range of 12 to 500 mm. Furthermore, it has been shown that a clearance of approximately 6 degrees also allows particularly good removal of drill cores from drill bits. For the purposes of the present invention, the machine tool is a core drilling device, the tool is a drill bit, and the diameter of the drill bit is preferably in the range of 12 to 500 mm. In a particularly preferred embodiment of the present invention, the diameter of the drill bit is in the range of 20 to 250 mm.

[0020] In the context of the present invention, a motor setpoint current is specified, the motor setpoint current having a frequency in the range of 7 to 60 Hz. The frequency preferably refers to the frequency at which the sign of the predetermined motor current changes ("sign change frequency"). The sign of the motor current changes to move the tool mount in a different rotational direction. If the drill bit is stuck, the drill bit cannot move but receives a transmitted torque. The transmission of torque in a different rotational direction causes a rocking motion acting on the drill bit, which can release the drill bit from a stuck position, as shown. In particular, the use of a brushless motor in the context of the present invention allows such rapid changes in current setting that can cause the described torque oscillations. In particular, rapid changes in the sign of the current setting of the machine tool motor can introduce torque peaks into the drive train, which results in a rocking motion to release the tool of the machine tool. For the purposes of the present invention, the machine tool motor is preferably a brushless DC motor.

[0021] In the context of the present invention, it is preferred that the motor torque follows the motor current very quickly, which in the sense of the present invention preferably means that the direction of rotation of the motor adapts particularly quickly to the changed sign setting of the motor current, i.e. the direction of rotation of the motor changes particularly quickly according to the changed sign setting of the motor current.

[0022] In addition to the motor, transmission mechanism, and pinion, the power transmission system may also include a spindle. The spindle preferably includes an output shaft. For purposes of the present invention, it is preferred that the motor torque multiplied by the transmission ratio n of the transmission mechanism of the power transmission system reaches the spindle of the machine tool. For example, if the motor of the machine tool can generate a peak torque of 5 Nm and the machine tool transmission mechanism has a transmission ratio of n=6, this results in a maximum motor torque of approximately 30 Nm, i.e., the product of the maximum torque and the transmission ratio. Such a value is usually too low to swing a stuck tool of the machine tool free. The inventors have recognized that by providing additional play in the power transmission system of the machine tool, this maximum motor torque can be significantly increased, and as a result, by providing additional play in the power transmission system, a motor torque sufficient to swing a stuck tool of the machine tool free can be generated. This swinging freeing can be advantageously used to free or remove a stuck drill bit from a borehole.

[0023] Additionally, the present invention advantageously provides a method for removing a stuck drill core from a drill bit. Such sticking of a drill core in a drill bit can occur, for example, due to deposits between the drill bit and the drill core, which often occur during the drilling process or operation. The deposits can make it difficult to remove or release the drill core from the drill bit. In the context of the present invention, the regularly changing sign of the motor setpoint current and the resulting rapid change in the rotational direction of the drill bit are utilized here to assist in removing a stuck drill core from the drill bit. In other words, the oscillatory rotational motion of the drill bit can be used to release a stuck drill core from the drill bit. The oscillatory rotational motion of the drill bit can also preferably be referred to as rocking. It has been shown that the oscillatory rotational motion of the drill bit can loosen deposits of workpiece material that lead to sticking of the drill core in the drill bit. This creates free space in the drill bit, which enables or facilitates the release of the drill core from the drill bit of the machine tool.

[0024] It has been found to be particularly advantageous if the frequency for changing the sign of the motor setpoint current to release the drill core from the drill bit is approximately 20 Hz. The oscillatory motion can consist of clockwise and counterclockwise rotations, with a distribution of approximately 30% counterclockwise and 70% clockwise rotations being found to be particularly suitable for making it much easier to remove the drill core from the drill hole. Such oscillatory motions, which are composed of different proportions of "clockwise" and "counterclockwise" rotations, are preferably referred to in the sense of the present invention as "asymmetrically configured movement" of the drill bit in the drill hole. For example, by dividing the rotation into approximately 30% left and 70% right, it is possible to provide a core drill and drill bit system in which the position of the drill bit relative to the borehole sidewall changes slightly during operation. Tests have shown that in this way the entire borehole wall is particularly uniformly contacted with the drill bit.

[0025] The present invention preferably relates to a method for releasing a drill core from a drill bit of a machine tool. In this method, a machine tool is provided, and play is provided in the power transmission system of the machine tool. After operation of the machine tool, i.e., after the drill core is removed from the substrate using the machine tool, if the drill core or a drill core remnant remains in the drill bit and cannot be easily released, the drill bit can be moved back and forth in a rotational motion characterized by a rapid change in direction. The rotational motion with a rapid change in direction can be achieved, in particular, by specifying a motor setpoint current for the machine tool's motor, the sign of which changes at a frequency in the range of 7 to 60 Hz. In the context of the method for loosening a drill core from a drill bit, it is particularly preferred that the drill bit rotates back and forth at a frequency of 10 to 30 Hz, most preferably at a frequency of about 20 Hz. This can be achieved in particular by transmitting torque from the motor to the drill bit, wherein when torque is transmitted from the motor to the drill bit, a rapidly changing sign of the motor setpoint current advantageously results in an oscillatory rotational movement of the drill bit of the machine tool, which oscillatory rotational movement can free the stuck drill core from the drill bit.

[0026] In the context of the present invention, the frequency at which the sign of the motor setpoint current setting changes is in the range of 7 to 60 Hz. However, within the meaning of the present invention, it may be preferable for the limits within this range to be adjustable. For example, an operating parameter of the machine tool can be determined, and the lower and / or upper limits of the sign-change frequency range can be set according to this operating parameter. The operating parameter may be, for example, the housing reaction force of the machine tool. Within the meaning of the present invention, the lower limit of the frequency range is preferably selected according to the natural frequency of the user's hand and arm of the machine tool. For example, the lower limit of the frequency range may correspond to twice the natural frequency of the user's hand and arm to ensure safe and gentle operation of the machine tool for the user. Preferably, the lower limit of the frequency range is approximately 7 Hz, i.e., the frequency at which the sign of the motor setpoint current changes 7 times per second. The unit hertz preferably represents the unit "1 / s" and is abbreviated as "Hz." Therefore, a sign-change frequency of 60 Hz represents 60 changes in the sign of the motor setpoint current per second.

[0027] In the context of the present invention, the motor setpoint current preferably has a substantially rectangular or substantially sinusoidal shape. Preferably, the motor setpoint current may have an offset. Regular sign changes of the motor setpoint current advantageously result in alternating torque peaks, while the offset may result in a holding torque that must be applied by the user of the machine tool. For the purposes of the present invention, the ratio of the torque of the motor ("motor torque") to the inertia of the motor is defined as 1,000 Nm / (kg m 2 ) The holding torque for the user of the machine tool is preferably derived from a time average of the motor torque or the housing reaction torque. This advantageously gives the user the feeling that they still have to hold the machine tool.

[0028] For the purposes of the present invention, the transmission mechanism of the machine tool preferably has a single-stage or multi-stage design. Preferably, the transmission mechanism can provide a transmission ratio in the range of n=1 to n=30, a value of n=1 preferably corresponding to direct drive. The transmission ratio of the transmission mechanism of the machine tool is not limited here to integer values ​​but can also be provided by rational numbers, such as 4.4 or 6.4. For the purposes of the present invention, it is very particularly preferred if the transmission ratio of the transmission mechanism of the machine tool is in the range of 1 to 30, preferably in the range of 3 to 10, particularly preferably in the range of 4 to 7.

[0029] For purposes of the present invention, the stiffness of the power train is preferably in the range of 1,000 to 100,000 Nm / rad. Here, the stiffness of the power train is preferably dominated by the stiffness of the output shaft, which, as explained above, is preferably considered a component of the power train in the context of the present invention. For purposes of the present invention, the output shaft of the machine tool preferably has a larger diameter than the motor shaft, and as a result, the stiffness of the output shaft is preferably significantly greater than the stiffness of the motor shaft. For purposes of the present invention, the stiffness of the motor shaft is preferably in the range of more than 50 Nm / rad. Therefore, the ratio of the stiffness of the power train of the machine tool to the stiffness of the motor shaft of the machine tool is preferably in the range of 20 to 2,000. In other words, the stiffness of the power train or output shaft can be 20 to 2,000 times greater than the stiffness of the rotor shaft of the machine tool.

[0030] For the purposes of the present invention, the aforementioned stiffness is preferably the torsional stiffness of the drive train, output shaft or motor shaft.

[0031] In a second aspect, the present invention relates to a method for operating a machine tool. The terms, definitions and technical advantages introduced with respect to the machine tool preferably apply equally to the method for operating the machine tool, which comprises the following method steps: a) preparing a machine tool, wherein a play is provided in a power transmission system of the machine tool, and the play is in the range of 2 to 10 degrees; b) specifying a motor setpoint current having a sign change frequency in the range of 7 to 60 hertz; c) transmitting a torque from the motor to a tool mount of the machine tool, the torque having a sign that changes at regular intervals according to a specified sign change frequency, thereby releasing the stuck tool from the borehole; It is characterized by:

[0032] The transmission of torque having a sign that changes at regular intervals according to a predetermined sign-change frequency preferably means, in the sense of the present invention, that the motor rotates based on the setting of the motor setpoint current, i.e., in a direction of rotation corresponding to the sign of the motor setpoint current. According to the present invention, this sign specification of the motor setpoint current changes regularly, the "regularity" resulting from the sign-change frequency. The sign-change frequency preferably indicates the time interval at which the sign of the motor setpoint current changes. The machine tool motor follows this changed specification by changing its direction of rotation. If the machine tool motor is a brushless DC motor, it can follow the changed motor setpoint current setting relatively quickly, and as a result, the use of a brushless DC motor is preferred in the context of the present invention.

[0033] When the motor changes its direction of rotation, this changed motion and the corresponding changed direction of torque are transmitted to the tool mount via the power transmission line. If the tool of the machine tool is not stuck in the borehole, the rapidly changing motion of the drill bit can, for example, generate a rocking motion that can rock a drill core located in the drill bit and release it from the drill bit. If the drill bit is stuck in the drill hole, the vibration motion can be used to rock the drill bit itself free from the drill hole and release the drill bit. In other words, the rocking motion can be used to release a stuck tool of the machine tool from the borehole. Therefore, the method of operating a machine tool can also preferably be referred to as a method of releasing a stuck tool of a machine tool from a borehole. Additionally, the present invention can advantageously be used to release a drill core from a drill bit without damaging the drill bit. Furthermore, no tools are required for the removal process, resulting in advantageous tool-less removal of the drill core from the drill bit. In the sense of the present invention, it is preferred that by changing the sign of the motor setpoint current, a movement of the tool of the machine tool can be brought about in a different direction of rotation, which movement can advantageously be used to free a stuck drill bit from a borehole or to free a drill core from a drill bit.

[0034] Introducing play into the driveline can significantly increase the maximum torque that can be transmitted from the motor to the tool mount. For example, 6 degrees of play has been shown to contribute to torque peaks that can occur when the tool or tool mount vibrates. Testing has shown that 6 degrees of play achieves the most significant increase in torque in the sign-change frequency range of 15 to 21 hertz.

[0035] For the purposes of the present invention, it is particularly preferred that play be provided between adjacent components in the drive train of the machine tool. However, for the purposes of the present invention, it may also be preferred that play be obtained within a component of the drive train of the machine tool.

[0036] Further advantages can be seen from the following description of the figures. The figures, the description and the claims contain a number of feature combinations. Those skilled in the art will also consider the features individually, as appropriate, and combine them to form suitable further combinations.

[0037] In the figures, the same and similar components are designated with the same reference numerals. [Brief explanation of the drawings]

[0038] [Figure 1] 1 shows a diagram of an exemplary preferred embodiment of the present invention; [Figure 2] 1 shows a diagram of an exemplary preferred embodiment of a drive train; DETAILED DESCRIPTION OF THE INVENTION

[0039] FIG. 1 illustrates a possible embodiment of the present invention. In particular, FIG. 1 shows a machine tool formed as a core drilling device 1 for cutting a drill core 5 from a hard substrate, such as concrete, stone, or masonry. The machine tool 1 is held by a handle 4 and can be switched on or off with the aid of a switching device 8. The tool of the core drilling device 1 is a drill bit 2, in which the drill core 5 is housed during the cutting process. The machine tool 1 has a motor 6 that receives specifications regarding the magnitude and direction of the motor current from a control device 7 of the machine tool 1. In the context of the proposed invention, a method for operating the core drilling machine 1 is proposed, in which the motor current specifications, and in particular its sign, are periodically changed. The frequency at which this change occurs is preferably referred to in the context of the present invention as the "sign change frequency." According to the present invention, the sign change frequency is in the range of 7 to 60 Hz.

[0040] The machine tool 1 includes a drive train 14 having a motor 6, a motor shaft 9, a transmission mechanism 10, and a pinion 11. The pinion 11 interacts with a larger gear wheel 12 arranged on an output shaft 13 of the machine tool 1. FIG. 2 shows a schematic diagram of a possible configuration of the drive train 14. For the purposes of the present invention, the larger wheel 12 and the output shaft 13 are preferably considered components of the drive train 14 of the machine tool 1. The output shaft 13 is preferably connected to the tool 2, in particular to the tool mount 3 of the machine tool 1. Play is provided in the drive train 14 of the machine tool 1. On the one hand, the term "play" in general terms refers to play in the conventional sense of the word, where two adjacent components of the drive train 14 can move at an angle of several degrees relative to each other. A particularly preferred play angle in the context of the present invention can be approximately 6 degrees. Such conventional play may exist, for example, between the output shaft 13 and the motor shaft 9 or in the region of the gear wheels 11, 12 of the drive train 14. In other words, a play angle of, for example, 6 degrees may be associated with the spindle 13, the tool mount 3 or the drill bit 5.

[0041] On the other hand, the general term "play" can refer to an abrupt change or difference in stiffness between the stiffness of two adjacent components of the drive train, for example between the output shaft 13 and the motor shaft 9. [Explanation of symbols]

[0042] 1 Core Drill Device 2 drill bits 3 Tool attachment part 4 Handle 5 Drill Core 6. Core drill device motor 7. Control device for core drill device 8 Switching Devices 9 Motor shaft 10 Transmission Mechanism 11 Pinion 12 Big Wheels 13 Output shaft 14 Power transmission system

Claims

1. A machine tool (1) having a tool (2), which can be connected to the machine tool (1) with the help of a tool attachment (3), and the machine tool (1) having a motor (6) for generating torque, which can be transmitted to the tool attachment (3) with the help of a power transmission system (14) of the machine tool (1), a play is provided in the power transmission system (14), and the setpoint current of the motor (6) of the machine tool (1) can be specified with a regularly alternating sign, the frequency for the change of sign of the motor setpoint current being in the range of 7 to 60 Hz, and the play being in the range of 2 to 10 degrees; characterized in that Machine tools (1).

2. The play is in the range of 3 to 9 degrees, preferably in the range of 5 to 7 degrees, and particularly preferably 6 degrees. A machine tool (1) according to claim 1.

3. the play is provided between adjacent components of the power transmission system (14) of the machine tool (1), A machine tool (1) according to claim 1 or 2.

4. The motor setpoint current has a substantially rectangular or substantially sinusoidal waveform. A machine tool (1) according to any one of claims 1 to 3.

5. The motor setpoint current has an offset. A machine tool (1) according to any one of claims 1 to 4.

6. the overall stiffness of the drive train (14) is less than the smallest individual stiffness of any component of the drive train (14); the play can cause abrupt changes in stiffness; and / or that the term "stiffness" means torsional stiffness; characterized by: A machine tool (1) according to any one of claims 1 to 5.

7. The motor (6) of the machine tool (1) is a brushless DC motor. A machine tool (1) according to any one of claims 1 to 6.

8. The ratio of the torque of the motor (6) to the inertia of the motor (6) is 1,000 Nm / (kg m ２ ) is greater than A machine tool (1) according to any one of claims 1 to 7.

9. the power transmission system (14) comprises the motor (6), a transmission mechanism (10) and a pinion (11), the pinion (11) being designed to drive a larger gear wheel (12), the larger gear wheel (12) being arranged on an output shaft (13), the output shaft (13) being designed to drive the tool (2) of the machine tool (10). A machine tool (1) according to any one of claims 1 to 8.

10. The transmission mechanism (10) is characterized in that it has a single-stage or multi-stage design. A machine tool (1) according to claim 9.

11. The rigidity of the power transmission system (14) is in the range of 1,000 to 100,000 Nm / rad. A machine tool (1) according to any one of claims 1 to 10.

12. The power transmission system (14) of the machine tool (1) comprises a motor shaft (9), and the stiffness of the motor shaft (9) is in a range exceeding 50 Nm / rad. A machine tool (1) according to any one of claims 1 to 11.

13. the play is a rotational play in the power transmission line (14) of the machine tool (1), in particular on the output shaft (13), A machine tool (1) according to any one of claims 1 to 12.

14. The following method steps: a) preparing the machine tool (1), wherein the power transmission system (14) of the machine tool (1) is provided with play, the play being in the range of 2 to 10 degrees; b) specifying a motor setpoint current having a sign change frequency in the range of 7 to 60 hertz; c) transmitting a torque having a sign that changes at regular intervals according to the specified sign-change frequency from the motor (6) to the tool mount (3) of the machine tool (1), thereby releasing a stuck tool (2) from the borehole; characterized by, A method for operating a machine tool (1) according to any one of claims 1 to 13.

15. a ratio of the rigidity of the power transmission system (14) of the machine tool (1) to the rigidity of the motor shaft (9) of the machine tool (1) is in the range of 20 to 2,000; 15. The method of claim 14.

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