Machine tool with a tool, and method for operating the machine tool

Abstract

The invention relates to a machine tool with a tool, wherein the tool can be connected to the machine tool using a tool receiving area, the machine tool has a motor for generating a torque, and the torque can be transferred to the tool receiving area by means of a powertrain of the machine tool. Play is provided in the powertrain, and a target current for the motor of the machine tool can be specified with a regularly changing sign, wherein the sign of the motor target current changes at a frequency ranging from 7 to 60 Hertz. A second aspect of the invention relates to a method for operating the machine tool. A motor target current with a frequency ranging from 7 to 60 Hertz is specified such that a torque in different rotational directions is transferred from the motor to the tool receiving area of the machine tool, and a clamped tool can be released from a borehole.

Description

[0001] MACHINE TOOL WITH A TOOL AND METHOD FOR OPERATING THE MACHINE TOOL

[0002] The present invention relates to a machine tool with a tool, wherein the tool can be connected to the machine tool by means of a tool holder, the machine tool has a motor for generating a torque, and wherein the torque can be transmitted to the tool holder by means of a drive train of the machine tool. A play is provided in the drive train, wherein a target current for the motor of the machine tool can be specified with a regularly alternating sign, wherein a frequency for the change in the sign of the target motor current lies in a range of 7 to 60 Hertz.In a second aspect, the invention relates to a method for operating the machine tool, wherein a motor target current is specified with a frequency in a range of 7 to 60 Hertz, so that a torque is transmitted in different directions of rotation from the motor to the tool holder of the machine tool, allowing a jammed tool to be released from a drilled hole. For example, the invention can also be used to release a jammed drill core from a drill bit.

[0003] Background of the invention:

[0004] Core drilling machines are known in the art for cutting cylindrical cores out of solid substrates such as concrete, masonry, or stone. Core drilling machines utilize a substantially cylindrical core bit that is hollow inside to accommodate the core. Core drilling machine users know from experience that removing the core from the bit once drilling has been successfully completed and the core has been cut out of the subsurface can be challenging. Furthermore, removing a jammed core bit from a borehole can be difficult. A common problem is that removing the core from the bit or removing the bit from the borehole takes longer than drilling the core itself.

[0005] For example, it is known in the art to remove the core from the core bit or the core bit from a borehole using mechanical means. This involves separating the core bit from the core drilling machine, for example, and attempting to loosen the core from the core bit by shaking or hammering and removing it from the interior of the core bit. This process can be very laborious and time-consuming under certain circumstances. Furthermore, the hammer blows can damage the core bit, shortening its lifespan.

[0006] To perform this kind of shaking-out process, a mechanical slip clutch is often used in machine tools. Mechanical slip clutches can generate auxiliary forces and torque peaks that can be used to shake the core from the drill bit. Alternatively, these auxiliary forces and torque peaks can be used to shake a jammed or stuck drill bit free from a borehole. Following this shaking-out process, drilling can then either be continued or the drill bit can be easily pulled out of the borehole.

[0007] However, with the advancement of technology in the field of machine tools, there is a move to no longer provide mechanical solutions for individual applications, but instead to use electronic and / or mechatronic solutions for freeing a drill bit. For example, electronic slip clutch solutions are known in the state of the art, as are solutions for regulating the torque in the machine tool. However, these electronic and / or mechatronic solutions are often unable to limit or effectively utilize the peak torques in the machine tool's drive train, which often occur very briefly. Furthermore, integrating a slip clutch into the drive train of a machine tool can be complex, so experts would welcome the possibility of dispensing with this additional component.

[0008] For example, DE 10 2018 216 702 A1 describes a method for controlling or regulating a handheld power tool, wherein a screwing means of the power tool can be subjected to two different torques. EP 4 082 703 A1 discloses a method for removing a drill core from a core bit of a core drilling machine.

[0009] The object on which the present invention is based is to overcome the disadvantages of the prior art described above and to provide a method for operating a core drilling machine with which the release of a jammed core bit from a borehole can be improved. Furthermore, those skilled in the art would welcome it if the method made it easier to release a core bit from a core bit and if a mechanical slip clutch could be dispensed with. Furthermore, the machine tool to be provided should be particularly light and compact, so that the handling of the machine tool is made easier and the period of time that a user can work with the machine tool can be extended. Furthermore, the removal of a core bit from a core bit orThe removal of a tool of the machine tool from a borehole can be carried out more quickly than with conventional machine tools known from the prior art. A further aspect of the invention is that a machine tool, in particular a core drilling machine, is provided for carrying out the method.

[0010] The problem is solved 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.

[0011] Description of the invention:

[0012] According to the invention, a machine tool is provided with a tool, wherein the tool can be connected to the machine tool by means of a tool holder. The machine tool has a motor for generating a torque, wherein the torque can be transmitted to the tool holder by means of a drive train of the machine tool and a play is provided in the drive train of the machine tool. A target current for the motor of the machine tool can be specified with a regularly alternating sign, wherein a frequency for the change of the sign of the motor target current lies in a range from 7 to 60 Hertz. The play lies in a range from 2 to 10 degrees. By providing the play and specifying the motor target current with different signs, particularly high torques, in particular torque peaks, can be transmitted from the motor of the machine tool in the direction of the tool holder.This creates a vibrating movement at the tool holder, which can be used to free a jammed tool from a drilled hole. The proposed machine tool advantageously does not require a mechanical slip clutch, so that a particularly compact and lightweight machine tool can be provided that ensures comfortable operation and handling. It has been shown that the proposed machine tool makes it possible to both facilitate the freeing of a jammed tool from a drilled hole and to simplify and significantly speed up the drilling of a core from a tool designed as a drill bit. This is because the vibrating movement, which is caused by the changing sign of the motor setpoint current, can be used to shake a drill bit out of a drilled hole if the drill bit had previously become jammed in the drilled hole.Secondly, the vibration movement can be used to release a drill core cut from the substrate from the interior of the drill bit after the drilling process has been completed, allowing a new drilling process to be started with an "empty" drill bit. Thus, the invention advantageously serves several purposes and improves various functions of the proposed machine tool.

[0013] The formulation of the "regularly alternating sign" in the sense of the invention preferably includes situations in which the direction of rotation of the motor changes from one direction of rotation to the other. In the context of the present invention, such a change in direction of rotation can be achieved by the motor setpoint current changing its sign from "plus" to "minus" or from "minus" to "plus" at regular intervals. However, the formulation of the "regularly alternating sign" preferably also includes situations in which the motor of the machine tool does not completely change its direction of rotation, but in which, for example, a motor setpoint current with a positive sign becomes "zero" and thus has no sign, or in which a motor setpoint current with a negative sign becomes "zero".Thus, the scope of the invention preferably also encompasses situations in which a motor target current setting other than "zero" returns to "zero" and thus to the neutral value. Preferably, the following sign sequences fall within the scope of the present invention: (+ / - / + / - / +), (+ / 0 / + / 0 / +), (- / 0 / - / 0 / -) or (+ / 0 / - / 0 / + / 0 / -).

[0014] According to the invention, it is preferred that the drive train of the machine tool comprises a motor, a gearbox, and a pinion, the pinion being configured to drive a larger gear, the larger gear being arranged on an output shaft, the output shaft driving the tool of the machine tool. The tool of the machine tool is preferably driven by a torque being transmitted from the motor of the machine tool to the tool, the torque initially being transmitted in particular to the tool holder of the machine tool. The pinion is preferably a first gear that is configured to drive a second gear, the first gear being somewhat smaller than the second gear. The gears belong together in the sense that the first gear drives the second gear.The second or larger gear can preferably also be referred to as a “large gear” in the sense of the invention.

[0015] Within the meaning of the invention, it is preferred that the larger gear and the output shaft are referred to as components of the drive train, even though, technically speaking, they form the output train of the machine tool (see Fig. 2). The term "drive train" within the meaning of the invention, as a generic term, refers to both the drive train and the output train of the machine tool. It is therefore preferred within the meaning of the invention that the drive train comprises the motor of the machine tool, the gearbox and the pinion on one side (drive side), as well as the larger gear and the output shaft on the other side (output side). Consequently, pairs of components from these two subgroups that are located next to one another can be "adjacent components of the drive train" within the meaning of the invention.

[0016] According to the invention, it is preferred that the clearance be provided between adjacent components in the drive train of the machine tool. However, according to the invention, it may also be preferred that the clearance be realized within a single component of the drive train of the machine tool.

[0017] It is particularly preferred within the meaning of the invention that the larger gear and the output shaft represent the "adjacent components of the drive train" within the meaning of the invention. It is preferred within the meaning of the invention that torque is transmitted between the large gear and the output shaft. Within the meaning of the invention, this preferably means that torque is transmitted from the drive shaft of the machine tool to the output shaft with the aid of the large gear. It is preferred within the meaning of the invention that the torque transmission between the adjacent components of the drive train of the machine tool, preferably the large gear and the output shaft, enables the introduction of a stiffness jump and / or play into the drive train. The stiffness jump can be made possible, for example, by the provision of one or more torsion springs.

[0018] The term "stiffness jump" in the sense of the invention preferably means that two components of the drivetrain have different stiffnesses. This results in a large stiffness difference between these components of the drivetrain, which is referred to as a "stiffness jump" in the sense of the invention. For example, the stiffness of the drivetrain can be in a range of 1,000 to 100,000 Nm / rad, while the stiffness of a motor shaft on the drive side of the drivetrain can be in a range of greater than 50 Nm / rad. The abbreviation "Nm" stands for the unit "Newton meter," which is a unit for torque, mechanical work, or energy. The abbreviation "rad" stands for the unit "radian," which is the angular or radian measure.Within the meaning of the invention, it is preferred that the rigidity of the drive train is preferably dominated by the rigidity of the output shaft, whereby the output shaft—as explained above—is preferably considered a component of the drive train in the context of the present invention. The motor shaft of the machine tool can also be referred to as the rotor shaft or drive shaft within the meaning of the invention. Within the meaning of the invention, it is preferred that the rotor shaft be significantly thinner than the output shaft of the machine tool.

[0019] According to the invention, it is preferred that the input shaft and / or the output shaft in the drive train are characterized by a specific stiffness, wherein the stiffness of the shafts is preferably specified in the unit Nm / rad. The overall stiffness of the drive train is preferably smaller than the smallest individual stiffness of a component within the drive train. This results from the fact that the overall stiffness of the drive train can be determined by an imaginary series connection of torsion springs. According to the invention, it is preferred that the stiffness jump arises from the play that is generated when the direction of rotation of the motor changes in combination with a rotation stop. According to the invention, this preferably means that the stiffness jump can preferably be brought about by the provision of the rotation stop.The rapidly changing direction of rotation of the engine can lead to a loading and unloading of the drive train components.

[0020] The term "play" is a generic term within the meaning of the invention and refers to two different situations: firstly, a play in the conventional sense of the word, in which two adjacent components of the drive train can move at a slight angle relative to each other. A particularly preferred play angle within the meaning of the invention can be approximately 6 degrees. Such conventional play can occur, for example, between the output shaft and the motor shaft or in the area of ​​the drive train gears. Secondly, the generic term "play" can refer to a stiffness jump or stiffness difference between the stiffnesses of two adjacent components of the drive train.Such a stiffness jump can occur, for example, between the stiffness of the output shaft (large diameter, high stiffness) and the motor shaft (smaller diameter, low stiffness), whereby the term "stiffness" in the context of the invention preferably refers to torsional stiffness. The invention thus preferably relates to a machine tool with a drive train that, due to its design, can implement a rapid change in the direction of the motor current setpoint without causing damage. To achieve this goal, a drive train with a certain amount of play has been shown to be particularly well suited.

[0021] It is preferred within the meaning of the invention that the backlash in the context of the present invention is rotational backlash in the drive train of the machine tool. It is particularly preferred within the meaning of the invention that the rotational backlash occurs on the output shaft of the drive train of the machine tool. In the meaning of the invention, this preferably means that the rotor shaft can rotate through a backlash angle without causing a rotation of the output shaft. This backlash angle preferably corresponds to a product of the backlash and the gear ratio of the machine tool. The backlash angle can, for example, be between 5 and 10 degrees, for example 6 degrees, 7 degrees, 8 degrees, 9 degrees or any value in between. If the rotor shaft strikes the above-mentioned rotation stop during its rotation, the backlash can advantageously be utilized by reversing the direction of rotation in the opposite direction.In the sense of the invention, it is particularly preferred to provide the play between the output shaft and the gear of the output shaft.

[0022] According to the invention, the play lies in a range of 2 to 10 degrees. The play can preferably lie in a range of 3 to 9 degrees, particularly preferably in a range of 5 to 7 degrees, and most preferably 6 degrees. A value of 6 degrees has proven particularly advantageous in order to enable particularly uncomplicated release of jammed tools, for example core bits, with different diameters. For example, the core bits used in the context of the present invention can have a diameter in a range of 12 to 500 mm. Furthermore, it has been shown that a play of approximately 6 degrees also enables the removal of a drill core from a core bit particularly well. Within the meaning of the invention, it is preferred that the machine tool is a core drilling machine and the tool is a core bit, wherein a diameter of the core bit lies in a range of 12 to 500 mm.In a particularly preferred embodiment of the invention, the diameter of the drill bit is in a range of 20 to 250 mm.

[0023] In the context of the present invention, a target motor current is specified, with the target motor current having a frequency in a range of 7 to 60 Hertz. The frequency preferably describes the frequency with which a sign of the specified motor current changes ("sign-changing frequency"). The sign of the motor current changes to cause the tool holder to move in different directions of rotation. If the drill bit is jammed, the drill bit cannot move but experiences the transmitted torque. By transmitting a torque with different directions of rotation, a shaking movement results, which acts on the drill bit and which - as has been shown - is capable of freeing the drill bit from a jam.In particular, the use of a brushless motor in the context of the present invention enables such rapid changes in the current setting, which can cause the described torque oscillations. In particular, the rapid change in the sign of the current setting for the machine tool motor can introduce torque peaks into the drive train, which lead to the shaking movement for releasing the machine tool's tool. It is preferred within the context of the invention for the machine tool motor to be a brushless DC motor.

[0024] According to the invention, it is preferred that the motor torque follows the motor current very quickly. This preferably means that the direction of rotation of the motor adapts particularly quickly to a changed preset sign for the motor current, i.e., that the direction of rotation of the motor changes particularly quickly according to a changed preset sign of the motor current.

[0025] In addition to the motor, the gearbox, and the pinion, the drive train can also include a spindle. The spindle preferably comprises the output shaft. According to the invention, it is preferred that the motor torque multiplied by the gear ratio n of the drive train's gearbox arrives at the spindle of the machine tool. For example, if the motor of the machine tool is capable of generating a peak torque of 5 Nm and the gearbox of the machine tool has a gear ratio n=6, this results in a maximum motor torque of approximately 30 Nm, i.e., the product of the maximum torque and the gear ratio. Such a value is usually too low to shake a jammed tool of the machine tool free.The inventors have recognized that by providing additional play in the drive train of the machine tool, this maximum motor torque can be significantly increased, so that by providing the additional play in the drive train, a motor torque can be generated that is advantageously sufficient to free a jammed tool of the machine tool. Such free vibration can advantageously be used to release or remove a jammed drill bit from a drilled hole.

[0026] Furthermore, the invention can advantageously provide a method for removing a jammed drill core from the drill bit. Such jamming of the drill core within the drill bit can occur, for example, due to deposits between the drill bit and the drill core, whereby such deposits often arise during a drilling process or drilling operation. The deposits can make it more 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 target current and the resulting rapid change in the direction of rotation of the drill bit are exploited to assist in releasing a jammed drill core from a drill bit. In other words, the oscillatory rotary movement of the drill bit can be used to release a jammed drill core from the drill bit.The oscillatory rotational movement of the core bit can also be referred to as shaking. It has been shown that the oscillatory rotational movement of the core bit can loosen the deposits of the drilling material that cause the core to jam in the core bit. This creates free spaces within the core bit that enable or facilitate the removal of the core from the machine tool's core bit.

[0027] For removing the core from the core bit, it has proven particularly advantageous if the frequency for changing the sign of the motor's nominal current is approximately 20 Hertz. The oscillating movement can be composed of a clockwise and a counterclockwise rotation, with a split of approximately 30% counterclockwise and 70% clockwise rotation having proven particularly suitable for significantly facilitating the removal of the core from the borehole. Such an oscillating movement, which is composed of different proportions of "clockwise" and "counterclockwise" rotation, is preferably referred to in the context of the invention as an "asymmetrically composed movement" of the core bit in the borehole. For example, with a split of approximately 30% counterclockwise and 70% clockwise rotation, a system comprising a core drilling machine and core bit can be provided in which the position of the core bit relative to the side walls of the borehole changes slightly during operation.Tests have shown that in this way the entire wall of the borehole has particularly even contact with the drill bit.

[0028] The invention preferably relates to a method for removing a drill core from a drill bit of a machine tool. In the method, a machine tool is provided, wherein a play is provided in the drive train of the machine tool. If, after operation of the machine tool, i.e. after a drill core has been cut out of a subsoil using the machine tool, a drill core or a drill core residue remains in the drill bit that cannot be easily removed, the drill bit can be moved back and forth with a rotary movement characterized by a rapid change of direction. The rotary movement with the rapid change of direction can be achieved in particular by specifying a target motor current to the motor of the machine tool, wherein the sign of the target motor current changes at a frequency in a range of 7 to 60 Hertz.In the context of the method for releasing 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 approximately 20 Hz. This can be achieved, in particular, by transmitting the torque from the motor to the drill bit. During the transmission of the torque from the motor to the drill bit, the rapidly changing sign of the motor target current advantageously leads to an oscillatory rotary movement of the drill bit of the machine tool, with which a jammed drill core can be released from the drill bit.

[0029] In the context of the present invention, the frequency at which the sign of the motor target current specification changes lies in a range from 7 to 60 Hz. However, it can also be preferred within the meaning of the invention for the limits to be adjustable within this range. For example, an operating parameter of the machine tool can be determined, wherein a lower and / or an upper limit of the range for the sign change frequency can be set depending on this operating parameter. The operating parameter can be, for example, a housing reaction of the machine tool. In the meaning of the invention, it is preferred that a lower limit of the frequency range is selected depending on a hand-arm natural frequency of a user of the machine tool.For example, the lower limit of the frequency range can correspond to twice the user's hand-arm natural frequency to ensure safe and gentle operation of the machine tool for the user. The lower limit of the frequency range is preferably approximately 7 Hertz, i.e., a frequency of 7 changes in the sign of the motor target current per second. The unit Hertz preferably represents the unit "1 / s" and is abbreviated to "Hz." Accordingly, a sign change frequency of 60 Hz represents 60 changes in the sign of the motor target current per second.

[0030] It is preferred according to the invention that the motor target current has a substantially rectangular or sinusoidal shape. Preferably, the motor target current can have an offset. The regular change in the sign of the motor target current advantageously leads to alternating torque peaks, while the offset can lead to a holding torque that must be applied by the user of the machine tool. It is preferred according to the invention that a ratio between a torque of the motor («motor torque») and a motor inertia is greater than 1,000 Nm / (kg-m 2 ). The holding torque for the machine tool user is preferably determined from the time-averaged value 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.

[0031] According to the invention, it is preferred that the transmission of the machine tool be single-stage or multi-stage. Preferably, the transmission can provide a ratio in a range from n=1 to n=30, with n=1 preferably corresponding to a direct drive. The transmission of the transmission of the machine tool is not limited to integer values, but rational numbers such as 4.4 or 6.4 can also occur. According to the invention, it is particularly preferred that the transmission of the machine tool be in a range from 1 to 30, preferably in a range from 3 to 10, and particularly preferably in a range from 4 to 7.

[0032] It is preferred within the meaning of the invention that the stiffness of the drive train lies in a range from 1,000 to 100,000 Nm / rad. The stiffness of the drive train of the machine tool is preferably dominated by the stiffness of the output shaft, whereby the output shaft—as explained above—is preferably considered as a component of the drive train in the context of the present invention. It is preferred within the meaning of the invention that the output shaft of the machine tool has a larger diameter than the motor shaft, so that the stiffness of the output shaft is significantly greater than the stiffness of the motor shaft. It is preferred within the meaning of the invention that the stiffness of the motor shaft lies in a range greater than 50 Nm / rad. This preferably results in a ratio between the stiffness of the drive train of the machine tool and the stiffness of the motor shaft of the machine tool lying in a range from 20 to 2,000.In other words, the stiffness of the drive train or output shaft can be 20 to 2,000 times greater than the stiffness of the rotor shaft of the machine tool.

[0033] It is preferred in the sense of the invention that the stiffnesses mentioned are torsional stiffnesses of the drive train, the output shaft or the motor shaft.

[0034] In a second aspect, the invention relates to a method for operating a machine tool. The terms, definitions, and technical advantages introduced for the machine tool preferably apply analogously to the operating method for the machine tool. The operating method is characterized by the following method steps: a) providing the machine tool, wherein a play is provided in the drive train of the machine tool, wherein the play lies in a range of 2 to 10 degrees, b) specifying a target motor current with a sign-alternating frequency in a range of 7 to 60 Hertz, c) transmitting a torque with a sign that changes at regular intervals according to the specified sign-alternating frequency from the motor to the tool holder of the machine tool, so that a jammed tool can be released from a drilled hole.

[0035] The transmission of torque with a sign changing at regular intervals according to the specified sign-changing frequency preferably means, in the sense of the invention, that the motor rotates based on the specification of the target motor current, specifically in a direction of rotation that corresponds to a sign of the target motor current. According to the present invention, the specification of this sign of the target motor current changes regularly, with the "regularity" resulting from the sign-changing frequency. The sign-changing frequency preferably indicates the time intervals at which the sign of the target motor current changes. The motor of the machine tool follows this changed specification by changing its direction of rotation.If the motor of the machine tool is a brushless DC motor, the motor of the machine tool can follow the changed motor target current specification comparatively quickly, so that the use of a brushless DC motor is preferred in the context of the present invention.

[0036] When the motor changes its direction of rotation, this changed movement and the changed direction of the corresponding torque are transferred via the drive train to the tool holder. If the tool of the machine tool is not jammed in a drill hole, the rapidly changing movements of the core bit can create a shaking movement that can, for example, shake a drill core that is contained in the core bit free and release it from the drill bit. If the core bit is jammed in a drill hole, the shaking movement can shake the core bit itself free and free it from the drill hole. In other words, the shaking movements can be used to free a jammed tool of the machine tool from a drill hole.Thus, the method for operating the machine tool can preferably also be referred to as a method for releasing a jammed tool of the machine tool from a drill hole. Furthermore, the invention can be used to release a drill core from the drill bit, advantageously without damaging the drill bit. Furthermore, no tool is required for the removal process, so that the drill core can advantageously be removed from the drill bit without tools. Within the meaning of the invention, it is preferred that by changing the sign of the desired motor current, a movement of the tool of the machine tool can be effected in different directions of rotation, which can advantageously be used to release a jammed drill bit from a drill hole or to release a drill core from the drill bit.Incorporating backlash in the drive train can significantly increase the maximum torque values ​​transmitted from the motor to the tool holder. It has been shown that a gear backlash of, for example, 6 degrees contributes to the generation of torque peaks when the tool or tool holder oscillates. Tests have shown that with a backlash of 6 degrees, the most significant torque increases can be achieved in a sign-change frequency range of 15 to 21 Hertz.

[0037] Within the meaning of the invention, it is particularly preferred that the clearance be provided between adjacent components of the drive train of the machine tool. However, within the meaning of the invention, it may also be preferred that the clearance be realized within one component of the drive train of the machine tool.

[0038] Further advantages emerge from the following description of the figures. The figures, the description, and the claims contain numerous features in combination. Those skilled in the art will expediently consider the features individually and combine them into further meaningful combinations. In the figures, identical and similar components are numbered with the same reference numerals.

[0039] It shows:

[0040] Fig. 1 View of an exemplary preferred embodiment of the machine tool

[0041] Fig. 2 View of an exemplary preferred embodiment of the drive train

[0042] Implementation example and figure description:

[0043] Figure 1 shows a possible embodiment of the invention. In particular, Fig. 1 shows a machine tool designed as a core drilling device 1 for cutting out drill cores 5 from a hard substrate, such as concrete, stone, or masonry. The machine tool 1 can be held by a user with a handle 4 and switched on or off with the aid of a switching device 8. The tool of the core drilling device 1 is a core bit 2, in which the drill core 5 is received during the cutting process. The machine tool 1 has a motor 6, which 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 a core drilling device 1 is proposed, in which the specification of the motor current and in particular its sign changes regularly.The frequency at which this change occurs is preferably referred to as the "sign change frequency" within the meaning of the invention. According to the invention, the sign change frequency lies in a range of 7 to 60 Hz.

[0044] The machine tool 1 comprises a drive train 14, which has the motor 6, a motor shaft 9, a gearbox 10, and a pinion 11. The pinion 11 interacts with a larger gear 12, which is arranged on an output shaft 13 of the machine tool 1. A possible embodiment of the drive train 14 is shown schematically in Figure 2. Within the meaning of the invention, it is preferred that the large gear 12 and the output shaft 13 are 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 holder 3 of the machine tool 1. Play is provided in the drive train 14 of the machine tool 1. The term "play" is a generic term that refers, on the one hand, to play in the conventional sense of the word, in which two adjacent components of the drive train 14 can move at an angle of several degrees relative to one another.A particularly preferred play angle within the meaning of the invention can be approximately 6 degrees. Such conventional play can be present, for example, between the output shaft 13 and the motor shaft 9 or in the area of ​​the gears 11, 12 of the drive train 14. In other words, the play angle of, for example, 6 degrees can be related to the spindle 13, the tool holder 3, or the drill bit 5.

[0045] On the other hand, the generic term "play" can refer to a stiffness jump or stiffness difference between the stiffnesses of two adjacent components of the drive train, which, for example, exists between the output shaft 13 and the motor shaft 9.

[0046] 1 core drilling machine

[0047] 2 core bits

[0048] 3 Tool holder 4 Handle

[0049] 5 drill core

[0050] 6 Core drilling rig motor

[0051] 7 Control device of the core drilling machine

[0052] 8 Switching device 9 Motor shaft

[0053] 10 gearboxes

[0054] 11 pinions

[0055] 12 large wheel

[0056] 13 Output shaft 14 Drive train

Claims

Patent claims 1. Machine tool (1) with a tool (2), wherein the tool (2) can be connected to the machine tool (1) by means of a tool holder (3), wherein the machine tool (1) has a motor (6) for generating a torque, wherein the torque can be transmitted to the tool holder (3) by means of a drive train (14) of the machine tool (1), characterized in that a play is provided in the drive train (14) and wherein a target current for the motor (6) of the machine tool (1) can be predetermined with a regularly alternating sign, wherein a sign-alternating frequency of the target motor current lies in a range from 7 to 60 Hertz, wherein the play lies in a range from 2 to 10 degrees.

2. Machine tool (1) according to claim 1, characterized in that the play is in a range of 3 to 9 degrees, preferably in a range of 5 to 7 degrees and particularly preferably 6 degrees.

3. Machine tool (1) according to claim 1 or 2, characterized in that the play is provided between adjacent components of the drive train (14) of the machine tool (1).

4. Machine tool (1) according to one of the preceding claims, characterized in that the motor target current has a substantially rectangular or sinusoidal shape.

5. Machine tool (1) according to one of the preceding claims, characterized in that the motor target current has an offset.

6. Machine tool (1) according to one of the preceding claims, characterized in that that a total stiffness of the drive train (14) is smaller than a smallest individual stiffness of a component of the drive train (14), that a stiffness jump can be generated by the play and / or that the term stiffness refers to a torsional stiffness.

7. Machine tool (1) according to one of the preceding claims, characterized in that the motor (6) of the machine tool (1) is a brushless DC motor.

8. Machine tool (1) according to one of the preceding claims, characterized in that a ratio between a torque of the motor (6) and an inertia of the motor (6) is greater than 1,000 Nm / (kg -m 2 ) is.

9. Machine tool (1) according to one of the preceding claims, characterized in that the drive train (14) has the motor (6), a gear (10) and a pinion (11), wherein the pinion (11) is designed to drive a larger gear (12), wherein the larger gear (12) is arranged on an output shaft (13), wherein the output shaft (13) is designed to drive the tool (2) of the machine tool (10).

10. Machine tool (1) according to claim 9, characterized in that the gear (10) is designed as a single-stage or multi-stage transmission.

11. Machine tool (1) according to one of the preceding claims, characterized in that a stiffness of the drive train (14) is in a range of 1,000 to 100,000 Nm / rad.

12. Machine tool (1) according to one of the preceding claims, characterized in that the drive train (14) of the machine tool (1) comprises a motor shaft (9), wherein a stiffness of the motor shaft (9) is in a range of greater than 50 Nm / rad.

13. Machine tool (1) according to one of the preceding claims, characterized in that the play is a rotational play in the drive train (14) of the machine tool (1), in particular on the output shaft (13).

14. Method for operating the machine tool (1) according to one of the preceding claims, characterized by the following method steps: a) providing the machine tool (1), wherein a play is provided in the drive train (14) of the machine tool (1), wherein the play is in a range of 2 to 10 degrees, b) specifying a motor target current with a sign-changing frequency in a range of 7 to 60 Hertz, c) transmitting a torque with a sign changing at regular intervals according to the specified sign-changing frequency from the motor (6) to the tool holder (3) of the machine tool (1), so that a jammed tool (2) can be released from a drill hole.

15. The method according to claim 14, characterized in that a ratio between a rigidity of the drive train (14) of the machine tool (1) and a motor shaft (9) of the machine tool (1) is in a range of 20 to 2,000.

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