MACHINE TOOL AND METHOD FOR OPERATING A MACHINE TOOL

Description

[0001] The invention relates to a machine tool comprising a tool and a motor, wherein the motor of the machine tool operates within a speed range of 2,000 to 30,000 rpm and wherein the inertia of the motor is in the range of 20 × 10⁻⁶ to 750 × 10⁻⁶ kg·m². In a second aspect, the invention relates to a method for operating a machine tool that operates within a speed range of 2,000 to 30,000 rpm, wherein the inertia of the motor is in the range of 20 × 10⁻⁶ to 750 × 10⁻⁶ kg·m². By selecting and specifying a set of parameters that describe the characteristics of the machine tool's motor, the machine tool can be designed and operated in such a way that a mechanical slip clutch is unnecessary. The motor parameters "speed" and "inertia" are selected, in particular, such that the maximum torque in a gearbox of the machine tool always remains below a defined upper limit.Furthermore, the invention enables particularly productive work with the machine tool, with tests having shown that the service intervals can advantageously be extended by omitting the mechanical slip clutch. Background of the invention:

[0002] Machine tools capable of performing various tasks are known in the prior art; see, for example, document US 3,714,994 A. Examples include rotary hammers, chisels, cut-off or angle grinders, screwdrivers, and core drills, each of which has a tool driven by a motor. Power can be supplied via a mains connection or with batteries or accumulators.

[0003] In existing devices, attempts are sometimes made to limit the maximum torque in the drive train when the device or its tool becomes jammed. This is primarily to protect the user and prevent injury to the user's arm, shoulder, or wrist if the device continues to rotate after the tool jams. Currently, mechanical slip clutches are used to achieve this limitation of the maximum torque and deflection of the machine tool and to protect the user from excessive strain. However, such mechanical slip clutches are expensive. Furthermore, they require frequent maintenance and short service intervals.Furthermore, high release speeds are observed in some slip clutches, which can have a detrimental effect on productivity when working with the machine tool.

[0004] To protect the user, prior art has proposed mechatronic solutions that, in particular, limit the device's impact on the user. However, no satisfactory solutions exist for limiting the peak torques that occur briefly in the drive train when the machine tool or its tool jams. This means that currently available machine tools, and especially their mechanical components, must be designed to be very robust in order to withstand the extreme loads that can occur with torque peaks in the event of a jam or tool binding. Consequently, the mechanics of such conventional machine tools, as known from the prior art, are over-engineered for most applications.Particularly in core drilling machines, which are used to cut cylindrical cores from a substrate, such torque peaks can be exceptionally high. This is primarily due to the torsional stiffness of the drill bit, which constitutes the tool of a core drilling machine. The object of the present invention is therefore to overcome the aforementioned shortcomings and disadvantages of the prior art and to provide an improved machine tool and a method for operating a machine tool, in which the torque peak can be limited in the event of blockage or jamming of the tool. A further objective of the invention is that the machine tool should operate without a mechanical slip clutch, without compromising the safety of the machine tool user.Furthermore, a compact and lightweight machine tool should be provided that allows for comfortable handling and requires very little maintenance.

[0005] The problem is solved by the subject matter of the independent claims. Advantageous embodiments of the subject matter according to the invention are described in the dependent claims. Description of the invention:

[0006] The problem is solved by a machine tool with a tool and a motor, wherein the motor can be operated in a speed range of 2,000 to 30,000 rpm, and wherein the motor's inertia lies in the range of 20 × 10⁻⁶ to 750 × 10⁻⁶ kg·m². The abbreviation rpm stands for the unit rounds per minute, i.e., the number of revolutions per minute. The inventors have recognized that the magnitude of the torque peaks that occur when the tool of the machine tool jams or locks depends on the inertia conditions within the machine tool. The invention is based on the idea that the magnitude of the maximum torque can be set and limited by a clever selection of motor parameters so that the maximum torque does not exceed a predetermined upper limit. It is in the sense of the invention that the upper limit represents a maximum value for the torque that can be generated by the machine tool.The maximum torque in the drive train of the machine tool is reached particularly when the tool jams or locks. The resulting high torque values ​​are preferably referred to as "torque peaks" within the meaning of the invention. The inventors have recognized, in particular, that the maximum torque depends on the inertia between the machine tool and its motor, as well as on the speed at which the tool locks and on the stiffness of the drive train. A fundamental aspect of the invention is that the maximum torque can be limited and kept below an upper limit if the machine tool is operated within a motor speed range of 2,000 to 30,000 rpm and the motor's inertia is within a range of 20 × 10⁻⁶ to 750 × 10⁻⁶ kg / m².

[0007] The invention consists of specifying the aforementioned parameter ranges for motor speed and motor inertia, such that the maximum torque of the machine tool's motor always remains below a defined upper limit. This enables particularly safe operation of the machine tool for the user. Typically, the time it takes for a jammed or blocked tool in a machine tool to come to a standstill is very short. This time span can, for example, be in the range of 5 milliseconds (ms). After the blocking event, the machine tool preferably continues to rotate at a predetermined initial speed. This movement is perceived by the machine tool user as a deflection of the machine tool.Tests have shown that this deflection of the machine tool, which in the past has frequently led to injuries in the arm, shoulder and hand area of ​​a user, can be significantly reduced with the invention.

[0008] The proposed machine tool could be, in particular, a core drilling machine. The tool of the machine tool would then preferably be a drill bit. The drill bit serves to cut cylindrical cores out of a solid substrate. However, the proposed machine tool could also be, for example, a hammer drill or a power drill.

[0009] According to the invention, a motor inertia range is described which, within the specified speed range, enables slip clutch-free operation of the machine tool. Thus, the invention eliminates the need for a mechanical slip clutch, allowing the machine tool to be manufactured more cost-effectively and designed more compactly. This advantageously leads to particularly convenient and easier handling of the machine tool. According to the invention, operating the machine tool within the motor speed range of 2,000 to 30,000 rpm and within the inertia range of 20 × 10⁻⁶ to 750 × 10⁻⁶ kg / m² enables the provision of a more productive and low-maintenance machine tool with longer service intervals.

[0010] For the purposes of the invention, it is preferred that the term "motor inertia" be understood as the moment of inertia of the motor, in particular as the moment of inertia of the rotating components of the motor about the axis of rotation of the motor shaft. The rotating components of the motor, which preferably rotate about the axis of rotation of the motor shaft, are preferably the rotor of the motor. Similarly, for the purposes of the invention, the term "inertia of the machine tool" is preferably understood as the moment of inertia of the machine tool, wherein the rotating components of the machine tool preferably rotate about the axis of rotation of the tool.

[0011] According to the invention, the upper limit for the torque lies in a range of 500 to 1,500 Nm, preferably in a range of 700 to 1,200 Nm, particularly preferably in a range of 850 to 950 Nm, and most preferably at 900 Nm. It is preferred, in accordance with the invention, that the level of the permissible maximum torque values ​​depends on the robustness of the machine tool's gearbox. The inventors have recognized that the tangential component of the acceleration of the side handle of the machine tool also plays a role in the maximum torque. This tangential component of the acceleration is referred to in the context of this invention as the so-called "level of pain" (LOP). It is preferred, in accordance with the invention, that this acceleration component is used as a measure of the ease of operation of the machine tool in the event of tool jamming. The inventors have recognized that the level of pain is related to the maximum torque, or rather, the tangential component of the acceleration of the side handle of the machine tool.its torque peaks are related to this. This relationship arises in particular from the inertia of the machine tool. Therefore, there is a correlation between the maximum permissible speed and the torque peaks within the machine tool. Thus, limiting the torque to values ​​below an upper limit advantageously also leads to a reduction in the level of discomfort and to improved user comfort of the machine tool compared to conventional machine tools known from the prior art.

[0012] It is preferred, according to the invention, that the machine tool has a gearbox with a transmission ratio. Preferably, the transmission ratio is derived from the motor characteristic curve, i.e., the characteristic curve of the machine tool's motor. It is preferred, according to the invention, that the motor characteristic curve describes the lowest speed at which the machine tool's motor can deliver the required power. The transmission ratio is particularly evident in the time lag between the standstill of the tool and the standstill of the machine tool's motor when the machine tool jams or binds. While the time for the tool to stand still is, for example, in the range of 5 ms, the time for the machine tool's motor to stand still can be in the range of 50 ms.The present invention relates in particular to the processes occurring during the aforementioned time periods after a tool of the machine tool has jammed. These time periods are defined in . Fig. 1 referred to as the second and third time periods.

[0013] In the context of the present invention, it was particularly recognized that the degree of pain, ease of use, and maximum torque can depend on the motor parameters speed, rotor inertia and / or peak torque.

[0014] According to the invention, the inertia of the machine tool lies in the range of 30,000 × 10⁻⁶ to 70,000 × 10⁻⁶ kg·m², preferably in the range of 40,000 × 10⁻⁶ to 60,000 × 10⁻⁶ kg·m², particularly preferably in the range of 45,000 × 10⁻⁶ to 55,000 × 10⁻⁶ kg·m², and most preferably at 50,000 × 10⁻⁶ kg·m². The aforementioned values ​​for the inertia of the machine tool are preferably used as input variables for determining the motor parameters speed and motor inertia.

[0015] Furthermore, the machine tool can have a spindle that transmits the rotation of the motor to the tool of the machine tool. The spindle speed can be in the range of 1,000 to 1,500 rpm, preferably 1,250 to 1,350 rpm, and particularly preferably 1,300 rpm.

[0016] In accordance with the invention, it is preferred that the spindle speed corresponds to the tool speed of the proposed machine tool. This means that the machine tool preferably rotates at a speed in the range of 1,000 to 1,500 rpm, more preferably in the range of 1,250 to 1,350 rpm, and most preferably at a speed of approximately 1,300 rpm. The spindle speed, or the tool speed, of the machine tool is coupled to the motor speed via the gear ratio in the transmission, with the gear ratio playing a significant role in the effective moment of inertia.

[0017] The invention also relates to a method for operating a machine tool. The machine tool comprises a tool and a motor, wherein the motor of the machine tool is operated in a speed range of 2,000 to 30,000 rpm and wherein the inertia of the motor lies in the range of 20 × 10⁻⁶ to 750 × 10⁻⁶ kg / m². The definitions, technical effects, and advantages described for the proposed machine tool apply analogously to the proposed operating method.

[0018] Further advantages will become apparent from the following description of the figures. The figures illustrate various embodiments of the present invention.

[0019] In the figures, identical and similar components are numbered with the same reference symbols.

[0020] They show: Fig. 1 Exemplary curves of the motor speed, the tool speed, the torque and the speed of the device versus time t. Fig. 2 Illustration of a preferred embodiment of a machine tool, in particular a core drilling device. Examples of implementation and description of figures:

[0021] Fig. 1The graph shows exemplary curves of the motor speed (1), the tool speed (2), the torque (3), and the machine tool speed (4) as a function of time t. The y-axis, from top to bottom, plots the motor speed (1), the tool speed (2), the torque (3), and the machine tool speed (4), while the x-axis plots time t. The graph is divided into three time periods, labeled I, II, and III with Roman numerals. The first period, I, covers the normal operation of the machine tool (10), during which the machine tool (10) is being used. During this first period, I, the curves shown in the graph are as follows: Fig. 1 The quantities shown (1-4) are essentially constant, although such an approximately constant course of the quantities (1-4) does not exclude fluctuations and deviations around a mean value.

[0022] Details of the machine tool (10) are given by way of example in Fig. 2 As shown. If the machine tool (10) is a core drilling machine, cylindrical cores can be cut out of a solid substrate using the drill bit (11). The drill bit, as the tool (11) of the machine tool (10), is driven by a motor (12) of the machine tool (10). The transmission of motion from the motor (12) to the tool (11) can be effected by means of a spindle (14). The machine tool (10) can also include a gearbox (13). In the Fig. 2 In the illustrated embodiment of the invention, the core drilling device (10) is attached to a drill stand, and the invention can be applied particularly to hand-held machine tools.

[0023] The second time period II begins with the blockage of the tool (11) of the machine tool (10). The start of the blockage of the tool (11) of the machine tool (10) is in Fig. 1The first dashed, vertical line represents the second time interval (II). During this second time interval, the rotational speeds of motor (1) and tool (2) decrease, while the torque (3) increases sharply. For example, the second time interval (II) lasts 5 ms. The end of the second time interval (II) is defined by the tool (11) of the machine tool (10) coming to a standstill. The motor (12) of the machine tool (10) requires more time to decelerate completely, with the standstill of the motor (12) of the machine tool (10) defining the end of the third time interval (III). The time difference between the standstill of the tool (11) and the motor (12) is determined by the gear ratio of the gearbox (13) of the machine tool (10).Overall, in the context of the invention, there is a transfer of momentum from the tool (11) of the machine tool (10) to the machine tool (10) itself, whereby it is an objective of the invention that the transfer of momentum and a deflection of the machine tool (10) are limited in such a way that no danger to the user emanates from the machine tool (10).

[0024] Approximately in the middle of the second time interval II, the torque (3) reaches its highest value (5), which simultaneously represents the upper limit (5) of the torque (3). This upper limit (5) of the torque (3) is in Fig. 1 through the upward-pointing block arrow in the upper right corner Fig. 1As indicated, a movement or deflection (4) of the machine tool (10) itself can also occur in the middle of the second time interval II. In the past, this deflection has led to injuries to the arms, shoulders, or wrists of users of the machine tool (10), which is why it is an objective of the present invention to minimize this deflection (4). It is preferred, in accordance with the invention, that a transfer of momentum occurs from the tool (11) of the machine tool (10) to the machine tool (10) itself. It is an objective of the invention that the transfer of momentum and the associated deflection of the machine tool (10) are limited so that no danger to the user emanates from the machine tool (10). It is a further objective of the invention that the torque (3) always remains below the upper limit (5) for the torque (3).According to the invention, this is achieved by operating the motor (12) of the machine tool (10) in a speed range (1) of 2,000 to 30,000 rpm and by having an inertia of the motor (12) of the machine tool (10) in a range of 20·10 -6< to 750·10 -6< kg·m 2<.

[0025] During the transition between the second time interval (II) and the third time interval (III), the machine tool (10) or its drive begins to brake. As a result, the torque (3) drops sharply during the third time interval (III). The transition between the second time interval (II) and the third time interval (III) is described in Fig. 1This is represented by the second dashed, vertical line. The rotational speed (1) of the motor (12) of the machine tool (10) also decreases during the third time interval III., with the decrease in motor speed (1) being approximately linear until the motor (12) has come to a complete standstill at the end of the third time interval III. The deflection (4) of the machine tool (10) is also stopped during the third time interval III. The third time interval III. can, for example, last 50 ms. Reference symbol list

[0026] 1. Motor speed 2. Tool speed 3. Torque or load 4. Machine tool speed 5. Upper torque limit 10. Machine tool 11. Tool 12. Motor 13. Gearbox 14. Spindle I. Machine tool operation II. Time it takes for the tool to come to a standstill in case of jamming III. Time it takes for the motor to come to a standstill in case of jamming

Claims

1. Power tool (10) having a tool (11) and a motor (12), wherein an inertia of the motor (12) is in a range of from 20·10-6 to 750·10-6 kg·m2, characterized in that the motor (12) can be operated in a speed range (1) of from 2000 to 30 000 rpm, wherein the power tool (10) has no mechanical slip clutch, wherein a torque (3) of the motor (12) of the power tool (10) does not exceed an upper limit value (5), wherein the upper limit value (5) for the torque (3) is in a range of from 500 to 1500 Nm, and wherein an inertia of the power tool (10) is in a range of from 30 000·10-6 to 70 000·10-6 kg·m2.

2. Power tool (10) according to one of the preceding claims, characterized in that the power tool (10) has a transmission (13) with a transmission ratio.

3. Power tool (10) according to one of the preceding claims, characterized in that the power tool (10) has a spindle (14) that can be used to transmit a rotation of the motor (12) to the tool (11) of the power tool (10), wherein a speed of the spindle (14) is in a range of from 1000 to 1500 rpm, preferably 1250 to 1350 rpm and particularly preferably is 1300 rpm.

4. Method for operating a power tool (10), wherein the power tool (10) has a tool (11) and a motor (12), wherein an inertia of the motor (12) is in a range of from 20·10-6 to 750·10-6 kg·m2, characterized in that the motor (12) of the power tool is operated in a speed range (1) of from 2000 to 30 000 rpm, wherein the power tool (10) has no mechanical slip clutch, wherein a torque (3) of the motor (12) of the power tool (10) does not exceed an upper limit value (5), wherein the upper limit value (5) for the torque (3) is in a range of from 500 to 1500 Nm, and wherein an inertia of the power tool (10) is in a range of from 30 000·10-6 to 70 000·10-6 kg·m2.