Control unit for an electric drive motor and machine tool

Abstract

Control device for controlling or regulating an electric drive motor (12) of a drive train (11) with a limiting device (31) for limiting an output torque (Mab) provided on the output side of the drive train (11) to a maximum torque value (Mmax, Mmax1, Mmax2) based on a motor current value (34) representing a motor current (Imot) for energizing the drive motor (12), wherein the limiting device (31) has comparison means (37) for comparing the maximum torque value (Mmax, Mmax1, Mmax2) with internal motor torque values ​​(36) that depend on the motor current (Imot), wherein, in the comparison to simulate the actual output torque (Mab), the respective internal motor torque value (36) is reduced by the limiting device (31) by an inertia moment value (43) that depends on an acceleration (a) of the drive train (11), or the maximum torque value (Mmax, Mmax1,Mmax2) is increased by the moment of inertia value (43) which depends on the acceleration (a) of the drive train (11), and wherein the limiting device (31) is configured to simulate the actual provided output torque (Mab) in order to reduce the respective internal motor torque value (36) by at least one frictional torque value (45) of the drive train (11) or to increase the maximum torque value (Mmax, Mmax1, Mmax2) by the at least one frictional torque value (45), characterized in that it has at least one input (56) for at least one temperature value (49) of the drive train (11), and that the limiting device (31) is configured to determine the at least one frictional torque value (45) of the drive train (11) as a function of the at least one temperature value (49).

Description

[0001] The invention relates to a control device for controlling or regulating an electric drive motor of a drive train of a machine tool, in particular a screw-driving machine tool, with a limiting device for limiting an output torque provided on the output side of the drive train to a maximum torque value based on a motor current value that represents a motor current for energizing the drive motor, according to the preamble of claim 1, and to a machine tool equipped therewith, in particular a hand-held machine tool.

[0002] Such a control device is known from DE 10 2007 000 281A1.

[0003] German patent application DE 103 41 975 A1 discloses a control system with a torque limiting device for an electric motor, particularly for an electric screwdriver. The drive train exhibits a torque component determined by the motor current of the drive motor, as well as kinetic energy from the rotating masses. The energy of these masses is determined as a function of rotational speed, for example, by calculation or based on a curve. The control system then sets the motor current, from which the torque component (dependent solely on the motor current) is derived, to a limit value such that, taking into account the speed-dependent kinetic torque component, the maximum permissible torque is not exceeded. Thus, in the event of a shutdown, the speed-dependent energy present in the drive train is, in effect, pre-calculated as the energy still available for screwdriving after the system is switched on.

[0004] It is therefore the object of the present invention to provide a control device and a machine tool equipped therewith with an improved torque limitation.

[0005] To solve the problem, a control device according to the technical teaching of claim 1 is provided.

[0006] The limiting device has, for example, generating means to generate output torque values ​​representing the actually provided output torque by reducing the internal motor torque values ​​of the drive motor, which depend on the motor current, by the inertial moment values ​​of the drive train, which depend on the acceleration of the drive train.

[0007] The control device according to the invention, which may, for example, contain hardware and / or software components, provides high dynamics. The torque limiting also functions at low maximum torque values.

[0008] Furthermore, the machine can start or accelerate rapidly without the torque limiter intervening unnecessarily. When the drivetrain accelerates, the internal motor torque is primarily required to overcome the drivetrain's inertia. This is advantageously taken into account by the control system. The torque limiter is based on the conditions dependent on the drivetrain's acceleration, rather than on a stationary, speed-dependent energy level. Therefore, instead of a largely stationary operating state, a dynamic operating condition is used as the basis for torque limiting.

[0009] Nevertheless, a sensitive and timely shutdown is easily possible even in so-called hard screwdriving cases, i.e., when spontaneous torque peaks occur.

[0010] The comparison methods compare output torque values, determined using the internal motor torque and optimally approximating the actual output torque value, with the respective set or specified maximum torque value. For this purpose, the so-called internal motor torque of the drive motor, which in itself depends only on the motor constant and the current used to power the drive motor, is adjusted for the moment of inertia values ​​of the drive train. The moment of inertia values ​​of the drive train include the dynamic component in the calculation, namely the acceleration of the drive train. This acceleration occurs, for example, when the machine tool is switched on or during intermediate acceleration of a particular drive train.Because the acceleration-dependent and thus dynamic components of the output torque are taken into account, the control device according to the invention reacts very quickly and switches off when the maximum torque value is reached.

[0011] The control device according to the invention can only operate with motor current values ​​without a corresponding motor voltage.

[0012] The comparison condition for limiting the torque is, for example: Mab≥M max where Mab is a calculated, or "simulated," output torque determined by the control unit, and Mmax is the maximum torque value. The internal torque Mi of the drive motor depends on the motor current Imot and a motor constant kt of the drive motor: Mab=kt*I mot

[0013] The control unit then calculates the output torque Mab according to the following formula: Mab=Mi−J*a where J is the moment of inertia of the drive train and a is its acceleration. The acceleration a is determined by the control unit according to the following formula as the time derivative of the rotational speed ω: a=dωdt

[0014] Using formula (4), the output torque Mab can be expressed according to formula (3) as follows: Mab=kt*I mot−J*dωdt

[0015] It is advantageous for the control unit to also consider other influences of the drivetrain that reduce the internal motor torque and are therefore not available on the output side. For example, the limiting device is designed to also take into account frictional torque values ​​of the drivetrain when generating the output torque values. Assuming essentially constant temperature and speed conditions, a frictional torque Mr of the drivetrain can be considered constant: Mab=kt*I mot−J*dωdt−Mr

[0016] It is advantageous, however, to consider influences on the frictional torque. These influences include, for example, temperatures in the drivetrain. For instance, a temperature T has a quadratic effect on the respective value of the frictional torque Mr. An oil or grease in the drivetrain, for example in a gearbox, becomes significantly more viscous at lower temperatures than at higher temperatures. It is therefore advantageous if the control device has an input for a temperature sensor. In the machine tool according to the invention, for example in an electric screwdriver, it is advantageous if the drive motor has a temperature sensor located near the gearbox. Thus, the temperature sensor detects the temperature of both the drive motor and the gearbox, which is advantageous when generating or calculating the frictional torque value or the frictional torque value profile.

[0017] Furthermore, the rotational speed ω of the drive motor and / or the gearbox affects the frictional torque Mr. This is also taken into account by the control device according to the invention. The rotational speed ω can also depend on the currently set gear ratio u of the gearbox. Mab=kt*I mot−J*dωdt−Mr(T,ω,u)

[0018] In the control device according to the invention, it is also advantageous if the limiting device for simulating the actually provided output torque Mab is designed as a function of a change in a target speed value. For example, the generating means for producing the output torque values ​​are designed as a function of a change in a target speed value. Whenever an increase in speed is desired, the motor current does indeed increase, for example, because a control device dictates this. However, the output speed of the drive train available does not increase immediately, for example, due to magnetic influences, friction, and the like. Acceleration values ​​are therefore initially unavailable or insufficient for determining a moment of inertia value.In the control device according to the invention, this is taken into account by a time-limited correction that begins with a request for acceleration.

[0019] Advantageously, the generating means for producing the output torque values ​​are designed by reducing the internal motor torque values ​​Mi by compensation values ​​K(t). These compensation values ​​K(t) serve to compensate for an increase in the motor current Imot after an increase in a target speed ωsoll for a predetermined time interval. During this time interval, the increase in the motor current Imot initially does not cause any change in the output-side available speed ω and thus no acceleration of the drive train. Mab=kt*I mot−J*dωdt−Mr(T,ω,u)−K(t)

[0020] Particularly when calculating output torque values ​​using sensor readings, implausible peak values ​​may occur. Therefore, it is advantageous for the control system to include plausibility checks, such as filters, integrators, and the like, to verify the plausibility of the output torque values ​​and / or the underlying sensor readings. For example, a single exceedance of the output torque values, which would immediately trigger a torque limitation of the drivetrain, can be filtered out in this way.

[0021] The plausibility check can, for example, take place on the side of the generating equipment, so that the generated output torque values ​​are used directly by the reference equipment. However, the plausibility check can also take place on the side of the reference equipment.

[0022] It is understood that, instead of reducing the internal motor torque Mi by inertia values ​​J*a of the drive train dependent on the acceleration of the drive train and / or by a frictional torque Mr and / or by compensation values ​​K(t), a control device according to the invention could also increase the maximum torque value by inertia values ​​dependent on the acceleration of the drive train and / or frictional torques and / or by compensation values ​​before comparing it with the internal motor torque Mi. This approach is equivalent.

[0023] The torque limitation of the control device according to the invention becomes particularly effective when it includes a switching device for switching the drive motor into braking mode when the output torque values ​​reach or exceed the maximum torque value. Thus, the drive train immediately enters braking mode and stops. This is particularly advantageous in a hard screwdriving application, which could, for example, lead to the destruction of the screw and / or a screwdriver bit. The switching device includes, for example, a switch for short-circuiting the drive motor. If the drive motor is an electronically commutated drive motor, it is also possible to apply current in the opposite direction of rotation until the drive train comes to a standstill.

[0024] The limiting device should preferably be switchable. A separate switch is preferably provided for this purpose. It is understood that, for example, a switch on which maximum torque values ​​can be set can also be used to switch off the limiting device.

[0025] When switching to braking mode, the drive motor expediently feeds electrical energy back into an electrical energy storage device, for example into the accumulator of a cordless screwdriver.

[0026] Neither switching off nor braking the drive motor or drive train by means of a short circuit of the drive motor may be sufficient to prevent, for example, the screw head from shearing off when it hits the workpiece, and / or the screw from penetrating too deeply into the workpiece, when a small screw is being screwed in at high speed but low torque.

[0027] The limiting device is therefore advantageously designed to send control commands to activate a power supply unit that energizes the drive motor, thereby initiating braking operation. In this braking operation, the power supply unit generates a rotating magnetic field that opposes the respective direction of rotation of the drive motor, thus braking the motor. To limit the output torque provided on the output side to the maximum torque value, the limiting device activates the power supply unit under at least one braking condition. Advantageously, the braking condition includes the requirement that the ratio of the output torque to the rotational energy present in the drive train is less than or equal to a maximum ratio.

[0028] The basic principle is that the power supply unit is controlled to initiate a braking operation, thereby generating a rotating magnetic field that opposes the direction of rotation of the drive motor. The drive motor is thus actively braked, so to speak.

[0029] However, such deceleration is not advantageous in all operating situations, for example because it increases the energy consumption of the handheld power tool, which is particularly undesirable when operating on a battery. Furthermore, the machine would heat up, increasing cooling requirements.

[0030] For example, if screws are being driven in with relatively high torque but low speed, such braking is not advantageous. When a large screw is driven into a workpiece, the drive motor typically rotates at a relatively low speed but generates high torque. While the motor current of the drive motor does increase when the screw is fully driven in, the limiting device then switches off the drive motor, for example, by comparing the maximum torque value with a motor current value or a value derived from it. Even if the drive train continues to rotate briefly afterward, this does not damage the screw.

[0031] The situation is different for small screws, especially when they encounter a hard, inflexible workpiece surface at the end of a screwing operation. Such a hard screwing scenario is detected by the control unit. The braking condition then stipulates that the output torque is relatively small compared to the rotational energy of the drive train during screwing, for example, according to the following formula: MabErot≤X max where Mab is the output torque, Erot is the rotational energy of the drivetrain, and Xmax is the maximum ratio.

[0032] The maximum torque ratio Xmax is preferably selected such that actively switching off the drive motor, i.e., energizing it in the opposite direction of rotation, prevents damage in the event of torque cut-off, particularly with sensitive workpieces and / or delicate screws. It is possible for the maximum torque ratio Xmax to be adjustable on the control unit or the machine tool, for example, by means of a suitable switch, parameterization software, or the like. In any case, the inventive approach takes into account that, for example, with small screws, the output torque Mab is relatively small, while the rotational speed ω of the drive train is comparatively large. The rotational speed of the drive train can be, for example, the rotational speed of the drive motor, the rotational speed of a tool holder, or the like, preferably taking gear ratios into account.

[0033] The following formula (b) illustrates the relationship between the rotational energy Erot and the rotational speed ω of the drive train: Erot=12Jω2 where J is the moment of inertia of the drive train and ω is the speed of the drive train, which the control device determines, for example, based on the speed of the drive motor or a tool holder.

[0034] The control device according to the invention, which may, for example, contain hardware and / or software components, provides high dynamics. The torque limiting also functions at low maximum torque values.

[0035] Nevertheless, a sensitive and timely shutdown is easily possible even in so-called hard screwdriving cases, i.e., when spontaneous torque peaks occur.

[0036] Accordingly, it is an advantageous braking condition if the output torque Mab is related to the rotational speed ω of the drive train, preferably to the first power of the rotational speed ω of the drive train. This is the case in the following formulas (c) and (d): Mabω≥Y max where Ymax is a ratio adjustable or set from the control device with respect to the rotational speed ω of the drive train and in the following formula (d) Zmax is a ratio with respect to the square of the rotational speed ω. Mabω2≥Z max

[0037] Another braking condition that is advantageous when switching to the advantageous braking mode is when the control device or the limiting device evaluates the respective rate of increase of the output torque. If the output torque increases sharply, which is usually only the case with relatively small screws, the limiting device will expediently take the following formula (e) into account: dMabdt≥H where H is the rate of increase of the output torque Mab.

[0038] Another advantageous braking condition is that the output torque reaches or exceeds the predetermined rate of increase, depending on a minimum speed of the drive motor. This means that active braking by counter-current is only activated by the control device when, for example, small screws are being turned at high speed. Active braking is particularly advantageous in such cases because there is a large amount of rotational energy in the drive train, which could damage the screw and / or the workpiece. The corresponding braking condition, which the limiting device then checks, is represented by the following formula (f): ω≥ω min where ω min is the minimum rotational speed.

[0039] As explained above, actively switching off the drive motor by counter-current is particularly advantageous when the output torque before switching off is relatively low, as is the case, for example, when tightening small screws. For instance, it is advantageous if at least one braking condition includes a predefinable or predetermined target maximum value Smax or output torque values ​​representing the output torque Mab, which must be equal to or less than a predetermined threshold torque value Ms before switching. The threshold torque value Ms is advantageous, for example, in the range of 2 to 5 Nm. This takes into account that switching off and counter-current is particularly advantageous when used with small screws that are tightened with low torque.

[0040] However, the braking condition can also include the condition that the maximum torque value at which the limiting device becomes active is below a threshold torque value. Mab≤Ms

[0041] Furthermore, it is advantageous if the limiting device for issuing control commands is designed to operate by means of reverse current flow depending on the braking profile of the drive train during braking. Thus, if, for example, the active braking of the drive train results in the maximum torque value not being reached or only being reached slowly, the limiting device advantageously reduces the braking effect and sends corresponding control commands to the current-generating device. Preferably, the limiting device is designed to control the braking profile. For example, the control device monitors the maximum torque value that is actually available on the output side or that is simulated by the control device and sends corresponding control commands to the current-generating device to adjust the braking rotating magnetic field depending on the output torque.In any case, it is advantageous if the limiting device regulates the braking process in such a way that the output torque quickly reaches the maximum torque value, but does not exceed it.

[0042] Furthermore, it is advantageous if the limiting device, at the start of braking, activates the current-generating device to apply stronger braking and subsequently reduces or regulates the braking force depending on the braking process. This reduction can, for example, occur gradually. This measure ensures that the maximum torque value is not exceeded if possible, but that optimal braking occurs at the start of braking to prevent exceeding the maximum torque value in any case.

[0043] The machine tool is preferably a hand-held machine tool. While the machine tool according to the invention is expediently a screwdriver, it can also be used in other applications where rapid, torque-dependent shutdown is desired, such as hedge trimmers.

[0044] An embodiment of the invention is explained below. The figures shown are: Fig. 1 an electrical functional circuit diagram of a machine tool with a control device according to the invention, Fig. 2 a schematic side view of the machine tool, Fig. 3 a curve of a delivery torque of the hand-held machine tool according to Fig. 1, Fig. 2 and further curves, Fig. 4 Curves of output torques during active braking by counter-current and Fig. 5 an excitation winding arrangement of the drive motor of the machine tool with current profiles during braking operation by short circuit and during active braking by counter-current.

[0045] A drive train 11 of a machine tool 10, for example an electric screwdriver, contains a drive motor 12 which drives a drive spindle 14 with a tool holder 15 via a gearbox 13. A screwdriver bit 16, for example, can be inserted into the tool holder 15 to drive a screw.

[0046] The drive train 11 is controlled by a control unit 17. The control unit 17 contains a microprocessor 18 for executing program code of a control module 19 and a limiting module 20, which limits an output torque Mab available at the drive train 11. The control module 19 and the limiting module 20 are stored, for example, in a memory 21 of the control unit 17.

[0047] Furthermore, the control unit 17 includes a power supply module 22 for generating, for example, a rotating magnetic field in a first direction 63 and / or a second direction 64 for the drive motor 12. The power supply module 22 can also include a pulse width modulator. The drive motor 12 can, for example, be a series-wound motor or an electronically commutated motor. Instead of the power supply module 22 integrated into the control unit 17, a separate power supply unit, controllable by the control unit 17, would also be possible.

[0048] The electrical drive energy for a machine tool according to the invention can, for example, be supplied by a power grid. However, in the case of the machine tool 10, an electrical energy storage device 23, for example a battery pack 24 attached to the bottom of a housing 25 of the machine tool 10, is provided to supply electrical operating energy for the machine tool 10. This functions as follows:

[0049] An operator of the machine tool 10 can, for example, specify target speed values ​​27 of a target speed ω on a speed encoder 26 containing a rotary and / or push-button switch. The control module 19 controls the drive motor 12 based on the target speed values ​​27 as well as on actual speed values ​​28, which represent an actual speed ω of the drive motor 12. For example, a speed sensor 29 detects the respective actual speed ω of the drive motor 12. The speed sensor 29 can form a component of the drive motor 12.

[0050] The control module 19 generates target current values ​​30 for the current supply module 22 based on the speed values ​​27, 28. The current supply module 22 sets a motor current Imot to supply the motor 12 based on the target current values ​​30.

[0051] The motor current Imot forms a first input value for the limiting module 20, which represents a limiting device 31 for limiting an output torque Mab at the drive train 11. A further input value for the limiting module 20, namely a maximum torque Mmax, which is to be available at the drive train 11, can be set via a shut-off torque sensor 32. The shut-off torque sensor 32 is, for example, a potentiometer switch on which an operator of the machine tool 10 can set a desired shut-off torque. It is understood that a fixed shut-off torque can also be provided in a control device according to the invention, for example, an absolute value. In the case of a screwdriver that is pre-configured for predetermined applications, for example, always for screws of the same screw type, it is even advantageous if the output torque Mab provided on the output side is fixed.

[0052] The current module 22 and / or a separate current sensor 33 generate motor current values ​​34, which represent the respective motor current Imot. The motor current value 34 forms an input value for a motor torque function 35, which generates motor torque values ​​36 representing the internal motor torque Mi of the drive motor 12.

[0053] An exemplary progression of the internal motor torque values ​​36 is shown in Fig. Figure 3 illustrates this. Starting at time t1, the internal motor torque Mi increases sharply until time t2, correlating with an acceleration a of the drive train 11, which begins at time t1. If a comparator function 38 of the limiting module 20, forming a comparator mean 37, were to directly compare the motor torque values ​​36 with the maximum torque value Mmax set on the cut-off torque sensor 32, it would detect an exceedance of the maximum torque value Mmax as early as time t1' and send a cut-off command 39 to the current control module 22 to switch off the current to the drive motor 12. The machine tool 10 would then prematurely terminate the screwing process. This is where the invention comes into play.

[0054] From the internal motor torque values ​​36, acceleration-dependent losses of the drivetrain 11 are subtracted. The motor torque function 35 forms a component of generating means 40, which also includes a generating function 41 for generating output torque values ​​42 according to formula (8) above. For this purpose, the generating function 41 receives the internal motor torque values ​​36, which it reduces by moment of inertia values ​​43. These moment of inertia values ​​are generated by an inertia function 44 based on the respective acceleration of the drivetrain 11 according to formulas (3) and (4) using the actual rotational speed values ​​28. The inertia function 44 calculates an acceleration-dependent moment of inertia for the drivetrain 11. It is understood that, alternatively or additionally, corresponding moment of inertia profiles can also be stored in the memory 21.

[0055] The generation function 41 reduces the internal motor torque values ​​36 according to formula (7) by friction torque values ​​45, which are generated by a friction torque function 46 and represent a friction torque Mr of the drive train 11.

[0056] The friction torque function 46 generates the friction torque values ​​based on the respective actual speed values ​​28 of the drive train 11. In addition, the friction torque function 46 takes into account a gear ratio u of the transmission 13, which is set in each case. When the transmission 13 rotates at higher speeds, this has a greater effect on the friction of the drive train 11. A gear ratio sensor 47 arranged on the transmission 13 detects the respective gear position of the transmission 13 and accordingly sends gear ratio values ​​48, representing the gear ratio u, to the friction torque function 46.

[0057] Furthermore, the friction torque function 46 takes into account temperature values ​​49, reported by a temperature sensor 50, when generating the friction torque values ​​45. The temperature sensor 50 is advantageously located in an area between the drive motor 12 and the gearbox 13 so that it can detect the temperature of both components. Advantageously, the temperature sensor 50 is even a component of the drive motor 12, for example, a sensor located in the excitation windings w1, w2, w3 and further excitation windings wn of the drive motor 12. Thus, the temperature sensor 50 detects the temperature of the drive motor 12 and simultaneously of the gearbox 13, for example, its lubricant.

[0058] Finally, the generating function 41 subtracts compensation values ​​51 from the internal motor torque values ​​36 of a compensation function 52. The compensation function 52 receives the target speed ωtarget and the actual speed ωact as input values. Based on an increase in the target speed ωtarget, the compensation function 52 recognizes a desired acceleration. Initially, after the target speed ωtarget increases, the motor current Imot increases, but the actual speed ωact does not. The compensation function 52 compensates for this by generating the compensation values ​​51, which it transmits to the generating function 41 for the output torque values ​​42. The generating function 41 subtracts the compensation values ​​51 from the internal motor torque values ​​36, thus realizing formula (8).

[0059] Furthermore, the generation function 41 expediently takes into account a respective transmission ratio u of the gearbox 13. By taking the transmission ratio u into account, the generation function 41 reduces a motor output torque Mmab available on the output side of the drive motor 12 and generates the output torque values ​​42, which replicate the actual output torque Mab.

[0060] The comparison function 38 now compares the output torque values ​​42 with the maximum torque value Mmax. While the internal motor torque Mi already exceeds the maximum torque Mmax between times t1 and t3, which would lead to premature shutdown of the drive train 11, the limiting device 31 now only switches off the drive motor 12 at time t4. Thus, the full output torque Mab, desired on the output side, is available until time t4, and the screw (not shown) can be tightened with maximum torque and high dynamics.

[0061] The control device 17 simply switches off the drive train 11 when the maximum torque value Mmax is reached.

[0062] Preferably, the control device 17 not only switches off the drive train 11, but also puts it into braking mode. A switching device 53, for example, short-circuits the drive motor 12. The switching device 53 has a switch 55, for example a relay or an electronic switch, for short-circuiting the drive motor 12. This also results in current being fed back into the electrical energy storage device 23, so that the machine tool 10 operates more efficiently.

[0063] For example, a stator of the drive motor 12 contains excitation windings w1, w2, w3-wn, which are energized by the current-sensing module 22. The respective excitation windings w1-wn are energized with excitation currents by the current-sensing module 22, which forms a current-sensing device. Fig. Figure 5 shows an example of an excitation current ID1 flowing through the excitation winding w1. For switching the excitation currents, the current-energizing module 22 has switches S11, S12, S13, S1n of a first switch group, which are connected on the input side to a supply potential Vcc and on the output side to the windings b1-bn, as well as switches S21-S2n of a second switch group, which are connected on the input side to the excitation windings w1-wn and on the output side to a ground potential Mp.

[0064] During braking, for example, switches S11-S1n are closed, so that short-circuit currents I11, I12, I13 flow through the excitation windings w1, w2, w3-wn in loops K11, K12, K13-Kn. It is also possible to close switches S21-S2n, so that short-circuit currents I21, I22, I23 can flow through loops K21, K22, K23-K2n.

[0065] The limiting device 31 can be switched off at a switch 54.

[0066] The control device 17 receives the temperature values ​​49 at an input 56 and also has an input 57 for the respective translation value 48.

[0067] In Fig. Figure 3 shows a curve of a total correction value Kges, which essentially correlates with the acceleration a of the drive train 11. Between times t1 and t3, between which the internal torque Mi is mainly used to accelerate the drive train 11 and is not available on the output side, a particularly strong correction or reduction of the internal motor torque Mi is required to determine the actual available output torque Mab.

[0068] It is understood that individual measurement or calculation errors may occur when acquiring sensor values ​​and / or determining the output torque Mab available on the output side of the drive train 11. To compensate for these errors, the generating means advantageously include plausibility check devices 58. These plausibility check devices 58 include, for example, a filter 59 that filters out implausible values, such as those for the output torque Mab. One such value is, for example, a peak output torque value 60 that exceeds the maximum torque value Mmax. This would normally lead to an immediate shutdown of the drive motor 12. However, the filter 59 compares the current output torque value 60 with previous output torque values ​​61 and 62 and filters out the "outlier" output torque value 60, which lies far outside the range of output torque Mab that can be determined by the output torque values ​​61 and 62.

[0069] In addition to the aforementioned short-circuit braking operation of the drive motor, the machine tool 10 is also designed for active braking by energizing the drive motor 12 in the opposite direction of rotation.

[0070] The current-energizing module 22 is designed to supply current to the drive motor 12, i.e., the excitation winding w1-wn, in a braking manner. The current-energizing module 22 generates, for example, a braking rotating magnetic field 64 that is opposite to the respective direction of rotation 63 of the drive motor 12. In this process, for example, an excitation current ID2 flows through the excitation winding w1, which flows in the opposite direction to the previously described excitation current ID1. The excitation currents ID1 and ID2 each flow at a comparable time but are associated with opposing rotating magnetic fields.

[0071] The limiting device 31 controls the current supply device 22 for braking operation, in which the rotating field 64 brakes the drive motor 12, by means of control commands 65.

[0072] The limiting device 31 sends the control commands 65 depending on the braking conditions explained above, in particular according to at least one of the formulas (a)-(g).

[0073] One in Fig. Curve 66, shown in Figure 4, illustrates, for example, the torque output Mab during the insertion of a relatively small screw. The torque output Mab is relatively low up to time t5. Up to this point, most of the energy is required to accelerate the drive train. From time t5 onwards, the drive rotor 12 turns the screw at a relatively high speed ω, with the torque increasing with increasing screw depth due to higher friction effects between time t5 and time t6.

[0074] Although the output torque Mab is relatively low between times t5 and t6 along curve 66, the rotational speed ω is high. Therefore, the rotational energy Erot present in the drive train 11 is relatively large. Given this initial situation, further rotation of the drive train 11 from time t6 onwards, at or immediately before reaching a maximum torque value Mmax1, would, for example, lead to the destruction of the screw, excessive screw penetration into the workpiece, or both. To remedy this situation, the limiting device 31 controls the current supply device or the current supply module 22 for the aforementioned braking operation using the counter-rotating magnetic field 64.The output torque Mab is small in relation to the rotational energy Erot present in the drive train in an operating case according to curve 66, so that the limiting device 31 determines the necessity of active braking operation on the basis of the braking condition (a).

[0075] The situation is different with, for example, a large screw. Fig. Figure 4 shows an example of the output torque curve 67. At time t5, the output torque Mab increases relatively sharply. At time t6, when a maximum torque value Mmax2 is reached, the limiting device 31 simply sends the shutdown command 39 to the power supply device 22, so that the drive motor 12 is switched off. Braking the drive motor 12 by means of a counter-rotating field 64 is not necessary in this operating condition and would only increase energy consumption and thus shorten the service life of the energy storage device 23.

[0076] It is particularly advantageous if the limiting device 31 controls the current supply device 22 or the current supply module for braking operation by means of the braking rotating field 64 when the output torque Mab increases particularly sharply. For example, if the head of a small screw strikes the workpiece, i.e., a hard screw impact occurs, a characteristic curve 68 of the output torque Mab may be established. In such cases, it is particularly advantageous if the limiting device 31 controls the current supply module 22 to generate the braking rotating field 64.

[0077] Furthermore, it is advantageous for the limiting device 31 to issue the control commands 65 depending on the braking profile of the drive train 11. For example, at time t6, the limiting device 31 controls the power supply device 22 in such a way that it brakes the drive motor 12 to its maximum extent. The output torque Mab therefore decreases very sharply from time t6 onwards, or ceases to increase, which is reflected in a braking profile 69 in Fig. Figure 4 illustrates this. From time t7, the limiting device 31 controls the current module 22 to a reduced braking operation, so that the output torque Mab increases from time t7 until it reaches the maximum torque value Mmax1 at time t8.

Claims

[1] Control device for controlling or regulating an electric drive motor (12) of a drive train (11) with a limiting device (31) for limiting an output torque (Mab) provided on the output side of the drive train (11) to a maximum torque value (Mmax, Mmax1, Mmax2) based on a motor current value (34) representing a motor current (Imot) for energizing the drive motor (12), wherein the limiting device (31) has comparison means (37) for comparing the maximum torque value (Mmax, Mmax1, Mmax2) with internal motor torque values ​​(36) that depend on the motor current (Imot), wherein, in the comparison to simulate the actual output torque (Mab), the respective internal motor torque value (36) is reduced by the limiting device (31) by an inertia moment value (43) that depends on an acceleration (a) of the drive train (11), or the maximum torque value (Mmax, Mmax1,Mmax2) is increased by the moment of inertia value (43) which depends on the acceleration (a) of the drive train (11), and wherein the limiting device (31) is designed to simulate the actual supplied output torque (Mab) by reducing the respective internal motor torque value (36) by at least one friction torque value (45) of the drive train (11) or by increasing the maximum torque value (Mmax, Mmax1, Mmax2) by the at least one friction torque value (45), , characterized by , that it has at least one input (56) for at least one temperature value (49) of the drive train (11), and that the limiting device (31) is designed to determine the at least one friction torque value (45) of the drive train (11) as a function of the at least one temperature value (49). [2] Control device according to claim 1, characterized by, that the limiting device (31) has generating means (40) for generating output torque values ​​(42) representing the actual output torque provided (Mab) by reducing the internal motor torque values ​​(36) of the drive motor (12) which depend on the motor current (Imot) by the moment of inertia values ​​(43) of the drive train (11) which depend on the acceleration (a) of the drive train (11), and that the comparison means (37) are designed for comparing the output torque values ​​(42) with the maximum torque value (Mmax, Mmax1, Mmax2). [3] Control device according to any of the preceding claims, characterized by , that the limiting device (31) is designed to determine at least one friction torque value (45) of the drive train (11) as a function of at least one speed value (28) of the drive train (11). [4] Control device according to any of the preceding claims, characterized by, that the drive train (11) has a transmission (13) downstream of the drive motor (12), and that the control device has an input (57) for a transmission value (48) or a sensor for determining the transmission value (48), wherein the transmission value (48) represents a transmission ratio (u) set on the transmission (13). [5] Control device according to claim 4, characterized by , that the limiting device (31) is designed to replicate the actual output torque (Mab) provided as a function of at least one transmission ratio (u) of the gearbox (13). [6] Control device according to claim 5, characterized by , that the limiting device (31) for generating the output torque values ​​(42) is designed depending on at least one transmission ratio (u) of the gearbox (13). [7] Control device according to any of the preceding claims, characterized by, that the limiting device (31) is designed to replicate the actual output torque (Mab) provided as a function of a change in a target speed value (27). [8] Control device according to any of the preceding claims, characterized by , that the limiting device (31) is designed to replicate the actual output torque (Mab) provided by reducing the internal motor torque values ​​(36) by compensation values ​​(51) or increasing the maximum torque value (Mmax, Mmax1, Mmax2) by compensation values ​​(51), wherein the compensation values ​​(51) represent an increase in the motor current (Imot) after an increase in a target speed value (27) for a predetermined time period in which the increase in the motor current (Imot) does not substantially change the output speed (ω) of the drive train (11). [9] Control device according to any of the preceding claims, characterized bythat it has plausibility testing equipment (58) for checking the plausibility of the output torque values ​​(42) and / or of sensor values ​​to be evaluated for determining the output torque values ​​(42). [10] Control device according to claim 9, characterized by , that plausibility check means (58) include filter means (59). [11] Control device according to any of the preceding claims, characterized by , that the comparison means (37) are designed to carry out a plausibility check when the maximum torque value (Mmax, Mmax1, Mmax2) is reached and / or exceeded by the output torque values ​​(42). [12] Control device according to any of the preceding claims, characterized by that it has a switching device (53) for switching the drive motor (12) into a braking operation when the output torque values ​​(42) reach or exceed the maximum torque value (Mmax, Mmax1, Mmax2). [13] Control device according to claim 10, characterized by that the switching device (53) has at least one switch (55) for short-circuiting the drive motor (12). [14] Control device according to any of the preceding claims, characterized by, that the limiting device (31) for sending control commands (65) for controlling a current-energizing device (22) supplying current to the drive motor (12) is configured in a braking mode in which the current-energizing device (22) generates a rotating field (64) that brakes the drive motor (12) and is opposite to a respective direction of rotation (63) of the drive motor (12), and that the limiting device (31) controls the current-energizing device (22) to the braking mode under at least one braking condition in order to limit the output torque (Mab) provided on the output side to the maximum torque value (Mmax, Mmax1, Mmax2), wherein the at least one braking condition includes that a quotient of the output torque (Mab) and a rotational energy (Erot) present in the drive train (11) is less than or equal to a maximum ratio (Xmax). [15] Control device according to claim 14, characterized by, that the at least one braking condition includes that the output torque (Mab) is below or equal to a predetermined or adjustable ratio (Ymax; Zmax) in relation to a rotational speed (ω) of the drive train (11) or in relation to the first power of a rotational speed (ω) of the drive train (11). [16] Control device according to claim 14 or 15, characterized by , that includes at least one braking condition that the output torque (Mab) reaches or exceeds a predetermined rate of increase (H). [17] Control device according to claim 16, characterized by , that the at least one braking condition includes that the output torque (Mab) reaches or exceeds the predetermined rate of increase (H) depending on a minimum rotational speed (ω min) of the drive motor (12). [18] Control device according to any one of claims 14 to 17, characterized by, that the at least one braking condition includes that a predefinable or predetermined target maximum value (SMmax) and / or output torque values ​​(42) representing the output torque (Mab) are equal to or less than a predetermined threshold torque value (Ms) before switching. [19] Control device according to any one of claims 14 to 18, characterized by , that it includes at least one braking condition that the maximum torque value (Mmax, Mmax1, Mmax2) is below a threshold torque value. [20] Control device according to one of claims 14 to 19, characterized by , that the limiting device (31) is designed to output the control commands (65) depending on a braking process (69) of the drive train (11) during braking operation. [21] Control device according to claim 20, characterized by , that the limiting device is designed to control the braking process (69). [22] Control device according to claim 21, characterized by , that the limiting device regulates the braking process (69) so that the output torque (Mab) reaches the maximum torque value (Mmax, Mmax1, Mmax2). [23] Control device according to one of claims 21 to 22, characterized by , that the limiting device, at the start of braking operation, controls the current supply device (22) to a stronger braking and subsequently reduces or regulates the braking depending on the braking process (69). [24] Control device according to any of the preceding claims, characterized by , that the limiting device (31) can be switched off. [25] Machine tool (10) with a drive train (11) comprising an electric drive motor (12), characterized by that it has a control device (17) according to one of the preceding claims for controlling or regulating the drive motor (12). [26] Machine tool according to claim 25, characterized by , that the drive train (11) has a gearbox (13) downstream of the drive motor (12), and that the drive motor (12) has at least one temperature sensor (50) arranged on a side of the drive motor (12) facing the gearbox (13), wherein the at least one temperature sensor (50) is connected to the control device (17) for transmitting temperature values ​​(49). [27] Machine tool according to claim 25 or 26, characterized by , that it is a hand-held power tool or a hand-held power tool (10) for drilling and / or screwing.

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