Method for calculating rotor position of a motor of a power tool and power tool

Abstract

The present invention relates to a method for calculating the rotor position of an electric motor 2 of an electric power tool 10, in particular an electric screwdriver, comprising a step S4 of checking whether a first motor current I1 is below a threshold value SW, and a step S5 of calculating the rotor position of the electric motor 2 based on the first motor current I1 and / or a second motor current in response to checking that the first motor current I1 is below the threshold value SW.

Description

[Technical field]

[0001] The present invention relates to a method for calculating the rotor position of an electric motor of an electric power tool, in particular an electric screwdriver. [Background technology]

[0002] EP 0579694, EP 1051801, EP 1746718 and EP 10201622275 each describe a method for calculating rotor position based on motor current. The method is based on the dependence of the winding inductance of a motor on the rotor position. If the rotor position changes, the winding inductance changes. If the winding inductance changes, the motor current changes.

[0003] Such rotor position capture based on the motor currents is also called sensorless detection of the rotor position. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] European Patent No. 0579694 [Patent Document 2] European Patent No. 1051801 [Patent Document 3] European Patent No. 1746718 [Patent Document 4] European Patent Application Publication No. 10201622275 Summary of the Invention [Problem to be solved by the invention]

[0005] The object of the invention is to provide a method which allows for an efficient and reliable determination of the rotor position. [Means for solving the problem]

[0006] This problem is solved by a method according to claim 1, comprising the steps of checking whether a first motor current is below a threshold value and, in response to checking that the first motor current is below the threshold value, calculating a rotor position of the motor based on the first motor current and / or the second motor current.

[0007] By performing the calculation of the rotor position based on the motor current, i.e. in particular in a sensorless manner, a sensor for calculating the rotor position, e.g. a signal generator, can be omitted. Preferably, the power tool does not have a sensor for detecting the rotor position, in particular a direct detection sensor. In particular, no sensor for detecting the rotor position, in particular a direct detection sensor, is used within the scope of the method.

[0008] Furthermore, by checking whether the motor current is below a threshold value, it is ensured that the rotor position calculation is reliable. Preferably, the motor current is used as an indicator for the magnetic saturation of the motor. Generally, when a motor is magnetically saturated, the winding inductance is less dependent or no longer dependent on the rotor position. Therefore, when a motor is magnetically saturated, the rotor position can usually no longer be reliably inferred from the motor current (which depends on the winding inductance).

[0009] Conventionally, to avoid this problem, the motor is designed to be large so that magnetic saturation does not occur during a given drive, thereby preventing the calculation of the rotor position based on the motor current from being adversely affected by magnetic saturation.

[0010] In contrast, in the method of the present invention, magnetic saturation is preferably allowed during a given operation, so that the motor of the power tool does not have to be designed to be large enough to prevent magnetic saturation from occurring during the given operation.

[0011] Nevertheless, the rotor position may be reliably calculated by the power tool. By checking whether the motor current is above a threshold before calculating the rotor position, and performing the rotor position calculation in response to the motor current being below the threshold, it may be beneficially ensured that the rotor position calculation is performed while the motor is not magnetically saturated and the rotor position calculation is beneficially not adversely affected. Thus, rotor position calculation may be accomplished efficiently.

[0012] Preferably, the electric motor is driven in a number of time-successive and non-overlapping drive phases, which drive phases in particular comprise a position calculation phase in which the rotor position is calculated, in which the first motor current is smaller than a threshold value. Preferably, these drive phases further comprise a rotational torque phase in which the rotor position is not calculated, in which the first motor current is larger than said threshold value. For controlling the electric motor, the power tool preferably uses in the rotational torque phase the rotor position calculated during the position calculation phase.

[0013] Advantageous further configurations are set forth in the dependent claims.

[0014] Furthermore, the present invention relates to a power tool, in particular a power screwdriver, having an electric motor, configured to calculate a rotor position of the motor based on a motor current, the power tool being configured to check whether a first motor current is below a threshold and, in response to checking that the first motor current is below the threshold, to calculate a rotor position of the motor based on the first motor current and / or a second motor current.

[0015] The present invention further relates to a controller for a power tool having an electric motor configured to determine whether a first motor current is below a threshold and, in response to determining that the first motor current is below the threshold, calculate a rotor position of the motor based on the first motor current and / or a second motor current.

[0016] Further representative details and exemplary embodiments are described below with reference to the drawings. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic diagram of a power tool. [Diagram 2] FIG. [Diagram 3] FIG. 2 is a circuit diagram of a control circuit. [Figure 4] 1 is a flowchart of a control procedure. [Diagram 5] This shows the time progression of the motor current. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] FIG. 1 shows a power tool 10 in a representative configuration. Here, the power tool 10 is configured as a power driver, in particular as a screwdriver. Alternatively, the power tool 10 may be configured as another power tool, in particular as a power tool with a rotating tool tip. The power tool may be configured as, for example, a saw, a disc grinder, a drill and / or a milling machine. The power tool 10 may in particular be a hand-operated power tool. Alternatively, the power tool 10 may be a fixed or semi-fixed power tool.

[0019] The power tool 10 includes an electric motor 2. The power tool 10 is configured to determine whether a first motor current I1 is less than a threshold value SW. A representative time course of the motor current I1 is shown in FIG. 5 together with the threshold value SW. The power tool 10 is configured to determine whether the first motor current I1 is less than the threshold value SW and then calculate a rotor position of the electric motor 2 based on the first motor current I1 and / or a second motor current. For example, the second motor current includes one or more branch currents of the branch currents IZ1, IZ2, IZ3 shown in FIG. 3 and / or includes a total current shown in FIG. 3.

[0020] In particular, the power tool 10 is configured to perform the calculation of the rotor position based on the first motor current and / or the second motor current after it has been determined that the motor current I1 is less than the threshold value SW. In particular, the power tool 10 is configured to not perform the calculation of the rotor position based on the first motor current and / or the second motor current after it has been determined that the motor current I1 is higher than the threshold value SW. In particular, the power tool 10 is configured to perform the calculation of the rotor position based on the first motor current and / or the second motor current only when it has been determined that the motor current I1 is less than the threshold value SW.

[0021] As already explained at the beginning, the first motor current I1 is used as an indicator for the magnetic saturation of the motor 2. By performing said rotor position calculation when the motor current I1 is below the threshold value SW - i.e. on the basis of a particular absence of (significant) magnetic saturation - it can be ensured that the rotor position calculation is not adversely influenced by the magnetic saturation of the motor 2.

[0022] Representative embodiments will be described in detail below.

[0023] First, regarding power tools: The power tool 10 comprises an electric drive 1. The electric drive 1 comprises an electric motor 2. Optionally, the electric drive 1 further comprises a gear mechanism (not shown). The power tool 10 is in particular configured as a brushless DC motor. The electric motor 2 is in particular a three-phase AC synchronous motor excited by permanent magnets. Preferably, the electric motor 2 is an EC motor (electronically commutated motor).

[0024] The power tool 10 further includes an accessory tool 3, for example an electric screwdriver, which may be driven by the electric motor 2. In particular, the accessory tool 3 may be rotated by the electric motor 2. In general, the accessory tool 3 is coupled to the electric motor 2 via a shaft 15 (and / or an optionally present gear mechanism).

[0025] Preferably, the power tool 10 further comprises a control device 4 and an operating device 5. Optionally, the power tool 10 further comprises an energy storage unit 6, for example a battery.

[0026] Preferably, the controller 4 comprises a processing device, e.g. a microcomputer. In particular, the controller 4 is used to check whether said first motor current I1 is below a threshold value SW and / or to perform a calculation of the rotor position based on said first motor current I1 and / or said second motor current. Preferably, the controller 4 comprises a control circuit 8 for providing a control voltage for the motor 2. A representative configuration of the control circuit 8 is shown in FIG. 3.

[0027] Typically, the operating device 5 includes a switch, in particular a trigger switch. Preferably, a user can control the driving of the tool accessory 3 by the electric motor 2 via the operating device, in particular the tool accessory 3 can be driven at its rotation speed and / or its rotation torque. Preferably, the control device 4 is configured to capture the operation of the operating device 5 and execute the control of the electric motor 2 according to the operation.

[0028] Preferably, energy for driving the power tool 10 , in particular the control device 4 and / or the electric motor 2 , is provided from an energy store 6 .

[0029] Generally, the power tool 10 includes a grip 7. The grip 7 of the power tool 10 is grasped by a user, particularly for use with one hand.

[0030] In general, the power tool 10 comprises a housing in which the electric drive 1, the control device 4 and / or the energy store 6 are arranged. In particular, the operating device 5 is arranged outside the housing. Preferably, a grip 7 forms part of the housing.

[0031] A representative configuration of the electric motor 2 will be described below with reference to FIG.

[0032] The electric motor 2 has a stator 9 and a rotor 11. The stator 9 includes a plurality of windings 12 arranged in a distributed manner around the rotation axis of the rotor 11. The rotor 11 includes a plurality of permanent magnets 14 arranged in a distributed manner around the rotation axis of the rotor 11.

[0033] In particular, the rotor 11 is not formed radially symmetrically, in particular with respect to the magnetic properties of the rotor 11. Depending on the rotor position of the rotor 11, the influence of said rotor on the inductance of the windings 12 varies. Preferably, the inductance of each of the windings 12 depends on the rotational position of the rotor 11. In particular, the term rotor position means the rotational position of the rotor 11 with respect to the rotational axis of the rotor 11. According to another configuration, the rotor 11 is formed radially symmetrically.

[0034] Preferably, the windings 12 are energized by the control circuit 7 to provide a rotating magnetic field that rotates about the axis of rotation of the rotor 11. The rotating magnetic field, through interaction with the permanent magnets 14, causes the rotor 11 to rotate about its axis of rotation.

[0035] Preferably, the stator 9 and / or the rotor 11 comprise a magnetizable material, in particular a ferromagnetic material, such as iron, which becomes magnetically saturated after a certain current strength of the current passing through the windings 12. The dependence of the inductance of these windings 12 - i.e. the current passing through these windings 12 - on the rotor position is reduced and / or eliminated upon magnetic saturation.

[0036] The magnetic saturation of the magnetizable material of the electric motor 2, in particular of said rotor 9 and / or stator 11, is indicated by a threshold value SW. Preferably, the threshold value SW corresponds to a current strength of the first motor current I1 at which the magnetizable material of the electric motor 2, in particular of said rotor 9 and / or stator 11, becomes magnetically saturated. Preferably, the threshold value SW is pre-calculated and stored in the power tool 10, in particular in the control device 4.

[0037] Preferably, first motor current I1 includes one, multiple, or all of the currents passing through multiple windings 12. For example, first motor current I1 is the sum of the currents passing through these windings 12. In particular, first motor current I1 is the sum of the currents flowing into and out of these windings 12.

[0038] The control of the electric motor 2 will be described in detail below with reference to FIG.

[0039] FIG. 3 shows a representative configuration of the control circuit 8. Preferably, the control circuit 8 is configured as an inverter. In particular, the control circuit 8 is used to provide a number of control signals for controlling the electric motor 2, in particular the number of windings 12. In general, the control circuit 8 provides three control signals. In general, the control circuit 8 has a first output U for providing a first control signal, a second output V for providing a second control signal, and a third output W for providing a third control signal.

[0040] Preferably, the control circuit 8 provides these control signals on the basis of a supply voltage Ud applied between the two connection points AP1, AP2. Preferably, the supply voltage Ud is a DC voltage.

[0041] The three control signals may also be called phases. These control signals are in particular voltage signals.

[0042] Generally, the control circuit 8 comprises one circuit branch SZ1, SZ2, SZ3 for each output U, V, W. These circuit branches SZ1, SZ2, SZ3 are respectively connected between both connection points AP1, AP2. Generally, these circuit branches SZ1, SZ2, SZ3 are respectively configured as half-bridges. Preferably, each circuit branch SZ1, SZ2, SZ3 comprises two switches - a first switch S11, S21, S31 and a second switch S12, S22, S32. Each output U, V, W can be connected to the first connection point AP1 via the respective first switch S11, S21, S31 and to the second connection point AP2 via the respective second switch S12, S22, S33.

[0043] To drive the rotor 11, preferably a plurality of AC signals, in particular a plurality of AC signals which are phase shifted with respect to one another, may be provided by controlling the first switches S11, S21, S31 and the second switches S12, S22, S32.

[0044] The power tool 10 is configured to capture a first motor current I1 and / or a second motor current, which is a current passing through one, a number of, or all of the windings 12 of the motor 2. The first motor current I1 and the second motor current may be the same current or may be different currents.

[0045] In general, the first motor current I1 is the total current passing through the multiple windings 12. In general, this current is captured as the total current passing through the second node AP2. Alternatively or in addition, the total current may be captured as the total current IS flowing into or out of the first node AP1.

[0046] Generally, the power tool 10, and in particular the control circuit 8, includes a total current measuring device SM for capturing the total current IS. Generally, the total current measuring device SM is connected between the second node AP2 and the second switches S12, S22, S32.

[0047] The first motor current I1 may further comprise one, several or all of the branch currents IZ1, IZ2, IZ3 conducted through the circuit branches SZ1, SZ2, SZ3. Preferably, the power tool 10 is configured to compare the one, several or all of the branch currents IZ1, IZ2, IZ3, respectively, with a threshold value SW and to perform a rotor position calculation in response to the compared respective branch current IZ1, IZ2, IZ3 being less than the threshold value SW.

[0048] In general, the power tool 10, and in particular the control circuit 8, includes a number of branch current measuring devices ZM1, ZM2, ZM3 for capturing respective branch currents IZ1, IZ2, IZ3, each of which is connected to a respective circuit branch SZ1, SZ2, SZ3.

[0049] Instead of the illustrated configuration in which only one branch current measuring device ZM1, ZM2, ZM3 is present for each circuit branch SZ1, SZ2, SZ3, there may also be a smaller number of branch current measuring devices than these circuit branches, for example no branch current measuring device may be present for one circuit branch, the branch current of this circuit branch then preferably being calculated by the power tool 10 in particular on the basis of the other branch currents and the total current.

[0050] In the following, calculation of the rotor position based on the first motor current and / or the second motor current will be described.

[0051] Preferably, the power tool 10 is configured to input a test signal to the motor 2 and to calculate a rotor position based on a response of the first motor current and / or the second motor current to the test signal. Preferably, the rotor 11 is not driven by the input of the test signal. Preferably, the test signal comprises a sequence of connection states and / or voltage values ​​for the outputs U, V, W obtained by controlling the first switches S11, S21, S31 and / or the second switches S12, S22, S32.

[0052] Specific test signals for controlling the electric motor 2 for the purpose of calculating the rotor position are described in the above-mentioned prior art. In particular, test signals according to the so-called "INFORM (Indirect Flux Detection by Online Reactance Measurement) method" are known. Preferably, the power tool 10 is configured to control the electric motor 2 by a test signal according to the INFORM method.

[0053] The first motor current and / or the second motor current may vary in response to the test signal. The power tool 10 is configured to capture the first motor current and / or the second motor current and to calculate a rotor position based on the captured motor currents. Preferably, the power tool 10 captures the branch currents IZ1, IZ2, IZ3 as the second motor current and calculates a rotor position based on the branch currents IZ1, IZ2, IZ3, in particular based on the time course of the branch currents IZ1, IZ2, IZ3 and / or on calculated signal characteristics.

[0054] Alternatively or additionally, the power tool 10 captures two of the branch currents IZ1, IZ2, IZ3 as a second motor current and calculates the rotor position based on the captured branch currents, in particular based on the time progression of the captured branch currents and / or the calculated signal characteristics.

[0055] Alternatively or additionally, the power tool 10 captures the total current IS as the second motor current and calculates the rotor position based on the total current IS, in particular based on the time profile of the total current IS and / or calculated signal characteristics.

[0056] A specific mathematical method for calculating the rotor position based on the multiple branch currents is described in the prior art above. In particular, this mathematical method is known from the INFORM method. Preferably, the power tool 10 is configured to mathematically calculate the rotor position according to the INFORM method.

[0057] In particular, the power tool 10 is configured to perform a control, in particular a commutation, of the electric motor 2 based on the calculated rotor position. In particular, the power tool 10 is configured to perform a sensorless commutation of the electric motor 2 using the calculated rotor position. In particular, the power tool 10 is configured to provide control signals provided at the outputs U, V, W based on the calculated rotor position. Preferably, the power tool 10 provides control signals provided at the outputs U, V, W based on the calculated rotor position and provides e.g. a requested rotation speed and / or a requested rotation torque based on a user input entered by the operating device 5.

[0058] Preferably, the power tool 10 is configured to continue the control, in particular the commutation, of the motor 2 based on the last calculated rotor position until a new rotor position is calculated. For example, when the first motor current I1 is above the threshold SW and for this reason the power tool 10 does not perform a rotor position calculation for this time, the power tool 10 continues to use the last calculated rotor position for this time to control the motor 2. Preferably, the power tool 10 electrically rotates the rotor 11 by 90° by controlling the motor 2 based on the calculated initial rotor position and continues said control based on said initial rotor position when a new rotor position of the rotor 11 has not been calculated. As a result, the rotor 11 remains electrically stopped after said 90° rotation until the power tool 10 calculates a new rotor position and performs said control based on said new rotor position. For example, a 90° rotation is electrically equivalent to a 45° rotation for a two mechanical pole pair and a 30° rotation for a three mechanical pole pair.

[0059] In the following, an exemplary control procedure AP for controlling the electric motor 2 is explained in detail with reference to Figures 4 and 5. The control procedure is an embodiment of a scheme for calculating the rotor position of the electric motor 2 of the power tool 10.

[0060] Preferably, the control procedure AP is executed by the power tool 10 , in particular by the control device 4 .

[0061] The control procedure AP starts with an optional step S1, in which the rotor position is preferably calculated based on the first motor current and / or the second motor current, while the rotor 11 is still not driven and preferably not running. After said rotor position calculation, an optional step S2 is performed, in which the motor 2 is started, i.e. in particular the first motor current is increased to such an extent that the rotor 11 is driven and preferably running.

[0062] If the control procedure AP is started while already running, steps S1 and S2 are unnecessary and preferably absent.

[0063] The control procedure AP continues with step S3, in which the motor 2 is controlled, in particular the winding 12 is energized, in order to generate a rotational torque for rotating the tool accessory 3. In step S3, the winding 12 is energized in such a way that the first motor current I1 increases above the threshold value SW or the first motor current I1 remains below the threshold value SW.

[0064] In particular, in step S3, control of the electric motor 2 is performed based on the rotor position calculated in the previous step (eg S2, S5 or S8).

[0065] In a fourth step, it is checked whether the first motor current I1 is smaller than the threshold value SW. If the check shows that the first motor current I1 is smaller than the threshold value SW, the control procedure continues with step S5. In step S5, the rotor position is calculated based on the first motor current and / or the second motor current. Preferably, in step S5, the motor 2, in particular the winding 12, is controlled by a test signal. Furthermore, in the case of step S5, the branch currents IZ1, IZ2, IZ3 which arise in response to the test signal are preferably captured and the rotor position is calculated based on these branch currents IZ1, IZ2, IZ3. The control procedure AP then preferably returns to step S3.

[0066] If the check shows that the first motor current I1 is greater than the threshold value SW, the control procedure continues with steps S6 and S7.

[0067] Preferably, the power tool 10 is configured in response to the motor current I1 being checked to be above the threshold SW such that a calculation of the rotor position is not performed based on the first motor current and / or the second motor current. In particular, when the motor current I1 is checked to be above the threshold SW, the power tool 10 is configured in such a way that a control of the motor 2 is not performed by means of a test signal and / or a capture of the branch currents IZ1, IZ2, IZ3 generated in response to the test signal and / or a calculation of the rotor position is not performed based on these branch currents IZ1, IZ2, IZ3. Thus, in steps S6 and S7, a calculation of the rotor position is not performed based on the first motor current and / or the second motor current.

[0068] Preferably, the power tool 10 is configured to, in response to the check finding that the motor current I1 is above the threshold SW, reduce the motor current I1 until the motor current I1 is below the threshold SW. In the control procedure AP, the reduction of the motor current I1 is generally performed by stopping the control of the motor 2 in step S6. For example, the motor phases of the motor 2, in particular the control signals, are interrupted. In general, the control circuit 8 is controlled such that the current passing through the winding 12 is reduced. For example, all the first switches S11, S21, S31 are opened (i.e. set to "non-conductive") and all the second switches S21, S22, S23 are closed (i.e. set to "conductive"). Alternatively, all the first switches S11, S21, S31 are closed and all the second switches S21, S22, S23 are opened.

[0069] In step S7, the still stopped control of eg motor 2 is maintained until the first motor current I1 falls below threshold value SW.

[0070] Preferably, the power tool 10 is configured to perform a rotor position calculation based on the first motor current and / or the second motor current after the first motor current I1 has decreased below the threshold value S. Typically, the rotor position calculation is performed in step S8.

[0071] The control procedure continues with step S3. Preferably, after the rotor position has been calculated, typically during step S3, the power tool is configured to increase the first motor current I1 above the threshold SW.

[0072] In the following, the different phases which proceed during the control of the motor, and in particular during the execution of the control procedure AP, will be explained with reference to FIG.

[0073] 5 shows the time course of the first motor current I1 together with successive driving phases of the power tool 10. In general, these driving phases include position calculation phases PP1, PP2, PP3, rotational torque phases DP1, DP2 and reduction phases RP1, RP2.

[0074] In general, the driving phases are executed in succession in the order of a position calculation phase, a rotational torque phase, and a reduction phase. Preferably, these driving phases are repeated several times, in particular successively, in the above-mentioned order. In the illustrated example, these driving phases are executed in succession in the order of a first position calculation phase PP1, a first rotational torque phase DP1, a first reduction phase RP1, a second position calculation phase PP2, a second rotational torque phase DP2, a second reduction phase RP2, and a third position calculation phase PP3.

[0075] Preferably, the power tool 10 is configured to start with a first position calculation phase PP1, during which the first motor current I1 is below the threshold SW. During the first position calculation phase PP1, the power tool 10 is configured to calculate the rotor position based on the first motor current and / or the second motor current.

[0076] In the first position calculation phase PP1, in particular step S2 is performed, with step S1 being performed as an option before step S2.

[0077] Preferably, the power tool 10 is configured to perform a rotation torque phase DP1 after the position calculation phase and to increase the first motor current I1 above the threshold value SW during the first position calculation phase PP1. Preferably, the power tool 10 is configured not to perform a rotor position calculation based on the first motor current and / or the second motor current during the first rotation torque phase DP1.

[0078] In the first rotational torque phase DP1, in particular steps S3 and S4 are executed.

[0079] Preferably, the power tool 10 uses the rotor position calculated during the first position calculation phase PP1 for controlling the electric motor 2 during the first rotation torque phase DP1.

[0080] Preferably, the power tool 10 is configured to execute a first reduction phase RP1 after the first rotation torque phase DP1 and to reduce the first motor current I1 below the threshold value SW during the first reduction phase RP1.

[0081] In the first decrease phase, in particular steps S6 and S7 are carried out.

[0082] In particular, when the power tool 10 determines during the test that the first motor current I1 is less than the threshold value SW, the power tool 10 preferably continues with the second position calculation phase PP2. The power tool 10 performs the second position calculation phase PP2 in a similar manner to the first position calculation phase PP1 and continues with the subsequent drive phases as described above. The present application relates to the invention described in the claims, but may also include the following configurations as other aspects. 1. A method for calculating the rotor position of an electric motor (2) of an electric power tool (10), in particular an electric screwdriver, comprising the steps of: The method comprises the step (S4) of checking whether a first motor current (I1) is below a threshold value (SW), and in response to checking that the first motor current (I1) is below the threshold value (SW), calculating (S5) a rotor position of the motor (2) based on the first motor current (I1) and / or the second motor current. 2. 2. The method according to claim 1, wherein the first motor current (I1) exceeding the threshold value (SW) is indicative of magnetic saturation of the motor (2). 3. 3. The method according to claim 1 or 2, further comprising checking (S4) whether the first motor current (I1) is below the threshold (SW), and in response to checking that the first motor current (I1) is above the threshold (SW), not calculating the rotor position based on the first motor current (I1) and / or the second motor current. 4. 4. The method according to any one of claims 1 to 3, further comprising, in response to determining that the first motor current (I1) is above the threshold (SW), reducing (S6, S7) the first motor current (I1) until the first motor current (I1) is below the threshold (SW). 5. 5. The method according to claim 4, further comprising, after reducing the first motor current (I1) below the threshold (SW), calculating the rotor position based on the first motor current and / or the second motor current. 6. 6. The method of claim 5, further comprising increasing the first motor current (I1) above the threshold (SW) after calculating the rotor position. 7. The method according to any one of 1 to 6 above, wherein a position calculation phase (PP1, PP2, PP3), a rotational torque phase (DP1, DP2), and a reduction phase (RP1, RP2) are successively executed during control of the electric motor (10). 8. 8. The method according to claim 7, wherein the position calculation phases (PP1, PP2, PP3) are executed in response to the first motor current (I1) being below the threshold value (SW), and during the position calculation phases (PP1, PP2, PP3) the rotor position is calculated based on the first motor current and / or the second motor current. 9. 9. The method according to claim 7 or 8, wherein the rotational torque phase (DP1, DP2) is performed after the position calculation phase (PP1, PP2, PP3), during the rotational torque phase (DP1, DP2) the first motor current (I1) is increased above the threshold value (SW), and during the position calculation phase (PP1, PP2, PP3) no calculation of the rotor position is performed based on the first motor current and / or the second motor current. 10. 10. The method according to any one of claims 7 to 9, wherein after the rotation torque phase (DP1, DP2), the reduction phase (RP1, RP2) is executed, and during the reduction phase (RP1, RP2), the first motor current (I1) is reduced to below the threshold value (SW). 11. 11. The method according to any one of claims 7 to 10, wherein the position calculation phase (PP1, PP2, PP3), the rotational torque phase (DP1, DP2), and the reduction phase (RP1, RP2) are repeated multiple times in the above order. 12. 12. The method according to any one of claims 1 to 11, wherein control, in particular commutation, of the electric motor (2) is performed based on the calculated rotor position. 13. 13. The method according to any one of the above 1 to 12, wherein the electric motor (2) is a brushless DC motor. 14. 14. The method according to any one of 1 to 13 above, further comprising inputting a test signal to the electric motor (2) and calculating a position of the rotor based on a response of the first motor current and / or the second motor current to the test signal. 15. A power tool (10), in particular a power screwdriver, having a motor (2), The power tool (10) is configured to check whether a first motor current (I1) is below a threshold (SW), and in response to checking that the first motor current (I1) is below the threshold (SW), calculate a rotor position of the motor (2) based on the first motor current (I1) and / or the second motor current. 16. 16. An electric power tool (10) according to claim 15, configured to carry out the method according to any one of claims 1 to 14. 17. A control device (4) for a power tool (10) having an electric motor (2), comprising: the control device (4) configured to check whether a first motor current (I1) is below a threshold (SW), and in response to checking that the first motor current (I1) is below the threshold (SW), calculate a rotor position of the motor (2) based on the first motor current (I1) and / or the second motor current. [Explanation of symbols]

[0083] 1 Electric drive unit 2 electric motor 3 Tip tool 4. Control device 5 Operating device 6 Energy storage unit 7 Grip 8 Control Circuit 9 Stator 10 Power tools 11 Rotor 12 Winding section 14 Permanent magnets 15-axis SW Threshold I1 1st motor current IZ1 Branch current IZ2 Branch Current IZ3 Branch current IS Total current U 1st output section V 2nd output section W 3rd output section AP1 First connection point AP2 Second connection point Ud supply voltage SZ1 Circuit branch SZ2 Circuit branch SZ3 Circuit branch S11 1st switch S21 1st Switch S31 1st Switch S12 Second switch S22 Second switch S32 2nd Switch ZM1 Branch Current Measuring Device ZM2 Branch Current Measuring Device ZM3 Branch Current Measuring Device SM total current measuring device IS Total current AP Control Procedure PP1, PP2, PP3 Position calculation phase DP1, DP2 Rotational torque phase RP1,RP2 Decrease Phase

Claims

1. 1. A method for calculating the position of a rotor of an electric motor of an electric power tool from the dependency between the inductance of one, several or all windings of a stator of the electric motor, i.e. the current passing through said windings, and the position of the rotor of the electric motor, comprising: A threshold value (SW) corresponding to the current intensity of the first motor current (I1) at which the electric motor (2) becomes magnetically saturated is calculated in advance; The threshold value (SW) is stored in the power tool (10), the first motor current (I1) exceeding the threshold value (SW) indicates magnetic saturation of the motor (2); (S4) determining whether the first motor current (I1) is below a threshold value (SW); in response to determining that the first motor current (I1) is below the threshold value (SW), calculating (S5) a position of the rotor of the motor (2) based on the first motor current (I1) and / or the second motor current, the currents passing through one, a number or all of the windings (12); in response to determining that the first motor current (I1) is above the threshold (SW), stopping control of the motor (2) (S6); subsequently, maintaining control of the electric motor (2) still stopped (S7) until the first motor current (I1) falls below the threshold value (SW); (S8) calculating the rotor position based on the first motor current (I1) and / or the second motor current after reducing the first motor current (I1) below the threshold value (SW); The method then comprises the step (S3) of continuing to control the electric motor (2).

2. 2. The method of claim 1, further comprising: determining (S4) whether the first motor current (I1) is below the threshold (SW); and in response to determining that the first motor current (I1) is above the threshold (SW), not calculating the rotor position based on the first motor current (I1) and / or the second motor current.

3. 3. The method of claim 1 or 2, further comprising, in response to determining that the first motor current (I1) is above the threshold (SW), decreasing (S6, S7) the first motor current (I1) until the first motor current (I1) is below the threshold (SW).

4. 4. The method of claim 3, further comprising, after reducing the first motor current (I1) below the threshold (SW), calculating the rotor position based on the first motor current and / or the second motor current.

5. 5. The method of claim 4, further comprising increasing the first motor current (I1) above the threshold (SW) after calculating the rotor position.

6. The method according to any one of claims 1 to 5, wherein during control of the electric motor (2), a position calculation phase (PP1, PP2, PP3), a rotational torque phase (DP1, DP2) and a reduction phase (RP1, RP2) are executed in succession.

7. 7. The method of claim 6, wherein in response to the first motor current (I1) being below the threshold value (SW), the position calculation phases (PP1, PP2, PP3) are executed, and during the position calculation phases (PP1, PP2, PP3) the rotor position is calculated based on the first motor current and / or the second motor current.

8. 8. The method according to claim 6 or 7, wherein the rotation torque phase (DP1, DP2) is performed after the position calculation phase (PP1, PP2, PP3), during which the first motor current (I1) is increased above the threshold value (SW), and during which no calculation of the rotor position is performed based on the first motor current and / or the second motor current.

9. 9. The method according to claim 6, wherein after said rotation torque phase (DP1, DP2) said reduction phase (RP1, RP2) is executed, and during said reduction phase (RP1, RP2) said first motor current (I1) is reduced below said threshold value (SW).

10. The method according to any one of claims 6 to 9, wherein the position calculation phase (PP1, PP2, PP3), the rotational torque phase (DP1, DP2) and the reduction phase (RP1, RP2) are repeated multiple times in succession in the above mentioned order.

11. A method according to any one of the preceding claims, wherein control or commutation of the electric motor (2) is performed on the basis of the calculated rotor position.

12. The method according to any one of the preceding claims, wherein the electric motor (2) is a brushless DC motor.

13. 13. The method of any one of claims 1 to 12, further comprising inputting a test signal to the electric motor (2) and calculating a position of the rotor based on a response of the first motor current and / or the second motor current to the test signal.

14. A power tool (10) having an electric motor (2), A threshold value (SW) corresponding to the current intensity of the first motor current (I1) at which the electric motor (2) becomes magnetically saturated is calculated in advance; The threshold value (SW) is stored in the power tool (10), the first motor current (I1) exceeding the threshold value (SW) indicates magnetic saturation of the motor (2); the power tool (10) checks whether the first motor current (I1) is below the threshold (SW), and in response to checking that the first motor current (I1) is below the threshold (SW), calculates a rotor position of the motor (2) based on the first motor current (I1) and / or the second motor current, which are currents passing through one, a plurality of or all of the windings (12); in response to determining that the first motor current (I1) is above the threshold (SW), stopping control of the motor (2) (S6); Subsequently, maintaining the still stopped control of the motor (2) until the first motor current (I1) falls below the threshold value (SW) (S7), After reducing the first motor current (I1) below the threshold value (SW), the rotor position is calculated based on the first motor current (I1) and / or the second motor current (S8); The power tool (10) is configured to continue controlling the electric motor (2) (S3).

15. A power tool (10) according to claim 14, configured to carry out the method according to any one of claims 1 to 13.

16. A control device (4) for a power tool (10) having an electric motor (2), comprising: A threshold value (SW) corresponding to the current intensity of the first motor current (I1) at which the electric motor (2) becomes magnetically saturated is calculated in advance; The threshold value (SW) is stored in the power tool (10), the first motor current (I1) exceeding the threshold value (SW) indicates magnetic saturation of the motor (2); the control device (4) checks whether the first motor current (I1) is below the threshold value (SW), and in response to checking that the first motor current (I1) is below the threshold value (SW), calculates a rotor position of the motor (2) based on the first motor current (I1) and / or the second motor current; in response to determining that the first motor current (I1) is above the threshold (SW), stopping control of the motor (2) (S6); Subsequently, maintaining the still stopped control of the motor (2) until the first motor current (I1) falls below the threshold value (SW) (S7), After reducing the first motor current (I1) below the threshold value (SW), the rotor position is calculated based on the first motor current (I1) and / or the second motor current (S8); The control device (4) is configured to continue controlling the electric motor (2) (S3).

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