Power tool, method, arrangement, computer program product and computer-readable medium

Abstract

To provide an improved power tool. [Solution] An electric power tool having a tool, an electric motor for driving the tool, and a control unit for controlling the electric motor, wherein the electric power tool is configured to be connected to a power supply voltage and includes a rectifier device having an intermediate circuit for providing an intermediate circuit voltage based on the power supply voltage, the intermediate circuit voltage having a plurality of voltage half-waves 16 successive to one another, the control unit is configured to provide a torque transition for control of the electric motor, the torque transition including a respective torque half-wave for each voltage half-wave 16, and the control unit is configured to detect a reverse voltage 34 induced in the electric motor and reduce a current torque value of the torque transition in response to the reverse voltage 34 being equal to or greater than the intermediate circuit voltage.

Description

[Technical Field]

[0001] The present invention relates to a power tool, in particular a handheld power tool, such as a grinding, polishing and / or sawing tool, comprising a tool, an electric motor for driving the tool and a control unit for controlling the electric motor. The power tool includes a rectifier device configured for connection to a mains voltage and having an intermediate circuit for providing an intermediate circuit voltage based on the mains voltage. [Background technology]

[0002] The intermediate circuit is, for example, a capacitor used to smooth a rectified supply voltage. There are various approaches to dimensioning the intermediate circuit. The first approach is to dimension it so that the intermediate circuit voltage is approximately constant. This allows, in particular, approximately constant phase currents for energizing the electric motor and, thus, an approximately constant torque profile of the electric motor. However, a large intermediate circuit leads to a poor power factor and a high harmonic content in the absorbed current. The second approach is to dimension it small so that the intermediate circuit voltage follows the supply voltage, in particular the rectified supply voltage. However, such a small intermediate circuit can lead to the induced reverse current of the electric motor exceeding the intermediate circuit voltage in conventional control of the electric motor, reaching a range where no current can flow through the motor. This can lead to torque ripple with twice the supply voltage. Furthermore, a small intermediate circuit can result in higher ohmic power losses in the motor windings, which requires the electric motor to be designed larger. Summary of the Invention [Problem to be solved by the invention]

[0003] SUMMARY OF THE INVENTION It is an object of the present invention to provide an improved power tool. [Means for solving the problem]

[0004] The problem is solved by a power tool according to claim 1.

[0005] In power tools, the intermediate circuit voltage has several successive voltage half-waves. In particular, the intermediate circuit, e.g., the capacitor, is small-sized so that the intermediate circuit voltage follows the rectified mains voltage, thereby forming voltage half-waves. The rectified mains voltage includes, in particular, a series of positive sine half-waves. For example, the intermediate circuit voltage follows the rectified mains voltage over at least 50% of the amplitude of the rectified mains voltage. For example, the intermediate circuit voltage follows the rectified mains voltage in the range of 140 to 320 V. A small intermediate circuit advantageously achieves a good power factor, e.g., a power factor of at least 0.70 or at least 0.75.

[0006] The control unit is configured to provide a torque transition for control of the electric motor, the torque transition including one torque half-wave for each voltage half-wave. The control unit is configured to detect a reverse voltage induced in the electric motor and, in response to the reverse voltage being equal to or greater than the intermediate circuit voltage, reduce a current torque value of the torque transition. In particular, the control unit reduces the current torque value so that braking torque and / or torque ripple is reduced or avoided.

[0007] Preferably, the control unit closes the loop to control the torque-generating current, i.e., in particular the q-current, to zero if the induced back voltage of the electric motor is equal to or greater than the intermediate circuit voltage. Expediently, the control unit maintains an electrical connection to the electric motor even when the induced back voltage of the electric motor is equal to or greater than the intermediate circuit voltage, so that a field-weakening current, i.e., in particular the d-current, or a torque-generating current, i.e., in particular the q-current, can always flow to the electric motor, and in particular braking torques can be avoided and / or the power factor can be dynamically adapted to the load.

[0008] Preferred developments are the subject of the dependent claims.

[0009] The invention also relates to a method for operating a power tool, in particular a handheld power tool, such as a sanding, grinding and / or sawing tool, comprising a tool, an electric motor for driving the tool and a control unit for controlling the electric motor, the method comprising the following steps: - providing an intermediate circuit voltage based on the mains voltage to which the power tool is connected using a rectifier device having an intermediate circuit, the intermediate circuit voltage comprising a number of successive voltage half-waves; - providing a torque profile for control of an electric motor, the torque profile including each torque half-wave for each voltage half-wave; - detecting a reverse voltage induced in the electric motor; - reducing a current torque value of the torque transition in response to the reverse voltage being equal to or greater than the intermediate circuit voltage; The present invention relates to a method comprising:

[0010] Expediently, the method is performed by the above-mentioned power tool and / or is designed to suit the above-mentioned configuration of the power tool.

[0011] The invention also relates to an arrangement including an electric motor for driving a tool and a control unit for controlling the electric motor, the control unit being configured to provide a torque transition for controlling the electric motor, the torque transition including one torque half-wave for each voltage half-wave of an intermediate circuit voltage, the control unit being configured to detect a reverse voltage induced in the electric motor and to reduce a current torque value of the torque transition in response to the reverse voltage being equal to or greater than the intermediate circuit voltage.

[0012] The present invention also relates to a computer program product comprising commands for causing a power tool to perform the above-mentioned method steps.

[0013] The invention also relates to a computer readable medium having a computer program product stored thereon.

[0014] The present invention also relates to a method comprising the step of installing a computer program product on a power tool.

[0015] Further exemplary details and exemplary embodiments are described below with reference to the drawings. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic diagram of a power tool configured as a grinding machine; [Figure 2] 1 is a schematic diagram of a power tool configured as a sawing device; [Figure 3] 1 is a diagram showing a schematic diagram of a commutation device, a control unit and an electric motor of a power tool; [Figure 4] FIG. 4 shows the time course of the intermediate circuit voltage; [Figure 5] FIG. 10 is a diagram showing a change in torque over time. [Figure 6] FIG. 1 is a block diagram of signal processing. DETAILED DESCRIPTION OF THE INVENTION

[0017] 1 and 2 show an exemplary configuration of a power tool 1. The power tool 1 is exemplarily configured as a handheld power tool. The power tool 1 can be held, carried, and / or handled by a user's hand. The power tool 1 can be configured, in particular, as a grinding machine 1A (see FIG. 1) or a sawing machine (saw machine) 1B (see FIG. 2). The grinding machine 1A is, for example, a grinding machine, in particular a rotary grinding device. The sawing machine 1B is, for example, a plunge circular saw. Alternatively, the power tool 1 can be configured as another power tool, for example, as a grinding machine, in particular a renovation grinder.

[0018] The power tool 1 includes a tool 2, which is exemplarily configured as an abrasive disc 2A or as a saw blade 2B. Alternatively, the tool 2 can be configured as another tool, for example as a grinding disc. In particular, the tool 2 is used for machining a workpiece, in particular in a state in which the tool 2 is subjected to a working movement, in particular a rotational movement, by an electric motor 3.

[0019] The power tool 1 includes an electric motor 3 for driving the tool 2. The electric motor 3 can in particular provide the driving rotary motion by which the tool 2 is driven. The electric motor 3 is, for example, configured as an EC motor, i.e., an electronically commutated motor. The electric motor 3 is in particular a brushless motor, preferably a brushless direct current motor, i.e., a BLDC motor.

[0020] The power tool 1 further includes a control unit 4 for controlling the electric motor 3. The control unit 4 includes, for example, a microcontroller and / or power electronics. In particular, the control unit 4 is configured to supply a plurality of motor currents I1, I2, I3, which are in particular out of phase with one another, to the electric motor 3 in order to control the electric motor 3 so as to appropriately cause the electric motor 3 to perform a driving rotary movement. The motor currents I1, I2, I3 may also be referred to as phase currents. The control unit 4 advantageously includes an inverter for providing the motor currents I1, I2, I3.

[0021] The power tool 1 exemplarily further includes a handle 5, by means of which a user can hold, carry, and / or handle the power tool 1. The power tool 1 exemplarily further includes an operating device 6, such as a button and / or a switch, by means of which a user can control the operation of the tool 2, in particular start and / or stop it. The operating device 6 is exemplarily arranged on the handle 5.

[0022] The power tool 1 expediently includes a shaft 7, via which the tool 2 is coupled to the electric motor 3 so that the tool 2 can be driven by the electric motor 3. The power tool 1 can optionally include a transmission, in particular an angle gear 8, via which the tool 2 is coupled to the electric motor 3. In FIG. 1 , the power tool 1 exemplarily includes a connecting shaft 9, via which the electric motor 3 is coupled to the angle gear 8. The angle gear 8 is exemplarily coupled to the tool 2 via the shaft 7. Alternatively, the electric motor 3 can be coupled directly to the tool 2, for example via the shaft 7.

[0023] The power tool 1 exemplarily comprises an outer housing 10, in which the electric motor 3, the control unit 4 and / or the commutation device 12 are expediently arranged. The handle 5 is exemplarily arranged on the outer housing 10. Alternatively, the handle 5 can be part of the outer housing 10.

[0024] The power tool 1 is configured to be connected to a power supply voltage V1 (see FIG. 2). The power supply voltage V1 is an AC voltage. The power supply voltage V1 is particularly sinusoidal and has, for example, an effective value of 230 V and / or a power supply frequency of 50 Hz. The power supply voltage V1 can also have an effective value of 120 V and / or a power supply frequency of 60 Hz. The power tool 1 includes a connection 11, for example a power plug and / or a power plug connection, via which the power tool 1 can be connected to the power supply voltage, for example a socket connector.

[0025] The power tool 1 includes a rectifier 12, exemplarily arranged in the outer housing 10. The rectifier 12 is shown, for example, in FIG. 3. The rectifier 12 is configured to provide an intermediate circuit voltage V2 based on a power supply voltage V1. The rectifier 12 includes a rectifier 14, exemplarily configured as a bridge rectifier. The rectifier 14 expediently includes four diodes connected as a bridge. The power supply voltage V1 is supplied to the rectifier 14, which provides a rectified power supply voltage based on the power supply voltage V1. The rectifier 12 further includes an intermediate circuit 15, exemplarily configured as a capacitor. The intermediate circuit 15 is connected to the output of the rectifier 14. The intermediate circuit 15 serves to smooth the rectified power supply voltage. The smoothed and rectified power supply voltage is also referred to as an intermediate circuit voltage V2. The intermediate circuit voltage V2 drops across the intermediate circuit 15, in particular across a capacitor.

[0026] The intermediate circuit 15, in particular the capacitor, is for example smaller than 100 μF, smaller than 50 μF, smaller than 30 μF, smaller than 20 μF or smaller than 10 μF.

[0027] An exemplary time course of the intermediate circuit voltage V2 is shown as a solid line in FIG. 4 . The intermediate circuit voltage V2 comprises several voltage half-waves 16 that follow one another. The voltage half-waves 16 exemplarily comprise one sinusoidal portion 17 each having the curved shape of a portion of a sinusoidal half-wave. The sinusoidal portion 17, in particular the portion, expediently comprises a maximum value 20 of the sinusoidal half-wave. Exemplarily, the intermediate circuit voltage V2 follows the rectified mains voltage in the sinusoidal portion 17. Exemplarily, the voltage half-wave 16 further comprises two transition portions 18, respectively, arranged before and after the sinusoidal portion 17. The transition portions 18 comprise a minimum value 19 of the intermediate circuit voltage V2. The voltage half-wave 16 exemplarily does not have the shape of a sinusoidal half-wave in the transition portions 18. In particular, the intermediate circuit voltage does not drop to zero in the transition portions 18. Exemplarily, the intermediate circuit voltage V2 does not follow the rectified mains voltage in the transition portions 18.

[0028] The minimum value 19 of each voltage half-wave 16 is expediently at least 20%, preferably at least 30%, of the maximum value 20. For example, the minimum value 19 of each voltage half-wave 16 is at least 90 V, at least 100 V. The minimum value 19 of each voltage half-wave 16 is also expediently at most 70%, in particular at most 50%, preferably at most 40% or at most 35% of the maximum value 20. For example, the minimum value 19 is at most 120 V or 110 V.

[0029] Preferably, the control unit 4 and / or the electric motor 3 are powered by the intermediate circuit 15. The control unit 4 is configured to generate and supply motor currents I1, I2, I3 to the electric motor 3 based on the electrical energy provided by the intermediate circuit 15, in particular based on the intermediate circuit voltage V2. Exemplarily, the control unit 4 provides three motor currents I1, I2, I3. For example, the motor currents I1, I2, I3 flow from the intermediate circuit 15.

[0030] The electric motor 3 illustratively includes a stator 43 and a rotor 21. The rotor 21 is coupled to the tool 2. Upon energizing the electric motor 3 with motor currents I1, I2, I3, the rotor 21 is driven to undergo a rotational movement relative to the stator 43.

[0031] The electric motor 3 is optionally equipped with a position sensor device 22, which is used to detect the position and / or movement, in particular the current angle, of the rotor 21. The position sensor device 22 includes, for example, a magnetic sensor, in particular a Hall sensor. The control unit 4 is expediently configured to detect the current angle of the rotor 21 by means of the position sensor device 22. The control unit 4 can also be configured to detect the current rotational speed of the electric motor 3 by means of the position sensor device 22.

[0032] Alternatively or additionally, the control unit 4 can be configured to detect the current angle of the rotor 21 and / or the current rotational speed of the electric motor 3. In this case, the position sensor device 22 is expediently not present. In particular, the control unit 4 is configured to detect, in particular measure, a back voltage 34 induced in the electric motor and to calculate the current angle of the rotor 21 and / or the current rotational speed of the electric motor 3 on the basis of the back voltage 34. In particular, the control unit 4 is configured to calculate the current angle of the rotor 21 and / or the current rotational speed of the electric motor 3 using the back-EMF principle, where "EMF" stands for "Electromotive Force".

[0033] FIG. 6 shows an exemplary block diagram of the signal processing performed by the control unit 4 for controlling the electric motor 3.

[0034] The control unit 4 is expediently configured to perform a closed-loop speed control of the electric motor 3. In particular, the control unit 4 is configured to provide motor currents I1, I2, I3 based on a target speed 23 and an actual speed 24. The target speed 23 is set by the control unit 4 according to a user input, for example, via the operating device 6. Alternatively or additionally, the target speed 23 can be pre-stored in the control unit 4 and / or calculated by the control unit 4. The actual speed 24 is the current speed of the electric motor 3 and is expediently obtained as described above, in particular using the position sensor device 22 and / or based on a sensorless principle, in particular based on the induced counter voltage 34. The actual speed 24 indicates how fast the rotor 21 is rotating relative to the stator 43.

[0035] The control unit 4 comprises a speed controller 25, to which a setpoint speed 23 and an actual speed 24 are supplied. Based on the setpoint speed 23 and the actual speed 24, and in particular on a comparison of the setpoint speed 23 and the actual speed 24, the speed controller 25 calculates a torque setpoint 26. The torque setpoint 26 defines the torque that should be exerted on the rotor 21 by energizing the electric motor 3 in order to achieve a change in the actual speed towards the setpoint speed.

[0036] The control unit 4 further comprises a torque curve calculation unit 27, which is configured to calculate a torque curve 28 over time based on the torque setpoint 26. The torque curve 28 can also be referred to as a torque signal. An exemplary torque curve 28 is shown in Fig. 5 as a solid line. By way of example, the torque curve 28 has a trapezoidal curve shape.

[0037] The control unit 4 further includes a motor current providing unit 31 configured to calculate motor currents I1, I2, and I3 based on the torque curve 28. Exemplarily, the motor current providing unit 31 includes a target current setting unit 32 configured to calculate a q (axis) current, particularly a q (axis) current target value, and a d (axis) current, particularly a d (axis) current target value, based on the torque curve 28. The d current and the q current are currents in a d / q (coordinate) system relative to the rotor 21 that rotates as the rotor 21 rotates. The d current forms a flow-forming component, and the q current forms a torque-forming component. The d current can be called a d component or field-weakening current, and the q current can be called a q component or torque-forming current. The target current setting unit 32 calculates the q current, particularly the q current target value, and the d current, particularly the d current target value, so as to achieve the torque curve 28 according to the q current, particularly the q current target value, and the d current, particularly the d current target value when the electric motor 3 is energized. Exemplarily, the time course of the calculated q current, in particular the q current setpoint, corresponds to the torque course 28. In particular, the q current, in particular the q current setpoint, has the same curve shape as the torque course 28.

[0038] The motor current providing unit 31 expediently further includes a current controller 33, which is configured to provide motor currents I1, I2, and I3. In particular, the current controller 33 is configured to perform closed-loop current control of the motor currents I1, I2, and I3. The motor currents I1, I2, and I3 are preferably pulse-width modulated. The current controller 33 provides the motor currents I1, I2, and I3 based on the q current and the d current, in particular by performing a transformation from a two-axis coordinate system to a three-axis coordinate system. The current controller 33 provides the motor currents I1, I2, and I3 so that the calculated q current and the calculated d current are achieved. The motor windings of the electric motor 3, in particular the stator 43, are energized with the motor currents I1, I2, and I3. The rotor 21, which illustratively includes permanent magnets, undergoes a driving rotational movement due to interaction with a magnetic field generated by energizing the motor windings.

[0039] Preferably, the current controller 33 performs closed-loop control of the q current, in particular the q current actual value, to the q current nominal value and / or closed-loop control of the d current, in particular the d current actual value, to the d current nominal value. Exemplarily, the motor current providing unit 31 calculates the d current actual value and / or the d current actual value based on the motor currents I1, I2, I3.

[0040] The torque transition 28 will be described in more detail below. An exemplary torque transition 28 is shown (as a solid line) in Figure 5. The torque transition 28 comprises a number of successive torque half-waves 36.

[0041] The torque curve 28 is provided, in particular calculated, by the control unit 4 for controlling the electric motor. The control unit 4 is configured to provide, in particular calculate, for each voltage half-wave 16 a respective torque half-wave 36. Expediently, each voltage half-wave 16 is assigned a respective torque half-wave 36, which in particular has the same period and / or the same phase angle as the voltage half-wave 16.

[0042] Preferably, the control unit 4 is configured to detect a reverse voltage 34 induced in the electric motor 3 and, in response to the reverse voltage 34 being greater than or equal to the intermediate circuit voltage V2, reduce the current torque value of the torque curve 28, exemplarily by means of the torque curve calculation unit 27, in particular by setting it to zero. In particular, the control unit 4 is configured to perform a comparison between the intermediate circuit voltage V2 and the reverse voltage 34 and, based on the result of the comparison, set the current torque value of the torque curve 28 to zero (if the reverse voltage 34 is greater than or equal to the intermediate circuit voltage). If the comparison between the intermediate circuit voltage V2 and the reverse voltage 34 results in the reverse voltage 34 being less than the intermediate circuit voltage, the control unit 4 expediently sets the current torque value of the torque curve 28 to zero.

[0043] Figure 4 shows an exemplary profile of the reverse voltage 34. The reverse voltage 34 is shown by a dashed line and is constant over the two voltage half-waves 16 shown by way of example in Figure 4. At the beginning and end of each voltage half-wave 16, i.e. at the minimum value 19, the intermediate circuit voltage V2 falls below the reverse voltage 34. Figure 5 shows the corresponding torque profile 28, which is set to zero at the time when the intermediate circuit voltage V2 falls below the reverse voltage 34.

[0044] A torque transition 28 occurs, which includes successive pulses 44. Each torque half-wave 36 has a pulse 44. Between the pulses 44, the torque transition 28 is continuously greater than zero. Each pulse 44 is trapezoidal in shape, for example. Alternatively, each pulse may be rectangular in shape. Between two pulses 44, the torque transition 28 is zero. The torque transition 28 is zero before and after each pulse. The part of the torque transition 28 where the torque transition 28 is zero is also referred to as a zero portion or torque minimum 41. The pulses 44 occur in a time portion where the intermediate circuit voltage V2 is greater than the reverse voltage 34. The torque minimum 44 occurs in a time portion where the intermediate circuit voltage V2 is less than the reverse voltage 34.

[0045] Preferably, the control unit 4 is configured to detect, in particular calculate, the induced reverse voltage 34 based on the rotational speed of the electric motor 3. The rotational speed of the electric motor 3 is measured in particular by means of the position sensor device 22, as described above. The control unit 4 can also be configured to measure the reverse voltage 34.

[0046] Preferably, the control unit 4 is configured to calculate a q current setpoint value according to the current torque value and to perform closed-loop control of the q current, in particular the q current actual value, to the q current setpoint value for controlling the electric motor 3. In particular, the control unit 4 is configured to set the q current setpoint value to zero and perform closed-loop control of the q current, in particular the q current actual value, to zero in response to the reverse voltage 34 being equal to or greater than the intermediate circuit voltage V2. Exemplarily, the setpoint current setting unit 32 sets the q current setpoint value to zero in response to the current torque value of the torque curve 28 being zero. Expediently, if the reverse voltage 34 is equal to or greater than the intermediate circuit voltage V2, the current controller 33 performs closed-loop control of the q current actual value to zero.

[0047] Also preferably, the control unit 4 is configured to, in response to the reverse voltage 34 being greater than or equal to the intermediate circuit voltage V2, preferably reduce the d current, in particular the d current setpoint, in particular set it to zero, preferably closed-loop controlled to zero.

[0048] Preferably, the control unit 4 is configured to maintain the electrical connection extending to the electric motor 3 and used to control the electric motor 3 when the reverse voltage 34 is equal to or greater than the intermediate circuit voltage V2. In particular, the power tool 1 does not continuously disconnect said connection in response to the reverse voltage 34 being equal to or greater than the intermediate circuit voltage V2. In particular, the control unit 4 is configured to continue and not stop closed-loop control of the torque-generating current when the induced reverse voltage 34 of the electric motor 3 is equal to or greater than the intermediate circuit voltage V2.

[0049] The control unit 4 is configured to provide, in particular calculate, for each voltage half-wave 16 a respective torque half-wave 36 for controlling the electric motor 3. Preferably, the curve shape of each torque half-wave is flattened compared to the curve shape of the (respectively assigned) voltage half-wave 16. Due to the flattened curve shape, when the electric motor 3 is energized, smaller ohmic power losses advantageously occur for the same average torque.

[0050] The control unit 4 expediently energizes the electric motor 3 in proportion to the torque half-wave. The larger the torque half-wave 36, the more the control unit 4 energizes the electric motor 3. Because ohmic power losses are a function of the square of the current applied to the electric motor 3, a larger current results in disproportionate ohmic power losses. The flattened curve shape of the torque half-wave 36 reduces the current maximum, which is important for ohmic power losses (due to its dependence on the square), so that ohmic power losses can be reduced, especially at smaller or less severe torque reductions. The flattened curve shape can also be referred to as an equalized curve shape. In particular, each torque half-wave 36 has a more equal curve shape than each voltage half-wave 16 and / or each (imaginary) sine half-wave 37 of the same period and / or area. Preferably, the standard deviation of each torque half-wave 36 is smaller than the standard deviation of each voltage half-wave 16 and / or each (imaginary) sine half-wave 37 of the same period and / or area.

[0051] In particular, the flattened curve shape has a smaller maximum value under the curve shape, especially compared to the (fictitious) sine half-wave 37, for the same area. FIG. 5 shows a reference curve 38 (as a dashed line) having a curve shape of a rectified sinusoid and including successive sine half-waves 37. The sine half-waves 37 each have the same period as the torque half-wave 36. The area under each sine half-wave 37, i.e., the integral over the period of the sine half-wave 37, is expediently the same as the area under each torque half-wave 36, i.e., the integral over the period of the torque half-wave 36. The maximum value of each torque half-wave 36 is expediently at least 10% smaller, or at least 20% smaller, than the maximum value of each sine half-wave 37. The sine half-waves 37 are used here in the mathematical definition of the flattened curve shape of the torque half-wave and do not necessarily have to be provided by the power tool 1. The flattened curve shape of each torque half-wave 36 is preferably mathematically defined to have a smaller maximum value than the (particularly fictitious) sine half-wave 37 at the same period and area as the sine half-wave 37.

[0052] For example, in a flattened curve profile, the ratio between the maximum value of the curve profile and the average value of the curve profile is reduced. Preferably, the ratio between the maximum value of the torque half-wave 36 and the average value of the torque half-wave 36 is smaller than the ratio between the maximum value 20 of the voltage half-wave 16 and the average value of the voltage half-wave 16.

[0053] The description of one torque half-wave 36 preferably applies to each torque half-wave 36. Preferably, the control unit 4 is configured to provide the torque half-waves 36 with a trapezoidal or rectangular curve shape. Illustratively, each torque half-wave 36 has a trapezoidal curve shape. Alternatively, the torque half-waves can have other curve shapes, for example, a rectangular curve shape.

[0054] The torque half-wave 37 expediently further comprises two torque minima 41, which represent the beginning and the end of the torque half-wave 36. Exemplarily, the torque is equal to zero at the torque minimum 41. The torque minimum 41 is in particular the time portion in which the induced counter voltage 34 is equal to or greater than the (assigned) voltage half-wave 16.

[0055] 4, the induced reverse voltage 34 is illustratively constant over the voltage half-wave 16. The minimum 19, particularly the transition portion 18, of the voltage half-wave 16 is illustratively below the induced reverse voltage 34. The maximum 20, particularly the sinusoidal portion 17, is illustratively above the induced reverse voltage 34.

[0056] The torque half-wave 36 has a plateau 39 that includes or represents the maximum value of the torque half-wave 36. The plateau 39 preferably has a zero slope and extends over at least 40%, at least 50%, at least 60%, at least 70%, or at least 80% of the period of the torque half-wave 36. Exemplarily, the maximum value 42 of the sine half-wave 37 is greater than that of the plateau 39. The torque half-wave 36 further has two side portions 40 surrounding the plateau 39. The side portions 40 have a slope (quantitatively) greater than that of the plateau 39, in particular a slope greater than that of the sine half-wave 37 and / or the voltage half-wave 16. According to one possible embodiment, the side portions 40 may be perpendicular, i.e., may have an infinite slope (quantitatively). Each pulse 44 is formed by one plateau 39 and two side portions 40. The torque half-wave 36 therefore comprises the following portions successive in time, in particular directly successive in the above mentioned order: a first torque minimum 41 (preferably equal to zero), a first flank portion 40 (preferably with a positive slope), a plateau portion 39 (preferably with a slope of zero), a second flank portion 40 (preferably with a negative slope) and a second torque minimum (preferably equal to zero). The torque minima 41 together extend in time over, in particular, at least 10%, at least 20% or at least 30% of the period of the torque half-wave 36.

[0057] Expediently, the control unit 4 is configured to provide torque half-waves 36 having the same period as each voltage half-wave 16. Preferably, the frequency of the torque transitions 28 is twice the frequency of the supply voltage V1. In particular, the frequency of the torque transitions 28 is 100 Hz or 120 Hz.

[0058] For example, the control unit 4 detects the period of the voltage half-wave 16 and / or the time interval between adjacent zero crossings of the supply voltage V1 and uses the detected period and / or time interval as the period for the torque half-wave 36. Expediently, the control unit 4 synchronizes the torque half-wave 36 with the supply voltage V1 and / or the voltage half-wave 16. For example, the control unit 4 synchronizes the minimum of the torque curve 28 with the zero crossings of the supply voltage V1 so that the minimum of the torque curve 28 coincides with the zero crossings of the supply voltage V2. The control unit 4 can also synchronize the minimum of the torque curve 28 with the minimum 19 of the intermediate circuit voltage V2 so that the minimum of the torque curve 28 coincides with the minimum of the intermediate circuit voltage V2. For example, the control unit 4 is configured to detect a phase angle 30 of the supply voltage V1 and / or the intermediate circuit voltage V2 and to provide the torque half-wave 36 in accordance with the phase angle 30, in particular so that the torque half-wave 36 is synchronized with the voltage half-wave 16 and / or the supply voltage V1. The torque curve 28 expediently has the same phase angle as the intermediate circuit voltage V2.

[0059] The control unit 4, in particular the torque curve calculation unit 27, is preferably configured to calculate the torque curve 28 on the basis of a curve shape profile 29. The curve shape profile is expediently stored in advance in the control unit 4 and / or is provided by the control unit 4. The curve shape profile 29 defines a flattened curve shape of the torque half-wave 36. For example, the curve shape profile 29 defines a trapezoidal or rectangular curve shape.

[0060] By way of example, the control unit 4 is configured to calculate the torque curve 28 taking into account the phase angle 30. In particular, the control unit 4 is configured to calculate a period for each torque half-wave 36 based on the phase angle 30 and to extend or compress the curved profile 29 in time according to the calculated period so that the period of the curved profile 29 is identical to the calculated period.

[0061] Expediently, the control unit 4 is further configured to calculate each torque half-wave 36 based on the torque setpoint 26. In particular, the control unit 4 is configured to calculate each torque half-wave 36 such that the mean value of the torque half-wave 36 is identical to the torque setpoint 26. In particular, the control unit 4 is configured to calculate each torque half-wave 36 by scaling the curve-shaped profile 29 in accordance with the torque setpoint 26. For example, the control unit 4 is configured to scale the curve-shaped profile 29 by the torque setpoint 26 or by a scaling factor that depends on the torque setpoint 26.

[0062] As mentioned above, the control unit 4 comprises a speed controller 25 for providing a torque setpoint 26, on the basis of which the control unit 4 provides the respective torque half-waves 36. In particular, the control unit 4 is configured to energize the electric motor 3 in accordance with the torque half-waves.

[0063] The provision of the torque half-wave 36 can also be called torque forming. Torque forming, especially in the case of trapezoidal or rectangular shapes, and the resulting current forming, can reduce ohmic power losses, i.e. copper losses, and therefore allow the electric motor 3 to be made smaller.

[0064] As already mentioned above, a small intermediate circuit 15 is expediently used so that the intermediate circuit voltage V2 corresponds mainly to the (rectified) mains voltage. A small intermediate circuit expediently makes it possible to reduce construction space and costs. In order to reduce copper losses in the electric motor 3, i.e. ohmic power losses, the torque of the electric motor 3 and thus the current flow, in particular the q current, are expediently controlled in a closed loop to a trapezoid or rectangular shape, preferably with double the mains frequency.

[0065] Copper loss is I 2 Since the torque plateau 39 of the trapezoidal torque half-wave 36 is calculated by *R, the torque plateau 39 should have as small a torque value as possible. This is preferably achieved by choosing as long as possible the time per half-wave during which current can flow in the electric motor 3, i.e. by choosing as large a time extension of the plateau 39 as possible. Expediently, the electric motor 3 is set at a voltage that is smaller than the supply voltage V1. Expediently, the counter voltage induced in the electric motor 3 by a change in the field-weakening current also varies depending on the intermediate circuit voltage V2.

[0066] Preferably, the control unit 4, in particular the setpoint current setting unit 32, is configured to calculate the d current, in particular the d current setpoint, taking into account the intermediate circuit voltage V2. In particular, the control unit 4 is configured to set the d current, in particular the d current setpoint, depending on the intermediate circuit voltage V2. For example, the control unit 4 is configured to quantitatively reduce the d current, in particular the d current setpoint, when the intermediate circuit voltage V2 is higher, and to quantitatively increase it when the intermediate circuit voltage V2 is lower. In particular, the control unit 4 is configured to set the d current, in particular the d current setpoint, based on the intermediate circuit voltage V2, such that the induced back voltage is reduced, in particular below the intermediate circuit voltage V2. The setting of the d current, in particular the d current setpoint, is, for example, inversely proportional to the intermediate circuit voltage V2. When the intermediate circuit voltage V2 increases, the d current, in particular the d current setpoint, is quantitatively reduced, and when the intermediate circuit voltage V2 decreases, the d current, in particular the d current setpoint, is quantitatively increased.

[0067] In particular, the control unit 4 is designed to constantly energize the electric motor according to the d-current and / or the q-current so that braking moments are avoided and in particular the power factor is dynamically adapted to the load.

[0068] In particular, the control unit 4 is configured to vary the d-current and the q-current in dependence on the intermediate circuit voltage V2 and / or the supply voltage V1 in order to always operate the motor optimally while requiring as little current as possible.

[0069] The power tool 1 can be operated in particular according to the method described below, which comprises the following steps: - providing an intermediate circuit voltage V2 based on a mains voltage V1 to which the power tool 1 is connected, using a rectifier device 12 with an intermediate circuit 15, the intermediate circuit voltage V2 comprising a number of successive voltage half-waves 16; - providing torque transitions (28) for controlling the electric motor (3), the torque transitions (28) including respective torque half-waves (36) for each voltage half-wave (16); - detecting the reverse voltage (34) induced in the electric motor (3); - reducing the current torque value of the torque transition (28) in response to the reverse voltage (34) being equal to or greater than the intermediate circuit voltage (V2); Includes.

[0070] Expediently, the method comprises a further step of energizing the electric motor 3 according to a torque half-wave 36 so that the rotor 21 is subjected to a driving rotational movement and thus the tool 2 is subjected to a working movement.

[0071] Expediently, the method comprises a further step of machining, in particular polishing, grinding or sawing, the workpiece by means of the tool 2 . The present invention may also include the following aspects: 1. A power tool (1), in particular a handheld power tool (1), such as a grinding tool (1A), a grinding tool and / or a sawing tool (1B), comprising a tool (2), an electric motor (3) for driving the tool (2), and a control unit (4) for controlling the electric motor (3), wherein the power tool (1) comprises a rectifier device (12) configured for connection to a power supply voltage (V1) and having an intermediate circuit (15) for providing an intermediate circuit voltage (V2) based on the power supply voltage (V1), and wherein the intermediate circuit voltage (V2) is 1. A power tool comprising: a power tool having a plurality of successive voltage half-waves (16); a control unit (4) configured to provide torque transitions (28) for control of an electric motor (3), the torque transitions (28) including respective torque half-waves (36) for each voltage half-wave (16); and the control unit (4) configured to detect a reverse voltage (34) induced in the electric motor (3) and to reduce a current torque value of the torque transitions (28) in response to the reverse voltage (34) being equal to or greater than an intermediate circuit voltage (V2). 2. The power tool (1) described in paragraph 1, wherein the control unit (4) is configured to set the current torque value of the torque profile (28) to zero in response to the reverse voltage (34) being equal to or greater than the intermediate circuit voltage (V2). 3. The power tool (1) described in 1. or 2. above, characterized in that the control unit (4) is configured to calculate a q current target value according to a current torque value and to perform closed-loop control of the q current to the q current target value for controlling the electric motor (3). 4. The power tool (1) described in 3. above, characterized in that the control unit (4) is configured to set the q current target value to zero in response to the reverse voltage (34) being equal to or greater than the intermediate circuit voltage (V2) and to perform closed-loop control of the q current to zero. 5. The power tool (1) according to any one of 1. to 4. above, characterized in that the control unit (4) is configured to maintain the electrical connection extending to the electric motor (3) and used to control the electric motor (3) when the reverse voltage (34) is equal to or greater than the intermediate circuit voltage (V2). 6. The power tool (1) according to any one of 1. to 5. above, characterized in that the control unit (4) is configured to detect the induced reverse voltage (34) based on the rotation speed of the electric motor (3). 7. The power tool (1) according to any one of 1. to 6. above, characterized in that the control unit (4) is configured to provide, for each voltage half-wave (16), each torque half-wave (36) for controlling the electric motor (3), the curve shape of which is flattened compared to the curve shape of the voltage half-wave (16). 8. The power tool (1) described in 7 above, characterized in that the control unit (4) is configured to provide a torque half-wave (36) having a curve shape with a smaller maximum value than the sine half-wave (37) in the same area as the sine half-wave (37). 9. The power tool (1) according to claim 7 or 8, wherein the control unit (4) is configured to provide a torque half-wave (36) having a trapezoidal curve shape or a rectangular curve shape. 10. The power tool (1) according to any one of 1. to 7. above, characterized in that the control unit (4) is configured to detect the phase angle (30) of the power supply voltage (V1) and / or the intermediate circuit voltage (V2) and provide a torque half-wave according to the phase angle (V2). 11. The power tool (1) according to any one of 1. to 8. above, characterized in that the control unit (4) is provided with a rotation speed controller (25) for providing a torque target value (26), and the control unit (4) provides each torque half-wave (36) based on the torque target value. 12. The power tool (1) according to any one of the above items 1 to 9, characterized in that the control unit (4) is configured to energize the electric motor (3) in accordance with a torque half-wave (36). 13. An electric power tool (1) according to any one of the above items 1 to 12, characterized in that the control unit (4) is configured to calculate the d current (Id) and the q current (Iq) for controlling the electric motor (3) and to adjust the d current (Id) in accordance with the intermediate circuit voltage (V2). 14. The power tool (1) according to claim 13, characterized in that the control unit (4) is configured to quantitatively reduce the d current (Id) when the intermediate circuit voltage (V2) is greater and to quantitatively increase the d current (Id) when the intermediate circuit voltage (V2) is smaller. 15. A method for operating a power tool (1), in particular a handheld power tool (1), such as a grinding tool (1A), a grinding tool and / or a sawing tool (1B), having a tool (2), an electric motor (3) for driving the tool (2), and a control unit (4) for controlling the electric motor (3), comprising the following steps: - providing an intermediate circuit voltage (V2) based on the mains voltage (V1) to which the power tool (1) is connected, using a rectifier device (12) having an intermediate circuit (15), the intermediate circuit voltage (V2) having a number of successive voltage half-waves (16); - providing a torque transition (28) for control of an electric motor (3), the torque transition (28) comprising a respective torque half-wave (36) for each voltage half-wave (16); - detecting the reverse voltage (34) induced in the electric motor (3); - reducing the current torque value of the torque transition (28) in response to the reverse voltage (34) being equal to or greater than the intermediate circuit voltage (V2); A method comprising: 16. The method of claim 15, wherein the current torque value of the torque profile (28) is set to zero in response to the reverse voltage (34) being greater than or equal to the intermediate circuit voltage (V2). 17. The method according to claim 15 or 16, characterized in that a q current target value is calculated according to a current torque value, and the q current is closed-loop controlled to the q current target value for controlling the electric motor. 18. The method of claim 17, wherein in response to the reverse voltage being equal to or greater than the intermediate circuit voltage, the q current target value is set to zero and the q current is closed-loop controlled to zero. 19. A method according to any one of claims 15 to 18, characterized in that when the reverse voltage (34) is equal to or greater than the intermediate circuit voltage (V2), the electrical connection extending to the electric motor (3) and used to control the electric motor (3) is maintained. 20. The method according to any one of items 15 to 19 above, wherein the induced reverse voltage is detected based on the rotation speed of the electric motor. 21. A method according to any one of claims 15 to 20, characterized in that for each voltage half-wave (16), a torque half-wave (36) for controlling the electric motor (3) is provided, the curve shape of which is flattened compared to the curve shape of the voltage half-wave (16). 22. The method according to claim 21, characterized in that a torque half-wave (36) is provided having a curve shape with a smaller maximum value than a sine half-wave (37) in the same area as the sine half-wave (37). 23. The method according to claim 21 or 22, characterized in that the control unit (4) is configured to provide a torque half-wave (36) having a trapezoidal or rectangular curve shape. 24. A method according to any one of items 15 to 23 above, characterized in that the phase angle (30) of the power supply voltage (V1) and / or the intermediate circuit voltage (V2) is detected, and a torque half-wave is provided according to the phase angle (V2). 25. The method according to any one of items 15 to 24 above, characterized in that each torque half-wave (36) is provided based on the torque target value (26) of the rotation speed controller (25). 26. The method according to any one of the above items 15 to 25, characterized in that the electric motor (3) is energized in accordance with a torque half-wave (36). 27. A method according to any one of claims 15 to 26, characterized in that a d current (Id) and a q current (Iq) are calculated for controlling the electric motor (3), and the d current (Id) is adjusted according to the intermediate circuit voltage (V2). 28. The method according to claim 27, characterized in that the current (Id) is quantitatively reduced when the intermediate circuit voltage (V2) is greater and quantitatively increased when the intermediate circuit voltage (V2) is smaller. 29. An arrangement including an electric motor for driving a tool and a control unit for controlling the electric motor, the control unit being configured to provide a torque transition for controlling the electric motor, the torque transition comprising one torque half-wave for each voltage half-wave of the intermediate circuit voltage, and the control unit being configured to detect a reverse voltage induced in the electric motor and to reduce a current torque value of the torque transition in response to the reverse voltage being equal to or greater than the intermediate circuit voltage. 30. A computer program product including commands for causing the power tool (1) described in 1. above to execute the method steps described in any one of 1. to 28. above. 31. A computer-readable medium on which the computer program product described in 30 above is stored. 32. A method comprising the step of installing the computer program product according to claim 30 on a power tool (1).

Claims

1. A power tool (1) having a tool (2), an electric motor (3) for driving the tool (2), and a control unit (4) for controlling the electric motor (3), wherein the power tool (1) is configured to be connected to a power supply voltage (V1) and includes a rectifier device (12) having an intermediate circuit (15) for providing an intermediate circuit voltage (V2) based on the power supply voltage (V1), the intermediate circuit voltage (V2) having a plurality of voltage half-waves (16) successive to one another, and the control unit (4) is configured to provide a target torque curve (28) for controlling the electric motor (3), the target torque curve (28) including a respective torque half-wave (36) for each voltage half-wave (16). a control unit (4) configured to detect a back electromotive force (34) induced in the electric motor (3) and reduce a current torque target value of the target torque profile (28) in response to the back electromotive force (34) being equal to or greater than the intermediate circuit voltage (V2); the control unit (4) is configured to calculate a q current target value according to the current torque target value and perform closed-loop control of the q current to the q current target value for controlling the electric motor (3); and the control unit (4) is configured to set the q current target value to zero in response to the back electromotive force (34) being equal to or greater than the intermediate circuit voltage (V2) and perform closed-loop control of the q current to zero.

2. The power tool (1) according to claim 1, characterized in that the power tool (1) is a handheld power tool (1), such as a grinding tool (1A), a grinding tool and / or a sawing tool (1B).

3. 3. The power tool according to claim 1, wherein the control unit is configured to set a current torque target value of the target torque profile to zero in response to the back electromotive force being equal to or greater than the intermediate circuit voltage.

4. 4. The power tool (1) according to claim 1, wherein the control unit (4) is configured to maintain an electrical connection extending from the power supply voltage (V1) to the electric motor (3) and used to control the electric motor (3) when the back electromotive force (34) is equal to or greater than the intermediate circuit voltage (V2).

5. The power tool (1) according to any one of claims 1 to 4, characterized in that the control unit (4) is configured to detect the induced back electromotive force (34) based on the rotation speed of the electric motor (3).

6. 6. The power tool (1) according to claim 1, wherein the control unit (4) is configured to provide, for each voltage half-wave (16), a respective torque half-wave (36) for controlling the electric motor (3), the curve shape of which is flattened compared to the curve shape of the voltage half-wave (16).

7. 7. The power tool (1) according to claim 6, characterized in that the control unit (4) is configured to provide a torque half-wave (36) having a curve shape with a smaller maximum value than the sine half-wave (37) in the same area as the sine half-wave (37).

8. 8. Power tool (1) according to claim 6 or 7, characterized in that the control unit (4) is configured to provide torque half-waves (36) having a trapezoidal or rectangular curve shape.

9. 9. The power tool (1) according to any one of claims 1 to 8, characterized in that the control unit (4) is configured to detect a phase angle (30) of the power supply voltage (V1) and / or the intermediate circuit voltage (V2) and to provide a torque half-wave according to the phase angle (V2).

10. 10. The power tool (1) according to any one of claims 1 to 9, characterized in that the control unit (4) comprises a speed controller (25) for providing a torque target value (26), and the control unit (4) provides each torque half-wave (36) based on the torque target value.

11. 11. The power tool (1) according to any one of the preceding claims, characterized in that the control unit (4) is configured to energize the electric motor (3) according to torque half-waves (36).

12. 12. The power tool (1) according to claim 1, wherein the control unit (4) is configured to calculate a d-current (Id) and a q-current (Iq) for controlling the electric motor (3) and to adjust the d-current (Id) depending on the intermediate circuit voltage (V2).

13. 13. The power tool (1) according to claim 12, characterized in that the control unit (4) is configured to quantitatively reduce the d current (Id) when the intermediate circuit voltage (V2) is higher and to quantitatively increase the d current (Id) when the intermediate circuit voltage (V2) is lower.

14. A method for operating a power tool (1) having a tool (2), an electric motor (3) for driving the tool (2), and a control unit (4) for controlling the electric motor (3), comprising the following steps: - providing an intermediate circuit voltage (V2) based on the mains voltage (V1) to which the power tool (1) is connected, using a rectifier device (12) having an intermediate circuit (15), the intermediate circuit voltage (V2) having a number of successive voltage half-waves (16); - providing a target torque profile (28) for controlling the electric motor (3), the target torque profile (28) comprising a respective torque half-wave (36) for each voltage half-wave (16); - detecting the back electromotive force (34) induced in the electric motor (3); - reducing the current torque target value of the target torque profile (28) in response to the back EMF voltage (34) being equal to or greater than the intermediate circuit voltage (V2); wherein a q current target value is calculated according to a current torque target value, and the q current is closed-loop controlled to the q current target value for control of the electric motor, and in response to the back EMF being equal to or greater than the intermediate circuit voltage, the q current target value is set to zero and the q current is closed-loop controlled to zero.

15. The method according to claim 14, characterized in that the power tool (1) is a hand-held power tool (1), such as a grinding tool (1A), a grinding tool and / or a sawing tool (1B).

16. A method as described in claim 14 or 15, characterized in that the current torque target value of the target torque profile (28) is set to zero in response to the back electromotive force (34) being greater than or equal to the intermediate circuit voltage (V2).

17. 17. The method according to claim 14, wherein the electrical connection extending from the supply voltage (V1) to the electric motor (3) and used for controlling the electric motor (3) is maintained if the back EMF (34) is equal to or greater than the intermediate circuit voltage (V2).

18. 18. The method according to claim 14, wherein the induced back electromotive force is detected based on the rotation speed of the electric motor.

19. 19. The method according to any one of claims 14 to 18, characterized in that for each voltage half-wave (16) a respective torque half-wave (36) for controlling the electric motor (3) is provided, the curve shape of which is flattened compared to the curve shape of the voltage half-wave (16).

20. 20. The method of claim 19, wherein a torque half-wave (36) is provided having a curve shape with a smaller maximum value than a sine half-wave (37) in the same area as the sine half-wave (37).

21. 21. A method according to claim 19 or 20, characterized in that the control unit (4) is configured to provide torque half-waves (36) having a trapezoidal or rectangular curve shape.

22. 22. The method according to any one of claims 14 to 21, characterized in that a phase angle (30) of the mains voltage (V1) and / or the intermediate circuit voltage (V2) is detected, and a torque half-wave is provided according to the phase angle (V2).

23. 23. The method according to claim 14, wherein each torque half-wave (36) is provided based on a torque setpoint (26) of a speed controller (25).

24. 24. The method according to any one of claims 14 to 23, characterized in that the electric motor (3) is energized according to a torque half-wave (36).

25. 25. The method according to claim 14, wherein a d-current (Id) and a q-current (Iq) are calculated for controlling the electric motor (3), and the d-current (Id) is adjusted depending on the intermediate circuit voltage (V2).

26. 26. The method according to claim 25, characterized in that the d current (Id) is quantitatively reduced when the intermediate circuit voltage (V2) is greater and quantitatively increased when the intermediate circuit voltage (V2) is smaller.

27. 1. An arrangement including an electric motor for driving a tool and a control unit for controlling the electric motor, the control unit being configured to provide a setpoint torque profile for controlling the electric motor, the setpoint torque profile comprising one torque half-wave for each voltage half-wave of an intermediate circuit voltage, the control unit being configured to detect a back electromotive force induced in the electric motor and to reduce a current setpoint torque value of the setpoint torque profile in response to the back electromotive force being equal to or greater than the intermediate circuit voltage.

28. A computer program product comprising commands to cause a power tool (1) according to claim 1 to carry out the method steps according to any one of claims 1 to 26.

29. 30. A computer readable medium having stored thereon the computer program product of claim 28.

30. 29. A method comprising the step of installing a computer program product according to claim 28 in a power tool (1).

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