POWER TOOL, METHOD, ARRANGEMENT, COMPUTER PROGRAM PRODUCT AND COMPUTER-READABLE MEDIUM

Abstract

The invention relates to an electric tool (1), in particular a hand-held electric tool, e.g. a polisher (1A), a grinder and / or a saw (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), the electric tool (1) being designed to be connected to a mains voltage (V1) and comprising a rectifier assembly (12) with a DC link (15) for supplying a DC link voltage (V2) on the basis of the mains voltage (V1), wherein the DC link voltage (V2) includes a plurality of successive voltage half-waves (16), the control unit (4) is configured to provide a torque curve (28) for controlling the electric motor (3), said torque curve (28) comprising a torque half-wave (36) for each voltage half-wave (16), and the control unit (4) is configured to ascertain a back electromotive force (34) induced in the electric motor (3), and if the back electromotive force (34) is greater than or equal to the DC link voltage (V2), to reduce a current torque value of the torque curve (28).

Description

[0001] Power tool, process, arrangement,

[0002] Computer program product and computer-readable medium

[0003] The invention relates to a power tool, in particular a hand-held power tool, for example a polishing device, a grinding device and / or a sawing device, comprising a tool, an electric motor for driving the tool and a control unit for controlling the electric motor. The power tool is designed for connection to a mains voltage and comprises a rectifier arrangement with an intermediate circuit for providing an intermediate circuit voltage based on the mains voltage.

[0004] The intermediate circuit, for example, is a capacitor which is used in particular to smooth the rectified mains voltage. There are various approaches to dimensioning the intermediate circuit. A first approach is to dimension the intermediate circuit large enough that the intermediate circuit voltage is almost constant. This enables almost constant phase currents for supplying current to the electric motor and a resulting almost constant torque curve of the electric motor. However, a large intermediate circuit leads to a poor power factor and to high harmonic components in the input current. A second approach is to dimension the intermediate circuit small so that the intermediate circuit voltage follows the mains voltage, in particular the rectified mains voltage.However, such a small DC link can result in areas where, with conventional control of the electric motor, the induced counter voltage of the electric motor becomes greater than or equal to the DC link voltage, and no current can flow into the motor. This behavior can lead to a torque ripple at twice the mains frequency. Furthermore, with a small DC link, the ohmic power loss in the motor windings can be greater, requiring a larger electric motor.

[0005] An object of the invention is to provide an improved power tool.

[0006] The object is achieved by a power tool according to claim 1.

[0007] In the case of the power tool, the intermediate circuit voltage has a plurality of successive voltage half-waves. In particular, the intermediate circuit, for example a capacitor, is dimensioned so small that the intermediate circuit voltage follows the rectified mains voltage and the voltage half-waves are formed in this way. The rectified mains voltage comprises in particular a sequence 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 a range from 140 V to 320 V. The small intermediate circuit expediently achieves a good power factor, for example a power factor of at least 0.70 or at least 0.75.The control unit is designed to provide a torque curve for controlling the electric motor. The torque curve comprises a respective torque half-wave for each voltage half-wave. The control unit is designed to determine a counter-voltage induced in the electric motor and, in response to the counter-voltage being greater than or equal to the intermediate circuit voltage, to reduce a current torque value of the torque curve. In particular, the control unit reduces the current torque value to such an extent that braking torques and / or torque ripples are reduced or avoided.

[0008] The control unit preferably regulates the torque-generating current - in particular a q-current - to zero when the induced countervoltage of the electric motor is greater than or equal to the intermediate circuit voltage. Expediently, the control unit maintains an electrical connection to the electric motor even when the induced countervoltage of the electric motor is greater than or equal to the intermediate circuit voltage, so that field-weakening current - in particular a d-current - or torque-generating current - in particular the q-current - can always flow to the electric motor, so that braking torques are prevented in particular and / or the power factor can be dynamically adapted to the load.

[0009] Advantageous further training is the subject of the subclaims.

[0010] The invention further relates to a method for operating a power tool, in particular a hand-held power tool, for example a polishing device, grinding device and / or sawing device, with a tool, an electric motor for driving the tool and a control unit for controlling the electric motor, comprising the steps:

[0011] - Providing, by means of a rectifier arrangement with an intermediate circuit, an intermediate circuit voltage based on a mains voltage to which the power tool is connected, wherein the intermediate circuit voltage has a plurality of successive voltage half-waves,

[0012] - Providing a torque curve for controlling the electric motor, wherein the torque curve for each voltage half-wave comprises a respective torque half-wave,

[0013] - Determination of a counter voltage induced in the electric motor and

[0014] - in response to the counter voltage being greater than or equal to the intermediate circuit voltage, reducing a current torque value of the torque curve.

[0015] The method is expediently carried out with the described power tool and / or is designed in accordance with a described embodiment of the power tool.

[0016] The invention further relates to an arrangement comprising an electric motor for driving a tool and a control unit for controlling the electric motor. The control unit is designed to provide a torque curve for controlling the electric motor, wherein the torque curve comprises a respective torque half-wave for each voltage half-wave of an intermediate circuit voltage, and wherein the control unit is designed to determine a counter-voltage induced in the electric motor and, in response to the counter-voltage being greater than or equal to the intermediate circuit voltage, to reduce a current torque value of the torque curve.

[0017] The invention further relates to a computer program product comprising instructions which cause the power tool to carry out the method steps mentioned above.

[0018] The invention further relates to a computer-readable medium on which the computer program is stored.

[0019] The invention further relates to a method comprising the step of: loading the computer program product onto a power tool.

[0020] Further exemplary details and exemplary embodiments are explained below with reference to the figures.

[0021] Figure 1 is a schematic representation of a power tool designed as a polishing device,

[0022] Figure 2 is a schematic representation of a power tool designed as a sawing device,

[0023] Figure 3 is a schematic representation of the rectifier arrangement, the control unit and the electric motor of the power tool,

[0024] Figure 4 shows a time course of an intermediate circuit voltage,

[0025] Figure 5 shows a time course of a torque and Figure 6 shows a block diagram of a signal processing system.

[0026] Figures 1 and 2 show exemplary embodiments of a power tool 1. By way of example, the power tool 1 is designed as a hand-held power tool. The power tool 1 can be gripped, carried and / or guided by a user by hand. The power tool 1 can be designed in particular as a polishing device 1A (see Figure 1) or as a sawing device 1B (see Figure 2). The polishing device 1A is, for example, a polishing machine, in particular a rotary polisher. The sawing device 1B is, for example, a plunge-cut saw. Alternatively, the power tool 1 can also be designed as a different power tool, for example as a sander, in particular as a renovation sander.

[0027] The power tool 1 comprises a tool 2. The tool 2 is embodied, for example, as a polishing disc 2A or a saw blade 2B. Alternatively, the tool 2 can also be embodied as another tool, for example as a grinding disc. The tool 2 serves, in particular, to machine a workpiece, in particular in a state in which the tool 2 is set into a working movement, in particular a rotary movement, by an electric motor 3.

[0028] The power tool 1 comprises the electric motor 3 for driving the tool 2. The electric motor 3 is particularly designed to provide the drive rotary movement on the basis of which the tool 2 is driven. The electric motor 3 is designed, for example, as an EC motor - that is to say as an electronically commutated motor. The electric motor 3 is, in particular, a brushless motor, preferably a brushless DC motor, BLDC motor. The power tool 1 further comprises a control unit 4 for controlling the electric motor 3. The control unit 4 comprises, for example, a microcontroller and / or power electronics. The control unit 4 is particularly designed to supply the electric motor 3 with a plurality of motor currents II, I2, I3, which are, in particular, phase-shifted with respect to one another, in order to expediently cause the electric motor 3 to carry out the drive rotary movement.The motor currents II, I2, I3 can also be referred to as phase currents. The control unit 4 expediently has an inverter for providing the motor currents II, I2, I3.

[0029] By way of example, the power tool 1 further comprises a handle 5 with which a user can manually grip, carry, and / or guide the power tool 1. The power tool 1 further comprises an operating device 6, for example a button and / or a switch, via which the user can control the drive of the tool 2, in particular start and / or stop it. By way of example, the operating device 6 is arranged on the handle 5.

[0030] The power tool 1 expediently comprises 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. Optionally, the power tool 1 can comprise a gear, in particular an angular gear 8, via which the tool 2 is coupled to the electric motor 3. In Figure 1, the power tool 1 exemplarily comprises a coupling shaft 9, via which the electric motor 3 is coupled to the angular gear 8. The angular 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. The power tool 1 exemplarily comprises an outer housing 10, in which the electric motor 3, the control unit 4 and / or a rectifier arrangement 12 are expediently arranged. By way of example, the handle 5 is arranged on the outer housing 10.Alternatively, the handle 5 can be part of the outer housing 10 .

[0031] The power tool 1 is designed for connection to a mains voltage VI (see Figure 2). The mains voltage VI is an alternating voltage. The mains voltage VI is in particular sinusoidal and has, for example, an effective value of 230 V and / or a mains frequency of 50 Hz. Furthermore, the mains voltage VI can have an effective value of 120 V and / or a mains frequency of 60 Hz. The power tool 1 comprises a connection 11, for example a mains plug and / or a mains plug connection, via which the power tool 1 can be connected to the mains voltage, for example to a socket.

[0032] The power tool 1 has the rectifier assembly 12, which is arranged, for example, in the outer housing 10. The rectifier assembly 12 is shown, for example, in Figure 3.

[0033] The rectifier arrangement 12 is designed to provide an intermediate circuit voltage V2 on the basis of the mains voltage VI. The rectifier arrangement 12 comprises a rectifier 14, which is exemplary designed as a bridge rectifier. The rectifier 14 expediently comprises four diodes, which are exemplary connected as a bridge. The mains voltage VI is fed to the rectifier 14, which provides a rectified mains voltage on the basis of the mains voltage VI. The rectifier arrangement 12 further comprises an intermediate circuit 15, which is exemplary designed 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 mains voltage. The smoothed rectified mains voltage should also be referred to as the intermediate circuit voltage V2. The intermediate circuit voltage V2 drops across the intermediate circuit 15, in particular across the capacitor.

[0034] The intermediate circuit 15, in particular the capacitor, is, for example, less than 100 / zF, less than 50 / zF, less than 30 / zF, less than 20 / zF or less than 10 / zF.

[0035] An exemplary temporal profile of the intermediate circuit voltage V2 is shown in Figure 4 as a solid line. The intermediate circuit voltage V2 comprises a plurality of successive voltage half-waves 16. By way of example, the voltage half-waves 16 each comprise a sine section 17 which has the curve shape of a partial section of a sine half-wave. The sine section 17, in particular the partial section, expediently comprises the maximum 20 of the sine half-wave. By way of example, the intermediate circuit voltage V2 follows the rectified mains voltage in the sine section 17. The voltage half-waves 16 further comprise, by way of example, each two transition sections 18 which are arranged before and after the sine section 17. The transition sections 18 comprise the minima 19 of the intermediate circuit voltage V2. In the transition sections 18, the voltage half-waves 16 do not have the shape of a sine half-wave.In particular, the intermediate circuit voltage does not drop to zero in the transition sections 18. For example, the intermediate circuit voltage V2 does not follow the rectified mains voltage in the transition sections 18. The minima 19 of each voltage half-wave 16 are expediently at least 20%, preferably at least 30%, of the maximum 20. For example, the minima 19 of each voltage half-wave 16 are at least 90 V or at least 100 V. Furthermore, the minima 19 of each voltage half-wave 16 are expediently at most 70%, in particular at most 50%, preferably at most 40% or at most 35%, of the maximum 20. For example, the minima 19 are at most 120 V or 110 V.

[0036] The control unit 4 and / or the electric motor 3 are preferably powered from the intermediate circuit 15. The control unit 4 is designed to generate motor currents II, I2, 13 based on the electrical energy provided by the intermediate circuit 15, in particular based on the intermediate circuit voltage V2, and to supply them to the electric motor 3. By way of example, the control unit 4 provides three motor currents II, I2, 13. For example, the motor currents II, I2, 13 flow from the intermediate circuit 15.

[0037] The electric motor 3 comprises, for example, a stator 43 and a rotor 21. The rotor 21 is coupled to the tool 2. By energizing the electric motor 3 with the motor currents II, I2, I3, the rotor 21 is set into the drive rotational movement relative to the stator 43.

[0038] Optionally, the electric motor 3 has a position sensor device 22, which serves to detect the position and / or movement, in particular the current angle, of the rotor 21. The position sensor device 22 comprises, for example, a magnetic sensor, in particular a Hall sensor. The control unit 4 is expediently designed to detect the current angle of the rotor 21 using the position sensor device 22. The control unit 4 can further be designed to detect the current rotational speed of the electric motor 3 using the position sensor device 22.

[0039] Alternatively or additionally, the control unit 4 can be designed to detect the current angle of the rotor 21 and / or the current speed of the electric motor 3 without the use of sensors. In this case, a position sensor device 22 is expediently not present. The control unit 4 is designed in particular to determine, in particular to measure, a counter voltage 34 induced in the electric motor and to calculate the current angle of the rotor 21 and / or the current speed of the electric motor 3 on the basis of the counter voltage 34. The control unit 4 is designed in particular to calculate the current angle of the rotor 21 and / or the current speed of the electric motor 3 using the back EMF principle, where "EMF" stands for "electromotive force".

[0040] Figure 6 shows an exemplary block diagram of the signal processing carried out by the control unit 4 for controlling the electric motor 3.

[0041] The control unit 4 is expediently designed to carry out a speed control of the electric motor 3. In particular, the control unit 4 is designed to provide the motor currents II, I2, I3 on ​​the basis of a target speed 23 and an actual speed 24. The target speed 23 is set by the control unit 4, for example, in accordance with a user input made using the operating device 6. Alternatively or additionally, the target speed 23 can be stored in the control unit 4 in advance 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 by means of the position sensor device 22 and / or on the basis of a sensorless principle, in particular on the basis of the induced counter voltage 34. The actual speed 24 describes how quickly the rotor 21 rotates relative to the stator 43.

[0042] The control unit 4 comprises a speed controller 25, to which the target speed 23 and the actual speed 24 are supplied. Based on the target speed 23 and the actual speed 24, in particular based on a comparison between the target speed 23 and the actual speed 24, the speed controller 25 calculates a torque target value 26. The torque target value 26 specifies the torque with which the rotor 21 is to be acted upon by energizing the electric motor 3 in order to achieve a change in the actual speed value towards the speed target value.

[0043] The control unit 4 further comprises a torque curve calculation unit 27, which is designed to calculate a temporal torque curve 28 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 Figure 5 as a solid line. As an example, the torque curve 28 has a trapezoidal curve shape.

[0044] The control unit 4 further comprises a motor current provision unit 31, which is designed to calculate the motor currents II, I2, I3 on ​​the basis of the torque curve s 28. By way of example, the motor current provision unit 31 comprises a target current specification unit 32, which is designed to calculate a q-current iq, in particular a q-current target value, and a d-current id, in particular a d-current target value, in particular on the basis of the torque curve s 28. The d-current and the q-current are currents in a rotor-related d / q system that rotates according to the rotation of the rotor 21. The d-current forms the flux-forming component and the q-current forms the torque-forming component. The d-current can be referred to as a d-component or as a field-weakening current, and the q-current can be referred to as a q-component or as a torque-forming current.The setpoint current specification unit 32 calculates the q-current, in particular the q-current setpoint, and the d-current, in particular the d-current setpoint, in such a way as to achieve the torque curve 28 when the electric motor 3 is energized according to the q-current, in particular the q-current setpoint, and the d-current, in particular the d-current setpoint. For example, the time profile of the calculated q-current, in particular the q-current setpoint, corresponds to the torque curve 28. In particular, the q-current, in particular the q-current setpoint, has the same curve shape as the torque curve 28.

[0045] The motor current supply unit 31 expediently comprises a current regulator 33 designed to provide the motor currents II, I2, 13. In particular, the current regulator 33 is designed to perform current control of the motor currents II, I2, 13. The motor currents II, I2, and I3 are preferably pulse-width modulated. The current regulator 33 provides the motor currents II, I2, 13 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 regulator 33 provides the motor currents II, I2, 13 such that the calculated q-current and the calculated d-current are achieved. The electric motor 3, in particular the motor windings of the stator 43, are energized with the motor currents II, I2, 13.The rotor 21 has, for example, a permanent magnet and is set into the drive rotational movement by an interaction of the permanent magnet with the magnetic field generated by the current supply to the motor windings.

[0046] The current controller 33 preferably regulates the q-current, in particular a q-current actual value, to the q-current setpoint and / or regulates the d-current, in particular a d-current actual value, to the d-current setpoint. For example, the motor current supply unit 31 calculates the q-current actual value and / or the d-current actual value based on the motor currents II, I2, I3.

[0047] The torque curve 28 will be discussed in more detail below. Figure 5 shows an exemplary torque curve 28 (as a solid line). The torque curve 28 has a plurality of consecutive torque half-waves 36.

[0048] The torque curve 28 is provided, in particular calculated, by the control unit 4 for controlling the electric motor. The control unit 4 is designed to provide, in particular to calculate, a respective torque half-wave 36 for each voltage half-wave 16. Each voltage half-wave 16 is expediently 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.

[0049] Preferably, the control unit 4 is designed to determine a counter voltage 34 induced in the electric motor 3 and, in response to the counter voltage 34 being greater than or equal to the intermediate circuit voltage V2, to reduce a current torque value of the torque curve 28, in particular to set it to zero, for example by means of the torque curve calculation unit 27. The control unit 4 is designed in particular to carry out a comparison between the intermediate circuit voltage V2 and the counter voltage 34 and, on the basis of the result of the comparison, to set the current torque value of the torque curve 28 to zero (if the counter voltage 34 is greater than or equal to the intermediate circuit voltage).If the comparison between the intermediate circuit voltage V2 and the counter voltage 34 shows that the counter voltage 34 is smaller than the intermediate circuit voltage , the control unit 4 expediently does not set the current torque value of the torque curve 28 to zero .

[0050] Figure 4 shows an example curve of the counter voltage 34. The counter voltage 34 is shown as a dashed line and is, by way of example, constant over the two voltage half-waves 16 shown in Figure 4. At the beginning and end of each voltage half-wave 16 - that is to say at the minima 19 - the intermediate circuit voltage V2 falls below the counter voltage 34. Figure 5 shows the associated torque curve 28, which is set to zero at the times at which the intermediate circuit voltage V2 is lower than the counter voltage 34.

[0051] This results in a torque curve 28 which comprises a plurality of successive pulses 44. Each torque half-wave 36 has a respective pulse 44. During each pulse 44, the torque curve 28 is continuously greater than zero. The pulses 44 are, for example, trapezoidal. Alternatively, the pulses can each be rectangular. Between two pulses 44, the torque curve 28 is 0. The torque curve 28 is zero before and after each pulse 44. The sections of the torque curve 28 in which the torque curve 28 is zero are also referred to as zero sections or torque minima 41. The pulses 44 result in the time sections in which the intermediate circuit voltage V2 is greater than the counter voltage 34. The torque minima 44 occur at the time intervals at which the intermediate circuit voltage V2 is smaller than the counter voltage 34 .

[0052] Preferably, the control unit 4 is configured to determine, in particular calculate, the induced countervoltage 34 based on the rotational speed of the electric motor 3. The rotational speed of the electric motor 3 is measured, in particular, as explained above, by means of the position sensor device 22. Furthermore, the control unit 4 can be configured to measure the countervoltage 34.

[0053] Preferably, the control unit 4 is designed to calculate a q-current setpoint value according to the current torque value and to regulate a q-current, in particular a q-current actual value, for controlling the electric motor 3 to the q-current setpoint value. In particular, the control unit 4 is designed to set the q-current setpoint value to zero and to regulate the q-current, in particular the q-current actual value, to zero in response to the counter voltage 34 being greater than or equal to the intermediate circuit voltage V2. For example, the setpoint current specification unit 32 sets the q-current setpoint value to zero in response to the current torque value of the torque curve 28 being equal to zero. Expediently, the current controller 33 regulates the q-current actual value to zero when the counter voltage 34 is greater than or equal to the intermediate circuit voltage V2.Furthermore, the control unit 4 is preferably designed, in response to the counter voltage 34 being greater than or equal to the intermediate circuit voltage V2, to preferably reduce the d-current, in particular the d-current setpoint, in particular to set it to zero, preferably to regulate it to zero.

[0054] Preferably, the control unit 4 is designed to maintain an electrical connection leading to the electric motor 3, which serves to control the electric motor 3, when the counter voltage 34 is greater than or equal to the intermediate circuit voltage V2. In particular, the power tool 1 does not continuously interrupt this connection in response to the counter voltage 34 being greater than or equal to the intermediate circuit voltage V2. In particular, the control unit 4 is designed to continue regulating the torque-generating current and not to switch it off when the induced counter voltage 34 of the electric motor 3 is greater than or equal to the intermediate circuit voltage V2.

[0055] The control unit 4 is designed to provide, in particular to calculate, a respective torque half-wave 36 for controlling the electric motor 3 for each voltage half-wave 16. The curve shape of the respective torque half-wave is preferably flattened compared to the curve shape of the (respectively assigned) voltage half-wave 16. The flattened curve shape results in particular in a lower ohmic power loss when energizing the electric motor 3, expediently with the same average torque.

[0056] The control unit 4 expediently supplies current to the electric motor 3 in proportion to the torque half-wave. If the torque half-wave 36 assumes larger values, the control unit 4 increases the current supply to the electric motor 3. The ohmic power loss is a function of the square of the current supply to the electric motor 3, so that larger currents lead to a disproportionately high ohmic power loss. The flattened curve shape of the torque half-waves 36 reduces the current maxima which are particularly significant for the ohmic power loss (due to the quadratic dependence), so that the ohmic power loss can be reduced, in particular when there is no or only a slight reduction in the torque. The flattened curve shape can also be referred to as a smoothed curve shape.In particular, each torque half-wave 36 has a more uniform curve shape than the respective voltage half-wave 16 and / or a respective (imaginary) sine half-wave 37 of the same period and / or the same area. Preferably, the standard deviation of the respective torque half-wave 36 is smaller than the standard deviation of the respective voltage half-wave 16 and / or a respective (imaginary) sine half-wave 37 of the same period and / or the same area.

[0057] In particular, the flattened curve shape is a curve shape which, with the same area under the curve shape, has a smaller maximum, in particular relative to an (imaginary) sine half-wave 37. Figure 5 shows a reference curve 38 (as a dashed line) which has the curve shape of a rectified sine curve and comprises successive sine half-waves 37. The sine half-waves 37 each have the same period as the torque half-waves 36. The area under each sine half-wave 37 - i.e. the integral over the period of the sine half-wave 37 - is expediently equal to the area under a respective torque half-wave 36 - i.e. equal to the integral over the period of a torque half-wave 36. The maximum of each torque half-wave 36 is expediently smaller, in particular at least 10% smaller or at least 20% smaller, than the maximum of the respective sine half-wave 37.The sine half-wave 37 serves at this point for the mathematical definition of the flattened curve shape of the torque half-wave and does not have to be provided by the power tool 1. The flattened curve shape of each torque half-wave 36 is preferably mathematically defined such that it has a smaller maximum than the sine half-wave 37 with the same period and the same area as a (particularly imaginary) sine half-wave 37.

[0058] For example, with the flattened waveform, the ratio between the maximum of the waveform and the average value of the waveform is reduced. Advantageously, the ratio between the maximum of the torque half-wave 36 and the average value of the torque half-wave 36 is smaller than the ratio between the maximum 20 of the voltage half-wave 16 and the average value of the voltage half-wave 16.

[0059] The explanation of a torque half-wave 36 preferably applies to each torque half-wave 36. Preferably, the control unit 4 is configured to provide the torque half-wave 36 with a trapezoidal waveform or a rectangular waveform. By way of example, the torque half-waves 36 each have a trapezoidal waveform. Alternatively, the torque half-waves can have a different waveform, for example, a rectangular waveform.

[0060] The torque half-wave 37 further expediently has two torque minima 41, which represent the beginning and the end of the torque half-wave 36. For example, the torque at the torque minima 41 is zero. The torque minima 41 are, in particular, those time periods in which the induced counter-voltage 34 is greater than or equal to the (associated) voltage half-wave 16.

[0061] As shown in Figure 4, the induced countervoltage 34 is, for example, constant over the voltage half-wave 16. The minima 19, in particular the transition sections 18, of the voltage half-wave 16 are, for example, below the induced countervoltage 34. The maximum 20, in particular the sinusoidal section 17, is, for example, above the induced countervoltage 34.

[0062] The torque half-wave 36 has a plateau section 39 which comprises or represents the maximum of the torque half-wave 36. The plateau section 39 preferably has a gradient of 0 and extends in particular 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. For example, the maximum 42 of the sine half-wave 37 is higher than the plateau section 39. The torque half-wave

[0063] 36 further comprises two flank sections 40 which surround the plateau section 39. The flank sections 40 have (in terms of magnitude) a higher gradient than the plateau section 39, in particular a higher gradient than the sine half-wave

[0064] 37 and / or the voltage half-wave 16. According to one possible embodiment, the flank sections 40 can be vertical - that is to say in particular they can have a gradient of (in terms of magnitude) infinity. Each pulse 44 is formed by a plateau section 39 and two flank sections 40. A torque half-wave 36 therefore comprises the following sections, which follow one another in the order mentioned, in particular directly one after the other: a first torque minimum 41 (preferably equal to zero), a first flank section 40 (preferably with a positive gradient), the plateau section 39 (preferably with a gradient of zero), a second flank section 40 (preferably with a negative gradient) and a second torque minimum (preferably equal to zero). The torque minima 41 extend together in time over in particular at least 10%, at least 20% or at least 30% of the period of the torque half-wave 36.

[0065] The control unit 4 is expediently designed to provide each torque half-wave 36 with a period equal to the period of a respective voltage half-wave 16. Preferably, the frequency of the torque curve 28 is twice as high as the frequency of the mains voltage VI. In particular, the frequency of the torque curve 28 is 100 Hz or 120 Hz.

[0066] For example, the control unit 4 records the period of the voltage half-waves 16 and / or the time interval between adjacent zero crossings of the mains voltage VI and uses the recorded period and / or the time interval as the period for the torque half-waves 36. The control unit 4 expediently synchronizes the torque half-waves 36 with the mains voltage VI and / or the voltage half-waves 16. For example, the control unit 4 synchronizes the minima of the torque curve s 28 with the zero crossings of the mains voltage VI, so that the minima of the torque curve s 28 occur at the same time as the zero crossings of the mains voltage V2. Furthermore, the control unit 4 can synchronize the minima of the torque curve s 28 with the minima 19 of the intermediate circuit voltage V2, so that the minima of the torque curve s 28 occur at the same time as the minima of the intermediate circuit voltage V2.For example, the control unit 4 is designed to determine a phase angle 30 of the mains voltage VI and / or the intermediate circuit voltage V2 and to provide the torque half-wave 36 according to the phase angle 30, in particular such that the torque half-wave 36 is synchronous with the voltage half-wave 16 and / or with the mains voltage VI. The torque curve 28 expediently has the same phase angle as the intermediate circuit voltage V2.

[0067] The control unit 4, in particular the torque curve calculation unit 27, is preferably designed to calculate the torque curve 28 on the basis of a curve profile 29. The curve profile is expediently stored in advance in the control unit 4 and / or is provided by the control unit 4. The curve profile 29 defines the flattened curve shape of the torque half-wave 36. For example, the curve profile 29 defines a trapezoidal curve shape or a rectangular curve shape.

[0068] The control unit 4 is designed, by way of example, to calculate the torque curve 28 taking into account the phase angle 30. In particular, the control unit 4 is designed to calculate the period for a respective torque half-wave 36 on the basis of the phase angle 30 and to stretch or compress the curve profile 29 in time according to the calculated period, so that the period of the curve profile 29 is equal to the calculated period.

[0069] The control unit 4 is expediently further designed to calculate the respective torque half-wave 36 on the basis of the torque setpoint 26. In particular, the control unit 4 is designed to calculate the respective torque half-wave 36 such that the average value of the torque half-wave 36 is equal to the torque setpoint 26. In particular, the control unit 4 is designed to calculate the respective torque half-wave 36 by scaling the curve profile 29 according to the torque setpoint 26. By way of example, the control unit 4 is designed to scale the curve profile 29 with the torque setpoint 26 or a scaling factor dependent on the torque setpoint 26.

[0070] As mentioned above, the control unit 4 has a speed controller 25 for providing the torque setpoint 26, on the basis of which the control unit 4 provides the respective torque half-wave 36. The control unit 4 is designed, in particular, to supply current to the electric motor 3 in accordance with the torque half-wave.

[0071] The provision of the torque half-wave 36 can also be referred to as torque shaping. Through torque shaping and the associated current shaping, particularly in the form of a trapezoid or a rectangle, the ohmic power loss—i.e., the copper losses—can be reduced, so that the electric motor 3 can be made smaller.

[0072] As already explained 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 can expediently save installation space and costs. In order to reduce copper losses - i.e. the ohmic power loss - in the electric motor 3, the torque and thus the current supply to the electric motor 3, in particular the q-current, is expediently regulated to a trapezoidal or rectangular wave, which preferably has twice the mains frequency. Since the copper losses are distributed over I 2*R, the plateau section 39 of the trapezoidal torque half-wave 36 should have the smallest possible torque value. This is preferably achieved by selecting the time per half-wave in which current can flow into the electric motor 3 as long as possible, i.e., by selecting a large temporal extension of the plateau section 39. The electric motor 3 is expediently designed for a lower voltage than the mains voltage VI. Furthermore, the induced counter-voltage of the electric motor 3 is expediently changed by varying the field-weakening current as a function of the intermediate circuit voltage V2.

[0073] Preferably, the control unit 4, in particular the target current specification unit 32, is designed to calculate the d-current, in particular the d-current target value, taking into account the intermediate circuit voltage V2. In particular, the control unit 4 is designed to set the d-current, in particular the d-current target value, in accordance with the intermediate circuit voltage V2. For example, the control unit 4 is designed to reduce the amount of the d-current, in particular the d-current target value, at a higher intermediate circuit voltage V2 and to increase it at a lower intermediate circuit voltage V2. In particular, the control unit 4 is designed to set the d-current, in particular the d-current target value, on the basis of the intermediate circuit voltage V2 such that the induced counter 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. With an increasing intermediate circuit voltage V2, the d-current, in particular the d-current setpoint, is reduced in magnitude, and with a decreasing intermediate circuit voltage V2, the d-current, in particular the d-current setpoint, is increased in magnitude.

[0074] In particular, the control unit 4 is designed to always supply current to the electric motor, specifically according to the d-current and / or the q-current, so that braking torques are prevented and, in particular, so that the power factor is dynamically adapted to the load.

[0075] In particular, the control unit 4 is designed to carry out a variation of d-current and q-current depending on the intermediate circuit voltage V2 and / or mains voltage VI in order to always control the motor optimally in order to require as little current as possible.

[0076] The power tool 1 can be operated in particular according to the method explained below. The method comprises the following steps:

[0077] - Providing, by means of the rectifier arrangement 12 with the intermediate circuit 15, the intermediate circuit voltage V2 on the basis of the mains voltage VI to which the power tool 1 is connected, wherein the intermediate circuit voltage V2 has a plurality of successive voltage half-waves 16,

[0078] - Providing the torque curve (28) for controlling the electric motor (3), wherein the torque curve (28) comprises a respective torque half-wave (36) for each voltage half-wave (16),

[0079] - Determining the counter voltage (34) induced in the electric motor (3) and - in response to the counter voltage (34) being greater than or equal to the intermediate circuit voltage (V2), reducing the current torque value of the torque curve (28).

[0080] The method expediently comprises a further step in which the electric motor 3 is energized according to the torque half-waves, so that the rotor 21 is set into the drive rotational movement and thereby the tool 2 is set into the working movement.

[0081] The method expediently comprises a further step in which a workpiece is machined, in particular polished, ground or sawn, using the tool 2.

Claims

27 Claims 1. Power tool (1), in particular hand-held power tool, for example polishing machine (1A), grinding machine and / or sawing machine (1B), with 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 designed for connection to a mains voltage (VI) and comprises a rectifier arrangement (12) with an intermediate circuit (15) for providing an intermediate circuit voltage (V2) based on the mains voltage (VI), wherein the intermediate circuit voltage (V2) has a plurality of successive voltage half-waves (16), wherein the control unit (4) is configured to provide a torque curve (28) for controlling the electric motor (3), wherein the torque curve (28) comprises a respective torque half-wave (36) for each voltage half-wave (16), and wherein the control unit (4) is configured to determine a back EMF (34) induced in the electric motor (3) and, in response to the fact that the back EMF (34) is greater than or equal to the DC link voltage (V2), to reduce a current torque value of the torque curve s (28).

2. Power tool (1) according to claim 1, wherein the control unit (4) is configured to respond to the fact that the counter-voltage (34) is greater than or equal to the The intermediate circuit voltage (V2) is to set the current torque value of the torque curve s (28) to zero.

3. Power tool (1) according to one of the preceding claims, wherein the control unit (4) is configured to calculate a q-current setpoint according to the current torque value and to regulate a q-current for controlling the electric motor (3) to the q-current setpoint.

4. Power tool (1) according to claim 3, wherein the control unit (4) is configured to set the q-current setpoint to zero and regulate the q-current to zero in response to the fact that the counter-voltage (34) is greater than or equal to the intermediate circuit voltage (V2).

5. Power tool (1) according to a preceding claim, wherein the control unit (4) is configured to maintain an electrical connection leading to the electric motor (3) for controlling the electric motor (3) when the counter voltage (34) is greater than or equal to the intermediate circuit voltage (V2).

6. Power tool (1) according to a preceding claim, wherein the control unit (4) is configured to determine the induced counter voltage (34) on the basis of a rotational speed of the electric motor (3).

7. Power tool (1) according to a preceding claim, 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 waveform of which is flattened compared to the waveform of the voltage half-wave (16).

8. Power tool (1) according to claim 7, wherein the control unit (4) is configured to provide the torque half-wave (36) with a curve shape which, for the same area as a sine half-wave (37), has a lower maximum than the sine half-wave (37).

9. Power tool (1) according to claim 7 or 8, wherein the control unit (4) is configured to provide the torque half-shaft (36) with a trapezoidal curve shape or a rectangular curve shape.

10. Power tool (1) according to a preceding claim, wherein the control unit (4) is configured to determine a phase angle (30) of the mains voltage (VI) and / or the intermediate circuit voltage (V2) and to provide the torque half-wave according to the phase angle (V2).

11. Power tool (1) according to a preceding claim, wherein the control unit (4) has a speed controller (25) for providing a torque setpoint (26), on the basis of which the control unit (4) provides the respective torque half-wave (36).

12. Power tool (1) according to a preceding claim, wherein the control unit (4) is configured to energize the electric motor (3) according to the torque half-shaft (36).

13. Power tool (1) according to a preceding claim, 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) according to the intermediate circuit voltage (V2).

14. Power tool (1) according to claim 13, wherein the control unit (4) is configured to reduce the magnitude of the d-current (Id) at higher intermediate circuit voltage (V2) and to increase it at lower intermediate circuit voltage (V2).

15. Method for operating an electric tool (1), in particular a hand-held electric tool, for example a polishing machine (1A), grinding machine and / or sawing machine (1B), with 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 steps: - Providing, by means of a rectifier arrangement (12) with an intermediate circuit (15), an intermediate circuit voltage (V2) based on a mains voltage (VI) to which the power tool (1) is connected, wherein the intermediate circuit voltage (V2) has a plurality of successive voltage half-waves (16), - Providing a torque curve s (28) for controlling the electric motor (3) , wherein the torque curve (28) comprises a respective torque half-wave (36) for each voltage half-wave (16), - Determining a reverse voltage (34) induced in the electric motor (3) and - in response to the fact that the counter-voltage (34) is greater than or equal to the intermediate circuit voltage (V2), reducing a current torque value of the torque curve s (28) . 31 16. Method according to claim 15, wherein the current torque value of the torque curve s (28) is set to zero in response to the fact that the counter-voltage (34) is greater than or equal to the intermediate circuit voltage (V2).

17. Method according to claim 15 or 16 wherein a q-current setpoint is calculated according to the current torque value and a q-current is regulated to the q-current setpoint for controlling the electric motor.

18. Method according to claim 17, wherein, in response to the fact that the counter-voltage is greater than or equal to the intermediate circuit voltage, the q-current setpoint is set to zero and the q-current is regulated to zero.

19. Method according to one of claims 15 to 18, wherein, when the counter voltage (34) is greater than or equal to the intermediate circuit voltage (V2), an electrical connection leading to the electric motor (3), which serves to control the electric motor (3), is maintained.

20. Method according to one of claims 15 to 19, wherein the induced back EMF is determined on the basis of a rotational speed of the electric motor.

21. Method according to one of claims 15 to 20, wherein for each voltage half-wave (16) a respective torque half-wave (36) is provided for controlling the electric motor (3), the waveform of which is flattened compared to the waveform of the voltage half-wave (16).

22. Method according to claim 21, wherein the torque half-shaft (36) is provided with a curve shape which 32 has a lower maximum than the sine half-wave (37) when the area is the same as a sine half-wave (37).

23. Method according to claim 21 or 22, wherein the control unit (4) is configured to provide the torque half-shaft (36) with a trapezoidal curve shape or a rectangular curve shape.

24. Method according to any one of claims 15 to 23, wherein a phase angle (30) of the mains voltage (VI) and / or the intermediate circuit voltage (V2) is determined and the torque half-wave is provided according to the phase angle (V2).

25. Method according to one of claims 15 to 24, wherein the respective torque half-wave (36) is provided on the basis of a torque setpoint (26) of a speed controller (25).

26. Method according to one of claims 15 to 25, wherein the electric motor (3) is energized according to the torque half-shaft (36).

27. Method according to one of claims 15 to 26, wherein a d-current (Id) and a q-current (Iq) are calculated for controlling the electric motor (3) and the d-current (Id) is set according to the intermediate circuit voltage (V2).

28. Method according to claim 27, wherein the d-current (Id) is reduced in magnitude at higher intermediate circuit voltage (V2) and increased in magnitude at lower intermediate circuit voltage (V2). 33 29. Arrangement comprising an electric motor for driving a tool and a control unit for controlling the electric motor, wherein the control unit is configured to provide a torque curve for controlling the electric motor, wherein the torque curve comprises a respective torque half-wave for each voltage half-wave of an intermediate circuit voltage, and wherein the control unit is configured to determine a back EMF induced in the electric motor and, in response to the fact that the back EMF is greater than or equal to the intermediate circuit voltage, to reduce an actual torque value of the torque curve.

30. Computer program product comprising commands that cause the power tool (1) according to claim 1 to perform the method steps according to any one of claims 1 to 28.

31. Computer-readable medium on which the computer program product according to claim 30 is stored.

32. Method comprising the step: Applying the computer program product according to claim 30 to a power tool ( 1) .