Patent ID: 12224697

DETAILED DESCRIPTION OF THE INVENTION

FIG.1shows a system1comprising a power tool2, a workpiece3and optionally a mobile device4. The system1represents a purely exemplary application environment for the power tool2. The power tool2can also be provided on its own—i.e. without the further components of the system1.

The power tool2is exemplarily a hand-held power tool. The power tool2can be gripped, carried and/or guided by a user with one or two hands. Exemplarily, the power tool2is a sander, in particular an eccentric sander. Exemplarily, the power tool2is a long-neck sander, in particular a long-neck eccentric sander. The power tool2may further be an eccentric polisher.

The power tool2comprises a tool5, which is exemplarily designed as a sanding tool, in particular as a sanding disc. The power tool2further comprises an electric motor6for driving the tool5. The electric motor6is exemplarily designed as an electronically commutated, in particular as a sensorless commutated electric motor. In particular, the electric motor6is designed as a brushless DC motor, BLDC motor. The electric motor6provides a rotary drive movement, on the basis of which the tool5is set into a working movement.

The power tool2further comprises a control unit7for driving the electric motor6with a motor current MI. The control unit7has a start-up mode in which the control unit7drives the electric motor6in such a way that the electric motor6goes through a rotational speed ramp DR during the start-up mode, in which rotational speed ramp DR the rotational speed of the electric motor6is continuously increased up to a working rotational speed ADZ. Exemplary rotational speed ramps DR are shown inFIG.4. The control unit7is configured to set the slope of the rotational speed ramp DR for the start-up mode on the basis of a detected temperature and/or to set the current strength of the motor current MI for the start-up mode on the basis of a/the detected temperature. By the current strength of the motor current MI is meant in particular the amplitude of the motor current MI.

Exemplarily, the power tool2comprises a head section8comprising the tool5. Preferably, the head section8comprises the electric motor6. According to an alternative embodiment, the electric motor6may be arranged in another section of the power tool2, for example in a user section9. Optionally, the head section8comprises a head section temperature sensor10, which may also be referred to as a second temperature sensor.

Exemplarily, the power tool2comprises the user section9. The user section9comprises, in particular, a handle section11which can be gripped by a user with his hand in order to carry and/or guide the power tool2. Exemplarily, the user section9comprises an operating device12, by means of which the drive of the tool5, which takes place by means of the electric motor6, can be switched on and/or switched off and/or by means of which a target rotational speed for the electric motor6can be set. In particular, the operating device12comprises a first operating element14, which is designed in particular as a switch and via which the drive of the tool5effected by means of the electric motor6can be switched on and/or switched off. Exemplarily, the operating device12comprises a second operating element16, which is designed in particular as a rotary wheel and via which the target rotational speed for the electric motor6can be expediently set.

Exemplarily, the user section9further comprises the control unit7. According to an alternative embodiment, the control unit7may be arranged in another section of the power tool2, in particular in the head section8. The power tool2, in particular the user section9, comprises a user section temperature sensor18, which may also be referred to as a first temperature sensor.

The power tool2is expediently configured to detect the temperature (on the basis of which the slope of the rotational speed ramp DR and/or the magnitude of the motor current MI is adjusted) with the first temperature sensor18. Exemplarily, the first temperature sensor18is arranged at a distance from the electric motor6. In particular, the first temperature sensor18is spaced apart from the electric motor6and/or thermally insulated so that the temperature detected by the first temperature sensor18is expediently not influenced by the heat emitted by the electric motor6. Exemplarily, the electric motor6is arranged on a first side of a neck section22and the first temperature sensor18is arranged on a second side of the neck section22, the second side facing away from the electric motor6.

Optionally, the user section9has a hose port19to which a suction hose can be connected. The hose port19is fluidically connected to a suction opening provided on the head section8via an air channel running through the power tool2.

Exemplarily, the user section9has a user section housing20. In particular, the control unit7and/or the first temperature sensor18are arranged in the user section housing20. Exemplarily, the operating device12, in particular the first operating element14and/or the second operating element16, is arranged on the user section housing20. Exemplarily, the handle section11is attached to the user section housing20. The hose port19is attached to the handle section11in an exemplary manner.

The head section8has, by way of example, a head section housing21in which, in particular, the electric motor6and/or the head section temperature sensor10are arranged.

According to a possible embodiment, the control unit7is designed to determine the temperature, on the basis of which the control unit7sets the slope of the rotational speed ramp DR and/or the strength of the motor current for the start-up mode, by means of a plurality of temperature sensors, in particular by means of the first temperature sensor18and the second temperature sensor. In particular, the control unit7detects a first temperature value via the first temperature sensor18and a second temperature value via the second temperature sensor and sets the slope of the rotational speed ramp DR and/or the strength of the motor current for the start-up mode based on the first temperature value and the second temperature value. For example, the control unit calculates the temperature on the basis of which the control unit7sets the slope of the rotational speed ramp DR and/or the strength of the motor current for the start-up mode from the first temperature value and the second temperature value, for example as an average value.

Exemplarily, the power tool2comprises the neck section22, which expediently comprises a neck element24, in particular of rod-shaped design. The neck section22, in particular the neck element24, connects the head section8, in particular the head section housing21, to the user section9, in particular the user section housing20. Expediently, an electrical line27runs through the neck section22, in particular through the neck element24, via which the control unit7supplies the motor current MI to the electric motor6. Furthermore, expediently, the aforementioned air channel runs through the neck section22, in particular through the neck element24.

The power tool2expediently has an elongated basic shape extending in a longitudinal direction. Exemplarily, the neck section22, in particular the neck element24, occupies at least 30%, at least 40% or at least 50% of the longitudinal extension of the power tool2.

The workpiece3shown inFIG.1has, by way of example, a workpiece surface24that can be machined, in particular sanded and/or polished, with the tool5. The workpiece3is, for example, a wall, in particular a ceiling wall and/or side wall, of a building. The surface of the wall is sanded with the tool5, in particular the sanding disc.

The mobile device4is expediently designed as a smartphone or tablet. In particular, the mobile device4is designed to communicate with the power tool2, in particular the control unit7, preferably wirelessly, for example via Bluetooth, NFC, WLAN and/or mobile radio.

FIG.2shows an exemplary detailed view of the head section8. The electric motor6comprises a stator25and a rotor26, which can be set into the drive rotary movement relative to the stator25. The rotor26is mounted for rotation about a rotor rotation axis28. The drive rotary movement of the rotor26takes place about this rotor rotation axis28.

The rotor26comprises an eccentric section29, which is arranged eccentrically to the rotor rotation axis28. When the rotor26performs its drive rotary movement about the rotor rotation axis28, the eccentric section29moves on a circular path about the rotor rotation axis28. The tool5is coupled to the eccentric section29, so that the tool5is set into working movement by the movement of the eccentric section29. Exemplarily, the power tool2has a pivot bearing30through which the tool5is coupled to the eccentric section29. The pivot bearing30defines a tool rotation axis33about which the tool5is rotatable relative to the eccentric section29. Exemplarily, the tool rotation axis33runs through the center of the tool5, which is in particular designed as a sanding disc. The tool rotation axis33is in particular aligned parallel to the rotor rotation axis28and arranged offset thereto. Due to the fact that the tool5is rotatably mounted relative to the eccentric section29, the tool5is in particular able to perform an unbound rotation as the working movement. In the unbound rotation, the own rotation of the tool5—that is, the rotation of the tool5about the tool rotation axis33—is expediently independent of the drive rotation movement.

The power tool2, in particular the head section8, expediently further has a braking device34which is designed to brake the tool5, in particular relative to a stationary section36of the power tool2. The braking device34can also be referred to as a disk brake. In particular, the braking device34serves to slow down the own rotation of the tool5(relative to the stationary section36) when the power tool2is idle, i.e. when the tool5is not yet in contact with the workpiece3, in particular the workpiece surface24. By slowing down the own rotation of the tool5, scoring that occurs when the tool5touches the workpiece3, in particular the workpiece surface24, can be reduced or prevented.

In particular, the stationary section36is stationary relative to the stator25and/or the head section housing21. The stationary section36does not follow the drive rotary movement. The stationary section36is, for example, disk-shaped and expediently has an opening38through which the rotor26, in particular the eccentric section29, is led out.

Exemplarily, the braking device34comprises a braking element37, which is arranged in particular between the tool5and the stationary section36. The braking element37is designed in particular to be elastic and/or ring-shaped. The braking element37is in particular designed as a rubber ring, preferably as an ring-shaped rubber sleeve. The braking element37is in particular a diaphragm and/or a lamella. The braking element37rotates around the tool rotation axis33. The braking element37is expediently attached to the tool5, so that it moves along with the tool5and in particular performs the working movement together with the tool5. Expediently, the braking element37rubs against the stationary section36, thereby braking the tool5relative to the stationary section36. According to an alternative embodiment, the braking element37is attached to the stationary section36and rubs against the tool5, thereby braking the tool5relative to the stationary section36.

The tool5is designed in particular as a sanding disc. The tool5has a in particular disk-shaped tool upper side40and/or a in particular disk-shaped tool lower side42. The tool upper side40and/or the tool lower side42are expediently aligned perpendicular to the tool rotation axis33. The tool upper side40is expediently in contact with the braking element37. For example, the braking element37is attached to the tool upper side40. Alternatively, the braking element37rubs against the tool upper side40. The tool lower side42is expediently formed by an sanding means, in particular a sanding disc. The power tool2can be placed with the tool lower side42on the workpiece3, in particular the workpiece surface24, in order to process the workpiece3, in particular to sand it.

FIG.3shows a schematic representation of the electric motor6, the control unit7, the first temperature sensor18and the operating device12.

The control unit7comprises, by way of example, a computer unit44and a power unit46. The computer unit44is designed in particular as a microcontroller and preferably comprises a processor. The power unit46is designed in particular as power electronics. The computer unit44is designed to calculate drive information AI, on the basis of which the power unit46drives the electric motor6. In particular, the power unit46provides the motor current MI on the basis of the drive information AI. Exemplarily, the motor current MI comprises three motor currents—a first motor current MI1, a second motor current MI2, and a third motor current MI3. The drive information AI expediently specifies frequency, amplitude and/or phase for the motor currents MI1, MI2, MI3. The electrical line running from the control unit7to the electric motor6expediently comprises at least three wires—a first wire51, a second wire52and a third wire53, with a respective motor current MI1, MI2, MI3being transmitted via each wire51,52,53.

The electric motor6, in particular the stator25, has a plurality of coils55, each of the coils55being energized with a respective motor current MI1, MI2, MI3to cause the drive rotation of the rotor26. The electric motor6, in particular the rotor26, has a permanent magnet56which expediently magnetically interacts with the magnetic field provided by the coils55and thereby results in the drive rotary movement of the rotor26.

The control unit7has the aforementioned start-up mode and a working mode, which will be explained in more detail below.

In the working mode, the rotor26rotates at a present rotational speed which is in particular greater than or equal to the working rotational speed ADZ. The present rotational speed is expediently equal to the target rotational speed. In the working mode, the working movement of the tool5is fast enough to machine the workpiece3.

The control unit7is designed to perform the commutation of the electric motor6in the working mode using a sensorless principle for determining a present angle of the rotor and/or a present rotational speed of the electric motor6. In particular, the control unit7is designed to commutate the electric motor in the working mode without a sensor—that is, on the basis of a sensorless principle. The sensorless principle is in particular a Back-EMF principle. Preferably, the power tool2does not have a position sensor for detecting the present rotor angle and/or the present rotational speed of the electric motor6.

For example, the control unit7determines the present rotor angle and/or the present rotational speed of the electric motor6on the basis of a countervoltage generated in the coils55(which can be tapped in particular via the electrical line27) and performs commutation of the electric motor6on the basis of the present rotor angle and/or the present rotational speed—for example, by providing the motor currents MI1, MI2, MI3.

In particular, the control unit7performs a closed-loop rotational speed control in the working mode, in which closed-loop rotational speed control the control unit7adjusts the motor currents MI1, MI2, MI3, in particular their frequency and/or current strength, so that the present rotational speed of the electric motor6detected (in particular without sensors) corresponds to the target rotational speed entered in particular via the operating device12. For example, the computer unit44calculates the drive information AI for the power unit46on the basis of the target rotational speed, the (in particular sensorless) detected present rotational speed and/or the (in particular sensorless) detected present rotor angle, and the power unit46provides the motor currents MI1, MI2, MI3on the basis of the drive information AI. The control information AI specifies, for example, the frequency, phase and/or current strength of the motor currents MI1, MI2, M3.

As an example, the sensorless principle for detecting the present rotor angle and/or the present rotational speed only functions once a minimum rotational speed—the working rotational speed ADZ—of the rotor26has been reached. The sensorless principle does not function below the working rotational speed ADZ.

In order to achieve the working rotational speed ADZ, the control unit7has the start-up mode in which the control unit7can increase the rotational speed of the rotor26up to the minimum rotational speed (in particular starting from a standstill of the rotor26) without detecting and/or taking into account the rotor angle and/or the rotational speed for this purpose. The control unit7is expediently designed to carry out the control of the electric motor6in the start-up mode without detecting and/or taking into account the present rotor angle of the electric motor6and/or the present rotational speed of the electric motor6. In particular, in the start-up mode, an “open-loop” control—i.e., in particular, a pure open-loop control (and no closed-loop control)—of the rotational speed of the rotor26is performed. The rotational speed ramp DR is not subject to any closed-loop control. Preferably, the control unit7determines the slope and/or current strength for the start-up mode in advance. In particular, the control unit7does not perform any adjustment of the slope of the rotational speed ramp and/or any change of the current strength, in particular of the amplitude, of the motor current MI during the execution of the rotational speed ramp.

FIG.4shows a diagram in which the rotational speed DZ of the rotor26is plotted versus the time t. The diagram includes a first rotational speed ramp DR1and a second rotational speed ramp DR2as examples of the rotational speed ramp DR. The explanations relating to the rotational speed ramp DR expediently apply to the first rotational speed ramp DR1and/or the second rotational speed ramp DR2. The rotational speed ramp DR is preferably monotonically increasing, in particular strictly monotonically increasing. Exemplarily, the rotational speed ramp DR is a straight line. In particular, the rotational speed ramp DR has a constant slope. The rotational speed ramp DR expediently starts at a rotational speed of 0 and runs at least up to the working rotational speed ADZ. The rotational speed ramp DR expediently comprises a temporal sequence of rotational speed values. The rotational speed values are shown inFIG.4as points lying on the rotational speed ramps DR1, DR2. The control unit7is designed in particular to provide a respective drive information AI for each rotational speed value, and to provide respective motor currents MI1, MI2, MI3on the basis of the respective drive information AI. Expediently, the control unit7is designed to provide the motor currents MI1, MI2, MI3with a continuously increasing frequency, so as to achieve a continuous increase in the rotational speed of the rotor26in accordance with the rotational speed ramp DR.

Expediently, the rotational speed ramp DR is already completely defined in the control unit7before the start of the rotational speed ramp DR—i.e. before the control unit7drives the electric motor6in accordance with the rotational speed ramp DR. For example, the rotational speed ramp DR, in particular the rotational speed values of the rotational speed ramp DR, is stored in the control unit7, and preferably before the control unit7drives the electric motor6according to the rotational speed ramp DR. Furthermore, it is possible that ramp information is stored in the control unit7(in particular before the start of the rotational speed ramp DR), by which the rotational speed ramp DR is determined. For example, the ramp information defines the slope of the rotational speed ramp DR. In particular, the ramp information comprises a ramp increment RI that describes, for example, the rotational speed difference between two rotational speed values that directly follow one another in time in the rotational speed ramp DR. Expediently, the rotational speed values are equally spaced apart in time.

Preferably, the control unit7is configured to switch from the start-up mode to the working mode when the working rotational speed ADZ is reached and to perform the driving of the electric motor6in the working mode using a sensorless principle, in particular using a Back-EMF principle, for determining a present rotor angle and/or a present rotational speed of the electric motor6. In particular, the control unit7performs closed-loop rotational speed control once the working rotational speed ADZ is reached. Provided that the target rotational speed SDZ is greater than the working rotational speed ADZ, the rotational speed can be further increased after reaching the working rotational speed ADZ in the working mode until the target rotational speed SDZ is reached. The further increase can be carried out with the same slope as the rotational speed ramp or with a different slope, as an example.

An internal mechanical load acts on the rotor26, which internal mechanical load counteracts the increase in the rotational speed of the rotor26and which internal mechanical load must be overcome in the start-up mode in order to be able to increase the rotational speed of the rotor26up to the working rotational speed ADZ. In particular, the internal mechanical load acting on the rotor26is temperature dependent, in particular such that the internal mechanical load decreases as the temperature increases and increases as the temperature decreases.

Exemplarily, the temperature-dependent internal mechanical load is the moment of inertia acting on the rotor26. In particular, this moment of inertia is dependent on the braking effect, expediently the braking force, of the braking device34. With a stronger braking effect, in particular with a stronger braking force, the moment of inertia acting on the rotor26is lower than with a weaker braking effect, in particular a weaker braking force. In particular, this is because the tool5is rotated less quickly about the tool rotation axis33(in particular, less quickly than the rotational speed of the rotor26) due to the greater braking effect. With a lower braking effect, in particular with a lower braking force, the moment of inertia acting on the rotor26is greater than with a stronger braking effect, in particular a greater braking force. This is due in particular to the fact that the tool5is rotated more quickly about the tool rotation axis33(for example, at the rotational speed of the rotor26) as a result of the lower braking effect.

Exemplarily, the braking effect, in particular the braking force, of the braking device34is temperature dependent. For example, the coefficient of friction provided with the braking element37is temperature dependent. For example, the braking effect, in particular the braking force, preferably the coefficient of friction increases with increasing temperature and decreases with decreasing temperature.

The control unit7is expediently configured to take this temperature dependence into account in the startup mode and, in particular, to compensate for it.

Preferably, the control unit7is configured to set the slope of the rotational speed ramp DR based on the detected temperature. For example, the control unit7is configured to set a higher slope of the rotational speed ramp DR at a higher detected temperature and to set a lower slope of the rotational speed ramp DR at a lower detected temperature.

In particular, the control unit7is configured to selectively set a first rotational speed ramp DR1with a first slope or a second rotational speed ramp DR2with a second slope on the basis of the detected temperature and to use the set rotational speed ramp for the startup mode. In an example, the second slope is smaller than the first slope.

In particular, the control unit7is configured to set the first rotational speed ramp DR1for the startup mode in response to the fact that the detected temperature is in a first temperature range, and to set the second rotational speed ramp DR2for the startup mode in response to the fact that the detected temperature is in a second temperature range. The temperatures contained in the first temperature range are expediently higher than the temperatures contained in the second temperature range. The first and second temperature ranges are preferably non-overlapping.

Expediently, the first rotational speed ramp DR1and the second rotational speed ramp DR2are completely defined in the control unit7, in particular before the start-up mode is performed. For example, the rotational speed ramps DR1, DR2, in particular the respective rotational speed values of the rotational speed ramps DR1, DR2are stored in the control unit7, preferably before the control unit7drives the electric motor6according to the selected rotational speed ramp. Furthermore, it is possible that a first ramp information and a second ramp information are stored in the control unit7(in particular before driving the electric motor6according to the selected rotational speed ramp). The first ramp information defines the first rotational speed ramp DR1, in particular its slope, and the second ramp information defines the second rotational speed ramp DR2, in particular its slope. Exemplarily, the first ramp information comprises a first ramp increment RI1and the second ramp information comprises a second ramp increment RI2. The first ramp increment RI1describes, for example, the rotational speed difference between two rotational speed values that directly follow each other in time in the first rotational speed ramp DR1. The second ramp increment RI2describes, for example, the rotational speed difference between two rotational speed values that directly follow each other in time in the second rotational speed ramp DR2. For example, the first ramp increment RI1is larger than the second ramp increment RI2.

Expediently, the control unit7is designed to selectively choose the first ramp information or the second ramp information based on the detected temperature and to generate the rotational speed ramp for the start-up mode based on the selected ramp information.

Preferably, the control unit7is configured to set the current strength of the motor current MI on the basis of the detected temperature. The current strength is set on the basis of the detected temperature in particular as an alternative to or in addition to the setting of the slope of the rotational speed ramp DR on the basis of the detected temperature explained above.

Preferably, the control unit7is configured to set the motor current MI with a lower current strength, in particular smaller amplitude, for a higher detected temperature and to set the motor current MI with a higher current strength, in particular larger amplitude, for a lower detected temperature. In particular, the control unit7is configured to set the first motor current MI1, second motor current MI2and third motor current MI3respectively with a higher current strength, in particular a larger amplitude, for a higher detected temperature, and to set them with a lower current strength, in particular a smaller amplitude, for a lower detected temperature.

In particular, the control unit7is configured to set the current strength, in particular the amplitude, of the motor currents MI1, MI2, MI3to a first value in response to the detected temperature being in a first temperature range and to set the current strength, in particular the amplitude, of the motor currents MI1, MI2, MI3to a second value in response to the detected temperature being in a second temperature range. The second value is expediently larger than the first value. The temperatures contained in the first temperature range are expediently higher than the temperatures contained in the second temperature range. The first and second temperature ranges are preferably non-overlapping.

Preferably, the start-up mode is configurable via the mobile device4. For example, via the mobile device4it is possible to activate and/or deactivate the consideration of the temperature when setting the slope of the rotational speed ramp DR and/or the strength of the motor current MI, in particular by an input of the user. Furthermore, it is expediently possible via the mobile device4to set the slope of the rotational speed ramp DR and/or the strength of the motor current MI, in particular by an input of the user.

Alternatively or additionally, it is preferably possible to configure the start-up mode via the operating device12, in particular in the aforementioned manner.

Preferably, the power tool2is operated according to the following method:

In a first step, the power tool2is switched on, in particular via the operating device12.

In a second step, a first temperature is detected, in particular with the first temperature sensor18. The detected first temperature is in particular an ambient temperature of the power tool2. The detected first temperature is preferably not a motor temperature of a running electric motor.

In a third step, the control unit7sets a first slope of a rotational speed ramp DR for the startup mode on the basis of the detected first temperature. Alternatively or additionally, the control unit7sets a first current strength, in particular a first amplitude, of the motor current MI for the startup mode on the basis of the detected first temperature.

In a fourth step, the control unit7provides the start-up mode with the set first slope of the rotational speed ramp DR and/or the set first current strength of the motor current MI. The rotational speed of the rotor26is increased according to the rotational speed ramp DR, at least until the working rotational speed ADZ is reached.

In an optional fifth step, the power tool2is switched off (in particular via the operating device12) and the rotational speed of the rotor26drops below the working rotational speed ADZ.

In an optional sixth step, the power tool2is switched on again.

In an optional seventh step, a second temperature is detected, in particular with the first temperature sensor18. The second temperature detected in the seventh step differs exemplarily (in its value) from the first temperature detected in the second step.

In an optional eighth step, the control unit7sets a second slope of the rotational speed ramp DR for the startup mode on the basis of the detected second temperature. Alternatively or additionally, the control unit7sets a second current strength, in particular a second amplitude, of the motor current MI for the startup mode on the basis of the detected second temperature. The second slope and/or second current strength set in the eighth step is expediently different from the first slope and/or first current strength set in the third step.

In an optional ninth step, the control unit7provides the start-up mode with the set second slope of the rotational speed ramp DR and/or the set second current strength of the motor current MI. The rotational speed of the rotor26is increased according to the rotational speed ramp DR, at least until the working rotational speed ADZ is reached.

In particular, the aforementioned steps are carried out sequentially in time, and in the order in which they are explained above.