METHOD FOR CONTROLLING AN ELECTRIC MOTOR OF A POWER TOOL

Description

[0001] The invention relates to a method for controlling an electric motor of a power tool according to claim 1, and a control unit according to claim 7. State of the art

[0002] It is known from the prior art to control the electric motor of a power tool depending on the actuation of a switch. The electric motor is controlled, for example, with a predetermined speed or torque. For instance, EP 1 510 299 A2 discloses a power tool that stores a selected operating mode depending on the direction of rotation and automatically restores it. WO 2011 / 122361 A1 discloses an impact tool that adjusts its impact frequency based on the measured motor current. Furthermore, JP H10 80828 A discloses a method that verifies the engagement of a tool by detecting a motor standstill at low torque before a loosening process is initiated. US 2002 / 134172 A1 further discloses a method for screwdrivers that ensure controlled loosening by monitoring the loosening angle, load torque, or the onset of free rotation.

[0003] The object of the invention is to provide an improved method for controlling the electric motor and an improved control unit. In a non-inventive embodiment, the object is further to provide an improved power tool. Disclosure of the invention

[0004] The object of the invention is solved by the method according to claim 1, and a control unit according to claim 7.

[0005] In a non-inventive embodiment, an advantage of the described method is that at least one parameter—the current of the electric motor and / or its rotational speed—is detected during impact operation, and a drive time for the impact operation is determined based on the detected parameter. This results in improved control of the electric motor, adapted to the specific tool. Consequently, the operation of the power tool is simplified.

[0006] In a further embodiment not according to the invention, the electric motor is operated in pulse mode for the defined drive time, and after the drive time, at least one torque or one speed of the electric motor is reduced. A clutch can be used to reduce the torque at the drive, or the electric motor can be switched off. For example, the electrical voltage supplied to the electric motor is reduced accordingly.

[0007] In a non-inventive embodiment, a torque and / or a speed can be set, depending on the detected parameter, with which the electric motor is driven during impact operation. This results in improved use of the power tool.

[0008] Preferably, a standard deviation of the electric motor current and / or the electric motor speed during a pulse operation of the electric motor is recorded as a parameter.

[0009] In a non-inventive embodiment, a calculation method and / or a table and / or a characteristic curve will be used to determine the control time and / or the torque and / or the speed for controlling the electric motor, depending on the parameter.

[0010] In a further embodiment not according to the invention, the electric motor is supplied with power by a battery, the battery voltage being determined, and the parameter being evaluated using the determined battery voltage, particularly when the battery voltage falls below a limit value. This allows a drop in battery voltage to be compensated for by evaluating the parameter.

[0011] In a further embodiment not according to the invention, the battery voltage and the drive time are corrected depending on the measured battery voltage. In another embodiment not according to the invention, the battery voltage is detected, compared with a reference value, and the drive time is corrected depending on a ratio of the measured battery voltage to the reference value. In this way, the magnitude of the control signal to the electric motor is compensated for a changing battery voltage. This further refines the driving of the electric motor.

[0012] In a further embodiment not according to the invention, a notification is issued to the operator when a measured battery voltage falls below a predefined limit. This ensures that the operator is alerted to the low battery voltage and the associated reduced drive power of the power tool. The notification can also include information that a predefined drive time should be adjusted due to the low battery voltage. If the operator has set the drive time, the notification allows them to adjust it if the battery voltage changes too drastically or falls below a predefined limit.

[0013] In a further embodiment not according to the invention, the drive time for a hammer operation is entered by an operator. The drive time is stored and taken into account by the control circuit when the electric motor is activated. This embodiment offers the advantage that the drive time does not have to be determined automatically, but can be easily set by the operator. The drive time refers to the time a screw is driven into a workpiece during a hammer operation before the torque of the electric motor is reduced, a clutch is opened, or the electric motor is completely switched off. In this way, damage to the tool, especially the screw, can be avoided. Furthermore, the workpiece can be protected from damage by preventing the screw from being driven in too deeply.In particular, the fastening of the screw in the workpiece can be improved by preventing the screw thread from slipping in the workpiece by setting the drive time during impact operation.

[0014] In a further embodiment not according to the invention, the electric motor is stopped if a predetermined torque is not reached when unscrewing a screw. The insufficient torque indicates a loosened screw. This ensures that the loosened screw is not completely unscrewed from the workpiece, but remains embedded. This reduces the risk of the screw being lost.

[0015] In a non-inventive embodiment, the delivered torque is detected by measuring the current drawn by the electric motor, with the electric motor being stopped when the current falls below a predetermined limit. The low current draw indicates that the screw turns easily, i.e., that it is already loose.

[0016] In a non-inventive embodiment, the electric motor stops when unscrewing a screw after the screw has been unscrewed a predetermined number of turns from a seated position following activation of the electric motor. Preferably, the number of turns can be set by an operator, for example, by inputting a value. This also reduces the risk of the screw being lost during unscrewing. Furthermore, it improves the handling of the power tool.

[0017] According to the invention, the method for controlling an electric motor of an electric tool with a holder for a tool for unscrewing a screw from a counterpart, wherein different control methods are used for unscrewing the screw or the workpiece depending on a seating torque of the screw.

[0018] In a further embodiment, depending on a speed of the electric motor specified by an operator and / or depending on the speed of actuation of a switch to specify the speed, different control methods for unscrewing the screw are selected.

[0019] In a further embodiment, the electric motor is controlled in a first phase according to a predetermined speed, wherein the current of the electric motor is detected during the first phase, wherein the detected current is compared with a limit value, wherein if the limit value is exceeded the electric motor is controlled during a subsequent second phase at a predetermined second speed, wherein the current of the electric motor is detected during the second phase, wherein, depending on the detected current of the second phase, a loosened screw is detected and the speed of the electric motor is at least reduced or stopped, and wherein the limit value depends on the seat torque and / or on the speed specified by the operator.

[0020] In one embodiment, the electric motor is controlled in a first phase according to a speed specified by an operator, wherein a time period is recorded, in particular by means of a counter, during which the electric motor remains in the first phase, wherein if a specified time period, in particular a counter reading, is exceeded, the electric motor is controlled during a subsequent second phase at a specified second speed, in particular at a maximum speed, wherein the current of the electric motor is recorded during the second phase, wherein, depending on the recorded current of the electric motor during the second phase, a loosened screw is detected and the speed of the electric motor is at least reduced or the electric motor is stopped.

[0021] According to the invention, depending on whether a predetermined current limit is undershot and / or depending on whether a predetermined negative time gradient is exceeded, a loosened screw is detected and the speed of the electric motor is at least reduced or the electric motor is stopped.

[0022] In another version, the seating torque of the screw is estimated based on the current drawn by the electric motor.

[0023] The described procedures can also be applied to unscrewing bolts, nuts, or other screwed parts.

[0024] The invention will be explained in more detail below with reference to the figures. They show Figure 1 a schematic cross-section through a power tool, Figure 2 a second cross-section through the power tool, Figure 3a schematic representation of a circuit arrangement for driving an electric motor of a power tool, Figure 4 a first schematic program sequence for operating the power tool, Figure 5 a second schematic program sequence for operating the power tool, Figure 6 a third schematic program sequence for operating the power tool, Figure 7 a fourth schematic program sequence for operating the power tool, Figure 8 a fifth schematic program sequence for operating the power tool, Figure 9 a sixth schematic program sequence for operating the power tool, Figure 10 a schematic representation of the time course of the current I for the electric motor when a screw is unscrewed, Figure 11 in a schematic representation a program sequence with which the unscrewing of a screw from a workpiece is influenced, and Figure 12 in a diagram the current I over time t for different methods for automatically unscrewing a screw.

[0025] Figure 1Figure 10 shows a schematic representation of a power tool 10 in the form of an impact wrench 10. The impact wrench 10 has a housing 11 comprising a cylindrical main body 12 and a handle 15 attached to it. A battery 19 is arranged opposite the main body 12. An electric motor 20, in the form of a brushless DC motor 20, is arranged in the main body 12. This motor includes a planetary gear 24, a spindle 25, an impact mechanism 26, and an anvil 27. The electric motor 20 serves as the drive source for the rotating impact mechanism 26. The speed of the electric motor 20 is reduced by means of the planetary gear 24 and then transmitted to the spindle 25. The rotational force of the spindle 25 is converted into a rotating impact force by the impact mechanism 26, for which a hammer 26h and a compression spring 26b are provided.The impact force of the hammer 26h is transferred to the anvil 27. The anvil 27 is rotatably mounted about an axis and is driven by the rotational impact force of the hammer 26h. The anvil 27 is rotatably held in the housing 11 by a bearing 12j, which is located on a front side of the main body 12. Thus, the anvil 27 can rotate about the axis of rotation but cannot move along it. A receptacle 27t is provided on a front side of the anvil 27 to accommodate, for example, a drill bit 60 or, via an insert, a screw 61. The drill bit 60 or the screw 61 constitutes the tool that is driven by the power tool.

[0026] The handle 15 of the housing 11 is gripped by an operator to use the power tool 10. The handle has a holding section 15h and a lower end section 15p, which connects to the lower end of the handle section 15h. The battery 19, which supplies power to the power tool 10, is located at the lower end section 15p. A main switch 18 is provided on the handle section 15h, which has a trigger 18t that can be actuated with a finger. The main switch 18 also has a switch unit 18s, which is used to switch the power tool on or off. The trigger 18t is used to increase the control signal to the electric motor 20 depending on the actuation distance of the trigger 18t. The trigger acts as a switch for setting the speed of the electric motor.The actuation path of the trigger 18t is detected, for example, as a resistance value using the switch unit 18s and sent to a control circuit (46, . Fig.3 ) reported. If the resistance value of the switch unit 18s of the main switch 18 changes according to the engagement state of the trigger switch 18t, then the control circuit (46, Fig.3 ) e.g. a speed of the control of the electric motor 20. In this way the speed and / or torque of the electric motor 20 can be controlled.

[0027] Furthermore, a direction switch 17 is provided above the main switch 18, which determines the direction of rotation of the holder 27t depending on its position. The direction switch 17 can be designed as a slide switch or a rotary switch. In a first position of the direction switch 17, the power tool 10 rotates clockwise when the main switch 18 is simultaneously actuated, i.e., in normal operation, e.g., for tightening a screw. In a second position of the direction switch 17 and when the main switch 18 is simultaneously actuated, the power tool 10 rotates counterclockwise in unscrewing or loosening mode for unscrewing or loosening a screw.

[0028] In addition, the power tool may have a switch 70. The switch 70 may be designed as a rotary or slide switch. The position of the switch 70 is controlled by the control circuit (46, Fig.3 ) reported. In a first position of the switch 70, when a screw is unscrewed, i.e., in a second position of the direction switch 17 and actuation of the main switch 18, a method for loosening a screw is carried out in which the unscrewing of the screw is influenced depending on at least one parameter. In particular, an automatic method is carried out in which a desired loosening state of the screw is to be achieved. Specifically, the screw should not be completely removed from the screw connection so that, for example, the screw is not lost. Depending on the chosen design, an indicator 71 can be provided that shows whether the automatic method for unscrewing a screw is activated. The indicator can be in the form of a lamp or an LED. The indicator can, for example, be integrated into the switch 70.

[0029] Furthermore, when loosening or unscrewing a screw, an automatic procedure for loosening a screw is initiated in the first position of switch 70.

[0030] Fig. 2A further cross-section shows additional details of the power tool 10. The hammer 26h of the impact mechanism 26 is connected to the spindle 25 via V-shaped first guide grooves 25v, V-shaped second guide grooves 26z, and steel balls 25r. The first guide grooves 25v are arranged on the outer surface of a front face of the spindle 25. These first guide grooves 25v have semicircular sections with the V-shaped openings facing outwards. Furthermore, the V-shaped second guide grooves 26z are arranged on an inner surface of the hammer 26h, opposite the first guide grooves 25v of the spindle 25. The second guide grooves 26z have a semicircular cross-section and open in a forward direction. The steel balls 25r are arranged between the first guide grooves 25v and the second guide grooves 26z.As a result, the hammer 26h is mounted to rotate about a predetermined angle with respect to a reference position of the spindle 25 and is able to move axially relative to a longitudinal axis of the spindle 25. Furthermore, the compression spring 26b is in contact with the outer surface of the spindle 25 and the hammer 26h, so that the hammer 26h is biased towards the spindle 25.

[0031] Striking projections 26w are formed on a front end face of the hammer 26h to generate impacts on the anvil 27 at two points offset by 180° from each other. Furthermore, the anvil 27 has striking arms 27d in the circumferential direction at the two points offset by 180° ( Fig.2The hammer 26h is formed by the preload force of the compression spring 26b, which receives the impacts of the striking projections 26w of the hammer 26h. The hammer 26h is held against the spindle 25 by the preload force of the compression spring 26b, so that the striking projections 26w of the hammer 26h bear against the striking arms 27d of the anvil 27. When the spindle 25 is rotated by the electric motor 20 in this state, the hammer 26h rotates together with the spindle 25, and the rotational force of the hammer 26h is transmitted to the anvil 27 via the striking projections 26w and the striking arms 27d. In this way, for example, a screw can be driven into a workpiece in impact mode.

[0032] As the screw is tightened, it can reach a position in the workpiece where the tightening resistance exceeds the torque of the hammer 26h. This tightening resistance is transmitted as torque to the anvil 27. As a result, the hammer 26h is retracted from the spindle against the preload force of the compression spring 26b, and the striking projections 26w of the hammer strike the striking arms 27d of the anvil 27. This releases the striking projections 26w from contact with the striking arms 27d, allowing them to rotate freely through a defined angle. As the striking projections 26w of the hammer 26h move over the striking arms 27d of the anvil 27, the hammer accelerates its rotation. The preload force of the compression spring 26b pushes the hammer 26h back towards the anvil 27 within the specified angle, so that the striking projections 26w of the hammer come back into contact with the striking arms 27d of the anvil 27.The impact of the striking projections 26w onto the striking arms 27d exerts an increased torque on the anvil 27 and thus on the holder 27t and the screw 61 or the drill bit 60. This process is continuously repeated during impact operation.

[0033] Furthermore, the power tool 10 can have an input unit 50 with which a user of the power tool can, for example, enter the maximum drive time for the electric motor, in particular the maximum drive time of the electric motor for impact operation. In addition, a user can enter a parameter for a size of the tool, in particular a diameter for a screw or a drill bit. The input unit 50 is connected to the electronic control circuit (46, Fig. 3 ) and / or with a memory (51, Fig. 3 ) tied together.

[0034] Figure 3 shows a schematic diagram of the circuit arrangement of the power tool 10. Figure 1for controlling the electric motor 20, which is designed, for example, as a brushless DC motor and is driven by a control circuit 40. The electric motor 20 has a rotor 22 with permanent magnets and a stator 23 with drive coils 23C. The control circuit 40 is an electrical circuit for controlling the electric motor 20 and has a three-phase bridge circuit 45, which has six switching elements 44, for example, in the form of field-effect transistors. Furthermore, a control circuit 46 is provided, which controls the switching elements 44 of the three-phase bridge circuit 45 depending on the switching unit 18s.

[0035] The three-phase bridge circuit 45 has three output lines 41, which are connected to the corresponding control coils 23c of the electric motor 20. The control circuit 46 is designed to control the switching elements 44 based on signals from magnetic sensors 32, such that an electric current flows sequentially through the drive coils 23c to rotate the rotor 22 at a desired speed and / or torque. The control circuit 46 can also measure the rotational speed of the electric motor 20 using the magnetic sensors 32. Furthermore, the control circuit 46 is connected to a measuring device 53, which detects the state of charge of the battery 19, in particular the voltage of the battery 19, and transmits this information to the control circuit 46. The control circuit 46 is connected to the switch 70.

[0036] Furthermore, the power tool has an input unit 50, which allows the user to input, for example, the maximum drive time for impact operation and / or a size, in particular a diameter, for a screw or drill bit. The input unit 50 is connected to the electronic control circuit 46. The electronic control circuit 46 is also connected to a memory 51. Data, characteristic curves, maps, and / or calculation methods are stored in the memory 51. The power tool also has an output 52, which can send a signal to the user, in particular a warning signal about a low battery charge. A limit value for the battery charge level is stored in the memory 51 for this purpose. The control circuit 46 uses the measuring device 53 to detect the current voltage of the battery 19 and compares the measured voltage with the limit value.If the charge level of battery 19 falls below the limit value, the control circuit 46 issues a corresponding warning visually, audibly, and / or haptically via output 52. Furthermore, the user can deactivate the automatic operation of the electric motor 20 by entering a corresponding command.

[0037] Furthermore, the control circuit 46 can detect the type of battery 19, which is indicated, for example, by a code on the battery, using a sensor, in particular an optical sensor. The type of battery 19 determines the battery voltage that corresponds to a sufficient state of charge. The memory 51 can store corresponding voltage thresholds for different codes or battery types, corresponding to a sufficient charge of the battery 19 for normal operation, especially for emergency operation. To determine the state of charge, the control circuit 46 uses the measuring device 53 to measure the charging voltage of the battery 19 and compares it with the stored thresholds. Preferably, the battery type can be taken into account to read precise thresholds for a sufficient state of charge of the battery 19 from the memory 51.Furthermore, the control circuit 46 can measure the current of the electric motor 20 with an ammeter 54 and / or the speed of the electric motor 20 with a tachometer 29. The current and / or speed can be used by the control circuit 46 to determine when the impact mode of the power tool begins. For this purpose, corresponding thresholds or limit values ​​for the current and speed of the electric motor are stored in the memory 51, which the electric motor 20 exceeds when an impact mode starts. The control circuit 46 is designed to determine a drive time for an impact mode depending on a detected parameter of the electric motor, in particular depending on the current and / or speed. The state of charge of the battery is preferably also taken into account. A characteristic map, a characteristic curve, a table, or a corresponding calculation method is used to determine the drive time.The characteristic map, curve, table, or calculation method defines a relationship between the current and / or rotational speed and the drive time. At the end of the drive time, i.e., at the end of the impact operation, the electric motor 20 is stopped by the control circuit 46, or an electronic clutch is engaged for a short period, and then the electric motor is completely stopped. The determined parameter for the tool size, in particular the diameter of the drill bit and / or screw, is stored in memory and used by the control circuit 46 for further drilling or screwdriving operations.

[0038] In a first embodiment, based on a first program sequence of the Figure 4As explained, the control circuit 46 determines a parameter at the start of an impact operation that depends on the size of the tool, in particular the diameter of a screw or drill bit, preferably within a predetermined initial time period. This initial period can last from the start of the impact operation, for example, up to 100 or 200 milliseconds or longer. Parameters such as the current and / or the speed of the electric motor are measured at defined intervals during this initial period. The measured values ​​for the electric motor current and / or speed are preferably filtered to remove unwanted error data. The speed and / or current are then used to determine a value, in particular a drive time, for controlling the electric motor, based on tables.Instead of a table, another calculation method and / or a characteristic curve can be used to determine the size for controlling the electric motor.

[0039] Furthermore, the magnitude of the electric motor's control signal can be determined in two other ways. A first method calculates a standard deviation of the measured current values ​​and / or a standard deviation of the measured rotational speed values ​​during the initial duration of the electric motor's control, particularly during the first 200 milliseconds after the electric motor 20 begins to operate.

[0040] The standard deviation can be calculated using the following formulas: The standard deviation σX a random variable X is defined as the square root of the variance Var( X ): σ X : = Var X .

[0041] The variance is Var X = E X − E X 2 = E X 2 − E X 2 from Xalways greater than or equal to 0. The symbol E(·) denotes the expected value.

[0042] In a second calculation method, the initial time period is divided into a predetermined number of sub-intervals, for example, ten sub-intervals. Then, for each sub-interval, a standard deviation is calculated for the measured values ​​of current and / or rotational speed. Finally, an average standard deviation for current and / or rotational speed is determined from these ten standard deviations by averaging them.

[0043] The standard deviation and / or the mean standard deviation of the speed and / or current are used to determine a control parameter for the electric motor using tables. Alternatively, another calculation method and / or a characteristic curve can be used to determine the control parameter for the electric motor.

[0044] The parameter can, for example, be the drive time used to power the electric motor. For instance, the drive time can define the duration the electric motor is powered when the button is pressed to drive a screw. After the drive time, the voltage supply to the electric motor 20 is reduced or cut off. The drive time is the duration the electric motor is powered during the impact operation of the power tool, specifically to drive a screw into a workpiece. Furthermore, the parameter controlling the electric motor can relate to a maximum speed and / or a maximum torque and / or a maximum current.

[0045] The program starts at program point 400. At the subsequent program point 410, it checks whether the rotational speed n is above a predefined limit W and whether the current i is above a predefined limit I. If both conditions are not met, program point 410 is executed again. If the check reveals that the rotational speed n is greater than the limit W and that the current i of the electric motor is greater than the limit I, the program branches to program point 420. The check at program point 410 verifies whether the power tool is already in a defined operating state, e.g., in impact mode, in which the hammer repeatedly strikes the anvil. Corresponding limit values ​​W and I are defined for the rotational speed and current and stored in memory 51. After the defined operating state is detected, the drive time for controlling the electric motor, specifically for impact mode, is started.

[0046] For example, it can be verified whether impact mode is active by checking if the time interval between two impacts is less than a first threshold. This first threshold can be in the range of 0.01 seconds to 0.05 seconds and is stored in memory 51. The impacts can be detected acoustically using sound sensors or by monitoring the current flow through the electric motor. Additionally, it can be checked whether a standard deviation of the measured rotational speed is less than a second threshold. This second threshold can be in the range of 30 to 90 and is also stored in memory 51. If both conditions are met, impact mode of the power tool is clearly identified. The thresholds are determined experimentally and can vary from one power tool to another, depending, for example, on the type of electric motor.

[0047] Furthermore, the program preferably branches automatically from program point 410 to program point 420 if a predetermined first period of time has elapsed since the operation of the electric motor, in particular since the start of the impact operation of the power tool, even if the conditions of program point 410 are not met.

[0048] In program step 420, at least one parameter of the electric motor is determined based on the measured values ​​for the current and / or the measured values ​​for the speed of the electric motor during an initial period. For example, the current and / or the speed of the electric motor are measured at defined time intervals during this initial period. This initial period can last, for example, from the start of the impact operation until 200 milliseconds after the start of the impact operation. The determined current and / or the determined speed and / or the standard deviation of the speed and / or the current and / or the average standard deviation of the speed and / or the current are calculated as described above and used to determine a control parameter for the electric motor using tables.Instead of a table, another calculation method and / or a characteristic curve can be used to determine the size for controlling the electric motor.

[0049] For example, depending on the parameter, a drive time of the electric motor during impact operation is defined. When the power tool is activated, particularly by pressing a switch, the electric motor is driven for the defined drive time, for example, to drive a screw into a workpiece using impact mode. The drive time may be extended by the initial duration, as the drive time is only calculated after this initial duration.

[0050] Furthermore, depending on the parameter, a torque and / or speed can be specified at which the electric motor is driven when the power tool is activated, particularly when a switch is pressed in impact mode. In one version, corresponding tables, characteristic curves, or formulas are stored to determine values ​​for the current and / or speed of the electric motor during impact operation, depending on the measured parameter.

[0051] Furthermore, the recorded parameter can be evaluated depending on the battery voltage of the power tool, especially if the battery voltage is below a specified limit.

[0052] For example, parameters such as a standard deviation of the current, and / or a mean standard deviation of the current, and / or a standard deviation of the rotational speed, and / or a mean standard deviation of the rotational speed are used. Furthermore, the parameter can be evaluated in relation to the battery's state of charge before a value for the electric motor's electrical control is determined based on the parameter(s).

[0053] Furthermore, the drive time during operation can be determined, for example, as a function of the standard deviation of the current, and / or as a function of the mean standard deviation of the current, and / or as a function of the standard deviation of the rotational speed, and / or as a function of the mean standard deviation of the rotational speed. For example, the battery's state of charge is also taken into account when determining the drive time. To determine the drive time, i.e., the duration of the drive time during operation, a characteristic map, a characteristic curve, or a corresponding calculation method is used, which determines the drive time as a function of the standard deviation of the current, and / or as a function of the mean standard deviation of the current, and / or as a function of the standard deviation of the rotational speed, and / or as a function of the mean standard deviation of the rotational speed.In addition, the battery's state of charge is taken into account. The determined driving time is stored in memory 51.

[0054] For example, the control circuit 46 can check whether, during a first time period at program point 420, the standard deviation of the current is greater than a first limit value X1 and / or whether the standard deviation of the rotational speed is greater than a first limit value Y1. If these conditions are not met, the program branches to program point 430 and the electric motor 20 is driven at a medium speed.

[0055] For example, the control circuit 46 can check whether, during a first time period at program point 420, the mean standard deviation of the current is greater than a second limit value X2, and / or whether the mean standard deviation of the rotational speed is greater than a second limit value Y2. If both conditions are not met, the program branches to program point 430 and the electric motor 20 is driven at a mean speed.

[0056] If the queries at program point 420 are met, the program branches to program point 440 and the electric motor 20 is driven at a high speed.

[0057] The program then branches to point 450. A high speed at point 440 is required to provide sufficiently high torque for a tool with a large diameter. Conversely, a medium speed at point 430 ensures that a tool with a smaller diameter does not break.

[0058] At program point 450, it is checked whether the determined drive time of the electric motor has been reached during the impact operation of the power tool. If so, at program point 460, the torque of the electric motor is reduced, a clutch is opened, or the electric motor is switched off. Similarly, during operation at a medium speed or rotational speed of the drive according to program point 430, at program point 450, it is checked whether the determined drive time has been reached during the impact operation of the power tool. If so, at program point 460, the torque of the electric motor is reduced, a clutch is opened, or the electric motor is switched off.

[0059] Depending on the chosen embodiment, other methods or calculation techniques can also be used to determine a parameter for controlling the electric motor, in particular a drive time for impact operation, based on the current and / or speed during the impact operation of the power tool. Furthermore, depending on the chosen design, the different speeds can be omitted, and the electric motor can be operated at a predetermined speed and / or torque during impact operation.

[0060] Figure 5Figure 5 shows another embodiment of the method. The program starts at program point 500. The power tool has an input unit 50, which an operator can use to enter a tool size, in particular the diameter of a drill bit or screw. The entered size is stored in memory 51. Preferably, the battery charge level is also determined at program point 500 when the program starts. Subsequently, at program point 510, it is checked whether the rotational speed n is greater than a first limit value W, and whether the current i of the electric motor is greater than a first limit value I. If both conditions are not met, program point 510 is executed again. Method step 510 determines whether the power tool is in a predefined operating state, in particular in impact mode. The limit values ​​W and I for the rotational speed and current are selected accordingly.If the check at program point 510 shows that the rotational speed n is greater than the limit value W, and that the current i of the electric motor is greater than the limit value I, then a predefined operating state, in particular a shock operation, is detected and the program branches to program point 520.

[0061] In another version, it can be checked whether a pulse-width oscillation is occurring by determining whether the time interval between two pulses is less than a first threshold value. This first threshold value can be in the range of 0.01 seconds to 0.05 seconds. The first threshold value is stored in memory 51. The pulses can be detected acoustically, for example, using sound sensors, or determined by monitoring the current flow through the electric motor over time. Additionally, it can be checked whether a standard deviation of the measured rotational speed is less than a second threshold value.

[0062] The second limit value can be in the range between 30 and 90. This second limit value is stored in memory 51. If both conditions are met, impact operation of the power tool is clearly detected. The limit values ​​are determined experimentally and can vary from power tool to power tool, e.g., depending on the type of electric motor.

[0063] At program point 520, a drive time for the electric motor is determined based on the entered tool size. To determine the drive time, i.e., the duration of the drive cycle, a characteristic map, a characteristic curve, or a corresponding calculation method is used, which defines the drive time depending on the tool size.

[0064] At program point 520, the system also checks whether the entered value is larger than a stored second reference value. If the check at program point 520 shows that the entered value is not larger than the second reference value, the system proceeds to program point 530. For example, the second reference value could correspond to a diameter of 14 mm. At program point 530, the electric motor is driven at a medium speed.

[0065] If the check at program point 520 shows that the entered value is greater than the second comparison value, the program branches to program point 540. At program point 540, the electric motor is driven at a high speed. Subsequently, after both program point 530 and program point 540, a check is performed at program point 550 to determine whether the measured drive time during the specified operating state, particularly during impact operation, is greater than the calculated drive time. If this is not the case, the tool continues to be driven by the electric motor.

[0066] If the check at program point 550 shows that the measured drive time is greater than the determined drive time, then at program point 560 the torque of the electric motor is reduced, a clutch is opened or the electric motor is switched off.

[0067] As already mentioned in the program schedule of the Figure 4 In this process, a high speed is required for a tool, especially a drill bit or a screw with a large diameter, to generate sufficient torque. The higher the rotational speed, the greater the torque.

[0068] In another embodiment, which is described in Figure 6As shown, the program starts at program point 600, where an operator of the power tool has entered a drive time for a predefined operating state, in particular a drive time for impact operation, via input unit 50. The drive time can be stored in memory 51. The drive time can, for example, be in the range of 10 seconds. The program then branches to program point 610. At program point 610, it is checked whether the rotational speed n of the electric motor is greater than a first limit value W, and whether the current i for the electric motor is above a first limit value I.

[0069] Program point 610 can be used to determine whether a predefined operating state, in particular impact mode of the power tool, is present. The limit values ​​W and I are selected accordingly. Other methods can also be used to detect impact mode. If impact mode is detected, the electric motor is operated with a defined torque and / or speed for the operator-specified drive time, depending on the tool size, in particular the diameter of the drill bit or screw. Subsequently, program point 620 checks whether the specified drive time has elapsed. If so, the electric motor's torque is reduced, and in particular, the electric motor is switched off at the following program point 630.

[0070] In further embodiments, the drive time, torque and / or speed of the electric motor are used for the methods according to the Figures 4 to 6 The control circuit 46 adjusts the operation depending on the battery's state of charge. Corresponding calculation methods, characteristic maps, and / or characteristic curves are stored in memory 51 for this purpose. This ensures that, regardless of the battery's state of charge, a drill bit and / or screw is driven a predetermined number of turns into a workpiece or tightened with a predetermined torque.

[0071] In another embodiment, the control circuit 46 issues a warning signal when the voltage of the battery 19 falls below a predetermined minimum value stored in the memory 51. This ensures that the user of the power tool has the opportunity to recharge the battery or adjust the drive time, rotational speed and / or torque accordingly to achieve the desired drilling or screwing result.

[0072] Depending on the chosen embodiment, an electronic clutch is activated before the electric motor is switched off, reducing the torque to the tool, and then the electric motor is switched off. Preferably, the battery's state of charge is determined at each start of a program sequence, for example, by measuring the battery voltage.

[0073] Subsequently, at program point 620, the operation of the electric motor is stopped when the predefined drive duration is reached. In another embodiment, the user-defined drive duration can be increased depending on the battery's state of charge if its state of charge has decreased compared to the reference value. For example, the drive duration can be increased by the percentage by which the battery's state of charge falls below the reference value. Depending on the chosen embodiment, other magnitudes or methods for adjusting the drive duration based on the current state of charge of the battery can also be selected. Furthermore, the control circuit 46 can output a signal if the current state of charge of the battery falls below a predefined minimum threshold.

[0074] Figure 7This shows a fourth method for operating the power tool. After starting at program point 700, a subsequent program point 710 checks whether the electric motor is in a counterclockwise rotation state, i.e., in a screw-removal mode, where a screw is being unscrewed from a workpiece. If this is the case, a subsequent program point 720 monitors whether the electric motor's current, and thus its torque, falls below a reference value. If this occurs, the program jumps to program point 730 and stops the electric motor. Additionally, depending on the selected embodiment, a maximum time for unscrewing a screw can be used, which is measured after the screw-removal mode is detected. The maximum time is stored, for example, in memory 51. If the maximum time is reached, the program jumps from process step 720 to process step 730 and stops the electric motor.When unscrewing a screw, an impact action is first used to loosen the screw from the workpiece. After a certain duration of the impact action, the screw is loosened and the torque holding the screw in the workpiece decreases significantly. The current of the electric motor 20 also decreases accordingly. The decrease in current is detected by the control circuit 46 using the ammeter 54, and the control circuit 46 terminates the screw unscrewing process according to procedure step 720 after the maximum time has elapsed or after the current drops below the reference value.

[0075] In another embodiment, after the electric motor is activated to unscrew a screw from a workpiece, a predetermined number of revolutions can be set, after which the electric motor stops. For example, the number of revolutions can be set by an operator. For instance, three levels can be preset: low, medium, and high. The low level corresponds to, for example, 3 revolutions, the medium level to, for example, 5 revolutions, and the high level to, for example, 8 revolutions. The number of revolutions is measured, for example, by a sensor or determined based on the current curve of the electric motor.

[0076] Figure 8 shows a further embodiment of the method according to Figure 7, wherein the electric motor 20 is not immediately stopped by the control circuit 46 when a current below the reference value is detected at process step 720, but is first slowed down by a corresponding voltage supply to the drive coils 23c in a subsequent process step 740 and then stopped in a subsequent process step 730. In any case, the electric motor 20 is stopped at program point 730 after reaching the maximum specified time duration.

[0077] Figure 9 shows another embodiment of the Figure 7 , whereby after program point 720, instead of a simple braking process according to program point 740, Figure 8The rotational speed of the electric motor is reduced by the control circuit 46 according to a predefined speed profile by appropriately controlling the drive coils 23c, and then the electric motor is stopped at a subsequent program step 730. The speed profile of program step 750 can, for example, consist of a linear decrease in speed or a stepwise decrease in the speed of the electric motor 20. Depending on the selected embodiment, other speed profiles can also be used.

[0078] Figure 10This schematic diagram shows the current I of an electric motor during the unscrewing of a screw embedded in a workpiece. The current I of the power tool's motor can be used to determine the screw's tightness. Depending on the type of fastener, various methods can be used to automatically unscrew the screw. Three key phases of the current curve can be considered for determining the tightness.

[0079] At time zero t0, the electric motor is not activated. At the subsequent first time t1, the direction of rotation of the power tool is set to counterclockwise, i.e., to unscrew a screw. Furthermore, at time t1, the electric motor is activated by means of the main switch 18 or the trigger 18t to unscrew the screw. In this example, the screw is firmly driven into a workpiece with a high torque. Thus, when the electric motor is activated to unscrew the screw, the current to the electric motor rises rapidly and significantly in an initial phase shortly after activation, resulting in a current spike 72 shortly after time t1, which is detected by the ammeter. The current spike 72 indicates that a screw is being loosened that is driven into a workpiece with a high torque.The current drops from its peak value after a short time. At a second time point, t2, the impact mode of the power tool is activated to loosen the stuck screw. The operation of the impact mechanism can be identified by a ripple in the current waveform and by a current increase between the second time point, t2, and a third time point, t3. The impact operation between the second and third time points represents the second phase. After the third time point, t3, the current drops abruptly to a lower value. This current drop can be 20% or more. The abrupt current drop indicates a third phase, in which the screw is loosened and the impact mode is no longer active. In the third phase, the screw can be unscrewed from the workpiece with less torque compared to the impact mode.Thus, the current drop after the third time point t3 indicates that the screw can now be unscrewed without impact operation. Between the third time point t3 and a fourth time point t4, at which the current drops, the screw is unscrewed from the workpiece with minimal resistance. This typical current profile when unscrewing a screw that is screwed into a workpiece can be used for an automated process that prevents the screw from being completely unscrewed from the workpiece, so that the screw does not detach completely from the workpiece.

[0080] For example, the speed of the electric motor is reduced, and in particular the electric motor is stopped, if the current value after the third time point t3 falls below a predefined limit. For example, the speed of the electric motor is reduced, and in particular the electric motor is stopped, if the negative time gradient of the current after the third time point t3 is greater than a reference gradient. Both the current limit and / or the reference gradient can depend on the current of the electric motor during the initial phase of unscrewing the screw. The current drawn by the electric motor depends on the tightening torque of the screw. The initial phase can begin after the first time point t1 and extend to the second and / or third time points t2, t3. Alternatively, the initial phase can also begin only at the second time point t2 and extend to the third time point t3.Furthermore, both the limit value for the current and / or the reference gradient can assume different values ​​depending on a speed of the electric motor specified by an operator and / or depending on the speed of actuation of a switch to specify the speed.

[0081] Furthermore, in one embodiment, after the third time t3, a loosened screw is detected depending on whether a predetermined current limit value is undershot and / or whether a predetermined negative time gradient of the current is exceeded, and the speed of the electric motor is at least reduced or the electric motor is stopped.

[0082] The tightening torque of the screw can be estimated based on the current drawn by the electric motor, particularly during the initial phase after the first time t1, and especially after the second time t2, when the screw is being unscrewed. The limit values ​​and reference gradients can also be determined experimentally, for example, in test series, and stored.

[0083] To implement an automatic unscrewing function, a soft braking method can be used at the end of the process to stop the electric motor. In a simple embodiment, for example, when the current drop is detected after the third time point t3, the motor speed can be reduced or braked to a predetermined low speed. The braking of the electric motor can continue until its speed is less than the mechanical resistance of the power tool. Subsequently, the motor speed is gradually reduced to zero. In this way, the motor is braked to zero speed more quickly. The braking of the electric motor can be achieved mechanically or by appropriate electrical control of the electric motor.

[0084] Figure 11A schematic diagram illustrates a program sequence that can influence the removal of a screw from a workpiece in such a way that the screw is not completely detached. This prevents the screw from coming completely loose. This is particularly advantageous when the screw is being loosened overhead with a power tool. It is also beneficial when loosening larger screws or bolts at great heights, for example, on the exterior of a building, where they could fall on passersby. Furthermore, the proposed methods avoid unnecessary limitation of the power tool's speed or its automatic shutdown, for example, when the power tool is operated without a load. This prevents the operator from being unsure about the power tool's functionality.The speed is limited or the electric motor is switched off when a loosened screw is detected. This allows the power tool to function even under light or no load.

[0085] In one embodiment, after detecting that the screw has loosened from its fixed position in the workpiece, based on the current drop after the third time point t3 ( Figure 10The number of screw rotations can be detected. For this purpose, the rotation of the electric motor can be detected using a sensor, e.g., a magnetic sensor. For example, after detecting the current drop at the third time point t3, following a predetermined number of 360° rotations of the screw, the control circuit can automatically terminate the electric motor's power supply. For example, after three, five, or eight rotations following the detection of the current drop at the third time point t3, the electric motor can be automatically switched off by the control circuit, even though the operator continues to actuate trigger 18t. Depending on the chosen configuration, the operator can use the input unit to define the number of rotations after which the electric motor is stopped following the detection of the current drop at the third time point t3.

[0086] With the help of the in Figure 11The depicted program sequence allows for the consideration of various operating situations during the automatic loosening of the screw. For example, depending on the load, i.e., the torque with which the screw is held in the workpiece, the control circuit 46 can execute different procedures to loosen the screw. Furthermore, the control circuit 46 can additionally or instead of considering the load, taking into account the type of actuation of the trigger 18t of the main switch 18 by an operator, in order to execute different automatic procedures to prevent the screw from completely detaching from the workpiece during the loosening process. The load is defined as the torque initially required to turn the screw that is held in the workpiece. The higher the seating torque with which the screw is screwed into the workpiece, the greater the load or torque that the electric motor must apply to turn the screw.

[0087] The following describes the program sequence for an initial operating scenario where a screw is stuck in the workpiece with high torque and a high speed is set by the operator on the power tool to loosen the screw. The program starts at program point 800, where the power tool is switched on. Switch 70 is in the position where the automatic procedure to prevent the screw from completely loosening from the workpiece is activated. Subsequently, at program point 810, it is checked whether the power tool is in the operating mode for loosening a screw or nut, i.e., in a counter-clockwise direction. If so, the program branches to the following program point 820 and a counter is reset to zero.

[0088] Program item 820 can also record the speed requested by the operator of the power tool. For example, an operator might set a low speed to loosen a screw. The desired speed can be recorded based on the way trigger 18t is actuated. In this case, trigger 18t is fully depressed to its stop, indicating that the operator is requesting maximum speed from the power tool's motor. Additionally, or instead of the type of partial or full depress of trigger 18t, the actuation speed of trigger 18t can also be recorded. The actuation speed of trigger 18t can be considered in the following automatic procedures, either in addition to or instead of the actuation distance of trigger 18t.The trigger actuation speed and / or the trigger travel can be detected by suitable sensors, such as an accelerometer or Hall sensor, and transmitted to the control circuit 46. The control circuit 46 detects a desired low speed when the trigger travel is less than 50% of the possible travel of the trigger 18t. The control circuit 46 detects a desired high speed, for example, when the trigger travel is more than 50% of the possible travel of the trigger 18t. Furthermore, the control circuit 46 can assume a low speed for a trigger 18t actuation speed if the actuation speed is below a stored reference value. Conversely, the control circuit 46 can assume a desired high speed for a trigger 18t actuation speed if the actuation speed is above the stored reference value.

[0089] In program point 820, one version sets the rotational speed of the electric motor proportionally to the actuation distance of trigger 18t. If trigger 18t is only half-pressed, the control circuit drives the electric motor at only half its maximum possible speed. If the trigger is fully pressed, the control circuit drives the electric motor at its maximum possible speed. The speed of trigger actuation can also be taken into account accordingly.

[0090] Subsequently, at program point 830, it is checked whether the current I of the electric motor is higher than a predefined first limit value I1 for a longer than a predefined initial time period t1. The initial time period t1 can, for example, be between 0.03 and 0.1 seconds. If this is the case, the program then branches to the following program point 840. If not, program point 820 is executed. At program point 840, the speed of the electric motor is still adjusted depending on the type of actuation of trigger 18t, as in program point 820.

[0091] At the following program point 850, it is checked whether the current of the electric motor exceeds a predefined third limit value I3. If this is the case, the counter is incremented by 1 to the value 1 and the program branches to the following program point 860. In the present first operating situation, this is the case.

[0092] If this is not the case, program point 840 continues to be executed. If the program remains at program point 840 for longer than a predefined second duration t2, program point 890 checks whether the current I of the electric motor is less than a predefined second limit value I2. If this is the case, the program branches back to program point 820. If this is not the case, program point 840 continues to be executed.

[0093] At program point 860, the speed of the electric motor continues to be controlled by the control circuit, depending on the type of actuation of trigger 18t, as in program point 820. At program point 860, program point 960 also checks whether the counter has a value of at least 3. If so, the program branches directly to program point 880. If not, the program remains at program point 860.

[0094] If the program remains at program point 860 for longer than a predefined second duration t2, it checks at program point 870 whether the electric motor current exceeds a predefined fourth limit value I4. Different values ​​for the fourth current value I4 can be stored, depending on the screw's tightening torque and / or the operator's desired rotational speed (i.e., the actuation path of trigger 18t) and / or the actuation speed of trigger 18t. This allows different operating situations to be handled with different automatic procedures. If the electric motor current exceeds a predefined fourth limit value I4, the program branches from program point 870 to program point 880. This is the case in the present first operating situation. If not, the program branches back to program point 840.

[0095] At program point 880, the electric motor is operated by the control circuit at its maximum speed. This sets the motor's speed to a high value, specifically 100% of the maximum possible speed, regardless of how the trigger is actuated. However, values ​​other than 100% of the maximum speed can also be used.

[0096] At program point 970, the program checks whether the counter has the value 1. If so, it then proceeds to program point 890. If not, the program remains at program point 880.

[0097] If the program remains at program point 880 after querying program point 970, it then checks at program point 950 whether the current I of the electric motor exhibits a greater rate of decay than a predefined reference value, i.e., whether the current of the electric motor decreases faster than the reference value. The reference value is stored in memory. If this is not the case, the program branches back to program point 880. If the query at program point 950 shows that the current I of the electric motor decreases faster, i.e., exhibits a greater negative rate of decay than the predefined reference value, the program branches to program point 910. If the negative rate of decay of the current is greater than the reference value, this indicates that the screw is loosened and can be turned with low torque.

[0098] At program point 890, the maximum speed for the electric motor is still set by control circuit 46. Furthermore, at the subsequent program point 900, it is checked whether the electric motor's current falls below a fifth limit value, I5. If this is the case, it means that the screw is loosened, and the program branches to the following program point 910. If this is not the case, program point 890 is executed.

[0099] At program point 910, the rotational speed is set to a predefined value, which is, for example, less than 50% of the maximum speed. The predefined value can be, for example, between 5% and 10% of the maximum speed or lower. Additionally, a revolution counter is reset to zero. Then, after a predefined third time interval t3 at program point 910, at the following program point 920, it is checked whether the screw has rotated at least a predefined number of revolutions. If this is the case, the program branches to program point 930 and at least reduces or switches off the current to the electric motor, or decelerates the electric motor. The program then terminates at program point 940.

[0100] The specified number of revolutions can, for example, be between three and eight whole revolutions. If the query at program point 920 indicates that the specified number of revolutions has not yet been reached, the electric motor continues to be driven according to program point 910, and the query at program point 920 is performed again until the specified number of revolutions is reached, at which point the program branches to program point 930.

[0101] In a second operating situation, where the screw is stuck in the workpiece with a small seating torque, and the operator desires a high speed of the power tool, the program sequence is carried out according to Figure 11The process is carried out as follows: The procedure corresponds to the described procedure for the first operating situation, except that the fourth current value I4 is chosen to be smaller than in the first operating situation due to the small insertion torque. For example, depending on the detected insertion torque of the screw and / or depending on the desired rotational speed of the operator, i.e., depending on the actuation path of trigger 18t, and / or depending on the speed of actuation of trigger 18t, different values ​​for the fourth current value I4 can be stored. The fourth current value I4 must be chosen such that the query at program point 870 shows that the measured current is greater than the fourth limit value I4, and therefore, after the second time period t2 in program point 860, the program branches to program point 880.At program point 880, the electric motor is again supplied with a predetermined high speed, specifically maximum speed for a predetermined duration. Since the counter has the value 1 in this case, the program branches to program point 890 based on the query at program point 970. This means that a state exists with a low screw torque and a high desired speed of the power tool. Subsequently, program points 900 and following are executed according to... Fig. 11 Completed.

[0102] Furthermore, for a low screw tightening torque, a smaller third limit value I3 for the current can be stored compared to the initial operating situation with a high tightening torque. For example, tables or diagrams can be stored in which different values ​​for the limit values ​​are stored depending on the detected screw tightening torque. The control circuit selects the corresponding limit values ​​depending on the screw tightening torque, which is estimated at the beginning of the program. The screw tightening torque can, for example, be estimated depending on the current or the current rise of the electric motor during the initial phase at program point 820. Corresponding diagrams, characteristic curves, or maps can be stored for this purpose, assigning a tightening torque to a current profile during program point 820.Furthermore, a torque sensor can be used on the power tool to measure the initial tightening torque of the screw. The limit values ​​can be determined or set by the control circuit based on the torque or tightening torque of the screw that occurs when the screw is first loosened. For example, different values ​​can be stored for the first, second, third, and / or fourth limit values ​​for predefined torque ranges. Otherwise, the procedure is carried out according to the first operating condition.

[0103] The procedure according to Figure 11For a third operating situation, in which the screw is in the workpiece without significant seating torque (i.e., no load) and a high desired speed is applied, the process is executed as follows: The procedure runs from program point 800 to program point 860 according to the second operating situation, as described above. At program point 860, the electric motor is operated by the control circuit 46 according to the operator's desired speed. Subsequently, at program point 870, a query is performed to determine whether the electric motor current is greater than the fourth limit value I4. The fourth limit value I4 depends on the existing seating torque; i.e., if there is no seating torque, it is selected to be even lower than in the second operating situation. Consequently, the query at program point 870 shows that the measured current is less than the fourth limit value I4. Therefore, the program branches back to program point 840, which is then executed.At the following program point 850, it is checked whether the current of the electric motor exceeds a predefined third limit value I3. If this is the case, the counter is incremented by 1 to the value 1, and the program branches to the following program point 860. At this point, the current is greater than the third limit value I3, so, due to the query at program point 850, the counter is incremented by 1 to the value 2.

[0104] At program point 860, the electric motor is then operated by the control circuit 46 according to the operator's desired speed. Additionally, at program point 860, program point 960 checks whether the counter has a value of at least 3. If so, the program branches to program point 880. However, this is not the case, so the program remains at program point 860. If the program remains at program point 860 for longer than the second time period t2, program point 870 checks whether the electric motor's current is greater than the fourth limit value I4. This is not the case, so the program branches back to program point 840.

[0105] Therefore, after program point 840, the program checks again at program point 850 whether the current is greater than the third limit value I3. In the current situation, the current is less than the third limit value I3, so the program remains at program point 840. If the check at program point 890 shows that the current is less than the second limit value I2, the program branches back to program point 820 and continues executing accordingly.

[0106] If the operator now activates trigger 18t to a maximum value, the program recognizes, for example, by a low current, that there is no load, i.e., no tightening torque on the screw. As a result, the program remains at program point 840, and the speed of the electric motor is controlled according to the activation of trigger 18t. Using this method, the user can operate the electric motor at the desired speed without activating the automatic speed limiters of the electric motor according to program points 910, 920, 930, and 940. This improves the user's intuitive handling of the power tool. Due to the lack of tightening torque, the control circuit recognizes that no screw should be loosened.

[0107] In a fourth operating situation, which corresponds to a medium to high load, i.e., a medium to high seating torque of the screw and a desired low to medium speed or a desired slow increase in speed by the operator, the program is run according to Figure 11 The process is as follows: The program starts at program point 800, where the power tool is switched on. Switch 70 is in the position where the automatic procedure to prevent the screw from completely loosening from the workpiece is activated. Then, at a subsequent program point 810, it is checked whether the power tool is in the operating mode for unscrewing a screw, i.e., counterclockwise rotation. If this is the case, a counter is reset to zero at a subsequent program point 820.

[0108] Program point 800 can also detect the speed and / or speed increase requested by the operator of the power tool. For example, an operator might set a low speed and / or a slow speed increase to loosen a screw. The speed can be detected by the control circuit based on the way trigger 18t is actuated. If trigger 18t is only pressed to a maximum of 60% of its stop, a desired low to medium speed of the electric motor is detected. In addition to, or instead of, the type of partial or full actuation of trigger 18t, the control circuit can also detect the speed at which trigger 18t is actuated. If trigger 18t is actuated slower than a stored reference speed, a desired slow speed increase is detected.In addition to or instead of the actuation travel of trigger 18t, the control circuit 46 can also take into account the speed of actuation of trigger 18t in the following automatic procedures. The speed of actuation of the trigger and / or the actuation travel of the trigger can be detected by appropriate sensors and transmitted to the control circuit 46. A low desired speed is detected by the control circuit, for example, if the operator only depresses trigger 18t to a maximum of 60% of its possible actuation travel. Due to the low desired speed, the control circuit can, at program point 820, control the electric motor at a speed between 0% and 60% of its maximum speed. This results in a slow increase in the speed of the electric motor.

[0109] Subsequently, at program point 830, it is checked whether the current I of the electric motor is higher than a predefined first limit value I1 for a longer than a predefined initial time period t1. The initial time period t1 can, for example, be between 0.03 and 0.1 seconds. If this is the case, the program then branches to the following program point 840. If not, program point 820 is executed. At program point 840, the speed of the electric motor is further adjusted depending on the type of actuation of trigger 18t.

[0110] The third current limit value I3 at program point 850 is selected, for example, to activate the impact mechanism of the power tool in this operating situation. At program point 840, the electric motor is controlled by the control circuit 46 according to the operator's desired speed. Subsequently, the query at program point 850 shows that the current is greater than the third limit value I3, so the program branches to program point 860. Simultaneously, the counter is incremented by 1 to its value of 1. Then, after the second time interval t2, at program point 870, the program checks whether the current is greater than the fourth limit value I4. The fourth limit value I4 is set higher than in the second operating situation. Therefore, at program point 870, the current is less than the fourth limit value I4, so the program branches back to program point 840.

[0111] At the following program point 850, the query again shows that the current is greater than the third limit value I3, so the counter is increased by the value 1 and thus now has the value 2.

[0112] The program then branches to point 860. After the second time interval t2, at point 870, a check is performed to see if the current is greater than the fourth limit value I4. At point 870, the current is found to be less than the fourth limit value I4. Since this is not the case, the program then branches back to point 840.

[0113] At the following program point 850, the query again shows that the current is greater than the third limit value I3, so the counter is increased by the value 1 and thus now has the value 3.

[0114] The program then branches to program point 860. At program point 860, the query at program point 960 shows that the counter has the value 3, so the program branches directly to program point 880. The counter value of 3 indicates that the screw might be loosened.

[0115] At program point 880, the electric motor is operated at its maximum speed. Then, at program point 950, it is checked whether the electric motor's current exhibits a greater drop in current over time than a predefined value. This predefined value for the current drop in time is stored in memory. If the query at program point 950 shows that the measured drop in current over time is less than the predefined value, the program returns to program point 880. If the query at program point 950 shows that the measured drop in current over time is greater than the predefined value, the program proceeds to program point 910. If the current drop in time is greater than the predefined value, this indicates that the screw has been loosened. Program points 910 through 940 are then executed accordingly.

[0116] In a fifth operating situation, which corresponds to no load and a low desired speed and / or a desired slow increase in speed, the program is... Figure 11 The process is as follows: The program starts at program point 800, where the power tool is switched on. Switch 70 is in the position where the automatic procedure to prevent the screw from completely loosening from the workpiece is activated. Then, at a subsequent program point 810, it is checked whether the power tool is in the operating mode for unscrewing a screw, i.e., counterclockwise rotation. If this is the case, a counter is reset to zero at a subsequent program point 820.

[0117] At program point 800, it is also possible to record the speed requested by the operator of the power tool. For example, an operator might set a low speed and / or a slow increase in speed to loosen a screw. The speed can be recorded based on the way trigger 18t is actuated. If trigger 18t is fully depressed to its stop, the operator requests maximum speed of the electric motor. In addition to or instead of the type of partial or full depress of trigger 18t, the speed of actuation of trigger 18t can also be recorded, and the speed of actuation of trigger 18t can also be taken into account in the subsequent automatic procedure, either additionally or instead of the actuation distance of trigger 18t.The speed of the trigger actuation and / or the actuation path of the trigger can be detected with appropriate sensors and transmitted to the control circuit 46.

[0118] At program point 820, the rotational speed of the electric motor is set proportionally to the actuation distance of trigger 18t. If trigger 18t is only half-pressed, the control circuit drives the electric motor at only half its maximum possible speed. If the trigger is fully pressed, the control circuit drives the electric motor at its maximum possible speed. The speed at which the trigger is actuated can also be taken into account.

[0119] In this state, program point 820 is maintained until the current exceeds the first limit value I1. The program then branches to program point 840. If the operator reduces the speed of the power tool during program point 840, the current falls below the second limit value I2, so that the query at program point 890 indicates that the program branches back to program point 820.

[0120] The program thus recognizes that the operator desires a low speed and / or a slow increase in speed, and that there is no load, i.e., no tightening torque on the screw. This could mean, for example, that there is no operative connection between the power tool and a screw or nut. Therefore, the operator can fully control the rotation of the power tool.

[0121] A sixth operating situation, corresponding to a low load and slow actuation of trigger 18t, is executed according to the program sequence shown in Figure 11 as follows: The program starts at program point 800, where the power tool is switched on. Switch 70 is in the position where the automatic procedure to prevent the screw from completely loosening from the workpiece is activated. Subsequently, at a later program point 810, it is checked whether the power tool is in the operating mode for unscrewing a screw, i.e., counterclockwise rotation. If this is the case, a counter is reset to zero at a later program point 820.

[0122] At program point 800, it is also possible to record the speed requested by the operator of the power tool. For example, an operator might set a slow increase in speed to loosen a screw. The speed can be determined based on the way trigger 18t is actuated. If trigger 18t is actuated slower than a stored reference speed, the operator requests a slow increase in the electric motor's speed. The actuation speed of trigger 18t is taken into account in the subsequent automatic procedure. The actuation speed and / or the actuation path of the trigger can be detected by appropriate sensors and transmitted to the control circuit 46.

[0123] In the following program step 820, the rotational speed of the electric motor, i.e., the rotational speed, is set proportionally to the actuation distance of trigger 18t. If trigger 18t is only half-pressed, the control circuit drives the electric motor at only half of its maximum possible speed. If the trigger is fully pressed, the control circuit drives the electric motor at its maximum possible speed. The speed of actuation of the trigger can also be taken into account accordingly.

[0124] Subsequently, at program point 830, it is checked whether the current I of the electric motor is higher than a predefined first limit value I1 for a longer than a predefined initial time period t1. The initial time period t1 can, for example, be between 0.03 and 0.1 seconds. If this is the case, the program then branches to the following program point 840. If not, program point 820 is executed. At program point 840, the speed of the electric motor is further adjusted depending on the type of actuation of trigger 18t.

[0125] At the following program point 850, it is checked whether the current of the electric motor exceeds a predefined third limit value I3. If this is the case, the counter is incremented by 1 to the value 1, and the program branches to the following program point 860. If this is not the case, program point 840 is executed. The third limit value I3 corresponds to the value that is just sufficient to execute a striking mechanism if the trigger 18t is only activated slowly, i.e., slower than the reference speed.

[0126] If the program remains at program point 840 for longer than a predefined second duration t2, program point 890 checks whether the current I of the electric motor is less than a predefined second limit value I2. If so, the program branches back to program point 820. If not, program point 840 is executed.

[0127] At program point 860, the speed of the electric motor continues to be controlled by the control circuit depending on the type of actuation of trigger 18t. At program point 860, program point 960 also checks whether the counter has a value of at least 3. If so, the program branches directly to program point 880. If not, the program remains at program point 860.

[0128] If the program remains at program point 860 for longer than a predetermined second time duration t2, then at program point 870 it is checked whether the current of the electric motor is greater than a predetermined fourth limit value I4.

[0129] The fourth limit value, I4, has a higher value than in the fourth operating situation. Therefore, the query at program point 870 shows that the current is less than the fourth limit value. Consequently, the program branches back to program point 840. At this point, the current is greater than the third limit value, I3, so, according to program point 850, the program branches again to program point 860. Additionally, the counter is incremented by 1 to the value 2. After the second time interval, t2, the query at program point 870 is performed. This query again shows that the current is less than the fourth limit value, I4, so the program then branches back to program point 840. The subsequent query at program point 850 again shows that the current is greater than the third limit value, I3, so the counter is incremented by 1 to the value 3, and the program branches back to program point 860.

[0130] At the following program point 860, the query at program point 960 detects that the counter value is 3. Therefore, the program branches directly to program point 880.

[0131] The fourth limit value, I4, must be chosen to be particularly small for this operating situation to allow a transition to program point 880. For example, the limit values, especially the fourth limit value, are determined experimentally and stored. A counter value of 3 indicates that a low load has been detected with a slight or slow actuation of trigger 18t. If the load is low, meaning, for example, that the screw is not fully or tightly tightened, then the current drops more quickly because the screw can be loosened more easily. After program point 880, the system checks at program point 950 because the counter value is not 1. At program point 950, it checks whether the current's rate of decay is less than a predefined reference value. The predefined reference value is stored in memory, for example, as the negative time gradient of the current.If the query at program point 950 shows that the measured rate of current decay is less than the reference value, the program branches to program point 910. Program points 910, 920, 930, and 940 are then executed as described.

[0132] The described methods can also be applied to unscrewing bolts, nuts, or other screwed parts. Thus, the term "screw" refers to any part that can be screwed or fastened to or into a counterpart.

[0133] Furthermore, the described automatic methods for unscrewing a screw can be used according to Fig. 11 The process can be terminated by a predefined input from the operator, for example by entering a predefined stop time.

[0134] Figure 12The diagram shows the current I over time t for various methods for automatically unscrewing a screw without completely removing the screw from the workpiece, according to the program sequence of Figure 11 can be carried out. A first characteristic curve 73 characterizes the first operating situation. A second characteristic curve 74 characterizes the second operating situation. A third characteristic curve 75 represents a third operating situation. The first three characteristic curves 73, 74, 75 are identical for the selected embodiments in an initial phase. A fourth characteristic curve 76 represents a fourth operating situation. A fifth characteristic curve 77 represents a fifth operating situation.

[0135] Furthermore, the diagram shows the first limit value I1, the second limit value I2, the third limit value I3, the fourth limit value I4, and the fifth limit value I5. It also includes examples of the first time duration t1, the second time duration t2, and the third time duration t3. The first time duration t1 can, for example, be between 0.03 and 0.1 seconds. The second time duration t2 can, for example, be between 0.01 and 0.05 seconds. The third time duration t3 can be between 0.01 and 0.05 seconds. In the example shown, the first limit value I1 is smaller than the third limit value I3. The third limit value I3 is smaller than the fourth limit value I4. The fourth limit value I4 is smaller than the fifth limit value I5. The second limit value I2 is smaller than the first limit value I1.

[0136] In the characteristic curves, E2 shows the occurrence of the query according to program point 830, asking whether the current exceeds the first limit value I1. E3 shows the occurrence of the query according to program point 850, asking whether the current exceeds the third limit value I3. E5 shows the occurrence of the query according to program point 870, asking whether the current exceeds the fourth limit value I4. E6, in the first characteristic curve 71, shows the query according to program point 950, asking whether the negative time gradient of the current is greater than the negative time gradient of the comparison curve, i.e., whether the current decreases more sharply than the comparison gradient. E7 shows the occurrence of the query according to program point 900, asking whether the current falls below the fifth limit value I5.

[0137] The first operating situation corresponds to a load, i.e., a high screw torque and a high desired speed of the power tool. The second operating situation corresponds to a low load, i.e., a low screw torque and a high desired speed of the power tool. The third operating situation corresponds to no load, i.e., no screw torque and a high speed of the power tool. The fourth operating situation corresponds to no significant load, i.e., no significant screw torque and a low desired speed, for example, less than 60% of the maximum speed. The fifth operating situation corresponds to no significant load, i.e., no significant screw torque and a low desired speed of the power tool.

[0138] As can be seen from the characteristic curves, the current waveforms for the first, second, and third operating situations are identical in the initial phase. However, over time, the current waveforms for the first, second, and third operating situations diverge. The current waveforms for the fourth and fifth operating situations are different from the outset.

Claims

1. Method for controlling an electric motor of a power tool with a holder for a tool for unscrewing a screw from a mating part, wherein different control methods for unscrewing the screw are used depending on a seating torque of the screw, characterized in that a loosened screw is identified and the rotational speed of the electric motor is at least reduced or the electric motor is stopped depending on a predetermined negative time gradient of the current being exceeded.

2. Method according to Claim 1, wherein different control methods for unscrewing the screw are selected depending on a rotational speed of the electric motor predetermined by an operator and / or depending on a speed of an actuation of a switch for predetermining the speed.

3. Method according to Claim 1 or 2, wherein the electric motor is actuated in a first phase according to a rotational speed predetermined by an operator, wherein the current of the electric motor during the first phase is measured, wherein the measured current is compared with a predetermined limit value, wherein, when the limit value is exceeded, the electric motor is actuated at a predetermined second rotational speed, in particular at a maximum rotational speed, during a subsequent second phase, wherein the current of the electric motor during the second phase is measured, wherein, depending on the current measured during the second phase, a loosened screw is identified and the rotational speed of the electric motor is at least reduced or the electric motor is stopped, and wherein the limit value depends on the seating torque and / or on the rotational speed predetermined by the operator.

4. Method according to Claim 1 or 2, wherein the electric motor is actuated in a first phase according to a rotational speed predetermined by an operator, wherein a period of time is measured in particular using a counter, during which period of time the electric motor is in the first phase, wherein, when a predetermined period of time is exceeded, the electric motor is actuated at a predetermined second rotational speed, in particular at a maximum rotational speed, during a subsequent second phase, wherein the current of the electric motor during the second phase is measured, wherein, depending on the measured current of the electric motor during the second phase, a loosened screw is identified and the speed of the electric motor is at least reduced or the electric motor is stopped.

5. Method according to any one of Claims 1 to 4, wherein a loosened screw is detected and the rotational speed of the electric motor is at least reduced or the electric motor is stopped depending on a predetermined current limit value being undershot.

6. Method according to any one of Claims 1 to 5, wherein the seating torque of the screw is estimated on the basis of a current which is received by the electric motor in particular in an initial phase when the screw is unscrewed.

7. Control unit comprising a current meter and a control circuit, which control unit is designed to carry out a method according to any one of the preceding claims.