EP3946818B1 - Method for detecting a first operating state of a handheld power tool - Google Patents

Description

The invention relates to a method for detecting a first operating state of a hand-held power tool, according to the preamble of patent claim 1, and to a hand-held power tool configured to carry out the method.

State of the art

From the state of the art, see for example EP 3 381 615 A1 , rotary impact wrenches for tightening screw elements, such as threaded nuts and screws, are known. A rotary impact wrench of this type comprises, for example, a structure in which an impact force in a direction of rotation is transmitted to a screw element by a rotary impact force of a hammer. The rotary impact wrench having this structure comprises a motor, a hammer driven by the motor, an anvil struck by the hammer, and a tool. In the rotary impact wrench, the motor built into a housing is driven, the hammer is driven by the motor, the anvil is struck by the rotating hammer, and an impact force is transmitted to the tool, whereby two different operating states can be distinguished, namely "no impact operation" and "impact operation".

In the EP 1 398 119 A1 , which discloses the preamble of patent claim 1, a safety shutdown system for electrically operated hand-held power tools is disclosed, wherein the hand-held power tool rotatably drives an insert tool and the safety shutdown system is provided to prevent injuries in the event of a blockage of the insert tool.

EN 10 2013 212506 A1 describes a machine tool switching device with at least one switching element for switching between at least two operating modes, and with at least one sensor unit which comprises at least one sensor element.

The WO 2013/174594 A1 discloses a percussion unit with a control unit which is intended to control a pneumatic percussion mechanism.

From the EP 2 599 589 B1 Also known is a rotary impact wrench with a motor, a hammer and a rotation speed detection unit, wherein the hammer is driven by the motor.

In order to provide intelligent tool functions, knowledge of the current operating state is required. In the current state of the art, this is identified, for example, by monitoring the operating variables of the electric motor, such as speed and electric motor current. The operating variables are examined to determine whether certain limit values and/or threshold values are reached. Corresponding evaluation methods work with absolute threshold values and/or signal gradients.

The disadvantage here is that a fixed limit and/or threshold value can practically only be perfectly set for one application. As soon as the application changes, the associated current or speed values or their temporal progressions also change and impact detection based on the set limit and/or threshold value or their temporal progressions no longer works.

For example, it may happen that an automatic shutdown based on the detection of impact operation switches off reliably in different speed ranges in individual application cases when self-tapping screws are used, but in other application cases when self-tapping screws are used, no shutdown occurs.

Other methods for determining operating modes in impact wrenches use additional sensors, such as acceleration sensors, to determine the current operating mode from the vibration conditions of the tool.

Disadvantages of these methods are additional costs for the sensors as well as losses in the robustness of the handheld power tool, since the number of installed components and electrical connections increases compared to handheld power tools without these sensors.

In principle, the problem of detecting operating states also exists with other hand-held power tools such as impact drills, so that the invention is not limited to impact wrenches.

Disclosure of the invention

The object of the invention is to provide a method for detecting operating states which is improved compared to the prior art and which at least partially eliminates the disadvantages mentioned above, or at least to provide an alternative to the prior art. A further object is to provide a corresponding hand-held power tool.

These objects are achieved by means of the respective subject matter of the independent claims. Advantageous embodiments of the invention are the subject matter of respective dependent subclaims.

• S1 Ermitteln eines Signals einer Betriebsgröße des Elektromotors;
• S2 Vergleichen des Signals der Betriebsgröße mit zumindest einer zustandstypischen Modellsignalform, wobei die zustandstypische Modellsignalform (240) dem ersten Betriebszustand zugeordnet ist;
• S3 Entscheiden, ob der erste Betriebszustand vorliegt, wobei die Entscheidung zumindest teilweise davon abhängt, ob in Schritt S2 die zustandstypische Modellsignalform im Signal der Betriebsgröße identifiziert wird.

According to the invention, a method for detecting a first operating state of a hand-held power tool is disclosed, wherein the hand-held power tool has an electric motor. The method comprises the steps:

• S1 Determining a signal of an operating variable of the electric motor;
• S2 comparing the signal of the operating variable with at least one state-typical model signal form, wherein the state-typical model signal form (240) is assigned to the first operating state;
• S3 Deciding whether the first operating state exists, the decision depending at least in part on whether the state-typical model signal shape is identified in the signal of the operating variable in step S2.

In this way, simple and safe monitoring and control can be carried out to detect the first operating state, whereby various operating variables can be considered as operating variables, which are recorded via a suitable sensor. It is particularly advantageous that no additional sensor is required in this regard, since various sensors, such as those for speed monitoring, preferably Hall sensors, are already built into electric motors.

The approach to detecting the first operating state using operating variables in the tool-internal measured variables, such as the speed of the electric motor, has proven to be particularly advantageous, since this method enables impact detection to be particularly reliable and largely independent of the general operating state of the tool or its application. In this case, there is essentially no need for additional sensor units for detecting the tool-internal measured variables, such as an acceleration sensor unit, so that essentially only the method according to the invention serves to detect the first operating state.

Furthermore, the method according to the invention enables the detection of the first operating state independently of at least one target speed of the electric motor, at least one starting characteristic of the electric motor and/or at least one charge state of a power supply, in particular a battery, of the hand-held power tool.

The method according to the invention enables the detection of the first operating state for applications in which a loose fastening element is screwed into a fastening support, as well as in which a fixed, in particular at least partially screwed, fastening element is screwed into a fastening support. The applications can include both hard and soft screwing cases, whereby a typical application can be, for example, a self-tapping screw connection or a wood screw connection.

The "loose fastening element" is to be understood as a fastening element that is essentially not screwed into the fastening carrier and that is to be screwed into the fastening carrier. The "fixed fastening element" is to be understood as a fastening element that is at least partially screwed into the fastening carrier or is essentially completely screwed into the fastening carrier.

In a further method step S0 preceding method steps S1 to S3, the at least one state-typical model signal form can be determined, wherein the state-typical model signal form is assigned to the first operating state. In this context, a limit and/or threshold value for an existing match or an existing error between the signal of the operating variable and the state-typical model signal form can represent an adjustable value for application cases for successful impact detection.

In particular, the state-typical model signal form is stored or saved internally in the device, alternatively and/or additionally provided to the hand-held power tool, in particular provided by an external data device.

In the context of the present invention, "determine" should in particular include measuring or recording, whereby "recording" should be understood in the sense of measuring and storing, and "determine" should also include possible signal processing of a measured signal.

Furthermore, "decide" should also be understood as recognizing or detecting, whereby a clear assignment should be achieved. "Identify" should be understood as recognizing a partial match with a pattern, which can be made possible, for example, by fitting a signal to the pattern, a Fourier analysis or the like. The "partial match" should be understood in such a way that the fitting has an error that is less than a predetermined threshold, in particular less than 30%, most particularly less than 20%.

The signal of the operating variable should be understood here as a temporal sequence of measured values. Alternatively and/or additionally, the signal of the operating variable can also be a frequency spectrum. Alternatively and/or additionally, the signal of the operating variable can also be reworked, for example smoothed, filtered, fitted and the like.

In one embodiment, the state-typical model signal shape is an oscillation curve around a mean value, in particular an essentially trigonometric oscillation curve. The state-typical model signal shape preferably represents an ideal impact operation of the hammer on the anvil of the rotary impact mechanism.

In a further embodiment, the operating variable is a speed of the electric motor or an operating variable that correlates with the speed. The rigid transmission ratio of the electric motor to the impact mechanism results in a direct dependency of the motor speed on the impact frequency, for example. Another conceivable operating variable that correlates with the speed is the motor current. A motor voltage, a Hall signal from the motor, a battery current or a battery voltage are also conceivable as an operating variable of the electric motor, whereby an acceleration of the electric motor, an acceleration of a tool holder or a sound signal from an impact mechanism of the hand-held power tool are also conceivable as the operating variable.

In a further embodiment, the signal of the operating variable in method step S1 is recorded as a time course of measured values of the operating variable, or as measured values of the operating variable as a variable of the electric motor that correlates with the time course, for example an acceleration, a jerk, in particular of a higher order, a power, an energy, an angle of rotation of the electric motor, an angle of rotation of the tool holder or a frequency.

In the latter embodiment, it can be ensured that a constant periodicity of the signal to be examined results regardless of the engine speed.

Alternatively, the signal of the operating variable is recorded in method step S1 as a time course of measured values of the operating variable, whereby in a step S1a following method step S1, due to the rigid transmission ratio of the transmission, a transformation of the time course of the measured values of the operating variable into a course of the measured values of the operating variable as a variable of the electric motor that correlates with the time course takes place. The same advantages arise as with the direct recording of the signal of the operating variable over time.

In a further embodiment, the signal of the operating variable is stored as a sequence of measured values in a memory, preferably a ring buffer, in particular of the hand-held power tool.

In a preferred embodiment, in method step S1, a segmentation of the measured values is carried out such that the signal of the operating variable always comprises a predetermined number of measured values.

In a particularly advantageous embodiment, in method step S2 the signal of the operating variable is compared using one of the comparison methods comprising at least one frequency-based comparison method and/or a comparative comparison method, wherein the comparison method compares the signal of the operating variable with the state-typical model signal form to determine whether at least one predetermined threshold value is met. The predetermined threshold value can be specified at the factory or can be set by a user.

In one embodiment, the frequency-based comparison method comprises at least bandpass filtering and/or frequency analysis, wherein the predetermined threshold value is at least 85%, in particular 90%, most particularly 95%, of a predetermined limit value.

In bandpass filtering, for example, the recorded signal of the operating variable is filtered via a bandpass whose passband matches the state-typical model signal shape. A corresponding amplitude in the resulting signal is to be expected in the first operating state, in particular in impact mode. The specified threshold value of the bandpass filtering can therefore be at least 85%, in particular 90%, very particularly 95%, of the corresponding amplitude in the first operating mode, in particular in impact mode. The specified limit value can be the corresponding amplitude in the resulting signal of an ideal first operating state, in particular an ideal impact mode.

Using the known frequency-based comparison method of frequency analysis, the previously defined state-typical model signal form, for example a frequency spectrum of the first operating state, in particular of impact operation, can be searched for in the recorded signals of the operating variable. A corresponding amplitude of the first operating state, in particular of impact operation, is to be expected in the recorded signals of the operating variable. The predetermined threshold value of the frequency analysis can be at least 85%, in particular 90%, very particularly 95%, of the corresponding amplitude in the first operating mode, in particular in impact operation. The predetermined limit value can be the corresponding amplitude in the recorded signals of an ideal first operating state, in particular of an ideal impact operation. In this case, appropriate segmentation of the recorded signal of the operating variable may be necessary.

In method step S3, the decision as to whether the first operating state has been identified in the signal of the operating variable can be made at least partially by means of the frequency-based comparison method, in particular the bandpass filtering and/or the frequency analysis.

In one embodiment, the comparative comparison method comprises at least the parameter estimation and/or the cross-correlation, wherein the predetermined threshold value is at least 50% of a match of the signal of the operating variable with the state-typical model signal shape.

The measured signal of the operating variable can be compared with the state-typical model signal form by means of the comparative comparison method. The measured signal of the operating variable is determined in such a way that it has essentially the same finite signal length as that of the state-typical model signal form. The comparison of the state-typical model signal form with the measured signal of the operating variable can be output as a signal of a finite length, in particular a discrete or continuous signal. Depending on the degree of agreement or deviation of the comparison, a result can be output as to whether the first operating state, in particular the impact operation, is present. If the measured If the signal of the operating variable corresponds at least 50% to the state-typical model signal form, the first operating state, in particular impact operation, may be present. It is also conceivable that the comparative method can output a degree of deviation from one another as a result of the comparison by comparing the measured signal of the operating variable with the state-typical model signal form. In this case, the deviation of at least 50% from one another can be a criterion for the presence of the first operating state, in particular impact operation.

With a parameter estimation, a comparison can be made in a simple manner between the previously defined state-typical model signal shape and the signal of the operating variable. For this purpose, estimated parameters of the state-typical model signal shape can be identified in order to adjust the state-typical model signal shape to the measured signal of the operating variables. By comparing the estimated parameters of the previously defined state-typical model signal shape and the signal of the operating variable, a result can be determined as to whether the first operating state, in particular impact operation, is present. The result of the comparison can then be evaluated to determine whether the specified threshold value has been reached. This evaluation can either be a quality determination of the estimated parameters or the deviation between the defined state-typical model signal shape and the recorded signal of the operating variable.

In a further embodiment, method step S2 contains a step S2a of determining the quality of the identification of the state-typical model signal form in the signal of the operating variable, wherein in method step S3 the decision as to whether the first operating state is present is made at least partially based on the quality determination. As a measure of the quality determination, a quality of fit of the estimated parameters can be determined.

In method step S3, the decision as to whether the first operating state has been identified in the signal of the operating variable can be made at least partially by means of the quality determination, in particular the measure of the quality.

In addition or as an alternative to the quality determination, method step S2a can include a deviation determination of the identification of the state-typical model signal form and the signal of the operating variable. The deviation of the estimated parameters of the state-typical model signal form from the measured signal of the operating variable can be, for example, 70%, in particular 60%, very particularly 50%. In method step S3, the decision as to whether the first operating state is present is made at least partially based on the deviation determination. The decision as to whether the first operating state is present can be made at the predetermined threshold value of at least 50% agreement between the measured signal of the operating variable and the state-typical model signal form.

With a cross-correlation, a comparison can be made between the previously defined state-typical model signal shape and the measured signal of the operating variable. With a cross-correlation, the previously defined state-typical model signal shape can be correlated with the measured signal of the operating variable. With a correlation of the state-typical model signal shape with the measured signal of the operating variable, a degree of agreement between the two signals can be determined. The degree of agreement can be, for example, 40%, in particular 50%, and most particularly 60%.

In method step S3 of the method according to the invention, the decision as to whether the first operating state is present can be made at least partially based on the cross-correlation of the state-typical model signal shape with the measured signal of the operating variable. The decision can be made at least partially based on the predetermined threshold value of at least 50% agreement between the measured signal of the operating variable and the state-typical model signal shape.

In a method step, the first operating state is determined based on less than ten impacts of a percussion mechanism of the hand-held power tool, in particular less than ten impact oscillation periods of the electric motor, preferably less than six impacts of a percussion mechanism of the hand-held power tool, in particular less than six impact oscillation periods of the electric motor, very preferably less than four impacts of a percussion mechanism, in particular less than four impact oscillation periods of the electric motor. In this case, a strike of the percussion mechanism is to be understood as an axial, radial, tangential and/or circumferentially directed strike of a percussion mechanism striker, in particular a hammer, on a percussion mechanism body, in particular an anvil. The impact oscillation period of the electric motor is correlated with the operating variable of the electric motor. An impact oscillation period of the electric motor can be determined based on operating variable fluctuations during the first operating state in the signal of the operating variable.

The identification of the impacts of the impact mechanism of the hand-held power tool, in particular the impact oscillation periods of the electric motor, can be achieved, for example, by using a Fas-Fitting algorithm, by means of which an evaluation of the impact detection can be made possible within less than 100 ms, in particular less than 60 ms, most particularly less than 40 ms. In this case, the inventive method enables the detection of the first operating state essentially for all of the above-mentioned applications and a screw connection for loose as well as fixed fastening elements in the fastening carrier.

Advantageously, the hand-held power tool is an impact wrench, in particular a rotary impact wrench, and the first operating state is an impact mode, in particular a rotary impact mode.

The present invention makes it possible to largely dispense with more complex methods of signal processing such as filters, signal loops, system models (static and adaptive) and signal tracking.

In addition, these methods allow an even faster identification of the impact operation or the work progress, which can cause an even faster reaction of the tool. This applies in particular to the number of impacts that have passed since the impact mechanism was used until identification and also in special operating situations such as the start-up phase of the drive motor. There is no need to limit the functionality of the tool, such as reducing the maximum drive speed.

In principle, no additional sensors (e.g. acceleration sensors) are necessary, but these evaluation methods can also be applied to signals from other sensors. Furthermore, in other engine concepts that do not require speed detection, for example, this method can also be used for other signals.

A further subject of the invention is a hand-held power tool according to claim 15, comprising an electric motor, a sensor for measuring an operating variable of the electric motor, and a motor controller, wherein the hand-held power tool is advantageously an impact wrench, in particular a rotary impact wrench, and the first operating state is an impact mode, in particular a rotary impact mode. The electric motor causes an input spindle to rotate, wherein an output spindle is connected to a tool holder. An anvil is connected to the output spindle in a rotationally fixed manner and a hammer is connected to the input spindle in such a way that, as a result of the rotation of the input spindle, it carries out an intermittent movement in the axial direction of the input spindle and an intermittent rotary movement around the input spindle, wherein the hammer intermittently strikes the anvil in this way and thus emits an impact and a rotational impulse to the anvil and thus to the output spindle. A first sensor transmits a first signal to the control unit, for example to determine a motor rotation angle. Furthermore, a second sensor can transmit a second signal to the control unit for determining an engine speed. The control unit is advantageously designed to carry out a method according to one of claims 1 to 14.

In a further embodiment, the hand-held power tool is a battery-operated hand-held power tool, in particular a battery-operated impact wrench. This ensures flexible and mains-independent use of the hand-held power tool.

In a preferred embodiment, the hand-held power tool is a cordless screwdriver, a drill, an impact drill or a hammer drill, whereby a drill, a core bit or various bit attachments can be used as a tool. The hand-held power tool according to the invention is designed in particular as an impact wrench tool, whereby the pulsed release of the motor energy generates a higher peak torque for screwing in or unscrewing a screw or a nut. In this context, the transmission of electrical energy is to be understood in particular as meaning that the hand-held power tool transmits energy to the body via a battery and/or via a power cable connection.

In addition, depending on the selected embodiment, the screwing tool can be designed to be flexible in the direction of rotation. In this way, the proposed method can be used both for screwing in and for unscrewing a screw or a nut.

Further features, possible applications and advantages of the invention emerge from the following description of the embodiment of the invention, which is shown in the drawing. It should be noted that the features described or shown in the figures, either individually or in any combination, are only descriptive of the subject matter of the invention, regardless of their summary in the patent claims or their reference, and regardless of their wording or representation in the description or in the drawing, and are not intended to limit the invention in any way.

Fig. 1

eine schematische Darstellung einer elektrischen Handwerkzeugmaschine;

Fig. 2(a)

eine schematische Darstellung eines Signals einer Betriebsgröße einer Handwerkzeugmaschine bei einem losen Befestigungselement;

Fig. 2(b)

eine schematische Darstellung eines Signals einer Betriebsgröße einer Handwerkzeugmaschine bei einem festen Befestigungselement;

Fig. 3

eine schematische Darstellung zweier verschiedener Aufzeichnungen des Signals der Betriebsgröße;

Fig. 4

ein Ablaufdiagramm eines erfindungsgemäßen Verfahrens; und

Fig. 5

eine gemeinsame Darstellung eines Signals einer Betriebsgröße und eines zustandstypischen Modellsignals für die Bandpassfilterung;

Fig. 6

eine gemeinsame Darstellung eines Signals einer Betriebsgröße und eines zustandstypischen Modellsignals für die Frequenzanalyse;

Fig. 7

eine gemeinsame Darstellung eines Signals einer Betriebsgröße und eines zustandstypischen Modellsignals für die Parameterschätzung;

Fig. 8

eine gemeinsame Darstellung eines Signals einer Betriebsgröße und eines zustandstypischen Modellsignals für die Kreuzkorrelation.

The invention is explained in more detail below with reference to the figures. They show:

Fig.1

a schematic representation of an electric hand tool;

Fig. 2(a)

a schematic representation of a signal of an operating variable of a hand-held power tool with a loose fastening element;

Fig. 2(b)

a schematic representation of a signal of an operating variable of a hand-held power tool with a fixed fastening element;

Fig.3

a schematic representation of two different recordings of the operating variable signal;

Fig.4

a flow chart of a method according to the invention; and

Fig.5

a joint representation of a signal of an operating variable and a state-typical model signal for bandpass filtering;

Fig.6

a joint representation of a signal of an operating variable and a state-typical model signal for frequency analysis;

Fig.7

a joint representation of a signal of an operating variable and a state-typical model signal for parameter estimation;

Fig.8

a joint representation of a signal of an operating variable and a state-typical model signal for the cross-correlation.

The Figure 1 shows a hand-held power tool 100 according to the invention, which has a housing 105 with a handle 115. According to the embodiment shown, the hand-held power tool 100 can be mechanically and electrically connected to a battery pack 190 for mains-independent power supply. In Fig.1 the hand-held power tool 100 is designed, for example, as a cordless impact wrench. However, it should be noted that the present invention is not limited to cordless impact wrenches, but can in principle be used in hand-held power tools 100 in which the detection of operating states is necessary, such as impact drills.

An electric motor 180, which is supplied with power by the battery pack 190, and a gear 170 are arranged in the housing 105. The electric motor 180 is connected to an input spindle via the gear 170. Furthermore A control unit 370 is arranged within the housing 105 in the area of the battery pack 190, which acts on the electric motor 180 and the transmission 170 for controlling and/or regulating them, for example by means of a set motor speed n, a selected angular momentum, a desired transmission gear x or the like.

The electric motor 180 can be operated, for example, via a manual switch 195, i.e. can be switched on and off, and can be any type of motor, for example an electronically commutated motor or a DC motor. In principle, the electric motor 180 can be electronically controlled or regulated in such a way that both reversing operation and specifications with regard to the desired motor speed n and the desired angular momentum can be implemented. The functioning and structure of a suitable electric motor are sufficiently known from the prior art, so that a detailed description is omitted here for the sake of brevity.

A tool holder 140 is rotatably mounted in the housing 105 via an input spindle and an output spindle. The tool holder 140 serves to hold a tool and can be molded directly onto the output spindle or connected to it in the form of an attachment.

The control unit 370 is connected to a power source and is designed such that it can control or regulate the electric motor 180 electronically using various current signals. The various current signals provide different rotational impulses for the electric motor 180, with the current signals being passed to the electric motor 180 via a control line. The power source can be designed, for example, as a battery or, as in the exemplary embodiment shown, as a battery pack 190 or as a mains connection.

Furthermore, control elements not shown in detail may be provided to set different operating modes and/or the direction of rotation of the electric motor 180.

In Figure 2 an example signal of an operating variable 200 of an electric motor 180 of a rotary impact wrench is shown, as it occurs in this or a similar form during the intended use of a rotary impact wrench. While the following statements refer to a rotary impact wrench, they also apply within the scope of the invention to other hand-held power tools 100 such as impact drills.

In this example, the abscissa x represents the Figure 2 the time is plotted as a reference value. In an alternative embodiment, however, a value correlated with time is plotted as a reference value, such as the angle of rotation of the tool holder 140 or the angle of rotation of the electric motor 180. The motor speed n present at any time is plotted on the ordinate f(x) in the figure. Instead of the motor speed, another operating value correlated with the motor speed can also be selected. In alternative embodiments of the invention, f(x) represents, for example, a signal of the motor current.

Motor speed and motor current are operating variables that are usually recorded by a control unit 370 in hand-held power tools 100 without any additional effort. The determination of the signal of an operating variable 200 of the electric motor 180 is in Figure 4 , which shows a schematic flow diagram of a method according to the invention, is identified as method step S1. In preferred embodiments of the invention, a user of the hand-held power tool 100 can select the operating variable on the basis of which the inventive method is to be carried out.

In Fig. 2(a) is an application of a loose fastening element, for example a screw, in a fastening support, for example a wooden board, is shown. You can see in Figure 2(a) that the signal comprises a first region 310, which is characterized by a monotonous increase in the engine speed, as well as a region of comparatively constant engine speed, which can also be referred to as a plateau. The intersection point between abscissa x and ordinate f(x) in Figure 2(a) corresponds to the start of the impact wrench during the screwing process.

In the first area 310, the impact wrench operates in the operating state of screwing without impact.

In a second area 320, the rotary impact wrench operates in rotary impact mode. Rotary impact mode is characterized by an oscillating course of the signal of operating variable 200, whereby the form of the oscillation can be trigonometric or otherwise oscillating, for example. In the present case, the oscillation has a course that can be described as a modified trigonometric function, whereby the upper half-wave of the oscillation has a pointed hat or tooth-like shape. This characteristic form of the signal of operating variable 200 in impact wrench mode is created by the winding up and free running of the impact mechanism striker and the system chain located between the impact mechanism and the electric motor 180, including the gear 170.

The qualitative signal form of the impact operation is therefore known in principle due to the inherent properties of the rotary impact wrench. In the method according to the invention of Figure 4 Based on this knowledge, at least one state-typical model signal form 240 is defined in a step S0, wherein the state-typical model signal form 240 corresponds to the first operating state, in the example of Figure 2(a) i.e. the impact wrench operation in the second area 320. In other words, the state-typical model signal shape 240 contains features typical for the first operating state, such as the presence of an oscillation curve, oscillation frequencies or amplitudes, or individual signal sequences in continuous, quasi-continuous or discrete form.

In other applications, the first operating state to be detected may be characterized by signal forms other than oscillations, such as discontinuities or growth rates in the function f(x). In such cases, the state-typical model signal form is characterized by these parameters instead of oscillations.

In Fig. 2(b) is an application of a fixed fastening element, such as a screw, in a mounting support, such as a wooden board, shown. Here, "fixed" means that the fastening element is at least partially screwed into the fastening carrier and an interrupted screwing process is to be continued. The reference numerals and designations of the first and second areas 310, 320 are as in Fig. 2(a) . The difference of the use case in Fig. 2(b) to Fig. 2(a) is that after a short start-up phase with the monotonically increasing speed, the rotary impact operation already starts during the monotonically increasing speed. In Fig. 2(b) It can be seen that there is essentially no plateau with the comparatively constant speed.

In a preferred embodiment of the inventive method, the state-typical model signal form 240 can be defined in method step S0. The state-typical model signal form 240 can be stored, calculated or saved internally in the device. In an alternative embodiment, the state-typical model signal form can alternatively and/or additionally be provided to the hand-held power tool 100, for example by an external data device.

In a method step S2 of the method according to the invention, the signal of the operating variable of the electric motor 180 is compared with the state-typical model signal form 240. In the context of the present invention, the feature "compare" should be interpreted broadly and in the sense of a signal analysis, so that a result of the comparison can in particular also be a partial or gradual match between the signal of the operating variable 200 of the electric motor 180 and the state-typical model signal form 240, wherein the degree of match between the two signals can be determined by various methods, which will be mentioned later.

In a method step S3 of the method according to the invention, the decision as to whether the first operating state is present is made at least partially based on the result of the comparison. The degree of agreement is a parameter that can be set at the factory or by the user to set a sensitivity for detecting the first operating state.

In practical applications, it can be provided that the method steps S1, S2 and S3 are carried out repeatedly during the operation of a hand-held power tool 100 in order to monitor the operation for the presence of the first operating state. For this purpose, the determined signal of the operating variable 200 can be segmented in method step S1, so that the method steps S2 and S3 are carried out on signal segments, preferably always of the same, fixed length.

For this purpose, the signal of the operating variable 200 can be stored as a sequence of measured values in a memory, preferably a ring buffer. In this embodiment, the hand-held power tool 100 comprises the memory, preferably the ring buffer.

As in connection with Figure 2 As already mentioned, in preferred embodiments of the invention in method step S1 the signal of the operating variable 200 is determined as a time course of measured values of the operating variable, or as measured values of the operating variable as a variable of the electric motor 180 that correlates with the time course. The measured values can be discrete, quasi-continuous or continuous.

One embodiment provides that the signal of the operating variable 200 is recorded in method step S1 as a time course of measured values of the operating variable and in a method step S1a following method step S1, a transformation of the time course of the measured values of the operating variable into a course of the measured values of the operating variable as a variable of the electric motor 180 that correlates with the time course, such as the angle of rotation of the tool holder 140 or the angle of rotation of the motor.

The advantages of this embodiment are explained below using Figure 3 described. Similar to Figure 2 shows Figure 3a Signals f(x) of an operating variable 200 over an abscissa x, in this case over time t. As in Figure 2 The operating variable can be an engine speed or a parameter correlated with the engine speed.

The figure contains two signal curves of operating size 200 in the first operating mode, in the case of a rotary impact wrench, in rotary impact wrench mode. In both cases, the signal comprises a wavelength of an oscillation curve assumed to be ideally sinusoidal, whereby the signal with the shorter wavelength, T1, has a curve with a higher impact frequency, and the signal with the longer wavelength, T2, has a curve with a lower impact frequency.

Both signals can be generated with the same hand-held power tool 100 at different motor speeds and depend, among other things, on the rotational speed requested by the user from the hand-held power tool 100 via the control switch.

If, for example, the parameter "wavelength" is to be used to define the state-typical model signal form 240, then in the present case at least two different wavelengths T1 and T2 would have to be stored as possible parts of the state-typical model signal form so that the comparison of the signal of the operating variable 200 with the state-typical model signal form 240 leads to the result "match" in both cases. Since the engine speed can change generally and to a large extent over time, this means that the wavelength sought also varies and the methods for detecting this beat frequency would therefore have to be adjusted accordingly.

If there were a large number of possible wavelengths, the complexity of the process and the programming would increase accordingly quickly.

In the preferred embodiment, the time values of the abscissa are therefore transformed into values that correlate with the time values, such as acceleration values, higher order jerk values, power values, energy values, frequency values, angle of rotation values of the tool holder 140 or angle of rotation values of the electric motor 180. This is possible because the rigid transmission ratio of the electric motor 180 to the impact mechanism and the tool holder 140 results in a direct, known dependence of the motor speed on the impact frequency. This standardization achieves a vibration signal of constant periodicity that is independent of the motor speed, which in figure 3b represented by the two signals resulting from the transformation of the signals belonging to T1 and T2, where both signals now have the same wavelength P1=P2.

Accordingly, in this embodiment of the invention, the state-typical model signal shape 240 can be defined valid for all speeds by a single parameter of the wavelength over the time-correlated quantity, such as the angle of rotation of the tool holder 140 or the motor angle of rotation.

In a preferred embodiment, the comparison of the signal of the operating variable 200 in method step S2 is carried out with a comparison method, wherein the comparison method comprises at least a frequency-based comparison method and/or a comparative comparison method. The comparison method compares the signal of the operating variable 200 with the state-typical model signal form 240 to determine whether at least one predetermined threshold value is met. The frequency-based comparison method comprises at least bandpass filtering and/or frequency analysis. The comparative comparison method comprises at least parameter estimation and/or cross-correlation. The frequency-based and comparative comparison methods are described in more detail below.

In embodiments with bandpass filtering, the input signal, optionally as described, transformed to a time-correlated quantity, is filtered via a bandpass whose passband represents the predetermined threshold value. The passband results from the state-typical model signal shape 240. It is also conceivable that the passband corresponds to a frequency defined in connection with the state-typical model signal shape 240. In the event that amplitudes of this frequency exceed a previously defined limit value, as is the case in the first operating state, the comparison in method step S2 then leads to the result that the signal of the operating quantity 200 is equal to the state-typical model signal shape 240, and that the first operating state is thus carried out. The definition of an amplitude limit value can be as a method step S2a following method step S2 of a quality determination of the correspondence of the state-typical model signal form 240 with the signal of the operating variable 200, on the basis of which it is decided in method step S3 whether the first operating state exists or not.

In embodiments that use frequency analysis as a frequency-based comparison method, the signal of the operating variable 200 is transformed from a time domain to the frequency domain with appropriate weighting of the frequencies on the basis of frequency analysis, for example the fast Fourier transformation (FFT), wherein at this point the term "time domain" is to be understood as both "course of the operating variable over time" and "course of the operating variable as a variable correlated with time" in accordance with the above explanations.

Frequency analysis in this form is well known as a mathematical tool for signal analysis in many areas of technology and is used, among other things, to approximate measured signals as series expansions of weighted periodic harmonic functions of different wavelengths. The weighting factors indicate whether and to what extent the corresponding harmonic functions of a certain wavelength are present in the signal under investigation.

In relation to the method according to the invention, frequency analysis can be used to determine whether and with what amplitude the frequency assigned to the state-typical model signal shape 240 is present in the signal of the operating variable 200. As mentioned in connection with the bandpass filtering, a limit value of the amplitude can be set, which is a measure of the degree of agreement between the signal of the operating variable 200 and the state-typical model signal shape 240. If the amplitude of the frequency assigned to the state-typical model signal shape 240 in the signal of the operating variable 200 exceeds this limit value, it is determined in method step S3 that the first operating state is present.

In embodiments in which the comparative comparison method is used, the signal of the operating variable 200 is compared with the state-typical model signal shape 240 in order to find out whether the measured signal of the operating variable 200 has at least a 50% match with the state-typical model signal shape 240 and thus the predetermined threshold value is reached. It is also conceivable that the signal of the operating variable 200 is compared with the state-typical model signal shape 240 in order to determine a deviation of the two signals from one another.

In embodiments of the method according to the invention in which the parameter estimation is used as a comparative comparison method, the measured signal of the operating variables 200 is compared with the state-typical model signal shape 240, wherein estimated parameters are identified for the state-typical model signal shape 240. With the help of the estimated parameters, a degree of agreement between the measured signal of the operating variables 200 and the state-typical model signal shape 240 can be determined as to whether the first operating state is present. The parameter estimation is based on the compensation calculation, which is a mathematical optimization method known to those skilled in the art. With the help of the estimated parameters, the mathematical optimization method makes it possible to adjust the state-typical model signal shape 240 to a series of measurement data of the signal of the operating variable 200. Depending on a degree of agreement between the estimated parameters of the state-typical model signal shape 240 and the measured signal of the operating variable 200, the decision as to whether the first operating state is present can be made.

With the help of the adjustment calculation of the comparative method of parameter estimation, a measure of a deviation of the estimated parameters of the state-typical model signal shape 240 from the measured signal of the operating variable 200 can also be determined.

In order to decide whether there is sufficient agreement or a sufficiently small deviation of the state-typical model signal shape 240 with the estimated parameters for the measured signal of the operating variable 200, a deviation determination is carried out in the method step S2 following method step S2. If the deviation of 70% from the state-typical model signal shape 240 to the measured signal of the operating variable is determined, the decision can be made as to whether the first operating state was identified in the signal of the operating variable and whether the first operating state is present.

In order to decide whether there is sufficient agreement between the state-typical model signal form 240 and the signal of the operating variable 200, in a further embodiment, a quality determination for the estimated parameters is carried out in a method step S2a following method step S2. During the quality determination, values for a quality between 0 and 1 are determined, with a higher value representing a higher agreement between the state-typical model signal form 240 and the signal of the operating variable 200. The decision as to whether the first operating state is present is made in the preferred embodiment in method step S3 at least partially based on the condition that the value of the quality is in a range of 50%.

In one embodiment of the inventive method, the cross-correlation method is used as a comparative comparison method in method step S2. Like the mathematical methods described above, the cross-correlation method is known per se to those skilled in the art. In the cross-correlation method, the state-typical model signal shape 240 is correlated with the measured signal of the operating variable 200.

In comparison to the parameter estimation method presented above, the result of the cross-correlation is again a signal sequence with an added signal length from a length of the signal of the operating variable 200 and the state-typical model signal form 240, which represents the similarity of the time-shifted input signals. The maximum of this output sequence represents the time of the highest agreement between the two signals, i.e. the signal of the operating variable 200 and the state-typical model signal form 240. and is thus also a measure of the correlation itself, which in this embodiment is used in method step S3 as a decision criterion for the presence of the first operating state. In the implementation in the method according to the invention, a significant difference to the parameter estimation is that any state-typical model signal shapes can be used for the cross-correlation, while in the parameter estimation the state-typical model signal shape 240 must be able to be represented by parameterizable mathematical functions.

Figure 5 shows the measured signal of the operating variable 200 for the case where bandpass filtering is used as the frequency-based comparison method. The time or a value correlated with time is plotted as the abscissa x. Figure 5a shows the measured signal of the operating variable, an input signal of the bandpass filtering, wherein in the first area 310 the hand-held power tool 100 is operated in screwing mode. In the second area 320 the hand-held power tool 100 is operated in rotary impact mode. Figure 5b represents the output signal after the bandpass has filtered the input signal.

Figure 6 represents the measured signal of the operating quantity 200 in the case that frequency analysis is used as the frequency-based comparison method. In Figure 6 a and b show the first area 310 in which the hand tool 100 is in screwing mode. On the abscissa x of the Figure 6a the time t or a time-correlated quantity is plotted. In Figure 6b The signal of the operating variable 200 is shown transformed, whereby, for example, it can be transformed from time to frequency using a fast Fourier transformation. On the abscissa x' of the Figure 6b For example, the frequency f is plotted so that the amplitudes of the signal of the operating variable 200 are shown. In the Figures 6c and d the second region 320 is shown, in which the hand-held power tool 100 is in rotary impact mode. Figure 6c shows the measured signal of the operating quantity 200 plotted over time in rotary impact operation. Figure 6d shows the transformed signal of the operating variable 200, where the signal of the operating variable 200 is plotted against the frequency f as abscissa x'. Figure 6d shows characteristic amplitudes for rotary impact operation.

Figure 7a shows a typical case of a comparison using the comparative comparison method of parameter estimation between the signal of an operating variable 200 and a state-typical model signal shape 240 in the first area 310 described in Figure 2. While the state-typical model signal shape 240 has an essentially trigonometric curve, the signal of the operating variable 200 has a curve that differs greatly from this. Regardless of the choice of one of the comparison methods described above, in this case the comparison carried out in method step S2 between the state-typical model signal shape 240 and the signal of the operating variable 200 results in the degree of agreement between the two signals being so low that the first operating state is not determined in method step S3.

In Figure 7b In contrast, the case is shown in which the first operating state is present and therefore the state-typical model signal form 240 and the signal of the operating variable 200 have a high degree of agreement overall, even if deviations can be detected at individual measuring points. In this way, the decision as to whether the first operating state is present can be made in the comparative comparison process of the parameter estimation.

Figure 8 shows the comparison of the state-typical model signal shape 240, see Figure 8b and e , with the measured signal of operating size 200, see Figure 8a and 8d , in case cross-correlation is used as a comparative comparison method. In the Figures 8a - f The time or a value correlated with time is plotted on the abscissa x. In the Figures 8 a - c the first area 310, the screwing operation, is shown. In the Figures 8 d - f the second area 320, the first operating state, is shown. As described above, the measured signal of the operating variable, Figure 8a and Figure 8d , with the state-typical model signal shape, Figure 8b and 8e , correlated. In the Figures 8c and 8f The respective results of the correlations are shown. Figure 8c shows the result of the correlation during the first range 310, where it can be seen that there is a slight agreement between the two signals. In Figure 8c Therefore, the screw operation is present. In Figure 8f the result of the correlation during the second area 320 is shown. It is in figure 8f It can be seen that there is a high degree of agreement, so that the hand-held power tool 100 is operated in the first operating state.

The invention is not limited to the embodiment described and illustrated. Rather, it also includes all specialist developments within the scope of the invention defined by the patent claims.

In addition to the embodiments described and illustrated, further embodiments are conceivable, which may include further modifications and combinations of features.

Claims (15)

1. Method for detecting a first operating state of a handheld power tool (100), the handheld power tool (100) including an electric motor (180), the method comprising the following step:

   S1 ascertaining a signal of an operating quantity (200) of the electric motor (180);

   wherein the method is characterized by the following steps:

   S2 comparing the signal of the operating quantity (200) with at least one state-typical model signal form (240), the state-typical model signal form (240) having been assigned to the first operating state;
   and

   S3 deciding whether the first operating state is present, the decision depending at least partially on whether the state-typical model signal form (240) is identified in the signal of the operating quantity (200) in step S2.
2. Method according to Claim 1, characterized in that the state-typical model signal form (240) is an oscillation curve, in particular a trigonometric oscillation curve.
3. Method according to Claim 1 or 2, characterized in that the operating quantity is a speed of the electric motor (180) or an operating quantity correlating with the speed.
4. Method according to one of the preceding claims, characterized in that the signal of the operating quantity (200) is recorded in method step S1 as a temporal progression of measured values of the operating quantity or as measured values of the operating quantity as a quantity of the electric motor (180) correlating with the temporal progression.
5. Method according to one of the preceding claims, characterized in that the signal of the operating quantity (200) is recorded in method step S1 as a temporal progression of measured values of the operating quantity, and, in a method step S1a following the method step, the temporal progression of the measured values of the operating quantity is transformed into a progression of the measured values of the operating quantity as a quantity of the electric motor (180) correlating with the temporal progression.
6. Method according to one of the preceding claims, characterized in that the signal of the operating quantity (200) is stored as a sequence of measured values in a memory, preferably a ring memory, in particular of the handheld power tool (100).
7. Method according to Claim 6, characterized in that in method step S1 the measured values are segmented in such a manner that the signal of the operating quantity (200) always comprises a predetermined number of measured values.
8. Method according to one of the preceding claims, characterized in that in method step S2 the signal of the operating quantity (200) is compared by means of one of the comparison methods encompassing at least one frequency-based comparison method and/or a comparative comparison method, the comparison method comparing the signal of the operating quantity (200) with the state-typical model signal form (240) in order to determine whether at least one predetermined threshold value is satisfied.
9. Method according to Claim 8, characterized in that the frequency-based comparison method encompasses at least bandpass filtering and/or frequency analysis, the predetermined threshold value amounting to at least 85%, in particular 90%, quite particularly 95%, of a predetermined limiting value.
10. Method according to Claim 8, characterized in that the comparative comparison method encompasses at least parameter estimation and/or crosscorrelation, the predetermined threshold value amounting to at least 50% of a concordance of the signal of the operating quantity (200) with the state-typical model signal form (240).
11. Method according to one of the preceding claims, characterized in that method step S2 includes a subsequent method step S2a of a determination of the quality of the identification of the state-typical model signal form (240) and of the signal of the operating quantity (200), the decision in method step S3 as to whether the first operating state is present being made at least partially on the basis of the quality determination.
12. Method according to one of the preceding claims, characterized in that method step S2 includes a subsequent method step S2a of a determination of the deviation of the identification of the state-typical model signal form (240) and of the signal of the operating quantity (200), the decision in method step S3 as to whether the first operating state is present being made at least partially on the basis of the deviation determination.
13. Method according to one of the preceding claims, characterized in that the first operating state is identified on the basis of fewer than ten impacts of an impact mechanism of the handheld power tool (100), in particular fewer than ten impact-oscillation periods of the electric motor (180), preferably fewer than six impacts of an impact mechanism of the handheld power tool (100), in particular fewer than six impact-oscillation periods of the electric motor (180), quite preferably fewer than four impacts of an impact mechanism of the handheld power tool (100), in particular fewer than four impact-oscillation periods of the electric motor (180).
14. Method according to one of the preceding claims, characterized in that the handheld power tool (100) is an impact wrench, in particular a rotary impact wrench, and the first operating state is an impact mode, in particular a rotary impact mode.
15. Handheld power tool (100) including an electric motor (180), a pick-up for a measured value of an operating quantity of the electric motor (180) and a control unit (370), characterized in that the control unit (370) has been set up to implement the method according to one of Claims 1 to 13.

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