Method for detecting abnormalities in the operation of an electric hand tool

Abstract

The invention relates to a computer-implemented method for detecting abnormalities in the operation of an electric hand tool, for the early detection of wear or fault states on the basis of monitoring of the cooling air flow for at least one electric motor of the electric hand tool controlled by an integrated control electronics, comprising the following steps: determining a first temperature in relation to the control electronics; measuring a second temperature with a temperature sensor arranged in the cooling air flow; comparing the time course of the estimated first temperature with the time course of the measured second temperature; evaluating the comparison data to determine whether the time point-related temperature difference between the first temperature and the second temperature rises above a specified threshold value, in order to deduce an abnormality that reduces or blocks the cooling air flow due to wear or a fault.

Description

[0001] Method for detecting abnormalities during operation of an electric hand tool

[0002] The present invention relates to a computer-implemented method for detecting abnormalities during the operation of an electric hand tool for the early detection of wear or fault conditions, an electric hand tool with an electric motor as a drive unit, and also a computer program embodying the method, which can be executed on a microprocessor-controlled control unit of the electric hand tool.

[0003] The field of application of the invention extends to electric hand tools, such as chisel and demolition hammers, hammer drills, drilling devices and the like, in which at least one electric motor is used as a drive unit.

[0004] High-performance power tools, in particular, require adequate cooling of the entire drive train to prevent wear or failures caused by overheating. For example, if a fan impeller integrated close to the motor fails due to blockage or contamination, or if it generates insufficient cooling airflow due to a lack of rotational speed, thermal overload of the motor windings and / or overheating of an impact mechanism unit are to be expected. The present invention is dedicated to the early detection of such abnormalities during the operation of a power tool, which, if they progress, would cause damage or failure.

[0005] State of the art

[0006] US 2022 / 0140758 A1 discloses a method for detecting abnormalities during the operation of a power hand tool for the early detection of wear or fault conditions. The known technical solution includes a driver circuit for a brushless DC motor (BLDC) as the drive unit, which comprises a power stage circuit configured to control the DC motor according to a pulse-width modulation signal. An additional abnormality diagnosis circuit is provided, which, while controlling a first parameter, determines an abnormality in the rotational state of the DC motor based on a second parameter.Both the first parameter and the second parameter correlate with the rotation of the DC motor and are selected from a parameter group comprising: speed of the DC motor, temperature of the DC motor, ambient temperature, operating current of the DC motor, operating voltage of the DC motor and duty cycle of the pulse width modulated signal controlling the DC motor.

[0007] An abnormal operating behavior is detected by controlling the first parameter at a constant level, and the abnormality diagnosis circuit detects a rotational abnormality of the DC motor by evaluating whether the second parameter exceeds a predetermined parameter range. For example, the two correlating parameters can be compared based on motor speed and motor temperature to determine whether an abnormal operating situation exists. In this case, a separate temperature sensor on the electric motor is required, as a conventional NTC resistor on the control board cannot provide the desired measured value.

[0008] The object of the present invention is to further improve a method for detecting abnormalities during the operation of a power tool for the early detection of wear or fault conditions, so that reliable indirect monitoring of the cooling air flow can be carried out using simple technical means. Summary of the Invention

[0009] The object is achieved by a computer-implemented method according to claim 1. With regard to an electric hand tool applying this method, reference is made to claim 8. Claim 10 specifies a computer program embodying the method steps according to the invention, which can be executed on a microprocessor-controlled control unit of an electric hand tool.

[0010] The invention includes the procedural teaching that the following steps are provided for detecting abnormalities during the operation of an electric hand tool for the early detection of wear or fault conditions based on the monitoring of a cooling air flow K for at least one electric motor of the electric hand tool controlled via the integrated control electronics:

[0011] - Determine a first temperature T e related to the control electronics;

[0012] Measuring a second temperature T m with a temperature sensor arranged in the cooling air flow K;

[0013] Comparing the time course of the estimated first temperature T e with the time course of the measured second temperature T m ;

[0014] Evaluate the comparison data to determine whether the time-related temperature difference between the first temperature T eand the second temperature T m a fixed threshold value A ma x in order to infer an abnormality that reduces or blocks the cooling air flow K and causes wear or failure.

[0015] The inventive solution is based on the realization that an air intake blockage in an electric hand tool represents an abnormality that damages the electric motor, even if the motor itself is functioning properly. Experience shows that such a malfunction in electric hand tools is caused by dust and dirt generated by the tool itself during operation or by the user holding the power tool incorrectly during use. The temperature comparison according to the invention and the associated special temperature difference analysis allow reliable conclusions to be drawn about a reduced or blocked cooling air flow K without the need for a special flow sensor.

[0016] Determining a first temperature T eThe temperature measured in relation to the control electronics can be determined by an NTC resistance value of the control electronics based on an electronic model. Alternatively, the determination of a first temperature T e The temperature sensor on the control electronics can be used, for example, on a MOSFET. It should be noted that the first temperature T e is detected at a point located in the cooling air flow.

[0017] In principle, according to the invention, it is assessed whether the measured second temperature of the cooling air flow is too far from the estimated temperature of the control electronics.

[0018] Preferably, the threshold value A ma x according to a first embodiment, a maximum permissible differential temperature AT max, the exceeding of which is classified as a wear- or error-causing abnormality. According to an alternative embodiment, the threshold value A ma x also a maximum permissible rate of increase of the difference of the temperature curves dT ma x, exceeding which is then also classified as a wear- or error-causing abnormality. The corresponding threshold values ​​A ma x are determined individually for each device through series of tests or can at least be based on empirical values.

[0019] The inventive estimation of the first temperature T e is preferably carried out using an electronic model that represents a data-driven first-order electronic model and processes the motor current IM, the motor speed nM, and the ambient temperature Tu as input values. The output value is the temperature T referred to the NTC resistor of the control electronics. eThe electronic model thus uses existing measurement data from the power tool's control system. The electronic model can be described using the following formula: x(t) = Ax(t) + Bit(t) y(t) = Cx(t) where: u = input values, y = output values, x = state values, and A1x1, B3x1, C1x1 represent system matrices that completely describe the system. The optimization algorithm runs offline at least once to determine the system parameters A, B, and C based on the measurement data.

[0020] As a measure to further improve the comparison step, it is proposed that this be carried out at a relatively high sampling rate between 0.5 and 100 Hz. Since the temperature estimation model requires very little computing capacity due to its small size, the comparison of the temporal temperature profiles can be carried out at a relatively high sampling rate, so that the detection of abnormalities can follow even highly dynamic profiles. Due to the high accuracy of the NTC signal estimated using the electronic model, the comparison of the temperature profiles according to the invention leads directly to the evaluation in the next step. The evaluation includes - as explained above - a test based on a threshold value, which can represent the difference temperature or the rate of increase of the temperature profiles occurring at a given point in time.

[0021] If the threshold value is exceeded, a further measure improving the invention can output a warning signal to the operator of the power tool. This gives the operator the opportunity to change the load on the power tool, its handling, or operating mode so that overloading is avoided in the future. Additionally or alternatively, the electric motor of the power tool can be automatically switched off, particularly if the threshold value is exceeded several times within a specified time interval. Restart can then be scheduled after a rest period or after maintenance personnel have reset the electronics. This allows, for example, a motor defect in the power tool to be proactively avoided.

[0022] Since electric hand tools of the type of interest here are already equipped with a microprocessor-equipped control board due to their integrated control electronics for a preferably brushless DC motor, the additional functionality according to the invention can be implemented therein, preferably in software, with little additional effort. For this purpose, a corresponding computer program comprises commands which, when executed by the microprocessor-controlled control unit of the electric hand tool, cause it to execute the method explained above.

[0023] Description based on drawing

[0024] Further measures improving the invention are presented in more detail below together with the description of a preferred embodiment of the invention with reference to the figures.

[0025] It shows:

[0026] Figure 1 is a schematic block diagram of an electric hand tool equipped with the range of functions according to the invention, and

[0027] Figure 2 shows a flow chart illustrating the steps of the computer-implemented method.

[0028] Example

[0029] According to Figure 1, an electric hand tool comprises a microprocessor-controlled electronics unit 1 for controlling an electric motor 2 designed as a brushless direct current (BLDC) motor. The electric motor 2 is cooled by a cooling air flow K, which is guided within the housing of the electric hand tool (not shown here). A temperature sensor 3 is arranged in the cooling air flow K, the measured values ​​of which are forwarded to the control electronics 1.

[0030] With this device, a method for detecting abnormalities during the operation of the power tool for the early detection of wear or fault conditions based on the monitoring of the cooling air flow K can be carried out as follows, as shown in Figure 2:

[0031] In process step I, a first temperature Te is estimated based on an NTC resistor of the control electronics using an electronic model. Subsequently, in process step II, a second temperature Tm is measured using the temperature sensor arranged in the cooling air flow K.

[0032] Subsequently, in process step III., a comparison of the temporal course of the estimated first temperature T e with the time course of the measured second temperature T mcarried out in order to finally evaluate the comparison data in process step IV to determine whether the time-related temperature difference between the first temperature T e and the second temperature T m rises above a specified threshold value Amax in order to conclude that there is an abnormality that reduces or blocks the cooling air flow K and causes wear or failure.

[0033] If the specified threshold A ma x is exceeded, in the following process step V. a warning signal is first given to the operator of the electric hand tool, who is then given the opportunity to change the operating situation of the electric hand tool. If the threshold value A max is exceeded several times, a final method step V.' in this embodiment involves shutting down the electric motor of the handheld tool. The solution according to the invention is not limited to the preferred embodiment described above. Rather, modifications thereof can also be made, which are also covered by the scope of the claims. For example, it is also possible to enter other input values ​​into the electronic model that are representative of an abnormality in the cooling air flow K.

[0034] List of reference symbols

[0035] 1 control electronics

[0036] 2 electric motor

[0037] 3 Temperature sensor

[0038] BLDC brushless DC motor

[0039] T e first temperature

[0040] T m second temperature

[0041] K Cooling air flow

[0042] Amax threshold

[0043] ÄTmax permissible differential temperature

[0044] (dTmax / dt) permissible rate of increase of the difference between the temperature curves

[0045] IM Motor current nM Motor speed

[0046] Tu ambient temperature

Claims

Patent claims 1. A computer-implemented method for detecting abnormalities during the operation of an electric hand tool for the early detection of wear or fault conditions based on monitoring the cooling air flow (K) for at least one electric motor (2) of the electric hand tool controlled by integrated control electronics (1), comprising the following steps: - Determine a first temperature T e related to the control electronics; - Measuring (II.) a second temperature (T m ) with a temperature sensor (3) arranged in the cooling air flow (K); - Compare (III.) the temporal course of the estimated first temperature (T e ) with the temporal course of the measured second temperature (T m ); - Evaluate the comparison data to determine whether the time-related temperature difference between the first temperature T e and the second temperature Tm a specified threshold A ma x in order to infer an abnormality that reduces or blocks the cooling air flow K and causes wear or failure.

2. Method according to claim 1, characterized in that the threshold value (A ma x) a maximum permissible differential temperature (AT ma x), the exceeding of which is classified as an abnormality caused by wear or failure.

3. Method according to claim 1, characterized in that the threshold value (A ma x) a maximum permissible rate of increase of the difference between the temperature profiles (dT ma x / dt), exceeding which is classified as an abnormality caused by wear or failure.

4. Method according to claim 1, characterized in that in step (I.) a data-driven electronic model of the first order processes the engine current (IM), the engine speed (OM) and the ambient temperature (Tu) as input values ​​in order to calculate the first temperature (T e ) as the output value.

5. Method according to claim 1, characterized in that in step (III.) the comparison of the temporal temperature profiles is carried out with a high sampling rate between 0.5 and 1000 Hz.

6. Method according to claim 1, characterized by: Outputting (V.) a warning signal to the operator of the power tool if the threshold value (A ma x) has been exceeded.

7. Method according to claim 1, characterized by: Outputting (V.') a switch-off signal for the electric motor (2) of the electric hand tool if the threshold value (A max) has been exceeded, preferably several times within a predetermined time interval.

8. Method according to claim 1, characterized by: Outputting (V.') a signal for the electric motor (2) of the electric hand tool to reduce the speed of the electric motor (2) if the threshold value (A ma x) has been exceeded, preferably several times within a predetermined time interval.

9. Electric hand tool with at least one electric motor (2) as a drive unit, which is controlled by a microprocessor-controlled control electronics (1) which carries out a method according to one of the preceding claims 1 to 7.

10. Electric hand tool according to claim 9, characterized in that the electric motor (2) is designed as a brushless direct current motor (BLDC) whose speed can be controlled via the control electronics (1).

11. A computer program comprising instructions which, when the program is executed by a microprocessor-controlled control unit (1) of an electric hand tool, cause the latter to carry out the method according to one of the preceding claims 1 to 8.

Images