Load dependent drive control for power tools

Abstract

The invention relates to a method and a corresponding drive arrangement for load-dependent drive control of an electric power tool during at least one start-up phase after switching on (I) an electric motor drive unit (5), the method comprising: starting (II) a speed-controlled electric motor drive unit (5) up to an initial start-up speed (vS) below a nominal speed (vN); monitoring (III) whether a motor reference current (IM) of the electric motor drive unit (5) exceeds a load limit value (IL) indicative of a load of the electric power tool; and increasing (IV) the drive speed from the starting speed (vS) to a nominal speed (vN) if the actual motor reference current (IM) exceeds the load limit (IL).

Description

Technical Field

[0001] The present invention relates to a method for load-dependent drive control of an electric power tool during at least one startup phase after an electric motor drive unit has been switched on. Furthermore, the present invention relates to a drive unit for speed control of an electric power tool for implementing the method, as well as to such an electric power tool itself. Furthermore, the present invention relates to a computer program or computer program product for implementing the method.

[0002] The field of application of the invention extends primarily to handheld power tools, such as rotary hammers, breaker hammers, but also, for example, electric screwdrivers. The power supply can be wireless via batteries or wired in a conventional manner.

[0003] As the power-to-weight ratio of the power tools discussed here increases, they become more difficult to operate. This is because lower inertia leads to erratic tool behavior, particularly when sudden loads are applied. Sudden loads occur when the tool strikes a workpiece with significant force. Therefore, soft-start functionality is desirable in electric power tools. Background Art

[0004] Document US 2018 / 0043521 A1 shows a handheld electric power tool of the type of interest here, the electric motor drive unit of which performs soft starting. To this end, a rotational motion sensor housed inside the handle of the machine housing detects the rotational movement of the machine housing around the working axis. The holding force is determined based on the amplitude of the rotational movement within a frequency range between 0.4 Hz and 4 Hz. If the determined rotational movement exceeds a limit value, the torque delivered by the electric power tool is reduced so that the triggering behavior is adapted to the user's determined holding force. The effect of the holding force on the average movement of the handheld power tool is not significantly different from the effect on other average movements. In particular, the various applications of the same power handheld power tool and the associated different typical movements make it difficult to identify the clamping force. According to the present technical solution, it has been found that, within a narrow frequency range, the rotational movement around the working axis is important for the holding force.

[0005] Document DE 10 2012 005 803 A1 describes another electric power tool in the form of a hammer drill with load-dependent stroke adjustment. Here, a force detection device detects the operator's squeezing force on the handle of the machine housing. If the detected squeezing force exceeds a predetermined operating impact force limit, the impact frequency of the impact mechanism is increased to a predetermined operating frequency. If the operator's detected squeezing force falls below a predetermined idle impact force limit, the impact frequency is reduced to a predetermined idle frequency. This ensures that the tool does not trip due to excessive impact force when applied to the workpiece being machined.

[0006] Document EP 2 324 961 B1 discloses another handheld power tool that utilizes a tool head removably mounted in a front end region of a tool body against a workpiece to perform a predetermined operation. The handheld power tool includes a plurality of different types of detection sensors that detect a number of load conditions that differ in the presence or absence and magnitude of a load applied to the tool head. For the same purpose as described above, an indication device indicates the load condition based on the results detected by the detection sensors, and a drive control device controls the drive of the tool head based on the results detected by the detection sensors.

[0007] All of the aforementioned technical solutions for load-dependent drive control of electric power tools require additional sensors and accessories to determine the current load state. Furthermore, the signals measured by the sensor elements must be analyzed and interpreted by additional signal processing components in order to generate appropriate control commands for the electric motor drive unit.

[0008] The object of the present invention is to further improve a method and a device for load-dependent drive control of a power tool in such a way that an improved power supply of an electric power tool is improved with less technical effort, in particular during the startup phase after switching on the electric motor drive unit. Summary of the Invention

[0009] This object is achieved by a method according to claim 1. The corresponding claim 5 specifies a speed-controlled drive device suitable for implementing the method. Claim 8 relates to an electric power tool having such a speed-controlled drive device, and claim 9 relates to a computer program product for implementing the method according to the invention, the steps of the method being implemented in the corresponding program code.

[0010] The invention includes the technical teaching that, at least during a starting phase after switching on an electric motor drive unit operated in a speed-controlled manner, the electric motor drive unit starts up to a speed below the nominal speed v N Initial starting speed v SThen, the motor reference current I of the electric motor drive unit is monitored. M Whether the load limit value I indicating the load of the electric power tool is exceeded L If the current motor reference current I M Exceeding the load limit I L , then the driving speed changes from the starting speed v S Increase to nominal speed v N Otherwise, maintain the starting speed v S .

[0011] The solution according to the invention is based on the knowledge that the motor reference current I M is functionally related, for example proportionally related, to the load on the electric power tool. If, for example, the load on the electric power tool increases because the tool is pressed against the workpiece to be machined, this can be seen from a correspondingly increased motor reference current I M Since the output power of the electric power tool is approximately proportional to the motor speed, the solution according to the invention controls the tool speed in order to improve the handling of the electric power tool by varying the drive speed. This is done by means of the load-dependent drive control of the drive speed according to the invention via detection of the motor reference current. No additional sensor elements and the signal processing required for this are required. The solution according to the invention relies solely on parameters that are already available within the scope of the speed control of the drive unit to set the desired drive speed, which enables a soft start of the electric power tool for improved handling. It also depends on the motor reference current I for detecting the application or removal of the load. M threshold level.

[0012] Preferably, a reduced starting speed v is maintained S , until the motor reference current I M Exceeding the load limit I L When the load is lowered again, for example by lowering the workpiece from the tool, it is possible to return to the starting speed v S .

[0013] According to a preferred embodiment of the present invention, the initial starting speed v S is set to the nominal speed v N 70% of the power tool, whereby a tolerance range of + / - 25% is preferably permissible. In order to enable a particularly effective soft start phase, a tolerance range of + / - 10% is optimal in order to ensure sufficient initial power of the electric power tool, which initial power is not so high as to significantly impair handling when the tool is placed on the workpiece.

[0014] Preferably, the load limit value I representing the load Lcorresponds to at least 60% of the full load of the electric power tool. This means that, starting from this limit value, the full nominal speed v N transitions to achieve a sufficiently soft startup phase.

[0015] For the same reason, it is also recommended that the driving speed be increased from the starting speed v S To nominal speed v N The speed control increase is implemented with a maximum gradient of 0.8. This allows a gradual increase to a higher nominal speed v N And thus prevent too sudden jumps in speed from occurring. Of course, this gradient also depends on the system inertia, so that in the case of particularly high rotating masses, the increase implemented by speed control can also be omitted if necessary.

[0016] The method according to the invention described above can be implemented using a drive device for speed control of an electric power tool, the drive device comprising an electric motor drive unit housed in a machine housing, the electric motor drive unit being switchable by an operator via an electric switch arranged on the machine housing. The electric control unit is configured to start the electric drive unit until the speed falls below a nominal speed v N Initial starting speed v S The comparison unit is provided for monitoring the motor reference current I M Whether the stored load limit value I representing the load of the electric power tool is exceeded L If the current motor reference current I M Exceeding the load limit I L , the control unit increases the driving speed to the nominal speed v N , thus providing the full power of the electric power tool.

[0017] Preferably, at least the load limit value I used for the described comparison purpose L is stored in the electronic memory unit. Load limit value I L is machine-specific and is stored at least once in the memory unit. In addition, the parameter startup speed v S Preferably stored in the same or another storage unit.

[0018] According to a preferred embodiment of the electric drive unit, it is designed as a brushless DC motor (BLDC) operated by an electronic speed control device as described above.

[0019] Furthermore, it should be pointed out that the method according to the invention for implementation in the above-described electronically speed-controlled drive device is designed as a software program with suitable program code. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Other technical features that improve the present invention are shown in more detail below together with the description of preferred embodiments of the present invention with reference to the accompanying drawings.

[0021] Figure 1 shows a schematic side view of an electric power tool having a drive member with speed control implemented herein, Figure 2 Shown according to Figure 1 The block diagram of the driving component, Figure 3 shows a schematic flow chart illustrating the process steps, and Figure 4 A graphical representation of speed control during the start-up phase of an electric motor drive unit is shown. DETAILED DESCRIPTION

[0022] Figure 1 A hammer drill is shown as an exemplary embodiment of a handheld power tool. The hammer drill includes a machine housing 1 for accommodating a drive member. The power tool also includes a tool holder 2, into which a shaft end 3 of a tool, such as a drill bit 4, can be inserted. An electric motor drive unit 5, which drives a hammer mechanism 6 and an output shaft 7, forms a primary drive device of the power tool. In this embodiment, the electric motor drive unit 5 is designed as a brushless DC motor. A battery pack 8 supplies power to the electric drive unit 5. A user can guide the power tool with the aid of a handle 9 and activate the power tool with the aid of an electric switch 10.

[0023] During operation, the power tool rotates the drill bit 4 about the working axis 11 and can thereby hammer the drill bit 4 into a workpiece along the working axis 11 in an impact direction 12. For controlling the electric motor drive unit 5, the electric power tool further comprises electronics 100.

[0024] according to Figure 2 The electronic device 100 comprises an electronic control unit 101 for speed control of the connected electric motor drive unit 5. After the electric motor drive unit 5 is switched on, the electronic control unit 101 initially causes the electric motor drive unit 5 to start until the speed falls below the nominal speed v N Initial starting speed v S , the initial starting speed is the nominal speed v N About 70% of

[0025] The comparison unit 102 connected to the electronic control unit 101 provides a reference value to the electronic control unit 101. The comparison unit 102 monitors the motor reference current I of the electric motor drive unit 5. M , and compares the motor reference current with the load limit value I stored in the memory unit 103 L If the actual motor reference current IM Exceeding the load limit I L , the driving speed is changed by the control unit 101 from the starting speed v S Increase to full rated speed v N .

[0026] according to Figure 3 The method for load-dependent drive control of a power tool according to the present invention comprises the following steps during at least the initial soft start phase: After the electric motor drive unit has been switched on (I), the electric motor drive unit 5 is started (II) to a speed below the nominal speed v N Initial starting speed v S . Then, monitor (III) the motor reference current I of the electric motor drive unit M Whether the load limit value I indicating the load of the electric power tool is exceeded L If the electric motor reference current I M Exceeding the load limit I L , the next step is to reduce the drive speed from the starting speed v S Increase to a higher nominal speed v N Otherwise, the electric motor drive unit continues at the starting speed v S operate.

[0027] Figure 4 The exemplary speed control timeline as described above is illustrated. At the start time t0, the electric motor drive unit starts until the nominal speed v N 70% until the first time point t1. This corresponds to the starting speed v S The starting speed v S is maintained until, based on the above monitoring of the motor reference current, a sufficient load on the electric power tool has been detected to reduce the drive speed from the starting speed v to the starting speed v at a second time point t2. S Increase to full nominal speed v N This feature is provided at least for the start-up phase of the electric power tool.

[0028] The present invention is not limited to the preferred embodiments described above. Modifications are also conceivable and are included within the scope of protection of the following claims. For example, it is also possible to repeat the load-dependent drive control process according to the invention after the tool has been removed from the workpiece. In this case, after the power tool is placed on the workpiece again, the electric motor drive unit will fall back to the starting speed v before the load on the power tool is repeated. S .

[0029] List of Reference Numerals 1. Machine casing 2 Tool holding part 3-axis end 4 drill bits 5Electric motor drive unit 6 Hammer mechanism 7 output shaft 8 battery packs 9 handles 10 Electric switch 11 working axis 12 Impact 100 electronic devices 101 control unit 102 comparison unit 103 memory cells v N Nominal speed v S Startup speed I M Motor reference current I L Load limiting current t0 start time t1 first time point t2 second time point

Claims

1. A method for load-dependent drive control of an electric power tool during at least one start-up phase after switching on (I) an electric motor drive unit (5), the method comprising the following steps: - Start (II) the speed-controlled electric motor drive unit (5) until the speed falls below the nominal speed (v N ) of the initial startup speed (v S ), - Monitoring (III) the motor reference current (I M ) exceeds the load limit value (I L ), - If the actual motor reference current (I M ) exceeds the load limit (I L ), the driving speed will be increased from the starting speed (v S ) increases (IV) to the nominal speed (v N ).

2. The method according to claim 1, It is characterized by: Maintain the starting speed (v S ) until the motor reference current (I M ) exceeds the load limit (I L ) at least once.

3. The method according to claim 1 or claim 2, It is characterized by: The initial starting speed (v S ) is set to the nominal speed (v N ), with a tolerance range of + / - 25%, preferably with a tolerance range of + / - 10%.

4. The method according to any one of the preceding claims, It is characterized by: The load limit value (I L ) corresponds to at least 60% of the full load of the electric power tool.

5. A drive device for an electric power tool for carrying out the method according to one of the preceding claims, the drive device comprising: - an electric motor drive unit (5) which is accommodated in a machine housing (1) and can be switched on by an electric switch (10) arranged on the machine housing (1), characterized in that - providing an electronic control unit (101) configured to start the electric drive unit (5) until the speed falls below the nominal speed (v N ) of the initial startup speed (v S ),in - providing a comparison unit (102) configured to monitor the motor reference current (I M ) exceeds a stored load limit value (I L ), where if the current motor reference current (I M ) exceeds the load limit value (I L ), the control unit (101) increases the driving speed to the nominal speed (v N ).

6. The driving device according to claim 5, It is characterized by: A memory unit (103) connected to the comparison unit (102) is provided for storing the load limit value (I L ).

7. The driving device according to claim 5 or claim 6, It is characterized by: The electric motor drive unit (5) is designed as a brushless DC motor.

8. An electric power tool having a speed-controlled drive according to one of claims 5 to 7.

9. A computer program comprising instructions which, when executed by a computer, cause the computer to perform the steps of the method according to any one of claims 1 to 4.

Images