EP3398725B1 - Oscillating driveable handheld tool and method for operating same - Google Patents

Description

The invention relates to a hand tool that can be driven in an oscillating manner, having a drive for driving a tool in an oscillating manner, and having at least one vibration sensor for monitoring vibrations, the output signals of which are fed to a control unit.

Such a hand tool is from DE 10 2007 014 891 A1 known.

In this case, the accelerations occurring are to be determined by means of a measuring device for determining the vibration exposure of persons and after a predetermined limit value has been exceeded, the hand tool can be switched off if necessary.

However, it essentially does this by sensing and summing the vibrations over an extended period of tool operation, and then shutting down when a time-weighted predetermined limit is reached.

It is not intended to switch off during operation if a certain limit value for vibrations is exceeded. According to the WO 2015/197753 A1 it is also known to use a sensor for detecting vibration values in a hand-held power tool in the form of a hammer drill in order to reduce the output power of the hand-held tool when a predetermined limit value is exceeded.

From the WO 2014/072044 A2 and the WO 2016/127936 A1 it is also known to switch off the machine after a cumulative vibration load has been reached in order to protect the user from excessive vibration load.

the US 2012/0318545 A1 shows a hand tool according to the preamble of claim 1 and a method according to the preamble of claim 15 of the present invention, in which the speed or the current is reduced when the vibrations occurring become too great. However, this reduction can be bypassed by the user using a switch.

Against this background, the invention is based on the object of specifying an oscillatingly drivable hand tool and a method for operating such a tool, the vibrations occurring during operation being monitored and when a predetermined value is exceeded Limit value is a limitation to reduce the level of vibration for a user to physiologically acceptable levels.

This object is achieved in the case of an oscillatingly drivable hand tool with a drive for oscillatingly driving a tool, with at least one vibration sensor for monitoring vibrations, the output signals of which are fed to a control unit, in that the control unit is designed to calculate a vibration characteristic from the output signals of the vibration sensor and then, when the vibration characteristic exceeds a maximum value, to switch off the drive and then to restart it automatically.

• Starten eines oszillierenden Antriebs;
• zyklische Messung der Beschleunigung in drei Raumrichtungen;
• Berechnen eines Vibrationskennwertes aus den Beschleunigungswerten in drei Raumrichtungen;
• Anhalten des Antriebs, sofern der Vibrationskennwert einen vorgegebenen Maximalwert überschreitet; und
• erneutes Starten des oszillierenden Antriebs nach Ablauf einer vorgegebenen Zeit.

With regard to the method, the object of the invention is also achieved by a method for operating a hand tool that can be driven in an oscillating manner with the following steps:

• starting an oscillating drive;
• cyclic measurement of acceleration in three spatial directions;
• calculating a vibration characteristic from the acceleration values in three spatial directions;
• Stopping the drive if the vibration characteristic exceeds a predetermined maximum value; and
• restarting the oscillating drive after a specified time has elapsed.

The object of the invention is achieved in this way.

According to the invention, careful monitoring ensures that the hand tool is not operated with excessive vibrations that exceed a physiologically safe limit value. Since the drive is automatically restarted after it has been switched off, the vibration limitation can be carried out unnoticed to a certain extent by the user.

For this purpose, the control unit can be designed, for example, to switch off the drive after it has been switched off within a period of time which is in the range from 2 seconds to 0.2 seconds, preferably between 1.5 and 0.5 seconds, particularly preferably between 1.2 and 0.8 seconds is to start again, preferably in a soft start, preferably up to a preset oscillation frequency of up to 25000 1 / min.

If the drive automatically restarts after such a short period of time, the restart can take place largely unnoticed by the user, especially if the start is soft, ie with increasing acceleration over time.

In an advantageous development of the invention, the sampling rate for determining the vibration characteristic is greater than the maximum oscillation frequency of the drive, with the ratio between the sampling rate and the maximum oscillation frequency preferably being greater than 2.

In this way, sufficiently frequent sampling for determining the vibration characteristic value is ensured in order to ensure the detection of the vibration characteristic value even with different maximum oscillation frequencies.

According to a further feature of the invention, the drive is designed with a drive motor for generating a rotationally oscillating drive movement of a tool spindle, on which a tool can be fixed, about a fixed axis, with the drive movement of the tool spindle preferably having a small pivoting angle in the range of 0.5° up to 5° and preferably with a high oscillation frequency of up to 25000 rpm, and wherein the drive motor is preferably coupled to an oscillation gear to generate the rotationally oscillating drive movement.

Usually, the drive consists of a combination of a drive motor and an oscillating gear, which converts the rotary movement of the motor shaft of the drive motor into the desired rotationally oscillating drive movement of the tool spindle about its longitudinal axis. In principle, however, drives are also conceivable in which the rotationally oscillating drive movement of the tool spindle is generated directly by a hydraulic motor, for example in the form of a vane motor, which is driven by a hydraulic generator with oscillating fluid energy, as is the case, for example, in WO 2015/071304 A1 is known.

According to a further embodiment of the invention, the drive is designed as an assembly which is coupled to a housing of the hand tool via at least one preferably elastic damping element.

With such an embodiment, limiting the vibrations to a predetermined maximum value is particularly effective. Hand tools in which the drive is arranged vibration-decoupled from the housing are known in principle, compare eg WO 2015/140029 A1 .

According to a further embodiment of the invention, the vibration sensor is rigidly connected to the housing.

In this way, the vibrations can be detected directly, even if the drive is connected to the housing in a vibration-decoupled manner by means of elastic damping elements.

The vibration sensor is preferably accommodated on an electronic circuit board which is rigidly connected to the housing.

More preferably, the vibration sensor is designed as an acceleration sensor that detects three mutually perpendicular sensor directions.

In this way, a conventional acceleration sensor can be used as the vibration sensor.

According to a further embodiment of the invention, the vibration sensor is aligned in such a way that at least one sensor device is angularly offset, preferably by 45°, relative to a main direction of the vibrations.

This measure has the advantage that less expensive vibration sensors can be used, which are only designed for a lower maximum vibration. Due to the angular offset in relation to the main direction of vibration, the recorded vibration values are lower. If the sensor direction is aligned at 45° to the main vibration direction, only one value is recorded from the assigned axes, which corresponds to the actual acceleration divided by the square root of 2, so only about 0.7 times. Thus, less expensive vibration sensors can be used.

According to a further embodiment of the invention, the control device is designed to separately evaluate and preferably smooth and filter the output signals of the vibration sensor for the three sensor directions and to calculate a sum signal therefrom which is used as a vibration parameter.

Such an evaluation method is particularly precise since all sensor directions are used.

According to a further embodiment of the invention, the control device is designed to first rectify and average the output signals of the vibration sensor before the vibration characteristic value is calculated therefrom.

This results in a particularly reliable determination of the vibration characteristic.

According to a further embodiment of the invention, the control device is designed to form the square for each output signal of the vibration sensor relating to each sensor direction and to use the root of the sum of the squares, each directed with a factor, as the vibration parameter.

Since the vibration is accompanied by the acceleration and the acceleration is proportional to the square of the speed values detected by the vibration sensor, such an evaluation results in a particularly correct approximation of the actual conditions in the case of vibrations.

According to a further embodiment of the invention, a modified vibration characteristic value is used which is dependent on an output power of the hand tool, preferably on the oscillation frequency and an input power of the drive motor.

In this way, the physiological relationship can be exploited that larger accelerations are tolerable at lower oscillation frequencies than at higher oscillation frequencies. The same applies to an increased output power, i.e. the higher the output power or power consumption of the drive, the lower the permissible vibration limit values.

For this purpose, a means for measuring the speed of the drive motor is preferably provided, with the control device also being designed to calculate a proportionality factor from the speed of the drive motor, with which the vibration parameter calculated from the output signals is weighted in order to obtain a speed-weighted vibration parameter which, when the maximum value is exceeded, the drive is switched off and then started, the proportionality factor preferably being less than 3, preferably less than 2.

In this way, an inversely proportional relationship between the speed of the drive motor and the permissible maximum vibration value can be used.

In an additional development of this embodiment, a means for measuring the current consumption of the drive motor is also provided, preferably by measuring the phase current, with the control device being designed to calculate a speed-weighted current consumption of the drive motor, in which a proportionality factor derived from the speed is used, which is preferably between 1.2 and 2.7, preferably between 1.5 and 2.5, the speed-weighted current consumption being used as an additional switch-off criterion for the speed-weighted vibration characteristic value and a switch-off only taking place if both the speed-weighted vibration characteristic value exceeds a predetermined maximum value, and the speed-weighted current consumption of the drive motor exceeds a predetermined maximum value.

In this way, both a dependence of the maximum permissible vibration on the rotational speed and on the power output of the hand tool can be used.

The predetermined maximum value for the vibration characteristic value or the speed-weighted vibration characteristic value is preferably at least 10 g (i.e. 10 times the acceleration due to gravity), preferably at least 12 g.

If a speed-weighted vibration parameter is used, this can tend to be somewhat higher, for example in the range between 14 g and 16 g.

It goes without saying that the features mentioned above in connection with the hand tool can also be used in connection with the above-mentioned method for operating a hand tool that can be driven in an oscillating manner. It is also understood that the features of the invention mentioned above and those yet to be explained below can be used not only in the respectively specified combination but also in other combinations or on their own without departing from the scope of the invention.

Fig. 1

eine perspektivische Darstellung eines erfindungsgemäßen Handwerkzeugs;

Fig. 2

eine Darstellung des Handwerkzeugs gemäß Fig. 1 nach Abnahme eines Teils des das Handwerkzeug umschließenden Gehäuses;

Fig. 3

eine Seitenansicht des Handwerkzeugs gemäß Fig. 1;

Fig. 4

einen Schnitt durch das Handwerkzeug gemäß Fig. 3 längs der Linie IV-IV;

Fig. 5

eine perspektivische Ansicht des Vibrationssensors in vergrößerter Darstellung;

Fig. 6

ein Ablaufdiagramm (Flow-Chart), das den grundsätzlichen Aufbau des Verfahrens zum Erfassen der Vibrationen mittels des Vibrationssensors und zur Berechnung des Vibrationskennwertes nebst Abschalten und Wiederanfahren im Falle einer Überschreitung des Grenzwertes zeigt;

Fig. 7

ein Ablaufdiagramm, das die Berechnung des Vibrationskennwertes aus den einzelnen Beschleunigungswerten im Detail erläutert; und

Fig. 8

ein Ablaufdiagramm für eine alternative Ausführung der Erfindung, bei welcher ein modifizierter Vibrationskennwert ermittelt und zur Abschaltung verwendet wird.

Further features and advantages of the invention result from the following description of preferred exemplary embodiments with reference to the drawing. Show it:

1

a perspective view of a hand tool according to the invention;

2

a representation of the hand tool according to FIG 1 after removing part of the housing enclosing the hand tool;

3

a side view of the hand tool according to FIG 1 ;

4

according to a section through the hand tool 3 along line IV-IV;

figure 5

a perspective view of the vibration sensor in an enlarged view;

6

a flow chart showing the basic structure of the method for detecting the vibrations by means of the vibration sensor and for calculating the vibration characteristic value together with switching off and restarting if the limit value is exceeded;

Figure 7

a flowchart that explains in detail the calculation of the vibration characteristic value from the individual acceleration values; and

8

a flowchart for an alternative embodiment of the invention, in which a modified vibration characteristic is determined and used for shutdown.

In 1 a perspective view of a hand tool according to the invention is shown, which is designed for the oscillating drive of a tool, for example in the form of a grinding, cutting or sawing tool.

The hand tool, designated overall by the number 10, has a housing 12, the rear region 14 of which can be gripped by one hand in order to be able to hold the hand tool 10 in one hand in a comfortable manner. An on/off switch 16, which is used to switch the hand tool 10 on and off, can be seen on the upper side of the housing. On the left longitudinal side of the handle area 14, a setting wheel 26 can be seen, which is used to set the oscillation frequency. This allows the oscillation frequency to be continuously adjusted between 0 and around 20,000 oscillations per minute.

A clamping lever 18 is accommodated at the top of the front region facing away from the handle region 14 and is used for quick clamping of a tool (not shown) at the outer end of a tool spindle 20 which protrudes at an angle from the front end of the hand tool 10 downwards. The tool spindle 20 can their longitudinal axis 22 are driven in a rotationally oscillating manner, as indicated by a double arrow 24 . In this case, the pivoting angle is relatively small (between approximately 0.5° and 5°), while the oscillation frequency, as already mentioned above, can be up to approximately 20,000 oscillations per minute.

2 shows the detailed structure of the hand tool 10 after removal of the rear housing part 14 in the handle area 14. A drive 28 is accommodated in the middle area of the hand tool 10, which is designed as a self-supporting structural unit and comprises a drive motor and an oscillating gear, as described below with reference to 4 is described in more detail.

In the rear area used by the tool spindle 20, an electronic circuit board 19 can be seen, on which the adjusting wheel 26 is accommodated, as well as a central control unit (not shown) and a vibration sensor 32.

The detailed structure of the hand tool 10 is from the Figures 3 and 4 apparent.

Out of 4 it can be seen that the drive 28 consists of the drive motor 34 and the oscillation gear 38 . The motor shaft 36 of the drive motor 34 drives an oscillating fork of the oscillating gear 38 via an eccentric and thus converts a rotational movement of the motor shaft 36 into a rotationally oscillating drive movement of the tool spindle 20 about its longitudinal axis.

The drive 28 is designed together with the drive motor 34 and the oscillation gear 38 as a self-supporting structural unit which is coupled to the housing 12 via a number of elastic damping elements 40, 42, 44, 46.

Vibrations that emanate from the drive 28 or from the tool held on the tool spindle 20 are thus only transmitted to the handle area 14 of the housing 12 in a damped manner.

In 4 Furthermore, the longitudinal axis of the hand tool 10, which is denoted by 48, and the main direction of the vibrations v, which is perpendicular to the longitudinal axis 48, can also be seen.

The central control unit 30, which comprises a microprocessor, and the vibration sensor 32 are accommodated on the electronic circuit board 19.

The vibration sensor 32, which can be designed as a piezo sensor, for example, is enlarged in figure 5 shown. The vibration sensor 32 has three sensor axes x, y, z, which are arranged at right angles to one another in a Cartesian coordinate system. The vibration sensor 32 is preferably mounted on the electronic circuit board 29 in such a way that the sensor axes x, y are arranged at an angle of 45° to the main direction v of the vibrations, i.e. angularly offset by 45° with respect to the longitudinal axis 48 of the hand tool 10.

The consequence of this is that the vibrations occurring in the main direction v are only detected in a weakened manner by the sensor axes x, y, namely reduced by a factor square root of 2. A relatively inexpensive vibration sensor 32 can thus be used which does not have to be designed for very high acceleration limit values.

The method used according to the invention, to detect vibrations of the hand tool 10 measured by the vibration sensor 32 and to limit the vibration of the hand tool 10 to a maximum permissible level, is described below with reference to FIG Figures 6 to 8 explained in more detail.

6 shows a flowchart (flow chart) from which the basic principle of the method according to the invention can be seen.

After starting at 60, the timer is set to 0 at 62 (t=0).

The acceleration in all three sensor axes v _x , v _y , v _z is then measured at 64 by means of the vibration sensor 32 .

From this, a resulting acceleration vector is determined at 66, which is then filtered at 68 in order to determine a vibration characteristic value vk therefrom.

The scanning rate with which the acceleration values v _x , v _y , v _z are recorded at 64 is approximately 1.5 kHz and is approximately twice the maximum oscillation frequency of approximately 20,000 rpm, which corresponds to approximately 335 Hz.

At 70, a query is then made as to whether the time Δt that has elapsed is greater than a predetermined time period of, for example, 1 s.

If this is the case (y), the further drive takes place in rated operation, which is indicated at 78 . In the subsequent query 80, it is checked whether the vibration characteristic value vk determined at 68 is greater than the maximum value vk _max . This can be, for example, 12.8 g (g=gravitational acceleration=9.81 m/s ² ). If this is the case (y), then there is a return loop 82 back to the initialization at 62. If this is not the case (n), the process continues at 74, ie with a speed control to a speed or oscillation frequency set by means of the adjusting wheel 26 . From there, there is a loopback 76 back to the acquisition of the acceleration values at 64.

If the elapsed time Δt in query 70 is less than 1 s (n), the speed is further increased at 72 (soft start/run-up) until the speed of the machine is regulated at 74 .

Out of 6 it can be seen that when the calculated vibration characteristic vk is greater than the predetermined maximum vibration characteristic vk _max , the drive is stopped and the machine is restarted.

The vibrations can thus be limited electronically to a maximum permissible value, this being largely unnoticed by the user, since the subsequent restart takes place in a period of time which is less than 1 s.

7 shows the flow chart for the cyclical measurement and processing of the vibration characteristic value vk 6 inserted practically between 64 and 68. The cyclical measurement and processing of the vibration characteristic value vk at 90 begins according to FIG 7 at 92 with the measurement of the acceleration values v _x , v _y , v _z for the three sensor axes x, y, z.

Then at 94 the squares of the measured values v _x ² , v _y ² , v _z ² are determined. These are then filtered at 96 for the individual sensor axes, resulting in the values av _x ² , av _y ² av _z ² . From this, the vibration characteristic value is calculated at 98 by preferably forming the sum of the values av _x ² + av _y ² + av _z ² and taking the root of this. In principle, of course, only a single axle or two axles could also be used. However, the measurement accuracy is highest when all sensor axes x, y, z are used.

After the calculation at 98, a loop 100 loops back to the start at 92.

As already mentioned above, the sampling rate of the acceleration measurement is higher than the maximum vibration frequency. The ratio is greater than 2:1.

A modification of the method described above is described below with reference to 8 explained.

8 shows the cyclical determination of a modified vibration characteristic, at which it is switched off, which is illustrated by 102 . At 104, the rotational speed n is first measured. This can be done using a separate speed sensor (not shown). However, since the drive motor is an EC motor is designed (electronically commutated motor), the control system basically knows the frequency anyway, so that it may be possible to dispense with an additional speed sensor.

At 106, a speed-proportional vibration value vkn is determined. In the previously based on 7 The speed with a proportionality factor p1 that is less than 2 is included in the determined vibration characteristic value vk.

At 108, the power consumption of the drive motor 34 is also measured, which is done by measuring the current phase current I.

At 110, a phase current switch-off value that is proportional to the speed is then determined from this, the speed preferably being included with a proportionality factor p2 between 1.5 and 2.5.

A shutdown of the drive (cf. 6 , query 80) occurs when the speed-weighted vibration characteristic value vkn is greater than the specified maximum value vkn _max and the speed-weighted current consumption I _n is also greater than the maximum specified current consumption I _max .

In this case, the phase current switch-off value I _max is preferably determined from a look-up table.

The maximum value for the speed-weighted vibration characteristic vkn _max is preferably determined from a look-up table.

The switch-off value vkn _max is preferably somewhat larger than in the case of the simplified method according to FIG 6 . As a result of the speed weighting, the switch-off value vkn _max is preferably in the range from 14 g to 16 g.

Claims (15)

1. Oscillating drivable hand tool, with a drive (28) for oscillating driving a tool, with at least one vibration sensor (32) for monitoring vibrations, whose output signals (v_x, v_y, v_z) are fed to a control unit (30) that is adapted to derive a vibration characteristic value (vk) from the output signals (v_x, v_y, v_z) of the vibration sensor (32) and then, when the vibration characteristic value (vk) exceeds a maximum value (vk_max), to switch off the drive (28), characterized in that the control unit (30) is adapted to subsequently automatically restart the drive (28).
2. Hand tool according to claim 1, characterized in that the sampling rate (f_T) for determining the vibration characteristic value (vk) is higher than the maximum oscillation frequency (f_max) of the drive (28), wherein the ratio between the sampling rate and the maximum oscillation frequency (f_T/f_max) is preferably greater than 2.
3. Hand tool according to claim 1 or 2, characterized in that the control unit (30) is adapted to restart the drive (30) after a shutdown within a period Δt, which is in the range of 2 seconds to 0.2 seconds, preferably between 1.5 seconds and 0.5 seconds, more preferably between 1.2 seconds and 0.8 seconds, preferably with a soft start, preferably to a preset oscillation frequency of up to 25.000 rpm.
4. Hand tool according to one of the preceding claims, characterized in that the drive (28) with a drive motor (34) is formed about a fixed axis (22) for generating a rotationally oscillating drive movement of a tool spindle (20), on which a tool is fixable, wherein the drive movement of the tool spindle (20) preferably occurs with a small pivoting angle in the range of 0.5 ° to 5 ° and preferably with a high oscillation frequency of up to 25.000 rpm, and wherein the drive motor (34) to generate the rotationally oscillating drive movement is preferably coupled to an oscillating gear (38).
5. Hand tool according to claim 4, characterized in that the drive (28) is adapted as an assembly which is coupled to a housing (12) of the hand tool (10) via at least one preferably elastic damping element (40, 42,44, 46).
6. Hand tool according to claim 4 or 5, characterized in that the vibration sensor (32) is rigidly connected to the housing (12), wherein the vibration sensor (32) preferably is accommodated on an electronic circuit board (30) which is rigidly connected to the housing (12).
7. Hand tool according to one of the preceding claims, characterized in that the vibration sensor (32) is adapted as an acceleration sensor which detects three mutually perpendicular sensor directions (x, y, z).
8. Hand tool according to claim 7, characterized in that the vibration sensor (32) is aligned such that at least one sensor direction (x, y) is angularly offset, preferably by 45°, relative to a main direction (v) of the vibrations.
9. Hand tool according to claim 7 or 8, characterized in that the control unit (30) is adapted to evaluate the three output signals of the vibration sensor for the sensor directions (x, y, z) separately and preferably to smooth and to filter, and to calculate therefrom a sum signal which is used as the vibration parameter (vk), wherein the control unit (30) is preferably adapted to calculate the sum signal from the output signals (v_x, v_y, v_z) for all three sensor directions (x, y, z) of the vibration sensor (32).
10. Hand tool according to one of the preceding claims, characterized in that the control unit (30) is adapted to initially rectify and average the output signals (v, y, v) of the vibration sensor (32) before the vibration characteristic value (vk) is calculated therefrom.
11. Hand tool according to claim 7, 8, 9 or 10, characterized in that the control unit (30) is adapted to, for each output signal (v_x, v_y, v_z) of the vibration sensor (32) relating to each sensor direction (x, y, z), form the square and to use the root of the sum of the squares (av_x ² + av_y ² + av_z ²)^1/2, each weighted with a factor, as the vibration parameter (vk).
12. Hand tool according to one of the preceding claims, characterized in that a modified vibration characteristic value is used which is dependent on an output power of the hand tool (10), preferably on the oscillation frequency (f_max) and a power consumption (P) of the drive motor (34).
13. Hand tool according to claim 12, characterized in that a means for measuring the speed (n) of the drive motor (34) is provided, and that the control unit (30) is adapted to calculate a proportionality factor (p1) with which the vibration characteristic value calculated from the output signals (v_x, v_y, v_z) is weighted in order to obtain a speed-weighted vibration characteristic value (vkn) at which, if the maximum value (vkn_max) is exceeded, the drive is switched off and then started (28), wherein the proportionality factor (p1) is preferably less than three, preferably less than two.
14. Hand tool according to claim 12 or 13, characterized in that a means for measuring the speed (n) of the drive motor (34) is provided, in that a means for measuring the current consumption of the drive motor (34), preferably by measuring the phase current (I), is provided, and that the control unit (30) is adapted to calculate a speed-weighted current consumption (In) of the drive motor (34), in which a proportionality factor (p2) derived from the speed (n) is used, which is preferably between 1.2 and 2.7, preferably between 1.5 and 2.5, with the speed-weighted current consumption (In) is used as an additional switch-off criterion for the speed-weighted vibration parameter (vkn) and a switch-off only occurs if both the speed-weighted vibration parameter (vkn) exceeds a predetermined maximum value (vkn_max), and the speed-weighted current consumption (In) of the drive motor exceeds a predetermined limit value (Imax), wherein preferably the specified maximum value (vk_max) for the vibration characteristic or the speed-weighted vibration characteristic (vkn_max) is at least 10 g, preferably between 14 g and 16 g.
15. Method for operating an oscillating drivable hand tool, with the following steps:

    - starting an oscillating drive (28);

    - cyclic measuring of acceleration (v_x, v_y, v_z) in three spatial directions;

    - calculating a vibration characteristic value (vk) from the acceleration values (v_x, v_y, v_z) in the three spatial directions (x, y, z); and

    - stopping the drive if the vibration characteristic value (vk) exceeds a specified limit value (vk_max);

    characterized in that

    - automatic restarting of the oscillating drive (28) before a predetermined time (Δt<t1).

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