EP2397258B1 - Screw driver - Google Patents

Description

1. (a) der Antrieb zunächst beschleunigt wird, bis die Drehzahl eine bestimmte erste Drehzahl erreicht hat;
2. (b) die Drehzahl anschließend mindestens um einen bestimmten Betrag innerhalb eines bestimmten Zeitinkrementes abfällt oder das Drehmoment wenigstens um einen bestimmten Betrag innerhalb eines bestimmten Zeitinkrementes ansteigt, der Antrieb abgebremst wird, bis die Drehzahl eine bestimmte zweite Drehzahl erreicht hat, die niedriger als die erste Drehzahl ist;
3. (c) wobei der Antrieb (17) danach für eine bestimmte Zeit auf die zweite Drehzahl (n₂) geregelt wird;
4. (d) und der Antrieb (17) nach dem Schritt (c) wieder beschleunigt wird, maximal bis die Drehzahl (n) die erste Drehzahl (n₁) erreicht.

The invention relates to a screwdriver with a drive of a tool spindle, with a controller for controlling the drive, and with a monitoring device for monitoring the rotational speed or the torque, which is coupled to the controller to turn off the drive upon reaching a shutdown criterion, wherein the controller programmed so that

1. (A) the drive is first accelerated until the speed has reached a certain first speed;
2. (B) the speed then decreases by at least a certain amount within a certain time increment or the torque increases at least by a certain amount within a certain time increment, the drive is decelerated until the speed has reached a certain second speed lower than the first Speed is;
3. (c) wherein the drive (17) is then controlled for a certain time to the second speed (n ₂ );
4. (D) and the drive (17) after the step (c) is accelerated again, at most until the rotational speed (n) reaches the first rotational speed (n ₁ ).

Such a screwdriver is from the EP 1 785 231 A2 known.

The well-known screwdriver has a control device by means of which the speed of the motor can be regulated and which reduces the speed when a trigger parameter is reached. In this case, an angular velocity change per unit of time is preferably used as the trigger parameter. If it is found that the angular velocity slows down, the speed is reduced, possibly in several stages, which should ensure a relatively accurate tightening torque for the screw connection. Here, the deviation of the torque between a hard and a soft screw should be low. A so-called "soft screw" means a screw, in which the torque steadily increases towards the end of the screw until the maximum torque is reached. In contrast, in the case of a "hard screwdriving case", the torque is initially relatively low and abruptly increases at the end of the screwing process.

In an alternative embodiment of the known screwdriver, the speed is lowered after reaching the trigger parameter to zero, the engine for operated for a certain time in the reverse direction, then reversed the direction of rotation and tightened the screw with a lower speed than the output speed.

In the known screwdriver, although a relatively uniform torque is achieved regardless of the type of screwing, however, the total time when tightening a screw especially in soft screwing is relatively high, as is always done at the end with a lower speed, which is sometimes further reduced , In the case of reversal of the direction of rotation, the total time for tightening the screw connection is increased even further.

From the DE 10 2008 033 866 A1 Another screwdriver is known, in which a limiting device for limiting a drive train in the output side provided output torque is provided to a maximum torque value, wherein the limiting device is configured for driving a current flowing to the drive motor energizing in a braking operation by the energizing a braking the drive motor, generates opposing rotating field to a respective direction of rotation of the drive motor. In the process, rotational energy present in the drive train is taken into account.

By this means in particular a too strong suit in a hard screwing can be avoided.

The said control of the screwdriver is constructed relatively complicated and nevertheless does not ensure for each application that the tightening torque is maintained precisely regardless of the type of screwing and at the same time the screw is completed in the shortest possible time.

Against this background, the invention has for its object to provide a screwdriver, in which, regardless of the type of Schraubfall a fast tightening a screw with the most accurate torque is guaranteed. Furthermore, a suitable method for controlling a screwdriver is to be specified, with which a fast and precise tightening a screw connection is made possible regardless of the type of screwing.

This object is achieved in a screwdriver according to the aforementioned type in that during the step (d) is monitored whether the speed (n) during acceleration drops by a certain amount within a certain time increment or the torque by a certain amount within a certain time increment increases, and upon fulfillment of this criterion, the drive is decelerated until the speed has reached the second speed (n ₂ ), which is lower than the first speed (n ₁ ).

1. (a) Beschleunigen des Antriebs, bis die Drehzahl eine bestimmte erste Drehzahl erreicht hat;
2. (b) sofern die Drehzahl mindestens um einen bestimmten Betrag innerhalb eines bestimmten Zeitinkrementes abfällt oder das Drehmoment mindestens um einen bestimmten Betrag innerhalb eines bestimmten Zeitinkrementes ansteigt, Abbremsen des Antriebs bis auf eine bestimmte zweite Drehzahl, die niedriger als die erste Drehzahl ist;
3. (c) Regeln des Antriebs für eine bestimmte Zeit auf die zweite Drehzahl;
4. (d) Beschleunigen des Antriebs, maximal bis auf die erste Drehzahl;

wobei während der vorgenannten Schritte ständig überwacht wird, ob die Abschalteinrichtung das Abschaltkriterium erreicht hat und der Antrieb dann abgeschaltet wird;
und wobei während des Schrittes (d) überwacht wird, ob die Drehzahl (n) während der Beschleunigung um einen bestimmten Betrag innerhalb eines bestimmten Zeitinkrementes abfällt oder das Drehmoment um einen bestimmten Betrag innerhalb eines bestimmten Zeitinkrementes ansteigt, und bei Erfüllung dieses Kriteriums der Antrieb abgebremst wird, bis die Drehzahl die zweite Drehzahl (n₂) erreicht hat, die niedriger als die erste Drehzahl (n₁) ist.With regard to the method, the object of the invention is further achieved by a method for controlling a screwdriver, with a drive for driving a tool spindle, and with a controller for controlling the drive, with a monitoring device for monitoring the rotational speed or the torque, and with a shutdown device for shutting down the drive upon reaching a shutdown criterion, the method comprising the steps of:

1. (a) accelerating the drive until the speed reaches a certain first speed;
2. (b) if the speed drops at least a certain amount within a certain time increment or the torque increases at least a certain amount within a certain time increment, braking the drive to a certain second speed lower than the first speed;
3. (c) controlling the drive for a certain time to the second speed;
4. (d) accelerating the drive, at most up to the first speed;

wherein during the aforementioned steps, it is constantly monitored whether the shutdown device has reached the shutdown criterion and the drive is then switched off;
and wherein it is monitored during step (d) whether the speed (n) falls during the acceleration by a certain amount within a certain time increment or the torque increases by a certain amount within a certain time increment, and brakes the drive when this criterion is met is until the speed has reached the second speed (n ₂ ), which is lower than the first speed (n ₁ ).

The object of the invention is achieved in this way.

Constant monitoring of the rotational speed or torque to detect a drop in torque or torque increase ensures timely deceleration of the drive to allow for excessive tightening of the screw even in a hard tightening event with rapid deceleration and torque increase, respectively avoid. On the other hand, characterized in that after the drive after detection of a speed drop is first decelerated to a lower speed and then accelerated again, even in the case of a soft Schraubfalls or a short-term speed drop, for example, as a result of contamination of the thread rapid tightening of the screw allows. At the same time a constant torque is guaranteed regardless of the type of screwdriving by the constant monitoring of the shutdown criterion and an immediate shutdown of the drive when reaching the shutdown criterion.

A "deceleration" is understood to mean a slowing down of the speed of the drive. This can be an active braking, for example by a self-excited or externally excited short-circuit braking, as is basically known in the prior art. Alternatively, the deceleration can also consist only in the removal of the drive energy or in a reduction of the phase angle in the case of pulse width modulation control.

According to the invention, it is therefore already monitored again during the acceleration process whether the criterion for braking the drive is fulfilled. So for example for the In the event that the speed has been erroneously lowered due to a threading error or contamination, for example, the speed will continue to be monitored in order to be able to react quickly in the event of a drop in speed, so that an over tightening of the screw connection is prevented in any case.

In a further advantageous embodiment of the invention is monitored as a shutdown criterion, whether the tightening torque of the screw reaches a certain preset value.

This monitoring of the shutdown criterion is carried out in parallel to the other operations described. For example, the achievement of the shutdown criterion for this purpose at certain time intervals, e.g. every 5 milliseconds, queried, so that at any time on reaching the shutdown criterion an immediate shutdown of the drive is guaranteed, so as to ensure a precise maintenance of a predetermined torque of the screw.

In a further advantageous embodiment of the invention, the drive has a separating clutch, which triggers when reaching the preset torque.

In this way, a specific torque can be maintained in a particularly precise manner.

In an advantageous embodiment of this embodiment, the drive is driven at release of the clutch at full power.

As a result, a precise triggering of the separating clutch is supported, since in particular when a rechargeable battery-powered screwdriver, the battery is almost exhausted, yet a precise release of the mechanical clutch is guaranteed, even if the speed is low.

Furthermore, the drive preferably has a shut-off device for switching off the drive, which triggers upon reaching a preset torque.

This avoids further running of the drive after release of the separating clutch.

In a further advantageous embodiment of the invention, the drive is switched off with a certain time delay after triggering the separating clutch.

As a result, defined conditions for the next start of the screwdriver, in particular for the separating clutch, guaranteed.

The screwdriver according to the invention has a monitoring device for monitoring the rotational speed or the torque. This may be e.g. a speed sensor for monitoring the speed of the drive or the tool spindle or a torque sensor for monitoring the torque of the drive or the tool spindle, e.g. in the form of a strain gauge or a Torsionssensors ,.

In a further advantageous embodiment of the invention, in step (b), the current rotational speed is compared with a plurality of rotational speed values which lie behind at different times, and the drive is decelerated if the current rotational speed is at least one of the rotational speed values at at least one of the previous points Speed difference has dropped.

In this way, a quick detection of hard screw is guaranteed because within a small time a large speed drop takes place. In a soft Schraubfall a speed drop is determined only after a long time, since this is the speed drop compared to a hard screw is not very large. An advantage, however, is that the speed always is lowered in time before it comes to triggering the separating clutch. This is based on the achievement of the headrest of a screw in a hard screwing very early and in a soft screwing a little later. This minimizes the tightening time and increases accuracy.

Fig. 1

eine stark vereinfachte, schematische Darstellung eines erfindungsgemäßen Schraubers;

Fig. 2a)

ein Ablaufdiagramm für ein erfindungsgemäßes Schraubverfahren;

Fig. 2b)

ein Ablaufdiagramm für die Überwachung des Abschaltkriteriums, das ständig zusätzlich während des Ablaufdiagramms gemäß Fig. 5a) durchlaufen wird;

Fig. 3

den Verlauf der Drehzahl n über der Zeit t bzw. dem Drehwinkel α bei einem weichen Schraubfall;

Fig. 4

den Verlauf der Drehzahl n über der Zeit t bzw. dem Drehwinkel α im Falle eines harten Schraubfalls und

Fig. 5

den Verlauf der Drehzahl n über der Zeit t bzw. dem Drehwinkel α im Falle einer fehlerhaften Abbremsung infolge eines kurzzeitigen Drehmomentanstiegs z.B. durch einen Gewindefehler, mit anschließender Beschleunigung.

Further features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the drawings. Show it:

Fig. 1

a highly simplified, schematic representation of a screwdriver according to the invention;

Fig. 2a)

a flow diagram for an inventive screwing method;

Fig. 2b)

a flow chart for the monitoring of the shutdown criterion, which is constantly in addition during the flowchart according to Fig. 5a ) will go through;

Fig. 3

the course of the rotational speed n over the time t or the rotational angle α in a soft screwing;

Fig. 4

the course of the speed n over the time t or the rotation angle α in the case of a hard screwdriving and

Fig. 5

the course of the rotational speed n over the time t or the rotational angle α in the event of an incorrect deceleration as a result of a short-term Torque increase, eg due to a thread error, with subsequent acceleration.

In Fig. 1 a screwdriver according to the invention is shown schematically and designated overall by the reference numeral 10.

The screwdriver 10 has a housing 12, which is designed pistol-shaped and at the lower end of a battery pack 16 is interchangeable added. The housing 12 has a handle 14 on which the screwdriver 10 are held and can be switched on and off by means of a switch button 28.

In the upper region of the housing 12, a motor 18, a gear 20 and a clutch 22 are successively added, which together form the drive 17. The output side of the separating clutch 22 is connected to a tool spindle 24, on which a tool holder 26 for receiving a tool, for example a bit, is provided. The motor 18 drives the transmission 20. The transmission 20 is finally coupled via the separating clutch 22 with the tool spindle 24.

The screwdriver 10 is controlled by a central control 30 which is received in the handle 14 and is connected via suitable lines to the accumulator package 16, the shift key 28, the motor 18, the transmission 20 and the disconnect clutch 22.

On the motor 18, a speed sensor 32 is further provided, which is formed for example as a Hall element and is also coupled to the controller 30 via suitable lines.

The transmission 20 may, as for example from EP 0 320 723 A2 known as planetary gear be formed and be provided with a torque shutdown. Upon reaching a certain torque coupled to the gear 20 switch 34 is actuated via a rotating fork and leads to the shutdown of the motor 18. To generate a restoring force, a torsion bar can be provided. As soon as the torque exceeds a preset torque value, the restoring force of the torsion spring rod is overcome and the shift fork is twisted, which leads to the operation of the switch 34.

Alternatively or additionally, the separating clutch 22 may be provided, via which, upon reaching a predetermined torque, the connection between the tool spindle 24 and the gear 20 is released by disengaging the separating clutch 22. Such tripping couplings have long been known in the art, for example, on the EP 0 990 488 A2 which is incorporated by reference in its entirety.

As an alternative to monitoring the torque on the transmission 20 by means of the torque-dependent triggerable switch 34, the separating clutch 22 can be monitored and a disengagement of the coupling half can be registered, which in turn can be used mechanically for actuating a switch.

The speed of the motor 18 is controlled by the controller 30 digital or analog.

For speed monitoring of the speed sensor 32 is provided which emits a pulse at each revolution of the motor shaft, which is supplied to a counter in the controller 30. If the number of pulses emitted by the sensor per unit time remains the same, the speed n of the motor 18 is constant. If the number of pulses per unit of time increases, the speed n increases, but decreases per unit of time, so the speed n drops. The number of pulses per unit time is used as the actual size or input from the controller 30. The screwdriver 10 is operated with a load-dependent motor characteristic.

The inventive control of the screwdriver 10 will be described below with reference to the two flowcharts according to Fig. 2a) and Fig. 2b ) explained in more detail.

In Fig. 2a ) is a flowchart 50 showing a part of the operation of the controller 30.

At certain times, the speed n is measured or calculated and the values stored in a ring buffer. For example, a speed measurement per millisecond can be done.

In addition to going through the flowchart 50 according to FIG Fig. 2a ), a monitoring of a shutdown criterion is constantly carried out, which takes place in the course of a separate flowchart 90, which in Fig. 2b ) is shown separately, but in the flowchart according to Fig. 2a ) is integrated and the regelmä-ßig, eg every 5 milliseconds, queried to turn off the screwdriver 10 as soon as the switch-off criterion is reached.

After the start 51 of a screwing process ("START"), an acceleration process 52 ("ACC") begins first. It is accelerated until the idling speed n _{1 is} reached. The acceleration process 52 is designed so that it is as pleasant as possible for the user, that is, a soft start is performed. As a result, high current peaks during startup are avoided.

It is now checked in the query 54, whether the idle speed n _{1 is} reached ("n = n ₁ ").

If this is not the case, the current speed value n is stored in the subsequent step 56 ("STORE n").

In the subsequent step 58, the current speed value n (i) is compared with a further past speed value n (im). If the current speed n (i) is smaller than the comparison value by a certain value x ₁ , this indicates a certain speed drop, and the screwdriver 10 is decelerated (step 66 "RET"). If this is not the case, the drive 17 is further accelerated (step 52). If it is determined in query 54 that the setpoint speed has been reached ("n = n ₁ "), then this speed value is stored (step 60 "STORE n").

In the following step 62, it is again queried whether the rotational speed has fallen by at least the amount x ₁ compared to the previous rotational speed. If this is not the case, then the screwdriver 10 is further operated at the same speed n ₁ , that is, it is branched back to step 60. If, on the other hand, it is determined in query 62 that a significant drop in rotational speed has occurred (n (i) + x ₁ <n (im)), a deceleration ("RET") takes place in step 66.

In order to cover a larger range of Schraubfallhärten, in the queries 58, 62 and 74, the current speed n (i) is compared not only with a past speed n (im). Rather, the current speed n (i) is compared with several different speeds in the past, speeds. For each comparison, there is a specific value x ₁ by which the speed must be dropped for deceleration to take place. Thus, hard screwdriving cases are quickly detected, as this takes place within a short time a large speed drop. In contrast, a soft screw is determined only after a long time, since in this case the speed drop is not very large compared to a soft screwing or this assumes a significant value only after a long time.

An advantage of this method is that the speed is always lowered in time before it comes to triggering the separator (mechanical disconnect clutch). This is, based on the achievement of the headrest of a screw, in a hard screwing very early and in a soft screw a little later. This minimizes the tightening time and increases accuracy.

The aforementioned braking operation in step 66 takes place until the rotational speed has fallen to a value n ₂ which is lower than the idling rotational speed n ₁ . If the speed n ₂ has not yet been reached, it is further delayed according to step 66. If the speed n _{2 has been} reached, this is regulated in step 68 ("CONTROL n").

The mentioned braking process can be done either by "active braking" or by simply reducing or removing the power supply.

If the speed n _{2 is} reached, it is held for a certain time, for example 30 ms-100 ms, preferably 60 milliseconds, or for a certain angle of rotation α, as checked in the query 70. If the time t has expired or the angle of rotation α has been reached, an acceleration ("ACC") takes place again in step 72.

The acceleration takes place in this case until the value n ₁ is reached again, which is checked in the query 76. If the idle speed n ₁ is reached again, it continues with step 60. If the idle speed n ₁ is not reached, it is checked in the query step 78, if the current speed deviates at least by a certain amount x ₂ from the idle speed n ₁ (n> n ₁ -x ₂ ). If this is not the case, then further accelerated in step 72. If the speed has reached the desired amount, the current speed is stored in step 80 ("STORE n").

In the following branch 74, it is again checked whether the braking criterion has been reached (n (i) + x ₁ <n (im)). If this is the case, the braking is initiated according to step 66. Otherwise, it is further accelerated in step 72.

The flowchart 50 described above is the flowchart 90 according to Fig. 2b ), which is polled regularly, eg every 1 to 30 ms, preferably every 5 milliseconds. Starting from any previous step 92 from the flowchart 50, a query is made in branch 94 as to whether the shutdown criterion has been reached.

In the present case, it is checked as Abschaltkriterium whether a preset torque is reached. This can be monitored by triggering the separating clutch 22 with a corresponding sensor. If there is no disconnect clutch 22, this could be checked, for example, by means of a torque sensor (e.g., strain gauges).

If the switch-off criterion is not reached, then the flowchart 50 is continued. If the switch-off criterion is reached, the motor power is fully activated in the subsequent step 96 ("PWM 100%"), that is, the pulse width modulation is fully controlled. This is useful in connection with a disconnect clutch, since, especially when the accumulator 16 is almost exhausted, a mechanical disconnect clutch does not properly or not safely triggers. A correct release results by skipping a cam. By this brief full control of the motor 18 as a safe release of the clutch 22 is ensured. After a deceleration step 98 lasting, for example, 10 ms-300 ms, preferably 50 ms (or a rotation angle of the separating clutch of 30 ° to 120 °, preferably 100 °), the motor is subsequently stopped in step 100 ("STOP motor"). ). This completes the cycle at 102 ("STOP").

By the algorithm described above, a quick tightening a screw regardless of the type of screwing and a precise maintenance of the tightening torque is guaranteed.

In the illustrated embodiment, the speed level for the idle speed n ₁ is about 800 to 1500 1 / min, preferably about 1000 1 / min, while the lowered second speed n ₂ in the range of 200 to 400 1 / min, preferably about 300 1 / min is, in each case measured on the separating clutch 22 and the tool spindle 24th

The following are some use cases based on the Fig. 3 to 5 explained in more detail.

Fig. 3 shows the application of a soft screwing operation. The tool spindle 24 is first driven at the speed n ₁ (see step 60). Subsequently, a speed drop Δn is detected. As soon as it exceeds the predetermined value x ₁ in step 62, the braking process begins, which is indicated by the arrow "RET". The braking process RET is continued until the speed n _{2 is} reached. This is controlled in step 68 for a certain period of time t or a certain angle of rotation α. After this time, an acceleration is again in step 72, and at most up to the speed n ₁ . If, however, the speed n is still smaller than the speed n ₁ minus a specific difference x ₂ , according to query 78 in step 72 the speed is further accelerated. In the illustrated soft screw the speed increases so during the final tightening of the screw gradually until, due to the increasing torque returns to a natural drop in speed. At the point "OFF" the switch-off criterion according to branch 94 is reached. That is, the disconnect clutch triggers, and the sequence of steps 96, 98, 100, 102 is passed through until the motor 18 is turned off and the screwing operation is completed.

In Fig. 4 is shown a hard screw case.

After the start 51 is first accelerated according to step 52 to the idle speed n ₁ and the speed value then stored according to step 60. If it is determined in the subsequent query in step 62, that the speed falls within a certain time by a certain amount, as by Δ n in Fig. 4 indicated or n (i) + x ₁ <n (im) in Fig. 2 , the braking is initiated according to step 66, as in Fig. 4 indicated by the arrow "RET". The braking process is continued until finally the speed n _{2 is} reached or fallen below and is regulated according to step 68. Subsequently, according to step 70, an expiring acceleration occurs again after the predetermined time has elapsed, until finally the switch-off criterion according to step 94 is reached and in which the arrow "OFF" in FIG Fig. 4 designated point the shutdown via the steps 96, 98, 100, 102 according to Fig. 2b ) is initiated.

In Fig. 5 Finally, another case of the algorithm is shown in which during the suit, first a speed drop is detected, which leads to a braking, but then accelerated back to the idle speed n ₁ . This could be, for example, a faulty thread, so that during the tightening process briefly increased torque and thus a drop in speed occurs, which is overcome again after a short time.

After the start 51 and the acceleration 52, the idling speed n ₁ is initially maintained (step 54). In the subsequent interrogation step 62, a speed drop Δn is detected which exceeds the value x ₁ at a certain point in time, which triggers the braking according to step 66, as indicated by the arrow "RET" in FIG Fig. 5 is indicated. The braking is continued until finally the speed n _{2 is} reached or fallen below and is controlled according to step 68 until a predetermined time t or a predetermined rotational angle α is exceeded. Thereafter, an acceleration "ACC" takes place according to step 72, until finally the idling speed n ₁ is reached again and this is followed by a hard or soft screw.

In contrast to the previously known screwdriver according to the EP 1 785 231 A2 During the entire control process, the speed is not lowered to zero or even a short-term drive in the opposite direction of rotation is performed before an acceleration takes place again. Rather, according to the invention, the speed is reduced in the case of deceleration only up to a predetermined positive speed value n ₂ , before either an acceleration or a shutdown follows.

Claims (13)

1. A screwdriver comprising a drive (17) for driving a tool spindle (24) having a controller (30) for controlling the drive (17), having a monitoring device (32) for monitoring the rotation speed or the torque, and having a monitoring device (34) for monitoring a switch-off criterion, which monitoring device (34) is coupled to the controller (30), in order to switch off the drive when the switch-off criterion is reached, with the controller (30) being designed such that

   (a) the drive (17) is first of all accelerated until the rotation speed (n) has reached a specific first rotation speed (n₁);

   (b) if the rotation speed (n) then falls by at least a specific amount within a specific time increment, or the torque rises by at least a specific amount within a specific time increment, the drive (17) is braked until the rotation speed (n) has reached a specific second rotation speed (n₂), which is lower than the first rotation speed (n₁);
   wherein

   (c) the drive (17) is then regulated at the second rotation speed (n₂) for a specific time;

   (d) after step (c), the drive (17) is accelerated again at most until the rotation speed (n) reaches the first rotation speed (n₁)

   characterized in that, monitoring is carried out during step (d) to determine whether the rotation speed (n) has fallen by a specific amount within a specific time increment during the acceleration or whether the torque has risen by a specific amount within a specific time increment and, if this criterion is satisfled, the drive is braked until the rotation speed has reached the second rotation speed (n₂), which is lower than the first rotation speed (n₁).
2. The screwdriver according to claim 1, characterized in that the switch-off criterion is to monitor whether the tightening torque for screwdriving reaches a specific preset value.
3. The screwdriver according to claim 2, characterized in that the drive (17) has a disconnecting clutch (22), which releases when the preset tightening torque (M_OFF) is reached.
4. The screwdriver according to claim 3, characterized in that, when the disconnecting clutch (22) is released, the drive (17) is operated at full power.
5. The screwdriver according to claim 2, 3 or 4, characterized in that the drive (17) has a switch-off device (34) for switching off the drive (17), which switch-off device (34) releases when the preset tightening torque (M_OFF) is reached.
6. The screwdriver according to claim 5, characterized in that the drive (17) is switched off with a specific time delay after release of the disconnecting clutch (22).
7. The screwdriver according to one of the preceding claims, characterized by a rotation speed sensor (32) for monitoring the rotation speed (n) of the drive (17) or of the tool spindle (24).
8. The screwdriver according to one of the preceding claims, characterized by a torque sensor for monitoring the torque (M) of the drive (17) or of the tool spindle (24).
9. The screwdriver according to one of the preceding claims, characterized in that, in step (b), the instantaneous rotation speed (n) is compared with a plurality of rotation speed values at various times in the past, and the drive (17) is braked if the instantaneous rotation speed (n) has in each case fallen by at least a specific rotation speed difference in comparison to the rotation speed value at at least one of the previous times.
10. The screwdriver according to one claims 1-8, characterized in that, in step (b), the instantaneous torque (M) is compared with a plurality of torque values at various times in the past, and the drive (17) is braked if the instantaneous torque value has risen by in each case at least one specific torque difference in comparison to the torque value at at least one of the previous times.
11. A method for controlling a screwdriver (10) having a drive (17) for driving a tool spindle (24) having a controller (30) for controlling the drive (17), having a monitoring device (32) for monitoring the rotation speed (n) or the torque (M), and having a switch-off device (22) for switching off the drive (17) when a switch-off criterion is reached, wherein the method comprises the following steps:

    (a) accelerating the drive (17) until the rotation speed (n) has reached a specific first rotation speed (n₁);

    (b) if the rotation speed (n) falls by at least a specific amount within a specific time increment, or the torque (M) rises by at least a specific amount within a specific time increment, braking the drive (17) to a specific second rotation speed (n₂), which is lower than the first rotation speed (n₁);

    (c) controlling the drive (17) at the second rotation speed (n₂) for a specific time;

    (d) accelerating the drive (17) to at most the first rotation speed (n₁);

    with continuous monitoring being carried out during the abovementioned steps to determine whether the switch-off device (22) has reached the switch-off criterion, and then switching off the drive (17);
    and wherein during step (d), monitoring is carried out to determine whether the rotation speed (n) has fallen by a specific amount within a specific time increment during the acceleration or whether the torque (M) has risen by a specific amount within a specific time increment and, if this criterion is satisfied, the drive (17) is braked to the specific second rotation speed (n₂), which is lower than the first rotation speed (n₁).
12. The method according to claim 11, in which, in step (b), the instantaneous rotation speed (n₁) is compared with a plurality of rotation speed values (n_i-1, n_i-2, ...) at various times in the past, and the drive (17) is braked if the instantaneous rotation speed (n_i) has fallen by at least one specific rotation speed difference in comparison to the rotation speed value (n_i-1, n_i-2, ...) at at least one of the previous times.
13. The method according to claim 11, in which, in step (b), the instantaneous torque (M_i) is compared with a plurality of torque values (M) at various times in the past, and the drive (17) is braked if the instantaneous torque value has risen by in each case at least one specific torque difference in comparison to the torque value (M) at at least one of the previous times.

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