EP1785231A2 - Screwdriver featuring rotational speed regulation and method of controlling the rotational speed of a screwdriver - Google Patents

Abstract

Screwdriver (10) has a speed controller, an engine (18) for actuation of tool drive shaft (24) and a control device (30) for control of speed of the engine. The control device supplies a value arrived from speed as trigger parameter for decreasing the speed. The control device is formed for decrease of speed with obtaining of trigger parameter. An independent claim is also included for the method for controlling of speed of screwdriver.

Description

The invention relates to a screwdriver with speed control, with a motor for driving a tool drive shaft, and with a control device by means of which the speed of the motor is regulated, wherein the control device is designed to reduce the speed upon reaching a trigger parameter.

The invention further relates to a method for speed control of a screwdriver, in which the speed of the motor is monitored and the speed of the motor is lowered upon reaching a trigger parameter.

Such a screwdriver and such a method for speed control are from the DE 42 25 157 A1 known.

The well-known screwdriver is designed as an electric screwdriver for drilling screws having a drill bit and a threaded portion, wherein when screwing the threaded portion of the required torque and thus the power consumption of the motor increases, and wherein an electronic control for keeping constant and a controllable switch for controlling the speed of Motors are provided. An electronic sensor is activated in response to the current consumption and actuates a switch, whereby the speed of the motor when screwing the threaded portion via an electronic control is reduced and kept constant.

Although such a screwdriver and such a method are suitable for the rapid insertion of self-drilling screws, but are less suitable for tightening fittings with a predetermined torque, which should be kept as accurate as possible. In particular, the tightening of a screw with the most accurate torque represents a major problem that has not been satisfactorily solved in the prior art. Here, in particular between the so-called "soft screw" and the so-called "hard screw" to distinguish. In soft tightening, the torque steadily increases towards the end of the fitting until the maximum tightening torque is reached. In the hard screw case, however, the torque is initially relatively low and increases abruptly at the end of Verschraubungsvorgangs towards, whereby the torque can usually not be met precisely. In both cases, it would be desirable to operate at a higher speed at the beginning of the tightening operation and at a lower speed at the end of the tightening operation, on the one hand to save time and on the other hand to achieve more precise tightening torques in both soft and hard tightening. However, this is not possible with the known screwdriver and the known method for speed control.

The invention is therefore based on the object to provide a screwdriver and a method for speed control of a screwdriver, which on the one hand initially a quick tightening the screw is made possible and on the other hand to the end the screwing down the screwdriver is controlled so that the most accurate tightening torque is ensured for a screw. Deviations of the tightening torque between a hard and a soft screw should be as low as possible.

This object is achieved in the screwdriver according to the aforementioned type according to the invention that the control device is derived from the speed derived value as a trigger parameter for reducing the speed.

The object of the invention is further achieved by a method for speed control of a screwdriver, in which the speed of the motor is monitored and upon reaching a trigger parameter, the speed of the motor is lowered, as a trigger parameter, the speed or derived from the speed Value is used.

The object of the invention is completely solved in this way. In accordance with the invention, a quick tightening of a screw connection is initially made possible, while a lower speed value is set when a specific trigger parameter, which is derived from the rotational speed, is reached. In this way, tightenings in the final phase can be tightened much more precisely than is the case with conventional screwdrivers, where the speed is reduced on the basis of the current consumption of the motor or possibly on the basis of the torque increase. Also, according to the invention can be minimized differences in the tightening torque of fittings, which result from differences between hard and soft screwing.

According to a further embodiment of the invention, the control device uses as a trigger parameter a speed change per unit time.

According to a further variant of the invention, the control device uses as a trigger parameter an angular velocity change per unit of time.

These measures ensure particularly precise speed control.

The screwdriver has according to a further embodiment of the invention, a speed sensor whose output signal is supplied to the control device.

The speed sensor can be designed, for example, as an incremental sensor with a light barrier (Hall element) of the like.

This results in a particularly simple construction of the speed sensor. If the control electronics are in any case designed for a digital control of the motor, the pulses recorded by the Hall element can be fed to a counter for simple further processing.

According to a further embodiment of the invention, the screwdriver on a shutdown device for switching off the motor upon reaching a predetermined torque.

As a result, a precise shutdown is guaranteed upon reaching the desired torque.

According to a further embodiment of the invention, a clutch for separating the tool drive shaft from the drive is provided upon reaching a predetermined tripping parameter.

This also makes it possible to ensure the most precise possible tightening torque of screwed connections.

According to a further development of the method according to the invention, when the trigger parameter is reached, the motor is regulated to a second speed, which is lower than the output speed.

According to a development of this embodiment, the speed is controlled on reaching another trigger parameter to a further speed, which is lower than the previous speed.

In this way, several speed stages can be adjusted in sequence speed-dependent, so that a very precise control of the screwing with different, each stepwise reduced speeds is possible. The speed reduction when a trigger parameter is reached can be repeated as often as required until a predetermined minimum speed has been reached. In this way, an n-stage speed control can be realized, which can be set very accurate compliance with a desired Schraubverlaufes.

According to a further embodiment of the invention, the control device is formed upon reaching the trigger parameter to reduce the speed to zero and the subsequent reversal of direction, followed by a further reversal of the direction of rotation.

In this way, a certain setting of the screw can be ensured for certain screwings by the short-term reversal of direction after the first tightening.

It is understood that the features of the invention mentioned above and those yet to be explained below can be used not only in the particular combination indicated but also in other combinations or in isolation, without departing from the scope of the invention.

Fig. 1

eine Darstellung des Drehmoment- und Drehzahl-Verlaufes in Abhängigkeit der Zeit für einen erfindungsgemäßen Schraubvorgang;

Fig. 2

eine stark vereinfachte, schematische Darstellung eines erfindungsgemäßen Schraubers;

Fig. 3

ein vereinfachtes Ablaufdiagramm für ein erfindungsgemäßes Schraubverfahren und

Fig. 4

eine Darstellung eines alternativen Schraubvorgangs, wobei der Drehmoment- und der Drehzahlverlauf in Abhängigkeit von der Zeit gezeigt ist.

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 representation of the torque and speed curve as a function of time for a screwing operation according to the invention;

Fig. 2

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

Fig. 3

a simplified flow diagram for an inventive screwing and

Fig. 4

a representation of an alternative screwing process, wherein the torque and the speed curve as a function of time is shown.

Fig. 1 shows a representation of the torque and the speed over time for a screwing operation according to the invention.

After the engine has been switched on, the nutrunner first runs at an initial speed n0 at the first tightening of the screw connection with a relatively low torque. Starting from the initial speed n0, the speed n drops only slightly in phase I at the beginning of the screwing. The torque M increases in phase I only slightly linear. As a trigger parameter Tpn for switching to a lower speed, the speed change dn / dt per unit time is monitored: $$\mathrm{dn}/\mathrm{dt}=\mathrm{.DELTA.n}/\mathrm{.delta.t}=\frac{n0-n1}{t0-t1}\mathrm{,}$$

If the speed drop dn within the time unit dt reaches the predetermined trigger parameter Tpn, the speed of the screwdriver is reduced and then regulated to a value n1. This speed value n1 is maintained in phase II, until the end of the screwing torque M increases up to a turn-off MA, resulting in the shutdown of the engine.

As can be seen from the illustration in FIG. 1, the torque in phase I initially rises to a certain value, followed by a greater increase towards the end of phase I. With the speed reduced to the value n1, the torque M increases in FIG Phase II then continue approximately linearly, but with a smaller increase than before, until finally the shutdown occurs when the torque limit MA is reached. The speed n is kept approximately constant in the phase II and possibly decreases at the end of the screwing process due to the higher load, until finally the value 0 is reached by the torque shutdown.

In Fig. 2, an inventive screwdriver is shown schematically and generally designated by the 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 can be held and by means of a switch button 28 on and off.

In the upper part of the housing 12, a motor 18, a gear 20 and a clutch 22 are successively added. The output side of the coupling is connected to a tool drive shaft 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 coupling 22 with the tool drive shaft 24.

The screwdriver 10 is controlled by a central electronic control device 30 which is received in the handle 14 and is connected via suitable lines to the battery pack 16, the shift key 28, the motor 18, the transmission 20 and optionally to the shut-off clutch 22.

On the motor 18, a speed sensor in the form of a Hall element is also provided, which is also coupled to the control device 30 via suitable lines.

The transmission 20 may, as for example EP 0 320 723 B1 be known to be formed as a planetary gear and be provided with a torque shutdown. Upon reaching a certain torque coupled to the planetary gear 20 switch 34 is actuated via a rotating fork and leads to the shutdown of the motor 18. To generate a restoring force may be provided a torsion spring rod. 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 release clutch 22 may be provided, on the connection between the tool drive shaft 24 and the gear 20 is released by disengaging the clutch 22 upon reaching a predetermined torque. Such tripping couplings have long been known in the art, for example, on the DE 10 2004 011 068 B3 is referenced.

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

The speed of the motor 18 is controlled digitally via the control device 30.

For monitoring the speed of the Hall element 32 is provided which emits a pulse at each revolution of the motor shaft, which is supplied to a counter in the control device or control electronics 30. If the number of pulses emitted by the Hall sensor per unit of time remains the same, then the speed n of the motor 18 is constant. If the number of pulses per unit of time increases, the speed increases, but decreases per unit of time, so the speed n drops. The number of pulses per unit of time is used as a manipulated variable by the digital electronic control device 30. The screwdriver is operated with a load-dependent motor characteristic.

The speed control of the motor 18 according to the invention will be described in more detail below with reference to a simplified flow diagram 40, which is shown in FIG. 3.

First, the engine is started. After a short time, an idling speed n0 comes on (step 42).

In the subsequent step 44, the value dn / dt = Δn / Δt is determined, for which purpose the number of pulses generated by the sensor 32 per unit of time is used.

In the following step 46, the speed drop dn per unit time dt is compared with a predetermined trigger parameter Tpn. As long as dn is less than the trigger parameter Tpn, step 44 is repeated. However, if dn is greater than or equal to Tpn, then in the following step 48, the rotational speed n is reduced until a predetermined lower value n1 is reached and maintained in step 50.

In a subsequent step 52, the torque M is determined and checked in a further step 54, whether the torque M exceeds the predetermined tripping torque MA. As long as this is not the case, the torque is still monitored. As soon as the torque M reaches the triggering torque MA, the motor is stopped in the subsequent step 56.

It is understood that the steps 52 and 54 can also be combined in one step by, for example, as already explained above, a torque-dependent triggering switch 34 is actuated.

It is further understood that the steps 44 to 50 can be repeated as often as desired in order to lower the rotational speed to a lower value, in each case after reaching a predetermined trigger parameter for dn, which can then be regulated. So can the speed value of a screwing in a row be lowered by successive speed levels until a predetermined minimum value of the speed is reached, which is maintained.

Also, the steps 44 to 50 could be used to a quasi-continuous speed reduction to a predetermined minimum value.

In principle, any value derived from the rotational speed can be used as the trigger parameter Tpx.

For example, the change in the angular velocity per unit time dω / dt could be used as a trigger parameter. If a controlled speed n0 is required in the first bolting stage, the relative change in the control variable of the control unit can also be used as the trigger parameter Tpx.

Overall, a slow tightening speed is achieved in the final phase of the screwing, resulting in a precise tightening torque. Also, the differences in the tightening torque, which naturally arise between hard and soft screwing, are reduced to a minimum.

An alternative screwing operation according to the invention is shown schematically in FIG.

Thereafter, in the first phase I of the screwing process, initially tightening takes place at an initial speed n0, which can easily drop until the trigger parameter is reached. When the trigger parameter Tpn is reached, a reduction first takes place to zero and immediately thereafter a reversal of the direction of rotation. The screw connection will be solved in the subsequent phase II for a short time. Thus, the torque initially drops again in phase II. Subsequently, for example, after a predetermined time has elapsed, a further reversal of the direction of rotation occurs so that the screwing in phase III is attracted at a lower rotational speed than the initial rotational speed until the switch-off torque MA is reached.

Phase II, for certain fittings, is designed to first allow some screwing to set before final tightening takes place in Phase III.

Claims (13)

Screwdriver with speed control, with a motor (18) for driving a tool drive shaft (24), and with a control device (30) by means of which the speed (n) of the motor (18) is controllable, wherein the control device for reducing the speed (n ) is formed upon reaching a trigger parameter (Tpx), characterized in that the control device (30) derived from the speed (n) value (dn, dω) as a trigger parameter (Tpx) for reducing the speed (n) is supplied. Screwdriver according to claim 1, characterized in that the control device (30) as a trigger parameter (Tpx) uses a speed change per unit time (dn / dt). Screwdriver according to claim 1, characterized in that the control device (30) as a trigger parameter (Tpx) uses an angular velocity change per unit time (dω / dt). Screwdriver according to one of the preceding claims, characterized in that a speed sensor (32) is provided, the output signal of the control device (30) is supplied. Screwdriver according to claim 4, characterized in that the rotational speed sensor (32) is designed as an incremental sensor, preferably as an incremental sensor with a light barrier, more preferably formed as a Hall element. Screwdriver according to one of the preceding claims, characterized in that a shut-off device (34) for switching off the motor (30) is provided upon reaching a predetermined tightening torque. Screwdriver according to one of the preceding claims, characterized by a coupling (22) for separating the tool drive shaft (24) from the drive upon reaching a predetermined tripping parameter. Screwdriver according to one of the preceding claims, characterized in that the control device (30) upon reaching the trigger parameter (Tpx) for reducing the rotational speed (n) to zero and subsequent rotation reversal, followed by a further reversal of rotation is formed. Method for speed control of a screwdriver, in which the speed (n) of the motor (18) is monitored and upon reaching a trigger parameter (Tpx), the speed of the motor (18) is lowered, as a trigger parameter (Tpx) the speed (n) or a derived from the speed (n) value (dn, dω) is used. Method according to Claim 10, in which, when the trigger parameter (Tpx) has been reached, the motor (18) is regulated to a second rotational speed (n1) which is lower than the output rotational speed (n0). Method according to Claim 10, in which, when another trigger parameter (Tpx) is reached, the rotational speed is regulated to a further rotational speed (n2) which is lower than the previous rotational speed (n1). Method according to one of Claims 9 to 11, in which the motor (18) is switched off when a predetermined torque (MA) is reached. Method according to one of claims 9 to 12, in which the speed is lowered after reaching the trigger parameter to zero, the motor is operated for a certain period of time with the reverse direction of rotation, then the direction of rotation is reversed again and the screw is tightened at a lower speed than at the output speed.

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