EP0463521B1 - Method and device for controlling the working of electrically powered hand-tools - Google Patents

Abstract

In an electrically powered hand-tool, in particular screwdriver and the like, in which a disconnect-type clutch, in particular in the form of a claw clutch, is situated between the drive motor and the tool output shaft, it is proposed to monitor the position of the claw clutch by means of a distance sensor and then to accelerate the drive motor, via a speed-control circuit, controlled by the distant sensor, for said drive motor, to high operating speed and optionally to maintain it at this speed whenever an inwardly directed pressure is exerted on the tool output shaft when screws and the like are being screwed in, by which pressure the disconnect-type clutch is simultaneously caused to close. <IMAGE>

Description

The invention is based on a method for controlling the operation of handheld electrical devices according to the preamble of claim 1 or a device which fulfills the same purpose according to the preamble of claim 4.

The invention relates specifically to the field of so-called screwdrivers as electrical handheld devices and is also explained in detail below with reference to a screwdriver, although it is understood that the basic concept of the invention is not limited to the screwdriver area, but advantageously also with any other electrical handheld devices, in particular Drills, rotary hammers and the like can be used.

It is common for screwdrivers to transmit the torque applied by an electric drive motor to provide at least one form-fitting coupling, for example and preferably a claw coupling. This claw coupling separates the positive connection between a gearbox on the drive motor side, if present, and the tool spindle when, for example, the tool spindle gradually slides axially forward in operative connection with a depth stop until the claws of the claw coupling separate from one another when a predetermined screwing depth is reached loosen and thereby end the screwing process.

It is not uncommon for such a claw coupling to form a functional unit together with a further device, for example a drag coupling (DE-PS 36 37 852), the effect of which is to complete the separation process of the claw coupling by an increase in distance which is immediately realized when this claw coupling slips through for the first time to prevent the individual claws from rattling past each other, especially when the claw coupling is released, and to avoid noise and wear.

This area of controlling the transmission of the torque in screwdrivers also includes the power-driven screwing tool in accordance with European patent application 90102260.8, in which the towing clutch responding when the limit torque is reached on the drive shaft-side coupling part of the claw coupling comprises at least one opening in the form of a guide pocket directed axially outward to the screwing tool , the recess base of which runs obliquely to the drive shaft longitudinal axis. In these The guide pocket engages with a cross pin that is non-rotatable on the drive shaft to form the towing coupling.

Also known is a motor-driven shut-off screwdriver (DE-OS 30 15 423), which, however, is intended so that when a preset limit torque is exceeded, the tool spindle is not stopped by switching off the electric motor, but by releasing a clutch, with further pressing in of the tool spindle lets the driver dome engage again beyond a position marked by the pressure point, but then into a position in which automatic uncoupling is no longer possible.

With such screwdrivers there is yet another problem, which occurs in particular when working professionally, if a screwdriver is placed in quick succession on the bit holder of the tool spindle or output shaft and the tool spindle is pressed axially backwards into the coupling position for the Claw clutch is brought. Such a procedure is also intended in itself, but becomes very problematic when the operators working with such a screwdriver have got used to working continuously with the switch-on or speed control switch depressed, so that the drive motor no longer at all when a new screw is inserted is switched off and is no longer brought down to idle speed, but the shaft standstill, which is necessary for inserting the screwdriver, is brought about by loosening the claw coupling and then, namely after inserting the screw with the drive motor continuing to turn up (control speeds for example 3000 to 5000 min⁻¹), the spindle is simply pressed again. As a result, the coupling process can be effected if you press firmly enough to strike the two claw coupling parts, so to speak. Nevertheless, it is unavoidable that the claws engage only poorly, since the claws of one claw coupling part have zero speed, while the other claw coupling part may even continue to run at maximum speed. You can achieve maximum screwdriving power, but you have to put up with a considerable amount of noise, since the corresponding hand tool is operated continuously at maximum working speed or close to it, while it can be assumed that even when screws are set quickly, a screwdriver per se only while 10% of the working time must run at high speed during the screwing-in process, while the other 90% are used to attach and remove the device or to insert new screws.

Another disadvantage is that due to the high idling speed maintained, not only a high clutch wear must be expected during clutch engagement, but also the service life of the other parts such as bearings, switches and the like. is reduced if the device is normally operated continuously at high speed in continuous operation, the resultant considerable noise being annoying and unpleasant. The invention is therefore based on the object to remedy this and an electric hand tool, especially screwdriver, drill, hammer drill and the like. To make available, on the one hand, a maximum screwing performance is possible, on the other hand but it is ensured that in the area of the positive coupling (claw coupling) there are no problems due to extreme differential speeds between the coupling parts.

Advantages of the invention

The invention solves this problem with the characterizing features of claim 1 and claim 4 and has the advantage that it is automatically ensured that the differential speed between the coupling parts is significantly reduced at the moment of engagement, even when the operator insists on maintaining the device in a fully switched-on state to maintain rapid progress in handling the hand tool. It is essential that the operator's intentions are not worked directly, so that the operator does not get the feeling that their own pace of work or the maximum possible screwing power is deliberately slowed down. The invention only ensures that at the moment of coupling for the device or for the coupling parts concerned there are optimal working conditions which, on the one hand, prevent tooth-on-tooth standing, which would prevent the coupling process, but, on the other hand, ensure that soft and engaged in the smooth transition and immediately after reaching a positive position of the claws with full force to the desired working speed, which for example can also correspond to the maximum speed of the device, is accelerated.

This also has the decisive advantage that in addition to the low differential speed Significant noise reduction can be achieved between the coupling parts and the much better coupling process achieved thereby, while at the same time being free from wear, since, according to a preferred embodiment of the invention, a reduced speed is maintained during the breaks between the individual screw connections.

Advantageous further developments and improvements of the invention specified in the main claim are possible through the measures listed in the subclaims. It is particularly advantageous that the reduced idling speed, which always occurs when the positive coupling (claw coupling) is released, significantly improves the service life of the other parts, i.e. bearings, switches, drive motors, collectors, also because none of the coupling area Shocks and vibrations are more to be expected. Furthermore, the low speed difference during the coupling process ensures a reduction in noise because now the individual parts can no longer rattle past each other at a high volume, but instead the coupling process proceeds smoothly and without problems. The invention therefore succeeds in reliably eliminating problems which occur especially with the so-called "professional devices" which are normally actually operated continuously in continuous operation.

drawing

Fig. 1

in einer schematisierten und lediglich wesentliche Teilbereiche im Schnitt darstellenden Seitenansicht eine mögliche Ausführungsform eines Schraubers;

Fig. 2

in Form eines Diagramms den durch die Erfindung automatisch vorgegebenen Drehzahlverlauf über der Zeit (abgesenkte Leerlaufdrehzahl - Arbeitsdrehzahl bzw. Maximaldrehzahl) und

Fig. 3

schematisiert und stark vereinfacht das Blockschaltbild zur Drehzahlsteuerung des Schraubers.

Exemplary embodiments of the invention are shown in the drawing and are explained in more detail in the following description. Show it:

Fig. 1

a possible embodiment of a screwdriver in a schematic side view, which shows only essential partial areas in section;

Fig. 2

in the form of a diagram, the speed curve automatically predetermined by the invention over time (reduced idle speed - working speed or maximum speed) and

Fig. 3

the block diagram for speed control of the screwdriver is schematized and greatly simplified.

Description of the embodiments

The basic idea of the present invention is to detect the clutch position and to give the start-up command to an, if desired, adjustable working speed or maximum speed at the moment of the coupling process of the positive coupling of a speed control for the electric drive motor of the device.

In this case, according to one embodiment of the invention, it is started up from a lower idling speed, so that firstly it is ensured that when the tool spindle is pressed on, i.e. when the screwing-in process begins, it can always be safely engaged and, secondly, it does not have to be started up from a complete standstill, but with full acceleration with the drive motor already idling, so that there is practically no work delay. In addition to the avoided clutch wear and the many other advantages achieved by the present invention, it is most likely that that the invention also optimizes the screwing-in process itself, since at the first moment of start-up there is still a lower speed, which is well suited to first allowing the screw to be gripped, for example predrilling an initial thread, in order then to be screwed in further at high speed.

The embodiment shown in FIG. 1 of a clutch position-controlled screwdriver is of a novel design in that the drive motor 11 of the screwdriver 10 is located in the handle of the screwdriver, which in the meantime has been designed like a pistol grip, as is the case with such devices.

The electric drive motor consists in the usual way of the A-bearing plate 11a, the B-bearing plate 11b, a stator 12 framed by the bearing plates and a rotor 13 with a rotor shaft 14 which rotates within the stator magnetic field and which on both sides in bearings 15a, 15b End shields 11a, 11b is mounted. The motor has yet another special feature, which is that the brush holder of the electric motor is designed as an inner, rotatable switching ring which works together with a punching plate and cooperates with an outer adjusting ring 16 through a housing recess, so that it is twisted by the adjusting ring 16 on the pistol handle of the device 10 is possible to freely select the desired direction of rotation of the screwdriver by turning the outer adjusting ring 16, it also being possible to switch the device off by means of a central adjusting ring position. This results in considerable simplifications of operation, but also simplifications in terms of structure Construction and assembly facilities. The rotor shaft 14 protrudes with a stub shaft 14a beyond the A-bearing 15a and in the exemplary embodiment shown drives a bevel gear 18 coaxial with the tool spindle 17 - it goes without saying that between the bevel gear 18 and the motor output shaft there is still a gear or other Device components can be interposed if desired. It also goes without saying that the bevel gear 18 does not necessarily have to sit on the device output shaft 17 (device spindle), as is the case in the exemplary embodiment shown; here, the bevel gear 18 is supported in a freely rotating manner via a needle bearing 19 by the device output shaft 17, which is itself supported in a further needle bearing 19 '.

In the embodiment shown in FIG. 1, the bevel gear 18 simultaneously forms the one coupling part of a form-fitting coupling 20, which is preferably designed as a claw coupling with claws 21b extending axially forward, while the other coupling part 22 is fixed with a claw ring 21a opposite the claws 21b is connected to the device output shaft 17.

The device output shaft 17 is biased, for example by spring pressure or in some other suitable manner to the outside, that is to the left in the plane of the drawing, so that the two claw rings 21a, 21b of the claw coupling 20 are kept at a distance from one another and the device output shaft 17 is therefore also at any speed rotating and the bevel gear 18 driving motor 11 stands still.

In this position, the user of the device can enter the Insert tool holder, not shown (screwdriver bit), a new screw, whereupon when using the device by pressing the screw onto the material into which it is to be screwed, the device output shaft 17 is also pushed back, so that the coupling parts 18 and 22 are moved towards each other or on another way, when the screw is pressed, the positive coupling (claw coupling) is closed. This is where the invention comes in, in that a distance sensor is provided at a suitable point, which is designed so that it can determine at what point in time or at what position distance the dog clutch 20 has effectively engaged, i.e. when that on the device output shaft 17 or one Other storage freely rotating, driven bevel gear 18 drives the transmission output shaft 17 as the first coupling part via the positive engagement with the second coupling part 22. At this moment, a speed acceleration signal is sent to a speed control circuit 23 which, according to FIG. 3, can consist of a speed control 23a and, for example, a phase control 23b controlled by the latter for the motor drive.

It is understood that the distance sensor can be designed in any way; it only has to be such that when the dog clutch is closed, that is to say when the device output shaft 17 is rotated, it generates such a signal that it can be interpreted and evaluated by the speed control circuit as a speed acceleration signal.

For this purpose, the distance sensor can be a simple mechanical switch, which triggers, for example, as a microswitch when the device output shaft 17 in the illustrated embodiment has moved so far to the rear, that is, to the right in the drawing plane, that the switch is actuated. However, it is also possible to design the distance sensor as a non-contact sensor, for example as an inductive or capacitive proximity switch, as a photo cell, in the form of a so-called Hall detector or as a pneumatic switch, the actual installation location of the distance sensor being arbitrary, for example, as in In the drawing, the distance sensor 24 specified there lies at the end of the device output shaft 17 or, for example, can be arranged in the region of the coupling as at 24 '(shown in broken lines).

The basic function of the invention can then be as follows. A speed control 23a (FIG. 3) receives the yes / no signal "engaged" or "not engaged" from the sensor 24, 24 '. The speed control 23a can consist of a simple resistor combination or other circuit elements which evaluate the corresponding signal of the distance sensor 24, 24 'and correspondingly control a phase control 23b which then in turn, ideally via a triac 25 which switches in both half-wave directions of the supplying mains voltage Motor 11 applied accordingly.

It is possible that the phase control 23b in connection with the speed control 23a is designed such that whenever the clutch is disengaged, the Electric drive motor rotates at a predetermined idling speed U _min (see FIG. 2); if the sensor 24, 24 'sends the signal "coupled" at time t1, then the speed control 23a switches up the motor 11 via the phase control 23b, so that it runs up to a predetermined working speed or to U _max , so that the motor runs in time t1-t2 applies the torque required for the screwing process.

Of course, it is possible that the screwing process is continued at maximum speed U _max for a predetermined period of time (dashed lines) and then the speed drop does not take place back to the preset idling speed until time t2 '. In any case, the return to the low-noise idling speed U _{min occurs} in that the coupling 20 is released again at the end of the screwing process, which is determined by the distance sensor and converted into a corresponding signal, as a result of which the leading edge control regulates back to the idling speed level. As is known in the case of such screwdrivers, this release of the coupling 20 determined by the distance sensor can take place in that a mechanical stop (depth stop) attached to the screwdriver at a predetermined point in time, for example also when a maximum torque is reached, due to the axial displacement of the device output shaft to the right 17, the dog clutch 20 opens again, which, after the screw has been displaced via the distance sensor, brings about an immediate automatic switchover to the reduced idling speed. This idle speed is also assumed by the speed control circuit 23 when the on / off switch 26 Mains separation is switched on - in any case, this represents a preferred setting of the device, it being understood that both the preferred idling speed U _min and the desired working speed U _{max can be} selected via further external actuators, for example potentiometer knurled wheel actuation 27 (FIG. 1) .

Alternatively, it is also possible, if no power is required from the device, to switch off the motor entirely via the speed control circuit, it being possible to ensure by selecting an appropriate mechanical claw coupling system that no "tooth-on-tooth" prevents the coupling process. Position "can occur. It is understood that the acceleration of the speed required for screwing on the motor, which is monitored by the speed control circuit, is also a function of the mechanics of the screwdriver and the respective screwing work to be carried out and can therefore be designed accordingly.

Claims (9)

1. A method of controlling the operation of electrically-powered hand tools, in particular nut runners, hand drilling machines, drill hammers and the like, by means of an axially displaceable tool output shaft driven by an electric motor via a coupling, the coupling closing in the event of axial pressure action on the output shaft, characterised in that the present tool output shaft position or coupling position is monitored by a distance sensor (24, 24') which - when the coupling (20) is closed and causing the tool output shaft to rotate along with it - supplies a speed acceleration signal to a speed control circuit (23) for the driving motor (11).
2. A method in accordance with Claim 1, characterised in that when the distance sensor (24, 24') is not actuated, the speed control circuit (23) triggers the driving motor (11) to adopt an adjustable idling speed (rev._min).
3. A method in accordance with Claim 1 or 2, characterised in that the tool output shaft (17) - spring-prestressed outwards - automatically transfers the claw coupling into the open position and the distance sensor (24, 24') - monitoring the output shaft position or coupling position - into its non-activated position, in such a manner that the driving motor runs at idling speed in the absence of operating contact pressure on the tool output shaft.
4. A device for controlling the operation of electrically-powered hand tools, in particular nut runners, hand drilling machines, drill hammers and the like, by means of an axially displaceable output shaft driven by an electric motor via a separating coupling (20), and by means of a speed control circuit for the electric motor, for the implementation of the method in accordance with any one of Claims 1 to 3, characterised in that a sensor (24, 24') is provided which monitors the state (open - closed) of the separating coupling and - when the coupling is closed and a closed driving connection is thereby produced from the electric driving motor to the tool bit - supplies a change-over signal to the speed control circuit (23) in such a manner that the electric motor is greatly accelerated by the speed control circuit and is held at a predetermined operating speed (rev._max).
5. A device in accordance with Claim 4, characterised in that the separating coupling is a claw coupling (20) whose first coupling part (18) is at least indirectly driven by the driving motor (11) and whose second coupling part is axially displaceable together with the tool output shaft (17) and is in the operating position - with the tool output shaft (17) pushed backwards - in a positive-locking operative connection with the first coupling part.
6. A device in accordance with Claim 4 or 5, characterised in that the electrically-powered hand tool is a nut runner (10) and on the nut-runner head there is arranged a mechanical stop which with a continuous screwing operation enables the gradual opening of the separating coupling (claw coupling 20) with progressive forwards travel of the tool output shaft (17), the distance sensor (24, 24') switching the driving motor (11) to idling speed via the speed control circuit (23) when the coupling is open.
7. A device in accordance with any one of Claims 4, 5 or 6, characterised in that the distance sensor is a mechanical switch, a microswitch, a non-contacting proximity switch, an optical sensor, a Hall detector, a pneumatic switch or the like.
8. A device in accordance with any one of Claims 4 to 7, characterised in that the tool output shaft (17) is under the effect of spring action causing automatic return motion and a disengagement of the coupling.
9. A device in accordance with one or a plurality of Claims 4 to 8, characterised in that the electrically-powered hand tool is constructed in the manner of a pistol handle with the driving motor being in the region of the pistol handle, in that the driving motor has an inner switching ring determining the rotational direction and the off/on position and being in a mechanical operative connection with an outer adjusting ring (16) on the housing in such a manner that the adjusting ring is as a rotary switch on the handle housing simultaneously used for reversing the direction of rotation and for switching on/off.

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