EP1180416A2 - Power tool with quick coupling means - Google Patents

Abstract

The circular tool (30) is clamped loosely between a flange (26) on a motor-driven hollow spindle (24) and a clamping flange (28), by a packet of Belleville washers (42). The final pressure is applied by pivoting a lever (32) operated cam (56), which acts on a tappet (58). The lever is moved from the closed position (Zu), to the open position (Auf). In the unclamped position, if the motor is energized, the tappet rotates, releasing the friction between it and the cam. The lever then moves into the clamped position.

Description

The invention relates to a power tool, in particular a Angle grinder, which is a quick release device for attachment of a tool on a spindle with a Clamping flange and a counter flange, between which the tool non-rotatable under the action of an elastic pressing means is clamped, an actuator that between a Clamping position and a release position is movable, in which Release position the tension between the counter flange and the Clamping flange against the action of the elastic pressure medium is lifted, and a cam acting on the clamping flange, the at least in the release position by a motor of the Power tool is rotatable and at least at the when transferring the actuator from the clamping position in the release position a trained on the actuator Tread engages, causing movement of the actuator can be implemented in an axial displacement of the clamping flange is and the actuating element in the release position with the engine stopped taking advantage of one between the cam and the friction force acting on the tread.

Such a power tool is known from EP 0 152 564 A2. This known power tool has a quick release device with which disc-shaped tools, e.g. Grinding discs or circular saw blades, quickly and easily replaced can be. The quick release includes this purpose a clamping flange designed as a nut and a counter flange, between which the disc-shaped tool is tensioned. The clamping flange is on a clamping bolt screwed on in one of the power tool's motor driven hollow spindle non-rotatably, but in the axial direction is arranged movably. The clamping bolt is opposite the Hollow spindle so clamped by means of a spring that due to the spring action of the clamping flange screwed onto the clamping bolt is pulled towards the counter flange.

By transferring an actuating element designed as a rotary lever from a clamping to a release position Remove tension between the clamping flange and the counter flange. For this purpose, a cylindrical socket is formed on the rotary lever, which is screwed into the housing of the power tool is. When the rotary lever is actuated, the nozzle is further in screwed the housing in until it finally touched the socket facing end of the clamping bolt and this, together with the clamping flange screwed onto it. So that the tension between the clamping flange and the counter flange, so that the clamping flange can now be unscrewed by hand from the clamping bolt. Subsequently the tool can be exchanged for another tool.

However, when operating such power tools shown that users occasionally from negligence or else turn the power tool motor out of curiosity, though the rotary lever is still in the release position. It can even if the clamping flange is only loosely on the clamping bolt screwed on, not to loosen the tool and thus endanger the user. However, since the neck is still in its lowered position, he presses the underside from above onto the clamping bolt, the now after switching on the engine at high speed rotates. Because of the comparatively high forces this can lead to welding or deformation.

In the quick release device known from EP 0 152 564 A2 are now the frictional relationships between each other facing surfaces of the approach and the clamping bolt so chosen that when starting the motor, the frictional force between the two surfaces is sufficient to turn the rotary lever into the To transfer the clamping position. So the rotary lever is one Such incorrect operation automatically returns to the clamping position recycled.

However, it has been shown that this return movement of the Rotary lever is relatively difficult to control. For one thing becomes a relatively strong one by starting the motor Transfer torque to the rotary lever because the one at the beginning Stiction between the two surfaces involved enables large power transmission. This sets the automatic Introduce with a very jerky movement that Can give rise to accidents.

On the other hand, the frictional relationships between the both surfaces involved after some time since the power transmission just takes advantage of the frictional force and thus wear of the surfaces is inevitable. This has the consequence that the power transmission and thus the Type of movement of the rotary lever changed over time.

Another power tool is known from EP 0 650 805 B1, the provided with a similar quick release device is. The actuator is there as a pivot lever, however executed, which is firmly connected to an eccentric. When the swivel lever is turned, the eccentric presses a but axially movable printhead down until it finally sits on a pressure piece into which the clamping flange is screwed in via a threaded bolt. Will the The clamping lever is pressed further, so the print head finally pushes the thrust piece and thus also the clamping flange against the Effect of disc springs down.

In this known power tool, the pivot lever is over a shift rod with a switch to turn on the engine connected in such a way that the motor can only be switched on can when the actuating element is in the clamping position. This measure prevents if the actuating element is in the release position, the lowered print head with its underside from above on the Pressure piece that presses with high after turning on the engine Speed would rotate. Without such a measure would be due to the comparatively high forces to weld or deformation between the printhead and the Pressure piece (or a friction plate attached to it). The mechanical connection between the actuator and the switch for switching on the motor is constructive comparatively complex.

It is therefore an object of the invention, a power tool the kind mentioned at the outset in such a way that damage is reliable be avoided if the motor of the power tool due to incorrect operation in the release position of the actuating element is switched on. The power tool should still simple construction and inexpensive to manufacture his.

With a generic power tool, this task solved in that the cam and the tread on each other are coordinated that in the release position by Turning the motor on caused the cam to rotate Frictional force between the cam and the tread is reduced so that in the release position of the elastic pressure means acted on cam the actuator from the Release position moved to the clamping position.

The principle of the solution underlying the invention draws consequently characterized in that for returning the actuating element in its clamping position not one generated by the motor Torque, but rather that of the elastic Pressing means exerted on the actuating element via the cams Pressure is exploited. As long as the cam is at rest, maintains the static friction between the cam and the tread the actuator in the release position. Only when the cam starts rotating when the motor starts the static friction goes into the much smaller one Over sliding friction, which is then no longer sufficient, the actuating element to hold in the release position. The engine does So just a change in the friction between the cam and the tread; a power transmission from Motor on the actuating element, however, finds - at least in significant extent - not taking place.

Compared to the known in EP 0 152 564 A2 mentioned at the outset This principle has the decisive advantage of the clamping device, that the speed of the actuator when returning practically no longer on the engine speed, but only from structurally definable, largely unchangeable in time Parameters.

These parameters are in particular those of the compressive force generated by the elastic pressure means, the moment of inertia of the actuator, the direction in which the Cam attacks on the tread on the actuator, and of course the friction between the cam and the tread. The latter in turn depend on both the type the materials used as well as their surface properties from.

By the way a flange and a counter flange are used here Every component understood that a tool is suitable to clamp a shaft. The clamping flange can especially a conventional nut that is screwed onto the shaft.

The terms tension and release position are not in the present case to understand the restrictive sense that this is an exact defined position should be designated. Under the clamping position is rather every position, also a larger position range, to understand the actuator, in which a at least partially bracing the clamping flange and counter flange is achieved. Are corresponding with the release position designated all positions where there is no tension exists between the clamping flange and the counter flange. If thus from a movement of the actuating element from the release Tensioned position is spoken, this ultimately means that the actuator is moved until the Tension has occurred at least partially. The reverse is true to relieve the components of the quick release device, so practical additional forces generated by the engine can no longer cause damage.

Here, each component is understood as a cam which is used for Power transmission on a trained on another component Surface, here called tread, attacks. A special Form should not be implied with the term cam. The The tread itself can be flat, but it can also be curved as desired, the curvatures also being developed as gradients of a Tread can be viewed.

It is particularly preferred if the tread at least has two sections of different slope.

This has the advantage that by varying the slope of the Tread the movement behavior of the actuator when automatically returning to the clamping position in certain Can have a constructive influence on boundaries. The slope affects the direction in which the cam moves over the Attacks the tread on the actuator. For example, it is possible a determination of the tread slope at which the actuator with an approximately constant speed is transferred from the release position to the clamping position.

In a preferred development of this embodiment, the Slope of the tread in the release position of the actuating element is smaller than the slope of the tread in the tensioned position.

This can be achieved that the power transmission to the Actuator is initially small, so that the return movement is slowly introduced into the clamping position. After that increases the slope of the tread so that the actuator accelerated more. This can be the case, for example be advantageous if the actuating element in the clamping position can be snapped into place. The speed of the actuator may then be sufficient to the locking resistance to overcome.

In another advantageous embodiment of the invention the tread at least two sections different Surface texture.

This has the advantage that even after the onset Return movement influenced the friction conditions can be. For example, be provided that the tread with a roughened section that has sliding friction so increased that the independent pivoting back of the Actuating elements braked or at least one more Acceleration is counteracted. The surface texture can also be changed by coating.

In a particularly preferred embodiment of the invention the tread is the rolling surface of the actuator trained eccentric rotatably mounted about an axis of rotation.

This has the advantage that the tread, so to speak, around the eccentric is wrapped around and in this way an essential has less "space" than a flat one Tread is the case, as e.g. on one as a slider trained actuator can be formed. The actuator can, for example, one on the side of the eccentric have trained rotary knob with which the eccentric can twist its axis of rotation.

In a preferred development of this embodiment includes however, the actuator one attached to the eccentric shaft Swivel lever that is about the axis of rotation of the eccentric is pivotable.

The use of a pivot lever has the advantage that so that much greater torques can be applied than this is the case with a rotary knob. In addition, through the sweeping swivel movement of the swivel lever when automatic Return to the user from the release position to the clamping position clearly indicated that he failed to Before operating the power tool Bring tension position. The attachment of the swivel lever on Eccentric can also be done via a freewheel. If that Actuator is in the release position, moves only the eccentric when starting the motor, not the one Swivel lever back to the clamping position.

In another advantageous development of this embodiment the eccentricity of the eccentric is between 1% and 20% of the largest diameter of the eccentric.

It has been shown that with such an eccentricity the eccentric a particularly reliable power transmission in the sense of the principle of the invention can be achieved.

In another preferred embodiment of the invention, the Eccentric offset in the direction of the axis of rotation of the eccentric Axis of rotation of the cam arranged.

Such a transverse offset leads to the fact that when the Motors in the release position of the rotating cam an additional Transmits torque to the eccentric, not to the elastic pressing means, but on the rotation of the cam as such declines. Whether this additional torque is from the torque generated by the elastic contact supports or counteracts this depends on which side the eccentric is offset in the direction of the eccentric axis of rotation is. The offset is preferably selected so that the Torque generated by the elastic pressing means supported is an additional acceleration of the actuator to achieve.

In a further preferred embodiment of the invention, the surfaces of the cam and the tread have a Vickers hardness of more than 54, preferably about 64, and a roughness depth R _z between 0.2 μm and 8 μm.

This is due to the great hardness of sufficient wear resistance given so that for the return of the Actuating element determining friction between the cam and the tread remain constant over time. On the other hand, such a roughness enables one sufficiently high static friction between the cam and the running surface, so that the actuator in the release position when standing Motor can be held by the cam. Such Surface quality can e.g. by hardening and grinding or by rolling (possibly sintered) steel parts become.

In a further advantageous embodiment of the invention the surfaces of the cam and the tread from one porous sintered material whose pores near the surface are covered with a Lubricants are filled up.

This measure, known per se, makes emergency lubrication between the cam and the tread. at the wear of the surfaces gradually opens up the pores, releasing the lubricant it contains becomes.

In another preferred embodiment of the invention spindle driven by the motor designed as a hollow spindle. The Cam acts on the clamping flange via a pressure piece on the the clamping flange is detachably fastened in the hollow spindle under the influence of the cam against the action of the elastic Pressure means slidably arranged in the axial direction is.

This measure, which is known per se, can be constructive simple way a very reliable quick release device realize. The cam can be part of the pressure piece or firmly with it be connected so that every movement of the actuator directly on the pressure piece and thus on it attached clamping flange transmits. But then it's for it To ensure that at least in the clamping position between the tread and the cam remain a short distance, so that it does not become a when operating the power tool permanent friction between the rotating cam and the Tread of the actuator comes.

In an advantageous development of this embodiment, the Cams, however, are not directly connected to the pressure piece. Rather, the cam is part of a printhead that is in a Sleeve is rotatably mounted and when the actuating element is transferred in the release position against the effect of a elastic pressing means that the cam of the print head presses the tread of the actuating element, axially so in Direction of the pressure piece is shifted so that the print head at least indirectly comes into frictional engagement with the pressure piece.

This has the advantage that the cam always has the running surface touches the actuator. This conveys a more pleasant one Feeling when operating the actuating element, as if this with its tread suddenly on the cam touches down. The frictional connection between the print head and the pressure piece facilitates in particular the changing of the tool, since the hollow spindle, which is connected to the pressure piece in a rotationally fixed manner is blocked against twisting due to the frictional engagement. To reduce the friction between the printhead and the pressure piece enlarge, the latter can be rotatably fixed at the end with a friction plate be connected. This has a surface with a sufficient high coefficient of friction and can, if they once should be worn, comparatively simply against a replacement plate Replace.

In a further advantageous embodiment of the invention an elastic return means acts on the actuating element, that has a force regardless of a rotation of the cam the actuator exerts a movement of the actuator supported from the release position to the clamping position.

With the help of such an additional return means, that the actuator even then by one Stop definable clamping position assumes when the actuator in an intermediate position between the clamping and Release position. This configuration is particularly useful in such designs where the actuator no printhead loaded by elastic pressure means attacks as described above.

It is understood that the above and those below Features to be explained not only in each case specified combination, but also in other combinations or can be used alone, without the scope of to leave the present invention.

Fig. 1

einen vereinfachten Längsschnitt durch ein erfindungsgemäßes Elektrowerkzeug im Bereich seines Getriebekopfes, wobei sich ein Betätigungselement für die Schnellspanneinrichtung in der Spannstellung befindet, in der ein Werkzeug zwischen einem Spannflansch und einem Gegenflansch drehfest eingespannt ist;

Fig. 2

das Elektrowerkzeug aus Fig. 1, bei dem das Betätigungselement in die Lösestellung überführt wurde, so daß die Verspannung zwischen dem Spannflansch und dem Gegenflansch aufgehoben ist;

Fig. 3

das Elektrowerkzeug aus den Fig. 1 und 2, bei dem in der Lösestellung des Betätigungselements der Spannflansch vollständig herausgeschraubt ist;

Fig. 4

einen schematischen Längsschnitt durch einen Exzenter mit daran angreifendem Nocken beim Überführen des Betätigungselements in die Lösestellung;

Fig. 5

eine Fig. 4 entsprechende Darstellung, bei der das Betätigungselement von der Löse- in die Spannstellung zurückgeführt wird;

Fig. 6

eine Ansicht von hinten auf den Exzenter aus Fig. 5, in der erkennbar ist, daß der Exzenter in Richtung der Exzenterdrehachse versetzt zum Nocken angeordnet ist;

Fig. 7

eine Abwicklung einer Exzenterabrollfläche;

Fig. 8

ein für das erfindungsgemäße Elektrowerkzeug geeignetes Betätigungselement in einer perspektivischen Darstellung;

Fig. 9a

ein stark vereinfachter Längsschnitt durch eine andere Ausführung eines für die Erfindung geeigneten Betätigungselements, welches sich in der Spannstellung befindet;

Fig. 9b

das Betätigungselement aus Fig. 9a in Draufsicht;

Fig. 10

das Betätigungselement aus Fig. 9a in der Lösestellung.

Preferred exemplary embodiments of the invention are explained in more detail below with reference to the drawing. In it show:

Fig. 1

a simplified longitudinal section through an electric tool according to the invention in the region of its gear head, an actuating element for the quick-action clamping device being in the clamping position in which a tool is clamped in a rotationally fixed manner between a clamping flange and a counter flange;

Fig. 2

the power tool of Figure 1, in which the actuating element has been transferred into the release position, so that the tension between the clamping flange and the counter flange is released;

Fig. 3

the power tool of Figures 1 and 2, in which the clamping flange is completely unscrewed in the release position of the actuating element.

Fig. 4

a schematic longitudinal section through an eccentric cam with it when transferring the actuating element into the release position;

Fig. 5

a Fig. 4 corresponding representation, in which the actuating element is returned from the release into the clamping position;

Fig. 6

a view from behind of the eccentric of Figure 5, in which it can be seen that the eccentric is arranged offset in the direction of the eccentric axis of rotation to the cam.

Fig. 7

a development of an eccentric rolling surface;

Fig. 8

a suitable for the power tool according to the invention actuator in a perspective view;

Fig. 9a

a greatly simplified longitudinal section through another embodiment of an actuating element suitable for the invention, which is in the clamping position;

Fig. 9b

the actuating element of Figure 9a in plan view.

Fig. 10

the actuating element from Fig. 9a in the release position.

A first embodiment for a power tool according to the invention in the form of an angle grinder is in total in Fig. 1 designated 10. Within a housing 12 of the power tool 10 there is a motor / transmission unit 14, which is shown in dashed lines for the sake of clarity. The motor / transmission unit 14 has an electric motor 16, whose motor shaft 18 is a pinion 20 for a bevel gear wearing. An output gear 22 of the bevel gear is rotationally fixed connected to a hollow spindle 24 which is not shown in FIG. 1 shown - ball bearings rotatably mounted about an axis of rotation 25 is. On a protruding out of the housing 12 A counter flange 26 is formed at the end of the hollow spindle 24, a clamping flange 28 for clamping a tool 30 assigned. Tool 30 is shown in FIG Embodiment around a grinding or cutting disc. To enable the tool 30 to be changed manually, a quick release device is provided, which among other things the counter flange 26, the clamping flange 28 and an actuating element 31 includes a pivot lever 32. By pressing of the actuator 31 is one between the counter flange 26 and the clamping flange 28 acting tension can be canceled.

For this purpose, the quick release device has a coaxial in the Hollow spindle 24 arranged pressure piece 34. The pressure piece 34 has approximately the shape of a cup and is not by means of guides shown in more detail in a rotationally fixed manner, but in the axial direction movably guided in the hollow spindle 24. Inside is the pressure piece 34 is provided with an internal thread 36 into which a clamping bolt 40 can be screwed in with an external thread 38 is. The clamping bolt 40 is in turn fixed to the clamping flange 28 connected or executed in one piece with this.

The a tight fit between the counter flange 26 and the Clamping flange 28 is caused by a bracing only schematically indicated disc spring assembly 42, which on one side on a rotating in the hollow spindle 24 Paragraph 44 attacks. Props on the opposite side the plate spring assembly 42 on the underside of the pressure piece 34 from. Because the top of the pressure piece 34 on a snap ring 45 strikes, the circumferential inside in the hollow spindle 24 Groove 46 is inserted, can from the pressure piece 34, the clamping bolt 40 and the clamping flange 28 unit formed only against the action of the plate spring assembly 42 in the direction the arrows labeled 48 are moved down.

A lifting of the tension caused by the plate spring assembly 42 is only possible with the aid of the actuating element 31, by the pivot lever 32 formed thereon in the by the Arrow 50 shown direction from that shown in FIG. 1 Clamping position in a release position shown in Fig. 2 is transferred.

The pivot lever 32 is firmly connected to an eccentric 52, which is rotatably mounted on a shaft 53 about an axis of rotation 54 is. A running surface forming the rolling surface of the eccentric 52 56 engages a cam 58 which is integral with a printhead 60 is formed. Printhead 60 is about the axis of rotation 25 rotatable in a self-lubricating bearing sleeve 62 axially movable added. With the help of a spiral compression spring 64, the between an annular shoulder 66 of the printhead 60 and one Projection 68 of the housing 12 is held, the printhead 60 pressed against the tread 56 of the eccentric 52, so that the printhead 60 is always in contact with the actuator 31 stands.

The function of the quick release device according to the invention is now explained in more detail with reference to FIGS. 2 and 3.

If the pivot lever 32 is flipped in the direction of the arrow 50, the eccentric 52 presses the cam over its running surface 56 58 due to the eccentricity down. This moves the printhead 60 down as a whole, contrary to the effect the spiral spring 64. About halfway through the swivel of the actuator 31 touches the lower tapered End of the print head 60 on a rotationally fixed to the hollow spindle the axial top of the pressure piece 34 attached friction plate 69th

If the pivot lever 32 is now pivoted further towards the release position, so the downward movement of the printhead 60 continues continued, which is now the pressure piece 34 against the action of the plate spring assembly 42 presses down in the direction of arrows 48. The screwed into the pressure piece 34 is also the same distance Clamping flange 28 moves down. This creates a small between the clamping flange 28 and the tool 30 Gap 70, which indicates that the tension between the counter flange 26 and the clamping flange 28 is now canceled. This State is shown in Fig. 2.

In this relaxed state there are no significant frictional forces more between the tool 30 and the clamping flange 28. The clamping flange 28 can therefore in this position Unscrew the hand from the pressure piece 34, as shown in FIG. 3 is indicated by the arrow 71. To unscrew it facilitate, the clamping flange is knurled on the circumference 72 provided.

In the embodiment shown in FIGS. 1 to 3, the Clamping flange 28 is not directly on the tool 30. Rather, it is based on the clamping flange 28 and the clamping bolt 40 unit formed, an intermediate flange 74 is rotatably received, that of a thin disc 76 and one from the center the disc 76 axially projecting projection 78. By the center of the disk 76 and the projection 78 is cylindrical Bore through which the clamping bolt 40 is guided. On the outside, the attachment 78 has the shape of a regular polygon. This polygonal shape has its counterpart in the section the hollow spindle 24 below the plate spring assembly 42, the inside is also designed accordingly polygonal. The intermediate flange 74 with its extension 78 can thereby so insert into this section of the hollow spindle 24 that a Form fit between the hollow spindle 24 and the intermediate flange 74 is achieved. Mutual twisting of the hollow spindle 24 and intermediate flange 74 is then not in the release position possible.

The tool is in the clamping position of the actuating element 31 30 between the counter flange 26 and the clamping flange 28 clamped. To create a positive connection between the Clamping flange 28 and the counter flange 26 in the clamping position ensure and thus a loosening of the clamping flange 28 under to avoid all operating conditions are preferably the mutually facing surfaces of the clamping flange 28 and intermediate flange 76 additionally with spur gears or similar Mistake. Consequently there is a continuous positive connection between the clamping flange 28 and the hollow spindle 24. Consequently it is not possible that the clamping flange 28 together with the Clamping pin 40 during use of the power tool Twisting releases from the pressure piece 34 by itself. Therefore, it is enough it also, after changing the tool, the clamping flange 28 only slightly tightened until the clamping flange 28 on the intermediate flange 76 strikes because after tightening the clamping flange 28 is held non-rotatably in any case and that of the disc spring package 42 practiced tension practically independently is how far the clamping bolt 40 is screwed into the pressure piece 34 is.

Since the clamping flange 28 is opposite after releasing the bracing can easily rotate the intermediate flange 76, can the clamping bolt 40 is unscrewed from the pressure piece 34, even if the intermediate flange 74 is still with its shoulder 78 is held non-rotatably in the hollow spindle 24. One on the clamping bolt 40 put on snap ring 80 leads when unscrewing of the clamping bolt 40 with the intermediate flange 74 until this finally reached the position shown in Fig. 3. The The clamping flange 28 can now, together with the intermediate flange 74 and the clamping bolt 40, completely in the direction of the arrows 48 are pulled out, causing the tool 30 from the counter flange 26 removed and replaced with a new tool can. The assembly is done in reverse order.

In the quick release device according to the invention, the Eccentric 52 together with the cam 58 so that when the actuating element 31 in that shown in FIGS. 2 and 3 Release position, the actuator 31st automatically returned to the clamping position is as soon as the motor 16 of the power tool 10 in motion is set. Since in the release position the print head 60 to the Pressure piece 34 is pressed, is transmitted in the event of an unintentional Switching on the motor 16 a movement of the hollow spindle 24 about an existing frictional connection to it non-rotatably arranged pressure piece 34 and thus on the print head 60 and the cam 58 formed thereon Rotation of the printhead 60 causes stiction, between the cam 58 and that formed on the eccentric 52 Tread 56 acts in a much smaller Sliding friction passes. While the printhead is at a standstill 60 acting static friction the actuator 31 in the release position held, the torque which the printhead 60 under the pressure of plate spring assembly 42 exerts on the cam 58 on the eccentric 52, the opposite acting torque, which is generated by the sliding friction becomes. The eccentric 52 therefore begins together with the Swivel lever 32 into that indicated by the dashed arrow 82 Direction to move back to the clamping position.

The processes that take place between the cam 58 and the eccentric 52 act, are explained in more detail below with reference to FIGS. 4 and 5.

4 shows the eccentric 52 and in solid lines the cam 58 formed on the pressure piece 60 in FIG. 1 shown clamping position. The pivot lever 32 is the overview not shown for the sake of it. The tread 56 of the eccentric 52nd describes in the embodiment shown in Fig. 4 the shape of a circular arc. The eccentricity denoted by e, i.e. the vertical distance between the center point 55 of the Circular arc and the axis of rotation 54 of the eccentric 52 in the clamping position, determines the amount by which the eccentric rotates 52 the cam 58 is pressed down. With a turn of the eccentric 52 by 180 °, this dimension is 2e.

4 shows the eccentric 52 at one Turn through approx. 45 ° to the release position. It can be seen how the tread 56 of the eccentric 52 moves down and the cam 58 in the position shown in dashed lines transferred. The print head 60 therefore moves through the Arrow 82 indicated downward direction.

Fig. 5 shows with solid lines the eccentric 52 in the Release position. Since the print head 60 from the plate spring assembly 42 in the direction indicated by arrow 84 pressed up a torque acts on the eccentric 52, which it in Would like to move in the direction of arrow 86 into the clamping position. This torque arises because the cam 58 on the Eccentric 52 exerts a force that is not central to the axis of rotation Eccentric 52 is directed. Rather, there is between the Contact line along which the eccentric 52 and the cam 58 touch, and the axis of rotation 54 of the eccentric an offset v. This offset v creates a lever arm that corresponds to the one addressed Torque leads. In the above In the exemplary embodiment, the circular arc diameter is 12.6 mm, the eccentricity e 1.2 mm and the offset v 0.2 mm.

As long as the print head 60 is at rest with the cam 58, this causes between the tread 56 of the eccentric 52 and the top of the cam 58 acting static friction that the eccentric 52 and so that the entire actuator 31 despite the acting Torque remains in its release position.

However, when the motor is actuated, the print head becomes 60 rotated together with the cam 58, so there is static friction between the tread 56 and the cam 58 into a sliding friction. If the cam 58 and the tread 56 are made of hardened ground steel, so the sliding friction is about an order of magnitude less than the static friction. The friction is no longer sufficient counteracting the torque exerted by the printhead, so that the eccentric 52 in the indicated by the arrow 86 Moved back towards the clamping position.

An eccentric 52 which is returned by approximately 60 ° is dashed in FIG. 5 indicated. It can be seen that the now In the direction of arrow 84 upward moving print head 60 the cams 58 formed thereon continue to have a torque exerts the eccentric 52, so that the actuating element 31 increasingly accelerates until it finally returns to that in FIG. 4 shown clamping position (or in a position shortly before) is transferred.

Fig. 6 shows a rear view of the eccentric 52, in which can be seen that the eccentric 52 in the direction of the axis of rotation 54 of the eccentric is offset from the cam 58. The The size of this offset is equal to the distance between the center plane 57 of the eccentric 52 and the axis of rotation 25 of the cam 58. Because of this offset, the line of contact between the eccentric 52 and cam 58 no longer symmetrical to the axis of rotation 25 of the cam 58 arranged. When cam 58 rotates an additional torque on the eccentric 52 exercised, the direction of which depends on whether the cam 58 rotates clockwise or counterclockwise about its longitudinal axis 25. In the illustrated embodiment, the cam rotates 58 in the direction indicated by arrow 59, whereby the Eccentric 52 in the direction of arrow 61 about its longitudinal axis 54 is moved back to the clamping position.

A similar effect is also produced when the Eccentric 52, seen in the direction of the axis of rotation 54, slightly conical is shaped. This also ensures that the contact line between the eccentric 52 and the cam 58, which are in this case shortened to a point of contact, not arranged more symmetrically to the axis of rotation 25 of the cam 58 is. The taper of the eccentric 52 can have values of approximately Accept 0.1 ° to 1 °, preferably of about 0.3 °.

Both the eccentric 52 and the pressure pin 60 with the cam 58 preferably consist of sintered rolled steel parts, the Vickers hardness of which is in the range of approximately 64 and the roughness depth R _z in the range of approximately 2 μm. As already mentioned above, this has the advantage that it creates a particularly large difference between static and sliding friction. In addition, due to the great hardness, the wear is low, so that the frictional relationships between the cam 58 and the running surface 56, which are decisive for the return of the actuating element 31, and on the other hand the stroke of the pressure pin 60 generated when the clamping lever 32 is pivoted remain constant over time. With such steel surfaces, when the plate spring assembly 42 generates a compressive force of approx. 3,000 N, the static friction force is approx. 300 N and the sliding friction force is approx. 40 N.

To the torque acting on the eccentric 52 during the To be able to influence swinging back into the clamping position can instead of an eccentric with an arc-shaped tread an eccentric can be used, the tread of which is not constant Has slope.

7, a rolling surface of such a modified eccentric is plotted over the swivel angle α. This shows that the gradient α _{2 of} the rolling surface at large swivel angles (release position) is smaller than the gradient α _{1 of} the rolling surface at smaller swivel angles (clamping position). This design of the rolling surface causes the actuating element 31 to first slowly move away from the released position after the motor is switched on and then accelerate more strongly. If desired, the final speed can be so great that the actuating element 31 finally transitions into an end position, in which it is sunk into a recess in the housing 12 of the power tool 10, by overcoming a latching resistance. With larger snap-in resistors, however, this can be inappropriate, since this may require such a great acceleration of the actuating element 31 that a danger to the user when swiveling back cannot be completely ruled out.

On the speed when swiveling the Actuator 31 can also by changing the surface quality the tread 56 can be influenced. For example, it can be provided that the tread between a swivel angle of 0 ° and 60 ° (from the clamping position seen, see Fig. 7) is roughened such that due to the greater sliding friction there, the automatic swing back movement of the actuating element 31 braked or at least one further acceleration is counteracted.

In the embodiment shown in FIGS. 1 to 3 the cam 58 is formed on a printhead 60, the first in the course of the pivoting of the actuating element 31 on the Pressure piece 34 attacks. Alternatively, it can also be provided be that the eccentric 52 acts directly on the pressure piece 34. This must then be carried out so that it faces upwards the hollow spindle 24 protrudes. On the pressure piece 34 can additionally a cam 58 may be formed. The cam 58 can but here as well as in the embodiment explained above in the sense that the entire pressure piece 34th or the print head 60 is regarded as a cam.

To in this alternative embodiment also in the Clamping position of the actuator 31 a constant friction between the pressure piece 34 and the one formed on the eccentric 52 To prevent tread 56 should be in the tensioned position a small between the eccentric 52 and the pressure piece 34 Leave gap. As a replacement for the effect of the spiral spring 64 can then a return spring acting on the actuating element 31 92 can be provided, as shown in FIG. 8. The Return spring 92 already acts on the actuating element 31 in its clamping position with a low spring force and ensures for the necessary distance to the pressure piece 34.

Finally, it is also conceivable instead of a swivel lever to use a rotary lever, as mentioned in the introduction EP 0 152 564 A2 is described. Which is in the release position mutually contacting surfaces of the rotary lever and the pressure piece (or a print head attacking it) and the Pitch of the thread over which the rotary lever with the housing is screwed, are then to be designed so that when the Motors of the rotary lever just not through a frictional force transmitted to the thrust piece on the rotary lever in motion is set. Rather, the parameters addressed are like this to determine that with a rotation of the pressure piece, the friction decreases at the contact surface, so that the rotary lever exclusively under the action of the elastic pressing elements from the Thread is unscrewed and thereby into its clamping position is returned. In this way, the rotary lever can be significantly return to the clamping position in a more controlled manner than if this is driven directly by the motor via a frictional connection becomes.

9a, 9b and 10 is an alternative embodiment schematically shown for an actuator 31. Instead of a swivel lever connected to an eccentric a slide 100 is used here as the actuating element, whose tapered underside forms a tread 102 which cooperates with a printhead 104. Different from the one above described print head 60, the print head 104 has a rounded Top 106 on, so that the print head 104 as a whole Cam works. The slider provided with a passage 108 100 is thus only schematically indicated between two Guides 110, 112 guided that it is in the arrow 116 indicated direction can move. Located in Fig. 9a the slider 100 shown in plan view in FIG. 9b is in the clamping position. Now he pulls on the handle 108 moved in the direction of arrow 116, so presses Tread 102 on the underside of the slide 100 den (without Guide shown) printhead 104 in the direction of the arrow 114 down. This will eventually cause the tension canceled between the clamping flange 28 and the counter flange 26, as detailed above with reference to FIGS. 1 to 3 has been described.

10, the slider 100 is in the release position. If the print head 60 is now rotated, it is reduced , as already described above, between the Top side 106 of the print head 60 and the tread 102 of the Slider 100 acting friction force, whereby the print head 60th now slide the slider 100 back into the clamping position can push, as indicated by arrow 118. Here, too, the tread 102 can of course be different Have slopes, as described above for FIG. 7 has been.

Claims (13)

Power tool (10), in particular an angle grinder, which has a quick-action clamping device for fastening a tool (30) to a spindle (24) with: a) a clamping flange (28) and a counter flange (26), between which the tool (30) can be non-rotatably clamped under the action of an elastic pressing means (42), b) an actuating element (31, 100) which can be moved between a clamping position and a release position, the tension between the counter flange (26) and the clamping flange (28) being released in the release position against the action of the elastic pressing means (42), and c) a cam (58, 106) acting on the clamping flange (28), i) which can be set in rotation at least in the release position by a motor (16) of the power tool (10) and ii) on which, at least when the actuating element (31, 100) is transferred from the tensioned position to the release position, a tread (56, 102) formed on the actuating element (31, 100) engages, thereby causing the actuating element (31, 100) to move axially Displacement of the clamping flange (28) can be implemented, and iii) which holds the actuating element (31, 100) in the release position when the motor (16) is stationary using a frictional force acting between the cam (58, 106) and the running surface (56, 102), characterized in that d) the cams (58, 106) and the running surface (56, 102) are matched to one another in such a way that in the release position a rotation of the cam (58, 106) caused by switching on the motor (16) reduces the frictional force between the cams (58 , 106) and the running surface (56, 102) so reduced that the cam (58, 106) acted upon in the release position by the elastic pressing means (42) moves the actuating element (31, 100) automatically from the release position to the clamping position. Power tool according to claim 1, characterized in that the tread (56, 102) has at least two sections of different pitch (α ₁ , α ₂ ). Power tool according to claim 2, characterized in that the slope (α ₂ ) of the tread (56, 102) in the release position of the actuating element (31, 100) is smaller than the slope (α ₁ ) of the tread (56, 102) in the clamping position. Power tool according to one of the preceding claims, characterized in that the tread (56, 102) has at least two sections of different surface properties. Power tool according to one of the preceding claims, characterized in that the running surface (56, 102) is the rolling surface of an eccentric (52) formed on the actuating element (31, 100) and rotatably mounted about an axis of rotation (54). Power tool according to Claim 5, characterized in that the actuating element (31, 100) comprises a pivot lever (32) which is fastened to the eccentric (52) and which can be pivoted about the axis of rotation (54) of the eccentric (52). Power tool according to Claim 6, characterized in that the eccentricity (e) of the eccentric (52) is between 1% and 20% of the largest diameter of the eccentric (52). Power tool according to one of claims 5 to 7, characterized in that the eccentric (52) is arranged offset in the direction of the axis of rotation (54) of the eccentric (52) to the axis of rotation (25) of the cam (58). Power tool according to one of the preceding claims, characterized in that the surfaces of the cam (58, 106) and the tread (56, 102) have a Vickers hardness of more than 54, preferably about 64, and a roughness depth R _z between 0.2 µm and 8 µm. Power tool according to one of the preceding claims, characterized in that the surfaces of the cam (58, 106) and the tread (56, 102) consist of a porous sintered material whose pores near the surface are filled with a lubricant. Power tool according to one of the preceding claims, characterized in that the spindle driven by the motor (16) is designed as a hollow spindle (24) and that the cam (58, 106) acts on the clamping flange (28) via a pressure piece (34) which the clamping flange (28) is releasably attached and which is arranged in the hollow spindle (24) under the influence of the cam (58, 106) against the action of the elastic pressing means (42) in the axial direction (48). Power tool according to Claim 11, characterized in that the cam (58, 106) is part of a print head (60) which is rotatably mounted in a sleeve (62) and which, when the actuating element (31, 100) is moved into the release position, counter to the Effect of an elastic pressing means (64), which presses the cams (58, 106) of the printhead (60) against the running surface (56, 102) of the actuating element (31, 100), is axially displaced in the direction of the pressure piece (34), that the print head (60) at least indirectly comes into frictional engagement with the pressure piece (34). Power tool according to one of the preceding claims, characterized in that an elastic return means (93) acts on the actuating element (31), which exerts a force on the actuating element (31), independent of a rotation of the cam (58, 106), which causes a movement the actuating element (31) is supported from the release position to the clamping position.

Images