Abrading – Frame or mount – Portable abrader
Reexamination Certificate
2001-08-16
2003-05-27
Hail, III, Joseph J. (Department: 3723)
Abrading
Frame or mount
Portable abrader
C451S359000, C451S363000, C451S508000, C451S510000, C451S523000
Reexamination Certificate
active
06569001
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a power tool, in particular to an angle grinder, comprising a quick clamping device for fastening of a tool onto a spindle, comprising a clamping flange and a counter flange, between which the tool under the effect of an elastic force means is clamped, an actuation element being movable between a clamping position and a release position, wherein in the release position the clamping between the counter flange and the clamping flange against the effect of the elastic force means is neutralized, and a cam acting on the clamping flange which can, at least in the release position, be rotated by a motor of the power tool, and on which acts at least, when the actuation element is transferred from the clamping position in the release position, a running surface designed on the actuation element, wherein a movement of the actuation element is transferred into an axial shift of the clamping flange; and which, in the release position, when the motor is idle, holds the actuation element under the action of a frictional force acting between the cam and the running surface.
RELATED PRIOR ART
Such a power tool is known from EP 0 152 564 A2. This known power tool has a quick clamping device, by means of which disk-shaped tools, e.g. abrasive wheels or circular saw blades, can be exchanged quickly and comfortably. The quick clamping device comprises, for that purpose, a clamping flange constructed as a nut, and a counter flange, between which the disk-shaped tool is clamped. In this way, the clamping flange is screwed upon a clamping pin, which is attached for common rotation to a hollow spindle driven by the motor of the power tool, but movable in axial direction. The clamping pin is clamped, with respect to the hollow spindle, by means of a spring in such a way that the clamping pin is pulled toward the counter flange, due to the bracing effect of the clamping flange.
By transferring an actuation element, which is configured as a pivot lever, from a clamping position into a release position, the clamping between the clamping flange and the counter flange can be neutralized. To this end, a cylindrical socket is arranged on the pivot lever, said socket being screwed into the housing of the power tool. If the pivot lever is actuated, the socket is screwed further into the housing, until it, finally, acts upon the end of the clamping pin facing towards the socket and presses down the clamping pin, together with the clamping flange screwed thereon. In that way, the clamping between the clamping flange and the counter flange is neutralized, so that the clamping flange can be unscrewed from the clamping pin manually. After that, the tool can be exchanged against another tool.
In the operation of such power tools it has turned out that users sometimes switch on, carelessly or curiously, the motor of the power tool, although the pivot lever is still in the release position. It is true that also when the clamping flange is only loosely screwed upon the clamping pin, this cannot result in detaching the tool and, thus, in endangering the user. As, however, the dog is still in its declined position, it presses, with its bottom part, from the top onto the clamping pin, which now, after switching on the motor, rotates with high speed. Due to the relatively high forces, welding or deformation may occur in this case.
In the quick clamping device known from EP 0 152 564 A2, the friction conditions between the areas facing each other of the dog are selected in such a way that, when the motor is started, the friction force between the two areas is high enough to transfer the pivot lever into the clamping position. The pivot lever is, thus, if such an operating error occurs, returned into the clamping position.
It has turned out, however, that this return movement is relatively hard to monitor. On the one hand namely, by starting the motor, a relatively high torque is transmitted onto the pivot lever, as the adhesive friction between the two engaged parts, existing at the beginning, allows a high force transmission. Thus, the self-instructed return process starts with a very abrupt movement, which may result in accidents.
On the other hand, the friction conditions between the two engaged surfaces change after a while, as the force transmission is performed exactly by making use of the friction force and, thus, a wear of the surfaces is inevitable. The result is that also the force transmission and, in connection therewith, the kind of movement of the pivot lever changes after a while.
From EP 0 650 805 B1, another power tool is known, which is equipped with a similar quick clamping device. The actuation element is in this case, however, configured as a pivot lever, which is firmly connected with an eccentric. When the pivot lever is pivoted, the eccentric presses down a pressure head which is guided axially movable, until the eccentric rests on a thrust piece, into which the clamping flange is screwed via a threaded bolt. If the clamping lever is further pivoted, the pressure head finally presses down the thrust piece and, thus, also the clamping flange, against the action of cup springs.
In this known power tool, the pivot lever is connected via a shifter bar with a switch for starting the motor in such a way that the motor can be switched on only when the actuation element is in the clamping position. With this measure, it is prevented that, if the actuation element is in the release position, the lowered pressure head presses, with its bottom part, onto the thrust piece, which would rotate at high speed after starting the motor. Without such a measure, there would be welding or deformation between the pressure head and the thrust piece (or a friction plate fastened onto it), due to the relatively high forces. The mechanical connection between the actuation element and the switch for switching on the motor is, however, relatively complicated in design.
SUMMARY OF THE INVENTION
It is thus an object of the invention to disclose an improved power tool which overcomes the drawbacks of the prior art. It is a further object of the invention to provide a power tool that reliably avoids failures when the motor of the power tool is switched on erroneously. The power tool shall be nevertheless simple in design, while allowing a cost effective manufacturing.
With respect to such a power tool as mentioned at the outset, this object is achieved by mating the cam and the running surface in such a way that, in the release position, a rotation of the cam caused by starting the motor reduces the frictional force between the cam and the running surface in such a way that the cam, which was prestressed by elastic force means, moves the actuation element from the release position into the direction of the clamping position on its own.
The solution principle underlying the invention is, consequently, distinguished by the fact that, for restoring the actuation element in its clamping position, not a torque generated by the motor is used, but, rather, the pressure exerted by the elastic force means via the cam onto the actuation element is used. As long as the cam rests, however, the adhesive friction force acting between the cam and the running surface keeps the actuation element in the release position. Only if the cam, when the motor is started, is set into rotation, the adhesive friction transitions into a distinctively smaller sliding friction, which is, then, not sufficient any more to keep the actuation element in the release position. The motor causes, thus, merely a modification of the friction conditions between the cam and the running surface; a force transmission from the motor to the actuation element, however,—at least in a significant amount—does not take place.
In comparison to the clamping device of EP 0 152 564 A2 mentioned at the outset, this principle has the decisive advantage that the speed of the actuation element, when being returned, is practically not dependent any more on the motor speed, but only depends on constructively determinable, mostly unchangea
Frenck Gerhard
Rudolf Boris
C. & E. Fein GmbH & Co. KG
Hail III Joseph J.
McDonald Shantese L
St. Onge Steward Johnston & Reens LLC
LandOfFree
Power tool having a quick clamping mechanism does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Power tool having a quick clamping mechanism, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Power tool having a quick clamping mechanism will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3001063