Electric machine tool

Details Electric machine tool Electric machine tool

1999-05-06

2001-03-13

Smith, Scott A. (Department: 3721)

Tool driving or impacting

Drive adjustable to completely change kind of drive

Adjustable to impacting device

C173S109000, C173S205000

Reexamination Certificate

active

06199640

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to an electric machine tool for tools which operate by rotation and/or percussion, such as a drill and/or riveting hammer or impact drilling machine.
In connection with a known drill and/or riveting hammer of this type (DE 41 21 279 A1), the drive unit comprises an eccentric seated on a gear shaft, which drives the work spindle via a gear wheel and, via a needle bearing, receives a coupling sleeve having an opening, as well as an elastically yielding driver member, which is seated, tiltable around an axis oriented transversely in relation to the gear shaft, in the machine housing. The driver member has a lever extending away from the axis toward the coupling sleeve, which engages the opening in the latter, and a two-legged hoop extending away from the axis, which is closed on its free end in a loop-like manner and is hinged with play between two collars formed on the beater. The beater is received with displacement play in the hollowly embodied drive spindle, wherein an inserted O-ring acts as a damper on the beater and prevents it from being displaced on its own. A header or a riveting bolt has been inserted between the tool shaft and the beater.
During operation, the driver member is driven via the eccentric in a back-and-forth movement, wherein only the vertical excursions of the eccentric are transmitted to the lever, while the transverse movements of the anchor sleeve do not reach the lever because of the opening, which is widened in this direction. Accordingly, the driver member performs a back-and-forth movement around its axis. At the moment of the impact of the beater on the header, and therefore on the tool, the driver member is at dead center on the tool side. Following the strong impact, the beater is reflected and flies backward toward the hoop of the driver member, which also moves backward. When the striking mechanism is well adjusted, the front collar touches the hoop of the driver member only slightly, or not at all. After passage through dead center on the motor side, the driver member again comes into contact with the front collar of the beater. Because of the kinetic energy of the beater, the hoop is bent backward in the process. Thus, the energy still stemming from the recoil of the beater is transferred to the elastic driver member and stored therein as spring energy. In the subsequent forward movement of the hoop, the latter accelerates the beater in the direction toward the tool, both because of the forward movement of the driver member and because of the backward springing hoop, wherein as a rule the beater attains higher velocities than the driving hoop. This leads to the separation of the beater from the driver member. The beater then flies freely over a defined distance, until another impact on the header and the tool takes place.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an electric machine tool which avoids the disadvantages of the prior art.
In keeping with these objects in the inventive electric machine tool the driver unit has a scanning member which rotates synchronously with the work spindle, is axially displaceably arranged, and is guided with axial plate between two circular-shaped curved paths, which are arranged fixed against relative twisting in respect to the work spindle and have elevations and depressions pointing in the axial direction of the work spindle.
The electric machine tool has the advantage, that because of the mechanical striking mechanism constructed in accordance with the invention it is possible to omit a gear shaft and therefore to achieve greater spindle rpm. By means of the selection of the axial elevations and depressions provided on the curved paths, a corresponding number of beats per spindle revolution is achieved. By means of the striking mechanism in accordance with the invention it is possible to produce an electric machine tool with the emphasis on small tool diameters in a very cost-efficient manner, wherein the lubrication outlay is very small.
In accordance with a preferred embodiment of the invention, the elevations and depressions of the curved paths, which extend parallel with the axial direction of the work spindle, are constituted by several periods of a sine-like curve, wherein the two curved paths extend parallel with or offset from each other. Three or five periods of a sine curve per curved path are preferred.
In accordance with an advantageous embodiment of the invention, the spring-loaded actuators are designed as contact springs, which can be simply and cost-effectively manufactured and installed.


REFERENCES:
patent: 5366025 (1994-11-01), Dutschk et al.
patent: 5427188 (1995-06-01), Fisher
patent: 5449044 (1995-09-01), Phillips
patent: 5513709 (1996-05-01), Fisher
patent: 5601149 (1997-02-01), Kawasaki et al.
patent: 2820125A (1979-11-01), None
patent: 41 21 279 A1 (1993-01-01), None

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