DE4225157A1 - Electric screwdriver for self tapping screws having drill tip and threaded part - has electronic sensor which is activated depending on current taken so that rpm of electric motor is reduced whilst thread is screwed in - Google Patents

Abstract

The screwdriver has an electronic regulator for controlling the rpm of the electric motor (2) drive. The rpm of the motor is reduced with the screwing in of the threaded part (6) of the screw (3) across a switch (8). The rpm is then maintained. The sensor (7) is activated depending on the gradient angle (alpha) of the current taken. A second sensor (9) is activated for the operation of the switch (8), depending on the level of the current taken. ADVANTAGE - Speed changeover results automatically and at correct time point. Electronic parts have low wt. and take up small space.

Description

The present invention relates to an electric screwdriver for self-drilling screws according to Preamble of claim 1.

To control the speed of the electric motor, it is known in drilling machines, initially drilling at an increased speed, the speed by an electronic Speed control is kept constant and in a second phase after actuation a manual control switch with increasing load at reduced speed finish drilling.

The hand screw is used to screw in self-drilling screws The control switch is unsuitable because the operator has the exact switching time cannot be strictly observed. If you switch to a lower speed too late the screw thread or the workpiece can then be damaged.

The object of the present invention is therefore to create an electric screwdriver of the type mentioned, in which the switching of the electric motor independently and done at the right time, with the electronic components a small Weight and need little space.

This object is achieved by the features in the characteristic of Claim 1.

When processing self-drilling screws, especially stainless steel self-drilling screws in Steel is initially a high speed when drilling, z. B. 2000 rpm is desired. This keeps the drilling time as short as possible. Would, however, with this high Speed also shaped the thread, so it would destroy the screw come.  

At the start of the thread forming process, the required torque and increases thus the current consumption increases steeply. This increase in power consumption can advantageously used to reduce the speed to a lower Value, e.g. B. 1000 rpm limit.

Thus, the switching starts exactly at the beginning of the thread area and one perfect shape of the thread is guaranteed.

The necessary electronic components are lightweight and a small footprint. The weight of the drill driver is therefore only slightly enlarged.

Both speeds are controlled by an electronic control system Current limited to a definable size and over a wide power range also kept.

A further sensor can be provided as an additional control option when a certain threshold of current consumption is exceeded, the switch reversed, this even with a relatively small slope of the current curve can be executed.

The following is an embodiment of the invention with reference to the Drawings described in more detail.

Show it:

Fig. 1 electric screwdriver schematically from the side;

Fig. 2 diagram for current consumption and speed over time when screwing in.

Fig. 1 shows an electric screwdriver 1 with an electric motor 2, can be screwed into the workpiece 4 with a drill screw. 3

For this purpose, the self-drilling screw 3 has a drill tip 5 and a threaded area 6 (see also FIG. 2), so that after the electric motor 2 is switched on, a hole is first drilled in the workpiece 4 and then the thread 6 is cut.

Fig. 2 shows the course of the current consumption 1 , corresponding to the required torque and speed n plotted over time t during the screwing process.

After switching on the electric motor 2 , the drill bit 5 of the self-drilling screw 3 drills a hole in the workpiece 4 at an engine speed of z. B. 2000 rpm.

If the threaded area 6 reaches the workpiece 4 , then the required torque and thus also the current consumption increases steeply at an angle α. If the slope of angle α exceeds a certain value, then a first electronic sensor 7 of the electric screwdriver 1 is activated, which switches the speed of the electric motor 2 to a low value, for example via a switch 8 . B. 1000 rpm. So that the thread in the workpiece 4 with the thread area 6 can cut perfectly and screw the self-drilling screw 3 .

With a second sensor 9, the switch 8 can also influence, said sensor 9 is responsive to a specific threshold value of the current consumption. This makes it possible to switch switch 8 even at a slope angle α of the current consumption which is below the slope angle triggering the sensor 1 .

There is one for limiting the respective speeds to a definable size known electronic control depending on the current consumption intended. This speed is simultaneously over a wide performance range also kept.

Claims (3)

1.Electric screwdriver for self-drilling screws, which have a drill tip and a threaded area, the required torque and thus the current consumption of the electric motor increase when the threaded area is screwed in, with an electronic control for keeping constant and with a controllable switch for controlling the speed of the electric motor , characterized in that a first electronic sensor ( 7 ) is activated as a function of the current consumption and actuates the switch ( 8 ) in such a way that the speed of the electric motor ( 2 ) is reduced and maintained when the threaded area ( 6 ) is screwed in via electronic control becomes. 2. Electric screwdriver according to claim 1, characterized in that the first sensor ( 7 ) is activated as a function of the pitch angle (α) of the current consumption. 3. Electric screwdriver according to claim 1 or 2, characterized in that a second sensor ( 9 ) for actuating the switch ( 8 ) is activated depending on the speed of the current consumption.