ELECTRIC POWER TOOL AND METHOD FOR OPERATING SAME

Abstract

In an electric power tool and a method for operating an electric power tool, a torque limitation of an electric motor reacts when a load moment exceeds a predetermined threshold and in which an output request is carried out by means of a switch. A supply of current to the motor is interrupted when a criterion for the reaction of the torque limitation is detected based on a speed detection of the motor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a preferred electric power tool with a battery unit for supplying current to the electric power tool,

FIG. 2 is a block circuit diagram for the implementation of the user function for an electric power tool with electronic speed limitation, and

FIG. 3 shows a curve of speed and torque as a function of time for a screwdriving operation with torque limitation and final screwdriving with visual monitoring of the results.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an electric power tool 100, which includes an electric motor 10, which can be supplied with current by a battery unit 14 situated in a handle 110 of the electric power tool 100. A switch 120 is provided for actuation of the electric power tool 100. If a torque limitation occurs during operation, then the connection can be interrupted between the battery unit 14 and motor 10, thus reducing demand on the battery unit 14.

FIG. 2 shows a block circuit diagram with the electric motor 10 preferably embodied as an EC motor, equipped with power electronics 12. The battery unit 14 supplies electrical power to the electric power tool. The motor 10, which is preferably embodied as an EC motor or DC motor, has a rotor position detection unit 20, which can detect the rotor position of a rotor of the motor 10. For example, the electric power tool 100 is a cordless drill.

An electronic unit 16 for controlling or regulating the electric power tool receives signals from the rotor position detection unit 20 that are used during normal operation to control of the motor 10, which is embodied as an EC motor.

A current measuring unit 22 detects the current output of the battery unit 14. The detected current value is transmitted to the electronic unit 16.

By means of a switch 18 preferably embodied as a pushbutton, the user sends the electronic unit 16 an output request, for example in order to drill a hole in a work piece that has been brought into operative connection with the drill bit of the electric power tool. The position of the switch 18 embodied as a pushbutton indicates the magnitude of the output request by the user. A speed n of the motor 10 or a conventional pulse width modulation of the current signal, which is supplied to the motor 10, is set proportional to the position of the switch. When the switch 18 embodied as a pushbutton is pressed to its maximum end position, the output request is at its maximum; in a middle position, the output request is correspondingly lower.

Preferably, the jamming detection, the switching off of the current, and the resumption of the current supply to the motor 10 are carried out by the electronic unit 16 and the power electronics unit 12 is triggered accordingly.

The supply of current to the motor 10 is interrupted if a criterion for the reaction of the torque limitation is detected based on a speed detection of the motor 10. A rapid drop in speed and/or a motor stoppage are suitable for use as the criterion.

After reaction of the torque limitation, the motor 10 can be supplied with current again when the output request is reduced, i.e. the switch 18 is released, and then increased again, i.e. the switch 18 is pressed again.

Alternatively, after reaction of the torque limitation, the motor 10 can be supplied with current again when a predetermined time span Δt has elapsed. This will be explained in conjunction with FIG. 3.

An upper characteristic curve 24a-26a indicates the progression of a speed n and a lower characteristic curve 24b-26b indicates the progression of a torque M over time t for a screwdriving operation with torque limitation. At a point 28, a criterion of the predetermined torque limitation 28b or of the predetermined speed drop 28a is reached within a predetermined time and the power electronics 12 interrupts the supply of current to the motor 10 (FIG. 1). The speed n and then the torque M quickly fall to zero.

During the time span Δt, current is not supplied even though the user continues to press the switch 18. After the time span Δt has elapsed, the supply of current to the motor 10 resumes, thus keeping its speed to low values while at the same time slowly increasing a threshold for the torque limitation. In this range, it is possible, for example, to execute a final screwdriving while visually monitoring the results.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of methods and constructions differing from the type described above.

While the invention has been illustrated and described as embodied in an electric power tool and method for operating same, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.

Claims

1. A method for operating an electric power tool, comprising the steps of reacting by a torque limitation of an electric motor when a load moment exceeds a predetermined threshold; carrying out an output request by a switch; interrupting a supply of current to the electric motor in at least partially automatic fashion when a criterion for a reaction of the torque limitation is detected.

2. A method as defined in claim 1; and further comprising interrupting a connection between the electric motor and a battery unit that powers the electric motor, a criterion for a reaction of the torque limitation is detected.

3. A method as defined in claim 1; and further comprising interrupting a connection between the electric motor and a battery unit that powers the electric motor in at least one partially automated fashion when a criterion for a reaction of the torque limitation is detected.

4. A method as defined in claim 1; and further comprising deriving the criterion from a speed detection of the electric motor.

5. A method as defined in claim 1; and further comprising using as the criterion a criterion selected from the group consisting of a rapid drop in a speed of the electric motor, a stoppage of the electric motor, and both.

6. A method a defined in claim 1; and further comprising after a reaction of the torque limitation, supplying the electric motor with current again when the output request is reduced and then increased again.

7. A method as defined in claim 1; and further comprising after a reaction of the torque limitation, supplying the electric motor with current again When a predetermined time span has elapsed.

8. A method as defined in claim 7; and further comprising selecting the time span by a user.

9. A method as defined in claim 7; and further comprising during the time span, maintaining the output request or increasing the output request.

10. A method as defined in claim 1; and further comprising after a resumption of the supply of current, increasing a limit value of the torque limitation.

11. A method as defined in claim 10; and further comprising limiting a speed of the electric motor.

12. An electric power tool, comprising an electric motor in which a torque limitation is provided when a load moment exceeds a predetermined threshold; a switch by which an output request of said electric motor is carried out; and means for interrupting a supply of current to said electric motor when a criterion for a reaction of the torque limitation is detectable.

13. An electric power tool as defined in claim 12; and further comprising means for interrupting a supply of current to said electric motor when a criterion for a reaction of the torque limitation is detected based on a speed detection of said electric motor.

14. An electric power tool as defined in claim 12; and further comprising means for detecting a rapid drop in a parameter selected from the group consisting of a speed of said electric motor, a stoppage of said electric motor, and both.

15. An electric power tool as defined in claim 12; and further comprising means for speed limitation upon resumption of a supply of current to said electric motor.

16. An electric power tool, comprising an electric motor in which a torque limitation is provided when a load moment exceeds a predetermined threshold; a switch by which an output request is carried out; and means for interrupting in an least partially automated fashion a connection between said electric motor and a battery unit that powers said electric motor when a criterion for a reaction of the torque limitation is detectable.

17. An electric power tool as defined in claim 16; and further comprising means for interrupting a supply of current to said electric motor when a criterion for a reaction of the torque limitation is detected based on a speed detection of said electric motor.

18. An electric power tool as defined in claim 16; and further comprising means for detecting a rapid drop in a parameter selected from the group consisting of a speed of said electric motor, a stoppage of said electric motor, and both.

19. An electric power tool as defined in claim 16; and further comprising means for speed limitation upon resumption of a supply of current to said electric motor.