Electric tool

Abstract

The invention discloses an electric tool. The electric tool comprises a shell, a motor, a transmission device, an output shaft, a control unit and a switch, wherein the motor, the transmission device,the output shaft, the control unit and the switch are located in the shell. The motor drives the output shaft to rotate through the transmission device. The control unit controls the motor to operateaccording to a switch state and comprises a current detecting unit, a storage unit and a judging unit. The current detecting unit is used for detecting the real time motor current value I. The storage unit is used for storing the maximum current value Imax. During reverse rotating of the motor, when the judging unit judges the situation that the current motor current value I is less than or equalto K times of the stored maximum current value Imax, the control unit cuts off the motor current, and the value range of K is from 0.3 to 0.7. According to the provided technical scheme of the electric tool, the reverse rotating self-stopping function of the tool can be achieved, and the risk that a bolt and a nut are fully separated and fall off is prevented.

Description

[technical field] [0001] The invention relates to an electric tool, in particular to an electric tool capable of automatic shutdown. [Background technique] [0002] At present, common electric tools, such as screwdrivers and impact wrenches, etc., are driven by a motor to rotate an output shaft to tighten or remove fasteners such as screws and bolts. When removing the fasteners, due to the high speed of the electric tool, the fasteners can be removed in a short time, which is easy to cause the problem that the fasteners fall off after removal. In order to solve this problem, China invented Patent announcement No. CN104656549B proposes a technical solution. By detecting the motor current value, the motor current value is compared with a preset threshold value. If it is less than or equal to the preset threshold value, the motor speed is changed or stopped. However, in reality, as the power tool is used longer, the permanent magnets of the motor will degrade to varying degree...

AI Technical Summary

Problems solved by technology

When removing the fasteners, due to the high speed of the electric tool, the fasteners can be removed in a short period of time, which may easily cause the problem that the fasteners will fall off after removal. To solve this problem, China invented Patent announcement No. CN104656549B proposes a technical solution. By detecting the motor current value, the motor current value is compared with the preset threshold value. If it is less than or equal to the preset threshold value, the motor speed is changed or the motor is stopped.

However, in reality, as the power tool is used longer, the permanent magnets of the motor will degrade to varying degrees, so that the output torque of the motor will decrease under the same current drive. If a fixed preset current threshold is used As a criterion for shutting down, after a long period of use of electric tools, the screws will be loosened excessively

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