Electric tool and controlling method thereof

摘要

A power tool including a motor for rotatably driving a tool bit at an attained rotational speed, a source for supplying an electric current to the motor, a sensor for measuring the current, and a control device. The control component fulfills the task of detecting a variation of the slope of the current in the course of time, and generates a control signal. The rotational speed of the tool is reduced in response to the control signal. The power tool automatically detects whether the work piece operated by the tool bit reaches a predetermined position by electronic control means. It may make sure that the screw is driven into a piece of wood and does not go beyond the predetermined position once it detects that the work piece reaches the position and carries out a changing action.

主权项

1. A method for controlling an electric tool, the electric tool comprising an electric motor and an output shaft which is driven by the electric motor and configured for outputting a rotary torque to drive a tool bit to work on a work piece, the method comprising:
measuring a current supplied to the electric tool in dependence on time, presetting a predetermined threshold value, calculating a second or higher derivative of the current in dependence on time, calculating a product of: i) the second or higher derivative and ii) the current, generating a control signal only when the absolute value of the product is greater than or equal to the predetermined threshold value, and changing a rotational speed of the electric tool in response to the control signal.