Method for determining rotational speed of an electric motor in a power tool
AssigneeBlack & Decker Inc.
InventorJohn C. Vanko
Life of this patent
Estimating the term…
Abstract
An overspeed protection subsystem is provided for a power tool having an electric motor. The overspeed protection subsystem is comprised of: a motor switch coupled in series with the motor; a motor control module interfaced with the motor switch to control switching operation of the motor switch; and an overspeed detection module that determines rotational speed of the motor and disables the power tool when the rotational speed of the motor exceeds a threshold.
Claims25
A method for determining rotational speed of an electric motor in a power tool powered by an alternating current (AC) input signal, comprising
- controlling voltage applied to the electric motor using a phase-controlled switch in accordance with a given firing angle of the phase-controlled switch corresponding to a conduction phase angle of the AC input signal, such that voltage of the AC input signal is applied through the phase-controlled switch to the electric motor, during each half cycle of the AC input signal, after the given firing angle but not before the given firing angle;
- measuring current through the electric motor;
- and
- determining, by a computer processor, rotational speed of the electric motor as a function of the given firing angle and the measured current, wherein the function is a linear combination of a first higher order polynomial related to the given firing angle and a second higher order polynomial related to the measured current, and wherein the computer processor resides in the power tool.
A power tool configured to receive an alternating current (AC) input signal, comprising:
- an electric motor;
- a sensor configured to a measure current through the electric motor;
- a controller configured to receive the measured current from the sensor and operable to control voltage applied to the electric motor using a phase-controlled switch in accordance with a given firing angle of the phase-controlled switch corresponding to a conduction phase angle of the AC input signal, such that the AC input signal is applied through the phase-controlled switch to the electric motor, during each half cycle of the AC input signal, after the given firing angle but not before the given firing angle;
- wherein the controller determines rotational speed of the electric motor as a function of the given firing angle and the measured current and is implemented by a computer processor in the power tool, the function being a linear combination of a first higher order polynomial related to the given firing angle and a second higher order polynomial related to the measured current.
A power tool configured to receive an alternating current (AC) input signal, comprising:
- an electric motor;
- a phase-controlled switch coupled in series with the motor;
- a motor control module interfaced with the phase-controlled switch and modulates the conductive state of the phase-controlled switch at a given firing angle corresponding to a conduction phase of the AC input signal, wherein the motor control module is implemented by computer executable instructions executed by a computer processor;
- and
- an overspeed detection module that is separate from the computer processor and configured to receive the given firing angle from the motor control module, the overspeed detection module operates to and measure current through the motor and the overspeed detection module operable to determine rotational speed of the motor as a function of the given firing angle and the measured current and to disable the power tool when the rotational speed of the motor exceeds a threshold, wherein the function is a linear combination of a first higher order polynomial related to the given firing angle and a second higher order polynomial related to the measured current.
Dependencies are inferred from the claim text.