Anti-kickback power tool control

A method of eliminating kickback in a power tool of the type having an implement driven by an electric motor, said electric motor being supplied with current from an AC source, the method comprising the steps of:

• (a) sampling successive periods of the current through said motor at determinate points in the current waveform;
• (b) filtering the sampled values of motor current;
• (c) measuring the rate of change of the results of said step of filtering;
• (d) comparing the measured rate of change with a threshold;
• and
• (e) inhibiting the supply of current to said motor if the measured rate of change exceeds said threshold.

A method of eliminating kickback in a power tool of the type having a rotary shaft connected to drive an implement and an electric motor coupled to said rotary shaft to impart a rotary motion thereto, said electric motor being periodically supplied with current through an electronic switching circuit, the method comprising the steps of:

• (a) sampling successive periods of the current through said motor at determinate points in the current waveform generated by said electronic switching circuits;
• (b) filtering the sampled values of motor current;
• (c) measuring the rate of change of the results of said step of filtering;
• (d) comparing the measured rate of change with a threshold;
• and
• (e) controlling said electronic switching circuit to block the supply of current to said electric motor if the measured rate of change exceeds said threshold.

A method of eliminating kickback in a power tool of the type having a rotary shaft connected to drive an implement and an electric motor coupled to said rotary shaft to impart a rotary motion thereto, said electric motor being supplied with current through an electric switching circuit, the method comprising the steps of:

• (a) closing a switch to generate a signal to said electronic switching circuit to cause said electric switching circuit to periodically supply current to said electric motor;
• (b) sampling successive periods of the current through said motor at determinate points in the current waveform;
• (c) filtering the sampled values of motor current;
• (d) measuring the rate of change of the results of said step of filtering;
• (e) comparing the measured rate of change with a threshold;
• and
• (f) controlling said electronic switching circuit to block the supply of current to said electric motor if the measured rate of change exceeds said threshold.

In a power tool of the type having an implement driven by an electric motor, said electric motor being supplied with current from an AC source, the improvement of a system for detecting an impending kickback condition in the power tool comprising:

• (a) sampling means for sampling successive periods of the current through said motor at determinate points in the current waveform;
• (b) filtering means for filtering the sampled values from said sampling means;
• (c) means connected to said filtering means for storing the results of filtering successive sampled values of motor current and for computing the difference between the stored results as a measure of the rate of change of said results of filtering;
• (d) comparing means for comparing said measure of the rate of change with a threshold to detect an impending kickback condition.

In a power tool of the type having an implement driven by an electric motor, said electric motor being supplied with current from an AC source, the improvement of an anti-kickback control system for said power tool comprising:

• (a) sampling means for sampling successive periods of the current through said motor at determinate points in the current waveform;
• (b) filtering means for filtering the sampled values from said sampling means;
• (c) means connected to said filtering means for storing the results of filtering successive sampled values of motor current and for computing the difference between the stored results as a measure of the rate of change of said results of filtering;
• (d) comparing means for comparing said measure of the rate of change with a threshold;
• and
• (e) means for inhibiting the supply of current to said motor if the measured rate of change exceeds said threshold.

In a power tool of the type having a rotary shaft connected to drive an implement and an electric motor coupled to said rotary shaft to impart a rotary motion thereto, said electric motor being supplied with current through an electronic switching circuit, the improvement of an anti-kickback control system for said power tool comprising:

• (a) sampling means for sampling successive periods of the current through said motor at determinate points in the current waveform generated by said electronic switching circuit;
• (b) filtering means for filtering the sampled values from said sampling means;
• (c) means connected to said filtering means for storing the results of filtering successive sampled values of motor current and for computing the difference between the stored results as a measure of the rate of change of said results of filtering;
• (d) comparing means for comparing said measure of the rate of change with a threshold;
• and
• (e) means for controlling said electronic switching circuit to block the supply of current to said electric motor if the measured rate of change exceeds said threshold.

In a power tool of the type having a rotary shaft connected to drive an implement and an electric motor coupled to said rotary shaft to impart a rotary motion thereto, said electric motor being supplied with current through an electronic switching circuit, the improvement of an anti-kickback control system for said power tool comprising:

• (a) a switch which when closed generates a signal to said electronic switching circuit to cause said electronic switching circuit to periodically supply current to said electric motor;
• (b) sampling means for sampling successive periods of the current through said motor at determinate points in the current waveform generated by said electronic switching circuit;
• (c) filtering means for filtering the sampled values from said sampling means;
• (d) means connected to said filtering means for storing the results of filtering successive sampled values of motor current and for computing the difference between the stored results as a measure of the rate of change of said results of filtering;
• (e) comparing means for comparing the measured rate of change with a threshold;
• and
• (f) means for controlling said electronic switching circuit to block the supply of current to said electric motor if the measured rate of change exceeds said threshold.

In a power tool of the type having an implement driven by an electric motor, the improvement of an anti-kickback control system for said power tool comprising:

• (a) monitoring means for monitoring a signal proportional to the current supplied to said electric motor;
• (b) a microprocessor connected to receive the signal from said monitoring means, said microprocessor being programmed to compute the rate of change of the signal from said monitoring means, compare the computed rate of change with a threshold value, and produce an inhibit output signal whenever the computed rate of change exceeds said threshold value;
• and
• (c) control means responsive to said inhibit output signal for inhibiting the coupling of power to said implement from said electric motor.