KICKBACK DETECTION METHOD AND APPARATUS

1 . A chainsaw comprising:

a housing containing an engine;

a guide bar extending from the housing;

a cutting chain that is movable by the engine around a perimeter of the guide bar;

a gyroscope configured to detect rotational velocity of the chainsaw about an axis of the chainsaw; and

a microprocessor configured to cause movement of the cutting chain to stop in response to a signal received from the gyroscope.

2 . The chainsaw of claim 1 , wherein the axis is a first axis and the signal is a first signal, the chainsaw further comprising:

an accelerometer configured to detect acceleration of the chainsaw in a direction parallel to a second axis of the chainsaw;

wherein the microprocessor is further configured to:

scale the first signal received from the gyroscope by a first weighting factor;

scale a second signal received from the accelerometer by a second weighting factor;

compare a combination of the scaled first signal and the scaled second signal to a threshold; and

cause movement of the cutting chain to stop where the combination exceeds the threshold.

3 . The chainsaw of claim 2 , wherein the first and second weighting factors are selected to maximize detection of actual kickback and minimize false alarms of kickback produced during normal operation of the chainsaw.

4 . The chainsaw of claim 2 , wherein the second axis is defined generally by the guide bar and is approximately perpendicular to the first axis.

5 . The chainsaw of claim 4 , wherein a ratio between the first weighting factor and the second weighting factor is between 1:2 and 1:3.

6 . The chainsaw of claim 2 , wherein the second axis is approximately perpendicular to both the first axis and a third axis defined by the guide bar.

7 . The chainsaw of claim 6 , wherein a ratio between the first weighting factor and the second weighting factor is approximately 4:1.

8 . The chainsaw of claim 2 , wherein the accelerometer is a first accelerometer and the second axis is approximately perpendicular to the first axis, the chainsaw further comprising a second accelerometer configured to detect acceleration of the chainsaw in a direction parallel to a third axis of the chainsaw that is perpendicular to both the first and second axes;

wherein the microprocessor is further configured to scale a third signal received from the second accelerometer by a third weighting factor.

9 . The chainsaw of claim 8 , wherein the signals from the first and second accelerometers are 180° out of phase.

10 . The chainsaw of claim 8 , wherein a ratio between the first weighting factor and both the second weighting factor and the third weighting factor is approximately 10:1.

11 . The chainsaw of claim 2 , wherein the microprocessor is further configured to cause the engine to shut down where the combination exceeds the threshold.

12 . The chainsaw of claim 2 , wherein one or more of the first signal and the second signal is passed through a low pass filter before being received by the microprocessor.

13 . The chainsaw of claim 12 , wherein the low pass filter has a frequency of about 150 Hz.

14 . A method, comprising:

receiving, by a microprocessor of a chainsaw, one or more signals from a gyroscope configured to detect rotational velocity about one or more axes of the chainsaw; and

activating, by the microprocessor, a braking system of the chainsaw to stop movement of a cutting chain around a perimeter of a guide bar in response to receiving the signal from the gyroscope.

15 . The method of claim 14 , further comprising:

scaling, by the microprocessor, a first signal received from the gyroscope by a first weighting factor;

scaling, by the microprocessor, a second signal received from an accelerometer configured to detect acceleration in one or more directions, by a second weighting factor;

comparing, by the microprocessor, a combination of the scaled first signal and the scaled second signal to a threshold; and

activating, by the microprocessor, the braking system of the chainsaw to stop movement of the cutting chain around the perimeter of the guide bar where the combination exceeds the threshold.

16 . The method of claim 15 , wherein the gyroscope is configured to detect rotational velocity about a Z-axis of the chainsaw and the accelerometer is configured to detect acceleration of the chainsaw in a direction parallel to a Y-axis of the chainsaw.

17 . The method of claim 15 , wherein a ratio between the first weighting factor and the second weighting factor is between 1:2 and 1:3.

18 . The method of claim 15 , wherein a ratio between the first weighting factor and the second weighting factor is approximately 4:1.

19 . The method of claim 15 , further comprising shutting down an engine of the chainsaw, by the microprocessor, where the combination exceeds the threshold.

20 . The method of claim 15 , further comprising passing the first and second signals through one or more low pass filters before sending the first and second signals to the microprocessor.

21 . The method of claim 15 , wherein the accelerometer is a first accelerometer, the method further comprising:

scaling, by the microprocessor, a third signal received from a second accelerometer configured to detect acceleration in one or more directions, by a third weighting factor;

wherein the gyroscope is configured to detect rotational velocity about a Z-axis of the chainsaw, the first accelerometer is configured to detect acceleration of the chainsaw in a direction parallel to an X-axis of the chainsaw, and the second accelerometer is configured to detect acceleration of the chainsaw in a direction parallel to a Y-axis of the chainsaw.