Electric power tool configured to detect twisted motion

An electric power tool comprising:

• a housing;
• a motor that is housed in the housing;
• an output shaft that is housed in the housing and includes a first end for attachment to a tool bit, the output shaft being configured to be rotatively driven by the motor and configured to rotate the tool bit about a Z-axis;
• and
• a twisted-motion detector that is configured to detect twisting of the housing, wherein the twisted motion detector includes:
• a three-axes acceleration sensor is configured to measure accelerations of the housing including a first axis acceleration along a first axis, a second acceleration along a second axis, and a third acceleration along a third axis;
• and
• an acceleration detection circuit configured to:
• calculate an angular acceleration of the housing about the Z-axis based on an input signal from the three-axes acceleration sensor;
• calculate a change in an angular velocity based on integrating the angular acceleration for a most recent period;
• determine a Z-axis angular velocity about the Z-axis as equal to the change in the angular velocity, without adding a previous change in the angular velocity from before the most recent period;
• and
• detect a twisted-motion of the housing based on the Z-axis angular velocity, and wherein:
• calculating the change in an angular velocity based on integrating the angular acceleration for the most recent period is defined as:
• integrating the angular acceleration during a first period while including a first weighting factor;
• and
• integrating the angular acceleration during a second period while including a second weighting factor,
• the second period occurs before the first period,
• the most recent period equals the second period plus the first period, and
• the second weighting factor is smaller than the first weighting factor.