Circular saws having a blade that moves relative to a stationary base structure during operative use of the circular saws to cut a workpiece and methods of detecting a kickback condition of such circular saws

A circular saw having a circular saw blade that moves relative to a base structure during operative use of the circular saw to cut a workpiece, the circular saw comprising:

• the base structure including a saw support and a workpiece support;
• a user-actuated assembly including a motor, an arbor, and a motion sensor, wherein the motor includes a motor shaft configured to rotate about a shaft rotational axis, and wherein the arbor is attached to the motor shaft and is configured to receive the circular saw blade and to rotate the circular saw within a blade rotation plane;
• an attachment structure, wherein the user-actuated assembly is attached to the base structure via the attachment structure such that the workpiece support faces toward the user-actuated assembly, and wherein the attachment structure is configured to permit constrained relative motion between the base structure and the user-actuated assembly in a motion direction and during operative use of the circular saw to cut the workpiece;
• and
• a controller,
• wherein the motion sensor is configured to detect motion of the user-actuated assembly along the motion direction and to generate a motion signal indicative of the motion of the user-actuated assembly along the motion direction,
• wherein the controller is programmed to receive the motion signal and to initiate a kickback response of the circular saw responsive to the motion signal being indicative of a kickback condition of the circular saw,
• wherein the motion direction includes a single linear motion component that is along a linear motion axis,
• wherein the attachment structure includes a linear guide configured to facilitate limited linear motion of the user-actuated assembly relative to the base structure along the linear motion axis,
• wherein the motion sensor includes a linear detection axis that is at least substantially aligned with the linear motion axis, wherein the linear detection axis is a first linear detection axis,
• wherein the motion sensor includes a second linear detection axis that is at least one of:
• (i) at least substantially perpendicular to the first linear detection axis;
• (ii) at least substantially aligned with a direction of gravity;
• (iii) at least substantially perpendicular to a horizontal direction;
• and
• (iv) at least substantially parallel to a workpiece support, and
• wherein the controller is programmed to initiate the kickback response when the motion signal indicates that at least one of:
• (i) a vector sum of linear acceleration along the first linear detection axis and linear acceleration along the second linear detection axis is greater than a threshold linear acceleration magnitude;
• and
• (ii) a scalar sum of an absolute value of linear acceleration along the first linear detection axis and an absolute value of linear acceleration along the second linear detection axis is greater than a threshold linear acceleration magnitude.