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

1 . 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, and

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, and

wherein the controller is programmed to initiate the kickback response when the motion signal indicates that linear acceleration along the linear detection axis is greater than a threshold linear acceleration magnitude.

2 . The circular saw of claim 1 , wherein the linear detection axis is a first linear detection axis, and 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.

3 . The circular saw of claim 1 , wherein the circular saw includes a linear motion axis braking structure configured to selectively resist motion of the user-actuated assembly along the linear motion axis, and wherein the controller is programmed to actuate the linear motion axis braking structure as the kickback response.

4 . The circular saw of claim 1 , wherein the motion direction includes a single rotary motion component that is about a rotary motion axis, and wherein the attachment structure includes a rotary element configured to facilitate limited rotary motion of the user-actuated assembly, relative to the base structure, about the rotary motion axis.

5 . The circular saw of claim 4 , wherein at least one of:

(i) the motion sensor is disposed on the linear motion axis;

(ii) the motion sensor is disposed on the rotary motion axis;

(iii) the motion sensor is disposed on a user-actuated assembly attached part of the linear guide such that the motion sensor is only exposed to linear motion; and

(iv) the motion sensor is disposed on a rotary element such that the motion sensor is only exposed to linear motion.

6 . The circular saw of claim 5 , wherein a battery pack is attached to at least one of:

(i) the user-actuated assembly; and

(ii) the user-actuated assembly attached part of the linear guide.

7 . The circular saw of claim 4 , wherein the circular saw includes a rotary motion axis braking structure configured to selectively resist motion of the user-actuated assembly about the rotary motion axis, and wherein the controller is programmed to actuate the rotary motion axis braking structure as the kickback response.

8 . The circular saw of claim 1 , wherein the controller is programmed to stop rotation of the circular saw blade as the kickback response.

9 . The circular saw of claim 1 , wherein the circular saw includes a brake assembly configured to be selectively actuated to stop rotation of the circular saw blade, and wherein the controller is programmed to actuate the brake assembly as the kickback response.

10 . The circular saw of claim 1 , wherein the controller is programmed to at least one of:

(i) cease supply of an electric current to the motor as the kickback response;

(ii) short circuit stator coils of the motor as the kickback response; and

(iii) short to ground stator coils of the motor as the kickback response.

11 . The circular saw of claim 1 , wherein the controller is programmed to determine a workpiece contact parameter, wherein, when the circular saw blade is in contact with the workpiece, the workpiece contact parameter is within a contact value range, wherein, when the circular saw blade is spaced apart from the workpiece, the workpiece contact parameter is within a no-contact value range, and wherein the controller is programmed to determine that the kickback condition exists only when the workpiece contact parameter is within the contact value range.

12 . The circular saw of claim 11 , wherein the workpiece contact parameter includes an angular velocity of at least one of the motor and the circular saw blade during operative use of the circular saw to cut the workpiece, wherein, when the circular saw blade is spaced apart from the workpiece, the angular velocity defines an average free angular velocity, and wherein the contact value range includes angular velocities that are at least 20 revolutions per minute below the average free angular velocity.

13 . The circular saw of claim 11 , wherein the workpiece contact parameter includes at least one of an electric current consumption and a power consumption of the circular saw blade during operative use of the circular saw to cut the workpiece, wherein the motor of the circular saw defines a maximum rated consumption, and wherein the contact value range includes a consumption that is greater than 50% of the maximum rated consumption.

14 . The circular saw of claim 11 , wherein the circular saw includes a contact detector configured to detect contact between the circular saw blade and the workpiece, and wherein the contact detector is configured to generate the workpiece contact parameter.

15 . 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.