The present invention relates to a miter saw, and more particularly, to such a miter saw having a turntable and a circular-saw unit.
Japanese Patent Application Publication No. 2000-254817 discloses a miter saw including a base section, a support section, and a circular saw unit. The base section includes a base and a turntable mounted on the base and rotatable about its axis. A workpiece is mounted on the turntable. The support section upwardly extends from the base section and laterally pivotable. The circular saw unit is positioned above the base section and is pivotally movably supported to the support section. The circular saw unit includes a circular saw blade and a motor for rotating the blade. Since the support section is pivotally movable in the lateral direction, the circular saw blade is laterally tiltable. Thus, an angle defined between a side surface of the circular saw blade and an upper surface of the base section can be changed.
A conventional miter saw includes a limiter arrangement for fixing the angular rotational position of the turntable at predetermined rotational positions such as 0 degree, 15 degrees, 30 degrees and 45 degrees. Further, the conventional miter saw also includes another limiter arrangement for fixing a tilting position of the circular saw blade at 0 degree and 45 degrees.
According to up to date electronic technology, it may be conceivable that a digital display portion is provided in the miter saw so as to display an angular rotation angle of the turntable and a tilting angle of the circular saw blade. To this effect, the miter saw must include detection units for detecting a rotation angle of the turntable and a tilting angle of the support section.
As a rotation angle detection unit, an optical sensor unit is conceivable. For example, the optical sensor unit includes a light emitting element, a disc like element, and an optical sensor. The disc like detected element is rotatable in synchronism with the rotation of the turntable and is formed with a plurality of slits arrayed in a circumferential direction of the disc and spaced away from each other by a constant distance in the circumferential direction. The disc like element generates optical pulse each time the light passes through each slit and non-slit region shuts off the light. The optical pulse is detected by the optical sensor. If slit distance is configured to generate a single pulse as a result of rotation of the turntable by 0.05 degrees, 900 pulses are theoretically generated if the turntable is angularly rotated from 0 degree to 45 degrees, the latter angle being regulated by the rotation limiter.
However, various machining errors are generated for the production of the various components and assembly of the miter saw. For example, the counted pulses may be 880 pulses in spite of the angular rotation to 45 degrees provided by the limiter. In this case, the display does not display 45 degrees but may display 44.8 degrees corresponding to 880 pulses. However, the user already knows that the turntable has been rotated by 45 degrees. Therefore, the user may have illusion that the miter saw is broken or defective. The same problem may be conceivable regarding the display of the tilting angle of the circular saw blade.