| 摘要 |
A screw-driving apparatus has a sprocket (21) causing the belt (70) to intermittently advance, and the sprocket is rotatably held on a transverse shaft (26) supported in a side wall of a slider (2) perpendicularly to a driver bit (7). The sprocket (21) is driven by a ratchet wheel (22) rotated by a pawl (24) swingably connected to a bell crank (23), the ratchet wheel (22) coaxial with the sprocket rotating only in one direction along with the sprocket. The bell crank (23) located near the sprocket is rockably held on the slider (2) and its one arm normally protrudes upwards to engage with a shoulder (35) formed in an upper wall of a casing (1), and the pawl (24) is pivoted to the bell crank's other arm. A spring means (33) always biases the pawl to engage with the ratchet wheel (22), so that as the slider (2) is forced back into the casing (1), the shoulder (35) pushes rotates the bell crank (23) and consequently the pawl (24) and the ratchet wheel make the belt (70) advance one pitch, such that the apparatus has a belt feeding mechanism (20) improved to render it smaller in size, lighter in weight and more convenient to use.
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