Patent ID: 7154639

Claim:
A transmission device for use in an image scanner, driven by a step motor to move a carriage to perform a scanning operation at a selected speed, and comprising: a transmission control set switched between a first and a second transmission states in response to a command for changing a moving speed of said carriage, and driven by said step motor to output a transmission power; a first transmission set of a first deceleration ratio, coupled with said transmission control set to receive said transmission power from said transmission control set in said first transmission state, and providing said transmission power for said carriage to have said carriage move at a first speed; and a second transmission set of a second deceleration ratio different from said first deceleration ratio, coupled with said transmission control set to receive said transmission power from said transmission control set in said second transmission state, and providing said transmission power for said carriage to have said carriage move at a second speed; wherein said transmission control set comprises: an active gear synchronously rotating with a shaft of said step motor; two follower gears engaging with said active gear to be transmitted by said active gear; and a swing arm connecting said two follower gears with each other, and swinging between a first position to allow said follower gears to engage with said first transmission set and a second position to allow said follower gears to engage with said second transmission set.