Image scanning apparatus having motor operating under improved drive control

Claim 1

An image scanning apparatus for scanning an original, comprising: original holding means having a platen for holding the original; scanning means for scanning the original on said platen; driving means for driving said scanning means in a plurality of driving modes in order to scan the original, including an electrical motor; generating means for generating encoder pulses corresponding to the rotation of the electrical motor, the encoder pulse width corresponding to the rotation speed of the motor; supplying means for supplying drive pulses to apply electric current to the motor; first detecting means for detecting the moving speed of said scanning means; second detecting means for detecting whether said scanning means is under a positive acceleration or a negative acceleration by comparing the encoder pulse widths and determining whether encoder pulse width has a tendency to increase or decrease; and control means for controlling said driving means when a detection is made that said scanning means is under an accelerating operation, and a detection is made that said detected moving speed becomes equal to or higher than a predetermined speed, and when a detection is made that said scanning means changes from the negative acceleration to the positive acceleration or becomes slower than a predetermined speed, the control means controlling the speed of the electrical motor by drive pulse width modulation in accordance with a time width of the drive which is supplied by the pulse supplying means, said control means providing a duty ratio of the drive pulse based on the encoder pulse width and supplying the drive pulse to the electrical motor according to the duty ratio so that an acceleration of the scanning system occurs when electric current is applied to the motor, and a deceleration occurs when electric current is not applied to the electrical motor.