Sheet transporting apparatus and image forming system

A sheet feeder comprising:

• a motor
• a feed roller connected to the motor;
• a sheet separator positioned downstream from the feed roller and configured to separate sheets;
• a sensor positioned downstream from the sheet separator and configured to output a detection signal in response to a leading head of the sheet passing therethrough
• an encoder positioned to detect a rotation of the motor or the feed roller, and
• a controller, the controller is configured to:
• input a first current to the motor;
• based on the output from the encoder during the rotation of the motor, measure a rotational amount of the motor or the feed roller;
• based on the measured rotational amount, update the first current;
• input the updated first current to the motor;
• receive the detection signal from the sensor;
• and
• after receiving the detection signal from the sensor, switch from inputting the updated first current to inputting the second current not based on the measured rotational amount to the motor.