Patent ID: 7424255

Claim:
A device for controlling speed of a belt, wherein a scale including a plurality of equally spaced marks is attached to the belt in a direction of movement of the belt such that a gap is formed between a first end and a second end of the scale, the device comprising: a first sensor configured to detect the marks on the scale and output a first signal upon detecting a mark among the marks; a second sensor configured to detect the marks on the scale and output a second signal upon detecting a mark among the marks, wherein the first sensor and the second sensor are located at different positions along the direction; said first and second sensors being configured to detect said gap; and a controlling unit that controls the speed based on any one of the first signals and the second signals according to a position of the gap detected by the first sensor and the second sensor, wherein the controlling unit switches from controlling the speed based on the first signals to controlling the speed based on the second signals at a timing immediately before the first end reaches the first sensor, wherein the timing is calculated when the second sensor detects the first end based on the distance corresponding to the space between the first sensor and the second sensor.