Patent ID: 8767028

Claim:
An image forming apparatus comprising: a light source for emitting a beam; a deflector for deflecting the beam; a light receiving element for receiving the beam and generating a detection signal; a converter for converting electric potentials of the detection signal into data values and generating time data associated with the data values; and a first calculator for calculating a position of center of the beam as the beam passes across the light receiving element, based on the data values and the time data, wherein the first calculator calculates the position of center xg of the beam by using the following expression, wherein d 1 to dn denote the data values, t 1 to tn denote the time data associated with the data values d 1 to dn, and v denotes travelling speed of the beam, xg = ∑ i = 1 n ⁢ ( di · xi ) ∑ i = 1 n ⁢ di · v .