Method of interpolating read-out signal of incremental encoder

A method of interpolating a read-out signal of an incremental encoder detecting a rotation angle by utilizing two pseudo sine wave signals having different phases, which are obtained from an incremental encoder including a dial board communicated with a rotation axis of a vertically rotating motor of a three-dimensional scanner, and a fixed scanning board, the method comprising:

• pulsing one of the pseudo sine wave signals as an angle signal;
• counting the pulsed angle signal;
• storing count values of a clock signal separately counted with respect to a timing of every rise of the angle signals, and with respect to a timing of every rise of signals of ordering detection of a rotation angle output from a controlling section of the three-dimensional scanner;
• and
• calculating a rotation angle “θ” at the timing of the rise of the signal of ordering the detection of the rotation angle, by means of an operational equation below by using a count value Ttrig i of the clock signal stored at the timing of the rise of the signal of ordering the detection of the rotation angle, a count value “i” of the pulsed angle signal counted immediately before the rise of the signal of ordering the detection of the rotation angle, respective count values Ti and Ti+1 of the clock signal stored at the timing of the rise of the respective angle signals which rise before and after the rise of the signal of ordering the detection of the rotation angle, and an angular pitch “λ” which is an angle of one pitch of plenty of slits acting as a main scale and disposed at regular intervals formed along a circular circumference of the dial board.
• θ={i+(Ttrig i−Ti)/(Ti+1−Ti)}×λ