APPARATUS FOR DETECTING PAPER WIDTH OF PRINTER AND METHOD THEREOF

PURPOSE:To avoid mistaking the black part for a paper end even in the paper wherein ruled lines or characters are printed by renewing the other end position of paper whenever optical sensor detecting signals change from white to black. CONSTITUTION:The carriage 5 is moved rightward by one step, and by adding one to the counter and ascertaining whether or not the detecting signals SS of an optical sensor 3 are changed from H to L, a value of the counter denoting the present position of the carriage 5 is stored In the right-hand end register PR within a paper position resister 9. The carriage 5 is checked up whether it reaches the right-hand end B of the movable range, and if not, the detecting operation is still continued. If the carriage 5 reaches the right-hand end B, a detecting control part 8 indicates putting out light to an element driving circuit, in order to put out a luminance element, thereby completing the detection of the paper position. Thereafter, the difference between the right-hand end register PR and the left-hand end resister PL is calculated, so as to decide the width of paper 2.