Position determining device and method for objects on a touch device having a stripped L-shaped reflecting mirror and a stripped retroreflector

A position determining method for objects, comprising following steps:

• (a) emitting light beam of a light emitting module from a reference point to illuminate or scan a work area entirely;
• (b) detecting a plurality of objects directly and indirectly blocking said light beam with a light detecting unit when the light beam is reflected by a reflecting mirror to said light detecting unit so as to obtain a first signal, and detecting said objects directly blocking said light beam with said light detecting unit when the light beam is retro-reflected by a retroreflector to said light detecting unit so as to obtain a second signal, wherein said first signal comprises a plurality of first weak signals corresponding to said objects and said second signal comprises at least one second weak signal corresponding to said objects;
• (c) processing said first signal and said second signal with a signal processing unit to obtain a plurality of included angles (A1) corresponding to said first weak signals according to where or when the first weak signals appear in the first signal and a plurality of included angles (A2) corresponding to said second weak signals according to where or when the second weak signals appear in the second signal, wherein the included angles (A1) and (A2) are formed by said blocked light beam intersecting with said first reflecting unit and said second reflecting unit respectively;
• (d) providing a microprocessor to arrange said included angles (A1) with each of said included angles (A2), respectively as a plurality of combinations of included angles, to convert said combinations to a plurality of coordinates, to compare said coordinates with one another, to select at least two coordinates with the same value, and to confirm corresponding coordinates of said object on said work area;
• wherein said work area is surrounded by a stripped L-shaped mixed-type reflecting unit, a stripped first reflecting unit and a stripped second reflecting unit, said first and second reflecting units are respectively positioned at two side ends of said mixed-type reflecting unit, a contact of said first reflecting unit and said second reflecting unit being a corner of said work area to be set as a reference point, said mixed-type reflecting unit comprising a reflecting mirror and a retroreflector, and said retroreflector being positioned above or below said reflecting mirror.