Measuring instrument of polygon-mirror motor
View Patent ↗A measuring instrument of polygon mirror motors includes a first light source, a first photo detecting element for detecting a first reflected light beam, i.e. first measuring light beam emitted from the first light source and reflected from the polygon mirror, a second light source, a second photo detecting element for detecting a second reflected light beam, i.e. second measuring light beam emitted from the second light source and reflected from the polygon mirror; and a calculator for performing a calculation based on a time difference between an output from the first photo detecting element and an output from the second photo detecting element. The calculator outputs at least one of an eccentricity and a level difference between facets of the polygon mirror.
1. A measuring instrument for a polygon-mirror motor spinning with a polygon mirror having a plurality of facets fixed to an output shaft of the motor, said measuring instrument comprising:
a first light source;
a first photo detecting element for detecting, via a first slit, a first light beam reflected from the polygon mirror after having been emitted as a first measuring light beam from said first light source;
a second light source;
a second photo detecting element for detecting a second light beam reflected from the polygon mirror after having been emitted as a second measuring light beam from said second light source;
a time difference detector for measuring a first time difference between an output signal from said first photo detecting element and an output signal from said second photo detecting element for each of the facets of the polygon mirror; and
a calculator that calculates at least one of the eccentricity and the level difference between facets based on the output of the time-difference detector and a second time difference, which is a difference between the first time difference of two of the facets, and outputs the at least one of the eccentricity and the level difference between facets of the polygon mirror; and
wherein said second photo detecting element outputs the output signal therefrom when the second measuring light beam is aligned with the second light beam on one straight line.
2. The measuring instrument according to claim 1 , further comprising:
a second slit, wherein the second light beam is to enter said second photo detecting element through said second slit.
3. The measuring instrument according to claim 1 , wherein
the first measuring light beam is to cross with the second measuring light beam at a given angle θ.
4. The measuring instrument according to claim 3 , wherein
the given angle θ falls within a range of 45±15 degrees.
5. The measuring instrument according to claim 3 , wherein
said calculator is for outputting at least one of an eccentricity and a level difference between facets of the polygon mirror after calculating the at least one of eccentricity and a level difference between facets of the polygon mirror as a function of the given angle θ.
6. The measuring instrument according to claim 1 , wherein
a displacement between an angular position of the polygon mirror, at which position said first photo detecting element is to detect the first light beam, and another angular position at which said second photo detecting element is to detect the second light beam, is not greater than 10 degrees at respective reflective surfaces of the polygon mirror.
7. The measuring instrument according to claim 1 , wherein
said first photo detecting element comprises a photo diode, and
said second photo detecting element comprises a photo diode.