Incident Angle Correction of Laser Beam using CCD Pattern of Reflected Beam

Abstract

Angle measurement and correction is an important technology used in various industries such as medical, research and manufacturing. Especially, as the introduction of automation factories that can increase the productivity and accuracy of products is accelerated, accurate angle measurement and correction technology of objects is required. There are two types by measuring angles: contact type and non-contact type. The contact type has a low flexibility and precision because it must be used in direct contact with the object and also can involve subjectivity of user. On the other hand, the non-contact angle measurement method is more flexible than the contact method by putting distance from the object. Among the non-contact angle systems, the system using light is advantageous in that it has high accuracy and long life-time because it's not influenced by on electromagnetic interference. Previously, the method using optical path difference and multiple laser displacement sensor have been mainly studied. The optical path difference method divides the light and measures the angle using the path difference depends on the angle of an object. Since the method using optical path uses additional optical component such as a beam splitter and a mirror, the system becomes bulky and a precise beam alignment is required for accurate measurement. In the method using multiple laser displacement sensors, the angle is measured using the distance between sensors and the distance information of object obtained from the displacement sensor. However, multiple displacement sensor system is high cost and complexity due to the difference in performance depending on the spacing and arrangement between sensors.

Therefore, in this thesis, we propose an angle correction system that estimates the angles and corrects at specific angles by using a single light source and Charge-Coupled Device (CCD). The proposed system can be implemented at relatively low cost and small volume because it uses only a single light source and CCD. Furthermore, if the CCD's viewing angle is secured, it can be measured over a wide range of measurement angles and distances of about 1 meter. The optical source of the proposed system uses red light with low loss in air and uses an obstacle that can form a ring shaped beam to calculate the change of reflected light pattern mathematically. In this way, the reflected light pattern on the CCD can be image-processed to estimate and correct the angle. As a result, we have demonstrated angle correction system that can correct at specific angle in real time within 0.5 degree error within 0~7.