Method and apparatus for measuring the surface of an object

A method of manufacturing an elongated article, having a circumferential surface, the steps comprising:

• continuously shaping said article,
• advancing the article past a measuring location,
• impinging at least one laser beam at an angle with the longitudinal axis of said article onto at least a portion of said circumferential surface of the measuring location to form an illuminated spot thereon, the characteristics of the laser rays reflected from the illuminated spot varying in dependence of the topography of said circumferential surface,
• scanning said part of said circumferential surface with the laser beam, the laser beam having a point of origin, measurable and reference distances being defined between said point of origin and said circumferential surface,
• reflecting the laser beam from said circumferential surface,
• focusing the reflected laser beam so as to obtain a focal image of the illuminated spot, said focal image having a substantially predetermined diameter and defining with the illuminated spot an optical axis, defocused spot regions existing on opposite sides of the focal image along the optical axis,
• measuring the light intensity within said predetermined diameter along said defocused spot regions and said focal image, the light intensity reaching a peak when said predetermined diameter coincides with said focal image, the peak corresponding to said reference distance being defined as the reference peak, the peaks corresponding to said measurable distances being defined as measured peaks, respectively, and
• measuring the time deviation between said reference peak and corresponding of said measured peaks, the distance from the origin of the laser beam to said circumferential surface being determinable solely as a function of said time deviation between said reference peak and corresponding of said measured peaks, and of said reference distance, respectively, and
• feeding back the results of the measuring step to the shaping step, so as to control the shaping step in dependence on the feedback results.

A laser-optical system for measuring the circumferential surface of an article moving continuously along a longitudinal axis thereof comprising, in combination:

• means for directing at least one laser beam at an angle with said longitudinal axis onto the circumferential surface to be measured to form an illuminated spot thereon, the laser rays reflected from the illuminated spot varying in dependence on the topography of the circumferential surface;
• means for scanning the laser beam across said circumferential surface, wherein said laser beam has a point of origin, a plurality of measurable distances, inclusive of a reference distance, being defined between said point of origin and said circumferential surface to be measured,
• means for measuring the characteristics of the laser rays reflected from the illuminated spot, including
• a light stop and
• moving means for periodically moving said light stop between two extreme positions in an additional light path, an intermediate point between said two extreme positions corresponding to said reference distance, the illuminated light spot being substantially focusable onto said light stop at a plurality of determinable distances from one of said extreme positions, so as to define peaks of light intensity occurring at measurable time deviations from respective predetermined time slots, each predetermined time slot corresponding to said reference distance, each measurable time deviation corresponding to a respective measurable incremental distance from said reference distance, the sum of respective incremental distances and of said reference distance corresponding to said measurable distances, whereby said measurable distances, and consequently, a contour of a cross-section of said article is obtainable from said measurable time deviations.

In a method of measuring and recording the circumferential surface of an article moving continuously along a longitudinal axis thereof, the steps comprising:

• impinging at least one laser beam at an angle with said longitudinal axis onto first and second positions of said circumferential surface to form illuminated spots thereon, the characteristics of the laser ray reflected from the illuminated spots varying in dependence of the topography of said circumferential surface,
• scanning said positions of said circumferential surface with the laser beam, the laser beam having a point of origin, measurable and reference distances being defined between said point of origin and said circumferential surface,
• reflecting the laser beam from said first and second positions of said circumferential surface,
• focusing the reflected laser beam so as to obtain focal images of the illuminated spots, each focal image having a substantially predetermined diameter and defining with each illuminated spot an optical axis, defocused spot regions existing on opposite sides of each focal image along the optical axis,
• measuring the light density within said predetermined diameter along corresponding of said defocused spot regions and said focal image, the light intensity reaching a peak when said predetermined diameter coincides with said focal image, the peak corresponding to said reference distance being defined as a reference peak, the peaks corresponding to said measurable distances being defined as measured peaks, respectively, and
• measuring the time deviation between said reference peak and corresponding of said measured peaks, the distance from the origin of the laser beam to said circumferential surface being determinable solely as a function of said time deviation between said reference peak and corresponding of said measured peaks, and said reference distance, respectively,
• transforming the measured time deviations into recordable electrical signals,
• recording said electrical signals, and
• synchronizing all of said impinging, measuring and scanning steps with one another.