Ever try to use a non-contact distance measurement sensor (or optical sensor) to measure the inside of a narrow hole or tube?
How about scanning undercuts or side walls of 3D objects?
If you have, you probably know that it is not an easy task and can be expensive and complicated. Typical triangulation-based sensors will certainly not capture these difficult shapes. Even collinear sensors won’t be able to measure the 90° angles and hidden surfaces completely.
So, you want to measure the shape of an object, perform a 3D surface scan or conduct surface metrology tests. Google tells us there are many measurement methods to achieve these goals. Problem is, which one’s best for you?
Object-measurement techniques can be divided into two basic categories: contact and non-contact. In the former, the object has to touch the sensor, which usually complicates the measurement process, slows it, and can possibly damage the object we examine. Moreover, if the measured object is a soft material, like rubber, textile or tissue, it can’t be measured at all. So here we’ll only discuss non-contact measurement sensors, in which the sensor and the object to be measured are separated from each other.
It all comes down to determining the precise distance between the two and moving one with respect to the other, in order to reconstruct the object’s shape. This goal can be achieved using various optical techniques, each best suited for a different type of application.