On the limitation of dual-view triangulation in reducing the measurement error induced by the speckle noise in scanning operations

A triangulation-based laser displacement sensor using the diffuse reflection light has a strong practical advantage in its robustness against the tilting of the object surface to the sensor’s sensitive direction. On the other hand, it is often subject to higher-frequency noise-like measurement error in scanning operations. This error is caused by the movement of the speckle in the reflected laser beam spot with the scanning operation. This paper first discusses how the dual-view triangulation, using two image sensors aligned symmetrically about the laser beam axis, can reduce the scanning noise in principle. Then, its inherent limitation is discussed. Since different points on the target surface cast the specular reflection to each image sensor, the influence of the sensor’s lateral movement cannot be canceled by comparing the reflected spot’s displacement on each image sensor. This issue can be observed clearer when measuring a surface of a less random surface profile. It is experimentally validated.