In previous works we reported several speckle interferometry methods applied to analyze paint drying processes. In this
paper we present the development of a low cost optoelectronic system for monitoring the drying status of different types
of paints. The system is composed by a laser diode, a linear CCD sensor and a microcontroller.
One of the key points of the system is the algorithm that processes the speckle patterns produced by the laser beam
scattered from the paint. The temporal evolution of the speckle carries information of the paint status. The proposed
algorithm modifies one of its parameters to follow the speckle rate of change, allowing a real-time measurement of the
The results obtained with this system are compared to the ones obtained by the method that measures the paint weight
loss in time, due to the solvent evaporation, and to the results from other methods that process the temporal evolution of
the speckle with different algorithms.
Nowadays most industrial and laboratory motion measuring equipment makes use of optical encoders to measure
rotation and linear displacements with sub-micrometrical resolution. In this work we introduce a new design of an optical
encoder based on a non diffractive beam, a binary amplitude grating and a monolithic photodetector. Two theoretical
models of the system are proposed and implemented to obtain numerical results. The performance of the design is also
investigated through experimental measurements. Finally, the experimental results are compared with the models
We present a study of the performance of an incremental optical encoder that works using speckle pattern illumination and a phase grating. The operational principle of the encoder lies in measuring the variations of a speckle pattern passing through the phase grating that can be displaced. This study is described theoretically by a model based on the scalar diffraction theory in the Fresnel zone. The intensity correlation of the modified speckle as a function of the grating displacement is obtained and compared with experimental results. Likewise, the mounting tolerances of the proposed system are analyzed.
A new design of an incremental optical encoder with a sub-micrometric resolution, composed of a divergent beam coming from an uncollimated laser diode, a sinusoidal phase diffraction grating and a detector consisting of a mask and a photodiode array is presented. It is modeled by the scalar theory of diffraction in the Fresnel approximation, obtaining the expression for the field at the detector plane. The tolerance of the system to rotations or displacements of its elements is analyzed. The output of the photodiode array is connected to an electronic interpolation circuit in order to verify the viability of the design.