Optical encoder based on a nondiffractive beam

Abstract

Optical encoders are used in industrial and laboratory motion equipment to measure rotations and linear displacements. We introduce a design of an optical encoder based on a nondiffractive beam. We expect that the invariant profile and radial symmetry of the nondiffractive beam provide the design with remarkable tolerance to mechanical perturbations. We experimentally demonstrate that the proposed design generates a suitable output sinusoidal signal with low harmonic distortion. Moreover, we present a numerical model of the system based on the angular spectrum approximation whose predictions are in excellent agreement with the experimental results.

Performance of an optical encoder based on a nondiffractive beam implemented with a specific photodetection integrated circuit and a diffractive optical element

“…The simulation through the propagation of the angular spectrum (not shown in Fig. 17) provides good estimation of the harmonic content [13] but predicts null intensity at frequencies other than multiples of the grating frequency; therefore, the spectral noise of the experimental results reveals that the grating used in the lab had some minor imperfections.…”

“…Optical encoders are rotation or linear displacement sensors that reach submicrometric resolution and are used in a wide variety of equipment such as printers, lathes, radars, robots, satellites, etc. There are several optical encoder designs, but all of them rely on the movement of an optical head with respect to a fixed scale [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. The optical head includes one or more light sources that shed some kind of structured light beam, which is shaped by the scale.…”

“…However, steel tape gratings are used for measuring displacements longer than 3 m. The influence of the steel roughness on the encoder performance for the aforementioned grating configurations has been studied [6]. Besides these common optical encoders, there are others based on interferential diffractive [7][8][9] and alternative [10][11][12][13] designs.…”

“…In 2008, we proposed an optical encoder based on a nondiffractive beam (NDB) [13] and presented some experimental results and a theoretical model to understand, analyze, and optimize its performance [18,19]. The main characteristic of this design is its excellent stability, which is due to the propagation invariance of the NDBs, thus allowing higher tolerances under variations in the distance between the scale and the moving head.…”

Self‐configuration system and frequency characterization of a programmable photodetector ASIC

“…Considering the system structure, the total frequency response shown in Figure 9A seems to be related mainly to the PMOS current mirrors dynamics. Under saturation condition, the current mirror response H CM can be modeled through the first-order transfer shown in Equation (1), where the single-pole frequency is defined by the input transistor transconductance g mX and its gate-source capacitance C gsX , while the higher single-zero frequency depends on the equivalent transconductance g mXi eq and the gate-drain capacitance C dgX ieq of the output transistors. 18,19…”