Miniature Reflection-Type Optical Displacement Sensor Incorporating a Projected Beam

Abstract

We embody a miniature reflection-type optical displacement sensor tapping into a projected beam that features high structural tolerance. A code scale with periodic patterns spatially encrypts the projected beam, which is established by imaging a collimated beam from a vertical-cavity surface-emitting laser via an aspheric lens, and linearly expands it, so as to be decoded by a receiver that comprises four serially cascaded identical photodetector cells. For the modulated beam, we observe a pitch increase with a rate of 18 μm/mm along the propagation direction. The two quadrature signals Sig-A and Sig-B derived from the PD signals exhibit a 90° phase relationship. The proposed sensor has been designed via ray-optic simulations and embodied through passive alignment, combined with plastic injection mold. We achieve a positional resolution of ∼10 μm from either of Sig-A and Sig-B. By concurrently considering the two quadrature outputs, we efficiently enhance the resolution to 2.5 μm, with the discovered direction of displacement. Finally, we thoroughly investigate the crucial dependence of the sensor performance on the positional tolerance pertaining to the constituent elements, which is discovered to be as large as +/-100 μm, under a certain resolution.