Miniaturized large-grating-clearance linear encoder based on beam-splitting optical system with MOEMS LD and wireless moving part for rebound nondestructive testing

One factor that limits use of grating linear encoders in rebound hammers for concrete nondestructive testing (NDT) is the lack of a sufficiently compact, dustproof and antiseismic structure. We investigate a miniaturized, large clearance and antiseismic beam-splitting-optical-system (BSOS) linear encoder using a wireless scanning unit and a scale unit. The scanning unit contains a scanning reticle and a total-reflection mirror. The scale unit contains a micro-opto-electro-mechanical systems (MOEMS) laser diode (LD), a photocell and a high strength steel tape scale. The BSOS reduces the linear encoder thickness to 1 cm, almost half that of the traditional one; the MOEMS LD enlarges the grating pair clearance by 1.4~2.4 times, improving durability and scratch resistance; and the wireless moving part enhances antiseismic performance. The linear encoder is integrated into a photoelectric digital rebound hammer to record, transform and digitize rebound displacement for NDT.